An impinging shock wave/turbulent boundary layer interaction over a compliant panel was experimentally examined in a Mach 4 Ludwieg Tube through simultaneous measurements of both the fluid and structure response. Synchronized measurements were obtained using colinear focused laser differential interferometry and high-speed schlieren together with single-camera stereo-photogrammetry. The static and dynamic behavior of the compliant panel itself was also characterized through response to pressurization, roving hammer, and panel flutter experiments.
\r\n\r\nWhen the compliant panel was subjected to shock impingement at the mid-chord and leading-edge locations, the initial panel response was dominated by oscillations at the fundamental vibration mode and was primarily governed by one-way uncoupled fluid-structure behavior. However, under leading-edge impingement, oscillations at the fundamental vibration mode eventually dampened, and a transition to a two-way coupled fluid-structure response was observed. Under two-way coupling, the interaction was characterized by a reduction in oscillation amplitudes and an increase in relative strength of high-order vibration modes.
\r\n\r\nPhase analysis at the fundamental vibration mode between the separation and reattachment shock motion revealed that the one-way uncoupled mid-chord impingement case exhibited a repeatable phase alignment, where the phase of the separation shock tended to lead that of the reattachment shock by approximately one quarter of a panel oscillation. However, consistent with the behavior in rigid wall shock wave/boundary layer interactions, the instantaneous reattachment motion was anti-correlated and led that of the separation shock in all compliant cases. The transition to a two-way coupled response strengthened the synchronization between the separation shock and panel motion compared to that of the one-way uncoupled response.
\r\n\r\nSpectral analysis of the mid- and high-frequency content of density fluctuations in the separation bubble and boundary layer showed that the spectral distributions were not significantly modified due to surface compliance. Instead, the magnitude of the density fluctuations inside the separation bubble were attenuated under mid-chord impingement compared to that of leading edge impingement. Moreover, in all compliant cases, surface compliance amplified the spectral energy in the boundary layer downstream of flow reattachment by over a factor two compared to that of the rigid case.
" }, { "name": "Ayling, Alex Eben", "degree": "PhD", "year": "2026", "title": "Scalable Arrays From Millimeter-Wave Sensing to Microwave Wireless Power Transfer", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:04072026-143808452", "creators": [ { "name": { "family": "Ayling", "given": "Alex Eben" }, "id": "Ayling-Alex-Eben", "orcid": "0009-0008-5440-7785", "display_name": "Ayling, Alex Eben" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Siegel", "given": "Peter H." }, "id": "Siegel-P-H", "orcid": "0000-0002-2539-4646", "role": "member", "display_name": "Siegel, Peter H." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/w440-k235", "abstract": "Wireless power transfer at a distance, long relegated to the realm of science fiction, has seen a resurgence in recent years. Chief among its promises is Space-Based Solar Power (SBSP), an ambitious project to deploy kilometer scale photovoltaic arrays in space and beam its power down to Earth using a complementary microwave phased array. The building blocks of the array are phased array tiles, which can be instantiated to produce larger apertures.
\r\n\r\nThe tile must be simultaneously lightweight and flexible for deployment in space, low-cost, high-performance, and scalable. First, the results of the MAPLE mission, which tested wireless power transfer in space using custom flexible arrays, are presented. Using the results of that mission, the design and testing of next-generation, fully flexible 8x8 element phased array tile are presented. The tile is driven by a custom 22-nm CMOS FDSOI RFIC that achieves record efficiency and performance. These results represent not only a step forward toward practical microwave wireless power transfer but offer new directions in communications and sensing driven by flexible arrays.
\r\n\r\nAdditionally, topics on maximum power point tracking in SBSP systems, transmitarrays for SBSP, and the design of a fully-integrated, scalable, and low-cost D-band (110-170GHz) radiator tile are discussed.
" }, { "name": "Bozkurt, Alk\u0131m Berke", "degree": "PhD", "year": "2026", "title": "Interfacing Long-Lived Mechanical Oscillators and Superconducting Quantum Circuits", "advisor": "Mirhosseini, Mohammad", "url": "https://resolver.caltech.edu/CaltechTHESIS:01262026-214753026", "creators": [ { "name": { "family": "Bozkurt", "given": "Alk\u0131m Berke" }, "id": "Bozkurt-Alk\u0131m-Berke", "orcid": "0000-0003-0633-8902", "display_name": "Bozkurt, Alk\u0131m Berke" } ], "advisors": [ { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "advisor", "display_name": "Mirhosseini, Mohammad" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/wz3n-fn09", "abstract": "Mechanical oscillators in the quantum regime hold promise for quantum sensing, frequency conversion and information processing. Because mechanical motion is linear, coupling to an external nonlinear system, such as a qubit, is essential for these applications. Recent advances in piezoelectric interfaces between mechanical oscillators and superconducting qubits have successfully demonstrated precise control of non-classical states of motion. However, challenges associated with heterogeneous integration of piezoelectric materials have limited mechanical quality factors in these systems to around one million, constraining their broader utility.
\r\n\r\nIn this thesis, we explore an alternative approach that harnesses the nonlinearity of electrostatic forces to engineer interactions between superconducting circuits and mechanical oscillators. This strategy allows us to employ mechanical oscillators made of silicon, a non-piezoelectric material with extremely low acoustic loss. We reach the strong coupling regime between a superconducting qubit and a long-lived mechanical oscillator with a quality-factor of around a billion. We employ this system to generate non-classical states of motion that exhibit clear signatures of quantum behavior. Furthermore, we explore the origins of acoustic decoherence and implement strategies to mitigate its impact.
\r\n\r\nThe mechanical lifetimes, which exceed those of best superconducting qubits, open new possibilities for storing and processing microwave quantum information in motional states. Furthermore, our material-agnostic approach is broadly applicable to a variety of material platforms that possess significance for quantum science but lack a piezoelectric response.
" }, { "name": "Bulfer, Steven Patrick", "degree": "PhD", "year": "2026", "title": "Energy Efficient On-Chip Neural Feature Extraction for Brain-Computer-Interfaces", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:11182025-233532194", "creators": [ { "name": { "family": "Bulfer", "given": "Steven Patrick" }, "id": "Bulfer-Steven-Patrick", "orcid": "0000-0001-9942-1195", "display_name": "Bulfer, Steven Patrick" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Pedroni", "given": "Volnei A." }, "id": "Pedroni-Volnei-Antonio", "role": "member", "display_name": "Pedroni, Volnei A." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" } ], "option_major": [ "eleceng" ], "doi": "10.7907/40as-d020", "abstract": "Neural interfaces are entering an era where what once was science fiction is becoming a reality. As neural interfaces move out of the lab and into people's lives, the stability of neural decoding algorithms becomes ever more pressing. It is an unfortunate reality that neural implants degrade from long-term exposure to the neurological environment, however prior work has shown enhanced decoding stability in the application of 1D convolutional neural networks to neural feature extraction. However, these algorithms have high memory and processing requirements, prohibiting them from meeting the low area and power restrictions of implantable brain-machine interface decoding pipelines.
\r\n\r\nThis dissertation addresses the difficulties of implementing these algorithms on streamed neural data with high parallelism and low area and power costs. We address the unique dataflow characteristics of the feature extraction workload by designing a tailored processing element that reduces the memory access requirements by 2x. We further reduce system memory requirements through efficient process scheduling and memory partitioning. We then address the model complexity through retraining and analysis of the effect of various system parameters on the accuracy of kinematic decoding and hardware performance.
\r\n\r\nResults show that these design choices were able to successfully implement these intensive but performant algorithms within the power and area budgets of implantable devices. The architecture supports 192 channels that achieve state-of-the-art decoding stability at 1.8 uW and 12801 um^2 per channel in 65 nm CMOS technology. The device is a fully configurable, scalable, area and power efficient solution that supports models with 2-8 feature layers and a total kernel length of up to 256. This architecture reduces caching requirements by 5x over conventional computation schemes. We show our hardware optimized models maintain superior stability over time using recorded data from tetraplegic human participants with spinal cord injury. The models and hardware were validated in real time with a human subject in online closed-loop center-out cursor control experiments with micro-electrode arrays that were implanted for 6 years. Decoders using features generated with this work substantially improve the viability of long-term neural implants compared to other feature extraction methods currently present in low-power BMI hardware.
" }, { "name": "Catherall, David Spencer", "degree": "PhD", "year": "2026", "title": "Threads in the Tapestry of Next Generation Nanodevices: Simulation and Thin Film Processing", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04202026-192826965", "creators": [ { "name": { "family": "Catherall", "given": "David Spencer" }, "id": "Catherall-David-Spencer", "orcid": "0000-0002-3540-2419", "display_name": "Catherall, David Spencer" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "chair", "display_name": "Falson, Joseph" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ye", "given": "Linda" }, "id": "Ye-Linda", "orcid": "0000-0001-7949-1356", "role": "member", "display_name": "Ye, Linda" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/bjfx-8519", "abstract": "Modern nanodevices such as silicon integrated circuits and superconducting quantum bits achieve their performance from the intrinsic properties of semiconducting, superconducting, and optical materials. Creating devices with improved performance, as well as creating new types of devices, requires an understanding of the fundamental material properties and the methods to actually grow and process these materials. For instance, in charge transport devices like transistors, phenomena such as hot carrier effects become relevant at the small length scales relevant in modern integrated circuits, necessitating new physical models and understanding during miniaturization. Additionally, as researchers seek to push the limits of device performance by reducing signal losses and by using novel materials, new etching and deposition technologies are needed to prepare ultra-high quality thin film materials to fabricate their devices. To this end, this thesis contains work in three facets of solid-state devices: simulation, etching, and deposition.
\r\n\r\nIn Chapter 2, we investigate the hot hole transport properties of silicon via a recently developed ab-initio formalism utilizing the Boltzmann transport equation. Hot carrier transport and fluctuations are of critical importance in essentially all modern transistors, and a thorough understanding of the underlying physics is central to their design and operation. In the hot carrier regime, electric fields are sufficiently strong to perturb the electron distribution function such that equilibrium relationships including Ohm's law, the Einstein diffusion relation, and Nyquist noise equation are no longer valid. In this non-equilibrium case, additional microscopic insight may be learned about the material system from the field-dependent mobility, diffusion coefficient, and noise spectrum. Here we develop and apply a first-principles approach to hot carrier transport that does not require any adjustable parameters, facilitating direct comparison to experiment. While this computational method has been applied to electrons in Si and GaAs, we apply it to holes in Si for the first time, calculating the anisotropic DC mobility, diffusion coefficient, and energy relaxation time. Furthermore, we extend the numerical theory underlying the solution to the linearized Boltzmann transport equation to achieve greater accuracy and allow for calculations at cryogenic temperatures. Using this modified theory, we successfully predict experimentally observed phenomena in the cryogenic field-dependent drift velocity and noise spectrum and elucidate their origin from the characteristics of the electron-phonon scattering rates and momentum relaxation time.
\r\n\r\nChapter 3 switches focus of the thesis to nanofabrication techniques for thin films; in this chapter we work with a process called atomic layer etching. Although this technique is practically the reverse of atomic layer deposition, which is now common in nanofabrication, atomic layer etching is only a recent development and still in its infancy. The process utilizes sequential, self-limited steps to modify and remove the surface of a material in a precise and controlled manner. Here we report a new process for etching silicon dioxide (SiO\u2082). This material is common in device fabrication as a dielectric, optical medium, or surface contaminant. Atomic layer etching has the unique properties of smoothing surfaces while exhibiting sub-angstrom precision. To this end, a technique utilizing less-hazardous reactants than prior works and performed using a commercial-scale tool is of interest to improve devices by smoothing SiO\u2082 interfaces. We develop and demonstrate such a process using trimethylaluminum (TMA) and an argon/sulfur hexafluoride/hydrogen (Ar/SF\u2086/H\u2082) plasma mixture, demonstrating the process window, step synergy, saturation curves, process parameter dependence, contamination from precursors, smoothing effect, and the influence of SiO\u2082 deposition method on the etch rate.
\r\n\r\nIn Chapter 4 we turn from etching to deposition techniques. This chapter focuses on a new physical vapor deposition method denoted thermal laser evaporation (also called thermal laser epitaxy). Physical vapor deposition techniques create thin films by the physical diffusion of material vapors onto a substrate. Common techniques included sputtering, electron beam evaporation, molecular beam epitaxy, and pulsed laser deposition. However, all of these come with various limitations. These limits include maximum process pressures, the use of reactive or fragile crucibles, and the maximum temperature of the deposition source. Thermal laser evaporation is an old technique which has long been neglected owing to the limits of laser technology and associated high cost. However, the recent development of 1070 nm fiber lasers has proven to be an enabling technology for this technique. In this chapter, we report the design and demonstration of a home-built thermal laser evaporation system. The system is among the first to be placed into operation in the modern era. We demonstrate its capabilities by evaporating nickel and perform roughness, compositional, and electrical characterization. We discuss lessons learned during system development and comment on both current and future designs.
" }, { "name": "Chen, Wenyuan", "degree": "PhD", "year": "2026", "title": "Additive Nanofabrication of 3D TiO\u2082 Metaoptics via Two-Photon Lithography", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072026-200423437", "creators": [ { "name": { "family": "Chen", "given": "Wenyuan" }, "id": "Chen-Wenyuan", "orcid": "0000-0002-0042-1118", "display_name": "Chen, Wenyuan" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/nyfd-tj09", "abstract": "Flat optics based on subwavelength metasurfaces has emerged as a powerful tool for compact and versatile wavefront control, enabling advances in imaging, sensing, displays, and communications. However, the functionality of single-layer metasurfaces is fundamentally limited by the finite degrees of freedom available in a single optical interaction. The growing demand for multifunctionality has motivated innovations in more complex designs involving multilayered structures. While cascaded or multilayer metasurfaces provide this additional design freedom, their realization through conventional top-down lithography is hindered by fabrication complexity and alignment challenges. Additive manufacturing, in particular two-photon lithography, has recently been explored to realize inverse-designed multilayered metaoptics, but such demonstrations have remained largely polymeric. High-index materials fabricated through TPL are still constrained to homogeneous lattices with uniform features. These challenges underscore the importance of alternative fabrication strategies that can expand the design space of multilayer and volumetric structures.
\r\n\r\nIn this dissertation, we establish a bottom-up platform for volumetric metaoptics based on nanoscale additive manufacturing (nano-AM) of TiO2. In Chapter 2, we develop a two-photon lithography framework that overcomes calcination-induced defects, enabling uniformly shrunk TiO2 lattices with lateral dimensions exceeding 90 \u03bcm and thicknesses up to 20 \u03bcm. In Chapter 3, we validate this platform by demonstrating metalenses operating at \u03bb = 4.5 \u03bcm with numerical aperture (NA) up to 0.74. In Chapter 4, we introduce heterogeneous multilayer stacking---achievable in a single lithography step---as a strategy to decouple phase, group delay, and higher-order dispersion control using simple cylindrical unit cells without height constraints. We experimentally realize broadband achromatic metalenses with NA = 0.25 and 0.49, exhibiting near-constant focal lengths across \u03bb = 4-5 \u03bcm. In Chapter 5, we further explore multifunctionality by demonstrating polarization-splitting metalenses and an inverse-designed color router, both fabricated in TiO2. Collectively, this work establishes nanoscale additive manufacturing of high-index oxides as a versatile route to functional multilayer and heterogeneous architectures, complementing existing polymer-based and subtractive approaches, and demonstrating new pathways toward compact, multifunctional, and volumetric optical devices.
" }, { "name": "Dai, Min", "degree": "PhD", "year": "2026", "title": "From Models to Data: Toward a Unified Framework for Agile and Safe Bipedal Locomotion", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03152026-044446970", "creators": [ { "name": { "family": "Dai", "given": "Min" }, "id": "Dai-Min", "orcid": "0009-0006-3674-0432", "display_name": "Dai, Min" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Niemeyer", "given": "Gunter" }, "id": "Niemeyer-Gunter", "role": "member", "display_name": "Niemeyer, Gunter" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/e1sk-7771", "abstract": "Achieving agile, efficient, and robust locomotion in bipedal robots remains a grand challenge of robotics. Traditional model-based control methods are theoretically grounded but are often sensitive to model mismatch and state-estimation uncertainty, limiting their adaptability to real-world environments. Conversely, data-driven approaches such as reinforcement learning produce remarkable behaviors but often lack interpretability, require non-trivial reward shaping, and raise safety concerns.
\r\n\r\nThis thesis bridges these two paradigms through a unified framework that begins with model-based behavior synthesis and culminates in data-driven adaptation. The first part focuses on constructing walking behaviors and controllers using reduced-order models of locomotion. A hierarchy of planners and controllers is developed to enable robust walking for flat-footed and multi-domain gaits, as well as safety-critical locomotion over constrained footholds such as stairs and stepping stones. Additionally, this work introduces RoMoCo, a modular open-source architecture, a modular open-source architecture designed to unify reduced-order planning, output synthesis, and whole-body control across multiple bipedal platforms.
\r\n\r\nBuilding on this foundation, the second part introduces data-driven mechanisms that enable robots to improve and personalize their behaviors through various forms of data. Episodic data collected during repeated executions are used to correct modeling errors and reduce constraint violations. Human preference data facilitates automatic gain tuning through interactive feedback. Online robot data enables adaptation of reduced-order models by learning step-to-step dynamics directly from real executions. Finally, large-scale simulation data support a reinforcement-learning framework designed for hardware deployment, where model-guided rewards enable efficient training and introduce perception inputs, yielding policies capable of dynamic stepping-stone traversal on real robots.
\r\n\r\nTogether, these contributions form a progression from theoretically grounded model-based control to data-enabled adaptation, demonstrating that reduced-order models and data-driven learning are complementary. Their integration enables bipedal robots such as Cassie and G1 to walk safely, robustly, and efficiently across diverse terrains, marking a step toward human-level agility in legged locomotion.
" }, { "name": "Davis, Branson William", "degree": "PhD", "year": "2026", "title": "Autoignition Modeling and a Generalized Hot Surface Ignition Criterion", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08262025-221106238", "creators": [ { "name": { "family": "Davis", "given": "Branson William" }, "id": "Davis-Branson-William", "orcid": "0000-0002-5288-7913", "display_name": "Davis, Branson William" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/meyv-1317", "abstract": "This work investigates the fundamental physics and predictive modeling of thermal ignition in heated volumes and near hot surfaces. Three-dimensional simulations of the ASTM-E659 apparatus revealed how natural convection and fuel stratification influence ignition timing and location, highlighting key limitations in standardized AIT testing. A one-dimensional analog further demonstrated the impact of radial temperature gradients on ignition behavior.
\r\n\r\nTo isolate the core mechanisms of thermal runaway, a canonical hot surface ignition problem was analyzed, showing that inclusion of low-temperature chemistry induces two-stage ignition and lowers critical surface temperatures. Building on insights from classical theory, a novel ignition model was developed based on chemical and thermal length scales. The model collapses ignition data across a wide range of configurations and defines a critical Damk\u00f6hler number. Despite some limitations for NTC fuels and catalytic effects, this unified framework represents a major advance over existing models.
" }, { "name": "Devey, Sean Patrick", "degree": "PhD", "year": "2026", "title": "Part I: A Novel Compact Water Tunnel. Part II: Evolution of Delta Wing Surface Contour from Flat Plates to Boxfish at Low Reynolds Numbers", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:09012025-210751150", "creators": [ { "name": { "family": "Devey", "given": "Sean Patrick" }, "id": "Devey-Sean-Patrick", "orcid": "0000-0002-8937-939X", "display_name": "Devey, Sean Patrick" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T-E", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rv8x-jm07", "abstract": "This thesis is presented in two parts.
\r\n\r\nPart I (Chapters 1\u20132) addresses a common challenge for experimentalists: the scarcity of laboratory space. Inspired by recent advances in fan-array wind tunnels, a novel, ultra-compact water tunnel was developed that uses an array of submerged thrusters to drive flow within a rectangular tank. Prioritizing space efficiency over power efficiency, the design achieves flow quality comparable to traditional facilities while occupying just 8% of the typical footprint. Flow characterization using particle image velocimetry (PIV), hot-film anemometry, and laser Doppler velocimetry (LDV) demonstrates the tunnel\u2019s effectiveness and suitability for fluid dynamic research.
\r\n\r\nPart II (Chapters 3\u20135) uses this new facility to investigate the aerodynamics of delta wings with extreme leeward surface contours in low Reynolds number subsonic flow. While the canonical delta wing flow field is dominated by a pair of counter-rotating leading-edge vortices (LEVs), similar vortex structures have been observed over a range of geometries\u2014including biological forms such as boxfish. However, the influence of non-uniform thickness and large leeward surface deformations on LEV behavior remains poorly understood.
\r\n\r\nTo address this, a family of 70\u00b0 sweep delta wing shapes was defined using B\u00e9zier splines, spanning a continuum from flat plates to forms approaching bluff bodies. Eight 3D-printed wing models were fabricated, with systematic variation in cross-sectional curvature and thickness, including a conical apex section with a thickness-to-span ratio of 0.5. Dye visualization, stereoscopic PIV (SPIV), and load cell measurements were used to examine LEV strength, position, and wing performance across multiple angles of attack. Results show that increasing the leeward surface height, effectively confining the LEV, leads to substantial reductions in vortex strength and shifts in vortex position. Experimental evidence of a dual primary vortex structure over thick delta wings is reported for the first time. Tomographic dye reconstructions reveal complex three-dimensional vortex behavior in the aft section of the wings, including flow separation patterns reminiscent of those seen in hatchbacks and Ahmed bodies. Force measurements reflect the observed flow field, with highly non-linear force evolution with angle of attack depending on model cross-sectional and longitudinal profiles. These findings provide new insight into the interplay between surface shape and vortex structure, and further demonstrate the capabilities of the compact flow facility.
" }, { "name": "Feng, Berthy T.", "degree": "PhD", "year": "2026", "title": "Advancing Scientific Computational Imaging Through Data-Driven and Physics-Based Priors", "advisor": "Bouman, Katherine L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08292025-040504302", "creators": [ { "name": { "family": "Feng", "given": "Berthy T." }, "id": "Feng-Berthy-T", "orcid": "0000-0002-1843-2165", "display_name": "Feng, Berthy T." } ], "advisors": [ { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "advisor", "display_name": "Bouman, Katherine L." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Freeman", "given": "William T." }, "id": "Freeman-William-T", "orcid": "0000-0002-2231-7995", "role": "member", "display_name": "Freeman, William T." }, { "name": { "family": "Gkioxari", "given": "Georgia" }, "id": "Gkioxari-Georgia", "role": "member", "display_name": "Gkioxari, Georgia" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "cms" ], "doi": "10.7907/cmed-tj81", "abstract": "The core idea of computational imaging is to supplement limited observable data\r\nwith human-imposed assumptions, or priors. One could formulate a prior as a statistical model or physics model of the object being imaged. However, incorporating such assumptions in the imaging process poses computational challenges, including efficiently expressing sophisticated priors, appropriately balancing priors with observations, and gently enforcing physics constraints. This thesis addresses such challenges with principled methods for bringing informative assumptions into computational imaging. We emphasize applications in scientific imaging, and we focus on two categories of priors as well as the intersection between them: data-driven statistics and physics knowledge.
\r\n\r\nOn the data-driven side, this thesis presents work on score-based priors, including a posterior-estimation method and results of re-imagining the famous M87* black hole from real data with score-based priors. On the physics-based side, we have been able to tackle extremely under-determined imaging problems by enforcing physics constraints, including performing single-viewpoint dynamic tomography of emission near a black hole and characterizing interior material properties from video. As a means towards integrating data-driven and physics-based assumptions, we have developed a method to enforce physics constraints on generative models. In this thesis, we explore each aforementioned project with an emphasis on technical novelty and experimental validation on simulated and real data. By opening new routes for bringing in both data-driven and physics-based assumptions, the methods presented in this thesis enable visualizing scientific phenomena beyond the reach of conventional sensors.
" }, { "name": "Flynn, Michael J.", "degree": "PhD", "year": "2026", "title": "Building to Understand MiRNA Circuits", "advisor": "Elowitz, Michael B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11072025-063320028", "creators": [ { "name": { "family": "Flynn", "given": "Michael J." }, "id": "Flynn-Michael-J", "orcid": "0009-0003-1186-957X", "display_name": "Flynn, Michael J." } ], "advisors": [ { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "advisor", "display_name": "Elowitz, Michael B." } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Gradinaru", "given": "Viviana" }, "id": "Gradinaru-V", "orcid": "0000-0001-5868-348X", "role": "member", "display_name": "Gradinaru, Viviana" }, { "name": { "family": "Hay", "given": "Bruce A." }, "id": "Hay-B-A", "orcid": "0000-0002-5486-0482", "role": "member", "display_name": "Hay, Bruce A." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3rb1-mk79", "abstract": "MicroRNA (miRNA) regulation is ubiquitous in human biology, with miRNAs playing a role in every developmental process. Despite the fact that deletion of miRNA genes typically derepress their targets by only 20%-50%, such deletions are often lethal. However, this raises the question of how such modest derepression can lead to severe phenotypic consequences. To better understand miRNA regulation, I took a \"build to understand\" approach: by building synthetic biological circuits using miRNA in two engineering projects, I put models of miRNA regulation to the test and created biological devices with practical applications. First, I developed miRNA incoherent feedforward loop (IFFL) circuits that enable precise control of therapeutic transgene expression to augment Rett syndrome gene therapy. Second, my colleagues and I systematically varied miRNA target complementarity and cooperativity to generate a toolkit of modular IFFL circuits, termed DIMMERs, that enabled precise, tunable control of transgene expression across diverse cell types to facilitate imaging, editing, and gene therapy. Together, these projects provided evidence that canonically-sized miRNAs can repress gene expression by more than 10-fold in the presence of three or more co-repressing miRNAs, but achieve little repression individually. This challenges previous models of miRNAs as subtle fine-tuners of gene expression, which may have underestimated miRNApotency by focusing on individual targets rather than those of cooperative groups." }, { "name": "Gandhi, Harshkooshal Kamlesh", "degree": "PhD", "year": "2026", "title": "Deep Stochastic Control for Regime-Dependent Utility Maximization Problems", "advisor": "Cvitani\u0107, Jak\u0161a", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222026-172512266", "creators": [ { "name": { "family": "Gandhi", "given": "Harshkooshal Kamlesh" }, "id": "Gandhi-Harshkooshal-Kamlesh", "orcid": "0000-0002-4624-2406", "display_name": "Gandhi, Harshkooshal Kamlesh" } ], "advisors": [ { "name": { "family": "Cvitani\u0107", "given": "Jak\u0161a" }, "id": "Cvitani\u0107-J", "orcid": "0000-0001-6651-3552", "role": "advisor", "display_name": "Cvitani\u0107, Jak\u0161a" } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Cvitani\u0107", "given": "Jak\u0161a" }, "id": "Cvitani\u0107-J", "orcid": "0000-0001-6651-3552", "role": "member", "display_name": "Cvitani\u0107, Jak\u0161a" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ebff-r716", "abstract": "We develop a unified framework for solving utility maximization problems (UMPs) in continuous-time stochastic control under high-dimensional, partially observed, and path-dependent uncertainty. Such settings arise in quantitative and engineering control problems where classical dynamic programming breaks down due to curse of dimensionality and non-Markovian structure. Our approach combines forward--backward stochastic differential equations (FBSDEs) with deep learning to construct scalable, simulation-based algorithms operating directly on trajectories. A central principle is the interplay between primal and dual formulations of stochastic control. We show that the duality gap, traditionally a post-hoc diagnostic, can be elevated to a principled driver of learning, yielding stable training and computable near-optimality. In regime-switching models, dynamic programming, convex duality and FBSDE representations yield a complete analytical and computational characterization. The framework extends to non-Markovian settings via filtering under latent regime uncertainty and functional It\\^{o} calculus for long-memory dynamics, with transformer-based architectures enabling efficient computation directly from trajectories. Structural correctness and adaptability is confirmed on classical engineering problems including the linear-quadratic regulator. Finally, we introduce a robust Minmax formulation under model ambiguity delivers algorithms that jointly learn optimal strategies and worst-case models. Overall, this work provides a unified, scalable approach to stochastic control in complex environments, bridging together modern machine learning and classical control theory for high-dimensional decision-making." }, { "name": "Gao, Angela Fang", "degree": "PhD", "year": "2026", "title": "Uncovering Hidden Structure in Data and the Physical World for Seismic Tomography and Beyond", "advisor": "Bouman, Katherine L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222026-052420973", "creators": [ { "name": { "family": "Gao", "given": "Angela Fang" }, "id": "Gao-Angela-Fang", "orcid": "0000-0001-8574-8728", "display_name": "Gao, Angela Fang" } ], "advisors": [ { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "advisor", "display_name": "Bouman, Katherine L." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Ross", "given": "Zachary E." }, "id": "Ross-Z-E", "orcid": "0000-0002-6343-8400", "role": "member", "display_name": "Ross, Zachary E." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." } ], "option_major": [ "cms" ], "doi": "10.7907/vcsd-dn14", "abstract": "Reliable and calibrated imaging strategies are essential for tackling challenging real-world imaging problems. Developing these strategies involves interdisciplinary approaches that translate inverse problem tooling into avenues for real scientific insight. However, raw scientific measurements present many challenges that modern imaging techniques do not adequately address. For instance, many state-of-the-art imaging methods struggle with seismic imaging problems due to several factors including non-linear forward models, uncalibrated noise, sensitivity to initial conditions, and limited angular observations. This thesis aims to overcome these challenges by presenting methods that image under uncertainty, leverage unconventional sources of regularization, and reshape the way we solve imaging inverse problems, ultimately enabling new scientific discoveries." }, { "name": "Garrett, David Christopher", "degree": "PhD", "year": "2026", "title": "Human-Scale Ultrasound, Thermoacoustic, and Photoacoustic Tomography", "advisor": "Wang, Lihong", "url": "https://resolver.caltech.edu/CaltechTHESIS:03092026-205538974", "creators": [ { "name": { "family": "Garrett", "given": "David Christopher" }, "id": "Garrett-David-Christopher", "orcid": "0000-0002-9747-8494", "display_name": "Garrett, David Christopher" } ], "advisors": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "advisor", "display_name": "Wang, Lihong" } ], "committee": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "chair", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "medeng" ], "doi": "10.7907/s8t2-qb10", "abstract": "Modern healthcare relies on imaging modalities that visualize internal anatomy and pathology. While X-ray computed tomography (CT) and magnetic resonance imaging (MRI) provide clinically useful imaging across many applications, they face significant barriers to more frequent use: ionizing radiation limits repeated CT scanning, and MRI\u2019s high cost and long acquisition times create access disparities. Conventional handheld ultrasonography enables rapid, low-cost imaging but remains limited by narrow fields of view, operator dependence, and challenging image interpretation. Photoacoustic tomography has emerged as a promising alternative that combines optical absorption contrast with acoustic detection, offering molecular specificity without ionizing radiation. However, conventional photoacoustic imaging remains limited to depths of several centimeters, inhibiting applications in deep-tissue imaging like gastrointestinal or whole-body assessment.
\r\n\r\nIn this thesis, we develop three approaches to extract clinically relevant information at human scales: ultrasound, thermoacoustic, and photoacoustic tomography. All three modalities leverage a custom 512-element, 60 cm diameter receiver array designed to detect acoustic signals across human-scale geometries. We validate these approaches through in vivo imaging, ex vivo tissue experiments, and phantom studies. First, we demonstrate ultrasound tomography of full human cross-sections in the abdomen and lower extremities, reconstructing backscatter contrast alongside quantitative maps of the speed of sound and attenuation coefficient. We show that ultrasound tomography enables visualization of features such as the liver, vasculature, muscle, and subcutaneous adipose across entire 2D human cross-sections. Second, we develop a thermoacoustic approach to guiding microwave ablation procedures. By modulating the microwave signal delivered through the probe, we record the generated thermoacoustic signals and use them to model the thermal dynamics during ablation. We show that this approach yields more accurate estimates of ablation zone geometry than standard look-up tables, which could allow for more precise ablation therapy. Third, we develop a method to extend the imaging depth of photoacoustic tomography using a wireless, ingestible capsule-based optical source. We demonstrate imaging depth up to 12 cm, which could open the door to photoacoustic imaging of regions like the gastrointestinal tract. Together, these approaches aim to expand the range of safe, informative, and accessible imaging modalities available to patients and clinicians.
" }, { "name": "Hossain, Azmain Abrawr", "degree": "PhD", "year": "2026", "title": "Atomic Layer Processing of Thin Film Superconductors for Superconducting Electronics", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03302026-202907452", "creators": [ { "name": { "family": "Hossain", "given": "Azmain Abrawr" }, "id": "Hossain-Azmain-Abrawr", "orcid": "0000-0002-8441-0183", "display_name": "Hossain, Azmain Abrawr" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "chair", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Kooi", "given": "Jacob W." }, "id": "Kooi-J-W", "orcid": "0000-0002-6610-0384", "role": "member", "display_name": "Kooi, Jacob W." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/pz9e-py53", "abstract": "State-of-the-art superconducting devices such as qubits, microwave kinetic inductance detectors (MKIDs), and superconducting-insulator-superconducting (SIS) mixers are fabricated using dry etching, typically reactive ion etching (RIE). The microwave performance of MKIDs and qubits is currently limited by interface and surface loss thought to arise from nanofabrication-induced damage and atmospheric exposure. For SIS mixers, it is important to fabricate layers with sub-nanometer etching precision and low surface roughness (< 0.5 nm). However, RIE is generally unable to meet these criteria due to the continuous nature of the etching process and the use of high energy ions. Additionally, RIE has been shown to lead to almost 10 nm of sub-surface damage, which can limit the performance of superconducting devices where the interfaces are critical to performance. In all of these devices, improving etch-depth control and achieving low surface roughness through a low-damage etching process is essential to improving state-of-the-art devices and enabling new device architectures.
\r\n\r\nIn this thesis, we investigate atomic layer processing techniques for thin-film metal nitride superconductors, namely atomic layer deposition (ALD) and atomic layer etching (ALE) being of special focus. ALD and ALE are nanofabrication methods capable of Angstrom-scale control and result in substantially less damage than standard methods such as RIE. Beyond ALD and ALE, we also develop and investigate a new plasma chemistry to etch magnesium diboride, which previously did not have a known chemical dry etch. We then use these techniques to fabricate superconductor-insulator-superconductor junctions and analyze their current-voltage characteristics.
" }, { "name": "Huang, Yu Xi (Max)", "degree": "PhD", "year": "2026", "title": "Signal in the Scatter: Advancing Speckle-Based Optical Sensing for Deep Cerebral Blood Flow Monitoring", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03102026-210243363", "creators": [ { "name": { "family": "Huang", "given": "Yu Xi (Max)" }, "id": "Huang-Yu-Xi-Max", "orcid": "0009-0000-0165-2084", "display_name": "Huang, Yu Xi (Max)" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Liu", "given": "Charles" }, "id": "Liu-Charles-Y", "orcid": "0000-0001-6423-8577", "role": "member", "display_name": "Liu, Charles" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/597j-zv94", "abstract": "This thesis presents the development and application of novel, non-invasive optical techniques for monitoring cerebral blood flow (CBF) and cerebral blood volume (CBV), addressing the critical need for cost-effective and scalable solutions in cerebrovascular health assessment. The research introduces advancements in interferometric speckle visibility spectroscopy (iSVS) and speckle contrast optical spectroscopy (SCOS) to overcome the challenges of signal attenuation and noise when measuring blood flow through the scalp and skull.
\r\n\r\nThe depth sensitivity of these optical methods was first experimentally determined. Using iSVS on phantoms, rabbits, and human subjects, a two-layer decay model was observed as the source-to-detector (S-D) distance was varied, allowing for the quantification of the transition point from superficial to cerebral signal detection. Complementing this, a multi-channel SCOS system was used with temporary occlusion of the superficial temporal artery to experimentally isolate and quantify the influence of scalp blood flow, providing direct evidence of brain-to-scalp signal sensitivity and establishing optimal S-D configurations.
\r\n\r\nAnother primary focus of this work was enhancing the signal-to-noise ratio (SNR) of deep-tissue measurements. A comprehensive theoretical framework for iSVS was developed to evaluate its SNR in the presence of detector noise, confirming its superiority in photon-limited regimes and revealing relaxed constraints on the reference beam. In parallel, a compact, fiber-free SCOS device was engineered, demonstrating a 70-fold increase in signal collection over traditional fiber-based systems with enhanced stability. The SNR for SCOS was further improved through an optimization-based, adaptive noise calibration framework that mitigates artifacts from cerebral blood volume fluctuations, significantly lowering the signal detection threshold for reliable CBF measurement.
\r\n\r\nBuilding upon these foundational advancements, the research progressed to clinical applications. The technology's modularity was demonstrated by engineering a portable, six-channel SCOS system for simultaneous, real-time measurements at multiple brain locations. This system was validated in a preliminary study on a patient with traumatic brain injury, demonstrating its potential for characterizing regional cerebrovascular dysfunction by comparing blood flow dynamics against structural MRI data. Furthermore, the compact SCOS device was used to assess stroke risk in a 50-person cohort by monitoring cerebrovascular reactivity during a breath-holding task; this revealed significant discrepancies between CBF and CBV responses that correlated with risk scores.
" }, { "name": "Jilani, Muhammad Musab", "degree": "PhD", "year": "2026", "title": "Dynamics of Microfabricated Enzyme Electrodes", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:08232025-011056106", "creators": [ { "name": { "family": "Jilani", "given": "Muhammad Musab" }, "id": "Jilani-Muhammad-Musab", "orcid": "0009-0008-0739-1418", "display_name": "Jilani, Muhammad Musab" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Petillo", "given": "Peter A." }, "id": "Petillo-Peter-A", "orcid": "0000-0001-7516-2221", "role": "member", "display_name": "Petillo, Peter A." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "medeng" ], "doi": "10.7907/5znv-n425", "abstract": "This work sets out to meet some of the demands created by advancements in glucose oxidase enzyme electrode fabrication techniques. The application of microfabrication techniques to enzyme electrodes has enabled not only greater control over enzyme geometry but also the possibility of monolithic low-power fully wireless implantable biosensors with sensor-on-CMOS construction. Such efforts must be guided by a strong grasp of the theory of diffusion-limited electrochemistry of the products of enzymatically catalyzed reactions. Low power requirements demand a full understanding of sensor turn-on transients and the reduced device size impacts diffusion phenomena and increases the importance of considerations such as oxygen recycling from the reaction at the working electrode. With analytical solutions to the nonlinear differential equations involved not forthcoming, there is a need for sophisticated simulation tools that build upon other efforts in the field and deliver novel capabilities. Such simulation tools must also be complemented by robust, convenient, reproducible, and ideally automated empirical measurement tools to enable the design-test-redesign iteration process to converge quickly to the desired outcomes.
\r\n\r\nThis work presents the development of finite element simulations of enzyme electrodes incorporating full two-substrate enzyme kinetics, a dynamic simulation of the sensor environment, and a full treatment of oxygen recycling at the working electrode. While the simulations presented in this work are carried out with axisymmetric RZ meshes, they are ready for use with full 3D meshes. It additionally presents the development of an automated wafer-scale measurement system enabling the testing of up to twenty sensors in parallel, still on the wafer on which they were fabricated. We present this with the hope that the ability to attack the problem from both sides --- better in silico simulation and faster and more controlled in vitro iteration --- should assist in the development of new sensing technologies.
\r\n\r\nWe also present selected results studied through the use of these tools, in particular the determination of the impact of enzyme geometry on sensor response. These results show the promise of thin-film deposition via spin-coating and vapor deposition crosslinking to enable the kind of fast response-time high-sensitivity electrodes that are needed for achieving monolithic wireless implantable biosensors.
" }, { "name": "Jimenez Rodriguez, Ivan Dario", "degree": "PhD", "year": "2026", "title": "Constructive Learning for Agile Underactuated Control", "advisor": "Yue, Yisong; Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01162026-051826165", "creators": [ { "name": { "family": "Jimenez Rodriguez", "given": "Ivan Dario" }, "id": "Jimenez-Rodriguez-Ivan-Dario-", "orcid": "0000-0002-7230-6733", "display_name": "Jimenez Rodriguez, Ivan Dario" } ], "advisors": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "co-advisor", "display_name": "Yue, Yisong" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "co-advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Culbertson", "given": "Preston" }, "id": "Culbertson-Preston", "orcid": "0000-0002-1403-8697", "role": "member", "display_name": "Culbertson, Preston" } ], "option_major": [ "cms" ], "doi": "10.7907/10aa-vg70", "abstract": "Learning-based methods have achieved remarkable performance in robotic control, yet providing formal guarantees for learned controllers remains an open challenge. The central question motivating this work is how control-theoretic structure can serve as an inductive bias for learning, producing controllers that are both flexible and certifiable.
\r\n\r\nThe key insight is that global properties such as stability and safety reduce to pointwise conditions that neural networks can learn to satisfy. A Lyapunov function certifies stability through a condition that must hold at every state in a region; a barrier function certifies safety through a condition that must hold throughout the safe set. Rather than optimizing over expensive trajectory rollouts, one can sample states and penalize violations of these pointwise conditions. If the conditions are satisfied throughout the relevant region of state space, the global guarantee follows.
\r\n\r\nThree complementary strategies are developed for integrating control structure with learning: training on pointwise certificate conditions, learning inputs to structured controllers that provide guarantees conditional on quantities like uncertainty estimates, and enforcing structure architecturally so that desired properties hold by construction. These strategies are validated on neural ordinary differential equations for certified stability and safety, stereo vision systems that learn perception uncertainty for safe quadruped navigation, and Koopman operator learning with guaranteed linear latent dynamics for predictive control of floating platforms.
\r\n\r\nThe primary application domain is underactuated legged locomotion. Zero dynamics, the residual dynamics that remain when controlled outputs have been driven to zero, provide a framework for coordinating actuated degrees of freedom with passive dynamics. A zero dynamics policy is a learned mapping from unactuated to actuated states that defines a stable invariant manifold. Theoretical results establish existence of such policies for locally controllable systems and prove that manifold stability implies full-state stability. Hardware experiments on a bipedal walker and a hopping robot validate these results: the hopper achieves over three thousand hops across stairs, ramps, and narrow bridges with robust disturbance rejection. These experiments demonstrate that control-theoretic structure and neural network learning can be combined to achieve both formal guarantees and robust physical performance.
" }, { "name": "Kim, Gihwan", "degree": "PhD", "year": "2026", "title": "Tailoring Tunable Interactions in Superconducting Circuits Using Many to No Modes", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152026-101519191", "creators": [ { "name": { "family": "Kim", "given": "Gihwan" }, "id": "Kim-Gihwan", "orcid": "0009-0009-3695-8118", "display_name": "Kim, Gihwan" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "chair", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Brandao", "given": "Fernando" }, "id": "Brand\u00e3o-F-G-S-L", "orcid": "0000-0003-3866-9378", "role": "member", "display_name": "Brandao, Fernando" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2td2-4z28", "abstract": "Tunable couplings are a central requirement for scalable quantum processing with superconducting quantum circuits. Practical quantum processors must dynamically reconfigure their interaction landscape to accommodate different quantum operations, including idle, single-qubit gates, two-qubit gates, readout, and reset, while maintaining high coherence and suppressing spurious couplings. While widely used tunable interaction approaches rely on single-mode mediation, they are often constrained by nearest-neighbor connectivity, limited on-off ratios, and stringent requirements on qubit frequency allocation.
\r\n\r\nThis thesis develops and studies novel strategies for tailoring tunable interactions by moving beyond single-mode mediation, spanning multimode engineered interactions and modeless interaction schemes (\"many to no modes\"), while accounting for realistic constraints in superconducting hardware. Using a microwave metamaterial waveguide realized by coupled resonator arrays, I demonstrate tunable dissipative interactions that allow on-demand, fast, and high switching-ratio photon emission from a transmon used as a multi-level quantum emitter. This capability is leveraged to achieve deterministic generation of multidimensional photonic cluster states, as well as unconditional reset and leakage reduction of frequency-tunable superconducting qubits.
\r\n\r\nComplementary to these multimode dissipative tunable interactions, this thesis also introduces architectures that realize tunable interactions mediated by many coherent modes or by no mediating modes. I discuss a long-range interaction scheme between superconducting dual-rail qubits mediated by spatially extended eigenmodes of a coupled-resonator array bus. Finally, I propose and analyze a novel modeless coupling architecture based on a SQUID coupler which provides intrinsic cross-Kerr interactions, enabling fast, hybridization-free CZ gates for far-detuned pairs, and discuss its implications for miniaturization of superconducting quantum processors.
" }, { "name": "Levin, Eitan", "degree": "PhD", "year": "2026", "title": "Any-Dimensional Data Science: Learning, Optimization, and Sampling", "advisor": "Chandrasekaran, Venkat; Tropp, Joel A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192026-033630765", "creators": [ { "name": { "family": "Levin", "given": "Eitan" }, "orcid": "009-0002-5789-4191", "display_name": "Levin, Eitan" } ], "advisors": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "advisor", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "co-advisor", "display_name": "Tropp, Joel A." } ], "committee": [ { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "chair", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/azc4-2j33", "abstract": "An exciting direction in computational math driven by recent trends in AI involves automating the solution process of entire problem classes. For example, algorithms for sophisticated data analysis tasks are increasingly being learned from training data instead of being designed by hand. There is also increasing interest in computationally producing proofs of mathematical theorems. However, computationally-derived algorithms and proofs, in sharp contrast to manually-designed ones, rarely generalize to inputs of size not seen during training. How can we train a model on inputs of a few small sizes, and generalize it to inputs of any other size? How can we computationally search over proofs of theorems that hold for objects of all sizes? This thesis develops foundations for tackling such any-dimensional problems by using random sampling maps to compare and summarize objects of different sizes. Our framework allows us to systematically derive finitely-parametrized families of functions that take inputs of any size, to prove inequalities between such functions, and to learn them from data. Our methodology leverages new de Finetti-type theorems and the recently-identified phenomenon of representation stability. We illustrate the resulting framework for any-dimensional problems in several applications." }, { "name": "Li, Jiahong", "degree": "PhD", "year": "2026", "title": "Multimodal Implantable Bioelectronics", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062026-201719589", "creators": [ { "name": { "family": "Li", "given": "Jiahong" }, "id": "Li-Jiahong", "orcid": "0000-0001-7938-9589", "display_name": "Li, Jiahong" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Zhang", "given": "Anqi" }, "id": "Zhang-Anqi", "orcid": "0000-0001-6121-8095", "role": "chair", "display_name": "Zhang, Anqi" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" } ], "option_major": [ "medee" ], "doi": "10.7907/a4af-sw77", "abstract": "Advances in bioelectronic technologies are transforming healthcare by enabling continuous monitoring and active modulation of physiological functions. However, conventional electronic materials are mechanically mismatched with soft biological tissues, which can lead to poor conformal contact, unstable signal acquisition, and adverse biological responses during long-term operation. This dissertation addresses these challenges through the development of multimodal bioelectronic systems that integrate soft materials, scalable fabrication strategies, and closed-loop therapeutic functionalities for next-generation health monitoring and intervention.
\r\n\r\nFirst, scalable fabrication strategies are developed to construct flexible and multimodal sensing platforms capable of detecting diverse physiological and environmental signals. Inkjet-printed sensor arrays incorporating nanomaterial-based electrochemical and physical sensors enable simultaneous measurement of temperature, pressure, and chemical biomarkers with high sensitivity and spatial resolution. These sensing systems can be integrated onto soft electronic skins and robotic platforms to provide real-time physicochemical perception in complex environments.
\r\n\r\nSecond, conformal bioelectronic interfaces are engineered to enable stable, long-term interactions with biological tissues. By tailoring material properties and device architectures, these interfaces achieve improved mechanical compatibility with soft tissues, facilitating reliable in vivo signal acquisition and stimulation while minimizing interfacial stress and biological reactions.
\r\n\r\nFinally, closed-loop bioelectronic systems are developed that combine continuous biosensing with responsive therapeutic stimulation. Integrated platforms capable of monitoring metabolic signals and triggering neuromodulation demonstrate the potential for automated therapeutic regulation. These systems highlight the feasibility of real-time physiological monitoring coupled with intelligent intervention.
\r\n\r\nTogether, the materials, device architectures, and system-level strategies presented in this dissertation establish a framework for scalable, conformal, and multifunctional bioelectronics. These technologies provide new opportunities for wearable and implantable systems capable of continuous health monitoring, autonomous therapy, and advanced human\u2013machine interfaces.
" }, { "name": "Luo, Ying", "degree": "PhD", "year": "2026", "title": "Near-Wake Structure and Dynamics of a Cylinder in Hypervelocity Flows", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03122026-190459583", "creators": [ { "name": { "family": "Luo", "given": "Ying" }, "id": "Luo-Ying", "orcid": "0009-0004-2832-7715", "display_name": "Luo, Ying" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/v935-3c96", "abstract": "The near-wake of a circular cylinder at hypersonic conditions was investigated experimentally to assess the influence of high stagnation enthalpy thermochemical effects on mean wake structure and near-wake dynamics. Experiments were conducted in the T5 Free-Piston Reflected Shock Tunnel and the Caltech Ludwieg Tube using high-speed schlieren and simultaneous focused laser differential interferometry and high-speed schlieren.
\r\n\r\nMean flow quantities, including the separation point, separation region size, shock angles, and neck width, were extracted from schlieren data. Relative to perfect-gas conditions, high stagnation enthalpy flow exhibited a downstream shift of the separation point and a reduction in the separation region size. These features retained a strong dependence on Reynolds number at high stagnation enthalpy. The recompression shock angle was found to be largely insensitive to key flow parameters, remaining approximately constant within experimental uncertainty, while the neck width decreased with increasing stagnation enthalpy and followed a Re-1/2 scaling consistent with laminar perfect gas behavior.
\r\n\r\nNear-wake dynamics were examined using power spectral density (PSD) analysis and Spectral Proper Orthogonal Decomposition (SPOD). A dominant shear layer frequency and a secondary frequency were identified in both facilities, with both remaining approximately constant along the shear layer. Although this frequency in high stagnation enthalpy flow was higher than that observed in perfect-gas experiments at similar Reynolds numbers, scaling by the shear layer length collapsed the data onto a Strouhal number consistent with previous studies.
\r\n \r\nPSD contours and SPOD modes at the dominant frequency revealed standing wave structures in the separation region and banded structures between the shear layer and the separation shock. SPOD, correlation analysis, and direct schlieren visualization revealed downstream-propagating disturbances consistent with the Kelvin Helmholtz instability, accompanied by waves indicative of Mach wave radiation; upstream-propagating waves between the shear layer and the separation shock, originating near the neck and hypothesized to be associated with upstream-traveling acoustic disturbances within the recirculation region; and stationary standing wave structures. These observations are consistent with a resonant aeroacoustic feedback mechanism in which downstream-propagating instabilities generate acoustic waves that travel upstream through the recirculation region and perturb the shear layer at separation. The physical origin of the secondary frequency remains uncertain; the data are analyzed in the context of existing theories to evaluate their consistency with current observations, although further data are required for conclusive identification.
" }, { "name": "Mandralis, Ioannis M.", "degree": "PhD", "year": "2026", "title": "Leveraging Aerial Transformation for Enhanced Air\u2013Ground Robotic Mobility", "advisor": "Gharib, Morteza; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11032025-192332480", "creators": [ { "name": { "family": "Mandralis", "given": "Ioannis M." }, "id": "Mandralis-Ioannis-M", "orcid": "0000-0001-5270-0672", "display_name": "Mandralis, Ioannis M." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "chair", "display_name": "Ames, Aaron D." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/srg8-sx98", "abstract": "Ground-aerial robots can extend endurance, versatility, and robustness by combining wheeled motion with flight, yet many flying-rolling robot designs add actuators that increase weight and reduce efficiency. Morphobots mitigate this by using multi-purpose actuators and body shape change to switch modes on the ground, but unpredictable vehicle-ground interactions can be an obstacle to robust operation. This dissertation develops the Aerially Transforming Morphobot (ATMO), a quadcopter that reconfigures in flight to land on wheels, enabling reliable air-ground transitions, mode switching without the hindrances of ground-morphing, and improved agility. We present ATMO\u2019s design and performance characterization, analyze its dynamics\u2013revealing transformation-induced couplings incompatible with standard quadcopter control\u2013and introduce a model-predictive control framework that stabilizes ATMO through aerial transformation to execute dynamic transitions. We then compare this approach with a learning-based controller that uses deep reinforcement learning for end-to-end morpho-transition, validating both experimentally. Finally, we revisit ATMO\u2019s design using aerodynamic principles to expand morphing flight through wake vectoring, showing that passive structures in the rotor wake substantially increase available thrust authority. Overall, we demonstrate that aerial shape change improves agility and reliability, highlighting a new direction for research in ground-aerial robotics." }, { "name": "McHaffie, Daniel Brendan", "degree": "PhD", "year": "2026", "title": "Computational and Data-Driven Discovery of Li Solid-State Electrolytes: From Representation to Experimental Realization", "advisor": "See, Kimberly", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072025-232922980", "creators": [ { "name": { "family": "McHaffie", "given": "Daniel Brendan" }, "id": "McHaffie-Daniel-Brendan", "orcid": "0000-0002-7265-7584", "display_name": "McHaffie, Daniel Brendan" } ], "advisors": [ { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "advisor", "display_name": "See, Kimberly" } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" } ], "option_major": [ "matsci" ], "doi": "10.7907/fn7h-vz84", "abstract": "Improvements in energy storage are required to facilitate the transition to renewable energy and the electrification of transport. Lithium-ion batteries (LIBs) are a promising solution, but the current leading chemistry, consisting of a layered oxide cathode and a graphite anode separated by a liquid electrolyte, has been optimized to near-theoretical limits. Replacing the graphitic carbon with Li metal would significantly improve energy density but the instability of the Li metal-electrolyte interface introduces performance and safety challenges. Using a solid-state electrolyte (SSE) to construct an all-solid-state battery (ASSB) could mitigate these issues. However, an ideal SSE material has yet to be identified.
\r\n \r\nThousands of known Li-containing materials have not yet been evaluated as SSEs. Data-driven methods could prioritize materials for experimental study but have historically lacked sufficient data and optimal representations. Chapter 2 presents the largest structure-ionic conductivity database to date and uses semi-supervised learning to determine the highest-performing descriptors. From ~26,000 Li-containing materials, 212 candidates are identified and screened using semi-empirical and first-principles calculations. Li3BS3 exhibits ionic conductivity above 10-3 S cm-1 with defect engineering through substitution and mechanical milling.
\r\n \r\nChapter 3 explores Cl, Al, and Si substitution in Li3BS3 to reveal mechanisms of ionic conductivity enhancement. At low substitution levels, conductivity improvements are driven by disordered environments from reduced crystallinity and microstructural effects. For Cl and Al, higher substitution generates fully amorphous phases with ionic conductivity above 10-4 S cm-1. Sufficient Si substitution produces novel crystalline phases with conductivities exceeding 10-3 S cm-1.
\r\n \r\nPrevious approaches, such as that in Chapter 2, could not represent disordered compounds, excluding much of the training data and candidate materials. This is particularly significant given the importance of disorder highlighted in Chapters 2 and 3 and the prevalence of disorder in known superionic conductors. Chapter 4 implements a transfer-learned graph representation compatible with disordered structures. A larger database is curated and used to train models for screening all known Li-containing materials. Experimental validation of superionic conductivity in an identified candidate demonstrates the utility of this graph-based approach for discovering experimentally relevant, high-performance materials.
" }, { "name": "Mizrahi, Oren Simon", "degree": "PhD", "year": "2026", "title": "Flexible Phased Arrays: Challenges & Opportunities", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:04072026-222438150", "creators": [ { "name": { "family": "Mizrahi", "given": "Oren Simon" }, "id": "Mizrahi-Oren-Simon", "orcid": "0000-0003-4271-8822", "display_name": "Mizrahi, Oren Simon" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "chair", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2bt7-3961", "abstract": "The history of technological progress can be seen through the lens of an interplay between utility and form factor: new applications inspire and/or demand new form factors, which in turn enable new applications, etc. This has long been the trajectory of antenna systems and phased arrays, which have scaled in form factor and broadened in adoption over the last century. Phased arrays currently straddle two regimes: highly scaled down for portable device compatibility or scaled up for array gain and complex functionality. Flexible phased arrays may be the next form factor to enable new applications: space solar power generation, high-bandwidth satellite communications, and others. However, challenges imposed by an array's flexibility, including radiator design, phase synchronization, and demonstrated viability, hinder the widespread adoption of flexible phased arrays. This thesis offers solutions to these challenges and discusses the opportunities flexible phased arrays offer for the future." }, { "name": "Mori Carroll, Alex Takuya", "degree": "PhD", "year": "2026", "title": "Thermochemical Modeling for Giant Planet Entry Flows", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292026-075758798", "creators": [ { "name": { "family": "Mori Carroll", "given": "Alex Takuya" }, "id": "Mori-Carroll-Alex-Takuya", "orcid": "0009-0003-0365-9142", "display_name": "Mori Carroll, Alex Takuya" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Brandis", "given": "Aaron M." }, "id": "Brandis-Aaron-M", "role": "member", "display_name": "Brandis, Aaron M." }, { "name": { "family": "Cruden", "given": "Brett A." }, "id": "Cruden-B-A", "orcid": "0000-0002-0634-3691", "role": "member", "display_name": "Cruden, Brett A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/z852-3v08", "abstract": "The four giant planets, Jupiter, Saturn, Uranus, and Neptune, contain most of the mass and angular momentum of our planetary system and thus are believed to have played a critical role in the formation and evolution of our solar system. Additionally, the giant planets represent the most frequently observed class of exoplanets, and therefore present a relatively accessible analog for exoplanetary research. Despite this, the giant planets are the least studied in our solar system. Our knowledge of them is primarily based on remote sensing from Earth-based observatories and space telescopes, which have inherent limitations when compared to in situ probe measurements. For these reasons, future probe missions to the giant planets have been identified as top priorities for the planetary science community.
\r\n\r\nThe upper atmospheres of the giant planets are primarily composed of gaseous hydrogen (H\u2082) and helium (He). During atmospheric entry, a shock wave forms in front of the probe. Under the high temperatures found in the post-shock region, H\u2082 molecules dissociate and H atoms become electronically excited, eventually ionizing to form protons and electrons. To predict heat loads and design mass-efficient thermal protection systems, it is necessary to model each of these non-equilibrium thermochemical processes accurately. The primary objective of this thesis is to investigate the thermochemistry of H\u2082/ He shock layers and to develop accurate yet computationally-efficient kinetic models for future giant planet probe missions.
\r\n\r\nFirst, a novel one-temperature diatomic dissociation model is developed to capture thermal non-equilibrium and non-Boltzmann effects for H\u2082 dissociation. In particular, the rovibrational state-specific master equations are used to derive macroscopic chemical source term and rovibrational energy expressions that are valid in all three key limits/ regimes of dissociation-dominated flows, i.e., the thermal equilibrium limit, the quasi-steady-state (QSS) regime, and the pre-QSS regime.
\r\n\r\nNext, optimal fits for H\u2082 dissociation rate constants are developed through a comprehensive literature review of available experimental and computational data. This includes data from high-temperature shock tube experiments (2,000 to 8,000 K), low-temperature discharge-flow tube experiments (below 350 K), and ab initio computational studies.
\r\n\r\nThen, a detailed literature review of the electronic excitation and ionization rate constants of atomic H (by both electron and heavy-particle impact) is performed. Using the best estimates of these rate constants along with the newly developed H\u2082 dissociation model, an 11-species thermochemical model with state-specific kinetics for atomic H is developed. To validate the kinetic model, 1-D steady shocks are simulated using a space-marching code that explicitly accounts for shock tube boundary layer effects. The resulting radiance profiles are compared to experimental data from the NASA Ames Electric Arc Shock Tube (EAST) facility, and are found to reproduce the measured values reasonably accurately while capturing the distinct induction zone behavior observed in the experiments.
\r\n\r\nFinally, a reduced-order non-Boltzmann kinetic model for H ionization is constructed using an analogous QSS framework to the one developed for diatomic dissociation. This model reproduces the majority of the results of the state-specific H ionization model, despite treating H as a single bulk species in the flowfield calculations.
" }, { "name": "Nicolov, Andr\u00e9", "degree": "PhD", "year": "2026", "title": "A Song of Ice and Plasma: The Formation and Behavior of Ice-Dusty Plasmas, from the Laboratory to the Edge of the Universe", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:11172025-005933174", "creators": [ { "name": { "family": "Nicolov", "given": "Andr\u00e9" }, "id": "Nicolov-Andr\u00e9", "orcid": "0000-0002-1197-4148", "display_name": "Nicolov, Andr\u00e9" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "orcid": "0000-0003-0787-1610", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/adns-n036", "abstract": "Much of the universe is partially ionized by stellar radiation, x-rays, or cosmic rays, forming weakly-ionized plasma. Many of these environments are also extremely cold, from Earth\u2019s upper atmosphere to planetary rings, protoplanetary disks, and interstellar clouds. Within these conditions, small grains of ice and dust can form and acquire electric charge by collecting free electrons and ions from the plasma.
\r\n \r\nThis thesis investigates these ice-dusty plasmas in the laboratory, observing the nucleation, growth, and dynamics of water-ice grains within extremely cold plasma. It details the construction and operation of a steady-state radio-frequency plasma in which the electrodes are cryogenically cooled by tandem cryostats; water vapor injected into the plasma spontaneously nucleates into ice grains which grow in dendritic fractal shapes to millimeters in length. Their electric charges confine them to the plasma, where they exhibit complex dynamics such as vortices, lattices, and instabilities.
\r\n\r\nNotably, ice grains nucleate homogeneously within the plasma: OH\u207b and H\u2083O\u207a ions, formed by reactions between water vapor and free electrons, attract water molecules via ion-dipole interactions to produce stable, electrically-charged molecule clusters that rapidly grow into ice grains. This process occurs regardless of the ice phase: amorphous ice forms at lower temperatures and transitions irreversibly to crystalline ice at higher temperatures or over time, mirroring processes seen in solar system ices. Further experiments reveal that the complex dynamics of the cloud of ice grains are strongly influenced by their fractal morphology, as the scaling laws of their masses, surface areas, and electric charges are vastly different during fractal growth. This allows them to strongly couple with ambient gas, enhancing momentum transfer between the grains and their surroundings and significantly increasing their charge-to-mass ratio.
\r\n\r\nThis research offers critical insights into the formation and behavior of ice grains in ionized environments, with wide-ranging implications across astrophysics, materials science, and plasma technology. Understanding these processes in a controlled laboratory setting offers a window into complex phenomena across the cosmos.
" }, { "name": "Sheng, Shawn JiaXiang", "degree": "PhD", "year": "2026", "title": "An Experimental Characterization of Atmospheric Turbulence Effects on Millimeter Wave Propagation in a Controlled Environment", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:11262025-191857258", "creators": [ { "name": { "family": "Sheng", "given": "Shawn JiaXiang" }, "id": "Sheng-Shawn-JiaXiang", "orcid": "0009-0004-5478-7184", "display_name": "Sheng, Shawn JiaXiang" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "orcid": "009-0002-2156-967X", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Cooper", "given": "Ken B." }, "id": "Cooper-Kenneth-Brian", "orcid": "0000-0001-9826-7157", "role": "member", "display_name": "Cooper, Ken B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/7sbc-5v10", "abstract": "Atmospheric turbulence significantly affects electromagnetic (EM) wave propagation, especially at millimeter-wave (mmWave) frequencies, resulting in scintillation. Developing a statistical channel model to characterize these effects is crucial for accurate prediction and mitigation across various applications. In radar and satellite systems, turbulence can degrade signal quality and reduce accuracy. As telecommunications advance toward higher EM frequencies, turbulence will significantly influence signal performance. Moreover, statistical analysis of a propagating EM wave provides a unique opportunity for the remote sensing of atmospheric turbulence dynamics. The push towards an improved understanding of the planetary boundary layer on a global scale motivates the development of next generation measurement techniques.
\r\n\r\nThis thesis presents a novel approach for studying and characterizing the physical effects of atmospheric turbulence on mmWave propagation in a controlled laboratory environment. The method combines theoretical modeling and experimental validation to link meteorological parameters and turbulence dynamics to the scintillation effects on the power spectrum of a radio frequency (RF) signal. The experimental setup employs a versatile fan array wind tunnel to generate repeatable and controllable turbulent flows. A W-band (95GHz) transceiver is used to propagate EM energy through the turbulent flow, with the received signal analyzed to characterize the effects of turbulence-induced scintillation. Additional components include utility heaters for generating strong temperature gradients, a thermal screen and infrared camera to measure the temperature profile of the flow with high spatial resolution, a high-speed anemometer for turbulence spectrum characterization, and barometers and hygrometers for pressure and humidity measurements.
\r\n\r\nThe effects of temperature gradients and wind speeds are shown to increase and shift the power spectrum of the RF signal across multiple turbulent scales. Meteorological and RF measurements are directly linked through an empirical model that builds upon existing theoretical frameworks to accurately determine flow dynamics based on the characteristics of the received signal. The results are shown to be consistent and repeatable across multiple days, ambient conditions, and experimental configurations. Improvements and future directions are discussed, including extending this experimental setup to practical applications and leveraging the controllability to develop more sophisticated models that advance the understanding of scintillation.
" }, { "name": "Sisler, Jared", "degree": "PhD", "year": "2026", "title": "Electrically Tunable Optical Active Metasurfaces in Space\r\nand Time", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:03252026-010757636", "creators": [ { "name": { "family": "Sisler", "given": "Jared" }, "id": "Sisler-Jared", "orcid": "0000-0002-0660-7909", "display_name": "Sisler, Jared" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/qr45-5670", "abstract": "Controlling the properties of light in space and time is fundamental to many areas of science and engineering. In recent years, actively tunable metasurfaces have enabled dynamic and precise manipulation of the wavefront of light in a compact form-factor, paving the way for a revolution in optics and photonics. This thesis furthers our understanding of such active nanophotonic devices and experimentally presents advanced control over light using two distinct material platforms: indium tin oxide (ITO) and liquid crystals (LCs). The conclusions from this work will enable the design and fabrication of more sophisticated active optical devices.
\r\n\r\nWe start with an introduction to metasurfaces by providing a brief history of their development and the physics of their operation. We then outline the subfield of active metasurfaces and provide the relevant background for the remainder of this thesis.
\r\n\r\nChapter 2 continues with a detailed background on ITO by summarizing its properties, common deposition methods, and methods of characterization. We then provide an in-depth analysis of how the properties of ITO can be changed through annealing in different material environments. This underpins much of the work that is presented in Chapters 3--5 of this thesis.
\r\n\r\nUsing the principles introduced in Chapter 2, we present a method to create precisely defined lateral doping gradients in a thin film of ITO. Our process selectively dopes regions of ITO via patterning a low-quality oxide layer on top of a planar film of ITO, followed by a low temperature (150 \u00b0C) anneal and the removal of the evaporated Al\u2082O\u2083. We fabricate reflective gratings of varying periodicity and demonstrate plasmonic guided modes in an unpatterned film of ITO. This work paves the way for ITO films to be integrated in more complex photonic devices such as on-chip modulators and free-space metasurfaces, as well as furthering our understanding of the material and optical properties of ITO.
\r\n\r\nNext, we demonstrate an ITO-based electrically tunable reflective metasurface in the midwave-infrared (mid-IR). This device operates by electrically modulating the carrier concentration in ITO when placed in a gap plasmon resonator to control the phase and amplitude of scattered light across a surface. Through appropriate electrical and optical design, we demonstrate the polarization-independent tunable diffraction of light in two dimensions (2D). This device represents a significant step forward for solid-state beam-steering devices in the mid-IR which are essential to applications such as thermal imaging and gas sensing.
\r\n\r\nIn Chapter 5, we experimentally show the electrical spatiotemporal modulation of an ITO-based metasurface in the near-infrared (near-IR) for the generation and tunable diffraction of high frequency signals. In this work, we use a similar device design as was used to demonstrate mid-IR beam-steering. We first modulate our device with frequencies up to 10 MHz to generate sidebands offset from the near-IR incident laser frequency. Through temporal waveform engineering, we generate select sidebands of interest and suppress unwanted sidebands. Finally, by spatially varying the time-delay of the temporal modulation, we can diffract --- or normally reflect --- each generated frequency. This device paves the way towards active metasurfaces for multi-beam, multi-frequency functionalities such as free-space optical communication.
\r\n\r\nFinally, we present a highly transmissive active metasurface enabling polarization rotation of near-IR light in 2D using a LC infiltrated titanium dioxide (TiO\u2082) metasurface. Our device consists of a subwavelength periodic array of TiO\u2082 nanopillars submerged in a thin (2 \u03bcm) LC layer and supports electric and magnetic dipole modes. Using a biased photoactive top contact, we spatially control the polarization rotation of transmitted light in 2D through the patterning of a 435 nm pump laser on the surface of the device. This work represents a significant contribution to LC-based optical devices through the detailed modeling of LC interactions with TiO\u2082 nanostructures to enable the efficient modulation of a large-area active metasurface.
\r\n\r\nThis thesis presents many aspects of materials fabrication, characterization, and modeling which are fundamental to the development of the next generation of active photonic devices.
" }, { "name": "Sleeman, Michael Kenneth Elliott", "degree": "PhD", "year": "2026", "title": "Nonlinear Disturbance Evolution in Boundary Layers Using the One-Way Navier-Stokes Equations", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:08132025-212958945", "creators": [ { "name": { "family": "Sleeman", "given": "Michael Kenneth Elliott" }, "id": "Sleeman-Michael-Kenneth-Elliott", "orcid": "0000-0001-5949-9289", "display_name": "Sleeman, Michael Kenneth Elliott" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/wwv8-v242", "abstract": "Laminar-turbulent transition prediction for boundary-layer flows is a pacing item in engineering design. This work extends the one-way Navier Stokes (OWNS) equations to support nonlinear interactions between waves of different frequencies which enables nonlinear disturbance evolution in spatially-developing shear flows, with the goal of predicting transition for a reduced computational cost relative to direct numerical simulation (DNS). The OWNS approach linearizes the Navier-Stokes equations about a user-specified equilibrium solution, and then evolves disturbances to the equilibrium solution by solving a spatial initial-value problem in the frequency domain. OWNS yields a reduced computational cost compared to global linear stability analysis, while also conferring numerous advantages over the parabolized stability equations (PSE) that we seek to extend to nonlinear OWNS (NOWNS). We validate NOWNS for two- and three-dimensional disturbances to a low-speed Blasius boundary layer by comparing to DNS results from the literature. We further demonstrate that NOWNS can be used to for transition prediction since it accurately predicts the onset of laminar-turbulent transition in low-speed boundary-layer flows, relative to DNS. Subsequently, we extend the approach to high-speed boundary-layer flows, where we apply it to study oblique-wave breakdown of Mack's first and second modes. Finally, we formulate a greedy algorithm for choosing optimal OWNS recursion parameters, which achieves rapid error convergence and a net decrease in computational cost compared to previous approaches to recursion parameter selection." }, { "name": "Smith, Richard Daniel", "degree": "PhD", "year": "2026", "title": "Techniques Toward the Wafer-Scale Fabrication of Enzyme-Based Sensors", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:02042026-041427925", "creators": [ { "name": { "family": "Smith", "given": "Richard Daniel" }, "id": "Smith-Richard-Daniel", "orcid": "0000-0001-9384-105X", "display_name": "Smith, Richard Daniel" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "member", "display_name": "Roukes, Michael Lee" } ], "option_major": [ "eleceng" ], "doi": "10.7907/b6e8-ws51", "abstract": "Wafer-scale fabrication of transducers directly on CMOS dies can minimize device size, increase the throughput and improve uniformity. Doing so with materials sensitive to the conditions encountered during typical microfabrication processes, such as enzymes, remains a challenge.
\r\n\r\nThis thesis investigates aspects of the performance and fabrication processes of electrochemical enzyme-based glucose-sensing transducers, intended for monolithic, implantable wireless sensors. The described work builds on past efforts in the Scherer group and focuses on the transducer fabrication compatible with CMOS wafers.
\r\n\r\nIn the first part, the pre-existing, enzyme-film lift-off patterning process is analyzed. The electrochemical processes of the three glucose oxidase-platinum electrodes are first investigated for the use in sensor diagnostics. The topography of the film is then related to the geometry of the patterns and to the performance of these transducers. Modifications are then made to reduce variation and improve yield. A process to optically profile such structures was also developed to better interpret the non-uniformity from thin film interference.
\r\n\r\nThe second part of this thesis describes the development and processing for plasma etch patterning the enzyme films. This aims to separate the uniformity of the film deposition from the definition of the boundaries, as occurs in many microfabrication processes with less sensitive materials. Strategies were developed that limit the optical, thermal, and chemical degradation of the enzyme activity. The resulting process demonstrated the feasibility of dry etch patterning functional enzyme films without loss of activity. Further, it clarified that improved structural uniformity can yield improved performance uniformity.
\r\n\r\nA final, tangential section investigates a positive tone electron beam lithography process that can be entirely performed in vacuum. Myo-inositol, an electron beam sensitive material, was unexpectedly found and refined. Dry processed negative tone resists avoid pattern collapse during wet development, but analogous positive-tone processes remain elusive. Myo-inositol films, deposited with thermal evaporation, were exposed with electron beams and then developed by subsequent heating. With dry etching and plasma stripping, the full dry process could be implemented in a vacuum cluster tool. While early in development and with challenges remaining, sub 100 nm features were transferred into an underlying thin metal film with this process.
" }, { "name": "Sonar, Sameer Anil", "degree": "PhD", "year": "2026", "title": "A High-Efficiency, Low-Noise Platform for Microwave-to-Optical Quantum Transduction", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06272025-211326959", "creators": [ { "name": { "family": "Sonar", "given": "Sameer Anil" }, "id": "Sonar-Sameer-Anil", "orcid": "0000-0002-1082-9360", "display_name": "Sonar, Sameer Anil" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/1cbe-vs09", "abstract": "Quantum computing platforms based on superconducting qubits have achieved remarkable progress in recent years, with significant advancements in quantum error correction, coherence times, and gate fidelities. However, the path to large-scale, fault-tolerant quantum computing faces a critical scaling bottleneck: the physical limits of single-chip architectures. Integrating millions of qubits on a single superconducting chip presents formidable engineering challenges, including increased thermal load, crosstalk, and complex wiring within the dilution refrigerator.
\r\n\r\nA promising approach to overcome these limitations is to interconnect multiple smaller superconducting quantum processors via a quantum network, allowing for distributed quantum computation. In this context, telecom-wavelength optical photons (around 1550 nm or 200 THz) are particularly attractive for transmitting quantum information across long distances due to their low propagation loss in optical fiber and negligible thermal occupation at room temperature. However, superconducting qubits typically operate at microwave frequencies (around 5-10 GHz), leading to a fundamental mismatch in operating frequencies that prevents direct coupling between these two domains.
\r\n\r\nThis five-orders-of-magnitude frequency mismatch poses a major challenge for coherent quantum transduction, requiring a highly efficient, low-noise interface to faithfully convert quantum states between microwave and optical photons. A leading approach for transduction involves piezo-optomechanical platforms, where an intermediary acoustic resonator facilitates the conversion between microwave photons and microwave acoustic phonons, which are then converted to optical photons. However, existing designs often suffer from poor conversion efficiency and added noise due to geometric constraints and substrate heating, limiting their scalability for real-world quantum networks. In the first part of this thesis, I will introduce an optimized two-dimensional optomechanical crystal platform with a side-coupled optical waveguide. This geometry significantly improves the noise-efficiency metric for optical photon-acoustic phonon conversion. I will then discuss the integration of piezo-acoustic circuits into these two-dimensional crystals to realize a full microwave-to-optical transducer. I will cover the underlying design principles, fabrication processes, and preliminary measurement results, highlighting the potential of this platform for enabling future quantum communication and distributed quantum computing.
\r\n\r\nAnother critical challenge in quantum networking is the frequency mismatch that arises when attempting to interfere photons emitted by different quantum nodes. This mismatch is primarily caused by variations in fabrication processes. In the second part of this thesis, I will present a novel post-fabrication tuning technique for piezo-optomechanical transducers, based on atomic force microscope (AFM) nano-oxidation. By applying a voltage bias to the AFM tip, we can selectively oxidize the surface of the dielectric device, introducing a controlled, localized change in refractive index and mechanical properties. This allows for precise tuning of both optical and acoustic resonance frequencies. I will demonstrate the effectiveness of this technique through experimental results at both room and cryogenic temperatures, highlighting its potential for scaling quantum networks.
" }, { "name": "Toledo Barrios, Patricia Amanda", "degree": "PhD", "year": "2026", "title": "Multiscale Response of Granular Materials under Cyclic Shear: Packing State, Force Chains, and Stress Transmission", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05122026-171140300", "creators": [ { "name": { "family": "Toledo Barrios", "given": "Patricia Amanda" }, "id": "Toledo-Barrios-Patricia-Amanda", "orcid": "0009-0000-2018-7616", "display_name": "Toledo Barrios, Patricia Amanda" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Shaikeea", "given": "Angkur" }, "id": "Shaikeea-Angkur-J", "orcid": "0000-0002-6706-0492", "role": "chair", "display_name": "Shaikeea, Angkur" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/eydy-1z48", "abstract": "Granular materials are widely encountered in natural and engineered systems, yet their behavior under cyclic loading remains difficult to predict because bulk response emerges from complex grain-scale interactions. Repeated loading can produce irreversible deformation, history dependence, and evolving internal load-transfer mechanisms that are not fully captured by macroscopic measurements alone. Although cyclic behavior has been studied extensively at the continuum scale, direct experimental characterization of the grain-scale processes governing cyclic response remains limited.
\r\n\r\nThis thesis investigates the multiscale behavior of dry, cohesionless granular materials subjected to quasi-static cyclic simple shear loading through laboratory experiments coupled with the Granular Element Method (GEM), a mechanics-based force-inference framework for estimating interparticle contact forces from experimentally measurable grain-scale data. An experimental framework was developed by upgrading an existing simple shear apparatus to enable controlled cyclic loading and by integrating imaging, tracking, and post-processing methods for multiscale measurements.
\r\n\r\nAt the macroscale, the experiments show that cyclic simple shear produces direction-dependent and history-dependent behavior. Repeated loading generates asymmetric stress and deformation responses, incomplete recovery of the initial state, and progressive changes that depend on packing condition and confinement level. Densely packed and loosely packed assemblies exhibit qualitatively different cyclic responses, while normal confinement primarily influences the strength and persistence of those responses.
\r\n\r\nAt the grain-scale, the results show that cyclic behavior is governed largely by the reorganization of the internal force network rather than by large changes in overall contact connectivity. Force chains evolve continuously with loading direction and cycle history, while anisotropy plays a central role in linking internal structure to bulk shear resistance. Dense systems initially develop stronger, more coherent load-bearing structures that weaken with repeated cycling, whereas loose systems deform via more distributed force transmission and progressive compaction.
\r\n\r\nOverall, this work provides a mechanistic framework for understanding how granular materials accumulate history, weaken, and reorganize under repeated shear. The combined experimental and GEM results also provide benchmark data to calibrate and validate physics-based particle models for broader granular systems and relevant engineering applications.
" }, { "name": "Tong, Xin", "degree": "PhD", "year": "2026", "title": "Advanced Imaging with Sound and Light: Photoacoustic Tomography and Quantum Microscopy", "advisor": "Wang, Lihong", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192026-220300004", "creators": [ { "name": { "family": "Tong", "given": "Xin" }, "id": "Tong-Xin", "orcid": "0000-0003-2002-5638", "display_name": "Tong, Xin" } ], "advisors": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "advisor", "display_name": "Wang, Lihong" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" } ], "option_major": [ "medee" ], "doi": "10.7907/013f-vd31", "abstract": "Optical imaging enables visualization of biological structure and function but is fundamentally limited by several physical constraints. Spatial resolution is bounded by optical diffraction, depth penetration is curtailed by strong absorption and scattering in tissue, and image contrast-to-noise ratio is often restricted by photon shot noise in low-light conditions. This thesis advances two novel directions\u2014photoacoustic imaging and quantum imaging\u2014to address these limitations.
\r\n \r\nIn photoacoustic imaging, we design and optimize high-speed photoacoustic computed tomography systems that enable deep, volumetric visualization of vasculature. By incorporating time-gated reconstruction and image-enhancement algorithms, these systems support small-animal imaging of cardiac structure, liver morphology, and brain hemodynamics non-invasively. Building on these foundations, we explore non-invasive breast photoacoustic imaging with high spatiotemporal resolution. Through integration with learning-based feature extraction, classification, and segmentation pipelines, we demonstrate the feasibility of applying photoacoustic imaging in clinical workflows to aid the characterization of breast tissue.
\r\n \r\nIn quantum imaging, we develop two complementary architectures that extend the state of the art in opposite but synergistic directions. The scanning quantum microscope scales up existing quantum imaging approaches, achieving the largest resolvable pixel counts to date by combining entangled-photon illumination with efficient coincidence detection. This platform enables the first demonstration of whole-organism imaging and shows potential in remote sensing and sub-shot-noise imaging. In contrast, the widefield quantum microscope scales down quantum imaging to the microscopic regime, integrating single-photon\u2013sensitive cameras with a covariance-based coincidence estimation algorithm. This approach enables cellular-level imaging and demonstrates quantum-enhanced resolution beyond the classical diffraction limit, establishing a practical pathway for quantum microscopy in biological imaging.
\r\n \r\nAcross both research directions, this thesis advances system design and engineering, quantitative characterization, calibration, reconstruction, and image-enhancement methodologies. Together, these developments establish pathways from physical principles to practical imaging systems, spanning laboratory prototypes through preclinical and clinical applications in biomedical imaging.
" }, { "name": "Wang, Canran", "degree": "PhD", "year": "2026", "title": "Smart Bandages for Chronic Wound Sampling, Monitoring, and Management", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05012026-185528615", "creators": [ { "name": { "family": "Wang", "given": "Canran" }, "id": "Wang-Canran", "orcid": "0000-0003-3297-9041", "display_name": "Wang, Canran" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Demirer", "given": "Gozde S." }, "id": "Demirer-G\u00f6zde-S", "orcid": "0000-0002-3007-1489", "role": "chair", "display_name": "Demirer, Gozde S." }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "member", "display_name": "Newman, Dianne K." }, { "name": { "family": "Mazmanian", "given": "Sarkis K." }, "id": "Mazmanian-S-K", "orcid": "0000-0003-2713-1513", "role": "member", "display_name": "Mazmanian, Sarkis K." }, { "name": { "family": "Zhang", "given": "Anqi" }, "id": "Zhang-Anqi", "orcid": "0000-0001-6121-8095", "role": "member", "display_name": "Zhang, Anqi" } ], "option_major": [ "medee" ], "doi": "10.7907/cq9y-x940", "abstract": "Chronic wounds are a major global health issue, incurring staggering economic costs and severely impacting patient well-being. Effective exudate management is crucial, yet current methods fail to balance moisture levels. Real-time analysis of biomarkers like reactive oxygen and nitrogen species could guide treatment, but existing systems lack the capacity required for continuous monitoring. Although wearable electronics have the potential to advance wound care, efficient management and analysis of wound exudate in real time remains challenging owing to its low secretion rate and complex composition. To address these issues, we introduce iCares, a wearable device for wound exudate management and continuous in situ analysis of crucial wound biomarkers. iCares contains a flexible nanoengineered sensor array that measures key reactive species such as NO, H\u2082O\u2082, and O\u2082, along with pH and temperature, providing multiparameter data to inform wound status. The device features a pump-free triad microfluidic modules with a superhydrophobic\u2013superhydrophilic Janus membrane, bioinspired wedge channels, and 3D graded micropillars for efficient unidirectional exudate collection, transport, and refreshing. The sensors demonstrate consistent response and analyte selectivity, validated in wound exudate. Rapidly manufacturable through advanced printing and laser-patterning techniques, iCares seamlessly integrates Bluetooth connectivity and enables scalable, wireless, long-term continuous reactive species monitoring without impeding daily activities. The iCares system was validated through in vivo testing in murine models of infection and fasting, where real-time monitoring was performed. In addition, clinical evaluation was conducted in 20 patients with chronic wounds, as well as in patients monitored before and after surgery, demonstrating the system\u2019s applicability across diverse wound conditions. iCares offers early infection detection and wound classification and outcome prediction using machine learning-enhanced data analysis." }, { "name": "Wang, Guanzhi", "degree": "PhD", "year": "2026", "title": "Building Foundation Agents with Internet Knowledge and Large Language Models", "advisor": "Gkioxari, Georgia; Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:01132026-015239964", "creators": [ { "name": { "family": "Wang", "given": "Guanzhi" }, "id": "Wang-Guanzhi", "orcid": "0009-0004-1921-1796", "display_name": "Wang, Guanzhi" } ], "advisors": [ { "name": { "family": "Gkioxari", "given": "Georgia" }, "id": "Gkioxari-Georgia", "role": "co-advisor", "display_name": "Gkioxari, Georgia" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "co-advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "chair", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Gkioxari", "given": "Georgia" }, "id": "Gkioxari-Georgia", "role": "member", "display_name": "Gkioxari, Georgia" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Fan", "given": "Jim" }, "id": "Fan-Jim", "role": "member", "display_name": "Fan, Jim" } ], "option_major": [ "cms" ], "doi": "10.7907/r2ax-s535", "abstract": "Autonomous agents that perceive, reason, and interact with the world promise a future where intelligent systems assist with daily activities, support work in homes and factories, and take on labor-intensive or repetitive tasks across diverse environments. Tremendous progress has been made across embodied AI, from self-driving cars and autonomous drones to whole-body locomotion and dexterous manipulation, yet building generalist agents that learn continually, generalize broadly, and operate reliably in open-world settings remains an open challenge. Modern systems face three key limitations: the scarcity and cost of collecting large-scale interactive experience; the difficulty of grounding high-level goals into long-horizon behavior; and the fragmentation of perception, language understanding, and motor control across modular, separately trained components.
\r\n\r\nThis dissertation explores a unified and scalable recipe for building foundation agents. The core premise is that internet-scale multimodal data, large language models as the embodied reasoning engine, and unified Vision-Language-Action (VLA) architectures together provide a powerful path toward open-ended embodied intelligence. First, internet-scale multimodal data, including gameplay videos, human activity datasets, online tutorials, and wiki documentation, offers unprecedented breadth, exposing agents to diverse strategies, affordances, and environment configurations that cannot be replicated through controlled robotic data collection alone. Second, large language models provide a flexible cognitive layer for planning, task decomposition, iterative self-improvement, tool use, reward generation, and continual skill acquisition without parameter updates. Third, VLA models unify perception, language grounding, and continuous low-level action, enabling fluid real-time behavior across simulation, gaming environments, and physical robotic platforms, while transferring effectively across task families and embodiments.
\r\n\r\nBy integrating these three components, this dissertation advances the development of embodied agents that can draw upon internet-scale knowledge, reason through language, and translate abstract plans into physical behavior. Together, these ideas aim to move us closer to general, open-ended agents that operate with the reliability, adaptability, and competence required to assist humans across a wide range of real-world tasks.
" }, { "name": "Wang, Yingjin", "degree": "PhD", "year": "2026", "title": "Additive Manufacturing and Characterization of Micro-Architected Lithium-ion Battery Electrodes", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04272026-182608505", "creators": [ { "name": { "family": "Wang", "given": "Yingjin" }, "id": "Wang-Yingjin", "orcid": "0009-0002-1239-3422", "display_name": "Wang, Yingjin" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/tkgq-7c28", "abstract": "Electrode structure is closely coupled with mechanical behavior, ion transport, and reaction uniformity during battery operation. In addition to conventional slurry-cast electrodes, emerging fabrication approaches provide new opportunities to study and design electrode architectures. This thesis investigates lithium-ion battery electrodes through two complementary perspectives related to the electrode structure: micro-scale mechanical characterization to elucidate degradation mechanisms and additive manufacturing of three-dimensional (3D) micro-architected electrodes to investigate structure-transport relationships.
\r\n\r\nIn Chapters 2 and 3, the mechanical behavior of lithium-ion battery electrodes was investigated using nanoindentation and micro-pillar compression experiments. State-of-charge-dependent mechanical properties of electroplated LiCoO2 (LCO) cathodes were quantified, revealing a decreasing tendency in elastic modulus and hardness during delithiation, which is attributed to the expansion of LCO layered structure. Fracture toughness distribution across the electrode thickness was analyzed to understand how structural heterogeneity contributes to the mechanical property landscape. In addition, we studied the deformation of lithium-based composite anodes, confirming that the Li/Na composite anode exhibits higher deformability at the electrode-electrolyte interface, which enhances interfacial contact.
\r\n\r\nThe interconnected pore structure and large surface-to-volume ratio of 3D architected battery electrodes render them promising for enhancing electrochemical performance via more efficient ionic transport. In Chapters 4 and 5, we develop a hydrogel infusion additive manufacturing (HIAM)-based approach to fabricate micro-architected LiFePO4 (LFP)/C composite electrodes with feature sizes down to 18 \u00b5m. The concomitant formation of carbon within the lattice enhances the mechanical strength, which preserves shape integrity of the 3D structure during cell assembly and function. We designed electrodes with different geometries, including tilted cubes, honeycombs, and triply periodic minimal surfaces (TPMS), to probe the influence of geometric factors on electrochemical performance under various charge-discharge rates. We propose an experimentally informed electrochemical model that demonstrates the roles of Li+ transport in the electrolyte and Li+ diffusion in the electrode in determining the utilization of active materials. This work introduces a versatile manufacturing platform for printing 3D battery components and provides insights into structure optimization for high-performance rechargeable batteries.
" }, { "name": "Wang, Yixuan", "degree": "PhD", "year": "2026", "title": "Singularity Formation: Synergy in Theoretical, Numerical and Machine Learning Approaches", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05042026-111930796", "creators": [ { "name": { "family": "Wang", "given": "Yixuan" }, "id": "Wang-Yixuan", "orcid": "0000-0001-7305-5422", "display_name": "Wang, Yixuan" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Hoffmann", "given": "Franca" }, "id": "Hoffmann-Franca", "orcid": "0000-0002-1182-5521", "role": "member", "display_name": "Hoffmann, Franca" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/gf82-wx70", "abstract": "This thesis develops numerical and theoretical approaches for understanding and analyzing singularity formation in Partial Differential Equations (PDEs). The singularity formation in the Navier-Stokes Equation (NSE) is famously challenging as one of the seven Clay Prize problems. Unlike simpler equations such as the Nonlinear Heat (NLH) or Keller-Segel (KS) equations, where formal asymptotics near blowup are better understood, the intrinsic complexity of NSE makes quantitative analytical treatment difficult, if not impossible, without numerical guidance.
\r\n\r\nBuilding on numerical insights, Chapter 2, 3 and 4 introduce a robust analytical framework to simplify and systematize pen-and-paper proofs for singular PDEs. We present a novel approach based on enforcing vanishing modulation conditions for perturbations around approximate blowup profiles, complemented by singularly weighted energy estimates. Blowups are proven with a clear notion of stability, with rates automatically inferred, without the need to know the asymptotics a priori or explicit spectral information of the linearized operator. We demonstrate the efficacy of our method on PDEs with complicated asymptotics, such as NLH and the Complex Ginzburg-Landau (CGL) equation, and address the open problem of singularity formation in the 3D KS equation with logistic damping. We also provide a roadmap for extending our techniques to singularities involving multiple scales.
\r\n\r\nIn Chapter 5 and 6, we develop and refine numerical approaches that facilitate deeper insights into singularity formation. We demonstrate that machine learning methods significantly enhance our capability to identify and characterize potential blowup solutions with high precision. We improve on existing Physics-Informed Neural Network (PINN) and Neural Operator (NO) frameworks. Moreover, we present a novel machine learning paradigm, the Kolmogorov-Arnold Network (KAN) architecture, whose interpretability and excellent scaling properties are achieved through learnable nonlinearities inspired by the Kolmogorov-Arnold representation theorem.
\r\n \r\n \r\nChapter 7 introduces Exponential Multiscale Finite Element Method (ExpMsFEM), developed to efficiently solve challenging multiscale PDEs beyond elliptic problems, such as the Helmholtz equation. We construct adaptive local bases, proving exponential convergence theoretically and demonstrating superior computational performance in practice. Like KAN, ExpMsFEM exemplifies how insights from theory can guide the design of high-performance solvers with theoretical guarantees.
" }, { "name": "Wu, Ailec", "degree": "PhD", "year": "2026", "title": "Enabling Technologies and Algorithms for Antenna Arrays", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:03302026-100637929", "creators": [ { "name": { "family": "Wu", "given": "Ailec" }, "id": "Wu-Ailec", "orcid": "0009-0008-7726-7842", "display_name": "Wu, Ailec" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/wram-da27", "abstract": "Phased arrays provide high angular resolution, efficient spatial power combining, and dynamic electronic beam-steering; although there are many applications of phased arrays, there are considerable challenges in their realization. This thesis summarizes the author's work in developing a novel phased array calibration method to address timing and synchronization challenges in phased arrays, as well as work exploring the usage of phased arrays in wireless power transfer in the context of the Caltech Space Solar Power Project. First, the calibration method is described, which involves usage of amplitude-only sensor placed in the proximal field of the array's radiators: to obtain array phase information from these sensors, machine learning is used to solve the phase retrieval problem generated from sensor raw data. Then the satellite payload producing the first in-orbit wireless power transfer demonstration is described. Finally, a method to address areal power matching issues between photovoltaic and wireless power transfer subsystems is described." }, { "name": "Wu, Zihui", "degree": "PhD", "year": "2026", "title": "Learning to Sample in Computational Imaging: Measurement Acquisition and Posterior Estimation", "advisor": "Bouman, Katherine L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09062025-050711919", "creators": [ { "name": { "family": "Wu", "given": "Zihui" }, "id": "Wu-Zihui", "orcid": "0000-0002-7622-3548", "display_name": "Wu, Zihui" } ], "advisors": [ { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "advisor", "display_name": "Bouman, Katherine L." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Song", "given": "Yang" }, "id": "Song-Yang", "orcid": "0000-0003-3193-1679", "role": "member", "display_name": "Song, Yang" } ], "option_major": [ "cms" ], "doi": "10.7907/j42z-s192", "abstract": "Many problems in science and engineering require visualizing objects that are not directly observable\u2014such as black holes that are millions of light-years away from the Earth or internal anatomical structures hidden within the human body. Computational imaging is a powerful paradigm that combines sensor design with advanced computational algorithms to make the invisible visible. The typical computational imaging pipeline involves first collecting indirect measurements of the target object and then solving a reconstruction problem. This thesis focuses on two core challenges about sampling along this pipeline: (1) optimizing the sampling process for measurement acquisition, and (2) sampling the posterior distribution of possible reconstructions given noisy measurements.
\r\n\r\nThe first part of the thesis investigates how to design adaptive and task-specific acquisition strategies for computational imaging systems, with a focus on compressed sensing magnetic resonance imaging (CS-MRI). We propose a sequential sampling method that learns to select measurements in multiple stages, and an approach that tailors sampling patterns for specific downstream tasks such as region-of-interest reconstruction, segmentation, and classification. These methods enable a better selection of measurements taken during acquisition, leading to improved performance compared to conventional baselines. We have also implemented our learned sequences on a real MRI scanner and verified their improvement in practice.
\r\n\r\nThe second part of the thesis develops a principled framework for posterior sampling using diffusion models (DMs)\u2014a state-of-the-art class of generative models. By revealing a key connection between DMs and the Split Gibbs Sampling, we introduce a posterior sampling method that rigorously incorporates pre-trained DMs as image priors for solving inverse problems, which exhibits strong performance on a variety of applications. We then show that this framework can be naturally extended into a series of instantiations for solving more general inverse problems, addressing topics like text conditioning, video inverse problems, non-differentiable forward models, and discrete-space sampling. We also present a comprehensive benchmark for systematically evaluating state-of-the-art DM-based posterior estimation methods.
\r\n\r\nBy leveraging machine learning to address challenges in both data acquisition and posterior estimation, this thesis provides new possibilities for building more intelligent and reliable imaging systems across science and engineering.
" }, { "name": "Yu, Kevin", "degree": "PhD", "year": "2026", "title": "Degradation Mechanisms of Oxide Ceramics Under Molten Regolith Electrolysis Conditions", "advisor": "Faber, Katherine T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12042025-001904943", "creators": [ { "name": { "family": "Yu", "given": "Kevin" }, "id": "Yu-Kevin", "orcid": "0000-0003-3130-4309", "display_name": "Yu, Kevin" } ], "advisors": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "advisor", "display_name": "Faber, Katherine T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "matsci" ], "doi": "10.7907/41bv-7696", "abstract": "Molten regolith electrolysis (MRE) is a promising in situ resource utilization process that produces both metals and O2 through the direct electrolysis of molten lunar regolith (dirt), in support of a permanent human presence on the Moon. However, MRE requires an operational temperature of 1600\u00b0C, involves contact with corrosive molten regolith, and causes an oxidizing atmosphere during electrolysis. These conditions prevent the usage of many refractory materials due to rapid degradation. Moreover, there are additional challenges associated with MRE, such as bubble detachment and O2 collection at the anode.
\r\n\r\nIn this thesis, a hollow anode design, composed of an oxygen-conducting yttria-stabilized zirconia (YSZ) shell and a platinum current collector, is presented to address the challenges of MRE. Research is performed to evaluate the performance of YSZ electrolytes and containment materials in the extreme MRE environment and identify the mechanisms governing their degradation. From these experiments, a laboratory-scale MRE cell is designed and fabricated to support hollow anode testing. Electrolysis experiments with lunar regolith simulants successfully demonstrate sustained oxygen production for up to 12 hours. Extended testing with a degradation mitigation strategy further increases O2 production efficiencies and enables cumulative operation of 40 hours, establishing design life estimates for YSZ hollow anodes and guidelines for integration into industrial-scale MRE systems.
\r\n\r\nA previously unreported Sc2O3-rich phase, silicon aluminum scandate (SAS), is discovered while performing materials compatibility testing. The crystal structure of SAS is solved using microcrystal electron diffraction, and its material properties are characterized. These results indicate that SAS is an entropy-stabilized oxide with potential applications as a thermally insulating, refractory oxide material.
\r\n\r\nUltimately, the work presented demonstrates the feasibility of YSZ hollow anodes for MRE and expands the understanding of ceramic behavior in molten oxide environments. The successful production of O2 with a hollow anode provides a foundation for scaling MRE toward industrial operation on the lunar surface, while the discovery of SAS highlights the potential for uncovering new oxide materials in extreme environments.
" }, { "name": "Yuksel, Mert", "degree": "PhD", "year": "2026", "title": "Interactions of Intrinsic Quantum Defects with a Nanoelectromechanical System", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechTHESIS:08262025-210340378", "creators": [ { "name": { "family": "Yuksel", "given": "Mert" }, "id": "Yuksel-Mert", "orcid": "0000-0002-4141-464", "display_name": "Yuksel, Mert" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Dykman", "given": "Mark" }, "id": "Dykman-Mark", "orcid": "0000-0003-3996-7932", "role": "member", "display_name": "Dykman, Mark" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3ypf-a284", "abstract": "Nanoelectromechanical systems (NEMS) resonators operating in the quantum regime provide a powerful platform for investigating mechanical motion at its most fundamental level. Their intrinsic ability to couple to environmental degrees of freedom, along with the long coherence times of their mechanical excitations (phonons), makes them particularly promising for quantum information and sensing applications. However, in this regime, the performance of NEMS resonators are predominantly affected by intrinsic material defects, acting as two-level systems (TLS). These quantum defects, ubiquitous in solid-state quantum devices at low temperatures, can exchange energy with their host field, causing dissipation and noise. Despite these dominant effects, the microscopic origin of such quantum defects is still unknown, and their interactions with phononic devices have been elusive.
\r\n\r\nHere, we present a detailed investigation into these interactions between quantum defects and phonons within piezoelectric lithium niobate NEMS resonator shielded by phononic crystals. We identify TLS defects as the primary source of excess noise at millikelvin temperatures, limiting their performance and sensitivity. By controlling the TLS frequency in situ with the application of electric field---and strain field due to piezoelectricity---we demonstrate strong resonant coupling between a mechanical mode of our NEMS resonator and a single, intrinsic TLS. Varying the resonant drive and/or temperature allows controlled ascent of the nonequidistant energy ladder and reveals the dressed states of the hybridized system. Fluctuations of the TLS on and off resonance with the mode induces switching between dressed and bare states; this elucidates the complex quantum nature of TLS-like defects in mesoscopic systems. We demonstrate that individual TLS defects can be precisely controlled and manipulated, transforming them from detrimental dissipation and noise sources into valuable quantum resources. The ability to harness this intrinsic nonlinearity of a nanomechanical resonator with quantum defects offers new directions towards quantum sensing and information.
" }, { "name": "Zellinger, Michael J.", "degree": "PhD", "year": "2026", "title": "White Elephants and Cash Cows: Economically Wrangling the Zoo of AI Models", "advisor": "Thomson, Matthew; B\u00fchlmann, Peter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07282025-205651638", "creators": [ { "name": { "family": "Zellinger", "given": "Michael J." }, "id": "Zellinger-Michael-J", "orcid": "0009-0001-7499-148X", "display_name": "Zellinger, Michael J." } ], "advisors": [ { "name": { "family": "Thomson", "given": "Matthew" }, "id": "Thomson-M-W", "orcid": "0000-0003-1021-1234", "role": "advisor", "display_name": "Thomson, Matthew" }, { "name": { "family": "B\u00fchlmann", "given": "Peter" }, "id": "B\u00fchlmann-Peter", "orcid": "0000-0002-1782-6015", "role": "co-advisor", "display_name": "B\u00fchlmann, Peter" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Thomson", "given": "Matthew" }, "id": "Thomson-M-W", "orcid": "0000-0003-1021-1234", "role": "member", "display_name": "Thomson, Matthew" }, { "name": { "family": "B\u00fchlmann", "given": "Peter" }, "id": "B\u00fchlmann-Peter", "orcid": "0000-0002-1782-6015", "role": "member", "display_name": "B\u00fchlmann, Peter" } ], "option_major": [ "cms" ], "doi": "10.7907/xj31-xm14", "abstract": "The capabilities of artificial intelligence are rapidly expanding, but deploying AI systems in practice still poses significant challenges. Specifically, practitioners find limited guidance on selecting the most suitable AI model for a concrete use case, balancing the economics of an AI deployment, and managing the risk of AI errors. These challenges call for a unified framework addressing pain points in a conceptually clear and statistically sound manner. In this thesis, we present several components of such a framework: 1) uncertainty-aware system optimization, 2) economic evaluation, 3) error reduction with human-in-the-loop, and 4) a proof-of-concept system for synthetic data generation. Our work presents novel technical and conceptual approaches for orchestrating natural language-based systems, advancing the economical and reliable deployment of artificial intelligence." }, { "name": "Zhou, Haowen", "degree": "PhD", "year": "2026", "title": "Synergizing Microscopy, Computation, and Artificial Intelligence to Advance Biomedical Research", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252026-183244369", "creators": [ { "name": { "family": "Zhou", "given": "Haowen" }, "id": "Zhou-Haowen", "orcid": "0000-0003-0955-4010", "display_name": "Zhou, Haowen" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "chair", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Wei", "given": "Lu" }, "id": "Wei-Lu", "orcid": "0000-0001-9170-2283", "role": "member", "display_name": "Wei, Lu" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0d6t-py79", "abstract": "Over the past century, microscopy has evolved significantly through advances in hardware design. However, pushing the boundaries of imaging performance using purely optical and mechanical innovations has become increasingly challenging. Meanwhile, the rapid growth in computational power has transformed the way we process and analyze imaging data, enabling a paradigm shift in microscopy. By offloading complexity from hardware to algorithms, computational microscopy -- a rising interdisciplinary field -- offers a powerful approach to simplify system design, correct aberrations, and extract more information from data. In this thesis, I will explore how computational techniques, including artificial intelligence, can enhance modern imaging systems and image analysis for biomedical research.
\r\n\r\nThis thesis develops physics-informed computational frameworks that extend the capabilities of optical imaging systems. By embedding physics models directly into reconstruction algorithms, I show how computational approaches can overcome traditional limitations in resolution and depth-of-field, through case studies in Fourier ptychographic microscopy and single-shot volumetric fluorescence imaging.
\r\n\r\nIn addition to reconstructions, this thesis advances analytic solutions with customized optical designs that leverage physical insight to enable robust, efficient, and automated microscopy. By identifying and exploiting principles in wave optics, analytic methods are developed for high-performance autofocusing and optimization-free volumetric refractive index imaging. These approaches improve robustness across imaging modalities.
\r\n\r\nFinally, this thesis demonstrates how artificial intelligence can be integrated with microscopic imaging to enable clinically relevant inference. Deep learning models are applied to digitized histopathology slides to predict progression risk in early-stage non-small-cell lung cancer patients, achieving performance that exceeds expert-level assessment. Beyond predictive accuracy, the models are systematically analyzed to identify the spatial feature scales that drive their predictions.
" }, { "name": "Aller, Brayden Gieschen", "degree": "PhD", "year": "2025", "title": "Strain Sensing in Thin Composite Laminates with Embedded Fiber Bragg Grating Sensors", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05012025-194857973", "creators": [ { "name": { "family": "Aller", "given": "Brayden Gieschen" }, "id": "Aller-Brayden-Gieschen", "orcid": "0000-0002-5258-4154", "display_name": "Aller, Brayden Gieschen" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "member", "display_name": "Watkins, Michael M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/zj2k-h305", "abstract": "Deployable structures are popular for space applications as they enable large, complex spacecraft structures to overcome the size constraints of launch vehicle fairings. Such structures are increasingly manufactured out of thin (< 200 \u03bcm thick) composite laminates as they have a high stiffness-to-weight ratio, the ability to withstand high curvatures during stowage, and the potential for self-deployment using stored strain energy. To ensure the reliability of these thin composite spacecraft structures in operation, it is of interest to be able to continuously monitor their internal strain state to detect potential changes or damage that may compromise their integrity.
\r\n \r\nAlthough there are a number of potential sensors that could be used for this, fiber Bragg grating (FBG) sensors are especially well suited for this task and have a track record of successfully monitoring both composite materials and large aerospace structures. However standard size FBG sensors, which have a cladding diameter of 125 \u03bcm, are too large to be integrated into the thin composite structures of interest. To overcome this, we worked with several suppliers to develop and manufacture ultra-thin FBG sensors (< 30 \u03bcm cladding diameter) for this work that are able to be successfully embedded into thin composite laminates.
\r\n\r\nThe primary objective of this thesis was to investigate the suitability of ultra-thin FBG sensors for the monitoring of strain changes in thin composite spacecraft structures. To this end, the work in this thesis first investigated how to best embed ultra-thin FBG sensors to be able to measure the internal strain changes of interest while minimizing their disruptions to the surrounding laminates. Second, mechanical testing was performed to assess the effect that the embedded ultra-thin FBG sensors have on the mechanical properties of thin laminates. Third, the ability of these sensors to detect and monitor for strain changes in thin composite laminates was assessed through further mechanical testing. Finally, the effects of temperature on ultra-thin FBG sensors were studied experimentally.
\r\n\r\nThrough this work, which was done at the coupon level, we sought to demonstrate the ability of these ultra-thin FBG sensors to monitor for strain changes in thin composite laminates and their potential for the health monitoring of thin composite spacecraft structures. It is our hope that our findings in this thesis help lay the groundwork for the future implementation of these sensors in not only thin composite spacecraft structures, but to many other composite materials and aerospace structures as well.
" }, { "name": "Armstrong, Stephen Lowell", "degree": "PhD", "year": "2025", "title": "Effects of Disorder on Quantum Phase Transitions and Quantum Dynamics", "advisor": "Rosenbaum, Thomas F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012025-033851773", "creators": [ { "name": { "family": "Armstrong", "given": "Stephen Lowell" }, "id": "Armstrong-Stephen-Lowell", "orcid": "0000-0001-7325-4763", "display_name": "Armstrong, Stephen Lowell" } ], "advisors": [ { "name": { "family": "Rosenbaum", "given": "Thomas F." }, "id": "Rosenbaum-T-F", "orcid": "0009-0008-6152-666X", "role": "advisor", "display_name": "Rosenbaum, Thomas F." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Alicea", "given": "Jason F." }, "id": "Alicea-J", "orcid": "0000-0001-9979-3423", "role": "member", "display_name": "Alicea, Jason F." }, { "name": { "family": "Jackson", "given": "Jennifer M." }, "id": "Jackson-J-M", "orcid": "0000-0002-8256-6336", "role": "member", "display_name": "Jackson, Jennifer M." }, { "name": { "family": "Rosenbaum", "given": "Thomas F." }, "id": "Rosenbaum-T-F", "orcid": "0009-0008-6152-666X", "role": "member", "display_name": "Rosenbaum, Thomas F." } ], "option_major": [ "matsci" ], "doi": "10.7907/yeaq-w360", "abstract": "We present experimental studies of the effects of disorder on the quantum phase transitions of antiferromagnetic LiErF\u2084 and of the dynamic behavior of LiHo0.2Y0.8F\u2084, which hosts a spin glass ground state due to the combination of substitutional disorder and magnetic frustration. Both compounds are insulating dipolar-coupled magnets that can be effectively treated as spin \u00bd systems.
\r\n\r\nTwo distinct quantum phase transitions can be induced in the easy-plane antiferromagnet LiErF\u2084, applying a magnetic field in the plane or perpendicular to it. The isotopic distribution of natural Er permits us to probe these transitions in the clean and dirty regimes. 167Er has a natural abundance of 23% and is the only stable isotope with a non-zero nuclear spin. At low temperatures, the nuclear spin slaves to the electronic spin and reduces the effective field felt by the electronic spin, thereby inducing random mass disorder in the dirty (low-temperature) regime. We use specific heat measurements to identify the temperature scale of the crossover between the dirty and clean regime as T=150 mK, and make ac magnetic susceptibility measurements to characterize the effects of disorder on the two quantum phase transitions. When the field is applied along the c-axis, the critical behavior is consistent with a violation of the Harris criterion in the clean regime and a change of universality class in the dirty regime. When the field is applied along the a-axis, the critical behavior is unchanged by the crossover between clean and dirty regimes.
\r\n\r\nWe use ac susceptibility measurements to conduct thermal memory dip experiments on the spin glass state of LiHo0.2Y0.8F\u2084 in zero magnetic field and find no apparent rejuvenation or memory. We perform an analogous \u201cquantum memory dip\u201d measurement which uses a transverse magnetic field rather than temperature to enter the spin glass state, and we find strong rejuvenation. The relaxation rate of the susceptibility decreases as the transverse field increases. This counterintuitive result is attributed to an increase in the variance of the random longitudinal field associated with increasing the transverse field and is supported by simulations. Finally, we perform a \"negative field cycle\" experiment which finds erasure of memory in the spin glass state. We establish a theoretical framework of quantum resonant tunneling to explain our results, rather than the conventional picture of a hierarchical free energy landscape associated with classical spin glasses.
" }, { "name": "Arun, Rahul", "degree": "PhD", "year": "2025", "title": "Beyond Symmetry: Normality-Based Analysis of Velocity Gradients in Turbulent Flows", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302025-232647443", "creators": [ { "name": { "family": "Arun", "given": "Rahul" }, "id": "Arun-Rahul", "orcid": "0000-0002-5942-169X", "display_name": "Arun, Rahul" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Lozano-Dur\u00e1n", "given": "Adri\u00e1n" }, "id": "Lozano-Duran-A", "orcid": "0000-0001-9306-0261", "role": "chair", "display_name": "Lozano-Dur\u00e1n, Adri\u00e1n" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3py1-wj85", "abstract": "Small-scale turbulence is a hallmark of countless natural and engineered flows. Its features are often described and modeled using the velocity gradient tensor (VGT), which is conventionally decomposed into the (symmetric) strain-rate tensor and the (antisymmetric) vorticity tensor. Although this symmetry-based decomposition has found use in areas such as vortex identification and closure modeling, it provides limited insight into local flow structure. A more refined description can be obtained by further distinguishing the normal and non-normal parts of the VGT. The resulting normality-based decomposition identifies contributions associated with normal straining (symmetric/normal), rigid rotation (antisymmetric/normal), and pure shearing (non-normal). We use this decomposition to identify flow features that are obscured by symmetry-based analyses yet have significant implications for efforts to understand and model turbulent flows.
\r\n\r\nWe first demonstrate that partitioning the strength of velocity gradients using our normality-based approach can distinguish between different regimes in various turbulent flows. In wall-bounded flows, the near-wall partitioning is dominated by shearing whereas the partitioning far from the wall collapses onto the partitioning associated with isotropic turbulence. In an unbounded vortex ring collision, our analysis distinguishes the initial vortex rings, which have a strong imprint from rigid rotation, from the decaying turbulent cloud produced by their collision, for which the partitioning is similar to that of isotropic turbulence. It also identifies enhanced shear\u2013rotation correlations as a distinctive fingerprint of the elliptic instability during transition, which can be interpreted using relevant geometric features of local streamlines. By deriving algebraic expressions for the partitioning constituents in terms of the invariants of the VGT and an additional parameter, which represents the alignment of shear vorticity with the local rotation axis, we identify a key facet of our analysis that goes beyond previous analyses of the VGT.
\r\n\r\nWe then apply our normality-based framework to filtered velocity gradients in direct and large-eddy simulations of isotropic turbulence. Our analysis enables shear layers, which are associated with shear vorticity, to be distinguished from vortex cores, which are associated with rigid rotation, in a multiscale setting. It reveals that filtering mitigates the relative contribution of shear layers in the subinertial range of the energy cascade. Moreover, it identifies crucial (yet perhaps overlooked) contributions from shear layers to fundamental energy transfer mechanisms, including strain self-amplification, vortex stretching, and backscatter associated with strain\u2013vorticity covariance. The dominant role of shear layers in the backscatter mechanism suggests that they contribute significantly to the bottleneck effect in the subinertial range of the cascade. Our analysis of large-eddy simulation data shows that they also amplify the artificial bottleneck effect produced by an eddy viscosity model in the inertial range. This reflects that the eddy viscosity model mimics an unfiltered direct numerical simulation at a lower Reynolds number. A mixed model can be used to mitigate the artificial bottleneck effect since it more accurately mimics a filtered direct numerical simulation.
" }, { "name": "Ballouz, Eric", "degree": "PhD", "year": "2025", "title": "Resolvent Analysis of Non-Stationary Turbulent Flows and Transient Flow Phenomena", "advisor": "Bae, H. Jane", "url": "https://resolver.caltech.edu/CaltechTHESIS:03102025-172015248", "creators": [ { "name": { "family": "Ballouz", "given": "Eric" }, "id": "Ballouz-Eric", "orcid": "0009-0003-7034-1898", "display_name": "Ballouz, Eric" } ], "advisors": [ { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "advisor", "display_name": "Bae, H. Jane" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Lozano-Duran", "given": "Adrian" }, "id": "Lozano-Duran-A", "orcid": "0000-0001-9306-0261", "role": "member", "display_name": "Lozano-Duran, Adrian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" } ], "option_major": [ "mecheng" ], "doi": "10.7907/t9sw-b215", "abstract": "In this work, we develop a wavelet-based formulation of resolvent analysis in order to extend the method to transient phenomena and non-stationary flows. We apply this method in two ways: first, to analyze systems that were not previously amenable to traditional resolvent analysis, and second, to probe the limits of the resolvent forcing modes' \"optimality\" in a nonlinear simulation as well as investigate the mechanisms that suppress their effectiveness. In wavelet-based resolvent analysis, the Navier-Stokes equations are linearized about a mean profile, Fourier-transformed in the homogeneous directions, and wavelet-transformed in time. The nonlinear terms are represented as forcing terms acting on the system, and a maximally perturbing forcing mode and the response it produces are then computed for this linear system. The wavelet formulation enables the forcing and response modes to represent transient trajectories. By windowing the wavelet-based resolvent operator, we can also compute optimal forcing modes restricted to a time-localized pulse along with their transient response.
\r\n\r\nFor the first application of the method, we use the windowing approach to study bursting in channel flow. The optimal response mode grows and decays in time scales that match turbulent data, and we show that this optimal burst exploits the Orr mechanism.\r\nWe also study channel flow subjected to a spanwise pressure gradient. The corresponding resolvent modes mirror the mean flow and gradually realign themselves according to the new flow conditions. More interestingly, they exhibit a collapse of the lift-up mechanism during this realignment, which offers an explanation to the depletion of tangential Reynolds stresses in the turbulent system.
\r\n\r\nFor the second application of the method, we inject time-localized resolvent forcing modes for the minimal flow unit into a simulation of the system, at different intensities. The principal resolvent forcing mode is much more effective than a randomly generated forcing structure at amplifying the near-wall streak. For initial times and close to the wall, the turbulent minimal flow unit matches the principal response mode well, but due to nonlinear effects, the response decays prematurely. By computing the nonlinear energy transfer to secondary scales, we find that the breakdown of the actuated mode proceeds similarly across all forcing intensities: in the near-wall region, the induced streak forks into two branches, while in the outer region, the streak breaks up in the streamwise direction. In both regions, spanwise gradients account for the dominant share of nonlinear energy transfer.
" }, { "name": "Batlle Franch, Pau", "degree": "PhD", "year": "2025", "title": "Optimization-Based Statistical Inference: Constrained Inverse Problems, Worst-Case Priors, and Kernel Regression", "advisor": "Owhadi, Houman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302025-005324047", "creators": [ { "name": { "family": "Batlle Franch", "given": "Pau" }, "id": "Batlle-Franch-Pau", "orcid": "0000-0003-4886-058X", "display_name": "Batlle Franch, Pau" } ], "advisors": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "advisor", "display_name": "Owhadi, Houman" } ], "committee": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "chair", "display_name": "Tropp, Joel A." }, { "name": { "family": "Hoffmann", "given": "Franca" }, "id": "Hoffmann-Franca", "orcid": "0000-0002-1182-5521", "role": "member", "display_name": "Hoffmann, Franca" }, { "name": { "family": "Braverman", "given": "Amy" }, "id": "Braverman-Amy", "orcid": "0000-0001-5127-9230", "role": "member", "display_name": "Braverman, Amy" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "cms" ], "doi": "10.7907/1v1b-6612", "abstract": "Optimization provides a worst-case framework for quantifying uncertainty in statistical inference, delivering robust and transparent performance guarantees. While this approach provides rigorous bounds, it cannot easily incorporate large-scale data or produce estimates at a prescribed confidence level. To bridge this gap, this thesis develops optimization-based methods that assimilate data while retaining worst-case robustness, exploring three different contexts: Ill-posed inverse problems, Bayesian inference with unknown priors, and Gaussian process regression.
\r\n\r\nIn the first, we introduce a new framework for frequentist, optimization-based intervals that provably achieves desired coverage. The framework unifies many previously proposed optimization-based intervals and disproves a conjecture dating back to 1965. In the second, we introduce data-likelihood constraints in Wald\u2019s two-player zero-sum game, which renders the game computationally tractable and provides explicit certificates of minimax optimality. In the third, we develop new Gaussian process (GP) based methods for learning and solving partial differential equations and operator learning. In each setting, our GP algorithms achieve stronger convergence guarantees than existing machine-learning techniques without sacrificing predictive accuracy.
\r\n\r\nAcross these three settings, estimates for the unknown quantity (a finite-dimensional parameter, a prior distribution, or a function, respectively) are obtained as the solution to an optimization problem that characterizes either worst-case or minimax optimality, therefore contributing towards a single optimization-centric view of uncertainty quantification.
" }, { "name": "Baumgart, Alexandra Rose", "degree": "PhD", "year": "2025", "title": "Numerical Stability and Reduced Order Chemistry Modeling in Detonation Simulations", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:08272024-002246183", "creators": [ { "name": { "family": "Baumgart", "given": "Alexandra Rose" }, "id": "Baumgart-Alexandra-Rose", "orcid": "0000-0001-8575-3404", "display_name": "Baumgart, Alexandra Rose" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/1vna-9r39", "abstract": "The coupling between shocks and chemistry in detonations poses a challenge for simulations. In this thesis, a simulation framework is developed to address key components of detonation modeling: numerical stability of shocks and discontinuities, and computational efficiency in chemistry modeling.
\r\n\r\nTo ensure numerical stability in the vicinity of shocks, a variety of methods have been used, including shock-capturing schemes such as weighted essentially non-oscillatory (WENO) schemes, as well as the addition of artificial diffusivities to the governing equations. In this work, all necessary viscous/diffusion terms are derived from first principles, and the performance of these analytical terms is demonstrated within a centered differencing framework. The physical Euler equations are spatially-filtered with a Gaussian-like filter. Sub-filter scale (SFS) terms arise in the momentum and energy equations. Analytical closure is provided for each of them by leveraging the jump conditions for a shock. No SFS terms are present in the continuity or species equations. For contact discontinuities, the analytical SFS terms are identically zero. However, numerically, the transport of a contact discontinuity may result in artificial oscillations due to dispersive errors. To treat contact discontinuities, a WENO-like correction term is applied to the enthalpy transport. Implemented within a centered difference code, this filtered framework performs well for a range of shock-dominated flows without introducing excessive diffusion. In addition to providing new insight into the placement and form of required diffusion terms in the governing equations, this framework is general and may be used with any numerical scheme.
\r\n\r\nChemistry modeling in detonations typically relies on two broad approaches: simplified models with one- or two-step chemistry, and detailed chemistry. These approaches require choosing between computational efficiency or physical accuracy. In detailed chemistry simulations, there are physical constraints that must be met when transporting species mass fractions; nonlinear transport schemes such as WENO do not satisfy these constraints automatically. A new method is presented to ensure that the sum of mass fractions equals 1, without penalizing inert species. The approach is better able to capture the physical instability expected for detonations. To reduce the cost of chemistry while maintaining accurate physics, tabulated chemistry has been used extensively for flames/deflagrations in the low Mach number framework. In the simplest tabulated chemistry model for premixed flames, a progress variable, describing the progress of reactions in the system, is transported in the simulation. This progress variable is then used to look up all other species, transport properties, and thermodynamic variables from a pre-computed table. Unfortunately, there is no existing tabulation approach designed specifically for detonations. As such, this work extends the tabulated chemistry method to detonations. To describe the enthalpy and specific heat capacity, the temperature is selected as a second table coordinate. The two table coordinates are able to capture virtually all variations in the progress variable source term. The Zel'dovich-von Neumann-D\u00f6ring (ZND) model is found to be the most appropriate one-dimensional problem for generation of the table. The ZND tabulation approach is validated for both one-dimensional stable and pulsating and two-dimensional regular and irregular detonations in various hydrogen-oxygen mixtures. The tabulated chemistry simulations are able to reproduce the detailed chemistry results in terms of propagation speed, cellular structures, and source term statistics at a reduced computational cost, demonstrating the benefits of this approach for predictive modeling of detonations.
" }, { "name": "Boddapati, Purna Chandra Jagannadh Kumar", "degree": "PhD", "year": "2025", "title": "Shear-Normal Coupled Deformations in Anisotropic Structured\r\nMaterials", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:08142024-070224435", "creators": [ { "name": { "family": "Boddapati", "given": "Purna Chandra Jagannadh Kumar" }, "id": "Boddapati-Purna-Chandra-Jagannadh-Kumar", "orcid": "0000-0001-8706-5963", "display_name": "Boddapati, Purna Chandra Jagannadh Kumar" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "mecheng" ], "doi": "10.7907/k1t8-4t34", "abstract": "The advent of additive manufacturing has allowed the design and engineering of a new class of materials known as metamaterials, or structured/architected materials. These metamaterials exhibit unique functionalities, such as ultrahigh strength-to-density ratios, which their base materials cannot achieve. Often designed to exhibit near-isotropic behavior, metamaterials derive their special properties from the distinctive deformation, dynamic motion, and elastic energy distribution of their micro- and meso-architectures. However, designing metamaterials for anisotropy, despite their ability to attain unique properties, is challenging. Fully characterizing anisotropic stiffness in planar loading requires six independent elastic tensor moduli. This high number of independent elastic stiffness parameters also expands the design space of structured materials and leads to unusual phenomena, such as materials that can shear under uniaxial compression. This direction-dependent shear-axial coupling is crucial for many applications such as shape-morphing, elastic wave manipulation devices and impact redirection.
\r\n\r\nThis thesis aims to understand the fundamental limits of shear-normal coupled deformations in anisotropic structured materials. Currently, there are no established upper and lower bounds on anisotropic moduli achieving extreme elastic anisotropy, similar to the Hashin-Shtrikman bounds in isotropic composites. This range is known as G-closure and provides limits for the achievable tensors. To date, there are no experimental methods that can measure the stiffness parameters of fully anisotropic structured materials from a single experiment. To address these challenges, we first introduce a method to generate two-phase periodic anisotropic unit cell geometries and construct a database of unit cells with a diverse range of effective elasticity tensors. The constructed database is compared with the properties achieved by hierarchical laminates and identify the regions where hierarchical designs are necessary to reach a specific extreme elasticity tensor.
\r\n\r\nWe then propose an experimental methodology to evaluate the anisotropic material properties. Our technique, which utilizes the virtual fields method, allows for the determination of six separate stiffness tensor parameters of two-dimensional structured materials using just one tension test. This method thus eliminates the need for multiple experiments as is typical in traditional methods. We show the accuracy of our method using synthetic data generated from finite element simulations as well as by conducting experiments on four additively manufactured specimens. The approach requires no stress data and uses the full-field displacement data measured using digital image correlation and global force data.
\r\n\r\nWe present a method for creating functionally graded anisotropic structures that smoothly transition between unit cells with distinct patterns. Isotropic materials with spatially varying density gradients have been shown to exhibit unique characteristics such as superior energy absorption. However, achieving smooth spatial gradients in the anisotropic mechanical properties while ensuring the connectivity of adjacent meso-architectures is non-trivial. This method allows for independent control of several functional gradients, such as porosity, anisotropic moduli, and symmetry. We show that certain nonlinearly graded structures when designed with unit cells positioned at distinct corners of the property space boundary exhibit novel mechanical behaviors. We conclude by designing specific functionally graded structures that demonstrate peculiar behaviors such as selective strain energy localization, localized rotations, compressive strains under tension, and longitudinal-shear wave mode conversion.
" }, { "name": "Chan, Miles J.", "degree": "PhD", "year": "2025", "title": "Reduced Order Modeling of Near-Wall and Roughness Sublayer Turbulence Using Resolvent Analysis", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222025-012553215", "creators": [ { "name": { "family": "Chan", "given": "Miles J." }, "id": "Chan-Miles-J", "orcid": "0009-0007-7898-3739", "display_name": "Chan, Miles J." } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Piomelli", "given": "Ugo" }, "id": "Piomelli-Ugo", "orcid": "0000-0002-7834-7894", "role": "member", "display_name": "Piomelli, Ugo" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5ycd-9x89", "abstract": "Modeling near-wall and roughness sublayer turbulence using physics-based methods remains a topic of paramount importance, since most engineering-relevant flows are turbulent and most surfaces are not smooth. While today there exists a wide range of empirical, data-driven modeling approaches for turbulence, these methods are limited because fully resolved turbulence data remains expensive to generate and burdensome to store and analyze. Therefore, the ability to predict out-of-sample is important, and since data-driven methods struggle to extrapolate, developing physics-based approximations that give useful, inexpensive predictions remains necessary. Yet the complexity of near-wall turbulence makes developing theoretical models difficult. This thesis tackles two main challenges. First, methods for reduced order modeling of the sensitivity of turbulence to multiscale, engineering-relevant roughness geometries are developed. In particular, a physics-based method for incorporating a drag-scaled, Reynolds-decomposed volume penalization into resolvent analysis yields a linear reduced order model that gives computationally inexpensive estimates for roughness sublayer fluctuations and dispersive stresses given a surface geometry and the mean flow profile in a rough wall channel flow. Then, an iterative method is developed to predict the mean flow profile, equivalent sand grain roughness, and Hama roughness function that utilizes the discovered relationship between the fluctuations and the mean flow. That model yields a closed-loop system for predicting roughness sublayer turbulence and the mean response given only a scan of the roughness geometry and a bulk Reynolds number in a rough wall channel flow. Second, a methodology for generating spatiotemporal representations of near-wall turbulence with very few degrees of freedom is developed. It utilizes a coarse-graining approach to reduce the number of modes required to describe a turbulent flow, selection criteria for picking descriptive modes, and Reynolds number scaling to provide predictions for an out-of-sample, higher Reynolds number flow. A spatiotemporal representation is generated, and results from Piomelli et al. that incorporate the modal representation into the wall layer of a wall modeled large eddy simulation are presented. Overall, this thesis contributes new reduced order modeling approaches that make use of physics-based insights to tackle outstanding problems in the prediction of near-wall and roughness sublayer turbulence." }, { "name": "Chen, Xiaoqiao", "degree": "PhD", "year": "2025", "title": "Active Acquisition Methods for Single Cell Genomics", "advisor": "Thomson, Matthew", "url": "https://resolver.caltech.edu/CaltechTHESIS:07052024-170119371", "creators": [ { "name": { "family": "Chen", "given": "Xiaoqiao" }, "id": "Chen-Xiaoqiao", "orcid": "0000-0003-4685-3466", "display_name": "Chen, Xiaoqiao" } ], "advisors": [ { "name": { "family": "Thomson", "given": "Matthew" }, "id": "Thomson-M-W", "orcid": "0000-0003-1021-1234", "role": "advisor", "display_name": "Thomson, Matthew" } ], "committee": [ { "name": { "family": "Cai", "given": "Long" }, "id": "Cai-Long", "orcid": "0000-0002-7154-5361", "role": "chair", "display_name": "Cai, Long" }, { "name": { "family": "Thomson", "given": "Matthew" }, "id": "Thomson-M-W", "orcid": "0000-0003-1021-1234", "role": "member", "display_name": "Thomson, Matthew" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." } ], "option_major": [ "cms" ], "doi": "10.7907/nsn8-nd79", "abstract": "We introduce two novel computational methodologies, ActiveSVM and Active Cell Inference, aimed at reducing the costs and enhancing the efficiency of single-cell mRNA sequencing and spatial transcriptomics, respectively. ActiveSVM employs an active learning approach to identify minimal yet highly informative gene sets for cell-type classification, physiological state identification, and genetic perturbation responses in single-cell datasets. By focusing on misclassified cells through an iterative process, ActiveSVM efficiently scales to analyze over a million cells, demonstrating around 90% accuracy across various datasets, including cell atlas and disease characterization studies.
\r\n\r\nActive Cell Inference complements this by utilizing ordered gene sets, developed through ActiveSVM, to streamline spatial genomics measurements. This end-to-end pipeline significantly reduces measurement time and costs by up to 100-fold in scientific and clinical settings. It optimizes the gene probing process by identifying well-classified cells early, allowing for targeted gene application based on cell classification certainty. This method's efficacy is further enhanced by a temporal scaling calibration scheme, improving calibration accuracy throughout its iterative process.
\r\n\r\nBoth methodologies were rigorously tested on the expansive Human Cell Atlas dataset, using the advanced computational tool, CellxGene-Census, involving over 60 million cells. This integration facilitated the creation of precise gene sets for various human tissues, dramatically improving the efficiency and reliability of these cutting-edge genomic techniques. Together, ActiveSVM and Active Cell Inference represent significant advancements in the application of genomics to clinical diagnostics, therapeutic discovery, and genetic screens, promising substantial reductions in the operational complexities and costs associated with next-generation sequencing technologies.
" }, { "name": "Choi, Changsoon", "degree": "PhD", "year": "2025", "title": "Techniques for Molecular Detection: From Mid-Infrared Spectrometers to Nanopore Devices", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012025-202413304", "creators": [ { "name": { "family": "Choi", "given": "Changsoon" }, "id": "Changsoon-Changsoon", "orcid": "0009-0005-4037-8643", "display_name": "Choi, Changsoon" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Petillo", "given": "Peter A." }, "id": "Petillo-Peter-A", "orcid": "0000-0001-7516-2221", "role": "member", "display_name": "Petillo, Peter A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/82w6-ka57", "abstract": "This thesis presents the development and characterization of three distinct molecular detection platforms aimed at improving accessibility and scalability. These systems utilize optical and electrical sensing techniques to analyze solid, liquid, and gas-phase samples, addressing challenges in portability, cost-effectiveness, and throughput.
\r\n\r\nFirst, a compact mid-infrared spectrometer was developed using a continuously variable filter composed of Ge/BaF2 distributed Bragg reflectors and a 2-D microbolometer array. This design enables high signal-to-noise ratio measurements across the long-wave infrared region (7.5 - 10.5 \u00b5m) without requiring moving parts. The system was calibrated using polymer samples and validated through spectral measurements of gases and liquids using gas cells and attenuated total reflection configurations. The results demonstrate good agreement with commercial Fourier transform infrared (FTIR) spectrometers while maintaining a significantly smaller form factor and lower cost.
\r\n\r\nNext, a tunable diode laser absorption spectroscopy system was implemented for methane detection. The system uses wavelength-modulated distributed feedback lasers and lock-in detection to achieve high sensitivity. Both free-space and fiber-optic configurations were developed, with detection limits down to 0.5 ppm-m for the free-space system. Real-time gas monitoring was demonstrated using retroreflectors and beam-steering optics, enabling multi-point detection with a single source-detector pair.
\r\n\r\nFinally, a design for a multiplexed nanopore detector was proposed to improve throughput. Electric properties of solid-state nanopores were investigated through analytical modeling, numerical simulations, and experimental conductance measurements. A new sensing architecture incorporating embedded electrodes was introduced. Simulations confirmed that this design enables independent detection of translocation events at each pore. Prototype devices were fabricated to validate the concept.
\r\n\r\nTogether, these platforms offer scalable and accessible alternatives to conventional molecular detection systems, with potential applications in environmental monitoring, industrial gas sensing, and real-time molecular diagnostics.
" }, { "name": "Christianson, Nicolas Henry", "degree": "PhD", "year": "2025", "title": "Machine Learning-Augmented Algorithms: Theory and Applications in Energy and Sustainability", "advisor": "Wierman, Adam C.; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-224128103", "creators": [ { "name": { "family": "Christianson", "given": "Nicolas Henry" }, "id": "Christianson-Nicolas-Henry", "orcid": "0000-0001-8330-8964", "display_name": "Christianson, Nicolas Henry" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "advisor", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "co-advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Mazumdar", "given": "Eric V." }, "id": "Mazumdar-E-V", "orcid": "0000-0002-1815-269X", "role": "chair", "display_name": "Mazumdar, Eric V." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Hajiesmaili", "given": "Mohammad H." }, "id": "Hajiesmaili-Mohammad-H", "orcid": "0000-0001-9278-2254", "role": "member", "display_name": "Hajiesmaili, Mohammad H." }, { "name": { "family": "Zhang", "given": "Baosen" }, "id": "Zhang-Baosen", "orcid": "0000-0003-4065-7341", "role": "member", "display_name": "Zhang, Baosen" } ], "option_major": [ "cms" ], "doi": "10.7907/nyn2-q614", "abstract": "Uncertainty poses a significant challenge for decision-makers in energy and sustainability domains. The ongoing energy transition—characterized by increasing penetrations of variable renewable generation, deployment of novel grid assets like battery energy storage systems, and growing risks from climate-driven natural disasters—introduces new, multifaceted uncertainties that traditional operational methods struggle to accommodate. While artificial intelligence (AI) and machine learning (ML) hold significant promise for navigating this transition and improving the efficiency of energy system operation, their direct deployment to high-stakes energy and sustainability problems presents substantial risks. In particular, current AI/ML tools typically lack guarantees on reliability, robustness, and safety, and thus pose a risk of poor performance or catastrophic failure if deployed in the real world. To make progress on decarbonization while maintaining reliability, new approaches are needed to enable the design of AI- and ML-augmented algorithms that achieve near-optimal performance while providing rigorous guarantees on robustness and reliability when deployed in real-world energy and sustainability problems.
\r\n\r\nThis thesis addresses this challenge from two complementary perspectives, seeking to bridge the gap between theoretical algorithmic insights and practical impact. In the first part, we develop learning-augmented algorithms that integrate black-box AI/ML \"advice\" into online optimization problems while ensuring provable, worst-case performance guarantees. We propose algorithms for several classes of problems—including cases with convex costs, nonconvex costs, and long-term deadline constraints—that obtain the provably optimal tradeoff between exploiting good AI performance and worst-case robustness. We demonstrate these algorithms' ability to improve operational efficiency in energy and sustainability domains through case studies on cogeneration power plant operation under high renewables penetration and carbon-aware workload shifting for geographically-distributed datacenters.
\r\n\r\nIn the second part of this thesis, we move beyond the \"black box\" model of AI/ML to explore how risk-awareness and reliability can be integrated as primary design criteria in AI/ML model training and algorithm development more generally. We consider this objective along several avenues, introducing new theoretical and methodological approaches for risk-aware optimization and uncertainty quantification, designing new mechanisms for pricing general forms of uncertainty in electricity markets, and developing new frameworks for training machine learning models with provable reliability guarantees. Throughout, we emphasize connections with and applications to energy and sustainability problems ranging from grid-scale battery storage operation to power grid contingency analysis. Together, these approaches highlight the challenges facing and benefits to risk- and reliability-aware learning and decision-making.
" }, { "name": "Cosner, Ryan Kazuo", "degree": "PhD", "year": "2025", "title": "Dynamic Safety Under Uncertainty: A Control Barrier Function Approach", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-015834886", "creators": [ { "name": { "family": "Cosner", "given": "Ryan Kazuo" }, "id": "Cosner-Ryan-Kazuo", "orcid": "0000-0002-4035-1425", "display_name": "Cosner, Ryan Kazuo" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Niemeyer", "given": "Gunter" }, "id": "Niemeyer-Gunter", "role": "member", "display_name": "Niemeyer, Gunter" }, { "name": { "family": "Culbertson", "given": "Preston" }, "id": "Culbterson-Preston", "orcid": "0000-0002-1403-8697", "role": "member", "display_name": "Culbertson, Preston" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/eee7-0m74", "abstract": "Modern technological achievements in robotics, machine learning, and control promise an exciting future where autonomous robots are a useful part of everyday life, from automated manufacturing and driverless cars to robotic healthcare and autonomous delivery drones. However, as robots are deployed in increasingly complex, uncertain, and human-interactive environments, safety becomes paramount; we cannot deploy these systems at scale unless we are rigorously assured of their safety. Despite the capabilities of modern robotics, practical real-world safety is often achieved through conservative hardware designs, confining deployment regulations, or restrictive assumptions that severely limit a robot's capabilities.
\r\n\r\nThe goal of this thesis is to develop methods for achieving dynamic safety: formal safety guarantees that preserve system performance and remain valid under uncertainty. To this end, this thesis advances the theory and practice of control barrier functions (CBFs), a leading framework for enforcing safety constraints on dynamical systems. While CBF-based methods offer strong theoretical guarantees, they do so by relying on several restrictive assumptions. Namely, they assume that the safety requirement and the system dynamics are compatible and that the dynamics model and state are perfectly known. These assumptions rarely hold in real-world settings and can result in false confidence and catastrophic safety failures when violated. This thesis addresses these gaps by systematically relaxing these assumptions and developing new theory to retain rigorous, deployable guarantees.
\r\n\r\nBy leveraging structural properties of several relevant classes of system dynamics, I first present a myriad of constructive synthesis methods that make CBF design feasible for a wide range of robots. I then develop robust control methods that retain their safety guarantees in the presence of bounded dynamics and measurement uncertainty. However, despite the utility of these methods in guaranteeing safety, they often lead to highly conservative behavior that compromises system performance. Thus, to mitigate this conservatism, I leverage machine learning techniques to reduce uncertainty and determine desired levels of robustness. While this unification of machine learning techniques with safety-critical control may sacrifice formal guarantees, it enables safe and performant behavior in practice. Moreover, the robust CBF framework provides a valuable degree of interpretability absent from typical end-to-end approaches.
\r\n\r\nNext, seeking a middle ground between conservative absolute guarantees and capable-but-heuristic methods, I adopt a probabilistic notion of safety that provides risk-based guarantees in the presence of unbounded disturbances. In particular, by illustrating the fundamental connection between DCBFs and supermartingales, I develop new theoretical guarantees and propose several algorithms to achieve safety in the presence of stochastic uncertainty. I then deploy these methods on several complex systems experiencing significant uncertainty, including a quadrotor robot with a slung payload, a humanoid robot walking in unstructured environments, and multiple robots performing dynamic collision avoidance. To achieve this, we use generative modeling techniques to capture the necessary understanding of the uncertainty distribution. Here, I also forego the traditional CBF-based safety filter paradigm and show the performance and safety improvements that can be gained through the unification of CBFs and horizon-based methods such as model predictive control (MPC).
\r\n\r\nTogether, the contributions of this thesis represent an advancement towards dynamic, safe, and capable robotic autonomy under uncertainty. The risk-aware, robust safety-critical control methods proposed here help close the gap between theoretical safety guarantees and the demands of real-world deployment.
" }, { "name": "Csomay-Shanklin, Noel V.", "degree": "PhD", "year": "2025", "title": "Layered Control Architectures: Constructive Theory and Application to Legged Robots", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032025-023615578", "creators": [ { "name": { "family": "Csomay-Shanklin", "given": "Noel V." }, "id": "Csomay-Shanklin-Noel-V", "orcid": "0000-0002-2361-1694", "display_name": "Csomay-Shanklin, Noel V." } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Niemeyer", "given": "Gunter" }, "id": "Niemeyer-Gunter", "role": "member", "display_name": "Niemeyer, Gunter" } ], "option_major": [ "cds" ], "doi": "10.7907/k0ns-c606", "abstract": "Fueled in part by the imagination of science fiction, every decade since the 1950s has expected robots to enter our everyday lives in the subsequent decade. Despite this anticipation, the widespread adoption of robots has consistently fallen short of societal expectations. This delay is attributable to the sheer variety of complexities in robotics --- perception, contact-rich dynamics, human-robot interactions. Each sub-discipline of robotics poses unique challenges that must be addressed to achieve general autonomy. As progress is made in these sub-fields, it is increasingly important to adopt a layered architecture perspective that combines isolated controller blocks into a unified framework.
\r\n\r\nThis thesis argues that on the road to general autonomy, adopting layered architectures enables three key benefits: efficiency, feasibility, and generalizability. We root our discussion in a general problem in robotics: the design of a controller that navigates a robot to a goal state while satisfying all state and input constraints that are present. Throughout the thesis, we focus on solutions that are both general --- applicable across a wide variety of robotic platforms --- and concrete --- deployed and tested on specific hardware platforms. As such, we aim to not only propose a framework for reasoning about this problem, but also methods to synthesize controllers that solve it in practice for legged robots.
\r\n\r\nWe begin by motivating and formalizing the notion of layered architectures and use this to build our control stack from the bottom up. We start with low-level planning and tracking layers that stabilize the system within a tracking tube for both the actuated and underactuated states of legged robots. We then introduce high-level planning and tracking layers that generate and follow sparse, dynamically feasible graphs for coarse global navigation through cluttered environments. By decomposing the global control problem into interacting levels and layers, each operating with disparate timescales and system abstractions, we enable tractable, reliable, and extensible robot autonomy.
\r\n\r\nThroughout this thesis, an emphasis will be placed on mathematical structure, constructive synthesis, and experimental validation. We demonstrate that adopting a layered architecture perspective is not merely an implementation convenience, but a fundamental organizing principle that can enable true robot autonomy.
" }, { "name": "Dassanayake, D. M. Sahangi Pulsarani", "degree": "PhD", "year": "2025", "title": "Space Legos: A Concept for In-Space Assembly of Large Structures with a Stationary Robot", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:11072024-033128289", "creators": [ { "name": { "family": "Dassanayake", "given": "D. M. Sahangi Pulsarani" }, "id": "Dassanayake-D-M-Sahangi-Pulsarani", "orcid": "0000-0002-1363-5764", "display_name": "Dassanayake, D. M. Sahangi Pulsarani" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/0pn5-3w42", "abstract": "Human nature is inherently driven by the desire to build; advancing from primitive shelters to skyscrapers, and extending this relentless pursuit of progress to space through technological innovations. As space missions require larger and more complex structures, traditional deployable systems face challenges due to constraints on launch mass, volume, and complex deployment mechanisms. In-space assembly (ISA) offers a promising solution for constructing large structures, such as telescopes and satellites, directly in space.
\r\n\r\nThis thesis introduces a novel ISA concept with a centralized `truss builder' for autonomous assembly of polygonal-ring structures, using simple, repetitive operations and focusing on scalable mesh reflectors for communication and imaging. Utilizing the standard AstroMesh architecture, a rapid generalized design method is developed. Through the analysis of reflector geometry, optimized cable prestress, structural design, and a high-fidelity finite element model, analytical scaling laws are derived for mass, stowed envelope, and natural frequency based on aperture diameter. A semi-analytical homogenization model is introduced to efficiently predict fundamental natural frequencies. Stowed volume is a key limitation for large deployable reflectors, approaching current and future launch capacity limits, while the proposed ISA reflectors face no such constraints for apertures up to 200 meters.
\r\n\r\nA two-dimensional finite element model simulates the assembly kinematics of large ring-like structures with the proposed ISA concept, enhancing understanding of the process and evaluating key design aspects of a stationary robot assembling scalable ring-like trusses. The model provides insights for optimizing autonomous assembly systems and underscores the need for advanced numerical simulations to ensure smooth assembly and stability during ISA, especially as structures scale.
\r\n\r\nLab-scale prototype testing validates the ISA concept, with results aligning qualitatively with simulations. Both experiments and simulations reveal a range of viable solutions, demonstrating flexibility for future mission designs. This research offers crucial insights into the design and scaling of mesh reflectors, setting the stage for comparing ISA with traditional deployable systems. The proposed ISA concept presents a practical solution for building high-precision, large-scale structures in space, advancing the field of space construction and supporting future extended space missions.
" }, { "name": "Desai, Dhruv Chimanbhai", "degree": "PhD", "year": "2025", "title": "First-Principles Calculations of Magnetotransport and Electron-Phonon Interactions in Semiconductors and Topological Materials", "advisor": "Bernardi, Marco", "url": "https://resolver.caltech.edu/CaltechTHESIS:09222024-203253433", "creators": [ { "name": { "family": "Desai", "given": "Dhruv Chimanbhai" }, "id": "Desai-Dhruv Chimanbhai", "orcid": "0009-0008-2898-9750", "display_name": "Desai, Dhruv Chimanbhai" } ], "advisors": [ { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "advisor", "display_name": "Bernardi, Marco" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Alicea", "given": "Jason F." }, "id": "Alicea-J", "orcid": "0000-0001-9979-3423", "role": "member", "display_name": "Alicea, Jason F." }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/s0ca-dg17", "abstract": "Understanding and predicting electron transport in novel materials is crucial to develop practical applications and accelerate materials discovery. Electron-phonon (e-ph) interactions are a key source of electron scattering and therefore play a dominant role in limiting electron transport under applied external fields. These interactions and the resulting phonon-limited charge transport can be calculated very accurately using ab-initio methods based on the semiclassical Boltzmann transport equation (BTE), where electron and phonon properties are obtained using density functional theory (DFT) and density functional perturbation theory (DFPT) techniques. Despite these advances, first-principles calculations of magnetotransport are still in their infancy, primarily due to technical challenges associated with solving the BTE in the presence of a magnetic field. Additionally, calculations of electrical charge transport and magnetotransport in topological materials are lacking because of various technical challenges, including computational cost and the absence of a unified formalism combining electron scattering and band topology in the BTE. In this work, we develop a framework that incorporates these effects into the BTE to compute charge transport, magnetotransport and topological transport regimes in several classes of conventional and quantum materials. Our magnetotransport calculations achieve excellent agreement with experiments, and we uncover an interplay of strong e-ph interactions and magnetic fields in graphene through a microsopic analysis of steady-state electron distributions. As a first step toward including band topology, we compute e-ph interactions and charge transport in the Dirac semimetal Na\u2083Bi and find that specific two-dimensional phonons control charge transport near room temperature. These lattice vibrations induce a dynamic phase transition to a Weyl semimetal, providing a platform for ultrafast control of dynamical phases in Na\u2083Bi. Expanding into more advanced phenomena, we incorporate the electron Berry curvature in the BTE formalism and study topological transport effects such as the chiral anomaly and nonlinear Hall effect (NLHE). Our calculations provide an accurate quantitative framework and demonstrate the importance of e-ph interactions in accurately describing topological transport in quantum materials. Lastly, we compute e-ph interactions in a novel correlated metal, RuO\u2082 which has been widely studied for its unconventional magnetism. We uncover various interesting properties such as phonon softening, strong e-ph band renormalization and a high superconducting Tc upon application of strain in RuO\u2082. Finally, we show a method to significantly accelerate all these calculations by compressing the matrices representing e-ph interactions. In summary, this work expands the scope of first-principles transport calculations to include magnetic fields and band topology. This enables future studies of electron dynamics in broad classes of novel quantum materials." }, { "name": "Epperly, Ethan Nicholas", "degree": "PhD", "year": "2025", "title": "Make the Most of What You Have: Resource-Efficient Randomized Algorithms for Matrix Computations", "advisor": "Tropp, Joel A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272025-233435853", "creators": [ { "name": { "family": "Epperly", "given": "Ethan Nicholas" }, "id": "Epperly-Ethan-Nicholas", "orcid": "0000-0003-0712-8296", "display_name": "Epperly, Ethan Nicholas" } ], "advisors": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "advisor", "display_name": "Tropp, Joel A." } ], "committee": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "chair", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Hoffmann", "given": "Franca" }, "id": "Hoffmann-Franca", "orcid": "0000-0002-1182-5521", "role": "member", "display_name": "Hoffmann, Franca" }, { "name": { "family": "Lin", "given": "Lin" }, "id": "Lin-Lin", "orcid": "0000-0001-6860-9566", "role": "member", "display_name": "Lin, Lin" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/pef3-mg80", "abstract": "In recent years, randomized algorithms have established themselves as fundamental tools in computational linear algebra, with applications in scientific computing, machine learning, and quantum information science. Many randomized matrix algorithms proceed by first collecting information about a matrix and then processing that data to perform some computational task. This thesis addresses the following question: How can one design algorithms that use this information as efficiently as possible, reliably achieving the greatest possible speed and accuracy for a limited data budget? This question is timely, as randomized algorithms are increasingly being deployed in production software and in applications where accuracy and reliability is critical.
\r\n\r\nThe first part of this thesis focuses on the problem of low-rank approximation for positive-semidefinite matrices, motivated by applications to accelerating kernel and Gaussian process machine learning methods. Here, the goal is to compute an accurate approximation to a matrix after accessing as few entries of the matrix as possible. This part of the thesis explores the randomly pivoted Cholesky (RPCholesky) algorithm for this task, which achieves a level of speed and reliability greater than other methods for the same problem.
\r\n\r\nThe second part of this thesis considers the task of estimating attributes of an implicit matrix accessible only by matrix\u2013vector products, motivated by applications in quantum physics, network science, and machine learning. This thesis describes the leave-one-out approach to developing matrix attribute estimation algorithms, and develops optimized trace, diagonal, and row-norm estimation algorithms for this computational model.
\r\n\r\nThe third part of this thesis considers randomized algorithms for overdetermined linear least squares problems, which arise in statistics and machine learning. Randomized algorithms for linear-least squares problems are asymptotically faster than any known deterministic algorithm, but recent work of [Meier et al., SIMAX '24] raised questions about the accuracy of these methods when implemented in floating point arithmetic. This thesis shows these issues are resolvable by developing fast randomized least-squares problem achieving backward stability, the gold-standard accuracy and stability guarantee for a numerical algorithm.
" }, { "name": "Fox, Chelsea Brae", "degree": "PhD", "year": "2025", "title": "Mechanical Characterization of Irregular Architected Two-Phase Materials", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272025-224848756", "creators": [ { "name": { "family": "Fox", "given": "Chelsea Brae" }, "id": "Fox-Chelsea-Brae", "orcid": "0009-0002-6612-8309", "display_name": "Fox, Chelsea Brae" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "member", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "mecheng" ], "doi": "10.7907/58vg-9217", "abstract": "Architected materials offer a wide range of mechanical properties through the choice of their constitutive materials and the design of their structure. Periodic architected materials are the most widely studied and used in practical applications, as their repeating unit cells are easy to design, fabricate, and analytically model, but these materials are only a small subset of the possible design space. Irregular architected materials, which are aperiodic but not necessarily stochastic, offer a way to achieve a wider design space of mechanical properties.
\r\n\r\nIn this thesis, we explore the design space of irregular architected materials and relate structural irregularity to the mechanical properties using measures of topology and geometry. We show that these measures of irregularity can be used to spatially and temporally control the mechanical response across linear and non-linear regimes, including fracture and dynamic impact, and we show that irregularity leads to improved mechanical properties when compared with periodic equivalents. To generate the irregular architected materials, we use a virtual growth algorithm, which imitates the stochastic growth process of biological structures by assembling a finite set of building blocks according to local connectivity rules. By varying the building blocks and connectivity rules, we show how to achieve a wide range of structures with varying degrees of irregularity all the way up to fully periodic structures. This thesis primarily focuses on the fabrication and characterization of additively manufactured two-phase polymer composites, but the design methods and irregular structure characterizations are material-agnostic, opening up a wide design space for future architected materials which use irregularity to achieve excellent mechanical performances.
" }, { "name": "Gao, Maodong", "degree": "PhD", "year": "2025", "title": "Physics and Applications of Compact Optical Frequency Comb", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08292024-234844580", "creators": [ { "name": { "family": "Gao", "given": "Maodong" }, "id": "Gao-Maodong", "orcid": "0000-0002-7791-0008", "display_name": "Gao, Maodong" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Beichman", "given": "Charles A." }, "id": "Beichman-C-A", "orcid": "0000-0002-5627-5471", "role": "member", "display_name": "Beichman, Charles A." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ck74-m354", "abstract": "Optical frequency combs (OFC) have been vastly developing and were awarded half of the Nobel Prize in 2005. OFCs are series of optical signals with distinct and equally spaced frequencies. One reason why OFCs are essential for modern optics and photonics engineering is that OFCs serve as a bridge between optical frequencies (hundreds of THz) and frequencies within the electronic bandwidth (from MHz to GHz, which is the distance between adjacent comb teeth). In this thesis, I first introduce some physical principles of optical resonators, which are critical components for confining optical energy and generating OFCs. Then, in the main body of this thesis, I study the physics and applications of two types of compact OFCs: soliton microcombs and electro-optical frequency combs.
\r\n\r\nMicrocombs are OFCs generated on integrated photonics devices. Here, I first develop a methodology to experimentally characterize two important physical properties (material absorption loss and optical nonlinearity) of integrated photonic materials. Next, I focus on a novel method to generate mode-locked soliton microcombs on ultra-low-loss Si3N4 material. It was considered challenging to support bright solitons due to its normal dispersion. This novel method involves two resonators that are partially coupled together, which can modify the dispersion through mode hybridization and feature symmetry breaking. Following this, I investigate two characteristics closely related to the symmetry breaking of this coupled-ring device: the observation of Kelly sidebands and multicolor bright soliton generation. Finally, I demonstrate bright soliton generation in Al0.2Ga0.8As resonators, which feature high nonlinearity but were considered difficult to support bright solitons at room temperature due to its high material loss. Here, we mitigate the effect of material loss by pulse-pumping operation.
\r\n\r\nElectro-optical frequency combs are OFCs generated by modulating a continuous wave laser using an external radio-frequency source. Taking advantage of low-noise radio frequency and stable continuous-wave laser frequency, this OFC can serve as a frequency reference for astronomical observation. In this thesis, I first introduce the physics and operating principle of electro-optical frequency combs in Chapter 1, then discuss developing and deploying the near-infrared laser frequency comb at the W.M. Keck Observatory in Chapter 7.
\r\n\r\nIn summary, the thesis discusses the physics and applications of mode-locked bright soliton microcombs, which can generate radio frequencies by taking the beat note of this OFC. I also discuss the physics and applications of electro-optical frequency combs, which are stable OFCs used for astronomical frequency references generated by radio-frequency modulation of continuous wave lasers. The critical role of OFCs as a bridge between optical frequencies and frequencies within the electronic bandwidth (MHz to GHz) is demonstrated, and their potential to revolutionize various fields, including high-precision metrology, telecommunications, and astrophysics, is highlighted.
" }, { "name": "Gray, Robert Matthew", "degree": "PhD", "year": "2025", "title": "Ultrafast Quadratic Nonlinear Dynamics and Soliton Formation in Parametric Amplifiers and Oscillators", "advisor": "Marandi, Alireza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092025-053621987", "creators": [ { "name": { "family": "Gray", "given": "Robert Matthew" }, "id": "Gray-Robert-Matthew", "orcid": "0000-0001-5980-8774", "display_name": "Gray, Robert Matthew" } ], "advisors": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "advisor", "display_name": "Marandi, Alireza" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7zzq-4w69", "abstract": "In the more than 60 years since the invention of the laser, complementary developments in nonlinear and ultrafast optics have revolutionized fundamental science and technology, enabling the measurement of atomic and electronic motion at their native timescales, optical timekeeping with unprecedented precision, information processing offering speeds beyond those attainable in electronics, and novel spectroscopy and sensing techniques capable of parallel detection of several analytes with fast acquisition times and high sensitivity. On the one hand, pulsed sources are particularly well-suited for driving nonlinear phenomena, as the strength of nonlinear interaction depends on the peak power of the optical input. Conversely, spectral broadening, pulse shaping, and temporal sampling mechanisms enabled by nonlinearity have been critical in developing ultrafast sources and systems.
\r\n\r\nIn this thesis, we further explore this synergistic relationship between nonlinear and ultrafast optics. We specifically study nonlinear dynamical phenomena such as soliton formation and supercontinuum generation in parametric amplifiers and oscillators exhibiting a quadratic (χ(2)) nonlinearity, and we show how these processes can be leveraged for the efficient generation of ultrashort pulses and coherent broadband spectra, with direct application in sensing and information processing. We begin by exploring the formation of mid-infrared temporal simultons in a free-space optical parametric oscillator, and we exploit their formation dynamics for enhanced molecular sensing. Next, we turn to the thin-film lithium niobate platform and demonstrate pJ pulse energy, two-color soliton pulse compression to the two-cycle regime in a dispersion-engineered waveguide. We additionally show that the strong nonlinearity in such waveguides enables the on-chip characterization of ultrashort, ultra-weak pulses. Next, we demonstrate a coherent, multi-octave frequency comb from a far-above-threshold nanophotonic parametric oscillator and investigate the dynamics underpinning its formation. Finally, we show simultaneous oscillation of 70 independent time-multiplexed parametric oscillators in a dispersion-engineered nanophotonic cavity. Our results pave the way to a new generation of scalable and efficient ultrafast sources, sensors, and information processing systems powered by quadratic nonlinearity.
." }, { "name": "Harms, Tanner David", "degree": "PhD", "year": "2025", "title": "Chasing After the Wind: Flow Structure Detection Strategies for Autonomous Mobile Flow Field Measurements", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09142024-001942971", "creators": [ { "name": { "family": "Harms", "given": "Tanner David" }, "id": "Harms-Tanner-David", "orcid": "0009-0003-2913-7414", "display_name": "Harms, Tanner David" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Brunton", "given": "Steven L." }, "id": "Brunton-S-L", "orcid": "0000-0002-6565-5118", "role": "member", "display_name": "Brunton, Steven L." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aerospace" ], "doi": "10.7907/vjvv-vb21", "abstract": "Modern flow measurement technology enables studies of fluid motion that, half a century ago, would have seemed unfathomable. However, despite staggering capabilities, measuring many natural flows in the field remains challenging. In particular, resolving coherent flow structures within physical scales ranging from meters to kilometers is not readily achieved. This dissertation proposes autonomous mobile flow field measurements (AMFM) as a paradigm for expanding flow field measurement capabilities into this range of scales. In the AMFM framework, a mobile platform such as a drone would identify critical flow structures and follow them autonomously as they evolve; the device would be taught, in a sense, to chase after the wind for the sake of measuring it. The greatest theoretical challenge to AMFM is that of flow structure detection: what, after all, should be identified in the flow? How is it to be measured? Answering these questions is the overarching motivation of this dissertation. In response, two principal contributions are developed. The first is a theoretical approach to gradient estimation labeled Lagrangian gradient regression (LGR), which enables instantaneous and finite-time flow gradients to be approximated from sparse flow observations. The second is a semantic approach to flow measurement, which provides the ability to discern fluid motion from complex natural images using arbitrarily defined flow tracers. Together, these tools enable a range of studies which would be difficult to conduct otherwise. To demonstrate their combined ability, two experiments are performed. The first examines the motion of imperfect surface tracers measured by the proposed methods relative to sub-surface flows measured by conventional techniques. The second experiment analyzes flow features in the Caltech turtle ponds using only tracers naturally occurring on its surface. While it is demonstrated that the methods and results obtained in this work are meritorious in their own right, they also provide a framework from which future AMFM technologies can be built." }, { "name": "Hatanp\u00e4\u00e4, Benjamin Henrik James", "degree": "PhD", "year": "2025", "title": "High-Field Charge Transport and Fluctuation Phenomena in Semiconductors from First Principles", "advisor": "Minnich, Austin J.", "url": "http://resolver.caltech.edu/CaltechTHESIS:09162024-212439874", "creators": [ { "name": { "family": "Hatanp\u00e4\u00e4", "given": "Benjamin Henrik James" }, "id": "Hatanp\u00e4\u00e4-Benjamin-Henrik-James", "orcid": "0000-0002-8441-0183", "display_name": "Hatanp\u00e4\u00e4, Benjamin Henrik James" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Ye", "given": "Linda" }, "id": "Ye-Linda", "orcid": "0000-0001-7949-1356", "role": "member", "display_name": "Ye, Linda" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/fc5a-5276", "abstract": "Charge transport and dynamics in semiconductors determine the limits of contemporary high-performance electronic devices. Previously, in order to understand the microscopic mechanisms underlying charge transport, and to efficiently find novel materials for new applications, computational methods were limited to using parameterized scattering rates and simplistic band structure models as inputs. However, with ab-initio methods, only the atomic identities and lattice vectors are needed as inputs. These methods have the capability of providing insights not possible with methods that rely on empirical data, and predicting properties for not-yet-synthesized materials.
\r\n\r\nWhile ab-initio computation of low-field transport properties have become common in recent years, these methods have not been extensively applied to non-equilibrium phenomena. In addition, the ab-initio simulation of fluctuational properties (such as the diffusion coefficient or power spectral density of current fluctuations) is an area that has been minimally explored. In order to approach quantum-limited noise levels in devices, a better understanding of the mechanisms that govern electronic noise away from equilibrium is needed.
\r\n\r\nThus, motivated by this, the overarching goal of this work is to develop and use first-principles methods to gain insight into the scattering processes that govern high-field electronic transport and noise in well-known semiconductors, and to use the same approach to make predictions and identify promising device applications for novel materials.
\r\n\r\nThe warm electron tensor is a quantity that describes the quadratic change of conductivity with electric field, which provides a quantitative way to examine the heating of the electron gas. However, this has not been examined from first-principles previously. In this work, we report the warm electron tensor of n-Si computed over a large temperature range, and find that the most commonly used order of perturbation theory only captures the qualitative change of the warm electron tensor with angle. However, by including the next-to-leading order two-phonon scattering term in our approach, we find near-quantitative agreement. This finding indicates that two-phonon scattering has a non-negligible role to play in transport in nonpolar semiconductors.
\r\n\r\nWe continue our investigation of n-Si by examining the diffusion coefficient and its anisotropy by applying our Boltzmann transport framework to fluctuational variables. We find that the qualitative features of the anisotropy are correct, but its magnitude is greatly underestimated in comparison to experimental data, while the onset of the noise is overestimated. While this suggests an incorrect description of f-type scattering in our work, by computing the frequency dependence of the diffusion coefficient as well as the piezoresistivity (two observables sensitive to the balance of f- and g-type scattering), we find that the qualitative agreement of these two observables with experiment shows that such a discrepancy cannot be due to an incorrect description. Instead, we suggest that the experiment contains charge transport phenomena not accounted for by our electron-phonon scattering framework.
\r\n\r\nFinally, we use the same approach to investigate the high-field transport and noise in the novel ultra-wide-bandgap semiconductor cubic boron nitride (c-BN). While c-BN is known for its excellent mechanical and thermal properties, its high predicted saturation velocity and breakdown field make it a promising candidate in high-power and high-frequency devices. However, very few experimental and theoretical studies have probed its transport properties. Here, we show that c-BN exhibits a negative differential resistance (NDR) region below 140 K, and show that the cause is due to an abrupt valley repopulation effect with applied electric field. We also show that the intervalley time in c-BN is extremely large, on the order of diamond, and that this large intervalley time causes a distinct noise peak, most prominent at low temperatures. We discuss how the NDR region and large intervalley time make c-BN a potential candidate for transferred-electron devices and Gunn oscillators, respectively.
" }, { "name": "Hatipo\u011flu, Utku", "degree": "PhD", "year": "2025", "title": "Tuning Hybrid Optomechanics for Remote Entanglement", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-181451042", "creators": [ { "name": { "family": "Hatipo\u011flu", "given": "Utku" }, "id": "Hatipo\u011flu-Utku", "orcid": "0000-0002-0511-9196", "display_name": "Hatipo\u011flu, Utku" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/cvzj-gx20", "abstract": "Superconducting microwave circuits are a leading platform for quantum computing, offering high coherence and controllability. However, their reliance on microwave photons, which are highly susceptible to thermal noise at room temperature due to their relatively low frequencies, necessitates operation at millikelvin temperatures. This requirement presents a major scalability challenge, particularly for connecting distant processors within a distributed quantum network. Microwave-optical transducers offer a promising solution by enabling coherent links between the microwave and optical domains, allowing quantum information to be shared via telecom-wavelength photons that propagate efficiently through low-loss optical fibers at room temperature. Among the various transduction platforms, hybrid piezo-optomechanical crystals (OMCs) are particularly promising due to their strong optomechanical and piezoelectric coupling and the potential for high-efficiency, low-noise transduction mediated by microwave frequency phonons. Proposed architectures for remote entanglement distribution rely on the interference of indistinguishable photons emitted from individual transducers. Although state-of-the-art fabrication techniques provide nanometer-level precision, achieving identical OMCs remains challenging, leading to device-to-device variations in optical and mechanical resonance frequencies. To enable scalable quantum networks based on optically mediated remote entanglement, a robust, selective, and precise post-fabrication tuning method is essential.
\r\n\r\nHere, we present an in situ, selective technique for tuning the optical and acoustic resonances of hybrid silicon optomechanical crystals through electric field-induced nano-oxidation using an atomic force microscope (AFM). The localized growth of a few-nanometer-thick silicon dioxide layer modifies the local permittivity, stiffness, and mass of the OMC at the oxidation region, consequently altering the optical and mechanical modes supported by the structure. Using this method, we demonstrate precise and targeted spectral alignment of both optical and mechanical modes across multiple devices within their respective mode linewidths. In addition, we extend this technique to achieve selective room-temperature pre-alignment of the optical mode of OMCs for precise wavelength alignment at millikelvin temperatures. This capability is essential for realizing indistinguishable photon emission from independently fabricated transducers toward entanglement of distant quantum processors in optically linked quantum networks.
\r\n\r\nIn the second part of this thesis, we present a side-coupled two-dimensional optomechanical cavity designed for high-efficiency, low-noise phonon\u2013photon transduction. This architecture enables near-unity conversion efficiency between optical photons and microwave frequency phonons while maintaining thermal occupancy of the phonon mode well below unity, an essential requirement for quantum-enabled operations. Finally, we describe the design, fabrication, and preliminary characterization of a microwave-to-optical transducer based on this new side-coupled 2D OMC platform.
" }, { "name": "Heidt, Liam Frank Raven", "degree": "PhD", "year": "2025", "title": "Modal Analysis of Harmonically Forced Turbulent Flows with Application to Jets", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:08072024-203148023", "creators": [ { "name": { "family": "Heidt", "given": "Liam Frank Raven" }, "id": "Heidt-Liam-Frank-Raven", "orcid": "0000-0003-1967-6847", "display_name": "Heidt, Liam Frank Raven" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "chair", "display_name": "Bae, H. Jane" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/e6fe-kz94", "abstract": "Many turbulent flows exhibit time-periodic statistics. These include flows in turbomachinery, the wakes of bluff bodies, and flows exposed to harmonic actuation. However, many existing techniques for identifying and modeling coherent structures, most notably spectral proper orthogonal decomposition (SPOD) and resolvent analysis, assume statistical stationarity. In this thesis, we develop extensions to study turbulent flows with periodic statistics. We focus on the application of turbulent jets and jet noise reduction through harmonic actuation, which is of interest for both commercial and military aviation due to its success in reducing noise by up to 5dB.
\r\n\r\nTo analyze the coherent structures in harmonically forced flows, we develop the cyclostationary spectral proper orthogonal decomposition (CS-SPOD). We examine the resulting properties of CS-SPOD and develop a theoretical connection between CS-SPOD and harmonic resolvent analysis (HRA), thereby providing the theoretical basis for HRA to be used as a model for coherent structures of cyclostationary flows. We develop and validate a computationally efficient algorithm and then illustrate its efficacy using the linearized (complex) Ginzburg-Landau equation.
\r\n\r\nWe next employ cyclostationary analysis to investigate the impact of an axisymmetric acoustic harmonic forcing on the mean, turbulence, and coherent structures of a round turbulent jet with a Mach number of 0.4 and a Reynolds number of 450000. We perform large-eddy simulations for four cases at two forcing frequencies and amplitudes. Both low-frequency (Strouhal number of 0.3) and high-frequency (Strouhal number of 1.5) forcing is found to generate an energetic, nonlinear, tonal response consisting of the rollup of vortices via the Kelvin-Helmholtz mechanism. However, the impact of forcing on the broadband turbulence and coherent structures is limited, particularly at the low forcing amplitude associated with jet-noise-reduction devices. Additionally, the dominant coherent structures for the forced jets are similar in their energy, structure, and mechanism. At high forcing amplitudes, phase-dependent features arise in the dominant coherent structures and are associated with coupling to the high-velocity/shear regions of the mean. Overall, our results support the existing hypotheses that jet noise reduction can be associated with the deformation of the mean flow field rather than through direct interaction between the forcing and the turbulence. Lastly, we find that HRA predicts the dominant coherent structures well. This shows that HRA can be used to develop models of forced jets in a similar manner to how resolvent is employed for natural jets, which may be useful to guide future sound-source models of jets subjected to active control.
" }, { "name": "Heng, Wenzheng", "degree": "PhD", "year": "2025", "title": "Smart Masks for in situ Exhaled Breath Condensate Harvesting and Analysis", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03172025-234845488", "creators": [ { "name": { "family": "Heng", "given": "Wenzheng" }, "id": "Heng-Wenzheng", "orcid": "0009-0009-5278-0727", "display_name": "Heng, Wenzheng" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Zhang", "given": "Anqi" }, "id": "Zhang-Anqi", "orcid": "0000-0001-6121-8095", "role": "member", "display_name": "Zhang, Anqi" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" } ], "option_major": [ "medeng" ], "doi": "10.7907/7kzx-ee44", "abstract": "With the growing focus on personalized breath health management and early detection of chronic pulmonary diseases, there is an urgent demand for noninvasive wearable technologies capable of continuous breath molecular monitoring during daily activities. Existing respiratory monitoring systems remain limited to physical signal tracking and lack the capability for real-time biochemical analysis of exhaled biomarkers. To address this critical gap, we developed EBCare, a fully integrated smart mask platform for automated in situ analysis of exhaled breath condensate (EBC) biomarkers. The system combines tandem passive cooling strategies (hydrogel evaporation and radiative metamaterials) with bioinspired microfluidics to enable sustainable breath condensation and efficient sample transport under real-world conditions. A multiplexed electrochemical sensor array functionalized with nanoengineered interfaces achieves selective detection of key inflammatory markers (nitrite, pH) and metabolic indicators (ammonia, alcohol), while an embedded wireless module facilitates continuous data transmission. System validation through controlled breathing experiments and field trials demonstrates reliable operation across diverse environments (10-35\u00b0C, 30-80% humidity). Clinical evaluations involving healthy subjects, COPD/asthma patients, and post-COVID cohorts reveal EBCare's ability to dynamically track airway inflammation patterns and metabolic shifts during daily tasks. This wearable EBC analysis platform bridges the gap between laboratory-based breath testing and real-world respiratory monitoring, offering a scalable solution for home-based management of chronic respiratory conditions and post-infection recovery tracking. The modular design and automated operation framework further support future expansion to monitor airborne pathogens and systemic metabolic disease biomarkers through exhaled breath." }, { "name": "Hooper, Meredith Leigh", "degree": "PhD", "year": "2025", "title": "Machine-Learned Propulsion Strategies: From Adaptive Damage Compensation to Advanced Aeromobility", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042025-002343274", "creators": [ { "name": { "family": "Hooper", "given": "Meredith Leigh" }, "id": "Hooper-Meredith-Leigh", "orcid": "0009-0004-4819-9941", "display_name": "Hooper, Meredith Leigh" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/79aa-ja50", "abstract": "Autonomous vehicles are regularly sent into \"dull, dirty, and dangerous\" environments where the risk of damage is high. Avoidance or mitigation of such damage is therefore paramount to maintain effective autonomy. In this thesis, we use machine learning to investigate two different propulsive strategies that may be used by autonomous vehicles. The first, flapping propulsion, shows remarkable ability in nature to recover from damage simply by altering stroke kinematics. Using machine learning, we ask whether and how such mitigation of damage would be possible for a robotic autonomous vehicle. The second propulsive strategy we investigate is single-rotor propulsion, most commonly seen in helicopters. With this system, we seek to avoid damage before it occurs by improving mobility and control authority via thrust vectoring.
\r\n\r\nIn Part I, we use an evolutionary strategy (CMA-ES) with hardware-in-the-loop to explore optimal machine-learned adaptations to propulsor damage. Experimental function evaluations are performed by a flexible propulsor actuated by a spherical parallel manipulator (SPM). The machine-learned forces and trajectory parameters are compared to in vivo observations in order to determine whether bio-inspired strategies to adapt to significant propulsor damage are the most efficient, or whether they may be affected by irrelevant evolutionary pressures. With amputation of approximately 50% of the propulsor, we find that a complete recovery in thrust production and fitness is made. Some characteristics of the recovered trajectory are similar to natural swimmers, while others differ. Recovery when producing side-force is even more complex. Not all trials are able to recover force production and fitness, and no clear strategy to modify amplitude or frequency is seen. We conclude Part I by using PIV measurements to detail the effect of compensatory strategies on hydrodynamics. Both amputated and intact trajectories clearly show utilization of a drag-based paddling strategy, but the hydrodynamics of the intact and amputated fins differ significantly. This suggests that the machine-learned trajectories are not simply reestablishing the same wake as the intact fin to achieve the same thrust and fitness.
\r\n\r\nGiven the success in applying machine learning in-the-loop to a complex propulsive system where fluid-structure interactions are significant, we utilize the same strategy in Part II to begin to explore helicopter aeromechanics. We built an independent blade control (IBC) system that interfaces with the CMA-ES algorithm to explore optimal blade pitch trajectories. Using this platform, we explore two preliminary optimizations designed to vector thrust; the first, for sustained thrust vectoring that might be utilized upon takeoff or landing, and the second, for short-time thrust vectoring that could be used for enhanced maneuverability. We present some preliminary results from these optimizations and lay out a foundation for future applications of this experimental system.
" }, { "name": "Hou, Wei", "degree": "PhD", "year": "2025", "title": "Fast Algorithms for Spanwise Periodic Incompressible External Flows: From Simulation to Analysis", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:03202025-173020131", "creators": [ { "name": { "family": "Hou", "given": "Wei" }, "id": "Hou-Wei", "orcid": "0000-0001-8023-6395", "display_name": "Hou, Wei" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/eygj-k325", "abstract": "External flows over spanwise-homogeneous geometries are ubiquitous in science and engineering applications. In this thesis, we propose algorithms to simulate and analyze these flows using the lattice Green's function (LGF) approach. The LGF is the analytical inverse of a discrete elliptic operator that automatically incorporates exact far-field boundary conditions and minimizes computational expense by allowing snug computational regions encompassing only vortical flow regions. By combining LGFs with adaptive mesh refinement (AMR) and immersed boundary (IB) methods, we present two numerical algorithms specially designed for spanwise periodic incompressible external flows: one to directly solve the nonlinear equations of motion and one to compute stability and resolvent analyses.
\r\n\r\nFor these algorithms, the LGFs of the screened Poisson equation must be computed at runtime. To enable efficient flow simulation and analysis algorithms, we propose a fast numerical algorithm to tabulate these LGFs. We derive convergence results for the algorithms and show that they are orders of magnitude faster than existing algorithms. Armed with the LGF for the screened Poisson equation, we further develop algorithms to solve the Navier-Stokes equations and associated linearized eigenvalue problems.
\r\n\r\nWe present two applications of these algorithms. We perform simulations to validate the starting vortex theory proposed by Pullin and Sader (2021), and we perform stability analyses of flow past a rotating cylinder with a control cylinder in its wake.
" }, { "name": "Huang, Yuting", "degree": "PhD", "year": "2025", "title": "Linear and Non-Linear Interactions Involving Large-Scale Structures in Turbulence", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10232024-033952961", "creators": [ { "name": { "family": "Huang", "given": "Yuting" }, "id": "Huang-Yuting", "orcid": "0000-0002-9457-7964", "display_name": "Huang, Yuting" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/739k-dj72", "abstract": "This thesis performs a linear resolvent analysis (McKeon and Sharma, 2010), and a novel quantitative non-linear analysis of the triadic interactions, to study the largescale structures in wall-bounded turbulence.
\r\n\r\nFirst, resolvent analysis is applied to a flow over spanwise periodic roughness, to model the large-scale counter-rotating rolls. The experimental data (Wangsawijaya et al., 2020) is utilized to examine both the predictive and data compression capabilities of the resolvent. The improvements by the inclusion of an eddy viscosity and a crude boundary geometry model are also demonstrated. Standard resolvent is able to qualitatively predict the shape of the counter-rotating rolls. The inclusion of eddy viscosity improves the quantitative predictions and combined with the boundary geometry model is able to efficiently represent the data with small differences using only a fraction of the degree of freedom.
\r\n\r\nNext, we developed a novel framework to quantitatively analyze the triadic non-linear contributions in a turbulent channel. We incorporated the linear resolvent operator to provide the missing link from energy transfer between modes to the effect on the spectral turbulent kinetic energy. The coefficients highlight the importance of interactions involving large-scale structures, for both the large and small-scale forcing and response, providing a natural connection to the modeling assumptions of the quasi-linear (QL) and generalized quasi-linear (GQL) analyses. Specifically, it is revealed that QL and GQL are efficiently capturing important triadic interactions in the flow, and the inclusion of small amounts of wavenumbers into the GQL large-scale base flow quickly captures most of the important triadic interactions.
\r\n\r\nFinally, by performing spatio-temporal analyses of the triadic contributions to a single mode, we demonstrated the spatio-temporal nature of the triadic interactions and the effect of the resolvent operator. It is shown that the energetic triadic interactions are concentrated in temporal frequencies around a plane where all three wavespeeds are the same, allowing for a truncation of the important triadic interactions. We also demonstrated the linear amplification mechanism of the resolvent, allowing certain triadic interactions to generate a stronger response even with a weak forcing, underscoring the different perspectives offered by the inclusion of the linear resolvent operator into the analyses of the non-linear triadic interactions.
" }, { "name": "Hwang, Emily Yoonju", "degree": "PhD", "year": "2025", "title": "Nonlinear Frequency Conversion in Lithium Niobate Nanophotonic Circuits for Quantum Spectroscopy", "advisor": "Cushing, Scott K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192025-200240351", "creators": [ { "name": { "family": "Hwang", "given": "Emily Yoonju" }, "id": "Hwang-Emily-Yoonju", "orcid": "0000-0002-9541-5887", "display_name": "Hwang, Emily Yoonju" } ], "advisors": [ { "name": { "family": "Cushing", "given": "Scott K." }, "id": "Cushing-Scott-K", "orcid": "0000-0003-3538-2259", "role": "advisor", "display_name": "Cushing, Scott K." } ], "committee": [ { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "chair", "display_name": "Falson, Joseph" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Cushing", "given": "Scott K." }, "id": "Cushing-Scott-K", "orcid": "0000-0003-3538-2259", "role": "member", "display_name": "Cushing, Scott K." } ], "option_major": [ "matsci" ], "doi": "10.7907/895c-5s83", "abstract": "Quantum light sources are becoming an increasingly popular alternative to pulsed lasers for spectroscopy, microscopy, and sensing. The inherent quantum correlations of entangled photons present unique advantages in spectroscopy, enabling high signal-to-noise ratios, low excitation fluxes, and time-resolved measurements without requiring a pulsed laser. Entangled photon sources for spectroscopic measurements typically consist of bulk crystals or ion-diffused waveguides. Integrated platforms such as thin-film lithium niobate have potential for highly efficient, tailored, and compact entangled photon sources through periodically poled nanophotonic waveguides. The advantageous nonlinear optical properties of lithium niobate coupled with the nanophotonic thin film platform allows for frequency conversion, quantum state generation, state manipulation, and sample interaction all on a single compact chip, demonstrating thin-film lithium niobate's potential for compact and portable integrated spectrometers.
\r\n\r\nHere, we present our work in frequency conversion and sample interactions in thin-film lithium niobate. Most of the previous demonstrations of nanophotonic lithium niobate waveguides have focused on infrared wavelengths for applications in quantum communication and computing, leaving the shorter wavelengths that are of interest for spectroscopy still a largely unexplored space. In this work, frequency conversion in thin-film lithium niobate is investigated from ultraviolet through telecom wavelengths. Periodically poled lithium niobate nanophotonic waveguides are fabricated for second harmonic generation in the ultraviolet-A region and entangled photon generation at visible and near-infrared wavelengths. Using a violet continuous wave laser, a waveguide with a fluorescent dye-doped polymer cladding layer is investigated for sample interactions. Finally, preliminary work in entangled photon triplet generation down to telecom wavelengths is explored. This work represents a step towards compact, on-chip spectrometers and sensors through lithium niobate photonic integrated circuits.
" }, { "name": "Im, Cheolmin", "degree": "PhD", "year": "2025", "title": "Simulation of Electrohydrodynamic Distortion Relevant to Liquid Metal Ion Sources", "advisor": "Troian, Sandra M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-014234039", "creators": [ { "name": { "family": "Im", "given": "Cheolmin" }, "id": "Im-Cheolmin", "orcid": "0000-0003-4063-2312", "display_name": "Im, Cheolmin" } ], "advisors": [ { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "advisor", "display_name": "Troian, Sandra M." } ], "committee": [ { "name": { "family": "Libbrecht", "given": "Kenneth George" }, "id": "Libbrecht-K-G", "orcid": "0000-0002-8744-3298", "role": "chair", "display_name": "Libbrecht, Kenneth George" }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/qs8q-wj55", "abstract": "The free surface of a liquid metal film in vacuum subject to an imbalance of destabilizing Maxwell (electric) and stabilizing capillary forces can undergo rapidly accelerating electrohydrodynamic (EHD) distortion which culminates in formation of protrusions from whose tips highly energetic ion beams are emitted. Such a phenomenon has been successfully leveraged into liquid metal ion sources (LMIS) which are fundamental to the operation of focused ion beam systems used for micro- and nanofabrication and even microarray devices actuating space micropropulsion. In this thesis, we have conducted a series of computational simulations using the arbitrary Lagrangian Eulerian finite element method designed to track the pre-emission EHD liquid distortion for realistic LMIS geometries characterizing a slender microemitter with a sharp (highly curved) tip positioned beneath an apertured extractor in vacuum.
\r\n \r\nThe simulations unveil various stable and unstable configurations whose protrusions can occur along the liquid surface. The particular configurations are found to correlate with the Reynolds number and electric Weber number based on a handful of initial values, namely the applied electric potential, emitter apex curvature radius and initial liquid thickness. For the parameter space explored, spectral analysis of the unstable configuration yields a dominant wavenumber in close agreement to that predicted from linear stability analysis of the flat liquid layer. This can be traced to the fact that a key aspect ratio indicates that the dynamics are in the flat liquid limit. Examination of the late stage dynamical behavior of the evolving protrusions reveals self-similar growth for all configurations examined. Values of the exponents extracted from the simulations are found to cluster neatly when plotted against Reynolds number and Weber number.
" }, { "name": "Ji, Qingxin", "degree": "PhD", "year": "2025", "title": "Optical Frequency Division Using High-Q Integrated Photonics", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312025-234853354", "creators": [ { "name": { "family": "Ji", "given": "Qingxin" }, "id": "Ji-Qingxin", "orcid": "0000-0002-6336-8350", "display_name": "Ji, Qingxin" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Leifer", "given": "Stephanie D." }, "id": "Leifer-Stephanie-D", "orcid": "0000-0002-8980-7825", "role": "member", "display_name": "Leifer, Stephanie D." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/wjew-9m88", "abstract": "Optical frequency division (OFD) coherently transfers the high spectral purity of optical transitions down to a microwave tone. This coherence transfer makes possible numerous modern technologies, including microwave synthesizing, optical atomic clocks, time and frequency transfer, optical frequency synthesizing, etc. In this thesis, I present advancements in using photonic-chip-based components to perform the OFD with high-performance. Along this pathway, chip-integrated, low-SWaP optical frequency combs are developed using coupled ring resonators. The key features include efficient dispersion tuning using the Moire speedup effect and ultra-high Q factor up to 100 million for an energy-efficient microcomb operation. To illustrate, recording low-noise microwave among those using integrated photonics are demonstrated. In moving towards a deliverable assembly, hybrid system packaging is demonstrated with characterized long-term stability. Ultrafast tuning control using integrated piezoelectric actuation simplifies the system architecture. In particular, an integrated, low-noise PDH locking system, and a full frequency-stabilized microcomb are demonstrated." }, { "name": "Jiang, Jiaqing", "degree": "PhD", "year": "2025", "title": "Computational Complexity and Quantum Gibbs Sampling for Local Hamiltonians", "advisor": "Vidick, Thomas G.; Mahadev, Urmila; Preskill, John P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05202025-023838413", "creators": [ { "name": { "family": "Jiang", "given": "Jiaqing" }, "id": "Jiang-Jiaqing", "orcid": "0000-0003-4055-1950", "display_name": "Jiang, Jiaqing" } ], "advisors": [ { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "advisor", "display_name": "Vidick, Thomas G." }, { "name": { "family": "Mahadev", "given": "Urmila" }, "id": "Mahadev-Urmila", "role": "co-advisor", "display_name": "Mahadev, Urmila" }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "co-advisor", "display_name": "Preskill, John P." } ], "committee": [ { "name": { "family": "Huang", "given": "Hsin-Yuan (Robert)" }, "id": "Huang-Hsin-Yuan", "orcid": "0000-0001-5317-2613", "role": "chair", "display_name": "Huang, Hsin-Yuan (Robert)" }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "member", "display_name": "Vidick, Thomas G." }, { "name": { "family": "Mahadev", "given": "Urmila" }, "id": "Mahadev-Urmila", "role": "member", "display_name": "Mahadev, Urmila" }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "member", "display_name": "Preskill, John P." } ], "option_major": [ "compsci" ], "doi": "10.7907/tthq-1471", "abstract": "One of the primary motivations for building quantum computers is to simulate quantum many-body systems. While significant progress has been made in simulating quantum dynamics, much less is known about simulating ground states and Gibbs states, an essential task for understanding the static properties of quantum many-body systems. From a computer science perspective, problems on ground states and Gibbs states are quantum analogues of the Boolean satisfiability problem (SAT) and classical Gibbs sampling, which have wide applications in optimization, machine learning, and computational complexity.
\r\n\r\nThis thesis leverages tools from computer science to explore the potential quantum advantage in simulating ground states and Gibbs states, through two complementary approaches: designing new quantum algorithms and evaluating the extent to which classical algorithms remain effective. In particular, \r\n
Autonomous systems are profoundly reshaping our societies, industries, and daily lives, delivering unprecedented levels of efficiency, innovation, and adaptability. From self-driving vehicles navigating dense urban traffic and coordinated swarms of search-and-rescue robots operating in hazardous environments, to next-generation intelligent power grids and high-precision industrial automation, these systems are increasingly deployed in safety-critical and high-stakes settings where they are routinely entrusted with split\u2011second decisions that carry profound economic and lethal consequences. In such contexts, the imperative for reliability, safety, and robustness is paramount: a single unanticipated failure within a power distribution network can trigger extensive blackouts, and a momentary lapse in decision-making or perception by an autonomous vehicle can endanger lives.
\r\n\r\nDespite their remarkable capabilities, securing such reliability guarantees faces formidable and multifaceted challenges. The environments in which these systems operate are characterized by unprecedented complexity, vast scale, and pervasive uncertainty as they frequently interact with numerous external entities such as humans or other autonomous agents whose behaviors may be volatile, adversarial, or fundamentally unknown. Explicitly and exhaustively modeling this complexity a priori is practically infeasible, compelling systems to infer, adapt, and respond to the novel environments by learning from data. Although contemporary machine\u2011learning models afford expressive representations, their assurances are limited by the scope and fidelity of their training data. Consequently, such models remain vulnerable to distribution shifts, rare events, or unmodeled edge cases, which can precipitate catastrophic failure.
\r\n\r\nFurther complicating matters, real-world applications frequently impose stringent resource constraints, including limited computation, memory, communication, and power. These constraints demand principled trade-offs between competing performance objectives and operational constraints such as safety, stability, robustness, and efficiency, especially in high-stakes and uncertainty-laden settings. This dissertation addresses these challenges by contributing fundamental theoretical results and practical computational tools towards provably reliable, resource\u2011efficient, and scalable autonomy.
\r\n\r\nOperating safely in dynamic and a priori unknown environments poses a fundamental challenge for autonomous systems: balancing exploration, i.e., the pursuit of long-term optimality by probing uncertain policy landscape at the risk of degraded safety, against exploitation, i.e., leveraging current knowledge to ensure short-term performance and stability at the expense of settling for a suboptimal policy. In Part 1, we study online reinforcement learning approaches for unknown linear dynamical systems to address this challenge. We present computationally efficient algorithms for online learning and control in both state-feedback and measurement-feedback settings that operate safely without any prior knowledge of the system. We rigorously establish their feasibility through finite-time guarantees on performance, computational complexity, and stability, matching the fundamental theoretical bounds.
\r\n\r\nStatistical models underlie every layer of an autonomous system, serving as representations of complex data-generating phenomena. Typically constructed from empirical data through a blend of explicit modeling, machine learning, and simulation, these models are vulnerable to distribution shift, i.e., discrepancies between design and deployment conditions, which can jeopardize both performance and safety. In Part 2, we investigate distributionally robust optimization (DRO) methods for control, prediction, communication, and unsupervised learning to guard against model misspecification and distribution shifts. DRO blends average-case optimality with worst\u2011case guarantees: by maximizing expected performance against the least\u2011favorable statistical model consistent with the available data, it strikes a balanced trade-off between robustness and performance informed by data.
\r\n\r\nAutonomous control systems must often balance several performance goals, such as cost efficiency, robustness, risk tolerance, and stability, while meeting practical constraints such as suitability for real\u2011time implementation and scalability. Because these design problems are inherently infinite\u2011dimensional, only a handful of special cases admit exact, tractable solutions (e.g., Linear\u2011Quadratic\u2011Gaussian, \u210b\u221e\u2011optimal, or regret\u2011optimal control) while widely studied formulations like mixed \u210b\u2082/\u210b\u221e control remain unresolved. In Part 3, we present non\u2011rational control, a unified framework that makes many such problems both solvable and implementable. The key is an optimize\u2011then\u2011approximate strategy that delivers provably near\u2011optimal, stabilizing, finite\u2011order (rational) controllers even when the true optimum resides in an infinite\u2011dimensional (non\u2011rational) policy space.
" }, { "name": "Kil, Yeokyoung (Anne)", "degree": "PhD", "year": "2025", "title": "Engineering and Computational Tools for Salivary Biomedicine", "advisor": "Pachter, Lior S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292025-233607669", "creators": [ { "name": { "family": "Kil", "given": "Yeokyoung (Anne)" }, "id": "Kil-Yeokyoung-Anne", "orcid": "0000-0002-1235-7379", "display_name": "Kil, Yeokyoung (Anne)" } ], "advisors": [ { "name": { "family": "Pachter", "given": "Lior S." }, "id": "Pachter-L", "orcid": "0000-0002-9164-6231", "role": "advisor", "display_name": "Pachter, Lior S." } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Wyllie", "given": "Anne L" }, "id": "Wyllie-A-L", "orcid": "0000-0001-6015-0279", "role": "member", "display_name": "Wyllie, Anne L" }, { "name": { "family": "Pachter", "given": "Lior S." }, "id": "Pachter-L", "orcid": "0000-0002-9164-6231", "role": "member", "display_name": "Pachter, Lior S." } ], "option_major": [ "medeng" ], "doi": "10.7907/8wdh-5v36", "abstract": "Saliva is emerging as a powerful biofluid for noninvasive diagnostics, offering a window into human health through its diverse biomolecular composition. This dissertation advances the field of salivary biomedicine by addressing critical challenges in saliva collection, processing, and analysis. First, a comparative analysis of five saliva collection devices highlighted key usability factors, informing the development of SalivaStraw--a novel device designed to improve collection efficiency and minimize leakage. Next, colosseum, a low-cost, open-source fraction collector, was designed and developed to facilitate scalable saliva processing and improve biomarker isolation. Finally, a computational framework leveraging spline regression was applied to longitudinal salivary transcriptomic data, enabling the identification of temporally regulated genes and underscoring saliva\u2019s potential for dynamic health monitoring. Collectively, this work contributes new tools and methodologies that strengthen the foundation of saliva-based diagnostics, broadening its applications in precision medicine and beyond." }, { "name": "Kim, Taeho", "degree": "PhD", "year": "2025", "title": "Modeling Frictional Processes in the Presence of Fluids: From Earthquakes in the Laboratory to Induced Seismicity in Geothermal Reservoirs", "advisor": "Lapusta, Nadia; Avouac, Jean-Philippe", "url": "https://resolver.caltech.edu/CaltechTHESIS:08132024-035518437", "creators": [ { "name": { "family": "Kim", "given": "Taeho" }, "id": "Kim-Taeho", "orcid": "0000-0002-2560-7728", "display_name": "Kim, Taeho" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "advisor", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "orcid": "0000-0002-3060-8442", "role": "co-advisor", "display_name": "Avouac, Jean-Philippe" } ], "committee": [ { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "chair", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Faulkner", "given": "Daniel R." }, "id": "Faulkner-Daniel-R", "orcid": "0000-0002-6750-3775", "role": "member", "display_name": "Faulkner, Daniel R." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "orcid": "0000-0002-3060-8442", "role": "member", "display_name": "Avouac, Jean-Philippe" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/pp3a-2609", "abstract": "Induced seismicity - earthquakes driven by injections of fluids into the subsurface - is of growing societal importance in its impact on clean energy technology. Advancements central to the world\u2019s transition to a greener economy such as geothermal energy and long-term geologic storage of CO2 are hampered by a lack of understanding and control of the associated seismic hazards. In its mechanics, frictional processes in the presence of fluids is a difficult problem to model given the challenges of studying frictionally unstable material in a controlled environment. Unstable gouge material is commonly found along faults in nature, due to pulverization of brittle rock in to granular layers called `gouge.' This thesis approaches the challenge at two different scales: 1. at the scale of the localized shear layer along the interface between two faults where we model laboratory earthquakes in the presence of pressurized fluids, and 2. at the scale of a reservoir where we model the rate of earthquakes given the injection/extraction schedule.
\r\n\r\nIn order to infer the frictional properties of unstable gouge material from laboratory experiments, we develop a probabilistic model based on a spring-slider representation of the experiment along with the rate-and-state friction law. Inversions indicate that the presence of pressurized pore fluids stabilizes the gouge - by an increase in the strength of the contacts and a lesser decrease in the grain size with slip - even under the same effective normal stress. Assuming purely slip-dependent healing of friction leads to an evolution of parameters with slip that is consistent with previously established interpretations of rate-and-state parameters. The best fitting spring-slider model still shows significant discrepancies to the experiment in the evolution of creep and in the dependence on loading rate. A quasi-static finite-element model with the same rate-and-state properties suggests that the gouge in the sample likely slides in a spatially uniform manner. Thus, the discrepancies between the spring-slider model and the experiment can likely be attributed to flaws in the rate-and-state formalism and the slip law rather than the idealization of a finite geometry to a single-degree-of-freedom system. The results prove that quantitative analysis of frictional processes of gouge in the unstable regime is possible, and that future development of constitutive relationships for friction should aim to reproduce key features of stick-slip in detail.
\r\n\r\nTo model seismicity induced by a geothermal well stimulation, we develop physical and statistical models of the seismicity rate. The physical models are based on rate-and-state friction and stress changes due to pore-pressure diffusion. The statistical model performs a convolution of a kernel function inspired by Omori law decay with the injection rate. Both models successfully reproduce the seismicity observed during the 2018 enhanced geothermal system (EGS) simulation in Otaniemi, Finland. We find that the effect of time-dependent nucleation from rate-and-state friction is crucial in reproducing the temporal and spatial patterns of the observed seismicity. We also find that the effect of finite nucleation cannot be approximated well by introducing a stress threshold in the standard Coulomb friction model, at least in the context of rapid variations of injection rates common in EGS operations.
\r\n\r\nWe highlight the major assumptions of the Dieterich seismicity rate model and examine how they may bias interpretations of induced seismicity observed in real reservoirs by comparing it directly to a Discrete Fault Network (DFN) model. The spatio-temporal pattern of seismicity in the finite setting is not only dependent on fluid transport properties and its combination with nucleation characteristics but also the distribution of initial conditions of the fault network. The back-propagation front, in particular, occurs co-injection if the time to instability for the minimum slip rate is shorter than the injection duration. The relocated catalogue of the 1993 GPK1 stimulation in Soultz-Sous-Forets shows such a back-front which can be fit qualitatively using the time to instability measure. A simple model for the rate of magnitudes that accounts for the evolution of frictional stability reproduces the apparent increase in the source radius of induced events in Soultz-Sous-Forets. The rate of larger events is overestimated by the model, possibly due to an overestimation of maximum magnitudes by the volume of stimulation. The comparisons reveal that parameters of the Dieterich model lack clear physical meaning in the finite analogue and highlight the importance of using realistic physics, especially in models at large scales where uncertainty due to assumptions at smaller scales may be amplified.
\r\n \r\nWe end the thesis with the application of rate-and-state friction to dynamic rupture modeling of seismic data from distributed acoustic sensing (DAS). The modeling of the high-frequency DAS recordings of a Magnitude 6.0 earthquake suggests a highly heterogeneous underlying fault with several prominent asperities and barriers that may control rupture dynamics. The model demonstrates how the high-stress patches both inhibit and promote the overall rupture, while also contributing to a significant amount of the energy release themselves. The successful interpretations of modern seismological data encourage future development efficient models that can be used for dynamic inversions.
" }, { "name": "King, William Robert", "degree": "PhD", "year": "2025", "title": "Advancing Applications of Quantum Computers in Quantum Simulation, Optimization, Learning, and Topological Data Analysis", "advisor": "Schulman, Leonard J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282025-173306123", "creators": [ { "name": { "family": "King", "given": "William Robert" }, "id": "King-William-Robert", "orcid": "0000-0002-8152-6340", "display_name": "King, William Robert" } ], "advisors": [ { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "advisor", "display_name": "Schulman, Leonard J." } ], "committee": [ { "name": { "family": "Vidick", "given": "Thomas Georges" }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "chair", "display_name": "Vidick, Thomas Georges" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "member", "display_name": "Preskill, John P." }, { "name": { "family": "Huang", "given": "Hsin-Yuan (Robert)" }, "id": "Huang-Hsin-Yuan", "orcid": "0000-0001-5317-2613", "role": "member", "display_name": "Huang, Hsin-Yuan (Robert)" }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "orcid": "0000-0002-6390-9401", "role": "member", "display_name": "Umans, Christopher M." } ], "option_major": [ "compsci" ], "doi": "10.7907/w905-b372", "abstract": "This thesis investigates novel directions for harnessing the potential of quantum computers in future applications. It is structured into three sections.
\r\n\r\nQuantum Simulation.
\r\nWe address two key questions: what systems exhibit quantum advantage in predicting ground state properties, and how can we reduce the cost of quantum simulations? For the former, we find that strongly interacting fermionic systems have promising characteristics for quantum advantage. For the latter, we develop an improved method for compiling block encodings using sum-of-squares optimization.
Learning with Entangled Measurements.
\r\nWe explore the benefits of leveraging entangled measurements on quantum states stored in quantum memory. These learning algorithms can be applied to the readout stage of quantum simulations, or to learn from quantum data from nature.
Topological Data Analysis.
\r\n\r\nUsing complexity-theoretic insights, we demonstrate that certain problems in topological data analysis possess a quantum mechanical structure, suggesting opportunities for quantum algorithms in this area.
Line spectrum signals appear in diverse application areas such as molecular dynamics, power electronics, speech processing, and target localization. They are composed of sums of complex exponentials with distinct frequencies. Identifying the parameters of these constituent complex exponentials has been a prominent research topic in signal processing for over four decades. In this thesis, we focus on two specific applications involving line spectrum signals: direction of arrival (DOA) estimation using sensor arrays, and denoising of discrete-time periodic signals.
\r\n\r\nThe main contribution of this thesis on the topic of DOA estimation is to propose unconventional sensor array geometries and algorithms in the presence of aperture constraints. In the first part, we demonstrate that under an aperture constraint, the traditional integer arrays (defined as arrays with sensors placed at integer multiples of the half-wavelength distance \u03bb/2) can perform only suboptimally because of the restrictive sensor placement at integer locations. To address this, we propose to use 'rational arrays' that can have sensors located at rational multiples of \u03bb/2. This offers greater flexibility in sensor placement under aperture constraints. In particular, we propose rational coprime arrays that can approach the Cram\u00e9r-Rao bound (CRB) even at low signal-to-noise ratio (SNR) and with a limited number of snapshots, and can outperform the integer arrays. Numerical simulations show that rational arrays are also better equipped to resolve closely separated DOAs. To enable the derivation of the theoretical results and identifiability guarantees for rational coprime arrays, we extend the number-theoretic concepts such as greatest common divisor and coprimality to the case of rational numbers, and prove several number-theoretic properties. Rational arrays are also demonstrated to have important advantages when the DOAs are known to lie in a sector of the space, and for identifying O(N2) uncorrelated sources using N sensors under aperture constraint.
\r\n\r\nIn the second part of the thesis, we propose modifications to the traditionally used sparse (integer) array design criteria. These modifications are aimed at mitigating the impact of mutual coupling on DOA estimation and reducing the required aperture. To reduce the impact of mutual coupling, we propose two types of sparse arrays that have either double or triple minimum inter-element spacing compared to the traditionally used \u03bb/2 spacing. This introduces 'holes' at lags 1 and 2 in the difference coarrays (defined as the set of differences in sensor locations). The first type of arrays, called weight-constrained sparse arrays, have O(N) aperture, making them suitable when the available aperture is constrained and the number of DOAs is small. A general array construction, to further reduce the weights at other coarray lags, is also proposed. The second type of arrays, called weight-constrained nested arrays, have O(N2) degrees of freedom and are suitable when there are no aperture restrictions. Extensive Monte-Carlo simulations demonstrate that the proposed arrays have significantly smaller DOA estimation errors compared to the well-known sparse arrays from the literature, in the presence of high mutual coupling.
\r\n\r\nBecause of the central holes in the difference coarrays of the weight-constrained arrays, there are two segments of consecutive entries in their coarrays: one on the positive side and the other on the negative side. To leverage these both, we propose to use an augmented coarray covariance matrix for the subspace-based algorithms such as multiple signal classification (MUSIC) and estimation of signal parameters via rotational invariance (ESPRIT). This further reduces the DOA estimation error for the weight-constrained arrays, and the computation time of augmented-MUSIC is significantly less than that of optimization-based methods, such as coarray interpolation and dictionary-based methods. We also develop methods to algorithmically interpolate the missing entries in the coarray at lags 1 and 2, to generate a larger coarray matrix. This approach demonstrates the capability to identify up to twice as many DOAs compared to what can be achieved using only the one-sided segment of consecutive lags in the coarray. This mitigates the main disadvantage of having central holes in the coarrays of weight-constrained arrays, while still benefiting from their advantage in reducing the impact of mutual coupling.
\r\n\r\nOne major drawback of using coarray-MUSIC for DOA estimation is its inefficiency (i.e., the mean squared error (MSE) does not approach CRB, even asymptotically). We conduct several experiments to provide new insights into the complex relationship of coarray-MUSIC MSE on several parameters, such as array geometry, DOA separation, and accuracy of the estimated array output correlations. Furthermore, we demonstrate that an alternative way of constructing the Toeplitz covariance matrix can greatly improve the MSE compared to coarray-MUSIC, and can lead to efficient DOA estimation. This approach is based on solving an optimization problem whose objective is derived using the asymptotic error distribution of the known entries from the covariance matrix. We also propose a modification to the Toeplitz covariance matrix construction approach to account for the presence of mutual coupling and provide simulations with different sparse arrays.
\r\n\r\nThe third part of the thesis is focused on developing a periodicity-aware signal denoising framework using Capon-optimized Ramanujan filter banks and pruned Ramanujan dictionaries. The signal reconstruction (synthesis) is done by solving a regularized optimization problem, based on the outputs of the analysis filter bank. This hybrid analysis-synthesis framework ensures that the denoised output is necessarily composed of discrete-time periodic components. Capon beamforming principles from array signal processing are utilized to optimize the Ramanujan filters to the incoming data. A computationally efficient way of obtaining the inverses of the required autocorrelation matrices is derived using Levinson\u2019s recursion. The proposed denoising method is observed to be effective even when the signal length is small and demonstrates a high SNR gain across a wide range of input signal SNRs. Furthermore, we derive several decimation properties of Ramanujan subspace signals, which help in reducing the required computations by appropriately downsampling the filter outputs without any loss of information.
\r\n\r\nTowards the end of the thesis, we theoretically investigate the locations of zeros of Ramanujan filters. Additionally, we propose an ideal interpolation filter model for Ramanujan subspace signals, which has potential application in developing a synthesis filter bank counterpart to the Ramanujan analysis filter bank for perfect signal reconstruction. We also explore the use of dictionary learning to represent periodic signals, and adapt a convolutional neural network based DOA estimation method to sparse arrays.
" }, { "name": "Ladygin, Vladimir Vladimirovich", "degree": "PhD", "year": "2025", "title": "Phonon-Phonon Interactions in Highly Anharmonic Systems", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312025-030423243", "creators": [ { "name": { "family": "Ladygin", "given": "Vladimir Vladimirovich" }, "id": "Ladygin-Vladimir-Vladimirovich", "orcid": "0000-0002-5697-6956", "display_name": "Ladygin, Vladimir Vladimirovich" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "chair", "display_name": "Falson, Joseph" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/sjpe-v132", "abstract": "The phonon, a quantum of atomic vibrations, is a core ingredient in the description of materials\u2019 behavior at both high and low temperatures. A harmonic theory of lattice dynamics treats phonons as independent, noninteracting normal modes with long lifetimes. The proper description of phenomena in solids requires the phonons to interact depending on temperature, or in other words, to act anharmonically. The phonon interaction in highly anharmonic crystals can result in intermodulation and an additional coherent scattering intensity at frequencies of the sums and differences of classical normal modes. At low temperatures, anharmonic interaction is triggered by nuclear quantum effects of zero-point motion, which can be observed\r\nas intermodulation and negative thermal expansion (NTE). In the thesis, I expand the general understanding of intermodulation phenomena using computational and experimental methods by adding missing parts expected in the theoretical intermodulation picture, such as phonon second harmonic generation and nuclear quantum intermodulation.
\r\n\r\nThe phenomenon of second harmonic generation (SHG) was found for phonons in anharmonic NaBr by inelastic neutron scattering. The temperature dependence of this phonon SHG was measured from 300 K to 650 K. At 300 K the second harmonic (SH) is seen as a high-energy branch around 33 meV, nearly independent of Q. The temperature effective potential (TDEP) method and classical molecular dynamics (MD) simulation with machine learning interatomic potential were able to reproduce the SH, and showed that SHG occurs with the flat transverse optical (TO) phonon branch. A classical model of a nonlinear medium explains the intensity and lifetime of the SH, compared to those of the TO modes. Also successful was a quantum model based on the Heisenberg-Langevin equation for interacting phonons coupled to a thermal bath, which also predicts a spectral distribution of the SH. The measured temperature dependence of the intensity of the second harmonic showed that it follows the Planck distribution of a one-phonon quasiparticle, and not two TO phonons.
\r\n\r\nThe anharmonic behavior of phonons and thermal expansion of hexagonal zinc were studied from 15 to 690 K by inelastic neutron scattering (INS) and ab initio simulations. Phonon spectra were measured for Q-points over the full Brillouin zone, giving the phonon density of states (DOS), and dispersions along high-symmetry directions. The dispersions were crisp at 15 K, but diffuse intensity was observed at energies above them. The dispersions broadened with temperature, T, and the diffuse intensity grew relatively stronger. This diffuse intensity appeared in all INS measurements and simulations, except for classical molecular dynamics at 15 K. The TDEP method was used to calculate the free energy and thermal expansion with the nuclear quantum effect from zero-point vibrational dynamics. For T < 100 K the nuclear quantum effect was essential for obtaining the negative thermal expansion, and path integral molecular dynamics (PIMD) was particularly effective for obtaining the negative thermal expansion in the basal plane. A Heisenberg-Langevin model for interacting phonons coupled to a thermal bath was able to reproduce the shape and intensity of the diffuse spectral features.
" }, { "name": "Lawlor, Barry Patrick", "degree": "PhD", "year": "2025", "title": "Full-Field Quantitative Visualization of Shock-Driven Pore Collapse in Solids: Mechanics of Deformation, Failure, and Interaction", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302025-081050551", "creators": [ { "name": { "family": "Lawlor", "given": "Barry Patrick" }, "id": "Lawlor-Barry-Patrick", "orcid": "0000-0003-4487-2129", "display_name": "Lawlor, Barry Patrick" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "role": "member", "display_name": "Mello, Michael" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/p8hs-da41", "abstract": "Porosity in solids is ubiquitous throughout engineering applications: inherent in energetic materials and exaggerated upon degradation, incorporated into shock-absorbing structures via materials such as metallic foams and metamaterials, and arising through manufacturing defects---especially in metal additive manufacturing methods. In these applications, many phenomena at both the macro- and meso-scale are critical to the operation under dynamic compression. Macroscopic shock wave structure, including shock attenuation and disruption are important for engineered structures like metallic foams, while mesoscopic localized shear deformation near porous defects can be a cause of failure in structures and is thought to be a mechanism for mechanically-induced hot spots in energetic materials which can dictate their ignition behavior. While the macroscopic shock response of porous materials has been well studied, the mesoscopic response has received less attention. Recent studies have improved the understanding through sophisticated numerical simulations and pore collapse experiments leveraging innovative high-speed imaging technologies, but many details of the mesoscopic response remain unclear.
\r\n\t\r\nThis thesis is focused on the mesoscopic domain, with an overarching goal of characterizing local details of pore collapse, such as the rate of collapse, pore geometry (asymmetry) evolution, deformation induced in the material surrounding the pore, localization/failure mechanisms, and interactions between pores. Fundamental understanding of these mesoscopic phenomena is a critical step toward unraveling the physics which couple the mesoscale and macroscale responses, enabling predictive modeling for the dynamic response of porous materials/structures, and developing innovative engineering designs with porous materials.
\r\n\t\r\nThe first part of this thesis develops a novel internal digital image correlation (DIC) technique for use in full-scale dynamic laboratory experiments, which enables investigation of phenomena which occur under confinement or are sensitive to boundary effects. The technique consists of manufacturing transparent specimens with an internally embedded speckle pattern, which is then dynamically deformed via the experiment of choice. During dynamic loading, the internal speckle pattern is visualized with a high-speed camera, after which DIC software is used to process the images and compute the displacement, velocity, and strain fields. The technique is implemented and validated using polymethyl methacrylate (PMMA) specimens under compression with split-Hopkinson (Kolsky) pressure bar and plate impact experiments---providing validation under both uniaxial stress and uniaxial strain conditions, at strain rates of 10\u00b3-10\u2076 s\u207b\u00b9 and impact stresses up to 0.65 GPa.
\r\n\t\r\nThe second part of the thesis implements the internal DIC technique to investigate the mechanics of a single spherical pore during collapse induced by weak shock loading up to 1 GPa impact stress in PMMA. The first of its kind internal strain measurements reveal concentrations around the collapsing pore, which are approximately consistent with elastostatic theory. Equivalent shear strain measurements uncover a transition from classical strain concentrations to the development of shear bands at 0.6 GPa, and raw deformation images show the development of fracture at 0.8 GPa---representing two distinct failure mechanisms arising within a small range of impact stresses. The shear bands arise due to large stress concentrations near the pore, which leads to plastic deformation and heating. Thermal softening generates local material instabilities, which can grow into regions of large, localized deformation. These bands are captured via explicit finite element analysis through a thermo-viscoplastic material model. The numerical simulations further indicate the crack to be a shear crack propagating through the weakened material of an adiabatic shear band. Finally, theoretical approaches elucidate the mechanics which govern the initiation of, spacing between, and preferred paths for these failure modes.
\r\n\t\r\nThe third part of the thesis follows a natural extension toward real porous media, investigating the collapse of pore arrays in PMMA with a focus on the role of interactions between pores on the localization and failure response. Experiments are conducted on pairs of pores in vertical and horizontal configurations. By utilizing internal DIC and shadowgraphy, the evolution of shear bands and cracks is visualized and measured. Further, apparent interactions between pores are identified through shifts in impact stress thresholds for failure initiation and through delayed crack growth. Baroclinicity, and accompanying baroclinic torque, is identified as the driving mechanism for crack propagation in these experiments. Finally, shear diffraction waves initiate upon plane wave interaction with pores and propagate toward neighboring pores. This is considered as a possible interaction mechanism between pores which alters the failure response.
\r\n\t\r\nThe work presented in this thesis enabled the first in-situ observation of adiabatic shear banding during pore collapse in addition to a much-improved spatiotemporal characterization of crack propagation compared to previous works. Analysis of the experimental results revealed the ability of theoretical and numerical (FEA) models to capture many details of shear localization in pore collapse. Further analysis unraveled mechanisms governing pore collapse and associated failure modes, including the importance of pore asymmetry during collapse as well as planar shock interaction with the pore and the resultant baroclinicity and diffracted shear waves.
" }, { "name": "Lee, Seola", "degree": "PhD", "year": "2025", "title": "Multiscale Design, Fabrication, and Mechanical Analysis of Structural Hierarchies in Functional Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312025-221040469", "creators": [ { "name": { "family": "Lee", "given": "Seola" }, "id": "Lee-Seola", "orcid": "0000-0002-4538-0890", "display_name": "Lee, Seola" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/1ee0-bc98", "abstract": "Hierarchical structuring has emerged as a powerful strategy in functional material design to enhance mechanical performance and impart functional properties across multiple scales. In architected materials, leveraging tessellated multiscale geometrical features enables unconventional properties such as ultra-low density and high energy absorption. Similarly, in functional polymers, rational design of molecular chemistries and polymer microstructures allows for tunable mechanical properties and stimuli-responsive behaviors. However, a substantial knowledge gap persists in understanding how multiscale interactions connect to determine the macroscale performance of these materials. This gap arises from challenges in scalable fabrication, multiscale characterization, and limited mechanistic insight from theory and simulations. To address these challenges, this thesis presents a comprehensive approach that integrates scalable fabrication, multiscale characterization, and theoretical modeling to develop hierarchical materials with tunable functionalities. Specifically, we (1) demonstrate scalable fabrication of hierarchical materials using additive manufacturing, (2) investigate the bulk mechanical responses by tuning the smallest level in hierarchical design, and (3) perform multiscale studies to bridge the gap between unit-level interactions and macroscale performance.
\r\n\r\nIn the first study, we explore the role of structural hierarchies in architected polymeric materials for enhanced energy dissipation. Using metasurface-based holographic lithography, we fabricate nano-architected polymeric sheets and demonstrate how geometrical parameters for unit cell design such as relative density and beam aspect ratio influence stiffness, energy dissipation, and deformation modes. These findings highlight the significance of hierarchical structuring in enhancing mechanical performance and establish design principles for scalable manufacturing. In the second study, we focus on dynamic polymers and examine how dynamic crosslinking at the molecular level influences macroscale material responses. A single-step stereolithography approach is developed to tune molecular-level controls in the material. Through multiscale modeling and experimental characterizations, we reveal how dynamic bonding mechanisms govern stiffness, stretchability, and fracture energy. The results underscore the significance of multiscale interactions in tuning mechanical behavior and suggest a pathway for designing materials with programmable responses. In the final study, we build on these insights by integrating molecular-level controls with nonlinear structural responses such as buckling and shape transformations. The central premise is that molecular interactions dictate local responsiveness, while structural geometries can amplify or suppress these responses through localized deformation or stress redistribution. As a demonstration, we explore how tailored viscoelasticity and controlled instabilities can determine the buckling mode of a structural beam. This synergistic interplay highlights the potential of the materials requiring programmed reconfigurability, shape morphing, and stimuli-responsive properties.
\r\n\r\nThe findings presented in this thesis offer a robust framework for bridging molecular-level design with macro-scale performance through scalable fabrication and characterization strategies. By expanding the design space of material-level behavior, this work lays the groundwork for developing next-generation materials with enhanced functionality, adaptability, and intelligence for applications such as soft robotics, healthcare, and sustainable materials.
" }, { "name": "Li, Gordon Han Ying", "degree": "PhD", "year": "2025", "title": "Ultrafast Computing with Nonlinear Photonics", "advisor": "Marandi, Alireza", "url": "https://resolver.caltech.edu/CaltechTHESIS:02032025-021547979", "creators": [ { "name": { "family": "Li", "given": "Gordon Han Ying" }, "id": "Li-Gordon-Han-Ying", "orcid": "0000-0001-8184-4915", "display_name": "Li, Gordon Han Ying" } ], "advisors": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "role": "advisor", "display_name": "Marandi, Alireza" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/g8re-9a27", "abstract": "Computers have revolutionized almost every facet of modern society, and as we approach the physical limits of digital electronics, it becomes imperative to investigate alternative computing hardware paradigms to enable the next generation of faster and more energy-efficient computers. This thesis embarks on building the foundation for a new kind of computer, based on ultrafast nonlinear photonics, aiming to overcome some of the limitations plaguing current computers. In particular, we primarily focus on the clock rate, which has stagnated at \u223c5 GHz for conventional microprocessors over the past two decades.
\r\n\r\nWe begin by identifying single nonlinear devices in lithium niobate nanophotonics that can act as essential building blocks for computers, showing a variety of nonlinear functions with operational speeds > 13 THz for artificial intelligence computing workloads. Then, we progress to small-scale photonic computing circuits combining both strong nonlinearity and memory feedback in a physical reservoir computer for temporal information processing with \u223c10 GHz clock rates. Additionally, we explore unconventional computer architectures such as Cellular Automata, which reveals key system-level considerations that maximize the benefits of ultrafast nonlinear photonics in large-scale computers. This culminates in the demonstration of truly end-to-end and all-optical computing with > 100 GHz clock rates, which represents over an order-of-magnitude advancement compared to existing electronic computers. Finally, we prove mathematically how coupled nonlinear optical resonators are Turing-complete computers.
\r\n\r\nOverall, this work builds on the recent advances in nonlinear photonics and highlights a path for a new class of ultrafast photonic computers that can surpass the clock rate and latency limits of electronic computers, hence enabling nascent applications requiring real-time control or information processing at picosecond timescales.
" }, { "name": "Li, Melissa", "degree": "PhD", "year": "2025", "title": "Atomically Thin Spatial Light Modulators with Excitonic Nanomaterials", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:02202025-192231690", "creators": [ { "name": { "family": "Li", "given": "Melissa" }, "id": "Li-Melissa", "orcid": "0000-0003-1534-4191", "display_name": "Li, Melissa" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "chair", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/5khv-t042", "abstract": "Achieving active control of light at the ultimate thickness limit\u2014a single atomic layer\u2014offers unprecedented opportunities for next-generation optoelectronic devices. The quest for ultrathin spatial light modulators has long relied on integrating tunable materials with plasmonic or high-index nanoantennas that serve as small, but three-dimensional optical resonators. As structures for controlling light become increasingly complex and compact, the geometrical constraints of these three-dimensional resonators will ultimately limit their scalability and versatility. A new avenue for device miniaturization emerges when harnessing electrically tunable resonances that are intrinsic to atomically thin materials.
\r\n \r\nThis thesis explores how exciton resonances, specifically in two-dimensional (2D) van der Waals materials, can serve as the central building blocks for future spatial light modulators that are as thin as atoms. We start by characterizing the gate-tunable optical properties of a monolayer molybdenum diselenide (MoSe\u2082), a 2D transition metal dichalcogenide. By tuning the exciton resonances with voltage, we demonstrate over 200% modulation in the real and imaginary part of the complex refractive index. We attribute this large tunability to the interplay between radiative and nonradiative decay channels of the excitons. The index modulation gives rise to amplitude and phase modulation of the scattered light, which is then used to engineer an electrically tunable phase gradient across a single monolayer MoSe\u2082 flake to dynamically steer the reflected beam.
\r\n \r\nNext, we present a theoretical analysis of the complex frequency response of a generalized excitonic heterostructure. We show how the spectral positions of the phase singularities, e.g. zeros and poles, can be dynamically controlled, their impacts on the real frequency phase response, and how they can be used in active metasurface design. Finally, we evaluate excitons in quantum dots as an alternative platform for room temperature optical modulators and show how they present different challenges in designing phase modulators.
\r\n\r\nOverall, our work highlights the novel functionalities enabled by exciton resonances for advanced light manipulation, underscoring their potential for atomically thin light modulators.
" }, { "name": "Li, Zongyi", "degree": "PhD", "year": "2025", "title": "Neural Operator for Scientific Computing", "advisor": "Anandkumar, Anima", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032025-033640769", "creators": [ { "name": { "family": "Li", "given": "Zongyi" }, "id": "Li-Zongyi", "orcid": "0000-0003-2081-9665", "display_name": "Li, Zongyi" } ], "advisors": [ { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "advisor", "display_name": "Anandkumar, Anima" } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Hassanzadeh", "given": "Pedram" }, "id": "Hassanzadeh-Pedram", "orcid": "0000-0001-9425-8085", "role": "member", "display_name": "Hassanzadeh, Pedram" } ], "option_major": [ "cms" ], "doi": "10.7907/fz9s-fq86", "abstract": "Scientific computing, which aims to accurately simulate complex physical phenomena, often requires substantial computational resources. By viewing data as continuous functions, we leverage the smoothness structures of function spaces to enable efficient large-scale simulations. We introduce the neural operator, a universal machine learning framework designed to approximate solution operators in infinite-dimensional spaces, achieving scalable physical simulations. The thesis begins with the introduction and definition of neural operators. Chapters 2-4 discuss architecture designs of neural operators including graph neural operator, multipole neural operator, and Fourier neural operator. Chapters 5-7 discuss physics-based learning techniques such as dissipative loss, physics-informed loss, and scale consistency loss. Chapters 8-10 discuss geometric neural operators with various boundary shapes, including latent space embedding, learned deformation, and optimal transport. Chapters 11-12 discuss further applications of neural operator in weather forecast and carbon capture storage." }, { "name": "Liang, Mingshu", "degree": "PhD", "year": "2025", "title": "Harvesting Insights from Advanced Microscope Acquisitions: Techniques and Applications", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:11072024-191407481", "creators": [ { "name": { "family": "Liang", "given": "Mingshu" }, "id": "Liang-Mingshu", "orcid": "0000-0001-7748-7652", "display_name": "Liang, Mingshu" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/aysy-jg55", "abstract": "Since their inception, microscopes have evolved significantly, becoming essential tools across various fields, from pathology diagnosis to biological studies. Morphological information that cannot be otherwise observed has always been regarded as the primary data a microscope could deliver. Yet microscopy data embodies further valuable information worth exploring. This thesis demonstrates extracting three types of information beyond morphology by modifying microscope systems, incorporating physical models, and applying image processing: 1) depth information, 2) object size information, and 3) object developmental information.
\r\n\r\nThe first part of the thesis describes an all-in-focus technique based on Fourier Ptychographic Microscopy (FPM) for depth information extraction. It synthesizes an all-in-focus image and depth map from an FPM-reconstructed multi-focal image stack. This technique benefits thyroid fine needle aspiration samples, relieving pathologists from the need to constantly adjust focal planes, enabling convenient data transfer, and potentially aiding machine learning tasks on cytology specimens.
\r\n\r\nThe second part of the thesis focuses on a non-destructive subvisible particle (SbVPs) analyzer for estimating size and concentrations of SbVPs in drug products. This analyzer aims to estimate the size and concentrations of SbVPs within a drug product while keeping the sample intact. Incorporating a light-sheet microscope with custom housings to compensate for container-induced astigmatism, it uses side-scattered light as a size indicator based on Mie scattering theory. Its functionality is demonstrated on polystyrene beads and biological drug products. Additionally, a new metric named the strip density is discovered from the same microscope images, which could serve as a more precise and robust size indicator beyond scattering light intensity. This new size indicator is used to train a particle detection neural network, verifying its effectiveness through good performance.
\r\n\r\nFor the final part, we focus on an embryo sex classification project, aiming to extract subtle developmental differences between male and female embryos from early development videos taken by Embryoscope. A combined convolutional and recurrent neural network structure is employed. While the prediction accuracy reaches 61%, which is not high, the deep learning model outperforms both human and random predictions, demonstrating its ability to acquire embryo developmental information from the Embryoscope videos to some extent.
" }, { "name": "Libersky, Matthew Murray", "degree": "PhD", "year": "2025", "title": "Microwave Spectroscopy for Probing Electronuclear Modes in Quantum Magnets", "advisor": "Rosenbaum, Thomas F.; Falson, Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072024-102144911", "creators": [ { "name": { "family": "Libersky", "given": "Matthew Murray" }, "id": "Libersky-Matthew-Murray", "orcid": "0000-0003-4140-360X", "display_name": "Libersky, Matthew Murray" } ], "advisors": [ { "name": { "family": "Rosenbaum", "given": "Thomas F." }, "id": "Rosenbaum-T-F", "orcid": "0009-0008-6152-666X", "role": "advisor", "display_name": "Rosenbaum, Thomas F." }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "co-advisor", "display_name": "Falson, Joseph" } ], "committee": [ { "name": { "family": "Motrunich", "given": "Olexei I." }, "id": "Motrunich-Olexei", "orcid": "0000-0001-8031-0022", "role": "chair", "display_name": "Motrunich, Olexei I." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Rosenbaum", "given": "Thomas F." }, "id": "Rosenbaum-T-F", "orcid": "0009-0008-6152-666X", "role": "member", "display_name": "Rosenbaum, Thomas F." }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/n5w4-ae93", "abstract": "Crystals with rare earth ions present an opportunity to explore a range of model magnetic systems, allowing for an experimental realization of several important physical concepts. For example, the compound LiHoF\u2084 is a transparent, insulating crystal which implements the transverse field Ising model (TFIM) with the Ho\u00b3\u207a spins. The TFIM is a well-known model which is one of the simplest systems to display quantum behavior, such as quantum phase transitions (QPTs). This makes LiHoF\u2084 very useful for investigating these and other quantum effects. LiHoF\u2084 ~also has strong hyperfine coupling to the nuclear spins, which means the excitations must be considered as composite of electronic and nuclear states (i.e., 'electronuclear'). This introduces a nuclear spin bath which modifies behavior near the QPT. In this work, we investigate the behavior of this QPT by probing the electronuclear states in LiHoF\u2084 at microwave frequencies. To accomplish this, we develop the use of loop-gap resonators which enable sensitive microwave measurements in LiHoF\u2084. We also extend the techniques to related systems, such as the 2-dimensional XY antiferromagnet LiErF\u2084. We then investigate ways to observe new phenomena in the LiHoF\u2084 system, namely improving superconducting resonators as one possible way to observe the dynamics of quantum quenching through the QPT." }, { "name": "Lin, Yiheng", "degree": "PhD", "year": "2025", "title": "Predictions and Policy Optimization in Online Decision Making", "advisor": "Wierman, Adam C.; Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292025-064811885", "creators": [ { "name": { "family": "Lin", "given": "Yiheng" }, "id": "Lin-Yiheng", "orcid": "0000-0001-6524-2877", "display_name": "Lin, Yiheng" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "advisor", "display_name": "Wierman, Adam C." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "co-advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Mazumdar", "given": "Eric V." }, "id": "Mazumdar-E-V", "orcid": "0000-0002-1815-269X", "role": "chair", "display_name": "Mazumdar, Eric V." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Srikant", "given": "Rayadurgam" }, "id": "Srikant-Rayadurgam", "orcid": "0000-0003-1483-5204", "role": "member", "display_name": "Srikant, Rayadurgam" } ], "option_major": [ "cms" ], "doi": "10.7907/37t0-7n77", "abstract": "Predictions are ubiquitous in modern systems, offering insights into how environments might evolve by encoding our prior knowledge and assumptions. Recent advances in artificial intelligence have significantly expanded the scope and accuracy of such models, creating vast new opportunities across domains. At the same time, online decision making remains a fundamental challenge in many real-world problems, concerned with challenges such as limited information, delayed feedback, and irrevocable actions. This dissertation focuses on the interplay between predictions and online decision making---how predictive information can be effectively leveraged to improve performance in dynamic, uncertain environments.
\r\n\r\nWhile incorporating predictions often enhances decision-making, the degree of improvement can vary substantially. This variability arises from two key factors. First, the potential benefit of using predictions is fundamentally determined by both the nature of the predictions (e.g., their targets, errors, and distributions) and the characteristics of the decision-making process (e.g., costs and dynamics). Second, standard predictive policies frequently fall short of realizing such potential, especially in changing environments or when critical system parameters are unknown.
\r\n\r\nThis dissertation introduces a unified theoretical framework to quantify the benefit of leveraging predictions across a broad range of online decision-making problems. To close the gap between the maximum potential and achievable performance, we formulate a general policy optimization framework and design efficient algorithms capable of tracking optimal (predictive) policies in time-varying settings. Additionally, we address practical considerations such as scalability and computational efficiency, enabling the application of our methods in large-scale networks and on resource-constrained devices.
" }, { "name": "Liu, Shengduo", "degree": "PhD", "year": "2025", "title": "Numerical Analyses of Frictional Sliding on Rate-and-State Interfaces: Fluid Effects, Dynamic Weakening, and Potential-Based Formulation Through Machine Learning", "advisor": "Lapusta, Nadia; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:08142024-141724425", "creators": [ { "name": { "family": "Liu", "given": "Shengduo" }, "id": "Liu-Shengduo", "orcid": "0009-0009-5259-0966", "display_name": "Liu, Shengduo" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "advisor", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "co-advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "chair", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/1tzb-pn69", "abstract": "Rate-and-state friction formulations have been widely used to reproduce a number of observations on faulting in the earth's crust, including earthquake nucleation, creeping fault segments, dynamic earthquake rupture, aftershock sequences, and episodic slow slip events. The formulations have also been used to explain the motion of landslides and glaciers. In this thesis, we use numerical simulations to study various factors that can affect the stability of fault slip with rate-and-state friction, including poroelastic bulk properties and dilatation/compaction of the fault material in the presence of fluids, fault healing, injection rate when there is fluid injected into the fault, as well as dynamic weakening of the fault gouge. We also seek to optimize simulations with rate-and-state friction by developing a potential-based formulation using machine learning.
\r\n\r\nFirst, we study the stability of frictional fault slip in the presence of fluids, with a focus on fault loading due to fluid injection into the fault as done in many field and laboratory experiments. In Chapter 2, we present a boundary-integral approach on simulating frictional fault slip in a permeable shear layer surrounded by poroelastic bulk. The approach is then used to explore the effects of poroelasticity and inelastic dilatancy on the stability of frictional fault slip in a fluid-injection problem. We find that the diffusion into and poroelastic properties of the bulk can significantly stabilize fault slip, with the stabilization by bulk diffusion and poroelastic properties comparable to the well-known stabilizing effects of the dilatancy mechanism.
\r\n \r\nIn Chapter 3, we further develop the boundary integral code to allow for purely elastic bulk with the same fluid transport properties as the poroelastic bulk material and consider the effect of fault healing and fluid injection rate on fault slip. We show that the poroelastic bulk effects can be very closely captured by using the undrained value of Poisson\u2019s ratio in an elastic bulk model with the same fluid mass diffusivity of the bulk. We find that fault healing significantly delays the onset of dynamic slip events and restricts their spatial extent, making the initial response of the fault to fluid injection much different than its longer-term response. While this is an expected conclusion, fault healing is not typically accounted for in fluid injection modeling which often uses simpler slip-dependent friction laws. We also find that faster or intermittent injection rates lead to more frequent but more spatially constrained dynamic slip events, for the same injected fluid mass, motivating further investigations into injection strategies that would optimize fault stability.
\r\n \r\nSecond, in Chapter 4, we numerically simulate a laboratory experiment of spontaneous dynamic rupture by developing a 3D finite-element model of the experiment with rate-and-state friction. In the experiment, a dynamic rupture is initiated on a Homalite-100 interface and then produces an intermittent slip in the rock gouge embedded into a part of the interface. Our simulations show that the laboratory findings are consistent with rock gouge which is rate-strengthening at low slip rates but dynamically weakening at high slip rates through the mechanism similar to flash heating. However, to fit the experimental results, the traditional flash-heating formulation needs to be substantially modified, potentially due to effects of localization and delocalization of slip in the rock gouge.
\r\n\r\nThe third part of the thesis focuses on identifying a potential-based formulation for the rate-and-state friction laws. Due to their empirical derivation, the rate-and-state friction laws cannot be written as the gradients of a potential, which leads to difficulties in implicit solution of dynamic frictional problems. In Chapter 5, we present a potential-based formulation for the rate-and-state friction law through Neural Network approximation and training on datasets generated by a one-degree of-freedom spring-slider system with the rate-and-state friction law. The learnt potential is able to reproduce the results with rate-and-state friction law, and indeed facilitates an implicit solution of dynamic problems. However, the training of the potential requires a much larger dataset than fitting the original rate-and-state friction law.
\r\n\r\nOverall, our modeling significantly advances our understanding of the factors that control stability of frictional sliding on natural faults and suggests promising machine-learning directions in replacing the empirical rate-and-state formulations with the ones based on thermodynamic potentials.
" }, { "name": "Llanos, Adrian Richard", "degree": "PhD", "year": "2025", "title": "New Structural and Electronic Degrees of Freedom in Epitaxial Square-Net Materials", "advisor": "Falson, Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:03232025-064022463", "creators": [ { "name": { "family": "Llanos", "given": "Adrian Richard" }, "id": "Llanos-Adrian Richard", "orcid": "0000-0002-5723-8007", "display_name": "Llanos, Adrian Richard" } ], "advisors": [ { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "advisor", "display_name": "Falson, Joseph" } ], "committee": [ { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "chair", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Ye", "given": "Linda" }, "id": "Ye-Linda", "orcid": "0000-0001-7949-1356", "role": "member", "display_name": "Ye, Linda" }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/41fj-5137", "abstract": "Materials belonging to the \"square-net\" (SN) family of crystal structures share the structural motif of highly conducting, 2D square-planar sheets sandwiched between complex spacer layers. Materials in this class have attracted attention for their diverse array of electronic properties such as topological, magnetic, charge/spin density wave (CDW/SDW) and superconducting ground states. Familiar examples include the cuprate and pnictide superconductors, the rare-earth tellurides and the Dirac semimetals such as ZrSiS. In this thesis we exploit the abilities of molecular beam epitaxy to synthesize and study ultra-thin films of the SN compounds and uncover several unexpected behaviors.
\r\n\r\nThe first compound we explore is DyTe\u2082, a member of the telluride family of SN materials known for their charge density wave ground states. We begin by describing the methods to fabricate epitaxial films using MBE. The high crystalline quality allows for characterization of subtle superlattice modulations with X-ray diffraction. Combinations of this experimental data with theoretical calculations reveal the origin of this superlattice to be an ordering of Te vacancies driven by Fermi-surface nesting.
\r\n\r\nWe then turn to the related compound LaSb\u2082. This material is thought to undergo a CDW transition that can be suppressed under pressure and replaced by a superconducting ground state. To our surprise, thin films of LaSb2 adopt a crystal structure distinct from that of the bulk crystals. We characterize this new structure comprehensively and find that concomitant with this new structure is an enhancement of superconducting Tc relative to the bulk.
\r\n\r\nFinally, we exploit this enhanced T\ua700 to observe magnetic field-induced superconductivity in ultra-thin LaSb2 doped with magnetic Ce dopants. This is the result of the unique robustness of the material to application of a parallel magnetic field. The combination of strong spin orbit coupling and reduced dimensionality allows the magnetic field to polarize paramagnetic spins, thereby reducing their deleterious impact on T\ua700, before the field itself destroys superconductivity. This allows a superconducting ground state to be induced from an otherwise normal metal ground state at T = 0.
\r\n\r\nThe results of this thesis highlight the unique degrees of freedom that can be accessed via epitaxial growth of single crystalline films of quantum materials.
" }, { "name": "Lu, Tracy", "degree": "PhD", "year": "2025", "title": "Variable-Stiffness and Shape-Morphing Structured Media", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:04022025-010011484", "creators": [ { "name": { "family": "Lu", "given": "Tracy" }, "id": "Lu-Tracy", "orcid": "0009-0004-4919-814X", "display_name": "Lu, Tracy" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Bordeenithikasem", "given": "Punnathat" }, "id": "Bordeenithikasem-Punnathat", "orcid": "0000-0002-0590-2447", "role": "member", "display_name": "Bordeenithikasem, Punnathat" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7wvv-cs52", "abstract": "Advancements in additive manufacturing and material synthesis with highly controlled geometries have enabled the creation of structured media, engineered materials with patterned micro- and meso-scale geometries that impart unique mechanical properties. By fine-tuning these architectures, structured materials can achieve properties beyond those of their base materials. A subcategory, structured fabrics, consists of discrete granular particles rather than continuous fibers. Their mechanical behavior is governed by jamming, a transition driven by geometric constraints, allowing them to switch between flexible and rigid states. By leveraging the interactions of the building blocks, structured fabrics enable tunable stiffness, global shape change, and adaptive functionalities, making them ideal for wearable, deployable, and morphing structures.
\r\n \r\nThe first structured fabric study explores a topologically interlocking material (TIM) system with adjustable bending stiffness controlled by external pre-stress. The system consists of truncated tetrahedral particles connected by tensioned nylon wires, allowing stiffness to be tuned by varying wire tension. Experiments examine the effects of surface friction and interlocking angle on bending response, guided by Level Set Discrete Element Method (LS-DEM) simulations. The second design presents deployable 3D structures that fold without rigid mechanisms, offering compact storage and stable deployment. The design consists of computationally generated rigid tiles adhered to a pre-stretched elastic sheet, which transforms from a flat state and jams into a predetermined 3D shape when released. Although the designs exhibited unique mechanical properties, experimentally understanding their internal mechanics was challenging due to limited visibility of the concealed membrane upon jamming. To optimize future designs, simulations were conducted to analyze the effects of various pattern designs and folding on membrane behavior.
" }, { "name": "Lukas, Heather Lauren", "degree": "PhD", "year": "2025", "title": "Engineering Bioaffinity Sensors toward Continuous Electrochemical Biosensing", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:09222024-230441454", "creators": [ { "name": { "family": "Lukas", "given": "Heather Lauren" }, "id": "Lukas-Heather-Lauren", "orcid": "0000-0002-8160-9066", "display_name": "Lukas, Heather Lauren" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Lester", "given": "Henry A." }, "id": "Lester-H-A", "orcid": "0000-0002-5470-5255", "role": "chair", "display_name": "Lester, Henry A." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" } ], "option_major": [ "medeng" ], "doi": "10.7907/2c89-k924", "abstract": "The rise of wearable sensing through smartwatches and continuous glucose monitors has made health data more widely accessible. Advances in machine learning have also been pivotal in identifying personalized health insights from biometric data streams. However, continuous biochemical data has been limited in sensor design by the availability of oxidoreductases (e.g., glucose oxidase, lactate dehydrogenase) to a given target. The challenge in engineering diverse oxidoreductase enzymes has led to the exploration of other generalized approaches to continuous electrochemical biosensing. To meet this need, we have explored a variety of bioaffinity sensing schemes using broad bioreceptor classes including antibodies, nucleic acids, and periplasmic binding proteins. We present a case study in electrochemical sensor design utilizing high-affinity antibodies for the rapid diagnosis of COVID-19 disease states. We then investigate the potential of nucleic acid-based electrochemical sensors for continuous sensing with a focus on structure-switching nucleic acid aptamers. The utility of aptamer sensors is demonstrated in the development of a serotonin aptamer sensor embedded in an ingestible capsule for continuous biosensing in the gastrointestinal tract. Applying the principles of electrochemical aptamer-based sensing, we explored the development of an electrochemical protein-based sensor for nicotine, which exploits the hinge-like binding motion of periplasmic binding proteins while also capitalizing on decades of protein evolution and characterization research. With the goal of continuous, noninvasive biochemical sensing, we evaluate the design considerations and translatability of these sensors for wearable sweat analysis. These biosensing techniques may enable the future hardware necessary to expand accessible biomedical data for the next wave of personalized health monitoring." }, { "name": "Lupu, Elena Sorina", "degree": "PhD", "year": "2025", "title": "Perception-Driven Autonomy and Learning Control for Ground Vehicles", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092025-020707222", "creators": [ { "name": { "family": "Lupu", "given": "Elena Sorina" }, "id": "Lupu-Elena-Sorina", "orcid": "0000-0002-3968-2630", "display_name": "Lupu, Elena Sorina" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Hadaegh", "given": "Fred" }, "id": "Fred-Hadaegh", "orcid": "0000-0002-0992-6323", "role": "member", "display_name": "Hadaegh, Fred" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "aerospace" ], "doi": "10.7907/79tk-eg16", "abstract": "Autonomous robots are widely recognized as highly valuable and are expected to become increasingly prevalent. They will play a critical role across a wide range of terrestrial applications in complex, unstructured environments, as well as in space, supporting infrastructure and exploration on various bodies throughout the solar system and beyond. Looking ahead, autonomous robots will play a crucial role in the search for extraterrestrial life by enabling exploration of remote and extreme environments beyond Earth.\r\nAs robots need to approach more complex tasks, the ability to rapidly perceive, understand, make real-time decisions, and operate at speed requires advances in perception-driven controls, improved predictability, and robustness to disturbances. \r\nTo enable these capabilities, the first part of this thesis proposes an innovative approach to enhancing ground vehicle mobility by integrating a vision-based control algorithm that adapts to changes in real-time. \r\nOur approach improves the vehicle's ability to assess and respond to complex terrains in real-time by leveraging visual information through visual foundation models and meta-learning.\r\nOur controller has provable guarantees of exponential stability and was validated on board two ground vehicles.\r\nNext, an extension of the previously mentioned method applied to detecting objects in space using a visual foundation model is presented. Our method was successfully demonstrated in space in early 2025 aboard the EdgeNode Lite spacecraft.\r\nEfficient operation comes from the synergy of suitable autonomy and control with a suitable robot body.\r\nFollowing this consideration, the second part of the thesis presents the design and control of multi-degrees of freedom robots designed for mobility in complex environments.\r\nIt presents a nonlinear tracking controller with adaptation to improve the walking performance of walking-flying robots. This is illustrated by our implementation on Leonardo, the first robot to combine walking with flying to create a new type of locomotion, which we showcase in complex acrobatic movements such as slacklining and skateboarding.\r\nIn a second case study, we aim to further understand and improve biped walking by introducing a bipedal robot designed to be lightweight, easily manufactured, and easily repaired, serving as a platform for testing learning-based controllers.\r\nWe introduce and demonstrate the performance of two controllers: a model-based and a learning-based control.\r\nThis work highlights the importance of tightly integrated perception, control, and electromechanical design in achieving robust autonomy: on Earth, in orbit, and beyond." }, { "name": "Mohebbi, Nina", "degree": "PhD", "year": "2025", "title": "Flow Induced by Collective Vertical Migration: Impact of Swimmer Distribution, Buoyancy, and Wake Interactions", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082025-223940273", "creators": [ { "name": { "family": "Mohebbi", "given": "Nina" }, "id": "Mohebbi-Nina", "orcid": "0000-0003-4014-6111", "display_name": "Mohebbi, Nina" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Lozano-Duran", "given": "Adrian" }, "id": "Lozano-Duran-A", "orcid": "0000-0001-9306-0261", "role": "member", "display_name": "Lozano-Duran, Adrian" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/hz5j-g795", "abstract": "Various animal species exhibit collective motion, characterized by coordinated movement within groups of organisms. A prominent oceanic example is diel vertical migration (DVM), wherein zooplankton migrate vertically from deeper waters during the day to shallower regions at night, often covering distances of approximately 1 kilometer. Despite numerous field measurements, laboratory observations, and theoretical studies of biogenic mixing resulting from collective swimming, the scale of fluid mixing induced by DVM remains unresolved. A key challenge is linking the behavior and flows created by large numbers of individual organisms to collective-scale fluid dynamics. Since most swimmers involved in DVM operate at intermediate Reynolds numbers, the dynamics of these systems are nonlinear and span a wide range of spatial and temporal scales.
\r\n\r\nThis thesis investigates flow scaling generated by vertical migration of brine shrimp (Artemia salina) aggregates, using laboratory measurements complemented by semi-analytical modeling. A volumetric laser scanning system first measured swimmer behaviors and flow interactions during laboratory-induced vertical migrations. Swimmers consistently maintained vertical swimming velocities under varying environmental conditions, showed a Gaussian horizontal distribution within the tank cross-section, and exhibited a pronounced tendency toward the tank center, where illumination was brightest. A scaling relationship between swimmer buoyancy, ascent speeds, and resulting flow velocities was developed to contextualize these results.
\r\n\r\nA semi-analytical model was then developed to estimate the flow generated by wakes of multiple swimmers in proximity. Individual swimmer behaviors were informed by empirical observations and combined through an iterative approach that conserves mass and momentum, providing an aggregation-scale flow solution. Numerical results indicated that induced upstream flows within the aggregation were relatively insensitive to downstream swimmer presence, that average flow speeds approached a plateau beyond a critical aggregation length, and that closer swimmer spacing significantly enhanced induced flow velocities.
" }, { "name": "Mukasa, Daniel", "degree": "PhD", "year": "2025", "title": "Computational Design of Wearable Chemical Sensors for Personalized Healthcare", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:06292024-045659387", "creators": [ { "name": { "family": "Mukasa", "given": "Daniel" }, "id": "Mukasa-Daniel", "orcid": "0000-0001-8379-3648", "display_name": "Mukasa, Daniel" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" } ], "option_major": [ "matsci" ], "doi": "10.7907/r46k-sw73", "abstract": "Wearable sweat sensors have the potential to revolutionize precision medicine as they can non-invasively collect molecular information closely associated with an individual\u2019s health status. However, the majority of clinically relevant biomarkers cannot be continuously detected in situ using existing wearable approaches. Molecularly imprinted polymers (MIPs) are a promising candidate to address this challenge but haven\u2019t yet gained widespread use due to their complex design and optimization process yielding variable selectivity. Despite their promise, MIPs have historically been known to be exceedingly difficult to optimize. Changes in the monomer/monomers used, polymerization solvent, and crosslinking agent have been shown to change the performance of MIP sensors significantly. This is particularly a concern in sweat-based sensors where the concentration of analytes is very low and chemical diversity is very high as a drop of sweat can contain vitamins, hormones, and amino acids. Consequentially, any sweat based sensor must exhibit high sensitivity (ability to detect low analyte concentrations) and selectivity (ability to distinguish one analyte from another). Computational methods have been introduced to design MIP sensitivity alone, however these prior methods do not cover all aspects essential for using a sensor in a wearable device such as selectivity optimization, detection of non-electroactive analytes, and scalable manufacturing. Here, we introduce a full computational method that allows for high throughput materials discovery for wearable devices. We will describe how to design novel sensing materials with QuantumDock, an automated computational framework for universal MIP development toward wearable applications. Then we delve into further technical details on signal transduction and scalable manufacturing approaches for these wearable devices. We present a number of novel devices designed with these computational methods including a wearable non-invasive phenylalanine monitoring system (the first of its kind), a wearable nutritional tracker \u2018Nutritrek\u2019 capable of monitoring a range of metabolic disorders, and an implantable pharmaceutical drug monitoring system for cancer patients." }, { "name": "Musgrave, Charles Bruce, III", "degree": "PhD", "year": "2025", "title": "Computational Approaches to Problems in Energy and Sustainability", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:07092024-152839479", "creators": [ { "name": { "family": "Musgrave", "given": "Charles Bruce, III" }, "id": "Musgrave-Charles-Bruce-III", "orcid": "0000-0002-5732-3180", "display_name": "Musgrave, Charles Bruce, III" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Manthiram", "given": "Karthish" }, "id": "Manthiram-Karthish", "orcid": "0000-0001-9260-3391", "role": "member", "display_name": "Manthiram, Karthish" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/hnc1-je90", "abstract": "The rapid development of modern society has been met by a fierce and overwhelming increase in fossil fuel utilization and the mass production of nonrenewable/recyclable materials. The escalating usage of fossil fuels results in rising greenhouse gas (GHG) emissions, while mass production of non-recyclable materials has led to unimaginable amounts of waste, which ultimately ends up in landfills or in the ocean. If we seek a sustainable future, it is imperative that we develop methods that can harness \u201cgreen\u201d electrons to generate power, particularly synthetic routes that selectively generate renewable materials via these electrons.
\r\n\r\nIn this thesis, we leverage theoretical methods to investigate several platforms for the conversion of GHGs to value-added products such as methanol, ethylene, methylacetic acid, styrene, etc. To generate these products, we use heterogeneous and homogeneous catalysts, with and without the assistance of an applied potential. The overarching goal of these methods is to remediate carbon and nitrogen cycles, such that generation of harmful carbon and nitrogen-based products is immediately followed by conversion of said products back to useful reactant species.
\r\n\r\nIn summation, this thesis provides several catalytic platforms for the selective and efficient production of useful fuels and feedstocks from harmful GHGs.
" }, { "name": "O'Gara, Stephanie Lea", "degree": "PhD", "year": "2025", "title": "Buoyancy-Driven Fluid Dynamics for Enhanced Ocular Drug Delivery", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282025-170616092", "creators": [ { "name": { "family": "O'Gara", "given": "Stephanie Lea" }, "id": "O'Gara-Stephanie-Lea", "orcid": "0009-0003-9826-6906", "display_name": "O'Gara, Stephanie Lea" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "member", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Koochesfahani", "given": "Manoochehr" }, "id": "Koochesfahani-Manoochehr", "orcid": "0000-0002-7001-8455", "role": "member", "display_name": "Koochesfahani, Manoochehr" }, { "name": { "family": "Humayun", "given": "Mark" }, "id": "Humayun-M", "orcid": "0000-0002-5830-5208", "role": "member", "display_name": "Humayun, Mark" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "mecheng" ], "doi": "10.7907/18vw-4r15", "abstract": "The CDC has identified vision loss as a growing public health concern, with eye disease prevalence on the rise. Three of the most common and vision-threatening eye diseases, wet age-related macular degeneration, proliferative diabetic retinopathy, and diabetic macular edema, are typically managed through periodic intravitreal injections. However, treatment effectiveness varies. Given that the half-life of the drug is limited, one possible cause of the ineffective treatment is inefficient delivery to the target region. This thesis investigates heat-induced convective flow in an in-vitro eye model as a method for enhancing drug delivery by accelerating fluid transport.
\r\n\r\nFirst, an optical distortion study was conducted to identify a vitreous model that matches both the viscosity of the human vitreous and the refractive index of the eye model. Next planar two-component and volumetric three-component flow visualization and measurement experiments capture the impact of thermal pad size on the resulting flow fields, with consideration given to particle trajectories for targeted delivery. Finally, a physics-informed neural network, trained on planar velocity data and tested against additional planes from volumetric measurements, demonstrates the potential for data-driven modeling to simplify future flow visualization experiments. The outcomes of this work further our fundamental understanding of fluid dynamics in the eye and encourage continued investigation into interdisciplinary approaches for improving drug delivery, and ultimately, patient outcomes.
" }, { "name": "Pederson, John Monroe Jr.", "degree": "PhD", "year": "2025", "title": "Thermoelastic Deflections of Thin-Shell Composite Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:12172024-163805389", "creators": [ { "name": { "family": "Pederson", "given": "John Monroe Jr." }, "id": "Pederson-John-Monroe-Jr", "orcid": "0009-0002-8500-2285", "display_name": "Pederson, John Monroe Jr." } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/xyry-w852", "abstract": "As space structures become larger, lighter, and deployable, thermal deflections induced by sunlight become a significant source of structural inaccuracy and even spacecraft vibration. Studying these deflections is notoriously difficult: analytical solutions rapidly become intractable, experiments under vacuum and cooling are low-visibility and expensive, and multiphysics finite-element simulations are computationally demanding and usually don\u2019t account for coupled thermo-structural analyses and/or changing radiation view factors.
\r\n\r\nThis work demonstrates key improvements in experimental methods and thermo-structural simulation of these thermal deflections. First, simultaneous full-field measurements of structural temperatures and deflections are achieved by constructing and using a custom vacuum chamber and heating setup; significant thermal gradients and repeatable thermal deformations are measured and analyzed, forming a ground truth for succeeding simulations. Second, multiphysics models of the experimental chamber are created in COMSOL Multiphysics and characterized, even accounting for residual convection, and used to inform prototype improvements and more advanced simulations. Third, based off such predictions, the unit structure prototype composite is improved by adding a layer of graphitized polymer film, with further experimentation showing a dramatic reduction in deflections.
\r\n\r\nFinally, the accumulated knowledge is used to simulate a satellite slew maneuver with realistic orbital heating; a custom technique to couple thermal (Thermal Desktop) and structural (Abaqus) finite-element software via a MATLAB script allows for the recalculation of radiation view factors during simulations, a feat necessary for accurate heating calculations on deployable structures. These results have immediate applicability in predicting structural temperatures and deflections during the satellite maneuvers proposed for the Caltech Space Solar Power Project, as well as suggesting critical improvements to ensure reliability and mission success.
" }, { "name": "Ragan, James Francis, III", "degree": "PhD", "year": "2025", "title": "Planning for an Uncertain Future: Tree-Based Methods for Real-Time Fault Estimation, Collision Avoidance, and Multi-Agent Reconfiguration", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:02252025-021704066", "creators": [ { "name": { "family": "Ragan", "given": "James Francis, III" }, "id": "Ragan-James-Francis-III", "orcid": "0009-0005-5680-9794", "display_name": "Ragan, James Francis, III" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "chair", "display_name": "Watkins, Michael M." }, { "name": { "family": "Hadaegh", "given": "Fred Y." }, "id": "Hadaegh-F-Y", "orcid": "0000-0002-0992-6323", "role": "member", "display_name": "Hadaegh, Fred Y." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "space" ], "doi": "10.7907/ptpk-d504", "abstract": "Autonomous spacecraft making independent high-level decisions present the promise of dramatically increased productivity in space for both exploration and economic activity. While autonomy has seen limited use in space to date owing to a lack of flight heritage, limited computational resources, and a traditionally risk adverse industry, the growing numbers of spacecraft and increasingly ambitious missions will soon render the current ground-intensive mode of space operation untenable.
\r\n \r\nIn this thesis, we develop two critical capabilities for an autonomous future in space. The first is proactive fault estimation, which seeks to rapidly and safely identify the root causes of onboard anomalies by planning sequences of test actions to gather information while probabilistically ensuring safety. The second is real-time reconfiguration to enable formations of spacecraft to respond quickly and effectively to changing environments or mission objectives.
\r\n\r\nWe achieve both goals using various forms of Monte-Carlo Tree Search planning. By formalizing each capability as sequential decision-making problems, and developing algorithms well suited to information gathering, we show that our algorithms provably converge to optimal solutions while maintaining the ability to run in real-time on robotic spacecraft simulators. We present several algorithmic innovations, including marginalized filtering, sampling-based chance constraint evaluation, and an array-based implementation of Monte-Carlo Tree Search. Through and numerical simulations and hardware experiments, we demonstrate that these modifications enable our algorithms to outperform existing tree search methods and achieve better scaling across system complexity, noise, and simulation depth.
" }, { "name": "Rajan, Aakila", "degree": "PhD", "year": "2025", "title": "Methods for Learning Mechanics: Inverse Problems, Constitutive Modeling, and Design", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262025-195518377", "creators": [ { "name": { "family": "Rajan", "given": "Aakila" }, "id": "Rajan-Aakila", "orcid": "0000-0001-9218-5062", "display_name": "Rajan, Aakila" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "chair", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Buskohl", "given": "Philip" }, "id": "Buskohl-Philip", "orcid": "0000-0001-5517-1956", "role": "member", "display_name": "Buskohl, Philip" } ], "option_major": [ "mecheng" ], "doi": "10.7907/caht-w798", "abstract": "Predicting the behavior of materials and structures under complex loading is a fundamental challenge in solid mechanics. Traditional techniques rely on idealized experiments, a priori information and are computationally intensive. This work introduces a unified framework for constitutive identification, multiscale modeling, and design optimization, grounded in physical laws and enhanced by machine learning.
\r\n\r\nWe first focus on the inverse problem of identifying constitutive behavior from experimental data. We formulate this task as an optimization problem with the governing equations of the experiment as a constraint. This allows us to infer material parameters from full-field or contact-based measurements. This approach enforces physical laws and accommodates complex loading, noise, and limited data. We apply it to recover properties for a history-dependent material using both synthetic and experimental datasets. We further extend the framework using recurrent neural operators to learn constitutive responses directly from data, bypassing the need for an explicit model form.
\r\n\r\nIn the second part of the thesis, we extend our focus to multiscale modeling and structural design. Neural operators are used to learn homogenized solutions of linear elliptic PDEs with discontinuous coefficients, eliminating the need to resolve fine-scale features during inference. For topology optimization, we develop reduced-order neural surrogates embedded within the design loop, achieving efficient yet accurate updates. Together, these contributions offer a cohesive, data-driven strategy for advancing modeling and design in solid mechanics.
" }, { "name": "Schoeffler, Donner Thomas", "degree": "PhD", "year": "2025", "title": "Measurement and Modeling of Detonation-Driven Shock Tube Flows", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272025-230901725", "creators": [ { "name": { "family": "Schoeffler", "given": "Donner Thomas" }, "id": "Schoeffler-Donner-Thomas", "orcid": "0000-0002-1932-5986", "display_name": "Schoeffler, Donner Thomas" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T-E", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/vedz-t661", "abstract": "The detonation driver is a device for generating the strong shock waves used in high-enthalpy hypersonic flow research facilities. The dynamic production of high-pressure and high-temperature driver gas has several advantages for shock-tube performance, however the unsteady gas dynamics of detonation waves also introduces several challenges. These are investigated here analytically and experimentally.
\r\n\r\nFor forward-mode operation, where the detonation propagates into the shock-tube diaphragm, the detonation Taylor wave attenuates the driven shock, and a model is needed to predict the resulting shock dynamics. This is accomplished by first analyzing the problem of plane shock decay generally. A new approximate solution is formulated for the classic piston start-stop problem and shown to be a significant advancement over predecessors. This result is applied to the shock decay from a detonation driver, and a two-parameter model is fit to simulation data, yielding a method for predicting shock trajectories from shock-tube initial conditions.
\r\n\r\nA small-scale shock tube is designed and constructed using a detonation driver that is operable in both the forward and reverse mode. A transparent driven section is used with large field-of-view shadowgraphy to perform novel time-resolved shock speed measurements. These are used to calibrate the decay model for a forward-mode driver and enable unique observations of shock-speed oscillations, resulting from diaphragm rupture and detonation initiation processes. Results are also obtained for shock tube operation with a conventional high-pressure helium driver.
\r\n\r\nThe gradients and fluctuations in post-shock flows are characterized using a heterodyne focused laser interferometer, a new instrument with advanced capabilities for measuring large phase changes with high resolution. As a development upon the FLDI, spatial filtering characteristics are preserved, and both differential and absolute phase data are acquired simultaneously, enabling a new technique for measurement of gas densities. The instrument is developed, experimentally validated, and then used to probe detonation-driven shock tube flows, achieving phase measurements of over 100 radians with milliradian resolution in a 10 MHz bandwidth. Results from forward-mode operation find that a hydrogen-oxygen driver produces remarkably disturbance-free flows. For reverse-mode operation, the amplitude of flow oscillations is found to be positively correlated with the contact-surface sound-speed ratio, and frequencies are consistent with first-order lateral acoustic waves.
" }, { "name": "Sekine, Ryoto", "degree": "PhD", "year": "2025", "title": "Lithium Niobate Nanophotonic Circuits for Information Processing", "advisor": "Marandi, Alireza", "url": "https://resolver.caltech.edu/CaltechTHESIS:07122024-082923823", "creators": [ { "name": { "family": "Sekine", "given": "Ryoto" }, "id": "Sekine-Ryoto", "orcid": "0000-0001-6135-8581", "display_name": "Sekine, Ryoto" } ], "advisors": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "advisor", "display_name": "Marandi, Alireza" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Cushing", "given": "Scott K." }, "id": "Cushing-Scott-K", "orcid": "0000-0003-3538-2259", "role": "member", "display_name": "Cushing, Scott K." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8vxv-eb34", "abstract": "In today's world, electronic information processors are ubiquitous. This dissertation explores an alternative paradigm of processing information using nanophotonics. We develop and investigate nanophotonic lithium niobate circuits leveraging strong \u03c7\u207d\u00b2\u207e nonlinearity for information processing. We demonstrate promising performance of nanophotonic circuits as building blocks of unconventional computing architectures that exploit the rich classical and quantum dynamics inherent to optics. Additionally, we introduce a new class of ultrafast nanophotonic sources, enabling novel opportunities for information processing. Ultimately, this dissertation puts forth the building blocks of next generation ultrafast photonic information processors in lithium niobate nanophotonics which may lead to photonic advantage." }, { "name": "Shayegan, Komron Joseph", "degree": "PhD", "year": "2025", "title": "Nanophotonic Engineering of Thermal Emitters", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-065031552", "creators": [ { "name": { "family": "Shayegan", "given": "Komron Joseph" }, "id": "Shayegan-Komron-Joseph", "orcid": "0000-0002-1532-357X", "display_name": "Shayegan, Komron Joseph" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1eap-d721", "abstract": "Thermal emission is our most ubiquitous light source, as all objects with non-zero temperature emit this type of radiation. Consequently, our ability to shape the spectral and directional properties of thermally emitted and absorbed light by structures is both intriguing at a fundamental level and has practical implications for infrared light sources, radiative cooling, and energy harvesting systems. To impart desired properties to emitted radiation, nanophotonic designs where subwavelength features are patterned into structures have proved effective in preliminary demonstrations of engineered nanoscale control of thermal emission.
\r\n\r\nIn this thesis, we leverage nanophotonic designs to demonstrate new phenomena in the context of thermal emission. We first use a guided-mode structure made of \u03b1-Si to resonantly couple to magneto-optically active InAs. The magneto-optic response is a common effect used in nonreciprocal optical elements, which we use here to directly observe a violation of the Kirchhoff thermal radiation law, a strict equality in the spectral, directional absorptivity and emissivity. This demonstration is significant in two ways: first, it opens new avenues to design thermal emitters with distinct spectral, directional emissivity and absorptivity properties, and second, it confirms theoretical predictions which have long lacked experimental confirmation.
\r\n\r\nWe then extend this experimental Kirchhoff violation to a broadband, directive thermal emitter. The nanophotonic design to achieve this is a deeply subwavelength structure of gradient epsilon-near-zero InAs layers that couple to a Berreman mode. The angular selectivity is determined by the stack thickness, while the broadband spectral range of the effect is imparted by the closely spectrally separated epsilon-near-zero wavelengths.
\r\n\r\nFinally, we theoretically and experimentally lay the groundwork for a thermal lens, where emitted radiation is directed to a focus a given distance above the surface of the structure. Using a combination of coupled dipole approximation, global optimization, and experimental measurements, we realize the necessary collective and local resonance conditions for this effect.
" }, { "name": "Shila, Kiran Arik", "degree": "PhD", "year": "2025", "title": "Low Noise at Low Cost for Large Radio Astronomy Arrays", "advisor": "Hallinan, Gregg W.; Padin, Stephen", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-173123134", "creators": [ { "name": { "family": "Shila", "given": "Kiran Arik" }, "id": "Shila-Kiran-Arik", "orcid": "0000-0003-4652-7038", "display_name": "Shila, Kiran Arik" } ], "advisors": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "advisor", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Padin", "given": "Stephen" }, "id": "Padin-Stephen", "orcid": "0009-0001-9993-4393", "role": "co-advisor", "display_name": "Padin, Stephen" } ], "committee": [ { "name": { "family": "Ravi", "given": "Vikram" }, "id": "Ravi-Vikram", "orcid": "0000-0002-7252-5485", "role": "chair", "display_name": "Ravi, Vikram" }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Padin", "given": "Stephen" }, "id": "Padin-Stephen", "orcid": "0009-0001-9993-4393", "role": "member", "display_name": "Padin, Stephen" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ng6s-6484", "abstract": "The 2020s is the decade of survey instruments in astronomy. Radio astronomy is no exception, with Caltech's proposed DSA-2000 being the most powerful radio interferometer in the world, costing much less than competing instruments. Key to this achievement are two core breakthroughs: a completely ambient-temperature receiver and a \u201cradio camera\u201d backend that images the sky in real time. DSA-2000 will have record-breaking survey speed and sensitivity, enabled by these two key breakthroughs, giving astronomers all over the world open access to exquisite all-sky maps to enable the discovery of billions of new radio sources, precise timing of pulsars, and localization of fast radio bursts. The array will produce enough data to keep astronomers busy for a century.
\r\n\r\nIn this thesis, we discuss the development of one of the key breakthroughs, the ambient-temperature receiver. Specifically, we focus on the design, testing, and implementation of the wideband, ambient-temperature low noise amplifier. We cover the design from analytic first principles through precision measurement of its performance. We follow this with a discussion of the design and implementation of the analog signal path, including a high performance, RF over fiber link. Finally, we discuss the Galactic Radio Explorer (GReX) instrument, designed as a global experiment probing the brightest radio transients in the local universe.
" }, { "name": "Slote, Joseph Alfred", "degree": "PhD", "year": "2025", "title": "Discrete Harmonic Analysis and its Applications to Testing, Learning, and Complexity", "advisor": "Umans, Christopher M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082025-235351698", "creators": [ { "name": { "family": "Slote", "given": "Joseph Alfred" }, "id": "Slote-Joseph-Alfred", "orcid": "0000-0002-6363-7821", "display_name": "Slote, Joseph Alfred" } ], "advisors": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "orcid": "0000-0002-6390-9401", "role": "advisor", "display_name": "Umans, Christopher M." } ], "committee": [ { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "chair", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Tamuz", "given": "Omer" }, "id": "Tamuz-O", "orcid": "0000-0002-0111-0418", "role": "member", "display_name": "Tamuz, Omer" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "orcid": "0000-0002-6390-9401", "role": "member", "display_name": "Umans, Christopher M." } ], "option_major": [ "cms" ], "doi": "10.7907/grjv-rz74", "abstract": "This thesis consists of two parts. In Part I we present a new class of norm discretization inequalities suited for low-degree polynomials in many dimensions, with applications to discrete harmonic analysis and to quantum and classical learning theory.
\r\n\r\nDiscretization inequalities (of Bernstein type) control the supremum norm of polynomials f by their supremum norms over certain finite subsets T of the domain. Unlike earlier multivariate Bernstein-type discretization inequalities we establish dimension-free comparisons for simple and generic T, such as product sets T=S\u2081 \u00d7 \u22c5\u22c5\u22c5 \u00d7 S\u2099 for S\u2c7c's consisting of well-spread points in R or C, in exchange for a constant that grows with deg(f).
\r\n\r\nOur results also introduce the notion of \"individual degree\"\u2014the maximum degree of f in any one variable\u2014as a fundamental parameter for discretization inequalities: we show for the first time that dimension-free discretizations of the uniform norm are possible for T with cardinality independent of deg(f), provided f has bounded individual degree.
\r\n\r\nOur work offers a new, high-dimensional perspective on discretization inequalities and yields several new results in analysis on the hypergrid (i.e., products of cyclic groups), including Bohnenblust\u2013Hille-type inequalities, dimension-free supremum norm bounds on level-k Fourier projections, and junta theorems. These estimates in turn provide the key analytic tools for extending recent breakthroughs in learning low-degree functions to the hypergrid and to its quantum analogue, local observables on K-level qudit systems.
\r\n\r\nIn Part II we apply ideas from analysis of Boolean functions to study other aspects of (quantum) computation: circuit complexity and property testing.
\r\n\r\nFirst, we introduce and study a deceptively simple model of constant-depth quantum circuits and begin the project of proving bounds on its capabilities, ultimately drawing on connections to nonlocal games and notions of approximate degree.
\r\n\r\nSecond, we introduce a new access model for property testing, quantum data, which allows for ultrafast testing algorithms where classical data provably yields no fast testers\u2014such as for monotonicity, symmetry, and triangle-freeness.
" }, { "name": "Solomon, Samuel Aaron", "degree": "PhD", "year": "2025", "title": "A Path Towards Wearable Affective General Intelligence", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082025-224903418", "creators": [ { "name": { "family": "Solomon", "given": "Samuel Aaron" }, "id": "Solomon-Samuel-Aaron", "orcid": "0000-0001-7199-6659", "display_name": "Solomon, Samuel Aaron" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" } ], "option_major": [ "medeng" ], "doi": "10.7907/2s0x-qq57", "abstract": "Artificial intelligence continues to support our daily decision-making tasks yet remains disconnected from our dynamic emotions driving these behaviors. Wearable technologies can supplement interactions with continuous emotion biofeedback, but existing models struggle to generalize across emerging biomarkers, platforms, and affective expressions. Here, we introduce a meta-analysis into embedding concurrent fragmented biosignals across 15 medical platforms, spanning five bodily locations, within a single profile that enables efficient and generalizable downstream affective analysis. We achieved this through a Lie manifold neural architecture that simultaneously reconstructs over 118,000 missing biometric details in 205 biomarkers and accurately forecasts 100 affective states across cohorts, questionnaires, and activities. We validated this framework across five datasets to propose a new skin-conformal, soft bioelectronic, affective computing platform that demonstrates closed-loop emotion modulation within thermal, audio, and visual interventions delivered through virtual, holographic, and conversational agents. Our framework establishes a new foundational bidirectional architecture for scalable, interpretable, and emotionally intelligent human-computer interactions." }, { "name": "Stroot, Gregory Matthew", "degree": "PhD", "year": "2025", "title": "Acoustic Radiation in Hypersonic Turbulent Boundary Layers: Deciphering Linear Dynamics", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05132025-002606572", "creators": [ { "name": { "family": "Stroot", "given": "Gregory Matthew" }, "id": "Stroot-Gregory-Matthew", "orcid": "0009-0004-7285-8281", "display_name": "Stroot, Gregory Matthew" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/agc2-at29", "abstract": "This thesis is primarily concerned with hypersonic turbulent boundary layers and the unique features \u2013 present in them. This problem is studied in three levels of varying fidelity \u2013 by means of linear resolvent analysis, a blended resolvent estimation approach, and direct decomposition of a temporally-resolved dataset. This thesis then explores three complementary research directions: (i) quantification of how streamwise development influences acoustic radiation across various parameter regimes, (ii) development of a forcing model that enables acoustic radiation estimation using only near-wall measurements, and (iii) evaluation of these findings through comparison with data-driven analysis techniques.
\r\n\r\nFirst, the resolvent analysis is performed on a turbulent hypersonic streamwise developing mean profile. It is shown that these (acoustically radiating) streamwise developing resolvent modes may be effectively modeled using resolvent modes around an assumed-parallel mean profile. Then this model is used to investigate the impact of streamwise development on acoustic radiation for varying bulk parameters.
\r\n\r\nSecond, the modeling of acoustic radiation from near-wall information is tackled. To achieve this, resolvent based estimation (RBE) is leveraged along with a small number of near-wall measurements. It is shown that RBE alone is insufficient to accurately predict the freestream power spectral density. Resolvent analysis around a streamwise developing mean profile is then analyzed by performing a Helmholtz decomposition, where it is shown that the solenoidal part of the resolvent forcing is primarily responsible for the linear amplification. This observation is used to develop an approximate forcing CSD method, which filters out any dilatational forcing, to supplement RBE. Using the approximate forcing with RBE shows significantly improved estimation of the freestream PSD.
\r\n\r\nFinally, spectral proper orthogonal decomposition (SPOD) is applied to a 3-D temporally-resolved dataset resulting from a direct numerical simulation of a hypersonic streamwise developing turbulent boundary layer. It is shown that the SPOD of the fluctuations around a streamwise developing mean extracts modes with a constant streamwise wavenumber and shows high-rank behavior. By further transforming the data in the streamwise direction, an SPOD of the fluctuations around a 1-D mean profile uncovers low-rank behavior and similar structures are seen between the resolvent and SPOD modes.
" }, { "name": "Tawney, Jacqueline Rose", "degree": "PhD", "year": "2025", "title": "Aqueous Metallo-Megasupramolecules: From Stability to Extensional Flow Properties", "advisor": "Kornfield, Julia A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-131020183", "creators": [ { "name": { "family": "Tawney", "given": "Jacqueline Rose" }, "id": "Tawney-Jacqueline-Rose", "orcid": "0000-0002-4276-0652", "display_name": "Tawney, Jacqueline Rose" } ], "advisors": [ { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "role": "advisor", "display_name": "Kornfield, Julia A." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Nelson", "given": "Chris W." }, "id": "Nelson-Chris-W", "role": "member", "display_name": "Nelson, Chris W." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." } ], "option_major": [ "aerospace" ], "doi": "10.7907/98fw-fx90", "abstract": "The addition of long, flexible polymers (> 1 Mg/mol) to a fluid is known to reduce turbulent drag and control droplet behavior, which has the potential to significantly enhance the efficiency of engineering flows across various industries, from agriculture to aviation. However, hydrodynamic forces can break the polymers and diminish their effectiveness, which is presently a major roadblock to their practical utilization in both applications and research. To address this challenge, the Kornfield group developed end-associative, self-healing polymers for use in fuel and, more recently, for use in water\u2014aqueous terpyridine-ended polyacrylamide (TPAM) supramolecules. This thesis examines the relationships between the molecular structure of TPAM, the amount of metal provided to link pairs of chain ends, and kinetic processes of the resulting supramolecules and the rheological properties and performance they provide. The most useful polymers for reducing turbulent drag, controlling mist, and tailoring droplet impact behavior combine high efficacy at low concentration (< 0.1 wt%), minimal impact on shear viscosity (< 2x), and long extensional relaxation time (> 1 ms), enabling them to stretch and resist elongational flow in turbulent eddies or fluid filaments. This thesis explores the fundamental nature of TPAM supramolecules and their potential utility as a rheological modifier, using measurements of molecular weight distributions and extensional relaxation times to illuminate the relationship between supramolecular structure and flow behavior.
\r\n\r\nFirst, we examine chemical degradation (desirable in the environment, but not during use), revealing that its rate can be controlled by limiting air exposure, avoiding an excess of metal ions relative to ligands, and storing samples in refrigerated conditions (4℃). Next, we assess how changes in metal-to-ligand ratios (M:L) and unimer lengths influence TPAM\u2019s megasupramolecular size, equilibration, and decay dynamics, showing that the presence of supramolecules comprising over 10 unimers gives rise to a relaxation time around 2 ms at 0.04 wt%\u2014long and dilute enough to cause drag reduction. In pursuit of even longer supramolecules (and thus longer relaxation times) with the same amount of TPAM, we modified the solution preparation protocol by introducing metal ions to a more concentrated TPAM solution prior to dilution. This exposed new and intriguing topologies with molecular weights extending beyond our measurable limit (10 Mg/mol), expanding the envelope of the longest accessible relaxation times (from ~2 to ~6 ms with M:L = 1:2 for Ni(II):terpyridine). We evaluated their potential as chain scission-resistant, turbulent drag-reducing agents. Initially, they reduce drag while maintaining backbone integrity; however, their supramolecular structure and extended relaxation time are not retained after multiple passes through contraction, turbulent, and expansion flows. The preservation of backbone integrity, along with the broad range of relaxation times achieved using more conventional linear topologies (up to ~3 ms), suggests that TPAM is a promising and robust rheological modifier worthy of continued investigation. Our findings enhance understanding of TPAM\u2019s structural and rheological properties under a range of conditions and lay the groundwork for further study of aqueous megasupramolecule dynamics and applications.
" }, { "name": "Thureja, Prachi", "degree": "PhD", "year": "2025", "title": "Electrically Reconfigurable Optical Metasurfaces for Universal Wavefront Shaping", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05022025-171646095", "creators": [ { "name": { "family": "Thureja", "given": "Prachi" }, "id": "Thureja-Prachi", "orcid": "0000-0003-3852-3395", "display_name": "Thureja, Prachi" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Polman", "given": "Albert" }, "id": "Polman-Albert", "orcid": "0000-0002-0685-3886", "role": "member", "display_name": "Polman, Albert" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/t5w7-xv05", "abstract": "The ability to control the properties of light in a compact, reconfigurable platform is essential for advancing nanophotonic technologies. Active metasurfaces --- flat optical components with tunable subwavelength elements --- enable real-time manipulation of wavefronts and thus offer a path toward versatile optical systems. This thesis furthers the development of electrically programmable metasurfaces as a step toward a universal platform for independent and comprehensive wavefront control. By integrating system-level optimization strategies, novel operation modes, and advanced material platforms, we establish a framework for next-generation, on-demand optical processing components.
\r\n\r\nFirst, we introduce an array-level inverse design approach for beam steering metasurfaces, that co-optimizes the spatial amplitude and phase responses to enhance target functionalities. Using the platform of a plasmonic, indium tin oxide (ITO)-based active metasurfaces, we demonstrate non-intuitive configurations that achieve high-directivity, continuous-angle beam steering up to 70\u00b0. Experimental validation confirms the effectiveness of this approach, which we further extend to advanced applications including flat-top beams, tunable beam widths, and multi-beam steering.
\r\n\r\nTo expand the functional channel capacity of active metasurfaces, we then explore space-time modulation as a means of enabling multi-frequency operation. By modulating ITO-based metasurfaces operating at near-infrared wavelengths with tailored waveforms at frequencies up to 10 MHz, we experimentally generate desired frequency harmonics, which appear as sidebands offset from the incident laser frequency. Introducing phase offsets between the driving waveforms enables tunable diffraction of frequency-shifted light. Theoretical extensions of this work highlight the potential of space-time metasurfaces to realize active multitasking components capable of dynamically performing multiple independent functions.
\r\n\r\nFor improved efficiency and broadband operation, we investigate electro-optically tunable metasurfaces based on the Pockels effect in barium titanate (BTO). We develop a scalable fabrication technique to obtain high-quality, thin-film BTO via stress-induced exfoliation from single-crystal substrates, preserving its bulk electro-optic properties. The experimentally measured Pockels coefficient r\u2083\u2083 exceeds that of commercially available thin-film lithium niobate, demonstrating the potential of this material platform for integration into high-speed, low-loss optical metasurfaces. Leveraging these properties, we design transmissive BTO-based metasurfaces for high efficiency beam steering at visible wavelengths.
\r\n\r\nThe results presented in this thesis lay the foundation for next-generation programmable metasurfaces by addressing key challenges in materials, design methodologies, and system-level control architectures. We conclude with a discussion of future directions, including the discovery of high-performance tunable materials, the development of advanced unit cell designs for independent control over multiple optical properties, and the miniaturization of control networks for large-scale metasurfaces. Ultimately, this work advances the development of reconfigurable and intelligent optical systems capable of adapting to diverse technological demands in a broad range of imaging, communication, and computing applications.
" }, { "name": "Tran, Thomas Tuan", "degree": "PhD", "year": "2025", "title": "Microstructural and Mechanical Characterization of Additively Manufactured Binary Metallic Alloys", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292025-003646523", "creators": [ { "name": { "family": "Tran", "given": "Thomas Tuan" }, "id": "Tran-Thomas-Tuan", "orcid": "0009-0003-7034-9486", "display_name": "Tran, Thomas Tuan" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Nelson", "given": "Hosea M." }, "id": "Nelson-H-M", "orcid": "0000-0002-4666-2793", "role": "member", "display_name": "Nelson, Hosea M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/ej4t-7e95", "abstract": "Hydrogel infusion-based additive manufacturing (HIAM) is a chemically versatile solid-state processing pathway that allows 3D structuring of ceramics and metals with micro-scale precision. Using controlled thermal treatments of 3D-printed metal ion-infused gels, this process generates intricate microstructures which are heavily influenced by the kinetics of gas-solid reactions and their subsequent phase evolution. This work seeks to refine our understanding of the process-structure-property relationships in HIAM-produced alloys and provide general insights for AM-enabled alloy development and microstructure design using metal oxide reduction.
\r\n\r\nThrough HIAM, we demonstrate the arbitrary alloying of CuxNi1-x binary alloys, where systematic characterization of microstructures down to the atomic scale revealed that reduction, or the lack thereof, drove the formation of chemically homogeneous alloy grains with numerous annealing twins and entrapped unreduced oxide nano-inclusions, resulting in a hierarchical two-phase composite. These features appear to elevate the average nanoindentation hardnesses by up to four times that of bulk annealed CuxNi1-x and lead to a composition dependence on the scaling of the \u201csmaller is stronger\u201d size effect in uniaxial micropillar compressions. This compositional dependence of hardness and deformation mechanisms arises from changes in reduction kinetics which influence the density of inclusions and voids developed by HIAM processing. As a result, HIAM demonstrates the capability to fabricate heterogeneous alloy systems as a result of their oxide reduction pathways, which are revealed by thermogravimetry experiments and kinetic analysis.
" }, { "name": "Trautner, Margaret Katherine", "degree": "PhD", "year": "2025", "title": "Operator Learning for Scientific Computing", "advisor": "Stuart, Andrew M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292025-172331972", "creators": [ { "name": { "family": "Trautner", "given": "Margaret Katherine" }, "id": "Trautner-Margaret-Katherine", "orcid": "000-0001-9937-8393", "display_name": "Trautner, Margaret Katherine" } ], "advisors": [ { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "advisor", "display_name": "Stuart, Andrew M." } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Hoffmann", "given": "Franca" }, "id": "Hoffmann-Franca", "orcid": "0000-0002-1182-5521", "role": "member", "display_name": "Hoffmann, Franca" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." } ], "option_major": [ "cms" ], "doi": "10.7907/s5p5-9j06", "abstract": "This thesis develops operator learning theory and methods for use in scientific computing. Operator learning uses data to approximate maps between infinite dimensional function spaces. As such, operator learning provides a natural framework for using machine learning in applications with partial differential equations (PDEs). While operator learning architectures have successfully modeled a variety of physical phenomena in practice, the theoretical foundations underpinning these successes remain in early stages of development.
\r\n \r\nThe present work takes a step towards a complete understanding of operator learning and its potential use in scientific applications. The thesis begins by studying multiscale constitutive modeling, where operator learning models can serve as surrogates to accelerate simulation and aid in model discovery of physical laws. The work proposes, and theoretically and numerically analyzes, an operator learning architecture for modeling history dependence in homogenized constitutive equations. The thesis then addresses learning solutions to an elliptic PDE in the presence of discontinuities and corner interfaces in two-dimensional materials. By proving a key continuity result for the underlying PDE, a universal approximation result is obtained. In its second half, the thesis moves on from the setting of homogenized constitutive laws and gives insight to operator learning from a broader perspective. First, error analysis bounds a form of discretization error that arises in implementations of the Fourier Neural Operator (FNO). Next, a modified form of the FNO, the Fourier Neural Mapping, accommodates finite-dimensional data while retaining the underlying function space structure. This modification allows applications where the map of interest is governed by an infinite-dimensional operator with data, such as parameters or summary statistics, in the form of finite vectors. Finally, the thesis extends a theory-to-practice gap result in finite dimensions to the infinite-dimensional operator learning setting, asserting that even for classes of architectures whose model expressivity scales well with model size, their error convergence with respect to data size scales poorly. In summary, this thesis builds understanding of operator learning from several perspectives and contributes both theoretical advancements and practical methodologies that improve the applicability of operator learning models to scientific problems.
" }, { "name": "Vafeidis, Panteleimon", "degree": "PhD", "year": "2025", "title": "Neural Network Models of Learning and Generalization", "advisor": "Rangel, Antonio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212025-232450900", "creators": [ { "name": { "family": "Vafeidis", "given": "Panteleimon" }, "id": "Vafeidis-Panteleimon", "orcid": "0000-0002-9768-0609", "display_name": "Vafeidis, Panteleimon" } ], "advisors": [ { "name": { "family": "Rangel", "given": "Antonio" }, "id": "Rangel-A", "role": "advisor", "display_name": "Rangel, Antonio" } ], "committee": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "orcid": "0000-0003-0016-3531", "role": "chair", "display_name": "O'Doherty, John P." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Rangel", "given": "Antonio" }, "id": "Rangel-A", "role": "member", "display_name": "Rangel, Antonio" } ], "option_major": [ "cns" ], "doi": "10.7907/cxs1-ss10", "abstract": "Neural networks have emerged as powerful models for understanding both biological and artificial intelligence. This thesis investigates fundamental principles of learning and generalization across four interconnected domains, bridging insights from theoretical neuroscience and machine learning to advance our understanding of intelligent systems.
\r\n \r\nChapter I addresses a central question in associative learning: how do neural circuits learn to associate concepts with one another? We combine two cortical inductive biases, namely mixed selectivity and predictive learning in compartmentalized neurons, to explain how the cortical architecture may confer significant evolutionary advantages for efficient learning and packing multiple associations within the same neuronal population. Our model achieves stimulus substitution, where neurons respond identically to a conditioned stimulus as they would to the associated unconditioned stimulus, a feat in which traditional, Hebb-based learning rules fail.
\r\n\r\nChapter II pivots from the static mappings between concepts learned in Chapter I to explore how neural systems develop the precise synaptic connectivity required to establish dynamic mappings for path integration\u2014the ability to maintain an internal sense of location without external cues. Applied to the Drosophila head direction system, our model develops connectivity patterns strikingly similar to those observed experimentally, with Continuous Attractor (CAN) dynamics emerging naturally from learning. This offers a novel perspective on how precisely calibrated neural circuits can develop through experience, rather than requiring genetic pre-specification, and explains experimental findings where animals adapt their internal representation when sensory experience changes.
\r\n\r\nIn Chapter III, we establish a theoretical framework explaining how disentangled representations\u2014internal models that isolate independent factors of variation in the world\u2014emerge from multi-task learning. We prove that any system competent at multiple related tasks must implicitly represent the underlying latent variables in a linearly decodable form. We experimentally confirm all major theoretical predictions, and reveal a fundamental connection between task diversity and representation quality, particularly explaining why modern transformer models may develop human-interpretable concepts. Furthermore, our work suggests that the massively parallel cortical architecture may be a key facilitator in the development of representations that enable the impressive zero-shot generalization ability that humans possess.
\r\n\r\nFinally, Chapter IV proposes leveraging Large Language Models (LLMs) as cognitive tools for evaluating latent factor hypotheses for psychology, leveraging the theoretical insights from Chapter III. It suggests that the self-consistency of an LLM's responses given hypothesized psychological factors could serve as a metric for psychological latent factor hypothesis evaluation. While preliminary, this approach represents a novel computational methodology for psychology that could transform how hypotheses for human cognition are developed and refined.
\r\n\r\nContinuous attractors display prominently in this thesis (Chapters II and III), yet these concepts are misunderstood, particularly in the experimental literature. Hence, in Appendix D of this thesis we provide important considerations about the detection and quantification of Continuous Attractors (CANs) from experimental data, considerations particularly important in order to avoid confusion when it comes to these concepts, leading to wasted efforts and resources in the experimental neuroscience community.
\r\n\r\nTogether, these investigations reveal complementary aspects of how intelligent systems develop useful, generalizable representations through learning. From biologically plausible learning rules to abstract computational principles, this thesis demonstrates how neural networks can illuminate fundamental mechanisms of intelligence across natural and artificial systems, contributing to a unified science of Neural Computation.
" }, { "name": "Williams, James Anthony", "degree": "PhD", "year": "2025", "title": "Ultrafast Quantum State Generation and Measurement in Nonlinear Nanophotonics", "advisor": "Marandi, Alireza", "url": "https://resolver.caltech.edu/CaltechTHESIS:04072025-222314586", "creators": [ { "name": { "family": "Williams", "given": "James Anthony" }, "id": "Williams-James-Anthony", "orcid": "0000-0001-9073-5745", "display_name": "Williams, James Anthony" } ], "advisors": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "advisor", "display_name": "Marandi, Alireza" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/s4n5-2405", "abstract": "While many physical systems, including superconductors, trapped atoms, molecules, and acoustic resonators can process quantum information, photonics holds several fundamental advantages. Most photonics systems not only offer the convenience of room temperature operation but also shed the scalability limitations imposed by cryogenic and high vacuum environments. Integrated photonics has shrunk room-sized experiments to a chip-scale device while improving performance and versatility. Operating at optical frequencies offers information bandwidths orders of magnitude larger than what is achievable with microwave or trapped atom experiments.
\r\n\r\nIn this thesis, we propose nanophotonic optical parametric amplifiers (OPAs) on a thin-film lithium niobate (TFLN) chip-scale platform for quantum information processing. Through dispersion-engineering, we achieve the distortion-free propagation of ultrafast pulses necessary for information clock rates above 1 THz. We investigate OPAs as ultrashort entangled pair sources and generate biphotons with a 165-fs temporal duration. We show that their generation efficiency and signal-to-noise performance is state-of-the-art at 2 \u00b5m and on-par with contemporary telecom-band sources. We explore OPAs as quantum measurement devices, and demonstrate all-optical single-photon level detection with a dead time of 75 fs. Finally, we show that OPAs can be used to recover continuous-variable quantum information by reconstructing the Wigner function of a 2.41 dB squeezed state encoded in a 154-fs pulse. This technique is loss-tolerant and offers a maximum clock speed of 6.5 THz. TFLN hosts a variety of high-performance optical devices including filters, modulators, resonators, III-V gain media, all of which are compatible with OPAs. Our results highlight ultrafast OPAs as the fundamental building blocks needed to realize large-scale circuits for all-optical quantum information processing.
" }, { "name": "Xie, Tian", "degree": "PhD", "year": "2025", "title": "Scalable On-Chip Platforms for Quantum Microwave-Optical Interface with Solid-State Ensembles", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03122025-171512282", "creators": [ { "name": { "family": "Xie", "given": "Tian" }, "id": "Xie-Tian", "orcid": "0000-0001-6154-1802", "display_name": "Xie, Tian" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/03kg-x059", "abstract": "Superconducting quantum circuits based on Josephson junctions are one of the most promising platforms for future quantum information processing. Tens of superconducting quantum bits have been integrated on a single chip with performances exceeding the most advanced classical computers. However, these new quantum machines operate at microwave frequencies, which have enormous thermal noise and photon loss at room temperature. This fundamentally limits the future application of this technology in distributed quantum computing and quantum networks. Conversely, optical photons are an ideal information carrier as the photon loss is extremely small in fibers and the thermal noise is negligible at room temperature. Therefore, a quantum transducer that converts between microwave and optical frequencies at the single-photon level is of great importance.
\r\n\r\nThis thesis is centered on building such chip-scale interfaces with rare-earth ion (REI) doped crystals. First, we focus on developing a theoretical understanding of microwave-to-optical transducers. Based on coupled mode theories, we derive a clean theoretical result of the on-resonance transduction model. This allows us to condense the relevant material properties for transduction into a single parameter, effective \u03c7\u207d\u00b2\u207e, describing the strength of the non-linearities provided by the rare-earth ion materials. Next, we designed, fabricated, and measured the chip under cryogenic temperatures, where percent-level efficiency and single-photon level of added noise referred to the input is achieved. To further demonstrate the unique advantage of atom-based platforms, we perform two transducer interference experiments, showing the scalability and capacity towards transducer-assisted remote entanglement of superconducting quantum bits. Lastly, with large microwave cooperativities achieved, we observe novel quantum electrodynamics enabled by controllable initialization of the excited-state spin system. By initializing the spins into spin-down and spin-up states, we observe collectively induced transparency and periodic superradiant emissions, respectively. Simulations are developed to explain the experimental results.
\r\n\r\nThese results establish REI doped crystals as a highly competitive platform for microwave-optical quantum interfaces and pave the way toward remote transducer-assisted entanglement of superconducting quantum machines.
" }, { "name": "Yu, Jing", "degree": "PhD", "year": "2025", "title": "Safe and Scalable Learning-Based Control: Theory and Application in Sustainable Energy Systems", "advisor": "Doyle, John Comstock; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechThesis:08192024-223132153", "creators": [ { "name": { "family": "Yu", "given": "Jing" }, "id": "Yu-Jing", "orcid": "0000-0003-1318-0189", "display_name": "Yu, Jing" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "co-advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cds" ], "doi": "10.7907/bgar-0602", "abstract": "From intelligent transportation systems to the smart grid, the next generation of cyber-physical systems (CPS) will substantially transform our society. It is vital that these systems are scalable and robust to uncertainties, with contextual awareness and fast adaptation. This dissertation presents progress towards addressing key challenges arising in the control of large-scale CPS, with a special focus on applications in sustainable energy systems.
\r\n\r\nLarge-scale CPS such as the smart grid often consist of numerous interconnected and heterogeneous subsystems that must coordinate to achieve global objectives by exchanging information over a communication network. \r\nTherefore, the first part of this thesis focuses on developing control algorithms that handle crucial design requirements emerging from scalability and communication constraints, such as disturbance localization, communication delay conformation, and distributed implementation.
\r\n\r\nSustainable energy systems are crucial for reducing greenhouse gas emissions and mitigating climate change. However, the inherent unpredictability and large uncertainties associated with renewable generation pose significant challenges for maintaining system stability and safety. Traditional control approaches, while robust and effective for known system models, often fall short when faced with the dynamic and uncertain nature of modern power systems. In the second part of the thesis, we address this challenge by integrating machine learning techniques with model-based control methods using uncertainty sets constructed from real-time data. In particular, we will introduce and provide convergence guarantees for a classic uncertainty set estimation method. Building on these uncertainty sets, we combine learning and control techniques to tackle core CPS control problems, such as adversarial stability certification for linear time-varying systems as well as networked systems under communication constraints where the system models are unknown.
\r\n\r\nThe final part of this thesis applies the developed methodologies to address the voltage control problem in power distribution networks with unknown grid topologies. We will combine online learning techniques and a robust predictive controller to achieve provably finite-time convergence to safe voltage limits, despite uncertainties in network topology and load variations. Our case study on a Southern California Edison 56-bus distribution system demonstrates the effectiveness of this approach in nonlinear, partial observation, and partial control settings.
" }, { "name": "Zhang, Wenxin", "degree": "PhD", "year": "2025", "title": "Advanced Nano Manufacturing Enables Probing Fundamental Mechanical Behaviors of Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03132025-055626664", "creators": [ { "name": { "family": "Zhang", "given": "Wenxin" }, "id": "Zhang-Wenxin", "orcid": "0000-0002-6318-0622", "display_name": "Zhang, Wenxin" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/fxq3-7817", "abstract": "The trend of miniaturization has revolutionized modern technologies, with micro- and nanoscale materials driving transformative advancements in high-tech industries and scientific discovery. Among the various properties and applications enabled at these small scales, nanomechanical properties play a fundamental role, underpinning the integrity and functionality of any structures or systems. However, despite advancements in both conventional and emerging micro- and nano-manufacturing strategies, there has remained a lack of direct \u201cbottom-up\u201d experimental pathways to fabricate and probe the mechanical responses of submicron-sized monolithic nano-specimens with unconventional microstructures and/or 3D nano-architectures with submicron-sized features, particularly for non-carbon materials.
\r\n\r\nIn this work, I will present novel nano-fabrication and manufacturing strategies and their applications in addressing these nanomechanical challenges through three key studies. In Chapter 2, the deformation characteristic of organic ice is studied via cryogenic micro-compression and molecular dynamics simulations, providing insights into a benzene-ring re-orientation-mediated densification deformation route and offering new insights into planetary geology for celestial bodies such as Titan. In Chapter 3, we experimentally unveiled unprecedented two-regime size effects in additively manufactured metallic nanopillars with hierarchical microstructures, revealing a nanocrystallinity-, nanoporosity-mediated plasticity mechanism through atomistic insights. In Chapter 4, we extended this nano-manufacturing approach to explore nanoporosity-driven deformation behaviors in nano-architected metals with in situ experiments and finite element analysis. Together, these studies not only elucidate previously unprobed fundamental small-scale mechanical behaviors but also lay the groundwork for developing an advanced micro-to-nanoscale manufacturing platform, enabling complex systems and functional applications such as energy storage, biomedical microrobots, nanophotonics, and beyond, which I will briefly discuss in Chapter 5 as an outlook with a few examples from metal/oxide nanocomposites to interpenetrated pyrolytic carbon microarchitectures.
" }, { "name": "Zhao, Jiawei", "degree": "PhD", "year": "2025", "title": "Understanding and Improving Efficiency in Training of Deep Neural Networks", "advisor": "Anandkumar, Anima", "url": "https://resolver.caltech.edu/CaltechTHESIS:02122025-201948305", "creators": [ { "name": { "family": "Zhao", "given": "Jiawei" }, "id": "Zhao-Jiawei", "orcid": "0000-0002-5726-6040", "display_name": "Zhao, Jiawei" } ], "advisors": [ { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "advisor", "display_name": "Anandkumar, Anima" } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Mazumdar", "given": "Eric V." }, "id": "Mazumdar-E-V", "orcid": "0000-0002-1815-269X", "role": "member", "display_name": "Mazumdar, Eric V." }, { "name": { "family": "Chen", "given": "Beidi" }, "id": "Chen-Beidi", "role": "member", "display_name": "Chen, Beidi" }, { "name": { "family": "Tian", "given": "Yuandong" }, "id": "Tian-Yuandong", "role": "member", "display_name": "Tian, Yuandong" } ], "option_major": [ "cms" ], "doi": "10.7907/jgq8-et91", "abstract": "As deep neural networks (DNNs) continue to drive progress in fields like computer vision and natural language processing, their increasing complexity presents significant challenges for training efficiency, particularly in large language models (LLMs). These challenges include memory limitations, energy consumption, and bandwidth constraints during training.
\r\n\r\nIn this thesis, I address these challenges by analyzing the training dynamics of DNNs and proposing hardware-efficient learning algorithms to enhance training efficiency. First, I focus on mitigating memory limitations in LLM training. Training large models like LLMs requires substantial memory for parameters, gradients, and optimizer states, often exceeding standard hardware capacity. To tackle this, I propose GaLore, a memory-efficient training algorithm that reduces the memory footprint of LLM training by up to 65.5% while preserving performance. Additionally, I introduce InRank, an incremental low-rank learning algorithm that further reduces memory usage by gradually increasing matrix rank.
\r\n\r\nNext, I address the issue of high energy consumption during training. Training large models like LLMs demands considerable energy, contributing to environmental impact. To mitigate this, I propose LNS-Madam, a low-precision training algorithm leveraging the logarithmic number system (LNS) to lower energy consumption without compromising accuracy. LNS-Madam achieves up to 90% energy savings compared to a full-precision baseline model.
\r\n\r\nFinally, I focus on bandwidth limitations in distributed training. Training LLMs often requires distributing computations across multiple devices to accelerate training. However, network bandwidth constraints can cause communication bottlenecks that slow down training. To resolve this, I introduce signSGD with Majority Vote, a communication-efficient training algorithm that reduces the overhead associated with distributed training.
" }, { "name": "Zhou, Ziran", "degree": "PhD", "year": "2025", "title": "Predictive Modeling of Architected Solids across Scales", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02242025-045741904", "creators": [ { "name": { "family": "Zhou", "given": "Ziran" }, "id": "Zhou-Ziran", "orcid": "0009-0008-9327-3505", "display_name": "Zhou, Ziran" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "chair", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "display_name": "Andrade, Jose E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/cn82-z804", "abstract": "Architected solids, comprising discrete or continuous materials and structures, are purposefully designed to achieve specific functional objectives, such as tailored mechanical properties or enhanced performance. The integration of architectural features and material science has revolutionized design and functionality across multiple length scales. However, experimental exploration of architected solids is often constrained by physical, financial, or technological limitations. To address these challenges, this study leverages computational models as powerful tools for validating and probing the behaviors of architected solids through three distinct case studies spanning different length scales.
\r\n\r\nThe first case study focuses on capturing the seismic performance of multiblock concrete structures at CERN for radiation shielding. The Level Set Discrete Element Method (LS-DEM), combined with Monte Carlo sampling of material properties, is employed to benchmark the displacement profiles of four concrete configurations against experimental data. In the second case study, a bonded LS-DEM model is utilized to investigate the bending response of a woven topological interlocking material (TIM). After validation against experimental results, the model is employed to explore how friction and contact area influence the bending resistance of the TIM system. The third case study introduces a 3D translational tensegrity structure modeled using the Finite Element Method (FEM). This model captures the deformation responses of single cells, monolayers, and multicellular spheroids under various loading conditions. Additionally, a data-driven (DD) framework with multiscale analysis is implemented, offering accurate results with enhanced computational efficiency. Through these three case studies, this research illustrates the evolution of computational models from tools for validating known behaviors to frameworks for exploring new phenomena.
" }, { "name": "de Jong, Emily Katherine", "degree": "PhD", "year": "2025", "title": "Cloudy with a Chance of Microphysics: Modeling Droplet Collisions for the Climate Scale", "advisor": "Schneider, Tapio", "url": "https://resolver.caltech.edu/CaltechTHESIS:09132024-172910003", "creators": [ { "name": { "family": "de Jong", "given": "Emily Katherine" }, "id": "de-Jong-Emily-Katherine", "orcid": "0000-0002-5310-4554", "display_name": "de Jong, Emily Katherine" } ], "advisors": [ { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "advisor", "display_name": "Schneider, Tapio" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "member", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Morrison", "given": "Hugh" }, "id": "Morrison-Hugh", "orcid": "0000-0001-8480-9787", "role": "member", "display_name": "Morrison, Hugh" }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" } ], "option_major": [ "mecheng" ], "doi": "10.7907/yv2y-kg55", "abstract": "Feedbacks between a warming atmosphere, emission of aerosols, and clouds and precipitation are some of the most difficult aspects for climate models to accurately capture. While climate models operate at resolutions of tens or hundreds of kilometers, many of the physics that determine how and where clouds form or precipitate function at the micron droplet scale. Due to this disparity in physical scales, most of these cloud physics must be modeled with only a few approximate quantities and physical equations. These simplifications lead to large uncertainties about climate forcings such as the sensitivity of global warming to human-emitted aerosols.
\r\n\r\nThis work presents several promising new techniques for modeling and understanding hydrometeors in the climate system, with a particular focus on processes that involve collisions between droplets. First, I extend a high-complexity high-fidelity Lagrangian microphysics method to represent the process of breakup, in which colliding droplets fragment upon collision. Next, I introduce two new methods which attempt to reduce the assumptions inherent to modeling droplet coalescence, in which colliding droplets combine to form a larger drop. The first method uses a spectral finite element approach, while the second generalizes this technique using a method of moments to create a fully flexible microphysics scheme. Finally, I turn to remote observations of clouds, aerosols, and lightning over busy shipping regions to offer new techniques for quantifying aerosol-cloud interactions from creative data resources. This combination of high-fidelity modeling tools, observational data, and efficient numerical methods offers a path toward improving our understanding of the role of cloud microphysics in our climate system.
" }, { "name": "Aghlmand, Fatemeh", "degree": "PhD", "year": "2024", "title": "Adaptive Optoelectronic Systems: From Bio- Sensing to Free-Space Optical Communication", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:08282023-193415593", "creators": [ { "name": { "family": "Aghlmand", "given": "Fatemeh" }, "id": "Aghlmand-Fatemeh", "orcid": "0000-0002-5103-9314", "display_name": "Aghlmand, Fatemeh" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" } ], "option_major": [ "eleceng" ], "doi": "10.7907/hj19-7516", "abstract": "Portable and point-of-care medical devices are becoming an essential part of today\u2019s medical technology. An affordable personal device that can diagnose and monitor a medical condition in real-time will improve the patient\u2019s life quality in many ways. Additionally, by autonomously providing the suitable treatment, a universal healthcare device can be accessible to most of the population at a low cost. Despite considerable efforts and great outcomes, most of the prior arts in realizing these devices have limitations that hinder their widespread use in portable applications. On the other hand, comprehensive environmental sensing has drawn great attention in the last few years. Monitoring the quality of water, soil, air, and waste is of utmost importance to study their effect on human life and also to recognize the consequence of human actions on the planet.
\r\n\r\nThe most important factors in developing a compact and portable device for medical and environmental applications are their integration level, ease of use with biomarkers, and reliability of the results. Detecting a specific chemical in the biology world relies on a biochemical reaction with a transducer that can convert the resulting signal into a measurable signal in various modalities, such as electrical, magnetic, or optical. Hence, the biosensing device is often a multidisciplinary apparatus that is not readily integrable due to the need for miniaturizing otherwise bulky optical or magnetic components. The key requirement in device miniaturization, though, is to use standard technologies to avoid extra cost and processing time for the device\u2019s mass production. The path towards achieving such a device needs revisiting the existing solutions and the capabilities of the powerful yet affordable CMOS technologies to seamlessly integrate various device components, namely electronics, biology, and optics/magnetics. This dissertation provides an overview of integrated biosensors and presents novel designs in optics and electronics to implement a fully integrated and miniaturized device for medical and environmental applications.
\r\n\r\nFluorescence sensing is one of the most reliable and widespread detection methods with well- established tools in synthetic biology. Specifically, bacterial-based fluorescence sensors offer unsurpassed advantages to labeled detection since bacterial cells, when engineered, can respond to various elements in their surroundings at a low cost and quite efficiently. The use of live bacterial cells is also of great importance in establishing the bidirectional link with the CMOS device. By monitoring the dynamics of the cells\u2019 growth and their protein expression, a desired biology response can be initiated upon receiving the stimulating signal from the device. The conventional methods in fluorescence sensing involve an elaborate setup with many external optical components unsuitable for portable and in vivo applications. Hence, integrating silicon chips and live bacterial biosensors in a miniaturized \"Silicon-Cell\" system can enable a wide range of applications for both sensing and remediation. Such integrated systems need on-chip optical filtering in the wavelength range compatible with fluorescent proteins, which are widely used signal reporters for bacterial biosensors.
\r\n\r\nIn the first part of this dissertation, we introduce a fully integrated fluorescence sensor in 65nm standard CMOS process comprising on-chip bandpass optical filters, photodiodes, and processing circuitry. The metal/dielectric layers in CMOS are employed to implement low- loss cavity-type optical filters, achieving a bandpass response at 600/700nm range suitable to work with fluorescent proteins. The sensitivity of the sensor is further improved in the electrical domain by using a C-TIA with variable switched capacitor gain, a voltage- controlled current source (VCCS), and feedback-controlled low-leakage switches, resulting in a minimum measured current of 1.05fA with SNR >18dB. The sensor can measure the statics/dynamics of the fluorescence signal as well as the growth of living E. coli bacterial cells. Using a differential design and layout, the sensor can distinguish two biochemical signals by measuring two fluorescent proteins encoded in a single bacterial strain. Furthermore, a proof of concept is demonstrated to establish bidirectional communication between living cells and the CMOS chip, using a fluorescent protein regulated by an optogenetic control.
\r\n\r\nIn the second part of this dissertation, we describe a fully integrated high-bandwidth optical receiver for RF-over-free-space optics (RoFSO). This work is motivated by the availability of a wide, unregulated bandwidth at the optical frequencies and the lower cost and setup time due to using atmosphere instead of fiber optics as the communication channel. Nonetheless, the atmospheric link poses serious challenges, including severe beam intensity and phase distortions. Here we present novel solutions at the system and circuit level to make the receiver adaptive and resilient to the mentioned distortions. The chip is designed and implemented in a 28nm CMOS process, and it is shown to achieve a measured gain of 58dB and bandwidth of 18GHz. The link performance is assessed by exposing the system to more than 26dB of optical loss, equivalent to 3.5km of free space distance under moderate visibility conditions. For a proof-of-concept demonstration, an 8Gbps non-coherent DPSK signal with an RF bandwidth of 10GHz is transmitted, resulting in a BER of 1 \u00d7 10\u207b\u2074 for a minimum received power of -30dBm and while consuming 19.2mW power at the receiver.
" }, { "name": "Akbari, Hamidreza", "degree": "PhD", "year": "2024", "title": "Characterization and Tuning of Quantum Emitters in Hexagonal Boron Nitride", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:02262024-184235077", "creators": [ { "name": { "family": "Akbari", "given": "Hamidreza" }, "id": "Akbari-Hamidreza", "orcid": "0000-0002-6073-3885", "display_name": "Akbari, Hamidreza" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/qz1v-3696", "abstract": "Hexagonal boron nitride (h-BN) is a two-dimensional material hosting atomic defects that serve as single-photon emitters, attributed to its large bandgap. Its high stability at room temperature, substantial Debye-Waller factor, and integrability into 2D devices make h-BN a compelling choice for quantum applications involving single-photon emitters.
\r\n\r\nInitially, we investigate the properties of emitters in h-BN to comprehend the limitations of their spectral linewidth. This study includes examining the effects of the host crystal's growth method, the emitter's environment (the substrate), and temperature. As a result, we identify two primary broadening regimes: thermal broadening and spectral diffusion. Secondly, we address spectral diffusion, the predominant broadening mechanism at cryogenic temperatures, which depends on local electrical charges near the emitter. We propose a device structure comprising graphene - emitter h-BN - buffer h-BN - graphene, designed to apply a DC electric field and suppress spectral diffusion. This approach leads to a dramatic two orders of magnitude reduction in linewidth, achieving Fourier transform-limited linewidth.
\r\n\r\nMoreover, we explored the 3D dipole orientation and axial location of emitters within an h-BN crystal slab by coupling them to a phase change material. We discovered that the dipole orientation of some emitters is predominantly out-of-plane, and these emitters tend to exist close to the crystal's surfaces. This insight aids in the quest to determine the atomic structure of the emitters.
\r\n\r\nFinally, we examine the photon statistics of single-photon beams generated by h-BN emitters. We demonstrate that these beams exhibit sub-Poissonian statistics with both pulsed and continuous-wave excitation. Our findings reveal that excitation power can serve as a control to alter photon statistics, and we utilize this dependency to illustrate how photon statistics influence the use of quantum emitters in quantum random number generation applications.
" }, { "name": "Badithela, Apurva Srinivas", "degree": "PhD", "year": "2024", "title": "Test and Evaluation of Autonomous Systems: Reactive Test Synthesis and Task-Relevant Evaluation of Perception", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022024-014038700", "creators": [ { "name": { "family": "Badithela", "given": "Apurva Srinivas" }, "id": "Apurva-Apurva-Srinivas", "orcid": "0000-0002-9788-2702", "display_name": "Badithela, Apurva Srinivas" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Wongpiromsarn", "given": "Tichakorn" }, "id": "Wongpiromsarn-Tichakorn", "role": "member", "display_name": "Wongpiromsarn, Tichakorn" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/e8qz-rd26", "abstract": "Autonomous robotic systems have potential for profound impact on our society -- legged and wheeled robots for search and rescue missions, drones for wildfire management, self-driving cars for improving mobility, and robotic space missions for exploration and repair of spacecraft. The complexity of these systems implies that formal guarantees during the design phase alone is not sufficient; mainstream deployment of these systems requires principled frameworks for test and evaluation, and verification and validation. This thesis studies two such challenges to mainstream deployment of these systems.
\r\n\r\nFirst, we consider the problem of evaluating perception models in a manner relevant to the system-level specification and the downstream planner. Perception and planning modules are often designed under different computational and mathematical paradigms. This talk will focus on evaluating models for classification and detection tasks, and leverages confusion matrices which are popularly used in computer vision to evaluate object detection models to derive probabilistic guarantees at the system-level. However, not all perception errors are equally safety-critical, and traditional confusion matrices account for all objects equally. Thus, task-relevant metrics such as proposition labeled confusion matrices are introduced. These are constructed by identifying propositional formulas relevant to the downstream planning logic and the system-level specification, and result in less conservative system-level guarantees. Using this analysis, fundamental tradeoffs in perception models are reflected in the tradeoffs of probabilistic guarantees. This framework is illustrated on a car-pedestrian example in simulation, and the confusion matrices are constructed from state-of-the-art detection models evaluated on the nuScenes dataset.
\r\n\r\nSecond, we consider the problem of automatically synthesizing tests for autonomous robotic systems. These systems reason over both discrete (e.g., navigate left or right around an obstacle) and continuous variables (e.g., continuous trajectories). This talk presents a flow-based approach for test environment synthesis which handles discrete variables and is also reactive to the system under test. Reactivity is important to account for uncertainties in system modeling, and to adapt to system behavior without knowledge of the system controller. These tests are synthesized from high-level specifications of desired behavior. Though the problem is shown to be NP-hard, a flow-based mixed-integer linear program formulation is used that scales well to medium-sized examples (e.g., >10,000 integer variables). The test environment can consist of static and reactive obstacles as well as dynamic test agents, whose strategies are synthesized to match the solution of the flow-based optimization. The overview of the approach is as follows. First, principles of automata theory are used to translate the high-level system and test objectives, and the non-deterministic abstraction of the system into a network flow optimization. The solution of this optimization is then parsed into GR(1) formulas in linear temporal logic. This GR(1) formula is used to synthesize reactive strategies of a dynamic test agent in a counterexample-guided fashion. We provide guarantees that the synthesized test strategy will realize the desired test behavior under the assumption of a well-designed system, the test strategy is reactive and least-restrictive,. This framework is illustrated on several simulation and hardware experiments with quadrupeds, showing promise towards a layered approach to test and evaluation.
" }, { "name": "Bernal-Choban, Camille Marie", "degree": "PhD", "year": "2024", "title": "Atomic Dynamics in Solids and Liquids from Inelastic Neutron Scattering", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09222023-185858765", "creators": [ { "name": { "family": "Bernal-Choban", "given": "Camille Marie" }, "id": "Bernal-Choban-Camille-Marie", "orcid": "0000-0001-7550-3153", "display_name": "Bernal-Choban, Camille Marie" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Granroth", "given": "Garrett" }, "id": "Granroth-Garrett", "orcid": "0000-0002-7583-8778", "role": "member", "display_name": "Granroth, Garrett" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/3nv3-g144", "abstract": "As temperature increases, atomic scale disorder, or entropy, drives the thermophysical properties of materials. One way it does this is by passing heat through materials in the form of vibrations. In solids, vibrational motions are called phonons, and their behaviors are used to predict macroscopic properties such as thermal expansion and thermal conductivity. Vibrational dynamics also exist in liquids but are traditionally less studied. Other forms of entropy include configurational and electronic entropy, which also evolve with temperature. Configurational changes in solids are often small, but in liquids, the prominence of diffusion makes this contribution significant. This dissertation addresses these atomistic components of entropy in two studies, one on bcc chromium and the other on the melting of monatomic systems.
\r\n\r\nIn the first study, phonon densities of states (DOS) of body-centered cubic chromium were measured by time-of-flight inelastic neutron scattering (INS) at temperatures up to 1493 K. Density functional theory calculations with both quasi-harmonic (QH) and anharmonic (AH) methods were performed at temperatures above the Neel temperature. Features in the phonon DOS decrease in energy (soften) substantially with temperature. A Born-von Karman analysis using fits to the experimental DOS reveals a softening of almost 17% of the high transverse phonon branch between 330 and 1493 K. The low transverse branch changes by approximately half this amount. The AH calculations capture the observed behavior of the two transverse phonon branches, but the QH calculations give some inverted trends. Vibrational entropies from phonons and electrons are obtained, and their sum is in excellent agreement with the entropy of chromium obtained by calorimetry, indicating that above 330 K, no explicit temperature-dependent magnetic contributions are necessary.
\r\n\r\nThe second investigation delves into the latent heat of melting, defined as TmΔSfus where Tm is the melting temperature and ΔSfus is the entropy of fusion. At the scale of atoms and electrons, ΔSfus has components from changes of atom configurations, atom vibrations, and thermal excitations of electrons. New data analyses were developed for inelastic neutron scattering to obtain changes in vibrational spectra upon melting. Combining these INS experiments with computational work using thermodynamic integration and molecular dynamics, components of ΔSfus were obtained for a total of six elements, Ge, Si, Bi, Sn, Pb, Li. Upon melting, there is always a positive change of configurational entropy, ΔSconfig. A baseline value of ΔSconfig=1.2kB/atom, approximately the value for Richard's rule, corresponds to zero change in the vibrational part of the entropy of fusion, ΔSvib. Elements having values of ΔSfus\r\nthat depart from this value of Richard's rule have both an additional ΔSvib and an additional ΔSconfig. Surprisingly, the extra ΔSconfig is close to 77% of ΔSvib, for both positive and negative deviations from Richard's rule. This implies a correlation between the change in the number of basins in a potential energy landscape and the change in the inverse of their curvature upon melting.
" }, { "name": "Burov, Dmitry Anatolyevich", "degree": "PhD", "year": "2024", "title": "Kernel Methods for Learning About Complex Dynamical Systems", "advisor": "Stuart, Andrew M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082024-115947714", "creators": [ { "name": { "family": "Burov", "given": "Dmitry Anatolyevich" }, "id": "Burov-Dmitry-Anatolyevich", "orcid": "0000-0002-5060-6794", "display_name": "Burov, Dmitry Anatolyevich" } ], "advisors": [ { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "advisor", "display_name": "Stuart, Andrew M." } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Hoffmann", "given": "Franca" }, "id": "Hoffmann-Franca", "orcid": "0000-0002-1182-5521", "role": "member", "display_name": "Hoffmann, Franca" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/zmmv-1a93", "abstract": "The ubiquitous spread of machine learning tools in natural sciences in recent years has seen trully exponential growth. What sounded like an expression from a sci-fi novel mere 7 years ago, \"solving PDEs with machine learning\" is hardly surprising to anyone today. The variety of methods is very large, but most of them revolve around the artificial neural networks. Despite tremendous success of applications to problems in natural sciences, and despite many strides towards a fundamental theory of neural networks, they still often lack interpretability and robustness of the results. An alternative, much narrower class of machine learning algorithms is comprised of the kernel methods. These methods, in contrast, offer deep analytical theory, with many approximation results and interpretable components. The firm foundation of the kernel methods, however, is offset by the practical difficulties, such as high computational cost, the burden of high-dimensional optimization and the necessity to manually choose kernel parametrization. This thesis explores a few applications of the kernel methods to dynamical systems, with the goal to address some of those issues. The comparison between the kernel analog forecasting and the plain Gaussian process regression is made, both from theoretical and practical sides, and a parametric extension of the former is proposed. An application of kernel methods to closures of dynamical systems is showcased. Finally, an application of data assimilation machinery to an epidemiological model is shown.
" }, { "name": "B\u00f6hme, Annette Ellen", "degree": "PhD", "year": "2024", "title": "Observation of the Microenvironment Around CO\u2082 Reduction Electrodes via Fluorescent Confocal Laser-Scanning Microscopy", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222024-182628149", "creators": [ { "name": { "family": "B\u00f6hme", "given": "Annette Ellen" }, "id": "B\u00f6hme-Annette-Ellen", "orcid": "0000-0003-1109-3428", "display_name": "B\u00f6hme, Annette Ellen" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Ardo", "given": "Shane" }, "id": "Ardo-Shane", "orcid": "0000-0001-7162-6826", "role": "member", "display_name": "Ardo, Shane" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ceqb-ew84", "abstract": "Electrochemical carbon dioxide reduction (CO\u2082R) is compelling because it enables the storage of renewable energy in the form of chemical bonds and offers the possibility to make carbon-based chemicals and fuels from a sustainable feedstock. A solid understanding of and control over the local microenvironment in and around CO\u2082R electrodes is crucial to optimize the device performance.
\r\n\r\nIn this work, we develop and refine a technique to observe the microenvironment around CO\u2082R electrodes via fluorescent confocal laser scanning microscopy with three-dimensional sub-micrometer spatial as well as temporal resolution. We combine two fluorescent pH probes, DHPDS and APTS, to resolve the local pH value around operando CO\u2082R electrodes. The pH plays an important role in determining the CO\u2082R activity and selectivity. In a first step, we image the local pH value in and around CO\u2082R GDEs with a random pattern of trenches and find that the pH is locally enhanced inside trenches. This effect becomes more pronounced for narrower trenches, reaching a maximum at a trench width of 5 \u00b5m. With the help of multiphysics simulations we can show that the high pH inside trenches is closely related to an enhanced C\u2082\u208a Faradaic efficiency. We harness this effect and fabricate CO\u2082R GDEs with tailored patterns of holes and trenches that allow a more systematic study of the influence of various micromorphology geometry parameters. We confirm experimentally that narrow holes and trenches exhibit a locally enhanced CO\u2082R selectivity and determine the most beneficial geometry parameters. We further use the developed technique to investigate the influence of a GDE's pore size on the local pH and with it, on the CO\u2082R selectivity. We observe that CO\u2082 transport is slower through smaller pores which can lead to switching of the reaction pathway and significantly alter the selectivity. We further investigate the importance of the microenvironment pH for CO\u2082R in acidic bulk electrolytes with the result that a non-acidic microenvironment pH, that can be reached at sufficiently high current densities, is required for the onset of CO\u2082R. Finally, we aim to extend the sensing capabilities and detect the local CO concentration in electrochemical devices but identify several challenges, including the probe reduction at the cathode.
\r\n\r\nOverall, we utilized fluorescent confocal laser-scanning microscopy to observe the microenvironment around CO\u2082R electrodes and correlate it with the CO\u2082R performance to gain a better mechanistic understanding of CO\u2082R and inform the design of future CO\u2082R electrodes.
" }, { "name": "Cao, Ruizhi", "degree": "PhD", "year": "2024", "title": "Dealing with Imperfections: From Aberration to Scattering", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:02152024-233300684", "creators": [ { "name": { "family": "Cao", "given": "Ruizhi" }, "id": "Ruizhi-Cao", "orcid": "0000-0003-3385-446X", "display_name": "Cao, Ruizhi" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/adgc-g315", "abstract": "Optical imaging has gained popularity in life science, biomedical imaging, fundamental physics research, and various other fields due to its non-invasive nature. In a carefully designed optical instrument operating in an ideal environment, the resolution of the optical imaging system is defined by its numerical aperture. However, practical manufacturing issues and inaccurate lens models make it challenging to achieve high resolution across a large area. High magnification lenses introduce aberrations that degrade image quality, prompting the use of complex lens systems dedicated to mitigating such aberrations. Furthermore, when a scattering medium is introduced into the imaging system, image formation becomes infeasible as light follows a complicated trajectory. These challenges pose great obstacles to the use of optical imaging methods in various scenarios. This thesis primarily consists of two parts, one aims to deal with aberration and the other tries to solve scattering induced imaging problems.
\r\n\r\nIn the first part of my thesis, I will discuss a technique called APIC (Angular Ptychographic Imaging with Closed-form method), which enables high-resolution imaging across a large field of view. To make APIC applicable in many non-ideal cases where aberrations (such as defocus) degrade image quality, we equip APIC with a closed-form aberration correction algorithm. We will demonstrate that APIC is unprecedentedly robust against aberrations and can retrieve high-resolution complex light fields using low magnification objectives.
\r\n\r\nIn the second part, we move on to dealing with scattering induced imaging problems. To form images where a scattering medium is present, we first explore the application of ultrasound modulation in optical imaging. We show that, by using ultrasound, we can image a hidden object in a highly scattering medium with ultrasonic resolution. Although this technique helps obtain clear images in the presence of a scattering medium, its resolution is limited. We then demonstrate a method in addressing another scattering problem, namely the non-line-of-sight (NLOS) imaging problem. In a general NLOS problem, modulation mechanisms such as the aforementioned ultrasound modulation are infeasible. We demonstrate that light can be directly focused on the hidden target with an optical diffraction-limited resolution by exploring the properties of the hidden target itself. We will show that this active focusing method possess remarkably improved resolution compared to existing methods and is able to image objects with large reflectance differences.
" }, { "name": "Chang, Benjamin K.", "degree": "PhD", "year": "2024", "title": "Electron-Phonon Interactions and Charge Transport in Organic Crystals and Transition Metal Oxides from First-Principles Calculations", "advisor": "Bernardi, Marco", "url": "https://resolver.caltech.edu/CaltechTHESIS:03232024-174719340", "creators": [ { "name": { "family": "Chang", "given": "Benjamin K." }, "id": "Chang-Benjamin-K", "orcid": "0000-0003-1304-9324", "display_name": "Chang, Benjamin K." } ], "advisors": [ { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "advisor", "display_name": "Bernardi, Marco" } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "member", "display_name": "Hsieh, David" }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/6zkq-2p13", "abstract": "Electron-phonon (e-ph) interactions play a critical role in determining material properties, such as charge and heat transport, optical response, and superconductivity. Recent advances in first-principles calculations based on density functional theory (DFT) enable quantitatively predictive studies of e-ph interactions and charge transport in a wide range of simple semiconductors and metals. However, certain technologically important materials, such as organic crystals and transition metal oxides (TMOs), remain less explored. Organic molecular crystals, known for their versatile electronic and mechanical properties, typically require high charge carrier mobility for practical applications. Yet accurately predicting the mobility and engineering approaches to improve it are challenging in organic crystals, because of their complex crystal structures with large unit cells and various charge transport regimes induced by e-ph interactions. Similarly, TMOs, both conventional and strongly correlated, are materials with broad applications and unique physics. A notable example are copper oxides (cuprate) superconductors, which are central to the study of high-temperature superconductivity and other exotic physical phenomena. Extensive experimental studies, particularly using photoemission techniques, have been employed to indirectly probe the e-ph interactions in TMOs. Nevertheless, many results are not fully understood, and calculations of e-ph coupling in TMOs are still scarce. This is mainly due to the strong correlation induced by d- and f-electrons posing a significant challenge to modeling.
\r\n\r\nThis thesis aims to develop state-of-the-art first-principles calculations to accurately describe e-ph interactions and the associated physical properties in organic crystals and TMOs. We focus on three research topics. First, we investigate the high-mobility bandlike transport regime in organic crystals. Using the formalism of the Boltzmann transport equation with electronic collisions computed from first principles, we study the mobility and its temperature dependence in benzene, anthracene, tetracene, pentacene, and biphenyl. Our results are in excellent agreement with experiments in all cases, and our pentacene calculation (72 atoms per unit cell) sets the record for the largest first-principles e-ph calculation to date. We find that the mobility is mainly regulated by e-ph scattering from low-frequency intermolecular phonons. Our analysis evidences the effectiveness of strain-based engineering to improve the mobility of organic crystals. Second, we propose a computational approach to study the intermediate polaronic transport regime in organic crystals. This method combines a finite-temperature cumulant-expansion approach for calculating electron spectral functions with the Kubo formula to compute the electronic conductivity and mobility. We show calculations of electron mobility in a naphthalene crystal in excellent agreement with experiments, and find that polaron effects, encoded in the satellites of the spectral functions, are induced by strong e-ph coupling of intramolecular hydrogen-atom vibrations. In the third and final topic, we study quantitatively the e-ph interactions in cuprate superconducting materials. Using the framework of Hubbard-corrected DFT, we focus on the prototypical parent (undoped) cuprate compound La2CuO4, which becomes superconducting upon doping. We show the first quantitative evidence of strong Fr\u00f6hlich-type e-ph interactions between holes and oxygen atomic vibrations, as well as polaron effects in hole spectral functions. Our findings explain a range of observations in photoemission experiments on both undoped and doped cuprates, suggesting the strong e-ph coupling is an intrinsic feature of the parent compounds rather than being induced by doping. The computational workflow presented in this work can be easily extended to a broad class of strongly-correlated oxides and insulators more generally. In summary, this thesis pushes the boundaries of first-principles calculations of e-ph interactions and transport, paving the way for a microscopic understanding of materials with large and complex unit cells, strong electronic correlations, and strong e-ph interactions.
" }, { "name": "Chang, Yi Hua", "degree": "PhD", "year": "2024", "title": "Studies of the Evolution and Stability of the Thin Film Equation for Externally Modulated Control of Electrohydrodynamic and Thermocapillary Patterning", "advisor": "Troian, Sandra M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05092024-225430822", "creators": [ { "name": { "family": "Chang", "given": "Yi Hua" }, "id": "Chang-Yi-Hua", "orcid": "0000-0003-0112-4139", "display_name": "Chang, Yi Hua" } ], "advisors": [ { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "advisor", "display_name": "Troian, Sandra M." } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Politzer", "given": "Hugh David" }, "id": "Politzer-H-D", "orcid": "0000-0002-4983-6621", "role": "member", "display_name": "Politzer, Hugh David" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/t65x-a578", "abstract": "It has been known for a couple decades, based on extensive experimental, theoretical and numerical studies, that a flat slender nanoscale viscous film in the absence of gravity always undergoes early time linear instability when subject to electrical or thermocapillary forces. The patterns resulting from a uniform transverse electric or thermal field resemble clusters of small rounded protrusions whose early time dynamics have been described by linear stability analysis of the governing fourth-order nonlinear interface equation -- the so-called thin film equation. However, the pattern formation process beyond early times generates larger amplitude protrusions prone to coalescence or an Oswald-like ripening of adjacent formations which destroy the pattern uniformity. Introduction of film interface modulation by external spatially periodic modulation offers a superior method for this type of lithographic patterning. The resulting linear and nonlinear response of the liquid layer can be tuned to corral the evolution of the liquid interface into periodic arrays containing identical components in certain parameter range. Conditions for achieving high-fidelity patterns are still not fully understood, however, rendering such technique not yet fully utilized in practical applications.
\r\n\r\nTo that end, we have conducted a number of analytical and numerical studies which elucidate various regimes leading to high-fidelity patterning by external spatial and temporal modulation. We focus on a single layer of viscous liquid film on a solid substrate which is described by the thin film equation derived under the long wavelength approximation. We first study the linear stability of periodic non-uniform stationary states subject to electrostatic stress and find that the necessary conditions for achieving stable states in 1D are the mass-limitation or saturation with a system-confining boundary (touching the mask) in order to suppress the coalescence and Ostwald-like-ripening modes. In 2D, stationary ridges are only achieved by saturation with a system-confining boundary in order to suppress its breakup. Time-dependent simulations further reveal inaccessible stationary states due to large electrode separation or large applied voltage. Exploratory studies on system subject to temperature gradient shows that the coalescence mode becomes unstable over a wider range of parameters due to thermocapillary stress. These findings result in phase diagrams relating the spatial modulation amplitude and electric Weber number or Marangoni number to the conditions for high-fidelity patterns which cannot be explained simply by matching the patterning and intrinsic instability wavelengths as previously claimed in literature.
\r\n\r\nWe then turn to the optimal control of electrohydrodynamic thin film patterning where the optimal strategy in deforming a flat film toward a desired shape is determined. A computational framework is derived which allows us to study the open-loop terminal control problem for thin liquid film. The approach allows us to quantify the best-possible outcome only constrained by the underlying physical mechanisms, and better understand the limitations of thin film patterning in relation to the choice of target shapes and system parameters. The impact of imperfect engineering and methods of mitigations are also discussed, which should prove useful to soft lithography and other applications.
" }, { "name": "Chen, Po-Chih", "degree": "PhD", "year": "2024", "title": "Signal Processing for Large Arrays: Convolutional Beamspace, Hybrid Analog and Digital Processing, and Distributed Algorithms", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05202024-212313617", "creators": [ { "name": { "family": "Chen", "given": "Po-Chih" }, "id": "Chen-Po-Chih", "orcid": "0000-0003-1637-9329", "display_name": "Chen, Po-Chih" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Tkacenko", "given": "Andre" }, "id": "Tkacenko-A", "role": "member", "display_name": "Tkacenko, Andre" } ], "option_major": [ "eleceng" ], "doi": "10.7907/m5ys-t440", "abstract": "The estimation of the directions of arrival (DOAs) of incoming waves for a passive antenna array has long been an important topic in array signal processing. Meanwhile, the estimation of the MIMO channel between a transmit antenna array and a receive antenna array is a key problem in wireless communications. In many recent works on these array processing tasks, people consider millimeter waves (mmWaves) due to their potential to offer more bandwidth than the already highly occupied lower-frequency bands. However, new challenges like strong path loss at the high frequencies of mmWaves arise. To compensate for the path loss, large arrays, or massive MIMO, are used to get large beamforming gain. It is practical due to the small sizes of mmWave antennas. When large arrays are used, it is important to develop efficient estimation algorithms with low computational and hardware complexity.
\r\n\r\nThe main contribution of this thesis is to propose low-complexity DOA and channel estimation methods that are especially effective for large arrays. To achieve low complexity, three main aspects are explored: beamspace methods, hybrid analog and digital processing, and distributed algorithms. First, a new beamspace method, convolutional beamspace (CBS), is proposed for DOA estimation based on passive arrays. In CBS, the array output is spatially filtered, followed by uniform decimation (downsampling) to achieve dimensionality reduction. No DOA ambiguity occurs since the filter output is represented only by the passband sources. CBS enjoys the advantages of classical beamspace such as lower computational complexity, increased parallelism of subband processing, and improved resolution threshold for DOA estimation. Moreover, unlike classical beamspace methods, it allows root-MUSIC and ESPRIT to be performed directly for uniform linear arrays without additional preparation since the Vandermonde structure is preserved under the CBS transformation. The method produces more accurate DOA estimates than classical beamspace, and for correlated sources, better estimates than element-space.
\r\n\r\nThe idea of hybrid analog and digital processing is then incorporated into CBS, leading to hybrid CBS for DOA estimation. In hybrid processing, an analog combiner is used to reduce the number of radio frequency (RF) chains and thus hardware complexity. Also for lowering hardware cost, the analog combiner is designed as a phase shifter network with unit-modulus entries. It is shown that any general (arbitrary coefficient) CBS filter can be implemented despite the unit-modulus constraints. Moreover, a new scheme of CBS is proposed based on nonuniform decimation and difference coarray method. This allows us to identify more sources than RF chains. The retained samples correspond to the sensor locations of a virtual sparse array, dilated by an integer factor, which results in larger coarray aperture and thus better estimation performance. Besides, with the use of random or deterministic filter delays that vary with snapshots, a new method is proposed to decorrelate sources for the coarray method to work.
\r\n\r\nNext, a 2-dimensional (2-D) hybrid CBS method is developed for mmWave MIMO channel estimation. Since mmWave channel estimation problems can be formulated as 2-D direction-of-departure (DOD) and DOA estimation, benefits of CBS such as low complexity are applicable here. The receiver operation is again filtering followed by decimation. A key novelty is the use of a proper counterpart of CBS at the transmitter\u2014expansion (upsampling) followed by filtering\u2014to reduce RF chains. The expansion and decimation can be either uniform or nonuniform. The nonuniform scheme is used with 2-D coarray method and requires fewer RF chains to achieve the same estimation performance as the uniform scheme. A method based on the introduction of filter delays is also proposed to decorrelate path gains, which is crucial to the success of coarray methods. It is shown that given fixed pilot overhead, 2-D hybrid CBS can yield more accurate channel estimates than previous methods.
\r\n\r\nFinally, distributed (decentralized) algorithms for array signal processing are studied. With the potential of reducing computation and communication complexity, distributed estimation of covariance, and distributed principal component analysis have been introduced and studied in the signal processing community in recent years. Applications in array processing have been also indicated in some detail. In this thesis, distributed algorithms are further developed for several well-known methods for DOA estimation and beamforming. New distributed algorithms are proposed for DOA estimation methods like root-MUSIC, total least squares ESPRIT, and FOCUSS. Other contributions include distributed design of the Capon beamformer from data, distributed implementation of the spatial smoothing method for coherent sources, and distributed realization of CBS. The proposed algorithms are fully distributed since average consensus (AC) is used to avoid the need for a fusion center. The algorithms are based on a finite-time version of AC which converges to the exact solution in a finite number of iterations. This enables the proposed distributed algorithms to achieve the same performance as the centralized counterparts, as demonstrated by simulations.
" }, { "name": "Deng, Weiting", "degree": "PhD", "year": "2024", "title": "Additive Manufacturing of 3D Micro-Architected Materials for Device Applications", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08212023-211243186", "creators": [ { "name": { "family": "Deng", "given": "Weiting" }, "id": "Deng-Weiting", "orcid": "0000-0003-0984-8027", "display_name": "Deng, Weiting" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "medeng" ], "doi": "10.7907/74dt-4442", "abstract": "Natural cellular biomaterials typically consist of hard and soft constituent materials that are hierarchically ordered to achieve outstanding mechanical properties, e.g., light weight, mechanical resilience, multi-functionality, etc. Architected materials are a new class of engineered materials with meticulously controlled internal structures that produce properties that differ from or exceed those of their constituent materials. Recent developments in additive manufacturing offer an extraordinary opportunity to rationally design the structure and chemical composition of architected materials to optimize properties and functionalities for a wide range of device applications. Here we first present a framework that combines an artificial intelligence tool and two-photon lithography in order to design and fabricate optimal porous structure with the desired anisotropic mechanical properties. The biomimetic and extremely tunable natural of the structures generated by the framework enables the great potential to be used as the bone scaffold design strategy which meets the requirements of complex anisotropic and heterogeneous mechanical properties of the vivo environment. The designed the architectures are meticulously verified by in situ Nanomechanics. These theory-informed experiments revealed close agreement between experimental data and artificial intelligence-predicted stiffness anisotropy, which opens a pathway for uncovering previous unattainable design space of elasticity vs. 3D architecture mapping in quantifiable and deterministic way. Besides, we explore the structural and material effects of additively manufactured microrobots which is powered by external physical fields for complex therapeutic assignments. The excellent movability and controllability permit the microrobots to be used as minimal invasive instruments for precise application in healthcare. The synergistically optimized microstructures and chemical composition enables the microrobots great potential to be applied to in vivo clinical applications." }, { "name": "Desai, Niyati K.", "degree": "PhD", "year": "2024", "title": "Scalar Vortex Coronagraphs for Imaging Habitable Exoplanets", "advisor": "Mawet, Dimitri", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282024-210649680", "creators": [ { "name": { "family": "Desai", "given": "Niyati K." }, "id": "Desai-Niyati-K", "orcid": "0000-0002-2843-8325", "display_name": "Desai, Niyati K." } ], "advisors": [ { "name": { "family": "Mawet", "given": "Dimitri" }, "id": "Mawet-D", "orcid": "0000-0002-8895-4735", "role": "advisor", "display_name": "Mawet, Dimitri" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bailey", "given": "Vanessa" }, "id": "Bailey-Vanessa", "orcid": "0000-0002-5407-2806", "role": "member", "display_name": "Bailey, Vanessa" }, { "name": { "family": "Mawet", "given": "Dimitri" }, "id": "Mawet-D", "orcid": "0000-0002-8895-4735", "role": "member", "display_name": "Mawet, Dimitri" } ], "option_major": [ "space" ], "doi": "10.7907/wnma-x832", "abstract": "Of the over 5,600 exoplanets detected to date, less than 2% have ever been directly imaged. Direct imaging is crucial for the study of habitable exoplanets around Sun-like stars because it offers the potential to characterize their atmospheres and detect biosignatures. However, the extreme contrast between star and planet light poses immense challenges which coronagraphs aim to address. Future telescopes, like NASA's upcoming Habitable Worlds Observatory, necessitate coronagraphs capable of suppressing starlight to contrast levels of 10-10 and operating in broadband light to directly image and characterize habitable planets. To meet these ambitious goals, innovations in focal plane mask technologies and wavefront sensing and control strategies are imperative.
\r\n\r\nThis thesis investigates the viability of scalar vortex coronagraphs for direct imaging of habitable exoplanets. The first part of this thesis focuses on simulation efforts for modeling various coronagraph mask topographies and laboratory testing. Analysis of current scalar vortex topographies found phase wrapping is favorable over classic vortex designs. The chromatic performance of one such design \u2014 the wrapped staircase scalar vortex coronagraph \u2014 is investigated and a laboratory demonstration is presented.
\r\n\r\nNext, this thesis explores the behavior of different wavefront sensing and control methods combined with the wrapped staircase scalar vortex coronagraph. Three techniques were implemented on a high contrast imaging testbed and competitive performance between model-free and model-based techniques was found, particularly with increasingly complex mask designs.
\r\n\r\nLastly, new scalar vortex mask designs which combine radially and azimuthally varying features are investigated. Specifically, the benefits of adding central phase dimples to scalar masks to improve broadband performance are explored. Hybrid designs incorporating phase dimples are found to suppress chromatic leakage and show substantial improvement in broadband contrast over current scalar vortex designs.
\r\n\r\nOverall, this thesis advances the understanding and development of scalar vortex coronagraphs for exoplanet direct imaging, explores their potential for future space telescopes and highlights avenues for further research and experimentation.
" }, { "name": "Esho, Iretomiwa", "degree": "PhD", "year": "2024", "title": "Investigation of Transport Phenomena in Semiconductors and Semiconductor Devices: Drain Noise, Two-Phonon Scattering, and Phonon Drag", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01242024-044612209", "creators": [ { "name": { "family": "Esho", "given": "Iretomiwa" }, "id": "Esho-Iretomiwa", "orcid": "0000-0002-3746-6571", "display_name": "Esho, Iretomiwa" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "chair", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Cleary", "given": "Kieran A." }, "id": "Cleary-K-A", "orcid": "0000-0002-8214-8265", "role": "member", "display_name": "Cleary, Kieran A." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/b30w-cr73", "abstract": "The dynamics of charge carriers in semiconductors set the foundation for semiconductor device performance. Devices crucial for fields like radio astronomy rely on transistor amplifiers where hot electron dynamics impact noise significantly. The overarching goal of this work is to contribute towards the development of better transistor amplifiers by investigating electron transport in existing devices and emerging materials.
\r\n\r\nThe physical mechanisms governing noise in a class of semiconductor devices called high electron mobility transistors (HEMTs) are not completely understood. HEMTs are transistors that use a junction between two materials of different band gaps as the channel. HEMTs are used as amplifiers by translating a small signal applied at the gate terminal to a large current at the drain terminal or output. The noise added at the input is well-characterized by the device physical temperature, while the origin of the noise added at the output is still up for debate. We attempt to fill this knowledge gap by proposing a theory of noise occurring at the drain terminal of these devices as a type of partition noise arising from two possible electron paths. This theory emphasizes the critical role of the conduction band offset between epitaxial layers of the device: a larger offset maximizes the channel sheet density and minimizes electron transfer between layers, potentially improving noise performance. The theory accounts for the magnitude and dependencies of the drain temperature and suggests strategies to realize devices with lower noise.
\r\n \r\nWe then investigate phonon-limited charge transport in the semiconductor boron arsenide. Boron arsenide has drawn significant interest due to reports of simultaneous high thermal conductivity and ambipolar charge mobility, desirable properties for integration in electronic devices. The theoretical prediction of high electron and hole mobility assumed the dominance of charge carrier scattering by one phonon. We consider the effects of two-phonon electron and hole scattering processes in boron arsenide, and find that inclusion of these higher-order processes reduces the computed room-temperature electron and hole mobility significantly from the one-phonon value. Despite its potential, our predictions of electron and hole mobility contradict recent experimental reports based on photoexcited charge carrier diffusion. Several factors may explain this discrepancy, including another type of two-phonon scattering not considered in this work, superdiffusion of hot carriers, induced carrier concentration, or a combination of all or some of the above elements.
\r\n \r\n\r\nAt high carrier concentrations, the phonon system may interact with the electron system on the timescale of the phonon-phonon interaction. When this happens, the nonequilibrium state of phonons becomes important for electron transport, and vice versa as these systems interact in a coupled manner. This coupled interaction could lead to an inflated value of the experimentally reported mobility. We quantify this effect, known as phonon drag, with a coupled electron-phonon Boltzmann transport equation framework and demonstrate that the electron mobility is indeed enhanced significantly at the relevant carrier densities.
" }, { "name": "Gomez De La Cruz, Salvador Rey", "degree": "PhD", "year": "2024", "title": "Linear Amplification in Nonequilibrium Turbulent Boundary Layers", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08312023-005517217", "creators": [ { "name": { "family": "Gomez De La Cruz", "given": "Salvador Rey" }, "id": "Gomez-De-La-Cruz-Salvador-Rey", "orcid": "0000-0002-7568-721X", "display_name": "Gomez De La Cruz, Salvador Rey" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Di Renzo", "given": "Mario" }, "id": "Di Renzo-Mario", "orcid": "0000-0003-0468-3606", "role": "member", "display_name": "Di Renzo, Mario" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/hn98-c285", "abstract": "Resolvent analysis is applied to nonequilibrium incompressible adverse pressure gradient (APG) turbulent boundary layers (TBL) and hypersonic boundary layers with high temperature real gas effects, including chemical nonequilibrium. Resolvent analysis is an equation-based, scale-dependent decomposition of the Navier Stokes equations, linearized about a known mean flow field. The decomposition identifies the optimal response and forcing modes, ranked by their linear amplification. To treat the nonequilibrium APG TBL, a biglobal resolvent analysis approach is used to account for the streamwise and wall-normal inhomogeneities in the streamwise developing flow. For the hypersonic boundary layer in chemical nonequilibrium, the resolvent analysis is constructed using a parallel flow assumption, incorporating N\u2082, O\u2082, NO, N, and O as a mixture of chemically reacting gases.
\r\n \r\nBiglobal resolvent analysis is first applied to the zero pressure gradient (ZPG) TBL. Scaling relationships are determined for the spanwise wavenumber and temporal frequency that admit self-similar resolvent modes in the inner layer, mesolayer, and outer layer regions of the ZPG TBL. The APG effects on the inner scaling of the biglobal modes are shown to diminish as their self-similarity improves with increased Reynolds number. An increase in APG strength is shown to increase the linear amplification of the large-scale biglobal modes in the outer region, similar to the energization of large scale modes observed in simulation. The linear amplification of these modes grows linearly with the APG history, measured as the streamwise averaged APG strength, and relates to a novel pressure-based velocity scale.
\r\n \r\nResolvent analysis is then used to identify the length scales most affected by the high-temperature gas effects in hypersonic TBLs. It is shown that the high-temperature gas effects primarily affect modes localized near the peak mean temperature. Due to the chemical nonequilibrium effects, the modes can be linearly amplified through changes in chemical concentration, which have non-negligible effects on the higher order modes. Correlations in the components of the small-scale resolvent modes agree qualitatively with similar correlations in simulation data.
\r\n\r\nFinally, efficient strategies for resolvent analysis are presented. These include an algorithm to autonomously sample the large amplification regions using a Bayesian Optimization-like approach and a projection-based method to approximate resolvent analysis through a reduced eigenvalue problem, derived from calculus of variations.
" }, { "name": "Graebener, Josefine Berta Marie", "degree": "PhD", "year": "2024", "title": "Formal Methods for Test and Evaluation: Reasoning over Tests, Automated Test Synthesis, and System Diagnostics", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312024-094443866", "creators": [ { "name": { "family": "Graebener", "given": "Josefine Berta Marie" }, "id": "Graebener-Josefine-Berta-Marie", "orcid": "0000-0002-1376-0741", "display_name": "Graebener, Josefine Berta Marie" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "aerospace" ], "doi": "10.7907/4xdc-b988", "abstract": "With the integration of autonomous systems into our everyday lives edging closer to reality, ensuring the safety of these systems is paramount. Part of the safety verification process is a rigorous testing procedure, which currently does not exist for autonomous vehicles. In this thesis, we aim to provide approaches using formal methods to increase the efficiency of testing campaigns.\r\nFirst, we provide a framework based on assume-guarantee contracts to specify tests in the form of a test structure. Using these test structures, we then show how to combine, split, and compare tests. Additionally, we characterize when tests can be combined and when the resulting test requires temporal constraints. Next, we demonstrate the approach on examples and find a strategy for a test agent using winning sets and Monte Carlo tree search.
\r\n\r\nSecond, we present a framework to automatically synthesize a test environment, consisting of static and reactive obstacles, and dynamic test agents. We characterize the desired test behavior in a system and a test objective in the form of a linear temporal logic specification, consisting of sub-tasks commonly used for robotic missions. This test environment must ensure that the test is not impossible (i.e. a correct system can pass the test), but also that every test execution that satisfies the system objective also satisfies the test objective. We use tools from automata theory to construct the virtual product graph that represents all possible test executions, and the virtual system graph, which corresponds to the system's perspective.\r\nWe formulate this routing problem as a network flow optimization on the virtual product graph in the form of a mixed integer linear program for different test environments. We show that this routing problem is NP-hard. We propose a counterexample-guided search using GR(1) synthesis to find a strategy for a test agent. This framework is demonstrated in several examples in simulation and hardware.
\r\n\r\nLastly, we present a framework to diagnose a system-level fault by identifying the component responsible for the failure. We make use of assume-guarantee contracts and Pacti, a tool for compositional system analysis and design, to construct a diagnostics map, which allows us to trace a system-level guarantee to possible causes. We show that this framework can reduce the number of statements that need to be checked in the diagnostics process. We illustrate this framework on several abstract examples and two examples inspired by a real-world autonomous system.
" }, { "name": "Gunnarson, Peter John", "degree": "PhD", "year": "2024", "title": "Autonomous Flow-Based Navigation in Unsteady Underwater Environments", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052024-052757779", "creators": [ { "name": { "family": "Gunnarson", "given": "Peter John" }, "id": "Gunnarson-Peter-John", "orcid": "0000-0002-4437-5379", "display_name": "Gunnarson, Peter John" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "chair", "display_name": "Bae, H. Jane" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/vnh6-3t44", "abstract": "Autonomous ocean-exploring robots promise to significantly enhance the rate at which we can explore ocean environments. However, the limited range and speed of existing autonomous underwater vehicles (AUVs) are barriers to comprehensive ocean exploration. To address these limitations, the work in this thesis investigates strategies for improving the capabilities of existing AUVs, such as targeted sampling and efficient navigation through background flows. Inspired by the ability of aquatic animals to navigate via flow sensing, hydrodynamic cues are investigated as a sensory input for accomplishing these feats of autonomous navigation using only onboard sensors. First, reinforcement learning (RL) is investigated as an algorithm for accomplishing efficient point-to-point navigation in simulated cylinder flow. The algorithm entails inputting point measurements of flow quantities such as velocity and vorticity into a deep neural network, which then determines a swimmer's actions. Using point velocity as the sensory input, the RL algorithm achieved a near 100 percent success rate in reaching the target locations while approaching the time-efficiency of optimal navigation trajectories. To test RL and flow-based navigation in a physical setting, we next developed the Caltech autonomous reinforcement learning robot (CARL), a palm-sized underwater robotic platform. As proof-of-concept analogy for tracking hydrothermal vent plumes in the ocean, the robot was tasked with locating the center of turbulent jet flows in a 13,000-liter water tank using data from onboard pressure sensors. Using a navigation policy trained with RL in a simulated flow environment, CARL successfully located the turbulent plumes at more than twice the rate of random searching by detecting mean flow gradients with the onboard pressure sensors. Lastly, combing both flow sensing and efficient navigation, the accelerometer onboard CARL was used to sense and exploit the flow from a passing vortex ring for energy-efficient propulsion. Body acceleration and rotation were shown to be effective methods of indirect flow sensing, which enabled the energy-efficient vortex ring surfing strategy. Throughout this work, efforts are made to understand the governing physics behind the discovered navigation strategies to generalize the results beyond a specific navigation problem, sensor type, or robotic implementation." }, { "name": "Guzman, Pedro", "degree": "PhD", "year": "2024", "title": "Developments in M\u00f6ssbauer Spectrometry: From Instrumentation to High Pressure Studies on Spins and Phonons", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302024-193052659", "creators": [ { "name": { "family": "Guzman", "given": "Pedro" }, "id": "Guzman-Pedro", "orcid": "0000-0002-9726-8315", "display_name": "Guzman, Pedro" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Scott", "given": "Valerie" }, "id": "Scott-Valerie", "orcid": "0000-0002-0267-9833", "role": "member", "display_name": "Scott, Valerie" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/hyry-q484", "abstract": "The well-established technique of 57Fe M\u00f6ssbauer spectrometry is used to investigate the local chemical environment in iron-containing materials. This technique relies on the recoil-free emission and absorption of \u03b3-rays by resonant nuclei within a solid. The key component of a M\u00f6ssbauer spectrometer is the velocity Doppler drive, which modulates the energy of the incident \u03b3-rays to detect the hyperfine structure of resonant nuclei. Since the 1970s, the conventional velocity Doppler drive has been constructed using a pair of electromagnetic coils, one for power and the second for feedback. An alternative M\u00f6ssbauer spectrometer was developed, utilizing an amplified piezoelectric actuator as the Doppler velocity drive under feedback control. The actuator, driven with a quadratic displacement waveform, produced a linear velocity profile and was optimized using measurements from a laser Doppler vibrometer (LDV). In transmission geometry, 57Fe M\u00f6ssbauer spectra of \u03b1-iron display minimal peak distortions, enabling M\u00f6ssbauer spectrometry in applications requiring compact size and low mass, such as geochemical studies on the Moon, Mars, or asteroids.
\r\n\r\nSynchrotron radiation is used for numerous experimental techniques, including X-ray diffraction (XRD), nuclear resonant inelastic X-ray scattering (NRIXS), and nuclear forward scattering (NFS), also known as synchrotron M\u00f6ssbauer spectrometry. Diamond-anvil cells, capable of reaching high pressures at various temperatures, combined with synchrotron experimental methods, provide the means to investigate the vibrational, magnetic, and thermophysical properties of materials. Measurements on 57Fe55Ni45 were conducted using synchrotron XRD, NRIXS, and NFS under various pressures and temperatures. XRD measurements at 298 K and 392 K under pressures up to 20 GPa confirmed a pressure-induced Invar effect between 7 GPa and 13 GPa, where the coefficient of thermal expansion is nearly zero. NFS measurements revealed a decrease in the magnetic moment of 57Fe under pressure, indicating an increase in magnetic entropy. The 57Fe phonon density of states (DOS) was measured with NRIXS from which a phonon entropy was extracted. Using thermodynamic Maxwell relations, magnetic and phonon contributions to thermal expansion were determined, demonstrating that the low thermal expansion in the pressure-induced Invar region stems from a competition between the thermal expansion from spins and from phonons.
" }, { "name": "Haghi, Benyamin Allahgholizadeh", "degree": "PhD", "year": "2024", "title": "Energy-Efficient and Robust Algorithms for Biomedical Applications", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:04072024-202335451", "creators": [ { "name": { "family": "Haghi", "given": "Benyamin Allahgholizadeh" }, "id": "Haghi-Benyamin-Allahgholizadeh", "orcid": "0000-0002-4839-7647", "display_name": "Haghi, Benyamin Allahgholizadeh" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" } ], "option_major": [ "eleceng" ], "doi": "10.7907/gkx4-s019", "abstract": "Medical devices play a critical role in improving the quality of life for patients and assisting physicians by monitoring, detecting, and helping manage chronic conditions such as epilepsy and spinal cord injuries. To perform these functions effectively, these devices must extract the most relevant information from complex medical data. However, the functionality of these medical devices has been limited by the existing challenges in medical applications. Some of these challenges include the complexity in the analysis of raw medical data, adaptability, non-stationarity, noise, large data volumes, real-time processing, limited resources, and high accuracy demands. Moreover, considering factors such as individual differences, environmental influences, and genetic variations, medical data will cause numerous variations and uncertainties in analyzing and interpreting the medical conditions in different biomedical applications. Medical data analysis is already complex and is further complicated by issues like non-stationarity and noise, especially when using traditional and manual methods. When it comes to the designing, implementation, and utilization of wearable and implantable medical devices, efficiency, accuracy, and adaptability become crucial. Particularly, applications that require fast control of equipment, such as brain-machine interfaces (BMIs), make the need for fast decision-making evident. Medical data have been conventionally managed by reliance on extensive manual labor. However, such manual data management techniques are not scalable, have inefficient procedures, and are more likely to produce errors. Therefore, more advanced, automated methods are required immediately considering the existing challenges of the current medical data analysis techniques.
\r\n\r\nSuch a shift in data processing and management will lead to more trustable procedures that can significantly improve the accuracy and efficiency of medical data analysis. Other than being just an improvement, such transformation signifies a noteworthy point in the development of medical devices. In this view, it is essential to introduce advanced technology and novel methods for medical data processing as well as automation. Therefore, it becomes critical that these high-performance and advanced techniques can efficiently be implemented with minimum effects on hardware for clinical applications. Currently, artificial intelligence (AI) and its subfield machine learning (ML) has led to major transformations in designing and utilization of various medical devices. Among all these biomedical applications, three major area are addressed in this thesis: Brain Machine Interfaces (BMIs), seizure detection, and classification of arrhythmias in cardiac rhythms. We selected these three applications due to their significance and ability to improve patient treatment further. Additionally, we showed how we used machine learning algorithms for each of these applications to address their current challenges.
\r\n\r\nIn our work related to Brain-Machine Interfaces (BMIs), we have been focused on improving the quality of life for individuals with spinal cord injury (SCI) through two studies. In our initial study, we have designed and implemented a deep multi-state Dynamic Recurrent Neural Network (DRNN) decoder for BMI applications. This algorithm decodes neural data recorded from the posterior parietal cortex (PPC) and the motor cortex (M1) of human participants to appropriate control signals to predict computer cursor kinematics on the computer screen. By reducing the amount of history used in predicting the movement kinematics from the recorded neural data, we have demonstrated that improved performance and robustness are preserved while memory and power consumption are reduced. We then compared the performance of DRNN with other decoding techniques to demonstrate that when operating on wavelet-based neural features, our proposed DRNN-based decoder outperforms other decoding techniques. Therefore, DRNN have the potential to be used for more efficient and effective BMIs. After developing DRNN as a decoding technique for BMI applications, we have implemented an efficient feature extraction technique, referred to as Feature Extraction Network (FENet), which has been designed by using convolutional neural networks for optimizing feature extraction and decoding to ensure consistency across electrodes when decoding the recorded neural data to the movement kinematics in BMI systems. After being tested with data recorded from the posterior parietal and motor cortices of three human participants, FENet outperformed existing feature extraction techniques such as threshold crossings and wavelet transforms, and it significantly enhanced both closed- and open-loop cursor controls. We have also evaluated the generalizability of FENet when applied to different datasets, brain regions, and participants. Therefore, the results of our research in BMI technology have the potential to promise the improvement of the quality of life for spinal cord injury (SCI) patients.
\r\n\r\nSecond, we co-designed EKGNet, a convolutional network that combines analog computing and deep learning for detecting heartbeat arrhythmia. EKGNet demonstrated high accuracy while minimizing power consumption, effectively overcoming challenges related to analog circuitry and real-time processing. The experimental findings, using PhysionNet\u2019s MIT-BIH and PTB Diagnostics datasets, showed an average balanced accuracy of 95% for intra-patient arrhythmia classification and 94.25% for myocardial infarction (MI) classification.
\r\n\r\nFinally, we designed a real-time seizure detector by using XGboost as a technique relies on gradient boosted trees, which can help with the fast and accurate diagnosis of seizure for epileptic patients. With an averaged detection latency of 1.1 seconds, this design attained average F1 scores of 99.23% and 87.86% under various data splitting methods. The energy-area-latency product was 27\u00d7 lower than the current state-of-the-art solutions, which allowed for adjustments that were specific to each patient and significantly reduced energy consumption.
\r\n\r\nThe results presented in this dissertation demonstrate the potential of AI in addressing the existing challenges in three biomedical applications: brain-machine interfaces (BMI), seizure detection, and heartbeat arrhythmia detection. By addressing these existing challenges including complex biological data management, real-time processing constraints, and limited resources in biomedical applications, AI has the potential to improve the quality of life for patients suffering from neurological disorders and medical conditions. Moreover, the improved precision, operational efficiency, and flexibility caused by the integration of AI into the design of the future biomedical systems will potentially assist healthcare providers to offer enhanced support and treatment to patients. While we have focused on the three above-mentioned biomedical applications, the principles learned from our analysis may be relevant and can be extended to other biomedical applications.
" }, { "name": "Ho, Dimitar Mi", "degree": "PhD", "year": "2024", "title": "Control of Unknown Dynamical Systems: Robustness and Online Learning of Feedback Control", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:09062023-095903699", "creators": [ { "name": { "family": "Ho", "given": "Dimitar Mi" }, "id": "Ho-Dimitar-Mi", "orcid": "0000-0002-7856-985X", "display_name": "Ho, Dimitar Mi" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "cds" ], "doi": "10.7907/fb64-vk24", "abstract": "Over the past few decades, our physical and digital worlds have become increasingly intertwined and reliant on each other. Advancements in areas such as machine learning, online optimization, and control theory, along with ubiquitous access to computational power, have played a crucial role in this technological evolution. As a result, we are now moving towards a future where complex and intelligent dynamical systems, with humans in the loop, govern our daily lives.
\r\n\r\nBuilding advanced control systems is a critical step in this journey, as they enable swift and data-informed decision-making. However, as we aim to create even more sophisticated closed-loop systems, we must proceed with a careful balance of ambition and caution. While the benefits of these interconnected systems are abundant and our dependence on them deepens, ensuring the actual reliability and safety of the systems becomes increasingly challenging due to the growing complexity of their dynamics. This challenge is particularly prominent in safety-critical applications involving physical systems, which often have strict and non-negotiable safety and performance requirements. To establish a harmonious relationship between our physical and digital worlds, it is crucial to develop intelligent closed-loop control systems that are not only fast and efficient, but also reliable and fault-tolerant.
\r\n\r\nThe title of this thesis, \"Control of Unknown Dynamical Systems: Robustness and Online Learning of Feedback Control,\" reflects the central focus of this work on addressing this pressing challenge. The thesis aims to develop theoretical frameworks and tools that provide insights and contribute new approaches to the design of control systems capable of handling the inherent uncertainty in real-world dynamical systems.
\r\n\r\nThe first part of the thesis focuses on the design of closed-loop systems that are robust to dynamic uncertainty, particularly in settings involving nonlinear dynamics and complex control constraints. The second part introduces a general framework for learning-to-control algorithms that provide worst-case guarantees, even in scenarios where the dynamic uncertainty is arbitrarily large. By addressing these key aspects, this work aims to advance our understanding and capabilities in designing control systems that can effectively deal with uncertainty.
" }, { "name": "Huang, Hsin-Yuan (Robert)", "degree": "PhD", "year": "2024", "title": "Learning in the Quantum Universe", "advisor": "Preskill, John P.; Vidick, Thomas G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032024-044352582", "creators": [ { "name": { "family": "Huang", "given": "Hsin-Yuan (Robert)" }, "id": "Huang-Hsin-Yuan", "orcid": "0000-0001-5317-2613", "display_name": "Huang, Hsin-Yuan (Robert)" } ], "advisors": [ { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "advisor", "display_name": "Preskill, John P." }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "co-advisor", "display_name": "Vidick, Thomas G." } ], "committee": [ { "name": { "family": "Brandao", "given": "Fernando" }, "id": "Brandao-Fernando", "orcid": "0000-0003-3866-9378", "role": "chair", "display_name": "Brandao, Fernando" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "member", "display_name": "Endres, Manuel A." }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "member", "display_name": "Preskill, John P." }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "member", "display_name": "Vidick, Thomas G." } ], "option_major": [ "cms" ], "doi": "10.7907/fgpv-3112", "abstract": "In this thesis, I will present our progress in building a rigorous theory to understand how scientists, machines, and future quantum computers could learn models of our quantum universe. The thesis begins with an experimentally feasible procedure for converting a quantum many-body system into a succinct classical description of the system, its classical shadow. Classical shadows can be applied to efficiently predict many properties of interest, including expectation values of local observables and few-body correlation functions. I will then build on the classical shadow formalism to answer two fundamental questions at the intersection of machine learning and quantum physics: Can classical machines learn to solve challenging problems in quantum physics? And can quantum machines learn exponentially faster and predict more accurately than classical machines? The thesis answers both questions positively through mathematical analysis and experimental demonstrations." }, { "name": "Huang, Yujia", "degree": "PhD", "year": "2024", "title": "Understanding and Improving Reliability of Inference Dynamics in Deep Neural Networks", "advisor": "Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:03052024-025023714", "creators": [ { "name": { "family": "Huang", "given": "Yujia" }, "id": "Huang-Yujia", "orcid": "0000-0001-7667-8342", "display_name": "Huang, Yujia" } ], "advisors": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "chair", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Gkioxari", "given": "Georgia" }, "id": "Gkioxari-Georgia", "role": "member", "display_name": "Gkioxari, Georgia" }, { "name": { "family": "Shi", "given": "Yuanyuan" }, "id": "Shi-Yuanyuan", "orcid": "0000-0002-6182-7664", "role": "member", "display_name": "Shi, Yuanyuan" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/77cc-6z86", "abstract": "Reliability is a crucial aspect for the successful deployment of deep learning systems across various domains. In generative modeling, it is essential to create content that adheres to specific rules. In the field of control, ensuring that robots operate safely without falling or entering hazardous areas is paramount. Similarly, in visual perception, the robustness of perception results against perturbations are vital.
\r\n\r\nIn this thesis, we explore the reliability of inference dynamics in deep neural networks such as ResNet, neural Ordinary Differential Equations (ODEs), and diffusion models.\r\nWe begin by examining the inference dynamics in standard networks with a discrete sequence of hidden layers, applying self-consistency and local Lipschitz bounds to enhance robustness against input perturbations. Our exploration then extends to neural ODEs, where the neural network specifies a vector field that continuously transforms the state. We employ forward invariance to achieve robustness, marking the first instance of training neural ODE policies with non-vacuous certified guarantees. The focus shifts next to diffusion models and their inference processes, particularly in adhering to symbolic constraints. For this, we introduce a novel sampling algorithm inspired by stochastic control principles. This algorithm not only guides these models in generating rule-specific content but also sets a new benchmark in symbolic music generation. Our work offers a cohesive understanding of inference dynamics in various deep learning architectures and propose new algorithms to significantly improve their reliability.
" }, { "name": "Iton, Zachery William Benjamin", "degree": "PhD", "year": "2024", "title": "Superionic Conduction of Next-Generation Mobile Ions in Solids Enabled by Coordinating Ligands", "advisor": "See, Kimberly", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302024-015407649", "creators": [ { "name": { "family": "Iton", "given": "Zachery William Benjamin" }, "id": "Iton-Zachery-William-Benjamin", "orcid": "https://orcid.org/0000-0002-2226-9006", "display_name": "Iton, Zachery William Benjamin" } ], "advisors": [ { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "advisor", "display_name": "See, Kimberly" } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" } ], "option_major": [ "matsci" ], "doi": "10.7907/fwyd-2w86", "abstract": "Advancements in battery technologies are a critical step towards meeting the growing demand for sustainable energy storage solutions. The development of next-generation battery technologies using \"beyond-Li\" ions, like Na\u207a, K\u207a, Mg\u00b2\u207a, Ca\u00b2\u207a, Zn\u00b2\u207a, and Al\u00b3\u207a, could potentially offer improved performance, safety, and cost-effectiveness over traditional lithium-ion systems. However, the realization of next-generation battery technology based on \"beyond-Li\" mobile ions is limited, in part, due to a lack of understanding of solid state conduction of next-generation ions, which governs ion transport in electrodes, interphases, and solid electrolytes. \u201cBeyond-Li\u201d ions tend to have relatively low mobility in solids due to: (1) the larger ionic radii (Na\u207a, K\u207a, Ca\u00b2\u207a), which limit the accessible migration pathways, or (2) higher charge densities (Mg\u00b2\u207a, Zn\u00b2\u207a Al\u00b3\u207a), which results in strong electrostatic interactions within the solid.
\r\n \r\nThis work discusses several structure-property relationships and structural modifications that are hypothesized to lead to facile conduction of next-generation working ions. A notable discovery is the superionic conductivity of ZnPS3 after exposure to humid environments. Water is introduced into the grain boundaries, thereby enabling Zn\u00b2\u207a ions from the material to migrate and conduct freely in the network of adsorbed water. The introduction of water leads to potential H\u207a, therefore a methodology for decoupling the contributions of Zn\u00b2\u207a and H\u207a in mixed ionic conducting solids using ion-selective EIS, transference number measurements, and deposition experiments is established.
\r\n \r\nFurther extending this approach, superionic conductivity of other next-generation ions in electronically-insulating inorganic solids is achieved by leveraging the established ion exchange/intercalation mechanism of MPS3 (M = Cd, Mn) materials. The mobile cations that are introduced are coordinated with H2O ligands which simultaneously increase the size of the bottlenecks within the migration pathway and screen the charge-dense ions resulting in high mobilities. Potential applications can be extended to water-incompatible systems by replacing the water ligands with aprotic molecules.
\r\n \r\nThese insights contribute significantly to the understanding and development of next-generation battery technologies, representing an important step toward the development of more sustainable and efficient energy storage solutions.
" }, { "name": "Ives, Craig Edward", "degree": "PhD", "year": "2024", "title": "Subtractive Photonics in Bulk CMOS", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272023-180554728", "creators": [ { "name": { "family": "Ives", "given": "Craig Edward" }, "id": "Ives-Craig-Edward", "orcid": "0009-0006-3893-541X", "display_name": "Ives, Craig Edward" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Sideris", "given": "Constantine" }, "id": "Sideris-Constantine", "orcid": "0000-0002-3042-4889", "role": "member", "display_name": "Sideris, Constantine" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/yrz7-ds33", "abstract": "Much of humanity's technological advancement over the last few decades may be attributed to exponentially increasing computing power, the bedrock of which is bulk CMOS technology. Exponentially increasing data rates in communications have also played an important role, facilitated by advancements in fiber optics and integrated photonics. However, efforts to capitalize on the complementary strengths of these two domains by merging them, an idea first envisioned almost 40 years ago, have so far proven inadequate. All previous attempts to integrate photonics in bulk CMOS have required either expensive process modification or resulted in waveguides with high loss.
\r\n\r\nIn this thesis, we discuss our investigations of a new method of integrating photonics into bulk CMOS, which we call the method of subtractive photonics. This method entails forming waveguides out of the back-end interconnect of an electronic chip. The interconnect metal is designed to wrap around dielectric channels such that when the metal is etched away, suspended dielectric waveguides remain. Although this method introduces a large, previously untapped design space, since there are many interconnect layers that can be used in photonic structures, it also introduces certain severe constraints. This thesis explores some of the possibilities this design space opens up, as well as some of the challenges involved in designing photonics in a process intended only for electronics. As part of this exploration, we demonstrate waveguides with an upper bound on loss that is significantly lower than the best previously published waveguide loss for unmodified bulk CMOS. We also demonstrate the first measurements of waveguide loss at visible and near-visible wavelengths in unmodified bulk CMOS, as well as the first measurements of waveguide coupled photodiodes in unmodified bulk CMOS. These proof-of-concept results may pave the way towards fully integrated electronic-photonic systems in unmodified bulk CMOS.
" }, { "name": "Jin, Zhiyang", "degree": "PhD", "year": "2024", "title": "Acoustic Biosensors for Noninvasive Imaging of Molecular Processes", "advisor": "Shapiro, Mikhail G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05152024-052419062", "creators": [ { "name": { "family": "Jin", "given": "Zhiyang" }, "id": "Jin-Zhiyang", "orcid": "0000-0002-4411-6991", "display_name": "Jin, Zhiyang" } ], "advisors": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "advisor", "display_name": "Shapiro, Mikhail G." } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Lester", "given": "Henry A." }, "id": "Lester-H-A", "orcid": "0000-0002-5470-5255", "role": "member", "display_name": "Lester, Henry A." }, { "name": { "family": "Gradinaru", "given": "Viviana" }, "id": "Gradinaru-V", "orcid": "0000-0001-5868-348X", "role": "member", "display_name": "Gradinaru, Viviana" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." } ], "option_major": [ "medeng" ], "doi": "10.7907/b51h-q307", "abstract": "Understanding biology in its native context has been a major scientific endeavor. Yet, it is challenging to visualize cellular dynamics at the molecular scale in the context of a living organism at the macroscopic scale. Ultrasound imaging represents a promising candidate to address this challenge, with its unique advantages of large imaging volume, deep penetration, and good spatiotemporal resolution. However, ultrasound was historically limited in retrieving molecular information that biology carries. Until very recently, the discovery of the first ultrasound-interacting biomolecules, gas vesicles (GVs), established a connection between connect cellular function and ultrasound signals, which later enabled ultrasound imaging of gene expression and thus the location of GV-expressing cells. Going beyond location tracking, this thesis describes the engineering of GV-based acoustic biosensors that made it possible to noninvasively image the dynamics of cellular signaling in living organisms.
\r\n \r\nGVs are genetically encoded intracellular air-filled \u201cballoons\u201d that are encapsulated by protein shells. The acoustic biosensor design leverages the GV surface protein GvpC, which controls GVs' ultrasound scattering by setting the stiffness of their protein shell. We developed the first acoustic biosensors by engineering GvpC to change its confirmation and thereby GVs\u2019 ultrasound contrast in response to the activity or concentration of specific molecules. Specifically, we first built the biosensors for three different types of enzymes and demonstrated noninvasive imaging of enzyme activity inside probiotic cells in the mouse colon in vivo. Next, we engineered the acoustic biosensors for calcium, a ubiquitous signaling molecule that is essential in many cellular processes (e.g., neural activity). With the first generation of this calcium sensor for ultrasound, we demonstrated imaging of receptor-specific calcium signaling deep inside the mouse brain through the intact skull noninvasively, which opened up the possibility of whole-brain neuroimaging that can lead to many breakthroughs in neuroscience. Last, we established a high-throughput engineering platform to develop all these GV-based imaging agents in a much shorter time frame. Collectively, this thesis presents the first demonstration of noninvasively imaging dynamic cellular signaling with acoustic biosensors and the feasibility of efficiently improving them for potential real-world applications with our engineering pipeline, opening up a new route towards understanding biology across scales.
" }, { "name": "Jurado Quiroga, Zoila Estefani", "degree": "PhD", "year": "2024", "title": "Towards a Synthetic Nucleus: Separating Transcription and Translation in Cell-Free Protein Expression Systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032024-141219249", "creators": [ { "name": { "family": "Jurado Quiroga", "given": "Zoila Estefani" }, "id": "Jurado-Quiroga-Zoila-Estefani", "orcid": "0000-0003-4160-5068", "display_name": "Jurado Quiroga, Zoila Estefani" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Voorhees", "given": "Rebecca M." }, "id": "Voorhees-R-M", "orcid": "0000-0003-1640-2293", "role": "member", "display_name": "Voorhees, Rebecca M." }, { "name": { "family": "Pandey", "given": "Ayush" }, "id": "Pandey-Ayush", "orcid": "0000-0003-3590-4459", "role": "member", "display_name": "Pandey, Ayush" } ], "option_major": [ "mecheng" ], "doi": "10.7907/kvq4-6132", "abstract": "Synthetic cells represent the culmination of decades of research aimed at deciphering the intricacies of life at its most basic level. The result of the fusion of biology, chemistry, physics, and engineering, synthetic cells promise to revolutionize biotechnology, medicine, and beyond. This thesis focuses on the ramifications of incorporating a synthetic nucleus within a synthetic cell.
\r\n\r\nTo experimentally study transcription and translation, we use a commercially available cell-free protein expression system comprising all the purified proteins essential for protein production (PURE), along with a fluorescent RNA aptamer--malachite green aptamer (MGapt), and a green fluorescent protein (deGFP). We observed that the chemical composition of the PURE system significantly impacts MGapt fluorescence, leading to inaccurate RNA calculations. We identify the reducing agent, dithiothreitol (DTT), to address this challenge as a crucial chemical affecting MGapt fluorescence. We propose a model that can reliably model MGapt measurements in commercial PURE. This investigation illuminates the intricate dynamics of MGapt in PURE and emphasizes the necessity of accounting for environmental factors in RNA measurements employing aptamers.
\r\n\r\n\r\nSubsequently, to advance our understanding of a synthetic nucleus and analyze the effects of separating transcription and translation in a cell-free protein expression, we propose and validate a chemical reaction network model for transcription (TX) in PURE. Additionally, we used open-source software to expand an existing translation (TL) model for any arbitrary DNA sequence to create a nearly complete model of TX-TL in PURE. Leveraging this model, we investigate the effect of introducing a synthetic nucleus by modulating the RNA diffusion rate and resource allocation. This detailed model showcases our capability to comprehensively model protein expression in PURE, enabling insights into the efficacy of segregating transcription and translation processes within the artificial cell environment. Lastly, we provide a perspective on the future of synthetic cells with an artificial nucleus and propose further steps to develop the proposed synthetic nucleus model.
" }, { "name": "Kaifu, Hiroki", "degree": "PhD", "year": "2024", "title": "Structural and Dynamical Correlations Linked to Smaller Thermal Resistance at a Classical Liquid/Solid Interface", "advisor": "Troian, Sandra M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012024-162517388", "creators": [ { "name": { "family": "Kaifu", "given": "Hiroki" }, "id": "Kaifu-Hiroki", "orcid": "0009-0003-2507-6810", "display_name": "Kaifu, Hiroki" } ], "advisors": [ { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "advisor", "display_name": "Troian, Sandra M." } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Motrunich", "given": "Olexei I." }, "id": "Motrunich-Olexei", "orcid": "0000-0001-8031-0022", "role": "member", "display_name": "Motrunich, Olexei I." }, { "name": { "family": "Porter", "given": "Frank C." }, "id": "Porter-F-C", "orcid": "0000-0003-1948-8889", "role": "member", "display_name": "Porter, Frank C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4z6h-v265", "abstract": "Ever more powerful and densely packed chips for applications like cryptocurrency mining and artificial intelligence generate such enormous heat fluxes that designers are pivoting from gas to liquid cooling to forestall damage from thermal runaway. Even with optimal flow patterns however, the intrinsic thermal boundary resistance at the liquid/solid (L/S) interface poses an additional source of thermal impedance. There is a lingering misconception in the field that the higher the liquid contact density, the more frequent the L/S collision rate and the smaller the thermal slip length. Here we present an insightful counterexample based on non-equilibrium molecular dynamics simulations of a classical liquid confined between different facets of a face centered cubic crystal held at different temperature. We have conducted a comprehensive study to quantify thermal exchange and propagation across the interface by varying the L/S interaction energy, L/S repulsive distance, facet orientation, thermal flux and local temperature with particular emphasis on the properties of the liquid contact layer (i.e., liquid monolayer adjacent to the solid surface). Numerous static and dynamic quantities characterizing the contact layer reveal the ways in which long range order, anisotropy of the L/S potential and correlated motion act to reduce the thermal slip length. Systems with the smallest thermal slip length exhibit two distinct features: 2D caged motion with string-like alignment of liquid particles unlike that observed in glassy systems and larger non-ergodicity parameter but shorter, not longer, caging times.
\r\n\r\nThese simulations have revealed two master curves which help unify the various influences at play. The first relation directly links the thermal slip length to the temperature modified 2D static structure factor representing long-range order in the contact layer. The second relation directly links the thermal slip length to the temperature modified dominant frequencies of the first solid and liquid layer as extracted from the density of states. These correlations, which represent power law dependencies, offer a new paradigm for the design of L/S interfaces to maximize thermal exchange across a classical L/S interface.
" }, { "name": "Kamakari, Hirsh", "degree": "PhD", "year": "2024", "title": "Investigation of Quantum Computers for Quantum Simulation and Machine Learning", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282024-002413905", "creators": [ { "name": { "family": "Kamakari", "given": "Hirsh" }, "id": "Kamakari-Hirsch", "orcid": "0000-0002-5377-9631", "display_name": "Kamakari, Hirsh" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "member", "display_name": "Endres, Manuel A." }, { "name": { "family": "Chen", "given": "Xie" }, "id": "Chen-Xie", "orcid": "0000-0003-2215-2497", "role": "member", "display_name": "Chen, Xie" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/rec5-4z30", "abstract": "The use of quantum mechanical phenomena for information processing has the potential to solve computational problems which are believed to be intractable for classical computers. Inspired by this potential, the last several decades has seen rapid development in both the theory and practice of quantum information processing. In this thesis, we explore three applications of quantum computing for the physical and computational sciences.
\r\n\r\nThe first potential application is for the simulation of open quantum systems. We introduce two algorithms for the simulation of open quantum systems governed by a Lindblad equation. Based on adaptations of the quantum imaginary time evolution algorithm, these methods transform non-unitary open system evolution into unitary evolution which can be implemented on contemporary quantum hardware. We demonstrate these algorithms on IBM's quantum hardware via the simulation of the spontaneous emission of a two-level system and the dissipative transverse field Ising model.
\r\n\r\nNext, we explore efficient methods to probe measurement induced phase transitions using superconducting circuits. These phase transitions occur in monitored quantum systems as the measurement rate of randomized single qubit measurements increases. We overcome two exponential bottlenecks which limited the system sizes of previous experiments on superconducting circuits by employing a cross-entropy benchmarking protocol and Clifford based circuit compression techniques. We observed measurement induced phase transitions on systems of up to 22 physical qubits.
\r\n\r\nFinally, we switch our attention to machine learning, where we prove rigorous quantum advantages for adversarially robust classification. By constructing a learning task based on widely accepted cryptographic assumptions, we show a necessary condition for the utility of quantum computers for robust classification. In particular, we show that for the learning task we construct, any efficient classical learner cannot robustly classify better than chance, whereas a quantum learner can efficiently and robustly classify data with high accuracy.
\r\n\r\nThrough these studies, we show that quantum computers have potential application in the physical and information sciences in both the near and long term.
" }, { "name": "Kili\u00e7, Korda\u011f Mehmet", "degree": "PhD", "year": "2024", "title": "On the Complexity of Neural Network Representations", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032024-055145735", "creators": [ { "name": { "family": "Kili\u00e7", "given": "Korda\u011f Mehmet" }, "id": "Kili\u00e7-Korda\u011f-Mehmet", "orcid": "0009-0005-6321-7113", "display_name": "Kili\u00e7, Korda\u011f Mehmet" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "orcid": "0000-0002-6390-9401", "role": "chair", "display_name": "Umans, Christopher M." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "eleceng" ], "doi": "10.7907/trse-ff38", "abstract": "The evolution of the human brain was one of the milestones in the history of information after the emergence of life. The underlying biological, chemical, and physical processes of the brain have amazed scientists for a long time. It is still a mystery how the human brain computes a simple arithmetical operation like 2 + 2 = 4. This enigma has spurred investigations into understanding the intrinsic architecture of the brain.
\r\n \r\nThis thesis delves into two primary models for brain architecture: Feedforward Neural Networks and Nearest Neighbor (NN) Representations. Both models are treated under the hypothesis that our brain does not work with \"large\" numbers and expressive power is derived from connectivity. Thus, when examining a network or, more precisely, a single neuron model, we strive to minimize the bit resolution of weights, potentially increasing depth or circuit complexity.
\r\n \r\nFor the NN representations, the memory is defined by a set of vectors in R\u207f (that we call anchors), computation is performed by convergence from an input vector to a nearest neighbor anchor, and the output is a label associated with an anchor. Limited bit resolution in the anchor entries may result in an increase of the size of the NN representation.
\r\n\r\nIn the digital age, computers universally employ the binary numeral system, ensuring the enduring relevance of Boolean functions. This study specifically explores the trade-off between resolution and size for the computation models for Boolean functions. It is established that \"low resolution\" models may require a polynomial or even an exponential increase in the size complexity of the \"high resolution\" model, potentially making the practical implementation infeasible. Building upon prior research, our goal is to optimize these blow-ups by narrowing the gaps between theoretical upper and lower bounds under various constraints. Additionally, we aim to establish connections between NN representations and neural network models by providing explicit NN representations for well-known Boolean functions in Circuit Complexity Theory.
" }, { "name": "Kim, Areum", "degree": "PhD", "year": "2024", "title": "Probing Active Nanophotonic Materials Phenomena Under Electrostatic Modulation", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302024-043707549", "creators": [ { "name": { "family": "Kim", "given": "Areum" }, "id": "Kim-Areum", "orcid": "0000-0001-9259-0906", "display_name": "Kim, Areum" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/16x8-7x89", "abstract": "Nanophotonic metastructured devices have gained significant attention due to their ability to manipulate properties of light such as the wavelength, amplitude, and phase. For photonic metastructures, these properties are typically fixed at the time of fabrication, as they depend on the geometrical parameters of resonant structures. Therefore, there is a growing interest in active nanophotonic devices, which can dynamically control the properties of light by incorporating active materials and applying external stimuli, in operation after fabrication.
\r\n\r\nThis thesis investigates the dynamic control of light through electrostatic modulation of metastructures containing indium tin oxide (ITO) and monolayer transition metal dichalcogenides (1L-TMDs) materials. Specifically, we analyze the dynamic behavior of these materials, characterizing their morphological, electrical, and optical properties within devices.
\r\n\r\nIn the first two chapters, we discuss the effects of ion migration on the electro-optic response of ITO-based active nanophotonic devices. Initially, we investigated uniformly deposited silver/dielectric/ITO heterostructures. Under electrical bias, silver ions and oxygen vacancies in the ITO actively migrate changing the device operating characteristics, resulting in hysteretic current-voltage curve behavior. Although optical modulation was barely observed, we explored the thermodynamic instability giving rise to electrical hysteresis in this volatile device. Furthermore, we investigated the impact of oxygen vacancy ion migration on the frequency response and phase modulation of ITO-based active metasurfaces. By annealing the devices, we were able to reduce the oxygen vacancy concentration, thereby improving the device high frequency performance.
\r\n\r\nIn the latter two chapters, we explore the electro-optic response of field effect heterostructures comprised of 1L-TMDs in high-Q resonators. We designed and simulated two distinct types of high-Q resonators: Fabry-Perot resonators and silicon pillar resonators. We optimized the geometrical parameters of these resonant structures embedded with 1L-TMDs to enhance device amplitude and phase modulation. Subsequently, we examined the potential for electro-optic modulation of TMDs in the telecommunication band, beyond their excitonic resonance wavelengths, by integrating them with Fabry-Perot resonators. We also discussed the compatibility of 1L-TMDs with gated heterostructure fabrication methods.
\r\n\r\nOverall, this thesis presents the application of electrical bias as a tool for the dynamic control of light in ITO and 1L-TMDs-based nanophotonic devices, with potential future applications in adaptive and reconfigurable photonic technologies.
" }, { "name": "Lee, Connor Tinghan", "degree": "PhD", "year": "2024", "title": "Learning-Based Perception for Robotics in Suboptimal Data Landscapes", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032024-181240783", "creators": [ { "name": { "family": "Lee", "given": "Connor Tinghan" }, "id": "Lee-Connor-Tinghan", "orcid": "0000-0002-5008-4092", "display_name": "Lee, Connor Tinghan" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "chair", "display_name": "Watkins, Michael M." }, { "name": { "family": "Gkioxari", "given": "Georgia" }, "id": "Gkioxari-Georgia", "role": "member", "display_name": "Gkioxari, Georgia" }, { "name": { "family": "Hadaegh", "given": "Fred Y." }, "id": "Hadaegh-F-Y", "orcid": "0000-0002-0992-6323", "role": "member", "display_name": "Hadaegh, Fred Y." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "space" ], "doi": "10.7907/v4yf-pj25", "abstract": "Autonomous robots are increasingly present in the world today, being used across a variety of settings and applications. In order to interact with their surroundings, robots typically use cameras to see the world, employing computer vision algorithms to comprehend rich, visual information. While contemporary, learning-based computer vision models provide robots with an accurate and robust understanding of their surroundings, most off-the-shelf methods rely on supervised deep learning techniques, requiring abundant labeled data in order to train and prevent overfitting. However, in many robotic applications and settings, the data landscape is characterized by data scarcity and/or the lack of apparent supervisory signals. Since custom perception solutions are often required for robotic applications, direct adoption of common computer vision methods proves challenging.
\r\n\r\nIn this thesis, we develop robotic perception approaches across three different applications that overcome the challenges of such data landscapes. First, we develop learning-based visual terrain-relative navigation (VTRN) approaches for high-altitude aerial vehicles. This is a problem for which relevant data is available, but made difficult by the lack of obvious supervisory signals related to the high-level navigation objective. In the first chapters of the thesis, we show the power of self-supervised learning approaches to increase VTRN robustness to seasonal and temporal variations that would otherwise debilitate such systems.
\r\n\r\nNext, we address the challenge of developing thermal semantic perception algorithms for aerial field robotics. Due to the specialized nature of field environments and the sensing modality, development of thermal vision algorithms under these conditions is often characterized by the lack of relevant data. We show how we develop various thermal semantic segmentation in response to the evolving data constraints inherent in field robotic projects. In the final part of the thesis, we develop data-efficient, multispectral deep learning algorithms for autonomous driving applications where the lack of data arises from the need for custom, multispectral datasets that are synchronized and coregistered.
" }, { "name": "Leefmans, Christian Richard", "degree": "PhD", "year": "2024", "title": "Topological Phenomena in Time-Multiplexed Resonator Networks", "advisor": "Marandi, Alireza", "url": "https://resolver.caltech.edu/CaltechTHESIS:12222023-012844057", "creators": [ { "name": { "family": "Leefmans", "given": "Christian Richard" }, "id": "Leefmans-Christian-Richard", "orcid": "0000-0002-7708-3727", "display_name": "Leefmans, Christian Richard" } ], "advisors": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "advisor", "display_name": "Marandi, Alireza" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2dp5-eb41", "abstract": "In 2008, the prediction that gyromagnetic photonic crystals could host analogs of the quantum Hall effect sparked a revolution in photonics, as it became apparent that the synergy between photonics and topological physics provides distinct opportunities for fundamental research and technological innovation. Since then, topological photonics has produced experimental realizations of numerous theories from topological condensed matter physics, while the inherent robustness of topological edge states has enabled novel devices like topological lasers and topological quantum sources. Despite this success, practical challenges limit the breadth of topological phenomena accessible to the existing experimental platforms for topological photonics. Therefore, to accelerate the pace of scientific discovery and to inspire the next generation of topological technologies, it is desirable to develop a platform that overcomes the limitations of traditional topological photonic architectures. In this thesis, I propose time-multiplexed resonator networks as a next-generation platform for topological photonics, and I present three experimental projects that demonstrate the diverse capabilities of this platform.
\r\n\r\nIn the first project, I use a time-multiplexed resonator network to demonstrate topological dissipation, in which nontrivial topology is encoded in the dissipation spectrum of a resonator array. I show measurements of dissipative topological phenomena in one- and two-dimensions and discuss how topological dissipation can be used to design resonator arrays with topologically robust quality factors. In the second project, I adapt a time-multiplexed resonator network to realize a topological mode-locked laser, and I show that this laser can realize non-Hermitian topological phenomena that had not previously been demonstrated in topological photonics. Finally, I experimentally study the dynamics of cavity solitons in a topological resonator array. This project demonstrates a general technique for realizing cavity solitons in large arrays of coupled resonators, which has become a relevant challenge in the soliton community over the past several years.
" }, { "name": "Lei, Mi", "degree": "PhD", "year": "2024", "title": "Many-Body Cavity Quantum Electrodynamics and Spin Dynamics with an Ensemble of Rare-Earth Ions", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04102024-171434556", "creators": [ { "name": { "family": "Lei", "given": "Mi" }, "id": "Lei-Mi", "orcid": "0009-0001-5484-7982", "display_name": "Lei, Mi" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "chair", "display_name": "Endres, Manuel A." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Yao", "given": "Norman Y." }, "id": "Yao-Norman-Y", "orcid": "0000-0003-0194-7266", "role": "member", "display_name": "Yao, Norman Y." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/gx1e-en28", "abstract": "Studying and controlling light-matter and matter-matter interactions is a central theme in quantum physics and provides the foundation for quantum applications. Rare-earth ions (REIs) doped in solids are promising candidates for engineering scalable quantum technologies, such as quantum memories and quantum transducers, and for exploring emerging fundamental phenomena. This is because REIs have highly stable optical and spin transitions at cryogenic temperatures, and as a solid-state platform, they are compatible for integrating with quantum devices using well-established semiconductor manufacturing techniques.
\r\n\r\nThis thesis is centered on nanophotonic devices coupling to an ensemble of REIs. To explore the light-matter interaction, we build a light-matter interface by coupling an inhomogeneously broadened ensemble of ytterbium-171 doped in yttrium orthovanadate to a nanophotonic cavity with high cooperativity. In this many-body cavity quantum electrodynamics (cavity QED) system, we observe the appearance of a narrow transparency window in the cavity reflection spectrum under optical driving (collectively induced transparency, CIT). This phenomenon results from the destructive interference between pairs of two-level emitters across the inhomogeneous line and the saturation of resonant ions. Furthermore, coherent excitation of the system within this transparency window enables us to observe highly nonlinear optical emission, spanning from fast superradiance to slow subradiance. To study matter-matter interactions, we shift the focus to the strongly interacting spins. These spins feature clock transitions and pure spin exchange interactions, leading to comparable magnitudes of interaction strength and on-site disorder. We characterize and control the many-body dynamics via Hamiltonian engineering and population initialization. Furthermore, we observe the emergence of robust subharmonic oscillations under Floquet driving, providing evidence for the presence of a discrete time crystal.
\r\n\r\nThe discoveries in many-body cavity QED enable new mechanisms for achieving slow light and frequency referencing, and they provide potential for superradiant lasers. Meanwhile, our studies on spin dynamics showcase REIs as a promising platform for the study of many-body physics, with potential applications in quantum sensing and quantum simulations. In general, our findings deepen the understanding for a disordered quantum system and offer valuable insights for development of quantum applications.
" }, { "name": "Leibovici, Daniel Victor", "degree": "PhD", "year": "2024", "title": "General Domain FC-Based Shock Dynamics Solver", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03152024-221312028", "creators": [ { "name": { "family": "Leibovici", "given": "Daniel Victor" }, "id": "Leibovici-Daniel-Victor", "orcid": "0009-0007-8267-4250", "display_name": "Leibovici, Daniel Victor" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "display_name": "Owhadi, Houman" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/bd5r-4q30", "abstract": "This thesis presents a novel FC-SDNN (Fourier Continuation Shock-detecting Neural Network) spectral scheme for the numerical solution of nonlinear conservation laws in general domains and under arbitrary boundary conditions, without the limiting CFL constraints inherent in other spectral schemes for general domains. The approach relies on the use of the Fourier Continuation (FC) method for spectral representation of non-periodic functions in conjunction with smooth artificial viscosity assignments localized in regions detected by means of a Shock-Detecting Neural Network (SDNN). Like previous shock capturing schemes and artificial viscosity techniques, the combined FC-SDNN strategy effectively controls spurious oscillations in the proximity of discontinuities. Thanks to its use of a localized but smooth artificial viscosity term, whose support is restricted to a vicinity of flow-discontinuity points, the algorithm enjoys spectral accuracy and low dissipation away from flow discontinuities, and, in such regions, it produces smooth numerical solutions\u2014as evidenced by an essential absence of spurious oscillations in contour levels. The FC-SDNN viscosity assignment, which does not require use of problem-dependent algorithmic parameters, induces a significantly lower overall dissipation than other methods, including the Fourier-spectral versions of the previous entropy viscosity method, especially in the vicinity of contact discontinuities. The approach, which does not require the use of otherwise ubiquitous positivity-preserving limiters, enjoys a great geometrical flexibility on the basis of an overlapping-patch discretization. This allows its application for the simulation of supersonic and hypersonic flows and shocks, including Euler simulations at significantly higher speeds than previously achieved, such as e.g. Mach 25 re-entry flow speeds, impinging upon complex physical obstacles. This multi-domain approach is suitable for efficient parallelization on large computer clusters, and the MPI implementation proposed in this thesis enjoys high parallel scalability and in particular perfect weak scaling, as demonstrated by simulations on general complex domains. The character of the proposed algorithm is demonstrated through a variety of numerical tests for the linear advection, Burgers and Euler equations in one and two-dimensional non-periodic spatial domains, with results in accordance with physical theory and prior experimental and computational results up to and including both supersonic and hypersonic regimes." }, { "name": "Li, Jing Shuang (Lisa)", "degree": "PhD", "year": "2024", "title": "Distributed Control Theory for Biological and Cyberphysical Systems", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:07062023-214417026", "creators": [ { "name": { "family": "Li", "given": "Jing Shuang (Lisa)" }, "id": "Li-Jing-Shuang-Lisa", "orcid": "0000-0003-4931-8709", "display_name": "Li, Jing Shuang (Lisa)" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Anderson", "given": "James" }, "id": "Anderson-James", "orcid": "0000-0001-8210-6527", "role": "member", "display_name": "Anderson, James" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "cds" ], "doi": "10.7907/p3k0-rv78", "abstract": "In engineering, control theory plays a crucial role in the design and analysis of robust and efficient systems --- including robots, spacecraft, and power grids. In biology, control theory underlies sensorimotor and locomotion models of organisms. Distributed control is particularly useful for large-scale cyber-physical systems and also in biological systems, where communication is more limited than in engineered counterparts. In this thesis, I provide a number of theoretical advances in distributed control theory on the relationship between communication within controllers vs. closed-loop behavior in both the online and offline settings, on the application of distributed methods to robust control, and on necessarily information flow within controllers subject to communication constraints. I then discuss the applications of these theoretical advances to the primate cortex, as well as to sensorimotor models of drosophila locomotion. Overall, the contributions outlined in this thesis facilitate modeling techniques and insights that were previously unavailable." }, { "name": "Liu, Mingchen", "degree": "PhD", "year": "2024", "title": "Nonlinear Enhancement of Optical Spectroscopy in the Mid-infrared", "advisor": "Marandi, Alireza", "url": "https://resolver.caltech.edu/CaltechTHESIS:03252024-002457591", "creators": [ { "name": { "family": "Liu", "given": "Mingchen" }, "id": "Liu-Mingchen", "orcid": "0000-0002-0649-8976", "display_name": "Liu, Mingchen" } ], "advisors": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "advisor", "display_name": "Marandi, Alireza" } ], "committee": [ { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "orcid": "0000-0001-6874-1137", "role": "chair", "display_name": "Okumura, Mitchio" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ffd0-yq96", "abstract": "Optical spectroscopy has long been a cornerstone in studying material properties, playing a pivotal role in the advancement of science and technology. It remains crucial in both research and industry, particularly in the mid-infrared (MIR) region, known for its unique molecular fingerprint capabilities. The emergence of optical frequency comb technology has set the stage for dual-comb spectroscopy (DCS) to revolutionize optical spectroscopy with its potential superiority in speed, resolution, sensitivity, precision, and compactness. However, practical implementation of DCS in the MIR region faces challenges due to its demanding requirements for sources, inefficient photodetection, and dynamic range \r\nlimitations, despite an exciting prospect. \r\nThis dissertation explores the use of quadratic optical nonlinearity to tackle these challenges. By manipulating energy and information flows between photons of different \r\nfrequencies through nonlinear optics, we leverage well-developed near-infrared (NIR) sources, detectors, and optics to address difficulties in the MIR region. We first \r\ndemonstrate optical parametric oscillators in the regime of simulton (quadratic soliton pair), achieving a high-power broadband MIR frequency comb with a remarkably high NIR-to-MIR power conversion efficiency. We also introduce cross-comb spectroscopy (CCS), which upconverts the MIR frequency comb to the NIR region and allows MIR spectral analysis with NIR photodetection. This novel approach can offer superior signal-to-noise ratio (SNR), dynamic range, and detection efficiency compared to conventional DCS, while providing wavelength flexibility. Additionally, we present a new method to facilitate the detection of trace samples with short-pulse optical parametric amplifiers, which can significantly enhance SNR and limit of detection of existing methods.\r\nOverall, this research demonstrates the capabilities of quadratic nonlinearity in enabling high-performance optical sensing in spectral regions where sources, detectors, and optics are less developed." }, { "name": "Lu, Chen-Hsuan", "degree": "PhD", "year": "2024", "title": "Strategic Advances in 2D Materials: Low-Temperature Plasma-Enhanced Chemical Vapor Deposition Growth of Graphene and Complementary Insights into MoS\u2082", "advisor": "Yeh, Nai-Chang", "url": "https://resolver.caltech.edu/CaltechTHESIS:11082023-043634180", "creators": [ { "name": { "family": "Lu", "given": "Chen-Hsuan" }, "id": "Lu-Chen-Hsuan", "orcid": "0000-0002-4802-1332", "display_name": "Lu, Chen-Hsuan" } ], "advisors": [ { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "advisor", "display_name": "Yeh, Nai-Chang" } ], "committee": [ { "name": { "family": "Fabe", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Fabe, Katherine T." }, { "name": { "family": "Falso", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falso, Joseph" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "member", "display_name": "Yeh, Nai-Chang" } ], "option_major": [ "matsci" ], "doi": "10.7907/cetf-ns02", "abstract": "This thesis explores the intricate details of the plasma-enhanced chemical vapor deposition (PECVD) technique for growing graphene on various substrates at low temperatures. The research begins by finely optimizing the PECVD growth conditions to produce high-quality graphene on copper ink, which can potentially be used in a wide range of flexible electronics and Internet of Things (IoT) devices. The study also showcases that PECVD is an effective technique for growing graphene directly on electroplated copper over polyimide substrates, which greatly improves the resilience and environmental stability of copper circuits.
\r\n\r\nFurthermore, the research investigates the possibility of using PECVD to grow graphene on gold, which can be a game-changer in anti-corrosion applications and increase the longevity of gold electrode-based biosensors. The study also makes a significant breakthrough by growing nanocrystalline multilayer graphene on silver in a single step, which demonstrates exceptional oxidation resistance and opens new opportunities for hybrid graphene-silver plasmonic technologies.
\r\n\r\nLastly, the thesis examines the potential and complexities of using electrodeposited (ED) copper foil as a graphene growth substrate, showing significant transformations in the properties of the ED copper foil post PECVD process. Towards the latter part of this work, attention is briefly shifted to explore the unique dipole ordering properties of monolayer molybdenum disulfide (MoS2) single crystals, which are synthesized using high-temperature chemical vapor deposition (CVD) and are van der Waals materials like graphene. Although not the main focus, this inclusion offers valuable insights into contrasting attributes and functionalities of graphene and MoS2, especially in areas like high-density data storage and non-volatile memories, and also compares the status of synthesis methods of these two types of van der Waals materials.
\r\n\r\nAlongside these investigations, the thesis also touches upon the prospects of both large-area PECVD graphene growth and interfacial graphene growth, identifying future paths for research and innovation. This comprehensive study highlights the versatility of low-temperature PECVD for graphene synthesis and provides insights that may reshape research and applications in flexible electronics, biosensing, and beyond. The findings of this research therefore pave ways for researchers, technology developers, and businesses to explore realistic technological applications of graphene and two-dimensional materials in various industries.
" }, { "name": "Mazaheri, Bijan Henrik Socrates", "degree": "PhD", "year": "2024", "title": "Combining Sources and Leveraging Contexts", "advisor": "Bruck, Jehoshua; Schulman, Leonard J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042024-004345614", "creators": [ { "name": { "family": "Mazaheri", "given": "Bijan Henrik Socrates" }, "id": "Mazaheri-Bijan-Henrik-Socrates", "orcid": "0000-0001-9690-8686", "display_name": "Mazaheri, Bijan Henrik Socrates" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "co-advisor", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "co-advisor", "display_name": "Schulman, Leonard J." } ], "committee": [ { "name": { "family": "Eberhardt", "given": "Frederick D." }, "id": "Eberhardt-F-D", "role": "chair", "display_name": "Eberhardt, Frederick D." }, { "name": { "family": "Janzing", "given": "Dominik" }, "id": "Janzing-Dominik", "orcid": "0000-0002-2126-5740", "role": "member", "display_name": "Janzing, Dominik" }, { "name": { "family": "Rabani", "given": "Yuval" }, "id": "Rabani-Yuval", "orcid": "0000-0001-7772-2544", "role": "member", "display_name": "Rabani, Yuval" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." } ], "option_major": [ "cms" ], "doi": "10.7907/7t4d-xg91", "abstract": "In this thesis we discuss two levels of knowledge beyond regression and classification. The first involves the identification of exchangeable scenarios or individuals from which causal relationships can be ascertained. We discuss one key difficulty of this task, the \"Multi-Source Conundrum,\" which emerges whenever data is merged from multiple sources. This motivates the \"Principle of Limited Latent Classes,\" an assumption which allows us to introduce new algorithms for deconfounding and causal structure learning.
\r\n\r\nThe second level of knowledge involves the expansion from contextual exchangeability to contextual synthesis. We will study a paradox of nontransitivity that occurs when combining multiple contexts, as well a demonstrating robustness gains from using context-dependent counterfactuals as training features. Through these points, we present contextual synthesis as a new frontier with promise for advances in out-of-distribution robustness, fairness, and privacy.
" }, { "name": "Min, Jihong", "degree": "PhD", "year": "2024", "title": "Innovations in Wireless Bioelectronics for Precision Medicine, from Sustainable Sweat Sensing to Ingestible Gut Monitoring", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:12052023-185529151", "creators": [ { "name": { "family": "Min", "given": "Jihong" }, "id": "Min-Jihong", "orcid": "0000-0002-5788-1473", "display_name": "Min, Jihong" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Lester", "given": "Henry A." }, "id": "Lester-H-A", "orcid": "0000-0002-5470-5255", "role": "member", "display_name": "Lester, Henry A." } ], "option_major": [ "medeng" ], "doi": "10.7907/kcm7-wz71", "abstract": "Biofluids, constituting about 60% of the human body, serve as treasure troves of biomarkers such as metabolites and electrolytes, shedding light on individual health conditions. Although blood and urine tests have been routinely utilized, they are limited by their invasive and episodic nature. However, the promise of continuous and noninvasive access to other biofluids like sweat, GI fluids, and saliva paves the way for real-time, onsite health monitoring. This thesis delves into the untapped potential of wearable sensors and noninvasive biofluid analysis, emphasizing the importance of continuous and sustainable monitoring for predictive personal healthcare. Chapter 1 introduces the paradigm of biofluid sensing, focusing on sweat as a key candidate for personalized healthcare applications. Chapter 2 delves into the physiology of sweat glands, highlighting the composition of sweat and the mechanisms behind sweat extraction, either through natural exercise or iontophoretic stimulation. Chapter 3 embarks on the development of innovative sensors designed for detecting clinically pertinent biomarkers in sweat, a step forward in predictive health analytics. In Chapter 4, the spotlight is on system integration, as the study emphasizes the need for miniaturized and reliable wireless sensor devices that ensure minimal discomfort and maximum reliability. Chapters 5 and 6 delve into strategies for sustainably powering wearable devices from energy harvested from body motions and from ambient light, respectively. The final chapter, Chapter 7, extrapolates the aforementioned technologies for the realm of ingestible devices, adapting them for electrochemical sensing in alternate media, primarily gastrointestinal fluids. This allows for enhanced detection of gastrointestinal diseases and a deeper understanding of the intricate gut-brain axis. The ultimate vision of this research is to equip individuals with wearable and ingestible sensors that can seamlessly monitor a broad spectrum of clinically relevant biomarkers. This continuous monitoring, coupled with data analytics, will potentially catalyze a shift from reactive to predictive healthcare, ushering in an era of personalized therapeutic interventions. As wearable sweat and ingestible sensors become mainstream, a confluence of biosensing mechanisms, materials science, and flexible electronics is anticipated enable continuous and unobtrusive acquisition of clinically relevant biomarkers over prolonged periods and large populations, further refining the nexus between health monitoring and precision medicine." }, { "name": "Moncada Lopez, Rigoberto", "degree": "PhD", "year": "2024", "title": "Sea Ice Discrete Element Modeling: Melt and Fracture of Floes and Sheets", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07032023-235459528", "creators": [ { "name": { "family": "Moncada Lopez", "given": "Rigoberto" }, "id": "Moncada Lopez-Rigoberto", "orcid": "0000-0001-7655-5406", "display_name": "Moncada Lopez, Rigoberto" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Thompson", "given": "Andrew F." }, "id": "Thompson-A-F", "orcid": "0000-0003-0322-4811", "role": "member", "display_name": "Thompson, Andrew F." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "civileng" ], "doi": "10.7907/erqr-cr51", "abstract": "Over the last 40 years, the Arctic Ocean has experienced a significant reduction in surface area and thickness of sea ice for its minimum summer and year-round values. Sea ice, existing both as continuous ice sheets and distinct broken floes or blocks, is disappearing earlier and faster over time. These changes are largely occurring within marginal ice zones, where ice is most vulnerable to thermal forcings from the sun, oceans, and atmosphere and wind and ocean currents. Given that sea ice plays a vital role in regulating climate by delaying global energy exchanges, its loss is a vital factor in increasing global temperatures and the frequency of extreme weather events. Understanding and projecting seasonal variations in sea ice is imperative to improve climate predictions. However, many of the processes in sea ice are not fully described by most existing models, due to the limitations of continuum sea ice approaches. As a result the use of discontinuum techniques on sea ice is a very active field. In this work, we combine discrete element methods with satellite image analysis to study changes in sea ice concentration and floe size distribution during the summer melt transition for ensembles of distinct floes decaying into open waters and continuous fast sea ice sheets breaking into multiple floes. For the pure floe-like behavior, we use the `Level Set Discrete Element Method for Sea Ice' or LS-ICE method. This model can resolve individual sea ice floes with realistic shapes, and represent their physical interactions by leveraging level-set functions to detect contacts. LS-ICE can also be coupled to atmospheric and oceanic heat and momentum forcings and simulate associated melt and breakage processes. With it, we are able to reproduce sea ice concentration decline for the summers of 2018 and 2020 at Baffin Bay. Using LS-ICE we also unveil the sensitivity of sea ice loss and floe size distribution to different intensities of fracturing and ocean/solar melt and how sea ice floe size determines which is more dominant. For monolithic landfast sea ice sheets, we use a bonded particle method within the level set discrete element model called LS-DEM-BPM. We explore the relationship between landfast sea ice breakage and area decline, ocean currents and floe size distribution for a region in Fram Strait in 2023. We also replicate its fracture characteristics, using idealized pulses and arbitrary eddying ocean currents, and unveil particular combinations of wavelengths and wave speeds that facilitate breakage. Our results give new insight on sea ice melt and breakage interactions and provide a numerical framework for simulating the complete transition of sea ice from intact sheets to open oceans." }, { "name": "Mueller, Andrew Sterling", "degree": "PhD", "year": "2024", "title": "Quantum Measurements with Superconducting Nanowire Single Photon Detectors", "advisor": "Spiropulu, Maria; Shaw, Matthew D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02092024-210936211", "creators": [ { "name": { "family": "Mueller", "given": "Andrew Sterling" }, "id": "Mueller-Andrew- Sterling", "orcid": "0000-0002-6598-9732", "display_name": "Mueller, Andrew Sterling" } ], "advisors": [ { "name": { "family": "Spiropulu", "given": "Maria" }, "id": "Spiropulu-M", "orcid": "0000-0001-8172-7081", "role": "advisor", "display_name": "Spiropulu, Maria" }, { "name": { "family": "Shaw", "given": "Matthew D." }, "id": "Shaw-M-D", "role": "advisor", "display_name": "Shaw, Matthew D." } ], "committee": [ { "name": { "family": "Hutzler", "given": "Nicholas R." }, "id": "Hutzler-N-R", "orcid": "0000-0002-5203-3635", "role": "chair", "display_name": "Hutzler, Nicholas R." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Shaw", "given": "Matthew D." }, "id": "Shaw-M-D", "role": "member", "display_name": "Shaw, Matthew D." }, { "name": { "family": "Spiropulu", "given": "Maria" }, "id": "Spiropulu-M", "orcid": "0000-0001-8172-7081", "role": "member", "display_name": "Spiropulu, Maria" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/tneb-9z27", "abstract": "Superconducting Nanowire Single-Photon Detectors (SNSPDs) are high-performance photon counting detectors, typically operated just a few degrees above absolute zero. Comprising a current-biased nanowire transitioning between superconducting and resistive states upon photon absorption, SNSPDs generate voltage pulses for precise photon arrival time measurement. Initially demonstrated in the 1990s, SNSPDs are now mature devices widely employed in various fields, including space communication, biological imaging, and quantum technology. This\u00a0thesis\u00a0explores techniques to enhance usable count rate, dark count rate, timing resolution, and photon number resolution for both emerging and established SNSPD designs. We introduce a free space optical filtering method to minimize SNSPD dark count rates which is competitive with the state-of-the-art for fiber coupled SNSPDs, and especially impactful for space communication applications. We go on to study dynamics that limit SNSPD maximum count rates, presenting a calibration and in-situ correction procedure to significantly reduce jitter at high rates without additional hardware or offline processing. With an eye towards space communication applications beyond NASA's Deep Space Optical Communication (DSOC) project, we present a high-rate Pulse Position Modulation communication demo with SNSPDs. In the process we uncover a rich photon-number dependent response in these detectors and devise methods to properly leverage and manage it. Finally, we employ low-jitter SNSPDs in a high-rate entanglement distribution system, achieving high entanglement visibilities, and distillable entanglement rates. \u00a0As this work focuses on optimizing SNSPD usage and analysis rather than device physics or fabrication, it is broadly applicable to any users of this single photon detection technology.
" }, { "name": "Naik, Nachiket Ramchandra", "degree": "PhD", "year": "2024", "title": "Charge Transport Phenomena in Cryogenic SiGe Heterojunction Bipolar Transistors", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04122024-211453536", "creators": [ { "name": { "family": "Naik", "given": "Nachiket Ramchandra" }, "id": "Naik-Nachiket-Ramchandra", "orcid": "0000-0001-8271-643X", "display_name": "Naik, Nachiket Ramchandra" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Cleary", "given": "Kieran A." }, "id": "Cleary-K-A", "orcid": "0000-0002-8214-8265", "role": "member", "display_name": "Cleary, Kieran A." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/f1tv-4w30", "abstract": "Silicon-germanium heterojunction bipolar transistors (HBTs) are widely used for high-speed communications and radar systems owing to the their low-cost and competitive performance relative to III-V compound semiconductor devices. Due to the higher cost and lower yield of III-V high electron mobility transistors (HEMTs) based on InGaAs quantum wells, SiGe HBTs operating at cryogenic temperatures are of significant interest for radio astronomy and quantum computing. However, their microwave noise performance has long been observed to be poorer than those of HEMTs. As a result, the physical mechanisms governing the cryogenic DC, microwave and noise performance of SiGe HBTS have been a topic of investigation for many years. Improved understanding of these mechanisms may ultimately allow for the realization of HBTs with noise performance rivaling those of HEMTs yet with lower cost, improved compatibility and integration with CMOS processes, and high yield.
\r\n \r\nThis thesis uses theoretical and experimental methods to examine cryogenic charge transport phenomena in SiGe HBTs which affect the microwave noise performance. A particular focus is on the anomalous electrical characteristics at cryogenic temperatures, in which pronounced deviations from the ideal drift-diffusion theory are observed. Various explanations for the observed anomalous cryogenic I-V behavior have been postulated, such as quasi-ballistic transport and electron tunneling, among others. Despite a number of works on this topic over the past three decades, none of the explanations has been unambiguously confirmed or excluded.
\r\n \r\nThe first contribution from this thesis is a study of the quasiballistic transport hypothesis using an exact, semi-analytic solution of the Boltzmann equation. Several prior studies have claimed quasiballistic electron transport across the base as the origin of cryogenic non-ideal current-voltage characteristics. Specifically, the observation of temperature independent DC performance below $\\sim 80$ K has been attributed partly to quasiballistic transport resulting in a presumed increase in electron temperature, but this hypothesis has been examined only using empirical models which leave ambiguity. We overcome this limitation by adapting an exact, semi-analytic solution to the Boltzmann equation based on an asymptotic expansion approach to describe electron transport across the base region of an HBT. With this exact solution, we computed macroscopic electrical properties such as collector current and transconductance which could be directly compared with experiments. We find that the computed transport characteristics are inconsistent with experiment, with the calculated transconductance following the ideal drift-diffusion inverse temperature dependence. This finding implies that quasiballistic electron transport is unlikely to be the origin of cryogenic non-ideal I-V characteristics.
\r\n\r\nNext, we study a previously unexplored explanation, the presence of lateral spatial inhomogeneities in the base-emitter junction potential height, as the origin for the observed non-ideal cryogenic current-voltage anomalies in SiGe HBTs. While this phenomenon has been established as the origin for similar cryogenic I-V anomalies observed in Schottky diodes, this possibility has not yet been considered for SiGe HBTs. We experimentally investigate this hypothesis by characterizing the base-emitter built-in potential and its temperature dependence using both capacitance-voltage and current-voltage characteristics. We observe a marked discrepancy in the built-in potential obtained using these two methods at cryogenic temperatures, a signature consistent with the presence of lateral inhomogeneities in the junction potential. We hypothesize that these inhomogeneities arise from clustering of Ge as a result of aggressive doping of modern devices, and propose future directions that allow direct probing of these inhomogeneities.
\r\n \r\nFinally, we explore the potential improvements in the minimum achievable noise temperature of HBT amplifiers by considering the effects of shot-noise correlation. We first model the expected reduction in cryogenic noise temperature of a state-of-the-art transistor as a result of shot-noise correlation. We then quantify the accuracy of the present noise measurement techniques that allow us to exploit the benefits of shot-noise correlation, and propose modifications to the noise measurement setup that will permit an unambiguous experimental determination of the magnitude of the effect.
" }, { "name": "Nelsen, Nicholas Hao", "degree": "PhD", "year": "2024", "title": "Statistical Foundations of Operator Learning", "advisor": "Stuart, Andrew M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142024-215222393", "creators": [ { "name": { "family": "Nelsen", "given": "Nicholas Hao" }, "id": "Nelsen-Nicholas-Hao", "orcid": "0000-0002-8328-1199", "display_name": "Nelsen, Nicholas Hao" } ], "advisors": [ { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "advisor", "display_name": "Stuart, Andrew M." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/0246-7574", "abstract": "This thesis studies operator learning from a statistical perspective. Operator learning uses observed data to estimate mappings between infinite-dimensional spaces. It does so at the conceptually continuum level, leading to discretization-independent machine learning methods when implemented in practice. Although this framework shows promise for physical model acceleration and discovery, the mathematical theory of operator learning lags behind its empirical success. Motivated by scientific computing and inverse problems where the available data are often scarce, this thesis develops scalable algorithms for operator learning and theoretical insights into their data efficiency.
\r\n\r\nThe thesis begins by introducing a convergent operator learning algorithm that is implementable on a computer with controlled complexity. The method is based on linear combinations of function-valued random features, enjoys efficient training via convex optimization, and accurately approximates nonlinear solution operators of parametric partial differential equations. A statistical analysis derives state-of-the-art error bounds for the method and establishes its robustness to errors stemming from noisy observations and model misspecification. Next, the thesis tackles fundamental statistical questions about how problem structure, data quality, and prior information influence learning accuracy. Specializing to a linear setting, a sharp Bayesian nonparametric analysis shows that continuum linear operators, such as the integration or differentiation of spatially varying functions, are provably learnable from noisy input-output pairs. The theory reveals that smoothing operators are easier to learn than unbounded ones and that training with rough or high-frequency input data improves sample complexity. When only specific linear functionals of the operator\u2019s output are the primary quantities of interest, the final part of the thesis proves that the smoothness of the functionals determines whether learning directly from these finite-dimensional observations carries a statistical advantage over plug-in estimators based on learning the entire operator. To validate the findings beyond linear problems, the thesis develops practical deep operator learning architectures for nonlinear mappings that send functions to vectors, or vice versa, and shows their corresponding universal approximation properties. Altogether, this thesis advances the reliability and efficiency of operator learning for continuum problems in the physical and data sciences.
" }, { "name": "Ogren, Alexander Charles", "degree": "PhD", "year": "2024", "title": "Machine Learning and Inference Methods for Surrogate Modeling and Inexpensive Characterization of Elastodynamic Systems", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042024-004152477", "creators": [ { "name": { "family": "Ogren", "given": "Alexander Charles" }, "id": "Ogren-Alexander-Charles", "orcid": "0000-0002-7277-0069", "display_name": "Ogren, Alexander Charles" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "chair", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Rudin", "given": "Cynthia" }, "id": "Rudin-Cynthia", "orcid": "0000-0003-4283-2780", "role": "member", "display_name": "Rudin, Cynthia" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "mecheng" ], "doi": "10.7907/dcbz-sj62", "abstract": "This thesis has two main focuses: (1) surrogate modeling of elastodynamic systems, and (2) inference methods for the inexpensive characterization of elastodynamic systems. Elastodynamics is the study of how and why materials move and deform when they are subject to time-varying loads, covering a wide range of applications from architected materials, to telecommunications, seismology, sound isolation, non-destructive evaluation, and medical imaging. Here, we explore how to more efficiently model elastodynamics, and what we can infer about our environment from observing them.
\r\n\r\nThe next generation of material engineering aims to leverage advanced multi-functional control over elastodynamic behaviors, but is currently limited by the large computational cost of purely physics-based modeling methods. Surrogate models aim to alleviate this cost by providing a data-driven approach to evaluate engineered material systems more efficiently. However, most current surrogate models lack certain useful traits, diminishing their potential for real-world use. This thesis begins by surveying the current state of surrogate modeling techniques, and establishes a set of state-of-the-art traits that greatly augment the utility of surrogate models, offering a perspective for the future direction of the field.
\r\n\r\nNext, a data-driven surrogate model based on Gaussian process regression for the computation of dispersion relations is developed, GPR-dispersion. The model exhibits several of the aforementioned traits, including representation invariance, data efficiency, incorporating direct use of physical theories, and the provision of both uncertainty estimates on its predictions and gradients for compatibility with gradient-based design optimization methods. GPR-dispersion is evaluated in comparison against both deep learning and traditional physics-based models.
\r\n\r\nThe thesis then pivots to inference methods for the inexpensive characterization of material systems via partial observation of elastodynamic behaviors. Tissue stiffness is a tremendously important biomarker for a long list of health conditions, but often needs to be evaluated in a medical clinic with expensive equipment and highly trained workers. At-home health monitoring is a major next-generation goal of healthcare, but the trajectories of current consumer-grade sensor technology and biomarker inference methods have not yet fully intersected.
\r\n\r\nInspired by a related work (Visual Vibration Tomography), Visual Surface Wave Tomography (VSWT) is proposed. VSWT observes partial information about the surface waves of layered elastodynamic systems (such as biological tissue) through monocular video to infer subsurface constitutive and geometrical information. Simulated experiments are presented to evaluate the accuracy, sensitivity, and limits of the method under ideal conditions. Real-world experimental results are presented using phantom materials that emulate biological tissue to demonstrate a practical proof of concept.
" }, { "name": "Pandey, Ayush", "degree": "PhD", "year": "2024", "title": "Modeling Frameworks for Modular and Scalable Biological Circuit Design", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062023-021337351", "creators": [ { "name": { "family": "Pandey", "given": "Ayush" }, "id": "Pandey-Ayush", "orcid": "0000-0003-3590-4459", "display_name": "Pandey, Ayush" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Del Vecchio", "given": "Domitilla" }, "id": "DelVecchio-D", "orcid": "0000-0001-6472-8576", "role": "member", "display_name": "Del Vecchio, Domitilla" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/qacp-dw76", "abstract": "Synthetic biology is a rapidly evolving interdisciplinary field that combines principles from biology, bioengineering, biochemistry, and computational sciences to design and engineer new biological systems for various applications. This thesis focuses on addressing the challenges in engineering large and complex biological circuits. We develop modular modeling frameworks, formal theory, and computer-assisted design (CAD) tools for design and analysis of biological systems at a larger scale.
\r\n\r\nThis thesis introduces a new problem of robustness in structured model reduction of dynamical systems and provides bounds on a robustness distance metric for linear and nonlinear systems. With this theory, we show the discrimination and quantification of different mathematical models, considering resource loading effects in biological circuits.
\r\n\r\nUsing our proposed model reduction robustness theory and its associated software development, we build a modeling, analysis, and parameter identification pipeline. This pipeline is demonstrated through the characterization of DNA recombination enzymes in a cell-free protein expression system. This pipeline is a general approach to systematically develop mathematical models, infer parameters from experimental data, and guide experimental design choices.
\r\n\r\nIdentification of parameters in detailed mathematical models is a major challenge in synthetic biology where only sparse data is available. This prevents the application of our detail-driven modeling approach to larger biological systems. Hence, to address this limitation, we present a formal methods-based approach for specifying and synthesizing implementations for the design of biological circuits. We present a contract-based design framework for synthetic biology. We write formal description of design objectives at a higher level of abstraction without modeling the details of each component. This design framework facilitates the design and prediction of complex synthetic biological circuits at scale.
\r\n\r\nOverall, this thesis contributes to the advancement of synthetic biology by providing novel modeling frameworks, analysis methods, and design approaches. These contributions aim to enable the design and analysis of complex biological systems and foster the systematic engineering of biological circuits.
" }, { "name": "Rivi\u00e8re, Benjamin Pierre", "degree": "PhD", "year": "2024", "title": "Do Robots Dream of Random Trees? Monte Carlo Tree Search for Dynamical, Partially Observable, and Multi-Agent Systems", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032024-152357240", "creators": [ { "name": { "family": "Rivi\u00e8re", "given": "Benjamin Pierre" }, "id": "Rivi\u00e8re-Benjamin-Pierre", "orcid": "0000-0002-0597-5400", "display_name": "Rivi\u00e8re, Benjamin Pierre" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Hadaegh", "given": "Fred" }, "id": "Fred-Hadaegh", "orcid": "0000-0002-0992-6323", "role": "member", "display_name": "Hadaegh, Fred" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/dbwa-we50", "abstract": "Autonomous robots are poised to transform various aspects of society, spanning transportation, labor, and scientific space exploration. A critical component to enable their capabilities is the algorithm that interprets sensor data to generate intelligent planned behavior. Although reinforcement learning methods that train parameterized policies offline from data have shown recent success, they are inherently limited when robots inevitably encounter situations outside their training domain. In contrast, optimal control techniques, which compute trajectories in real-time using numerical optimization, typically yield only locally optimal solutions.
\r\n\r\nThis research endeavors to bridge the gap by developing algorithms that compute trajectories in real-time while converging towards globally optimal solutions. Building upon the Monte Carlo Tree Search (MCTS) framework\u2014a stochastic tree search method that simulates future trajectories while balancing exploration and exploitation\u2014the research focus is twofold: (i) constructing an efficient discrete representation of continuous systems in a decision trees, and (ii) searching on the resulting tree while balancing exploration and exploitation to achieve global optimality.
\r\n\r\nThe study spans theoretical analysis, algorithmic design, and hardware demonstrations across dynamical, partially observable, and multi-agent systems. By addressing these critical questions, this research aims to advance the field of autonomous robotics, enabling the deployment of intelligent robots in complex and diverse environments.
" }, { "name": "Roberts, Gregory David", "degree": "PhD", "year": "2024", "title": "Design, Realization, and Applications of 3D Multifunctional Nanophotonics", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:08232023-220808049", "creators": [ { "name": { "family": "Roberts", "given": "Gregory David" }, "id": "Roberts-Gregory-David", "orcid": "0009-0002-0720-3938", "display_name": "Roberts, Gregory David" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/1r1w-0234", "abstract": "Metaoptics leverages electromagnetic phenomena and the advanced abilities of modern nanofabrication to replicate traditional optical devices in a fraction of the thickness and to realize novel, compact, multifunctional devices with no known bulk equivalent. Motivated by the expanding role of optics in modern technologies, this field has seen a rise in design techniques for realizing increasingly powerful photonic structures. Three-dimensional (3D) devices, with refractive index distributions patterned at subwavelength scales, represent an enormous design space capable of achieving highly efficient, free space, multifunctional structures. By utilizing a gradient-based, iterative optimization algorithm, a technique for nanophotonic inverse design, we demonstrate scattering structures with unique responses to all the fundamental properties of light. The algorithm is constrained such that resulting devices can be made with realistic multilayer fabrication processes. We present dielectric structures that can be placed directly on top of image sensor arrays and sort light to different pixels based on its wavelength, polarization, and angular momentum, thus enabling efficient and exotic camera technologies. The following work contains fabrication and measurement of 3D devices in the mid-infrared, practical evaluations of devices for visible light imaging applications, and visualizations of underlying structure of photonic design optimization problems.
" }, { "name": "Ruskuc, Andrei", "degree": "PhD", "year": "2024", "title": "Single Rare-Earth Ions in Solid-State Hosts: A Platform for Quantum Networks", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:10202023-123922325", "creators": [ { "name": { "family": "Ruskuc", "given": "Andrei" }, "id": "Ruskuc-Andrei", "orcid": "0000-0001-7684-7409", "display_name": "Ruskuc, Andrei" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "chair", "display_name": "Endres, Manuel A." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Hutzler", "given": "Nicholas R." }, "id": "Hutzler-N-R", "orcid": "0000-0002-5203-3635", "role": "member", "display_name": "Hutzler, Nicholas R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ecn2-pp53", "abstract": "Solid-state defects have emerged as leading candidates for quantum network nodes due to their compatibility with scalable device engineering and local nuclear spins for quantum processing. Rare-earth ions in crystalline hosts are particularly attractive due to their long optical and spin coherence times at cryogenic temperatures. However, until recently, detection and utilization of single rare-earth ions in quantum technologies has been hindered by their inherently weak optical transitions. In this thesis I present progress towards realizing a novel quantum network node architecture using single \u00b97\u00b9Yb\u00b3\u207a ions in YVO\u2084, coupled to a nanophotonic cavity.
\r\n\r\nFirst, we demonstrate coherent operation of single \u00b97\u00b9Yb\u00b3\u207a ions as optically addressed qubits. To do this, we leverage first order insensitivity of optical and spin transitions to electric and magnetic fields, thereby protecting the qubits from environmental noise. We demonstrate initialization, high fidelity control and readout of a hyperfine spin qubit with long quantum storage times. We also characterize the optical transitions and find a lifetime-limited echo coherence, thereby enabling a coherent spin-photon interface.
\r\n\r\nNext, we focus on realizing an auxiliary quantum register. The high-fidelity spin control of our \u00b97\u00b9Yb\u00b3\u207a qubit is leveraged to access local nuclear spins. These spins comprise a dense ensemble which serves as a deterministic quantum resource. We utilize Hamiltonian engineering to generate tailored interactions, enabling polarization, coherent control and preparation of many-body nuclear spin states. Finally, we implement a spin-wave based memory protocol and demonstrate storage and retrieval of quantum states.
\r\n\r\nMoving beyond a single quantum node, in the final section of this thesis we will realize a small-scale quantum network using this platform. As a first step we demonstrate time-resolved quantum interference between photons emitted by ions in two separate devices. Then, we demonstrate a novel heralded entanglement protocol which incorporates optical dynamical decoupling and frequency erasure via precise photon detection. This protocol counteracts both static and dynamic inhomogeneity in the ions\u2019 optical transition frequencies, thereby enabling entanglement generation between any pair of qubits in a scalable fashion.
\r\n\r\nThese results showcase single rare-earth ions as a promising platform for the future quantum internet.
" }, { "name": "Shang, Kuang-Ming", "degree": "PhD", "year": "2024", "title": "Oxygen-Regulating MEMS Devices for Cell Transplantation to Cure Type 1 Diabetes", "advisor": "Tai, Yu-Chong; Komatsu, Hirotake", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212024-231923059", "creators": [ { "name": { "family": "Shang", "given": "Kuang-Ming" }, "id": "Shang-Kuang-Ming", "orcid": "0000-0001-5065-7607", "display_name": "Shang, Kuang-Ming" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Komatsu", "given": "Hirotake" }, "id": "Komatsu-Hirotake", "orcid": "0000-0003-0876-4809", "role": "co-advisor", "display_name": "Komatsu, Hirotake" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Komatsu", "given": "Hirotake" }, "id": "Komatsu-Hirotake", "orcid": "0000-0003-0876-4809", "role": "member", "display_name": "Komatsu, Hirotake" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "medeng" ], "doi": "10.7907/xf5z-0p34", "abstract": "Type 1 diabetes is an autoimmune disease in which immune cells specifically attack and destroy the insulin-producing beta cells in the pancreatic islets that regulate blood glucose levels. Traditionally managed with frequent injections of exogenous insulin, beta cell replacement therapy\u2014also known as islet transplantation\u2014has emerged as an alternative clinical option. Recently, the focus has shifted toward subcutaneous islet transplantation, offering a promising and minimally invasive therapy. However, the survival of transplanted islets has been shown to be significantly challenged by hypoxia-induced graft loss stemming from inadequate oxygen supply.
\r\n\r\nTo address this issue, we have developed innovative hollow mesh devices that regulate oxygen. These devices can either bring oxygen from the adjacent oxygen-rich tissue or draw additional oxygen from ambient air to improve oxygen delivery to the hypoxic microenvironment of islet grafts. Fabricated using MEMS techniques and biocompatible materials, these devices feature a network of unobstructed air-containing microchannels. Utilizing the property that oxygen diffuses 10,000 times faster in air than in interstitial fluids, these devices effectively overcome oxygen supply barriers when co-transplanted with islet grafts. By integrating these hollow meshes with the islet grafts, oxygen can be rapidly redistributed throughout the graft, establishing local oxygen balance and regulation. This approach significantly reduces hypoxia-induced graft loss and improves the efficacy of post-transplant blood glucose regulation in recipients.
\r\n\r\nIn this thesis, we first delved into the physiology of oxygen transport within an islet, establishing the critical oxygen threshold necessary for islet cell survival. We developed equivalent circuit models for oxygen diffusion and constructed oxygen-regulating hollow mesh MEMS devices based on these models. We investigated the effects of oxygenation through both computational models and benchtop experiments. Finally, using our device, we demonstrated enhanced survival of islet grafts in diabetic rodent models, successfully achieving a long-term cure for diabetes.
\r\n\r\nWith the preclinical success of this oxygen-regulating hollow mesh in mitigating cellular oxygen deficiency, we also explored and proposed future pathways toward clinical effectiveness. Our device holds significant therapeutic potential to revolutionize clinical outcomes in islet transplantation with the ultimate goal of curing type 1 diabetes.
" }, { "name": "Simon, Christopher", "degree": "PhD", "year": "2024", "title": "Non-Equilibrium Quantum Dynamics in a Disordered Ising Magnet", "advisor": "Rosenbaum, Thomas F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182023-202554036", "creators": [ { "name": { "family": "Simon", "given": "Christopher" }, "id": "Simon-Christopher", "orcid": "0009-0003-6129-2078", "display_name": "Simon, Christopher" } ], "advisors": [ { "name": { "family": "Rosenbaum", "given": "Thomas F." }, "id": "Rosenbaum-T-F", "orcid": "0009-0008-6152-666X", "role": "advisor", "display_name": "Rosenbaum, Thomas F." } ], "committee": [ { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "chair", "display_name": "Endres, Manuel A." }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Rosenbaum", "given": "Thomas F." }, "id": "Rosenbaum-T-F", "orcid": "0009-0008-6152-666X", "role": "member", "display_name": "Rosenbaum, Thomas F." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/tm3k-yk55", "abstract": "The quantum two-level system, or \u201cqubit,\u201d is a simple platform that nonetheless displays fundamentally non-trivial quantum behavior. The rare-earth magnet LiHoF\u2084 is a natural physical representation of a system of coupled qubits. With its uncommonly high crystal anisotropy, LiHoF\u2084 can be mapped to the problem of the Ising model in a transverse field. However, while this Ising approximation can quantitatively predict much of the equilibrium behavior, quantum corrections, originating from off-diagonal terms in the dipolar interaction that generate quantum fluctuations, are crucial in driving non-equilibrium dynamics when subject to an external drive. Furthermore, quenched disorder can be introduced through chemical substitution, which, through the dipolar interaction, generates spatially random pinning fields, as well as internal transverse fields, which drive quantum fluctuations. Noise measurements on the disordered ferromagnet LiHo0.65Y0.35F4 show critical behavior, whose statistics are driven from the underlying pinning distribution, while measurements on LiHo0.40Y0.60F4 display non-critical behavior that can only be attributed to quantum co-tunneling processes. This is the first demonstration of crackling noise in a ferromagnet in the purely quantum regime. Furthermore, pump-probe susceptibility measurements on the decoupled cluster glass show the system being driven out of equilibrium with astonishingly weak drives, due to resonant transitions arising from off-diagonal dipolar terms \u03c3iz \u03c3jx. Non-linear sample response is observable in inelastic Raman scattering measurements, and these spin clusters also exhibit asymmetric Fano resonances with high Q-factors of ~10\u2075. Quantum interference effects can be tuned to fully decouple one of the dressed states from the others, rendering the sample transparent to the drive. This is analogous to optical systems that display electromagnetically-induced transparency, but at 100 Hz frequencies!" }, { "name": "Soliman, Yousuf Mounir", "degree": "PhD", "year": "2024", "title": "Discrete Constrained Willmore Surfaces", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232024-182937115", "creators": [ { "name": { "family": "Soliman", "given": "Yousuf Mounir" }, "id": "Soliman-Yousuf-Mounir", "orcid": "0000-0003-4023-5026", "display_name": "Soliman, Yousuf Mounir" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Pinkall", "given": "Ulrich" }, "id": "Pinkall-U", "orcid": "0000-0002-2087-6435", "role": "member", "display_name": "Pinkall, Ulrich" }, { "name": { "family": "Tamuz", "given": "Omer" }, "id": "Tamuz-O", "orcid": "0000-0002-0111-0418", "role": "member", "display_name": "Tamuz, Omer" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/ks49-mj38", "abstract": "This thesis introduces discrete conformal variational problems as a versatile toolkit for the construction and manipulation of smooth surfaces in three-dimensions. Smooth curves and surfaces can be characterized as minimizers of squared curvature bending energies subject to constraints. In the univariate case with an isometry (length) constraint this leads to classic non-linear splines. For surfaces, isometry is too rigid a constraint, so we instead ask for minimizers of the Willmore (squared mean curvature) energy subject to a conformality constraint. Conformal transformations are desirable in applications because they preserve angles, and consequentially also mesh quality and the fidelity of geometric data. The conformal structure of a surface can be specified in terms of finitely many geometric parameters, and therefore provides a suitable interface for the free form design of surfaces. We term these surfaces conformal surface splines. Until now, however, there has been no systematic study of discrete conformal variational problems.
\r\n\r\nThe main contribution of this thesis is analysis and numerical computation of discrete constrained Willmore surfaces. We present an efficient algorithm for computing discrete (conformally) constrained Willmore surfaces using triangle meshes of arbitrary topology. We also introduce free boundary conditions and point constraints for conformal immersions that increase the controllability of surfaces defined as minimizers of conformal variational problems. We demonstrate the applicability of our framework to geometric modeling and mathematical visualization.
\r\n\r\nTo understand the M\u00f6bius invariant discretization of the Willmore energy underlying conformal surface splines, we describe a new quaternionic description of the conformal three-sphere, along with realizations of the spaces of circles, spheres, and point pairs in Euclidean three-space. We give an interpretation of the Willmore energy as the curvature of a quaternionic connection that has a clear geometric interpretation in terms of mean curvature spheres rolling over the surface. Building on this interpretation, we prove that the M\u00f6bius invariant discretization of the Willmore energy is equal to the curvature of a discrete connection defined by rolling the edge circumspheres. Conservation laws for discrete Willmore surfaces are also derived, finding applications in the prescription of tangent planes at point constraints.
" }, { "name": "Spratt, Jean-S\u00e9bastien Alexandre", "degree": "PhD", "year": "2024", "title": "Numerical Simulations of Cavitating Bubbles in Elastic and Viscoelastic Materials for Biomedical Applications", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162023-141935060", "creators": [ { "name": { "family": "Spratt", "given": "Jean-S\u00e9bastien Alexandre" }, "id": "Spratt-Jean-S\u00e9bastien-Alexandre", "orcid": "0000-0002-1962-4214", "display_name": "Spratt, Jean-S\u00e9bastien Alexandre" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "space" ], "doi": "10.7907/g34e-6p65", "abstract": "The interactions of cavitating bubbles with elastic and viscoelastic materials play a central role in many biomedical applications. This thesis makes use of numerical modeling and data-driven approaches to characterize soft biomaterials at high strain rates via observation of bubble dynamics, and to model burst-wave lithotripsy, a focused ultrasound therapy to break kidney stones.
\r\n\r\nIn the first part of the thesis, a data assimilation framework is developed for cavitation rheometry, a technique that uses bubble dynamics to characterize soft, viscoelastic materials at high strain-rates. This framework aims to determine material properties that best fit observed cavitating bubble dynamics. We propose ensemble-based data assimilation methods to solve this inverse problem. This approach is validated with surrogate data generated by adding random noise to simulated bubble radius time histories, and we show that we can confidently and efficiently estimate parameters of interest within 5% given an iterative Kalman smoother approach and an ensemble- based 4D-Var hybrid technique. The developed framework is applied to experimental data in three distinct settings, with varying bubble nucleation methods, cavitation media, and using different material constitutive models. We demonstrate that the mechanical properties of gels used in each experiment can be estimated quickly and accurately despite experimental inconsistencies, model error, and noisy data. The framework is used to further our understanding of the underlying physics and identify limitations of our bubble dynamics model for violent bubble collapse.
\r\n\r\nIn the second part of the thesis, we simulate burst-wave lithotripsy (BWL), a non- invasive treatment for kidney stones that relies on repeated short bursts of focused ultrasound. Numerical approaches to study BWL require simulation of acoustic waves interacting with solid stones as well as bubble clouds which can nucleate ahead of the stone. We implement and validate a hypoelastic material model, which, with the addition of a continuum damage model and calibration of a spherically- focused transducer array, enables us to determine how effective various treatment strategies are with arbitrary stones. We present a preliminary investigation of the bubble dynamics occurring during treatment, and their impact on damage to the stone. Finally, we propose a strategy to reduce shielding by collapsing bubbles ahead of the stone via introduction of a secondary, low-frequency ultrasound pulse during treatment.
" }, { "name": "Su, Magel Powei", "degree": "PhD", "year": "2024", "title": "Exploring Thermal Photonics for Sustainability: From Selective Solar Absorbers to Terrestrial Radiative Cooling", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032024-223707990", "creators": [ { "name": { "family": "Su", "given": "Magel Powei" }, "id": "Su-Magel-Powei", "orcid": "0000-0003-4898-5024", "display_name": "Su, Magel Powei" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/rrf2-4979", "abstract": "Photonic materials for thermal emission control have attracted much attention in sustainable technologies where energy and heat management are highly desirable. Controlling the frequency dependency of emissivity enables passive suppression or enhancement of thermal emission which can be used to exploit thermodynamically favorable conditions.
\r\n\r\nIn Part I, we present the development of a selective solar absorber which suppresses thermal emission for efficient conversion of solar energy into thermal energy. Our absorber uses an ultrathin metal layer and an antireflective coating to suppress thermal emission and enhance solar absorption, respectively. Furthermore, we constructed a novel scalable photothermal reactor which utilizes the selective solar absorber for thermocatalytic processes. Thermochemical processes provide a sustainable alternative for fuel synthesis compared to traditional industrial methods, and catalyzed processes operate at reduced temperatures and pressures allowing them to be powered solely by direct solar thermal energy. Using sunlight, we synthesized C\u2086 \u2013 C\u2082\u2084 carbon chain length olefins from ethylene gas with Ni-catalyzed ethylene oligomerization, demonstrating a vital step for direct CO\u2082 to sustainable aviation fuel synthesis.
\r\n\r\nIn Part II, we present silicon oxide and silicon nitride bilayer laminate nanoparticle films as scalable efficient daytime terrestrial radiative coolers which couple enhanced thermal emission with the cold background of space. We show experimentally that laminate nanoparticle films deposited from a nonthermal plasma are well described by effective medium mixing models, and their fill fraction tunability enables them to spectrally match more efficiently to the atmospheric transmission window than conventional dense laminate thin films. During this process, we realized a need for directly measuring thermal emission in a controlled ambient to facilitate inter-comparisons between radiative cooling performances. In response, we constructed a new instrument for direct spectrally and angularly resolved radiative emission measurements, providing a new avenue to study the thermal emission behavior of photonic materials.
" }, { "name": "Sun, Jennifer Jianing", "degree": "PhD", "year": "2024", "title": "AI for Scientists: Accelerating Discovery Through Knowledge, Data, and Learning", "advisor": "Perona, Pietro; Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:11162023-054627670", "creators": [ { "name": { "family": "Sun", "given": "Jennifer Jianing" }, "id": "Sun-Jennifer-Jianing", "orcid": "0000-0002-0906-6589", "display_name": "Sun, Jennifer Jianing" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "co-advisor", "display_name": "Perona, Pietro" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "co-advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "chair", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Chaudhuri", "given": "Swarat" }, "id": "Chaudhuri-Swarat", "orcid": "0000-0002-6859-1391", "role": "member", "display_name": "Chaudhuri, Swarat" }, { "name": { "family": "Kennedy", "given": "Ann" }, "id": "Kennedy-Ann", "role": "member", "display_name": "Kennedy, Ann" } ], "option_major": [ "cms" ], "doi": "10.7907/d6y8-4590", "abstract": "With rapidly growing amounts of experimental data, machine learning is increasingly crucial for automating scientific data analysis. However, many real-world workflows demand expert-in-the-loop attention and require models that not only interface with data, but also with experts and domain knowledge. My research develops full stack solutions that enable scientists to scalably extract insights from diverse and messy experimental data with minimal supervision. My approaches learn from both data and expert knowledge, while exploiting the right level of domain knowledge for generalization. This thesis presents progress towards developing automated scientist-in-the-loop solutions, including methods that automatically discover meaningful structure from data such as self-supervised keypoints from videos of diverse behaving organisms. We will then discuss methods that use these interpretable structures to inject domain knowledge into the learning process, such as guiding representation learning using symbolic programs of behavioral features computed from keypoints. This work is the result of close collaborations with domain experts, such as behavioral neuroscientists, in order to identify bottlenecks and integrate these methods in real-world workflows. My aim is to enable AI that collaborates with scientists to accelerate the scientific process." }, { "name": "Sun, Shi-Ning", "degree": "PhD", "year": "2024", "title": "Digital Quantum Simulation of Quantum Many-Body Systems", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292024-213136069", "creators": [ { "name": { "family": "Sun", "given": "Shi-Ning" }, "id": "Sun-Shi-Ning", "orcid": "0000-0002-5984-780X", "display_name": "Sun, Shi-Ning" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-G-K", "orcid": "0000-0001-8009-6038", "role": "member", "display_name": "Chan, Garnet K." }, { "name": { "family": "Chen", "given": "Xie" }, "id": "Chen-Xie", "orcid": "0000-0003-2215-2497", "role": "member", "display_name": "Chen, Xie" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/xm9j-9x23", "abstract": "Quantum computing has emerged as a promising technology, heralding a new era of computational capabilities, with the simulation of quantum many-body systems as one of its primary objectives. Although fault-tolerant quantum computers are still years away, noisy intermediate-scale quantum (NISQ) devices have been fabricated and leveraged to perform small-scale quantum simulations. In this thesis, we demonstrate simulations of quantum many-body systems on these near-term quantum computers. We specifically focus on physical quantities pertaining to the linear-response framework, which include two-point correlation functions and Green's functions, of small-scale spin and molecular models. Additionally, as quantum hardware increases in qubit count, simulation of these quantum algorithms on classical computers that closely resemble those planned for execution on quantum hardware becomes increasingly critical. The final part of this thesis examines such a simulation using tensor network algorithms on classical computers.
\r\n\r\nWe first present the study of finite-temperature physics of spin models on quantum hardware. Employing the quantum imaginary time evolution (QITE) algorithm, we demonstrate the computation of diverse finite-temperature observables, including energy, static and dynamical correlation functions, and excitation spectra of the Heisenberg model and the transverse-field Ising model of up to four sites on five-qubit IBM Quantum devices. Accurate determination of these finite-temperature properties on quantum computers is made possible by several algorithmic improvements, including a method to exploit symmetries that reduces the quantum resources required by QITE, circuit optimization procedures to reduce circuit depth, and error-mitigation techniques to improve the quality of raw hardware data. This work demonstrates that the ansatz-independent QITE algorithm is capable of computing diverse finite-temperature observables on near-term quantum devices.
\r\n\r\nThe second work implements an algorithm for frequency-domain response properties of diatomic molecules using a novel high-fidelity three-qubit iToffoli gate. Although it is natural to compute response properties in the time domain due to the natural ability of quantum computers to apply unitary time evolutions, obtaining the frequency-domain properties from the time-domain properties typically requires a time duration that results in quantum circuits exceeding the circuit depth limitations of near-term quantum computers. In this work, we carry out computations of the response properties directly in the frequency domain using the linear combination of unitaries (LCU) algorithm. Execution of the LCU-based protocol on quantum hardware is enabled by the iToffoli gate, which enables a ~50\\% reduction in circuit depth and ~40\\% reduction in circuit execution time in the LCU circuits compared to the traditional gate set. We show that the molecular properties obtained with the iToffoli gate exhibit comparable or better agreement with analytical results than those obtained when CZ gates are the only multi-qubit gates. This work is among the first demonstrations of the practical usage of a native multi-qubit gate in quantum simulation, with diverse potential applications to near-term quantum computation.
\r\n\r\nFinally, this thesis conducts a tensor network simulation of measurement-induced state preparation on classical computers. Specifically, we simulate the phase transition in random-bond Ising models (RBIM) by performing measurements on the cluster states. The simulation is carried out on NVIDIA H100 graphical processing units (GPUs) using the cuQuantum library. We present simulation of correlation functions in one dimension (1D) and ferromagnetic susceptibilities in two dimensions (2D), observing a phase transition from the ferromagnetic phase to spin-glass phase in the 2D model. The tensor network simulation incorporates up to 176 qubits on the 2D lattice. This work paves the way for future explorations of tensor network simulations of measurement-induced quantum computation protocols with GPU-accelerated tensor network libraries.
" }, { "name": "Sun, Yuchun", "degree": "PhD", "year": "2024", "title": "3D Micro-Architected Materials for Batteries", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04162024-184348195", "creators": [ { "name": { "family": "Sun", "given": "Yuchun" }, "id": "Sun-Yuchun", "orcid": "0000-0002-7028-3523", "display_name": "Sun, Yuchun" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "West", "given": "William C." }, "id": "West-W-C", "orcid": "0000-0001-6417-8930", "role": "member", "display_name": "West, William C." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/y6bt-xb40", "abstract": "Additive manufacturing (AM) enables three-dimensional micro-patterning of battery electrode materials, permitting complex structural designs beyond those of traditional slurry electrodes. We demonstrate two novel AM approaches for architecting electrode materials in lithium-ion batteries. First, we introduce a process for fabricating 3D micro-architected cathodes utilizing gel infusion additive manufacturing, and demonstrate this technique with lithium cobalt oxide (LCO). This method combines VP-based 3D printing with subsequent ion infusion and calcination processes. It starts with the printing of a blank organogel structure using a customized acrylate-based photoresin. This organogel is then converted into a hydrogel, infused with lithium and cobalt precursors, and finally subjected to calcination to form the LCO structure. This technique achieves 3D micro-architected LCO lattices with beam diameters of 45 \u03bcm, and maintains the designed architecture with tunable microstructures. By fabricating 3D micro-architected LiNi0.33Mn0.33Co0.33O2 (NMC111) through a very similar process, we demonstrate the potential for this gel infusion additive manufacturing method to engineer a variety of cathode materials for lithium-ion batteries in 3D.
\r\n\r\nWe also develop a fabrication method to create 3D lithium anodes supported by micro-architected carbon scaffold. By pyrolyzing 3D printed polymer microlattices, mechanically robust carbon electrodes are produced. Their micro-scale features and flexible structural control make them suitable as scaffolds for lithium-metal anodes. Surface functionalization and lithium electrodeposition are explored for dense lithium nucleation and uniform epitaxial growth on the carbon framework, resulting in micro-architected lithium/carbon anodes. With the rapid development of high-resolution AM techniques in recent decades, these approaches to additively manufacture cathode and anode materials provide promising pathways to build batteries with customizable 3D designs, and pursue higher energy and power densities for different applications.
" }, { "name": "Tu, Jiaobing", "degree": "PhD", "year": "2024", "title": "Wearable Sweat Sensors for Disease Monitoring and Management", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062023-050222447", "creators": [ { "name": { "family": "Tu", "given": "Jiaobing" }, "id": "Tu-Jiaobing", "orcid": "0000-0002-7653-6640", "display_name": "Tu, Jiaobing" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "chair", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" } ], "option_major": [ "medeng" ], "doi": "10.7907/7jdg-z479", "abstract": "With the emphasis of healthcare shifting towards prevention and early detection of diseases and monitoring of chronic conditions, there is a growing need for hassle\u2010free telemedicine sensor technologies that can be seamlessly integrated into daily life. While significant progress has been made in the development of wearable sweat and salivary biosensors to meet this need for rapid, real-time collection of physiological information, the majority of current epidermal sensing systems are unable to detect trace-level disease-relevant biomarkers accurately in biofluids and cannot be mass produced. To meet this demand for low-cost, mass-producible mHealth devices for at-home settings, we developed several fully integrated laser-engraved graphene-based biosensors for the detection of low-concentration sweat and saliva analytes including hormones (cortisol) and proteins (C-reactive protein). Several graphene surface engineering strategies are investigated for the sensitive and selective detection of targets. System-level engineering and microfluidic designs are explored to achieve on-demand sweat induction and harvesting under sedentary settings and automated sweat and reagent routing and in situ signal correction and analysis for facile operation on the skin. The utility of these fully integrated flexible mHealth systems is evaluated through multiple human studies involving healthy and various patient subgroups towards stress assessment, as well as the monitoring and management of various chronic conditions including chronic obstructive pulmonary disease, heart failure, and inflammatory bowel diseases. These fully integrated mHealth devices demonstrate a technology that can be easily adapted to monitor a broad spectrum of disease-specific proteins, cytokines, and hormones, thus advancing future applications in personalized disease diagnosis, management, and prevention." }, { "name": "Villafuerte, Fernando Joaquin", "degree": "PhD", "year": "2024", "title": "Additive Manufacturing of Batteries and IR-Active Microparticles: Polyborane-Based Electrolytes for Solid State Batteries and Additively Manufactured, TiN-Coated Microbridges", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10222023-023442759", "creators": [ { "name": { "family": "Villafuerte", "given": "Fernando Joaquin" }, "id": "Villafuerte-Fernando-Joaquin", "orcid": "0000-0003-0958-7111", "display_name": "Villafuerte, Fernando Joaquin" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/jc8h-gs34", "abstract": "Advances in additive manufacturing (AM) processes are continuously opening up the material design space, providing scientists with opportunities to explore the relationship between structure, processing, and materials properties in new contexts. The first project presented in this thesis presents the design and refinement of a novel, polyborane-based solid electrolyte, whose design and investigation were motivated by the advent of additively manufactured, 3D electrodes, which could play a pivotal role in enabling next-generation batteries that can store more energy without sacrificing power. The first iteration of this electrolyte was synthesized by hydroborating polybutadiene with 9-borabicyclo(3.3.1)nonane (9-BBN). The resultant poly(9-BBN) was then reacted with precise amounts of n-butyllithium (n-BuLi), an organolithium reagent, to create the final polymer electrolyte. The polymer electrolyte films were assembled into a custom apparatus for impedance measurements, and though found to be ionically conductive, these measurements were not consistent, even within films made from the same batch of polymer in solution.
\r\n\r\nThis necessitated the modification of the electrolyte into a UV-cured version, which was achieved by hydroboration of polybutadiene using 9-BBN. The resulting poly(9BBN)-co-polybutadiene is treated with lithium tert-butoxide (LiOtBu) and crosslinked to produce a precursor resin, which is then drop cast onto PTFE spacers, UV-cured for 5 minutes, dried, and assembled into coin cells for electrochemical impedance spectroscopy (EIS) and into pans for differential scanning calorimetry (DSC). The ionic conductivity of the PBEs as measured by EIS as a function of molar salt ratio, r = molLi/molB, does not track with their measured glass transition temperatures, Tg or the activation energies, Ea, extracted from fitting the Vogel-Tammann-Fulcher (VTF) equation to the conductivity data. Beyond r = 0.33, values for Tg and Ea demonstrate insensitivity to increasing concentration, while conductivity continues to change with concentration and reaches a maximum at r = 0.75. Moreover, measurement of ionic conductivity of control PBE films without boron on the polybutadiene backbone confirms that the presence of Lewis-acidic boron groups is necessary for ionic solvation and conduction. Further analysis that compared the PBEs to a well-studied PEO-based electrolyte in the literature through the calculation of a reduced conductivity to control for polymer viscosity and segmental motion revealed that PBEs obtain optimal conductivity at higher salt concentrations than PEO, and that their ionic conductivities are far below that of PEO. We posit that we are observing a mechanism of ionic conduction in a glassy regime partially decoupled from the relaxation of the polymer host. We attribute these effects to the strong interaction between the Lewis-acidic boron centers and the strongly Lewis-basic tert-butoxide anions, which limits ionic conductivity by suppressing motion of the anions and presenting a large activation barrier for motion of Li+, which is optimized at high concentrations where the distance between the boron-anion centers is sufficiently small to increase the probability of a hopping event from one center to another.
\r\n\r\nNanorods fashioned from noble metals are ideal for maximizing extinction of electromagnetic radiation, which is necessary for plasmonically active materials in numerous applications, from contrast agents for biological imaging to effective obscurants. Key challenges that prevent nanorods from being employed for these technological applications include the prohibitively expensive cost of Au and Ag, their lack of requisite thermal and chemical stability, and the limitations in resolution and attainable feature sizes produced by existing wet chemistry techniques. The second project in this thesis focuses on the development of an AM process to create arrays of TiN-coated microbridges with lengths of 4.749 microns, cross-sections with dimensions of 0.692 by 2.256 microns, and effective aspect ratios of 3.368, that are capable of attenuating light reflected from a TiN-coated sapphire substrate by more than 80% in the mid-infrared (mid-IR), as measured by Fourier Transform Infrared (FTIR) spectroscopy. FTIR spectroscopy measurements further reveal attenuation of light transmitted through the same TiN-coated structures by up to 35% in the near- to mid-IR. These results indicate a promising pathway for AM of plasmonically active microparticles with broad reflectance and transmittance attenuation of light in the near- and mid-IR.
" }, { "name": "Voloshin, Cameron", "degree": "PhD", "year": "2024", "title": "Guaranteed Policy Performance in Reinforcement Learning", "advisor": "Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062024-061120491", "creators": [ { "name": { "family": "Voloshin", "given": "Cameron" }, "id": "Voloshin-Cameron", "orcid": "0009-0007-7725-6660", "display_name": "Voloshin, Cameron" } ], "advisors": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Chaudhuri", "given": "Swarat" }, "id": "Chaudhuri-Swarat", "orcid": "0000-0002-6859-1391", "role": "member", "display_name": "Chaudhuri, Swarat" } ], "option_major": [ "cms" ], "doi": "10.7907/n2fg-e554", "abstract": "Decision-making is ubiquitous in everyday life. Increasingly, researchers are seeking answers on how to optimally solve sequential decision-making tasks. Thanks to recent availability of computation, advances in deep learning, and released open-sourced code, it has become easy to train a computational agent to make decisions in many domains. Nevertheless, in realistic scenarios where the consequences of failure are high, running a trained computational agent in the wild poses substantial risk.
\r\n\r\nThe goal of this thesis is to develop and advance techniques that guarantee a learned agent does what we expect it to do. The thesis tackles two central questions:
\r\n\r\n1) Given an agent, how can we predict if it will perform desirably?
\r\n\r\n2) Can we structure the learning process to guarantee desirable post-learning performance?
\r\n\r\nOn the former question, this thesis proposes multiple algorithms to evaluate such agents, finds factors that have high influence on the success of agent evaluation, and open-sources benchmarks for further development in the space.
\r\n\r\nOn the latter question, this thesis formulates desirable agent behavior as a constrained optimization with varying types of constraints depending on the structure afforded to the practitioner. Constraining the search space over the learning process ensures post-learning behaviors will, by definition, perform as desired.
" }, { "name": "Wei, Skylar Xueyao", "degree": "PhD", "year": "2024", "title": "Data-Driven Safety-Critical Autonomy in Unknown, Unstructured, and Dynamic Environments", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:03042024-201031352", "creators": [ { "name": { "family": "Wei", "given": "Skylar Xueyao" }, "id": "Wei-Skylar-Xueyao", "orcid": "000-0002-6336-9433", "display_name": "Wei, Skylar Xueyao" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "chair", "display_name": "Ames, Aaron D." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Brunton", "given": "Steven L." }, "id": "Brunton-S-L", "orcid": "0000-0002-6565-5118", "role": "member", "display_name": "Brunton, Steven L." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "cds" ], "doi": "10.7907/qpbp-0x81", "abstract": "This thesis addresses the critical challenge of ensuring safety in autonomous exploration within unknown, unstructured, dynamic environments, a domain filled with various types of uncertainties. These include model uncertainties in system dynamics, localization uncertainties stemming from measurement noises, and the risks of collision in environments with dynamic obstacles. Traditional models for vehicle planning and control are often simplified for computational feasibility, but this simplification without careful analysis can compromise safety and system stability. My research introduces a novel, comprehensive framework to provide probabilistically safe planning and control for robot autonomy, structured around three components:
\r\n\r\n(1) Probabilistic Uncertainty Quantification for Model Mismatches:
\r\nThis segment focuses on identifying model discrepancies given closed-loop tracking data in an unstructured environment where a reduced-order robot model is used for planning and control. The disturbance is modeled as a scalar-valued stochastic process of a norm on the difference between the reduce-order robot model and actual system evolution. In an online and risk-aware framework, Gaussian Process Regression is employed to extract the probabilistic upper bound to such stochastic process, referred to as the Surface-at-Risk. Theoretical guarantees on the accuracy of the fitted discrepancy surface are analyzed and verified to the data sets collected during system operation.
\r\n\r\nIn an offline setting, conformal prediction, a statistical inference tool, is employed to obtain probabilistic upper bounds of matched and unmatched model disturbance in the system from data, without any assumption of the latent probability distribution governing these discrepancies. Building on these bounds, the robot's nominal ancillary controller is augmented for extending robustness and stability guarantees of the closed-loop system in the face of such discrepancies. Additionally, a maximum tracking error tube is constructed along the planned trajectory using the reduced-order model. Such error tubes describe the maximum permissible deviation in actual trajectory tracking under the augmented ancillary controller and the worst-case matched and unmatched model uncertainties, thereby delineating safe operational boundaries for the system.
\r\n\r\n(2) Data-Driven Unsafe Set Prediction for Dynamic Obstacles:
\r\nThis thesis topic develops an online, data-driven predictive model for dynamic obstacles, accounting for measurement noise and low-frequency data rates. \r\n First inspired by singular spectrum analysis (SSA), a time-series forecast technique, obstacle models characterized by linear recurrence relationships are extracted from real-time position observables. Using the statistical bootstrap technique, a set of predicted obstacle trajectories are constructed, which in turn are reformulated into deterministic distributionally robust obstacle avoidance constraints, reflecting a user-defined risk tolerance.
\r\nFurther refining the obstacle predictor for intention-unknown obstacles, a linear, time-varying model is learned from data using time-delay embedding of obstacle position observables. Additive process and measurement noises are anticipated in the learned model, where their intensities are estimated from data. For inferring prediction uncertainties, a companion data-driven Kalman Filter (DDKF) is constructed to forecast obstacle positions and uncertainties. This \"heuristic unsafe set\" from DDKF is then dynamically calibrated using adaptive conformal prediction, ensuring safety without relying on any distribution assumptions regarding the uncertainties or model accuracy. The calibrated sets, called conformal prediction sets, are then reformulated into convex state constraints.
\r\n\r\n(3) Safety-Critical Planning:
\r\nThe thesis proposes two methods for ensuring safety in planning and navigation: Probabilistic-Safe Model Predictive Control (MPC) and Probabilistic-Safe Model Predictive Path Integral (MPPI) given uncertainties arising from operating in unknown, unstructured, and dynamic environments. The MPC approach integrates the quantified obstacle avoidance constraints into a convex program to balance computational tractability while providing probabilistic safety guarantees. In contrast, the MPPI method, a sampling-based strategy, incorporating unsafe sets into a cost map derived from sensory data, optimizes reference tracking trajectory while guaranteeing collision avoidance up to a user-defined risk tolerance.
\r\n\r\nIn unknown and cluttered environments automatically, the proposed framework learns an upper bound on model residuals from data and systematically calculates the safety buffers needed to provide the desired probabilistic safe navigation of robotics systems. Additionally, in the presence of dynamic obstacles, the proposed data-driven predictor systematically extracts an obstacle model and makes obstacle-occupied unsafe set forecasts. These features largely eliminate the \"hand tuning\" of the underlying planner and controller that is normally required in heuristic-based algorithms. The efficacy of these proposed frameworks is empirically validated through Monte Carlo Simulations, alongside hardware validations on both ground and aerial vehicles, demonstrating their robustness, versatility, and applicability in real-world scenarios.
" }, { "name": "Wen, Alexander Huai-Cheng", "degree": "PhD", "year": "2024", "title": "Vibration Damping of Coiled Structures Through Frictional Slip", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132023-225911259", "creators": [ { "name": { "family": "Wen", "given": "Alexander Huai-Cheng" }, "id": "Wen-Alexander-Huai-Cheng", "orcid": "0009-0008-9038-3039", "display_name": "Wen, Alexander Huai-Cheng" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "member", "display_name": "Watkins, Michael M." } ], "option_major": [ "aerospace" ], "doi": "10.7907/gvps-8x65", "abstract": "Vibration management is important for the survivability of structures. The response of a structure under vibration is dependent upon interaction between the excitation environment and the properties of the structure. If the input excitation cannot be adjusted, then the structure must be engineered to survive. One approach to engineering structures to reduce vibration response is through damping, which is achieved by adding damping devices or materials to covert kinetic energy into heat, where removing energy from the system reduces the amplitude of response. There are a variety of existing vibration damping concepts and techniques, however, conventional methods of these approaches are subject to limitations such as compromising stiffness for increased damping and performance that is excitation profile dependent.
\r\n\r\nThis research proposes a novel, passive vibration damping concept which is motivated by recent deployable structures for space that use coiling as a packaging architecture. The proposed concept, referred to as \"wound roll damping\", is a friction-based damping scheme for coiled structures, where the structure is wound around a mandrel with tension that allows interlayer slip during vibration. The friction between slipping layers provides an energy dissipation mechanism, which reduces the overall level of response. The concept was developed with the challenges of mitigating spacecraft launch vibration and the limitations of conventional damping techniques in mind.
\r\n\r\nUnderstanding of the working principle and performance of this damping concept is achieved using a combination of experiments, analysis, and FEA. A method for determining the locations of slip within a wound roll under vibration is presented. This consists of modeling the interlayer friction forces, using analytical expressions for the stress fields that arise during tension winding of wound rolls, and comparing these values against loading estimates obtained from analysis and FEA. The locations of slip for wound rolls supported by a cantilevered mandrel with bending vibration modes are towards the root of the wound roll structure, near the inner layers.
\r\n\r\nExperimental studies that demonstrate the performance and properties of this damping concept are presented in this work. A wound roll test sample is subjected to a range of excitation profiles including: sine sweep, sine dwell, random, and shock with varying levels of sample winding tension and excitation amplitude. Using these experiments, this concept is demonstrated to not be subject to the limitations of conventional damping schemes. This scheme is observed to be capable of significantly increasing the overall stiffness while providing elevated damping levels, with a performance that is tunable with winding tension, independent of excitation profile, and scales with excitation amplitude. The locations of slip are observed to be consistent with predictions from FEA and analysis.
\r\n\r\nTwo approaches to simulate and model the wound roll damper are developed to both better understand the physical mechanism of this concept and provide analysis tools. The first method is an FEA model, consisting of the base vibration of concentric shells and solids that have frictional contact interactions. The second method is a 2-DoF reduced order model that simulates the frictional contact between two mass-spring-damper systems. Both methods are demonstrated to have good correlation with experimental measurements.\r\n
\r\n\r\nA majority of this work demonstrates the performance of this concept, using both experiments and simulation at lab scales. This work also presents simulation studies that demonstrate the viability of this concept at realistic scales. Using simulations scaled to recent coilable space structures, both implemented and proposed, the wound roll damping concept is demonstrated to provide significant stiffness and damping.
" }, { "name": "Wood, Steven Andrew", "degree": "PhD", "year": "2024", "title": "Quantum Microwave to Optical Transduction with Light-Robust Superconducting Circuits", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03222024-181941076", "creators": [ { "name": { "family": "Wood", "given": "Steven Andrew" }, "id": "Wood-Steven-Andrew", "orcid": "0009-0004-2582-0627", "display_name": "Wood, Steven Andrew" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/kkbj-ex94", "abstract": "Modern computing and communication technologies such as supercomputers and the internet are based on optically connected networks of microwave frequency information processors. In recent years, an analogous architecture has emerged for quantum networks with optically distributed entanglement between remote superconducting quantum processors, a leading platform for quantum computing. The high coherence, controllability and scalability of microwave frequency superconducting circuits are ideal test-beds for nodes of a quantum network, however, microwave photons are not well suited for transmission of quantum information over long distances due to the presence of a large thermal background at room temperature. Optical photons are ideal for quantum communication applications due to their low propagation loss and negligible thermal occupation at room temperature. Coherent transduction of single photons from the microwave to the optical domain has the potential to play a key role in quantum networking and distributed quantum computing. In this thesis, we present the design of a piezo-optomechanical quantum transducer where transduction is mediated by a strongly hybridized acoustic mode of a piezoacoustic cavity attached to an optomechanical crystal. Our design involves on-chip integration of a light-robust superconducting circuit with the piezo-optomechanical transducer. Absorption of stray photons from the optical pump used in the transduction process is known to cause excess decoherence and noise in the superconducting circuit. The recovery time of the superconducting circuit after the optical pulse sets a limit on the transducer repetition rate. We fabricate niobium nitride based superconducting circuits and test their response to illumination by a 1550nm laser. We find a bandwidth-limited recovery time of $\\sim$ 1us, indicating that a repetition rate exceeding 10kHz should be possible. Combined with the expected efficiency and noise metrics of our design, we expect that a transducer in this parameter regime would be suitable to realize probabilistic schemes for remote entanglement of superconducting quantum processors. We show non-classical microwave-optical photon correlations of the niobium nitride aluminum nitride transducer operated as a spontaneous parametric down conversion source. We go on to show the preparation and characterization of microwave-optical Bell states prepared by the transducer. And finally, we conclude by discussing the challenges with fabricating niobium nitride superconducting circuits and lithium niobate piezoacoustic devices on silicon-on-insulator substrates and provide steps towards realizing our enhanced transducer design." }, { "name": "Wray, Parker Ryan", "degree": "PhD", "year": "2024", "title": "How to Make Small Things Do Big Things: Exploring Engineered Disorder for Massively Scalable Metasurfaces and Metamaterials", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:01032024-012340742", "creators": [ { "name": { "family": "Wray", "given": "Parker Ryan" }, "id": "Wray-Parker-Ryan", "orcid": "0000-0003-3384-0826", "display_name": "Wray, Parker Ryan" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "eleceng" ], "doi": "10.7907/kvz3-jn93", "abstract": "This work presents a collection of topics related to anomalous electromagnetic scattering, emission, and absorption states formed from random systems. The underlying motivation is to explore to what extent metasurface and metamaterial concepts could be applied at a massively large scale; by identifying emergent properties in systems that do not require careful fabrication. Emphasis is placed on exploring theoretical descriptions for systems that do not conform well to existing simpler models. Covered topics include random metasurfaces for spectral filtering and polarization invariance, random nanoparticle films for radiative cooling, broadband polarization and angle invariant absorption using random fractals, effective medium models beyond traditional assumptions, a mathematical transform to understand highly directional scattering/emission in complex systems, and optical metrology and characterization techniques for random systems." }, { "name": "Wu, Lue Leo", "degree": "PhD", "year": "2024", "title": "Greater Than One Billion Optical Q Factor for On-Chip Microresonators", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042024-003837900", "creators": [ { "name": { "family": "Wu", "given": "Lue Leo" }, "id": "Wu-Lue-Leo", "orcid": "0000-0002-7503-7057", "display_name": "Wu, Lue Leo" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/n1cn-tn34", "abstract": "This thesis is focused on making ultra-high-Q optical microresonators on silicon chips based on design and constructing ultra-low-loss optical waveguides (with losses around 20 dB/km), their fabrication process development, and device applications in on-chip nonlinear optics, including frequency combs, low-noise microwave generation, and narrow-linewidth lasers.
\r\n\r\nFirst, using thermally grown oxide (thermal silica) and wedge microresonator structure, a record Q factor exceeding 1.1 billion is achieved. Then, the limitations of the Q-factor due to surface roughness scattering loss and OH absorption loss are investigated and identified. Absorption limited Q-factor of 8 billion mainly attributed to OH ions is measured. To further explore the potential of thick thermal silica as under cladding material, wedge resonator fabricated in 25-\u00b5m-thick thermal silica achieves a Q-factor of over 60 million, along with a sixfold improvement in thermal stability and a 5 billion absorption-limited Q-factor. Subsequently, low noise microwave signal generation is demonstrated using these devices in a fully optical packaged form, operating soliton microcomb to generate beatnote microwave signals. Noise limitations arising from dispersive waves induced by distinct transverse modes are identified. Additionally, a low-fundamental-linewidth microcavity Brillouin laser is demonstrated, benefiting from device high Q-factor. The noise limits stemming from thermal refractive fluctuation at low offset frequencies and laser output power at high offset frequencies are identified. To improve device integration level, an engineered reduction of interface scattering using TM mode enables a demonstration of 700 million Q factor in a fully-integrated high-aspect-ratio thin SiN platform fabricated in a CMOS foundry. To add one more thing, room temperature soliton microcomb generation is demonstrated for the first time in high-Q AlGaAs microresonators.
" }, { "name": "Xu, Changhao", "degree": "PhD", "year": "2024", "title": "Electronic Skin in Robotics and Healthcare: Towards Multimodal Sensing and Intelligent Analysis", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:02182024-070645738", "creators": [ { "name": { "family": "Xu", "given": "Changhao" }, "id": "Xu-Changhao", "orcid": "0000-0002-6817-3341", "display_name": "Xu, Changhao" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" } ], "option_major": [ "medeng" ], "doi": "10.7907/en0a-ep72", "abstract": "Skin-interfaced electronics is gradually transforming robotic and medical fields by enabling noninvasive and continuous monitoring of physiological and biochemical information. Despite their promise, current wearable technologies face challenges in several disciplines: Physical sensors are prone to motion-induced noise and lack the capability for effective disease detection, while existing wearable biochemical sensors suffer from operational instability in biofluids, limiting their practicality. Conventional electronic skin contains only a limited category of sensors that are not sufficient for practical applications, and conventional data processing methods for these wearables necessitate manual intervention to filter noise and decipher health-related information.
\r\n\r\nThis thesis presents advances in electronic skin within robotics and healthcare, emphasizing multimodal sensing and data analysis through machine intelligence. Chapter 1 introduces the concept of electronic skin, outlining the emerging sensor technologies and a general machine learning pipeline for data processing. Chapter 2 details the development of multimodal physiological and biochemical sensors that enable long-term continuous monitoring with high sensitivity and stability. Chapter 3 explores the application of integrated electronic skin in robotics, prosthetics, and human machine interactions. Chapter 4 showcases practical implementations of integrated electronic skin with robust sensors for wound monitoring and treatment. Chapter 5 highlights the transformative deployment of artificial intelligence in deconvoluting health profiles on mental health. The last chapter, Chapter 6, delves into the challenges and prospects of artificial intelligence-powered electronic skins, offering predictions for the evolution of smart electronic skins. We envision that multimodal sensing and machine intelligence in electronic skin could significantly advance the field of human machine interactions and personalized healthcare.
" }, { "name": "Yao, Matthew Xuhuai", "degree": "PhD", "year": "2024", "title": "Lean Premixed Hydrogen Flames: Turbulence, Chemistry, and Modelling", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292024-213954509", "creators": [ { "name": { "family": "Yao", "given": "Matthew Xuhuai" }, "id": "Yao-Matthew-Xuhuai", "orcid": "0000-0001-6141-1477", "display_name": "Yao, Matthew Xuhuai" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/yjzw-vp60", "abstract": "Lean turbulent premixed hydrogen/air flames have substantially increased flame speeds, a behaviour which is attributed to differential diffusion effects. In this thesis, the relationships between turbulence, chemistry, and modelling are studied through direct numerical simulation (DNS) and large eddy simulation (LES).
\r\n\r\nThe effect of turbulence on lean hydrogen combustion is studied through DNS using detailed chemistry and detailed transport. Simulations are conducted at six Karlovitz numbers and four integral length scales. A general expression for the burning efficiency is proposed which depends on the conditional mean chemical source term and gradient of a progress variable. At a fixed Karlovitz number, the normalized turbulent flame speed and area both increase almost linearly with the integral length scale ratio. The effect on the mean source term profile is minimal, indicating that the increase in flame speed can solely be attributed to the increase in flame area. At a fixed integral length scale, both the flame speed and area first increase with Karlovitz number before decreasing. Neglecting Soret diffusion is shown to reduce the flame speed, area, and burning efficiency. At higher Karlovitz numbers, the diffusivity is enhanced due to penetration of turbulence into the reaction zone, significantly dampening differential diffusion effects.
\r\n\r\nThe structure of lean hydrogen flames, namely the species mass fraction dependence on the local temperature, differs significantly from that of unity Lewis number fuels due to thermodiffusive instabilities. When subjected to turbulence, the conditional mean species mass fraction profiles are observed to transition from the laminar mixture-averaged flamelet solution to the unity Lewis number flamelet solution. We assess the impact of Soret diffusion and integral length scales on an effective Lewis number model. The results show that the turbulent flame structure can be mapped onto laminar flamelets via the use of effective Lewis numbers, which are expressed by an a priori Karlovitz number model. Although the flame structure is altered by Soret diffusion, there is still strong agreement with previously derived Karlovitz number models for effective Lewis numbers. To map the turbulent flames onto laminar flames with effective Lewis numbers, the relative impact of Soret diffusion needs to be proportionally reduced.
\r\n\r\nTo assess the LES modelling of lean hydrogen flames, we simulate a low-swirl burner, an alternative means of clean energy generation. The LES modelling of these flows remains challenging because the transition of small-scale instabilities into large-scale turbulent structures cannot be modelled by conventional strategies. Traditional one-equation tabulated chemistry formulations require only a progress variable, and cannot capture differential diffusion and curvature effects. In this work, we study the effects of tabulating different conditional mean source terms. It is shown that tabulating the appropriate conditional mean source term leads to improvements in the flow field prediction, however, key features such as the main recirculation region are not reproduced. Then, a two-equation tabulated chemistry model which accounts for differential diffusion and curvature effects is tested. This model provides the best agreement with experimental results. The work is a first effort in evaluating the performance of the two-equation model in the LES framework.
" }, { "name": "Yu, Wesley Minlai", "degree": "PhD", "year": "2024", "title": "Experiments on Separation Shear Layer Instabilities in Hypervelocity Flows", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05202024-181545768", "creators": [ { "name": { "family": "Yu", "given": "Wesley Minlai" }, "id": "Yu-Wesley-Minlai", "orcid": "0000-0002-1133-3199", "display_name": "Yu, Wesley Minlai" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1m4t-5n55", "abstract": "Shock-boundary layer interactions (SBLI) are complex fluid dynamic phenomena that occur when shocks are generated near corners and irregular geometries on vehicles flying near or above supersonic speeds, causing external flow distortion and possible boundary layer separation. Accurate prediction of the mean and unsteady SBLI surface interaction is imperative to avoid failure from highly localized aerodynamic and heating loads, and loss of authority near a control surface. For hypersonic flight-enthalpy matched conditions, current SBLI simulations tend to under-predict thermal loads and have significant disagreements with ground-based experiments in separation location, and location and magnitude of peak heating. These discrepancies are potentially largely due to uncertainties in the modeling and recreation of the coupled real-gas (thermochemical) molecular and gas dynamic processes. To address this issue, efforts have been placed on developing and validating thermochemical gas models, which presents a need for off-surface experimental data. The disagreement between simulations and high-enthalpy ground test experiments have also highlighted the need to better characterize the freestream thermodynamic, velocity, and noise conditions.
\r\n\r\nExtensive freestream characterization of the T5 Free-Piston Reflected Shock Tunnel was performed over the course of numerous experimental campaigns using high-speed shadowgraph/schlieren imaging, static and pitot pressure probes, tunable diode laser absorption spectroscopy (TDLAS), and focused laser differential interferometry (FLDI). Accurate time-resolved static pressure measurements are key to characterizing the operation and freestream thermodynamic state in hypervelocity reflected shock tunnels, through both direct measurement and for interpretation of TDLAS signals. A series of three static pressure probes were built for use in T5 at a range of conditions from 8-16 MJ/kg stagnation enthalpies, and measurements agreed well with TDLAS-inferred pressure and numerical simulations of the static probe response. At higher enthalpy conditions, TDLAS measurements showed a substantial decrease in freestream temperature (~1000 K) while velocity was constant. This finding motivated the need for a method to characterize the arrival time and degree of driver gas contamination in T5. An opposing-wedge detector was designed to leverage the sensitivity of the canonical Mach stem flow to the freestream \u03b3, such that the flow would choke at a prescribed increase in \u03b3 corresponding to the arrival of a specific mole fraction of monatomic driver gas. With high-speed schlieren/shadowgraph imaging, driver gas arrival times and mole fractions were obtained for the 8 MJ/kg test condition.
\r\n\r\nInformed by these freestream characterization experiments, near-surface FLDI measurements of instabilities in a separation shear layer on a 25\u00b0-55\u00b0 double-cone model were performed with simultaneous static pressure and freestream tunnel noise measurements in hypervelocity conditions. Three main frequency regimes were considered: i) low-frequency content associated with Kelvin-Helmholtz instabilities and streamwise acoustic disturbances along the shear layer, ii) a strong medium-frequency (peak ~370-450 kHz) signal associated with shear layer instabilities communicating with the model surface, and iii) high-frequency features associated with Mack (second-mode) disturbances. Length scaling arguments are discussed for each case, informed by axisymmetric simulations of the mean flow over the double-cone. A ray-tracing model was used to simulate the FLDI response to certain disturbances. The low-frequency Kelvin-Helmholtz and streamwise acoustic disturbance frequencies did not vary beyond uncertainty bounds along the shear layer. The medium-frequency content had a clear dependence on the local separation height, with the mean frequency decreasing with streamwise position. The high-frequency Mack mode disturbances were only observed in some experiments, suggesting the disturbance is limited only to within the shear layer, making detection difficult if any bulk shear layer motion occurs relative to the FLDI beam positions. This study provides the first known FLDI data on shear layers in hypervelocity flows, together with simultaneous freestream characterization, with the aim to inform future experiments in hypervelocity ground testing facilities and high-resolution numerical simulations.
" }, { "name": "Yuan, Zhiquan", "degree": "PhD", "year": "2024", "title": "Physics and Applications of Optical Nonlinearity in High-Q Microresonators", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01262024-232942660", "creators": [ { "name": { "family": "Yuan", "given": "Zhiquan" }, "id": "Yuan-Zhiquan", "orcid": "0000-0001-9054-6004", "display_name": "Yuan, Zhiquan" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/vj6e-wr82", "abstract": "Optical microresonators trap light in compact volumes at discrete resonant frequencies. Benefiting from the ultra-low propagation loss, the electromagnetic wave intensity is greatly enhanced. Due to the pronounced light confinement, nonlinear optical effects are significantly magnified in the microresonators. In this thesis, I investigate various nonlinear optical phenomena using high quality factor silica wedge and fully-integrated thin film silicon nitride microresonators. The exploration begins with Kerr nonlinearity-induced soliton microcombs followed by their application in mid-IR band gas spectroscopy. The generation of solitons under normal dispersion conditions, which frustrate soliton formation, is then considered. Subsequently, attention is directed towards stimulated Brillouin lasers and their frequency noise performance, including long-term frequency stabilization based on the built-in temperature reference and validation of two modification factors affecting short-term fundamental linewidth. Along this journey, a novel method for calibrating ultra-narrow laser linewidths is introduced. Lastly, this method is employed to measure the narrow linewidth of a visible laser generated through second harmonic generation in silicon nitride resonators." }, { "name": "Zhang, Yang", "degree": "PhD", "year": "2024", "title": "Understanding the Plasma Universe through Laboratory Experiments and Related Models", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032024-042422418", "creators": [ { "name": { "family": "Zhang", "given": "Yang" }, "id": "Zhang-Yang", "orcid": "0000-0002-4168-9225", "display_name": "Zhang, Yang" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Batygin", "given": "Konstantin" }, "id": "Batygin-K", "orcid": "0000-0002-7094-7908", "role": "member", "display_name": "Batygin, Konstantin" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/gc8w-6n85", "abstract": "Laboratory experiments and the models they inspire are powerful tools for studying the plasma universe. This dissertation details possible solutions to two important problems in the plasma universe, namely how solar flares are generated and how accretion disks transport angular momentum and generate astrophysical jets.
\r\n\r\nAddressing the first problem, solar coronal loop physics is simulated in a laboratory experiment. The loop structure composed of braided strands is replicated. The MHD kink instability and the magnetic Rayleigh Taylor instability (MRTI) are observed to disrupt the loop structure. The dependence of the MRTI wavelength on the axial magnetic field is studied. Transient, localized 7.6-keV X-ray bursts and a several-kilovolt voltage spike are observed to be associated with the breaking of braided magnetic flux ropes containing 2 eV plasma. These spikes occur when the braid strand radius is choked down to be at the kinetic scale by either MHD kink or magnetic Rayleigh\u2013Taylor instabilities. The observed sequence reveals an MHD to non-MHD cross-scale coupling that is likely responsible for generating solar energetic particles and X-ray bursts. All the essential components of this mechanism have been separately observed in the solar corona.
\r\n\r\nMagnetic flux ropes, the fundamental building block of magnetohydrodynamic plasma configurations, have often been observed to wrap around each other to form a helical braided structure with net axial current as observed from the laboratory experiment and solar coronal loops. Braiding phenomena extend to astrophysical jets, double helix nebula, and fusion plasma experiments. The equilibrium of braided flux ropes is more complicated than familiar axisymmetric systems because it requires balancing forces between the individual braids. A novel method for constructing these equilibria is developed. This method generates a double helix equilibrium with net axial current which is characteristic of observed solar loops and of laboratory-produced braided magnetic flux ropes. To the best of our knowledge, no previous model has been able to describe braided structures with net axial current. The net-axial-current equilibrium presented here reproduces the observed braided structure of the double helix nebula and is expected to be a powerful tool in other contexts.
\r\n\r\nAddressing the second problem, the dissertation introduces a first-principles angular momentum transport mechanism based only on collisions between neutrals and charged particles in the presence of gravitational and magnetic fields. The mechanism is demonstrated by a 2D N-body simulation of a weakly-ionized system. It is found that ions and electrons drift in opposite radial directions as a result of colliding with Kepler-motion neutrals. This reduces the ordinary angular momentum of neutrals and increases the canonical angular momentum of charged particles in a manner such that the net global canonical angular momentum is conserved. The accumulation of ions at small radius and electrons at large radius produces a radially outward electric field, while current from the separation of ions and electrons is radially inward. Consequently, this process provides a gravitational dynamo converting gravitational energy into the electric energy that powers an astrophysical jet. Because this neutral angular momentum loss depends only on neutrals colliding with charged particles, it should be ubiquitous. The model predicts an accretion rate of 3 \u00d7 10\u22128 solar mass per year in good agreement with observed accretion rates.
\r\n\r\nBased on the conservation of canonical angular momentum and dynamics of charged particles under collisions with infalling neutrals, the dissertation also investigates the origin of angular momentum in astrophysical systems. A weakly-ionized, initially non-rotating cloud of neutral particles is shown to spontaneously start rotating when infalling. Quantitative scaling predicts an angular momentum generation rate sufficient to convert neutral infall motion into neutral Keplerian rotation in the outer region of a protoplanetary accretion disk.
" }, { "name": "Zheng, Tianzhe", "degree": "PhD", "year": "2024", "title": "Reconfigurable Metasurfaces in Nanoelectromechanical and Silicon-Organic Systems", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03062024-043923772", "creators": [ { "name": { "family": "Zheng", "given": "Tianzhe" }, "id": "Zheng-Tianzhe", "orcid": "0000-0001-7058-5196", "display_name": "Zheng, Tianzhe" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry" }, "id": "Vahaha-K", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2kmq-da15", "abstract": "Over the past decade, metasurfaces, a technology referring to 2D or 3D engineered nanostructures, has demonstrated itself as a groundbreaking solution for creating compact and multifunctional optical devices. Moreover, the integration of metasurfaces with various modulation techniques enables compact yet high-performance active optical systems. In this thesis I explore various optical modes in engineered nanostructures and apply different design techniques to improve the amplitude and phase response of free-space modulators.
\r\n\r\nIn Chapter 1 and 2, we first briefly introduce the concept of reconfigurable metasurfaces and its state of art. Then we introduce several nanophotonic concepts that will be used frequently in later projects and discuss the potential directions to improve modulator's performance.
\r\n\r\nIn Chapter 3, we find that the dual-mode resonant metasurfaces could improve the phase response in the nanoelectromechanical system(NEMS). The interaction between the quasi-bond state in the continuum and guided mode resonance boosts the phase response up to 144 degrees.
\r\n\r\nIn Chapter 4, the design target is to utilize the high-Q mode to decrease the driving voltage of the NEMS system to CMOS level. Motivated by the low-index confinement property of the slot mode, the device achieves over 10% reflection amplitude modulation with only 1.5V in the experiment. In addition, by adding a bottom gold mirror, 1.8\u03c0 phase response is numerically observed. Based on the success of this device, we propose a design that could achieve subwavelength wavefront control. As a example, we show a 3-pixel optical beam deflector with 75% diffraction efficiency.
\r\n\r\nIn Chapter 5, we extend the use of the slot mode into silicon-organic hybrid devices. The utilization of the slot mode achieves efficient electro-optic tuning under 17V in free space with a MHz modulation speed. We also explored various methods to enhance its phase response and discuss its feasibility. The spatial phase modulation design is also proposed with a 12-period supercell pixel. The beam deflector achieves 70% diffraction efficiency numerically.
\r\n\r\nIn Chapter 6, we bring this dissertation to a close and outline potential directions for future research.
\r\n\r\nThis thesis provides a foundation for the development of high-resolution and power-efficient one-dimensional spatial light modulators and showcases the potential of reconfigurable metasurfaces.
" }, { "name": "Akella, Prithvi", "degree": "PhD", "year": "2023", "title": "Reliable Controller Synthesis: Guarantees for Safety-Critical System Testing and Verification", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122023-162907795", "creators": [ { "name": { "family": "Akella", "given": "Prithvi" }, "id": "Akella-Prithvi", "orcid": "0000-0003-4375-0015", "display_name": "Akella, Prithvi" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/jej3-4444", "abstract": "The well-known quote by George Box states that \"All models are wrong, but some are useful\", and the controls and robotics communities alike have followed a similar paradigm to make significant theoretical and practical advances in the study of controllable systems to date. However, recent robotic system requirements include formal considerations for system safety, especially as we engineer systems that are required to work alongside us in our daily lives. As such, current research directions require analyses that consider these inaccurate system models, our inaccurate understanding of the environments in which these systems operate, and their combined effects on safe, effective system operation, e.g. the canonical autonomous driving problem in exceedingly difficult-to-model urban environments. Recently, this has led to burgeoning efforts in a formal study of controller verification. Specifically, verification denotes the process of determining whether a controller steers its system to exhibit desired behaviors despite the variety of environments the system might face during operation, e.g. whether the autonomous car's controller successfully drives the car to a destination without crashing into obstacles or pedestrians along the way. However, formalization of such a verification pipeline has proved difficult to date, especially since both the models we use for controller synthesis and our understanding of system environments are typically inaccurate.
\r\n \r\nAs a result, this thesis describes our efforts in the development of a formal verification pipeline that addresses a few key challenges in traditional approaches to safety-critical system verification. The first contribution centers on difficult, reactive test synthesis. By test synthesis, we mean the construction of a (potentially difficult) environment in which we require the system under test to perform its objective, e.g. placement of parked cars around which an autonomous vehicle must park. Typically phrased as an optimization problem over the space of allowable environments, these tests are \"static\" insofar as they do not react to the system's choices made during the test. We posit that such reactivity could more accurately identify worst-case system behavior. As a result, we phrase reactive, maximally difficult test synthesis as a game-theoretic optimization problem, leveraging the same control theoretic tools that facilitate safety-critical controller synthesis - control barrier functions and signal temporal logic. We prove that our proposed synthesis technique is always solvable and always produces a realizable test environment. Finally, we showcase our results by synthesizing reactive tests for both single and multi-agent systems.
\r\n\r\nThe second set of contributions centers on our efforts in uncertainty quantification. Due to un-modeled system and environmental aspects affecting system evolution in unpredictable ways, real-life systems need not realize the same paths every time. As such, typical analyses phrase verification as an optimization problem minimizing the expected value of a function over system trajectories with the expectation taken over this path variability, the distribution for which is assumed to be known. However, we posit that such an analysis should be risk-aware, i.e. account for this variability in a more principled fashion than an expectation-specific analysis, and should not assume apriori knowledge of the distribution corresponding to path variability, as it will be unknown in practice. To that end, we develop methods to bound a subset of risk measures for random variables whose distributions are unknown. This subset includes both Value-at-Risk and other, coherent risk measures heavily utilized in the controls and robotics communities. Simultaneously, we note that the same procedure can be applied to a wide class of non-convex optimization problems. In doing so, we develop a percentile-based optimization approach that rapidly identifies percentile solutions to optimization problems, i.e. a 90-th percentile solution is as good as 90% of solutions in the considered decision space.
\r\n\r\nThe third set of contributions focuses on the application of the prior mathematical developments to facilitate both risk-aware safety-critical system verification and controller synthesis. We phrase risk-aware controller verification as a risk-measure identification problem and utilize the prior bounding results to provide an efficient, dimensionally-independent verification procedure. Then, we phrase risk-aware controller synthesis as an optimization problem maximizing the bound provided by our risk-aware verification method, and show that this problem is solvable by the percentile optimization methods mentioned prior. Finally, we lay the foundation for the utilization of the aforementioned mathematical developments in other aspects of controls and robotics and communities more broadly. We show how risk-measure bounding can augment models both offline and online to robustify safety-critical controllers, how percentile optimization can facilitate \"optimal\" input selection and guarantee generation for non-convex finite-time optimal controllers, and how multiple applications of the percentile approach can also bound the optimality gap of reported percentile solutions. We showcase all these results on hardware for multiple systems and highlight the data efficiency of our proposed approaches.
" }, { "name": "Akerson, Andrew James", "degree": "PhD", "year": "2023", "title": "Optimal Design of Soft Responsive Actuators and Impact Resistant Structures", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-013553184", "creators": [ { "name": { "family": "Akerson", "given": "Andrew James" }, "id": "Akerson-Andrew-James", "orcid": "0000-0002-4382-1226", "display_name": "Akerson, Andrew James" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "chair", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Watkins", "given": "Ryan" }, "id": "Watkins-Ryan", "orcid": "0000-0002-1883-5714", "role": "member", "display_name": "Watkins, Ryan" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/dx05-p030", "abstract": "The rapid pace of development of new responsive and structural materials along with significant advances in synthesis techniques, which may incorporate multiple materials in complex architectures, provides an opportunity to design functional devices and structures of unprecedented performance. These include implantable medical devices, soft-robotic actuators, wearable haptic devices, mechanical protection, and energy storage or conversion devices. However, the full realization of the potential of these emerging techniques requires a robust, reliable, and systematic design approach. This thesis explores this through optimal design methods. By investigating pressing engineering problems which exploit these advances in materials and manufacturing, we develop optimal design methods to realize next-generation structures.
\r\n\t\t\r\nWe begin by reviewing classical optimal design methods, the mathematical difficulties they raise, and the practical approaches of overcoming these difficulties. We introduce the canonical problem of compliance minimization of a linear elastic structure. After illustrating the intricacies of this seemingly simple problem, we detail contemporary methods used to address the underlying mathematical issues.
\r\n\r\nWe then turn to extending these classical methods for emerging materials and technologies. We must incorporate optimal design with rich physical models, develop computational approaches for efficient numerics, and study mathematical regularization to obtain well-posed optimization problems. Additionally, care must be taken when selecting an application-tailored objective function which captures the desired behavior. Finally, we must also take into account manufacturing constraints in scenarios where the fabrication pathway affects the structural layout. We address these issues by exploring model optimal design problems. While these serve to ground the fundamental study, they are also relevant, pressing engineering problems.
\r\n\t\t\r\nThe first application we consider is the design of responsive structures. Recent developments in material synthesis and 3D printing of anisotropic materials, such as liquid crystal elastomers (LCE), have facilitated the realization of structures with arbitrary morphology and tailored material orientation. These methods may also produce integrated structures of passive and active material. This creates a trade-off between stiffness and actuation flexibility when designing such structures. Thus, we turn to optimal design. This is complicated by anisotropic behavior and finite deformations, manufacturing constraints, and choice of objective function. Like many optimal design problems, the naive formulations are ill-posed giving rise to mesh dependence, lack of convergence, and other numerical deficiencies. So, starting with a simple setting using linear kinematics and working all the way to finite deformation, we develop a systematic mathematical theory that motivates, and then rigorously proves, an alternate well-posed formulation. We examine suitable objective functions, before studying a series of examples in both small and finite deformation. However, the manufacturing process constrains the design as extrusion-based 3D printing aligns nematic directors along the print path. We extended the formulation with these considerations to produce print-aware designs while also recovering the fabrication pathway. We demonstrate the formulation by designing and producing physical realizations of these actuators.
\t\t\r\n\t\t\r\nNext, we explore optimal design of impact resistant structures. The complex physics and numerous failure modes of structural impact creates challenges when designing for impact resistance. Here, we apply gradient-based topology optimization to the design of such structures. We start by constructing a variational model of an elastic-plastic material enriched with gradient phase-field damage, and present a novel method to accurately and efficiently compute its transient dynamic time evolution. Sensitivities over this trajectory are computed through the adjoint method, and we develop a numerical method to solve the resulting adjoint dynamical system. We demonstrate this formulation by studying the optimal design of 2D solid-void structures undergoing blast loading. Then, we explore the trade-offs between strength and toughness in the design of a spall-resistant structure composed of two materials of differing properties undergoing dynamic impact.
\r\n\t\t\r\nWe conclude by summarizing the presented work and discuss the contribution towards the overarching goal of optimal design for emerging materials technologies. From our study, key issues have arose which must be addressed to further progress the field. We examine these and lay a pathway for future studies which will allow optimal design to tackle complicated, pressing engineering problems.
" }, { "name": "Amo Alonso, Carmen", "degree": "PhD", "year": "2023", "title": "Distributed and Localized Model Predictive Control", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-203113987", "creators": [ { "name": { "family": "Amo Alonso", "given": "Carmen" }, "id": "Amo-Alonso-Carmen", "orcid": "0000-0001-7593-5992", "display_name": "Amo Alonso, Carmen" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Mazumdar", "given": "Eric V." }, "id": "Mazumdar-E-V", "orcid": "0000-0002-1815-269X", "role": "member", "display_name": "Mazumdar, Eric V." }, { "name": { "family": "Matni", "given": "Nikolai" }, "id": "Matni-Nikolai", "orcid": "0000-0003-4936-3921", "role": "member", "display_name": "Matni, Nikolai" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "cds" ], "doi": "10.7907/6pje-yd82", "abstract": "The increasing presence of large-scale distributed systems highlights the need for scalable control strategies where only local communication is required. Moreover, in safety-critical systems it is imperative that such control strategies handle constraints in the presence of disturbances and enjoy theoretical and performance guarantees. In response to this need, we present the Distributed and Localized Model Predictive Control (DLMPC) algorithm for large-scale linear systems. DLMPC is a distributed closed-loop model predictive control (MPC) scheme wherein only local state and model information needs to be exchanged between subsystems for the computation and implementation of control actions. The resulting distributed algorithms tackle various types of additive disturbances and enjoy recursive feasibility and asymptotic stability guarantees that introduce minimal conservatism and can be computed in an offline fashion without adding to the computational burden. We also provide analysis and guarantees on the global performance of DLMPC, and demonstrate that in cases where the underlying topology of the system is sparse (as is the case in most large-scale networks), the inclusion of local communication constraints does not result in a suboptimal solution. Moreover, we show that when no noise is present, this algorithm can be extended to the purely data-driven case where all previous guarantees hold and the need for a model is fully replaced by past-trajectory data. We show that the amount of data needed for our synthesis problem is independent of the size of the global system. Lastly, we explore the potential of DLMPC for hardware accelerated implementation in GPU by exploiting the fact that the structure of the DLMPC problem captures some of the limitations of GPU computations. In all algorithmic and theoretical results presented in this thesis, only local information exchange is necessary, and computational complexity is independent of the global system size. DLMPC is the first MPC algorithm that allows for the scalable, efficient and data-driven computation and implementation of distributed closed-loop control policies and enjoys theoretical guarantees." }, { "name": "Bauinger, Christoph", "degree": "PhD", "year": "2023", "title": "The \"Interpolated Factored Green Function\" Method", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07072022-003500251", "creators": [ { "name": { "family": "Bauinger", "given": "Christoph" }, "id": "Bauinger-Christoph", "display_name": "Bauinger, Christoph" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/1cnc-s558", "abstract": "This thesis presents a novel Interpolated Factored Green Function (IFGF) method for the accelerated evaluation of the integral operators in scattering theory and other areas. Like existing acceleration methods in these fields, the IFGF algorithm evaluates the action of Green function-based integral operators at a cost of O(N log N) operations for an N-point surface mesh. The IFGF strategy capitalizes on slow variations inherent in a certain Green function analytic factor, which is analytic up to and including infinity, and which therefore allows for accelerated evaluation of fields produced by groups of sources on the basis of a recursive application of classical interpolation methods. Unlike other approaches, the IFGF method does not utilize the Fast Fourier Transform (FFT), and it is thus better suited than other methods for efficient parallelization in distributed-memory computer systems. In fact, a (hybrid MPI-OpenMP) parallel implementation of the IFGF algorithm is proposed in this thesis which results in highly efficient data communication, and which exhibits in practice excellent parallel scaling up to large numbers of cores -- without any hard limitations on the number of cores concurrently employed with high efficiency. Moreover, on any given number of cores, the proposed parallel approach preserves the linearithmic (O(N log N)) computing cost inherent in the sequential version of the IFGF algorithm. This thesis additionally introduces a complete acoustic scattering solver that incorporates the IFGF method in conjunction with a suitable singular integration scheme. A variety of numerical results presented in this thesis illustrate the character of the proposed parallel IFGF-accelerated acoustic solver. These results include applications to several highly relevant engineering problems, e.g., problems concerning acoustic scattering by structures such as a submarine and an aircraft-nacelle geometry, thus establishing the suitability of the IFGF method in the context of real-world engineering problems. The theoretical properties of the IFGF method, finally, are demonstrated by means of a variety of numerical experiments which display the method's serial and parallel linearithmic scaling as well as its excellent weak and strong parallel scaling -- for problems of up to 4,096 wavelengths in acoustic size, and scaling tests spanning from 1 compute core to all 1,680 cores available in the High Performance Computing cluster used.
" }, { "name": "Beery, Sara Meghan", "degree": "PhD", "year": "2023", "title": "Where the Wild Things Are: Computer Vision for Global-Scale Biodiversity Monitoring", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:04242022-005200355", "creators": [ { "name": { "family": "Beery", "given": "Sara Meghan" }, "id": "Beery-Sara-Meghan", "orcid": "0000-0002-2544-1844", "display_name": "Beery, Sara Meghan" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Belongie", "given": "Serge J." }, "id": "Belongie-S-J", "orcid": "0000-0002-0388-5217", "role": "member", "display_name": "Belongie, Serge J." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cms" ], "doi": "10.7907/m4mt-2q51", "abstract": "We require a real-time, modular earth observation system that unites efforts across research groups in order to provide the necessary information necessary for global-scale impact in sustainability and conservation in the face of climate change. The development of such systems requires collaborative, interdisciplinary approaches that translate diverse sources of raw information into accessible scientific insight. For example, we need to monitor species in real time and in greater detail to quickly understand which conservation efforts are most effective and take corrective action. Current ecological monitoring systems generate data far faster than researchers can analyze it, making scaling up impossible without automated data processing. However, ecological data collected in the field presents a number of challenges that current methods, like deep learning, are not designed to tackle. These include strong spatiotemporal correlations, imperfect data quality, fine-grained categories, and long-tailed distributions. Our work seeks to overcome these challenges, and this thesis includes methods which can learn from imperfect data, systematic frameworks and benchmarks for measuring and overcoming performance drops due to domain shift, and the development and deployment of efficient human-AI systems that have made significant real-world conservation impact." }, { "name": "Biswas, Souvik", "degree": "PhD", "year": "2023", "title": "Electro-Optic Excitations in van der Waals Materials for Active Nanophotonics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:04032023-062047194", "creators": [ { "name": { "family": "Biswas", "given": "Souvik" }, "id": "Biswas-Souvik", "orcid": "0000-0002-8021-7271", "display_name": "Biswas, Souvik" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "chair", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "member", "display_name": "Hsieh, David" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "da Jornada", "given": "Felipe H." }, "id": "da-Jornada-FElipe-H", "orcid": "0000-0001-6712-7151", "role": "member", "display_name": "da Jornada, Felipe H." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/tz4z-ed06", "abstract": "van der Waals materials are emerging due to their unique properties such as atomic thickness, diverse quasiparticle optical resonances, and no requirement for lattice matching. While there is a vast variety of materials, semiconductors hold a special place for opto-electronic and linear/non-linear optical studies. Black phosphorus (BP), a 2D quantum-well with direct bandgap and puckered crystal structure, is a compelling platform for this research direction. In this thesis, we investigate fundamental optical excitations in novel low-dimensional quantum materials to achieve strong light-matter interaction and integrate with nanophotonic motifs for low-footprint, reconfigurable optical technology, focusing primarily on black phosphorus and transition metal dichalcogenides.
\r\n\r\nThe thesis begins with the 'thin film limit' of van der Waals materials, between 5 and 20 nm thickness range. Chapters 2 and 3 explore how few-layer black phosphorus hosts interband and intraband optical excitations that can be strongly modified with gate-controlled doping and electric field, displaying epsilon near zero and hyperbolic behavior in the mid and far-infrared. In atomic thickness, strongly bound excitonic quasiparticles dominate the optical response. In Chapter 4, we investigate electrically tunable excitons in tri-layer black phosphorus, demonstrating a reconfigurable birefringent material that, when coupled with a Fabry-Perot cavity, enables the realization of a versatile and broadband polarization modulator. In Chapter 5, we examine the ultimate limit of a monolayer, studying MoTe2 via photoluminescence measurements and first-principles GW+BSE calculations, highlighting the Rydberg series associated with the exciton and its gate-tunability to understand strong electron-exciton interactions. In Chapter 6, we show how such excitons in monolayer black phosphorus can be strongly quantum confined at natural edges of exfoliated flakes, leading to highly temporally coherent emission. This emission is gate-tunable and understood via transmission electron microscopy and first-principles GW+BSE calculations of phosphorene nanoribbons to be originating from atomic reconstructions of the edge coupled with strain and screening effects.
\r\n\r\nOverall, our work highlights the potential of van der Waals materials for various electro-optical excitations and their applications in active nanophotonics.\r\n
" }, { "name": "Buarque de Macedo, Robert Andrew", "degree": "PhD", "year": "2023", "title": "Methods for Control of Granular Material Attributes", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172022-000450303", "creators": [ { "name": { "family": "Buarque de Macedo", "given": "Robert Andrew" }, "id": "Buarque-de-Macedo-Robert-Andrew", "orcid": "0000-0002-2218-4117", "display_name": "Buarque de Macedo, Robert Andrew" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "member", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Parker", "given": "Joseph" }, "id": "Parker-J", "orcid": "0000-0001-9598-2454", "role": "member", "display_name": "Parker, Joseph" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/1h8f-se14", "abstract": "A granular material is a collection of discrete, solid particles. This substance is ubiquitous in nature and industry, with examples ranging from soils, jointed rocks, foodstuffs, ball bearings, powders, and even asteroids. As such, understanding granular materials is necessary for making sense of the physical world. Tremendous progress has been made in directly simulating granular materials in the previous decades, in particular via the discrete element method (DEM). Nevertheless, there remains ample opportunity for manipulating granular materials to achieve specific outcomes by leveraging the DEM. The research presented in this thesis utilizes DEM simulations to develop tools and strategies for manipulating granular material to achieve desired attributes. These attributes include the shape of individual grains, the structure of granular tunnels, and mesoscopic packing characteristics such as packing fraction and coordination number. Optimization of granular materials is considered at 3 different scales: at the single grain scale (100 grains), at the scale of granular structures such as arches (101 grains), and at the mesoscopic scale (103 grains). The first component of this thesis considers automated design of individual grain shapes that embody user-specified morphological properties via genetic algorithms. Next, excavation in granular materials is considered. It is studied how ants can so successfully manipulate granular materials to achieve stable systems by mapping the forces around real ant tunnels. Ant tunnels are simulated using a DEM which can handle arbitrary shaped grains: the Level-Set Discrete Element Method (LS-DEM). Finally, tools are developed for controlling mesoscopic attributes of granular materials as a function of grain shape. To do so, genetic algorithms and a deep generative model are combined with LS-DEM. The methodologies introduced in this thesis serve as a foundation for controlling granular material attributes. Such techniques can be leveraged to engineer granular materials, with applications ranging from swarm robotics, robotic grippers, mechanically tunable fabrics for armor, and robotic excavation." }, { "name": "Canales Escobedo, Fabricio Gianfranco", "degree": "PhD", "year": "2023", "title": "Numerical Analysis of Folding and Deployment Dynamics of Thin Shell Structures with Localized Folds", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-233806562", "creators": [ { "name": { "family": "Canales Escobedo", "given": "Fabricio Gianfranco" }, "id": "Canales-Escobedo-Fabricio-Gianfranco", "orcid": "0000-0001-9071-3263", "display_name": "Canales Escobedo, Fabricio Gianfranco" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/gt81-0s18", "abstract": "This thesis focuses on the analysis of tape springs folded in the opposite sense and their dynamic deployment, and aims to use methods to reduce the computational cost of the analysis. The tape spring is a thin shell deployable structure that has features in common with other deployable structures. The deployment process of such structures can be difficult to predict, and the use of numerical models can be a more cost-effective alternative to experimental testing. Approaches to reduce the computational cost of the analysis of tape springs are investigated such as adaptive meshing and reduced order models. The thesis also presents an accurate analysis of tape spring deployment and a detailed study of the energies and the physics of the deployment. This is used to investigate the energy leak observed in previous tape spring deployment work. Overall, this thesis contributes to improving the efficiency and accuracy of the analysis of deployable structures, particularly tape springs, which can have significant applications in spacecraft technology." }, { "name": "Chari, Celia S.", "degree": "PhD", "year": "2023", "title": "Degradation of Ceramic Surfaces and its Mitigation: From Electric Propulsion to Cultural Heritage", "advisor": "Faber, Katherine T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08312022-141029875", "creators": [ { "name": { "family": "Chari", "given": "Celia S." }, "id": "Chari-Celia-S", "orcid": "0000-0001-6404-4203", "display_name": "Chari, Celia S." } ], "advisors": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "advisor", "display_name": "Faber, Katherine T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "McEnerney", "given": "Bryan W." }, "id": "McEnerney-B-W", "orcid": "0000-0003-0869-0686", "role": "member", "display_name": "McEnerney, Bryan W." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "matsci" ], "doi": "10.7907/22st-q436", "abstract": "Ceramics have played an evolving role throughout human history, with the earliest known fired clay figurines dating back to 29,000-25,000 BCE in what is today the Czech Republic. Such examples of porous, low-fired potteries transitioned into vitreous and heat-resistant porcelain with the advancements of kiln technologies, which steadily grew to reach temperatures up to 1270 \u00b0C by the time of the Song Dynasty (960-1279 CE). In the modern-age, furnaces technologies have become exceedingly more sophisticated, reaching ultra-high temperatures of up to 3000 \u00b0C with dedicated calibration systems. With the advancement of firing technologies came the advancement of materials processing methods, which have transformed the role of ceramics in everyday applications: from ceramic fibers used in tennis racquets, to ceramics used in space shuttle tiles and even in artificial joints. Indeed, ceramics are candidate solutions to the most stringent material problems faced today, including high-temperature applications like electric propulsion and turbine engine systems. However, in order to improve the long-term use and sustainability of ceramics, it is essential to evaluate both their performance and their eventual degradation from mechanical wear and chemical erosion.
\r\n\r\nThis work explores the processing-microstructure-performance relationship of ceramics to better understand the performance and degradation mechanisms of ceramic surfaces. This relationship is investigated using a series of material case studies, including (i) advanced high-temperature ceramics composed of h-BN rich composites, and (ii) historic ceramics, ranging from low-fired pottery to porcelain. Details are provided for the design and manufacturing of novel high-performing ceramics, while simultaneously referring to ceramics of the past to understand how their surfaces have altered over their lifetime. Highlights of this work include the innovative use of carbothermic reactions to create h-BN surface layers for electric propulsion; self-healing strategies from AlN/BN composites; DFT-supported analysis of pottery corrosion in acidic soils; and nanoscale processing of historic porcelain glazes. These analyses provide us with an opportunity to learn from materials of the past to create more sustainable materials for the future, with an emphasis on ways of mitigating degradation by controlling processing conditions and environmental exposures.
" }, { "name": "Chen, Amylynn C.", "degree": "PhD", "year": "2023", "title": "3D in situ Chemical Synthesis: Additive Manufacturing of Functional Polymeric Materials via Vat Photo-polymerization", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-145117270", "creators": [ { "name": { "family": "Chen", "given": "Amylynn C." }, "id": "Chen-Amylynn-C", "orcid": "0000-0002-8112-5862", "display_name": "Chen, Amylynn C." } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/ca3e-rc06", "abstract": "As additively manufacturing gains popularity in rapid-prototyping, manufacturing and customized production, there is a continuous demand in seeking for new materials with advanced functionalities to satisfy the wide range of applications in aerospace, construction, optics, actuation, dentistry, biomedical practices and even food industry. Vat photopolymerization (VP), a light-enabled AM technique, is particularly promising due to its ability to achieve good surface quality, high resolution, and large volumetric throughput. The vast majority of materials obtained by VP are covalently-crosslinked thermosets with nondegradable carbon backbones. This highly crosslinked molecular structure gives rise to stiff and brittle materials, limiting the structural functionality in desired applications.
\r\n\r\nThis thesis explores a variety of molecular structures for new VP photopolymers: a) dynamically-crosslinked compliant polymer, b) interpenetrating network (IPN) hydrogel, and c) covalently-crosslinked polymer with labile group (ex. ester) insertion to polymer backbone. With the dynamic crosslinking system, we demonstrate tunable mechanical behaviors of the metal-coordinated supramolecular polymers. These materials display a range of failure strain of 450% - 940% and ultimate tensile strength of 12.4 - 2.2 MPa with varying resin compositions. To incorporate multifunctionality, we design thermoresponsive IPN hydrogels by fabricating a hydrophilic host polymer network via VP and a subsequent formation a thermoresponsive 2nd network (poly(N-Isopropylacrylamide)). The architected IPNs consistently display strong polymer-liquid phase separation behavior and a tunable water release behavior with volumetric shrinkage between 30% and 70% upon heating at 50oC. Finally, to promote the degradability of the acylate-based photoresin, we demonstrated successful incorporation for ester functional groups into the polymer backbone via radical ring opening polymerization of cyclic ketene acetals. The obtained polymer undergoes 84% mass loss within 7 hours under hydrolytic degradation condition. Overall, we demonstrated VP as a powerful technique to achieve one-pot synthesis and fabrication of functional materials. Our explorations on the development of degradable photopolymers, thermoresponsive double-network hydrogels, and metal-coordinated supramolecular polymers provide valuable insights into the impact of resin formulation on mechanical properties. From analyzing the molecular weight of 3DP materials to finetuning of phase separation behavior and degradability, we demonstrate that VP provides a new platform to inspire advanced photoresin design strategies for desirable mechanical performance.
" }, { "name": "Chen, Yifan", "degree": "PhD", "year": "2023", "title": "On Multiscale and Statistical Numerical Methods for PDEs and Inverse Problems", "advisor": "Hou, Thomas Y.; Owhadi, Houman; Stuart, Andrew M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292023-175108484", "creators": [ { "name": { "family": "Chen", "given": "Yifan" }, "id": "Chen-Yifan", "orcid": "0000-0001-5494-4435", "display_name": "Chen, Yifan" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "advisor", "display_name": "Owhadi, Houman" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "advisor", "display_name": "Stuart, Andrew M." } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/83p4-c644", "abstract": "This thesis focuses on numerical methods for scientific computing and scientific machine learning, specifically on solving partial differential equations and inverse problems. The design of numerical algorithms usually encompasses a spectrum that ranges from specialization to generality. Classical approaches, such as finite element methods, and contemporary scientific machine learning approaches, like neural nets, can be viewed as lying at relatively opposite ends of this spectrum. Throughout this thesis, we tackle mathematical challenges associated with both ends by advancing rigorous multiscale and statistical numerical methods.
\r\n\r\nRegarding the multiscale numerical methods, we present an exponentially convergent multiscale finite element method for solving high-frequency Helmholtz's equation with rough coefficients. To achieve this, we first identify the local low-complexity structure of Helmholtz's equations when the resolution is smaller than the wavelength. Then, we construct local basis functions by solving local spectral problems and couple them globally through non-overlapped domain decomposition and Galerkin's method. This results in a numerical method that achieves nearly exponentially convergent accuracy regarding the number of local basis functions, even when the solution is highly non-smooth. We also analyze the role of a subsampled lengthscale in variational multiscale methods, characterizing the tradeoff between accuracy and efficiency in the numerical upscaling of heterogeneous PDEs and scattered data approximation.
\r\n\r\nAs for the statistical numerical methods, we discuss using Gaussian processes and kernel methods to solve nonlinear PDEs and inverse problems. This framework incorporates the flavor of scientific machine learning automation and extends classical meshless solvers. It transforms general PDE problems into quadratic optimization with nonlinear constraints. We present the theoretical underpinning of the methodology. For the scalability of the method, we develop state-of-the-art algorithms to handle dense kernel matrices in both low and high-dimensional scientific problems. For adaptivity, we analyze the convergence and consistency of hierarchical learning algorithms that adaptively select kernel functions. Additionally, we note that statistical numerical methods offer natural uncertainty quantification within the Bayesian framework. In this regard, our further work contributes to some new understanding of efficient statistical sampling techniques based on gradient flows.
" }, { "name": "Cole, Elijah Henry John", "degree": "PhD", "year": "2023", "title": "Visual and Spatial Representation Learning with Applications in Ecology", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072023-210232983", "creators": [ { "name": { "family": "Cole", "given": "Elijah Henry John" }, "id": "Cole-Elijah-Henry-John", "orcid": "0000000166230966", "display_name": "Cole, Elijah Henry John" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Belongie", "given": "Serge J." }, "id": "Belongie-S-J", "orcid": "0000-0002-0388-5217", "role": "member", "display_name": "Belongie, Serge J." } ], "option_major": [ "cms" ], "doi": "10.7907/xp2k-es46", "abstract": "Machine learning has the potential to empower scientists, physicians, and other human experts working to solve problems of societal importance. To realize this goal, we need algorithms that can distill useful knowledge from real-world data. However, most machine learning research focuses on benchmarks that seldom reflect real-world challenges, such as learning from limited, noisy, or weak supervision. This thesis develops new benchmarks, algorithms, and problem settings that link fundamental machine learning research to impactful applications in ecology. In Part I, we provide context and motivation for our work. How and why should machine learning researchers work with domain experts on real-world problems? What is the appeal of ecology specifically Part II focuses on visual representation learning with an emphasis on label efficiency. We discuss the strengths and limitations of self-supervised learning, the relationship between concept specificity and representation learning, and multi-label learning with minimal labeled data. Part III covers our work in the emerging field on spatial representation learning. In particular, we consider the problem of modeling the spatial distribution of plant and animal species. We review this important ecological problem from a machine learning perspective before showing how deep learning can transform the way these models are applied (using spatial models to assist image classifiers) and developed (jointly learning spatial distributions and representations). Finally, Part IV concludes and highlights opportunities for future work." }, { "name": "De Rose, Luc\u00eda Bel\u00e9n", "degree": "PhD", "year": "2023", "title": "Nanoscale Field Emission Devices for High-Temperature and High-Frequency Operation", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312023-192646665", "creators": [ { "name": { "family": "De Rose", "given": "Luc\u00eda Bel\u00e9n" }, "id": "De-Rose-Luc\u00eda-Bel\u00e9n", "orcid": "0000-0002-1432-8248", "display_name": "De Rose, Luc\u00eda Bel\u00e9n" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "DeRose", "given": "Guy A." }, "id": "DeRose-Guy-A", "orcid": "0000-0003-0916-5015", "role": "member", "display_name": "DeRose, Guy A." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8qa5-kn97", "abstract": "Field emission\u2014the quantum-mechanical tunneling of electrons from the surface of a material into vacuum by means of a strong electric field\u2014has been studied for over a century. However, the usage of devices based on this mechanism has been limited to a handful of niche applications such as high-power RF systems and field emission displays. The preference for solid-state devices relies on their low cost, long lifetimes, reduced power consumption, ease of integrability, and simple and scalable fabrication. Nonetheless, with the advent of modern fabrication techniques, it has been possible to build field emission devices with nanoscale dimensions that offer several advantages over traditional semiconductor devices. The use of vacuum allows ballistic transport with no lattice scattering. As device capacitance can be engineered by tuning the geometry, these devices are appealing for high-frequency operation. Vacuum is also inherently immune to harsh operating conditions such as high temperature and radiation, which is desirable for aerospace, nuclear, and military applications. In addition, even though field emission requires substantial electric fields, by exploiting the nanoscale gaps that can be easily fabricated with state-of-the-art lithographic capabilities, we can expect operating voltages comparable to CMOS. Thus, vacuum emission devices have the potential to greatly improve upon the limitations of current technologies.
\r\n\r\nIn this work, we experimentally demonstrate various design paradigms to develop nanoscale field emission devices for high-temperature environments and high-frequency operation. First, we propose suspended lateral two- and four-terminal devices. By removing the underlying solid substrate, we aim to increase the resistance of the leakage current pathways that emerge at elevated temperatures. Tungsten is the chosen electrode material due to its low work function and ability to withstand high temperatures. Our next architecture consists of a multi-tip two-terminal array, which exclusively relies on the inherent fast response of field emission. Due to the strong non-linearity in the emission characteristic, frequency mixing is measured. Lastly, we combine field emission with plasmonics to conceive devices that can be modulated both electrically and optically at telecommunication wavelength. By taking advantage of the strong confinement and significant optical field enhancement of surface plasmon polaritons, we seek to minimize the applied voltages required for field emission as well as the necessary laser powers for photoemission towards the development of high-speed, low-power, nanoscale optoelectronic systems.
" }, { "name": "Dixit, Anushri C.", "degree": "PhD", "year": "2023", "title": "Risk-Aware Planning and Control in Extreme Environments", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:02082023-223824752", "creators": [ { "name": { "family": "Dixit", "given": "Anushri C." }, "id": "Dixit-Anushri-C", "orcid": "0000-0002-9698-2189", "display_name": "Dixit, Anushri C." } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Mazumdar", "given": "Eric V." }, "id": "Mazumdar-E-V", "orcid": "0000-0002-1815-269X", "role": "member", "display_name": "Mazumdar, Eric V." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "cds" ], "doi": "10.7907/xv2b-tj24", "abstract": "Safety-critical control and planning for autonomous systems operating in unstructured environments is a challenging problem must be addressed as autonomous vehicles, surgical robots, and autonomous industrial robots become more pervasive. This thesis addresses some of the issues in safety critical autonomy by introducing new techniques for computationally tractable and efficient safety-critical control. The approach developed in this thesis arises from taking a deeper look at two questions: 1) How can we obtain better uncertainty quantification of the disturbances that affect autonomous systems either as a result of unmodeled changes in the environment or due to sensor imperfections? 2) Given richer uncertainty quantification techniques, how do incorporate the diverse uncertainty descriptions into the control and planning framework without sacrificing the tractability and efficiency of existing approaches?
\r\n\r\nI address the above two questions by developing risk-aware control and planning techniques for traversal of a mobile robot over static but extreme terrain and in the presence of dynamic obstacles. We first look at algorithms for risk-aware terrain assessment, and extensively test them on wheeled and legged robots that were deployed in subterranean tunnel, urban, and cave environments for search and rescue operations in the DARPA Subterranean Challenge. I then present a theory for risk-aware model predictive control in static environments and in the presence of dynamic obstacles. Coherent risk measures are applied to this planning and control framework in order to account for diverse uncertainty descriptions. Computationally tractable reformulations of the optimal control problem are realized through constraint tightening techniques.
\r\n \r\nI then investigate algorithms for uncertainty assessment and prediction of apriori unknown, dynamic obstacles using data-driven techniques. We use a technique from signal processing literature called Singular Spectrum Analysis for making linear predictions of dynamic obstacles. The obstacle motion predictions are equipped with error predictions to account for the uncertainty in the sensing heuristically using bootstrapping techniques. We use a statistical tool, Adaptive Conformal Inference, to further calibrate the heuristic error prediction online to obtain true uncertainty prediction while using nonstationary data to analyze the performance of the data-driven predictor. These techniques provide reactive, real-time, risk-aware obstacle avoidance in dynamic environments.
" }, { "name": "Dorobantu, Victor David", "degree": "PhD", "year": "2023", "title": "Geometry and Dynamical Systems in Machine Learning and Control", "advisor": "Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-194820518", "creators": [ { "name": { "family": "Dorobantu", "given": "Victor David" }, "id": "Dorobantu-Victor-David", "orcid": "0000-0002-2797-7802", "display_name": "Dorobantu, Victor David" } ], "advisors": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Azizzadenesheli", "given": "Kamyar" }, "id": "Azizzadenesheli-Kamyar", "orcid": "0000-0001-8507-1868", "role": "member", "display_name": "Azizzadenesheli, Kamyar" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cms" ], "doi": "10.7907/x271-r088", "abstract": "For many problems of interest in machine learning and control, we have access to rich information about underlying geometry and dynamics; we can leverage this information to build robust and performant solutions in new algorithms, optimizations, and designs. In this thesis we study four problem settings to stress this central assumption. First, we study conformal generative modeling, using computational geometry techniques to simplify and register complex 2D surfaces and enabling the use of a variety of flow-based generative models as plug-and-play subroutines. Second, we study data-driven robust optimization problems in control, modeling the precise impact of dynamics uncertainty in several control frameworks using convex geometry. Third, we study compactly-restrictable policy optimization, constraining the available states and actions in reinforcement learning and optimal control problems to be consistent with the inherent dynamics of the systems to be controlled. Finally, we study nonlinear model predictive control on Lie groups as applied to a 3D hopping robot platform, developing a control methodology compatible with nontrivial state space geometry and hybrid system dynamics." }, { "name": "Eldjarn Hjoerleifsson, Kristjan", "degree": "PhD", "year": "2023", "title": "Graph Modeling for Genomics and Epidemiology", "advisor": "Pachter, Lior S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02122023-103759689", "creators": [ { "name": { "family": "Eldjarn Hjoerleifsson", "given": "Kristjan" }, "id": "Eldjarn-Hjoerleifsson-Kristjan", "orcid": "0000-0002-7851-1818", "display_name": "Eldjarn Hjoerleifsson, Kristjan" } ], "advisors": [ { "name": { "family": "Pachter", "given": "Lior S." }, "id": "Pachter-L", "orcid": "0000-0002-9164-6231", "role": "advisor", "display_name": "Pachter, Lior S." } ], "committee": [ { "name": { "family": "Wold", "given": "Barbara J." }, "id": "Wold-B-J", "orcid": "0000-0003-3235-8130", "role": "chair", "display_name": "Wold, Barbara J." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Melsted", "given": "Pall" }, "id": "Melsted-Pall", "orcid": "0000-0002-8418-6724", "role": "member", "display_name": "Melsted, Pall" }, { "name": { "family": "Pachter", "given": "Lior S." }, "id": "Pachter-L", "orcid": "0000-0002-9164-6231", "role": "member", "display_name": "Pachter, Lior S." } ], "option_major": [ "cms" ], "doi": "10.7907/s32c-a211", "abstract": "The last decades have seen great leaps made in the development of RNA sequencing technologies, yielding lower cost and greater throughput of experiments, to the point where the scale of the data produced on a daily basis is staggering. While computational hardware is also continuously improving, famously (or perhaps infamously) described by Gordon Moore (Moore, 1965), the rate at which data are produced eclipses advances on the hardware front. Over the last few years, many new methods have been proposed for bridging that ever-widening chasm, more than a few of which harness the latent graphical structure of genomic data to reduce the number of calculations required and pack the data tighter in memory. This body of work continues this development on three different, but related, fronts. Firstly, I present developments that greatly improve upon the efficiency of state-of-the-art methods for the quantification of RNA-seq reads, and describe a method that improves the accuracy of quantification without substantially increasing the computational over- head. Secondly, I introduce a procedure for the discovery of associations between novel gene isoforms and phenotypes, without prior knowledge of those isoforms. Lastly, I present the largest reconstruction of the transmission tree of a viral outbreak to date, modeled from viral genome sequences, contact tracing, and symptom data. I then use the reconstructed transmission tree to assess the efficacy of different vaccination strategies." }, { "name": "Gallivan, Rebecca Anne", "degree": "PhD", "year": "2023", "title": "The Role of Boundaries and Other Microstructural Features on Emergent Mechanical and Mechanically-Coupled Phenomena at the Nanoscale", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07112022-193425820", "creators": [ { "name": { "family": "Gallivan", "given": "Rebecca Anne" }, "id": "Gallivan-Rebecca-Anne", "orcid": "0000-0001-6516-2180", "display_name": "Gallivan, Rebecca Anne" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "chair", "display_name": "Falson, Joseph" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/gv3v-9k07", "abstract": "As nanotechnology continues to advance, the need for smaller, structurally complex materials has grown. However, these microscopic (10\u2076) and nanoscopic (10\u2079) structures often display unexpected changes in mechanical properties as compared to their macroscopic counterparts. Nanomechanical studies investigating size-effects in stiffness, strength, recoverability, ductility, and fracture, reveal an intimate interplay between the breakdown in continuum behavior and the energetic landscape of microstructural mechanisms. Additive manufacturing opens new opportunities to explore this microstructure-mechanics relationship as it enables the micro- and nano-scale production of novel materials and microstructures. While existing studies on structural and functional materials highlight the unique size-scale behavior, a large gap remains in our understanding of the complex relationship between microstructure and material performance. This work investigates the interactions and mechanisms that give rise to emergent nanoscale phenomena. With microstructural characterizations, we demonstrate the role of boundaries and interfaces on mechanical and mechanically-coupled behavior in (1) dense nanowire arrays, (2) nano-architected nanocrystalline zinc oxide, and (3) highly-twinned additively manufactured metallic systems. This work provides critical insights into the mechanisms underlying the observed emergent phenomena and further opens our fundamental intuition for microstructure-mechanics relationships in materials at the nanoscale." }, { "name": "Gandhi, Vatsa Bhupeshkumar", "degree": "PhD", "year": "2023", "title": "Shock Compression of Body-Centered Cubic Metals from the Atomistic to Continuum Scale: Iron and Molybdenum", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05052023-185856720", "creators": [ { "name": { "family": "Gandhi", "given": "Vatsa Bhupeshkumar" }, "id": "Gandhi-Vatsa-Bhupeshkumar", "orcid": "0000-0002-6752-113X", "display_name": "Gandhi, Vatsa Bhupeshkumar" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "role": "member", "display_name": "Mello, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/kwf1-7y79", "abstract": "Fundamental understanding of material behavior under extreme conditions is crucial for designing high strength, light weight, and high temperature resistance materials, and for modeling planetary physics problems such as behavior of the core and impact phenomena. Under extreme conditions, materials not only exhibit a different mechanical, thermal, and failure response but can also undergo structural changes, such as phase transformations, which significantly alters their material properties. This motivates studying their dynamic response and developing constitutive models for applications such as hypersonics, high speed manufacturing, impact and blast of structures, aircraft and spacecraft shielding, meteorite impact, and collision of planets. Despite the importance, experimental investigations of shock induced phase transitions, inelastic material behavior, and elastic-plastic anisotropy under multi-axial stress states and at microscopic length scales of metals still remains largely unexplored. Thus, the focus of this thesis is on the shock compression behavior of body-centered cubic (BCC) metals, specifically iron and molybdenum, under compression-shear loading and at the atomistic-continuum spatial scales. In particular, the role of solid-solid phase transformation of body-centered cubic (BCC) iron on material strength and the orientation dependence of single crystal molybdenum on its elastic-plastic transition is investigated.
\r\n\t \r\nIron in its high pressure hexagonal close-packed (HCP) \u03f5-phase is critical in geological and planetary applications such as inner cores of rocky planets and hypervelocity impacts of asteroids, and meteorites. Thus, understanding plasticity behavior of iron under these condensed matter states is important to develop more accurate models for such applications and to understand deformation mechanisms of inner planetary cores. Because the \u03f5-phase is unstable, iron reverts to its ambient \u03b1-phase (BCC) upon release making it difficult to probe the strength behavior using conventional methods. Additionally, solid-solid phase transformations provide a unique opportunity to study material strength as they are crucial for expanding the design space for various load-bearing applications. In the first part of the thesis, the pressure dependent dynamic strength behavior of both the ambient BCC \u03b1-phase and high-pressure HCP \u03f5-phase of iron at strain rates on the order of 1 X 10\u2075 s\u207b\u00b9 and pressures up to 42 GPa is investigated. Pressure shear plate impact experiments are conducted using a sandwich configuration to decouple the effect of pressure and shear thereby allowing to probe shear strength once the sample reaches an equilibrated state of pressure but prior to release. The strength of the \u03f5-phase is observed to be more than double the strength of \u03b1-phase possibly due to microstructural evolution during phase transformation. Additionally, the evolution of yield properties with pressure, temperature, and strain is presented for the first time, enabling more accurate modeling of extreme deformation phenomena associated with iron-rich celestial bodies such as planetary collisions.
\r\n\t\r\nMolybdenum, its alloys, and other body-centered cubic (BCC) refractory metals are critical in geological and planetary applications such as structural properties of terrestrial planetary composition, formation of the earth-moon system, and hypervelocity impacts of rocky planets. Additionally, the high temperature specific strength, creep resistance, and ductility of BCC refractory metals make them ideal for aerospace and armor/anti-armor applications. Under high strain-rate inelastic loadings, the macroscopic response of these metals is often influenced by the atomistic mechanisms including dislocation motion and deformation twinning. Current material models rely on investigations that involve continuum measurements followed by postmortem microstructural analysis of recovered samples. However, these may not reflect the material behavior during the passage of the shock wave and, thus, requires real-time in-situ atomistic characterization to link the microstructure to macroscopic response. In the second part of the thesis, plate impact experiments coupled with both laser interferometry continuum measurements and in-situ dynamic Laue x-ray diffraction (XRD), at the Advanced Photon Source (APS), are conducted on single crystal molybdenum. Here, the role of crystal orientation, either [100] or [111], on deformation mechanisms during the elastic-plastic transition and the steady state response is explored at pressures ranging from 9-19 GPa. Complementary simulation methodology is developed to analyze the evolution of the Laue diffraction spots captured during impact. By extracting the lattice strain and stresses from XRD images, dislocation slip along [110]\u2329111\u232a and [112]\u2329111\u232a is found to be the probable deformation mechanism during compression with negligible anisotropy observed at the Hugoniot state. For the first time, real-time evidence of molybdenum undergoing deformation twinning along [112\u0305]\u2329111\u232a during shock release beyond a critical pressure of 16 GPa irrespective of the loading orientation is presented.
" }, { "name": "Gehlhar, Rachel", "degree": "PhD", "year": "2023", "title": "Model-Based Lower-Limb Powered Prosthesis Control: Developing and Realizing Nonlinear Subsystem Control Methods for Generalizable Prosthesis Control", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01072023-214003146", "creators": [ { "name": { "family": "Gehlhar", "given": "Rachel" }, "id": "Gehlhar-Rachel", "orcid": "0000-0002-4838-8839", "display_name": "Gehlhar, Rachel" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/6724-6e14", "abstract": "While there are over 600,000 lower-limb amputees in the US, commercially available prostheses remain limited to mostly passive devices. People that walk with a passive prosthesis experience an increase in energy expenditure, a decrease in comfortable walking speed, and gait asymmetry which leads to degenerative conditions. To address these limitations, researchers have developed powered prostheses with the aim of replicating the net positive energy biological limbs supply to humans in walking. These active devices have been shown to decrease users' metabolic cost and increase their comfortable walking speed. However, the control methods to achieve these results typically require hours of heuristic tuning for every user and every behavior. This motivates developing more formal prosthesis control methods that generalize between users.
\r\n\r\nFormal nonlinear control methods have been developed to realize energy efficient, human-like walking on bipedal robots. These model-based approaches provide a systematic approach to generate and realize provably stable walking gaits. However, these methods cannot be directly applied to prostheses since they depend on a dynamic model of the entire system, and in the case of the prosthesis, the human dynamics are unknown.
\r\n\r\nTo address this challenge, we develop a theoretical framework to translate model-based bipedal control methods to prostheses with the aim of realizing a generalizable prosthesis control method. We separate the prosthesis subsystem from the remaining human portion of the system and model the human's impact on the prosthesis dynamics with a measure of the interaction forces between the human and the prosthesis. We theoretically prove that a model-based controller developed in this separable subsystem framework is equivalent to one developed with knowledge of the full-order human-prosthesis system. With control Lyapunov functions, we develop a wider class of subsystem controllers that solely depend on local information but provide full-order system guarantees, even in the presence of force estimate errors. This work bridges the gap between bipedal control methods and prostheses, allowing us to leverage the benefits of model-based approaches on prostheses.
\r\n\r\nWe demonstrated a controller of this class through an online optimization-based approach on a powered knee-ankle prosthesis, realizing the first model-dependent lower-limb prosthesis controller that accounts for the interaction force between the human and the prosthesis. For a first pass, a force-estimation method was used that yields improved tracking of the desired trajectories over model-independent prosthesis control methods. Then, we incorporated a load cell into the prosthesis platform at the human-prosthesis attachment point to measure the interaction forces, and an inertial measurement to measure the rotation and velocity of the human's thigh. These two sensors completed the prosthesis dynamics model. A pressure sensor incorporated into the prosthesis' shoe measured the ground reaction forces, enabling the prosthesis to respond to its real-world environment, proving robust to 4 different terrains. We extended this controller to a multi-domain hybrid system approach to model the changing contact points occurring in human heel-toe roll. By allowing the prosthesis to sense the human's large varying dynamic load and respond accordingly, this model-based prosthesis controller emulated subject-specific human kinematic trends on a knee-ankle prosthesis for two subjects with no tuning in between, suggesting this approach could yield a method that generalizes between users.
" }, { "name": "Gordon, Spencer Lane", "degree": "PhD", "year": "2023", "title": "The Identification of Discrete Mixture Models", "advisor": "Vidick, Thomas G.; Schulman, Leonard J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072023-112938936", "creators": [ { "name": { "family": "Gordon", "given": "Spencer Lane" }, "id": "Gordon-Spencer-Lane", "orcid": "0000-0002-7101-2370", "display_name": "Gordon, Spencer Lane" } ], "advisors": [ { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "co-advisor", "display_name": "Vidick, Thomas G." }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "co-advisor", "display_name": "Schulman, Leonard J." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "member", "display_name": "Vidick, Thomas G." }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "compsci" ], "doi": "10.7907/ebf5-0b48", "abstract": "In this thesis we discuss a variety of results on learning and identifying discrete mixture models, i.e., distributions that are a convex combination of k from a known class C of distributions. We first consider the case where C is the class of binomial distributions, before generalizing to the case of product distributions. We provide a necessary condition for identifiability of mixture of products distributions as well as a generalization to structured mixtures over multiple latent variables." }, { "name": "Gu, Zichen", "degree": "PhD", "year": "2023", "title": "Interparticle Forces and Stress Transfer in Saturated and Unsaturated Granular Systems", "advisor": "Ravichandran, Guruswami; Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232023-164041915", "creators": [ { "name": { "family": "Gu", "given": "Zichen" }, "id": "Gu-Zichen", "orcid": "0000-0002-6345-0178", "display_name": "Gu, Zichen" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "co-advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "orcid": "0000-0003-3741-0364", "role": "chair", "display_name": "Andrade, Jose E." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Rittel", "given": "Daniel" }, "id": "Rittel-D", "role": "member", "display_name": "Rittel, Daniel" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/rgys-kh14", "abstract": "Granular systems are ubiquitous in nature and engineering applications. The macroscopic behavior of such systems is governed by the behavior at the grain-scale, including force transfer between adjacent grains. The correlation between continuum behavior and interparticle forces in granular systems is yet to be fully understood. For a saturated or unsaturated granular system under external load, it is important to decode stress partition and transfer in the solid, fluid, and gas phases. In the meantime, the presence of the fluid phase and gas phase greatly increases the difficulty of measuring interparticle forces in opaque granular systems. This thesis describes the theoretical and experimental works on interparticle forces and effective stresses in two types of granular systems: i) fully saturated granular media, and ii) unsaturated granular media.
\r\n\r\nThe first part of the thesis focuses on the direct measurement of interparticle forces and the experimental validation of the concept of effective stress introduced by Karl Terzaghi. The grain-scale expression of Terzaghi's effective stress for saturated granular media under small deformation and quasi-static state is derived using stress decomposition and balance of forces and moments. For the experimental validation of the analytical solution, an experimental setup was designed to study 2D saturated rubber rod packing under classic 1D consolidation. A hybrid optical-mechanical method based on the Granular element method (GEM) and Digital image correlation (DIC) is applied. The interparticle forces are directly computed from 2D strain distribution of the grains, and the effective stress is calculated using the grain-scale forces. With pore water pressure measured by a pressure sensor, the summation of the effective stress and the pore water pressure is then compared with the external load applied in the 1D consolidation experiment, which is the core of Terzaghi's principle. The 1D consolidation experiment is also compared with the 1D consolidation model and matches the results from Discrete element simulations (DEM).
\r\n\r\nThe second part of the thesis investigates the measurement of interparticle forces in more complex unsaturated granular systems consisting of solid, pore fluid, and pore air phases. In the case of quasi-static, point contact, and low saturation, an expression for the partition of stress is derived as a function of interparticle forces. To simplify the expression of the stress partition equation, capillary bridges, which are integral parts of unsaturated systems under low saturation condition, are simulated numerically using 2D finite element method (FEM) to further understand the influence of gravity on pore fluid clusters. As the original GEM for fully saturated systems focuses on interparticle interactions, the GEM is further developed for unsaturated systems based on the original GEM and considering capillary forces. Finally, a hybrid optical-mechanical approach combined with the granular element method (GEM) is developed to extract interparticle forces in a classic 1D consolidation experiment. The partition of stresses is determined by experimental results and compared with the analytical results.
\r\n\r\nThe major contributions of this thesis are the theoretical derivation and experimental validation of the link between the grain-scale properties (interparticle forces, branch vectors, etc.) and the stress transfer in fully saturated and unsaturated systems. The theoretical and experimental methodology employed in the thesis could pave the way for exploring the mechanics and physics behind the constitutive behaviors of a variety of poromechanical systems.
" }, { "name": "Guo, Nian", "degree": "PhD", "year": "2023", "title": "Causal Sampling, Compressing, and Channel Coding of Streaming Data", "advisor": "Kostina, Victoria", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182022-183119533", "creators": [ { "name": { "family": "Guo", "given": "Nian" }, "id": "Guo-Nian", "orcid": "0000-0003-4490-328X", "display_name": "Guo, Nian" } ], "advisors": [ { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "advisor", "display_name": "Kostina, Victoria" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "member", "display_name": "Kostina, Victoria" } ], "option_major": [ "eleceng" ], "doi": "10.7907/n201-ca08", "abstract": "With the emergence of the Internet of Things, communication systems, such as those employed in distributed control and tracking scenarios, are becoming increasingly dynamic, interactive, and delay-sensitive. The data in such real-time systems arrive at the encoder progressively in a streaming fashion. An intriguing question is: what codes can transmit streaming data with both high reliability and low latency? Classical non-causal (block) encoding schemes can transmit data reliably but under the assumption that the encoder knows the entire data block before the transmission. While this is a realistic assumption in delay-tolerant systems, it is ill-suited to real-time systems due to the delay introduced by collecting data into a block. This thesis studies causal encoding: the encoder transmits information based on the causally received data while the data is still streaming in and immediately incorporates the newly received data into a continuing transmission on the fly.
\r\n\r\nThis thesis investigates causal encoding of streaming data in three scenarios: causal sampling, causal lossy compressing, and causal joint source-channel coding (JSCC). In the causal sampling scenario, a sampler observes a continuous-time source process and causally decides when to transmit real-valued samples of it under a constraint on the average number of samples per second; an estimator uses the causally received samples to approximate the source process in real time. We propose a causal sampling policy that achieves the best tradeoff between the sampling frequency and the end-to-end real-time estimation distortion for a class of continuous Markov processes. In the causal lossy compressing scenario, the sampling frequency constraint in the causal sampling scenario is replaced by a rate constraint on the average number of bits per second. We propose a causal code that achieves the best causal distortion-rate tradeoff for the same class of processes. In the causal JSCC scenario, the noiseless channel and the continuous-time process in the previous scenarios are replaced by a discrete memoryless channel with feedback and a sequence of streaming symbols, respectively. We propose a causal joint sourcechannel code that achieves the maximum exponentially decaying rate of the error probability compatible with a given rate. Remarkably, the fundamental limits in the causal lossy compressing and the causal JSCC scenarios achieved by our causal codes are no worse than those achieved by the best non-causal codes. In addition to deriving the fundamental limits and presenting the causal codes that achieve the limits, we also show that our codes apply to control systems, are resilient to system deficiencies such as channel delay and noise, and have low complexities.
" }, { "name": "Han, SooJean", "degree": "PhD", "year": "2023", "title": "Control and State-Estimation of Jump Stochastic Systems by Learning Recurrent Spatiotemporal Patterns", "advisor": "Doyle, John Comstock; Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:01302023-023806052", "creators": [ { "name": { "family": "Han", "given": "SooJean" }, "id": "Han-SooJean", "orcid": "0000-0003-1195-6465", "display_name": "Han, SooJean" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "co-advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "co-advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "cds" ], "doi": "10.7907/gyae-jv94", "abstract": "This thesis establishes control and estimation architectures that combine both model-based and model-free methods by theoretically characterizing several types of jump stochastic systems (JSSs), i.e., systems with random and repetitive jump phenomena. By expanding the capabilities of model-based stochastic control and estimation, there is potential for artificial intelligence to be implemented as a supplement to theory-influenced design instead of being used end-to-end. We begin by deriving sufficient conditions for stochastic incremental stability for nonlinear systems perturbed by two types of non-Gaussian noise: 1) shot noise processes represented as compound Poisson processes, and 2) finite-measure L\u00e9vy processes constructed as affine combinations of Gaussian white and Poisson shot noise processes. We then present a controller architecture based on a concept we call pattern-learning for prediction (PLP) for discrete-time/discrete-event systems, in which we can take advantage of the fact that the underlying jump process is a sequence of random variables that occurs as repeated patterns of interest. Finally, we demonstrate control and estimation for JSSs in three real-world applications. First, we consider the control of networks with dynamic topology (e.g., power grid with fault-tolerance to downed lines), for which PLP is integrated with variations of the novel system-level synthesis framework for disturbance-rejection. Second, we perform congestion control of vehicle traffic flow over metropolitan intersection networks, for which PLP is extended to pattern-learning with memory and prediction (PLMP) via the inclusion of episodic control, designed to reduce memory consumption by exploiting structural symmetries and temporal repetition in the network. Third, we perform estimation and forecasting (the dual problem to control) for epidemic spread throughout a population network under jump phenomena such as superspreader effects and the emergence of variant viruses. Our results indicate that learning patterns in the jump process makes controller/observer design efficient in data-consumption and computation time, which suggests that it can potentially be used for other JSSs in the real world." }, { "name": "Hashemi Talkhooncheh, Arian", "degree": "PhD", "year": "2023", "title": "Holistic Design in High-Speed Silicon Photonics and Low-Power Electronics Platforms", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122023-184556858", "creators": [ { "name": { "family": "Hashemi Talkhooncheh", "given": "Arian" }, "id": "Hashemi-Talkhooncheh-Arian", "orcid": "0000-0001-8946-5047", "display_name": "Hashemi Talkhooncheh, Arian" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Zilkie", "given": "Aaron" }, "id": "Zilkie-A", "orcid": "0000-0002-4114-2297", "role": "member", "display_name": "Zilkie, Aaron" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8yj9-2a62", "abstract": "High-speed interconnects are of vital importance to the operation of high-performance computing and communication systems, determining the ultimate bandwidth or data rates at which the information can be exchanged. Optical interconnects and the employment of high order modulation formats are considered as the solutions to fulfilling the envisioned speed and power efficiency of future interconnects. One area of growing importance in optical interconnects is the design and optimization of energy-efficient transmitters with superior power efficiency. Enhancing the electro-optical bandwidth density while keeping the power efficiency optimized, requires improvement in the optical power penalty of photonic integrated circuits. Moreover, co-optimization of electronics and photonics enables a path towards sub-pJ/b transmission efficiency. In this dissertation, architectural and circuit-level energy-efficient techniques serving these goals are presented.\r\n\r\nFirst, an integrated DAC-less PAM-4 transmitter in a multi-micron silicon photonics platform using 2 binary-driven uneven-length SiGe EAMs in an unbalanced MZI is presented. The optical transmitter exhibits 5.5dB ER at 100 Gb/s with 2.1dB SNR improvement compared to single EAMs driven by PAM-4 signals. Also, A DAC-less 200Gb/s QAM-16 transmitter in a multi-micron silicon-photonics platform using 4 binary-driven SiGe EAMs in an unbalanced MZI is presented. The transmitter exhibits bit-error rates of 3\u00d710-4 and 2.8\u00d710-4 for square and hexagonal constellations.\r\n\r\nSecond, a 100Gb/s PAM4 optical transmitter system implemented in a 3D-integrated Silicon Photonics-CMOS platform is presented. The photonics chip includes a push-pull segmented Mach-Zehnder Modulator (MZM) structure using highly capacitive (415fF to 1.1pF), yet optically efficient (V\u03c0L= 0.8 V.cm) metal-oxide-silicon capacitor (MOSCAP) phase modulators. Two pairs of U-shaped modulator segments with effective lengths of 170\u00b5m and 450\u00b5m are driven at 50 Gbaud by a dual-channel 28nm CMOS driver, which is flip-chip bonded to the photonics chip. The driver cores utilize digitally controllable pre-distortion and inductive peaking to achieve sufficient electro-optical bandwidth. The drivers deliver 1.2Vppd swing to modulators using a 0.9V supply and on-chip serializers that generate 50Gb/s data streams. The electronics chip consumes 240mW achieving 2.4pJ/bit energy efficiency. The overall electro-optical bandwidth (EOBW), without any pre-distortion, is increased by approximately 56% and 48% for the 170\u00b5m and 450\u00b5m segments, respectively, when compared to their EOBW measured by 65GHz 50-Ohm terminated probes. The optical input power to the photonics chip is +10dBm and an erbium-doped fiber amplifier amplifies output signals by 11dB. The 50Gb/s NRZ optical raw eye diagram exhibits 4.3dB extinction ratio (ER) and 1.2dBm of optical modulation amplitude (OMA). The 100Gb/s PAM4 optical raw eye diagram shows 4.3dB ER and 1.4dBm OMA with a transmitter dispersion eye closure quaternary (TDECQ) of 1.53dB after a 5-tap feed-forward-equalization (FFE) filter. The PAM4 TDECQ changes by 53% when the temperature is increased from 30\u00baC to 90 \u00baC at the optimum forward bias voltage of 1V.\r\n\r\nThird, an efficient cold-starting energy harvester system, fabricated in 65nm CMOS is presented. The proposed harvester uses no external electrical components and is compatible with biofuel-cell voltage and power ranges. A power-efficient system architecture is proposed to keep the internal circuitry operating at 0.4V while regulating the output voltage at 1V using switched-capacitor DC-DC converters and a hysteretic controller. A startup enhancement block is presented to facilitate cold startup with any arbitrary input voltage. A real-time on-chip 2D maximum power point tracking with source degradation tracing is also implemented to maintain power efficiency maximized over time. The system performs cold startup with a minimum input voltage of 0.39V and continues its operation if the input voltage degrades to as low as 0.25V. Peak power efficiency of 86% is achieved at 0.39V of input voltage and 1.34\u03bcW of output power with 220nW of average power consumption of the chip. The end-to-end power efficiency is kept above 70% for a wide range of loading powers from 1\u03bcW to 12\u03bcW. The chip is integrated with a pair of lactate biofuel-cell electrodes with 2mm of diameter on a prototype printed circuit board (PCB). Integrated operation of the chip with the electrodes and a lactate solution is demonstrated." }, { "name": "Hirokawa, Soichi", "degree": "PhD", "year": "2023", "title": "Dynamics of Protein-Mediated Polymer Coupling and their Implications in Antibody Production and Emergent Patterning", "advisor": "Phillips, Robert B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08252022-153300158", "creators": [ { "name": { "family": "Hirokawa", "given": "Soichi" }, "id": "Hirokawa-Soichi", "orcid": "0000-0001-5584-2676", "display_name": "Hirokawa, Soichi" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "advisor", "display_name": "Phillips, Robert B." } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Thomson", "given": "Matthew" }, "id": "Thomson-M-W", "orcid": "0000-0003-1021-1234", "role": "member", "display_name": "Thomson, Matthew" }, { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "member", "display_name": "Hsieh, David" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/fpmm-a552", "abstract": "Proteins serve a wide range of functions in and out of the cell, from signaling and gene regulation to transport and structural reinforcement. These functions are usually carried out from interactions with other molecules in the surrounding medium such as other proteins, small molecules, or DNA. One such class of proteins are what I will call polymer-coupling proteins: these proteins intentionally link identical polymers or two regions of the same polymer together so that their coupled interactions critically affect the state of the biological system. A vast array of such proteins exist in nature with roles such as the looping of DNA to physically inhibit the expression of a gene or the formation of the cytoskeleton which provides a cell with its shape. In this thesis, I use in vitro experimental methods to explore two cases of coupling proteins and understand their roles not only in reorganizing their complementary polymers but influencing the final state of their respective systems.
\r\n\r\nIn Chapter 2, I examine the starting process for the assembly of an antibody-encoding gene in developing immune cells. Motivated by data suggesting that some antibodies are less likely to be made than others, I explore how the early steps of constructing an antibody-encoding gene affect this uneven frequency of assembly. To initiate recombination, the recombination-activating gene (RAG) protein complex simultaneously binds and cuts two well-recognized sequences neighboring two antibody-encoding gene segments in order to allow other proteins to combine these exposed segments together. The sequences to which the RAG protein performs its binding and cutting functions have certain identifiable sequence patterns but can still vary. Through a single-molecule experimental method known as tethered particle motion (TPM) I show how changes to the binding site sequence can enhance or diminish the propensity of the RAG protein to bind and cut the DNA and thus explore the consequences of these altered interactions in the unequal selection for certain antibody gene segments over others.
\r\n\r\nIn Chapter 3, I turn to questions of the emergence of order from self-organization in biological systems. From the molecular to the population scale, biology constantly demonstrates that with an injection of energy, systems can be driven out of equilibrium and allow for the organization of its constituents. A case of such organization in cells is the coupling of microtubules by motor proteins to create and maintain the mitotic spindle, a critical biological architecture for ensuring that each cell obtains a copy of the genome during division. In vitro experiments that exploit similar motor-microtubule interactions have become a convenient way to identify the effects of perturbing a key player such as motor properties or boundary conditions of the system on the spatiotemporal extent of organization. However, in many instances, the dynamics under which such cytoskeletal systems reduce their entropy over the course of creating order have not been carefully examined in experimental systems. Here, I use engineered light-dimerizable motors that can give rise to the formation of a highly connected network that compacts to form a dense, organized structure, and through the use of a noninvasive imaging technique observe how the polymers that make up the network continually reorganize in the bulk during a global contraction of the network.
" }, { "name": "Hu, Peng", "degree": "PhD", "year": "2023", "title": "Computational Compensation for Model Imperfections in Photoacoustic Computed Tomography", "advisor": "Wang, Lihong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-051815823", "creators": [ { "name": { "family": "Hu", "given": "Peng" }, "id": "Hu-Peng", "orcid": "0000-0002-2933-1239", "display_name": "Hu, Peng" } ], "advisors": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "advisor", "display_name": "Wang, Lihong" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" } ], "option_major": [ "medeng" ], "doi": "10.7907/6hdm-ar41", "abstract": "Photoacoustic computed tomography (PACT) images biological tissues\u2019 optical absorption through detection of photon-absorption-induced ultrasonic waves. Various systems have been proposed for PACT and they are described by different mathematical models to reconstruct from detected ultrasonic signals the photon-absorption-induced initial pressure, the main contrast in PACT. Accurate image reconstruction has high requirements for the system and the mathematical model, which is often imperfect in practice due to multiple factors, e.g., limited transducer bandwidth, finite transducer element size, sparse spatial sampling, partial-view detection, and tissue motion. The focus of this dissertation is on using computational methods to compensate for these model imperfections.
\r\n\r\nFirst, for a human breast imaging system based on a full-ring transducer array, we incorporate the limited transducer bandwidth into the model for spatiotemporal analysis to clarify the aliasing due to sparse spatial sampling and propose (1) two methods (radius-dependent spatiotemporal antialiasing and location-dependent spatiotemporal antialiasing) to mitigate these artifacts. Second, for an isotropic-resolution 3D PACT system formed by four arc arrays, we consider both the limited transducer bandwidth and the finite transducer element size and (2) compress the system matrix through singular value decomposition and fast Fourier transform for its efficient explicit expression. Enabled by this expression, we then propose (3) fast sparsely sampling functional imaging by incorporating a densely sampled prior image into the system matrix, which maintains the critical linearity while mitigating artifacts, and (4) intra-image nonrigid motion correction by incorporating the motion as subdomain translations into the system matrix and reconstructing the translations together with the image iteratively. Finally, for a single-shot 3D PACT system based on a single ultrasonic transducer, we propose (5) a fast implementation of the forward model by connecting traditional PACT with virtual detector responses through fast Fourier transform, and we iteratively reconstruct the image from signals with extremely compressed sensing and partial-view detection.
\r\n\r\nAll these proposed methods enable image reconstruction or significantly improve image quality in numerical simulations, phantom experiments, and in vivo experiments. Although they are demonstrated only for certain PACT systems, they are directly applicable to other systems and can be extended to other tomographic imaging modalities such as X-ray computed tomography (X-ray CT) and magnetic resonance imaging (MRI).
" }, { "name": "H\u00e4geli Lohaus, Stefan P.", "degree": "PhD", "year": "2023", "title": "Experimental Study on the Thermodynamic Interactions of Phonons and Magnetism in Fe Systems", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-173549089", "creators": [ { "name": { "family": "H\u00e4geli Lohaus", "given": "Stefan P." }, "id": "H\u00e4geli-Lohaus-Stefan-P-H\u00e4geli", "orcid": "0000-0002-4430-3834", "display_name": "H\u00e4geli Lohaus, Stefan P." } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Alp", "given": "Esen E." }, "id": "Alp-Esen-E", "role": "member", "display_name": "Alp, Esen E." }, { "name": { "family": "Scott", "given": "Valerie" }, "id": "Scott-Valerie", "role": "member", "display_name": "Scott, Valerie" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/5sb5-fm96", "abstract": "The macroscopic thermophysical behavior of materials is governed by their atomic level excitations and how they store heat. Most of the thermal energy excites oscillations of the atoms, quantized as phonons, but in magnetic materials a considerable amount of heat is also absorbed by fluctuations of the electronic spins. This thesis explores the thermodynamics of phonons and magnetic spins in Fe-systems: we investigate the coupling between these excitations in Fe, Fe-Ni, and Fe-C, quantify their size dependency in nanocrystalline in Ni\u2083Fe, and assess their individual roles in the anomalous thermal expansion of Fe-Ni Invar.
\r\n \r\nMost materials expand when heated due to enhanced atomic oscillations. However, in 1895 C.E. Guillaume combined Fe and Ni to discover a material with near-zero thermal expansion, called Invar. This discovery was awarded the 1920 Physics Nobel Prize and sparked thousands of scientific investigations. Since the anomalous Invar effect is associated with magnetism, nearly all studies have focused on the electronic and spin structure of Fe-Ni. But phonons are needed to complete the picture, and to date, the anomalous Invar behavior is not fully understood. Here, we explore a method for measuring thermal expansion that is capable of isolating contributions from phonons and spins. Since the thermal energy of materials is related to entropy, the thermal expansion can be indirectly determined through individual entropic contributions by using a Maxwell relation. The phonon and magnetic entropies were measured by combining two nuclear resonant x-ray scattering techniques, with samples under pressure in diamond-anvil cells. We show that the Invar behavior stems from a competition between phonons and spins, that oppose each other for near-zero thermal expansion. A spin-phonon coupling improves the precision of this cancellation, extending the range of Invar behavior.
\r\n \r\nSuch a coupling of phonons and spin was also observed in pure Fe and Fe\u2083C cementite, as their phonon energies correlate to the change in magnetization. This motivated us to develop a magnetic quasi-harmonic model for Fe and Fe\u2083C, which accounts well for the deviation of phonon energies from pure volumetric effects of the conventional quasi-harmonic approximation.
\r\n\r\nThe thermodynamics of materials is also affected by the size of their crystallites. We determined the size effects on the heat absorption by phonons, electrons, and spins in nanocrystalline Ni\u2083Fe. All excitations become enhanced in the nanomaterial. In particular, the redistribution of spectral weights amplifies the phonon entropy. This helps stabilize the nanostructure against the enthalpy from its extra grain boundaries. However, the nanostructure is meta-stable, and the grains will grow into their bulk counterpart when diffusion is enabled at elevated temperatures.
" }, { "name": "Kamal, Omar", "degree": "PhD", "year": "2023", "title": "Optimal Receptivity and the Generalization of the One-Way Navier-Stokes (OWNS) Equations to Complex High-Speed Boundary Layers and Jets", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:01162023-041217909", "creators": [ { "name": { "family": "Kamal", "given": "Omar" }, "id": "Kamal-Omar", "orcid": "0000-0002-3431-2964", "display_name": "Kamal, Omar" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Hussain", "given": "Fazle" }, "id": "Hussain-F", "orcid": "0000-0002-2209-9270", "role": "member", "display_name": "Hussain, Fazle" } ], "option_major": [ "mecheng" ], "doi": "10.7907/haet-h558", "abstract": "Prediction of the linear amplification of disturbances in hypersonic boundary layers is challenging due to the presence and interactions of discrete modes (e.g. Tollmien-Schlichting and Mack) and continuous modes (entropic, vortical, and acoustic). While direct numerical simulations (DNS) and global analysis can be used, the large grids required make the stability calculations expensive, particularly when a large parameter space is required. At the same time, parabolized stability equations are non-convergent and unreliable for problems involving multi-modal and non-modal interactions. We therefore apply the One-Way Navier-Stokes (OWNS) Equations to study transitional hypersonic boundary layers. OWNS is based on a rigorous, approximate parabolization of the equations of motion that removes disturbances with upstream group velocity using a higher-order recursive filter. We extend the original algorithm by considering non-orthogonal curvilinear coordinates and incorporate full compressibility with temperature-dependent fluid properties. The generalized OWNS methodology is validated by comparing to DNS data for flat plates and a sharp cone, and to linear stability theory results for local disturbances on the centerline of the Mach 6 HIFiRE-5 elliptic cone. OWNS provides DNS-quality results for the former flows at a small fraction of the computational expense. We further demonstrate the capability of OWNS to track fully 3D instabilities by applying the algorithm to a complex Mach 6 finned-cone geometry as well as a 3D Mach 1.5 turbulent jet.
\r\n\r\nIt is often desirable, especially for design purposes, to compute worst-case disturbances, i.e. solving the inverse problem, otherwise known as resolvent or input-output analysis. While DNS and global analysis can be used to compute optimal forced responses, their large computational expense render these tools less practical for large design parameter spaces. We address this issue by modifying the original OWNS framework to find the optimal forcing and responses using Lagrangian multipliers via an iterative, adjoint-based, space-marching technique that appreciably reduces the computational burden compared to the global approach that uses singular value decomposition without sacrificing accuracy. The input-output OWNS model is validated against optimal forcings and responses of a Mach 4.5 flat-plate boundary layer from literature and a Mach 1.5 turbulent jet. We then apply these equations to study worst-case disturbances on the centerline of the Mach 6 HIFiRE-5 elliptic cone and on a highly cooled Mach 6 flat-plate boundary layer.
\r\n \r\nAlthough the worst-case forcings are theoretically informative, they are not physically realizable. In natural receptivity analysis, disturbances are forced by matching local solutions within the boundary layer to outer solutions consisting of free-stream vortical, entropic, and acoustic disturbances. We pose a scattering formalism to restrict the input forcing to a set of realizable disturbances associated with plane-wave solutions of the outer problem. The formulation is validated by comparing with DNS of a Mach 4.5 flat-plate boundary layer. We show that the method provides insight into transition mechanisms by identifying those linear combinations of plane-wave disturbances that maximize energy amplification over a range of frequencies. We also discuss how the framework can be extended to accommodate scattering from shocks and in shock layers for supersonic flow.
" }, { "name": "Kim, Brian Lee Kiwon", "degree": "PhD", "year": "2023", "title": "Dynamics of Time-Varying and Nonlinear Phononic Lattices", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05042023-201010843", "creators": [ { "name": { "family": "Kim", "given": "Brian Lee Kiwon" }, "id": "Kim-Brian-Lee-Kiwon", "orcid": "0000-0002-2403-8703", "display_name": "Kim, Brian Lee Kiwon" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Chong", "given": "Christopher" }, "id": "Chong-C", "orcid": "0000-0002-4908-3252", "role": "member", "display_name": "Chong, Christopher" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "mecheng" ], "doi": "10.7907/n7mv-eg68", "abstract": "The control of waves and vibrations in materials and structures underpins both the most common and the most advanced technologies. Spatially structured and periodic media have been widely studied and applied to signal processing, vibration mitigation, focusing, and other applications beyond the capabilities of bulk materials. Recently, interest has grown in the effects of temporal variation of material and medium properties on wave propagation. Temporal variations serve as an additional dimension for the design and structure of materials, further expanding potential functionalities and performance. Many of the concepts of waves in time-varying media have been developed in photonics and other electromagnetic systems, but the same fundamental dynamics govern acoustic and elastic systems, which provide alternative opportunities for implementation and new applications of time-varying media. In this thesis, we employ a one-dimensional phononic lattice composed of repelling ring magnets with electromagnetic coils that act as time-dependent grounding stiffness. The lattice provides an excellent platform for studying waves in time-varying media, with implementation and modeling of time-variation of elastic properties made simple by its discreteness. In addition, the repelling force between the magnets allows not only for the study of the linear dynamics of time-varying systems for small displacements but also for the exploration of the interaction between time-variation and nonlinear effects. We first present novel demonstrations of two types of time-varying wave phenomena in acoustic or elastic systems. First, the measurement of the propagation of waves across a temporal discontinuity in elastic properties demonstrates the temporal analog to refraction across a spatial boundary. Second, the experimental reconstruction of the dispersion relation of a time-periodic periodic medium shows the opening of wavenumber band gaps. We then characterize the dynamic stability of the time-periodic lattice and consider the role of nonlinearity. Finally, we investigate the possible existence of wavenumber gap breathers, temporally localized solutions of the discrete, nonlinear system.
" }, { "name": "Kim, Gunho", "degree": "PhD", "year": "2023", "title": "Wave Propagation in Periodic Acoustic Metamaterials: from 1D to 3D", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:03022023-175118888", "creators": [ { "name": { "family": "Kim", "given": "Gunho" }, "id": "Kim-Gunho", "orcid": "0000-0003-1796-0908", "display_name": "Kim, Gunho" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "chair", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" } ], "option_major": [ "mecheng" ], "doi": "10.7907/dyq0-vm69", "abstract": "Wave propagation in periodic structures has been studied for centuries; for example, Newton derived the velocity of sound based on a linear lattice. Recently, advanced manufacturing techniques have led to the fabrication of geometrically complex architected materials with acoustic properties unattainable by their constituent materials. Such rationally designed structures are often called acoustic metamaterials and they can be engineered to transmit, block, amplify, or redirect acoustic waves. Subwave-length building blocks, typically periodic (but not necessarily so), can be assembled into effectively continuous materials to manipulate dispersive properties of vibrational waves in ways that differ substantially in conventional media. This thesis investigates rationally designed acoustic metamaterials, ranging from 1D to 3D, and how acoustic wave propagation can be controlled by these artificially structured composite materials for ultrasound-related biomedical applications.
\r\n\r\nI first explore 1D wave propagation in acoustic metamaterials to study the basic mechanics and relevant analysis skills. Bio-inspired helical mechanical metamaterials are designed and their normal modes are investigated. I demonstrate the ability to vary the acoustic properties of the helical metamaterials by perturbing the geometrical structure and mass distribution. By locally adding eccentric and denser elements in the unit cells, I change the moment of inertia of the system and introduce centro-asymmetry. This allows me to control the degree of mode coupling and the width of subwavelength band gaps in the dispersion relation, which are the product of enhanced local resonance hybridization.
\r\n\r\nThen I study 2D wave propagation in microlattice acoustic metamaterials for ultra- sound manipulation. When coupled with pressure waves in the surrounding fluid, the dynamic behavior of microlattices in the long wavelength limit can be explained in the context of Biot\u2019s theory of poroelasticity. I exploit elastoacoustic wave propagation within 3D-printed polymeric microlattices to design a gradient refractive index lens for underwater wave focusing. A modified Luneburg lens index profile adapted for ultrasonic wave lensing is demonstrated via the finite element method and underwater testing, showcasing a computationally efficient poroelasticity-based design approach that enables accelerated design of acoustic wave manipulation devices.
\r\n\r\nLastly, I show that tailorable 3D wave propagation can be achieved based on the findings from the previous chapters. Functional ultrasound imaging enables sensitive, high-resolution imaging of neural activity in freely behaving animals and human patients. However, the skull acts as an aberrant and absorbing layer for sound waves, leading to most functional ultrasound experiments being conducted after skull removal. A microscale 2-photon polymerization technique is adopted to fabricate a conformal acoustic window with a high stiffness-to-density ratio and sonotransparency. Long-term biocompatibility and lasting signal sensitivity are demonstrated over a long period of time (> 4 months) by conducting ultrasound imaging in mouse models implanted with the metamaterial skull prosthesis.
" }, { "name": "Korner, Kevin Andreas", "degree": "PhD", "year": "2023", "title": "Modeling Deformations of Active Rods, Ribbons, and Plates", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:07202022-212008345", "creators": [ { "name": { "family": "Korner", "given": "Kevin Andreas" }, "id": "Korner-Kevin-Andreas", "orcid": "0000-0002-2967-9657", "display_name": "Korner, Kevin Andreas" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "member", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/2zb0-m166", "abstract": "Slender structures are mechanical components which have at least one spatial dimension much smaller than another. Some canonical examples are beams, rods, ribbons, plates, and shells. Although these systems have been studied for many centuries, the focus of development has generally been limited to small strains and the onset of buckling modes. Outside of this regime, both geometric and material non-linearities contribute significant complexity to the analytical and computational techniques which can be applied to these problems. Despite this, large deformations demonstrate tremendous potential in engineering applications, particularly with soft materials. This thesis examines various methods of modeling slender structures. We focus on large strain behaviors, often accentuated by spontaneous strains generated with active materials. These systems demonstrate a wide range of interesting and useful behaviors, such as bifurcations, snap-through, and cyclic deformations.
" }, { "name": "Lale, Ali Sahin", "degree": "PhD", "year": "2023", "title": "Learning and Control of Dynamical Systems", "advisor": "Anandkumar, Anima", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282023-011333603", "creators": [ { "name": { "family": "Lale", "given": "Ali Sahin" }, "id": "Lale-Ali-Sahin", "orcid": "0000-0002-7191-346X", "display_name": "Lale, Ali Sahin" } ], "advisors": [ { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "advisor", "display_name": "Anandkumar, Anima" } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/rdhq-8a88", "abstract": "Despite the remarkable success of machine learning in various domains in recent years, our understanding of its fundamental limitations remains incomplete. This knowledge gap poses a grand challenge when deploying machine learning methods in critical decision-making tasks, where incorrect decisions can have catastrophic consequences. To effectively utilize these learning-based methods in such contexts, it is crucial to explicitly characterize their performance. Over the years, significant research efforts have been dedicated to learning and control of dynamical systems where the underlying dynamics are unknown or only partially known a priori, and must be inferred from collected data. However, much of these classical results have focused on asymptotic guarantees, providing limited insights into the amount of data required to achieve desired control performance while satisfying operational constraints such as safety and stability, especially in the presence of statistical noise.
\r\n\r\nIn this thesis, we study the statistical complexity of learning and control of unknown dynamical systems. By utilizing recent advances in statistical learning theory, high-dimensional statistics, and control theoretic tools, we aim to establish a fundamental understanding of the number of samples required to achieve desired (i) accuracy in learning the unknown dynamics, (ii) performance in the control of the underlying system, and (iii) satisfaction of the operational constraints such as safety and stability. We provide finite-sample guarantees for these objectives and propose efficient learning and control algorithms that achieve the desired performance at these statistical limits in various dynamical systems. Our investigation covers a broad range of dynamical systems, starting from fully observable linear dynamical systems to partially observable linear dynamical systems, and ultimately, nonlinear systems.
\r\n\r\nWe deploy our learning and control algorithms in various adaptive control tasks in real-world control systems and demonstrate their strong empirical performance along with their learning, robustness, and stability guarantees. In particular, we implement one of our proposed methods, Fourier Adaptive Learning and Control (FALCON), on an experimental aerodynamic testbed under extreme turbulent flow dynamics in a wind tunnel. The results show that FALCON achieves state-of-the-art stabilization performance and consistently outperforms conventional and other learning-based methods by at least 37%, despite using 8 times less data. The superior performance of FALCON arises from its physically and theoretically accurate modeling of the underlying nonlinear turbulent dynamics, which yields rigorous finite-sample learning and performance guarantees. These findings underscore the importance of characterizing the statistical complexity of learning and control of unknown dynamical systems.
" }, { "name": "Learsch, Robert Whitson", "degree": "PhD", "year": "2023", "title": "Droplet Control in Aqueous and Hydrocarbon Fluids: Long, End-Associative Polymers Dictate Fluid Behavior Under Elongational Flows", "advisor": "Kornfield, Julia A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05102023-041835603", "creators": [ { "name": { "family": "Learsch", "given": "Robert Whitson" }, "id": "Learsch-Robert-Whitson", "orcid": "0000-0001-6329-5879", "display_name": "Learsch, Robert Whitson" } ], "advisors": [ { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "advisor", "display_name": "Kornfield, Julia A." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Nelson", "given": "Chris W." }, "id": "Nelson-Chris-W", "role": "member", "display_name": "Nelson, Chris W." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." } ], "option_major": [ "matsci" ], "doi": "10.7907/zkpd-bq33", "abstract": "Modifying elongational flows seen in sprayed mists, turbulent flows, and droplet spreading and retraction following impact, is of interest in diverse industries, including agriculture and aviation. Long flexible polymers (with fully extended lengths 1 to 10 \u00b5m) modify the elongational flow behavior of a fluid to which they are added. At low concentrations (1 to 10% of their overlap concentrations), their effect is mild under shear flow (shear viscosity increases < 50%), but dramatic under elongational flows (extensional viscosity increases \u2265 300).
\r\n\r\nThese long polymers are not widely used in practice because they degrade under strong flows, such as passing through pumps and filters, that typically precede spray. Pairwise end-associative polymers can overcome this limitation. Pulling apart non-covalent associative bonds under such strong flow conditions relieves the tension along the polymer backbone. The pairwise end-associative polymers that are effective in mist control and drag reduction are individually short enough to avoid chain scission in flows that would break long covalent polymers, yet long enough that 6 to 8 associative polymers connected end-to-end create supermolecules that are as effective as their long covalent counterparts.
\r\n\r\nThis thesis systematically compares the effect of long covalent and long end-associative polymers on the fluid\u2019s extensional flow properties and the polymers' performance in controlling droplet impact and spray breakup. To measure the elongational flow properties, I implemented and enhanced the Dripping onto Substrate Extensional Rheometry (DoSER) technique (Chapter 2) and applied it to long covalent polymers (Chapter 3) and to end-to-end associative polymers (Chapter 4). Preparing solutions in which the polymers negligibly affect the interfacial tension (< 10%) allows us to explore the relationship between extensional flow properties and droplet impact (Chapter 5) and spray (Chapter 6).
\r\n\r\nBy combining the quantitative measurements of extensional viscosity and extensional relaxation time with the corresponding behavior in impact and spray, I correlate the structure of polymers to the solution behavior in droplet rebound and spray breakup. This work has the potential to reduce pesticide contamination of soil, water, and air from agricultural sprays and fire hazard associated with hydrocarbon lubricants.
" }, { "name": "Ledezma, Luis M.", "degree": "PhD", "year": "2023", "title": "Towards Universal Integrated Laser Sources with Nonlinear Photonics", "advisor": "Marandi, Alireza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242023-033922764", "creators": [ { "name": { "family": "Ledezma", "given": "Luis M." }, "id": "Ledezma-Luis-M", "orcid": "0000-0002-0365-1672", "display_name": "Ledezma, Luis M." } ], "advisors": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "advisor", "display_name": "Marandi, Alireza" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ag5t-r511", "abstract": "Lasers are ubiquitous in modern technology with different applications typically requiring different laser wavelengths. However, a given laser can operate only in a relatively narrow spectral region given by the particular material used to build the laser. This leads to using several lasers when several wavelengths are required. Nonlinear photonic devices pose a solution to this problem by transferring energy from single lasers to vast regions of the electromagnetic spectrum. But, despite more than 60 years of development in nonlinear photonics, most nonlinear devices remain large, expensive, and confined to research laboratories.
\r\n\r\nIn this dissertation, we demonstrate a new generation of integrated nonlinear photonic devices based on the quadratic \u03c7(2) nonlinearity. Using the up-and-coming thin-film lithium niobate platform, we demonstrate ultrafast optical parametric amplifiers, parametric generation of ultrashort mid-infrared pulses, long pulses and frequency combs tunable over an octave bandwidth, and the first \u03c7(2) CW parametric oscillator directly pumped by a single commercial diode laser. These results represent key milestones towards compact and inexpensive universal laser sources.
" }, { "name": "Levine, Matthew Emanuel", "degree": "PhD", "year": "2023", "title": "Machine Learning and Data Assimilation for Blending Incomplete Models and Noisy Data", "advisor": "Stuart, Andrew M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-213052258", "creators": [ { "name": { "family": "Levine", "given": "Matthew Emanuel" }, "id": "Levine-Matthew-Emanuel", "orcid": "0000-0002-5627-3169", "display_name": "Levine, Matthew Emanuel" } ], "advisors": [ { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "advisor", "display_name": "Stuart, Andrew M." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." } ], "option_major": [ "cms" ], "doi": "10.7907/b82h-ye78", "abstract": "The prediction and inference of dynamical systems is of widespread interest across scientific and engineering disciplines. Data assimilation (DA) offers a well-established and successful paradigm for blending such models with noisy observational data. However, traditional DA-based inference often fails when available data are insufficiently informative. Chapter 2 copes with this challenge by introducing constraints into Ensemble Kalman Filtering, which is shown to improve forecasting of glucose dynamics in real patient-level clinical data. Chapter 3 addresses this identifiability challenge by instead developing a simplified, reduced-order stochastic model for glucose dynamics that is more easily identified from patient data. Despite these successes, the forecasting performance of the methods are fundamentally limited by the fidelity of the employed model, which is often not fully understood a priori.
\r\n\r\nChapter 4 presents a general picture of how noisy, partially-observed time-series data can be used to learn flexible (e.g., neural network-based) corrections to a pre-specified mechanistic model. In Chapter 5, the proposed methodology is then validated in simulated settings for glucose-insulin models. Chapter 6 provides further perspective on learning flexible model corrections, comparing approaches that use i) gradient-based or gradient-free optimization, ii) temporal or time-averaged data, iii) different model parameterizations, iv) deterministic and stochastic corrections, and v) physical conservation laws to constrain inference.
\r\n\r\nChapter 7 studies how these perspectives on machine learning and dynamical systems can help us understand the roles of biochemical networks. In particular, it considers protein dimerization networks from the lens of approximation theory and evaluates how the equilibria of these networks can be fine-tuned to perform a variety of biological computations.
" }, { "name": "Li, Tongxin", "degree": "PhD", "year": "2023", "title": "Learning-Augmented Control and Decision-Making: Theory and Applications in Smart Grids", "advisor": "Low, Steven H.; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechThesis:07202022-040725024", "creators": [ { "name": { "family": "Li", "given": "Tongxin" }, "id": "Li-Tongxin", "orcid": "0000-0002-9806-8964", "display_name": "Li, Tongxin" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Mazumdar", "given": "Eric V." }, "id": "Mazumdar-E-V", "orcid": "0000-0002-1815-269X", "role": "member", "display_name": "Mazumdar, Eric V." } ], "option_major": [ "cms" ], "doi": "10.7907/cdf6-0w78", "abstract": "Achieving carbon neutrality by 2050 does not only lead to the increasing penetration of renewable energy, but also an explosive growth of smart meter data. Recently, augmenting classical methods in real-world cyber-physical systems such as smart grids with black-box AI tools, forecasts, and ML algorithms has attracted a lot of growing interest. Integrating AI techniques into smart grids, on the one hand, provides a new approach to handle the uncertainties caused by renewable resources and human behaviors, but on the other hand, creates practical issues such as reliability, stability, privacy, and scalability, etc. to the AI-integrated algorithms.
\r\n\r\nThis dissertation focuses on solving problems raised in designing learning-augmented control and decision-making algorithms.
\r\n \r\nThe results presented in this dissertation are three-fold. We first study a problem in linear quadratic control, where imperfect/untrusted AI predictions of system perturbations are available. We show that it is possible to design a learning-augmented algorithm with performance guarantees that is aggressive if the predictions are accurate and conservative if they are imperfect. Machine-learned black-box policies are ubiquitous for nonlinear control problems. Meanwhile, crude model information is often available for these problems from, e.g., linear approximations of nonlinear dynamics. We next study the problem of equipping a black-box control policy with model-based advice for nonlinear control on a single trajectory. We first show a general negative result that a naive convex combination of a black-box policy and a linear model-based policy can lead to instability, even if the two policies are both stabilizing. We then propose an adaptive \u03bb-confident policy, with a coefficient \u03bb indicating the confidence in a black-box policy, and prove its stability. With bounded nonlinearity, in addition, we show that the adaptive \u03bb-confident policy achieves a bounded competitive ratio when a black-box policy is near-optimal. Finally, we propose an online learning approach to implement the adaptive \u03bb-confident policy and verify its efficacy in case studies about the Cart-Pole problem and a real-world electric vehicle (EV) charging problem with data bias due to COVID-19.
\r\n\r\nAggregators have emerged as crucial tools for the coordination of distributed, controllable loads. To be used effectively, an aggregator must be able to communicate the available flexibility of the loads they control, known as the aggregate flexibility to a system operator. However, most existing aggregate flexibility measures often are slow-timescale estimations and much less attention has been paid to real-time coordination between an aggregator and an operator. In the second part of this dissertation, we consider solving an online decision-making problem in a closed-loop system and present a design of real-time aggregate flexibility feedback, termed the maximum entropy feedback (MEF). In addition to deriving analytic properties of the MEF, combining learning and control, we show that it can be approximated using reinforcement learning and used as a penalty term in a novel control algorithm--the penalized predictive control (PPC) that enables efficient communication, fast computation, and lower costs. We illustrate the efficacy of the PPC using a dataset from an adaptive electric vehicle charging network and show that PPC outperforms classical MPC. We show that under certain regularity assumptions, the PPC is optimal. We illustrate the efficacy of the PPC using a dataset from an adaptive electric vehicle charging network and show that PPC outperforms classical model predictive control (MPC). In a theoretical perspective, a two-controller problem is formulated. A central controller chooses an action from a feasible set that is determined by time-varying and coupling constraints, which depend on all past actions and states. The central controller's goal is to minimize the cumulative cost; however, the controller has access to neither the feasible set nor the dynamics directly, which are determined by a remote local controller. Instead, the central controller receives only an aggregate summary of the feasibility information from the local controller, which does not know the system costs. We show that it is possible for an online algorithm using feasibility information to nearly match the dynamic regret of an online algorithm using perfect information whenever the feasible sets satisfy some criterion, which is satisfied by inventory and tracking constraints.
\r\n\r\nThe third part of this dissertation consists of examples of learning, inference, and data analysis methods for power system identification and electric charging. We present a power system identification problem with noisy nodal measurements and efficient algorithms, based on fundamental trade-offs between the number of measurements, the complexity of the graph class, and the probability of error. Next, we specifically consider prediction and unsupervised learning tasks in EV charging. We provide basic data analysis results of a public dataset released by Caltech and develop a novel iterative clustering method for classifying time series of EV charging rates.
" }, { "name": "Lucas, \u00c9owyn", "degree": "PhD", "year": "2023", "title": "Advancement of Asymmetric Bipolar Membranes for Tailoring Chemical Environments in Electrochemical Systems", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:02162023-233344819", "creators": [ { "name": { "family": "Lucas", "given": "\u00c9owyn" }, "id": "Lucas-\u00c9owyn", "orcid": "0000-0002-8743-5722", "display_name": "Lucas, \u00c9owyn" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Xiang", "given": "Chengxiang" }, "id": "Xiang-Chengxiang", "orcid": "0000-0002-1698-6754", "role": "member", "display_name": "Xiang, Chengxiang" }, { "name": { "family": "Manthiram", "given": "Karthish" }, "id": "Manthiram-Karthish", "orcid": "0000-0001-9260-3391", "role": "member", "display_name": "Manthiram, Karthish" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/jken-ty64", "abstract": "Under reverse bias, bipolar membranes (BPMs) enhance water dissociation (WD) at the junction between a cation exchange layer (CEL) and an anion exchange layer (AEL), often with additional improvement from an integrated WD catalyst. Recent research has shown promise for developing and implementing BPMs in renewable energy systems, such as carbon removal, water and CO\u2082 electrolysis, and energy storage. The economic feasibility of these carbon capture and conversion systems with incorporated BPMs, however, relies on BPMs to maintain stable operation at high current densities (>100 mA cm\u207b\u00b2) and low overpotentials. Existing commercial BPMs are limited to current densities of \u2264100 mA cm\u207b\u00b2 as water transport through the CEL and AEL cannot keep up with the increased rate of WD at the junction at higher current densities. In this work, we present a freestanding, high current density BPM (HCD-BPM) with a thin AEL (15 \u03bcm, PiperION 15R), a graphene oxide (GrOx) catalyst layer, and a mechanically supportive CEL (50 \u03bcm, Nafion 212) specifically designed to overcome water transport limitations. When tested under reverse bias in a custom electrodialysis cell with Luggin capillaries, this HCD-BPM demonstrates the lowest published overpotentials up to 1 A cm\u207b\u00b2. Furthermore, the HCD-BPM exhibits stabilities of >1000 hour at 80 mA cm\u207b\u00b2, >100 hours at 500 mA cm\u207b\u00b2, and >60 hours at 1 A cm\u207b\u00b2, Faradaic efficiencies for H\u207a and OH\u207b of >95%, and successful implementation into a multi-cell electrodialysis stack designed for integration into a DOC system. Additional characterization, such as SEM, Confocal microscopy, and titration, was performed to understand the structure and performance of the HCD-BPM. Additionally, the BPM was tested in forward bias to investigate its use for acid/base flow batteries. Overall, this thesis presents a novel BPM with record performance in multiple electrochemical systems that mitigate anthropogenic CO\u2082 emissions.
" }, { "name": "Martin, Conor Daniel", "degree": "PhD", "year": "2023", "title": "Experiments in Thermal Ignition: Influence of Natural Convection on Properties of Gaseous Explosions", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-192522565", "creators": [ { "name": { "family": "Martin", "given": "Conor Daniel" }, "id": "Martin-Conor-Daniel", "orcid": "0000-0003-2332-7383", "display_name": "Martin, Conor Daniel" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/twcf-m219", "abstract": "Explosion hazards exist in many industrial sectors including chemical processing, mining, nuclear power, and aviation. Thermal ignition is the name given to the particular case where the initiation energy is supplied via thermal heating of a gas. The critical conditions leading to thermal ignition are in general highly configuration dependent and require a broad set of experimentation to investigate the influence of wide ranging physical processes on ignition. To aid this effort the present work comprises three main experiments covering a range of thermal ignition hazards. First, a heated atmosphere test with fuel injection (ASTM-E659) was implemented to enable the study of heavy hydrocarbon fuels such as Jet A and multicomponent surrogates. This approach showed the existence of cool flame ignition modes near the ignition thresholds for most fuels. The autoignition temperature (AIT) of commodity Jet A was found to be reasonably reproducible by most alkane fuels including n-hexane. Multicomponent surrogates were also able to match the cool flame ignition regimes reasonably well.
\r\n\r\nNext, ignition using a vertical heated surface in a cold reactive atmosphere was studied in the laminar flow regime. The effects of dilution with nitrogen and reduced pressure were explored for n-hexane/oxygen/nitrogen mixtures. Results found a modest dependence of minimum ignition temperatures on pressure and nitrogen fraction however, with a significant reduction in explosion severity as measured by the maximum overpressure and transient duration. At sufficiently reduced oxygen concentrations, localized weakly propagating flames were found to form in the thermal layer near the surface and produce sustained puffing flame instabilities. One-dimensional flame simulations with detailed kinetics were conducted to supplement and aid in interpretation of the experimental measurements for diluted mixtures. Correlation of ignition thresholds were found to be possible using simplified flame properties and laminar natural convection boundary layer theory.
\r\n\r\nFinally, a novel experiment was designed to explore the effects of turbulent transition and confinement of large heated surfaces on ignition thresholds. Modeling of the energy balance for resistive heating showed that cylinders up to 36 in. long could be heated using modest power supplies. Six cylinder sizes of varying length were chosen based on this analysis to explore laminar, transitional, and turbulent flow regimes. A large scale flow visualization system was created to study these flow regimes and found that turbulent transition occurred for cylinders as small as 10 in. long for wall temperatures of 1000 K. A study of the transitional dependence on temperatures for large temperature difference (T = 555--1140 K), highly non-Boussinesq conditions found that the transitional Rayleigh number decreased by two orders of magnitude in this regime. The thermal layer thickness at the transition height was estimated in order to obtain a relevant length scale to the boundary layer transition problem. Using this a more consistent transition criteria was obtained (Ra using the thermal thickness length scale) and found to vary by only a factor of two in the high temperature cases studied.
\r\n\r\nThe implementation of these cylinders in ignition testing revealed that there was a strong influence of heating rate due to confinement. The use of absorption spectroscopy showed that for low heating rates the fuel was mostly consumed in low temperature reactions prior to or in place of rapid ignition. This resulted in larger ignition temperatures and weak flames which propagate only in the thermal boundary layer. This effect was explained as a consequence of reduced flow recirculation times due to confinement. A strong influence of turbulence was also found for ignition thresholds when compared with other data for ignition by vertical hot surfaces in the laminar regime. Turbulence was also found to strongly influence the explosion properties due to turbulent flame acceleration. This resulted in larger explosion pressures, shorter transients, and faster flames.
" }, { "name": "Matsuka, Kai", "degree": "PhD", "year": "2023", "title": "Vision-Based Navigation and Large-Scale Estimation for Spacecraft Swarms", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-235550987", "creators": [ { "name": { "family": "Matsuka", "given": "Kai" }, "id": "Matsuka-Kai", "orcid": "0000-0003-2116-9756", "display_name": "Matsuka, Kai" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "member", "display_name": "Watkins, Michael M." }, { "name": { "family": "Hadaegh", "given": "Fred" }, "id": "Fred-Hadaegh", "orcid": "0000-0002-0992-6323", "role": "member", "display_name": "Hadaegh, Fred" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "space" ], "doi": "10.7907/spf8-8p84", "abstract": "There has been dramatic growth in the space industry over the past 20 years. Around the same time, robotics and autonomy research has advanced significantly, resulting in a plethora of new mission concepts employing autonomy, such as on-orbit inspection, mission extension, space structure assembly, and orbital debris removal becoming within the realm of possibility. Two of the key autonomous technologies that are critical to the success of these missions are (1) advanced coordination of multi-agent systems and (2) robust vision-based navigation for on-orbit servicing in close proximity. However, there are challenges to simply applying the existing technology to space systems. First, there are domain-specific challenges that are unique to space, such as orbital mechanics and harsh lighting conditions. Second, even at a theoretical level, previous works in the controls and robotics literature are limited when applied to large-scale, locally coupled systems such as spacecraft swarms. To this end, this thesis develops novel algorithms for addressing these gaps.
\r\n\r\nIn the first part of the thesis, we present a decentralized, scalable algorithm for swarm localization, called the Decentralized Pose Estimation (DPE) algorithm. With the DPE algorithm, each spacecraft computes relative navigation estimates with respect to others in the swarm but achieves higher performance through the benefit of multi-agent coordination. The DPE algorithm considers both communication and relative sensing graphs and defines an observable local formation. Each spacecraft jointly localizes its local subset of spacecraft using direct and communicated measurements. Since the algorithm is local, the algorithm complexity does not grow with the number of spacecraft in the swarm. As part of the DPE, we present the Swarm Reference Frame Estimation (SRFE) algorithm, a distributed consensus algorithm to co-estimate a common Local-Vertical, Local-Horizontal frame. The DPE combined with the SRFE provides a scalable, fully-decentralized navigation solution that improves the estimation accuracy compared to when without multi-agent coordination. Numerical simulations and experiments using Caltech's robotic spacecraft simulators are presented to validate the effectiveness and scalability of the DPE algorithm. We show that DPE has much higher accuracy than the best possible estimate without any coordination, while simultaneously being scalable to an arbitrarily large number of agents.
\r\n\r\nIn the second part of the thesis, we propose a novel computer vision algorithm to track the pose of an unknown and uncooperative target using multiple decentralized observers. Vision-based pose determination of an unknown target is challenging due to factors such as lack of cooperative visual markers and harsh lighting conditions of space, and the problem is even harder for distributed observers. To address this challenge, we develop the algorithm called the Multi-Spacecraft Simultaneous Estimation of Pose and Shape algorithm or MSEPS. Within MSEPS, a team of chaser spacecraft, each equipped with a monocular camera, exchange information over a local network to jointly estimate the relative kinematic state of the target and its sparse shape landmarks. In this approach, each spacecraft processes its images and extracts its own set of visual keypoints in parallel. Then, the team uses the local network to jointly estimate the target pose and shape in a distributed fashion by applying the consensus algorithm over the inter-spacecraft communication links. To the best of the authors' knowledge, this is the first cooperative vision-based algorithm for estimating the pose and shape of a space object by means of an arbitrary number of spacecraft.\r\nWe validate our algorithm using simulations of relative orbits and observations captured by each chaser spacecraft and show the multiple observers successfully agree on a consistent estimate and track the target pose accurately.
\r\n\r\nIn the third part of the thesis, we develop some new simulation tools that bridge the gap between robotics and space technology. When developing robotics algorithms for on-orbit systems such as DPE and MSEPS, we identified a need for new simulation tools that tightly integrate robotics algorithms with high-fidelity models of space environments such as astrodynamics effects and visual conditions. To this end, we first develop a ROS2-compatible software interface for Basilisk, the open-source astrodynamics simulation software. This tool allows running Basilisk in parallel with ROS2 in real-time and translates messages between Basilisk modules and ROS2 modules, such that control algorithms implemented in ROS2 can interact with the high-fidelity dynamics within Basilisk in a closed-loop fashion. Second, we develop a ROS2-compatible camera simulation module that uses the Neural Radiance Fields (NeRF) to rapidly generate novel images. These synthetic images are used as inputs to validate the vision-based navigation algorithm in a closed-loop fashion. To validate these simulation tools, we also developed a set of autonomous algorithms for on-orbit inspection and use the simulated measurements as inputs to the algorithm. The real-time numerical simulations demonstrate that our tools can be integrated with autonomy algorithms implemented in ROS2 in a closed-loop fashion to validate the feasibility of the mission.
\r\n\r\nIn the process of addressing some lessons learned from DPE and MSEPS works, we identified that there is a gap in general frameworks for solving the optimal estimation problems for probabilistic inference of large-scale problems involving networked systems. This gap is not just applicable to spacecraft swarms, but also to a general class of large-scale, multi-agent problems in robotics and controls such as localization and mapping, wireless sensor networks, and electrical power grids. Therefore, in the fourth part of the thesis, we address this fundamental gap by developing novel algorithms for Distributed Factor Graph Optimization (DFGO) problems that arise in large-scale networked systems. We develop algorithms for both batch and real-time problems. First, for the batch DFGO problem, we derive a type of the Alternating Direction Method of Multipliers (ADMM) algorithm called the Local Consensus ADMM (LC-ADMM). LC-ADMM is fully localized; therefore, the computational effort, communication bandwidth, and memory for each agent scale like O(1) with respect to the network size. We establish two new theoretical results for LC-ADMM: (1) exponential convergence when the objective is strongly convex and has a Lipschitz continuous subdifferential, and (2) o(1/k) when the objective is convex and has a unique solution. We also show that LC-ADMM allows the use of non-quadratic loss functions, such as l1-norm and Huber loss. Second, we also develop the Incremental DFGO algorithm (iDFGO) for real-time problems by combining the ideas from LC-ADMM and the Bayes tree. To derive a time-scalable algorithm, we exploit the temporal sparsity of the real-time factor graph and the convergence of the augmented factors of LC-ADMM. The iDFGO algorithm incrementally recomputes estimates when new factors are added to the graph and is scalable with respect to both network size and time. We validate LC-ADMM and iDFGO in simulations with examples from multi-agent Simultaneous Localization and Mapping (SLAM) and power grids.
" }, { "name": "Moestopo, Widianto Putra", "degree": "PhD", "year": "2023", "title": "Design, Fabrication, and Mechanical Analysis of Intertwined and Frictional Micro-Architected Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06242022-190238579", "creators": [ { "name": { "family": "Moestopo", "given": "Widianto Putra" }, "id": "Moestopo-Widianto-Putra", "orcid": "0000-0002-7617-4280", "display_name": "Moestopo, Widianto Putra" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "chair", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/ycqd-1f27", "abstract": "Natural biomaterials, e.g., shells, bone, and wood, are typically comprised of hard and soft constituent materials that are hierarchically ordered to achieve mechanical resilience, light weight, and multifunctionality. Advanced fabrication techniques have enabled the creation of precisely architected materials with exceptional mechanical properties unattainable by their constituent materials, yet they are often designed with fully interconnected structural members whose junctions are detrimental to their performance because they serve as stress concentrations for damage accumulation and lower mechanical resilience. Most studies have also focused on understanding the stretching, bending, and buckling of the structural members, while explorations toward contact interactions within structural members remain limited. We address these challenges by (i) introducing a new three-dimensional (3D) hierarchical architecture in which fibers are interwoven to construct effective beams, (ii) introducing the concept of knots into the hierarchical architecture framework, and (iii) developing a model to study the effects of structural element length scale on the energy dissipation capability of a frictional architected material.
\r\n\r\nWe first explore the effective lattice response of hierarchical woven microlattices, and we demonstrate the superior ability of woven architectures to achieve high tensile and compressive strains via smooth reconfiguration of woven microfibers in the effective beams and junctions without failure events. We study how fiber topology and constituent materials influence the mechanical behaviors of hierarchical intertwined structures, and we compare our results with theory. Our study reveals that knot topology allows a new regime of deformation capable of shape-retention, leading to increased absorbed energy and failure strain compared to structures with woven topology. Agreements between experimental results and a model for long overhand knots suggest that the model can aid the optimization of the mechanical performance of microwoven materials. We then adapt classical contact mechanics and adhesion models to explore the influence of the size of structural elements in a frictional architected material on its energy dissipation capability. Our model shows that the energy dissipation capability of our frictional architected material can be significantly increased when it is scaled down from the mm-scale to the sub-micron length scale.
\r\n\r\nOur woven hierarchical design offers a pathway to make traditionally stiff and brittle materials more deformable and introduces a new building block for 3D architected materials with complex nonlinear mechanics. The unique tightening mechanism introduced by knotted topology unlocks new ways to create shape-reconfigurable, highly extensible, and extremely energy-absorbing bulk, 3D architected materials with mechanical properties that can be tuned not only by their geometries and bulk properties, but also by the surface interactions experienced by the structural elements. Lastly, our modeling work shows the potential of creating highly dissipative architected materials with shape-retention capability via carefully architected structural elements.
" }, { "name": "Mohamed Soliman, Ahmed Mohamed", "degree": "PhD", "year": "2023", "title": "BICEP Array Detectors and Instrumentation at 30/40 GHz: Design, Performance, and Deployment to the South Pole for Constraining Primordial Gravitational Waves", "advisor": "Bock, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232023-174453276", "creators": [ { "name": { "family": "Mohamed Soliman", "given": "Ahmed Mohamed" }, "id": "Mohamed-Soliman-Ahmed-Mohamed", "orcid": "0009-0007-9335-1326", "display_name": "Mohamed Soliman, Ahmed Mohamed" } ], "advisors": [ { "name": { "family": "Bock", "given": "James J." }, "id": "Bock-J-J", "orcid": "0000-0002-5710-5212", "role": "advisor", "display_name": "Bock, James J." } ], "committee": [ { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "orcid": "0000-0002-1098-7174", "role": "chair", "display_name": "Golwala, Sunil" }, { "name": { "family": "Barish", "given": "Barry C." }, "id": "Barish-B-C", "orcid": "0000-0001-6386-7371", "role": "member", "display_name": "Barish, Barry C." }, { "name": { "family": "O'Brient", "given": "Roger" }, "id": "O'Brient-Roger", "orcid": "0000-0002-4987-6375", "role": "member", "display_name": "O'Brient, Roger" }, { "name": { "family": "Bock", "given": "James J." }, "id": "Bock-J-J", "orcid": "0000-0002-5710-5212", "role": "member", "display_name": "Bock, James J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/srdx-w019", "abstract": "The discovery of the Cosmic Microwave Background (CMB) in the 1960s has provided strong observational evidence for the Big Bang cosmological model to describe the origin and evolution of the universe. The theory of cosmic inflation was developed in the 1980s to account for the initial density perturbations by a period of exponential expansion in the early Universe to solve the horizon, flatness and monopole problems. Many inflation models predict potentially detectable primordial gravitational-waves (PGWs) background that imprint a B-mode polarization pattern in the CMB. The amplitude of the inflationary B-mode polarization depends on the energy scale of inflation and is parameterized by the tensor-to-scalar ratio r. The detection of a B-mode pattern would open a new window to probe the energy scale at the beginning of time when the universe was a mere fraction of a second old after the Big Bang.
\r\n\r\nThe BICEP/Keck collaboration is building a series of experiments located at the Amundsen-Scott South Pole Station to map the polarization of the CMB at degree angular scales using small-aperture telescopes. Our latest BICEP/Keck publications use data collected through 2018 and report the strongest constraints r0.05 < 0.036 at 95% confidence. The current sensitivity on r is limited by the variance from the gravitational lensing. BICEP/Keck is starting a collaboration with the South Pole Telescope (SPT) team to develop delensing techniques to improve future constraints on r. Characterizing Galactic foregrounds, especially synchrotron emission, remains a priority in order to improve constraints as statistical sensitivity continues to improve. The motivation for this thesis is to develop a highly sensitive receiver at 30 and 40 GHz, at frequencies where the synchrotron foreground dominates. BICEP Array represents the latest phase in the BICEP/Keck experiments, and will map the polarization of the CMB at 30/40, 95, 150, and 220/270 GHz. BICEP Array will search for PGWs with unprecedented sensitivity levels on r by characterizing and removing Galactic synchrotron and dust emission from our maps of the CMB.
\r\n\r\nMy PhD thesis focuses on the technology development for high sensitivity detectors and instrumentation to successfully deploy the first BICEP Array receiver at 30 GHz and 40 GHz to the South Pole in order to constrain the Galactic synchrotron foreground. My dissertation presents the receiver design and performance. I will first explain the engineering design principles, the fabrication and a laboratory demonstration of single-color antenna-coupled Transition Edge Sensor (TES) bolometers. Secondly, I will discuss the design and demonstration of dual-color detectors at 30 and 40 GHz that gain receiver sensitivity by increasing the optical throughput and bandwidth of each pixel. I also developed microstrip diplexer circuits that divide the detector bandwidth into two CMB observing channels. I optimized this approach to design the dual-color bowtie-coupled detector at 90/150 GHz. Thirdly, I will introduce a new wide-band corrugated focal plane module design to minimize the beam mismatch systematic at 30 and 40 GHz bands simultaneously. Our receivers map polarization of the CMB by taking the difference between co-located and orthogonally polarized pair of detectors. Polarized beam difference measurements show a differential beam response due to a shift between the polarization beam centers within a pixel due to an electromagnetic interaction with the focal plane frame. The residual beams leak a temperature to polarization (T-P) in the CMB polarization maps and can produce a false B-mode signal that introduces non-negligible systematic errors for BICEP Array measurements to come with improved sensitivity. The wide-band design reduces this effect and associated systematic errors for 30 and 40 GHz receiver. I also developed a new single-band corrugated focal plane module design for 150 GHz receiver. I performed laboratory measurements of these designs at 30, 40, and 150 GHz to verify the modelled response. The corrugation design will also be extended to the 220/270 GHz receiver. Fourthly, I will show my contributions to the receiver deployment, integration and calibration during the first 2020 observing season. The measurements will include the full optical characterization of the detector camera, in-lab and on-sky sensitivity at the South Pole. I will also describe the tests done to diagnose the challenges during the first season and new upgrades during the second 2022 season to improve the overall sensitivity of the receiver. Improved detector modules have been installed during the 2023 season to further boost the mapping speed for measuring the synchrotron foreground.
\r\n\r\nThe technologies developed for BICEP Array feed into capabilities for the upcoming CMB-S4 program. For example, I used similar methods to design a diplexer for a CMB-S4 dual-color feedhorn-coupled detector design at 90/150 GHz. I will also detail my work on the cryogenic implementation and test of an Adiabatic Demagnetization Refrigerator suitable for demonstrating 100 mK CMB-S4 detector arrays in a prototype 95/150 GHz telescope planned to observe on the BICEP Array.
" }, { "name": "O'Connell, Michael Thomas", "degree": "PhD", "year": "2023", "title": "Methods for Robust Learning-Based Control", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072023-134620248", "creators": [ { "name": { "family": "O'Connell", "given": "Michael Thomas" }, "id": "O'Connell-Michael-Thomas", "orcid": "0000-0001-6681-8823", "display_name": "O'Connell, Michael Thomas" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "space" ], "doi": "10.7907/2xnc-t162", "abstract": "This thesis addresses the general problem of improving control, safety, and reliability of multi-rotor drones in various challenging conditions by introducing novel deep-learning-based approaches. These approaches are designed to tackle specific issues that multi-rotor drones face during operation, such as near-ground trajectory control, high-speed wind disturbances, actuation delays, and motor failures. The thesis is organized into four main chapters, plus an introduction and conclusion. Each of the main chapters focuses on a unique approach to address a particular challenge of deep-learning-based control methods. Chapter 2 presents Neural-Lander, a deep-learning-based robust nonlinear controller that significantly improves quadrotor control performance during landing by accounting for complex aerodynamic effects. This chapter addresses key challenges to incorporating learned residual dynamics into a control architecture, laying the groundwork for the subsequent chapters. Chapters 3 and 4 introduce Neural-Fly, a learning-based approach that uses Domain Adversarially Invariant Meta-Learning (DAIML) and adaptive control to enable rapid online learning and precise flight control under a wide range of wind conditions. Chapter 5 proposes a lightweight augmentation method that enhances trajectory tracking performance for UAVs by effectively compensating for motor dynamics and digital transport delays. This method is extensible to a range of control methods, including learning-based approaches. Chapter 6 explores a novel sparse failure identification method for detecting and compensating for motor failures in over-actuated UAVs, contributing to the development of robust fault detection and compensation strategies for a safer and more reliable operation. This method builds on the Neural-Fly online learning framework and extends it to handle a wider range of conditions, including complete actuator failures. Together, these chapters address key challenges in safe and reliable learning-based control and demonstrate the potential of deep-learning-based control methods.
" }, { "name": "Ocegueda, Eric", "degree": "PhD", "year": "2023", "title": "Physics-Based and Data-Driven Computational Models of Inelastic Deformations", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312023-212652388", "creators": [ { "name": { "family": "Ocegueda", "given": "Eric" }, "id": "Ocegueda-Eric", "orcid": "0000-0001-7845-6890", "display_name": "Ocegueda, Eric" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/3gqd-zp93", "abstract": "Crystalline materials inevitably exhibit inelastic deformation when applied to large enough loads. The behavior in this inelastic regime is a coupling of physics across several length scales: from initiating as defects at the atomic scale, interacting with crystal defects, and finally spanning multiple grains and influencing macroscopic stress behavior. These length-scale interactions make predicting material response an open challenge and an avenue for leveraging microscale physics for material design. This thesis examines developing physics-based and data-driven computational models to capture complex inelastic behavior at appropriate length scales.
\r\n\r\nFirst, we present a mesoscale model for capturing deformation twinning physics at the polycrystal scale. Mechanical twinning is a form of inelastic deformation observed in low-symmetry crystals, such as magnesium and other hexagonal close-packed (hcp) metals. Twinning, unlike slip, forms as bands collectively across grains with complex local morphology propagating into bulk behavior, drastically affecting strength and ductility. We, thus, propose a model where twinning is treated using a phase-field approach, while dislocation slip is considered using crystal plasticity. Lattice reorientation, length-scale effects, interactions between dislocations and twin boundaries, and twin and slip interactions with grain boundaries are all carefully considered. We first outline the model and its implementation using a novel approach of accelerated computational micromechanics in a two-dimensional, single twin-slip system, polycrystal case to demonstrate its capabilities. Finally, we consider multiple twin-slip systems and conduct three-dimensional simulations of polycrystalline magnesium. We summarize the insights gained from these studies and the implications on the macroscale behavior of hcp materials.
\r\n\r\nThe second part of the thesis focuses on data-driven models for capturing microscopic history-dependent phenomena for multiscale modeling applications. The multiscale modeling framework has seen increased usage over the last few decades for its ability to capture complex material behavior over a range of time/length scales by solving a macroscale problem directly with a constitutive relation defined implicitly by the solution of a microscale problem. However, this implementation is computationally expensive -- needing to solve a microscale problem at each point and time of the macroscopic calculation. In this study, we examine the use of machine learning by utilizing data generated through repeated solutions of a microscale problem to: (i) gain insights into the history dependent macroscopic internal variables that govern the response and (ii) create a computationally efficient surrogate. We do so by introducing a recurrent neural operator, which can provide accurate approximations of the stress response and insights into the physics of the macroscopic problem. We illustrate these capabilities on a laminate composite and polycrystal made of elasto-viscoplastic materials, summarize insights on the learned internal variables, and accuracy of stress predictions.
" }, { "name": "Oshima, Emile Kazuo", "degree": "PhD", "year": "2023", "title": "Experimental Studies of Flow Control Techniques for Future Aircraft", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:02042023-015312785", "creators": [ { "name": { "family": "Oshima", "given": "Emile Kazuo" }, "id": "Oshima-Emile-Kazuo", "orcid": "0000-0002-1689-3726", "display_name": "Oshima, Emile Kazuo" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "member", "display_name": "Bae, H. Jane" }, { "name": { "family": "Wygnanski", "given": "Israel J." }, "id": "Wygnanski-I-J", "orcid": "0009-0001-5711-7029", "role": "member", "display_name": "Wygnanski, Israel J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/fpcj-w268", "abstract": "From the signing of the Paris Agreement to the COVID-19 outbreak, the past decade has truly challenged the aviation industry to adapt. New technologies need to be developed constantly to meet the increasing commercial and defense demands for more efficient, quiet, safe, and agile aircraft. To keep up with these rapidly changing times, an approach that marries a fundamental understanding of aerodynamics with systems design and optimization is necessary. This thesis explores two promising concepts for controlling flow over next-generation aircraft: active control on a swept wing for airplane applications, and passive control on a rotating blade for drone applications. In each, force measurements are combined with advanced flow visualization techniques to create a research framework that is both data-driven and physics-informed.
\r\n\r\nIn Part I, a comprehensive wind tunnel campaign is carried out on a swept wing model of modular geometry equipped with an array of sweeping jet actuators, which have demonstrated tremendous promise for flow control authority in both laboratory settings and full-scale flight tests. The flow physics and performance of the wing is investigated first without actuation, revealing separation behaviors at both the leading and trailing edges that are crucial to consider when flow control is applied. This paves the way for an optimization study in a newly proposed framework that relies on fluid power coefficients rather than the momentum coefficient that has been the accepted parameter of choice for characterizing blowing systems over the past seven decades of active flow control research.
\r\n\r\nPart II explores the feasibility of a \"prop-shroud\" concept for small-scale aerial vehicles, in which the shroud is directly attached to the blade tips and thus co-rotates with the propeller. Such a configuration has the potential to provide the various aerodynamic and engineering benefits of a shrouded propeller without the associated costs and complexities of its installation. The hover efficiency of a prop-shroud is shown to be comparable to commercially available drone propellers, even without a rigorous optimization of its geometry. The effect of the co-rotating shroud is then analyzed in detail on the time-averaged, phase-averaged, and unsteady features of the flow field. A model based on vortex formation time is developed, laying out a foundation for future research and understanding.
" }, { "name": "Palmer, Emily Hope", "degree": "PhD", "year": "2023", "title": "Locomotory Control Algorithms and Their Neuronal Implementation in Drosophila melanogaster", "advisor": "Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192023-015643241", "creators": [ { "name": { "family": "Palmer", "given": "Emily Hope" }, "id": "Palmer-Emily-Hope", "orcid": "0009-0006-8370-4709", "display_name": "Palmer, Emily Hope" } ], "advisors": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/yyjd-a554", "abstract": "Scientists and engineers alike have long looked to animals in their pursuit of understanding the natural world and how best to interact with it. While researchers have looked across diverse classes, insects have been extensively studied for their rich diversity of life histories and abilities to perform at spatial and temporal scales difficult for engineered systems. Within insects, the fruit fly, Drosophila melanogaster, is a particularly well-studied organism because of its experimental tractability and status as a genetic model organism, providing both detailed descriptions of a broad suite of behaviors and access to and control over specific sets of tissue. In this work, we make use of these tools to study two behaviors in Drosophila, local search, the behavior in which walking flies will search the area around a food site in search of other food sources nearby, and the optomotor response, wherein they will stabilize in response to visual motion during flight. In these studies, we will use modern techniques from both biology and engineering, to exhaustively characterize and describe the observed behaviors and attempt to untangle the underlying algorithms and their neuronal implementation.
\r\n\r\nFirst, we explore the algorithmic structure of local search in fruit flies. When flies encounter a piece of food, they will often perform walking searches nearby; as food tends to be patchy in natural settings, searches may allow flies to locate other food sites in the area. We induce local search using optogenetic stimulation of sugar-sensing neurons and constrain the flies to a dark, annular arena. These experimental details result in a simplified behavior, as the fly has access to a limited sensory environment, so that the search can be interpreted as an example of idiothetic path integration, and the search itself is one-dimensionalized and therefore more easily analyzed. Our experiments, in tandem with complementary modeling using a state transition diagram formalization of the behaviors, generate two principle findings. First, flies can integrate their location in two dimensions--after the optogenetic activation is disabled and the flies can no longer receive the food stimulus, they will continue to search over the former food site even after completing a full revolution of the annular arena. Second, when multiple food sites are present, they search over a center of the food sites, rather than over one distinct food site. These results both provide insights into the algorithmic structure of local search and an experimental and descriptive paradigm for further inquiries into the behavior.
\r\n\r\nSecond, we investigate the role of a population of neurons, the DNg02s, in the optomotor response. In response to visual patterns of wide-field motion, such that the entire world is moving in the fly-centric reference frame, the animal will attempt to steer to cancel the visual motion, as the most parsimonious explanation of the motion is that the fly itself is moving in the global reference frame. We demonstrate that the DNg02 neurons are a required component in the neural circuitry underlying the optomotor response, but that they are insufficient to induce steering behaviors. We conclude with a set of models that fully recapitulate the collected dataset. With current techniques, distinguishing between the two possible models of the downstream connectivity from the DNg02s to the motor neurons associated with wing motor output is not possible. However, as new datasets become available, particularly complete connectomes of the Drosophila nervous system, the neuronal pathways from the DNg02s to the motor systems may be elucidated.
" }, { "name": "Phelan, Megan Elisabeth", "degree": "PhD", "year": "2023", "title": "Optimization of Photovoltaic Performance for Luminescent Solar Concentrator Systems", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:02232023-035632589", "creators": [ { "name": { "family": "Phelan", "given": "Megan Elisabeth" }, "id": "Phelan-Megan-Elisabeth", "orcid": "0000-0002-4968-7128", "display_name": "Phelan, Megan Elisabeth" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Nuzzo", "given": "Ralph G." }, "id": "Nuzzo-Ralph-G", "orcid": "0000-0003-2310-2045", "role": "member", "display_name": "Nuzzo, Ralph G." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/aqhb-s069", "abstract": "The luminescent solar concentrator (LSC), an emerging photovoltaic (PV) technology with myriad potential application areas, could help further spur global solar adoption. At its core, an LSC absorbs and down-shifts incident irradiation via luminophores, and then redirects the emitted photoluminescence through a dielectric waveguide towards small-area PV cells. Given this design, an LSC describes a planar concentrating technology that i) maintains low system costs by using small amounts of high-efficiency PV material and ii) enables concentration of both direct and diffuse irradiation. The underlying structure of an LSC\u2014including flexibility, material versatility, and variable transparency\u2014facilitates application areas that span utility, building integrated, and space-based solar power.
\r\n\r\nThis thesis explores the optimization of LSC systems, measured based on photovoltaic performance, across each application area. We begin by examining photovoltaic device considerations for LSC integration, including device form factor, luminophore pairing, and microcell fabrication. We outline ideal component parameters for optimal LSC performance and fabricate a silicon heterojunction microcell with a record VOC of 588mV. Next, we design and fabricate single-junction LSCs for two application areas: building-integrated PV and space-based solar power. Through simulations and technoeconomic analyses, we find that such designs are able to achieve 7% efficiency with a forecasted cost as low as 2.22 $/W for the building-integrated application, and a specific power up to 11.55 kW/kg with an associated cost as low as 0.24 $/W for the space-based application. Finally, we investigate the potential to combine luminescent concentration with conventional solar technologies, including each a silicon subcell and geometric concentrators. We demonstrate that hybridization of luminescent concentrators with certain conventional designs has the potential to boost PV performance in both direct and diffuse lighting.
\r\n\r\nWe conclude by investigating future directions for LSCs, including improved overall system performance, as well as next-generation designs for each building-integrated and space-based applications.
" }, { "name": "Polski, Robert Michael", "degree": "PhD", "year": "2023", "title": "Electronic Correlations and Topology in Graphene Moir\u00e9 Multilayers and InAs/GaSb-Derivative Systems", "advisor": "Nadj-Perge, Stevan", "url": "https://resolver.caltech.edu/CaltechTHESIS:01052023-230400021", "creators": [ { "name": { "family": "Polski", "given": "Robert Michael" }, "id": "Polski-Robert-Michael", "orcid": "0000-0003-0887-8099", "display_name": "Polski, Robert Michael" } ], "advisors": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "advisor", "display_name": "Nadj-Perge, Stevan" } ], "committee": [ { "name": { "family": "Alicea", "given": "Jason F." }, "id": "Alicea-J", "orcid": "0000-0001-9979-3423", "role": "chair", "display_name": "Alicea, Jason F." }, { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "member", "display_name": "Hsieh, David" }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/yhws-0f08", "abstract": "Twisted bilayer graphene (TBG) near the magic angle exhibits a wide variety of correlated and topological phases such as superconductivity, correlated insulators, and orbital ferromagnetism. We show using electrical transport measurements that adding a layer of tungsten diselenide in proximity to twisted bilayer graphene stabilizes superconductivity to twist angles significantly below the magic angle despite the disappearance of correlated insulators and insulators at full moir\u00e9 filling. These findings--along with our report of a relationship between superconductivity and symmetry breaking Fermi surface reconstruction--suggest constraints on theories of the origin of superconductivity in TBG. In the context of this TBG-tungsten diselenide system, we study how the correlated phases evolve over a wide twist angle range and classify them into a hierarchy based on where they occur relative to the magic angle (or where bands have been maximally flattened). While effects such as orbital ferromagnetism near one electron per moir\u00e9 unit cell and gapped correlated insulators only exist in close proximity to the magic angle, superconductivity and high-temperature cascade transitions survive in a wider twist angle range.
\r\n\r\nWe also analyze the structures of twisted trilayer, quadrilayer, and pentalayer graphene (and all proximitized to tungsten diselenide) near their respective theoretical magic angles, revealing robust electron- and hole-side superconductivity in each heterostructure. We additionally find previously unreported insulating states in twisted trilayer and quadrilayer graphene along with an enlarged filling range of superconductivity in pentalayer. Our studies on twisted graphene multilayers beyond two layers allow us to generalize the correlated physics found in TBG and consider the role of the additional bands introduced.
\r\n\r\nIn the last part of this thesis, we measure the two-dimensional topological insulator candidate system InAs/GaSb with added stoichiometric impurities. Previous studies in pure InAs/GaSb structures have revealed low bulk resistivity and edge states that arise from trivial effects which can be easily mistaken for topological effects. Due, in part, to the strain effects of Indium impurities added to GaSb, our results show high bulk resistivity. We also, due to the wide gate-tunability in our devices, are able to measure the expected spin-orbit-split valence band structure. Our development of highly tunable InAs/GaSb-derivative structures paves the way for another look at two-dimensional topological insulator behavior in these systems and for their integration into superconducting devices.
" }, { "name": "Poremba, Alexander Mario", "degree": "PhD", "year": "2023", "title": "Revocable Cryptography in a Quantum World", "advisor": "Vidick, Thomas G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-202038500", "creators": [ { "name": { "family": "Poremba", "given": "Alexander Mario" }, "id": "Poremba-Alexander-Mario", "orcid": "0000-0002-7330-1539", "display_name": "Poremba, Alexander Mario" } ], "advisors": [ { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "advisor", "display_name": "Vidick, Thomas G." } ], "committee": [ { "name": { "family": "Mahadev", "given": "Urmila" }, "id": "Mahadev-Urmila", "role": "chair", "display_name": "Mahadev, Urmila" }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "member", "display_name": "Preskill, John P." }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "orcid": "0000-0002-6390-9401", "role": "member", "display_name": "Umans, Christopher M." }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "member", "display_name": "Vidick, Thomas G." } ], "option_major": [ "compsci" ], "doi": "10.7907/y62s-j417", "abstract": "Quantum cryptography leverages unique features of quantum mechanics in order to construct cryptographic primitives which are oftentimes impossible for digital computers. Cryptographic applications of quantum computers therefore have the potential for useful quantum advantage---entirely without computational speed-ups. Can we use the power of quantum states to address fundamental limitations in the world of classical cryptography, such as the intricate problem of ``revoking'' information from an untrusted party? This thesis undertakes a systematic study of how to delegate and revoke privileges in a world in which quantum computers become widely available. As part of a single framework we call revocable cryptography, we show how to revoke programs, encrypted data, and even cryptographic keys under standard assumptions.
\r\n\r\nIn the first part of this thesis, we focus on the following question: can we use the no-cloning principle of quantum mechanics and encode a program in such a way that it can be evaluated, yet it cannot be pirated? Naturally, we would also like to ensure that, once the program is ``returned,'' the recipient loses its ability to evaluate it. While this quantum notion of secure software leasing (SSL) was shown to be impossible for general programs by Ananth and La Placa (Eurocrypt 2021), their work left open the possibility that it is achievable for more primitive classes of programs. We construct an SSL scheme for a large class of evasive functions known as compute-and-compare programs---a more expressive generalization of point functions. Our scheme can be instantiated with any cryptographic hash function, and we prove its security in the quantum random oracle model. As a complementary result, we also construct a quantum copy-protection scheme for multi-bit point functions, which achieves a related but stronger notion of software protection previously introduced by Aaronson (CCC 2009).
\r\n\r\nIn the second part of this thesis, we ask: is it possible to provably delete information by leveraging the laws of quantum mechanics? We revisit a cryptographic notion called certified deletion, which was proposed by Broadbent and Islam (TCC 2020). While this remarkable notion allows a classical verifier to be convinced that quantum ciphertext has been deleted by an untrusted party, it offers no additional layer of functionality. We use Gaussian superpositions over lattices to construct the first fully homomorphic encryption scheme with certified deletion -- a protocol which allows an untrusted quantum server to compute on encrypted data and to also prove data deletion to a client. Our scheme has the desirable property that verification of a deletion certificate is public; meaning anyone can verify whether deletion has taken place. Assuming the quantum subexponential hardness of the learning with errors problem (Regev, STOC 2005), we can prove that our scheme achieves a particularly strong information-theoretic deletion guarantee; namely, once a valid deletion certificate is presented, the plaintext remains hidden even if the adversary is subsequently allowed to run in unbounded time.
\r\n\r\nIn the final part of this thesis, we ask: is it possible to revoke a crytographic key by using the power of quantum information? We give an affirmative answer to this question and design cryptosystems with key-revocation capabilities; specifically, we consider schemes with the guarantee that, once the secret key (represented as a quantum state) is successfully revoked from a user, they no longer have the ability to perform the same functionality as before. We define and construct several fundamental cryptographic primitives with key-revocation capabilities, namely pseudorandom functions, secret-key and public-key encryption, and even fully homomorphic encryption, assuming the subexponential hardness of the learning with errors problem. Central to all our constructions is our approach for making the Dual-Regev encryption scheme (Gentry, Peikert and Vaikuntanathan, STOC 2008) revocable.
" }, { "name": "Quine, Cullen Mackenzie", "degree": "PhD", "year": "2023", "title": "Tunability of Gas Adsorption Enthalpies in Carbonaceous Materials for Energy-Related Applications", "advisor": "Fultz, Brent T.; Ahn, Channing C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292023-054311609", "creators": [ { "name": { "family": "Quine", "given": "Cullen Mackenzie" }, "id": "Quine-Cullen-Mackenzie", "orcid": "0000-0002-7301-0969", "display_name": "Quine, Cullen Mackenzie" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "co-advisor", "display_name": "Ahn, Channing C." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Stadie", "given": "Nicholas" }, "id": "Stadie-P-Nicholas", "orcid": "0000-0002-1139-7846", "role": "member", "display_name": "Stadie, Nicholas" }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "member", "display_name": "Ahn, Channing C." } ], "option_major": [ "matsci" ], "doi": "10.7907/r5ad-1j85", "abstract": "Carbonaceous materials provide a porous, high surface area framework for the adsorption of gases through physisorption. Physisorption operates through van der Waals forces, resulting in highly reversible, densified gas storage. The density of adsorbed gas species approaches the bulk liquid density, providing a method to increase the volumetric energy density of hydrogen and natural gas at conditions where the adsorbate is a non-liquid in the bulk phase. This dissertation explores the tunability of the strength of gas adsorption to surfaces of carbon adsorbents, known as the enthalpy of adsorption. Two methods are studied: modification of the surface atomic composition and microstructural changes to the carbon porosity. Applications are considered for both energy storage and carbon capture applications.
\r\n\r\nThe first chapter presents a brief overview of the energy storage field, with emphasis on non-conventional methods to store gases efficiently. Chapter 2 provides the thermodynamic and statistical mechanical derivations used throughout this work, and the assumptions that go into the models used to analyze adsorption data. Chapter 3 reports work on a copper-modified commercial carbon MSC-30 for hydrogen storage, which exhibits an activated dissociative chemisorption desorption feature around ambient temperature. Chapter 4 presents the densification of a novel architected carbon structure, zeolite-templated carbon, for adsorbed natural gas storage. Through the pelletization process, the pore morphology of the underlying adsorbent framework is compressed, resulting in increased adsorption enthalpies with applied pelletization pressure. Chapter 5 focuses on the tunability of pore structure through potassium hydroxide activation, and the resulting adsorption properties pertinent to carbon dioxide capture from a simulated flue-gas stream. The last chapter provides insight into the work as a whole and identifies areas of future work that would improve the fundamental understanding and broader impact of adsorbent materials.
" }, { "name": "Reddy, Narravula Harshavardhan", "degree": "PhD", "year": "2023", "title": "Folding and Dynamic Deployment of Ultralight Thin-Shell Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292023-160132013", "creators": [ { "name": { "family": "Reddy", "given": "Narravula Harshavardhan" }, "id": "Reddy-Narravula-Harshavardhan", "orcid": "0000-0003-3897-8162", "display_name": "Reddy, Narravula Harshavardhan" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/m7rd-6s86", "abstract": "Thin-shell structures are becoming increasingly popular for space missions due to their high stiffness-to-mass ratio, easy folding and coiling, and self-deployment using stored strain energy. Broadly, two deployment strategies exist: 1) controlled or deterministic, and 2) unconstrained. Controlled deployment involves carefully orchestrated events using control or guidance systems, while in unconstrained deployment, the structure is simply allowed to self-deploy with minimal guidance. Unconstrained deployment offers lighter deployment mechanisms and better packaging efficiency but the unpredictability of this process has been a significant obstacle to its adoption.
\r\n\r\nThis study focuses on demonstrating the predictability of unconstrained dynamic deployment of thin-shell structures, using the Caltech Space Solar Power Project (SSPP) structures as a case study. The Caltech SSPP uses composite triangular rollable and coilable longerons as the primary building blocks to create large bending-stiff structures. The specific objective is to improve the predictability and robustness of the unconstrained dynamic deployment of the Caltech SSPP structures. Deployment is influenced by the initial conditions and the interaction between the structure and the mechanism during the deployment. To understand these effects, high-fidelity numerical simulations are developed and validated against experiments. The study also examines the sensitivity of deployment characteristics to various design parameters and external influences to ensure the robustness of deployment.
\r\n\r\nThis research demonstrates that the interaction between the structure and the deployment mechanism must be minimal to ensure the predictability of deployment, as thin-shell structures can self-deploy using stored strain energy. This study's sensitivity analysis will inform the design of future SSPP deployment mechanisms and structures. Additionally, the numerical simulation techniques developed have broader applicability beyond this specific case study to any deployable thin-shell structure.
\r\n\r\nDue to the large aspect ratios of thin-shell structures, a very fine finite element mesh is required to model them accurately. A dense finite element mesh is also required to model the contact interactions between the structure and the rigid components of the deployment mechanism. As large spacecraft structures become increasingly complex, full-scale numerical modeling becomes impractical, necessitating the search for more computationally efficient finite element methods. In this study, NURBS-based isogeometric analysis is explored, and it is shown that it is not yet worth switching to NURBS-based elements for the analysis of thin-shell deployable structures. In addition, h-adaptive meshing for quadrilateral shell elements is investigated, and more efficient refinement indicators and solution mapping techniques for nonlinear analyses are proposed and their superior performance is demonstrated using a test case of quasi-static folding of a tape spring.
\r\n\r\nThis thesis fills a gap in the literature on unconstrained dynamic deployment of space structures, providing crucial insights and numerical modeling tools for further research. It establishes a knowledge and resource foundation to advance space structure design and promote more frequent use of unconstrained deployment, marking a pivotal contribution to the field and enabling safe and efficient space structure deployment. Furthermore, the study provides insights into more computationally efficient finite element methods, such as h-adaptive meshing. These insights are broadly applicable and can inform the design of future deployable structures beyond the tested cases.
" }, { "name": "Renn, Peter Ian James", "degree": "PhD", "year": "2023", "title": "Applied Machine Learning for Prediction and Control of Fluid Flows", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:02272023-230531120", "creators": [ { "name": { "family": "Renn", "given": "Peter Ian James" }, "id": "Renn-Peter-Ian-James", "orcid": "0000-0002-5735-3873", "display_name": "Renn, Peter Ian James" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Bae", "given": "H. Jane" }, "id": "Bae-H-J", "orcid": "0000-0001-6789-6209", "role": "chair", "display_name": "Bae, H. Jane" }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/smnv-tz73", "abstract": "Modern aerodynamic technologies such as unmanned aerial systems and horizontal axis wind turbines must regularly contend with forces from highly stochastic and turbulent atmospheric gusts. Conventional methods for modeling and controlling fluid flows are limited in their ability to mitigate these aerodynamic forces in real-time. By applying modern machine learning techniques in an experimental setting, this thesis demonstrates the utility of machine learning in addressing these important problems. We follow two complementary approaches towards this goal.
\r\n\r\nFirst, we find an end-to-end solution for control in a gusty environment with model-free reinforcement learning. We deploy state-of-the-art reinforcement learning algorithms on a generalized aerodynamic test-bed consisting of an airfoil with motorized trailing edge flaps. The system features embedded flow sensors, enabling the inclusion of flow measurements in state observations. We place this system in a highly irregular wake behind a bluff-body, dynamically mounted on elastic bands and therefore free to oscillate, and train reinforcement learning agents to minimize the net lifting force on the system by controlling the position of the trailing edge flaps. We find that model-free reinforcement learning agents can outperform basic linear controllers in this gusty, turbulent environment. We also show that augmenting state observations with flow measurements can lead to more consistent learning of the system dynamics.
\r\n\r\nNext, we explore Fourier neural operators (FNOs) as a method for forecasting the time evolution of turbulent fluid flows. FNOs are capable of learning underlying operator solutions to families of partial differential equations and can be evaluated in just milliseconds. We specifically focus on training FNOs with experimentally measured velocity fields of bluff body wakes in the subcritical regime. To the best of our knowledge, this is the first application of operator learning for fluid mechanics that features experimental measurements. We find that FNOs can accurately predict the evolution of these turbulent wakes even when trained with imperfect measurements. We then show that FNOs can quickly adapt to unseen conditions with minimal data and training through transfer learning. Finally, we consider the performance of FNOs over longer prediction horizons. This approach could enable real-time gust prediction capabilities and monitoring for applied aerodynamic systems.
" }, { "name": "Rosakis, Alexandros Yiannis", "degree": "PhD", "year": "2023", "title": "The Hemodynamics of Native and Surgical Aortic Valves with Regards to Wall Shear Stress and Residence Time", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:10032022-224522966", "creators": [ { "name": { "family": "Rosakis", "given": "Alexandros Yiannis" }, "id": "Rosakis-Alexandros-Yiannis", "orcid": "0000-0001-9170-1002", "display_name": "Rosakis, Alexandros Yiannis" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Koochesfahani", "given": "Manoochehr" }, "id": "Koochesfahani-Manoochehr", "orcid": "0000-0002-7001-8455", "role": "member", "display_name": "Koochesfahani, Manoochehr" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "medeng" ], "doi": "10.7907/exsa-nm30", "abstract": "Cardiovascular diseases are the leading causes of illness and death all around the world. The third most common cardiovascular disease is aortic stenosis (AS). AS is most commonly characterized as a stiffening of the native trileaflet aortic valve, which impedes blood flow into the aorta and puts extra stress on the heart. The aorta is the main artery that supplies oxygenated blood to the body. AS has been widely studied in the past. However, there has been little work in understanding the complex effects that non uniform stiffening of the aortic valve can have on the hemodynamics inside the aorta.\r\n\r\nThe most effective treatment for AS is to replace the stiffened valve with a prosthetic valve. Care must be taken to ensure that the replacement actually performs better hemodynamically. A major metric for prosthetic valve performance is the transvalvular pressure drop which is a measure of how much pressure, and energy, is lost as the heart pumps blood through the valve. Generally speaking, larger valves exhibit a smaller pressure drop because they restrict the flow to a lesser degree. This phenomenon has led to a trend for surgeons to implant the largest prosthetic valve possible, and in some cases, to expanding the aorta to fit even larger valves. However, there has been relatively little work done on determining the effects of valve oversizing on the blood flow inside the Aorta. \r\n\r\nThe aims of this study were two-fold. First, a model of AS was tested inside an in vitro aortic simulator in order to identify how different individual leaflet stiffnesses would affect blood flow. Digital particle image velocimetry (DPIV) was used to measure velocity profiles inside a model aorta. The DPIV results were used to estimate the wall shear stress and blood residence time. Our analysis suggests that leaflet asymmetry greatly affects the amount of WSS by vectoring the systolic jet and that stiffened leaflets have an increased residence time. This study indicates that valve leaflets with different stiffness conditions can have a more significant impact on wall shear stress than stenosis caused by the uniform increase in all three leaflets (and the subsequent increased systolic velocity) alone. Second, the experimental apparatus was used to test different prosthetic valve sizes and valve mounting methods in order to identify how they affected residence time inside the sinus bulge. Dye residence experiments and DPIV were used to measure fluid stasis in several different combinations of prosthetic valve sizes, sinus sizes, and valve mounting methods. Our results indicate that valve to sinus sizing and mounting method is very important and can lead to greatly increased residence time and thrombosis risk. We have also identified a metric that can predict the threshold at which valves become oversized." }, { "name": "Roy, Arkadev", "degree": "PhD", "year": "2023", "title": "Parametrically-Driven Nonlinear Optical Resonators and their Networks for Sensing and Computing", "advisor": "Marandi, Alireza", "url": "https://resolver.caltech.edu/CaltechTHESIS:03142023-213121023", "creators": [ { "name": { "family": "Roy", "given": "Arkadev" }, "id": "Roy-Arkadev", "orcid": "0000-0001-5659-8388", "display_name": "Roy, Arkadev" } ], "advisors": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "advisor", "display_name": "Marandi, Alireza" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/xsyc-6668", "abstract": "New physics and novel applications in various fields ranging from biology, and spectroscopy, to manipulation of quantum systems are driven by the availability of coherent light sources including frequency combs in the visible and mid-infrared spectral regimes. Nonlinear optical systems, that are parametrically driven by technologically mature near-infrared lasers, are leveraged in this regard to access challenging wavelengths where conventional lasers may be unavailable. It is of paramount importance to miniaturize these systems and replace the traditional bulky setups thereby paving the way for a plethora of applications. Optical parametric oscillators are among the most prominent examples of such nonlinear systems and beyond their indispensable usage as light sources (both classical and quantum) their unique non-equilibrium dynamics can endow a wealth of functionalities absent in their linear counterparts. These properties can be engineered and utilized for realizing highly sensitive sensors as well as special-purpose computing hardware that may outperform conventional digital computers. A network of these coupled parametric oscillators can be made to interact leading to emergent behaviors that are not expected from the individual constituents.
\r\n\r\nIn this work, we experimentally and theoretically study the dynamics of individual and coupled optical parametric oscillators towards sensing and computing applications. We explore a previously avoided regime of operation for generating ultra-short pulses from these parametrically driven nonlinear resonators that lead to extreme pulse compression. We engineer the nonlinear dynamics of these systems to realize all-optical spectral phase transitions (both first-order and second-order) that behave as highly-sensitive sensors. We show how these critical phenomena can be utilized to enhance the solution accuracy of physics-based solvers in finding optimum solutions to combinatorial optimization problems in the context of coherent Ising machines. We also realize optical parametric oscillators in integrated lithium-niobate nanophotonic platform and demonstrate a mid-infrared frequency comb source that is widely tunable over an octave accompanied by visible frequency comb generation. We develop a comprehensive description to investigate the noise properties of optical parametric oscillators that provide new insights into the phase noise behavior of optical parametric oscillators in their various operating regimes. Finally, we propose a system of parametrically driven resonators as a synthetic medium with highly reconfigurable interactions that can host a plethora of emergent phenomena ranging from topological behaviors to non-Hermitian dynamics. These networks of nonlinear resonators display intriguing dynamical properties in contrast to their static counterparts in condensed-matter physics with implications in quantum sensing and robust device functionality.
" }, { "name": "Sharma, Saransh", "degree": "PhD", "year": "2023", "title": "Low-Power and Miniaturized Medical Electronics for In-Vivo Localization and Tracking", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312023-034316442", "creators": [ { "name": { "family": "Sharma", "given": "Saransh" }, "id": "Sharma-Saransh", "orcid": "0000-0002-5052-4932", "display_name": "Sharma, Saransh" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "chair", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Traverso", "given": "Giovanni" }, "id": "Traverso-Giovanni", "orcid": "0000-0001-7851-4077", "role": "member", "display_name": "Traverso, Giovanni" } ], "option_major": [ "eleceng" ], "doi": "10.7907/xrw0-k789", "abstract": "Medical electronic devices are an integral part of the healthcare system today. Significant advances have been made over the past few decades to yield highly miniaturized and low-power medical devices that are suitable for implantable, ingestible, or wearable applications. A key feature of medical devices that is central to their use in many applications is the capability to locate them precisely inside the body, and quite a lot of research effort has been expended in this direction. Location sensing is crucial for several applications: tracking pills in the GI tract, navigation during precision surgeries, endovascular procedures, robotic and minimally invasive surgery, and targeted therapy. The current gold-standard solutions for these procedures include invasive techniques such as endoscopy, or procedures that require repeated use of potentially harmful X-ray radiation such as CT scans. These techniques also require repeated evaluation in a hospital setting and are not conducive for non-clinical environments. While there are several alternative non-ionizing methods for imaging and localization based on electromagnetic tracking, radio-frequency, ultrasound, and optical tracking, none of them are able to simultaneously achieve a high field-of-view of tracking, high spatiotemporal resolution, fully wireless operation and miniaturization of the sensing devices, and system scalability with the number of devices. In this dissertation, we present a radiation-free system for high-precision localization and tracking of miniaturized wireless devices in vivo, using harmless magnetic field gradients.
\r\n\r\nFirst, we demonstrate our system for precision surgery applications. We designed highly miniaturized, wireless and battery-less microdevices, capable of measuring and transmitting their local magnetic field. One such device can be attached to an implant inside the body and another to a surgical tool, such that both can simultaneously measure and communicate the magnetic field at their respective locations to an external receiver. The relative location of the two devices on a real-time display can enable precise surgical navigation without using X-ray fluoroscopy. The prototype device consists of a micro-chip fabricated in 65nm CMOS technology, a 3D magnetic sensor and an inductor-coil. The chip performs wireless power management, wireless bi-directional data-telemetry, and I2C communication with the sensor. Planar electromagnetic coils are designed for creating monotonically varying magnetic fields in the X, Y, and Z directions, resulting in field gradients that encode each spatial point with a unique magnetic field value. The concept of gradient-based spatial encoding is inspired by MRI. The system is tested in vitro to demonstrate a localization accuracy of <100\u00b5m in 3D, the highest reported to the best of our knowledge.
\r\n\r\nSecond, we demonstrate our system for localization and tracking of ingestible microdevices in the GI tract, which is valuable for the diagnosis and treatment of GI disorders. We designed highly miniaturized, low-power, and wireless ingestible devices to sense and transmit their local magnetic field as they travel through the GI tract. These devices consist of a 3D magnetic sensor, a Bluetooth microprocessor and a 2.4GHz Bluetooth antenna for wireless communication, all packaged into a 000-size capsule. The magnetic field sensed by the devices is created by using high-efficiency planar electromagnetic coils that encode each spatial point with a distinct magnetic field magnitude, allowing us to track the location of the devices unambiguously. The system functionality is demonstrated in vivo in large animals under different chronic conditions and disease models to show 3D localization and tracking in real time and in non-clinical settings, with mm-scale spatial resolution, and without using any X-ray radiation. This has the potential for significant clinical benefit for quantitative assessment of GI transit-time, motility disorders, constipation, incontinence, medication adherence monitoring, anatomic targeting for drug delivery, and targeted stimulation therapy.
\r\n\r\nThird, in order to further miniaturize the devices developed for the above two applications and to make them even more low-power, we present a monolithic 3D magnetic sensor in 65nm CMOS technology that measures <5mm\u00b2 in area and consumes 14.8\u00b5W in power while achieving <10\u03bcTrms noise. Our novel 3D magnetic sensor overcomes the challenges faced by traditional magnetic sensors by being fully CMOS compatible and achieving high sensitivity with only \u00b5W-level power, which is in sharp contrast with Hall and Fluxgate sensors. The sensor is comprised of three orthogonal and highly dense metal coils implemented in the 65nm node, which generate a voltage signal in response to AC magnetic fields by electromagnetic induction. The EMF voltage signal is processed by on-chip circuitry that performs low-noise amplification, filtering, peak detection, and 12-bit digitization. Though the sensor can be used for a variety of applications that require AC field sensing, it is particularly useful for biomedical applications\u2014tracking catheters and guidewires during endovascular procedures, minimally invasive surgeries, targeted radiotherapy, and for use as fiducial markers during preoperative planning. The proposed magnetic sensor is demonstrated for use in 3D tracking of catheters using the magnetic-field gradient-based spatial encoding scheme, and achieves 500\u00b5m of mean 3D localization accuracy.
" }, { "name": "Shen, Cheng", "degree": "PhD", "year": "2023", "title": "Computational Imaging for Phase Retrieval and Biomedical Applications", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272023-062623589", "creators": [ { "name": { "family": "Shen", "given": "Cheng" }, "id": "Shen-Cheng", "orcid": "0000-0001-7136-4715", "display_name": "Shen, Cheng" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Zernicka-Goetz", "given": "Magdalena" }, "id": "Zernicka-Goetz-M", "orcid": "0000-0002-7004-2471", "role": "member", "display_name": "Zernicka-Goetz, Magdalena" } ], "option_major": [ "eleceng" ], "doi": "10.7907/pahb-cx81", "abstract": "In conventional imaging, optimizing hardware is prioritized to enhance image quality directly. Digital signal processing is viewed as supplementary. Computational imaging intentionally distorts images through modulation schemes in illumination or sensing. Then its reconstruction algorithms extract desired object information from raw data afterwards. Co-designing hardware and algorithms reduces demands on hardware and achieves the same or even better image quality. Algorithm design is at the heart of computational imaging, with model-based inverse problem or data-driven deep learning methods as approaches. This thesis presents research work from both perspectives, with a primary focus on the phase retrieval issue in computational microscopy and the application of deep learning techniques to address biomedical imaging challenges.
\r\n\r\nThe first half of the thesis begins with Fourier ptychography, which was employed to overcome chromatic aberration problems in multispectral imaging. Then, we proposed a novel computational coherent imaging modality based on Kramers-Kronig relations, aiming to replace Fourier ptychography as a non-iterative method. While this approach showed promise, it lacks certain essential characteristics of the original Fourier ptychography. To address this limitation, we introduced two additional algorithms to form a whole package scheme. Through comprehensive evaluation, we demonstrated that the combined scheme outperforms Fourier ptychography in achieving high-resolution, large field-of-view, aberration-free coherent imaging.
\r\n\r\nThe second half of the thesis shifts focus to deep-learning-based methods. In one project, we optimized the scanning strategy and image processing pipeline of an epifluorescence microscope to address focus issues. Additionally, we leveraged deep-learning-based object detection models to automate cell analysis tasks. In another project, we predicted the polarity status of mouse embryos from bright field images using adapted deep learning models. These findings highlight the capability of computational imaging to automate labor-intensive processes, and even outperform humans in challenging tasks.
" }, { "name": "Shi, Guanya", "degree": "PhD", "year": "2023", "title": "Reliable Learning and Control in Dynamic Environments: Towards Unified Theory and Learned Robotic Agility", "advisor": "Chung, Soon-Jo; Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:08052022-231458463", "creators": [ { "name": { "family": "Shi", "given": "Guanya" }, "id": "Shi-Guanya", "orcid": "0000-0002-9075-3705", "display_name": "Shi, Guanya" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "co-advisor", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "co-advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cds" ], "doi": "10.7907/8rz4-7b35", "abstract": "Recent breathtaking advances in machine learning beckon to their applications in a wide range of real-world autonomous systems. However, for safety-critical settings such as agile robotic control in hazardous environments, we must confront several key challenges before widespread deployment. Most importantly, the learning system must interact with the rest of the autonomous system (e.g., highly nonlinear and non-stationary dynamics) in a way that safeguards against catastrophic failures with formal guarantees. In addition, from both computational and statistical standpoints, the learning system must incorporate prior knowledge for efficiency and generalizability.
\r\n\r\nThis thesis presents progress towards establishing a unified framework that fundamentally connects learning and control. First, Part I motivates the benefit and necessity of such a unified framework by the Neural-Control Family, a family of nonlinear deep-learning-based control methods with not only stability and robustness guarantees but also new capabilities in agile robotic control. Then Part II discusses three unifying interfaces between learning and control: (1) online meta-adaptive control, (2) competitive online optimization and control, and (3) online learning perspectives on model predictive control. All interfaces yield settings that jointly admit both learning-theoretic and control-theoretic guarantees.
" }, { "name": "Tamborini, Alessio", "degree": "PhD", "year": "2023", "title": "A Novel Approach to Cardiac Health Assessment Using a Redesign of the Brachial Cuff Device", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-001712615", "creators": [ { "name": { "family": "Tamborini", "given": "Alessio" }, "id": "Tamborini-Alessio", "orcid": "0000-0001-7651-3505", "display_name": "Tamborini, Alessio" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "medeng" ], "doi": "10.7907/rp22-me93", "abstract": "Current diagnostic methodologies in cardiology face large tradeoffs between procedure invasiveness and diagnostic reliability, ultimately requiring individuals to undergo cardiac catheterization for accurate diagnosis. Given the current societal burden of cardiovascular disease, there is a need for translational medical devices that bridge the accuracy gap between invasive and non-invasive measurements in the assessment of heart health. This thesis focuses on the development and validation of a high-resolution cuff-based system for assessment of central cardiovascular health.
\r\n\r\nTraditional pressure cuffs suffer low signal resolution when applied to non-invasive pulse waveform acquisition. In the first section of this thesis, we develop a cuff-based device with a pneumatic filter for high fidelity pulse waveform acquisition. This work discusses the design and functionality of the cuff-device, and investigates the repeatability of the cuff-based measurement. Furthermore, the derived mathematical model of the pneumatic filter is shown to have an equivalent behavior to an electrical low-pass filter inclusive of a time constant and a frequency response curve.
\r\n\r\nThe accuracy and reliability of the pulse waveform features from the cuff-device are evaluated with human study data. Firstly, an IRB study is performed at Caltech on a young and healthy population showing that the cuff-device data lies within a narrow distribution indicative of the healthy nature of the population. Secondly, data from a clinical trial collecting simultaneous invasive catheter, cuff, and ECG is analyzed. The first analysis compared waveform parameters from the cuff in sSBP hold pressure with simultaneous aortic catheter, showing strong correlations between the two measurement modalities for both magnitude and fluctuations thereof.
\r\n\r\nLastly, this work investigated the relationship between cuff-based parameters and left ventricular functions. We introduced a cuff-based method for extraction of the pressure-sound waveform, a pressure based surrogate of heart sounds. The results from this analysis showed that the pressure-sound features correlate with the strength of the left ventricular isovolumetric contraction and relaxation. Other important results from this work demonstrated the correlations between the heart-lung interactions in the left ventricle and cuff parameters: breathing fluctuations proportionally affect LV pressures and cuff sSBP waveform parameters. Overall these results support the accuracy and reliability of a cuff-based device for central cardiovascular health assessments.
" }, { "name": "Tan Teck Keng, Adrian", "degree": "PhD", "year": "2023", "title": "Digital Quantum Simulation of Physical Systems on Noisy Intermediate-Scale Quantum Computers", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05072023-204014466", "creators": [ { "name": { "family": "Tan Teck Keng", "given": "Adrian" }, "id": "Tan-Teck-Keng-Adrian", "orcid": "0000-0002-6660-0397", "display_name": "Tan Teck Keng, Adrian" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-G-K", "orcid": "0000-0001-8009-6038", "role": "member", "display_name": "Chan, Garnet K." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/wget-ws64", "abstract": "Current quantum computers are characterized as having the order of 5-100 qubits, with limited connectivity restricting two-qubit operations to nearest neighbors, and with too much noise to achieve fault-tolerance. Such devices, called noisy intermediate-scale quantum (NISQ) devices, have been demonstrated to have sufficient coherent lifetime to perform interesting experiments motivated by quantum information sciences. This motivates the question of whether such devices can be utilized to study physical systems commonly encountered in condensed matter and quantum chemistry.
\r\n\r\nIn this thesis, we address the open problem of identifying approaches to perform quantum simulations of physical systems on NISQ devices. We begin our study by considering the Hamiltonian ground state problem, a task routinely solved in numerical studies of materials and molecules. We provided a new quantum primitive, the quantum imaginary time evolution (QITE), that provides a practical approach to solve the Hamiltonian ground state problem. In addition, the QITE subroutine can be used in a Lanczos scheme to speed up convergence time.
\r\n \r\nNext, we consider the problem of performing finite temperature simulations and demonstrate how QITE can be used as a subroutine to develop scalable and feasible approaches to perform such calculations on a quantum computer. More specifically, we develop routines to obtain thermal averages by sampling minimally entangled thermal states, and also free energy by evaluating the partition function directly.
\r\n \r\nIn our final study, we consider the study of topological states of matter, which do not fit within the Landau paradigm of local order parameters associated with symmetry breaking, and have been shown to exhibit unusual behavior. We show how a specific class of topological states of matter, the symmetry-protected topological states can be feasibly realized on present NISQ devices and their unusual behavior experimentally validated. Our study provides a benchmark of capabilities of state-of-the-art NISQ devices to study these interesting phases of matter.
" }, { "name": "Tang, Ellande", "degree": "PhD", "year": "2023", "title": "Studies on Off-Nominal Rotor Aerodynamics for eVTOL Aircraft", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:12222022-065507477", "creators": [ { "name": { "family": "Tang", "given": "Ellande" }, "id": "Tang-Ellande", "orcid": "0000-0001-5933-4716", "display_name": "Tang, Ellande" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Tokumaru", "given": "Phil" }, "id": "Tokumaru-P", "role": "member", "display_name": "Tokumaru, Phil" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "mecheng" ], "doi": "10.7907/eytr-nd50", "abstract": "As electric Vertical Takeoff and Landing (eVTOL) aircraft become increasingly common, improved understanding of rotor aerodynamics in off-nominal conditions becomes ever more important. A better fundamental understanding of these effects can help inform vehicle design, leading to lower power consumption and improved performance. This thesis will cover a selection of topics to gain a better understanding of the expected rotor aerodynamics associated with use in this class of vehicle, as well as the development of tools to aid in the studies and an analysis of the impact of the effects.
\r\n\r\nTo consider special effects on a rotor in hover on such a vehicle, Chapter 2 is the study of obstructions in the upstream of a propeller, representing the effects of a wing or fuselage blocking a propeller\u2019s inlet. The next is the effect of forward flight on the forces produced by a rotor. Lifting rotors are often used in eVTOL aircraft as the craft transitions to forward flight, so a study of their performance in forward flight as well as a model are presented in Chapter 3. Having examined rotor-wing interactions in hover and isolated rotor performance in forward flight, the next step is to examine rotor-wing interactions in forward flight. Chapter 6 shows the design of an integrated test stand for studying the aerodynamic interactions between lifting propellers and a wing in low-speed, transitional forward flight, as well as the subsequent results.
\r\n\r\nThis thesis also describes the development and implementation of two tools to aid in the work herein. The first (Chapter 4) is a rapid, low-cost method of extracting the geometry of a propeller using photogrammetry which is subsequently used in simulations. The second (Chapter 5) is low-cost and accessible multi-axis force sensor used in the integrated test stand for propeller-wing interaction studies. To assess the impact of the findings, the experimental results and models developed are then taken into consideration by applying them to models of existing eVTOL aircraft in Chapter 7. The change in modeling of hover and transition performance is studied with and without the additional modeling.
" }, { "name": "Taylor, Andrew James", "degree": "PhD", "year": "2023", "title": "Robust Safety-Critical Control: A Lyapunov and Barrier Approach", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-032907616", "creators": [ { "name": { "family": "Taylor", "given": "Andrew James" }, "id": "Taylor-Andrew-James", "orcid": "0000-0002-5990-590X", "display_name": "Taylor, Andrew James" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "cds" ], "doi": "10.7907/bpht-by81", "abstract": "Accompanying the technological advances of the past decade has been the promise for widespread growth of autonomous systems into nearly all domains of human society, including manufacturing, transportation, and healthcare. At the same time, there have been several tragic failures that reveal potential risks with the expansion of autonomous systems into everyday life, and indicate that it is vital for safety to be accounted for in the design of control systems.
\r\n\r\nThis thesis seeks to develop a theory of robust safety-critical control for autonomous systems. This theory will be built upon the foundational tools of Control Lyapunov Functions (CLFs) and Control Barrier Functions (CBFs), which provide a powerful paradigm for the design of model-based safety-critical controllers. The dependence of CLF and CBF-based controllers on a system model makes them susceptible to modeling inaccuracies, potentially resulting in unsafe behavior when deploying these controllers on real-world systems.
\r\n\r\nIn this thesis I present methods for resolving four classes of model inaccuracies referred to as model error, disturbances, measurement error, and input sampling, which are commonly faced challenges when designing controllers for robotic systems. The proposed methods are unified by their shared use of CLFs and CBFs to produce controllers possessing rigorous and robust safety guarantees that can be demonstrated in simulation or experimentally. A hallmark of these methods is a focus on enabling control synthesis through convex optimization, which ensures that controllers can be efficiently computed on real-world robotic hardware platforms.
\r\n\r\nIn addressing model error, I consider both data-driven learning approaches and adaptive control approaches. I present three episodic learning frameworks that iteratively augment existing CLF and CBF-based controllers specified via convex optimization problems to improve the stability and safety properties of a system, which I demonstrate in simulation and experimentally. I also establish a relationship between the degradation of stability and safety properties with the magnitude of residual learning error through the perspective of Input-to-State Stability (ISS) and Input-to-State Safety (ISSf). Lastly, I develop an adaptive safety-critical control framework for systems with parametric model error through the notion of adaptive CBFs.
\r\n\r\nIn addressing disturbances, I resolve challenges in balancing performance and robustness with ISSf-based controllers through the notion of Tunable Input-to-State Safety (TISSf), which permits prioritizing robustness to disturbances only when safety requirements are close to being violated. I demonstrate the capabilities of TISSf-based control design experimentally on an autonomous semi-trailer truck system that is subject to input disturbances due to complex unmodeled actuator dynamics. Lastly, I develop a framework for achieving ISSf-like finite-time safety guarantees for discrete-time systems subject to stochastic disturbances through the use of CBFs and convex optimization.
\r\n\r\nIn addressing measurement error, I develop the notion of Measurement-Robust CBFs (MR-CBFs), which permit control synthesis through convex optimization in the presence of imperfect measurements. I demonstrate the capability of MR-CBFs on an experimental Segway system using a vision-based measurement system, validating the tractability of using controllers specified through increasingly complex classes of convex optimization problems on real-world systems. Lastly, I present an application of Preference Based Learning (PBL) in tuning the robustness parameters of a CBF-based controller, demonstrating the first use of PBL with CBFs and providing a tool for tuning the safety and performance of the robust controllers proposed in this thesis.
\r\n\r\nIn addressing input sampling, I consider both sampled-data and event-triggered paradigms for modeling input sampling. I provide a method for synthesizing CLF-based controllers for sampled-data systems by integrating feedback linearization with approximate discrete-time models, leading to a significant improvement over continuous-time CLF-based controllers implemented with input sampling. I then develop a framework for achieving safety of sampled-data systems through approximate discrete-time models through the notion of practical safety and Sampled-Data CBFs (SD-CBFs), which I demonstrate with convex-optimization based controllers in simulation. Lastly, I develop a method for event-triggered safety-critical control that uses ISSf to achieve safety while satisfying the requirement of a minimum interevent time.
\r\n\r\nCollectively, these contributions constitute a significant advance in the theory of robust safety-critical control by establishing a framework, unified by the use of CLFs and CBFs in conjunction with convex optimization, that addresses a wide class of challenges faced in the design of safety-critical control systems.
" }, { "name": "Tsukamoto, Hiroyasu", "degree": "PhD", "year": "2023", "title": "Contraction Theory for Robust Learning-Based Control: Toward Aerospace and Robotic Autonomy", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262023-141116640", "creators": [ { "name": { "family": "Tsukamoto", "given": "Hiroyasu" }, "id": "Tsukamoto-Hiroyasu", "orcid": "0000-0002-6337-266", "display_name": "Tsukamoto, Hiroyasu" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "chair", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Doyle", "given": "John C." }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John C." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Watkins", "given": "Michael M." }, "id": "Watkins-M-M", "role": "member", "display_name": "Watkins, Michael M." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "space" ], "doi": "10.7907/rznp-g568", "abstract": "Machine learning and AI have been used for achieving autonomy in various aerospace and robotic systems. In next-generation research tasks, which could involve highly nonlinear, complicated, and large-scale decision-making problems in safety-critical situations, however, the existing performance guarantees of black-box AI approaches may not be sufficiently powerful. This thesis gives a mathematical overview of contraction theory, with some practical examples drawn from joint projects with NASA JPL, for enjoying formal guarantees of nonlinear control theory even with the use of machine learning-based and data-driven methods. This is not to argue that these methods are always better than conventional approaches, but to provide formal tools to investigate their performance for further discussion, so we can design and operate truly autonomous aerospace and robotic systems safely, robustly, adaptively, and intelligently in real-time.
\r\n\r\nContraction theory is an analytical tool to study differential dynamics of a non-autonomous (i.e., time-varying) nonlinear system under a contraction metric defined with a uniformly positive definite matrix, the existence of which results in a necessary and sufficient characterization of incremental exponential stability of multiple solution trajectories with respect to each other. Its nonlinear stability analysis boils down to finding a suitable contraction metric that satisfies a stability condition expressed as a linear matrix inequality, resulting in many parallels drawn between linear systems theory and contraction theory for nonlinear systems. This yields much-needed safety and stability guarantees for neural network-based control and estimation schemes, without resorting to a more involved method of using uniform asymptotic stability for input-to-state stability. Such distinctive features permit the systematic construction of a contraction metric via convex optimization, thereby obtaining an explicit exponential bound on the distance between a time-varying target trajectory and solution trajectories perturbed externally due to disturbances and learning errors. The first two parts of this thesis are about a theoretical overview of contraction theory and its advantages, with an emphasis on deriving formal robustness and stability guarantees for deep learning-based 1) feedback control, 2) state estimation, 3) motion planning, 4) multi-agent collision avoidance and robust tracking augmentation, 5) adaptive control, 6) neural net-based system identification and control, for nonlinear systems perturbed externally by deterministic and stochastic disturbances. In particular, we provide a detailed review of techniques for finding contraction metrics and associated control and estimation laws using deep neural networks.
\r\n\r\nIn the third part of the thesis, we present several numerical simulations and empirical validation of our proposed approaches to assess the impact of our findings on realizing aerospace and robotic autonomy. We mainly focus on the two joint projects with NASA JPL: 1) Science-Infused Spacecraft Autonomy for Interstellar Object Exploration and 2) Constellation Autonomous Space Technology Demonstration of Orbital Reconfiguration (CASTOR), where we also perform hardware demonstrations of our methods using our thruster-based spacecraft simulators (M-STAR) and in high-conflict, distributed, intelligent UAV swarm reconfiguration with up to 20 UAVs (crazyflies).
" }, { "name": "Tucker, Maegan Lindsay", "degree": "PhD", "year": "2023", "title": "Enabling Robust and User-Customized Bipedal Locomotion on Lower-Body Assistive Devices via Hybrid System Theory and Preference-Based Learning", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292023-003436131", "creators": [ { "name": { "family": "Tucker", "given": "Maegan Lindsay" }, "id": "Tucker-Maegan-Lindsay", "orcid": "0000-0001-7363-6809", "display_name": "Tucker, Maegan Lindsay" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "mecheng" ], "doi": "10.7907/j9hk-xa17", "abstract": "Practical robotic assistive devices have the potential to transform many aspects of our society, from enabling locomotive autonomy to facilitating rehabilitation. However, as is typically the case when having autonomous systems interact closely with humans, one must simultaneously solve multiple grand challenges. My work focuses specifically on 1) leveraging hybrid system theory to achieve stable and robust walking that generalizes well across various human models and environmental conditions, and 2) developing an online learning strategy to customize the experimental walking for individual user comfort. The presented methodology is grounded in realizing lower-body exoskeleton locomotion for subjects with motor complete paraplegia, with extensions to other robotic applications. The contributions are broken down as follows.
\r\n\r\nFirst, by leveraging tools from nonlinear control theory, I propose techniques for systematically addressing locomotive robustness. These techniques include: using saltation matrices to generate robust gaits with experimental demonstrations on the Atalante lower-body exoskeleton; and developing an input-to-state stability perspective to certify robustness to uncertain impact events. Importantly, these methods aim to better understand the mathematical conditions underlying robust locomotion -- a necessary step towards realizing safe locomotion across varying human models and environmental conditions. Second, I develop a preference-based learning framework to explicitly optimize user comfort during exoskeleton locomotion (achieved using the aforementioned nonlinear control methodology) by learning directly from subjective feedback. This framework is implemented in real-world settings, including the clinical realization of user-preferred locomotion for two subjects with motor complete paraplegia.Third, the extensibility of this framework is demonstrated through three general robotic applications: tuning constraints of the gait generation optimization problem with demonstrations on a planar biped; tuning Lyapunov-based controller gains on a 3D biped; and tuning control barrier function parameters for performant yet safe exploration on a quadrupedal platform. Lastly, I discuss other relevant clinical considerations for lower-body assistive devices including how exoskeleton locomotion influences metabolic cost of transport, the study of latent factors underlying user-preferred walking, and embedding musculoskeletal models directly in the gait generation process.
" }, { "name": "Ubamanyu, Kanthasamy (Uba)", "degree": "PhD", "year": "2023", "title": "Time-Dependent Failure of Thin-Ply Composite Laminates", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312023-210300139", "creators": [ { "name": { "family": "Ubamanyu", "given": "Kanthasamy (Uba)" }, "id": "Ubamanyu-Kanthasamy-Uba", "orcid": "0000-0002-3679-6173", "display_name": "Ubamanyu, Kanthasamy (Uba)" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/x286-g488", "abstract": "The demand for larger and lighter structures for next-generation space designs necessitates the use of deployable structures. Among the materials that hold promise for such applications, thin-laminate fiber composites with thicknesses less than 200 μm stand out due to their strength-to-weight ratio, packaging efficiency, and ability to deploy using stored strain energy. However, designing deployable structures with thin-laminate composites is challenging as they need to be stiff enough to withstand loads during deployment while also having a small volume in the packaged configuration. Complicating matters further, stress relaxation of the polymer matrix within the composite during long-term stowage in response to an imposed curvature can drastically impact both the deployment process and the performance of the structure in its deployed state, even leading to catastrophic failure in the stowed configuration.
\r\n\r\nThis thesis presents a comprehensive study of the time-dependent failure behavior of thin-laminate fiber composites under bending, with a focus on a fundamental material-level understanding. The work is divided into three main parts. First, a novel test method called Flattening to Rupture (FTR) test was developed to effectively load composite coupons under long-term bending, enabling the measurement of time-dependent rupture and identification of the underlying failure mechanisms. Second, numerical simulations using the Abaqus/Standard finite element software were developed to understand the sequence of rupture events and the influence of several parameters that affect time-dependent rupture. Finally, a statistical approach was proposed to model the stochastic nature of the failure of thin composite laminates.
\r\n\r\nThe contributions of this thesis extend the understanding of the microscale failure mechanisms involved in the time-dependent failure of fiber composites. These new insights pave the way for the efficient design of tightly and safely packaged deployable structures under long-term loading. The findings of this research can be utilized to optimize the design and performance of deployable space structures made of fiber composites, leading to new technologies that can advance space exploration.
" }, { "name": "Wang, Linghui", "degree": "PhD", "year": "2023", "title": "Ion Transport in Temperature Sensitive Polyelectrolytes", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142023-192053975", "creators": [ { "name": { "family": "Wang", "given": "Linghui" }, "id": "Wang-Linghui", "orcid": "0000-0003-2492-7364", "display_name": "Wang, Linghui" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/zsat-9s73", "abstract": "Temperature sensors are widely employed and play a key role in many industries, such as automotive vehicles, medical devices, environmental monitoring, and process control. The state-of-the-art thermal sensing elements are made of rigid and costly inorganic materials, such as vanadium oxide and platinum. These materials have limitations for emerging applications such as wearable devices and prosthetic devices. Ideal temperature sensing materials for such applications need to be flexible, reliable under mechanical deformation, and suitable for large-area production. Electrical conductive polymers were found to be a promising solution because of their flexibility and solution processability. However, they often lag in temperature resolution compared to their inorganic counterparts.
\r\n \r\nA recent discovery revealed that the ionic conductivity of crosslinked pectin, a biopolymer extracted from plant cell walls, has a record-high temperature response. It is biocompatible, flexible when hydrated, and solution-processable, making it a strong candidate for wearable temperature sensing and conformal temperature mapping. However, open questions remain about the origin of its temperature sensitivity and the principles governing its ion transport. Furthermore, the heterogeneity of the complex molecular structure of pectin presents challenges to its integration in sensing devices.
\r\n \r\nIn this thesis, we study the origin of the high thermal sensitivity in pectin and develop a synthetic polyelectrolyte that mimics its key structure and properties. In Chapter 3, we focus on the ion transport mechanism in crosslinked pectin. We show that the binding between multivalent ions and certain chemical functional groups of pectin plays a critical role in its temperature sensitivity. In Chapter 4, the impact of water content on the ion transport and dielectric processes in crosslinked pectin is also investigated. In the following chapter, we present a novel synthetic polyelectrolyte designed to mimic pectin with a simpler structure. It has superior flexibility, high temperature sensitivity, and is stable under mechanical deformation. To further study this new material, we examine its ion transport dynamics under varying humidity and temperature conditions in Chapter 7. We discover that temperature and humidity have a similar effect on ion transport. Overall, we showed a biomimetic approach to design temperature sensitive polymers where the strong ion-polymer binding is the key to the ultrahigh temperature response.
" }, { "name": "Wang, Ziyi", "degree": "PhD", "year": "2023", "title": "Temperature Dependence of Gas Physisorption Energy: Experimental and Computational Studies of Krypton on Porous Carbon", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162023-225200255", "creators": [ { "name": { "family": "Wang", "given": "Ziyi" }, "id": "Wang-Ziyi", "orcid": "0000-0003-0811-921X", "display_name": "Wang, Ziyi" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Stadie", "given": "Nicholas" }, "id": "Stadie-P-Nicholas", "orcid": "0000-0002-1139-7846", "role": "member", "display_name": "Stadie, Nicholas" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "abstract": "This work comprehensively investigated the temperature dependence of physical adsorption energy, combining theoretical, computational, and experimental approaches. A thermodynamic analysis of the 2D ideal gas and the slit-pore models highlighted the role of van der Waal potentials in the adsorption energy and isotherm fitting methods, especially Henry's law. Experimental data of krypton adsorption on CNS-201 and MSC-30 porous carbon materials revealed a significant weakening in the isosteric adsorption energy with temperatures from 250 K to 330 K. Using the zero-coverage Henry's constants and Clausius\u2013Clapeyron equation, the adsorption energies weaken for 13% and 15% for CNS-201 and MSC-30. The corresponding changing rates are 4.35k_B for CNS-201 and 3.65k_B for MSC-30.
\r\n\r\nThe DFT-based computational study with the slit-pore model showed the van der Waal potentials of different-sized pores. Then it showed how the structures of the pores significantly influence the surface dynamics and the internal energies of the adsorbates at different temperatures. Gas molecules adsorbed in pores of different sizes have different heat capacities larger than the gas phase, leading to a temperature dependence of adsorption energy. Monte Carlo calculation indicated that displacements of adsorbent atoms caused by thermal vibration slightly weaken the van der Waal potentials but have a negligible effect on the temperature dependence of the adsorption energy.
\r\n\r\nThe distribution of pore sizes plays a crucial role in the temperature dependence of the overall adsorption energy. With increasing temperature, the pores with higher energy states become more accessible due to the Boltzmann distribution, weakening the statistically averaged internal energy. Adsorption energy weakening of 5% and 15% for CNS-201 and MSC-30 are given by combining the computational van der Waal potentials and experimentally measured pore sizes. The changing rates are 0.62k_B and 2.03k_B.
" }, { "name": "Weeks, John Stephen IV", "degree": "PhD", "year": "2023", "title": "Mechanical Response of Lattice Structures under High Strain-Rate and Shock Loading", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:09152022-195715025", "creators": [ { "name": { "family": "Weeks", "given": "John Stephen IV" }, "id": "Weeks-John-Stephen", "orcid": "0000-0002-7971-5919", "display_name": "Weeks, John Stephen IV" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9v5k-1157", "abstract": "Lattice structures are a class of architected cellular materials composed of similar unit cells with structural components of rods, plates, or sheets. Current additive manufacturing (AM) techniques allow control and tunability of unit cell geometries, which enable lattice structures to demonstrate exceptional mechanical properties such as high stiffness- and strength-to-mass ratios and energy absorption. Lattice structures exist on two length scales corresponding to the unit cell and continuum material, and therefore demonstrate mechanical behavior dependent on structural geometry and base material. These effects extend to the dynamic regime where lattice structures demonstrate distinct deformation modes under varying strain-rate loading. Experimental investigation of the dynamic and shock compression behavior of lattice structures remains largely unstudied and is the central focus of this thesis where the high strain-rate, transient dynamic, and shock compression behaviors of different topologies of lattice materials are explored.
\r\n\r\nThe first part of this thesis investigates the high strain-rate behavior of lattice structures via polymeric Kelvin lattices with rod- and plate-based geometries and relative densities of 15-30%. High strain-rate behavior is characterized by deformation modes similar to that of low strain-rate behavior. High strain-rate experiments (1000/s) are performed and validated using a viscoelastic polycarbonate split-Hopkinson (Kolsky) pressure bar system coupled with high-speed imaging. Both low and high strain-rate experiments show the formation of a localized deformation band which initiates in the middle of the specimen. Strain-rate effects of lattice specimens are observed to correlate with effects of the base polymer material and mechanical properties depend strongly on the relative density of the lattice specimen and exhibit distinct scaling with geometry type (rod, plate) and loading rate despite a similar unit cell shape. Explicit finite element simulations with a tensile failure material model are then used to validate deformation modes and scaling/property trends, and match those observed in experiments.
\r\n\r\nThe second part of this thesis explores the transient dynamic and transition to shock compression behavior of lattice structures using polymeric lattices with cubic, Kelvin, and octet-truss topologies with relative densities of about 8%. Transient dynamic behavior is characterized by a compaction wave initiating at an impact surface and additional deformation bands with modes similar to low strain-rate modes of deformation. Dynamic testing is conducted through gas gun direct impact experiments (25 - 70 m/s) with high-speed imaging coupled with digital image correlation (DIC) and a polycarbonate Hopkinson pressure bar. Full-field DIC measurements are used to characterize distinct mechanical behaviors induced by topology such as elastic wave speeds, deformation modes, and particle velocities. At lower impact velocities, a transient dynamic response is observed. At higher impact velocities, shock compression behavior occurs and is characterized by a sole compaction wave initiating and propagating from the impact surface of the lattice. One-dimensional continuum shock theory with Eulerian forms of the Rankine-Hugoniot jump conditions is used with full-field measurements to quantify a non-steady shock response and the varied effect of topology on material behaviors.
\r\n\r\nThe final part of this thesis examines the steady-state shock compression behavior of lattice structures through stainless steel 316L (SS316L) octet-truss lattices with relative densities of 10-30%. Powder gun plate impact experiments (270 - 390 m/s) with high-speed imaging and DIC are conducted and reveal a two-wave structure consisting of an elastic precursor wave and a planar compaction (shock) wave. Local shock parameters of lattice structures are defined using full-field DIC measurements and a linear shock velocity (us) versus particle velocity (up) relation is found to approximate measurements with a unit slope and linear fit constant equal to the crushing speed. One-dimensional continuum shock analysis is again performed using Eulerian forms of the Rankine-Hugoniot jump conditions to extract relevant mechanical quantities. Explicit finite element simulations of the lattice specimens using the Johnson-Cook constitutive model exhibit similar shock behavior to experiments. The simulations reveal a linear us-up relation and corresponding Hugoniot calculations agree with experimental trends. Notably, 1D shock theory is applied to simulations without resorting to a us-up relation for the base material, which characterizes this deformation regime and compaction wave as a `structural shock.'
\r\n\r\nMajor contributions of this thesis include experimental demonstration of ranged strain-rate behaviors for lattice structures of various base materials and topologies including low strain-rate, high strain-rate, transient dynamic, and shock compression regimes; use of full-field quantitative visualization techniques for local mechanical behavior and shock analysis; and finally, characterization of a 'structural' shock compression regime in lattice structures.
" }, { "name": "Wei, Nathaniel James", "degree": "PhD", "year": "2023", "title": "Dynamics and Performance of Wind-Energy Systems in Unsteady Flow Conditions", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-233342281", "creators": [ { "name": { "family": "Wei", "given": "Nathaniel James" }, "id": "Wei-Nathaniel-James", "orcid": "0000-0001-5846-6485", "display_name": "Wei, Nathaniel James" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/d9wh-pj98", "abstract": "Wind energy is poised to play a considerable role in the global transition to clean-energy technologies within the next few decades. Modern wind turbines, like aircraft and other aerodynamic structures, are typically designed with the assumption that the flows they encounter will be uniform and steady. However, atmospheric flows are highly unsteady, and systems operating within them must contend with gust disturbances that can lead to performance losses and structural damage. Therefore, the next generation of wind-energy systems requires physics-informed design principles that effectively account for and even leverage these unsteady flow phenomena for enhanced power generation, robustness, and operational longevity. Accordingly, this work details experimental and analytical efforts to characterize unsteady aerodynamics in wind-turbine contexts. First, the effects of unsteady streamwise motion on turbine performance are studied, as recent work has suggested that these dynamics may enable time-averaged efficiencies that exceed the steady-flow Betz limit on turbine efficiency. The power production of and flow around a periodically surging wind turbine are thus investigated using wind-tunnel experiments, which suggest that turbines in these flow conditions could leverage unsteady surge motions for power-extraction gains of up to 6.4% over the stationary case. Linearized and nonlinear dynamical models of the response of the turbine to these time-varying flows are derived and validated against the experimental data. These models are also coupled with a potential-flow model of the upstream induction zone of the turbine in order to predict temporal variations in the flow velocities and pressures in this region. Unsteady contributions to the time-averaged efficiency are also considered through theoretical potential-flow derivations. Additionally, a novel three-dimensional particle-tracking velocimetry approach using artificial snow as seeding particles is deployed to obtain volumetric flow measurements in the wakes of full-scale vertical-axis wind turbines in field conditions. These measurements yield insights into the effects of unsteady vortex dynamics on the structure of the near wake, with implications for the performance of turbines in wind-farm arrays. These investigations provide the analytical and experimental foundations for future studies of unsteady atmospheric flows, and will lead to the development of principles and techniques for wind-farm siting, control, and optimization." }, { "name": "Werner, Lucien Desloge", "degree": "PhD", "year": "2023", "title": "Uncertainty and Decentralization: Two Themes in an Energy Transformation", "advisor": "Low, Steven H.; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122023-232029846", "creators": [ { "name": { "family": "Werner", "given": "Lucien Desloge" }, "id": "Werner-Lucien-Desloge", "orcid": "0000-0003-1613-1702", "display_name": "Werner, Lucien Desloge" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "cms" ], "doi": "10.7907/scmm-p028", "abstract": "Over the last two decades, the rapidly decreasing units costs of solar, wind, and energy storage technologies have launched a fundamental transformation in how electric power is produced, distributed, and consumed. Proliferation of these technologies has effected a shift towards a more decentralized, flexible, and sustainable energy system that can meet the growing demand for energy while reducing greenhouse gas emissions from fossil fuels. The work in this thesis studies two principal themes in this transformation: uncertainty and decentralization.
\r\n\r\nUncertainty is a key challenge in the modern grid resulting from the weather dependence of variable renewables and volatile loads like electric vehicles distributed throughout the grid. Electricity markets, whose function is to regulate the precise balance of supply and demand across the system, face a pressing need for dispatch mechanisms that account for uncertainty while providing participation incentives for generators and loads. We introduce a framework for multi-stage market dispatch and pricing under a general description of forecast uncertainty that enables system operators to explicitly incorporate uncertainty into market-clearing prices. In related work, we study mechanisms that guarantee feasibility of multi-interval dispatch under robust uncertainty and provide participation incentives for shiftable demand response in forward multi-interval markets.
\r\n\r\nThe trend towards a more decentralized energy system stems from the inherent modularity of distributed energy resources (DERs), such as solar and storage, as well as the persistent growth in end-use loads. This evolution presents significant challenges to system operators who typically lack the tools and processes for managing a complex, distributed power system. To fill this gap, we introduce and implement a Microgrid Operating System (OS), a software platform for monitoring, modeling, and optimizing microgrids and distribution systems. The Microgrid OS is a central layer that links DER hardware, such as batteries, solar, and flexible loads, to energy applications like cost minimization, emissions reduction, and wholesale market participation. The core functions it provides are data acquisition and processing, system modeling and learning, and optimization and control. We present key modules of the Microgrid OS in the context of several implementation projects in microgrids, commercial buildings, and distribution networks.
" }, { "name": "Wu, Chun-Wei Vince", "degree": "PhD", "year": "2023", "title": "Freeze Casting - from Battery Separators to Ceramic Scaffolds", "advisor": "Faber, Katherine T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092023-230729474", "creators": [ { "name": { "family": "Wu", "given": "Chun-Wei Vince" }, "id": "Wu-Chun-Wei-Vince", "orcid": "0009-0002-4509-9713", "display_name": "Wu, Chun-Wei Vince" } ], "advisors": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "advisor", "display_name": "Faber, Katherine T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Liu", "given": "Hansan" }, "id": "Liu-Hansan", "role": "member", "display_name": "Liu, Hansan" } ], "option_major": [ "matsci" ], "doi": "10.7907/ghvz-q712", "abstract": "Freeze casting is a versatile pore-forming technique which allows tunability of pore structures including pore size, size distribution, morphology, and alignment in various material systems. It is that versatility that makes freeze casting a prospective candidate for fabrication of porous components used in a wide range of fields, ranging from biomaterials to supercapacitors. This work explores freeze casting as the processing route to fabricate battery separators and ceramic scaffolds.
\r\n\r\nThe first part of this study assesses the feasibility of tape/freeze casting, a combination of tape casting and freeze casting, in fabricating battery separators for sodium-ion batteries. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is chosen as the separator material due to its chemical inertness in battery environments, and dioxane is selected as the solvent for PVDF-HFP owing to its dendritic crystal structure and the absence of demixing upon freezing the solution. PVDF-HFP membranes fabricated by a bi-directional tape/freeze casting with dioxane exhibit through-thickness, directionally aligned pore structures. Although PVDF-HFP is shown to surpass reference separators in electrolyte affinity and electrochemical performance, composite strategies are designed to provide enhanced mechanical and electrochemical properties.
\r\n\r\nFirstly, the effects of alumina, a reinforcing agent introduced via ball milling with dioxane to form suspensions prior to tape/freeze casting, are examined. Composite PVDF- HFP/Al2O3 membranes show similar microstructures to their polymer counterpart, with enhanced resistance to thermal shrinkage, elastic modulus, electrolyte uptake, and ionic conductivity. Moreover, coin cells made with composite membranes deliver better rate performance and cycling stability than those with polymer membranes and filter paper reference materials.
\r\n\r\nSecondly, an alternative route to incorporate inorganic reinforcing elements into PVDF- HFP membranes is found through a co-solvent process. Silica particles from a sol-gel reaction of tetraethoxysilane (TEOS) are introduced into PVDF-HFP membranes via a co- solvent method in conjunction with dimethyl sulfoxide (DMSO). The tape/freeze-cast PVDF-HFP membranes fabricated with DMSO alone exhibit directionally aligned pores, while a hierarchical pore morphology with circular pores on the aligned pore walls is observed in composite membranes fabricated with TEOS, and hence, silica additions.\r\nComposite PVDF-HFP/SiO\u2082 membranes outperform their unreinforced polymer counterpart in terms of elastic modulus, thermal stability, electrolyte affinity, and ionic conductivity, along with capacity retention and cycling performance when assembled into coin cells.
\r\n\r\nThe final portion of this study evaluates the capability of freeze casting for highly permeable ceramic scaffolds using a polymethylsiloxane preceramic polymer with tert- butyl alcohol (TBA), a solvent creating prismatic pores without side arms that affords high permeability. A double-sided freeze-casting configuration results in more controlled freezing of the polymer solutions in comparison with the conventional single-sided counterpart, and hence a more aligned pore structure is obtained. Further improvement in pore alignment accompanied by an eight-fold increase in water permeability is realized by templating the substrate in freeze-casting molds.
" }, { "name": "Xiong, Lealia Li", "degree": "PhD", "year": "2023", "title": "Expanding the Toolbox for Thermal Control of E. coli: Cold-Activated Transcription with Applications in Temperature Self-Regulation", "advisor": "Shapiro, Mikhail G.; Kornfield, Julia A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272023-161541041", "creators": [ { "name": { "family": "Xiong", "given": "Lealia Li" }, "id": "Xiong-Lealia-Li", "orcid": "0000-0001-7636-5936", "display_name": "Xiong, Lealia Li" } ], "advisors": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "co-advisor", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "co-advisor", "display_name": "Kornfield, Julia A." } ], "committee": [ { "name": { "family": "Gradinaru", "given": "Viviana" }, "id": "Gradinaru-V", "orcid": "0000-0001-5868-348X", "role": "chair", "display_name": "Gradinaru, Viviana" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." } ], "option_major": [ "medeng" ], "doi": "10.7907/5w59-0667", "abstract": "Temperature can be used to control engineered E. coli \u2014 for example, the living component of an engineered living material (ELM) - through the use of thermolabile transcription factors. Sharp induction of gene expression with heat has been established using these bacteria- and phage-derived proteins. Here, we expand the toolbox for thermal control of E. coli through both direct cold-induced gene expression and through the construction of genetic circuits to invert heat-induced gene expression.
\r\n\r\nWe accomplish direct induction at low temperatures through the use of temperature-sensitive mutants of Lambda repressor as transcriptional activators. In addition, we show that a temperature-sensitive mutant of Lambda repressor can serve as an activator and a repressor of different genes simultaneously in one genetic circuit, leading to opposite thermal responses and serving as a temperature switch.
\r\n\r\nNext, we demonstrate inversion of a temperature-sensitive repressor using a temperature insensitive repressor. We apply this multicomponent switch to engineer a temperature self-regulation circuit for E. coli-based ELMs. Seasonal variation in ambient temperature presents a challenge in deploying ELMs outside of a laboratory environment, because E. coli growth rate is impaired both below and above 37\u00b0C. Our construct enables E. coli to produce a light-absorptive pigment in response to environmental temperature below 36\u00b0C with the goal of allowing the cells to absorb sunlight and locally warm to their optimal growth temperature. We demonstrate the efficacy of our pigment temperature switch in a model flat ELM growing at 32\u00b0C and 42\u00b0C in a home-built illuminated growth chamber. Below 36\u00b0C, our engineered E. coli increase in pigmentation, causing an increase in sample temperature and growth rate above non-pigmented bacteria. On the other hand, above 36\u00b0C, they decrease in pigmentation, protecting their growth compared to bacteria with temperature- independent high pigmentation. Integrating our temperature homeostasis circuit into an ELM has the potential to improve ELM performance by optimizing growth and protein production in the face of seasonal temperature changes.
" }, { "name": "Yang, Yiran (Isabella)", "degree": "PhD", "year": "2023", "title": "Laser-Engraved Wearable Sweat Sensor for Metabolic Monitoring", "advisor": "Gao, Wei", "url": "https://resolver.caltech.edu/CaltechTHESIS:02082023-162753604", "creators": [ { "name": { "family": "Yang", "given": "Yiran (Isabella)" }, "id": "Yang-Yiran-Isabella", "orcid": "0000-0001-8770-8746", "display_name": "Yang, Yiran (Isabella)" } ], "advisors": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "advisor", "display_name": "Gao, Wei" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" } ], "option_major": [ "medeng" ], "doi": "10.7907/5yfm-tt16", "abstract": "Wearable sensors have shown great potential in health diagnostics and monitoring. Continuous monitoring of metabolites in sweat could potentially offer great insight into a person\u2019s health, but current sweat sensing technology faces challenges in different realms: The sensing strategies are limited and there is a need to achieve high sensitivity for low-concentration targets and widen the detection spectrum of chemical targets. The lack of efficient sweat sampling creates inaccurate sensing results from sweat mixing with skin contaminants or sensing byproducts. Moreover, the lack of evaluation of sweat metabolites with respect to relevant clinical conditions and the lack of scalable fabrication technique pose hurdles in the eventual applications of non-invasive sweat monitoring. In this thesis, efforts advancing progress in these fronts are presented. Chapter 1 establishes a brief topical overview of the sweat-sensing background. In Chapter 2, we demonstrate how to utilize laser-engraving technique to achieve high-performance graphene sensors for electroactive metabolite sensing and vital signs detection. Chapter 3 describes subsequent efforts built on laser-engraved graphene sensors to improve sensing selectivity and widen the detection spectrum to detect non-electroactive targets in sweat. In Chapter 4, design and performance of our laser-engraved microfluidics are described and shown to improve sweat sampling in both exercise-induced and iontophoresis-induced sweating individuals. Chapter 5 presents our endeavors in evaluating sweat biomarkers with clinical conditions in pilot studies involving individuals with gout and metabolic syndrome. In total, the works summarized here expand biology, chemistry, material science, and mechanical engineering, and could potentially facilitate future applications in precision nutrition." }, { "name": "Yavas, Recep Can", "degree": "PhD", "year": "2023", "title": "Non-Asymptotic Analysis of Single-Receiver Channels with Limited Feedback", "advisor": "Effros, Michelle; Kostina, Victoria", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-003751035", "creators": [ { "name": { "family": "Yavas", "given": "Recep Can" }, "id": "Yavas-Recep-Can", "orcid": "0000-0002-5640-515X", "display_name": "Yavas, Recep Can" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "co-advisor", "display_name": "Effros, Michelle" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "co-advisor", "display_name": "Kostina, Victoria" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" } ], "option_major": [ "eleceng" ], "doi": "10.7907/a9e9-he45", "abstract": "Emerging Internet of Things, machine-type communication, and ultra-reliable low-latency communication in 5G demand codes that operate at short blocklengths, have low error probability and low energy consumption, and can handle the random activity of a large number of communicating devices. Since many of the applications have a single central device, e.g., a base station, that resolves the communication and a varying number of users, these requirements on the code design motivate interest in the non-asymptotic analysis of codes in a variety of single-receiver channels. This thesis investigates three channel coding problems with the goals of understanding the fundamental limits of channel coding under stringent requirements on reliability, delay, and power, and proposes novel coding architectures that employ constrained feedback to attain those limits. In the first part, we consider point-to-point channels without feedback, and analyze the non-asymptotic limits in the moderate deviations regime in probability theory. The moderate deviations regime is suitable for accurately approximating the maximum achievable coding rate in the operational regimes of practical interest because it simultaneously considers high rates and low error probabilities. We propose a new quantity, channel skewness, which governs the fundamental limit at short blocklengths and low error probabilities. Our approximation is the tightest among the state-of-the-art approximations for most error probability and latency constraints of interest. In the second part, we investigate rateless channel coding with limited feedback. Here, rateless means that decoding can occur at multiple decoding times. In our code design, feedback is limited both in frequency and content; it is sparse, meaning that it is available only at a few instants throughout the communication epoch; and it is stop-feedback, meaning that the receiver informs the transmitters only about whether decoding has occurred rather than what symbols it has received. Our results demonstrate that sporadically sending a few bits is almost as efficient as sending feedback at every time instant. In the third part, we focus on rateless random access channel codes, where the number of active transmitters is unknown to both the transmitters and the receiver. Our rateless code design that reserves a decoding time for each possible number of active transmitters achieves the same first two terms in the asymptotic expansion of the achievable rate as codes where the transmitter activity is known a priori. This means that, remarkably, the random transmitter activity has almost no effect on achievable rates.
\r\n\r\nTo obtain tight channel coding bounds, we analyze some non-asymptotic and asymptotic state-of-the-art bounds on the probability of the sum of independent and identical random variables, whose applications extend to source coding, hypothesis testing, and many others. In the scenarios where these tools are not directly applicable such as for the Gaussian channel, we propose new techniques to overcome that difficulty.
" }, { "name": "Yurk, Dominic Jeffrey", "degree": "PhD", "year": "2023", "title": "Advancements in Hemodynamic Measurement: Arterial Resonance, Ultrasound, and Machine Learning", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-215651797", "creators": [ { "name": { "family": "Yurk", "given": "Dominic Jeffrey" }, "id": "Yurk-Dominic-Jeffrey", "orcid": "0000-0002-2276-4189", "display_name": "Yurk, Dominic Jeffrey" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Rajagopal", "given": "Aditya" }, "id": "Rajagopal-Aditya", "orcid": "0000-0002-7768-2463", "role": "member", "display_name": "Rajagopal, Aditya" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/q7j4-vj19", "abstract": "This thesis covers two separate projects which both use ultrasound to measure a form of blood pressure in very different ways. The first project focuses on the noninvasive measurement of continuous arterial blood pressure via the previously unstudied phenomenon of arterial resonance. While prior research efforts have attempted many methods of noninvasive blood pressure measurement, none has been able to generate continuous, calibration-free measurements based on a first-principles physical model. This work describes the derivation of this resonance-based model, its in vitro validation, and its in vivo testing on 60 subjects. This testing resulted in robust resonance detection and accurate calculation of BP in the large majority of evaluated subjects, representing very promising performance for the first test of a new biomedical technology. The second study changes focus to the measurement of blood pressure in the right atrium of the heart, an important clinical indicator in heart disease patients. Rather than developing a new physical approach, this project used machine learning to model the existing assessments made by cardiologists. Comparison to gold standard invasive catheter measurements showed that model predictions were statistically indistinguishable from cardiologist measurements. Both of these projects represent significant advances in expanding precise blood pressure measurements beyond critical care units and expanding access to a much broader population.
" }, { "name": "Zhang, Shumao", "degree": "PhD", "year": "2023", "title": "Singularity Formation in the High-Dimensional Euler Equations and Sampling of High-Dimensional Distributions by Deep Generative Networks", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09202022-034157716", "creators": [ { "name": { "family": "Zhang", "given": "Shumao" }, "id": "Zhang-Shumao", "orcid": "0000-0003-3071-3362", "display_name": "Zhang, Shumao" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/8had-3a90", "abstract": "High dimensionality brings both opportunities and challenges to the study of applied mathematics. This thesis consists of two parts. The first part explores the singularity formation of the axisymmetric incompressible Euler equations with no swirl in \u211d\u207f, which is closely related to the Millennium Prize Problem on the global singularity of the Navier-Stokes equations. In this part, the high dimensionality contributes to the singularity formation in finite time by enhancing the strength of the vortex stretching term. The second part focuses on sampling from a high-dimensional distribution using deep generative networks, which has wide applications in the Bayesian inverse problem and the image synthesis task. The high dimensionality in this part becomes a significant challenge to the numerical algorithms, known as the curse of dimensionality.
\r\n \r\nIn the first part of this thesis, we consider the singularity formation in two scenarios. In the first scenario, for the axisymmetric Euler equations with no swirl, we consider the case when the initial condition for the angular vorticity is C\u03b1 H\u00f6lder continuous. We provide convincing numerical examples where the solutions develop potential self-similar blow-up in finite time when the H\u00f6lder exponent \u03b1 < \u03b1*, and this upper bound \u03b1* can asymptotically approach 1 - 2/n. This result supports a conjecture from Drivas and Elgindi [37], and generalizes it to the high-dimensional case. This potential blow-up is insensitive to the perturbation of initial data. Based on assumptions summarized from numerical experiments, we study a limiting case of the Euler equations, and obtain \u03b1* = 1 - 2/n which agrees with the numerical result. For the general case, we propose a relatively simple one-dimensional model and numerically verify its approximation to the Euler equations. This one-dimensional model might suggest a possible way to show this finite-time blow-up scenario analytically. Compared to the first proved blow-up result of the 3D axisymmetric Euler equations with no swirl and H\u00f6lder continuous initial data by Elgindi in [40], our potential blow-up scenario has completely different scaling behavior and regularity of the initial condition. In the second scenario, we consider using smooth initial data, but modify the Euler equations by adding a factor \u03b5 as the coefficient of the convection terms to weaken the convection effect. The new model is called the weak convection model. We provide convincing numerical examples of the weak convection model where the solutions develop potential self-similar blow-up in finite time when the convection strength \u03b5 < \u03b5*, and this upper bound \u03b5* should be close to 1 - 2/n. This result is closely related to the infinite-dimensional case of an open question [37] stated by Drivas and Elgindi. Our numerical observations also inspire us to approximate the weak convection model with a one-dimensional model. We give a rigorous proof that the one-dimensional model will develop finite-time blow-up if \u03b5 < 1 - 2/n, and study the approximation quality of the one-dimensional model to the weak convection model numerically, which could be beneficial to a rigorous proof of the potential finite-time blow-up.
\r\n \r\nIn the second part of the thesis, we propose the Multiscale Invertible Generative Network (MsIGN) to sample from high-dimensional distributions by exploring the low-dimensional structure in the target distribution. The MsIGN models a transport map from a known reference distribution to the target distribution, and thus is very efficient in generating uncorrelated samples compared to MCMC-type methods. The MsIGN captures multiple modes in the target distribution by generating new samples hierarchically from a coarse scale to a fine scale with the help of a novel prior conditioning layer. The hierarchical structure of the MsIGN also allows training in a coarse-to-fine scale manner. The Jeffreys divergence is used as the objective function in training to avoid mode collapse. Importance sampling based on the prior conditioning layer is leveraged to estimate the Jeffreys divergence, which is intractable in previous deep generative networks. Numerically, when applied to two Bayesian inverse problems, the MsIGN clearly captures multiple modes in the high-dimensional posterior and approximates the posterior accurately, demonstrating its superior performance compared with previous methods. We also provide an ablation study to show the necessity of our proposed network architecture and training algorithm for the good numerical performance. Moreover, we also apply the MsIGN to the image synthesis task, where it achieves superior performance in terms of bits-per-dimension value over other flow-based generative models and yields very good interpretability of its neurons in intermediate layers.
" }, { "name": "Zhang, Xueyue", "degree": "PhD", "year": "2023", "title": "Superconducting Circuit Architectures Based on Waveguide Quantum Electrodynamics", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03112023-174134421", "creators": [ { "name": { "family": "Zhang", "given": "Xueyue" }, "id": "Xueyue-Sherry-Zhang", "orcid": "0000-0001-8994-0629", "display_name": "Zhang, Xueyue" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "member", "display_name": "Endres, Manuel A." }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/c7d8-nn87", "abstract": "Quantum science and technology provides new possibilities in processing information, simulating novel materials, and answering fundamental questions beyond the reach of classical methods. Realizing these goals relies on the advancement of physical platforms, among which superconducting circuits have been one of the leading candidates offering complete control and read-out over individual qubits and the potential to scale up. However, most circuit-based multi-qubit architectures only include nearest-neighbor (NN) coupling between qubits, which limits the efficient implementation of low-overhead quantum error correction and access to a wide range of physical models using analog quantum simulation.
\r\n\r\nThis challenge can be overcome by introducing non-local degrees of freedom. For example, photons in a shared channel between qubits can mediate long-range qubit-qubit coupling arising from light-matter interaction. In addition, constructing a scalable architecture requires this channel to be intrinsically extensible, in which case a one-dimensional waveguide is an ideal structure providing the extensible direction as well as strong light-matter interaction.
\r\n\r\nIn this thesis, we explore superconducting circuit architectures based on light-matter interactions in waveguide quantum electrodynamics (QED) systems. These architectures in return allow us to study light-matter interaction, demonstrating strong coupling in the open environment of a waveguide by employing sub-radiant states resulting from collective effects. We further engineer the waveguide dispersion to enter the topological photonics regime, exploring interactions between qubits that are mediated by photons with topological properties. Finally, towards the goals of quantum information processing and simulation, we settle into a multi-qubit architecture where the photon-mediated interaction between qubits exhibits tunable range and strength. We use this multi-qubit architecture to construct a lattice with tunable connectivity for strongly interacting microwave photons, synthesizing a quantum many-body model to explore chaotic dynamics. The architectures in this thesis introduce scalable beyond-NN coupling between superconducting qubits, opening the door to the exploration of many-body physics with long-range coupling and efficient implementation of quantum information processing protocols.
" }, { "name": "Zhang, Ziyun", "degree": "PhD", "year": "2023", "title": "Low-Rank Matrix Recovery: Manifold Geometry and Global Convergence", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302023-222447373", "creators": [ { "name": { "family": "Zhang", "given": "Ziyun" }, "id": "Zhang-Ziyun", "orcid": "0000-0002-5794-2387", "display_name": "Zhang, Ziyun" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "chair", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/hd6q-g460", "abstract": "Low-rank matrix recovery problems are prevalent in modern data science, machine learning, and artificial intelligence, and the low-rank property of matrices is widely exploited to extract the hidden low-complexity structure in massive datasets. Compared with Burer-Monteiro factorization in the Euclidean space, using the low-rank matrix manifold has its unique advantages, as it eliminates duplicated spurious points and reduces the polynomial order of the objective function. Yet a few fundamental questions have remained unanswered until recently. We highlight two problems here in particular, which are the global geometry of the manifold and the global convergence guarantee.
\r\n\r\nAs for the global geometry, we point out that there exist some spurious critical points on the boundary of the low-rank matrix manifold M\u1d63, which have rank smaller than r but can serve as limit points of iterative sequences in the manifold M\u1d63. For the least squares loss function, the spurious critical points are rank-deficient matrices that capture part of the eigen spaces of the ground truth. Unlike classical strict saddle points, their Riemannian gradient is singular and their Riemannian Hessian is unbounded.
\r\n\r\nWe show that randomly initialized Riemannian gradient descent almost surely escapes some of the spurious critical points. To prove this result, we first establish the asymptotic escape of classical strict saddle sets consisting of non-isolated strict critical submanifolds on Riemannian manifolds. We then use a dynamical low-rank approximation to parameterize the manifold M\u1d63 and map the spurious critical points to strict critical submanifolds in the classical sense in the parameterized domain, which leads to the desired result. Our result is the first to partially overcome the nonclosedness of the low-rank matrix manifold without altering the vanilla gradient descent algorithm. Numerical experiments are provided to support our theoretical findings.
\r\n\r\nAs for the global convergence guarantee, we point out that earlier approaches to many of the low-rank recovery problems only imply a geometric convergence rate toward a second-order stationary point. This is in contrast to the numerical evidence, which suggests a nearly linear convergence rate starting from a global random initialization. To establish the nearly linear convergence guarantee, we propose a unified framework for a class of low-rank matrix recovery problems including matrix sensing, matrix completion, and phase retrieval. All of them can be considered as random sensing problems of low-rank matrices with a linear measurement operator from some random ensembles. These problems share similar population loss functions that are either least squares or its variant.
\r\n\r\nWe show that under some assumptions, for the population loss function, the Riemannian gradient descent starting from a random initialization with high probability converges to the ground truth in a nearly linear convergence rate, i.e., it takes O(log 1/\u03f5 + log n) iterations to reach an \u03f5-accurate solution. The key to establishing a nearly optimal convergence guarantee is closely intertwined with the analysis of the spurious critical points S_# on M\u1d63. Outside the local neighborhoods of spurious critical points, we use the fundamental convergence tool by the \u0141ojasiewicz inequality to derive a linear convergence rate. In the spurious regions in the neighborhood of spurious critical points, the Riemannian gradient becomes degenerate and the \u0141ojasiewicz inequality could fail. By tracking the dynamics of the trajectory in three stages, we are able to show that with high probability, Riemannian gradient descent escapes the spurious regions in a small number of steps.
\r\n\r\nAfter addressing the two problems of global geometry and global convergence guarantee, we use two applications to demonstrate the broad applicability of our analytical tools. The first is the robust principal component analysis problem on the manifold M\u1d63 with the Riemannian subgradient method. The second application is the convergence rate analysis of the Sobolev gradient descent method for the nonlinear Gross-Pitaevskii eigenvalue problem on the infinite dimensional sphere manifold. These two examples demonstrate that the analysis of manifold first-order algorithms can be extended beyond the previous framework, to nonsmooth functions and subgradient methods, and to infinite dimensional Hilbert manifolds. This exemplifies that the insights gained and tools developed for the low-rank matrix manifold M\u1d63 can be extended to broader scientific and technological fields.
" }, { "name": "Zhou, Yi", "degree": "PhD", "year": "2023", "title": "Experimental and Theoretical Studies of Unstable Dynamics of Caltech\u2019s Plasma Jet: X-Rays, Ultraviolet, and Visible Light", "advisor": "Bellan, Paul M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262023-165151068", "creators": [ { "name": { "family": "Zhou", "given": "Yi" }, "id": "Zhou-Yi", "orcid": "0000-0001-5315-9101", "display_name": "Zhou, Yi" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul M." }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul M." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bellan", "given": "Paul M." }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul M." }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "role": "member", "display_name": "Hillenbrand, Lynne A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/yfha-cs19", "abstract": "The Caltech plasma jet experiment launches a laboratory plasma jet that is analogous to an astrophysical jet. Even though the temperature of the plasma jet is around 2 eV, 6 keV X-rays and 20--60 eV extreme ultraviolet (EUV) radiation were detected when the plasma jet was perturbed by magnetohydrodynamic instabilities. How charged particles in a plasma are accelerated to suprathermal energy has been a key question in plasma physics, solar physics, and astrophysics. Studying these surprisingly energetic radiations from Caltech\u2019s plasma jet can help answer this question. Toward this goal, this thesis contains an experimental study of the X-rays and a theoretical study of the EUV radiation.
\r\n\r\nIn the experimental study, a PIN-diode-based 1D X-ray camera has been developed to spatially, temporally, and spectrally resolve the transient, low-intensity, and suprathermal X-rays detected to be simultaneous with magnetohydrodynamic instabilities that disrupt the plasma jet. This X-ray camera has high detection efficiency over the 5\u201310 keV X-ray band, an over 20-degree field of view (FOV), and the capability to produce more than 50 time-resolved frames with a submicrosecond time resolution. The X-ray images are formed by a pinhole or by a coded aperture placed outside the vacuum chamber in which the plasma jet is launched. The 1D imaging shows that the location of the X-ray source is either a few centimeters away from an inner disk electrode or near a spatially translatable metal frame that is 30\u201340 cm away from the electrode.
\r\n\r\nIn the theoretical study, we propose a collisional two-fluid model which involves a novel two-stream instability that is indifferent to collisions, even though collisions have been traditionally presumed to damp the two-stream instability. This model is used to explain previously observed localized dimming of visible light and a simultaneous, localized burst of EUV radiation from a plasma jet the cross section of which is constricted by a kink-instigated Rayleigh-Taylor instability. On being triggered by the constriction of the plasma cross section, the proposed two-stream instability produces a region of low density where an electric double layer leads to localized electron heating. The low-density region is consistent with and so likely explains the visible light dimming, and the localized electron heating is consistent with and likely explains the EUV radiation. The numerical solution of the collisional two-fluid model demonstrates good agreement with the apparent electron velocity and density profiles in the plasma jet.
" }, { "name": "Ambrose, Eric Ryan", "degree": "PhD", "year": "2022", "title": "Creating ARCHER: A 3D Hopping Robot with Flywheels for Attitude Control", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012022-061623441", "creators": [ { "name": { "family": "Ambrose", "given": "Eric Ryan" }, "id": "Ambrose-Eric-Ryan", "orcid": "0000-000194335650", "display_name": "Ambrose, Eric Ryan" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Niemeyer", "given": "Gunter" }, "id": "Niemeyer-G", "role": "member", "display_name": "Niemeyer, Gunter" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/gbts-va63", "abstract": "The field of robotic hopping began over 40 years ago, when it was first shown that robust hopping could be achieved on real hardware. In the years since then, it's become clear that hopping requires high performance and precision from its actuation and planning, due to its extreme interactions with the environment occurring over periodic, yet very short durations of time. Despite being of lower dimensionality than many other legged robots, hoppers are very underactuated, which only adds to the difficulty of planning motions quickly for real-time needs.
\r\n\r\nThe studies of robotic hopping presented in this thesis start with a look into two different actuation styles for creating vertical periodic motion: a compress-release mechanism and a moving-mass mechanism. The dynamics of each were examined from the perspective of stability and robustness to uncertainties in the model and measurements. The compress-release hopper (CRH) was found to be very stable, simple to control, and robust to all uncertainties, but inherently had some inefficiencies due to the requirement of holding compression during portions of the aerial phase. The moving-mass hopper (MMH) required optimization to generate the proper cyclic motions as well as closed-loop control to make them stable. Furthermore, the original configuration of the MMH was also less energetically efficient and robust to uncertainty than the CRH.
\r\n\r\nIn an effort to improve the efficiency of the MMH, a second-generation robot was designed using the principle of parallel elasticity. This involved placing a second spring in parallel to the actuator which would naturally guide the motion of the moving-mass into an optimal path, eliminating a significant portion of actuation effort and improving the overall efficiency. An added benefit of this change was that the robot no longer required closed loop control to create stable hopping. This new robot was built and tested in the lab showing a dramatic improvement over the previous design. The principle of controlling the compliance in the actuator for efficient motion was then taken one step further by creating custom, nonlinear stiffness springs which would provide a more ideal trajectory of motion. This process utilized a design-in-the-loop optimization strategy that would both design these springs as well as the motions of the moving-mass to yield better actuation efficiency. A set of these springs was created and attached to the second-gen MMH, replacing the lower spring, and tested in the lab. These springs did slightly improve the efficiency of the robot, but were restricted by the material selection of the springs due to manufacturing limitations.
\r\n\r\nMoving into the realm of 3-Dimensional hopping, a final robot was designed and built: ARCHER. Unlike traditional hopping robots which use a torso with very large inertia to control the leg motion and balance, ARCHER uses a set of three flywheels. The goal of this robot was twofold: to study the feasibility of using flywheels alone to control attitude, and to take advantage of the principle of decoupled systems. By using strategically placed flywheels, the dynamics of the leg and the attitude subsystems were decoupled, meaning their actuation did not have a direct influence on each other. This allows for simpler motion planning and control. The culmination of this thesis was running experiments with this robot, showing its initial performance and ability to hop with separate controllers for each subsystem.
" }, { "name": "Ardizzi, Anthony Joseph", "degree": "PhD", "year": "2022", "title": "Self-Heating of HEMT Low-Noise Amplifiers in Liquid Cryogenic Environments and the Limits of Microwave Noise Performance", "advisor": "Minnich, Austin J.; Schwab, Keith C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272022-180844058", "creators": [ { "name": { "family": "Ardizzi", "given": "Anthony Joseph" }, "id": "Ardizzi-Anthony-Joseph", "orcid": "0000-0001-8667-1208", "display_name": "Ardizzi, Anthony Joseph" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "co-advisor", "display_name": "Minnich, Austin J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "co-advisor", "display_name": "Schwab, Keith C." } ], "committee": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "chair", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/9va8-tc64", "abstract": "Detection and processing of microwave signals is of substantial scientific importance in fields ranging from radio astronomy to quantum computing. An essential component of the signal processing chain is the microwave amplifier, which adds gain to the signal so that it may be processed by subsequent microwave components. However, the amplifier itself adds its own internally generated noise into the measurement chain. As a result, amplifiers which add a minimal amount of noise are crucial to any high precision measurement scheme. A device which is commonly employed for this task is the high-electron-mobility transistor (HEMT) amplifier. Understanding the fundamental limits of the microwave noise performance of HEMT amplifiers is highly desirable. Noise temperatures in these devices as low as 3 times the quantum limit have been observed in the last decade, but the lack of understanding of the origin of the excess noise has hindered further improvements. Noise in HEMTs is attributed to a generator at the output, known as drain noise; and a generator at the input, which is attributed to thermal noise of the gate. At cryogenic temperatures of ~4 K, thermal noise is predicted to be negligible. However, a plateau in noise temperature has been observed at physical temperatures below ~20 K, with a negligible improvement in noise performance upon further cooling.
\r\n \r\nThe primary noise mechanism responsible for this plateau is believed to be ohmic heating of the HEMT structure induced by current in the active device channel, a process known as self-heating. At room temperature the ambient thermal noise dominates the amplifier\u2019s overall noise performance, but at the cryogenic temperatures required to achieve low-noise performance the self-heating effect produces thermal noise at the input of the HEMT gate which contributes significantly to the total noise. A potential mechanism to mitigate self-heating is to provide an additional thermal dissipation path for the Joule heating in the channel. However, given the sub-micron length scales and buried gate structure of HEMTs, thermal management is challenging. The primary heat conduction pathway, that of phonons travelling through the bulk HEMT substrate, decreases rapidly in magnitude at cryogenic temperatures. An alternative option is to submerge the HEMT in a cryogenic fluid, thereby presenting an alternate thermal conduction route through the HEMT surface into the fluid. This technique, while commonly employed in cryogenic thermal management of superconducting magnets, has not been investigated for HEMTs.
\r\n \r\nIn this work we explore the use of liquid cryogenic cooling to directly mitigate the effect of HEMT self-heating. We test in particular the effectiveness of cooling using superfluid helium-4, which has the highest known thermal conductivity of any known substance. We report a systematic experimental investigation of the noise performance of a cryogenic packaged two-stage HEMT low-noise amplifier over a wide range of biases in a 4.0 - 5.5 GHz frequency band, with the device immersed in a variety of cryogenic baths including helium-4 vapor, liquid helium-4, superfluid helium-4, and vacuum. We present the details of the experimental apparatus which was constructed to perform microwave noise measurements of the low-noise amplifier when submerged in a liquid cryogen environment. We interpret our results using a small-signal model of the amplifier and compare our findings with the predictions of a phonon radiation model of heat dissipation. We find that liquid cryogenic cooling is unable to mitigate the thermal noise associated with self-heating. Considering this finding, we examine the implications for the lower bounds of cryogenic noise performance in HEMTs by incorporating the effects of self-heating into the existing noise modelling of HEMT amplifiers. Our analysis supports the general design principle for cryogenic HEMTs of maximizing gain at the lowest possible power.
" }, { "name": "Ayoubi, Peyman", "degree": "PhD", "year": "2022", "title": "Modeling and Parameterization of Basin Effects for Engineering Design Applications", "advisor": "Asimaki, Domniki", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312022-021127047", "creators": [ { "name": { "family": "Ayoubi", "given": "Peyman" }, "id": "Ayoubi-Peyman", "orcid": "0000-0001-6795-4923", "display_name": "Ayoubi, Peyman" } ], "advisors": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "advisor", "display_name": "Asimaki, Domniki" } ], "committee": [ { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "orcid": "0000-0002-3060-8442", "role": "chair", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "orcid": "0000-0002-4703-190X", "role": "member", "display_name": "Kohler, Monica D." }, { "name": { "family": "Ross", "given": "Zachary E." }, "id": "Ross-Z-E", "orcid": "0000-0002-6343-8400", "role": "member", "display_name": "Ross, Zachary E." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" } ], "option_major": [ "civileng" ], "doi": "10.7907/4e61-q346", "abstract": "The term \"Basin effects\" refers to trapped and reverberating earthquake waves in soft sedimentary deposits overlying convex depressions of the basement bedrock, which significantly alter the frequency content, amplitude, and duration of seismic waves. This has played an important role in shaking duration and intensity in past earthquakes such as the Mw 8.0 1985 Micho\u00e1can, Mexico, Mw 6.9 1995 Kobe, Japan, and Mw 7.8 2015 Gorkha, Nepal earthquakes. While the standard practice is to perform a 1D analysis of a soil column, edge-effect and surface waves are among the key contributors to the surface ground motion within a basin. This thesis studies basin effects in a 2D medium to help better understand the phenomena, better parameterize them, and suggest a path to appropriately incorporate them in ground motion prediction equations and building design codes. After the introduction in Chapter 1, I present the results in three main parts as follows:
\r\n\r\nIn Chapter 2, we perform an extensive parametric study on the characteristics of surface ground motion associated with basin effects. We use an elastic idealized-shaped medium subjected to vertically propagating SV plane waves and examine the effects of basin geometry and material properties. We specifically study the effects of four dimensionless parameters, the width-to-depth (aspect) ratio, the rock-to-soil material contrast, a dimensionless frequency that quantifies the depth of the basin relative to the dominant incident wavelength, and a dimensionless distance that quantifies the distance of the basin edges relative to the dominant wavelength. Our results show that basin effects can be reasonably characterized using at least three independent parameters, each of which can significantly alter the resultant ground motion. To demonstrate the application of dimensional analysis applied here, we investigate the response of the Kathmandu Valley during the 2015 Mw 7.8 Gorkha Earthquake in Nepal using an idealized basin geometry and soil properties. Our results show that a simplified model can capture notable ground motion characteristics associated with basin effects.
\r\n\r\nChapter 3 uses the identified parameters from the previous chapter to estimate surface acceleration time-series given earthquake frequency content, basin geometry and material properties, and location inside a basin. This is of practical use when the amount of available data is limited or the fast estimation of time-series is desirable. For that, we train a neural network to estimate surface ground acceleration time-series across a basin. Three input parameters are needed for the estimation: basin-to-bedrock shear wave velocity ratio, aspect ratio of the basin, and dimensionless location. These parameters define an idealized-shaped basin and the location at which the time-series are to be computed. It will be shown that the model performs with high accuracy in comparison to the result of a full-fidelity Finite Element (FE) simulation (ground truth) and generalizes reasonably well for input parameters outside of the training set. Moreover, we will also use the model for the case of Kathmandu Valley, Nepal during the 2015 Mw 7.8 Gorkha earthquake and compare the results of NN versus recordings of the mainshock, similarly to Chapter 2.
\r\n\r\nOnce we have studied basin behavior in a homogeneous case in previous chapters, we focus on material representation inside a basin in Chapter 4. Here, we study basin effects for the cases where high-frequency response and realistic material representation are desirable. However, the lack of sufficient information about the material properties and stratigraphy of a basin prevents accurate simulation of the phenomena. To do that, we perform a stochastic analysis using the Monte Carlo technique, where a random field represents basin material. Similarly to the previous chapters, we use a 2D FE model with an idealized basin subjected to vertically propagating SV plane waves and investigate the spatial variation of surface ground motion (SGM) associated with basin effects by assuming different realizations of the correlated random field. We then study various correlation lengths, coefficients of variations, and autocorrelation functions to evaluate their contribution to SGM. We show that the coefficient of variation is the most influential parameter on SGM, followed by correlation lengths and type of autocorrelation function. Increasing the coefficient of variation not only affects the mean surface amplification, but also results in a dramatic change in the standard deviation. Correlation lengths and autocorrelation functions, on the other hand, are of less importance for the cases we examine in this study.
" }, { "name": "Ballew, Conner Kiley", "degree": "PhD", "year": "2022", "title": "Multifunctional Volumetric Metaoptics", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:08272021-165922711", "creators": [ { "name": { "family": "Ballew", "given": "Conner Kiley" }, "id": "Ballew-Conner-Kiley", "orcid": "0000-0003-4854-8342", "display_name": "Ballew, Conner Kiley" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "orcid": "0000-0002-1098-7174", "role": "member", "display_name": "Golwala, Sunil" } ], "option_major": [ "eleceng" ], "doi": "10.7907/dn7h-6r72", "abstract": "Optical systems are often comprised of modular arrangements of components, and the improvement of these systems has historically leaned on the precise manufacturing and alignment of the comprising elements. This provides an intuitive pathway to optical design, but ultimately yields systems that are far bulkier than required by the laws of physics. It is often the case that the required degrees of freedom to achieve complex tasks is present within dielectric volumes that are only several wavelengths per side, and these degrees of freedom can be accessed by patterning the dielectric volume with subwavelength resolution. Even in such small volumes, all of the fundamental properties of light (wavelength, polarization, k-vector) can be controlled which opens the possibility for extremely multifunctional, compact image sensor elements. The determination of the refractive index distribution of these devices has historically been a challenging inverse-design problem, and the fabrication of 3D dielectric devices is a challenge unique to different regimes of the electromagnetic spectrum. This thesis utilizes current state-of-the-art optimization techniques to design multifunctional volumetric devices, and theoretically expands upon the techniques to facilitate the optimization of high index contrast structures. Multiple microwave prototypes are measured, devices operating at terahertz frequencies are fabricated using silicon micromachining, and optical devices with resolutions achievable with CMOS processing techniques are studied for next-generation camera sensors.
" }, { "name": "Banker, Jash Haren", "degree": "PhD", "year": "2022", "title": "Photonic and Phononic Band Gap Engineering for Circuit Quantum Electrodynamics and Quantum Transduction", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01222022-151042739", "creators": [ { "name": { "family": "Banker", "given": "Jash Haren" }, "id": "Banker-Jash-Haren", "orcid": "0000-0002-2130-0825", "display_name": "Banker, Jash Haren" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/jrf3-gx27", "abstract": "The ability to pattern materials at the wavelength and sub-wavelength scale has led to the concept of photonic crystals and metamaterials - artificially engineered structures that exhibit electromagnetic properties not found in conventional materials. Such engineered structures offer the ability to slow down and even inhibit the propagation of electromagnetic waves giving rise to a photonic band gap and a sharply varying photonic density of states.
\r\n\r\nQuantum emitters in the presence of an electromagnetic reservoir with varying density of states can undergo a rich set of dynamical behavior. In particular, the reservoir can be tailored to have a memory of past interactions with emitters, in contrast to memory-less Markovian dynamics of typical open systems. In part 1 of this thesis, we investigate the non-Markovian dynamics of a superconducting qubit strongly coupled to a superconducting metamaterial waveguide engineered to have both a sharp spectral variation in its transmission properties and a slowing of light by a factor of 650. Tuning the qubit into the spectral vicinity of the passband of this slow-light waveguide reservoir, we observe a 400-fold change in the emission rate of the qubit, along with oscillatory energy relaxation of the qubit resulting from the beating of bound and radiative dressed qubit-photon states. Further, upon addition of a reflective boundary to one end of the waveguide, we observe revivals in the qubit population on a timescale 30 times longer than the inverse of the qubit\u2019s emission rate, corresponding to the round-trip travel time of an emitted photon. With this superconducting circuit platform, future studies of multi-qubit interactions via highly structured reservoirs and the generation of multi-photon highly entangled states are possible.
\r\n\r\nWhile microwave frequency superconducting circuits are near ideal testbeds for quantum electrodynamics experiments of the type discussed in part 1, microwave photons are not well suited for transmission of quantum information over long distances due to the presence of a large thermal background at room temperature. Optical photons are ideal for quantum communication applications due to their low propagation loss at room temperature. Coherent transduction of single photons from the microwave to the optical domain has the potential to play a key role in quantum networking and distributed quantum computing. In part 2 of this thesis, we extend the notion of band gap engineering to the optical and acoustic domain and present the design of a piezo-optomechanical quantum transducer where transduction is mediated by a strongly hybridized acoustic mode of a lithium niobate piezoacoustic cavity attached to a silicon optomechanical crystal patterned on a silicon-on-insulator substrate. We estimate an intrinsic transduction efficiency of 29% with <0.5 added noise quanta when our transducer is resonantly coupled to a superconducting transmon qubit and operated in pulsed mode. Our design involves on-chip integration of a superconducting qubit with the piezo-optomechanical transducer. Absorption of stray photons from the optical pump used in the transduction process is known to cause excess decoherence and noise in the superconducting circuit. The recovery time of the superconducting circuit after the optical pulse sets a limit on the transducer repetition rate. We fabricate niobium based superconducting circuits on a silicon substrate and test their response to illumination by a 1550 nm laser. We find a recovery time of ~ 10 \u03bcs, indicating that a repetition rate of 10 kHz should be possible. Combined with the expected efficiency and noise metrics of our design, we expect that a transducer in this parameter regime would be suitable to realize probabilistic schemes for remote entanglement of superconducting quantum processors. We conclude by discussing some of the challenges associated with fabricating niobium superconducting qubits and lithium niobate piezoacoustic devices on silicon-on-insulator substrates and provide initial steps towards realizing our transducer design in the lab.
" }, { "name": "Barthel, Benedikt", "degree": "PhD", "year": "2022", "title": "On the Variational Principles of Linear and Nonlinear Resolvent Analysis", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03222022-135834919", "creators": [ { "name": { "family": "Barthel", "given": "Benedikt" }, "id": "Barthel-Benedikt", "orcid": "0000-0002-6890-5047", "display_name": "Barthel, Benedikt" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Chini", "given": "Gregory" }, "id": "Chini-Gregory", "orcid": "0000-0001-5539-3364", "role": "member", "display_name": "Chini, Gregory" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/sy44-d841", "abstract": "Despite decades of research, the accurate and efficient modeling of turbulent flows remains a challenge. However, one promising avenue of research has been the resolvent analysis framework pioneered by McKeon and Sharma (2010) which interprets the nonlinearity of the Navier-Stokes equations (NSE) as an intrinsic forcing to the linear dynamics. This thesis contributes to the advancement of both the linear and nonlinear aspects of resolvent analysis (RA) based modeling of wall bounded turbulent flows. On the linear front, we suggest an alternative definition of the resolvent basis based on the calculus of variations. The proposed formulation circumvents the reliance on the inversion of the linear operator and is inherently compatible with any arbitrary choice of norm. This definition, which defines resolvent modes as stationary points of an operator norm, allows for more tractable analytical manipulation and leads to a straightforward approach to approximate the resolvent (response) modes of complex flows as expansions in any arbitrary basis. The proposed method avoids matrix inversions and requires only the spectral decomposition of a matrix of significantly reduced size as compared to the original system, thus having the potential to open up RA to the investigation of larger domains and more complex flow configurations. These analytical and numerical advantages are illustrated through a series of examples in one and two dimensions. The nonlinear aspects of RA are addressed in the context of Taylor vortex flow. Highly truncated and fully nonlinear solutions are computed by treating the nonlinearity not as an inherent part of the governing equations but rather as a triadic constraint which must be satisfied by the model solution. Our results show that as the Reynolds number increases, the flow undergoes a fundamental transition from a classical weakly nonlinear regime, where the forcing cascade is strictly down scale, to a fully nonlinear regime characterized by the emergence of an inverse (up scale) forcing cascade. It is shown analytically that this is a direct consequence of the structure of the quadratic nonlinearity of the NSE formulated in Fourier space. Finally, we suggest an algorithm based on the energy conserving nature of the nonlinearity of the NSE to reconstruct the phase information, and thus higher order statistics, from knowledge of solely the velocity spectrum. We demonstrate the potential of the proposed algorithm through a series of examples and discuss the challenges and potential applications to the study and simulation of turbulent flows.
" }, { "name": "Bauser, Haley Coddington", "degree": "PhD", "year": "2022", "title": "High Contrast Nanophotonics for Scalable Photovoltaics and Solar Fuels", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242022-235412996", "creators": [ { "name": { "family": "Bauser", "given": "Haley Coddington" }, "id": "Bauser-Haley-Coddington", "orcid": "0000-0002-9677-3301", "display_name": "Bauser, Haley Coddington" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2xqd-c773", "abstract": "Anthropogenic climate change is a massive threat to our planet\u2019s stability and habitability. Carbon dioxide makes up the majority of the greenhouse gas emissions leading to rising global temperatures. In order to reduce the global temperature, it is imperative to reduce dependency on fossil fuels by mass adaptation of renewable energy with net-zero carbon emissions. In this work, we present designs to convert incident solar energy to power through scalable nanophotonic systems.
\r\n\r\nWe first introduce a tandem luminescent solar concentrator (LSC). LSCs are of interest due to their ability to concentrate both direct and diffuse light expanding the regions in which LSCs can be deployed. The tandem LSC uses a novel architecture in which InGaP micro-cells lie co-planar and optically coupled to the waveguide as opposed to the traditional edge-lined LSC. The waveguide consists of highly efficient CdSe/CdS quantum dots with emissions tuned to the band edge of the InGaP cells. This LSC is then coupled to a Si sub-cell allowing the tandem LSC to effectively convert a greater portion of the incident solar spectrum. We fabricate and perform outdoor testing on the first co-planar tandem LSC demonstrating a path to high efficiency LSCs.
\r\n\r\nWe then introduce two methods to more efficiently trap light within the LSC. The first is a high contrast grating spectrally selective reflector. By using a high contrast grating, we can achieve high reflectivity with a single layer of high index materially patterned at a sub-wavelength scale on a low index substrate. While we explore both AlSb and a-SiC:H as grating materials, we pursue a-SiC:H and fabricate such a spectrally selective reflector with over 94% reflectivity at 642 nm. We then move to eliminate the need for spectrally selective filters by using photonic crystal waveguides to trap quantum dot emission within the LSC. We present two designs in which over 90% of emission remains trapped in the photonic crystal waveguide and is therefore able to travel to the photovoltaic material. We demonstrate how such a design can be used for LSCs in terrestrial and space solar power applications.
\r\n\r\nLastly, we expand on the photonic crystal waveguide and introduce a thermal concentrator for production of scalable solar fuels. The thermal concentrator absorbs incident sunlight and traps the generated heat within the photonic crystal. This elevates the temperature within the thermal concentrator creating conditions under which catalytic reactions producing solar fuels can occur. We design a thermal concentrator that can heat up to 507.3 Kelvin under 1 sun illumination and 729.4 Kelvin under 3 sun illumination.
" }, { "name": "Booeshaghi, Ali Sina", "degree": "PhD", "year": "2022", "title": "Foundations and Applications of Single-Cell RNA Sequencing", "advisor": "Pachter, Lior S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292022-204424650", "creators": [ { "name": { "family": "Booeshaghi", "given": "Ali Sina" }, "id": "Booeshaghi-Ali-Sina", "orcid": "0000-0002-6442-4502", "display_name": "Booeshaghi, Ali Sina" } ], "advisors": [ { "name": { "family": "Pachter", "given": "Lior S." }, "id": "Pachter-L", "orcid": "0000-0002-9164-6231", "role": "advisor", "display_name": "Pachter, Lior S." } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Melsted", "given": "P\u00e1ll" }, "id": "Melsted-P\u00e1ll", "orcid": "0000-0002-8418-6724", "role": "member", "display_name": "Melsted, P\u00e1ll" }, { "name": { "family": "Pachter", "given": "Lior S." }, "id": "Pachter-L", "orcid": "0000-0002-9164-6231", "role": "member", "display_name": "Pachter, Lior S." } ], "option_major": [ "mecheng" ], "doi": "10.7907/ptbp-a779", "abstract": "Single-cell RNA-sequencing is an experimental technique for studying cellular gene expression, with a multitude of engineering challenges. These challenges transcend the boundaries of traditional academic disciplines and the field of mechanical engineering, that aims to address roadblocks in critical technologies towards engineering our environment, is central to this endeavor.
\r\n\r\nThis thesis addresses three engineering challenges that must be met in order to realize the goal of bringing single-cell RNA sequencing to the clinic. The first is scalable cellular isolation and sampling. Chapter 2 describes the poseidon and colosseum instruments that enable massive scale single-cell isolation and collection. They each have novel design elements that reduce cost and enable modularity, at a similar accuracy to expensive commercial alternatives.
\r\n\r\nThe second challenge is the rapid preprocessing of single-cell RNA-sequencing data. Chapter 3 describes the kallisto | bustools command-line tools that make scalable scRNAseq analysis fast and efficient. These tools implement novel algorithms for sequence read-alignment, barcode error correction, and molecular counting that helps resolve ambiguities in sequence mapping.
\r\n\r\nThe third challenge is refining gene expression data to the isoform level. This refinement is crucial for understanding transcriptional regulation and the effects of alternative splicing in biological processes. Towards that end, I have extended the kallisto | bustools workflow to process full-length scRNAseq data taking advantage of expectation maximization algorithm to disambiguate sequence alignments. Chapter four describes how I used these tools to assemble the first ever spatially-resolved single-cell isoform atlas, and in particular one of great interest in the neuroscience community (the mouse primary motor cortex) with data generated with three RNA-sequencing assays.
" }, { "name": "Bouman, Amanda Rose", "degree": "PhD", "year": "2022", "title": "Autonomous Mission-Driven Robots in Extreme Environments", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05172022-043237609", "creators": [ { "name": { "family": "Bouman", "given": "Amanda Rose" }, "id": "Bouman-Amanda-Rose", "orcid": "0000-0002-4215-2913", "display_name": "Bouman, Amanda Rose" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "chair", "display_name": "Ames, Aaron D." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Agha-Mohammadi", "given": "Ali-Akbar" }, "id": "Agha-Mohammadi-A-A", "orcid": "0000-0001-5509-1841", "role": "member", "display_name": "Agha-Mohammadi, Ali-Akbar" } ], "option_major": [ "mecheng" ], "doi": "10.7907/a78d-kv42", "abstract": "Robotic autonomy systems that can negotiate harsh environments under time and communication constraints are critical to accomplishing many real-world missions. Such systems require an integrated software-hardware solution capable of robustly reasoning about a time-limited mission across a complex environment and negotiating extreme physical conditions during mission execution. To this end, I will discus the development of two field-tested systems designed for operation in GPS-denied areas: (i) a coverage planning framework that enables efficient exploration of large, unknown environments, and (ii) a ballistically-launched aircraft that converts to an autonomous, free-flying multirotor in order to provide rapid aerial surveillance.
\r\n\r\nThe first system addresses the time-limited exploration problem by providing a planning strategy that seeks to maximize the area covered by a robot\u2019s sensor footprint along a planned trajectory. In order to find solutions over large spatial extents (>1 km) and long temporal horizons (>1 hour), this coverage problem is decomposed into tractable subproblems by introducing spatial and temporal abstractions. Spatially, the robot-world belief is approximated by a task-dependent structure, enriched with environment map estimates. Temporally, the belief is approximated by the aggregation of multiple structures, each spanning a different spatial range. Cascaded uncertainty-aware solvers return a coverage plan over the stratified belief in real time. \r\nCoverage policies are constructed in a receding horizon fashion to ensure motion smoothness and resiliency to real-world stochasticity in perception and control. This coverage planning framework was extensively tested on physical robots in various real-world environments (caves, mines, subway systems, etc.) and served as the exploration strategy for a competing entry in the DARPA Subterranean Challenge.
\r\n\r\nThe second system addresses rapid multirotor deployment for aerial data collection during emergencies. While multirotors are advantageous over fixed-winged systems due to their high maneuverability, their rotating blades are hazardous and require stable, uncluttered takeoff sites. To overcome this issue, a ballistically-launched, autonomously-stabilizing multirotor (SQUID -- Streamlined Quick Unfolding Investigation Drone) was designed, fabricated, and tested. SQUID follows a deterministic trajectory, transitioning from a folded launch configuration to an autonomous, fully-controllable hexacopter. The entire process from launch to position stabilization requires no user- or GPS-input and demonstrates the viability of using ballistically-launched multirotors to achieve safe and rapid deployment from moving vehicles.
" }, { "name": "Chen, Jiajie", "degree": "PhD", "year": "2022", "title": "Singularity Formation in Incompressible Fluids and Related Models", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05172022-223804694", "creators": [ { "name": { "family": "Chen", "given": "Jiajie" }, "id": "Chen-Jiajie", "orcid": "0000-0002-0194-1975", "display_name": "Chen, Jiajie" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "chair", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Isett", "given": "Philip" }, "id": "Isett-Phlip", "orcid": "0000-0001-9038-5546", "role": "member", "display_name": "Isett, Philip" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/nqff-dh92", "abstract": "Whether the three-dimensional (3D) incompressible Euler equations can develop a finite-time singularity from smooth initial data with finite energy is a major open problem in partial differential equations. A few years ago, Tom Hou and Guo Luo obtained strong numerical evidence of a potential finite time singularity of the 3D axisymmetric Euler equations with boundary from smooth initial data. So far, there is no rigorous justification. In this thesis, we develop a framework to study the Hou-Luo blowup scenario and singularity formation in related equations and models. In addition, we analyze the obstacle to singularity formation.
\r\n\r\nIn the first part, we propose a novel framework of analysis based on the dynamic rescaling formulation to study singularity formation. Our strategy is to reformulate the problem of proving finite time blowup into the problem of establishing the nonlinear stability of an approximate self-similar blowup profile using the dynamic rescaling equations. Then we prove finite time blowup of the 2D Boussinesq and the 3D Euler equations with C1,\u03b1 velocity and boundary. This result provides the first rigorous justification of the Hou-Luo scenario using C1,\u03b1 velocity.
\r\n\r\nIn the second part, we further develop the framework for smooth data. The method in the first part relies crucially on the low regularity of the data, and there are several essential difficulties to generalize it to study the Hou-Luo scenario with smooth data. We demonstrate that some of the challenges can be overcome by proving the asymptotically self-similar blowup of the Hou-Luo model. Applying this framework, we establish the finite time blowup of the De Gregorio (DG) model on the real line (\u211d) with smooth data. Our result resolves the open problem on the regularity of this model on \u211d that has been open for quite a long time.
\r\n\r\nIn the third part, we investigate the competition between advection and vortex stretching, an essential difficulty in studying the regularity of the 3D Euler equations. This competition can be modeled by the DG model on S1. We consider odd initial data with a specific sign property and show that the regularity of the initial data in this class determines the competition between advection and vortex stretching. For any 0 < \u03b1 < 1, we construct a finite time blowup solution from some C\u03b1 initial data. On the other hand, we prove that the solution exists globally for C1 initial data. Our results resolve some conjecture on the finite time blowup of this model and imply that singularities developed in the DG model and the generalized Constantin-Lax-Majda model on S1 can be prevented by stronger advection.
" }, { "name": "Chen, Kuan-Chang", "degree": "PhD", "year": "2022", "title": "Energy-Efficient Receiver Design for High-Speed Interconnects", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:08042021-231915829", "creators": [ { "name": { "family": "Chen", "given": "Kuan-Chang" }, "id": "Chen-Kuan-Chang", "orcid": "0000-0003-2968-4656", "display_name": "Chen, Kuan-Chang" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Nelson", "given": "David" }, "id": "Nelson-David", "role": "member", "display_name": "Nelson, David" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ntem-sn47", "abstract": "High-speed interconnects are of vital importance to the operation of high-performance computing and communication systems, determining the ultimate bandwidth or data rates at which the information can be exchanged. Optical interconnects and the employment of high-order modulation formats are considered as the solutions to fulfilling the envisioned speed and power efficiency of future interconnects. One common key factor in bringing the success is the availability of energy-efficient receivers with superior sensitivity. To enhance the receiver sensitivity, improvement in the signal-to-noise ratio (SNR) of the front-end circuits, or equalization that mitigates the detrimental inter-symbol interference (ISI) is required. In this dissertation, architectural and circuit-level energy-efficient techniques serving these goals are presented.
\r\n\r\nFirst, an avalanche photodetector (APD)-based optical receiver is described, which utilizes non-return-to-zero (NRZ) modulation and is applicable to burst-mode operation. For the purposes of improving the overall optical link energy efficiency as well as the link bandwidth, this optical receiver is designed to achieve high sensitivity and high reconfiguration speed. The high sensitivity is enabled by optimizing the SNR at the front-end through adjusting the APD responsivity via its reverse bias voltage, along with the incorporation of 2-tap feedforward equalization (FFE) and 2-tap decision feedback equalization (DFE) implemented in current-integrating fashion. The high reconfiguration speed is empowered by the proposed integrating dc and amplitude comparators, which eliminate the RC settling time constraints. The receiver circuits, excluding the APD die, are fabricated in 28-nm CMOS technology. The optical receiver achieves bit-error-rate (BER) better than 1E\u221212 at \u221216-dBm optical modulation amplitude (OMA), 2.24-ns reconfiguration time with 5-dB dynamic range, and 1.37-pJ/b energy efficiency at 25 Gb/s.
\r\n\r\nSecond, a 4-level pulse amplitude modulation (PAM4) wireline receiver is described, which incorporates continuous time linear equalizers (CTLEs) and a 2-tap direct DFE dedicated to the compensation for the first and second post-cursor ISI. The direct DFE in a PAM4 receiver (PAM4-DFE) is made possible by the proposed CMOS track-and-regenerate slicer. This proposed slicer offers rail-to-rail digital feedback signals with significantly improved clock-to-Q delay performance. The reduced slicer delay relaxes the settling time constraint of the summer circuits and allows the stringent DFE timing constraint to be satisfied. With the availability of a direct DFE employing the proposed slicer, inductor-based bandwidth enhancement and loop-unrolling techniques, which can be power/area intensive, are not required. Fabricated in 28-nm CMOS technology, the PAM4 receiver achieves BER better than 1E\u221212 and 1.1-pJ/b energy efficiency at 60 Gb/s, measured over a channel with 8.2-dB loss at Nyquist frequency.
\r\n\r\nThird, digital neural-network-enhanced FFEs (NN-FFEs) for PAM4 analog-to-digital converter (ADC)-based optical interconnects are described. The proposed NN-FFEs employ a custom learnable piecewise linear (PWL) activation function to tackle the nonlinearities with short memory lengths. In contrast to the conventional Volterra equalizers where multipliers are utilized to generate the nonlinear terms, the proposed NN-FFEs leverage the custom PWL activation function for nonlinear operations and reduce the required number of multipliers, thereby improving the area and power efficiencies. Applications in the optical interconnects based on micro-ring modulators (MRMs) are demonstrated with simulation results of 50-Gb/s and 100-Gb/s links adopting PAM4 signaling. The proposed NN-FFEs and the conventional Volterra equalizers are synthesized with the standard-cell libraries in a commercial 28-nm CMOS technology, and their power consumptions and performance are compared. Better than 37% lower power overhead can be achieved by employing the proposed NN-FFEs, in comparison with the Volterra equalizer that leads to similar improvement in the symbol-error-rate (SER) performance.
" }, { "name": "Cheng, Peishi Stephen", "degree": "PhD", "year": "2022", "title": "Charge and Heat Transport in Non-Metallic Crystals Using First-Principles Boltzmann Transport Theory", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082022-230903229", "creators": [ { "name": { "family": "Cheng", "given": "Peishi Stephen" }, "id": "Cheng-Peishi-Stephen", "orcid": "0000-0002-3513-9972", "display_name": "Cheng, Peishi Stephen" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/45fv-ja45", "abstract": "Phonon-phonon and electron-phonon interactions underlie many fundamental transport properties like thermal conductivity and electrical mobility, and models of these properties provide information about the underlying microscopic interactions present in the materials. Many of these models use the Boltzmann transport equation where the choice of the expression for the collision integral is the most important and challenging aspect since it should capture all of the relevant interactions. In the past the expressions were semi-empirical, but in recent decades first principles models with no fitting parameters have become more commonplace, leading to discovery of new materials or providing deeper insights into the relevant mechanisms governing transport. This thesis presents first-principles calculations of thermal conductivity in polymer crystals, and charge transport at high electric fields in semiconductors in the Boltzmann transport framework.
\r\n\r\nPolymers are thermally insulating in their typical amorphous form, but it is known that their thermal conductivity can be enhanced through drawing and aligning of their polymer chains. With perfect chain alignment, the structures can be described as polymer crystals, which tend to contain many atoms per unit cell. However, the conventional understanding of thermal transport in crystals predicts low thermal conductivity for complex, many atom unit cells. It is known from simple models that phonon focusing redirects the heat flow into the polymer chain direction, but the extent to which phonon focusing plays a role in setting the intrinsic upper limits of polymer thermal conductivity has not been assessed from a first principles standpoint. We calculate the ab initio lattice conductivity of polythiophene, a complex molecular crystal with 28 atoms per unit cell, using the temperature dependent effective potential (TDEP) method to obtain finite temperature phonon properties taking into account the large quantum nuclear motion of hydrogen atoms present in polymers. We find a high thermal conductivity due to phonon focusing and stiff branches that overcome the expected low phonon lifetimes. The phonon focusing aligns group velocities along the chain axis throughout the Brillouin zone, even for states with wave vector almost orthogonal to the chain axis.
\r\n\r\nFor charge transport, ab initio calculations focus almost exclusively on low field mobility, but technologically relevant phenomena like negative differential resistance manifest only at high fields far from equilibrium. Further, there are no ab initio calculations of non-equilibrium electronic noise, which differs qualitatively from transport observables at high fields. We report a methodological advance that obtains both the high-field transport properties and the non-equilibrium noise using an ab initio Boltzmann transport approach. Our method extends the collision integral to high fields by making physically motivated approximations to account for the non-linearities at high fields.
\r\n\r\nUsing our method, we calculate the high-field noise and transport properties in GaAs and find that the 1ph level of theory is inadequate. Thus, we implement an approximate form of higher order interactions where electrons are scattered consecutively by two phonons (2ph) and find that these 2ph processes qualitatively alter the energy relaxation of the electron system compared to 1ph scattering, resolving a long-standing discrepancy in the strength of intervalley scattering inferred from different experiments. We also calculate non-equilibrium electronic noise from first principles for the first time. However, we are not able to reproduce experimental trends, and we suggest that 2ph processes beyond our approximation may be necessary to obtain experimental agreement. Our calculation shows how noise provides a new observable against which the accuracy of first-principles methods can be measured.
" }, { "name": "Choi, Alexander Youngsoo", "degree": "PhD", "year": "2022", "title": "Investigation of Electronic Fluctuations in Semiconductor Materials and Devices through First-Principles Simulations and Experiments in Transistor Amplifiers", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12172021-224454947", "creators": [ { "name": { "family": "Choi", "given": "Alexander Youngsoo" }, "id": "Choi-Alexander-Youngsoo", "orcid": "0000-0003-2006-168X", "display_name": "Choi, Alexander Youngsoo" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/tba0-pd94", "abstract": "Electronic noise, or stochasticity in the current, voltage, and frequency of a carrier signal is caused by microscopic fluctuations in the occupation of quantum electronic states. In the context of scientific instrumentation, understanding the physical origin of these fluctuations is of paramount importance since the associated stochasticity ultimately limits the fidelity of information transmitted through electronically processed-signals. The unifying theme of the work presented in this thesis is the study of electronic fluctuations in semiconductor materials and devices. Our interest in this topic is twofold. First, while the Nyquist law dictates the equivalence of noise and transport properties for systems in thermal equilibrium, this relationship breaks down for systems driven out of equilibrium by external forcing. Simulating non-equilibrium electronic fluctuations can therefore provide new insights into the microscopic processes that control energy and momentum relaxation which would not be available from conventional studies of transport alone. Furthermore, because noise properties are sensitive to the microscopic details of the bandstructure and scattering, ab initio simulations of noise observables provide a more rigorous test of the accepted theory of charge transport and carrier scattering in materials. Second, cryogenic low noise amplifiers based on high electron mobility transistors (HEMTs) are widely used in electromagnetic detector chains in applications such as radio astronomy, deep space communications, and quantum computing. The design and optimization of HEMT devices have conventionally relied upon empirical circuit-level models of fluctuations in devices. As the noise performance of modern low-noise amplifiers has saturated to levels five to ten times above the standard quantum limit, these empirical models are unable to resolve the microscopic origin of the limiting excess noise. Identifying the microscopic mechanisms underpinning noise in modern amplifiers is therefore necessary to produce better devices for scientific instrumentation. In this work, we investigate electronic noise in semiconductor materials and devices with a combination of first-principles simulations and Schottky thermometry experiments in transistor amplifiers.
\r\n\r\nFirst, we present our work on the development of novel parameter-free simulations of non-equilibrium noise in semiconductor materials. While the ab initio theory of low-field electronic transport properties such as carrier mobility is well-established, an equivalent treatment of electronic fluctuations about a non-equilibrium steady state has remained less explored. Starting from the Boltzmann Transport Equation, we develop an ab initio method for hot electron noise in semiconductors. In contrast with the typical numerical methods used for electronic noise such as Monte Carlo techniques, no adjustable parameters are required in the present formalism with the electronic band structure and scattering rates calculated from first-principles. Our formalism enables a parameter-free approach to probe the microscopic transport processes that give rise to electronic noise in semiconductors. Next, we apply the developed method to compute the spectral noise power in two materials of technological interest, GaAs and Si. In our first study in GaAs, we show that despite the well-known dominance of optical phonon scattering, the spectral features in AC transport properties and noise originate from a surprising quasi-elasticity in the scattering of warm electrons with the lattice. In our second study, we apply the method to Si which possesses a more complicated multivalley conduction band. This study demonstrates that the widely-accepted one-phonon scattering approximation is insufficient to reproduce the warm electron tensor and that incorporating second-order mechanisms, such as two-phonon scattering, may be critical to obtain an accurate description of noise in such materials.
\r\n \r\nFinally, we discuss our work on developing deeper understandings of electronic noise in real devices with a focus on transistor amplifiers. While the first-principles work described above is appropriate for evaluating noise in ideal materials, in real semiconductor devices, charge carriers are influenced by mechanisms such as defect scattering, size effects, and reflections at interfaces. Owing to the complexity of these mechanisms, HEMT noise is typically treated with empirical models, where the physical noise sources are reduced to fitting parameters. Existing models of HEMT noise, such as the Pospieszalski model, are unable to resolve the mechanisms that set the noise floor of modern transistor amplifiers. In particular, the magnitude of the contribution of thermal noise from the gate at cryogenic temperatures remains unclear owing to a lack of experimental measurements of thermal resistance under these conditions. We report measurements of gate junction temperature and thermal resistance in a HEMT at cryogenic and room temperatures using a Schottky thermometry method. Based on our findings, we develop a phonon radiation model of heat transfer in the device and estimate that the thermal noise from the gate is several times larger than previously assumed. Our work suggests that self-heating results in a practical lower limit for the microwave noise figure of HEMTs at cryogenic temperatures.
" }, { "name": "Chou, Tzu-Chieh", "degree": "PhD", "year": "2022", "title": "Wearable Inductive Damping Sensors for Skin Edema Quantification", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:01152020-143207091", "creators": [ { "name": { "family": "Chou", "given": "Tzu-Chieh" }, "id": "Chou-Tzu-Chieh", "orcid": "0000-0002-6074-8286", "display_name": "Chou, Tzu-Chieh" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/q77f-me73", "abstract": "The electrical conductivity of human organs is closely related to the physiological or pathological changes occurring within the organ. For example, metastatic liver tumors significantly increase electrical conductivity compared to healthy liver tissues over a wide frequency range. Therefore, knowing when and where these conductivity changes happen within an organ is highly valuable for disease monitoring.
\r\n \r\nSkin is the largest human organ by surface area, and under its large surface, there are numerous tiny blood and lymphatic vessels that circulate body fluid and dissipate heat. Therefore, it contains critical information about systemic circulation. Diseases such as congestive heart failure, acute renal injury, and liver failure disturb the systemic circulation and allow extra interstitial fluid to accumulate in the form of peripheral skin edema. As the interstitial fluid is highly conductive, the overall skin conductivity significantly increases when edema occurs.
\r\n\r\nConsequently, quantification of skin edema allows us to track the progression of these diseases and is the main goal to pursue in this study. The current clinical standard uses a 0-to-4 grade system to quantify the severity of edema based on how the skin responds to a pressing force. However, it requires in-person examination and has relatively large inter-examiner variations, making it less suitable for real-time edema monitoring.
\r\n\r\nTo solve the unmet need to quantify edema in real-time, I present a skin edema model that relates skin conductivity to the interstitial fluid volume fraction. The latter is used to quantify the severity of edema. Furthermore, I developed a wearable coil sensor that provides accurate real-time conductivity measurements on subcutis, a significant portion of the skin where edema typically occurs. The coil sensor uses alternating magnetic fields to induce eddy currents in the skin and measures the skin conductivity as a function of coil resistance change. The experimental results suggested that when grade-1 edema occurs, the subcutis conductivity increases from the average value of 0.09 S/m to 0.25 S/m. This change corresponds to an increase of interstitial volume fraction from 10% to 20% in the subcutis. These quantitative results are consistent with finite element simulations and allow direct comparison with ultrasonography measurements. Due to its high accuracy and portability, the proposed wearable sensor opens a new possibility for continuous monitoring of skin edema.
" }, { "name": "Corona, Sydney Lea", "degree": "PhD", "year": "2022", "title": "Emerging Evidence of a Second Glass Phase in Strong to Ultra-Fragile Bulk Metallic Glass-Forming Liquids", "advisor": "Johnson, William Lewis; Samwer, Konrad", "url": "https://resolver.caltech.edu/CaltechTHESIS:04132022-221839497", "creators": [ { "name": { "family": "Corona", "given": "Sydney Lea" }, "id": "Corona-Sydney-Lea", "orcid": "0000-0002-4962-619X", "display_name": "Corona, Sydney Lea" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Samwer", "given": "Konrad" }, "id": "Samwer-K", "orcid": "0000-0003-4266-449X", "role": "co-advisor", "display_name": "Samwer, Konrad" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Samwer", "given": "Konrad" }, "id": "Samwer-K", "orcid": "0000-0003-4266-449X", "role": "member", "display_name": "Samwer, Konrad" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "matsci" ], "doi": "10.7907/9bvb-2d78", "abstract": "This thesis compiles three experimental works that provide evidence for distinct bulk metallic glass (BMG) phases across a range of kinetic fragilities. Motivated by An et al.\u2019s computational discovery of a secondary heterogeneous glass phase in pure Ag and binary AgCu and CuZr, the thesis reports the distinct glass phases in the high and ultra-high fragile regime with a tunable Pt80-XCuXP20 system, and the\r\nkinetically strong Ni71.4Cr5.64Nb3.46P16.5B3 (Ni208) BMG.
\r\n\r\n\r\nThe high-fragility work utilizes direct measurement techniques for liquid configurational enthalpy as a function of temperature on anneal-equilibrated samples (Chapter 2). An apparent first-order glass-melting transition is revealed across kinetic fragilities ranging from m = 60 to over 90. The glass-melting temperature, Tgm, traverses up the\u2000\u2206T region with increasing Cu content, X. A further experimental study of PtCuP explored the traditional and second glass phases to determine if they are in fact equivalent to the two glasses of An et al. (Chapter 3). Hardness data reveal that while the high-fragility samples grow the second glass during anneal, it forms in the ultra-fragile samples on quenching. Further, this apparent glass-melting transition is visible via traditional thermodynamic methods in ultra-fragile samples. For X = 20, where Tgm is in the inaccessible \u2206T region, rapid capacitive discharge heating visualizes Tgm as well.
\r\n\r\nInvestigation of a kinetically stronger Ni-based BMG connects the presence of the secondary glass to the embrittlement transition in Ni208 (Chapter 4). Inclusions are only present in embrittled samples, and are suppressed to lower temperatures when the initial melt is overheated above a critical toughening temperature. The inclusions show a heterogeneous structure and 30% increased hardness, similar to the computational Ag secondary glass phase.
\r\n\r\nThese works provide compelling evidence for the existence of a secondary glass phase across the spectrum from strong to ultra-fragile glasses, and validates the initial computational discovery. This proves to be a significant work, as it presents direct experimental evidence of a novel phenomenon in metallic liquids, and presents a new solid-like glass phase.
" }, { "name": "Costanza, Vincenzo", "degree": "PhD", "year": "2022", "title": "Thermally Responsive Polymers for Wearable Calorimeters", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272022-085102678", "creators": [ { "name": { "family": "Costanza", "given": "Vincenzo" }, "id": "Costanza-Vincenzo", "orcid": "0000-0002-2409-0632", "display_name": "Costanza, Vincenzo" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "medeng" ], "doi": "10.7907/0hf9-8m62", "abstract": "The measurement of the body core temperature (BCT) can provide insightful health information spanning from hypothermia and heat stroke to inflammations and infections. In addition, the continuous monitoring of the BCT can unlock new possibilities for people\u2019s well-being such counting of burnt calories, prediction of the ovulation period in the female population, and for the assessment of mental health issues. However, the integration of a BCT sensor in wearable devices is extremely challenging, since standard methods cannot combine minimal invasiveness with high measurement accuracy. Dual heat flux (DHF) thermometry is a novel technique that allows the precise estimation of BCT from the measurement of skin temperature. Nevertheless, the limited precision of currently available temperature sensors has not favored the wide spread of devices based on this architecture. In this thesis, we present the fabrication of a fully wearable DHF thermometer realized by integrating new polymers with a remarkable temperature sensitivity. In these particular polymers, an increase in temperature results in a change of the ionic conductivity. In the first part of this work, we focus on the understanding of the ion transport mechanism in these polymers and, in particular, on the nature of the interaction between the functional groups present on the polymer backbone and the conducting species (i.e. metal cations and water molecules). We show that the ion\u2019s coordinating environment is the key to make these materials highly sensitive to temperature. The second part of the thesis tackles the fabrication of a BCT sensor, integrating these temperature responsive polymers in an ultrathin DHF thermometer. Building on the understanding of the nature of the temperature response, we optimize the polymer\u2019s composition to obtain a thermal sensitivity that allows a good precision when measuring the BCT. Finally, we characterize the performance of the fabricated DHF thermometer in different conditions, assessing the sensor\u2019s accuracy and response time." }, { "name": "Cua, Eunice Michelle Chua", "degree": "PhD", "year": "2022", "title": "Exploiting Speckle to Image Deeper in Scattering Media", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:09152021-000948244", "creators": [ { "name": { "family": "Cua", "given": "Eunice Michelle Chua" }, "id": "Cua-Eunice-Michelle-Chua", "orcid": "0000-0002-0394-757X", "display_name": "Cua, Eunice Michelle Chua" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/rcsj-a410", "abstract": "Optical methods for imaging and focusing are advantageous in many scenarios as optics can provide exquisite spatial resolution, has multiple sources of contrast, and does not impart ionizing radiation. However, optical scattering remains a fundamental challenge which limits the depth at which we can perform imaging with good spatial resolution. This challenge motivated our investigations into methods that could make use of the scattered light in order to extend the depth of imaging through or within scattering media. In particular, we focus on answering: (1) Can one 'unscramble' the scattered light in order to recover information about the otherwise hidden object?; and (2) Can we preferentially detect the more forward scattered photons in an efficient manner in order to allow deeper penetration with modest resolution? These two questions are explored in the first two projects of the thesis:
\r\n\r\n1. The development of an imaging system that detects the scattered light and exploits correlations within the scattering process to enable imaging through scattering media at diffraction-limited resolution.
\r\n\r\n2. The introduction of a novel method, termed Speckle-Resolved Optical Coherence Tomography, that sensitively and preferentially detects the more forward scattered photons in a coherent, speckle-resolved fashion to allow deeper imaging at moderate resolution.
\r\n\r\nOptical methods offer the benefit of visualizing samples that would otherwise appear transparent. Using light, one is able to visualize and measure the thickness of transparent films and coatings in a non-contact manner. The third project in my thesis focuses on using light to non-destructively visualize and characterize the evenness of the silicone oil layer that typically coats the inner surface of prefilled syringes. Characterizing the evenness of this silicone oil layer is important as it impacts the functionality of the prefilled syringe and may correlate with particle formation, which is undesirable as the number of particles in a syringe is regulated due to potential health concerns.
" }, { "name": "Dobreva, Tatyana", "degree": "PhD", "year": "2022", "title": "Engineering Tools to Probe and Manipulate the Immune System at Single-Cell Resolution", "advisor": "Thomson, Matthew; Gradinaru, Viviana", "url": "https://resolver.caltech.edu/CaltechTHESIS:10172021-215439860", "creators": [ { "name": { "family": "Dobreva", "given": "Tatyana" }, "id": "Dobreva-Tatyana", "orcid": "0000-0002-2625-8873", "display_name": "Dobreva, Tatyana" } ], "advisors": [ { "name": { "family": "Thomson", "given": "Matthew" }, "id": "Thomson-M-W", "orcid": "0000-0003-1021-1234", "role": "advisor", "display_name": "Thomson, Matthew" }, { "name": { "family": "Gradinaru", "given": "Viviana" }, "id": "Gradinaru-V", "orcid": "0000-0001-5868-348X", "role": "co-advisor", "display_name": "Gradinaru, Viviana" } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Gradinaru", "given": "Viviana" }, "id": "Gradinaru-V", "orcid": "0000-0001-5868-348X", "role": "member", "display_name": "Gradinaru, Viviana" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Thomson", "given": "Matthew" }, "id": "Thomson-M-W", "orcid": "0000-0003-1021-1234", "role": "member", "display_name": "Thomson, Matthew" } ], "option_major": [ "medeng" ], "doi": "10.7907/n3rs-ft69", "abstract": "My thesis focuses on developing experimental and computational tools to probe and manipulate cellular transcriptomes in the context of human health and disease. Chapter 1 and 2 focus on published work where we leverage single-cell RNA sequencing (scRNA-seq) to understand human immune variability, characterize cell-type specific biases of multiple viral variants within an animal, and assess temporal immune response in the brain to delivery of genetic cargo via an adeno-associated virus (AAV). Chapter 3 and 4 present progress I have made on tools for exporting RNA extracellularly and engineering of a transcription factor for modulating macrophage state.
\r\n\r\nFor probing cellular transcriptome states, we have developed a platform using multiplexed single-cell sequencing and out-of-clinic capillary blood extraction to understand temporal and inter-individual variability of gene expression within immune cell types. Our platform enables simplified, cost-effective profiling of the human immune system across subjects and time at single-cell resolution. To demonstrate the power of our platform, we performed a three day time-of-day study of four healthy individuals, generating gene expression data for 24,087 cells across 22 samples. We detected genes with cell type-specific time-of-day expression and identified robust genes and pathways particular to each individual, all of which could have been missed if analyzed with bulk RNA-sequencing. Also, using scRNA-seq, we have developed a method to screen and characterize cellular tropism of multiple AAV variants. Additionally, I have looked at AAV-mediated transcriptomic changes in animals injected with AAV-PHP.eB three days and twenty-five days post-injection. I have found that there is an upregulation of genes involved in p53 signaling in endothelial cells three days post-injection.
\r\n\r\nIn the context of manipulating cellular transcriptomic states, I demonstrate that a fusion between RNA targeting enzyme, dCas13, and capsid-forming neuronal protein, Arc, is able to form a capsid-like structure capable of encapsulating RNA. I also present methods and preliminary data for tuning macrophage states through mutations in transcription factor EB (TFEB) using scRNA-seq as a readout.
" }, { "name": "Dorn, Charles Jacob", "degree": "PhD", "year": "2022", "title": "Geometry Synthesis and Multi-Configuration Rigidity of Reconfigurable Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:09182021-045958776", "creators": [ { "name": { "family": "Dorn", "given": "Charles Jacob" }, "id": "Dorn-Charles-Jacob", "orcid": "0000-0001-6516-2586", "display_name": "Dorn, Charles Jacob" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/ph2w-9a34", "abstract": "Reconfigurable structures are structures that can change their shapes to change their functionalities. Origami-inspired folding offers a path to achieving shape changes that enables multi-functional structures in electronics, robotics, architecture and beyond. Folding structures with many kinematic degrees of freedom are appealing because they are capable of achieving drastic shape changes, but are consequently highly flexible and therefore challenging to implement as load-bearing engineering structures. This thesis presents two contributions with the aim of enabling folding structures with many degrees of freedom to be load-bearing engineering structures.
\r\n\r\nThe first contribution is the synthesis of kirigami patterns capable of achieving multiple target surfaces. The inverse design problem of generating origami or kirigami patterns to achieve a single target shape has been extensively studied. However, the problem of designing a single fold pattern capable of achieving multiple target surfaces has received little attention. In this work, a constrained optimization framework is presented to generate kirigami fold patterns that can transform between several target surfaces with varying Gaussian curvature. The resulting fold patterns have many kinematic degrees of freedom to achieve these drastic geometric changes, complicating their use in the design of practical load-bearing structures.
\r\n\r\nTo address this challenge, the second part of this thesis introduces the concept of multi-configuration rigidity as a means of achieving load-bearing capabilities in structures with multiple degrees of freedom. By embedding springs and unilateral constraints, multiple configurations are rigidly held due to the prestress between the springs and unilateral constraints. This results in a structure capable of rigidly supporting finite loads in multiple configurations so long as the loads do not exceed some threshold magnitude. A theoretical framework for rigidity due to embedded springs and unilateral constraints is developed, followed by a systematic method for designing springs to maximize the load-bearing capacity in a set of target configurations. An experimental study then validates theoretical predictions for a linkage structure. Together, the application of geometry synthesis and multi-configuration rigidity constitute a path towards engineering reconfigurable load-bearing structures.
" }, { "name": "Dougherty, Christopher John", "degree": "PhD", "year": "2022", "title": "On the Experimental Simulation of Atmospheric-Like Disturbances Near the Surface", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272022-085410375", "creators": [ { "name": { "family": "Dougherty", "given": "Christopher John" }, "id": "Dougherty-Christopher-John", "orcid": "0000-0002-0974-5696", "display_name": "Dougherty, Christopher John" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Brown", "given": "Garry L." }, "id": "Brown-Garry-L", "role": "member", "display_name": "Brown, Garry L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/293w-ev66", "abstract": "Any and every 'decision-maker'\u2019 gravity-bound to the planetary surface (or very nearly so) must contend with the frictional complexities confined to its relatively small surface layer. From the perspective of the near-surface bound small autonomous flyer, it is the microclimatic local set of atmospheric conditions (i.e. the weather), characterized by moisture, temperature, and the parameters describing wind, that determines the baseline flowfields within which these flyers must navigate and negotiate. Unlike their human-on-board counterparts, mission parameters relegate small (nearly) massless autonomous flyers to the lower regions of the atmospheric boundary layer, where they may not be fortuned enough to soar above the effects of friction or wait for clearer skies. Relatively little focus has been placed on the experimental strategies of how these machines might learn to function in challenging scenarios well-before encountering them in the real-world. To address such shortcomings, this work focuses on the experimental simulation of flight-relevant environments through the development of multi-source wind generating apparatuses (i.e. fan arrays) that can initialize velocity distributions discretely-individually or in-concert to produce appropriate mean and fluctuating velocities through an ample open-air test envelope that enables full-scale conventional statically-mounted aerodynamic-characterizations up through free-flight autonomous vehicle testing. Though outside the scope of current experimental work, as full of an environmental description (i.e. moisture, temperature, and wind) is given as possible, prior to ultimately reducing the scope to a neutrally stable atmosphere devoid of any major weather events other than a reasonably strong prevailing wind. Nearly always set amongst the backdrop of a high Reynolds number turbulent flowfield, two primary prototypical flowfields (continuous-gust and discrete-gust) are identified as meriting consideration for mainstay experimental simulation. The core features within the spectral overlap of these windy disturbance environments with the response characteristics of flyers of interest ensure that the turbulence of consideration is nearly always of the mechanical-type. Unlike air motions far above local effects in the inertial sublayer (ISL), the dominant flow mechanism within regions of interest near canopied surfaces is augmented by the presence of coherent structures due to the prevalence of locally initiated mixing layers and wakes such that the task becomes one of simulation of suitable forcing spectra in the physical domain for the regions of interest during anticipated times-of-flight.
\r\n\r\nLikely to prove challenging to the small autonomous flyer are encounters of a change in wind state that occur upon piercing the dividing streamline of air masses of two different velocities. From the view of the flyer navigating the built-up environment, intermittent free shear layers due to wind-interactions with surface roughness elements are unavoidable and are experienced discretely when the flyer and shear layer dynamics are decoupled. Fan array techniques for the generation of mixing layers, the basic building block of any such free shear layer, is explored as a candidate flowfield for the experimental simulation of a discrete gust forcing input for the flyer near the surface. Both initialized dual-stream and triple-stream mixing layers at flight-relevant freestream velocity differences are explored and found to principally behave like the mixing layers developed in a more conventional splitterplate experiment. The Reynolds number Reδω based on the velocity difference ΔU and vorticity thickness δω (both outer scale parameters) is shown to linearly increase with downstream development as the vorticity thickness increases commensurately. The spectral analysis along the centerline confirms local isotropy for every tested case.
\r\n\r\nThe continuous-gust flowfield (simply referred to as 'turbulence) is prevalent throughout the atmospheric boundary layer as are quasi-coherent flowfields of superimposed wakes within canopied environments. Because velocity fluctuations manifest as (predominantly) random deviations at any given instant, these flowfields are good candidates for statistical analysis. Generation techniques to produce such turbulent flowfields are introduced and compared against the uniform flow modality (i.e. all fan units set to produce nominally the same initial velocity condition to develop a well-mixed turbulent flowfield beyond x/L \u223c 0.5 with ReλT = 135). The random-phase (R-P) perturbation technique proves useful in increasing ReλT upwards of nearly sevenfold with only a slight further-loss-of-uniformity (to within 3.7% of the mean). The uniform flow modality with the (R-P) perturbation activated is shown, through the presence of a -5/3 slope power law region, to be locally isotropic at relevant freestream velocities. Significant increases in ReλT are made through a static-reconfiguring of the discrete source fan units into a so called quasi-grid (Q-G) configuration. The highest recorded Taylor microscale Reynolds number was found to be ReλT = 2700, likely accompanied by a non-negligible loss of uniformity at the fixed measurement location, though traverses were not undertaken during this campaign so no direct statement of homogeneity is put forth.
\r\n\r\nFor all the flow modalities presented (i.e uniform, pseudo-random, quasi-coherent, and mixing layer), the high-Re number criteria (Reδω \u2248 104 , ReλT \u2248 102) has been met. This serves, then, as a necessary minimum benchmark in the development of multi-source wind tunnels with intended use as environmental simulators for flyers near the surface and also provides the basis for a spectral framework of comparison to enable systematic development of flowfields in future work. Characteristics of the evolving flowfields can further be tuned through the introduction of perturbation techniques applied as initial conditions to both increase the standard deviation of the fluctuating velocities about a desired mean as well as to initiate, evolve, and combine flowfields in representative ways. A preliminary example of one such combination of flow modalities (pseudo-random and mixing layer) indicates significant alteration of flow development compared to a nominal mixing layer case.
" }, { "name": "Ferreira, Vinicius Thaddeu dos Santos", "degree": "PhD", "year": "2022", "title": "Waveguide Quantum Electrodynamics with Superconducting Slow-Light Waveguide Circuits", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312022-105606161", "creators": [ { "name": { "family": "Ferreira", "given": "Vinicius Thaddeu dos Santos" }, "id": "Ferreira-Vinicius-Thaddeu-dos-Santos", "orcid": "0000-0002-9522-2567", "display_name": "Ferreira, Vinicius Thaddeu dos Santos" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Brandao", "given": "Fernando" }, "id": "Brand\u00e3o-F-G-S-L", "orcid": "0000-0003-3866-9378", "role": "member", "display_name": "Brandao, Fernando" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/y4vk-a827", "abstract": "Waveguide quantum electrodynamics (QED) refers to the study of quantum emitters (qubits) coupled to a single mode waveguide - a 1D electromagnetic reservoir with a continuum of states. This paradigmatic quantum-optical system can serve as a test-bed for experimental investigations in many-body physics, quantum non-linear optics, reservoir engineering, non-Markovian physics, quantum networks, and quantum computing. While such a system can be realized in a variety of physical platforms, superconducting quantum circuits are well suited to the study of waveguide QED due their readily available strong light-matter interaction strengths.
\r\n\r\nOf particular interest is the ability to tailor the dispersion relation and modal properties of the waveguide beyond that of a conventional waveguide with linear dispersion. For example, through periodic modulation of the geometry of a waveguide, or through the fabrication of an array of coupled resonant elements, novel electromagnetic responses can be engineered. These include spectral constriction of the 1D continuum to a transmission band of finite bandwidth, enhanced or suppressed emission rates of quantum emitters into the waveguide that are dependent on their frequencies, and extreme slowing of the velocity of light. Such attributes of dispersive waveguides can be leveraged to substantially enrich the physics and applications of qubit-waveguide systems.
\r\n\r\nIn this thesis, we demonstrate the design, fabrication, and characterization of a slow-light waveguide (SLWG) comprised of an array of coupled lumped-element superconducting microwave resonators, and present on various experiments involving superconducting transmon qubits coupled to the SLWG. We investigate the physics of a qubit strongly coupled to the SLWG reservoir by tuning its frequency across the passband of this waveguide, where we find substantial changes to the qubit emission rate, along with oscillatory energy relaxation of the qubit resulting from the beating of bound and radiative dressed qubit-photon states. Further, upon addition of a reflective boundary to one end of the waveguide, we observe revivals in the qubit population on a timescale 30 times longer than the inverse of the qubit's emission rate, corresponding to the round-trip travel time of an emitted photon.
\r\n\r\nIn addition, we show how we leveraged the ability to induce this non-Markovian time-delayed feedback via the SLWG's long delay to generate multidimensional cluster states of itinerant microwave photonic qubits. By utilizing the SLWG as a delay line with 240 ns round-trip delay, a single flux-tunable transmon qubit as a quantum emitter, and a second auxiliary transmon as a switchable mirror, we achieve rapid, shaped emission of entangled photon wavepackets, and effect time-delayed feedback within the waveguide between previously emitted photons and the emitter qubit. We leverage these capabilities to generate a 2D cluster state of four photons with 70% fidelity, as verified by tomographic reconstruction of the quantum state. We conclude by discussing directly realizable novel follow-up experiments that involve a continuously driven qubit in the presence of time-delayed feedback, and discuss how our cluster-state generation scheme could be straightforwardly extended to generation of even larger multidimensional cluster states, thereby enabling utilization of such states for quantum information processing techniques in the microwave domain.
" }, { "name": "Fikes, Austin Covey", "degree": "PhD", "year": "2022", "title": "Future Microwave Arrays Take Shape", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:02092022-003219315", "creators": [ { "name": { "family": "Fikes", "given": "Austin Covey" }, "id": "Fikes-Austin-Covey", "orcid": "0000-0003-4889-5782", "display_name": "Fikes, Austin Covey" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/h541-3e28", "abstract": "Phased arrays provide high gain electronically steerable beams and are powerful systems for sensing and communication. Existing phased arrays are typically small, rigid, and planar which limits their possible use cases. This thesis describes the author's contributions to the creation of novel phased array architectures which can enable new phased array systems and applications. The first chapter describes the design, testing, and use of the scalable router. Scalable routers are a time delay array relay used to reroute signals a microwave frequencies. The second chapter describes the development of large scale flexible phased arrays, first in the context the Caltech Space Solar Power Project, and then in an exploration of a technique for determining the shape of arrays using only mutual coupling between elements. Finally, a guide for developing electronics for academic space payloads is included as an appendix.
" }, { "name": "Folkestad, Carl A. A.", "degree": "PhD", "year": "2022", "title": "Koopman-based Learning and Control of Agile Robotic Systems", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122021-213903517", "creators": [ { "name": { "family": "Folkestad", "given": "Carl A. A." }, "id": "Folkestad-Carl-A-A", "orcid": "0000-0002-3436-8247", "display_name": "Folkestad, Carl A. A." } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "chair", "display_name": "Ames, Aaron D." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cds" ], "doi": "10.7907/2t6d-j206", "abstract": "Learning methods to enable high performance control systems have recently shown promising results in selected environments and applications. These advances promote the next generation of autonomous robots capable of significantly improving efficiency, cost, and safety in their respective domains. Importantly, these systems are safety-critical and operate in proximity to humans in diverse and uncertain environments. As a result, operational failures may cause significant material and societal losses. Additionally, robot learning and control are further complicated by requiring fast controller update rates and operational constraint satisfaction.
\r\n\r\nTo address these challenges, this thesis presents multiple methods based on Koopman operator theory. The first approach develops algorithms to learn lifted-dimensional models of nonlinear systems and leverages the models in model predictive control (MPC) design. Koopman-based methods typically employ hand-crafted observable functions to \"lift\" the state variables to the higher dimensional space. For most systems, this leads to poor prediction performance and inefficient use of data and computational resources. Instead, I present methods that generate observable functions from data, both based on underlying theory and by incorporating the observable functions and model structure in a neural network model. This allows lower dimensional models, important for real-time control, and enables the nonlinearities of control-affine dynamics to be captured, crucial to describing many robotic systems. I use quadrotor drones to experimentally demonstrate that the learned models combined with MPC can achieve close to optimal behavior while respecting important operational constraints.
\r\n \r\nThe last part of the thesis is concerned with endowing systems with an arbitrary nominal control policy with safety guarantees. Control barrier functions (CBFs) are a powerful tool to achieve this, yet they rely on the computation of control invariant sets, which is notoriously difficult. To avoid this, a backup strategy can be used to implicitly define a control invariant set. However, this requires forward integration of the system dynamics under a backup controller, which is prohibitively expensive for realistic systems. I present a method that replaces the expensive integration using learned Koopman operators of the closed-loop dynamics. As a result, the online computation time required to evaluate the controller is drastically reduced, enabling real-time use. I also derive an error bound on the unmodeled dynamics in order to robustify the CBF controller and demonstrate the method on multi-agent collision avoidance for wheeled robots and quadrotors.
" }, { "name": "Gao, Yang", "degree": "PhD", "year": "2022", "title": "Extending the Capability of Classical Quantum Many-Body Methods", "advisor": "Chan, Garnet K.; Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01032022-192500728", "creators": [ { "name": { "family": "Gao", "given": "Yang" }, "id": "Gao-Yang", "orcid": "0000-0003-2320-2839", "display_name": "Gao, Yang" } ], "advisors": [ { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-Garnet-K-L", "orcid": "0000-0001-8009-6038", "role": "co-advisor", "display_name": "Chan, Garnet K." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "co-advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-Garnet-K-L", "orcid": "0000-0001-8009-6038", "role": "member", "display_name": "Chan, Garnet K." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" } ], "option_major": [ "matsci" ], "doi": "10.7907/15dc-sd19", "abstract": "This thesis discusses several topics in extending the capability of conventional quantum many-body methods. The first project focuses on extending quantum chemical methods, namely coupled cluster theory, to the correlated systems in the condensed phase. We consider bulk nickel oxide and manganese oxide, which are two paradigmatic correlated electron materials that pose challenges to traditional density functional theory-based simulation framework. We adapted molecular coupled cluster singles and doubles theory using Gaussian basis sets with translational symmetry and norm-conserving pseudopotential. This allowed us to carry a detailed study on the ground and excited states of the two materials.
\r\n \r\nThe second project investigates numerical optimization techniques for Abelien group symmetric tensor contractions. In many-body quantum simulations, group symmetries in states and operators often lead to block sparse structure in the representing tensors. Exploiting this opportunity can significantly reduce the computation cost and memory footprint in tensor contractions. We consider cyclic group symmetry and introduce an efficient remapping scheme to express the sparse tensor contractions almost fully in terms of dense tensor operations.
\r\n \r\nThe third project is devising a wavefunction-based method for coupled electrons and phonons. We are interested in simulating the interacting electrons and phonons at the same footing using coupled cluster methods. The ground state and excited state of two types of systems are investigated in this work: the Hubbard Holstein model and diamond crystal in ab initio setting.
\r\n \r\nFinally, the fourth project is to develop a generic framework for tensor network simulation on fermionic systems. Tensor network methods are powerful tools to study strongly correlated physical systems. However, traditionally these methods have been developed with commutative algebraic rules, which are commensurate with bosons but not compatible with anti-symmetric fermions. Our approach encodes the fermion statistics directly in the block sparse tensor backend so the tensors behave just like anti-commuting fermion operators.
" }, { "name": "Goel, Gautam", "degree": "PhD", "year": "2022", "title": "Regret-Optimal Control", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-021936716", "creators": [ { "name": { "family": "Goel", "given": "Gautam" }, "id": "Goel-Gautam", "orcid": "000-0002-7054-7218", "display_name": "Goel, Gautam" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Hazan", "given": "Elad" }, "id": "Hazan-Elad", "orcid": "0000-0002-1566-3216", "role": "member", "display_name": "Hazan, Elad" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" } ], "option_major": [ "cms" ], "doi": "10.7907/8t6d-4t53", "abstract": "Optimal controllers are usually designed to minimize cost under the assumption that the disturbance they encounter is drawn from some specific class. For example, in H\u2082 control the disturbance is assumed to be generated by a stochastic process and the controller is designed to minimize its expected cost, while in H\u221e control the disturbance is assumed to be generated adversarially and the controller is designed to minimize its worst-case cost. This approach suffers from an obvious drawback: a controller which encounters a disturbance which falls outside of the class it was designed to handle may perform poorly. This observation naturally motivates the design of adaptive controllers which dynamically adjust their control strategy as they causally observe the disturbance instead of blindly following a prescribed strategy.
\r\n\r\nInspired by online learning, we propose data-dependent regret as a criterion for controller design. In the regret-optimal control paradigm, causal controllers are designed to minimize regret against a hypothetical optimal noncausal controller, which selects the cost-minimizing sequence of control actions given noncausal access to the disturbance sequence. Controllers with low regret retain a performance guarantee irrespective of how the disturbance is generated; it is this universality which makes our approach an attractive alternative to traditional H\u2082 and H\u221e control. The regret of the causal controller is bounded by some measure of the complexity of the disturbance sequence; we consider several different complexity measures, including the energy of the disturbance sequence, which measures the size of the disturbance, and the pathlength of the disturbance, which measures its variation over time. We also consider the alternative metric of competitive ratio, which is the worst-case ratio between the cost incurred by the causal controller and the cost incurred by the optimal noncausal controller. This metric can also be viewed as a special case of data-dependent regret, where the complexity measure is simply the offline optimal cost. For each of these complexity measures, we derive a corresponding control algorithm with optimal data-dependent regret. The key technique we introduce is an operator-theoretic reduction from regret-optimal control to H\u221e control; each of the regret-optimal controllers we obtain can be interpreted as an H\u221e controller in a synthetic system of larger dimension. We also extend regret-optimal control to the more challenging measurement-feedback setting, where the online controller must choose control actions without directly observing the disturbance sequence, using only noisy linear measurements of the state.
\r\n\r\nWe show that the competitive controller can be arbitrarily well-approximated by the class of disturbance-action-controller (DAC) policies. The convexity of this class of policies makes it amenable to online optimization via a reduction to online convex optimization with memory, and this class has hence attracted much recent attention in online learning. Using our approximation result, we show how to obtain algorithms which achieve the \"best-of-both-worlds\": sublinear policy regret against DAC policies and approximate competitive ratio. These performance guarantees can even be extended to the \"adaptive control\" setting, where the controller does not know the system dynamics ahead of time and must perform online system identification.
\r\n\r\nWe present numerical experiments in a linear dynamical system which demonstrate how the performance of regret-optimal controllers varies as a function of the complexity of the disturbance. We extend regret-optimal control to nonlinear dynamical systems using model-predictive control (MPC) and present experiments which suggest that regret-optimal control is a promising approach to adapting to model error in nonlinear control.
" }, { "name": "Hanania, Haeri Park", "degree": "PhD", "year": "2022", "title": "Nanophotonic Application to Biomedical Devices", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:02182022-230421298", "creators": [ { "name": { "family": "Hanania", "given": "Haeri Park" }, "id": "Hanania-Haeri-Park", "orcid": "0000-0002-2206-5732", "display_name": "Hanania, Haeri Park" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "orcid": "0000-0002-8903-7939", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "medeng" ], "doi": "10.7907/tzpw-pt75", "abstract": "Nanophotonics is the study of interactions between nanoscale structures and light. It has greatly expanded the fields of application over the past decades, taking advantage of the advancement in MEMS technology. The most common nanophotonic structures consist of either dielectrics, metals, or both. When a nanophotonic structure contains metals, it is considered as a plasmonic structure. Plasmonics is a field of light-metal interactions. Due to the negative permittivity of metals, the electromagnetic energy of light is focused at the metal-dielectric interface and creates plasmons-a collective motion of electrons in the conduction band of metals. By shaping metals into different structures to achieve a desired performance, plasmonics have been successfully applied to many fields including photovoltaics, spectroscopy, and biomedical devices.
\r\n\r\nThis thesis provides 3 different applications of biomedical devices in which nanophotonics-articularly plasmonics-was applied. Chapter 1 discusses the application of nanophotonics to molecular sensing. In this chapter, an open-top, tapered waveguide that serves as a 3-dimensional plasmon cavity is demonstrated and achieves a near or single molecular detection. Chapter 2 discusses the application of nanophotonics to an implantable intraocular pressure sensor. In this chapter, an array of gold nanodots are introduced on a flexible membrane to optimize the performance of the sensor. Chapter 3 discusses the application of nanophotonics to angle-and-polarization independent pressure or strain sensing, which reduces the need for precise alignment or a trained technician, and therefore can be easily applied to moving subjects in diverse environments. Inspired by the geometry and optical principles of butterfly corneas, an array of gold paraboloids is designed to support a surface plasmon resonance that is angle-and-polarization independent. This array is integrated onto a hermetically sealed cavity with a flexible membrane and enables angle-and-polarization independent pressure/strain sensing.
" }, { "name": "Harmon, John Michael", "degree": "PhD", "year": "2022", "title": "Predicting the Strength of Planetary Surfaces", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10152021-195617065", "creators": [ { "name": { "family": "Harmon", "given": "John Michael" }, "id": "Harmon-John-Michael", "orcid": "0000-0002-8323-3488", "display_name": "Harmon, John Michael" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/r9zm-kp19", "abstract": "Our curiosity and spirit for exploration has fueled advancements towards visiting Earth's neighbors in the solar system. Environments outside of Earth are extreme, however, and it is far from guaranteed that landing and operating on the surface of these bodies is an easy task. Conditions such as reduced gravity, extreme temperatures and sparse atmospheres play a role in the compressive, shear, and tensile strength of a surface. These environmental factors make experiments that work to inform design decisions for spacecraft-surface interaction difficult and expensive. In order to better ensure successful mission operations in the future, this thesis focuses on the development of a platform of numerical modeling for planetary surface interaction.
\r\n \r\nDry regolith and water ice are two surface materials that are pervasive in the solar system. For each, the mechanical properties are heavily reliant on features at the microscale that are insufficiently modeled. The first part of the thesis will focus on crushable dry regolith. There will be two chapters on this topic, the first of which discusses the development of the modeling capability to capture both the highly irregular particle shapes and the brittle nature of regolith. The second chapter on regolith will focus on the validation of this method on a crushable sand sample experiment. This model demonstrates excellent predictive capability for the constituitive relationship, the evolution of particle sizes, and the evolution of particle shape in the sample. Further, evidence from the forces between the particles shows that despite larger particles being weaker on average, many survive due to two reasons. One, the surviving particles are generally on the stronger side of the particle strength distribution, and second, that larger particles have a higher coordination number producing a more isotropic stress state in the particle.
\r\n \r\nUnlike dry regolith, distinct neighboring water ice particles will sinter together over time at varying rates depending on their environment. This leads to a large amount of the water ice surfaces that are of interest to future missions, having a highly varied and many times unknown levels of strength. The contact interaction between water ice particles at the microscale will be handled the same as regolith, however a modification was added to account for sintering. The strong cohesiveness sintering generates is modeled by placing massless bonds where sinters would form. The cross-sectional area of the bond represents the amount of sintering that has taken place and can be thought of as a representation of the neck geometry that early stage sintering is described as. The bonds used are linear elastic and breakable in order to capture the crushable nature of porous ice. Three chapters are dedicated to ice modeling. First, the model development will be shown with verification examples for its use. Second, the model will be used to predict cone penetration tests on ice that were previously conducted in experiment. Comparisons show that the model can produce similar stresses and qualitative features observed in the experiment. A sensitivity analysis is conducted and shows that the most important controlling parameters are the ice\u2019s critical strength and the sinter's neck thickness. The relation of the bond characteristics to the sintering process is discussed. In the third chapter on water ice, the landing of a footpad on the surface of Enceladus is modeled. The model predicts that a lack of sintering could result in catastrophic sinkage, however even moderate sintering provides enough strength to support a lander. Also the model predicts landing on inclined surfaces and shows that landing could be possible at angles as high as 20 degrees.
" }, { "name": "Herren, Benjamin Riley", "degree": "PhD", "year": "2022", "title": "Oxidative and Internal Stress Effects of Dopants in Multilayer Yb\u2082Si\u2082O\u2087 Environmental Barrier Coatings", "advisor": "Faber, Katherine T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012022-214247822", "creators": [ { "name": { "family": "Herren", "given": "Benjamin Riley" }, "id": "Herren-Benjamin-Riley", "orcid": "0000-0002-6011-710", "display_name": "Herren, Benjamin Riley" } ], "advisors": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "advisor", "display_name": "Faber, Katherine T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Almer", "given": "Jonathan D." }, "id": "Almer-Jonathan-D", "orcid": "0000-0002-1900-2271", "role": "member", "display_name": "Almer, Jonathan D." }, { "name": { "family": "Lee", "given": "Kang N." }, "id": "Lee-Kang-N", "orcid": "0000-0003-1215-0228", "role": "member", "display_name": "Lee, Kang N." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "matsci" ], "doi": "10.7907/4cm0-8e79", "abstract": "One of the best approaches to improving the efficiency of turbine engines is to increase their operating temperatures. A revolutionary improvement toward this goal will be the replacement of structural metallic components with silicon-based ceramic-matrix composites (CMCs). However, corrosive chemistries in combustion engines necessitate chemical protection of the structural material. Environmental Barrier Coatings (EBCs) are designed for this purpose through thermomechanical and chemical compatibility with the system. High-temperature, humid oxidation of the EBC bondcoat, a silicon layer which adheres the topcoat to the substrate, remains a critical failure mode EBC systems.
\r\n\r\nThis work studies the effects of chemical modifications on bondcoat oxidation during steam cycling in a current state-of-the-art EBC (Yb\u2082Si\u2082O\u2087/Si), and the implications for the durability of the system. Chemically modified EBCs have been shown to decrease oxide growth by more than 85 percent after 1000 hours of steam cycling. Post-exposure analyses are used to investigate the effects of chemistry on thermal oxide thickness and microstructure. Synchrotron X-ray scattering at the Advanced Photon Source, Argonne National Laboratory, is used to observe internal strains, connected to oxidation and chemistry through microstructure. Compared internal stresses, oxidation, and microstructure between baseline and modified EBCs promote the effectiveness of topcoat chemical modifications as they may apply to EBC durability. Microindentation, nanoindentation, and ongoing beam-bending experiments are also used to assess EBC interface toughness in a baseline EBC system. Additionally, a custom induction furnace has been designed and tested for in-situ steam cycling at the synchrotron. Traits facilitating the use of the custom furnace at the synchrotron make for convenient steam-cycling and other exposures in conventional laboratory settings, as well, with enhanced customizability and flexibility.
" }, { "name": "Hooper, Morgan Louise", "degree": "PhD", "year": "2022", "title": "Characterization and Optimization of a Fully Passive Flapping Foil in an Unsteady Environment for Power Production and Propulsion", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312022-024822211", "creators": [ { "name": { "family": "Hooper", "given": "Morgan Louise" }, "id": "Hooper-Morgan-Louise", "display_name": "Hooper, Morgan Louise" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Brunton", "given": "Steven L." }, "id": "Brunton-S-L", "role": "member", "display_name": "Brunton, Steven L." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/tymc-1985", "abstract": "This thesis provides an experimental window into the duality between thrust production and energy harvesting by a flapping foil subject to unsteadiness in an oncoming flow. In particular, an airfoil is placed downstream of a circular cylinder, and allowed to interact with the vorticity shed in its wake to produce motions in both the transverse and streamwise directions. It is confirmed that under the right conditions, passive fluid-structure interactions arising from such a configuration give rise to simultaneous extraction of energy from the flow, coupled with net thrust larger than net drag experienced by the airfoil.
\r\n\r\nMeasurements of forces acting on the airfoil and the motion that arises are presented, for cases where the flapping motion is both active (the foil is driven through a pre-planned trajectory) and fully passive (the foil is allowed to react to the fluid forcing it experiences). These are coupled with simultaneous Particle Image Velocimetry (PIV) measurements of the flow field in the region of the airfoil. These measurements allow for direct observation of fluid-structure interactions which give rise to both thrust production and power extraction potential, illuminating the mechanisms driving each. The dynamics of a fully passive flapping foil are largely determined by the mounting system used to facilitate its motion. It is shown that by leveraging Cyber-Physical Fluid Dynamics (CPFD) capabilities to tune these mounting parameters, the behaviour of a fully passive flapping foil can be made similar to that of a representative driven system. A framework based on a simplified linear model for mounting system dynamics is presented, to allow for the optimization of such a system for power extraction potential subject to relevant engineering constraints. The effects of nonlinearity on airfoil behaviour, particularly those due to friction in the mechanism(s) permitting passive flapping, are also explored. Finally, two-dimensional motion of a fully passive flapping foil is demonstrated, allowing for the foil to travel upstream against the oncoming flow solely due to forces induced by interactions with oncoming unsteadiness.
" }, { "name": "Huang, Zi-Yu", "degree": "PhD", "year": "2022", "title": "Electrical Impedance Spectroscopy-Derived 3D Conductivity Tomography for Atherosclerosis Detection", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:12202021-172349636", "creators": [ { "name": { "family": "Huang", "given": "Zi-Yu" }, "id": "Huang-Zi-Yu", "orcid": "0000-0001-5998-3097", "display_name": "Huang, Zi-Yu" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "medeng" ], "doi": "10.7907/n0md-h379", "abstract": "Electrical impedance tomography (EIT) utilizes voltage/current data measured from the surface of interest to reconstruct the electrical conductivity distribution. This results in a noninvasive medical imaging procedure with many applications. Some examples would be: lung ventilation monitoring, breast cancer detection, and fatty liver detection. Non-alcoholic fatty liver disease (NAFLD) is one of the most common causes of cardiometabolic diseases in overweight individuals. The gold standard for NAFLD diagnosis is a liver biopsy which is a risky and invasive procedure. A non-invasive and cost effective method to detect fatty liver is an important unmet clinical need. Due to the distinct electrical properties of fatty tissue versus normal tissue, EIT can be applied to detect the fat infiltrate in the liver. We conducted EIT measurements and reconstructions on 19 subjects where the fat infiltrate was validated by MRI proton-density fat fraction (PDFF). The liver EIT conductivity was shown to be inversely correlated with MRI PDFF, demonstrating the ability of EIT to detect fatty infiltrate in the liver.
\r\n\r\nThis thesis also extends the EIT reconstruction to detect atherosclerosis, which is a build-up of fatty tissue in the arteries (plaque). Some plaques are prone to rupture and the current gold standard has a false negative rate of 20 % when distinguishing between vulnerable plaque and stable plaque. We sought to use EIT to detect the fatty content (mainly oxidize LDL) inside these vulnerable plaques. Therefore, the reconstruction method was modified into an outward setting that can measure from the inner surface of interest. Ex vivo experiments have demonstrated the ability to detect the location of fatty tissue in swine aorta. This technique has the potential to detect vulnerable plaque. However, the dimension of the device and the required electrode number limits the application from in vivo animal artery experiments.
\r\n\r\nFinally EIS-derived EIT, a new method we proposed, utilizes impedance values at a fixed frequency to solve for the conductivity distribution. This approach circumvents the mathematically ill-posed problem found when performing traditional EIT methods. We designed a 6-point EIS electrode array that was circumferentially configured to a balloon catheter and deployed in Yorkshire mini-pigs with induced stenosis in the right carotid artery. The EIS spectra demonstrated an elevated impedance in the right carotid arteries and the EIS-derived EIT mappings were reconstructed. The low conductivity regions in the EIS-derived EIT mappings were correlated with the positive E06 immunostaining for oxLDL-laden regions. Thus, we establish the capability of 3D EIS-derived EIT to detect oxLDL-laden arterial walls with translational implication to predict metabolically active plaques prone to acute coronary syndromes.
" }, { "name": "Jahelka, Phillip Robert", "degree": "PhD", "year": "2022", "title": "Progress in Low-Cost Gallium Arsenide Solar Cells", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242022-235428954", "creators": [ { "name": { "family": "Jahelka", "given": "Phillip Robert" }, "id": "Jahelka-Phillip-Robert", "orcid": "0000-0002-1460-7933", "display_name": "Jahelka, Phillip Robert" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/btbp-6h76", "abstract": "In order to prevent disastrous global warming the manufacturing capacity of renewable energy power sources must grow rapidly. Solar photovoltaics will likely be one of humanity's main sources of energy in the future due to the enormous available resource but increasing the manufacturing capacity of solar panels is hamstrung by both the limited profit margins of the highly-competitive renewable energy market and the enormous capital cost of building the factories that convert sand into semiconductor-grade silicon. Gallium arsenide is a material that can potentially help with the capital bottleneck because it absorbs light much more strongly than silicon and so the capital cost per unit weight of making the semiconductor can be spread over a larger number of devices and therefore effectively reduced. We present a number of results aimed at enabling low capital-cost GaAs solar cell manufacturing. First is a technique for open-tube, vapor phase zinc diffusion in GaAs. This method is dramatically simpler than its historical counterparts. Second, we use this technique to fabricate solar cells with Voc's greater than 960 mV and uncertified efficiencies over 23%, large improvements over the state of the art. We further demonstrate a base-metal, air-tolerant ohmic contact to n-type GaAs which is an improvement over traditional contacts that require noble metals and inert atmospheres. We also found the existence of melt-grown n-type GaAs with minority carrier diffusion length comparable to vapor grown material which helps with the economic viability of these devices. We also performed a technoeconomic analysis on our proposed devices and find that they satisfy the desired properties of both the capital and electricity being cheaper than silicon solar cells. We also demonstrate the first n-on-p diffused junction GaAs solar cells.
\r\n\r\nAs a parallel path to low capital intensity GaAs solar cells we also investigated non-epitaxial heterojunction devices. In the course of this work we both developed and characterized passivation chemistries for GaAs. Results in include the first use of a carbene and dithiothreitol for GaAs passivation and achieving surface recombination velocities comparable to GaInP passivation. With passivated organic heterojunction solar cells we were able to achieve a Voc of 840 mV which is a record for this class of devices, but its unclear how to improve the result to make them competitive with diffused junctions.
\r\n\r\nWe also explored nanowire solar cells as an alternative strategy to reducing material usage by exploiting their strong light-absorption. We developed a computational model for a non-epitaxial GaAs heterojunction nanowire solar cell and predict an optimized efficiency over 30%. Towards fabrication we used metal-assisted-chemical-etching to make nanowire arrays and found we were able to cleanly cleave the nanowires embedded in a polymer from a 110 oriented wafer.
\r\n\r\n\r\nWe also share some preliminary work on using total internal reflection in a solar cell encapsulant to mitigate shading loss due to the contacts on the front of a solar cell. We developed a computational model arguing that these structures could increase energy yield by 8% and demonstrated proof-of-principle experiments.
\r\n\r\nFinally, we share work on designing solar cells for operation on Venus. We developed models for the optical properties and recombination that correctly model the temperature dependence of a reference solar cell and using that model predict that a GaInP single-junction solar cell is a good solar-cell design for general usage in the atmosphere.
" }, { "name": "Kim, Eun Jong", "degree": "PhD", "year": "2022", "title": "Waveguide Quantum Electrodynamics in Superconducting Circuits", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02122022-205429202", "creators": [ { "name": { "family": "Kim", "given": "Eun Jong" }, "id": "Kim-Eun-Jong", "orcid": "0000-0003-4879-8819", "display_name": "Kim, Eun Jong" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Brandao", "given": "Fernando" }, "id": "Brand\u00e3o-F-G-S-L", "orcid": "0000-0003-3866-9378", "role": "member", "display_name": "Brandao, Fernando" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "member", "display_name": "Preskill, John P." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/bscv-b073", "abstract": "Achieving an efficient interface of light and matter has been a principal goal in the field of quantum optics. A burgeoning paradigm in the study of light-matter interface is waveguide quantum electrodynamics (QED), where quantum emitters are coupled to a common one-dimensional waveguide channel. In this scenario, cooperative effects among quantum emitters emerge as a result of real and virtual exchange of photons, giving rise to new ways of controlling matter.
\r\n\r\nSuperconducting quantum circuits offer an exciting platform to study quantum optics in the microwave domain with artificial quantum emitters interfaced to engineered photonic structures on chip. Beyond revisiting the experiments performed in atom-based platforms, superconducting circuits enable exploration of novel regimes in quantum optics that are otherwise prohibitively challenging to achieve. Moreover, the unprecedented level of control over individual quantum degrees of freedom and good scalability of the system provided by state-of-the-art circuit QED toolbox set a promising direction towards the study of quantum many-body phenomena.
\r\n\r\nIn this thesis, I discuss waveguide QED experiments performed in superconducting quantum circuits where transmon qubits are coupled to engineered microwave waveguides. Employing the high flexibility and controllability of superconducting quantum circuits, we realize and explore various schemes for generating waveguide-mediated interactions between superconducting qubits. We also demonstrate an intermediate-scale quantum processor based on a dispersive waveguide QED system involving ten superconducting qubits, exploring quantum many-body dynamics in a highly controllable fashion. The work described in the thesis marks an important step towards the construction of scalable architectures for quantum simulation of many-body models and realization of efficient coupling schemes for quantum computation.
" }, { "name": "Kim, Yonghwi", "degree": "PhD", "year": "2022", "title": "Light Modulation with Vanadium Dioxide-Based Optical Devices", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06232021-050358035", "creators": [ { "name": { "family": "Kim", "given": "Yonghwi" }, "id": "Kim-Yonghwi", "orcid": "0000-0002-6652-7994", "display_name": "Kim, Yonghwi" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/pkxj-9584", "abstract": "This thesis focuses on active material-based tunable optical devices. In particular, I have been working on tunable optical devices based on vanadium dioxide (VO2), which can produce tunable optical responses, such as amplitude, phase, thermal emission, and quantum emission. The modulations of light are achieved by coupling the phase-transition material with the precisely designed resonant structures or by placing it close to quantum emitters. This thesis presents three research streams, which aim at experimentally demonstrating the dynamically tunable optical responses using VO2. First, we propose and experimentally demonstrate an electrically tunable VO2-based reflectarray metasurface that exhibits largely tunable optical responses in the near-infrared region. We incorporate VO2 directly into the plasmonic resonator, which undergoes a phase transition triggered by Joule heating. The induced plasmonic resonance modulation is accompanied by a large and continuous modulation in optical responses, such as amplitude, resonance wavelength, and phase. Second, we propose and demonstrate an active tuning of thermal emission from VO2-based metasurfaces. We introduce a thin VO2 film as an absorbing layer on top of a metal reflector. This layer is coupled with a dielectric resonator, with a dielectric spacer placed between them. Upon undergoing a phase transition triggered by heating, the induced absorption tuning of the VO2 layer is accompanied by modulation in the absorption spectra of the coupled structure. We experimentally show narrowband absorption spectra, which can be tuned by controlling the VO2 temperature. Finally, we experimentally demonstrate the axial position of quantum emitters in a multilayered hexagonal boron nitride (hBN) flake with nanoscale accuracy, which is enabled through the modification of a photonic density of states by introducing VO2. Furthermore, we observe a sharp distance-dependent photoluminescence response by modulating the optical environment of an emitter placed close to the hBN/VO2 interface.
" }, { "name": "Kovachki, Nikola Borislavov", "degree": "PhD", "year": "2022", "title": "Machine Learning and Scientific Computing", "advisor": "Stuart, Andrew M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252022-180406320", "creators": [ { "name": { "family": "Kovachki", "given": "Nikola Borislavov" }, "id": "Kovachki-Nikola-Borislavov", "orcid": "0000-0002-3650-2972", "display_name": "Kovachki, Nikola Borislavov" } ], "advisors": [ { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "advisor", "display_name": "Stuart, Andrew M." } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/8nc5-cc67", "abstract": "The remarkable success of machine learning methods for tacking problems in computer vision and natural language processing has made them auspicious tools for applications to scientific computing tasks. The present work advances both machine learning techniques by using ideas from numerical analysis, inverse problems, and data assimilation and introduces new machine learning based tools for accurate and computationally efficient scientific computing. Chapters 2 and 3 introduce new methods and analyze existing methods for the optimization of deep neural networks. Chapters 4 and 5 formulate approximation architectures acting between infinite dimensional functions spaces for applications to parametric PDE problems. Chapter 6 demonstrates how to re-formulate GAN(s) so they can condition on continuous data and exhibits applications to Bayesian inverse problems. In Chapter 7, we present a novel regression-clustering method and apply it to the problem of predicting molecular activation energies.
" }, { "name": "Lee, Marcus Kuok Kuan", "degree": "PhD", "year": "2022", "title": "Instabilities in the Flow Over a Spinning Disk at Angle of Attack", "advisor": "Colonius, Tim; McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282021-234035965", "creators": [ { "name": { "family": "Lee", "given": "Marcus Kuok Kuan" }, "id": "Lee-Marcus-Kuok-Kuan", "orcid": "0000-0003-3972-843X", "display_name": "Lee, Marcus Kuok Kuan" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "co-advisor", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "co-advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/kmhn-7e49", "abstract": "Micro air vehicles (MAVs) face stability issues, especially as they continue to decrease in size. A spinning disk is inherently robust to external disturbances due to its spin stabilization, and therefore is a potential design for stable MAV flight. However, controlled flight of a spinning disk requires a detailed understanding of the underlying flow structures that determine the aerodynamic behavior. A spinning disk acts to rotate and propel nearby flow tangentially outwards, while drawing in fluid from above. In this way, spin acts as an additional source of both angular and linear momentum from the disk's surface, which can alter the wake structure significantly. In this thesis, we explore how spin affects the aerodynamic forces on a disk and characterize several instabilities that occur. To this end, we use the immersed-boundary Lattice Green's function (IBLGF) method to simulate flow over a spinning disk at angle of attack for Reynolds numbers of O(102) and tip-speed ratios (non-dimensional spin rate) up to 3.
\r\n\r\nAt these Reynolds numbers, the steady flow first undergoes a bifurcation associated with wake instability, giving rise to vortex shedding. Increasing tip-speed ratio leads to monotonic increases in both lift and drag, although the lift-to-drag ratio remains fairly constant. We also identify several distinct wake regimes, including a region of vortex-shedding suppression, and the appearance of a distinct corkscrew-like short-wavelength instability in the advancing tip vortex. To understand the mechanism leading to suppression of vortex shedding, we study the streamlines and vortex lines in the wake. We show that the vorticity produced by the spinning disk strengthens the tip vortices, inducing a spanwise flow in the trailing edge vortex sheet. This helps to dissipate the vorticity, which in turn prevents roll up and thus suppresses vortex shedding. For the short-wavelength instability, we use spectral proper orthogonal decomposition (SPOD) to identify the most energetic modes and compare it to elliptic instabilities seen in counter-rotating vortex pairs with axial flow. The addition of vorticity from the disk rotation significantly alters the circulation and axial velocity in the tip vortices, giving rise to elliptic instability despite its absence in the non-spinning case. We also observe lock-in between the frequency of the elliptic instability and twice the spin frequency, indicating that disk rotation acts as an additional forcing for the elliptic instability. Many of these phenomena are consistent with observations in high Reynolds number studies and for other bluff body geometries. As a result, the mechanisms proposed here may serve as a basis for understanding and predicting the changing wake structures in more complex flow configurations.
" }, { "name": "Liang, Chen", "degree": "PhD", "year": "2022", "title": "Cascading Failures in Power Systems: Modeling, Characterization, and Mitigation", "advisor": "Low, Steven H.; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032022-035416994", "creators": [ { "name": { "family": "Liang", "given": "Chen" }, "id": "Liang-Chen", "orcid": "0000-0002-0015-7206", "display_name": "Liang, Chen" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" } ], "option_major": [ "cms" ], "doi": "10.7907/8817-xy25", "abstract": "Reliability is a critical goal for power systems. Due to the connectivity of power grids, an initial failure may trigger a cascade of failures and eventually lead to a large-scale blackout, causing significant economic and social impacts. Cascading failure analysis thus draws wide attention from power system practitioners and researchers. A well-known observation is that cascading failures in power systems propagate non-locally because of the complex mechanism of power grids. Such non-local propagation makes it particularly challenging to model, analyze and control the failure process. In this thesis, we tackle these challenges by establishing a mathematical theory to model and characterize failure patterns, discover structural properties of failure propagation, and design novel techniques for failure mitigation.
\r\n\r\nFirst, we propose a failure propagation model considering both fast-timescale system frequency dynamics and the slow-timescale line tripping process. This model provides mathematical justifications to the widely used static DC model and can be generalized to capture a variety of failure propagation patterns induced by different control mechanisms of the power grid. More importantly, this model provides flexibility to design real-time control algorithms for failure mitigation and localization.
\r\n\r\nSecond, we provide a complete characterization of line failures under the static DC model. Our results unveil a deep connection between the power redistribution patterns and the network block decomposition. More specifically, we show that a non-cut line failure in a block will only impact the branch power flows on the transmission lines within the block. In contrast, a cut set line failure will propagate globally depending on both the power balancing rules and the network topological structure. Further, we discuss three types of interface networks to connect the sub-grids, all achieving better failure localization performance.
\r\n\r\nThird, we study corrective control algorithms for failure mitigation. We integrate a distributed frequency control strategy with the network block decomposition to provide provable failure mitigation and localization guarantees on line failures. This strategy operates on the frequency control timescale and supplements existing corrective mechanisms, improving grid reliability and operational efficiency. We further explore the failure mitigation approach with direct post-contingency injection adjustments. Specifically, we propose an optimization-based control method with strong structural properties, which is highly desirable in large-scale power networks.
" }, { "name": "Loke, Samuel Pei Hao", "degree": "PhD", "year": "2022", "title": "Photovoltaic Technologies Developed for Space-Based Solar Power", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142022-060038327", "creators": [ { "name": { "family": "Loke", "given": "Samuel Pei Hao" }, "id": "Loke-Samuel- Pei-Hao", "orcid": "0000-0003-1856-3605", "display_name": "Loke, Samuel Pei Hao" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/6jhy-2623", "abstract": "In this thesis, photovoltaic technologies were developed for space-based solar power. Two methods of realizing SBSP were introduced, namely concentrated photovoltaics (CPV) and radiation hard flat panel photovoltaics. Both techniques are instrumental to realizing SBSP as they are pathways to realizing high specific power and lower launch costs. Technologies developed to support these two forms of SBSP were then reported.
\r\n\r\nIn support of CPV, ultralight broadband mid-infrared coatings were developed for the concentrating mirrors used in our project. This was done to create radiative pathways for heat loss to ensure that the solar cells do not overheat. Using the rigorous coupled wave analysis technique, we optimized a backside single-layer coating using 2nm Cr/ 2\u03bcm CP1/ 500nm Ag that had an mIR emissivity of 0.6. Adding a second layer of this coating, we predicted that a 0.5nm Cr/ 1.9\u00b5m CP1/ 3nm Cr/ 2\u00b5m CP1/ 500nm Ag screen could achieve an emissivity of 0.8. We also optimized a 10nm ITO/ 2 \u03bcm CP1/ 500nm Ag frontside emitter which had a visible reflectivity of 0.896 and a mIR emissivity of 0.554. A backside emitter coating that was 0.927 emissive in the mIR with areal density 6.0 gm\u207b\u00b2 was successfully fabricated, as was a frontside mirror emitter coating with visible reflectivity of 0.896 and a mIR emissivity of 0.582 with areal density 4.1 gm\u207b\u00b2.
\r\n\r\nIn support of radiation hard photovoltaics, organo-lead halide perovskites (OHLP) were investigated. Challenges facing their fabrication were explored, with special focus on the electron transport layer PCBM as well as OHLP formulation. It was found that doping PCBM with a surfactant CTAB was beneficial, but did not work with all surfaces. An ITO/NiOx/MAPbI3/CTAB+PCBM/Cu device with in-house champion efficiency of 12.41% was achieved, and an ITO/NiOx/FA0.85Cs0.15PbI3/PCBM/Cu device with in-house champion efficiency of 11.81% was achieved. Time-dependant drift diffusion modelling was employed to account for the S-kink arising from poor PCBM carrier concentration.
\r\n\r\nFinally, the proton degradation of OHLP devices and constituent transport layers were investigated to shed better light on how OHLP devices degrade under proton irradiation. Films of ITO, PEDOT, NiOx, PCBM, and PTCDi were found to degrade under 30keV and 75keV protons of up to 1.4 x 10\u00b9\u2074 p\u207acm\u207b\u00b2 fluence, but their electrical resistivity and optical transmissivity were not found to impact the cell as much as the OHLP absorber layer itself. Observing the light IV and EQE degradation of OHLP cells, it is evident that proton deposition in the OHLP layer itself causes the most damage, especially at 30keV and 75keV protons with fluences from 4.3 x 10\u00b9\u00b3 p\u207acm\u207b\u00b2 to 1.7 x 10\u00b9\u2074 p\u207acm\u207b\u00b2. By considering the discrepancy in trends between Jsc and EQE, we concluded that the protons much accelerate intensity-based metastable photodegradation. Finally, by observing their anneal recovery, we concluded that it was temperature dependant and that maximum irrecoverable damage occurs at the OHLP/HTL interface.
" }, { "name": "Marshall, Michael Aaron", "degree": "PhD", "year": "2022", "title": "Dynamics of Ultralight Flexible Spacecraft During Slew Maneuvers", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262022-221946560", "creators": [ { "name": { "family": "Marshall", "given": "Michael Aaron" }, "id": "Marshall-Michael-Aaron", "orcid": "0000-0002-4259-2484", "display_name": "Marshall, Michael Aaron" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Braun", "given": "Robert D." }, "id": "Braun-R-D", "role": "member", "display_name": "Braun, Robert D." }, { "name": { "family": "Leyendecker", "given": "Sigrid" }, "id": "Leyendecker-S", "role": "member", "display_name": "Leyendecker, Sigrid" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/w6na-w476", "abstract": "Traditional spacecraft design paradigms rely on stiff structures with comparatively flexible appendages. More recent trends, however, trade deployed stiffness for packaging efficiency to stow increasingly large-area apertures inside existing launch vehicles. By leveraging recent advances in materials and structures, these ultralight, packageable, and deployable spacecraft, hereafter referred to as ultralight flexible spacecraft, are up to several orders of magnitude lighter and more flexible than the current state-of-the-art. They promise to deliver higher performance for a wide range of applications, but this comes at a cost, in this case, due to their very low-frequency structural dynamics. Structural dynamics can negatively interact with spacecraft attitude control systems and degrade pointing performance.
\r\n\r\nThese developments motivate the main objective of this thesis: to demonstrate the feasibility and limitations of maneuvering next-generation ultralight flexible spacecraft. To that end, the thesis proposes a quantitative method for determining structure-based performance limits for flexible spacecraft slew maneuvers using reduced-order modal models. It then develops a geometrically nonlinear flexible multibody dynamics finite element model of a representative ultralight flexible spacecraft based on the Caltech Space Solar Power Project architecture to validate this method. The results demonstrate that contrary to common assumptions, other constraints impose more restrictive limits on slew maneuver performance than the dynamics of the structure. In particular, they show that the available attitude control system momentum and torque are often significantly more limiting than the structure. Consequently, these results suggest that spacecraft structures can either be (i) maneuvered significantly faster, assuming suitable actuators are available, or (ii) built using lighter-weight, less-stiff, and lower-cost construction that moves the structure-based performance limits closer to those of the rest of the system. Thus, there is a significant opportunity to design less-conservative, higher-performance space systems.
" }, { "name": "McMahan, Connor Glenn", "degree": "PhD", "year": "2022", "title": "Modeling and Programming Shape-Morphing Structured Media", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282021-231505066", "creators": [ { "name": { "family": "McMahan", "given": "Connor Glenn" }, "id": "McMahan-Connor-Glenn", "orcid": "0000-0001-5024-6138", "display_name": "McMahan, Connor Glenn" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "mecheng" ], "doi": "10.7907/rcw1-r139", "abstract": "Shape-morphing and self-propelled locomotion are examples of mechanical behaviors that can be \"programmed\" in structured media by designing geometric features at micro- and mesostructural length scales. This programmability is possible because the small-scale geometry often imposes local kinematic modes that are strongly favored over other deformations. In turn, global behaviors are influenced by local kinematic preferences over the extent of the structured medium and by the kinematic compatibility (or incompatibility) between neighboring regions of the domain. This considerably expands the design space for effective mechanical properties, since objects made of the same bulk material but with different internal geometry will generally display very different behaviors. This motivates pursuing a mechanistic understanding of the connection between small-scale geometry and global kinematic behaviors. This thesis addresses challenges pertaining to the modeling and design of structured media that undergo large deformations.
\r\n\r\nThe first part of the thesis focuses on the relation between micro- or mesoscale patterning and energetically favored modes of deformation. This is first discussed within the context of twisted bulk metallic glass ribbons whose edges display periodic undulations. The undulations cause twist concentrations in the narrower regions of the structural element, delaying the onset of material failure and permitting the design of structures whose deployment and compaction emerge from the ribbons' chirality. Following this discussion of a periodic system, we study sheets with non-uniform cut patterns that buckle out-of-plane. Motivated by computational challenges associated with the presence of geometric features at disparate length scales, we construct an effective continuum model for these non-periodic systems, allowing us to simulate their post-buckling behavior efficiently and with good accuracy.
\r\n\r\nThe second part of the thesis discusses ways to leverage the connection between micro/mesoscale geometry and energetically favorable local kinematics to create \"programmable matter\" that undergo prescribed shape changes or self-propelled locomotion when exposed to an environmental stimulus. We first demonstrate the capabilities of an inverse design method that automates the design of structured plates that morph into target 3D geometries over time-dependent actuation paths. Finally, we present devices made of 3D-printed liquid crystal elastomer (LCE) hinges that change shape and self-propel when heated.
" }, { "name": "Mehta, Jenish Chetan", "degree": "PhD", "year": "2022", "title": "Combinatorial and Algebraic Propeties of Nonnegative Matrices", "advisor": "Schulman, Leonard J.; Vidick, Thomas G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-043503154", "creators": [ { "name": { "family": "Mehta", "given": "Jenish Chetan" }, "id": "Mehta-Jenish-Chetan", "display_name": "Mehta, Jenish Chetan" } ], "advisors": [ { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "advisor", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "advisor", "display_name": "Vidick, Thomas G." } ], "committee": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "chair", "display_name": "Umans, Christopher M." }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "member", "display_name": "Vidick, Thomas G." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "compsci" ], "doi": "10.7907/3vxb-6778", "abstract": "We study the combinatorial and algebraic properties of Nonnegative Matrices. Our results are divided into three different categories.
\r\n\r\n1. We show the first quantitative generalization of the 100 year-old Perron-Frobenius theorem, a fundamental theorem which has been used within diverse areas of mathematics. The Perron-Frobenius theorem shows that any irreducible nonnegative matrix R will have a largest positive eigenvalue r, and every other eigenvalue \u03bb is such that Re\u03bb < R and |\u03bb| \u2264 r. We capture the notion of irreducibility through the widely studied notion of edge expansion \u03c6 of R which intuitively measures how well-connected the underlying digraph of R is, and show a quantitative relation between the spectral gap \u0394 = 1-Re\u03bb/r (where \u03bb \u2260 r has the largest real part) of R to the edge expansion \u03c6 as follows.
\r\n\r\n(1/15) \u2022 [(\u0394(R))/n] \u2264 \u03c6(R) \u2264 \u221a[2 \u2022 \u0394(R)].
\r\n\r\nThis also provides a more general result than the Cheeger-Buser inequalities since it applies to any nonnegative matrix.
\r\n\r\n2. We study constructions of specific nonsymmetric matrices (or nonreversible Markov Chains) that have small edge expansion but large spectral gap, taking us in a direction more novel and unexplored than studying symmetric matrices with constant edge expansion that have been extensively studied. We first analyze some known but less studied Markov Chains, and then provide a novel construction of a nonreversible chain for which
\r\n\r\n\u03c6(R) \u2264 [(\u0394(R))/\u221an],
\r\n\r\nobtaining a bound exponentially better than known bounds. We also present a candidate construction of matrices for which
\r\n\r\n\u03c6(R) \u2264 2[(\u0394(R))/n]
\r\n\r\nwhich is the most beautiful contribution of this thesis. We believe these matrices have properties remarkable enough to deserve study in their own right.
\r\n\r\n3. We connect the edge expansion and spectral gap to other combinatorial properties of nonsymmetric matrices. The most well-studied property is mixing time, and we provide elementary proofs of the relation between mixing time and the edge expansion, and also other bounds relating the mixing time of a nonreversible chain to the spectral gap and to its additive symmetrization. Further, we provide a unified view of the notion of capacity and normalized capacity, and show the monotonicity of capacity of nonreversible chains amongst other results for nonsymmetric matrices. We finally discuss and prove interesting lemmas about different notions of expansion and show the first results for tensor walks or nonnegative tensors.
" }, { "name": "Needell, David Robert", "degree": "PhD", "year": "2022", "title": "High-Efficiency Luminescent Solar Concentrators for Photovoltaic Applications", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072021-154010065", "creators": [ { "name": { "family": "Needell", "given": "David Robert" }, "id": "Needell-David-Robert", "orcid": "0000-0001-8343-5883", "display_name": "Needell, David Robert" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "chair", "display_name": "Falson, Joseph" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/5r7z-zd88", "abstract": "Despite an overwhelming abundance of crude solar energy, current photovoltaic systems worldwide harness less than 1% of this available power. As such, emerging solar generation technology must be developed to further spur global adoption -- whereby increased sunlight to power conversion efficiency alongside decreased system costs constitute the primary methods to accomplish this goal. The luminescent solar concentrator (LSC) offers a unique approach to collecting and redirecting large areas of incident light onto small-area solar cells. Relying upon photoluminescent materials (i.e., luminophores) suspended within a dielectric waveguide, the LSC absorbs high energy irradiance and re-emits photons at down-shifted energies into optical waveguide modes.
\r\n\t \r\nThis thesis presents analytical, computational, and experimental work to illustrate the technical power conversion efficiency limits for LSC-based photovoltaic devices. We begin with a technical description of two LSC numerical models -- a stochastic Monte Carlo ray-trace and a deterministic closed-form approach. We apply these models to quantify the effects of system and component parameters on power conversion efficiency for a number of end-use applications. To validate our modeling and unveil current practical material limits, we fabricate CdSe/CdS and CuInS2/ZnS core/shell quantum dot waveguides hosting embedded InGaP and GaAs photovoltaic cells, respectively. From these measurements, we observe close model-to-experiment matching and report a world-record LSC power conversion efficiency reaching approximately 10% under 1-sun illumination at modest incident to outgoing radiance areas.
\r\n\t \r\nHerein we consider four distinct applications for the LSC: (i) single junction LSC devices for terrestrial-based energy generation, (ii) building-integrated LSC form factors for on-site electricity, (iii) multijunction LSC modules for utility-scale installations at high power conversion efficiency, and (iv) ultra-light structures for on-board power in aerospace settings. We organize each chapter according to its end-use application.
" }, { "name": "Park, Jinsoo", "degree": "PhD", "year": "2022", "title": "Spin-Phonon Interactions and Spin Decoherence from First Principles", "advisor": "Bernardi, Marco", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052022-215214933", "creators": [ { "name": { "family": "Park", "given": "Jinsoo" }, "id": "Park-Jinsoo", "orcid": "0000-0002-1763-5788", "display_name": "Park, Jinsoo" } ], "advisors": [ { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "advisor", "display_name": "Bernardi, Marco" } ], "committee": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "chair", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Alicea", "given": "Jason F." }, "id": "Alicea-J", "orcid": "0000-0001-9979-3423", "role": "member", "display_name": "Alicea, Jason F." }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "member", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/80bd-x991", "abstract": "Developing a microscopic understanding of spin decoherence is essential to advancing quantum technologies. Electron spin decoherence due to atomic vibrations (phonons) plays a special role as it sets an intrinsic limit to the performance of spin-based quantum devices. Two main sources of phonon-induced spin decoherence, the Elliott-Yafet (EY) and Dyakonov-Perel (DP) mechanisms, have distinct physical origins and theoretical treatments. First-principles calculations of electron-phonon (e-ph) interactions combined with many-body perturbation theory are promising to study phonon-induced spin decoherence. However, predicting the spin response in materials remains an open challenge; methods for quantifying spin-dependent e-ph interactions in materials, as well as a linear response framework for spins in the presence of e-ph interaction is missing. In this thesis, we provide a first-principles framework for computing the relativistic spin-dependent electron-phonon interactions. We develop a formalism that unifies the modeling of EY and DP spin decoherence, and provide a rigorous many-body perturbation theory for obtaining the spin-spin correlation function including the vertex corrections due to e-ph interactions. We compute the phonon-dressed vertex of the spin-spin correlation function with a treatment analogous to the calculation of the anomalous electron magnetic moment in QED. We find that the vertex correction provides a giant renormalization of the electron spin dynamics in solids, greater by many orders of magnitude than the corresponding correction from photons in vacuum. We further identify the long-range quadrupole e-ph interaction in materials, and demonstrate its importance in the description of phonon-induced spin decoherence. We show first-principle calculations of spin-dependent e-ph interactions in correlated electron systems, using the framework of Hubbard-corrected density functional theory. Lastly, we provide technical details in the implementation of ab-initio e-ph interaction in PERTURBO, a software package for first-principles calculations of charge transport, spin dynamics, and ultrafast carrier dynamics in materials. In summary, the thesis demonstrates a general approach for quantitative analysis of spin decoherence in materials, advancing the quest for spin-based quantum technologies.
" }, { "name": "Porsandeh Khial, Parham", "degree": "PhD", "year": "2022", "title": "High Sensitivity Time-Varying Systems In Photonics and Electronics", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242021-181127485", "creators": [ { "name": { "family": "Porsandeh Khial", "given": "Parham" }, "id": "Porsandeh-Khial-Parham", "orcid": "0000-0002-3242-8541", "display_name": "Porsandeh Khial, Parham" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/qzj9-rz93", "abstract": "Integrated electronics and photonics have been revolutionizing our daily lives for decades. However, the demand for high-speed communications, low-latency networks, and high-performance optical and electrical sensors continues to grow. In order to keep up with this demand as well as be able to address upcoming and unknown challenges, we need to explore unconventional solutions. Moving away from existing systems and traditional architectures allows us to take a deeper look at these challenges and potentially come up with nontrivial answers. In this thesis, unconventional approaches to implementing high-performance optical and electrical sensors and systems are investigated. Among these unorthodox solutions are time-varying architectures which led to completely new devices, sensors with dramatically improved sensitivity, and the breaking of known trade-offs.
\r\n\r\nBy developing a time-varying method that we call reciprocal sensitivity enhancement, we demonstrated a nanophotonic optical gyroscope (NOG) for the first time. The efficacy of this method is borne out by its ability to improve the performance of optical gyroscopes by two orders of magnitude. This sensitivity-enhancement method filters out reciprocal imperfections and noise, thereby increasing the overall signal-to-noise ratio. Next, the same approach is used to boost the performance of resonance-based magnetic biosensors. By merging two biosensors and taking advantage of the frequency response of magnetic beads, time-division switching cancels out most of the correlated noise. This solution pushes the sensitivity of this sensor below parts-per-million (PPM) levels for long periods of time \u2014 a property which is desirable in many biosensing applications.
\r\n\r\nAdditionally, an electrical scalable router that mitigates line-of-sight issues in next-generation wireless systems is introduced. This novel design does not require any shared timing reference to form a coherent array and uses a time-varying baseband to create a proper true-time delay. Next, we discuss how radiating elements in silicon-photonics platforms can be engineered to create a passive lensless camera. By applying a robust reconstruction algorithm, the captured image can be faithfully recovered. The same concept can be used in multi-mode nanophotonic antennas to alleviate the field-of-view (FOV)-aperture trade-off.
\r\n\r\nFinally, a hybrid photonic transmitter/receiver architecture, an electrical full-duplex transceiver with one nonreciprocal element, and a nested-ring optical modulator are presented.
" }, { "name": "Qin, Yidan", "degree": "PhD", "year": "2022", "title": "Autonomous Temporal Understanding and State Estimation during Robot-Assisted Surgery", "advisor": "Burdick, Joel W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272022-171138586", "creators": [ { "name": { "family": "Qin", "given": "Yidan" }, "id": "Qin-Yidan", "orcid": "0000-0002-7766-1021", "display_name": "Qin, Yidan" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel W." }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel W." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/n58k-tr61", "abstract": "Robot-Assisted Surgery (RAS) has become increasingly important in modern surgical practice for its many benefits and advantages for both the patient and the healthcare professionals, as compared to traditional open surgeries and minimally invasive surgeries such as laparoscopy. Artificial intelligence applications during RAS and post-operative analysis can provide various surgeon-assisting functionalities and could potentially achieve a better surgery outcome. These applications, ranging from providing surgeons with advisory information during RAS and post-operative analysis to virtual fixture and supervised autonomous surgical tasks, share a necessary prerequisite of a comprehensive understanding of the current surgical scene. This understanding should include the knowledge of the current surgical task being performed, the surgeon's actions and gestures, the state of the patient, etc. Currently, there is yet to be a unified effort to achieve the autonomous temporal understanding and perception of an RAS at the high accuracy and efficiency required in the highly safety-critical field of medicine.
\r\n\r\nThis thesis develops novel modeling methodologies and deep learning-based models for the autonomous perception and temporal segmentation of the current surgical scene during an RAS. An RAS procedure is modeled as a hierarchical system consisting of discrete surgical states at multiple levels of temporal granularity. These surgical states take the form of surgical tasks, operational steps, fine-grained surgical actions, etc. A broad range of computational experiments were performed to develop methods that achieve an accurate, robust, and efficient estimation of these surgical states. Multiple novel deep learning-based models for feature extraction, noise elimination, and efficient training were proposed and tested. This thesis also shows the significant benefits of incorporating multiple types of data streams recorded by the surgical robotic system to a more accurate surgical state estimation effort.
\r\n\r\nTwo new RAS datasets that contains real-world RAS procedures and diverse experimental settings were collected and annotated--filling a gap in the data sets available for the development and testing of of robust surgical state estimation models. The performance and robustness of models in this thesis work were showcased with these highly complex and dynamic real-world RAS datasets and compared against state-of-the-art methods. A significant model performance improvement was observed in both surgical state estimation accuracy and efficiency. The modeling methodologies and deep learning-based models developed in this work have diverse potential applications to the development of a next-generation surgical robotic systems.
" }, { "name": "Rochman, Jake Herschel Lebi", "degree": "PhD", "year": "2022", "title": "Microwave-to-Optical Transduction Using Rare-Earth Ions", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05152022-181826611", "creators": [ { "name": { "family": "Rochman", "given": "Jake Herschel Lebi" }, "id": "Rochman-Jake-Herschel-Lebi", "orcid": "0000-0002-8475-3389", "display_name": "Rochman, Jake Herschel Lebi" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4h2f-wj87", "abstract": "Superconducting qubits that operate at microwave frequencies are one of the most promising platforms for quantum information processing. However, connecting distant processors with microwave photons is challenging since microwave photons suffer from thermal noise and large propagation losses in room temperature components.
\r\n\r\nConversely, optical photons within the telecommunications band are known to have extremely low loss in optical fiber and the thermal noise is minuscule at room temperature. In order to interface superconducting qubits with room temperature optical photons, a quantum transducer is required that can convert photons between microwave and optical frequencies.
\r\n\r\nThis thesis describes the development of a microwave-to-optical transducer using an ensemble of erbium ions, doped within a yttrium orthovanadate crystal, that are simultaneously coupled to a superconducting microwave resonator and a photonic crystal optical resonator. The erbium ions have spin transitions that couple to the microwave resonator and optical transitions at telecom wavelengths that couple to the optical resonator.
" }, { "name": "Ryou, Serim", "degree": "PhD", "year": "2022", "title": "Representation of the Semantic Structures: from Discovery to Applications", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092021-125955775", "creators": [ { "name": { "family": "Ryou", "given": "Serim" }, "id": "Ryou-Serim", "orcid": "0000-0003-1344-1158", "display_name": "Ryou, Serim" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." } ], "option_major": [ "eleceng" ], "doi": "10.7907/rvnc-dp57", "abstract": "The world surrounding us is full of structured entities. Scenes can be structured as the sum of objects arranged in space, objects can be decomposed into parts, and even small molecules are composed of atoms. As humans can organize and structure many concepts into smaller components, structural representation has become a powerful tool for various applications. Computer vision utilizes the part-based representation for classical object detection and categorization tasks, and computational neuroscientists use the structural representation to achieve an interpretable and low-dimensional encoding for behavior analysis. Furthermore, structural encoding of the molecules allows the application of machine learning models to optimize experimental reaction conditions in organic chemistry.
\r\n\r\nTo perform the high-level tasks described above, accurate detection of the structural component should be accomplished in advance. In this dissertation, we first propose methods to improve the pose estimation algorithm, where the task is to localize the semantic parts of the target instance from a 2D image. As the collection of a large number of human annotations is a prerequisite for the task to be successful, we aim to design a model that automatically discovers the structure information from the visual inputs without supervision. Lastly, we demonstrate the efficacy of the structural representation by applying it to various scientific applications such as behavior analysis and organic chemistry.
" }, { "name": "Saunders, Claire Nicole", "degree": "PhD", "year": "2022", "title": "Thermal Behavior of Cuprous Oxide: a Comprehensive Study of Three-Body Phonon Effects and Beyond", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262022-015714738", "creators": [ { "name": { "family": "Saunders", "given": "Claire Nicole" }, "id": "Saunders-Claire-Nicole", "orcid": "0000-0001-7973-3722", "display_name": "Saunders, Claire Nicole" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Granroth", "given": "Garrett" }, "id": "Granroth-Garrett", "orcid": "0000-0002-7583-8778", "role": "member", "display_name": "Granroth, Garrett" } ], "option_major": [ "matsci" ], "doi": "10.7907/mate-2v65", "abstract": "Phonons, or quantized normal modes of crystal vibrations, are responsible for much of the thermophysical behavior in solid-state systems. This behavior includes properties like thermal expansion, defined as the change in material volume in response to temperature. Typically, materials expand upon heating and contract upon cooling; however, some undergo anomalous or negative thermal expansion (NTE). This study focuses on a material with NTE, cuprous oxide (Cu2O), commonly known as cuprite. Using computational and experimental methods, we identify the underlying mechanisms of the NTE and how these mechanisms relate to temperature-dependent phonon behavior with temperature, using both computational and experimental methods.
\r\n\r\nComputationally, we interpret temperature-dependent changes in phonon energies with perturbation theory. Assuming that the bonds between atoms behave like simple harmonic oscillators, we model the observed random motion of the atoms around their equilibrium positions with quasi-harmonic (QH) and anharmonic (AH) approximations. Furthermore, the perturbations in the atom position allow us to model phonon energy changes in response to temperatures.
\r\n\r\nWhile these models, particularly AH models, have proven accurate in predicting the phonon behavior, experimental methods, like inelastic neutron scattering (INS), remain the gold standard for validation. This study presents INS data from single-crystal cuprite measured on the Wide-Angular Range Chopper Spectrometer (ARCS) at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS). We present INS data collected at 10 K, 300 K, 700 K, and 900 K. The post-processing workflow included: (1) binning with the software package Mantid, (2) reducing with a multiphonon background correction for polyatomic crystals, and (3) condensing into a single irreducible wedge in the first Brillouin zone (BZ). From this, we obtain a four-dimensional scattering function S(Q, E). Our AH calculations use the stochastic-Temperature Dependent Effective Potential (sTDEP) and the Machine Learning Interatomic Potential (MLIP) methods. The former method uses perturbation theory to include cubic and quartic AH contributions. The latter uses machine learning (ML), which in principle, includes all orders of AH terms.
\r\n\r\nThis investigation of the NTE of cuprite demonstrates that QH and AH models successfully predict anomalous NTE behavior. However, only AH calculations show the temperature-dependent phonon behavior seen in INS results. This discrepancy likely stems from a fortuitous cancellation of cubic and quartic AH terms giving an apparent success of QH models for the NTE. Ultimately, a correct prediction of thermal expansion with incorrect phonons reinforces the need to look at the role of higher-order terms in the temperature-dependent behavior of this material.
\r\n\r\nDespite the success of sTDEP at predicting phonon frequency shifts, it could not account for the newly observed diffuse inelastic intensity (DII) in the INS phonon spectra. For this, MLIP was more effective.
\r\n\r\nThis work provides complementary models to explain the origins of the DII, which is likely an emerging category of AH feature best described as a local nonlinear many-body process. We investigate phonon dissipation, the dynamics of systems coupled to their environments, Brownian motion, and discontinuities due to impulse transfer effects. We conclude by addressing the potential applications of the results and their role in future work on thermal lattice dynamics.
" }, { "name": "Sima, Jin", "degree": "PhD", "year": "2022", "title": "Correcting Errors in DNA Storage", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-185003284", "creators": [ { "name": { "family": "Sima", "given": "Jin" }, "id": "Sima-Jin", "orcid": "0000-0003-4588-9790", "display_name": "Sima, Jin" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "chair", "display_name": "Kostina, Victoria" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Raviv", "given": "Netanel" }, "id": "Raviv-N", "orcid": "0000-0002-1686-1994", "role": "member", "display_name": "Raviv, Netanel" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "eleceng" ], "doi": "10.7907/kdph-6z71", "abstract": "DNA-based storage has potentially unprecedented advantages of high information density and long duration, and is one of the promising techniques to meet the ever-growing demands to keep data in the future. As noise and errors are present in almost every procedure during reading, writing, and storing of information in DNA storage systems, error correction is inevitable to guarantee reliable data storage in DNA. Moreover, it is often required that error correction is done in an efficient manner to reduce the cost and time needed for reading and writing data. Due to the technology constraints and physical limitations, error correction in DNA-based storage poses the following challenges that differ from those in traditional digital data transmission and storage systems.
\r\n\r\n1. A combination of deletion, insertion, and substitution errors present. The goal is to construct efficient codes correcting these errors. While substitution errors are special cases of deletion and insertion errors, and are well studied under the current theory and practice frameworks, deletion and insertion errors are much more difficult to deal with, and less understanding was gained for deletion and insertion errors.
\r\n\r\n2. Error correction is over an unordered set of strings, rather than over a single string, which can be regarded as a set of ordered strings. The latter, which includes the above deletion/insertion coding problem, is commonly studied for current digital communication and storage systems. Our goal is to extend the deletion/insertion correction capability for a single string to a set of unordered strings.
\r\n\r\n3. The decoder observes multiple noisy copies of every coded string. The problem is to deduce a set of strings (or a single string) from a collection of their noisy samples, also studied as the population recovery (or trace reconstruction for a single string) problem. The problem is well answered with substitution errors only and becomes elusive with the introduction of deletion and insertion errors.
\r\n\r\nThis thesis tries to address the above challenges. For the first challenge, we proposed binary codes correct any constant number of deletions and/or insertions with order-wise optimal redundancy, which made a step toward a solution to a longstanding open problem introduced by Levenshtein in 1960s. We also extended it to different settings, in particular, non-binary deletin/insertion correcting codes suitable for DNA storage applications.
\r\n\r\nFor the second challenge, we established lower and upper bounds on the optimal redundancy of codes correcting any number of substitution, deletion, and insertion errors and found that the redundancy needed for coding over an unordered set of strings is order-wise the same as that needed for coding over a ordered set of strings. Using our results for the first challenge, we proposed codes correcting any constant number of deletion/insertion errors with order-wise optimal redundancy under some parametter settings.
\r\n\r\nFor the third challenge, we studied the problem of trace reconstruction, which asks the number of noisy samples needed to reconstruct a single string. While there is a exponential gap between upper and lower bounds on sample complexities in general, we showed that a polynomial number of samples suffice, given a reference string that is within constant edit distance from the target string.
\r\n\r\nApart from dealing with the above challenges, we investigated error correction for multi-head racetrack memory applications. The problem can be considered as correcting any constant number of deletions/insertions in a single string with multiple noisy copies, with the help of coding. Different from the settings we considered above in the trace reconstruction problem, where noisy copies are independent given the target string, in racetrack memory, the noisy copies are correlated, and the number of errors is small compared to the trace reconstruction problem. We derived a lower bound on redundancy and proposed a code correcting any number of deletions/insertions with order-wise optimal redundancy.
" }, { "name": "Singletary, Andrew Wills", "degree": "PhD", "year": "2022", "title": "Safe Input Regulation for Robotic Systems", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022022-064735213", "creators": [ { "name": { "family": "Singletary", "given": "Andrew Wills" }, "id": "Singletary-Andrew-Wills", "orcid": "0000-0001-6635-4256", "display_name": "Singletary, Andrew Wills" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Feron", "given": "Eric M." }, "id": "Feron-E-M", "orcid": "0000-0001-7717-2159", "role": "member", "display_name": "Feron, Eric M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/zz10-gv06", "abstract": "The safety of robotic systems is paramount to their continued emergence into our lives. From collaborative industrial manipulators to drone deliveries to autonomous vehicles, safety is the primary concern when it comes to the continued adoption of these technologies. While a number of techniques can be used to design safe controllers and planners that govern the actions of these robots, few are able to provide the type of safety guarantee needed to bring these technologies into reality.
\r\n\r\nThe goal of this thesis is to provide a framework for regulating, or filtering, existing control inputs before they are applied by the robot, in order to ensure that safety is upheld. To illustrate this, consider one of the primary applications for this method: human-operated robotic platforms. For vehicles, this framework would modify the throttle, braking, and steering commands from a human driver to prevent him from driving off the road or into other cars. However, when the human is operating the vehicle safely, his commands should go unaltered. This illustrates the idea of a minimally invasive safety regulator: one that only engages when absolutely necessary to ensure safety.
\r\n\r\nWithin the last decade, the mathematical framework that allows us to achieve this result, control barrier functions, was introduced. Its adoption among the nonlinear controls community has been rapid, and the method has been used to create controllers that guarantee safety on a large class of systems. Despite this, real-world implementations of control barrier functions are less common, since they require a very accurate model of the system, and they can be difficult to formulate properly. This work provides several major extensions, improvements, and modifications of control barrier functions that allow them to be utilized on a variety of real-world robotic systems.
\r\n\r\nThe first major contribution of this thesis is a set of formulations for safety regulators that do not depend on complete knowledge of the underlying dynamical systems. Three unique formulations are proposed, whose usages depend on the level of knowledge of the underlying system. The resulting performance and safety guarantees are analyzed in real-world applications of quadrotor collision avoidance and fast-food frying with industrial manipulators. The second major contribution is a set of two safety filtering frameworks that utilize knowledge of the full-order dynamics, but allow for guaranteed safety in the presence of input constraints on high-dimensional systems. Two formulations are given, with one designed for use on microcontrollers with minimal computational resources. Both formulations utilize the knowledge of an existing \"backup controller\" that attempts to take the system into a small, safe \"backup set\". This method is demonstrated in simulation on a robotic manipulator and a Segway robot, and on hardware for collision avoidance and geofencing of single and multi-agent racing drones. The third major contribution is a novel discrete-time formulation of control barrier functions that allow for safety regulation of discrete-time systems. We show how safety constraints can be encoded as temporal logic specifications that are enforced over discrete-time models of the systems and their environments. The fourth and final major contribution is a unified, multi-rate control framework that guarantees safety at both the high-level, in discrete-time, and the low-level, in continuous-time. A mid-level Model Predictive Controller (MPC) is used to generate reference signals based on the high-level planner which are tracked by the low-level controller.
\r\n\r\nTogether, these four major contributions result in safe input regulation on a wide variety of robotic systems. Since no single method can reliably enforce safety on such a wide range of systems with different requirements, this thesis provides the smallest collection of methods that applies to the largest classes of systems.
" }, { "name": "Song, Yichuan", "degree": "PhD", "year": "2022", "title": "Rheological Measurements in Moderate Reynolds Number Liquid-Solid Flows", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-033735914", "creators": [ { "name": { "family": "Song", "given": "Yichuan" }, "id": "Yichuan-Song", "orcid": "0000-0001-7276-2029", "display_name": "Song, Yichuan" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5ey8-v324", "abstract": "Liquid-solid flows with inertial and viscous effects are critical for many engineering and geophysical applications, such as the processing of biomass slurry and the control of debris flows. However, modeling the rheological behaviors of these complex flows remains a challenge. Prior investigations on the liquid-solid flows typically cover suspensions in which the particle Reynolds numbers (Re) based on the particle diameter and shear rate are less than 1. Limited prior study at Caltech focuses on particle Reynolds numbers above 10. This thesis focuses on rheological experiments for the moderate Reynolds number regime where both inertial and viscous effects are important, with particle Reynolds numbers from 0.5 to 800. The rheological experiments include torque measurements of mm scale-sized polystyrene and SAN particles with a range of solid fractions from 10% to 50%, considering both neutrally-buoyant and settling suspensions with density ratios of 1 and 1.05. This thesis discusses rheological measurements of three different fields: pure fluids, neutrally-buoyant suspensions, and non-neutrally-buoyant suspensions.
\r\n\r\nThe pure fluids measurements determine the flow starts to transition to turbulent flow for gap Reynolds numbers above 6500 in the Caltech Couette flow device. For suspensions with matched particle and fluid densities and solid fractions less than 40%, we find that the effective viscosity only depends on the particle solid fraction until we observe the shear-thickening behaviors for Re of approximately 10. For the intermediate Re from 10 to 100 and lower solid fractions, the effective viscosity not only depends on the particle solid fraction, but also shows increased dependence on Re. For Re greater than 100, the liquid-solid flows transition to the turbulent regime, similar to what we see for the pure fluids. At the maximum solid fraction of 50%, the magnitude of the effective viscosity has increased by a factor of 20 as compared to the results of the 10% solid fraction, but the effective viscosity is nearly independent of Re. A particle Reynolds number (Re') based on the maximum shear flow velocity and the particle diameter is introduced to examine the effective viscosity of the suspensions. Since the present studies use particles with different sizes, Re' is found to be a better way to correlate the effective viscosity than the traditional Re. For the analysis of liquid-solid flows with a density ratio of 1.05, the effective viscosity of the particulate flow increases with the Stokes number for loading fractions of 10% and 20%, while the dependence is reversed for higher solid fractions.
" }, { "name": "Stevens, Benjamin Carter", "degree": "PhD", "year": "2022", "title": "Applications of Machine Learning to Finite Volume Methods", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:02062022-203334930", "creators": [ { "name": { "family": "Stevens", "given": "Benjamin Carter" }, "id": "Stevens-Benjamin-Carter", "orcid": "0000-0002-3410-5922", "display_name": "Stevens, Benjamin Carter" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/41qn-7n22", "abstract": "The finite volume method (FVM) has been one of the primary tools of computational fluid dynamics (CFD) for many decades. This method allows for the approximate solution of a partial differential equation (PDE) to be determined by breaking up a problem with no analytical solution into smaller pieces that can be solved together to get a physically realistic simulation. These algorithms can even be used for PDEs with discontinuous solutions, though they must be carefully designed for those situations because they cannot assume any level of smoothness in the solution. An FVM that has been designed for PDEs with discontinuous solutions is referred to as a shock-capturing method. For most of their history, FVM algorithms have been developed using rigorous mathematical arguments to formally maximize the order of convergence of the solution as the grid is refined. However, these arguments depend on the solution to the PDE being smooth, and therefore do not apply to shock-capturing methods. Instead, shock-capturing methods have traditionally been designed using human intuition to create algorithms that then perform well empirically. In this thesis, we instead follow a data-driven approach to train neural networks to use for enhanced FVM methods.
\r\n\r\nBy including a neural network in our FVM, we can use empirical data to optimize the algorithm. We can also utilize ideas from traditional FVM algorithms to create hybrid methods that have tunable parameters and maintain convergence guarantees present in FVMs that have been designed by hand. We explore these hybrid methods in a variety of settings. First, we create a general-purpose shock-capturing method WENO-NN by hybridizing the popular shock-capturing method WENO-JS with a neural network. Additionally, we develop a network architecture, called FiniteNet, that can be used to learn a coarse-graining model associated with a specific PDE and embed it into an FVM scheme. Finally, we also explore the idea of using transfer learning to further improve the WENO-NN for specific problems and name the resulting algorithm WENO-TL. We demonstrate experimentally that this hybrid approach results in methods that can offer similar error levels as traditional FVMs at less computational cost. Although the neural network increases the computational cost of one evaluation of our hybrid FVM, these methods also allow the simulation to be carried out on a coarser grid, leading to a net reduction in both simulation time and memory usage.
" }, { "name": "Sudhir, Kavya", "degree": "PhD", "year": "2022", "title": "Slip Patterns on Heterogeneous Frictional Interfaces", "advisor": "Lapusta, Nadia", "url": "https://resolver.caltech.edu/CaltechTHESIS:02232022-193800084", "creators": [ { "name": { "family": "Sudhir", "given": "Kavya" }, "id": "Sudhir-Kavya", "orcid": "0000-0001-6673-0979", "display_name": "Sudhir, Kavya" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "advisor", "display_name": "Lapusta, Nadia" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "orcid": "0000-0002-3060-8442", "role": "member", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "mecheng" ], "doi": "10.7907/xkbp-ks08", "abstract": "Understanding the implications of heterogeneity on frictional interfaces for the resulting slip patterns is a challenging, highly nonlinear, and dynamic problem with special relevance to earthquake source processes. Natural fault surfaces are rarely homogeneous and host a spectrum of slip behaviors in response to slow tectonic loading where slow steady slip and earthquake ruptures are just the end members. Understanding how heterogeneous frictional properties translate into different slip patterns would enable us to constrain the heterogeneity of natural faults and get an insight into processes that are difficult to observe in the field such as earthquake nucleation, with important implications for the assessment of seismic hazard.
\r\n\r\nIn this thesis, we advance our understanding of fault heterogeneity and its effects by conducting numerical simulations of long-term slip histories on heterogeneous frictional interfaces. We first focus on how irregular fault geometry affects the variability in repeating sequences by investigating a specific example of the SF-LA repeaters in the Parkfield segment of the San Andreas Fault (SAF) in California. We then investigate the effect of increasing heterogeneity in the effective normal stress on earthquake nucleation processes, complexity of earthquake sequences, and features of larger-scale ruptures. In both cases, we incorporate the heterogeneity in physical properties into 2D planar faults governed by rate-and-state friction and embedded into 3D homogeneous elastic bulk. Fully dynamic simulations are used to numerically solve the resulting elastodynamic problems with friction as a nonlinear boundary condition.
\r\n\r\nOur models reproduce many observations about SF-LA repeating sequences, in- cluding their mean moment, mean recurrence times, stress drops, the observed non- trivial scaling between the seismic moment and recurrence times of the repeaters, the ranges of variability in moment and recurrence time, and the ranges of triggering times between the two sequences. Multiple models produce slip behaviors com- parable to observations, indicating that the models cannot be uniquely constrained based on available observations. We also study how small-scale features of hetero- geneity affect model response. We find that smoothing the distribution over scales smaller than governing length scales in the problem, such as the nucleation size in our case, changes the specific evolution of slip, but preserves its key characteristics, such as the range of event variability and triggering times between events. However, smoothing the distribution on larger scales modifies the response qualitatively.
\r\n\r\nOur study of the earthquake initiation processes on interfaces with normal stress heterogeneity reveals that systematic increase in heterogeneity induces a continuum of behaviors, ranging from purely fault-spanning events to persistent foreshock-like events interspersed between fault-spanning mainshocks. In models with strong heterogeneity, most smaller-scale and larger-scale events initiate from scales much smaller than the nucleation size estimates calculated for uniform interfaces with equivalent average properties. While the variations in normal stress induce inversely proportional variations in the instability length scale often called nucleation size, we find that the nucleation-size variations by themselves are insufficient to cause such behavior, and that the associated strong heterogeneity in frictional strength is also required. In models with uniform friction strength but the same nucleation-size variation, the nucleation processes of larger-scale events are similar to those on uniform interfaces, with an addition of multiple triggered small-scale earthquakes. Our simulations show that several hypothesized scenarios of earthquake nucleation and foreshocks on natural faults may be viable and reflect different types and levels of heterogeneity on different faults the effects of which, in addition, vary as fault conditions evolve. For example, even with strong fault heterogeneity, some large- scale events have foreshocks and some do not, in the same simulation.
\r\n\r\nThe increasing fault heterogeneity generally leads to increasing complexity of the resulting earthquake sequences and moment-rate release (also called source-time function) of large-scale, fault-spanning events, as intuitively expected, although with some saturation at the higher heterogeneity levels. We find that, in the presence of significant normal-stress heterogeneity, source-time functions of many larger-scale events exhibit prolonged seismic initiation phases, similar to some observations, as the events nucleate from the heterogeneity scale and re-rupture the areas pres-lipped quasi-statically and in foreshocks. The source-time functions also reveal that larger-scale events in our models -- that are arrested by velocity-strengthening barriers -- have a more abrupt arrest phase than natural earthquakes, which places constraints on rupture-arresting mechanisms that should be used in modeling. The initial moment rates are similar for events of different eventual sizes on interfaces with strong heterogeneity, implying that, in those cases, large events are just small events that ran away.
" }, { "name": "Szoke, Szilard", "degree": "PhD", "year": "2022", "title": "Entangled Photon Interferometry: Development of Photonic Systems Towards Quantum Spectroscopy", "advisor": "Cushing, Scott K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02162022-092446660", "creators": [ { "name": { "family": "Szoke", "given": "Szilard" }, "id": "Szoke-Szilard", "orcid": "0000-0001-7860-4638", "display_name": "Szoke, Szilard" } ], "advisors": [ { "name": { "family": "Cushing", "given": "Scott K." }, "id": "Cushing-Scott-K", "orcid": "0000-0003-3538-2259", "role": "advisor", "display_name": "Cushing, Scott K." } ], "committee": [ { "name": { "family": "Hadt", "given": "Ryan G." }, "id": "Hadt-Ryan-G", "orcid": "0000-0001-6026-1358", "role": "chair", "display_name": "Hadt, Ryan G." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Cushing", "given": "Scott K." }, "id": "Cushing-Scott-K", "orcid": "0000-0003-3538-2259", "role": "member", "display_name": "Cushing, Scott K." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/brct-zh28", "abstract": "Entangled photon spectroscopy is an emergent field offering the potential to perform nonlinear and non-classical measurements at low photon fluxes. The entangled photon pairs which are generated using a continuous-wave laser pumped spontaneous parametric downconversion (SPDC) process simultaneously display strong correlations in time and anti-correlations in frequency space. Measuring changes in these correlations provides classical and non-classical information about the underlying dynamics and fluctuations of the sample-system. Further, because these two variables are not Fourier conjugates, entangled photon spectroscopy makes it possible to exploit the spectral resolution of continuous-wave lasers, while leveraging the temporal relationship of the near-simultaneously generated photon pairs which effectively mimics an ultrafast pulsed laser experiment. Nonlinear and ultrafast measurements can therefore be performed with low-power sources while also achieving superior signal-to-noise ratios due to the underlying quantum statistics. As photons in a pair can be separately manipulated, spectroscopic setups using these quantum states of light have marked benefits in contrast to measurements performed using traditional single photon states.
\r\n\r\nHere, we describe our efforts towards implementing quantum interferometers to test the abilities of entangled photon pairs in nonlinear spectroscopic studies. Specifically, we present work on the development of free-space, fiber-optic, and nanophotonic systems that leverage nonlinear materials to generate narrow to broadband entangled photon pairs via SPDC. The numerical methods used for designing and tailoring these entangled photon sources are outlined together with associated experimental limitations. The spectral-temporal correlations of the two-photon states are characterized using fourth-order interferometry, demonstrating Hong-Ou-Mandel interference with picoseconds to femtoseconds coherence times, and wavelengths ranging from the IR to the UV. A monolithic nanophotonics architecture is proposed for completely on-chip, entangled, ultrafast, and nonlinear spectroscopy.
" }, { "name": "Veismann, Marcel", "degree": "PhD", "year": "2022", "title": "Axial Descent of Multirotor Configurations -- Experimental Studies for Terrestrial and Extraterrestrial Applications", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:01252022-055518852", "creators": [ { "name": { "family": "Veismann", "given": "Marcel" }, "id": "Veismann-Marcel", "orcid": "0000-0001-8106-6738", "display_name": "Veismann, Marcel" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/w49w-qy54", "abstract": "Axial descent, specifically the vortex ring state (VRS), poses great challenges for rotorcraft operation as this flight stage is typically accompanied by severe aerodynamic losses and excessive vibrational loads due to the re-ingestion of rotor downwash. Given the hazardous nature of this flight stage, its fluid dynamic properties in regards to single, large-scale rotors have been extensively investigated since the early stages of manned helicopter flight. In light of the rapidly expanding use of small-scale multirotor systems, the field of VRS research has recently received increased interest, with a shifted focus towards small-scale rotors, as the thrust generation and stability of these aerial systems have also been shown to be adversely affected by complex descent aerodynamics. While experimental studies have started examining low Reynolds number rotor aerodynamics in steep or vertical descent, the influence of small-scale rotor geometry and aerodynamic coupling between neighboring rotors have not yet been sufficiently explored.
\r\n\r\nThe objective of this work is, therefore, to extend the current understanding of rotorcraft vortex ring state aerodynamics to low Reynolds number multirotor systems. A series of experimental studies employing various wind tunnel setups and flow visualization techniques is presented with the aim of identifying the underlying \ufb02uid-structure interactions, and quantifying rotor performance losses during multirotor axial descent. The work is divided into two fundamental experimental approaches, one utilizing statically mounted rotor systems and one utilizing free-flight testing.
\r\n\r\nThe first part of this work (Chapters 4 and 5) presents the results of wind-tunnel tested statically-mounted rotors for precise aerodynamic identification of rotor performance under simulated descent conditions. Chapter 4 covers a parametric analysis to comprehensively assess the extent to which relevant geometric parameters of a small-scale rotor influence its descent characteristic. Chapter 5 then explores the influence of separation between rotors and identifies potential rotor-rotor interactions in the VRS. The studies in this part of the thesis also make use of PIV setups for visualizing the flow field around small-scale rotors in the axial descent regime, subject to changing geometric parameters and rotor separation.
\r\n\r\nIn the second part (Chapters 6 and 7), a series of free-flight investigations is described for realistically simulated axial descent scenarios. Chapter 6 introduces the methodology for quantifying thrust generation of a multirotor in free-flight without rigid attachment to a load cell, and presents the results of exploratory axial flight studies. Chapter 7 discusses a study on axial descent of variable-pitch multirotor configurations, which was carried out to evaluate the feasibility of deploying a future Mars helicopter in mid air. Findings from this study helped to inform the entry descent and landing (EDL) strategy for JPL's future Martian rotorcraft missions.
" }, { "name": "Welch, Alexandra Justine", "degree": "PhD", "year": "2022", "title": "Understanding and Optimizing the Local Catalyst Environment in CO\u2082 Reduction Electrodes", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062021-151820825", "creators": [ { "name": { "family": "Welch", "given": "Alexandra Justine" }, "id": "Welch-Alexandra-Justine", "orcid": "0000-0003-2132-9617", "display_name": "Welch, Alexandra Justine" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4s78-cq55", "abstract": "Understanding and managing the local microenvironments in carbon dioxide reduction catalysts is crucial for optimizing device performance. In particular a locally high pH can increase catalyst selectivity and activity, as well as indicate which part of the catalyst is most active. In this thesis we begin by studying how nanoporous catalysts can induce this locally high pH in an aqueous system. We observe an increase in both Faradaic efficiency and partial current density for carbon monoxide in the nanoporous system relative to a planar metal film. We then show that this same nanoporous architecture can be used for improved device performance in a gas diffusion electrode configuration. We also perform copper underpotential deposition and secondary ion mass spectroscopy to show that almost half of the catalyst is not in contact with the electrolyte in this configuration. Then we use confocal fluorescent microscopy to image the local pH in a gas diffusion electrode to determine which parts of the electrode are most active. Through a combination of experiment and simulations we find that the catalyst within thin cracks of the microporous layer is most active for carbon dioxide reduction. While the study of local pH and wetting is the main focus of this thesis, we also explore how light can be used to improve selectivity and activity. In particular we study gold nanoparticles on p-type gallium nitride and copper nanoparticles on p-type nickel oxide. Finally, this thesis also explores how carbon dioxide conversion can actually be deployed. We discuss opportunities for combining carbon dioxide capture and conversion, as well as evaluate different pathways for renewable methane generation.
\r\n\r\nThis thesis gives in depth analysis of electrochemical carbon dioxide reduction catalysts as well as putting this research into the larger context of how such devices can be deployed. We hope that by combining systems level thinking and specific device studies better carbon dioxide conversion systems can be realized.
" }, { "name": "White, Nicholas Conlan", "degree": "PhD", "year": "2022", "title": "Nonlinear Dynamics and Stability of Viscous Free-Surface Microcapillary Flows in V-Shaped Channels and on Curved Surfaces", "advisor": "Troian, Sandra M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292022-001428228", "creators": [ { "name": { "family": "White", "given": "Nicholas Conlan" }, "id": "White-Nicholas-Conlan", "orcid": "0000-0002-7603-9329", "display_name": "White, Nicholas Conlan" } ], "advisors": [ { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "advisor", "display_name": "Troian, Sandra M." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "orcid": "0000-0002-1225-4695", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/yd3w-ck87", "abstract": "The last two decades have brought a revolution in miniaturization of space technology. Thanks to improved microelectronic sensors and MEMS devices, nanosatellites can perform communication and scientific studies previously limited to large satellites, significantly reducing the financial barriers to space access. But development of a reliable, long-running, small-scale propulsion system for orbital maneuvers remains a key challenge. One solution is the microfluidic electrospray propulsion (MEP) thruster under development at NASA's Jet Propulsion Laboratory (JPL).
\r\n\r\nThis thesis analytically addresses aspects of the MEP system's propellant management, specifically, capillary flow in the groove network delivering fluid propellant from the reservoir to the emitters. Building upon the reduced-order model of viscous capillary flow in straight V-shaped channels (\"V-grooves\") of Weislogel (1996) and Romero and Yost (1996), we prove stability of steady-state and self-similar flows. Because the MEP design requires an electric field above the grooves, and further calls for grooves which curve and bend in three dimensions, we extend earlier V-groove models to include these effects, and also perform stability analyses of the new models. The results not only validate the use of V-grooves as a robust propellant delivery system, but also provide a theoretical basis for the design of future microfluidic devices with compact, three-dimensional designs and electric fields.
\r\n\r\nIn order to lay the groundwork for future studies of early-time behavior of propellant on emitter tips before the Taylor cone necessary for ion emission is formed, we develop the technique of generalized linear stability analysis (Farrell and Ioannou, 1996) of capillary flow of thin viscous films coating curved surfaces (governed by the equation first developed by Roy and Schwartz, 1997). This methodology was first applied to films coating cylinders and spheres by Balestra et al. (2016, 2018); we instead apply the technique and analyze for the first time a viscous-capillary instability arising on a torus coated with a uniform thin film.
\r\n\r\nBesides the capillary fluid dynamics results, two additional pieces of work are included in the thesis. First, in an unorthodox application of Noether's Theorem to non-Lagrangian gradient flow equations, we show that each variational symmetry of the governing functional induces a constraint on the evolution of the system. Second, to support JPL's efforts to directly detect a \"fifth force,\" we introduce and implement numerical methods for computation of the scalar Cubic Galileon Gravity (CGG) field at solar system scales.
" }, { "name": "Williams, David Elliott", "degree": "PhD", "year": "2022", "title": "Shape-Changing Phased Arrays", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312022-192034489", "creators": [ { "name": { "family": "Williams", "given": "David Elliott" }, "id": "Williams-David-Elliott", "orcid": "0000-0002-6213-4712", "display_name": "Williams, David Elliott" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/r6f1-zq65", "abstract": "Historically, increasing the degrees of freedom in electromagnetic structures has revolutionized the capabilities of wireless systems and introduced new applications. While research on phased arrays has explored everything from antenna drive settings to the element placement, the array geometry is assumed to be a fixed parameter. This thesis summarizes the author's work developing shape-changing phased arrays. It demonstrates the fundamental trade-off between gain and steering range for a given geometry. Measurements of the first shape-changing phased array both verify this theory and demonstrate the ability to break this trade-off using geometric reconfiguration. In addition, the mathematical consequences of shape-change and their impact on the arrays electromagnetic properties are discussed. Programmable passive switching networks on flexible sheets embedded in the array are proposed to address these challenges. The ability of these structures to enhance array performance is demonstrated by in-situ optimization experiments on a demonstration array. The associated optimization problem is characterized with a statistical analysis on a simulated array. Finally, avenues for further research are proposed.
" }, { "name": "Wong, Joeson", "degree": "PhD", "year": "2022", "title": "Optoelectronic Physics and Engineering of Atomically Thin Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132021-004403821", "creators": [ { "name": { "family": "Wong", "given": "Joeson" }, "id": "Wong-Joeson", "orcid": "0000-0002-6304-7602", "display_name": "Wong, Joeson" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "chair", "display_name": "Falson, Joseph" }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Heinz", "given": "Tony F." }, "id": "Heinz-Tony-F", "orcid": "0000-0003-1365-9464", "role": "member", "display_name": "Heinz, Tony F." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/pxk0-3d19", "abstract": "Materials that are atomically thin behave substantially different than those of their bulk counterparts. However, when most materials become thinner, their surface-to-volume ratio increases and the number of unpassivated dangling bonds at the surface approaches the number of internal crystalline bonds, which prevents examining the intrinsic properties of most ultrathin materials. The recent discovery of layered materials, whose crystal structures have naturally passivated basal planes, has enabled the possibility to examine materials\u2019 thicknesses that approach a single atomic layer.
\r\n\r\nIn this thesis, we examine and explore the consequence of this new regime of thickness for active layers in photovoltaic applications. Specifically, we focus on the three aspects that define photovoltaic operation and explore their differences in these ultrathin materials: optical absorption of photons, subsequent carrier generation and transport, and finally, free energy extraction of collected carriers. We first discuss the implications of band-edge abruptness on the maximum efficiency of a solar cell. Then, we show that optical absorption in these ultrathin materials is dominated by cavity wave optics, and design structures that enable near-unity absorption in both ultrathin (~10 nm) and atomically-thin (~7 \u00c5) active layers. Using these optical design rules, we design heterostructures with record incident photon to electron conversion efficiency (>50%). Next, we examine new methods of creating electrical junctions by using thickness to vary the amount of band bending in a material. We spatiotemporally image these 'band-bending junctions' for the first time. Finally, we argue that photoluminescence can be used as a direct readout of the open circuit voltage potential, and motivate examination of monolayer materials which have substantially higher radiative efficiency. We therefore examine the strain tuning of photoluminescence properties of both monolayer TMDC and heterobilayer TMDC systems. This work illustrates that van der Waals materials are an ideal system for examining the novel optoelectronic physics of atomically thin photovoltaics.
" }, { "name": "Zhan, Eric", "degree": "PhD", "year": "2022", "title": "New Algorithms for Programmatic Deep Learning with Applications to Behavior Modeling", "advisor": "Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302021-224628633", "creators": [ { "name": { "family": "Zhan", "given": "Eric" }, "id": "Zhan-Eric", "orcid": "0000-0003-0521-5329", "display_name": "Zhan, Eric" } ], "advisors": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Chaudhuri", "given": "Swarat" }, "id": "Chaudhuri-Swarat", "orcid": "0000-0002-6859-1391", "role": "member", "display_name": "Chaudhuri, Swarat" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cms" ], "doi": "10.7907/5n5q-x203", "abstract": "Raw behavioral data is becoming increasingly more abundant and more easily obtainable in spatiotemporal domains such as sports, video games, navigation & driving, motion capture, and animal science. How can we best use this data to advance their respective domains forward? For instance, researchers for self-driving vehicles would like to identify the key features of the environment state that impact decision-making the most; game developers would like to populate their games with characters that have unique and diverse behaviors to create a more immersive gaming experience; and behavioral neuroscientists would like to uncover the underlying mechanisms that drive learning in animals. Machine learning, the science of developing models and algorithms to identify and leverage patterns in data, is well-equipped to aid in these endeavors. But how do we integrate machine learning with these spatiotemporal domains in a principled way? In this dissertation, we develop and introduce new algorithms in programmatic deep learning that tackle some of the new challenges encountered in behavior modeling.
\r\n\r\nOur work in programmatic deep learning comprises two main themes: in the first, we show how to use expert-written programs as sources of weak labels in domains where manually-annotated expert labels are scarce; in the second, we explore programs as a flexible function class with human-interpretable structure and show how to learn them via neurosymbolic program learning. Augmenting deep learning with programmatic structure allows domain experts to easily incorporate domain knowledge into machine learning models; we show that this results in significant improvements in many behavior modeling applications like imitation learning, controllable generation, counterfactual analysis, and unsupervised clustering.
" }, { "name": "Zhou, Fengyu", "degree": "PhD", "year": "2022", "title": "Optimization of Distribution Power Networks: from Single-Phase to Multi-Phase", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012022-005449566", "creators": [ { "name": { "family": "Zhou", "given": "Fengyu" }, "id": "Zhou-Fengyu", "orcid": "0000-0002-2639-6491", "display_name": "Zhou, Fengyu" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Anderson", "given": "James" }, "id": "Anderson-James", "orcid": "0000-0001-8210-6527", "role": "member", "display_name": "Anderson, James" } ], "option_major": [ "eleceng" ], "doi": "10.7907/tg26-9857", "abstract": "Distributed energy resources play an important role in today's distribution power system. The Optimal Power Flow (OPF) problem is fundamental in power systems as many important applications such as economic dispatch, battery displacement, unit commitment, and voltage control can be formulated as an OPF. A paradoxical observation is the problem's complexity in theory but simplicity in practice. On the one hand, the problem is well known to be non-convex and NP-hard, so it is likely that no simple algorithms can solve all problem instances efficiently. On the other hand, there are many known algorithms which perform extremely well in practice for both standard test cases and real-world systems. This thesis attempts to reconcile this seeming contradiction.
\r\n\r\nSpecifically, this thesis focuses on two types of properties that may underlie the simplicity in practice of OPF problems. The first property is the exactness of relaxations, meaning that one can find a convex relaxation of the original non-convex problem such that the two problems share the same optimal solution. This property would allow us to convexify the non-convex problem without altering the optimal solution and cost. The second property is that all locally optimal solutions of the non-convex problem are also globally optimal. This property allows us to apply local algorithms such as gradient descent without being trapped at some spurious local optima. We focus on distribution systems with radial networks (i.e., the underlying graphs are trees). We consider both single-phase models and unbalanced multi-phase models, since most real-world distribution systems are multi-phase unbalanced, and distributed energy resources (DERs) can be connected in either Wye or Delta configurations.
\r\n\r\nThe main results of this thesis are two-fold. In the first half, we propose a class of sufficient conditions for a non-convex problem to simultaneously have exact relaxation and no spurious local optima. Then we apply the result to single-phase system and conclude that if all buses have no injection lowerbounds, then both properties (exactness and global optimality) can be achieved. While the same condition is already known to be sufficient for exactness, our work is the first to extend it to global optimality. In the second half, we focus on the exactness property for multi-phase systems. For systems without Delta connections, the exactness can be guaranteed if 1) the binding constraints are sparse in the network at optimality; or 2) all nodal prices fall within a narrow range. Using the DC model as an approximation, we further analyze the OPF sensitivity and explain why nodal prices tend to be close to each other. In the presence of Delta connections, we conclude that the inexactness can be resolved by either postprocessing an optimal solution, or adding a new regularization term in the cost function. Both methods achieve global optimality for IEEE standard test cases.
" }, { "name": "Zhou, Hao", "degree": "PhD", "year": "2022", "title": "Accelerated Computational Micromechanics", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:03112022-002649428", "creators": [ { "name": { "family": "Zhou", "given": "Hao" }, "id": "Zhou-Hao", "orcid": "0000-0002-6011-6422", "display_name": "Zhou, Hao" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "member", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Lebensohn", "given": "Ricardo A." }, "id": "Lebensohn-R-A", "orcid": "0000-0002-3152-9105", "role": "member", "display_name": "Lebensohn, Ricardo A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/r4jb-4e98", "abstract": "The development of new materials is an important component of many cutting edge technologies such as space technology, electronics and medical devices. The properties of advanced materials involve phenomena across multiple scales. The material may be heterogeneous on a scale that is small compared to that of applications, or may spontaneously develop fine-scale structure. Numerical simulation of such phenomena can be an effective tool in understanding the complex physics underlying these materials, thereby assisting the development and refinement of such materials, but can also be challenging.
\r\n\r\nThis thesis develops a new method to exploit the use of graphical processing units and other accelerators for the computational study of complex phenomena in heterogeneous materials. The governing equations are nonlinear partial differential equations, typically second order in space and first order in time. We propose an operator-splitting scheme to solve these equations by observing that these equations come about by a composition of linear differential constraints like kinematic compatibility and balance laws, and nonlinear but local constitutive equations. We formulate the governing equation as an incremental variational principle. We treat both the deformation and the deformation gradient as independent variables, but enforce kinematic compatibility between them as a constraint using an augmented Lagrangian. The resulting local-global problem is solved using the alternating direction method of multipliers. This enables efficient implementation on massively parallel graphical processing units and other accelerators. We use the study of elastic composites in finite elasticity to verify the method, and to demonstrate its numerical performance. We also compare the performance of the proposed method with that of other emerging approaches.
\r\n\r\nWe apply the method to understand the mechanisms responsible for a remarkable in-plane liquid-like property of liquid crystal elastomers (LCEs). LCEs are rubber-like solids where rod-like nematic molecules are incorporated into the main or a side polymer chain. They undergo isotropic to nematic phase transition accompanied by spontaneous deformation which can be exploited for actuation. Further, they display a soft behavior at low temperatures due to the reorientation of the nematic directors. Recent experiments show that LCEs exhibit an in-plane liquid-like behavior under multiaxial loading, where there is shear strain with no shear stress. Our numerical studies of LCEs provides insights into the director distribution and reorientation in polydomain specimens, and how these lead to the observed liquid-like behavior. The results show good agreement with experimental observations. In addition to providing insight, this demonstrates the ability of our computational approach to study multiple coupled fields.
\r\n\r\nThe core ideas behind the method developed in this thesis are then applied elsewhere. First, we use it to study multi-stable deployable engineering structures motivated by origami. The approach uses two descriptions of origami kinematics, angle/face based approach and vertex/truss based approach independently, and enforces the relationship between them as a constraint. This is analogous to the treatment of kinematic compatibility above where both the deformation and deformation gradient are used as independent variables. The constraint is treated using a penalty. Stable and rigid-foldable configurations are identified by minimizing the penalty using alternate directions, and pathways between stable states are found using the nudged elastic band method. The approach is demonstrated using various examples.
\r\n\r\nSecond, we use a balance law or equilibrium to the problem of determining the stress field from high resolution x-ray diffraction. This experimental approach determines the stress field locally, and errors lead to non-equilibriated fields. It is hypothesized that imposing equilibrium leads to a more accurate stress reconstruction. We use Hodge decomposition to project a non-equilibriated stress field onto the divergence-free (equilibriated) subspace. This projection is numerically implemented using fast Fourier transforms. This method is first verified using synthetic data, and then applied to experimental data obtained from a beta-Ti alloy. It results in large corrections near grain boundaries.
" }, { "name": "Anderson, Thomas Geoffrey", "degree": "PhD", "year": "2021", "title": "Hybrid Frequency-Time Analysis and Numerical Methods for Time-Dependent Wave Propagation", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09042020-172204130", "creators": [ { "name": { "family": "Anderson", "given": "Thomas Geoffrey" }, "id": "Anderson-Thomas-Geoffrey", "orcid": "0000-0002-0643-2571", "display_name": "Anderson, Thomas Geoffrey" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/hmv1-r869", "abstract": "This thesis focuses on the solution of causal, time-dependent wave propagation and scattering problems, in two- and three-dimensional spatial domains. This important and long-lasting problem has attracted a great deal of interest reflecting not only its use as a model problem but also the prevalence of wave phenomena in diverse areas of modern science, technology and engineering. Essentially all prior methods rely on \"time-stepping\" in one form or another, which involves local-in-time approximation of the evolution of the solution of the partial differential equation (PDE) based on the immediate time history and temporal finite-difference approximation. In addition to the need to manage the accumulation of (dispersion) error and the burdensome increase in computational cost over time, there are additionally difficult issues of stability, time-domain boundary conditions, and absorbing boundary conditions which often need to be addressed.
\r\n\r\nTo sidestep many of these problems, this thesis develops a novel highly-efficient approach for time-dependent wave scattering problems employing the global-in-time techniques of Fourier transformation and leading to a frequency/time hybrid method for the time-dependent wave equation. Thus, relying on Fourier Transformation in time and utilizing a fixed (time-independent) number of frequency-domain solutions, the method evaluates the desired time-domain evolution with errors that both, decay faster than any negative power of the temporal sampling rate, and that, for a given sampling rate, are additionally uniform in time for all time. The fast error decay guarantees that high accuracies can be attained on the basis of relatively coarse temporal and frequency discretizations. The uniformity of the error for all time with fixed sampling rate, a property known as dispersionlessness, plays a crucial role, together with other properties of the Fourier transform, in enabling the evaluation of solutions for long times at O(1) cost. In particular, this thesis demonstrates the significant advantages enjoyed by the proposed methods over alternative approaches based on volumetric discretizations, time-domain integral equations, and convolution-quadrature.
\r\n\r\nThe approach relies on two main elements, namely, 1) A smooth time-windowing methodology that enables accurate band-limited representations for arbitrarily-long time signals, and 2) A novel Fourier transform approach which, in a time-parallel manner and without causing spurious periodicity effects, delivers numerically dispersionless spectrally-accurate solutions. A similar hybrid technique can be obtained on the basis of Laplace transforms instead of Fourier transforms, but we do not consider in detail the Laplace-based method, and only briefly point out its essential features and associated challenges.
\r\n\r\nThe proposed frequency/time Fourier-transform methods for obstacle scattering problems are easily generalizable to any linear partial differential equation in the time domain for which frequency-domain solutions can readily be obtained, including e.g. the time-domain Maxwell equations, the linear elasticity equations, inhomogeneous and/or frequency-dependent dispersive media, etc. Further, the proposed approach can tackle complex physical structures, it enables parallelization in time in a straightforward manner, and it allows for time leaping\u2014that is, solution sampling at any given time T at O(1)-bounded sampling cost, for arbitrarily large values of T, and without requirement of evaluation of the solution at intermediate times. In particular, effective algorithms are introduced that, relying on use of time-asymptotics, compute two-dimensional solutions at O(1) cost despite the very slow time-decay that takes place in the two-dimensional case.
\r\n\r\nA significant portion of this thesis is devoted to a theoretical study of the validity of a certain stopping criterion used by the algorithm, which guarantees that certain field contributions can safely be neglected after certain stopping times. Roughly speaking, the theoretical results guarantee that, after the incident field is turned off, the magnitude of the future scattering density (and thus the magnitudes of the fields) can be estimated by the magnitude of the integral density over a time period comparable to the time required by a wave to travel a distance equal to the diameter of the scatterer. The criterion, which is crucial in ensuring the O(1) computational cost of the algorithm, is closely related to the well-known scattering theory developed in the 1960s and '70s by Lax, Morawetz, Phillips, Strauss and others. Our approach to the decay problem is based on use of frequency-domain estimates (developed previously in the context of numerical analysis of frequency-domain problems) on integral operators in the high-frequency regime for obstacles of various trapping classes. In particular, our theory yields, for the first time, decay estimates for a class of connected trapping obstacles: all previous estimates of scattered-field decay for connected obstacles are restricted to nontrapping structures.
\r\n\r\nIn all, the proposed approach leverages the power of the Fourier transformation together with a range of newly developed spectrally convergent numerical methods in both the frequency and time domain and a variety of novel theoretical results in the general area of scattering theory to produce a radically-new framework for the solution of time-dependent wave propagation and scattering problems.
" }, { "name": "Arai, Noriaki", "degree": "PhD", "year": "2021", "title": "Freeze Casting of Ceramics: Pore Design from Solidification Principles", "advisor": "Faber, Katherine T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062020-163041829", "creators": [ { "name": { "family": "Arai", "given": "Noriaki" }, "id": "Arai-Noriaki", "orcid": "0000-0002-3040-2997", "display_name": "Arai, Noriaki" } ], "advisors": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "advisor", "display_name": "Faber, Katherine T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "matsci" ], "doi": "10.7907/3rmr-cz93", "abstract": "Freeze casting is a porous material processing method which allows the creation of directionally aligned pores by the solidification process. Pores are generated by sublimation of solidified crystals which reject suspending particles or dissolved solutes during freezing. Although freeze-cast ceramics have been identified for applications such as filtration and bioceramics, the lack of understanding of the process often results in a discrepancy between the desired pore structure and the fabricated structures.
\r\n\r\nSince solidification is the foundation upon which freeze casting is built, this work seeks to understand the solidification process, especially the growth and time evolution of dendrites. To understand the dendritic growth process, two solidification parameters, freezing front velocity and temperature gradient, are independently controlled to investigate the effects of each parameter. Dendritic pore size changes with solidification parameters and shows good agreement with dendrite growth theory. The theory of constitutional supercooling serves as a guide to control pore morphology between dendritic pores and cellular pores. Furthermore, dendrite growth under the effects of the gravitational force is investigated by changing the solidification direction with respect to the gravity direction. Convection changes the degree of constitutional supercooling, and results in different pore sizes as well as pore morphology.
\r\n\r\nTime evolution of dendrites through isothermal coarsening is investigated. During the coarsening of dendrites, they are transformed to cylinder-like crystals, which yield honeycomb-like structures. Moreover, dendrite size changes linearly with the cube root of coarsening time. Both findings are well-established phenomena in alloy solidification. Further comparison with alloy systems are achieved with tomography-based analysis where similar microstructural evolution with alloy system is demonstrated.
\r\n\r\nBased upon the understanding of underlying solidification principles in freeze casting, three applications are explored. First, the freeze-cast structure is designed to improve shape-memory properties. Processing variables are controlled such that shape-memory porous zirconia can enable martensitic phase transformations and shape deformation without fracture. Other applications utilize unique pore space. Dendritic pores are investigated for size-based filtration to preferentially capture small particles. Flow-through experiments and in-situ observation by confocal microscopy confirm that pores created by secondary dendrites capture small particles. Finally, honeycomb-like structures are filled with functional microgels to create a ceramic/polymer composite as an application for membrane chromatography. The fabricated composite demonstrates advantages such as mechanical stability during the fluid flow.
" }, { "name": "Azizan Ruhi, Navid", "degree": "PhD", "year": "2021", "title": "Large-Scale Intelligent Systems: From Network Dynamics to Optimization Algorithms", "advisor": "Wierman, Adam C.; Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:11182020-210226861", "creators": [ { "name": { "family": "Azizan Ruhi", "given": "Navid" }, "id": "Azizan-Ruhi-Navid", "orcid": "0000-0002-4299-2963", "display_name": "Azizan Ruhi, Navid" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-Steven-H", "orcid": "0000-0001-6476-3048", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cms" ], "doi": "10.7907/j494-j572", "abstract": "The expansion of large-scale technological systems such as electrical grids, transportation networks, health care systems, telecommunication networks, the Internet (of things), and other societal networks has created numerous challenges and opportunities at the same time. These systems are often not yet as robust, efficient, sustainable, or smart as we would want them to be. Fueled by the massive amounts of data generated by all these systems, and with the recent advances in making sense out of data, there is a strong desire to make them more intelligent. However, developing large-scale intelligent systems is a multifaceted problem, involving several major challenges. First, large-scale systems typically exhibit complex dynamics due to the large number of entities interacting over a network. Second, because the system is composed of many interacting entities, that make decentralized (and often self-interested) decisions, one has to properly design incentives and markets for such systems. Third, the massive computational needs caused by the scale of the system necessitate performing computations in a distributed fashion, which in turn requires devising new algorithms. Finally, one has to create algorithms that can learn from the copious amounts of data and generalize well. This thesis makes several contributions related to each of these four challenges.
\r\n\r\nAnalyzing and understanding the network dynamics exhibited in societal systems is crucial for developing systems that are robust and efficient. In Part I of this thesis, we study one of the most important families of network dynamics, namely, that of epidemics, or spreading processes. Studying such processes is relevant for understanding and controlling the spread of, e.g., contagious diseases among people, ideas or fake news in online social networks, computer viruses in computer networks, or cascading failures in societal networks. We establish several results on the exact Markov chain model and the nonlinear \"mean-field\" approximations for various kinds of epidemics (i.e., SIS, SIRS, SEIRS, SIV, SEIV, and their variants).
\r\n\r\nDesigning incentives and markets for large-scale systems is critical for their efficient operation and ensuring an alignment between the agents' decentralized decisions and the global goals of the system. To that end, in Part II of this thesis, we study these issues in markets with non-convex costs as well as networked markets, which are of vital importance for, e.g., the smart grid. We propose novel pricing schemes for such markets, which satisfy all the desired market properties. We also reveal issues in the current incentives for distributed energy resources, such as renewables, and design optimization algorithms for efficient management of aggregators of such resources.
\r\n\r\nWith the growing amounts of data generated by large-scale systems, and the fact that the data may already be dispersed across many units, it is becoming increasingly necessary to run computational tasks in a distributed fashion. Part III concerns developing algorithms for distributed computation. We propose a novel consensus-based algorithm for the task of solving large-scale systems of linear equations, which is one of the most fundamental problems in linear algebra, and a key step at the heart of many algorithms in scientific computing, machine learning, and beyond. In addition, in order to deal with the issue of heterogeneous delays in distributed computation, caused by slow machines, we develop a new coded computation technique. In both cases, the proposed methods offer significant speed-ups relative to the existing approaches.
\r\n\r\nOver the past decade, deep learning methods have become the most successful learning algorithms in a wide variety of tasks. However, the reasons behind their success (as well as their failures in some respects) are largely unexplained. It is widely believed that the success of deep learning is not just due to the deep architecture of the models, but also due to the behavior of the optimization algorithms, such as stochastic gradient descent (SGD), used for training them. In Part IV of this thesis, we characterize several properties, such as minimax optimality and implicit regularization, of SGD, and more generally, of the family of stochastic mirror descent (SMD). While SGD performs an implicit regularization, this regularization can be effectively controlled using SMD with a proper choice of mirror, which in turn can improve the generalization error.
" }, { "name": "Beardsell, Guillaume", "degree": "PhD", "year": "2021", "title": "Numerical Investigation of Compressibility Effects in Reacting Subsonic Flows", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:11102020-065104205", "creators": [ { "name": { "family": "Beardsell", "given": "Guillaume" }, "id": "Beardsell-Guillaume", "orcid": "0000-0001-7138-488X", "display_name": "Beardsell, Guillaume" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Pullin", "given": "Dale I." }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale I." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/dtfx-gy14", "abstract": "Direct numerical simulations (DNS) of reacting flows are routinely performed either by solving the fully compressible Navier-Stokes equations or using the low Mach number approximation. The latter is obtained by performing a Mach number expansion of the Navier-Stokes equations for small Mach numbers. These two frameworks differ by their ability to capture compressibility effects, which can be broadly defined as phenomena that are not captured by the low Mach number approximation. These phenomena include acoustics, compressible turbulence, and shocks. In this thesis, we systematically isolate compressibility effects in subsonic flows by performing two sets of DNS: one using the fully compressible framework, and one using the low Mach number approximation. We are specifically interested in the interactions between turbulence, acoustics, and flames.
\r\n\r\nThe addition of detailed chemistry in the compressible flow solver required the development of a novel time integration scheme. This scheme combines an iterative semi-implicit method for the integration of the species transport equations, and the classical Runge-Kutta method for the integration of the other flow quantities. It is found to perform well, yielding time steps limited by the acoustic CFL only. Furthermore, the computational cost per iteration of this hybrid scheme is low, being comparable to the one for the classical Runge-Kutta method.
\r\n\r\nAfter extensive validation, the first application is the investigation of flame-acoustics interactions in laminar premixed flames. The thermodynamic fluctuations that accompany the acoustic wave are shown to significantly impact the flame response. Using the Rayleigh criterion, the flame-acoustics system is found to be thermo-acoustically unstable for various fuels, flow conditions, and acoustic frequencies. As expected, the low Mach number approximation and the fully compressible framework are in good agreement at low frequencies, since the flame is very thin compared to the acoustic wavelength. The two frameworks differ for very large acoustic frequencies only. In the high frequency limit, the gain reaches a plateau using the low Mach number approximation, while it goes to zero using the fully compressible framework. This is related to the spatial variations in the acoustic pressure field, which are not present in the low Mach number approximation. However, for practically relevant acoustic frequencies, the low Mach number framework is found to yield accurate results.
\r\n\r\nNext, a numerical methodology to simulate compressible flows in geometries that lack a natural turbulence generation mechanism is presented. It is found that, unlike in incompressible flows, special care must be taken regarding the energy equation and the presence of standing acoustic modes. When using periodic boundary conditions, forcing the dilatational velocity field promotes the growth of unstable modes. This is explained by extracting the eigenvalues of the linearized forced Navier-Stokes equations. Based on these observations, it is found necessary to force the solenoidal velocity field only. This methodology is applied first to simulations of subsonic homogeneous non-reacting turbulence. We present simulations results for turbulent Mach numbers varying from 0.02 to 0.65. The Mach number dependence of various quantities, such as the dilatational to solenoidal kinetic energy ratio, is extracted. The Mach number scaling of all quantities of interest is found to be readily explained by the low Mach number expansion, specifically the zeroth and first order sets of equations, for turbulent Mach numbers up to 0.1.
\r\n\r\nFinally, the interaction between subsonic compressible turbulence and premixed flames is investigated. Compressibility effects are isolated by comparing results obtained with the low Mach number approximation and the fully compressible framework, at the same flow conditions. Compressibility effects on chemistry are found to be limited for turbulent Mach numbers at least up to 0.4, especially when contrasted with the large impact of the Karlovitz number. Compressibility effects give rise to significant thermodynamic fluctuations away from the flame front, but these remain small compared to the large fluctuations due to the presence of the turbulent flame brush. The low Mach number approximation thus remains a valid framework for the Mach numbers considered, when the primary goal is to characterize the impact of turbulence on the chemical processes at play.
" }, { "name": "Buabthong, Pakpoom (Pai)", "degree": "PhD", "year": "2021", "title": "Stability and Protective Coatings of Semiconductor Electrodes for Solar Fuel Devices", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312021-211620881", "creators": [ { "name": { "family": "Buabthong", "given": "Pakpoom (Pai)" }, "id": "Buabthong-Pakpoom-Pai", "orcid": "0000-0001-5538-138X", "display_name": "Buabthong, Pakpoom (Pai)" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "chair", "display_name": "Gray, Harry B." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "matsci" ], "doi": "10.7907/dx7s-fh20", "abstract": "Climate change and increasing global energy consumption drive the need for clean and renewable alternatives to fossil fuels. Photoelectrochemical solar fuel devices offer a potential solution to capture and store clean and renewable solar energy in chemical bonds. Nevertheless, degradation of semiconductor electrodes is one of the major impediments to the implementation of practical stable solar fuels systems.
\r\n\r\nerein, we investigate the corrosion mechanisms and the corrosion kinetics of CdTe and ZnTe cathodes under the conditions for hydrogen-evolution reaction in strong acid and strong alkaline media. The effects of catalyst over-layer on CdTe\u2019s and ZnTe\u2019s corrosion pathways are discussed as well as potential protective coatings for ZnTe cathodes. Then, we address the original physical pinhole defects in amorphous a TiO\u2082 grown by atomic-layer deposition (ALD) on GaAs anodes. In addition, we explore new pinhole formation during electrochemical experiments and provide simulation for the propagation of the corroding GaAs substrate after new exposure to the electrolyte through microscopic pinholes. Finally, we develop a fabrication procedure for GaAs micro-island structures to provide defect isolation on the a TiO\u2082 film. The micro-island structures combined with dissolution measurements of the ALD a TiO\u2082 films were used to study the distribution and the evolution of pinholes from pre-existing defect spots in the protective coatings.
" }, { "name": "Cai, Karena Xin", "degree": "PhD", "year": "2021", "title": "Safe and Interpretable Autonomous Systems Design: Behavioral Contracts and Semantic-Based Perception", "advisor": "Murray, Richard M.; Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:04022021-033321217", "creators": [ { "name": { "family": "Cai", "given": "Karena Xin" }, "id": "Cai-Karena-Xin", "orcid": "0000-0002-8392-4158", "display_name": "Cai, Karena Xin" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "co-advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "co-advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "cds" ], "doi": "10.7907/w3m8-es32", "abstract": "We are on the verge of experiencing a new, integrated society where autonomous vehicles will become a fabric of our everyday lives. And yet, seamless integration of autonomous vehicles into our society will require vehicles to interface safely with humans in an incredibly complex, fast-paced, and dynamic environment. Premature deployment of these new autonomous systems \u2014 without safety guarantees or interpretability of algorithms, could prove catastrophic. How can algorithms governing vehicle behavior be designed in a way that guarantees safety, performance, interpretability and scalability? This is the question this thesis seeks to answer.
\r\n\r\nFirst, we present a framework for architecting the decision-making module of autonomous vehicles so that safety and progress of agents can be formally guaranteed. In particular, all agents are defined to act according to what is termed an assume-guarantee contract, which is broadly defined as a set of behavioral preferences. The first version of the assume-guarantee contract is a behavioral profile, which is a set of ordered rules that agents must use to select actions in a way that is interpretable. With all agents operating according to a behavioral profile, the interactions however, are not necessarily coordinated. We then constrain agent behavior with an additional set of interaction rules. The behavioral profile combined with these additional constraints, are what we term a behavioral protocol. With all agents operating according to a local, decentralized behavioral protocol, we can provide formal proofs of the correctness of agent behavior, i.e. all agents will never collide and agents will make it to their respective destinations. Not only does the protocol so\u00a0defined allow us to make formal guarantees, but it is also designed in a way that scales well in the number of agents and provides interpretability of agent\u00a0behaviors. Safety and progress guarantees are proven and verified in simulation.
\r\n\r\nSecond, we focus on using information from object classifiers to enhance an autonomous vehicle's ability to localize where it is within its environment. The proposed approach for incorporating this semantic information is based on solving the maximum likelihood problem. With a hierarchical formulation, we are not only able to improve upon the accuracy of traditional localization techniques, but we are also able to improve our confidence in the accuracy of object detection classifications. The improvement in robustness and accuracy of these algorithms are shown in simulation.
" }, { "name": "Chen, Yalu", "degree": "PhD", "year": "2021", "title": "Computational Investigation of Nanoscale Electrocatalysts for Clean Energy Conversion", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:12152020-221422639", "creators": [ { "name": { "family": "Chen", "given": "Yalu" }, "id": "Chen-Yalu", "orcid": "0000-0002-0589-845X", "display_name": "Chen, Yalu" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "chair", "display_name": "Gray, Harry B." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/tgw8-c485", "abstract": "Electrocatalysis provides a practical solution to the increasing global energy demand while maintaining a sustainable environment. Recently nanoscale catalysts (nanoparticles, nanowires, and dealloyed surfaces) have been shown to have experimentally far superior performance than metallic crystals at sustainable energy conversion. However, the surface feature of these improved catalysts is still unknown, as the detection of the active sites directly from experiment has not been possible.
\r\n\r\nIn this thesis work, we discuss using the quantum mechanics based muitiscale simulations and machine learning to understand the nature of these superior materials. We first studied jagged Pt nanowire (J-PtNW), which was shown to have performance at oxygen reduction reactions (ORR) 50 times better than Pt/C. We used multiscale simulations (reactive force field, and density functional theory) to explain this remarkably accelerated ORR activity from an atomistic perspective. Next, we looked into the irregular gold surfaces and copper surfaces (nanoparticles and dealloyed surfaces), which showed dramatically improved performance at CO2 reduction reactions (CO2RR) and CO reduction reactions (CORR). We developed the strategy to combine the reactive force field, density functional theory, and machine learning to identify the active sites responsible for their improved performance. This approach provided the possibility to understand the highly irregular and disordered surface, which is impossible with surface science experiments or with quantum mechanics. The identification of the active sites provides insights into new design concepts (alloys, NP, NW, and electrolytes such as ionic liquids) aimed at increasing product selectivity and rates simultaneously with reducing energy requirements.
" }, { "name": "Chen, Yikai (Katie)", "degree": "PhD", "year": "2021", "title": "Numerical Simulation of Performance and Solar-to-Fuel Conversion Efficiency for Photoelectrochemical Devices", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082021-054649127", "creators": [ { "name": { "family": "Chen", "given": "Yikai (Katie)" }, "id": "Chen-Yikai-Katie", "orcid": "0000-0002-2955-9671", "display_name": "Chen, Yikai (Katie)" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Brunschwig", "given": "Bruce S." }, "id": "Brunschwig-B-S", "orcid": "0000-0002-6135-6727", "role": "member", "display_name": "Brunschwig, Bruce S." } ], "option_major": [ "mecheng" ], "doi": "10.7907/65pq-7d93", "abstract": "The Industrial Revolution was energized by coal, petroleum, and natural gas. It is clear that fossil fuels, which drive steam and electrical engines, made possible a monumental increase in the amount of productive energy available to humans. But in the meantime, the constant burning of fossil fuels has changed the natural greenhouse, intensified global warming, deteriorated air quality, and eventually caused irreversible environmental damage on our planet. Renewable energy especially solar energy offers a desirable approach toward meeting our growing energy needs while largely reducing fossil fuel burning. The major problems in terms of harvesting energy directly from sunlight turn out to be low energy concentration and intermittency. Building solar-fuel generators, which stores solar energy in chemical bonds, similar to photosynthesis in nature, provides a possible solution to these two problems. Carbon-free chemicals, such as hydrogen gas, which are produced by solar-driven water-splitting, or carbon-neutral chemicals, such as methane and ethylene, which are produced by solar-driven CO\u2082 reduction, are all promising clean fuels for solar storage.
\r\n\r\nThis thesis is focused on studying the performance and solar to fuel conversion efficiency of existing and hypothetical test-bed photoelectrochemical prototypes using multi-physics modeling and simulation to lay a foundation for future implementation and scale-up of the integrated, solar-driven systems. For water-splitting systems, a sensitivity analysis has been made to assess the relative importance of improvements in electrocatalysts, light absorbers, and system geometry on the efficiency of solar-to-hydrogen generators. Besides, an integrated photoelectrolysis system sustained by water vapor is designed and modeled. Under concentrated sunlight, the performance of the photoelectrochemical system with 10\u00d7 solar concentrators was simulated and the impact of hydrogen bubbles that are generated inside the cathodic chamber on the performance of the photoelectrolysis system was evaluated. For CO\u2082 reduction systems, operational constraints and strategies for systems to effect the sustainable, solar-driven reduction of atmospheric CO\u2082 were investigated. The spatial and light-intensity dependence of product distributions in an integrated photoelectrochemical CO\u2082 reduction system was modeled and simulated. Finally, the performance a flow-through gas diffusion electrode for electrochemical reduction of CO or CO\u2082 was evaluated.
\r\n\r\nThis thesis can be divided into three parts. The first part discusses the importance of solar energy. The second part includes Chapter II, Chapter III, Chapter IV, and Chapter V, which deals with solar-driven water-splitting cells, and the third part includes Chapter VI, Chapter VII, and Chapter VIII, which deals with solar-driven CO\u2082 reduction cells.
" }, { "name": "Cheng, Richard", "degree": "PhD", "year": "2021", "title": "Assuring Safety under Uncertainty in Learning-Based Control Systems", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:01052021-195655093", "creators": [ { "name": { "family": "Cheng", "given": "Richard" }, "id": "Cheng-Richard", "orcid": "0000-0001-8301-9169", "display_name": "Cheng, Richard" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9kye-rn93", "abstract": "Learning-based controllers have recently shown impressive results for different robotic tasks in well-defined environments, successfully solving a Rubiks cube and sorting objects in a bin. These advancements promise to enable a host of new capabilities for complex robotic systems. However, these learning-based controllers cannot yet be deployed in highly uncertain environments due to significant issues relating to learning reliability, robustness, and safety.
\r\n\r\nTo overcome these issues, this thesis proposes new methods for integrating model information (e.g. model-based control priors) into the reinforcement learning framework, which is crucial to ensuring reliability and safety. I show, both empirically and theoretically, that this model information greatly reduces variance in learning and can effectively constrain the policy search space, thus enabling significant improvements in sample complexity for the underlying RL algorithms. Furthermore, by leveraging control barrier functions and Gaussian process uncertainty models, I show how system safety can be maintained under uncertainty without interfering with the learning process (e.g. distorting the policy gradients).
\r\n\r\nThe last part of the thesis will discuss fundamental limitations that arise when utilizing machine learning to derive safety guarantees. In particular, I show that widely used uncertainty models can be highly inaccurate when predicting rare events, and examine the implications of this for safe learning. To overcome some of these limitations, a novel framework is developed based on assume-guarantee contracts in order to ensure safety in multi-agent human environments. The proposed approach utilizes contracts to impose loose responsibilities on agents in the environment, which are learned from data. Imposing these responsibilities on agents, rather than treating their uncertainty as a purely random process, allows us to achieve both safety and efficiency in interactions.
" }, { "name": "Edwards, Bryce Walker", "degree": "PhD", "year": "2021", "title": "Mechanical Investigations: Experimental Fracture Techniques and Frozen Small-Molecule Organics", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012021-150444627", "creators": [ { "name": { "family": "Edwards", "given": "Bryce Walker" }, "id": "Edwards-Bryce-Walker", "orcid": "0000-0002-2393-5488", "display_name": "Edwards, Bryce Walker" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/8f8y-5h58", "abstract": "Fracture of architected lattices: Three-dimensional diamond, kagome, and octet lattices were prepared for validation of a standard compact tension fracture experiment at two different length scales. Solid polymer lattices were written via two-photon lithography at the microscale, and solid polymer lattices are printed via digital light processing at the macroscale. Several of the macrolattices were pyrolyzed into carbon lattices to yield a brittle material for testing. The scaling laws of fracture toughness with relative density are explored, and this offers one of the first experimental studies of a fully 3D kagome lattice.
\r\n\r\nMechanical properties of solid benzene: We explore the mechanical properties and deformation of 10 um-sized cuboid-shaped solid benzene crystals made by freezing directly onto a liquid-nitrogen-cooled sample stage and compressed quasi-statically to 10% strain at 125 K with an in-situ nanomechanical instrument inside a Scanning Electron Microscope (SEM). Cryo-Transmission Electron Microscopy (cryo-TEM) and diffraction of frozen benzene confirms the orthorhombic crystal structure of benzene. Compressive contact pressure-strain response generated from load-displacement data suggests the deformation mechanism to occur via densification, with a loading modulus of 9 GPa, slightly larger than that of other small molecules composed of aromatic rings, such as naphthalene and biphenyl. Molecular dynamics (MD) simulations of experimentally equivalent compressions of 10-30 nm benzene samples of the same crystal structure and geometry along the principal lattice directions at 10-30 K suggest densification could, initially, occur by local amorphization of the compressed region. The discovered deformation mechanism, stiffness, and strength of benzene at 125 K can inform our understanding of geological processes on cold planetary bodies. For example, the surface of Saturn\u2019s moon Titan is teeming with solid organics at an ambient temperature of 95 K; this work will have significant impact on designing in-situ sampling tools for future missions to Titan and to substantiate speculative surface compositions.
" }, { "name": "Elliott, Luizetta Vadimovna", "degree": "PhD", "year": "2021", "title": "Stimuli Responsive Micro-Architected Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01082021-041336404", "creators": [ { "name": { "family": "Elliott", "given": "Luizetta Vadimovna" }, "id": "Elliott-Luizetta-Vadimovna", "orcid": "0000-0002-6411-0239", "display_name": "Elliott, Luizetta Vadimovna" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "medeng" ], "doi": "10.7907/bnfv-9c75", "abstract": "Shape memory polymers (SMPs) respond to heat by generating programmable movement useful in devices that require substantial deformation and operate at transient temperatures, including stents, embolization coils, and robotic grippers. Transitioning these materials to the microscale can result in expanded potential applications, such as clot removal from retinal vasculature, neural probe delivery, and responsive metamaterials. To achieve these goals, shape transformation must occur in SMPs with complex 3D geometries and nanoscale features.
\r\n\r\nThis thesis describes the synthesis and sculpting of a benzyl methacrylate-based SMP into 3D structures with <800nm characteristic critical dimensions via two photon lithography. The glass transition based shape memory mechanism of these materials is explored through dynamic nanomechanical analysis of 8\u00b5m-diameter cylindrical pillars, which revealed the initiation of a tunable glass transition at 60\u00b0C not present in highly crosslinked materials. Shape memory programming of the characterized pillars as well as complex 3D architectures, including flowers with 500nm thick petals and cubic lattices with 2.5\u00b5m unit cells and overall dimensions of 4.5\u00b5m x 4.5\u00b5m x 10\u00b5m, demonstrated an 86 +/- 4% characteristic shape recovery ratio. These results reveal a pathway towards SMP devices with nanoscale features and arbitrary 3D geometries changing shape in response to temperature.
\r\n\r\nThis thesis subsequently focuses on a particular potential application for such materials: neural probes designed for deployment in primate brains. Architected shape memory structures have the potential to create favorable long-term recording environments through softening triggered by biological conditions, deployment to beyond tissue damage during initial electrode positioning, and architectural features designed for optimal scaffold-tissue interactions. This thesis addresses one of the barriers to the deployment of such structures: the high loading during centimeter scale insertions required for primate brain targeting is incompatible with buckling free-insertion of low stiffness and/or cross sectional area probes required for minimizing the foreign body response.
\r\n\r\nLamb brain tissue model experiments with 280\u00b5m diameter platinum coated carbon fiber probes demonstrate that 59+/- 3% of the work during 3cm probe insertion is attributable to friction, suggesting that friction reduction is a favorable approach to load minimization. A phosphorylcholine-based ~100nm low friction coating is used to reduce the shear stress at the probe-brain interface by 20+/-7 %, demonstrating a facile method for friction reduction that has minimal impacts on probe cross sectional area. Surgical validation of probe insertion in a porcine head model reveals that these probes are suitable for whole brain penetration of brains at the primate scale (~10\u00b2g). These results show that loading requirements during whole brain penetration can be reduced through addressing the contribution of friction and introduce a viable vehicle for recording electrode delivery to large scale brains.
\r\n\r\nIn summary, this thesis provides the foundation for developing stimuli responsive microscale devices and materials and, in the case of deep brain neural recording, the building blocks for the design of an integrated shape memory/ low friction carbon fiber electrode delivery device. Future research on the scalable fabrication of architected shape memory polymers could enable the widespread application of such materials.
" }, { "name": "Faraji Dana, Mohammad Sadegh", "degree": "PhD", "year": "2021", "title": "From Metasurfaces to Compact Optical Metasystems", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:08042020-093945451", "creators": [ { "name": { "family": "Faraji Dana", "given": "Mohammad Sadegh" }, "id": "Faraji-Dana-Mohammad-Sadegh", "orcid": "0000-0002-8012-1253", "display_name": "Faraji Dana, Mohammad Sadegh" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/kvsy-ve81", "abstract": "Optical metasurfaces are a class of ultra-thin diffractive optical elements, which can control different properties of light such as amplitude, phase, polarization and direction at various wavelengths. The compatibility of optical metasurfaces with standard micro- and nano-fabrication processes makes them highly-suitable for realization of compact and planar form optical devices and systems. In addition, optical metasurfaces have achieved unique and unprecedented functionalities not possible by conventional diffractive or refractive optical elements. In this thesis, after a short review on the history and state of the art optical metasurfaces, I will discuss the systems consisting of optical metasurfaces, called optical meta-systems, which allow for implementations of complicated optical functions, such as wide field of view imaging and projection, tunable cameras, retro-reflection, phase-imaging, multi-color imaging, etc. Thereafter, the concept of folded metasurface optics is introduced and a compact folded metasurface spectrometer is showcased to demonstrate how the folded meta-systems can be designed, fabricated and practically utilized for real-life applications. Furthermore, different approaches for implementation of miniaturized hyperspectral imagers are investigated, among which the folded metasurface optics and a computational scheme using a random metasurface mask will be highlighted. Other potentials of optical metasurfaces achieved by the employment of optimization techniques to improve their multi-functional performances, as well as example applications in realizing optical vortex cornographs are studied. Finally, I will conclude the dissertation with an outlook on further applications of optical metasurfaces, where they can surpass the performance of current optical devices and systems and what limitations are still to be overcome before we can expect their wide-spread applications in our daily life.
" }, { "name": "Fatemi, Seyed Mohammadreza", "degree": "PhD", "year": "2021", "title": "Active Flat Optics Wavefront Manipulation for Imaging, Ranging, and Sensing", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:09182020-074010855", "creators": [ { "name": { "family": "Fatemi", "given": "Seyed Mohammadreza" }, "id": "Fatemi-Seyed-Mohammadreza", "orcid": "0000-0001-9081-2608", "display_name": "Fatemi, Seyed Mohammadreza" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7e5p-9r23", "abstract": "The emergence and maturity of integrated photonic platforms over the past decade allowed for reliable integration of a large number of photonic components on a single substrate. This ability to process and control coherent light on a chip is a potential pathway for the realization of novel low-cost systems capable of non-conventional functionalities for optical wavefront engineering. In this thesis, integrated active flat optics architectures for generation, manipulation, and reception of optical wavefronts are investigated. In particular, the application of such systems for imaging, ranging, and sensing are studied and multiple photonic systems including a large scale transmitter, a high-sensitivity receiver, and a high-resolution transceiver are demonstrated.
\r\n\r\nFor generation of optical wavefronts, solutions for engineering a radiative optical waveform via emission by an array of nano-photonic antennas are studied and a chip-scale photonic transmitter is implemented. The transmitter forms an optical phased array with a novel architecture in a CMOS compatible silicon photonics process which not only dispenses with the limitations of previously demonstrated systems but also yields a narrower beamwidth leading to a higher resolution. Moreover, an integrated adaptive flat optical receiver architecture that collects samples of the incident light and processes it on-chip with high detection sensitivity is implemented. To detect the optical samples with a high signal to noise ratio, an optoelectronic mixer is proposed and designed that down-converts the optical signals received by each antenna to a radio frequency signal in the electronic domain, provides conversion gain, and rejects interferers. This system allows arbitrary wavefront manipulation of the received signal by adapting itself to new conditions \u2014 a capability that does not exist in conventional cameras. Using this system, we realized the first high-sensitivity optical phased array receivers with one-dimensional and two-dimensional apertures and the functionality of the chips as ultra-thin lens-less cameras were demonstrated. To achieve a high-resolution integrated photonic 3D imager with low system complexity, a double spectral sampling method is developed through a special wavefront sampling arrangement on the transmitter and receiver apertures. This transceiver architecture includes a multi-beam transmitter and a high-sensitivity receiver that can distinguish the illuminated points separately and process them simultaneously using a digital signal processor.
\r\n\r\nMoreover, novel ultra-low power architectures for generation and reception of short RF/microwave pulses are explored. Such systems have a broad range of applications including imaging and ranging. In this study, the capability of generating and receiving orthogonal Hermite pulses of various orders using a capacitor-only time-varying network is demonstrated.
" }, { "name": "Filippitzis, Filippos", "degree": "PhD", "year": "2021", "title": "Identification of Structural Damage, Ground Motion Response, and the Benefits of Dense Seismic Instrumentation", "advisor": "Heaton, Thomas H.; Kohler, Monica D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11052020-043034327", "creators": [ { "name": { "family": "Filippitzis", "given": "Filippos" }, "id": "Filippitzis-Filippos", "orcid": "0000-0001-8377-4914", "display_name": "Filippitzis, Filippos" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "advisor", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "orcid": "0000-0002-4703-190X", "role": "co-advisor", "display_name": "Kohler, Monica D." } ], "committee": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "chair", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "orcid": "0000-0002-4703-190X", "role": "member", "display_name": "Kohler, Monica D." }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "orcid": "0000-0003-3323-3508", "role": "member", "display_name": "Clayton, Robert W." } ], "option_major": [ "mecheng" ], "doi": "10.7907/x0sf-pq18", "abstract": "This study explores the problems of identifying structural damage in steel frame buildings, through the use of dense instrumentation over the height of the building, and of characterizing the ground motion response in urban Los Angeles following the 2019 Ridgecrest earthquakes, through the use of dense instrumentation from available seismic networks, including the very dense Community Seismic Network.
\r\n\r\nFirst we explore the possibility of tracing possible nonlinear behavior of a structure by updating an equivalent linear system model in short time segments of the earthquake-induced excitation and response time histories, using a moving time window approach. The stiffness and damping related parameters of the equivalent linear model are estimated by minimizing a measure of fit between the measured and model predicted response time histories for each time window. We explore the effectiveness of the methodology for two example applications, a single-story and a six-story steel moment frame building. For the single-story building, the methodology is shown to be very effective in tracing the nonlinearities, while the six-story building is designed to also reveal the limitations of the methodology, mainly arising from the different types of model errors manifested in the formulation.
\r\n\r\nNext, we investigate the problem of structural damage identification through the use of sparse Bayesian learning (SBL) techniques. This is based on the premise that damage in a structure appears only in a limited number of locations. SBL methods that had been previously applied for structural damage identification used measurements related to modal properties and were thus limited to linear models. Here we present a methodology that allows for the application of SBL in non-linear models, using time history measurements recorded from a dense network of sensors installed along the building height. We develop a two-step optimization algorithm in which the most probable values of the structural model parameters and the hyper-parameters are iteratively obtained. An equivalent single-objective minimization problem that results in the most probable model parameter values is also derived. We consider the example problem of identifying damage in the form of weld fractures in a 15-story moment resisting steel frame building, using a nonlinear finite element model and simulated acceleration data. Fiber elements and a bilinear material model are used in order to account for the change of local stiffness when cracks at the welds are subjected to tension and the model parameters characterize the loss of stiffness as the crack opens under tension. The damage identification results demonstrate the effectiveness and robustness of the proposed methodology in identifying the existence, location, and severity of damage for a variety of different damage scenarios, and degrees of model and measurement errors. The results show the great promise of the SBL methodology for damage identification by integrating nonlinear finite element models and response time history measurements.
\r\n\r\nThe final part of the thesis involves studying the ground motion response in urban Los Angeles during the two largest events (M7.1 and M6.4) of the 2019 Ridgecrest earthquake sequence using recordings from multiple regional seismic networks as well as a subset of 350 stations from the much denser Community Seismic Network. The response spectral (pseudo) accelerations for a selection of periods of engineering significance are calculated. Significant spectral acceleration amplification is present and reproducible between the two events. For the longer periods, coherent spectral acceleration patterns are visible throughout the Los Angeles Basin, while for the shorter periods, the motions are less spatially coherent. The dense Community Seismic Network instrumentation allows us to observe smaller-scale coherence even for these shorter periods. Examining possible correlations of the computed response spectral accelerations with basement depth and Vs30, we find the correlations to be stronger for the longer periods. Furthermore, we study the performance of two state-of-the-art methods for estimating ground motions for the largest event of the Ridgecrest earthquake sequence, namely 3D finite difference simulations and ground motion prediction equations. For the simulations, we are interested in the performance of the two Southern California Earthquake Center 3D Community Velocity Models (CVM-S and CVM-H). For the ground motion prediction equations, we consider four of the 2014 Next Generation Attenuation-West2 Project equations. For some cases, the methods match the observations reasonably well; however, neither approach is able to reproduce the specific locations of the maximum response spectral accelerations, or match the details of the observed amplification patterns.
" }, { "name": "Gal-Katziri, Matan", "degree": "PhD", "year": "2021", "title": "Precision at Scale: System Design from Tiny Biosensors to Giant Arrays", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172020-115024354", "creators": [ { "name": { "family": "Gal-Katziri", "given": "Matan" }, "id": "Gal-Katziri-Matan", "orcid": "0000-0001-9100-1188", "display_name": "Gal-Katziri, Matan" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/t3cz-c785", "abstract": "In order to change the world, technological advancements must be made affordable and available for the general public to use. In other words, we must be able to scale our inventions effectively. Silicon integrated circuits are crucial components in scaling electronic systems because they are mass producible and offer a phenomenal cost-to-complexity ratio. This thesis summarizes the author\u2019s work on highly scalable sensor and array systems. It presents three high precision systems, that demonstrate how the use of highly functional radio-frequency integrated circuits enables the realization of previously unfeasible architectures." }, { "name": "Ginsberg, Leah Morgan", "degree": "PhD", "year": "2021", "title": "Multiscale Mechanical Characterization of Subcellular Structures in Living Walled Cells", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:03262021-224805539", "creators": [ { "name": { "family": "Ginsberg", "given": "Leah Morgan" }, "id": "Ginsberg-Leah-Morgan", "orcid": "0000-0001-9685-7014", "display_name": "Ginsberg, Leah Morgan" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Roumeli", "given": "Eleftheria" }, "id": "Roumeli-Eleftheria", "orcid": "0000-0002-2828-1428", "role": "member", "display_name": "Roumeli, Eleftheria" } ], "option_major": [ "mecheng" ], "doi": "10.7907/avj4-ve78", "abstract": "The physiology of walled cells is dramatically different from that of human cells, but the biomechanics of walled cells are far less studied. Most bacterial, fungal, and plant cells have a strong cell wall (CW), which allows them to withstand large hydrostatic pressures in the cytoplasm, called turgor. Turgor pressure conflates the mechanics of subcellular components and complicates the characterization of the cell. In this dissertation, new models are introduced and explored for single cells to investigate the multiscale mechanics of plant and bacterial cells using micro- and nano-indentation experiments.
\r\n\r\nA multi-scale biomechanical assay is used to study the mechanical properties of plant cells. The plant CW is typically around 5% of the width of the entire cell, and is thought to carry most of the mechanical load. Large-scale indentations using a micro-indentation system probe the behavior of the overall cell structure, and atomic-force microscopy (AFM) nano-scale indentations are used to isolate the CW response. To determine the effect of external osmotic pressure, indentations are performed on cells in different osmotic conditions: hypotonic, isotonic, and hypertonic. The cell is idealized as two springs acting in series, one to represent the CW and one to represent the cytoplasm. The model uses the experimentally determined initial stiffnesses as input to the model to determine the relative stiffness contributions of the CW and the cytoplasm.
\r\n\r\nThe first type of walled cells investigated is the xylem vessel element of Arabidopsis thaliana. The xylem is responsible for transporting water through the stem of any vascular plant (more commonly known as a land plant), and hence it must maintain structural integrity against high internal pressures while transporting water from the roots to the leaves. For extra structural support, xylem vessel elements develop secondary cell walls (SCWs), which are known to be a key component for mediating mechanical strength and stiffness in vascular plants. The structure and biomechanics of cultured plant cells are investigated during the cellular developmental stages associated with SCW formation using the multi-scale biomechanical assay described above. To determine the effect of morphological changes during differentiation, micro- and nano-indentations are performed on cells in different observed stages of the differentiation process.Prior to triggering differentiation, cells in hypotonic pressure conditions are significantly stiffer than cells in isotonic or hypertonic conditions, highlighting the dominant role of turgor pressure. Plasmolyzed cells with a SCW reach similar levels of stiffness as cells with maximum turgor pressure. Analysis using the two-spring model shows that the stiffness of the primary CW in all of these conditions is lower than the stiffness of the fully-formed SCW. These results provide the first experimental characterization of the mechanics of SCW formation at the single-cell level in plant cells.
\r\n\r\nNext, the mechanical response of individual Nicotiana tabacum cells from a suspension culture is studied using the same multi-scale biomechanical assay. The role played by the microtubules (MTs) and actin filaments (AFs) is determined through the use of drug treatments which selectively remove MTs and AFs. A generative statistical model is added to the two-spring model to quantify the stiffnesses of the CW, cytoplasm, turgor pressure, MTs, and AFs. Analysis of the initial stiffness and energy dissipation calculated from micro-indentation experiments indicates that the MTs and AFs contribute significantly to the mechanical response of a cell under compression. Micro- and nano-indentation tests confirm that turgor pressure is the most significant contributor to the stiffness response of turgid cells in compression. Finally, the results reveal that turgor pressure exerts stress on the CW, which leads to a measurable stiffening of the CW.
\r\n\r\nThe studies described above focused on developing a discrete model to describe the mechanics of a cell in indentation experiments. However, the most common type of model used to evaluate the mechanics of a cell are continuum models. Continuum models are also necessary to decouple the material properties of subcellular components from their structure. In the final section, AFM indentations are simulated on a gram-negative bacterium, Escherichia coli, and a sensitivity study and inverse analysis are performed to solve for the CW elastic modulus and turgor pressure simultaneously. Sensitivity study results reveal that uncertainty in turgor pressure and CW elasticity indeed contribute the most to variability in force spectra from AFM measurements. The parameter space of possible values for CW elastic modulus and turgor pressure is discretized using triangular elements. \"Simulated experiments\" are tested throughout the parameter space, and correlations between the CW elastic modulus and turgor pressure, which depend on the type of objective function, are investigated. Two unique objective functions are tested in the inverse analysis, and a third objective function, which is a weighted sum of the first two, is found to reduce errors in estimated CW elastic modulus and turgor pressure by 20% and 11%, respectively. The use of this type of inverse analysis has the potential to elucidate the material properties of CWs using a single indentation measurement and reliably decouple these properties from the high turgor pressures inside walled cells.
" }, { "name": "Injeti, Sai Sharan", "degree": "PhD", "year": "2021", "title": "Multi-Functional Metamaterials", "advisor": "Bhattacharya, Kaushik; Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062021-023201965", "creators": [ { "name": { "family": "Injeti", "given": "Sai Sharan" }, "id": "Injeti-Sai-Sharan", "orcid": "0000-0003-1941-9752", "display_name": "Injeti, Sai Sharan" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "mecheng" ], "doi": "10.7907/3rfm-1x78", "abstract": "Optimally designing interdependent mechanical properties in a structure allows for it to be used in application where an arbitrary combination of properties is desired. Architected materials have proven to be an effective way of attaining mechanical behaviors that are unattainable using their constituent materials alone, such as unusual static mechanical properties, unusual wave propagation behavior, and shape morphing. The advent of 3-D printing has allowed for fabricating metamaterials with complex topologies that display engineered mechanics. However, much of the current efforts have focused on optimally designing simple mechanical behaviors such as designing for stiffness and weight, particular frequency bandgaps, or bi-stability. In this work, we study two metamaterial systems where we control and optimize a wide set of static and dynamic properties, and one complex multi-stable structure.
\r\n\r\nMost studies on the optimal design of static properties have focused on engineering stiffness and weight, and much remains unknown about ways to decouple the critical load to failure from stiffness and weight. This is the focus of the first part of our work. We show that the addition of local internal pre-stress in selected regions of architected materials enables the design of materials where the critical load to failure can be optimized independently from the density and/or quasistatic stiffness. We propose a method to optimize the specific load to failure and specific stiffness using sensitivity analysis, and derive the maximum bounds on the attainable properties. We demonstrate the method in a 2-D triangular lattice and a 3-D octahedral truss, showing excellent agreement between experimental and theoretical results. The method can be used to design materials with predetermined fracture load, failure location and fracture paths.
\r\n\r\nFor the second part of our work, we focus on designing acoustically transparent structures, by engineering the acoustic impedance -- a combination of wave speed and density, to match that of the surroundings. Owing to the strong correlation between acoustic wave speed and static stiffness, it is challenging to design acoustically transparent materials in a fluid, while maintaining their high structural rigidity. We provide a sensitivity analysis to optimize these properties with respect to design parameters of the structure, that include localized masses at specific positions. We demonstrate the method on five different periodic, three dimensional lattices, to calculate bounds on the longitudinal wave speed as a function of their density and stiffness. We then perform experiments on 3-D printed structures, to validate our numerical simulations. Further, using the sensitivity analysis together with a data-driven approach, we design and demonstrate a mode demultiplexer, that is capable of splitting arbitrarily mixed modes. The tools developed in this work allow for designing structures in a plethora of applications, including ultrasound imaging, wave filtering, and waveguiding.
\r\n\r\nFinally, most multi-stable structures are limited by bi-stability either at the macroscopic or the unit cell level owing to the difficulty in engineering a highly non-linear energy landscape using just elements that display convex energy landscapes. We demonstrate a method to design arbitrarily complex multi-stable shape morphing structures, by introducing rigid kinematic constraints together with disengaging energy storing elements. We present the idea on a kagome lattice configuration, producing a quadri-stable unit cell and complex stable topologies with larger tessellations, validated by demonstrations on 3-D printed structures. Most designs that use passive actuation address one-way shape morphing along the direction of least resistance. We demonstrate reversible, thermally actuated shape morphing between stable open and closed topologies using shape memory springs. The designs can be extended to non-planar structures and fabricated at vastly different length scales.
" }, { "name": "Jones, Silken Michelle", "degree": "PhD", "year": "2021", "title": "Thermal Ignition by Vertical Cylinders", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182020-055522985", "creators": [ { "name": { "family": "Jones", "given": "Silken Michelle" }, "id": "Jones-Silken-Michelle", "orcid": "0000-0003-3496-7191", "display_name": "Jones, Silken Michelle" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverly J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverly J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9g5j-2b97", "abstract": "Accidental thermal ignition events present a significant hazard to the aviation industry. There is scarcity of experimental data on ignition by external natural convection flows for surface areas larger than 10 cm\u00b2. In this work, thermal ignition of external natural convection flows by vertical cylinders is investigated. The effect of geometry is studied by resistively heating stainless steel cylinders of various sizes in a stoichiometric n-hexane and air mixture at 298 K and 1 bar. Cylinder lengths range from 12.7 to 25.4 cm, and cylinder surface areas vary from 25 to 200 cm\u00b2. Logistic regression is used to provide statistical information about the ignition threshold (50% probability of ignition). The maximum ignition threshold found is 1117 K for a cylinder 12.7 cm long and 50 cm\u00b2 in surface area. The minimum ignition threshold found is 1019 K for a cylinder 25.4 cm long and 200 cm\u00b2 in surface area. The maximum uncertainty on these ignition thresholds is \u00b129 K, which comes from the maximum uncertainty on the pyrometer measurement used to record cylinder surface temperatures. \r\nThe dependence of ignition threshold on both surface area and length of a cylinder is found to be minor. High speed visualizations of ignition indicated that ignition occurs near the top edge of all cylinders.
\r\n \r\nThe entire experimental setup is heated to allow for ignition tests with multi-component, heavy-hydrocarbon fuels including Jet A and two surrogate fuels, Aachen and JI. The cylinder used for all testing of heavier fuels is 25.4 cm long and 200 cm\u00b2 in surface area. Hexane is also tested with the heated vessel to investigate the effect of ambient temperature on ignition. At an ambient temperature of 393 K, the ignition threshold of hexane is 933 K. Aachen has an ignition threshold of 947 K at an ambient temperature of 373 K. JI has an ignition temperature of 984 K at an ambient temperature of 393 K. Jet A has an ignition temperature of 971 K at an ambient temperature of 333 K. The maximum uncertainty on these thresholds is \u00b129 K. JI is found to be the most appropriate surrogate for Jet A.
\r\n \r\nFrom the experiments, two main conclusions are reached. Ignition threshold temperatures in external natural convection flows are very weakly correlated with surface area. The observed ignition thresholds do not show the drastic transition of ignition temperature with surface area that is observed in internal natural convection situations. Observed ignition thresholds for comparable surface areas (100 to 200 cm\u00b2) are 500 to 600 K higher for external natural convection than internal natural convection. Hexane was found to be a reasonable surrogate for Jet A (38 K difference in ignition threshold) in external natural convection ignition testing. The more complex multi-component JI surrogate, while having an ignition threshold more comparable to Jet A (13 K difference in ignition threshold), requires heating the experimental apparatus and associated difficulties of fuel handling as well as the soot generation by combustion.
\r\n \r\nTwo simplified models of ignition are explored. The first is an investigation of ignition chemistry using a zero-dimensional reactor and a detailed kinetic mechanism for hexane. The temperature history of the reactor is prescribed by an artificial streamline whose rate of temperature increase is parametrically varied. The results from the zero-dimensional reactor computation reveal that a gradually heated streamline exhibits two-stage ignition behavior, while a rapidly heated streamline only experiences one ignition event. The second model of ignition is a one-dimensional simulation of ignition adjacent to a cylinder at a prescribed temperature. The formulation included diffusion of species and thermal energy as well as chemical reaction and employed Lagrangian coordinates. The chemistry is modeled with a reaction mechanism for hydrogen to reduce numerical demand. Heat flux and energy balance are analysed to gain insight into the ignition dynamics. Initially, heat transfer is from the wall into the gas, and a mostly nonreactive thermal boundary layer develops around the cylinder. As reaction in the gas near the surface begins to release energy, the heat transfer decreases, and, near the critical temperature for ignition, the direction of heat flux reverses and is from the gas into the wall. In a case where ignition takes place, there is rapid rise in temperature in the gas within the thermal layer, and a propagating flame is observed to emerge into surrounding cold gas. The heat transfer from the hot combustion products results in a continuous heat flux from the gas into the wall. In a case where ignition does not take place, no flame is observed and the heat flux at the wall is slightly positive. For the critical condition just below the ignition threshold, a balance between energy release and diffusion in the adjacent gas results in a small temperature rise in the thermal layer, but a propagating flame is not created. The Van't Hoff ignition criterion of vanishing heat flux at the ignition threshold is approximately but not exactly satisfied. Contrasting the two modeling ideas, we observe that modeling adiabatic flows along computed nonreactive streamlines is useful in examining the role of detailed chemistry but lacks important diffusion effects. Including mass and thermal transport provides more insight into important ignition dynamics but comes at the expense of increased computational complexity.
" }, { "name": "Joshi, Akshay", "degree": "PhD", "year": "2021", "title": "A Shock Compression Investigation of Failure Waves and Phase Transition in Soda-Lime Glass", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282021-233441075", "creators": [ { "name": { "family": "Joshi", "given": "Akshay" }, "id": "Joshi-Akshay", "orcid": "0000-0001-8347-8357", "display_name": "Joshi, Akshay" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "role": "member", "display_name": "Mello, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/b8xs-8r91", "abstract": "Soda-lime glass (SLG) and other silica glasses find use in many technological applications involving high pressures and strain rates, such as systems with laser-matter interactions, transparent armor, etc. An experimentally validated constitutive model for these glasses is required for modeling their mechanical behavior at high pressures and strain rates. Also, due to the abundance of silica in the earth's crust, understanding the behavior of these glasses at high pressures can provide significant insights into many geophysical processes. To this end, shock compression experiments are carried out on SLG to study the material's behavior under impact stresses of 5-10 GPa. These experiments are accompanied by numerical simulations and constitutive modeling of SLG to gain further insights into the reported failure-wave phenomenon and phase transitions associated with the material.
\r\n\r\nThe significant findings of this study in relation to the failure-wave phenomenon were the sudden densification/compaction of SLG associated with the failure-wave and the disappearance of the failure-wave phenomenon for impact stresses above 10 GPa. When viewed in the context of the findings from past experiments, these results seem to suggest that localized densification/compaction of SLG causes nucleation of cracks and subsequent comminution in the material under shock compression. These results and observations offer a potential explanation of the mechanism underlying the failure-wave phenomenon.
\r\n\r\nFurther, the shock compression and release experiments performed in this work provided significant insights into the onset of possible phase-transition in SLG under shock compression. A loading-unloading hysteresis is observed in the material\u2019s stress-strain curve for impact stresses higher than 5.8 GPa, with the permanent/residual strain increasing with impact stress. Further analysis of these results strongly indicates that the hysteresis is more likely due to a gradual, irreversible phase transition of SLG than due to regular inelastic behavior. Thus, the results suggest that the SLG undergoes a gradual phase transition to a stiffer phase, although other properties of this phase remain unclear. It can also be noted that this phase transition is postulated to start occurring under shock compression of SLG to stresses above 5 GPa, which is also the threshold stress for the onset of the failure-wave phenomenon. It is, therefore, possible that the two phenomena are interrelated. The experimental results from this study are further used to construct a constitutive model to capture the unloading behavior of SLG.
" }, { "name": "Kafaie Shirmanesh, Ghazaleh", "degree": "PhD", "year": "2021", "title": "Electro-Optically Tunable Metasurfaces for a Comprehensive Control of Properties of Light", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:09172020-190836007", "creators": [ { "name": { "family": "Kafaie Shirmanesh", "given": "Ghazaleh" }, "id": "Kafaie-Shirmanesh-Ghazaleh", "orcid": "0000-0003-1666-3215", "display_name": "Kafaie Shirmanesh, Ghazaleh" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/m554-as73", "abstract": "The ability to control electromagnetic wavefront is a central key in optics. Conventional optical components rely on the gradual accumulation of the phase of light as it passes through an optical medium. However, since the accumulated phase is limited by the permittivity of naturally existing materials, such a mechanism often results in bulky devices that are much thicker than the operating wavelength.
\r\n\r\nDuring the last several years, metasurfaces (quasi-2D nanophotonic structures) have attracted a great deal of attention owing to their promise to manipulate constitutive properties of electromagnetic waves such as amplitude, phase, and polarization. Metasurfaces are ultrathin arrays of subwavelength resonators, called meta-atoms, where each meta-atom imposes a predefined change on the properties of the scattered light. By precisely designing the optical response of these meta-atoms to an incident wave, metasurfaces can introduce abrupt changes to the properties of the transmitted, reflected, or scattered light, and hence, can flexibly shape the out-going wavefront at a subwavelength scale. This enables metasurfaces to replace conventional bulky optical components such as prisms or lenses by their flat, low-profile analogs. Furthermore, a single metasurface can perform optical functions typically attained by using a combination of multiple bulky optical elements, offering tremendous opportunities for flat optics.
\r\n\r\nThe optical response of a metasurface is typically dictated by the geometrical parameters of the subwavelength scatterers. As a result, most of the reported metasurfaces have been passive, namely have functions that are entirely fixed at the time of fabrication. By making the metasurfaces reconfigurable in their phase, amplitude, and polarization response, one can achieve real-time control of optical functions, and indeed, achieve multi-functional characteristics after fabrication. Dynamical control of the properties of the scattered light is possible by using external stimuli such as electrical biasing, optical pumping, heating, or elastic strain that can give rise to changes in the dielectric function or physical dimensions of the metasurface elements.
\r\n\r\nIn this dissertation, we present the opportunities and challenges towards achieving reconfigurable metasurfaces. We introduce a paradigm of active metasurfaces for real-time control of the wavefront of light at a subwavelength scale by investigating different modulation mechanisms and possible metasurface designs and material platforms that let us effectively employ the desired modulation mechanism. We will present multiple electro-optically tunable metasurface platforms. These electronically-tunable schemes are of great interest owing to their robustness, high energy-efficiency, and reproducibility. We will also show the design and experimental demonstration of active metasurfaces for which the tunable optical response can be tailored in a pixel-by-pixel configuration.
\r\n\r\nThe ability to individually control the optical response of metasurface elements has made active optical metasurfaces to be progressively ubiquitous by enabling a wide range of optical functions such as dynamic holography, light fidelity (Li-Fi), focusing, and beam steering. As a result, reconfigurable metasurfaces can hold an extraordinary promise for optical component miniaturization and on-chip photonic integration. Such compact and high-performance devices with reduced size, weight, and power (SWaP) can be used in future free-space optical communications or light detection and ranging (LiDAR) systems.
" }, { "name": "Karapiperis, Konstantinos", "degree": "PhD", "year": "2021", "title": "Multiscale, Data-Driven and Nonlocal Modeling of Granular Materials", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182020-181342301", "creators": [ { "name": { "family": "Karapiperis", "given": "Konstantinos" }, "id": "Karapiperis-Konstantinos", "orcid": "0000-0002-6796-8900", "display_name": "Karapiperis, Konstantinos" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/7rtg-x780", "abstract": "Granular materials are ubiquitous in both nature and technology. They play a key role in many applications ranging from storing food and energy to building reusable habitats and soft robots. Yet, predicting the continuum mechanical response of granular materials continues to present extraordinary challenges, despite the apparently simple laws that govern particle-scale interactions. This is largely due to the complex history dependence arising from the continuous rearrangement of their internal structure, and the nonlocality emerging from their self-organization. There is clearly an urge to develop methods that adequately address these two aspects, while bridging the long-standing divide between the grain- and the continuum scale.
\r\n\r\nThis dissertation introduces novel theoretical and computational approaches for behavior prediction in granular solids. To begin with, we develop a framework for investigating their incremental behavior from the perspective of plasticity theory. It relies on systematically probing, through level-set discrete element calculations, the response of granular assemblies from the same initial state to multiple directions is stress space. We then extract the state- and history-dependent elasticity and plastic flow, and investigate the evolution of pertinent internal variables. We specifically study assemblies of sand particles characterized by X-ray computed tomography, as well as morphologically simpler counterparts of the same systems. Naturally arising from this investigation is the concept of a granular genome. Next, inspired by the abundance of generated high-fidelity micromechanical data, we develop an alternative data-driven approach for behavior prediction. This new multiscale modeling paradigm completely bypasses the need to define a constitutive law. Instead, the problem is directly formulated on a material data set, generated by grain-scale calculations, while pertinent constraints and conservation laws are enforced. We particularly focus on the sampling of the mechanical phase space, and develop two methods for parametrizing material history, one thermodynamically motivated and one statistically inspired. In the remainder of the thesis, we direct our attention to the understanding and modeling of nonlocality. We base our investigation on data derived from a discrete element simulation of a sample of sand subjected to triaxial compression and undergoing shear banding. By representing the granular system as a complex network, we study the self-organized and cooperative evolution of topology, kinematics and kinetics within the shear band. We specifically characterize the evolution of fundamental topological structures called force cycles, and propose a novel order parameter for the system, the minimal cycle coefficient. We find that this coefficient governs the stability of force chains, which succumb to buckling as they grow beyond a characteristic maximum length. We also analyze the statistics of nonaffine kinematics, which involve rotational and vortical particle motion. Finally, inspired by these findings, we extend the previously introduced data-driven paradigm to include nonaffine kinematics within a weakly nonlocal micropolar continuum description. By formulating the problem on a phase space augmented by higher-order kinematics and their conjugate kinetics, we bypass for the first time the need to define an internal length scale, which is instead discovered from the data. By carrying out a data-driven prediction of shear banding, we find that this nonlocal extension of the framework resolves the ill-posedness inherent to the classical continuum description. Finally, by comparing with available experimental data on the same problem, we are able to validate our theoretical developments.
" }, { "name": "Kennedy, Kathleen Marie", "degree": "PhD", "year": "2021", "title": "Renewable Energy Generation and Storage: From Microwires to Macro-Energy Systems", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:10142020-161631454", "creators": [ { "name": { "family": "Kennedy", "given": "Kathleen Marie" }, "id": "Kennedy-Kathleen-Marie", "orcid": "0000-0002-7125-4871", "display_name": "Kennedy, Kathleen Marie" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "matsci" ], "doi": "10.7907/nsmj-tq29", "abstract": "Current trajectories require urgent action to reach net-zero greenhouse gas emissions targets. This thesis focuses on efforts to support decarbonization through the development of solar fuels devices to produce green hydrogen and through macro-energy systems modeling.
\r\n\r\nLong-term stability of light-absorbing materials remains a substantial barrier to the viability of solar fuel devices. In this thesis, we identify corrosion pathways in TiO\u2082-protected silicon microwire arrays in a polymer membrane either attached to a substrate or free-standing. Both top-down and bottom-up corrosion processes were observed in both morphologies, with top-down corrosion arising from defects in the TiO\u2082 protection layer and bottom-up corrosion occurring through the substrate and membrane.
\r\n\r\nMoving to a systems perspective, we use a macro-scale energy model with historical demand in conjunction with hourly historical weather data to analyze the role of concentrated solar power (CSP) with thermal energy storage (TES) relative to photovoltaics (PV) and batteries in an idealized least-cost wind/solar/storage system that reliably meets hourly demand. We find that CSP+TES occupies a small niche providing valuable grid services by adding flexibility due to the favorable cost of storing energy in TES compared to batteries. Consequently, CSP does not compete directly with PV, but rather TES competes with short-duration storage from batteries, with the coupled CSP technology providing cost-effective grid services to achieve reliability. A cost-sensitivity analysis shows that penetration of CSP+TES in this idealized wind/solar/storage electricity system is primarily limited by the relatively high current CSP generation costs.
" }, { "name": "Khachaturian, Aroutin", "degree": "PhD", "year": "2021", "title": "Large-Scale Photonics Integration: Data Communications to Optical Beamforming", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:02162021-124026838", "creators": [ { "name": { "family": "Khachaturian", "given": "Aroutin" }, "id": "Khachaturian-Aroutin", "orcid": "0000-0001-8304-3302", "display_name": "Khachaturian, Aroutin" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "eleceng" ], "doi": "10.7907/xjby-xn13", "abstract": "Integrated photonics is an emerging technology that has begun to transform our way of life with the same amount of impact that integrated CMOS electronics has. Currently, photonics integration is orders of magnitude less complicated than its electronics counterparts. Nonetheless, it serves as one of the main driving forces to meet the exponentially increasing demand for high-speed and low-cost data transfer in the Information Age. It also promises to provide solutions for next-generation high-sensitivity image sensors and precision metrology and spectroscopy instruments. In this thesis, integrated photonics architectures for solid-state photonic beamforming and processing are investigated for high-resolution and high sensitivity lens-free transceiver applications. Furthermore, high-efficiency integrated electro-optical modulators aiming to meet the demand of high-density photonic integration with improved modulation efficiency, small footprint, and lower insertion loss are investigated.
\r\n\r\nTwo integrated photonic solid-state beamforming architectures incorporating two-dimensional apertures are explored. First, a novel transceiver architecture for remote sensing, coherent imaging, and ranging applications is demonstrated. It reduces system implementation complexity and offers a methodology for very-large-scale coherent transceiver beamforming applications. Next, a transmitter beamforming architecture inspired by the diffraction pattern of the slit annular ring is analyzed and demonstrated. This transceiver architecture can be used for coherent beamforming applications such as imaging and point-to-point optical communication. Finally, a coherent imager architecture for high-sensitivity three-dimensional imaging and remote-sensing applications is present. This novel architecture can suppress undesired phase fluctuations of the optical carrier signal in the illumination and reference paths, providing higher resolution and higher acquisition speed than previous implementations.
\r\n\r\nMoreover, several compact, high-speed CMOS compatible modulators that enable high-density photonic integration are explored. Ultra-compact and low insertion loss silicon-organic-hybrid modulators are designed and implemented for high-speed beamforming and high-efficiency complex signal modulation applications. Finally, a novel integrated nested-ring assisted modulator topology is analyzed and implemented for high-density and high modulation efficiency applications.
" }, { "name": "Kim, Taeyong", "degree": "PhD", "year": "2021", "title": "Investigation of Transport Phenomena of Thermal Acoustic Excitations in Semi-Crystalline and Amorphous Materials Using Transient Grating Spectroscopy", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162020-115452109", "creators": [ { "name": { "family": "Kim", "given": "Taeyong" }, "id": "Kim-Taeyong", "orcid": "0000-0003-2452-1065", "display_name": "Kim, Taeyong" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/k364-ga14", "abstract": "The physics of transport of heat-carrying atomic vibrations in amorphous and semi-crystalline solids is a topic of fundamental interest. Diverse tools have been employed to study thermal transport in these materials, including cryogenic thermal conductivity measurements and various inelastic scattering tools. However, unambiguously identifying the damping mechanisms of few THz and smaller frequency excitations remains difficult owing to the lack of the experimental probes in the frequency band. As a result, debate has remained regarding the microscopic origin of weak acoustic damping in amorphous silicon (Si), the unusually high thermal conductivity of ultra-drawn polyethylene, and other topics.
\r\n\r\nIn this thesis, we investigate the transport properties of heat-carrying acoustic excitations in semi-crystalline and amorphous solids using transient grating spectroscopy. This optical method permits the creation of thermal gradients over sub-micron length scales which may be comparable to the attenuation lengths of the excitations. We show how these measurements can be used to constrain the damping mechanisms in the sub-THz range that has been historically inaccessible by typical methods such as inelastic scattering.
\r\n\r\nFirst, we report measurements of the bulk thermal conductivity and elastic properties of MoS\u2082 thin films. Specifically, we use TG to measure the in-plane longitudinal sound velocity and thermal conductivity. We do not observe any size effects of thermal conductivity with grating period, indicating that the propagating distance of heat-carrying acoustic phonons are smaller than the thermal length scale accessible in the experiment. This result is consistent with the mean free paths predicted from ab-initio numerical methods.
\r\n\r\nSecond, we utilize the capability of TG to resolve the microscopic heat transport properties of phonons in highly oriented semi-crystalline polyethylene (PE). Earlier experimental studies have reported thermal conductivities of up to ~ 100 Wm\u207b\u00b9 K\u207b\u00b9 crystalline polyethylene, orders of magnitude larger than the bulk value of ~ 0.4 Wm\u207b\u00b9 K\u207b\u00b9. However, the microscopic origin of the high thermal conductivity remains unclear. We address this question by applying TG to highly oriented polyethylene to show that mean free paths on micron length scales are the dominant heat carriers. Using a low-energy anisotropic Debye model to interpret these data, we find evidence of one-dimensional phonon density of states for excitations of frequency less than ~ 2 THz. This transition frequency is consistent with the unique features of ultradrawn PE, in particular the stiff longitudinal branch leading to wavelengths of 8 nm at 2 THz frequency; and fiber diameters < 10 nm observed in prior structural studies of ultradrawn polymers; so that the wavelength does indeed exceed the fiber diameter at the relevant frequencies.
\r\n\r\nFinally, we report the measurements of the frequency-resolved mean free path of heat-carrying acoustic excitation in amorphous silicon (aSi), for the first time. The heat-carrying acoustic excitations of amorphous silicon are of interest because their mean free paths approach the micron scale at room temperature. Despite extensive investigation, the origin of the weak acoustic damping in the heat-carrying frequencies remains a topic of debate for decades. A prior study suggested a framework of classifying the vibrations into propagons, diffusons, and locons. Propagons were considered phonon-like, delocalized, propagating vibrations; locons as localized vibrations, and diffusons as delocalized yet non-propagating vibrations. Following the framework, numerous works have predicted mechanism of acoustic damping in aSi, but the predictions have contradicted to observations in experiments. In this work, we obtained measurements of the frequency-dependent mean free path in amorphous silicon thin films from ~0.1-3 THz and over temperatures from 60 - 315 K using picosecond acoustics (PSA) and transient grating spectroscopy. We first describe our PSA experiments to resolve the attenuation of 0.1 THz acoustic excitations in aSi. We then present our table-top approach to resolve MFP of heat-carrying acoustic excitation between ~ 0.1-3 using TG spectroscopy. The mean free paths are independent of temperature and exhibit a Rayleigh scattering trend over most of this frequency range. The observed trend is inconsistent with the predictions of numerical studies based on normal mode analysis, but agrees with diverse measurements on other glasses. The micron-scale MFPs in amorphous Si arise from the absence of Akhiezer and two-level system damping in the sub-THz frequencies, leading to heat-carrying acoustic excitations with room-temperature damping comparable to that of other glasses at cryogenic temperatures. Our results allow us to establish a clear picture for the origin of micron-scale damping in aSi by understanding vibrations as acoustic excitation rather than propagons, diffusons, and locons.
" }, { "name": "Kishore Kumar, Deepan", "degree": "PhD", "year": "2021", "title": "Novel Light-Matter Interaction in Quasi-One-Dimensional Graphene Nanomaterials for Photonics", "advisor": "Yeh, Nai-Chang", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282021-182147719", "creators": [ { "name": { "family": "Kishore Kumar", "given": "Deepan" }, "id": "Kishore-Kumar-Deepan", "orcid": "0000-0003-0236-8805", "display_name": "Kishore Kumar, Deepan" } ], "advisors": [ { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "advisor", "display_name": "Yeh, Nai-Chang" } ], "committee": [ { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "chair", "display_name": "Marandi, Alireza" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Mirhosseini", "given": "Mohammad" }, "id": "Mirhosseini-M", "orcid": "0000-0002-9084-6880", "role": "member", "display_name": "Mirhosseini, Mohammad" }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "member", "display_name": "Yeh, Nai-Chang" } ], "option_major": [ "eleceng" ], "doi": "10.7907/y5a2-zx57", "abstract": "Nonlinear light-matter interaction in two-dimensional (2D) materials like graphene with unique nanostructured quasi-one-dimensionality (quasi-1D) holds the potential to address major technology opportunities in photonics from on-chip photo detection, modulation of light, and even possibly coherent light sources. In this work, we propose to use graphene, a gapless two-dimensional nanomaterial, for both nano-photonic applications and potentially energy harvesting by nano-structuring the material into nearly quasi-one-dimensional effective optical cavities with defects that act like color centers. These defects are naturally formed during its synthesis or can be engineered in the material by selective plasma radiation, is found to support a broad spectral distribution of color centers that exhibit excitation dependent photoluminescence. Through detailed investigation on the temperature and power dependence of photoluminescence from such defects, excitation dependent photoluminescence emission, we have established that these graphene nanomaterials with metastable energy states can support material excitations (e.g., excitons) that are strongly coupled to the optical modes confined within the nanostructured cavities to produce polaritonic quasiparticles, leading to many interesting nonlinear behaviors. In particular, the manifestation of blue-shifted photoluminescence, polariton lasing-like emission, multimode lasing-like emission, and distinct interference fringes, all points to the presence of novel light-matter interaction in quasi-one-dimensional graphene. Such novel light matter interactions can be exploited, among other applications, within photonic integrated circuits (PIC) by directly synthesizing graphene on silicon from a low temperature, single-step, plasma-enhanced chemical vapor deposition (PECVD) with feedstock gases of methane and hydrogen.
" }, { "name": "Kuo, Claire Taijung", "degree": "PhD", "year": "2021", "title": "Customized Porosity in Ceramic Composites via Freeze Casting", "advisor": "Faber, Katherine T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12242020-000539491", "creators": [ { "name": { "family": "Kuo", "given": "Claire Taijung" }, "id": "Kuo-Claire-Taijung", "orcid": "0000-0002-3720-968X", "display_name": "Kuo, Claire Taijung" } ], "advisors": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "advisor", "display_name": "Faber, Katherine T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "matsci" ], "doi": "10.7907/88p1-5v79", "abstract": "Freeze casting is a facile pore-forming technique for ceramics as it affords great tunability in pore structure including size, morphology, wall thickness, tortuosity, and alignment. Nevertheless, similar to any other pore-forming techniques, it has limitations in terms of the range of accessible properties. For example, a porous lamellar structure is highly permeable but easily fractures, while the dendritic structure is the opposite. This research seeks to provide strategies used with freeze casting to achieve a combination of properties that go beyond the current limitations and create optimized pore structures with a specific focus on three properties: strength, permeability, and surface area.
\r\n\r\nSuch strategies utilize two composite material principles. First, particle reinforcement was implemented to optimize the mechanical and transport properties. Second, surface area was increased with hierarchical design for enhanced capture or catalysis applications. To optimize the mechanical and transport properties, we reinforced high-permeability lamellar structures with reinforcement fillers of silicon carbide (SiC) whiskers and carbon nanotubes (CNTs). The two fillers afford two different mechanisms of reinforcement: structural and material reinforcement.
\r\n\r\nAdditions of 30 vol.% SiC whiskers increased the compressive strength by 325% at a small expense in permeability. Shear failure, common in lamellar structures, was prevented by the interwall bridges produced via particle engulfment during freezing. These bridges were demonstrated by the change in microstructure, stress-strain behavior, and fracture surfaces. A 2D in-situ solidification experiment was conducted to observe solidification and particle engulfment directly. We proposed a modified engulfment model to account for the complexity stemming from high-aspect ratio particles and non-planar freezing fronts. Reasonable agreement was found between the model, the simulation based on the model, and the experimental values from the freeze-casting and 2D-solidification experiments.
\r\n\r\nFreeze-casting with CNTs was explored as an alternative reinforcement strategy, but one which maintains the original pore structure. CNTs were pushed aside by the freezing front to pore walls due to their small diameters for low CNT concentration composites (<4.5 wt.%) such that the original pore structures remained. The compressive strength increased, albeit by smaller percentages (118% for 4.3 wt.%) than those with SiC whiskers. The increase was attributed to the toughening of pore walls with no diminishing effect on permeability. In addition, CNTs changed the electrical conductivity by ten orders of magnitude with the addition of 8.2 wt.% of the reinforcement.
\r\n\r\nFinally, conformal coatings via self-assembly of block copolymers (BCP) were produced by infiltration into a freeze-cast lamellar structure and significantly increased the surface area of the underlying scaffold. A bimodal pore size distribution with nanometer-size pores from the BCP self-assembly and micron-size pores from freeze casting was observed. An increase in compressive strengths was achieved with the introduction of pore hierarchy while retaining permeability of the macroporous structure due to enlarged lamellar spacings from the infiltration process.
" }, { "name": "Kusanovic, Danilo Smiljan", "degree": "PhD", "year": "2021", "title": "Improving Reduced Order Models of Soil-Structure Interaction Using an Ensemble Kalman Inversion Finite Element Model Updating Framework", "advisor": "Asimaki, Domniki", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092020-002934412", "creators": [ { "name": { "family": "Kusanovic", "given": "Danilo Smiljan" }, "id": "Kusanovic-Danilo-Smiljan", "orcid": "0000-0002-0935-2577", "display_name": "Kusanovic, Danilo Smiljan" } ], "advisors": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "advisor", "display_name": "Asimaki, Domniki" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" } ], "option_major": [ "civileng" ], "doi": "10.7907/m2qj-s182", "abstract": "In civil engineering, almost all structures are somehow in contact with soil - i.e., have foundations or support elements that either rest on or are embedded in soil. Thus, their seismic response is governed by the interaction between the structure, the non-structural components, the foundation, and the surrounding soil. Predicting such interaction becomes increasingly complex when uncertainties of soil and structural material, ground motion variability, and dissipation mechanisms are considered. The accuracy of numerical models to predict the linear or nonlinear responses of structures depends not only on how well the uncertainties in the material properties and input motion are estimated, but also on how well the various sources of energy dissipation and their interaction are modeled. Therefore, high-fidelity simulation of soil-structure interaction (SSI) problems require advanced models that can capture the nonlinear behavior of soils and structures, and parallel computing capabilities to optimize the cost associated with large scale problems. In spite of this fact, SSI in practice is widely accounted for using fixed-base building and reduced-order-models (ROM) which usually trade accurate solution for fast ones. Unfortunately, if SSI effects are neglected or poorly estimated, then critical response measures of a structure can be over- or under-estimated, which in turn can lead to unsafe or overly\r\nconservative designs.
\r\n\r\nMotivated by the previous challenge, in this thesis work we present a robust and efficient framework for finite element model (FEM) updating based on ensemble-Kalman inversion (EnKI). The EnKI-FEM updating framework is used to obtain suitable parameters to inform a ROM from data generated using high-fidelity FEM simulations. Since high-fidelity SSI simulations call for accurate and computationally efficient capabilities, as a part of this work, we developed Seismo-VLAB, a simple, fast, and extendable C++ finite element software to optimize large-scale simulations of dynamic and nonlinear SSI problems. The EnKI-FEM updating framework is thus integrated in Seismo-VLAB allowing to identify any parameter of the ROM without compromising accuracy. The so-generated ROM are finally employed to propose a new dimensionless frequency mapping to estimate the soil impedance for time domain analysis and to investigate soil-structure-interaction effects at a regional-scale. The presented methodology is general enough and it can be extended to more complex structural and/or geotechnical systems, allowing to construct highly-accurate ROM in a simple manner.
" }, { "name": "Kwon, Hyounghan", "degree": "PhD", "year": "2021", "title": "Dielectric Metasurfaces for Integrated Imaging Devices and Active Optical Elements", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112021-170331252", "creators": [ { "name": { "family": "Kwon", "given": "Hyounghan" }, "id": "Hyounghan-Kwon", "orcid": "0000-0002-9257-687X", "display_name": "Kwon, Hyounghan" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/j08n-0q77", "abstract": "Optical dielectric metasurfaces have shown great advances in the last two decades and become promising candidates for next-generation free-space optical elements. In addition to their compatibility with scalable semiconductor fabrication technology, metasurfaces have provided new and efficient ways to manipulate diverse characteristics of light. In this thesis, we demonstrate the potential of dielectric metastructures in the realization of compact imaging devices, reconfigurable optical elements, and multi-layer inverse-designed metasurfaces. With the metasurfaces\u2019 extreme capability to simultaneously control phase and polarization, we first showcase their potential toward optical field imaging applications. In this regard, we demonstrate a system of dielectric metasurfaces and designed random metasurfaces for single-shot phase gradient microscopes and computational complex field imaging system, respectively. Then, we propose nano-electromechanically tunable resonant dielectric metasurfaces as a general platform for active metasurfaces. For example, we demonstrate two different types of the phase and amplitude modulators. While one utilizes resonant eigenmodes in the lattice such as leaky guided mode resonances and bound-states in the continuum modes, the other is based on the high-Q Mie resonances in the dielectric nanostructures where symmetry is broken. In addition to the modulation of the phase and amplitude, we also show tuning of strong chiroptical responses in dielectric chiral metasurfaces. Next, we experimentally demonstrate inverse-designed multi-layer metasurfaces. Not only do they provide increased degree of freedom in the design space, but also overcome limits of conventional design methods of the metasurfaces. Finally, we summarize the presented works and conclude this thesis with a brief outlook on what aspects of the metasurfaces can be important for their real-world applications in the future and what challenges and opportunities remain.
" }, { "name": "Lawson, Joel Michael", "degree": "PhD", "year": "2021", "title": "Focused Laser Differential Interferometry", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05132021-180953405", "creators": [ { "name": { "family": "Lawson", "given": "Joel Michael" }, "id": "Lawson-Joel-Michael", "orcid": "0000-0002-3042-0909", "display_name": "Lawson, Joel Michael" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5thh-f652", "abstract": "The focused laser differential interferometer (FLDI) is a non-imaging optical diagnostic that is sensitive to density disturbances. A distinguishing feature is reduced sensitivity away from the focal plane of its beams. The spatial resolution is sub-mm, and the temporal resolution is restricted only by photodetector bandwidth, typically >10 MHz. These traits make FLDI particularly suited to measurements in hypervelocity ground-testing facilities, where the low densities, short time-scales, and harsh environments preclude the use of intrusive diagnostics. Line of sight integration issues associated with other optical techniques are therefore minimized, a distinct advantage for measurements in impulse facilities, where the core flow of interest is often surrounded by highly-turbulent shear layers.
\r\n\r\nThe systematic design principles for single and double FLDI systems are discussed, based on ray transfer matrix analysis combined with Gaussian optics. A detailed guide is presented for the practicalities of aligning, calibrating, and operating an FLDI.
\r\n\r\nA modular numerical implementation of Schmidt and Shepherd's FLDI ray-tracing model is developed, capable of accepting arbitrary flow-fields defined via analytical expressions, simulation coupling, or experimental datasets. This numerical implementation is used to perform the first comprehensive experimental validation of the model, using known static and dynamic phase objects. Quantitatively-accurate predictions of the response of real FLDI systems are obtained. Importantly, the spatial sensitivity of the instrument is found to be dependent on disturbance wavelength, with scaling matching that predicted analytically from the model. Propagating shock waves are used as another highly-dynamic test phase object, and it is shown that FLDI maintains its theoretical performance at sub-μs time-scales.
\r\n\r\nThe validated ray-tracing model is used to develop analytical expressions for the response of FLDI to propagating plane waves, extending on the results of Schmidt and Shepherd, and Settles and Fulghum. For the first time, the inverse problem is solved for this class of flow-field, allowing the density fluctuation spectrum to be recovered quantitatively from FLDI phase shift data. This approach is validated using synthetic flow-fields with the numerical ray-tracing scheme, and is also compared with the approximate approach introduced by Parziale et al.
\r\n\r\nFLDI is used to make freestream density fluctuation measurements on two facilities: a conventional blowdown tunnel, and an expansion tube. On the conventional tunnel, a comparison is made between pitot-probe and FLDI measurements after converting both to freestream pressure fluctuation spectra. A modification of Stainback and Wagner's theory, incorporating recent numerical results from Chaudhry et al., is used to interpret the pitot data, while the new inversion algorithm is applied to the FLDI data. Close agreement is found between the two sets of spectra, showing that accurate quantitative data can be obtained with FLDI, and used to extend spectra beyond the pitot bandwidth.
\r\n\r\nOn the expansion tube, the theory of Paull and Stalker for freestream noise originating in the driver gas is investigated. Their proposed relationship between freestream density fluctuations and the primary interface sound speed ratio is not observed. Spectral banding is also absent, however this is expected due to the relatively low secondary expansion strengths. The envelope of accessible conditions is somewhat restricted due to the low mean freestream densities that lead to signal-to-noise issues.
\r\n\r\nSignificant performance improvements can still be made to FLDI, in terms of its noise and bandwidth limitations, and to the spatial localization of its sensitive region; suggestions are given for possible approaches. With the ray-tracing model now validated, it can be used to optimize FLDI, or even to suggest derivative instruments based on similar principles.
" }, { "name": "Lee, Victoria Jin-Young", "degree": "PhD", "year": "2021", "title": "Theoretical, Computational, and Experimental Characterization of Nematic Elastomers", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042021-213808812", "creators": [ { "name": { "family": "Lee", "given": "Victoria Jin-Young" }, "id": "Lee-Victoria-Jin-Young", "orcid": "0000-0002-2748-0089", "display_name": "Lee, Victoria Jin-Young" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/f2hp-qe09", "abstract": "Nematic elastomers are programmable soft materials that display large, reversible, and predictable deformation under an external stimulus such as a change in temperature or light. They are composed of a lightly crosslinked polymer network with stiff, rod-like liquid crystal molecules incorporated within the polymer chains. In thermotropic nematic elastomers, the liquid crystals undergo a continuous and reversible phase transition between the randomly oriented isotropic state and the highly oriented nematic state. Further, there is a direct thermo-mechanical coupling between the underlying temperature-responsive orientational order of the liquid crystal molecules and the macroscopic shape change of the surrounding elastomer chains. Finally, these materials display an unusually soft behavior. These remarkable properties make them promising materials for applications in aerospace as deployable structures and skins, in biomedical engineering as a soft pump, and in communications as the actuation mechanism in a reconfigurable antenna. Motivated by these applications, this thesis discusses the theoretical, computational, and experimental characterization of nematic elastomers.
\r\n\r\nWe begin by investigating an example of actuation that takes advantage of the programmable, soft nature of these materials as well as instabilities associated with large deformation. We outline the multi-stable equilibrium solutions to a cylindrical balloon subjected to internal inflation, the material's microstructure formation due to this deformation, and its use as a soft pump with large ejection fraction, which involves a snap-through instability. Then we extend the Agostiniani-DeSimone-Dolzmann relaxed energy to a generalized Mooney-Rivlin constitutive relation and study four examples of Ericksen's universal deformations -- the inflation of cylindrical and spherical balloons, the cavitation of a disk, and the bending of a block.
\r\n\r\nWe then move beyond the modeling of ideal materials and present a new constitutive relation for isotropic-genesis polydomain nematic elastomers. It is based on internal variables that describe the fine-scale domain patterns and evolve according to a kinetic process with dissipation. We discuss the model's implementation in the commercial finite-element software, ABAQUS, and study the problem of torsion of a cylinder. We identify an interesting instability at large torsional strains as a result of the Poynting effect. Finally, we present the design of a thermo-mechanical tensile setup and the experimental results for strain-rate dependence and temperature-dependence of samples that we synthesize in-house.
" }, { "name": "Lee, Zachary Jordan", "degree": "PhD", "year": "2021", "title": "The Adaptive Charging Network Research Portal: Systems, Tools, and Algorithms", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282021-174411678", "creators": [ { "name": { "family": "Lee", "given": "Zachary Jordan" }, "id": "Lee-Zachary-Jordan", "orcid": "0000-0002-5358-2388", "display_name": "Lee, Zachary Jordan" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/8eqg-e110", "abstract": "Millions of electric vehicles (EVs) will enter service in the next decade, generating gigawatt-hours of additional energy demand. Charging these EVs cleanly, affordably, and without excessive stress on the grid will require advances in charging system design, hardware, monitoring, and control. Collectively, we refer to these advances as smart charging. While researchers have explored smart charging for over a decade, very few smart charging systems have been deployed in practice, leaving a sizeable gap between the research literature and the real world. In particular, we find that research is often based on simplified theoretical models. These simple models make analysis tractable but do not account for the complexities of physical systems. Moreover, researchers often lack the data needed to evaluate the performance of their algorithms on real workloads or apply techniques like machine learning. Even when promising algorithms are developed, they are rarely deployed since field tests can be costly and time-consuming.
\r\n \r\nThe goal of this thesis is to develop systems, tools, and algorithms to bridge these gaps between theory and practice.
\r\n\r\nFirst, we describe the architecture of a first-of-its-kind smart charging system we call the Adaptive Charging Network (ACN). \r\nNext, we use data and models from the ACN to develop a suite of tools to help researchers. These tools include ACN-Data, a public dataset of over 80,000 charging sessions; ACN-Sim, an open-source simulator based on realistic models; and ACN-Live, a platform for field testing algorithms on the ACN. Finally, we describe the algorithms we have developed using these tools. For example, we propose a practical and robust algorithm based on model predictive control, which can reduce infrastructure requirements by over 75%, increase operator profits by up to 3.4 times, and significantly reduce strain on the electric power grid. Other examples include a pricing scheme that fairly allocates costs to users considering time-of-use tariffs and demand charges and a data-driven approach to optimally size on-site solar generation with smart EV charging systems.
" }, { "name": "Lin, Wei-Hsiang", "degree": "PhD", "year": "2021", "title": "Synthesis of 2D Quantum Materials for Nanoelectronic and Nanophotonic Applications", "advisor": "Atwater, Harry Albert; Yeh, Nai-Chang", "url": "https://resolver.caltech.edu/CaltechTHESIS:04262021-085536699", "creators": [ { "name": { "family": "Lin", "given": "Wei-Hsiang" }, "id": "Lin-Wei-Hsiang", "orcid": "0000-0003-0037-1277", "display_name": "Lin, Wei-Hsiang" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "co-advisor", "display_name": "Yeh, Nai-Chang" } ], "committee": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "chair", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "member", "display_name": "Yeh, Nai-Chang" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/vh7k-4w84", "abstract": "2D materials have attracted tremendous attention for a variety of properties such as ultra-low body thickness, ultra-high mobility, and tunable bandgap. These unique merits of the 2D materials bring in the significant improvements and new perspectives in the digital CMOS scaling, analog performance, as well as the 3D integration of wafer stacking.
\r\n\r\nIn this thesis, we explore van der Waals materials for future CMOS technologies. Chapter 2 introduces a compatible and a single-step method for synthesizing high-mobility monolayer graphene (MLG) in merely a few minutes by means of plasma-enhanced chemical vapor deposition (PECVD) techniques without the need of active heating. This environment enables graphene growth on different surfaces at relatively low temperatures, which paves ways to a CMOS-compatible approach to graphene synthesis. Chapter 3 describes the development of a synthesis method that controls the growth of large-area h-BN films from monolayer to 30 atomic layers, and summarizes the characterizations of the properties of these h-BN films that demonstrate the high-quality of these materials.
\r\n\r\nNew degrees of freedom possess the immense potential and attract huge attentions as the imminent end of \"Moore's Law\". Compared with the traditional charge degree of freedom, spin and valley are the other two additional internal degree of freedom in solid-state electronics which enable the spintronic and valleytronic devices with high integration density, fast processing speed, low power dissipation, and non-volatility. Monolayer transition-metal dichalcogenides (TMDCs) in the 2H-phase are semiconductors promising for opto-valleytronic and opto-spintronic applications because of their strong spin-valley coupling. In chapter 4, we report detailed studies of opto-valleytronic properties of heterogeneous domains in CVD-grown monolayer WS\u2082 single crystals. By illuminating WS\u2082 with off-resonance circularly-polarized light and measuring the resulting spatially resolved circularly-polarized emission (Pcirc), we find large circular polarization increases significantly to nearly 90% at 80 K. In Chapter 5, it is reported that valley polarized PL of monolayer WS\u2082 can be efficiently tailored at room temperature (RT) through the surface plasmon-exciton interaction with plasmonic Archimedes spiral (PAS) nanostructures. The DVP of WS\u2082 using 2 turns (2T) and 4 turns (4T) of PAS can reach up to 40% and 50% at RT, respectively. Further enhancement and continuous control of excitonic valley polarization in electrostatically doped monolayer WS\u2082 are demonstrated. Under the circularly polarized light on WS\u2082-2TPAS heterostructure, 40% valley polarization of exciton without electrostatic doping is icreased to 70% by modulating the carrier doping via a backgate. This enhancement of valley polarization may be attributed to the screening of momentum-dependent long-range electron-hole exchange interactions. The demonstration of electrical tunability in the valley-polarized emission from WS\u2082-PAS heterostructures provides new strategies to harness valley excitons for application in ultrathin valleytronic devices.
\r\n\r\nIn contrast to future optical switch applications, in Chpater 6, it is reported that Ternary tellurides based on alloying different 2D transition metal dichalcogenides can result in interesting new 2D materials with tunable optical and electrical properties. Additionally, such alloys can provide opportunities for significantly improving the electrical contact properties at the metal-semiconductor interface. In particular, realization of practical devices based on the 2D materials will require overcoming the typical Fermi-level pinning limitations of the electrical contacts at the metal-semiconductor interface and ultimately approaching the ideal Schottky-Mott limit. In this work, we develop a simple method of stacking 3D/2D electrical metal contacts onto dangling-bond-free 2D semiconductors in order to surmount the typical issue of Fermi-level pinning. Specifically, contacts of Au, graphene/Au, and WTe\u2082/Au are transferred onto WS1.94Te0.06 alloy-based devices via a new transfer method. The WS1.94Te0.06 field-effect transistors (FETs) with WTe\u2082/Au contacts reveal a field-effect mobility of 25 cm\u00b2V\u207b\u00b9s\u207b\u00b9, an on/off current ratio of 10\u2076, and extremely low contact resistance of 8 k\u03a9 \u03bcm. These electrical properties are far more superior to similar devices with either Au or graphene/Au contacts, which may be attributed to the fact that the work function of WTe\u2082 is close to the band edge of the WS1.94Te0.06 alloy so that the resulting metal-semiconductor interface of the FETs are free from Fermi-level pinning. The Schottky barrier heights of the WS1.94Te0.06-FETs with WTe\u2082/Au contacts also follow the general trend of the Schottky-Mott limit, implying high-quality electrical contacts. Finally, in Chapter 7, several promising opportunities were proposed for future CMOS integrated circuits based on monolayer semiconductors.
" }, { "name": "London, Palma Alise den Nijs", "degree": "PhD", "year": "2021", "title": "Frameworks for High Dimensional Convex Optimization", "advisor": "Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08162020-233437139", "creators": [ { "name": { "family": "London", "given": "Palma Alise den Nijs" }, "id": "London-Palma-Alise-den-Nijs", "orcid": "0000-0001-6472-8293", "display_name": "London, Palma Alise den Nijs" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "compsci" ], "doi": "10.7907/db29-am33", "abstract": "We present novel, efficient algorithms for solving extremely large optimization problems. A significant bottleneck today is that as the size of datasets grow, researchers across disciplines desire to solve prohibitively massive optimization problems. In this thesis, we present methods to compress optimization problems. The general goal is to represent a huge problem as a smaller problem or set of smaller problems, while still retaining enough information to ensure provable guarantees on solution quality and run time. We apply this approach to the following three settings.
\r\n\r\nFirst, we propose a framework for accelerating both linear program solvers and convex solvers for problems with linear constraints. Our focus is on a class of problems for which data is either very costly, or hard to obtain. In these situations, the number of data points m available is much smaller than the number of variables, n. In a machine learning setting, this regime is increasingly prevalent since it is often advantageous to consider larger and larger feature spaces, while not necessarily obtaining proportionally more data. Analytically, we provide worst-case guarantees on both the runtime and the quality of the solution produced. Empirically, we show that our framework speeds up state-of-the-art commercial solvers by two orders of magnitude, while maintaining a near-optimal solution.
\r\n\r\nSecond, we propose a novel approach for distributed optimization which uses far fewer messages than existing methods. We consider a setting in which the problem data are distributed over the nodes. We provide worst-case guarantees on the performance with respect to the amount of communication it requires and the quality of the solution. The algorithm uses O(log(n+m)) messages with high probability. We note that this is an exponential reduction compared to the O(n) communication required during each round of traditional consensus based approaches. In terms of solution quality, our algorithm produces a feasible, near optimal solution. Numeric results demonstrate that the approximation error matches that of ADMM in many cases, while using orders-of-magnitude less communication.
\r\n\r\nLastly, we propose and analyze a provably accurate long-step infeasible Interior Point Algorithm (IPM) for linear programming. The core computational bottleneck in IPMs is the need to solve a linear system of equations at each iteration. We employ sketching techniques to make the linear system computation lighter, by handling well-known ill-conditioning problems that occur when using iterative solvers in IPMs for LPs. In particular, we propose a preconditioned Conjugate Gradient iterative solver for the linear system. Our sketching strategy makes the condition number of the preconditioned system provably small. In practice we demonstrate that our approach significantly reduces the condition number of the linear system, and thus allows for more efficient solving on a range of benchmark datasets.
\r\n" }, { "name": "Ma, Wen-Loong", "degree": "PhD", "year": "2021", "title": "From Bipedal to Quadrupedal Locomotion, Experimental Realization of Lyapunov Approaches", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05042021-155258800", "creators": [ { "name": { "family": "Ma", "given": "Wen-Loong" }, "id": "Ma-Wen-Loong", "orcid": "0000-0002-0115-5632", "display_name": "Ma, Wen-Loong" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "mecheng" ], "doi": "10.7907/j1ty-zb28", "abstract": "Possibly one of the most significant innovations of the past decade is the hybrid zero dynamics (HZD) framework, which formally and rigorously designs a control algorithm for robotic walking. In this methodology, Lyapunov stability, which is often used to certificate a dynamical system's stability, was introduced to the control law design for a hybrid control system. However, the prerequisites of precise modeling to apply the HZD methodology can often be too restrictive to design controllers for uncertain and complex real-world hardware experiments. This thesis addresses the problem raised by noisy measurements and the intricate hybrid structure of locomotion dynamics.
\r\n\r\nFirst, the HZD methodology's construction is based on the full-order, hybrid dynamics of legged locomotion, which can be intractable for control synthesis for high-dimensional systems. This thesis studies the general structure of hybrid control systems for walking systems, ranging from 1D hopping, 2D walking, 2D running, and 3D quadrupedal locomotion on rough terrains. Further, we characterize a walking behavior--gait--as a solution (execution) to a hybrid control system. To find these solutions, which represent a \"gait,\" we employed advanced numerical methods such as collocation methods to parse the solution-finding problem into the open- and closed-loop trajectory optimization problems. The result is that we can find versatile gaits for ten different robotic platforms efficiently. This includes bipedal running, bipedal walking on slippery surfaces, and quadrupedal robots walking on sloped terrains. The numerous solution-finding examples expand the applicability of the HZD framework towards more complex dynamical systems.
\r\n\r\nFurther, for the uncertain and noisy real-world implementation, the exponential stability of the continuous dynamics is an ideal but restrictive condition for hybrid stability. This condition is especially challenging to satisfy for highly dynamical behaviors such as bipedal running, which loses ground support for a short period. This thesis observes the destabilizing effect of the noisy measurements of the phasing variable. By reformulating the traditional input-to-state stability (ISS) concept into phase-uncertainty to state stability, we are able to synthesize a robust controller for bipedal running on DURUS-2D. This time+state-based controller formally guarantees stability under noisy measurements and stabilizes the 1.75 m/s running experiments.
\r\n\r\nLastly, robotic dynamics have long been characterized as the interconnection of rigid-body dynamics. We take this perspective one step further and incorporate controller design into the formulation of coupled control systems (CCS). We first view a quadrupedal robot as two bipedal robots connected via some holonomic constraints. In a dimensional reduction manner, we develop a novel optimization framework, and the computational performance is reduced to a few seconds for gait generation. Furthermore, we can design local controllers for each bipedal subsystem and still guarantee the overall system's stability. This is done by combining the HZD framework and the ISS properties to contain the disturbance induced by the other subsystems' inputs. Utilizing the proposed CCS methods, we will experimentally realize quadrupedal walking on various outdoor rough terrains.
" }, { "name": "Murray, Riley John", "degree": "PhD", "year": "2021", "title": "Applications of Convex Analysis to Signomial and Polynomial Nonnegativity Problems", "advisor": "Chandrasekaran, Venkat; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05202021-194439071", "creators": [ { "name": { "family": "Murray", "given": "Riley John" }, "id": "Murray-Riley-John", "orcid": "0000-0003-1461-6458", "display_name": "Murray, Riley John" } ], "advisors": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "co-advisor", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "chair", "display_name": "Tropp, Joel A." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "cms" ], "doi": "10.7907/vn9x-xj10", "abstract": "Here is a question that is easy to state, but often hard to answer:
\r\n\r\nIs this function nonnegative on this set?
\r\n\r\nWhen faced with such a question, one often makes appeals to known inequalities. One crafts arguments that are sufficient to establish the nonnegativity of the function, rather than determining the function's precise range of values. This thesis studies sufficient conditions for nonnegativity of signomials and polynomials. Conceptually, signomials may be viewed as generalized polynomials that feature arbitrary real exponents, but with variables restricted to the positive orthant.
\r\n\r\nOur methods leverage efficient algorithms for a type of convex optimization known as relative entropy programming (REP). By virtue of this integration with REP, our methods can help answer questions like the following:
\r\n\r\nIs there some function, in this particular space of functions, that is nonnegative on this set?
\r\n\r\nThe ability to answer such questions is extremely useful in applied mathematics.\r\nAlternative approaches in this same vein (e.g., methods for polynomials based on semidefinite programming)\r\nhave been used successfully as convex relaxation frameworks for nonconvex optimization, as mechanisms for analyzing dynamical systems, and even as tools for solving nonlinear partial differential equations.
\r\n\r\nThis thesis builds from the sums of arithmetic-geometric exponentials or SAGE approach to signomial nonnegativity. The term \"exponential\" appears in the SAGE acronym because SAGE parameterizes signomials in terms of exponential functions.
\r\n\r\nOur first round of contributions concern the original SAGE approach. We employ basic techniques in convex analysis and convex geometry to derive structural results for spaces of SAGE signomials and exactness results for SAGE-based REP relaxations of nonconvex signomial optimization problems.\r\nWe frame our analysis primarily in terms of the coefficients of a signomial's basis expansion rather than in terms of signomials themselves.\r\nThe effect of this framing is that our results for signomials readily transfer to polynomials. In particular, we are led to define a new concept of SAGE polynomials. For sparse polynomials, this method offers an exponential efficiency improvement relative to certificates of nonnegativity obtained through semidefinite programming.
\r\n\r\nWe go on to create the conditional SAGE methodology for exploiting convex substructure in constrained signomial nonnegativity problems.\r\nThe basic insight here is that since the standard relative entropy representation of SAGE signomials is obtained by a suitable application of convex duality, we are free to add additional convex constraints into the duality argument. In the course of explaining this idea we provide some illustrative examples in signomial optimization and analysis of chemical dynamics.
\r\n\r\nThe majority of this thesis is dedicated to exploring fundamental questions surrounding conditional SAGE signomials. We approach these questions through analysis frameworks of sublinear circuits and signomial rings. These sublinear circuits generalize simplicial circuits of affine-linear matroids, and lead to rich modes of analysis for sets that are simultaneously convex in the usual sense and convex under a logarithmic transformation. The concept of signomial rings lets us develop a powerful signomial Positivstellensatz and an elementary signomial moment theory. The Positivstellensatz provides for an effective hierarchy of REP relaxations for approaching the value of a nonconvex signomial minimization problem from below, as well as a first-of-its-kind hierarchy for approaching the same value from above.
\r\n\r\nIn parallel with our mathematical work, we have developed the sageopt python package. Sageopt drives all the examples and experiments used throughout this thesis, and has been used by engineers to solve high-degree polynomial optimization problems at scales unattainable by alternative methods.\r\nWe conclude this thesis with an explanation of how our theoretical results affected sageopt's design.
" }, { "name": "Nakka, Yashwanth Kumar", "degree": "PhD", "year": "2021", "title": "Spacecraft Motion Planning and Control under Probabilistic Uncertainty for Coordinated Inspection and Safe Learning", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142021-163257155", "creators": [ { "name": { "family": "Nakka", "given": "Yashwanth Kumar" }, "id": "Nakka-Yashwanth-Kumar", "orcid": "0000-0001-7897-3644", "display_name": "Nakka, Yashwanth Kumar" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Hadaegh", "given": "Fred" }, "id": "Fred-Hadaegh", "role": "member", "display_name": "Hadaegh, Fred" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "space" ], "doi": "10.7907/6329-sf68", "abstract": "During a spacecraft mission design process, engineers often balance the following three criteria: science return, optimality in performance, and safety. Given a science criterion, engineers design the orbit parameters with predefined performance and safety. Often in this approach, the spacecraft has no understanding of the expected outcome or the knowledge of the mission safety criteria. Autonomous science-driven orbit (or goal) selection and planning for safety under uncertainty enable efficient and adaptable missions. To this end, we propose an architecture for information-based guidance and control for coordinated inspection, motion planning and control algorithms for safe and optimal guidance under uncertainty, and architecture for safe exploration.
\r\n\r\nIn the first part of this thesis, we present an architecture for inspection or mapping of a target spacecraft in a low Earth orbit using multiple observer spacecraft. We use an information gain approach to directly consider the trade-off between gathered data and fuel/energy cost. The estimated information gain is a crucial input to the motion planner, which computes orbits and reconfiguration strategies for each of the observers to maximize the information gain from distributed observations of the target spacecraft. The resulting motion trajectories jointly consider observational coverage of the target spacecraft and fuel/energy cost. We validate our architecture in a mission simulation to visually inspect the target spacecraft and on the three degree-of-freedom robotic spacecraft dynamics simulator testbed.
\r\n\r\nIn the second part of the thesis, we present gPC-SCP, Generalized Polynomial Chaos-based Sequential Convex Programming method, to compute a sub-optimal solution for a continuous-time chance-constrained stochastic nonlinear optimal control (SNOC) problem. The approach enables motion planning and control of robotic systems under uncertainty. The proposed method involves two steps. The first step is to derive a deterministic nonlinear optimal control problem (DNOC) with convex constraints that are surrogate to the SNOC by using gPC expansion and the distributionally-robust convex subset of the chance constraints. The second step is to solve the DNOC problem using sequential convex programming (SCP) for trajectory generation and control. We prove that in the unconstrained case, the optimal value of the DNOC converges to that of SNOC asymptotically and that any feasible solution of the constrained DNOC is a feasible solution of the chance-constrained SNOC. We derive a stable stochastic model predictive controller using the gPC-SCP for tracking a potentially unsafe trajectory in the presence of uncertainty. We empirically demonstrate the efficacy of the gPC-SCP method for the following three test cases: 1) collision checking under uncertainty in actuation, 2) collision checking with stochastic obstacles, and 3) safe trajectory tracking under uncertainty in the dynamics and obstacle location by using a receding horizon control approach. We validate the effectiveness of the gPC-SCP method on the robotic spacecraft testbed.
\r\n\r\n\r\nIn the third part of this thesis, we present a new approach for optimal motion planning for safe exploration that integrates the chance-constrained stochastic optimal control with dynamics learning and feedback control. We derive an iterative convex optimization algorithm that solves an Information-cost Stochastic Nonlinear Optimal Control problem (Info-SNOC). The optimization objective encodes control cost for performance and exploration cost for learning, and the safety is incorporated as distributionally robust chance constraints. The dynamics are predicted from a robust regression model that is learned from data. The Info-SNOC algorithm is used to compute a sub-optimal pool of safe motion plans that aid in exploration for learning unknown residual dynamics under safety constraints. A stable feedback controller is used to execute the motion plan and collect data for model learning. We prove the safety of rollout from our exploration method and reduction in uncertainty over epochs, thereby guaranteeing the consistency of our learning method. We validate the effectiveness of Info-SNOC by designing and implementing a pool of safe trajectories for a planar robot. We demonstrate that our approach has a higher success rate in ensuring safety when compared to a deterministic trajectory optimization approach.
" }, { "name": "Narasimhan, Vinayak", "degree": "PhD", "year": "2021", "title": "Bioinspired Nanostructures for Biomedical Applications", "advisor": "Choo, Hyuck; Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:07242020-111050846", "creators": [ { "name": { "family": "Narasimhan", "given": "Vinayak" }, "id": "Narasimhan-Vinayak", "orcid": "0000-0003-4165-402X", "display_name": "Narasimhan, Vinayak" } ], "advisors": [ { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "orcid": "0000-0002-8903-7939", "role": "advisor", "display_name": "Choo, Hyuck" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "co-advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "orcid": "0000-0002-8903-7939", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Siddique", "given": "Radwanul Hasan" }, "id": "Siddique-Radwanul-Hasan", "orcid": "0000-0001-7494-5857", "role": "member", "display_name": "Siddique, Radwanul Hasan" } ], "option_major": [ "medeng" ], "doi": "10.7907/atnt-8p46", "abstract": "Nature boasts a myriad examples of coloration achieved purely through the physical interaction of light with nano-scale features also known as biophotonic nanostructures. From reptiles to insects, birds to flora, structural coloration has been achieved through a variety of fascinating nano-architectures that leverage different physics. Beyond structural coloration, these nanostructures are often truly multifunctional. For instance, biophotonic nanostructures can also serve as self-cleaning and bactericidal surfaces, gas and thermal sensors, waveguides and beam splitters. With the growing need for robust and compact biomedical devices, the requirement to embed multiple functionalities towards sensing, monitoring, diagnostics and therapeutics within a diminutive device footprint becomes crucial. In this regard, inspiration from the multifunctionality of biophotonic nanostructures can prove to be greatly beneficial for medical applications. Consequently, this work attempts to showcase various examples of the utilization of nanostructures inspired from biophotonic nanostructures for biomedical applications under various overlapping themes such as ophthalmic sensors, bioinspired optics and plasmonic biosensing.
\r\n\r\nThis thesis is summarized in two parts. The first part (Chapters 2--4) introduces a proof-of-concept optical intraocular pressure (IOP) sensor implant and various challenges faced during its in vivo implementation. In Chapter 3, nanostructures inspired by light-trapping epidermal micro-/nanostructures on flower petals are proposed and embedded onto the sensor platform to improve its in vivo optical signal-to-noise ratio and biocompatibility. Chapter 4 covers nanostructures inspired by biophotonic nanostructures on longtail glasswing butterfly wings that improve the in vivo angle of acceptance and biocompatibility of the sensor.
\r\n\r\nThe second part (Chapters 5 and 6) presents the use of bioinspired nanostructures in plasmonic biosensors. Chapter 5 discusses an on-chip platform consisting of bioinspired plasmonic nanostructures to detect various nucleic acid sequences of relevance in the pathogenesis of HIV-1 via plasmon-enhanced fluorescence. Chapter 6 describes the employment of bioinspired quasi-ordered nanostructuring on flexible substrates for broadband surface-enhanced Raman spectroscopy (SERS). Here, SERS-based biosensing enabled by quasi-ordering is used to detect uric acid -- a biomarker of various pathologies in human tears.
" }, { "name": "Narita, Kai", "degree": "PhD", "year": "2021", "title": "3D Architected Battery Electrodes for Exploring Battery Kinetics from Nano to Millimeter", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05012021-183915976", "creators": [ { "name": { "family": "Narita", "given": "Kai" }, "id": "Narita-Kai", "orcid": "0000-0002-3867-8234", "display_name": "Narita, Kai" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/dr3b-2d27", "abstract": "The ability to design a particular geometry of porous electrodes at multiple length scales in a lithium-ion battery can significantly and positively influence battery performance because it enables control over kinetics and trajectories of ion and electron transport. None of the existing methods of engineering electrode structure is capable of creating 3D architected electrodes designed with independent and flexible form-factors at multiscale that are also resilient against cell packaging pressure. In addition, battery kinetics coupled at multiscale from ion transport in an electrolyte to solid electrolyte interphase (SEI) growth has only been studied by numerical simulations, but has never been experimentally explored.
\r\n\r\nIn this thesis, we demonstrate an additive manufacturing technique to engineer porous electrode structure in 3D and explore battery kinetics at multiscale. First, we develop 3D architected carbon electrodes, whose structural factors are independently controlled and whose dimensions span microns to centimeters, using digital light processing and pyrolysis.\r\nThese free-standing lattice electrodes are disordered graphitic carbon composed of several stacked graphitic layers that are mechanically robust. Galvanostatic cycling using these architected carbon electrodes showed sloping capacity, typically observed in pyrolyzed carbon electrodes. We discuss the modified rate performance of the 3D architected carbon electrodes in the framework of ion transport kinetics in the electrode vs. electrolyte and overpotential, enabled by controlling structural factors of battery electrodes, including porosity, surface morphology, electrode thickness, and beam diameter, whose length scales range from nano to millimeter.
\r\n\r\nWe then explore battery kinetics associated with SEI using deterministic, mechanically resilient, and thick 3D architected carbon electrodes, which allow us to study the formation, structure-resistance relationship, and position-dependent growth of SEI by combining the newly developed in operando DC-based technique and post-characterization using secondary ion mass spectroscopy. The amount of Li in SEI agrees with capacity losses, and the amount of F in SEI showed a strong linear correlation with SEI resistance evolutions. The position-dependent SEI growth was experimentally explored; the Li amount in SEI along the electrode thickness agrees with the simulation results in prior work, but the F amount in SEI showed the opposite tendency, suggesting modeling of multilayer SEI is necessary to predict precisely battery aging especially for thick electrodes. Our work demonstrates the use of 3D architected electrodes as a model system to explore multiscale kinetics in Li-ion batteries.
" }, { "name": "Novoseller, Ellen Rachel", "degree": "PhD", "year": "2021", "title": "Online Learning from Human Feedback with Applications to Exoskeleton Gait Optimization", "advisor": "Burdick, Joel W.; Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092020-162149429", "creators": [ { "name": { "family": "Novoseller", "given": "Ellen Rachel" }, "id": "Novoseller-Ellen-Rachel", "orcid": "0000-0001-5263-0598", "display_name": "Novoseller, Ellen Rachel" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel W." }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel W." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "co-advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "chair", "display_name": "Ames, Aaron D." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Sadigh", "given": "Dorsa" }, "id": "Sadigh-Dorsa", "orcid": "0000-0002-7802-9183", "role": "member", "display_name": "Sadigh, Dorsa" } ], "option_major": [ "cds" ], "doi": "10.7907/gvtx-1586", "abstract": "Systems that intelligently interact with humans could improve people's lives in numerous ways and in numerous settings, such as households, hospitals, and workplaces. Yet, developing algorithms that reliably and efficiently personalize their interactions with people in real-world environments remains challenging. In particular, one major difficulty lies in adapting to human-in-the-loop feedback, in which an algorithm makes sequential decisions while receiving online feedback from humans; throughout this interaction, the algorithm seeks to optimize its decision-making quality, as measured by the utility of its performance to the human users. Such algorithms must balance between exploration and exploitation: on one hand, the algorithm must select uncertain strategies to fully explore the environment and the interacting human's preferences, while on the other hand, it must exploit the empirically-best-performing strategies to maximize its cumulative performance.
\r\n\r\nLearning from human feedback can be difficult, as people are often unreliable in specifying numerical scores. In contrast, humans can often more accurately provide various types of qualitative feedback, for instance pairwise preferences. Yet, sample efficiency is a significant concern in human-in-the-loop settings, as qualitative feedback is less informative than absolute metrics, and algorithms can typically pose only limited queries to human users. Thus, there is a need to create theoretically-grounded online learning algorithms that efficiently, reliably, and robustly optimize their interactions with humans while learning from online qualitative feedback.
\r\n\r\nThis dissertation makes several contributions to algorithm design for human-in-the-loop learning. Firstly, this work develops the Dueling Posterior Sampling (DPS) algorithmic framework, a model-based, Bayesian approach for online learning in the settings of preference-based reinforcement learning and generalized linear dueling bandits. DPS is developed together with a theoretical regret analysis framework, and yields competitive empirical performance in a range of simulations. Additionally, this thesis presents the CoSpar and LineCoSpar algorithms for sample-efficient, mixed-initiative learning from pairwise preferences and coactive feedback. CoSpar and LineCoSpar are both deployed in human subject experiments with a lower-body exoskeleton to identify optimal, user-preferred exoskeleton walking gaits. This work presents the first demonstration of preference-based learning for optimizing dynamic crutchless exoskeleton walking for user comfort, and makes progress toward customizing exoskeletons and other assistive devices for individual users.
" }, { "name": "Pastor, Daniel", "degree": "PhD", "year": "2021", "title": "Towards Learning Robotic Dynamics: Application to Multirotor Takeoff and Landing", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:03152021-082447788", "creators": [ { "name": { "family": "Pastor", "given": "Daniel" }, "id": "Pastor-Daniel", "orcid": "0000-0003-3452-0605", "display_name": "Pastor, Daniel" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "chair", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "space" ], "doi": "10.7907/199j-dk87", "abstract": "Multirotors have become widespread but their usage is still limited. Ensuring safety during take-off and landing is still an open problem. Towards this goal this thesis proposes two different solutions to address this problem. The two approaches complement each other and they are tested on hardware.
\r\n \r\nThe first approach is to design a vehicle that is stable during take-off, despite hardware failures or unsteady take-off platforms. A solution is to use a ballistic launch to impose a deterministic path, preventing collisions with its environment. Following this approach led to the development of several SQUID (Streamlined Quick Unfolding Investigation Drone) vehicles. The main challenges are the ballistic initial flight, large accelerations during launch, and limited volume. A first prototype was developed, which is able to transition mid-flight from stable ballistic flight to a fully controllable multirotor. The system has been fabricated and field tested from a moving vehicle up to 50mph to successfully demonstrate the feasibility of the concept and experimentally validate the design's aerodynamic stability and deployment reliability. A second prototype expanded the first one's capabilities incorporating fully-autonomous vision-based navigation, while keeping the ballistic passive stability and stable transition abilities. The new design includes a more reliable plate-based structure and more effective folding fins.
\r\n \r\nThe second approach focuses on designing controllers that are safe regardless of the platform. For that purpose, a Model Predictive Control (MPC) is used to ensure state and input constraints. Given the highly non-linear dynamics platforms and fast dynamics that require a quick controller evaluation, the work in this thesis is built using Koopman Operator theory, which allows tools from linear analysis to be applied to systems with inherently non-linear dynamics. One of the main contributions is a novel method to find Koopman Eigenfunctions directly from data. Another key contribution is an episodic approach to model non-linear actuation dynamics. The proposed method is first tested on simulation and it outperforms comparable approaches. The method is also demonstrated on-board a multirotor for a fast landing application, where the nonlinear ground effect is learned and used to improve landing speed and quality. An additional extension considers model uncertainty in the MPC architecture, where an Ensemble Kalman Sampler is used to learn the uncertainty distribution.
" }, { "name": "Pedivellano, Antonio", "degree": "PhD", "year": "2021", "title": "Deployment Dynamics of Thin-Shell Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012021-002457442", "creators": [ { "name": { "family": "Pedivellano", "given": "Antonio" }, "id": "Pedivellano-Antonio", "orcid": "0000-0003-2321-7301", "display_name": "Pedivellano, Antonio" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/4zbq-g037", "abstract": "Thin-shell structures provide a lightweight solution for deployable structure applications. Despite being only few tens of microns thick, these structures provide excellent bending stiffness, thanks to their curved cross-section. Their thinness also allows them to be elastically packaged into small volumes to fit into a launch vehicle; once in space, they can be self-deployed by releasing their stored elastic energy.
\r\n\r\nMost space applications use thin-shell structures to deploy and tension thin membranes, such as solar sails, drag sails, and solar arrays. Recently, a novel space solar power architecture has been developed at Caltech, and it relies on distributed thin-shell components, connected in a space frame, to create large-area deployable structures. Thanks to the unique properties of thin shells, these structure provide superior stiffness-to-mass ratio and self-deployment capabilities. However, to demonstrate their reliability and enable their use on space missions, their deployment dynamics must be understood and predicted.
\r\n\r\nGround testing is the established approach to verify a structure throughout its design and qualification process. However, replicating the space environment in a laboratory setting is generally not possible, especially for lightweight structures, which are very sensitive to the effects of gravity and air. Numerical models are therefore the only tool to predict the behavior of a structure in space. However, validation with ground experiments is necessary to build confidence in the models, which must be able to capture the complexity of the interaction with air, gravity, and the suspension system that supports the weight of the structure.
\r\n\r\nThe goal of this thesis is to develop high-fidelity models for large space structures, where multiple thin-shell components are folded together and deploy by releasing their strain energy. This overall objective is achieved in 3 steps. First, a ladder-type rectangular strip is introduced, as a building block for more complex architectures. The strip is composed by two thin-shell longerons, symmetrically folded at two locations. The deployment dynamics of this structure is investigated through experiments on 1 m-scale prototypes, both in air and in vacuum. A detailed analysis of its elastic folds is performed using full-field displacement measurements from Digital Image Correlation. A finite element model of this strip is presented, and it is shown to accurately capture the dynamics of the strip for all tested conditions. Then, the implementation of the packaging and deployment scheme of a space solar power spacecraft, composed of multiple strips, is discussed. A kinematic model of the structure is proposed as a design tool to achieve systematic folding. A novel concept of a deployment mechanism to coil the structure in a robust and reliable way is proposed. Also, a staged deployment scheme is demonstrated, to reduce the uncertainty of strain-energy deployment for large space structures. Finally, the deployment dynamics of a 2 m-scale space structural prototype, based on the space solar power architecture, is investigated. A full-scale finite element model of the structure is implemented to replicate its complex folding scheme and capture the deployment process, including the interaction with the deployment mechanism and the suspension system. The simulations predict well the behavior of the structure observed in experiments through motion capture techniques.
\r\n\r\nThe work presented in this thesis advances previous studies on the deployment dynamics of simple thin-shell components, and demonstrates that even complex thin-shell architectures can be packaged and deployed in a controlled and predictable way. The solutions proposed in this thesis have guided the packaging process and the design of the deployment mechanism for DOLCE, an upcoming flight demonstration of the space solar power architecture described in this work. However, this research has much broader implications, as the experimental and numerical framework presented herein can be generalized to different shell-based architectures, and contributes to enabling a new generation of lightweight deployable structures for future space applications.
" }, { "name": "Phan-Minh, Tung", "degree": "PhD", "year": "2021", "title": "Contract-Based Design: Theories and Applications", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01132021-065636010", "creators": [ { "name": { "family": "Phan-Minh", "given": "Tung" }, "id": "Phan-Minh-Tung", "orcid": "000-0002-1403-5197", "display_name": "Phan-Minh, Tung" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/8vp7-kd82", "abstract": "Most things we know only exist in relation to one another. Their states are strongly coupled due to dependencies that arise from such relations. For a system designer, acknowledging the presence of these dependencies is as crucial to guaranteeing performance as studying them. As the roles played by technology in fields such as transportation, healthcare, and finance continue to be more profound and diverse, modern engineering systems have grown to be more reliant on the integration of technologies across multiple disciplines and their requirements. The need to ensure proper division of labor, integration of system modules, and attribution of legal responsibility calls for a more methodological look into co-design considerations. Originally conceived in computer programming, contract-based reasoning is a design approach whose promise of a formal compositional paradigm is receiving attention from a broader engineering community. Our work is dedicated to narrowing the gap between the theory and application of this yet nascent framework.
\r\n\r\nIn the first half of this dissertation, we introduce a model interface contract theory for input/output automata with guards and a formalization of the directive-response architecture using assume-guarantee contracts and show how these may be used to guide the formal design of a traffic intersection and an automated valet parking system respectively. Next, we address a major drawback of assume-guarantee contracts, i.e., the problem of a void contract due to antecedent failure. Our proposed solution is a reactive version of assume-guarantee contracts that enables direct specification at the assumption and guarantee level along with a novel synthesis algorithm that exposes the effects of failures on the contract structure. This is then used to help optimize, adapt, and robustify our design against an uncertain environment.
\r\n\r\nIn light of ongoing development of autonomous driving technologies and its potential impact on the safety of future transportation, the second half of this work is dedicated to the application of the design-by-contract framework to the distributed control of autonomous vehicles. We start by defining and proving properties of \"assume-guarantee profiles,\" our proposed approach to transparent distributed multi-agent decision making and behavior prediction. Next, we provide a local conflict resolution algorithm in the context of a quasi-simultaneous game which guarantees safety and liveness to the composition of autonomous vehicle systems in this game. Finally, to facilitate the extension of these frameworks to real-life urban driving settings, we also supply an effective method to predict agent behavior that utilizes recent advances in machine learning research.
" }, { "name": "Pickering, Ethan Marcus", "degree": "PhD", "year": "2021", "title": "Resolvent Modeling of Turbulent Jets", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:03022021-005902351", "creators": [ { "name": { "family": "Pickering", "given": "Ethan Marcus" }, "id": "Pickering-Ethan-Marcus", "orcid": "0000-0002-4485-6359", "display_name": "Pickering, Ethan Marcus" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/szxb-f168", "abstract": "Optimal control of turbulent flows requires a detailed prediction of the unsteady, three-dimensional turbulent structures that govern quantities of interest like noise, drag, and mixing efficiency. There is a need for physics-based, reduced-order models of turbulent structure for those cases where direct simulation of the flow would be computationally prohibitive. In this thesis, we explore resolvent analysis as a framework for such models. Based on a linearization about the turbulent mean flow field, the resolvent finds optimal (highest gain) forcing functions that give rise, through linear amplification mechanisms, to energetic coherent structures. The forcing functions represent the nonlinear interactions between the coherent structures as well as with background incoherent turbulence. While the high-gain structures capture many characteristics of the observed turbulent coherent structures in both wall-bounded and free-shear flows, closures for the forcing function are required to make these models predictive and thus utilize them for flow control.
\r\n\r\nIn the first part of this thesis, we examine a linear model for the resolvent forcing by adapting the concept of a turbulent (eddy) viscosity from classical Reynolds-Averaged Navier--Stokes (RANS) turbulence modeling. We present a data-driven approach to identify an optimal eddy-viscosity field that best matches the resolvent prediction to the most energetic coherent structure educed via spectral proper orthogonal decomposition (SPOD) of data from high-fidelity simulations. We analyze the specific case of turbulent jets spanning a range of Mach numbers from subsonic to supersonic. We find the optimal eddy-viscosity field to be effective at matching both the shape and energy distribution of structures. More importantly, we find that calibrated eddy-viscosity fields predicted using standard eddy-viscosity models (utilizing only quantities available from RANS) yield results that are close to optimal.
\r\n\r\nWe use the resulting resolvent model together with the high-fidelity data to investigate the full spectrum of amplification mechanisms and coherent structures present in turbulent jets. The addition of a turbulence model provides a clear separation between two established mechanisms in turbulent jets (Kelvin-Helmholtz and Orr) and leads to the identification of a third mechanism known as lift-up. Lift-up becomes the dominant mechanism at low-frequency limits for nonzero azimuthal wavenumbers, generating elongated, streaky structures. We find these streaks to be the most energetic structures in the jet, and that their presence has implications for altering the mean flow and controlling noise.
\r\n\r\nFinally, we extend resolvent analysis to that of an acoustic analogy that relates the near-field forcing to the far-field acoustics 100 diameters from the nozzle. We again leverage high-fidelity data to produce an ensemble of realizations of the acoustic field and find that only a few resolvent modes are necessary for reconstruction. Ultimately, we find that a resolvent model based solely upon RANS quantities can reconstruct and predict the peak acoustic field at rank-1 to within 2 decibels for both the supersonic and transonic jets.
" }, { "name": "Reher, Jenna", "degree": "PhD", "year": "2021", "title": "Dynamic Bipedal Locomotion: From Hybrid Zero Dynamics to Control Lyapunov Functions via Experimentally Realizable Methods", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282021-062435188", "creators": [ { "name": { "family": "Reher", "given": "Jenna" }, "id": "Reher-Jenna", "orcid": "0000-0002-8297-3847", "display_name": "Reher, Jenna" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/h8v0-vd47", "abstract": "Robotic bipedal locomotion has become a rapidly growing field of research as humans increasingly look to augment their natural environments with intelligent machines. In order for these robotic systems to navigate the often unstructured environments of the world and perform tasks, they must first have the capability to dynamically, reliably, and efficiently locomote. Due to the inherently hybrid and underactuated nature of dynamic bipedal walking, the greatest experimental successes in the field have often been achieved by considering all aspects of the problem; with explicit consideration of the interplay between modeling, trajectory planning, and feedback control.
\r\n\r\nThe methodology and developments presented in this thesis begin with the modeling and design of dynamic walking gaits on bipedal robots through hybrid zero dynamics (HZD), a mathematical framework that utilizes hybrid system models coupled with nonlinear controllers that results in stable locomotion. This will form the first half of the thesis, and will be used to develop a solid foundation of HZD trajectory optimization tools and algorithms for efficient synthesis of accurate hybrid motion plans for locomotion on two underactuated and compliant 3D bipeds. While HZD and the associated trajectory optimization are an existing framework, the resulting behaviors shown in these preliminary experiments will extend the limits of what HZD has demonstrated is possible thus far in the literature. Specifically, the core results of this thesis demonstrate the first experimental multi-contact humanoid walking with HZD on the DURUS robot and then through the first compliant HZD motion library for walking over a continuum of walking speeds on the Cassie robot.
\r\n \r\nOn the theoretical front, a novel formulation of an optimization-based control framework is introduced that couples convergence constraints from control Lyapunov functions (CLF)s with desirable formulations existing in other areas of the bipedal locomotion field that have proven successful in practice, such as inverse dynamics control and quadratic programming approaches. The theoretical analysis and experimental validation of this controller thus forms the second half of this thesis. First, a theoretical analysis is developed which demonstrates several useful properties of the approach for tuning and implementation, and the stability of the controller for HZD locomotion is proven. This is then extended to a relaxed version of the CLF controller, which removes a convergence inequality constraint in lieu of a conservative CLF cost within a quadratic program to achieve tracking. It is then explored how this new CLF formulation can fully leverage the planned HZD walking gaits to achieve the target performance on physical hardware. Towards this goal, an experimental implementation of the CLF controller is derived for the Cassie robot, with the resulting experiments demonstrating the first successful realization of a CLF controller for a 3D biped on hardware in the literature. The accuracy of the robot model and synthesized HZD motion library allow the real-time control implementation to regularize the CLF optimization cost about the nominal walking gait. This drives the controller to choose smooth input torques and anticipated spring torques, as well as regulate an optimal distribution of feasible ground reaction forces on hardware while reliably tracking the planned virtual constraints. These final results demonstrate how each component of this thesis were brought together to form an effective end-to-end implementation of a nonlinear control framework for underactuated locomotion on a bipedal robot through modeling, trajectory optimization, and then ultimately real-time control.
" }, { "name": "Ren, Xinying (Cindy)", "degree": "PhD", "year": "2021", "title": "Principles for Designing Robust and Stable Synthetic Microbial Consortia", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262021-072231177", "creators": [ { "name": { "family": "Ren", "given": "Xinying (Cindy)" }, "id": "Ren-Xinying-Cindy", "orcid": "0000-0002-8852-6722", "display_name": "Ren, Xinying (Cindy)" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Franco", "given": "Elisa" }, "id": "Franco-Elisa", "role": "member", "display_name": "Franco, Elisa" } ], "option_major": [ "cds" ], "doi": "10.7907/hc8x-3280", "abstract": "Engineering stable microbial consortia with robust functions are useful in many areas, including bioproduction and human health. Robust and stable properties depend on proper control of dynamics ranging from single cell-level to population-environment interactions. In this thesis, I discuss principles of building microbial consortia with synthetic circuits in two design scenarios.
\r\n\r\nFirst, for one microbial population, strong disturbances in environments often severely perturb cell states and lead to heterogeneous responses. Single cell-level design of control circuits may fail to induce a uniform response as needed. I demonstrate that cell-cell signaling systems can facilitate coordination among cells and achieve robust population-level behaviors. Moreover, I show that heterogeneity can be harnessed for robust adaptation at population-level via a bistable state switch.
\r\n\r\nSecond, multi-pecies consortia are intrinsically unstable due to competitive exclusion. Previous theoretical investigations based on models of pairwise interactions mainly explored what interaction network topology ensures stable coexistence. Yet neglecting detailed interaction mechanisms and spatial context results in contradictory predictions. Focusing on chemical-mediated interaction, I show that detailed mechanisms of chemical consumption/accumulation and chemical-induced growth/death, interaction network topology and spatial structures of environments all are critical factors to maintain stable coexistence. With a two population-system, I demonstrate that the same interaction network topology can exhibit qualitatively different or even opposite behaviors due to interaction mechanisms and spatial conditions.
" }, { "name": "Roh, Becky", "degree": "PhD", "year": "2021", "title": "Matching Waveform Envelopes for Earthquake Early Warning", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11112020-213135157", "creators": [ { "name": { "family": "Roh", "given": "Becky" }, "id": "Roh-Becky", "orcid": "0000-0002-3905-0086", "display_name": "Roh, Becky" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "chair", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Ross", "given": "Zachary E." }, "id": "Ross-Z-E", "orcid": "0000-0002-6343-8400", "role": "member", "display_name": "Ross, Zachary E." }, { "name": { "family": "Allen", "given": "Richard Harvey" }, "id": "Allen-Richard-Harvey", "orcid": "0000-0003-4293-9772", "role": "member", "display_name": "Allen, Richard Harvey" }, { "name": { "family": "Minson", "given": "Sarah" }, "id": "Minson-Sarah", "orcid": "0000-0001-5869-3477", "role": "member", "display_name": "Minson, Sarah" } ], "option_major": [ "civileng" ], "doi": "10.7907/hw8k-zx98", "abstract": "Current earthquake early warning (EEW) algorithms are continuously optimized to strive for fast, accurate source parameter estimates for the rupturing earthquake (i.e. magnitude, location), which are then used to predict ground motions expected at a site. However, they may still struggle with challenging cases, such as offshore events and complex sequences. An envelope-based two-part search algorithm is developed to handle such cases. This algorithm matches different templates to the incoming observed ground motion envelopes to find the optimal earthquake source parameter estimates.
\r\n\r\nThe algorithm consists of two methods. Method I is the standard grid search, and it uses Cua-Heaton ground motion envelopes as its templates; Method II is the extended catalog search, and its templates are waveform envelopes from past real and synthetic earthquakes. The grid search is intended for robustness and provides approximate average solutions, whereas the extended catalog search matches envelopes considering the station\u2019s specific site and path effects. In parallel execution, Methods I and II work together \u2013 either by confirming each other\u2019s solutions or accepting the solution with stronger fits \u2013 to provide the best parameter estimates based on waveform-based data.
\r\n\r\nThe main advantage of the two-part search algorithm is its ability to find parameter estimates of reduced uncertainties using the P-wave data from a single station. Many algorithms wait until multiple stations are triggered to reduce tradeoffs between the magnitude and location. This waiting time, however, is detrimental in EEW, for it jeopardizes the warning time that can be issued to nearby regions expected to experience strong shaking. The use of a single station would virtually eliminate this waiting time, maximizing the warning time without the cost in accuracy of the estimates.
\r\n\r\nBecause EEW is a race against time, further actions are taken for more rapid estimation of the earthquake source parameters. A Bayesian approach using prior information has the potential to reduce uncertainties that arise in the initial time points due to tradeoffs between the magnitude and location. This essentially increases the confidence of the initial parameter estimates, allowing alerts to be issued faster. A KD tree nearest neighbor search is also introduced to reduce latency in the time it takes to find the best-fitting solutions. In comparison to an exhaustive, brute-force search, it cuts the searching time by only examining through a fraction of the total database.
\r\n\r\nAn envelope-based algorithm examines the shape and relative frequency content and makes appropriate judgments, just as a human seismologist would; it also addresses the issue of data transmission latencies. Overall, this algorithm is able to interpret the complexity of earthquakes and assess the features they hold to ultimately communicate information of significant ground shaking to different regions.
" }, { "name": "Royer, Fabien A.", "degree": "PhD", "year": "2021", "title": "Probing the Buckling of Thin-Shell Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312021-185024653", "creators": [ { "name": { "family": "Royer", "given": "Fabien A." }, "id": "Royer-Fabien-A", "orcid": "0000-0003-2452-2893", "display_name": "Royer, Fabien A." } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/ksn2-t598", "abstract": "The overarching goal of the research presented in this dissertation is to apply and extend a newly developed methodology to understand the buckling of complex thin shell structures. This methodology enables the determination of tighter buckling criteria and paves the way to the development of more efficient structures, used closer than ever to their buckling load and even beyond. It would result in dramatically lighter structures to be built and has the potential to enable new applications, such as extremely large aperture satellites.
\r\n\r\nWe first analyze the stability of open section thin shell structures under a pure bending moment, through simulations. These structures are composed of longitudinal thin-shell elements connected transversely by thin rods, and inspired by real spacecraft structures. The present study applies and extends recent work on the stability of cylindrical and spherical shells. The role of localization in the buckling of these structures is investigated and early transitions into the post-buckling regime are unveiled using a probe that locally displaces the structure. The probing method enables the computation of the energy input needed to transition early into a post-buckling state, which is central to determining the critical buckling mechanism for the structure. We show that the structure follows stability landscapes also found in cylindrical and spherical shell buckling problems. This initial computational study is the basis for the first ever probing experiment on a complex structure.
\r\n\r\nIn order to test these new structures under bending, a new bending apparatus is designed and implemented. The boundary conditions are chosen such that the apparatus is statically determinate (isostatic), and no state of self stress can develop in the sample during its mounting and testing. This feature is especially desirable in the study of thin shell structures and their elastic instabilities, for which imperfection sensitivity plays a crucial role in the buckling transition and the post-buckling regime. The accuracy of the isostatic bending machine is first assessed through the testing of rods, and its imperfection insensitive behavior is then highlighted in experiments on tape springs, and through numerical studies of the same structures.
\r\n\r\nThe new bending machine is complemented by a probing apparatus, and the stability of the open section thin-shell structures subjected to a pure bending moment is studied experimentally. The experiment confirms that localization of deformations plays a paramount role in the structure's nonlinear post-buckling regime and is extremely sensitive to imperfections. This characteristic is investigated through probing experiments. The range of moments for which the early buckling of the structure can be triggered using this probe perturbation is determined, as well as the energy barrier separating the pre-buckling and post-buckling states. The stability of the local buckling mode is then illustrated by an experimental stability landscape of shell buckling, and probing is then extended to the entire structure to reveal alternate buckling modes disconnected from the structure's fundamental path. These results can be used to elaborate efficient buckling criteria for this type of structures, through the use of transition diagrams determined experimentally.
\r\n\r\nFinally, the buckling and post-buckling behavior of ultralight ladder-type coilable structures is investigated. These specific structures are used in the Space Solar Power Project at Caltech and are referred to as strips. Similarly to the previous studies, the stability of strip structures loaded by normal pressure is computationally studied by applying controlled perturbations through localized probing. The probing technique is generalized to higher-order bifurcations along the post-buckling path, and low-energy escape paths into buckling that cannot be predicted by a classical eigenvalue formulation are identified. It is shown that the stability landscape for a pressure-loaded strip is similar to the landscape for classical shells, and the open section thin shell structure studied initially in this thesis. While classical shell structures buckle catastrophically, strip structures feature a large stable post-buckling range. Probing enables the full characterization of the structure's unstable behavior, which paves the way to extend its operation closer than ever to the buckling load, and even in the post-buckling regime. It would enable the design of more efficient structures by dramatically reducing their mass, therefore enabling new large spacecraft to be built.
" }, { "name": "Ruan, Joseph Y.", "degree": "PhD", "year": "2021", "title": "Streamwise Homogeneous Turbulent Boundary Layers", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062021-094519451", "creators": [ { "name": { "family": "Ruan", "given": "Joseph Y." }, "id": "Ruan-Joseph-Y", "orcid": "0000-0002-9110-0458", "display_name": "Ruan, Joseph Y." } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/qjfk-5q05", "abstract": "Boundary layers are everywhere and computing direct numerical simulations (DNS) of them is crucial for drag reduction. However, traditional DNS of flat-plate boundary layers are prohibitively expensive. Due to the streamwise inhomogeneity of the boundary layer, simulations of spatially growing boundary layer simulations require long domains and long convergence times. Current methods to overcome streamwise inhomogeneity (and allow for shorter streamwise domains) either suffer from a lack of stationarity or have difficult numerical implementation. The goal of this thesis is to develop and validate a more efficient method for simulating boundary layers that will be both statistically stationary and streamwise homogeneous.
\r\n\r\nThe current methodology is developed and validated for the flat plate, zero pressure gradient, incompressible boundary layer. The Navier-Stokes equations are rescaled by a boundary layer thickness to produce a new set of governing equations that resemble the original Navier-Stokes equations with additional source terms. Streamwise homogeneity and statistical stationarity are verified through non-periodic and periodic simulations, respectively. To test the accuracy of the methodology, a sweep of Reynolds number simulations is conducted in streamwise periodic domains for Re\u03b4*=1460-5650. The global quantities show excellent agreement with established empirical values: the computed shape factor and skin friction coefficient for all cases are within 3% and 1% of empirical values, respectively. Furthermore, to obtain accurate two-point correlations, it is sufficient to have a computational domain of length 14\u03b499 and width 5\u03b499, thus, leading to large computational savings by one-to-two orders of magnitude. This translates into increasing the largest possible Reynolds number one could simulate by about a factor of 3.
\r\n\r\nThanks to the streamwise homogeneous nature of the simulation results, it is now possible to apply cost-efficient data-driven techniques like spectral proper orthogonal decomposition (SPOD; Towne et al. 2018) to extract turbulent structures. Particular emphasis is place on identifying structures for waves in the inner and outer layers. To interpret these structures, 1D resolvent analysis (McKeon and Sharma 2010) is leveraged. The peak location for the extracted inner wave is captured by traditional resolvent analysis, assuming a parallel flow. However, the peak location for the extracted outer wave differs from that predicted by the classic 1D resolvent analysis by 20%. Recovering the peak location requires including in the resolvent operator the mean wall-normal velocity profile and the streamwise growth of the boundary layer.
\t\r\n\r\nThis methodology has natural extensions to slowly growing boundary layer flows, including thermal boundary layers, rough wall boundary layers and mild pressure gradient flows.
" }, { "name": "Salehi, Fariborz", "degree": "PhD", "year": "2021", "title": "Structured Signal Recovery from Nonlinear Measurements with Applications in Phase Retrieval and Linear Classification", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:05172021-044724906", "creators": [ { "name": { "family": "Salehi", "given": "Fariborz" }, "id": "Salehi-Fariborz", "orcid": "0000-0002-9679-1016", "display_name": "Salehi, Fariborz" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "chair", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "member", "display_name": "Kostina, Victoria" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1c69-wq71", "abstract": "Nonlinear models are widely used in signal processing, statistics, and machine learning to model real-world applications. A popular class of such models is the single-index model where the response variable is related to a linear combination of dependent variables through a link function. In other words, if x \u2208 Rp denotes the input signal, the posterior mean of the generated output y has the form, E[y|x] = \u03c1(xTw), where \u03c1 :R \u2192 R is a known function (referred to as the link function), and w \u2208 Rp is the vector of unknown parameters. When \u03c1(\u2022) is invertible, this class of models is called generalized linear models (GLMs). GLMs are commonly used in statistics and are often viewed as flexible generalizations of linear regression. Given n measurements (samples) from this model, D = {(xi, yi) | 1 \u2264q i \u2264 n}, the goal is to estimate the parameter vector w. While the model parameters are assumed to be unknown, in many applications these parameters follow certain structures (sparse, low-rank, group-sparse, etc.) The knowledge on this structure can be used to form more accurate estimators.
\r\n\r\nThe main contribution of this thesis is to provide a precise performance analysis for convex optimization programs that are used for parameter estimation in two important classes of single-index models. These classes are: (1) phase retrieval in signal processing, and (2) binary classification in statistical learning.
\r\n\r\nThe first class of models studied in this thesis is the phase retrieval problem, where the goal is to recover a discrete complex-valued signal from amplitudes of its linear combinations. Methods based on convex optimization have recently gained significant attentions in the literature. The conventional convex-optimization-based methods resort to the idea of lifting which makes them computationally inefficient. In addition to providing an analysis of the recovery threshold for the semidefinite-programming-based methods, this thesis studies the performance of a new convex relaxation for the phase retrieval problem, known as phasemax, which is computationally more efficient as it does not lift the signal to higher dimensions. Furthermore, to address the case of structured signals, regularized phasemax is introduced along with a precise characterization of the conditions for its perfect recovery in the asymptotic regime.
\r\n\r\nThe next important application studied in this thesis is the binary classification in statistical learning. While classification models have been studied in the literature since 1950's, the understanding of their performance has been incomplete until very recently. Inspired by the maximum likelihood (ML) estimator in logistic models, we analyze a class of optimization programs that attempts to find the model parameters by minimizing an objective that consists of a loss function (which is often inspired by the ML estimator) and an additive regularization term that enforces our knowledge on the structure. There are two operating regimes for this problem depending on the separability of the training data set D. In the asymptotic regime, where the number of samples and the number of parameters grow to infinity, a phase transition phenomenon is demonstrated that happens at a certain over-parameterization ratio. We compute this phase transition for the setting where the underlying data is drawn from a Gaussian distribution.
\r\n\r\nIn the case where the data is non-separable, the ML estimator is well-defined, and its attributes have been studied in the classical statistics. However, these classical results fail to provide reasonable estimate in the regime where the number of data points is proportional to the number of samples. One contribution of this thesis is to provide an exact analysis on the performance of the regularized logistic regression when the number of training data is proportional to the number of samples. When the data is separable (a.k.a. the interpolating regime), there exist multiple linear classifiers that perfectly fit the training data. In this regime, we introduce and analyze the performance of \"extended margin maximizers\" (EMMs). Inspired by the max-margin classifier, EMM classifiers simultaneously consider maximizing the margin and the structure of the parameter. Lastly, we discuss another generalization to the max-margin classifier, referred to as the robust max-margin classifier, that takes into account the perturbations by an adversary. It is shown that for a broad class of loss functions, gradient descent iterates (with proper step sizes) converge to the robust max-margin classifier.
" }, { "name": "Sch\u00e4fer, Florian Tobias", "degree": "PhD", "year": "2021", "title": "Inference, Computation, and Games", "advisor": "Owhadi, Houman", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082021-005706263", "creators": [ { "name": { "family": "Sch\u00e4fer", "given": "Florian Tobias" }, "id": "Sch\u00e4fer-Florian-Tobias", "orcid": "0000-0002-4891-0172", "display_name": "Sch\u00e4fer, Florian Tobias" } ], "advisors": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "advisor", "display_name": "Owhadi, Houman" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/esyv-2181", "abstract": "In this thesis, we use statistical inference and competitive games to design algorithms for computational mathematics.
\r\n\r\nIn the first part, comprising chapters two through six, we use ideas from Gaussian process statistics to obtain fast solvers for differential and integral equations. We begin by observing the equivalence of conditional (near-)independence of Gaussian processes and the (near-)sparsity of the Cholesky factors of its precision and covariance matrices. This implies the existence of a large class of dense matrices with almost sparse Cholesky factors, thereby greatly increasing the scope of application of sparse Cholesky factorization. Using an elimination ordering and sparsity pattern motivated by the screening effect in spatial statistics, we can compute approximate Cholesky factors of the covariance matrices of Gaussian processes admitting a screening effect in near-linear computational complexity. These include many popular smoothness priors such as the Mat\u00e9rn class of covariance functions. \r\nIn the special case of Green's matrices of elliptic boundary value problems (with possibly unknown elliptic operators of arbitrarily high order, with possibly rough coefficients), we can use tools from numerical homogenization to prove the exponential accuracy of our method. This result improves the state-of-the-art for solving general elliptic integral equations and provides the first proof of an exponential screening effect. We also derive a fast solver for elliptic partial differential equations, with accuracy-vs-complexity guarantees that improve upon the state-of-the-art. Furthermore, the resulting solver is performant in practice, frequently beating established algebraic multigrid libraries such as AMGCL and Trilinos on a series of challenging problems in two and three dimensions.\r\nFinally, for any given covariance matrix, we obtain a closed-form expression for its optimal (in terms of Kullback-Leibler divergence) approximate inverse-Cholesky factorization subject to a sparsity constraint, recovering Vecchia approximation and factorized sparse approximate inverses. Our method is highly robust, embarrassingly parallel, and further improves our asymptotic results on the solution of elliptic integral equations. We also provide a way to apply our techniques to sums of independent Gaussian processes, resolving a major limitation of existing methods based on the screening effect. As a result, we obtain fast algorithms for large-scale Gaussian process regression problems with possibly noisy measurements.
\r\n\r\nIn the second part of this thesis, comprising chapters seven through nine, we study continuous optimization through the lens of competitive games. In particular, we consider competitive optimization, where multiple agents attempt to minimize conflicting objectives. In the single-agent case, the updates of gradient descent are minimizers of quadratically regularized linearizations of the loss function. We propose to generalize this idea by using the Nash equilibria of quadratically regularized linearizations of the competitive game as updates (linearize the game). We provide fundamental reasons why the natural notion of linearization for competitive optimization problems is given by the multilinear (as opposed to linear) approximation of the agents' loss functions. The resulting algorithm, which we call competitive gradient descent, thus provides a natural generalization of gradient descent to competitive optimization. By using ideas from information geometry, we extend CGD to competitive mirror descent (CMD) that can be applied to a vast range of constrained competitive optimization problems. CGD and CMD resolve the cycling problem of simultaneous gradient descent and show promising results on problems arising in constrained optimization, robust control theory, and generative adversarial networks. Finally, we point out the GAN-dilemma that refutes the common interpretation of GANs as approximate minimizers of a divergence obtained in the limit of a fully trained discriminator. Instead, we argue that GAN performance relies on the implicit competitive regularization (ICR) due to the simultaneous optimization of generator and discriminator and support this hypothesis with results on low-dimensional model problems and GANs on CIFAR10.
" }, { "name": "Shahrestani, Shane Shayan", "degree": "PhD", "year": "2021", "title": "Eddy Current Damping Stroke Sensor", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:01132021-224837966", "creators": [ { "name": { "family": "Shahrestani", "given": "Shane Shayan" }, "id": "Shahrestani-Shane-Shayan", "orcid": "0000-0001-7561-4590", "display_name": "Shahrestani, Shane Shayan" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "chair", "display_name": "Gao, Wei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Zada", "given": "Gabriel" }, "id": "Zada-Gabriel", "role": "member", "display_name": "Zada, Gabriel" } ], "option_major": [ "medeng" ], "doi": "10.7907/zxdh-ej95", "abstract": "Existing paradigms for stroke diagnosis typically involve computed tomography (CT) or magnetic resonance (MR) imaging to classify ischemic versus hemorrhagic stroke variants, as treatment for these subtypes varies widely. Delays in diagnosis and issues related to transport of unstable patients may worsen neurological status. As such, translational medical devices that accelerate time to treatment in the field or hospital setting have the potential to lower morbidity and mortality in stroke patients. We demonstrated feasibility of rapid and accurate bedside stroke detection using a novel, handheld portable eddy current damping imaging device in laboratory benchtop as well as live human clinical ischemic and hemorrhagic stroke settings. We show that diagnosis of stroke may potentially be reduced from several hours to minutes, with additional spatial localization of intracranial hemorrhage, thereby rapidly guiding time-sensitive medical decisions for clinical intervention such as tissue plasminogen activator (tPA). The sensor additionally detects ischemic and hemorrhagic lesions located deep inside the brain, and its range can be selectively tuned during sensor design and fabrication.
" }, { "name": "Shamai, Maysam", "degree": "PhD", "year": "2021", "title": "Complexity Reduction of Fluid-Structure Systems at Low Forcing Frequencies", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282021-215050622", "creators": [ { "name": { "family": "Shamai", "given": "Maysam" }, "id": "Shamai-Maysam", "orcid": "0000-0002-1099-1456", "display_name": "Shamai, Maysam" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Plesniak", "given": "Michael W." }, "id": "Plesniak-M-W", "orcid": "0000-0001-6575-5074", "role": "member", "display_name": "Plesniak, Michael W." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rhs5-yq49", "abstract": "This thesis addresses complexity reduction in periodic fluid-structure systems at low forcing frequencies. A novel quasi-steady time scaling framework is developed to relate the dynamics of a forced system to a corresponding unforced system.
\r\n\r\nParticle Image Velocimetry and dye flow visualization are used to study the streamwise-oscillating cylinder's wake at a mean Reynolds number of 900. Forcing frequencies both one and two orders of magnitude below the stationary shedding frequency are considered. Forcing amplitudes are such that the instantaneous Reynolds number remains above the critical value at all times. It is shown that this forcing regime is synonymous with the development of both frequency and amplitude modulation in the wake. While frequency modulation is linked to vortex shedding, amplitude modulation arises due to symmetric reorganization of the wake at certain phases in the forcing cycle. Furthermore, Dynamic Mode Decomposition is used to extract underlying flow structures and quasi-steady time scaling is employed to relate dynamics to the corresponding unforced system. Specifically, forcing regimes where quasi-steady shedding can develop are identified and time is scaled to transform the system to resemble the stationary cylinder at the same mean Reynolds number.
\r\n\r\nExperimental flowfields are also used to analyze the wake of a surface mounted hemisphere subject to a highly pulsatile freestream, characterized by a forcing amplitude equal to the mean. Although this flow sees regular shedding of hairpin vortices in the unforced case, pulsatile forcing leads to significant deviations. For a nominal mean Reynolds number of 1000, analysis of the wake shows that forcing at a frequency much smaller than that associated with hairpin shedding can lead to frequency modulated shedding. Consequently, time scaling is employed to reduce system complexity associated with hairpin shedding and to relate wake dynamics to the analogous unforced system.
" }, { "name": "Shen, Boqiang", "degree": "PhD", "year": "2021", "title": "Applications and Integration of Optical Frequency Combs", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292021-053844660", "creators": [ { "name": { "family": "Shen", "given": "Boqiang" }, "id": "Shen-Boqiang", "orcid": "0000-0003-0697-508X", "display_name": "Shen, Boqiang" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Leifer", "given": "Stephanie D." }, "id": "Leifer-Stephanie-D", "orcid": "0000-0002-8980-7825", "role": "member", "display_name": "Leifer, Stephanie D." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/p5z5-n346", "abstract": "Optical frequency combs have a wide range of applications in science and technology, including but not limited to timekeeping, optical frequency synthesis, spectroscopy, searching for exoplanets, ranging, and microwave generation. The integration of microresonator with other photonic components enables the high-volume production of wafer-scale optical frequency combs, soliton microcombs. However, it faces two considerable obstacles: optical isolation, which is challenging to integrate on-chip at acceptable performance levels, and power-hungry electronic control circuits, which are required for the generation and stabilization of soliton microcombs. In this thesis, we describe the design and early commissioning of the laser frequency comb for astronomical calibration using electro-optic modulation. We also focus on the realization of a novel and compact chip-scale optical frequency comb, soliton microcomb, including the progress made towards the visible soliton microcomb generation and the demonstration of low power operation of a soliton microcomb along contours of constant power in the phase space. We introduce a soliton spectrometer using dual-locked counter-propagating soliton microcombs to provide high-resolution frequency measurement. Finally, we look into the integration of lasers and high-Q microresonators. The self-injection locking process has been shown to create a new turnkey soliton operating point that eliminates difficult-to-integrate optical isolation as well as complex startup and feedback loops. Moreover, this technique also simplifies the access to high-efficiency dark soliton states without special dispersion engineering of microresonators." }, { "name": "Shen, Naijian", "degree": "PhD", "year": "2021", "title": "Part I: The Equations of Plasma Physics and the Richtmyer-Meshkov Instability in Magnetohydrodynamics. Part II: Evolution of Perturbed Planar Shockwaves.", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:10042020-174941725", "creators": [ { "name": { "family": "Shen", "given": "Naijian" }, "id": "Shen-Naijian", "orcid": "0000-0002-0533-8081", "display_name": "Shen, Naijian" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/e9b8-y318", "abstract": "Part I: Mitigating the Richtmyer-Meshkov instability (RMI) is critical for energy production in inertial confinement fusion. Suitable plasma models are required to study the hydrodynamic and electromagnetic interactions associated with the RMI in a conducting medium. First, a sequence of asymptotic expansions in several small parameters, as formal limits of the non-dissipative and non-resistive two-fluid plasma equations, leads to five simplified plasma/magnetohydrodynamics (MHD) systems. Each system is characterized by its own physical range of validity and dispersion relations, and includes the widely used magnetohydrodynamic (MHD) and Hall-MHD equations. Next we focus on the RMI in MHD. Using ideal MHD, it has been shown that the RMI is suppressed by the presence of an external magnetic field. We utilize the incompressible, Hall-MHD model to investigate the stabilization mechanism when the plasma ion skin depth and Larmor radius are nonzero. The evolution of an impulsively accelerated, sinusoidally perturbed density interface between two conducting fluids is solved as a linearized initial-value problem. An initially uniform background magnetic field of arbitrary orientation is applied. The incipient RMI is found suppressed through oscillatory motions of the interface due to the ion cyclotron effect. This suppression is most effective for near tangential magnetic fields but becomes less effective with increasing plasma length scales. The vorticity dynamics that facilitates the stabilization is discussed.
\r\n\r\nPart II: We consider the evolution of a planar gas-dynamic shock wave subject to smooth initial perturbations in both Mach number and shock shape profile. A complex variable formulation for the general shock motion is developed based on an expansion of the Euler equations proposed by Best [Shock Waves, {1}: 251-273, (1991)]. The zeroth-order truncation of Best's system is related to the well-known geometrical shock dynamics (GSD) equations while higher-order corrections provide a hierarchy of closed systems, as detailed initial flow conditions immediately behind the shock are prescribed. Solutions to Best's generalized GSD system for the evolution of two-dimensional perturbations are explored numerically up to second order in the weak and strong shock limits. Two specific problems are investigated: a shock generated by an impulsively accelerated piston with a corrugated surface, and a shock traversing a density gradient. For the piston-driven flow, it is shown that this approach allows full determination of derivative jump conditions across the shock required to specify initial conditions for the retained, higher-order correction equations. In both cases, spontaneous development of curvature singularity in the shock shape is detected. The critical time at which a singularity occurs follows a scaling inversely proportional to the initial perturbation size. This result agrees with the weakly nonlinear GSD analysis of Mostert et al. [J. Fluid Mech., {846}: 536-562, (2018)].
" }, { "name": "Shi, Xichen", "degree": "PhD", "year": "2021", "title": "Intelligent Control for Fixed-Wing eVTOL Aircraft", "advisor": "Chung, Soon-Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:02182021-040721884", "creators": [ { "name": { "family": "Shi", "given": "Xichen" }, "id": "Shi-Xichen", "orcid": "0000-0002-5366-9256", "display_name": "Shi, Xichen" } ], "advisors": [ { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "advisor", "display_name": "Chung, Soon-Jo" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "space" ], "doi": "10.7907/51c6-aa57", "abstract": "Urban Air Mobility (UAM) holds promise for personal air transportation by deploying \"flying cars\" over cities. As such, fixed-wing electric vertical take-off and landing (eVTOL) aircraft has gained popularity as they can swiftly traverse cluttered areas, while also efficiently covering longer distances. These modes of operation call for an enhanced level of precision, safety, and intelligence for flight control. The hybrid nature of these aircraft poses a unique challenge that stems from complex aerodynamic interactions between wings, rotors, and the environment. Thus accurate estimation of external forces is indispensable for a high performance flight. However, traditional methods that stitch together different control schemes often fall short during hybrid flight modes. On the other hand, learning-based approaches circumvent modeling complexities, but they often lack theoretical guarantees for stability.
\r\n\r\nIn the first part of this thesis, we study the theoretical benefits of these fixed-wing eVTOL aircraft, followed by the derivation of a novel unified control framework. It consists of nonlinear position and attitude controllers using forces and moments as inputs; and control allocation modules that determine desired attitudes and thruster signals. Next, we present a composite adaptation scheme for linear-in-parameter (LiP) dynamics models, which provides accurate realtime estimation for wing and rotor forces based on measurements from a three-dimensional airflow sensor. Then, we introduce a design method to optimize multirotor configuration that ensures a property of robustness against rotor failures.
\r\n\r\nIn the second part of the thesis, we use deep neural networks (DNN) to learn part of unmodeled dynamics of the flight vehicles. Spectral normalization that regulates the Lipschitz constants of the neural network is applied for better generalization outside the training domain. The resultant network is utilized in a nonlinear feedback controller with a contraction mapping update, solving the nonaffine-in-control issue that arises. Next, we formulate general methods for designing and training DNN-based dynamics, controller, and observer. The general framework can theoretically handle any nonlinear dynamics with prior knowledge of its structure. Finally, we establish a delay compensation technique that transforms nominal controllers for an undelayed system into a sample-based predictive controller with numerical integration. The proposed method handles both first-order and transport delays in actuators and balances between numerical accuracy and computational efficiency to guarantee stability under strict hardware limitations.
" }, { "name": "Song, Jialin", "degree": "PhD", "year": "2021", "title": "Learning to Optimize: from Theory to Practice", "advisor": "Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022021-223508132", "creators": [ { "name": { "family": "Song", "given": "Jialin" }, "id": "Song-Jialin", "orcid": "0000-0001-5633-9909", "display_name": "Song, Jialin" } ], "advisors": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Dilkina", "given": "Bistra" }, "id": "Dilkina-Bistra", "orcid": "0000-0002-6784-473X", "role": "member", "display_name": "Dilkina, Bistra" } ], "option_major": [ "cms" ], "doi": "10.7907/7qaw-kd75", "abstract": "Optimization is at the heart of everyday applications, from finding the fastest route for navigation to designing efficient drugs for diseases. The study of optimization algorithms has focused on developing general approaches that do not adapt to specific problem instances. While they enjoy wide applicability, they forgo the potentially useful information embedded in the structure of an instance. Furthermore, as new optimization problems appear, the algorithm development process relies heavily on domain expertise to identify special properties and design methods to exploit them. Such design philosophy is labor-intensive and difficult to deploy efficiently to a broad range of domain-specific optimization problems, which are becoming ubiquitous in the pursuit of ever more personalized applications.
\r\n \r\nIn this dissertation, we consider different hybrid versions of classical optimization algorithms with data-driven techniques. We aim to equip classical algorithms with the ability to adapt their behaviors on the fly based on specific problem instances. A common theme in our approaches is to train the data-driven components on a pre-collected batch of representative problem instances to optimize some performance metrics, e.g., wall-clock time. Varying the integration details, we present several approaches to learning data-driven optimization modules for combinatorial optimization problems and study the corresponding fundamental research questions on policy learning. We provide multiple practical experimental results to showcase the practicality of our methods which lead to state-of-the-art performance on some classes of problems.
" }, { "name": "Su, Yu", "degree": "PhD", "year": "2021", "title": "Optimizing Cloud AI Platforms: Resource Allocation and Market Design", "advisor": "Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072021-172842077", "creators": [ { "name": { "family": "Su", "given": "Yu" }, "id": "Su-Yu", "orcid": "0000-0002-7159-4542", "display_name": "Su, Yu" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "cms" ], "doi": "10.7907/bc2t-er54", "abstract": "The numerous applications of data-driven algorithms and tools across diverse industries have led to tremendous successes in recent years. As the volume of massive data that is created, collected, and consumed continues to grow, there are many new imposed challenges faced by today's cloud AI platforms that support the deployment of machine learning algorithms on a large scale. In this thesis, we tackle the emerging challenges within cloud AI systems and beyond by adopting approaches from the fields of resource allocation and market design.
\r\n\r\nFirst, we propose a new scheduler, Generalized Earliest Time First (GETF), and provide the provable, worst-case approximation guarantees for the goals of minimizing both makespan and total weighted completion time of tasks with precedence constraints on related machines with machine-dependent communication times. These two results address long-standing open problems. Further, we adopt the classic speed scaling function to model power consumption and use mean response time to measure the performance. We propose the concept of pseudo-size to quantify importance of tasks and design a family of two-stage scheduling frameworks based on the approximation of pseudo-size. Assuming a good approximation of pseudo-size, we are able to provide the first provable bound of a linear combination of performance and energy goals under this setting.
\r\n\r\nSecond, we study the design of mechanisms for data acquisition in settings with information leakage and verifiable data. We provide the first characterization of an optimal mechanism for data acquisition if agents are concerned about privacy and their data is correlated with each other. Additionally, the mechanism allows, for the first time, a trade-off between the bias and variance of the estimator. Transitioning from the data market into the energy market, we propose a new pricing scheme, which is applicable to general non-convex costs, and allows using general parametric pricing functions. Optimizing for the quantities and the price parameters simultaneously, and the ability to use general parametric pricing functions allows our scheme to find prices that are typically economically more efficient and less discriminatory than those of the existing schemes while still supporting a competitive equilibrium. In addition, we supplement the proposed method with a computationally efficient polynomial-time approximation algorithm, which can be used to approximate the optimal quantities and prices for general non-convex cost functions.
" }, { "name": "Teh, Ying Shi", "degree": "PhD", "year": "2021", "title": "Understanding Imperfections and Instabilities in Crystals via Physics-Based and Data-Driven Models", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:04202021-184720643", "creators": [ { "name": { "family": "Teh", "given": "Ying Shi" }, "id": "Ying-Shi-Teh", "orcid": "0000-0003-1743-4158", "display_name": "Teh, Ying Shi" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/kd3n-eq78", "abstract": "In crystals, atoms are arranged in a periodic manner in space. However in reality, imperfections and instabilities exist and this repeated arrangement is never perfect. The coupling between crystal defects, lattice instabilities, other defects like domain walls and domain patterns, and material properties generates interesting phenomena that can be leveraged on for future materials design. Nevertheless, the coupling of different scales and processes also makes the modeling and understanding of these materials an open challenge. This thesis examines these various aspects of crystalline solids through the development of both physics-based and data-driven computational models at the appropriate length scales.
\r\n\r\nAbove-bandgap photovoltaic (PV) effect has been observed experimentally in multi-domain ferroelectric perovskites, but the underlying working mechanisms are not well understood. The first part of the thesis presents a device model to study the role of ferroelectric domain walls in the observed PV effect. The model accounts for the intricate interplay between ferroelectric polarization, space charges, photo-generation, and electronic transport. When applied to bismuth ferrite, results show a significant electric potential step across both 71\u00b0 and 109\u00b0 domain walls, which in turn contributes to the PV effect. The domain-wall-driven PV effect is further shown to be additive in nature, allowing for the possibility of generating the above-bandgap voltage.
\r\n\r\nIn the second part, we present a lattice model incorporating random fields and long-range interactions where a frustrated state emerges at a specific composition, but is suppressed elsewhere. The model is motivated by perovskite solid solutions, and explains the phase diagram in such materials including the morphotropic phase boundary (MPB) that plays a critical role in applications for its enhanced dielectric, piezoelectric, and optical properties. Further, the model also suggests the possibility of entirely new phenomena by exploiting MPBs.
\r\n\r\nThe final part of the thesis focuses on constructing data-driven models from first principles calculations, particularly density functional theory (DFT) for studying crystalline materials. Specifically we propose an approach that exploits machine learning to approximate electronic fields in crystalline solids subjected to deformation. When demonstrated on magnesium---a promising light weight structural material---our model predicts the energy and electronic fields to the level of chemical accuracy, and it even captures lattice instabilities. This DFT-based machine learning approach can be very useful in methods that require repeated DFT calculations of unit cell subjected to strain, especially multi-resolution studies of crystal defects and strain engineering that is emerging as a widely used method for tuning material properties.
" }, { "name": "Teke, Oguzhan", "degree": "PhD", "year": "2021", "title": "Signals on Networks: Random Asynchronous and Multirate Processing, and Uncertainty Principles", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242020-094028488", "creators": [ { "name": { "family": "Teke", "given": "Oguzhan" }, "id": "Teke-Oguzhan", "orcid": "0000-0002-1131-5206", "display_name": "Teke, Oguzhan" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "chair", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/44dx-3g83", "abstract": "The processing of signals defined on graphs has been of interest for many years, and finds applications in a diverse set of fields such as sensor networks, social and economic networks, and biological networks. In graph signal processing applications, signals are not defined as functions on a uniform time-domain grid but they are defined as vectors indexed by the vertices of a graph, where the underlying graph is assumed to model the irregular signal domain. Although analysis of such networked models is not new (it can be traced back to the consensus problem studied more than four decades ago), such models are studied recently from the view-point of signal processing, in which the analysis is based on the \"graph operator\" whose eigenvectors serve as a Fourier basis for the graph of interest. With the help of graph Fourier basis, a number of topics from classical signal processing (such as sampling, reconstruction, filtering, etc.) are extended to the case of graphs.
\r\n\r\nThe main contribution of this thesis is to provide new directions in the field of graph signal processing and provide further extensions of topics in classical signal processing. The first part of this thesis focuses on a random and asynchronous variant of \"graph shift,\" i.e., localized communication between neighboring nodes. Since the dynamical behavior of randomized asynchronous updates is very different from standard graph shift (i.e., state-space models), this part of the thesis focuses on the convergence and stability behavior of such random asynchronous recursions. Although non-random variants of asynchronous state recursions (possibly with non-linear updates) are well-studied problems with early results dating back to the late 60's, this thesis considers the convergence (and stability) in the statistical mean-squared sense and presents the precise conditions for the stability by drawing parallels with switching systems. It is also shown that systems exhibit unexpected behavior under randomized asynchronicity: an unstable system (in the synchronous world) may be stabilized simply by the use of randomized asynchronicity. Moreover, randomized asynchronicity may result in a lower total computational complexity in certain parameter settings. The thesis presents applications of the random asynchronous model in the context of graph signal processing including an autonomous clustering of network of agents, and a node-asynchronous communication protocol that implements a given rational filter on the graph.
\r\n\r\nThe second part of the thesis focuses on extensions of the following topics in classical signal processing to the case of graph: multirate processing and filter banks, discrete uncertainty principles, and energy compaction filters for optimal filter design. The thesis also considers an application to the heat diffusion over networks.
\r\n\r\nMultirate systems and filter banks find many applications in signal processing theory and implementations. Despite the possibility of extending 2-channel filter banks to bipartite graphs, this thesis shows that this relation cannot be generalized to M-channel systems on M-partite graphs. As a result, the extension of classical multirate theory to graphs is nontrivial, and such extensions cannot be obtained without certain mathematical restrictions on the graph. The thesis provides the necessary conditions on the graph such that fundamental building blocks of multirate processing remain valid in the graph domain. In particular, it is shown that when the underlying graph satisfies a condition called M-block cyclic property, classical multirate theory can be extended to the graphs.
\r\n\r\nThe uncertainty principle is an essential mathematical concept in science and engineering, and uncertainty principles generally state that a signal cannot have an arbitrarily \"short\" description in the original basis and in the Fourier basis simultaneously. Based on the fact that graph signal processing proposes two different bases (i.e., vertex and the graph Fourier domains) to represent graph signals, this thesis shows that the total number of nonzero elements of a graph signal and its representation in the graph Fourier domain is lower bounded by a quantity depending on the underlying graph. The thesis also presents the necessary and sufficient condition for the existence of 2-sparse and 3-sparse eigenvectors of a connected graph. When such eigenvectors exist, the uncertainty bound is very low, tight, and independent of the global structure of the graph.
\r\n\r\nThe thesis also considers the classical spectral concentration problem. In the context of polynomial graph filters, the problem reduces to the polynomial concentration problem studied more generally by Slepian in the 70's. The thesis studies the asymptotic behavior of the optimal solution in the case of narrow bandwidth. Different examples of graphs are also compared in order to show that the maximum energy compaction and the optimal filter depends heavily on the graph spectrum.
\r\n\r\nIn the last part, the thesis considers the estimation of the starting time of a heat diffusion process from its noisy measurements when there is a single point source located on a known vertex of a graph with unknown starting time. In particular, the Cram\u00e9r-Rao lower bound for the estimation problem is derived, and it is shown that for graphs with higher connectivity the problem has a larger lower bound making the estimation problem more difficult.
" }, { "name": "Toedtli, Simon Silvio", "degree": "PhD", "year": "2021", "title": "Control of Wall-Bounded Turbulence Through Closed-Loop Wall Transpiration", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272021-055610816", "creators": [ { "name": { "family": "Toedtli", "given": "Simon Silvio" }, "id": "Toedtli-Simon-Silvio", "orcid": "0000-0001-9371-9572", "display_name": "Toedtli, Simon Silvio" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Hutchins", "given": "Nicholas" }, "id": "Hutchins-Nicholas", "role": "member", "display_name": "Hutchins, Nicholas" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/me3y-te05", "abstract": "Many wall-bounded flows of practical relevance are turbulent, including the flows past airplanes and ships. The turbulent motions enhance momentum mixing and, as a result, the drag force on the engineering surface increases, for transportation vessels typically by at least a factor of two compared to laminar flow. Turbulent flow control aimed at drag reduction therefore has the potential to deliver enormous energetic and economic savings, but many challenges remain despite active research for well over a century. The present thesis aims to contribute towards two open questions of the field: first, what are suitable controller design tools for high Reynolds number flows? And second, how does actuation through closed-loop wall transpiration change the flow physics? We investigate aspects of these questions through direct numerical simulation (DNS) and modal analyses of an example control scheme, which is applied to a low Reynolds number turbulent channel flow. The controller is a generalization of the opposition control scheme, and introduces a phase shift between the Fourier transformed sensor measurement and actuator response.
\r\n\r\nThe first part of the thesis demonstrates that a low-order model based on the resolvent framework is able to approximate the drag reduction results of DNS over the entire parameter space considered. The model is about two orders of magnitude cheaper to evaluate than DNS at low Reynolds numbers, and we present a strategy based on subsampling of the wave number space and analytical scaling laws that enables model-based flow control design at technologically relevant Reynolds numbers. The second part of the thesis shows that the physics of the controlled flow can be understood from two distinct families of spatial scales, termed streamwise-elongated and spanwise-elongated scales, respectively. Wall transpiration with streamwise-elongated scales attenuates or amplifies the near-wall cycle and therefore leads to drag reduction or increase, depending on the phase shift. In contrast, wall transpiration with spanwise-elongated scales only leads to drag increase, which occurs at positive phase shifts and is due to the appearance of spanwise rollers which largely enhance momentum mixing. Both patterns are robust features of flows with closed-loop wall transpiration, and the present study offers a simple explanation of their origin in terms of phase relations at distinct spatial scales. The findings of this study may set the stage for a unifying framework for various forms of wall transpiration, and implications for future flow control design are discussed.
" }, { "name": "Wang, Heming", "degree": "PhD", "year": "2021", "title": "Kerr Solitons and Brillouin Lasers in Optical Microresonators", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282021-193431717", "creators": [ { "name": { "family": "Wang", "given": "Heming" }, "id": "Wang-Heming", "orcid": "0000-0003-3861-0624", "display_name": "Wang, Heming" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/g1kf-5t57", "abstract": "Optical resonators are capable of storing electromagnetic energies in the visible and infrared band. The light intensity is greatly enhanced within the resonator, which makes them suitable as a platform for nonlinear optics studies. Here, using silica microresonators as platforms, we explore the fundamental nonlinear dynamics of light induced by Kerr nonlinearity and Brillouin scattering. The first half of the thesis analyzes optical solitons as a result of Kerr nonlinearity, including its universal scaling, its dynamics in the presence of laser feedback, the analytical properties of its relativistic counterpart, as well as its applications as a wavelength reference. The second half of the thesis focuses on stimulated Brillouin lasers and their linewidth performance, demonstrating new performance levels of the Brillouin laser and two correction factors to its linewidth that have been established for semiconductor lasers.
" }, { "name": "Wu, Di", "degree": "PhD", "year": "2021", "title": "Biomolecular Tools for Noninvasive Imaging and Manipulation of Engineered Cells", "advisor": "Shapiro, Mikhail G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262021-021059637", "creators": [ { "name": { "family": "Wu", "given": "Di" }, "id": "Wu-Di", "orcid": "0000-0002-6848-668X", "display_name": "Wu, Di" } ], "advisors": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "advisor", "display_name": "Shapiro, Mikhail G." } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." } ], "option_major": [ "medeng" ], "doi": "10.7907/dt22-nv14", "abstract": "Today\u2019s most advanced tools for imaging and controlling cellular function are based on fluorescent or light-controlled proteins, which have limited utility in large organisms or engineered living materials due to the scattering of photons. Deeply penetrant forms of energy such as magnetic fields and sound waves, while routinely used to monitor and treat diseases on the tissue and organism level, do not process the equivalent set of biomolecular tools for interfacing with biology on the molecular and cellular level. Emerging technologies discussed in this thesis aim to bridge this gap by harnessing biomolecules that have the appropriate physical properties to interact with sound waves or magnetic fields in such a way that enables the visualization and control of specific cells (Chapter 1). We describe two additions to the expanding toolkit for noninvasive imaging and control. In the first case, we show that gas vesicles, a class of hollow protein nanostructures naturally found in aquatic single-cell organisms, can be used as acoustic actuators to enable the control of cellular forces, movement, and patterning using ultrasound (Chapter 2). In the second case, we show that aquaporins, a class of membrane water channels, can be used to alter cellular permeability and serve as genetic reporters for magnetic resonance imaging (Chapter 3). These tools provide critical capabilities for interfacing with cellular function noninvasively and could open the door to applications in various research, biomedical, and industrial settings." }, { "name": "Xiong, Xiaobin", "degree": "PhD", "year": "2021", "title": "Reduced Order Model Inspired Robotic Bipedal Walking: A Step-to-step Dynamics Approximation based Approach", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022021-035141903", "creators": [ { "name": { "family": "Xiong", "given": "Xiaobin" }, "id": "Xiong-Xiaobin", "orcid": "0000-0002-6275-3900", "display_name": "Xiong, Xiaobin" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Sreenath", "given": "Koushil" }, "id": "Sreenath-S", "role": "member", "display_name": "Sreenath, Koushil" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/9bz9-x102", "abstract": "Controlling bipedal robotic walking is a challenging task. The dynamics is hybrid, nonlinear, high-dimensional, and typically underactuated. Complex physical constraints have to be satisfied in the walking generation. The stability in terms of not-falling is also hard to be encoded in the walking synthesis. Canonical approaches for enabling robotic walking typically rely on large-scale trajectory optimizations for generating optimal periodic behaviors on the full-dimensional model of the system; then the stabilities of the controlled behaviors are analyzed through the numerically derived Poincar\u00e9 maps. This full-dimensional periodic behavior based synthesis, despite being theoretically rigorous, suffers from several disadvantages. The trajectory optimization problem is computationally challenging to solve. Non-trivial expert-tuning is required on the cost, constraints, and initial conditions to avoid infeasibilities and local optimality. It is cumbersome for realizing non-periodical behaviors, and the synthesized walking can be sensitive to model uncertainties.
\r\n \r\nIn this thesis, we propose an alternative approach of walking synthesis that is based on reduced order modeling and dynamics approximation. We formulate a discrete step-to-step (S2S) dynamics of walking, where the step size is treated as the control input to stabilize the pre-impact horizontal center of mass (COM) state of the robot. Stepping planning thus is converted into a feedback control problem. To effectively and efficiently solve this feedback stepping planning problem, an underactuated Hybrid Linear Inverted Pendulum (H-LIP) model is proposed to approximate the dynamics of underactuated bipedal walking; the linear S2S dynamics of the H-LIP then approximates the robot S2S dynamics. The H-LIP based stepping controller is hence utilized to plan the desired step sizes on the robot to control its pre-impact horizontal COM state. Stable walking behaviors are consequently generating by realizing the desired step size in the output construction and stabilizing the output via optimization-based controllers. We evaluate this approach successfully on several bipedal walking systems with an increase in the system complexity: a planar five-linkage walker AMBER, an actuated version of the Spring Loaded Inverted Pendulum (aSLIP) in both 2D and 3D, and finally the 3D underactuated robot Cassie. The generated dynamic walking behaviors on these systems are shown to be highly versatile and robust. Furthermore, we show that this approach can be effectively extended to realizing more complex walking tasks such as global trajectory tracking and walking on rough terrain.
" }, { "name": "Xu, Jian", "degree": "PhD", "year": "2021", "title": "Optical Light Manipulation and Imaging Through Scattering Media", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:09092020-162015646", "creators": [ { "name": { "family": "Xu", "given": "Jian" }, "id": "Xu-Jian", "orcid": "0000-0002-4743-2471", "display_name": "Xu, Jian" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "orcid": "0000-0002-9730-9463", "role": "member", "display_name": "Chen, Yanbei" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4hkq-dz43", "abstract": "Typical optical systems are designed to be implemented in free space or clean media. However, the presence of optical scattering media scrambles light waves and becomes a problem in light field control, optical imaging, and sensing.
\r\n\r\nTo address the problem caused by optical scattering media, we discuss two types of solutions in this thesis. One type of solution is active control, where active modulators are used to modulate the light wave to compensate the wave distortion caused by optical scattering. The other type of solution is computational optics, where physical and mathematical models are built to computationally reconstruct the information from the measured distorted wavefront.
\r\n\r\nIn the part of active control, we first demonstrate coherent light focusing through scattering media by transmission matrix inversion. The transmission matrix inversion approach can realize coherent light control through scattering media with higher fidelity compared to conventional transmission matrix approaches. Then, by combining the pre-designed scattering metasurface with wavefront shaping, we demonstrate a beam steering system with large angular and high angular resolution. Next, we present optical-channel-based intensity streaming (OCIS), which uses only intensity information of light fields to realize light control through scattering media. This solution can be used to control spatially incoherent light propagating through scattering media. In the part of computational optics, we first demonstrate the idea of interferometric speckle visibility spectroscopy (ISVS) to measure the information cerebral blood flow. In ISVS, a camera records the speckle frames of diffused light from the human subject interferometrically, and the speckle statistics is used to calculate the speckle decorrelation time and consequently the blood flow index. Then, we compare the two methods of decorrelation time measurements - temporal sampling methods and spatial ensemble methods - and derive unified mathematical expressions for them in terms of measurement accuracy. Based on current technology of camera sensors and single detectors, our results indicate that spatial ensemble methods can have higher decorrelation time measurement accuracy compared to commonly used temporal sampling methods.
" }, { "name": "Ye, Erika", "degree": "PhD", "year": "2021", "title": "Reducing Computational Costs for Many-Body Physics Problems", "advisor": "Chan, Garnet K.; Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112021-235754667", "creators": [ { "name": { "family": "Ye", "given": "Erika" }, "id": "Ye-Erika", "orcid": "0000-0001-9694-568X", "display_name": "Ye, Erika" } ], "advisors": [ { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-Garnet-K-L", "orcid": "0000-0001-8009-6038", "role": "co-advisor", "display_name": "Chan, Garnet K." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "co-advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Motrunich", "given": "Olexei I." }, "id": "Motrunich-Olexei", "orcid": "0000-0001-8031-0022", "role": "chair", "display_name": "Motrunich, Olexei I." }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-Garnet-K-L", "orcid": "0000-0001-8009-6038", "role": "member", "display_name": "Chan, Garnet K." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/xpvv-ar02", "abstract": "Three different computational physics problems are discussed. The first project is solving the semi-classical Boltzmann transport equation (BTE) to compute the thermal conductivity of 1-D superlattices. We consider various spectral scattering models at each interface. This computation requires the inversion of a matrix whose size scales with the number of points used in the discretization of the Brillouin zone. We use spatial symmetries to reduce the size of data points and make the computation manageable. The other two projects involve quantum systems. Simulating quantum systems can potentially require exponential resources because of the exponential scaling of Hilbert space with system size. However, it has been observed that many physical systems, which typically exhibit locality in space or time, require much fewer resources to accurately simulate within some small error tolerance. The second project in the thesis is a two-step factorization of the electronic structure Hamiltonian that allows for efficient implementation on a quantum computer and also systematic truncation of small contributions. By using truncations that only incur errors below chemical accuracy, one is able to reduce the number of terms in the Hamiltonian from O(N\u2074) to O(N\u00b3), where N is the number of molecular orbitals in the system. The third project is a tensor network algorithm based on the concept of influence functionals (IFs) to compute long-time dynamics of single-site observables. IFs are high-dimensional objects that describe the influence of the bath on the dynamics of the subsystem of interest over all times, and we are interested in their low-rank approximations. We study two numerical models, the spin-boson model and a model of interacting hard-core bosons in a 1D harmonic trap, and find that the IFs can be efficiently computed and represented using tensor network methods. Consistent with physical intuition, the correlations in the IFs appear to decrease with increased bath sizes, suggesting that the low-rank nature of the IF is due to nontrivial cancellations in the bath.
" }, { "name": "Yildiz, Hikmet", "degree": "PhD", "year": "2021", "title": "Linear Codes with Constrained Generator Matrices", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242021-223430388", "creators": [ { "name": { "family": "Yildiz", "given": "Hikmet" }, "id": "Yildiz-Hikmet", "orcid": "0000-0002-0891-3352", "display_name": "Yildiz, Hikmet" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "orcid": "0000-0002-2406-7440", "role": "chair", "display_name": "Kostina, Victoria" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" } ], "option_major": [ "eleceng" ], "doi": "10.7907/qz6m-wp22", "abstract": "Designing good error correcting codes whose generator matrix has a support constraint, i.e., one for which only certain entries of the generator matrix are allowed to be nonzero, has found many recent applications, including in distributed coding and storage, linear network coding, multiple access networks, and weakly secure data exchange. The dual problem, where the parity check matrix has a support constraint, comes up in the design of locally repairable codes. The central problem here is to design codes with the largest possible minimum distance, subject to the given support constraint on the generator matrix. When the distance metric is the Hamming distance, the codes of interest are Reed-Solomon codes, for which case, the problem was formulated as the \"GM-MDS conjecture.\" In the rank metric case, the same problem can be considered for Gabidulin codes. This thesis provides solutions to these problems and discusses the remaining open problems.
" }, { "name": "Yu, Ke", "degree": "PhD", "year": "2021", "title": "Multi-Resolution Lattice Green's Function Method for High Reynolds Number External Flows", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072021-162542722", "creators": [ { "name": { "family": "Yu", "given": "Ke" }, "id": "Yu-Ke", "orcid": "0000-0003-0157-4471", "display_name": "Yu, Ke" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/wkc8-se35", "abstract": "This work expands the state-of-the-art computational fluid dynamics (CFD) methods for simulating three-dimensional, turbulent, external flows by further developing the immersed boundary (IB) Lattice Green's function (LGF) method. \r\nThe original IB-LGF method applies an exact far-field boundary condition using fundamental solutions on regular Cartesian grids and allows active computational cells to be restricted to vortical flow regions in an adaptive fashion as the flow evolves. The combination of spatial adaptivity and regular Cartesian structure leads to superior efficiency, scalability, and robustness, but necessitates uniform grid spacing. However, the scale separation associated with thin boundary layers and turbulence at higher Reynolds numbers favors a more flexible distribution of elements/cells, which is achieved in this thesis by developing a multi-resolution LGF approach that permits block-wise grid refinement while maintaining the important properties of the original scheme. We further show that the multi-resolution LGF method can be fruitfully combined with the IB method to simulate external flows around complex geometries at high Reynolds numbers. This novel multi-resolution IB-LGF scheme retains good efficiency, parallel scaling as well as robustness (conservation and stability properties). DNS of bluff and streamlined bodies at Reynolds numbers O(104) are conducted and the new multi-resolution scheme is shown to reduce the total number of computational cells up to 99.87%.
\r\n\r\nWe also extended this method to large-eddy simulation (LES) with the stretched-vortex sub-grid-scale model. In validating the LES implementation, we considered an isolated spherical region of turbulence in free space. The initial condition is spherically windowed, isotropic homogeneous incompressible turbulence. We study the spectrum and statistics of the decaying turbulence and compare the results with decaying isotropic turbulence, including cases representing different low wavenumber behavior of the energy spectrum (i.e. k2 versus k4). At late times the turbulent sphere expands with both mean radius and integral scale showing similar time-wise growth exponents. The low wavenumber behavior has little effect on the inertial scales, and we find that decay rates follow Saffman's predictions in both cases, at least until about 400 initial eddy turnover times. The boundary of the spherical region develops intermittency and features ejections of vortex rings. These are shown to occur at the integral scale of the initial turbulence field and are hypothesized to occur due to a local imbalance of impulse on this scale.
" }, { "name": "Zhang, Haolu Jane", "degree": "PhD", "year": "2021", "title": "Microstructure-Enabled Plasticity in Nano-to-Microscale Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02232021-081136982", "creators": [ { "name": { "family": "Zhang", "given": "Haolu Jane" }, "id": "Zhang-Haolu-Jane", "orcid": "0000-0002-2871-5169", "display_name": "Zhang, Haolu Jane" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "James", "given": "Richard D." }, "id": "James-Richard-D", "role": "member", "display_name": "James, Richard D." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/0zvc-tc14", "abstract": "Microstructure-governed damage resistance in materials enables a variety of functional applications, such as durable biomedical implants and robust product packaging. For example, the refined phase compatibility qualifies NiTi for artery stents, while carbon fiber reinforced polymers improve structural strength in aerospace engineering. As the overall size of industrial applications continue to decrease, it has become increasingly apparent that when a material's external structural size and internal microstructural size become comparable, its mechanical behavior starts to deviate from that of bulk, such as the smaller-is-stronger size-effect in metals. This elucidation necessitates the characterization of materials at lengthscales relevant to their internal microstructure to guarantee accuracy in the design of real-world applications.
\r\n\r\nThis thesis aims at deciphering the microstructure-mechanics relationship for materials at lengthscales bridging the gap between 1nm and 1\u00b5m, with shape memory ceramics, scorpion shells, and jellyfish biogel as sample systems. We use electron and x-ray diffraction to characterize microstructures such as twinning, defects, and fiber organization, while revealing strength, toughness, and other deformation mechanisms through in-situ nanomechanical experiments. We show improved shape recovery in an otherwise brittle ceramic by tuning its phase compatibility at the nanoscale and reveal unprecedented smaller-is-stronger size-dependence for its twinning-induced plasticity. We then unveil competing fiber orientations in Scorpion shells that follow fiber-mechanics principles and demonstrate a combined poroelasticity/viscoelasticity constitutive relation in jellyfish that explains their self-healing behavior. The correlation between microstructure and mechanical behavior unveils unique damage mitigation and energy dissipation techniques in both brittle ceramics and natural biomaterials at each order of lengthscale, paving the road to designing macroscopic materials with hierarchical mechanical behavior and improved plasticity.
" }, { "name": "Zhang, Zhewei", "degree": "PhD", "year": "2021", "title": "Hybrid Si/III-V Lasers for Next-generation Coherent Optical Communication", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:02222021-054057067", "creators": [ { "name": { "family": "Zhang", "given": "Zhewei" }, "id": "Zhang-Zhewei", "orcid": "0000-0002-1211-7957", "display_name": "Zhang, Zhewei" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/y85t-nj39", "abstract": "The most important application of semiconductor lasers is, without doubt, optical communication, the backbone of the information age. In the past few decades, incoherent optical communication with conventional semiconductor lasers, the III-V distributed feedback (DFB) lasers, has successfully fulfilled the global demand for the data rate. However, in order to support the rapidly growing Internet traffic of the 21st century, the transition from incoherent to coherent optical communication is inevitable, requiring new types of lasers, as the conventional III-V DFB lasers lack the phase coherence needed to serve as the light sources in coherent optical communication. The existent alternatives with high phase coherence are external cavity lasers (ECLs) and fiber lasers, whose high price and bulky size effectively thwart the upgrade of the current communication networks. This is the main motivation for us to develop high-coherence semiconductor lasers.
\r\n\r\nTo achieve the goal, we shall rethink and redesign semiconductor lasers. Advanced modern fabrication technology helps us to turn bold ideas into reality. Not only do we build semiconductor lasers on hybrid platforms, but also engineer elaborately the optical mode to enhance the lasers\u2019 phase coherence. The newly developed semiconductor lasers, hybrid Si/III-V lasers, are the core of the entire thesis. Their design principles, fabrication process, properties and performance in the coherent optical communication system will be presented and discussed. The experimental results show the Si/III-V lasers' superiority to their conventional counterparts.
\r\n\r\nAside from possessing high phase coherence, the Si/III-V lasers have great potential to be the light sources on the integrated photonic platforms. The fundamental obstacle thwarting photonic integration is optical feedback, to which the conventional semiconductor lasers are very sensitive. Without the protection provided by optical isolators, which unfortunately cannot be fabricated on chip, the performance of the conventional III-V DFB lasers could get significantly degraded by optical feedback. The Si/III-V lasers, with their built-in high-Q resonators, are very robust against optical feedback and can function properly in the isolator-free coherent optical communication systems. Thus, the cost of future optical networks can be further reduced by monolithically integrating passive photonic devices such as modulators and demodulators with the Si/III-V lasers.
\r\n\r\nFinally, all the studies centered on laser coherence trigger us to think deeply about the underlying relation between different means of characterizing laser coherence. A rigorous mathematical relation, the Central Relation, has been derived here, which not only unveils the fundamental relation between laser lineshape and frequency noise power spectral density (PSD) but also provides new methods of frequency noise controlling like optical filtering.
" }, { "name": "Abbasi, Ehsan", "degree": "PhD", "year": "2020", "title": "Universality Laws and Performance Analysis of the Generalized Linear Models", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092020-005908250", "creators": [ { "name": { "family": "Abbasi", "given": "Ehsan" }, "id": "Abbasi-Ehsan", "orcid": "0000-0002-0185-7933", "display_name": "Abbasi, Ehsan" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" } ], "option_major": [ "eleceng" ], "doi": "10.7907/873c-ej41", "abstract": "In the past couple of decades, non-smooth convex optimization has emerged as a powerful tool for the recovery of structured signals (sparse, low rank, etc.) from noisy linear or non-linear measurements in a variety of applications in genomics, signal processing, wireless communications, machine learning, etc.. Taking advantage of the particular structure of the unknown signal of interest is critical since in most of these applications, the dimension p of the signal to be estimated is comparable, or even larger than the number of observations n. With the advent of Compressive Sensing there has been a very large number of theoretical results that study the estimation performance of non-smooth convex optimization in such a high-dimensional setting.
\r\n\r\nA popular approach for estimating an unknown signal \u03b2\u2080 \u03f5 \u211d\u1d56 in a generalized linear model, with observations y = g(X\u03b2\u2080) \u03f5 \u211d\u207f, is via solving the estimator \u03b2̂ = arg min\u03b2 L(y, X\u03b2 + \u03bbf(\u03b2). Here, L(\u2022,\u2022) is a loss function which is convex with respect to its second argument, and f(\u2022) is a regularizer that enforces the structure of the unknown \u03b2\u2080. We first analyze the generalization error performance of this estimator, for the case where the entries of X are drawn independently from real standard Gaussian distribution. The precise nature of our analysis permits an accurate performance comparison between different instances of these estimators, and allows to optimally tune the hyperparameters based on the model parameters. We apply our result to some of the most popular cases of generalized linear models, such as M-estimators in linear regression, logistic regression and generalized margin maximizers in binary classification problems, and Poisson regression in count data models. The key ingredient of our proof is the Convex Gaussian Min-max Theorem (CGMT), which is a tight version of the Gaussian comparison inequality proved by Gordon in 1988. Unfortunately, having real iid entries in the features matrix X is crucial in this theorem, and it cannot be naturally extended to other cases.
\r\n\r\nBut for some special cases, we prove some universality properties and indirectly extend these results to more general designs of the features matrix X, where the entries are not necessarily real, independent, or identically distributed. This extension, enables us to analyze problems that CGMT was incapable of, such as models with quadratic measurements, phase-lift in phase retrieval, and data recovery in massive MIMO, and help us settle a few long standing open problems in these areas.
" }, { "name": "Albertson, Theodore Glenn", "degree": "PhD", "year": "2020", "title": "Simulations of Conic Cusp Formation, Growth, and Instability in Electrified Viscous Liquid Metals on Flat and Curved Surfaces", "advisor": "Troian, Sandra M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182020-133853408", "creators": [ { "name": { "family": "Albertson", "given": "Theodore Glenn" }, "id": "Albertson-Theodore-Glenn", "display_name": "Albertson, Theodore Glenn" } ], "advisors": [ { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "advisor", "display_name": "Troian, Sandra M." } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Marrese-Reading", "given": "Colleen M." }, "id": "Marrese-Reading-Colleen-M", "role": "member", "display_name": "Marrese-Reading, Colleen M." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "orcid": "0000-0002-1225-4695", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/thhf-5478", "abstract": "It is well known that above a critical field strength sufficiently large to overcome damping by capillary forces, the free surface of a perfectly conducting liquid will spontaneously deform into one or more sharp protrusions known as conic cusps. Such cusps undergo tip sharpening while rapidly accelerating toward regions of highest electric field strength, eventually giving rise to beams of ions and/or charged droplets . These charged beams form the basis for liquid metal ion sources (LMIS) commonly used in focused ion beam systems, scanning ion microscopy, micromilling, ion mass spectrometry, implantation, and lithography. During the past few decades, there has been growing interest in optimizing the formation, growth, and stability of conic cusps in liquid metals for a new class of efficient and highly miniaturizable satellite micropropulsion devices consisting of microarrays of externally wetted solid needles coated with a film of liquid metal propellant. The thrust levels generated by such microarrays is suitable for propulsion of small satellites and precision pointing maneuvers for larger satellites.
\r\n\r\nThis thesis addresses the formation, growth, and instability of conic cusp formations in perfectly conducting, electrified viscous liquids on flat and curved surfaces. We use finite element simulations based on the arbitrary Lagrangian-Eulerian (ALE) method for coupling the vacuum and liquid domains across the accelerating interface. The simulations in Chapters 2\u20134 describe the evolution of liquid flow subject to electric field distributions generated by opposing flat parallel and solid electrodes. In particular, we examine in Chapter 2 the growth of a small liquid protuberance on an otherwise flat viscous liquid layer of perfectly conducting fluid subject to an initial uniform electric field. Previous studies in the literature have established that tip sharpening proceeds via a self-similar process in two distinct limits: the Stokes regime at Re = 0 and the inviscid regime Re \u2192 \u221e. These simulations, conducted at fixed capillary number Ca and for 0.1 \u2264 Re \u2264 50,000, which span the viscous to inviscid regimes, demonstrate that the conic tip always undergoes self-similar growth irrespective of Reynolds number. Field self-enhancement due to conic cusp tip sharpening is shown to generate divergent power law growth in finite time (so-called blowup behavior) of the interfacial and volumetric forces acting at the advancing tip. The computed blow up exponents at the tip surface associated with the various terms in the Navier-Stokes equation and interface normal stress condition reveal the different forces at play as Re increases. Rescaling of the tip shape by the capillary stress exponent yields excellent collapse onto a universal conic tip shape with interior half-angle dependent on the magnitude of the Maxwell stress. The simulations clearly show that the interior cone angle adopts values both above and below the Taylor cone angle value of 49.3\u00b0. Additional details of the modeled flow dispel prevailing misconceptions that dynamic cones resemble conventional Taylor cones or that viscous stresses at finite Re can be neglected. In Chapter 3, we demonstrate how the rapid acceleration of the curved liquid interface also generates a thin surface boundary layer with very high local strain rate in the vicinity of the conic tip. The value of the surface vorticity along the moving interface is shown to be in excellent agreement with theoretical predictions. More importantly, the results in Chapters 2 and 3 demonstrate that the velocity streamlines are always at an oblique angle to the moving interface, contrary to commonly held belief that the streamlines always lie tangent to the moving boundary. In Chapter 4, we extend the simulations to include variation of the capillary number and find that for sufficiently high Re and Ca, the advancing interface develops significant oscillations. Fourier analysis of these interface oscillations indicates that the extracted instability wavelength characteristic of flows at smaller values of Re tends to exceed the simplified theoretical prediction based on inviscid flow. By contrast, the extracted instability wavelength for the largest values of Re examined tends to fall below the inviscid prediction.
\r\n\r\nIn Chapter 5, we explore the effect of substrate curvature on the flow and stability of electrified films by examining the behavior of a thin viscous film of perfectly conducting liquid on two types of curved surfaces. These shapes, which include a solid conical needle with a spherical cap tip and a solid parabolic needle, are intended to mimic substrates used in some externally wetted microemitter arrays in LMIS systems. For the simulations in Chapter 5, the needle is situated below a counter electrode perforated with a circular aperture. The films are shown to develop both on-axis and off-axis cusp-like protrusions depending on the parameter range examined. In particular, the formation of off-axis protrusions are directly traced to substrate shapes which manifest an abrupt change in curvature, as present in a solid conical needle with a spherical cap tip. The simulations reported here are anticipated to help optimize fabrication of externally wetted needle shapes for use in a variety of LMIS systems.
" }, { "name": "Allmaras, Jason Paul", "degree": "PhD", "year": "2020", "title": "Modeling and Development of Superconducting Nanowire Single-Photon Detectors", "advisor": "Schwab, Keith C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312020-201105584", "creators": [ { "name": { "family": "Allmaras", "given": "Jason Paul" }, "id": "Allmaras-Jason-Paul", "orcid": "0000-0001-9621-289X", "display_name": "Allmaras, Jason Paul" } ], "advisors": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "advisor", "display_name": "Schwab, Keith C." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Shaw", "given": "Matthew D." }, "id": "Shaw-M-D", "role": "member", "display_name": "Shaw, Matthew D." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/wgak-vs11", "abstract": "Superconducting nanowire single-photon detectors (SNSPDs) have demonstrated remarkable efficiency, timing resolution, and intrinsic dark count rate properties, but the SNSPD community currently lacks a comprehensive model of the single-photon detection process. In this work, we conduct a detailed examination of the current detection mechanism models and compare their predictions to new experimental measurements of the intrinsic timing properties and polarization dependence of specialized NbN test devices. First, we consider the energy downconversion cascade using the kinetic equations to describe the non-equilibrium electron and phonon systems immediately following photon absorption. These calculations provide estimates for the energy loss and fluctuations during this process, and provide qualitative information about the way energy is partitioned between the electron and phonon systems. To study the suppression of superconductivity following downconversion, we apply the most advanced existing model, that of Vodolazov (2017), but find it inadequate to quantitatively describe the timing properties of these detectors. By extending the model to use the generalized time-dependent Ginzburg-Landau equations, we achieve better quantitative agreement with experiment. However, the generalized model still provides only a qualitative picture of the detection process.
\r\n\r\nWe also conduct an experimental examination of the heat transfer process in WSi nanowires by examining the nanowire reset dynamics, steady-state dissipation, and crosstalk between elements of an array. The results are compared to existing electrothermal models, but these models fail to adequately describe the dynamics of the system. A generalized form of the electrothermal model provides better fitting to experiment, but incorporation of non-equilibrium effects is likely needed to provide a fully quantitative description of the system. These results are directly connected to some of the thermal challenges of SNSPD array development. Informed by the crosstalk results, we demonstrate a new multiplexing technique based on thermal coupling between two active nanowire layers, known as the thermal row-column. This method promises to enable kilopixel to megapixel scale imaging arrays for low photon-flux applications. Finally, we discuss the design and characterization of the ground detector for the Deep Space Optical Communication (DSOC) demonstration mission.
" }, { "name": "Arora, Harpreet Singh", "degree": "PhD", "year": "2020", "title": "Superconductivity in Graphene Hetero-Structures: From Fundamental Physics to Functional Devices", "advisor": "Nadj-Perge, Stevan", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052020-175219708", "creators": [ { "name": { "family": "Arora", "given": "Harpreet Singh" }, "id": "Arora-Harpreet-Singh", "orcid": "0000-0002-7674-735X", "display_name": "Arora, Harpreet Singh" } ], "advisors": [ { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "advisor", "display_name": "Nadj-Perge, Stevan" } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Rosenbaum", "given": "Thomas F." }, "id": "Rosenbaum-T-F", "orcid": "0009-0008-6152-666X", "role": "member", "display_name": "Rosenbaum, Thomas F." }, { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "member", "display_name": "Hsieh, David" }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/nc05-gr15", "abstract": "While graphene has been dubbed as a \"wonder material\" because of its amazing characteristics, such as the ability to conduct electricity better than copper and being two hundred times stronger than steel, until recently, the key quantum phenomenon of superconductivity was missing from the list of properties exhibited by graphene. In 2018, an astonishing discovery showed that by placing two sheets of graphene on top of each other in a structure known as Twisted Bilayer Graphene, it is possible to realize superconductivity when the rotation angle between the sheets is close to the \"Magic Angle\" value of 1.1\u00b0. More surprisingly, superconductivity in the initial reports was observed in close proximity to insulating states - resembling the phase diagram of High Tc superconductors. This sparked a fierce debate about its origin and its possible relation to High Tc superconductors. In this thesis, we show that by carefully engineering the dielectric environment of TBG, it is possible to stabilize superconductivity in non-magic angle TBG devices without the presence of any insulating states. This discovery imposes severe constraints on the origin of superconductivity in TBG. We also report, for the first time, the successful induction of spin-orbit coupling in TBG and discuss its implications.
\r\n\r\nSuperconductivity can also be induced into graphene via coupling to conventional superconductors, and the strength of the induced supercurrent depends strongly on temperature. We employ this thermal dependence by integrating graphene into superconducting circuits that serves two purposes a) to investigate graphene's thermal behavior at milliKelvin temperatures and b) to utilize its extremely low heat capacity in making functional devices that have the potential to achieve ultra-high thermal sensitivity.
" }, { "name": "Bedrossian, Manuel M.", "degree": "PhD", "year": "2020", "title": "A Novel Digital Holographic Microscope (DHM) to Investigate and Characterize Microbial Motility in Extreme Aquatic Environments", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:04272020-152058259", "creators": [ { "name": { "family": "Bedrossian", "given": "Manuel M." }, "id": "Bedrossian-Manuel-M", "orcid": "0000-0003-2524-3765", "display_name": "Bedrossian, Manuel M." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "chair", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Ismagilov", "given": "Rustem F." }, "id": "Ismagilov-R-F", "orcid": "0000-0002-3680-4399", "role": "member", "display_name": "Ismagilov, Rustem F." }, { "name": { "family": "Nadeau", "given": "Jay L." }, "id": "Nadeau-Jay-L", "orcid": "0000-0001-5258-0076", "role": "member", "display_name": "Nadeau, Jay L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "medeng" ], "doi": "10.7907/m3a3-4610", "abstract": "Recent shifts in the astrobiological community have prompted the development of methods for the direct search for extant life within our solar system. In order to look for life elsewhere in our solar system, it is important to also investigate the broad spectrum of extant life on Earth. Over millions of years of evolution, life has continually adapted such that an 'extreme' environment has become a relative term. What is considered extreme for one type of organism is home to another and vice versa. Furthermore, very little is known about the organisms that inhabit these extreme environments, and even less in known about their in situ behavior. Investigating various extreme environments around Earth in order to understand the in situ behavior of organisms that inhabit it will better inform the astrobiological community when planning future space missions for the direct search for extant life within our solar system. However, no suitable instrument exists to conduct these in situ field campaigns, while also being physically robust enough to withstand the rugged terrains that can be expected from extreme environments.
\r\n\r\nThis thesis describes the development of a novel off-axis digital holographic microscope (DHM) for the direct in situ observation of microscale organisms in extreme aquatic environments. The hardware developments of this instrument are introduced and validated experimentally as well as software developments including autonomous particle detection and tracking algorithms. This instrument is then used in novel laboratory experiments involving the development of optical phase contrast agents, as well as deployed to multiple field campaigns where off-axis DHM is used to observe the in situ behavior of microorgansisms in various extreme aquatic environments around North America.
" }, { "name": "Bowkett, Joseph John Douglas", "degree": "PhD", "year": "2020", "title": "Functional Autonomy Techniques for Manipulation in Uncertain Environments", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082020-104419929", "creators": [ { "name": { "family": "Bowkett", "given": "Joseph John Douglas" }, "id": "Bowkett-Joseph-John-Douglas", "orcid": "0000-0002-3101-489X", "display_name": "Bowkett, Joseph John Douglas" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "chair", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Backes", "given": "Paul G." }, "id": "Backes-Paul-G", "role": "member", "display_name": "Backes, Paul G." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/0kgt-yg76", "abstract": "As robotic platforms are put to work in an ever more diverse array of environments, their ability to deploy visuomotor capabilities without supervision is complicated by the potential for unforeseen operating conditions. This is a particular challenge within the domain of manipulation, where significant geometric, semantic, and kinetic understanding across the space of possible manipulands is necessary to allow effective interaction. To facilitate adoption of robotic platforms in such environments, this work investigates the application of functional, or behavior level, autonomy to the task of manipulation in uncertain environments. Three functional autonomy techniques are presented to address subproblems within the domain.
\r\n\r\nThe task of reactive selection between a set of actions that incur a probabilistic cost to advance the same goal metric in the presence of an operator action preference is formulated as the Obedient Multi-Armed Bandit (OMAB) problem, under the purview of Reinforcement Learning. A policy for the problem is presented and evaluated against a novel performance metric, disappointment (analogous to prototypical MAB's regret), in comparison to adaptations of existing MAB policies. This is posed for both stationary and non-stationary cost distributions, within the context of two example planetary exploration applications of multi-modal mobility, and surface excavation.
\r\n\r\nSecond, a computational model that derives semantic meaning from the outcome of manipulation tasks is developed, which leverages physics simulation and clustering to learn symbolic failure modes. A deep network extracts visual signatures for each mode that may then guide failure recovery. The model is demonstrated through application to the archetypal manipulation task of placing objects into a container, as well as stacking of cuboids, and evaluated against both synthetic verification sets and real depth images.
\r\n\r\nThird, an approach is presented for visual estimation of the minimum magnitude grasping wrench necessary to extract massive objects from an unstructured pile, subject to a given end effector's grasping limits, that is formulated for each object as a \"wrench space stiction manifold\". Properties are estimated from segmented RGBD point clouds, and a geometric adjacency graph used to infer incident wrenches upon each object, allowing candidate extraction object/force-vector pairs to be selected from the pile that are likely to be within the system's capability.
" }, { "name": "Brodnik, Neal Ryan", "degree": "PhD", "year": "2020", "title": "Fracture and Toughening of Brittle Structures with Designed Anisotropy", "advisor": "Faber, Katherine T.; Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:11122019-171331857", "creators": [ { "name": { "family": "Brodnik", "given": "Neal Ryan" }, "id": "Brodnik-Neal-Ryan", "orcid": "0000-0002-4426-5997", "display_name": "Brodnik, Neal Ryan" } ], "advisors": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "advisor", "display_name": "Faber, Katherine T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "co-advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/ET0C-MK61", "abstract": "Despite good thermal and chemical properties, the use of ceramic materials in structural applications is limited by their inherently brittle nature. Efforts have been made to improve the toughness of ceramics through composite design, but recent developments in net shape processing such as additive manufacturing have significantly expanded this design space. Where composite topologies and morphologies were previously limited by material composition and thermodynamics, tools like 3D printing now allow for the design of composite structures of nearly any shape or arrangement.
\r\n\r\nThis work seeks to understand how these processing advances might be utilized to improve the toughness of brittle composites by exploring how previously inaccessible anisotropic inclusion structures might influence fracture behavior. The study begins with the evaluation of printed photopolymer structures as model brittle materials. First, printed structures are used to explore how elastic contrast between inclusions and matrix can affect crack propagation and improve toughness. Here, anisotropy presents an opportunity to achieve similar toughness to isotropic structures at smaller volume fractions by virtue of topologies that only exhibit toughening only in a singular direction, but require significantly less material to do so. Next, the effect of anisotropic voids is explored as a means of controlling crack nucleation and growth. With consideration of both compliance and directional propagation, a \"fracture diode\" that exhibits controlled, predictable fracture 100% of the time can be realized.
\r\n\r\nAfter exploring brittle polymers, ceramics systems with similar toughness and higher stiffness are considered. First, a model layered system of mica is explored, where wedge splitting can be used achieve stable crack growth. This allows for the evaluation of how changes in compliance can improve the interlayer toughness without directly interacting with the crack. Finally, this study extends further into ceramics by exploring silicon oxycarbide (SiOC) truss structures and truss elements produced from 3D printed preceramic polymers. In addition to considering the material itself, changes in truss structure are explored as a means of changing deformation mode, and by consequence, failure strength. These model experiments suggest that if trusses are compatible, they can be interchanged to control failure of the bulk structure.
\r\n\r\nThis study demonstrates how designed heterogeneities with anisotropic structure can be used to both enhance the toughness of brittle composites as well achieve a greater degree of control over both crack nucleation and propagation in brittle systems where predicting failure is otherwise difficult. Looking forward, new processing tools like additive manufacturing present major opportunities for expanding the design space of brittle composites to achieve higher toughness and better fracture control than previously available. These new techniques may be able to expand the mechanical viability of ceramics, and make them better suited to mechanically demanding applications in the future.
" }, { "name": "Candogan, Utkan Onur", "degree": "PhD", "year": "2020", "title": "Convex Relaxations for Graph and Inverse Eigenvalue Problems", "advisor": "Chandrasekaran, Venkat", "url": "https://resolver.caltech.edu/CaltechTHESIS:01152020-210801253", "creators": [ { "name": { "family": "Candogan", "given": "Utkan Onur" }, "id": "Candogan-Utkan-Onur", "orcid": "0000-0002-1416-4909", "display_name": "Candogan, Utkan Onur" } ], "advisors": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "advisor", "display_name": "Chandrasekaran, Venkat" } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZV0D-SW58", "abstract": "This thesis is concerned with presenting convex optimization based tractable solutions for three fundamental problems:
\r\n\r\n1. Planted subgraph problem: Given two graphs, identifying the subset of vertices of the larger graph corresponding to the smaller one.
\r\n\r\n2. Graph edit distance problem: Given two graphs, calculating the number of edge/vertex additions and deletions required to transform one graph into the other.
\r\n\r\n3. Affine inverse eigenvalue problem: Given a subspace \u03b5 \u2282 𝕊\u207f and a vector of eigenvalues \u03bb \u2208 \u211d\u207f, finding a symmetric matrix with spectrum \u03bb contained in \u03b5.
\r\n\r\nThese combinatorial and algebraic problems frequently arise in various application domains such as social networks, computational biology, chemoinformatics, and control theory. Nevertheless, exactly solving them in practice is only possible for very small instances due to their complexity. For each of these problems, we introduce convex relaxations which succeed in providing exact or approximate solutions in a computationally tractable manner.
\r\n\r\nOur relaxations for the two graph problems are based on convex graph invariants, which are functions of graphs that do not depend on a particular labeling. One of these convex relaxations, coined the Schur-Horn orbitope, corresponds to the convex hull of all matrices with a given spectrum, and plays a prominent role in this thesis. Specifically, we utilize relaxations based on the Schur-Horn orbitope in the context of the planted subgraph problem and the graph edit distance problem. For both of these problems, we identify conditions under which the Schur-Horn orbitope based relaxations exactly solve the corresponding problem with overwhelming probability. Specifically, we demonstrate that these relaxations turn out to be particularly effective when the underlying graph has a spectrum comprised of few distinct eigenvalues with high multiplicities. In addition to relaxations based on the Schur-Horn orbitope, we also consider outer-approximations based on other convex graph invariants such as the stability number and the maximum-cut value for the graph edit distance problem. On the other hand, for the inverse eigenvalue problem, we investigate two relaxations arising from a sum of squares hierarchy. These relaxations have different approximation qualities, and accordingly induce different computational costs. We utilize our framework to generate solutions for, or certify unsolvability of the underlying inverse eigenvalue problem.
\r\n\r\nWe particularly emphasize the computational aspect of our relaxations throughout this thesis. We corroborate the utility of our methods with various numerical experiments.
" }, { "name": "Cheng, Wen-Hui (Sophia)", "degree": "PhD", "year": "2020", "title": "Towards High Solar to Fuel Efficiency: From Photonic Design, Interface Study, to Device Integration", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282020-183139057", "creators": [ { "name": { "family": "Cheng", "given": "Wen-Hui (Sophia)" }, "id": "Cheng-Wen-Hui-Sophia", "orcid": "0000-0003-3233-4606", "display_name": "Cheng, Wen-Hui (Sophia)" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Houle", "given": "Frances A." }, "id": "Houle-Frances-A", "orcid": "0000-0001-5571-2548", "role": "member", "display_name": "Houle, Frances A." } ], "option_major": [ "matsci" ], "doi": "10.7907/kd6a-xt88", "abstract": "Efficient unassisted solar fuel generation, a pathway to storable renewable energy in the form of chemical bonds, requires optimization of a photoelectrochemical device based on photonic design and interface study. We first focused on enhancing absorption via nanophotonic design of light absorbers. Near-unity, broadband absorption in sparse InP nanowire arrays with multi-radii and tapered nanowire array designs are simulated and experimentally demonstrated. Later, a few strategies are introduced to achieved high solar-to-fuel efficiency.
\r\n\r\nOptically, photoelectrochemical device would require the catalyst ensembles to be highly transparent. We report a record solar-to-hydrogen efficiency by integrating Rh nanoparticle catalysts onto photocathodes with minimal parasitic absorption and reflection losses in the visible range. The other two light management strategies have been developed and experimentally verified to create highly active and effectively transparent catalyst structures: i) arrays of mesophotonic dielectric cone structures that serve as tapered waveguide light couplers to efficiently guide incident light through apertures in an opaque catalyst into the light absorber, and ii) an effectively transparent catalyst consisting of arrays of micron-scale triangular cross-sectional metal grid fingers, which are capable of redirecting the incoming light to the open areas of the PEC cell without shadow loss.
\r\n\r\nThe electronic properties of the surface films exposed to the electrolyte are also critical. The anatase TiO\u2082 protection layer on the photocathode creates a favorable internal band alignment for hydrogen evolution, promoting the transport of the excess electrons and inhibiting voltage drops. The interfacial conduction mechanism between the defected TiO\u2082 and metal catalysts is investigated. A combinatorial approach of electrochemistry, X-ray photoelectron spectroscopy, and resonant X-ray spectroscopy reveals the correlation between the interfacial quasi-metal phase with TiO\u2082 properties. By careful control of gas diffusion electrode assembling to maintain appropriate wetted catalyst interface, another record solar-to-CO efficiency with extended stability can be realized.
" }, { "name": "Cho, Hyunjun", "degree": "PhD", "year": "2020", "title": "Real-Time Biosensing and Energy Harvesting on Human Body", "advisor": "Choo, Hyuck; Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:07252019-145728798", "creators": [ { "name": { "family": "Cho", "given": "Hyunjun" }, "id": "Cho-Hyunjun", "orcid": "0000-0002-8963-5525", "display_name": "Cho, Hyunjun" } ], "advisors": [ { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "orcid": "0000-0002-8903-7939", "role": "advisor", "display_name": "Choo, Hyuck" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "orcid": "0000-0002-8903-7939", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZN7F-ZF71", "abstract": "This thesis covers two technologies that can be applied to the human body for real-time applicable usages: biosensors and energy harvesters. The first part of the thesis describes optical biosensing techniques based on surface-enhanced Raman spectroscopy (SERS). Our large-scale spatially uniform Raman enhancing substrates allow low-level bio molecule detection due to their strong plasmonic enhancement of the 3D Au-NP clusters. This method also enables low-level insulin sensing as well as insulin concentration analysis in islet secretion. These results can lead to developing simple and easy biosensing methods allowing real-time biosensing applications including convenient monitoring of health, early disease detection, and diabetes-related clinical measurements.
\r\n\r\nThe second part of the thesis suggests an energy harvesting method using vocal vibrations. The vocal folds produce mechanical vibrations that can serve as an energy source with consistent amplitude and frequency. The vibration hotspots exist at various locations on the human upper body. The energy harvesting system consisting of piezoelectric devices and energy harvesting circuits generates 3.99 mW of electrical power. The amount of energy generated from vocal vibrations is sufficient to charge a Li-Po battery which can drive an LCD display or charge Bluetooth headphones. This method demonstrating a relatively high power generation and convenience of practical use can provide a real-time complementary charging technique for wearable electronics like wireless headphones and smart glasses as well as medical implantable devices such as deep brain stimulators, cochlear implants and pacemakers.
" }, { "name": "Citrin, Michael Andrew", "degree": "PhD", "year": "2020", "title": "Nanomechanical Properties of Electrodeposited Li and Fabrication of 3D Architected Cathodes for Li-Based Batteries", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12032019-200437699", "creators": [ { "name": { "family": "Citrin", "given": "Michael Andrew" }, "id": "Citrin-Michael-Andrew", "orcid": "0000-0001-8183-5437", "display_name": "Citrin, Michael Andrew" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/YD18-8N08", "abstract": "Advancements in the active materials of Li-based batteries provide a promising route to significantly improve electrochemical performance. Li metal has a 10x increase in gravimetric capacity compared to conventional graphite anodes and can be utilized with a solid electrolyte. However, current solid-state Li metal anode batteries cannot reliably cycle large amounts of Li due to chemical and mechanical degradation at the solid electrolyte / Li interface. One key factor in the failure of solid electrolytes is the dearth of mechanical data on Li at the relevant length scales and microstructures to solid-state batteries. The initial stages of Li formation at the solid electrolyte / Li interface also require further exploration to help improve the performance of solid-state Li batteries.
\r\n\r\nIn the first part of the thesis, we will discuss the methods used to investigate Li electrodeposited in-situ in a scanning electron microscope (SEM) chamber from a thin film solid-state battery. We probed the formation of this Li and found preferential growth at the domain boundaries of the surface of the cell, corroborated by electrochemical simulations. Cryogenic electron microscopy was determined to be the optimal method for examining the microstructure of Li and was utilized to reveal the single crystalline microstructure of Li pillars. Uniaxial compression experiments were performed on single crystalline Li pillars that grew from these batteries. We found that Li pillars with diameters of 360-759 nm first deformed elastically, then yielded and flowed plastically, with an average yield stress of 16.0 \u00b1 6.82 MPa, 24x stronger than bulk polycrystalline Li. The mechanical results are discussed in the framework of dislocation starvation and nucleation, in addition to thermally activated deformation processes.
\r\n\r\nNext generation battery systems may also utilize 3D electrodes to allow for both high energy (large mass loading) and power densities (small diffusion lengths). The last section of the thesis investigates the fabrication of 3D architected LiCoO2 structures and their performance as Li-ion battery cathodes. Using a novel hydrogel photoresin with relevant salt contents, the structures were fabricated using digital light processing and calcination. The electrochemical performance of the architected cathodes was examined and the electrodes exhibited a relatively high areal capacity up to \u223c8 mAh/cm2 and a capacity retention of 82% after 100 cycles.
" }, { "name": "Coladangelo, Andrea Wei", "degree": "PhD", "year": "2020", "title": "Quantum Correlations, Certifying Quantum Devices, and the Quest for Infinite Entanglement", "advisor": "Vidick, Thomas G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01162020-013448014", "creators": [ { "name": { "family": "Coladangelo", "given": "Andrea Wei" }, "id": "Coladangelo-Andrea-Wei", "orcid": "0000-0002-6773-2711", "display_name": "Coladangelo, Andrea Wei" } ], "advisors": [ { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "advisor", "display_name": "Vidick, Thomas G." } ], "committee": [ { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "chair", "display_name": "Preskill, John P." }, { "name": { "family": "Chen", "given": "Xie" }, "id": "Chen-Xie", "orcid": "0000-0003-2215-2497", "role": "member", "display_name": "Chen, Xie" }, { "name": { "family": "Brandao", "given": "Fernando" }, "id": "Brand\u00e3o-F-G-S-L", "orcid": "0000-0003-3866-9378", "role": "member", "display_name": "Brandao, Fernando" }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "member", "display_name": "Vidick, Thomas G." } ], "option_major": [ "cms" ], "doi": "10.7907/VQC0-ZK80", "abstract": "Quantum information has the potential to disrupt the present computational landscape. Much of this potential rests on the existence of efficient quantum algorithms for classically intractable problems and of quantum cryptographic protocols for tasks that are provably impossible to realize classically. At the heart of many quantum advantages is one of the most counterintuitive features of quantum mechanics, known as entanglement. The central motivating question of this thesis is the following: if quantum devices will perform tasks that are beyond the reach of classical devices, can we hope to certify that they are performing these tasks correctly? Bell's theorem, a landmark result in physics, provides a partial answer to this question: it asserts that measurements on spatially isolated, but entangled, particles can result in outcomes that are correlated in a way that cannot be explained by any local hidden variable theory (such as Newtonian physics). A direct operational consequence of this theorem is that one can devise a statistical test to certify the presence of entanglement (and hence of genuine quantumness). Remarkably, nature allows us to take this certification one step further: in some cases, the correlation of measurement outcomes is sufficient to single out a unique quantum setup compatible with this correlation. This phenomenon is often referred to as self-testing, and is the central topic of this thesis.
\r\n\r\nIn the first part of this thesis, we review the basic terminology and results in the theory of self-testing. We then explore a concrete application to the problem of verifiably delegating a quantum computation. Our main technical contribution is a test that robustly certifies products of single-qubit Clifford measurements on many EPR pairs. We employ this test to obtain a protocol which allows a classical user to verifiably delegate her quantum computation to two spatially isolated quantum servers. The overall complexity of our protocol is near-optimal, requiring resources that scale almost linearly in the size of the circuit being delegated.
\r\n\r\nIn the second part of this thesis, the driving question is the following: what is the class of quantum states and measurements that can be certified through self-testing? Does self-testing only apply to a few special cases, like EPR pairs or copies of EPR pairs, or are these instances of a more general phenomenon? One of the main results of this thesis is that we settle this question for the case of bipartite states. We show the existence of a self-testing correlation for any pure bipartite entangled state of any finite local dimension. We then move on to explore the multipartite case, and we show that a significantly larger class of states can be self-tested than was previously known. This includes all multipartite partially entangled GHZ states, and more generally all multipartite qudit states which admit a Schmidt decomposition.
\r\n\r\nIn the final part of this thesis, we explore connections of the theory of self-testing to basic questions about entanglement and quantum correlation sets. In particular, we set out to understand the expressive power of infinite-dimensional quantum systems. We consider two questions: can spatially isolated quantum systems of infinite dimension produce correlations that are unattainable by finite-dimensional systems? Does there exist a correlation that cannot be attained exactly by spatially isolated quantum systems (not even infinite-dimensional ones), but can be approximated arbitrarily well by a sequence of finite or infinite-dimensional systems? The first question was posed by Tsirelson in 1993, and its answer has been elusive. One of the main results of this thesis is a resolution of this question. The second question is better known as the \"non-closure of the set of quantum correlations\", and was answered affirmatively in a breakthrough of Slofstra. We give a new elementary proof of this result which leverages one of our self-testing results and a phenomenon known as embezzlement.
\r\n" }, { "name": "Craiciu, Ioana", "degree": "PhD", "year": "2020", "title": "Quantum Storage of Light Using Nanophotonic Resonators Coupled to Erbium Ion Ensembles", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-134801698", "creators": [ { "name": { "family": "Craiciu", "given": "Ioana" }, "id": "Craiciu-Ioana", "orcid": "0000-0002-8670-0715", "display_name": "Craiciu, Ioana" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "member", "display_name": "Endres, Manuel A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/yn6n-7x40", "abstract": "This thesis presents on-chip quantum storage of telecommunication wavelength light using nanophotonic resonators coupled to erbium ions. Storage of light in an optical quantum memory has applications in quantum information and quantum communication. For example, long distance quantum communication using quantum repeater protocols is enabled by quantum memories. Efficient and broadband quantum memories can be made from resonators coupled to ensembles of atoms. Like other rare earth ions, erbium is appealing for quantum applications due to its long optical and hyperfine coherence times in the solid state at low temperatures. However, erbium is unique among rare earth ions in having an optical transition in the telecommunication C band (1540 nm), making it particularly appealing for quantum communication applications. In this work, we use nano-scale resonators coupled to erbium-167 ions in yttrium orthosilicate crystals (167Er 3+:Y2SiO5).
\r\n\r\nWe demonstrate quantum storage in two types of resonators. In a nanobeam photonic crystal resonator milled directly in 167Er 3+:Y2SiO5, we show storage of weak coherent states using the atomic frequency comb protocol. The storage fidelity for single photon states is estimated to be at least 93.7% ± 2.4% using decoy state analysis, Storage of up to 10 μs and multimode storage are demonstrated. Using a hybrid amorphous silicon 167Er 3+:Y2SiO5 resonator and on-chip electrodes, we demonstrate a multifunctional memory using the atomic frequency comb protocol with DC Stark shift control. In addition dynamic control of memory time, Stark shift control allows modifications to the frequency and bandwidth of stored light. We show tuning of the output pulse by ± 20 MHz relative to the input pulse, and broadening of the pulse bandwidth by more than a factor of three. The storage efficiency in both devices was limited to < 1%.
\r\n\r\nOn the way to these results, we describe 167Er 3+:Y2SiO5 spectroscopy measurements including optical coherence times and hyperfine lifetimes below 1 K, and we estimate the linear DC stark shift along two crystal directions. The design and fabrication of the on-chip resonators is presented. We discuss the limitations to storage time and efficiency, including superhyperfine coupling and resonator parameters, and we outline a path forward for improving the storage efficiency in these types of devices.
" }, { "name": "Cvitkovic, Michael William (Milan0", "degree": "PhD", "year": "2020", "title": "Deep Learning in Unconventional Domains", "advisor": "Vidick, Thomas G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082020-095943405", "creators": [ { "name": { "family": "Cvitkovic", "given": "Michael William (Milan0" }, "id": "Cvitkovic-Michael-William-Milan", "orcid": "0000-0003-4188-452X", "display_name": "Cvitkovic, Michael William (Milan0" } ], "advisors": [ { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "advisor", "display_name": "Vidick, Thomas G." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "member", "display_name": "Vidick, Thomas G." }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" } ], "option_major": [ "cms" ], "doi": "10.7907/v7dm-6r52", "abstract": "Machine learning methods have dramatically improved in recent years thanks to advances in deep learning (LeCun et al., 2015), a set of methods for training high-dimensional, highly-parameterized, nonlinear functions. Yet deep learning progress has been concentrated in the domains of computer vision, vision-based reinforcement learning, and natural language processing. This dissertation is an attempt to extend deep learning into domains where it has thus far had little impact or has never been applied. It presents new deep learning algorithms and state-of-the-art results on tasks in the domains of source-code analysis, relational databases, and tabular data.
" }, { "name": "Dathathri, Sumanth", "degree": "PhD", "year": "2020", "title": "Scalable Synthesis and Verification: Towards Reliable Autonomy", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292020-165136662", "creators": [ { "name": { "family": "Dathathri", "given": "Sumanth" }, "id": "Dathathri-Sumanth", "display_name": "Dathathri, Sumanth" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Gao", "given": "Sicun" }, "id": "Gao-Sicun", "role": "member", "display_name": "Gao, Sicun" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cms" ], "doi": "10.7907/4j39-v857", "abstract": "We have seen the growing deployment of autonomous systems in our daily life, ranging from safety-critical self-driving cars to dialogue agents. While impactful and impressive, these systems do not often come with guarantees and are not rigorously evaluated for failure cases. This is in part due to the limited scalability of tools available for designing correct-by-construction systems, or verifying them posthoc. Another key limitation is the lack of availability of models for the complex environments with which autonomous systems often have to interact with. In the direction of overcoming these above mentioned bottlenecks to designing reliable autonomous systems, this thesis makes contributions along three fronts.
\r\n\r\nFirst, we develop an approach for parallelized synthesis from linear-time temporal logic Specifications corresponding to the generalized reactivity (1) fragment. We begin by identifying a special case corresponding to singleton liveness goals that allows for a decomposition of the synthesis problem, which facilitates parallelized synthesis. Based on the intuition from this special case, we propose a more generalized approach for parallelized synthesis that relies on identifying equicontrollable states.
\r\n\r\nSecond, we consider learning-based approaches to enable verification at scale for complex systems, and for autonomous systems that interact with black-box environments. For the former, we propose a new abstraction refinement procedure based on machine learning to improve the performance of nonlinear constraint solving algorithms on large-scale problems. For the latter, we present a data-driven approach based on chance-constrained optimization that allows for a system to be evaluated for specification conformance without an accurate model of the environment. We demonstrate this approach on several tasks, including a lane-change scenario with real-world driving data.
\r\n\r\nLastly, we consider the problem of interpreting and verifying learning-based components such as neural networks. We introduce a new method based on Craig's interpolants for computing compact symbolic abstractions of pre-images for neural networks. Our approach relies on iteratively computing approximations that provably overapproximate and underapproximate the pre-images at all layers. Further, building on existing work for training neural networks for verifiability in the classification setting, we propose extensions that allow us to generalize the approach to more general architectures and temporal specifications.
" }, { "name": "Douik, Ahmed", "degree": "PhD", "year": "2020", "title": "Riemannian Optimization for Convex and Non-Convex Signal Processing and Machine Learning Applications", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-120425051", "creators": [ { "name": { "family": "Douik", "given": "Ahmed" }, "id": "Douik-Ahmed", "orcid": "0000-0001-7791-9443", "display_name": "Douik, Ahmed" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" } ], "option_major": [ "eleceng" ], "doi": "10.7907/jt3c-0m30", "abstract": "The performance of most algorithms for signal processing and machine learning applications highly depends on the underlying optimization algorithms. Multiple techniques have been proposed for solving convex and non-convex problems such as interior-point methods and semidefinite programming. However, it is well known that these algorithms are not ideally suited for large-scale optimization with a high number of variables and/or constraints. This thesis exploits a novel optimization method, known as Riemannian optimization, for efficiently solving convex and non-convex problems with signal processing and machine learning applications. Unlike most optimization techniques whose complexities increase with the number of constraints, Riemannian methods smartly exploit the structure of the search space, a.k.a., the set of feasible solutions, to reduce the embedded dimension and efficiently solve optimization problems in a reasonable time. However, such efficiency comes at the expense of universality as the geometry of each manifold needs to be investigated individually. This thesis explains the steps of designing first and second-order Riemannian optimization methods for smooth matrix manifolds through the study and design of optimization algorithms for various applications. In particular, the paper is interested in contemporary applications in signal processing and machine learning, such as community detection, graph-based clustering, phase retrieval, and indoor and outdoor location determination. Simulation results are provided to attest to the efficiency of the proposed methods against popular generic and specialized solvers for each of the above applications." }, { "name": "Fang, Michael Tianyu", "degree": "PhD", "year": "2020", "title": "Suspended Trace Air-Gap Resonators for Low Loss Superconducting Circuits", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312020-215457608", "creators": [ { "name": { "family": "Fang", "given": "Michael Tianyu" }, "id": "Fang-Michael-Tianyu", "orcid": "0000-0003-2321-1321", "display_name": "Fang, Michael Tianyu" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Brandao", "given": "Fernando" }, "id": "Brand\u00e3o-F-G-S-L", "orcid": "0000-0003-3866-9378", "role": "member", "display_name": "Brandao, Fernando" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/6teq-md72", "abstract": "Quantum memories and networks for distributed quantum information processing require links between the microwave, mechanical, and optical domains. Coherent integration of long-lived superconducting qubits (SCQs) with optomechanical and photonic devices (OMPDs) remains an outstanding challenge. We present a step towards coherent integration using a suspended trace air-gap resonator (STAR): a superconducting resonator on a silicon-on-insulator (SOI) substrate with the signal trace suspended by silicon tethers above and between galvanically connected ground metal planes. As a result, the electric field energy is closely confined within the microwave structure, yielding lower crosstalk compared to conventional coplanar waveguides (CPW). An order of magnitude improvement in the quality factors for STAR over previous work on SOI is achieved, in a transverse cross-sectional area that is an order of magnitude more compact. Electric field participation in lossy bulk dielectrics, a dominant source of energy leakage in previous measurements of aluminum CPW resonators on SOI, is virtually eliminated in STAR. The loss from the metal-air interface now dominates, but can be reduced by several factors using superconductors with better surface properties. Most importantly, STAR fabrication is compatible with Josephson junction and air-bridge deposition for highly coherent integration of SCQs and OMPDs to realize proposals for quantum information storage and networking.
" }, { "name": "Fernandez-Lado, Agustin Gabriel", "degree": "PhD", "year": "2020", "title": "Wave-Scattering by Periodic Media", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08252019-170117522", "creators": [ { "name": { "family": "Fernandez-Lado", "given": "Agustin Gabriel" }, "id": "Fernandez-Lado-Agustin- Gabriel", "orcid": "0000-0002-8141-3792", "display_name": "Fernandez-Lado, Agustin Gabriel" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "chair", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/G7XQ-RT85", "abstract": "This thesis presents a full-spectrum, well-conditioned, Green-function methodology for evaluation of scattering by general periodic structures, which remains applicable on a set of challenging singular configurations, usually called Rayleigh-Wood (RW) anomalies, where most existing methods break down. After reviewing a variety of existing fast-converging numerical procedures commonly used to compute the classical quasi-periodic Green-function, the present work explores the difficulties they present around RW-anomalies and introduces the concept of hybrid \"spatial/spectral\" representations. Such expressions allow both the modification of existing methods to obtain convergence at RW-anomalies as well as the application of a slight generalization of the Woodbury-Sherman-Morrison formulae together with a limiting procedure to bypass the singularities. Although, for definiteness, the overall approach is applied to the scalar (acoustic) wave-scattering problem in the frequency domain, the approach can be extended in a straightforward manner to the harmonic Maxwell's and elasticity equations. Ultimately, the thorough understanding of RW-anomalies this thesis provides yields fast and highly-accurate solvers, which are demonstrated with a variety of simulations of wave-scattering phenomena by arrays of particles, crossed impenetrable and penetrable diffraction gratings, and other related structures. In particular, the methods developed in this thesis can be used to \"upgrade\" classical approaches, resulting in algorithms that are applicable throughout the spectrum, and it provides new methods for cases where previous approaches are either costly or fail altogether. In particular, it is suggested that the proposed shifted Green function approach may provide the only viable alternative for treatment of three-dimensional high-frequency configurations. A variety of computational examples are presented which demonstrate the flexibility of the overall approach, including, in particular, a problem of diffraction by a double-helix structure, for which numerical simulations did not previously exist, and for which the scattering pattern presented in this thesis closely resembles those obtained in crystallography experiments for DNA molecules.
\r\n" }, { "name": "Ferraro, Serena", "degree": "PhD", "year": "2020", "title": "Topology Optimization and Failure Analysis of Deployable Thin Shells with Cutouts", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:02032020-164711057", "creators": [ { "name": { "family": "Ferraro", "given": "Serena" }, "id": "Ferraro-Serena", "orcid": "0000-0002-6038-7863", "display_name": "Ferraro, Serena" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/9VZ4-3E71", "abstract": "Shell structures with cutouts are widely used in architectural and engineering applications. For thin, lightweight, and deployable space structures, cutouts are cleverly positioned to fold and store the structure in a small volume. To maintain shape accuracy, these structures must fold without becoming damaged and must be stiff in their deployed configurations. Intuitive designs often fail to satisfy these two requirements. This research proposes solutions to the topology optimization of composite, thin shell structures with cutouts.
\r\n\r\nA novel optimization algorithm was developed that makes no assumptions on the initial number, shape, and location of cutouts on deployable thin shells. The algorithm uses a density-based approach, which distributes the material within the structure by assigning a density parameter to discretized locations. This parametrization of the design domain allows for the finding of new features and the connectivity of the domain, thus providing a completely general formulation to the optimization problem. The goal is to study the effects of volume and stress constraints imposed in a deformed configuration of thin shell structures. While classical topology optimization studies focus on finding solutions to linear problems, this method is applicable to geometrically nonlinear problems and implements stress constraints in the deformed, and hence most stressed, configuration of these shells. A mathematical formulation of the optimization problem and interpolation schemes for stiffness tensor, volume, and stress are presented. A sensitivity analysis of objective function, volume, and stress constraints is provided. Finally, solutions for a thin plate and a tape spring are proposed.
\r\n\r\nDensity-based methods are computationally expensive when applied to large structures and complex shapes because of the large number of design variables. To address these challenges, two optimization methods that provide more specific solutions to the problem of composite, deployable shells are proposed. The first method uses level sets to parametrize the cutouts, thereby restricting the design space and simultaneously limiting the number of design variables. This greatly reduces the computational cost. Using this approach, successful solutions are found for stiff, composite, thin shells with complex shapes that can fold without becoming damaged. The second method uses a spline representation of the contour of a single cutout on the shell, thus performing fine tuning of the shape of the cutout. Modeling techniques that simulate localized strain and experimental methods for studying the quasi-static folding of these composite shells are developed. A laminate failure criterion suitable for thin, plain-weave composites is used in simulations to predict the onset of failure in folded shells. Numerical results are validated with folding experiments that demonstrated good agreement with numerical solutions.
\r\n\r\nLastly, it was discovered that many of the best performing solutions have multiple closely spaced cutouts, as opposed to current designs for deployable space structures that have fewer large cutouts. This leads to the formation of small strips of material between cutouts. Hence, the behavior of thin, plain-weave composite material was characterized and the first study on size-scaling effects at small length scales (\u2264 15 mm) in this type of material was performed. Size-scaling effects on stiffness and strength shown in this study were introduced in numerical simulations of deployable thin shells. The study demonstrates that the prediction of the onset of failure in folded shells strongly depends on these size effects. Numerical predictions are corroborated by an experimental investigation of localized damage in thin strips of material forming between cutouts. Deployable shells resulting from the optimization studies are built and tested and localized damage is measured via digital volume correlation techniques.
" }, { "name": "Figueroa-Schibber, Erika", "degree": "PhD", "year": "2020", "title": "High-Cycle Dynamic Cell Fatigue with Applications on Oncotripsy", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:01202020-210729635", "creators": [ { "name": { "family": "Figueroa-Schibber", "given": "Erika" }, "id": "Figueroa-Schibber-Erika", "orcid": "0000-00002-6629-297X", "display_name": "Figueroa-Schibber, Erika" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "chair", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "space" ], "doi": "10.7907/0425-SN62", "abstract": "The method of oncotripsy (from Greek, onco- meaning \"tumor\" and \u2013tripsy \"to break\") exploits aberrations in the material properties and morphology of cancerous cells to target them selectively using tuned low-intensity pulsed ultrasound. Compared to other noninvasive ultrasound treatments that ablate malignant tissue, oncotripsy has the capability of targeting unhealthy tissue with minimal damage to healthy cells in the ablation process.
\r\n\r\nWe propose a model of oncotripsy that follows as an application of cell dynamics, statistical mechanical theory of network elasticity and 'birth-death' kinetics to describe processes of damage and repair of the cytoskeleton. We also develop a reduced dynamical model that approximates the three-dimensional dynamics of the cell and facilitates parameter studies, including sensitivity analysis and process optimization.
\r\n\r\nThe dynamical system encompasses the relative motion of the nucleus to the cell membrane and a state variable measuring the extent of damage to the cytoskeleton. The dynamical system evolves in time as a result of structural dynamics and kinetics of cytoskeletal damage and repair. The resulting dynamics are complex and exhibits behavior on multiple time scales, including the period of vibration and attenuation, the characteristic time of cytoskeletal healing, the pulsing period and the time of exposure to the ultrasound. Damage on the cells develops in the order of millions of ultrasound cycles, and the failure mechanism is explained as a fatigue process. We also account for cell variability and estimate the attendant variance of the time-to-death of a cell population. We show that the dynamical model predicts \u2014 and provides a conceptual basis for understanding \u2014 the oncotripsy effect and other trends observed in experiments.
" }, { "name": "Garc\u00eda Su\u00e1rez, Antonio Joaqu\u00edn", "degree": "PhD", "year": "2020", "title": "Application of Path-Independent Integrals to Soil-Structure Interaction", "advisor": "Asimaki, Domniki", "url": "https://resolver.caltech.edu/CaltechTHESIS:11212019-100323260", "creators": [ { "name": { "family": "Garc\u00eda Su\u00e1rez", "given": "Antonio Joaqu\u00edn" }, "id": "Garc\u00eda-Su\u00e1rez-Antonio-Joaqu\u00edn", "orcid": "0000-0001-8830-4348", "display_name": "Garc\u00eda Su\u00e1rez, Antonio Joaqu\u00edn" } ], "advisors": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "advisor", "display_name": "Asimaki, Domniki" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MMWW-B046", "abstract": "Assessing seismic pressure increment on buried structures is a critical step in the design of infrastructure in earthquake-prone areas. Due to intrinsic complexities derived from the need to match the solution in the far-field to the localized solution around the structure, the near-field, researchers have aimed at finding simplified models focused on engineering variables as the seismic earth thrust. One such model is the so-called Younan-Veletsos model, which pivots on a stringent assumption on the stress tensor.
\r\n\r\nAt the same time, the might of the path-independent integrals of solid mechanics to deal with problems in Geotechnical Engineering at large, and Soil-Structure Interaction in particular, has remained unexplored, despite of a rich landscape of potential applications. The unbridled success of these path-independent integrals in Fracture Mechanics, a discipline which cannot be understood without them currently, may be mirrored in problems in Geotechnical Engineering, since the two fields, despite appearing very detached from each other at first glance, share deep traits: in both cases, the system under consideration can be conceptualized as a domain with simple, easy-to-assess regions (the areas where remote loading is applied and the far-field, respectively) and also with other complex, hard-to-understand regions (the crack tip, the near-field).
\r\n\r\nWe present the first derivation of the exact solution of the Younan-Veletsos problem, which is later analyzed to reveal phenomena not captured by previous approximate solutions. Then, we introduce a novel model which relies on the path-independent Rice\u2019s J-integral, a customary tool in Fracture Mechanics, which is applied here in the Soil-structure Interaction context for the first time. This novel model captures those features of the exact solution that were missed by prior approximations. The capabilities of the J-integral to, first, find an upper bound of the force induced by earthquakes over the walls of underground structures, under some conditions, and, second, to understand the soil-structure kinematic interaction phenomenon are also assessed.
\r\n\r\nAdditionally, the intermediate step of analyzing of the far-field yielded some results concerning Site Response Analysis which are also included in the text.
" }, { "name": "Garza Gonzalez, Emmanuel", "degree": "PhD", "year": "2020", "title": "Boundary Integral Equation Methods for Simulation and Design of Photonic Devices", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01092020-141256074", "creators": [ { "name": { "family": "Garza Gonzalez", "given": "Emmanuel" }, "id": "Garza-Gonzalez-Emmanuel", "orcid": "0000-0003-1687-8216", "display_name": "Garza Gonzalez, Emmanuel" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Sideris", "given": "Constantine" }, "id": "Sideris-Constantine", "role": "member", "display_name": "Sideris, Constantine" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/XXPX-9H78", "abstract": "This thesis presents novel boundary integral equation (BIE) and associated optimization methodologies for photonic devices. The simulation and optimization of such structures is a vast and rapidly growing engineering area, which impacts on design of optical devices such as waveguide splitters, tapers, grating couplers, and metamaterial structures, all of which are commonly used as elements in the field of integrated photonics. The design process has been significantly facilitated in recent years on the basis of a variety of methods in computational electromagnetic (EM) simulation and design. Unfortunately, however, the expense required by previous simulation tools has limited the extent and complexity of the structures that can be treated. The methods presented in this thesis represent the results of our efforts towards accomplishing the dual goals of 1) Accurate and efficient EM simulation for general, highly-complex three-dimensional problems, and 2) Development of effective optimization methods leading to an improved state of the art in EM design.
\r\n\r\nOne of the main proposed elements utilizes BIE in conjunction with a modified-search algorithm to obtain the modes of uniform waveguides with arbitrary cross sections. This method avoids spurious solutions by means of a certain normalization procedure for the fields within the waveguides. In order to handle problems including nonuniform waveguide structures, we introduce the windowed Green function (WGF) method, which used in conjunction with auxiliary integral representations for bound mode excitations, has enabled accurate simulation of a wide variety of waveguide problems on the basis of highly accurate and efficient BIE, in two and three spatial dimensions. The \"rectangular-polar\" method provides the basic high-order singular-integration engine. Based on non-overlapping Chebyshev-discretized patches, the rectangular-polar method underlies the accuracy and efficiency of the proposed general-geometry three-dimensional BIE approach. Finally, we introduce a three-dimensional BIE framework for the efficient computation of sensitivities \u2014 i.e. gradients with respect to design parameters \u2014 via adjoint techniques. This methodology is then applied to the design of metalenses including up to a thousand parameters, where the overall optimization process takes in the order of three hours using five hundred computing cores. Forthcoming work along the lines of this effort seeks to extend and apply these methodologies to some of the most challenging and exciting design problems in electromagnetics in general, and photonics in particular.
" }, { "name": "Gurriet, Thomas", "degree": "PhD", "year": "2020", "title": "Applied Safety Critical Control", "advisor": "Ames, Aaron D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022020-154234707", "creators": [ { "name": { "family": "Gurriet", "given": "Thomas" }, "id": "Gurriet-Thomas", "orcid": "0000-0002-5240-3720", "display_name": "Gurriet, Thomas" } ], "advisors": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "role": "advisor", "display_name": "Ames, Aaron D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Feron", "given": "Eric M." }, "id": "Feron-E-M", "role": "member", "display_name": "Feron, Eric M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/y97v-b205", "abstract": "There is currently a clear gap between control-theoretical results and the reality of robotic implementation, in the sense that it is very difficult to transfer analytical guarantees to practical ones. This is especially problematic when trying to design safety-critical systems where failure is not an option. While there is a vast body of work on safety and reliability in control theory, very little of it is actually used in practice where safety margins are typically empiric and/or heuristic. Nevertheless, it is still widely accepted that a solution to these problems can only emerge from rigorous analysis, mathematics, and methods. In this work, we therefore seek to help bridge this gap by revisiting and expanding existing theoretical results in light of the complexity of hardware implementation.
\r\n\r\nTo that end, we begin by making a clear theoretical distinction between systems and models, and outline how the two need to be related for guarantees to transfer from the latter to the former. We then formalize various imperfections of reality that need to be accounted for at a model level to provide theoretical results with better applicability. We then discuss the reality of digital controller implementation and present the mathematical constraints that theoretical control laws must satisfy for them to be implementable on real hardware. In light of these discussions, we derive new realizable set-invariance conditions that, if properly enforced, can guarantee safety with an arbitrary high levels of confidence. We then discuss how these conditions can be rigorously enforced in a systematic and minimally invasive way through convex optimization-based Safety Filters. Multiple safety filter formulations are proposed with varying levels of complexity and applicability. To enable the use of these safety filters, a new algorithm is presented to compute appropriate control invariant sets and guarantee feasibility of the optimization problem defining these filters. The effectiveness of this approach is demonstrated in simulation on a nonlinear inverted pendulum and experimentally on a simple vehicle. The aptitude of the framework to handle a system's dynamics uncertainty is illustrated by varying the mass of the vehicle and showcasing when safety is conserved. Then, the aptitude of this approach to provide guarantees that account for controller implementation's constraints is illustrated by varying the frequency of the control loop and again showcasing when safety is conserved.
\r\n\r\nIn the second part of this work, we revisit the safety filtering approach in a way that addresses the scalability issues of the first part of this work. There are two main approaches to safety-critical control. The first one relies on computation of control invariant sets and was presented in the first part of this work. The second approach draws from the topic of optimal control and relies on the ability to realize Model-Predictive-Controllers online to guarantee the safety of a system. In that online approach, safety is ensured at a planning stage by solving the control problem subject for some explicitly defined constraints on the state and control input. Both approaches have distinct advantages but also major drawbacks that hinder their practical effectiveness, namely scalability for the first one and computational complexity for the second one. We therefore present an approach that draws from the advantages of both approaches to deliver efficient and scalable methods of ensuring safety for nonlinear dynamical systems. In particular, we show that identifying a backup control law that stabilizes the system is in fact sufficient to exploit some of the set-invariance conditions presented in the first part of this work. Indeed, one only needs to be able to numerically integrate the closed-loop dynamics of the system over a finite horizon under this backup law to compute all the information necessary for evaluating the regulation map and enforcing safety.\r\nThe effect of relaxing the stabilization requirements of the backup law is also studied, and weaker but more practical safety guarantees are brought forward. We then explore the relationship between the optimality of the backup law and how conservative the resulting safety filter is. Finally, methods of selecting a safe input with varying levels of trade-off between conservativeness and computational complexity are proposed and illustrated on multiple robotic systems, namely: a two-wheeled inverted pendulum (Segway), an industrial manipulator, a quadrotor, and a lower body exoskeleton.
" }, { "name": "Herriman, Jane Elizabeth", "degree": "PhD", "year": "2020", "title": "Phonon Thermodynamics and Elastic Behavior of GaN and GaAs at High Temperatures and Pressures", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03042020-145654151", "creators": [ { "name": { "family": "Herriman", "given": "Jane Elizabeth" }, "id": "Herriman-Jane-Elizabeth", "orcid": "0000-0003-4769-1403", "display_name": "Herriman, Jane Elizabeth" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Jackson", "given": "Jennifer M." }, "id": "Jackson-J-M", "role": "member", "display_name": "Jackson, Jennifer M." }, { "name": { "family": "Correa", "given": "Alfredo" }, "id": "Correa-Alfredo", "role": "member", "display_name": "Correa, Alfredo" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/HJ36-P349", "abstract": "The work herein studies how high temperatures and pressure impact the properties of four materials: two phases of Gallium Nitride (GaN) and two phases of Gallium Arsenide (GaAs). The particular phases we study are the wurtzite and zinc blende phases of each chemical composition. The properties we study concern (1) the phonon thermodynamics and (2) the elastic behavior. In particular, phonons were calculated at simultaneously elevated temperature and pressure, and elastic constants were calculated as functions of pressure at 0 K.
\r\n\r\nOur studies of phonon thermodynamics included comparing the results of phonon calculations accounting for full temperature effects to the results of a quasiharmonic approximation (QHA) for each material, allowing us to assess the importance of explicitly anharmonic contributions to the phonons with changing temperature and pressure.\r\nIn GaN, the QHA gave reasonable results for the temperature dependence of the phonon DOS at zero pressure, but unreliably predicted the combined effects of temperature and pressure.\r\nPressure was found to change the explicit anharmonicity, altering the thermal shifts of phonons, and more notably qualitatively changing the evolution of phonon lifetimes with increasing temperature. These effects were largest for the optical modes, and phonon frequencies below approximately 5 THz were adequately predicted with the QHA.\r\nIn GaAs, the QHA failed to account for temperature-induced phonon frequency shifts at all pressures. As in GaN, the QHA was not able to predict the combined effects of temperature and pressure. In GaAs, the QHA clearly became less reliable with elevated pressure. In particular, the number of three-phonon processes increased with pressure, thereby increasing the temperature-driven broadening of phonon spectral lineshapes.
\r\n\r\nSo, why did pressure change the possible three-phonon processes in both GaN and GaAs, but cause them to net increase in GaAs? In all materials, the frequencies of phonon branches were sensitive to pressure to varying degrees. Showing the greatest contrast, transverse acoustic modes in all four materials softened with increasing pressure, whereas all other modes stiffened, albeit at different rates. If the frequencies of all modes scaled uniformly with pressure, we might expect that phonon decay channels consisting of equivalent input and output total phonon frequencies would persist independent of pressure; non-uniform frequency scaling, however, destroys some phonon decay channels and creates others in order to conserve energy. The dissimilar atomic masses of Ga and N create a phonon bandgap in GaN that increased with pressure. The increasing phonon bandgap frequently pushed some of the high frequency optical modes out of range of previously available down-conversion processes, ultimately causing GaN to become more quasiharmonic with pressure. More similar atomic masses in GaAs, however, prevent GaAs from exhibiting a true phonon bandgap; in this case, pressure was not able to drive the acoustic and optical branches away from each other, and instead created more opportunities for conversion.
\r\n\r\nOur understanding of the elastic behavior of each material derived from both calculations of the elastic constants and from additional information we could extract from the phonons. We used elastic constants to study elastic anisotropy and to predict the onset of elastic instability using the Born stability criteria. In GaN, elastic anisotropy increased with pressure until reaching elastic instabilities at 65 GPa (wurtzite) and 40 GPa (zinc blende). In GaAs, elastic anisotropy again increased with pressure through the onset of lattice instability, but the Born stability criteria failed to accurately predict this instability. Instead, pressure caused instabilities of shorter-wavelength transverse acoustic modes in both phases of GaAs that preceded the onset of instability predicted by the Born stability criteria, which depend on elastic constants and thereby only long wavelength phonons. In particular, pressure drove the frequencies of shorter-wavelength transverse acoustic phonon instabilities down until they reached 0 THz, inducing instability at 18 GPa (wurtzite) and 20 GPa (zinc blende). Interestingly, temperature caused a significant stabilization of these phonon modes, however, slowing their softening with pressure.
" }, { "name": "Huang, De", "degree": "PhD", "year": "2020", "title": "Positive Definite Matrices: Compression, Decomposition, Eigensolver, and Concentration", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222020-162227420", "creators": [ { "name": { "family": "Huang", "given": "De" }, "id": "Huang-De", "orcid": "0000-0003-4023-9895", "display_name": "Huang, De" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/g2nt-yy27", "abstract": "For many decades, the study of positive-definite (PD) matrices has been one of the most popular subjects among a wide range of scientific researches. A huge mass of successful models on PD matrices has been proposed and developed in the fields of mathematics, physics, biology, etc., leading to a celebrated richness of theories and algorithms. In this thesis, we draw our attention to a general class of PD matrices that can be decomposed as the sum of a sequence of positive-semidefinite matrices. For this class of PD matrices, we will develop theories and algorithms on operator compression, multilevel decomposition, eigenpair computation, and spectrum concentration. We divide these contents into three main parts.
\r\n\r\nIn the first part, we propose an adaptive fast solver for the preceding class of PD matrices which includes the well-known graph Laplacians. We achieve this by establishing an adaptive operator compression scheme and a multiresolution matrix factorization algorithm which have nearly optimal performance on both complexity and well-posedness. To develop our methods, we introduce a novel notion of energy decomposition for PD matrices and two important local measurement quantities, which provide theoretical guarantee and computational guidance for the construction of an appropriate partition and a nested adaptive basis.
\r\n\r\nIn the second part, we propose a new iterative method to hierarchically compute a relatively large number of leftmost eigenpairs of a sparse PD matrix under the multiresolution matrix compression framework. We exploit the well-conditioned property of every decomposition components by integrating the multiresolution framework into the Implicitly Restarted Lanczos method. We achieve this combination by proposing an extension-refinement iterative scheme, in which the intrinsic idea is to decompose the target spectrum into several segments such that the corresponding eigenproblem in each segment is well-conditioned.
\r\n\r\nIn the third part, we derive concentration inequalities on partial sums of eigenvalues of random PD matrices by introducing the notion of k-trace. For this purpose, we establish a generalized Lieb's concavity theorem, which extends the original Lieb's concavity theorem from the normal trace to k-traces. Our argument employs a variety of matrix techniques and concepts, including exterior algebra, mixed discriminant, and operator interpolation.
" }, { "name": "Huang, Jinglin Alice", "degree": "PhD", "year": "2020", "title": "Investigations of Different Methods to Promote Drug Mixing in the Eye", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:12122019-162434400", "creators": [ { "name": { "family": "Huang", "given": "Jinglin Alice" }, "id": "Huang-Jinglin-Alice", "orcid": "0000-0003-0760-4950", "display_name": "Huang, Jinglin Alice" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Petrasek", "given": "Danny" }, "id": "Petrasek-Danny", "role": "member", "display_name": "Petrasek, Danny" }, { "name": { "family": "Schwartz", "given": "Daniel M." }, "id": "Schwartz-Daniel-M", "role": "member", "display_name": "Schwartz, Daniel M." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "medeng" ], "doi": "10.7907/741T-MN38", "abstract": "Age-related macular degeneration (AMD) is the leading cause of central vision loss in the developed world. In the case of wet AMD, it can be managed through serial intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) agents. However, sometimes the treatment is ineffective. Given that half-life time of the drug is limited, one possible cause of the ineffective treatment is inefficient drug mixing in the eye. Here, we focus on the understanding of drug mixing in vitreous chamber and parameters that could potentially influence mixing profiles. Both movement-driven method and thermal-driven method are explored. The in-vitro study outcomes will not only be useful for achieving fundamental understandings of fluid dynamics in the eye, but also helpful in developing a better strategy for intravitreal injection and improving the quality of care for patients." }, { "name": "Kwong, Anthony Herman Fu-Hao", "degree": "PhD", "year": "2020", "title": "Mechanical Properties of Small-Scale Sputtered Metallic Glasses", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09252020-152536826", "creators": [ { "name": { "family": "Kwong", "given": "Anthony Herman Fu-Hao" }, "id": "Kwong-Anthony-Herman-Fu-Hao", "orcid": "0000-0001-6389-1443", "display_name": "Kwong, Anthony Herman Fu-Hao" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Falson", "given": "Joseph" }, "id": "Falson-Joseph", "orcid": "0000-0003-3183-9864", "role": "member", "display_name": "Falson, Joseph" } ], "option_major": [ "matsci" ], "doi": "10.7907/4nv1-1f26", "abstract": "Sputtered metallic glasses (MGs) represent a unique class of materials because their nonperiodic arrangements are far from equilibrium. This microstructure gives rise to their exceptional mechanical properties; for example, experiments and simulations on the deformation of small-scale sputtered Zr-based MGs demonstrate their exceptional compressive and tensile strengths in excess of 1 GPa and exceptional tensile ductility of ~150%.
\r\n\r\nWe report a new property that emerges in sputtered MGs: age-induced strengthening. We measured the compressive strengths of cylindrical pillars with diameters between 300 nm to 1.1 \u03bcm, which were carved from a 5 \u03bcm-thick sputtered Zr\u2013Ni\u2013Al thin film that was aged in a nitrogen environment for three years. Nanomechanical experiments revealed that the aged samples had a stiffness of 91 \u00b1 4 GPa and a yield strength of 2.7 \u00b1 0.2 GPa for all cylinder sizes, which represents a nearly 43% increase in yield strength and a 31% increase in the elastic modulus compared to equivalently sized as-sputtered samples. We also observed nano-sized induced failure suppression: samples with diameters below 600 nm deformed smoothly and noncatastrophically. Those with larger diameters deformed via a series of observable and detectable shear bands that propagated to the surfaces. Molecular dynamics (MD) simulations of uniaxial compression of chemically equivalent Zr\u2013Ni\u2013Al MG nanowires revealed that the underlying physics of enhanced strengths involves the evolution of local disorder that can be quantified in the number of fivefold atomic bonds. The average amount of fivefold bonding increased systematically with energetic relaxation and the maximum compressive stress. Dynamic mechanical analysis (DMA) revealed the presence of hydrides within the MG. Hydrogen diffusion into the host matrix resulted in an increase in the local volume such that more\u2013mobile atoms (i.e., Ni and Al) can redistribute and relax into a more\u2013energetically favorable configuration.
\r\n\r\nExperiments and simulations in this work demonstrate that sputtered MGs strength by 43% when solely aged for three years, i.e., without any accompanying annealing or mechanical treatment, which originates from atomic-level microstructural relaxation in these materials. This provides a useful foundation for simple design of advanced materials whose mechanical properties can be predicted and prescribed a priori using physical principles of atomic-level relaxation.
" }, { "name": "Le, Hoang Minh", "degree": "PhD", "year": "2020", "title": "New Frameworks for Structured Policy Learning", "advisor": "Yue, Yisong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092020-121556493", "creators": [ { "name": { "family": "Le", "given": "Hoang Minh" }, "id": "Le-Hoang-Minh", "orcid": "0000-0002-5521-5856", "display_name": "Le, Hoang Minh" } ], "advisors": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "advisor", "display_name": "Yue, Yisong" } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Anandkumar", "given": "Anima" }, "id": "Anandkumar-A", "orcid": "0000-0002-6974-6797", "role": "member", "display_name": "Anandkumar, Anima" }, { "name": { "family": "Daum\u00e9", "given": "Hal, III" }, "id": "Daum\u00e9-Hal-III", "orcid": "0000-0002-3760-345X", "role": "member", "display_name": "Daum\u00e9, Hal, III" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cms" ], "doi": "10.7907/rz4w-k233", "abstract": "Sequential decision making applications are playing an increasingly important role in everyday life. Research interest in machine learning approaches to sequential decision making has surged thanks to recent empirical successes of reinforcement learning and imitation learning techniques, partly fueled by recent advances in deep learning-based function approximation. However in many real-world sequential decision making applications, relying purely on black box policy learning is often insufficient, due to practical requirements of data efficiency, interpretability, safety guarantees, etc. These challenges collectively make it difficult for many existing policy learning methods to find success in realistic applications.
\r\n\r\nIn this dissertation, we present recent advances in structured policy learning, which are new machine learning frameworks that integrate policy learning with principled notions of domain knowledge, which spans value-based, policy-based, and model-based structures. Our framework takes flexible reduction-style approaches that can integrate structure with reinforcement learning, imitation learning and robust control techniques. In addition to methodological advances, we demonstrate several successful applications of the new policy learning frameworks.
" }, { "name": "Leclerc, Christophe", "degree": "PhD", "year": "2020", "title": "Mechanics of Ultra-Thin Composite Coilable Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:01232020-134850757", "creators": [ { "name": { "family": "Leclerc", "given": "Christophe" }, "id": "Leclerc-Christophe", "orcid": "0000-0003-1999-4757", "display_name": "Leclerc, Christophe" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/X60S-BR30", "abstract": "Coilable structures are thin-shell structures that can be coiled around a hub by flattening their cross-section. They are attractive for multiple space applications as they allow efficient packaging and deployment of large planar structures. Reducing the shell thickness enables smaller coiling radius and more efficient packaging.
\r\n\r\nThis thesis investigates TRAC structures, a type of coilable structure, made of ultra-thin composite materials. A design using a laminate made of glass fiber plainweave fabric and carbon fiber unidirectional tape is proposed, leading to a shell thickness of 0.08 mm. An in-autoclave, two-cure manufacturing process is presented, and a shape measurement method is used to mitigate post-cure shape changes due to residual stresses.
\r\n\r\nA study of the structure behavior in its deployed configuration is performed. First, the behavior when subjected to pure bending is investigated experimentally for structures with a length of 575 mm. Two regimes are observed, with a pre-buckling phase transitioning to a stable post-buckling phase after an initial buckling event. The ultimate buckling moment following the stable post-buckling regime can be as high as four times the initial buckling moment. A finite element model is developed and is able to reproduce all the features observed experimentally, except the ultimate buckling. This simulation model is used to study the effect of varying the structure length from 300 mm to 5000 mm on the initial buckling moment. Results show that nonlinearities in the pre-buckling deformations of the flanges under compression lead to a constant wavelength lateral-torsional buckling mode for which the critical moment is mostly constant across the range of length. The torsional behavior of the TRAC structure is also investigated. Good agreement is obtained between experiments and numerical simulations, and initial twist in the structure is shown to have little effect on the overall behavior due to the small torsional stiffness in the underformed configuration.
\r\n\r\nAn analytical method to predict the buckling load of a TRAC structure under pure bending is presented. It is achieved by considering only one flange of the structure and solving the problem of a cylindrical shell panel with a longitudinal free edge under non-uniform axial compression. Partially uncoupled stability equations for a balanced laminate are derived and are used in conjunction with the Rayleigh-Ritz method to approximate the buckling load. This method overestimates the buckling load by 44% in the case of a 500 mm TRAC structure made with ultra-thin composite materials.
\r\n\r\nA study of the coiling behavior is also presented. High localized curvature in the transition region between the coiled and deployed regions is observed in experiments, leading to material failure for a structure made only of carbon fiber unidirectional tape. A numerical framework is developed and reproduces the localized curvature observed in experiments, predicting stress concentration at this location. The study shows that changing the laminate to a a single ply of carbon fiber unidirectional tape sandwiched between plies of glass fiber plainweave fabrics reduces significantly the maximum stress in the transition region, to the extent that the highest stress is now in the fully coiled region and can be accurately predicted using simple equations based on the change of curvatures due to the coiling process.
" }, { "name": "Leibowitz, Matthew Gregory", "degree": "PhD", "year": "2020", "title": "Hypervelocity Shock Tunnel Studies of Blunt Body Aerothermodynamics in Carbon Dioxide for Mars Entry", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272020-173051776", "creators": [ { "name": { "family": "Leibowitz", "given": "Matthew Gregory" }, "id": "Leibowitz-Matthew-Gregory", "orcid": "0000-0002-7297-2592", "display_name": "Leibowitz, Matthew Gregory" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/chyn-ea06", "abstract": "A low mass and reliable thermal protection system for Martian atmospheric entry requires an accurate prediction of the aerothermal environment encountered by the spacecraft. In order to move forward with predictive models for larger vehicles needed for manned and sample return missions, anomalous data needs to be resolved.\r\nThis work aims to address two critical problems relevant for Mars missions.
\r\n\r\nI) We investigate significant discrepancies between experimental and simulated blunt body bow shock standoff distance in ground test facilities. Experiments using high-speed and high-resolution schlieren imaging are conducted in the T5 reflected shock tunnel and the Hypervelocity Expansion Tube (HET) to examine facility\r\nindependence of the measurements. A recently-developed model for sphere and sphere-cone behavior is in good agreement with experiments, and with predictions from Navier-Stokes simulations with thermal and chemical nonequilibrium. The need to account for the divergence of the streamlines in conical nozzles is highlighted.\r\nThe contributions of vibrational and chemical nonequilibrium to the stagnation-line density profile are quantified using the simulation results in order to compare different reaction rate models.
\r\n\r\nII) We measure and characterize carbon dioxide mid-wave infrared radiation in hypervelocity flow. Initially assumed negligible in the design of the Mars Science Laboratory (MSL) mission heat shield, this mechanism of heating must be considered for accurate predictions of the heating environment. Specifically, carbon dioxide radiation can be a dominant source of heating in the afterbody, particularly later in the trajectory at lower velocities. Presented are spectral measurements of the 4.3 \u03bcm fundamental band of carbon dioxide radiation measured using fiber optics embedded on the surface of an MSL scaled heat shield model. When comparing experiments and simulations, good agreement is found when running the HET in shock tube mode where the shock layer is optically thick, while discrepancies are observed in expansion tube mode where the shock layer is optically thin. A thorough analysis of flow features in the line-of-sight including freestream uncertainties is performed to explore possible reasons for this discrepancy. After developing the spectroscopic calibration technique and obtaining forebody measurements in the expansion tube, an experimental campaign is completed in the T5 Reflected Shock Tunnel to measure spectral radiation in the forebody and afterbody. The accompanying T5 simulations needed for radiation predictions are being carried out by NASA Ames.
" }, { "name": "Li, Liuchi", "degree": "PhD", "year": "2020", "title": "Linking Micro-Structure to Macro-Behavior of Granular Matter: From Flowing Heterogeneously to Morphing Adaptively", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04232020-202440477", "creators": [ { "name": { "family": "Li", "given": "Liuchi" }, "id": "Li-Liuchi", "orcid": "0000-0002-1360-4757", "display_name": "Li, Liuchi" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/pbec-dk61", "abstract": "From concrete gravels unloaded from trucks to wheat seeds discharged through funnels, from polymeric beads filled in shoe cushions to metallic pellets packed in robotic grippers, granular matter is becoming increasingly relevant in coping with our evolvingly sophisticated societal needs in many respects (e.g. expanding urbanization, growing population and advancing manufacturing). This increasing relevance urges developing micro-structural understandings of granular matter regarding its two basic macro-scale behaviors: flowing heterogeneously and morphing adaptively. However, findings in this regard so far suffered from a disconnection in length-scale - some adopting a top-down perspective lacking predictability due to few insights taken from underpinning micro-scale details (e.g. particle shape), while others adopting a bottom-up perspective lacking practicality due to few specificities incorporated from overlaying macro-scale conditions (e.g. heterogeneities).
\r\n\r\nIn this dissertation, via Discrete Element Method (DEM) simulations, we bridge the divide between length-scales in this regard by revealing the fundamental role of microstructures. To begin with, we evaluate and verify the robustness of DEM in capturing granular microstructures, by systematically comparing simulation results with experimental measurements on quasi-statically sheared granular assemblies. Then, we first numerically study spatial phase transitions in heterogeneous granular flows from a top-down perspective. We start by calibrating and validating a DEM model using experiments we perform on fluidizing spherical particle pile formed in a rotating drum. We next take the validated model to produce flows with different microstructures by systematically varying boundary condition and loading rate, and lastly we study their correlations with phase transitions ranging from gas-like layers near the free surface, to underneath liquid-like layers, and to solid-like layers deep in the bulk. We propose a micro-scale parameter quantifying the level of structural anisotropy, that can for the first time elucidate the spatial phase transitions between these layers independent of imposed boundary conditions and loading rates. Further, we find that, in solid-like layers, this micro-structural quantity correlates to bulk effective friction, an integral macro-scale quantity in constitutive modeling. Next, we numerically study bending modulus adaptations in shape-morphing granular sheets from a bottom-up perspective. We start by calibrating and validating a DEM model using experiments we perform on bending 3D printed granular sheets enclosed in a flexible membrane. We next take the validated model to construct granular sheets with different microstructures by varying constituent particle shape, initial configuration and confining pressure. Lastly we study the correlation between microstructure variations and modulus adaptations. We discover a universal power-law correlation between bending modulus (a macro-scale quantity) and coordination number (a micro-scale quantity) in reminiscence of the canonical power-law scaling for packings of frictionless sphere near jamming. We also find larger coordination number favors interlocked particles over non-interlocked ones, leading to significantly better shape-morphing performance of chain-like sheets over discrete assemblies.
" }, { "name": "Lim, Yu Xian", "degree": "PhD", "year": "2020", "title": "L-Band Multi-Polarization Radar Scatterometry over Global Forests: Modelling, Analysis, and Applications", "advisor": "van Zyl, Jakob J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07252019-221240608", "creators": [ { "name": { "family": "Lim", "given": "Yu Xian" }, "id": "Lim-Yu-Xian", "orcid": "0000-0002-3777-7986", "display_name": "Lim, Yu Xian" } ], "advisors": [ { "name": { "family": "van Zyl", "given": "Jakob J." }, "id": "van-Zyl-J-J", "role": "advisor", "display_name": "van Zyl, Jakob J." } ], "committee": [ { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "chair", "display_name": "Elachi, Charles" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "van Zyl", "given": "Jakob J." }, "id": "van-Zyl-J-J", "role": "member", "display_name": "van Zyl, Jakob J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/7Y4D-JD17", "abstract": "Spaceborne L-band radars have the ability to penetrate vegetation canopies over forested areas, suggesting a potential for regular and frequent global monitoring of both the vegetation state and the subcanopy soil moisture. However, L-band radar\u2019s sensitivity to both vegetation and ground also complicates the relationship between the radar observations and the ecological and geophysical parameters. Accurate yet parsimonious forward models of the radar backscatter are valuable to building an understanding of these relationships. In the first part of this thesis, a model of L-band multi-polarization radar backscatter from forests, intended for use at regional to global spatial scales, is presented. Novel developments in the model include the consideration of multiple scattering within the dense vegetation canopy, and the application of a general model of plant allometry to mitigate the need for much intensive field data for training or over-tuning towards specific sites and tree species.
\r\n\r\nAided by our model, in the remainder and majority of the thesis, a detailed analysis and interpretation of L-band backscatter over global forests is performed, using data from the Aquarius and SMAP missions. Quantitative differences in backscatter predicted by our model due to freeze/thaw states, branch orientation, and flooding are partially verified against the data, and fitted values of aboveground-biomass and microwave vegetation optical depths are comparable to independent estimates in the literature. Polarization information is used to help distinguish vegetation and ground effects on spatial and temporal variations. We show that neither vegetation nor ground effects alone can explain spatial variations within the same land cover class. For temporal variations during unfrozen periods, soil moisture is found to often be an important factor at timescales of a week to several months, although vegetation changes remain a non-negligible factor. We report the observation of significant differences in backscatter depending on beam azimuthal angle, possibly due to plant phototropism.
\r\n\r\nWe also investigated diurnal variations, which have the potential to reveal signals related to plant transpiration. SMAP data from May-July 2015 showed that globally, co-polarized backscatter was generally higher at 6PM compared to 6AM over boreal forests, which is not what one might expect based on previous studies. Based on our modelling, increased canopy extinction at 6AM is a possible cause, but this is unproven and its true underlying physical cause undetermined.
\r\n\r\nFinally, by making simplifying approximations on our forward model, we propose and explore algorithms for soil moisture retrieval under forest canopies using L-band scatterometry, with preliminary evaluations suggesting improved performance over existing algorithms.
" }, { "name": "Lin, Li", "degree": "PhD", "year": "2020", "title": "Photoacoustic Tomography: From Bench to Bedside", "advisor": "Wang, Lihong", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092019-113537728", "creators": [ { "name": { "family": "Lin", "given": "Li" }, "id": "Lin-Li", "orcid": "0000-0002-0517-8436", "display_name": "Lin, Li" } ], "advisors": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "advisor", "display_name": "Wang, Lihong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" } ], "option_major": [ "medeng" ], "doi": "10.7907/1DGY-T168", "abstract": "Photoacoustic imaging (PAI) is an emerging imaging modality that shows great potential for preclinical research and clinical practice. As a hybrid technique, PAI uniquely combines the advantages of optical excitation and of acoustic detection. Optical absorption provides a rich contrast mechanism from either endogenous chromophores or exogenous contrast agents. Because ultrasound scatters much less than light in tissue, PAI generates high-resolution images in both the optical ballistic and diffusive regimes, overcoming the limitations imposed by light scattering in deep biological tissues. PAI has led to a variety of exciting discoveries and applications from laboratory research to clinical patient care.
\r\n\r\nTo translate photoacoustic technology from the bench to the bedside, this thesis focuses on efforts to increase the imaging depth, provide clinically useful information (i.e., relevant imaging contrast), reduce system size, and improve system reliability. Assisted by powerful pulsed lasers and advanced data acquisition circuits, modern PAI has achieved applications such as functional imaging of the whole rat brain, revealing detailed angiography and functional connectivity at high spatiotemporal resolution. The advancement of deep imaging in small animal PAI has been transferred to human breast and brain imaging, showing early promise for clinical practice. To further extend the imaging depth and provide dielectric imaging contrast, microwave-based thermoacoustic tomography has been demonstrated in vivo. To map further physiological contrasts, spectroscopic PAI has been performed to image the oxygenation states of hemoglobin and myoglobin. In addition to the effort towards deep penetration and multiple contrasts, benchtop photoacoustic microscopy has been minimized to a handheld probe for human skin imaging. As a rapidly evolving imaging technology, PAI is being translated from the bench to the bedside and promises exciting and useful clinical applications.
\r\n" }, { "name": "Liu, Yang", "degree": "PhD", "year": "2020", "title": "From Restoring Human Vision to Enhancing Computer Vision", "advisor": "Meister, Markus", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092020-120629159", "creators": [ { "name": { "family": "Liu", "given": "Yang" }, "id": "Liu-Yang-CNS", "orcid": "0000-0002-8155-9134", "display_name": "Liu, Yang" } ], "advisors": [ { "name": { "family": "Meister", "given": "Markus" }, "id": "Meister-M", "role": "advisor", "display_name": "Meister, Markus" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "member", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Meister", "given": "Markus" }, "id": "Meister-M", "role": "member", "display_name": "Meister, Markus" } ], "option_major": [ "cns" ], "doi": "10.7907/sq58-z682", "abstract": "The central theme of this work is enabling vision, which includes two subtopics: restoring vision for blind humans, and enhancing computer vision models in visual recognition. Chapter 1 first provides a gentle introduction to relevant high level principles of human visual computations and summarizes two fundamental questions that vision answers: \"what\" and \"where.\" Chapters 2, 3, and 4 contain three published projects that are anchored by those two fundamental questions.
\r\n \r\nChapter 2 introduces a cognitive assistant to restore visual function for blind humans by focusing on an interface powered by audio augmented reality. The assistant communicates the \"what\" and \"where\" aspects of visual scenes by a combination of natural language and spatialized sound. We experimentally demonstrated that the assistant enables many aspects of visual functions for naive blind users.
\r\n \r\nChapters 3 and 4 develop data augmentation methods to address the data inefficiency problem in neural network based computer visual recognition models. In Chapter 3, a 3D-simulation based data augmentation method is developed for improving the generalization of visual classification models for rare classes. In Chapter 4, a fast and efficient data augmentation method is developed for the newly formulated panoptic segmentation task. The method improves performance of state-of-the-art panoptic segmentation models and generalizes across dataset domains, sizes, model architectures, and backbones.
" }, { "name": "Lu, I-Te", "degree": "PhD", "year": "2020", "title": "First-Principles Calculations of Electron-Defect Interactions and Defect-Limited Charge Transport", "advisor": "Bernardi, Marco", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302020-181136654", "creators": [ { "name": { "family": "Lu", "given": "I-Te" }, "id": "Lu-I-Te", "orcid": "0000-0003-1649-7931", "display_name": "Lu, I-Te" } ], "advisors": [ { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "advisor", "display_name": "Bernardi, Marco" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" } ], "option_major": [ "matsci" ], "doi": "10.7907/gjx3-qh49", "abstract": "Crystallographic defects and impurities govern charge transport at low temperature, where the electron-defect (e-d) interactions limit the carrier mobility and manifest themselves in a wide range of phenomena of broad relevance in condensed matter physics. Theoretical treatments of e-d interactions have so far relied on heuristic approaches and analytic models. However, the band structure, electronic wave functions, and defect perturbation potential are far more complex in real materials than in these simplified models. First-principles calculations can provide atomistic details of the atomic and electronic structures of the material and make accurate predictions of their properties. Yet, ab initio calculations of e-d interactions are still in their infancy, mainly because they require large simulation cells and computationally expensive workflows. This thesis aims to overcome the open challenge of computing the e-d interactions and the associated e-d matrix elements, e-d relaxation times, and defect-limited mobility using first-principles methods. We develop an efficient first-principles method to compute the e-d matrix elements and apply it to neutral vacancy and interstitial defects in silicon. Using the new approach, we demonstrate systematic convergence of the e-d relaxation times with respect to supercell size, defect position, and Brillouin zone sampling. To speed up the e-d calculations, we formulate and implement an interpolation scheme to compute the e-d matrix elements using maximally-localized Wannier functions. We show for the first time fully ab initio calculations of the temperature dependent defect-limited carrier mobility and investigate its numerical convergence. To treat charged defects, we develop a different interpolation method and apply it to a charged point defect in silicon. We use this approach together with importance sampling integration to effectively compute the e-d relaxation times for charged defects. Finally, we provide technical details of the e-d routines and discuss their integration in the open source code PERTURBO developed in the Bernardi group. In summary, the methods developed in this thesis have laid a solid foundation for future ab initio e-d interaction calculations, which can be applied broadly to address materials design challenges in electronics, energy, and quantum technologies.
" }, { "name": "Luan, Xingsheng", "degree": "PhD", "year": "2020", "title": "Towards Atom Assembly on Nanophotonic Structures with Optical Tweezers", "advisor": "Kimble, H. Jeff", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312020-151115988", "creators": [ { "name": { "family": "Luan", "given": "Xingsheng" }, "id": "Luan-Xingsheng", "orcid": "0000-0003-0649-2221", "display_name": "Luan, Xingsheng" } ], "advisors": [ { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "advisor", "display_name": "Kimble, H. Jeff" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Chen", "given": "Xie" }, "id": "Chen-Xie", "orcid": "0000-0003-2215-2497", "role": "member", "display_name": "Chen, Xie" }, { "name": { "family": "Endres", "given": "Manuel A." }, "id": "Endres-M", "orcid": "0000-0002-4461-224X", "role": "member", "display_name": "Endres, Manuel A." }, { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "member", "display_name": "Kimble, H. Jeff" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/08q5-0w11", "abstract": "The integration of atomic physics and nanophotonics combines the best of two worlds. With atoms as the naturally existing qubits and nanophotonic devices as the engineered interaction medium, new frontiers can be explored for building novel quantum optical circuits for non-conventional quantum optics and exotic quantum many-body physics, as well as potentially serving as a fundamental building block for quantum computation and communication with neutral atoms. While important experimental milestones towards this goal have been reached, a grand challenge for experiments in this new field is the loading and trapping of atomic arrays with high fractional filling near complex nanophotonic structures. In this thesis, we have proposed a novel protocol for atom assembly on nanophotonic structures by integrating optical tweezer arrays and photonic crystal waveguides. This research is inspired by recent exciting progress in free-space atom assembly. However, different from the free-space counterpart, our new proposal should enable subwavelength atom arrays with complex patterns defined by precision nanofabrication. To demonstrate the basic principles behind this new proposal, we have designed and built an advanced apparatus with compact footprint that overcomes several significant experimental barriers in previous experiments. To achieve efficient atom delivery and assembly of arrays for more complex nanostructures, we have proposed a novel direct delivery scheme with optical tweezers by exploiting the rapid spatial variation of the Gouy phase of radial Laguerre-Gauss beams. With reduced dimension in the axial direction, the optical tweezer formed by supposed Laguerre-Gauss beams may find important applications in the communities of general atomic physics and super-resolution imaging. Finally, we have investigated the optomechanical properties of our nanophotonic devices for trapping atoms and evaluated potential heating mechanisms for trapped atoms. The studies presented in this thesis should provide important guidance to future atom-nanophotonic experiments.
" }, { "name": "Luo, Jie", "degree": "PhD", "year": "2020", "title": "Integrating Quantum Optical and Superconducting Circuits with Quantum Acoustics for Scalable Quantum Network and Computation", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08282019-141610693", "creators": [ { "name": { "family": "Luo", "given": "Jie" }, "id": "Luo-Jie", "orcid": "0000-0002-6464-2761", "display_name": "Luo, Jie" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/P0YC-CQ43", "abstract": "Due to its high coherence in transmission over a large distance in the ambient environment, the quantum optical system has been a prevailing platform for long-distance quantum communication, which was recently realized over a continental distance with a low earth orbit satellite and ground stations [102, 70]. However, the pure quantum optical system has so far shown weak interactions between photon and matter, which makes it inefficient in carrying out deterministic quantum gates for quantum repeater based scalable quantum network and quantum computing. On the other hand, superconducting quantum systems operating in the microwave domain with Josephson junction transmon qubits have proven to be capable of efficient deterministic quantum operations on quantum states [86, 87, 66]. Nevertheless, such architecture is prone to errors and decoherence due to cross-talk between microwave elements in a large-scale superconducting quantum circuit. Furthermore, superconducting systems, in general, also have large footprint (100s um) elements (resonators and superconducting quantum bits) [92, 60] that limit the ability to scale up a superconducting quantum system. Moreover, microwave quantum circuits require cooling to around 10 mK, making it unsuitable for communicating quantum information outside a dilution refrigerator (DF). Micro- and nano- acoustic elements have been extensively used in conventional integrated information processing systems due to their compactness and high coherence [97]. Acoustic systems in quantum engineering also have the advantage of being a platform for universal couplings between various quantum systems including spins, optical photons, and superconducting circuits. As it will be discussed in this thesis, elements critical to scalable optical quantum network and superconducting quantum circuit can be constructed relying on the cavity optomechanics and piezoelectric interactions.
\r\n\r\nOptomechanical interaction is concerned with the light pressure coupling of cavity mechanical deformation to a strong optical \ufb01eld. This interaction has allowed the close to mechanical ground state cooling of mechanical resonators using laser and the ultra-sensitive displacement measurement that led to the detection of gravitational waves in the LIGO collaboration [125, 25]. Optomechanical crystals (OMCs) are lithographically patterned devices which contain a periodic structure that host bandgaps for both optical band electromagnetic waves and microwave band acoustic waves. A properly engineered defect in the crystal can con\ufb01ne and localize acoustic and electromagnetic modes of similar wavelengths into a small mode volume [17, 20, 21]. A strong optomechanical coupling, which can be achieved between such strongly con\ufb01ned co-localized optical and acoustic modes, can be used in engineering the quantum state of mechanical motion to realize useful quantum devices such as a high-coherence quantum memory [74] and an optomechanical high efficiency optical isolator for unidirectionally connecting distant optical cavities via an acoustic bus [37].
\r\n\r\nTo strongly couple the mechanical degree of freedom with a superconducting quantum circuit, various methods can be used, ranging from electromechanic coupling (electric coupling to a mechanically compliant capacitor), magnetomechanical coupling (magnetic coupling to a vibrating SQUID loop), and piezoelectric coupling. The recent advent of quantum acoustics [23, 8, 9] was realized with the strong piezoelectric coupling between a superconducting transmon qubit and a high-coherence mechanical resonator. The engineered strong piezoacoustic coupling provides the possibility to carry out deterministic ultra-high \ufb01delity two-qubit quantum gates on non-classical mechanical quantum states [52]. This ability together with the recent demonstration of ultra-long phonon lifetime mechanical resonators show the possibility of integrating the ultra-high quality mechanical resonator as a compact quantum memory element and even a new ultra-compact (10s um) quantum bit architecture for scalable superconducting quantum circuits. Furthermore, the strong piezoelectric coupling that can transduce quantum state in a superconducting circuit into mechanical wave also makes it possible to efficiently transduce a quantum state between a superconducting quantum circuit and a telecommunication band optical channel via a mechanical waveguide connected to an optomechanical crystal cavity.
\r\n" }, { "name": "Mac Donald, Kimberley Ann", "degree": "PhD", "year": "2020", "title": "Three-Dimensional Quantitative Visualization for Mechanics of Discontinuous Materials", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:08092019-151803660", "creators": [ { "name": { "family": "Mac Donald", "given": "Kimberley Ann" }, "id": "Mac-Donald-Kimberley-Kimberley-Ann", "orcid": "0000-0003-4512-9740", "display_name": "Mac Donald, Kimberley Ann" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/0M4F-FG13", "abstract": "The complexity and multiscale nature of material microstructures introduces significant intricacies to many mechanics problems for which we do not have a full theoretical understanding. Under loading, these microstructures can introduce significant nonlinearities that cannot be described sufficiently by current theories and models. This leads us to consider experiments we could perform to improve our understanding of such effects. This thesis describes the design of experiments exploring two aspects of material microstructure effects: (i) crack propagation and renucleation in soft brittle polymers and (ii) interparticle forces in granular materials.
\r\n\r\nFirst, experimental and analysis methods are developed to study fracture mechanics in soft brittle polymers with the goal of developing a more detailed understanding of the effects of microstructural heterogeneities on crack propagation and renucleation in three-dimensions. To better understand these processes, experiments on crack propagation in thin soft polymers using confocal microscopy images are conducted. Traditional metrics associated with crack propagation including stress intensity factor (SIF, K) and energy release rate (ERR, G) are calculated by direct measurement of the crack tip opening displacement (CTOD, \u03b4t) on the sub-millimeter scale. Errors in these calculations are comparable to those reported in the literature for more traditional fracture experiment geometries. Fluorescent speckle images are captured using confocal microscopy imaging, a fast and low cost 3D optical imaging technique, to study crack geometry during propagation. Images of renucleation events are also captured allowing investigation of factors contributing to slow crack roughening observed by earlier researchers. The goal of this study is to provide an experimental method to enhance understanding of crack interactions with microstructural heterogeneities and of renucleation events, which can significantly improve our ability to design material toughness.
\r\n\r\nTo begin to understand the effects of engineered microstructural heterogeneities such as inclusions in materials, we must be able to produce such engineered systems and understand the interparticle interactions. To this end, a method to manufacture volumetrically speckled spheres in-house with controlled diameters was developed. Additionally, an experimental method combining confocal microscopy with digital volume correlation (DVC) was also used to study interparticle force transmission in 3D. Analysis of an in-plane 2D projection of volumetric surface data shows that three-dimensional effects play a significant role in the deformation of granular assemblies. Study of a single grain in 3D demonstrates progress in experimental capabilities and highlights the need for more studies to validate existing numerical models and theories for granular matter. Analysis of particle scale deformations and strains with the Granular Element Method (GEM) allows us to determine interparticle forces and understand the development and evolution of force chains in a granular assembly under a wide variety of loading conditions. These experiments can also lead to development of new understanding of the effects of inclusions on material properties, processes, and damage evolution.
" }, { "name": "Marshall, Ryan Scott", "degree": "PhD", "year": "2020", "title": "Developing Plasma Spectroscopy and Imaging Diagnostics to Understand Astrophysically-Relevant Plasma Experiments: Megameters, Femtometers, and Everything in Between", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082020-085730717", "creators": [ { "name": { "family": "Marshall", "given": "Ryan Scott" }, "id": "Marshall-Ryan-Scott", "orcid": "0000-0003-0429-3923", "display_name": "Marshall, Ryan Scott" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "orcid": "0000-0003-0787-1610", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Harrison", "given": "Fiona A." }, "id": "Harrison-F-A", "orcid": "0000-0003-2992-8024", "role": "member", "display_name": "Harrison, Fiona A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/gfcd-4q50", "abstract": "One of the main attractions of using laboratory experiments as a proxy to study solar and astrophysical plasmas is the ability to build diagnostics that directly measure things. This cannot be done on actual solar and astrophysical plasmas as they are either i) extremely distant, ii) in an extreme environment, or iii) both. Fortunately, the lack of intrinsic scales in the MHD equations means that a plasma created in the laboratory with similar \u03b2, S, and magnetic topology will evolve similarly to its astrophysical analogs. Thus the use of diagnostics in the laboratory to understand the evolution of laboratory plasmas can assist in understanding complicated astrophysical plasma dynamics.
\r\n\r\nThis thesis is broken up into three main areas. The first is about the development of and results from two new custom X-ray scintillator detectors and a CMOS camera repurposed into an X-ray spectrometer mounted on the Caltech Astrophysical Jet Experiment. Next, water-ice grain growth in a cold dusty plasma is quantified by analyzing the frames in a movie recorded by an ultra-high-speed camera. Finally, the development of and results from a custom, motorized Laser-Induced Fluorescence diagnostic that measures the temperature and flow speed of neutral argon atoms in the dusty plasma experiment are presented.
\r\n\r\nTwo custom-built X-ray scintillator detectors mounted on the jet experiment detect a burst of hard X-rays establishing that this burst occurs simultaneously with a fast magnetic reconnection event taking place in the T = 2 eV plasma. A repurposed windowless CMOS camera acting as an X-ray spectrometer confirms the burst consists of non-mono-energetic photons around 6 keV energy. This magnetic reconnection event is triggered after the jet undergoes an ideal MHD kink instability which accelerates the jet laterally inducing a fast-growing secondary Rayleigh-Taylor instability. The Rayleigh-Taylor instability causes the ideal MHD treatment of the jet to be violated when it pinches the jet diameter past c/\u03c9pi causing it to break apart. As it breaks apart, a burst of hard X-rays are detected. These findings lead to the conclusion that an inductive electric field arises at the location of the reconnection event that accelerates a small fraction of electrons to keV energy despite the plasma being so collisional that acceleration is unexpected. This theory leads to the hypothesis that the fine structure of solar prominences consists of many Litz-wire like strands of plasma each on the order of a few ion skin depths in diameter, as opposed to the traditional picture of one monolithic arch.
\r\n\r\nAnalysis of a high-speed video of ice grains growing from 20 to 80 \u00b5m inside the dusty plasma experiment leads to the conclusion that the charged ice grains in the experiment grow via accretion of water molecules. The video challenges the common astrophysical assumption that the dusts in dusty plasmas are spherical as they are clearly seen to be elongated, fractal structures in the movie. Another commonly made assumption is that the grains grow via agglomerating collisions and that this results in the grains having a power law dependence on radius. Video of the grains in the Caltech experiment shows a log-normal dependence and absolutely no evidence of agglomerating collisions; or even a case of two grains approaching with a large relative velocity, and then scattering. It is believed that the grains have a large negative charge resulting in strong mutual repulsion and this, combined with their nearly non-existent relative velocities due to undergoing oscillatory motion by a relatively coherent wave, prevents them from agglomerating. This combined with a detailed study of Coulomb repulsion between the grains leads to the conclusion that direct accretion of water molecules is likely the dominant contribution to the observed ice grain growth.
\r\n\r\nLastly, a Laser-Induced Fluorescence diagnostic has been developed for the dusty plasma experiment. Whereas the first two projects rely on passive detection instruments, the LIF diagnostic actively uses a pump beam to excite atoms in the plasma, and then detects the resulting emission. The diagnostic is motorized and automated with Labview so that the plasma volume can be scanned in three dimensions. Argon neutral temperature is measured to be slightly above room temperature on the Caltech experiment and the PK4 experimental setup at Baylor University. Challenges such as the lack of absolute calibration of diode lasers and wavelength drift due to slight changes in ambient room conditions are overcome to measure sub-linewidth bulk neutral flow speeds on the order of 1-2 m/s with resolution on the order of 2/3 of a meter per second. The competing influences of a density gradient and wavelength dependent absorption broadening mechanism are separated and quantified. High-speed video shows that introducing an argon flow to a cloud of ice grains causes the cloud of ice grains to move and change shape. This motion is analyzed and found to show agreement with neutral LIF flow measurements. Surprisingly, when the flow ceases, the ice grain cloud reverts to its original location and shape.
" }, { "name": "McMullen, Ryan Michael", "degree": "PhD", "year": "2020", "title": "Aspects of Reduced-Order Modeling of Turbulent Channel Flows: From Linear Mechanisms to Data-Driven Approaches", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282020-161209039", "creators": [ { "name": { "family": "McMullen", "given": "Ryan Michael" }, "id": "McMullen-Ryan-Michael", "orcid": "0000-0003-1371-7150", "display_name": "McMullen, Ryan Michael" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Graham", "given": "Michael D." }, "id": "Graham-Michael-D", "role": "member", "display_name": "Graham, Michael D." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wayx-eh75", "abstract": "This thesis concerns three key aspects of reduced-order modeling for turbulent shear flows. They are linear mechanisms, nonlinear interactions, and data-driven techniques. Each aspect is explored by way of example through analysis of three different problems relevant to the broad area of turbulent channel flow.
\r\n\r\nFirst, linear analyses are used to both describe and better understand the dominant flow structures in elastoinertial turbulence of dilute polymer solutions. It is demonstrated that the most-amplified mode predicted by resolvent analysis (McKeon and Sharma, 2010) strongly resembles these features. Then, the origin of these\r\nstructures is investigated, and it is shown that they are likely linked to the classical Tollmien-Schichting waves.
\r\n\r\nSecond, resolvent analysis is again utilized to investigate nonlinear interactions in Newtonian turbulence. An alternative decomposition of the resolvent operator into Orr-Sommerfeld and Squire families (Rosenberg and McKeon, 2019b) enables a highly accurate low-order representation of the second-order turbulence statistics. The reason for its excellent performance is argued to result from the fact that the decomposition enables a competition mechanism between the Orr-Sommerfeld and Squire vorticity responses. This insight is then leveraged to make predictions about how resolvent mode weights belonging to several special classes scale with increasing Reynolds number.
\r\n\r\nThe final application concerns special solutions of the Navier-Stokes equations known as exact coherent states. Specifically, we detail a proof of concept for a data-driven method centered around a neural network to generate good initial guesses for upper-branch equilibria in Couette flow. It is demonstrated that the neural network is capable of producing upper-branch solution predictions that successfully converge to numerical solutions of the governing equations over a limited range of Reynolds numbers. These converged solutions are then analyzed, with a particular emphasis on symmetries. Interestingly, they do not share any symmetries with the known equilibria used to train the network. The implications of this finding, as well as broader outlook for the scope of the proposed method, are discussed.
" }, { "name": "Mitskovets, Anna", "degree": "PhD", "year": "2020", "title": "Using DNA Origami to Create Hybrid Nanophotonic Architectures for Single-Photon Emitters", "advisor": "Atwater, Harry Albert; Rothemund, Paul W. K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312020-234931669", "creators": [ { "name": { "family": "Mitskovets", "given": "Anna" }, "id": "Mitskovets-Anna", "orcid": "0000-0003-1967-5334", "display_name": "Mitskovets, Anna" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Rothemund", "given": "Paul W. K." }, "id": "Rothemund-P-W-K", "role": "co-advisor", "display_name": "Rothemund, Paul W. K." } ], "committee": [ { "name": { "family": "Gopinath", "given": "Ashwin" }, "id": "Gopinath-Ashwin", "role": "chair", "display_name": "Gopinath, Ashwin" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Rothemund", "given": "Paul W. K." }, "id": "Rothemund-P-W-K", "role": "member", "display_name": "Rothemund, Paul W. K." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/kqaj-ex65", "abstract": "The limitations in physical dimensions of silicon transistors give us a stimulus to explore alternative systems for better computational performance. The most promising system that received a lot of attention in the past few years is a quantum computer. Ideally, a nanophotonic quantum computer would consist of hundreds of single-photon emitters, optical or plasmonic resonators, optical waveguides and interconnects. The main difficulty in large-scale production of such quantum photonic networks is the integration and deterministic coupling of single-photon sources to photonic elements.
\r\n\r\nIn the first part of this thesis, we utilize spontaneous parametric down-conversion to create correlated pairs of indistinguishable photons. These photons are generated by bismuth borate nonlinear crystal and then are coupled to a photonic chip where they interfere at directional couplers to produce a path-entangled state. Our photonic chip consists of waveguides, directional couplers, and a single Mach-Zender interferometer with a thermo-optic phase shifter. When a part of the waveguide connecting directional couplers is replace with a plasmonic waveguide, quantum state of photons is converted to plasmonic state. Here we report a measurement of path entanglement between surface plasmons with 95% contrast, confirming that a path-entangled state can indeed survive without measurable decoherence. Our measurement suggests that elastic scattering mechanisms of the type that might cause pure dephasing in plasmonic systems must be weak enough not to significantly perturb the state of the metal under the experimental conditions we investigated.
\r\n\r\nThe second part of this work is dedicated to the study of a novel DNA origami self-assembly technique for creating hybrid nanophotonic architectures to create single-photon emitters. DNA origami is a modular platform for the combination of molecular and colloidal components to create optical, electronic, and biological devices. We present a DNA origami molecule that can be deterministically positioned on a silicon chip within 3.2\u00b0 alignment. Orientation is absolute (all degrees of freedom are speci\ufb01ed) and arbitrary (every molecule\u2019s orientation is independently speci\ufb01ed). The use of orientation to optimize device performance is shown by aligning \ufb02uorescent emission dipoles within microfabricated optical cavities. Large-scale integration is demonstrated via an array of 3,456 DNA origami with 12 distinct orientations, which indicates the polarization of the excitation light. Following this experiment, we explore how many molecular emitters can be coupled to this DNA origami shape and discover interesting interactions between ssDNA extensions that can cause origami to fold along its seam. Finally, we examine DNA origami self-assembly methods that can be used to deterministically couple single-photon emitters to resonators in order to decrease pure-dephasing rates and increase indistinguishability of emitted photons.
" }, { "name": "Mittelstein, David Reza", "degree": "PhD", "year": "2020", "title": "Modifying Ultrasound Waveform Parameters to Control, Influence, or Disrupt Cells", "advisor": "Gharib, Morteza; Shapiro, Mikhail G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242020-045332969", "creators": [ { "name": { "family": "Mittelstein", "given": "David Reza" }, "id": "Mittelstein-David-Reza", "orcid": "0000-0001-8747-0483", "display_name": "Mittelstein, David Reza" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "co-advisor", "display_name": "Gharib, Morteza" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "co-advisor", "display_name": "Shapiro, Mikhail G." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "medeng" ], "doi": "10.7907/71ak-w328", "abstract": "Ultrasound can be focused into deep tissues with millimeter precision to perform non-invasive ablative therapy for diseases such as cancer. In most cases, this ablation uses high intensity ultrasound to deposit non-selective thermal or mechanical energy at the ultrasound focus, damaging both healthy bystander tissue and cancer cells. Here we describe an alternative low intensity pulsed ultrasound approach known as \u201concotripsy\u201d that leverages the distinct mechanical properties of neoplastic cells to achieve inherent cancer selectivity. We show that when applied at a specific frequency and pulse duration, focused ultrasound selectively disrupts a panel of breast, colon, and leukemia cancer cell models in suspension without significantly damaging healthy immune or red blood cells. Mechanistic experiments reveal that the formation of acoustic standing waves and the emergence of cell-seeded cavitation lead to cytoskeletal disruption, expression of apoptotic markers, and cell death. The inherent selectivity of this low intensity pulsed ultrasound approach offers a potentially safer and thus more broadly applicable alternative to non-selective high intensity ultrasound ablation.
\r\n\r\nIn this dissertation, I describe the oncotripsy theory in its initial formulation, the experimental validation and investigation of testable predictions from that theory, and the refinement of said theory with new experimental evidence. Throughout, I describe how careful modifications to the ultrasound waveform directly can significantly impact how the ultrasound bio-effects control, influence, or disrupt cells in a selective and controlled manner.
\r\n" }, { "name": "Moon, Jaeyun", "degree": "PhD", "year": "2020", "title": "Thermal Conduction in Amorphous Materials and the Role of Collective Excitations", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01162020-015608435", "creators": [ { "name": { "family": "Moon", "given": "Jaeyun" }, "id": "Moon-Jaeyun", "orcid": "0000-0001-8199-5588", "display_name": "Moon, Jaeyun" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z23D-Z566", "abstract": "The atomic vibrations and thermal properties of amorphous dielectric solids are of fundamental and practical interest. For applications, amorphous solids are widely used as thermal insulators in thermopile and other detectors where low thermal conductivity directly sets the sensitivity of the detector. Amorphous solids are of fundamental interest themselves because the lack of atomic periodicity complicates theoretical development. As a result, the lower limits of thermal conductivity in solids as well as the nature of the vibrational excitations that carry heat remain active topics of research.
\r\n\r\nIn this thesis, we use numerical and experimental methods to investigate the thermal conduction in amorphous dielectrics. We begin by using molecular dynamics to investigate the thermal conductivity of amorphous nanocomposites. We find that mismatching the vibrational density of states of constituent materials in the composite is an effective route to achieve exceptionally low thermal conductivity in fully dense solids.
\r\n\r\nWe then transition to examining the properties of the atomic vibrations transporting heat in amorphous solids. For decades, normal mode methods have been used extensively to study thermal transport in amorphous solids. These methods naturally assume that normal modes are the fundamental vibrational excitations transporting heat. We examine the predictions from normal mode analysis that are now able to be tested against experiments, and we find that the predictions from these methods do not agree with experimental observations. For instance, normal mode methods predict that the low frequency normal modes are scattered by anharmonic interactions as in single crystalline solids. However, temperature dependent thermal conductivity measurements demonstrate a typical glassy temperature dependence inconsistent with normal modes scattering through anharmonic interactions. These discrepancies suggest that normal modes are not the fundamental heat carriers in amorphous dielectrics.
\r\n\r\nTo identify the actual heat carriers, we draw on fundamental concepts from many- body physics and inelastic scattering theory that dictate that the excitation energies of a many-body interacting system are given by the poles of the single-particle Green's function. The imaginary part of this function is proportional to the dynamic structure factor that is directly measured in inelastic scattering experiments. Collective excitations of a given energy and wavevector can thus be identified from peaks in the dynamic structure factor; their damping is given by the broadening of the peak. Using these concepts from many-body physics, the physical picture that emerges is that heat is carried in large part by a gas of weakly interacting collective excitations with a cutoff frequency that depends on the atomic structure and composition of the glass.
\r\n\r\nWe test this picture using numerical and experimental inelastic scattering measurements on amorphous silicon, a commonly studied amorphous solid. We observe collective excitations up to 10 THz, well into the thermal spectrum, and far higher than previous inelastic scattering measurements on other glasses. Our numerical and experimental evidence also confirms that the collective excitations are damped by structural disorder rather than anharmonic interactions and that they dominate the thermal conduction in amorphous silicon. Subsequent analysis shows that these high frequency acoustic excitations are supported in amorphous silicon due to a large sound velocity and monatomic composition, suggesting that other monatomic amorphous solids with large sound velocities may also support these thermal excitations.
\r\n\r\nOverall, our results provide strong evidence that the heat carriers in amorphous dielectrics are collective excitations rather than normal modes. This change in physical picture advances our understanding of atomic dynamics in glasses and also provides a foundation for realizing dielectric solids with ultralow thermal conductivity.
" }, { "name": "Nguyen, Kien Trung", "degree": "PhD", "year": "2020", "title": "Reduced-Order Model for Dynamic Soil-Pipe Interaction Analysis", "advisor": "Asimaki, Domniki", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-154218098", "creators": [ { "name": { "family": "Nguyen", "given": "Kien Trung" }, "id": "Nguyen-Kien-Trung", "orcid": "0000-0001-5761-3156", "display_name": "Nguyen, Kien Trung" } ], "advisors": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "advisor", "display_name": "Asimaki, Domniki" } ], "committee": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "chair", "display_name": "Andrade, Jose E." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" } ], "option_major": [ "civileng" ], "doi": "10.7907/mekk-dc25", "abstract": "Pipelines are very vulnerable infrastructure components to geohazard-induced ground deformation and failure. How soil transmits loads on pipelines and vice versa, known as soil-pipe interaction (SPI), thus is very important for the assessment and design of resilient pipeline systems.
\r\n\r\nIn the first part, this work proposes a simplified macroelement designed to capture SPI in cohesionless soils subjected to arbitrary loading normal to the pipeline axis. We present the development of a uniaxial hysteresis model that can capture the smooth nonlinear reaction force-relative displacement curves (FDCs) of SPI problems. Using the unscented Kalman filter, we derived the model parameter κ that controls the smoothness of the transition zone from linear to plastic using published experimental data. We extended this uniaxial model to biaxial loading effects and showed that the macroelement can capture effects such as pinching and shear-dilation coupling. The model input parameters were calibrated using finite element (FE) analyses validated by experiments. The FDCs of the biaxial model were verified by comparison with FE and smoothed-particle hydrodynamic (SPH) simulations for different loading patterns: cyclic uniaxial, 0-shaped, 8-shaped, and transient loading. Accounting for smooth nonlinearity, hysteresis, pinching, and coupling effects, the proposed biaxial macroelement shows good agreement with FE and SPH analyses, while maintaining the computational efficiency and simplicity of beam-on-nonlinear-Winkler foundation models, as well as a small number of input parameters.
\r\n\r\nNext, this work presents analytical solutions for computing frequency-domain axial and in-plane soil impedance functions (SIFs) for an infinitely long rigid circular structure buried horizontally in homogeneous elastic half-space. Using Hankel— and Bessel—Fourier series expansion, we solved a mixed-boundary-value problem considering a harmonic displacement at the structure boundary and traction-free boundary condition at the half-space free surface. We then verified our analytical solutions using results obtained from FE simulations. The SIFs of a buried structure in a homogeneous elastic half-space calculated by these two approaches are in perfect agreement with each other. In addition, we used analytical solutions and FE simulations to comprehensively investigate factors that affect the SIFs in homogeneous and two-layered half-spaces, respectively. The parametric study shows that SIFs of buried structures in elastic half-space primarily depend on frequency of excitation, shear modulus and Poisson's ratio of the half-space, burial depth and radius of the structure. In a two-layered soil domain, SIFs depend also on material contrast and the distance from the structure location to the interface between soil layers.
\r\n\r\nLastly, it demonstrates how the SIFs obtained previously can be incorporated into a reduced-order model to analyze SPI problems, specifically a straight pipe subjected to Rayleigh surface wave propagating through homogeneous and heterogeneous elastic half-spaces. Calculated displacement time histories at the control points are shown to agree well with those computed by direct two-dimensional FE analyses.
" }, { "name": "Oniyama, Tomoyuki", "degree": "PhD", "year": "2020", "title": "Shock Compression of Molybdenum Single Crystals to High Stresses", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192020-135417079", "creators": [ { "name": { "family": "Oniyama", "given": "Tomoyuki" }, "id": "Oniyama-Tomoyuki", "orcid": "0000-0001-6097-9917", "display_name": "Oniyama, Tomoyuki" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/YWPJ-5379", "abstract": "To investigate the role of crystal anisotropy and the impact stress on the shock induced elastic-plastic deformation of BCC single crystals at high stresses, molybdenum single crystals were shock compressed along [100], [111], and [110] orientations. A series of plate impact experiments were conducted with various impact stresses (23 - 190 GPa) along each orientation. Along the [100] and [111] orientations, two-wave structure - an elastic shock wave trailed by a plastic shock wave - was observed to 110 GPa. Along the [110] orientation, the two-wave structure was observed only up to 90 GPa.
\r\n\r\nBased on the measured quantities, in-material quantities at the elastic limit and at the peak state were calculated. The elastic wave amplitudes were analyzed to determine the crystal anisotropy effects, the impact stress dependence, and the activated slip systems on the elastic limit. The elastic wave amplitude increased linearly with\r\nincreasing impact stress, and that was significantly larger along the [111] orientation compared to the other orientations. The difference between calculated maximum resolved shear stresses at the elastic limit and corresponding Peierls stress suggested the activation of {110}<111> slip systems.
\r\n\r\nAt the peak state, the Hugoniot relations were calculated along each orientation and compared with polycrystalline molybdenum Hugoniot relations. The Hugoniot relations along three orientations were in agreement within experimental uncertainties, even though the elastic limit showed considerable anisotropy. Also, they agreed reasonably well with the polycrystalline molybdenum data. This implied that the in-material quantities at the peak state do not depend on crystal orientation or the presence of grain boundaries.
\r\n\r\nIn addition to the plate impact experiments, finite element simulations of shock compressed molybdenum single crystals were conducted using Abaqus Explicit in order to gain insight into deformation mechanisms activated during the elasticplastic\r\ndeformation. Shear strains on slip systems were explicitly considered by the crystal plasticity model implemented using Abaqus VUMAT subroutine. The results of FEM simulations indicated that {110}<111> systems were likely to be operating at the elastic limit. This observation was consistent with the experimental results from the present study.
" }, { "name": "Pajunen, Kirsti Mari", "degree": "PhD", "year": "2020", "title": "Dynamics of Lightweight Tensegrity-Inspired Metamaterials Fabricated with 3D-Printing", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-003455628", "creators": [ { "name": { "family": "Pajunen", "given": "Kirsti Mari" }, "id": "Pajunen-Kirsti-Mari", "orcid": "0000-0002-5366-1190", "display_name": "Pajunen, Kirsti Mari" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Hofmann", "given": "Douglas C." }, "id": "Hofmann-D-C", "role": "member", "display_name": "Hofmann, Douglas C." } ], "option_major": [ "space" ], "doi": "10.7907/wm2f-4013", "abstract": "Tensegrity structures and lattices have been of interest in engineering applications for decades, with their dynamics becoming a thriving field of study. Tensegrities consist of structural members under purely axial loading, either tension or compression, and obtain their stability from prestress. They possess unique characteristics such as high strength-to-weight ratio, nonlinear behavior, and elastic response under severe deformation. Tensegrity lattices (or metamaterials) have been shown to exhibit appealing dynamic attributes such as continuous tunability with prestress, impact mitigation, energy trapping and lensing, and nonlinear wave propagation, to name a few. However, their pin-jointed and prestressed nature presents significant manufacturing limitations, especially in the formation of lattices with large numbers of tessellated unit cells. Therefore, experimental validation of the dynamics of tensegrity metamaterials has remained elusive. For lattices with tensegrity-like characteristics to be manifested for real-world applications, a method for producing tensegrity-like metamaterials at multiple length scales is needed.
\r\n\r\nIn this thesis, we present a design for a 3D-printable tensegrity-inspired structure with the equivalent strain energy capacity and stress-strain response as a pin-jointed tensegrity. Using this structure as a building block for multidimensional lattices, we subject them to a range of dynamic loading conditions to study their response. First, we perform experiments and simulations to obtain the dispersion relations for 1D and 3D lattices. We demonstrate the lattices\u2019 ability to continuously tune the dispersion characteristics (e.g., band gap and wave speed) under precompression. This trait shows potential for acoustic lensing and dispersive wave propagation. In 3D, we show that the lattice shows the same type of unique properties, such as faster shear speed than longitudinal speed, as pin-jointed tensegrity lattices. Next, we study the lattices under impact loading. Long-duration impact experiments on baseline unit cells and 1D lattices show their resilience to repeated deformation, elasticity, and load limitation behaviors. Short-duration impulse experiments and simulations exhibit a wealth of desirable properties, such as high force transmission reduction, highly dispersive wave propagation, tunable wave speeds, energy trapping, and redirection of energy. We demonstrate that these tensegrity-inspired metamaterials not only exhibit and experimentally demonstrate tensegrity-like characteristics, but open a new range of lightweight metamaterials with unprecedented dynamic properties.
" }, { "name": "Rah, Kyupaeck Jeff", "degree": "PhD", "year": "2020", "title": "Derivation of Realistic Forcing Schemes to Reproduce Turbulent Characteristics of Round Jets on Centerline", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:08262019-191842947", "creators": [ { "name": { "family": "Rah", "given": "Kyupaeck Jeff" }, "id": "Rah-Kyupaeck-Jeff", "orcid": "0000-0003-1898-2930", "display_name": "Rah, Kyupaeck Jeff" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7SXH-V275", "abstract": "Turbulence forcing techniques are often required in the numerical simulation of statistically stationary turbulent flows. However, the existing forcing techniques are not based on physics, but rather arbitrary numerical methods that sustain the turbulent kinetic energy. In this work, a realistic forcing technique is devised to reproduce the centerline turbulent characteristics of round jets in a triply periodic box.
\r\n\r\nA velocity forcing term is derived from the Navier-Stokes equations by applying a Reynolds decomposition with the mean velocity of the axisymmetric jet. The result is an anisotropic linear forcing term. A series of direct numerical simulations (DNS) are performed over a range of Reynolds numbers by applying the derived velocity forcing term in a 3D cubic box. The budget of the terms in the kinetic energy equation is found to be very close to the experimental measurement on the centerline. The anisotropy ratio, kinetic energy, and dissipation rate of the simulations are also comparable to experimental values. Finally, the kinetic energy spectrum in the axial direction is presented. With appropriate normalizations, the spectrum agrees well with the round jet spectrum on its centerline.
\r\n\r\nA similar procedure is applied to passive scalars to derive a scalar forcing term to simulate the centerline mixing properties of round jets. The term is derived from the scalar transport equation using a Reynolds-like decomposition of the scalar field. The equation is closed by applying the known mean velocity and scalar profiles of axisymmetric jets. The result is a combination of a mean gradient term and a linear scalar term. DNS at different Reynolds numbers have been performed with these source terms for unity Schmidt number. Scalar flux values and scaling exponents of scalar energy spectra from simulations are comparable to experimental values. In addition, a dimensional analysis shows that the normalized scalar statistics, such as variance, flux, and dissipation rate, should only be a function of Reynolds number; indeed, such quantities computed from our simulations approach constant values as the Reynolds number increases. The effects of velocity forcing on scalar fields are also investigated; changing velocity forcing terms may result in unstable scalar fields even under the same scalar forcing.
\r\n\r\nMore computations on higher Schmidt number scalars are performed with the same velocity and scalar forcing terms. It is found that the scalar flux values decrease with increasing Schmidt number for low Reynolds number flows, and reach plateaus as the Schmidt number increases. The flux values also increase with the Reynolds number for all non-unity Schmidt numbers. The scaling exponents of scalar energy spectra are found to decrease with increasing Schmidt number for all Reynolds numbers.
" }, { "name": "Ren, Hengjiang", "degree": "PhD", "year": "2020", "title": "Cavity Optomechanics for Hybrid Quantum Systems", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082020-144243454", "creators": [ { "name": { "family": "Ren", "given": "Hengjiang" }, "id": "Ren-Hengjiang", "orcid": "0000-0002-5612-8287", "display_name": "Ren, Hengjiang" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/vr67-w986", "abstract": "Recent advances in optomechanical systems have led to a series of scientific and technical advances. In addition, they have demonstrated macroscopic quantum phenomena, including probabilistic preparation of quantum states, squeezed light, and coherent transduction between photons with different energies. There are advantages in using phonons within a quantum information network. Within the solid state, all optical and electronic phenomena strongly depend on the local distortions of the crystal lattice, i.e. mechanical phonons, hence could connect dissimilar degrees of freedom such as superconducting qubits operating at gigahertz frequencies with atomic/optical states. Also, unlike photons, phonons do not radiate into free space. Energy damping of phonon can occur through radiation into bulk structure which support the mechanical resonator, through impurities and defects in the material, and due to the inherent anharmonic motion of atoms within solid-state materials.
\r\n\r\nIn this thesis, we explore the limits of acoustic damping and coherence of a microwave-frequency acoustic nanocavity with a phononic crystal shield that possesses a wide bandgap for all polarizations of acoustic waves. The nanocavity is formed from an optomechanical crystal (OMC) nanobeam resonator. It supports an acoustic breathing mode at ~ 5 GHz and a co-localized telecom optical resonant mode which allows us to excite and readout mechanical motion using radiation pressure from a pulsed laser source. This minimally invasive pulsed measurement technique avoids a slew of parasitic damping effects - typically associated with electrode materials and mechanical contact, or probe fields for continuous readout - and allows for the sensitive measurement of motion at the single phonon level. The results of acoustic ringdown measurements at millikelvin temperatures show that damping due to radiation is effectively suppressed by the phononic shield, with breathing mode quality factors reaching mechanical quality factor Q = 4.9 x 1010, corresponding to an unprecedented frequency-Q product of f-Q = 2.6 x 1020 and an effective phonon propagation length of several kilometers. Measurement of the frequency jitter of the acoustic resonance is also performed, indicating telegraph-like noise corresponding to a coherence time of ~ 130 \u00b5s. The observed breathing mode behavior can be explained by TLS interactions when taking into account the highly modified density of phonon states in the shielded OMC cavity, which are most likely present in the amorphous etch-damaged region of the silicon surface. In particular, we find that damping due to nearly resonant TLS is suppressed due to the bandgap of the phononic shield, and that relaxation damping from non-resonant TLS can explain the magnitude, low temperature dependence of the breathing mode damping, and lack of saturation of the damping with both temperature and acoustic amplitude.
\r\n\r\nThe extremely small motional mass and narrow linewidth of the OMC cavity make it ideal for precision mass sensing and in exploring limits to alternative quantum collapse models.
\r\n\r\nOur mechanical modes exist in the same frequency range as common superconducting qubits, suggesting a possibility for creating a hybrid quantum architecture consisting of acoustic and superconducting quantum circuits, where the small scale, reduced cross-talk, and ultralong coherence time of quantum acoustic devices may provide significant improvements in connectivity and performance of current quantum hardware. A proposal of mechanical quantum memory based on ultra-high-Q mechanical model and piezo-electrical coupling is also discussed in this work. \r\nOne remaining roadblock, which significantly compromises the utility of OMCs integration with superconducting circuits, is the very weak, yet non-negligible parasitic optical absorption, which is thought to occur due to surface defect states, and together with inefficient thermalization can yield significant heating of the hypersonic mechanical mode of the device at ultralow temperatures, where microwave systems can be reliably operated as quantum devices. In 1D OMC experiments, the quantum cooperativity (Ceff), which corresponds to the standard photon-phonon cooperativity divided by the Bose factor of the thermal bath and is the most relevant figure-of-merit for operation of optomechanical systems at ultralow temperatures, was lower than unity for all but a microsecond around the time an optical pulse is applied. This limits quantum optomechanical experiments to schemes with short pulses. Increased Ceff can be achieved with improved thermalization, for example, by employing a two-dimensional (2D) OMC cavity.
\r\n\r\nIn this thesis, we demonstrate an improved silicon quasi-2D OMC with an over 50-fold improvement in back-action per photon over previous reports. We are able to measure the dynamics of the internal cavity acoustic modes of both 1D nanobeam and quasi-2D OMCs. Quasi-2D OMC shows much lower bath occupancy compared to 1D structures. Most importantly, quasi-2D OMCs demonstrated a Ceff greater than unity under steady-state optical pumping, a crucial threshold for realizing a variety of optomechanical applications. For example, bi-directional transduction or amplification of continuous quantum signals require the optomechanical device to be operated in a continuous mode. An analysis of piezo-optomechanical bi-directional microwave to optics transducer is also presented in this thesis.
" }, { "name": "Ronchi, Matteo Ruggero", "degree": "PhD", "year": "2020", "title": "Vision for Social Robots: Human Perception and Pose Estimation", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212020-155425112", "creators": [ { "name": { "family": "Ronchi", "given": "Matteo Ruggero" }, "id": "Ronchi-Matteo-Ruggero", "orcid": "0000-0002-4277-3314", "display_name": "Ronchi, Matteo Ruggero" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "orcid": "0000-0003-0848-3177", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Papon", "given": "Jeremie" }, "id": "Papon-Jeremie", "role": "member", "display_name": "Papon, Jeremie" } ], "option_major": [ "compsci" ], "doi": "10.7907/n2v1-1g79", "abstract": "In order to extract the underlying meaning from a scene captured from the surrounding world in a single still image, social robots will need to learn the human ability to detect different objects, understand their arrangement and relationships relative both to their own parts and to each other, and infer the dynamics under which they are evolving. Furthermore, they will need to develop and hold a notion of context to allow assigning different meanings (semantics) to the same visual configuration (syntax) of a scene.
\r\n\r\nThe underlying thread of this Thesis is the investigation of new ways for enabling interactions between social robots and humans, by advancing the visual perception capabilities of robots when they process images and videos in which humans are the main focus of attention.
\r\n\r\nFirst, we analyze the general problem of scene understanding, as social robots moving through the world need to be able to interpret scenes without having been assigned a specific preset goal. Throughout this line of research, i) we observe that human actions and interactions which can be visually discriminated from an image follow a very heavy-tailed distribution; ii) we develop an algorithm that can obtain a spatial understanding of a scene by only using cues arising from the effect of perspective on a picture of a person\u2019s face; and iii) we define a novel taxonomy of errors for the task of estimating the 2D body pose of people in images to better explain the behavior of algorithms and highlight their underlying causes of error.
\r\n\r\nSecond, we focus on the specific task of 3D human pose and motion estimation from monocular 2D images using weakly supervised training data, as accurately predicting human pose will open up the possibility of richer interactions between humans and social robots. We show that when 3D ground-truth data is only available in small quantities, or not at all, it is possible to leverage knowledge about the physical properties of the human body, along with additional constraints related to alternative types of supervisory signals, to learn models that can regress the full 3D pose of the human body and predict its motions from monocular 2D images.
\r\n\r\nTaken in its entirety, the intent of this Thesis is to highlight the importance of, and provide novel methodologies for, social robots' ability to interpret their surrounding environment, learn in a way that is robust to low data availability, and generalize previously observed behaviors to unknown situations in a similar way to humans.
" }, { "name": "Schill, William Joseph", "degree": "PhD", "year": "2020", "title": "Variational and Multiscale Modeling of Amorphous Silica Glass", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:07202019-135213721", "creators": [ { "name": { "family": "Schill", "given": "William Joseph" }, "id": "Schill-William-Joseph", "orcid": "0000-0003-0950-7433", "display_name": "Schill, William Joseph" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Stainier", "given": "Laurent F." }, "id": "Stainier-Laurent-F", "role": "member", "display_name": "Stainier, Laurent F." } ], "option_major": [ "mecheng" ], "doi": "10.7907/B2A9-RQ38", "abstract": "We develop a critical-state model of fused silica plasticity on the basis of data mined from molecular dynamics (MD) calculations. The MD data is suggestive of an irreversible densification transition in volumetric compression resulting in permanent, or plastic, densification upon unloading. Moreover, this data exhibits dependence on temperature and the rate of deformation. We show that these characteristic behaviors are well-captured by a critical state model of plasticity, where the densification law for glass takes the place of the classical consolidation law of granular media and the locus of constant volume states denotes the critical-state line. A salient feature of the critical-state line of fused silica, as identified from the MD data, that renders its yield behavior anomalous is that it is strongly non-convex, owing to the existence of two well-differentiated phases at low and high pressures. We argue that this strong non-convexity of yield explains the patterning that is observed in molecular dynamics calculations of amorphous solids deforming in shear. We employ an explicit and exact rank-2 envelope construction to upscale the microscopic critical-state model to the macroscale. Remarkably, owing to the equilibrium constraint the resulting effective macroscopic behavior is still characterized by a non-convex critical-state line. Despite this lack of convexity, the effective macroscopic model is stable against microstructure formation and defines well-posed boundary-value problems. We present examples of ballistic impact of silica glass rods by way of the optimal transport meshfree method. We extend the study of the inelastic behavior of silica glass to include the effect of many different temperatures, pressures, and strain rates using MD and maximum entropy atomistics (MXE) calculations. Owing to the temperature dependence of the model, the macroscopic model becomes unstable against adiabatic shear localization. Thus, the material adopts small inter-facial regions where the shear strain is extremely high. We characterize the shear band size, thereby predicting a yield knockdown factor at the macroscale, and compare the results to behavior reported in flyer plate impact experiments.
" }, { "name": "Shen, Yang", "degree": "PhD", "year": "2020", "title": "Phonon Anharmonicity at the Limits of Perturbation Theory", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292020-150856962", "creators": [ { "name": { "family": "Shen", "given": "Yang" }, "id": "Shen-Yang", "orcid": "0000-0001-6838-0925", "display_name": "Shen, Yang" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Hellman", "given": "Bj\u00f6rn O." }, "id": "Hellman-B-O", "orcid": "0000-0002-3429-7856", "role": "member", "display_name": "Hellman, Bj\u00f6rn O." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/e48r-2j94", "abstract": "Phonons, as the building blocks of solid-state physics, have been studied for almost one hundred years. The harmonic model is helpful when introducing the concepts and offering a basic physics picture of atomic vibrations. However, there are many properties that cannot be explained by the harmonic model or its extension to the quasiharmonic approximation (QHA), which ignores the pure temperature dependence of phonon frequencies. The rapid development of materials science requests a deep understanding of the phonon behaviors at elevated temperatures, where phonon-phonon interactions, as a main source of phonon anharmonicity, account for a number of abnormal phonon behaviors and the thermodynamical properties of many materials. In this thesis, I present the phonon anharmonicity in metals of Pd and Pt, the metallic compound FeGe2, and the polar material NaBr to show the limitation of the harmonic or QH model and the importance of taking anharmonic effects into consideration.
\r\n\r\nInelastic neutron scattering (INS) was used to measure the phonon density of states (DOS) in fcc Pd and Pt metal at temperatures from 7 K to 1576 K. Both phonon-phonon interactions and electron-phonon interactions were calculated by methods based on density functional theory (DFT) and were consistent with the measured shifts and broadenings of phonons with temperature. Contributions to the entropy from phonons and electrons were assessed and summed to obtain excellent agreement with prior calorimetric data. The QH entropy is positive for both phonons and electrons but larger for phonons. The anharmonic phonon entropy is negative in Pt, but in Pd it changes from positive to negative with increasing temperature.
\r\n \r\nPhonon dispersions in a single crystal of FeGe2 with the C16 structure at 300, 500, and 635 K were measured by INS. Phonon DOS were also measured on polycrystalline FeGe2 from 325 to 1050 K, and the Fe partial DOS was obtained from polycrystalline 57FeGe2 at 300 K using nuclear resonant inelastic X-ray scattering (NRIXS). The dominant feature in the temperature dependence of the phonon spectrum is thermal broadening of high-energy modes. The energy shifts of the low- and high-energy parts of the spectrum were almost the same. DFT calculations performed with the QHA gave results in moderate agreement with the experimental thermal energy shifts, although the isobaric Gr\u00fcneisen parameter calculated from the quasiharmonic model was smaller than that from measurements. The thermal broadening of the phonon spectrum and dispersions, especially at high energies, indicates a cubic anharmonicity to second order that should also induce phonon shifts. There are cancellations of different anharmonic contributions to energy shifts, giving average phonon shifts in moderate agreement to calculations with the QHA. The different parts of the large phonon contribution to the entropy are separated for FeGe2, showing modest but interpretable anharmonic contributions.
\r\n\r\nAll phonons in a single crystal of NaBr were measured by INS at temperatures of 10, 300 and 700 K. Even at 300 K the phonons, especially the longitudinal optical (LO) phonons, showed large shifts in frequencies, and showed large broadenings in energy owing to anharmonicity. The QHA was an unqualified failure for predicting the temperature dependence of phonon frequencies, even at 300K, and it predicted a thermal expansion that was in error by a factor of four. Ab initio computations that included both anharmonicity and quasiharmonicity successfully predicted both the temperature dependence of phonons and the large thermal expansion of NaBr. The frequencies of LO phonon modes decrease significantly with temperature owing to the real part of the phonon self-energy from explicit anharmonicity. The origin of the large cubic anharmonicity was identified with nearest-neighbor Na-Br bonds. Anharmonicity is not a small correction to the QHA predictions of thermal expansion and thermal phonon shifts, but anharmonicity dominates the behavior.
\r\n\r\nNew spectral features were found in phonon dispersions of NaBr at 300 K. Ab initio calculations based on anharmonic perturbation theory also showed these spectral features as \"many-body effects\". Their physical origin is better elucidated with a Langevin model, similar that in recent work in optomechanics. The transverse optic (TO) part of the new features originates from phonon intermodulation between the transverse acoustic (TA) and TO phonons. The LO spectral features originate from three-phonon coupling between the TA modes and the TO lattice modes.
" }, { "name": "Taeb, Armeen", "degree": "PhD", "year": "2020", "title": "Latent-Variable Modeling: Algorithms, Inference, and Applications", "advisor": "Chandrasekaran, Venkat", "url": "https://resolver.caltech.edu/CaltechTHESIS:09222019-132051506", "creators": [ { "name": { "family": "Taeb", "given": "Armeen" }, "id": "Taeb-Armeen", "orcid": "0000-0002-5647-3160", "display_name": "Taeb, Armeen" } ], "advisors": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "advisor", "display_name": "Chandrasekaran, Venkat" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Pachter", "given": "Lior S." }, "id": "Pachter-L", "orcid": "0000-0002-9164-6231", "role": "member", "display_name": "Pachter, Lior S." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" } ], "option_major": [ "eleceng" ], "doi": "10.7907/YRF1-7W29", "abstract": "Many driving factors of physical systems are often latent or unobserved. Thus, understanding such systems crucially relies on accounting for the influence of the latent structure. This thesis makes advances in three aspects of latent-variable modeling: inference, algorithms, and applications. Specifically, we develop and explore latent-variable techniques that a) ensure interpretable and statistically significant models, b) can be efficiently optimized to identify best fit to data, and c) provide useful insights in real-world applications. The specific contributions of this thesis are:
\r\n\r\n1. We employ a latent-variable graphical modeling technique to develop the first state-wide statistical model of the California reservoir network. With this model, we precisely characterize the system-wide behavior of the network to hypothetical drought conditions, and proposed guidelines for more sustainable reservoir management.
\r\n\r\n2. Motivated by the previous application, we provide a geometric framework to assess the extent to which our latent variable model has learned true or false discoveries about the relevant physical phenomena. Our approach generalizes the classical notions of true and false discoveries in mathematical statistics that rely on the discrete structure of the decision space to settings where the decision space is continuous and more complicated. We highlight the utility of this viewpoint in problems involving subspace selection and low-rank estimation.
\r\n\r\n3. We propose a convex optimization procedure to fit a latent-variable graphical model for generalized linear models. This framework provides a flexible approach to model non-Gaussian variables including Poisson, Bernoulli, and exponential variables. A particularly novel aspect of our formulation is that it incorporates regularizers that are tailored to the type of latent variables.
\r\n\r\n4. We describe a computationally efficient framework to learn a latent-variable model with high-dimensional and non-iid data. This framework is based on factoriable precision operators that decouple the component associated with the observational dependencies and the component associated to interdependencies among the variables.
\r\n\r\n5. We propose a convex optimization technique to provide semantics to latent variables of a factor model. This approach is based on linking auxiliary variables -- chosen based on domain expertise -- to these latent variables.
" }, { "name": "Talon, Thibaud", "degree": "PhD", "year": "2020", "title": "Surface Reconstruction from Distributed Angle Measurements", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:02282020-192725947", "creators": [ { "name": { "family": "Talon", "given": "Thibaud" }, "id": "Talon-Thibaud", "orcid": "0000-0002-8240-1101", "display_name": "Talon, Thibaud" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/ZG2D-2K77", "abstract": "This thesis presents an innovative solution to the shape measurement of large structures for space applications. The current state-of-the-art heavily relies on optical solutions such as cameras or lasers to recover the shape of a surface. Because of the impracticality of placing a system in front of a large structure flying in space, new solutions need to be developed. The proposed solution is to embed angular sensors (such as sun sensors) directly on the surface. The sensors provide a collection of distributed measurements that form a discrete map of the angular orientation of the structure. An integration scheme can then estimate the 3D shape of the surface.
\r\n\r\nA mathematical model to perform the integration from angle measurements to the shape of a 3D surface is presented first. This model is purely geometric and serves as a basis for similar concepts. The surface is known in a reference configuration and is assumed to have deformed inextensibly to its current shape. Inextensibility conditions are enforced through a discretization of the metric tensor generating a finite number of constraints. This model parameterizes the shape of the surface using a small number of unknowns, and thus requires a small number of sensors. We study the singularities of the equations and derive necessary conditions for the problem to be well-posed. The limitations of the algorithm are highlighted. Simulations are performed on developable surfaces to analyze the performance of the method and to show the influence of the parameters used in the algorithm. Optimal schemes which lower the RMS error between the reconstructed shape and the actual one are presented.
\r\n\r\nAn experimental validation of the proposed solution and algorithm is performed on a 1.3 x 0.25 m structure with 14 embedded sun sensors. The sensors measure the two local angles of the surface from a light source placed in front of the surface. A small, lightweight and expandable design of the sensors is shown in this thesis. A calibration procedure accurately correlates the output of the sensor with a 0.5\u00b0 precision. The procedure also highlights the limitations of the design. The structure was deformed in bending and torsion with amplitudes of a few centimeters, and its shape was reconstructed to an accuracy on the order of a millimeter.
\r\n\r\nThe accuracy of the initial algorithm is found to be limited by local shape deformations caused by the mechanical response of the structure. A new algorithm, replacing the discrete inextensibility conditions with the equilibrium equations derived from a finite-element model, is shown. This new algorithm is tested on the experimental structure and the accuracy of the reconstruction is increased by a factor of 2. The RMS error is under a millimeter on average over the different applied shapes and goes as low as 0.3 mm.
\r\n\r\nTo understand how this solution can apply to large space structures, simulations are performed on a model of a large planar spacecraft. A 25 x 25 m structure representing the current concept for the Caltech Space Solar Power Project satellite is used as an example. Sensors with similar noise properties as the ones built for the experiment are placed on the spacecraft. A finite-element model combining the vibration of the spacecraft with large rigid body rotations is presented. This model is used in a Kalman filter that estimates the shape of the structure by iterative prediction from the dynamic finite-element model and correction from the angle measurements. Simulations are performed around the thruster actuation applied at the corner of the structure to follow a specific guidance scheme that is optimal for space solar power satellites. The actuation creates both vibrations of the structure with amplitudes of few centimeters and large rotations of the spacecraft. The designed Kalman filter can accurately estimate both effects and it is shown that millimeter accuracy is achievable. The relationship between the number of sensors, the reconstructed shape error, as well as potential stiffness deviations in the FE model is studied. The results provide first order estimates of the performance of this measurement system, in order to enable the design of future space missions.
" }, { "name": "Tanner, Melissa Midori", "degree": "PhD", "year": "2020", "title": "Tethered Motion Planning for a Rappelling Robot", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012020-230913819", "creators": [ { "name": { "family": "Tanner", "given": "Melissa Midori" }, "id": "Tanner-Melissa-Midori", "orcid": "0000-0003-4610-1379", "display_name": "Tanner, Melissa Midori" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Nesnas", "given": "Issa A." }, "id": "Nesnas-I-A", "role": "member", "display_name": "Nesnas, Issa A." }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/h7d4-ww72", "abstract": "The Jet Propulsion Laboratory and Caltech developed the Axel rover to investigate and demonstrate the potential for tethered extreme terrain mobility, such as allowing access to science targets on the steep crater walls of other planets. Tether management is a key issue for Axel and other rappelling rovers. Avoiding tether entanglement constrains the robot's valid motions to the set of outgoing and returning path pairs that are homotopic to each other. In the case of a robot on a steep slope, a motion planner must additionally ensure that this ascent-descent path pair is feasible, based on the climbing forces provided by the tether. This feasibility check relies on the taut tether configuration, which is the shortest path in the homotopy class of the ascent-descent path pair.
\r\n\r\nThis dissertation presents a novel algorithm for tethered motion planning in extreme terrains, produced by combining shortest-homotopic-path algorithms from the topology and computational geometry communities with traditional graph search methods. The resulting tethered motion planning algorithm searches for this shortest path, checks for feasibility, and then generates waypoints for an ascent-descent path pair in the same homotopy class. I demonstrate the implementation of this algorithm on a Martian crater data set such as might be seen for a typical mission. By searching only for the shortest path, and ordering that search according to a heuristic, this algorithm proceeds more efficiently than previous tethered path-planning algorithms for extreme terrain.
\r\n\r\nFrictional tether-terrain interaction may cause dangerously intermittent and unstable tether obstacles, which can be categorized based on their stability. Force-balance equations from the rope physics literature provide a set of tether and terrain conditions for static equilibrium, which can be used to determine if a given tether configuration will stick to a given surface based on tether tension. By estimating the tension of Axel's tether when driving, I divide potential tether tension obstacles into the following categories: acting as obstacles, acting as non-obstacles, and hazardous intermittent obstacles where it is uncertain whether the tether would slip or stick under normal driving tension variance. This dissertation describes how to modify the obstacle map as the categorization of obstacles fluctuates, and how to alter a motion plan around the dangerous tether friction obstacles. Together, these algorithms and methods form a framework for tethered motion planning on extreme terrain.
" }, { "name": "Tokpanov, Yury", "degree": "PhD", "year": "2020", "title": "Towards Next Generation of Optoelectronics: from Quantum Plasmonics and 2D Materials to Advanced Optimization Techniques of Nanophotonic Devices", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechThesis:06012020-093627645", "creators": [ { "name": { "family": "Tokpanov", "given": "Yury" }, "id": "Tokpanov-Yury", "orcid": "0000-0001-5123-7428", "display_name": "Tokpanov, Yury" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/tg1b-hn35", "abstract": "In this thesis, we explore different novel concepts and materials for the next-generation of nanophotonic and optoelectronic devices that could be used both in classical and quantum settings.
\r\n\r\nFirst, we study quantum coherence properties of surface plasmon polaritons (SPPs) in the regime of extreme dispersion. Most experiments to date, that tested quantum coherence properties of SPPs, used essentially weakly-confined plasmons, which experience limited light-matter hybridization, thus restricting the potential for decoherence. Our setup is based on a hole-array chip supporting SPPs near the surface plasma frequency, where plasmonic dispersion and confinement is much stronger than in previous experiments, making the plasmons much more susceptible for decoherence processes. We generated polarization-entangled pairs of photons and transmitted one of the photons through this plasmonic hole array. Our results show that the quality of photon entanglement after the highly-dispersive plasmonic channel is unperturbed. Our findings provide a lower bound of 100 femtoseconds for the pure dephasing time of dispersive plasmons in our materials, and show that even in a highly dispersive regime, surface plasmons preserve quantum mechanical correlations, making possible harnessing the power of extreme light confinement for integrated quantum photonics.
\r\n\r\nSecond, we systematically study different passivation schemes of sulfur vacancies in 2D molybdenum disulfide using first-principles calculations based on density functional theory. We aim at building a microscopic understanding of passivation mechanisms of treatment with TFSI superacid - a popular approach of to improve optical properties. Since superacids have a strong ability to donate protons, we consider hydrogenation and protonation of sulfur vacancies as a possible passivation scheme. Our calculations show that effects of protonation and hydrogenation on properties of 2D molybdenum disulfide are very similar. Moreover, we find that four hydrogen atoms can fully \"heal\" sulfur vacancies in this material. Our results are an important step towards controllable defects design in 2D transition metal dichalcogenides.
\r\n\r\nAnd third, we study applications of advanced methods of optimization and machine learning to the design of different nanophotonic devices. We explore feasibility of using novel multi-fidelity Gaussian processes optimization technique to optimize plasmonic mirror filters for hyperspectral imaging. We compare our results with other common optimization approaches. Then we apply deep-learning inspired techniques to optimize control voltages of individual pixels of active metasurfaces to achieve dynamic beamsteering. We obtain interesting results that pave the way for future experiments both in nanophotonics and machine learning fields.
" }, { "name": "Vyatskikh, Andrey", "degree": "PhD", "year": "2020", "title": "Additive Manufacturing of 3D Nano-Architected Metals and Ceramics", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252020-134146453", "creators": [ { "name": { "family": "Vyatskikh", "given": "Andrey" }, "id": "Vyatskikh-Andrey", "orcid": "0000-0002-6917-6931", "display_name": "Vyatskikh, Andrey" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "chair", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "medeng" ], "doi": "10.7907/pdz2-dd59", "abstract": "Additive manufacturing (AM) represents a set of manufacturing processes that create complex 3D parts out of polymers, metals, and ceramics. AM of metals and ceramics is widely used to produce parts for aerospace, automotive, and medical applications. At the micro- and nano-scales, AM is poised to become the enabling technology for efficient 3D microelectromechanical systems (MEMS), 3D micro-battery electrodes, 3D electrically small antennae, micro-optical components, and photonics. Today, the minimum feature size for most commercially available metal and ceramic AM is limited to ~20-50 \u03bcm. Currently, no established processes can reliably produce complex 3D metal and ceramic parts with sub-micron features.
\r\n\r\nIn this thesis, we first demonstrate a nanoscale metal AM process that can produce ~300 nm features out of nanocrystalline, nanoporous nickel using synthesized hybrid organic-inorganic materials, two-photon lithography, and pyrolysis. We study microstructure and mechanical properties of as-fabricated nickel architectures and compare their structural strength to established AM processes. We then show how this process can be extended to other metals and metalloids, including Mg, Ge, Si, and Ti.
\r\n\r\nThis study extends further into nanoscale AM of transparent, high refractive index materials for micro-optics and photonic crystals. We develop an AM process to 3D print fully dense nanocrystalline rutile titanium dioxide (TiO\u2082) with feature dimensions down to ~120 nm. We carefully study and model the relationship between feature dimensions and process parameters to achieve a <2% variation in critical dimensions. We then use this understanding of the process to fabricate and study 3D dielectric photonic crystals with a full photonic bandgap in the infrared.
\r\n\r\nFinally, a microscale AM process of titanium dioxide is demonstrated for photocatalytic water treatment. We show how synthesized hybrid organic-inorganic materials can be applied for stereolithography to print TiO\u2082 architectures with 100 \u03bcm features. We use the developed 3D printing process to investigate the effect of 3D architecture on the efficiency of photocatalytic water treatment.
\r\n\r\nThis work establishes a versatile and efficient pathway to create three-dimensional nano-architected metals and ceramics and to investigate their properties for applications in 3D MEMS, micro-optics, photonics, and photocatalysis.
\r\n" }, { "name": "Wang, Chuting", "degree": "PhD", "year": "2020", "title": "On-Chip Photonic Devices for Coupling to Color Centers in Silicon Carbide", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04122020-055837611", "creators": [ { "name": { "family": "Wang", "given": "Chuting" }, "id": "Wang-Chuting", "orcid": "0000-0002-3711-682X", "display_name": "Wang, Chuting" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/m2p0-6t37", "abstract": "Optical quantum networks are important for global use of quantum computers, and secure quantum communication. Those networks require storage devices for synchronizing or making queues of processing transferred quantum information. Practical quantum information networks should minimize loss of transmitted data (photons) and have high efficiency mapping when writing data on memories (solid state qubits). This requires strong light-matter interaction that is enabled by coupling qubits to optical cavities.
\r\n\r\nThe first half of the thesis focuses on emerging candidates for promising qubits in silicon carbide (SiC). The optical and quantum properties of these color centers are discussed with focus on divacancies in 4H-SiC due to their long spin coherence time. Optically detected magnetic resonance of divacancies is shown, an essential technique for reading out the qubit state using the intensity of optical emission.
\r\n\r\nThe second half of the thesis focuses on hybrid photonic devices for coupling to silicon carbide qubits. Hybrid devices are made of another layer of high refractive index material other than the qubit hosting material. Evanescent coupling to qubits close to the surface can be achieved without damaging the host material. Mainly the silicon (Si) on 4H-SiC hybrid ring resonator architecture is discussed starting from design, simulation to fabrication. The fabrication includes Si membrane transfer that is an important step to create a light confining layer on 4H-SiC. The final ring resonator device shows quality factors as high as 23000.
" }, { "name": "Wongwaitayakornkul, Pakorn", "degree": "PhD", "year": "2020", "title": "Dynamics of an Arched Magnetically-Twisted Current-Carrying Plasma", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:03042020-114816620", "creators": [ { "name": { "family": "Wongwaitayakornkul", "given": "Pakorn" }, "id": "Wongwaitayakornkul-Pakorn", "orcid": "0000-0001-7455-8582", "display_name": "Wongwaitayakornkul, Pakorn" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "orcid": "0000-0001-8638-0320", "role": "chair", "display_name": "Hillenbrand, Lynne A." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/6Q9D-JH07", "abstract": "Experimental and numerical studies of a dense magnetically-twisted plasma and their applications to solar plasmas are the subject of this dissertation. In the corona, plasma lies in a low-beta, high Lundquist number regime, meaning that it is magnetically dominated and the magnetic fields are well frozen into the plasma. Understanding the dynamics of these plasmas help us predict and prevent damage from future catastrophic solar eruption events. In situ measurements from satellite and ground-based observation provide limited information that is not controllable nor reproducible. The research objective in this thesis is to produce a miniature-scaled plasma with the same dimensionless parameters as the space plasmas. Along with numerical simulation, theoretical study, and observational data, the laboratory plasma can give novel insights into the physics of solar plasma.
\r\n\r\nFirst, an experimental dip on a flux rope, previously thought to be caused by a kink instability, is discussed and explained. We find that the apex cusp is in fact caused by the differential acceleration due to a non-uniform density. The pileup density results from a nonlinear interaction of the neutral gas. This result introduces a new method to impose effective gravity on the arched plasma and explains the suppression of kink instability. Second, a model for a morphology of CME and its shock driving mechanism is investigated. In the experiment, the chamber is prefilled with neutral gas, leading to an observation of a density cavity. Because the plasma is flux conserving, injecting a current into the plasma induces an opposite eddy current in front of the flux rope. The two opposing currents repel and leave a low density region in between. This feature is often observed in CMEs. We propose this mechanism to be the model of the CME 3-part structure formation. The opposite eddy current acts as a current piston driving an MHD perturbation/shock, which is often observed on the sun as an EUV wave.
\r\n\r\nA Magnetic Rayleigh-Taylor instability has been observed in the arched plasma loop. For the first time, the magnetic effect of the MRT instability is shown when the wavelength observed depends on the initial magnetic field initially injected into the system. In several years of working with the experiment in the Bellan plasma group, I designed and constructed several diagnostics, such as Langmuir probes, magnetic probes, and a coded aperture camera. Together with fast multi-images camera and spectroscopy techniques, plasma parameters are measured and compared to verify the models.
\r\n\r\nThe 3D MHD numerical simulation was performed using the supercomputer from the Los Alamos National Laboratory. The initial condition and injection routines were modified to appropriately replicate the experiment. The code has been significant in improving our understanding of the physical phenomena we observed in the experiment. We attain a proper initial distribution of the mass density and the initial and injected current density. In addition to simulating an arched flux rope experiment, we use this tool to replicate MHD instabilities detected in the astrophysical jet experiment. Specifically, both a sausage-to-kink and kink-to-Rayleigh-Taylor instability have been reproduced using the numerical simulation. Each process thins the plasma current channel to be below the ion skin depth. The kinetic effect then gives rise to magnetic reconnection. An anomalous resistivity is added to simulate this process.
\r\n\r\nIn conclusion, an interdisciplinary approach, through experimental, numerical, observational, and theoretical studies, is presented. It improves our understanding of the underlying mechanism for solar eruptions. A magnetically-twisted current-carrying flux rope, once formed, could exhibit dips and cavity. Its evolution could a drive shock and instabilities, which ultimately cause particle acceleration.
" }, { "name": "Yanes, Nelson Javier", "degree": "PhD", "year": "2020", "title": "Ultraviolet Radiation of Hypervelocity Stagnation Flows and Shock/Boundary-Layer Interactions", "advisor": "Austin, Joanna M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02112020-170613058", "creators": [ { "name": { "family": "Yanes", "given": "Nelson Javier" }, "id": "Yanes-Nelson-Javier", "orcid": "0000-0001-8423-6958", "display_name": "Yanes, Nelson Javier" } ], "advisors": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "advisor", "display_name": "Austin, Joanna M." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "orcid": "0000-0002-1225-4695", "role": "member", "display_name": "Polk, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WYHM-1218", "abstract": "Shock/boundary-layer interactions can induce flow distortion, create flow separation with loss of control authority, and result in high thermal loads. Correct prediction of the flow structure and heating loads is vital for vehicle survival. However, a recent NATO workshop revealed severe underprediction of thermal loads and discrepancies in the location of separation by simulations of high enthalpy air flows. Due to the coupling between thermochemistry and fluid mechanics, a substantial effort has been placed on the development and validation of thermochemical models. As a result, there is a need for experimental data that are more than mean flow surface measurements.
\r\n\r\nSpatially resolved emission spectra are collected in the post-shock regime of hypervelocity flow over a circular cylinder and a 30-55 degree double wedge. The Hypervelocity Expansion Tube (HET) is used to generate high Mach number, high enthalpy flow (Mach numbers 5 - 7, h\u2080 = 4 - 8 MJ/kg) with minimal freestream dissociation. The NO \u03b3 band (A\u00b2\u03a3\u207a - X\u00b2\u03a0) emission is measured in the ultraviolet range of 210-250 nm at downstream locations behind shock waves. Excitation temperatures are extracted from the NO \u03b3 emission from spectrum fitting. The result is a temperature relaxation profile that quantifies the state thermal non-equilibrium. Profiles of vibrational band intensity as a function of streamwise distance are used as direct measurements of chemical non-equilibrium in the flow.
\r\n\r\nCylinder experiments are performed with varying freestream total enthalpy, Mach number, and test gas O\u2082 mole fraction to examine changes in relaxation profile. Schlieren images are used to accurately measure standoff distance. Temperature measurements are compared against a zero-dimensional state-to-state model. Strategies for spectrum fitting are presented for cases where the gas is not optically thin and for radiation containing multiple electronic states. For freestream mixtures with reduced oxygen mole fraction, an electronic excitation temperature is required to describe the radiation of the NO \u03b3, \u03b2 (B\u00b2\u03a0 - X\u00b2\u03a0), and \u03b4 (C\u00b2\u03a0 - X\u00b2\u03a0) transitions. The creation of electronically excited NO is discussed in the context of measured vibrational band intensities and computed NO(A) number density profiles using a two-temperature reactive Landau-Teller model.
\r\n\r\nEmission spectra are collected in the post bow shock and reattachment shock region of hypervelocity flow over a double wedge. High speed schlieren imaging is performed to investigate facility startup effects and for tracking features in a shock/boundary-layer interaction. Detector exposures occur at select times throughout the flow development process to study temporal changes in thermal and chemical non-equilibrium. Time evolution of temperatures at strategic locations of the flow is obtained from spectrum fitting. Two-temperature calculations of the oblique shock system are compared against the emission results. Radiation data are discussed in the context of recent simulation efforts.
" }, { "name": "Yee, Daryl Wei Liang", "degree": "PhD", "year": "2020", "title": "Additive Manufacturing of 3D Functional Materials: From Surface Chemistry to Combustion-Derived Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042020-112316408", "creators": [ { "name": { "family": "Yee", "given": "Daryl Wei Liang" }, "id": "Yee-Daryl-Wei-Liang", "orcid": "0000-0002-4114-6167", "display_name": "Yee, Daryl Wei Liang" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "member", "display_name": "Grubbs, Robert H." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/ya58-cn88", "abstract": "Over the past decade, additive manufacturing has emerged as one of the most powerful manufacturing tools available today. Vat photopolymerization techniques, in particular, are especially promising as they are capable of achieving high resolutions and throughputs. However, the vast majority of materials that are compatible with them only have structural functionality. The fabrication of functional materials still remains a challenge in the field: functional polymers often require a complex multi-step synthesis. Ceramics-based photoresins are limited in composition and are challenging to use or synthesize. Metals have also been hardly explored with vat photopolymerization techniques.
\r\n\r\nThis thesis explores methods of fabricating functional materials with vat photopolymerization. We develop accessible techniques for the fabrication of functional polymers, ceramics, metals, and multimaterials at a variety of length scales, from sub-micron to centimeter scales. On the polymer front, we first explore how surface coatings can be an accessible method of introducing chemical functionality to a material. In particular, we demonstrate the surface coating of genomic DNA on an architected polymeric structure and show how it can be used as a drug capture device to reduce off-target toxicity in chemotherapy. We also explore the use of click chemistry, the thiol-Michael reaction in particular, in the facile synthesis of acrylate monomers with a variety of functional groups. We demonstrate the compatibility of these functionalized monomers with two-photon lithography and highlight some potential applications of these functional polymers structures.
\r\n\r\nIn the fabrication of ceramics and metals, we present a novel technique called photopolymer complex synthesis that combines solution combustion synthesis with vat photopolymerization to enable their fabrication. We illustrate the use of this technique by first fabricating piezoelectric zinc oxide architected structures with sub-micron features using two-photon lithography. Following that, we fabricate lithium cobalt oxide structures using digital light processing printing and highlight their use as architected lithium-ion battery cathodes. Lastly, we show how photopolymer complex synthesis can be expanded to fabricate metal and multimaterial architected structures. Our work highlights the use of polymer chemistry and materials science in expanding the range of materials that are compatible with vat photopolymerization, with the vision of democratizing the fabrication of advanced functional materials and enabling the production of previously impossible 3D devices.
" }, { "name": "Yoon, Young Dae", "degree": "PhD", "year": "2020", "title": "Probing the Progression, Properties, and Progenies of Magnetic Reconnection", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:04302020-151019178", "creators": [ { "name": { "family": "Yoon", "given": "Young Dae" }, "id": "Yoon-Young-Dae", "orcid": "0000-0001-8394-2076", "display_name": "Yoon, Young Dae" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "role": "chair", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Velli", "given": "Marco" }, "id": "Velli-Marco", "role": "member", "display_name": "Velli, Marco" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/hqwx-r892", "abstract": "Magnetic reconnection is a plasma phenomenon in which opposing magnetic fields annihilate and release their magnetic energy into other forms of energy. In this thesis, various aspects of collisionless magnetic reconnection are studied analytically and numerically, and an experimental diagnostic for magnetic fields in a plasma is described.
\r\n \r\nThe progression of magnetic reconnection is first illustrated through the formulation of a framework that revolves around canonical vorticity flux, which is ideally a conserved quantity. The reconnection instability, electron acceleration, and whistler wave generation are explained in an intuitive manner by analyzing the dynamics of canonical vorticity flux tubes. The validity of the framework is then extended down to first principles by the inclusion of the electron canonical battery effect. The importance of this effect during reconnection determines the overall structure and evolution of the process.
\r\n \r\nA crucial property of magnetic reconnection is its accompaniment by anomalous ion heating much faster than conventional collisional heating. Stochastic heating is a mechanism in which, under a sufficiently strong electric field, particles undergo chaotic motion in phase space and heat up dramatically. Using the previously established canonical vorticity framework, it is demonstrated that the Hall electric fields that develop during reconnection satisfy the stochastic ion heating criterion and that the ions involved indeed undergo chaotic motion. This mechanism is then kinetically verified via exact analyses and particle simulations and is thus ultimately established as the main ion heating mechanism in magnetic reconnection.
\r\n \r\nAn important progeny of magnetic reconnection is whistler waves. These waves interact with energetic particles and scatter their pitch-angles, triggering losses of magnetic confinement. A previous study demonstrated via exact relativistic analyses that if a particle undergoes a \"two-valley\" motion, it undergoes drastic changes in its pitch-angle. This analysis is extended to a relativistic thermal distribution of particles. The condition for two-valley motion is first derived; it is then shown that a significant fraction of the particle distribution meets this condition and thus undergoes large pitch-angle scatterings. The scaling of this fraction with the wave amplitude suggests that relativistic microburst events may be explained by the two-valley mechanism. It is also found that the widely-used second-order trapping theory is an inaccurate approximation of the theory presented.
\r\n \r\nA new method of probing the magnetic field in a plasma is described and developed to some extent. It utilizes the two-photon Doppler-free laser-induced fluorescence technique, where two counter-propagating laser beams effectively cancel out the Doppler effect and excite electron populations. The fluorescence resulting from the subsequent de-excitation is then measured, enabling the resolution of Zeeman splitting of the spectral lines from which the magnetic field information can be inferred. A high-power, repetitively-pulsed radio-frequency plasma source was developed as the subject of diagnosis, and preliminary results are presented.
" }, { "name": "Adalian, Dvin Artashes-Boghos", "degree": "PhD", "year": "2019", "title": "Development and Dynamics of Microfabricated Enzymatic Biosensors", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102019-031412552", "creators": [ { "name": { "family": "Adalian", "given": "Dvin Artashes-Boghos" }, "id": "Adalian-Dvin-Artashes-Boghos", "display_name": "Adalian, Dvin Artashes-Boghos" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7GHS-NX49", "abstract": "We have extended the application of microfabrication techniques to all parts of electrochemical enzymatic sensor processing and characterized the behavior of the resulting new sensor geometries. Improved and parallelized enzyme immobilization techniques utilizing spin coating along with porous sputtered platinum barrier layers are implemented on microfabricated platinum electrodes on silicon wafer substrates as well as on millimeter-scale wireless CMOS potentiostats. Functional biosensor sensitivities and linear ranges were observed with multi-month lifetimes, demonstrating that the enzyme layer fabrication process is compatible with precise and massively parallelized CMOS fabrication, making further progress toward the production of low cost and low-tissue impact fully implantable miniaturized biosensors." }, { "name": "Arbabi, Ehsan", "degree": "PhD", "year": "2019", "title": "Metasurfaces: Beyond Diffractive and Refractive Optics", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04222019-151834122", "creators": [ { "name": { "family": "Arbabi", "given": "Ehsan" }, "id": "Arbabi-Ehsan", "orcid": "0000-0002-5328-3863", "display_name": "Arbabi, Ehsan" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/EQEY-KZ52", "abstract": "Optical metasurfaces are a category of thin diffractive optical elements, fabricated using the standard micro- and nano-fabrication techniques. They provide new ways of controlling the flow of light based on various properties such as polarization, wavelength, and propagation direction. In addition, their compatibility with standard micro-fabrication techniques and compact form factor allows for the development of several novel platforms for the design and implementation of various complicated optical elements and systems. In this thesis, I first give a short overview and a brief history of the works on optical metasurfaces. Then I discuss the capabilities of metasurfaces in controlling the polarization and phase of light, and showcase their potential applications through the cases of polarimetric imaging and vectorial holography. Then, a discussion of the chromatic dispersion in optical metasurfaces is given, followed by three methods that can be utilized to design metasurfaces working at multiple discrete wavelengths. As a potential application of such metasurfaces, I present results of using them as objective lenses in two-photon microscopy. In addition, I discuss how metasurfaces enable the at-will control of chromatic dispersion in diffractive optical elements, demonstrate metasurfaces with controlled dispersion, and provide a discussion of their limitations. Integration of multiple metasurfaces into metasystems allows for implementation of complicated optical functions such as imaging and spectrometry. In this regard, I present several examples of how such metasystems can be designed, fabricated, and utilized to provide wide field of view imaging and projection, microelectromechanically tunable lenses, optical spectrometers, and retroreflectors. I conclude with an outlook on where metasurfaces can be most useful, and what limitations should be overcome before they can find wide-spread application.
" }, { "name": "Brake, Joshua Harris", "degree": "PhD", "year": "2019", "title": "Seeing Through the Fog: Using Scattered Light to Peer Deeper into Biological Tissue\r ", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282019-104728085", "creators": [ { "name": { "family": "Brake", "given": "Joshua Harris" }, "id": "Brake-Joshua-Harris", "orcid": "0000-0002-5113-6886", "display_name": "Brake, Joshua Harris" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Gradinaru", "given": "Viviana" }, "id": "Gradinaru-V", "role": "member", "display_name": "Gradinaru, Viviana" }, { "name": { "family": "Chung", "given": "Euiheon" }, "id": "Chung-Euiheon", "role": "member", "display_name": "Chung, Euiheon" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0PP8-2E39", "abstract": "Optical scattering is a fundamental problem in biomedical optics and limits most optical techniques to shallow operating depths less than 1 millimeter. However, although the scattering behavior of tissue scrambles the information it contains, it does not destroy it. Therefore, if you can unscramble the scattered light, it increases the accessible imaging depths up the absorption limit of light (several centimeters deep).
\r\n\r\nOne such way to beat optical scattering is using wavefront shaping. Borrowing ideas from adaptive optics in astronomy and phased arrays in radar and ultrasonic imaging, the basic concept of wavefront shaping is to control the phase and amplitude of the light field in order to harness scattered light. Using wavefront shaping techniques, scattered light can be used to form focal spots or transmit information through or inside optically scattering media. Furthermore, even without correcting for scattering directly by shaping the input light field, the properties of the scattered light can be analyzed to recover information about the structure and dynamic properties of a sample using methods from diffuse optics.
\r\n\r\nThe main contributions of this thesis are along these two lines of research: moving wavefront shaping toward more practical applications and developing new techniques to recover useful physiological information from scattered light. This is developed through three main projects: (1) an investigation of how dynamic samples impact the scattering process and the practical implications of these dynamics on wavefront shaping systems, (2) the development of a wavefront shaping system combining light and ultrasound to focus light inside acute brain slices to improve light delivery for optogenetics, (3) a novel method to sensitively detect the dynamics of scattered light and use it to tease out information about the flow of blood within the tissue sample of interest.
" }, { "name": "Brouillet, Jeremy Jean", "degree": "PhD", "year": "2019", "title": "Graphene-Mediated Light-Matter Interaction", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022019-011156429", "creators": [ { "name": { "family": "Brouillet", "given": "Jeremy Jean" }, "id": "Brouillet-Jeremy-Jean", "orcid": "0000-0001-6664-5643", "display_name": "Brouillet, Jeremy Jean" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/VRFE-ZY57", "abstract": "Advances in 2D materials have opened a wealth of possibilities for the control of emission and propagation of light on length scales much smaller than the wavelength of light. Graphene, with highly-confined electrostatically tunable plasmons, provides a strong platform for explore a number of avenues.
\r\n\r\nWe show that graphene that can increase the luminescence of erbium by 80%, can induce population inversion in a three-level system, speed up the response time by over an order of magnitude, and has modulation depth of up to 14 dB for luminescence.
\r\n\r\nWe experimentally demonstrated a tunable epsilon-near-zero metamaterial with a elliptic-to-hyperbolic transition. The device had been theorized for many years and we provide the first experimental realization.
\r\n\r\nWe explore the properties of an isotropic tunable 2D heterostructure composed of black phosphorus, hexagonal boron nitride, and graphene. These symmetry-breaking materials create an effective permittivity that is biaxially anistropic and tunable. This material supports tunable beam steering based on propagation of energy along the hyperbolic dispersion lines.
" }, { "name": "Budninskiy, Maxim A.", "degree": "PhD", "year": "2019", "title": "Geometry-Driven Model Reduction", "advisor": "Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:12102018-011614041", "creators": [ { "name": { "family": "Budninskiy", "given": "Maxim A." }, "id": "Budninskiy-Maxim-A", "orcid": "0000-0002-9288-0249", "display_name": "Budninskiy, Maxim A." } ], "advisors": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/0RCX-0369", "abstract": "In this thesis we bring discrete differential geometry to bear on model reduction, both in the context of data analysis and numerical simulation of physical phenomena.
\r\n\r\nFirst, we present a novel controllable as-isometric-as-possible embedding method for low- and high-dimensional geometric datasets through sparse matrix eigenanalysis. This approach is equally suitable for performing nonlinear dimensionality reduction on big data and nonlinear shape editing of 3D meshes and pointsets. At the core of our approach is the construction of a \"multi-Laplacian\" quadratic form that is assembled from local operators whose kernels only contain locally affine functions. Minimizing this quadratic form produces an embedding that best preserves all relative coordinates of points within their local neighborhoods. We demonstrate the improvements that our approach brings over existing nonlinear local manifold learning methods on a number of datasets, and formulate the first eigen-based as-rigid-as-possible shape deformation technique by applying our affine-kernel embedding approach to 3D data augmented with user-imposed constraints on select vertices.
\r\n\r\nSecond, we introduce a new global manifold learning approach based on metric connection for generating a quasi-isometric, low-dimensional mapping from a sparse and irregular sampling of an arbitrary low-dimensional manifold embedded in a high-dimensional space. Our geometric procedure computes a low-dimensional embedding that best preserves all pairwise geodesic distances over the input pointset similarly to one of the staples of manifold learning, the Isomap algorithm, and exhibits the same strong resilience to noise. While Isomap relies on Dijkstra's shortest path algorithm to approximate geodesic distances over the input pointset, we instead propose to compute them through \"parallel transport unfolding,\" a discrete form of Cartan's development, to offer robustness to poor sampling and arbitrary topology. Our novel approach to evaluating geodesic distances using discrete differential geometry results in a markedly improved robustness to irregularities and sampling voids. In particular, it does not suffer from Isomap's limitation to geodesically convex sampled domains. Moreover, it involves only simple linear algebra, significantly improves the accuracy of all pairwise geodesic distance approximations, and has the same computational complexity as Isomap. We also show that our connection-based distance estimation can be used for faster variants of Isomap such as Landmark-Isomap.
\r\n\r\nFinally, we introduce an operator-adapted multiresolution analysis for finite-element differential forms. From a given continuous, linear, bijective, and self-adjoint positive-definite operator L, a hierarchy of basis functions and associated wavelets for discrete differential forms is constructed in a fine-to-coarse fashion and in quasilinear time. The resulting wavelets are L-orthogonal across all scales, and can be used to obtain a Galerkin discretization of the operator with a block diagonal stiffness matrix composed of uniformly well-conditioned and sparse blocks. Because our approach applies to arbitrary differential p-forms, we can derive both scalar-valued and vector-valued wavelets that block diagonalize a prescribed operator. Our construction applies to various types of computational grids, offers arbitrary smoothness orders of basis functions and wavelets, and can accommodate linear differential constraints such as divergence-freeness. We also demonstrate the benefits of the operator-adapted multiresolution decomposition for coarse-graining and model reduction of linear and nonlinear partial differential equations.
\r\n\r\nWe conclude with a short discussion on how future work in geometric model reduction may impact other related topics such as semi-supervised learning.
" }, { "name": "Bukowsky, Courtney Roberta", "degree": "PhD", "year": "2019", "title": "Scalable Nanophotonic Light Management Design for Solar Cells", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012019-002405475", "creators": [ { "name": { "family": "Bukowsky", "given": "Courtney Roberta" }, "id": "Bukowsky-Courtney-Roberta", "orcid": "0000-0003-3577-8050", "display_name": "Bukowsky, Courtney Roberta" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "co-chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/J5FG-1B48", "abstract": "The current trend in wide adoption of solar energy is encouraging in the context of current projections of increasing energy consumption and the dire need to decrease carbon emissions. The solar industry has expanded due to scientific advances in the power conversion efficiency of solar modules. In order maintain a rapid pace of adoption and further decrease electricity costs, converting each photon becomes increasingly important. This work focuses on nanophotonic approaches to increasing the power conversion efficiency of different solar photovoltaic designs. The projects voluntarily impose certain design constraints in order to be compatible with the large scale manufacturing needed by the solar industry. A focus was given to designs that can leverage the promising technology of nanoimprint lithography. Amorphous silicon tandem cells with embedded nanophotonic patterning attempted to increase absorption while minimizing materials and time costs. Simulated designs of Copper Indium Gallium Diselenide absorbers showed that the management of excited carriers is equally as important as light management in decreasingly thin absorber layers. Near perfect anti-reflection structures were given a detailed physical analysis to better describe the fundamental physics of near zero reflection due to nanocones printed on solar cell encapsulation glass. Experimental results agreed with the theoretical analysis, and showed that these nanostructures further increased absorbed photocurrent by trapping light in the encapsulation glass. Finally, a unique device in the form of a tandem luminescent solar concentrator/silicon solar module was proposed and analyzed as a low cost and adaptable technology for increased solar power conversion efficiency. Key to this design was discovery of new, near-perfect components for light management. Exciting and innovative designs are proposed to control the light-matter interaction within these devices. Study of a photonic luminescent solar concentrator predicted that luminescence can be trapped in photonic crystal slab waveguides with near zero loss. Rigorous experimental efforts to characterize a multitude of near-perfect samples help guide these designs toward their final goals." }, { "name": "Chung, Jaebum", "degree": "PhD", "year": "2019", "title": "Computational Imaging: a Quest for the Perfect Image", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05202019-151055724", "creators": [ { "name": { "family": "Chung", "given": "Jaebum" }, "id": "Chung-Jaebum", "orcid": "0000-0003-3932-8428", "display_name": "Chung, Jaebum" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Zheng", "given": "Guoan" }, "id": "Zheng-Guoan", "role": "member", "display_name": "Zheng, Guoan" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8W3A-HE02", "abstract": "A physical lens is limited in its ability to capture an image that is both high- resolution and wide-field due to aberrations even with a sophisticated lens design. This thesis explores computational methods that expand on the recently developed Fourier ptychographic microscopy (FPM) to overcome the physical limitations. New algorithms and imaging methods extend the computational aberration correction to more general imaging modalities including fluorescence microscopy and incoherent bright-field imaging so as to allow even a crude lens to perform like an ideal lens. This paradigm shift from the lens design to computational algorithms democratizes high-resolution imaging by making it easier to use and less complicated to build." }, { "name": "Cook, Colin Andrew", "degree": "PhD", "year": "2019", "title": "Phototherapeutic Devices for the Treatment of Diabetic Retinopathy", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:01102019-190818557", "creators": [ { "name": { "family": "Cook", "given": "Colin Andrew" }, "id": "Cook-Colin-Andrew", "orcid": "0000-0002-6283-5105", "display_name": "Cook, Colin Andrew" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "chair", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Martinez-Camarillo", "given": "Juan Carlos" }, "id": "Martinez-Camarillo-Juan-Carlos", "role": "member", "display_name": "Martinez-Camarillo, Juan Carlos" } ], "option_major": [ "medeng" ], "doi": "10.7907/62R5-RF78", "abstract": "Diabetic retinopathy is a microvascular disease of the retina and a leading cause of vision loss worldwide. In the non-proliferative phase, diabetes-induced degradation of the retinal blood supply leads to edema and progressive tissue hypoxia. In response, the retinal tissue expresses proangiogenic growth factors (e.g. vascular endothelial growth factor), which drive proliferation of aberrant blood vessels within the eye. These poorly formed vessels leak fluid and blood cells into the eye and grow into the vitreous, which puts traction on the retina and leads to detachment. Given the hypoxic etiology, retinal oxygen tension and metabolism have received considerable attention. Dark-adapted conditions drive the retina to a significantly lower oxygen tension compared to light- adapted conditions as rod cells consume more energy in order to boost sensitivity. While tolerable in the healthy retina, it has been hypothesized that increased nightly metabolism overwhelms the compromised oxygen supply in the diabetic retina, leading to hypoxia and pathological vascular endothelial growth factor expression.
\r\n\r\nThis thesis develops ocular devices that shine light onto the retina to modulate rod metabolism, reducing oxygen demand and mitigating nightly hypoxia. The phototherapeutic effect is characterized through mathematical modeling of retinal metabolism and in vivo testing. Implantable phototherapy devices are designed, fabricated, and evaluated. This thesis also develops overnight phototherapeutic contact lenses utilizing radioluminescence, chemiluminescence, and electroluminescence approaches. Phototherapy holds promise as a non-invasive, preventative therapy for the treatment of hypoxic retinal diseases such as diabetic retinopathy.
" }, { "name": "Deffo Nde, Arnold Durel", "degree": "PhD", "year": "2019", "title": "A Line-Free Method of Monopoles for 3D Dislocation Dynamics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:08042018-083338014", "creators": [ { "name": { "family": "Deffo Nde", "given": "Arnold Durel" }, "id": "Deffo-Nde-Arnold-Durel", "orcid": "0000-0001-9077-8315", "display_name": "Deffo Nde, Arnold Durel" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ariza", "given": "Pilar" }, "id": "Ariza-Pilar", "role": "member", "display_name": "Ariza, Pilar" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/23YV-3312", "abstract": "Despite the emergence of architected materials for various applications, metals still play a key role in engineering in general and aeronautics in particular. Turbine blades in jets engines for instance are made from single-crystal Nickel superalloys. As a result, studying the failure mechanism of these crystalline materials would help understand the limits of their applications. At the core of this mechanism are line defects called dislocations. Indeed, the plastic deformation of metals is governed by the motion of dislocation ensembles inside the crystal. In this thesis, we propose a novel approach to dislocation dynamics through the method of monopoles. In this approach, we discretize the dislocation line as a collection of points (or monopoles), each of which carries a Burgers \"charge\" and an element of line. The fundamental difference between our method and current methods for dislocation dynamics lies in the fact that the latter discretize the dislocation as a collection of line segments from which spans a need to keep track of the connectivity of the nodes. In our approach, we propose a \"line-free\" discretization where a linear connectivity or sequence between monopoles need not be defined. This attribute of the formulation offers significant computational advantages in terms of simplicity and efficiency. Through verification examples, we show that our method is consistent with existing results for simple configurations. We then build on this success to investigate increasingly complex examples, this with the ultimate goal of simulating the plastic deformation of a BCC grain in an elastic matrix.
" }, { "name": "Dhandapani, Chandru", "degree": "PhD", "year": "2019", "title": "Using the Force: Applications and Implications of Turbulence Forcing Terms in Direct Numerical Simulations", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102019-185605511", "creators": [ { "name": { "family": "Dhandapani", "given": "Chandru" }, "id": "Dhandapani-Chandru", "orcid": "0000-0002-7319-557X", "display_name": "Dhandapani, Chandru" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FH31-4468", "abstract": "Most energy requirements of modern life can be fulfilled by renewable energy sources, but it is impossible in the near future to provide an alternative energy source to combustion for airplanes. That being said, combustion in aviation can be made more sustainable by using alternative jet fuels, which are made from renewable sources like agricultural wastes, solid wastes, oils, and sugars. These alternative fuels can be used in commercial flights only after a long certification process by the Federal Aviation Agency (FAA) and ASTM International. Unfortunately, in over 50 years of fuel research, only five fuels have been certified.\r\nThis research project aims to speed up the certification process with quicker testing of alternative fuels. Engine testing and even laboratory testing require large amounts of time and fuel. Simulations can make the process much more efficient, but accurately simulating highly turbulent flames in such complex geometries would need large amounts of computational resources. The goal of this thesis is to create an efficient computational framework, that can replicate different engine-like turbulent flow conditions in simple geometries with numerical tractability.
\r\n\r\nThe central idea is to decompose the flow field into ensemble mean and fluctuating quantities. The simulations then resolve only the fluctuations using simple computational domains, while emulating the effect of the mean flow using \"forcing\" terms. These forcing terms are calculated first for incompressible turbulence, and this method is later extended to turbulent reacting flows. In incompressible turbulence, Direct Numerical Simulations (DNS) performed on simple triply periodic cubic domains reasonably capture the statistically stationary shear turbulence, that is observed in free shear flows. The simulations are also performed in cuboidal domains, that are longer in one direction and with an inflow/outflow along it. Both changes are observed to not have a significant impact on the turbulence statistics. Finally, shear convection is applied to the turbulence simulations with inflow/outflow, which has a significant impact on the turbulence. These simulations accurately capture the turbulence anisotropy in free-shear flows.
\r\n\r\nThe study is extended to DNS of highly turbulent n-heptane-air flames performed under different flow conditions. Turbulent flames involve two-way coupling between fluid mechanics and combustion. The effects of the flame on the turbulence and the impact of the turbulent flow conditions on the flame behavior are analyzed. The focus is placed on the effects of turbulence production, shear convection, and pressure gradients. The anisotropy produced in the turbulence due to the different flow conditions and the flame are also compared and contrasted. While the global behavior and flow anisotropy were affected by these conditions, the local chemistry effects were unaffected, and depend only on the laminar flame properties and turbulence intensity. These findings can help predict turbulent flame behavior, and can expedite the search and testing of sustainable alternatives to conventional jet fuels.
" }, { "name": "Edlund, Jeffrey Andrews", "degree": "PhD", "year": "2019", "title": "Numerical Investigation of Spinal Neuron Facilitation with Multi-electrode Epidural Stimulation", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302018-185025297", "creators": [ { "name": { "family": "Edlund", "given": "Jeffrey Andrews" }, "id": "Edlund-Jeffrey-Andrews", "orcid": "0000-0003-3092-4493", "display_name": "Edlund, Jeffrey Andrews" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "role": "chair", "display_name": "Ames, Aaron D." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Edgerton", "given": "V. Reggie" }, "id": "Edgerton-V-R", "role": "member", "display_name": "Edgerton, V. Reggie" } ], "option_major": [ "cns" ], "doi": "10.7907/2DVK-G212", "abstract": "Approximately 1,275,000 people in the US have a spinal cord injury severe enough to cause some paralysis of the arms and/or legs. Epidural stimulation using implanted multi-electrode stimulating arrays over the lumbosacral spinal cord has recently shown promise in assisting individuals with severe spinal cord injuries to stand, walk, and even facilitate voluntary movement. Both animal model and human studies have shown that sub-threshold facilitation of motor recovery gives the best results. The underlying neural mechanisms by which sub-threshold epidural stimulation leads to motor recovery are incompletely known.
\r\n\r\nThis thesis uses computational methods to study the facilitation effect. A neuron is facilitated if a sub-threshold synaptic input can cause a neuronal output under the influence of a stimulating electric field. The analysis in this thesis is based on a computational model of the epidural spinal stimulation process in the rat spinal cord. This model includes a time-domain finite element simulation (using COMSOL\u00ae) of the various tissues in the spinal cord with the appropriate anisotropic and frequency-dependent complex relative permittivities. The voltages obtained from the finite element simulations were used as the extracellular voltage in NEURON simulations.
\r\n\r\nA population of neurons were simulated under a wide variety of conditions. These simulations highlight the effect of neuron orientation, location, and synaptic timing as key parameters which influence facilitation.
\r\n\r\nThis study indicates that regions of the spinal cord that have previously been ignored may be actively involved in motor recovery. These results may also enable the design of specialized epidural electrode arrays and the design of new stimulation protocols.
" }, { "name": "Filippidis, Ioannis", "degree": "PhD", "year": "2019", "title": "Decomposing Formal Specifications Into Assume-Guarantee Contracts for Hierarchical System Design", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07202018-115217471", "creators": [ { "name": { "family": "Filippidis", "given": "Ioannis" }, "id": "Filippidis-Ioannis", "orcid": "0000-0003-4704-3334", "display_name": "Filippidis, Ioannis" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Holzmann", "given": "Gerard J." }, "id": "Holzmann-G-J", "role": "member", "display_name": "Holzmann, Gerard J." } ], "option_major": [ "cds" ], "doi": "10.7907/Z9Q52MTD", "abstract": "Specifications for complex engineering systems are typically decomposed into specifications for individual subsystems in a way that ensures they are implementable and simpler to develop further. We describe a method to algorithmically construct specifications for components that should implement a given specification when assembled. By eliminating variables that are irrelevant to realizability of each component, we simplify the specifications and reduce the amount of information necessary for operation.\r\nTo identify these variables, we parametrize the information flow between components.
\r\n\r\n\r\nThe specifications are written in the Temporal Logic of Actions, TLA+, with liveness properties restricted to an implication of conjoined recurrence properties, known as GR(1). We study whether GR(1) contracts exist in the presence of full information, and prove that memoryless GR(1) contracts that preserve safety do not always exist, whereas contracts in GR(1) with history-determined variables added do exist. We observe that timed stutter-invariant specifications of open-systems in general require GR(2) liveness properties for expressing them.
\r\n\r\n\r\nWe formalize a definition of realizability in TLA+, and define an operator for forming open-systems from closed-systems, based on a variant of the while-plus operator. The resulting open-system properties are realizable when expected to be. We compare stepwise implication operators from the literature, and establish relations between them, and examine the arity required for expressing these operators. We examine which symmetric combinations of stepwise implication and implementation kind avoid circular dependence, and show that only Moore components specified by strictly causal stepwise implication avoid circular dependence.
\r\n\r\n\r\nThe proposed approach relies on symbolic algorithms for computing specifications. To convert the generated specifications from binary decision diagrams to readable formulas over integer variables, we symbolically solve a minimal covering problem. We implemented an algorithm for minimal covering over lattices originally proposed for two-level logic minimization. We formalized the computation of essential elements and cyclic core that is part of this algorithm, and machine-checked the proofs of safety properties using a proof assistant. Proofs supporting the thesis are organized as TLA+ modules in appendices.
" }, { "name": "Fleischman, Dagny", "degree": "PhD", "year": "2019", "title": "Nanophotonic Structures: Fundamentals and Applications in Narrowband Transmission Color Filtering", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:12032018-173954965", "creators": [ { "name": { "family": "Fleischman", "given": "Dagny" }, "id": "Fleischman-Dagny", "orcid": "0000-0003-2913-657X", "display_name": "Fleischman, Dagny" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/RA1G-GS84", "abstract": "The optical properties of materials can be manipulated by structures roughly the size of the wavelength of light of interest. For visible wavelengths, many different types of structures sized on the order of 10s-100s of nanometers have been used to engineer materials to produce a targeted optical response. Multilayer stacks of nanoscale metal and dielectric films are a widely explored geometry that has been used to make composite materials with effective optical properties that vary significantly from their constituent films. In this thesis, carefully designed multilayer stacks were used to induce artificial magnetism in non-magnetic materials, opening new directions for tailoring wave propagation in optical media. By perforating these multilayer structures with an array of sub-wavelength slits, these nanophotonic structures were shown to be able to function as narrowband transmission color filters. Using numerical optimization methods, these narrowband filterswere further refined and simplified to only require a single thin film sandwiched between two mirrors to achieve this high resolution spectral filtering. Novel methods were used to fabricate these ultracompact narrowband transmission color filters, which were shown to possess extremely narrow transmission resonances that can be controllably pushed across the visible and near IR parts of the spectrum. These mirrored color filters have footprints as small as 400 nm, well below the size of state-of-the-art CMOS pixels, inviting the possibility for integrating multi- and hyperspectral imaging capabilities into small portable electronic devices.
" }, { "name": "Fu, Zhongzheng", "degree": "PhD", "year": "2019", "title": "Representations of Action Monitoring and Cognitive Control by Single Neurons in the Human Brain", "advisor": "Adolphs, Ralph; Rutishauser, Ueli", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012019-234115726", "creators": [ { "name": { "family": "Fu", "given": "Zhongzheng" }, "id": "Fu-Zhongzheng", "orcid": "0000-0002-2572-6284", "display_name": "Fu, Zhongzheng" } ], "advisors": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "advisor", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Rutishauser", "given": "Ueli" }, "id": "Rutishauser-U", "role": "co-advisor", "display_name": "Rutishauser, Ueli" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Rutishauser", "given": "Ueli" }, "id": "Rutishauser-U", "role": "member", "display_name": "Rutishauser, Ueli" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" } ], "option_major": [ "cds" ], "doi": "10.7907/RG37-G744", "abstract": "Cognitive control arises whenever a prepotent and often automatic response needs to be overcome by another response. Control is usually effortful and relies on monitoring processes that detect when control is needed and/or when it failed. Control is one of the most important aspects of human behavior in everyday life and is a critical component of executive function. In a series of three empirical chapters, I present results from invasive single-neuron recordings from the frontal cortex of neurosurgical human patients while they perform tasks requiring cognitive control. I show that a substantial proportion of neurons in the pre-supplementary motor area (pre-SMA), and in the dorsal anterior cingulate cortex (dACC), signal response errors shortly after they occurred, but well before onset of feedback. Here I demonstrate that these error neurons signal self-detected errors and that they were separate from neurons signaling conflict. The response of error neurons correlated trial-by-trial with the simultaneously recorded intracranial error-related negativity (iERN), thereby establishing a single-neuron correlate of this important scalp potential. iERN-error neuron synchrony in dACC, but not pre-SMA, predicted whether post-error slowing, which is a measure of control, occurred or not. Spike-field coherence between action potentials and local field potentials in specific frequency bands, and latency differences between the different brain regions, suggest a mechanistic model whereby information relevant to control is passed between sectors of the medial frontal cortex. Multiplexing of different ex-post monitoring signals by individual neurons further documents that control relies on multiple sources of information, which can be dynamically routed in the brain depending on task demands. These findings provide the most complete set of single-neuron data on how errors and conflict signals at the single neuron level contribute to cognitive controls in humans. They provide a first-single neuron correlate of an extensively utilized scalp EEG potential. Together, this work provides a strong complement to investigations of this topic using fMRI in humans, and using electrophysiology in monkeys, and suggests specific future directions." }, { "name": "Georgiev, Nikola-Zlatkov", "degree": "PhD", "year": "2019", "title": "Towards High Performance Robotic Actuation", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222019-132217207", "creators": [ { "name": { "family": "Georgiev", "given": "Nikola-Zlatkov" }, "id": "Georgiev-Nikola-Zlatkov", "orcid": "0000-0002-7997-5577", "display_name": "Georgiev, Nikola-Zlatkov" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "role": "chair", "display_name": "Ames, Aaron D." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "role": "member", "display_name": "Mello, Michael" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/W64Q-1R69", "abstract": "The main objective of this thesis is to enable development of high performance actuation for legged, limbed and mobile robots. Due to the fact that such robots need to support their own weight, their actuators need to be light weight, compact and efficient. Furthermore, a dynamics analysis, shows that the actuators' design may have significant impact on a robot's dynamics sensitivity. These consideration motivate improvements in all actuator design aspects.
\r\n\r\nFirst, the application-specific design of outer rotor motors with concentrated windings is considered. It is shown that an intrinsic design trade-off exists between a motor's copper loss, core loss and mass, which allows development of motors with superior performance for a particular application. The three main application categories of interest are: electric vehicles, drones and robotic joints. Due to their outstanding torque density, high pole count outer rotor motors are analysed in terms of their design and optimization for robotic applications. Motor design scaling modes are also described in order to outline the main challenges in the implementation of high torque motors.
\r\n\r\nNext, the design of gearboxes for robotic actuation is discussed. A novel type of high reduction Bearingless Planetary Gearbox is introduced which allows large range of reduction ratios to be achieved in a compound planetary stage. In this concept, all gear components float in an unconstrained manner as the planet carrier is substituted with a secondary sun gear. The advantages of the Bearingless Planetary Gearbox over current approaches in terms of improved robustness, load distribution, manufacturability, and assembly are outlined.
\r\n\r\nFinally, analysis, design, and prototyping of rotary planar springs for rotary series elastic actuators is described. A mathematical model, based on curved beam theory, that allows rapid design, analysis, and comparison of rotary springs is developed. Mass reduction techniques based on composite arm structures are introduced and internal arm contact modeling is presented. Motivated by strain energy density analysis, an optimization based spring design approach is developed that allows significant increase in the torque and torque density.
\r\n" }, { "name": "Giwa, Adenike Monsurat", "degree": "PhD", "year": "2019", "title": "Microstructure and Small-Scale Deformation of Al\u2080.\u2087CoCrFeNi High-Entropy Alloy", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06252018-172548450", "creators": [ { "name": { "family": "Giwa", "given": "Adenike Monsurat" }, "id": "Giwa-Adenike-Monsurat", "orcid": "0000-0002-1229-7505", "display_name": "Giwa, Adenike Monsurat" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/PSWX-RY20", "abstract": "Novel engineering materials are continuously being designed for structural applications, particularly for improved mechanical properties such as high strength, enhanced ductility, and great thermal stability. High entropy alloys (HEAs) as an emerging material can be distinguished from other metal systems as a five-or-more-component alloy in which the constituents are in equiatomic or near equiatomic proportions, thereby maximizing the configurational entropy.
\r\n\r\nThis thesis is focused on understanding the microstructure of an aluminum-containing HEA in relation to its small-scale mechanical properties. Physical phenomena such as size-effect, slip sizes, temperature effect, crystallographic orientation effect, influence of interface, and small perturbations in atom motions are studied.
\r\n\r\nUniaxial compression experiments were conducted on nanopillars fabricated from the individual phases (i.e. Face Centered Cubic (FCC) and Body Cubic Centered (BCC) present in the Al0.7CoCrFeNi HEA. We observed the presence of a size-effect in both phases, with smaller pillars having substantially greater strengths compared with bulk and with larger sized samples. The size-effect power law exponent m in \u03c4y \u03b1 D-m for the BCC phase was \u2212 0.28, which is lower than that of most pure BCC metals, and the FCC phase had m = \u2212 0.66, which is equivalent to most pure FCC metals. These results are discussed in the framework of nano-scale plasticity and the intrinsic lattice resistance through the interplay of the internal (microstructural) and external (dimensional) size effects.
\r\n\r\nIn addition to higher stresses observed at cryogenic temperature in both phases, the microstructural analysis of the deformed pillar via Transmission Electron Microscopy (TEM) showed that FCC pillars undergo deformation by planar-slip dislocation activities even at temperatures of 40 K. Bulk FCC HEAs have been studied to deform via twinning mechanism at low temperatures. The BCC phase, however, confirms dislocation\u2013driven plasticity and twinning at 40 K. These results are explained from the intrinsic nature of the dislocation structure of both phases at low temperatures.
\r\n\r\nThe effect of an 'interphase' in micron-sized HEA pillars was studied from different orientation configurations of the BCC | FCC phases. Slip transmission across the phases was observed in high symmetry orientation combination of both phases. Configurations having a mixture of both low and high symmetry orientations vary in deformation mechanisms. We explain these findings in relation to crystal orientation effect of the combining half pillars, competing plastic mechanisms, dislocation \u2013 boundary interactions and how these findings correlate with their mechanical response.
\r\n\r\nAlso, we conducted dynamic mechanical analysis on the FCC and BCC HEA nanopillars to reveal their damping properties. Higher storage modulus and damping factor values were observed in FCC and BCC the nanopillars. Storage Moduli in the nano-sized HEAs are a factor of 2 greater than both bulk BCC and FCC HEA counterparts. The difference is due to greater surface contribution of the external atoms in the small-sized HEAs.
" }, { "name": "Guerrero Vela, Pedro Pablo", "degree": "PhD", "year": "2019", "title": "Plasma Surface Interactions in LaB\u2086 Hollow Cathodes with Internal Xe Gas Discharge", "advisor": "Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032019-100503451", "creators": [ { "name": { "family": "Guerrero Vela", "given": "Pedro Pablo" }, "id": "Guerrero-Vela-Pedro-Pablo", "orcid": "0000-0001-5766-2038", "display_name": "Guerrero Vela, Pedro Pablo" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "orcid": "0000-0002-1225-4695", "role": "member", "display_name": "Polk, James E." } ], "option_major": [ "space" ], "doi": "10.7907/4CW7-2K35", "abstract": "The ultimate goals of space vehicles are to move faster, further, and more reliably in the space environment. Electric propulsion (EP) has proven to be a necessary technology in the exploration of our solar system ever since its working principle was empirically tested in space in 1964. Thanks to the high exhaust velocities of ionized propellant gases, EP enables efficient utilization of the limited supply of propellant aboard spacecrafts. This technology has opened the possibility of long distance autonomous space missions.
\r\n\r\nEP devices require electron sources to ionize the propellant gas and to neutralize charges that are leaving the spacecraft. In modern EP thrusters, this is achieved by the use of hollow cathodes -- complex devices that employ low work function materials to emit electrons. Hollow cathodes using polycrystalline LaB6 inserts are attractive candidates for long duration EP based space missions. However, the physics behind LaB6 hollow cathode operation has not been studied in detail, which limits the possibility of their optimization. This work presents an integrated experimental and computational approach to investigate LaB6 hollow cathode thermal behaviour and the interplay between LaB6 insert surface chemistry and xenon plasma.
\r\n\r\nOur investigation of the thermal behaviour of LaB6 cathodes led to the unexpected discovery of a thermal transient when a new insert is first used. Specifically, we observed that the cathode temperature decreases by approximately 300 degrees over 50 hours before reaching steady state. This finding suggests a beneficial dynamic evolution of the cathode's chemical state when it interacts with its own plasma. This evolution is intrinsic to cathode operation and can only be precisely understood when the multiphysic nature of the cathode is self-consistently simulated. Thus, we built a numerical platform capable of combining the plasma, thermal and chemical behavior of a discharging hollow cathode. Simulations incorporating different neutralization models, inelastic ion-surface interaction and heterogeneous chemical evolution led to two major conclusions. First, simulations predicted a significant reduction of the LaB6 work function (0.42~eV) compared to previously reported baseline values, which is of paramount importance for EP thruster efficiency and operational lifetimes. Second, simulations suggested that the interaction between xenon low energy ions (<\t50 eV) and the LaB6 surface occurs following a two step neutralization mechanism. The predicted work function reduction was experimentally confirmed by photoemission spectroscopy. Furthermore, using a combination of crystallographic analysis, scanning electron microscopy and profilometry, we demonstrated that work function reduction is caused by the creation of a crystallographic texture at the LaB6 surface upon interaction with Xe plasma. In addition, we postulated the existence of a work function enhancing mechanism of secondary importance, which can be explained by forced cationic termination of plasma exposed crystals.
\r\n\r\nOur results revealed the unexpected phenomenon of work function reduction upon plasma exposure of LaB6. These findings suggest that LaB6 hollow cathodes may outperform current technologies and become the component of choice in EP thrusters for future space missions.
" }, { "name": "Guo, Linqi", "degree": "PhD", "year": "2019", "title": "Impact of Transmission Network Topology on Electrical Power Systems", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312019-191005982", "creators": [ { "name": { "family": "Guo", "given": "Linqi" }, "id": "Guo-Linqi", "orcid": "0000-0001-5771-2752", "display_name": "Guo, Linqi" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Doyle", "given": "John C." }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "cms" ], "doi": "10.7907/EN8K-W872", "abstract": "Power system reliability is a crucial component in the development of sustainable infrastructure. Because of the intricate interactions among power system components, it is often difficult to make general inferences on how the transmission network topology impacts performance of the grid in different scenarios. This complexity poses significant challenges for researches in the modeling, control, and management of power systems.
\r\n\r\nIn this work, we develop a theory that aims to address this challenge from both the fast-timescale and steady state aspects of power grids. Our analysis builds upon the transmission network Laplacian matrix, and reveals new properties of this well-studied concept in spectral graph theory that are specifically tailored to the power system context. A common theme of this work is the representation of certain physical quantities in terms of graphical structures, which allows us to establish algebraic results on power grid performance using purely topological information. This view is particularly powerful and often leads to surprisingly simple characterizations of complicated system behaviors. Depending on the timescale of the underlying problem, our results can be roughly categorized into the study of frequency regulation and the study of cascading failures.
\r\n\r\nFast-timescale: Frequency Regulation. We first study how the transmission network impacts power system robustness against disturbances in transient phase. Towards this goal, we develop a framework based on the Laplacian spectrum that captures the interplay among network topology, system inertia, and generator/load damping. This framework shows that the impact of network topology in frequency regulation can be quantified through the network Laplacian eigenvalues, and that such eigenvalues fully determine the grid robustness against low frequency perturbations. Moreover, we can explicitly decompose the frequency signal along scaled Laplacian eigenvectors when damping-inertia ratios are uniform across the buses. The insights revealed by this framework explain why load-side participation in frequency regulation not only makes the system respond faster, but also helps lower the system nadir after a disturbance, providing useful guidelines in the controller design. We simulate an improved controller reverse engineered from our results on the IEEE 39-bus New England interconnection system, and illustrate its robustness against high frequency oscillations compared to both the conventional droop control and a recent controller design.
\r\n\r\nWe then switch to a more combinatorial problem that seeks to characterize the controllability and observability of the power system in frequency regulation if only a subset of buses are equipped with controllers/sensors. Our results show that the controllability/observability of the system depends on two orthogonal conditions: (a) intrinsic structure of the system graph, and (b) algebraic coverage of buses with controllers/sensors. Condition (a) encodes information on graph symmetry and is shown to hold for almost all practical systems. Condition (b) captures how buses interact with each other through the network and can be verified using the eigenvectors of the graph Laplacian matrix. Based on this characterization, the optimal placement of controllers and sensors in the network can be formulated as a set cover problem. We demonstrate how our results identify the critical buses in real systems using a simulation in the IEEE 39-bus New England interconnection test system. In particular, for this testbed a single well chosen bus is capable of providing full controllability and observability.
\r\n\r\nSteady State: Cascading Failures. Cascading failures in power systems exhibit non-monotonic, non-local propagation patterns which make the analysis and mitigation of failures difficult. By studying the transmission network Laplacian matrix, we reveal two useful structures that make the analysis of this complex evolution more tractable: (a) In contrast to the lack of monotonicity in the physical system, there is a rich collection of monotonicity we can explore in the spectrum of the Laplacian matrix. This allows us to systematically design topological measures that are monotonic over the cascading event. (b) Power redistribution patterns are closely related to the distribution of different types of trees in the power network topology. Such graphical interpretation captures the Kirchhoff's Law in a precise way and naturally suggests that we can eliminate long-distance propagation of system disturbances by forming a tree-partition.
\r\n\r\nWe then show that the tree-partition of transmission networks provides a precise analytical characterization of line failure localizability. Specifically, when a non-bridge line is tripped, the impact of this failure only propagates within well-defined components, which we refer to as cells, of the tree-partition defined by the bridges. In contrast, when a bridge line is tripped, the impact of this failure propagates globally across the network, affecting the power flow on all remaining transmission lines. This characterization suggests that it is possible to improve the system robustness by switching off certain transmission lines, so as to create more, smaller components in the tree-partition; thus spatially localizing line failures and making the grid less vulnerable to large-scale outages. We illustrate this approach using the IEEE 118-bus test system and demonstrate that switching off a negligible portion of transmission lines allows the impact of line failures to be significantly more localized without substantial changes in line congestion.
\r\n\r\nUnified Controller on Tree-partitions. Combining our results from both the fast-timescale and steady state behaviors of power grids, we propose a distributed control strategy that offers strong guarantees in both the mitigation and localization of cascading failures in power systems. This control strategy leverages a new controller design known as Unified Controller (UC) from frequency regulation literature, and revolves around the powerful properties that emerge when the management areas that UC operates over form a tree-partition. After an initial failure, the proposed strategy always prevents successive failures from happening, and regulates the system to the desired steady state where the impact of initial failures are localized as much as possible. For extreme failures that cannot be localized, the proposed framework has a configurable design that progressively involves and coordinates across more control areas for failure mitigation and, as a last resort, imposes minimal load shedding. We compare the proposed control framework with the classical Automatic Generation Control (AGC) on the IEEE 118-bus test system. Simulation results show that our novel control greatly improves the system robustness in terms of the N-1 security standard, and localizes the impact of initial failures in majority of the load profiles that are examined. Moreover, the proposed framework incurs significantly less load loss, if any, compared to AGC, in all of our case studies.
" }, { "name": "Helou, Bassam Mohamad", "degree": "PhD", "year": "2019", "title": "Testing Alternative Theories of Quantum Mechanics with Optomechanics, and Effective Modes for Gaussian Linear Optomechanics", "advisor": "Chen, Yanbei", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182018-142547647", "creators": [ { "name": { "family": "Helou", "given": "Bassam Mohamad" }, "id": "Helou-Bassam-Mohamad", "orcid": "0000-0003-2760-7622", "display_name": "Helou, Bassam Mohamad" } ], "advisors": [ { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "role": "advisor", "display_name": "Chen, Yanbei" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Miao", "given": "Hiaoxing" }, "id": "Miao-Hiaoxing", "role": "member", "display_name": "Miao, Hiaoxing" }, { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "role": "member", "display_name": "Chen, Yanbei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/KJ1K-9268", "abstract": "Optomechanics has made great strides in theory and experiments over the past decade, which culminated in the first direct detection of gravitational waves in 2015 by LIGO. This thesis explores how optomechanics can be used to test fundamental physics other than the theory of general relativity. Our emphasis will be on falsifiable theories (ultimately, only experiments can decide whether a theory is correct) that address two outstanding issues in quantum mechanics: the measurement problem, and reconciling quantum mechanics with the theory of general relativity. In particular, we show that the space experiment LISA pathfinder places aggressive bounds on two objective collapse models, which are non-linear stochastic modifications of the Schroedinger equation that can resolve the measurement problem. Moreover, we show that state-of-the-art torsion pendulum experiments can test the Schroedinger-Newton theory, which is the non-relativistic limit of a non-linear theory combining quantum mechanics with a fundamentally classical spacetime.
\r\n\r\nAlong the way, we propose how to resolve two major difficulties with determining the predictions of non-linear quantum mechanics in an actual experiment. First, we cannot use the density matrix formalism in non-linear quantum mechanics and so we have to suggest and justify a particular ensemble for the thermal bath. Separating out quantum and classical fluctuations helped us propose a reasonable ensemble. Second, most researchers believe that deterministic non-linear quantum mechanics must violate the no-signaling condition. We show this isn't necessarily the case because different interpretations of quantum mechanics make different predictions in non-linear quantum mechanics. We propose an interpretation, the causal-conditional prescription, that doesn't violate causality by noticing that once we fix an initial state, the evolution of a system under many non-linear theories is equivalent to evolution under a linear Hamiltonian with feedback. The mapping allows us to leverage the tools of quantum control, and it tells us that if the non-linear parameters of a non-linear Hamiltonian respond causally (i.e. with an appropriate delay) to measurement results, then the theory can be made causal.
\r\n\r\nWe also contribute to the theory of quantum optomechanics. We introduce two new bases that one can view environment modes with. In linear optomechanics a system interacts with an infinite number of bath modes. We show that the interaction can be reduced to one with finite degrees of freedom. Moreover, at any particular time, the system is correlated with only a finite number of bath modes. We show that if we make the assumption that we can measure any commuting environment modes, then this basis allows us to understand the one-shot quantum Cramer-Rao bound in a simple way, and allows us to sweep large parameter regimes and so find promising optomechanics topologies for quantum state preparation tasks that we can then analyze without the assumption of being able to measure any observable of the environment. We also use this basis to show that when we are interested in the conditional dynamics of a test mass, we can only adiabatically eliminate a lossy cavity when we measure the optomechanical system at a slow enough rate. Finally, we develop an analytic filter for obtaining the state of a generic optomechanical system that interacts linearly with its environment and is driven by Gaussian states, and where the outgoing light is measured with a non-linear photon-counting measurement. We hope that our work will help researchers explore optomechanics topologies that make use of photon counters.
\r\n" }, { "name": "Hong, Brian Daffern", "degree": "PhD", "year": "2019", "title": "Periodically Disturbed Oscillators", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:07262018-030251324", "creators": [ { "name": { "family": "Hong", "given": "Brian Daffern" }, "id": "Hong-Brian-Daffern", "orcid": "0000-0001-8099-0312", "display_name": "Hong, Brian Daffern" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/W0A7-4258", "abstract": "By controlling the timing of events and enabling the transmission of data over long distances, oscillators can be considered to generate the \"heartbeat\" of modern electronic systems. Their utility, however, is boosted significantly by their peculiar ability to synchronize to external signals that are themselves periodic in time. Although this fascinating phenomenon has been studied by scientists since the 1600s, models for describing this behavior have seen a disconnect between the rigorous, methodical approaches taken by mathematicians and the design-oriented, physically-based analyses carried out by engineers. While the analytical power of the former is often concealed by an inundation of abstract mathematical machinery, the accuracy and generality of the latter are constrained by the empirical nature of the ensuing derivations. We hope to bridge that gap here.
\r\n\r\nIn this thesis, a general theory of electrical oscillators under the influence of a periodic injection is developed from first principles. Our approach leads to a fundamental yet intuitive understanding of the process by which oscillators lock to a periodic injection, as well as what happens when synchronization fails and the oscillator is instead injection pulled. By considering the autonomous and periodically time-varying nature that underlies all oscillators, we build a time-synchronous model that is valid for oscillators of any topology and periodic disturbances of any shape. A single first-order differential equation is shown to be capable of making accurate, quantitative predictions about a wide array of properties of periodically disturbed oscillators: the range of injection frequencies for which synchronization occurs, the phase difference between the injection and the oscillator under lock, stable vs. unstable modes of locking, the pull-in process toward lock, the dynamics of injection pulling, as well as phase noise in both free-running and injection-locked oscillators. The framework also naturally accommodates superharmonic injection-locked frequency division, subharmonic injection-locked frequency multiplication, and the general case of an arbitrary rational relationship between the injection and oscillation frequencies. A number of novel insights for improving the performance of systems that utilize injection locking are also elucidated. In particular, we explore how both the injection waveform and the oscillator's design can be modified to optimize the lock range. The resultant design techniques are employed in the implementation of a dual-moduli prescaler for frequency synthesis applications which features low power consumption, a wide operating range, and a small chip area.
\r\n\r\nFor the commonly used inductor-capacitor (LC) oscillator, we make a simple modification to our framework that takes the oscillation amplitude into account, greatly enhancing the model's accuracy for large injections. The augmented theory uniquely captures the asymmetry of the lock range as well as the distinct characteristics exhibited by different types of LC oscillators. Existing injection locking and pulling theories in the available literature are subsumed as special cases of our model. It is important to note that even though the veracity of our theoretical predictions degrades as the size of the injection grows due to our framework's linearization with respect to the disturbance, our model's validity across a broad range of practical injection strengths are borne out by simulations and measurements on a diverse collection of integrated LC, ring, and relaxation oscillators. Lastly, we also present a phasor-based analysis of LC and ring oscillators which yields a novel perspective into how the injection current interacts with the oscillator's core nonlinearity to facilitate injection locking.
" }, { "name": "Huertas-Cerdeira, Cecilia", "degree": "PhD", "year": "2019", "title": "On the Dynamics of Flat Plates in a Fluid Environment: A Study of Inverted Flag Flapping and Caudal Fin Maneuvering", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-103225366", "creators": [ { "name": { "family": "Huertas-Cerdeira", "given": "Cecilia" }, "id": "Huertas-Cerdeira-Cecilia", "orcid": "0000-0003-4553-0470", "display_name": "Huertas-Cerdeira, Cecilia" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/326X-M576", "abstract": "Despite serving analogous functions, the mechanical designs conceived by human engineering and those that result from natural evolution often possess fundamentally differing properties. This thesis explores the use of principles that stem from natural evolution to improve the performance of engineered mechanisms, focusing on systems whose role is to interact with a fluid environment. Two different principles are considered: the use of compliance, abundant in nature's structures, and the use of flapping propulsion, prevalent among nature's swimmers.
\r\n\r\nThe first part of this thesis is dedicated to investigating the physics that govern the behavior of an inverted-flag energy harvester; an unactuated flexible cantilever plate that is clamped at its trailing edge and submerged in a flow. The resonance between solid motion and fluid forcing generates large-amplitude unsteady deformations of the structure that may be used for energy harvesting purposes. The effect of the flag's aspect ratio on its stability is first evaluated. Flags of very small aspect ratio are demonstrated to undergo a saddle-node bifurcation instead of a divergence instability. The angle of attack of the flag is then modified to reveal the existence of dynamical regimes additional to those present at zero angle of attack. A side-by-side flag configuration is finally explored, highlighting the presence of an energetically favorable symmetric flapping mode among other coupled dynamics.
\r\n\r\nThe second part of this thesis delves into the analysis of underwater flapping propellers and the optimization of their three-dimensional motion to generate desired maneuvering forces, with the objective of obtaining an appendage for use in autonomous underwater vehicles that can perform both fast maneuvering and efficient propulsion. An experimental optimization procedure is employed to obtain the most efficient trajectory that generates a specified side force. The effect of increasing the fin's aspect ratio is examined, and a highly efficient trajectory, that makes use of high three-dimensionality and rotation angles, is obtained for a fin of AR=4. The use of a flexible fin is then analyzed and shown to be detrimental to the maneuvering efficiency of the system.
" }, { "name": "Huynh, David Pham", "degree": "PhD", "year": "2019", "title": "Spatio-Temporal Response of a Compliant-Wall, Turbulent Boundary Layer System to Dynamic Roughness Forcing", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04232019-162807004", "creators": [ { "name": { "family": "Huynh", "given": "David Pham" }, "id": "Huynh-David-Pham", "orcid": "0000-0002-8430-6255", "display_name": "Huynh, David Pham" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A5PS-GT54", "abstract": "This thesis investigates the interaction between an elastic compliant surface and a turbulent boundary layer exposed to dynamic roughness forcing. The goals are to explore a unique perspective of this fluid-structural problem through narrow-band forcing, and to further develop the understanding of dynamic roughness. Water tunnel experiments are designed with flow and surface measurements, both phase-locked to the roughness actuation. This enables a phase-averaged analysis, which leverages the deterministic input to isolate the temporally correlated components of the flow and surface response. Identifying the directly interacting velocity and deformation modes allows the complex, fluid-structural system to be studied in a more tractable, input-output manner.
\r\n\r\nThe first experiment is conducted with a smooth-wall turbulent boundary layer forced by dynamic roughness, and contributes to the knowledge of this type of forcing through structure-resolved particle image velocimetry. This allows for the streamwise-spatial nature and the wall-normal velocity component (v) of the roughness-forced flow to be explored, which had not been previously studied. A spatial amplitude modulation is observed in the synthetic structure and investigated directly through the spatial spectra. Through a parametric study and an empirical fit, the forcing frequency may now be selected to target a particular streamwise length scale.
\r\n\r\nThe second experiment implements a gelatin sample subject to an unforced turbulent boundary layer. The surface response is characterized and serves as a base case with which to identify the roughness-forced component of the deformations. This naturally leads to the third experiment, where the full compliant-wall, dynamic-roughness-forced turbulent boundary layer system is considered. The surface response to the synthetic flow structure is confirmed, which sets the stage for a comparison between the smooth-wall and compliant-wall data to study the effect of the compliant surface.
\r\n\r\nThe smooth/compliant comparison is guided by a resolvent analysis, which predicts a virtual wall feature in the v velocity mode for the elastic material under consideration. Using this prediction to inform a conditional average, the virtual wall is revealed in the experimental data. Thus, the action of the elastic surface is interpreted as opposing the v velocity near the wall, in a manner similar to wall-jet opposition control.\r\nPrevious experimental studies of viscoelastic compliant surfaces have demonstrated the potential for turbulent drag reduction, though either indirectly via the turbulence intensities or with relatively high skin friction measurement error. A common observation in these studies was the importance of the interaction between the surface and the coherent structures in the flow. To that end, this study has isolated and modeled the behavior of the fluid-structural system with a single spatio-temporal scale generated by dynamic roughness forcing. The results provide a physical interpretation of the effect of an elastic surface on turbulent boundary layer flow structures and informs the ongoing development of a reduced-order modeling tool in the resolvent analysis.
" }, { "name": "Jain, Siddharth", "degree": "PhD", "year": "2019", "title": "Decoding the Past", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechTHESIS:04032019-102853075", "creators": [ { "name": { "family": "Jain", "given": "Siddharth" }, "id": "Jain-Siddharth", "orcid": "0000-0002-9164-6119", "display_name": "Jain, Siddharth" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Schwartz", "given": "Moshe" }, "id": "Schwartz-Moshe", "role": "member", "display_name": "Schwartz, Moshe" } ], "option_major": [ "eleceng" ], "doi": "10.7907/K286-5N63", "abstract": "The human genome is continuously evolving, hence the sequenced genome is a snapshot in time of this evolving entity. Over time, the genome accumulates mutations that can be associated with different phenotypes - like physical traits, diseases, etc. Underlying mutation accumulation is an evolution channel (the term channel is motivated by the notion of communication channel introduced by Shannon [1] in 1948 and started the area of Information Theory), which is controlled by hereditary, environmental, and stochastic factors. The premise of this thesis is to understand the human genome using information theory framework. In particular, it focuses on: (i) the analysis and characterization of the evolution channel using measures of capacity, expressiveness, evolution distance, and uniqueness of ancestry and uses these insights for (ii) the design of error correcting codes for DNA storage, (iii) inversion symmetry in the genome and (iv) cancer classification.
\r\n\r\nThe mutational events characterizing this evolution channel can be divided into two categories, namely point mutations and duplications. While evolution through point mutations is unconstrained, giving rise to combinatorially many possibilities of what could have happened in the past, evolution through duplications adds constraints limiting the number of those possibilities. Further, more than 50% of the genome has been observed to consist of repeated sequences. We focus on the much constrained form of duplications known as tandem duplications in order to understand the limits of evolution by duplication. Our sequence evolution model consists of a starting sequence called seed and a set of tandem duplication rules. We find limits on the diversity of sequences that can be generated by tandem duplications using measures of capacity and expressiveness. Additionally, we calculate bounds on the duplication distance which is used to measure the timing of generation by these duplications. We also ask questions about the uniqueness of seed for a given sequence and completely characterize the duplication length sets where the seed is unique or non-unique. These insights also led us to design error correcting codes for any number of tandem duplication errors that are useful for DNA-storage based applications. For uniform duplication length and duplication length bounded by 2, our designed codes achieve channel capacity. We also define and measure uncertainty in decoding when the duplication channel is misinformed. Moreover, we add substitutions to our tandem duplication model and calculate sequence generation diversity for a given budget of substitutions.
\r\n\r\nWe also use our duplication model to explain the inversion symmetry observed in the genome of many species. The inversion symmetry is popularly known as the 2nd Chargaff Rule, according to which in a single strand DNA, the frequency of a k-mer is almost the same as the frequency of its reverse complement. The insights gained by these problems led us to investigate the tandem repeat regions in the genome. Tandem repeat regions in the genome can be traced back in time algorithmically to make inference about the effect of the hereditary, environmental and stochastic factors on the mutation rate of the genome. By inferring the evolutionary history of the tandem repeat regions, we show how this knowledge can be used to make predictions about the risk of incurring a mutation based disease, specifically cancer. More precisely, we introduce the concept of mutation profiles that are computed without any comparative analysis, but instead by analyzing the short tandem repeat regions in a single healthy genome and capturing information about the individual's evolution channel. Using gradient boosting on data from more than 5,000 TCGA (The Cancer Genome Atlas) cancer patients, we demonstrate that these mutation profiles can accurately distinguish between patients with various types of cancer. For example, the pairwise validation accuracy of the classifier between PAAD (pancreas) patients and GBM (brain) patients is 93%. Our results show that healthy unaffected cells still contain a cancer-specific signal, which opens the possibility of cancer prediction from a healthy genome.
" }, { "name": "Jhalani, Vatsal A.", "degree": "PhD", "year": "2019", "title": "Light Emission and Ultrafast Carrier Dynamics in III-V Semiconductors from First Principles", "advisor": "Bernardi, Marco", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062019-155629104", "creators": [ { "name": { "family": "Jhalani", "given": "Vatsal A." }, "id": "Jhalani-Vatsal-A", "orcid": "0000-0003-0866-0858", "display_name": "Jhalani, Vatsal A." } ], "advisors": [ { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "display_name": "Bernardi, Marco" } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/9E0D-KX54", "abstract": "The III-V semiconductors are a broad class of technologically important materials which have seen immense research interest in academia and industry due to their electronic, optoelectronic, and photovoltaic properties. In particular, GaN and the III-nitride family of wide bandgap semiconductors have emerged as promising candidates for the next generation of high-efficiency power electronics and light-emitting devices. Their device operation and macroscopic properties are governed by the dynamics of charge carriers and their microscopic scattering processes. Near room temperature, the carriers are scattered by lattice vibrations (phonons) at ultrafast timescales of order fs-ps. Microscopic understanding of carrier dynamics is challenging due to both the ultrafast time scale at play and to the presence of defects, interfaces, and impurities affecting transport and spectroscopy measurements. Typical theoretical treatments of carrier dynamics and light emission employ empirical models to interpret and fit experimental results. Over the last few years, so-called first-principles (or \"ab initio\") methods to accurately compute ultrafast carrier dynamics, transport, and light emission have seen a rapid rise. These approaches do not employ parameters from experiments, and using only the structure of the material as input, together with quantum mechanics and condensed matter theory, are enabling accurate predictions of carrier dynamics in a wide range of materials and are shedding light on microscopic details such as which electronic states, phonon modes and dissipative processes are responsible for the observed charge transport and light emission properties.
\r\n\r\n\r\nHere, we present first-principles calculations of different aspects of ultrafast carrier dynamics and light emission in III-V semiconductors of technological relevance, focusing on GaN, a key material for solid-state light emission technology. We first present a study of the ultrafast nonequilibrium dynamics of excited (so-called \"hot\") carriers in GaN, with a focus on electron-phonon scattering and the nanometer scale transport of carriers in GaN light emitting devices (LEDs). Using cutting-edge first-principles methods developed in this work, we find an asymmetry between the time scale of hot electron and hole thermalization which provides a possible explanation on a major open problem in the efficiency and energy losses of GaN LEDs. We then develop and apply a new rigorous first-principles approach for computing light emission and the radiative recombination lifetimes in bulk crystals, nanomaterials and isolated systems. Our approach is based on the Bethe-Salpeter equation (BSE), and it accurately includes excitons, namely electron-hole states bound by the Coulomb interaction that play a key role in light-matter interactions. Using this method, we carry out benchmark calculations of radiative lifetimes in GaAs and GaN. In GaN, our computed radiative lifetimes are in excellent agreement with experiment (within a factor of two), and our calculations further highlight the importance of including excitonic effects and spin-orbit coupling to obtain accurate radiative. We also employ a model to account for exciton thermal dissociation at high temperature, finding excellent agreement with spectroscopic measurements. Lastly, we discuss ongoing work on computing the intrinsic (phonon-limited) mobility in bulk GaN from first principles, focusing on efforts to include piezoelectric electron-phonon interactions, which are important for acoustic phonon modes in GaN. We compute the electron and hole mobilities in GaN and obtain excellent agreement with experiment. Our calculations shed light on which phonon modes scatter the carriers, providing new microscopic insight into charge carrier dynamics in GaN and related III-V semiconductors.
" }, { "name": "Kalaee, Mahmoud", "degree": "PhD", "year": "2019", "title": "Superconducting Electromechanical and Nanophotonic Devices for Quantum Measurement and Conversion", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10252018-150052650", "creators": [ { "name": { "family": "Kalaee", "given": "Mahmoud" }, "id": "Kalaee-Mahmoud", "display_name": "Kalaee, Mahmoud" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3PMX-2Y88", "abstract": "Microscale and nanoscale mechanical resonators have been used in advanced technological applications, from high precision time keeping and mass sensing, to processing high frequency signals in mobile communications. In the last few decades, they have been an important part of progress in the field of quantum information and metrology and have been proposed as quantum memories or transducers for measuring or connecting different types of quantum systems.
\r\n\r\nThe field of cavity optomechanics and electromechanics is concerned with coupling the electromagnetic field of a resonant optical cavity or electrical circuit to mechanical motion. These systems provide potential means to control and engineer the state of a mechanical object at the quantum level. This thesis contains the description of mechanical systems in megahertz to a few hundred megahertz frequency range formed by nano-fabricating photonic, phononic, and electrical circuits on a chip. These structures are designed to provide a large radiation pressure coupling between mechanical motion and electromagnetic fields to address and manipulate motional degrees of freedom. Qualitatively novel quantum effects are expected when one takes a step beyond linear coupling and exploits higher order interactions. To that end, we integrate electrical, mechanical and photonic structures in a multimode photonic crystal structure to observe \"x2-coupling\", where the optical cavity frequency is coupled to the square of the mechanical displacement. Moreover, we have developed two integrated on-chip platforms based on Si3N4 and Si nanomembranes capable of interfacing superconducting qubits and optical photons and realizing reversible microwave-to-optical conversion. We employ radiation pressure to cool these mechanical resonators to their quantum ground state. Finally, we demonstrate a form of electromechanical crystal for coupling microwave photons and hypersonic phonons of frequency \u03c9m/2\u03c0 = 0.425 GHz by capacitively coupling a phononic crystal acoustic cavity to a superconducting microwave resonator. Moving to higher frequency acoustic cavities not only facilitates the integration of electromechanical circuits and nanophotonic systems capable of operation in the resolved sideband limit of optomechanics for noise-free quantum signal conversion, but it opens up the possibility of using phonons as information carriers via phononic circuits. Utilizing a two-photon resonance condition for efficient microwave pumping and phononic bandgap shield to eliminate acoustic radiation, we achieve large cooperative electromechanical coupling (C \u2248 30) and intrinsic decay time of 2.3 ms. Moreover, electrical read-out of the phonon occupancy shows that the acoustic mode thermalizes close to its quantum ground-state of motion (phonon occupancy nm=1.5) at a fridge temperature of Tf = 10 mK. We conclude by considering several designs and fabrication improvements to the hypersonic electromechanical crystals that would enable them to perform quantum conversion between the electrical and acoustic\r\ndomain.
\r\n" }, { "name": "Kamali, Seyedeh Mahsa", "degree": "PhD", "year": "2019", "title": "Dielectric Metasurfaces from Fundamentals to Applications", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112019-120905666", "creators": [ { "name": { "family": "Kamali", "given": "Seyedeh Mahsa" }, "id": "Kamali-Seyedeh-Mahsa", "orcid": "0000-0002-6968-811X", "display_name": "Kamali, Seyedeh Mahsa" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/TPN1-XA53", "abstract": "In the past few decades, the advancements in nanotechnology have significantly altered many fields of science and technology, especially electronics and integrated photonics. Free-space optics, on the other hand, has remained mostly unaffected, and even today \"optics\" reminds us of carefully shaped and polished pieces of various types of glasses and crystals lumped into lenses and beam shapers. Several of these devices are then combined into more complicated optical systems like microscopes and pulse shapers that are expensive, bulky, sensitive to various environmental factors, and require several alignment steps. This thesis contains my work on designing and utilizing structures engineered at the nano-scale, which are called metasurfaces, to implement compact optical elements and systems with capabilities beyond those of conventional refractive and diffractive optics. My contributions to this field are two-fold: I have developed and contributed to the development of new concepts that take metasurfaces beyond conventional difractive optics in various aspects, in addition to paradigm changing platforms for optical element and system design. Here, I first give an overview and a brief history about optical metasurfaces. Next I discuss the unprecedented capabilities of metasurfaces in controlling light based on its degrees of freedom like illumination angle and polarization. Then, I will focus on various novel metasurface platforms of conformal and tunable metasurfaces, 3D metasurface beam shapers, and integrated metasurfaces. I conclude with an outlook on future potentials and challenges that need to be overcome for realizing their wide-spread applications." }, { "name": "Kettenbeil, Christian", "degree": "PhD", "year": "2019", "title": "Dynamic Strength of Silica Glasses at High Pressures and Strain Rates", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:02202019-104738145", "creators": [ { "name": { "family": "Kettenbeil", "given": "Christian" }, "id": "Kettenbeil-Christian", "orcid": "0000-0003-0301-3678", "display_name": "Kettenbeil, Christian" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "role": "member", "display_name": "Mello, Michael" }, { "name": { "family": "Clifton", "given": "Rodney J." }, "id": "Clifton-Rodney-J", "role": "member", "display_name": "Clifton, Rodney J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/RZJW-MX30", "abstract": "Understanding the behavior of silica glasses at high pressures and strain rates is of great importance for geological processes and highly relevant to many technological applications including high-powered laser-matter interactions in optical elements and impact/blast damage in defense systems. Materials typically experience large inelastic deformations at high pressures, which are strongly affected by strength-related phenomena such as work hardening, damage and thermal softening. The pressure-shear plate impact experiment (PSPI) provides detailed information on the pressure and strain rate dependent strength properties of materials subjected to uniaxial compression. However, its range of attainable pressures has so far been limited and the assumptions required for its analysis become invalid at pressures beyond the Hugoniot elastic limit of the anvil materials. In this dissertation, a high-pressure PSPI (HP-PSPI) technique is developed that greatly extends the range of attainable experimental conditions by achieving higher terminal projectile velocities in a powder gun setup. A novel fiber-optic heterodyne transverse velocimeter (HTV) is developed to enable the use of robust frequency-based data reduction techniques, which reduce the effect of signal noise and light coupling losses. A forward analysis method, based on finite element simulations, is employed to match the experimentally observed material response during HP-PSPI experiments on soda-lime glass samples while considering the inelastic deformation of the utilized tungsten carbide anvils. Symmetric HP-PSPI experiments on tungsten carbide revealed a loss of strength at normal stresses exceeding 25 GPa, which hint at active damage or softening mechanisms under nominally uniaxial strain compression. A pressure-dependent strain softening model transitions soda-lime glass from an intact strength of 2.8 GPa, below strains of 10-30%, to a failed granular state following extensive inelastic shear deformation, which accurately predicts the measured response over a wide range of stresses (9-21 GPa) and strain rates (3\u2022105-2\u2022107s-1). Extending the range of previously attainable pressures and strain rates in PSPI experiments, combined with more robust diagnostics and analysis tools, will greatly benefit our understanding of material strength in extreme environments and enables the investigation of material behavior in a currently unexplored range of pressures and strain rates.
" }, { "name": "Kim, Laura", "degree": "PhD", "year": "2019", "title": "Novel Light Emitting Mechanisms Originating from Graphene Plasmons Near and Far from Equilibrium", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062019-203520662", "creators": [ { "name": { "family": "Kim", "given": "Laura" }, "id": "Kim-Laura", "orcid": "0000-0002-9745-3668", "display_name": "Kim, Laura" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" } ], "option_major": [ "matsci" ], "doi": "10.7907/1CDC-HV37", "abstract": "Graphene supports surface plasmons bound to an atomically thin layer of carbon, characterized by tunable propagation characteristics and distinctly strong spatial confinement of the electromagnetic energy. Such collective excitations in graphene enable the strong interactions of massless Dirac fermions with light. In this work, I explore fundamental properties and applications of graphene plasmons both near and far from equilibrium. I discuss the ability of graphene plasmons to interact with its local environment in various forms of mid-infrared, optically active excitations, demonstrated by tunable graphene plasmon dispersions and an emergence of a new mode via addition of a monoatomic dielectric layer. Furthermore, the viability of graphene for optics-based applications and large-scale integration is epitomized by the experimental demonstration of perfect tunable absorption in a large-area chemically grown graphene by using a noble-metal-graphene metasurfaces. Using these properties of graphene plasmons, electronically tunable thermal radiation is demonstrated. Finally, I present theoretical predictions and experimental validations of nonequilibrium graphene plasmon excitations via ultrafast optical excitation, originating from a previously unobserved decay channel: hot plasmons generated from optically excited carriers. These studies reveal novel infrared light emitting processes, both spontaneous and stimulated, and provide a platform for achieving ultrafast, ultrabright mid-infrared light sources.
" }, { "name": "Kindem, Jonathan Miners", "degree": "PhD", "year": "2019", "title": "Quantum Nanophotonics with Ytterbium in Yttrium Orthovanadate", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03132019-062905529", "creators": [ { "name": { "family": "Kindem", "given": "Jonathan Miners" }, "id": "Kindem-Jonathan-Miners", "orcid": "0000-0002-7737-9368", "display_name": "Kindem, Jonathan Miners" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Hutzler", "given": "Nicholas R." }, "id": "Hutzler-N-R", "role": "member", "display_name": "Hutzler, Nicholas R." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Q40T-8907", "abstract": "Quantum light-matter interfaces that can reversibly map quantum information between photons and atoms are essential for building future quantum networks. Crystals doped with rare-earth ions (REIs) are an attractive solid-state platform for such light-matter interfaces due to their exceptional optical and spin coherence properties at cryogenic temperatures. Building scalable REI-based technology has proven to be challenging due to the inherently weak coupling of REIs with light. This thesis explores the integration of REIs with nanophotonic resonators to overcome this weak light-matter interaction and enable efficient, scalable quantum light-matter interfaces. Specifically, this work focuses on the development of quantum nanophotonics with ytterbium in yttrium orthovanadate.
\r\n \r\nThis thesis begins with an introduction to a nanophotonic platform based on photonic crystal cavities fabricated directly in rare-earth host materials and highlights the initial successes of this platform with neodymium-doped materials. This motivates an examination of the optical and spin coherence properties of 171Yb:YVO4, a REI material that was previously unexplored for quantum technology applications. This material is found to have strong optical transitions compared to other REI-doped materials, a simple energy level structure, and long optical and spin coherence lifetimes.
\r\n\r\nThe focus then turns to the detection and coherent manipulation of single ytterbium ions coupled to nanophotonic cavities. The Purcell-enhancement in these cavities enables efficient optical detection and spin initialization of individual ytterbium ions. We identify ions corresponding to different isotopes of ytterbium and show that the coupling of electron and nuclear spin in ytterbium-171 at zero-field gives rise to strong electron-spin-like transitions that are first-order insensitive to magnetic field fluctuations. This allows for coherent microwave control and the observation of long spin coherence lifetimes at temperatures up to 1 K. We then make use of the optical selection rules and energy structure of 171Yb:YVO4 to demonstrate high-fidelity single-shot optical readout of the spin state. These results establish nanophotonic devices in 171Yb:YVO4 as a promising platform for solid-state quantum light-matter interfaces.
" }, { "name": "Kou, Junlong", "degree": "PhD", "year": "2019", "title": "Tailoring Thermal Radiation from Near Field to Far Field", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302019-214849044", "creators": [ { "name": { "family": "Kou", "given": "Junlong" }, "id": "Kou-Junlong", "orcid": "0000-0002-0481-5149", "display_name": "Kou, Junlong" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "chair", "display_name": "Wang, Lihong" }, { "name": { "family": "Marandi", "given": "Alireza" }, "id": "Marandi-A", "orcid": "0000-0002-0470-0050", "role": "member", "display_name": "Marandi, Alireza" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MCZC-7E85", "abstract": "Control of heat flow in both near and far field through thermal radiation is of fundamental interest for applications in thermal management and energy conversion.
\r\n\r\nOne challenge is how we can realize high contrast control of heat flow with high temporal frequencies and without moving parts. We try to resolve this problem and propose two schemes in the near field: one based on electrical tuning of silicon and the other based on optical pumping of doped silicon slabs. Both methods rely on the change of free carriers, leading to tuning of the plasma frequency, resulting in modulation of near-field thermal radiation. Calculations based on fluctuational electrodynamics show that the electric method gives 10% tuning range. On the other hand, heat transfer coefficient between two silicon films can be tuned from near zero to 600 Wm-2K-1 with a gap distance of 100 nm at room temperature with the optical pumping method.
\r\n\r\nIn the far field, we predict and demonstrate two spectrally selective absorbers based on semiconductors, by utilizing their band gap properties and dedicated photonic structure design. The germanium photonic crystals have around 95% absorption from 500 nm to 1000 \u00b5m and over 0.9 over the entire visible and near infrared spectrum. The effective absorptivity is as high as 0.91. The black silicon achieves 100% absorption for light with wavelength under 1 \u00b5m. The effective absorptivity is as high as 0.96. Field test shows that black silicon is able to maintain at 130 degrees Celcius under unconcentrated condition.
\r\n\r\nAnother interesting topic is to achieve over 100 Wm-2 electricity-free cooling power density with simple fabrication method by passive radiative cooling under direction sunlight. We theoretically predicted three schemes for achieving this goal and experimentally demonstrate that a polymer-coated fused silica mirror, as a near-ideal black-body in the mid-infrared and near-ideal reflector in the solar spectrum, achieves radiative cooling below ambient air temperature under direct sunlight (8.2 \u00b0C) and at night (8.4 \u00b0C). Its performance exceeds that of a multi-layer thin film stack fabricated using vacuum deposition methods by nearly 3 \u00b0C. Furthermore, we estimate the cooler has an average net cooling power of about 127 Wm-2 during daytime at ambient temperature, more than twice that reported previously, even considering the significant influence of external conduction and convection. Our work demonstrates that abundant materials and straight-forward fabrication can be used to achieve daytime radiative cooling, advancing applications such as dry cooling of thermal power plants.
" }, { "name": "Kumar, Siddhant", "degree": "PhD", "year": "2019", "title": "An Enhanced Maximum-Entropy Based Meshfree Method: Theory and Applications", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062019-043913897", "creators": [ { "name": { "family": "Kumar", "given": "Siddhant" }, "id": "Kumar-Siddhant", "orcid": "0000-0003-1602-8641", "display_name": "Kumar, Siddhant" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Danas", "given": "Konstantinos" }, "id": "Danas-Konstantinos", "role": "member", "display_name": "Danas, Konstantinos" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0AP6-5F94", "abstract": "This thesis develops an enhanced meshfree method based on the local maximum-entropy (max-ent) approximation and explores its applications. The proposed method offers an adaptive approximation that addresses the tensile instability which arises in updated-Lagrangian meshfree methods during severe, finite deformations. The proposed method achieves robust stability in the updated-Lagrangian setting and fully realizes the potential of meshfree methods in simulating large-deformation mechanics, as shown for benchmark problems of severe elastic and elastoplastic deformations. The improved local maximum-entropy approximation method is of a general construct and has a wide variety of applications. This thesis presents an extensive study of two applications - the modeling of equal-channel angular extrusion (ECAE) based on high-fidelity plasticity models, and the numerical relaxation of nonconvex energy potentials. In ECAE, the aforementioned enhanced maximum-entropy scheme allows the stable simulation of large deformations at the macroscale. This scheme is especially suitable for ECAE as the latter falls into the category of severe plastic deformation processes where simulations using mesh-based methods (e.g. the finite element method (FEM)) are limited due to severe mesh distortions. In the second application, the aforementioned max-ent meshfree method outperforms FEM and FFT-based schemes in numerical relaxation of nonconvex energy potentials, which is essential in discovering the effective response and associated energy-minimizing microstructures and patterns. The results from both of these applications show that the proposed method brings new possibilities to the subject of computational solid mechanics that are not within the reach of traditional mesh-based and meshfree methods.
\r\n" }, { "name": "Lai, Yu-Hung", "degree": "PhD", "year": "2019", "title": "Microresonator Brillouin Laser Gyroscope", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282019-120721714", "creators": [ { "name": { "family": "Lai", "given": "Yu-Hung" }, "id": "Lai-Yu-Hung", "orcid": "0000-0002-9639-6569", "display_name": "Lai, Yu-Hung" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/10XE-G776", "abstract": "Optical Gyroscopes are among the most accurate rotation-measuring devices and are widely used for navigation and accurate compasses. With the advent of integrated photonics for complex telecommunication chips, there has been interest in the possibility of chip-scale optical gyroscopes. Besides the potential benefits of miniaturization, such solid-state systems would be robust and resistant to shock. In this thesis, we investigate a chip-based optical gyroscope using counter-propagating Brillouin lasers on a monolithic silicon chip. The near-degenerate lasers mimic a commercial ring laser gyroscope including the existence of a locking band. By using physical properties associated with the Brillouin process, a solid-state unlocking method is demonstrated. We focus on three topics to explore the potential of the counter-propagating Brillouin-laser gyroscope. First, we explore the physics of the counter-propagating Brillouin lasers by deriving the theory to link the passive cavity mode with the lasing gain medium. We explicitly show how the dispersion, Kerr nonlinearity, dissipative coupling, and Sagnac sensing affect the beating frequency of the Brillouin lasers. Second, we experimentally demonstrate the performance of the gyroscope. Most notably, the gyroscope is used to measure the rotation of the Earth, representing an important milestone for chip-scale optical gyroscopes. Third, we investigate the non-Hermitian interaction between the counter-propagating Brillouin lasers. We test the recent prediction of the EP-enhanced Sagnac effect, and observe a Sagnac scale factor boost by over 4X by measurement of rotations applied to the resonator. Our research shows the feasibility of the chip-based Brillouin laser gyroscope. This gyroscope paves the way towards an all-optical inertial guidance system.
" }, { "name": "Li, Lei", "degree": "PhD", "year": "2019", "title": "Multi-Contrast Photoacoustic Computed Tomography", "advisor": "Wang, Lihong", "url": "https://resolver.caltech.edu/CaltechTHESIS:05072019-120355881", "creators": [ { "name": { "family": "Li", "given": "Lei" }, "id": "Li-Lei", "orcid": "0000-0001-6164-2646", "display_name": "Li, Lei" } ], "advisors": [ { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "advisor", "display_name": "Wang, Lihong" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "orcid": "0000-0001-9783-4383", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Oka", "given": "Yuki" }, "id": "Oka-Yuki", "orcid": "0000-0003-2686-0677", "role": "member", "display_name": "Oka, Yuki" } ], "option_major": [ "eleceng" ], "doi": "10.7907/FYGX-7M29", "abstract": "Imaging of small animals has played an indispensable role in preclinical research by providing high dimensional physiological, pathological, and phenotypic insights with clinical relevance. Yet pure optical imaging suffers from either shallow penetration (up to ~1\u20132 mm) or a poor depth-to-resolution ratio (~3), and non-optical techniques for whole-body imaging of small animals lack either spatiotemporal resolution or functional contrast. A stand-alone single-impulse photoacoustic computed tomography (PACT) system has been built, which successfully mitigates these limitations by integrating high spatiotemporal resolution, deep penetration, and full-view fidelity, as well as anatomical, dynamical, and functional contrasts. Based on hemoglobin absorption contrast, the whole-body dynamics and large scale brain functions of rodents have been imaged in real time. The absorption contrast between cytochrome and lipid has enabled PACT to resolve MRI-like whole brain structures. Taking advantage of the distinct absorption signature of melanin, unlabeled circulating melanoma cells have been tracked in real time in vivo.
\r\n\r\nAssisted by near-infrared dyes, the perfusion processes have been visualized in rodents. By localizing single-dyed droplets, the spatial resolution of PACT has been improved by six-fold in vivo. The migration of metallic-based microrobots toward the targeted regions in the intestines has been monitored in real time. Genetically encoded photochromic proteins benefit PACT in detection sensitivity and specificity. The unique photoswitching characteristics of different photochromic proteins allow quantitative multi-contrast imaging at depths. A split version of the photochromic protein has permitted PA detection of protein-protein interactions in deep-seated tumors. The photochromic behaviors have also been utilized to guide photons to form an optical focus inside live tissue. As a rapidly evolving imaging technique, PACT promises pre-clinical applications and clinical translation.
\r\n" }, { "name": "Lifson, Max Louis", "degree": "PhD", "year": "2019", "title": "Electromechanical Properties of 3D Multifunctional Nano-Architected Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01182019-105653047", "creators": [ { "name": { "family": "Lifson", "given": "Max Louis" }, "id": "Lifson-Max-Louis", "orcid": "0000-0002-0382-182X", "display_name": "Lifson, Max Louis" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/D0AD-4T88", "abstract": "In this thesis, we explore the fabrication and characterization of 3D architected multifunctional materials in three different categories: varied density for tailored mechanical response, stiff ultra low-k dielectric materials, and direct laser writing of piezoelectric structures at the micron scale. The density of an architected material plays a large role in determining its effective Young\u2019s modulus, strength, and deformation behavior. The first section of this work explores the effect of incorporating two density regions into hollow nanolattices, which results in two distinct mechanical response regions for horizontal interfaces and a combined varying response for a diagonal interface. The second section of this work describes low dielectric constant (low-k) materials, which have gained increasing popularity because of their critical role in developing faster, smaller, and higher performance devices. We report the fabrication of 3D nanoarchitected hollow-beam alumina dielectrics with a k value of 1.06 - 1.10 at 1 MHz that is stable over the voltage range of -20 to 20 V and a frequency range of 100 kHz to 10 MHz, with an effective Young\u2019s modulus of 30 MPa, a strength of 1.07 MPa, a nearly full shape recoverability to its original size after >50% compressions, and outstanding thermal stability with a thermal coefficient of dielectric constant (TCK) of 2.43 x 10-5K-1 up to 800\u00b0 C. Finally, we report the fabrication of monolithic piezoelectric ZnO structures of arbitrary shape via a polymer complex route. We have confirmed the microstructure using XRD, TEM, and SAED, and have observed its electromechanical response using a novel in-situ experiment.
" }, { "name": "Mauser, Kelly Ann Weekley", "degree": "PhD", "year": "2019", "title": "Resonant Thermoelectric Nanophotonics: Applications in Spectral and Thermal Sensing", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062019-191307495", "creators": [ { "name": { "family": "Mauser", "given": "Kelly Ann Weekley" }, "id": "Mauser-Kelly-Ann-Weekley", "orcid": "0000-0001-9903-8559", "display_name": "Mauser, Kelly Ann Weekley" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/0HJF-X691", "abstract": "Plasmon excitation enables extreme light confinement at the nanoscale, localizing energy in subwavelength volumes and thus can enable increased absorption in photovoltaic or photoconductive detectors. Nonetheless, plasmon decay also results in energy transfer to the lattice as heat which is detrimental to photovoltaic detector performance. However, heat generation in resonant subwavelength nanostructures also represents an energy source for voltage generation, as we demonstrate in the first part of this thesis via design of resonant thermoelectric (TE) plasmonic absorbers for optical detection. Though TEs have been used to observe resonantly coupled surface plasmon polaritons in noble-metal thin films and microelectrodes, they have not been employed previously as resonant absorbers in functional TE nanophotonic structures.
\r\n\r\nWe demonstrate nanostructures composed of TE thermocouple junctions using established TE materials \u2013 chromel/alumel and bismuth telluride/antimony telluride \u2013 but patterned so as to support guided mode resonances with sharp absorption profiles, and which thus generate large thermal gradients upon optical excitation and localized heat generation in the TE material. Unlike previous TE absorbers, our structures feature tunable narrowband absorption and measured single junction responsivities 4 times higher than the most similar (albeit broadband) graphene structures, with potential for much higher responsivities in thermopile architectures. For bismuth telluride \u2013 antimony telluride single thermocouple structures, we measure a maximum responsivity of 38 V/W, referenced to incident illumination power. We also find that the small heat capacity of optically resonant TE nanowires enables a fast, 3 kHz temporal response, 10-100 times faster than conventional TE detectors. We show that TE nanophotonic structures are tunable from the visible to the MIR, with small structure sizes of 50 microns x 100 micons. Our nanophotonic TE structures are suspended on thin membranes to reduce substrate heat losses and improve thermal isolation between TE structures arranged in arrays suitable for imaging or spectroscopy. Whereas photoconductive and photovoltaic detectors are typically insensitive to sub-bandgap radiation, nanophotonic TEs can be designed to be sensitive to any specific wavelength dictated by nanoscale geometry, without bandgap wavelength cutoff limitations. From the point of view of imaging and spectroscopy, they enable integration of filter and photodetector functions into a single structure. Other thermoelectric nanophotonic motifs are also explored.
\r\n\r\nGenerating localized, high electric field intensity in nanophotonic and plasmonic devices has many applications, from enhancing chemical reaction rates, to thermal radiation steering, to chemical sensing, and to photovoltaics. Along with a strongly localized electric field comes a temperature rise in non-lossless photonic materials, which can affect reaction rate, photovoltaic efficiency, or other properties of the system. Measuring temperature rises in nanophotonic structures is difficult, and methods commonly employed suffer from various limitations, such as low spatial resolution (Fourier transform infrared microscopy), bulky and expensive setups (scanning thermal microscopy), intrusive methods that interfere with nanophotonic structures (Pt resistive thermometry), or the need for specialized materials (temperature dependent photoluminescence).
\r\n\r\nIn the second part of this thesis, we overcome these limitations with the first-ever demonstration of temperature measurements of nanophotonic structures by employing both room temperature noise thermometry and the thermoelectric effect under ambient conditions without external probes by utilizing the properties of the materials that make up the nanophotonic structure itself. We have previously estimated the \u0394 T in a nanophotonic device using the thermoelectric effect, but could not determine the absolute temperature of the system. In the application we will discuss, the absolute electron temperature of the nanophotonic material itself is measured. Because Johnson-Nyquist noise is material independent and is a fundamental measure of absolute temperature, there is theoretically no need for calibration as in the case of resistive thermometry. To measure the temperature rise of a nanophotonic resonant region remotely, the Seebeck coefficient of the material is first carefully measured using noise thermometry, then the thermoelectric voltage generated in the nanophotonic materials themselves is measured from electrical leads spanning the resonantly excited region. To accomplish this, we have developed a metrology technique capable of simultaneously measuring electrical noise at two locations on the nanophotonic structure as well as the electrical potential between the two points, under chopped laser illumination that heats the structure via nanophotonic absorption, thus providing drift-corrected light on/off temperature information.
" }, { "name": "Mazur, Paul Antoine Benoit", "degree": "PhD", "year": "2019", "title": "Controlling the Buckling Behavior of Bilayered Systems", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272018-211547049", "creators": [ { "name": { "family": "Mazur", "given": "Paul Antoine Benoit" }, "id": "Mazur-Paul-Antoine-Benoit", "orcid": "0000-0002-2837-9716", "display_name": "Mazur, Paul Antoine Benoit" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Audoly", "given": "Basile" }, "id": "Audoly-Basile", "role": "member", "display_name": "Audoly, Basile" } ], "option_major": [ "mecheng" ], "doi": "10.7907/C70B-K221", "abstract": "A bilayered system is an assembly of two different materials and has the form of flat and thin layers. The two materials are attached to each other at the surface. The attachment method varies depending on the materials properties. Bilayered systems made of materials with different dimensions and stiffness have been widely studied and used for different applications. The characteristic scale of this kind of system can go from hundreds of km in the case of geological layers on the Earth surface to some \u00b5m in the case of very small electronic systems or microlenses.
\r\n\r\nThe behavior of a bilayered system, when submitted to a stimulus, is characterized by the conflict between the preferred response of each material and the constraint that one imposes on the other. As a result, the deformation of the bilayered system will be different from that which could be obtained when the materials are taken separately. Of particular interest is the buckling of such systems: when submitted to a particular stress distribution, one material will expand significantly more than the other, but as the two materials are attached at the interface surface, the material displacements must be continuous through this interface. The conflict between the continuity of displacement and the need to expand differently may result in nonlinear patterns at this interface. Those unstable situations can be used to define a limit of constraint for the materials or can be used as actuators for a desired surface pattern. Many studies have focused on characterizing homogeneous buckling within an entire surface due to homogeneous strain distribution within the top surface. This characterization was performed theoretically, numerically, and experimentally. But, some studies have shown different possibilities of evolution of the buckling patterns known today. As a consequence, we can pose two questions: 1) Is there a possibility to modify non-linear patterns regardless of what is imposed by mechanical properties and dimensions? 2) What happens in the case of a non-uniform state of constraints within the bilayered system?
\r\n\r\nThis thesis explores those questions for the case of a thin stiff film attached to a compliant thick substrate. The first part of this thesis serves to describe the initial buckling theory in the case of uniform strain and explains how to define the loading threshold resulting in uniform buckling at the surface characterized by a finite number of spatial frequencies. The second part of the thesis studies the consequences of a non-uniform loading within the surface. A numerical method based on the theory of the first part is implemented to show the emergence of new frequencies due to the discontinuous loading distribution. The third part focuses on the possibility of tuning a uniform buckling by including an electromechanical coupling into the bilayered system. This coupling makes the materials sensitive to electric fields, thus creating a new energy term to interfere with the mechanical energy of deformation, thereby modifying the resulting spatial frequency of the buckling. This study is done theoretically and numerically by finite element modeling.
" }, { "name": "Morgan, Jonathan Philip", "degree": "PhD", "year": "2019", "title": "Linear and Non-linear Interactions in a Rough-Wall Turbulent Boundary Layer", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04112019-234812867", "creators": [ { "name": { "family": "Morgan", "given": "Jonathan Philip" }, "id": "Morgan-Jonathan-Philip", "orcid": "0000-0003-2898-4868", "display_name": "Morgan, Jonathan Philip" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7RSR-3277", "abstract": "This thesis explores the linear and non-linear interactions which take place in a rough-wall turbulent boundary through experiments and modeling. In order to derive physics-based models for the relation between roughness geometry and flow physics, two very simple periodic roughnesses were 3D printed and placed in a boundary layer wind tunnel for separate experiments. Hot-wire measurements were taken at a grid of points within a single period of the roughness in order to map the spatial variation of important flow statistics in way that allows correlation back to the roughness geometry. Time averaged streamwise velocity and the power spectrum of instantaneous streamwise velocity were both found to vary coherently with the roughness. The spatial variation of the time averaged velocity was identified as the linear result of the roughness, as it has identical wavenumber and frequency to the static roughness geometry. Modeling the time-averaged velocity field as a response mode of the linear resolvent operator was found to be reasonable for certain wavenumbers. The spatial distribution of the power spectrum was shown to be a non-linear effect of the roughness; the power spectrum only measures the energy of convecting modes, which necessarily have non-zero frequency and cannot correlate linearly to the static roughness. The spatial modulation of the power spectrum was found to be indicative of non-linear triadic interactions between the static velocity Fourier modes and pairs of convecting modes, as allowed by the Navier-Stokes equations. A low-order model for these interactions, and their effect on the power spectrum, was constructed using resolvent response modes to represent all velocity Fourier modes. The model was found to qualitatively predict the modulation of the power spectrum for several sets of wavenumbers. The success of such a simple model suggests that it presents a useful low-order understanding of non-linear forcing between scales in rough-wall boundary layers.
" }, { "name": "Nakahira, Yorie", "degree": "PhD", "year": "2019", "title": "Connecting the Speed-Accuracy Trade-Offs in Sensorimotor Control and Neurophysiology Reveals Diversity Sweet Spots in Layered Control Architectures", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-083145024", "creators": [ { "name": { "family": "Nakahira", "given": "Yorie" }, "id": "Nakahira-Yorie", "orcid": "0000-0003-3324-4602", "display_name": "Nakahira, Yorie" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "role": "member", "display_name": "Adami, Christoph Carl" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "cds" ], "doi": "10.7907/VYQY-DF47", "abstract": "Nervous systems sense, communicate, compute, and actuate movement using distributed components with trade-offs in speed, accuracy, sparsity, noise, and saturation. Nevertheless, the resulting control can achieve remarkably fast, accurate, and robust performance due to a highly effective layered control architecture. However, this architecture has received little attention from the existing research. This is in part because of the lack of theory that connects speed-accuracy trade-offs (SATs) in the components neurophysiology with system-level sensorimotor control and characterizes the overall system performance when different layers (planning vs. reflex layer) act work jointly. In thesis, we present a theoretical framework that provides a synthetic perspective of both levels and layers. We then use this framework to clarify the properties of effective layered architectures and explain why there exists extreme diversity across layers (planning vs. reflex layers) and within levels (sensorimotor versus neural/muscle hardware levels). The framework characterizes how the sensorimotor SATs are constrained by the component SATs of neurons communicating with spikes and their sensory and muscle endpoints, in both stochastic and deterministic models. The theoretical predictions are also verified using driving experiments. Our results lead to a novel concept, termed ``diversity sweet spots (DSSs)'': the appropriate diversity in the properties of neurons and muscles across layers and within levels help create systems that are both fast and accurate despite being built from components that are individually slow or inaccurate. At the component level, this concept explains why there are extreme heterogeneities in the neural or muscle composition. At the system level, DSSs explain the benefits of layering to allow extreme heterogeneities in speed and accuracy in different sensorimotor loops. Similar issues and properties also extend down to the cellular level in biology and outward to our most advanced network technologies from smart grid to the Internet of Things. We present our initial step in expanding our framework to that area and widely-open area of research for future direction. " }, { "name": "Olsman, Noah Andrew", "degree": "PhD", "year": "2019", "title": "Architecture, Design, and Tradeoffs in Biomolecular Feedback Systems", "advisor": "Goentoro, Lea A.; Doyle, John C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11262018-100422941", "creators": [ { "name": { "family": "Olsman", "given": "Noah Andrew" }, "id": "Olsman-Noah-Andrew", "orcid": "0000-0002-4351-3880", "display_name": "Olsman, Noah Andrew" } ], "advisors": [ { "name": { "family": "Goentoro", "given": "Lea A." }, "id": "Goentoro-L-A", "orcid": "0000-0002-3904-0195", "role": "co-advisor", "display_name": "Goentoro, Lea A." }, { "name": { "family": "Doyle", "given": "John C." }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "co-advisor", "display_name": "Doyle, John C." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Bois", "given": "Justin S." }, "id": "Bois-J-S", "orcid": "0000-0001-7137-8746", "role": "member", "display_name": "Bois, Justin S." }, { "name": { "family": "Doyle", "given": "John C." }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John C." }, { "name": { "family": "Goentoro", "given": "Lea A." }, "id": "Goentoro-L-A", "orcid": "0000-0002-3904-0195", "role": "member", "display_name": "Goentoro, Lea A." } ], "option_major": [ "cds" ], "doi": "10.7907/DGPY-1679", "abstract": "A core pursuit in systems and synthetic biology is the analysis of the connection between the low-level structure and parameters of a biomolecular network and its high-level function and performance. Elucidating this mapping has become increasingly feasible as precise measurements of both input parameters and output dynamics become abundant. At the same time, cross-pollination between biology and engineering has led to the realization that many of the mathematical tools from control theory are well-suited to analyze biological processes.
\r\n\r\nThe goal of this thesis is to use tools from control theory to analyze a variety of biomolecular systems from both natural and synthetic settings, and subsequently yield insight into the architecture, tradeoffs, and limitations of biological network. In Chapter 2, I demonstrate how allosteric proteins can be used to respond logarithmically to changes in signal. In Chapter 3, I show how control theoretic techniques can be used to inform the design of synthetic integral feedback networks that implement feedback with a sequestration mechanism. Finally, in Chapter 4 I present a novel simplified model of the E. coli heat shock response system and show how the the mapping of circuit parameters to function depends on the network's architecture.
\r\n\r\nThe unifying theme of this research is that the conceptual framework used to study engineered systems is remarkably well-suited to biology. That being said, it is important to apply these tools in a way that is informed by the molecular details of biological processes. By combining structural and biochemical data with the functional perspective of engineering, it is possible to understand the architectural principles that underlie living systems.
" }, { "name": "Omelchenko, Stefan Thomas", "degree": "PhD", "year": "2019", "title": "Towards a Net-zero Carbon Energy System: High Efficiency Photovoltaics and Electrocatalysts", "advisor": "Lewis, Nathan Saul; Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022019-111830413", "creators": [ { "name": { "family": "Omelchenko", "given": "Stefan Thomas" }, "id": "Omelchenko-Stefan-Thomas", "orcid": "0000-0003-1104-9291", "display_name": "Omelchenko, Stefan Thomas" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "co-advisor", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "co-advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/B6AS-EA22", "abstract": "Modern society is dependent on energy. Despite increases in energy efficiency, human development and economic goals are expected to increase the global demand for energy by almost 30% in the next 20 years. At the same time, anthropogenic carbon dioxide emissions must approach zero to stabilize global temperatures below the 2\u00b0C target set out by international climate agreements. Realizing a net-zero carbon energy system will depend on the development of a highly reliable, sustainable electricity grid to power society and the ability to produce chemicals and fuels in a carbon-free manner. Developing cheap, efficient solar photovoltaics and highly active and selective electrocatalysts is thus pivotal to achieving this goal.
\r\n\r\nIn this work, we address issues limiting photovoltaics and electrocatalysts. Our work on photovoltaics analyzes two effects often neglected in the evaluation of efficiency limits for photovoltaic materials. We show that the shape of the band tail and, in particular, the extent of sub-gap absorption, controls the open-circuit voltage, emission, and ultimately the achievable efficiency of a solar cell. These findings are generalizable to any luminescent material and our analysis suggests that efficiency limits for a material can be determined through simple experimental characterization. In addition, we develop a device physics model which accounts for the presence of excitons, which are the fundamental excitation in a host of emerging photovoltaic materials. A case study in cuprous oxide shows that excitonic effects can play a large role in the device physics of materials with large exciton binding energies and that standard models can drastically underestimate the efficiency limits in these systems. Our work on photovoltaics, culminates in the realization of a novel device architecture for tandem silicon/perovskite solar cells that opens the possibility of achieving efficiencies >30%. Finally, we develop a method to tune the catalytic activity of electrocatalysts for the oxygen-evolution and chlorine-evolution reactions. Our method is based on group electronegativity and is likely generalizable to other reactions and catalysts. The analyses and technologies developed herein are promising steps towards a zero-carbon energy system.
" }, { "name": "Paik, Haemin", "degree": "PhD", "year": "2019", "title": "Development of Electrocatalysts in Solid Acid Fuel Cells", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-011829568", "creators": [ { "name": { "family": "Paik", "given": "Haemin" }, "id": "Paik-Haemin", "orcid": "0000-0001-8358-6067", "display_name": "Paik, Haemin" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "matsci" ], "doi": "10.7907/C96K-Z389", "abstract": "Solid acid fuel cells (SAFCs) can operate at intermediate temperature (near 250 \u00baC) using a non-toxic, solid proton-conducting electrolyte, CsH2PO4, which allows for fuel flexibility, high efficiency, inexpensive auxiliary components, and easy on-off cycling. Despite these features, large activation overpotentials at the electrodes require high Pt loadings in order to achieve acceptable power output. Few alternatives to Pt have emerged for either the hydrogen oxidation reaction or the oxygen reduction reaction in SAFCs. This thesis explores the use of Pd and Pd-containing alloys for electrocatalysis in SAFCs to reduce overall precious metal loading and therefore reduce cost to commercialization.
\r\n\r\nFirst, this work explores the use of Pd at the SAFC anode, assessing both catalytic activity for hydrogen electro-oxidation and reactivity with the CsH2PO4 electrolyte. A thin film geometry, in which nanometric layers of metal were deposited onto a polycrystalline disk of CsH2PO4 was used to simplify the device and facilitate interpretation electrochemical behavior. Using a symmetric geometry, the cells were examined under a uniform hydrogen-rich gas. It was found that Pd reacts with CsH2PO4, forming palladium phosphide (Pd-P) at the metal-electrolyte interface. With the aim studying the behavior of Pd in the absence of this reactivity, Pd overlain on Pt was examined in a bilayer geometry of Pd | Pt | CsH2PO4 | Pt | Pd. The bilayer Pt | Pd films show much higher activity for hydrogen electro-oxidation than films of Pt alone, as measured by AC impedance spectroscopy. Ex-situ low energy ion scattering and scanning transmission electron microscopy revealed that Pd diffused into the Pt layer under operating conditions. The extremely high activity of the interdiffused films suggest that Pd catalyzes reactions at both the metal-gas and metal-electrolyte interfaces, and furthermore facilitates rapid hydrogen diffusion rates through the films.
\r\n\r\nThe high activity of Pt | Pd films, in which Pd eventually contacts the underlying electrolyte due to interdiffusion of the metals, motivates an investigation of Pd-based catalysts (Pd and Pd-P) for hydrogen electro-oxidation in a fuel cell relevant configuration. Working electrodes were formed from a mixture of Pd on carbon and the electrolyte material. The hydrogen oxidation kinetics from Pd, Pd6P, and Pd3P0.8 were observed to be comparable. The result is consistent with the observation that Pd catalyst reacts with CsH2PO4 and converts into Pd-P during cell operation. Both Pd and Pd-P appear to be more effective electrocatalysts for hydrogen oxidation than the equivalent mole percent of Pt supported on carbon. Further enhancement of Pd catalytic activity is achieved by reducing its crystallite size.
\r\n\r\nLastly, this work examines the catalytic activity of Pd for oxygen reduction at the SAFC cathode. Evaluation of this system is complicated by the instability of Pd on CsH2PO4 under oxidizing conditions, which causes microstructure collapse and performance degradation. A SnO2 thin film was introduced as a barrier layer to inhibit Pd reactivity with CsH2PO4 and as a structural support for the catalyst. Employing atomic layer deposition, a SnO2 thin film was deposited either between the Pd and CsH2PO4 interface, or over the Pd catalyst. Both Pd-SnO2 bilayers show improved fuel cell performance stability compared to a Pd-only control, forming Pd-Sn alloys under cathode conditions. This suggests that the formation of Pd-Sn alloy stabilizes the metallic phase of Pd, improving catalytic activity. This work presents a new approach for designing the cathode materials for SAFCs.
" }, { "name": "Pang, John Zhen Fu", "degree": "PhD", "year": "2019", "title": "Online Platforms in Networked Markets: Transparency, Anticipation and Demand Management", "advisor": "Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03132019-143428796", "creators": [ { "name": { "family": "Pang", "given": "John Zhen Fu" }, "id": "Pang-John-Zhen-Fu", "orcid": "0000-0002-6485-7922", "display_name": "Pang, John Zhen Fu" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "chair", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Doval", "given": "Laura" }, "id": "Doval-Laura", "role": "member", "display_name": "Doval, Laura" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "cms" ], "doi": "10.7907/XY8M-8D94", "abstract": "The global economy has been transformed by the introduction of online platforms in the past two decades. These companies, such as Uber and Amazon, have benefited and undergone massive growth, and are a critical part of the world economy today. Understanding these online platforms, their designs and how participation change with anticipation and uncertainty can help us identify the necessary ingredients for successful implementation of online platforms in the future, especially for those with underlying network constraints, e.g., the electricity grid.
\r\n\r\nThis thesis makes three main contributions. First, we identify and compare common access and allocation control designs for online platforms, and highlight their trade-offs between transparency and control. We make these comparisons under a networked Cournot competition model and consider three popular designs: (i) open access, (ii) discriminatory access, and (iii) controlled allocation. Our findings reveal that designs that control over access are more efficient than designs that control over allocations, but open access designs are susceptible to substantial search costs. Next, we study the impact of demand management in a networked Stackelberg model considering network constraints and producer anticipation. We provide insights on limiting manipulation under these constrained networked marketplaces with nodal prices, and show that demand management mechanisms that traditionally aid system stability also help plays a vital role economically. In particular, we show that demand management empower consumers and give them \"market power\" to counter that of producers, limiting the impact of their anticipation and their potential for manipulation. Lastly, we study how participants (e.g., drivers on Uber) make competitive real-time production (driving) decisions. To that end, we design a novel pursuit algorithm for making online optimization under limited inventory constraints. Our analysis yields an algorithm that is competitive and applicable to achieve optimal results in the well known one-way trading problem, and new variants of the original problem.
" }, { "name": "Phlipot, Gregory Paul", "degree": "PhD", "year": "2019", "title": "A Fully-Nonlocal Quasicontinuum Method to Model the Nonlinear Response of Periodic Truss Lattices", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242019-115317802", "creators": [ { "name": { "family": "Phlipot", "given": "Gregory Paul" }, "id": "Phlipot-Gregory-Paul", "orcid": "0000-0003-2721-8678", "display_name": "Phlipot, Gregory Paul" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "space" ], "doi": "10.7907/3MPP-Q119", "abstract": "We present a framework for the efficient, yet accurate description of general periodic truss networks based on concepts of the quasicontinuum (QC) method. Previous research in coarse-grained truss models has focused either on simple bar trusses or on two-dimensional beam lattices undergoing small deformations. Here, we extend the truss QC methodology to nonlinear deformations, general periodic beam lattices, and three dimensions. We introduce geometric nonlinearity into the model by using a corotational beam description at the level of individual truss members. Coarse-graining is achieved by the introduction of representative unit cells and a polynomial interpolation analogous to traditional QC. General periodic lattices defined by the periodic assembly of a single unit cell are modeled by retaining all unique degrees of freedom of the unit cell (identified by a lattice decomposition into simple Bravais lattices) at each macroscopic point in the simulation, and interpolating each degree of freedom individually. We show that this interpolation scheme accurately captures the homogenized properties of periodic truss lattices for uniform deformations. In order to showcase the efficiency and accuracy of the method, we compare coarse-grained simulations to fully-resolved simulations for various test problems, including: brittle fracture toughness prediction, static and dynamic indentation with geometric and material nonlinearities, and uniaxial tension of a truss lattice plate with a cylindrical hole. We also discover the notion of stretch locking --- a phenomenon where certain lattice topologies are over-constrained, resulting in artificially stiff behavior similar to volumetric locking in finite elements --- and show that using higher-order interpolation instead of affine interpolation significantly reduces the error in the presence of stretch locking in 2D and 3D. Overall, the new technique shows convincing agreement with exact, discrete results for a wide variety of lattice architectures, and offers opportunities to reduce computational expenses in structural lattice simulations and thus to efficiently extract the effective mechanical performance of discrete networks." }, { "name": "Portela G., Carlos Mauricio", "degree": "PhD", "year": "2019", "title": "Fabrication, Mechanical Characterization, and Modeling of 3D Architected Materials upon Static and Dynamic Loading", "advisor": "Greer, Julia R.; Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052019-161606954", "creators": [ { "name": { "family": "Portela G.", "given": "Carlos Mauricio" }, "id": "Portela-G-Carlos-M", "orcid": "0000-0002-2649-4235", "display_name": "Portela G., Carlos Mauricio" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "co-advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/75S6-SB32", "abstract": "Architected materials have been ubiquitous in nature, enabling unique properties that are unachievable by monolithic, homogeneous materials. Inspired by natural processes, man-made three-dimensional (3D) architected materials have been reported to enable novel mechanical properties such as high stiffness- and strength-to-density ratios, extreme resilience, or high energy absorption. Furthermore, advanced fabrication techniques have enabled architected materials with feature sizes at the nanometer-scale, which exploit material size effects to approach theoretical bounds. However, most architected materials have relied on symmetry, periodicity, and lack of defects to achieve the desired mechanical response, resulting in sub-optimal mechanical response under the presence of inevitable defects. Additionally, most of these nano- and micro-architected materials have only been studied in the static regime, leaving the dynamic parameter space unexplored.
\r\n\r\nIn this work, we address these issues by: (i) proposing numerical and theoretical tools that predict the behavior of architected materials with non-ideal geometries, (ii) presenting a pathway for scalable fabrication of tunable nano-architected materials, and (iii) exploring the response of nano- and micro-architected materials under three types of dynamic loading. We first explore lattice architectures with features at the micro- and millimeter scales and provide an extension to the classical stiffness scaling laws, enabled by reduced-order numerical models and experiments at both scales. After discussing the effect of nodes (i.e., junctions) on the mechanical response of lattice architectures, we propose alternative node-less geometries that eliminate the stress concentrations associated with nodes to provide extreme resilience. Using natural processes such as spinodal decomposition, we present pathways to fabricate a version of these materials with samples sizes on the order of cubic centimeters while achieving feature sizes on the order of tens of nanometers. In the dynamic regime, we design, fabricate, and test micro-architected materials with tunable vibrational band gaps through the use of architectural reconfiguration and local resonance. Lastly, we present methods to fabricate carbon-based materials at the nano- and centimeter scales and test them under supersonic impact and blast conditions, respectively. Our work provides explorations into pathways that could enable the use of nano- and micro-architected materials for applications that go beyond small-volume, quasi-static mechanical regimes.
" }, { "name": "Qian, Jin", "degree": "PhD", "year": "2019", "title": "From Quantum Mechanics to Experimental Observables: Computational Investigations of Energy-Related Heterogeneous Catalysts", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072018-215548214", "creators": [ { "name": { "family": "Qian", "given": "Jin" }, "id": "Qian-Jin", "orcid": "0000-0002-0162-0477", "display_name": "Qian, Jin" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Soriaga", "given": "Manuel P." }, "id": "Soriaga-M-P", "role": "member", "display_name": "Soriaga, Manuel P." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/SPEJ-5X35", "abstract": "One of the most severe challenges in this decade is assuring more secure, more efficient, cleaner, and more sustainable energy to power our world. This work takes a catalytic approach to help overcome this challenge.
\r\n\r\nThe Haber Bosch process is one of the towering achievements of industrial chemistry. It consumes a huge amount of energy due to the high temperature and high pressure reaction condition, and in turn, has enabled us to produce enough nitrogen fertilizer to feed the current world population. An essential goal of present research is therefore to dramatically reduce Haber Bosch energy cost by improving the catalytic performance of the presently used Fe-based heterogeneous catalysts. We use quantum mechanics (QM) and kinetic Monte Carlo (kMC) to predict reaction mechanisms and kinetics for NH3 synthesis on Fe(111) \u2013 the best Fe single crystal surface for NH3 synthesis. We find excellent agreement with a predicted turnover frequency (TOF) of 17.7 sec-1 per 2x2 site (5.3 x 10-9 moles/cm2/sec) compared to TOF=10 sec-1 per site from experiment, and we further predict that top-layer Co doping leads to an acceleration by a factor of 2.3 in reaction rates of ammonia synthesis.
\r\n\r\nCompared to the industrialized Haber Bosch reaction, renewable energy technologies are still in their infancy with a great deal of questions unanswered, as well as a lot of barriers to overcome. Here we report our atomistic understanding of how CO2 and H2O molecules adsorb on the catalyst surface and interact to initiate CO2 dissociation and subsequent product formation. Using synergistic experimental and theoretical analyses, we show that Cu and Ag operate entirely differently for the first step of activating CO2. We develop a method of predicting the ambient pressure XPS spectrum in an ab-initio multiscale fashion: from electronic structure, to atomic picture, to chemical reaction network (CRN), and eventually to the experimental observable. We bridge both the qualitative and quantitative gap from quantum mechanics to XPS, and demonstrate our approach by decoding the initial H2O adsorption and complex formation on Ag(111) surface, which we encourage to be the new standard protocol in this field.
\r\n" }, { "name": "Ratnaswamy, Vishagan", "degree": "PhD", "year": "2019", "title": "Constraining the Mantle's Rheology Using Methods in Uncertainty Quantification", "advisor": "Gurnis, Michael C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05132019-143045769", "creators": [ { "name": { "family": "Ratnaswamy", "given": "Vishagan" }, "id": "Ratnaswamy-Vishagan", "orcid": "0000-0002-2371-807X", "display_name": "Ratnaswamy, Vishagan" } ], "advisors": [ { "name": { "family": "Gurnis", "given": "Michael C." }, "id": "Gurnis-M-C", "role": "advisor", "display_name": "Gurnis, Michael C." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Simons", "given": "Mark" }, "id": "Simons-M", "role": "member", "display_name": "Simons, Mark" }, { "name": { "family": "Gurnis", "given": "Michael C." }, "id": "Gurnis-M-C", "role": "member", "display_name": "Gurnis, Michael C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F6FW-T648", "abstract": "An accurate estimation of the large-scale forces in the mantle has been difficult to obtain as numerical models either do not use an accurate rheology nor reproduce surface observations. While much work has been done in developing high-fidelity forward models that capture the salient physics of shear-thinning and dynamic weakening, they fail to reproduce observations such as plate motions and topography. In this thesis, we develop an optimization methodology that minimizes the misfit in surface observations such as plate motions and average effective viscosity for certain regions of the mantle. We utilize adjoints to calculate the gradient, while using second-order adjoints to construct the Hessian so as to infer the rheological parameters of the mantle's rheology. Furthermore, we build on this optimization scheme by constructing the Gaussian approximation of the posterior distribution for the inferred rheological parameters using the Hessian and establish the trade-offs between each parameter through their conditional distributions. We further extend this Gaussian approximation to infer extrinsic quantities such as the stresses in the fault zones and the average effective viscosity in the hinge zones to not only quantify the uncertainty, but also to see partitioning of the coupling of each subduction zone. " }, { "name": "Robbins, Andrew Beyer", "degree": "PhD", "year": "2019", "title": "Exploring Microscopic Thermal Transport Properties of Molecular Crystals with Simulations and Experiments", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02062019-144758624", "creators": [ { "name": { "family": "Robbins", "given": "Andrew Beyer" }, "id": "Robbins-Andrew-Beyer", "orcid": "0000-0002-8328-1762", "display_name": "Robbins, Andrew Beyer" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/ZZJ3-0K58", "abstract": "Polymers are widely used in applications due to their diverse and controllable properties in many physical domains. However, polymers have not historically been used in applications for which a high thermal conductivity is required as bulk polymers are typically thermal insulators. However, research in recent decades on a handful of highly oriented or semi-crystalline polymers has shown the potential for dramatically increased uniaxial thermal conductivity by factors exceeding 100. This dramatic increase in thermal conductivity is because heat is conducted by atomic vibrations along the covalently bonded polymer backbone rather than across chains by weak van der Waals bonds as in unoriented polymers. While it is known that polymers can be processed to yield these properties, much remains unknown about the microscopic transport properties of atomic vibrations in these materials and the true upper limits to thermal conductivity. In this thesis, we address these knowledge gaps by using a combination of simulations and experiments to investigate thermal conduction in semi-crystalline and crystalline polymers.
\r\n\r\nFirst, we present molecular dynamics simulations of a perfect polymer crystal, polynorbornene. While polymer crystals studied typically exhibit substantially enhanced thermal conductivities above those of the amorphous form, polynorbornene exhibits a glass-like thermal conductivity of less than 1 Wm-1K-1 even as a perfect crystal. This unusual behavior occurs despite the polymer satisfying many of the conventional criteria for high thermal conductivity. Using our simulations, we show that the origin of this unusual behavior is excessively anharmonic bonds and a complex unit cell.
\r\n\r\nSecond, we move to experimental studies of thermal transport in polymers. A key requirement to perform materials science is a method to routinely and easily characterize the property of interest in diverse samples. For polymers, this property is typically the in-plane thermal conductivity. This property turns out to be surprisingly difficult to measure using conventional thermal characterization methods. In this work, we adapt transient grating spectroscopy (TG), a well-known method in the chemistry community, to perform in-plane thermal conductivity measurements of polymer films. TG can resolve the in-plane thermal anisotropy of a sample without any physical contact and at tunable length scales, a substantial advance in capability over all prior characterization methods. We extend the application of TG to probe sub-\u00b5m length scales, and we successfully apply the technique to numerous poor quality polymer samples as well as thin films.
\r\n\r\nFinally, we exploit the capability of TG to probe thermal conduction over sub-\u00b5m length scales to provide the first experimentally resolved microscopic transport properties of atomic vibrations in semi-crystalline polyethylene (PE). Despite the intense interest over decades in PE due to its high intrinsic thermal conductivity, no experimental measurement has yet been able to directly probe the heat-carrying phonons, leading to many questions about the relevant scattering mechanisms and absolute upper limits of thermal conductivity in real samples. Using TG, we present the first observation of quasi-ballistic thermal transport at sub-\u00b5m length scales, from which we obtain the phonon mean free path spectra of a semi-crystalline PE sample. Further, we pair these results with Small-Angle X-ray Scattering measurements to show that thermal phonons propagate ballistically within and across nanocrystalline domains, contrary to the conventional viewpoint. These results provide an unprecedented microscopic view of thermal transport in polymer crystals that was previously experimentally inaccessible.
" }, { "name": "Scianmarello, Nicholas E.", "degree": "PhD", "year": "2019", "title": "Oxygen Transporter and Generator Devices to Treat Diabetic Retinopathy", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282019-074707723", "creators": [ { "name": { "family": "Scianmarello", "given": "Nicholas E." }, "id": "Scianmarello-Nicholas-E", "orcid": "0000-0002-1207-4029", "display_name": "Scianmarello, Nicholas E." } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Humayun", "given": "Mark" }, "id": "Humayun-M", "role": "member", "display_name": "Humayun, Mark" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "role": "member", "display_name": "Wang, Lihong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JCS2-8E12", "abstract": "In recent years, Micro-Electrical Mechanical Systems (MEMS) have opened new areas of the human body to non-pharmacological treatment. Miniaturized implants have started to appear in volume or power constrained areas, such as the eye and the heart. In particular, the eye benefits from miniaturization, as it is very sensitive to pressure and volumetric changes, which can affect eyesight and blood flow.
\r\n\r\nDiabetic retinopathy is the worldwide leading cause of blindness among working age adults. As the numbers of diabetics increases, so does the number of retinopathies. By 2030, 191 million people are expected to be affected by the disease. As a patient\u2019s retinopathy progresses, the chronic hyperglycemia from diabetes causes permanent changes to the vasculature; vessels become leaky and occluded, tissue becomes hypoxic due to this ischemia and begins to release vascular endothelial growth factor (VEGF) to promote angiogenesis.
\r\n\r\nCurrently, treatments exist only for severe non-proliferative or proliferative DR, and rely on blocking VEGF (vascular endothelial growth factor) or panretinal laser photocoagulation to reduce retinal metabolic demand. VEGF antagonists are expensive; costing up to $164k per quality life adjusted year and must be administered by intravitreal injections monthly. Laser photocoagulation also requires retreatment and is known to reduce peripheral vision\u2014up to 20% of the peripheral retina is ablated. Another treatment approach may be to supply oxygen. Oxygen is a strong vasoconstrictor and suppresses the hypoxic signaling that leads to release of VEGF. These two effects reduce the plasma volume leaked into tissue, which in turn reduces edema, and may help prevent ischemic related cell death. Literature supports this assertion. A study of nasally inspired oxygen in patients with macular edema showed a reduction of edema and improvement of visual acuity following 3 months of treatment. Another study on rabbits with an induced ischemia demonstrated that intravitreal oxygenation maintained the retina to a near healthy condition.
\r\n\r\nIn this thesis, two devices, the oxytransporter and oxygenerator, that treat diabetic retinopathy are designed and tested. The former shuttles oxygen from areas of high concentration to the ischemic retina. The latter generates oxygen by electrolysis.
\r\n\r\nThis thesis is grounded on a computational model of oxygen consumption in the retina. To estimate the oxygen consumption, the model accounts for the anatomical distribution of tissue and vasculature in the retina. Previous models in literature averaged over the effects in the inner retina. The model estimates that the devices must supply 0.25nmol/s of oxygen to the human macula with an oxygen tension dependent on the degree of ischemia.
\r\n\r\nA nanoporous filler material was developed and integrated into the oxytransporter to allow this device to operate in the high humidity environment of the eye. The material is capable of withstanding an environment with water vapor 1.4 times the bulk saturation pressure. Theory behind the material was tested and compared to simulation. Benchtop testing over a month demonstrated the stability of the device in conditions similar to the eye. This oxytransporter was implanted in rabbits and the diffusor, or output membrane, reached the favorable mark of 100mmHg in the vitreous humor from atmospheric oxygen alone. This is estimated to be sufficient to treat a mild to moderate ischemia in humans.
\r\n\r\nThe oxygenerator is powered from a coil up to 3cm away, and can provide 0.25nmol/s continuously with an oxygen tension of up to 300mmHg for a human sized diffusor. A steady state test demonstrated the capability of maintaining the oxygen tension in the device by modulating the input power. The device is replenished through osmosis from the vitreous humor, and can absorb moisture at a rate comparable to the required oxygen consumption. One week implantation in vivo in rabbits demonstrated that the oxygen tension exceeded 200mmHg at the diffusor, which is estimated to be sufficient to treat severe ischemia.\r\nFuture work should involve a study of the long term effects of oxygen in an ischemic animal model.
" }, { "name": "Shan, Kevin Qing", "degree": "PhD", "year": "2019", "title": "Sparse Deconvolution with Applications to Spike Sorting", "advisor": "Siapas, Athanassios G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292019-161916232", "creators": [ { "name": { "family": "Shan", "given": "Kevin Qing" }, "id": "Shan-Kevin-Qing", "orcid": "0000-0002-2621-1274", "display_name": "Shan, Kevin Qing" } ], "advisors": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "advisor", "display_name": "Siapas, Athanassios G." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "member", "display_name": "Siapas, Athanassios G." } ], "option_major": [ "cds" ], "doi": "10.7907/3JQS-BT21", "abstract": "Chronic extracellular recording is the use of implanted electrodes to measure the electrical activity of nearby neurons over a long period of time. It presents an unparalleled view of neural activity over a broad range of time scales, offering sub-millisecond resolution of single action potentials while also allowing for continuous recording over the course of many months. These recordings pick up a rich collection of neural phenomena -- spikes, ripples, and theta oscillations, to name a few -- that can elucidate the activity of individual neurons and local circuits.
\r\n\r\nHowever, this also presents an interesting challenge for data analysis. Chronic extracellular recordings contain overlapping signals from multiple sources, requiring these signals to be detected and classified before they can be properly analyzed. The combination of fine temporal resolution with long recording durations produces large datasets, requiring efficient algorithms that can operate at scale.
\r\n\r\nIn this thesis, I consider the problem of spike sorting: detecting spikes (the extracellular signatures of individual neurons' action potentials) and clustering them according to their putative source. First, I introduce a sparse deconvolution approach to spike detection, which seeks to detect spikes and represent them as the linear combination of basis waveforms.\tThis approach is able to separate overlapping spikes without the need for source templates, and produces an output that can be used with a variety of clustering algorithms.
\r\n\r\nSecond, I introduce a clustering algorithm based around a mixture of drifting t-distributions. This model captures two features of chronic extracellular recordings -- cluster drift over time and heavy-tailed residuals in the distribution of spikes -- that are missing from previous models. This enables us to reliably track individual neurons over longer periods of time. I will also show that this model produces more accurate estimates of classification error, which is an important component to proper interpretation of the spike sorting output.
\r\n\r\nFinally, I present a few theoretical results that may assist in the efficient implementation of sparse deconvolution.
" }, { "name": "Shapero, Aubrey Michael", "degree": "PhD", "year": "2019", "title": "Long Term Implantable Pressure Sensors", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302019-123348477", "creators": [ { "name": { "family": "Shapero", "given": "Aubrey Michael" }, "id": "Shapero-Aubrey-Michael", "orcid": "0000-0002-8036-3623", "display_name": "Shapero, Aubrey Michael" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Humayun", "given": "Mark" }, "id": "Humayun-M", "role": "member", "display_name": "Humayun, Mark" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SX5J-VM54", "abstract": "The benefits of implantable pressure sensors for continuous monitoring of diseases like glaucoma or hydrocephalus has been well established, but it has been difficult to achieve accurate pressure sensing in the body for more than one month. In this thesis, a general MEMS pressure sensor packaging method called parylene-oil-encapsulation is developed and analyzed in order to make commercial barometers for use in air suitable for implantation inside the body long term. Accelerated aging bench top data is presented and a wireless implantable intraocular pressure sensor has been built towards proving the viability of the packaging method in vivo.
" }, { "name": "Shi, Jian", "degree": "PhD", "year": "2019", "title": "Improving Site Response Analysis for Earthquake Ground Motion Modeling", "advisor": "Asimaki, Domniki", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302019-150220368", "creators": [ { "name": { "family": "Shi", "given": "Jian" }, "id": "Shi-Jian", "orcid": "0000-0002-1969-7579", "display_name": "Shi, Jian" } ], "advisors": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "advisor", "display_name": "Asimaki, Domniki" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Graves", "given": "Robert W." }, "id": "Graves-R-W", "role": "member", "display_name": "Graves, Robert W." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" } ], "option_major": [ "civileng" ], "doi": "10.7907/X5NZ-DQ21", "abstract": "The modeling of earthquake-induced ground motions plays an important role in the quantification of seismic hazards, which contributes to the ultimate goal of saving lives and reducing economic loss. Site response is a natural phenomenon in which soils in the earth\u2019s shallow crust alter the amplitude, frequency content, and duration of earthquake-induced ground motions. Therefore, improvements in the research of site response directly contribute to ground motion modeling, and eventually to seismic hazard quantification.
\r\n\r\nThis thesis presents two models that advance the current research in site response.
\r\n\r\nThe first model provides a tool to predict near-surface shear-wave velocity profiles from Vs30 (a proxy that represents the general stiffness of a site). This model bridges the gap between the lack of information about near-surface soil properties and the need to model site response on a regional scale (city, county, or above).
\r\n\r\nThe second model is a stress-strain model for describing 1D shearing behaviors of soils. It is capable of capturing both the small-strain and the large-strain behaviors, which makes it suitable for modeling very strong ground motions. More importantly, this model enables seismologists to construct stress-strain curves from only shear-wave velocity information, again improving our ability to model site response on a regional scale. Our validation study shows that this model outperforms the prevalent stress-strain model (namely, the MKZ model) by a considerable margin.
\r\n\r\nLastly, we demonstrate how the two models above can improve earthquake ground motion modeling: we develop an improved version of site factors for the Western United States. These site factors are provided as Fourier spectral ratios, and phase factors are provided for the first time, which enables the time delay of earthquake waves to be modeled. They can be used for incorporating site response in earthquake ground motion simulations, as well as for improving seismic hazard maps for the Western United States.
" }, { "name": "Soh, Yong Sheng", "degree": "PhD", "year": "2019", "title": "Fitting Convex Sets to Data: Algorithms and Applications", "advisor": "Chandrasekaran, Venkat", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282018-091842941", "creators": [ { "name": { "family": "Soh", "given": "Yong Sheng" }, "id": "Soh-Yong-Sheng", "orcid": "0000-0003-3367-1401", "display_name": "Soh, Yong Sheng" } ], "advisors": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "advisor", "display_name": "Chandrasekaran, Venkat" } ], "committee": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "chair", "display_name": "Tropp, Joel A." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/jkmq-b430", "abstract": "This thesis concerns the geometric problem of finding a convex set that best fits a given dataset. Our question serves as an abstraction for data-analytical tasks arising in a range of scientific and engineering applications. We focus on two specific instances:
\r\n\r\n1. A key challenge that arises in solving inverse problems is ill-posedness due to a lack of measurements. A prominent family of methods for addressing such issues is based on augmenting optimization-based approaches with a convex penalty function so as to induce a desired structure in the solution. These functions are typically chosen using prior knowledge about the data. In Chapter 2, we study the problem of learning convex penalty functions directly from data for settings in which we lack the domain expertise to choose a penalty function. Our solution relies on suitably transforming the problem of learning a penalty function into a fitting task.
\r\n\r\n2. In Chapter 3, we study the problem of fitting tractably-described convex sets given the optimal value of linear functionals evaluated in different directions.
\r\n\r\nOur computational procedures for fitting convex sets are based on a broader framework in which we search among families of sets that are parameterized as linear projections of a fixed structured convex set. The utility of such a framework is that our procedures reduce to the computation of simple primitives at each iteration, and these primitives can be further performed in parallel. In addition, by choosing structured sets that are non-polyhedral, our framework provides a principled way to search over expressive collections of non-polyhedral descriptions; in particular, convex sets that can be described via semidefinite programming provide a rich source of non-polyhedral sets, and such sets feature prominently in this thesis.
\r\n \r\nWe provide performance guarantees for our procedures. Our analyses rely on understanding geometrical aspects of determinantal varieties, building on ideas from empirical processes as well as random matrix theory. We demonstrate the utility of our framework with numerical experiments on synthetic data as well as applications in image denoising and computational geometry.
\r\n\r\nAs secondary contributions, we consider the following:
\r\n\r\n1. In Chapter 4, we consider the problem of optimally approximating a convex set as a spectrahedron of a given size. Spectrahedra are sets that can be expressed as feasible regions of a semidefinite program.
\r\n\r\n2. In Chapter 5, we consider change-point estimation in a sequence of high-dimensional signals given noisy observations. Our method integrates classical approaches with a convex optimization-based step that is useful for exploiting structure in high-dimensional data.
" }, { "name": "Sridhar, Akshay", "degree": "PhD", "year": "2019", "title": "Large-Eddy Simulation of Turbulent Boundary Layers with Spatially Varying Roughness", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:09082018-212920204", "creators": [ { "name": { "family": "Sridhar", "given": "Akshay" }, "id": "Sridhar-Akshay", "orcid": "0000-0002-2642-8246", "display_name": "Sridhar, Akshay" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Callies", "given": "Joern" }, "id": "Callies-J", "orcid": "0000-0002-6815-1230", "role": "member", "display_name": "Callies, Joern" } ], "option_major": [ "space" ], "doi": "10.7907/8YWS-B862", "abstract": "This dissertation addresses high Reynolds number turbulent boundary layers flows with different inhomogeneous surface roughness distributions using large eddy simulations. The stretched vortex subgrid scale model for the outer flow LES is coupled with a virtual-wall model for the friction velocity with a correction accounting for local roughness effects.
\r\n\r\nA semi-empirical model that describes a fully developed rough-walled turbulent boundary layer with sand-grain roughness length-scale ks = \u03b1x that varies linearly with streamwise distance is first developed, with \u03b1 a dimensionless constant. For large Rex and a free-stream velocity U\u221e ~ xm, a simple log-wake model of the local turbulent mean-velocity profile is used that contains a standard mean-velocity correction for the asymptotic, fully rough regime. A two parameter (\u03b1; m) family of solutions is obtained for which U\u221e+ (or equivalently Cf) and boundary-layer measures can be calculated. These correspond to perfectly self-similar boundary-layer growth in the streamwise direction with similarity variable z/ks where z is the wall-normal co-ordinate. Results over a range of \u03b1 are discussed for cases including the zero-pressure gradient (m = 0) and sink-flow (m = -1) boundary layers. Model trends are supported by high Re wall-modeled LES. Linear streamwise growth of boundary layer measures is confirmed, while for each \u03b1, mean-velocity profiles and streamwise turbulent stresses are shown to collapse against z/(\u03b1x). Inner scaled velocity defects are shown to collapse against z/\u0394, where \u0394 is the Rotta-Clauser parameter. The present results suggest that these flows may be interpreted as the fully-rough limit for boundary layers in the presence of small-scale, linear roughness.
\r\n\r\nNext, an LES study of a flat-plate turbulent boundary layer at high Re under nonequilibrium flow conditions due to the presence of abrupt changes in surface roughness is presented. Two specific cases, smooth-rough (SR) and rough-smooth (RS) transition are examined in detail. Streamwise developing velocity and turbulent stress profiles are considered and sharp departures from equilibrium flow properties with subsequent relaxation are shown downstream. Relaxation trends are studied using integral parameters and higher-order mean flow statistics with emphasis on Re\u03c4 and ks+ dependence. Results are compared with RS experiments at matched Re\u03c4, and show good agreement in terms of recovery rates.
\r\n\r\nFinally, the case of static, impulsive wall-roughness in flows at high Re is addressed using the same LES framework. The initial perturbation from smooth-to-rough appears to dominate the flow behaviour with the length of the impulsive patch showing little effect on recovery rates at matched Re\u03c4 and ks+. The resulting trends show good agreement with low Re experiments and support the wall-modeled LES framework as a suitable method for analysing high Re flows in practical applications.
" }, { "name": "Tan, Wei Lin", "degree": "PhD", "year": "2019", "title": "Polycrystalline Perovskite Ferroelectrics: Microstructural Origins of the Macroscale Electromechanical Response", "advisor": "Kochmann, Dennis M.; Faber, Katherine T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082019-133053987", "creators": [ { "name": { "family": "Tan", "given": "Wei Lin" }, "id": "Tan-Wei-Lin", "orcid": "0000-0001-6855-8340", "display_name": "Tan, Wei Lin" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "co-advisor", "display_name": "Faber, Katherine T." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" } ], "option_major": [ "matsci" ], "doi": "10.7907/J2W5-XA95", "abstract": "Ferroelectrics are a class of electromechanically coupled materials which possess an electric dipole polarization that can be permanently reoriented by applied electric and mechanical stress fields. Their reorientable polarization results in complex, nano- to micrometer scale domain structures whose evolution under electric and mechanical stress fields alters the material's overall time-dependent electrical and viscoelastic properties. To understand domain structure evolution, in-situ microscopy of domain switching processes in ferroelectric thin films, single crystals and nanoparticles have been well-studied in the past. However, domain evolution in bulk polycrystals is less well understood as their local stress and electric field environment differs from thin specimens.
\r\n\t\r\nThis work seeks to understand ferroelectric domain evolution in bulk ferroelectric perovskite polycrystals using a combination of a recently-developed electromechanical characterization technique, Broadband Electromechanical Spectroscopy (BES), and theoretical-computational predictions. A constitutive material model for polycrystalline ferroelectrics is first developed and applied to simulate barium titanate single crystals and polycrystals. Simulated polarization, strain and energy dissipation hysteresis curves show good qualitative agreement to experimental data and demonstrate that macroscale properties can be efficiently predicted from microscale physics to some extent.
\r\n\t\r\nThe microstructural origins of fatigue behavior in bulk polycrystalline lead zirconate titanate (PZT) are investigated using a combination of macroscale electrical and viscoelastic property characterization via BES, and scanning electron microscopy (SEM) imaging of microstructure. The evolution of electrical and viscoelastic properties during bipolar electrical fatigue show differences in the effects of electrical vs. mechanical fatigue processes, and the latter is verified through SEM imaging and measurement of microcracks.
\r\n\t\r\nFinally, the same electromechanical BES characterizations are performed on specimens of bulk polycrystalline barium titanate (BT). Results reveal stark qualitative differences in electrical and viscoelastic responses from PZT despite both materials being perovskite ferroelectrics. A growth vs. nucleation hypothesis is proposed to explain the observed results, guided by preliminary imaging of domain microstructure.
\r\n\t\r\nIn summary, the BES is a powerful tool to elucidate domain switching processes within bulk ferroelectric specimens, while a computational method which bridges the micro- and macroscale further adds to the diagnostic toolbox of understanding bulk ferroelectric domain switching mechanisms. This opens the pathway to designing future applications which make use of the unique electrical and viscoelastic properties of ferroelectric switching.
" }, { "name": "Tang, Yujie", "degree": "PhD", "year": "2019", "title": "Time-Varying Optimization and Its Application to Power System Operation", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01222019-221628111", "creators": [ { "name": { "family": "Tang", "given": "Yujie" }, "id": "Tang-Yujie", "orcid": "0000-0002-4921-8372", "display_name": "Tang, Yujie" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6N9W-3J20", "abstract": "The main topic of this thesis is time-varying optimization, which studies algorithms that can track optimal trajectories of optimization problems that evolve with time. A typical time-varying optimization algorithm is implemented in a running fashion in the sense that the underlying optimization problem is updated during the iterations of the algorithm, and is especially suitable for optimizing large-scale fast varying systems. Motivated by applications in power system operation, we propose and analyze first-order and second-order running algorithms for time-varying nonconvex optimization problems.\r\n\r\nThe first-order algorithm we propose is the regularized proximal primal-dual gradient algorithm, and we develop a comprehensive theory on its tracking performance. Specifically, we provide analytical results in terms of tracking a KKT point, and derive bounds for the tracking error defined as the distance between the algorithmic iterates and a KKT trajectory. We then provide sufficient conditions under which there exists a set of algorithmic parameters that guarantee that the tracking error bound holds. Qualitatively, the sufficient conditions for the existence of feasible parameters suggest that the problem should be \"sufficiently convex\" around a KKT trajectory to overcome the nonlinearity of the nonconvex constraints. The study of feasible algorithmic parameters motivates us to analyze the continuous-time limit of the discrete-time algorithm, which we formulate as a system of differential inclusions; results on its tracking performance as well as feasible and optimal algorithmic parameters are also derived. Finally, we derive conditions under which the KKT points for a given time instant will always be isolated so that bifurcations or merging of KKT trajectories do not happen.\r\n\r\nThe second-order algorithms we develop are approximate Newton methods that incorporate second-order information. We first propose the approximate Newton method for a special case where there are no explicit inequality or equality constraints. It is shown that good estimation of second-order information is important for achieving satisfactory tracking performance. We also propose a specific version of the approximate Newton method based on L-BFGS-B that handles box constraints. Then, we propose two variants of the approximate Newton method that handle explicit inequality and equality constraints. The first variant employs penalty functions to obtain a modified version of the original problem, so that the approximate Newton method for the special case can be applied. The second variant can be viewed as an extension of the sequential quadratic program in the time-varying setting.\r\n\r\nFinally, we discuss application of the proposed algorithms to power system operation. We formulate the time-varying optimal power flow problem, and introduce partition of the decision variables that enables us to model the power system by an implicit power flow map. The implicit power flow map allows us to incorporate real-time feedback measurements naturally in the algorithm. The use of real-time feedback measurement is a central idea in real-time optimal power flow algorithms, as it helps reduce the computation burden and potentially improve robustness against model mismatch. We then present in detail two real-time optimal power flow algorithms, one based on the regularized proximal primal-dual gradient algorithm, and the other based on the approximate Newton method with the penalty approach." }, { "name": "Tertuliano, Ottman Aeman", "degree": "PhD", "year": "2019", "title": "Small-Scale Deformation and Fracture of Hard Biomaterials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162018-124906600", "creators": [ { "name": { "family": "Tertuliano", "given": "Ottman Aeman" }, "id": "Tertuliano-Ottman-Aeman", "orcid": "0000-0003-0524-3944", "display_name": "Tertuliano, Ottman Aeman" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/CAPE-5661", "abstract": "Structural materials engineering often aims to realize materials that are simultaneously strong, tough, and lightweight \u2014 a combination classically considered mutually exclusive. Natural composite materials such as bone exhibit a combination of these properties far exceeding that of their constituents, a feat generally credited to their hierarchical structure \u2014 all the way down the nanoscale. To date, a quantitative description of how this property combination arises in such microstructurally complex materials has remained elusive due to challenges in experimentally isolating and probing the salient deformation and toughening mechanisms at the micro and nanometer scales \u2014 length scales on the order the constituents of many natural composites.
\r\n\r\nIn this thesis, we first investigate the site-specific nanoscale structure of human bone using transmission electron microscopy. We show the presence of previously undiscovered disordered arrangement of collagen and mineral \u2014 alongside a well known ordered structure \u2014 within the trabecular architecture of bone. We perform micro- and nano-mechanical compression experiments to probe strength and deformation of each of these microstructures, revealing a size-dependent strength of bone attributed to the limited number of failure-initiating critical defects (e.g pores) in the small-scale samples relative to macro-scale tissue.
\r\n\r\nUnlike experiments for investigating strength at small-scales, fracture experiments are standardized for the macroscale. To address this, we developed an in situ SEM/nanoindenter methodology that enables 3-point bending fracture experiments with observation and measurement of crack growth and toughening behavior at nano and micrometer scales. Using this technique, we discuss the crack initiation and growth toughness arising primarily from the underlying fibril microstructure in bone. In the context of a crack growth resistance, we describe a transition in the toughening behavior of bone originating from different levels of hierarchy. Given its versatility, this experimental technique establishes a platform for understanding the coupling between structure and fracture behavior of micron-sized materials.
" }, { "name": "Thomas, Nathan Hoover", "degree": "PhD", "year": "2019", "title": "Passive and Active Control of Radiative Heat Flow", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02102019-152730366", "creators": [ { "name": { "family": "Thomas", "given": "Nathan Hoover" }, "id": "Thomas-Nathan-Hoover", "orcid": "0000-0003-4648-5325", "display_name": "Thomas, Nathan Hoover" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/FGWC-0244", "abstract": "Materials that control the absorption and emission of thermal radiation have attracted renewed interest for energy applications. Materials of interest include those with static optical properties that vary with photon wavelength in a desired manner as well as those with dynamic properties that can be actively tuned by external stimuli. The research in this thesis focuses on creating materials in both categories.
\r\n\r\nFirst, we examine selective absorbers for solar thermal energy conversion with high absorptivity in solar wavelengths and low emissivity in infrared wavelengths. Achieving stagnation temperatures exceeding 200 \u00b0C with unconcentrated sunlight, pertinent to technologies like industrial process heat, air conditioning, and electricity generation, requires better spectrally selective absorbers with ultra-low thermal emittance. Current state-of-art surfaces are based on ceramic-metal mixtures and patterned metal or metal-dielectric structures. Semiconductor based selective surfaces with near zero absorption below the bandgap offer the potential for lower thermal emittance than that achieved with such surfaces that employ metals in the primary absorbing medium. In this thesis, we report a semiconductor-based multilayer selective absorber that exploits the sharp drop in optical absorption at the band gap energy to achieve a measured absorptance of 76% at solar wavelengths and a low emittance of approximately 5% at thermal wavelengths. In field tests, we obtain a peak temperature of 225 \u00b0C, comparable to that achieved with state-of-the-art selective surfaces. With straightforward optimization to improve solar absorption, our work shows the potential for unconcentrated solar thermal systems to reach stag- nation temperatures exceeding 300 \u00b0C, higher than any available selective surface. Our surface would eliminate the need for solar concentrators for mid-temperature solar applications such as supplying process heat.
\r\n\r\nSecond, we theoretically propose and experimentally implement a thermal switch for near-field radiative transfer. In the field of active thermal materials for manipulating heat flow in a controllable and reversible manner, numerous approaches to perform thermal switching have been reported. However, they typically suffer from various limitations, including small switching ratio or requiring large temperature differentials. We report the experimental implementation of a scheme to electrostatically control near-field radiative transfer in a graphene field effect heterostructure. We measure a maximum heat flux modulation of 4 \u00b1 3% and an absolute heat flux modulation rate of 24 \u00b1 7 mWm\u22122 per V bias. Employing gate dielectrics with lower surface warp and higher dielectric breakdown strength as well as reducing conductive losses would enable modulations up to 100%, substantially exceeding the switching ratios achievable by other methods. Our work paves the way for electrostatic control of near-field radiative transfer using two-dimensional materials.
" }, { "name": "Thompson, Jonathan Ross", "degree": "PhD", "year": "2019", "title": "Unconventional Approaches to Structured Semiconductors", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:07272018-145200158", "creators": [ { "name": { "family": "Thompson", "given": "Jonathan Ross" }, "id": "Thompson-Jonathan-Ross", "display_name": "Thompson, Jonathan Ross" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "matsci" ], "doi": "10.7907/YW6M-H367", "abstract": "The function of semiconductor devices is intrinsically tied to their structure. While there are already myriad techniques in use today to fabricate an extreme diversity of devices, new processes are regularly developed to make the production of previously unrealizable structures, and consequently devices, possible.
\r\n\r\nThis dissertation deals with several unconventional approaches to generating ordered semiconductor structures. One chapter discusses a novel technique to measure the various forces that impede the alignment of randomly dispersed microstructures. The technique made it possible to both determine the magnitude of the interactions that the particles must overcome in order to be organized into a useful structure and assess the functional form of the forces that the microstructure is experiencing, thereby giving insight into the physical origin of said forces.
\r\n\r\nThe following chapter deal with the spontaneous structure formation seen in photoelectrodeposited semiconductor films. One chapter investigates how the natural tendency of these films to form oriented, high aspect ratio structures can be coupled to the geometry of the substrate on which they are grown. This work demonstrates that extremely straight, high aspect ratio structures can be grown over macroscopic areas by making simple modifications of the substrate.
\r\n\r\nThe final chapter characterizes the iridescence that these films exhibit. A simple physical explanation for the origin of the coloration is posited and verified. Then the information gleaned about the optical response of these films is used to generate vibrant, colorful patterns on electrode using consumer electronics.
" }, { "name": "Tosi, Lu\u00eds Phillipe Costa Ferreira", "degree": "PhD", "year": "2019", "title": "Fluid-Structure Instability in an Internal Flow Energy Harvester", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:09122018-201219035", "creators": [ { "name": { "family": "Tosi", "given": "Lu\u00eds Phillipe Costa Ferreira" }, "id": "Tosi-Lu\u00eds-Phillipe-Costa-Ferreira", "orcid": "0000-0002-0819-4765", "display_name": "Tosi, Lu\u00eds Phillipe Costa Ferreira" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Hall", "given": "Jeffery" }, "id": "Hall-J-L", "orcid": "0000-0002-8835-2830", "role": "member", "display_name": "Hall, Jeffery" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Y0KG-Y197", "abstract": "Access to reliable power sources in remote locations is a recurring engineering challenge for both large and small applications. The developing world struggles with power connectivity in remote villages, while sensor networks strain with power limitations of batteries or short-lived turbines. Energy harvesting based on fluid-induced vibration provides a potential robust alternative for in-situ power generation, furnishing means for a decades long supply of power. Yet, one of the main challenges in the design of flow energy harvesters is understanding the mechanisms that drive their motion. Fluid-structure interaction problems often span a large parametric space and require considerable computational resources to resolve the necessary dynamic details for reliable designs.
\r\n\r\nThis thesis aims to address this challenge for a piezoelectric internal flow energy harvester developed in conjunction with NASA Jet Propulsion Laboratory for in-well, deepwater sensor and actuator systems. Through exploratory experimentation, a configuration consisting of a piezoelectric beam within a converging-diverging channel in axial flow generated considerable power at moderate flow velocities when compared to other devices of the same size. The current device, though adapted to a more robust configuration based on flextensional actuators, still maintains the same fluid-structure interaction: the instability that ensues forces the system into self-sustained oscillations that produces consistent power output for flow rates above a critical threshold.
\r\n\r\nTo understand and quantify this behavior, we develop an analytical framework based on a leakage-flow type instability, which curtails the shortcomings of expensive numerical simulations once verified. The formulation consists of a quasi one-dimensional simplification of coupled fluid-structure equations, which are linearized for classical stability analysis. The stability boundary and critical property predictions are verified through a set of fully coupled fluid-structure immersed boundary direct numerical simulations. Experiments are carried out in tandem to quantify the dynamics of the harvester, specifically targeting the critical flow rate threshold. The analytical framework is expanded to include flow in the spanwise direction of the beam, and results to a simplified geometry of the harvester compared with those from experiments. Agreement between predicted critical values suggest that leakage-flow may be the principal mechanism for fluid-induced vibration within our device. The model can serve as the foundation of initial exploration of design parameters, and perhaps more powerful devices in future endeavors.
" }, { "name": "Tutcuoglu, Abbas Davud", "degree": "PhD", "year": "2019", "title": "Stochastic Multiscale Modeling of Dynamic Recrystallization", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242019-144233476", "creators": [ { "name": { "family": "Tutcuoglu", "given": "Abbas Davud" }, "id": "Tutcuoglu-Abbas-Davud", "orcid": "0000-0003-2360-706X", "display_name": "Tutcuoglu, Abbas Davud" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "space" ], "doi": "10.7907/1VVP-T060", "abstract": "Materials by design is a core driver in enhancing sustainability and improving efficiency in a broad spectrum of industries. To this end, thermo-mechanical processes and many of the underlying phenomena were studied extensively in the context of specific cases. The goal of this thesis is threefold: First, we aim to establish a novel numerical model on the micro- and mesoscale that captures dynamic recrystallization in a generalized framework. Based on the inheritance of the idea of state switches, we term this scheme Field-Monte-Carlo Potts method. We employ a finite deformation framework in conjunction with a continuum-scale crystal plasticity formulation and extend the idea of state switches to cover both grain migration and nucleation. We introduce physically-motivated state-switch rules, based on which we achieve a natural marriage between the deterministic nature of crystal plasticity and the stochastic nature of dynamic recrystallization. Using a novel approach to undertake the states-switches in a transient manner, the new scheme benefits from enhanced stability and can, therefore, handle arbitrary levels of anisotropy. We demonstrate this functionality at the example of pure Mg at room temperature, which experiences strong anisotropy through the different hardening behavior on the \u2329c+a\u232a-pyramidal and prismatic slip systems as opposed to the basal slip systems as well as through the presence of twinning as an alternative strain accommodating mechanisms. Building on this generalized approach, we demonstrate spatial convergence of the scheme along with the ability to capture the transformation from single- to multi-peak stress-strain behavior.
\r\n\r\nSecond, motivated by the lack of transparency concerning the benefits of high-fidelity approaches in the modeling of dynamic recrystallization, we present two derivative models of the Field-Monte-Carlo Potts method, both of which afford reduced computational expense. One model preserves the spatial interpretation of grains, but imposes a Taylor assumption regarding the distribution of strain; the other reduces the spatial notion of a grain to a volume fraction in the idea of a Taylor model. In order to concentrate on the differences in accuracy between the various approaches, we fit all three schemes to experimental data for pure copper, which allows us to employ a well-understood crystal plasticity-based constitutive model and to simultaneously provide sufficient data for the analysis of the texture, stress and grain-size evolution. Owing to the large strains attained in these simulations, using the FFT-based scheme, we achieve capturing a precursor of continuous dynamic recrystallization. For low temperatures, the Taylor model fails to replicate the nucleation-dominated recrystallization process, whereas, at high temperatures, it shows compelling agreement with experiments and the two higher-fidelity models both in terms of the homogenized stress-evolution and the microstructural evolution.
\r\n\r\nFinally, we present a novel multiscale analysis of thermo-mechanical processes through coupling of the computationally efficient Taylor model for modeling dynamic recrystallization on the mesoscale to a max-ent based meshfree approach on the macroscale in the idea of vertical homogenization. We analyze the severe plastic deformation-based process of equal channel angular extrusion, which is intriguing from a numerical perspective due to the heavily localized zone of extensive shear deformation. By employing novel tools on the microscale regarding the stable update of internal variables as well as a careful interpretation of macroscale boundary conditions, we present the first multiscale analysis of a severe plastic deformation process informing simultaneously about the evolution of stress, texture and grain refinement. We attain convincing qualitative agreements for the evolution of the plunger force and texture. As an outlook on future investigations, we analyze multiple passes of the same billet in the form of route C with emphasis on the texture evolution after the second pass.
" }, { "name": "Van Horn, Grant Richard", "degree": "PhD", "year": "2019", "title": "Towards a Visipedia: Combining Computer Vision and Communities of Experts", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082019-103122440", "creators": [ { "name": { "family": "Van Horn", "given": "Grant Richard" }, "id": "Van-Horn-Grant-Richard", "orcid": "0000-0003-2953-9651", "display_name": "Van Horn, Grant Richard" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Belongie", "given": "Serge J." }, "id": "Belongie-S-J", "role": "member", "display_name": "Belongie, Serge J." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "compsci" ], "doi": "10.7907/20DQ-Y220", "abstract": "Motivated by the idea of a Visipedia, where users can search and explore by image, this thesis presents tools and techniques for empowering expert communities through computer vision. The collective aim of this work is to provide a scalable foundation upon which an application like Visipedia can be built. We conduct experiments using two highly motivated communities, the birding community and the naturalist community, and report results and lessons on how to build the necessary components of a Visipedia. First, we conduct experiments analyzing the behavior of state-of-the-art computer vision classifiers on long tailed datasets. We find poor feature sharing between classes, potentially limiting the applicability of these models and emphasizing the ability to intelligently direct data collection resources. Second, we devise online crowdsourcing algorithms to make dataset collection for binary labels, multiclass labels, keypoints, and mulit-instance bounding boxes faster, cheaper, and more accurate. These methods jointly estimate labels, worker skills, and train computer vision models for these tasks. Experiments show that we can achieve significant cost savings compared to traditional data collection techniques, and that we can produce a more accurate dataset compared to traditional data collection techniques. Third, we present two fine-grained datasets, detail how they were constructed, and analyze the test accuracy of state-of-the-art methods. These datasets are then used to create applications that help users identify species in their photographs: Merlin, an app assisting users in identifying birds species, and iNaturalist, an app that assists users in identifying a broad variety of species. Finally, we present work aimed at reducing the computational burden of large scale classification with the goal of creating an application that allows users to classify tens of thousands of species in real time on their mobile device. As a whole, the lessons learned and the techniques presented in this thesis bring us closer to the realization of a Visipedia.
" }, { "name": "Veilleux, Jean-Christophe", "degree": "PhD", "year": "2019", "title": "Pressure and Stress Transients in Autoinjector Devices", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02172019-174051312", "creators": [ { "name": { "family": "Veilleux", "given": "Jean-Christophe" }, "id": "Veilleux-Jean-Christophe", "orcid": "0000-0002-5420-9411", "display_name": "Veilleux, Jean-Christophe" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VJSH-TF65", "abstract": "The viscosity of drug solutions delivered parenterally has been increasing over the years. Injecting viscous drug solutions using spring-actuated autoinjector devices is challenging due to a number of technical and human factor constraints. Some of the related challenges are investigated in this thesis.
\r\n\r\nActuation of autoinjector devices powered using stiff springs can create deleterious pressure and stress transients which are not needed to achieve the normal functions of the device. Experimental measurements have shown that peak pressures and stresses substantially larger than what is needed to achieve the normal device function can occur during the actuation phase, creating unnecessary potential for device failure.
\r\n\r\nThe acceleration of the syringe during actuation can be very large, often creating transient cavitation in the cone region. The occurrence or absence of cavitation is determined by the relative timing of syringe pressurization and syringe acceleration, which is affected by several factors such as the presence, location, and size of an air gap inside the syringe, and the friction between the plunger-stopper and the syringe.
\r\n\r\nExperiments and numerical simulations have shown that sharp pressure waves traveling inside the syringe can be amplified within the cone terminating the syringe. Despite the potential for shock focusing, the impulsive pressurization and the rapid deceleration of pre-filled syringes create a potential for failure which is localized in the syringe shoulder and at the junction between the flange and the barrel, not inside the cone. The cavitation events, on the other hand, create a potential for failure which is limited to a region in close proximity of the bubble upon collapse. The collapse of cavitation bubbles located within the syringe cone can be enhanced due to geometrical effects, and the resulting stresses can be large enough to cause syringe failure.
\r\n\r\nThis thesis demonstrates that static and quasi-static analyses do not provide accurate estimates of the peak pressures and stresses occurring within the device. The pressure and stresses created by the highly dynamic events occurring during actuation need to be accounted for during device design in order to improve device reliability, the user's experience, and patient's adherence to prescribed treatments. The findings discussed in this work provide insights and guidance as to how the transient events can be mitigated.
" }, { "name": "Vidyasagar, A.", "degree": "PhD", "year": "2019", "title": "Predicting Microstructural Pattern Formation Using Stabilized Spectral Homogenization", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03272019-170619076", "creators": [ { "name": { "family": "Vidyasagar", "given": "A." }, "id": "Vidyasagar-A", "orcid": "0000-0003-0262-5429", "display_name": "Vidyasagar, A." } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F1VN-1X80", "abstract": "Instability-induced patterns are ubiquitous in nature, from phase transformations and ferroelectric switching to spinodal decomposition and cellular organization. While the mathematical basis for pattern formation has been well-established, autonomous numerical prediction of complex pattern formation has remained an open challenge. This work aims to simulate realistic pattern evolution in material systems exhibiting non-(quasi)convex energy landscapes. These simulations are performed using fast Fourier spectral techniques, developed for high-resolution numerical homogenization. In a departure from previous efforts, compositions of standard FFT-based spectral techniques with finite-difference schemes are used to overcome ringing artifacts while adding grid-dependent implicit regularization.
\r\n\r\nThe resulting spectral homogenization strategies are first validated using benchmark energy minimization examples involving non-convex energy landscapes. The first investigation involves the St. Venant-Kirchhoff model, and is followed by a novel phase transformation model and finally a finite-strain single-slip crystal plasticity model. In all these examples, numerical approximations of energy envelopes, computed through homogenization, are compared to laminate constructions and, where available, analytical quasiconvex hulls.
\r\n\r\nSubsequently, as an extension of single-slip plasticity, a finite-strain viscoplastic formulation for hexagonal-closed-packed magnesium is presented. Microscale intragranular inelastic behavior is captured through high-fidelity simulations, providing insight into the micromechanical deformation and failure mechanisms in magnesium. Studies of numerical homogenization in polycrystals, with varying numbers of grains and textures, are also performed to quantify convergence statistics for the macroscopic viscoplastic response.
\r\n\r\nIn order to simulate the kinetics of pattern evolution, stabilized spectral techniques are utilized to solve phase-field equations. As an example of conservative gradient-flow kinetics, phase separation by anisotropic spinodal decomposition is shown to result in cellular structures with tunable elastic properties and promise for metamaterial design. Finally, as an example of nonconservative kinetics, the study of domain wall motion in polycrystalline ferroelectric ceramics predicts electromechanical hysteresis behavior under large bias fields. A first-principles approach using DFT-informed model constants is outlined for lead zirconate titanate, producing results showing convincing qualitative agreement with in-house experiments. Overall, these examples demonstrate the promise of the stabilized spectral scheme in predicting pattern evolution as well as effective homogenized response in systems with non-quasiconvex energy landscapes.
" }, { "name": "Wang, Cong", "degree": "PhD", "year": "2019", "title": "On the Manipulation of a Turbulent Boundary Layer by Unsteady Boundary Conditions", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-114300433", "creators": [ { "name": { "family": "Wang", "given": "Cong" }, "id": "Wang-Cong", "orcid": "0000-0002-8271-5637", "display_name": "Wang, Cong" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Brown", "given": "Garry L." }, "id": "Brown-Garry-L", "role": "member", "display_name": "Brown, Garry L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FT8M-PM75", "abstract": "Reducing the frictional drag generated by a turbulent boundary layer (TBL) is critical for many engineering applications. Motivated by existing turbulent drag reduction methods, this study explores the possibility of sustaining wall-attached air-films and manipulating the near-wall turbulence in hydrodynamic TBL. An innovative air-retaining system is designed to sustain and dynamically modulate the wall-attached air-films in TBL. In still water, the oscillating air-films induce vortical motions in the near-region of air-films. In TBL, phenomena such as Stokes-type oscillatory motion, zero- shear-stress layer, 'inactive' turbulence and reduced viscous shear stress are observed in the vicinity region of air-films. The analysis shows that TBL momentum transfer toward the wall is suppressed and a turbulence re-laminarization mechanism is induced in the near-wall region. One potential physical mechanism points to the process of vorticity generation in the near-region of oscillating air-films, which 'pushes' the TBL near-wall vortical structures away from the wall. With this viewpoint, the phenomena mentioned above can be explained. The modified momentum transfer mechanism and turbulence re-laminarization process are shown to be the potential cause of suppressed viscous shear stress in the near-wall region. Estimated using the Clauser chart method, the turbulent wall-skin friction shows a noticeable decrease in the presence of air-films.
" }, { "name": "Weadock, Nicholas Joseph", "degree": "PhD", "year": "2019", "title": "Addressing Thermodynamic Inefficiencies of Hydrogen Storage in Transition Metal Hydrides", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02112019-143327096", "creators": [ { "name": { "family": "Weadock", "given": "Nicholas Joseph" }, "id": "Weadock-Nicholas-Joseph", "orcid": "0000-0002-1178-7641", "display_name": "Weadock, Nicholas Joseph" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/ANY4-VA70", "abstract": "Transition metal hydrides (MH) are an attractive class of materials for several energy technologies. Primary benefits include their large volumetric storage capacity (often exceeding that of liquid hydrogen) and capability to absorb and desorb hydrogen for hundreds of cycles. In this thesis, we set out to understand two of the thermodynamic inefficiencies of MH: the pressure hysteresis associated with hydrogen absorption and desorption and the corrosion and dissolution of high capacity MH alloys in high pH electrolyte environments.
\r\n\r\nThe volume change associated with hydriding transitions can exceed 10%, and a macroscopic nucleation barrier resulting from coherency strains has been proposed as the origin of the pressure hysteresis. We investigated this hypothesis for the palladium-hydrogen system. The hysteresis and phase transformation characteristics of bulk and nanocrystalline PdH were characterized with coupled in situ X-ray diffraction and pressure composition isotherm measurements. Size effects are observed in the total hydrogen uptake and hydrogen solubility in the hydride phases. Experimentally determined hysteresis energies were found to be comparable to the misfit strain between the Pd and PdH phases and much larger than the energy for dislocation formation. Theoretical predictions of pressure hysteresis overestimate the experimentally measured hysteresis, and we suggest methods of accommodation which could explain the discrepancy. Finally, we propose that an effect of the nucleation barrier is to split the coherent spinodal phase diagram and introduce directionally dependent phase boundaries.
\r\n\r\nWe report a successful development of Ti29V62-xNi9Crx (x = 0, 6, 12) body-centered cubic (BCC) MH electrodes for MH batteries by addressing vanadium corrosion and dissolution in potassium hydroxide electrolytes. The effectiveness of a limited oxygen environment and vanadate ion addition against corrosion are compared to the effects of Cr substitution. By identifying oxygen as the primary source of corrosion and eliminating oxygen with an Ar-purged cell, the Cr-free alloy electrode achieved a maximum capacity of 594 mAh/g, double the capacity of commercial AB5 MH electrodes. With modified coin cells suppressing oxygen evolution, the cycle stability of the Ti29V62Ni9 alloy electrode was greatly improved with either vanadate ion additions to the electrolyte or Cr-substitution in the alloy. Both approaches lead to reversible capacity of 500 mAh/g for 200 cycles.
" }, { "name": "Wei, Yuchen", "degree": "PhD", "year": "2019", "title": "Deployable Piezoelectric Thin Shell Structures: Concepts, Characterization and Vibration Control", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-114129662", "creators": [ { "name": { "family": "Wei", "given": "Yuchen" }, "id": "Wei-Yuchen", "orcid": "0000-0002-7669-020X", "display_name": "Wei, Yuchen" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/4DRX-2X87", "abstract": "The thesis presents three interconnected technology paths to the design and realization of novel deployable active thin shell structures. The baseline concept envisioned is built upon a deployable ultra-thin piezoelectric active thin shell architecture, with segmented tessellations. This vision is motivated by the need to deploy and control large, curved and precise surfaces for a variety of applications including future space telescopes, and is made possible by recent progress in ultra-thin high-performance composites and active material technologies. The thesis uses a combination of heuristic design, theoretical analysis, numerical modeling and novel experimental techniques to construct and validate proposed concepts for deployable piezoelectric thin shells.
\r\n\r\nSpecifically, the thesis answers the following questions: i) How to design and manufacture precise, foldable and curved piezoelectric shells. ii) How to deploy these shells reliably and maintain shape correctability in the deployed state. iii) How to synthesize large, curved deployable surfaces with the aforementioned advantages. iv) How to characterize and predict the nonlinear behavior of piezoelectric materials and thin structures under high electric field actuation and large bending deformations. v) How to improve the shape stability of piezoelectric active thin shells under dynamic disturbances without introducing external sensors.
\r\n\r\nFirst, the thesis proposes new methodologies and design criteria to synthesize deployable, modular edge-supported thin shells based on a combination of origami-inspired folding patterns and spatial mechanisms. In contrast to traditional deployable surface designs, which attach rigid shells to deployable trusses, the proposed methodology enables concurrent folding of flat or curved shells along with the support structures. Starting from a basic module, a variety of deployable surface concepts are proposed through tessellations of the module.
\r\n\r\nA piezoelectric material unimorph architecture is further introduced, providing global curvature and shape correction capabilities. All components of the basic concept are validated through model prototyping and material folding tests, and it is discovered that both the ultra thin carbon fiber composites and piezoelectric ceramic materials can achieve a small folding radius without failure. A composite, doubly-curved foldable shell is also designed and manufactured while still maintaining low shape error. These efforts have led to a new family of deployable piezoelectric thin shell structures that integrate low areal density, high shape accuracy, and structural foldability to an unprecedented degree.
\r\n\r\nThe thesis then tackles the challenge of estimating the actuation response and residual structural deformation of unimorph active thin shells under high electric field and large bending motion. A rate-independent, full field phenomenological constitutive model for a polycrystalline piezoelectric material is characterized experimentally. It successfully captures both the observed ferroelectric and ferroelastic domain switching effects. To overcome the difficulty of testing ultra thin piezoelectric plates, a set of novel characterization techniques is developed and implemented to measure the dielectric and mechanical responses of this material. The characterized material constitutive relation is implemented in an efficient model for estimating the structural response of unimorph thin shells under general electric and mechanical loading. The complete set of governing equations is integrated with a Backward-Euler algorithm, reproducing the measured responses of both the material and the structure under complex loading sequences.
\r\n\r\nActive vibration damping based on self-sensing piezoelectric thin shells is then analyzed and demonstrated on testbed. The self-sensing architecture removes redundant external sensors by making dual use of the piezoelectric layer of the active shell. An adaptive identification method with the associated hardware to track the evolution of field dependent piezoelectric capacitance is implemented, and a new identification strategy is proposed. Closed loop damping with in-situ capacitance adaptation is conducted in bench tests on self-sensing cantilever beams and achieves -12~dB attenuation at the resonance frequency. A highly efficient modeling technique for general self-sensing piezoelectric thin shell structures is proposed which is able to construct closed loop dynamic models based on the vibration eigenmodes and actuation responses obtained from commercial finite element software. These validated modeling techniques are extended to a multi-electrode doubly curved thin shell, where the improvements of shape stability under closed loop damping are evaluated through simulations. It is discovered that the electrode pattern of the self-sensing piezoelectric layer determines the damping performance under the specific boundary conditions of the shell.
" }, { "name": "Xia, Xiaoxing", "degree": "PhD", "year": "2019", "title": "Adaptive and Reconfigurable Architected Materials Driven by Electrochemistry", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012019-140706232", "creators": [ { "name": { "family": "Xia", "given": "Xiaoxing" }, "id": "Xia-Xiaoxing", "orcid": "0000-0003-1255-3289", "display_name": "Xia, Xiaoxing" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "matsci" ], "doi": "10.7907/Q092-P711", "abstract": "Architected materials are a new class of engineered materials with carefully controlled internal structures that give rise to properties that differ from or surpass those of their constituent materials. Recent advances in additive manufacturing provide an extraordinary opportunity to rationally design the structure and the chemical composition of architected materials across multiple length scales to optimize properties and functionalities for a variety of applications. These functional architected materials are capable of decoupling critical trade-offs, such as strength vs. density, to reach new regions of the material property space, and enabling exotic properties that rarely exist in classical materials such as negative refraction and negative thermal expansion.
\r\n\r\nThis thesis probes into the dynamic behaviors of architected materials undergoing electrochemical reactions and aims to provide an in-depth understanding of the underlying mechanisms as well as design principles generalizable for other functional architected material systems. We developed novel fabrication methods based on two-photon lithography and various physical and chemical post-processing techniques to create architected materials with multi-level design freedom including feature sizes, structural geometries, and material compositions, which resonates with the multi-faceted challenges in electrochemical systems. We demonstrated that architected materials provide a new platform to design battery electrodes that could accommodate the large volumetric changes associated with conversion-based electrode materials, while decoupling the longstanding trade-off between active material loading and transport kinetics in batteries. Furthermore, we presented a new class of electrochemically reconfigurable architected materials that could transform their structures in a programmable, reversible and non-volatile fashion, which provide new vistas for designing mechanical metamaterials with tunable phononic bandgaps and deployable micro-devices for biomedical applications.
\r\n\r\nThe multi-scale and multi-physics nature of these electrochemically driven architected materials prompted us to develop a toolset of (1) in situ SEM and optical microscopy to visualize the dynamic responses, (2) coupled chemo-mechanical finite element analysis to reconstruct detailed mechanical evolution as electrochemical reactions proceed, and (3) a statistical mechanics framework to capture the transient interactions between coupled mechanical instabilities. Using these tools, we investigated lithiation-induced cooperative beam buckling in tetragonal Si microlattices: from the deformation mechanisms of individual beams and the cooperative coupling between buckling directions of neighboring beams to the lithiation rate-dependent distribution of ordered buckling domains separated by distorted domain boundaries. Results indicate that local defects and stochastic energy fluctuations play a critical role in the dynamic response of architected materials in a way analogous to that during phase transformations of classical materials. These connections have profound implications on how we could understand and design architected materials by drawing inspiration from established theories in materials science.
\r\n" }, { "name": "Yalamanchili, Sisir", "degree": "PhD", "year": "2019", "title": "Light Management in Photovoltaics and Photoelectrochemical Cells using Tapered Micro and Nano Structures", "advisor": "Atwater, Harry Albert; Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182018-111020369", "creators": [ { "name": { "family": "Yalamanchili", "given": "Sisir" }, "id": "Yalamanchili-Sisir", "display_name": "Yalamanchili, Sisir" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "matsci" ], "doi": "10.7907/RRYM-VK03", "abstract": "Enhancing the efficiency and reducing the cost of solar photovoltaic (PV) systems is critical for increasing their penetration into energy generation market. The intermittency of energy generation from such systems due to diurnal, seasonal, and weather-related variation of sunlight limits them to low capacity factors (typically ~ 25%). Therefore, despite the cost of electricity from solar PV systems being cost competitive, further reductions are necessary to incorporate storage and increase the fraction of solar energy in total energy generation. An integrated photoelectrochemical (PEC) system that can generate fuel directly from sunlight could potentially reduce the balance of systems cost that dominates current PV systems, and provide an alternative way for energy storage. PEC systems are currently in research stage.
\r\n\r\nIn this work conical and triangular micro-nano structures are utilized to explore optical solutions for maximizing the light absorption and therefore enhancing the efficiencies of both PV and PEC systems. Silicon (Si) based micro conical arrays demonstrate < 1 % Spectrum-and-Angle-Averaged reflection, and absorption nearing ray optic light trapping limit in a 20 \u00b5m effectively thick Si substrates. Si microcone based photocathodes prepared for performing hydrogen evolution reaction (HER) show that thick layers of light blocking Pt and Co-P catalysts can be incorporated with only a 6 % photocurrent loss. The light trapping properties of Si micro-cones are a result of efficient coupling of light to available waveguide modes in a conical geometry. Alternatively, TiO2 based dielectric nano-conical arrays are shown to couple the light to waveguide modes and transmit the light into a planar Si substrate despite covering 54 % of the planar front surface with a light blocking Ni catalyst as an alternative way of light trapping without texturing the light absorber.
\r\n\r\nTriangular silver (Ag) front contacts in place of conventional flat contacts over PV cells are shown as another alternative for reducing front contact reflection losses and enhancing the efficiency by ~ 1% in Si heterojunction solar cells. These structures are implemented using a polymer stamp prepared from a Si master with triangular groves, and by flowing Ag ink through them. A Si master fabrication method is shown for fabrication of multiple configurations of triangular Ag contacts which can potentially be applied to other PV and PEC systems to enhance their efficiency.
\r\n" }, { "name": "Yang, Fred Chae-Reem", "degree": "PhD", "year": "2019", "title": "High Temperature Electron-Phonon and Magnon-Phonon Interactions", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03272019-174351662", "creators": [ { "name": { "family": "Yang", "given": "Fred Chae-Reem" }, "id": "Yang-Fred-Chae-Reem", "orcid": "0000-0002-5615-5170", "display_name": "Yang, Fred Chae-Reem" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/1KP5-CJ98", "abstract": "Computational materials discovery and design has emerged in order to meet the surge in demand for new materials for applications ranging from clean alternative energy to human welfare. This acceleration of materials discovery is exhilarating, but the applications of new advanced materials can be limited by their thermodynamic stability. Accurate calculations of the Gibbs free energy, a measure of thermodynamic stability, require a deep understanding of atomic vibrations, a main source of entropy in materials. This deep understanding of atomic vibrations requires us to treat phonons (quantized lattice vibrations) beyond the harmonic model by considering their interactions with various excitations. In this thesis, I present the effects of high temperature interactions of phonons with electrons and magnetic excitations on the thermodynamics of FeTi, vanadium, and Pd3Fe.
\r\n\r\nA combination of ab initio calculations, inelastic neutron scattering (INS), and nuclear resonant inelastic x-ray scattering (NRIXS) showed an anomalous thermal softening of the M5\u2212 phonon mode in B2-ordered FeTi and a thermal stiffening of the longitudinal acoustic N phonon mode in body-centered-cubic vanadium. Computational investigations involving electronic band unfolding were performed to identify the nesting features on Fermi surfaces crucial to high temperature electron-phonon interactions in FeTi and vanadium. These investigations showed that the Fermi surface of FeTi undergoes a novel thermally driven electronic topological transition (ETT), in which new features of the Fermi surface arise at elevated temperatures. This ETT was also observed in vanadium, but the effects were overtaken by the thermal smearing of the Fermi surface that decreased the rate of electron-phonon scattering.
\r\n\r\nIron phonon partial densities of states of Pd3Fe were measured with NRIXS from room temperature through the Curie transition at 500 K. The experimental results were compared to ab initio spin-polarized calculations that modeled the finite-temperature thermodynamic properties of Pd3Fe with magnetic special quasirandom structures (SQSs) of magnetic moments. The scattering measurements and first-principles calculations showed that the iron partial vibrational entropy is close to what is predicted by the quasiharmonic approximation owing to a cancellation of effects: phonon-phonon and magnon-phonon interactions approximately cancel a ferromagnetic optical phonon stiffening.
" }, { "name": "Yang, Jin", "degree": "PhD", "year": "2019", "title": "Fast Adaptive Augmented Lagrangian Digital Image Correlation", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162018-093212227", "creators": [ { "name": { "family": "Yang", "given": "Jin" }, "id": "Yang-Jin", "orcid": "0000-0002-5967-980X", "display_name": "Yang, Jin" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "role": "member", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/MZ5G-PS98", "abstract": "Digital image correlation (DIC) is a powerful experimental technique for measuring full-field displacement and strain. The basic idea of the method is to compare images of an object decorated with a speckle pattern before and after deformation in order to compute the displacement and strain fields. Local Subset DIC and finite element-based Global DIC are two widely used image matching methods; however there are some drawbacks to these methods. In Local Subset DIC, the computed displacement field may not satisfy compatibility, and the deformation gradient may be noisy, especially when the subset size is small. Global DIC incorporates displacement compatibility, but can be computationally expensive. In this thesis, we propose a new method, the augmented-Lagrangian digital image correlation (ALDIC), that combines the advantages of both the local (fast and in parallel) and global (compatible) methods. We demonstrate that ALDIC has higher accuracy and behaves more robustly compared to both Local Subset DIC and Global DIC.
\r\n\r\nDIC requires a large number of high resolution images, which imposes significant needs on data storage and transmission. We combined DIC algorithms with image compression techniques and show that it is possible to obtain accurate displace- ment and strain fields with only 5 % of the original image size. We studied two compression techniques \u2013 discrete cosine transform (DCT) and wavelet transform, and three DIC algorithms \u2013 Local Subset DIC, Global DIC and our newly proposed augmented Lagrangian DIC (ALDIC). We found the Local Subset DIC leads to the largest errors and ALDIC to the smallest when compressed images are used. We also found wavelet-based image compression introduces less error compared to DCT image compression.
\r\n\r\nTo further speed up and improve the accuracy of DIC algorithms, especially in the study of complex heterogeneous strain fields at various length scales, we apply an adaptive finite element mesh to DIC methods. We develop a new h-adaptive technique and apply it to ALDIC. We show that this adaptive mesh ALDIC algorithm significantly decreases computation time with no loss (and some gain) in accuracy.
" }, { "name": "Yang, Qifan", "degree": "PhD", "year": "2019", "title": "Nonlinear Physics in Soliton Microcombs", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192019-220451795", "creators": [ { "name": { "family": "Yang", "given": "Qifan" }, "id": "Yang-Qifan", "orcid": "0000-0002-7036-1712", "display_name": "Yang, Qifan" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/DWMX-S056", "abstract": "Like rulers of light, optical frequency combs consist of hundreds to millions of coherent laser lines, which are capable of measuring time and frequency with the highest degree of accuracy. Used to rely on table-top mode-locked lasers, optical frequency combs have been recently realized in a miniaturized form, namely the microcomb, using monolithic microresonators. Besides a reduction of footprint, microcombs could also achieve parity with traditional frequency combs in performance by mode-locking through the formation of \"light bullets\" called dissipative Kerr solitons. These soliton microcombs not only serve as a unique platform to study nonlinear physics, but also offer scalable and cost-effective solutions to many groundbreaking applications, spanning spectroscopy to time standards. In this thesis I will trace the physical origin of soliton microcombs, followed by their experimental realization in high-Q silica microresonators. The impact of several nonlinear process on solitons will be discussed, which leads to novel soliton systems, e.g., Stokes solitons and counter-propagating solitons. Utilizing these nonlinear properties, we show that soliton microcombs can be adapted for high-precision spectroscopic applications. In the end, a real-time method for monitoring transient behavior of solitons will be presented." }, { "name": "Ziani, Juba", "degree": "PhD", "year": "2019", "title": "Data: Implications for Markets and for Society", "advisor": "Ligett, Katrina A.; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292019-162418941", "creators": [ { "name": { "family": "Ziani", "given": "Juba" }, "id": "Ziani-Juba", "orcid": "0000-0002-3324-4349", "display_name": "Ziani, Juba" } ], "advisors": [ { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-Katrina-A", "role": "advisor", "display_name": "Ligett, Katrina A." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Echenique", "given": "Federico" }, "id": "Echenique-F", "role": "chair", "display_name": "Echenique, Federico" }, { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-K-A", "role": "member", "display_name": "Ligett, Katrina A." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Doval", "given": "Laura" }, "id": "Doval-Laura", "role": "member", "display_name": "Doval, Laura" }, { "name": { "family": "Roth", "given": "Aaron" }, "id": "Roth-Aaron", "role": "member", "display_name": "Roth, Aaron" } ], "option_major": [ "compsci" ], "doi": "10.7907/XZHX-1M46", "abstract": "Every day, massive amounts of data are gathered, exchanged, and used to run statistical computations, train machine learning algorithms, and inform decisions on individuals and populations. The quick rise of data, the need to exchange and process it, to take data privacy concerns into account, and to understand how it affects decision-making, introduce many new and interesting economic, game theoretic, and algorithmic challenges.
\r\n\r\nThe goal of this thesis is to provide theoretical foundations to approach these challenges. The first part of this thesis focuses on the design of mechanisms that purchase then aggregate data from many sources, in order to perform statistical tasks. The second part of this thesis revolves around the societal concerns associated with the use of individuals' data. The first such concern we examine is that of privacy, when using sensitive data about individuals in statistical computations; we focus our attention on how privacy constraints interact with the task of designing mechanisms for acquisition and aggregation of sensitive data. The second concern we focus on is that of fairness in decision-making: we aim to provide tools to society that help prevent discrimination against individuals and populations based on sensitive attributes in their data, when making important decisions about them. Finally, we end this thesis on a study of the interactions between data and strategic behavior. There, we see data as a source of information that informs and affects agents' incentives; we study how information revelation impacts agent behavior in auctions, and in turn how a seller should design auctions that take such information revelation into account.
" }, { "name": "da Silva, Andre Fernando de Castro", "degree": "PhD", "year": "2019", "title": "An EnKF-Based Flow State Estimator for Aerodynamic Problems", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:09072018-105527896", "creators": [ { "name": { "family": "da Silva", "given": "Andre Fernando de Castro" }, "id": "da-Silva-Andre-Fernando-de-Castro", "orcid": "0000-0002-8125-6010", "display_name": "da Silva, Andre Fernando de Castro" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/W327-VF41", "abstract": "Regardless of the plant model, robust flow estimation based on limited measurements remains a major challenge in successful flow control applications. Aiming to combine the robustness of a high-dimensional representation of the dynamics with the cost efficiency of a low-order approximation of the state covariance matrix, a flow state estimator based on the Ensemble Kalman Filter (EnKF) is applied to two-dimensional flow past a cylinder and an airfoil at high angle of attack and low Reynolds number. For development purposes, we use the numerical algorithm as both the estimator and as a surrogate for the measurements. In a perfect-model framework, a reduced number of either pressure sensors on the surface of the body or sparsely placed velocity probes in the wake are sufficient to accurately estimate the instantaneous flow state. Because the dynamics of these flows are restricted to a low-dimensional manifold of the state space, a small ensemble size is sufficient to yield the correct asymptotic behavior. The relative importance of each sensor location is evaluated by analyzing how they influence the estimated flow field, and optimal locations for pressure sensors are determined.
\r\n\r\nHowever, model inaccuracies are ubiquitous in practical applications. Covariance inflation is used to enhance the estimator performance in the presence of unmodeled freestream perturbations. A combination of parametric modeling and augmented state methodology is used to successfully estimate the forces on immersed bodies subjected to deterministic and random gusts. The robustness of high-dimensional representation of the dynamics to the choice of parameters such as the Reynolds number is inherited by the estimator, which was shown to successfully estimate the reference Reynolds number on the fly. Spatial and temporal discretization can constitute a second source of errors which can render numerical solutions a biased representation of reality. Left unaccounted for, biased forecast and observation models can lead to poor estimator performance. In this work, we propose a low-rank representation for the bias whose dynamics are represented by a colored-noise process. System state and bias parameters are simultaneously tracked online with the Ensemble Kalman Filter (EnKF) algorithm. The proposed methodology is demonstrated to achieve a 70% error reduction for the problem of estimating the state of the two-dimensional low-Re flow past a flat plate at high angle of attack using an ensemble of coarse-mesh simulations and pressure measurements at the surface of the body, compared to a bias-blind estimator. Strategies to determine the bias statistics and to deal with nonlinear observation functions in the context of ensemble methods are discussed.
" }, { "name": "Aasen, David", "degree": "PhD", "year": "2018", "title": "Super Pivotal Categories, Fermion Condensation, and Fermionic Topological Phases", "advisor": "Alicea, Jason F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-132922155", "creators": [ { "name": { "family": "Aasen", "given": "David" }, "id": "Aasen-David", "orcid": "0000-0002-6552-488X", "display_name": "Aasen, David" } ], "advisors": [ { "name": { "family": "Alicea", "given": "Jason F." }, "id": "Alicea-J", "orcid": "0000-0001-9979-3423", "role": "advisor", "display_name": "Alicea, Jason F." } ], "committee": [ { "name": { "family": "Alicea", "given": "Jason F." }, "id": "Alicea-J", "orcid": "0000-0001-9979-3423", "role": "chair", "display_name": "Alicea, Jason F." }, { "name": { "family": "Motrunich", "given": "Olexei I." }, "id": "Motrunich-Olexei", "orcid": "0000-0001-8031-0022", "role": "member", "display_name": "Motrunich, Olexei I." }, { "name": { "family": "Chen", "given": "Xie" }, "id": "Chen-Xie", "orcid": "0000-0003-2215-2497", "role": "member", "display_name": "Chen, Xie" }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/P9A4-MH26", "abstract": "We describe a systematic way of producing fermionic topological phases using the technique of fermion condensation. We give a prescription for performing fermion condensation in bosonic topological phases which contain an emergent fermion. Our approach to fermion condensation can roughly be understood as coupling the parent bosonic topological phase to a phase of physical fermions, and condensing pairs of physical and emergent fermions. There are two distinct types of objects in fermionic theories, which we call “m-type” and “q-type” particles. The endomorphism algebras of q-type particles are complex Clifford algebras, and they have no analogues in bosonic theories. We construct a fermionic generalization of the tube category, which allows us to compute the quasiparticle excitations in fermionic topological phases. We then prove a series of results relating data in condensed theories to data in their parent theories; for example, if C is a modular tensor category containing a fermion, then the tube category of the condensed theory satisfies Tube(C/ψ) ≅ C × C/ψ. We also study how modular transformations, fusion rules, and coherence relations are modified in the fermionic setting, prove a fermionic version of the Verlinde dimension formula, construct a commuting projector lattice Hamiltonian for fermionic theories, and write down a fermionic version of the Turaev-Viro-Barrett-Westbury state sum.
" }, { "name": "Abiri, Behrooz", "degree": "PhD", "year": "2018", "title": "Silicon Integrated Arrays: From Microwave to IR", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042018-194533722", "creators": [ { "name": { "family": "Abiri", "given": "Behrooz" }, "id": "Abiri-Behrooz", "orcid": "0000-0002-3317-2752", "display_name": "Abiri, Behrooz" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MNYK-Y158", "abstract": "Integrated chips have enabled realization and mass production of complex systems in a small form factor. Through process miniaturization many novel applications in silicon photonics and electronic systems have been enabled. In this thesis I have provided several examples of innovations that are only enabled by integration. I have also demonstrated how electronics and photonics circuits can complement each other to achieve a system with superior performance.
" }, { "name": "Avellar, Louisa Taylor", "degree": "PhD", "year": "2018", "title": "Observations of Failure Phenomena in Periodic Media", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282018-024934056", "creators": [ { "name": { "family": "Avellar", "given": "Louisa Taylor" }, "id": "Avellar-Louisa-Taylor", "orcid": "0000-0003-1299-5343", "display_name": "Avellar, Louisa Taylor" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/8N81-MV74", "abstract": "New manufacturing techniques, such as 3D printing, allow for greater control over material properties and can be used to create custom heterogeneous materials. Heterogeneities can be leveraged to increase fracture toughness by redistributing the stresses, such as due to an elastic heterogeneity, or by impeding crack propagation, such as the renucleation at a material interface or edge of a void. The goal of this research is to study the mechanisms by which heterogeneities work to make composite materials more resistant to fracture than either of the individual base materials.
\r\n\r\nThe influence of heterogeneities on the deformation and fracture of 3D printed fracture specimens is investigated. Brick-like heterogeneities are studied in compact tension and plate specimens with soft, stiff, and void heterogeneities. Horizontally layered heterogeneities are studied in compact tension specimens. The specimens are manufactured using a printer capable of printing multiple materials. The specimens are loaded until failure, and full-field displacement and strain data are collected using digital image correlation. The evolution of resistance to fracture is quantified by the energy release rate and fracture toughness values calculated using load, load-point displacement measurements, and crack extension data determined from images of the specimen. Both in soft specimens with stiff heterogeneities and in stiff specimens with soft heterogeneities, stresses are observed to be higher in the stiffer material. Fracture toughness is observed to increase in the presence of stiff inclusions and voids, although in the case of voids this is due to the crack terminating at the edge of the void and renucleating at the other edge.
\r\n\r\nThe effects of interfaces on crack propagation in periodic media are experimentally studied. Comparative experiments on two proposed heterogeneity architectures aim to separate the effects of elastic deformation caused by heterogeneous inclusions in a composite from the effects of passing through an interface during crack propagation. The first, 'stripe' specimens, alternate equal width stripes perpendicular to the plane of the crack. The second, 'cross' specimens, have the same stripe pattern but with a narrow strip of one of the constituent materials in the plane of crack propagation. The 'cross' is wide enough to contain the crack to an area without material interfaces but thin enough that its overall effect on elastic deformation is minimal. Specimens are manufactured from two polymers using polyjet 3D printing. Energy release rate for fracture is calculated from load and displacement measurements. Digital image correlation is used to study strain and stress fields during crack propagation. While the stress fields during crack propagation appear similar, the fracture toughness in the 'stripe' specimens was found to be higher than that of the 'cross' specimens, indicating that fracture toughness is enhanced by renucleation at the interfaces. Additionally, the amount of enhancement was observed to depend on the width of the heterogeneous layers.
\r\n\r\nThe interaction between the cohesive zone and elastic stiffness heterogeneity in the peeling of an adhesive tape from a rigid substrate is examined experimentally and with finite element simulations. It is understood that elastic stiffness heterogeneities can greatly enhance the adhesion of a tape without changing the properties of the interface. However, in peeling experiments performed on pressure sensitive adhesive tapes with both an elastic stiffness heterogeneity and a substantial cohesive zone, muted adhesion enhancement was observed. It is proposed that the cohesive zone acts to smooth out the effect of the discontinuity at the edge of the elastic stiffness heterogeneities, suppressing their effect on peel force enhancement. The results of numerical simulations show that the peel force enhancement depends on the strength of the adhesive and the size of the cohesive zone.
" }, { "name": "Baetica, Ania-Ariadna", "degree": "PhD", "year": "2018", "title": "Design, Analysis, And Computational Methods For Engineering Synthetic Biological Networks", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042018-171639726", "creators": [ { "name": { "family": "Baetica", "given": "Ania-Ariadna" }, "id": "Baetica-Ania-Ariadna", "orcid": "0000-0003-0421-8181", "display_name": "Baetica, Ania-Ariadna" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Munsky", "given": "Brian" }, "id": "Munsky-Brian", "role": "member", "display_name": "Munsky, Brian" } ], "option_major": [ "cds" ], "doi": "10.7907/98qt-zv92", "abstract": "This thesis advances our understanding of three important aspects of biological systems engineering: analysis, design, and computational methods. First, biological circuit design is necessary to engineer biological systems that behave consistently and follow our design specifications. We contribute by formulating and solving novel problems in stochastic biological circuit design. Second, computational methods for solving biological systems are often limited by the nonlinearity and high dimensionality of the system\u2019s dynamics. This problem is particularly extreme for the parameter identification of stochastic, nonlinear systems. Thus, we develop a method for parameter identification that relies on data-driven stochastic model reduction. Finally, biological system analysis encompasses understanding the stability, performance, and robustness of these systems, which is critical for their implementation. We analyze a sequestration feedback motif for implementing biological control.
\r\n\r\nFirst, we discuss biological circuit design for the stationary and the transient distributional responses of stochastic biochemical systems. Noise is often indispensable to key cellular activities, such as gene expression, necessitating the use of stochastic models to capture their dynamics. The chemical master equation is a commonly used stochastic model that describes how the probability distribution of a chemically reacting system varies with time. Here we design the distributional response of these stochastic models by formulating and solving it as a constrained optimization problem.
\r\n\r\nSecond, we analyze the stability and the performance of a biological controller implemented by a sequestration feedback network motif. Sequestration feedback networks have been implemented in synthetic biology using an array of biological parts. However, their properties of stability and performance are poorly understood. We provide insight into the stability and performance of sequestration feedback networks. Additionally, we provide guidelines for the implementation of sequestration feedback networks.
\r\n\r\nThird, we develop computational methods for the parameter identification of stochastic models of biochemical reaction networks. It is often not possible to find analytic solutions to problems where the dynamics of the underlying biological circuit are stochastic, nonlinear or both. Stochastic models are often challenging due to their high dimensionality and their nonlinearity, which further limits the availability of analytical tools. To address these challenges, we develop a computational method for data-driven stochastic model reduction and we use it to perform parameter identification. Last, we provide concluding remarks and future research directions.
" }, { "name": "Braun, Noah Oakley", "degree": "PhD", "year": "2018", "title": "An LES and RANS Study of the Canonical Shock-Turbulence Interaction", "advisor": "Pullin, Dale Ian; Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212018-165403115", "creators": [ { "name": { "family": "Braun", "given": "Noah Oakley" }, "id": "Braun-Noah-Oakley", "orcid": "0000-0002-9710-0686", "display_name": "Braun, Noah Oakley" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "co-advisor", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "co-advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Gore", "given": "Robert A." }, "id": "Gore-Robert-A", "role": "member", "display_name": "Gore, Robert A." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BGX1-C128", "abstract": "The canonical problem of a nearly stationary, nearly planar shockwave passing through isotropic turbulence is investigated within high Reynolds number regimes. The subject flow contains a wide range of turbulent scales and is addressed in Large Eddy Simulation (LES) to relax the otherwise prohibitive computational cost of simulating these flows. Aliasing errors in the LES of the upstream isotropic turbulence are shown to interact with the mean compression of the shock in a problematic matter, and may result in nonphysical behavior such as a reduction in the dissipation rate as the flow crosses the shock. A method for the regularization of LES of shock-turbulence interactions is presented which is constructed to enforce that the energy content in the highest resolved wavenumbers decays as k-5/3, and is computed locally in physical space at low computational cost. The application of the regularization to an existing subgrid scale model is shown to remove high wavenumber errors while maintaining agreement with DNS of forced and decaying isotropic turbulence. Comparisons to analytical models suggest that the regularization significantly improves the ability of the LES to predict amplifications in subgrid terms over the modeled shockwave.
\r\n\r\nThe regularization method is then employed in high resolution LES intended to illustrate the physical behavior of the shocked, turbulent flow. Turbulent statistics downstream of the interaction are provided for a range of weakly compressible upstream turbulent Mach numbers Mt = 0.03 - 0.18, shock Mach numbers Ms = 1.2 - 3.0, and Taylor-based Reynolds numbers Re\u03bb = 20 - 2500. The LES displays minimal Reynolds number effects once an inertial range has developed for Re\u03bb > 100. The inertial range scales of the turbulence are shown to quickly return to isotropy, and downstream of sufficiently strong shocks this process generates a net transfer of energy from transverse into streamwise velocity fluctuations. The streamwise shock displacements are shown to approximately follow a k-11/3 decay with wavenumber as predicted by linear analysis. In conjunction with other statistics this suggests that the instantaneous interaction of the shock with the upstream turbulence proceeds in an approximately linear manner, but nonlinear effects immediately downstream of the shock significantly modify the flow even at the lowest considered turbulent Mach numbers.
\r\n\r\nLES allows consideration of high Re\u03bb flows, but remains expensive to compute relative to lower cost modeling approaches such as Reynolds-Averaged Navier Stokes (RANS). Conventional RANS models are often not well suited for simulations containing discontinuous features such as shocks and, in an effort to improve the performance of RANS, models for averaged shock corrugation effects and the impact of turbulent entropy or acoustic modes on the energy equation are presented. Unlike previous RANS work that has focused on the modification of turbulent statistics by the shock, the proposed models are introduced to capture the effects of the turbulence on the profiles of primitive variables --- mean density, velocity, and pressure. By producing accurate profiles for the primitive variables, it is shown that the proposed models improve numerical convergence behavior with mesh refinement about a shock, and introduce the physical effects of shock asphericity in a converging shock geometry. These effects are achieved by local closures to turbulent statistics in the averaged Navier-Stokes equations, and can be applied in conjunction with existing Reynolds stress closures that have been constructed for broader applications beyond shock-turbulence interactions.
" }, { "name": "Brooks, Daniel James", "degree": "PhD", "year": "2018", "title": "Computational Investigation of Ionic Diffusion in Polymer Electrolytes for Lithium-Ion Batteries", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012018-042437640", "creators": [ { "name": { "family": "Brooks", "given": "Daniel James" }, "id": "Brooks-Daniel-James", "display_name": "Brooks, Daniel James" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Wise", "given": "Mark B." }, "id": "Wise-M-B", "orcid": "0000-0002-9125-801X", "role": "member", "display_name": "Wise, Mark B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ZE9T-V407", "abstract": "Energy storage is a critical problem in the 21st century and improvements in battery technology are required for the next generation of electric cars and electronic devices. Solid polymer electrolytes show promise as a material for use in long-lifetime, high energy density lithium-ion batteries. Improvements in ionic conductivity, however, for the development of commercially viable materials, and, to this end, a series of computational studies of ionic diffusion were performed. First, pulsed charging is examined as a technique for inhibiting the growth of potentially dangerous lithium dendrites. The effective timescale for pulse lengths is determined as a function of cell geometry. Next, the atomistic diffusion mechanism in the leading polymer electrolyte, PEO-LiTFSI, is characterized as a function of temperature, molecular weight, and ionic concentration using molecular dynamics simulations. A novel model for describing coordination of lithium to the polymer structure is developed which describes two types of interchain motion \"hops\" and \"shifts,\" the former of which is shown to contribute significantly to ionic diffusion. The methodology developed in this study is then applied to a new problem \u2013 the adsorption of CO2 at the surface of semi-permeable polymer membranes. Finally, a new method, PQEq, is developed, which provides an improved description of electrostatic interactions with the inclusion of explicit polarization, Gaussian shielding, and charge equilibration. The dipole interaction energies obtained from PQEq are shown to be in excellent agreement with QM and a preliminary application of PQEq to a polymer electrolyte suggest that it can provide an improved description of ionic diffusion. Taken as a whole, these techniques show promise as tools to explore and characterize novel materials for lithium-ion batteries. " }, { "name": "Burali, Nicholas", "degree": "PhD", "year": "2018", "title": "Towards a priori Models for Differential Diffusion in Turbulent Non-Premixed Flames", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062018-163232775", "creators": [ { "name": { "family": "Burali", "given": "Nicholas" }, "id": "Burali-Nicholas", "orcid": "0000-0002-0733-0577", "display_name": "Burali, Nicholas" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/N3VJ-BE39", "abstract": "In this work, progress is made towards the correct modeling of differential diffusion, both for resolved simulations, and for reduced-order combustion models. For resolved simulations, the validity and the limitations of the constant non-unity Lewis number approach in the description of molecular mixing in laminar and turbulent flames is studied. Three test cases are selected, including a lean, highly unstable, premixed hydrogen/air flame, a lean turbulent premixed n-heptane/air flame, and a laminar ethylene/air coflow diffusion flame. For the hydrogen flame, both a laminar and a turbulent configuration are considered. The three flames are characterized by Lewis numbers which are less than unity, greater than unity, and close to unity, respectively. For each flame, mixture-averaged transport simulations are carried out and used as reference data. The analysis suggests that, for numerous combustion configurations, the constant non-unity Lewis number approximation leads to small errors when the set of Lewis numbers is chosen properly. For the selected test cases and our numerical framework, the reduction of computational cost is found to be minimal. Two different methods of evaluating the Lewis numbers are tested, with both performing well, and neither consistently better than the other.
\r\n\r\nThe flamelet-based chemistry tabulation technique is a popular reduced-order chemical model for non-premixed turbulent flames. In this approach, the correct choice of the species Lewis numbers in the flamelet equations plays an important role. Experimental results have highlighted that, in turbulent non-premixed jet flames, turbulent transport becomes gradually dominant over molecular mixing with (i) increasing axial distance from the burner exit plane, and (ii) increasing jet Reynolds number. In the current work, this transition is characterized and a priori models for the effective species Lewis numbers in turbulent non-premixed flames are assessed.
\r\n\r\nFirst, a flamelet-based methodology is proposed to extract these effective Lewis numbers from data sets of turbulent non-premixed flames. This methodology is then applied to the Sandia non-premixed methane/air jet flames B, C, D, and E (R. Barlow, Int. Work. Meas. Comput. Turb. Non-Prem. Flames, 2003). The effective Lewis numbers are found to transition from their laminar values, close to the burner exit plane, to unity further downstream. Previously-suggested scalings for the effective Lewis numbers are then assessed.
\r\n\r\nTo overcome the limitations associated with the experimental data, a campaign of Direct Numerical Simulations (DNS) of Sandia flame B is carried out. A baseline grid is carefully designed, and grid independence is assessed through simulations using refined grids in the axial, radial and azimuthal directions. Radiation and differential diffusion effects are systematically isolated by considering radiating and unity Lewis number cases, respectively. The DNS database is then validated using available measured statistics for flame B, and comparisons to the higher Reynolds number flames are carried out. Effective Lewis numbers extracted from the DNS data are found to transition to unity with increasing downstream distance. Finally, the scalings for the effective Lewis numbers are re-computed from the DNS data base, and compared to the higher Reynolds number flames.
" }, { "name": "Burkhardt, Matthew Ryan", "degree": "PhD", "year": "2018", "title": "Dynamic Modeling and Control of Spherical Robots", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302018-110559204", "creators": [ { "name": { "family": "Burkhardt", "given": "Matthew Ryan" }, "id": "Burkhardt-Matthew-Ryan", "display_name": "Burkhardt, Matthew Ryan" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "role": "member", "display_name": "Ames, Aaron D." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Backes", "given": "Paul G." }, "id": "Backes-Paul-G", "role": "member", "display_name": "Backes, Paul G." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/E5CW-8H41", "abstract": "In this work, a rigorous framework is developed for the modeling and control of spherical robotic vehicles. Motivation for this work stems from the development of Moball, which is a self-propelled sensor platform that harvests kinetic energy from local wind fields. To study Moball's dynamics, the processes of Lagrangian reduction and reconstruction are extended to robotic systems with symmetry-breaking potential energies, in order to simplify the resulting dynamic equations and expose mathematical structures that play an important role in subsequent control-theoretic tasks. These results apply to robotic systems beyond spherical robots. A formulaic procedure is introduced to derive the reduced equations of motion of most spherical robots from inspection of the Lagrangian. This adaptable procedure is applied to a diverse set of robotic systems, including multirotor aerial vehicles.
\r\n\r\nSmall time local controllability (STLC) results are derived for barycentric spherical robots (BSR), which are spherical vehicles whose locomotion depends on actuating the vehicle's center of mass (COM) location. STLC theorems are introduced for an arbitrary BSR on flat, sloped, or smooth terrain. I show that STLC depends on the surjectivity of a simple steering matrix. An STLC theorem is also derived for a class of commonly encountered multirotor vehicles.
\r\n\r\nFeedback linearizing and PID controllers are proposed to stabilize an arbitrary spherical robot to a desired trajectory over smooth terrain, and direct collocation is used to develop a feedforward controller for Moball specifically. Moball's COM is manipulated by a novel system of magnets and solenoids, which are actuated by a \"ballistic-impulse\" controller that is also presented. Lastly, a motion planner is developed for energy-harvesting vehicles. This planner charts a path over smooth terrain while balancing the desire to achieve scientific objectives, avoid hazards, and the imperative of exposing the vehicle to environmental sources of energy such as local wind fields and topology. Moball's design details and experimental results establishing Moball's energy-harvesting performance (7W while rolling at a speed of 2 m/s), are contained in an Appendix.
" }, { "name": "Buyco, John Kenneth", "degree": "PhD", "year": "2018", "title": "Improving Seismic Collapse Risk Assessments of Steel Moment Frame Buildings", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012018-015306089", "creators": [ { "name": { "family": "Buyco", "given": "John Kenneth" }, "id": "Buyco-John-Kenneth", "orcid": "0000-0002-8182-7119", "display_name": "Buyco, John Kenneth" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "chair", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "orcid": "0000-0002-4703-190X", "role": "member", "display_name": "Kohler, Monica D." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/2SFH-WP06", "abstract": "It is important to be able to accurately assess seismic risk so that vulnerabilities can be prioritized for retrofit, emergency response procedures can be properly informed, and insurance rates can be sustainably priced to manage risk. To assess the risk of a building (or class of buildings) collapsing in a seismic event, procedures exist for creating one or more mathematical models of the structure of interest and performing nonlinear time history analysis with a large suite of input ground motions to calculate the building's seismic fragility and collapse risk. In this dissertation, three aspects of these procedures for assessing seismic collapse risk are investigated for the purpose of improving their accuracy.
\r\n\r\nIt is common to use spectral acceleration with a damping ratio of 5% as a ground motion intensity measure (IM) for assessing collapse fragility. In this dissertation, the use of 70%-damped spectral acceleration as an IM is investigated, with a focus on evaluating its sufficiency and efficiency. Incremental dynamic analysis (IDA) is performed for 22 steel moment frame (SMF) models with 50 biaxial ground motion records to formally evaluate the performance of 70%-damped spectral acceleration as an IM for highly nonlinear response and collapse. It is found that 70%-damped spectral acceleration is much more efficient than 5%-damped spectral acceleration and much more sufficient with respect to epsilon for all considered levels of highly nonlinear response. Its efficiency and sufficiency compares also compares well with more advanced IMs such as average spectral acceleration.
\r\n\r\nWhen selecting input ground motions for nonlinear time history analysis, most engineers select ground motion records from the NGA-West2 database, which are processed with high-pass filters to remove long-period noise. In this dissertation, the extent to which these filters remove actual ground motion that is relevant to nonlinear time history analysis is evaluated. 52 near-source ground motion records from large-magnitude events are considered. Some records are processed by applying high-pass filters and others are processed by record-specific tilt corrections. Raw and NGA-West2 records are also considered. IDA is performed for 9-, 20-, and 55-story steel moment frame models with these processed records to assess the effects of ground motion processing on the calculated collapse capacity. It is found that if the cutoff period (Tc) is at least 40 seconds, then applying a high-pass filter does not have more than a negligible effect on collapse capacity for any of the considered records or building models. For shorter Tc (e.g. 10 or 15 seconds), it is found that the filters sometimes have a large effect on calculated collapse capacity, in some cases by over 50%, even if Tc is much larger than the building\u2019s fundamental period. Of the considered ground motions, simply using the raw, uncorrected records usually yields more accurate results than using ground motions that have been processed with Tc less than or equal to 20 seconds.
\r\n\r\nFor an existing building with unknown design plans, one might perform a collapse risk assessment using an archetype model for which the specific member sizes are assumed based on the relevant design code and building site. In this dissertation, the sensitivity of seismic collapse risk estimates to design criteria and procedures are evaluated for six 9-story and four 20-story post-Northridge SMFs. These SMFs are designed for downtown Los Angeles using different design procedures according to ASCE 7-05 and ASCE 7-10. Seismic risk analysis is performed using the results of IDA with 44 ground motion records and the results are compared to those of pre-Northridge models. It is found that the collapse risk of 9-story SMFs designed according to performance-based design vary by 3x, owing to differences in GMPEs used to generate site-specific response spectra. There is generally less variation in the collapse risk estimates of 20-story post-Northridge SMFs when compared to 9-story post-Northridge SMFs because wind drift limits control the design of many members of the 20-story SMFs. Differences in collapse risk between pre- and post-Northridge SMFs are found to be at least 4x and 8x for the 9- and 20-story models, respectively. Furthermore, in response to four strong ground motion records from large-magnitude events, some of the 9-story and all of the 20-story pre-Northridge SMFs experience collapse and most of the post-Northridge SMFs experience significant damage (MIDR > 0.03).
" }, { "name": "Chen, Niangjun", "degree": "PhD", "year": "2018", "title": "Online Algorithms: From Prediction to Decision\r ", "advisor": "Wierman, Adam C.; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10182017-210853845", "creators": [ { "name": { "family": "Chen", "given": "Niangjun" }, "id": "Chen-Niangjun", "orcid": "0000-0002-2289-9737", "display_name": "Chen, Niangjun" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "co-advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "compsci" ], "doi": "10.7907/Z95M63W4", "abstract": "Making use of predictions is a crucial, but under-explored, area of sequential decision problems with limited information. While in practice most online algorithms rely on predictions to make real time decisions, in theory their performance is only analyzed in simplified models of prediction noise, either adversarial or i.i.d. The goal of this thesis is to bridge this divide between theory and practice: to study online algorithm under more practical predictions models, gain better understanding about the value of prediction, and design online algorithms that make the best use of predictions.
\r\n\r\nThis thesis makes three main contributions. First, we propose a stochastic prediction error model that generalizes prior models in the learning and stochastic control communities, incorporates correlation among prediction errors, and captures the fact that predictions improve as time passes. Using this general prediction model, we prove that Averaging Fixed Horizon Control (AFHC) can simultaneously achieve sublinear regret and constant competitive ratio in expectation using only a constant- sized prediction window, overcoming the hardnesss results in adversarial prediction models. Second, to understand the optimal use of noisy prediction, we introduce a new class of policies, Committed Horizon Control (CHC), that generalizes both popular policies Receding Horizon Control (RHC) and Averaging Fixed Horizon Control (AFHC). Our results provide explicit results characterizing the optimal use of prediction in CHC policy as a function of properties of the prediction noise, e.g., variance and correlation structure. Third, we apply the general prediction model and algorithm design framework to the deferrable load control problem in power systems. Our proposed model predictive algorithm provides significant reduction in variance of total load in the power system. Throughout this thesis, we provide both average-case analysis and concentration results for our proposed online algorithms, highlighting that the typical performance is tightly concentrated around the average-case performance.
" }, { "name": "Chernow, Victoria Fay", "degree": "PhD", "year": "2018", "title": "Design, Fabrication, and Characterization of 3D Nanolattice Photonic Crystals for Bandgap and Refractive Index Engineering", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112018-154344223", "creators": [ { "name": { "family": "Chernow", "given": "Victoria Fay" }, "id": "Chernow-Victoria-Fay", "orcid": "0000-0001-5405-1928", "display_name": "Chernow, Victoria Fay" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/FK5P-FA29", "abstract": "Three-dimensional (3D) photonic crystals (PhCs) have been the focus of ever-increasing interest in the scientific community given their potential to impact areas spanning energy conversion to analyte sensing. These architected materials are defined by a refractive index that is spatially modulated with a period comparable to that of the electromagnetic wavelength. As a result, constructive and destructive interference due to multiple scattering gives rise to a band structure for photons which may contain gaps. Both bands and bandgaps can be engineered to specifically manipulate light propagation by 3D PhCs. In this work we explore the effect of lattice architecture, finite-size effects, and material constraints on stopband position and emergence of band dispersion phenomena like negative refraction. We show that uniaxial mechanical compression can be used to stably and reversibly tune stopband position in 3D polymer nanolattice PhCs with octahedron unit-cell geometry. We then explore how lattice architecture, namely the differences in 3D cubic space group and finite size effects impact experimentally observable stopbands, and assess the degree to which the stopband behavior of real PhCs can be adequately described by the photonic band structure for an infinite, ideal PhC. Finally, we discuss the design, fabrication, and characterization of a core-shell 3D nanolattice PhC which exhibits an effective negative refractive index in the mid-infrared range.
" }, { "name": "Cid, Cl\u00e9ment Antoine Fran\u00e7ois", "degree": "PhD", "year": "2018", "title": "Development, Implementation, and Improvements on an Effective Electrochemical Wastewater Treatment and Recycling Unit as a Sustainable Sanitation Solution for the Developing World", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02152018-165139157", "creators": [ { "name": { "family": "Cid", "given": "Cl\u00e9ment Antoine Fran\u00e7ois" }, "id": "Cid-Cl\u00e9ment-Antoine-Fran\u00e7ois", "orcid": "0000-0002-7293-035X", "display_name": "Cid, Cl\u00e9ment Antoine Fran\u00e7ois" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "role": "chair", "display_name": "Okumura, Mitchio" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Diallo", "given": "Mamadou S." }, "id": "Diallo-Mamadou-S", "role": "member", "display_name": "Diallo, Mamadou S." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/Z9BG2M61", "abstract": "In this thesis, I present my work on the development of a self-contained toilet wastewater treatment and recycling system, the \u201cCaltech Solar Toilet\u201d. The Caltech Solar Toilet technology is based on electrolysis of toilet wastewater with TiO2-coated semiconductor anodes and stainless steel cathodes. This is a potentially viable onsite sanitation solution in parts of the world that lack the needed infrastructure for centralized wastewater treatment.
\r\n\r\nPrototypes of Caltech Solar Toilets were designed to fit in shipping containers in order to provide toilets and onsite wastewater treatment with clean water recycling. Units were designed to handle the waste of 25 users per day (or 130 L of toilet wastewater). The various prototypes were able to provide for the disinfection of pathogens, reduction of chemical oxygen demand (COD), [NH3], and color at an average energy consumption of 35 Wh L-1. The treated wastewater was recycled for use as toilet flushing water.
\r\n\r\nThe addition of a microbial fuel cell system for urine pre-treatment was investigated to lower the overall energy consumption of the Solar Toilets. The microbial fuel cell system used consisted of two stacks of 32 cells connected in parallel. An average power density of 23 mW m\u20112 was produced at an effective current density of 65\u00a0mA\u00a0m\u20112 for more than 120 days. [NH3], total inorganic carbon, COD, and total organic carbon levels were monitored frequently to understand the chemical energy conversion to electricity as well as to determine the best electrical configuration of the stacks. Archaeal and bacterial population on selected anode felts and in the anolyte of both stacks were investigated as well.
\r\n\r\nIn addition to treating toilet wastewater, pilot-scale and bench-scale experiments demonstrated that electrolysis can remove phosphate by cathodic precipitation as hydroxyapatite at no additional energy cost. Phosphate removal could be predicted based on initial phosphate and calcium concentrations, and up to 80% total phosphate removal was achieved. While calcium was critical for phosphate removal, magnesium and bicarbonate had only minor impacts on phosphate removal rates at concentrations typical of toilet wastewater.
" }, { "name": "Dou, Nicholas Gang", "degree": "PhD", "year": "2018", "title": "Thermal Transport in Three-Dimensional Nanoarchitected Materials", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022018-070416991", "creators": [ { "name": { "family": "Dou", "given": "Nicholas Gang" }, "id": "Dou-Nicholas-Gang", "orcid": "0000-0001-8199-5588", "display_name": "Dou, Nicholas Gang" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/TPC8-VH59", "abstract": "Materials that simultaneously possess ultralow thermal conductivity, high stiffness, and damage tolerance are highly desirable for engineering applications. However, this combination of properties has never been demonstrated in a single material because thermal and mechanical properties are coupled in most fully dense and porous solids. A new class of lattice materials with nanoscale features, called nanolattices, can fill this void in the material property space by virtue of their architecture and nanoscale dimensions. Extensive work on nanolattice mechanical properties report their excellent stiffness-to-density ratio and recoverability from large compressive strains. In contrast, the framework for studying their thermal properties has not been established. Our work develops the computational and experimental tools necessary to study heat conduction in nanoarchitected materials and applies those tools to prove the viability of octet-truss nanolattices as multifunctional thermal insulators.
\r\n\r\nWe implement significant improvements to a phonon Monte Carlo method to solve the Boltzmann transport equation (BTE) in highly complex geometries like the octet-truss. No prior works solve the BTE in a domain as intricate as a nanolattice, so we create a geometry representation scheme that can model any arbitrary 3-D body. Our enhanced variance-reduced Monte Carlo code incorporates this scheme, allowing us to predict the thermal conductivity of nanolattices and analyze the phonon transport behavior in them. Results suggest that hollow-beam silicon nanolattices indeed reach ultralow thermal conductivities. Based on Monte Carlo and finite element simulations, we develop a predictive thermal conductivity model that accounts for both diffusive and radiative phonon transport in nanolattices.
\r\n\r\nWe also devise custom modifications to the 3\u03c9 method to experimentally measure the thermal conductivity of additively manufactured nanolattices. Since the serial fabrication process of nanolattices makes it costly to cover large areas, we design a specialized 3\u03c9 sample that minimizes the required structure size while maintaining good experimental sensitivity. We derive a new thermal model to account for conductive losses through the heater line in our novel sample geometry. 3\u03c9 measurements and compression tests of hollow-beam alumina nanolattices show that they combine ultralow thermal conductivity with excellent mechanical stiffness and resilience, which proves that nanolattices occupy a previously unreachable region in material property space. Our work provides motivation to further investigate and improve the thermal properties of architected materials.
\r\n" }, { "name": "Floyd, Michael Cameron Dawley", "degree": "PhD", "year": "2018", "title": "Development of Ferromagnetic Metallic Glasses into Low Loss Power Transformer Cores", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262017-091901955", "creators": [ { "name": { "family": "Floyd", "given": "Michael Cameron Dawley" }, "id": "Floyd-Michael-Cameron-Dawley", "display_name": "Floyd, Michael Cameron Dawley" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Demetriou", "given": "Marios D." }, "id": "Demetriou-M-D", "role": "member", "display_name": "Demetriou, Marios D." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9QF8R27", "abstract": "Currently, 3% of energy losses in the U.S. electrical grid occur at power transformers. With a transition to Metglas, transformer efficiency could be increased, but is Metglas the best replacement material for power transformers?
\r\n\r\nWith this in mind we develop a Fe-based metallic glass for its glass forming ability and soft magnetic properties. During this development we identify a redox reaction of boron oxide by Si during melt fluxing of the Fe-based glass, which promotes an unexpected exchange of Si and B in the alloy. Taking this reaction into account, a unique optimization strategy is implemented, enabling oxide purification of the melt coupled with a significant but predictable shift in composition. This leads to an optimized Fe-based glass demonstrating a global peak in glass forming ability. Following boron oxide fluxing in the high temperature melt, alloy with composition Fe57.5Co20.2Si10.2B2.05P10.05 transforms to Fe57Co19.2Si6.8B7.4P9.6, and increases its critical rod diameter from 1 mm to 5 mm. The alloy also demonstrates excellent soft ferromagnetic performance characterized by a magnetic saturation of 1.53 T.
\r\n\r\nWhile developing the above alloy, we also analyzed the effect of varying thickness of a Fe68Mo4Ni3Co5Si1P11.5C5B2.5 transformer core as a function of frequency to discover if there was a minimum in the losses. We did not find a single minimum, but found that the optimal thickness exhibits a logarithmic dependency on frequency. This dependence suggests the optimal thickness of a core ranges from 100\u2212400\u03bcm, instead of in the < 50\u03bcm range currently used. These larger optimal thicknesses are unexpected if anomalous losses are not considered, but the dominance of the anomalous losses at low frequencies, or for thin samples, validates the need for thicker power transformers. While other amorphous metals and casting techniques will yield varying results, the logarithmic dependence on frequency and the 100\u2212400\u03bcm optimal thickness range should be broadly applicable.
\r\n" }, { "name": "Fragoso, Anthony Thomas", "degree": "PhD", "year": "2018", "title": "Egospace Motion Planning Representations for Micro Air Vehicles", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10242017-193520989", "creators": [ { "name": { "family": "Fragoso", "given": "Anthony Thomas" }, "id": "Fragoso-Anthony-Thomas", "orcid": "0000-0002-5805-9668", "display_name": "Fragoso, Anthony Thomas" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "role": "member", "display_name": "Chung, Soon-Jo" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Matthies", "given": "Larry H." }, "id": "Matthies-L-H", "role": "member", "display_name": "Matthies, Larry H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9GX48RJ", "abstract": "Navigation of micro air vehicles (MAVs) in unknown environments is a complex sensing and trajectory generation task, particularly at high velocities. In this work, we introduce an efficient sense-and-avoid pipeline that compactly represents range measurements from multiple sensors, trajectory generation, and motion planning in a 2.5\u2013dimensional projective data structure called an egospace representation. Egospace coordinates generalize depth image obstacle representations and are a particularly convenient choice for configuration flat mobile robots, which are differentially flat in their configuration variables and include a number of commonly used MAV plant models. After characterizing egospace obstacle avoidance for robots with trivial dynamics and establishing limits on applicability and performance, we generalize to motion planning over full configuration flat dynamics using motion primitives expressed directly in egospace coordinates. In comparison to approaches based on world coordinates, egospace uses the natural sensor geometry to combine the benefits of a multi-resolution and multi-sensor representation architecture into a single simple and efficient layer.\r\nWe also present an experimental implementation, based on perception with stereo vision and an egocylinder obstacle representation, that demonstrates the specialization of our theoretical results to particular mission scenarios. The natural pixel parameterization of the egocylinder is used to quickly identify dynamically feasible maneuvers onto radial paths, expressed directly in egocylinder coordinates, that enable finely detailed planning at extreme ranges within milliseconds. We have implemented our obstacle avoidance pipeline with an Asctec Pelican quadcopter, and demonstrate the efficiency of our approach experimentally with a set of challenging field scenarios. The scalability potential of our system is discussed in terms of sensor horizon, actuation, and computational limitations and the speed limits that each imposes, and its generality to more challenging environments with multiple moving obstacles is developed as an immediate extension to the static framework." }, { "name": "Gat, Ilana Batya", "degree": "PhD", "year": "2018", "title": "Investigations of Incompressible Variable-Density Turbulence in an External Acceleration Field", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12052017-154614667", "creators": [ { "name": { "family": "Gat", "given": "Ilana Batya" }, "id": "Gat-Ilana-Batya", "orcid": "0000-0003-0223-0507", "display_name": "Gat, Ilana Batya" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Matheou", "given": "Georgios" }, "id": "Matheou-Georgios", "role": "member", "display_name": "Matheou, Georgios" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9JM27V7", "abstract": "Of interest to turbulence modeling is the behavior of variable-density flow at high Reynolds numbers - a flow difficult to model. This thesis provides insight into variable-density flow behavior by examining the dynamics and mixing of variable-density turbulence subject to an externally imposed acceleration field. The flow is studied in the zero-Mach-number limit with a series of direct numerical simulations. The flow configuration consists of alternating slabs of high- and low-density fluid in a triply periodic domain. Density ratios in the range of 1.005 to 10 are investigated. The flow produces temporally evolving shear layers.
\r\n\r\nA perpendicular mean density\u2013pressure gradient is maintained as the flow evolves, with multi-scale baroclinic torques generated in the turbulent flow that ensues. For all density ratios studied, the simulations attain Reynolds numbers at the beginning of the fully developed turbulence regime.
\r\n\r\nAn empirical relation for the convection velocity predicts the observed entrainment-ratio and dominant mixed-fluid composition statistics. Two mixing-layer temporal evolution regimes are identified: an initial diffusion-dominated regime with a growth rate with the square-root of time followed by a turbulence-dominated regime with a cubic growth rate in time. In the turbulent regime, composition probability density functions within the shear layers exhibit a slightly tilted ('non-marching') hump, corresponding to the most probable mole fraction. The shear layers preferentially entrain low-density fluid by volume at all density ratios, which is reflected in the mixed-fluid composition.
\r\n\r\nThe mixed-fluid orientations of vorticity, baroclinic torques, density gradients, and pressure gradients are presented. Baroclinic torques, the cross product of the density and pressure gradients, tend to be aligned with positive or negative vorticity direction, with vorticity preferentially aligning with the intermediate eigenvector of the local strain-rate tensor, with some variance.
" }, { "name": "Gori, Marcello", "degree": "PhD", "year": "2018", "title": "Laboratory Investigation of Shear Ruptures: Supersonic Propagation and Nucleation by Fluid Injection", "advisor": "Rosakis, Ares J.; Lapusta, Nadia", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-150338327", "creators": [ { "name": { "family": "Gori", "given": "Marcello" }, "id": "Gori-Marcello", "orcid": "0000-0002-7380-3723", "display_name": "Gori, Marcello" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "co-advisor", "display_name": "Lapusta, Nadia" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AH9X-V905", "abstract": "Shear rupture nucleation and dynamic propagation is a challenging, non- linear, highly interactive process with important practical implications. Here we focus on two aspects of this problem: propagation speeds and shock front radiation from the dynamic crack tip as well as nucleation of dynamic rupture due to fluid injection.
\r\n\r\nSpontaneously propagating cracks in solids emit pressure and shear waves and are, in part, driven by energy transfer due to them. When a shear crack propagates faster than the shear wave speed of the material, the coalescence of the shear wavelets emitted by the near-crack-tip region forms a shock front that significantly concentrates particle motion. The equivalent scenario involving a pressure shock front should not be possible, since cracks should not be able to exceed the pressure wave speed, at least in an isotropic linear-elastic solid. Here we present full-field experimental evidence of dynamic shear cracks in viscoelastic polymers that result in the formation of a pressure shock front, in addition to the shear one. In that sense, the crack appears to be supersonic. The apparent violation of classic theories is explained by the strain-rate-dependent material behavior of polymers: the increased wave speeds within the highly- strained region around the crack tip allow for supersonic crack propagation with respect to the (lower) wave speeds at short distances away from the interface, resulting in the formation of the pressure shock front. The crack speed remains below the pressure wave speed prevailing locally, about its tip, in agreement with basic physics and energy considerations of linear-elastic theories.
\r\n\r\nWe find that the shock fronts emitted by the shear cracks in the viscoelastic materials are curved and propose a novel method to quantify the viscoelastic wave speeds of the solids in the dynamic range of strain rates based on the curvature. Only kinematic relationships are used in the method, without the need for the constitutive relationship of the material. Measuring or inferring the material properties at elevated strain rates in viscoelastic solids is a difficult task, because of practical limitations of obtaining accurate measurements in that regime. Under the quasi-elastic solid approximation, in which the strain-rate history is neglected, we use the pressure-wave speed measurements to infer the associated value of the Young\u2019s modulus, estimated by assuming a constant value of the Poisson\u2019s ratio. We complement these results with the characterization of the Young\u2019s modulus at lower strain rates via canonical compressive tests. Our results not only confirm previous findings that the Young\u2019s modulus dependence on the strain rate in PMMA is significant but also demonstrate that its variation is more pronounced in the dynamic strain-rate range, with important consequences for the design of structures employing viscoelastic materials that are required to withstand elevated strain rates.
\r\n\r\nThe second part of the study concentrates on the nucleation of shear dynamic rupture due to fluid injection or, more broadly, on the interaction of frictional faulting with fluids. Fluid overpressure is recognized to play a fundamental role in promoting fault motion. A large number of observations has shed light on the interplay between fluids and faulting, both in natural events and in earth-quakes induced by human activities, such as wastewater disposal associated with oil and gas extraction. Fluids can induce a variety of earthquake source behaviors ranging from unstable, dynamic motions to stable, quasi-static ones, which a number of field studies suggests that can coexist on the same fault areas at different times, depending on the local conditions. In fact, a higher pore pres-sure plays the dual role of reducing the frictional strength of the fault and of increasing the nucleation size, e.g., the critical length for a shear crack to transition from quasi-static to dynamic motions. However, due to the complexity of the frictional problem at the fault interface, the understanding of which of these two effects prevails remains elusive. The assumption of a critical nucleation length represents a powerful, yet simplified concept, which currently does not include the dependence on the rate of the pore pressure increase.
\r\n\r\nHere, we explore the effect of the rate of the pore pressure increase on the rupture nucleation. We find that elevated injection rates induce triggering of the rupture at lower pressure values and minimal volumes of the injected fluid, if compared to slow injection rates. For the slow injection rates, we experimentally observe a much larger portion of interface wetted by the fluid and a phase of accelerated slip prior to the dynamic event (quasi-dynamic nucleation process). In some cases, we record much smaller foreshock-like events at the injection site. These findings suggest the presence of a prominent quasi-static nucleation process over the interface. In cases of rapid pore pressure increase, the nucleation process is much shorter in time and much more compact in space, being highly concentrated around the injection location. The dynamic events, once initiated, are qualitatively similar across different injection rates, but quantitatively different, with the slow-injection ones experiencing higher stress drops and higher slips, perhaps due to the effect of fluids on the friction properties.\r\nThese findings suggest the need to develop nucleation size estimates that include the rate of the pore pressure increase and motivate further investigation of how friction properties depend on the presence of fluids. The details of the obtained experimental findings, once analyzed through numerical modeling, will place important constrains on the forms of the acceptable friction laws, including the effects of pore fluid pressure and its rate of change.
" }, { "name": "Goza, Andres Jared", "degree": "PhD", "year": "2018", "title": "Numerical Methods for Fluid-Structure Interaction, and their Application to Flag Flapping", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122017-095438989", "creators": [ { "name": { "family": "Goza", "given": "Andres Jared" }, "id": "Goza-Andres-Jared", "display_name": "Goza, Andres Jared" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z95T3HPB", "abstract": "This thesis is divided into two parts. Part I is devoted to the development of numerical techniques for simulating fluid-structure interaction (FSI) systems and for educing important physical mechanisms that drive these systems\u2019 behavior; part II discusses the application of many of these techniques to investigate a specific FSI system.
\r\n\r\nWithin part I, we first describe a procedure for accurately computing the stresses on an immersed surface using the immersed-boundary method. This is a key step to simulating FSI problems, as the surface stresses simultaneously dictate the motion of the structure and enforce the no-slip boundary condition on the fluid. At the same time, accurate stress computations are also important for applications involving rigid bodies that are either stationary or moving with prescribed kinematics (e.g., characterizing the performance of wings and aerodynamic bodies in unsteady flows or understanding and controlling flow separation around bluff bodies). Thus, the method is first formulated for the rigid-body prescribed-kinematics case. The procedure described therein is subsequently incorporated into an immersed boundary method for efficiently simulating FSI problems involving arbitrarily large structural motions and rotations.
\r\n\r\nWhile these techniques can be used to perform high-fidelity simulations of FSI systems, the resulting data often involves a range of spatial and temporal scales in both the structure and the fluid and are thus typically difficult to interpret directly. The remainder of part I is therefore devoted to extending tools regularly used for understanding complex flows to FSI systems. We focus in particular on the application of global linear stability analysis and snapshot-based data analysis (such as dynamic mode decomposition and proper orthogonal decomposition) to FSI problems. To our knowledge, these techniques had not been applied to deforming-body problems in a manner that that accounts for both the fluid and structure leading up to this work.
\r\n\r\nThroughout part I, our methods are derived in the context of fairly general FSI systems and are validated using results from the literature for flapping flags in both the conventional configuration (in which the flag is pinned or clamped at its leading edge with respect to the oncoming flow) and the inverted configuration (in which the flag is clamped at its trailing edge). In part II, we apply many of the techniques developed in part I to uncover new physical mechanisms about inverted-flag flapping. We identify the instability-driving mechanism responsible for the initiation of flapping and further characterize the large-amplitude and chaotic flapping regimes that the system undergoes for a range of physical parameters.
" }, { "name": "Grivel, Morgane Anne Marie", "degree": "PhD", "year": "2018", "title": "On the Effect of Large-Scale Patterned Wettability on Contact Line Hydrodynamics", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182017-103752052", "creators": [ { "name": { "family": "Grivel", "given": "Morgane Anne Marie" }, "id": "Grivel-Morgane-Anne-Marie", "orcid": "0000-0002-4391-799X", "display_name": "Grivel, Morgane Anne Marie" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9736P2V", "abstract": "Numerous studies have investigated how liquid water behaves on solid surfaces with uniformly hydrophilic or uniformly hydrophobic wetting properties. In particular, uniformly hydrophobic surfaces have been widely studied for modifying flow behavior of rivulets and drops at smaller scales, as well as for drag reduction on ships or other free-surface-piercing bodies at larger scales. Despite the extensive body of work on surfaces with uniform wetting properties, minimal work has been done to investigate how combining hydrophilic and hydrophobic regions onto a single surface to create macroscopic non-uniform wetting properties affects flows. Research in this vein has predominantly focused on low Reynolds number flows, such as in microfluidic channels or droplet impacts.
\r\n\r\nThis thesis expands on the current literature by investigating contact line dynamics and global flow behavior on surfaces with larger-scale non-uniform wetting properties. Experiments were first carried out to study thin sheet flow down an inclined plate at Re ~ 50 - 1200. The plate's wetting condition was changed by introducing alternating hydrophilic and hydrophobic bands 2-25 mm wide oriented at different angles with respect to the flow direction. Results show that the contact line of such flows is heavily modified compared to the uniform cases. At low Reynolds numbers, large-scale wettability heterogeneities are observed to tune the fingering instability wavelength if the bands are parallel to the flow direction and to dampen finger oscillations if the bands are perpendicular to the flow direction. At higher Reynolds numbers, roller structures are introduced at every hydrophilic-to-hydrophobic junction, modifying the global flow morphology. Entrained air bubbles are also captured and observed to coalesce if the bands are perpendicular to the flow direction.
\r\n\r\nThese experiments were then extended to a surface-piercing hydrofoil coated with alternating hydrophilic and hydrophobic bands. Experiments were run in Caltech's Free Surface Laboratory water tunnel for Re on the order of 104 to 105. The experiments demonstrate that the contact line is modulated in this context, alternating from concave to convex over the different wettability regions. The modulation of the contact line propagates to the rest of the water free-surface via the generation of standing waves and further modifies the free-surface separation point's location and steadiness. In addition, changes in wettability are observed to generate side force, which is of interest for vessel maneuvers in naval applications.
" }, { "name": "Harfouche, Mark", "degree": "PhD", "year": "2018", "title": "The Coherence Collapse Regime of High-Coherence Si/III-V Lasers and the Use of Swept Frequency Semiconductor Lasers for Full Field 3D Imaging", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:10242017-104926655", "creators": [ { "name": { "family": "Harfouche", "given": "Mark" }, "id": "Harfouche-Mark", "orcid": "0000-0002-4657-4603", "display_name": "Harfouche, Mark" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9W66J07", "abstract": "The semiconductor laser is the linchpin of optical communication and is now also penetrating a wide spectrum of new applications such as biomedical sensing, coherent communication, metrology, and time keeping. These require a higher degree of temporal coherence than is available from the present generation. Recently, it has been proposed and shown that heterogeneously integrated lasers on silicon and InGaAsP can be used to design high coherence single mode lasers with a much narrower linewidth than their all InGaAsP counterparts. Unfortunately, these lasers suffer from large thermal impedances and their optical feedback characteristics have not yet been explored. In the first part of this thesis, we will explore how flip chip bonding can help decrease the thermal impedance of these lasers to improve their overall performance and show that these lasers can provide up to 20 dB of optical isolation compared to their all III-V counterparts.
\r\n\r\nIn the second part of this thesis, we will report on the use of commercially available semiconductor lasers, in conjunction with an optical modulator to obtain high-resolution tomographic images in one shot without any moving parts. The electronic control over the imaged depth of this novel tomographic imaging camera enables it to monitor arbitrary depth slices in rapid succession over a depth range limited only by the coherence length of the laser. Not only does this imaging modality acquire the transverse image intensity (x,y) distribution of the light reflected from a particular depth, but also the phase of the reflected light enabling imaging beyond the conventional depth of field of the lens. This has important implications in applications requiring high lateral resolution images where the shallow depth of field would often require mechanical scanning of the lens elements to change the imaged depth.
" }, { "name": "Haw, Magnus Albert", "degree": "PhD", "year": "2018", "title": "Experimental and Numerical Studies of Cavities, Flows, and Waves in Arched Flux Ropes", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012018-131846705", "creators": [ { "name": { "family": "Haw", "given": "Magnus Albert" }, "id": "Haw-Magnus-Albert", "orcid": "0000-0001-5739-5160", "display_name": "Haw, Magnus Albert" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Fuller", "given": "James" }, "id": "Fuller-J", "orcid": "0000-0002-4544-0750", "role": "member", "display_name": "Fuller, James" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3AX5-EN61", "abstract": "This dissertation details various studies of arched flux ropes using both scalable laboratory experiments and numerical simulations. This work can be divided into three major classes: studies of flux rope motion and shape, development of supporting simulations, and development of new experimental diagnostics.
\r\n\r\nThe primary scientific results in this work are the characterization of new mechanisms for flux rope motion and morphology. These studies are done on two separate experiments, the single loop and double loop, which produce arched flux ropes with non-dimensional evolution equivalent to solar prominences. Measurements taken on these experiments characterize three flux rope mechanisms: (1) how variation in a flux rope minor radius can drive axial flows and collimation, (2) how non-uniform axial density can perturb flux rope shape and inhibit the kink instability, and (3) how changing flux rope current can repel background plasma and form density cavities around the flux rope. These mechanisms are each relevant to a different aspect of solar prominences: the collimation mechansim (1) can explain why solar loops are denser and more collimated than expected, the work on density perturbations (2) puts a higher limit on prominence stability, and the cavity mechanism (3) provides the first model to explain why coronal mass ejections (CMEs) are observed to have a three part structure.
\r\n\r\nTwo numerical simulations were developed in support of the experiments: a 3D magnetohydrodynamic (MHD) simulation of the single loop experiment and a 3D spline model simulating flux ropes as interacting current carrying wires. The MHD simulation uses the solver module from the Los Alamos COMPutational Astrophysics Simulation Suite (LA-COMPASS) to evolve B, v, rho, and P on a 96^3 Cartesian grid using the dimensionless ideal MHD equations. The resulting simulation has excellent agreement with experimental observations in shape, velocity, and magnetic field and quantitatively reproduces the mechanisms (2,3) observed in the single loop experiment. The spline simulation models the flux ropes experiments as plasma systems of thin current paths in a 3D space with no background plasma. This model is shown to be useful for reproducing flux rope evolution, testing new experimental configurations, evaluating the magnetic fields generated from complex 3D current paths, and testing the robustness of analytic flux rope models.
\r\n\r\nThe last body of work concerns the development of two novel diagnostics: a high frequency (1-100 MHz) wave probe designed to measure both the magnetic field B, and current density J, of passing waves and a high frequency (100 MHz) 1D coded aperture camera. The wave probe consists of four 3-axis Bdot-probes arranged in a tetrahedron. This additional spatial resolution allows the calculation of both J and the wavevector k. Measurements taken by this probe on the plasma jet experiment identify short whistler wave pulses emitted from magnetic reconnection events. These waves are identified by measurements of the background conditions, the wave polarization, and comparisons with the theoretical whistler dispersion relation. The pulses also occur simultaneously with bursts of X-ray emissions, indicating that non-MHD physics (i.e. two-fluid or kinetic effects) are important during the reconnection event. The coded aperture camera is a fast (100MHz) 1D visible light system developed as a prototype for imaging plasma experiments in the EUV/X-ray bands. In the low signal limit, the system demonstrates 40-fold increase in throughput and a signal-to-noise gain of ~7 over that of a pinhole camera of equivalent parameters.
" }, { "name": "Hoff, Andrew Taylor", "degree": "PhD", "year": "2018", "title": "Understanding the Origin of Glass Forming Ability in Metallic Glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082018-081351539", "creators": [ { "name": { "family": "Hoff", "given": "Andrew Taylor" }, "id": "Hoff-Andrew-Taylor", "display_name": "Hoff, Andrew Taylor" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z7Y5-0B62", "abstract": "The glass forming ability of metallic glasses has been one of their most studied yet least understood properties. Crystal nucleation in a recently development Ni-based metallic glass was studied by undercooling in a DSC under a variety of conditions and showed stochastic very deep undercooling behavior. The glass forming ability of a family of Ni-based alloys was analyzed and was found to depend only on two experimentally accessible factors, the reduced glass transition temperature and the liquid fragility. Neutron scattering experiments showed that in two model glass formers vibrational entropy had essentially no change through the glass transition, demonstrating that the change in entropy through the glass transition is due almost entirely to configurational entropy. The configurational enthalpy of a pair of recently developed Pt-based metallic glasses show almost no change in the undercooled liquid between the liquidus and TTT-nose, demonstrating the inability of current models to explain the thermodynamics of supercooled liquids. " }, { "name": "Horie, Yu", "degree": "PhD", "year": "2018", "title": "Controlling the Flow of Light Using High-Contrast Metastructures", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:09202017-124555409", "creators": [ { "name": { "family": "Horie", "given": "Yu" }, "id": "Horie-Yu", "orcid": "0000-0001-7083-1270", "display_name": "Horie, Yu" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "chair", "display_name": "Faraon, Andrei" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z94X5604", "abstract": "A new class of planar optical components and devices has emerged using subwavelength metastructures with a strong contrast in refractive indices. High-contrast metastructures have shown promises to manipulate optical fields in an extraordinary way and to replace conventional bulky optical elements by their low-profile analogs, typically with subwavelength-scale features. We elucidate the underlying principle, how these seemingly low-profile geometries render unique optical responses, using the coupled-mode analysis in a multimode waveguide. Moreover, strong field localization in high-index structures allows us to interpret each single element in the metastructures as a low-quality-factor resonator (or a localized scatterer), permitting us to realize designer surface that shapes phase, amplitude, and polarization of light in free space, also known as an optical metasurface. The remainder of the thesis is devoted to explore novel applications in optics using high-contrast metastructures. One of the particularly interesting applications is to use them in an optical resonator. Specifically, we demonstrate to incorporate high-contrast subwavelength grating reflectors and dielectric metasufaces in a vertical Fabry\u2013Perot cavity, and show that we can flexibly tune the resonance frequency by the subwavelength patterning. With this technique, we envision the realization of compact, on-chip spectrometers when integrating them on a photodetector array. Secondly, we investigate the use of high-contrast subwavelength gratings in visible wavelengths. We perform the optimization of their geometries and demonstrate a set of RGB color filters, down to near a micrometer in the pixel size. This platform exhibits unique performances such as high efficiency, angular insensitivity, and color tunability by the design. A novel device concept is also explored, where a high-contrast subwavelength grating reflector is integrated on a silicon platform to constitute an active resonant antenna, enabling high-speed, phase-dominant modulation by means of thermo-optic effect of silicon. We demonstrate an array of such active antennas, yielding a beam deflection capability. This justifies the robustness of our device design, enabling a large-scale integration of high-speed, phase-dominant spatial light modulators. Finally, we introduce a disorder-engineered metasurface in the context of wavefront shaping. Recently, wavefront shaping with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics, but translating this class of technology into a practical use has remained challenging due to enormous amounts of information needed to be characterized as the input-output responses. As a paradigm shift, we propose the use of disorder-engineered metasurface in wavefront shaping, where the disorder is programmatically designed and makes the system characterization-free prior to use. With this approach, we demonstrate high numerical aperture focusing in an extended volume as well as wide-field fluorescence imaging with unprecedented performances.
" }, { "name": "Jiang, Jingjing", "degree": "PhD", "year": "2018", "title": "Interfacial and Stability Studies of Photocathodes for Hydrogen Evolution", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112018-153323554", "creators": [ { "name": { "family": "Jiang", "given": "Jingjing" }, "id": "Jiang-Jingjing", "orcid": "0000-0002-3109-229X", "display_name": "Jiang, Jingjing" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "chair", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." } ], "option_major": [ "matsci" ], "doi": "10.7907/SBJ9-D062", "abstract": "Photoelectrochemical (PEC) water splitting is a promising way to generate clean hydrogen fuel from water and sunlight. The ideal photocathodes for hydrogen evolution reaction (HER) should have good electrical contact and mechanical adhesion on the interface between the semiconductor and the catalyst, and be stable during operation. However, the interfacial properties and the stability have not been intensively studied. We investigated the electrical and mechanical properties on the nanoscale of the interface of commonly used Si/Pt nanoparticles (Pt-NPs) electrodes with Pt-NPs as a catalyst, and showed that the Pt-NPs have a weaker adhesion in electrolyte than in air, and less than half of the Pt-NPs carry high currents, limiting the performance of the common Si/Pt-NPs electrodes. Furthermore, we explored the interfacial engineering of using TiO2 deposited by atomic layer deposition (ALD), and showed that annealed TiO2 led to higher open circuit voltages than the as grown ones by the possible formation of an interfacial Si-O-Ti mixture layer. Besides, the stability and corrosion behavior of CdTe electrodes for HER in the dark was studied in 1.0 M H2SO4(aq) and 1.0 M KOH(aq). The conditions studied herein include the electrochemical corrosion when biased at -100 mV vs. the reversible hydrogen electrode (RHE), the chemical corrosion when left at open circuit voltage (OCV), and the electrochemical corrosion with an active HER Pt catalyst overlayer when biased at -100 mV vs. RHE. The corrosion comes mostly from chemical corrosion and is reduced at negative bias in electrochemical condition. With a Pt catalyst overlayer at -100 mV vs. RHE, the corrosion rate is further reduced, indicating the promising utilization of CdTe for HER in PEC cells.
" }, { "name": "Jones, William Maxwell", "degree": "PhD", "year": "2018", "title": "Nanoscale Field Emission Devices", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132017-132404589", "creators": [ { "name": { "family": "Jones", "given": "William Maxwell" }, "id": "Jones-William-Maxwell", "orcid": "0000-0002-8610-2176", "display_name": "Jones, William Maxwell" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "DeRose", "given": "Guy A." }, "id": "DeRose-Guy-A", "role": "member", "display_name": "DeRose, Guy A." }, { "name": { "family": "Neches", "given": "Philip M." }, "id": "Neches-Philip-M", "role": "member", "display_name": "Neches, Philip M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z94B2ZHZ", "abstract": "This thesis outlines work done to produce in-plane nanoscale field emission devices. Field emission, the process of quantum tunneling electrons from a conductor into a vacuum, has been theorized as a device concept for almost as long as integrated circuits have existed. This is because the micro- and nanoscale dimensions of integrated circuits make field emission possible at modest voltages, and because the physics of field emission and conduction in a vacuum channel suggest that field emission devices can operate at extremely high frequencies and in harsh environments where CMOS devices face challenges. Yet despite many attempts to make practical field emission devices none have risen to the level of commercial products. These attempts were stymied by short lifetimes, high operating voltages, and the necessity for vacuum enclosure. In this thesis work, I outline how new fabrication technologies like high resolution electron beam lithography, atomic layer deposition, and refinement in reactive ion etching make lateral field emission devices with extremely short vacuum channels practical. The demonstrated devices can operate at near CMOS voltages and at atmospheric pressures, and are robust to emitting tip destruction. These devices are prime candidates for integration into demonstration circuits.
\r\n\r\nThe second part of this thesis outlines work done in an emerging field to combine field emission with plasmonics for practical devices. The tunneling process in field emission depends exponentially on the magnitude of the instantaneous electric field, either static or time-varying, at the emitting surface. While it has long been known that using extremely powerful pulsed lasers one can field emit electrons from a metallic surface, the combination of plasmonics into a field emitting device has the potential to dramatically lower the incident optical power needed to produce field emission. This could enable extremely fast opto-electronic devices. This thesis presents work in progress to realize a plasmonically enhanced field emission opto-electronic modulator that is designed to operate at 1550 nm and is integratable with existing silicon photonics platforms.
" }, { "name": "Kang, Stephen Dongmin", "degree": "PhD", "year": "2018", "title": "Charge Transport Analysis Using the Seebeck Coefficient-Conductivity Relation", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292018-140812451", "creators": [ { "name": { "family": "Kang", "given": "Stephen Dongmin" }, "id": "Kang-Stephen-Dongmin", "orcid": "0000-0002-7491-7933", "display_name": "Kang, Stephen Dongmin" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "orcid": "0000-0003-1414-8682", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "orcid": "0000-0003-1414-8682", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/ZAQP-MN67", "abstract": "Charge transport properties like electrical conductivity or the Seebeck coefficient are defined phenomenologically from near-equilibrium thermodynamics, while the analysis or modeling of them often involves a physical model based on mechanistic principles. In other words, physical models connect microscopic and physical parameters to phenomenological and experimental properties. One of the challenges is that the complexity of solid state requires many physical parameters, whereas the measurable properties which help to determine those parameters are limited. The interrelations of measured properties are very important to overcome this challenge, but this aspect is not well recognized in conventional analysis themes. In this thesis, the concept of using a phenomenological transport function is devised to help combine a collection of measurements into an intermediate level of phenomenology, relevant for Fermion transport but not dependent on a particular physical model. This phenomenological transport function can be determined by examining the electrical conductivity, the Seebeck coefficient, and potentially the Lorenz number. Because the phenomenological transport function combines information from a set of multiple measurable properties, a direct comparison to the transport function of a physical model serves as a strong test for the model.
\r\n\r\nParticular usefulness comes from extracting transport functions from the Seebeck coefficient-conductivity relation, especially in doped semiconductors. This approach is applied to contrast CeO2-x and n-type SrTiO3 as narrow and dispersive transport function materials, each consistent with polaron and band conduction, respectively. In band conductors such as SrTiO3 and Mg3Sb2, the approach is used to test and refute previous claims about the scattering mechanism and find consistency with deformation potential scattering in both cases. In conducting polymers, which do not resemble any other type of conventional conductors, the Seebeck-conductivity relation reveals a qualitative disagreement with the commonly cited Mott's models. For the case of Cu2Se, a peculiar band conductor which shows anomalies in the Hall measurement of the high temperature phase and also in other transport properties at the phase transition, the transport function approach is applied as a workaround for modeling. On the practical side, for thermoelectric applications, the transport function approach is used to characterize material quality factors for both majority carrier conduction and bipolar conduction. Finally, experimental efforts for improving the accuracy and applicability of Seebeck measurements is discussed.
" }, { "name": "Kawamoto, Reid Yoshio", "degree": "PhD", "year": "2018", "title": "The Avatar Paradigm in Granular Materials", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072018-230955387", "creators": [ { "name": { "family": "Kawamoto", "given": "Reid Yoshio" }, "id": "Kawamoto-Reid-Yoshio", "orcid": "0000-0002-4936-5321", "display_name": "Kawamoto, Reid Yoshio" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/4fr8-bn91", "abstract": "Granular materials are ubiquitous in both everyday life and various engineering and industrial applications, ranging from breakfast cereal to sand to rice to medical pills. However, despite the familiarity of granular materials, their behavior is complex and efforts to characterize them are currently broad research areas in physics and engineering. Research of granular materials, as is the case with the research of other engineering materials such as rocks and metals, is beset with two gaps: the gap between reconciling macroscopic behavior with microscale (particle-scale, in the case of granular materials) behavior, and the gap between reconciling experimental and computational results. In this dissertation, we bridge these gaps through the \"avatar paradigm.\" The avatar paradigm is a two-step process that numerically characterizes (from experimental images) and simulates the shapes and behavior of individual particles, which we call avatars. First, we validate that our avatars are indeed capable of faithfully capturing particle kinematics and interparticle contact, then apply the characterization process, level set imaging (LS-imaging), to two experimental specimens to compute particle kinematics and contact statistics. We then detail a computational method, the level set discrete element method (LS-DEM), that is able to simulate the behavior of avatars, and apply it (and LS-imaging) to two other experimental specimens, calibrating the model to one specimen and using the results to predict the behavior of the other, thus providing some reconciliation between experimental and computational results. Finally, we use the avatar process to characterize and simulate yet another experimental specimen, this time analyzing the results at length scales ranging from particle behavior to local behavior to macroscopic behavior, further validating the ability of the avatar paradigm to bridge experiments and computations and showing its power to reconcile different length scales." }, { "name": "Kim, Dennis Sungtae", "degree": "PhD", "year": "2018", "title": "Silicon Revisited: Understanding Pure Phonon Anharmonicity and the Effects on Thermophysical Properties", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechThesis:02202018-144811029", "creators": [ { "name": { "family": "Kim", "given": "Dennis Sungtae" }, "id": "Kim-Dennis-Sungtae", "orcid": "0000-0002-5707-2609", "display_name": "Kim, Dennis Sungtae" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Nadj-Perge", "given": "Stevan" }, "id": "Nadj-Perge-S", "orcid": "0000-0002-2394-9070", "role": "member", "display_name": "Nadj-Perge, Stevan" }, { "name": { "family": "Hellman", "given": "Bjoern O." }, "id": "Hellman-B-O", "role": "member", "display_name": "Hellman, Bjoern O." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9C827HR", "abstract": "Phonons, quantized lattice vibrations, govern most of the thermophysical properties of solid-state materials such that understanding the temperature dependent lattice dynamics is of great technological importance. I performed inelastic neutron scattering measurements at the Spallation Neutron Source on ARCS, a wide-angular chopper spectrometer, to measure phonon dispersions and density of states over a wide range of temperatures. Large phonon anharmonicities manifested by phonon energy shifts and broadenings were observed in both measured phonon dispersions and phonon density of states. The sources of deviations from the simple harmonic model with temperature were elucidated using experimentally assessed lattice dynamics coupled with ab initio methods. Pure anharmonicity dominates the changes in lattice dynamics with temperature and therefore drive the entropy and thermophysical properties of thermal expansion and thermal conductivity. Crystal structure, anharmonicity, and nuclear quantum effects all play important roles in the thermal expansion of silicon, and a simple mechanical explanation is inappropriate. The quantum effect of nuclear vibrations is also expected to be important for thermal expansion of many materials. My experimental techniques capture the linewidth broadenings from phonon anharmonicity needed to calculate thermal conductivity. The methods developed for data reduction on single crystal inelastic neutron scattering data and predicting macroscopic quantities should also be useful for understanding microscopic mechanisms behind thermophysical properties for materials." }, { "name": "Kim, Dongwan", "degree": "PhD", "year": "2018", "title": "Frequency Noise Control of Heterogeneous Si/III-V Lasers ", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262017-003847721", "creators": [ { "name": { "family": "Kim", "given": "Dongwan" }, "id": "Kim-Dongwan", "orcid": "0000-0002-5661-2503", "display_name": "Kim, Dongwan" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z90Z71G6", "abstract": "Narrow-linewidth lasers have many applications including optical telecommunication, laser spectroscopy, atomic clocks, and light detection and ranging. Conventionally, narrow linewidth lasers have been realized in the form of fiber-based or solid-state lasers. These lasers are bulky and relatively expensive, limiting their usage as bench-top systems in laboratory environments. Historically, semiconductor lasers, also known as laser diodes, have served applications where size and cost are important factors, including fiber optic communications. The linewidth of the semiconductor lasers, however, has been limited to the MHz-level, due to high loss in laser cavities and small size.
\r\n\r\nRecently, reduction of the frequency fluctuations in the semiconductor lasers has been achieved, obtaining tens of kHz linewidth, using the heterogeneous Silicon/III-V platform with a new design strategy. In this design, the majority of the optical energy is stored in the low-loss high-Q silicon resonator away from the high-loss III-V active region, requiring the minimal gain from the active region to overcome the reduced modal loss.
\r\n\r\nThis work explores the new design strategy further, and demonstrates theoretically and experimentally that the strategy eliminates the frequency fluctuations arising from the amplitude-phase coupling by placing a relaxation resonance frequency at frequencies of a few hundred MHz. Consequently, it becomes possible to obtain a semiconductor laser device possessing sub-kHz quantum-limited linewidths at frequencies of a few GHz (the frequencies of interest in optical telecommunication).
\r\n\r\nIn addition to the frequency noise reduction, the strategy turns out to have the additional benefit of accomplishing a coherent and stable lasing operation, even under external reflections. Thus, the new design strategy has the potential to replace the costly, but currently indispensable external optical isolators, which have been traditionally used to maintain the consistent performance of semiconductor lasers in the presence of external reflection.
\r\n\r\nThis work paves the way for the design of narrow-linewidth and stable semiconductor lasers that can function without the use of the bulky and costly external components, such as external cavities or optical isolators.
" }, { "name": "Kirchdoerfer, Trenton Thomas", "degree": "PhD", "year": "2018", "title": "Data Driven Computing", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:09122017-092017294", "creators": [ { "name": { "family": "Kirchdoerfer", "given": "Trenton Thomas" }, "id": "Kirchdoerfer-Trenton-Thomas", "orcid": "0000-0003-2290-1857", "display_name": "Kirchdoerfer, Trenton Thomas" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Z899MV", "abstract": "Data Driven Computing is a new field of computational analysis which uses provided data to directly produce predictive outcomes. This thesis first establishes definitions of Data-Driven solvers and working examples of static mechanics problems to demonstrate efficacy. Significant extensions are then explored to both accommodate noisy data sets and apply the deveoloped methods to dynamic problems within mechanics. Possible method improvements discuss incorporation of data quality metrics and adaptive data sampling, while new applications focus on multi-scale analysis and the need for public databases to support constitutive data collaboration.\r\n" }, { "name": "Korlakai Vinayak, Ramya", "degree": "PhD", "year": "2018", "title": "Graph Clustering: Algorithms, Analysis and Query Design", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:09222017-130217881", "creators": [ { "name": { "family": "Korlakai Vinayak", "given": "Ramya" }, "id": "Korlakai-Vinayak-Ramya", "orcid": "0000-0003-0248-9551", "display_name": "Korlakai Vinayak, Ramya" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9RR1WFK", "abstract": "A wide range of applications in engineering as well as the natural and social sciences have datasets that are unlabeled. Clustering plays a major role in exploring structure in such unlabeled datasets. Owing to the heterogeneity in the applications and the types of datasets available, there are plenty of clustering objectives and algorithms. In this thesis we focus on two such clustering problems: Graph Clustering and Crowdsourced Clustering.
\r\n\r\nIn the first part, we consider the problem of graph clustering and study convex-optimization-based clustering algorithms. Datasets are often messy -- ridden with noise, outliers (items that do not belong to any clusters), and missing data. Therefore, we are interested in algorithms that are robust to such discrepancies. We present and analyze convex-optimization-based clustering algorithms which aim to recover the low-rank matrix that encodes the underlying cluster structure for two clustering objectives: clustering partially observed graphs and clustering similarity matrices with outliers. Using block models as generative models, we characterize the performance of these convex clustering algorithms. In particular, we provide explicit bounds, without any large unknown constants, on the problem parameters that determine the success and failure of these convex approaches.
\r\n\r\nIn the second part, we consider the problem of crowdsourced clustering -- the task of clustering items using answers from non-expert crowd workers who can answer similarity comparison queries. Since the workers are not experts, they provide noisy answers. Further, due to budget constraints, we cannot make all possible comparisons between items in the dataset. Thus, it is important to design queries that can reduce the noise in the responses and design algorithms that can work with noisy and partial data. We demonstrate that random triangle queries (where three items are compared per query) provide less noisy data as well as greater quantity of data, for a fixed query budget, as compared to random edge queries (where two items are compared per query). We extend the analysis of convex clustering algorithms to show that the exact recovery guarantees hold for triangle queries despite involving dependent edges. In addition to random querying strategies, we also present a novel active querying algorithm that is guaranteed to find all the clusters regardless of their sizes and without the knowledge of any parameters as long as the workers are better than random guessers. We also provide a tight upper bound on the number of queries made by the proposed active querying algorithm. Apart from providing theoretical guarantees for the clustering algorithms we also apply our algorithms to real datasets.
" }, { "name": "Kucharczyk, Christopher James", "degree": "PhD", "year": "2018", "title": "High-throughput Characterization of Solid Oxide Fuel Cell Cathode Materials", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302018-201642452", "creators": [ { "name": { "family": "Kucharczyk", "given": "Christopher James" }, "id": "Kucharczyk-Christopher-James", "orcid": "0000-0002-4712-839X", "display_name": "Kucharczyk, Christopher James" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z094-9907", "abstract": "Solid oxide fuel cells are electrochemical devices which convert chemical energy directly to electricity. The extreme environments in which these devices operate require the use of expensive components to withstand degradation. To lower operating temperatures and therefore cost, materials discovery efforts have targeted new electrodes with high ionic and electronic conductivity, but these studies often convolute electrode morphology and performance, masking the inherent activity of electrode materials. In this work, a high-throughput experimental technique utilizing a robotic scanning impedance probe is applied to materials libraries to rigorously compare the performance of electrode materials and characterize fundamental electrode properties.
\r\n\r\nTwo cathode materials libraries are studied in-depth: the perovskite material La1-xSrxCo1-yFeyO3-\u03b4 (LSCF) and the double perovskite material PrBa0.5Sr0.5Co2-xFexO5+\u03b4 (PBSCF). Each materials library is investigated through the entire regime of cobalt and iron doping and results are obtained on both oxide-ion- and proton-conducting electrolyte materials. For LSCF, a four-fold increase in electrochemical resistance is observed from the cobalt-dominant endmember LSC64 to the iron-dominant endmember LSF64 on an oxygen-ion conducting substrate, concurrent with a decrease in chemical capacitance indicating lower oxygen vacancy concentration. For PBSCF, proton conductivity is observed through the bulk of the film, leading to its use in a real proton-conducting ceramic fuel cell that demonstrates exceptional performance at low temperatures (> 500mW/cm2 at 500\u00b0C) while remaining stable over hundreds of hours of testing. These results demonstrate the power and robustness of this high-throughput approach in characterizing both well-known and novel materials, and show great promise for future targeted searches of high-performance materials.
" }, { "name": "Leong, Yoke Peng", "degree": "PhD", "year": "2018", "title": "Optimal Controller Synthesis for Nonlinear Systems", "advisor": "Burdick, Joel Wakeman; Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162017-121220572", "creators": [ { "name": { "family": "Leong", "given": "Yoke Peng" }, "id": "Leong-Yoke-Peng", "orcid": "0000-0001-8560-8856", "display_name": "Leong, Yoke Peng" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "co-advisor", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "co-advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Ames", "given": "Aaron D." }, "id": "Ames-A-D", "role": "member", "display_name": "Ames, Aaron D." } ], "option_major": [ "cds" ], "doi": "10.7907/Z9TX3CK8", "abstract": "Optimal controller synthesis is a challenging problem to solve. However, in many applications such as robotics, nonlinearity is unavoidable. Apart from optimality, correctness of the system behaviors with respect to system specifications such as stability and obstacle avoidance is vital for engineering applications. Many existing techniques consider either the optimality or the correctness of system behavior. Rarely, a tool exists that considers both. Furthermore, most existing optimal controller synthesis techniques are not scalable because they either require ad-hoc design or they suffer from the curse of dimensionality.
\r\n\r\nThis thesis aims to close these gaps by proposing optimal controller synthesis techniques for two classes of nonlinear systems: linearly solvable nonlinear systems and hybrid nonlinear systems. Linearly solvable systems have associated Hamilton- Jacobi-Bellman (HJB) equations that can be transformed from the original nonlinear partial differential equation (PDE) into a linear PDE through a logarithmic transformation. The first part of this thesis presets two methods to synthesize optimal controller for linearly solvable nonlinear systems. The first technique uses a hierarchy of sums-of-square programs to compute a sequence of suboptimal controllers that have non-increasing suboptimality for first exit and finite horizon problems. This technique is the first systematic approach to provide stability and suboptimal performance guarantees for stochastic nonlinear systems in one framework. The second technique uses the low rank tensor decomposition framework to solve the linear HJB equation for first exit, finite horizon, and infinite horizon problems. This technique scale linearly with dimensions, alleviating the curse of dimensionality and enabling us to solve the linear HJB equation for a quadcopter model that is a twelve-dimensional system on a personal laptop. A new algorithm is proposed for a key step in the controller synthesis algorithm to solve the ill-conditioning issue that arises in the original algorithm. A MATLAB toolbox that implements the algorithms is developed, and the performance of these algorithms is illustrated by a few engineering examples.
\r\n\r\nApart from stability, in many applications, more complex specifications such as obstacle avoidance, reachability, and surveillance are required. The second part of the thesis describes methods to synthesize optimal controllers for hybrid nonlinear systems with quantitative objectives (i.e., minimizing cost) and qualitative objectives (i.e., satisfying specifications). This thesis focuses on two types of qualitative objectives, regular objectives, and \u03c9-regular objectives. Regular objectives capture bounded time behavior such as reachability, and ω-regular objectives capture long term behavior such as surveillance. For both types of objectives, an abstraction-refinement procedure that preserves the cost is developed. A two-player game is solved on the product of the abstract system and the given objectives to synthesize the suboptimal controller for the hybrid nonlinear system. By refining the abstract system, the algorithms are guaranteed to converge to the optimal cost and return the optimal controller if the original systems are robust with respect to the initial states and the optimal controller inputs. The proposed technique is the first abstraction-refinement based technique to combine both quantitative and qualitative objectives into one framework. A Python implementation of the algorithms are developed, and a few engineering examples are presented to illustrate the performance of these algorithms.
" }, { "name": "Liu, Chun-Lin", "degree": "PhD", "year": "2018", "title": "Sparse Array Signal Processing: New Array Geometries, Parameter Estimation, and Theoretical Analysis", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302018-095132389", "creators": [ { "name": { "family": "Liu", "given": "Chun-Lin" }, "id": "Liu-Chun-Lin", "orcid": "0000-0003-3135-9684", "display_name": "Liu, Chun-Lin" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" } ], "option_major": [ "eleceng" ], "doi": "10.7907/NSTQ-SD57", "abstract": "Array signal processing focuses on an array of sensors receiving the incoming waveforms in the environment, from which source information, such as directions of arrival (DOA), signal power, amplitude, polarization, and velocity, can be estimated. This topic finds ubiquitous applications in radar, astronomy, tomography, imaging, and communications. In these applications, sparse arrays have recently attracted considerable attention, since they are capable of resolving O(N2) uncorrelated source directions with N physical sensors. This is unlike the uniform linear arrays (ULA), which identify at most N-1 uncorrelated sources with N sensors. These sparse arrays include minimum redundancy arrays (MRA), nested arrays, and coprime arrays. All these arrays have an O(N2)-long central ULA segment in the difference coarray, which is defined as the set of differences between sensor locations. This O(N2) property makes it possible to resolve O(N2) uncorrelated sources, using only N physical sensors.
\r\n\r\nThe main contribution of this thesis is to provide a new direction for array geometry and performance analysis of sparse arrays in the presence of nonidealities. The first part of this thesis focuses on designing novel array geometries that are robust to effects of mutual coupling. It is known that, mutual coupling between sensors has an adverse effect on the estimation of DOA. While there are methods to counteract this through appropriate modeling and calibration, they are usually computationally expensive, and sensitive to model mismatch. On the other hand, sparse arrays, such as MRA, nested arrays, and coprime arrays, have reduced mutual coupling compared to ULA, but all of these have their own disadvantages. This thesis introduces a new array called the super nested array, which has many of the good properties of the nested array, and at the same time achieves reduced mutual coupling. Many theoretical properties are proved and simulations are included to demonstrate the superior performance of super nested arrays in the presence of mutual coupling.
\r\n\r\nTwo-dimensional planar sparse arrays with large difference coarrays have also been known for a long time. These include billboard arrays, open box arrays (OBA), and 2D nested arrays. However, all of them have considerable mutual coupling. This thesis proposes new planar sparse arrays with the same large difference coarrays as the OBA, but with reduced mutual coupling. The new arrays include half open box arrays (HOBA), half open box arrays with two layers (HOBA-2), and hourglass arrays. Among these, simulations show that hourglass arrays have the best estimation performance in presence of mutual coupling.
\r\n\r\nThe second part of this thesis analyzes the performance of sparse arrays from a theoretical perspective. We first study the Cram\u00e9r-Rao bound (CRB) for sparse arrays, which poses a lower bound on the variances of unbiased DOA estimators. While there exist landmark papers on the study of the CRB in the context of array processing, the closed-form expressions available in the literature are not applicable in the context of sparse arrays for which the number of identifiable sources exceeds the number of sensors. This thesis derives a new expression for the CRB to fill this gap. Based on the proposed CRB expression, it is possible to prove the previously known experimental observation that, when there are more sources than sensors, the CRB stagnates to a constant value as the SNR tends to infinity. It is also possible to precisely specify the relation between the number of sensors and the number of uncorrelated sources such that these sources could be resolved.
\r\n\r\nRecently, it has been shown that correlation subspaces, which reveal the structure of the covariance matrix, help to improve some existing DOA estimators. However, the bases, the dimension, and other theoretical properties of correlation subspaces remain to be investigated. This thesis proposes generalized correlation subspaces in one and multiple dimensions. This leads to new insights into correlation subspaces and DOA estimation with prior knowledge. First, it is shown that the bases and the dimension of correlation subspaces are fundamentally related to difference coarrays, which were previously found to be important in the study of sparse arrays. Furthermore, generalized correlation subspaces can handle certain forms of prior knowledge about source directions. These results allow one to derive a broad class of DOA estimators with improved performance.
\r\n\r\nIt is empirically known that the coarray structure is susceptible to sensor failures, and the reliability of sparse arrays remains a significant but challenging topic for investigation. This thesis advances a general theory for quantifying such robustness, by studying the effect of sensor failure on the difference coarray. We first present the (k-)essentialness property, which characterizes the combinations of the faulty sensors that shrink the difference coarray. Based on this, the notion of (k-)fragility is proposed to quantify the reliability of sparse arrays with faulty sensors, along with comprehensive studies of their properties. These novel concepts provide quite a few insights into the interplay between the array geometry and its robustness. For instance, for the same number of sensors, it can be proved that ULA is more robust than the coprime array, and the coprime array is more robust than the nested array. Rigorous development of these ideas leads to expressions for the probability of coarray failure, as a function of the probability of sensor failure.
\r\n\r\nThe thesis concludes with some remarks on future directions and open problems.
" }, { "name": "Lloyd, John Vickery", "degree": "PhD", "year": "2018", "title": "Optoelectronic Design and Prototyping of Spectrum-Splitting Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212018-185007265", "creators": [ { "name": { "family": "Lloyd", "given": "John Vickery" }, "id": "Lloyd-John-Vickery", "display_name": "Lloyd, John Vickery" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" } ], "option_major": [ "matsci" ], "doi": "10.7907/G1CG-E962", "abstract": "Global energy production is dominated by the combustion of fossil fuels but in order to avoid the projected consequences of anthropogenic climate change it is necessary that humankind reduce the carbon intensity of its energy supply. Fortunately the sun supplies a ubiquitous flow of energy of with excellent thermodynamic quality to earth. Massive investment and manufacturing scale has driven the costs of photovoltaic systems to levels competitive with fossil fuel generation, and yet commercial photovoltaic systems convert power from the sun into electricity with less than 20% efficiency. In this thesis we consider the thermodynamic and practical limits to the power conversion efficiency of photovoltaic systems and seek to design systems that address the greatest sources of loss, namely the lack of sub-bandgap absorption and the thermalization of excited carriers. We present several designs of spectrum-splitting systems that utilize optical structures to allocate incident broadband solar radiation into narrower spectral bands which can be converted by multiple distinct photovoltaic cells at greater efficiency. Furthermore, we report on the design and fabrication of thin film III-V single-junction cells at bandgaps spanning the solar spectrum for incorporation within spectrum-splitting systems. These devices were fabricated by utilizing epitaxial lift-off processes from both GaAs and InP wafers as proof of scalability. We additionally report on the fabrication and characterization of series of a spectrum-splitting prototypes. This design featured seven distinct spectral bands with single-junction photovoltaic cells designed to convert them with highest possible efficiency, and the ultimate prototype exhibited an 84.5% spectrum splitting efficiency and 30.2% power conversion efficiency under a standard AM1.5D solar spectrum. We also report a technical pathway to raise the prototype efficiency to a record breaking 45.2%. Finally, we present an optical design of a spectrum-splitting module that is informed by a technoeconomic analysis which drastically reduces the complexity and cost relative to the fabricated prototype.
" }, { "name": "Luo, Shi", "degree": "PhD", "year": "2018", "title": "Microstructural Effects on Diffusion and Mechanical Properties in Different Material Systems", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01082018-142110350", "creators": [ { "name": { "family": "Luo", "given": "Shi" }, "id": "Luo-Shi", "display_name": "Luo, Shi" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z90G3HBV", "abstract": "Material microstructures is a very broad subject that encompasses most of the field of materials science. Advances in materials characterization and small scale mechanical experiments have brought about progress in the understanding of microstructural features and mechanisms down to the nanometer scale. In contrast to bulk features and properties, the small length scale of these microstructures lead to many interesting properties, and often requires a material-by-material, and even localized region-by-region study. While a thorough understanding of microstructural effects even in one material system is way beyond the scope of this thesis, there are nonetheless many common themes and properties that link together microstructures and their effects on different materials, especially in terms of mechanical properties.
\r\n\r\nIn this thesis, the effects of microstructural features such as grain boundaries, surface modification and structural hierarchy are investigated using two sample material systems: Cu-In-Ga-Se (CIGS) thin films and marine diatom frustules. We find that grain structures (or a lack there of) play a major role in both systems, and lead to differences in material stiffness, strength, and diffusion of species. The latter is also significantly affected by material defects across length scales, exemplified in CIGS by both microscopic voids and pores, and atomic scale like substitutional point defects. On the other hand, in diatoms, a low flaw density combined with an effective hierarchical design can propel the mechanical property of relatively simple ingredients like amorphous silica, to achieve extraordinary mechanical strength. We will conclude by showcasing that we can generalize some of these knowledge on microstructural effects across material systems, to help designing manmade structures that fully capture the material-level and structural-level properties of natural marine diatoms.
" }, { "name": "Maeda, Kazuki", "degree": "PhD", "year": "2018", "title": "Simulation, Experiments, and Modeling of Cloud Cavitation with Application to Burst Wave Lithotripsy", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012018-165819361", "creators": [ { "name": { "family": "Maeda", "given": "Kazuki" }, "id": "Maeda-Kazuki", "orcid": "0000-0002-5729-6194", "display_name": "Maeda, Kazuki" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "chair", "display_name": "Brady, John F." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "orcid": "0000-0002-0291-4215", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/N7JK-F529", "abstract": "Modeling, numerical simulations, and experiments are used to investigate the dynamics of cavitation bubble clouds induced by strong ultrasound waves.
\r\n\r\nA major application of this work is burst wave lithotripsy (BWL), recently proposed method of lithotripsy that uses pulses (typically 10 wavelengths each) of highintensity, focused ultrasound at a frequency of O(100) kHz and an amplitude of O(1) MPa to break kidney stones. BWL is an alternative to standard shockwave lithotripsy (SWL), which uses much higher amplitude shock waves delivered at a typically much lower rate. In both SWL and BWL, the tensile component of the pressure can nucleate cavitation bubbles in the human body. For SWL, cavitation is a significant mechanism in stone communition, but also causes tissue injury. By contrast, little is yet known about cavitation in BWL.
\r\n\r\nTo investigate cloud cavitation in BWL, two numerical tools are developed: a model of ultrasound generation from a medical transducer, and a method of simulating clouds of cavitation bubbles in the focal region of the ultrasound. The numerical tools enable simulation of the cavitation growth and collapse of individual bubbles, their mutual interactions, and the resulting bubble-scattered acoustics. The numerics are implemented in a massively parallel framework to enable large-scale, three-dimensional simulations. Next, the numerical tools are applied to bubble clouds associated with BWL. Additionally, laboratory experiments are conducted in vitro in order to calibrate and validate the simulations. A major feature of the resulting bubble clouds is that the cloud size is similar to the ultrasound wavelength. This results in an anisotropic structure where the bubbles closest to the wave source grow to larger size and oscillate more rapidly. A new scaling parameter is introduced to characterize the nonlinear bubble cloud dynamics that generalizes the cloud interaction parameter of d'Agostino and Brennen (1989) defined for weak (linearized), bubble cloud dynamics excited uniformly by long-wavelength pressure waves. The mechanisms leading to the observed bubble dynamics are identified. The results further show that bubble clouds can scatter a large portion of incident ultrasound and consequently shield distal regions, including kidney stones, from irradiation. This energy shielding is quantified, and the simulations show that even a thin layer of bubbles can scatter up to 90% of the incident wave energy. A strong correlation is identified between the magnitude of energy shielding and the amplitude of the bubble-scattered acoustics. The correlation may be of use to control cavitation in the human body in real time by ultrasound monitoring for better outcomes of BWL.
" }, { "name": "Maggi, Alessandro", "degree": "PhD", "year": "2018", "title": "Three-Dimensional Nano-Architected Materials as Platforms for Designing Effective Bone Implants", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12242017-060345135", "creators": [ { "name": { "family": "Maggi", "given": "Alessandro" }, "id": "Maggi-Alessandro", "display_name": "Maggi, Alessandro" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "medeng" ], "doi": "10.7907/Z947482K", "abstract": "The growing world population coupled with longer human life expectancy warrants the need for better medical implant development. Recent advances in lithographic techniques have opened the door to a variety of approaches to tackle the aforementioned issue. However, several scientific hurdles must be overcome before patients can use fully synthetic and effective implants.
\r\n\r\nIdentifying the optimal material, porosity, and mechanical properties of the scaffold to induce cell functionality are key obstacles. Limitations in established fabrication techniques have hindered the ability to fully understand cell behavior on 3D substrates. 3D printing is limited to feature sizes that are at least one order of magnitude larger than a single cell (~10\u03bcm); electrospinning is able to yield features that are on the same scale as cells, but its stochastic nature leads to scaffolds with poor mechanical properties; salt leeching doesn\u2019t allow for control of pore size and distribution which have detrimental effects on nutrient diffusion and cell ingrowth, thereby thwarting the formation of functional tissue.
\r\n\r\nMuch effort has been made to create a suitable platform for regenerating a relatively less complex organ, such as bone, yet the inability to fully understand cell mechanics on 3D scaffolds has curbed the fabrication of effective bone implants.
\r\n\r\nThe first part of this thesis focuses on the suitability of nanoarchitected materials as 3D platforms for bone-tissue growth. We employed two-photon lithography to create polymeric and hydroxyapatite-coated 3D nanolattices to explore scaffold biocompatibility and material effects on osteoblast attachment and growth. Our experiments showed that the unit cell geometry, tetrakaidekahedron, and size, 25\u03bcm, were adequate for cell attachment and infiltration, which are hallmark signs of biocompatibility. Our study also corroborated previous findings that mammalian cells respond differently to different materials that they come in contact with. To isolate structural effects, we fabricated nanolattices coated with a uniform 20nm-thick outermost layer of TiO2. These nanolattices, which had fixed porosity and unit cell size (25\u03bcm) while they varied in structural stiffness (~2-9MPa) were used to explore the influence of scaffold properties on the viability of osteoblasts in a microenvironment similar to that of natural bone. Upon growing osteogenic cells on the nanolattices, significant cell attachment and presence of various calcium phosphate species, which are commonly found in natural bone, were observed. These findings suggest that 3-dimensional nano-architected materials can be used as effective scaffolds for bone cell growth and proliferation.
\r\n\r\nThe second part of the thesis investigates the effects of nanolattice structural stiffness and loading conditions on osteoblast behavior. We fabricated nanolattices with stiffness ranging from ~0.7MPa to 100MPa. Experiments done by seeding osteoblast-like cells on these nanolattices revealed that both stress fiber concentration and bioapatite deposition were higher on the most compliant nanolattice, (0.7 MPa) by ~20% and ~40% respectively. These results provide insights into cell behavior in 3D microenvironments which can lead to a better understanding of stress shielding at the cellular level. Preventing stress shielding by creating scaffolds with structural stiffness and porosity that enhances osteoblasts activity could lead to the creation of effective implants with improved mechanical stability which ultimately improves osteointegration.
\r\n\r\nIn addition to investigating static cell-scaffold interactions we took advantage of the nanolattices tunability to study the effects of dynamic loading on cell behavior. Bone adaptation is driven by dynamic, rather than static loading, however there is still wide controversy on whether stress, strain or loading frequency plays the most significant role in bone remodeling, which drives bone healing.
\r\n\r\nIn order to understand cell sensitivity to varying loads, displacements and frequencies, we fabricated hollow TiO2 nanolattices with stiffness ranging from ~0.7-35MPa which were populated with osteoblast-like cells and subjected to cyclic compression to either a constant stress or strain. After seeding SAOS-2 cells on the nanolattices for 12 days different dynamic loading conditions were tested: (1) cyclic uniaxial compressions to strains ranging from ~0.3-2% strain were carried out to investigate the effects of strain magnitude on cell behavior. (2) Cyclic uniaxial compressions to stresses spanning from ~0.02-1MPa were performed to explore the role of stress magnitude on the cells\u2019 stress fibers formation. (3) The nanolattices were cyclically loaded at different frequencies, ~0.1-3Hz, while maintaining stress and strain constant, which provided insights into how loading frequency affects osteoblasts behavior.
\r\n\r\nCell activity, which was measured by monitoring f-actin and vinculin fluorescence intensity, revealed increased fluorescence in those cells that were mechanically stimulated as opposed to those that were statically grown on the nanolattices regardless of loading condition. Cell response was most drastically affected by varying the loading frequency. A ~30% increase in f-actin fluorescence was observed in the cells grown on the nanolattices that were loaded at ~3Hz compared to those that were grown on the nanolattices that were cyclically compressed at ~0.1Hz.
\r\n\r\nThe last part of this thesis is focused on developing a three-dimensional architected capacitor that could be used as a strain gauge to further our understanding of cell mechanics in 3D. We took advantage of the mechanical tunability of the nanolattices to fabricate a 3D parallel-plate capacitor with a basal capacitance of ~280fF and able to sense forces as low as ~30\u03bcN. This work points to nano-architected materials as promising candidates for ideal platforms to investigate more realistic cellular conditions which can immensely benefit the field of tissue engineering.
" }, { "name": "Marteau, Elo\u00efse Sophie H\u00e9l\u00e8ne", "degree": "PhD", "year": "2018", "title": "Laboratory Studies of Granular Materials Under Shear: From Avalanches to Force Chains", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142018-133453405", "creators": [ { "name": { "family": "Marteau", "given": "Elo\u00efse Sophie H\u00e9l\u00e8ne" }, "id": "Marteau-Elo\u00efse-Sophie-H\u00e9l\u00e8ne", "orcid": "0000-0001-7696-6264", "display_name": "Marteau, Elo\u00efse Sophie H\u00e9l\u00e8ne" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/FKM0-P754", "abstract": "Granular materials reveal their complexity and some of their unique features when subjected to shear deformation. They can dilate, behave like a solid or a fluid, and are known to carry external forces preferentially as force chains. In this dissertation, we employ laboratory experiments to study the complex behavior of granular materials under shear. We introduce a multiscale approach in which the underlying grain-scale mechanics are experimentally measured and homogenized to obtain enriched macroscopic quantities. First, we investigate granular avalanches spontaneously generated by a rotating drum. Measurements of grain kinematics are directly incorporated into a rate-dependent plasticity model that explains and reproduces the life cycle of laboratory avalanches. The results presented here feature dilatancy as the key material parameter governing the triggering of an avalanche. Second, we report a set of experiments performed on a custom-built mechanical device that allows a specimen composed of a two-dimensional analogue granular assembly to be subjected to quasi-static shear conditions. A numerical force inference technique, the Granular Element Method (GEM), provides direct observation and quantitative characterization of force chain structures in assemblies made of realistic grains. Equipped with a complete description of the grain-scale mechanics, we show that shear deformation creates geometrical (fabric) and mechanical (force) anisotropy. Finally, the influence of grain shape on grain-scale processes is studied. We find that grain interlocking is a prominent deformation mechanism for non-circular grains that ultimately promotes a significant increase in macroscopic shear strength. By seamlessly connecting grain-scale information to continuum scale experiments, this dissertation sheds light on the multiscale mechanical behavior of granular assemblies under shear.
" }, { "name": "Martin, Nathan Koon-Hung", "degree": "PhD", "year": "2018", "title": "Analysis of Flapping Propulsion: Comparison, Characterization, and Optimization", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072018-133402239", "creators": [ { "name": { "family": "Martin", "given": "Nathan Koon-Hung" }, "id": "Martin-Nathan-Koon-Hung", "orcid": "0000-0001-6038-6177", "display_name": "Martin, Nathan Koon-Hung" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q6CG-QY57", "abstract": "In recent decades, the development of autonomous underwater vehicles (AUVs) has rapidly increased and inspiration for novel designs has recently come from nature, primarily based on the fast, efficient, and maneuverable flapping motion of fish. Due to its potential, flapping propulsion is investigated through three studies.
\r\n\r\nThe first study involves the comparison between swimming by flapping and by periodic contractions. A direct comparison is made between the two propulsion mechanisms by simplifying the motions, utilizing a machine that can operate in either mode of propulsion, and evaluating the average thrust generated and the average input power required per cycle between the two mechanisms when the overall kinematics are identical. The two propulsion mechanisms are tested using a variety of overall kinematics, flexible plates, and modified duty cycles, all of which suggest that flapping propulsion is the more efficient; however, periodic contractions with a modified duty cycle are shown to generate more thrust per cycle.
\r\n\r\nThe second study involves the characterization of the impact of chord-wise curvature on the hydrodynamic forces and torques, motivated by the dorso-ventral bending of a fish's caudal fin during locomotion. The impact of curvature is shown to depend on the planform area of the flapping plate. Plates with a smaller or an identical planform area compared with a baseline rigid flat rectangular plate either decrease or increase the generated thrust, respectively. These phenomena are utilized to develop an actuated plate for velocity modulation and a snap-buckling plate to provide a greater thrust and efficiency compared with a rigid plate propulsor.
\r\n\r\nThe third study involves the development and demonstration of a method to experimentally optimize an arbitrary three-dimensional trajectory for a flapping propulsor. The trajectory is parameterized by variables inspired by birds and fish, executed by a mechanism that can actuate an arbitrary motion in a hemisphere, and optimized using an adaptive evolutionary strategy. The trajectories are scored based upon their difference from a desired force set-point and their efficiency. All trajectory searches demonstrate good convergence properties and match the desired force set-point almost immediately. Additional generations primarily improve the efficiency. This novel approach finds optimal trajectories for generating side-forces, similar to how a fish's pectoral fin or a bird's wing functions, and for generating thrust, similar to how a fish's caudal fin operates.
" }, { "name": "Massari, Anthony Thomas", "degree": "PhD", "year": "2018", "title": "Achieving Higher Fidelity Building Response through Emerging Technologies and Analytical Techniques", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07262017-074416397", "creators": [ { "name": { "family": "Massari", "given": "Anthony Thomas" }, "id": "Massari-Anthony-Thomas", "orcid": "0000-0002-6561-4674", "display_name": "Massari, Anthony Thomas" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "orcid": "0000-0003-3363-2197", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "orcid": "0000-0003-3323-3508", "role": "member", "display_name": "Clayton, Robert W." }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "orcid": "0000-0002-4703-190X", "role": "member", "display_name": "Kohler, Monica D." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9HH6H7N", "abstract": "The integration of sensor technology into the built environment has created an opportunity for a new approach to infrastructure development and management. Using collected data and principles of general physics, we discuss means and methods of using low cost dense instrumentation to perform damage detection, structural identification, and the benefits of cyber physical systems to community resilience. A nonlinear damping strategy for braced frame structures is introduced incorporating capped levels of damping forces. The study shows the effect of having control of damping forces in nonlinear analysis and the importance of limiting energy dissipation to rational levels. The issue of sliding mass is also studied to determine the contribution to energy loss and the effect to overall response. The results indicate a need to incorporate this effect in stiff structures with intentionally decoupled mass such as data centers. Finally, a discussion on dual system structures under plastic deformation in a post event deformed configuration is presented. A suggested displacement based method for design is suggested for implementation into future editions of the building code." }, { "name": "Mateos Arrieta, Arturo Jos\u00e9", "degree": "PhD", "year": "2018", "title": "Tensile Failure and Fracture of Three-Dimensional Brittle Nanolattices", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122018-094549478", "creators": [ { "name": { "family": "Mateos Arrieta", "given": "Arturo Jos\u00e9" }, "id": "Mateos-Arrieta-Arturo-Jos\u00e9", "orcid": "0000-0002-9306-3531", "display_name": "Mateos Arrieta, Arturo Jos\u00e9" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AZXG-NB17", "abstract": "The emergence of a new class of cellular solids, i.e., nano- and micro-architected materials, poses the question of whether they can be characterized as a continuum solid. Extensive research has shown that these ultralight and strong structural metamaterials are particularly attractive for mechanically-demanding applications; yet their susceptibility to flaws, fracture behavior, and discrete-continuum duality remains relatively unexplored. In the course of this work, we report the fabrication and tensile-to-failure response of three-dimensional ceramic nanolattices, comprised of 50nm-thick alumina tubes that are arranged into periodic 5um-wide octet-truss unit cells, with and without pre-fabricated through-thickness center notches oriented at different angles to the loading direction. In-situ uniaxial tensile experiments revealed that for all notch orientations, failure always initiated at the notch root, as would be in a monolithic material, with the tube walls at nodal junctions fracturing first, followed by instantaneous crack propagation through the discrete lattice architecture along nodal planes orthogonal to the loading direction. Measured tensile strength of 27.4 MPa was highest for the unnotched samples and decreased systematically with the increase of notch orientation to its minimum of 7.2 MPa in the orthogonally-notched samples. We found the specific tensile strength of hollow-tube octet alumina nanolattices to be 4 times higher than what has been reported for architected and bulk materials at similar low densities. Three-dimensional finite element simulations closely reproduce the observed failure mechanism and trends in failure strength. A direct comparison is made between the experimental measurements, finite element simulations, and predictions of linear elastic fracture mechanics for a self-similar monolithic tensile samples made out of an ideally-brittle solid. Results are in good agreement with the scaling of failure strengths from classical mode I fracture criteria and suggest that trajectory of crack propagation can be adequately explained by considering the connectivity of the lattice architecture. These findings imply that the continuum nature of nano-architected materials offers predictability of failure stresses, which helps enable the development of advanced materials through informed architectural design." }, { "name": "Minxha, Juri", "degree": "PhD", "year": "2018", "title": "Single-Neuron Correlates of Visual Object Representation in the Human Brain: Effects of Attention, Memory, and Choice", "advisor": "Adolphs, Ralph; Rutishauser, Ueli", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082018-133105605", "creators": [ { "name": { "family": "Minxha", "given": "Juri" }, "id": "Minxha-Juri", "display_name": "Minxha, Juri" } ], "advisors": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "advisor", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Rutishauser", "given": "Ueli" }, "id": "Rutishauser-U", "role": "advisor", "display_name": "Rutishauser, Ueli" } ], "committee": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "chair", "display_name": "O'Doherty, John P." }, { "name": { "family": "Rutishauser", "given": "Ueli" }, "id": "Rutishauser-U", "role": "member", "display_name": "Rutishauser, Ueli" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Tsao", "given": "Doris Y." }, "id": "Tsao-D-Y", "role": "member", "display_name": "Tsao, Doris Y." } ], "option_major": [ "cns" ], "doi": "10.7907/8f55-zz50", "abstract": "Neurons in the medial temporal lobe (amygdala and hippocampus) are known to respond selectively to specific object categories, such as faces. This dissertation investigates two novel extensions of this work: (1) how are such neuronal responses influenced by where we attend; (2) how is category information used by the brain to make decisions.
\r\n\r\nThe first question evaluated the representation of faces in the primate amygdala during naturalistic conditions, by recording from both human and macaque amygdala neurons during free viewing of arrays of images with concurrent eye tracking. We found that category-selective responses were very strongly modulated by where people, or monkeys, fixated (overt attention). Subsequent experiments in humans only further demonstrated that this effect holds even when people allocate visual attention while keeping central fixation (covert attention). In both monkeys and humans, the majority of face-selective neurons preferred faces of conspecifics, a bias also seen behaviorally in first fixation preferences. Response latencies, relative to fixation onset, were shortest for conspecific-selective neurons. Response latencies were also notably shorter in monkeys than in humans. To answer the second question, we investigated how visual representations in the medial temporal lobe are subsequently used to make two types of decisions: a recognition memory choice (\"have you seen this image before?\"), and a stimulus categorization choice (\"Is this a face?\"). We show that (i) there are distinct populations of cells in the medial frontal cortex (including anterior cingulate cortex, and supplementary motor cortex) encoding recognition memory or categorization-based choices; (ii) category-selective cells in the medial temporal lobe are insensitive to such task conditions; and (iii) spike-field coherence between field potentials in the medial temporal lobe and action potentials in the medial frontal cortex is enhanced during recognition memory choices. This suggests that inter-areal communication between these two brain regions may be facilitated selectively in tasks that rely on recognition memory-based information. Taken together these two components of this dissertation provide novel insights into how visual object representations in the human brain are gated by attention, and how they are used in decisions. This work thus for the first time provides a comprehensive characterization of how single neurons in the human brain participate in the cycle from perception to action.
" }, { "name": "Monroe, Ryan McKay", "degree": "PhD", "year": "2018", "title": "Gigahertz Bandwidth and Nanosecond Timescales: New Frontiers in Radio Astronomy Through Peak Performance Signal Processing", "advisor": "Hallinan, Gregg W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042018-004220017", "creators": [ { "name": { "family": "Monroe", "given": "Ryan McKay" }, "id": "Monroe-Ryan-McKay", "orcid": "0000-0002-0026-4546", "display_name": "Monroe, Ryan McKay" } ], "advisors": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "role": "advisor", "display_name": "Hallinan, Gregg W." } ], "committee": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "role": "chair", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "D'Addario", "given": "Larry R." }, "id": "D'Addario-L-R", "role": "member", "display_name": "D'Addario, Larry R." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/25DP-J474", "abstract": "Abstract In the past decade, there has been a revolution in radio-astronomy signal processing. High bandwidth receivers coupled with fast ADCs have enabled the collection of tremendous instantaneous bandwidth, but streaming computational resources are struggling to catch up and serve these new capabilities. As a consequence, there is a need for novel signal processing algorithms capable of maximizing these resources. This thesis responds to the demand by presenting FPGA implementations of a Polyphase Filter Bank which are an order of magnitude more efficient than previous algorithms while exhibiting similar noise performance. These algorithms are showcased together alongside a broadband RF front-end in Starburst: a 5 GHz instantaneous bandwidth two-element interferometer, the first broadband digital sideband separating astronomical interferometer.\u00a0 Starburst technology has been applied to three instruments to date.
\r\n\r\nAbstract Wielding tremendous computational power and precisely calibrated hardware, low frequency radio telescope arrays have potential greatly exceeding their current applications.\u00a0 This thesis presents new modes for low frequency radio-telescopes, dramatically extending their original capabilities.\u00a0 A microsecond-scale time/frequency mode empowered the Owens Valley Long Wavelength Array to inspect not just the radio sky by enabling the testing of novel imaging techniques and detecting overhead beacon satellites, but also the terrestrial neighborhood, allowing for the characterization and mitigation of nearby sources of radio frequency interference (RFI).\u00a0 This characterization led to insights prompting a nanosecond-scale observing mode to be developed, opening new avenues in high energy astrophysics, specifically related to the radio frequency detection of ultra-high energy cosmic rays and neutrinos.
\r\n\r\nAbstract Measurement of the flux spectrum, composition, and origin of the highest energy cosmic ray events is a lofty goal in high energy astrophysics. One of the most powerful new windows has been the detection of associated extensive air showers at radio frequencies. However, all current ground-based systems must trigger off an expensive and insensitive external source such as particle detectors - making detection of the rare, high energy events uneconomical.\u00a0 Attempts to make a direct detection in radio-only data have been unsuccessful despite numerous efforts. The problem is even more severe in the case of radio detection of ultra-high energy neutrino events, which cannot rely on in-situ particle detectors as a triggering mechanism. This thesis combines the aforementioned nanosecond-scale observing mode with real-time, on-FPGA RFI mitigation and sophisticated offline post-processing.\u00a0 The resulting system has produced the first successful ground based detection of cosmic rays using only radio instruments. Design and measurements of cosmic ray detections are discussed, as well as recommendations for future cosmic ray experiments.\u00a0 The presented future designs allow for another order of magnitude improvement in both sensitivity and output data-rate, paving the way for the economical ground-based detection of the highest energy neutrinos.
" }, { "name": "Newman, Matthew Gregory", "degree": "PhD", "year": "2018", "title": "On the Kinetics of Materials of Geophysical Interest", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:08282017-105838669", "creators": [ { "name": { "family": "Newman", "given": "Matthew Gregory" }, "id": "Newman-Matthew-Gregory", "orcid": "0000-0003-2752-0121", "display_name": "Newman, Matthew Gregory" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kraus", "given": "Richard" }, "id": "Kraus-Richard", "role": "member", "display_name": "Kraus, Richard" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9319T35", "abstract": "Knowledge of the equation of state and phase diagram of magnesium silicates and light iron alloys is important for understanding the thermal evolution and interior structure of terrestrial planets. Dynamic compression techniques are the primary viable methods to create the temperature and pressure conditions that are relevant to Earth and super-Earth (1-10 Earth mass) sized planets. However, due to the kinetic constraints imposed by the timescale of dynamic compression experiments, the nature of the state within the dynamically compressed sample (whether equilibrium or metastable) is uncertain. Here, we present the results of a series of dynamic compression experiments performed on both laser driven compression and plate impact facilities to study the nanosecond to microsecond response of forsterite and iron silicide. In situ x-ray diffraction measurements are used to probe the crystal structure of solid phases and test for the presence of melt, from which we investigate the decomposition of forsterite and iron silicide into compositionally distinct phases at high pressure. For forsterite, we do not observe chemical segregation in the solid phase, however the presence of melt speeds up the kinetics and allows chemical segregation to occur on nanosecond timescales. For iron silicide, our results show a textured solid phase upon shock compression to pressures ranging from 166(14) to 282(24) GPa consistent with cubic and hcp structures in coexistence. Above 313(29) GPa, the intense and textured solid diffraction peaks give way to a diffuse scattering feature and loss of texture, consistent with melting along the Hugoniot." }, { "name": "Ni, Xiaoyue", "degree": "PhD", "year": "2018", "title": "Probing Microplastic Deformation in Metallic Materials", "advisor": "Greer, Julia R.; Adhikari, Rana", "url": "https://resolver.caltech.edu/CaltechTHESIS:09202017-020239229", "creators": [ { "name": { "family": "Ni", "given": "Xiaoyue" }, "id": "Ni-Xiaoyue", "orcid": "0000-0002-1822-1122", "display_name": "Ni, Xiaoyue" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "role": "co-advisor", "display_name": "Adhikari, Rana" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Dahmen", "given": "Karin A." }, "id": "Dahmen-Karin-A", "role": "member", "display_name": "Dahmen, Karin A." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "role": "member", "display_name": "Adhikari, Rana" } ], "option_major": [ "matsci" ], "doi": "10.7907/F38W-6N47", "abstract": "Metallic materials deform through discrete displacement bursts that are commonly associated with abrupt dislocation activities, i.e. avalanches, during plastic flow. Dislocations might be active prior to the textbook yielding, but it is unclear whether these activities can be discerned as smaller strain events, i.e. microplasticity. Novel experimental approaches involving nanomechanical experiments are developed to detect and to quantify microplastic deformation that occurs during compression of micron- and sub-micron sized single crystalline copper nano-pillars. The experiment, focusing on metals\u2019 pre-yield regime, reveals an evolving dissipation component in the storage and loss moduli that likely corresponds to a smooth transition from perfect elasticity to avalanche-dominated plastic deformation. This experimental investigation is corroborated by mesoscopic plasticity simulations, which apply to a minimal model that combines fast avalanche dynamics and slow relaxation processes of dislocations. The model's predictions are consistent with the microscopic experiments and provide constitutive relationship predicting microplastic crackling noise being upconverted by small stress perturbations. Another experimental investigation on unload-reload cyclic behavior of copper nano-pillars post yielding shows a decaying microplastic hysteresis with emergent power laws and scaling features, which signifies an ever-explored reversible-to- irreversible transitions in metal deformation, as seen in other nonequilibrium systems. To study microplasticity in macroscopic metallic samples, an instrument is custom-built based on Michelson interferometer and achieves unprecedented high displacement noise resolution of 10\u221214m/\u221aHz in the frequency range of 10 \u2013 1000 Hz. The macroscopic experiment has resolved a driving-modulated microplastic noise in bulk cantilever steel samples under nominal elastic loading. The characteristics of the noise resemble those of the microplastic noise predicted from the micromechanical simulations developed from microscopic experiments." }, { "name": "Oh, Dong Yoon", "degree": "PhD", "year": "2018", "title": "Integrated Nonlinear Photonic Devices", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11122017-215023206", "creators": [ { "name": { "family": "Oh", "given": "Dong Yoon" }, "id": "Oh-Dong-Yoon", "orcid": "0000-0001-6716-1851", "display_name": "Oh, Dong Yoon" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z95H7DGT", "abstract": "Chip-scale nonlinear optics can provide important new functions in communications, frequency metrology and spectroscopy. Optical microcavities enhance nonlinear optical effects through resonant recirculation. This recirculation dramatically reduces the required power in applications and also lowers signal noise. A key figure-of-merit is the optical Q factor, which provides a dimensionless scale of optical storage time within the microcavity. In this thesis, a novel integrated ultra-high-Q microcavity with Q as high as 230 million is presented. The device is applied to demonstrate multiple functions including electronic-rate soliton microcomb generation and stimulated Brillouin laser operation. For soliton generation, the resonator must be engineered to produce optical mode families that feature anomalous dispersion. This engineering is applied to generate solitons at wavelengths of 1064 nm and 778 nm. Systems-on-a-chip applications of these devices are discussed including compact optical synthesizers, optical clocks and rotation sensors. Finally, a compact array of silica ridge waveguides is described and applied for efficient and coherent ultraviolet-to-visible comb generation by dispersive-wave generation. Unlike other devices used to broaden spectra such as micro-structured fibers, these arrays provide a wide range of emission wavelength choices on a single chip. The arrays can also enable mode-locked lasers to attain greatly extended spectral reach for spectroscopy, bioimaging, tomography and metrology. " }, { "name": "Papadakis, Georgia Theano", "degree": "PhD", "year": "2018", "title": "Optical Response in Planar Heterostructures: From Artificial Magnetism to Angstrom-Scale Metamaterials", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:03082018-161639906", "creators": [ { "name": { "family": "Papadakis", "given": "Georgia Theano" }, "id": "Papadakis-Georgia-Theano", "orcid": "0000-0001-8107-9221", "display_name": "Papadakis, Georgia Theano" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z97H1GS1", "abstract": "The idea of expanding the range of properties of natural substances with artificial matter was introduced by V. G. Veselago in 1967. Since then, the field of metamaterials has dramatically advanced. Man-made structures can now exhibit a plethora of extraordinary electromagnetic properties, such as negative refraction, optical magnetism, and super-resolution imaging. Typical metamaterial motifs include split ring resonators, dielectric and plasmonic particles, fishnet and wire arrays. The principle of operation of these elements is now well-understood, and they are being exploited for practical applications on a global scale, ranging from telecommunications to sensing and biomedicine, in the radio frequency and terahertz domains. Accessing and controlling optical and near-infrared phenomena requires scaling down the dimensions of meta- materials to the nanometer regime, pushing the limits of state-of-the-art nano- lithography and requiring structurally less complex geometries. Hence, within the last decade, research in metamaterials has revisited a simpler, lithography- free structure, particularly planar arrangements of alternating metal and dielectric layers, termed hyperbolic metamaterials. Such media are readily realizable with well-established thin-film deposition techniques. They support a rich canvas of properties ranging from surface plasmonic propagation to negative refraction, and they can enhance the photoluminescence properties of quantum emitters at any frequency range.
\r\n\r\nHere, we introduce a computational approach that allows tailoring the dielectric and magnetic effective properties of planar metamaterials. Previously, planar hyperbolic metamaterials have been considered non-magnetic. In contrast, we show theoretically and experimentally that planar arrangements com- posed of non-magnetic constituents can be engineered to exhibit a non-trivial magnetic response. This realization simplifies the structural requirements for tailoring optical magnetism up to very high frequencies. It also provides access to previously unexplored phenomena, for example artificially magnetic plasmons, for which we perform an analysis on the basis of available materials for achieving polarization-insensitive surface wave propagation. By combining the concept of metamaterials\u2019 homogenization with previous transfer matrix approaches, we develop a general computational method for surface waves calculations that is free of previous assumptions, for example infinite or purely periodic media. Furthermore, we theoretically demonstrate that hyperbolic metamaterials can be dynamically tunable via carrier injection through external bias, using transparent conductive oxides and graphene, at visible and infrared frequencies, respectively. Lastly, we demonstrate that planar graphene-based van der Waals heterostructures behave effectively as supermetals, exhibiting reflective properties that surpass the reflectivity of gold and silver that are currently considered the state-of-the-art materials for mirroring applications in space applications. The (meta)materials we introduce exhibit an order-of-magnitude lower mass density, making them suitable candidates for future light-sail technologies intended for space exploration.
" }, { "name": "Ren, Xiaoqi", "degree": "PhD", "year": "2018", "title": "Optimizing Resource Management in Cloud Analytics Services", "advisor": "Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-080301508", "creators": [ { "name": { "family": "Ren", "given": "Xiaoqi" }, "id": "Ren-Xiaoqi", "orcid": "0000-0002-1121-9046", "display_name": "Ren, Xiaoqi" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "compsci" ], "doi": "10.7907/K62Y-FV39", "abstract": "The fundamental challenge in the cloud today is how to build and optimize machine learning and data analytical services. Machine learning and data analytical platforms are changing computing infrastructure from expensive private data centers to easily accessible online services. These services pack user requests as jobs and run them on thousands of machines in parallel in geo-distributed clusters. The scale and the complexity of emerging jobs lead to increasing challenges for the clusters at all levels, from power infrastructure to system architecture and corresponding software framework design.
\r\n\r\nThese challenges come in many forms. Today's clusters are built on commodity hardware and hardware failures are unavoidable. Resource competition, network congestion, and mixed generations of hardware make the hardware environment complex and hard to model and predict. Such heterogeneity becomes a crucial roadblock for efficient parallelization on both the task level and job level. Another challenge comes from the increasing complexity of the applications. For example, machine learning services run jobs made up of multiple tasks with complex dependency structures. This complexity leads to difficulties in framework designs. The scale, especially when services span geo-distributed clusters, leads to another important hurdle for cluster design. Challenges also come from the power infrastructure. Power infrastructure is very expensive and accounts for more than 20% of the total costs to build a cluster. Power sharing optimization to maximize the facility utilization and smooth peak hour usages is another roadblock for cluster design.
\r\n\r\nIn this thesis, we focus on solutions for these challenges at the task level, on the job level, with respect to the geo-distributed data cloud design and for power management in colocation data centers.
\r\n\r\nAt the task level, a crucial hurdle to achieving predictable performance is stragglers, i.e., tasks that take significantly longer than expected to run. At this point, speculative execution has been widely adopted to mitigate the impact of stragglers in simple workloads. We apply straggler mitigation for approximation jobs for the first time. We present GRASS, which carefully uses speculation to mitigate the impact of stragglers in approximation jobs. GRASS's design is based on the analysis of a model we develop to capture the optimal speculation levels for approximation jobs. Evaluations with production workloads from Facebook and Microsoft Bing in an EC2 cluster of 200 nodes show that GRASS increases accuracy of deadline-bound jobs by 47% and speeds up error-bound jobs by 38%.
\r\n\r\nMoving from task level to job level, task level speculation mechanisms are designed and operated independently of job scheduling when, in fact, scheduling a speculative copy of a task has a direct impact on the resources available for other jobs. Thus, we present Hopper, a job-level speculation-aware scheduler that integrates the tradeoffs associated with speculation into job scheduling decisions based on a model generalized from the task-level speculation model. We implement both centralized and decentralized prototypes of the Hopper scheduler and show that 50% (66%) improvements over state-of-the-art centralized (decentralized) schedulers and speculation strategies can be achieved through the coordination of scheduling and speculation.
\r\n\r\nAs computing resources move from local clusters to geo-distributed cloud services, we are expecting the same transformation for data storage. We study two crucial pieces of a geo-distributed data cloud system: data acquisition and data placement. Starting from developing the optimal algorithm for the case of a data cloud made up of a single data center, we propose a near-optimal, polynomial-time algorithm for a geo-distributed data cloud in general. We show, via a case study, that the resulting design, Datum, is near-optimal (within 1.6%) in practical settings.
\r\n \r\nEfficient power management is a fundamental challenge for data centers when providing reliable services. Power oversubscription in data centers is very common and may occasionally trigger an emergency when the aggregate power demand exceeds the capacity. We study power capping solutions for handling such emergencies in a colocation data center, where the operator supplies power to multiple tenants. We propose a novel market mechanism based on supply function bidding, called COOP, to financially incentivize and coordinate tenants' power reduction for minimizing total performance loss while satisfying multiple power capping constraints. We demonstrate that COOP is \"win-win\", increasing the operator's profit (through oversubscription) and reducing tenants' costs (through financial compensation for their power reduction during emergencies).
" }, { "name": "Rosenberg, Kevin Thomas", "degree": "PhD", "year": "2018", "title": "Resolvent-Based Modeling of Flows in a Channel", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012018-114927289", "creators": [ { "name": { "family": "Rosenberg", "given": "Kevin Thomas" }, "id": "Rosenberg-Kevin-Thomas", "orcid": "0000-0001-6101-3823", "display_name": "Rosenberg, Kevin Thomas" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PHDW-Z389", "abstract": "This thesis concerns the continued development of the resolvent framework (McKeon and Sharma, 2010) to model wall-bounded turbulent flows. Herein, we introduce novel modifications and extensions of the framework to improve the compact representation of flows in a channel. In particular, inspired by ideas rooted in classical linear stability theory, we introduce a decomposition of the velocity field into Orr-Sommerfeld (OS) and Squire (SQ) modes in a nonlinear context via the resolvent operator. We demonstrate through the analysis of a number of exact coherent states (ECS) of the Navier-Stokes equations (NSE) in Couette and Poiseuille flow that this decomposition offers a significant improvement in the low-dimensional representation of these flows. With this efficient basis, we are able to develop through the notion of interaction coefficients a method to compute accurate, self-consistent solutions of the NSE with knowledge of only the mean velocity profile. We also highlight the role of the solenoidal component of the nonlinear forcing in the solution process. In addition, the resolvent framework is extended to the analysis of 2D/3C flows. This approach, again applied to ECS, sheds light on the underlying scale interactions which sustain these solutions. Notably, it reveals that lower branch ECS can be effectively described in their entirety with a single resolvent response mode. This discovery is leveraged to construct a method to compute accurate approximations of ECS starting from a laminar profile using a single parameter model. This thesis also utilizes a constant time-step DNS of a turbulent channel to perform a direct characterization of the nonlinear forcing terms. We compute power spectra and confirm that the nonlinear forcing has a non-trivial signature in the wavenumber-frequency domain. We also compute and analyze spectra for the OS/SQ vorticity and discuss the potential benefit of this decomposition technique to the study of fully turbulent flows as well.
" }, { "name": "Sakovsky, Maria", "degree": "PhD", "year": "2018", "title": "Design and Characterization of Dual-Matrix Composite Deployable Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302018-165415595", "creators": [ { "name": { "family": "Sakovsky", "given": "Maria" }, "id": "Sakovsky-Maria", "orcid": "0000-0002-3683-8505", "display_name": "Sakovsky, Maria" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/CNPY-A883", "abstract": "Dual-matrix composites are a promising approach to deployable high performance antennas for small satellites. Several techniques exist for packaging large antenna apertures. Assemblies of rigid bars and hinges obtain high deployed precision but are heavy and mechanically complex. Thin shell structures deployed using stored strain energy are a lightweight alternative offering efficient packaging but reduced surface precision. Moreover, elastomer composites shells attain even smaller fold radii upon packaging but are limited by the deployed structure's stiffness. Dual-matrix composites combine the advantages of several of these approaches to enable larger antenna apertures. They consist of a continuous woven fiber reinforcement with an elastomer matrix embedded in localized hinge regions and a stiff epoxy resin elsewhere. Such structures can achieve small fold radii, are strain energy deployable, and promise high deployed stiffness.
\r\n\r\nThis research demonstrates the capabilities of the proposed dual-matrix structures through direct comparison to existing antenna designs. Analytic scaling relations between structural and electromagnetic performance of various deployable antenna designs are developed. These are used to rapidly predict achievable antenna performance as a function of a common set of antenna geometric parameters. Plotting of this data on a coordinated set of 2D design plots enables the direct comparison of antenna concepts and the selection of specific designs meeting all requirements. This methodology was used to design a deployable dual-matrix composite conical log spiral (CLS) antenna for use on CubeSats which outperformed existing off-the-shelf designs through higher gain, higher bandwidth, and more efficient packaging.
\r\n\r\nStarting from this initial design, the antenna is tuned to maximize performance and an assembly including the CubeSat, dual-matrix antenna, dual-matrix hinge for antenna deployment, and a flexible feeding network is developed. All portions of the assembly are prototyped and tested. The antenna electromagnetic performance is predicted using ANSYS HFSS and verified by testing in an anaechoic chamber with antenna gains predicted within 4% of measured values. Structural stiffness is characterized through the antenna's fundamental frequency with simulated performance in the Abaqus finite element software within 6% of measured values. Comparison of antenna performance before and after packaging and deployment shows the structural frequency, antenna gain, and antenna bandwidth are unaffected by folding, demonstrating that dual-matrix composites are appropriate for use as deployable structures.
\r\n\r\nTechniques for the quasi-static deployment of dual-matrix composites are presented. An analytic minimum energy method, which accounts for fiber microbuckling in regions of high curvature, is used to predict the folded shape and deployment moments of a dual-matrix hinge. The model shows excellent agreement with LS-Dyna finite element simulations for a variety of material properties. Comparison with experimental characterization demonstrates the capability of the models to predict folded radii and deployment moment of a prototype hinge withing 5% of measured values. The developed analysis tool-set enables a design of deployment restraints and mechanisms.
\r\n\r\nThe woven elastomer composites forming the fold regions in dual-matrix composites have been the subject of very few studies. Existing methods for predicting the stiffness of woven epoxy composites are applied to elastomer composites here and show poor agreement with measurements. A novel approach is presented for the prediction of tow stiffness in elastomer composites using a semi-empirical approach. The reinforcing efficiency parameter in the well-established Halpin-Tsai model for tow homogenization is estimated using experimental measurements of stiffnesses of several laminates. It is shown that for elastomer composites, the parameter values are orders of magnitude higher than the heuristic values used for epoxy composites. The method is used to predict the stiffness of woven epoxy and elastomer composites making up the dual-matrix structures studied in this work showing agreement withing 15% of experimental measurements for arbitrary layups. The method is extended to the prediction of viscoelastic behavior of dual-matrix structures to enable investigation of deployment reliability after long storage times.
" }, { "name": "Saxton-Fox, Theresa Ann", "degree": "PhD", "year": "2018", "title": "Coherent Structures, their Interactions, and their Effects on Passive Scalar Transport and Aero-Optic Distortion in a Turbulent Boundary Layer", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11272017-152918929", "creators": [ { "name": { "family": "Saxton-Fox", "given": "Theresa Ann" }, "id": "Saxton-Fox-Theresa-Ann", "orcid": "0000-0003-1328-4148", "display_name": "Saxton-Fox, Theresa Ann" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9W0943P", "abstract": "This thesis focused on the characterization of coherent structures and their interactions in a turbulent boundary layer using data from particle image velocimetry (PIV) measurements performed at Caltech and from a direct numerical simulation (DNS) of Wu et al. (2017). Connections were identified between instantaneous and statistical descriptions of coherent velocity structures, through the analysis of representative models for their structures derived from the resolvent analysis of McKeon and Sharma (2010). The representative models were used in a novel conditional averaging technique to identify the average behavior of small scales about variations in the large-scale streamwise velocity field. Based upon the results of this analysis, a hypothesis for a scale interaction mechanism was proposed involving three-dimensional critical layers. The modeling and analysis methods were then applied to the aero-optic problem in which optical beams are observed to be distorted after passing through variable-density turbulent flows. Measurements using simultaneous PIV and an aero-optic sensor called a Malley probe (Malley, Sutton, and Kincheloe, 1992) were conducted in an incompressible, mildly-heated turbulent boundary layer with Prandtl number of 0.7. A conditional averaging analysis of the data identified that the nonlinear interaction of two scales was most correlated to the aero-optic distortion. The modeling of this interaction using resolvent modes led to new insights regarding the instantaneous relationship between the velocity and scalar fields over a range of Prandtl numbers.
" }, { "name": "Schaal, Natalie Sarah Ann", "degree": "PhD", "year": "2018", "title": "Modeling of Nucleation and Dynamic Rupture on Heterogeneous Frictional Interfaces with Applications to Foreshocks", "advisor": "Lapusta, Nadia", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272018-175543580", "creators": [ { "name": { "family": "Schaal", "given": "Natalie Sarah Ann" }, "id": "Schaal-Natalie-Sarah-Ann", "orcid": "0000-0003-4825-4344", "display_name": "Schaal, Natalie Sarah Ann" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "advisor", "display_name": "Lapusta, Nadia" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "role": "member", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "mecheng" ], "doi": "10.7907/YCVJ-PM21", "abstract": "While many large earthquakes are preceded by observable foreshocks, the mechanisms responsible for the occurrence of these smaller-scale seismic events remain uncertain. One physical explanation of foreshocks with growing support is that they are produced by the interaction of slow slip, due to the nucleation of the upcoming mainshock, with fault patches of different properties. Having a better understanding of how earthquakes nucleate on heterogeneous faults would increase our capacity to forecast potentially hazardous events.\r\n
\r\n\r\nWith this motivation in mind, we seek to understand what conditions produce isolated microseismicity within the nucleating region of the mainshock and to study the mechanics of the resulting events. Inspired by the suggestion from laboratory experiments that foreshocks occur on asperities, i.e., local deviations from planarity that are flattened by the overall compression, we explore the behavior of asperity-type patches of higher compressive stress embedded in the larger seismogenic region of a rate-and-state fault model by conducting 3D numerical simulations of their slip over long-term sequences of aseismic and seismic slip. Our models do produce smaller-scale seismicity during the aseismic nucleation of much larger seismic events, and we explore their properties as well as the separation in length scales needed to produce them. These foreshock-like events have stress drops that are consistent with laboratory and field observations and approximately constant, despite the highly elevated compression assigned to the source patches. Two main factors contributing to the reasonable stress drops are the significant extent of the rupture into the region surrounding the patch and the aseismic stress release just prior to the seismic event.
\r\n\r\n\r\nWe also investigate the seismologically-derived properties of the asperity-type events using the spectral analysis commonly applied to natural microseismic events. We find that the seismological methods cannot adequately capture the properties of the simulated events. In part, the seismological estimates of their stress drops are significantly different from the actual stress drops determined from the on-fault stress changes. This is because our sources have more complex features than the standard models from which the current seismological methods have been built, including heterogeneous stress change over the rupture area with much larger initial stress change, and heterogeneous rupture speed. We identify features in the far-field seismograms of the asperity-type sources that differ from the standard models and can be potentially characteristic of the asperity-type sources.\r\n
\r\n\r\n\r\nOur asperity-type models of microseismicity sources provide insight into the conditions conducive for generating foreshocks on both natural and laboratory faults and the properties of the resulting events. The conclusions provided jointly by the two perspectives in this study -- dynamically simulating the behavior of seismic sources within heterogeneous fault models and seismologically analyzing their far-field source spectra -- have important implications that warrant further study. Topics for future research include the interaction among smaller-scale seismic events and their role in the mainshock nucleation process, the effect of timing on their source properties, and relation to the so-called seismic nucleation phase of the subsequent mainshock.\r\n
\r\n" }, { "name": "Schlup, Jason Robert", "degree": "PhD", "year": "2018", "title": "Numerical Investigations of Transport and Chemistry Modeling for Lean Premixed Hydrogen Combustion", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-170312588", "creators": [ { "name": { "family": "Schlup", "given": "Jason Robert" }, "id": "Schlup-Jason-Robert", "orcid": "0000-0002-3121-3477", "display_name": "Schlup, Jason Robert" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KFN6-7K54", "abstract": "The use of hydrogen as a fuel for power generation applications has been suggested as an additive to, or replacement of, hydrocarbon fuels. The safety of hydrogen combustion has also received recent attention due to nuclear power plant disasters and the rise of hydrogen refuelling stations. In these uses and scenarios, lean hydrogen--air flames are prone to thermo-diffusive instabilities which can be dangerous to equipment and personnel. These instabilities are heavily influenced by two mechanisms: transport properties (e.g., diffusion) and chemical species production rates. This thesis investigates lean premixed hydrogen combustion using direct numerical simulations. A wide range of flame configurations are considered, spanning one-dimensional steady configurations to three-dimensional unsteady laminar and turbulent flames with high curvature. In particular, the two controlling mechanisms of thermo-diffusive instabilities are carefully investigated.
\r\n\t\r\nThe effects of transport properties, in particular the importance of thermal diffusion in these mixtures, are quantified through global and local evaluations. Thermal diffusion is found to change flame speeds in one-dimensional flat flames, and also modify species profiles due to the increased diffusivity of light reactants. The impact of thermal diffusion is greatly enhanced in the presence of flame curvature, resulting in higher flame speeds (20% to 30% for two- and three-dimensional laminar and turbulent flames), fuel consumption, and flame surface area relative to simulations neglecting thermal diffusion. The mixture-averaged thermal diffusion model proposed by Chapman and Cowling (1970) is found to accurately reproduce global and local flame statistics (including enhanced burning and local extinction) computed using multicomponent transport at significantly reduced costs. Further cost reductions of the mixture-averaged thermal diffusion method are undertaken, and a new model is developed with constant computational requirements for large (~100 species) chemical models. The resulting reduced thermal diffusion model additionally improves upon the accuracy of the mixture-averaged thermal diffusion technique.
\r\n\t\r\nThe effects of fluctuating chemical source terms on flame instabilities are then investigated using tabulated chemistry. One-dimensional unstretched flames including non-equal diffusion and thermal diffusion are incorporated into a chemistry table. This table successfully captures the interaction of differential diffusion and flame curvature. The chemistry tabulation approach is applied to a similar set of flame configurations, and accurate predictions of global and local statistics are found. The tabulated chemistry method reproduces flame curvature, local enhanced burning, and local extinction of unstable flames using one-dimensional, flat, burning flames in its construction. The proposed reduced-order thermal diffusion and chemistry tabulation models significantly reduce computational costs while simultaneously including physical properties necessary to predict lean premixed hydrogen--air flame instabilities.
" }, { "name": "Seetharam, Karthik Iyengar", "degree": "PhD", "year": "2018", "title": "Thermalization in Periodically-Driven Interacting Quantum Systems", "advisor": "Refael, Gil", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062018-171256773", "creators": [ { "name": { "family": "Seetharam", "given": "Karthik Iyengar" }, "id": "Seetharam-Karthik-Iyengar", "orcid": "0000-0003-1928-8019", "display_name": "Seetharam, Karthik Iyengar" } ], "advisors": [ { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "advisor", "display_name": "Refael, Gil" } ], "committee": [ { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "chair", "display_name": "Refael, Gil" }, { "name": { "family": "Motrunich", "given": "Olexei I." }, "id": "Motrunich-Olexei", "orcid": "0000-0001-8031-0022", "role": "member", "display_name": "Motrunich, Olexei I." }, { "name": { "family": "Alicea", "given": "Jason F." }, "id": "Alicea-J", "orcid": "0000-0001-9979-3423", "role": "member", "display_name": "Alicea, Jason F." }, { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "member", "display_name": "Hsieh, David" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3G0V-TW52", "abstract": "Periodically-driven (Floquet) quantum systems are ubiquitous in science and technology. For example, when a laser illuminates a material or an AC voltage is applied to a device, the system is well-described by a time-periodic Hamiltonian. In recent years, periodic driving has been proposed, not just as a tool to excite and probe devices, but actually as a mechanism of engineering new phases of matter, some of which have no equilibrium analog. However, with this promise comes a serious problem. Intuitively, if energy is injected into and distributed throughout a system, it is no surprise that it tends to heat up indefinitely to infinite temperature.
\r\n\r\nIn this thesis, we study the mechanisms of heating, i.e. the process of thermalization, in Floquet systems and propose methods to control them. Specifically, for non-interacting Floquet systems that are coupled to external bosonic and fermionic baths (e.g. laser-driven electrons in a semiconductor that interact with phonons and an external lead), we classify the relevant scattering processes that contribute to cooling/heating in the Floquet bands and suggest methods to suppress heating via bandwidth-restrictions on the baths. We find that is possible, with appropriate dissipative engineering, to stabilize a controlled incompressible nonequilibrium steady-state resembling a ground state - a state we term the \"Floquet insulator.\" We extend this analysis to include short-range interactions that contribute additional heating processes and show, under the same framework, that heating can be controlled with dissipation. In the process, we develop a simple effective model for the Floquet band densities that captures the essence of all the Floquet scattering processes and that is useful for ballparking experimentally-relevant estimates of heating. Next, we turn our attention to strongly-interacting closed Floquet systems and study how heating emerges through a proliferation of resonances. We find a novel integrable point governing the strong-interaction limit of the Floquet system and examine the breakdown of integrability via the proliferation of resonances. We observe two distinct scaling regimes, attributed to non-thermal and thermal behavior, and discover a power-law scaling of the crossover between them as a function of system size. The lingering ergodicity-breaking effects of the conserved quantities in the vicinity (in parameter space) of the integrable point at finite size is a phenomena we term \"near-integrability.\" These results suggest that small quantum systems, which are accessible currently in many platforms (e.g. trapped ions, cold atoms, superconducting devices), intrinsically host non-thermal states that one may be able to utilize to avoid heating. Furthermore, our results suggest a \"dual\" interpretation, in the thermodynamic limit, that a periodically-driven system exhibits prethermalization as a power-law in interaction strength.
" }, { "name": "Sherrott, Michelle Caroline", "degree": "PhD", "year": "2018", "title": "Active Infrared Nanophotonics in van der Waals Materials", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:01262018-171457982", "creators": [ { "name": { "family": "Sherrott", "given": "Michelle Caroline" }, "id": "Sherrott-Michelle-Caroline", "orcid": "0000-0002-7503-9714", "display_name": "Sherrott, Michelle Caroline" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9J964M8", "abstract": "Two-dimensional van der Waals materials have recently been introduced into the field of nanophotonics, creating opportunities to explore novel physics and realize first-of-their kind devices. By reducing the thickness of these materials, novel optical properties emerge due to the introduction of vertical quantum confinement. Unlike most materials, which suffer from a reduction in quality as they are thinned, layered van der Waals materials have naturally passivated surfaces that preserve their performance in monolayer form. Moreover, because the thickness of these materials is below typical charge carrier screening lengths, it is possible to actively control their optical properties with an external gate voltage. By combining these unique properties with the subwavelength control of light-matter interactions provided by nanophotonics, new device architectures can be realized.
\r\n\r\nIn this thesis, we explore van der Waals materials for active infrared nanophotonics, focusing on monolayer graphene and few-layer black phosphorus. Chapter 2 introduces gate-tunable graphene plasmons that interact strongly with their environment and can be combined with an external cavity to reach large absorption strengths in a single atomic layer. Chapter 3 builds on this, using graphene plasmons to control the spectral character and polarization state of thermal radiation. In Chapter 4, we complete the story of actively controlling infrared light using graphene-based structures, introducing graphene into a resonant gold structure to enable active control of phase. By combining these resonant structures together into a multi-pixel array, we realize an actively tunable meta-device for active beam steering in the infrared. In Chapters 5 and 6, we present few layer black phosphorus (BP) as a novel material for active infrared nanophotonics. We study the different electro-optic effects of the material from the visible to mid-infrared. We additionally examine the polarization-dependent response of few-layer BP, observing that we can tune its optical response from being highly anisotropic to nearly isotropic in plane. Finally, Chapter 7 comments on the challenges and opportunities for graphene- and BP-integrated nanophotonic structures and devices.
" }, { "name": "Sun, Dingyi", "degree": "PhD", "year": "2018", "title": "Proliferation of Twinning in Metals: Application to Magnesium Alloys", "advisor": "Bhattacharya, Kaushik; Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:08042017-190200194", "creators": [ { "name": { "family": "Sun", "given": "Dingyi" }, "id": "Sun-Dingyi", "orcid": "0000-0003-2109-7123", "display_name": "Sun, Dingyi" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "co-advisor", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "co-advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ponga", "given": "Mauricio" }, "id": "Ponga-M", "role": "member", "display_name": "Ponga, Mauricio" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z93B5XB4", "abstract": "In the search for new alloys with a great strength-to-weight ratio, magnesium has emerged at the forefront. With a strength rivaling that of steel and aluminum alloys --- materials which are deployed widely in real world applications today --- but only a fraction of the density, magnesium holds great promise in a variety of next-generation applications. Unfortunately, the widespread adoption of magnesium is hindered by the fact that it fails in a brittle fashion, which is undesirable when it comes to plastic deformation mechanisms. Consequently, one must design magnesium alloys to navigate around this shortcoming and fail in a more ductile fashion.
\r\n\r\nHowever, such designs are not possible without a thorough understanding of the underlying mechanisms of deformation in magnesium, which is somewhat contested at the moment. In addition to slip, which is one of the dominant mechanisms in metallic alloys, a mechanism known as twinning is also present, especially in hexagonal close-packed (HCP) materials such as magnesium. Twinning involves the reorientation of the material lattice about a planar discontinuity and has been shown as one of the preferred mechanisms by which magnesium accommodates out-of-plane deformation. Unfortunately, twinning is not particularly well-understood in magnesium, and needs to be addressed before progress can be made in materials design. In particular, though two specific modes of twinning have been acknowledged, various works in the literature have identified a host of additional modes, many of which have been cast aside as \"anomalous\" observations.
\r\n\r\nTo this end, we introduce a new framework for predicting the modes by which a material can twin, for any given material. Focusing on magnesium, we begin our investigation by introducing a kinematic framework that predicts novel twin configurations, cataloging these twins modes by their planar normal and twinning shear. We then subject the predicted twin modes to a series of atomistic simulations, primarily in molecular statics but with supplementary calculations using density functional theory, giving us insight on both the energy of the twin interface and barriers to formation. We then perform a stress analysis and identify the twin modes which are most likely to be activated, thus finding the ones most likely to affect the yield surface of magnesium.
\r\n\r\nOver the course of our investigation, we show that many different modes actually participate on the yield surface of magnesium; the two classical modes which are accepted by the community are confirmed, but many additional modes --- some of which are close to modes which have been previously regarded as anomalies --- are also observed. We also perform some extensional work, showing the flexibility of our framework in predicting twins in other materials and in other environments and highlighting the complicated nature of twinning, especially in HCP materials.
" }, { "name": "Swaminathan, Anandh", "degree": "PhD", "year": "2018", "title": "Application, Computation, and Theory for Synthetic Gene Circuits", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132017-121914940", "creators": [ { "name": { "family": "Swaminathan", "given": "Anandh" }, "id": "Swaminathan-Anandh", "orcid": "0000-0001-9935-6530", "display_name": "Swaminathan, Anandh" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Goentoro", "given": "Lea A." }, "id": "Goentoro-L-A", "role": "member", "display_name": "Goentoro, Lea A." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "cds" ], "doi": "10.7907/Z9833Q67", "abstract": "The field of synthetic gene circuits is concerned with engineering novel gene expression dynamics into organisms. This field, a subset of synthetic biology, was started almost two decades ago with the creation of two synthetic circuits: a bistable toggle switch and an oscillator. From the very outset, modeling has played a role in the development of synthetic circuits. However, modeling has been used to gain qualitative insight into dynamics, and actual quantitative modeling has been lagging behind.
\r\n\r\nParameters for quantitative models for biological systems often cannot be adequately estimated from measured data, because far too many sets of parameters can produce the same set of limited measured outputs. Additionally, models for synthetic gene circuits are often not correct the first time, and iterating on cycles of modeling and parameter estimation is difficult. Finally, there is a gap between development of modeling and system identification tools and their application to experiments on actual synthetic gene circuits.
\r\n\r\nThis thesis attempts to work towards addressing these issues with quantitative modeling for synthetic gene circuits. First, we derive theoretical conditions for identifiability of stochastic linear systems from heterogenous types of measurement data. These identifiability conditions can provide insight into what type of model to use and what measurements to collect in order to ensure that the resulting model can be identified.
\r\n\r\nSecond, we develop a software package for fast and flexible modeling and parameter estimation for synthetic gene circuits. The user can input models into our software using a simple text format and perform simulations of all types at optimized speeds. By inputting measured experimental data along with the model, the software can be used to perform Bayesian parameter estimation in an automated manner. To bridge the gap between computation and application, we apply this software to parameter estimation of DNA recombinase dynamics using real experimental data collected in an in vitro cell extract.
\r\n\r\nFinally, we use modeling to guide the design of an improved single gene synthetic oscillator. While the original synthetic genetic oscillator contained three genes, we show that a simple circuit with a single gene can produce robust and synchronized oscillations across a population.
\r\n\r\nOur results constitute an additional step towards the incorporation of quantitative modeling and parameter inference as part of the design-build-test cycle for synthetic gene circuits.
" }, { "name": "Symon, Sean Pearson", "degree": "PhD", "year": "2018", "title": "Reconstruction and Estimation of Flows Using Resolvent Analysis and Data-Assimilation", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302018-181049042", "creators": [ { "name": { "family": "Symon", "given": "Sean Pearson" }, "id": "Symon-Sean-Pearson", "orcid": "0000-0001-9085-0778", "display_name": "Symon, Sean Pearson" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B4K7-K876", "abstract": "A flow reconstruction methodology is presented for incompressible, statistically stationary flows using resolvent analysis and data-assimilation. The only inputs necessary for the procedure are a rough approximation of the mean profile and a single time-resolved measurement. The objective is to estimate both the mean and fluctuating states of experimental flows with limited measurements which do not include pressure. The input data may be incomplete, in the sense that measurements near a body are difficult to obtain with techniques such as particle image velocimetry (PIV), or contaminated by noise. The tools developed in this thesis are capable of filling in missing data and reducing the amount of measurement noise by leveraging the governing equations. The reconstructed flow is capable of estimating fluctuations where time-resolved data are not available and solving the flow on larger domains where the mean profile is not known.
\r\n\r\nThe first part of the thesis focuses on how resolvent analysis of the mean flow selects amplification mechanisms. Eigenspectra and pseudospectra of the mean linear Navier-Stokes (LNS) operator are used to characterize amplification mechanisms in flows where linear mechanisms are important. The real parts of the eigenvalues are responsible for resonant amplification and the resolvent operator is low-rank when the eigenvalues are sufficiently separated in the spectrum. Two test cases are studied: low Reynolds number cylinder flow and turbulent channel flow. The latter is studied by considering well-known turbulent structures while the former contains a marginally stable eigenvalue which drowns out the effect of other eigenvalues over a large range of temporal frequencies. There is a geometric manifestation of this dominant mode in the mean profile, suggesting that it leaves a significant footprint on the time-averaged flow that the resolvent can identify. The resolvent does not provide an efficient basis at temporal frequencies where there is no separation of singular values. It can still be leveraged, nevertheless, to identify coherent structures in the flow by approximating the nonlinear forcing from the interaction of highly amplified coherent structures.
\r\n\r\nThe second part of the thesis extends the framework of Foures et al. (2014), who data-assimilated the mean cylinder wake at very low Reynolds numbers. The contributions presented here are to assess the minimum domain for successfully reconstructing Reynolds stress gradients, modifying the algorithm to assimilate mean pressure, determining whether weighting input measurements contributes to improved performance, and adapting the method to experimental data at higher Reynolds numbers. The results from data-assimilating the mean cylinder wake at low Reynolds numbers suggest that the measurement domain needs to coincide with the spatial support of the Reynolds stress gradients while point weighting has a minimal impact on the performance. Finally, a smoothing procedure adapted from Foures et al. (2014) is proposed to cope with data-assimilating an experimental mean profile obtained from PIV data. The data-assimilated mean profiles for an idealized airfoil and NACA 0018 airfoil are solved on a large domain making the mean profile suitable for global resolvent analysis. Data-assimilation is also able to fill in missing or unreliable vectors near the airfoil surface.
\r\n\r\nThe final piece of the thesis is to synthesize the knowledge and techniques developed in the first two parts to reconstruct the experimental flow around a NACA 0018 airfoil. Preliminary results are presented for the case where \u03b1 = 0\u00b0 and Re = 10250. The mean profile is data-assimilated and used as an input to resolvent analysis to educe coherent structures in the flow. The resolvent operator for non- amplified temporal frequencies is forced by an approximated nonlinear forcing. The amplitude and phase of the modes are obtained from the discrete Fourier-transform of a time-resolved probe point measurement. The final reconstruction contains less measurement noise compared to the PIV snapshots and obeys the incompressible Navier-Stokes equations (NSE). The thesis concludes with a discussion of how elements of this methodology can be incorporated into the development of estimators for turbulent flows at high Reynolds numbers.
" }, { "name": "Tembhekar, Ishan", "degree": "PhD", "year": "2018", "title": "The Fully Nonlocal, Finite-Temperature, Adaptive 3D Quasicontinuum Method for Bridging Across Scales", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04222018-122438253", "creators": [ { "name": { "family": "Tembhekar", "given": "Ishan" }, "id": "Tembhekar-Ishan", "orcid": "0000-0001-5123-1958", "display_name": "Tembhekar, Ishan" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "mecheng" ], "doi": "10.7907/RF27-NA04", "abstract": "Computational modeling of metallic materials across various length and time scales has been on the rise since the advent of efficient, fast computing machines. From atomistic methods like molecular statics and dynamics at the nanoscale to continuum mechanics modeled by finite element methods at the macroscale, various techniques have been established that describe and predict the mechanics of materials. Many recent technologies, however, fall into a gap between length scales (referred to as mesoscales), with microstructural features on the order of nanometers (thereby requiring full atomistic resolution) but large representative volumes on the order of micrometers (beyond the scope of molecular dynamics). There is an urgent need to predict material behavior using scale-bridging techniques that build up from the atomic level and reach larger length and time scales. To this end, there is extensive ongoing research in building hierarchical and concurrent scale-bridging techniques to master the gap between atomistics and the continuum, but robust, adaptive schemes with finite-temperature modeling at realistic length and time scales are still missing.
\r\n\r\nIn this thesis, we use the quasicontinuum (QC) method, a concurrent scale-bridging technique that extends atomistic accuracy to significantly larger length scales by reducing the full atomic ensemble to a small set of representative atoms, and using interpolation to recover the motion of all lattice sites where full atomistic resolution is not necessary. We develop automatic model adaptivity by adding mesh refinement and adaptive neighborhood updates to the new fully nonlocal energy-based 3D QC framework, which allows for automatic resolution to full atomistics around regions of interest such as nanovoids and moving lattice defects. By comparison to molecular dynamics (MD), we show that these additions allow for a successful and computationally efficient coarse graining of atomistic ensembles while maintaining the same atomistic accuracy.
\r\n\r\nWe further extend the fully nonlocal QC formulation to finite temperature (termed hotQC) using the principle of maximum entropy in statistical mechanics and averaging the thermal motion of atoms to obtain a temperature-dependent free energy using numerical quadrature. This hotQC formulation implements recently developed optimal summation rules and successfully captures temperature-dependent elastic constants and thermal expansion. We report for the first time the influence of temperature on force artifacts and conclude that our novel finite-temperature adaptive nonlocal QC shows minimal force artifacts and outperforms existing formulations. We also highlight the influence of quadrature in phase space on simulation outcomes.
\r\n\r\nWe study 3D grain boundaries in the nonlocal hotQC framework (previously limited to single-crystals) by modeling coarse-grained symmetric-tilt grain boundaries in coincidence site lattice (CSL) based bicrystals. We predict relaxed energy states of various \u03a3-boundaries with reasonable accuracy by comparing grain boundary energies to MD simulations and outline a framework to model polycrystalline materials that surpasses both spatial and temporal limitations of traditional MD.
" }, { "name": "Tenneti, Srikanth Venkata", "degree": "PhD", "year": "2018", "title": "The Nested Periodic Subspaces: Extensions of Ramanujan Sums for Period Estimation", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062018-132643508", "creators": [ { "name": { "family": "Tenneti", "given": "Srikanth Venkata" }, "id": "Tenneti-Srikanth-Venkata", "orcid": "0000-0002-5415-3681", "display_name": "Tenneti, Srikanth Venkata" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/1n4t-5876", "abstract": "In the year 1918, the Indian mathematician Srinivasa Ramanujan proposed a set of sequences called Ramanujan Sums as bases to expand arithmetic functions in number theory. Today, exactly a 100 years later, we will show that these sequences re-emerge as exciting tools in a completely different context: For the extraction of periodic patterns in data. Combined with the state-of-the-art techniques of DSP, Ramanujan Sums can be used as the starting point for developing powerful algorithms for periodicity applications.
\r\n\r\nThe primary inspiration for this thesis comes from a recent extension of Ramanujan sums to subspaces known as the Ramanujan subspaces. These subspaces were designed to span any sequence with integer periodicity, and have many interesting properties. Starting with Ramanujan subspaces, this thesis first develops an entire family of such subspace representations for periodic sequences. This family, called Nested Periodic Subspaces due to their unique structure, turns out to be the least redundant sets of subspaces that can span periodic sequences.
\r\n\r\nThree classes of new algorithms are proposed using the Nested Periodic Subspaces: dictionaries, filter banks, and eigen-space methods based on the auto-correlation matrix of the signal. It will be shown that these methods are especially advantageous to use when the data-length is short, or when the signal is a mixture of multiple hidden periods. The dictionary techniques were inspired by recent advances in sparsity based compressed sensing. Apart from the l1 norm based convex programs currently used in other applications, our dictionaries can admit l2 norm formulations that have linear and closed form solutions, even when the systems is under-determined. A new filter bank is also proposed using the Ramanujan sums. This, named the Ramanujan Filter Bank, can accurately track the instantaneous period for signals that exhibit time varying periodic nature. The filters in the Ramanujan Filter Bank have simple integer valued coefficients, and directly tile the period vs time plane, unlike classical STFT (Short Time Fourier Transform) and wavelets, which tile the time-frequency plane. The third family of techniques developed here are a generalization of the classic MUSIC (MUltiple SIgnal Classification) algorithm for periodic signals. MUSIC is one of the most popular techniques today for line spectral estimation. However, periodic signals are not just any unstructured line spectral signals. There is a nice harmonic spacing between the lines which is not exploited by plain MUSIC. We will show that one can design much more accurate adaptations of MUSIC using Nested Periodic Subspaces. Compared to prior variants of MUSIC for the periodicity problem, our approach is much faster and yields much more accurate results for signals with integer periods. This work is also the first extension of MUSIC that uses simple integer valued basis vectors instead of using traditional complex-exponentials to span the signal subspace. The advantages of the new methods are demonstrated both on simulations, as well as real world applications such as DNA micro-satellites, protein repeats and absence seizures.
\r\n\r\nApart from practical contributions, the theory of Nested Periodic Subspaces offers answers to a number of fundamental questions that were previously unanswered. For example, what is the minimum contiguous data-length needed to be able to identify the period of a signal unambiguously? Notice that the answer we seek is a fundamental identifiability bound independent of any particular period estimation technique. Surprisingly, this basic question has never been answered before. In this thesis, we will derive precise expressions for the minimum necessary and sufficient datalengths for this question. We also extend these bounds to the context of mixtures of periodic signals. Once again, even though mixtures of periodic signals often occur in many applications, aspects such as the unique identifiability of the component periods were never rigorously analyzed before. We will present such an analysis as well.
\r\n\r\nWhile the above question deals with the minimum contiguous datalength required for period estimation, one may ask a slightly different question: If we are allowed to pick the samples of a signal in a non-contiguous fashion, how should we pick them so that we can estimate the period using the least number of samples? This question will be shown to be quite difficult to answer in general. In this thesis, we analyze a smaller case in this regard, namely, that of resolving between two periods. It will be shown that the analysis is quite involved even in this case, and the optimal sampling pattern takes an interesting form of sparsely located bunches. This result can also be extended to the case of multi-dimensional periodic signals.
\r\n\r\nWe very briefly address multi-dimensional periodicity in this thesis. Most prior DSP literature on multi-dimensional discrete time periodic signals assumes the period to be parallelepipeds. But as shown by the artist M. C. Escher, one can tile the space using a much more diverse variety of shapes. Is it always possible to account for such other periodic shapes using the traditional notion of parallelepiped periods? An interesting analysis in this regard is presented towards the end of the thesis.
\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n" }, { "name": "Tozier, Dylan Douglas", "degree": "PhD", "year": "2018", "title": "Cathode Design for High Energy Molten Salt Lithium-Oxygen Batteries", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072018-140534228", "creators": [ { "name": { "family": "Tozier", "given": "Dylan Douglas" }, "id": "Tozier-Dylan-Douglas", "orcid": "0000-0001-9489-8824", "display_name": "Tozier, Dylan Douglas" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" } ], "option_major": [ "matsci" ], "doi": "10.7907/TG0K-8776", "abstract": "State of the art commercial lithium ion batteries use cathodes such as lithium cobalt oxide which rely on insertion and removal of lithium ions from a host material. However, insertion cathode materials are limited in their capacity, and replacing them with a cathode that employs growth and dissolution of new phases could significantly increase a battery\u2019s energy density. For example, oxygen and sulfur cathodes have been widely researched to this end, with both cases involving the growth of a lithium-rich compound on a current collector/catalyst support.
\r\n\r\nWe begin by describing the effect of using a molten salt electrolyte in a lithium-oxygen battery. In particular, we focus on how the electrochemical performance and discharge product, lithium peroxide, differ from that of a traditional organic electrolyte. In addition, we discuss the enhanced peroxide solubility in a molten salt and its implications for lithium peroxide growth and coulombic efficiency. Finally, we address the cell death of a galvanostatically cycled battery.
\r\n\r\nWe then introduce a similar phase-forming conversion chemistry, whereby a molten nitrate salt serves as both an active material and the electrolyte. Molten nitrate salts were previously studied as an active material in a primary lithium battery where lithium oxide irreversibly forms as nitrate reduces to nitrite. We will describe how the use of a nanoparticle heterogeneous catalyst allows the reversible growth and dissolution of micron-scale lithium oxide crystals in this system.
\r\n\r\nAfter introducing these molten salt lithium batteries, we address the effect of cathode geometry on electrochemical performance. In particular, we note that the growth of such large, solid phase species on the surface of the catalyst support imposes new design restrictions when optimizing a cathode for energy density. As a proof of concept, we design and implement an architected electrode with large pore volume and relatively small surface area, comparing it with the more typical geometries of thin films and nanoparticles.
" }, { "name": "Yang, Kiyoul", "degree": "PhD", "year": "2018", "title": "Integrated Ultra-High-Q Nonlinear Photonic Platform for On-Chip Optoelectronic Systems", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechThesis:10042017-102201104", "creators": [ { "name": { "family": "Yang", "given": "Kiyoul" }, "id": "Yang-Kiyoul", "orcid": "0000-0002-0587-3201", "display_name": "Yang, Kiyoul" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z96T0JTQ", "abstract": "Silicon technology provided a concrete basis of the integrated microelectronics revolution, and it might usher disruptive advances in photonics again. An integrated photonic system can potentially revolutionize instrumentation, time standards, spectroscopy, and navigation. Driven by these applications, various high-Q platforms have emerged over the last decade. However, applications require to satisfy challenging combinations of ultra-high-Q (UHQ) cavity performance, monolithic integration, and nonlinear cavity designs: the monolithic integration of UHQ devices still remains elusive. In this thesis, an integrated UHQ microcavity is demonstrated for the first time. A silicon nitride waveguide is monolithically integrated with a silicon oxide cavity, and the integrated waveguide can provide nearly universal interface to other photonic devices. Significantly, this thesis discusses far beyond setting a new record for integrated Q factor: the integrated UHQ cavity provides functionality as soliton source with electronic-repetition-rates. Demonstration of low-pump-power soliton generation at 15 GHz was previously possible in only discrete devices but essentially required for integrated self-referenced comb, which can unlock new level of performance and scale in an optoelectronic system. In addition, nonlinear cavity design is another outstanding challenge towards a further development on the optoelectronic system, and will be discussed in this thesis. The dispersion-engineered platform can potentially tailor the spectral bandwidth of frequency comb, and extend the frequency comb to visible and ultraviolet band. Importantly, the design methods are directly transferable to the integrated platform." }, { "name": "Yin, Lucy", "degree": "PhD", "year": "2018", "title": "Reducing Latencies in Earthquake Early Warning", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242017-121200052", "creators": [ { "name": { "family": "Yin", "given": "Lucy" }, "id": "Yin-Lucy", "orcid": "0000-0002-0652-9330", "display_name": "Yin, Lucy" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "chair", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Ampuero", "given": "Jean-Paul" }, "id": "Ampuero-J-P", "orcid": "0000-0002-4827-7987", "role": "member", "display_name": "Ampuero, Jean-Paul" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Page", "given": "Morgan" }, "id": "Page-Morgan", "role": "member", "display_name": "Page, Morgan" } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9TH8JW4", "abstract": "Existing Earthquake Early Warning (EEW) algorithms use waveform analysis for earthquake detections, estimation of source parameters (i.e., magnitude and hypocenter location), and prediction of peak ground motions at sites near the source. The latency of warning delivery due to data collection significantly restricts the usefulness of the system, especially for users in the vicinity of the earthquake source, as the warning may not arrive before the strong shaking. This presentation discusses several methods to reduce the warning latency, while maintaining reliability and robustness, so that the warning time can be maximized for users to take appropriate actions to reduce causalities and economic losses.
\r\n\r\nFirstly, we incorporated the seismicity forecast information from Epidemic-Type Aftershock Sequence (ETAS) model into EEW as prior information, under the Bayesian probabilistic inference framework. Similar to human\u2019s decision-making process, the Bayesian approach updates the probability of the estimations as more information becomes available. This allows us to reduce the required time for reliable earthquake signal detection from at least 3 seconds to 0.5 second. Furthermore, the initial error of hypocenter location estimation is reduced by 58%. The performance of the algorithm is further improved during aftershock sequences and swarm earthquakes.
\r\n\r\nSecondly, we introduce the use of multidimensional (KD tree) data structure to organize seismic database, so that the querying time can be reduced for the nearest neighbor search during earthquake source parameter estimation. The processing time of KD tree is approximately 15% of the processing time of linear exhaustive search, which allows the potential use of large seismic databases in real-time.
\r\n\r\nEEW is an interdisciplinary subject that involves collaboration among different scientific and engineering communities. Only by optimizing the warning time, such a unified system could be successful in taking protective actions before, during, and after earthquake natural disasters.
" }, { "name": "Zhou, Xinghao", "degree": "PhD", "year": "2018", "title": "Performance and Stability Optimization of Solar Fuel Devices", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062018-164727269", "creators": [ { "name": { "family": "Zhou", "given": "Xinghao" }, "id": "Zhou-Xinghao", "orcid": "0000-0001-9229-7670", "display_name": "Zhou, Xinghao" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "chair", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/SSNP-XW29", "abstract": "Fossil fuels enabled the Industrial Revolution, and have been the most important power for promoting the world's economic growth ever since. However, burning fossil fuels have also been causing severe air pollution, and global warming is also related to excessive use of fossil fuels. Solar energy is considered to be the largest renewable clean energy resource. The principal problems of solar energy are low energy concentration and intermittency. Storing solar energy in chemical bonds, similar to photosynthesis in nature, is a possible way to overcome these two problems. Carbon-free chemicals, like hydrogen gas produced by solar-driven water splitting, or carbon-neutral chemicals, like methane, ethylene, formic acid, carbon monoxide, etc. produced from solar-driven CO2 reduction, are all promising clean fuels for solar storage, as they feature high energy/power intensity, are easy and cheap to store and transport, and have direct interface with existing infrastructures.
\r\n\r\nIn this thesis, we focus on improving the efficiency and stability of the solar-driven fuel generation devices, which consist of (photo-)anode and (photo-)cathode. For the anode part, cobalt oxide Co3O4 ultrathin (2 nm) films by atomic layer deposition (ALD) were deposited onto silicon photoanode prior to deposition of thick nickel oxide (NiOx) layers. The photovoltage of the photoanode increased from 200 mV to 580 mV after including the interfacial Co3O4 layer, and the anode was stable in 1.0 M KOH(aq) for 1700 hours, which was equivalent to one year of operation in the field at a maximum photocurrent density of 30 mA/cm2 assuming a 20% solar capacity factor. Furthermore, the non-uniform sputtered (NiOx) layer of the n-Si/SiOx/Co3O4/NiOx photoanode was removed, and the 2 nm Co3O4 film was thickened to 50 nm, and the stability of n-Si/SiOx/50 nm-Co3O4 was improved to 2500 hours with lower efficiency decay rate. For the cathode part, an optimized Pd/C nanoparticle coated Ti mesh cathode exhibited < 100 mV overpotential at 8.5 mA/cm2 current density, and > 94% Faradaic efficiency for the reduction of 1 atm of CO2(g) to formate in 2.8 M KHCO3. A solar-driven CO2 reduction (CO2R) cell was constructed with this cathode, showing 10% solar-to-fuels conversion efficiency.
\r\n\r\nThis thesis can be divided into three parts. The first part discusses importance of solar fuels, as well as gives an introduction of solar-fuel generators. The second part includes Chapter II and Chapter III, which deal with performance improvement of silicon photoanode with ALD Co3O4 thin films. The third part is Chapter IV, in which we study the cathode for CO2 reduction to formate, and demonstrate a 10% efficiency solar-driven CO2 reduction cell with the cathode.
" }, { "name": "Appel, Ron", "degree": "PhD", "year": "2017", "title": "Boosting Boosting", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052017-221842127", "creators": [ { "name": { "family": "Appel", "given": "Ron" }, "id": "Appel-Ron", "display_name": "Appel, Ron" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9N29V0J", "abstract": "Machine learning is becoming prevalent in all aspects of our lives. For some applications, there is a need for simple but accurate white-box systems that are able to train efficiently and with little data.
\r\n\r\n\"Boosting\" is an intuitive method, combining many simple (possibly inaccurate) predictors to form a powerful, accurate classifier. Boosted classifiers are intuitive, easy to use, and exhibit the fastest speeds at test-time when implemented as a cascade. However, they have a few drawbacks: training decision trees is a relatively slow procedure, and from a theoretical standpoint, no simple unified framework for cost-sensitive multi-class boosting exists. Furthermore, (axis-aligned) decision trees may be inadequate in some situations, thereby stalling training; and even in cases where they are sufficiently useful, they don't capture the intrinsic nature of the data, as they tend to form boundaries that overfit.
\r\n\r\nMy thesis focuses on remedying these three drawbacks of boosting.\r\nCh.III outlines a method (called QuickBoost) that trains identical classifiers at an order of magnitude faster than before, based on a proof of a bound. In Ch.IV, a unified framework for cost-sensitive multi-class boosting (called REBEL) is proposed, both advancing theory and demonstrating empirical gains. Finally, Ch.V describes a novel family of weak learners (called Localized Similarities) that guarantee theoretical bounds and outperform decision trees and Neural Nets (as well as several other commonly used classification methods) on a range of datasets.
\r\n\r\nThe culmination of my work is an easy-to-use, fast-training, cost-sensitive multi-class boosting framework whose functionality is interpretable (since each weak learner is a simple comparison of similarity), and whose performance is better than Neural Networks and other competing methods. It is the tool that everyone should have in their toolbox and the first one they try.
" }, { "name": "Batara, Nicolas Anthony", "degree": "PhD", "year": "2017", "title": "Spontaneous Pattern Formation in Photoelectrodeposited Semiconductor Films", "advisor": "Atwater, Harry Albert; Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032017-161239736", "creators": [ { "name": { "family": "Batara", "given": "Nicolas Anthony" }, "id": "Batara-Nicolas-Anthony", "orcid": "0000-0002-9154-4577", "display_name": "Batara, Nicolas Anthony" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "co-advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "co-advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z98S4MZ4", "abstract": "The ability to manipulate matter with ever-increasing precision has enabled the fabrication of nanoscale structures with unprecedented utility. Scalable patterning technologies have dramatically transformed diverse application spaces such as computing and photonics, in part due to diminishing cost per unit area. The work in this thesis presents a template-free, bottom-up technique based on photoelectrodeposition which allows the direct fabrication of periodically nanostructured thin films of semiconductor material over large areas.
\r\n \r\nFirst, we examine the effects of wavelength, polarization and incidence angle of illumination on the film morphology. We develop an understanding of the pattern formation to be the result of interference of light scattered across the surface of the growing interface. We also examine the morphological effects of more complex illumination conditions. For example, when deposited under two different illumination wavelengths, the period of patterned films self-optimizes to concentrate light absorption to the tips of the nanostructures . Additionally, we find that the relative polarization angles and phases of two illumination sources can be tuned to produce film morphologies ranging from isotropic mesh-type patterns to orthogonally arranged, intersecting lamellar structures with independent periodicities.
\r\n\r\nWe deepen our understanding of these observations by building a probabilistic computational model that correlates the local light absorption with a local growth probability at the interface of the film with few material parameters. We find that this model is able to reproduce experimentally observed morphological features for all illumination conditions investigated in this work. Through Fourier analysis, we find quantitative agreement between the simulated and experimental periods. Separately, we use electrodynamic simulations on idealized lamellar structures to understand the effect of two coincident illumination sources on the spatial absorption profile.
" }, { "name": "Bhattacharyya, Pinaky", "degree": "PhD", "year": "2017", "title": "Optimal Sensor Placement for Bayesian Parametric Identification of Structures", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182017-090742614", "creators": [ { "name": { "family": "Bhattacharyya", "given": "Pinaky" }, "id": "Bhattacharyya-Pinaky", "orcid": "0000-0003-3773-0392", "display_name": "Bhattacharyya, Pinaky" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9H41PG5", "abstract": "There exists a choice in where to place sensors to collect data for Bayesian model updating and system identification of structures. It is desirable to use an available deterministic predictive model, such as a finite-element model, along with prior information on the uncertain model parameters and the uncertain accuracy of the predictive model, to determine which optimal sensor locations should be instrumented in the structure. In this thesis, an information-theoretic framework for optimality is considered.
\r\n\r\nThe mutual information between the uncertain model predictions for the data and the uncertain model parameters is presented as a natural measure of reduction in uncertainty to maximize over sensor configurations. A combinatorial search over all sensor configurations is usually prohibitively expensive. A convex optimization method is developed to provide a fast sub-optimal, but possibly optimal, sensor configuration when certain simplifying assumptions can be made about the chosen stochastic model class for the structure. The optimization method is demonstrated to work for a 50-story uniform shear building, with 20 sensors to be installed.
\r\n\r\nThe stability of optimal sensor configurations under refinement of the mesh of the underlying finite-element model is investigated and related to the choice of prediction-error correlations in the model. An example problem of placement of a single sensor on the continuum of an elastic axial bar is solved analytically.
\r\n\r\nIn order to solve the optimal sensor placement problem in the more general case, numerical estimation of mutual information between the model predictions for the data and the model parameters becomes necessary. To this end, a thermodynamic integration scheme based on path sampling is developed with the aim of estimating the entropy of the data prediction distribution. The scheme is demonstrated to work for an example that uses synthetic data for model class comparison between linear and Duffing oscillator model classes. The thermodynamic integration method is then used to determine the optimal location of a single sensor for a two degree-of-freedom oscillator model.
\r\n" }, { "name": "Bhui, Rahul Brian", "degree": "PhD", "year": "2017", "title": "Essays on Timing and Economic Behavior", "advisor": "Camerer, Colin F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07292016-015158537", "creators": [ { "name": { "family": "Bhui", "given": "Rahul Brian" }, "id": "Bhui-Rahul-Brian", "orcid": "0000-0002-6303-8837", "display_name": "Bhui, Rahul Brian" } ], "advisors": [ { "name": { "family": "Camerer", "given": "Colin F." }, "id": "Camerer-C-F", "orcid": "0000-0003-4049-1871", "role": "advisor", "display_name": "Camerer, Colin F." } ], "committee": [ { "name": { "family": "Shum", "given": "Matthew S." }, "id": "Shum-M-S", "orcid": "0000-0002-6262-915X", "role": "chair", "display_name": "Shum, Matthew S." }, { "name": { "family": "Camerer", "given": "Colin F." }, "id": "Camerer-C-F", "orcid": "0000-0003-4049-1871", "role": "member", "display_name": "Camerer, Colin F." }, { "name": { "family": "Sherman", "given": "Robert P." }, "id": "Sherman-R-P", "role": "member", "display_name": "Sherman, Robert P." }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Krajbich", "given": "Ian M." }, "id": "Krajbich-I-M", "role": "member", "display_name": "Krajbich, Ian M." } ], "option_major": [ "cns" ], "doi": "10.7907/Z9959FJP", "abstract": "Economic activities unfold over time. How does timing influence our choices? How do we control our timing? Economic agents are considered to satisfy their preferences in an optimal fashion subject to constraints. Each chapter in this thesis tackles a different one of these three elements where the timing of behavior is central.
\r\n\r\nIn the first chapter, I study the impact of loss aversion on preferences for labor versus leisure. In a real-effort lab experiment, I show that a worker's willingness to persevere in a task is influenced by information about task completion time. To directly assess the location and impact of reference dependence, I structurally estimate labor-leisure preferences with a novel econometric approach drawing on computational neuroscience. Once participants exceed an expectations-based reference point, their subjective values of time rise sharply, and they speed up at the cost of reduced work quality and forgone earnings.
\r\n\r\nIn the second chapter, I propose and implement a method to test the optimality of individual deliberative time allocation. I also conduct experiments to study perceptual decision making in both simple decisions, where the difference in values between better and worse choices is known, and complex decisions, where this value difference is uncertain. The test reveals significant departures from optimality when task difficulty and monetary incentives are varied. However, a recently developed model based on optimality provides an improvement in fit over its predecessor.
\r\n\r\nIn the third chapter, I investigate the effects of memory constraints on choice over sequentially presented options. In a study that combines experimental paradigms used to analyze memory and judgment separately, I find a close link between order effects in choice and in memory. I show that cognitive load stemming from either an externally-imposed distractor or naturally-occuring fatigue substantially weakens primacy effects. Thus disrupting memory encoding and consolidation can potentially alleviate bias in judgment.
" }, { "name": "Bruer, John Jacob", "degree": "PhD", "year": "2017", "title": "Recovering Structured Low-rank Operators Using Nuclear Norms", "advisor": "Tropp, Joel A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02082017-062956314", "creators": [ { "name": { "family": "Bruer", "given": "John Jacob" }, "id": "Bruer-John-Jacob", "orcid": "0000-0003-4590-3038", "display_name": "Bruer, John Jacob" } ], "advisors": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "advisor", "display_name": "Tropp, Joel A." } ], "committee": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "chair", "display_name": "Tropp, Joel A." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z9F18WQS", "abstract": "This work considers the problem of recovering matrices and operators from limited and/or noisy observations. Whereas matrices result from summing tensor products of vectors, operators result from summing tensor products of matrices. These constructions lead to viewing both matrices and operators as the sum of \"simple\" rank-1 factors.
\r\n\r\nA popular line of work in this direction is low-rank matrix recovery, i.e., using linear measurements of a matrix to reconstruct it as the sum of few rank-1 factors. Rank minimization problems are hard in general, and a popular approach to avoid them is convex relaxation. Using the trace norm as a surrogate for rank, the low-rank matrix recovery problem becomes convex.
\r\n \r\nWhile the trace norm has received much attention in the literature, other convexifications are possible. This thesis focuses on the class of nuclear norms\u2014a class that includes the trace norm itself. Much as the trace norm is a convex surrogate for the matrix rank, other nuclear norms provide convex complexity measures for additional matrix structure. Namely, nuclear norms measure the structure of the factors used to construct the matrix.
\r\n\r\nTransitioning to the operator framework allows for novel uses of nuclear norms in recovering these structured matrices. In particular, this thesis shows how to lift structured matrix factorization problems to rank-1 operator recovery problems. This new viewpoint allows nuclear norms to measure richer types of structures present in matrix factorizations.
\r\n\r\nThis work also includes a Python software package to model and solve structured operator recovery problems. Systematic numerical experiments in operator denoising demonstrate the effectiveness of nuclear norms in recovering structured operators. In particular, choosing a specific nuclear norm that corresponds to the underlying factor structure of the operator improves the performance of the recovery procedures when compared, for instance, to the trace norm.\r\nApplications in hyperspectral imaging and self-calibration demonstrate the additional flexibility gained by utilizing operator (as opposed to matrix) factorization models.
" }, { "name": "Catanach, Thomas Anthony", "degree": "PhD", "year": "2017", "title": "Computational Methods for Bayesian Inference in Complex Systems", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042017-011739366", "creators": [ { "name": { "family": "Catanach", "given": "Thomas Anthony" }, "id": "Catanach-Thomas-Anthony", "orcid": "0000-0002-4321-3159", "display_name": "Catanach, Thomas Anthony" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "orcid": "0000-0001-5227-8037", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "chair", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Simons", "given": "Mark" }, "id": "Simons-M", "orcid": "0000-0003-1412-6395", "role": "member", "display_name": "Simons, Mark" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "orcid": "0000-0001-5227-8037", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z9RX9948", "abstract": "Bayesian methods are critical for the complete understanding of complex systems. In this approach, we capture all of our uncertainty about a system\u2019s properties using a probability distribution and update this understanding as new information becomes available. By taking the Bayesian perspective, we are able to effectively incorporate our prior knowledge about a model and to rigorously assess the plausibility of candidate models based upon observed data from the system. We can then make probabilistic predictions that incorporate uncertainties, which allows for better decision making and design. However, while these Bayesian methods are critical, they are often computationally intensive, thus necessitating the development of new approaches and algorithms.
\r\n\r\nIn this work, we discuss two approaches to Markov Chain Monte Carlo (MCMC). For many statistical inference and system identification problems, the development of MCMC made the Bayesian approach possible. However, as the size and complexity of inference problems has dramatically increased, improved MCMC methods are required. First, we present Second-Order Langevin MCMC (SOL-MC), a stochastic dynamical system-based MCMC algorithm that uses the damped second-order Langevin stochastic differential equation (SDE) to sample a desired posterior distribution. Since this method is based on an underlying dynamical system, we can utilize existing work in the theory for dynamical systems to develop, implement, and optimize the sampler's performance. Second, we present advances and theoretical results for Sequential Tempered MCMC (ST-MCMC) algorithms. Sequential Tempered MCMC is a family of parallelizable algorithms, based upon Transitional MCMC and Sequential Monte Carlo, that gradually transform a population of samples from the prior to the posterior through a series of intermediate distributions. Since the method is population-based, it can easily be parallelized. In this work, we derive theoretical results to help tune parameters within the algorithm. We also introduce a new sampling algorithm for ST-MCMC called the Rank-One Modified Metropolis Algorithm (ROMMA). This algorithm improves sampling efficiency for inference problems where the prior distribution constrains the posterior. In particular, this is shown to be relevant for problems in geophysics.
\r\n\r\nWe also discuss the application of Bayesian methods to state estimation, disturbance detection, and system identification problems in complex systems. We introduce a Bayesian perspective on learning models and properties of physical systems based upon a layered architecture that can learn quickly and flexibly. We then apply this architecture to detecting and characterizing changes in physical systems with applications to power systems and biology. In power systems, we develop a new formulation of the Extended Kalman Filter for estimating dynamic states described by differential algebraic equations. This filter is then used as the basis for sub-second fault detection and classification. In synthetic biology, we use a Bayesian approach to detect and identify unknown chemical inputs in a biosensor system implemented in a cell population. This approach uses the tools of Bayesian model selection.
" }, { "name": "Chalupka, Krzysztof", "degree": "PhD", "year": "2017", "title": "Automated Macro-scale Causal Hypothesis Formation Based on Micro-scale Observation", "advisor": "Perona, Pietro; Eberhardt, Frederick", "url": "https://resolver.caltech.edu/CaltechTHESIS:11292016-204528802", "creators": [ { "name": { "family": "Chalupka", "given": "Krzysztof" }, "id": "Chalupka-Krzysztof", "display_name": "Chalupka, Krzysztof" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" }, { "name": { "family": "Eberhardt", "given": "Frederick" }, "id": "Eberhardt-F", "role": "co-advisor", "display_name": "Eberhardt, Frederick" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Eberhardt", "given": "Frederick D." }, "id": "Eberhardt-F-D", "role": "member", "display_name": "Eberhardt, Frederick D." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Tsao", "given": "Doris Y." }, "id": "Tsao-D-Y", "role": "member", "display_name": "Tsao, Doris Y." } ], "option_major": [ "cns" ], "doi": "10.7907/Z9MW2F4P", "abstract": "This book introduces new concepts at the intersection of machine learning, causal inference and philosophy of science: the macrovariable cause and effect. Methods for learning such from microvariable data are introduced. The learning process proposes a minimal number of guided experiments that recover the macrovariable cause from observational data.
\r\n\r\nMathematical definitions of a micro- and macro- scale manipulation, an observational and causal partition, and a subsidiary variable are given. These concepts provide a link to previous work in causal inference and machine learning.
\r\n\r\nThe main theoretical result is the Causal Coarsening Theorem, a new insight into the measure-theoretic structure of probability spaces and structural equation models. The theorem provides grounds for automatic causal hypothesis formation from data. Other results concern the minimality and sufficiency of representations created in accordance with the theorem.
\r\n\r\nFinally, this book proposes the first algorithms for supervised and unsupervised causal macrovariable discovery. These algorithms bridge large-scale, multidimensional machine learning and causal inference. In an application to climate science, the algorithms re-discover a known causal mechanism as a viable causal hypothesis. In a psychophysical experiment, the algorithms learn to minimally change visual stimuli to achieve a desired effect on human perception.
" }, { "name": "Chen, Yuhua Richard", "degree": "PhD", "year": "2017", "title": "Concentration Inequalities of Random Matrices and Solving Ptychography with a Convex Relaxation", "advisor": "Tropp, Joel A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09022016-135721172", "creators": [ { "name": { "family": "Chen", "given": "Yuhua Richard" }, "id": "Chen-Yuhua-Richard", "display_name": "Chen, Yuhua Richard" } ], "advisors": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "advisor", "display_name": "Tropp, Joel A." } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z9M906MF", "abstract": "Random matrix theory has seen rapid development in recent years. In particular, researchers have developed many non-asymptotic matrix concentration inequalities that parallel powerful scalar concentration inequalities. In this thesis, we focus on three topics: 1) estimating sparse covariance matrix using matrix concentration inequalities, 2) constructing the matrix phi-entropy to derive matrix concentration inequalities, 3) developing scalable algorithms to solve the phase recovery problem of ptychography based on low-rank matrix factorization.
\r\n\r\nEstimation of covariance matrix is an important subject. In the setting of high dimensional statistics, the number of samples can be small in comparison to the dimension of the problem, thus estimating the complete covariance matrix is unfeasible. By assuming that the covariance matrix satisfies some sparsity assumptions, prior work has proved that it is feasible to estimate the sparse covariance matrix of Gaussian distribution using the masked sample covariance estimator. In this thesis, we use a new approach and apply non-asymptotic matrix concentration inequalities to obtain tight sample bounds for estimating the sparse covariance matrix of subgaussian distributions.
\r\n\r\nThe entropy method is a powerful approach in developing scalar concentration inequalities. The key ingredient is the subadditivity property that scalar entropy function exhibits. In this thesis, we construct a new concept of matrix phi-entropy and prove that matrix phi-entropy also satisfies a subadditivity property similar to the scalar form. We apply this new concept of matrix phi-entropy to derive non-asymptotic matrix concentration inequalities.
\r\n\r\nPtychography is a computational imaging technique which transforms low-resolution intensity-only images into a high-resolution complex recovery of the signal. Conventional algorithms are based on alternating projection, which lacks theoretical guarantees for their performance. In this thesis, we construct two new algorithms. The first algorithm relies on a convex formulation of the ptychography problem and on low-rank matrix recovery. This algorithm improves traditional approaches' performance but has high computational cost. The second algorithm achieves near-linear runtime and memory complexity by factorizing the objective matrix into its low-rank components and approximates the first algorithm's imaging quality.
" }, { "name": "Chern, Albert Ren-Haur", "degree": "PhD", "year": "2017", "title": "Fluid Dynamics with Incompressible Schr\u00f6dinger Flow", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052017-102338732", "creators": [ { "name": { "family": "Chern", "given": "Albert Ren-Haur" }, "id": "Chern-Albert-Ren-Haur", "orcid": "0000-0002-9802-3619", "display_name": "Chern, Albert Ren-Haur" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Pinkall", "given": "Ulrich" }, "id": "Pinkall-U", "orcid": "0000-0002-2087-6435", "role": "member", "display_name": "Pinkall, Ulrich" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z98050N3", "abstract": "This thesis introduces a new way of looking at incompressible fluid dynamics. Specifically, we formulate and simulate classical fluids using a Schr\u00f6dinger equation subject to an incompressibility constraint. We call such a fluid flow an incompressible Schr\u00f6dinger flow (ISF). The approach is motivated by Madelung's hydrodynamical form of quantum mechanics, and we show that it can simulate classical fluids with particular advantage in its simplicity and its ability of capturing thin vortex dynamics. The effective dynamics under an ISF is shown to be an Euler equation modified with a Landau-Lifshitz term. We show that the modifying term not only enhances the dynamics of vortex filaments, but also regularizes the potentially singular behavior of incompressible flows.
\r\n \r\nAnother contribution of this thesis is the elucidation of a general, geometric notion of Clebsch variables. A geometric Clebsch variable is useful for analyzing the dynamics of ISF, as well as representing vortical structures in a general flow field. We also develop an algorithm of approximating a \"spherical\" Clebsch map for an arbitrarily given flow field, which leads to a new tool for visualizing, analyzing, and processing the vortex structure in a fluid data.
" }, { "name": "Chu, Hao", "degree": "PhD", "year": "2017", "title": "Nonlinear and Ultrafast Optical Investigations of Correlated Materials", "advisor": "Hsieh, David", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092017-141136995", "creators": [ { "name": { "family": "Chu", "given": "Hao" }, "id": "Chu-Hao", "display_name": "Chu, Hao" } ], "advisors": [ { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "role": "advisor", "display_name": "Hsieh, David" } ], "committee": [ { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "role": "chair", "display_name": "Hsieh, David" }, { "name": { "family": "Eisenstein", "given": "James P." }, "id": "Eisenstein-J-P", "role": "member", "display_name": "Eisenstein, James P." }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "role": "member", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9VD6WHV", "abstract": "This thesis comprises studies of 3d-5d transition metal oxides with various degrees of electronic correlation using nonlinear harmonic generation rotational anisotropy as well as time-resolved optical reflectivity methods. Specifically, we explored photo-induced phase transition in Ca2RuO4 and Sr2IrO4, discovered novel electronic phases in doped Sr2IrO4 and Sr3Ir2O7, and investigated different types of antiferromagnetic orders in transition metal trichalcogenides MPX3.
\r\n" }, { "name": "Collins, Lincoln Nash", "degree": "PhD", "year": "2017", "title": "Optimal Design of Materials for Energy Conversion\r ", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06132017-164608976", "creators": [ { "name": { "family": "Collins", "given": "Lincoln Nash" }, "id": "Collins-Lincoln-Nash", "display_name": "Collins, Lincoln Nash" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9X928B7", "abstract": "The efficiency of fuel cells, batteries and thermochemical energy conversion devices depends on inherent material characteristics that govern the complex chemistry and transport of multiple species as well as the spatial arrangement of the various materials. Therefore, optimization of the spatial arrangement is a recurrent theme in energy conversion devices. Traditional methods of synthesis offer limited control of the microstructure and there has been much work in advanced imaging for these uncontrolled microstructures and optimizing gross features. However, the growing ability for directed synthesis allows us to ask the question of what microgeometries are optimal for particular applications. Through this work, we study problems motivated by metal oxides used in solar-driven thermochemical conversion devices designed to split water or carbon dioxide into fuels. We seek to understand the arrangement of the solid and porous regions to maximize the transport given sources and sinks for the gaseous oxygen and vacancies. Three related problems are investigated with the common theme of understanding the role of microstructure design.
\r\n\r\nWe derive the transport equations for electrons and oxygen vacancies through ceria under an externally-applied electric potential in an oxygen environment using various balance laws and constitutive equations. From this, we obtain various thermodynamic potentials that take into consideration the thermal, chemical, and mechanical state of the material. Accordingly, we obtain a system of partial differential equations describing ambipolar diffusion. We present the applicability of strain-engineering as a way to design systems to improve the behavior of thermochemical conversion devices. We look at an idealized thin film of mixed conductor attached to an inert substrate with a thermal mismatch as a way to induce strain into the film. The resulting impact on equilibrium non-stoichiometry is analyzed using data describing non-stoichiometry in ceria as a function of oxygen pressure and temperature.
\r\n\r\nThe optimal design of material microstructure for thermochemical conversion is addressed from two standpoints: the mathematical homogenization of associated transport models, and from topology optimization. We present the homogenization of coupled transport through porous media consisting of linearized Stokes flow, convective diffusion, and diffusion in the solid phase with interface reaction. Depending on the strength of the interface chemistry, different forms of effective behavior are described at the macroscale, and we gain insight into the impact cell-design and pore shape has on the behavior.
\r\n\r\nThe topology optimization of a model energy-conversion reactor is then presented. We express the problem of optimal design of the material arrangement as a saddle point problem and obtain an effective functional which shows that regions with very fine phase mixtures of the material arise naturally. To explore this further, we introduce a phase-field formulation of the optimal design problem, and numerically study selected examples. We find that zig-zag interfaces develop to balance mass transport and interface exchange.
" }, { "name": "Cummings, Rachel Autumn Dixon", "degree": "PhD", "year": "2017", "title": "The Implications of Privacy-Aware Choice", "advisor": "Ligett, Katrina A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03232017-160527848", "creators": [ { "name": { "family": "Cummings", "given": "Rachel Autumn Dixon" }, "id": "Cummings-Rachel-Autumn-Dixon", "orcid": "0000-0002-1196-1515", "display_name": "Cummings, Rachel Autumn Dixon" } ], "advisors": [ { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-Katrina-A", "role": "advisor", "display_name": "Ligett, Katrina A." } ], "committee": [ { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-K-A", "role": "chair", "display_name": "Ligett, Katrina A." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Echenique", "given": "Federico" }, "id": "Echenique-F", "role": "member", "display_name": "Echenique, Federico" }, { "name": { "family": "Roth", "given": "Aaron" }, "id": "Roth-Aaron", "role": "member", "display_name": "Roth, Aaron" }, { "name": { "family": "Vohra", "given": "Rakesh" }, "id": "Vohra-Rakesh", "role": "member", "display_name": "Vohra, Rakesh" } ], "option_major": [ "cms" ], "doi": "10.7907/Z9057CZP", "abstract": "Privacy concerns are becoming a major obstacle to using data in the way that we want. It's often unclear how current regulations should translate into technology, and the changing legal landscape surrounding privacy can cause valuable data to go unused. In addition, when people know that their current choices may have future consequences, they might modify their behavior to ensure that their data reveal less---or perhaps, more favorable---information about themselves. Given these concerns, how can we continue to make use of potentially sensitive data, while providing satisfactory privacy guarantees to the people whose data we are using? Answering this question requires an understanding of how people reason about their privacy and how privacy concerns affect behavior.
\r\n\r\nIn this thesis, we study how strategic and human aspects of privacy interact with existing tools for data collection and analysis. We begin by adapting the standard model of consumer choice theory to a setting where consumers are aware of, and have preferences over, the information revealed by their choices. In this model of privacy-aware choice, we show that little can be inferred about a consumer's preferences once we introduce the possibility that she has concerns about privacy, even when her preferences are assumed to satisfy relatively strong structural properties. Next, we analyze how privacy technologies affect behavior in a simple economic model of data-driven decision making. Intuition suggests that strengthening privacy protections will both increase utility for the individuals providing data and decrease usefulness of the computation. However, we demonstrate that this intuition can fail when strategic concerns affect consumer behavior. Finally, we study the problem an analyst faces when purchasing and aggregating data from strategic individuals with complex incentives and privacy concerns. For this problem, we provide both mechanisms for eliciting data that satisfy the necessary desiderata, and impossibility results showing the limitations of privacy-preserving data collection.
" }, { "name": "Darbe, Sunita", "degree": "PhD", "year": "2017", "title": "Optics for High-Efficiency Full Spectrum Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:01032017-032640614", "creators": [ { "name": { "family": "Darbe", "given": "Sunita" }, "id": "Darbe-Sunita", "orcid": "0000-0002-8099-1814", "display_name": "Darbe, Sunita" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z96W9833", "abstract": "While the price of solar energy has dropped dramatically in the last few years, costs must be further reduced to reach wide-scale adoption. One strategy to decrease cost is to increase efficiency. Photovoltaic energy conversion is most efficient for a narrow frequency range. Lack of absorption of low energy photons and thermalization of high-energy photons leads lead to a loss of over 40% of incident solar power on a silicon cell. Current-matching and lattice-matching restrictions limit the efficiency of traditional monolithic multijunction solar cells. In order to avoid these limitations and realize ultrahigh efficiency (close to 50%), this thesis explores use of optical elements to split broadband sunlight into multiple spectral bands that can each be sent to physically separated solar cells tuned to best convert that band.
\r\n\r\nDesign of a holographic diffraction grating based spectrum-splitting system resulted in a simulated module efficiency of 37%, meeting the efficiency of state-of-the-art modules. One of four holographic grating stacks is experimentally characterized. Next, a design incorporating dichroic filters, seven subcells with bandgaps spanning the solar spectrum, and concentrators with efficiency potential exceeding 45% module efficiency is presented. While prototyping this design, we also used on-going cost-modeling to ensure that our design was on-track to be a high-volume technology with low lifetime energy cost.
\r\n\r\nFinally, high-contrast gratings are used as resonant, dielectric spectrally selective mirrors in a tandem luminescent solar concentrator and as alternatives to Bragg reflectors. Gratings can have omnidirectional, high reflectivity by appropriately offsetting grating resonances in nano-patterned subwavelength thickness high-refractive index material. Subwavelength feature sizes suppress diffraction, and the high-refractive index of the grating layer leads to relatively angle-insensitive reflectance. Gratings can be fabricated by nanoimprint lithography, making them a scalable and economical option for photovoltaic applications. Simulations show hemispherically average reflectivity near 90% possible from a single subwavelength thickness layer. These properties are well suited for a variety of applications including multiple spectrum-splitting device architectures.
" }, { "name": "Delapierre, M\u00e9lanie", "degree": "PhD", "year": "2017", "title": "Dynamics and Stability of Spinning Membranes", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222017-093718571", "creators": [ { "name": { "family": "Delapierre", "given": "M\u00e9lanie" }, "id": "Delapierre-M\u00e9lanie", "display_name": "Delapierre, M\u00e9lanie" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/Z9HT2MC8", "abstract": "Many future space missions require large structures subject to stringent shape accuracy requirements. Spinning membrane-like structures are a cost effective solution for these applications. However, any small deflection of a spinning structure, due to maneuvers or solar radiation pressure, leads to geometrically nonlinear effects on its stability and dynamics. Accurate experiments, simulation tools, and models are required to ensure that buckling and vibrations will not affect mission objectives.
\r\n \r\nWe first focus on the influence of transverse uniform loads on the dynamics and stability of spinning isotropic uniform membranes. A transverse uniform load models the effect of a transverse light beam on flat membranes with small deflections. We present experimental measurements of the angular velocities at which various membranes become wrinkled, and of the wrinkling mode transitions that occur upon spin down. A theoretical formulation to predict the critical angular velocities and critical transverse loads is also presented. The transition between bending dominated and in-plane dominated behavior is identified, and the wrinkling modes are obtained. Next, deflected, non-buckled membranes are further analyzed. Axisymmetric nonlinear oscillations are studied analytically, and a reduced-order model is presented. This model predicts that the deflection of the membrane introduces a hardening behavior at low angular velocities and a softening behavior at high angular velocities. This model is validated through experiments and FEM simulations.
\r\n \r\nThen, we relax the assumption of uniform membranes loaded by transverse light beams. We present an Abaqus model of foldable membranes and show that for particular types of hinges and at high angular velocities, these structures behave like uniform membranes. Finally, we derive an FEM model for solar radiation pressure for quadrilateral surface elements and 3D problems and present its implementation in Abaqus. We show that this follower load introduces an unsymmetric stiffness matrix and that instabilities known as solarelastic flutter can develop. This new FEM capability enables equilibrium and frequency-based stability analyses for a wide range of spacecraft.
" }, { "name": "Ding, Ding", "degree": "PhD", "year": "2017", "title": "Nanoscale Thermal Transport with Photons and Phonons", "advisor": "Minnich, Austin", "url": "https://resolver.caltech.edu/CaltechTHESIS:01062017-221235563", "creators": [ { "name": { "family": "Ding", "given": "Ding" }, "id": "Ding-Ding", "display_name": "Ding, Ding" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin" }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "advisor", "display_name": "Minnich, Austin" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z94Q7RZ0", "abstract": "Recent progress in nanosciences challenges the conventional understanding of Fourier's law for heat conduction and Planck's law for thermal radiation, calling for theoretical and experimental advancement to improve our understanding at these length scales. Advances in both theoretical and experimental progress at these length scale have been made in the past two decades, but there are still many challenges and possibilities in further understanding how heat conducts or radiates at these length scales.
\r\n\r\nThe first half of this thesis focuses on topics in nanoscale thermal radiation. First, we will discuss an effort to modify thermal emission using a hyperbolic metamaterial (HMM). Recent efforts in utilizing different metamaterial designs to modify thermal emission has led to greater control over the spectral and directional properties of thermal radiation, and the HMM is one such metamaterial. HMM is typically made up of sub-wavelength alternating layers of metal and dielectric that result in an anisotropic permittivity. Here we demonstrate that an annular, transparent HMM lens enables selective controlling of the plasmonic resonance such that a nanowire emitter, surrounded by an HMM, appears dark to incoming radiation from an adjacent nanowire emitter unless the second emitter is surrounded by an identical lens.
\r\n\r\nWhile many metamaterial schemes exist to modify thermal emission, these schemes are ultimately limited by the maximum possible emission of a blackbody. In an effort to further increase radiative thermal emission, we made another effort to explore the possibility of removing the enhanced but trapped thermal radiation energy density at sub-wavelength distances. Here, we propose and numerically demonstrate an active scheme that exploits the monochromatic nature of near-field thermal radiation to drive a transition in a laser gain medium, which, when coupled with external optical pumping, allows the resonant surface mode to be emitted into the far-field. We compare this proposed active radiative cooling (ARC) approach to the better-understood laser cooling of solids (LCS) technique, which achieves cooling by extracting phonons instead of thermal radiation. We show that LCS and ARC can be described with the same mathematical formalism and find that ARC can achieve higher efficiency and extracted power over a wide range of conditions.
\r\n\r\nIn the second half of thesis, we switch our attention to nanoscale heat conduction where phonons are the dominant heat carriers. Phonons require a medium to travel, unlike thermal radiation, and thus experience much stronger interaction with the medium. Typical assumptions of many scattering events of phonons at the larger length scales break down at the nanoscale when phonon transport can no longer be accurately described by diffusion theory. Here, we present a numerical modeling effort using the Boltzmann Transport Equation to accurately model nanoscale phonon transport of a recent experiment. We show a calculated trend of pump beam size dependence on thermal conductivity similar to results from the time-domain thermal reflectance (TDTR) experiment. We also identify the radial suppression function that describes the suppression in heat flux, compared to Fourier's law, that occurs due to quasiballistic transport and demonstrate good agreement with experimental data.
\r\n\r\nWhile time-domain thermal reflectance (TDTR) experiment is widely used to characterize thermal transport, it is not ideal for in-plane thermal measurements compared to the transient grating (TG) techniques which utilize interference of two beams to create a in-plane grating pattern for thermal measurements. In the last part of my thesis, we highlight details of an experimental effort to develop the ultra-fast transient grating (TG) technique capable of measuring fast thermal decays. We will then highlight the results of thermal and acoustic measurements of molybdenum disulphide that can be obtained from this technique. Our results are in good agreement with other measurements and calculations.
\r\n\r\nWith nanosciences paving way for the future of technology, understanding thermal management at the nanoscale is crucial for device performance and reducing energy waste. We believe that these results in thermal radiation and conduction will benefit thermal management at the nanoscale.
\r\n" }, { "name": "Eyjolfsdottir, Eyrun-Arna", "degree": "PhD", "year": "2017", "title": "Computational Methods for Behavior Analysis", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052017-121818057", "creators": [ { "name": { "family": "Eyjolfsdottir", "given": "Eyrun-Arna" }, "id": "Eyjolfsdottir-Eyrun-Arna", "display_name": "Eyjolfsdottir, Eyrun-Arna" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Anderson", "given": "David J." }, "id": "Anderson-D-J", "role": "member", "display_name": "Anderson, David J." }, { "name": { "family": "Fowlkes", "given": "Charless C." }, "id": "Fowlkes-C-C", "role": "member", "display_name": "Fowlkes, Charless C." } ], "option_major": [ "compsci" ], "doi": "10.7907/Z9445JJH", "abstract": "Behavioral scientists strive to decode the functional relationship between sensory input and motor output of the brain, which requires quantitive measurement of animal behavior. Artificial intelligence researchers aim to build intelligent systems, capable of understanding, predicting, and generating behavior. Our research lies on the intersection of the two fields; our goal is to automate measurement of animal behavior and to model their sensory-motor relationship using machine learning.
\r\n\r\nWe have developed a tool that tracks the pose of multiple fruit flies and aims to maintain their identity throughout a video. It outputs motion trajectories that can be used to quantify behavioral differences between individuals, for example by comparing histograms of velocities and wing angles. We show that the tool also works well on non-fly-like animals such as zebrafish larvae.
\r\n\r\nEmbedded in these motion trajectories are temporal patterns that constitute actions. We developed two supervised learning frameworks for action detection: a sliding window framework and a structured output framework. Both frameworks learn to classify actions from motion trajectories and expert annotated action intervals. Our results show that the simpler sliding window framework achievers better results in spite of being much faster to train, reaching 90% of human performance.
\r\n\r\nSupervised learning requires a lot of training data which involves time consuming and painstaking annotation. To alleviate that we have built a semi-supervised neural network framework that, in addition to classifying actions, learns to predict how an animal will move next given its motion and sensory inputs so far. Our model archives as good results as its supervised counterpart with only half of the expert labels. \r\nIn addition, we show that motion prediction can be used to generate convincing simulations of fruit fly behavior and handwritten text, and that our model learns to represent high level information, such as identity, when trained unsupervised.
\r\n\r\nAlthough developed for animal behavior, our methods are general and could be applied to other motion data. We hope that this thesis demonstrates the value of studying animal behavior for the development of artificial intelligence.
" }, { "name": "Guo, Zeyu", "degree": "PhD", "year": "2017", "title": "P-Schemes and Deterministic Polynomial Factoring Over Finite Fields", "advisor": "Umans, Christopher M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012017-013622968", "creators": [ { "name": { "family": "Guo", "given": "Zeyu" }, "id": "Guo-Zeyu", "orcid": "0000-0001-7893-4346", "display_name": "Guo, Zeyu" } ], "advisors": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "orcid": "0000-0002-6390-9401", "role": "advisor", "display_name": "Umans, Christopher M." } ], "committee": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "orcid": "0000-0002-6390-9401", "role": "chair", "display_name": "Umans, Christopher M." }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Vidick", "given": "Thomas G." }, "id": "Vidick-T", "orcid": "0000-0002-6405-365X", "role": "member", "display_name": "Vidick, Thomas G." }, { "name": { "family": "Huang", "given": "Ming-Deh" }, "id": "Huang-Ming-Deh", "role": "member", "display_name": "Huang, Ming-Deh" } ], "option_major": [ "compsci" ], "doi": "10.7907/Z94F1NSG", "abstract": "We introduce a family of mathematical objects called P-schemes, where P is a poset of subgroups of a finite group G. A P-scheme is a collection of partitions of the right coset spaces H\\G, indexed by H\u2208P, that satisfies a list of axioms. These objects generalize the classical notion of association schemes [BI84] as well as the notion of m-schemes [IKS09].
\r\n\r\nBased on P-schemes, we develop a unifying framework for the problem of deterministic factoring of univariate polynomials over finite field under the generalized Riemann hypothesis (GRH). More specifically, our results include the following:
\r\n\r\nWe show an equivalence between m-scheme as introduced in [IKS09] and P-schemes in the special setting that G is an multiply transitive permutation group and P is a poset of pointwise stabilizers, and therefore realize the theory of m-schemes as part of the richer theory of P-schemes.
\r\n\r\nWe give a generic deterministic algorithm that computes the factorization of the input polynomial \u0192(X) \u2208 Fq[X] given a \"lifted polynomial\" \u0192~(X) of \u0192(X) and a collection F of \"effectively constructible\" subfields of the splitting field of \u0192~(X) over a certain base field. It is routine to compute \u0192~(X) from \u0192(X) by lifting the coefficients of \u0192(X) to a number ring. The algorithm then successfully factorizes \u0192(X) under GRH in time polynomial in the size of \u0192~(X) and F, provided that a certain condition concerning P-schemes is satisfied, for P being the poset of subgroups of the Galois group G of \u0192~(X) defined by F via the Galois correspondence. By considering various choices of G, P and verifying the condition, we are able to derive the main results of known (GRH-based) deterministic factoring algorithms [Hua91a; Hua91b; Ron88; Ron92; Evd92; Evd94; IKS09] from our generic algorithm in a uniform way.
\r\n \r\nWe investigate the schemes conjecture in [IKS09] and formulate analogous conjectures associated with various families of permutation groups, each of which has applications on deterministic polynomial factoring. Using a technique called induction of P-schemes, we establish reductions among these conjectures and show that they form a hierarchy of relaxations of the original schemes conjecture.
\r\n\r\nWe connect the complexity of deterministic polynomial factoring with the complexity of the Galois group G of \u0192~(X). Specifically, using techniques from permutation group theory, we obtain a (GRH-based) deterministic factoring algorithm whose running time is bounded in terms of the noncyclic composition factors of G. In particular, this algorithm runs in polynomial time if G is in \u0393k for some k=2O(\u221a(log n), where \u0393k denotes the family of finite groups whose noncyclic composition factors are all isomorphic of subgroups of the symmetric group of degree k. Previously, polynomial-time algorithms for \u0393k were known only for bounded k.
\r\n\r\nWe discuss various aspects of the theory of P-schemes, including techniques of constructing new P-schemes from old ones, P-schemes for symmetric groups and linear groups, orbit P-schemes, etc. For the closely related theory of m-schemes, we provide explicit constructions of strongly antisymmetric homogeneous m-schemes for m\u22643. We also show that all antisymmetric homogeneous orbit 3-schemes have a matching for m\u22653, improving a result in [IKS09] that confirms the same statement for m\u22654.
\r\n\r\nIn summary, our framework reduces the algorithmic problem of deterministic polynomial factoring over finite fields to a combinatorial problem concerning P-schemes, allowing us to not only recover most of the known results but also discover new ones. We believe progress in understanding P-schemes associated with various families of permutation groups will shed some light on the ultimate goal of solving deterministic polynomial factoring over finite fields in polynomial time.
" }, { "name": "Halbawi, Wael", "degree": "PhD", "year": "2017", "title": "Error-Correcting Codes for Networks, Storage and Computation", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092017-013147699", "creators": [ { "name": { "family": "Halbawi", "given": "Wael" }, "id": "Halbawi-Wael", "orcid": "0000-0001-5951-7002", "display_name": "Halbawi, Wael" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Dimakis", "given": "Alexandros G." }, "id": "Dimakis-A-G", "role": "member", "display_name": "Dimakis, Alexandros G." }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9J67F08", "abstract": "The advent of the information age has bestowed upon us three challenges related to the way we deal with data. Firstly, there is an unprecedented demand for transmitting data at high rates. Secondly, the massive amounts of data being collected from various sources needs to be stored across time. Thirdly, there is a need to process the data collected and perform computations on it in order to extract meaningful information out of it. The interconnected nature of modern systems designed to perform these tasks has unraveled new difficulties when it comes to ensuring their resilience against sources of performance degradation. In the context of network communication and distributed data storage, system-level noise and adversarial errors have to be combated with efficient error correction schemes. In the case of distributed computation, the heterogeneous nature of computing clusters can potentially diminish the speedups promised by parallel algorithms, calling for schemes that mitigate the effect of slow machines and communication delay.
\r\n\r\nThis thesis addresses the problem of designing efficient fault tolerance schemes for the three scenarios just described. In the network communication setting, a family of multiple-source multicast networks that employ linear network coding is considered for which capacity-achieving distributed error-correcting codes, based on classical algebraic constructions, are designed. The codes require no coordination between the source nodes and are end to end: except for the source nodes and the destination node, the operation of the network remains unchanged.
\r\n\r\nIn the context of data storage, balanced error-correcting codes are constructed so that the encoding effort required is balanced out across the storage nodes. In particular, it is shown that for a fixed row weight, any cyclic Reed-Solomon code possesses a generator matrix in which the number of nonzeros is the same across the columns. In the balanced and sparsest case, where each row of the generator matrix is a minimum distance codeword, the maximal encoding time over the storage nodes is minimized, a property that is appealing in write-intensive settings. Analogous constructions are presented for a locally recoverable code construction due to Tamo and Barg.
\r\n\r\nLastly, the problem of mitigating stragglers in a distributed computation setup is addressed, where a function of some dataset is computed in parallel. Using Reed-Solomon coding techniques, a scheme is proposed that allows for the recovery of the function under consideration from the minimum number of machines possible. The only assumption made on the function is that it is additively separable, which renders the scheme useful in distributed gradient descent implementations. Furthermore, a theoretical model for the run time of the scheme is presented. When the return time of the machines is modeled probabilistically, the model can be used to optimally pick the scheme's parameters so that the expected computation time is minimized. The recovery is performed using an algorithm that runs in quadratic time and linear space, a notable improvement compared to state-of-the-art schemes.
\r\n\r\nThe unifying theme of the three scenarios is the construction of error-correcting codes whose encoding functions adhere to certain constraints. It is shown that in many cases, these constraints can be satisfied by classical constructions. As a result, the schemes presented are deterministic, operate over small finite fields and can be decoded using efficient algorithms.
" }, { "name": "Hall, David Christopher", "degree": "PhD", "year": "2017", "title": "Advancing a Machine's Visual Awareness of People", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292017-224523022", "creators": [ { "name": { "family": "Hall", "given": "David Christopher" }, "id": "Hall-David-Christopher", "orcid": "0000-0003-3244-5744", "display_name": "Hall, David Christopher" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Munich", "given": "Mario E." }, "id": "Munich-M-E", "role": "member", "display_name": "Munich, Mario E." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9ST7MWC", "abstract": "Methods to advance a machine's visual awareness of people with a focus on understanding 'who is where' in video are presented. 'Who' is used in a broad sense that includes not only the identity of a person but attributes of that person as well. Efforts are focused on improving algorithms in four areas of visual recognition: detection, tracking, fine-grained classification and person reidentification.
\r\n\r\nEach of these problems appear to be quite different on the surface; however, there are two broader questions that are answered across each of the works. The first, the machine is able to make better predictions when it has access to the extra information that is available in video. The second, that it is possible to learn on-the-fly from single examples. How each work contributes to answering these over-arching questions as well as its specific contributions to the relevant problem domain are as follows:
\r\n\r\nThe first problem studied is one-shot, real-time, instance detection. Given a single image of a person, the task for the machine is to learn a detector that is specific to that individual rather than to an entire category such as faces or pedestrians. In subsequent images, the individual detector indicates the size and location of that particular person in the image. The learning must be done in real-time. To solve this problem, the proposed method starts with a pre-trained boosted category detector from which an individual-object detector is trained, with near-zero computational cost, through elementary manipulations of the thresholds of the category detector. Experiments on two challenging pedestrian and face datasets indicate that it is indeed possible to learn identity classifiers in real-time; besides being faster-trained, the proposed classifier has better detection rates than previous methods.
\r\n\r\nThe second problem studied is real-time tracking. Given the initial location of a target person, the task for the machine is to determine the size and location of the target person in subsequent video frames, in real-time. The method proposed for solving this problem treats tracking as a repeated detection problem where potential targets are identified with a pre-trained boosted person detector and identity across frames is established by individual-specific detectors. The individual-specific detectors are learnt using the method proposed to solve the first problem. The proposed algorithm runs in real-time and is robust to drift. The tracking algorithm is benchmarked against nine state-of-the-art trackers on two benchmark datasets. Results show that the proposed method is 10% more accurate and nearly as fast as the fastest of the competing algorithms, and it is as accurate but 20 times faster than the most accurate of the competing algorithms.
\r\n\r\nThe third problem studied is the fine-grained classification of people. Given an image of a person, the task for the machine is to estimate characteristics of that person such as age, clothing style, sex, occupation, social status, ethnicity, emotional state and/or body type. Since fine-grained classification using the entire human body is a relatively unexplored area, a large video dataset was collected. To solve this problem, a method that uses deep neural networks and video of a person is proposed. Results show that the class average accuracy when combining information from a sequence of images of an individual and then predicting the label is 3.5-7.1% better than independently predicting the label of each image, when severely under-represented classes are ignored.
\r\n\r\nThe final problem studied is person reidentification. Given an image of a person, the task for the machine is to find images that match the identity of that person from a large set of candidate images. This is a challenging task since images of the same individual can vary significantly due to changes in clothing, viewpoint, pose, lighting and background. The method proposed for solving this problem is a two-stage deep neural network architecture that uses body part patches as inputs rather than an entire image of a person. Experiments show that rank-1 matching rates increase by 22-25.6% on benchmark datasets when compared to state-of-the-art methods.
" }, { "name": "Hirsch, Damian George", "degree": "PhD", "year": "2017", "title": "An Experimental and Theoretical Study of Active Flow Control", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092017-112408552", "creators": [ { "name": { "family": "Hirsch", "given": "Damian George" }, "id": "Hirsch-Damian-George", "display_name": "Hirsch, Damian George" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Wygnanski", "given": "Israel J." }, "id": "Wygnanski-I-J", "orcid": "0009-0001-5711-7029", "role": "member", "display_name": "Wygnanski, Israel J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9N014KR", "abstract": "The accelerating growth of environmental awareness has not stopped at the aerospace industry. The need for greener and more efficient airplanes threatens to outpace the flow of new technology. This has ignited development in several fields, one of which is active flow control (AFC). Active flow control has quickly proven its tremendous potential for real applications. Even though the roots of this technology date back a century, we still lack fundamental understanding. This thesis combines both modern and traditional approaches to lay out a new foundation for future research.
\r\n\r\nThe thesis first focuses on the rising stars of active flow control: the so-called fluidic oscillators or sweeping jet actuators. These devices consist of simple, rigid internal geometries that create a sweeping output jet motion. The fluid dynamic interactions with the internal geometry are studied in detail using high-speed Schlieren imaging. Additionally, the influence of adjacent sweeping jets is investigated. It is revealed that the internal driving mechanism is far stronger than the fluid dynamic interactions at the outlet, resulting in a completely independent jet behavior.
\r\n\r\nNext, a high-lift airfoil design is combined with active flow control, and an extensive wind tunnel study is carried out. It is shown that for the given wing design active flow control leads to much higher lift benefits when applied to the trailing edge. Applied to the leading edge active flow control disrupts the vortex lift of the high-lift airfoil, resulting in a deleterious lift effect; however, it shows potential for pitch moment control. This project also underlines the advantages of jet-like active flow control over steady blowing actuation at limited available mass flow rates.
\r\n\r\nThe momentum input coefficient as an important parameter in active flow control is discussed in detail, identifying common misconceptions and difficulties that hinder its proper calculation. An innovative, much simpler approach is introduced. This allows a detailed study of the underlying physics, unveiling unknown limitations of active flow control. The approach is then used as a model to derive the novel concept of thermal active flow control. Experimental studies, including a wind tunnel test campaign, are performed to confirm the viability of the concept for practical applications.
\r\n\r\nThe new calculation method of the input momentum coefficient emphasizes its weakness as a similarity parameter in active flow control studies. The extended mass flow coefficient is introduced as a new parameter. It is shown that it can overcome the deficiencies of the input momentum coefficient without suffering other disadvantages. Its further investigation leads to a deeper understanding of active flow control, which is supported by PIV experiments. The main findings of this investigation divide active flow control into three different \"states\": boundary layer thickening, separation control, and supercirculation.
" }, { "name": "Hogstrom, Kristina", "degree": "PhD", "year": "2017", "title": "Robotically Assembled Space Telescopes with Deployable Modules: Concepts and Design Methodologies", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182016-100030713", "creators": [ { "name": { "family": "Hogstrom", "given": "Kristina" }, "id": "Hogstrom-Kristina", "display_name": "Hogstrom, Kristina" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "space" ], "doi": "10.7907/Z9T151NT", "abstract": "This thesis first presents a novel architecture for robotically assembled optical telescopes with apertures between 20 m and 100 m, that utilizes only currently available technology. In this architecture, the primary mirror consists of two layers: a reflective layer and a truss backplane layer. The reflective layer is divided into mirror modules, or groups of mirror segments and actuators. The truss backplane layer is divided into truss modules that fold compactly for launch and are deployed in space by the robot. In this thesis, the design methodology of the mirror modules and truss modules is detailed. The ability of the designed truss layer to maintain precision requirements in the presence of typical space environment loads is demonstrated.
\r\n \r\nThis architecture requires the deployment of many truss modules, and thus the deployment must be reliable despite errors introduced during manufacturing. In this thesis, a new simulation-based toolkit for estimating deployment reliability is described, including the experimental validation of the deployment simulation and the Monte Carlo-style method for repeating deployment simulations with different distributions of random fabrication errors to statistically estimate reliability. Using the toolkit, a set of reliability trade studies are then presented, revealing how different types of errors and design parameters affect reliability. Finally, the manufacturing tolerances and design modifications required to ensure high reliability are proposed.
\r\n \r\nEven if all modules deploy successfully, fabrication errors will still be present and may affect the assembly process. In this thesis, a new simulation method is presented that can model the step-by-step assembly of flexible modules with errors. The method is used to reveal that overall shape errors grow with the number of connections, resulting in significantly decreased surface precision and large-scale deformations from the nominal backplane shape as the size of the backplane increases. The misalignment at each individual connection does not increase as the backplane increases, but can still be much larger than the applied manufacturing tolerances simply due to random combinations. A simple design for the interconnects between modules is then tested, with simulation results demonstrating that it is unlikely to fully engage when the expected errors are present. With this information, a requirement on the complexity of the interconnect design is inferred, and potential modifications that may increase its efficacy are suggested.
" }, { "name": "Hsueh, Chun-Jen", "degree": "PhD", "year": "2017", "title": "Effective Toughness of Heterogeneous Materials", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042017-165228124", "creators": [ { "name": { "family": "Hsueh", "given": "Chun-Jen" }, "id": "Hsueh-Chun-Jen", "orcid": "0000-0001-6522-4505", "display_name": "Hsueh, Chun-Jen" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bourdin", "given": "Blaise" }, "id": "Bourdin-B", "role": "member", "display_name": "Bourdin, Blaise" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9HH6H49", "abstract": "Composite materials are widely used because of their extraordinary performance. It is understood that the heterogeneity / microstructure can dramatically affect the effective behavior of materials. Although there is a well-developed theory for this relation in elasticity, there is no similar theory in fracture mechanics. Therefore, we use theoretical, numerical, and experimental approaches to study the relationship between heterogeneity / microstructure and the effective fracture behavior in this thesis.
\r\n\r\nWe use the surfing boundary condition, a boundary condition that ensures the macroscopic steady crack growth, and then define the effective toughness of heterogeneous materials as the peak energy release rate during crack propagation. We also use the homogenization theory to prove that the effective J-integral in heterogeneous materials is well defined, and that it can be calculated by the homogenized stress and strain field.
\r\n\r\nIn order to study the relationship between heterogeneities and effective toughness, we first use the semi-analytical method under the assumption of small elastic contrast to study selected examples. For strong heterogeneities, we use the phase field fracture method to study the crack propagation numerically. We then optimize the microstructure with respect to effective stiffness and effective toughness in a certain class of microgeometries. We show that it is possible to significantly enhance toughness without significant loss of stiffness. We also design materials with asymmetric toughness.
\r\n\r\nWe develop a new experimental configuration that can measure the effective toughness of specimens with arbitrary heterogeneities. We confirm through preliminary tests that the heterogeneities can enhance the effective toughness.
\r\n\r\nBesides study the effective toughness of heterogeneous materials, we also study a model problem of peeling a thin sheet from a heterogeneous substrate. We develop a methodology to systematically optimize microstructure.
" }, { "name": "Huang, Wentao", "degree": "PhD", "year": "2017", "title": "Coding for Security and Reliability in Distributed Systems", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042017-212503971", "creators": [ { "name": { "family": "Huang", "given": "Wentao" }, "id": "Huang-Wentao", "orcid": "0000-0003-0963-3624", "display_name": "Huang, Wentao" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Langberg", "given": "Michael" }, "id": "Langberg-M", "role": "member", "display_name": "Langberg, Michael" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9P26W5C", "abstract": "This dissertation studies the use of coding techniques to improve the reliability and security of distributed systems. The first three parts focus on distributed storage systems, and study schemes that encode a message into n shares, assigned to n nodes, such that any n - r nodes can decode the message (reliability) and any colluding z nodes cannot infer any information about the message (security). The objective is to optimize the computational, implementation, communication and access complexity of the schemes during the process of encoding, decoding and repair. These are the key metrics of the schemes so that when they are applied in practical distributed storage systems, the systems are not only reliable and secure, but also fast and cost-effective.
\r\n\r\nSchemes with highly efficient computation and implementation are studied in Part I. For the practical high rate case of r \u2264 3 and z \u2264 3, we construct schemes that require only r + z XORs to encode and z XORs to decode each message bit, based on practical erasure codes including the B, EVENODD and STAR codes. This encoding and decoding complexity is shown to be optimal. For general r and z, we design schemes over a special ring from Cauchy matrices and Vandermonde matrices. Both schemes can be efficiently encoded and decoded due to the structure of the ring. We also discuss methods to shorten the proposed schemes.
\r\n\r\nPart II studies schemes that are efficient in terms of communication and access complexity. We derive a lower bound on the decoding bandwidth, and design schemes achieving the optimal decoding bandwidth and access. We then design schemes that achieve the optimal bandwidth and access not only for decoding, but also for repair. Furthermore, we present a family of Shamir's schemes with asymptotically optimal decoding bandwidth.
\r\n\r\nPart III studies the problem of secure repair, i.e., reconstructing the share of a (failed) node without leaking any information about the message. We present generic secure repair protocols that can securely repair any linear schemes. We derive a lower bound on the secure repair bandwidth and show that the proposed protocols are essentially optimal in terms of bandwidth.
\r\n\r\nIn the final part of the dissertation, we study the use of coding techniques to improve the reliability and security of network communication.
\r\n\r\nSpecifically, in Part IV we draw connections between several important problems in network coding. We present reductions that map an arbitrary multiple-unicast network coding instance to a unicast secure network coding instance in which at most one link is eavesdropped, or a unicast network error correction instance in which at most one link is erroneous, such that a rate tuple is achievable in the multiple-unicast network coding instance if and only if a corresponding rate is achievable in the unicast secure network coding instance, or in the unicast network error correction instance. Conversely, we show that an arbitrary unicast secure network coding instance in which at most one link is eavesdropped can be reduced back to a multiple-unicast network coding instance. Additionally, we show that the capacity of a unicast network error correction instance in general is not (exactly) achievable. We derive upper bounds on the secrecy capacity for the secure network coding problem, based on cut-sets and the connectivity of links. Finally, we study optimal coding schemes for the network error correction problem, in the setting that the network and adversary parameters are not known a priori.
" }, { "name": "Hufstedler, Esteban Antonio Lemus", "degree": "PhD", "year": "2017", "title": "Experimental Generation and Modeling of Vortical Gusts and Their Interactions with an Airfoil", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232017-111820349", "creators": [ { "name": { "family": "Hufstedler", "given": "Esteban Antonio Lemus" }, "id": "Hufstedler-Esteban-Antonio-Lemus", "orcid": "0000-0001-7162-920X", "display_name": "Hufstedler, Esteban Antonio Lemus" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Q52MN5", "abstract": "This thesis examines two methods of vortical gust generation and the interaction between these gusts and an airfoil. These flows were studied with both experiments at a Reynolds number of 20,000 and with potential-flow based simulations.
\r\n\r\nThe standard method of generating a vortical gust has been to rapidly pitch an airfoil. A novel approach is presented: heaving a plate across the tunnel, and changing direction rapidly to release a vortex. This method is motivated by the desire to limit a test article's exposure to the wake of the gust generator by moving it to the side of the tunnel.
\r\n\r\nA series of potential flow models were used to examine these flows: steady and unsteady thin airfoil theory, an extension of Tchieu and Leonard's unsteady airfoil model, and an unsteady vortex panel method.
\r\n\r\nExperiments characterized the generated gusts and verified that the strength of the shed vortices approximately matched the theoretical predictions. The inviscid simulations were unable to predict viscous effects like the wakes of the generators. The pitching airfoil resulted in a persistent wake in the test section, whereas the wake of the heaving plate only temporarily disturbed the flow.
\r\n\r\nThe vortex-wing interaction was examined using both mechanisms. When the wake of the generator was far from the wing, the unsteady simulations provided reasonable estimates for the early variation in lift. This demonstrated that the initial lift peak is due to inviscid effects. Each of the potential flow methods with wake models provided reasonable estimates of this lift. The simplicity of the unsteady thin airfoil theory model recommends its use for examining early vortex-wing interactions.
\r\n\r\nWith the test article mounted at the midline of the tunnel, the wakes had substantial effects when the pitching generator was near the midline of the tunnel, or when the heaving plate passed the midline. The simulations were not able to capture the effects of the wakes or predict the effects of the airfoil's angle of attack. This had the largest effect on the timescale of the post-gust approach to the final forces. With the airfoil at \u03b1=0\u00b0, this was 5-10 convective time units, which is characteristic of attached flows. The airfoil at \u03b1=10\u00b0 needed double the time to approach its final state after perturbations due to its separated flow. The heaving plate's withdrawal allowed for measurement of the resumption of vortex shedding, which was impossible with the pitching airfoil's persistent wake.
" }, { "name": "Ji, Ho-Il", "degree": "PhD", "year": "2017", "title": "Redox Kinetics of Nonstoichiometric Oxides", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182017-225415095", "creators": [ { "name": { "family": "Ji", "given": "Ho-Il" }, "id": "Ji-Ho-Il", "orcid": "0000-0002-6194-991X", "display_name": "Ji, Ho-Il" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z98913W2", "abstract": "Cerium oxide (CeO2-\u03b4) and its derivatives are the most attractive materials under consideration for solar-driven thermochemical production of chemical fuels. Understanding the rate-limiting factors in fuel production is essential for maximizing the efficacy of the thermochemical process.
\r\n\r\nThe rate of response of the porous ceria structured with architectural features typical of those employed in solar reactors was measured via electrical conductance relaxation methods. A transition from behavior controlled by material surface reaction kinetics to that controlled by sweep-gas supply rates is observed on increasing temperature, increasing volume specific surface area, and decreasing normalized gas flow rate. The transition behavior is relevant not only for optimal reactor operation and architectural design of material, but also for accurate measurement of material properties.
\r\n\r\nThe redox kinetics of undoped ceria, CeO2-\u03b4 at extreme high temperature (1400 \u00b0C) was investigated using the electrical conductivity relaxation method, and those of 10% Pr doped ceria at low temperature (700 \u00b0C) were done using the mass relaxation method. It was demonstrated under sufficiently high gas flow rates relative to the mass of the oxide, which is required in order to overcome gas phase limitations and access the material kinetic properties. Furthermore, the surface reaction rate constant of undoped ceria, ,kChem, was investigated at high temperature (1400 \u00b0C) in humidified gas atmosphere, in consideration of the operating conditions in thermochemical fuel production system. It was demonstrated that H2O potentially plays a role of oxidants as increasing temperature and/or decreasing oxygen partial pressure; thus in such thermodynamic conditions, pH2O, besides temperature and pO2, needs to be carefully considered in surface reaction study.
\r\n\r\nIn addition to relaxation experiments under small driving force for redox reaction, the kinetics of surface related oxidation reaction under large chemical driving force (large \u0394pO2 change) was investigated by mass relaxation method. Based on the normalized reaction rates of several possible rate determining steps, the relaxation behavior in oxygen concentration for all possible rate determining steps was computed. On the comparison with the experimental results, the most probable rate determining step was suggested (reduction of diatomic oxygen from neutral oxygen molecule to superoxide), and the oxidation kinetics under large driving force was explained.
\r\n" }, { "name": "Johnson, Samantha Jo Iva", "degree": "PhD", "year": "2017", "title": "Computational Investigation of Small Molecule Catalysis by Cobalt, Rhodium, and Iridium Molecular Catalysts ", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:12082016-154933538", "creators": [ { "name": { "family": "Johnson", "given": "Samantha Jo Iva" }, "id": "Johnson-Samantha-Jo-Iva", "orcid": "0000-0001-6495-9892", "display_name": "Johnson, Samantha Jo Iva" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Persson", "given": "Petter" }, "id": "Persson-Petter", "role": "member", "display_name": "Persson, Petter" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9TD9V9K", "abstract": "Global energy demands are predicted to increase through 2040. In the spirit of meeting these demands, work focusing on increasing the efficiency of existing energy technologies, as well as improving energy storage is necessary. This work takes a catalytic approach to these challenges, focusing on Co, Rh, and Ir catalysts with pincer and bipyridine ligands. Density functional theory (DFT) can be used in order to gain a deeper understanding of how these catalysts behave. In the realm of improving existing technologies, the mechanism for oxidation of methane to methanol by Phebox Ir (Phebox = bis(oxazolinyl)phenyl) is investigated with a focus on understanding how subtle substitutions to the ligand can help or hinder this reaction. It is shown that in this catalyst, two unwanted intermediates on the potential energy surface (an IrIV state leading to catalyst deactivation and an IrV state leading to over-oxidation) can potentially be avoided by adding trifluoromethyl groups to the ligand. For production of fuels from solar energy, two reactions are studied. Experimentally, CO2 reduction to formate by (POCOP)Ir (POCOP = C6H3-2,6-[OP(tBu)2]2) has been shown to selectively occur at moderate potentials. The mechanism by which this catalyst reduces CO2 is elucidated. In particular, the impressive product selectivity afforded this catalyst for formate over hydrogen production is rooted in kinetics: high barriers for protonation inhibit the creation of H2 adducts. In addition to this, substitutions to the ligand and metal center are investigated to further illuminate the relationship between kinetics and thermodynamics. Hydrogen evolution in Cp*Rh(bpy) (bpy = 2,2'-bipyridine, Cp* = pentamethylcyclopentadienyl) is investigated, centering on unexpected protonation at the Cp* ligand rather than the metal center. This state is on the path for hydrogen evolution in the case of using weak acids, but in the presence of strong acids, the path through the traditional hydride is most likely. Finally, the attachment of these catalysts to electrode surfaces is discussed with the aim of making molecular catalysts a more viable option in industry It is shown that chlorine present in the attachment process enables easy catalyst dissociation from the surface. Several non-halogen options are discussed as replacements. Throughout the thesis two themes emerge: the constant interaction between thermodynamics and kinetics to control mechanistic paths and products, and the ability of small modifications to have huge impacts on catalytic cycles. " }, { "name": "Kher, Aditya Shreyas", "degree": "PhD", "year": "2017", "title": "Superconducting Nonlinear Kinetic Inductance Devices", "advisor": "Zmuidzinas, Jonas", "url": "https://resolver.caltech.edu/CaltechTHESIS:02062017-171647432", "creators": [ { "name": { "family": "Kher", "given": "Aditya Shreyas" }, "id": "Kher-Aditya-Shreyas", "orcid": "0000-0002-5994-428X", "display_name": "Kher, Aditya Shreyas" } ], "advisors": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "orcid": "0000-0002-3330-5439", "role": "advisor", "display_name": "Zmuidzinas, Jonas" } ], "committee": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "orcid": "0000-0002-3330-5439", "role": "chair", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Bock", "given": "James J." }, "id": "Bock-J-J", "orcid": "0000-0002-5710-5212", "role": "member", "display_name": "Bock, James J." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9JQ0Z1F", "abstract": "We describe a novel class of devices based on the nonlinearity of the kinetic inductance of a superconducting thin film. By placing a current-dependent inductance in a microwave resonator, small currents can be measured through their effect on the resonator\u2019s frequency. By using a high-resistivity material for the film and nanowires as kinetic inductors, we can achieve a large coefficient of nonlinearity to improve device sensitivity. We demonstrate a current sensitivity of 8 pA/√Hz, making this device useful for transition-edge sensor (TES) readout and other cutting-edge applications. An advantage of these devices is their natural ability to be multiplexed in the frequency domain, enabling large detector arrays for TES-based instruments. A traveling-wave version of the device, consisting of a thin-film microwave transmission line, is also sensitive to small currents as they change the phase length of the line due to their effect on its inductance. We demonstrate a current sensitivity of 5 pA/√Hz for this version of the device, making it also suitable for TES readout as well as other current-detection applications. It has the advantage of multi-gigahertz bandwidth and greater dynamic range, offering a different approach to the resonator version of the device. Finally, we also demonstrate a transmission-line resonator version of the device that combines some of the advantages of the nanowire resonator and the traveling-wave device. This version of the device has high dynamic range but can also be easily multiplexed in the frequency domain.
\r\n\r\nA lumped-element resonator similar to the first device can be placed in a loop configuration to make it sensitive to magnetic fields. We demonstrate an example of such a device whose sensitivity could ultimately reach levels similar to those of state-of-the-art DC SQUIDs, making it potentially useful for many magnetometry applications given its ease of multiplexing. Finally, a similar microwave resonator is shown to exhibit parametric gain of up to 29 dB in the presence of a strong pump tone. The noise performance of this parametric amplifier approaches the quantum limit, making it useful for applications in quantum information and metrology.
" }, { "name": "Kim, Jinho", "degree": "PhD", "year": "2017", "title": "Compact Microscope System for Biomedical Applications", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04262017-114441886", "creators": [ { "name": { "family": "Kim", "given": "Jinho" }, "id": "Kim-Jinho", "display_name": "Kim, Jinho" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Lester", "given": "Henry A." }, "id": "Lester-H-A", "role": "member", "display_name": "Lester, Henry A." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9H9937R", "abstract": "Demands for an imaging system which has high space-bandwidth product (SBP) are increasing in modern biomedical research as the amount of information to be dealt with is increasing. However, conventional microscopy has a limited SBP of about 10 mega pixels, and as such if a user wants an image in high resolution, the field of view (FOV) of the image is reduced, or if a wide FOV is necessary, the user needs to give up the resolution of image. A common way of overcoming this SBP limit in the conventional microscopy is to use mechanical moving stages and scan through wide sample area, however, it is time consuming to image large area using a high numerical aperture (NA) objective lens. This thesis presents compact imaging systems based on Fourier ptychographic microscopy for biomedical applications which are able to increase SBP without having any mechanical moving parts: one imaging system for an incubator embedded imaging system to be used in in-vitro cell culture monitoring, and the other for a high throughput 96 well plate imaging system for fast drug screening.
" }, { "name": "Kim, Seyoon", "degree": "PhD", "year": "2017", "title": "Electronically Tunable Light Modulation with Graphene and Noble Metal Plasmonics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:02152017-220505611", "creators": [ { "name": { "family": "Kim", "given": "Seyoon" }, "id": "Kim-Seyoon", "orcid": "0000-0002-8040-9521", "display_name": "Kim, Seyoon" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9ZW1HXJ", "abstract": "Graphene is a monolayer of carbon atoms constructing a two-dimensional honeycomb structure, and it has an excellent carrier mobility and a very high thermal conductivity. Remarkably, it has been experimentally demonstrated that a monolayer graphene exhibits an exotic optical properties. To be specific, the plasmonic dispersion relation of a transverse magnetic graphene plasmon is electronically tunable by adjusting carrier density in graphene with external gate bias, and graphene plasmonic nano cavities have been utilized to modulate mid-infrared light.
\r\n\r\nIn this thesis, we present how to efficiently modulate mid-infrared light by combining graphene plasmonic ribbons with noble metal plasmonic structures.
\r\n\r\nFirst, we propose and demonstrate electronically tunable resonant perfect absorption in graphene plasmonic metasurface enhanced by noble metal plasmonic effect, which results in modulating reflecting light. In this device, we improve coupling efficiency of free-space photons into graphene plasmons by reducing wavevector mismatching with a low permittivity substrate. In addition, the graphene plasmonic resonance is significantly enhanced by plasmonic light focusing effect of the coupled subwavelength metallic slit structure, which results in strongly fortifying resonance absorption in the graphene plasmonic metasurface. In the proposed device, theoretical calculation expects that perfect absorption in the graphene plasmonic metasurface is achievable with low graphene carrier mobility. We also present an analytical model based on surface admittance in order to fully understand how this enhancement occurs.
\r\n\r\nIn the second device, we propose and demonstrate a transmission type light modulator by combining graphene plasmonic ribbons with subwavelength metal slit arrays. In this device, extraordinary optical transmission resonance is coupled to graphene plasmonic ribbons to create electrostatic modulation of mid-infrared light. Absorption in graphene plasmonic ribbons situated inside metallic slits can efficiently block the coupling channel for resonant transmission, leading to a suppression of transmission. This phenomenon is also interpreted by anti-crossing between the graphene plasmonic resonance in the ribbons and the noble metal plasmonic resonance in the subwavelength metal slit arrays.
\r\n\r\nFinally, we devise a platform to demonstrate graphene plasmonic resonance energy transport along graphene plasmonic ribbons. In this device, two metal-insulator-metal waveguides are connected by a subwavelength metal slit, and graphene plasmonic ribbons are located inside this slit. Due to the large impedance mismatch at the junction, light coupling efficiency across the junction is poor. If the graphene plasmonic ribbons are tuned to support strong graphene plasmonic resonances, the light energy can be transferred via graphene plasmons along the ribbons, and it leads to significant improvement in the light coupling efficiency across the junction. In addition to enhanced light coupling efficiency, we also present how to totally suppress the transmission by inducing a Fano resonance between a non-resonant propagation mode across the junction and a resonant graphene plasmonic transport mode, which can be utilized to efficiently modulate light in a noble metal plasmonic waveguide with the graphene plasmon resonance energy transfer.
" }, { "name": "Liu, Pengfei", "degree": "PhD", "year": "2017", "title": "Spatial Profiles in the Singular Solutions of the 3D Euler Equations and Simplified Models", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09092016-000915850", "creators": [ { "name": { "family": "Liu", "given": "Pengfei" }, "id": "Liu-Pengfei", "orcid": "0000-0002-6714-7387", "display_name": "Liu, Pengfei" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z9V9862G", "abstract": "The partial differential equations (PDE) governing the motions of incompressible ideal fluid in three dimensional (3D) space are among the most fundamental nonlinear PDEs in nature and have found a lot of important applications. Due to the presence of super-critical non-linearity, the fundamental question of global well-posedness still remains open and is generally viewed as one of the most outstanding open questions in mathematics. In this thesis, we investigate the potential finite-time singularity formation of the 3D Euler equations and simplified models by studying the self-similar spatial profiles in the potentially singular solutions.
\r\n\r\nIn the first part, we study the self-similar singularity of two 1D models, the CKY model and the HL model, which approximate the dynamics of the 3D axisymmtric Euler equations on the solid boundary of a cylindrical domain. The two models are both numerically observed to develop self-similar singularity. We prove the existence of a discrete family of self-similar profiles for the CKY model, using a combination of analysis and computer-aided verification. Then we employ a dynamic rescaling formulation to numerically study the evolution of the spatial profiles for the two 1D models, and demonstrate the stability of the self-similar singularity. We also study a singularity scenario for the HL model with multi-scale feature.
\r\n\r\nIn the second part, we study the self-similar singularity for the 3D axisymmetric Euler equations. We first prove the local existence of a family of analytic self-similar profiles using a modified Cauchy-Kowalevski majorization argument. Then we use the dynamic rescaling formulation to investigate two types of initial data with different leading order properties. The first initial data correspond to the singularity scenario reported by Luo and Hou. We demonstrate that the self-similar profiles enjoy certain stability, which confirms the finite-time singularity reported by Luo and Hou. For the second initial data, we show that the solutions develop singularity in a different manner from the first case, which is unknown previously. The spatial profiles in the solutions become singular themselves, which means that the solutions to the Euler equations develop singularity at multiple spatial scales.
\r\n\r\nIn the third part, we propose a family of 3D models for the 3D axisymmetric Euler and Navier-Stokes equations by modifying the amplitude of the convection terms. The family of models share several regularity results with the original Euler and Navier-Stokes equations, and we study the potential finite-time singularity of the models numerically. We show that for small convection, the solutions of the inviscid model develop self-similar singularity and the profiles behave like travelling waves. As we increase the amplitude of the velocity field, we find a critical value, after which the travelling wave self-similar singularity scenario disappears. Our numerical results reveal the potential stabilizing effect the convection terms.
" }, { "name": "Miyazono, Evan Tsugio", "degree": "PhD", "year": "2017", "title": "Nanophotonic Resonators for Optical Quantum Memories based on Rare-Earth-Doped Materials", "advisor": "Faraon, Andrei", "url": "https://resolver.caltech.edu/CaltechTHESIS:03152017-114949088", "creators": [ { "name": { "family": "Miyazono", "given": "Evan Tsugio" }, "id": "Miyazono-Evan-Tsugio", "orcid": "0000-0003-2176-0335", "display_name": "Miyazono, Evan Tsugio" } ], "advisors": [ { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "advisor", "display_name": "Faraon, Andrei" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z98K773F", "abstract": "The growing interest in optical quantum systems has led to the exploration of multiple platforms. Though pioneering experiments were performed in trapped atom and trapped ion systems, solid state systems show promise of being scalable and robust. Rare earth dopants in crystalline hosts are an appealing option because they possess a rich spectrum of energy levels that result from a partially filled electron orbital. While level structure varies across the period, all elements possess crystal field splittings corresponding to near infra-red or optical frequencies, as well as Zeeman and often hyperfine levels separated by radio frequency and microwave frequencies. These levels demonstrate long excited-state lifetimes and coherence times and have been used in diverse applications, including demonstrating storage of a photonic state, converting of optical to microwave photons, and manipulating a single ion as a single qubit. The ions' weak interaction with their environment results in low coupling to optical fields, which had previously required measurements with macroscopically large ensembles of ions. Coupling the ions to an optical cavity enables the use of a smaller ensemble, which is required for the development of the aforementioned technologies in an on-chip scalable architecture.
\r\n\r\nThis thesis contains recent progress towards fabricating optical micro and nanocavities coupled to ensembles of erbium ions, mainly erbium in yttrium orthosilicate. In one design, focused ion beam milling was used to create a triangular nanobeam photonic crystal cavity in a bulk erbium-doped substrate. A second design leveraged the fabrication capabilities of silicon photonics, defining amorphous silicon ring resonators using electron beam lithography and dry etching. These devices coupled evanescently to erbium ions below the ring, in the bulk substrate. Simulation, design, fabrication, and characterization of both resonators are discussed. Coupling between the ions and the resonator is demonstrated for each, and capabilities offered by these devices are described. Preliminary work implementing coherent control of erbium ions is presented. Lastly, alternative substrates are evaluated for possible future solid-state erbium systems.
" }, { "name": "Monge Osorio, Manuel Alejandro", "degree": "PhD", "year": "2017", "title": "Localization and Stimulation Techniques for Implantable Medical Electronics", "advisor": "Emami, Azita; Shapiro, Mikhail G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312017-143935777", "creators": [ { "name": { "family": "Monge Osorio", "given": "Manuel Alejandro" }, "id": "Monge-Osorio-Manuel-Alejandro", "orcid": "0000-0001-9799-0693", "display_name": "Monge Osorio, Manuel Alejandro" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "advisor", "display_name": "Emami, Azita" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "co-advisor", "display_name": "Shapiro, Mikhail G." } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9P55KJ7", "abstract": "Implantable medical devices (IMDs) are emerging as one of the keystones of tomorrow\u2019s medical technology. Although they have enabled a revolution in medicine, from research to diagnosis to treatment, most of today\u2019s devices have critical limitations. They are bulky, have low resolution, and, in some cases, are limited to basic functionality. Miniaturization of IMDs will have an enormous impact not only on the technology itself and the medical procedures they enable, but also on the lives of patients, who will be more comfortable, have greater confidence in their medical treatments, and enjoy an overall improvement in their quality of life. The path towards miniaturized bioelectronic devices requires a reevaluation of existing paradigms to reach a seamless integration of electronics and biology. Miniaturization of medical electronics then involves an exploration of advanced integrated circuit processes and novel circuit and system level architectures. In this dissertation, we provide an overview of implantable medical devices and present novel circuit and system level techniques for the miniaturization of medical electronics.
\r\n\r\nThe function of wireless miniaturized medical devices such as capsule endoscopes, biosensors, and drug delivery systems depends critically on their location inside the body. However, existing electromagnetic, acoustic, and imaging-based methods for localizing and communicating with such devices with spatial selectivity are limited by the physical properties of tissue or imaging modality performance. In the first part of this dissertation, we introduce a new approach for microscale device localization by embodying the principles of nuclear magnetic resonance in a silicon integrated circuit. By analogy to the behavior of nuclear spins, we engineer miniaturized RF transmitters that encode their location in space by shifting their output frequency in proportion to the local magnetic field. The application of external field gradients then allows each device\u2019s location to be determined precisely from the frequency of its signal. We demonstrate the core capabilities of these devices, which we call addressable transmitters operated as magnetic spins (ATOMS), in an integrated circuit smaller than 0.7 mm^3, manufactured through a standard 180 nm complementary metal-oxide-semiconductor (CMOS) process. We show that ATOMS are capable of sub-millimeter localization in vitro and in vivo. As a technology that is inherently robust to tissue properties and scalable to multiple devices, ATOMS localization provides an enabling capability for the development of microscale devices to monitor and treat disease.
\r\n\r\nIn neuroprosthetics, retinal prostheses aim to restore vision in patients suffering from advanced stages of retinal degeneration (e.g., retinitis pigmentosa) by bypassing the damaged photoreceptors and directly stimulating the remaining healthy neurons. In the second part of this dissertation, we describe a fully intraocular self-calibrating epiretinal prosthesis that reduces area and power consumption, and increases the functionality and resolution of traditional implementations. We introduce a novel novel digital calibration technique that matches the biphasic stimulation currents of each channel independently while sharing the calibration circuitry among every 4 channels. The system-on-chip presents dual-band telemetry for power and data with on-chip rectifier and clock recovery. These techniques reduce the number of off-chip components and achieve a power conversion efficiency >80% and supporting data rates up to 20 Mb/s. The system occupies an area of 4.5 x 3.1 mm2 and is implemented in 65 nm CMOS . It features 512 independent channels with a pixel size of 0.0169 mm2 and arbitrary waveform generation per channel. The chip is integrated with flexible MEMS origami coils and parylene substrate to provide a fully intraocular implant.
" }, { "name": "Murialdo, Maxwell Robert", "degree": "PhD", "year": "2017", "title": "Anomalous Thermodynamics of Nonideal Gas Physisorption on Nanostructured Carbons", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08292016-233907648", "creators": [ { "name": { "family": "Murialdo", "given": "Maxwell Robert" }, "id": "Murialdo-Maxwell-Robert", "display_name": "Murialdo, Maxwell Robert" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9GH9FXM", "abstract": "Mesoporous and microporous adsorbents play critical roles in gas storage and separation applications. This thesis describes previously unexplored anomalous thermodynamics in the field of gas physisorption and their impact on energy relevant gases including methane, ethane, krypton and carbon dioxide. Physisorption occurs when an adsorbent induces gas molecules to form a locally densified layer at its surface due to physical interactions. This increases gas storage capacity over pure compression and its efficacy is dependent on the surface area of the adsorbent and the isosteric heat of adsorption. The isosteric heat of adsorption is the molar change in the enthalpy of the adsorptive species upon adsorption and serves as a measure of adsorbent-adsorbate binding strength.
\r\n\r\nUnlike conventional adsorbate-adsorbent systems, which have isosteric heats of adsorption that decrease with surface loading, zeolite-templated carbon is shown to have isosteric heats of methane, ethane and krypton adsorption that increase with surface loading. This is a largely beneficial effect that can enhance gas storage and separation. The unique nanostructure and uniform pore periodicity of the zeolite-templated carbon promote lateral interactions among the adsorbed molecules that cause the isosteric heats of adsorption to increase with loading. These results have been tested and corroborated by developing robust fitting techniques and thermodynamics analyses. The anomalous thermodynamics are shown to result from cooperative adsorbate-adsorbate interactions among the nonideal species and are modeled with an Ising-type model.
\r\n\r\nAs a second theme of this thesis, the study of nonideal gas adsorption has enabled the development of a Generalized Law of Corresponding States for Physisorption. A predictive understanding of high-pressure physisorption on a variety of adsorbents would facilitate the further development of tailored adsorbents and adsorption analysis. Prior attempts at developing a predictive understanding, however, have been hindered by nonideal gas effects.
\r\n\r\nBy approaching physisorption from both empirical and fundamental perspectives, a Generalized Law of Corresponding States for Physisorption was established that accounts for a number of nonideal effects. This new Law of Corresponding States allows one to predict adsorption isotherms for a variety of classical gases from data measured with a single gas. In brief: \"At corresponding conditions on the same adsorbent, classical gases physisorb to the same fractional occupancy.\"
\r\n\r\nCorresponding conditions are met when the reduced variables of each nonideal gas are equivalent, and fractional occupancy gives the fraction of occupied adsorption sites. This Law of Corresponding States for Physisorption is determined using monolayer, BET and Dubinin-Polanyi adsorption theories along with measured adsorption isotherms across a number of conditions and adsorbents. Furthermore, the anomalous cooperative adsorbate-adsorbate interactions discussed in this thesis are shown to be consistent with the Generalized Law of Corresponding States for Physisorption.
\r\n" }, { "name": "Nadkarni, Neel P.", "degree": "PhD", "year": "2017", "title": "Nonlinear Dynamics of Transition Waves in Multi-Stable Discrete and Continuous Media", "advisor": "Kochmann, Dennis M.; Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:01132017-035026894", "creators": [ { "name": { "family": "Nadkarni", "given": "Neel P." }, "id": "Nadkarni-Neel-P", "orcid": "0000-0002-4311-2817", "display_name": "Nadkarni, Neel P." } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Abeyaratne", "given": "Rohan" }, "id": "Abeyaratne-R", "role": "member", "display_name": "Abeyaratne, Rohan" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9DR2SG2", "abstract": "The concept of phase transitions, i.e., switching between two or more different equilibrium states of a system, is commonly encountered in many physical, chemical and biological phenomena. The exact mechanism of this switching is a highly nonlinear dynamical process that is accommodated by the propagation of a localized wave. The characteristics of the nonlinear wave such as its profile, velocity, energy, and width of transition are governed by the type and specifics of the system that it is propagating through which may be conservative, dissipative, or diffusive in nature. The goal of this thesis is to develop a fundamental understanding of the dynamics of such processes in general nonlinear systems capable of undergoing phase transitions and the application of new theories to elucidate the kinetic and energetic properties of transition waves in different scenarios. In conservative systems, we show that there are three different modes of stable wave propagation that we analytically solve for and validate computationally. In contrast, dissipative and diffusive systems allow the stable propagation of only the strongly nonlinear kink mode whose kinetic energy and propagation velocity are linked through a linear relation. We further validate our results in dissipative systems experimentally by fabricating and testing a strongly nonlinear lattice and show that transition waves are unidirectional in nature, as predicted by theory. Finally, as an application, we devise a strategy of using the physics of dissipative phase transitions to propagate stable mechanical signals in highly dissipative media such as soft polymers which effectively damp out small-amplitude linear waves." }, { "name": "Noorzad, Parham", "degree": "PhD", "year": "2017", "title": "Network Effects in Small Networks: A Study of Cooperation", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062017-101123885", "creators": [ { "name": { "family": "Noorzad", "given": "Parham" }, "id": "Noorzad-Parham", "orcid": "0000-0002-0201-3791", "display_name": "Noorzad, Parham" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Langberg", "given": "Michael" }, "id": "Langberg-M", "role": "member", "display_name": "Langberg, Michael" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-K-A", "role": "member", "display_name": "Ligett, Katrina A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9M32STV", "abstract": "Communication over a point-to-point link is relatively well understood. However, when such a link is part of a larger network, our understanding is far from complete. Nonetheless, progress in this area has important consequences in both the theoretical and practical aspects of communication networks.
\r\n\r\nIn this work, we focus on the role of a single link in networks that in addition to point-to-point links, contain \"multi-terminal components.\" An example of a network consisting of a single multi-terminal component is the uplink in a wireless communication network where multiple transmitters communicate with a single receiver over a shared medium. We demonstrate the existence of a class of such networks where a finite capacity link results in a rate gain for each source that far exceeds the capacity of that link. This is an example of a \"network effect\": the phenomenon where a resource, here link capacity, is significantly more valuable in a network than in isolation. Here we measure the \"value\" of the finite capacity link by the sum-capacity gain per source that it enables.
\r\n\r\nThe central idea behind the construction of networks that exhibit such effects is the introduction of a node, referred to as the \"cooperation facilitator\" (CF), that allows other network nodes to work together to reduce interference. In the setting of the classical multiple access channel (MAC), an example of a CF is a node that receives rate-limited information from each transmitter and broadcasts rate-limited information back to the transmitters through a common bottleneck link. Let the \"cooperation rate\" be the capacity of the CF bottleneck link. We show that for a class of MACs, the presence of a CF\r\nleads to a sum-capacity gain that, as a function of the cooperation rate, has an infinite slope at cooperation rate zero. This means that the bottleneck link of the CF is significantly more valuable in some networks than in isolation. This class of MACs includes well-known examples such as the Gaussian MAC and the binary adder MAC.
\r\n\r\nIn addition to sum-capacity gain, cooperation under the CF model also improves reliability. Specifically, in the case of the MAC with two transmitters, whenever the CF has full access to both messages, the maximal- and average error capacity regions coincide. This effect is observed even when the cooperation rate is \"negligible\"; that is, the cooperation rate grows sublinearly in the number of channel uses. An implication of this result is the existence of a network whose maximal-error sum-capacity is not continuous with respect to the capacities of its edges; this means that in some networks, even a negligible cooperation rate leads to a positive sum-capacity gain.
" }, { "name": "Ohno, Saneyuki", "degree": "PhD", "year": "2017", "title": "Phase Boundary Mapping for Exploring New Thermoelectric Zintl Compounds", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-235716123", "creators": [ { "name": { "family": "Ohno", "given": "Saneyuki" }, "id": "Saneyuki-Ohno", "orcid": "0000-0001-8192-996X", "display_name": "Ohno, Saneyuki" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Bux", "given": "Sabah K." }, "id": "Bux-S-K", "role": "member", "display_name": "Bux, Sabah K." }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9H70CWG", "abstract": "Understanding and controlling the defect chemistry of bulk materials can vastly increase the opportunities for discovering highly efficient thermoelectrics. Good thermoelectrics are degenerate semiconductors and there are two types: n-type thermoelectrics, whose charge carriers are electrons, and p-type thermoelectrics conducting holes as carriers. Although normally one type can attain superior thermoelectric properties to the other depending on the electronic band structure of a material, a formation of the unfavorable defects sometimes prevents a material from obtaining the desired type. Similarly, even if the desired carrier type is realized, the Fermi level, which is a measure of the carrier density, could be kept from the optimum due to the formation of compensating defects. It has been known from growing binary semiconductors for electronics and optoelectronics such as GaAs and GaN that a growth condition can substantially alter the defect concentration of resulting samples. This is primarily due to the change in the reference atomic chemical potentials, but such defect engineering has not been utilized for the bulk thermoelectric research, resulting in overlooking the promising candidate materials.
\r\n\r\nIn this work, we established an experimental methodology to fully explore all the accessible variations in chemical potentials of a target phase and demonstrated its implementation. Although a pursuance of purity of samples to be measured is a common experimental concept in solid-state chemistry, in practice, a small single-phase region of semiconductors allows samples to have a certain amount of impurities. Since different multi-phase equilibria have discrete chemical potentials, only when all the boundaries of the multi-phase equilibria around target phase are mapped out in nominal composition space are the measured transport properties of resulting samples properly correlated with their atomic chemical potential.
\r\n\r\nUtilizing this experimental concept we call \"phase boundary mapping\", we have identified the mechanism of obtaining the superior n-type conduction in Mg3Sb2-based compounds. To achieve their exceptionally high thermoelectric figure-of-merit (zT = 1.5 at 750 K), the formation energy of Mg-vacancy needs to be suppressed with excess Mg but this condition had been missing for over 80 years due to the absence of experimental concept to fully investigate properties of a material. Implementing phase boundary mapping has also allowed an inexpensive thermoelectric Zintl compound Ca9Zn4+xSb9 to be one of the best thermoelectrics in the intermediate temperature range (zT = 1.1). We have also successfully reduced the carrier concentration of Yb9Zn4+xSb9, which was originally thought to be impossible, leading to zT increased by a factor of five.
" }, { "name": "Palm, Steven Leslie", "degree": "PhD", "year": "2017", "title": "Thermo-Acoustic Coupling and Dynamic Response of a Premixed Methane-Air Flame", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302017-214955280", "creators": [ { "name": { "family": "Palm", "given": "Steven Leslie" }, "id": "Palm-Steven-Leslie", "orcid": "0000-0003-3095-0368", "display_name": "Palm, Steven Leslie" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Yang", "given": "Vigor" }, "id": "Yang-Vigor", "role": "member", "display_name": "Yang, Vigor" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9V12309", "abstract": "The work herein generally applies to the problem of combustion instability. Combustion instabilities first arose in engineering practice in the 1940s when they were experienced during the development of solid and liquid propellant rocket engines. Later, similar problems arose in gas turbine combustors and afterburners. However, the earliest technical case of the phenomenon dates back to Rijke in 1859 with his \"singing\" tube.
\r\n\r\nThe presented work focuses on the study of a simple, stagnation plane stabilized, laminar, flat-flame burner. In particular the dynamic response of the burner is examined under excitation by a driven acoustic field. After characterization of the burner\u2019s operational range, the response of the system is measured from 20 Hz to nearly 2000 Hz over the span of operating parameters using an optically filtered PMT and lens combination. A library of the collected and reduced data is generated.
\r\n\r\nA deeper investigation of the burner dynamics at a given reference operating condition is performed using phase-resolved PLIF. Fluctuations in the spatial distributions of the LIF signals for several target species (OH, CH, CH2O) under acoustic forcing are measured. In addition, visualization of the unsteady reactant flow using precision acetone seeding and PLIF at 277 nm is performed. Subsequent cinematographic sequences are produced along with spatially resolved plots of the combustion response function and the forced Rayleigh index for numerous drive frequencies. A library of the collected and reduced data is assembled.
\r\n\r\nAnalysis of the collected data reveals two principal mechanisms contributing to the unsteady response of the flame. Structure development in (and subsequent convention along) the unsteady shear layer of the laminar jet dominates the response at the outer reaches of the flame. The inner region of the flame is driven largely by the Helmholtz response of the burner nozzle cavity. These two operations mutually contribute to produce the general shape of the combustion response curve. Ultimately, the data is used to construct a simplified model for the combustion response function. The model is enhanced with two additional revisions guided by the improved understanding of the mechanisms involved.
\r\n\r\nThe document ends with numerous appendices describing, in detail, the equipment used, much of which was fabricated specifically for this work. These appendices, in combination with information presented in the chapters, provide substantial detail regarding the experimental configuration and operating conditions. Great effort was made to provide the necessary information to allow replication of the experiments as well as to support future modeling endeavors as a validation dataset.
\r\n" }, { "name": "Plucinsky, Paul P.", "degree": "PhD", "year": "2017", "title": "The Deformations of Thin Nematic Elastomer Sheets", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022017-081925673", "creators": [ { "name": { "family": "Plucinsky", "given": "Paul P." }, "id": "Plucinsky-Paul-P", "orcid": "0000-0003-2060-8657", "display_name": "Plucinsky, Paul P." } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9765CCT", "abstract": "Thin structures exhibit a broad range of mechanical responses as the competition between stretching and bending in these structures can result in buckling and localized deformations like folding and tension wrinkling. Active materials also exhibit a broad range of mechanical responses as features that manifest themselves at the microscale in these materials result in mechanical couplings at the engineering scale (thermal/electrical/dissipative) and novel function (e.g., the shape memory effect and piezoelectricity in select metal alloys and the immense fracture toughness of hydrogels). Given this richness in behaviors, my research broadly aims to address the following questions: What happens when active materials are incorporated into thin structures? Do phenomena inherent to these materials compete with or enhance those inherent to thin structures? Does this interplay result in entirely new and unexpected phenomena? And can all this be exploited to design new functions in engineering systems?
\r\n\r\nIn this thesis, we explore these questions in the context of a theoretical study of thin sheets of nematic liquid crystal elastomer. These materials are active rubbery solids made of cross-linked polymer chains that have liquid crystals either incorporated into the main chain or pendent from them. Their structure enables a coupling between the mechanical elasticity of the polymer network and the ordering of the liquid crystals, and this in turn results in fairly complex mechanical behavior including large spontaneous distortion due to temperature change, soft-elasticity and fine-scale microstructure.
\r\n\r\nWe study thin sheets of nematic elastomer. First, we show that thin of sheets of a particular class of nematic elastomer can resist wrinkling when stretched. Second, we show that thin sheets of another class of nematic elastomer can be actuated into a multitude of complex shapes. In order to obtain these results, we systematically develop two dimensional theories for thin sheets starting from a well-accepted first principles theory for nematic elastomers. These characterize (i) the mechanical response due to instabilities such as structural wrinkling and fine-scale material microstructure, and (ii) thermal actuation of heterogeneously patterned sheets. For the latter, we show that the theory, which comes in the form of a two dimensional metric constraint, admits two broad classes of designable actuation in nonisometric origami and lifted surface. For the former, we show that taut and appreciably stressed sheets of nematic elastomer are capable of suppressing wrinkling by modifying the expected state of stress through the formation of microstructure.
" }, { "name": "Popescu, Paula Flor", "degree": "PhD", "year": "2017", "title": "An Optofluidic Ring Resonator Platform for Rapid and Robust Sensing", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12012016-194127904", "creators": [ { "name": { "family": "Popescu", "given": "Paula Flor" }, "id": "Popescu-Paula-Flor", "display_name": "Popescu, Paula Flor" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9H41PFQ", "abstract": "Ring resonators show great potential as sensitive optical detectors for studies of biomolecular interactions, drug screening, and point-of-care diagnostics. They are sensitive to minute changes in the refractive index of the surrounding medium, which enables them to detect and quantify sub-femtomolar concentrations of target molecules. This thesis investigates the advantages of an optofluidic ring resonator platform that employs a differential measurement scheme for reducing environmental noise due to temperature and pressure fluctuations. Through simulations and experiments, I determine the sensitivity of the platform to changes in the target analyte concentration and to environmental noise, and demonstrate the benefits of employing a second, reference, ring resonator.
\r\n\r\nA crucial step in achieving versatile biosensing platforms is the integration of the high sensitivity resonators into platforms with short assay times and robust chemical functionalization. I focus on the development of robust chemistry protocols for depositing linker silane layers for biomolecular interaction studies. Moreover, since the fluid handling scheme strongly influences the response time of the platform, I design and test two fluidic platforms integrated with elastomeric valves that show excellent response times. To further increase the response time of the sensing platform, I explore the effects of a patterned channel geometry on the enhancement of mass transport to the sensor in low Reynolds number flows.
" }, { "name": "P\u00e9rez Arancibia, Carlos Andr\u00e9s", "degree": "PhD", "year": "2017", "title": "Windowed Integral Equation Methods for Problems of Scattering by Defects and Obstacles in Layered Media", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182016-124629380", "creators": [ { "name": { "family": "P\u00e9rez Arancibia", "given": "Carlos Andr\u00e9s" }, "id": "Perez-Arancibia-Carlos-Andr\u00e9s", "orcid": "0000-0003-1647-4019", "display_name": "P\u00e9rez Arancibia, Carlos Andr\u00e9s" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z9GQ6VQT", "abstract": "This thesis concerns development of efficient high-order boundary integral equation methods for the numerical solution of problems of acoustic and electromagnetic scattering in the presence of planar layered media in two and three spatial dimensions. The interest in such problems arises from application areas that benefit from accurate numerical modeling of the layered media scattering phenomena, such as electronics, near-field optics, plasmonics and photonics as well as communications, radar and remote sensing.
\r\n\r\nA number of efficient algorithms applicable to various problems in these areas are pre- sented in this thesis, including (i) A Sommerfeld integral based high-order integral equation method for problems of scattering by defects in presence of infinite ground and other layered media, (ii) Studies of resonances and near resonances and their impact on the absorptive properties of rough surfaces, and (iii) A novel Window Green Function Method (WGF) for problems of scattering by obstacles and defects in the presence of layered media. The WGF approach makes it possible to completely avoid use of expensive Sommerfeld integrals that are typically utilized in layer-media simulations. In fact, the methods and studies referred in points (i) and (ii) above motivated the development of the markedly more efficient WGF alternative.
" }, { "name": "Ravichandran, Navaneetha Krishnan", "degree": "PhD", "year": "2017", "title": "Theoretical and Experimental Investigation of Phonon Boundary Scattering in Thin Silicon Membranes", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01172017-145551495", "creators": [ { "name": { "family": "Ravichandran", "given": "Navaneetha Krishnan" }, "id": "Ravichandran-Navaneetha-Krishnan", "display_name": "Ravichandran, Navaneetha Krishnan" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9SJ1HK2", "abstract": "The thermal transport properties of thin semiconductor membranes play an important role in the performance of many technologies like micro-electronics and solid-state energy conversion. The dominant resistance to heat flow in thin membranes is offered by the scattering of thermal phonons at the membrane boundaries. In this dissertation, we examine the nature of microscopic phonon boundary scattering processes and their effect on the thermal conductivity of the thin membranes using a pump-probe experimental technique and computationally efficient solutions of the phonon Boltzmann transport equation (BTE).
\r\n\r\nFirst, we investigate the boundary scattering-limited thermal transport in nanostructures using an efficient variance-reduced Monte Carlo (MC) solution of the BTE to elucidate the impact of specular and diffuse phonon boundary scattering events on the thermal conductivity of the nanostructures. To directly measure the relative frequency of these two boundary scattering events, called the phonon specularity parameter, we design, implement and characterize a non-contact laser-based pump-probe experiment called the transient grating (TG) to perform phonon mode-dependent measurements of the specularity parameter in suspended free-standing thin silicon membranes. We describe the phenomenon of quasiballistic heat conduction, which enables the phonon mode-dependent measurements of the specularity parameter, and derive a transfer function based on the BTE with ab-initio phonon properties as inputs, to connect the specularity parameter with the experimentally measured thermal conductivity of the thin membranes.
\r\n\r\nFinally, we present the methodology adopted to invert the BTE transfer function to extract the phonon specularity parameter from the thermal conductivity measurements in the TG experiment, while rigorously accounting for the experimental uncertainties. We find that the observed magnitudes and trends of the thermal conductivity of the thin membranes cannot be explained by the 50-year old Ziman's model for the phonon specularity parameter and the Fuchs-Sondheimer theory of phonon boundary scattering. We also find that the partially specular boundary scattering picture of phonon boundary interactions works well for one of the membranes, enabling a direct measurement of the mode-dependent phonon specularity parameter for the first time in an experiment. We discuss the possibility of phonon mode conversion at the boundaries of a few membranes for which the partially specular phonon boundary scattering picture fails to explain the observed thermal conductivity trends. Considering the importance of understanding phonon boundary scattering to engineer and improve nanoscale device performance, we expect that the new experimental and computational tools developed in this work will advance a variety of nanoscale energy applications and further our understanding of nanoscale heat transport.
" }, { "name": "Roh, Chris", "degree": "PhD", "year": "2017", "title": "Hydrodynamics of Insects. Part 1. Jetting of the Dragonfly Larvae. Part 2. Honeybee at the Air-water Interface: Surfing with the Capillary Wave", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-183218154", "creators": [ { "name": { "family": "Roh", "given": "Chris" }, "id": "Roh-Chris", "orcid": "0000-0002-5681-0040", "display_name": "Roh, Chris" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "chair", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z97P8WFW", "abstract": "This thesis presents the study on the hydrodynamics of two insects commonly known for their aerial adaptation: the dragonfly and the honeybee.
\r\n\r\nPart 1: Anisopteran dragonflies live underwater in their larval stages. The key factor for their aquatic adaptation is the modified hindgut chamber that is used as a pump. The two main functions of this biological pump are jet propulsion and respiration. Both functions involve jetting and refilling of the chamber through an orifice guard by a tri-leaflet anal valve. Despite it being a unique machinery among insects, associated hydrodynamic studies are limited thus far. In the first part of this thesis, various aspects of the hydrodynamics of the dragonfly larvae\u2019s ventilatory flow are studied. The flow visualization showed that the respiratory flow is laminar but the propulsion flow is turbulent. The hydrodynamic force analysis showed that jetting and refilling phase forces are dominated by quasi-steady momentum flux and unsteady acceleration, respectively. Finally, simultaneous measurement of the anal valve kinematics and jet flow showed that the larvae could influence the direction and magnitude of the jet by controlling the anal valve leaflets.
\r\n\r\nPart 2: Water-collecting honeybees often fall onto water surfaces. However, bees trapped by the \u201cstickiness\u201d of the water can propel by vibrating their wings, often making it to shore. In the second part of this thesis, the honeybee\u2019s propulsion mechanisms at the air\u2013water interface is studied. The result shows that the bees can achieve three body-lengths per second propulsion speed. High-speed video of their wing motion shows that honeybee\u2019s propulsion involves pulling blobs of water with the underside of the wing, while pushing on a surface wave with its trailing edge. This propulsion mechanism resembles surfing on a self-generated capillary wave. Moreover, their wing vibration generates complicated surface waves and flows, below which the deeper water flow shows a single jet stream. From the wave and flow field measurements, the average force imparted to the surrounding fluid is estimated and compared to the average force calculated from the bee\u2019s body motion. The resulting average forces are of the same order of magnitude, which means that generating wave and flow are both important for the bee\u2019s propulsion.
" }, { "name": "Rufat, Dzhelil Sabahatin", "degree": "PhD", "year": "2017", "title": "Spectral Exterior Calculus and its Implementation", "advisor": "Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302017-094600781", "creators": [ { "name": { "family": "Rufat", "given": "Dzhelil Sabahatin" }, "id": "Rufat-Dzhelil-Sabahatin", "orcid": "0000-0001-8766-2338", "display_name": "Rufat, Dzhelil Sabahatin" } ], "advisors": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "chair", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Porter", "given": "Frank C." }, "id": "Porter-F-C", "orcid": "0000-0003-1948-8889", "role": "member", "display_name": "Porter, Frank C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9VX0DKV", "abstract": "Preserving geometric, topological and algebraic structures at play in partial differential equations has proven to be a fruitful guiding principle for computational methods in a variety of scientific fields. However, structure-preserving numerical methods have traditionally used spaces of piecewise polynomial basis functions with local support to interpolate differential forms. When solutions are known to be smooth, a spectral treatment is often preferred instead as it brings exponential convergence. While recent works have established spectral variants of discrete exterior calculus, no existing approach offers the full breadth of exterior calculus operators and a clear distinction between vectors and covectors. We present such a unified approach to spectral exterior calculus (SPEX) and provide detail on its implementation. Notably, our approach leverages Poincare duality through the use of a primal grid and its dual (with a natural handling of boundaries to facilitate the treatment of boundary conditions), and uses a twin representation of differential forms as both integrated and pointwise values. Through its reliance on the fast Fourier transform, the resulting framework enables computations in arbitrary dimensions that are both efficient and have excellent convergence properties." }, { "name": "Saadi, Fadl Hussein", "degree": "PhD", "year": "2017", "title": "Acid-Stable Electrocatalysts for the Solar Production of Fuels", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:01132017-091611769", "creators": [ { "name": { "family": "Saadi", "given": "Fadl Hussein" }, "id": "Saadi-Fadl-Hussein", "orcid": "0000-0003-3941-0464", "display_name": "Saadi, Fadl Hussein" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "chair", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Soriaga", "given": "Manuel" }, "id": "Soriaga-M-P", "role": "member", "display_name": "Soriaga, Manuel" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9QF8QV4", "abstract": "Sunlight is one of the few renewable resources that can meet global energy demand. Unfortunately, while solar energy has grown in the past few years, several economic and scientific constraints have hindered mass adoption. One of the main obstacles solar energy faces is the lack of economically competitive storage technologies. Artificial photosynthesis is a potential solution in which solar energy is directly converted into energy dense chemical bonds that can be easily stored and transported.
\r\n\r\nOne impediment facing the commercialization of artificial photosynthesis is the use of expensive and rare precious metals as catalysts. This dissertation focuses on the achievements of the past five years in characterizing novel, earth-abundant, acid-stable hydrogen evolution catalysts. While nickel alloys have long been known as catalysts for the hydrogen evolution reaction in basic media, it has only been in the past decade that earth abundant catalysts that are stable in acidic media have been reported. These discoveries are critically important as the many proposed artificial photosynthetic devices require the use of acidic media.
\r\n\r\nIn this dissertation we examine two families of hydrogen evolution catalysts: transition metal chalcogenides (namely molybdenum and cobalt selenide) as well as transition metal phosphides (cobalt phosphide). In addition to the electrochemical characterization of these catalysts, spectroscopic characterizations were performed in order to carefully examine the chemical compositions of these catalysts before, after and during the hydrogen evolution reaction. This analysis elucidated both chemical, and structural changes that occurred after the catalysts had been subject to the hydrogen evolution reaction conditions.
\r\n\r\nThe final chapter in this thesis delves into the techno-economic realities of energy transportation via different fuels. Due to the strong interest in renewable energy, several future energy transportation scenarios, including 100% grid electrification and widespread installation of hydrogen pipelines, have been proposed. In order to get a fuller understanding of such potential infrastructure alternatives, we report their differing energy transportation costs.
" }, { "name": "Sadek, Akram Sarwat", "degree": "PhD", "year": "2017", "title": "Wireless Nano and Molecular Scale Neural Interfacing", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162016-094948729", "creators": [ { "name": { "family": "Sadek", "given": "Akram Sarwat" }, "id": "Sadek-Akram-Sarwat", "display_name": "Sadek, Akram Sarwat" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9RJ4GG4", "abstract": "Nanoscale circuits and sensors built from silicon nanowires, carbon nanotubes and other devices will require methods for unobtrusive interconnection with the macroscopic world to fully realise their potential; the size of conventional wires precludes their integration into dense, miniature systems. The same wiring problem presents an obstacle in our attempts to understand the brain by means of massively deployed nanodevices, for multiplexed recording and stimulation in vivo. We report on a nanoelectromechanical system that ameliorates wiring constraints, enabling highly integrated sensors to be read in parallel through a single output. Its basis is an effect in piezoelectric nanomechanical resonators that allows sensitive, linear and real-time transduction of electrical potentials. We interface multiple signals through a mechanical Fourier transform using tuneable resonators of different frequency and extract the signals from the system optically. With this method we demonstrate the direct transduction of neuronal action potentials from an extracellular microelectrode. We further extend this approach to incorporate nanophotonics for an all-optical system, coupled via a single optical fibre. Here, the mechanical resonators are both driven and probed optically, but modulated locally by the voltage sensors via the piezoelectric effect. Such piezophotonic nanoelectromechanical systems may be integrated with nanophotonic resonators, allowing concordant multiplexing in both the radiofrequency and optical bandwidths. In principle, this would allow billions of sensor channels to be multiplexed on an optical fibre. With view to eventually integrating such technology into a neural probe, we develop fabrication methods for crafting wired silicon neural probes via photolithography and electron beam lithography. Finally, to complement recording, we propose novel ideas for wireless, multiplexed neural stimulation through the use of radiofrequency-sensitive molecular scale resonators." }, { "name": "Safaripour Tabbalvandani, Amirreza", "degree": "PhD", "year": "2017", "title": "Proximal-Field Radiation Sensors for Dynamically Controllable and Self-Correcting Integrated Radiators", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162017-205230203", "creators": [ { "name": { "family": "Safaripour Tabbalvandani", "given": "Amirreza" }, "id": "Safaripour-Tabbalvandani-Amirreza", "orcid": "0000-0001-9758-6156", "display_name": "Safaripour Tabbalvandani, Amirreza" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9DR2SJZ", "abstract": "One of the major challenges in the design of integrated radiators at mm-wave frequencies is the generation of surface waves in the dielectric substrate by the on-chip antennas. Since dielectric substrates are excellent surface waveguides with a fundamental mode with no cutoff frequency, there is always some energy trapped in them due to the surface waves and the excited substrate modes. This phenomenon is a significant cause of reduced radiation efficiency for mm-wave integrated radiators. However, in this thesis, we use this as an opportunity. We show that the excited substrate modes in the dielectric substrate of an integrated antenna contain valuable information regarding its far-field radiation properties. We introduce Proximal-Field Radiation Sensors (PFRS) as a number of small sensing antennas that are placed strategically on the same substrate as the integrated antenna and measure electromagnetic waves in its immediate proximity. These sensors extract the existing information in the substrate modes and use it to predict the far-field radiation properties of the integrated antenna in real-time based on in-situ measurements in the close proximity of the antennas, without any need to use additional test equipment and without removing the antenna from its operating environment or interfering with its operation in a wireless system. In other words, PFRS enables self-calibration, self-correction, and self-monitoring of the performance of the integrated antennas. Design intuition and a variety of data processing schemes for these sensors are discussed. Two proof-of-concept prototypes are fabricated on printed circuit board (PCB) and integrated circuit (IC) and both verify PFRS capabilities in prediction of radiation properties solely based on in-situ measurements.
\r\n\r\nDynamically controllable integrated radiators would significantly benefit from PFRS, These radiators are capable of controlling their radiation parameters such as polarization and beam steering angle through their actuators and control units. In these cases, PFRS serves as a tool for real-time monitoring of their radiation parameters, so that without direct measurement of the far-field properties through bulky equipment the required information for the control units and the actuators are provided.
\r\n\r\nDynamically controllable integrated radiators can be designed using the additional design space provided by Multi-Port Driven (MPD) radiator methodology. After a review of advantages of MPD design over the traditional single-port design, we show that a slot-based MPD radiator would have the additional advantage of reduced exclusive use area compared to the original wire-based MPD radiator, through demonstration of a 134.5-GHz integrated slot-based MPD radiator with a measured single-element EIRP of +6.0 dBm and a total radiated power of -1.3 dBm.
\r\n\r\nWe discuss how MPD methodology enables the new concept of Dynamic Polarization Control, as a method to ensure polarization matching of the transmitter antenna to the receiver antenna, regardless of the polarization and orientation of the receiver antenna in space. A DPC antenna design using the MPD methodology is described and a 105.5-GHz 2x1 integrated DPC radiator array with a maximum EIRP of +7.8 dBm and a total radiated power of 0.9 mW is presented as the first demonstration of an integrated radiator with DPC capability. This prototype can control the polarization angle across the entire tuning range of 0 to 180 degrees while maintaining axial ratios above 10 dB, and control the axial ratio from 2.4 dB (near circular) to 14 dB (linear). We also demonstrate how simultaneous two-dimensional beam steering and DPC capabilities can even match the polarization to a mobile receiver antenna through a prototype 123-GHz 2x2 integrated DPC radiator array with a maximum EIRP of +12.3 dBm, polarization angle control across the full range of 0to 180 degrees as well as tunable axial ratio down to 1.2 dB and beam steering of up to 15 degrees in both dimensions. We also use slot-based DPC antennas to fabricate a 120-GHz integrated slot-based DPC radiator array, expected to have a maximum EIRP of +15.5 dBm.
\r\n\r\nWe also introduce a new modulation scheme called Polarization Modulation (Pol-M) as a result of DPC capability, where the polarization itself is used for encoding the data. Pol-M is a spatial modulation method and is orthogonal to the existing phase and amplitude modulation schemes. Thus, it could be added on top of those schemes to enable creation of 4-D data constellations, or it can be used as the only basis for modulation to increase the stream security by misleading the undesired receivers. We discuss how DPC antenna enables Pol-M and also present PCB prototypes for Pol-M transmitter and receiver units operating at 2.4 GHz.
\r\n" }, { "name": "Sideris, Constantine", "degree": "PhD", "year": "2017", "title": "Electromagnetic Field Manipulation: Biosensing to Antennas", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-193807440", "creators": [ { "name": { "family": "Sideris", "given": "Constantine" }, "id": "Sideris-Constantine", "display_name": "Sideris, Constantine" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Alon", "given": "Elad" }, "id": "Alon-E", "role": "member", "display_name": "Alon, Elad" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9RN35XW", "abstract": "We will explore how understanding and controlling electromagnetic fields can provide significant impact across a multitude of applications throughout the whole frequency spectrum from DC to daylight. Starting from the DC end of the electromagnetic spectrum, we motivate the design of a new integrated magnetic biosensing design as well as various improvements to the initial design based on spatial and temporal manipulations of the magnetic fields. Next, we look into the RF domain and develop maximal performance bounds for antennas and other electromagnetic structures. We develop rapid simulation techniques which when coupled with heuristic optimization algorithms can quickly and effectively produce new antenna structures with little to no manual intervention. We demonstrate the efficacy of these techniques in the context of on-chip antenna designs and a 3D printed coupling antenna for a dielectric waveguide communication link. We present the design of a 120GHz dual-channel 100Gbps QPSK/64QAM transceiver IC developed in a standard 28nm bulk CMOS process. Finally, we explore the higher THz regime in the context of photonic device optimization. We optimize compact photonic multiplexer devices which are fabricated in a standard foundry process and evaluate their performance against simulation results." }, { "name": "Sternberger, Zachary Martin Murphy", "degree": "PhD", "year": "2017", "title": "Determining Strength of Materials Under Dynamic Loading Conditions Using Hydrodynamic Instabilities", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182017-095600418", "creators": [ { "name": { "family": "Sternberger", "given": "Zachary Martin Murphy" }, "id": "Sternberger-Zachary-Martin-Murphy", "orcid": "0000-0002-7612-673X", "display_name": "Sternberger, Zachary Martin Murphy" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9N877T5", "abstract": "Hydrodynamic instability experiments allow access to material properties at extreme conditions where the pressure exceeds 100 GPa and the strain rate exceeds 106 1/s. Laser ablation dynamically loads a sample, causing a manufactured initial perturbation to grow due to hydrodynamic instability. The instability growth rate depends on the strength of the sample. Material strength can then be inferred from a measurement of the instability growth. Past experiments relied on in-flight diagnostics to measure the amplitude growth, which are not available at all facilities.
\r\n\r\nRecovery instability experiments, where the initial and final amplitude of the instability are measured before and after the sample is dynamically loaded, obviate the need for in-flight diagnostics. Recovery targets containing copper and tantalum samples coined with 2D (hill and valley) and 3D (eggcrate) initial perturbations were dynamically loaded using the Janus laser at the Jupiter Laser Facility, Lawrence Livermore National Laboratory. The energy of the laser pulse was varied to cover a range of conditions in the dynamically compressed sample with pressures in the range 10 GPa to 150 GPa and strain rates in the range 105 1/s to 108 1/s.
\r\n\r\nThe coupling of laser energy into a loading wave was studied with a combination of laser-matter interaction simulations (Hyades) and velocity interferometry data (VISAR). Laser ablation of the recovery targets generated a blast wave, loading the coined initial perturbations with a shock wave followed by a release wave. Different ablator materials and variations in the amount of laser energy deposited in the ablator lead to variations in the loading wave and consequently variations in instability growth.
\r\n\r\nThe growth of the initial perturbation amplitude from initial to final conditions was studied with hydrocode simulations (CTH). During dynamic loading of the sample, the shock wave caused amplitude growth due to hydrodynamic instability. The release wave accelerated the perturbed interface and slowed amplitude growth, in some cases reversing growth.
\r\n\r\nThe sensitivity of the instability growth to coarse changes in the strength model was demonstrated. However, uncertainty in modeling the laser ablation loading prevented a definitive comparison between simulation and experiment.
" }, { "name": "Suh, Myoung-Gyun", "degree": "PhD", "year": "2017", "title": "Nonlinear Optics in Chip-based Microresonators and their Applications", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012017-163114372", "creators": [ { "name": { "family": "Suh", "given": "Myoung-Gyun" }, "id": "Suh-Myoung-Gyun", "orcid": "0000-0002-9527-0585", "display_name": "Suh, Myoung-Gyun" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z92F7KG8", "abstract": "Optical micro-resonators have been studied for decades as a platform to investigate optical physics, and to miniaturize bulky optical systems. In the last decade, optical frequency combs, which have revolutionized the precision measurement of time and frequency, have been demonstrated in optical micro-resonators via the combined effect of parametric oscillation and cascaded four-wave mixing. More recently, soliton mode-locking has made possible low-noise/reproducible generation of these miniature combs (microcombs). In this thesis, we demonstrated the generation of soliton microcombs from silica wedge disk micro-resonators and the characteristics of the soliton microcombs are described. We also applied soliton microcombs to dual-comb spectroscopy and distance measurement (LIDAR) for the first time. Also, ways to improve spectral resolution, signal-to-noise ratio, and spectral coverage are discussed. In addition to soliton microcombs, a novel spiral resonator is studied as a stable optical frequency reference. Combined with a frequency comb, this new type of chip-based reference cavity is also applied to generate stable microwaves via optical frequency division. Lastly, we generated a stimulated Brillouin laser (SBL) from the optical micro-resonator and its phonon-limited linewidth is studied. Application of the SBL for rotation measurement is also demonstrated. This thesis is organized into six chapters. Throughout the thesis, the implication and potential of my PhD work toward chip-based advanced optics system are discussed.
" }, { "name": "Sui, Yanan", "degree": "PhD", "year": "2017", "title": "Online Learning for the Control of Human Standing via Spinal Cord Stimulation", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:04172017-163725367", "creators": [ { "name": { "family": "Sui", "given": "Yanan" }, "id": "Sui-Yanan", "orcid": "0000-0002-9480-627X", "display_name": "Sui, Yanan" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9BK19DN", "abstract": "Many applications in recommender systems or experimental design need to make decisions online. Each decision leads to a stochastic reward with initially unknown distribution, while new decisions are made based on the observations of previous rewards. To maximize the total reward, one needs to balance between exploring different strategies and exploiting currently optimal strategies within a given set of strategies. This is the underlying trade-off of a number of clinical neural engineering problems, including brain-computer interface, deep brain stimulation, and spinal cord injury therapy. In these systems, complex electronic and computational systems interact with the human central nervous system. A critical issue is how to control the agents to produce results which are optimal under some measure, for example, efficiently decoding the user's intention in a brain-computer interface or performs temporal and spatial specific stimulation in deep brain stimulation. This dissertation is motivated by electrical sipnal cord stimulation with high dimensional inputs(multi-electrode arrays). The stimulation is applied to promote the function and rehabilitation of the remaining neural circuitry below the spinal cord injury, and enable complex motor behaviors such as stepping and standing. To enable the careful tuning of these stimuli for each patient, the electrode arrays which deliver these stimuli have become increasingly more sophisticated, with a corresponding increase in the number of free parameters over which the stimuli need to be optimized. Since the number of stimuli is growing exponentially with the number of electrodes, algorithmic methods of selecting stimuli is necessary, particularly when the feedback is expensive to get.
\r\n\r\nIn many online learning settings, particularly those that involve human feedback, reliable feedback is often limited to pairwise preferences instead of real valued feedback. Examples include implicit or subjective feedback for information retrieval and recommender systems, such as clicks on search results, and subjective feedback on the quality of recommended care. Sometimes with real valued feedback, we require that the sampled function values exceed some prespecified ``safety'' threshold, a requirement that existing algorithms fail to meet. Examples include medical applications where the patients' comfort must be guaranteed; recommender systems aiming to avoid user dissatisfaction; and robotic control, where one seeks to avoid controls that cause physical harm to the platform.
\r\n\r\nThis dissertation provides online learning algorithms for several specific online decision-making problems. \\selfsparring optimizes the cumulative reward with relative feedback. RankComparison deals with ranking feedback. \\safeopt considers the optimization with real valued feedback and safety constraints. \\cduel is designed for specific spinal cord injury therapy.
\r\n\r\nA variant of \\cduel was implemented in closed-loop human experiments, controlling which epidural stimulating electrodes are used in the spinal cord of SCI patients. The results obtained are compared with concurrent stimulus tuning carried out by human experimenter. These experiments show that this algorithm is at least as effective as the human experimenter, suggesting that this algorithm can be applied to the more challenging problems of enabling and optimizing complex, sensory-dependent behaviors, such as stepping and standing in SCI patients.
\r\n\r\nIn order to get reliable quantitative measurements besides comparisons, the standing behaviors of paralyzed patients under spinal cord stimulation are evaluated. The potential of quantifying the quality of bipedal standing in an automatic approach is also shown in this work.
" }, { "name": "Summy, Dustin Phillip", "degree": "PhD", "year": "2017", "title": "Maximum Entropy Reconstruction for Gas Dynamics", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262017-215132894", "creators": [ { "name": { "family": "Summy", "given": "Dustin Phillip" }, "id": "Summy-Dustin-Phillip", "orcid": "0000-0002-6383-0621", "display_name": "Summy, Dustin Phillip" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9GT5K7W", "abstract": "We present a method for selecting a unique and natural probability distribution function (PDF) which satisfies a given number of known moments and apply it for use in the closure of moment-based schemes for approximately solving the Boltzmann equation in gas dynamics.
\r\n\r\nThe method used for determining the PDF is the Maximum Entropy Reconstruction (MER) procedure, which determines the PDF with maximum entropy which satisfies a given set of constraining moments. For the five-moment truncated Hamburger moment problem in one dimension, the MER takes the form of the exponential of a quartic polynomial. This implies a bimodal structure which gives rise to a small-amplitude packet of PDF-density sitting quite far from the mean. This is referred to as the Itinerant Moment Packet (IMP). It is shown by asymptotic analysis that the IMP gives rise to a solution that, in the space of constraining moments, is singular along a line emanating from, but not including, the point representing thermodynamic equilibrium. We use this analysis of the IMP to develop a numerical regularization of the MER, creating a procedure we call the Hybrid MER (HMER). Compared with the MER, the HMER is a significant improvement in terms of robustness and efficiency while preserving accuracy in its prediction of other important distribution features, such as higher order moments.
\r\n\r\nWe apply the one-dimensional HMER to close a fourth order moment system derived from the Boltzmann equation by using a specific set of moment constraints which allow the full, three-dimensional velocity PDF to be treated as a product of three independent, one-dimensional PDFs. From this system, we extract solutions to the problem of spatially homogeneous relaxation and find excellent agreement with a standard method of solution. We further apply this method to the problem of computing the profile within a normal shock wave, and find that solutions exist only within a finite shock Mach number interval. We examine the structure of this solution and find that it has interesting behavior connected to the singularity of the MER and the IMP. Comparison is made to standard solution methods. It is determined that the use of the MER in gas dynamics remains uncertain and possible avenues for further progress are discussed.
" }, { "name": "Verlage, Erik A.", "degree": "PhD", "year": "2017", "title": "High-Efficiency Solar Fuel Devices: Protection and Light Management Utilizing TiO2", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012017-152250262", "creators": [ { "name": { "family": "Verlage", "given": "Erik A." }, "id": "Verlage-Erik-A", "orcid": "0000-0001-5940-0859", "display_name": "Verlage, Erik A." } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9MC8X2P", "abstract": "Global climate change coupled with increasing global energy consumption drives the need for renewable and carbon-neutral alternatives to fossil fuels. Photoelectrochemical devices store solar energy in chemical bonds, and have the potential to provide cost-effective fuel for grid-scale energy storage as well as to serve as a feedstock for the production of carbon-neutral transportation fuels. A widely recognized goal is the demonstration of a monolithically-integrated solar-fuels system that is simultaneously efficient, stable, intrinsically safe, and scalably manufacturable. This thesis presents the development of three separate high-efficiency solar fuel devices protected by thin films of amorphous TiO2, and develops light management strategies to increase the performance of these devices.
\r\n\r\nFirst, high-efficiency monolithic cells were designed to perform solar water-splitting and CO2 reduction. These designs are driven by high-quality single-crystalline III-V semiconductors that are unstable when placed in direct contact with aqueous electrolytes but can be protected against corrosion by hole-conducting amorphous films. Experimental fabrication and characterization of this tandem device was realized in the form of a fully-integrated water-splitting prototype with a solar-to-hydrogen efficiency of 10% showing stability for over 80 hours of operation. This was followed by the demonstration of water-splitting and CO2 reduction devices enabled by bipolar membranes, which increased stability and alleviated materials-compatibility constraints by creating a pH difference between the anolyte and catholyte, maintained at steady-state. Finally, universal light management strategies were developed using high-aspect-ratio TiO2 nanocones, resulting in an increase in catalyst loading with ultrahigh broadband transmission.
" }, { "name": "Wang, Yuh-Shyang", "degree": "PhD", "year": "2017", "title": "A System Level Approach to Optimal Controller Design for Large-Scale Distributed Systems", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:12122016-113630092", "creators": [ { "name": { "family": "Wang", "given": "Yuh-Shyang" }, "id": "Wang-Yuh-Shyang", "orcid": "0000-0001-7357-7247", "display_name": "Wang, Yuh-Shyang" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chung", "given": "Soon-Jo" }, "id": "Chung-Soon-Jo", "orcid": "0000-0002-6657-3907", "role": "member", "display_name": "Chung, Soon-Jo" } ], "option_major": [ "cds" ], "doi": "10.7907/Z95M63PF", "abstract": "Modern cyber-physical systems, such as the smart grid, software-defined networks, and automated highway systems, are large-scale, physically distributed, and interconnected. The scale of these systems poses fundamental challenges for controller design: the traditional optimal control methods are globally centralized, which require solving a large-scale optimization problem with the knowledge of the global plant model, and collecting global measurement instantaneously during implementation. The ultimate goal of distributed control design is to provide a local, distributed, scalable, and coordinated control scheme to achieve centralized control objectives with nearly global transient optimality.
\r\n\r\nThis dissertation provides a novel theoretical and computational contribution to the area of constrained linear optimal control, with a particular emphasis on addressing the scalability of controller design and implementation for large-scale distributed systems. Our approach provides a fundamental rethinking of controller design: we extend a control design problem to a system level design problem, where we directly optimize the desired closed loop behavior of the feedback system. We show that many traditional topics in the optimal control literature, including the parameterization of stabilizing controller and the synthesis of centralized and distributed controller, can all be cast as a special case of a system level design problem. The system level approach therefore unifies many existing results in the field of distributed optimal control, and solves many previously open problems.
\r\n\r\nOur system level approach has at least the following four technical merits. First, we characterize the broadest known class of constrained linear optimal control problem that admits a convex formulation. Specifically, we show that the set of convex system level design problems is a strict superset of those that can be parameterized using quadratic invariance. Second, we identify a class of system level design problems, which we called the localized optimal control problems, that are scalable to arbitrary large-scale systems. In particular, the parallel synthesis and implementation complexity of the localized optimal controller are O(1) compared to the size of the networked system. Third, we provide a unified framework to simultaneously incorporate user-specified design specification on the closed loop and the hardware implementation constraints on the controller into the optimal controller design process. Lastly, we provide a system level approach that supports the co-design of optimal controller and its sensing and actuating architecture.
\r\n\r\nWe demonstrate the effectiveness of our method on a 51200-state randomized heterogeneous power network model, and show that the system level approach provides superior scalability over the centralized and distributed method. For such a large-scale example, the theoretical computation time for the centralized scheme is more than 200 days, and the distributed optimal control scheme is intractable. In contrast, it only takes 38 minutes to synthesize a localized optimal controller that achieves at least 99% global optimality guarantee.
" }, { "name": "Wilson, Lee L.", "degree": "PhD", "year": "2017", "title": "Analysis of Packaging and Deployment of Ultralight Space Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242017-230338904", "creators": [ { "name": { "family": "Wilson", "given": "Lee L." }, "id": "Wilson-Lee-L", "orcid": "0000-0002-5865-9903", "display_name": "Wilson, Lee L." } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "space" ], "doi": "10.7907/Z9B27S96", "abstract": "This thesis presents a new approach to modeling in finite element analysis (FEA) creased thin-film sheets such as those used for drag sails, as well as modeling the packaging behavior of coilable deployable booms. This is highly advantageous because these deployable space structures are challenging to test on the ground due to their lightweight nature and the effects of gravity and air resistance. Such structures are utilized in the space industry due to their low mass and ability to be packaged into a small volume during their launch into space.
\r\n\r\nIt is shown that removing the crease bending stiffness in creased sheets still allows the deployment behavior of a benchmark problem to be captured, including deployment forces and equilibrium configurations. In addition, folding creased sheets from a flat state into a packaged configuration can result in crease crumpling and excessive wrinkling. To avoid this the Momentless Crease Force Folding (MCFF) technique is developed.
\r\n\r\nFurther presented is the behavior of tape springs and Tubular Rollable and Coilable (TRAC) booms when coiled to radii greater than their natural bend radius. Under these conditions the booms can form multiple localized folds which may jam during boom deployment. Understanding this behavior is important for extending the use of these booms to large scale space structures such as orbital solar power stations.
\r\n\r\nA useful analytical model is developed determining when the localized folds in a tape spring will bifurcate and is verified against simulation results. Additionally, a numerical model of the wrapping an isotropic tape spring around a hub with a radius greater than the localized fold radii is validated against physical experiments. This model is used to predict trends in the force required to fully wrap a tape spring around a given hub radii.
\r\n\r\nFinally, when examining the coiling and uncoiling behavior of TRAC booms it was found that the tension force required to keep a TRAC boom tightly coiled is significantly less than the force required to initially coil the boom.
" }, { "name": "Wong, Ming Fai", "degree": "PhD", "year": "2017", "title": "A Study of Communication Networks through the Lens of Reduction", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072017-154010713", "creators": [ { "name": { "family": "Wong", "given": "Ming Fai" }, "id": "Wong-Ming-Fai", "orcid": "0000-0002-9191-1277", "display_name": "Wong, Ming Fai" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Langberg", "given": "Michael" }, "id": "Langberg-M", "role": "member", "display_name": "Langberg, Michael" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9348HFK", "abstract": "A central goal of information theory is to characterize the capacity regions of communication networks. Due to the difficulty of the general problem, research is primarily focused on families of problems defined by various classifiers. These classifiers include the channel transition function (i.e., noisy, deterministic, network coding), demand type (i.e., single-source, 2-unicast), network topology (i.e. acyclic network coding, index coding). To date, the families of networks that are fully solved remain limited. Moreover, results derived for one specific family often do not extend easily to other families of problems.
\r\n\r\nOur work shifts from the traditional focus on solving example networks to one that builds connections between problem solutions so that we can say where and when solving a problem in one domain would also solve a corresponding problem in another domain. Central to our approach is a technique called \"reduction\", in which we connect the solutions and results of communication problems. We say that problem A reduces to problem B when A can be solved by first transforming it to B and then applying a solution for B. We focus on two notions of reduction: reduction in code design and reduction in capacity region.
\r\n\r\nOur central results demonstrate reductions with respect to a variety of classifiers. We show that finding multiple multicast network capacity regions reduces to finding multiple unicast network capacity regions both when capacity is defined as the maximal rate over all possible codes and when capacity is defined as the optimal rate over linear codes. As a corollary to this result, we show that the same capacity reduction holds for when network types are limited to either network coding networks or index coding networks. In several instances, we show that a reduction in code design extends to a reduction in capacity region if and only if the edge removal conjecture holds. Here, the edge removal conjecture states that removing an edge of negligible capacity from a network does not change its capacity region.
\r\n\r\nOne of the key challenges in network coding research is how to handle networks containing cycles. As a result, many papers on network coding restrict attention to acyclic networks and some results derived for acyclic networks do not extend to networks containing cycles. We consider a streaming model for network communication where information is streamed to its destination under a constraint on maximal delay at the decoder. Restricting our attention to this scenario enables us to prove a code reduction from network coding to index coding in both acyclic and cyclic networks. Since index coding networks are acyclic, a consequence of this reduction is that under the streaming model, there is no fundamental difference between acyclic and cyclic networks.
" }, { "name": "Xu, Chen", "degree": "PhD", "year": "2017", "title": "The Catalytic and Mechanical Properties of Lithium Battery Electrodes", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062016-104329889", "creators": [ { "name": { "family": "Xu", "given": "Chen" }, "id": "Xu-Chen", "orcid": "0000-0002-9427-0161", "display_name": "Xu, Chen" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "role": "member", "display_name": "Miller, Thomas F." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9XG9P4W", "abstract": "The mass adoption of electric vehicles warrants higher energy densities at lower costs. Novel chemistries such as Li-S or Li-air, high energy density anodes such as lithium (Li) metal are some of the ways to address the aforementioned issue. However, many scientific challenges must be overcome in order to achieve the successful commercialization of these batteries. For Li-air, poor cyclability and low coulumbic efficiency are key obstacles. The search for cathode materials that exhibit high capacity, low discharge/charge overpotential and chemical stability over many cycles is a major area of interest in the field. On the anode side, the application of Li metal is stumped by uncontrollable dendrite growth during the charging, and existing methods such as pulsed charging, physical suppression, and additives in the electrolyte have only had alleviating effects.
\r\n\r\nThe first part of this thesis investigates the suitability of various materials as Li-air cathodes. We fabricated 3-dimensional architected electrodes using a variety of materials including Au, Ni, Ti, LaCoO3 (LCO), LaNiO3 (LNO), and LaNi0.5Co0.5O3 (LNCO). Their performances in capacity, overpotential, and cyclability were assessed using galvanostatic battery testing methods. The reaction products were investigated using spectroscopic techniques such as FTIR and Raman. Our experiments corroborated recent findings that even trace moisture contamination can dramatically influence discharge product composition and morphology. Furthermore, Ni nanoparticles may serve as a carbon substitute in investigating the properties of non-conductive catalysts under specific potential windows. By incorporation the perovskites into a Ni based conductive mesh, we found the oxygen reduction reaction capability of the three materials to be ranked as LCO>LNCO>LNO, and the chemical stability ranked as LCO>LNO>LNCO. The instability of DMSO due to chemical reactions with discharge products is observed and discussed in the context of the solution-mediated mechanism of Li2O2 growth. The second part of the thesis investigates the nano-mechanical properties of Li (bcc), as a function of size, temperature, and crystal grain orientation. At room temperature the power law exponent of the strength vs. size log-log plot is -0.68, while at 90\u00b0C this value is increased to -1.00. A factor of 3 decrease in the yield strength at 90\u00b0C is observed, and the morphology of deformation was found to transition from localized slip planes to homogeneous barreling. Our collaborators at Carnegie Mellon University calculated the elastic constants of Li from 78 K to 440 K (melting temperature of Li is 453 K), and is found to be within reasonable agreement with existing experimental data where applicable (78 -300 K). We proceeded to calculate the elastic and shear moduli of single crystal Li as a function of temperature and orientation. We found that due to the extreme anisotropy of Li, there is a factor of ~4 difference between the strongest and weakest orientation of both the elastic and shear moduli. Our findings are discussed in the context of Li anodes, where we highlight the importance of taking into consideration the size-effect and anisotropy when designing solid electrolytes, or modeling dendrite growth behavior.
\r\n" }, { "name": "Yi, Xu", "degree": "PhD", "year": "2017", "title": "Physics and Applications of Microresonator Solitons and Electro-optic Frequency Combs", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232017-161027761", "creators": [ { "name": { "family": "Yi", "given": "Xu" }, "id": "Yi-Xu", "orcid": "0000-0002-2485-1104", "display_name": "Yi, Xu" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Beichman", "given": "Charles A." }, "id": "Beichman-C-A", "orcid": "0000-0002-5627-5471", "role": "member", "display_name": "Beichman, Charles A." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9FT8J22", "abstract": "Frequency combs are having a broad impact on science and technology because they provide a way to coherently link radio/microwave-rate electrical signals with optical-rate signals derived from lasers and atomic transitions. A new, miniature realization, the microcomb, that uses chip-based microresonators can potentially revolutionize instrumentation, time keeping, spectroscopy, and navigation. Microcombs were first demonstrated using a form of cascaded four-wave mixing. However, the recent discovery of dissipative soliton microcombs enables phase-locked spectra with reproducible envelopes, as required in many frequency comb applications. In addition, these solitons are confined in a high-Q microresonator, thereby creating a rich landscape for research in nonlinear optical phenomena. In this thesis, these solitons are demonstrated for the first time in a silica microcavity. Significantly, the device provides a microwave-detectable soliton repetition rate, which is essential to many comb applications. The unusual properties of the solitons are studied from a theoretical viewpoint using a Lagrangian formalism and predictions of the theory are confirmed experimentally. In the course of this work, a new optical soliton, the Stokes soliton, was also discovered. In addition to soliton mode locking, another novel and compact platform, the electro-optical modulation frequency comb, was studied. This type of frequency comb was used to demonstrate a novel electro-optic form of frequency division for stable microwave synthesis. It was also modified to perform astronomical calibration for exoplanet detection at the Keck Observatory in Hawaii.
" }, { "name": "Zelhofer, Alex James", "degree": "PhD", "year": "2017", "title": "Computational Modeling of the Mechanics of Elastic Structural Lattices: Effects of Lattice Architecture and Hierarchy", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042017-210215990", "creators": [ { "name": { "family": "Zelhofer", "given": "Alex James" }, "id": "Zelhofer-Alex-James", "orcid": "0000-0002-8064-2876", "display_name": "Zelhofer, Alex James" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z91G0J90", "abstract": "This thesis establishes advanced theoretical-computational techniques to understand and predict the mechanical properties of structural lattice metamaterials with a focus on the effective elastic properties. First, attention is devoted to the effective stiffness of hierarchical nanolattices, which depends on lattice topology, architecture, and inherent geometric imperfections. A computational substructuring technique is applied to predict the mechanics of hierarchical truss networks containing thousands to millions of truss members, with each solid, hollow-tube, or composite truss member requiring full-detail 3D resolution. By applying this methodology to hierarchical nanolattices structural hierarchy is shown to span several decades of relative density and effective stiffness with near-ideal effective stiffness scaling. Comparisons between experimental data and model predictions show convincing agreement and highlight the lattice sensitivity to fabrication-induced geometric imperfection. Second, elastic stress wave propagation in structural lattices is investigated with a focus on wave beaming (i.e., directional energy flow) under harmonic mechanical excitation. A new technique is introduced to obtain pseudo-continuous maps of group velocity magnitude vs. propagation direction vs. frequency to predict directional wave propagation, demonstrating traditional beaming prediction techniques are insufficient for many scenarios. The method is applied to two-dimensional structural lattices to predict directional energy flow. Predictions are verified by comparison to explicit dynamic simulations showing the limitations of the classical dispersion relation method. Overall, improved computational techniques are presented to better described, understand, predict and optimize the elastic behavior of truss lattices.\r\n" }, { "name": "Zhang, Pengchuan", "degree": "PhD", "year": "2017", "title": "Compressing Positive Semidefinite Operators with Sparse/Localized Bases", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312017-000636495", "creators": [ { "name": { "family": "Zhang", "given": "Pengchuan" }, "id": "Zhang-Pengchuan", "orcid": "0000-0003-1155-9507", "display_name": "Zhang, Pengchuan" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "orcid": "0000-0001-5227-8037", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z91N7Z5J", "abstract": "Given a positive semidefinite (PSD) operator, such as a PSD matrix, an elliptic operator with rough coefficients, a covariance operator of a random field, or the Hamiltonian of a quantum system, we would like to find its best finite rank approximation with a given rank. One way to achieve this objective is to project the operator to its eigenspace that corresponds to the smallest or largest eigenvalues, depending on the setting. The eigenfunctions are typically global, i.e. nonzero almost everywhere, but our interest is to find the sparsest or most localized bases for these subspaces. The sparse/localized basis functions lead to better physical interpretation and preserve some sparsity structure in the original operator. Moreover, sparse/localized basis functions also enable us to develop more efficient numerical algorithms to solve these problems.
\r\n\r\nIn this thesis, we present two methods for this purpose, namely the sparse operator compression (Sparse OC) and the intrinsic sparse mode decomposition (ISMD). The Sparse OC is a general strategy to construct finite rank approximations to PSD operators, for which the range space of the finite rank approximation is spanned by a set of sparse/localized basis functions. The basis functions are energy minimizing functions on local patches. When applied to approximate the solution operator of elliptic operators with rough coefficients and various homogeneous boundary conditions, the Sparse OC achieves the optimal convergence rate with nearly optimally localized basis functions. Our localized basis functions can be used as multiscale basis functions to solve elliptic equations with multiscale coefficients and provide the optimal convergence rate O(hk) for 2k'th order elliptic problems in the energy norm. From the perspective of operator compression, these localized basis functions provide an efficient and optimal way to approximate the principal eigen-space of the elliptic operators. From the perspective of the Sparse PCA, we can approximate a large set of covariance functions by a rank-n operator with a localized basis and with the optimal accuracy. While the Sparse OC works well on the solution operator of elliptic operators, we also propose the ISMD that works well on low rank or nearly low rank PSD operators. Given a rank-n PSD operator, say a N-by-N PSD matrix A (n \u2264 N), the ISMD decomposes it into n rank-one matrices \u03a3ni=1gigTi where the mode {gi}ni=1 are required to be as sparse as possible. Under the regular-sparse assumption (see Definition 1.3.2), we have proved that the ISMD gives the optimal patchwise sparse decomposition, and is stable to small perturbations in the matrix to be decomposed. We provide several applications in both the physical and data sciences to demonstrate the effectiveness of the proposed strategies.
" }, { "name": "Zhang, Shell Xiaoxiao", "degree": "PhD", "year": "2017", "title": "Electrical Impedance Based Spectroscopy and Tomography Techniques for Obesity and Heart Diseases", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292016-114827320", "creators": [ { "name": { "family": "Zhang", "given": "Shell Xiaoxiao" }, "id": "Zhang-Shell-Xiaoxiao", "display_name": "Zhang, Shell Xiaoxiao" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Hsiai", "given": "Tzung" }, "id": "Hsiai-Tzung", "role": "member", "display_name": "Hsiai, Tzung" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9CC0XPJ", "abstract": "Despite advances in diagnosis and therapy, atherosclerosis cardiovascular disease remains the leading cause of morbidity and mortality. Predicting metabolically active atherosclerotic lesions has remained an unmet clinical need. Specially, atherosclerotic plaques that are prone to rupture are of extremely high-risk and can cause detrimental heart attacks and/or strokes, leading to sudden death. It has been shown that atheroscleroses is correlated to the level of obesity of an individual [1] Usually in clinical practice, the doctor will assess a patient's \"risk factor\" based on his or her Body Mass Index (BMS), and measurement of the waist circumference. Meanwhile the level of fatty droplet deposits in the liver is an important bio-marker to assess the patient's risk factor, however the patient will need to undergo radiation imaging such as CT scan or MRI scan.
\r\n\r\nFor the vulnerable plaques that can lead to sudden rupture, the ability to distinguish them at an early stage remains largely lacking. Therefore it is of great clinical interest to find improved diagnostic techniques to identify and localize such vulnerable plaques. Meanwhile, lipid has significantly lower electrical impedance than the rest of the vessel tissues in certain frequency bands [2]. In this thesis we explore spectroscopic and tomographic methods to characterize such plaques. In addition, with the Electrical Impedance Tomography method we will propose a novel method to detect fatty liver in an early stage with non-radiating and non-invasive manner.
" }, { "name": "Zhou, Edward Haojiang", "degree": "PhD", "year": "2017", "title": "Optical Focusing and Imaging through Scattering Media", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05172017-103505376", "creators": [ { "name": { "family": "Zhou", "given": "Edward Haojiang" }, "id": "Zhou-Edward-Haojiang", "orcid": "0000-0001-7020-9502", "display_name": "Zhou, Edward Haojiang" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Judkewitz", "given": "Benjamin" }, "id": "Judkewitz-Benjamin", "role": "member", "display_name": "Judkewitz, Benjamin" }, { "name": { "family": "Wang", "given": "Lihong" }, "id": "Wang-Lihong", "role": "member", "display_name": "Wang, Lihong" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Cai", "given": "Long" }, "id": "Cai-Long", "role": "member", "display_name": "Cai, Long" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9TX3CD1", "abstract": "Optical techniques, which have been widely used in various fields including bio-medicine, remote sensing, astronomy, and industrial production, play an important role in modern life. Optical focusing and imaging, which correspond to the basic methods of utilizing light, are key to the implementation of optical techniques. In free space or a nearly transparent medium, optical imaging and focusing can be easily realized by using conventional optical elements, such as lenses and mirrors, due to the ballistic propagation of light in these media. However, in scattering media like biological tissue and fog, refractive index inhomogeneities cause diffusive propagation of light that increases with depth, which restricts the use of optical methods in thick, scattering media. Generally speaking, scattering media poses three challenges to optical focusing and imaging: wavefront aberrations, glare, and decorrelation. Wavefront aberrations can randomize light traveling through a scattering medium, disrupt the formation of focus, and break the conjugate relation in imaging. Glare caused by backscattering will largely impair the visibility of imaging, and decorrelation in dynamic media requires systems that counter the effect of scattering to operate faster than the decorrelation time. In this thesis, we explored solutions to the problem of scattering from different aspects. We presented Time Reversal by Analysis of Changing wavefronts from Kinetic targets (TRACK) technique to realize noninvasive optical focusing through a scattering medium. We showed that by taking the difference between time-varying scattering fields caused by a moving object and applying optical phase conjugation, light can be focused back to the location previously occupied by the object. To tackle the decorrelation of living tissue, we built up a fast digital optical phase conjugation (DOPC) system based on FPGA and DMD, which has a response time of 5.3 ms and was the fastest DOPC system in the world before 2017. We demonstrated that the system is fast enough to focus light through 2.3mm-thick living mouse skin. As for glare, inspired by noise canceling headphones, we invented an optical analogue termed coherence gated negation (CGN) technique. CGN can optically cancel out the glare in an active illumination imaging scenario to realize imaging through scattering media, like fog. In the experiment, we suppressed the glare by an order of magnitude and allowed improved imaging of a weak target. Finally, we demonstrated a method to image a moving target through scattering media noninvasively. Its principle roots are in the speckle-correlation-based imaging (SCI) invented by Ori Katz. We improved the technique and extended its application to bright field imaging of a moving target.
" }, { "name": "Agrawal, Vinamra", "degree": "PhD", "year": "2016", "title": "Shock Wave Propagation in Composites and Electro-Thermomechanical Coupling of Ferroelectric Materials", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-104209268", "creators": [ { "name": { "family": "Agrawal", "given": "Vinamra" }, "id": "Agrawal-Vinamra", "orcid": "0000-0002-1698-1371", "display_name": "Agrawal, Vinamra" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z98G8HN8", "abstract": "How is material behavior at the macro scale influenced by its properties and structure at the micro and meso-scales? How do heterogeneities influence the properties and the response of a material? How does nonlinear coupling of electro-thermo-mechanical properties influence the behavior of a ferroelectric material? How can design at the micro-scale be exploited to obtain selective response? These questions have been topics of significant interest in the materials and mechanics community. Recently, new materials like multifunctional composites and metamaterials have been developed, targeted at selective applications. These materials find applications in areas like energy harvesting, damage mitigation, biomedical devices, and various aerospace applications. The current thesis explores these questions with two major thrusts: (i) internal reflects of shocks in composite media and (ii) shocks in ferroelectric media.
\r\n\r\nUnder the application of high-pressure, high strain rate loading, such as during high velocity impact, shock waves are generated in the material. They can cause the material to achieve very high stress states, and if transmitted without mitigation, can lead to failure of key components. An important question here is 'Can we design materials which can successfully mitigate damage due to shocks?' In a heterogeneous material, like a layered composite, the traveling waves undergo scattering due to internal reflections. In order to understand internal reflections, an idealized problem that focuses on nonlinear shocks and ignores less important elastic waves was formulated and studied in detail. The problem is studied by classifying all possible interactions in the material and then solving corresponding Riemann problems. Using dynamic programming tools, a new algorithm is designed that uses these solutions to generate a complete picture of the impact process. Different laminate designs are explored to study optimal design, by varying individual layer properties and their arrangement. Phenomena like spallation and delamination are also investigated.
\r\n\r\nUpon high strain rate loading, ferroelectric materials like lead zirconate titanate (PZT) undergo ferroelectric to anti-ferroelectric phase transition leading to large pulsed current output. These materials have thus found applications as pulsed power generators. The problem of shock induced depolarization and the associated electro-thermo-mechanical coupling of ferroelectric materials is studied in this thesis using theoretical and numerical methods. A large deformation dynamic analysis of such materials is conducted to study phase boundary propagation in the medium. The presence of high electrical fields can lead to formation of charges in the material, such as surface charge on the phase boundary. Using conservation laws and the second law of thermodynamics, a set of governing equations are formulated that dictate the phase boundary propagation in isothermal and adiabatic environments. Due to the possibility of surface charges on the phase boundary, the curvature of the phase boundary starts to play a role in the driving force acting on the phase boundary. The equations of motion and driving force see the contribution of nonlinear electro-thermomechanical coupling in the material. Using the equations derived, a canonical problem of impact on a ferroelectric material is studied. A new finite-volume, front-tracking method is developed to solve these equations. Finally, results from numerical simulations are compared to the experimental results.
" }, { "name": "Akhmetgaliyev, Eldar", "degree": "PhD", "year": "2016", "title": "Fast Numerical Methods for Mixed, Singular Helmholtz Boundary Value Problems and Laplace Eigenvalue Problems - with Applications to Antenna Design, Sloshing, Electromagnetic Scattering and Spectral Geometry", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202015-162838809", "creators": [ { "name": { "family": "Akhmetgaliyev", "given": "Eldar" }, "id": "Akhmetgaliyev-Eldar", "display_name": "Akhmetgaliyev, Eldar" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Simon", "given": "Barry M." }, "id": "Simon-B", "orcid": "0000-0003-2561-8539", "role": "member", "display_name": "Simon, Barry M." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z97P8W93", "abstract": "This thesis presents a novel class of algorithms for the solution of scattering and eigenvalue problems on general two-dimensional domains under a variety of boundary conditions, including non-smooth domains and certain \"Zaremba\" boundary conditions - for which Dirichlet and Neumann conditions are specified on various portions of the domain boundary. The theoretical basis of the methods for the Zaremba problems on smooth domains concern detailed information, which is put forth for the first time in this thesis, about the singularity structure of solutions of the Laplace operator under boundary conditions of Zaremba type. The new methods, which are based on use of Green functions and integral equations, incorporate a number of algorithmic innovations, including a fast and robust eigenvalue-search algorithm, use of the Fourier Continuation method for regularization of all smooth-domain Zaremba singularities, and newly derived quadrature rules which give rise to high-order convergence even around singular points for the Zaremba problem. The resulting algorithms enjoy high-order convergence, and they can tackle a variety of elliptic problems under general boundary conditions, including, for example, eigenvalue problems, scattering problems, and, in particular, eigenfunction expansion for time-domain problems in non-separable physical domains with mixed boundary conditions." }, { "name": "Allen, Thomas F.", "degree": "PhD", "year": "2016", "title": "Two and Three Finger Caging of Polygons and Polyhedra", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:12062015-164238181", "creators": [ { "name": { "family": "Allen", "given": "Thomas F." }, "id": "Allen-Thomas-F", "display_name": "Allen, Thomas F." } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z93X84KR ", "abstract": "Multi-finger caging offers a rigorous and robust approach to robot grasping. This thesis provides several novel algorithms for caging polygons and polyhedra in two and three dimensions. Caging refers to a robotic grasp that does not necessarily immobilize an object, but prevents it from escaping to infinity. The first algorithm considers caging a polygon in two dimensions using two point fingers. The second algorithm extends the first to three dimensions. The third algorithm considers caging a convex polygon in two dimensions using three point fingers, and considers robustness of this cage to variations in the relative positions of the fingers.
\r\n\r\nThis thesis describes an algorithm for finding all two-finger cage formations of planar polygonal objects based on a contact-space formulation. It shows that two-finger cages have several useful properties in contact space. First, the critical points of the cage representation in the hand\u2019s configuration space appear as critical points of the inter-finger distance function in contact space. Second, these critical points can be graphically characterized directly on the object\u2019s boundary. Third, contact space admits a natural rectangular decomposition such that all critical points lie on the rectangle boundaries, and the sublevel sets of contact space and free space are topologically equivalent. These properties lead to a caging graph that can be readily constructed in contact space. Starting from a desired immobilizing grasp of a polygonal object, the caging graph is searched for the minimal, intermediate, and maximal caging regions surrounding the immobilizing grasp. An example constructed from real-world data illustrates and validates the method.
\r\n\r\nA second algorithm is developed for finding caging formations of a 3D polyhedron for two point fingers using a lower dimensional contact-space formulation. Results from the two-dimensional algorithm are extended to three dimension. Critical points of the inter-finger distance function are shown to be identical to the critical points of the cage. A decomposition of contact space into 4D regions having useful properties is demonstrated. A geometric analysis of the critical points of the inter-finger distance function results in a catalog of grasps in which the cages change topology, leading to a simple test to classify critical points. With these properties established, the search algorithm from the two-dimensional case may be applied to the three-dimensional problem. An implemented example demonstrates the method.
\r\n\r\nThis thesis also presents a study of cages of convex polygonal objects using three point fingers. It considers a three-parameter model of the relative position of the fingers, which gives complete generality for three point fingers in the plane. It analyzes robustness of caging grasps to variations in the relative position of the fingers without breaking the cage. Using a simple decomposition of free space around the polygon, we present an algorithm which gives all caging placements of the fingers and a characterization of the robustness of these cages.
" }, { "name": "Amelang, Jeffrey Scott", "degree": "PhD", "year": "2016", "title": "A Fully-Nonlocal Energy-based Formulation and High-performance Realization of the Quasicontinuum Method", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09152015-212147583", "creators": [ { "name": { "family": "Amelang", "given": "Jeffrey Scott" }, "id": "Amelang-Jeffrey-Scott", "display_name": "Amelang, Jeffrey Scott" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9SB43PH", "abstract": "The quasicontinuum (QC) method was introduced to coarse-grain crystalline atomic ensembles in order to bridge the scales from individual atoms to the micro- and mesoscales. Though many QC formulations have been proposed with varying characteristics and capabilities, a crucial cornerstone of all QC techniques is the concept of summation rules, which attempt to efficiently approximate the total Hamiltonian of a crystalline atomic ensemble by a weighted sum over a small subset of atoms. In this work we propose a novel, fully-nonlocal, energy-based formulation of the QC method with support for legacy and new summation rules through a general energy-sampling scheme. Our formulation does not conceptually differentiate between atomistic and coarse-grained regions and thus allows for seamless bridging without domain-coupling interfaces. Within this structure, we introduce a new class of summation rules which leverage the affine kinematics of this QC formulation to most accurately integrate thermodynamic quantities of interest. By comparing this new class of summation rules to commonly-employed rules through analysis of energy and spurious force errors, we find that the new rules produce no residual or spurious force artifacts in the large-element limit under arbitrary affine deformation, while allowing us to seamlessly bridge to full atomistics. We verify that the new summation rules exhibit significantly smaller force artifacts and energy approximation errors than all comparable previous summation rules through a comprehensive suite of examples with spatially non-uniform QC discretizations in two and three dimensions. Due to the unique structure of these summation rules, we also use the new formulation to study scenarios with large regions of free surface, a class of problems previously out of reach of the QC method. Lastly, we present the key components of a high-performance, distributed-memory realization of the new method, including a novel algorithm for supporting unparalleled levels of deformation. Overall, this new formulation and implementation allows us to efficiently perform simulations containing an unprecedented number of degrees of freedom with low approximation error." }, { "name": "Araya, Daniel Borsodi", "degree": "PhD", "year": "2016", "title": "Aerodynamics of Vertical-Axis Wind Turbines in Full-Scale and Laboratory-Scale Experiments", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12022015-023535926", "creators": [ { "name": { "family": "Araya", "given": "Daniel Borsodi" }, "id": "Araya-Daniel-Borsodi", "display_name": "Araya, Daniel Borsodi" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9VD6WC2 ", "abstract": "Within a wind farm, multiple turbine wakes can interact and have a substantial effect on the overall power production. This makes an understanding of the wake recovery process critically important to optimizing wind farm efficiency. Vertical-axis wind turbines (VAWTs) exhibit features that are amenable to dramatically improving this efficiency. However, the physics of the flow around VAWTs is not well understood, especially as it pertains to wake interactions, and it is the goal of this thesis to partially fill this void. This objective is approached from two broadly different perspectives: a low-order view of wind farm aerodynamics, and a detailed experimental analysis of the VAWT wake.
\r\n\r\nOne of the contributions of this thesis is the development of a semi-empirical model of wind farm aerodynamics, known as the LRB model, that is able to predict turbine array configurations to leading order accuracy. Another contribution is the characterization of the VAWT wake as a function of turbine solidity. It was found that three distinct regions of flow exist in the VAWT wake: (1) the near wake, where periodic blade shedding of vorticity dominates; (2) a transition region, where growth of a shear-layer instability occurs; (3) the far wake, where bluff-body oscillations dominate. The wake transition can be predicted using a new parameter, the dynamic solidity, which establishes a quantitative connection between the wake of a VAWT and that of a circular cylinder. The results provide insight into the mechanism of the VAWT wake recovery and the potential means to control it.
" }, { "name": "Arya, Manan", "degree": "PhD", "year": "2016", "title": "Packaging and Deployment of Large Planar Spacecraft Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232016-115519723", "creators": [ { "name": { "family": "Arya", "given": "Manan" }, "id": "Arya-Manan", "orcid": "0000-0003-3522-6010", "display_name": "Arya, Manan" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/Z9Z60M0D", "abstract": "This thesis presents a set of novel methods to biaxially package planar structures by folding and wrapping. The structure is divided into strips connected by folds that can slip during wrapping to accommodate material thickness. These packaging schemes are highly efficient, with theoretical packaging efficiencies approaching 100%. Packaging tests on meter-scale physical models have demonstrated packaging efficiencies of up to 83%. These methods avoid permanent deformation of the structure, allowing an initially flat structure to be deployed to a flat state.
\r\n\r\nAlso presented are structural architectures and deployment schemes that are compatible with these packaging methods. These structural architectures use either in-plane pretension -- suitable for membrane structures -- or out-of-plane bending stiffness to resist loading. Physical models are constructed to realize these structural architectures. The deployment of these types of structures is shown to be controllable and repeatable by conducting experiments on lab-scale models.
\r\n\r\nThese packaging methods, structural architectures, and deployment schemes are applicable to a variety of spacecraft structures such as solar power arrays, solar sails, antenna arrays, and drag sails; they have the potential to enable larger variants of these structures while reducing the packaging volume required. In this thesis, these methods are applied to the preliminary structural design of a space solar power satellite. This deployable spacecraft, measuring 60 m x 60 m, can be packaged into a cylinder measuring 1.5 m in height and 1 m in diameter. It can be deployed to a flat configuration, where it acts as a stiff lightweight support framework for multifunctional tiles that collect sunlight, generate electric power, and transmit it to a ground station on Earth.
" }, { "name": "Bajaj, Saurabh", "degree": "PhD", "year": "2016", "title": "Phase Diagrams and Defect Thermodynamics to Devise Doping Strategies in Lead Chalcogenide Thermoelectric Materials and its Alloys", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:10212015-101150451", "creators": [ { "name": { "family": "Bajaj", "given": "Saurabh" }, "id": "Bajaj-Saurabh", "orcid": "0000-0003-0216-9697", "display_name": "Bajaj, Saurabh" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9DF6P6N", "abstract": "This thesis discusses the application of phase diagrams and the associated thermodynamics to semiconductor materials through theoretical computational calculations. The majority of work is focused on thermoelectric semiconducting materials that enable direct inter-conversion between electrical and thermal energy. First, one of the most efficient thermoelectric material, PbTe, is picked to demonstrate the assessment of unknown phase diagrams by combining two methods - DFT and CALPHAD. Since there had been no previous investigations of defect stability in this material using computations, DFT is used to deduce the stability of various intrinsic point defects, and in turn attribute origins of n- and p-type conductivity to the most stable defects. Then, the calculated defect formation energies are used in the Pb-Te thermodynamic model built using the CALPHAD method to compare the estimated solubility lines and non-stoichiometric range of the PbTe phase with experimental data. Next, another lead chalcogenide, PbSe, is picked to explore the phase stability of the PbSe phase upon the addition of dopants (Br, Cl, I, Na, Sb, Bi, In), which is a common strategy to make thermoelectric materials and devices more efficient. The range of efficiencies and thermoelectric properties as functions of composition and temperature that can be achieved depends on the amount of dopant that can be added without precipitating secondary phases. Also, depending on the system and its phase diagram, there can be more than one way of doping a material. To help detail which method(s) of doping into PbSe will result in maximum dopant solubility, a procedure similar to the above for PbTe is followed by using DFT in combination with Boltzmann statistics to map solvus boundaries of the PbSe phase, but now in the ternary phase space of composition and temperature. This method also helps predict electrical conductivity, n- or p-type, in each region of the phase diagrams that represent different doping methods.
\r\n\r\nLastly, the role of surface energy contributions in changing phase stability at nano-dimensions is explored. The CALPHAD approach is employed to investigate these changes in three systems by calculating their phase diagrams at nano dimensions and comparing them with their bulk counterparts.
" }, { "name": "Billeh, Yazan Nicola", "degree": "PhD", "year": "2016", "title": "Functional, Clustered, Feedforward, and Mesoscale Brain Networks", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162016-100757711", "creators": [ { "name": { "family": "Billeh", "given": "Yazan Nicola" }, "id": "Billeh-Yazan-Nicola", "orcid": "0000-0001-5200-4992", "display_name": "Billeh, Yazan Nicola" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "orcid": "0000-0001-8837-678X", "role": "chair", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Meister", "given": "Markus" }, "id": "Meister-M", "orcid": "0000-0003-2136-6506", "role": "member", "display_name": "Meister, Markus" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9DB7ZSX", "abstract": "The brain is a network spanning multiple scales from subcellular to macroscopic. In this thesis I present four projects studying brain networks at different levels of abstraction. The first involves determining a functional connectivity network based on neural spike trains and using a graph theoretical method to cluster groups of neurons into putative cell assemblies. In the second project I model neural networks at a microscopic level. Using diferent clustered wiring schemes, I show that almost identical spatiotemporal activity patterns can be observed, demonstrating that there is a broad neuro-architectural basis to attain structured spatiotemporal dynamics. Remarkably, irrespective of the precise topological mechanism, this behavior can be predicted by examining the spectral properties of the synaptic weight matrix. The third project introduces, via two circuit architectures, a new paradigm for feedforward processing in which inhibitory neurons have the complex and pivotal role in governing information flow in cortical network models. Finally, I analyze axonal projections in sleep deprived mice using data collected as part of the Allen Institute's Mesoscopic Connectivity Atlas. After normalizing for experimental variability, the results indicate there is no single explanatory difference in the mesoscale network between control and sleep deprived mice. Using machine learning techniques, however, animal classification could be done at levels significantly above chance. This reveals that intricate changes in connectivity do occur due to chronic sleep deprivation." }, { "name": "Bobbitt, Brock Douglas", "degree": "PhD", "year": "2016", "title": "Small Scale Turbulence in High Karlovitz Number Premixed Flames", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:03102016-211538603", "creators": [ { "name": { "family": "Bobbitt", "given": "Brock Douglas" }, "id": "Bobbitt-Brock-Douglas", "display_name": "Bobbitt, Brock Douglas" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9Z03649", "abstract": "The purpose of this thesis is to characterize the behavior of the smallest turbulent scales in high Karlovitz number (Ka) premixed flames. These scales are particularly important in the two-way coupling between turbulence and chemistry and better understanding of these scales will support future modeling efforts using large eddy simulations (LES). The smallest turbulent scales are studied by considering the vorticity vector, \u03c9, and its transport equation.
\r\n\r\nDue to the complexity of turbulent combustion introduced by the wide range of length and time scales, the two-dimensional vortex-flame interaction is first studied as a simplified test case. Numerical and analytical techniques are used to discern the dominate transport terms and their effects on vorticity based on the initial size and strength of the vortex. This description of the effects of the flame on a vortex provides a foundation for investigating vorticity in turbulent combustion.
\r\n\r\nSubsequently, enstrophy, \u03c92 = \u03c9 \u2022 \u03c9, and its transport equation are investigated in premixed turbulent combustion. For this purpose, a series of direct numerical simulations (DNS) of premixed n-heptane/air flames are performed, the conditions of which span a wide range of unburnt Karlovitz numbers and turbulent Reynolds numbers. Theoretical scaling analysis along with the DNS results support that, at high Karlovitz number, enstrophy transport is controlled by the viscous dissipation and vortex stretching/production terms. As a result, vorticity scales throughout the flame with the inverse of the Kolmogorov time scale, \u03c4\u03b7, just as in homogeneous isotropic turbulence. As \u03c4\u03b7 is only a function of the viscosity and dissipation rate, this supports the validity of Kolmogorov\u2019s first similarity hypothesis for sufficiently high Ka numbers (Ka \u2273 100). These conclusions are in contrast to low Karlovitz number behavior, where dilatation and baroclinic torque have a significant impact on vorticity within the flame. Results are unaffected by the transport model, chemical model, turbulent Reynolds number, and lastly the physical configuration.
\r\n\r\nNext, the isotropy of vorticity is assessed. It is found that given a sufficiently large value of the Karlovitz number (Ka \u2273 100) the vorticity is isotropic. At lower Karlovitz numbers, anisotropy develops due to the effects of the flame on the vortex stretching/production term. In this case, the local dynamics of vorticity in the strain-rate tensor, S, eigenframe are altered by the flame. At sufficiently high Karlovitz numbers, the dynamics of vorticity in this eigenframe resemble that of homogeneous isotropic turbulence.
\r\n\r\nCombined, the results of this thesis support that both the magnitude and orientation of vorticity resemble the behavior of homogeneous isotropic turbulence, given a sufficiently high Karlovitz number (Ka \u2273 100). This supports the validity of Kolmogorov\u2019s first similarity hypothesis and the hypothesis of local isotropy under these condition. However, dramatically different behavior is found at lower Karlovitz numbers. These conclusions provides/suggests directions for modeling high Karlovitz number premixed flames using LES. With more accurate models, the design of aircraft combustors and other combustion based devices may better mitigate the detrimental effects of combustion, from reducing CO2 and soot production to increasing engine efficiency.
" }, { "name": "Brown, Ana Maii", "degree": "PhD", "year": "2016", "title": "Classical and Quantum Effects in Plasmonic Metals", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:04242016-093536420", "creators": [ { "name": { "family": "Brown", "given": "Ana Maii" }, "id": "Brown-Ana-Maii", "orcid": "0000-0003-3008-2310", "display_name": "Brown, Ana Maii" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9QV3JHT", "abstract": "The field of plasmonics exploits the unique optical properties of metallic nanostructures to concentrate and manipulate light at subwavelength length scales. Metallic nanostructures get their unique properties from their ability to support surface plasmons\u2013 coherent wave-like oscillations of the free electrons at the interface between a conductive and dielectric medium. Recent advancements in the ability to fabricate metallic nanostructures with subwavelength length scales have created new possibilities in technology and research in a broad range of applications.
\r\n\r\nIn the first part of this thesis, we present two investigations of the relationship between the charge state and optical state of plasmonic metal nanoparticles. Using experimental bias-dependent extinction measurements, we derive a potential- dependent dielectric function for Au nanoparticles that accounts for changes in the physical properties due to an applied bias that contribute to the optical extinction. We also present theory and experiment for the reverse effect\u2013 the manipulation of the carrier density of Au nanoparticles via controlled optical excitation. This plasmoelectric effect takes advantage of the strong resonant properties of plasmonic materials and the relationship between charge state and optical properties to eluci- date a new avenue for conversion of optical power to electrical potential.
\r\n\r\nThe second topic of this thesis is the non-radiative decay of plasmons to a hot-carrier distribution, and the distribution\u2019s subsequent relaxation. We present first-principles calculations that capture all of the significant microscopic mechanisms underlying surface plasmon decay and predict the initial excited carrier distributions so generated. We also preform ab initio calculations of the electron-temperature dependent heat capacities and electron-phonon coupling coefficients of plasmonic metals. We extend these first-principle methods to calculate the electron-temperature dependent dielectric response of hot electrons in plasmonic metals, including direct interband and phonon-assisted intraband transitions. Finally, we combine these first-principles calculations of carrier dynamics and optical response to produce a complete theoretical description of ultrafast pump-probe measurements, free of any fitting parameters that are typical in previous analyses.
" }, { "name": "Burgoyne, Hayden Andrew", "degree": "PhD", "year": "2016", "title": "Dynamics of Granular Crystals with Elastic-Plastic Contacts", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182016-164150213", "creators": [ { "name": { "family": "Burgoyne", "given": "Hayden Andrew" }, "id": "Burgoyne-Hayden-Andrew", "orcid": "0000-0003-0891-6411", "display_name": "Burgoyne, Hayden Andrew" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Newman", "given": "John A." }, "id": "Newman-J-A", "role": "member", "display_name": "Newman, John A." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "space" ], "doi": "10.7907/Z9J38QG6", "abstract": "We study the behavior of granular crystals subjected to impact loading that creates plastic deformation at the contacts between constituent particles. Granular crystals are highly periodic arrangements of spherical particles, arranged into densely packed structures resembling crystals. This special class of granular materials has been shown to have unique dynamics with suggested applications in impact protection. However, previous work has focused on very low amplitude impacts where every contact point can be described using the Hertzian contact law, valid only for purely elastic deformation. In this thesis, we extend previous investigation of the dynamics of granular crystals to significantly higher impact energies more suitable for the majority of applications. Additionally, we demonstrate new properties specific to elastic-plastic granular crystals and discuss their potential applications as well. We first develop a new contact law to describe the interaction between particles for large amplitude compression of elastic-plastic spherical particles including a formulation for strain-rate dependent plasticity. We numerically and experimentally demonstrate the applicability of this contact law to a variety of materials typically used in granular crystals. We then extend our investigation to one-dimensional chains of elastic-plastic particles, including chains of alternating dissimilar materials. We show that, using the new elastic-plastic contact law, we can predict the speed at which impact waves with plastic dissipation propagate based on the material properties of the constituent particles. Finally, we experimentally and numerically investigate the dynamics of two-dimensional and three-dimensional granular crystals with elastic-plastic contacts. We first show that the predicted wave speeds for 1D granular crystals can be extended to 2D and 3D materials. We then investigate the behavior of waves propagating across oblique interfaces of dissimilar particles. We show that the character of the refracted wave can be predicted using an analog to Snell's law for elastic-plastic granular crystals and ultimately show how it can be used to design impact guiding \"lenses\" for mitigation applications." }, { "name": "Cai, Wuhan Desmond", "degree": "PhD", "year": "2016", "title": "Electricity Markets for the Smart Grid: Networks, Timescales, and Integration with Control", "advisor": "Low, Steven H.; Wierman, Adam C.; Chandy, K. Mani; Ledyard, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262016-112813537", "creators": [ { "name": { "family": "Cai", "given": "Wuhan Desmond" }, "id": "Cai-Wuhan-Desmond", "orcid": "0000-0001-9207-1890", "display_name": "Cai, Wuhan Desmond" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "co-advisor", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "co-advisor", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "co-advisor", "display_name": "Ledyard, John O." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9BG2KZG", "abstract": "We are at the dawn of a significant transformation in the electric industry. Renewable generation and customer participation in grid operations and markets have been growing at tremendous rates in recent years and these trends are expected to continue. These trends are likely to be accompanied by both engineering and market integration challenges. Therefore, to incorporate these resources efficiently into the grid, it is important to deal with the inefficiencies in existing markets. The goal of this thesis is to contribute new insights towards improving the design of electricity markets.
\r\n\r\nThis thesis makes three main contributions. First, we provide insights into how the economic dispatch mechanism could be designed to account for price-anticipating participants. We study this problem in the context of a networked Cournot competition with a market maker and we give an algorithm to find improved market clearing designs. Our findings illustrate the potential inefficiencies in existing markets and provides a framework for improving the design of the markets. Second, we provide insights into the strategic interactions between generation flexibility and forward markets. Our key insight is an observation that spot market capacity constraints can significantly impact the efficiency and existence of equilibrium in forward markets, as they give producers incentives to strategically withhold offers from the markets. Third, we provide insights into how optimization decomposition theory can guide optimal design of the architecture of power systems control. In particular, we illustrate a context where decomposition theory enables us to jointly design market and control mechanisms to allocate resources efficiently across both the economic dispatch and frequency regulation timescales.\r\n
" }, { "name": "Chang, Yingrui (Ray)", "degree": "PhD", "year": "2016", "title": "A Continuum Model for Slip-Twinning Interactions in Magnesium and Magnesium Alloys", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01252016-164549986", "creators": [ { "name": { "family": "Chang", "given": "Yingrui (Ray)" }, "id": "Chang-Yingrui-Ray", "display_name": "Chang, Yingrui (Ray)" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Lloyd", "given": "Jeffrey T." }, "id": "Lloyd-J-T", "role": "member", "display_name": "Lloyd, Jeffrey T." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z96M34RX", "abstract": "Due to their high specific strength and low density, magnesium and magnesium-based alloys have gained great technological importance in recent years. However, their underlying hexagonal crystal structure furnishes Mg and its alloys with a complex mechanical behavior because of their comparably smaller number of energetically favorable slip systems. Besides the commonly studied slip mechanism, another way to accomplish general deformation is through the additional mechanism of deformation-induced twinning. The main aim of this thesis research is to develop an efficient continuum model to understand and ultimately predict the material response resulting from the interaction between these two mechanisms.
\r\n\r\nThe constitutive model we present is based on variational constitutive updates of plastic slips and twin volume fractions and accounts for the related lattice reorientation mechanisms. The model is applied to single- and polycrystalline pure magnesium. We outline the finite-deformation plasticity model combining basal, pyramidal, and prismatic dislocation activity as well as a convexification based approach for deformation twinning. A comparison with experimental data from single-crystal tension-compression experiments validates the model and serves for parameter identification. The extension to polycrystals via both Taylor-type modeling and finite element simulations shows a\r\ncharacteristic stress-strain response that agrees well with experimental observations for polycrystalline magnesium. The presented continuum model does not aim to represent the full details of individual twin-dislocation interactions, yet it is sufficiently efficient to allow for finite element simulations while qualitatively capturing the underlying microstructural deformation mechanisms.
" }, { "name": "Chen, Bo", "degree": "PhD", "year": "2016", "title": "Quantum of Vision", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252016-140422108", "creators": [ { "name": { "family": "Chen", "given": "Bo" }, "id": "Chen-Bo", "orcid": "0000-0001-5566-7361", "display_name": "Chen, Bo" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Meister", "given": "Markus" }, "id": "Meister-M", "role": "member", "display_name": "Meister, Markus" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Rutishauser", "given": "Ueli" }, "id": "Rutishauser-U", "role": "member", "display_name": "Rutishauser, Ueli" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9057CWS", "abstract": "Visual inputs to artificial and biological visual systems are often quantized: cameras accumulate photons from the visual world, and the brain receives action potentials from visual sensory neurons. Collecting more information quanta leads to a longer acquisition time and better performance. In many visual tasks, collecting a small number of quanta is sufficient to solve the task well. The ability to determine the right number of quanta is pivotal in situations where visual information is costly to obtain, such as photon-starved or time-critical environments. In these situations, conventional vision systems that always collect a fixed and large amount of information are infeasible. I develop a framework that judiciously determines the number of information quanta to observe based on the cost of observation and the requirement for accuracy. The framework implements the optimal speed versus accuracy tradeoff when two assumptions are met, namely that the task is fully specified probabilistically and constant over time. I also extend the framework to address scenarios that violate the assumptions. I deploy the framework to three recognition tasks: visual search (where both assumptions are satisfied), scotopic visual recognition (where the model is not specified), and visual discrimination with unknown stimulus onset (where the model is dynamic over time). Scotopic classification experiments suggest that the framework leads to dramatic improvement in photon-efficiency compared to conventional computer vision algorithms. Human psychophysics experiments confirmed that the framework provides a parsimonious and versatile explanation for human behavior under time pressure in both static and dynamic environments." }, { "name": "Chen, Christopher Tien", "degree": "PhD", "year": "2016", "title": "Heteroepitaxy of Group IV and Group III-V semiconductor alloys for photovoltaic applications", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062015-161003458", "creators": [ { "name": { "family": "Chen", "given": "Christopher Tien" }, "id": "Chen-Christopher-Tien", "orcid": "0000-0001-5848-961X", "display_name": "Chen, Christopher Tien" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9KW5CX0", "abstract": "Photovoltaic energy conversion represents a economically viable technology for realizing collection of the largest energy resource known to the Earth -- the sun. Energy conversion efficiency is the most leveraging factor in the price of energy derived from this process. This thesis focuses on two routes for high efficiency, low cost devices: first, to use Group IV semiconductor alloy wire array bottom cells and epitaxially grown Group III-V compound semiconductor alloy top cells in a tandem configuration, and second, GaP growth on planar Si for heterojunction and tandem cell applications.
\r\n\r\nMetal catalyzed vapor-liquid-solid grown microwire arrays are an intriguing alternative for wafer-free Si and SiGe materials which can be removed as flexible membranes. Selected area Cu-catalyzed vapor-liquid solid growth of SiGe microwires is achieved using chlorosilane and chlorogermane precursors. The composition can be tuned up to 12% Ge with a simultaneous decrease in the growth rate from 7 to 1 \u03bcm/min-1. Significant changes to the morphology were observed, including tapering and faceting on the sidewalls and along the lengths of the wires. Characterization of axial and radial cross sections with transmission electron microscopy revealed no evidence of defects at facet corners and edges, and the tapering is shown to be due to in-situ removal of catalyst material during growth. X-ray diffraction and transmission electron microscopy reveal a Ge-rich crystal at the tip of the wires, strongly suggesting that the Ge incorporation is limited by the crystallization rate.
\r\n\r\nTandem Ga1-xInxP/Si microwire array solar cells are a route towards a high efficiency, low cost, flexible, wafer-free solar technology. Realizing tandem Group III-V compound semiconductor/Si wire array devices requires optimization of materials growth and device performance. GaP and Ga1-xInxP layers were grown heteroepitaxially with metalorganic chemical vapor deposition on Si microwire array substrates. The layer morphology and crystalline quality have been studied with scanning electron microscopy and transmission electron microscopy, and they provide a baseline for the growth and characterization of a full device stack. Ultimately, the complexity of the substrates and the prevalence of defects resulted in material without detectable photoluminescence, unsuitable for optoelectronic applications.
\r\n\r\nCoupled full-field optical and device physics simulations of a Ga0.51In0.49P/Si wire array tandem are used to predict device performance. A 500 nm thick, highly doped \"buffer\" layer between the bottom cell and tunnel junction is assumed to harbor a high density of lattice mismatch and heteroepitaxial defects. Under simulated AM1.5G illumination, the device structure explored in this work has a simulated efficiency of 23.84% with realistic top cell SRH lifetimes and surface recombination velocities. The relative insensitivity to surface recombination is likely due to optical generation further away from the free surfaces and interfaces of the device structure.
\r\n\r\nFinally, GaP has been grown free of antiphase domains on Si (112) oriented substrates using metalorganic chemical vapor deposition. Low temperature pulsed nucleation is followed by high temperature continuous growth, yielding smooth, specular thin films. Atomic force microscopy topography mapping showed very smooth surfaces (4-6 \u00c5 RMS roughness) with small depressions in the surface. Thin films (~ 50 nm) were pseudomorphic, as confirmed by high resolution x-ray diffraction reciprocal space mapping, and 200 nm thick films showed full relaxation. Transmission electron microscopy showed no evidence of antiphase domain formation, but there is a population of microtwin and stacking fault defects.
" }, { "name": "Chen, David Zhaoyue", "degree": "PhD", "year": "2016", "title": "Atomic-Level Structure and Deformation in Metallic Glasses", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252016-155624343", "creators": [ { "name": { "family": "Chen", "given": "David Zhaoyue" }, "id": "Chen-David-Zhaoyue", "orcid": "0000-0001-5732-5015", "display_name": "Chen, David Zhaoyue" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "role": "member", "display_name": "Miller, Thomas F." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z95Q4T2B", "abstract": "Metallic glasses (MGs) are a relatively new class of materials discovered in 1960\r\nand lauded for its high strengths and superior elastic properties. Three major obstacles\r\nprevent their widespread use as engineering materials for nanotechnology and\r\nindustry: 1) their lack of plasticity mechanisms for deformation beyond the elastic\r\nlimit, 2) their disordered atomic structure, which prevents effective study of their\r\nstructure-to-property relationships, and 3) their poor glass forming ability, which\r\nlimits bulk metallic glasses to sizes on the order of centimeters. We focused on\r\nunderstanding the first two major challenges by observing the mechanical properties\r\nof nanoscale metallic glasses in order to gain insight into its atomic-level structure\r\nand deformation mechanisms. We found that anomalous stable plastic flow emerges\r\nin room-temperature MGs at the nanoscale in wires as little as ~100 nanometers\r\nwide regardless of fabrication route (ion-irradiated or not). To circumvent experimental\r\nchallenges in characterizing the atomic-level structure, extensive molecular\r\ndynamics simulations were conducted using approximated (embedded atom\r\nmethod) potentials to probe the underlying processes that give rise to plasticity in\r\nnanowires. Simulated results showed that mechanisms of relaxation via the sample\r\nfree surfaces contribute to tensile ductility in these nanowires. Continuing with characterizing\r\nnanoscale properties, we studied the fracture properties of nano-notched\r\nMGnanowires and the compressive response of MG nanolattices at cryogenic (~130\r\nK) temperatures. We learned from these experiments that nanowires are sensitive\r\nto flaws when the (amorphous) microstructure does not contribute stress concentrations,\r\nand that nano-architected structures with MG nanoribbons are brittle at low\r\ntemperatures except when elastic shell buckling mechanisms dominate at low ribbon\r\nthicknesses (~20 nm), which instead gives rise to fully recoverable nanostructures regardless\r\nof temperature. Finally, motivated by understanding structure-to-property\r\nrelationships in MGs, we studied the disordered atomic structure using a combination\r\nof in-situ X-ray tomography and X-ray diffraction in a diamond anvil cell\r\nand molecular dynamics simulations. Synchrotron X-ray experiments showed the\r\nprogression of the atomic-level structure (in momentum space) and macroscale volume\r\nunder increasing hydrostatic pressures. Corresponding simulations provided\r\ninformation on the real space structure, and we found that the samples displayed\r\nfractal scaling (rd ∝ V, d < 3) at short length scales (< ~8 \u00c5), and exhibited a\r\ncrossover to a homogeneous scaling (d = 3) at long length scales. We examined\r\nthis underlying fractal structure of MGs with parallels to percolation clusters and\r\ndiscuss the implications of this structural analogy to MG properties and the glass\r\ntransition phenomenon." }, { "name": "Choi, Jeesoon", "degree": "PhD", "year": "2016", "title": "Unsteady Aerodynamics and Optimal Control of an Airfoil at Low Reynolds Number", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-220450949", "creators": [ { "name": { "family": "Choi", "given": "Jeesoon" }, "id": "Choi-Jeesoon", "display_name": "Choi, Jeesoon" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Williams", "given": "David R." }, "id": "Williams-D-R", "role": "member", "display_name": "Williams, David R." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9J1014Q", "abstract": "As opposed to conventional air vehicles that have fixed wings, small birds and insects are known to flap their wings at higher angles of attack. The vortex produced at the tip of the wing, known as the leading-edge vortex (LEV), plays an important role to enhance lift during its flight. In this thesis, we analyze the influence of these vortices on aerodynamic forces that could be beneficial to micro-air vehicle performance and efficiency. The flow structures associated with simple harmonic motions of an airfoil are first investigated. The characteristics of the time-averaged and fluctuating forces are explained by analyzing vortical flow features, such as vortex lock-in, leading-edge vortex synchronization, and vortex formation time. Specific frequency regions where the wake instability locks in to the unsteady motion of the airfoil are identified, and these lead to significant changes in the mean forces. A detailed study of the flow structures associated with the LEV acting either in- or out-of-phase with the quasi-steady component of the forces is performed to quantify the amplification and attenuation behavior of the fluctuating forces. An inherent time scale of the LEV associated with its formation and detachment (LEV formation time) is shown to control the time-averaged forces. With these results, several optimal flow control problems are formulated. Adjoint-based optimal control is applied to an airfoil moving at a constant velocity and also to a reciprocating airfoil with no forward velocity. In both cases, we maximize lift by controlling the pitch rate of the airfoil. For the former case, the static map of lift at various angles of attack is additionally examined to find the static angle that provides maximum lift and also to confirm whether the optimizations perform according to the static map. For the latter case, we obtain a solution of the optimized motion of the flapping airfoil which resembles that of a hovering insect." }, { "name": "Coronel, Naomi Cristina", "degree": "PhD", "year": "2016", "title": "Earth-Abundant Zinc-IV-Nitride Semiconductors", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252016-080726422", "creators": [ { "name": { "family": "Coronel", "given": "Naomi Cristina" }, "id": "Coronel-Naomi-Cristina", "display_name": "Coronel, Naomi Cristina" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9CF9N28", "abstract": "This investigation is motivated by the need for new visible frequency direct bandgap semiconductor materials that are abundant and low-cost to meet the increasing demand for optoelectronic devices in applications such as solid state lighting and solar energy conversion. Proposed here is the utilization of zinc-IV-nitride materials, where group IV elements include silicon, germanium, and tin, as earth-abundant alternatives to the more common III-nitrides in optoelectronic devices. These compound semiconductors were synthesized under optimized conditions using reactive radio frequency magnetron sputter deposition. Single phase ZnSnN2, having limited experimental accounts in literature, is validated by identification of the wurtzite-derived crystalline structure predicted by theory through X-ray and electron diffraction studies. With the addition of germanium, bandgap tunability of ZnSnxGe1-xN2 alloys is demonstrated without observation of phase separation, giving these materials a distinct advantage over InxGa1-xN alloys. The accessible bandgaps range from 1.8 to 3.1 eV, which spans the majority of the visible spectrum. Electron densities, measured using the Hall effect, were found to be as high as 1022 cm\u22123 and indicate that the compounds are unintentionally degenerately doped. Given these high carrier concentrations, a Burstein-Moss shift is likely affecting the optical bandgap measurements. The discoveries made in this thesis suggest that with some improvements in material quality, zinc-IV-nitrides have the potential to enable cost-effective and scalable optoelectronic devices." }, { "name": "Coronel, Stephanie Alexandra", "degree": "PhD", "year": "2016", "title": "Thermal Ignition Using Moving Hot Particles", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032016-210051818", "creators": [ { "name": { "family": "Coronel", "given": "Stephanie Alexandra" }, "id": "Coronel-Stephanie-Alexandra", "orcid": "0000-0002-7088-7976", "display_name": "Coronel, Stephanie Alexandra" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9W37T9X", "abstract": "In this work, ignition of n-hexane-air mixtures was investigated using moving hot spheres of various diameters and surface temperatures. Alumina spheres of 1.8-6 mm diameter were heated using a high power CO2 laser and injected with an average velocity of 2.4 m/s into a premixed n-hexane-air mixture at a nominal initial temperature and pressure of 298 K and 100 kPa, respectively. The 90% probability of ignition using a 6 mm diameter sphere was 1224 K. High-speed experimental visualizations using interferometry indicated that ignition occurred in the vicinity of the separation point in the boundary layer of the sphere when the sphere surface temperature was near the ignition threshold. Additionally, the ignition threshold was found to be insensitive to the mixture composition and showed little variation with sphere diameter.
\r\n\r\nNumerical simulations of a transient one-dimensional boundary layer using detailed chemistry in a gas a layer adjacent to a hot wall indicated that ignition takes place away from the hot surface; the igniting gas that is a distance away from the surface can overcome diffusive heat losses back to the wall when there is heat release due to chemical activity. Finally, a simple approximation of the thermal and momentum boundary layer profiles indicated that the residence time within a boundary layer varies drastically, for example, a fluid parcel originating at very close to the wall has a residence time that is 65x longer than the residence time of a fluid parcel traveling along the edge of the momentum boundary layer.
\r\n\r\nA non-linear methodology was developed for the extraction of laminar flame properties from synthetic spherically expanding flames. The results indicated that for accurate measurements of the flame speed and Markstein length, a minimum of 50 points is needed in the data set (flame radius vs. time) and a minimum range of 48 mm in the flame radius. The non-linear methodology was applied to experimental n-hexane-air spherically expanding flames. The measured flame speed was insensitive to the mixture initial pressure from 50 to 100 kPa and increased with increasing mixture initial temperature. One-dimensional freely-propagating flame calculations showed excellent agreement with the experimental flame speeds using the JetSurF and CaltechMech chemical mechanisms.
" }, { "name": "Cymbalist, Niccolo", "degree": "PhD", "year": "2016", "title": "Mixing, Chemical Reactions, and Combustion in Supersonic Flows", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242016-143905617", "creators": [ { "name": { "family": "Cymbalist", "given": "Niccolo" }, "id": "Cymbalist-Niccolo", "display_name": "Cymbalist, Niccolo" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9G73BNR", "abstract": "Experiments were conducted at the GALCIT supersonic shear-layer facility to investigate\r\naspects of reacting transverse jets in supersonic crossflow using chemiluminescence and schlieren\r\nimage-correlation velocimetry. In particular, experiments were designed to examine mixing-delay\r\nlength dependencies on jet-fluid molar mass, jet diameter, and jet inclination.
\r\n\r\nThe experimental results show that mixing-delay length depends on jet Reynolds number, when\r\nappropriately normalized, up to a jet Reynolds number of 500,000. Jet inclination increases the\r\nmixing-delay length, but causes less disturbance to the crossflow when compared to normal jet\r\ninjection. This can be explained, in part, in terms of a control-volume analysis that relates jet\r\ninclination to flow conditions downstream of injection.
\r\n\r\nIn the second part of this thesis, a combustion-modeling framework is proposed and developed\r\nthat is tailored to large-eddy simulations of turbulent combustion in high-speed flows. Scaling arguments place supersonic hydrocarbon combustion in a regime of autoignition-dominated distributed\r\nreaction zones (DRZ). The proposed evolution-variable manifold (EVM) framework incorporates an\r\nignition-delay data-driven induction model with a post-ignition manifold that uses a Lagrangian\r\nconvected 'balloon' reactor model for chemistry tabulation. A large-eddy simulation incorporating\r\nthe EVM framework captures several important reacting-flow features of a transverse hydrogen jet\r\nin heated-air crossflow experiment.
" }, { "name": "De Lorenzo, Laura Anne", "degree": "PhD", "year": "2016", "title": "Optomechanics with Superfluid Helium-4", "advisor": "Schwab, Keith C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-075803376", "creators": [ { "name": { "family": "De Lorenzo", "given": "Laura Anne" }, "id": "Delorenzo-Laura-Anne", "display_name": "De Lorenzo, Laura Anne" } ], "advisors": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "advisor", "display_name": "Schwab, Keith C." } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "role": "member", "display_name": "Chen, Yanbei" }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "role": "member", "display_name": "Adhikari, Rana" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9RJ4GD7", "abstract": "We demonstrate the utility of superfluid helium-4 as an extremely low loss optomechanical element. We form an optomechanical system with a cylindrical niobium superconducting TE011 resonator whose 40 cm3 inner cylindrical cavity is filled with 4He. [1] Coupling is realized via the variations in permittivity resulting from the density profile of the acoustic modes. Acoustic losses in helium-4 below 500 mK are governed by the intrinsic nonlinearity of sound, leading to an attenuation which drops as T 4, indicating the possibility of quality factors (Q) over 1010 at 10 mK. In our lowest loss mode, we demonstrate this T 4 law down to 50 mK, realizing an acoustic Q of 1.35·108 at 8.1 kHz. When coupled with a low phase noise microwave source, we expect this system to be utilized as a probe of macroscopic quantized motion, for precision measurements to search for fundamental physical length scales, and as a continuous gravitational wave detector. Our estimates suggest that a resonant superfluid acoustic system could exceed the sensitivity of current broad-band detectors for narrow-band sources such as pulsars [2]." }, { "name": "Dizon, Abel Bermie Roberto", "degree": "PhD", "year": "2016", "title": "A Hybrid-Parallel Framework for the Nonlinear Seismic Analysis of Very Tall Buildings", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12142015-083607823", "creators": [ { "name": { "family": "Dizon", "given": "Abel Bermie Roberto" }, "id": "Dizon-Abel-Bermie-Roberto", "display_name": "Dizon, Abel Bermie Roberto" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "chair", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "civileng" ], "doi": "10.7907/Z96Q1V58", "abstract": "FRAME3D, a program for the nonlinear seismic analysis of steel structures, has previously been used to study the collapse mechanisms of steel buildings up to 20 stories tall. The present thesis is inspired by the need to conduct similar analysis for much taller structures. It improves FRAME3D in two primary ways.
\r\n\r\nFirst, FRAME3D is revised to address specific nonlinear situations involving large displacement/rotation increments, the backup-subdivide algorithm, element failure, and extremely narrow joint hysteresis. The revisions result in superior convergence capabilities when modeling earthquake-induced collapse. The material model of a steel fiber is also modified to allow for post-rupture compressive strength.
\r\n\r\nSecond, a parallel FRAME3D (PFRAME3D) is developed. The serial code is optimized and then parallelized. A distributed-memory divide-and-conquer approach is used for both the global direct solver and element-state updates. The result is an implicit finite-element hybrid-parallel program that takes advantage of the narrow-band nature of very tall buildings and uses nearest-neighbor-only communication patterns.
\r\n\r\nUsing three structures of varied sized, PFRAME3D is shown to compute reproducible results that agree with that of the optimized 1-core version (displacement time-history response root-mean-squared errors are ~\u301610\u3017^(-5) m) with much less wall time (e.g., a dynamic time-history collapse simulation of a 60-story building is computed in 5.69 hrs with 128 cores\u2014a speedup of 14.7 vs. the optimized 1-core version). The maximum speedups attained are shown to increase with building height (as the total number of cores used also increases), and the parallel framework can be expected to be suitable for buildings taller than the ones presented here.
\r\n\r\nPFRAME3D is used to analyze a hypothetical 60-story steel moment-frame tube building (fundamental period of 6.16 sec) designed according to the 1994 Uniform Building Code. Dynamic pushover and time-history analyses are conducted. Multi-story shear-band collapse mechanisms are observed around mid-height of the building. The use of closely-spaced columns and deep beams is found to contribute to the building's \u201csomewhat brittle\u201d behavior (ductility ratio ~2.0). Overall building strength is observed to be sensitive to whether a model is fracture-capable.
" }, { "name": "Dunne, Reeve", "degree": "PhD", "year": "2016", "title": "Dynamic Stall on Vertical Axis Wind Turbines", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09042015-152813860", "creators": [ { "name": { "family": "Dunne", "given": "Reeve" }, "id": "Dunne-Reeve", "display_name": "Dunne, Reeve" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z92Z13FX", "abstract": "In this study the dynamics of flow over the blades of vertical axis wind turbines was investigated using a simplified periodic motion to uncover the fundamental flow physics and provide insight into the design of more efficient turbines. Time-resolved, two-dimensional velocity measurements were made with particle image velocimetry on a wing undergoing pitching and surging motion to mimic the flow on a turbine blade in a non-rotating frame. Dynamic stall prior to maximum angle of attack and a leading edge vortex development were identified in the phase-averaged flow field and captured by a simple model with five modes, including the first two harmonics of the pitch/surge frequency identified using the dynamic mode decomposition. Analysis of these modes identified vortical structures corresponding to both frequencies that led the separation and reattachment processes, while their phase relationship determined the evolution of the flow.
\r\n\r\nDetailed analysis of the leading edge vortex found multiple regimes of vortex development coupled to the time-varying flow field on the airfoil. The vortex was shown to grow on the airfoil for four convection times, before shedding and causing dynamic stall in agreement with 'optimal' vortex formation theory. Vortex shedding from the trailing edge was identified from instantaneous velocity fields prior to separation. This shedding was found to be in agreement with classical Strouhal frequency scaling and was removed by phase averaging, which indicates that it is not exactly coupled to the phase of the airfoil motion.
\r\n\r\nThe flow field over an airfoil undergoing solely pitch motion was shown to develop similarly to the pitch/surge motion; however, flow separation took place earlier, corresponding to the earlier formation of the leading edge vortex. A similar reduced-order model to the pitch/surge case was developed, with similar vortical structures leading separation and reattachment; however, the relative phase lead of the separation mode, corresponding to earlier separation, necessitated that a third frequency to be incorporated into the reattachment mode to provide a relative lag in reattachment.
\r\n\r\nFinally, the results are returned to the rotating frame and the effects of each flow phenomena on the turbine are estimated, suggesting kinematic criteria for the design of improved turbines.
" }, { "name": "Dunne, Simon G.", "degree": "PhD", "year": "2016", "title": "Neural and Hormonal Systems Underlying Human Reward-Seeking Behavior", "advisor": "O'Doherty, John P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-152546060", "creators": [ { "name": { "family": "Dunne", "given": "Simon G." }, "id": "Dunne-Simon-G", "orcid": "0000-0003-4875-7953", "display_name": "Dunne, Simon G." } ], "advisors": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "advisor", "display_name": "O'Doherty, John P." } ], "committee": [ { "name": { "family": "Camerer", "given": "Colin F." }, "id": "Camerer-C-F", "role": "chair", "display_name": "Camerer, Colin F." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "member", "display_name": "O'Doherty, John P." } ], "option_major": [ "cns" ], "doi": "10.7907/Z9SN06ZX", "abstract": "Our evolutionary history has endowed us with biological systems for identifying those elements of the environment that contribute to our biological fitness and for modifying our behaviors to allow us to acquire them.
\r\n\r\nTheoretical propositions suggest that the ability to detect changes in the statistics underlying in the environment may be useful for rapidly adapting our behaviors. However, little is known about the neural representation of the quantity representing the evidence for a change point: unexpected uncertainty. In Chapter 2, I describe a study in which humans interact with an unstable reward environment while undergoing fMRI. Representations of unexpected uncertainty were found in multiple cortical areas, as well as the noradrenergic brainstem nucleus locus coeruleus. Other unique cortical regions were found to encode estimation uncertainty, or the uncertainty in one\u2019s estimates of the reward contingencies, and risk, or one\u2019s estimate of the stochasticity of the environment. Collectively, these findings support theoretical models in which uncertainty computations determine the speed of learning.
\r\n\r\nAlthough learning from direct experience in this way is vital to our survival, humans are also particularly adept at learning from conspecifics. However, it is not known whether differing computational strategies thought to support experiential learning, model-based and model-free learning, also support learning by observation. Chapter 3 describes a study in which human participants played a multi-armed bandit task that encouraged them to employ both experiential and observational learning while they underwent fMRI. Model-based learning signals are found during both observational and experiential learning in the intraparietal sulcus. However, unlike in experiential learning, model-free learning signals in the ventral striatum were not detectable during observational learning. These results provide insight into the flexibilty of the model-based learning system, and further suggest that the model-free learning system may be less flexible with regard to its involvement in observational learning.
\r\n\r\nWhile Chapters 2 and 3 are concerned with modifying reward-seeking behavior in reponse to changes in the external environment, Chapter 4 examines a modification of reward-seeking behavior in response to changes in the internal hormonal environment. Specifically, it describes how the behavior of human males in a simple economic game was influenced by the administration of testosterone. Although a popular view on the role of testosterone in human social behaviour proposes that it increases aggression, a recent theory states that it instead promotes behaviors that enhance social status. In a double-blind, placebo-controlled between-subjects design, administration of testosterone increased punishment of players who treat the participants unfairly but also increased reward of those who treat them generously. Our findings are inconsistent with the view that testosterone simply increases aggression and provides causal evidence for the social-status hypothesis in men.
\r\n\r\nIn Chapter 5, I describe an investigation of the phenomenon of \u2018choking under pressure\u2019, in which reward-seeking behavior is compromised by the promise of high reward for successful performance. A novel approach to attenuating such 'choking under pressure' using cognitive reappraisal of the incentive is described and tested. When participants performed a demanding motor task under reappraisal, choking was indeed significantly reduced, with the magnitude of this reduction being predicted by the striatal BOLD response to incentive magnitude. In addition, application of the reappraisal strategy was associated with reduced sympathetic arousal during trials on which performance failed at high levels of incentive. These results suggest that reappraisal of the incentive is indeed a promising intervention for attenuating choking under pressure.
" }, { "name": "Duvvuri, Subrahmanyam", "degree": "PhD", "year": "2016", "title": "Non-Linear Scale Interactions in a Forced Turbulent Boundary Layer", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02292016-143116051", "creators": [ { "name": { "family": "Duvvuri", "given": "Subrahmanyam" }, "id": "Duvvuri-Subrahmanyam", "display_name": "Duvvuri, Subrahmanyam" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Z31WKP ", "abstract": "This thesis explores the dynamics of scale interactions in a turbulent boundary layer through a forcing-response type experimental study. An emphasis is placed on the analysis of triadic wavenumber interactions since the governing Navier-Stokes equations for the flow necessitate a direct coupling between triadically consist scales. Two sets of experiments were performed in which deterministic disturbances were introduced into the flow using a spatially-impulsive dynamic wall perturbation. Hotwire anemometry was employed to measure the downstream turbulent velocity and study the flow response to the external forcing. In the first set of experiments, which were based on a recent investigation of dynamic forcing effects in a turbulent boundary layer, a 2D (spanwise constant) spatio-temporal normal mode was excited in the flow; the streamwise length and time scales of the synthetic mode roughly correspond to the very-large-scale-motions (VLSM) found naturally in canonical flows. Correlation studies between the large- and small-scale velocity signals reveal an alteration of the natural phase relations between scales by the synthetic mode. In particular, a strong phase-locking or organizing effect is seen on directly coupled small-scales through triadic interactions. Having characterized the bulk influence of a single energetic mode on the flow dynamics, a second set of experiments aimed at isolating specific triadic interactions was performed. Two distinct 2D large-scale normal modes were excited in the flow, and the response at the corresponding sum and difference wavenumbers was isolated from the turbulent signals. Results from this experiment serve as an unique demonstration of direct non-linear interactions in a fully turbulent wall-bounded flow, and allow for examination of phase relationships involving specific interacting scales. A direct connection is also made to the Navier-Stokes resolvent operator framework developed in recent literature. Results and analysis from the present work offer insights into the dynamical structure of wall turbulence, and have interesting implications for design of practical turbulence manipulation or control strategies." }, { "name": "Emmer, Hal S.", "degree": "PhD", "year": "2016", "title": "Paths Towards High Efficiency Silicon Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:04102016-142401400", "creators": [ { "name": { "family": "Emmer", "given": "Hal S." }, "id": "Emmer-Hal-S", "display_name": "Emmer, Hal S." } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9RV0KN6", "abstract": "While photovoltaics hold much promise as a sustainable electricity source, continued cost reduction is necessary to continue the current growth in deployment. A promising path to continuing to reduce total system cost is by increasing device efficiency. This thesis explores several silicon-based photovoltaic technologies with the potential to reach high power conversion efficiencies. Silicon microwire arrays, formed by joining millions of micron diameter wires together, were developed as a low cost, low efficiency solar technology. The feasibility of transitioning this to a high efficiency technology was explored. In order to achieve high efficiency, high quality silicon material must be used. Lifetimes and diffusion lengths in these wires were measured and the action of various surface passivation treatments studied. While long lifetimes were not achieved, strong inversion at the silicon / hydrofluoric acid interface was measured, which is important for understanding a common measurement used in solar materials characterization.
\r\n\r\nCryogenic deep reactive ion etching was then explored as a method for fabricating high quality wires and improved lifetimes were measured. As another way to reach high efficiency, growth of silicon-germanium alloy wires was explored as a substrate for a III-V on Si tandem device. Patterned arrays of wires with up to 12% germanium incorporation were grown. This alloy is more closely lattice matched to GaP than silicon and allows for improvements in III-V integration on silicon.
\r\n\r\nHeterojunctions of silicon are another promising path towards achieving high efficiency devices. The GaP/Si heterointerface and properties of GaP grown on silicon were studied. Additionally, a substrate removal process was developed which allows the formation of high quality free standing GaP films and has wide applications in the field of optics.
\r\n\r\nFinally, the effect of defects at the interface of the amorphous silicon heterojuction cell was studied. Excellent voltages, and thus efficiencies, are achievable with this system, but the voltage is very sensitive to growth conditions. We directly measured lateral transport lengths at the heterointerface on the order of tens to hundreds of microns, which allows carriers to travel towards any defects that are present and recombine. This measurement adds to the understanding of these types of high efficiency devices and may aid in future device design.
\r\n" }, { "name": "Farivar, Masoud", "degree": "PhD", "year": "2016", "title": "Optimization and Control of Power Flow in Distribution Networks", "advisor": "Hassibi, Babak; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092015-021431773", "creators": [ { "name": { "family": "Farivar", "given": "Masoud" }, "id": "Farivar-Masoud", "orcid": "0000-0001-7298-3526", "display_name": "Farivar, Masoud" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "co-advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Chen", "given": "Lijun" }, "id": "Chen-Lijun", "role": "member", "display_name": "Chen, Lijun" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9JW8BSM", "abstract": "Climate change is arguably the most critical issue facing our generation and the next. As we move towards a sustainable future, the grid is rapidly evolving with the integration of more and more renewable energy resources and the emergence of electric vehicles. In particular, large scale adoption of residential and commercial solar photovoltaics (PV) plants is completely changing the traditional slowly-varying unidirectional power flow nature of distribution systems. High share of intermittent renewables pose several technical challenges, including voltage and frequency control. But along with these challenges, renewable generators also bring with them millions of new DC-AC inverter controllers each year. These fast power electronic devices can provide an unprecedented opportunity to increase energy efficiency and improve power quality, if combined with well-designed inverter control algorithms. The main goal of this dissertation is to develop scalable power flow optimization and control methods that achieve system-wide efficiency, reliability, and robustness for power distribution networks of future with high penetration of distributed inverter-based renewable generators.
\r\n\r\nProposed solutions to power flow control problems in the literature range from fully centralized to fully local ones. In this thesis, we will focus on the two ends of this spectrum. In the first half of this thesis (chapters 2 and 3), we seek optimal solutions to voltage control problems provided a centralized architecture with complete information. These solutions are particularly important for better understanding the overall system behavior and can serve as a benchmark to compare the performance of other control methods against. To this end, we first propose a branch flow model (BFM) for the analysis and optimization of radial and meshed networks. This model leads to a new approach to solve optimal power flow (OPF) problems using a two step relaxation procedure, which has proven to be both reliable and computationally efficient in dealing with the non-convexity of power flow equations in radial and weakly-meshed distribution networks. We will then apply the results to fast time- scale inverter var control problem and evaluate the performance on real-world circuits in Southern California Edison\u2019s service territory.
\r\n\r\nThe second half (chapters 4 and 5), however, is dedicated to study local control approaches, as they are the only options available for immediate implementation on today\u2019s distribution networks that lack sufficient monitoring and communication infrastructure. In particular, we will follow a reverse and forward engineering approach to study the recently proposed piecewise linear volt/var control curves. It is the aim of this dissertation to tackle some key problems in these two areas and contribute by providing rigorous theoretical basis for future work.
" }, { "name": "Ha, Quoc Bao Nguyen", "degree": "PhD", "year": "2016", "title": "Plasma Loop and Strapping Field Dynamics: Reproducing Solar Eruptions in the Laboratory", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:07162015-193957726", "creators": [ { "name": { "family": "Ha", "given": "Quoc Bao Nguyen" }, "id": "Ha-Quoc-Bao-Nguyen", "display_name": "Ha, Quoc Bao Nguyen" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "role": "member", "display_name": "Hallinan, Gregg W." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z99G5JR6", "abstract": "Coronal mass ejections (CMEs) are dramatic eruptions of large, plasma structures from the Sun. These eruptions are important because they can harm astronauts, damage electrical infrastructure, and cause auroras. A mysterious feature of these eruptions is that plasma-filled solar flux tubes first evolve slowly, but then suddenly erupt. One model, torus instability, predicts an explosive-like transition from slow expansion to fast acceleration, if the spatial decay of the ambient magnetic field exceeds a threshold.
\r\n\r\nWe create arched, plasma filled, magnetic flux ropes similar to CMEs. Small, independently-powered auxiliary coils placed inside the vacuum chamber produce magnetic fields above the decay threshold that are strong enough to act on the plasma. When the strapping field is not too strong and not too weak, expansion force build up while the flux rope is in the strapping field region. When the flux rope moves to a critical height, the plasma accelerates quickly, corresponding to the observed slow-rise to fast-acceleration of most solar eruptions. This behavior is in agreement with the predictions of torus instability.
\r\n\r\nHistorically, eruptions have been separated into gradual CMEs and impulsive CMEs, depending on the acceleration profile. Recent numerical studies question this separation. One study varies the strapping field profile to produce gradual eruptions and impulsive eruptions, while another study varies the temporal profile of the voltage applied to the flux tube footpoints to produce the two eruption types. Our experiment reproduced these different eruptions by changing the strapping field magnitude, and the temporal profile of the current trace. This suggests that the same physics underlies both types of CME and that the separation between impulsive and gradual classes of eruption is artificial.
" }, { "name": "Horstmeyer, Roarke William", "degree": "PhD", "year": "2016", "title": "Computational Microscopy: Turning Megapixels into Gigapixels", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:10202015-173005082", "creators": [ { "name": { "family": "Horstmeyer", "given": "Roarke William" }, "id": "Horstmeyer-Roarke-William", "orcid": "0000-0002-2480-9141", "display_name": "Horstmeyer, Roarke William" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Zheng", "given": "Guoan" }, "id": "Zheng-Guoan", "role": "member", "display_name": "Zheng, Guoan" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z95Q4T1W", "abstract": "The layout of a typical optical microscope has remained effectively unchanged over the past century. Besides the widespread adoption of digital focal plane arrays, relatively few innovations have helped improve standard imaging with bright-field microscopes. This thesis presents a new microscope imaging method, termed Fourier ptychography, which uses an LED to provide variable sample illumination and post-processing algorithms to recover useful sample information. Examples include increasing the resolution of megapixel-scale images to one gigapixel, measuring quantitative phase, achieving oil-immersion quality resolution without an immersion medium, and recovering complex\r\nthree dimensional sample structure." }, { "name": "Hua, Chengyun", "degree": "PhD", "year": "2016", "title": "Exploring Thermal Phonon Transport from Atomic to Macroscopic Scales for Energy Conversion and Management", "advisor": "Minnich, Austin", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032016-104118221", "creators": [ { "name": { "family": "Hua", "given": "Chengyun" }, "id": "Hua-Chengyun", "display_name": "Hua, Chengyun" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin" }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin" } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z96H4FDH", "abstract": "Heat is one of the most fundamental forms of energy, and the ability to control heat plays a critical role in most current and future energy applications. Recently, interface engineering between heterogeneous solids has provided new approaches to manipulate heat transport at the scales of the energy carriers in solids, i.e. phonons which are quantized lattice vibrations. For example, nanocrystalline materials, which are polycrystalline materials with nanoscale grain sizes, are promising thermoelectric (TE) materials that have achieved substantially improved figure of merits compared to their bulk counterparts. This enhancement is typically attributed to a reduction in lattice thermal conductivity by phonon scattering at grain boundaries. On the other hand, inefficient heat dissipation across interfaces has been a long-standing problem that shortens the lifetime of electronics such as light-emitting diodes.
\r\n\r\nDespite the importance of interfaces, we still lack a comprehensive understanding of interfacial thermal phonon transport. For instance, the Fresnel coefficients enable the straightforward mathematical description of light as it moves between media of differing dielectric constants. Similarly, interfacial phonon transport can also be characterized by transmission coefficients that vary over the broad phonon spectrum in an analogous manner to Fresnel coefficients for light. However, despite decades of work, the spectral profile of these coefficients and how the profile is influenced by the atomic structure of actual interfaces remains unclear. As a result, the basic phenomenon of interfacial heat transport remains among the most poorly understood transport processes.
\r\n\r\nTo elucidate this process, in this thesis we investigate interfacial thermal phonon transport using both modeling and experiment. The first portion of the thesis examines the impact of frequency-dependent grain boundary scattering in nanocrystalline silicon and silicon-germanium alloys using a novel computational method. We find that the grain boundary may not be as effective as commonly considered in scattering certain phonons, with a substantial amount of heat being carried by low frequency phonons with mean free paths longer than the grain size. Our result will help guide the design of more efficient TEs.
\r\n\r\nThe second part of the thesis focuses on studying heat conduction using the Boltzmann transport equation (BTE), which is the governing equation of energy transport at length scales comparable to phonon mean free paths. The BTE is an integro-differential equation of time, real space, and phase space. Due to its high dimensionality, it is extremely challenging to solve. Here, we develop analytical methods to solve the frequency-dependent BTE, which allow us to obtain simple, closed-form solutions to complex multidimensional problems that have previously been possible to solve only with computationally expensive numerical simulations. We demonstrate that the solution leads to a more accurate measurement of phonon MFP spectra in thermal transient grating experiments.
\r\n\r\nFinally, we report the first measurements of thermal phonon transmission coefficients at a metal-semiconductor interface using ab-initio phonon transport modeling based on the BTE we develop in the second part and a thermal characterization technique, time-domain thermoreflectance. With our approach, we are able to directly link the atomic structure of an interface to the spectral content of the heat crossing it for the first time. Our work realizes the long-standing goal of directly measuring thermal phonon transmission coefficients and demonstrates a general route to study microscopic processes governing interfacial heat conduction.
\r\n" }, { "name": "Hung, Peter Shek-Ho", "degree": "PhD", "year": "2016", "title": "Advanced Applications of Nanoelectromechanical Systems", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-154210811", "creators": [ { "name": { "family": "Hung", "given": "Peter Shek-Ho" }, "id": "Hung-Peter-Shek-Ho", "orcid": "0000-0002-9034-5330", "display_name": "Hung, Peter Shek-Ho" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "role": "member", "display_name": "Yeh, Nai-Chang" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9J38QJ3", "abstract": "Nanoelectromechanical systems (NEMS) have advanced the technologies in a wide spectrum of fields, including nonlinear dynamics, sensors for force detection, mass spectrometry, inertial imaging, calorimetry, and charge sensing. Due to their low power consumption, fast response time, large dynamic range, high quality factor, and low mass, NEMS have achieved unprecedented measurement sensitivity. For optimized system functionalization and design, precise characterization of material properties at the nanoscale is essential. In this thesis, we will discuss three applications of NEMS: mechanical switches, using anharmonic nonlinearity to measure device and material properties, and mass spectrometry and inertial imaging.
\r\n\r\nThe first application of NEMS we discuss is NEMS switches, switches with physical moving parts. Conventional electronics, based largely on silicon transistors, is reaching a physical limit in both size and power consumption. Mechanical switches provide a promising solution to surpass this limit by forcing a jump between the on and off states. Graphene, which is a single sheet of carbon atoms arranged in a hexagonal structure, has high mechanical strength and strong planar bonding, making it an ideal candidate for nanoelectromechanical switches. In addition, graphene is conductive, which decreases resistive heating at the contact area, therefore reducing bonding issues and subsequently reducing degradation. We demonstrate using exfoliated graphene to fabricate suspended graphene NEMS switches with successful switching.
\r\n\r\nThe second application of NEMS we discuss in this thesis is the use of mechanical nonlinearity to measure device and material properties. While the nonlinear dynamics of NEMS have been used previously to investigate the longitudinal speed of sound of materials at nano- and micro-scales, we correct a previously attempted method that employs the anharmonicity of NEMS arising from deflection-dependent stress to interrogate the transport of RF acoustic phonons at nanometer scales. In contrast to existing approaches, this decouples intrinsic material properties, such as longitudinal speed of sound, from properties associated with linear dynamics, such as tension, of the structure. We demonstrate this approach through measurements of the longitudinal speed of sound in several NEMS devices composed of single crystal silicon along different crystal orientations. Good agreement with literature values is reported.
\r\n\r\nThe third application of NEMS we discuss is mass spectrometry and inertial imaging. Currently, only doubly clamped beams and cantilevers have been experimentally demonstrated for mass spectrometry. We extend the one-dimension model for mass spectrometry to a novel method for inertial imaging. We further extend the theory of mass spectrometry and inertial imaging to two dimensions by using a plate geometry. We show that the mode shape is critical in performing NEMS mass spectrometry and inertial imaging, and that the mode shapes in plates deviate from the ideal scenario with isotropic stress. We experiment with various non-ideal conditions to match non-ideal mode shape observed.
" }, { "name": "Hurley, Ryan Colt", "degree": "PhD", "year": "2016", "title": "Force Chains, Friction, and Flow: Behavior of Granular Media across Length Scales", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09212015-105224808", "creators": [ { "name": { "family": "Hurley", "given": "Ryan Colt" }, "id": "Hurley-Ryan-Colt", "display_name": "Hurley, Ryan Colt" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lamb", "given": "Michael P." }, "id": "Lamb-M-P", "role": "member", "display_name": "Lamb, Michael P." }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/Z91Z429J", "abstract": "We study the behavior of granular materials at three length scales. At the smallest length scale, the grain-scale, we study inter-particle forces and \"force chains\". Inter-particle forces are the natural building blocks of constitutive laws for granular materials. Force chains are a key signature of the heterogeneity of granular systems. Despite their fundamental importance for calibrating grain-scale numerical models and elucidating constitutive laws, inter-particle forces have not been fully quantified in natural granular materials. We present a numerical force inference technique for determining inter-particle forces from experimental data and apply the technique to two-dimensional and three-dimensional systems under quasi-static and dynamic load. These experiments validate the technique and provide insight into the quasi-static and dynamic behavior of granular materials.
\r\n\r\nAt a larger length scale, the mesoscale, we study the emergent frictional behavior of a collection of grains. Properties of granular materials at this intermediate scale are crucial inputs for macro-scale continuum models. We derive friction laws for granular materials at the mesoscale by applying averaging techniques to grain-scale quantities. These laws portray the nature of steady-state frictional strength as a competition between steady-state dilation and grain-scale dissipation rates. The laws also directly link the rate of dilation to the non-steady-state frictional strength.
\r\n\r\nAt the macro-scale, we investigate continuum modeling techniques capable of simulating the distinct solid-like, liquid-like, and gas-like behaviors exhibited by granular materials in a single computational domain. We propose a Smoothed Particle Hydrodynamics (SPH) approach for granular materials with a viscoplastic constitutive law. The constitutive law uses a rate-dependent and dilation-dependent friction law. We provide a theoretical basis for a dilation-dependent friction law using similar analysis to that performed at the mesoscale. We provide several qualitative and quantitative validations of the technique and discuss ongoing work aiming to couple the granular flow with gas and fluid flows.
" }, { "name": "Jaganathan, Kishore", "degree": "PhD", "year": "2016", "title": "Convex Programming-Based Phase Retrieval: Theory and Applications", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312016-051759406", "creators": [ { "name": { "family": "Jaganathan", "given": "Kishore" }, "id": "Jaganathan-Kishore", "display_name": "Jaganathan, Kishore" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9C82775", "abstract": "Phase retrieval is the problem of recovering a signal from its Fourier magnitude. This inverse problem arises in many areas of engineering and applied physics, and has been studied for nearly a century. Due to the absence of Fourier phase, the available information is incomplete in general. Classic identifiability results state that phase retrieval of one-dimensional signals is impossible, and that phase retrieval of higher-dimensional signals is almost surely possible under mild conditions. However, there are no efficient recovery algorithms with theoretical guarantees. Classic algorithms are based on the method of alternating projections. These algorithms do not have theoretical guarantees, and have limited recovery abilities due to the issue of convergence to local optima.
\r\n\r\nRecently, there has been a renewed interest in phase retrieval due to technological advances in measurement systems and theoretical developments in structured signal recovery. In particular, it is now possible to obtain specific kinds of additional magnitude-only information about the signal, depending on the application. The premise is that, by carefully redesigning the measurement process, one could potentially overcome the issues of phase retrieval. To this end, another approach could be to impose certain kinds of prior on the signal, depending on the application. On the algorithmic side, convex programming based approaches have played a key role in modern phase retrieval, inspired by their success in provably solving several quadratic constrained problems.
\r\n\r\nIn this work, we study several variants of phase retrieval using modern tools, with focus on applications like X-ray crystallography, diffraction imaging, optics, astronomy and radar. In the one-dimensional setup, we first develop conditions, which when satisfied, allow unique reconstruction. Then, we develop efficient recovery algorithms based on convex programming, and provide theoretical guarantees. The theory and algorithms we develop are independent of the dimension of the signal, and hence can be used in all the aforementioned applications. We also perform a comparative numerical study of the convex programming and the alternating projection based algorithms. Numerical simulations clearly demonstrate the superior ability of the convex programming based methods, both in terms of successful recovery in the noiseless setting and stable reconstruction in the noisy setting.
" }, { "name": "Jang, Mooseok", "degree": "PhD", "year": "2016", "title": "Optical Phase Conjugation and Its Applications in Biology", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262016-142345346", "creators": [ { "name": { "family": "Jang", "given": "Mooseok" }, "id": "Jang-Mooseok", "orcid": "0000-0003-1977-9539", "display_name": "Jang, Mooseok" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vellekoop", "given": "Ivo" }, "id": "Vellekoop-I", "role": "member", "display_name": "Vellekoop, Ivo" }, { "name": { "family": "Gradinaru", "given": "Viviana" }, "id": "Gradinaru-V", "role": "member", "display_name": "Gradinaru, Viviana" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z99G5JSN", "abstract": "Optical phase conjugation is a process where an incoming electromagnetic wave is reflected with a reversed phase. The propagation direction of an incoming beam (equivalently, local phase gradient) can thereby be precisely reversed by the phase conjugate beam. This intriguing effect, so called \"time-reversal of electromagnetic waves,\" allows cancellation of spatial distortion introduced into the incoming beam. Recently, this concept has provided a new avenue to overcome or utilize random scattering in the field of biophotonics.
\r\n\r\nThis thesis discusses a number of interrelated topics regarding optical phase conjugation and its applications in biology. First, two examples of exploiting optical phase conjugation for light focusing are presented. The first example shows that the axial resolution can be improved based on the counter-propagating property of the phase-conjugate beam, and the second example demonstrates how the random scattering media can be used to enhance the flexibility in focusing range. We then discuss a new class of techniques that involves the use of guidestars in the phase conjugation process for deep tissue (> 1mm) light focusing and imaging. In the context of in vivo application, we model and estimate the penetration depth limit of one prominent example of this approach, time-reversed ultrasonically encoded (TRUE) optical focusing. Based on the analysis, we show that the iteration of phase conjugation operation can improve the contrast and resolution of the focal spot created inside deep tissue. We also present a new kind of guidestar-assisted method, time-reversed ultrasound microbubble encoded (TRUME) light focusing, which can focus light with sub-ultrasound wavelength resolution. At last, the effect of dynamic scatterers on time-reversal fidelity is studied to explore the possibility of applying the optical phase conjugation techniques in living tissue.
" }, { "name": "Janover, Christopher George", "degree": "PhD", "year": "2016", "title": "SteelConverter and Caltech VirtualShaker: Rapid Nonlinear Cloud-Based Structural Model Conversion and Analysis", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052015-133333291", "creators": [ { "name": { "family": "Janover", "given": "Christopher George" }, "id": "Janover-Christopher-George", "display_name": "Janover, Christopher George" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "orcid": "0000-0002-4703-190X", "role": "member", "display_name": "Kohler, Monica D." } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9SF2T3V", "abstract": "STEEL, the Caltech created nonlinear large displacement analysis software, is currently used by a large number of researchers at Caltech. However, due to its complexity, lack of visualization tools (such as pre- and post-processing capabilities) rapid creation and analysis of models using this software was difficult. SteelConverter was created as a means to facilitate model creation through the use of the industry standard finite element solver ETABS. This software allows users to create models in ETABS and intelligently convert model information such as geometry, loading, releases, fixity, etc., into a format that STEEL understands. Models that would take several days to create and verify now take several hours or less. The productivity of the researcher as well as the level of confidence in the model being analyzed is greatly increased.
\r\n\t\r\nIt has always been a major goal of Caltech to spread the knowledge created here to other universities. However, due to the complexity of STEEL it was difficult for researchers or engineers from other universities to conduct analyses. While SteelConverter did help researchers at Caltech improve their research, sending SteelConverter and its documentation to other universities was less than ideal. Issues of version control, individual computer requirements, and the difficulty of releasing updates made a more centralized solution preferred. This is where the idea for Caltech VirtualShaker was born. Through the creation of a centralized website where users could log in, submit, analyze, and process models in the cloud, all of the major concerns associated with the utilization of SteelConverter were eliminated. Caltech VirtualShaker allows users to create profiles where defaults associated with their most commonly run models are saved, and allows them to submit multiple jobs to an online virtual server to be analyzed and post-processed. The creation of this website not only allowed for more rapid distribution of this tool, but also created a means for engineers and researchers with no access to powerful computer clusters to run computationally intensive analyses without the excessive cost of building and maintaining a computer cluster.
\r\n\t\r\nIn order to increase confidence in the use of STEEL as an analysis system, as well as verify the conversion tools, a series of comparisons were done between STEEL and ETABS. Six models of increasing complexity, ranging from a cantilever column to a twenty-story moment frame, were analyzed to determine the ability of STEEL to accurately calculate basic model properties such as elastic stiffness and damping through a free vibration analysis as well as more complex structural properties such as overall structural capacity through a pushover analysis. These analyses showed a very strong agreement between the two softwares on every aspect of each analysis. However, these analyses also showed the ability of the STEEL analysis algorithm to converge at significantly larger drifts than ETABS when using the more computationally expensive and structurally realistic fiber hinges. Following the ETABS analysis, it was decided to repeat the comparisons in a software more capable of conducting highly nonlinear analysis, called Perform. These analyses again showed a very strong agreement between the two softwares in every aspect of each analysis through instability. However, due to some limitations in Perform, free vibration analyses for the three story one bay chevron brace frame, two bay chevron brace frame, and twenty story moment frame could not be conducted. With the current trend towards ultimate capacity analysis, the ability to use fiber based models allows engineers to gain a better understanding of a building\u2019s behavior under these extreme load scenarios.
\r\n\t\r\nFollowing this, a final study was done on Hall\u2019s U20 structure [1] where the structure was analyzed in all three softwares and their results compared. The pushover curves from each software were compared and the differences caused by variations in software implementation explained. From this, conclusions can be drawn on the effectiveness of each analysis tool when attempting to analyze structures through the point of geometric instability. The analyses show that while ETABS was capable of accurately determining the elastic stiffness of the model, following the onset of inelastic behavior the analysis tool failed to converge. However, for the small number of time steps the ETABS analysis was converging, its results exactly matched those of STEEL, leading to the conclusion that ETABS is not an appropriate analysis package for analyzing a structure through the point of collapse when using fiber elements throughout the model. The analyses also showed that while Perform was capable of calculating the response of the structure accurately, restrictions in the material model resulted in a pushover curve that did not match that of STEEL exactly, particularly post collapse. However, such problems could be alleviated by choosing a more simplistic material model.
\r\n" }, { "name": "Jerves Cobo, Alex Xavier", "degree": "PhD", "year": "2016", "title": "Microscopic Origin of Macroscopic Strength in Granular Media: A Numerical and Analytical Approach", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05042016-174005898", "creators": [ { "name": { "family": "Jerves Cobo", "given": "Alex Xavier" }, "id": "Jerves-Cobo-Alex-Xavier", "orcid": "0000-0002-6556-8727", "display_name": "Jerves Cobo, Alex Xavier" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/Z9GB2211", "abstract": "Constitutive modeling in granular materials has historically been based on macroscopic experimental observations that, while being usually effective at predicting the bulk behavior of these type of materials, suffer important limitations when it comes to understanding the physics behind grain-to-grain interactions that induce the material to macroscopically behave in a given way when subjected to certain boundary conditions.
\r\n\t\r\nThe advent of the discrete element method (DEM) in the late 1970s helped scientists and engineers to gain a deeper insight into some of the most fundamental mechanisms furnishing the grain scale. However, one of the most critical limitations of classical DEM schemes has been their inability to account for complex grain morphologies. Instead, simplified geometries such as discs, spheres, and polyhedra have typically been used. Fortunately, in the last fifteen years, there has been an increasing development of new computational as well as experimental techniques, such as non-uniform rational basis splines (NURBS) and 3D X-ray Computed Tomography (3DXRCT), which are contributing to create new tools that enable the inclusion of complex grain morphologies into DEM schemes.
\r\n\t\r\nYet, as the scientific community is still developing these new tools, there is still a gap in thoroughly understanding the physical relations connecting grain and continuum scales as well as in the development of discrete techniques that can predict the emergent behavior of granular materials without resorting to phenomenology, but rather can directly unravel the micro-mechanical origin of macroscopic behavior.
\r\n\t\r\nIn order to contribute towards closing the aforementioned gap, we have developed a micro-mechanical analysis of macroscopic peak strength, critical state, and residual strength in two-dimensional non-cohesive granular media, where typical continuum constitutive quantities such as frictional strength and dilation angle are explicitly related to their corresponding grain-scale counterparts (e.g., inter-particle contact forces, fabric, particle displacements, and velocities), providing an across-the-scale basis for better understanding and modeling granular media.
\r\n\t\r\nIn the same way, we utilize a new DEM scheme (LS-DEM) that takes advantage of a mathematical technique called level set (LS) to enable the inclusion of real grain shapes into a classical discrete element method. After calibrating LS-DEM with respect to real experimental results, we exploit part of its potential to study the dependency of critical state (CS) parameters such as the critical state line (CSL) slope, CSL intercept, and CS friction angle on the grain's morphology, i.e., sphericity, roundness, and regularity.
\r\n\t\r\nFinally, we introduce a first computational algorithm to ``clone'' the grain morphologies of a sample of real digital grains. This cloning algorithm allows us to generate an arbitrary number of cloned grains that satisfy the same morphological features (e.g., roundness and aspect ratio) displayed by their real parents and can be included into a DEM simulation of a given mechanical phenomenon. In turn, this will help with the development of discrete techniques that can directly predict the engineering scale behavior of granular media without resorting to phenomenology.
\r\n" }, { "name": "Jonsson, Vanessa Danielle", "degree": "PhD", "year": "2016", "title": "Robust Control of Evolutionary Dynamics", "advisor": "Murray, Richard M.; Baltimore, David L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10132015-121212703", "creators": [ { "name": { "family": "Jonsson", "given": "Vanessa Danielle" }, "id": "Jonsson-Vanessa-Danielle", "display_name": "Jonsson, Vanessa Danielle" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Baltimore", "given": "David L." }, "id": "Baltimore-D-L", "role": "co-advisor", "display_name": "Baltimore, David L." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Baltimore", "given": "David L." }, "id": "Baltimore-D-L", "role": "member", "display_name": "Baltimore, David L." }, { "name": { "family": "Bjorkman", "given": "Pamela J." }, "id": "Bjorkman-P-J", "role": "member", "display_name": "Bjorkman, Pamela J." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "cds" ], "doi": "10.7907/Z9NP22CH", "abstract": "The application of principles from evolutionary biology has long been used to gain new insights into the progression and clinical control of both infectious diseases and neoplasms. This iterative evolutionary process consists of expansion, diversification and selection within an adaptive landscape - species are subject to random genetic or epigenetic alterations that result in variations; genetic information is inherited through asexual reproduction and strong selective pressures such as therapeutic intervention can lead to the adaptation and expansion of resistant variants. These principles lie at the center of modern evolutionary synthesis and constitute the primary reasons for the development of resistance and therapeutic failure, but also provide a framework that allows for more effective control.
\r\n\r\nA model system for studying the evolution of resistance and control of therapeutic failure is the treatment of chronic HIV-1 infection by broadly neutralizing antibody (bNAb) therapy. A relatively recent discovery is that a minority of HIV-infected individuals can produce broadly neutralizing antibodies, that is, antibodies that inhibit infection by many strains of HIV. Passive transfer of human antibodies for the prevention and treatment of HIV-1 infection is increasingly being considered as an alternative to a conventional vaccine. However, recent evolution studies have uncovered that antibody treatment can exert selective pressure on virus that results in the rapid evolution of resistance. In certain cases, complete resistance to an antibody is conferred with a single amino acid substitution on the viral envelope of HIV.
\r\n\r\nThe challenges in uncovering resistance mechanisms and designing effective combination strategies to control evolutionary processes and prevent therapeutic failure apply more broadly. We are motivated by two questions: Can we predict the evolution to resistance by characterizing genetic alterations that contribute to modified phenotypic fitness? Given an evolutionary landscape and a set of candidate therapies, can we computationally synthesize treatment strategies that control evolution to resistance?
\r\n\r\nTo address the first question, we propose a mathematical framework to reason about evolutionary dynamics of HIV from computationally derived Gibbs energy fitness landscapes -- expanding the theoretical concept of an evolutionary landscape originally conceived by Sewall Wright to a computable, quantifiable, multidimensional, structurally defined fitness surface upon which to study complex HIV evolutionary outcomes.
\r\n\r\nTo design combination treatment strategies that control evolution to resistance, we propose a methodology that solves for optimal combinations and concentrations of candidate therapies, and allows for the ability to quantifiably explore tradeoffs in treatment design, such as limiting the number of candidate therapies in the combination, dosage constraints and robustness to error. Our algorithm is based on the application of recent results in optimal control to an HIV evolutionary dynamics model and is constructed from experimentally derived antibody resistant phenotypes and their single antibody pharmacodynamics. This method represents a first step towards integrating principled engineering techniques with an experimentally based mathematical model in the rational design of combination treatment strategies and offers predictive understanding of the effects of combination therapies of evolutionary dynamics and resistance of HIV. Preliminary in vitro studies suggest that the combination antibody therapies predicted by our algorithm can neutralize heterogeneous viral populations despite containing resistant mutations.
" }, { "name": "Kaltenboeck, Georg", "degree": "PhD", "year": "2016", "title": "Investigation of Capacitive Discharge Heating of Metallic Glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechTHESIS:05122016-150703449", "creators": [ { "name": { "family": "Kaltenboeck", "given": "Georg" }, "id": "Kaltenboeck-Georg", "display_name": "Kaltenboeck, Georg" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Demetriou", "given": "Marios D." }, "id": "Demetriou-M-D", "role": "member", "display_name": "Demetriou, Marios D." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9251G5Z", "abstract": "In recent years, the discovery of bulk metallic glasses with exceptional properties has generated much interest. One of their most intriguing features is their capacity for viscous flow above the glass transition temperature. This characteristic allows metallic glasses to be formed like plastics at modest temperatures. However, crystallization of supercooled metallic liquids in the best bulk metallic glass-formers is much more rapid than in most polymers and silicate glass-forming liquids. The short times to crystallization impairs experimentation on and processing of supercooled glass-forming metallic liquids. A technique to rapidly and uniformly heat metallic glasses at rates of 105 to 106 kelvin per second is presented. A capacitive discharge is used to ohmically heat metallic glasses to temperatures in the super cooled liquid region in millisecond time-scales. By heating samples rapidly, the most time-consuming step in experiments on supercooled metallic liquids is reduced orders of magnitude in length. This allows for experimentation on and processing of metallic liquids in temperature ranges that were previously inaccessible because of crystallization.
\r\n\r\nA variety of forming techniques, including injection molding and forging, were coupled with capacitive discharge heating to produce near net-shaped metallic glass parts. In addition, a new forming technique, which combines a magnetic field with the heating current to produce a forming force, was developed. Viscosities were measured in previously inaccessible temperature ranges using parallel plate rheometry combined with capacitive discharge heating. Lastly, a rapid pulse calorimeter was developed with this technique to investigate the thermophysical behavior of metallic glasses at these rapid heating rates.
" }, { "name": "Karakus, Gokcan", "degree": "PhD", "year": "2016", "title": "Real-Time Bayesian Analysis of Ground Motion Envelopes for Earthquake Early Warning", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02242016-172347324", "creators": [ { "name": { "family": "Karakus", "given": "Gokcan" }, "id": "Karakus-Gokcan", "display_name": "Karakus, Gokcan" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Ampuero", "given": "Jean-Paul" }, "id": "Ampuero-J-P", "orcid": "0000-0002-4827-7987", "role": "member", "display_name": "Ampuero, Jean-Paul" }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9PN93JS", "abstract": "Current earthquake early warning systems usually make magnitude and location predictions and send out a warning to the users based on those predictions. We describe an algorithm that assesses the validity of the predictions in real-time. Our algorithm monitors the envelopes of horizontal and vertical acceleration, velocity, and displacement. We compare the observed envelopes with the ones predicted by Cua & Heaton's envelope ground motion prediction equations (Cua 2005). We define a \"test function\" as the logarithm of the ratio between observed and predicted envelopes at every second in real-time. Once the envelopes deviate beyond an acceptable threshold, we declare a misfit. Kurtosis and skewness of a time evolving test function are used to rapidly identify a misfit. Real-time kurtosis and skewness calculations are also inputs to both probabilistic (Logistic Regression and Bayesian Logistic Regression) and nonprobabilistic (Least Squares and Linear Discriminant Analysis) models that ultimately decide if there is an unacceptable level of misfit. This algorithm is designed to work at a wide range of amplitude scales. When tested with synthetic and actual seismic signals from past events, it works for both small and large events." }, { "name": "Kim, Hyun-Sik", "degree": "PhD", "year": "2016", "title": "Thermoelectric Properties of Bismuth Antimony Telluride Alloys", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262016-230647147", "creators": [ { "name": { "family": "Kim", "given": "Hyun-Sik" }, "id": "Kim-Hyun-Sik", "orcid": "0000-0001-8934-4042", "display_name": "Kim, Hyun-Sik" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William L." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9RN35V0", "abstract": "Commonly used ozone-depleting refrigerants in refrigerators will be completely phased out in less than 15 years according to the Montreal Protocol. This imminent challenge can be tackled effectively by replacing the current vapor-compression cooling with environmentally sustainable thermoelectric cooling. P-type (Bi0.25Sb0.75)2Te3 alloys have been intensively studied over the past 50 years for cooling applications because of their high thermoelectric performance near room temperature. However, the electronic origin of the high thermoelectric efficiency of (Bi0.25Sb0.75)2Te3 alloys is often understated or ignored completely. In this thesis, the underlying physics of high electronic performance observed in the particular alloy composition, (Bi2Te3).25\u2013(Sb2Te3).75, is investigated. It was demonstrated with two-band transport calculation that the convergence of bands occurred at (Bi2Te3).25\u2013(Sb2Te3).75. A zT improvement of 17 % was also achieved in zone-levelled (Bi0.25Sb.75)2Te3 crystals by controlling their carrier concentration while using the two-band model as a guide. With the optimum electronic efficiency theoretically calculated and achieved experimentally, the thesis moves on to minimize lattice thermal conductivity of (Bi0.25Sb.75)2Te3 for the maximum zT. A new liquid compaction method was devised to produce dense arrays of dislocations in grain boundaries of nanostructured (Bi0.25Sb.75)2Te3. The grain boundary dislocations were found to be highly effective in scattering phonons and a substantial improvement in zT was possible (zT = 1.86 at 320 K). The understanding of phonon scattering by dislocations was in turn applied to phonon scattering at grain boundaries of polycrystalline materials. By demonstrating that the frequency-dependent dislocation scattering can replace the commonly used frequency-independent boundary scattering by Casimir, this thesis suggests that the grain boundary dislocation scattering may be responsible for the mechanism of phonon scattering at grain boundaries. " }, { "name": "Lapointe, Simon", "degree": "PhD", "year": "2016", "title": "Simulation of Premixed Hydrocarbon Flames at High Turbulence Intensities", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-105842881", "creators": [ { "name": { "family": "Lapointe", "given": "Simon" }, "id": "Lapointe-Simon", "display_name": "Lapointe, Simon" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z90V89SW", "abstract": "Turbulent premixed hydrocarbon flames in the thin and distributed reaction zones regimes are simulated using both Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). A series of DNS is performed to study the transition from the thin reaction zones regime to the distributed reaction zones regime. Differential diffusion effects, distributed burning, and local extinctions are quantified. Different fuels, chemical mechanisms, and equivalence ratios are considered. The fuel Lewis number significantly influences the chemical source terms and turbulent flame speeds. More precisely, simulations with differential diffusion effects exhibit lower mean fuel consumption and heat release rates than their unity Lewis number counterparts. However, the differences are reduced as the reaction zone Karlovitz number is increased. The turbulent reaction zone surface areas increase with the turbulence intensity but aren't strongly affected by fuel, equivalence ratio, chemical mechanism, or differential diffusion. Unsurprisingly, changes in the integral length at a fixed Karlovitz number do not affect the chemical source terms but lead to an increase in flame surface area. Assumptions behind closure models for the filtered source term are then studied a priori using the DNS results. Using the concept of optimal estimators, it is shown that a tabulation approach using a progress variable and its variance can predict accurately the filtered progress variable source term. The filtered source terms are compared to predictions from two common presumed sub-filter Probability Density Functions (PDF) models. Both models show deviations from the filtered DNS source terms but predict accurately the mean turbulent flame speed. Finally, LES of experimentally-studied piloted premixed jet flames are performed using tabulated chemistry. Velocity and flame height measurements from simulations and experiments are compared. The LES are in good agreement with the experimental results for the four different hydrocarbon fuels and three different Reynolds numbers simulated. This corroborates that fuel and chemistry effects in turbulent flames are limited to effects present in laminar flames." }, { "name": "Liska, Sebastian", "degree": "PhD", "year": "2016", "title": "Fast Lattice Green's Function Methods for Viscous Incompressible Flows on Unbounded Domains", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:04062016-223108239", "creators": [ { "name": { "family": "Liska", "given": "Sebastian" }, "id": "Liska-Sebastian", "orcid": "0000-0003-4139-9364", "display_name": "Liska, Sebastian" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9ZC80TG", "abstract": "In this thesis, a collection of novel numerical techniques culminating in a fast, parallel method for the direct numerical simulation of incompressible viscous flows around surfaces immersed in unbounded fluid domains is presented. At the core of all these techniques is the use of the fundamental solutions, or lattice Green\u2019s functions, of discrete operators to solve inhomogeneous elliptic difference equations arising in the discretization of the three-dimensional incompressible Navier-Stokes equations on unbounded regular grids. In addition to automatically enforcing the natural free-space boundary conditions, these new lattice Green\u2019s function techniques facilitate the implementation of robust staggered-Cartesian-grid flow solvers with efficient nodal distributions and fast multipole methods. The provable conservation and stability properties of the appropriately combined discretization and solution techniques ensure robust numerical solutions. Numerical experiments on thin vortex rings, low-aspect-ratio flat plates, and spheres are used verify the accuracy, physical fidelity, and computational efficiency of the present formulations." }, { "name": "Liu, Yang", "degree": "PhD", "year": "2016", "title": "Novel Parylene Filters for Biomedical Applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262016-210208370", "creators": [ { "name": { "family": "Liu", "given": "Yang" }, "id": "Liu-Yang-Electrical-Engineering", "display_name": "Liu, Yang" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Goldkorn", "given": "Amir" }, "id": "Goldkorn-A", "role": "member", "display_name": "Goldkorn, Amir" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z97P8WDF", "abstract": "Medical engineering plays a more and more important role in driving the fundamental biology research moving forward. The work presented in this thesis targets at engineer smart parylene filters for various biomedical applications. Three novel parylene membranes are discussed. The first device is parylene magnesium-embedded filter for circulating tumor cells isolation. Circulating tumor cells (CTCs) are cells that slough off the edges of a primary tumor and are swept away by the bloodstream or lymphatic system into the vasculature. They constitute seeds for subsequent growth of additional tumors in vital distant organs, triggering a mechanism that is responsible for the vast majority of cancer-related deaths. Thus CTCs in peripheral blood have been investigated as a valuable biomarker for patients with various types of cancers. However, CTCs are difficult targets to probe owing to their extremely low concentration in peripheral blood. Although rare, CTCs represent a potential approach for the detection, characterization and monitoring of non-haematologic cancers. Therefore, CTCs capture from whole blood has been identified to be an unmet need for cancer research and effective cell separation methods are required to facilitate the study of CTCs. In this study, we developed a novel design applying a buried sacrificial Magnesium (Mg) layer underneath the original microfilter. After filtration, the filter was immersed in DMEM. When the thin-film Mg was dissolved, the cells were released and thus were ready for further biology analysis.
\r\n\r\nThe second device is parylene based microelectrode filter for single-islet electroisletogram. Other than direct insulin injection, one promising treatment for Type I diabetes is islet transplantation. However, one of the key lacking technologies of islet transplantation is high-throughput islet screening since each transplantation requires about one million islets. Islets, which are heterogeneous by nature, are currently screened as whole populations containing a range of functioning and dysfunctional characteristics. This work represents the first attempt to develop a MEMS technology for the screening of every single islet so as to guarantee no bad islet at all, which should improve results of islet transplant therapy. Here we report the first MEMS device designed for in vitro measuring of electroisletogram (EIG) of individual rat islets. Strong EIG signals in millivolt range are obtained. This work proves the feasibility of using MEMS and EIG for high-throughput screening, in contrast to patch-clamp measurements, of islets for transplantation to treat diabetes.
\r\n\r\nThe third device is parylene-on-PDMS membrane for vaccine production. A parylene-on-PDMS design is proposed to supply oxygen to CV-1 cells for vaccine production. Because the cells are seeded and attached right onto the surface of the device, extra oxygen is provided through permeation from the PDMS and thin parylene layers. The permeation is studied and cell growth experiments are performed to demonstrate the feasibility of the device. Compared to commercialized bioreactors, this novel design could have large cell density because oxygen are supplied locally and shear force is not a limiting factor any more.
\r\n\r\nBesides the three devices, parylene properties are also studied and a novel origami design is proposed, which can potentially increase the surface areas of the membranes by fold the 2D flat film into 3D structures. Details are discussed in the following chapters.
" }, { "name": "Liu, Zhao", "degree": "PhD", "year": "2016", "title": "Electromyographic Signal Processing With Application To Spinal Cord Injury", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312016-211459301", "creators": [ { "name": { "family": "Liu", "given": "Zhao" }, "id": "Liu-Zhao", "display_name": "Liu, Zhao" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Edgerton", "given": "V. Reggie" }, "id": "Edgerton-V-R", "role": "member", "display_name": "Edgerton, V. Reggie" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9QJ7F99", "abstract": "An Electromyogram or Electromyographic (EMG) signal is the recording of the electrical activity produced by muscles. It measures the electric currents generated in muscles during their contraction. The EMG signal provides insight into the neural activation and dynamics of the muscles, and is therefore important for many different applications, such as in clinical investigations that attempt to diagnose neuromuscular deficiencies. In particular, the work in this thesis is motivated by rehabilitation for patients with spinal cord injury. The EMG signal is very important for researchers and practitioners to monitor and evaluate the effect of the rehabilitation training and the condition of muscles, as the EMG signal provides information that helps infer the neural activity in the spinal cord. Before the work in this thesis, EMG analysis required significant amounts of manual labeling of interesting signal features. The motivation of this thesis is to fully automate the EMG analysis tasks and yield accurate, consistent results.
\r\n\r\nThe EMG signal contains multiple muscle responses. The difficulty in processing the EMG signal arises from the fact that the transient muscle response is a transient signal with unknown arrival time, unknown duration, and unknown shape. In addition, the EMG signal recorded from patients with spinal cord injury during rehabilitation is very different from the EMG signal of normal healthy people undergoing the same motions. For example, some of the muscle responses are very weak and thus hard to detect. Because of this, general EMG processing tools and methods are either not applicable or insufficient.
\r\n\r\nThe primary contribution of this thesis is the development of a wavelet-based, double-threshold algorithm for the detection of transient peaks in the EMG signal. The application of wavelet transform in the detection of transient signals has been studied extensively and employed successfully. However, most of the theories assume certain knowledge about the shapes of the transient signals, which makes it hard to be generalized to the transient signals with arbitrary shapes. The proposed detection scheme focuses on the more fundamental feature of most transient signals (in particular the EMG signal): peaks, instead of the shapes. The continuous wavelet transform with Mexican Hat wavelet is employed. This thesis theoretically derived a framework for selecting a set of scales based on the frequency domain information. Ridges are identified in the time-scale space to combine the wavelet coefficients from different scales. By imposing two thresholds, one on the wavelet coefficient and one on the ridge length, the proposed detection scheme can achieve both high recall and high precision. A systematic approach for selecting the optimal parameters via simulation is proposed and demonstrated. Comparing with other state-of-the-art detection methods, the proposed method in this thesis yields a better detection performance, especially in the low Signal-to-Noise-Ratio (SNR) environment.
\r\n\r\nBased on the transient peak detection result, the EMG signal is further segmented and classified into various groups of monosynaptic Motor Evoked Potentials (MEPs) and polysynaptic MEPs using techniques stemming from Principal Component Analysis (PCA), hierarchical clustering, and Gaussian mixture model (GMM). A theoretical framework is proposed to segment the EMG signal based on the detected peaks. The scale information of the detected peak is used to derive a measure for its effective support. Several different techniques have been adapted together to solve the clustering problem. An initial hierarchical clustering is first performed to obtain most of the monosynaptic MEPs. PCA is used to reduce the number of features and the effect of the noise. The reduced feature set is then fed to a GMM to further divide the MEPs into different groups of similar shapes. The method of breaking down a segment of multiple consecutive MEPs into individual MEPs is derived.
\r\n\r\nA software with graphic user interface has been implemented in Matlab. The software implements the proposed peak detection algorithm, and enables the physiologists to visualize the detection results and modify them if necessary. The solutions proposed in this thesis are not only helpful to the rehabilitation after spinal cord injury, but applicable to other general processing tasks on transient signals, especially on biological signals.
" }, { "name": "Livingston, Scott Carlton", "degree": "PhD", "year": "2016", "title": "Incremental Control Synthesis for Robotics in the Presence of Temporal Logic Specifications", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12312015-131513787", "creators": [ { "name": { "family": "Livingston", "given": "Scott Carlton" }, "id": "Livingston-Scott-Carlton", "display_name": "Livingston, Scott Carlton" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Holzmann", "given": "Gerard J." }, "id": "Holzmann-G-J", "role": "member", "display_name": "Holzmann, Gerard J." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cds" ], "doi": "10.7907/Z94Q7RW3", "abstract": "This thesis presents methods for incrementally constructing controllers in the presence of uncertainty and nonlinear dynamics. The basic setting is motion planning subject to temporal logic specifications. Broadly, two categories of problems are treated. The first is reactive formal synthesis when so-called discrete abstractions are available. The fragment of linear-time temporal logic (LTL) known as GR(1) is used to express assumptions about an adversarial environment and requirements of the controller. Two problems of changes to a specification are posed that concern the two major aspects of GR(1): safety and liveness. Algorithms providing incremental updates to strategies are presented as solutions. In support of these, an annotation of strategies is developed that facilitates repeated modifications. A variety of properties are proven about it, including necessity of existence and sufficiency for a strategy to be winning. The second category of problems considered is non-reactive (open-loop) synthesis in the absence of a discrete abstraction. Instead, the presented stochastic optimization methods directly construct a control input sequence that achieves low cost and satisfies a LTL formula. Several relaxations are considered as heuristics to address the rarity of sampling trajectories that satisfy an LTL formula and demonstrated to improve convergence rates for Dubins car and single-integrators subject to a recurrence task." }, { "name": "Martinez-Ortiz, Monica Paola", "degree": "PhD", "year": "2016", "title": "Fluid Transport by Aggregations of Small Swimming Organisms", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12232015-091951061", "creators": [ { "name": { "family": "Martinez-Ortiz", "given": "Monica Paola" }, "id": "Martinez-Ortiz-Monica-Paola", "display_name": "Martinez-Ortiz, Monica Paola" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Thompson", "given": "Andrew F." }, "id": "Thompson-A-F", "orcid": "0000-0003-0322-4811", "role": "member", "display_name": "Thompson, Andrew F." }, { "name": { "family": "Zenit Camacho", "given": "Jose Roberto" }, "id": "Zenit-Camacho-J-R", "orcid": "0000-0002-2717-4954", "role": "member", "display_name": "Zenit Camacho, Jose Roberto" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9057CX7", "abstract": "Diel vertical migration of zooplankton has been proposed to affect global ocean circulation to a degree comparable to physical phenomena. Almost a decade after shipboard measurements showed high kinetic energy dissipation rates in the vicinity of migrating krill swarms, the hypothesis that biogenic mixing is relevant to ocean dynamics and local fluid transport has remained controversial due to the inability to directly measure the efficiency of this biological process. In situ field measurements of individual swimming jellyfish have demonstrated large-scale fluid transport via Darwinian drift, but it has remained an open question how this transport mechanism is manifested in smaller species of vertically-migrating zooplankton that are sufficient in number to be accountable in the dynamics. The goals of the present study are, first, to devise and implement experimental instruments and develop methodologies to investigate this biological process in a laboratory setting and, second, to determine whether efficient fluid transport mechanisms become available during vertical collective motion and, if so, analyze how energy is distributed within the flow. By leveraging the phototactic abilities of zooplankton, a multi-laser guidance system was developed to achieve controllable vertical migrations of A. salina concurrently with laser velocimetry of the surrounding flow. Measurements show that the hydrodynamic interactions between neighboring swimmers during vertical migration result in the development of a pronounced jet opposite to animal motion. In non-stratified fluid, this hydrodynamic feature is shown to trigger a Kelvin-Helmholtz instability that results in the generation of eddy-like structures with characteristic length scales much larger than the individual size of the organisms. Experiments in a thermally stratified water column also display the presence of a downward jet despite the strong stable stratification. Furthermore, overturning regions larger than the size of an individual organism are observed adjacent to the migrating aggregation, suggesting an alternate energy transfer route from the small scale of individual swimmers to significantly larger scales, at which mixing can be efficient via a Rayleigh-Taylor instability. The computed velocity spectrum is consistent with these findings and displays energy input at scales larger than the body length of a single swimmer. The mixing efficiency, inferred from the spectral energy distribution with and without stratification, matches experimentally achieved mixing efficiencies via a Rayleigh-Taylor instability within a stable stratification. According to our findings, biogenic mixing does have the potential to redistribute temperature, salinity and nutrients effectively. We propose the employment of laser control to examine additional species as well as alternative oceanic environments and interrogate its effect on the efficiency of biogenic mixing.\r\n" }, { "name": "Matni, Nikolai", "degree": "PhD", "year": "2016", "title": "Distributed Optimal Control of Cyber-Physical Systems: Controller Synthesis, Architecture Design and System Identification", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312016-100604768", "creators": [ { "name": { "family": "Matni", "given": "Nikolai" }, "id": "Matni-Nikolai", "orcid": "0000-0003-4936-3921", "display_name": "Matni, Nikolai" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/Z99884Z0", "abstract": "The centralized paradigm of a single controller and a single plant upon which modern control theory is built is no longer applicable to modern cyber-physical systems of interest, such as the power-grid, software defined networks or automated highways systems, as these are all large-scale and spatially distributed. Both the scale and the distributed nature of these systems has motivated the decentralization of control schemes into local sub-controllers that measure, exchange and act on locally available subsets of the globally available system information. This decentralization of control logic leads to different decision makers acting on asymmetric information sets, introduces the need for coordination between them, and perhaps not surprisingly makes the resulting optimal control problem much harder to solve. In fact, shortly after such questions were posed, it was realized that seemingly simple decentralized optimal control problems are computationally intractable to solve, with the Wistenhausen counterexample being a famous instance of this phenomenon. Spurred on by this perhaps discouraging result, a concerted 40 year effort to identify tractable classes of distributed optimal control problems culminated in the notion of quadratic invariance, which loosely states that if sub-controllers can exchange information with each other at least as quickly as the effect of their control actions propagates through the plant, then the resulting distributed optimal control problem admits a convex formulation.
\r\n\r\nThe identification of quadratic invariance as an appropriate means of \"convexifying\" distributed optimal control problems led to a renewed enthusiasm in the controller synthesis community, resulting in a rich set of results over the past decade. The contributions of this thesis can be seen as being a part of this broader family of results, with a particular focus on closing the gap between theory and practice by relaxing or removing assumptions made in the traditional distributed optimal control framework. Our contributions are to the foundational theory of distributed optimal control, and fall under three broad categories, namely controller synthesis, architecture design and system identification.
\r\n\r\nWe begin by providing two novel controller synthesis algorithms. The first is a solution to the distributed H\u221e optimal control problem subject to delay constraints, and provides the only known exact characterization of delay-constrained distributed controllers satisfying an H\u221e norm bound. The second is an explicit dynamic programming solution to a two player LQR state-feedback problem with varying delays. Accommodating varying delays represents an important first step in combining distributed optimal control theory with the area of Networked Control Systems that considers lossy channels in the feedback loop. Our next set of results are concerned with controller architecture design. When designing controllers for large-scale systems, the architectural aspects of the controller such as the placement of actuators, sensors, and the communication links between them can no longer be taken as given -- indeed the task of designing this architecture is now as important as the design of the control laws themselves. To address this task, we formulate the Regularization for Design (RFD) framework, which is a unifying computationally tractable approach, based on the model matching framework and atomic norm regularization, for the simultaneous co-design of a structured optimal controller and the architecture needed to implement it. Our final result is a contribution to distributed system identification. Traditional system identification techniques such as subspace identification are not computationally scalable, and destroy rather than leverage any a priori information about the system's interconnection structure. We argue that in the context of system identification, an essential building block of any scalable algorithm is the ability to estimate local dynamics within a large interconnected system. To that end we propose a promising heuristic for identifying the dynamics of a subsystem that is still connected to a large system. We exploit the fact that the transfer function of the local dynamics is low-order, but full-rank, while the transfer function of the global dynamics is high-order, but low-rank, to formulate this separation task as a nuclear norm minimization problem. Finally, we conclude with a brief discussion of future research directions, with a particular emphasis on how to incorporate the results of this thesis, and those of optimal control theory in general, into a broader theory of dynamics, control and optimization in layered architectures.
" }, { "name": "Meng, Jomela Chen-Chen", "degree": "PhD", "year": "2016", "title": "Numerical Simulations of Droplet Aerobreakup", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262016-092840941", "creators": [ { "name": { "family": "Meng", "given": "Jomela Chen-Chen" }, "id": "Meng-Jomela-Chen-Chen", "display_name": "Meng, Jomela Chen-Chen" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "member", "display_name": "Austin, Joanna M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9KW5D09", "abstract": "The work presented in this thesis aims to bridge an existing gap in the state of droplet aerobreakup knowledge associated with the fundamental flow physics that govern the experimentally observable droplet morphologies. Using direct numerical simulations of the aerobreakup of water cylinders and droplets in the flow behind shock waves in air, we investigate the behavior of the surrounding gas flow to gain insight into the droplet\u2019s deformation and evolution in the stripping breakup regime. The compressible multicomponent Navier-Stokes equations are solved using the Multicomponent Flow Code \u2014 a high-order accurate structured finite-volume flow solver with shock- and interface-capturing. Following qualitative descriptions of the aerobreakup process, comparisons are made with available experimental data. In 2D, accurate measurements of the cylinder\u2019s center-of-mass acceleration across a range of incident shock Mach numbers allow characterization of the unsteady drag coefficient. Additionally, mass loss measurements from viscous simulations refute a well-known boundary layer stripping theory. The results of a 3D nonaxisymmetric aerobreakup simulation are presented with an emphasis on describing the intricate flow phenomena observable in the wake region. Subsequent analyses of the surface instabilities and a Fourier decomposition of the flow field reveal asymmetrical azimuthal modulations and broadband instability growth that result in the devolution of the wake region into chaotic flow." }, { "name": "Meza, Lucas Rosendo", "degree": "PhD", "year": "2016", "title": "Design, Fabrication, and Mechanical Property Analysis of 3D Nanoarchitected Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232016-115645913", "creators": [ { "name": { "family": "Meza", "given": "Lucas Rosendo" }, "id": "Meza-Lucas-Rosendo", "orcid": "0000-0003-0250-2621", "display_name": "Meza, Lucas Rosendo" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9154F1K", "abstract": "Recent developments in micro- and nanoscale 3D fabrication techniques have enabled the creation of materials with a controllable nanoarchitecture that can have structural features spanning 5 orders of magnitude from tens of nanometers to millimeters. These fabrication methods in conjunction with nanomaterial processing techniques permit a nearly unbounded design space through which new combinations of nanomaterials and architecture can be realized. In the course of this work, we designed, fabricated, and mechanically analyzed a wide range of nanoarchitected materials in the form of nanolattices made from polymer, composite, and hollow ceramic beams. Using a combination of two-photon lithography and atomic layer deposition, we fabricated samples with periodic and hierarchical architectures spanning densities over 4 orders of magnitude from \u03c1=0.3-300kg/m3 and with features as small as 5nm. Uniaxial compression and cyclic loading tests performed on different nanolattice topologies revealed a range of novel mechanical properties: the constituent nanoceramics used here have size-enhanced strengths that approach the theoretical limit of materials strength; hollow aluminum oxide (Al2O3) nanolattices exhibited ductile-like deformation and recovered nearly completely after compression to 50% strain when their wall thicknesses were reduced below 20nm due to the activation of shell buckling; hierarchical nanolattices exhibited enhanced recoverability and a near linear scaling of strength and stiffness with relative density, with E\u221d\u03c11.04 and \u03c3y\u221d\u03c11.17 for hollow Al2O3 samples; periodic rigid and non-rigid nanolattice topologies were tested and showed a nearly uniform scaling of strength and stiffness with relative density, marking a significant deviation from traditional theories on \u201cbending\u201d and \u201cstretching\u201d dominated cellular solids; and the mechanical behavior across all topologies was highly tunable and was observed to strongly correlate with the slenderness \u03bb and the wall thickness-to-radius ratio t/a of the beams. These results demonstrate the potential of nanoarchitected materials to create new highly tunable mechanical metamaterials with previously unattainable properties." }, { "name": "Mital, Utkarsh", "degree": "PhD", "year": "2016", "title": "Understanding Micro- and Macro-Mechanics of Soil Liquefaction: A Necessary Step for Field-Scale Assessment", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05092016-151847908", "creators": [ { "name": { "family": "Mital", "given": "Utkarsh" }, "id": "Mital-Utkarsh", "orcid": "0000-0001-9794-382X", "display_name": "Mital, Utkarsh" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Ampuero", "given": "Jean-Paul" }, "id": "Ampuero-J-P", "orcid": "0000-0002-4827-7987", "role": "member", "display_name": "Ampuero, Jean-Paul" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/Z9PV6HB0", "abstract": "Liquefaction is a devastating instability associated with saturated, loose, and cohesionless soils. It poses a significant risk to distributed infrastructure systems that are vital for the security, economy, safety, health, and welfare of societies. In order to make our cities resilient to the effects of liquefaction, it is important to be able to identify areas that are most susceptible. Some of the prevalent methodologies employed to identify susceptible areas include conventional slope stability analysis and the use of so-called liquefaction charts. However, these methodologies have some limitations, which motivate our research objectives. In this dissertation, we investigate the mechanics of origin of liquefaction in a laboratory test using grain-scale simulations, which helps (i) understand why certain soils liquefy under certain conditions, and (ii) identify a necessary precursor for onset of flow liquefaction. Furthermore, we investigate the mechanics of liquefaction charts using a continuum plasticity model; this can help in modeling the surface hazards of liquefaction following an earthquake. Finally, we also investigate the microscopic definition of soil shear wave velocity, a soil property that is used as an index to quantify liquefaction resistance of soil. We show that anisotropy in fabric, or grain arrangement can be correlated with anisotropy in shear wave velocity. This has the potential to quantify the effects of sample disturbance when a soil specimen is extracted from the field. In conclusion, by developing a more fundamental understanding of soil liquefaction, this dissertation takes necessary steps for a more physical assessment of liquefaction susceptibility at the field-scale." }, { "name": "Mitchell, Sarah Louise", "degree": "PhD", "year": "2016", "title": "Topology Optimization of Silicon Anode Structures for Lithium-Ion Battery Applications", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:02292016-100659735", "creators": [ { "name": { "family": "Mitchell", "given": "Sarah Louise" }, "id": "Mitchell-Sarah-Louise", "display_name": "Mitchell, Sarah Louise" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "chair", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Cirak", "given": "Fehmi" }, "id": "Cirak-F", "role": "member", "display_name": "Cirak, Fehmi" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9JW8BT2", "abstract": "This thesis presents a topology optimization methodology for the systematic design of optimal multifunctional silicon anode structures in lithium-ion batteries. In order to develop next generation high performance lithium-ion batteries, key design challenges relating to the silicon anode structure must be addressed, namely the lithiation-induced mechanical degradation and the low intrinsic electrical conductivity of silicon. As such, this work considers two design objectives of minimum compliance under design dependent volume expansion, and maximum electrical conduction through the structure, both of which are subject to a constraint on material volume. Density-based topology optimization methods are employed in conjunction with regularization techniques, a continuation scheme, and mathematical programming methods. The objectives are first considered individually, during which the iteration history, mesh independence, and influence of prescribed volume fraction and minimum length scale are investigated. The methodology is subsequently extended to a bi-objective formulation to simultaneously address both the compliance and conduction design criteria. A weighting method is used to derive the Pareto fronts, which demonstrate a clear trade-off between the competing design objectives. Furthermore, a systematic parameter study is undertaken to determine the influence of the prescribed volume fraction and minimum length scale on the optimal combined topologies. The developments presented in this work provide a foundation for the informed design and development of silicon anode structures for high performance lithium-ion batteries. " }, { "name": "Mitchell, Stephanie Jane", "degree": "PhD", "year": "2016", "title": "Metaconcrete: Engineered Aggregates for Enhanced Dynamic Performance", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:07072015-124133131", "creators": [ { "name": { "family": "Mitchell", "given": "Stephanie Jane" }, "id": "Mitchell-Stephanie-Jane", "orcid": "0000-0002-7303-8216", "display_name": "Mitchell, Stephanie Jane" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pandolfi", "given": "Anna" }, "id": "Pandolfi-A", "role": "member", "display_name": "Pandolfi, Anna" } ], "option_major": [ "space" ], "doi": "10.7907/Z9H12ZXN", "abstract": "This work presents the development and investigation of a new type of concrete for the attenuation of waves induced by dynamic excitation. Recent progress in the field of metamaterials science has led to a range of novel composites which display unusual properties when interacting with electromagnetic, acoustic, and elastic waves. A new structural metamaterial with enhanced properties for dynamic loading applications is presented, which is named metaconcrete. In this new composite material the standard stone and gravel aggregates of regular concrete are replaced with spherical engineered inclusions. Each metaconcrete aggregate has a layered structure, consisting of a heavy core and a thin compliant outer coating. This structure allows for resonance at or near the eigenfrequencies of the inclusions, and the aggregates can be tuned so that resonant oscillations will be activated by particular frequencies of an applied dynamic loading. The activation of resonance within the aggregates causes the overall system to exhibit negative effective mass, which leads to attenuation of the applied wave motion. To investigate the behavior of metaconcrete slabs under a variety of different loading conditions a finite element slab model containing a periodic array of aggregates is utilized. The frequency dependent nature of metaconcrete is investigated by considering the transmission of wave energy through a slab, which indicates the presence of large attenuation bands near the resonant frequencies of the aggregates. Applying a blast wave loading to both an elastic slab and a slab model that incorporates the fracture characteristics of the mortar matrix reveals that a significant portion of the supplied energy can be absorbed by aggregates which are activated by the chosen blast wave profile. The transfer of energy from the mortar matrix to the metaconcrete aggregates leads to a significant reduction in the maximum longitudinal stress, greatly improving the ability of the material to resist damage induced by a propagating shock wave. The various analyses presented in this work provide the theoretical and numerical background necessary for the informed design and development of metaconcrete aggregates for dynamic loading applications, such as blast shielding, impact protection, and seismic mitigation." }, { "name": "Montemayor, Lauren Christine", "degree": "PhD", "year": "2016", "title": "Fabrication, Characterization, And Deformation of 3D Structural Meta-Materials ", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07132015-150843708", "creators": [ { "name": { "family": "Montemayor", "given": "Lauren Christine" }, "id": "Montemayor-Lauren-Christine", "display_name": "Montemayor, Lauren Christine" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "space" ], "doi": "10.7907/Z9D21VH2", "abstract": "Current technological advances in fabrication methods have provided pathways to creating architected structural meta-materials similar to those found in natural organisms that are structurally robust and lightweight, such as diatoms. Structural meta-materials are materials with mechanical properties that are determined by material properties at various length scales, which range from the material microstructure (nm) to the macro-scale architecture (\u03bcm \u2013 mm). It is now possible to exploit material size effect, which emerge at the nanometer length scale, as well as structural effects to tune the material properties and failure mechanisms of small-scale cellular solids, such as nanolattices. \r\nThis work demonstrates the fabrication and mechanical properties of 3-dimensional hollow nanolattices in both tension and compression. Hollow gold nanolattices loaded in uniaxial compression demonstrate that strength and stiffness vary as a function of geometry and tube wall thickness. Structural effects were explored by increasing the unit cell angle from 30\u00b0 to 60\u00b0 while keeping all other parameters constant; material size effects were probed by varying the tube wall thickness, t, from 200nm to 635nm, at a constant relative density and grain size. In-situ uniaxial compression experiments reveal an order-of-magnitude increase in yield stress and modulus in nanolattices with greater lattice angles, and a 150% increase in the yield strength without a concomitant change in modulus in thicker-walled nanolattices for fixed lattice angles. These results imply that independent control of structural and material size effects enables tunability of mechanical properties of 3-dimensional architected meta-materials and highlight the importance of material, geometric, and microstructural effects in small-scale mechanics. \r\nThis work also explores the flaw tolerance of 3D hollow-tube alumina kagome nanolattices with and without pre-fabricated notches, both in experiment and simulation. Experiments demonstrate that the hollow kagome nanolattices in uniaxial tension always fail at the same load when the ratio of notch length (a) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. For notches with (a/w) > 1/3, the samples fail at lower peak loads and this is attributed to the increased compliance as fewer unit cells span the un-notched region. Finite element simulations of the kagome tension samples show that the failure is governed by tensile loading for (a/w) < 1/3 but as (a/w) increases, bending begins to play a significant role in the failure. This work explores the flaw sensitivity of hollow alumina kagome nanolattices in tension, using experiments and simulations, and demonstrates that the discrete-continuum duality of architected structural meta-materials gives rise to their flaw insensitivity even when made entirely of intrinsically brittle materials.\r\n" }, { "name": "Natsiavas, Panagiotis Philippos", "degree": "PhD", "year": "2016", "title": "Stability of Electrode-Electrolyte Interfaces During Charging in Lithium Batteries", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:11222015-173649284", "creators": [ { "name": { "family": "Natsiavas", "given": "Panagiotis Philippos" }, "id": "Natsiavas-Panagiotis-Philippos", "display_name": "Natsiavas, Panagiotis Philippos" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Weinberg", "given": "Kerstin" }, "id": "Weinberg-K", "role": "member", "display_name": "Weinberg, Kerstin" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z93R0QR8", "abstract": "In this thesis we study the growth of a Li electrode-electrolyte interface in the presence of an elastic prestress. In particular, we focus our interest on Li-air batteries with a solid electrolyte, LIPON, which is a new type of secondary or rechargeable battery. Theoretical studies and experimental evidence show that during the process of charging the battery the replated lithium adds unevenly to the electrode surface. This phenomenon eventually leads to dendrite formation as the battery is charged and discharged numerous times. In order to suppress or alleviate this deleterious effect of dendrite growth, we put forth a study based on a linear stability analysis. Taking into account all the mechanisms of mass transport and interfacial kinetics, we model the evolution of the interface. We find that, in the absence of stress, the stability of a planar interface depends on interfacial diffusion properties and interfacial energy. Specifically, if Herring-Mullins capillarity-driven interfacial diffusion is accounted for, interfaces are unstable against all perturbations of wavenumber larger than a critical value. We find that the effect of an elastic prestress is always to stabilize planar interfacial growth by increasing the critical wavenumber for instability. A parametric study results in quantifying the extent of the prestress stabilization in a manner that can potentially be used in the design of Li-air batteries. Moreover, employing the theory of finite differences we numerically solve the equation that describes the evolution of the surface profile and present visualization results of the surface evolution by time. Lastly, numerical simulations performed in a commercial finite element software validate the theoretical formulation of the interfacial elastic energy change with respect to the planar interface." }, { "name": "Ou, Xiaoze", "degree": "PhD", "year": "2016", "title": "Computational Microscopy: Breaking the Limit of Conventional Optics", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04282016-051723211", "creators": [ { "name": { "family": "Ou", "given": "Xiaoze" }, "id": "Ou-Xiaoze", "orcid": "0000-0001-9918-0221", "display_name": "Ou, Xiaoze" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "member", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Cai", "given": "Long" }, "id": "Cai-Long", "role": "member", "display_name": "Cai, Long" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9M32SRZ", "abstract": "Computational imaging is flourishing thanks to the recent advancement in array photodetectors and image processing algorithms. This thesis presents Fourier ptychography, which is a computational imaging technique implemented in microscopy to break the limit of conventional optics. With the implementation of Fourier ptychography, the resolution of the imaging system can surpass the diffraction limit of the objective lens's numerical aperture; the quantitative phase information of a sample can be reconstructed from intensity-only measurements; and the aberration of a microscope system can be characterized and computationally corrected. This computational microscopy technique enhances the performance of conventional optical systems and expands the scope of their applications." }, { "name": "Papusha, Ivan Igorevych", "degree": "PhD", "year": "2016", "title": "Robustness, Adaptation, and Learning in Optimal Control", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032016-102336160", "creators": [ { "name": { "family": "Papusha", "given": "Ivan Igorevych" }, "id": "Papusha-Ivan-Igorevych", "display_name": "Papusha, Ivan Igorevych" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Lavretsky", "given": "Eugene" }, "id": "Lavretsky-Eugene", "role": "member", "display_name": "Lavretsky, Eugene" } ], "option_major": [ "cds" ], "doi": "10.7907/Z9F18WPB", "abstract": "Recent technological advances have opened the door to a wide variety of dynamic control applications, which are enabled by increasing computational power in ever smaller devices. These advances are backed by reliable optimization algorithms that allow specification, synthesis, and embedded implementation of sophisticated learning-based controllers. However, as control systems become more pervasive, dynamic, and complex, the control algorithms governing them become more complex to design and analyze. In many cases, optimal control policies are practically impossible to determine unless the state dimension is small, or the dynamics are simple. Thus, in order to make implementation progress, the control designer must specialize to suboptimal architectures and approximate control. The major engineering challenge in the upcoming decades will be how to cope with the complexity of designing implementable control architectures for these smart systems while certifying their safety, robustness, and performance.
\r\n\r\nThis thesis tackles the design and verification complexity by carefully employing tractable lower and upper bounds on the Lyapunov function, while making connections to robust control, formal synthesis, and machine learning. Specifically, optimization-based upper bounds are used to specify robust controllers, while lower bounds are used to obtain performance bounds and to synthesize approximately optimal policies. Implementation of these bounds depends critically on carrying out learning and optimization in the loop. Examples in aerospace, formal methods, hybrid systems, and networked adaptive systems are given, and novel sources of identifiability and persistence of excitation are discussed.
" }, { "name": "Park, Soyoung", "degree": "PhD", "year": "2016", "title": "Connectivity and Function of the Primate Insula", "advisor": "Allman, John Morgan; Adolphs, Ralph", "url": "https://resolver.caltech.edu/CaltechTHESIS:01242016-181117777", "creators": [ { "name": { "family": "Park", "given": "Soyoung" }, "id": "Park-Soyoung", "orcid": "0000-0002-3761-7229", "display_name": "Park, Soyoung" } ], "advisors": [ { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "advisor", "display_name": "Allman, John Morgan" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "advisor", "display_name": "Adolphs, Ralph" } ], "committee": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "chair", "display_name": "O'Doherty, John P." }, { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "member", "display_name": "Quartz, Steven R." }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "member", "display_name": "Adolphs, Ralph" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9F47M2M", "abstract": "The insula is a mammalian cortical structure that has been implicated in a wide range of low- and high-level functions governing one\u2019s sensory, emotional, and cognitive experiences. One particular role of this region is considered to be processing of olfactory stimuli. The ability to detect and evaluate odors has significant effects on an organism\u2019s eating behavior and survival and, in case of humans, on complex decision making. Despite such importance of this function, the mechanism in which olfactory information is processed in the insula has not been thoroughly studied. Moreover, due to the structure\u2019s close spatial relationship with the neighboring claustrum, it is not entirely clear whether the connectivity and olfactory functions attributed to the insula are truly those of the insula, rather than of the claustrum. My graduate work, consisting of two studies, seeks to help fill these gaps. In the first, the structural connectivity patterns of the insula and the claustrum in a non-human primate brain is assayed using an ultra-high-quality diffusion magnetic resonance image, and the results suggest dissociation of connectivity \u2014 and hence function \u2014 between the two structures. In the second study, a functional neuroimaging experiment investigates the insular activity during odor evaluation tasks in humans, and uncovers a potential spatial organization within the anterior portion of the insula for processing different aspects of odor characteristics." }, { "name": "Peng, Qiuyu", "degree": "PhD", "year": "2016", "title": "Distributed Control and Optimization for Communication and Power Systems", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01262016-194420781", "creators": [ { "name": { "family": "Peng", "given": "Qiuyu" }, "id": "Peng-Qiuyu", "display_name": "Peng, Qiuyu" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z99C6VBW", "abstract": "We are at the cusp of a historic transformation of both communication system and electricity system. This creates challenges as well as opportunities for the study of networked systems. Problems of these systems typically involve a huge number of end points that require intelligent coordination in a distributed manner. In this thesis, we develop models, theories, and scalable distributed optimization and control algorithms to overcome these challenges.
\r\n\r\nThis thesis focuses on two specific areas: multi-path TCP (Transmission Control Protocol) and electricity distribution system operation and control. Multi-path TCP (MP-TCP) is a TCP extension that allows a single data stream to be split across multiple paths. MP-TCP has the potential to greatly improve reliability as well as efficiency of communication devices. We propose a fluid model for a large class of MP-TCP algorithms and identify design criteria that guarantee the existence, uniqueness, and stability of system equilibrium. We clarify how algorithm parameters impact TCP-friendliness, responsiveness, and window oscillation and demonstrate an inevitable tradeoff among these properties. We discuss the implications of these properties on the behavior of existing algorithms and motivate a new algorithm Balia (balanced linked adaptation) which generalizes existing algorithms and strikes a good balance among TCP-friendliness, responsiveness, and window oscillation. We have implemented Balia in the Linux kernel. We use our prototype to compare the new proposed algorithm Balia with existing MP-TCP algorithms.
\r\n\r\nOur second focus is on designing computationally efficient algorithms for electricity distribution system operation and control. First, we develop efficient algorithms for feeder reconfiguration in distribution networks. The feeder reconfiguration problem chooses the on/off status of the switches in a distribution network in order to minimize a certain cost such as power loss. It is a mixed integer nonlinear program and hence hard to solve. We propose a heuristic algorithm that is based on the recently developed convex relaxation of the optimal power flow problem. The algorithm is efficient and can successfully computes an optimal configuration on all networks that we have tested. Moreover we prove that the algorithm solves the feeder reconfiguration problem optimally under certain conditions. We also propose a more efficient algorithm and it incurs a loss in optimality of less than 3% on the test networks.
\r\n\r\nSecond, we develop efficient distributed algorithms that solve the optimal power flow (OPF) problem on distribution networks. The OPF problem determines a network operating point that minimizes a certain objective such as generation cost or power loss. Traditionally OPF is solved in a centralized manner. With increasing penetration of volatile renewable energy resources in distribution systems, we need faster and distributed solutions for real-time feedback control. This is difficult because power flow equations are nonlinear and kirchhoff's law is global. We propose solutions for both balanced and unbalanced radial distribution networks. They exploit recent results that suggest solving for a globally optimal solution of OPF over a radial network through a second-order cone program (SOCP) or semi-definite program (SDP) relaxation. Our distributed algorithms are based on the alternating direction method of multiplier (ADMM), but unlike standard ADMM-based distributed OPF algorithms that require solving optimization subproblems using iterative methods, the proposed solutions exploit the problem structure that greatly reduce the computation time. Specifically, for balanced networks, our decomposition allows us to derive closed form solutions for these subproblems and it speeds up the convergence by 1000x times in simulations. For unbalanced networks, the subproblems reduce to either closed form solutions or eigenvalue problems whose size remains constant as the network scales up and computation time is reduced by 100x compared with iterative methods.
" }, { "name": "Runnels, Brandon Scott", "degree": "PhD", "year": "2016", "title": "A Model for Energy and Morphology of Crystalline Grain Boundaries with Arbitrary Geometric Character", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:07082015-130125061", "creators": [ { "name": { "family": "Runnels", "given": "Brandon Scott" }, "id": "Runnels-Brandon-Scott", "orcid": "0000-0003-3043-5227", "display_name": "Runnels, Brandon Scott" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9KS6PHP ", "abstract": "It has been well-established that interfaces in crystalline materials are key players in the mechanics of a variety of mesoscopic processes such as solidification, recrystallization, grain boundary migration, and severe plastic deformation. In particular, interfaces with complex morphologies have been observed to play a crucial role in many micromechanical phenomena such as grain boundary migration, stability, and twinning. Interfaces are a unique type of material defect in that they demonstrate a breadth of behavior and characteristics eluding simplified descriptions. Indeed, modeling the complex and diverse behavior of interfaces is still an active area of research, and to the author's knowledge there are as yet no predictive models for the energy and morphology of interfaces with arbitrary character. The aim of this thesis is to develop a novel model for interface energy and morphology that i) provides accurate results (especially regarding \"energy cusp\" locations) for interfaces with arbitrary character, ii) depends on a small set of material parameters, and iii) is fast enough to incorporate into large scale simulations.
\r\n\r\nIn the first half of the work, a model for planar, immiscible grain boundary is formulated. By building on the assumption that anisotropic grain boundary energetics are dominated by geometry and crystallography, a construction on lattice density functions (referred to as \"covariance\") is introduced that provides a geometric measure of the order of an interface. Covariance forms the basis for a fully general model of the energy of a planar interface, and it is demonstrated by comparison with a wide selection of molecular dynamics energy data for FCC and BCC tilt and twist boundaries that the model accurately reproduces the energy landscape using only three material parameters. It is observed that the planar constraint on the model is, in some cases, over-restrictive; this motivates an extension of the model.
\r\n\r\nIn the second half of the work, the theory of faceting in interfaces is developed and applied to the planar interface model for grain boundaries. Building on previous work in mathematics and materials science, an algorithm is formulated that returns the minimal possible energy attainable by relaxation and the corresponding relaxed morphology for a given planar energy model. It is shown that the relaxation significantly improves the energy results of the planar covariance model for FCC and BCC tilt and twist boundaries. The ability of the model to accurately predict faceting patterns is demonstrated by comparison to molecular dynamics energy data and experimental morphological observation for asymmetric tilt grain boundaries. It is also demonstrated that by varying the temperature in the planar covariance model, it is possible to reproduce a priori the experimentally observed effects of temperature on facet formation.
\r\n\r\nFinally, the range and scope of the covariance and relaxation models, having been demonstrated by means of extensive MD and experimental comparison, future applications and implementations of the model are explored.
" }, { "name": "Saeedi, Saman", "degree": "PhD", "year": "2016", "title": "Holistic Design In High-Speed Optical Interconnects", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:10212015-150203289", "creators": [ { "name": { "family": "Saeedi", "given": "Saman" }, "id": "Saeedi-Saman", "display_name": "Saeedi, Saman" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9K935HH", "abstract": "Integrated circuit scaling has enabled a huge growth in processing capability, which necessitates a corresponding increase in inter-chip communication bandwidth. As bandwidth requirements for chip-to-chip interconnection scale, deficiencies of electrical channels become more apparent. Optical links present a viable alternative due to their low frequency-dependent loss and higher bandwidth density in the form of wavelength division multiplexing. As integrated photonics and bonding technologies are maturing, commercialization of hybrid-integrated optical links are becoming a reality. Increasing silicon integration leads to better performance in optical links but necessitates a corresponding co-design strategy in both electronics and photonics. In this light, holistic design of high-speed optical links with an in-depth understanding of photonics and state-of-the-art electronics brings their performance to unprecedented levels. This thesis presents developments in high-speed optical links by co-designing and co-integrating the primary elements of an optical link: receiver, transmitter, and clocking.
\r\n\r\nIn the first part of this thesis a 3D-integrated CMOS/Silicon-photonic receiver will be presented. The electronic chip features a novel design that employs a low-bandwidth TIA front-end, double-sampling and equalization through dynamic offset modulation. Measured results show -14.9dBm of sensitivity and energy efficiency of 170fJ/b at 25Gb/s. The same receiver front-end is also used to implement source-synchronous 4-channel WDM-based parallel optical receiver. Quadrature ILO-based clocking is employed for synchronization and a novel frequency-tracking method that exploits the dynamics of IL in a quadrature ring oscillator to increase the effective locking range. An adaptive body-biasing circuit is designed to maintain the per-bit-energy consumption constant across wide data-rates. The prototype measurements indicate a record-low power consumption of 153fJ/b at 32Gb/s. The receiver sensitivity is measured to be -8.8dBm at 32Gb/s.
\r\n\r\nNext, on the optical transmitter side, three new techniques will be presented. First one is a differential ring modulator that breaks the optical bandwidth/quality factor trade-off known to limit the speed of high-Q ring modulators. This structure maintains a constant energy in the ring to avoid pattern-dependent power droop. As a first proof of concept, a prototype has been fabricated and measured up to 10Gb/s. The second technique is thermal stabilization of micro-ring resonator modulators through direct measurement of temperature using a monolithic PTAT temperature sensor. The measured temperature is used in a feedback loop to adjust the thermal tuner of the ring. A prototype is fabricated and a closed-loop feedback system is demonstrated to operate at 20Gb/s in the presence of temperature fluctuations. The third technique is a switched-capacitor based pre-emphasis technique designed to extend the inherently low bandwidth of carrier injection micro-ring modulators. A measured prototype of the optical transmitter achieves energy efficiency of 342fJ/bit at 10Gb/s and the wavelength stabilization circuit based on the monolithic PTAT sensor consumes 0.29mW.
\r\n\r\nLastly, a first-order frequency synthesizer that is suitable for high-speed on-chip clock generation will be discussed. The proposed design features an architecture combining an LC quadrature VCO, two sample-and-holds, a PI, digital coarse-tuning, and rotational frequency detection for fine-tuning. In addition to an electrical reference clock, as an extra feature, the prototype chip is capable of receiving a low jitter optical reference clock generated by a high-repetition-rate mode-locked laser. The output clock at 8GHz has an integrated RMS jitter of 490fs, peak-to-peak periodic jitter of 2.06ps, and total RMS jitter of 680fs. The reference spurs are measured to be \u201364.3dB below the carrier frequency. At 8GHz the system consumes 2.49mW from a 1V supply.
" }, { "name": "Sauerbrei, Britton Alan", "degree": "PhD", "year": "2016", "title": "Firing Patterns of Cerebellar Purkinje Cells During Locomotion and Sleep", "advisor": "Siapas, Athanassios G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12012015-143528464", "creators": [ { "name": { "family": "Sauerbrei", "given": "Britton Alan" }, "id": "Sauerbrei-Britton-Alan", "display_name": "Sauerbrei, Britton Alan" } ], "advisors": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "advisor", "display_name": "Siapas, Athanassios G." } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "role": "member", "display_name": "Sternberg, Paul W." }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "member", "display_name": "Siapas, Athanassios G." } ], "option_major": [ "cns" ], "doi": "10.7907/Z9G15XS8", "abstract": "The cerebellum is a major supraspinal center involved in the coordination of movement. The principal neurons of the cerebellar cortex, Purkinje cells, receive excitatory synaptic input from two sources: the parallel and climbing fibers. These pathways have markedly different effects: the parallel fibers control the rate of simple sodium spikes, while the climbing fibers induce characteristic complex spike bursts, which are accompanied by dendritic calcium transients and play a key role in regulating synaptic plasticity. While many studies using a variety of species, behaviors, and cerebellar regions have documented modulation in Purkinje cell activity during movement, few have attempted to record from these neurons in unrestrained rodents. In this dissertation, we use chronic, multi-tetrode recording in freely-behaving rats to study simple and complex spike firing patterns during locomotion and sleep. Purkinje cells discharge rhythmically during stepping, but this activity is highly variable across steps. We show that behavioral variables systematically influence the step-locked firing rate in a step-phase-dependent way, revealing a functional clustering of Purkinje cells. Furthermore, we find a pronounced disassociation between patterns of variability driven by the parallel and climbing fibers, as well as functional differences between cerebellar lobules. These results suggest that Purkinje cell activity not only represents step phase within each cycle, but is also shaped by behavior across steps, facilitating control of movement under dynamic conditions. During sleep, we observe an attenuation of both simple and complex spiking, relative to awake behavior. Although firing rates during slow wave sleep (SWS) and rapid eye movement sleep (REM) are similar, simple spike activity is highly regular in SWS, while REM is characterized by phasic increases and pauses in simple spiking. This phasic activity in REM is associated with pontine waves, which propagate into the cerebellar cortex and modulate both simple and complex spiking. Such a temporal coincidence between parallel and climbing fiber activity is known to drive plasticity at parallel fiber synapses; consequently, pontocerebellar waves may provide a mechanism for tuning synaptic weights in the cerebellum during active sleep." }, { "name": "Schmidt, Bryan Eric", "degree": "PhD", "year": "2016", "title": "On the Stability of Supersonic Boundary Layers with Injection", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252016-141702166", "creators": [ { "name": { "family": "Schmidt", "given": "Bryan Eric" }, "id": "Schmidt-Bryan-Eric", "orcid": "0000-0001-9193-7760", "display_name": "Schmidt, Bryan Eric" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Austin", "given": "Joanna M." }, "id": "Austin-J-M", "orcid": "0000-0003-3129-5035", "role": "chair", "display_name": "Austin, Joanna M." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z93X84M6", "abstract": "The problem of supersonic flow over a 5 degree half-angle cone with injection of gas through a porous section on the body into the boundary layer is studied experimentally. Three injected gases are used: helium, nitrogen, and RC318 (octafluorocyclobutane). Experiments are performed in a Mach 4 Ludwieg tube with nitrogen as the free stream gas. Shaping of the injector section relative to the rest of the body is found to admit a \"tuned\" injection rate which minimizes the strength of shock waves formed by injection. A high-speed schlieren imaging system with a framing rate of 290 kHz is used to study the instability in the region of flow downstream of\r\ninjection, referred to as the injection layer. This work provides the first experimental data on the wavelength, convective speed, and frequency of the instability in such a flow. The stability characteristics of the injection layer are found to be very similar to those of a free shear layer. The findings of this work present a new paradigm for future stability analyses of supersonic flow with injection." }, { "name": "Shankar, Krishna", "degree": "PhD", "year": "2016", "title": "Kinematics and Local Motion Planning for Quasi-static Whole-body Mobile Manipulation", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222016-095145651", "creators": [ { "name": { "family": "Shankar", "given": "Krishna" }, "id": "Shankar-Krishna", "display_name": "Shankar, Krishna" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Hudson", "given": "Nicolas H." }, "id": "Hudson-N-H", "role": "member", "display_name": "Hudson, Nicolas H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9KK98RX", "abstract": "This thesis studies mobile robotic manipulators, where one or more robot manipulator arms are\r\nintegrated with a mobile robotic base. The base could be a wheeled or tracked vehicle, or it might be a\r\nmulti-limbed locomotor. As robots are increasingly deployed in complex and unstructured environments,\r\nthe need for mobile manipulation increases. Mobile robotic assistants have the potential to revolutionize human\r\nlives in a large variety of settings including home, industrial and outdoor environments.
\r\n\r\nMobile Manipulation is the use or study of such mobile robots as they interact with physical\r\nobjects in their environment. As compared to fixed base manipulators, mobile manipulators can take\r\nadvantage of the base mechanism\u2019s added degrees of freedom in the task planning and execution process.\r\nBut their use also poses new problems in the analysis and control of base system stability, and the\r\nplanning of coordinated base and arm motions. For mobile manipulators to be successfully and\r\nefficiently used, a thorough understanding of their kinematics, stability, and capabilities is required.\r\nMoreover, because mobile manipulators typically possess a large number of actuators, new and efficient\r\nmethods to coordinate their large numbers of degrees of freedom are needed to make them practically\r\ndeployable. This thesis develops new kinematic and stability analyses of mobile manipulation, and new\r\nalgorithms to efficiently plan their motions.
\r\n\r\nI first develop detailed and novel descriptions of the kinematics governing the operation of multi-\r\nlimbed legged robots working in the presence of gravity, and whose limbs may also be simultaneously\r\nused for manipulation. The fundamental stance constraint that arises from simple assumptions about\r\nfriction and the ground contact and feasible motions is derived. Thereafter, a local relationship between\r\njoint motions and motions of the robot abdomen and reaching limbs is developed. Baseeon these\r\nrelationships, one can define and analyze local kinematic qualities including limberness, wrench\r\nresistance and local dexterity. While previous researchers have noted the similarity between multi-\r\nfingered grasping and quasi-static manipulation, this thesis makes explicit connections between these two\r\nproblems.
\r\n\r\nThe kinematic expressions form the basis for a local motion planning problem that that\r\ndetermines the joint motions to achieve several simultaneous objectives while maintaining stance stability\r\nin the presence of gravity. This problem is translated into a convex quadratic program entitled the\r\nbalanced priority solution, whose existence and uniqueness properties are developed. This problem is\r\nrelated in spirit to the classical redundancy resoxlution and task-priority approaches. With some simple\r\nmodifications, this local planning and optimization problem can be extended to handle a large variety of\r\ngoals and constraints that arise in mobile-manipulation. This local planning problem applies readily to\r\nother mobile bases including wheeled and articulated bases. This thesis describes the use of the local\r\nplanning techniques to generate global plans, as well as for use within a feedback loop. The work in this\r\nthesis is motivated in part by many practical tasks involving the Surrogate and RoboSimian robots at\r\nNASA/JPL, and a large number of examples involving the two robots, both real and simulated, are\r\nprovided.
\r\n\r\nFinally, this thesis provides an analysis of simultaneous force and motion control for multi-\r\nlimbed legged robots. Starting with a classical linear stiffness relationship, an analysis of this problem for\r\nmultiple point contacts is described. The local velocity planning problem is extended to include\r\ngeneration of forces, as well as to maintain stability using force-feedback. This thesis also provides a\r\nconcise, novel definition of static stability, and proves some conditions under which it is satisfied.
" }, { "name": "Shing, Amanda M.", "degree": "PhD", "year": "2016", "title": "Development of Zn-IV-Nitride Semiconductor Materials and Devices", "advisor": "Lewis, Nathan Saul; Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-161721247", "creators": [ { "name": { "family": "Shing", "given": "Amanda M." }, "id": "Shing-Amanda-M", "display_name": "Shing, Amanda M." } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "co-advisor", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "co-advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "chair", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "co-chair", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z94Q7RXJ", "abstract": "This thesis details explorations of the materials and device fabrication of Zn-IV-Nitride thin-films. Motivation in studying this materials series originates from its analgous properties to the III-Nitride semiconductor materials and its potential applications in photonic devices such as solar cells, light emitting diodes, and optical sensors. Building off of initial fabrication work from Coronel, Lahourcade et al., ZnSnxGe1-xN2 thin-films have shown to be a non-phase-segregating, tunable alloy series and a possible earth-abundant alternative to InxGa1-xN alloys. This thesis discusses further developments in fabrication of ZnSnxGe1-xN2 alloys by three-target co-sputtering and molecular beam epitaxy, and the resulting structural and optoelectronic characterization. Devices from these developed alloys are also highlighted.
\r\n\r\nInitial fabrication was based on the reactive radio-frequency (RF) sputtering technique and was limited to two-target sources and produced nanocrystalline films. Progression to three-target reactive RF co-sputtering for ZnSnxGe1-xN2 (x < 1) alloys is presented, where three-target co-sputtered alloys follow the structural and optoelectronic trends of the initial alloy series. However, three-target co-sputtering further enabled synthesis of alloys having < 10% atomic composition (x < 0.4) of tin, exhibiting non-degenerate doping. The electronic structure of sputtered thin-film surfaces for the alloy series were also characterized by photoelectron spectroscopy to measure their work functions and relative band alignment for device implementation.
\r\n\r\nLow electronic mobilities, degenerate carrier concentrations, and limited photoresponse may stem from the defective and nanocrystalline nature of the sputtered films. To improve crystalline quality, films were grown by molecular beam epitaxy (MBE). MBE ZnSnxGe1-xN2 films on sapphire and GaN were epitaxially grown, overall displaying single-crystalline quality films, higher electronic mobilities, and lower carrier concentrations. Througout experimentation, devices from both sputter deposited and MBE ZnSnxGe1-xN2 alloys films were constructed. Attempts at solid-state and electrochemical devices are described. Devices exhibited some photoresponse, providing a positive outlook for employment of ZnSnxGe1-xN2 alloys in solar cells or photon sensors.
\r\n" }, { "name": "Tang, Yinglu", "degree": "PhD", "year": "2016", "title": "Thermoelectric Skutterudites: Why and How High zT Can Be Achieved", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:04192016-013400484", "creators": [ { "name": { "family": "Tang", "given": "Yinglu" }, "id": "Tang-Yinglu", "display_name": "Tang, Yinglu" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William L." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9TD9VB1", "abstract": "Thermoelectric materials have been widely studied over the past few decades due to their ability to convert waste heat into useful electricity. Among various thermoelectric materials, skutterudite distinguishes itself in both space and terrestrial applications with its excellent thermoelectric performance, robust mechanical properties, and thermal stability. The thermoelectric excellence of skutterudites is mostly attributed to the low thermal conductivity due to the addition of filler atoms (R) into the void (one per primitive cell Co4Sb12). Essential though this is to high zT, the importance of the intrinsic electronic structure in skutterudites is often understated or ignored completely. In this thesis, by combining experimental and computational studies, the electronic origin of high thermoelectric performance of CoSb3-based skutterudites is investigated. The high zT was shown to be a direct result of the high valley degeneracy inherent to CoSb3, which is further enhanced by band convergence at high temperatures. This successfully explains why the optimum doping carrier concentration in n-CoSb3 skutterudites is independent on the type of fillers. With the electronic origin of high thermoelectric performance clarified, the thesis moves on to elaborate how to achieve high zT in skutterudite with the aid of phase diagram study. By mapping out the phase regions near the skutterudite phase on the isothermal section of the R-Co-Sb ternary phase diagram, the solubility region of the CoSb3 skutterudite phase can be determined along with the solubility limit of R, both of which are often determined in stable compositions resulting in a synthesis window. The temperature dependence of the filler solubility is also demonstrated experimentally. This overturns the general understanding that the filler solubility is a single value only dependent on the filler type. The temperature dependence of stable compositions enables easy carrier concentration tuning which allows the optimization of thermoelectric performance. High zT values are achieved in single In, Yb, Ce-CoSb3 skutterudites. The methodology applied here are not confined to n-CoSb3, but can be generalized to any other ternary systems." }, { "name": "Thill, Matthew David", "degree": "PhD", "year": "2016", "title": "Algebraic Techniques in Coding Theory: Entropy Vectors, Frames, and Constrained Coding", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:09042015-171723764", "creators": [ { "name": { "family": "Thill", "given": "Matthew David" }, "id": "Thill-Matthew-David", "orcid": "0000-0003-0885-6260", "display_name": "Thill, Matthew David" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9F18WNW", "abstract": "The study of codes, classically motivated by the need to communicate information reliably in the presence of error, has found new life in fields as diverse as network communication, distributed storage of data, and even has connections to the design of linear measurements used in compressive sensing. But in all contexts, a code typically involves exploiting the algebraic or geometric structure underlying an application. In this thesis, we examine several problems in coding theory, and try to gain some insight into the algebraic structure behind them.
\r\n\r\nThe first is the study of the entropy region - the space of all possible vectors of joint entropies which can arise from a set of discrete random variables. Understanding this region is essentially the key to optimizing network codes for a given network. To this end, we employ a group-theoretic method of constructing random variables producing so-called \"group-characterizable\" entropy vectors, which are capable of approximating any point in the entropy region. We show how small groups can be used to produce entropy vectors which violate the Ingleton inequality, a fundamental bound on entropy vectors arising from the random variables involved in linear network codes. We discuss the suitability of these groups to design codes for networks which could potentially outperform linear coding.
\r\n\r\nThe second topic we discuss is the design of frames with low coherence, closely related to finding spherical codes in which the codewords are unit vectors spaced out around the unit sphere so as to minimize the magnitudes of their mutual inner products. We show how to build frames by selecting a cleverly chosen set of representations of a finite group to produce a \"group code\" as described by Slepian decades ago. We go on to reinterpret our method as selecting a subset of rows of a group Fourier matrix, allowing us to study and bound our frames' coherences using character theory. We discuss the usefulness of our frames in sparse signal recovery using linear measurements.
\r\n\r\nThe final problem we investigate is that of coding with constraints, most recently motivated by the demand for ways to encode large amounts of data using error-correcting codes so that any small loss can be recovered from a small set of surviving data. Most often, this involves using a systematic linear error-correcting code in which each parity symbol is constrained to be a function of some subset of the message symbols. We derive bounds on the minimum distance of such a code based on its constraints, and characterize when these bounds can be achieved using subcodes of Reed-Solomon codes.
" }, { "name": "Thrampoulidis, Christos", "degree": "PhD", "year": "2016", "title": "Recovering Structured Signals in High Dimensions via Non-Smooth Convex Optimization: Precise Performance Analysis", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032016-144604076", "creators": [ { "name": { "family": "Thrampoulidis", "given": "Christos" }, "id": "Thrampoulidis-Christos", "orcid": "0000-0001-9053-9365", "display_name": "Thrampoulidis, Christos" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z998850V", "abstract": "The typical scenario that arises in modern large-scale inference problems is one where the ambient dimension of the unknown signal is very large (e.g., high-resolution images, recommendation systems), yet its desired properties lie in some low-dimensional structure such as, sparsity or low-rankness. In the past couple of decades, non-smooth convex optimization methods have emerged as a powerful tool to extract those structures, since they are often computationally efficient, and also they offer enough flexibility while simultaneously being amenable to performance analysis. Especially, since the advent of Compressed Sensing (CS) there has been significant progress towards this direction. One of the key ideas is that random linear measurements offer an efficient way to acquire structured signals. When the measurement matrix has entries iid from a wide class of distributions (including Gaussians), a series of recent works have established a complete and transparent theory that precisely captures the performance in the noiseless setting. In the more practical scenario of noisy measurements the performance analysis task becomes significantly more challenging and corresponding precise and unifying results have hitherto remained scarce. The available class of optimization methods, often referred to as regularized M-estimators, is now richer; additional factors (e.g., the noise distribution, the loss function, and the regularizer parameter) and several different measures of performance (e.g., squared-error, probability of support recovery) need to be taken into account.
\r\n\r\nThis thesis develops a novel analytical framework that overcomes these challenges, and establishes {precise asymptotic performance guarantees for regularized M-estimators under Gaussian measurement matrices. In particular, the framework allows for a unifying analysis among different instances (such as the Generalized LASSO, and the LAD, to name a few) and accounts for a wide class of performance measures. Among others, we show results on the mean-squared-error of the Generalized-LASSO method and make insightful connections to the classical theory of ordinary least squares and to noiseless CS. Empirical evidence is presented that suggests the Gaussian assumption is not necessary. Beyond iid measurement matrices, motivated by practical considerations, we study certain classes of random matrices with orthogonal rows and establish their superior performance when compared to Gaussians.
\r\n\r\nA prominent application of this generic theory is on the analysis of the bit-error rate (BER) of the popular convex-relaxation of the Maximum Likelihood decoder for recovering BPSK signals in a massive Multiple Input Multiple Output setting. Our precise BER analysis allows comparison of these schemes to the unattainable Matched-filter bound, and further suggests means to provably boost their performance.
\r\n\r\nThe last challenge is to evaluate the performance under non-linear measurements. For the Generalized LASSO, it is shown that this is (asymptotically) equivalent to the one under noisy linear measurements with appropriately scaled variance. This encompasses state-of-the art theoretical results of one-bit CS , and is also used to prove that the optimal quantizer of the measurements that minimizes the estimation error of the Generalized LASSO is the celebrated Lloyd-Max quantizer.
\r\n\r\nThe framework is based on Gaussian process methods; in particular, on a new strong and tight version of a classical comparison inequality (due to Gordon, 1988) in the presence of additional convexity assumptions. We call this the Convex Gaussian Min-max Theorem (CGMT).
" }, { "name": "Tolstova, Yulia", "degree": "PhD", "year": "2016", "title": "Cu\u2082O Heterojunction Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012016-163813213", "creators": [ { "name": { "family": "Tolstova", "given": "Yulia" }, "id": "Tolstova-Yulia", "display_name": "Tolstova, Yulia" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z92V2D22", "abstract": "Cuprous oxide (Cu2O) is an earth abundant semiconductor that has several promising photovoltaic properties, including high absorption in the visible range, high minority carrier diffusion length, and high majority carrier mobility. Cu2O can be easily synthesized by oxidation of copper foils in air. One important advantage that makes Cu2O highly relevant to today's solar cell markets dominated by crystalline silicon is its wide bandgap of 1.9 eV at room temperature, which makes it an ideal candidate for a top cell in tandem with a crystalline silicon bottom cell. The detailed balance efficiency of such a device exceeds 44%. \r\nIn this work we aim to understand and address several issues that have limited Cu2O solar cell efficiency. We address the intrinsic p-type nature and chemical instability of Cu2O by pairing it with an appropriate n-type heterojunction partner Zn(O,S), which allows us to achieve devices with open circuit voltages exceeding 1 V. We identify presence of a current blocking layer and reduce it, which results in more than doubling the short circuit current to exceed 5 mA/cm2. Light beam induced current measurements highlight some of the issues inherent to polycrystalline Cu2O solar cells, including grain dependent collection and current losses due to presence of grain boundaries. \r\nIn order to address the issues affecting Cu2O made by thermal oxidation we also develop thin film growth of Cu2O by molecular beam epitaxy on several substrates including MgO and heteroepitaxial noble metal templates that act as ohmic back contacts. These studies culminate in achievement of the first Cu2O/Zn(O,S) solar cells incorporating an absorber layer grown by molecular beam epitaxy.\r\n\r\n" }, { "name": "Towne, Aaron S.", "degree": "PhD", "year": "2016", "title": "Advancements in Jet Turbulence and Noise Modeling: Accurate One-Way Solutions and Empirical Evaluation of the Nonlinear Forcing of Wavepackets", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:01062016-163653523", "creators": [ { "name": { "family": "Towne", "given": "Aaron S." }, "id": "Towne-Aaron-S", "orcid": "0000-0002-7315-5375", "display_name": "Towne, Aaron S." } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Hussain", "given": "Fazle" }, "id": "Hussain-F", "orcid": "0000-0002-2209-9270", "role": "member", "display_name": "Hussain, Fazle" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z99884XJ", "abstract": "Jet noise reduction is an important goal within both commercial and military aviation. Although large-scale numerical simulations are now able to simultaneously compute turbulent jets and their radiated sound, lost-cost, physically-motivated models are needed to guide noise-reduction efforts. A particularly promising modeling approach centers around certain large-scale coherent structures, called wavepackets, that are observed in jets and their radiated sound. The typical approach to modeling wavepackets is to approximate them as linear modal solutions of the Euler or Navier-Stokes equations linearized about the long-time mean of the turbulent flow field. The near-field wavepackets obtained from these models show compelling agreement with those educed from experimental and simulation data for both subsonic and supersonic jets, but the acoustic radiation is severely under-predicted in the subsonic case. This thesis contributes to two aspects of these models. First, two new solution methods are developed that can be used to efficiently compute wavepackets and their acoustic radiation, reducing the computational cost of the model by more than an order of magnitude. The new techniques are spatial integration methods and constitute a well-posed, convergent alternative to the frequently used parabolized stability equations. Using concepts related to well-posed boundary conditions, the methods are formulated for general hyperbolic equations and thus have potential applications in many fields of physics and engineering. Second, the nonlinear and stochastic forcing of wavepackets is investigated with the goal of identifying and characterizing the missing dynamics responsible for the under-prediction of acoustic radiation by linear wavepacket models for subsonic jets. Specifically, we use ensembles of large-eddy-simulation flow and force data along with two data decomposition techniques to educe the actual nonlinear forcing experienced by wavepackets in a Mach 0.9 turbulent jet. Modes with high energy are extracted using proper orthogonal decomposition, while high gain modes are identified using a novel technique called empirical resolvent-mode decomposition. In contrast to the flow and acoustic fields, the forcing field is characterized by a lack of energetic coherent structures. Furthermore, the structures that do exist are largely uncorrelated with the acoustic field. Instead, the forces that most efficiently excite an acoustic response appear to take the form of random turbulent fluctuations, implying that direct feedback from nonlinear interactions amongst wavepackets is not an essential noise source mechanism. This suggests that the essential ingredients of sound generation in high Reynolds number jets are contained within the linearized Navier-Stokes operator rather than in the nonlinear forcing terms, a conclusion that has important implications for jet noise modeling." }, { "name": "Tracy, Sally June", "degree": "PhD", "year": "2016", "title": "Polaron Hopping in Olivine Phosphates Studied by Nuclear Resonant Scattering", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062015-165650934", "creators": [ { "name": { "family": "Tracy", "given": "Sally June" }, "id": "Tracy-Sally-June", "orcid": "0000-0002-6428-284X", "display_name": "Tracy, Sally June" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z95H7D67", "abstract": "Valence fluctuations of Fe2+ and Fe3+ were studied in a solid solution of LixFePO4 by nuclear resonant forward scattering of synchrotron x rays while the sample was heated in a diamond-anvil pressure cell. The spectra acquired at different temperatures and pressures were analyzed for the frequencies of valence changes using the Blume-Tjon model of a system with a fluctuating Hamil- tonian. These frequencies were analyzed to obtain activation energies and an activation volume for polaron hopping. There was a large suppression of hopping frequency with pressure, giving an anomalously large activation volume. This large, positive value is typical of ion diffusion, which indicates correlated motions of polarons, and Li+ ions that alter the dynamics of both.
\r\n\r\nIn a parallel study of NaxFePO4, the interplay between sodium ordering and electron mobility was investigated using a combination of synchrotron x-ray diffraction and nuclear resonant scattering. Conventional Mossbauer spectra were collected while the sample was heated in a resistive furnace. An analysis of the temperature evolution of the spectral shapes was used to identify the onset of fast electron hopping and determine the polaron hopping rate. Synchrotron x-ray diffraction measurements were carried out in the same temperature range. Reitveld analysis of the diffraction patterns was used to determine the temperature of sodium redistribution on the lattice. The diffraction analysis also provides new information about the phase stability of the system. The temperature evolution of the iron site occupancies from the Mossbauer measurements, combined with the synchrotron diffraction results give strong evidence for a relationship between the onset of fast electron dynamics and the redistribution of sodium in the lattice.
\r\n\r\nMeasurements of activation barriers for polaron hopping gave fundamental insights about the correlation between electronic carriers and mobile ions. This work established that polaron-ion interactions can alter the local dynamics of electron and ion transport. These types of coupled processes may be common in many materials used for battery electrodes, and new details concerning the influence of polaron-ion interactions on the charge dynamics are relevant to optimizing their electrochemical performance.
" }, { "name": "Tsai, Hsieh-Chen", "degree": "PhD", "year": "2016", "title": "Numerical Investigation of Vertical-Axis Wind Turbines at Low Reynolds Number", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-150613633", "creators": [ { "name": { "family": "Tsai", "given": "Hsieh-Chen" }, "id": "Tsai-Hsieh-Chen", "display_name": "Tsai, Hsieh-Chen" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9SF2T5R", "abstract": "This thesis is aimed at numerically investigating the aerodynamics and the starting of a vertical-axis wind turbine at low Reynolds number using the immersed boundary method. The influence of the Coriolis effect on dynamic stall is isolated by comparing the rotating airfoil to one undergoing an equivalent planar motion that is composed of surging and pitching motions that produce an equivalent speed and angle of attack variation over a cycle. At lower tip-speed ratios, the Coriolis force leads to the capture of a vortex pair which results in a significant decrease in lift when the angle of attack of a rotating airfoil begins to decrease in the upwind half cycle. In the absence of the wake-capturing, the equivalent planar motion is a good approximation to a rotating blade in a vertical-axis wind turbine.
\r\n\r\nAnalysis on the starting torque shows that when the turbine solidity is lower than about 0.5, the starting torque distribution can be well-modeled by considering a single blade at different orientations, and starting torque distributions for multi-bladed turbines can be constructed by linearly combining the torques at the respective positions of the blades. Using this model, optimal configurations to start a multi-bladed low-solidity vertical-axis wind turbine is proposed.
\r\n\r\nA preliminary study is made to determine an optimal blade pitch for a single-bladed motor-driven turbine using optimal control theory. When the input power is minimized directly, the solution seems to converge to only a local minimum due to a lower input power reduction than that obtained by maximizing the mean tangential force. After a transient, both controls converge to time-invariant pitch angles of about the same magnitude but with opposite signs. The wake-capturing phenomenon observed in the uncontrolled case necessitates large input power. Under active control, the disappearance of wake-capturing and attendant changes in the flow field collectively result in a reduction of required input power.
" }, { "name": "Weinstein, Aaron Jacob", "degree": "PhD", "year": "2016", "title": "Quantum Electromechanics with Two Tone Drive", "advisor": "Schwab, Keith C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01072016-143812513", "creators": [ { "name": { "family": "Weinstein", "given": "Aaron Jacob" }, "id": "Weinstein-Aaron-Jacob", "orcid": "0000-0002-2354-0777", "display_name": "Weinstein, Aaron Jacob" } ], "advisors": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "advisor", "display_name": "Schwab, Keith C." } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "role": "member", "display_name": "Adhikari, Rana" }, { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "role": "member", "display_name": "Chen, Yanbei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z95M63MJ", "abstract": "In the field of mechanics, it is a long standing goal to measure quantum behavior in ever larger and more massive objects. It may now seem like an obvious conclusion, but until recently it was not clear whether a macroscopic mechanical resonator -- built up from nearly 1013 atoms -- could be fully described as an ideal quantum harmonic oscillator. With recent advances in the fields of opto- and electro-mechanics, such systems offer a unique advantage in probing the quantum noise properties of macroscopic electrical and mechanical devices, properties that ultimately stem from Heisenberg's uncertainty relations. Given the rapid progress in device capabilities, landmark results of quantum optics are now being extended into the regime of macroscopic mechanics.
\r\n\r\nThe purpose of this dissertation is to describe three experiments -- motional sideband asymmetry, back-action evasion (BAE) detection, and mechanical squeezing -- that are directly related to the topic of measuring quantum noise with mechanical detection. These measurements all share three pertinent features: they explore quantum noise properties in a macroscopic electromechanical device driven by a minimum of two microwave drive tones, hence the title of this work: \"Quantum electromechanics with two tone drive\".
\r\n\r\nIn the following, we will first introduce a quantum input-output framework that we use to model the electromechanical interaction and capture subtleties related to interpreting different microwave noise detection techniques. Next, we will discuss the fabrication and measurement details that we use to cool and probe these devices with coherent and incoherent microwave drive signals. Having developed our tools for signal modeling and detection, we explore the three-wave mixing interaction between the microwave and mechanical modes, whereby mechanical motion generates motional sidebands corresponding to up-down frequency conversions of microwave photons. Because of quantum vacuum noise, the rates of these processes are expected to be unequal. We will discuss the measurement and interpretation of this asymmetric motional noise in a electromechanical device cooled near the ground state of motion.
\r\n\r\nNext, we consider an overlapped two tone pump configuration that produces a time-modulated electromechanical interaction. By careful control of this drive field, we report a quantum non-demolition (QND) measurement of a single motional quadrature. Incorporating a second pair of drive tones, we directly measure the measurement back-action associated with both classical and quantum noise of the microwave cavity. Lastly, we slightly modify our drive scheme to generate quantum squeezing in a macroscopic mechanical resonator. Here, we will focus on data analysis techniques that we use to estimate the quadrature occupations. We incorporate Bayesian spectrum fitting and parameter estimation that serve as powerful tools for incorporating many known sources of measurement and fit error that are unavoidable in such work.
" }, { "name": "Yan, Wen", "degree": "PhD", "year": "2016", "title": "Dynamics of Chemically Active Suspensions", "advisor": "Brady, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242016-214836974", "creators": [ { "name": { "family": "Yan", "given": "Wen" }, "id": "Yan-Wen", "orcid": "0000-0002-9189-0840", "display_name": "Yan, Wen" } ], "advisors": [ { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "advisor", "display_name": "Brady, John F." } ], "committee": [ { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "chair", "display_name": "Brady, John F." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9Z60M1V", "abstract": "Chemically active particles may swim by self-diffusiophoresis in a concentration gradient of chemical solutes they created themselves by patterned surface catalytic reactions. Those particles can also interact via normal diffusiophoresis in the same solute concentration field. The interaction can be attractive or repulsive. This 'field-driven' nature of the system makes its dynamics different from a thermodynamic system and is analyzed with a new simulation method. Simulations show that attractive active particles exhibit coexistence of dense and dilute regions, but it is different from a liquid-gas phase equilibrium. To explain the behavior, a continuum mechanics theory is developed based on the minimal Active Brownian Particles (ABP) model. In the continuum description, the surface force is found to be the swim stress, which can be anisotropic. The body force includes the average swim force as an internal contribution and an 'activity-gradient' force contribution. Further, behaviors of active matter at the sub-continuum scale are also analyzed. The continuum mechanics theory is shown to accurately describe the behaviors of chemically active particles. Particle clustering is explained with a linear stability analysis, and the steady state is explained with a sedimentation-like mechanical force balance." }, { "name": "Yeung, Enoch Ho-Yee", "degree": "PhD", "year": "2016", "title": "Reverse Engineering and Quantifying Context Effects in Synthetic Gene Networks", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechThesis:05272016-145559554", "creators": [ { "name": { "family": "Yeung", "given": "Enoch Ho-Yee" }, "id": "Yeung-Enoch-Ho-Yee", "orcid": "0000-0001-7630-7429", "display_name": "Yeung, Enoch Ho-Yee" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Doyle", "given": "John C." }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John C." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Goentoro", "given": "Lea A." }, "id": "Goentoro-L-A", "role": "member", "display_name": "Goentoro, Lea A." } ], "option_major": [ "cds" ], "doi": "10.7907/Z9Z31WM4", "abstract": "In the first part of this thesis, we undertake a quantitative investigation of how compositional context, the spatial arrangement and relative orientation of genes, affects individual gene expression in a genetic network. Taking a synthetic biology approach, we construct a series of simple two-reporter biocircuits, each expressing either an mRNA aptamer or a fluorescent protein, and show that by varying the relative orientation of the two genes we obtain a wide range of gene expression profiles, including context-dependent bimodality. We develop a mathematical model to describe the experimental trends observed based on concepts from DNA supercoiling theory. We validate the model through a series of in vitro supercoiling experiments and show that by relaxing positive supercoiling in the plasmids, we can significantly reduce the context effects in gene expression. Most importantly, these insights provide a framework for understanding how compositional context and supercoiling can impose feedback on the intended architecture of a synthetic gene network. As a proof of concept, we engineer a genetic toggle switch exploiting compositional context effects to improve its threshold detection and memory capabilities.
\r\n\r\nIn the second part of this thesis, we examine a series of theoretical and computational tools from dynamical systems theory that assist in engineering novel biochemical reaction networks. We briefly review the concept of dynamical structure functions and network reconstruction as tools for understanding biochemical reaction networks. In particular, we review the concept of resource-loading, show that resource-loading can lead to coupling interactions among biochemical species, and that by estimating a dynamical structure function from experimental data, it is possible to quantify resource loading effects in practice. We illustrate the importance of knowing these loading effects through several example systems, showing that crosstalk imbalance in feed-forward loops can lead to performance limitations. However, since biochemical reaction networks are generally large, in practice, only portions of the global network can be reconstructed at a time. We show, with a combination of theory, simulation, modeling and experiments, it is possible to reconstruct the dynamical structure function of a large-scale biochemical network using a series of network reconstruction experiments. We then demonstrate how the dynamical structure function can be used to analyze context interference and how these perturbations interfere with performance. We illustrate these ideas with several classes of standard biological networks, e.g. autocatalytic systems, cascade systems, and input-coupled systems.
\r\n\r\nFinally, in the third part of this thesis, we consider models for context interference in stochastic chemical reaction networks. We address the problem of representing a biological system and its environment using a stochastic modeling framework. We first introduce a decomposition of the global chemical reaction system into two systems: a system of interest and its environment. We then present and derive a decomposition of the chemical master equation to achieve a representation describing the dynamics of the system of interest, perturbed by an environmental disturbance. We use this decomposition to model examples of two types of environmental disturbances: the disturbance a system experiences through loading effects from limited resources and the disturbance a system experiences when perturbed by an antibiotic that modifies transcription or translation rates.
" }, { "name": "You, Seungil", "degree": "PhD", "year": "2016", "title": "A Direct Approach to Robustness Optimization", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:08122015-172710296", "creators": [ { "name": { "family": "You", "given": "Seungil" }, "id": "You-Seungil", "display_name": "You, Seungil" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" } ], "option_major": [ "cds" ], "doi": "10.7907/Z9X34VDV", "abstract": "This dissertation reformulates and streamlines the core tools of robustness analysis for linear time invariant systems using now-standard methods in convex optimization. In particular, robust performance analysis can be formulated as a primal convex optimization in the form of a semidefinite program using a semidefinite representation of a set of Gramians. The same approach with semidefinite programming duality is applied to develop a linear matrix inequality test for well-connectedness analysis, and many existing results such as the Kalman-Yakubovich--Popov lemma and various scaled small gain tests are derived in an elegant fashion. More importantly, unlike the classical approach, a decision variable in this novel optimization framework contains all inner products of signals in a system, and an algorithm for constructing an input and state pair of a system corresponding to the optimal solution of robustness optimization is presented based on this information. This insight may open up new research directions, and as one such example, this dissertation proposes a semidefinite programming relaxation of a cardinality constrained variant of the H \u221e norm, which we term sparse H \u221e analysis, where an adversarial disturbance can use only a limited number of channels. Finally, sparse H \u221e analysis is applied to the linearized swing dynamics in order to detect potential vulnerable spots in power networks.\r\n" }, { "name": "Zhao, Changhong", "degree": "PhD", "year": "2016", "title": "Real-Time Load-Side Control of Electric Power Systems", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232016-160307020", "creators": [ { "name": { "family": "Zhao", "given": "Changhong" }, "id": "Zhao-Changhong", "orcid": "0000-0003-0539-8591", "display_name": "Zhao, Changhong" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9RN35TJ", "abstract": "Two trends are emerging from modern electric power systems: the growth of renewable (e.g., solar and wind) generation, and the integration of information technologies and advanced power electronics. The former introduces large, rapid, and random fluctuations in power supply, demand, frequency, and voltage, which become a major challenge for real-time operation of power systems. The latter creates a tremendous number of controllable intelligent endpoints such as smart buildings and appliances, electric vehicles, energy storage devices, and power electronic devices that can sense, compute, communicate, and actuate. Most of these endpoints are distributed on the load side of power systems, in contrast to traditional control resources such as centralized bulk generators. This thesis focuses on controlling power systems in real time, using these load side resources. Specifically, it studies two problems.
\r\n\r\n(1) Distributed load-side frequency control: We establish a mathematical framework to design distributed frequency control algorithms for flexible electric loads. In this framework, we formulate a category of optimization problems, called optimal load control (OLC), to incorporate the goals of frequency control, such as balancing power supply and demand, restoring frequency to its nominal value, restoring inter-area power flows, etc., in a way that minimizes total disutility for the loads to participate in frequency control by deviating from their nominal power usage. By exploiting distributed algorithms to solve OLC and analyzing convergence of these algorithms, we design distributed load-side controllers and prove stability of closed-loop power systems governed by these controllers. This general framework is adapted and applied to different types of power systems described by different models, or to achieve different levels of control goals under different operation scenarios. We first consider a dynamically coherent power system which can be equivalently modeled with a single synchronous machine. We then extend our framework to a multi-machine power network, where we consider primary and secondary frequency controls, linear and nonlinear power flow models, and the interactions between generator dynamics and load control.
\r\n\r\n(2) Two-timescale voltage control: The voltage of a power distribution system must be maintained closely around its nominal value in real time, even in the presence of highly volatile power supply or demand. For this purpose, we jointly control two types of reactive power sources: a capacitor operating at a slow timescale, and a power electronic device, such as a smart inverter or a D-STATCOM, operating at a fast timescale. Their control actions are solved from optimal power flow problems at two timescales. Specifically, the slow-timescale problem is a chance-constrained optimization, which minimizes power loss and regulates the voltage at the current time instant while limiting the probability of future voltage violations due to stochastic changes in power supply or demand. This control framework forms the basis of an optimal sizing problem, which determines the installation capacities of the control devices by minimizing the sum of power loss and capital cost. We develop computationally efficient heuristics to solve the optimal sizing problem and implement real-time control. Numerical experiments show that the proposed sizing and control schemes significantly improve the reliability of voltage control with a moderate increase in cost.
" }, { "name": "Zhao, Sinan", "degree": "PhD", "year": "2016", "title": "Advanced Monte Carlo Simulation and Machine Learning for Frequency Domain Optical Coherence Tomography", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:03022016-094235703", "creators": [ { "name": { "family": "Zhao", "given": "Sinan" }, "id": "Zhao-Sinan", "display_name": "Zhao, Sinan" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Ng", "given": "Willie" }, "id": "Ng-Willie", "role": "member", "display_name": "Ng, Willie" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9X63JVM", "abstract": "Optical Coherence Tomography(OCT) is a popular, rapidly growing imaging technique with an increasing number of bio-medical applications due to its noninvasive nature. However, there are three major challenges in understanding and improving an OCT system: (1) Obtaining an OCT image is not easy. It either takes a real medical experiment or requires days of computer simulation. Without much data, it is difficult to study the physical processes underlying OCT imaging of different objects simply because there aren't many imaged objects. (2) Interpretation of an OCT image is also hard. This challenge is more profound than it appears. For instance, it would require a trained expert to tell from an OCT image of human skin whether there is a lesion or not. This is expensive in its own right, but even the expert cannot be sure about the exact size of the lesion or the width of the various skin layers. The take-away message is that analyzing an OCT image even from a high level would usually require a trained expert, and pixel-level interpretation is simply unrealistic. The reason is simple: we have OCT images but not their underlying ground-truth structure, so there is nothing to learn from. (3) The imaging depth of OCT is very limited (millimeter or sub-millimeter on human tissues). While OCT utilizes infrared light for illumination to stay noninvasive, the downside of this is that photons at such long wavelengths can only penetrate a limited depth into the tissue before getting back-scattered. To image a particular region of a tissue, photons first need to reach that region. As a result, OCT signals from deeper regions of the tissue are both weak (since few photons reached there) and distorted (due to multiple scatterings of the contributing photons). This fact alone makes OCT images very hard to interpret.
\r\n\r\nThis thesis addresses the above challenges by successfully developing an advanced Monte Carlo simulation platform which is 10000 times faster than the state-of-the-art simulator in the literature, bringing down the simulation time from 360 hours to a single minute. This powerful simulation tool not only enables us to efficiently generate as many OCT images of objects with arbitrary structure and shape as we want on a common desktop computer, but it also provides us the underlying ground-truth of the simulated images at the same time because we dictate them at the beginning of the simulation. This is one of the key contributions of this thesis. What allows us to build such a powerful simulation tool includes a thorough understanding of the signal formation process, clever implementation of the importance sampling/photon splitting procedure, efficient use of a voxel-based mesh system in determining photon-mesh interception, and a parallel computation of different A-scans that consist a full OCT image, among other programming and mathematical tricks, which will be explained in detail later in the thesis.
\r\n\r\nNext we aim at the inverse problem: given an OCT image, predict/reconstruct its ground-truth structure on a pixel level. By solving this problem we would be able to interpret an OCT image completely and precisely without the help from a trained expert. It turns out that we can do much better. For simple structures we are able to reconstruct the ground-truth of an OCT image more than 98% correctly, and for more complicated structures (e.g., a multi-layered brain structure) we are looking at 93%. We achieved this through extensive uses of Machine Learning. The success of the Monte Carlo simulation already puts us in a great position by providing us with a great deal of data (effectively unlimited), in the form of (image, truth) pairs. Through a transformation of the high-dimensional response variable, we convert the learning task into a multi-output multi-class classification problem and a multi-output regression problem. We then build a hierarchy architecture of machine learning models (committee of experts) and train different parts of the architecture with specifically designed data sets. In prediction, an unseen OCT image first goes through a classification model to determine its structure (e.g., the number and the types of layers present in the image); then the image is handed to a regression model that is trained specifically for that particular structure to predict the length of the different layers and by doing so reconstruct the ground-truth of the image. We also demonstrate that ideas from Deep Learning can be useful to further improve the performance.
\r\n\r\nIt is worth pointing out that solving the inverse problem automatically improves the imaging depth, since previously the lower half of an OCT image (i.e., greater depth) can be hardly seen but now becomes fully resolved. Interestingly, although OCT signals consisting the lower half of the image are weak, messy, and uninterpretable to human eyes, they still carry enough information which when fed into a well-trained machine learning model spits out precisely the true structure of the object being imaged. This is just another case where Artificial Intelligence (AI) outperforms human. To the best knowledge of the author, this thesis is not only a success but also the first attempt to reconstruct an OCT image at a pixel level. To even give a try on this kind of task, it would require fully annotated OCT images and a lot of them (hundreds or even thousands). This is clearly impossible without a powerful simulation tool like the one developed in this thesis.
" }, { "name": "Aitken, Zachary Howard", "degree": "PhD", "year": "2015", "title": "Effect of Microstructural Interfaces on the Mechanical Response of Crystalline Metallic Materials", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04302015-143917971", "creators": [ { "name": { "family": "Aitken", "given": "Zachary Howard" }, "id": "Aitken-Zachary-Howard", "display_name": "Aitken, Zachary Howard" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9C24TCP", "abstract": "Advances in nano-scale mechanical testing have brought about progress in the understanding of physical phenomena in materials and a measure of control in the fabrication of novel materials. In contrast to bulk materials that display size-invariant mechanical properties, sub-micron metallic samples show a critical dependence on sample size. The strength of nano-scale single crystalline metals is well-described by a power-law function, \u03c3\u03b1D-n, where D is a critical sample size and n is a experimentally-fit positive exponent. This relationship is attributed to source-driven plasticity and demonstrates a strengthening as the decreasing sample size begins to limit the size and number of dislocation sources. A full understanding of this size-dependence is complicated by the presence of microstructural features such as interfaces that can compete with the dominant dislocation-based deformation mechanisms. In this thesis, the effects of microstructural features such as grain boundaries and anisotropic crystallinity on nano-scale metals are investigated through uniaxial compression testing. We find that nano-sized Cu covered by a hard coating displays a Bauschinger effect and the emergence of this behavior can be explained through a simple dislocation-based analytic model. Al nano-pillars containing a single vertically-oriented coincident site lattice grain boundary are found to show similar deformation to single-crystalline nano-pillars with slip traces passing through the grain boundary. With increasing tilt angle of the grain boundary from the pillar axis, we observe a transition from dislocation-dominated deformation to grain boundary sliding. Crystallites are observed to shear along the grain boundary and molecular dynamics simulations reveal a mechanism of atomic migration that accommodates boundary sliding. We conclude with an analysis of the effects of inherent crystal anisotropy and alloying on the mechanical behavior of the Mg alloy, AZ31. Through comparison to pure Mg, we show that the size effect dominates the strength of samples below 10 \u03bcm, that differences in the size effect between hexagonal slip systems is due to the inherent crystal anisotropy, suggesting that the fundamental mechanism of the size effect in these slip systems is the same." }, { "name": "Aryanfar, Asghar", "degree": "PhD", "year": "2015", "title": "Dendrites Inhibition in Rechargeable Lithium Metal Batteries", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05012015-161434189", "creators": [ { "name": { "family": "Aryanfar", "given": "Asghar" }, "id": "Aryanfar-Asghar", "orcid": "0000-0002-8890-077X", "display_name": "Aryanfar, Asghar" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "chair", "display_name": "Andrade, Jose E." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9ZK5DMP", "abstract": "The specific high energy and power capacities of rechargeable lithium metal (Li0) batteries are ideally suited to portable devices and are valuable as storage units for intermittent renewable energy sources. Lithium, the lightest and most electropositive metal, would be the optimal anode material for rechargeable batteries if it were not for the fact that such devices fail unexpectedly by short-circuiting via the dendrites that grow across electrodes upon recharging. This phenomenon poses a major safety issue because it triggers a series of adverse events that start with overheating, potentially followed by the thermal decomposition and ultimately the ignition of the organic solvents used in such devices.
\r\n\r\nIn this thesis, we developed experimental platform for monitoring and quantifying the dendrite populations grown in a Li battery prototype upon charging under various conditions. We explored the effects of pulse charging in the kHz range and temperature on dendrite growth, and also on loss capacity into detached \u201cdead\u201d lithium particles.
\r\n\r\nSimultaneously, we developed a computational framework for understanding the dynamics of dendrite propagation. The coarse-grained Monte Carlo model assisted us in the interpretation of pulsing experiments, whereas MD calculations provided insights into the mechanism of dendrites thermal relaxation. We also developed a computational framework for measuring the dead lithium crystals from the experimental images.
\r\n" }, { "name": "Asimakopoulos, Aristotelis", "degree": "PhD", "year": "2015", "title": "Macroscopically Dissipative Systems with Underlying Microscopic Dynamics : Properties and Limits of Measurement", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:09082014-135331211", "creators": [ { "name": { "family": "Asimakopoulos", "given": "Aristotelis" }, "id": "Asimakopoulos-Aristotelis", "display_name": "Asimakopoulos, Aristotelis" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9V40S4N", "abstract": "While some of the deepest results in nature are those that give explicit bounds between important physical quantities, some of the most intriguing and celebrated of such bounds come from fields where there is still a great deal of disagreement and confusion regarding even the most fundamental aspects of the theories. For example, in quantum mechanics, there is still no complete consensus as to whether the limitations associated with Heisenberg's Uncertainty Principle derive from an inherent randomness in physics, or rather from limitations in the measurement process itself, resulting from phenomena like back action. Likewise, the second law of thermodynamics makes a statement regarding the increase in entropy of closed systems, yet the theory itself has neither a universally-accepted definition of equilibrium, nor an adequate explanation of how a system with underlying microscopically Hamiltonian dynamics (reversible) settles into a fixed distribution.
\r\n\r\nMotivated by these physical theories, and perhaps their inconsistencies, in this thesis we use dynamical systems theory to investigate how the very simplest of systems, even with no physical constraints, are characterized by bounds that give limits to the ability to make measurements on them. Using an existing interpretation, we start by examining how dissipative systems can be viewed as high-dimensional lossless systems, and how taking this view necessarily implies the existence of a noise process that results from the uncertainty in the initial system state. This fluctuation-dissipation result plays a central role in a measurement model that we examine, in particular describing how noise is inevitably injected into a system during a measurement, noise that can be viewed as originating either from the randomness of the many degrees of freedom of the measurement device, or of the environment. This noise constitutes one component of measurement back action, and ultimately imposes limits on measurement uncertainty. Depending on the assumptions we make about active devices, and their limitations, this back action can be offset to varying degrees via control. It turns out that using active devices to reduce measurement back action leads to estimation problems that have non-zero uncertainty lower bounds, the most interesting of which arise when the observed system is lossless. One such lower bound, a main contribution of this work, can be viewed as a classical version of a Heisenberg uncertainty relation between the system's position and momentum. We finally also revisit the murky question of how macroscopic dissipation appears from lossless dynamics, and propose alternative approaches for framing the question using existing systematic methods of model reduction.
" }, { "name": "Balaji Gopal, Chirranjeevi", "degree": "PhD", "year": "2015", "title": "Ab-Initio and Experimental Techniques for Studying Non-Stoichiometry and Oxygen Transport in Mixed Conducting Oxides", "advisor": "Haile, Sossina M.; van de Walle, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:08292014-092737024", "creators": [ { "name": { "family": "Balaji Gopal", "given": "Chirranjeevi" }, "id": "Balaji-Gopal-Chirranjeevi", "display_name": "Balaji Gopal, Chirranjeevi" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." }, { "name": { "family": "van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "advisor", "display_name": "van de Walle, Axel" } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "member", "display_name": "van de Walle, Axel" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9TT4NWZ", "abstract": "The ability of cerium oxide (CeO2-\u03b4, also called ceria), to vary its oxygen stoichiometry in response to changes in temperature or oxygen activity is key to many of its applications in catalysis and electrochemical energy storage and conversion. This thesis explores ab initio and experimental approaches to study the fundamental thermodynamic and oxygen transport properties of ceria (MxCe1-xOO2-\u03b4), but the methods are applicable to other mixed conducting oxides as well.
\r\n\r\nIn the first part of the thesis, a computational thermodynamics approach that integrates quantum mechanical and statistical ensemble-based simulations is used to calculate the reduction-oxidation thermodynamics of non-stoichiometric ceria entirely from first principles. This procedure is well understood and has been successfully implemented for metallic alloys, but has not been extended to correlated electron systems such as ceria, for which the physics of electronic structure calculations is significantly more complicated. Density functional calculations were used to obtain the ground state energies of ceria with vacancy concentrations ranging from fully stoichiometric up to \u03b4=0.25$. For each \u03b4, numerous vacancy configurations were sampled to capture the interactions between vacancies and other atoms. Using the frozen phonon method, lattice dynamical calculations of phonon density of states were performed for various \u03b4. Based on the ground state energies of nearly 40 structures, a cluster expansion Hamiltonian was used to parametrize the energy as a polynomial in occupation variables. The vibrational energies were used to make the Hamiltoninan temperature dependent. Lattice Monte Carlo (MC) simulations using the cluster expansion Hamiltonian were then used to study, for the first time, the effect of temperature and chemical potential on the vacancy concentration in ceria from first principles. The temperature composition phase diagram constructed from the MC simulations successfully reproduced the experimentally reported miscibility gap. The inclusion of vibrational and electronic contributions to the entropy made the agreement quantitative. Further, the partial molar enthalpy and entropy of reduction as a function of \u03b4 were extracted and found to deviate significantly from those of an ideally behaved system. The deviations were quantified by calculating the Warren-Cowley short range order parameters. This was the first demonstration of an ab initio approach being used to accurately model the defect thermodynamics of a correlated electron system without resorting to experimental inputs. Using ceria as benchmark material, this project lays the groundwork for a computational approach to screen new oxides for thermochemical cycling.
\r\n\r\nThe rest of the thesis describes experimental investigations of oxygen transport and non-stoichiometry in doped and undoped ceria. Oxygen transport studies were performed using electrical conductivity relaxation (ECR). In ECR, a small step change in pO2 forces the sample non-stoichiometry \u03b4, and other dependent properties such as electrical conductivity, to equilibrate to a new value. The rate of this re-equilibration is governed by the bulk oxygen diffusivity, DChem, and surface reaction rate constant, kS -- the two principal kinetic properties. By fitting the solution to Fick's second law, with the appropriate boundary conditions, to the conductivity relaxation profile, DChem and kS can be extracted. The instrumental capability for performing electrical conductivity relaxation experiments was set up and a systematic data analysis procedure was developed to reliably and accurately extract DChem and or kS. The experimental and data analytical methodologies were successfully benchmarked with 15 mol% Sm doped ceria, for which approximate values of the two principal transport properties, bulk oxygen diffusivity, DChem, and surface reaction rate constant, kS, can be found in the literature. An unexpectedly high p-type electronic transference number enabled ECR measurements under oxidizing conditions. A systematic data analysis procedure was developed to permit reliable extraction of the kinetic parameters even in the general case of simultaneous bulk and surface limitation. When the surface kinetics were too sluggish compared to bulk diffusion, Pt catalyst nanoparticles were sputtered to catalyze the surface reaction and enable extraction of DChem. The DChem from this study showed excellent qualitative and quantitative agreement with expected values, falling in the range from ~ 2 x 10-5 to 2 x 10-4 cm2/s. The surface reaction constant under H2/H2O mixtures also showed good agreement with literature results. Remarkably, this value increased by a factor of 40 under mixtures of CO/CO2 or O2/Ar. This observation suggests kinetic advantages for production of CO rather than H2 in a two-step solar-driven thermochemical process based on samarium doped ceria.
\r\n\r\nUsing ECR, the effect of 20% Zr addition on the electrical conductivity and oxygen transport properties of ceria as a function of pO2 and T was investigated. Under oxidizing conditions, both CeO2-\u03b4 and Zr0.2Ce0.8O2-\u03b4(ZDC20) showed n type, mixed conduction. The conductivity of ZDC20 was two orders of magnitude higher than that of undoped ceria. Contrary to previous studies, we found that Zr addition does not change the electronic mobility in this pO2 regime. The enhancement in conductivity is a consequence of higher vacancy concentration in ZDC20 under identical conditions compared to ceria. Under reducing conditions, while the n-type conductivity of ceria continued to increase with decreasing pO2, that of ZDC20 reached a broad maximum, eventually decreasing with pO2 (p-type) despite increasing carrier concentration. We show that the electronic mobility becomes strongly concentration dependent at high oxygen non-stoichiometry. This leads to a marked decrease in mobility with increase in \u03b4, causing the conductivity to roll over from n to p type. The chemical diffusion coefficient and surface reaction rate constant of both ceria and ZDC20 showed strong dependence on pO2 under oxidizing conditions, decreasing by nearly an order of magnitude between 10-2 atm and 10-5 atm. The unexpectedly high sensitivity to pO2 was ascribed to the effect of extrinsic vacancies generated by trace quantities of lower valence cation impurities, that dramatically increase both the absolute value of the thermodynamic factor and its sensitivity to pO2 close to stoichiometry. Overall, the addition of Zr lowers the DChem and kS of ceria in the temperature and oxygen partial pressure range of this study, the effect being more pronounced under reducing conditions. Beyond its relevance to ceria, this work demonstrates the potential of ECR to isolate the effect of kinetics from thermodynamics of the real thermochemical cycle, reveal the limiting transport parameters, and ultimately guide microstructure design for maximizing the rate of fuel production.
\r\n \r\nLastly, we improve upon an existing formalism to calculate the oxygen non-stoichiometry in thin films of mixed conducting oxides using AC impedance spectroscopy. Cerium oxide was once again chosen as the benchmarking material, since it shows both ideal and non-ideal thermodynamic behavior under different conditions, and has been well studied in its bulk form. In this method, the impedance response of dense, thin films of CeO2-\u03b4 deposited on a Y0.84Zr0.16O1.92> (YSZ) substrate was measured using AC impedance spectroscopy. To explore potential grain boundary effects on bulk thermodynamic properties. A physically derived equivalent circuit model was fit to the impedance response to extract a quantity called the 'chemical capacitance', which was subsequently related to the non-stoichiometry. Previous studies employing this method were restricted to systems that can be described using ideal solution thermodynamics, which allows simplifications to the theoretical treatment of their capacitance. Apart from extending this technique to a non-ideally behaved oxide, we report excellent agreement between the non-stoichiometry of single crystal and polycrystalline films and that of bulk ceria. By virtue of using thin films, equilibration times are dramatically decreased, enabling faster measurements compared to bulk techniques like thermogravimetry and coulometric titration. Further, the electrochemical method is ideal for thin films, for which the mass changes are below the detection limits of bulk techniques.
\r\n" }, { "name": "Bitter, Neal Phillip", "degree": "PhD", "year": "2015", "title": "Stability of Hypervelocity Boundary Layers", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052015-111128842", "creators": [ { "name": { "family": "Bitter", "given": "Neal Phillip" }, "id": "Bitter-Neal-Phillip", "display_name": "Bitter, Neal Phillip" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Q23X5Z", "abstract": "The early stage of laminar-turbulent transition in a hypervelocity boundary layer is studied using a combination of modal linear stability analysis, transient growth analysis, and direct numerical simulation. Modal stability analysis is used to clarify the behavior of first and second mode instabilities on flat plates and sharp cones for a wide range of high enthalpy flow conditions relevant to experiments in impulse facilities. Vibrational nonequilibrium is included in this analysis, its influence on the stability properties is investigated, and simple models for predicting when it is important are described.
\r\n\r\nTransient growth analysis is used to determine the optimal initial conditions that lead to the largest possible energy amplification within the flow. Such analysis is performed for both spatially and temporally evolving disturbances. The analysis again targets flows that have large stagnation enthalpy, such as those found in shock tunnels, expansion tubes, and atmospheric flight at high Mach numbers, and clarifies the effects of Mach number and wall temperature on the amplification achieved. Direct comparisons between modal and non-modal growth are made to determine the relative importance of these mechanisms under different flow regimes.
\r\n\r\nConventional stability analysis employs the assumption that disturbances evolve with either a fixed frequency (spatial analysis) or a fixed wavenumber (temporal analysis). Direct numerical simulations are employed to relax these assumptions and investigate the downstream propagation of wave packets that are localized in space and time, and hence contain a distribution of frequencies and wavenumbers. Such wave packets are commonly observed in experiments and hence their amplification is highly relevant to boundary layer transition prediction. It is demonstrated that such localized wave packets experience much less growth than is predicted by spatial stability analysis, and therefore it is essential that the bandwidth of localized noise sources that excite the instability be taken into account in making transition estimates. A simple model based on linear stability theory is also developed which yields comparable results with an enormous reduction in computational expense. This enables the amplification of finite-width wave packets to be taken into account in transition prediction.
" }, { "name": "Brown, David Ross", "degree": "PhD", "year": "2015", "title": "Enhanced Thermoelectric Performance at the Superionic Phase Transitions of Mixed Ion-Electron Conducting Materials", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:08112014-121653693", "creators": [ { "name": { "family": "Brown", "given": "David Ross" }, "id": "Brown-David-Ross", "display_name": "Brown, David Ross" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9B56GNM", "abstract": "The quality of a thermoelectric material is judged by the size of its temperature de- pendent thermoeletric-figure-of-merit (zT ). Superionic materials, particularly Zn4Sb3 and Cu2Se, are of current interest for the high zT and low thermal conductivity of their disordered, superionic phase. In this work it is reported that the super-ionic materials Ag2Se, Cu2Se and Cu1.97Ag0.03Se show enhanced zT in their ordered, normal ion-conducting phases. The zT of Ag2Se is increased by 30% in its ordered phase as compared to its disordered phase, as measured just below and above its first order phase transition. The zT \u2019s of Cu2Se and Cu1.97Ag0.03Se both increase by more than 100% over a 30 K temperatures range just below their super-ionic phase transitions. The peak zT of Cu2Se is 0.7 at 406 K and of Cu1.97Ag0.03Se is 1.0 at 400 K. In all three materials these enhancements are due to anomalous increases in their Seebeck coefficients, beyond that predicted by carrier concentration measurements and band structure modeling. As the Seebeck coefficient is the entropy transported per carrier, this suggests that there is an additional quantity of entropy co-transported with charge carriers. Such co-transport has been previously observed via co-transport of vibrational entropy in bipolaron conductors and spin-state entropy in NaxCo2O4. The correlation of the temperature profile of the increases in each material with the nature of their phase transitions indicates that the entropy is associated with the thermodynamcis of ion-ordering. This suggests a new mechanism by which high thermoelectric performance may be understood and engineered." }, { "name": "Callahan, Dennis Michael", "degree": "PhD", "year": "2015", "title": "Nanophotonic Light Trapping In Thin Solar Cells", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:10082014-105407332", "creators": [ { "name": { "family": "Callahan", "given": "Dennis Michael" }, "id": "Callahan-Dennis-Michael", "display_name": "Callahan, Dennis Michael" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z92N506Z", "abstract": "Over the last several decades there have been significant advances in the study and understanding of light behavior in nanoscale geometries. Entire fields such as those based on photonic crystals, plasmonics and metamaterials have been developed, accelerating the growth of knowledge related to nanoscale light manipulation. Coupled with recent interest in cheap, reliable renewable energy, a new field has blossomed, that of nanophotonic solar cells.
\r\n\r\nIn this thesis, we examine important properties of thin-film solar cells from a nanophotonics perspective. We identify key differences between nanophotonic devices and traditional, thick solar cells. We propose a new way of understanding and describing limits to light trapping and show that certain nanophotonic solar cell designs can have light trapping limits above the so called ray-optic or ergodic limit. We propose that a necessary requisite to exceed the traditional light trapping limit is that the active region of the solar cell must possess a local density of optical states (LDOS) higher than that of the corresponding, bulk material. Additionally, we show that in addition to having an increased density of states, the absorber must have an appropriate incoupling mechanism to transfer light from free space into the optical modes of the device. We outline a portfolio of new solar cell designs that have potential to exceed the traditional light trapping limit and numerically validate our predictions for select cases.
\r\n\r\nWe emphasize the importance of thinking about light trapping in terms of maximizing the optical modes of the device and efficiently coupling light into them from free space. To further explore these two concepts, we optimize patterns of superlattices of air holes in thin slabs of Si and show that by adding a roughened incoupling layer the total absorbed current can be increased synergistically. We suggest that the addition of a random scattering surface to a periodic patterning can increase incoupling by lifting the constraint of selective mode occupation associated with periodic systems.
\r\n\r\nLastly, through experiment and simulation, we investigate a potential high efficiency solar cell architecture that can be improved with the nanophotonic light trapping concepts described in this thesis. Optically thin GaAs solar cells are prepared by the epitaxial liftoff process by removal from their growth substrate and addition of a metallic back reflector. A process of depositing large area nano patterns on the surface of the cells is developed using nano imprint lithography and implemented on the thin GaAs cells.
" }, { "name": "Chang, Chieh-Feng", "degree": "PhD", "year": "2015", "title": "Wafer-Scalable Fabrication of Metal Nanostructures for Plasmonics-Assisted Biomedical Sensing Applications", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022015-015750109", "creators": [ { "name": { "family": "Chang", "given": "Chieh-Feng" }, "id": "Chang-Chieh-Feng", "display_name": "Chang, Chieh-Feng" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Walavalkar", "given": "Sameer S." }, "id": "Walavalkar-S-S", "role": "member", "display_name": "Walavalkar, Sameer S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9K935FM", "abstract": "Plasmonics provides many opportunities of sensing and detection since it combines the nanoscale spatial confinement and the optical temporal resolution. The wireless nature of photonic investigation, moreover, is very desirable for biomedical applications. Plasmonic metals, however, are difficult to pattern with great nanoscopic precision, and traditional approaches were time-consuming, non-scalable, stochastically-manufactured, or highly-limiting in the pattern designs. In this work, wafer-scalable nanofabrication methods are presented for various plasmonic structures for biomedical sensing applications. The fabrication steps have ready counterparts in commercial semiconductor foundries and therefore can be directly applied for mass production.
\r\n\r\nThe fabrication and measurement of extraordinary transmission (EOT) are discussed in Chapter 2. Fabrication options are available for substrates like silicon-on-sapphire and silicon-on-glass, so that the devices can be mechanically robust for user-friendliness. The metal layer can also be varied for EOT applications in different ranges of wavelengths. The EOT nanostructures can be fabricated to be polarization-sensitive, and the concept of fluorescence-based EOT assays is demonstrated.
\r\n\r\nThe fabrication and applications of surface-enhanced Raman spectroscopy (SERS) are then discussed. With a hybrid approach, the top-down designing defines uniform SERS nanostructures on a chip, while the bottom-up process of thermal reflow increases the fabrication precision beyond the lithography resolution limit. Based on the thiophenol study, an enhancement factor greater than 1010 can be achieved. The first Raman spectrum of tracheal cytotoxin is demonstrated without any special sample preparation, and thrombin binding could be easily resolved through chip functionalization. The binding dynamics of ethyl mercaptan, which is similar to the highly toxic gas of hydrogen sulfide, can be detected with a good resolution in time at a low concentration.
\r\n\r\nWith a few more steps of fabrication, the plasmonic structures can be integrated into systems that do not call for laboratory infrastructures. A built-in micro-channel on a chip can make the device useful without dedicated support of a microscope or additional microfluidic structures. The nanostructures can also be transferred onto flexible substrates for better conformity onto various surfaces. Finally, the SERS structures can be transferred onto a fiber tip for in-field or through-the-needle applications, especially when combined with a portable Raman-scope.
" }, { "name": "Coralic, Vedran", "degree": "PhD", "year": "2015", "title": "Simulation of Shock-Induced Bubble Collapse with Application to Vascular Injury in Shockwave Lithotripsy", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:01222015-234921548", "creators": [ { "name": { "family": "Coralic", "given": "Vedran" }, "id": "Coralic-Vedran", "display_name": "Coralic, Vedran" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z91N7Z26", "abstract": "Shockwave lithotripsy is a noninvasive medical procedure wherein shockwaves are repeatedly focused at the location of kidney stones in order to pulverize them. Stone comminution is thought to be the product of two mechanisms: the propagation of stress waves within the stone and cavitation erosion. However, the latter mechanism has also been implicated in vascular injury. In the present work, shock-induced bubble collapse is studied in order to understand the role that it might play in inducing vascular injury. A high-order accurate, shock- and interface-capturing numerical scheme is developed to simulate the three-dimensional collapse of the bubble in both the free-field and inside a vessel phantom. The primary contributions of the numerical study are the characterization of the shock-bubble and shock-bubble-vessel interactions across a large parameter space that includes clinical shockwave lithotripsy pressure amplitudes, problem geometry and tissue viscoelasticity, and the subsequent correlation of these interactions to vascular injury. Specifically, measurements of the vessel wall pressures and displacements, as well as the finite strains in the fluid surrounding the bubble, are utilized with available experiments in tissue to evaluate damage potential. Estimates are made of the smallest injurious bubbles in the microvasculature during both the collapse and jetting phases of the bubble's life cycle. The present results suggest that bubbles larger than 1 \u03bcm in diameter could rupture blood vessels under clinical SWL conditions." }, { "name": "Cubillos-Moraga, Max Anton", "degree": "PhD", "year": "2015", "title": "General-Domain Compressible Navier-Stokes Solvers Exhibiting Quasi-Unconditional Stability and High Order Accuracy in Space and Time", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082015-184801592", "creators": [ { "name": { "family": "Cubillos-Moraga", "given": "Max Anton" }, "id": "Cubillos-Moraga-Max-Anton", "display_name": "Cubillos-Moraga, Max Anton" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z9WW7FKW", "abstract": "This thesis presents a new class of solvers for the subsonic compressible Navier-Stokes equations in general two- and three-dimensional spatial domains. The proposed methodology incorporates: 1) A novel linear-cost implicit solver based on use of higher-order backward differentiation formulae (BDF) and the alternating direction implicit approach (ADI); 2) A fast explicit solver; 3) Dispersionless spectral spatial discretizations; and 4) A domain decomposition strategy that negotiates the interactions between the implicit and explicit domains. In particular, the implicit methodology is quasi-unconditionally stable (it does not suffer from CFL constraints for adequately resolved flows), and it can deliver orders of time accuracy between two and six in the presence of general boundary conditions. In fact this thesis presents, for the first time in the literature, high-order time-convergence curves for Navier-Stokes solvers based on the ADI strategy---previous ADI solvers for the Navier-Stokes equations have not demonstrated orders of temporal accuracy higher than one. An extended discussion is presented in this thesis which places on a solid theoretical basis the observed quasi-unconditional stability of the methods of orders two through six. The performance of the proposed solvers is favorable. For example, a two-dimensional rough-surface configuration including boundary layer effects at Reynolds number equal to one million and Mach number 0.85 (with a well-resolved boundary layer, run up to a sufficiently long time that single vortices travel the entire spatial extent of the domain, and with spatial mesh sizes near the wall of the order of one hundred-thousandth the length of the domain) was successfully tackled in a relatively short (approximately thirty-hour) single-core run; for such discretizations an explicit solver would require truly prohibitive computing times. As demonstrated via a variety of numerical experiments in two- and three-dimensions, further, the proposed multi-domain parallel implicit-explicit implementations exhibit high-order convergence in space and time, useful stability properties, limited dispersion, and high parallel efficiency." }, { "name": "Dasgupta, Kaushik", "degree": "PhD", "year": "2015", "title": "Self-Healing Techniques for RF and mm-Wave Transmitters and Receivers", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:10282014-113257585", "creators": [ { "name": { "family": "Dasgupta", "given": "Kaushik" }, "id": "Dasgupta-Kaushik", "display_name": "Dasgupta, Kaushik" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9HQ3WTR", "abstract": "With continuing advances in CMOS technology, feature sizes of modern Silicon chip-sets have gone down drastically over the past decade. In addition to desktops and laptop processors, a vast majority of these chips are also being deployed in mobile communication devices like smart-phones and tablets, where multiple radio-frequency integrated circuits (RFICs) must be integrated into one device to cater to a wide variety of applications such as Wi-Fi, Bluetooth, NFC, wireless charging, etc. While a small feature size enables higher integration levels leading to billions of transistors co-existing on a single chip, it also makes these Silicon ICs more susceptible to variations. A part of these variations can be attributed to the manufacturing process itself, particularly due to the stringent dimensional tolerances associated with the lithographic steps in modern processes. Additionally, RF or millimeter-wave communication chip-sets are subject to another type of variation caused by dynamic changes in the operating environment. Another bottleneck in the development of high performance RF/mm-wave Silicon ICs is the lack of accurate analog/high-frequency models in nanometer CMOS processes. This can be primarily attributed to the fact that most cutting edge processes are geared towards digital system implementation and as such there is little model-to-hardware correlation at RF frequencies.
\r\n\r\nAll these issues have significantly degraded yield of high performance mm-wave and RF CMOS systems which often require multiple trial-and-error based Silicon validations, thereby incurring additional production costs. This dissertation proposes a low overhead technique which attempts to counter the detrimental effects of these variations, thereby improving both performance and yield of chips post fabrication in a systematic way. The key idea behind this approach is to dynamically sense the performance of the system, identify when a problem has occurred, and then actuate it back to its desired performance level through an intelligent on-chip optimization algorithm. We term this technique as self-healing drawing inspiration from nature's own way of healing the body against adverse environmental effects. To effectively demonstrate the efficacy of self-healing in CMOS systems, several representative examples are designed, fabricated, and measured against a variety of operating conditions.
\r\n\r\nWe demonstrate a high-power mm-wave segmented power mixer array based transmitter architecture that is capable of generating high-speed and non-constant envelope modulations at higher efficiencies compared to existing conventional designs. We then incorporate several sensors and actuators into the design and demonstrate closed-loop healing against a wide variety of non-ideal operating conditions. We also demonstrate fully-integrated self-healing in the context of another mm-wave power amplifier, where measurements were performed across several chips, showing significant improvements in performance as well as reduced variability in the presence of process variations and load impedance mismatch, as well as catastrophic transistor failure. Finally, on the receiver side, a closed-loop self-healing phase synthesis scheme is demonstrated in conjunction with a wide-band voltage controlled oscillator to generate phase shifter local oscillator (LO) signals for a phased array receiver. The system is shown to heal against non-idealities in the LO signal generation and distribution, significantly reducing phase errors across a wide range of frequencies.
" }, { "name": "Duan, Ran", "degree": "PhD", "year": "2015", "title": "Instrumentation for Kinetic-Inductance-Detector-Based Submillimeter Radio Astronomy", "advisor": "Golwala, Sunil", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282015-141343540", "creators": [ { "name": { "family": "Duan", "given": "Ran" }, "id": "Duan-Ran", "display_name": "Duan, Ran" } ], "advisors": [ { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "role": "advisor", "display_name": "Golwala, Sunil" } ], "committee": [ { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "role": "chair", "display_name": "Golwala, Sunil" }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z90P0WXZ", "abstract": "A substantial amount of important scientific information is contained within astronomical data at the submillimeter and far-infrared (FIR) wavelengths, including information regarding dusty galaxies, galaxy clusters, and star-forming regions; however, these wavelengths are among the least-explored\r\nfields in astronomy because of the technological difficulties involved in such research. Over the past 20 years, considerable efforts have been devoted to developing submillimeter- and millimeter-wavelength astronomical instruments and telescopes.
\r\n\r\nThe number of detectors is an important property of such instruments and is the subject of the current study. Future telescopes will require as many as hundreds of thousands of detectors to meet the necessary requirements in terms of the field of view, scan speed, and resolution. A large pixel count is one benefit of the development of multiplexable detectors that use kinetic inductance detector (KID) technology.
\r\n\r\nThis dissertation presents the development of a KID-based instrument including a portion of the millimeter-wave bandpass filters and all aspects of the readout electronics, which together enabled one of the largest detector counts achieved to date in submillimeter-/millimeter-wavelength imaging arrays: a total of 2304 detectors. The work presented in this dissertation has been implemented in the MUltiwavelength Submillimeter Inductance Camera (MUSIC), a new instrument for the Caltech Submillimeter Observatory (CSO).
" }, { "name": "En Gad, Eyal", "degree": "PhD", "year": "2015", "title": "Rewriting Schemes for Flash Memory", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082015-142940694", "creators": [ { "name": { "family": "En Gad", "given": "Eyal" }, "id": "En-Gad-Eyal", "display_name": "En Gad, Eyal" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Langberg", "given": "Michael" }, "id": "Langberg-M", "role": "member", "display_name": "Langberg, Michael" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9R49NQ3", "abstract": "Flash memory is a leading storage media with excellent features such as random access and\r\nhigh storage density. However, it also faces significant reliability and endurance challenges.\r\nIn flash memory, the charge level in the cells can be easily increased, but removing charge\r\nrequires an expensive erasure operation. In this thesis we study rewriting schemes that\r\nenable the data stored in a set of cells to be rewritten by only increasing the charge level\r\nin the cells. We consider two types of modulation scheme; a convectional modulation based\r\non the absolute levels of the cells, and a recently-proposed scheme based on the relative cell\r\nlevels, called rank modulation. The contributions of this thesis to the study of rewriting\r\nschemes for rank modulation include the following: we
\r\n\r\n•propose a new method of rewriting in rank modulation, beyond the previously proposed\r\nmethod of \u201cpush-to-the-top\u201d;
\r\n•study the limits of rewriting with the newly proposed method, and derive a tight upper\r\nbound of 1 bit per cell;
\r\n•extend the rank-modulation scheme to support rankings with repetitions, in order to\r\nimprove the storage density;
\r\n•derive a tight upper bound of 2 bits per cell for rewriting in rank modulation with\r\nrepetitions;
\r\n•construct an efficient rewriting scheme that asymptotically approaches the upper bound\r\nof 2 bit per cell.
\r\n\r\nThe next part of this thesis studies rewriting schemes for a conventional absolute-levels\r\nmodulation. The considered model is called \u201cwrite-once memory\u201d (WOM). We focus on\r\nWOM schemes that achieve the capacity of the model. In recent years several capacity-achieving\r\nWOM schemes were proposed, based on polar codes and randomness extractors.\r\nThe contributions of this thesis to the study of WOM scheme include the following: we
\r\n\r\n•propose a new capacity-achievingWOM scheme based on sparse-graph codes, and show\r\nits attractive properties for practical implementation;
\r\n•improve the design of polarWOMschemes to remove the reliance on shared randomness\r\nand include an error-correction capability.
\r\n\r\nThe last part of the thesis studies the local rank-modulation (LRM) scheme, in which a\r\nsliding window going over a sequence of real-valued variables induces a sequence of permutations.\r\nThe LRM scheme is used to simulate a single conventional multi-level flash cell.\r\nThe simulated cell is realized by a Gray code traversing all the relative-value states where,\r\nphysically, the transition between two adjacent states in the Gray code is achieved by using\r\na single \u201cpush-to-the-top\u201d operation. The main results of the last part of the thesis are two\r\nconstructions of Gray codes with asymptotically-optimal rate.
" }, { "name": "Fakonas, James Spencer", "degree": "PhD", "year": "2015", "title": "Quantum Interference and Entanglement of Surface Plasmons", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:12052014-101005469", "creators": [ { "name": { "family": "Fakonas", "given": "James Spencer" }, "id": "Fakonas-James-Spencer", "display_name": "Fakonas, James Spencer" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9MG7MD3", "abstract": "Surface plasma waves arise from the collective oscillations of billions of electrons at the surface of a metal in unison. The simplest way to quantize these waves is by direct analogy to electromagnetic fields in free space, with the surface plasmon, the quantum of the surface plasma wave, playing the same role as the photon. It follows that surface plasmons should exhibit all of the same quantum phenomena that photons do, including quantum interference and entanglement.
\r\n\r\nUnlike photons, however, surface plasmons suffer strong losses that arise from the scattering of free electrons from other electrons, phonons, and surfaces. Under some circumstances, these interactions might also cause \u201cpure dephasing,\u201d which entails a loss of coherence without absorption. Quantum descriptions of plasmons usually do not account for these effects explicitly, and sometimes ignore them altogether. In light of this extra microscopic complexity, it is necessary for experiments to test quantum models of surface plasmons.
\r\n\r\nIn this thesis, I describe two such tests that my collaborators and I performed. The first was a plasmonic version of the Hong-Ou-Mandel experiment, in which we observed two-particle quantum interference between plasmons with a visibility of 93 \u00b1 1%. This measurement confirms that surface plasmons faithfully reproduce this effect with the same visibility and mutual coherence time, to within measurement error, as in the photonic case.
\r\n\r\nThe second experiment demonstrated path entanglement between surface plasmons with a visibility of 95 \u00b1 2%, confirming that a path-entangled state can indeed survive without measurable decoherence. This measurement suggests that elastic scattering mechanisms of the type that might cause pure dephasing must have been weak enough not to significantly perturb the state of the metal under the experimental conditions we investigated.
\r\n\r\nThese two experiments add quantum interference and path entanglement to a growing list of quantum phenomena that surface plasmons appear to exhibit just as clearly as photons, confirming the predictions of the simplest quantum models.
" }, { "name": "Gabuchian, Vahe", "degree": "PhD", "year": "2015", "title": "Experimental Investigation of Thrust Fault Rupture Mechanics", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04222014-195027916", "creators": [ { "name": { "family": "Gabuchian", "given": "Vahe" }, "id": "Gabuchian-Vahe", "orcid": "0000-0001-7457-5921", "display_name": "Gabuchian, Vahe" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Bhat", "given": "Harsha S." }, "id": "Bhat-H-S", "role": "member", "display_name": "Bhat, Harsha S." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9J96497", "abstract": "Thrust fault earthquakes are investigated in the laboratory by generating dynamic shear ruptures along pre-existing frictional faults in rectangular plates. A considerable body of evidence suggests that dip-slip earthquakes exhibit enhanced ground motions in the acute hanging wall wedge as an outcome of broken symmetry between hanging and foot wall plates with respect to the earth surface. To understand the physical behavior of thrust fault earthquakes, particularly ground motions near the earth surface, ruptures are nucleated in analog laboratory experiments and guided up-dip towards the simulated earth surface. The transient slip event and emitted radiation mimic a natural thrust earthquake. High-speed photography and laser velocimeters capture the rupture evolution, outputting a full-field view of photo-elastic fringe contours proportional to maximum shearing stresses as well as continuous ground motion velocity records at discrete points on the specimen. Earth surface-normal measurements validate selective enhancement of hanging wall ground motions for both sub-Rayleigh and super-shear rupture speeds. The earth surface breaks upon rupture tip arrival to the fault trace, generating prominent Rayleigh surface waves. A rupture wave is sensed in the hanging wall but is, however, absent from the foot wall plate: a direct consequence of proximity from fault to seismometer. Signatures in earth surface-normal records attenuate with distance from the fault trace. Super-shear earthquakes feature greater amplitudes of ground shaking profiles, as expected from the increased tectonic pressures required to induce super-shear transition. Paired stations measure fault parallel and fault normal ground motions at various depths, which yield slip and opening rates through direct subtraction of like components. Peak fault slip and opening rates associated with the rupture tip increase with proximity to the fault trace, a result of selective ground motion amplification in the hanging wall. Fault opening rates indicate that the hanging and foot walls detach near the earth surface, a phenomenon promoted by a decrease in magnitude of far-field tectonic loads. Subsequent shutting of the fault sends an opening pulse back down-dip. In case of a sub-Rayleigh earthquake, feedback from the reflected S wave re-ruptures the locked fault at super-shear speeds, providing another mechanism of super-shear transition." }, { "name": "Gan, Lingwen", "degree": "PhD", "year": "2015", "title": "Distributed Load Control in Multiphase Radial Networks", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01272015-214848277", "creators": [ { "name": { "family": "Gan", "given": "Lingwen" }, "id": "Gan-Lingwen", "display_name": "Gan, Lingwen" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9FQ9TJ0", "abstract": "The current power grid is on the cusp of modernization due to the emergence of distributed generation and controllable loads, as well as renewable energy. On one hand, distributed and renewable generation is volatile and difficult to dispatch. On the other hand, controllable loads provide significant potential for compensating for the uncertainties. In a future grid where there are thousands or millions of controllable loads and a large portion of the generation comes from volatile sources like wind and solar, distributed control that shifts or reduces the power consumption of electric loads in a reliable and economic way would be highly valuable.
\r\n\r\nLoad control needs to be conducted with network awareness. Otherwise, voltage violations and overloading of circuit devices are likely. To model these effects, network power flows and voltages have to be considered explicitly. However, the physical laws that determine power flows and voltages are nonlinear. Furthermore, while distributed generation and controllable loads are mostly located in distribution networks that are multiphase and radial, most of the power flow studies focus on single-phase networks.
\r\n\r\nThis thesis focuses on distributed load control in multiphase radial distribution networks. In particular, we first study distributed load control without considering network constraints, and then consider network-aware distributed load control.
\r\n\r\nDistributed implementation of load control is the main challenge if network constraints can be ignored. In this case, we first ignore the uncertainties in renewable generation and load arrivals, and propose a distributed load control algorithm, Algorithm 1, that optimally schedules the deferrable loads to shape the net electricity demand. Deferrable loads refer to loads whose total energy consumption is fixed, but energy usage can be shifted over time in response to network conditions. Algorithm 1 is a distributed gradient decent algorithm, and empirically converges to optimal deferrable load schedules within 15 iterations.
\r\n\r\nWe then extend Algorithm 1 to a real-time setup where deferrable loads arrive over time, and only imprecise predictions about future renewable generation and load are available at the time of decision making. The real-time algorithm Algorithm 2 is based on model-predictive control: Algorithm 2 uses updated predictions on renewable generation as the true values, and computes a pseudo load to simulate future deferrable load. The pseudo load consumes 0 power at the current time step, and its total energy consumption equals the expectation of future deferrable load total energy request.
\r\n\r\nNetwork constraints, e.g., transformer loading constraints and voltage regulation constraints, bring significant challenge to the load control problem since power flows and voltages are governed by nonlinear physical laws. Remarkably, distribution networks are usually multiphase and radial. Two approaches are explored to overcome this challenge: one based on convex relaxation and the other that seeks a locally optimal load schedule.
\r\n\r\nTo explore the convex relaxation approach, a novel but equivalent power flow model, the branch flow model, is developed, and a semidefinite programming relaxation, called BFM-SDP, is obtained using the branch flow model. BFM-SDP is mathematically equivalent to a standard convex relaxation proposed in the literature, but numerically is much more stable. Empirical studies show that BFM-SDP is numerically exact for the IEEE 13-, 34-, 37-, 123-bus networks and a real-world 2065-bus network, while the standard convex relaxation is numerically exact for only two of these networks.
\r\n\r\nTheoretical guarantees on the exactness of convex relaxations are provided for two types of networks: single-phase radial alternative-current (AC) networks, and single-phase mesh direct-current (DC) networks. In particular, for single-phase radial AC networks, we prove that a second-order cone program (SOCP) relaxation is exact if voltage upper bounds are not binding; we also modify the optimal load control problem so that its SOCP relaxation is always exact. For single-phase mesh DC networks, we prove that an SOCP relaxation is exact if 1) voltage upper bounds are not binding, or 2) voltage upper bounds are uniform and power injection lower bounds are strictly negative; we also modify the optimal load control problem so that its SOCP relaxation is always exact.
\r\n\r\nTo seek a locally optimal load schedule, a distributed gradient-decent algorithm, Algorithm 9, is proposed. The suboptimality gap of the algorithm is rigorously characterized and close to 0 for practical networks. Furthermore, unlike the convex relaxation approach, Algorithm 9 ensures a feasible solution. The gradients used in Algorithm 9 are estimated based on a linear approximation of the power flow, which is derived with the following assumptions: 1) line losses are negligible; and 2) voltages are reasonably balanced. Both assumptions are satisfied in practical distribution networks. Empirical results show that Algorithm 9 obtains 70+ times speed up over the convex relaxation approach, at the cost of a suboptimality within numerical precision.
" }, { "name": "Gomez, Marcella Mary", "degree": "PhD", "year": "2015", "title": "On the Role of Delays in Biological Systems : Analysis and Design", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08282014-165029252", "creators": [ { "name": { "family": "Gomez", "given": "Marcella Mary" }, "id": "Gomez-Marcella-Mary", "display_name": "Gomez, Marcella Mary" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Balas", "given": "Mark J." }, "id": "Balas-M-J", "role": "member", "display_name": "Balas, Mark J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9JH3J4W", "abstract": "This work quantifies the nature of delays in genetic regulatory networks and their effect on system dynamics. It is known that a time lag can emerge from a sequence of biochemical reactions. Applying this modeling framework to the protein production processes, delay distributions are derived in a stochastic (probability density function) and deterministic setting (impulse function), whilst being shown to be equivalent under different assumptions. The dependence of the distribution properties on rate constants, gene length, and time-varying temperatures is investigated. Overall, the distribution of the delay in the context of protein production processes is shown to be highly dependent on the size of the genes and mRNA strands as well as the reaction rates. Results suggest longer genes have delay distributions with a smaller relative variance, and hence, less uncertainty in the completion times, however, they lead to larger delays. On the other hand large uncertainties may actually play a positive role, as broader distributions can lead to larger stability regions when this formalization of the protein production delays is incorporated into a feedback system.
\r\n\r\nFurthermore, evidence suggests that delays may play a role as an explicit design into existing controlling mechanisms. Accordingly, the reccurring dual-feedback motif is also investigated with delays incorporated into the feedback channels. The dual-delayed feedback is shown to have stabilizing effects through a control theoretic approach. Lastly, a distributed delay based controller design method is proposed as a potential design tool. In a preliminary study, the dual-delayed feedback system re-emerges as an effective controller design.
" }, { "name": "Gonz\u00e1lez Palacios, Carlos Roberto", "degree": "PhD", "year": "2015", "title": "Optimal Data Distributions in Machine Learning", "advisor": "Abu-Mostafa, Yaser S.; Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262015-094933189", "creators": [ { "name": { "family": "Gonz\u00e1lez Palacios", "given": "Carlos Roberto" }, "id": "Gonz\u00e1lez-Palacios-Carlos-Roberto", "display_name": "Gonz\u00e1lez Palacios, Carlos Roberto" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "co-advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "co-chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9DR2SD5", "abstract": "In the first part of the thesis we explore three fundamental questions that arise naturally when we conceive a machine learning scenario where the training and test distributions can differ. Contrary to conventional wisdom, we show that in fact mismatched training and test distribution can yield better out-of-sample performance. This optimal performance can be obtained by training with the dual distribution. This optimal training distribution depends on the test distribution set by the problem, but not on the target function that we want to learn. We show how to obtain this distribution in both discrete and continuous input spaces, as well as how to approximate it in a practical scenario. Benefits of using this distribution are exemplified in both synthetic and real data sets.
\r\n\r\nIn order to apply the dual distribution in the supervised learning scenario where the training data set is fixed, it is necessary to use weights to make the sample appear as if it came from the dual distribution. We explore the negative effect that weighting a sample can have. The theoretical decomposition of the use of weights regarding its effect on the out-of-sample error is easy to understand but not actionable in practice, as the quantities involved cannot be computed. Hence, we propose the Targeted Weighting algorithm that determines if, for a given set of weights, the out-of-sample performance will improve or not in a practical setting. This is necessary as the setting assumes there are no labeled points distributed according to the test distribution, only unlabeled samples.
\r\n\r\nFinally, we propose a new class of matching algorithms that can be used to match the training set to a desired distribution, such as the dual distribution (or the test distribution). These algorithms can be applied to very large datasets, and we show how they lead to improved performance in a large real dataset such as the Netflix dataset. Their computational complexity is the main reason for their advantage over previous algorithms proposed in the covariate shift literature.
\r\n\r\nIn the second part of the thesis we apply Machine Learning to the problem of behavior recognition. We develop a specific behavior classifier to study fly aggression, and we develop a system that allows analyzing behavior in videos of animals, with minimal supervision. The system, which we call CUBA (Caltech Unsupervised Behavior Analysis), allows detecting movemes, actions, and stories from time series describing the position of animals in videos. The method summarizes the data, as well as it provides biologists with a mathematical tool to test new hypotheses. Other benefits of CUBA include finding classifiers for specific behaviors without the need for annotation, as well as providing means to discriminate groups of animals, for example, according to their genetic line.
" }, { "name": "Han, Chao", "degree": "PhD", "year": "2015", "title": "Wide Field-of-View Microscopes and Endoscopes for Time-Lapse Imaging and High-Throughput Screening", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:01302015-101318815", "creators": [ { "name": { "family": "Han", "given": "Chao" }, "id": "Han-Chao", "display_name": "Han, Chao" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Ismagilov", "given": "Rustem F." }, "id": "Ismagilov-R-F", "role": "member", "display_name": "Ismagilov, Rustem F." }, { "name": { "family": "Lai", "given": "Lily L." }, "id": "Lai-Lily-L", "role": "member", "display_name": "Lai, Lily L." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9SF2T49", "abstract": "Wide field-of-view (FOV) microscopy is of high importance to biological research and clinical diagnosis where a high-throughput screening of samples is needed. This thesis presents the development of several novel wide FOV imaging technologies and demonstrates their capabilities in longitudinal imaging of living organisms, on the scale of viral plaques to live cells and tissues.
\r\n\r\nThe ePetri Dish is a wide FOV on-chip bright-field microscope. Here we applied an ePetri platform for plaque analysis of murine norovirus 1 (MNV-1). The ePetri offers the ability to dynamically track plaques at the individual cell death event level over a wide FOV of 6 mm \u00d7 4 mm at 30 min intervals. A density-based clustering algorithm is used to analyze the spatial-temporal distribution of cell death events to identify plaques at their earliest stages. We also demonstrate the capabilities of the ePetri in viral titer count and dynamically monitoring plaque formation, growth, and the influence of antiviral drugs.
\r\n\r\nWe developed another wide FOV imaging technique, the Talbot microscope, for the fluorescence imaging of live cells. The Talbot microscope takes advantage of the Talbot effect and can generate a focal spot array to scan the fluorescence samples directly on-chip. It has a resolution of 1.2 \u03bcm and a FOV of ~13 mm2. We further upgraded the Talbot microscope for the long-term time-lapse fluorescence imaging of live cell cultures, and analyzed the cells\u2019 dynamic response to an anticancer drug.
\r\n \r\nWe present two wide FOV endoscopes for tissue imaging, named the AnCam and the PanCam. The AnCam is based on the contact image sensor (CIS) technology, and can scan the whole anal canal within 10 seconds with a resolution of 89 \u03bcm, a maximum FOV of 100 mm \u00d7 120 mm, and a depth-of-field (DOF) of 0.65 mm. We also demonstrate the performance of the AnCam in whole anal canal imaging in both animal models and real patients. In addition to this, the PanCam is based on a smartphone platform integrated with a panoramic annular lens (PAL), and can capture a FOV of 18 mm \u00d7 120 mm in a single shot with a resolution of 100\u2500140 \u03bcm. In this work we demonstrate the PanCam\u2019s performance in imaging a stained tissue sample.
" }, { "name": "Harrison, Laura Anne", "degree": "PhD", "year": "2015", "title": "Real-World Social Cognition: Context Effects in Face and Threat Processing", "advisor": "Adolphs, Ralph", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292015-165113710", "creators": [ { "name": { "family": "Harrison", "given": "Laura Anne" }, "id": "Harrison-Laura-Anne", "orcid": "0000-0001-5383-7769", "display_name": "Harrison, Laura Anne" } ], "advisors": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "advisor", "display_name": "Adolphs, Ralph" } ], "committee": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "chair", "display_name": "O'Doherty, John P." }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Tsao", "given": "Doris Y." }, "id": "Tsao-D-Y", "role": "member", "display_name": "Tsao, Doris Y." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/Z95H7D7P", "abstract": "As borne out by everyday social experience, social cognition is highly dependent on context, modulated by a host of factors that arise from the social environment in which we live. While streamlined laboratory research provides excellent experimental control, it can be limited to telling us about the capabilities of the brain under artificial conditions, rather than elucidating the processes that come into play in the real world. Consideration of the impact of ecologically valid contextual cues on social cognition will improve the generalizability of social neuroscience findings also to pathology, e.g., to psychiatric illnesses. To help bridge between laboratory research and social cognition as we experience it in the real world, this thesis investigates three themes: (1) increasing the naturalness of stimuli with richer contextual cues, (2) the potentially special contextual case of social cognition when two people interact directly, and (3) a third theme of experimental believability, which runs in parallel to the first two themes. Focusing on the first two themes, in work with two patient populations, we explore neural contributions to two topics in social cognition. First, we document a basic approach bias in rare patients with bilateral lesions of the amygdala. This finding is then related to the contextual factor of ambiguity, and further investigated together with other contextual cues in a sample of healthy individuals tested over the internet, finally yielding a hierarchical decision tree for social threat evaluation. Second, we demonstrate that neural processing of eye gaze in brain structures related to face, gaze, and social processing is differently modulated by the direct presence of another live person. This question is investigated using fMRI in people with autism and controls. Across a range of topics, we demonstrate that two themes of ecological validity \u2014 integration of naturalistic contextual cues, and social interaction \u2014 influence social cognition, that particular brain structures mediate this processing, and that it will be crucial to study interaction in order to understand disorders of social interaction such as autism. " }, { "name": "Heyden, Stefanie", "degree": "PhD", "year": "2015", "title": "Micromechanical Damage and Fracture in Elastomeric Polymers", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:12202014-233824767", "creators": [ { "name": { "family": "Heyden", "given": "Stefanie" }, "id": "Heyden-Stefanie", "display_name": "Heyden, Stefanie" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Weinberg", "given": "Kerstin" }, "id": "Weinberg-K", "role": "member", "display_name": "Weinberg, Kerstin" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/Z9HX19NS", "abstract": "This thesis aims at a simple one-parameter macroscopic model of distributed damage and fracture of polymers that is amenable to a straightforward and efficient numerical implementation. The failure model is motivated by post-mortem fractographic observations of void nucleation, growth and coalescence in polyurea stretched to failure, and accounts for the specific fracture energy per unit area attendant to rupture of the material.
\r\n\r\nFurthermore, it is shown that the macroscopic model can be rigorously derived, in the sense of optimal scaling, from a micromechanical model of chain elasticity and failure regularized by means of fractional strain-gradient elasticity. Optimal scaling laws that supply a link between the single parameter of the macroscopic model, namely the critical energy-release rate of the material, and micromechanical parameters pertaining to the elasticity and strength of the polymer chains, and to the strain-gradient elasticity regularization, are derived. Based on optimal scaling laws, it is shown how the critical energy-release rate of specific materials can be determined from test data. In addition, the scope and fidelity of the model is demonstrated by means of an example of application, namely Taylor-impact experiments of polyurea rods. Hereby, optimal transportation meshfree approximation schemes using maximum-entropy interpolation functions are employed.
\r\n\r\nFinally, a different crazing model using full derivatives of the deformation gradient and a core cut-off is presented, along with a numerical non-local regularization model. The numerical model takes into account higher-order deformation gradients in a finite element framework. It is shown how the introduction of non-locality into the model stabilizes the effect of strain localization to small volumes in materials undergoing softening. From an investigation of craze formation in the limit of large deformations, convergence studies verifying scaling properties of both local- and non-local energy contributions are presented.
" }, { "name": "Hoenselaar, Andreas", "degree": "PhD", "year": "2015", "title": "The Structure of Hippocampal Activity During REM Sleep", "advisor": "Siapas, Athanassios G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11172014-000718184", "creators": [ { "name": { "family": "Hoenselaar", "given": "Andreas" }, "id": "Hoenselaar-Andreas", "display_name": "Hoenselaar, Andreas" } ], "advisors": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "advisor", "display_name": "Siapas, Athanassios G." } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "member", "display_name": "Siapas, Athanassios G." } ], "option_major": [ "cns" ], "doi": "10.7907/Z98W3B8H", "abstract": "The hippocampus is a brain structure critical for the formation of long-term episodic memories. The current predominant theory is that memories are gradually established across neocortical networks under the influence of hippocampal activity. This process of memory consolidation is conjectured to occur during sleep, which is characterized by two different modes of activation: slow-wave sleep (SWS) and rapid eye movement (REM) sleep. The functional roles of these two different sleep states remain unknown. Paradoxically, REM sleep exhibits the main features of awake activity, and is the stage of sleep when most dreams occur. Despite decades of study, the organization and function of REM sleep activity remains poorly understood. The goal of this thesis is to achieve a deeper quantitative understanding of the patterns of firing in area CA1 of the hippocampus during REM sleep using chronic multi-tetrode recordings from freely behaving and naturally sleeping rats. Our analysis shows that CA1 neurons significantly elevate their firing rate for periods that are short in relation to the duration of the REM sleep episode. Furthermore, for the majority of neurons, there is exactly one such burst per REM episode. This leads to lower overall firing rates and sparser population activity in CA1 compared to SWS. The time of onset of these bursts defines a natural order of firing across the population of recorded neurons within each REM episode. We demonstrate that this order does not repeat across REM episodes. Our results suggest that CA1 neurons are activated in random sequences across REM episodes, resulting in sparse patterns with only a small fraction of neurons active at any given time." }, { "name": "Homyk, Andrew P.", "degree": "PhD", "year": "2015", "title": "Scalable Methods for Deterministic Integration of Quantum Emitters in Photonic Crystal Cavities", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022015-141742970", "creators": [ { "name": { "family": "Homyk", "given": "Andrew P." }, "id": "Homyk-Andrew-P", "display_name": "Homyk, Andrew P." } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "orcid": "0000-0002-8903-7939", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Walavalkar", "given": "Sameer S." }, "id": "Walavalkar-S-S", "role": "member", "display_name": "Walavalkar, Sameer S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9D50JXC", "abstract": "We investigated four unique methods for achieving scalable, deterministic integration of quantum emitters into ultra-high Q{V photonic crystal cavities, including selective area heteroepitaxy, engineered photoemission from silicon nanostructures, wafer bonding and dimensional reduction of III-V quantum wells, and cavity-enhanced optical trapping. In these areas, we were able to demonstrate site-selective heteroepitaxy, size-tunable photoluminescence from silicon nanostructures, Purcell modification of QW emission spectra, and limits of cavity-enhanced optical trapping designs which exceed any reports in the literature and suggest the feasibility of capturing- and detecting nanostructures with dimensions below 10 nm. In addition to process scalability and the requirement for achieving accurate spectral- and spatial overlap between the emitter and cavity, these techniques paid specific attention to the ability to separate the cavity and emitter material systems in order to allow optimal selection of these independently, and eventually enable monolithic integration with other photonic and electronic circuitry.
\r\n\r\nWe also developed an analytic photonic crystal design process yielding optimized cavity tapers with minimal computational effort, and reported on a general cavity modification which exhibits improved fabrication tolerance by relying exclusively on positional- rather than dimensional tapering. We compared several experimental coupling techniques for device characterization. Significant efforts were devoted to optimizing cavity fabrication, including the use of atomic layer deposition to improve surface quality, exploration into factors affecting the design fracturing, and automated analysis of SEM images. Using optimized fabrication procedures, we experimentally demonstrated 1D photonic crystal nanobeam cavities exhibiting the highest Q/V reported on substrate. Finally, we analyzed the bistable behavior of the devices to quantify the nonlinear optical response of our cavities.
" }, { "name": "Hulikal Sampath Kumaran, Srivatsan", "degree": "PhD", "year": "2015", "title": "Collective Behavior of Asperities as a Model for Friction and Adhesion", "advisor": "Lapusta, Nadia; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:05172015-152006825", "creators": [ { "name": { "family": "Hulikal Sampath Kumaran", "given": "Srivatsan" }, "id": "Hulikal-Sampath-Kumaran-Srivatsan", "display_name": "Hulikal Sampath Kumaran, Srivatsan" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "co-advisor", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "co-advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z94M92HM", "abstract": "Understanding friction and adhesion in static and sliding contact of surfaces is important in numerous physical phenomena and technological applications. Most surfaces are rough at the microscale, and thus the real area of contact is only a fraction of the nominal area. The macroscopic frictional and adhesive response is determined by the collective behavior of the population of evolving and interacting microscopic contacts. This collective behavior can be very different from the behavior of individual contacts. It is thus important to understand how the macroscopic response emerges from the microscopic one.
\r\n\r\nIn this thesis, we develop a theoretical and computational framework to study the collective behavior. Our philosophy is to assume a simple behavior of a single asperity and study the collective response of an ensemble. Our work bridges the existing well-developed studies of single asperities with phenomenological laws that describe macroscopic rate-and-state behavior of frictional interfaces. We find that many aspects of the macroscopic behavior are robust with respect to the microscopic response. This explains why qualitatively similar frictional features are seen for a diverse range of materials.
\r\n\r\nWe first show that the collective response of an ensemble of one-dimensional independent viscoelastic elements interacting through a mean field reproduces many qualitative features of static and sliding friction evolution. The resulting macroscopic behavior is different from the microscopic one: for example, even if each contact is velocity-strengthening, the macroscopic behavior can be velocity-weakening. The framework is then extended to incorporate three-dimensional rough surfaces, long- range elastic interactions between contacts, and time-dependent material behaviors such as viscoelasticity and viscoplasticity. Interestingly, the mean field behavior dominates and the elastic interactions, though important from a quantitative perspective, do not change the qualitative macroscopic response. Finally, we examine the effect of adhesion on the frictional response as well as develop a force threshold model for adhesion and mode I interfacial cracks.
" }, { "name": "Ji, Chenguang", "degree": "PhD", "year": "2015", "title": "Design of Antenna-Coupled Lumped-Element Titanium Nitride KIDs for LongWavelength Multi-Band Continuum Imaging", "advisor": "Golwala, Sunil", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282015-121920930", "creators": [ { "name": { "family": "Ji", "given": "Chenguang" }, "id": "Ji-Chenguang", "display_name": "Ji, Chenguang" } ], "advisors": [ { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "role": "advisor", "display_name": "Golwala, Sunil" } ], "committee": [ { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "role": "chair", "display_name": "Golwala, Sunil" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9W66HQ7", "abstract": "Many applications in cosmology and astrophysics at millimeter wavelengths including CMB polarization, studies of galaxy clusters using the Sunyaev-Zeldovich effect (SZE), and studies of star formation at high redshift and in our local universe and our galaxy, require large-format arrays of millimeter-wave detectors. Feedhorn and phased-array antenna architectures for receiving mm-wave light present numerous advantages for control of systematics, for simultaneous coverage of both polarizations and/or multiple spectral bands, and for preserving the coherent nature of the incoming light. This enables the application of many traditional \"RF\" structures such as hybrids, switches,\r\nand lumped-element or microstrip band-defining filters.
\r\n\r\nSimultaneously, kinetic inductance detectors (KIDs) using high-resistivity materials like titanium nitride are an attractive sensor option for large-format arrays because they are highly multiplexable and because they can have sensitivities reaching the condition of background-limited detection. A\r\nKID is a LC resonator. Its inductance includes the geometric inductance and kinetic inductance of the inductor in the superconducting phase. A photon absorbed by the superconductor breaks a Cooper pair into normal-state electrons and perturbs its kinetic inductance, rendering it a detector\r\nof light. The responsivity of KID is given by the fractional frequency shift of the LC resonator per unit optical power.
\r\n\r\nHowever, coupling these types of optical reception elements to KIDs is a challenge because of the impedance mismatch between the microstrip transmission line exiting these architectures and the high resistivity of titanium nitride. Mitigating direct absorption of light through free space coupling to the inductor of KID is another challenge. We present a detailed titanium nitride KID\r\ndesign that addresses these challenges. The KID inductor is capacitively coupled to the microstrip in such a way as to form a lossy termination without creating an impedance mismatch. A parallel plate capacitor design mitigates direct absorption, uses hydrogenated amorphous silicon, and yields acceptable noise. We show that the optimized design can yield expected sensitivities very close to\r\nthe fundamental limit for a long wavelength imager (LWCam) that covers six spectral bands from 90 to 400 GHz for SZE studies.
\r\n\r\nExcess phase (frequency) noise has been observed in KID and is very likely caused by two-level systems (TLS) in dielectric materials. The TLS hypothesis is supported by the measured dependence of the noise on resonator internal power and temperature. However, there is still a lack of a unified microscopic theory which can quantitatively model the properties of the TLS noise. In this thesis we\r\nderive the noise power spectral density due to the coupling of TLS with phonon bath based on an existing model and compare the theoretical predictions about power and temperature dependences with experimental data. We discuss the limitation of such a model and propose the direction for future study.
" }, { "name": "Kang, Dongyang", "degree": "PhD", "year": "2015", "title": "MEMS for Diabetic Retinopathy", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042015-065451017", "creators": [ { "name": { "family": "Kang", "given": "Dongyang" }, "id": "Kang-Dongyang", "display_name": "Kang, Dongyang" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "chair", "display_name": "Choo, Hyuck" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Humayun", "given": "Mark" }, "id": "Humayun-M", "role": "member", "display_name": "Humayun, Mark" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z97D2S34", "abstract": "As the worldwide prevalence of diabetes mellitus continues to increase, diabetic retinopathy remains the leading cause of visual impairment and blindness in many developed countries. Between 32 to 40 percent of about 246 million people with diabetes develop diabetic retinopathy. Approximately 4.1 million American adults 40 years and older are affected by diabetic retinopathy. This glucose-induced microvascular disease progressively damages the tiny blood vessels that nourish the retina, the light-sensitive tissue at the back of the eye, leading to retinal ischemia (i.e., inadequate blood flow), retinal hypoxia (i.e., oxygen deprivation), and retinal nerve cell degeneration or death. It is a most serious sight-threatening complication of diabetes, resulting in significant irreversible vision loss, and even total blindness.
\r\n\r\nUnfortunately, although current treatments of diabetic retinopathy (i.e., laser therapy, vitrectomy surgery and anti-VEGF therapy) can reduce vision loss, they only slow down but cannot stop the degradation of the retina. Patients require repeated treatment to protect their sight. The current treatments also have significant drawbacks. Laser therapy is focused on preserving the macula, the area of the retina that is responsible for sharp, clear, central vision, by sacrificing the peripheral retina since there is only limited oxygen supply. Therefore, laser therapy results in a constricted peripheral visual field, reduced color vision, delayed dark adaptation, and weakened night vision. Vitrectomy surgery increases the risk of neovascular glaucoma, another devastating ocular disease, characterized by the proliferation of fibrovascular tissue in the anterior chamber angle. Anti-VEGF agents have potential adverse effects, and currently there is insufficient evidence to recommend their routine use.
\r\n\r\nIn this work, for the first time, a paradigm shift in the treatment of diabetic retinopathy is proposed: providing localized, supplemental oxygen to the ischemic tissue via an implantable MEMS device. The retinal architecture (e.g., thickness, cell densities, layered structure, etc.) of the rabbit eye exposed to ischemic hypoxic injuries was well preserved after targeted oxygen delivery to the hypoxic tissue, showing that the use of an external source of oxygen could improve the retinal oxygenation and prevent the progression of the ischemic cascade.
\r\n\r\nThe proposed MEMS device transports oxygen from an oxygen-rich space to the oxygen-deficient vitreous, the gel-like fluid that fills the inside of the eye, and then to the ischemic retina. This oxygen transport process is purely passive and completely driven by the gradient of oxygen partial pressure (pO2). Two types of devices were designed. For the first type, the oxygen-rich space is underneath the conjunctiva, a membrane covering the sclera (white part of the eye), beneath the eyelids and highly permeable to oxygen in the atmosphere when the eye is open. Therefore, sub-conjunctival pO2 is very high during the daytime. For the second type, the oxygen-rich space is inside the device since pure oxygen is needle-injected into the device on a regular basis.
\r\nTo prevent too fast or too slow permeation of oxygen through the device that is made of parylene and silicone (two widely used biocompatible polymers in medical devices), the material properties of the hybrid parylene/silicone were investigated, including mechanical behaviors, permeation rates, and adhesive forces. Then the thicknesses of parylene and silicone became important design parameters that were fine-tuned to reach the optimal oxygen permeation rate.
\r\n\r\nThe passive MEMS oxygen transporter devices were designed, built, and tested in both bench-top artificial eye models and in-vitro porcine cadaver eyes. The 3D unsteady saccade-induced laminar flow of water inside the eye model was modeled by computational fluid dynamics to study the convective transport of oxygen inside the eye induced by saccade (rapid eye movement). The saccade-enhanced transport effect was also demonstrated experimentally. Acute in-vivo animal experiments were performed in rabbits and dogs to verify the surgical procedure and the device functionality. Various hypotheses were confirmed both experimentally and computationally, suggesting that both the two types of devices are very promising to cure diabetic retinopathy. The chronic implantation of devices in ischemic dog eyes is still underway.
\r\nThe proposed MEMS oxygen transporter devices can be also applied to treat other ocular and systemic diseases accompanied by retinal ischemia, such as central retinal artery occlusion, carotid artery disease, and some form of glaucoma.
\r\n" }, { "name": "Kozachkov, Henry", "degree": "PhD", "year": "2015", "title": "Modifying Bulk Metallic Glasses: Composites and Configurational States", "advisor": "Johnson, William Lewis; Hofmann, Douglas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04022015-231633336", "creators": [ { "name": { "family": "Kozachkov", "given": "Henry" }, "id": "Kozachkov-Henry", "display_name": "Kozachkov, Henry" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "co-advisor", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Hofmann", "given": "Douglas C." }, "id": "Hofmann-D-C", "role": "co-advisor", "display_name": "Hofmann, Douglas C." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Hofmann", "given": "Douglas C." }, "id": "Hofmann-D-C", "role": "member", "display_name": "Hofmann, Douglas C." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9JQ0XZ4", "abstract": "Bulk metallic glasses (BMGs) maybe be considered to share some of the same inherent trade-offs as engineering ceramics. While BMGs typically exhibit high yield strengths, and while some have surprising fracture toughness, they exhibiting little to no tensile ductility, and fail in a brittle manner under uniaxial loading. Speaking broadly, there are two complimentary approaches to improving on these shortcomings: 1) create bulk metallic glass matrix composites (BMGMCs) and 2) improve the properties of a monolithic BMG. The structure of this thesis mirrors this division, with chapters 2-7 focusing on creating and processing amorphous metal matrix composites, and chapter 8 focusing on modifying the properties of a monolithic BGM by altering its configurational state through irradiation." }, { "name": "Krause, Alexander Grey", "degree": "PhD", "year": "2015", "title": "Acceleration Sensing, Feedback Cooling, and Nonlinear Dynamics with Nanoscale Cavity-Optomechanical Devices", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01162015-120819334", "creators": [ { "name": { "family": "Krause", "given": "Alexander Grey" }, "id": "Krause-Alexander-Grey", "display_name": "Krause, Alexander Grey" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "role": "member", "display_name": "Chen, Yanbei" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z98K771J", "abstract": "Light has long been used for the precise measurement of moving bodies, but the burgeoning field of optomechanics is concerned with the interaction of light and matter in a regime where the typically weak radiation pressure force of light is able to push back on the moving object. This field began with the realization in the late 1960's that the momentum imparted by a recoiling photon on a mirror would place fundamental limits on the smallest measurable displacement of that mirror. This coupling between the frequency of light and the motion of a mechanical object does much more than simply add noise, however. It has been used to cool objects to their quantum ground state, demonstrate electromagnetically-induced-transparency, and modify the damping and spring constant of the resonator. Amazingly, these radiation pressure effects have now been demonstrated in systems ranging 18 orders of magnitude in mass (kg to fg).
\r\n\r\nIn this work we will focus on three diverse experiments in three different optomechanical devices which span the fields of inertial sensors, closed-loop feedback, and nonlinear dynamics. The mechanical elements presented cover 6 orders of magnitude in mass (ng to fg), but they all employ nano-scale photonic crystals to trap light and resonantly enhance the light-matter interaction. In the first experiment we take advantage of the sub-femtometer displacement resolution of our photonic crystals to demonstrate a sensitive chip-scale optical accelerometer with a kHz-frequency mechanical resonator. This sensor has a noise density of approximately 10 micro-g/rt-Hz over a useable bandwidth of approximately 20 kHz and we demonstrate at least 50 dB of linear dynamic sensor range. We also discuss methods to further improve performance of this device by a factor of 10.
\r\n\r\nIn the second experiment, we used a closed-loop measurement and feedback system to damp and cool a room-temperature MHz-frequency mechanical oscillator from a phonon occupation of 6.5 million down to just 66. At the time of the experiment, this represented a world-record result for the laser cooling of a macroscopic mechanical element without the aid of cryogenic pre-cooling. Furthermore, this closed-loop damping yields a high-resolution force sensor with a practical bandwidth of 200 kHZ and the method has applications to other optomechanical sensors.
\r\n\r\nThe final experiment contains results from a GHz-frequency mechanical resonator in a regime where the nonlinearity of the radiation-pressure interaction dominates the system dynamics. In this device we show self-oscillations of the mechanical element that are driven by multi-photon-phonon scattering. Control of the system allows us to initialize the mechanical oscillator into a stable high-amplitude attractor which would otherwise be inaccessible. To provide context, we begin this work by first presenting an intuitive overview of optomechanical systems and then providing an extended discussion of the principles underlying the design and fabrication of our optomechanical devices.
" }, { "name": "Lim, Keng-Wit", "degree": "PhD", "year": "2015", "title": "Discrete Modeling of Granular Media: A NURBS-based Approach", "advisor": "Andrade, Jose E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12042014-104112714", "creators": [ { "name": { "family": "Lim", "given": "Keng-Wit" }, "id": "Lim-Keng-Wit", "display_name": "Lim, Keng-Wit" } ], "advisors": [ { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "advisor", "display_name": "Andrade, Jose E." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ampuero", "given": "Jean-Paul" }, "id": "Ampuero-J-P", "role": "member", "display_name": "Ampuero, Jean-Paul" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/Z9W093V4", "abstract": "This dissertation is concerned with the development of a new discrete element method (DEM) based on Non-Uniform Rational Basis Splines (NURBS). With NURBS, the new DEM is able to capture sphericity and angularity, the two particle morphological measures used in characterizing real grain geometries. By taking advantage of the parametric nature of NURBS, the Lipschitzian dividing rectangle (DIRECT) global optimization procedure is employed as a solution procedure to the closest-point projection problem, which enables the contact treatment of non-convex particles. A contact dynamics (CD) approach to the NURBS-based discrete method is also formulated. By combining particle shape flexibility, properties of implicit time-integration, and non-penetrating constraints, we target applications in which the classical DEM either performs poorly or simply fails, i.e., in granular systems composed of rigid or highly stiff angular particles and subjected to quasistatic or dynamic flow conditions. The CD implementation is made simple by adopting a variational framework, which enables the resulting discrete problem to be readily solved using off-the-shelf mathematical programming solvers. The capabilities of the NURBS-based DEM are demonstrated through 2D numerical examples that highlight the effects of particle morphology on the macroscopic response of granular assemblies under quasistatic and dynamic flow conditions, and a 3D characterization of material response in the shear band of a real triaxial specimen." }, { "name": "Linares-Guerrero, Esperanza Crystal", "degree": "PhD", "year": "2015", "title": "Experimental Study on Inertial Effects in Liquid-Solid Flows", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042015-153430245", "creators": [ { "name": { "family": "Linares-Guerrero", "given": "Esperanza Crystal" }, "id": "Linares-Guerrero-Esperanza-Crystal", "display_name": "Linares-Guerrero, Esperanza Crystal" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "chair", "display_name": "Brady, John F." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Lamb", "given": "Michael P." }, "id": "Lamb-M-P", "role": "member", "display_name": "Lamb, Michael P." }, { "name": { "family": "Zenit Camacho", "given": "Jose Roberto" }, "id": "Zenit-Camacho-J-R", "role": "member", "display_name": "Zenit Camacho, Jose Roberto" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9GT5K4J", "abstract": "This thesis presents experimental measurements of the rheological behavior of liquid-solid mixtures at moderate Reynolds (defined by the shear rate and particle diameter) and Stokes numbers, ranging from 3 ≤ Re ≤ 1.6 × 103 and 0.4 ≤ St ≤ 195. The experiments use a specifically designed Couette cylindrical rheometer that allows for probing the transition from transporting a pure liquid to transporting a dense suspension of particles. Measurements of the shear stress are presented for a wide range of particle concentration (10 to 60% in volume) and for particle to fluid density ratio between 1 and 1.05. The effective relative viscosity exhibits a strong dependence on the solid fraction for all density ratios tested. For density ratio of 1 the effective viscosity increases with Stokes number (St) for volume fractions (φ) lower than 40% and becomes constant for higher φ. When the particles are denser than the liquid, the effective viscosity shows a stronger dependance on St. An analysis of the particle resuspension for the case with a density ratio of 1.05 is presented and used to predict the local volume fraction where the shear stress measurements take place. When the local volume fraction is considered, the effective viscosity for settling and no settling particles is consistent, indicating that the effective viscosity is independent of differences in density between the solid and liquid phase. Shear stress measurements of pure fluids (no particles) were performed using the same rheometer, and a deviation from laminar behavior is observed for gap Reynolds numbers above 4× 103, indicating the presence of hydrodynamic instabilities associated with the rotation of the outer cylinder. The increase on the effective viscosity with Stokes numbers observed for mixtures with φ ≤ 30% appears to be affected by such hydrodynamic instabilities. The effective viscosity for the current experiments is considerably higher than the one reported in non-inertial suspensions. " }, { "name": "Lydon, Joseph John II", "degree": "PhD", "year": "2015", "title": "Nonlinear Effects in Granular Crystals with Broken Periodicity", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:01212015-023955427", "creators": [ { "name": { "family": "Lydon", "given": "Joseph John II" }, "id": "Lydon-JJoseph-John-II", "display_name": "Lydon, Joseph John II" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z93J39XM", "abstract": "When studying physical systems, it is common to make approximations: the contact interaction is linear, the crystal is periodic, the variations occurs slowly, the mass of a particle is constant with velocity, or the position of a particle is exactly known are just a few examples. These approximations help us simplify complex systems to make them more comprehensible while still demonstrating interesting physics. But what happens when these assumptions break down? This question becomes particularly interesting in the materials science community in designing new materials structures with exotic properties In this thesis, we study the mechanical response and dynamics in granular crystals, in which the approximation of linearity and infinite size break down. The system is inherently finite, and contact interaction can be tuned to access different nonlinear regimes. When the assumptions of linearity and perfect periodicity are no longer valid, a host of interesting physical phenomena presents itself. The advantage of using a granular crystal is in its experimental feasibility and its similarity to many other materials systems. This allows us to both leverage past experience in the condensed matter physics and materials science communities while also presenting results with implications beyond the narrower granular physics community. In addition, we bring tools from the nonlinear systems community to study the dynamics in finite lattices, where there are inherently more degrees of freedom. This approach leads to the major contributions of this thesis in broken periodic systems. We demonstrate the first defect mode whose spatial profile can be tuned from highly localized to completely delocalized by simply tuning an external parameter. Using the sensitive dynamics near bifurcation points, we present a completely new approach to modifying the incremental stiffness of a lattice to arbitrary values. We show how using nonlinear defect modes, the incremental stiffness can be tuned to anywhere in the force-displacement relation. Other contributions include demonstrating nonlinear breakdown of mechanical filters as a result of finite size, and the presents of frequency attenuation bands in essentially nonlinear materials. We finish by presenting two new energy harvesting systems based on our experience with instabilities in weakly nonlinear systems. " }, { "name": "Mahdavi, Alborz", "degree": "PhD", "year": "2015", "title": "Synthetic Biology Tools for Targeted Incorporation of Non-Canonical Amino Acids into Cellular Proteins", "advisor": "Tirrell, David A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12052014-154140797", "creators": [ { "name": { "family": "Mahdavi", "given": "Alborz" }, "id": "Mahdavi-Alborz", "orcid": "0000-0002-8790-8112", "display_name": "Mahdavi, Alborz" } ], "advisors": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "orcid": "0000-0003-3175-4596", "role": "advisor", "display_name": "Tirrell, David A." } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "orcid": "0000-0003-3175-4596", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Mazmanian", "given": "Sarkis K." }, "id": "Mazmanian-S-K", "orcid": "0000-0003-2713-1513", "role": "member", "display_name": "Mazmanian, Sarkis K." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "bioeng" ], "doi": "10.7907/Z9W66HS4", "abstract": "Proteins mediate many essential functions in cells, and methods to profile cellular proteins are of great interest for biological discovery. Whereas all of the cells in an organism share the same genome, the landscape of proteins (the proteome) varies between different cell types and over the lifetime of the organism. Rapid progress in mass spectrometers is enabling the detailed analysis of cellular proteomes. Whereas better instruments increase coverage, throughput, and measurement precision, new chemical reporters, metabolic tags, and synthetic biology techniques are required to enhance the specificity and spatiotemporal resolution of protein labeling and detection. This work introduces methods for cell-selective proteome analysis through the incorporation of non-canonical amino acids into newly synthesized proteins.
\r\n \r\nChapter I provides an overview of current technologies for translational profiling and proteomic analysis in cells. Strategies for the residue-specific incorporation of non-canonical amino acids and bioorthogonal non-canonical amino acid tagging are discussed. Chapter II introduces a new approach for the identification of secreted bacterial proteins from infected host cells using non-canonical amino acid labeling. This work demonstrates an application of cell-selective proteome labeling. Selectivity is achieved through controlled expression of a mutant aminoacyl tRNA synthetase (aaRS) enzyme that enables the metabolic incorporation of a non-canonical amino acid.
\r\n \r\nIdeally, the activity of multiple genes should be used to genetically control the extent of proteome labeling in cells. This is useful because many cell states are characterized by the activity of multiple genes and identified based on the expression of several proteins. Therefore chapter III introduces a novel approach to control proteome labeling as a function of multiple promoters using a genetically encoded AND gate based on a bisected methionyl-tRNA synthetase, a class I aaRS. Cellular protein labeling occurs only upon activation of two different promoters that drive expression of the N- and C-terminal fragments of this bisected aaRS. The utility of this tool is demonstrated by the selective labeling of proteins in subpopulations of bacterial cells in a laminar-flow microfluidic channel.
\r\n \r\nChapter IV extends the cell-selective incorporation of non-canonical amino acids from bacterial systems to mammalian cells by introducing a mutant mammalian methionyl-tRNA synthetase for cell-targeted proteome labeling. This enzyme is genetically encoded and can be conditionally activated for time-resolved and cell-targeted proteome analysis in a variety of different mammalian cell types. Chapter V uses this enzyme for lineage-specific proteomic analysis of mouse embryonic stem cells during differentiation to cardiac and mesoderm lineages. This approach for lineage-specific protein labeling enables the unbiased and comprehensive analysis of proteomic changes that occur during stem cell differentiation and cell-fate commitment.
\r\n \r\nAppendices A-G provide brief summaries of publications and research efforts during my PhD that are not directly related to this thesis. These publications are the result of a number of collaborations that I have been fortunate to be involved with during my graduate research.
\r\n\r\nThe technologies and methods introduced in this thesis provide versatile tools for the comprehensive and unbiased detection and identification of newly synthesized proteins in complex multicellular systems. Time-resolved, genetically encoded, and spatially defined non-canonical amino acid incorporation enables the identification of proteins involved in cell-cell interactions and the proteins made during specific cell states.
\r\n" }, { "name": "Mao, Wei", "degree": "PhD", "year": "2015", "title": "Information-Theoretic Studies and Capacity Bounds: Group Network Codes and Energy Harvesting Communication Systems", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:04272015-133555770", "creators": [ { "name": { "family": "Mao", "given": "Wei" }, "id": "Mao-Wei", "display_name": "Mao, Wei" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Kostina", "given": "Victoria" }, "id": "Kostina-V", "role": "member", "display_name": "Kostina, Victoria" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9ZS2TFB", "abstract": "Network information theory and channels with memory are two important but difficult frontiers of information theory. In this two-parted dissertation, we study these two areas, each comprising one part. For the first area we study the so-called entropy vectors via finite group theory, and the network codes constructed from finite groups. In particular, we identify the smallest finite group that violates the Ingleton inequality, an inequality respected by all linear network codes, but not satisfied by all entropy vectors. Based on the analysis of this group we generalize it to several families of Ingleton-violating groups, which may be used to design good network codes. Regarding that aspect, we study the network codes constructed with finite groups, and especially show that linear network codes are embedded in the group network codes constructed with these Ingleton-violating families. Furthermore, such codes are strictly more powerful than linear network codes, as they are able to violate the Ingleton inequality while linear network codes cannot. For the second area, we study the impact of memory to the channel capacity through a novel communication system: the energy harvesting channel. Different from traditional communication systems, the transmitter of an energy harvesting channel is powered by an exogenous energy harvesting device and a finite-sized battery. As a consequence, each time the system can only transmit a symbol whose energy consumption is no more than the energy currently available. This new type of power supply introduces an unprecedented input constraint for the channel, which is random, instantaneous, and has memory. Furthermore, naturally, the energy harvesting process is observed causally at the transmitter, but no such information is provided to the receiver. Both of these features pose great challenges for the analysis of the channel capacity. In this work we use techniques from channels with side information, and finite state channels, to obtain lower and upper bounds of the energy harvesting channel. In particular, we study the stationarity and ergodicity conditions of a surrogate channel to compute and optimize the achievable rates for the original channel. In addition, for practical code design of the system we study the pairwise error probabilities of the input sequences." }, { "name": "Mason, Gemma Ellen", "degree": "PhD", "year": "2015", "title": "Full and Model-Reduced Structure-Preserving Simulation of Incompressible Fluids", "advisor": "Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312015-134909133", "creators": [ { "name": { "family": "Mason", "given": "Gemma Ellen" }, "id": "Mason-Gemma-Ellen", "display_name": "Mason, Gemma Ellen" } ], "advisors": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z9KK98QG", "abstract": "This thesis outlines the construction of several types of structured integrators for incompressible fluids. We first present a vorticity integrator, which is the Hamiltonian counterpart of the existing Lagrangian-based fluid integrator. We next present a model-reduced variational Eulerian integrator for incompressible fluids, which combines the efficiency gains of dimension reduction, the qualitative robustness to coarse spatial and temporal resolutions of geometric integrators, and the simplicity of homogenized boundary conditions on regular grids to deal with arbitrarily-shaped domains with sub-grid accuracy.
\r\n\r\nBoth these numerical methods involve approximating the Lie group of volume-preserving diffeomorphisms by a finite-dimensional Lie-group and then restricting the resulting variational principle by means of a non-holonomic constraint. Advantages and limitations of this discretization method will be outlined. It will be seen that these derivation techniques are unable to yield symplectic integrators, but that energy conservation is easily obtained, as is a discretized version of Kelvin's circulation theorem.
\r\n\r\nFinally, we outline the basis of a spectral discrete exterior calculus, which may be a useful element in producing structured numerical methods for fluids in the future.
" }, { "name": "Mauger, Lisa Mary", "degree": "PhD", "year": "2015", "title": "The Phonon Thermodynamics of Iron and Cementite", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092015-103051110", "creators": [ { "name": { "family": "Mauger", "given": "Lisa Mary" }, "id": "Mauger-Lisa-Mary", "display_name": "Mauger, Lisa Mary" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Jackson", "given": "Jennifer M." }, "id": "Jackson-J-M", "role": "member", "display_name": "Jackson, Jennifer M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9TQ5ZH3", "abstract": "The vibrational properties of materials are essential to understanding material stability and thermodynamics. In this thesis I outline vibrational thermodynamic models and the experimental tools that provide evidence on phonon behavior. The introductory section discusses the history of metallurgy and thermodynamic theory, with an emphasis on the role of iron and cementite, two important components of steels. The thermodynamic framework for understanding vibrational material behavior is provided alongside the growing body of experimental and computational tools that provide physical insight on vibrational properties. The high temperature vibrational behavior of iron and cementite are explored within this context in the final chapters.
\r\n\r\nBody-centered-cubic iron exhibits decreasing phonon energies at elevated temperatures. The observed energy change in not uniform across phonon modes in iron, and specific phonon modes show significant decreases in energy that are not explained by simple vibrational models. This anomalously\r\nenergy decrease is linked to the second-nearest-neighbor interactions in the bcc structure, through examination of fitted interatomic force constants. The large changes in phonon energy result in a significant increase in the vibrational entropy, called the nonharmonic vibrational entropy, which emulates the temperature behavior of the magnetic entropy across the Curie temperature. The nonharmonic vibrational entropy is attributed to interactions between the vibrations and state of magnetic disorder in the material, which persists above the magnetic transitions and extends the stability region of the bcc phase.
\r\n\r\nOrthorombic cementite, Fe3C, exhibits anisotropic magneto-volume behavior in the ferromagnetic phase including regions very low thermal expansion. The phonon modes of cementite show anomalous temperature dependence, with low energy phonon modes increasing their energy at elevated temperatures in the ferromagnetic phase. This behavior is reversed after the magnetic transition and these same phonon modes lower their energies with temperature, consistent with observed thermal expansion. This atypical phonon behavior lowers the vibrational entropy of cementite up to the Curie temperature. The experimentally observed increase in low energy acoustic phonons affects the elastic behavior of Fe3C, increasing the isotropy of elastic response. First principles calculations link the observed phonon energy increases to specific vibrational modes that are polarized along the b-axis, which aligns with the closest Fe-Fe bonding direction. The nonharmonic behavior of the vibrational modes are discussed in the context of other observations of anomalous anisotropic magneto-volume behavior in Fe3C.
" }, { "name": "Mbengue, Cheikh Oumar", "degree": "PhD", "year": "2015", "title": "Storm Track Response to Perturbations in Climate", "advisor": "Schneider, Tapio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112015-075223217", "creators": [ { "name": { "family": "Mbengue", "given": "Cheikh Oumar" }, "id": "Mbengue-Cheikh-Oumar", "display_name": "Mbengue, Cheikh Oumar" } ], "advisors": [ { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "advisor", "display_name": "Schneider, Tapio" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Teixeira", "given": "Joao" }, "id": "Teixeira-Joao", "role": "member", "display_name": "Teixeira, Joao" }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9FT8J05", "abstract": "This thesis advances our understanding of midlatitude storm tracks and how they respond to perturbations in the climate system. The midlatitude storm tracks are regions of maximal turbulent kinetic energy in the atmosphere. Through them, the bulk of the atmospheric transport of energy, water vapor, and angular momentum occurs in midlatitudes. Therefore, they are important regulators of climate, controlling basic features such as the distribution of surface temperatures, precipitation, and winds in midlatitudes. Storm tracks are robustly projected to shift poleward in global-warming simulations with current climate models. Yet the reasons for this shift have remained unclear. Here we show that this shift occurs even in extremely idealized (but still three-dimensional) simulations of dry atmospheres. We use these simulations to develop an understanding of the processes responsible for the shift and develop a conceptual model that accounts for it.
\r\n\r\nWe demonstrate that changes in the convective static stability in the deep tropics alone can drive remote shifts in the midlatitude storm tracks. Through simulations with a dry idealized general circulation model (GCM), midlatitude storm tracks are shown to be located where the mean available potential energy (MAPE, a measure of the potential energy available to be converted into kinetic energy) is maximal. As the climate varies, even if only driven by tropical static stability changes, the MAPE maximum shifts primarily because of shifts of the maximum of near-surface meridional temperature gradients. The temperature gradients shift in response to changes in the width of the tropical Hadley circulation, whose width is affected by the tropical static stability. Storm tracks generally shift in tandem with shifts of the subtropical terminus of the Hadley circulation.
\r\n\r\nWe develop a one-dimensional diffusive energy-balance model that links changes in the Hadley circulation to midlatitude temperature gradients and so to the storm tracks. It is the first conceptual model to incorporate a dynamical coupling between the tropical Hadley circulation and midlatitude turbulent energy transport. Numerical and analytical solutions of the model elucidate the circumstances of when and how the storm tracks shift in tandem with the terminus of the Hadley circulation. They illustrate how an increase of only the convective static stability in the deep tropics can lead to an expansion of the Hadley circulation and a poleward shift of storm tracks.
\r\n\r\nThe simulations with the idealized GCM and the conceptual energy-balance model demonstrate a clear link between Hadley circulation dynamics and midlatitude storm track position. With the help of the hierarchy of models presented in this thesis, we obtain a closed theory of storm track shifts in dry climates. The relevance of this theory for more realistic moist climates is discussed.
" }, { "name": "McNamee, Daniel Ciar\u00e1n", "degree": "PhD", "year": "2015", "title": "Neural and Computational Representations of Decision Variables", "advisor": "O'Doherty, John P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02242015-022259327", "creators": [ { "name": { "family": "McNamee", "given": "Daniel Ciar\u00e1n" }, "id": "McNamee-Daniel-Ciar\u00e1n", "orcid": "0000-0001-9928-4960", "display_name": "McNamee, Daniel Ciar\u00e1n" } ], "advisors": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "advisor", "display_name": "O'Doherty, John P." } ], "committee": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "chair", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Rangel", "given": "Antonio" }, "id": "Rangel-A", "role": "member", "display_name": "Rangel, Antonio" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "member", "display_name": "O'Doherty, John P." } ], "option_major": [ "cns" ], "doi": "10.7907/Z96971HZ", "abstract": "These studies explore how, where, and when representations of variables critical to decision-making are represented in the brain. In order to produce a decision, humans must first determine the relevant stimuli, actions, and possible outcomes before applying an algorithm that will select an action from those available. When choosing amongst alternative stimuli, the framework of value-based decision-making proposes that values are assigned to the stimuli and that these values are then compared in an abstract \u201cvalue space\u201d in order to produce a decision. Despite much progress, in particular regarding the pinpointing of ventromedial prefrontal cortex (vmPFC) as a region that encodes the value, many basic questions remain. In Chapter 2, I show that distributed BOLD signaling in vmPFC represents the value of stimuli under consideration in a manner that is independent of the type of stimulus it is. Thus the open question of whether value is represented in abstraction, a key tenet of value-based decision-making, is confirmed. However, I also show that stimulus-dependent value representations are also present in the brain during decision-making and suggest a potential neural pathway for stimulus-to-value transformations that integrates these two results.
\r\n\r\nMore broadly speaking, there is both neural and behavioral evidence that two distinct control systems are at work during action selection. These two systems compose the \u201cgoal-directed system\u201d, which selects actions based on an internal model of the environment, and the \u201chabitual\u201d system, which generates responses based on antecedent stimuli only. Computational characterizations of these two systems imply that they have different informational requirements in terms of input stimuli, actions, and possible outcomes. Associative learning theory predicts that the habitual system should utilize stimulus and action information only, while goal-directed behavior requires that outcomes as well as stimuli and actions be processed. In Chapter 3, I test whether areas of the brain hypothesized to be involved in habitual versus goal-directed control represent the corresponding theorized variables.
\r\n\r\nThe question of whether one or both of these neural systems drives Pavlovian conditioning is less well-studied. Chapter 4 describes an experiment in which subjects were scanned while engaged in a Pavlovian task with a simple non-trivial structure. After comparing a variety of model-based and model-free learning algorithms (thought to underpin goal-directed and habitual decision-making, respectively), it was found that subjects\u2019 reaction times were better explained by a model-based system. In addition, neural signaling of precision, a variable based on a representation of a world model, was found in the amygdala. These data indicate that the influence of model-based representations of the environment can extend even to the most basic learning processes.
\r\n\r\nKnowledge of the state of hidden variables in an environment is required for optimal inference regarding the abstract decision structure of a given environment and therefore can be crucial to decision-making in a wide range of situations. Inferring the state of an abstract variable requires the generation and manipulation of an internal representation of beliefs over the values of the hidden variable. In Chapter 5, I describe behavioral and neural results regarding the learning strategies employed by human subjects in a hierarchical state-estimation task. In particular, a comprehensive model fit and comparison process pointed to the use of \"belief thresholding\". This implies that subjects tended to eliminate low-probability hypotheses regarding the state of the environment from their internal model and ceased to update the corresponding variables. Thus, in concert with incremental Bayesian learning, humans explicitly manipulate their internal model of the generative process during hierarchical inference consistent with a serial hypothesis testing strategy.
" }, { "name": "Meenehan, Sean Michael", "degree": "PhD", "year": "2015", "title": "Cavity Optomechanics at Millikelvin Temperatures", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03132015-135949868", "creators": [ { "name": { "family": "Meenehan", "given": "Sean Michael" }, "id": "Meenehan-Sean-Michael", "display_name": "Meenehan, Sean Michael" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z92J68S7", "abstract": "The field of cavity optomechanics, which concerns the coupling of a mechanical object's motion to the electromagnetic field of a high finesse cavity, allows for exquisitely sensitive measurements of mechanical motion, from large-scale gravitational wave detection to microscale accelerometers. Moreover, it provides a potential means to control and engineer the state of a macroscopic mechanical object at the quantum level, provided one can realize sufficiently strong interaction strengths relative to the ambient thermal noise. Recent experiments utilizing the optomechanical interaction to cool mechanical resonators to their motional quantum ground state allow for a variety of quantum engineering applications, including preparation of non-classical mechanical states and coherent optical to microwave conversion. Optomechanical crystals (OMCs), in which bandgaps for both optical and mechanical waves can be introduced through patterning of a material, provide one particularly attractive means for realizing strong interactions between high-frequency mechanical resonators and near-infrared light. Beyond the usual paradigm of cavity optomechanics involving isolated single mechanical elements, OMCs can also be fashioned into planar circuits for photons and phonons, and arrays of optomechanical elements can be interconnected via optical and acoustic waveguides. Such coupled OMC arrays have been proposed as a way to realize quantum optomechanical memories, nanomechanical circuits for continuous variable quantum information processing and phononic quantum networks, and as a platform for engineering and studying quantum many-body physics of optomechanical meta-materials.
\r\n\r\nHowever, while ground state occupancies (that is, average phonon occupancies less than one) have been achieved in OMC cavities utilizing laser cooling techniques, parasitic absorption and the concomitant degradation of the mechanical quality factor fundamentally limit this approach. On the other hand, the high mechanical frequency of these systems allows for the possibility of using a dilution refrigerator to simultaneously achieve low thermal occupancy and long mechanical coherence time by passively cooling the device to the millikelvin regime. This thesis describes efforts to realize the measurement of OMC cavities inside a dilution refrigerator, including the development of fridge-compatible optical coupling schemes and the characterization of the heating dynamics of the mechanical resonator at sub-kelvin temperatures.
\r\n\r\nWe will begin by summarizing the theoretical framework used to describe cavity optomechanical systems, as well as a handful of the quantum applications envisioned for such devices. Then, we will present background on the design of the nanobeam OMC cavities used for this work, along with details of the design and characterization of tapered fiber couplers for optical coupling inside the fridge. Finally, we will present measurements of the devices at fridge base temperatures of Tf = 10 mK, using both heterodyne spectroscopy and time-resolved sideband photon counting, as well as detailed analysis of the prospects for future quantum applications based on the observed optically-induced heating.
" }, { "name": "Mourhatch, Ramses", "degree": "PhD", "year": "2015", "title": "Quantifying Earthquake Collapse Risk of Tall Steel Braced Frame Buildings Using Rupture-to-Rafters Simulations", "advisor": "Heaton, Thomas H.; Krishnan, Swaminathan", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252015-122512887", "creators": [ { "name": { "family": "Mourhatch", "given": "Ramses" }, "id": "Mourhatch-Ramses", "orcid": "0000-0001-8037-726X", "display_name": "Mourhatch, Ramses" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "co-advisor", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "orcid": "0000-0002-2594-1523", "role": "co-advisor", "display_name": "Krishnan, Swaminathan" } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "orcid": "0000-0002-2594-1523", "role": "member", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Graves", "given": "Robert W." }, "id": "Graves-R-W", "role": "member", "display_name": "Graves, Robert W." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9DV1GTG", "abstract": "This thesis examines collapse risk of tall steel braced frame buildings using rupture-to-rafters simulations due to suite of San Andreas earthquakes. Two key advancements in this work are the development of (i) a rational methodology for assigning scenario earthquake probabilities and (ii) an artificial correction-free approach to broadband ground motion simulation. The work can be divided into the following sections: earthquake source modeling, earthquake probability calculations, ground motion simulations, building response, and performance analysis.
\r\n\r\nAs a first step the kinematic source inversions of past earthquakes in the magnitude range of 6-8 are used to simulate 60 scenario earthquakes on the San Andreas fault. For each scenario earthquake a 30-year occurrence probability is calculated and we present a rational method to redistribute the forecast earthquake probabilities from UCERF to the simulated scenario earthquake. We illustrate the inner workings of the method through an example involving earthquakes on the San Andreas fault in southern California.
\r\n\r\nNext, three-component broadband ground motion histories are computed at 636 sites in the greater Los Angeles metropolitan area by superposing short-period (0.2~s-2.0~s) empirical Green's function synthetics on top of long-period ($>$ 2.0~s) spectral element synthetics. We superimpose these seismograms on low-frequency seismograms, computed from kinematic source models using the spectral element method, to produce broadband seismograms.
\r\n\r\nUsing the ground motions at 636 sites for the 60 scenario earthquakes, 3-D nonlinear analysis of several variants of an 18-story steel braced frame building, designed for three soil types using the 1994 and 1997 Uniform Building Code provisions and subjected to these ground motions, are conducted. Model performance is classified into one of five performance levels: Immediate Occupancy, Life Safety, Collapse Prevention, Red-Tagged, and Model Collapse. The results are combined with the 30-year probability of occurrence of the San Andreas scenario earthquakes using the PEER performance based earthquake engineering framework to determine the probability of exceedance of these limit states over the next 30 years.
" }, { "name": "Nandra, Mandheerej Singh", "degree": "PhD", "year": "2015", "title": "Microelectrode Implants for Spinal Cord Stimulation in Rats ", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052015-084726649", "creators": [ { "name": { "family": "Nandra", "given": "Mandheerej Singh" }, "id": "Nandra-Mandheerej-Singh", "display_name": "Nandra, Mandheerej Singh" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Edgerton", "given": "V. Reggie" }, "id": "Edgerton-V-R", "role": "member", "display_name": "Edgerton, V. Reggie" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9930R3G", "abstract": "Paralysis is a debilitating condition afflicting millions of people across the globe, and is particularly deleterious to quality of life when motor function of the legs is severely impaired or completely absent. Fortunately, spinal cord stimulation has shown great potential for improving motor function after spinal cord injury and other pathological conditions. Many animal studies have shown stimulation of the neural networks in the spinal cord can improve motor ability so dramatically that the animals can even stand and step after a complete spinal cord transaction.
\r\n\r\nThis thesis presents work to successfully provide a chronically implantable device for rats that greatly enhances the ability to control the site of spinal cord stimulation. This is achieved through the use of a parylene-C based microelectrode array, which enables a density of stimulation sites unattainable with conventional wire electrodes. While many microelectrode devices have been proposed in the past, the spinal cord is a particularly challenging environment due to the bending and movement it undergoes in a live animal. The developed microelectrode array is the first to have been implanted in vivo while retaining functionality for over a month. In doing so, different neural pathways can be selectively activated to facilitate standing and stepping in spinalized rats using various electrode combinations, and important differences in responses are observed.
\r\n\r\nAn engineering challenge for the usability of any high density electrode array is connecting the numerous electrodes to a stimulation source. This thesis develops several technologies to address this challenge, beginning with a fully passive implant that uses one wire per electrode to connect to an external stimulation source. The number of wires passing through the body and the skin proved to be a hazard for the health of the animal, so a multiplexed implant was devised in which active electronics reduce the number of wires. Finally, a fully wireless implant was developed. As these implants are tested in vivo, encapsulation is of critical importance to retain functionality in a chronic experiment, especially for the active implants, and it was achieved without the use of costly ceramic or metallic hermetic packaging. Active implants were built that retained functionality 8 weeks after implantation, and achieved stepping in spinalized rats after just 8-10 days, which is far sooner than wire-based electrical stimulation has achieved in prior work.
" }, { "name": "Narang, Prineha", "degree": "PhD", "year": "2015", "title": "Light-Matter Interactions in Semiconductors and Metals: From Nitride Optoelectronics to Quantum Plasmonics", "advisor": "Atwater, Harry Albert; Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052015-164458210", "creators": [ { "name": { "family": "Narang", "given": "Prineha" }, "id": "Narang-Prineha", "orcid": "0000-0003-3956-4594", "display_name": "Narang, Prineha" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "co-advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9513W4S", "abstract": "This thesis puts forth a theory-directed approach coupled with spectroscopy aimed at the discovery and understanding of light-matter interactions in semiconductors and metals.
\r\n\r\nThe first part of the thesis presents the discovery and development of Zn-IV nitride materials.The commercial prominence in the optoelectronics industry of tunable semiconductor alloy materials based on nitride semiconductor devices, specifically InGaN, motivates the search for earth-abundant alternatives for use in efficient, high-quality optoelectronic devices. II-IV-N2 compounds, which are closely related to the wurtzite-structured III-N semiconductors, have similar electronic and optical properties to InGaN namely direct band gaps, high quantum efficiencies and large optical absorption coefficients. The choice of different group II and group IV elements provides chemical diversity that can be exploited to tune the structural and electronic properties through the series of alloys. The first theoretical and experimental investigation of the ZnSnxGe1\u2212xN2 series as a replacement for III-nitrides is discussed here.
\r\n\r\nThe second half of the thesis shows ab\u2212initio calculations for surface plasmons and plasmonic hot carrier dynamics. Surface plasmons, electromagnetic modes confined to the surface of a conductor-dielectric interface, have sparked renewed interest because of their quantum nature and their broad range of applications. The decay of surface plasmons is usually a detriment in the field of plasmonics, but the possibility to capture the energy normally lost to heat would open new opportunities in photon sensors, energy conversion devices and switching. A theoretical understanding of plasmon-driven hot carrier generation and relaxation dynamics in the ultrafast regime is presented here. Additionally calculations for plasmon-mediated upconversion as well as an energy-dependent transport model for these non-equilibrium carriers are shown.
\r\n\r\nFinally, this thesis gives an outlook on the potential of non-equilibrium phenomena in metals and semiconductors for future light-based technologies.
" }, { "name": "Ning, Xin", "degree": "PhD", "year": "2015", "title": "Imperfection Insensitive Thin Shells", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212015-174045815", "creators": [ { "name": { "family": "Ning", "given": "Xin" }, "id": "Ning-Xin", "display_name": "Ning, Xin" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "space" ], "doi": "10.7907/Z91J97P9", "abstract": "The buckling of axially compressed cylindrical shells and externally pressurized spherical shells is extremely sensitive to even very small geometric imperfections. In practice this issue is addressed by either using overly conservative knockdown factors, while keeping perfect axial or spherical symmetry, or adding closely and equally spaced stiffeners on shell surface. The influence of imperfection-sensitivity is mitigated, but the shells designed from these approaches are either too heavy or very expensive and are still sensitive to imperfections. Despite their drawbacks, these approaches have been used for more than half a century.
\r\n\r\nThis thesis proposes a novel method to design imperfection-insensitive cylindrical shells subject to axial compression. Instead of following the classical paths, focused on axially symmetric or high-order rotationally symmetric cross-sections, the method in this thesis adopts optimal symmetry-breaking wavy cross-sections (wavy shells). The avoidance of imperfection sensitivity is achieved by searching with an evolutionary algorithm for smooth cross-sectional shapes that maximize the minimum among the buckling loads of geometrically perfect and imperfect wavy shells. It is found that the shells designed through this approach can achieve higher critical stresses and knockdown factors than any previously known monocoque cylindrical shells. It is also found that these shells have superior mass efficiency to almost all previously reported stiffened shells.
\r\n\r\nExperimental studies on a design of composite wavy shell obtained through the proposed method are presented in this thesis. A method of making composite wavy shells and a photogrametry technique of measuring full-field geometric imperfections have been developed. Numerical predictions based on the measured geometric imperfections match remarkably well with the experiments. Experimental results confirm that the wavy shells are not sensitive to imperfections and can carry axial compression with superior mass efficiency.
\r\n\r\nAn efficient computational method for the buckling analysis of corrugated and stiffened cylindrical shells subject to axial compression has been developed in this thesis. This method modifies the traditional Bloch wave method based on the stiffness matrix method of rotationally periodic structures. A highly efficient algorithm has been developed to implement the modified Bloch wave method. This method is applied in buckling analyses of a series of corrugated composite cylindrical shells and a large-scale orthogonally stiffened aluminum cylindrical shell. Numerical examples show that the modified Bloch wave method can achieve very high accuracy and require much less computational time than linear and nonlinear analyses of detailed full finite element models.
\r\n\r\nThis thesis presents parametric studies on a series of externally pressurized pseudo-spherical shells, i.e., polyhedral shells, including icosahedron, geodesic shells, and triambic icosahedra. Several optimization methods have been developed to further improve the performance of pseudo-spherical shells under external pressure. It has been shown that the buckling pressures of the shell designs obtained from the optimizations are much higher than the spherical shells and not sensitive to imperfections.
\r\n" }, { "name": "Oymak, Samet", "degree": "PhD", "year": "2015", "title": "Convex Relaxation for Low-Dimensional Representation: Phase Transitions and Limitations", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182014-091546460", "creators": [ { "name": { "family": "Oymak", "given": "Samet" }, "id": "Oymak-Samet", "display_name": "Oymak, Samet" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Fazel", "given": "Maryam" }, "id": "Fazel-M", "role": "member", "display_name": "Fazel, Maryam" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9S46PWX", "abstract": "There is a growing interest in taking advantage of possible patterns and structures in data so as to extract the desired information and overcome the curse of dimensionality. In a wide range of applications, including computer vision, machine learning, medical imaging, and social networks, the signal that gives rise to the observations can be modeled to be approximately sparse and exploiting this fact can be very beneficial. This has led to an immense interest in the problem of efficiently reconstructing a sparse signal from limited linear observations. More recently, low-rank approximation techniques have become prominent tools to approach problems arising in machine learning, system identification and quantum tomography.
\r\n\r\nIn sparse and low-rank estimation problems, the challenge is the inherent intractability of the objective function, and one needs efficient methods to capture the low-dimensionality of these models. Convex optimization is often a promising tool to attack such problems. An intractable problem with a combinatorial objective can often be \"relaxed\" to obtain a tractable but almost as powerful convex optimization problem. This dissertation studies convex optimization techniques that can take advantage of low-dimensional representations of the underlying high-dimensional data. We provide provable guarantees that ensure that the proposed algorithms will succeed under reasonable conditions, and answer questions of the following flavor:
\r\nMore specifically, i) Focusing on linear inverse problems, we generalize the classical error bounds known for the least-squares technique to the lasso formulation, which incorporates the signal model. ii) We show that intuitive convex approaches do not perform as well as expected when it comes to signals that have multiple low-dimensional structures simultaneously. iii) Finally, we propose convex relaxations for the graph clustering problem and give sharp performance guarantees for a family of graphs arising from the so-called stochastic block model. We pay particular attention to the following aspects. For i) and ii), we aim to provide a general geometric framework, in which the results on sparse and low-rank estimation can be obtained as special cases. For i) and iii), we investigate the precise performance characterization, which yields the right constants in our bounds and the true dependence between the problem parameters.
" }, { "name": "Pai, Alex Hao-Yu", "degree": "PhD", "year": "2015", "title": "Sensing and Actuation from Biology to Electronics", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302015-005943888", "creators": [ { "name": { "family": "Pai", "given": "Alex Hao-Yu" }, "id": "Pai-Alex-Hao-Yu", "display_name": "Pai, Alex Hao-Yu" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9NC5Z5M", "abstract": "We introduce an in vitro diagnostic magnetic biosensing platform for immunoassay and nucleic acid detection. The platform has key characteristics for a point-of-use (POU) diagnostic: portability, low-power consumption, low cost, and multiplexing capability. As a demonstration of capabilities, we use this platform for the room temperature, amplification-free detection of a 31 bp DNA oligomer and interferon-gamma (a protein relevant for tuberculosis diagnosis). Reliable assay measurements down to 100 pM for the DNA and 1 pM for the protein are demonstrated. We introduce a novel \"magnetic freezing\" technique for baseline measurement elimination and to enable spatial multiplexing. We have created a general protocol for adapting integrated circuit (IC) sensors to any of hundreds of commercially available immunoassay kits and custom designed DNA sequences.
\r\n\r\nWe also introduce a method for immunotherapy treatment of malignant gliomas. We utilize leukocytes internalized with immunostimulatory nanoparticle-oligonucleotide conjugates to localize and retain immune cells near the tumor site. As a proof-of-principle, we develop a novel cell imaging and incubation chamber for in vitro magnetic motility experiments. We use the apparatus to demonstrate the controlled movement of magnetically loaded THP-1 leukocytes.
\r\n\r\nFinally, we introduce an IC transmitter and power ampli er (PA) that utilizes electronic digital infrastructure, sensors, and actuators to self-heal and adapt to process, dynamic, and environmental variation. Traditional IC design has achieved incredible degrees of reliability by ensuring that billions of transistors on a single IC die are all simultaneously functional. Reliability becomes increasingly difficult as the size of a transistor shrinks. Self-healing can mitigate these variations.
" }, { "name": "Raj, Mayank", "degree": "PhD", "year": "2015", "title": "Injection Locked Clocking and Transmitter Equalization Techniques for Chip to Chip Interconnects", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062014-090236636", "creators": [ { "name": { "family": "Raj", "given": "Mayank" }, "id": "Raj-Mayank", "display_name": "Raj, Mayank" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z90P0WZD", "abstract": "Semiconductor technology scaling has enabled drastic growth in the computational capacity of integrated circuits (ICs). This constant growth drives an increasing demand for high bandwidth communication between ICs. Electrical channel bandwidth has not been able to keep up with this demand, making I/O link design more challenging. Interconnects which employ optical channels have negligible frequency dependent loss and provide a potential solution to this I/O bandwidth problem. Apart from the type of channel, efficient high-speed communication also relies on generation and distribution of multi-phase, high-speed, and high-quality clock signals. In the multi-gigahertz frequency range, conventional clocking techniques have encountered several design challenges in terms of power consumption, skew and jitter. Injection-locking is a promising technique to address these design challenges for gigahertz clocking. However, its small locking range has been a major contributor in preventing its ubiquitous acceptance.
\r\n \r\nIn the first part of this dissertation we describe a wideband injection locking scheme in an LC oscillator. Phase locked loop (PLL) and injection locking elements are combined symbiotically to achieve wide locking range while retaining the simplicity of the latter. This method does not require a phase frequency detector or a loop filter to achieve phase lock. A mathematical analysis of the system is presented and the expression for new locking range is derived. A locking range of 13.4 GHz\u201317.2 GHz (25%) and an average jitter tracking bandwidth of up to 400 MHz are measured in a high-Q LC oscillator. This architecture is used to generate quadrature phases from a single clock without any frequency division. It also provides high frequency jitter filtering while retaining the low frequency correlated jitter essential for forwarded clock receivers.
\r\n\r\nTo improve the locking range of an injection locked ring oscillator; QLL (Quadrature locked loop) is introduced. The inherent dynamics of injection locked quadrature ring oscillator are used to improve its locking range from 5% (7-7.4GHz) to 90% (4-11GHz). The QLL is used to generate accurate clock phases for a four channel optical receiver using a forwarded clock at quarter-rate. The QLL drives an injection locked oscillator (ILO) at each channel without any repeaters for local quadrature clock generation. Each local ILO has deskew capability for phase alignment. The optical-receiver uses the inherent frequency to voltage conversion provided by the QLL to dynamically body bias its devices. A wide locking range of the QLL helps to achieve a reliable data-rate of 16-32Gb/s and adaptive body biasing aids in maintaining an ultra-low power consumption of 153pJ/bit.
\r\n \r\nFrom the optical receiver we move on to discussing a non-linear equalization technique for a vertical-cavity surface-emitting laser (VCSEL) based optical transmitter, to enable low-power, high-speed optical transmission. A non-linear time domain optical model of the VCSEL is built and evaluated for accuracy. The modelling shows that, while conventional FIR-based pre-emphasis works well for LTI electrical channels, it is not optimum for the non-linear optical frequency response of the VCSEL. Based on the simulations of the model an optimum equalization methodology is derived. The equalization technique is used to achieve a data-rate of 20Gb/s with power efficiency of 0.77pJ/bit.
\r\n" }, { "name": "Rauls, Michael Brian", "degree": "PhD", "year": "2015", "title": "Shock Wave Behavior of Particulate Composites", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292015-170754625", "creators": [ { "name": { "family": "Rauls", "given": "Michael Brian" }, "id": "Rauls-Michael-Brian", "display_name": "Rauls, Michael Brian" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Neel", "given": "Christopher H." }, "id": "Neel-C-H", "role": "member", "display_name": "Neel, Christopher H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z98P5XHC", "abstract": "Material heterogeneity at some scale is common in present engineering and structural materials as a means of strength improvement, weight reduction, and performance enhancement in a great many applications such as impact and blast protection, construction, and aerospace. While the benefits of transitioning toward composites in practical applications is obvious, the methods of measurement and optimization required to handle spatial heterogeneity and bridge length scale differences across multiple orders of magnitude are not. This is especially true as loading rates transition into the shock regime. Composite materials, such as concrete, have advantages afforded to them by their microstructure that allow them to dissipate and scatter impact energy. The mechanical mismatch between constituent phases in composites (mortar and cement paste in concrete, crystals and binder in polymer bonded explosives, ceramic powder and epoxy in potting materials, etc.) provides the interfaces required for shock wave reflection. The degree to which a shock is disrupted from its accepted form as a propagating discontinuity in stress and particle velocity is highly dependent upon the size, shape, and density of the interfaces present.
\r\n\r\nThe experimental and computer aided simulations in this thesis seek to establish a scaling relationship between composite microstructure and shock front disruption in terms of particulate size and density through the use of multi-point heterodyne velocity interferometry. A model particulate composite has been developed to mimic the wave reflection properties of materials such as Ultra High Performace Composite (UHPC) concrete and polymer bonded explosives, while also being simple to source and manufacture repeatably. Polymethyl Methacrylate (PMMA), a thermoplastic polymer, and silica glass spheres satisfy the manufacturing constraints with a shock impedance mismatch of 4.1, when placed in-between the shock impedance of UHPC concretes (~ 10) and polymer bondedexplosives (~ 2). The flexibility afforded by the model composite allows for the use of mono-disperse bead particle diameter distributions centered at 5 discrete diameters centered in the range associated with high scattering effectiveness (5-50 times the shock thickness in the pure matrix material). Shock front disruption is measured at multiple points on the rear surface of a plate impact target to observe shock spreading and spatial heterogeneity in material response due to random particle placement.
\r\n\r\nShock rise times are reported for composites of 30% and 40% glass spheres by volume, with glass spheres of 100, 300, 500, 700, and 1000 micron diameter. Composites with single mode as well as bi-modal bead diameter distributions are subjected to plate impact loading at an average pressure of 5 GPa. In single mode composites, a linear dependence of shock wave rise time on particle diameter is observed, with a constant of proportionality equal to the bulk shock speed in the material. Bi-modal bead diameter composites were fabricated in order to achieve higher volume fractions without composite degradation. The addition of a second phase to a base 30% glass by volume composite mix results in significant increases in shock wave rise time for base mixes of 500 micron beads, while a point of maximum scattering effectiveness is observed for base mixes\r\nof 1000 micron diameter beads.
\r\n\r\nA comprehensive two dimensional series of CTH hydrocode simulations has been completed in tandem with experiments. An evaluation of the discrepancies in simulation and experimental results is presented. Shock disruption mechanisms and matrix/interface damage effects are discussed as possible sources of error and potential avenues for model improvement. The scaling arguments and model deficiency corrections made in this thesis have the potential to drive the development of new approaches of modeling shock waves in heterogeneous materials as well as optimization of microstructure for maximum shock front disruption.
" }, { "name": "Revechkis, Boris", "degree": "PhD", "year": "2015", "title": "Neural Prosthetics and Parietal Cortex", "advisor": "Andersen, Richard A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292015-193747262", "creators": [ { "name": { "family": "Revechkis", "given": "Boris" }, "id": "Revechkis-Boris", "display_name": "Revechkis, Boris" } ], "advisors": [ { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "advisor", "display_name": "Andersen, Richard A." } ], "committee": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "chair", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "member", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." } ], "option_major": [ "cns" ], "doi": "10.7907/Z9Z31WNK", "abstract": "In the last decade, research efforts into directly interfacing with the neurons of individuals with motor deficits have increased. The goal of such research is clear: Enable individuals affected by paralysis or amputation to regain control of their environments by manipulating external devices with thought alone. Though the motor cortices are the usual brain areas upon which neural prosthetics depend, research into the parietal lobe and its subregions, primarily in non-human primates, has uncovered alternative areas that could also benefit neural interfaces. Similar to the motor cortical areas, parietal regions can supply information about the trajectories of movements. In addition, the parietal lobe also contains cognitive signals like movement goals and intentions. But, these areas are also known to be tuned to saccadic eye movements, which could interfere with the function of a prosthetic designed to capture motor intentions only. In this thesis, we develop and examine the functionality of a neural prosthetic with a non-human primate model using the superior parietal lobe to examine the effectiveness of such an interface and the effects of unconstrained eye movements in a task that more closely simulates clinical applications. Additionally, we examine methods for improving usability of such interfaces.
\r\n\r\nThe parietal cortex is also believed to contain neural signals relating to monitoring of the state of the limbs through visual and somatosensory feedback. In one of the world\u2019s first clinical neural prosthetics based on the human parietal lobe, we examine the extent to which feedback regarding the state of a movement effector alters parietal neural signals and what the implications are for motor neural prosthetics and how this informs our understanding of this area of the human brain.
" }, { "name": "Savard, Bruno", "degree": "PhD", "year": "2015", "title": "Characterization and Modeling of Premixed Turbulent n-Heptane Flames in the Thin Reaction Zone Regime", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282015-154709861", "creators": [ { "name": { "family": "Savard", "given": "Bruno" }, "id": "Savard-Bruno", "display_name": "Savard, Bruno" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "space" ], "doi": "10.7907/Z9GM858F", "abstract": "n-heptane/air premixed turbulent flames in the high-Karlovitz portion of the thin reaction zone regime are characterized and modeled in this thesis using Direct Numerical Simulations (DNS) with detailed chemistry. In order to perform these simulations, a time-integration scheme that can efficiently handle the stiffness of the equations solved is developed first. A first simulation with unity Lewis number is considered in order to assess the effect of turbulence on the flame in the absence of differential diffusion. A second simulation with non-unity Lewis numbers is considered to study how turbulence affects differential diffusion. In the absence of differential diffusion, minimal departure from the 1D unstretched flame structure (species vs. temperature profiles) is observed. In the non-unity Lewis number case, the flame structure lies between that of 1D unstretched flames with \"laminar\" non-unity Lewis numbers and unity Lewis number. This is attributed to effective Lewis numbers resulting from intense turbulent mixing and a first model is proposed. The reaction zone is shown to be thin for both flames, yet large chemical source term fluctuations are observed. The fuel consumption rate is found to be only weakly correlated with stretch, although local extinctions in the non-unity Lewis number case are well correlated with high curvature. These results explain the apparent turbulent flame speeds. Other variables that better correlate with this fuel burning rate are identified through a coordinate transformation. It is shown that the unity Lewis number turbulent flames can be accurately described by a set of 1D (in progress variable space) flamelet equations parameterized by the dissipation rate of the progress variable. In the non-unity Lewis number flames, the flamelet equations suggest a dependence on a second parameter, the diffusion of the progress variable. A new tabulation approach is proposed for the simulation of such flames with these dimensionally-reduced manifolds." }, { "name": "Siriki, Hemanth", "degree": "PhD", "year": "2015", "title": "Quantifying Earthquake Collapse Risk of Tall Steel Moment Frame Buildings Using Rupture-to-Rafters Simulations", "advisor": "Krishnan, Swaminathan; Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042015-132126668", "creators": [ { "name": { "family": "Siriki", "given": "Hemanth" }, "id": "Siriki-Hemanth", "display_name": "Siriki, Hemanth" } ], "advisors": [ { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "orcid": "0000-0002-2594-1523", "role": "advisor", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "orcid": "0000-0002-2594-1523", "role": "member", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9TX3CB4", "abstract": "There is a sparse number of credible source models available from large-magnitude past earthquakes. A stochastic source model generation algorithm thus becomes necessary for robust risk quantification using scenario earthquakes. We present an algorithm that combines the physics of fault ruptures as imaged in laboratory earthquakes with stress estimates on the fault constrained by field observations to generate stochastic source models for large-magnitude (Mw 6.0-8.0) strike-slip earthquakes. The algorithm is validated through a statistical comparison of synthetic ground motion histories from a stochastically generated source model for a magnitude 7.90 earthquake and a kinematic finite-source inversion of an equivalent magnitude past earthquake on a geometrically similar fault. The synthetic dataset comprises of three-component ground motion waveforms, computed at 636 sites in southern California, for ten hypothetical rupture scenarios (five hypocenters, each with two rupture directions) on the southern San Andreas fault. A similar validation exercise is conducted for a magnitude 6.0 earthquake, the lower magnitude limit for the algorithm. Additionally, ground motions from the Mw7.9\r\nearthquake simulations are compared against predictions by the Campbell-Bozorgnia NGA relation as well as the ShakeOut scenario earthquake. The algorithm is then applied to generate fifty source models for a hypothetical magnitude 7.9 earthquake originating at Parkfield, with rupture propagating from north to south (towards Wrightwood), similar to the 1857 Fort Tejon earthquake. Using the spectral element method, three-component ground motion waveforms are computed in the Los Angeles basin for each scenario earthquake and the sensitivity of ground shaking intensity to seismic source parameters (such as the percentage of asperity area relative to the fault area, rupture speed, and risetime) is studied.
\r\n\r\nUnder plausible San Andreas fault earthquakes in the next 30 years, modeled using the stochastic source algorithm, the performance of two 18-story steel moment frame buildings (UBC 1982 and 1997 designs) in southern California is quantified. The approach integrates rupture-to-rafters simulations into the PEER performance based earthquake engineering (PBEE) framework. Using stochastic sources and computational seismic wave propagation, three-component ground motion histories at 636 sites in southern California are generated for sixty scenario earthquakes on the San Andreas fault. The\r\nruptures, with moment magnitudes in the range of 6.0-8.0, are assumed to occur at five locations on the southern section of the fault. Two unilateral rupture propagation directions are considered. The 30-year probabilities of all plausible ruptures in this magnitude range and in that section of the fault,\r\nas forecast by the United States Geological Survey, are distributed among these 60 earthquakes based on proximity and moment release. The response of the two 18-story buildings hypothetically located at each of the 636 sites under 3-component shaking from all 60 events is computed using 3-D nonlinear time-history analysis. Using these results, the probability of the structural response exceeding Immediate Occupancy (IO), Life-Safety (LS), and Collapse Prevention (CP) performance levels under San Andreas fault earthquakes over the next thirty years is evaluated.
\r\n\r\nFurthermore, the conditional and marginal probability distributions of peak ground velocity\r\n(PGV) and displacement (PGD) in Los Angeles and surrounding basins due to earthquakes occurring primarily on the mid-section of southern San Andreas fault are determined using Bayesian model class identification. Simulated ground motions at sites within 55-75km from the source from a suite of 60 earthquakes (Mw 6.0 \u2212 8.0) primarily rupturing mid-section of San Andreas fault are considered for PGV and PGD data.
" }, { "name": "Srinivas, Niranjan", "degree": "PhD", "year": "2015", "title": "Programming Chemical Kinetics: Engineering Dynamic Reaction Networks with DNA Strand Displacement", "advisor": "Winfree, Erik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012015-171243593", "creators": [ { "name": { "family": "Srinivas", "given": "Niranjan" }, "id": "Srinivas-Niranjan", "display_name": "Srinivas, Niranjan" } ], "advisors": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "advisor", "display_name": "Winfree, Erik" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Rothemund", "given": "Paul W. K." }, "id": "Rothemund-P-W-K", "role": "member", "display_name": "Rothemund, Paul W. K." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Seelig", "given": "Georg" }, "id": "Seelig-G", "role": "member", "display_name": "Seelig, Georg" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9KD1VVJ", "abstract": "Over the last century, the silicon revolution has enabled us to build faster, smaller and more sophisticated computers. Today, these computers control phones, cars, satellites, assembly lines, and other electromechanical devices. Just as electrical wiring controls electromechanical devices, living organisms employ \"chemical wiring\" to make decisions about their environment and control physical processes. Currently, the big difference between these two substrates is that while we have the abstractions, design principles, verification and fabrication techniques in place for programming with silicon, we have no comparable understanding or expertise for programming chemistry.
\r\n\r\nIn this thesis we take a small step towards the goal of learning how to systematically engineer prescribed non-equilibrium dynamical behaviors in chemical systems. We use the formalism of chemical reaction networks (CRNs), combined with mass-action kinetics, as our programming language for specifying dynamical behaviors. Leveraging the tools of nucleic acid nanotechnology (introduced in Chapter 1), we employ synthetic DNA molecules as our molecular architecture and toehold-mediated DNA strand displacement as our reaction primitive.
\r\n\r\nAbstraction, modular design and systematic fabrication can work only with well-understood and quantitatively characterized tools. Therefore, we embark on a detailed study of the \"device physics\" of DNA strand displacement (Chapter 2). We present a unified view of strand displacement biophysics and kinetics by studying the process at multiple levels of detail, using an intuitive model of a random walk on a 1-dimensional energy landscape, a secondary structure kinetics model with single base-pair steps, and a coarse-grained molecular model that incorporates three-dimensional geometric and steric effects. Further, we experimentally investigate the thermodynamics of three-way branch migration. Our findings are consistent with previously measured or inferred rates for hybridization, fraying, and branch migration, and provide a biophysical explanation of strand displacement kinetics. Our work paves the way for accurate modeling of strand displacement cascades, which would facilitate the simulation and construction of more complex molecular systems.
\r\n\r\nIn Chapters 3 and 4, we identify and overcome the crucial experimental challenges involved in using our general DNA-based technology for engineering dynamical behaviors in the test tube. In this process, we identify important design rules that inform our choice of molecular motifs and our algorithms for designing and verifying DNA sequences for our molecular implementation. We also develop flexible molecular strategies for \"tuning\" our reaction rates and stoichiometries in order to compensate for unavoidable non-idealities in the molecular implementation, such as imperfectly synthesized molecules and spurious \"leak\" pathways that compete with desired pathways.
\r\n\r\nWe successfully implement three distinct autocatalytic reactions, which we then combine into a de novo chemical oscillator. Unlike biological networks, which use sophisticated evolved molecules (like proteins) to realize such behavior, our test tube realization is the first to demonstrate that Watson-Crick base pairing interactions alone suffice for oscillatory dynamics. Since our design pipeline is general and applicable to any CRN, our experimental demonstration of a de novo chemical oscillator could enable the systematic construction of CRNs with other dynamic behaviors.
" }, { "name": "Steeves, John Bradley", "degree": "PhD", "year": "2015", "title": "Multilayer Active Shell Mirrors", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282015-145339959", "creators": [ { "name": { "family": "Steeves", "given": "John Bradley" }, "id": "Steeves-John-Bradley", "display_name": "Steeves, John Bradley" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "space" ], "doi": "10.7907/Z99W0CFB", "abstract": "This thesis presents a novel active mirror technology based on carbon fiber composites and replication manufacturing processes. Multiple additional layers are implemented into the structure in order to provide the reflective layer, actuation capabilities and electrode routing. The mirror is thin, lightweight, and has large actuation capabilities. These features, along with the associated manufacturing processes, represent a significant change in design compared to traditional optics. Structural redundancy in the form of added material or support structures is replaced by thin, unsupported lightweight substrates with large actuation capabilities.
\r\n\r\nSeveral studies motivated by the desire to improve as-manufactured figure quality are performed. Firstly, imperfections in thin CFRP laminates and their effect on post-cure shape errors are studied. Numerical models are developed and compared to experimental measurements on flat laminates. Techniques to mitigate figure errors for thicker laminates are also identified. A method of properly integrating the reflective facesheet onto the front surface of the CFRP substrate is also presented. Finally, the effect of bonding multiple initially flat active plates to the backside of a curved CFRP substrate is studied. Figure deformations along with local surface defects are predicted and characterized experimentally. By understanding the mechanics behind these processes, significant improvements to the overall figure quality have been made.
\r\n\r\nStudies related to the actuation response of the mirror are also performed. The active properties of two materials are characterized and compared. Optimal active layer thicknesses for thin surface-parallel schemes are determined. Finite element simulations are used to make predictions on shape correction capabilities, demonstrating high correctabiliity and stroke over low-order modes. The effect of actuator saturation is studied and shown to significantly degrade shape correction performance.
\r\n\r\nThe initial figure as well as actuation capabilities of a fully-integrated active mirror prototype are characterized experimentally using a Projected Hartmann test. A description of the test apparatus is presented along with two verification measurements. The apparatus is shown to accurately capture both high-amplitude low spatial-frequency figure errors as well as those at lower amplitudes but higher spatial frequencies. A closed-loop figure correction is performed, reducing figure errors by 94%.
" }, { "name": "Stiles, Noelle Rebecca Barry", "degree": "PhD", "year": "2015", "title": "Behavioral and fMRI Measures of Crossmodal Plasticity Induced by Auditory Sensory Substitution", "advisor": "Shimojo, Shinsuke", "url": "https://resolver.caltech.edu/CaltechTHESIS:11072014-145237990", "creators": [ { "name": { "family": "Stiles", "given": "Noelle Rebecca Barry" }, "id": "Stiles-Noelle-Rebecca-Barry", "display_name": "Stiles, Noelle Rebecca Barry" } ], "advisors": [ { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "advisor", "display_name": "Shimojo, Shinsuke" } ], "committee": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "chair", "display_name": "O'Doherty, John P." }, { "name": { "family": "Lester", "given": "Henry A." }, "id": "Lester-H-A", "role": "member", "display_name": "Lester, Henry A." }, { "name": { "family": "Tsao", "given": "Doris Y." }, "id": "Tsao-D-Y", "role": "member", "display_name": "Tsao, Doris Y." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9N29TZP", "abstract": "Thirty nine million people are blind worldwide. Sensory Substitution (SS) attempts to aid the blind by translating images into sound and thereby restoring visual function. Previous studies have found that training on SS generates crossmodal neural changes allowing for activation in early visual regions in response to SS sounds. Unfortunately, training on auditory sensory substitution to become proficient at basic visual tasks takes 1 week to 3 months and even then is slow, inaccurate, and attention-intensive. In this thesis it was studied if SS interpretation could be performed by entirely naive users automatically, and if the crossmodal plasticity engendered through training could be engaged automatically. In contrast to the top-down SS interpretation, we have found that SS interpretation can be effortless and automatic in entirely naive individuals when crossmodally intuitive stimuli that contain crossmodal mappings are used. Crossmodal mappings are pre-existing associations in all individuals of images and sounds that were found to be used for entirely naive interpretation of SS. This result indicates that SS could potentially be made more useful to the blind with appropriate training and translation algorithms. We also studied if the crossmodal plasticity generated by SS training can also be activated automatically in trained blind and sighted device users. We found that crossmodal plasticity engendered through a week of training could be triggered automatically by SS stimuli. This indicates that crossmodal plasticity does not require an attention-intensive task be used and therefore is not entirely top-down cognitive. It might be possible to tap into this automatic processing in visual cortex of SS stimuli to make SS interpretation less effortful and more perceptual following the appropriate training. Overall, this thesis attempts to use SS to understand crossmodal neural processing and plasticity, and to through this broadened knowledge restore some visual function to the entirely blind." }, { "name": "Sullivan, Nicolette Jean", "degree": "PhD", "year": "2015", "title": "The Neurocomputational Basis of Self-Control Success and Failure", "advisor": "Rangel, Antonio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292015-162052753", "creators": [ { "name": { "family": "Sullivan", "given": "Nicolette Jean" }, "id": "Sullivan-Nicolette-Jean", "display_name": "Sullivan, Nicolette Jean" } ], "advisors": [ { "name": { "family": "Rangel", "given": "Antonio" }, "id": "Rangel-A", "role": "advisor", "display_name": "Rangel, Antonio" } ], "committee": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "chair", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "member", "display_name": "Quartz, Steven R." }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "member", "display_name": "O'Doherty, John P." }, { "name": { "family": "Camerer", "given": "Colin F." }, "id": "Camerer-C-F", "role": "member", "display_name": "Camerer, Colin F." } ], "option_major": [ "cns" ], "doi": "10.7907/Z90P0X8V", "abstract": "Individuals often have difficulty delaying gratification \u2013 that is, forging smaller sooner rewards in favor of larger rewards delivered at a delay. Common examples of this deficit in self-control are difficulties in saving for retirement, going to the gym, or eating healthy foods. Despite an extensive literature on the neural substrates of decision-making, relatively little is still known about the sources of underlying individual variation in the ability to successfully execute self-control. This manuscript presents three studies examining the sources of individual differences in delay of gratification, with the goal of obtaining a more complete understanding of the neural mechanisms underlying choice. The main question this thesis addresses is: what features of the brain\u2019s decision process allow individuals to down-regulate the appeal of smaller sooner rewards, in order to forgo them in favor of greater future reward?
\r\n\r\nIn the first study, I present a novel method of measuring decision process dynamics, in which we harness the power of fine temporal resolution in recording computer mouse movements in dietary choices. We find that up to 39% of individual variation in dietary self-control can be explained by differences in the speed with which the decision-making circuitry processes basic attributes, such as tastiness, versus more complex, abstract, attributes, such as healthfulness.
\r\n\r\nIn the second study, we extend this novel approach to a classic experimental economics paradigm, intertemporal choice. We found large individual variance in the speeds with which immediate and delayed reward values were processed. We found that about 25% of the individual differences can be explained by differences in the speed at which delayed rewards are processed. We also found that the relative speed at which immediate and delayed rewards are processed fluctuated across trials: subjects processed delayed rewards faster than immediate rewards when they made patient choices, but the order of processing speeds was reversed during impulsive choices. Together, these results show that a sizable fraction of variation in the ability to postpone gratification might be attributable to variables that affect the speed at which different types of rewards are processed, and not to differences on deep preference parameters like the temporal discount rate used by the brain\u2019s valuation systems.
\r\n\r\nAcross the lifespan, self-control improves in many choice domains. The third and final study capitalizes on this phenomenon of behavioral change with age to investigate the neural mechanisms underlying improvements in self-control. I use functional magnetic resonance imaging (fMRI) to examine the neural correlates of changes in discounting of future monetary rewards across the lifespan from adolescents (13 years old) to seniors (70 years old). We find that neural response to value in reward-related striatal brain regions dramatically decrease with age. In contrast, we find that the left dorsolateral prefrontal cortex, often found to be related to successful self-control, increases its functional connectivity to key valuation, reward, and future-thinking brain regions with age during very tempting trials. These results suggest a mechanism through which increased self-control is improved.
\r\n\r\nTaken together, these studies argue that individual features of the decision process have a large influence on the overall ability to exert self-control in both dietary and monetary choice domains. Specifically, we find that the speed with which abstract future attributes such as health information, relative to more concrete attributes such as taste, are processed have a large influence on individual self-control ability. We also find that decreased reward sensitivity, paired with increased effective connectivity between control and valuation regions specifically when control is required most, allow for increased ability to delay gratification with age.
" }, { "name": "Thevamaran, Ramathasan", "degree": "PhD", "year": "2015", "title": "Rate and Microstructure Effects on the Dynamics of Carbon Nanotube Foams", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162014-104834622", "creators": [ { "name": { "family": "Thevamaran", "given": "Ramathasan" }, "id": "Thevamaran-Ramathasan", "orcid": "0000-0001-5058-6167", "display_name": "Thevamaran, Ramathasan" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9DB7ZRG ", "abstract": "Soft hierarchical materials often present unique functional properties that are sensitive to the geometry and organization of their micro- and nano-structural features across different lengthscales. Carbon Nanotube (CNT) foams are hierarchical materials with fibrous morphology that are known for their remarkable physical, chemical and electrical properties. Their complex microstructure has led them to exhibit intriguing mechanical responses at different length-scales and in different loading regimes. Even though these materials have been studied for mechanical behavior over the past few years, their response at high-rate finite deformations and the influence of their microstructure on bulk mechanical behavior and energy dissipative characteristics remain elusive.
\r\n\r\nIn this dissertation, we study the response of aligned CNT foams at the high strain-rate regime of 102 - 104 s-1. We investigate their bulk dynamic response and the fundamental deformation mechanisms at different lengthscales, and correlate them to the microstructural characteristics of the foams. We develop an experimental platform, with which to study the mechanics of CNT foams in high-rate deformations, that includes direct measurements of the strain and transmitted forces, and allows for a full field visualization of the sample\u2019s deformation through high-speed microscopy.
\r\n\r\nWe synthesize various CNT foams (e.g., vertically aligned CNT (VACNT) foams, helical CNT foams, micro-architectured VACNT foams and VACNT foams with microscale heterogeneities) and show that the bulk functional properties of these materials are highly tunable either by tailoring their microstructure during synthesis or by designing micro-architectures that exploit the principles of structural mechanics. We also develop numerical models to describe the bulk dynamic response using multiscale mass-spring models and identify the mechanical properties at length scales that are smaller than the sample height.
\r\n\r\nThe ability to control the geometry of microstructural features, and their local interactions, allows the creation of novel hierarchical materials with desired functional properties. The fundamental understanding provided by this work on the key structure-function relations that govern the bulk response of CNT foams can be extended to other fibrous, soft and hierarchical materials. The findings can be used to design materials with tailored properties for different engineering applications, like vibration damping, impact mitigation and packaging.
" }, { "name": "Tsai, Ho-Cheng", "degree": "PhD", "year": "2015", "title": "Quantum Mechanics Studies of Fuel Cell Catalysts and Proton Conducting Ceramics with Validation by Experiment", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012015-203513094", "creators": [ { "name": { "family": "Tsai", "given": "Ho-Cheng" }, "id": "Tsai-Ho-Cheng", "display_name": "Tsai, Ho-Cheng" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9P55KFW", "abstract": "We carried out quantum mechanics (QM) studies aimed at improving the performance of hydrogen fuel cells. This led to predictions of improved materials, some of which were subsequently validated with experiments by our collaborators.
\r\n\r\nIn part I, the challenge was to find a replacement for the Pt cathode that would lead to improved performance for the Oxygen Reduction Reaction (ORR) while remaining stable under operational conditions and decreasing cost. Our design strategy was to find an alloy with composition Pt3M that would lead to surface segregation such that the top layer would be pure Pt, with the second and subsequent layers richer in M. Under operating conditions we expect the surface to have significant O and/or OH chemisorbed on the surface, and hence we searched for M that would remain segregated under these conditions. Using QM we examined surface segregation for 28 Pt3M alloys, where M is a transition metal. We found that only Pt3Os and Pt3Ir showed significant surface segregation when O and OH are chemisorbed on the catalyst surfaces. This result indicates that Pt3Os and Pt3Ir favor formation of a Pt-skin surface layer structure that would resist the acidic electrolyte corrosion during fuel cell operation environments. We chose to focus on Os because the phase diagram for Pt-Ir indicated that Pt-Ir could not form a homogeneous alloy at lower temperature. To determine the performance for ORR, we used QM to examine all intermediates, reaction pathways, and reaction barriers involved in the processes for which protons from the anode reactions react with O2 to form H2O. These QM calculations used our Poisson-Boltzmann implicit solvation model include the effects of the solvent (water with dielectric constant 78 with pH 7 at 298K). We found that the rate determination step (RDS) was the Oad hydration reaction (Oad + H2Oad -> OHad + OHad) in both cases, but that the barrier for pure Pt of 0.50 eV is reduced to 0.48 eV for Pt3Os, which at 80 degrees C would increase the rate by 218%. We collaborated with the Pu-Wei Wu\u2019s group to carry out experiments, where we found that the dealloying process-treated Pt2Os catalyst showed two-fold higher activity at 25 degrees C than pure Pt and that the alloy had 272% improved stability, validating our theoretical predictions.
\r\n\r\nWe also carried out similar QM studies followed by experimental validation for the Os/Pt core-shell catalyst fabricated by the underpotential deposition (UPD) method. The QM results indicated that the RDS for ORR is a compromise between the OOH formation step (0.37 eV for Pt, 0.23 eV for Pt2ML/Os core-shell) and H2O formation steps (0.32 eV for Pt, 0.22 eV for Pt2ML/Os core-shell). We found that Pt2ML/Os has the highest activity (compared to pure Pt and to the Pt3Os alloy) because the 0.37 eV barrier decreases to 0.23 eV. To understand what aspects of the core shell structure lead to this improved performance, we considered the effect on ORR of compressing the alloy slab to the dimensions of pure Pt. However this had little effect, with the same RDS barrier 0.37 eV. This shows that the ligand effect (the electronic structure modification resulting from the Os substrate) plays a more important role than the strain effect, and is responsible for the improved activity of the core- shell catalyst. Experimental materials characterization proves the core-shell feature of our catalyst. The electrochemical experiment for Pt2ML/Os/C showed 3.5 to 5 times better ORR activity at 0.9V (vs. NHE) in 0.1M HClO4 solution at 25 degrees C as compared to those of commercially available Pt/C. The excellent correlation between experimental half potential and the OH binding energies and RDS barriers validate the feasibility of predicting catalyst activity using QM calculation and a simple Langmuir\u2013Hinshelwood model.
\r\n\r\nIn part II, we used QM calculations to study methane stream reforming on a Ni-alloy catalyst surfaces for solid oxide fuel cell (SOFC) application. SOFC has wide fuel adaptability but the coking and sulfur poisoning will reduce its stability. Experimental results suggested that the Ni4Fe alloy improves both its activity and stability compared to pure Ni. To understand the atomistic origin of this, we carried out QM calculations on surface segregation and found that the most stable configuration for Ni4Fe has a Fe atom distribution of (0%, 50%, 25%, 25%, 0%) starting at the bottom layer. We calculated that the binding of C atoms on the Ni4Fe surface is 142.9 Kcal/mol, which is about 10 Kcal/mol weaker compared to the pure Ni surface. This weaker C binding energy is expected to make coke formation less favorable, explaining why Ni4Fe has better coking resistance. This result confirms the experimental observation. The reaction energy barriers for CHx decomposition and C binding on various alloy surface, Ni4X (X=Fe, Co, Mn, and Mo), showed Ni4Fe, Ni4Co, and Fe4Mn all have better coking resistance than pure Ni, but that only Ni4Fe and Fe4Mn have (slightly) improved activity compared to pure Ni.
\r\n\r\nIn part III, we used QM to examine the proton transport in doped perovskite-ceramics. Here we used a 2x2x2 supercell of perovskite with composition Ba8X7M1(OH)1O23 where X=Ce or Zr and M=Y, Gd, or Dy. Thus in each case a 4+ X is replace by a 3+ M plus a proton on one O. Here we predicted the barriers for proton diffusion allowing both includes intra-octahedron and inter-octahedra proton transfer. Without any restriction, we only observed the inter-octahedra proton transfer with similar energy barrier as previous computational work but 0.2 eV higher than experimental result for Y doped zirconate. For one restriction in our calculations is that the Odonor-Oacceptor atoms were kept at fixed distances, we found that the barrier difference between cerates/zirconates with various dopants are only 0.02~0.03 eV. To fully address performance one would need to examine proton transfer at grain boundaries, which will require larger scale ReaxFF reactive dynamics for systems with millions of atoms. The QM calculations used here will be used to train the ReaxFF force field.
\r\n \r\n" }, { "name": "Usiskin, Robert Ezra", "degree": "PhD", "year": "2015", "title": "Surface Activity and Bulk Defect Chemistry of Solid Oxide Fuel Cell Cathodes", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10032014-161017442", "creators": [ { "name": { "family": "Usiskin", "given": "Robert Ezra" }, "id": "Usiskin-Robert-Ezra", "display_name": "Usiskin, Robert Ezra" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z91N7Z3N", "abstract": "In the first half of this thesis, a new robotic instrument called a scanning impedance probe is presented that can acquire electrochemical impedance spectra in automated fashion from hundreds of thin film microelectrodes with systematically varied properties. Results from this instrument are presented for three catalyst compositions that are commonly considered for use in state-of-the-art solid oxide fuel cell cathodes. For (La0.8Sr0.2)0.95MnO3+\u03b4 (LSM), the impedance spectra are well fit by a through-the-film reaction pathway. Transport rates are extracted, and the surface activity towards oxygen reduction is found to be correlated with the number of exposed grain boundary sites, suggesting that grain boundaries are more surface-active than grains. For La0.5Sr0.5CoO3-\u03b4 (LSC), the surface activity degrades ~50x initially and then stabilizes at a comparable activity to that of previously measured Ba0.5Sr0.5Co0.8Fe0.2O3-\u03b4 films. For Sr0.06Nb0.06Bi1.87O3 (SNB), an example of a doped bismuth oxide, the activity of the metal-SNB boundary is measured.
\r\n\r\nIn the second half of this thesis, SrCo0.9Nb0.1O3-\u03b4 is selected as a case study of perovskites containing Sr and Co, which are the most active oxygen reduction catalysts known. Several bulk properties are measured, and synchrotron data are presented that provide strong evidence of substantial cobalt-oxygen covalency at high temperatures. This covalent bonding may be the underlying source of the high surface activity.
\r\n" }, { "name": "Veeraraghavan, Swetha", "degree": "PhD", "year": "2015", "title": "Toppling Analysis of Precariously Balanced Rocks under Earthquake Excitation", "advisor": "Krishnan, Swaminathan; Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252015-121408938", "creators": [ { "name": { "family": "Veeraraghavan", "given": "Swetha" }, "id": "Veeraraghavan-Swetha", "display_name": "Veeraraghavan, Swetha" } ], "advisors": [ { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "orcid": "0000-0002-2594-1523", "role": "advisor", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "co-advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "chair", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Asimaki", "given": "Domniki" }, "id": "Asimaki-D", "orcid": "0000-0002-3008-8088", "role": "member", "display_name": "Asimaki, Domniki" }, { "name": { "family": "Hudnut", "given": "Kenneth W." }, "id": "Hudnut-K-W", "orcid": "0000-0002-3168-4797", "role": "member", "display_name": "Hudnut, Kenneth W." }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "orcid": "0000-0002-2594-1523", "role": "member", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "civileng" ], "doi": "10.7907/Z98W3B9Z", "abstract": "Toppling analysis of a precariously balanced rock (PBR) can provide insights into the nature of ground motion that has not occurred at that location in the past and, by extension, realistic constraints on peak ground motions for use in engineering design. Earlier approaches have targeted simplistic 2-D models of the rock or modeled the rock-pedestal contact using spring-damper assemblies that require re-calibration for each rock. These analyses also assume that the rock does not slide on the pedestal. Here, a method to model PBRs in three dimensions is presented. The 3-D model is created from a point cloud of the rock, the pedestal, and their interface, obtained using Terrestrial Laser Scanning (TLS). The dynamic response of the model under earthquake excitation is simulated using a rigid body dynamics algorithm. The veracity of this approach is demonstrated by comparisons against data from shake table experiments. Fragility maps for toppling probability of the Echo Cliff PBR and the Pacifico PBR as a function of various ground motion parameters, rock-pedestal interface friction coefficient, and excitation direction are presented. The seismic hazard at these PBR locations is estimated using these maps. Additionally, these maps are used to assess whether the synthetic ground motions at these locations resulting from scenario earthquakes on the San Andreas Fault are realistic (toppling would indicate that the ground motions are unrealistically high)." }, { "name": "Vilenchik, Yaakov", "degree": "PhD", "year": "2015", "title": "Narrow-Linewidth Si/III-V Lasers: a Study of Laser Dynamics and Nonlinear Effects", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042015-232226135", "creators": [ { "name": { "family": "Vilenchik", "given": "Yaakov" }, "id": "Vilenchik-Yaakov", "display_name": "Vilenchik, Yaakov" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9513W57", "abstract": "Narrow-linewidth lasers play an important role in a wide variety of applications, from sensing and spectroscopy to optical communication and on-chip clocks. Current narrow-linewidth systems are usually implemented in doped fibers and are big, expensive, and power-hungry. Semiconductor lasers compete favorably in size, cost, and power consumption, but their linewidth is historically limited to the sub-MHz regime. However, it has been recently demonstrated that a new design paradigm, in which the optical energy is stored away from the active region in a composite high-Q resonator, has the potential to dramatically improve the coherence of the laser.
\r\n \r\nThis work explores this design paradigm, as applied on the hybrid Si/III-V platform. It demonstrates a record sub-KHz white-noise-floor linewidth. It further shows, both theoretically and experimentally, that this strategy practically eliminates Henry\u2019s linewidth enhancement by positioning a damped relaxation resonance at frequencies as low as 70 MHz, yielding truly quantum limited devices at frequencies of interest.
\r\n\r\nIn addition to this empirical contribution, this work explores the limits of performance of this platform. Here, the effect of two-photon-absorption and free-carrier-absorption are analyzed, using modified rate equations and Langevin force approach. The analysis predicts that as the intra-cavity field intensity builds up in the high-Q resonator, non-linear effects cause a new domain of performance-limiting factors. Steady-state behavior, laser dynamics, and frequency noise performance are examined in the context of this unique platform, pointing at the importance of nonlinear effects.
\r\n\r\nThis work offers a theoretical model predicting laser performance in light of nonlinear effects, obtaining a good agreement with experimental results from fabricated high-Q Si/III-V lasers. In addition to demonstrating unprecedented semiconductor laser performance, this work establishes a first attempt to predict and demonstrate the key impact of nonlinear effects on silicon-based lasers.
" }, { "name": "Wang, Xin C.", "degree": "PhD", "year": "2015", "title": "A Variational Framework for Spectral Discretization of the Density Matrix in Kohn-Sham Density Functional Theory", "advisor": "Bhattacharya, Kaushik; Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:04132015-160812309", "creators": [ { "name": { "family": "Wang", "given": "Xin C." }, "id": "Wang-Xin-C", "orcid": "0000-0003-3854-4831", "display_name": "Wang, Xin C." } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "co-advisor", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "co-advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z99021QK", "abstract": "Kohn-Sham density functional theory (KSDFT) is currently the main work-horse of quantum\r\nmechanical calculations in physics, chemistry, and materials science. From a mechanical\r\nengineering perspective, we are interested in studying the role of defects in the\r\nmechanical properties in materials. In real materials, defects are typically found at \r\nvery small concentrations e.g., vacancies occur at parts per million,\r\ndislocation density in metals ranges from $10^{10} m^{-2}$ to $10^{15} m^{-2}$,\r\nand grain sizes vary from nanometers to micrometers in polycrystalline materials, etc. In order to model materials at\r\nrealistic defect concentrations using DFT, we would need\r\nto work with system sizes beyond millions of atoms. Due to the cubic-scaling\r\ncomputational cost with respect to the number of atoms in conventional DFT implementations, such system sizes are\r\nunreachable. Since the early 1990s, there has been a huge interest in developing DFT\r\nimplementations that have linear-scaling computational cost. A promising\r\napproach to achieving linear-scaling cost is to approximate the density matrix in\r\nKSDFT. The focus of this\r\nthesis is to provide a firm mathematical framework to study the convergence of\r\nthese approximations. We reformulate the Kohn-Sham density\r\nfunctional theory as a nested variational problem in the density matrix,\r\nthe electrostatic potential, and a field dual to the electron density. The\r\ncorresponding functional is linear in the density matrix and thus amenable to\r\nspectral representation. Based on this reformulation, we introduce a new\r\napproximation scheme, called spectral binning, which does not require smoothing\r\nof the occupancy function and thus applies at arbitrarily low temperatures. We\r\nproof convergence of the approximate solutions with respect to spectral binning\r\nand with respect to an additional spatial discretization of the domain. For a\r\nstandard one-dimensional benchmark problem, we present numerical experiments for\r\nwhich spectral binning exhibits excellent convergence characteristics and\r\noutperforms other linear-scaling methods. " }, { "name": "Wilson, Samantha Stricklin", "degree": "PhD", "year": "2015", "title": "Zn-VI/Cu2O Heterojunctions for Earth-Abundant Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212015-091546304", "creators": [ { "name": { "family": "Wilson", "given": "Samantha Stricklin" }, "id": "Wilson-Samantha-Stricklin", "display_name": "Wilson, Samantha Stricklin" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9N58J9H ", "abstract": "The need for sustainable energy production motivates the study of photovoltaic materials, which convert energy from sunlight directly into electricity. This work has focused on the development of Cu2O as an earth-abundant solar absorber due to the abundance of its constituent elements in the earth's crust, its suitable band gap, and its potential for low cost processing. Crystalline wafers of Cu2O with minority carrier diffusion lengths on the order of microns can be manufactured in a uniquely simple fashion \u2014 directly from copper foils by thermal oxidation. Furthermore, Cu2O has an optical band gap of 1.9 eV, which gives it a detailed balance energy conversion efficiency of 24.7% and the possibility for an independently connected Si/Cu2O dual junction with a detailed balance efficiency of 44.3%.
\r\n\r\nHowever, the highest energy conversion efficiency achieved in a photovoltaic device with a Cu2O absorber layer is currently only 5.38% despite the favorable optical and electronic properties listed above. There are several challenges to making a Cu2O photovoltaic device, including an inability to dope the material, its relatively low chemical stability compared to other oxides, and a lack of suitable heterojunction partners due to an unusually small electron affinity. We have addressed the low chemical stability, namely the fact that Cu2O is an especially reactive oxide due to its low enthalpy of formation (\u0394Hf0 = -168.7 kJ/mol), by developing a novel surface preparation technique. We have addressed the lack of suitable heterojunction partners by investigating the heterojunction band alignment of several Zn-VI materials with Cu2O. Finally, We have addressed the typically high series resistance of Cu2O wafers by developing methods to make very thin, bulk Cu2O, including devices on Cu2O wafers as thin as 20 microns. Using these methods we have been able to achieve photovoltages over 1 V, and have demonstrated the potential of a new heterojunction material, Zn(O,S).
" }, { "name": "Wojnar, Charles Stanley", "degree": "PhD", "year": "2015", "title": "Exploring the Kinetics of Domain Switching in Ferroelectrics for Structural Applications", "advisor": "Kochmann, Dennis M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302015-221358386", "creators": [ { "name": { "family": "Wojnar", "given": "Charles Stanley" }, "id": "Wojnar-Charles-Stanley", "display_name": "Wojnar, Charles Stanley" } ], "advisors": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "advisor", "display_name": "Kochmann, Dennis M." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9HD7SM7", "abstract": "The complex domain structure in ferroelectrics gives rise to electromechanical coupling, and its evolution (via domain switching) results in a time-dependent (i.e. viscoelastic) response. Although ferroelectrics are used in many technological applications, most do not attempt to exploit the viscoelastic response of ferroelectrics, mainly due to a lack of understanding and accurate models for their description and prediction. Thus, the aim of this thesis research is to gain better understanding of the influence of domain evolution in ferroelectrics on their dynamic mechanical response.\r\n\r\nThere have been few studies on the viscoelastic properties of ferroelectrics, mainly due to a lack of experimental methods. Therefore, an apparatus and method called Broadband Electromechanical Spectroscopy (BES) was designed and built. BES allows for the simultaneous application of dynamic mechanical and electrical loading in a vacuum environment. Using BES, the dynamic stiffness and loss tangent in bending and torsion of a particular ferroelectric, viz. lead zirconate titanate (PZT), was characterized for different combinations of electrical and mechanical loading frequencies throughout the entire electric displacement hysteresis. Experimental results showed significant increases in loss tangent (by nearly an order of magnitude) and compliance during domain switching, which shows promise as a new approach to structural damping.\r\n\r\nA continuum model of the viscoelasticity of ferroelectrics was developed, which incorporates microstructural evolution via internal variables and associated kinetic relations. For the first time, through a new linearization process, the incremental dynamic stiffness and loss tangent of materials were computed throughout the entire electric displacement hysteresis for different combinations of mechanical and electrical loading frequencies. The model accurately captured experimental results.\r\n\r\nUsing the understanding gained from the characterization and modeling of PZT, two applications of domain switching kinetics were explored by using Micro Fiber Composites (MFCs). Proofs of concept of set-and-hold actuation and structural damping using MFCs were demonstrated." }, { "name": "Yang, Chih-Kai", "degree": "PhD", "year": "2015", "title": "An Exploration of Perovskite Materials for Thermochemical Water Splitting", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09082014-140216721", "creators": [ { "name": { "family": "Yang", "given": "Chih-Kai" }, "id": "Yang-Chih-Kai", "display_name": "Yang, Chih-Kai" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z91834GB", "abstract": "Two-step thermochemical water splitting is a promising technology for the hydrogen production of solar energy. This process possesses the advantages of utilizing the full solar spectrum, producing flexible fuels, and requiring no precious metal catalysts. It furthermore temporally separates the oxygen release and hydrogen production steps, eliminating the possibility of O2 and H2 recombination. Ceria, which undergoes non-stoichiometric changes in oxygen content, has been demonstrated as an effective material for solar-driven thermochemical fuel production, but the process requires extremely high temperatures (~ 1600 degrees C), leading to efficiency penalties and challenges in reactor design and construction. Accordingly, the objective of this work is the development of new thermochemical reaction substrate materials which enable operation at lower temperatures and ideally increase fuel productivity and efficiency. Here we explore perovskite systems, specifically La1-xSrxMnO3-\u03b4, La0.8Sr0.2Mn1-yFeyO3-\u03b4, and La0.8Sr0.2Mn1-yAlyO3-\u03b4. The link between the solid-state chemistry, redox properties, hydrogen production, and reaction kinetic limitations will be discussed. This study aims to learn how to design and tailor the good catalytic oxides for solar-driven thermochemical water splitting application." }, { "name": "Zhai, Xiang", "degree": "PhD", "year": "2015", "title": "Experimental, Numerical and Analytical Studies of the MHD-Driven Plasma Jet, Instabilities and Waves", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092015-162916583", "creators": [ { "name": { "family": "Zhai", "given": "Xiang" }, "id": "Zhai-Xiang", "display_name": "Zhai, Xiang" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Ott", "given": "Christian D." }, "id": "Ott-C-D", "role": "member", "display_name": "Ott, Christian D." }, { "name": { "family": "Tsurutani", "given": "Bruce" }, "id": "Tsurutani-B", "role": "member", "display_name": "Tsurutani, Bruce" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z90G3H3Q", "abstract": "This thesis describes a series of experimental, numerical, and analytical studies involving the Caltech magnetohydrodynamically (MHD)-driven plasma jet experiment. The plasma jet is created via a capacitor discharge that powers a magnetized coaxial planar electrodes system. The jet is collimated and accelerated by the MHD forces.
\r\n\r\nWe present three-dimensional ideal MHD finite-volume simulations of the plasma jet experiment using an astrophysical magnetic tower as the baseline model. A compact magnetic energy/helicity injection is exploited in the simulation analogous to both the experiment and to astrophysical situations. Detailed analysis provides a comprehensive description of the interplay of magnetic force, pressure, and flow effects. We delineate both the jet structure and the transition process that converts the injected magnetic energy to other forms.
\r\n\r\nWhen the experimental jet is sufficiently long, it undergoes a global kink instability and then a secondary local Rayleigh-Taylor instability caused by lateral acceleration of the kink instability. We present an MHD theory of the Rayleigh-Taylor instability on the cylindrical surface of a plasma flux rope in the presence of a lateral external gravity. The Rayleigh-Taylor instability is found to couple to the classic current-driven instability, resulting in a new type of hybrid instability. The coupled instability, produced by combination of helical magnetic field, curvature of the cylindrical geometry, and lateral gravity, is fundamentally different from the classic magnetic Rayleigh-Taylor instability occurring at a two-dimensional planar interface.
\r\n\r\nIn the experiment, this instability cascade from macro-scale to micro-scale eventually leads to the failure of MHD. When the Rayleigh-Taylor instability becomes nonlinear, it compresses and pinches the plasma jet to a scale smaller than the ion skin depth and triggers a fast magnetic reconnection. We built a specially designed high-speed 3D magnetic probe and successfully detected the high frequency magnetic fluctuations of broadband whistler waves associated with the fast reconnection. The magnetic fluctuations exhibit power-law spectra. The magnetic components of single-frequency whistler waves are found to be circularly polarized regardless of the angle between the wave propagation direction and the background magnetic field.
\r\n" }, { "name": "Zhang, Xuan", "degree": "PhD", "year": "2015", "title": "Investigation of Fundamental Processes Governing Secondary Organic Aerosol Formation in Laboratory Chambers", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282015-214235298", "creators": [ { "name": { "family": "Zhang", "given": "Xuan" }, "id": "Zhang-Xuan", "orcid": "0000-0003-1548-8021", "display_name": "Zhang, Xuan" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "chair", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/Z9QZ27WP", "abstract": "Our understanding of the processes and mechanisms by which secondary organic aerosol (SOA) is formed is derived from laboratory chamber studies. In the atmosphere, SOA formation is primarily driven by progressive photooxidation of SOA precursors, coupled with their gas-particle partitioning. In the chamber environment, SOA-forming vapors undergo multiple chemical and physical processes that involve production and removal via gas-phase reactions; partitioning onto suspended particles vs. particles deposited on the chamber wall; and direct deposition on the chamber wall. The main focus of this dissertation is to characterize the interactions of organic vapors with suspended particles and the chamber wall and explore how these intertwined processes in laboratory chambers govern SOA formation and evolution.
\r\n \r\nA Functional Group Oxidation Model (FGOM) that represents SOA formation and evolution in terms of the competition between functionalization and fragmentation, the extent of oxygen atom addition, and the change of volatility, is developed. The FGOM contains a set of parameters that are to be determined by fitting of the model to laboratory chamber data. The sensitivity of the model prediction to variation of the adjustable parameters allows one to assess the relative importance of various pathways involved in SOA formation.
\r\n \r\nA critical aspect of the environmental chamber is the presence of the wall, which can induce deposition of SOA-forming vapors and promote heterogeneous reactions. An experimental protocol and model framework are first developed to constrain the vapor-wall interactions. By optimal fitting the model predictions to the observed wall-induced decay profiles of 25 oxidized organic compounds, the dominant parameter governing the extent of wall deposition of a compound is identified, i.e., wall accommodation coefficient. By correlating this parameter with the molecular properties of a compound via its volatility, the wall-induced deposition rate of an organic compound can be predicted based on its carbon and oxygen numbers in the molecule.
\r\n \r\nHeterogeneous transformation of \u03b4-hydroxycarbonyl, a major first-generation product from long-chain alkane photochemistry, is observed on the surface of particles and walls. The uniqueness of this reaction scheme is the production of substituted dihydrofuran, which is highly reactive towards ozone, OH, and NO3, thereby opening a reaction pathway that is not usually accessible to alkanes. A spectrum of highly-oxygenated products with carboxylic acid, ester, and ether functional groups is produced from the substituted dihydrofuran chemistry, thereby affecting the average oxidation state of the alkane-derived SOA.
\r\n \r\nThe vapor wall loss correction is applied to several chamber-derived SOA systems generated from both anthropogenic and biogenic sources. Experimental and modeling approaches are employed to constrain the partitioning behavior of SOA-forming vapors onto suspended particles vs. chamber walls. It is demonstrated that deposition of SOA-forming vapors to the chamber wall during photooxidation experiments can lead to substantial and systematic underestimation of SOA. Therefore, it is likely that a lack of proper accounting for vapor wall losses that suppress chamber-derived SOA yields contribute substantially to the underprediction of ambient SOA concentrations in atmospheric models.
\r\n" }, { "name": "Ahn, Hyoung Jun", "degree": "PhD", "year": "2014", "title": "Random Propagation in Complex Systems: Nonlinear Matrix Recursions and Epidemic Spread\r ", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232014-172754261", "creators": [ { "name": { "family": "Ahn", "given": "Hyoung Jun" }, "id": "Ahn-Hyoung-Jun", "display_name": "Ahn, Hyoung Jun" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-K-A", "role": "member", "display_name": "Ligett, Katrina A." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/MC7M-EE22", "abstract": "This dissertation studies long-term behavior of random Riccati recursions and mathematical epidemic model. Riccati recursions are derived from Kalman filtering. The error covariance matrix of Kalman filtering satisfies Riccati recursions. Convergence condition of time-invariant Riccati recursions are well-studied by researchers. We focus on time-varying case, and assume that regressor matrix is random and identical and independently distributed according to given distribution whose probability distribution function is continuous, supported on whole space, and decaying faster than any polynomial. We study the geometric convergence of the probability distribution. We also study the global dynamics of the epidemic spread over complex networks for various models. For instance, in the discrete-time Markov chain model, each node is either healthy or infected at any given time. In this setting, the number of the state increases exponentially as the size of the network increases. The Markov chain has a unique stationary distribution where all the nodes are healthy with probability 1. Since the probability distribution of Markov chain defined on finite state converges to the stationary distribution, this Markov chain model concludes that epidemic disease dies out after long enough time. To analyze the Markov chain model, we study nonlinear epidemic model whose state at any given time is the vector obtained from the marginal probability of infection of each node in the network at that time. Convergence to the origin in the epidemic map implies the extinction of epidemics. The nonlinear model is upper-bounded by linearizing the model at the origin. As a result, the origin is the globally stable unique fixed point of the nonlinear model if the linear upper bound is stable. The nonlinear model has a second fixed point when the linear upper bound is unstable. We work on stability analysis of the second fixed point for both discrete-time and continuous-time models. Returning back to the Markov chain model, we claim that the stability of linear upper bound for nonlinear model is strongly related with the extinction time of the Markov chain. We show that stable linear upper bound is sufficient condition of fast extinction and the probability of survival is bounded by nonlinear epidemic map." }, { "name": "Amlani, Faisal", "degree": "PhD", "year": "2014", "title": "A New High-Order Fourier Continuation-Based Elasticity Solver for Complex Three-Dimensional Geometries", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10082013-093825165", "creators": [ { "name": { "family": "Amlani", "given": "Faisal" }, "id": "Amlani-Faisal", "display_name": "Amlani, Faisal" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/V9DQ-P103", "abstract": "This thesis presents a new approach for the numerical solution of three-dimensional problems in elastodynamics. The new methodology, which is based on a recently introduced Fourier continuation (FC) algorithm for the solution of Partial Differential Equations on the basis of accurate Fourier expansions of possibly non-periodic functions, enables fast, high-order solutions of the time-dependent elastic wave equation in a nearly dispersionless manner, and it requires use of CFL constraints that scale only linearly with spatial discretizations. A new FC operator is introduced to treat Neumann and traction boundary conditions, and a block-decomposed (sub-patch) overset strategy is presented for implementation of general, complex geometries in distributed-memory parallel computing environments. Our treatment of the elastic wave equation, which is formulated as a complex system of variable-coefficient PDEs that includes possibly heterogeneous and spatially varying material constants, represents the first fully-realized three-dimensional extension of FC-based solvers to date. Challenges for three-dimensional elastodynamics simulations such as treatment of corners and edges in three-dimensional geometries, the existence of variable coefficients arising from physical configurations and/or use of curvilinear coordinate systems and treatment of boundary conditions, are all addressed. The broad applicability of our new FC elasticity solver is demonstrated through application to realistic problems concerning seismic wave motion on three-dimensional topographies as well as applications to non-destructive evaluation where, for the first time, we present three-dimensional simulations for comparison to experimental studies of guided-wave scattering by through-thickness holes in thin plates." }, { "name": "Bjornsson, Arnar Bjorn", "degree": "PhD", "year": "2014", "title": "A Retrofitting Framework for Pre-Northridge Steel Moment-Frame Buildings", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302014-102237282", "creators": [ { "name": { "family": "Bjornsson", "given": "Arnar Bjorn" }, "id": "Bjornsson-Arnar-Bjorn", "display_name": "Bjornsson, Arnar Bjorn" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "chair", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Graves", "given": "Robert W." }, "id": "Graves-R-W", "role": "member", "display_name": "Graves, Robert W." } ], "option_major": [ "civileng" ], "doi": "10.7907/3Z6T-2H83", "abstract": "In the 1994 Mw 6.7 Northridge and 1995 Mw 6.9 Kobe earthquakes,\r\nsteel moment-frame buildings were exposed to an unexpected flaw. The commonly utilized\r\nwelded unreinforced flange, bolted web connections\r\nwere observed to experience brittle fractures in a number of buildings, even at\r\nlow levels of seismic demand. A majority of these buildings have not been retrofitted\r\nand may be susceptible to structural collapse in a major earthquake.
\r\n\r\nThis dissertation presents a case study of retrofitting a 20-story pre-Northridge steel\r\nmoment-frame building. Twelve retrofit schemes are developed that present some\r\nrange in degree of intervention. Three retrofitting techniques are considered: upgrading\r\nthe brittle beam-to-column moment resisting connections, and implementing either conventional\r\nor buckling-restrained brace elements within the existing moment-frame bays.\r\nThe retrofit schemes include some that are designed to the\r\nbasic safety objective of ASCE-41 Seismic Rehabilitation of Existing Buildings.
\r\n\r\nDetailed finite element models of the base line building and the retrofit schemes\r\nare constructed. The models include considerations of brittle\r\nbeam-to-column moment resisting connection fractures, column splice fractures,\r\ncolumn baseplate fractures, accidental contributions from ``simple'' non-moment resisting\r\nbeam-to-column connections to the lateral force-resisting system, and composite\r\nactions of beams with the overlying floor system.\r\nIn addition, foundation interaction is included through nonlinear translational springs\r\nunderneath basement columns.
\r\n\r\nTo investigate the effectiveness of the retrofit schemes, the building models are\r\nanalyzed under ground motions from three large magnitude simulated earthquakes that\r\ncause intense shaking in the greater Los Angeles metropolitan area, and under\r\nrecorded ground motions from actual earthquakes.\r\nIt is found that retrofit schemes that convert the existing moment-frames into braced-frames\r\nby implementing either conventional or buckling-restrained braces are effective in limiting\r\nstructural damage and mitigating structural collapse. In the three simulated earthquakes,\r\na 20% chance of simulated collapse is realized at PGV of around 0.6 m/s for the base line model,\r\nbut at PGV of around 1.8 m/s for some of the retrofit schemes. However, conventional braces are observed\r\nto deteriorate rapidly. Hence, if a braced-frame that employs conventional braces survives\r\na large earthquake, it is questionable how much service the braces provide in potential\r\naftershocks.
" }, { "name": "Bose, Subhonmesh", "degree": "PhD", "year": "2014", "title": "An Integrated Design Approach to Power Systems: From Power Flows to Electricity Markets", "advisor": "Low, Steven H.; Wierman, Adam C.; Chandy, K. Mani; Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012014-040224456", "creators": [ { "name": { "family": "Bose", "given": "Subhonmesh" }, "id": "Bose-Subhonmesh", "display_name": "Bose, Subhonmesh" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "co-advisor", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "co-advisor", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "co-advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." }, { "name": { "family": "Baldick", "given": "Ross" }, "id": "Baldick-R", "role": "member", "display_name": "Baldick, Ross" } ], "option_major": [ "eleceng" ], "doi": "10.7907/FRGW-AF26", "abstract": "Power system is at the brink of change. Engineering needs, economic forces and environmental factors are the main drivers of this change. The vision is to build a smart electrical grid and a smarter market mechanism around it to fulfill mandates on clean energy. Looking at engineering and economic issues in isolation is no longer an option today; it needs an integrated design approach. In this thesis, I shall revisit some of the classical questions on the engineering operation of power systems that deals with the nonconvexity of power flow equations. Then I shall explore some issues of the interaction of these power flow equations on the electricity markets to address the fundamental issue of market power in a deregulated market environment. Finally, motivated by the emergence of new storage technologies, I present an interesting result on the investment decision problem of placing storage over a power network. The goal of this study is to demonstrate that modern optimization and game theory can provide unique insights into this complex system. Some of the ideas carry over to applications beyond power systems." }, { "name": "Bowers, Steven Michael", "degree": "PhD", "year": "2014", "title": "Dynamically Controllable Integrated Radiation and Self-Correcting Power Generation in mm-Wave Circuits and Systems", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:10102013-145125571", "creators": [ { "name": { "family": "Bowers", "given": "Steven Michael" }, "id": "Bowers-Steven-Michael", "display_name": "Bowers, Steven Michael" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9MP518K", "abstract": "This thesis presents novel design methodologies for integrated radiators and power generation at mm-wave frequencies that are enabled by the continued integration of various electronic and electromagnetic (EM) structures onto the same substrate. Beginning with the observation that transistors and their connections to EM radiating structures on an integrated substrate are essentially free, the concept of multi-port driven (MPD) radiators is introduced, which opens a vast design space that has been generally ignored due to the cost structure associated with discrete components that favors fewer transistors connected to antennas through a single port.
\r\n\r\nFrom Maxwell's equations, a new antenna architecture, the radial MPD antennas based on the concept of MPD radiators, is analyzed to gain intuition as to the important design parameters that explain the wide-band nature of the antenna itself. The radiator is then designed and implemented at 160 GHz in a 0.13 um SiGe BiCMOS process, and the single element design has a measured effective isotropic radiated power (EIRP) of +4.6 dBm with a total radiated power of 0.63 mW.
\r\n\r\nNext, the radial MPD radiator is adapted to enable dynamic polarization control (DPC). A DPC antenna is capable of controlling its radiated polarization dynamically, and entirely electronically, with no mechanical reconfiguration required. This can be done by having multiple antennas with different polarizations, or within a single antenna that has multiple drive points, as in the case of the MPD radiator with DPC. This radiator changes its polarization by adjusting the relative phase and amplitude of its multiple ports to produce polarizations with any polarization angle, and a wide range of axial ratios. A 2x1 MPD radiator array with DPC at 105 GHz is presented whose measurements show control of the polarization angle throughout the entire 0 degree through 180 degree range while in the linear polarization mode and maintaining axial ratios above 10 dB in all cases. Control of the axial ratio is also demonstrated with a measured range from 2.4 dB through 14 dB, while maintaining a fixed polarization angle. The radiator itself has a measured maximum EIRP of +7.8 dBm, with a total radiated power of 0.9 mW, and is capable of beam steering.
\r\n \r\nMPD radiators were also applied in the domain of integrated silicon photonics. For these designs, the driver transistor circuitry was replaced with silicon optical waveguides and photodiodes to produce a 350 GHz signal. Three of these optical MPD radiator designs have been implemented as 2x2 arrays at 350 GHz. The first is a beam forming array that has a simulated gain of 12.1 dBi with a simulated EIRP of -2 dBm. The second has the same simulated performance, but includes optical phase modulators that enable two-dimensional beam steering. Finally, a third design incorporates multi-antenna DPC by combining the outputs of both left and right handed circularly polarized MPD antennas to produce a linear polarization with controllable polarization angle, and has a simulated gain of 11.9 dBi and EIRP of -3 dBm. In simulation, it can tune the polarization from 0 degrees through 180 degrees while maintaining a radiated power that has a 0.35 dB maximum deviation from the mean.
\r\n\r\nThe reliability of mm-wave radiators and power amplifiers was also investigated, and two self-healing systems have been proposed. Self-healing is a global feedback method where integrated sensors detect the performance of the circuit after fabrication and report that data to a digital control algorithm. The algorithm then is capable of setting actuators that can control the performance of the mm-wave circuit and counteract any performance degradation that is observed by the sensors. The first system is for a MPD radiator array with a partially integrated self-healing system. The self-healing MPD radiator senses substrate modes through substrate mode pickup sensors and infers the far-field radiated pattern from those sensors. DC current sensors are also included to determine the DC power consumption of the system. Actuators are implemented in the form of phase and amplitude control of the multiple drive points.
\r\n\r\nThe second self-healing system is a fully integrated self-healing power amplifier (PA) at 28 GHz. This system measures the output power, gain and efficiency of the PA using radio frequency (RF) power sensors, DC current sensors and junction temperature sensors. The digital block is synthesized from VHDL code on-chip and it can actuate the output power combining matching network using tunable transmission line stubs, as well as the DC operating point of the amplifying transistors through bias control. Measurements of 20 chips confirm self-healing for two different algorithms for process variation and transistor mismatch, while measurements from 10 chips show healing for load impedance mismatch, and linearity healing. Laser induced partial and total transistor failure show the benefit of self-healing in the case of catastrophic failure, with improvements of up to 3.9 dB over the default case. An exemplary yield specification shows self-healing improving the yield from 0% up through 80%.
" }, { "name": "Carroll, Phares Lynn", "degree": "PhD", "year": "2014", "title": "Towards Understanding the Mixing Characteristics of Turbulent Buoyant Flows", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212014-101703985", "creators": [ { "name": { "family": "Carroll", "given": "Phares Lynn" }, "id": "Carroll-Phares-Lynn", "display_name": "Carroll, Phares Lynn" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/RDHJ-3X60", "abstract": "This work proposes a new simulation methodology in which variable density turbulent flows can be studied in the context of a mixing layer with or without the presence of gravity. Specifically, this methodology is developed to probe the nature of non-buoyantly-driven (i.e. isotropically-driven) or buoyantly-driven mixing deep inside a mixing layer. Numerical forcing methods are incorporated into both the velocity and scalar fields, which extends the length of time over which mixing physics can be studied. The simulation framework is designed to allow for independent variation of four non-dimensional parameters, including the Reynolds, Richardson, Atwood, and Schmidt numbers. Additionally, the governing equations are integrated in such a way to allow for the relative magnitude of buoyant energy production and non-buoyant energy production to be varied.
\r\n\r\n\r\nThe computational requirements needed to implement the proposed configuration are presented. They are justified in terms of grid resolution, order of accuracy, and transport scheme. Canonical features of turbulent buoyant flows are reproduced as validation of the proposed methodology. These features include the recovery of isotropic Kolmogorov scales under buoyant and non-buoyant conditions, the recovery of anisotropic one-dimensional energy spectra under buoyant conditions, and the preservation of known statistical distributions in the scalar field, as found in other DNS studies.
\r\n\r\n\r\nThis simulation methodology is used to perform a parametric study of turbulent buoyant flows to discern the effects of varying the Reynolds, Richardson, and Atwood numbers on the resulting state of mixing. The effects of the Reynolds and Atwood numbers are isolated by looking at two energy dissipation rate conditions under non-buoyant (variable density) and constant density conditions. The effects of Richardson number are isolated by varying the ratio of buoyant energy production to total energy production from zero (non-buoyant) to one (entirely buoyant) under constant Atwood number, Schmidt number, and energy dissipation rate conditions. It is found that the major differences between non-buoyant and buoyant turbulent flows are contained in the transfer spectrum and longitudinal structure functions, while all other metrics are largely similar (e.g. energy spectra, alignment characteristics of the strain-rate tensor). Also, despite the differences noted between fully buoyant and non-buoyant turbulent fields, the scalar field, in all cases, is unchanged by these. The mixing dynamics in the scalar field are found to be insensitive to the source of turbulent kinetic energy production (non-buoyant vs. buoyant).
\r\n" }, { "name": "Chang, Jan Han-Chieh", "degree": "PhD", "year": "2014", "title": "Wireless Parylene-Based Retinal Implant", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202013-193131878", "creators": [ { "name": { "family": "Chang", "given": "Jan Han-Chieh" }, "id": "Chang-Jan-Han-Chieh", "display_name": "Chang, Jan Han-Chieh" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Weiland", "given": "James D." }, "id": "Weiland-J-D", "role": "member", "display_name": "Weiland, James D." } ], "option_major": [ "eleceng" ], "doi": "10.7907/YTN7-ZA05", "abstract": "The degeneration of the outer retina usually causes blindness by affecting the photoreceptor cells. However, the ganglion cells, which consist of optic nerves, on the middle and inner retina layers are often intact. The retinal implant, which can partially restore vision by electrical stimulation, soon becomes a focus for research. Although many groups worldwide have spent a lot of effort on building devices for retinal implant, current state-of-the-art technologies still lack a reliable packaging scheme for devices with desirable high-density multi-channel features. Wireless flexible retinal implants have always been the ultimate goal for retinal prosthesis. In this dissertation, the reliable packaging scheme for a wireless flexible parylene-based retinal implants has been well developed. It can not only provide stable electrical and mechanical connections to the high-density multi-channel (1000+ channels on 5 mm \u00d7 5 mm chip area) IC chips, but also survive for more than 10 years in the human body with corrosive fluids.
\r\n\r\nThe device is based on a parylene-metal-parylene sandwich structure. In which, the adhesion between the parylene layers and the metals embedded in the parylene layers have been studied. Integration technology for high-density multi-channel IC chips has also been addressed and tested with dummy and real 268-channel and 1024-channel retinal IC chips. In addition, different protection schemes have been tried in application to IC chips and discrete components to gain the longest lifetime. The effectiveness has been confirmed by the accelerated and active lifetime soaking test in saline solution. Surgical mockups have also been designed and successfully implanted inside dog's and pig's eyes. Additionally, the electrodes used to stimulate the ganglion cells have been modified to lower the interface impedance and shaped to better fit the retina. Finally, all the developed technologies have been applied on the final device with a dual-metal-layer structure.
\r\n" }, { "name": "Cheng, Ming Hei", "degree": "PhD", "year": "2014", "title": "New Applications that Come from Extending Seismic Networks into Buildings", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03182014-225151551", "creators": [ { "name": { "family": "Cheng", "given": "Ming Hei" }, "id": "Cheng-Ming-Hei", "display_name": "Cheng, Ming Hei" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "role": "member", "display_name": "Kohler, Monica D." } ], "option_major": [ "civileng" ], "doi": "10.7907/STB2-XR07", "abstract": "This thesis describes engineering applications that come from extending seismic networks into building structures. The proposed applications will benefit the data from the newly developed crowd-sourced seismic networks which are composed of low-cost accelerometers. An overview of the Community Seismic Network and the earthquake detection method are addressed. In the structural array components of crowd-sourced seismic networks, there may be instances in which a single seismometer is the only data source that is available from a building. A simple prismatic Timoshenko beam model with soil-structure interaction (SSI) is developed to approximate mode shapes of buildings using natural frequency ratios. A closed form solution with complete vibration modes is derived. In addition, a new method to rapidly estimate total displacement response of a building based on limited observational data, in some cases from a single seismometer, is presented. The total response of a building is modeled by the combination of the initial vibrating motion due to an upward traveling wave, and the subsequent motion as the low-frequency resonant mode response. Furthermore, the expected shaking intensities in tall buildings will be significantly different from that on the ground during earthquakes. Examples are included to estimate the characteristics of shaking that can be expected in mid-rise to high-rise buildings. Development of engineering applications (e.g., human comfort prediction and automated elevator control) for earthquake early warning system using probabilistic framework and statistical learning technique is addressed. " }, { "name": "Ci, Maolin", "degree": "PhD", "year": "2014", "title": "Multiscale Model Reduction Methods for Deterministic and Stochastic Partial Differential Equations", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312014-014047677", "creators": [ { "name": { "family": "Ci", "given": "Maolin" }, "id": "Ci-Maolin", "display_name": "Ci, Maolin" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/06ND-CY07", "abstract": "Partial differential equations (PDEs) with multiscale coefficients are very difficult to solve due to the wide range of scales in the solutions. In the thesis, we propose some efficient numerical methods for both deterministic and stochastic PDEs based on the model reduction technique.
\r\n\r\nFor the deterministic PDEs, the main purpose of our method is to derive an effective equation for the multiscale problem. An essential ingredient is to decompose the harmonic coordinate into a smooth part and a highly oscillatory part of which the magnitude is small. Such a decomposition plays a key role in our construction of the effective equation. We show that the solution to the effective equation is smooth, and could be resolved on a regular coarse mesh grid. Furthermore, we provide error analysis and show that the solution to the effective equation plus a correction term is close to the original multiscale solution.
\r\n\r\nFor the stochastic PDEs, we propose the model reduction based data-driven stochastic method and multilevel Monte Carlo method. In the multiquery, setting and on the assumption that the ratio of the smallest scale and largest scale is not too small, we propose the multiscale data-driven stochastic method. We construct a data-driven stochastic basis and solve the coupled deterministic PDEs to obtain the solutions. For the tougher problems, we propose the multiscale multilevel Monte Carlo method. We apply the multilevel scheme to the effective equations and assemble the stiffness matrices efficiently on each coarse mesh grid. In both methods, the $\\KL$ expansion plays an important role in extracting the main parts of some stochastic quantities.
\r\n\r\nFor both the deterministic and stochastic PDEs, numerical results are presented to demonstrate the accuracy and robustness of the methods. We also show the computational time cost reduction in the numerical examples.
" }, { "name": "Coss\u00e9, Julia Theresa", "degree": "PhD", "year": "2014", "title": "On the Behavior of Pliable Plate Dynamics in Wind: Application to Vertical Axis Wind Turbines", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272014-160129404", "creators": [ { "name": { "family": "Coss\u00e9", "given": "Julia Theresa" }, "id": "Coss\u00e9-Julia-Theresa", "display_name": "Coss\u00e9, Julia Theresa" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Sader", "given": "John E." }, "id": "Sader-J-E", "orcid": "0000-0002-7096-0627", "role": "member", "display_name": "Sader, John E." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X7S3-CS74", "abstract": "Numerous studies have shown that flexible materials improve resilience and durability of a structure. Several studies have investigated the behavior of elastic plates under the influence of a free stream, such as studies of the fluttering flag and others of shape reconfiguration, due to a free stream.
\r\n\r\nThe principle engineering contribution of this thesis is the design and development of a vertical axis wind turbine that features pliable blades which undergo various modes of behavior, ultimately leading to rotational propulsion of the turbine. The wind turbine design was tested in a wind tunnel and at the Caltech Laboratory for Optimized Wind Energy. Ultimately, the flexible blade vertical axis wind turbine proved to be an effective way of harnessing the power of the wind.
\r\n\r\nIn addition, this body of work builds on the current knowledge of elastic cantilever plates in a free stream flow by investigating the inverted flag. While previous studies have focused on the fluid structure interaction of a free stream on elastic cantilever plates, none had studied the plate configuration where the trailing edge was clamped, leaving the leading edge free to move. Furthermore, the studies presented in this thesis establish the geometric boundaries of where the large-amplitude flapping occurs.
" }, { "name": "Della Rocca, Gerry V.", "degree": "PhD", "year": "2014", "title": "A Novel Methodology for Simulating Contact-Line Behavior in Capillary-Driven Flows", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262014-160059300", "creators": [ { "name": { "family": "Della Rocca", "given": "Gerry V." }, "id": "Della-Rocca-Gerry-V", "display_name": "Della Rocca, Gerry V." } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9CN71WW", "abstract": "Despite the wide swath of applications where multiphase fluid contact lines exist, there is still no consensus on an accurate and general simulation methodology. Most prior numerical work has imposed one of the many dynamic contact-angle theories at solid walls. Such approaches are inherently limited by the theory accuracy. In fact, when inertial effects are important, the contact angle may be history dependent and, thus, any single mathematical function is inappropriate. Given these limitations, the present work has two primary goals: 1) create a numerical framework that allows the contact angle to evolve naturally with appropriate contact-line physics and 2) develop equations and numerical methods such that contact-line simulations may be performed on coarse computational meshes.
\r\n\r\nFluid flows affected by contact lines are dominated by capillary stresses and require accurate curvature calculations. The level set method was chosen to track the fluid interfaces because it is easy to calculate interface curvature accurately. Unfortunately, the level set reinitialization suffers from an ill-posed mathematical problem at contact lines: a ``blind spot'' exists. Standard techniques to handle this deficiency are shown to introduce parasitic velocity currents that artificially deform freely floating (non-prescribed) contact angles. As an alternative, a new relaxation equation reinitialization is proposed to remove these spurious velocity currents and its concept is further explored with level-set extension velocities.
\r\n\r\nTo capture contact-line physics, two classical boundary conditions, the Navier-slip velocity boundary condition and a fixed contact angle, are implemented in direct numerical simulations (DNS). DNS are found to converge only if the slip length is well resolved by the computational mesh. Unfortunately, since the slip length is often very small compared to fluid structures, these simulations are not computationally feasible for large systems. To address the second goal, a new methodology is proposed which relies on the volumetric-filtered Navier-Stokes equations. Two unclosed terms, an average curvature and a viscous shear VS, are proposed to represent the missing microscale physics on a coarse mesh.
\r\n\r\nAll of these components are then combined into a single framework and tested for a water droplet impacting a partially-wetting substrate. Very good agreement is found for the evolution of the contact diameter in time between the experimental measurements and the numerical simulation. Such comparison would not be possible with prior methods, since the Reynolds number Re and capillary number Ca are large. Furthermore, the experimentally approximated slip length ratio is well outside of the range currently achievable by DNS. This framework is a promising first step towards simulating complex physics in capillary-dominated flows at a reasonable computational expense.
" }, { "name": "Demers, Steven Brian", "degree": "PhD", "year": "2014", "title": "Advanced Density Functional Theory Methods tor Materials Science", "advisor": "van de Walle, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032014-224426152", "creators": [ { "name": { "family": "Demers", "given": "Steven Brian" }, "id": "Demers-Steven-Brian", "display_name": "Demers, Steven Brian" } ], "advisors": [ { "name": { "family": "van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "advisor", "display_name": "van de Walle, Axel" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" }, { "name": { "family": "van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "member", "display_name": "van de Walle, Axel" } ], "option_major": [ "matsci" ], "doi": "10.7907/KNJR-6F80", "abstract": "In this work we chiefly deal with two broad classes of problems in computational materials science, determining the doping mechanism in a semiconductor and developing an extreme condition equation of state. While solving certain aspects of these questions is well-trodden ground, both require extending the reach of existing methods to fully answer them. Here we choose to build upon the framework of density functional theory (DFT) which provides an efficient means to investigate a system from a quantum mechanics description.
\r\n\r\nZinc Phosphide (Zn3P2) could be the basis for cheap and highly efficient solar cells. Its use in this regard is limited by the difficulty in n-type doping the material. In an effort to understand the mechanism behind this, the energetics and electronic structure of intrinsic point defects in zinc phosphide are studied using generalized Kohn-Sham theory and utilizing the Heyd, Scuseria, and Ernzerhof (HSE) hybrid functional for exchange and correlation. Novel 'perturbation extrapolation' is utilized to extend the use of the computationally expensive HSE functional to this large-scale defect system. According to calculations, the formation energy of charged phosphorus interstitial defects are very low in n-type Zn3P2 and act as 'electron sinks', nullifying the desired doping and lowering the fermi-level back towards the p-type regime. Going forward, this insight provides clues to fabricating useful zinc phosphide based devices. In addition, the methodology developed for this work can be applied to further doping studies in other systems.
\r\n\r\nAccurate determination of high pressure and temperature equations of state is fundamental in a variety of fields. However, it is often very difficult to cover a wide range of temperatures and pressures in an laboratory setting. Here we develop methods to determine a multi-phase equation of state for Ta through computation. The typical means of investigating thermodynamic properties is via \u2019classical\u2019 molecular dynamics where the atomic motion is calculated from Newtonian mechanics with the electronic effects abstracted away into an interatomic potential function. For our purposes, a \u2019first principles\u2019 approach such as DFT is useful as a classical potential is typically valid for only a portion of the phase diagram (i.e. whatever part it has been fit to). Furthermore, for extremes of temperature and pressure quantum effects become critical to accurately capture an equation of state and are very hard to capture in even complex model potentials. This requires extending the inherently zero temperature DFT to predict the finite temperature response of the system. Statistical modelling and thermodynamic integration is used to extend our results over all phases, as well as phase-coexistence regions which are at the limits of typical DFT validity. We deliver the most comprehensive and accurate equation of state that has been done for Ta. This work also lends insights that can be applied to further equation of state work in many other materials.
" }, { "name": "Desautels, Thomas Anthony", "degree": "PhD", "year": "2014", "title": "Spinal Cord Injury Therapy through Active Learning", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:07252013-120308708", "creators": [ { "name": { "family": "Desautels", "given": "Thomas Anthony" }, "id": "Desautels-Thomas-Anthony", "display_name": "Desautels, Thomas Anthony" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Edgerton", "given": "V. Reggie" }, "id": "Edgerton-V-R", "role": "member", "display_name": "Edgerton, V. Reggie" } ], "option_major": [ "mecheng" ], "doi": "10.7907/X5M7-EC09", "abstract": "Therapy employing epidural electrostimulation holds great potential for improving therapy for patients with spinal cord injury (SCI) (Harkema et al., 2011). Further promising results from combined therapies using electrostimulation have also been recently obtained (e.g., van den Brand et al., 2012). The devices being developed to deliver the stimulation are highly flexible, capable of delivering any individual stimulus among a combinatorially large set of stimuli (Gad et al., 2013). While this extreme flexibility is very useful for ensuring that the device can deliver an appropriate stimulus, the challenge of choosing good stimuli is quite substantial, even for expert human experimenters. To develop a fully implantable, autonomous device which can provide useful therapy, it is necessary to design an algorithmic method for choosing the stimulus parameters. Such a method can be used in a clinical setting, by caregivers who are not experts in the neurostimulator's use, and to allow the system to adapt autonomously between visits to the clinic. To create such an algorithm, this dissertation pursues the general class of active learning algorithms that includes Gaussian Process Upper Confidence Bound (GP-UCB, Srinivas et al., 2010), developing the Gaussian Process Batch Upper Confidence Bound (GP-BUCB, Desautels et al., 2012) and Gaussian Process Adaptive Upper Confidence Bound (GP-AUCB) algorithms. This dissertation develops new theoretical bounds for the performance of these and similar algorithms, empirically assesses these algorithms against a number of competitors in simulation, and applies a variant of the GP-BUCB algorithm in closed-loop to control SCI therapy via epidural electrostimulation in four live rats. The algorithm was tasked with maximizing the amplitude of evoked potentials in the rats' left tibialis anterior muscle. These experiments show that the algorithm is capable of directing these experiments sensibly, finding effective stimuli in all four animals. Further, in direct competition with an expert human experimenter, the algorithm produced superior performance in terms of average reward and comparable or superior performance in terms of maximum reward. These results indicate that variants of GP-BUCB may be suitable for autonomously directing SCI therapy." }, { "name": "Faulkner, Matthew Nicholas", "degree": "PhD", "year": "2014", "title": "Community Sense and Response Systems", "advisor": "Krause, R. Andreas; Chandy, K. Mani; Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152014-111007328", "creators": [ { "name": { "family": "Faulkner", "given": "Matthew Nicholas" }, "id": "Faulkner-Matthew-Nicholas", "display_name": "Faulkner, Matthew Nicholas" } ], "advisors": [ { "name": { "family": "Krause", "given": "R. Andreas" }, "id": "Krause-R-A", "role": "advisor", "display_name": "Krause, R. Andreas" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Krause", "given": "R. Andreas" }, "id": "Krause-R-A", "role": "chair", "display_name": "Krause, R. Andreas" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/QFM5-FH06", "abstract": "The proliferation of smartphones and other internet-enabled, sensor-equipped consumer devices enables us to sense and act upon the physical environment in unprecedented ways. This thesis considers Community Sense-and-Response (CSR) systems, a new class of web application for acting on sensory data gathered from participants' personal smart devices. The thesis describes how rare events can be reliably detected using a decentralized anomaly detection architecture that performs client-side anomaly detection and server-side event detection. After analyzing this decentralized anomaly detection approach, the thesis describes how weak but spatially structured events can be detected, despite significant noise, when the events have a sparse representation in an alternative basis. Finally, the thesis describes how the statistical models needed for client-side anomaly detection may be learned efficiently, using limited space, via coresets.
\r\n \r\nThe Caltech Community Seismic Network (CSN) is a prototypical example of a CSR system that harnesses accelerometers in volunteers' smartphones and consumer electronics. Using CSN, this thesis presents the systems and algorithmic techniques to design, build and evaluate a scalable network for real-time awareness of spatial phenomena such as dangerous earthquakes.
" }, { "name": "Fefferman, William Jason", "degree": "PhD", "year": "2014", "title": "The Power of Quantum Fourier Sampling", "advisor": "Umans, Christopher M.; Kitaev, Alexei", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302014-131308138", "creators": [ { "name": { "family": "Fefferman", "given": "William Jason" }, "id": "Fefferman-William-Jason", "display_name": "Fefferman, William Jason" } ], "advisors": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "co-advisor", "display_name": "Umans, Christopher M." }, { "name": { "family": "Kitaev", "given": "Alexei" }, "id": "Kitaev-A", "role": "co-advisor", "display_name": "Kitaev, Alexei" } ], "committee": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "chair", "display_name": "Umans, Christopher M." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "role": "member", "display_name": "Preskill, John P." }, { "name": { "family": "Kitaev", "given": "Alexei" }, "id": "Kitaev-A", "role": "member", "display_name": "Kitaev, Alexei" } ], "option_major": [ "compsci" ], "doi": "10.7907/6HJB-MC69", "abstract": "How powerful are Quantum Computers? Despite the prevailing belief that Quantum Computers are more powerful than their classical counterparts, this remains a conjecture backed by little formal evidence. Shor's famous factoring algorithm [Shor97] gives an example of a problem that can be solved efficiently on a quantum computer with no known efficient classical algorithm. Factoring, however, is unlikely to be NP-Hard, meaning that few unexpected formal consequences would arise, should such a classical algorithm be discovered. Could it then be the case that any quantum algorithm can be simulated efficiently classically? Likewise, could it be the case that Quantum Computers can quickly solve problems much harder than factoring? If so, where does this power come from, and what classical computational resources do we need to solve the hardest problems for which there exist efficient quantum algorithms?
\r\n\r\nWe make progress toward understanding these questions through studying the relationship between classical nondeterminism and quantum computing. In particular, is there a problem that can be solved efficiently on a Quantum Computer that cannot be efficiently solved using nondeterminism? In this thesis we address this problem from the perspective of sampling problems. Namely, we give evidence that approximately sampling the Quantum Fourier Transform of an efficiently computable function, while easy quantumly, is hard for any classical machine in the Polynomial Time Hierarchy. In particular, we prove the existence of a class of distributions that can be sampled efficiently by a Quantum Computer, that likely cannot be approximately sampled in randomized polynomial time with an oracle for the Polynomial Time Hierarchy.
\r\n\r\nOur work complements and generalizes the evidence given in Aaronson and Arkhipov's work [AA2013] where a different distribution with the same computational properties was given. Our result is more general than theirs, but requires a more powerful quantum sampler.
\r\n" }, { "name": "Ferrari de Goes, Fernando", "degree": "PhD", "year": "2014", "title": "Geometric Discretization through Primal-Dual Meshes", "advisor": "Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222014-134831171", "creators": [ { "name": { "family": "Ferrari de Goes", "given": "Fernando" }, "id": "Ferrari-de-Goes-Fernando-Ferrari", "display_name": "Ferrari de Goes, Fernando" } ], "advisors": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "chair", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Alliez", "given": "Pierre" }, "id": "Alliez-P", "role": "member", "display_name": "Alliez, Pierre" } ], "option_major": [ "compsci" ], "doi": "10.7907/32CA-7376", "abstract": "This thesis introduces new tools for geometric discretization in computer graphics and computational physics. Our work builds upon the duality between weighted triangulations and power diagrams to provide concise, yet expressive discretization of manifolds and differential operators. Our exposition begins with a review of the construction of power diagrams, followed by novel optimization procedures to fully control the local volume and spatial distribution of power cells. Based on this power diagram framework, we develop a new family of discrete differential operators, an effective stippling algorithm, as well as a new fluid solver for Lagrangian particles. We then turn our attention to applications in geometry processing. We show that orthogonal primal-dual meshes augment the notion of local metric in non-flat discrete surfaces. In particular, we introduce a reduced set of coordinates for the construction of orthogonal primal-dual structures of arbitrary topology, and provide alternative metric characterizations through convex optimizations. We finally leverage these novel theoretical contributions to generate well-centered primal-dual meshes, sphere packing on surfaces, and self-supporting triangulations." }, { "name": "Florian, Mihai", "degree": "PhD", "year": "2014", "title": "Analysis-Aware Design of Embedded Systems Software", "advisor": "Holzmann, Gerard J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10142013-111401153", "creators": [ { "name": { "family": "Florian", "given": "Mihai" }, "id": "Florian-Mihai", "display_name": "Florian, Mihai" } ], "advisors": [ { "name": { "family": "Holzmann", "given": "Gerard J." }, "id": "Holzmann-G-J", "role": "advisor", "display_name": "Holzmann, Gerard J." } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Holzmann", "given": "Gerard J." }, "id": "Holzmann-G-J", "role": "member", "display_name": "Holzmann, Gerard J." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Havelund", "given": "Klaus" }, "id": "Havelund-K", "role": "member", "display_name": "Havelund, Klaus" }, { "name": { "family": "Joshi", "given": "Rajeev" }, "id": "Joshi-R", "role": "member", "display_name": "Joshi, Rajeev" } ], "option_major": [ "compsci" ], "doi": "10.7907/VB1N-Y042", "abstract": "In the past many different methodologies have been devised to support software development and different sets of methodologies have been developed to support the analysis of software artefacts. We have identified this mismatch as one of the causes of the poor reliability of embedded systems software. The issue with software development styles is that they are ``analysis-agnostic.'' They do not try to structure the code in a way that lends itself to analysis. The analysis is usually applied post-mortem after the software was developed and it requires a large amount of effort. The issue with software analysis methodologies is that they do not exploit available information about the system being analyzed.
\r\n\r\nIn this thesis we address the above issues by developing a new methodology, called \"analysis-aware\" design, that links software development styles with the capabilities of analysis tools. This methodology forms the basis of a framework for interactive software development. The framework consists of an executable specification language and a set of analysis tools based on static analysis, testing, and model checking. The language enforces an analysis-friendly code structure and offers primitives that allow users to implement their own testers and model checkers directly in the language. We introduce a new approach to static analysis that takes advantage of the capabilities of a rule-based engine. We have applied the analysis-aware methodology to the development of a smart home application.
" }, { "name": "Fokoua Djodom, Landry", "degree": "PhD", "year": "2014", "title": "Optimal Scaling in Ductile Fracture", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162013-221817628", "creators": [ { "name": { "family": "Fokoua Djodom", "given": "Landry" }, "id": "Fokoua-Djodom-Landry", "display_name": "Fokoua Djodom, Landry" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Weinberg", "given": "Kerstin" }, "id": "Weinberg-K", "role": "member", "display_name": "Weinberg, Kerstin" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B1TW-2D81", "abstract": "This work is concerned with the derivation of optimal scaling laws, in the sense of matching lower and upper bounds on the energy, for a solid undergoing ductile fracture. The specific problem considered concerns a material sample in the form of an infinite slab of finite thickness subjected to prescribed opening displacements on its two surfaces. The solid is assumed to obey deformation-theory of plasticity and, in order to further simplify the analysis, we assume isotropic rigid-plastic deformations with zero plastic spin. When hardening exponents are given values consistent with observation, the energy is found to exhibit sublinear growth. We regularize the energy through the addition of nonlocal energy terms of the strain-gradient plasticity type. This nonlocal regularization has the effect of introducing an intrinsic length scale into the energy. We also put forth a physical argument that identifies the intrinsic length and suggests a linear growth of the nonlocal energy. Under these assumptions, ductile fracture emerges as the net result of two competing effects: whereas the sublinear growth of the local energy promotes localization of deformation to failure planes, the nonlocal regularization stabilizes this process, thus resulting in an orderly progression towards failure and a well-defined specific fracture energy. The optimal scaling laws derived here show that ductile fracture results from localization of deformations to void sheets, and that it requires a well-defined energy per unit fracture area. In particular, fractal modes of fracture are ruled out under the assumptions of the analysis. The optimal scaling laws additionally show that ductile fracture is cohesive in nature, i.e., it obeys a well-defined relation between tractions and opening displacements. Finally, the scaling laws supply a link between micromechanical properties and macroscopic fracture properties. In particular, they reveal the relative roles that surface energy and microplasticity play as contributors to the specific fracture energy of the material. Next, we present an experimental assessment of the optimal scaling laws. We show that when the specific fracture energy is renormalized in a manner suggested by the optimal scaling laws, the data falls within the bounds predicted by the analysis and, moreover, they ostensibly collapse---with allowances made for experimental scatter---on a master curve dependent on the hardening exponent, but otherwise material independent." }, { "name": "Griffith, Virgil", "degree": "PhD", "year": "2014", "title": "Quantifying Synergistic Information", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132013-161604752", "creators": [ { "name": { "family": "Griffith", "given": "Virgil" }, "id": "Griffith-Virgil", "display_name": "Griffith, Virgil" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "cns" ], "doi": "10.7907/ZS2T-XQ55", "abstract": "Within the microcosm of information theory, I explore what it means for a system to be functionally irreducible. This is operationalized as quantifying the extent to which cooperative or \"synergistic\" effects enable random variables X1, ... , Xn to predict (have mutual information about) a single target random variable Y . In Chapter 1, we introduce the problem with some emblematic examples. In Chapter 2, we show how six different measures from the existing literature fail to quantify this notion of synergistic mutual information. In Chapter 3 we take a step towards a measure of synergy which yields the first nontrivial lowerbound on synergistic mutual information. In Chapter 4, we find that synergy is but the weakest notion of a broader concept of irreducibility. In Chapter 5, we apply our results from Chapters 3 and 4 towards grounding Giulio Tononi\u2019s ambitious \u03c6 measure which attempts to quantify the magnitude of consciousness experience.
" }, { "name": "Hakimi, Shabnam", "degree": "PhD", "year": "2014", "title": "Characterization of the Neural Mechanisms Supporting the Implementation of Cognitive Control in Human Decision Making", "advisor": "O'Doherty, John P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052013-125503107", "creators": [ { "name": { "family": "Hakimi", "given": "Shabnam" }, "id": "Hakimi-Shabnam", "display_name": "Hakimi, Shabnam" } ], "advisors": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "advisor", "display_name": "O'Doherty, John P." } ], "committee": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "chair", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Camerer", "given": "Colin F." }, "id": "Camerer-C-F", "role": "member", "display_name": "Camerer, Colin F." }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "member", "display_name": "O'Doherty, John P." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/W6VP-VM56", "abstract": "Humans are particularly adept at modifying their behavior in accordance with changing environmental demands. Through various mechanisms of cognitive control, individuals are able to tailor actions to fit complex short- and long-term goals. The research described in this thesis uses functional magnetic resonance imaging to characterize the neural correlates of cognitive control at two levels of complexity: response inhibition and self-control in intertemporal choice. First, we examined changes in neural response associated with increased experience and skill in response inhibition; successful response inhibition was associated with decreased neural response over time in the right ventrolateral prefrontal cortex, a region widely implicated in cognitive control, providing evidence for increased neural efficiency with learned automaticity. We also examined a more abstract form of cognitive control using intertemporal choice. In two experiments, we identified putative neural substrates for individual differences in temporal discounting, or the tendency to prefer immediate to delayed rewards. Using dynamic causal models, we characterized the neural circuit between ventromedial prefrontal cortex, an area involved in valuation, and dorsolateral prefrontal cortex, a region implicated in self-control in intertemporal and dietary choice, and found that connectivity from dorsolateral prefrontal cortex to ventromedial prefrontal cortex increases at the time of choice, particularly when delayed rewards are chosen. Moreover, estimates of the strength of connectivity predicted out-of-sample individual rates of temporal discounting, suggesting a neurocomputational mechanism for variation in the ability to delay gratification. Next, we interrogated the hypothesis that individual differences in temporal discounting are in part explained by the ability to imagine future reward outcomes. Using a novel paradigm, we imaged neural response during the imagining of primary rewards, and identified negative correlations between activity in regions associated the processing of both real and imagined rewards (lateral orbitofrontal cortex and ventromedial prefrontal cortex, respectively) and the individual temporal discounting parameters estimated in the previous experiment. These data suggest that individuals who are better able to represent reward outcomes neurally are less susceptible to temporal discounting. Together, these findings provide further insight into role of the prefrontal cortex in implementing cognitive control, and propose neurobiological substrates for individual variation." }, { "name": "Han, Shuo", "degree": "PhD", "year": "2014", "title": "Optimal Uncertainty Quantification via Convex Optimization and Relaxation", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162013-111333269", "creators": [ { "name": { "family": "Han", "given": "Shuo" }, "id": "Han-Shuo", "display_name": "Han, Shuo" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "eleceng" ], "doi": "10.7907/X00K-T615", "abstract": "Many engineering applications face the problem of bounding the expected value of a quantity of interest (performance, risk, cost, etc.) that depends on stochastic uncertainties whose probability distribution is not known exactly. Optimal uncertainty quantification (OUQ) is a framework that aims at obtaining the best bound in these situations by explicitly incorporating available information about the distribution. Unfortunately, this often leads to non-convex optimization problems that are numerically expensive to solve.
\r\n\r\nThis thesis emphasizes on efficient numerical algorithms for OUQ problems. It begins by investigating several classes of OUQ problems that can be reformulated as convex optimization problems. Conditions on the objective function and information constraints under which a convex formulation exists are presented. Since the size of the optimization problem can become quite large, solutions for scaling up are also discussed. Finally, the capability of analyzing a practical system through such convex formulations is demonstrated by a numerical example of energy storage placement in power grids.
\r\n\r\nWhen an equivalent convex formulation is unavailable, it is possible to find a convex problem that provides a meaningful bound for the original problem, also known as a convex relaxation. As an example, the thesis investigates the setting used in Hoeffding's inequality. The naive formulation requires solving a collection of non-convex polynomial optimization problems whose number grows doubly exponentially. After structures such as symmetry are exploited, it is shown that both the number and the size of the polynomial optimization problems can be reduced significantly. Each polynomial optimization problem is then bounded by its convex relaxation using sums-of-squares. These bounds are found to be tight in all the numerical examples tested in the thesis and are significantly better than Hoeffding's bounds.
" }, { "name": "Heckman, Vanessa Mary", "degree": "PhD", "year": "2014", "title": "Damage Detection in Civil Structures using High-Frequency Seismograms", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12192013-162221707", "creators": [ { "name": { "family": "Heckman", "given": "Vanessa Mary" }, "id": "Heckman-Vanessa-Mary", "display_name": "Heckman, Vanessa Mary" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "role": "member", "display_name": "Clayton, Robert W." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "role": "member", "display_name": "Kohler, Monica D." }, { "name": { "family": "Tsai", "given": "Victor C." }, "id": "Tsai-V-C", "role": "member", "display_name": "Tsai, Victor C." } ], "option_major": [ "civileng" ], "doi": "10.7907/NVKN-8D47", "abstract": "The dynamic properties of a structure are a function of its physical properties, and changes in the physical properties of the structure, including the introduction of structural damage, can cause changes in its dynamic behavior. Structural health monitoring (SHM) and damage detection methods provide a means to assess the structural integrity and safety of a civil structure using measurements of its dynamic properties. In particular, these techniques enable a quick damage assessment following a seismic event. In this thesis, the application of high-frequency seismograms to damage detection in civil structures is investigated.
\r\n\r\nTwo novel methods for SHM are developed and validated using small-scale experimental testing, existing structures in situ, and numerical testing. The first method is developed for pre-Northridge steel-moment-resisting frame buildings that are susceptible to weld fracture at beam-column connections. The method is based on using the response of a structure to a nondestructive force (i.e., a hammer blow) to approximate the response of the structure to a damage event (i.e., weld fracture). The method is applied to a small-scale experimental frame, where the impulse response functions of the frame are generated during an impact hammer test. The method is also applied to a numerical model of a steel frame, in which weld fracture is modeled as the tensile opening of a Mode I crack. Impulse response functions are experimentally obtained for a steel moment-resisting frame building in situ. Results indicate that while acceleration and velocity records generated by a damage event are best approximated by the acceleration and velocity records generated by a colocated hammer blow, the method may not be robust to noise. The method seems to be better suited for damage localization, where information such as arrival times and peak accelerations can also provide indication of the damage location. This is of significance for sparsely-instrumented civil structures.
\r\n\r\nThe second SHM method is designed to extract features from high-frequency acceleration records that may indicate the presence of damage. As short-duration high-frequency signals (i.e., pulses) can be indicative of damage, this method relies on the identification and classification of pulses in the acceleration records. It is recommended that, in practice, the method be combined with a vibration-based method that can be used to estimate the loss of stiffness. Briefly, pulses observed in the acceleration time series when the structure is known to be in an undamaged state are compared with pulses observed when the structure is in a potentially damaged state. By comparing the pulse signatures from these two situations, changes in the high-frequency dynamic behavior of the structure can be identified, and damage signals can be extracted and subjected to further analysis. The method is successfully applied to a small-scale experimental shear beam that is dynamically excited at its base using a shake table and damaged by loosening a screw to create a moving part. Although the damage is aperiodic and nonlinear in nature, the damage signals are accurately identified, and the location of damage is determined using the amplitudes and arrival times of the damage signal. The method is also successfully applied to detect the occurrence of damage in a test bed data set provided by the Los Alamos National Laboratory, in which nonlinear damage is introduced into a small-scale steel frame by installing a bumper mechanism that inhibits the amount of motion between two floors. The method is successfully applied and is robust despite a low sampling rate, though false negatives (undetected damage signals) begin to occur at high levels of damage when the frequency of damage events increases. The method is also applied to acceleration data recorded on a damaged cable-stayed bridge in China, provided by the Center of Structural Monitoring and Control at the Harbin Institute of Technology. Acceleration records recorded after the date of damage show a clear increase in high-frequency short-duration pulses compared to those previously recorded. One undamage pulse and two damage pulses are identified from the data. The occurrence of the detected damage pulses is consistent with a progression of damage and matches the known chronology of damage.
\r\n" }, { "name": "Heinz, Nicholas A.", "degree": "PhD", "year": "2014", "title": "Microstructure Control and Iodine Doping of Bismuth Telluride", "advisor": "Snyder, G. Jeffrey; Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112014-114312386", "creators": [ { "name": { "family": "Heinz", "given": "Nicholas A." }, "id": "Heinz-Nicholas-A", "display_name": "Heinz, Nicholas A." } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "co-advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/HKX2-QG08", "abstract": "On the materials scale, thermoelectric efficiency is defined by the dimensionless figure of merit zT. This value is made up of three material components in the form zT = Tα2/ρκ, where α is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the total thermal conductivity. Therefore, in order to improve zT would require the reduction of κ and ρ while increasing α. However due to the inter-relation of the electrical and thermal properties of materials, typical routes to thermoelectric enhancement come in one of two forms. The first is to isolate the electronic properties and increase α without negatively affecting ρ. Techniques like electron filtering, quantum confinement, and density of states distortions have been proposed to enhance the Seebeck coefficient in thermoelectric materials. However, it has been difficult to prove the efficacy of these techniques. More recently efforts to manipulate the band degeneracy in semiconductors has been explored as a means to enhance α.
\r\n\r\nThe other route to thermoelectric enhancement is through minimizing the thermal conductivity, κ. More specifically, thermal conductivity can be broken into two parts, an electronic and lattice term, κe and κl respectively. From a functional materials standpoint, the reduction in lattice thermal conductivity should have a minimal effect on the electronic properties. Most routes incorporate techniques that focus on the reduction of the lattice thermal conductivity. The components that make up κl (κl = 1/3Cνl) are the heat capacity (C), phonon group velocity (ν), and phonon mean free path (l). Since the difficulty is extreme in altering the heat capacity and group velocity, the phonon mean free path is most often the source of reduction.
\r\n\r\nPast routes to decreasing the phonon mean free path has been by alloying and grain size reduction. However, in these techniques the electron mobility is often negatively affected because in alloying any perturbation to the periodic potential can cause additional adverse carrier scattering. Grain size reduction has been another successful route to enhancing zT because of the significant difference in electron and phonon mean free paths. However, grain size reduction is erratic in anisotropic materials due to the orientation dependent transport properties. However, microstructure formation in both equilibrium and nonequilibrium processing routines can be used to effectively reduce the phonon mean free path as a route to enhance the figure of merit.
\r\n\r\nThis work starts with a discussion of several different deliberate microstructure varieties. Control of the morphology and finally structure size and spacing is discussed at length. Since the material example used throughout this thesis is anisotropic a short primer on zone melting is presented as an effective route to growing homogeneous and oriented polycrystalline material. The resulting microstructure formation and control is presented specifically in the case of In2Te3-Bi2Te3 composites and the transport properties pertinent to thermoelectric materials is presented. Finally, the transport and discussion of iodine doped Bi2Te3 is presented as a re-evaluation of the literature data and what is known today.
\r\n" }, { "name": "Horowitz, Matanya Benasher", "degree": "PhD", "year": "2014", "title": "Efficient Methods for Stochastic Optimal Control", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312014-011052261", "creators": [ { "name": { "family": "Horowitz", "given": "Matanya Benasher" }, "id": "Horowitz-Matanya-Benasher", "display_name": "Horowitz, Matanya Benasher" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" } ], "option_major": [ "cds" ], "doi": "10.7907/D40A-9E03", "abstract": "The Hamilton Jacobi Bellman (HJB) equation is central to stochastic optimal control (SOC) theory, yielding the optimal solution to general problems specified by known dynamics and a specified cost functional. Given the assumption of quadratic cost on the control input, it is well known that the HJB reduces to a particular partial differential equation (PDE). While powerful, this reduction is not commonly used as the PDE is of second order, is nonlinear, and examples exist where the problem may not have a solution in a classical sense. Furthermore, each state of the system appears as another dimension of the PDE, giving rise to the curse of dimensionality. Since the number of degrees of freedom required to solve the optimal control problem grows exponentially with dimension, the problem becomes intractable for systems with all but modest dimension.
\r\n\r\nIn the last decade researchers have found that under certain, fairly non-restrictive structural assumptions, the HJB may be transformed into a linear PDE, with an interesting analogue in the discretized domain of Markov Decision Processes (MDP). The work presented in this thesis uses the linearity of this particular form of the HJB PDE to push the computational boundaries of stochastic optimal control.
\r\n\r\nThis is done by crafting together previously disjoint lines of research in computation. The first of these is the use of Sum of Squares (SOS) techniques for synthesis of control policies. A candidate polynomial with variable coefficients is proposed as the solution to the stochastic optimal control problem. An SOS relaxation is then taken to the partial differential constraints, leading to a hierarchy of semidefinite relaxations with improving sub-optimality gap. The resulting approximate solutions are shown to be guaranteed over- and under-approximations for the optimal value function. It is shown that these results extend to arbitrary parabolic and elliptic PDEs, yielding a novel method for Uncertainty Quantification (UQ) of systems governed by partial differential constraints. Domain decomposition techniques are also made available, allowing for such problems to be solved via parallelization and low-order polynomials.
\r\n\r\nThe optimization-based SOS technique is then contrasted with the Separated Representation (SR) approach from the applied mathematics community. The technique allows for systems of equations to be solved through a low-rank decomposition that results in algorithms that scale linearly with dimensionality. Its application in stochastic optimal control allows for previously uncomputable problems to be solved quickly, scaling to such complex systems as the Quadcopter and VTOL aircraft. This technique may be combined with the SOS approach, yielding not only a numerical technique, but also an analytical one that allows for entirely new classes of systems to be studied and for stability properties to be guaranteed.
\r\n\r\nThe analysis of the linear HJB is completed by the study of its implications in application. It is shown that the HJB and a popular technique in robotics, the use of navigation functions, sit on opposite ends of a spectrum of optimization problems, upon which tradeoffs may be made in problem complexity. Analytical solutions to the HJB in these settings are available in simplified domains, yielding guidance towards optimality for approximation schemes. Finally, the use of HJB equations in temporal multi-task planning problems is investigated. It is demonstrated that such problems are reducible to a sequence of SOC problems linked via boundary conditions. The linearity of the PDE allows us to pre-compute control policy primitives and then compose them, at essentially zero cost, to satisfy a complex temporal logic specification.
" }, { "name": "Hou, Xiaodi", "degree": "PhD", "year": "2014", "title": "Computational Modeling and Psvchophysics in Low- and Mid-Level Vision", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142014-044033712", "creators": [ { "name": { "family": "Hou", "given": "Xiaodi" }, "id": "Hou-Xiaodi", "display_name": "Hou, Xiaodi" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Yuille", "given": "Alan L." }, "id": "Yuille-A-L", "role": "member", "display_name": "Yuille, Alan L." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/1H1Q-J703", "abstract": "This thesis addresses a series of topics related to the question of how people find the foreground objects from complex scenes. With both computer vision modeling, as well as psychophysical analyses, we explore the computational principles for low- and mid-level vision.
\r\n\r\nWe first explore the computational methods of generating saliency maps from images and image sequences. We propose an extremely fast algorithm called Image Signature that detects the locations in the image that attract human eye gazes. With a series of experimental validations based on human behavioral data collected from various psychophysical experiments, we conclude that the Image Signature and its spatial-temporal extension, the Phase Discrepancy, are among the most accurate algorithms for saliency detection under various conditions.
\r\n\r\nIn the second part, we bridge the gap between fixation prediction and salient object segmentation with two efforts. First, we propose a new dataset that contains both fixation and object segmentation information. By simultaneously presenting the two types of human data in the same dataset, we are able to analyze their intrinsic connection, as well as understanding the drawbacks of today\u2019s \u201cstandard\u201d but inappropriately labeled salient object segmentation dataset. Second, we also propose an algorithm of salient object segmentation. Based on our novel discoveries on the connections of fixation data and salient object segmentation data, our model significantly outperforms all existing models on all 3 datasets with large margins.
\r\n\r\nIn the third part of the thesis, we discuss topics around the human factors of boundary analysis. Closely related to salient object segmentation, boundary analysis focuses on delimiting the local contours of an object. We identify the potential pitfalls of algorithm evaluation for the problem of boundary detection. Our analysis indicates that today\u2019s popular boundary detection datasets contain significant level of noise, which may severely influence the benchmarking results. To give further insights on the labeling process, we propose a model to characterize the principles of the human factors during the labeling process.
\r\n\r\nThe analyses reported in this thesis offer new perspectives to a series of interrelating issues in low- and mid-level vision. It gives warning signs to some of today\u2019s \u201cstandard\u201d procedures, while proposing new directions to encourage future research.
\r\n" }, { "name": "Jewell, Joseph Stephen", "degree": "PhD", "year": "2014", "title": "Boundary-Layer Transition on a Slender Cone in Hypervelocity Flow with Real Gas Effects", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292014-220110640", "creators": [ { "name": { "family": "Jewell", "given": "Joseph Stephen" }, "id": "Jewell-Joseph-Stephen", "orcid": "0000-0002-4047-9998", "display_name": "Jewell, Joseph Stephen" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leyva", "given": "Ivett A." }, "id": "Leyva-I-A", "role": "member", "display_name": "Leyva, Ivett A." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9H9935V", "abstract": "The laminar to turbulent transition process in boundary layer flows in thermochemical nonequilibrium at high enthalpy is measured and characterized. Experiments are performed in the T5 Hypervelocity Reflected Shock Tunnel at Caltech, using a 1 m length 5-degree half angle axisymmetric cone instrumented with 80 fast-response annular thermocouples, complemented by boundary layer stability computations using the STABL software suite. A new mixing tank is added to the shock tube fill apparatus for premixed freestream gas experiments, and a new cleaning procedure results in more consistent transition measurements. Transition location is nondimensionalized using a scaling with the boundary layer thickness, which is correlated with the acoustic properties of the boundary layer, and compared with parabolized stability equation (PSE) analysis. In these nondimensionalized terms, transition delay with increasing CO2 concentration is observed: tests in 100% and 50% CO2, by mass, transition up to 25% and 15% later, respectively, than air experiments. These results are consistent with previous work indicating that CO2 molecules at elevated temperatures absorb acoustic instabilities in the MHz range, which is the expected frequency of the Mack second-mode instability at these conditions, and also consistent with predictions from PSE analysis. A strong unit Reynolds number effect is observed, which is believed to arise from tunnel noise. NTr for air from 5.4 to 13.2 is computed, substantially higher than previously reported for noisy facilities. Time- and spatially-resolved heat transfer traces are used to track the propagation of turbulent spots, and convection rates at 90%, 76%, and 63% of the boundary layer edge velocity, respectively, are observed for the leading edge, centroid, and trailing edge of the spots. A model constructed with these spot propagation parameters is used to infer spot generation rates from measured transition onset to completion distance. Finally, a novel method to control transition location with boundary layer gas injection is investigated. An appropriate porous-metal injector section for the cone is designed and fabricated, and the efficacy of injected CO2 for delaying transition is gauged at various mass flow rates, and compared with both no injection and chemically inert argon injection cases. While CO2 injection seems to delay transition, and argon injection seems to promote it, the experimental results are inconclusive and matching computations do not predict a reduction in N factor from any CO2 injection condition computed.
" }, { "name": "John, Kristen Kathleen", "degree": "PhD", "year": "2014", "title": "Strength of Tantalum at High Pressures through Richtmyer-Meshkov Laser Compression Experiments and Simulations", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:08092014-195153430", "creators": [ { "name": { "family": "John", "given": "Kristen Kathleen" }, "id": "John-Kristen-Kathleen", "display_name": "John, Kristen Kathleen" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NE7Y-CK04", "abstract": "Strength at extreme pressures (>1 Mbar or 100 GPa) and high strain rates (106-108 s-1) of materials is not well characterized. The goal of the research outlined in this thesis is to study the strength of tantalum (Ta) at these conditions. The Omega Laser in the Laboratory for Laser Energetics in Rochester, New York is used to create such extreme conditions. Targets are designed with ripples or waves on the surface, and these samples are subjected to high pressures using Omega\u2019s high energy laser beams. In these experiments, the observational parameter is the Richtmyer-Meshkov (RM) instability in the form of ripple growth on single-mode ripples. The experimental platform used for these experiments is the \u201cride-along\u201d laser compression recovery experiments, which provide a way to recover the specimens having been subjected to high pressures. Six different experiments are performed on the Omega laser using single-mode tantalum targets at different laser energies. The energy indicates the amount of laser energy that impinges the target. For each target, values for growth factor are obtained by comparing the profile of ripples before and after the experiment. With increasing energy, the growth factor increased.
\r\n \r\nEngineering simulations are used to interpret and correlate the measurements of growth factor to a measure of strength. In order to validate the engineering constitutive model for tantalum, a series of simulations are performed using the code Eureka, based on the Optimal Transportation Meshfree (OTM) method. Two different configurations are studied in the simulations: RM instabilities in single and multimode ripples. Six different simulations are performed for the single ripple configuration of the RM instability experiment, with drives corresponding to laser energies used in the experiments. Each successive simulation is performed at higher drive energy, and it is observed that with increasing energy, the growth factor increases. Overall, there is favorable agreement between the data from the simulations and the experiments. The peak growth factors from the simulations and the experiments are within 10% agreement. For the multimode simulations, the goal is to assist in the design of the laser driven experiments using the Omega laser. A series of three-mode and four-mode patterns are simulated at various energies and the resulting growth of the RM instability is computed. Based on the results of the simulations, a configuration is selected for the multimode experiments. These simulations also serve as validation for the constitutive model and the material parameters for tantalum that are used in the simulations.
\r\n\r\nBy designing samples with initial perturbations in the form of single-mode and multimode ripples and subjecting these samples to high pressures, the Richtmyer-Meshkov instability is investigated in both laser compression experiments and simulations. By correlating the growth of these ripples to measures of strength, a better understanding of the strength of tantalum at high pressures is achieved.
\r\n" }, { "name": "Jones, Daniel Lawson III", "degree": "PhD", "year": "2014", "title": "Sequence-Function Relationships in E. coli Transcriptional Regulation", "advisor": "Phillips, Robert B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022014-165211576", "creators": [ { "name": { "family": "Jones", "given": "Daniel Lawson III" }, "id": "Jones-Daniel-Lawson-III", "display_name": "Jones, Daniel Lawson III" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "advisor", "display_name": "Phillips, Robert B." } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "member", "display_name": "Winfree, Erik" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4J7V-WD59", "abstract": "Understanding how transcriptional regulatory sequence maps to regulatory function remains a difficult problem in regulatory biology. Given a particular DNA sequence for a bacterial promoter region, we would like to be able to say which transcription factors bind there, how strongly they bind, and whether they interact with each other and/or RNA polymerase, with the ultimate objective of integrating knowledge of these parameters into a prediction of gene expression levels. The theoretical framework of statistical thermodynamics provides a useful framework for doing so, enabling us to predict how gene expression levels depend on transcription factor binding energies and concentrations. We used thermodynamic models, coupled with models of the sequence-dependent binding energies of transcription factors and RNAP, to construct a genotype to phenotype map for the level of repression exhibited by the lac promoter, and tested it experimentally using a set of promoter variants from E. coli strains isolated from different natural environments. For this work, we sought to ``reverse engineer'' naturally occurring promoter sequences to understand how variations in promoter sequence affects gene expression. The natural inverse of this approach is to ``forward engineer'' promoter sequences to obtain targeted levels of gene expression. We used a high precision model of RNAP-DNA sequence dependent binding energy, coupled with a thermodynamic model relating binding energy to gene expression, to predictively design and verify a suite of synthetic E. coli promoters whose expression varied over nearly three orders of magnitude.
\r\n\r\nHowever, although thermodynamic models enable predictions of mean levels of gene expression, it has become evident that cell-to-cell variability or ``noise'' in gene expression can also play a biologically important role. In order to address this aspect of gene regulation, we developed models based on the chemical master equation framework and used them to explore the noise properties of a number of common E. coli regulatory motifs; these properties included the dependence of the noise on parameters such as transcription factor binding strength and copy number. We then performed experiments in which these parameters were systematically varied and measured the level of variability using mRNA FISH. The results showed a clear dependence of the noise on these parameters, in accord with model predictions.
\r\n\r\nFinally, one shortcoming of the preceding modeling frameworks is that their applicability is largely limited to systems that are already well-characterized, such as the lac promoter. Motivated by this fact, we used a high throughput promoter mutagenesis assay called Sort-Seq to explore the completely uncharacterized transcriptional regulatory DNA of the E. coli mechanosensitive channel of large conductance (MscL). We identified several candidate transcription factor binding sites, and work is continuing to identify the associated proteins.
" }, { "name": "Keller, Sean Jason", "degree": "PhD", "year": "2014", "title": "Robust Near-Threshold QDI Circuit Analysis and Design", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172013-192316055", "creators": [ { "name": { "family": "Keller", "given": "Sean Jason" }, "id": "Keller-Sean-Jason", "display_name": "Keller, Sean Jason" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Harris", "given": "David Money" }, "id": "Harris-D-M", "role": "member", "display_name": "Harris, David Money" } ], "option_major": [ "compsci" ], "doi": "10.7907/79EJ-Q945", "abstract": "The two most important digital-system design goals today are to reduce power consumption and to increase reliability. Reductions in power consumption improve battery life in the mobile space and reductions in energy lower operating costs in the datacenter. Increased robustness and reliability shorten down time, improve yield, and are invaluable in the context of safety-critical systems. While optimizing towards these two goals is important at all design levels, optimizations at the circuit level have the furthest reaching effects; they apply to all digital systems. This dissertation presents a study of robust minimum-energy digital circuit design and analysis. It introduces new device models, metrics, and methods of calculation\u2014all necessary first steps towards building better systems\u2014and demonstrates how to apply these techniques. It analyzes a fabricated chip (a full-custom QDI microcontroller designed at Caltech and taped-out in 40-nm silicon) by calculating the minimum energy operating point and quantifying the chip\u2019s robustness in the face of both timing and functional failures." }, { "name": "Kim, Kun Woo", "degree": "PhD", "year": "2014", "title": "Electronic States in Disordered Topological Insulators", "advisor": "Refael, Gil", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022014-093929164", "creators": [ { "name": { "family": "Kim", "given": "Kun Woo" }, "id": "Kim-Kun-Woo", "display_name": "Kim, Kun Woo" } ], "advisors": [ { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "advisor", "display_name": "Refael, Gil" } ], "committee": [ { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "chair", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Motrunich", "given": "Olexei I." }, "id": "Motrunich-Olexei", "orcid": "0000-0001-8031-0022", "role": "member", "display_name": "Motrunich, Olexei I." }, { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "member", "display_name": "Hsieh, David" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "member", "display_name": "Refael, Gil" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/BSH1-AA62", "abstract": "We present a theoretical study of electronic states in topological insulators with impurities. Chiral edge states in 2d topological insulators and helical surface states in 3d topological insulators show a robust transport against nonmagnetic impurities. Such a nontrivial character inspired physicists to come up with applications such as spintronic devices [1], thermoelectric materials [2], photovoltaics [3], and quantum computation [4]. Not only has it provided new opportunities from a practical point of view, but its theoretical study has deepened the understanding of the topological nature of condensed matter systems. However, experimental realizations of topological insulators have been challenging. For example, a 2d topological insulator fabricated in a HeTe quantum well structure by Konig et al. [5] shows a longitudinal conductance which is not well quantized and varies with temperature. 3d topological insulators such as Bi2Se3 and Bi2Te3 exhibit not only a signature of surface states, but they also show a bulk conduction [6]. The series of experiments motivated us to study the effects of impurities and coexisting bulk Fermi surface in topological insulators. We first address a single impurity problem in a topological insulator using a semiclassical approach. Then we study the conductance behavior of a disordered topological-metal strip where bulk modes are associated with the transport of edge modes via impurity scattering. We verify that the conduction through a chiral edge channel retains its topological signature, and we discovered that the transmission can be succinctly expressed in a closed form as a ratio of determinants of the bulk Green's function and impurity potentials. We further study the transport of 1d systems which can be decomposed in terms of chiral modes. Lastly, the surface impurity effect on the local density of surface states over layers into the bulk is studied between weak and strong disorder strength limits." }, { "name": "Lan, Tian", "degree": "PhD", "year": "2014", "title": "Studies of Phonon Anharmonicity in Solids", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142014-120832065", "creators": [ { "name": { "family": "Lan", "given": "Tian" }, "id": "Lan-Tian", "display_name": "Lan, Tian" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Marcus", "given": "Rudolph A." }, "id": "Marcus-R-A", "role": "member", "display_name": "Marcus, Rudolph A." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/AB7A-FP25", "abstract": "Today our understanding of the vibrational thermodynamics of materials at low temperatures is emerging nicely, based on the harmonic model in which phonons are independent. At high temperatures, however, this understanding must accommodate how phonons interact with other phonons or with other excitations. We shall see that the phonon-phonon interactions give rise to interesting coupling problems, and essentially modify the equilibrium and non-equilibrium properties of materials, e.g., thermodynamic stability, heat capacity, optical properties and thermal transport of materials. Despite its great importance, to date the anharmonic lattice dynamics is poorly understood and most studies on lattice dynamics still rely on the harmonic or quasiharmonic models. There have been very few studies on the pure phonon anharmonicity and phonon-phonon interactions. The work presented in this thesis is devoted to the development of experimental and computational methods on this subject.
\r\n\r\nModern inelastic scattering techniques with neutrons or photons are ideal for sorting out the anharmonic contribution. Analysis of the experimental data can generate vibrational spectra of the materials, i.e., their phonon densities of states or phonon dispersion relations. We obtained high quality data from laser Raman spectrometer, Fourier transform infrared spectrometer and inelastic neutron spectrometer. With accurate phonon spectra data, we obtained the energy shifts and lifetime broadenings of the interacting phonons, and the vibrational entropies of different materials. The understanding of them then relies on the development of the fundamental theories and the computational methods.
\r\n\r\nWe developed an efficient post-processor for analyzing the anharmonic vibrations from the molecular dynamics (MD) calculations. Currently, most first principles methods are not capable of dealing with strong anharmonicity, because the interactions of phonons are ignored at finite temperatures. Our method adopts the Fourier transformed velocity autocorrelation method to handle the big data of time-dependent atomic velocities from MD calculations, and efficiently reconstructs the phonon DOS and phonon dispersion relations. Our calculations can reproduce the phonon frequency shifts and lifetime broadenings very well at various temperatures.
\r\n\r\nTo understand non-harmonic interactions in a microscopic way, we have developed a numerical fitting method to analyze the decay channels of phonon-phonon interactions. Based on the quantum perturbation theory of many-body interactions, this method is used to calculate the three-phonon and four-phonon kinematics subject to the conservation of energy and momentum, taking into account the weight of phonon couplings. We can assess the strengths of phonon-phonon interactions of different channels and anharmonic orders with the calculated two-phonon DOS. This method, with high computational efficiency, is a promising direction to advance our understandings of non-harmonic lattice dynamics and thermal transport properties.
\r\n\r\nThese experimental techniques and theoretical methods have been successfully performed in the study of anharmonic behaviors of metal oxides, including rutile and cuprite stuctures, and will be discussed in detail in Chapters 4 to 6. For example, for rutile titanium dioxide (TiO2), we found that the anomalous anharmonic behavior of the B1g mode can be explained by the volume effects on quasiharmonic force constants, and by the explicit cubic and quartic anharmonicity. For rutile tin dioxide (SnO2), the broadening of the B2g mode with temperature showed an unusual concave downwards curvature. This curvature was caused by a change with temperature in the number of down-conversion decay channels, originating with the wide band gap in the phonon dispersions. For silver oxide (Ag2O), strong anharmonic effects were found for both phonons and for the negative thermal expansion.
" }, { "name": "LeBon, Lauren E.", "degree": "PhD", "year": "2014", "title": "The Logic of Receptor-Ligand Interactions in the Notch Signaling Pathway", "advisor": "Elowitz, Michael B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212014-094412950", "creators": [ { "name": { "family": "LeBon", "given": "Lauren E." }, "id": "LeBon-Lauren-E", "display_name": "LeBon, Lauren E." } ], "advisors": [ { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "advisor", "display_name": "Elowitz, Michael B." } ], "committee": [ { "name": { "family": "Hay", "given": "Bruce A." }, "id": "Hay-B-A", "role": "chair", "display_name": "Hay, Bruce A." }, { "name": { "family": "Weinmaster", "given": "Geraldine" }, "id": "Weinmaster-G", "role": "member", "display_name": "Weinmaster, Geraldine" }, { "name": { "family": "Anderson", "given": "David J." }, "id": "Anderson-D-J", "role": "member", "display_name": "Anderson, David J." }, { "name": { "family": "Goentoro", "given": "Lea A." }, "id": "Goentoro-L-A", "role": "member", "display_name": "Goentoro, Lea A." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." } ], "option_major": [ "cns" ], "doi": "10.7907/83PA-9833", "abstract": "The Notch signaling pathway enables neighboring cells to coordinate developmental fates in diverse processes such as angiogenesis, neuronal differentiation, and immune system development. Although key components and interactions in the Notch pathway are known, it remains unclear how they work together to determine a cell's signaling state, defined as its quantitative ability to send and receive signals using particular Notch receptors and ligands. Recent work suggests that several aspects of the system can lead to complex signaling behaviors: First, receptors and ligands interact in two distinct ways, inhibiting each other in the same cell (in cis) while productively interacting between cells (in trans) to signal. The ability of a cell to send or receive signals depends strongly on both types of interactions. Second, mammals have multiple types of receptors and ligands, which interact with different strengths, and are frequently co-expressed in natural systems. Third, the three mammalian Fringe proteins can modify receptor-ligand interaction strengths in distinct and ligand-specific ways. Consequently, cells can exhibit non-intuitive signaling states even with relatively few components.
\r\n\r\nIn order to understand what signaling states occur in natural processes, and what types of signaling behaviors they enable, this thesis puts forward a quantitative and predictive model of how the Notch signaling state is determined by the expression levels of receptors, ligands, and Fringe proteins. To specify the parameters of the model, we constructed a set of cell lines that allow control of ligand and Fringe expression level, and readout of the resulting Notch activity. We subjected these cell lines to an assay to quantitatively assess the levels of Notch ligands and receptors on the surface of individual cells. We further analyzed the dependence of these interactions on the level and type of Fringe expression. We developed a mathematical modeling framework that uses these data to predict the signaling states of individual cells from component expression levels. These methods allow us to reconstitute and analyze a diverse set of Notch signaling configurations from the bottom up, and provide a comprehensive view of the signaling repertoire of this major signaling pathway.
" }, { "name": "Lee, Seung Ah", "degree": "PhD", "year": "2014", "title": "Bright-Field and Fluorescence Chip-Scale Microscopy for Biological Imaging", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:02212014-174719213", "creators": [ { "name": { "family": "Lee", "given": "Seung Ah" }, "id": "Lee-Seung-Ah", "display_name": "Lee, Seung Ah" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Ismagilov", "given": "Rustem F." }, "id": "Ismagilov-R-F", "role": "member", "display_name": "Ismagilov, Rustem F." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/HNWJ-J182", "abstract": "Optical microscopy is an essential tool in biological science and one of the gold standards for medical examinations. Miniaturization of microscopes can be a crucial stepping stone towards realizing compact, cost-effective and portable platforms for biomedical research and healthcare. This thesis reports on implementations of bright-field and fluorescence chip-scale microscopes for a variety of biological imaging applications. The term \u201cchip-scale microscopy\u201d refers to lensless imaging techniques realized in the form of mass-producible semiconductor devices, which transforms the fundamental design of optical microscopes.
\r\n\r\nOur strategy for chip-scale microscopy involves utilization of low-cost Complementary metal Oxide Semiconductor (CMOS) image sensors, computational image processing and micro-fabricated structural components. First, the sub-pixel resolving optofluidic microscope (SROFM), will be presented, which combines microfluidics and pixel super-resolution image reconstruction to perform high-throughput imaging of fluidic samples, such as blood cells. We discuss design parameters and construction of the device, as well as the resulting images and the resolution of the device, which was 0.66 \u00b5m at the highest acuity. The potential applications of SROFM for clinical diagnosis of malaria in the resource-limited settings is discussed.
\r\n\r\nNext, the implementations of ePetri, a self-imaging Petri dish platform with microscopy resolution, are presented. Here, we simply place the sample of interest on the surface of the image sensor and capture the direct shadow images under the illumination. By taking advantage of the inherent motion of the microorganisms, we achieve high resolution (~1 \u00b5m) imaging and long term culture of motile microorganisms over ultra large field-of-view (5.7 mm \u00d7 4.4 mm) in a specialized ePetri platform. We apply the pixel super-resolution reconstruction to a set of low-resolution shadow images of the microorganisms as they move across the sensing area of an image sensor chip and render an improved resolution image. We perform longitudinal study of Euglena gracilis cultured in an ePetri platform and image based analysis on the motion and morphology of the cells. The ePetri device for imaging non-motile cells are also demonstrated, by using the sweeping illumination of a light emitting diode (LED) matrix for pixel super-resolution reconstruction of sub-pixel shifted shadow images. Using this prototype device, we demonstrate the detection of waterborne parasites for the effective diagnosis of enteric parasite infection in resource-limited settings.
\r\n\r\nThen, we demonstrate the adaptation of a smartphone\u2019s camera to function as a compact lensless microscope, which uses ambient illumination as its light source and does not require the incorporation of a dedicated light source. The method is also based on the image reconstruction with sweeping illumination technique, where the sequence of images are captured while the user is manually tilting the device around any ambient light source, such as the sun or a lamp. Image acquisition and reconstruction is performed on the device using a custom-built android application, constructing a stand-alone imaging device for field applications. We discuss the construction of the device using a commercial smartphone and demonstrate the imaging capabilities of our system.
\r\n\r\nFinally, we report on the implementation of fluorescence chip-scale microscope, based on a silo-filter structure fabricated on the pixel array of a CMOS image sensor. The extruded pixel design with metal walls between neighboring pixels successfully guides fluorescence emission through the thick absorptive filter to the photodiode layer of a pixel. Our silo-filter CMOS image sensor prototype achieves 13-\u00b5m resolution for fluorescence imaging over a wide field-of-view (4.8 mm \u00d7 4.4 mm). Here, we demonstrate bright-field and fluorescence longitudinal imaging of living cells in a compact, low-cost configuration.
\r\n" }, { "name": "Liu, Xiao", "degree": "PhD", "year": "2014", "title": "A Study on Iron-Based Amorphous Alloys: Alloy Development, Thermodynamics and Soft Magnetism", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechTHESIS:11222013-151337813", "creators": [ { "name": { "family": "Liu", "given": "Xiao" }, "id": "Liu-Xiao", "display_name": "Liu, Xiao" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/X2WM-RA54", "abstract": "Metallic glass has since its debut been of great research interest due to its profound scientific significance. Magnetic metallic glasses are of special interest because of their promising technological applications. In this thesis, we introduced a novel series of Fe-based alloys and offer a holistic review of the physics and properties of these alloys. A systematic alloy development and optimization method was introduced, with experimental implementation on transition metal based alloying system. A deep understanding on the influencing factors of glass forming ability was brought up and discussed, based on classical nucleation theory. Experimental data of the new Fe-based amorphous alloys were interpreted to further analyze those influencing factors, including reduced glass transition temperature, fragility, and liquid-crystal interface free energy. Various treatments (fluxing, overheating, etc.) were discussed for their impacts on the alloying systems' thermodynamics and glass forming ability. Multiple experimental characterization methods were discussed to measure the alloys' soft magnetic properties. In addition to theoretical and experimental investigation, we also gave a detailed numerical analysis on the rapid-discharge-heating-and-forming platform. It is a novel experimental system which offers extremely fast heating rate for calorimetric characterization and alloy deformation. " }, { "name": "Liu, Zhenhua", "degree": "PhD", "year": "2014", "title": "Sustainable IT and IT for Sustainability", "advisor": "Wierman, Adam C.; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312014-215801543", "creators": [ { "name": { "family": "Liu", "given": "Zhenhua" }, "id": "Liu-Zhenhua", "display_name": "Liu, Zhenhua" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "co-advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Liu", "given": "Xue" }, "id": "Liu-X", "role": "member", "display_name": "Liu, Xue" } ], "option_major": [ "compsci" ], "doi": "10.7907/296T-HR79", "abstract": "Energy and sustainability have become one of the most critical issues of our generation. While the abundant potential of renewable energy such as solar and wind provides a real opportunity for sustainability, their intermittency and uncertainty present a daunting operating challenge. This thesis aims to develop analytical models, deployable algorithms, and real systems to enable efficient integration of renewable energy into complex distributed systems with limited information.
\r\n\r\nThe first thrust of the thesis is to make IT systems more sustainable by facilitating the integration of renewable energy into these systems. IT represents the fastest growing sectors in energy usage and greenhouse gas pollution. Over the last decade there are dramatic improvements in the energy efficiency of IT systems, but the efficiency improvements do not necessarily lead to reduction in energy consumption because more servers are demanded. Further, little effort has been put in making IT more sustainable, and most of the improvements are from improved \"engineering\" rather than improved \"algorithms\". In contrast, my work focuses on developing algorithms with rigorous theoretical analysis that improve the sustainability of IT. In particular, this thesis seeks to exploit the flexibilities of cloud workloads both (i) in time by scheduling delay-tolerant workloads and (ii) in space by routing requests to geographically diverse data centers. These opportunities allow data centers to adaptively respond to renewable availability, varying cooling efficiency, and fluctuating energy prices, while still meeting performance requirements. The design of the enabling algorithms is however very challenging because of limited information, non-smooth objective functions and the need for distributed control. Novel distributed algorithms are developed with theoretically provable guarantees to enable the \"follow the renewables\" routing. Moving from theory to practice, I helped HP design and implement industry's first Net-zero Energy Data Center.
\r\n\r\nThe second thrust of this thesis is to use IT systems to improve the sustainability and efficiency of our energy infrastructure through data center demand response. The main challenges as we integrate more renewable sources to the existing power grid come from the fluctuation and unpredictability of renewable generation. Although energy storage and reserves can potentially solve the issues, they are very costly. One promising alternative is to make the cloud data centers demand responsive. The potential of such an approach is huge.
\r\n\r\nTo realize this potential, we need adaptive and distributed control of cloud data centers and new electricity market designs for distributed electricity resources. My work is progressing in both directions. In particular, I have designed online algorithms with theoretically guaranteed performance for data center operators to deal with uncertainties under popular demand response programs. Based on local control rules of customers, I have further designed new pricing schemes for demand response to align the interests of customers, utility companies, and the society to improve social welfare.
" }, { "name": "Lucey, Kaitlyn Shae", "degree": "PhD", "year": "2014", "title": "Catechol 2,3-Dioxygenase-Assisted Cleavage of Aromatics by \"Anaerobic\" Termite Gut Spirochetes and Genomic Evidence of a Complete Meta-Pathway", "advisor": "Leadbetter, Jared R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262013-152651094", "creators": [ { "name": { "family": "Lucey", "given": "Kaitlyn Shae" }, "id": "Lucey-Kaitlyn-Shae", "display_name": "Lucey, Kaitlyn Shae" } ], "advisors": [ { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "advisor", "display_name": "Leadbetter, Jared R." } ], "committee": [ { "name": { "family": "Orphan", "given": "Victoria J." }, "id": "Orphan-V-J", "orcid": "0000-0002-5374-6178", "role": "chair", "display_name": "Orphan, Victoria J." }, { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "member", "display_name": "Leadbetter, Jared R." }, { "name": { "family": "Mazmanian", "given": "Sarkis K." }, "id": "Mazmanian-S-K", "orcid": "0000-0003-2713-1513", "role": "member", "display_name": "Mazmanian, Sarkis K." }, { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "member", "display_name": "Newman, Dianne K." } ], "option_major": [ "envreng" ], "doi": "10.7907/KQB3-7010", "abstract": "The termite hindgut microbial ecosystem functions like a miniature lignocellulose-metabolizing natural bioreactor, has significant implications to nutrient cycling in the terrestrial environment, and represents an array of microbial metabolic diversity. Deciphering the intricacies of this microbial community to obtain as complete a picture as possible of how it functions as a whole, requires a combination of various traditional and cutting-edge bioinformatic, molecular, physiological, and culturing approaches. Isolates from this ecosystem, including Treponema primitia str. ZAS-1 and ZAS-2 as well as T. azotonutricium str. ZAS-9, have been significant resources for better understanding the termite system. While not all functions predicted by the genomes of these three isolates are demonstrated in vitro, these isolates do have the capacity for several metabolisms unique to spirochetes and critical to the termite system\u2019s reliance upon lignocellulose. In this thesis, work culturing, enriching for, and isolating diverse microorganisms from the termite hindgut is discussed. Additionally, strategies of members of the termite hindgut microbial community to defend against O2-stress and to generate acetate, the \u201cbiofuel\u201d of the termite system, are proposed. In particular, catechol 2,3-dioxygenase and other meta-cleavage catabolic pathway genes are described in the \u201canaerobic\u201d termite hindgut spirochetes T. primitia str. ZAS-1 and ZAS-2, and the first evidence for aromatic ring cleavage in the phylum (division) Spirochetes is also presented. These results suggest that the potential for O2-dependent, yet nonrespiratory, metabolisms of plant-derived aromatics should be re-evaluated in termite hindgut communities. Potential future work is also illustrated." }, { "name": "Lyon, Bradley Joseph", "degree": "PhD", "year": "2014", "title": "A Multi-Scale Approach to Shaping Carbon Nanotube Structures for Hollow Microneedles", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302014-012121120", "creators": [ { "name": { "family": "Lyon", "given": "Bradley Joseph" }, "id": "Lyon-Bradley-Joseph", "display_name": "Lyon, Bradley Joseph" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BJGT-TB74", "abstract": "The concept of a carbon nanotube microneedle array is explored in this thesis from multiple perspectives including microneedle fabrication, physical aspects of transdermal delivery, and in vivo transdermal drug delivery experiments. Starting with standard techniques in carbon nanotube (CNT) fabrication, including catalyst patterning and chemical vapor deposition, vertically-aligned carbon nanotubes are utilized as a scaffold to define the shape of the hollow microneedle. Passive, scalable techniques based on capillary action and unique photolithographic methods are utilized to produce a CNT-polymer composite microneedle. Specific examples of CNT-polyimide and CNT-epoxy microneedles are investigated. Further analysis of the transport properties of polymer resins reveals general requirements for applying arbitrary polymers to the fabrication process.
\r\n\r\nThe bottom-up fabrication approach embodied by vertically-aligned carbon nanotubes allows for more direct construction of complex high-aspect ratio features than standard top-down fabrication approaches, making microneedles an ideal application for CNTs. However, current vertically-aligned CNT fabrication techniques only allow for the production of extruded geometries with a constant cross-sectional area, such as cylinders. To rectify this limitation, isotropic oxygen etching is introduced as a novel fabrication technique to create true 3D CNT geometry. Oxygen etching is utilized to create a conical geometry from a cylindrical CNT structure as well as create complex shape transformations in other CNT geometries.
\r\n\r\nCNT-polymer composite microneedles are anchored onto a common polymer base less than 50 \u00b5m thick, which allows for the microneedles to be incorporated into multiple drug delivery platforms, including modified hypodermic syringes and silicone skin patches. Cylindrical microneedles are fabricated with 100 \u00b5m outer diameter and height of 200-250 \u00b5m with a central cavity, or lumen, diameter of 30 \u00b5m to facilitate liquid drug flow. In vitro delivery experiments in swine skin demonstrate the ability of the microneedles to successfully penetrate the skin and deliver aqueous solutions.
\r\n\r\nAn in vivo study was performed to assess the ability of the CNT-polymer microneedles to deliver drugs transdermally. CNT-polymer microneedles are attached to a hand actuated silicone skin patch that holds a liquid reservoir of drugs. Fentanyl, a potent analgesic, was administered to New Zealand White Rabbits through 3 routes of delivery: topical patch, CNT-polymer microneedles, and subcutaneous hypodermic injection. Results demonstrate that the CNT-polymer microneedles have a similar onset of action as the topical patch. CNT-polymer microneedles were also vetted as a painless delivery approach compared to hypodermic injection. Comparative analysis with contemporary microneedle designs demonstrates that the delivery achieved through CNT-polymer microneedles is akin to current hollow microneedle architectures. The inherent advantage of applying a bottom-up fabrication approach alongside similar delivery performance to contemporary microneedle designs demonstrates that the CNT-polymer composite microneedle is a viable architecture in the emerging field of painless transdermal delivery.
\r\n" }, { "name": "Malik, Imran Raouf", "degree": "PhD", "year": "2014", "title": "Point of Care Molecular Diagnostics for Humanity", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062014-102704108", "creators": [ { "name": { "family": "Malik", "given": "Imran Raouf" }, "id": "Malik-Imran-Raouf", "display_name": "Malik, Imran Raouf" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Joyce", "given": "Gerald" }, "id": "Joyce-G", "role": "member", "display_name": "Joyce, Gerald" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9HH6H2D", "abstract": "Diagnostics of disease at POC (point of care) has been declared one of the Grand Challenge by the Bill and Melina Gates Foundation (BMGF). Infectious diseases constitute a major cause of disease burden and cause more than half a billion Disability-Adjusted Life Years (DALYs) and millions of deaths each year. They have an especially large effect on children under 5 years of age. We have analyzed data from the GBD 2010 (Global Burden of Disease) project to emphasize the damage caused by infectious diseases, and highlight the opportunity of using diagnostic tools to rapidly identify and treat diseases. To motivate the work of this thesis, we quantify the expected impact of appropriate diagnostic technologies.
\r\n\r\nWe have also analyzed the requirements that a diagnostic tool should meet to generate the maximal global impact. We present various existing TPPs (Target Product Profiles) from different organizations and suggest some additions to these existing TPPs. We explain the particular molecular pathology technologies which have the potential to allow deployment of functional products in the developing world for point-of-care pathogen detection, especially in low-resource settings.
\r\n \r\nWe perform a detailed analysis on existing polymerase chain reaction (PCR) systems and describe the problems caused with thermal performance and optical interrogation. We list the requirements that disposable cartridges for such instruments should meet and suggest a metal base design with polymer top. After detailed FEA simulations, we demonstrate that the thermal response can be modeled using a one-dimensional (1D) lumped element system. We show improvements in thermal response due to using a metal base and the effect of fluid height. We also performed thermal-structural simulations to quantify the stresses on the adhesive bonds of metal/polymer cartridges.\r\nNext, we explain fabrication of these cartridges. We show methods to dispense adhesive using a robot and a custom made jig to spread the adhesive during curing. The cartridge was tested with different PCR reagents and we obtained reaction efficiencies approaching those of the commercial real time PCR machines. Our fabrication technique is useful to join dissimilar materials and is production friendly. By developing custom software, we observed the cartridge performance in a continuous manner. We could see the thermal response of cartridges by continuous fluorescence monitoring, and used reflective aluminum which increase light collection efficiency.
\r\n\r\nWe then present a simple and robust new way for thermal cycling. Robust thermal cycling has been a major challenge conducting PCR, especially in point of care situations. Here, we suggest a contact cooling approach, in which the cartridge rests on a thin metal plate with an integrated thin heater constructed from flexible printed circuit board (PCB) material. We use a solenoid to move a metal plate to cool down the sample cartridge during cycling. The metal plate then rests on a larger heat sink to disperse the shuttled heat. Our design is dust and water proof and was verified on a bench-top prototype.
\r\n\r\nA novel optical design for fluorescence detection during qPCR is also described. We suggest a lateral illumination waveguide geometry with prism coupling that eliminates lenses and is integrated into an injection molded cartridge. The light is homogenized using a light guide, and we quantify the sources of scattered stray light from the chamber edge by performing ray tracing simulations to optimize the precise geometry. The design is tolerant to misalignments and enables easy coupling of LED light into the chamber. As the light collection efficiency is high, the size of the chamber can be very small. We tested real PCR reactions using this concept and observed a rapid integration time, enabling very fast reading.
\r\n\r\nSample preparation has been another challenge for all point-of-care (POC) lab-on-chip devices for many years. Here, we propose a new design which is robust, fast, flexible and simple, and uses a sliding seal to move the collected sample between various reservoir chambers. The sample moves on a slider sandwiched between seals that shuttles a DNA binding membrane between different reactions. Thus, size and volumes of reagents can be increased without increasing dead volumes. This design is easily automated, and positive displacement of fluids can work with many reagents without worrying about their characteristics such as foaming. The speed of the sample preparation protocols is high and complex protocols can be ported on this design concept, which we tested on real clinical samples and obtained impressive results. We designed and injection molded devices to test and verify this concept.
\r\n\r\nFinally, we focus on instrumentation and software required to allow our technology to be used at the POC. We describe our embedded electronics and describe the powerful micro-controller and various high performance ICs that are used to construct a fully functional for sample to answer instrument. We developed various versions of software. The developer software allows us to control our system and bench top setup. Our end user product includes a tablet and cell phone software interface. Software was developed for a windows 8 tablet, windows 8 phone and an Android based devices.
\r\n\r\nTo conclude, we very briefly describe the POC systems that are under development: A portable qPCR system with a separate cartridge design, and a universal sample to answer system that performs qPCR, sample preparation and sample to answer protocols in one box depending on the cartridge.
\r\n\r\nAs per best of our knowledge the cost of this technology is much lower than any other option in its class. The sample to answer instrument is expected to cost less than $500. The test cost is expected to be less than $5. The performance is not compromised. We hope that this work can help bring a transformative change in the practice of pathology especially in the developing world.
\r\n" }, { "name": "Maqueda Jim\u00e9nez, Ignacio", "degree": "PhD", "year": "2014", "title": "High Strain Composites and Dual-Matrix Composite Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292014-191924394", "creators": [ { "name": { "family": "Maqueda Jim\u00e9nez", "given": "Ignacio" }, "id": "Maqueda-Jim\u00e9nez-Ignacio", "display_name": "Maqueda Jim\u00e9nez, Ignacio" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Murphey", "given": "Thomas" }, "id": "Murphey-T", "role": "member", "display_name": "Murphey, Thomas" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z34C-NY82", "abstract": "Most space applications require deployable structures due to the limiting size of current launch vehicles. Specifically, payloads in nanosatellites such as CubeSats require very high compaction ratios due to the very limited space available in this typo of platform. Strain-energy-storing deployable structures can be suitable for these applications, but the curvature to which these structures can be folded is limited to the elastic range. Thanks to fiber microbuckling, high-strain composite materials can be folded into much higher curvatures without showing significant damage, which makes them suitable for very high compaction deployable structure applications. However, in applications that require carrying loads in compression, fiber microbuckling also dominates the strength of the material. A good understanding of the strength in compression of high-strain composites is then needed to determine how suitable they are for this type of application.
\r\n\r\nThe goal of this thesis is to investigate, experimentally and numerically, the microbuckling in compression of high-strain composites. Particularly, the behavior in compression of unidirectional carbon fiber reinforced silicone rods (CFRS) is studied. Experimental testing of the compression failure of CFRS rods showed a higher strength in compression than the strength estimated by analytical models, which is unusual in standard polymer composites. This effect, first discovered in the present research, was attributed to the variation in random carbon fiber angles respect to the nominal direction. This is an important effect, as it implies that microbuckling strength might be increased by controlling the fiber angles. With a higher microbuckling strength, high-strain materials could carry loads in compression without reaching microbuckling and therefore be suitable for several space applications.
\r\n\r\nA finite element model was developed to predict the homogenized stiffness of the CFRS, and the homogenization results were used in another finite element model that simulated a homogenized rod under axial compression. A statistical representation of the fiber angles was implemented in the model. The presence of fiber angles increased the longitudinal shear stiffness of the material, resulting in a higher strength in compression. The simulations showed a large increase of the strength in compression for lower values of the standard deviation of the fiber angle, and a slight decrease of strength in compression for lower values of the mean fiber angle. The strength observed in the experiments was achieved with the minimum local angle standard deviation observed in the CFRS rods, whereas the shear stiffness measured in torsion tests was achieved with the overall fiber angle distribution observed in the CFRS rods.
\r\n\r\nHigh strain composites exhibit good bending capabilities, but they tend to be soft out-of-plane. To achieve a higher out-of-plane stiffness, the concept of dual-matrix composites is introduced. Dual-matrix composites are foldable composites which are soft in the crease regions and stiff elsewhere. Previous attempts to fabricate continuous dual-matrix fiber composite shells had limited performance due to excessive resin flow and matrix mixing. An alternative method, presented in this thesis uses UV-cure silicone and fiberglass to avoid these problems. Preliminary experiments on the effect of folding on the out-of-plane stiffness are presented. An application to a conical log-periodic antenna for CubeSats is proposed, using origami-inspired stowing schemes, that allow a conical dual-matrix composite shell to reach very high compaction ratios.
" }, { "name": "Miller, Madeline Diane", "degree": "PhD", "year": "2014", "title": "The Deep Ocean Density Structure at the Last Glacial Maximum: What Was It and Why?", "advisor": "Adkins, Jess F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10312013-000733635", "creators": [ { "name": { "family": "Miller", "given": "Madeline Diane" }, "id": "Miller-Madeline-Diane", "display_name": "Miller, Madeline Diane" } ], "advisors": [ { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "advisor", "display_name": "Adkins, Jess F." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "member", "display_name": "Adkins, Jess F." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Charles", "given": "Christopher D." }, "id": "Charles-C-D", "role": "member", "display_name": "Charles, Christopher D." }, { "name": { "family": "Simons", "given": "Mark" }, "id": "Simons-M", "role": "member", "display_name": "Simons, Mark" } ], "option_major": [ "mecheng" ], "doi": "10.7907/QHD5-FH77", "abstract": "The search for reliable proxies of past deep ocean temperature and salinity has proved difficult, thereby limiting our ability to understand the coupling of ocean circulation and climate over glacial-interglacial timescales. Previous inferences of deep ocean temperature and salinity from sediment pore fluid oxygen isotopes and chlorinity indicate that the deep ocean density structure at the Last Glacial Maximum (LGM, approximately 20,000 years BP) was set by salinity, and that the density contrast between northern and southern sourced deep waters was markedly greater than in the modern ocean. High density stratification could help explain the marked contrast in carbon isotope distribution recorded in the LGM ocean relative to that we observe today, but what made the ocean's density structure so different at the LGM? How did it evolve from one state to another? Further, given the sparsity of the LGM temperature and salinity data set, what else can we learn by increasing the spatial density of proxy records?
\r\n\r\nWe investigate the cause and feasibility of a highly and salinity stratified deep ocean at the LGM and we work to increase the amount of information we can glean about the past ocean from pore fluid profiles of oxygen isotopes and chloride. Using a coupled ocean--sea ice--ice shelf cavity model we test whether the deep ocean density structure at the LGM can be explained by ice--ocean interactions over the Antarctic continental shelves, and show that a large contribution of the LGM salinity stratification can be explained through lower ocean temperature. In order to extract the maximum information from pore fluid profiles of oxygen isotopes and chloride we evaluate several inverse methods for ill-posed problems and their ability to recover bottom water histories from sediment pore fluid profiles. We demonstrate that Bayesian Markov Chain Monte Carlo parameter estimation techniques enable us to robustly recover the full solution space of bottom water histories, not only at the LGM, but through the most recent deglaciation and the Holocene up to the present. Finally, we evaluate a non-destructive pore fluid sampling technique, Rhizon samplers, in comparison to traditional squeezing methods and show that despite their promise, Rhizons are unlikely to be a good sampling tool for pore fluid measurements of oxygen isotopes and chloride.
" }, { "name": "Mohan, Nisha", "degree": "PhD", "year": "2014", "title": "Extracting Material Response from Simple Mechanical Tests on Hardening-Softening-Hardening Viscoplastic Solids", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142014-151151819", "creators": [ { "name": { "family": "Mohan", "given": "Nisha" }, "id": "Mohan-Nisha", "display_name": "Mohan, Nisha" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "space" ], "doi": "10.7907/MMTW-FF91", "abstract": "Compliant foams are usually characterized by a wide range of desirable mechanical properties. These properties include viscoelasticity at different temperatures, energy absorption, recoverability under cyclic loading, impact resistance, and thermal, electrical, acoustic and radiation-resistance. Some foams contain nano-sized features and are used in small-scale devices. This implies that the characteristic dimensions of foams span multiple length scales, rendering modeling their mechanical properties difficult. Continuum mechanics-based models capture some salient experimental features like the linear elastic regime, followed by non-linear plateau stress regime. However, they lack mesostructural physical details. This makes them incapable of accurately predicting local peaks in stress and strain distributions, which significantly affect the deformation paths. Atomistic methods are capable of capturing the physical origins of deformation at smaller scales, but suffer from impractical computational intensity. Capturing deformation at the so-called meso-scale, which is capable of describing the phenomenon at a continuum level, but with some physical insights, requires developing new theoretical approaches.
\r\n\r\nA fundamental question that motivates the modeling of foams is \u2018how to extract the intrinsic material response from simple mechanical test data, such as stress vs. strain response?\u2019 A 3D model was developed to simulate the mechanical response of foam-type materials. The novelty of this model includes unique features such as the hardening-softening-hardening material response, strain rate-dependence, and plastically compressible solids with plastic non-normality. Suggestive links from atomistic simulations of foams were borrowed to formulate a physically informed hardening material input function. Motivated by a model that qualitatively captured the response of foam-type vertically aligned carbon nanotube (VACNT) pillars under uniaxial compression [2011,\u201cAnalysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes,\u201d J. Mech.Phys. Solids, 59, pp. 2227\u20132237, Erratum 60, 1753\u20131756 (2012)], the property space exploration was advanced to three types of simple mechanical tests: 1) uniaxial compression, 2) uniaxial tension, and 3) nanoindentation with a conical and a flat-punch tip. The simulations attempt to explain some of the salient features in experimental data, like
\r\n1) The initial linear elastic response.
\r\n2) One or more nonlinear instabilities, yielding, and hardening.
The model-inherent relationships between the material properties and the overall stress-strain behavior were validated against the available experimental data. The material properties include the gradient in stiffness along the height, plastic and elastic compressibility, and hardening. Each of these tests was evaluated in terms of their efficiency in extracting material properties. The uniaxial simulation results proved to be a combination of structural and material influences. Out of all deformation paths, flat-punch indentation proved to be superior since it is the most sensitive in capturing the material properties.
" }, { "name": "Mujeeb-U-Rahman, Muhammad", "degree": "PhD", "year": "2014", "title": "Integrated Microsystems for Wireless Sensing Applications", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062014-160929992", "creators": [ { "name": { "family": "Mujeeb-U-Rahman", "given": "Muhammad" }, "id": "Mujeeb-U-Rahman-Muhammad", "display_name": "Mujeeb-U-Rahman, Muhammad" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z98050MN", "abstract": "Personal health monitoring is being considered the future of a sustainable health care system. Biosensing platforms are a very important component of this system. Real-time and accurate sensing is essential for the success of personal health care model. Currently, there are many efforts going on to make these sensors practical and more useful for such measurements. Implantable sensors are considered the most widely applicable and most reliable sensors for such accurate health monitoring applications. However, macroscopic (cm scale) size has proved to be a limiting factor for successful use of these systems for long time and in large numbers. This work is focused to resolve the issues related with miniaturizing these devices to a microscopic (mm scale) size scale which can minimize many practical difficulties associated with their larger counterparts currently.
\r\n\r\nTo accomplish this goal of miniaturization while retaining or even improving on the necessary capabilities for such sensing platforms, an integrated approach is presented which focuses on system-level miniaturization using standard fabrication procedures. First, it is shown that a completely integrated and wireless system is the best solution to achieve desired miniaturization without sacrificing the functionality of the system. Hence, design and implementation of the different components comprising the complete system needs to be done according to the requirements of the overall integrated system. This leads to the need of on-chip functional sensors, integrated wireless power supply, integrated wireless communication and integrated control system for realization of such system. In this work, different options for implementation of each of these subsystems are compared and an optimal solution is presented for each subsystem. For such complex systems, it is imperative to use a standard fabrication process which can provide the required functionality for all subsystems at smallest possible size scale. Complementary Metal Oxide Semiconductor (CMOS) process is the most appropriate of the technologies in this regard and has enabled incredible miniaturization of the computing industry. It also provides options for designing different subsystems on the same platform in a monolithic process with very high yield. This choice then leads to actual designs of subsystems in the CMOS technology using different possible methods. Careful comparison of these subsystems provides insights into different design adjustments that are made until the desired functions are achieved at the desired size scale. Integration of all these compatible subsystems in the same platform is shown to provide the smallest possible sensing platform to date.
\r\n\r\nThe completely wireless system can measure a host of different important analyte and can transmit the data to an external device which can use it for appropriate purpose. Results on measurements in phosphate buffer solution, blood serum and whole blood along with wireless communication in real biological tissues are provided. Specific examples of glucose and DNA sensors are presented and the use for many other relevant applications is also proposed. Finally, insights into animal model studies and future directions of the research are discussed.
\r\n" }, { "name": "Olson, Michael James", "degree": "PhD", "year": "2014", "title": "Cloud Computing Services for Seismic Networks", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechTHESIS:08242013-182604077", "creators": [ { "name": { "family": "Olson", "given": "Michael James" }, "id": "Olson-Michael-James", "display_name": "Olson, Michael James" } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Billock", "given": "Joseph Gregory" }, "id": "Billock-J-G", "role": "member", "display_name": "Billock, Joseph Gregory" }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "role": "member", "display_name": "Clayton, Robert W." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "compsci" ], "doi": "10.7907/5D60-FG88", "abstract": "This thesis describes a compositional framework for developing situation awareness applications: applications that provide ongoing information about a user's changing environment. The thesis describes how the framework is used to develop a situation awareness application for earthquakes. The applications are implemented as Cloud computing services connected to sensors and actuators. The architecture and design of the Cloud services are described and measurements of performance metrics are provided. The thesis includes results of experiments on earthquake monitoring conducted over a year. The applications developed by the framework are (1) the CSN --- the Community Seismic Network --- which uses relatively low-cost sensors deployed by members of the community, and (2) SAF --- the Situation Awareness Framework --- which integrates data from multiple sources, including the CSN, CISN --- the California Integrated Seismic Network, a network consisting of high-quality seismometers deployed carefully by professionals in the CISN organization and spread across Southern California --- and prototypes of multi-sensor platforms that include carbon monoxide, methane, dust and radiation sensors." }, { "name": "Patterson, Keith D.", "degree": "PhD", "year": "2014", "title": "Lightweight Deformable Mirrors for Future Space Telescopes", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182013-094108778", "creators": [ { "name": { "family": "Patterson", "given": "Keith D." }, "id": "Patterson-Keith-D", "display_name": "Patterson, Keith D." } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/S7JS-A837", "abstract": "This thesis presents a concept for ultra-lightweight deformable mirrors based on a thin substrate of optical surface quality coated with continuous active piezopolymer layers that provide modes of actuation and shape correction. This concept eliminates any kind of stiff backing structure for the mirror surface and exploits micro-fabrication technologies to provide a tight integration of the active materials into the mirror structure, to avoid actuator print-through effects. Proof-of-concept, 10-cm-diameter mirrors with a low areal density of about 0.5 kg/m² have been designed, built and tested to measure their shape-correction performance and verify the models used for design. The low cost manufacturing scheme uses replication techniques, and strives for minimizing residual stresses that deviate the optical figure from the master mandrel. It does not require precision tolerancing, is lightweight, and is therefore potentially scalable to larger diameters for use in large, modular space telescopes. Other potential applications for such a laminate could include ground-based mirrors for solar energy collection, adaptive optics for atmospheric turbulence, laser communications, and other shape control applications.
\r\n\r\nThe immediate application for these mirrors is for the Autonomous Assembly and Reconfiguration of a Space Telescope (AAReST) mission, which is a university mission under development by Caltech, the University of Surrey, and JPL. The design concept, fabrication methodology, material behaviors and measurements, mirror modeling, mounting and control electronics design, shape control experiments, predictive performance analysis, and remaining challenges are presented herein. The experiments have validated numerical models of the mirror, and the mirror models have been used within a model of the telescope in order to predict the optical performance. A demonstration of this mirror concept, along with other new telescope technologies, is planned to take place during the AAReST mission.
\r\n\r\n" }, { "name": "Rabinovitch, Jason", "degree": "PhD", "year": "2014", "title": "Advancing EDL Technologies for Future Space Missions: From Ground Testing Facilities to Ablative Heatshields", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302014-140011538", "creators": [ { "name": { "family": "Rabinovitch", "given": "Jason" }, "id": "Rabinovitch-Jason", "orcid": "0000-0002-1914-7964", "display_name": "Rabinovitch, Jason" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XKM7-7368", "abstract": "Motivated by recent MSL results where the ablation rate of the PICA heatshield was over-predicted, and staying true to the objectives outlined in the NASA Space Technology Roadmaps and Priorities report, this work focuses on advancing EDL technologies for future space missions.
\r\n\r\nDue to the difficulties in performing flight tests in the hypervelocity regime, a new ground testing facility called the vertical expansion tunnel is proposed. The adverse effects from secondary diaphragm rupture in an expansion tunnel may be reduced or eliminated by orienting the tunnel vertically, matching the test gas pressure and the accelerator gas pressure, and initially separating the test gas from the accelerator gas by density stratification. If some sacrifice of the reservoir conditions can be made, the VET can be utilized in hypervelocity ground testing, without the problems associated with secondary diaphragm rupture.
\r\n\r\nThe performance of different constraints for the Rate-Controlled Constrained-Equilibrium (RCCE) method is investigated in the context of modeling reacting flows characteristic to ground testing facilities, and re-entry conditions. The effectiveness of different constraints are isolated, and new constraints previously unmentioned in the literature are introduced. Three main benefits from the RCCE method were determined: 1) the reduction in number of equations that need to be solved to model a reacting flow; 2) the reduction in stiffness of the system of equations needed to be solved; and 3) the ability to tabulate chemical properties as a function of a constraint once, prior to running a simulation, along with the ability to use the same table for multiple simulations.
\r\n\r\nFinally, published physical properties of PICA are compiled, and the composition of the pyrolysis gases that form at high temperatures internal to a heatshield is investigated. A necessary link between the composition of the solid resin, and the composition of the pyrolysis gases created is provided. This link, combined with a detailed investigation into a reacting pyrolysis gas mixture, allows a much needed consistent, and thorough description of many of the physical phenomena occurring in a PICA heatshield, and their implications, to be presented.
\r\n\r\nThrough the use of computational fluid mechanics and computational chemistry methods, significant contributions have been made to advancing ground testing facilities, computational methods for reacting flows, and ablation modeling.
" }, { "name": "Rajagopal, Aditya", "degree": "PhD", "year": "2014", "title": "Microfabricated Tools and Engineering Methods for Sensing Bioanalytes", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052014-214022941", "creators": [ { "name": { "family": "Rajagopal", "given": "Aditya" }, "id": "Rajagopal-Aditya", "display_name": "Rajagopal, Aditya" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "chair", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Baltimore", "given": "David L." }, "id": "Baltimore-D-L", "role": "member", "display_name": "Baltimore, David L." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9W9575D", "abstract": "There is a convergence between the needs of the medical community and the capabilities of the engineering community. For example, the scale of biomedical devices and sensors allow for finer, more cost-effective quantification of biological and chemical targets. By using micro-fabrication techniques, we design and demonstrate a variety of microfluidic sensors and actuators that allow us to interact with a biochemical environment. We demonstrate the performance of microfluidic blood-filtrations chips, immune-diagnostic assays, and evaporative coolers. Furthermore, we show how micro-fabricated platinum filaments can be used for highly localized heating and temperature measurement. We demonstrate that these filaments can be used as miniature IR spectroscopic sources. Finally, we describe and demonstrate novel combinatorial coding methods for increasing the information extracted from biochemical reactions. We show proof-principle of these techniques in the context of Taqman PCR as well as persistence length PCR." }, { "name": "Ray, Debajyoti", "degree": "PhD", "year": "2014", "title": "Efficient Methods for Empirical Tests of Behavioral Economics Theories in Laboratory and Field Experiments", "advisor": "Camerer, Colin F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272014-001635343", "creators": [ { "name": { "family": "Ray", "given": "Debajyoti" }, "id": "Ray-Debajyoti", "orcid": "0000-0002-3833-1062", "display_name": "Ray, Debajyoti" } ], "advisors": [ { "name": { "family": "Camerer", "given": "Colin F." }, "id": "Camerer-C-F", "role": "advisor", "display_name": "Camerer, Colin F." } ], "committee": [ { "name": { "family": "Camerer", "given": "Colin F." }, "id": "Camerer-C-F", "role": "chair", "display_name": "Camerer, Colin F." }, { "name": { "family": "Shum", "given": "Matthew S." }, "id": "Shum-M-S", "role": "member", "display_name": "Shum, Matthew S." }, { "name": { "family": "Bossaerts", "given": "Peter L." }, "id": "Bossaerts-P-L", "role": "member", "display_name": "Bossaerts, Peter L." }, { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-K-A", "role": "member", "display_name": "Ligett, Katrina A." }, { "name": { "family": "Krause", "given": "Andreas" }, "id": "Krause-A", "role": "member", "display_name": "Krause, Andreas" }, { "name": { "family": "Weber", "given": "Romann M." }, "id": "Weber-R-M", "role": "member", "display_name": "Weber, Romann M." } ], "option_major": [ "cns" ], "doi": "10.7907/V184-1318", "abstract": "In the quest for a descriptive theory of decision-making, the rational actor model in economics imposes rather unrealistic expectations and abilities on human decision makers. The further we move from idealized scenarios, such as perfectly competitive markets, and ambitiously extend the reach of the theory to describe everyday decision making situations, the less sense these assumptions make. Behavioural economics has instead proposed models based on assumptions that are more psychologically realistic, with the aim of gaining more precision and descriptive power. Increased psychological realism, however, comes at the cost of a greater number of parameters and model complexity. Now there are a plethora of models, based on different assumptions, applicable in differing contextual settings, and selecting the right model to use tends to be an ad-hoc process. In this thesis, we develop optimal experimental design methods and evaluate different behavioral theories against evidence from lab and field experiments.
\r\n\r\nWe look at evidence from controlled laboratory experiments. Subjects are presented with choices between monetary gambles or lotteries. Different decision-making theories evaluate the choices differently and would make distinct predictions about the subjects' choices. Theories whose predictions are inconsistent with the actual choices can be systematically eliminated. Behavioural theories can have multiple parameters requiring complex experimental designs with a very large number of possible choice tests. This imposes computational and economic constraints on using classical experimental design methods. We develop a methodology of adaptive tests: Bayesian Rapid Optimal Adaptive Designs (BROAD) that sequentially chooses the \"most informative\" test at each stage, and based on the response updates its posterior beliefs over the theories, which informs the next most informative test to run. BROAD utilizes the Equivalent Class Edge Cutting (EC2) criteria to select tests. We prove that the EC2 criteria is adaptively submodular, which allows us to prove theoretical guarantees against the Bayes-optimal testing sequence even in the presence of noisy responses. In simulated ground-truth experiments, we find that the EC2 criteria recovers the true hypotheses with significantly fewer tests than more widely used criteria such as Information Gain and Generalized Binary Search. We show, theoretically as well as experimentally, that surprisingly these popular criteria can perform poorly in the presence of noise, or subject errors. Furthermore, we use the adaptive submodular property of EC2 to implement an accelerated greedy version of BROAD which leads to orders of magnitude speedup over other methods.
\r\n\r\nWe use BROAD to perform two experiments. First, we compare the main classes of theories for decision-making under risk, namely: expected value, prospect theory, constant relative risk aversion (CRRA) and moments models. Subjects are given an initial endowment, and sequentially presented choices between two lotteries, with the possibility of losses. The lotteries are selected using BROAD, and 57 subjects from Caltech and UCLA are incentivized by randomly realizing one of the lotteries chosen. Aggregate posterior probabilities over the theories show limited evidence in favour of CRRA and moments' models. Classifying the subjects into types showed that most subjects are described by prospect theory, followed by expected value. Adaptive experimental design raises the possibility that subjects could engage in strategic manipulation, i.e. subjects could mask their true preferences and choose differently in order to obtain more favourable tests in later rounds thereby increasing their payoffs. We pay close attention to this problem; strategic manipulation is ruled out since it is infeasible in practice, and also since we do not find any signatures of it in our data.
\r\n\r\nIn the second experiment, we compare the main theories of time preference: exponential discounting, hyperbolic discounting, \"present bias\" models: quasi-hyperbolic (α, β) discounting and fixed cost discounting, and generalized-hyperbolic discounting. 40 subjects from UCLA were given choices between 2 options: a smaller but more immediate payoff versus a larger but later payoff. We found very limited evidence for present bias models and hyperbolic discounting, and most subjects were classified as generalized hyperbolic discounting types, followed by exponential discounting.
\r\n\r\nIn these models the passage of time is linear. We instead consider a psychological model where the perception of time is subjective. We prove that when the biological (subjective) time is positively dependent, it gives rise to hyperbolic discounting and temporal choice inconsistency.
\r\n\r\nWe also test the predictions of behavioral theories in the \"wild\". We pay attention to prospect theory, which emerged as the dominant theory in our lab experiments of risky choice. Loss aversion and reference dependence predicts that consumers will behave in a uniquely distinct way than the standard rational model predicts. Specifically, loss aversion predicts that when an item is being offered at a discount, the demand for it will be greater than that explained by its price elasticity. Even more importantly, when the item is no longer discounted, demand for its close substitute would increase excessively. We tested this prediction using a discrete choice model with loss-averse utility function on data from a large eCommerce retailer. Not only did we identify loss aversion, but we also found that the effect decreased with consumers' experience. We outline the policy implications that consumer loss aversion entails, and strategies for competitive pricing.
\r\n\r\nIn future work, BROAD can be widely applicable for testing different behavioural models, e.g. in social preference and game theory, and in different contextual settings. Additional measurements beyond choice data, including biological measurements such as skin conductance, can be used to more rapidly eliminate hypothesis and speed up model comparison. Discrete choice models also provide a framework for testing behavioural models with field data, and encourage combined lab-field experiments.
" }, { "name": "Richmond, Victoria Stolyar", "degree": "PhD", "year": "2014", "title": "Techniques for Strength Measurement at High Pressures and Strain-Rates using Transverse Waves", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:01152014-115401299", "creators": [ { "name": { "family": "Richmond", "given": "Victoria Stolyar" }, "id": "Richmond-Victoria-Stolyar", "display_name": "Richmond, Victoria Stolyar" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "space" ], "doi": "10.7907/SH60-5659", "abstract": "The study of the strength of a material is relevant to a variety of applications including automobile collisions, armor penetration and inertial confinement fusion. Although dynamic behavior of materials at high pressures and strain-rates has been studied extensively using plate impact experiments, the results provide measurements in one direction only. Material behavior that is dependent on strength is unaccounted for. The research in this study proposes two novel configurations to mitigate this problem.
\r\n\r\nThe first configuration introduced is the oblique wedge experiment, which is comprised of a driver material, an angled target of interest and a backing material used to measure in-situ velocities. Upon impact, a shock wave is generated in the driver material. As the shock encounters the angled target, it is reflected back into the driver and transmitted into the target. Due to the angle of obliquity of the incident wave, a transverse wave is generated that allows the target to be subjected to shear while being compressed by the initial longitudinal shock such that the material does not slip. Using numerical simulations, this study shows that a variety of oblique wedge configurations can be used to study the shear response of materials and this can be extended to strength measurement as well. Experiments were performed on an oblique wedge setup with a copper impactor, polymethylmethacrylate driver, aluminum 6061-t6 target, and a lithium fluoride window. Particle velocities were measured using laser interferometry and results agree well with the simulations.
\r\n\r\nThe second novel configuration is the y-cut quartz sandwich design, which uses the anisotropic properties of y-cut quartz to generate a shear wave that is transmitted into a thin sample. By using an anvil material to back the thin sample, particle velocities measured at the rear surface of the backing plate can be implemented to calculate the shear stress in the material and subsequently the strength. Numerical simulations were conducted to show that this configuration has the ability to measure the strength for a variety of materials.
\r\n" }, { "name": "Roberts, Scott Nolan", "degree": "PhD", "year": "2014", "title": "Developing and Characterizing Bulk Metallic Glasses for Extreme Applications", "advisor": "Johnson, William Lewis; Hofmann, Douglas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01072014-174255218", "creators": [ { "name": { "family": "Roberts", "given": "Scott Nolan" }, "id": "Roberts-Scott-Nolan", "display_name": "Roberts, Scott Nolan" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Hofmann", "given": "Douglas C." }, "id": "Hofmann-D-C", "role": "co-advisor", "display_name": "Hofmann, Douglas C." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Hofmann", "given": "Douglas C." }, "id": "Hofmann-D-C", "role": "member", "display_name": "Hofmann, Douglas C." } ], "option_major": [ "matsci" ], "doi": "10.7907/FPNT-FT46", "abstract": "Metallic glasses have typically been treated as a \u201cone size fits all\u201d type of material. Every alloy is considered to have high strength, high hardness, large elastic limits, corrosion resistance, etc. However, similar to traditional crystalline materials, properties are strongly dependent upon the constituent elements, how it was processed, and the conditions under which it will be used. An important distinction which can be made is between metallic glasses and their composites. Charpy impact toughness measurements are performed to determine the effect processing and microstructure have on bulk metallic glass matrix composites (BMGMCs). Samples are suction cast, machined from commercial plates, and semi-solidly forged (SSF). The SSF specimens have been found to have the highest impact toughness due to the coarsening of the dendrites, which occurs during the semi-solid processing stages. Ductile to brittle transition (DTBT) temperatures are measured for a BMGMC. While at room temperature the BMGMC is highly toughened compared to a fully glassy alloy, it undergoes a DTBT by 250 K. At this point, its impact toughness mirrors that of the constituent glassy matrix. In the following chapter, BMGMCs are shown to have the capability of being capacitively welded to form single, monolithic structures. Shear measurements are performed across welded samples, and, at sufficient weld energies, are found to retain the strength of the parent alloy. Cross-sections are inspected via SEM and no visible crystallization of the matrix occurs.
\r\n\r\nNext, metallic glasses and BMGMCs are formed into sheets and eggbox structures are tested in hypervelocity impacts. Metallic glasses are ideal candidates for protection against micrometeorite orbital debris due to their high hardness and relatively low density. A flat single layer, flat BMG is compared to a BMGMC eggbox and the latter creates a more diffuse projectile cloud after penetration. A three tiered eggbox structure is also tested by firing a 3.17 mm aluminum sphere at 2.7 km/s at it. The projectile penetrates the first two layers, but is successfully contained by the third.
\r\n\r\nA large series of metallic glass alloys are created and their wear loss is measured in a pin on disk test. Wear is found to vary dramatically among different metallic glasses, with some considerably outperforming the current state-of-the-art crystalline material (most notably Cu\u2084\u2083Zr\u2084\u2083Al\u2087Be\u2087). Others, on the other hand, suffered extensive wear loss. Commercially available Vitreloy 1 lost nearly three times as much mass in wear as alloy prepared in a laboratory setting. No conclusive correlations can be found between any set of mechanical properties (hardness, density, elastic, bulk, or shear modulus, Poisson\u2019s ratio, frictional force, and run in time) and wear loss. Heat treatments are performed on Vitreloy 1 and Cu\u2084\u2083Zr\u2084\u2083Al\u2087Be\u2087. Anneals near the glass transition temperature are found to increase hardness slightly, but decrease wear loss significantly. Crystallization of both alloys leads to dramatic increases in wear resistance. Finally, wear tests under vacuum are performed on the two alloys above. Vitreloy 1 experiences a dramatic decrease in wear loss, while Cu\u2084\u2083Zr\u2084\u2083Al\u2087Be\u2087 has a moderate increase. Meanwhile, gears are fabricated through three techniques: electrical discharge machining of 1 cm by 3 mm cylinders, semisolid forging, and copper mold suction casting. Initial testing finds the pin on disk test to be an accurate predictor of wear performance in gears.
\r\n\r\nThe final chapter explores an exciting technique in the field of additive manufacturing. Laser engineered net shaping (LENS) is a method whereby small amounts of metallic powders are melted by a laser such that shapes and designs can be built layer by layer into a final part. The technique is extended to mixing different powders during melting, so that compositional gradients can be created across a manufactured part. Two compositional gradients are fabricated and characterized. Ti 6Al\u00ac 4V to pure vanadium was chosen for its combination of high strength and light weight on one end, and high melting point on the other. It was inspected by cross-sectional x-ray diffraction, and only the anticipated phases were present. 304L stainless steel to Invar 36 was created in both pillar and as a radial gradient. It combines strength and weldability along with a zero coefficient of thermal expansion material. Only the austenite phase is found to be present via x-ray diffraction. Coefficient of thermal expansion is measured for four compositions, and it is found to be tunable depending on composition.
" }, { "name": "Saito, Namiko", "degree": "PhD", "year": "2014", "title": "Large-Eddy Simulations of Fully Developed Turbulent Channel and Pipe Flows with Smooth and Rough Walls", "advisor": "Pullin, Dale I.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02142014-112419793", "creators": [ { "name": { "family": "Saito", "given": "Namiko" }, "id": "Saito-Namiko", "display_name": "Saito, Namiko" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale I." }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WKNJ-ET18", "abstract": "Studies in turbulence often focus on two flow conditions, both of which occur frequently in real-world flows and are sought-after for their value in advancing turbulence theory. These are the high Reynolds number regime and the effect of wall surface roughness. In this dissertation, a Large-Eddy Simulation (LES) recreates both conditions over a wide range of Reynolds numbers Reτ = O(102)-O(108) and accounts for roughness by locally modeling the statistical effects of near-wall anisotropic fine scales in a thin layer immediately above the rough surface. A subgrid, roughness-corrected wall model is introduced to dynamically transmit this modeled information from the wall to the outer LES, which uses a stretched-vortex subgrid-scale model operating in the bulk of the flow. Of primary interest is the Reynolds number and roughness dependence of these flows in terms of first and second order statistics. The LES is first applied to a fully turbulent uniformly-smooth/rough channel flow to capture the flow dynamics over smooth, transitionally rough and fully rough regimes. Results include a Moody-like diagram for the wall averaged friction factor, believed to be the first of its kind obtained from LES. Confirmation is found for experimentally observed logarithmic behavior in the normalized stream-wise turbulent intensities. Tight logarithmic collapse, scaled on the wall friction velocity, is found for smooth-wall flows when Reτ ≥ O(106) and in fully rough cases. Since the wall model operates locally and dynamically, the framework is used to investigate non-uniform roughness distribution cases in a channel, where the flow adjustments to sudden surface changes are investigated. Recovery of mean quantities and turbulent statistics after transitions are discussed qualitatively and quantitatively at various roughness and Reynolds number levels. The internal boundary layer, which is defined as the border between the flow affected by the new surface condition and the unaffected part, is computed, and a collapse of the profiles on a length scale containing the logarithm of friction Reynolds number is presented. Finally, we turn to the possibility of expanding the present framework to accommodate more general geometries. As a first step, the whole LES framework is modified for use in the curvilinear geometry of a fully-developed turbulent pipe flow, with implementation carried out in a spectral element solver capable of handling complex wall profiles. The friction factors have shown favorable agreement with the superpipe data, and the LES estimates of the Karman constant and additive constant of the log-law closely match values obtained from experiment." }, { "name": "Sanan, Patrick David", "degree": "PhD", "year": "2014", "title": "Geometric Elasticity for Graphics, Simulation, and Computation", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechTHESIS:12052013-121547860", "creators": [ { "name": { "family": "Sanan", "given": "Patrick David" }, "id": "Sanan-Patrick-David", "display_name": "Sanan, Patrick David" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/DF7X-F354", "abstract": "We develop new algorithms which combine the rigorous theory of mathematical elasticity with the geometric underpinnings and computational attractiveness of modern tools in geometry processing. We develop a simple elastic energy based on the Biot strain measure, which improves on state-of-the-art methods in geometry processing. We use this energy within a constrained optimization problem to, for the first time, provide surface parameterization tools which guarantee injectivity and bounded distortion, are user-directable, and which scale to large meshes. With the help of some new generalizations in the computation of matrix functions and their derivative, we extend our methods to a large class of hyperelastic stored energy functions quadratic in piecewise analytic strain measures, including the Hencky (logarithmic) strain, opening up a wide range of possibilities for robust and efficient nonlinear elastic simulation and geometry processing by elastic analogy. " }, { "name": "Satsanarukkit, Penvipha", "degree": "PhD", "year": "2014", "title": "Development of Integrated Parylene Fluidic Devices for Use as a Microbial Monitoring System in Wastewater Treatment", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312014-143352981", "creators": [ { "name": { "family": "Satsanarukkit", "given": "Penvipha" }, "id": "Satsanarukkit-Penvipha", "display_name": "Satsanarukkit, Penvipha" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "member", "display_name": "Newman, Dianne K." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z98G8HPQ", "abstract": "[Abstract Embargoed]" }, { "name": "Sharan, Rangoli", "degree": "PhD", "year": "2014", "title": "Formal Methods for Control Synthesis in Partially Observed Environments: Application to Autonomous Robotic Manipulation", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292014-063852576", "creators": [ { "name": { "family": "Sharan", "given": "Rangoli" }, "id": "Sharan-Rangoli", "display_name": "Sharan, Rangoli" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hudson", "given": "Nicolas H." }, "id": "Hudson-N-H", "role": "member", "display_name": "Hudson, Nicolas H." } ], "option_major": [ "cds" ], "doi": "10.7907/RQKC-N871", "abstract": "Modern robots are increasingly expected to function in uncertain and dynamically challenging environments, often in proximity with humans. In addition, wide scale adoption of robots requires on-the-fly adaptability of software for diverse application. These requirements strongly suggest the need to adopt formal representations of high level goals and safety specifications, especially as temporal logic formulas. This approach allows for the use of formal verification techniques for controller synthesis that can give guarantees for safety and performance. Robots operating in unstructured environments also face limited sensing capability. Correctly inferring a robot's progress toward high level goal can be challenging.
\r\n\r\nThis thesis develops new algorithms for synthesizing discrete controllers in partially known environments under specifications represented as linear temporal logic (LTL) formulas. It is inspired by recent developments in finite abstraction techniques for hybrid systems and motion planning problems. The robot and its environment is assumed to have a finite abstraction as a Partially Observable Markov Decision Process (POMDP), which is a powerful model class capable of representing a wide variety of problems. However, synthesizing controllers that satisfy LTL goals over POMDPs is a challenging problem which has received only limited attention.
\r\n\r\nThis thesis proposes tractable, approximate algorithms for the control synthesis problem using Finite State Controllers (FSCs). The use of FSCs to control finite POMDPs allows for the closed system to be analyzed as finite global Markov chain. The thesis explicitly shows how transient and steady state behavior of the global Markov chains can be related to two different criteria with respect to satisfaction of LTL formulas. First, the maximization of the probability of LTL satisfaction is related to an optimization problem over a parametrization of the FSC. Analytic computation of gradients are derived which allows the use of first order optimization techniques.
\r\n\r\nThe second criterion encourages rapid and frequent visits to a restricted set of states over infinite executions. It is formulated as a constrained optimization problem with a discounted long term reward objective by the novel utilization of a fundamental equation for Markov chains - the Poisson equation. A new constrained policy iteration technique is proposed to solve the resulting dynamic program, which also provides a way to escape local maxima.
\r\n\r\nThe algorithms proposed in the thesis are applied to the task planning and execution challenges faced during the DARPA Autonomous Robotic Manipulation - Software challenge.
" }, { "name": "Smith, Hillary Leigh", "degree": "PhD", "year": "2014", "title": "Phase Transformations and Entropy of Non-Equilibrium Materials", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102014-162104359", "creators": [ { "name": { "family": "Smith", "given": "Hillary Leigh" }, "id": "Smith-Hillary-Leigh", "display_name": "Smith, Hillary Leigh" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Demetriou", "given": "Marios D." }, "id": "Demetriou-M-D", "role": "member", "display_name": "Demetriou, Marios D." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Jackson", "given": "Jennifer M." }, "id": "Jackson-J-M", "role": "member", "display_name": "Jackson, Jennifer M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9FB50W7", "abstract": "Time-resolved vibrational spectra through the glass transition in the bulk metallic glass CuZr were acquired with inelastic neutron scattering. Vibrational density of states (DOS) in ranges as small as 4K were extracted from continuous heating through the glass transition. For each temperature interval, the vibrational entropy is calculated from the DOS. This provides a detailed characterization of how the vibrational entropy contributes to the large jump in heat capacity that characterizes the glass transition in amorphous materials. This change in heat capacity has been attributed to combinations of configurational and vibrational entropy. However, the role of vibrational entropy in this transition has never been demonstrated for all vibrational modes in an amorphous material. This work provides the first experimental measurement of the change in vibrational entropy through the glass transition. We found the unique contributions of both the vibrational and configurational entropy and find that the change in vibrational entropy can be bound at less than 0.01 kB per atom. By elimination, this means that the configurational entropy is dominant, putting to rest a controversial debate over the role of entropy through the glass transition.
\r\n\r\nThe changes in vibrational entropy during the early stages of chemical unmixing was studied in a nanocrystalline fcc solid solution of 6%-Fe in Cu. Material prepared by high-energy ball milling was annealed at temperatures from 200 to 360\u00b0C to induce chemical unmixing. Nuclear resonant inelastic x-ray scattering spectra yield the phonon partial density of states (pDOS) of 57Fe. The pDOS of the as-prepared material is that of an fcc crystal. In the earliest stages of unmixing, the features of the pDOS broaden, with only small changes in average phonon frequencies, until the bcc phase begins to form. The chemical state of the material was characterized by three-dimensional atom probe microscopy, M\u04e7ssbauer spectrometry, and x-ray powder diffractometry. The unmixing was heterogeneous, with iron atoms forming iron-rich zones that thicken with further annealing. The vibrational entropy calculated from the pDOS underwent little change during the early stage of unmixing, but decreased rapidly when the bcc phase formed in the material.
\r\n\r\nElectrochemical cycling of lithium ion batteries causes fundamental structural changes and the formation of new phases in cathode materials. The reversibility of these transitions is often critical to the viability of cathode materials for long-term performance. The cycle lives for cathodes of nanocrystalline iron trifluoride (FeF3) were measured in rechargeable lithium batteries at different depths of discharge. When the discharge was limited to less than one Li+ ion per FeF3, both the cycle life and energy efficiency were considerably greater than when converting FeF3 into Fe and LiF in deep discharge. An in situ X-ray diffractometry (XRD) study of the FeF3 cathode during its initial discharge to LiFeF3 showed a continuous change of the FeF3 diffraction pattern, indicating Li+ insertion into the rhombohedral FeF3 causing distortion of its lattice parameters. Electrochemical cycling is most reversible when this mechanism occurs in the absence of other changes in the crystal structure.
" }, { "name": "Song, Shiyan", "degree": "PhD", "year": "2014", "title": "A New Ground Motion Intensity Measure, Peak Filtered Acceleration (PFA), to Estimate Collapse Vulnerability of Buildings in Earthquakes", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10212013-164416621", "creators": [ { "name": { "family": "Song", "given": "Shiyan" }, "id": "Song-Shiyan", "display_name": "Song, Shiyan" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Zareian", "given": "Farzin" }, "id": "Zareian-F", "role": "member", "display_name": "Zareian, Farzin" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/J5YB-AR86", "abstract": "In this thesis, we develop an efficient collapse prediction model, the PFA (Peak Filtered Acceleration) model, for buildings subjected to different types of ground motions.
\r\n\r\nFor the structural system, the PFA model covers modern steel and reinforced concrete moment-resisting frame buildings (potentially reinforced concrete shear wall buildings). For ground motions, the PFA model covers ramp-pulse-like ground motions, long-period ground motions, and short-period ground motions.
\r\n\r\nTo predict whether a building will collapse in response to a given ground motion, we first extract long-period components from the ground motion using a Butterworth low-pass filter with suggested order and cutoff frequency. The order depends on the type of ground motion, and the cutoff frequency depends on the building\u2019s natural frequency and ductility. We then compare the filtered acceleration time history with the capacity of the building. The capacity of the building is a constant for 2-dimentional buildings and a limit domain for 3-dimentional buildings. If the filtered acceleration exceeds the building\u2019s capacity, the building is predicted to collapse. Otherwise, it is expected to survive the ground motion.
\r\n\r\nThe parameters used in PFA model, which include fundamental period, global ductility and lateral capacity, can be obtained either from numerical analysis or interpolation based on the reference building system proposed in this thesis.
\r\n\r\nThe PFA collapse prediction model greatly reduces computational complexity while archiving good accuracy. It is verified by FEM simulations of 13 frame building models and 150 ground motion records.
\r\n\r\nBased on the developed collapse prediction model, we propose to use PFA (Peak Filtered Acceleration) as a new ground motion intensity measure for collapse prediction. We compare PFA with traditional intensity measures PGA, PGV, PGD, and Sa in collapse prediction and find that PFA has the best performance among all the intensity measures.
\r\n\r\nWe also provide a close form in term of a vector intensity measure (PGV, PGD) of the PFA collapse prediction model for practical collapse risk assessment.
" }, { "name": "Steger, Scott Tiedeman", "degree": "PhD", "year": "2014", "title": "A Fundamental Approach to Phase Noise Reduction in Hybrid Si/III-V Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212014-113511509", "creators": [ { "name": { "family": "Steger", "given": "Scott Tiedeman" }, "id": "Steger-Scott-Tiedeman", "display_name": "Steger, Scott Tiedeman" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" } ], "option_major": [ "eleceng" ], "doi": "10.7907/91CD-6H86", "abstract": "Spontaneous emission into the lasing mode fundamentally limits laser linewidths. Reducing cavity losses provides two benefits to linewidth: (1) fewer excited carriers are needed to reach threshold, resulting in less phase-corrupting spontaneous emission into the laser mode, and (2) more photons are stored in the laser cavity, such that each individual spontaneous emission event disturbs the phase of the field less. Strong optical absorption in III-V materials causes high losses, preventing currently-available semiconductor lasers from achieving ultra-narrow linewidths. This absorption is a natural consequence of the compromise between efficient electrical and efficient optical performance in a semiconductor laser. Some of the III-V layers must be heavily doped in order to funnel excited carriers into the active region, which has the side effect of making the material strongly absorbing.
\r\n\r\nThis thesis presents a new technique, called modal engineering, to remove modal energy from the lossy region and store it in an adjacent low-loss material, thereby reducing overall optical absorption. A quantum mechanical analysis of modal engineering shows that modal gain and spontaneous emission rate into the laser mode are both proportional to the normalized intensity of that mode at the active region. If optical absorption near the active region dominates the total losses of the laser cavity, shifting modal energy from the lossy region to the low-loss region will reduce modal gain, total loss, and the spontaneous emission rate into the mode by the same factor, so that linewidth decreases while the threshold inversion remains constant. The total spontaneous emission rate into all other modes is unchanged.
\r\n\r\nModal engineering is demonstrated using the Si/III-V platform, in which light is generated in the III-V material and stored in the low-loss silicon material. The silicon is patterned as a high-Q resonator to minimize all sources of loss. Fabricated lasers employing modal engineering to concentrate light in silicon demonstrate linewidths at least 5 times smaller than lasers without modal engineering at the same pump level above threshold, while maintaining the same thresholds.
" }, { "name": "Suver, Marie Patricia", "degree": "PhD", "year": "2014", "title": "Octopamine Neurons Mediate Flight-Induced Modulation of Visual Processing in Drosophila melanogaster", "advisor": "Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08162013-150835965", "creators": [ { "name": { "family": "Suver", "given": "Marie Patricia" }, "id": "Suver-Marie-Patricia", "display_name": "Suver, Marie Patricia" } ], "advisors": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "chair", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Meister", "given": "Markus" }, "id": "Meister-M", "role": "member", "display_name": "Meister, Markus" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "role": "member", "display_name": "Sternberg, Paul W." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "cns" ], "doi": "10.7907/DJKK-TC21", "abstract": "Activity-dependent modulation of sensory systems has been documented in many organisms, and is likely to be essential for appropriate processing of information during different behavioral states. However, the mechanisms underlying these phenomena, and often their functional consequences, remain poorly characterized. I investigated the role of octopamine neurons in the flight-dependent modulation observed in visual interneurons in the fruit fly Drosophila melanogaster. The vertical system (VS) cells exhibit a boost in their response to visual motion during flight compared to quiescence. Pharmacological application of octopamine evokes responses in quiescent flies that mimic those observed during flight, and octopamine neurons that project to the optic lobes increase in activity during flight. Using genetic tools to manipulate the activity of octopamine neurons, I find that they are both necessary and sufficient for the flight-induced visual boost. This work provides the first evidence that endogenous release of octopamine is involved in state-dependent modulation of visual interneurons in flies. Further, I investigated the role of a single pair of octopamine neurons that project to the optic lobes, and found no evidence that chemical synaptic transmission via these neurons is necessary for the flight boost. However, I found some evidence that activation of these neurons may contribute to the flight boost. Wind stimuli alone are sufficient to generate transient increases in the VS cell response to motion vision, but result in no increase in baseline membrane potential. These results suggest that the flight boost originates not from a central command signal during flight, but from mechanosensory stimuli relayed via the octopamine system. Lastly, in an attempt to understand the functional consequences of the flight boost observed in visual interneurons, we measured the effect of inactivating octopamine neurons in freely flying flies. We found that flies whose octopamine neurons we silenced accelerate less than wild-type flies, consistent with the hypothesis that the flight boost we observe in VS cells is indicative of a gain control mechanism mediated by octopamine neurons. Together, this work serves as the basis for a mechanistic and functional understanding of octopaminergic modulation of vision in flying flies." }, { "name": "Tavallali, Peyman", "degree": "PhD", "year": "2014", "title": "Sparse Time-Frequency Data Analysis: A Multi-Scale Approach", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05152014-141711934", "creators": [ { "name": { "family": "Tavallali", "given": "Peyman" }, "id": "Tavallali-Peyman", "display_name": "Tavallali, Peyman" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z9TT4NXD", "abstract": "In this work, we further extend the recently developed adaptive data analysis method, the Sparse Time-Frequency Representation (STFR) method. This method is based on the assumption that many physical signals inherently contain AM-FM representations. We propose a sparse optimization method to extract the AM-FM representations of such signals. We prove the convergence of the method for periodic signals under certain assumptions and provide practical algorithms specifically for the non-periodic STFR, which extends the method to tackle problems that former STFR methods could not handle, including stability to noise and non-periodic data analysis. This is a significant improvement since many adaptive and non-adaptive signal processing methods are not fully capable of handling non-periodic signals. Moreover, we propose a new STFR algorithm to study intrawave signals with strong frequency modulation and analyze the convergence of this new algorithm for periodic signals. Such signals have previously remained a bottleneck for all signal processing methods. Furthermore, we propose a modified version of STFR that facilitates the extraction of intrawaves that have overlaping frequency content. We show that the STFR methods can be applied to the realm of dynamical systems and cardiovascular signals. In particular, we present a simplified and modified version of the STFR algorithm that is potentially useful for the diagnosis of some cardiovascular diseases. We further explain some preliminary work on the nature of Intrinsic Mode Functions (IMFs) and how they can have different representations in different phase coordinates. This analysis shows that the uncertainty principle is fundamental to all oscillating signals." }, { "name": "Tyranowski, Tomasz Michal", "degree": "PhD", "year": "2014", "title": "Geometric Integration Applied to Moving Mesh Methods and Degenerate Lagrangians", "advisor": "Marsden, Jerrold E.; Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:12042013-185815472", "creators": [ { "name": { "family": "Tyranowski", "given": "Tomasz Michal" }, "id": "Tyranowski-Tomasz-Michal", "display_name": "Tyranowski, Tomasz Michal" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "chair", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/PH3X-YH23", "abstract": "Moving mesh methods (also called r-adaptive methods) are space-adaptive strategies used for the numerical simulation of time-dependent partial differential equations. These methods keep the total number of mesh points fixed during the simulation, but redistribute them over time to follow the areas where a higher mesh point density is required. There are a very limited number of moving mesh methods designed for solving field-theoretic partial differential equations, and the numerical analysis of the resulting schemes is challenging. In this thesis we present two ways to construct r-adaptive variational and multisymplectic integrators for (1+1)-dimensional Lagrangian field theories. The first method uses a variational discretization of the physical equations and the mesh equations are then coupled in a way typical of the existing r-adaptive schemes. The second method treats the mesh points as pseudo-particles and incorporates their dynamics directly into the variational principle. A user-specified adaptation strategy is then enforced through Lagrange multipliers as a constraint on the dynamics of both the physical field and the mesh points. We discuss the advantages and limitations of our methods. The proposed methods are readily applicable to (weakly) non-degenerate field theories---numerical results for the Sine-Gordon equation are presented.
\r\n\r\nIn an attempt to extend our approach to degenerate field theories, in the last part of this thesis we construct higher-order variational integrators for a class of degenerate systems described by Lagrangians that are linear in velocities. We analyze the geometry underlying such systems and develop the appropriate theory for variational integration. Our main observation is that the evolution takes place on the primary constraint and the 'Hamiltonian' equations of motion can be formulated as an index 1 differential-algebraic system. We then proceed to construct variational Runge-Kutta methods and analyze their properties. The general properties of Runge-Kutta methods depend on the 'velocity' part of the Lagrangian. If the 'velocity' part is also linear in the position coordinate, then we show that non-partitioned variational Runge-Kutta methods are equivalent to integration of the corresponding first-order Euler-Lagrange equations, which have the form of a Poisson system with a constant structure matrix, and the classical properties of the Runge-Kutta method are retained. If the 'velocity' part is nonlinear in the position coordinate, we observe a reduction of the order of convergence, which is typical of numerical integration of DAEs. We also apply our methods to several models and present the results of our numerical experiments.
" }, { "name": "Verma, Siddhartha", "degree": "PhD", "year": "2014", "title": "Velocity Resolved - Scalar Modeled Simulations of High Schmidt Number Turbulent Transport", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042014-163735743", "creators": [ { "name": { "family": "Verma", "given": "Siddhartha" }, "id": "Verma-Siddhartha", "display_name": "Verma, Siddhartha" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PTD9-W004", "abstract": "The objective of this thesis is to develop a framework to conduct velocity resolved - scalar modeled (VR-SM) simulations, which will enable accurate simulations at higher Reynolds and Schmidt (Sc) numbers than are currently feasible. The framework established will serve as a first step to enable future simulation studies for practical applications. To achieve this goal, in-depth analyses of the physical, numerical, and modeling aspects related to Sc>>1 are presented, specifically when modeling in the viscous-convective subrange. Transport characteristics are scrutinized by examining scalar-velocity Fourier mode interactions in Direct Numerical Simulation (DNS) datasets and suggest that scalar modes in the viscous-convective subrange do not directly affect large-scale transport for high Sc. Further observations confirm that discretization errors inherent in numerical schemes can be sufficiently large to wipe out any meaningful contribution from subfilter models. This provides strong incentive to develop more effective numerical schemes to support high Sc simulations. To lower numerical dissipation while maintaining physically and mathematically appropriate scalar bounds during the convection step, a novel method of enforcing bounds is formulated, specifically for use with cubic Hermite polynomials. Boundedness of the scalar being transported is effected by applying derivative limiting techniques, and physically plausible single sub-cell extrema are allowed to exist to help minimize numerical dissipation. The proposed bounding algorithm results in significant performance gain in DNS of turbulent mixing layers and of homogeneous isotropic turbulence. Next, the combined physical/mathematical behavior of the subfilter scalar-flux vector is analyzed in homogeneous isotropic turbulence, by examining vector orientation in the strain-rate eigenframe. The results indicate no discernible dependence on the modeled scalar field, and lead to the identification of the tensor-diffusivity model as a good representation of the subfilter flux. Velocity resolved - scalar modeled simulations of homogeneous isotropic turbulence are conducted to confirm the behavior theorized in these a priori analyses, and suggest that the tensor-diffusivity model is ideal for use in the viscous-convective subrange. Simulations of a turbulent mixing layer are also discussed, with the partial objective of analyzing Schmidt number dependence of a variety of scalar statistics. Large-scale statistics are confirmed to be relatively independent of the Schmidt number for Sc>>1, which is explained by the dominance of subfilter dissipation over resolved molecular dissipation in the simulations. Overall, the VR-SM framework presented is quite effective in predicting large-scale transport characteristics of high Schmidt number scalars, however, it is determined that prediction of subfilter quantities would entail additional modeling intended specifically for this purpose. The VR-SM simulations presented in this thesis provide us with the opportunity to overlap with experimental studies, while at the same time creating an assortment of baseline datasets for future validation of LES models, thereby satisfying the objectives outlined for this work." }, { "name": "Wang, Heng", "degree": "PhD", "year": "2014", "title": "High Temperature Transport Properties of Lead Chalcogenides and Their Alloys", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292014-133349910", "creators": [ { "name": { "family": "Wang", "given": "Heng" }, "id": "Wang-Heng", "display_name": "Wang, Heng" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/BBQ6-8X60", "abstract": "This thesis describes a series of experimental studies of lead chalcogenide thermoelectric semiconductors, mainly PbSe. Focusing on a well-studied semiconductor and reporting good but not extraordinary zT, this thesis distinguishes itself by answering the following questions that haven\u2019t been answered: What represents the thermoelectric performance of PbSe? Where does the high zT come from? How (and how much) can we make it better? For the first question, samples were made with highest quality. Each transport property was carefully measured, cross-verified and compared with both historical and contemporary report to overturn commonly believed underestimation of zT. For n- and p-type PbSe zT at 850 K can be 1.1 and 1.0, respectively. For the second question, a systematic approach of quality factor B was used. In n-type PbSe zT is benefited from its high-quality conduction band that combines good degeneracy, low band mass and low deformation potential, whereas zT of p-type is boosted when two mediocre valence bands converge (in band edge energy). In both cases the thermal conductivity from PbSe lattice is inherently low. For the third question, the use of solid solution lead chalcogenide alloys was first evaluated. Simple criteria were proposed to help quickly evaluate the potential of improving zT by introducing atomic disorder. For both PbTe1-xSex and PbSe1-xSx, the impacts in electron and phonon transport compensate each other. Thus, zT in each case was roughly the average of two binary compounds. In p-type Pb1-xSrxSe alloys an improvement of zT from 1.1 to 1.5 at 900 K was achieved, due to the band engineering effect that moves the two valence bands closer in energy. To date, making n-type PbSe better hasn\u2019t been accomplished, but possible strategy is discussed." }, { "name": "Wang, Shuo", "degree": "PhD", "year": "2014", "title": "Social Saliency: Visual Psychophysics and Single-Neuron Recordings in Humans", "advisor": "Adolphs, Ralph", "url": "https://resolver.caltech.edu/CaltechTHESIS:05122014-203347930", "creators": [ { "name": { "family": "Wang", "given": "Shuo" }, "id": "Wang-Shuo", "display_name": "Wang, Shuo" } ], "advisors": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "advisor", "display_name": "Adolphs, Ralph" } ], "committee": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "orcid": "0000-0003-0016-3531", "role": "chair", "display_name": "O'Doherty, John P." }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Tsao", "given": "Doris Y." }, "id": "Tsao-D-Y", "orcid": "0000-0003-1083-1919", "role": "member", "display_name": "Tsao, Doris Y." }, { "name": { "family": "Rutishauser", "given": "Ueli" }, "id": "Rutishauser-U", "orcid": "0000-0002-9207-7069", "role": "member", "display_name": "Rutishauser, Ueli" } ], "option_major": [ "cns" ], "doi": "10.7907/Z90Z718H", "abstract": "My thesis studies how people pay attention to other people and the environment. How does the brain figure out what is important and what are the neural mechanisms underlying attention? What is special about salient social cues compared to salient non-social cues? In Chapter I, I review social cues that attract attention, with an emphasis on the neurobiology of these social cues. I also review neurological and psychiatric links: the relationship between saliency, the amygdala and autism. The first empirical chapter then begins by noting that people constantly move in the environment. In Chapter II, I study the spatial cues that attract attention during locomotion using a cued speeded discrimination task. I found that when the motion was expansive, attention was attracted towards the singular point of the optic flow (the focus of expansion, FOE) in a sustained fashion. The more ecologically valid the motion features became (e.g., temporal expansion of each object, spatial depth structure implied by distribution of the size of the objects), the stronger the attentional effects. However, compared to inanimate objects and cues, people preferentially attend to animals and faces, a process in which the amygdala is thought to play an important role. To directly compare social cues and non-social cues in the same experiment and investigate the neural structures processing social cues, in Chapter III, I employ a change detection task and test four rare patients with bilateral amygdala lesions. All four amygdala patients showed a normal pattern of reliably faster and more accurate detection of animate stimuli, suggesting that advantageous processing of social cues can be preserved even without the amygdala, a key structure of the \u201csocial brain\u201d. People not only attend to faces, but also pay attention to others\u2019 facial emotions and analyze faces in great detail. Humans have a dedicated system for processing faces and the amygdala has long been associated with a key role in recognizing facial emotions. In Chapter IV, I study the neural mechanisms of emotion perception and find that single neurons in the human amygdala are selective for subjective judgment of others\u2019 emotions. Lastly, people typically pay special attention to faces and people, but people with autism spectrum disorders (ASD) might not. To further study social attention and explore possible deficits of social attention in autism, in Chapter V, I employ a visual search task and show that people with ASD have reduced attention, especially social attention, to target-congruent objects in the search array. This deficit cannot be explained by low-level visual properties of the stimuli and is independent of the amygdala, but it is dependent on task demands. Overall, through visual psychophysics with concurrent eye-tracking, my thesis found and analyzed socially salient cues and compared social vs. non-social cues and healthy vs. clinical populations. Neural mechanisms underlying social saliency were elucidated through electrophysiology and lesion studies. I finally propose further research questions based on the findings in my thesis and introduce my follow-up studies and preliminary results beyond the scope of this thesis in the very last section, Future Directions." }, { "name": "Warmann, Emily Cathryn", "degree": "PhD", "year": "2014", "title": "Design Strategies for Ultra-High Efficiency Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052014-163757869", "creators": [ { "name": { "family": "Warmann", "given": "Emily Cathryn" }, "id": "Warmann-Emily-Cathryn", "display_name": "Warmann, Emily Cathryn" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "mecheng" ], "doi": "10.7907/0K8F-9871", "abstract": "While concentrator photovoltaic cells have shown significant improvements in efficiency in the past ten years, once these cells are integrated into concentrating optics, connected to a power conditioning system and deployed in the field, the overall module efficiency drops to only 34 to 36%. This efficiency is impressive compared to conventional flat plate modules, but it is far short of the theoretical limits for solar energy conversion. Designing a system capable of achieving ultra high efficiency of 50% or greater cannot be achieved by refinement and iteration of current design approaches.
\r\n\r\nThis thesis takes a systems approach to designing a photovoltaic system capable of 50% efficient performance using conventional diode-based solar cells. The effort began with an exploration of the limiting efficiency of spectrum splitting ensembles with 2 to 20 sub cells in different electrical configurations. Incorporating realistic non-ideal performance with the computationally simple detailed balance approach resulted in practical limits that are useful to identify specific cell performance requirements. This effort quantified the relative benefit of additional cells and concentration for system efficiency, which will help in designing practical optical systems.
\r\n\r\nEfforts to improve the quality of the solar cells themselves focused on the development of tunable lattice constant epitaxial templates. Initially intended to enable lattice matched multijunction solar cells, these templates would enable increased flexibility in band gap selection for spectrum splitting ensembles and enhanced radiative quality relative to metamorphic growth. The III-V material family is commonly used for multijunction solar cells both for its high radiative quality and for the ease of integrating multiple band gaps into one monolithic growth. The band gap flexibility is limited by the lattice constant of available growth templates. The virtual substrate consists of a thin III-V film with the desired lattice constant. The film is grown strained on an available wafer substrate, but the thickness is below the dislocation nucleation threshold. By removing the film from the growth substrate, allowing the strain to relax elastically, and bonding it to a supportive handle, a template with the desired lattice constant is formed. Experimental efforts towards this structure and initial proof of concept are presented.
\r\n\r\nCells with high radiative quality present the opportunity to recover a large amount of their radiative losses if they are incorporated in an ensemble that couples emission from one cell to another. This effect is well known, but has been explored previously in the context of sub cells that independently operate at their maximum power point. This analysis explicitly accounts for the system interaction and identifies ways to enhance overall performance by operating some cells in an ensemble at voltages that reduce the power converted in the individual cell. Series connected multijunctions, which by their nature facilitate strong optical coupling between sub-cells, are reoptimized with substantial performance benefit.
\r\n\r\nPhotovoltaic efficiency is usually measured relative to a standard incident spectrum to allow comparison between systems. Deployed in the field systems may differ in energy production due to sensitivity to changes in the spectrum. The series connection constraint in particular causes system efficiency to decrease as the incident spectrum deviates from the standard spectral composition. This thesis performs a case study comparing performance of systems over a year at a particular location to identify the energy production penalty caused by series connection relative to independent electrical connection.
\r\n" }, { "name": "Wei, Wei", "degree": "PhD", "year": "2014", "title": "Microfluidics-Based Single-Cell Functional Proteomics Microchip for Portraying Protein Signal Transduction Networks within the Framework of Physicochemical Principles, with Applications in Fundamental and Translational Cancer Research", "advisor": "Heath, James R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03062014-172332538", "creators": [ { "name": { "family": "Wei", "given": "Wei" }, "id": "Wei-Wei", "orcid": "0000-0002-1018-7708", "display_name": "Wei, Wei" } ], "advisors": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "advisor", "display_name": "Heath, James R." } ], "committee": [ { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William L." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Davis", "given": "Mark E." }, "id": "Davis-M-E", "role": "member", "display_name": "Davis, Mark E." }, { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "member", "display_name": "Heath, James R." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9WS8R7G", "abstract": "Single-cell functional proteomics assays can connect genomic information to biological function through quantitative and multiplex protein measurements. Tools for single-cell proteomics have developed rapidly over the past 5 years and are providing unique opportunities. This thesis describes an emerging microfluidics-based toolkit for single cell functional proteomics, focusing on the development of the single cell barcode chips (SCBCs) with applications in fundamental and translational cancer research.
\r\n\r\nThe microchip designed to simultaneously quantify a panel of secreted, cytoplasmic and membrane proteins from single cells will be discussed at the beginning, which is the prototype for subsequent proteomic microchips with more sophisticated design in preclinical cancer research or clinical applications. The SCBCs are a highly versatile and information rich tool for single-cell functional proteomics. They are based upon isolating individual cells, or defined number of cells, within microchambers, each of which is equipped with a large antibody microarray (the barcode), with between a few hundred to ten thousand microchambers included within a single microchip. Functional proteomics assays at single-cell resolution yield unique pieces of information that significantly shape the way of thinking on cancer research. An in-depth discussion about analysis and interpretation of the unique information such as functional protein fluctuations and protein-protein correlative interactions will follow.
\r\n\r\nThe SCBC is a powerful tool to resolve the functional heterogeneity of cancer cells. It has the capacity to extract a comprehensive picture of the signal transduction network from single tumor cells and thus provides insight into the effect of targeted therapies on protein signaling networks. We will demonstrate this point through applying the SCBCs to investigate three isogenic cell lines of glioblastoma multiforme (GBM).
\r\n\r\nThe cancer cell population is highly heterogeneous with high-amplitude fluctuation at the single cell level, which in turn grants the robustness of the entire population. The concept that a stable population existing in the presence of random fluctuations is reminiscent of many physical systems that are successfully understood using statistical physics. Thus, tools derived from that field can probably be applied to using fluctuations to determine the nature of signaling networks. In the second part of the thesis, we will focus on such a case to use thermodynamics-motivated principles to understand cancer cell hypoxia, where single cell proteomics assays coupled with a quantitative version of Le Chatelier's principle derived from statistical mechanics yield detailed and surprising predictions, which were found to be correct in both cell line and primary tumor model.
\r\n\r\nThe third part of the thesis demonstrates the application of this technology in the preclinical cancer research to study the GBM cancer cell resistance to molecular targeted therapy. Physical approaches to anticipate therapy resistance and to identify effective therapy combinations will be discussed in detail. Our approach is based upon elucidating the signaling coordination within the phosphoprotein signaling pathways that are hyperactivated in human GBMs, and interrogating how that coordination responds to the perturbation of targeted inhibitor. Strongly coupled protein-protein interactions constitute most signaling cascades. A physical analogy of such a system is the strongly coupled atom-atom interactions in a crystal lattice. Similar to decomposing the atomic interactions into a series of independent normal vibrational modes, a simplified picture of signaling network coordination can also be achieved by diagonalizing protein-protein correlation or covariance matrices to decompose the pairwise correlative interactions into a set of distinct linear combinations of signaling proteins (i.e. independent signaling modes). By doing so, two independent signaling modes \u2013 one associated with mTOR signaling and a second associated with ERK/Src signaling have been resolved, which in turn allow us to anticipate resistance, and to design combination therapies that are effective, as well as identify those therapies and therapy combinations that will be ineffective. We validated our predictions in mouse tumor models and all predictions were borne out.
\r\n\r\nIn the last part, some preliminary results about the clinical translation of single-cell proteomics chips will be presented. The successful demonstration of our work on human-derived xenografts provides the rationale to extend our current work into the clinic. It will enable us to interrogate GBM tumor samples in a way that could potentially yield a straightforward, rapid interpretation so that we can give therapeutic guidance to the attending physicians within a clinical relevant time scale. The technical challenges of the clinical translation will be presented and our solutions to address the challenges will be discussed as well. A clinical case study will then follow, where some preliminary data collected from a pediatric GBM patient bearing an EGFR amplified tumor will be presented to demonstrate the general protocol and the workflow of the proposed clinical studies.
\r\n" }, { "name": "Wolff, Eric McKenzie", "degree": "PhD", "year": "2014", "title": "Control of Dynamical Systems with Temporal Logic Specifications", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02172014-121159358", "creators": [ { "name": { "family": "Wolff", "given": "Eric McKenzie" }, "id": "Wolff-Eric-McKenzie", "display_name": "Wolff, Eric McKenzie" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Topcu", "given": "Ufuk" }, "id": "Topcu-U", "role": "member", "display_name": "Topcu, Ufuk" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "cds" ], "doi": "10.7907/TGFR-SS39", "abstract": "This thesis is motivated by safety-critical applications involving autonomous air, ground, and space vehicles carrying out complex tasks in uncertain and adversarial environments. We use temporal logic as a language to formally specify complex tasks and system properties. Temporal logic specifications generalize the classical notions of stability and reachability that are studied in the control and hybrid systems communities. Given a system model and a formal task specification, the goal is to automatically synthesize a control policy for the system that ensures that the system satisfies the specification. This thesis presents novel control policy synthesis algorithms for optimal and robust control of dynamical systems with temporal logic specifications. Furthermore, it introduces algorithms that are efficient and extend to high-dimensional dynamical systems.
\r\n\r\nThe first contribution of this thesis is the generalization of a classical linear temporal logic (LTL) control synthesis approach to optimal and robust control. We show how we can extend automata-based synthesis techniques for discrete abstractions of dynamical systems to create optimal and robust controllers that are guaranteed to satisfy an LTL specification. Such optimal and robust controllers can be computed at little extra computational cost compared to computing a feasible controller.
\r\n\r\nThe second contribution of this thesis addresses the scalability of control synthesis with LTL specifications. A major limitation of the standard automaton-based approach for control with LTL specifications is that the automaton might be doubly-exponential in the size of the LTL specification. We introduce a fragment of LTL for which one can compute feasible control policies in time polynomial in the size of the system and specification. Additionally, we show how to compute optimal control policies for a variety of cost functions, and identify interesting cases when this can be done in polynomial time. These techniques are particularly relevant for online control, as one can guarantee that a feasible solution can be found quickly, and then iteratively improve on the quality as time permits.
\r\n\r\nThe final contribution of this thesis is a set of algorithms for computing feasible trajectories for high-dimensional, nonlinear systems with LTL specifications. These algorithms avoid a potentially computationally-expensive process of computing a discrete abstraction, and instead compute directly on the system's continuous state space. The first method uses an automaton representing the specification to directly encode a series of constrained-reachability subproblems, which can be solved in a modular fashion by using standard techniques. The second method encodes an LTL formula as mixed-integer linear programming constraints on the dynamical system. We demonstrate these approaches with numerical experiments on temporal logic motion planning problems with high-dimensional (10+ states) continuous systems.
" }, { "name": "Wu, Stephen", "degree": "PhD", "year": "2014", "title": "Future of Earthquake Early Warning: Quantifying Uncertainty and Making Fast Automated Decisions for Applications", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192014-145205444", "creators": [ { "name": { "family": "Wu", "given": "Stephen" }, "id": "Wu-Stephen", "display_name": "Wu, Stephen" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "chair", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Cochran", "given": "Elizabeth S." }, "id": "Cochran-E-S", "role": "member", "display_name": "Cochran, Elizabeth S." }, { "name": { "family": "Gillen", "given": "Benjamin J." }, "id": "Gillen-B-J", "role": "member", "display_name": "Gillen, Benjamin J." } ], "option_major": [ "civileng" ], "doi": "10.7907/EK7V-7A89", "abstract": "Earthquake early warning (EEW) systems have been rapidly developing over the past decade. Japan Meteorological Agency (JMA) has an EEW system that was operating during the 2011 M9 Tohoku earthquake in Japan, and this increased the awareness of EEW systems around the world. While longer-time earthquake prediction still faces many challenges to be practical, the availability of shorter-time EEW opens up a new door for earthquake loss mitigation. After an earthquake fault begins rupturing, an EEW system utilizes the first few seconds of recorded seismic waveform data to quickly predict the hypocenter location, magnitude, origin time and the expected shaking intensity level around the region. This early warning information is broadcast to different sites before the strong shaking arrives. The warning lead time of such a system is short, typically a few seconds to a minute or so, and the information is uncertain. These factors limit human intervention to activate mitigation actions and this must be addressed for engineering applications of EEW. This study applies a Bayesian probabilistic approach along with machine learning techniques and decision theories from economics to improve different aspects of EEW operation, including extending it to engineering applications.
\r\n\r\nExisting EEW systems are often based on a deterministic approach. Often, they assume that only a single event occurs within a short period of time, which led to many false alarms after the Tohoku earthquake in Japan. This study develops a probability-based EEW algorithm based on an existing deterministic model to extend the EEW system to the case of concurrent events, which are often observed during the aftershock sequence after a large earthquake.
\r\n\r\nTo overcome the challenge of uncertain information and short lead time of EEW, this study also develops an earthquake probability-based automated decision-making (ePAD) framework to make robust decision for EEW mitigation applications. A cost-benefit model that can capture the uncertainties in EEW information and the decision process is used. This approach is called the Performance-Based Earthquake Early Warning, which is based on the PEER Performance-Based Earthquake Engineering method. Use of surrogate models is suggested to improve computational efficiency. Also, new models are proposed to add the influence of lead time into the cost-benefit analysis. For example, a value of information model is used to quantify the potential value of delaying the activation of a mitigation action for a possible reduction of the uncertainty of EEW information in the next update. Two practical examples, evacuation alert and elevator control, are studied to illustrate the ePAD framework. Potential advanced EEW applications, such as the case of multiple-action decisions and the synergy of EEW and structural health monitoring systems, are also discussed.
" }, { "name": "Xuan, Yuan", "degree": "PhD", "year": "2014", "title": "Progress in Numerical Modeling of Non-Premixed Combustion", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292014-112456783", "creators": [ { "name": { "family": "Xuan", "given": "Yuan" }, "id": "Xuan-Yuan", "orcid": "0000-0001-9326-2197", "display_name": "Xuan, Yuan" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZED4-A872", "abstract": "Progress is made on the numerical modeling of both laminar and turbulent non-premixed flames. Instead of solving the transport equations for the numerous species involved in the combustion process, the present study proposes reduced-order combustion models based on local flame structures.
\r\n\r\nFor laminar non-premixed flames, curvature and multi-dimensional diffusion effects are found critical for the accurate prediction of sooting tendencies. A new numerical model based on modified flamelet equations is proposed. Sooting tendencies are calculated numerically using the proposed model for a wide range of species. These first numerically-computed sooting tendencies are in good agreement with experimental data. To further quantify curvature and multi-dimensional effects, a general flamelet formulation is derived mathematically. A budget analysis of the general flamelet equations is performed on an axisymmetric laminar diffusion flame. A new chemistry tabulation method based on the general flamelet formulation is proposed. This new tabulation method is applied to the same flame and demonstrates significant improvement compared to previous techniques.
\r\n\r\nFor turbulent non-premixed flames, a new model to account for chemistry-turbulence interactions is proposed. %It is found that these interactions are not important for radicals and small species, but substantial for aromatic species. The validity of various existing flamelet-based chemistry tabulation methods is examined, and a new linear relaxation model is proposed for aromatic species. The proposed relaxation model is validated against full chemistry calculations. To further quantify the importance of aromatic chemistry-turbulence interactions, Large-Eddy Simulations (LES) have been performed on a turbulent sooting jet flame. %The aforementioned relaxation model is used to provide closure for the chemical source terms of transported aromatic species. The effects of turbulent unsteadiness on soot are highlighted by comparing the LES results with a separate LES using fully-tabulated chemistry. It is shown that turbulent unsteady effects are of critical importance for the accurate prediction of not only the inception locations, but also the magnitude and fluctuations of soot.
" }, { "name": "Zevalkink, Alexandra", "degree": "PhD", "year": "2014", "title": "Chain-Forming Zintl Antimonidcs as Novel Thermoelectric Materials", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:10182013-151558126", "creators": [ { "name": { "family": "Zevalkink", "given": "Alexandra" }, "id": "Zevalkink-Alexandra", "display_name": "Zevalkink, Alexandra" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/YDSW-A554", "abstract": "Zintl phases, a subset of intermetallic compounds characterized by covalently-bonded \"sub-structures,\" surrounded by highly electropositive cations, exhibit precisely the characteristics desired for thermoelectric applications. The requirement that Zintl compounds satisfy the valence of anions through the formation of covalent substructures leads to many unique, complex crystal structures. Such complexity often leads to exceptionally low lattice thermal conductivity due to the containment of heat in low velocity optical modes in the phonon dispersion. To date, excellent thermoelectric properties have been demonstrated in several Zintl compounds. However, compared with the large number of known Zintl phases, very few have been investigated as thermoelectric materials.
\r\n\r\nFrom this pool of uninvestigated compounds, we selected a class of Zintl antimonides that share a common structural motif: anionic moieties resembling infinite chains of linked MSb4 tetrahedra, where $M$ is a triel element. The compounds discussed in this thesis (
The work in this thesis develops two types of microimplants for the application of cardiovascular in vivo biomedical sensing, one for short-term diagnosis and the other for long-term monitoring.
\r\n\r\nDespite advances in diagnosis and therapy, atherosclerotic cardiovascular disease remains the leading cause of morbidity and mortality in the Western world. Predicting metabolically active atherosclerotic plaques has remained an unmet clinical need. A stretchable impedance sensor manifested as a pair of quasi-concentric microelectrodes was developed to detect unstable intravascular. By integrating the impedance sensor with a cardiac catheter, high-resolution Electrochemical Impedance Spectroscopy (EIS) measurements can be conducted during cardiac catheterization. An inflatable silicone balloon is added to the sensor to secure a well-controlled contact with the plaque under test in vivo. By deploying the device to the explants of NZW rabbit aorta and live animals, distinct EIS measurements were observed for unstable atherosclerotic plaques that harbored active lipids and inflammatory cells.
\r\n\r\nOn the other hand, zebrafish (Danio rerio) is an emerging genetic model for heart regenerative medicine. In humans, myocardial infarction results in the irreversible loss of cardiomyocytes. Zebrafish hearts can fully regenerate after two months with 20% ventricular resection. Long-term electrocardiogram (ECG) recording can characterize the heart regeneration in a functional dimension. A flexible microelectrode membrane was developed to be percutaneously implanted onto a zebrafish heart and record epicardial ECG signals from specific regions on it. Region-specific aberrant cardiac signals were obtained from injured and regenerated hearts. Following that, in order to achieve continuous and wireless recording from non-sedated and non-restricted small animal models, a wireless ECG recording system was designed for the microelectrode membrane, prototyped on a printed circuit board and demonstrated on a one-day-old neonatal mouse. Furthermore, a flexible and compact parylene C printed circuit membrane was used as the integration platform for the wireless ECG recording electronics. A substantially miniature wireless ECG recording system was achieved.
" }, { "name": "van Breugel, Floris", "degree": "PhD", "year": "2014", "title": "Complex Behavior and Perception in Drosophila Emerges from Iterative Feedback-Regulated Reflexes", "advisor": "Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01032014-164946523", "creators": [ { "name": { "family": "van Breugel", "given": "Floris" }, "id": "van-Breugel-Floris", "orcid": "0000-0001-6538-7179", "display_name": "van Breugel, Floris" } ], "advisors": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Riffell", "given": "Jeff" }, "id": "Riffell-J", "role": "member", "display_name": "Riffell, Jeff" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "cds" ], "doi": "10.7907/WSE4-WG98", "abstract": "For a hungry fruit fly, locating and landing on a fermenting fruit where it can feed, find mates, and lay eggs, is an essential and difficult task requiring the integration of both olfactory and visual cues. Understanding how flies accomplish this will help provide a comprehensive ethological context for the expanding knowledge of their neural circuits involved in processing olfaction and vision, as well as inspire novel engineering solutions for control and estimation in computationally limited robotic applications. In this thesis, I use novel high throughput methods to develop a detailed overview of how flies track odor plumes, land, and regulate flight speed. Finally, I provide an example of how these insights can be applied to robotic applications to simplify complicated estimation problems. To localize an odor source, flies exhibit three iterative, reflex-driven behaviors. Upon encountering an attractive plume, flies increase their flight speed and turn upwind using visual cues. After losing the plume, flies begin zigzagging crosswind, again using visual cues to control their heading. After sensing an attractive odor, flies become more attracted to small visual features, which increases their chances of finding the plume source. Their changes in heading are largely controlled by open-loop maneuvers called saccades, which they direct towards and away from visual features. If a fly decides to land on an object, it begins to decelerate so as to maintain a stereotypical ratio of expansion to retinal size. Once they reach a stereotypical distance from the target, flies extend their legs in preparation for touchdown. Although it is unclear what cues they use to trigger this behavior, previous studies have indicated that it is likely under visual control. In Chapter 3, I use a nonlinear control theoretic analysis and robotic testbed to propose a novel and putative mechanism for how a fly might visually estimate distance by actively decelerating according to a visual control law. Throughout these behaviors, a common theme is the visual control of flight speed. Using genetic tools I show that the neuromodulator octopamine plays an important role in regulating flight speed, and propose a neural circuit for how this controller might be implemented in the flies brain. Two general biological and engineering principles are evident across my experiments: (1) complex behaviors, such as foraging, can emerge from the interactions of simple independent sensory-motor modules; (2) flies control their behavior in such a way that simplifies complex estimation problems.
" }, { "name": "Akgiray, Ahmed Halid", "degree": "PhD", "year": "2013", "title": "New Technologies Driving Decade-Bandwidth Radio Astronomy: Quad-ridged Flared Horn and Compound-Semiconductor LNAs", "advisor": "Weinreb, Sander", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292013-140750287", "creators": [ { "name": { "family": "Akgiray", "given": "Ahmed Halid" }, "id": "Akgiray-Ahmed-Halid", "display_name": "Akgiray, Ahmed Halid" } ], "advisors": [ { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "advisor", "display_name": "Weinreb, Sander" } ], "committee": [ { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "chair", "display_name": "Weinreb, Sander" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Imbriale", "given": "William A." }, "id": "Imbriale-W-A", "role": "member", "display_name": "Imbriale, William A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/TYX5-2C48", "abstract": "Among the branches of astronomy, radio astronomy is unique in that it spans the largest portion of the electromagnetic spectrum, e.g., from about 10 MHz to 300 GHz. On the other hand, due to scientific priorities as well as technological limitations, radio astronomy receivers have traditionally covered only about an octave bandwidth. This approach of \"one specialized receiver for one primary science goal\" is, however, not only becoming too expensive for next-generation radio telescopes comprising thousands of small antennas, but also is inadequate to answer some of the scientific questions of today which require simultaneous coverage of very large bandwidths.
\r\n\r\nThis thesis presents significant improvements on the state of the art of two key receiver components in pursuit of decade-bandwidth radio astronomy: 1) reflector feed antennas; 2) low-noise amplifiers on compound-semiconductor technologies. The first part of this thesis introduces the quadruple-ridged flared horn, a flexible, dual linear-polarization reflector feed antenna that achieves 5:1-7:1 frequency bandwidths while maintaining near-constant beamwidth. The horn is unique in that it is the only wideband feed antenna suitable for radio astronomy that: 1) can be designed to have nominal 10 dB beamwidth between 30 and 150 degrees; 2) requires one single-ended 50 Ohm low-noise amplifier per polarization. Design, analysis, and measurements of several quad-ridged horns are presented to demonstrate its feasibility and flexibility.
\r\n\r\nThe second part of the thesis focuses on modeling and measurements of discrete high-electron mobility transistors (HEMTs) and their applications in wideband, extremely low-noise amplifiers. The transistors and microwave monolithic integrated circuit low-noise amplifiers described herein have been fabricated on two state-of-the-art HEMT processes: 1) 35 nm indium phosphide; 2) 70 nm gallium arsenide. DC and microwave performance of transistors from both processes at room and cryogenic temperatures are included, as well as first-reported measurements of detailed noise characterization of the sub-micron HEMTs at both temperatures. Design and measurements of two low-noise amplifiers covering 1--20 and 8\u201450 GHz fabricated on both processes are also provided, which show that the 1--20 GHz amplifier improves the state of the art in cryogenic noise and bandwidth, while the 8--50 GHz amplifier achieves noise performance only slightly worse than the best published results but does so with nearly a decade bandwidth.
\r\n" }, { "name": "Aria, Adrianus Indrat", "degree": "PhD", "year": "2013", "title": "Control of Wettability of Carbon Nanotube Array by Reversible Dry Oxidation for Superhydrophobic Coating and Supercapacitor Applications", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012013-192515668", "creators": [ { "name": { "family": "Aria", "given": "Adrianus Indrat" }, "id": "Aria-Adrianus-Indrat", "display_name": "Aria, Adrianus Indrat" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "orcid": "0000-0001-5356-4385", "role": "member", "display_name": "Heath, James R." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B6MF-FX89", "abstract": "In this thesis, dry chemical modification methods involving UV/ozone, oxygen plasma, and vacuum annealing treatments are explored to precisely control the wettability of CNT arrays. By varying the exposure time of these treatments the surface concentration of oxygenated groups adsorbed on the CNT arrays can be controlled. CNT arrays with very low amount of oxygenated groups exhibit a superhydrophobic behavior. In addition to their extremely high static contact angle, they cannot be dispersed in DI water and their impedance in aqueous electrolytes is extremely high. These arrays have an extreme water repellency capability such that a water droplet will bounce off of their surface upon impact and a thin film of air is formed on their surface as they are immersed in a deep pool of water. In contrast, CNT arrays with very high surface concentration of oxygenated functional groups exhibit an extreme hydrophilic behavior. In addition to their extremely low static contact angle, they can be dispersed easily in DI water and their impedance in aqueous electrolytes is tremendously low. Since the bulk structure of the CNT arrays are preserved during the UV/ozone, oxygen plasma, and vacuum annealing treatments, all CNT arrays can be repeatedly switched between superhydrophilic and superhydrophobic, as long as their O/C ratio is kept below 18%.
\r\n\r\nThe effect of oxidation using UV/ozone and oxygen plasma treatments is highly reversible as long as the O/C ratio of the CNT arrays is kept below 18%. At O/C ratios higher than 18%, the effect of oxidation is no longer reversible. This irreversible oxidation is caused by irreversible changes to the CNT atomic structure during the oxidation process. During the oxidation process, CNT arrays undergo three different processes. For CNT arrays with O/C ratios lower than 40%, the oxidation process results in the functionalization of CNT outer walls by oxygenated groups. Although this functionalization process introduces defects, vacancies and micropores opening, the graphitic structure of the CNT is still largely intact. For CNT arrays with O/C ratios between 40% and 45%, the oxidation process results in the etching of CNT outer walls. This etching process introduces large scale defects and holes that can be obviously seen under TEM at high magnification. Most of these holes are found to be several layers deep and, in some cases, a large portion of the CNT side walls are cut open. For CNT arrays with O/C ratios higher than 45%, the oxidation process results in the exfoliation of the CNT walls and amorphization of the remaining CNT structure. This amorphization process can be implied from the disappearance of C-C sp2 peak in the XPS spectra associated with the pi-bond network.
\r\n\r\nThe impact behavior of water droplet impinging on superhydrophobic CNT arrays in a low viscosity regime is investigated for the first time. Here, the experimental data are presented in the form of several important impact behavior characteristics including critical Weber number, volume ratio, restitution coefficient, and maximum spreading diameter. As observed experimentally, three different impact regimes are identified while another impact regime is proposed. These regimes are partitioned by three critical Weber numbers, two of which are experimentally observed. The volume ratio between the primary and the secondary droplets is found to decrease with the increase of Weber number in all impact regimes other than the first one. In the first impact regime, this is found to be independent of Weber number since the droplet remains intact during and subsequent to the impingement. Experimental data show that the coefficient of restitution decreases with the increase of Weber number in all impact regimes. The rate of decrease of the coefficient of restitution in the high Weber number regime is found to be higher than that in the low and moderate Weber number. Experimental data also show that the maximum spreading factor increases with the increase of Weber number in all impact regimes. The rate of increase of the maximum spreading factor in the high Weber number regime is found to be higher than that in the low and moderate Weber number. Phenomenological approximations and interpretations of the experimental data, as well as brief comparisons to the previously proposed scaling laws, are shown here.
\r\n\r\nDry oxidation methods are used for the first time to characterize the influence of oxidation on the capacitive behavior of CNT array EDLCs. The capacitive behavior of CNT array EDLCs can be tailored by varying their oxygen content, represented by their O/C ratio. The specific capacitance of these CNT arrays increases with the increase of their oxygen content in both KOH and Et4NBF4/PC electrolytes. As a result, their gravimetric energy density increases with the increase of their oxygen content. However, their gravimetric power density decreases with the increase of their oxygen content. The optimally oxidized CNT arrays are able to withstand more than 35,000 charge/discharge cycles in Et4NBF4/PC at a current density of 5 A/g while only losing 10% of their original capacitance.
" }, { "name": "Azizgolshani, Hesham", "degree": "PhD", "year": "2013", "title": "Tissue Engineering Active Biological Machines: Bio-Inspired Design, Directed Self-Assembly, and Characterization of Muscular Pumps Simulating the Embryonic Heart", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232013-150116734", "creators": [ { "name": { "family": "Azizgolshani", "given": "Hesham" }, "id": "Azizgolshani-Hesham", "display_name": "Azizgolshani, Hesham" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "bioeng" ], "doi": "10.7907/2C8T-TB84", "abstract": "Biological machines are active devices that are comprised of cells and other biological components. These functional devices are best suited for physiological environments that support cellular function and survival. Biological machines have the potential to revolutionize the engineering of biomedical devices intended for implantation, where the human body can provide the required physiological environment. For engineering such cell-based machines, bio-inspired design can serve as a guiding platform as it provides functionally proven designs that are attainable by living cells. In the present work, a systematic approach was used to tissue engineer one such machine by exclusively using biological building blocks and by employing a bio-inspired design. Valveless impedance pumps were constructed based on the working principles of the embryonic vertebrate heart and by using cells and tissue derived from rats. The function of these tissue-engineered muscular pumps was characterized by exploring their spatiotemporal and flow behavior in order to better understand the capabilities and limitations of cells when used as the engines of biological machines." }, { "name": "Bourguignon, Jean-Loup", "degree": "PhD", "year": "2013", "title": "Models of Turbulent Pipe Flow", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11272012-130849053", "creators": [ { "name": { "family": "Bourguignon", "given": "Jean-Loup" }, "id": "Bourguignon-Jean-Loup", "display_name": "Bourguignon, Jean-Loup" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BPEZ-VM28", "abstract": "The physics of turbulent pipe flow was investigated via the use of two models based on simplified versions of the Navier-Stokes equations. The first model was a streamwise-constant projection of these equations, and was used to study the change in mean flow that occurs during transition to turbulence. The second model was based on the analysis of the turbulent pipe flow resolvent, and provided a radial basis for the modal decomposition of turbulent pipe flow. The two models were tested numerically and validated against experimental and numerical data.
\r\n\r\nAnalysis of the streamwise-constant model showed that both non-normal and nonlinear effects are required to capture the blunting of the velocity profile, which occurs during pipe flow transition. The model generated flow fields characterized by the presence of high- and low-speed streaks, whose distribution over the cross-section of the pipe was remarkably similar to the one observed in the velocity field near the trailing edge of the puff structures present in pipe flow transition.
\r\n\r\nA modal decomposition of turbulent pipe flow, in the three spatial directions and in time, was performed, and made possible by the significant reduction in data requirements achieved via the use of compressive sampling and model-based radial basis functions. The application and efficiency of compressive sampling in wall-bounded turbulence was demonstrated.
\r\n\r\nApproximately sparse representations of turbulent pipe flow by propagating waves with model-based radial basis functions, were derived. The basis functions, obtained by singular value decomposition of the resolvent, captured the wall-normal coherence of the flow; and provided a link between the propagating waves and the governing equations, allowing for the identification of the dominant mechanims sustaining the waves, as a function of their streamwise wavenumber.
\r\n\r\nAnalysis of the resolvent showed that the long streamwise waves are amplified mainly via non-normality effects, and are also constrained to be tall in the wall-normal direction, which decreases the influence of viscous dissipation. The short streamwise waves were shown to be localized near the critical-layer (defined as the wall-normal location where the convection velocity of the wave equals the local mean velocity), and thus exhibit amplification with a large contribution from criticality. The work in this thesis allows the reconciliation of the well-known results concerning optimal disturbance amplification due to non-normal effects with recent resolvent analyses, which highlighted the importance of criticality effects.
\r\n" }, { "name": "Burgos, Stanley P.", "degree": "PhD", "year": "2013", "title": "Coupled Plasmonic Systems and Devices: Applications in Visible Metamaterials, Nanophotonic Circuits, and CMOS Imaging", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042013-150337959", "creators": [ { "name": { "family": "Burgos", "given": "Stanley P." }, "id": "Burgos-Stanley-P", "display_name": "Burgos, Stanley P." } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/N2JK-5318", "abstract": "With the size of transistors approaching the sub-nanometer scale and Si-based photonics pinned at the micrometer scale due to the diffraction limit of light, we are unable to easily integrate the high transfer speeds of this comparably bulky technology with the increasingly smaller architecture of state-of-the-art processors. However, we find that we can bridge the gap between these two technologies by directly coupling electrons to photons through the use of dispersive metals in optics. Doing so allows us to access the surface electromagnetic wave excitations that arise at a metal/dielectric interface, a feature which both confines and enhances light in subwavelength dimensions - two promising characteristics for the development of integrated chip technology. This platform is known as plasmonics, and it allows us to design a broad range of complex metal/dielectric systems, all having different nanophotonic responses, but all originating from our ability to engineer the system surface plasmon resonances and interactions. In this thesis, we demonstrate how plasmonics can be used to develop coupled metal-dielectric systems to function as tunable plasmonic hole array color filters for CMOS image sensing, visible metamaterials composed of coupled negative-index plasmonic coaxial waveguides, and programmable plasmonic waveguide network systems to serve as color routers and logic devices at telecommunication wavelengths. " }, { "name": "Censi, Andrea", "degree": "PhD", "year": "2013", "title": "Bootstrapping Vehicles: A Formal Approach to Unsupervised Sensorimotor Learning Based on Invariance", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10282012-082208075", "creators": [ { "name": { "family": "Censi", "given": "Andrea" }, "id": "Censi-Andrea", "display_name": "Censi, Andrea" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Soatto", "given": "Stefano" }, "id": "Soatto-Stefano", "role": "member", "display_name": "Soatto, Stefano" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "cds" ], "doi": "10.7907/PWVS-2Q74", "abstract": "Could a \"brain in a jar\" be able to control an unknown robotic body to which it is connected, and use it to achieve useful tasks, without any prior assumptions on the body's sensors and actuators? Other than of purely intellectual interest, this question is relevant to the medium-term challenges of robotics: as the complexity of robotics applications grows, automated learning techniques might reduce design effort and increase the robustness and reliability of the solutions. In this work, the problem of \"bootstrapping\" is studied in the context of the Vehicles universe, which is an idealization of simple mobile robots, after the work of Braitenberg. The first thread of results consists in analyzing such simple sensorimotor cascades and proposing models of varying complexity that can be learned from data. The second thread regards how to properly formalize the notions of \"absence of assumptions\", as a particular form of invariance that the bootstrapping agent must satisfy, and proposes some invariance-based design techniques." }, { "name": "Chandra, Fiona Adriani", "degree": "PhD", "year": "2013", "title": "Limits and Tradeoffs in the Control of Autocatalytic Systems", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032013-143158080", "creators": [ { "name": { "family": "Chandra", "given": "Fiona Adriani" }, "id": "Chandra-Fiona-Adriani", "display_name": "Chandra, Fiona Adriani" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "DiStefano", "given": "Joseph" }, "id": "DiStefano-J-D", "role": "member", "display_name": "DiStefano, Joseph" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "bioeng" ], "doi": "10.7907/Z1BQ-ZX85", "abstract": "Despite the complexity of biological networks, we find that certain common architectures govern network structures. These architectures impose fundamental constraints on system performance and create tradeoffs that the system must balance in the face of uncertainty in the environment. This means that while a system may be optimized for a specific function through evolution, the optimal achievable state must follow these constraints. One such constraining architecture is autocatalysis, as seen in many biological networks including glycolysis and ribosomal protein synthesis. Using a minimal model, we show that ATP autocatalysis in glycolysis imposes stability and performance constraints and that the experimentally well-studied glycolytic oscillations are in fact a consequence of a tradeoff between error minimization and stability. We also show that additional complexity in the network results in increased robustness. Ribosome synthesis is also autocatalytic where ribosomes must be used to make more ribosomal proteins. When ribosomes have higher protein content, the autocatalysis is increased. We show that this autocatalysis destabilizes the system, slows down response, and also constrains the system\u2019s performance. On a larger scale, transcriptional regulation of whole organisms also follows architectural constraints and this can be seen in the differences between bacterial and yeast transcription networks. We show that the degree distributions of bacterial transcription network follow a power law distribution while the yeast network follows an exponential distribution. We then explored the evolutionary models that have previously been proposed and show that neither the preferential linking model nor the duplication-divergence model of network evolution generates the power-law, hierarchical structure found in bacteria. However, in real biological systems, the generation of new nodes occurs through both duplication and horizontal gene transfers, and we show that a biologically reasonable combination of the two mechanisms generates the desired network." }, { "name": "Chen, Tong", "degree": "PhD", "year": "2013", "title": "Ultralow-Loss Silica Resonators and Waveguides on a Silicon Chip", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072013-163825736", "creators": [ { "name": { "family": "Chen", "given": "Tong" }, "id": "Chen-Tong", "display_name": "Chen, Tong" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/QBR4-3980", "abstract": "Compared to fiber optic systems, on-chip optical devices provide reasonable optical performance and mechanical stability in a smaller footprint and at a lower cost. Such devices, including resonators and waveguides, have been applied in diverse areas of scientific research, including quantum information, nonlinear optics, cavity optomechanics, telecommunications, biodetection, rotation sensing, high stability microwave oscillators, and all-optical signal processing. As performance demands on these applications increase, resonators and waveguides with ultralow propagation loss become critical.
\r\n \r\nIn this thesis, we first demonstrate a new resonator with a record Q factor of 875 million for on-chip devices. The fabrication of our device avoids the requirement for a specialized processing step, which in microtoroid resonators has made it difficult to control their size and achieve millimeter- and centimeter-scale diameters. Attaining these sizes is important in applications such as microcombs. The resonators not only set a new benchmark for the Q factor on a chip, but also provide, for the first time, full compatibility of this important device class with conventional semiconductor processing.
\r\n\r\nMeanwhile, we demonstrate a monolithic waveguide as long as 27 m (39 m optical path length), and featuring broadband loss rate values of (0.08 \u00b1 0.01) dB/m measured over 7 m by optical backscattering. Resonator measurements show a further reduction of loss to 0.037 dB/m, close to that of optical fibers when first considered a viable technology. Scaling this waveguide to integrated spans exceeding 250 m and attenuation rates below 0.01 dB/m is discussed. This chip-based waveguide and resonator improve shock resistance, and afford the possibility of integration for system-on-a chip functionality.
\r\n\r\nWe finally demonstrate a highly sensitive nanoparticle and virus detection method by using a thermal-stabilized reference interferometer in conjunction with an ultrahigh-Q microcavity. Sensitivity is sufficient to resolve shifts caused by binding of individual nanobeads in solution down to a record radius of 12.5 nm, a size approaching that of single protein molecules. A histogram of wavelength shift versus nanoparticle radius shows that particle size can be inferred from shift maxima.
" }, { "name": "Cheng, Mulin", "degree": "PhD", "year": "2013", "title": "Adaptive Methods Exploring Intrinsic Sparse Structures of Stochastic Partial Differential Equations", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09182012-175436855", "creators": [ { "name": { "family": "Cheng", "given": "Mulin" }, "id": "Cheng-Mulin", "display_name": "Cheng, Mulin" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/V638-V403", "abstract": "Many physical and engineering problems involving uncertainty enjoy certain low-dimensional structures, e.g., in the sense of Karhunen-Loeve expansions (KLEs), which in turn indicate the existence of reduced-order models and better formulations for efficient numerical simulations. In this thesis, we target a class of time-dependent stochastic partial differential equations whose solutions enjoy such structures at any time and propose a new methodology (DyBO) to derive equivalent systems whose solutions closely follow KL expansions of the original stochastic solutions. KL expansions are known to be the most compact representations of stochastic processes in an L2 sense. Our methods explore such sparsity and offer great computational benefits compared to other popular generic methods, such as traditional Monte Carlo (MC), generalized Polynomial Chaos (gPC) method, and generalized Stochastic Collocation (gSC) method. Such benefits are demonstrated through various numerical examples ranging from spatially one-dimensional examples, such as stochastic Burgers' equations and stochastic transport equations to spatially two-dimensional examples, such as stochastic flows in 2D unit square. Parallelization is also discussed, aiming toward future industrial-scale applications. In addition to numerical examples, theoretical aspects of DyBO are also carefully analyzed, such as preservation of bi-orthogonality, error propagation, and computational complexity. Based on theoretical analysis, strategies are proposed to overcome difficulties in numerical implementations, such as eigenvalue crossing and adaptively adding or removing mode pairs. The effectiveness of the proposed strategies is numerically verified. Generalization to a system of SPDEs is considered as well in the thesis, and its success is demonstrated by applications to stochastic Boussinesq convection problems. Other generalizations, such as generalized stochastic collocation formulation of DyBO method, are also discussed. " }, { "name": "Crane, Keenan Michael", "degree": "PhD", "year": "2013", "title": "Conformal Geometry Processing", "advisor": "Schroeder, Peter; Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052013-020706629", "creators": [ { "name": { "family": "Crane", "given": "Keenan Michael" }, "id": "Crane-Keenan-Michael", "display_name": "Crane, Keenan Michael" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "role": "advisor", "display_name": "Schroeder, Peter" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "co-advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Markovic", "given": "Vladimir" }, "id": "Markovic-V", "role": "member", "display_name": "Markovic, Vladimir" }, { "name": { "family": "Pinkall", "given": "Ulrich" }, "id": "Pinkall-U", "orcid": "0000-0002-2087-6435", "role": "member", "display_name": "Pinkall, Ulrich" } ], "option_major": [ "compsci" ], "doi": "10.7907/8V9Z-N286", "abstract": "This thesis introduces fundamental equations and numerical methods for manipulating surfaces in three dimensions via conformal transformations. Conformal transformations are valuable in applications because they naturally preserve the integrity of geometric data. To date, however, there has been no clearly stated and consistent theory of conformal transformations that can be used to develop general-purpose geometry processing algorithms: previous methods for computing conformal maps have been restricted to the flat two-dimensional plane, or other spaces of constant curvature. In contrast, our formulation can be used to produce---for the first time---general surface deformations that are perfectly conformal in the limit of refinement. It is for this reason that we commandeer the title Conformal Geometry Processing.
\r\n\r\nThe main contribution of this thesis is analysis and discretization of a certain time-independent Dirac equation, which plays a central role in our theory. Given an immersed surface, we wish to construct new immersions that (i) induce a conformally equivalent metric and (ii) exhibit a prescribed change in extrinsic curvature. Curvature determines the potential in the Dirac equation; the solution of this equation determines the geometry of the new surface. We derive the precise conditions under which curvature is allowed to evolve, and develop efficient numerical algorithms for solving the Dirac equation on triangulated surfaces.
\r\n\r\nFrom a practical perspective, this theory has a variety of benefits: conformal maps are desirable in geometry processing because they do not exhibit shear, and therefore preserve textures as well as the quality of the mesh itself. Our discretization yields a sparse linear system that is simple to build and can be used to efficiently edit surfaces by manipulating curvature and boundary data, as demonstrated via several mesh processing applications. We also present a formulation of Willmore flow for triangulated surfaces that permits extraordinarily large time steps and apply this algorithm to surface fairing, geometric modeling, and construction of constant mean curvature (CMC) surfaces.
" }, { "name": "Dabby, Nadine L.", "degree": "PhD", "year": "2013", "title": "Synthetic Molecular Machines for Active Self-Assembly: Prototype Algorithms, Designs, and Experimental Study", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05122013-221658522", "creators": [ { "name": { "family": "Dabby", "given": "Nadine L." }, "id": "Dabby-Nadine-L", "display_name": "Dabby, Nadine L." } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Stojanovic", "given": "Milan N." }, "id": "Stojanovic-M-N", "role": "member", "display_name": "Stojanovic, Milan N." }, { "name": { "family": "Fygenson", "given": "Deborah K." }, "id": "Fygenson-D-K", "role": "member", "display_name": "Fygenson, Deborah K." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cns" ], "doi": "10.7907/T0ZG-PA07", "abstract": "Computer science and electrical engineering have been the great success story of the twentieth century. The neat modularity and mapping of a language onto circuits has led to robots on Mars, desktop computers and smartphones. But these devices are not yet able to do some of the things that life takes for granted: repair a scratch, reproduce, regenerate, or grow exponentially fast\u2013all while remaining functional.
\r\n\r\nThis thesis explores and develops algorithms, molecular implementations, and theoretical proofs in the context of \u201cactive self-assembly\u201d of molecular systems. The long-term vision of active self-assembly is the theoretical and physical implementation of materials that are composed of reconfigurable units with the programmability and adaptability of biology\u2019s numerous molecular machines. En route to this goal, we must first find a way to overcome the memory limitations of molecular systems, and to discover the limits of complexity that can be achieved with individual molecules.
\r\n\r\nOne of the main thrusts in molecular programming is to use computer science as a tool for figuring out what can be achieved. While molecular systems that are Turing-complete have been demonstrated [Winfree, 1996], these systems still cannot achieve some of the feats biology has achieved.
\r\n\r\nOne might think that because a system is Turing-complete, capable of computing \u201canything,\u201d that it can do any arbitrary task. But while it can simulate any digital computational problem, there are many behaviors that are not \u201ccomputations\u201d in a classical sense, and cannot be directly implemented. Examples include exponential growth and molecular motion relative to a surface.
\r\n\r\n\r\nPassive self-assembly systems cannot implement these behaviors because (a) molecular motion relative to a surface requires a source of fuel that is external to the system, and (b) passive systems are too slow to assemble exponentially-fast-growing structures. We call these behaviors \u201cenergetically incomplete\u201d programmable behaviors. This class of behaviors includes any behavior where a passive physical system simply does not have enough physical energy to perform the specified tasks in the requisite amount of time.
\r\n\r\n\r\nAs we will demonstrate and prove, a sufficiently expressive implementation of an \u201cactive\u201d molecular self-assembly approach can achieve these behaviors. Using an external source of fuel solves part of the the problem, so the system is not \u201cenergetically incomplete.\u201d But the programmable system also needs to have sufficient expressive power to achieve the specified behaviors. Perhaps surprisingly, some of these systems do not even require Turing completeness to be sufficiently expressive.
\r\n\r\n\r\nBuilding on a large variety of work by other scientists in the fields of DNA nanotechnology, chemistry and reconfigurable robotics, this thesis introduces several research contributions in the context of active self-assembly.
\r\n\r\n\r\nWe show that simple primitives such as insertion and deletion are able to generate complex and interesting results such as the growth of a linear polymer in logarithmic time and the ability of a linear polymer to treadmill. To this end we developed a formal model for active-self assembly that is directly implementable with DNA molecules. We show that this model is computationally equivalent to a machine capable of producing strings that are stronger than regular languages and, at most, as strong as context-free grammars. This is a great advance in the theory of active self- assembly as prior models were either entirely theoretical or only implementable in the context of macro-scale robotics.
\r\n\r\n\r\nWe developed a chain reaction method for the autonomous exponential growth of a linear DNA polymer. Our method is based on the insertion of molecules into the assembly, which generates two new insertion sites for every initial one employed. The building of a line in logarithmic time is a first step toward building a shape in logarithmic time. We demonstrate the first construction of a synthetic linear polymer that grows exponentially fast via insertion. We show that monomer molecules are converted into the polymer in logarithmic time via spectrofluorimetry and gel electrophoresis experiments. We also demonstrate the division of these polymers via the addition of a single DNA complex that competes with the insertion mechanism. This shows the growth of a population of polymers in logarithmic time. We characterize the DNA insertion mechanism that we utilize in Chapter 4. We experimentally demonstrate that we can control the kinetics of this re- action over at least seven orders of magnitude, by programming the sequences of DNA that initiate the reaction.
\r\n\r\n\r\nIn addition, we review co-authored work on programming molecular robots using prescriptive landscapes of DNA origami; this was the first microscopic demonstration of programming a molec- ular robot to walk on a 2-dimensional surface. We developed a snapshot method for imaging these random walking molecular robots and a CAPTCHA-like analysis method for difficult-to-interpret imaging data.
" }, { "name": "Damazo, Jason Scott", "degree": "PhD", "year": "2013", "title": "Planar Reflection of Gaseous Detonation", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112013-153305610", "creators": [ { "name": { "family": "Damazo", "given": "Jason Scott" }, "id": "Damazo-Jason-Scott", "orcid": "0000-0002-4155-7177", "display_name": "Damazo, Jason Scott" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4QW7-TK55", "abstract": "Pipes containing flammable gaseous mixtures may be subjected to internal detonation. When the detonation normally impinges on a closed end, a reflected shock wave is created to bring the flow back to rest. This study built on the work of Karnesky (2010) and examined deformation of thin-walled stainless steel tubes subjected to internal reflected gaseous detonations. A ripple pattern was observed in the tube wall for certain fill pressures, and a criterion was developed that predicted when the ripple pattern would form. A two-dimensional finite element analysis was performed using Johnson-Cook material properties; the pressure loading created by reflected gaseous detonations was accounted for with a previously developed pressure model. The residual plastic strain between experiments and computations was in good agreement.
\r\n\r\nDuring the examination of detonation-driven deformation, discrepancies were discovered in our understanding of reflected gaseous detonation behavior. Previous models did not accurately describe the nature of the reflected shock wave, which motivated further experiments in a detonation tube with optical access. Pressure sensors and schlieren images were used to examine reflected shock behavior, and it was determined that the discrepancies were related to the reaction zone thickness extant behind the detonation front. During these experiments reflected shock bifurcation did not appear to occur, but the unfocused visualization system made certainty impossible. This prompted construction of a focused schlieren system that investigated possible shock wave-boundary layer interaction, and heat-flux gauges analyzed the boundary layer behind the detonation front. Using these data with an analytical boundary layer solution, it was determined that the strong thermal boundary layer present behind the detonation front inhibits the development of reflected shock wave bifurcation.
" }, { "name": "Darvish, Davis Solomon", "degree": "PhD", "year": "2013", "title": "Cu\u2082O Substrates and Epitaxial Cu\u2082O/ZnO Thin Film Heterostructures for Solar Energy Conversion", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042013-144822210", "creators": [ { "name": { "family": "Darvish", "given": "Davis Solomon" }, "id": "Darvish-Davis-Solomon", "display_name": "Darvish, Davis Solomon" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/0KEM-KG56", "abstract": "Future fossil fuel scarcity and environmental degradation have demonstrated the need for renewable, low-carbon sources of energy to power an increasingly industrialized world. Solar energy with its infinite supply makes it an extraordinary resource that should not go unused. However with current materials, adoption is limited by cost and so a paradigm shift must occur to get everyone on the same page embracing solar technology. Cuprous Oxide (Cu\u2082O) is a promising earth abundant material that can be a great alternative to traditional thin-film photovoltaic materials like CIGS, CdTe, etc. We have prepared Cu\u2082O bulk substrates by the thermal oxidation of copper foils as well Cu\u2082O thin films deposited via plasma-assisted Molecular Beam Epitaxy. From preliminary Hall measurements it was determined that Cu\u2082O would need to be doped extrinsically. This was further confirmed by simulations of ZnO/Cu\u2082O heterojunctions. A cyclic interdependence between, defect concentration, minority carrier lifetime, film thickness, and carrier concentration manifests itself a primary reason for why efficiencies greater than 4% has yet to be realized. Our growth methodology for our thin-film heterostructures allow precise control of the number of defects that incorporate into our film during both equilibrium and nonequilibrium growth. We also report process flow/device design/fabrication techniques in order to create a device. A typical device without any optimizations exhibited open-circuit voltages Voc, values in excess 500mV; nearly 18% greater than previous solid state devices. " }, { "name": "DeLorimier, Michael John", "degree": "PhD", "year": "2013", "title": "GRAph Parallel Actor Language: A Programming Language for Parallel Graph Algorithms", "advisor": "DeHon, Andre; Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192012-145253489", "creators": [ { "name": { "family": "DeLorimier", "given": "Michael John" }, "id": "DeLorimier-Michael-John", "display_name": "DeLorimier, Michael John" } ], "advisors": [ { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "advisor", "display_name": "DeHon, Andre" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "co-advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "chair", "display_name": "DeHon, Andre" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shrobe", "given": "Howard" }, "id": "Shrobe-H", "role": "member", "display_name": "Shrobe, Howard" } ], "option_major": [ "compsci" ], "doi": "10.7907/M3TW-7Y53", "abstract": "We introduce a domain-specific language, GRAph Parallel Actor Language, that enables parallel graph algorithms to be written in a natural, high-level form. GRAPAL is based on our GraphStep compute model, which enables a wide range of parallel graph algorithms that are high-level, deterministic, free from race conditions, and free from deadlock. Programs written in GRAPAL are easy for a compiler and runtime to map to efficient parallel field programmable gate array (FPGA) implementations. We show that the GRAPAL compiler can verify that the structure of operations conforms to the GraphStep model. We allocate many small processing elements in each FPGA that take advantage of the high on-chip memory bandwidth (5x the sequential processor) and process one graph edge per clock cycle per processing element. We show how to automatically choose parameters for the logic architecture so the high-level GRAPAL programming model is independent of the target FPGA architecture. We compare our GRAPAL applications mapped to a platform with four 65 nm Virtex-5 SX95T FPGAs to sequential programs run on a single 65 nm Xeon 5160. Our implementation achieves a total mean speedup of 8x with a maximum speedup of 28x. The speedup per chip is 2x with a maximum of 7x. The ratio of energy used by our GRAPAL implementation over the sequential implementation has a mean of 1/10 with a minimum of 1/80." }, { "name": "Deceglie, Michael Gardner", "degree": "PhD", "year": "2013", "title": "Advanced Silicon Solar Cell Device Physics and Design", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:02152013-094838378", "creators": [ { "name": { "family": "Deceglie", "given": "Michael Gardner" }, "id": "Deceglie-Michael-Gardner", "display_name": "Deceglie, Michael Gardner" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/PV2J-1429", "abstract": "A fundamental challenge in the development and deployment of solar photovoltaic technology is a reduction in cost enabling direct competition with fossil-fuel-based energy sources. A key driver in this cost reduction is optimized device efficiency, because increased energy output leverages all photovoltaic system costs, from raw materials and module manufacturing to installation and maintenance. To continue progress toward higher conversion efficiencies, solar cells are being fabricated with increasingly complex designs, including engineered nanostructures, heterojunctions, and novel contacting and passivation schemes. Such advanced designs require a comprehensive and unified understanding of the optical and electrical device physics at the microscopic scale. This thesis focuses on a microscopic understanding of solar cell optoelectronic performance and its impact on cell optimization. We consider this in three solar cell platforms: thin-film crystalline silicon, amorphous/crystalline silicon heterojunctions, and thin-film cells with nanophotonic light trapping. The work described in this thesis represents a powerful design paradigm, based on a detailed physical understanding of the mechanisms governing solar cell performance. Furthermore, we demonstrate the importance of understanding not just the individual mechanisms, but also their interactions. Such an approach to device optimization is critical for the efficiency and competitiveness of future generations of solar cells." }, { "name": "Dikaliotis, Theodoros K.", "degree": "PhD", "year": "2013", "title": "On Delay and Security in Network Coding", "advisor": "Ho, Tracey C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292012-041022964", "creators": [ { "name": { "family": "Dikaliotis", "given": "Theodoros K." }, "id": "Dikaliotis-Theodoros-K", "display_name": "Dikaliotis, Theodoros K." } ], "advisors": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "advisor", "display_name": "Ho, Tracey C." } ], "committee": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "chair", "display_name": "Ho, Tracey C." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/1KE1-DW91", "abstract": "In this thesis, delay and security issues in network coding are considered. First, we study the delay incurred in the transmission of a fixed number of packets through acyclic networks comprised of erasure links. The two transmission schemes studied are routing with hop-by-hop retransmissions, where every node in the network simply stores and forwards its received packets, and linear coding, where nodes mix their packets by forwarding linear combinations of all their previously received packets. We show that even though the achievable rates of coding and routing are the same, network coding can have an increasingly better performance than routing as the number of packets increases.
\r\n\r\nSecondly, we investigate the security benefits of network coding. We investigate the achievable secrecy rate region in a general network of noisy wiretap channels with general communication demands. The eavesdropper has access to an unknown set of links, and on the wiretapped links observes a degraded version of the intended receiver's observation. While characterizing the capacity in general is an open problem, in the noise-free case there exist inner and outer bounds. In the noisy case, we show how one can change any of the wiretap channels to a noiseless degraded broadcast channel, so that the derived network's rate region bounds, and under certain conditions is equivalent, to that of the initial network. Specifically, we showed that in case the eavesdropper can choose only a single link to wiretap at each time, then one can change all the links in the network with corresponding noiseless ones, creating an equivalent noiseless secrecy problem. In the case where the eavesdropper can wiretap multiple links simultaneously, we derive upper and lower bounding noiseless network problems.
\r\n\r\nFinally, we consider design practical code design for the detection of adversarial errors in a distributed storage system. We build on work of functions that can fool linear polynomials to create and communicate hash functions of the data in order to detect with high probability the maliciously attacked nodes in the system.
" }, { "name": "Dubois, Julien Christian Roger", "degree": "PhD", "year": "2013", "title": "Studying Conscious and Unconscious Vision with Functional Magnetic Resonance Imaging : the BOLD Promise", "advisor": "Koch, Christof; Adolphs, Ralph", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-191910347", "creators": [ { "name": { "family": "Dubois", "given": "Julien Christian Roger" }, "id": "Dubois-Julien-Christian-Roger", "orcid": "0000-0002-3029-173X", "display_name": "Dubois, Julien Christian Roger" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "co-advisor", "display_name": "Adolphs, Ralph" } ], "committee": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "orcid": "0000-0003-0016-3531", "role": "chair", "display_name": "O'Doherty, John P." }, { "name": { "family": "Tsao", "given": "Doris Y." }, "id": "Tsao-D-Y", "orcid": "0000-0003-1083-1919", "role": "member", "display_name": "Tsao, Doris Y." }, { "name": { "family": "Tyszka", "given": "Julian Michael" }, "id": "Tyszka-J-M", "role": "member", "display_name": "Tyszka, Julian Michael" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "member", "display_name": "Adolphs, Ralph" } ], "option_major": [ "cns" ], "doi": "10.7907/7EGE-FG03", "abstract": "Waking up from a dreamless sleep, I open my eyes, recognize my wife\u2019s face and am filled with joy. In this thesis, I used functional Magnetic Resonance Imaging (fMRI) to gain insights into the mechanisms involved in this seemingly simple daily occurrence, which poses at least three great challenges to neuroscience: how does conscious experience arise from the activity of the brain? How does the brain process visual input to the point of recognizing individual faces? How does the brain store semantic knowledge about people that we know? To start tackling the first question, I studied the neural correlates of unconscious processing of invisible faces. I was unable to image significant activations related to the processing of completely invisible faces, despite existing reports in the literature. I thus moved on to the next question and studied how recognition of a familiar person was achieved in the brain; I focused on finding invariant representations of person identity \u2013 representations that would be activated any time we think of a familiar person, read their name, see their picture, hear them talk, etc. There again, I could not find significant evidence for such representations with fMRI, even in regions where they had previously been found with single unit recordings in human patients (the Jennifer Aniston neurons). Faced with these null outcomes, the scope of my investigations eventually turned back towards the technique that I had been using, fMRI, and the recently praised analytical tools that I had been trusting, Multivariate Pattern Analysis. After a mostly disappointing attempt at replicating a strong single unit finding of a categorical response to animals in the right human amygdala with fMRI, I put fMRI decoding to an ultimate test with a unique dataset acquired in the macaque monkey. There I showed a dissociation between the ability of fMRI to pick up face viewpoint information and its inability to pick up face identity information, which I mostly traced back to the poor clustering of identity selective units. Though fMRI decoding is a powerful new analytical tool, it does not rid fMRI of its inherent limitations as a hemodynamics-based measure." }, { "name": "Elling, Timothy James", "degree": "PhD", "year": "2013", "title": "GPU-Accelerated Fourier-Continuation Solvers and Physically Exact Computational Boundary Conditions for Wave Scattering Problems", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07092012-144406693", "creators": [ { "name": { "family": "Elling", "given": "Timothy James" }, "id": "Elling-Timothy-James", "display_name": "Elling, Timothy James" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/A5ZM-NK18", "abstract": "Many important engineering problems, ranging from antenna design to seismic imaging, require the numerical solution of problems of time-domain propagation and scattering of acoustic, electromagnetic, elastic waves, etc. These problems present several key difficulties, including numerical dispersion, the need for computational boundary conditions, and the extensive computational cost that arises from the extremely large number of unknowns that are often required for adequate spatial resolution of the underlying three-dimensional space. In this thesis a new class of numerical methods is developed. Based on the recently introduced Fourier continuation (FC) methodology (which eliminates the Gibbs phenomenon and thus facilitates accurate Fourier expansion of nonperiodic functions), these new methods enable fast spectral solution of wave propagation problems in the time domain. In particular, unlike finite difference or finite element approaches, these methods are very nearly dispersionless---a highly desirable property indeed, which guarantees that fixed numbers of points per wavelength suffice to solve problems of arbitrarily large extent. This thesis further puts forth the mathematical and algorithmic elements necessary to produce highly scalable implementations of these algorithms in challenging parallel computing environments---such as those arising in GPU architectures---while preserving their useful properties regarding convergence and dispersion.
\r\n \r\nAdditionally, this thesis develops a fast method for evaluation of computational boundary conditions which is based on Kirchhoff's integral formula in conjunction with the FC methodology and an accelerated equivalent source integration method introduced recently for solution of integral equation problems. The combination of these ideas gives rise to a physically exact radiating boundary condition that is nonlocal but fast. The only known alternatives that provide all three of these features are only applicable to a highly restrictive class of domains such as spheres or cylinders, whereas the Kirchhoff-based approach considered here only requires a bounded domain with nonvanishing thickness. As is the case with the FC scattering solvers mentioned above, the boundary-conditions algorithm is modified into a formulation that admits efficient implementation in GPU and other parallel infrastructures.
\r\n\r\nFinally, this thesis illustrates the character of the newly developed algorithms, in both GPU and parallel CPU infrastructures, with a variety of numerical examples. In particular, it is shown that the GPU implementations result in thirty- to fiftyfold speedups over the corresponding single CPU implementations. An extension of the boundary-condition algorithm, further, is demonstrated, which enables for propagation of time-domain solutions over arbitrarily large spans of empty space at essentially null computational cost. Finally, a hybridization of the FC and boundary condition algorithm is presented, which is also part of this thesis work, and which provides an interface of the newly developed algorithms with legacy finite-element representations of geometries and engineering structures. Thus, combining spectral and classical PDE solvers and propagation methods with novel GPU and parallel CPU implementations, this thesis demonstrates a computational capability that enables solution, in novel computational architectures, of some of the most challenging problems in the broad field of computational wave propagation and scattering.
\r\n" }, { "name": "Elzinga, Michael John", "degree": "PhD", "year": "2013", "title": "Flight Dynamics in Drosophila Through a Dynamically-scaled Robotic Approach", "advisor": "Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072013-110839676", "creators": [ { "name": { "family": "Elzinga", "given": "Michael John" }, "id": "Elzinga-Michael-John", "display_name": "Elzinga, Michael John" } ], "advisors": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/MSRS-JG88", "abstract": "Flies are particularly adept at balancing the competing demands of delay tolerance, performance, and robustness during flight, which invites thoughtful examination of their multimodal feedback architecture. This dissertation examines stabilization requirements for inner-loop feedback strategies in the flapping flight of Drosophila, the fruit fly, against the backdrop of sensorimotor transformations present in the animal. Flies have evolved multiple specializations to reduce sensorimotor latency, but sensory delay during flight is still significant on the timescale of body dynamics. I explored the effect of sensor delay on flight stability and performance for yaw turns using a dynamically-scaled robot equipped with a real-time feedback system that performed active turns in response to measured yaw torque. The results show a fundamental tradeoff between sensor delay and permissible feedback gain, and suggest that fast mechanosensory feedback provides a source of active damping that compliments that contributed by passive effects. Presented in the context of these findings, a control architecture whereby a haltere-mediated inner-loop proportional controller provides damping for slower visually-mediated feedback is consistent with tethered-flight measurements, free-flight observations, and engineering design principles.
\r\n\r\nAdditionally, I investigated how flies adjust stroke features to regulate and stabilize level forward flight. The results suggest that few changes to hovering kinematics are actually required to meet steady-state lift and thrust requirements at different flight speeds, and the primary driver of equilibrium velocity is the aerodynamic pitch moment. This finding is consistent with prior hypotheses and observations regarding the relationship between body pitch and flight speed in fruit flies. The results also show that the dynamics may be stabilized with additional pitch damping, but the magnitude of required damping increases with flight speed. I posit that differences in stroke deviation between the upstroke and downstroke might play a critical role in this stabilization. Fast mechanosensory feedback of the pitch rate could enable active damping, which would inherently exhibit gain scheduling with flight speed if pitch torque is regulated by adjusting stroke deviation. Such a control scheme would provide an elegant solution for flight stabilization across a wide range of flight speeds.
\r\n" }, { "name": "Garrett, Glenn Robert", "degree": "PhD", "year": "2013", "title": "Study of the Origins of Toughness in Amorphous Metals", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252013-065528171", "creators": [ { "name": { "family": "Garrett", "given": "Glenn Robert" }, "id": "Garrett-Glenn-Robert", "display_name": "Garrett, Glenn Robert" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Demetriou", "given": "Marios D." }, "id": "Demetriou-M-D", "role": "member", "display_name": "Demetriou, Marios D." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9JD4TRM", "abstract": "Amorphous metals that form fully glassy parts over a few millimeters in thickness are still relatively new materials. Their glassy structure gives them particularly high strengths, high yield strains, high hardness values, high resilience, and low damping losses, but this can also result in an extremely low tolerance to the presence of flaws in the material. Since this glassy structure lacks the ordered crystal structure, it also lacks the crystalline defect (dislocations) that provides the micromechanism of toughening and flaw insensitivity in conventional metals. Without a sufficient and reliable toughness that results in a large tolerance of damage in the material, metallic glasses will struggle to be adopted commercially. Here, we identify the origin of toughness in metallic glass as the competition between the intrinsic toughening mechanism of shear banding ahead of a crack and crack propagation by the cavitation of the liquid inside the shear bands. We present a detailed study over the first three chapters mainly focusing on the process of shear banding; its crucial role in giving rise to one of the most damage-tolerant materials known, its extreme sensitivity to the configurational state of a glass with moderate toughness, and how the configurational state can be changed with the addition of minor elements. The last chapter is a novel investigation into the cavitation barrier in glass-forming liquids, the competing process to shear banding. The combination of our results represents an increased understanding of the major influences on the fracture toughness of metallic glasses and thus provides a path for the improvement and development of tougher metallic glasses. " }, { "name": "Gdoutos, Eleftherios E.", "degree": "PhD", "year": "2013", "title": "Thin Metastructures with Engineered Thermal Expansion", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292013-162505920", "creators": [ { "name": { "family": "Gdoutos", "given": "Eleftherios E." }, "id": "Gdoutos-Eleftherios-E", "display_name": "Gdoutos, Eleftherios E." } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "chair", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Shapiro", "given": "Andrew A." }, "id": "Shapiro-A-A", "role": "member", "display_name": "Shapiro, Andrew A." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M69R-3A76", "abstract": "The geometry and constituent materials of metastructures can be used to engineer the thermal expansion coefficient. In this thesis, we design, fabricate, and test thin thermally stable metastructures consisting of bi-metallic unit cells and show how the coefficient of thermal expansion (CTE) of these metastructures can be finely and coarsely tuned by varying the CTE of the constituent materials and the unit cell geometry. Planar and three-dimensional finite element method modeling is used to drive the design and inform experiments, and predict the response of these metastructures. We demonstrate computationally the significance of out-of-plane effects in the metastructure response. We develop an experimental setup using digital image correlation and an infrared camera to experimentally measure full displacement and temperature fields during testing and accurately measure the metastructures\u2019 CTE. We experimentally demonstrate high aspect ratio metastructures of Ti/Al and Kovar/Al which exhibit near-zero and negative CTE, respectively. We demonstrate robust fabrication procedures for thermally stable samples with high aspect ratios in thin foil and thin film scales. We investigate the lattice structure and mechanical properties of thin films comprising a near-zero CTE metastructure. The mechanics developed in this work can be used to engineer metastructures of arbitrary CTE and can be extended to three dimensions." }, { "name": "Giang, Ha Thanh", "degree": "PhD", "year": "2013", "title": "Coupled Effects of Mechanics, Geometry, and Chemistry on Bio-Membrane Behavior", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062013-102758695", "creators": [ { "name": { "family": "Giang", "given": "Ha Thanh" }, "id": "Giang-Ha-Thanh", "display_name": "Giang, Ha Thanh" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/BVSK-K782", "abstract": "Lipid bilayer membranes are models for cell membranes--the structure that helps regulate cell function. Cell membranes are heterogeneous, and the coupling between composition and shape gives rise to complex behaviors that are important to regulation. This thesis seeks to systematically build and analyze complete models to understand the behavior of multi-component membranes.
\r\n\r\nWe propose a model and use it to derive the equilibrium and stability conditions for a general class of closed multi-component biological membranes. Our analysis shows that the critical modes of these membranes have high frequencies, unlike single-component vesicles, and their stability depends on system size, unlike in systems undergoing spinodal decomposition in flat space. An important implication is that small perturbations may nucleate localized but very large deformations. We compare these results with experimental observations.
\r\n\r\nWe also study open membranes to gain insight into long tubular membranes that arise for example in nerve cells. We derive a complete system of equations for open membranes by using the principle of virtual work. Our linear stability analysis predicts that the tubular membranes tend to have coiling shapes if the tension is small, cylindrical shapes if the tension is moderate, and beading shapes if the tension is large. This is consistent with experimental observations reported in the literature in nerve fibers. Further, we provide numerical solutions to the fully nonlinear equilibrium equations in some problems, and show that the observed mode shapes are consistent with those suggested by linear stability. Our work also proves that beadings of nerve fibers can appear purely as a mechanical response of the membrane.
" }, { "name": "Gittens, Alex A.", "degree": "PhD", "year": "2013", "title": "Topics in Randomized Numerical Linear Algebra", "advisor": "Tropp, Joel A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102013-100609092", "creators": [ { "name": { "family": "Gittens", "given": "Alex A." }, "id": "Gittens-Alex-A", "display_name": "Gittens, Alex A." } ], "advisors": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "advisor", "display_name": "Tropp, Joel A." } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/3K1S-R458", "abstract": "This thesis studies three classes of randomized numerical linear algebra algorithms, namely: (i) randomized matrix sparsification algorithms, (ii) low-rank approximation algorithms that use randomized unitary transformations, and (iii) low-rank approximation algorithms for positive-semidefinite (PSD) matrices.
\r\n\r\nRandomized matrix sparsification algorithms set randomly chosen entries of the input matrix to zero. When the approximant is substituted for the original matrix in computations, its sparsity allows one to employ faster sparsity-exploiting algorithms. This thesis contributes bounds on the approximation error of nonuniform randomized sparsification schemes, measured in the spectral norm and two NP-hard norms that are of interest in computational graph theory and subset selection applications.
\r\n\r\nLow-rank approximations based on randomized unitary transformations have several desirable properties: they have low communication costs, are amenable to parallel implementation, and exploit the existence of fast transform algorithms. This thesis investigates the tradeoff between the accuracy and cost of generating such approximations. State-of-the-art spectral and Frobenius-norm error bounds are provided.
\r\n\r\nThe last class of algorithms considered are SPSD \"sketching\" algorithms. Such sketches can be computed faster than approximations based on projecting onto mixtures of the columns of the matrix. The performance of several such sketching schemes is empirically evaluated using a suite of canonical matrices drawn from machine learning and data analysis applications, and a framework is developed for establishing theoretical error bounds.
\r\n\r\nIn addition to studying these algorithms, this thesis extends the Matrix Laplace Transform framework to derive Chernoff and Bernstein inequalities that apply to all the eigenvalues of certain classes of random matrices. These inequalities are used to investigate the behavior of the singular values of a matrix under random sampling, and to derive convergence rates for each individual eigenvalue of a sample covariance matrix.
" }, { "name": "Gopalakrishnan, Ragavendran", "degree": "PhD", "year": "2013", "title": "Characterizing Distribution Rules for Cost Sharing Games", "advisor": "Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032013-104204451", "creators": [ { "name": { "family": "Gopalakrishnan", "given": "Ragavendran" }, "id": "Gopalakrishnan-Ragavendran", "display_name": "Gopalakrishnan, Ragavendran" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." }, { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-K-A", "role": "member", "display_name": "Ligett, Katrina A." }, { "name": { "family": "Marden", "given": "Jason R." }, "id": "Marden-J-R", "role": "member", "display_name": "Marden, Jason R." } ], "option_major": [ "compsci" ], "doi": "10.7907/AWE2-H976", "abstract": "In noncooperative cost sharing games, individually strategic agents choose resources based on how the welfare (cost or revenue) generated at each resource (which depends on the set of agents that choose the resource) is distributed. The focus is on finding distribution rules that lead to stable allocations, which is formalized by the concept of Nash equilibrium, e.g., Shapley value (budget-balanced) and marginal contribution (not budget-balanced) rules.
\r\n\r\nRecent work that seeks to characterize the space of all such rules shows that the only budget-balanced distribution rules that guarantee equilibrium existence in all welfare sharing games are generalized weighted Shapley values (GWSVs), by exhibiting a specific 'worst-case' welfare function which requires that GWSV rules be used. Our work provides an exact characterization of the space of distribution rules (not necessarily budget-balanced) for any specific local welfare functions remains, for a general class of scalable and separable games with well-known applications, e.g., facility location, routing, network formation, and coverage games.
\r\n\r\nWe show that all games conditioned on any fixed local welfare functions possess an equilibrium if and only if the distribution rules are equivalent to GWSV rules on some 'ground' welfare functions. Therefore, it is neither the existence of some worst-case welfare function, nor the restriction of budget-balance, which limits the design to GWSVs. Also, in order to guarantee equilibrium existence, it is necessary to work within the class of potential games, since GWSVs result in (weighted) potential games.
\r\n\r\nWe also provide an alternative characterization—all games conditioned on any fixed local welfare functions possess an equilibrium if and only if the distribution rules are equivalent to generalized weighted marginal contribution (GWMC) rules on some 'ground' welfare functions. This result is due to a deeper fundamental connection between Shapley values and marginal contributions that our proofs expose—they are equivalent given a transformation connecting their ground welfare functions. (This connection leads to novel closed-form expressions for the GWSV potential function.) Since GWMCs are more tractable than GWSVs, a designer can tradeoff budget-balance with computational tractability in deciding which rule to implement.
" }, { "name": "Griffin, Gregory Scott", "degree": "PhD", "year": "2013", "title": "Learning and Using Taxonomies for Visual and Olfactory Classification", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162013-152639568", "creators": [ { "name": { "family": "Griffin", "given": "Gregory Scott" }, "id": "Griffin-Gregory-Scott", "display_name": "Griffin, Gregory Scott" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Nguyen", "given": "Hien Trong" }, "id": "Nguyen-Hien-Trong", "role": "member", "display_name": "Nguyen, Hien Trong" } ], "option_major": [ "cns" ], "doi": "10.7907/YTZH-HA75", "abstract": "Humans are able of distinguishing more than 5000 visual categories even in complex environments using a variety of different visual systems all working in tandem. We seem to be capable of distinguishing thousands of different odors as well. In the machine learning community, many commonly used multi-class classifiers do not scale well to such large numbers of categories. This thesis demonstrates a method of automatically creating application-specific taxonomies to aid in scaling classification algorithms to more than 100 cate- gories using both visual and olfactory data. The visual data consists of images collected online and pollen slides scanned under a microscope. The olfactory data was acquired by constructing a small portable sniffing apparatus which draws air over 10 carbon black polymer composite sensors. We investigate performance when classifying 256 visual categories, 8 or more species of pollen and 130 olfactory categories sampled from common household items and a standardized scratch-and-sniff test. Taxonomies are employed in a divide-and-conquer classification framework which improves classification time while allowing the end user to trade performance for specificity as needed. Before classification can even take place, the pollen counter and electronic nose must filter out a high volume of background \u201cclutter\u201d to detect the categories of interest. In the case of pollen this is done with an efficient cascade of classifiers that rule out most non-pollen before invoking slower multi-class classifiers. In the case of the electronic nose, much of the extraneous noise encountered in outdoor environments can be filtered using a sniffing strategy which preferentially samples the visensor response at frequencies that are relatively immune to background contributions from ambient water vapor. This combination of efficient background rejection with scalable classification algorithms is tested in detail for three separate projects: 1) the Caltech-256 Image Dataset, 2) the Caltech Automated Pollen Identification and Counting System (CAPICS) and 3) a portable electronic nose specially constructed for outdoor use." }, { "name": "Hebert, Paul", "degree": "PhD", "year": "2013", "title": "Estimation and Inference for Grasping and Manipulation Tasks Using Vision and Kinesthetic Sensors", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:04052013-105520483", "creators": [ { "name": { "family": "Hebert", "given": "Paul" }, "id": "Hebert-Paul", "display_name": "Hebert, Paul" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hudson", "given": "Nicolas H." }, "id": "Hudson-N-H", "role": "member", "display_name": "Hudson, Nicolas H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/PZB6-QJ39", "abstract": "This thesis presents a novel framework for state estimation in the context of robotic grasping and manipulation. The overall estimation approach is based on fusing various visual cues for manipulator tracking, namely appearance and feature-based, shape-based, and silhouette-based visual cues. Similarly, a framework is developed to fuse the above visual cues, but also kinesthetic cues such as force-torque and tactile measurements, for in-hand object pose estimation. The cues are extracted from multiple sensor modalities and are fused in a variety of Kalman filters.
\r\n\r\nA hybrid estimator is developed to estimate both a continuous state (robot and object states) and discrete states, called contact modes, which specify how each finger contacts a particular object surface. A static multiple model estimator is used to compute and maintain this mode probability. The thesis also develops an estimation framework for estimating model parameters associated with object grasping. Dual and joint state-parameter estimation is explored for parameter estimation of a grasped object's mass and center of mass. Experimental results demonstrate simultaneous object localization and center of mass estimation.
\r\n\r\nDual-arm estimation is developed for two arm robotic manipulation tasks. Two types of filters are explored; the first is an augmented filter that contains both arms in the state vector while the second runs two filters in parallel, one for each arm. These two frameworks and their performance is compared in a dual-arm task of removing a wheel from a hub.
\r\n\r\nThis thesis also presents a new method for action selection involving touch. This next best touch method selects an available action for interacting with an object that will gain the most information. The algorithm employs information theory to compute an information gain metric that is based on a probabilistic belief suitable for the task. An estimation framework is used to maintain this belief over time. Kinesthetic measurements such as contact and tactile measurements are used to update the state belief after every interactive action. Simulation and experimental results are demonstrated using next best touch for object localization, specifically a door handle on a door.\r\nThe next best touch theory is extended for model parameter determination. Since many objects within a particular object category share the same rough shape, principle component analysis may be used to parametrize the object mesh models. These parameters can be estimated using the action selection technique that selects the touching action which best both localizes and estimates these parameters. Simulation results are then presented involving localizing and determining a parameter of a screwdriver.
\r\n\r\nLastly, the next best touch theory is further extended to model classes. Instead of estimating parameters, object class determination is incorporated into the information gain metric calculation. The best touching action is selected in order to best discern between the possible model classes. Simulation results are presented to validate the theory.
" }, { "name": "Hill, Jeffrey Thomas", "degree": "PhD", "year": "2013", "title": "Nonlinear Optics and Wavelength Translation Via Cavity-Optomechanics", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-144103500", "creators": [ { "name": { "family": "Hill", "given": "Jeffrey Thomas" }, "id": "Hill-Jeffrey-Thomas", "display_name": "Hill, Jeffrey Thomas" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/DKW6-TF64", "abstract": "The field of cavity-optomechanics explores the interaction of light with sound in an ever increasing array of devices. This interaction allows the mechanical system to be both sensed and controlled by the optical system, opening up a wide variety of experiments including the cooling of the mechanical resonator to its quantum mechanical ground state and the squeezing of the optical field upon interaction with the mechanical resonator, to name two.
\r\n\r\nIn this work we explore two very different systems with different types of optomechanical coupling. The first system consists of two microdisk optical resonators stacked on top of each other and separated by a very small slot. The interaction of the disks causes their optical resonance frequencies to be extremely sensitive to the gap between the disks. By careful control of the gap between the disks, the optomechanical coupling can be made to be quadratic to first order which is uncommon in optomechanical systems. With this quadratic coupling the light field is now sensitive to the energy of the mechanical resonator and can directly control the potential energy trapping the mechanical motion. This ability to directly control the spring constant without modifying the energy of the mechanical system, unlike in linear optomechanical coupling, is explored.
\r\n\r\nNext, the bulk of this thesis deals with a high mechanical frequency optomechanical crystal which is used to coherently convert photons between different frequencies. This is accomplished via the engineered linear optomechanical coupling in these devices. Both classical and quantum systems utilize the interaction of light and matter across a wide range of energies. These systems are often not naturally compatible with one another and require a means of converting photons of dissimilar wavelengths to combine and exploit their different strengths. Here we theoretically propose and experimentally demonstrate coherent wavelength conversion of optical photons using photon-phonon translation in a cavity-optomechanical system. For an engineered silicon optomechanical crystal nanocavity supporting a 4 GHz localized phonon mode, optical signals in a 1.5 MHz bandwidth are coherently converted over a 11.2 THz frequency span between one cavity mode at wavelength 1460 nm and a second cavity mode at 1545 nm with a 93% internal (2% external) peak efficiency. The thermal and quantum limiting noise involved in the conversion process is also analyzed and, in terms of an equivalent photon number signal level, are found to correspond to an internal noise level of only 6 and 4 times 10x^-3 quanta, respectively.
\r\n\r\nWe begin by developing the requisite theoretical background to describe the system. A significant amount of time is then spent describing the fabrication of these silicon nanobeams, with an emphasis on understanding the specifics and motivation. The experimental demonstration of wavelength conversion is then described and analyzed. It is determined that the method of getting photons into the cavity and collected from the cavity is a fundamental limiting factor in the overall efficiency. Finally, a new coupling scheme is designed, fabricated, and tested that provides a means of coupling greater than 90% of photons into and out of the cavity, addressing one of the largest obstacles with the initial wavelength conversion experiment.
" }, { "name": "Honarvar Nazari, Meisam", "degree": "PhD", "year": "2013", "title": "Electrical and Optical Interconnects for High-Performance Computing", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282013-164038057", "creators": [ { "name": { "family": "Honarvar Nazari", "given": "Meisam" }, "id": "Honarvar-Nazari-Meisam", "display_name": "Honarvar Nazari, Meisam" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TSX2-EE48", "abstract": "Technology scaling has enabled drastic growth in the computational and storage capacity of integrated circuits (ICs). This constant growth drives an increasing demand for high-bandwidth communication between and within ICs. In this dissertation we focus on low-power solutions that address this demand. We divide communication links into three subcategories depending on the communication distance. Each category has a different set of challenges and requirements and is affected by CMOS technology scaling in a different manner. We start with short-range chip-to-chip links for board-level communication. Next we will discuss board-to-board links, which demand a longer communication range. Finally on-chip links with communication ranges of a few millimeters are discussed.
\r\n\r\nElectrical signaling is a natural choice for chip-to-chip communication due to efficient integration and low cost. IO data rates have increased to the point where electrical signaling is now limited by the channel bandwidth. In order to achieve multi-Gb/s data rates, complex designs that equalize the channel are necessary. In addition, a high level of parallelism is central to sustaining bandwidth growth. Decision feedback equalization (DFE) is one of the most commonly employed techniques to overcome the limited bandwidth problem of the electrical channels. A linear and low-power summer is the central block of a DFE. Conventional approaches employ current-mode techniques to implement the summer, which require high power consumption. In order to achieve low-power operation we propose performing the summation in the charge domain. This approach enables a low-power and compact realization of the DFE as well as crosstalk cancellation. A prototype receiver was fabricated in 45nm SOI CMOS to validate the functionality of the proposed technique and was tested over channels with different levels of loss and coupling. Measurement results show that the receiver can equalize channels with maximum 21dB loss while consuming about 7.5mW from a 1.2V supply. We also introduce a compact, low-power transmitter employing passive equalization. The efficacy of the proposed technique is demonstrated through implementation of a prototype in 65nm CMOS. The design achieves up to 20Gb/s data rate while consuming less than 10mW.
\r\n \r\nAn alternative to electrical signaling is to employ optical signaling for chip-to-chip interconnections, which offers low channel loss and cross-talk while providing high communication bandwidth. In this work we demonstrate the possibility of building compact and low-power optical receivers. A novel RC front-end is proposed that combines dynamic offset modulation and double-sampling techniques to eliminate the need for a short time constant at the input of the receiver. Unlike conventional designs, this receiver does not require a high-gain stage that runs at the data rate, making it suitable for low-power implementations. In addition, it allows time-division multiplexing to support very high data rates. A prototype was implemented in 65nm CMOS and achieved up to 24Gb/s with less than 0.4pJ/b power efficiency per channel. As the proposed design mainly employs digital blocks, it benefits greatly from technology scaling in terms of power and area saving.
\r\n\r\nAs the technology scales, the number of transistors on the chip grows. This necessitates a corresponding increase in the bandwidth of the on-chip wires. In this dissertation, we take a close look at wire scaling and investigate its effect on wire performance metrics. We explore a novel on-chip communication link based on a double-sampling architecture and dynamic offset modulation technique that enables low power consumption and high data rates while achieving high bandwidth density in 28nm CMOS technology. The functionality of the link is demonstrated using different length minimum-pitch on-chip wires. Measurement results show that the link achieves up to 20Gb/s of data rate (12.5Gb/s/$\\mu$m) with better than 136fJ/b of power efficiency.
" }, { "name": "Hong, Ting", "degree": "PhD", "year": "2013", "title": "Brownian Thermal Noise in Interferometric Gravitational Wave Detectors and Single Photon Optomechanics", "advisor": "Chen, Yanbei", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182012-212554378", "creators": [ { "name": { "family": "Hong", "given": "Ting" }, "id": "Hong-Ting", "display_name": "Hong, Ting" } ], "advisors": [ { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "role": "advisor", "display_name": "Chen, Yanbei" } ], "committee": [ { "name": { "family": "Chen", "given": "Yanbei" }, "id": "Chen-Yanbei", "role": "chair", "display_name": "Chen, Yanbei" }, { "name": { "family": "Adhikari", "given": "Rana" }, "id": "Adhikari-R", "role": "member", "display_name": "Adhikari, Rana" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/B83T-7730", "abstract": "The Laser Interferometric Gravitational-Wave Observatory (LIGO) is designed to detect the Gravitational Waves (GW) predicted by Albert Einstein\u2019s general theory of relativity. The advanced LIGO project is ongoing an upgrade to increase the detection sensitivity by more than a factor of 10, which will make the events detection a routine occurrence. In addition to using higher power lasers, heavier test mass, and better isolation systems, several new designs and techniques are proposed in the long-term upgrade, such as modifying the optics configuration to reduce the quantum noise, active noise cancellation of the Newtonian noise, optimizing the coating structure, and employing non-Guassian laser beams etc.
\r\n\r\nIn the first part of my thesis (Chapters 2 and 3), I apply statistical mechanics and elastostatics to the LIGO coated mirrors, and study the thermal fluctuations that dominate advanced LIGO\u2019s most sensitive frequency band from 40 Hz to 200 Hz.
\r\n\r\nIn particular, in Chapter 2, I study the so-called coating Brownian noise, fluctuations of mirrors coated with multiple layers of dielectrics due to internal friction. Assuming coating materials to be isotropic and homogeneous, I calculate the cross spectra of Brownian fluctuations in the bulk and shear strains of the coating layers, as well as fluctuations in the height of the coating-substrate interface. The additional phase shifting and back-scattering caused by photo elastic effects are also considered for the first time.
\r\n\r\nIn Chapter 3, I study whether it is realistic to adopt higher-order Laguerre-Gauss modes in LIGO, in order to mitigate the effect of mirror thermal noise. We investigate the effect on the detector\u2019s contrast defect caused by the mode degeneracy. With both analytical calculation and numerical simulation, we show that with this approach, the detector\u2019s susceptibility to mirror figure errors is reduced greatly compared to using the nondegenerate modes, therefore making it unacceptable for LIGO requirements.
\r\n\r\nFor the future GW detectors, with much lower noises and higher sensitivity, this might be used to investigate the quantum behaviors of macroscopic mechanical objects. In recent years the linear optomechanical systems with cavity modes coupling to a mechanical oscillator have been studied extensively. In the second part of my thesis (Chapter 4), I study the interaction between a single photon and a high-finesse cavity with a movable mirror, in the so-called strong coupling regime, where the recoil of the photon can cause significant change in the momentum of the mirror. The results are applied to analyze the case with a Fabry-Perot cavity. We also present that with engineering the photon wave function, it is possible to prepare the oscillator into an arbitrary quantum state.
" }, { "name": "Ikeda, Ayako", "degree": "PhD", "year": "2013", "title": "Superprotonic Solid Acids: Thermochemistry, Structure, and Conductivity", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09142012-115522353", "creators": [ { "name": { "family": "Ikeda", "given": "Ayako" }, "id": "Ikeda-Ayako", "display_name": "Ikeda, Ayako" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "matsci" ], "doi": "10.7907/R1SG-VY83", "abstract": "In this work, in order to investigate the thermochemistry and property of the superprotonic solid acid compounds, the measurement methods were established for
The thermodynamic and kinetics of the dehydration and hydration of CsH2PO4 is investigated by TG, DSC, and XRD analysis. By making use of the enhanced kinetics afforded by SiO2, the phase boundary between CsH2PO4, CsPO3, and dehydrated liquid was precisely determined. The stability of CsH2PO4 and the liquid dehydrate, CsH2(1-x)PO4-x(l), were confirmed by the complete reversal of dehydration to recover these phases in the appropriate temperature and water partial pressure ranges. Rehydration and conversion of CsPO3(s) to CsH2PO4(s) occurs over a period of several hours, depending on temperature, water partial pressure, and morphology of the metaphosphate. High and small particles favor rapid dehydration, whereas the temperature dependence of the rehydration kinetics is nonmonotonic, reaching its fastest rate in the vicinity of the superprotonic transition.
\r\n\r\nDoping Rb and K into CDP was examined and the stable region of Cs1-xRbxH2PO4 and Cs1-xKxH2PO4 are determined by in situ XRD and DSC measurement. Then the effects of doping to the structure and conductivity are discussed. It was found that Rb has whole-range solubility for both cubic and monoclinic CDP. Ts increases and Td decrease with Rb content. K has 27% solubility for cubic CDP, Ts and Td decrease with K content. The eutectic temperature is 208 \u00b1 2\u00b0C. The lattice size of Rb- or K- doped CDP depends on the averaged cation size. Conductivity linearly decreases by dopant concentration. The impact of K doping is deeper than that of Rb for the equivalent averaged cation size.
\r\n \r\nThe zero-pressure gradient turbulent boundary layer at Reynolds numbers (based on momentum thickness) ranging from 2700--4100 was perturbed using an impulsively short patch of two-dimensional, spanwise roughness elements. A spatial perturbation was considered in which the roughness patch was held statically on the flat-plate, and the flow downstream of the perturbation was measured by hotwire and particle-image velocimetry. A dynamic perturbation, in which the roughness patch was actuated periodically in time, was also studied, and additional measurements were taken by phase-locking to the dynamic actuation itself.
\r\n\r\nThe static perturbation distorted the boundary layer through the generation of a `stress bore' which modified the mean streamwise velocity gradient. The effect of this stress bore was observed in a modification of statistical and spectral measures of the turbulence, as well as a redistribution of coherent structures in the boundary layer. The characterization of the statically perturbed boundary layer provided a base flow from which to consider the dynamically perturbed flow. The dynamically perturbed flow manifested both effects analogous to the static perturbation, as well as a coherent, periodic, large-scale velocity fluctuation. The extent to which these two features could be treated as linearly independent was studied by a variety of statistical and spectral means. Moreover, the very large scale motion synthesized by the dynamic perturbation was isolated by phase-locked measurement, and its behavior was predicted with reasonable success by employing a resolvent operator approach to a forced version of the Orr-Sommerfeld equation.
\r\n\r\nThe relationship between large-scale motions and an envelope of small-scale motions in the turbulent boundary layer was studied in both the unperturbed and perturbed flows. A variety of correlation techniques were used to interpret the interaction between the different scale motions in the context of a phase-relationship between large and small scales. This phase relationship was shown to provide a physically-grounded perspective on the relationship between the synthetic very large scale motion produced by the dynamic perturbation and the smaller scales in the flow, and was able to provide a foundation for thinking about new approaches to controlling turbulence through large-scale forcing.
" }, { "name": "Jang, Min Seok", "degree": "PhD", "year": "2013", "title": "Plasmonics and Electron Optics in Graphene", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:11262012-160659812", "creators": [ { "name": { "family": "Jang", "given": "Min Seok" }, "id": "Jang-Min-Seok", "display_name": "Jang, Min Seok" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/59RB-9653", "abstract": "The field of plasmonics has been attracting wide interest because it has provided routes to guide and localize light at nanoscales by utilizing metals as its major building block. Meanwhile, graphene, a two-dimensional lattice of carbon atoms, has been regarded as an ideal material for electronic applications owing to its remarkably high carrier mobility and superior thermal properties. Both research fields have been growing rapidly, but quite independently. However, a closer look reveals that there are actually numerous similarities between them, and it is possible to extract useful applications from these analogies. Even more interestingly, these research fields are recently overlapping to create a new field of research, namely graphene plasmonics.
\r\n\r\nIn this thesis, we present a few examples of these intertwined topics. First, we investigate \"rainbow trapping\" structures, broadband plasmonic slow light systems composed of single or double negative materials. We clarify the mode-conversion mechanism and the light-trapping performance by analyzing the dispersion relation. We then show that electrons in graphene exhibit photonlike dynamics including Goos-Hanchen effect and the rainbow trapping effect, but quantitatively differently. To study the dynamics of graphene electrons numerically, we develop a finite-difference time domain simulator. We also present a way to enhance electron backscattering in graphene by engineering the dispersion of electron eigenmodes in a Kronig-Penney potential. Finally, we discuss physics of graphene plasmon cavities. We report the resonant mid-infrared transmission across a plasmonic waveguide gap that is governed by the Fano interference between transmission through plasmon modes in graphene and nonresonant background transmission. An ultracompact graphene plasmon cavity, which resonates at near-infrared telecommunication frequencies, is also proposed.
" }, { "name": "Johnson, Gwendolyn Brook", "degree": "PhD", "year": "2013", "title": "Modeling, Simulation, and Design of Self-Assembling Space Systems: Accurate Collision Detection, Robust Time Integration, and Optimal Control", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:09132012-125328533", "creators": [ { "name": { "family": "Johnson", "given": "Gwendolyn Brook" }, "id": "Johnson-G-B", "display_name": "Johnson, Gwendolyn Brook" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Leyendecker", "given": "Sigrid" }, "id": "Leyendecker-S", "role": "member", "display_name": "Leyendecker, Sigrid" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/73S0-Y593", "abstract": "Motivated by issues inherent in modeling and designing self-assembling systems (e.g. multiple collisions, collisions between non-smooth bodies, clumping and jamming behaviors, etc.), the goal of this thesis is to develop robust numerical tools that enable ecient and accurate direct simulation of self assembling systems and the application of optimal control methods to this type of system. The systems will be alternately modeled using linear nite elements, rigid bodies, or chains of rigid bodies. To this end, this work begins with development of a linear programming based collision detection algorithm for general convex polyhedral bodies. The resulting linear program has several features which render it extremely useful in determining the force system at the time of contact in numerical collision integrators. With robust collision detection in hand, three related numerical integration methods for dynamics with collisions are treated; a direct potential-based approach, and exact collision integrator in a discrete variational setting, and a decomposition-based algorithm, again in the discrete variational setting. Finally, several control problems are treated in the Discrete Mechanics and Optimal Control{Constrained (DMOCC) framework in which collisions between non-smooth bodies either need to be avoided or explicitly included in the optimal control problem. A globally stable feedback controller and a family of trajectories for spacecraft docking are also developed and tested with an accurate representation of an optimized CubeSat docking system." }, { "name": "Kim, Justin Young-Hyun", "degree": "PhD", "year": "2013", "title": "Parylene-C as a New Piezoelectric Material", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142013-075702623", "creators": [ { "name": { "family": "Kim", "given": "Justin Young-Hyun" }, "id": "Kim-Justin-Young-Hyun", "display_name": "Kim, Justin Young-Hyun" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1VEH-EP90", "abstract": "The goal of this thesis is to develop a proper microelectromechanical systems (MEMS) process to manufacture piezoelectric Parylene-C (PA-C), which is famous for its chemical inertness, mechanical and thermal properties and electrical insulation. Furthermore, piezoelectric PA-C is used to build miniature, inexpensive, non-biased piezoelectric microphones.
\r\n \r\nThese piezoelectric PA-C MEMS microphones are to be used in any application where a conventional piezoelectric and electret microphone can be used, such as in cell phones and hearing aids. However, they have the advantage of a simplified fabrication process compared with existing technology. In addition, as a piezoelectric polymer, PA-C has varieties of applications due to its low dielectric constant, low elastic stiffness, low density, high voltage sensitivity, high temperature stability and low acoustic and mechanical impedance. Furthermore, PA-C is an FDA approved biocompatible material and is able to maintain operate at a high temperature.
\r\n\r\nTo accomplish piezoelectric PA-C, a MEMS-compatible poling technology has been developed. The PA-C film is poled by applying electrical field during heating. The piezoelectric coefficient, -3.75pC/N, is obtained without film stretching.
\r\n\r\nThe millimeter-scale piezoelectric PA-C microphone is fabricated with an in-plane spiral arrangement of two electrodes. The dynamic range is from less than 30 dB to above 110 dB SPL (referenced 20 \u00b5Pa) and the open-circuit sensitivities are from 0.001 \u2013 0.11 mV/Pa over a frequency range of 1 - 10 kHz. The total harmonic distortion of the device is less than 20% at 110 dB SPL and 1 kHz.
" }, { "name": "Kwok, Kawai", "degree": "PhD", "year": "2013", "title": "Mechanics of Viscoelastic Thin-Walled Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122012-184825377", "creators": [ { "name": { "family": "Kwok", "given": "Kawai" }, "id": "Kwok-Kawai", "orcid": "0000-0001-6876-4267", "display_name": "Kwok, Kawai" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Andrade", "given": "Jose E." }, "id": "Andrade-J-E", "role": "member", "display_name": "Andrade, Jose E." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RSSF-1C35", "abstract": "Thin-walled structures made of polymers and reinforced polymer composites are prominent candidates for constructing large lightweight structures. A major challenge in designing polymer-based thin-walled structures is their time and temperature dependent behavior originating from material viscoelasticity and its interaction with the highly geometrically nonlinear response due to thinness of the walls. Although polymer viscoelasticity and geometric nonlinearity have been extensively studied, the mechanics of structures exhibiting both phenomena are not well understood.
\r\n\r\nThis thesis presents a combination of experimental, numerical, and analytical investigations of the behavior of viscoelastic thin-walled structures. The first goal of this research is to establish general methods of analysis for two types of structural components, namely composite shells and polymer membranes, that will serve as the basis for full-scale structural analysis. The second goal is to demonstrate the capability of the developed methods by analyzing time and temperature dependent behavior of deployable structures and balloon structures.
\r\n\r\nIn the study of deployable structures, the deployment and shape recovery processes after stowage are investigated. Fundamental features of viscoelastic deployable structures are studied first with homogeneous polymer beams and shells. A simple closed-form solution describing the shape evolution of a beam after stowage is proposed. The effects of rate and temperature on the bending instability of shells are revealed. Building on the understanding gained from the analysis of homogeneous structures, modeling techniques are developed for polymer composite structures. A micromechanical viscoelastic model for carbon fiber reinforced polymer thin shells is established through finite element homogenization and applied to evaluate the effects of long-term stowage in a representative composite deployable structure.
\r\n\r\nIn the study of balloon structures, a membrane model is developed to study polymer balloon films with stress concentrations due to thickness variation. A nonlinear viscoelastic constitutive model is first formulated for the film material. The wrinkling instability behavior is incorporated into the model through correction of stress and strain states in the presence of wrinkling. Stress concentration factors in balloon films are predicted and measured with the membrane model and full-field displacement measurement techniques, respectively.
" }, { "name": "Leenheer, Andrew Jay", "degree": "PhD", "year": "2013", "title": "Light to Electrons to Bonds: Imaging Water Splitting and Collecting Photoexcited Electrons", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:12102012-191527683", "creators": [ { "name": { "family": "Leenheer", "given": "Andrew Jay" }, "id": "Leenheer-Andrew-Jay", "display_name": "Leenheer, Andrew Jay" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Lewis", "given": "Nathan S." }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan S." } ], "option_major": [ "matsci" ], "doi": "10.7907/A8ZZ-Z189", "abstract": "Photoelectrochemical devices can store solar energy as chemical bonds in fuels, but more control over the materials involved is needed for economic feasibility. Both efficient capture of photon energy into electron energy and subsequent electron transfer and bond formation are necessary, and this thesis explores various steps of the process. To look at the electrochemical fuel formation step, the spatially-resolved reaction rate on a water-splitting electrode was imaged during operation at a few-micron scale using optical microscopy. One method involved localized excitation of a semiconductor photoanode and recording the growth rate of bubbles to determine the local reaction rate. A second method imaged the reactant profile with a pH-sensitive fluorophore in the electrolyte to determine the local three-dimensional pH profile at patterned electrocatalysts in a confocal microscope. These methods provide insight on surface features optimal for efficient electron transfer into fuel products.
\r\n\r\nA second set of studies examined the initial process of photoexcited electron transport and collection. An independent method to measure the minority carrier diffusion length in semiconductor photoelectrodes was developed, in which a wedge geometry is back illuminated with a small scanned spot. The diffusion length can be determined from the exponential decrease of photocurrent with thickness, and the method was demonstrated on solid-state silicon wedge diodes, as well as tungsten oxide thin-film wedge photoanodes. Finally, the possibility of absorbing and collecting sub-bandgap illumination via plasmon-enhanced hot carrier internal photoemission was modeled to predict the energy conversion efficiency. The effect of photon polarization on emission yield was experimentally tested using gold nanoantennas buried in silicon, and the correlation was found to be small.
" }, { "name": "Leonard, Andrea Beth", "degree": "PhD", "year": "2013", "title": "Controlling Wave Propagation through Nonlinear Engineered Granular Systems", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122013-030022149", "creators": [ { "name": { "family": "Leonard", "given": "Andrea Beth" }, "id": "Leonard-Andrea-Beth", "display_name": "Leonard, Andrea Beth" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/NF5J-5W42", "abstract": "We study the fundamental dynamic behavior of a special class of ordered granular systems in order to design new, structured materials with unique physical properties. The dynamic properties of granular systems are dictated by the nonlinear, Hertzian, potential in compression and zero tensile strength resulting from the discrete material structure. Engineering the underlying particle arrangement of granular systems allows for unique dynamic properties, not observed in natural, disordered granular media. While extensive studies on 1D granular crystals have suggested their usefulness for a variety of engineering applications, considerably less attention has been given to higher-dimensional systems. The extension of these studies in higher dimensions could enable the discovery of richer physical phenomena not possible in 1D, such as spatial redirection and anisotropic energy trapping. We present experiments, numerical simulation (based on a discrete particle model), and in some cases theoretical predictions for several engineered granular systems, studying the effects of particle arrangement on the highly nonlinear transient wave propagation to develop means for controlling the wave propagation pathways. The first component of this thesis studies the stress wave propagation resulting from a localized impulsive loading for three different 2D particle lattice structures: square, centered square, and hexagonal granular crystals. By varying the lattice structure, we observe a wide range of properties for the propagating stress waves: quasi-1D solitary wave propagation, fully 2D wave propagation with tunable wave front shapes, and 2D pulsed wave propagation. Additionally the effects of weak disorder, inevitably present in real granular systems, are investigated. The second half of this thesis studies the solitary wave propagation through 2D and 3D ordered networks of granular chains, reducing the effective density compared to granular crystals by selectively placing wave guiding chains to control the acoustic wave transmission. The rapid wave front amplitude decay exhibited by these granular networks makes them highly attractive for impact mitigation applications. The agreement between experiments, numerical simulations, and applicable theoretical predictions validates the wave guiding capabilities of these engineered granular crystals and networks and opens a wide range of possibilities for the realization of increasingly complex granular material design." }, { "name": "Leong, Derek", "degree": "PhD", "year": "2013", "title": "On Erasure Coding for Distributed Storage and Streaming Communications", "advisor": "Ho, Tracey C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-162820930", "creators": [ { "name": { "family": "Leong", "given": "Derek" }, "id": "Leong-Derek", "display_name": "Leong, Derek" } ], "advisors": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "advisor", "display_name": "Ho, Tracey C." } ], "committee": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "chair", "display_name": "Ho, Tracey C." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Dimakis", "given": "Alexandros G." }, "id": "Dimakis-A-G", "orcid": "0000-0002-4244-7033", "role": "member", "display_name": "Dimakis, Alexandros G." } ], "option_major": [ "eleceng" ], "doi": "10.7907/PZJ8-F333", "abstract": "The work presented in this thesis revolves around erasure correction coding, as applied to distributed data storage and real-time streaming communications.
\r\n\r\nFirst, we examine the problem of allocating a given storage budget over a set of nodes for maximum reliability.\r\nThe objective is to find an allocation of the budget that maximizes the probability of successful recovery by a data collector accessing a random subset of the nodes.\r\nThis optimization problem is challenging in general because of its combinatorial nature, despite its simple formulation.\r\nWe study several variations of the problem, assuming different allocation models and access models, and determine the optimal allocation and the optimal symmetric allocation (in which all nonempty nodes store the same amount of data) for a variety of cases.\r\nAlthough the optimal allocation can have nonintuitive structure and can be difficult to find in general, our results suggest that, as a simple heuristic, reliable storage can be achieved by spreading the budget maximally over all nodes when the budget is large, and spreading it minimally over a few nodes when it is small.\r\nCoding would therefore be beneficial in the former case, while uncoded replication would suffice in the latter case.
\r\n\r\nSecond, we study how distributed storage allocations affect the recovery delay in a mobile setting.\r\nSpecifically, two recovery delay optimization problems are considered for a network of mobile storage nodes:\r\nthe maximization of the probability of successful recovery by a given deadline, and the minimization of the expected recovery delay.\r\nWe show that the first problem is closely related to the earlier allocation problem, and solve the second problem completely for the case of symmetric allocations.\r\nIt turns out that the optimal allocations for the two problems can be quite different.\r\nIn a simulation study, we evaluated the performance of a simple data dissemination and storage protocol for mobile delay-tolerant networks, and observed that the choice of allocation can have a significant impact on the recovery delay under a variety of scenarios.
\r\n\r\nThird, we consider a real-time streaming system where messages created at regular time intervals at a source are encoded for transmission to a receiver over a packet erasure link;\r\nthe receiver must subsequently decode each message within a given delay from its creation time.\r\nFor erasure models containing a limited number of erasures per coding window, per sliding window, and containing erasure bursts whose maximum length is sufficiently short or long, we show that a time-invariant intrasession code asymptotically achieves the maximum message size among all codes that allow decoding under all admissible erasure patterns.\r\nFor the bursty erasure model, we also show that diagonally interleaved codes derived from specific systematic block codes are asymptotically optimal over all codes in certain cases.\r\nWe also study an i.i.d. erasure model in which each transmitted packet is erased independently with the same probability;\r\nthe objective is to maximize the decoding probability for a given message size.\r\nWe derive an upper bound on the decoding probability for any time-invariant code, and show that the gap between this bound and the performance of a family of time-invariant intrasession codes is small when the message size and packet erasure probability are small.\r\nIn a simulation study, these codes performed well against a family of random time-invariant convolutional codes under a number of scenarios.
\r\n\r\nFinally, we consider the joint problems of routing and caching for named data networking.\r\nWe propose a backpressure-based policy that employs virtual interest packets to make routing and caching decisions.\r\nIn a packet-level simulation, the proposed policy outperformed a basic protocol that combines shortest-path routing with least-recently-used (LRU) cache replacement.
" }, { "name": "Li, Jiang", "degree": "PhD", "year": "2013", "title": "Nonlinear Optics in Planar Silica-on-Silicon Disk Resonators", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-151745220", "creators": [ { "name": { "family": "Li", "given": "Jiang" }, "id": "Li-Jiang", "display_name": "Li, Jiang" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/20G7-EM85", "abstract": "Optical frequency combs (OFCs) provide direct phase-coherent link between optical and RF frequencies, and enable precision measurement of optical frequencies. In recent years, a new class of frequency combs (microcombs) have emerged based on parametric frequency conversions in dielectric microresonators. Micocombs have large line spacing from 10's to 100's GHz, allowing easy access to individual comb lines for arbitrary waveform synthesis. They also provide broadband parametric gain bandwidth, not limited by specific atomic or molecular transitions in conventional OFCs. The emerging applications of microcombs include low noise microwave generation, astronomical spectrograph calibration, direct comb spectroscopy, and high capacity telecommunications.
\r\n\r\nIn this thesis, research is presented starting with the introduction of a new type of chemically etched, planar silica-on-silicon disk resonator. A record Q factor of 875 million is achieved for on-chip devices. A simple and accurate approach to characterize the FSR and dispersion of microcavities is demonstrated. Microresonator-based frequency combs (microcombs) are demonstrated with microwave repetition rate less than 80 GHz on a chip for the first time. Overall low threshold power (as low as 1 mW) of microcombs across a wide range of resonator FSRs from 2.6 to 220 GHz in surface-loss-limited disk resonators is demonstrated. The rich and complex dynamics of microcomb RF noise are studied. High-coherence, RF phase-locking of microcombs is demonstrated where injection locking of the subcomb offset frequencies are observed by pump-detuning-alignment. Moreover, temporal mode locking, featuring subpicosecond pulses from a parametric 22 GHz microcomb, is observed. We further demonstrated a shot-noise-limited white phase noise of microcomb for the first time. Finally, stabilization of the microcomb repetition rate is realized by phase lock loop control.
\r\n\r\nFor another major nonlinear optical application of disk resonators, highly coherent, simulated Brillouin lasers (SBL) on silicon are also demonstrated, with record low Schawlow-Townes noise less than 0.1 Hz^2/Hz for any chip-based lasers and low technical noise comparable to commercial narrow-linewidth fiber lasers. The SBL devices are efficient, featuring more than 90% quantum efficiency and threshold as low as 60 microwatts. Moreover, novel properties of the SBL are studied, including cascaded operation, threshold tuning, and mode-pulling phenomena. Furthermore, high performance microwave generation using on-chip cascaded Brillouin oscillation is demonstrated. It is also robust enough to enable incorporation as the optical voltage-controlled-oscillator in the first demonstration of a photonic-based, microwave frequency synthesizer. Finally, applications of microresonators as frequency reference cavities and low-phase-noise optomechanical oscillators are presented.
" }, { "name": "Li, Na (Lina)", "degree": "PhD", "year": "2013", "title": "Distributed Optimization in Power Networks and General Multi-agent Systems", "advisor": "Doyle, John Comstock; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-122007615", "creators": [ { "name": { "family": "Li", "given": "Na (Lina)" }, "id": "Li-Na-Lina", "display_name": "Li, Na (Lina)" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "co-advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "co-chair", "display_name": "Low, Steven H." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Marden", "given": "Jason R." }, "id": "Marden-J-R", "role": "member", "display_name": "Marden, Jason R." } ], "option_major": [ "cds" ], "doi": "10.7907/NHVJ-FX37", "abstract": "The dissertation studies the general area of complex networked systems that consist of interconnected and active heterogeneous components and usually operate in uncertain environments and with incomplete information. Problems associated with those systems are typically large-scale and computationally intractable, yet they are also very well-structured and have features that can be exploited by appropriate modeling and computational methods. The goal of this thesis is to develop foundational theories and tools to exploit those structures that can lead to computationally-efficient and distributed solutions, and apply them to improve systems operations and architecture.
\r\n\r\nSpecifically, the thesis focuses on two concrete areas. The first one is to design distributed rules to manage distributed energy resources in the power network. The power network is undergoing a fundamental transformation. The future smart grid, especially on the distribution system, will be a large-scale network of distributed energy resources (DERs), each introducing random and rapid fluctuations in power supply, demand, voltage and frequency. These DERs provide a tremendous opportunity for sustainability, efficiency, and power reliability. However, there are daunting technical challenges in managing these DERs and optimizing their operation. The focus of this dissertation is to develop scalable, distributed, and real-time control and optimization to achieve system-wide efficiency, reliability, and robustness for the future power grid. In particular, we will present how to explore the power network structure to design efficient and distributed market and algorithms for the energy management. We will also show how to connect the algorithms with physical dynamics and existing control mechanisms for real-time control in power networks.
\r\n\r\nThe second focus is to develop distributed optimization rules for general multi-agent engineering systems. A central goal in multiagent systems is to design local control laws for the individual agents to ensure that the emergent global behavior is desirable with respect to the given system level objective. Ideally, a system designer seeks to satisfy this goal while conditioning each agent\u2019s control on the least amount of information possible. Our work focused on achieving this goal using the framework of game theory. In particular, we derived a systematic methodology for designing local agent objective functions that guarantees (i) an equivalence between the resulting game-theoretic equilibria and the system level design objective and (ii) that the resulting game possesses an inherent structure that can be exploited for distributed learning, e.g., potential games. The control design can then be completed by applying any distributed learning algorithm that guarantees convergence to the game-theoretic equilibrium. One main advantage of this game theoretic approach is that it provides a hierarchical decomposition between the decomposition of the systemic objective (game design) and the specific local decision rules (distributed learning algorithms). This decomposition provides the system designer with tremendous flexibility to meet the design objectives and constraints inherent in a broad class of multiagent systems. Furthermore, in many settings the resulting controllers will be inherently robust to a host of uncertainties including asynchronous clock rates, delays in information, and component failures.
" }, { "name": "Lin, Minghong", "degree": "PhD", "year": "2013", "title": "Algorithmic Challenges in Green Data Centers", "advisor": "Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-223354639", "creators": [ { "name": { "family": "Lin", "given": "Minghong" }, "id": "Lin-Minghong", "display_name": "Lin, Minghong" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Lui", "given": "John C. S." }, "id": "Lui-J-CS", "role": "member", "display_name": "Lui, John C. S." } ], "option_major": [ "compsci" ], "doi": "10.7907/NRXJ-JB76", "abstract": "With data centers being the supporting infrastructure for a wide range of IT services, their efficiency has become a big concern to operators, as well as to society, for both economic and environmental reasons. The goal of this thesis is to design energy-efficient algorithms that reduce energy cost while minimizing compromise to service. We focus on the algorithmic challenges at different levels of energy optimization across the data center stack. The algorithmic challenge at the device level is to improve the energy efficiency of a single computational device via techniques such as job scheduling and speed scaling. We analyze the common speed scaling algorithms in both the worst-case model and stochastic model to answer some fundamental issues in the design of speed scaling algorithms. The algorithmic challenge at the local data center level is to dynamically allocate resources (e.g., servers) and to dispatch the workload in a data center. We develop an online algorithm to make a data center more power-proportional by dynamically adapting the number of active servers. The algorithmic challenge at the global data center level is to dispatch the workload across multiple data centers, considering the geographical diversity of electricity price, availability of renewable energy, and network propagation delay. We propose algorithms to jointly optimize routing and provisioning in an online manner. Motivated by the above online decision problems, we move on to study a general class of online problem named \"smoothed online convex optimization\", which seeks to minimize the sum of a sequence of convex functions when \"smooth\" solutions are preferred. This model allows us to bridge different research communities and help us get a more fundamental understanding of general online decision problems." }, { "name": "Liu, Annie Hsin-Wen", "degree": "PhD", "year": "2013", "title": "Sensor Networks for Geospatial Event Detection - Theory and Applications", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062013-224746692", "creators": [ { "name": { "family": "Liu", "given": "Annie Hsin-Wen" }, "id": "Liu-Annie-Hsin-Wen", "display_name": "Liu, Annie Hsin-Wen" } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "role": "member", "display_name": "Clayton, Robert W." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "compsci" ], "doi": "10.7907/MZWJ-T222", "abstract": "This thesis presents theories, analyses, and algorithms for detecting and estimating parameters of geospatial events with today's large, noisy sensor networks. A geospatial event is initiated by a significant change in the state of points in a region in a 3-D space over an interval of time. After the event is initiated it may change the state of points over larger regions and longer periods of time.
\r\n\r\nNetworked sensing is a typical approach for geospatial event detection. In contrast to traditional sensor networks comprised of a small number of high quality (and expensive) sensors, trends in personal computing devices and consumer electronics have made it possible to build large, dense networks at a low cost. The changes in sensor capability, network composition, and system constraints call for new models and algorithms suited to the opportunities and challenges of the new generation of sensor networks.
\r\n\r\nThis thesis offers a single unifying model and a Bayesian framework for analyzing different types of geospatial events in such noisy sensor networks. It presents algorithms and theories for estimating the speed and accuracy of detecting geospatial events as a function of parameters from both the underlying geospatial system and the sensor network. Furthermore, the thesis addresses network scalability issues by presenting rigorous scalable algorithms for data aggregation for detection. These studies provide insights to the design of networked sensing systems for detecting geospatial events.
\r\n\r\nIn addition to providing an overarching framework, this thesis presents theories and experimental results for two very different geospatial problems: detecting earthquakes and hazardous radiation. The general framework is applied to these specific problems, and predictions based on the theories are validated against measurements of systems in the laboratory and in the field.
" }, { "name": "Liu, Chih-Hao", "degree": "PhD", "year": "2013", "title": "Transceiver Designs and Analysis for LTI, LTV and Broadcast Channels - New Matrix Decompositions and Majorization Theory", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282013-115316389", "creators": [ { "name": { "family": "Liu", "given": "Chih-Hao" }, "id": "Liu-Chih-Hao", "display_name": "Liu, Chih-Hao" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Quirk", "given": "Kevin J." }, "id": "Quirk-K-J", "role": "member", "display_name": "Quirk, Kevin J." }, { "name": { "family": "Tkacenko", "given": "Andre" }, "id": "Tkacenko-A", "role": "member", "display_name": "Tkacenko, Andre" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2VFF-SZ70", "abstract": "Signal processing techniques play important roles in the design of digital communication systems. These include information manipulation, transmitter signal processing, channel estimation, channel equalization and receiver signal processing. By interacting with communication theory and system implementing technologies, signal processing specialists develop efficient schemes for various communication problems by wisely exploiting various mathematical tools such as analysis, probability theory, matrix theory, optimization theory, and many others. In recent years, researchers realized that multiple-input multiple-output (MIMO) channel models are applicable to a wide range of different physical communications channels. Using the elegant matrix-vector notations, many MIMO transceiver (including the precoder and equalizer) design problems can be solved by matrix and optimization theory. Furthermore, the researchers showed that the majorization theory and matrix decompositions, such as singular value decomposition (SVD), geometric mean decomposition (GMD) and generalized triangular decomposition (GTD), provide unified frameworks for solving many of the point-to-point MIMO transceiver design problems.
\r\n\r\nIn this thesis, we consider the transceiver design problems for linear time invariant (LTI) flat MIMO channels, linear time-varying narrowband MIMO channels, flat MIMO broadcast channels, and doubly selective scalar channels. Additionally, the channel estimation problem is also considered. The main contributions of this dissertation are the development of new matrix decompositions, and the uses of the matrix decompositions and majorization theory toward the practical transmit-receive scheme designs for transceiver optimization problems. Elegant solutions are obtained, novel transceiver structures are developed, ingenious algorithms are proposed, and performance analyses are derived.
\r\n\r\nThe first part of the thesis focuses on transceiver design with LTI flat MIMO channels. We propose a novel matrix decomposition which decomposes a complex matrix as a product of several sets of semi-unitary matrices and upper triangular matrices in an iterative manner. The complexity of the new decomposition, generalized geometric mean decomposition (GGMD), is always less than or equal to that of geometric mean decomposition (GMD). The optimal GGMD parameters which yield the minimal complexity are derived. Based on the channel state information (CSI) at both the transmitter (CSIT) and receiver (CSIR), GGMD is used to design a butterfly structured decision feedback equalizer (DFE) MIMO transceiver which achieves the minimum average mean square error (MSE) under the total transmit power constraint. A novel iterative receiving detection algorithm for the specific receiver is also proposed. For the application to cyclic prefix (CP) systems in which the SVD of the equivalent channel matrix can be easily computed, the proposed GGMD transceiver has K/log_2(K) times complexity advantage over the GMD transceiver, where K is the number of data symbols per data block and is a power of 2. The performance analysis shows that the GGMD DFE transceiver can convert a MIMO channel into a set of parallel subchannels with the same bias and signal to interference plus noise ratios (SINRs). Hence, the average bit rate error (BER) is automatically minimized without the need for bit allocation. Moreover, the proposed transceiver can achieve the channel capacity simply by applying independent scalar Gaussian codes of the same rate at subchannels.
\r\n\r\nIn the second part of the thesis, we focus on MIMO transceiver design for slowly time-varying MIMO channels with zero-forcing or MMSE criterion. Even though the GGMD/GMD DFE transceivers work for slowly time-varying MIMO channels by exploiting the instantaneous CSI at both ends, their performance is by no means optimal since the temporal diversity of the time-varying channels is not exploited. Based on the GTD, we develop space-time GTD (ST-GTD) for the decomposition of linear time-varying flat MIMO channels. \r\nUnder the assumption that CSIT, CSIR and channel prediction are available, by using the proposed ST-GTD, we develop space-time geometric mean decomposition (ST-GMD) DFE transceivers under the zero-forcing or MMSE criterion. Under perfect channel prediction, the new system minimizes both the average MSE at the detector in each space-time (ST) block (which consists of several coherence blocks), and the average per ST-block BER in the moderate high SNR region. Moreover, the ST-GMD DFE transceiver designed under an MMSE criterion maximizes Gaussian mutual information over the equivalent channel seen by each ST-block. In general, the newly proposed transceivers perform better than the GGMD-based systems since the super-imposed temporal precoder is able to exploit the temporal diversity of time-varying channels. For practical applications, a novel ST-GTD based system which does not require channel prediction but shares the same asymptotic BER performance with the ST-GMD DFE transceiver is also proposed.
\r\n\r\nThe third part of the thesis considers two quality of service (QoS) transceiver design problems for flat MIMO broadcast channels. The first one is the power minimization problem (min-power) with a total bitrate constraint and per-stream BER constraints. The second problem is the rate maximization problem (max-rate) with a total transmit power constraint and per-stream BER constraints. Exploiting a particular class of joint triangularization (JT), we are able to jointly optimize the bit allocation and the broadcast DFE transceiver for the min-power and max-rate problems. The resulting optimal designs are called the minimum power JT broadcast DFE transceiver (MPJT) and maximum rate JT broadcast DFE transceiver (MRJT), respectively. In addition to the optimal designs, two suboptimal designs based on QR decomposition are proposed. They are realizable for arbitrary number of users.
\r\n\r\nFinally, we investigate the design of a discrete Fourier transform (DFT) modulated filterbank transceiver (DFT-FBT) with LTV scalar channels. For both cases with known LTV channels and unknown wide sense stationary uncorrelated scattering (WSSUS) statistical channels, we show how to optimize the transmitting and receiving prototypes of a DFT-FBT such that the SINR at the receiver is maximized. Also, a novel pilot-aided subspace channel estimation algorithm is proposed for the orthogonal frequency division multiplexing (OFDM) systems with quasi-stationary multi-path Rayleigh fading channels. Using the concept of a difference co-array, the new technique can construct M^2 co-pilots from M physical pilot tones with alternating pilot placement. Subspace methods, such as MUSIC and ESPRIT, can be used to estimate the multipath delays and the number of identifiable paths is up to O(M^2), theoretically. With the delay information, a MMSE estimator for frequency response is derived. It is shown through simulations that the proposed method outperforms the conventional subspace channel estimator when the number of multipaths is greater than or equal to the number of physical pilots minus one.
\r\n" }, { "name": "Loh Rui Yan, Matthew", "degree": "PhD", "year": "2013", "title": "Dense, Efficient Chip-to-Chip Communication at the Extremes of Computing", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082013-113725728", "creators": [ { "name": { "family": "Loh Rui Yan", "given": "Matthew" }, "id": "Loh-Rui-Yan-Matthew", "display_name": "Loh Rui Yan, Matthew" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/FQ18-2X96", "abstract": "The scalability of CMOS technology has driven computation into a diverse range of applications across the power consumption, performance and size spectra. Communication is a necessary adjunct to computation, and whether this is to push data from node-to-node in a high-performance computing cluster or from the receiver of wireless link to a neural stimulator in a biomedical implant, interconnect can take up a significant portion of the overall system power budget. Although a single interconnect methodology cannot address such a broad range of systems efficiently, there are a number of key design concepts that enable good interconnect design in the age of highly-scaled CMOS: an emphasis on highly-digital approaches to solving \u2018analog\u2019 problems, hardware sharing between links as well as between different functions (such as equalization and synchronization) in the same link, and adaptive hardware that changes its operating parameters to mitigate not only variation in the fabrication of the link, but also link conditions that change over time. These concepts are demonstrated through the use of two design examples, at the extremes of the power and performance spectra.
\r\n\r\nA novel all-digital clock and data recovery technique for high-performance, high density interconnect has been developed. Two independently adjustable clock phases are generated from a delay line calibrated to 2 UI. One clock phase is placed in the middle of the eye to recover the data, while the other is swept across the delay line. The samples produced by the two clocks are compared to generate eye information, which is used to determine the best phase for data recovery. The functions of the two clocks are swapped after the data phase is updated; this ping-pong action allows an infinite delay range without the use of a PLL or DLL. The scheme's generalized sampling and retiming architecture is used in a sharing technique that saves power and area in high-density interconnect. The eye information generated is also useful for tuning an adaptive equalizer, circumventing the need for dedicated adaptation hardware.
\r\n\r\nOn the other side of the performance/power spectra, a capacitive proximity interconnect has been developed to support 3D integration of biomedical implants. In order to integrate more functionality while staying within size limits, implant electronics can be embedded onto a foldable parylene (\u2018origami\u2019) substrate. Many of the ICs in an origami implant will be placed face-to-face with each other, so wireless proximity interconnect can be used to increase communication density while decreasing implant size, as well as facilitate a modular approach to implant design, where pre-fabricated parylene-and-IC modules are assembled together on-demand to make custom implants. Such an interconnect needs to be able to sense and adapt to changes in alignment. The proposed array uses a TDC-like structure to realize both communication and alignment sensing within the same set of plates, increasing communication density and eliminating the need to infer link quality from a separate alignment block. In order to distinguish the communication plates from the nearby ground plane, a stimulus is applied to the transmitter plate, which is rectified at the receiver to bias a delay generation block. This delay is in turn converted into a digital word using a TDC, providing alignment information.
\r\n" }, { "name": "Lopez Ortega, Alejandro", "degree": "PhD", "year": "2013", "title": "Simulation of Richtmyer-Meshkov Flows for Elastic-Plastic Solids in Planar and Converging Geometries Using an Eulerian Framework", "advisor": "Pullin, Dale Ian; Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02202013-185004693", "creators": [ { "name": { "family": "Lopez Ortega", "given": "Alejandro" }, "id": "Lopez-Ortega-Alejandro", "display_name": "Lopez Ortega, Alejandro" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "co-advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4WJ6-D795", "abstract": "This thesis presents a numerical and analytical study of two problems of interest involving shock waves propagating through elastic-plastic media: the motion of converging (imploding) shocks and the Richtmyer-Meshkov (RM) instability. Since the stress conditions encountered in these cases normally produce large deformations in the materials, an Eulerian description, in which the spatial coordinates are fixed, is employed. This formulation enables a direct comparison of similarities and differences between the present study of phenomena driven by shock-loading in elastic-plastic solids, and in fluids, where they have been studied extensively. In the first application, Whitham's shock dynamics (WSD) theory is employed for obtaining an approximate description of the motion of an elastic-plastic material processed by a cylindrically/spherically converging shock. Comparison with numerical simulations of the full set of equations of motion reveal that WSD is an accurate tool for characterizing the evolution of converging shocks at all stages. The study of the Richtmyer-Meshkov flow (i.e., interaction between the interface separating two materials of different density and a shock wave incoming at an angle) in solids is performed by means of analytical models for purely elastic solids and numerical simulations when plasticity is included in the material model. To this effect, an updated version of a previously developed multi-material, level-set-based, Eulerian framework for solid mechanics is employed. The revised code includes the use of a multi-material HLLD Riemann problem for imposing material boundary conditions, and a new formulation of the equations of motion that makes use of the stretch tensor while avoiding the degeneracy of the stress tensor under rotation. Results reveal that the interface separating two elastic solids always behaves in a stable oscillatory or decaying oscillatory manner due to the existence of shear waves, which are able to transport the initial vorticity away from the interface. In the case of elastic-plastic materials, the interface behaves at first in an unstable manner similar to a fluid. Ejecta formation is appreciated under certain initial conditions while in other conditions, after an initial period of growth, the interface displays a quasi-stationary long-term behavior due to stress relaxation. The effect of secondary shock-interface interactions (re-shocks) in converging geometries is also studied. A turbulent mixing zone, similar to what is observed in gas--gas interfaces, is created, especially when materials with low strength driven by moderate to strong shocks are considered." }, { "name": "McCoy, Michael Brian", "degree": "PhD", "year": "2013", "title": "A Geometric Analysis of Convex Demixing", "advisor": "Tropp, Joel A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05202013-091317123", "creators": [ { "name": { "family": "McCoy", "given": "Michael Brian" }, "id": "McCoy-Michael-Brian", "orcid": "0000-0002-9479-2090", "display_name": "McCoy, Michael Brian" } ], "advisors": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "advisor", "display_name": "Tropp, Joel A." } ], "committee": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "chair", "display_name": "Tropp, Joel A." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "role": "member", "display_name": "Schulman, Leonard J." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/156S-EZ89", "abstract": "Demixing is the task of identifying multiple signals given only their sum and prior information about their structures. Examples of demixing problems include (i) separating a signal that is sparse with respect to one basis from a signal that is sparse with respect to a second basis; (ii) decomposing an observed matrix into low-rank and sparse components; and (iii) identifying a binary codeword with impulsive corruptions. This thesis describes and analyzes a convex optimization framework for solving an array of demixing problems.
\r\n \r\nOur framework includes a random orientation model for the constituent signals that ensures the structures are incoherent. This work introduces a summary parameter, the statistical dimension, that reflects the intrinsic complexity of a signal. The main result indicates that the difficulty of demixing under this random model depends only on the total complexity of the constituent signals involved: demixing succeeds with high probability when the sum of the complexities is less than the ambient dimension; otherwise, it fails with high probability.
\r\n\r\nThe fact that a phase transition between success and failure occurs in demixing is a consequence of a new inequality in conic integral geometry. Roughly speaking, this inequality asserts that a convex cone behaves like a subspace whose dimension is equal to the statistical dimension of the cone. When combined with a geometric optimality condition for demixing, this inequality provides precise quantitative information about the phase transition, including the location and width of the transition region.
" }, { "name": "Mehta, Nikil", "degree": "PhD", "year": "2013", "title": "An Ultra-Low-Energy, Variation-Tolerant FPGA Architecture Using Component-Specific Mapping", "advisor": "DeHon, Andre", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072012-230900231", "creators": [ { "name": { "family": "Mehta", "given": "Nikil" }, "id": "Mehta-Nikil", "display_name": "Mehta, Nikil" } ], "advisors": [ { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "advisor", "display_name": "DeHon, Andre" } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "member", "display_name": "DeHon, Andre" }, { "name": { "family": "Calhoun", "given": "Benton H." }, "id": "Calhoun-B-H", "role": "member", "display_name": "Calhoun, Benton H." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "compsci" ], "doi": "10.7907/358S-CW22", "abstract": "As feature sizes scale toward atomic limits, parameter variation continues to increase, leading to increased margins in both delay and energy. Parameter variation both slows down devices and causes devices to fail. For applications that require high performance, the possibility of very slow devices on critical paths forces designers to reduce clock speed in order to meet timing. For an important and emerging class of applications that target energy-minimal operation at the cost of delay, the impact of variation-induced defects at very low voltages mandates the sizing up of transistors and operation at higher voltages to maintain functionality.
\r\n\r\nWith post-fabrication configurability, FPGAs have the opportunity to self-measure the impact of variation, determining the speed and functionality of each individual resource. Given that information, a delay-aware router can use slow devices on non-critical paths, fast devices on critical paths, and avoid known defects. By mapping each component individually and customizing designs to a component's unique physical characteristics, we demonstrate that we can eliminate delay margins and reduce energy margins caused by variation.
\r\n\r\nTo quantify the potential benefit we might gain from component-specific mapping, we first measure the margins associated with parameter variation, and then focus primarily on the energy benefits of FPGA delay-aware routing over a wide range of predictive technologies (45 nm--12 nm) for the Toronto20 benchmark set. We show that relative to delay-oblivious routing, delay-aware routing without any significant optimizations can reduce minimum energy/operation by 1.72x at 22 nm. We demonstrate how to construct an FPGA architecture specifically tailored to further increase the minimum energy savings of component-specific mapping by using the following techniques: power gating, gate sizing, interconnect sparing, and LUT remapping. With all optimizations considered we show a minimum energy/operation savings of 2.66x at 22 nm, or 1.68--2.95x when considered across 45--12 nm. As there are many challenges to measuring resource delays and mapping per chip, we discuss methods that may make component-specific mapping more practical. We demonstrate that a simpler, defect-aware routing achieves 70% of the energy savings of delay-aware routing. Finally, we show that without variation tolerance, scaling from 16 nm to 12 nm results in a net increase in minimum energy/operation; component-specific mapping, however, can extend minimum energy/operation scaling to 12 nm and possibly beyond.
\r\n" }, { "name": "Mihaly, Jonathan Michael", "degree": "PhD", "year": "2013", "title": "Investigation of Hypervelocity Impact Phenomena Using Real-time Concurrent Diagnostics", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072013-143355354", "creators": [ { "name": { "family": "Mihaly", "given": "Jonathan Michael" }, "id": "Mihaly-Jonathan-Michael", "display_name": "Mihaly, Jonathan Michael" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V3A7-7686", "abstract": "Hypervelocity impact of meteoroids and orbital debris poses a serious and growing threat to spacecraft. To study hypervelocity impact phenomena, a comprehensive ensemble of real-time concurrently operated diagnostics has been developed and implemented in the Small Particle Hypervelocity Impact Range (SPHIR) facility. This suite of simultaneously operated instrumentation provides multiple complementary measurements that facilitate the characterization of many impact phenomena in a single experiment. The investigation of hypervelocity impact phenomena described in this work focuses on normal impacts of 1.8 mm nylon 6/6 cylinder projectiles and variable thickness aluminum targets. The SPHIR facility two-stage light-gas gun is capable of routinely launching 5.5 mg nylon impactors to speeds of 5 to 7 km/s. Refinement of legacy SPHIR operation procedures and the investigation of first-stage pressure have improved the velocity performance of the facility, resulting in an increase in average impact velocity of at least 0.57 km/s. Results for the perforation area indicate the considered range of target thicknesses represent multiple regimes describing the non-monotonic scaling of target perforation with decreasing target thickness. The laser side-lighting (LSL) system has been developed to provide ultra-high-speed shadowgraph images of the impact event. This novel optical technique is demonstrated to characterize the propagation velocity and two-dimensional optical density of impact-generated debris clouds. Additionally, a debris capture system is located behind the target during every experiment to provide complementary information regarding the trajectory distribution and penetration depth of individual debris particles. The utilization of a coherent, collimated illumination source in the LSL system facilitates the simultaneous measurement of impact phenomena with near-IR and UV-vis spectrograph systems. Comparison of LSL images to concurrent IR results indicates two distinctly different phenomena. A high-speed, pressure-dependent IR-emitting cloud is observed in experiments to expand at velocities much higher than the debris and ejecta phenomena observed using the LSL system. In double-plate target configurations, this phenomena is observed to interact with the rear-wall several micro-seconds before the subsequent arrival of the debris cloud. Additionally, dimensional analysis presented by Whitham for blast waves is shown to describe the pressure-dependent radial expansion of the observed IR-emitting phenomena. Although this work focuses on a single hypervelocity impact configuration, the diagnostic capabilities and techniques described can be used with a wide variety of impactors, materials, and geometries to investigate any number of engineering and scientific problems." }, { "name": "Mishra, Himanshu", "degree": "PhD", "year": "2013", "title": "Proton Transfers at the Air-Water Interface", "advisor": "Goddard, William A., III; Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05092013-220921048", "creators": [ { "name": { "family": "Mishra", "given": "Himanshu" }, "id": "Mishra-Himanshu", "display_name": "Mishra, Himanshu" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "co-advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "matsci" ], "doi": "10.7907/A9HR-PN89", "abstract": "Proton transfer reactions at the interface of water with hydrophobic media, such as air or lipids, are ubiquitous on our planet. These reactions orchestrate a host of vital phenomena in the environment including, for example, acidification of clouds, enzymatic catalysis, chemistries of aerosol and atmospheric gases, and bioenergetic transduction. Despite their importance, however, quantitative details underlying these interactions have remained unclear. Deeper insight into these interfacial reactions is also required in addressing challenges in green chemistry, improved water quality, self-assembly of materials, the next generation of micro-nanofluidics, adhesives, coatings, catalysts, and electrodes. This thesis describes experimental and theoretical investigation of proton transfer reactions at the air-water interface as a function of hydration gradients, electrochemical potential, and electrostatics. Since emerging insights hold at the lipid-water interface as well, this work is also expected to aid understanding of complex biological phenomena associated with proton migration across membranes.
\r\n\r\nBased on our current understanding, it is known that the physicochemical properties of the gas-phase water are drastically different from those of bulk water. For example, the gas-phase hydronium ion, H3O+(g), can protonate most (non-alkane) organic species, whereas H3O+(aq) can neutralize only relatively strong bases. Thus, to be able to understand and engineer water-hydrophobe interfaces, it is imperative to investigate this fluctuating region of molecular thickness wherein the \u2018function\u2019 of chemical species transitions from one phase to another via steep gradients in hydration, dielectric constant, and density. Aqueous interfaces are difficult to approach by current experimental techniques because designing experiments to specifically sample interfacial layers (< 1 nm thick) is an arduous task. While recent advances in surface-specific spectroscopies have provided valuable information regarding the structure of aqueous interfaces, but structure alone is inadequate to decipher the function. By similar analogy, theoretical predictions based on classical molecular dynamics have remained limited in their scope.
\r\n\r\nRecently, we have adapted an analytical electrospray ionization mass spectrometer (ESIMS) for probing reactions at the gas-liquid interface in real time. This technique is direct, surface-specific,and provides unambiguous mass-to-charge ratios of interfacial species. With this innovation, we have been able to investigate the following:
\r\n\r\n1. How do anions mediate proton transfers at the air-water interface?
\r\n\r\n2. What is the basis for the negative surface potential at the air-water interface?
\r\n\r\n3. What is the mechanism for catalysis \u2018on-water\u2019?
\r\n\r\nIn addition to our experiments with the ESIMS, we applied quantum mechanics and molecular dynamics to simulate our experiments toward gaining insight at the molecular scale. Our results unambiguously demonstrated the role of electrostatic-reorganization of interfacial water during proton transfer events. With our experimental and theoretical results on the \u2018superacidity\u2019 of the surface of mildly acidic water, we also explored implications on atmospheric chemistry and green chemistry. Our most recent results explained the basis for the negative charge of the air-water interface and showed that the water-hydrophobe interface could serve as a site for enhanced autodissociation of water compared to the condensed phase.
" }, { "name": "Moeller, Robert Carlos", "degree": "PhD", "year": "2013", "title": "Current Transport and Onset-Related Phenomena in an MPD Thruster Modified by Applied Magnetic Fields", "advisor": "Shepherd, Joseph E.; Polk, James E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01252013-171305685", "creators": [ { "name": { "family": "Moeller", "given": "Robert Carlos" }, "id": "Moeller-Robert-Carlos", "display_name": "Moeller, Robert Carlos" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "co-advisor", "display_name": "Polk, James E." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/39VT-GB93", "abstract": "This work investigated the effects of tailored, externally-applied magnetic fields on current transport and near-anode processes in the plasma discharge of a magnetoplasmadynamic thruster (MPDT). Electrical and plasma diagnostics were used to determine whether applied magnetic fields could mitigate the effects of the \"onset\" phenomena, including large-amplitude terminal voltage fluctuations and high anode fall voltages associated with unstable operation and anode erosion. A new MPDT was developed and operated with quasi-steady 1 ms pulses from 36 kW to 3.3 MW with argon propellant. Three magnetic configurations studied included self-field operation (without external electromagnets) and two applied poloidal magnetic fields. One configuration used magnetic field lines tangential to the anode lip (and intersecting the anode further upstream) and the other created a magnetic cusp intersecting the anode downstream.
\r\n\r\nThe influence of the applied fields on the discharge current streamlines, current densities, and key plasma properties (electron temperature, number density, and plasma potential) was studied. Key findings included that the current pattern and current densities redistributed to follow the applied magnetic field lines. Also, the anode fall voltage was substantially reduced with both applied fields over a large range of currents (and eliminated at 8 kA). These results occurred because applied magnetic field lines intersecting the anode provided a high conductivity path and reduced the local electric field required to sustain the radial current densities. The applied fields reduced the amplitude and frequency of the terminal voltage fluctuations (up to 49%) over a broad range of currents and also decreased transients in the ion saturation current, which suggest reduction of current filamentation and surface-eroding anode spots. Additionally, the cusp field reduced mean terminal voltages over the entire range of discharge currents (up to 31%), and the tangential field lowered terminal voltages below 10.7 kA. These significant reductions in onset-related behaviors should lead to improved thruster lifetime and increased efficiency. These results suggest a distinctive and more effective approach to influencing the near-anode phenomena and mitigating the effects of onset with appropriately designed applied magnetic fields that differ from those used in the vast majority of conventional, so-called \"applied-field MPD thrusters.\"
" }, { "name": "Mu\u00f1oz, Jorge Alberto", "degree": "PhD", "year": "2013", "title": "Electronic Structure and Phonon Thermodynamics of Iron Alloys", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-184738559", "creators": [ { "name": { "family": "Mu\u00f1oz", "given": "Jorge Alberto" }, "id": "Mu\u00f1oz-Jorge-Alberto", "display_name": "Mu\u00f1oz, Jorge Alberto" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/7EJD-RP70", "abstract": "Inelastic neutron scattering (INS) and nuclear-resonant inelastic x-ray scattering (NRIXS) were used to measure phonon spectra of FeV as a B2- ordered compound and as a bcc solid solution. Contrary to the behavior of ordering alloys studied to date, the phonons in the B2-ordered phase are softer than in the solid solution. Ordering increases the vibrational entropy, which stabilizes the ordered phase to higher temperatures. Ab initio calculations show that the number of electronic states at the Fermi level increases upon ordering, enhancing the screening between ions, and reducing the interatomic force constants. The effect of screening is larger at the V atomic sites than at the Fe atomic sites.
\r\n\r\nThe phonon spectra of Au-rich alloys of fcc Au-Fe were also measured. The main effect on the vibrational entropy of alloying comes from a stiffening of the Au partial phonon density of states (DOS) with Fe concentration that increases the miscibility gap temperature. The magnitude of the effect is non- linear and it is reduced at higher Fe concentrations. Force constants were calculated for several compositions and show a local stiffening of Au\u2013Au bonds close to Fe atoms, but Au\u2013Au bonds that are farther away do not show this effect. Phonon DOS curves calculated from the force constants reproduced the experimental trends. The Au\u2013Fe bond is soft and favors ordering, but a charge transfer from the Fe to the Au atoms stiffens the Au\u2013Au bonds enough to favor unmixing. The stiffening is attributed to two main effects comparable in magnitude: an increase in electron density in the free-electron-like states, and stronger sd-hybridization.
\r\n\r\nINS and NRIXS measurements were performed at elevated temperatures on B2-ordered FeTi and NRIXS measurements were performed at high pressures. The high-pressure behavior is quasi- harmonic. The softening of the phonon DOS curves with temperature is strongly nonharmonic. Calculations of the force constants and Born-von Karman fits to the experimental data show that the bonds between second nearest neighbors (2nn) are much stiffer than those between 1nn, but fits to the high temperature data show that the former softens at a faster rate with temperature. The Fe\u2013Fe bond softens more than the Ti\u2013Ti bond. The unusual stiffness of the 2nn bond is explained by the calculated charge distribution, which is highly aspherical and localized preferentially in the t2g orbitals. Ab initio molecular dynamics (AIMD) simulations show a charge transfer from the t2g orbitals to the eg orbitals at elevated temperatures. The asphericity decreases linearly with temperature and is more severe at the Fe sites.
" }, { "name": "Notbohm, Jacob K.", "degree": "PhD", "year": "2013", "title": "Dynamics of Cell\u2013Matrix Mechanical Interactions in Three Dimensions ", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-133431536", "creators": [ { "name": { "family": "Notbohm", "given": "Jacob K." }, "id": "Notbohm-Jacob-K", "display_name": "Notbohm, Jacob K." } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "member", "display_name": "Tirrell, David A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/AXD0-2D10", "abstract": "The forces cells apply to their surroundings control biological processes such as growth, adhesion, development, and migration. In the past 20 years, a number of experimental techniques have been developed to measure such cell tractions. These approaches have primarily measured the tractions applied by cells to synthetic two-dimensional substrates, which do not mimic in vivo conditions for most cell types. Many cell types live in a fibrous three-dimensional (3D) matrix environment. While studying cell behavior in such 3D matrices will provide valuable insights for the mechanobiology and tissue engineering communities, no experimental approaches have yet measured cell tractions in a fibrous 3D matrix.
\r\n\r\nThis thesis describes the development and application of an experimental technique for quantifying cellular forces in a natural 3D matrix. Cells and their surrounding matrix are imaged in three dimensions with high speed confocal microscopy. The cell-induced matrix displacements are computed from the 3D image volumes using digital volume correlation. The strain tensor in the 3D matrix is computed by differentiating the displacements, and the stress tensor is computed by applying a constitutive law. Finally, tractions applied by the cells to the matrix are computed directly from the stress tensor.
\r\n\r\nThe 3D traction measurement approach is used to investigate how cells mechanically interact with the matrix in biologically relevant processes such as division and invasion. During division, a single mother cell undergoes a drastic morphological change to split into two daughter cells. In a 3D matrix, dividing cells apply tensile force to the matrix through thin, persistent extensions that in turn direct the orientation and location of the daughter cells. Cell invasion into a 3D matrix is the first step required for cell migration in three dimensions. During invasion, cells initially apply minimal tractions to the matrix as they extend thin protrusions into the matrix fiber network. The invading cells anchor themselves to the matrix using these protrusions, and subsequently pull on the matrix to propel themselves forward.
\r\n\r\nLastly, this thesis describes a constitutive model for the 3D fibrous matrix that uses a finite element (FE) approach. The FE model simulates the fibrous microstructure of the matrix and matches the cell-induced matrix displacements observed experimentally using digital volume correlation. The model is applied to predict how cells mechanically sense one another in a 3D matrix. It is found that cell-induced matrix displacements localize along linear paths. These linear paths propagate over a long range through the fibrous matrix, and provide a mechanism for cell-cell signaling and mechanosensing. The FE model developed here has the potential to reveal the effects of matrix density, inhomogeneity, and anisotropy in signaling cell behavior through mechanotransduction.
" }, { "name": "O'Farrell, Clara", "degree": "PhD", "year": "2013", "title": "A Dynamical Systems Analysis of Vortex Pinch-Off", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032013-161632237", "creators": [ { "name": { "family": "O'Farrell", "given": "Clara" }, "id": "O'Farrell-Clara", "display_name": "O'Farrell, Clara" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "cds" ], "doi": "10.7907/AFAA-KF43", "abstract": "Vortex rings constitute the main structure in the wakes of a wide class of swimming and flying animals, as well as in cardiac flows and in the jets generated by some moss and fungi. However, there is a physical limit, determined by an energy maximization principle called the Kelvin-Benjamin principle, to the size that axisymmetric vortex rings can achieve. The existence of this limit is known to lead to the separation of a growing vortex ring from the shear layer feeding it, a process known as `vortex pinch-off', and characterized by the dimensionless vortex formation number. The goal of this thesis is to improve our understanding of vortex pinch-off as it relates to biological propulsion, and to provide future researchers with tools to assist in identifying and predicting pinch-off in biological flows.
\r\n\r\nTo this end, we introduce a method for identifying pinch-off in starting jets using the Lagrangian coherent structures in the flow, and apply this criterion to an experimentally generated starting jet. Since most naturally occurring vortex rings are not circular, we extend the definition of the vortex formation number to include non-axisymmetric vortex rings, and find that the formation number for moderately non-axisymmetric vortices is similar to that of circular vortex rings. This suggests that naturally occurring vortex rings may be modeled as axisymmetric vortex rings. Therefore, we consider the perturbation response of the Norbury family of axisymmetric vortex rings. This family is chosen to model vortex rings of increasing thickness and circulation, and their response to prolate shape perturbations is simulated using contour dynamics. Finally, the response of more realistic models for vortex rings, constructed from experimental data using nested contours, to perturbations which resemble those encountered by forming vortices more closely, is simulated using contour dynamics. In both families of models, a change in response analogous to pinch-off is found as members of the family with progressively thicker cores are considered. We posit that this analogy may be exploited to understand and predict pinch-off in complex biological flows, where current methods are not applicable in practice, and criteria based on the properties of vortex rings alone are necessary.
" }, { "name": "Oh, Tae-Sik", "degree": "PhD", "year": "2013", "title": "Electrical, Electrochemical, and Optical Characterization of Ceria Films", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05202013-113539414", "creators": [ { "name": { "family": "Oh", "given": "Tae-Sik" }, "id": "Oh-Tae-Sik", "display_name": "Oh, Tae-Sik" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Giapis", "given": "Konstantinos P." }, "id": "Giapis-K-P", "role": "member", "display_name": "Giapis, Konstantinos P." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" } ], "option_major": [ "matsci" ], "doi": "10.7907/139F-KV81", "abstract": "Acceptor-doped ceria has been recognized as a promising intermediate temperature solid oxide fuel cell electrode/electrolyte material. For practical implementation of ceria as a fuel cell electrolyte and for designing model experiments for electrochemical activity, it is necessary to fabricate thin films of ceria. Here, metal-organic chemical vapor deposition was carried out in a homemade reactor to grow ceria films for further electrical, electrochemical, and optical characterization. Doped/undoped ceria films are grown on single crystalline oxide wafers with/without Pt line pattern or Pt solid layer. Deposition conditions were varied to see the effect on the resultant film property. Recently, proton conduction in nanograined polycrystalline pellets of ceria drew much interest. Thickness-mode (through-plane, z-direction) electrical measurements were made to confirm the existence of proton conductivity and investigate the nature of the conduction pathway: exposed grain surfaces and parallel grain boundaries. Columnar structure presumably favors proton conduction, and we have found measurable proton conductivity enhancement. Electrochemical property of gas-columnar ceria interface on the hydrogen electrooxidation is studied by AC impedance spectroscopy. Isothermal gas composition dependence of the electrode resistance was studied to elucidate Sm doping level effect and microstructure effect. Significantly, preferred orientation is shown to affect the gas dependence and performance of the fuel cell anode. A hypothesis is proposed to explain the origin of this behavior. Lastly, an optical transmittance based methodology was developed to obtain reference refractive index and microstructural parameters (thickness, roughness, porosity) of ceria films via subsequent fitting procedure." }, { "name": "Pahlevan, Niema Mohammed", "degree": "PhD", "year": "2013", "title": "A Systems Approach to Cardiovascular Health and Disease with a Focus on Aortic Wave Dynamics", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082013-152249157", "creators": [ { "name": { "family": "Pahlevan", "given": "Niema Mohammed" }, "id": "Pahlevan-Niema-Mohammed", "display_name": "Pahlevan, Niema Mohammed" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "chair", "display_name": "Pierce, Niles A." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Hussain", "given": "Fazle" }, "id": "Hussain-F", "orcid": "0000-0002-2209-9270", "role": "member", "display_name": "Hussain, Fazle" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "bioeng" ], "doi": "10.7907/Z9DR2SFM", "abstract": "Cardiovascular diseases (CVDs) have reached an epidemic proportion in the US and worldwide with serious consequences in terms of human suffering and economic impact. More than one third of American adults are suffering from CVDs. The total direct and indirect costs of CVDs are more than $500 billion per year. Therefore, there is an urgent need to develop noninvasive diagnostics methods, to design minimally invasive assist devices, and to develop economical and easy-to-use monitoring systems for cardiovascular diseases. In order to achieve these goals, it is necessary to gain a better understanding of the subsystems that constitute the cardiovascular system. The aorta is one of these subsystems whose role in cardiovascular functioning has been underestimated. Traditionally, the aorta and its branches have been viewed as resistive conduits connected to an active pump (left ventricle of the heart). However, this perception fails to explain many observed physiological results. My goal in this thesis is to demonstrate the subtle but important role of the aorta as a system, with focus on the wave dynamics in the aorta.
\r\n\r\nThe operation of a healthy heart is based on an optimized balance between its pumping characteristics and the hemodynamics of the aorta and vascular branches. The delicate balance between the aorta and heart can be impaired due to aging, smoking, or disease. The heart generates pulsatile flow that produces pressure and flow waves as it enters into the compliant aorta. These aortic waves propagate and reflect from reflection sites (bifurcations and tapering). They can act constructively and assist the blood circulation. However, they may act destructively, promoting diseases or initiating sudden cardiac death. These waves also carry information about the diseases of the heart, vascular disease, and coupling of heart and aorta. In order to elucidate the role of the aorta as a dynamic system, the interplay between the dominant wave dynamic parameters is investigated in this study. These parameters are heart rate, aortic compliance (wave speed), and locations of reflection sites. Both computational and experimental approaches have been used in this research. In some cases, the results are further explained using theoretical models.
\r\n \r\nThe main findings of this study are as follows: (i) developing a physiologically realistic outflow boundary condition for blood flow modeling in a compliant vasculature; (ii) demonstrating that pulse pressure as a single index cannot predict the true level of pulsatile workload on the left ventricle; (iii) proving that there is an optimum heart rate in which the pulsatile workload of the heart is minimized and that the optimum heart rate shifts to a higher value as aortic rigidity increases; (iv) introducing a simple bio-inspired device for correction and optimization of aortic wave reflection that reduces the workload on the heart; (v) deriving a non-dimensional number that can predict the optimum wave dynamic state in a mammalian cardiovascular system; (vi) demonstrating that waves can create a pumping effect in the aorta; (vii) introducing a system parameter and a new medical index, Intrinsic Frequency, that can be used for noninvasive diagnosis of heart and vascular diseases; and (viii) proposing a new medical hypothesis for sudden cardiac death in young athletes.
\r\n" }, { "name": "Pal, Piya", "degree": "PhD", "year": "2013", "title": "New Directions In Sparse Sampling and Estimation For Underdetermined Systems", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072013-153438961", "creators": [ { "name": { "family": "Pal", "given": "Piya" }, "id": "Pal-Piya", "display_name": "Pal, Piya" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "van Zyl", "given": "Jakob J." }, "id": "van-Zyl-J-J", "role": "member", "display_name": "van Zyl, Jakob J." }, { "name": { "family": "Tkacenko", "given": "Andre" }, "id": "Tkacenko-A", "role": "member", "display_name": "Tkacenko, Andre" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/P0E1-5G05", "abstract": "A central objective in signal processing is to infer meaningful information from a set of measurements or data. While most signal models have an overdetermined structure (the number of unknowns less than the number of equations), traditionally very few statistical estimation problems have considered a data model which is underdetermined (number of unknowns more than the number of equations). However, in recent times, an explosion of theoretical and computational methods have been developed primarily to study underdetermined systems by imposing sparsity on the unknown variables. This is motivated by the observation that inspite of the huge volume of data that arises in sensor networks, genomics, imaging, particle physics, web search etc., their information content is often much smaller compared to the number of raw measurements. This has given rise to the possibility of reducing the number of measurements by down sampling the data, which automatically gives rise to underdetermined systems.
\r\n\r\nIn this thesis, we provide new directions for estimation in an underdetermined system, both for a class of parameter estimation problems and also for the problem of sparse recovery in compressive sensing. There are two main contributions of the thesis: design of new sampling and statistical estimation algorithms for array processing, and development of improved guarantees for sparse reconstruction by introducing a statistical framework to the recovery problem.
\r\n\r\nWe consider underdetermined observation models in array processing where the number of unknown sources simultaneously received by the array can be considerably larger than the number of physical sensors. We study new sparse spatial sampling schemes (array geometries) as well as propose new recovery algorithms that can exploit priors on the unknown signals and unambiguously identify all the sources. The proposed sampling structure is generic enough to be extended to multiple dimensions as well as to exploit different kinds of priors in the model such as correlation, higher order moments, etc.
\r\n\r\nRecognizing the role of correlation priors and suitable sampling schemes for underdetermined estimation in array processing, we introduce a correlation aware framework for recovering sparse support in compressive sensing. We show that it is possible to strictly increase the size of the recoverable sparse support using this framework provided the measurement matrix is suitably designed. The proposed nested and coprime arrays are shown to be appropriate candidates in this regard. We also provide new guarantees for convex and greedy formulations of the support recovery problem and demonstrate that it is possible to strictly improve upon existing guarantees.
\r\n\r\nThis new paradigm of underdetermined estimation that explicitly establishes the fundamental interplay between sampling, statistical priors and the underlying sparsity, leads to exciting future research directions in a variety of application areas, and also gives rise to new questions that can lead to stand-alone theoretical results in their own right.
\r\n\r\n" }, { "name": "Pang, Shuo", "degree": "PhD", "year": "2013", "title": "Fluorescence Optofluidic Microscopy and Fluorescence Microscopy Based on the Talbot Effect", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04132013-185824588", "creators": [ { "name": { "family": "Pang", "given": "Shuo" }, "id": "Pang-Shuo", "display_name": "Pang, Shuo" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "role": "member", "display_name": "Sternberg, Paul W." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WWFF-7S14", "abstract": "Light microscopy has been one of the most common tools in biological research, because of its high resolution and non-invasive nature of the light. Due to its high sensitivity and specificity, fluorescence is one of the most important readout modes of light microscopy. This thesis presents two new fluorescence microscopic imaging techniques: fluorescence optofluidic microscopy and fluorescent Talbot microscopy. The designs of the two systems are fundamentally different from conventional microscopy, which makes compact and portable devices possible. The components of the devices are suitable for mass-production, making the microscopic imaging system more affordable for biological research and clinical diagnostics.
\r\n\r\nFluorescence optofluidic microscopy (FOFM) is capable of imaging fluorescent samples in fluid media. The FOFM employs an array of Fresnel zone plates (FZP) to generate an array of focused light spots within a microfluidic channel. As a sample flows through the channel and across the array of focused light spots, a filter-coated CMOS sensor collects the fluorescence emissions. The collected data can then be processed to render a fluorescence microscopic image. The resolution, which is determined by the focused light spot size, is experimentally measured to be 0.65 \u03bcm.
\r\n\r\nFluorescence Talbot microscopy (FTM) is a fluorescence chip-scale microscopy technique that enables large field-of-view (FOV) and high-resolution imaging. The FTM method utilizes the Talbot effect to project a grid of focused excitation light spots onto the sample. The sample is placed on a filter-coated CMOS sensor chip. The fluorescence emissions associated with each focal spot are collected by the sensor chip and are composed into a sparsely sampled fluorescence image. By raster scanning the Talbot focal spot grid across the sample and collecting a sequence of sparse images, a filled-in high-resolution fluorescence image can be reconstructed. In contrast to a conventional microscope, a collection efficiency, resolution, and FOV are not tied to each other for this technique. The FOV of FTM is directly scalable. Our FTM prototype has demonstrated a resolution of 1.2 \u03bcm, and the collection efficiency equivalent to a conventional microscope objective with a 0.70 N.A. The FOV is 3.9 mm \u00d7 3.5 mm, which is 100 times larger than that of a 20X/0.40 N.A. conventional microscope objective. Due to its large FOV, high collection efficiency, compactness, and its potential for integration with other on-chip devices, FTM is suitable for diverse applications, such as point-of-care diagnostics, large-scale functional screens, and long-term automated imaging.
" }, { "name": "Panithipongwut, Chatr", "degree": "PhD", "year": "2013", "title": "Phase Behavior of Complex Superprotonic Solid Acids", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-183134007", "creators": [ { "name": { "family": "Panithipongwut", "given": "Chatr" }, "id": "Panithipongwut-Chatr", "display_name": "Panithipongwut, Chatr" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/NXG8-TY79", "abstract": "Superprotonic phase transitions and thermal behaviors of three complex solid acid systems are presented, namely Rb3H(SO4)2-RbHSO4 system, Rb3H(SeO4)22-Cs3H(SeO4)2 solid solution system, and Cs6(H2SO4)3(H1.5PO4)4. These material systems present a rich set of phase transition characteristics that set them apart from other, simpler solid acids. A.C. impedance spectroscopy, high-temperature X-ray powder diffraction, and thermal analysis, as well as other characterization techniques, were employed to investigate the phase behavior of these systems.
\r\n\r\nRb3H(SO4)2 is an atypical member of the M3H(XO4)2 class of compounds (M = alkali metal or NH4+ and X = S or Se) in that a transition to a high-conductivity state involves disproportionation into two phases rather than a simple polymorphic transition [1]. In the present work, investigations of the Rb3H(SO4)2-RbHSO4 system have revealed the disproportionation products to be Rb2SO4 and the previously unknown compound Rb5H3(SO4)4. The new compound becomes stable at a temperature between 25 and 140 \u00b0C and is isostructural to a recently reported trigonal phase with space group P3\u0305m of Cs5H3(SO4)4 [2]. At 185 \u00b0C the compound undergoes an apparently polymorphic transformation with a heat of transition of 23.8 kJ/mol and a slight additional increase in conductivity.
\r\n\r\nThe compounds Rb3H(SeO4)2 and Cs3H(SeO4)2, though not isomorphous at ambient temperatures, are quintessential examples of superprotonic materials. Both adopt monoclinic structures at ambient temperatures and ultimately transform to a trigonal (R3\u0305m) superprotonic structure at slightly elevated temperatures, 178 and 183 \u00b0C, respectively. The compounds are completely miscible above the superprotonic transition and show extensive solubility below it. Beyond a careful determination of the phase boundaries, we find a remarkable 40-fold increase in the superprotonic conductivity in intermediate compositions rich in Rb as compared to either end-member.
\r\n\r\nThe compound Cs6(H2SO4)3(H1.5PO4)4 is unusual amongst solid acid compounds in that it has a complex cubic structure at ambient temperature and apparently transforms to a simpler cubic structure of the CsCl-type (isostructural with CsH2PO4) at its transition temperature of 100-120 \u00b0C [3]. Here it is found that, depending on the level of humidification, the superprotonic transition of this material is superimposed with a decomposition reaction, which involves both exsolution of (liquid) acid and loss of H2O. This reaction can be suppressed by application of sufficiently high humidity, in which case Cs6(H2SO4)3(H1.5PO4)4 undergoes a true superprotonic transition. It is proposed that, under conditions of low humidity, the decomposition/dehydration reaction transforms the compound to Cs6(H2-0.5xSO4)3(H1.51.5PO4)4-x, also of the CsCl structure type at the temperatures of interest, but with a smaller unit cell. With increasing temperature, the decomposition/dehydration proceeds to greater and greater extent and unit cell of the solid phase decreases. This is identified to be the source of the apparent negative thermal expansion behavior.
\r\n\r\nReferences:
\r\n[1]\tL.A. Cowan, R.M. Morcos, N. Hatada, A. Navrotsky, S.M. Haile, Solid State Ionics 179 (2008) (9-10) 305.
\r\n[2]\tM. Sakashita, H. Fujihisa, K.I. Suzuki, S. Hayashi, K. Honda, Solid State Ionics 178 (2007) (21-22) 1262.
\r\n[3]\tC.R.I. Chisholm, Superprotonic Phase Transitions in Solid Acids: Parameters affecting the presence and stability of superprotonic transitions in the MHnXO4 family of compounds (X=S, Se, P, As; M=Li, Na, K, NH4, Rb, Cs), Materials Science, California Institute of Technology, Pasadena, California (2003).
With novel application of optical techniques, the slender-body hypervelocity boundary-layer instability is characterized in the previously unexplored regime where thermo-chemical effects are important. Narrowband disturbances (500-3000 kHz) are measured in boundary layers with edge velocities of up to 5~km/s at two points along the generator of a 5 degree half angle cone. Experimental amplification factor spectra are presented. Linear stability and PSE analysis is performed, with fair prediction of the frequency content of the disturbances; however, the analysis over-predicts the amplification of disturbances. The results of this work have two key implications: 1) the acoustic instability is present and may be studied in a large-scale hypervelocity reflected-shock tunnel, and 2) the new data set provides a new basis on which the instability can be studied.
" }, { "name": "Penmecha, Bharat Prasad", "degree": "PhD", "year": "2013", "title": "Fracture of Materials Undergoing Solid-Solid Phase Transformation", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-233635296", "creators": [ { "name": { "family": "Penmecha", "given": "Bharat Prasad" }, "id": "Penmecha-Bharat-Prasad", "display_name": "Penmecha, Bharat Prasad" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/FNTG-9T08", "abstract": "A large number of technologically important materials undergo solid-solid phase transformations. Examples range from ferroelectrics (transducers and memory devices), zirconia (Thermal Barrier Coatings) to nickel superalloys and (lithium) iron phosphate (Li-ion batteries). These transformations involve a change in the crystal structure either through diffusion of species or local rearrangement of atoms. This change of crystal structure leads to a macroscopic change of shape or volume or both and results in internal stresses during the transformation. In certain situations this stress field gives rise to cracks (tin, iron phosphate etc.) which continue to propagate as the transformation front traverses the material. In other materials the transformation modifies the stress field around cracks and effects crack growth behavior (zirconia, ferroelectrics). These observations serve as our motivation to study cracks in solids undergoing phase transformations. Understanding these effects will help in improving the mechanical reliability of the devices employing these materials.
\r\n\r\nIn this thesis we present work on two problems concerning the interplay between cracks and phase transformations. First, we consider the directional growth of a set of parallel edge cracks due to a solid-solid transformation. We conclude from our analysis that phase transformations can lead to formation of parallel edge cracks when the transformation strain satisfies certain conditions and the resulting cracks grow all the way till their tips cross over the phase boundary. Moreover the cracks continue to grow as the phase boundary traverses into the interior of the body at a uniform spacing without any instabilities. There exists an optimal value for the spacing between the cracks. We ascertain these conclusion by performing numerical simulations using finite elements.
\r\n\r\nSecond, we model the effect of the semiconducting nature and dopants on cracks in ferroelectric perovskite materials, particularly barium titanate. Traditional approaches to model fracture in these materials have treated them as insulators. In reality, they are wide bandgap semiconductors with oxygen vacancies and trace impurities acting as dopants. We incorporate the space charge arising due the semiconducting effect and dopant ionization in a phase field model for the ferroelectric. We derive the governing equations by invoking the dissipation inequality over a ferroelectric domain containing a crack. This approach also yields the driving force acting on the crack. Our phase field simulations of polarization domain evolution around a crack show the accumulation of electronic charge on the crack surface making it more permeable than was previously believed so, as seen in recent experiments. We also discuss the effect the space charge has on domain formation and the crack driving force.
" }, { "name": "Pomrehn, Gregory Schoelerman", "degree": "PhD", "year": "2013", "title": "Phase Stability and Defect Behavior in Complex Thermoelectric Zinc-Antimonides", "advisor": "van de Walle, Axel; Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:01252013-135311552", "creators": [ { "name": { "family": "Pomrehn", "given": "Gregory Schoelerman" }, "id": "Pomrehn-Gregory-Schoelerman", "display_name": "Pomrehn, Gregory Schoelerman" } ], "advisors": [ { "name": { "family": "van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "co-advisor", "display_name": "van de Walle, Axel" }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "co-advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "member", "display_name": "van de Walle, Axel" }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/0AWH-4P69", "abstract": "The Zn-Sb binary phase system has been of interest for many years in the search for efficient and low-cost thermoelectric materials. Of primary interest has been the Zn4Sb3 phase which exhibits a thermoelectric figure of merit, zT, in excess of 1 in an intermediate temperature range. In this study, Zn4Sb3 is shown to be entropically stabilized with respect to decomposition to Zn and ZnSb through the effects of configurational disorder and phonon free energy. Single-phase stability is predicted for a range of compositions and temperatures. Retrograde solubility of Zn is predicted on the two-phase boundary region between Zn4Sb3 and Zn. The complex temperature-dependent solubility can be used to explain the variety of nanoparticle formation observed in the system: formation of ZnSb on the Sb-rich side, Zn on the far Zn-rich side, and nano-void formation due to Zn precipitates being reabsorbed at lower temperatures.
\r\n\r\nA new binary compound, Zn8Sb7, known only in nanoparticulate form, is also studied using density functional calculations. The free energies of formation, including effects from vibrations and configurational disorder, are calculated to compare with the relevant phases ZnSb, Zn, and Zn4Sb3, yielding insight into the phase stability of Zn8Sb7. Band structure calculations predict Zn8Sb7, much like ZnSb and Zn4Sb3, to be an intermetallic semiconductor with similar thermoelectric properties. If sufficient entropy or surface energy exists to stabilize the bulk material, it would be stable in a limited temperature window at high temperature.
\r\n\r\nIn the AZn2Sb2 series of materials—A = Ca, Sr, Yb, and Eu—I show that a large concentration of thermodynamically stable cation vacancies leads to high extrinsic carrier concentrations. The stable defect level depends on the choice of A, and is consistent with experimentally observed carrier concentrations in these materials. These results demonstrate that point defects are the primary mechanism by which the covalency of the cation bond can influence carrier concentration in nominally valence-precise AZn2Sb2compounds. This mechanism may be generally applicable to other Zintl phases, perhaps explaining similar trends seen in A14MSb11, A2MSb2 (A=2+ cation, M = 2+ or 3+ metal),and similar materials.
" }, { "name": "Ren, Jian", "degree": "PhD", "year": "2013", "title": "Endoscopic Optical Coherence Tomography: Design and Application", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:06172013-155313179", "creators": [ { "name": { "family": "Ren", "given": "Jian" }, "id": "Ren-Jian", "display_name": "Ren, Jian" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Humayun", "given": "Mark" }, "id": "Humayun-M", "role": "member", "display_name": "Humayun, Mark" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9445JF5", "abstract": "This thesis presents an investigation on endoscopic optical coherence tomography (OCT). As a noninvasive imaging modality, OCT emerges as an increasingly important diagnostic tool for many clinical applications. Despite of many of its merits, such as high resolution and depth resolvability, a major limitation is the relatively shallow penetration depth in tissue (about 2\u223c3 mm). This is mainly due to tissue scattering and absorption. To overcome this limitation, people have been developing many different endoscopic OCT systems. By utilizing a minimally invasive endoscope, the OCT probing beam can be brought to the close vicinity of the tissue of interest and bypass the scattering of intervening tissues so that it can collect the reflected light signal from desired depth and provide a clear image representing the physiological structure of the region, which can not be disclosed by traditional OCT. In this thesis, three endoscope designs have been studied. While they rely on vastly different principles, they all converge to solve this long-standing problem.
\r\n\r\nA hand-held endoscope with manual scanning is first explored. When a user is holding a hand- held endoscope to examine samples, the movement of the device provides a natural scanning. We proposed and implemented an optical tracking system to estimate and record the trajectory of the device. By registering the OCT axial scan with the spatial information obtained from the tracking system, one can use this system to simply \u2018paint\u2019 a desired volume and get any arbitrary scanning pattern by manually waving the endoscope over the region of interest. The accuracy of the tracking system was measured to be about 10 microns, which is comparable to the lateral resolution of most OCT system. Targeted phantom sample and biological samples were manually scanned and the reconstructed images verified the method.
\r\n\r\nNext, we investigated a mechanical way to steer the beam in an OCT endoscope, which is termed as Paired-angle-rotation scanning (PARS). This concept was proposed by my colleague and we further developed this technology by enhancing the longevity of the device, reducing the diameter of the probe, and shrinking down the form factor of the hand-piece. Several families of probes have been designed and fabricated with various optical performances. They have been applied to different applications, including the collector channel examination for glaucoma stent implantation, and vitreous remnant detection during live animal vitrectomy.
\r\n\r\nLastly a novel non-moving scanning method has been devised. This approach is based on the EO effect of a KTN crystal. With Ohmic contact of the electrodes, the KTN crystal can exhibit a special mode of EO effect, termed as space-charge-controlled electro-optic effect, where the carrier electron will be injected into the material via the Ohmic contact. By applying a high voltage across the material, a linear phase profile can be built under this mode, which in turn deflects the light beam passing through. We constructed a relay telescope to adapt the KTN deflector into a bench top OCT scanning system. One of major technical challenges for this system is the strong chromatic dispersion of KTN crystal within the wavelength band of OCT system. We investigated its impact on the acquired OCT images and proposed a new approach to estimate and compensate the actual dispersion. Comparing with traditional methods, the new method is more computational efficient and accurate. Some biological samples were scanned by this KTN based system. The acquired images justified the feasibility of the usage of this system into a endoscopy setting.\r\nMy research above all aims to provide solutions to implement an OCT endoscope. As technology evolves from manual, to mechanical, and to electrical approaches, different solutions are presented. Since all have their own advantages and disadvantages, one has to determine the actual requirements and select the best fit for a specific application.
" }, { "name": "Richards, Andrew Walter", "degree": "PhD", "year": "2013", "title": "Interplay of Martensitic Phase Transformation and Plastic Slip in Polycrystals ", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072013-023915252", "creators": [ { "name": { "family": "Richards", "given": "Andrew Walter" }, "id": "Richards-Andrew-Walter", "display_name": "Richards, Andrew Walter" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lebensohn", "given": "Ricardo A." }, "id": "Lebensohn-R-A", "role": "member", "display_name": "Lebensohn, Ricardo A." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/MM8X-BZ69", "abstract": "Inspired by key experimental and analytical results regarding Shape Memory Alloys (SMAs), we propose a modelling framework to explore the interplay between martensitic phase transformations and plastic slip in polycrystalline materials, with an eye towards computational efficiency. The resulting framework uses a convexified potential for the internal energy density to capture the stored energy associated with transformation at the meso-scale, and introduces kinetic potentials to govern the evolution of transformation and plastic slip. The framework is novel in the way it treats plasticity on par with transformation.
\r\n\r\nWe implement the framework in the setting of anti-plane shear, using a staggered implicit/explict update: we first use a Fast-Fourier Transform (FFT) solver based on an Augmented Lagrangian formulation to implicitly solve for the full-field displacements of a simulated polycrystal, then explicitly update the volume fraction of martensite and plastic slip using their respective stick-slip type kinetic laws. We observe that, even in this simple setting with an idealized material comprising four martensitic variants and four slip systems, the model recovers a rich variety of SMA type behaviors. We use this model to gain insight into the isothermal behavior of stress-stabilized martensite, looking at the effects of the relative plastic yield strength, the memory of deformation history under non-proportional loading, and several others.
\r\n\r\nWe extend the framework to the generalized 3-D setting, for which the convexified potential is a lower bound on the actual internal energy, and show that the fully implicit discrete time formulation of the framework is governed by a variational principle for mechanical equilibrium. We further propose an extension of the method to finite deformations via an exponential mapping. We implement the generalized framework using an existing Optimal Transport Mesh-free (OTM) solver. We then model the $\\alpha$--$\\gamma$ and $\\alpha$--$\\varepsilon$ transformations in pure iron, with an initial attempt in the latter to account for twinning in the parent phase. We demonstrate the scalability of the framework to large scale computing by simulating Taylor impact experiments, observing nearly linear (ideal) speed-up through 256 MPI tasks. Finally, we present preliminary results of a simulated Split-Hopkinson Pressure Bar (SHPB) experiment using the $\\alpha$--$\\varepsilon$ model.
\r\n" }, { "name": "Russell, Damon Stuart", "degree": "PhD", "year": "2013", "title": "Technology Advances for Radio Astronomy", "advisor": "Weinreb, Sander", "url": "https://resolver.caltech.edu/CaltechTHESIS:11262012-212534634", "creators": [ { "name": { "family": "Russell", "given": "Damon Stuart" }, "id": "Russell-Damon-Stuart", "display_name": "Russell, Damon Stuart" } ], "advisors": [ { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "advisor", "display_name": "Weinreb, Sander" } ], "committee": [ { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "chair", "display_name": "Weinreb, Sander" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Gaier", "given": "Todd C." }, "id": "Gaier-T-C", "role": "member", "display_name": "Gaier, Todd C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/MW3P-2S22", "abstract": "The field of radio astronomy continues to provide fundamental contributions to the understanding of the evolution, and inner workings of, our universe. It has done so from its humble beginnings, where single antennas and receivers were used for observation, to today's focal plane arrays and interferometers. The number of receiving elements (pixels) in these instruments is quickly growing, currently approaching one hundred. For the instruments of tomorrow, the number of receiving elements will be in the thousands. Such instruments will enable researchers to peer deeper into the fabric of our universe and do so at faster survey speeds. They will provide enormous capability, both for unraveling today's mysteries as well as for the discovery of new phenomena.
\r\n \r\nAmong other challenges, producing the large numbers of low-noise amplifiers required for these instruments will be no easy task. The work described in this thesis advances the state of the art in three critical areas, technological advancements necessary for the future design and manufacturing of thousands of low-noise amplifiers. These areas being: the automated, cryogenic, probing of $\\diameter100$ mm indium phosphide wafers; a system for measuring the noise parameters of devices at cryogenic temperatures; and the development of low-noise, silicon germanium amplifiers for terahertz mixer receivers. The four chapters that comprise the body of this work detail the background, design, assembly, and testing involved in these contributions. Also included is a brief survey of noise parameters, the knowledge of which is fundamental to the design of low-noise amplifiers and the optimization of the system noise temperature for large, dense, interferometers.
" }, { "name": "Safavi-Naeini, Amir Hossein", "degree": "PhD", "year": "2013", "title": "Quantum Optomechanics with Silicon Nanostructures", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-145253965", "creators": [ { "name": { "family": "Safavi-Naeini", "given": "Amir Hossein" }, "id": "Safavi-Naeini-Amir-Hossein", "display_name": "Safavi-Naeini, Amir Hossein" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "member", "display_name": "Kimble, H. Jeff" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/VZW9-1Z52", "abstract": "Mechanical resonators are the most basic and ubiquitous physical systems known. In on-chip form, they are used to process high frequency signals in every cell phone, television, and laptop. They have also been in the last few decades in different shapes and forms, a critical part of progress in quantum information sciences with kilogram-scale mirrors for gravitational wave detection measuring motion at its quantum limits, and the motion of single ions being used to link qubits for quantum computation.
\r\n\r\nOptomechanics is a field primarily concerned with coupling light to the motion of mechanical structures. This thesis contains descriptions of recent work with mechanical systems in the megahertz to gigahertz frequency range, formed by nanofabricating novel photonic/phononic structures on a silicon chip. These structures are designed to have both optical and mechanical resonances, and laser light is used to address and manipulate their motional degrees of freedom through radiation pressure forces. We laser cool these mechanical resonators to their ground states, and observe for the first time the quantum zero-point motion of a nanomechanical resonator. Conversely, we show that engineered mechanical resonances drastically modify the optical response of our structures, creating large effective optical nonlinearities not present in bulk silicon. We experimentally demonstrate aspects of these nonlinearities by proposing and observing ``electromagnetically induced transparency'' and light slowed down to 6 m/s, as well as wavelength conversion, and generation of nonclassical optical radiation. Finally, the application of optomechanics to longstanding problems in quantum and classical communications are proposed and investigated.
\r\n" }, { "name": "Santis, Christos Theodoros", "degree": "PhD", "year": "2013", "title": "High-Coherence Hybrid Si/III-V Semiconductor Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-151934307", "creators": [ { "name": { "family": "Santis", "given": "Christos Theodoros" }, "id": "Santis-Christos-Theodoros", "orcid": "0000-0001-8636-1613", "display_name": "Santis, Christos Theodoros" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" } ], "option_major": [ "eleceng" ], "doi": "10.7907/M4KJ-8H56", "abstract": "The relentlessly increasing demand for network bandwidth, driven primarily by Internet-based services such as mobile computing, cloud storage and video-on-demand, calls for more efficient utilization of the available communication spectrum, as that afforded by the resurging DSP-powered coherent optical communications. Encoding information in the phase of the optical carrier, using multilevel phase modulationformats, and employing coherent detection at the receiver allows for enhanced spectral efficiency and thus enables increased network capacity. The distributed feedback semiconductor laser (DFB) has served as the near exclusive light source powering the fiber optic, long-haul network for over 30 years. The transition to coherent communication systems is pushing the DFB laser to the limits of its abilities. This is due to its limited temporal coherence that directly translates into the number of different phases that can be imparted to a single optical pulse and thus to the data capacity. Temporal coherence, most commonly quantified in the spectral linewidth \u0394\u03bd, is limited by phase noise, result of quantum-mandated spontaneous emission of photons due to random recombination of carriers in the active region of the laser.
\r\n\r\nIn this work we develop a generically new type of semiconductor laser with the requisite coherence properties. We demonstrate electrically driven lasers characterized by a quantum noise-limited spectral linewidth as low as 18 kHz. This narrow linewidth is result of a fundamentally new laser design philosophy that separates the functions of photon generation and storage and is enabled by a hybrid Si/III-V integration platform. Photons generated in the active region of the III-V material are readily stored away in the low loss Si that hosts the bulk of the laser field, thereby enabling high-Q photon storage. The storage of a large number of coherent quanta acts as an optical flywheel, which by its inertia reduces the effect of the spontaneous emission-mandated phase perturbations on the laser field, while the enhanced photon lifetime effectively reduces the emission rate of incoherent quanta into the lasing mode. Narrow linewidths are obtained over a wavelength bandwidth spanning the entire optical communication C-band (1530-1575nm) at only a fraction of the input power required by conventional DFB lasers. The results presented in this thesis hold great promise for the large scale integration of lithographically tuned, high-coherence laser arrays for use in coherent communications, that will enable Tb/s-scale data capacities.
" }, { "name": "Schaeffer, Joseph Malcolm", "degree": "PhD", "year": "2013", "title": "Stochastic Simulation of the Kinetics of Multiple Interacting Nucleic Acid Strands", "advisor": "Winfree, Erik", "url": "https://resolver.caltech.edu/CaltechTHESIS:02042013-110332492", "creators": [ { "name": { "family": "Schaeffer", "given": "Joseph Malcolm" }, "id": "Schaeffer-Joseph-Malcolm", "display_name": "Schaeffer, Joseph Malcolm" } ], "advisors": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "advisor", "display_name": "Winfree, Erik" } ], "committee": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "chair", "display_name": "Winfree, Erik" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "compsci" ], "doi": "10.7907/JEBY-6X69", "abstract": "DNA nanotechnology is an emerging field which utilizes the unique structural properties of nucleic acids in order to build nanoscale devices, such as logic gates, motors, walkers, and algorithmic structures. Predicting the structure and interactions of a DNA device requires good modeling of both the thermodynamics and the kinetics of the DNA strands within the system. The kinetics of a set of DNA strands can be modeled as a continuous time Markov process through the state space of all secondary structures. The primary means of exploring the kinetics of a DNA system is by simulating trajectories through the state space and aggregating data over many such trajectories.
\r\n\r\nWe expand on previous work by extending the thermodynamics and kinetics models to handle multiple strands in a fixed volume, and show that the new models are consistent with previous models. We developed data structures and algorithms that allow us to take advantage of local properties of secondary structure, improving the efficiency of the simulator so that we can handle larger systems. The new kinetic parameters in our model were calibrated by analyzing simulator results on experimental systems that measure basic kinetic rates of various processes. Finally, we apply the new simulator to explore a case study on toehold-mediated four-way branch migration.
" }, { "name": "Sendowski, Jacob Benjamin", "degree": "PhD", "year": "2013", "title": "On-Chip Integrated Label-Free Optical Biosensing", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-213433052", "creators": [ { "name": { "family": "Sendowski", "given": "Jacob Benjamin" }, "id": "Sendowski-Jacob-Benjamin", "display_name": "Sendowski, Jacob Benjamin" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2H9Y-AB63", "abstract": "This thesis investigates the design and implementation of a label-free optical biosensing system utilizing a robust on-chip integrated platform. The goal has been to transition optical micro-resonator based label-free biosensing from a laborious and delicate laboratory demonstration to a tool for the analytical life scientist. This has been pursued along four avenues: (1) the design and fabrication of high-$Q$ integrated planar microdisk optical resonators in silicon nitride on silica, (2) the demonstration of a high speed optoelectronic swept frequency laser source, (3) the development and integration of a microfluidic analyte delivery system, and (4) the introduction of a novel differential measurement technique for the reduction of environmental noise.
\r\n\r\nThe optical part of this system combines the results of two major recent developments in the field of optical and laser physics: the high-$Q$ optical resonator and the phase-locked electronically controlled swept-frequency semiconductor laser. The laser operates at a wavelength relevant for aqueous sensing, and replaces expensive and fragile mechanically-tuned laser sources whose frequency sweeps have limited speed, accuracy and reliability. The high-$Q$ optical resonator is part of a monolithic unit with an integrated optical waveguide, and is fabricated using standard semiconductor lithography methods. Monolithic integration makes the system significantly more robust and flexible compared to current, fragile embodiments that rely on the precarious coupling of fragile optical fibers to resonators. The silicon nitride on silica material system allows for future manifestations at shorter wavelengths. The sensor also includes an integrated microfluidic flow cell for precise and low volume delivery of analytes to the resonator surface. We demonstrate the refractive index sensing action of the system as well as the specific and nonspecific adsorption of proteins onto the resonator surface with high sensitivity. Measurement challenges due to environmental noise that hamper system performance are discussed and a differential sensing measurement is proposed, implemented, and demonstrated resulting in the restoration of a high performance sensing measurement.
\r\n\r\nThe instrument developed in this work represents an adaptable and cost-effective platform capable of various sensitive, label-free measurements relevant to the study of biophysics, biomolecular interactions, cell signaling, and a wide range of other life science fields. Further development is necessary for it to be capable of binding assays, or thermodynamic and kinetics measurements; however, this work has laid the foundation for the demonstration of these applications.
" }, { "name": "Shi, Wendian (Leo)", "degree": "PhD", "year": "2013", "title": "Blood Cell Count On-a-Chip", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06252012-171451630", "creators": [ { "name": { "family": "Shi", "given": "Wendian (Leo)" }, "id": "Shi-Wendian-Leo", "display_name": "Shi, Wendian (Leo)" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "eleceng" ], "doi": "10.7907/6YF1-WR04", "abstract": "White blood cell (WBC) count is one of the most frequently ordered clinical tests in hospitals. There are five types of WBCs in the circulating blood, including lymphocyte, monocyte, neutrophil, eosinophil and basophil. The WBC count test enumerates not only the total number of WBCs in per volume blood, but also the percentage of each WBC type. A portable instrument for the WBC count test is currently in demand by the NASA human spaceflight, and also by the on-earth telemedicine application. However, the commercially available tests do not meet the requirement of the portable applications, because of their large instrument size and the large reagent volume consumed per test.
\r\n\r\nThis study describes the development of a WBC count technology optimized for portable applications. First, a sheathless microfluidic cytometer is developed for WBC count. This technology consumes only a small amount of blood (5 microlitre) and a minimal volume of reagents (50 microlitre). Second, fluorescent dye assays are developed for the WBC differential count by measuring fluorescent emissions on the microfluidic cytometer. Based on this technology, a portable instrument is built with high test accuracy (maximum error less than 10%).
\r\n \r\nFurthermore, this study explores two key components for future integrating this technology into a self-contained chip. First, a microvalve actuated by thermal blood clogging is developed. This valve has a simple structure suitable for on-chip integration. Second, a micromixer is used to demonstrate the staining of blood with dye assays, and the following fluorescent detection of WBCs on the cytometer.
\r\n" }, { "name": "Smith, Matthew Alexander", "degree": "PhD", "year": "2013", "title": "Non-Contiguous Protein Recombination", "advisor": "Arnold, Frances Hamilton", "url": "https://resolver.caltech.edu/CaltechTHESIS:04102013-164733450", "creators": [ { "name": { "family": "Smith", "given": "Matthew Alexander" }, "id": "Smith-Matthew-Alexander", "display_name": "Smith, Matthew Alexander" } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "orcid": "0000-0003-3175-4596", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Marcus", "given": "Rudolph A." }, "id": "Marcus-R-A", "orcid": "0000-0001-6547-1469", "role": "member", "display_name": "Marcus, Rudolph A." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" } ], "option_major": [ "bioeng" ], "doi": "10.7907/4B8E-ZH08", "abstract": "Swapping sequence elements among related proteins can produce chimeric proteins with novel behaviors and improved properties such as enhanced stability. Although homologous mutations are much more conservative than random mutations, chimeras of distantly-related proteins have a low probability of retaining fold and function. Here, I introduce a new tool for protein recombination that identifies structural blocks that can be swapped among homologous proteins with minimal disruption. This non-contiguous recombination approach enables design of chimeras and libraries of chimeras with less disruption than can be achieved by swapping blocks of sequence. Less disruption means that one can generate libraries with higher fractions of functional enzymes and enables recombination of more distant homologs.
\r\n\r\nUsing this new tool I design and construct many functional chimeric cellulases. I illustrate the structurally conservative nature of this recombination by creating a functional prokaryotic-eukaryotic chimera and solving its structure. I also show how non-contiguous recombination can be used to efficiently identify stabilizing mutations that have been incorporated into homologs in nature.
" }, { "name": "Sojoudi, Somayeh", "degree": "PhD", "year": "2013", "title": "Mathematical Study of Complex Networks: Brain, Internet, and Power Grid", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252013-081655550", "creators": [ { "name": { "family": "Sojoudi", "given": "Somayeh" }, "id": "Sojoudi-Somayeh", "display_name": "Sojoudi, Somayeh" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "cds" ], "doi": "10.7907/E750-2M74", "abstract": "The dissertation is concerned with the mathematical study of various network problems. First, three real-world networks are considered: (i) the human brain network (ii) communication networks, (iii) electric power networks. Although these networks perform very different tasks, they share similar mathematical foundations. The high-level goal is to analyze and/or synthesis each of these systems from a \u201ccontrol and optimization\u201d point of view. After studying these three real-world networks, two abstract network problems are also explored, which are motivated by power systems. The first one is \u201cflow optimization over a flow network\u201d and the second one is \u201cnonlinear optimization over a generalized weighted graph\u201d. The results derived in this dissertation are summarized below.
\r\n\r\nBrain Networks: Neuroimaging data reveals the coordinated activity of spatially distinct brain regions, which may be represented mathematically as a network of nodes (brain regions) and links (interdependencies). To obtain the brain connectivity network, the graphs associated with the correlation matrix and the inverse covariance matrix\u2014describing marginal and conditional dependencies between brain regions\u2014have been proposed in the literature. A question arises as to whether any of these graphs provides useful information about the brain connectivity. Due to the electrical properties of the brain, this problem will be investigated in the context of electrical circuits. First, we consider an electric circuit model and show that the inverse covariance matrix of the node voltages reveals the topology of the circuit. Second, we study the problem of finding the topology of the circuit based on only measurement. In this case, by assuming that the circuit is hidden inside a black box and only the nodal signals are available for measurement, the aim is to find the topology of the circuit when a limited number of samples are available. For this purpose, we deploy the graphical lasso technique to estimate a sparse inverse covariance matrix. It is shown that the graphical lasso may find most of the circuit topology if the exact covariance matrix is well-conditioned. However, it may fail to work well when this matrix is ill-conditioned. To deal with ill-conditioned matrices, we propose a small modification to the graphical lasso algorithm and demonstrate its performance. Finally, the technique developed in this work will be applied to the resting-state fMRI data of a number of healthy subjects.
\r\n\r\nCommunication Networks: Congestion control techniques aim to adjust the transmission rates of competing users in the Internet in such a way that the network resources are shared efficiently. Despite the progress in the analysis and synthesis of the Internet congestion control, almost all existing fluid models of congestion control assume that every link in the path of a flow observes the original source rate. To address this issue, a more accurate model is derived in this work for the behavior of the network under an arbitrary congestion controller, which takes into account of the effect of buffering (queueing) on data flows. Using this model, it is proved that the well-known Internet congestion control algorithms may no longer be stable for the common pricing schemes, unless a sufficient condition is satisfied. It is also shown that these algorithms are guaranteed to be stable if a new pricing mechanism is used.
\r\n\r\nElectrical Power Networks: Optimal power flow (OPF) has been one of the most studied problems for power systems since its introduction by Carpentier in 1962. This problem is concerned with finding an optimal operating point of a power network minimizing the total power generation cost subject to network and physical constraints. It is well known that OPF is computationally hard to solve due to the nonlinear interrelation among the optimization variables. The objective is to identify a large class of networks over which every OPF problem can be solved in polynomial time. To this end, a convex relaxation is proposed, which solves the OPF problem exactly for every radial network and every meshed network with a sufficient number of phase shifters, provided power over-delivery is allowed. The concept of \u201cpower over-delivery\u201d is equivalent to relaxing the power balance equations to inequality constraints.
\r\n\r\nFlow Networks: In this part of the dissertation, the minimum-cost flow problem over an arbitrary flow network is considered. In this problem, each node is associated with some possibly unknown injection, each line has two unknown flows at its ends related to each other via a nonlinear function, and all injections and flows need to satisfy certain box constraints. This problem, named generalized network flow (GNF), is highly non-convex due to its nonlinear equality constraints. Under the assumption of monotonicity and convexity of the flow and cost functions, a convex relaxation is proposed, which always finds the optimal injections. A primary application of this work is in the OPF problem. The results of this work on GNF prove that the relaxation on power balance equations (i.e., load over-delivery) is not needed in practice under a very mild angle assumption.
\r\n\r\nGeneralized Weighted Graphs: Motivated by power optimizations, this part aims to find a global optimization technique for a nonlinear optimization defined over a generalized weighted graph. Every edge of this type of graph is associated with a weight set corresponding to the known parameters of the optimization (e.g., the coefficients). The motivation behind this problem is to investigate how the (hidden) structure of a given real/complex valued optimization makes the problem easy to solve, and indeed the generalized weighted graph is introduced to capture the structure of an optimization. Various sufficient conditions are derived, which relate the polynomial-time solvability of different classes of optimization problems to weak properties of the generalized weighted graph such as its topology and the sign definiteness of its weight sets. As an application, it is proved that a broad class of real and complex optimizations over power networks are polynomial-time solvable due to the passivity of transmission lines and transformers.
" }, { "name": "Somala, Surendra Nadh", "degree": "PhD", "year": "2013", "title": "Source Imaging with Dense Sensor Networks: Inversions Based on Adjoint Methods", "advisor": "Ampuero, Jean-Paul; Lapusta, Nadia", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-210319511", "creators": [ { "name": { "family": "Somala", "given": "Surendra Nadh" }, "id": "Somala-Surendra-Nadh", "display_name": "Somala, Surendra Nadh" } ], "advisors": [ { "name": { "family": "Ampuero", "given": "Jean-Paul" }, "id": "Ampuero-J-P", "role": "advisor", "display_name": "Ampuero, Jean-Paul" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "advisor", "display_name": "Lapusta, Nadia" } ], "committee": [ { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "role": "chair", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "role": "member", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Ampuero", "given": "Jean-Paul" }, "id": "Ampuero-J-P", "role": "member", "display_name": "Ampuero, Jean-Paul" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9WQ01S7", "abstract": "Inversions of earthquake source slip from the recorded ground motions typically impose a number of restrictions on the source parameterization, which are needed to stabilize the inverse problem with sparse data. Such restrictions may include smoothing, causality considerations, predetermined shapes of the local source-time function, and constant rupture speed. The best regional networks have sensor spacing in the tens of kilometers range, much larger than the wavelengths relevant to key aspects of earthquake physics. Novel approaches to providing orders-of-magnitude denser sensing include low-cost sensors (Community Seismic Network) and space-based optical imaging (Geostationary Optical Seismometer). This thesis aims to understand whether the inversion results could be substantially improved, with fewer constraints, by the availability of much denser sensor networks than currently available.
\r\n\r\nInversions that involve large number of sensors and 3D crustal velocity models are intractable with the current source inversion codes. Hence we have developed a new approach that can handle thousands of sensors in heterogeneous media. It employs iterative conjugate gradient optimization based on an adjoint method and involves iterative time-reversed 3D wave propagation simulations using the spectral element method (SPECFEM3D). We have also developed a variant of this adjoint-based method for layered media that utilizes pre-computed Green\u2019s functions instead of the time-reversed wave propagation. The developed methods have been applied to two problems: impact of crustal structure uncertainties on source inversion and resolution of rise time as a function of network spacing and rupture velocity. In the first part, we show that typical uncertainties in crustal velocity models represented by a von Karman distribution of 5 km correlation length and 5% standard deviation (with Hurst exponent of zero), severely degrade the quality of source inversion. However, if the velocity uncertainties have a correlation of 500 m or a standard deviation of 1%, then source inversion has an adequate quality. In the second part we find that supershear ruptures show almost identical source recovery in terms of width of the slip pulse for network spacings ranging from few km to tens of km, even for rise times as short as 1 sec, while subshear ruptures require a network spacing finer than a penetration length that depends on rupture velocity and rise time, as their peak ground velocity decay rapidly with distance from the fault.
\r\n\r\nIn summary, we have developed scalable source inversion tools that will enable exploiting the next generation of very dense earthquake observation systems, improvements in regional scale 3D tomography models and accelerated advancements in computing capabilities. These developments will be critical in resolving the fine spatio-temporal features of earthquake sources that are pertinent to fracture mechanics and earthquake physics. With the 3D iterative time-reversal imaging, one could aspire for extracting more information from the high frequency wavefield by considering joint improvement of source and structure.
\r\n" }, { "name": "Stadie, Nicholas P.", "degree": "PhD", "year": "2013", "title": "Synthesis and Thermodynamic Studies of Physisorptive Energy Storage Materials", "advisor": "Fultz, Brent T.; Ahn, Channing C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09092012-010239493", "creators": [ { "name": { "family": "Stadie", "given": "Nicholas P." }, "id": "Stadie-Nicholas-P", "display_name": "Stadie, Nicholas P." } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "co-advisor", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "co-advisor", "display_name": "Ahn, Channing C." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "member", "display_name": "Ahn, Channing C." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Davis", "given": "Mark E." }, "id": "Davis-M-E", "role": "member", "display_name": "Davis, Mark E." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/ZK3P-CV60", "abstract": "Physical adsorption of hydrogen or other chemical fuels on the surface of carbonaceous materials offers a promising avenue for energy storage applications. The addition of a well-chosen sorbent material to a compressed gas tank increases the volumetric energy density of the system while still permitting fast refueling, simplicity of design, complete reversibility, high cyclability, and low overall cost of materials. While physical adsorption is most effective at temperatures below ambient, effective storage technologies are possible at room temperature and modestly high pressure. A volumetric Sieverts apparatus was designed, constructed, and commissioned to accurately measure adsorption uptake at high pressures and an appropriate thermodynamic treatment of the experimental data is presented.
\r\n\r\nIn Chapter 1, the problem of energy storage is introduced in the context of hydrogen as an ideal alternative fuel for future mobile vehicle applications, and with methane in mind as a near-term solution. The theory of physical adsorption that is relevant to this work is covered in Chapter 2. In-depth studies of two classes of materials are presented in the final chapters. Chapter 3 presents a study of the dissociative \u201chydrogen spillover\u201d effect in the context of its viability as a practical hydrogen storage solution at room temperature. Chapters 4-5 deal with zeolite-templated carbon, an extremely high surface-area material which shows promise for hydrogen and methane storage applications. Studies of hydrogen adsorption at high pressure (Chapter 4) and anomalous thermodynamic properties of methane adsorption (Chapter 5) on ZTCs are presented. The concluding chapter discusses the impact of and possible future directions for this work.
" }, { "name": "Sternberg, Jonathan Ben-Zion", "degree": "PhD", "year": "2013", "title": "Signal Transduction with Hybridization Chain Reactions", "advisor": "Pierce, Niles/ A", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072013-170244348", "creators": [ { "name": { "family": "Sternberg", "given": "Jonathan Ben-Zion" }, "id": "Sternberg-Jonathan-Ben-Zion", "display_name": "Sternberg, Jonathan Ben-Zion" } ], "advisors": [ { "name": { "family": "Pierce", "given": "Niles/ A" }, "id": "Pierce-N-A", "role": "advisor", "display_name": "Pierce, Niles/ A" } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." } ], "option_major": [ "bioeng" ], "doi": "10.7907/Z90Z719Z", "abstract": "Some of the most exciting developments in the field of nucleic acid engineering include the utilization of synthetic nucleic acid molecular devices as gene regulators, as disease marker detectors, and most recently, as therapeutic agents. The common thread between these technologies is their reliance on the detection of specific nucleic acid input markers to generate some desirable output, such as a change in the copy number of an mRNA (for gene regulation), a change in the emitted light intensity (for some diagnostics), and a change in cell state within an organism (for therapeutics). The research presented in this thesis likewise focuses on engineering molecular tools that detect specific nucleic acid inputs, and respond with useful outputs.
\r\n\r\nFour contributions to the field of nucleic acid engineering are presented: (1) the construction of a single nucleotide polymorphism (SNP) detector based on the mechanism of hybridization chain reaction (HCR); (2) the utilization of a single-stranded oligonucleotide molecular Scavenger as a means of enhancing HCR selectivity; (3) the implementation of Quenched HCR, a technique that facilitates transduction of a nucleic acid chemical input into an optical (light) output, and (4) the engineering of conditional probes that function as sequence transducers, receiving target signal as input and providing a sequence of choice as output. These programmable molecular systems are conceptually well-suited for performing wash-free, highly selective rapid genotyping and expression profiling in vitro, in situ, and potentially in living cells.
" }, { "name": "Stobbe, Peter", "degree": "PhD", "year": "2013", "title": "Convex Analysis for Minimizing and Learning Submodular Set Functions ", "advisor": "Krause, R. Andreas", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-151014984", "creators": [ { "name": { "family": "Stobbe", "given": "Peter" }, "id": "Stobbe-Peter", "display_name": "Stobbe, Peter" } ], "advisors": [ { "name": { "family": "Krause", "given": "R. Andreas" }, "id": "Krause-R-A", "role": "advisor", "display_name": "Krause, R. Andreas" } ], "committee": [ { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "chair", "display_name": "Tropp, Joel A." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Krause", "given": "R. Andreas" }, "id": "Krause-R-A", "role": "member", "display_name": "Krause, R. Andreas" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/1A1J-SA64", "abstract": "The connections between convexity and submodularity are explored, for purposes of minimizing and learning submodular set functions.
\r\n\r\nFirst, we develop a novel method for minimizing a particular class of submodular functions, which can be expressed as a sum of concave functions composed with modular functions. The basic algorithm uses an accelerated first order method applied to a smoothed version of its convex extension. The smoothing algorithm is particularly novel as it allows us to treat general concave potentials without needing to construct a piecewise linear approximation as with graph-based techniques.
\r\n\r\nSecond, we derive the general conditions under which it is possible to find a minimizer of a submodular function via a convex problem. This provides a framework for developing submodular minimization algorithms. The framework is then used to develop several algorithms that can be run in a distributed fashion. This is particularly useful for applications where the submodular objective function consists of a sum of many terms, each term dependent on a small part of a large data set.
\r\n\r\nLastly, we approach the problem of learning set functions from an unorthodox perspective---sparse reconstruction. We demonstrate an explicit connection between the problem of learning set functions from random evaluations and that of sparse signals. Based on the observation that the Fourier transform for set functions satisfies exactly the conditions needed for sparse reconstruction algorithms to work, we examine some different function classes under which uniform reconstruction is possible.
\r\n" }, { "name": "Szelengowicz, Ivan Michel Nicolas", "degree": "PhD", "year": "2013", "title": "Analysis and Optimization of Stress Wave Propagation in Two-Dimensional Granular Crystals with Defects", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05082013-161911202", "creators": [ { "name": { "family": "Szelengowicz", "given": "Ivan Michel Nicolas" }, "id": "Szelengowicz-Ivan-Michel-Nicolas", "display_name": "Szelengowicz, Ivan Michel Nicolas" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TE86-1A15", "abstract": "Granular crystals are compact periodic assemblies of elastic particles in Hertzian contact whose dynamic response can be tuned from strongly nonlinear to linear by the addition of a static precompression force. This unique feature allows for a wide range of studies that include the investigation of new fundamental nonlinear phenomena in discrete systems such as solitary waves, shock waves, discrete breathers and other defect modes. In the absence of precompression, a particularly interesting property of these systems is their ability to support the formation and propagation of spatially localized soliton-like waves with highly tunable properties. The wealth of parameters one can modify (particle size, geometry and material properties, periodicity of the crystal, presence of a static force, type of excitation, etc.) makes them ideal candidates for the design of new materials for practical applications. This thesis describes several ways to optimally control and tailor the propagation of stress waves in granular crystals through the use of heterogeneities (interstitial defect particles and material heterogeneities) in otherwise perfectly ordered systems. We focus on uncompressed two-dimensional granular crystals with interstitial spherical intruders and composite hexagonal packings and study their dynamic response using a combination of experimental, numerical and analytical techniques. We first investigate the interaction of defect particles with a solitary wave and utilize this fundamental knowledge in the optimal design of novel composite wave guides, shock or vibration absorbers obtained using gradient-based optimization methods." }, { "name": "Tootoonian, Sina", "degree": "PhD", "year": "2013", "title": "On the Analysis and Design of the Locust Olfactory System", "advisor": "Laurent, Gilles J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12282012-075056374", "creators": [ { "name": { "family": "Tootoonian", "given": "Sina" }, "id": "Tootoonian-Sina", "display_name": "Tootoonian, Sina" } ], "advisors": [ { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "advisor", "display_name": "Laurent, Gilles J." } ], "committee": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "orcid": "0000-0001-8837-678X", "role": "chair", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "member", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "member", "display_name": "Laurent, Gilles J." } ], "option_major": [ "cns" ], "doi": "10.7907/MAWA-GD04", "abstract": "The ~ 830 projection neurons (PNs) of the locust antennal lobe respond to odors with dense, odor-specific spatio-temporal activity patterns that are mapped via intrinsic and circuit properties into a sparse representation by the Kenyon cells of the mushroom body, which are in turn read out by the beta-lobe neurons (bLNs). In this thesis we present several analyses of this system. First, we describe metrics for quantifying the geometric properties of PN population responses in the full response space that verify the structures revealed by locally linear embedding. Second, we analyze the mixture responses of single PNs and find that in many cases the mixture response can be explained using one of the component responses. Grouping PNs by their single component preferences reveals a potentially simple substrate for olfactory computations. Third, we look for evidence of cycle-by-cycle decoding of PNs by KCs. We show that much of the variance in single KC responses can be explained using small numbers of PNs, and conversely, that PN odor response trajectories can be reconstructed using KC responses. Finally, in a theoretical / computational analysis, we assemble some of the basic biological facts about the locust olfactory system into an architecture for the online learning of arbitrary mappings from odors to valences." }, { "name": "Trautman, Peter", "degree": "PhD", "year": "2013", "title": "Robot Navigation in Dense Crowds: Statistical Models and Experimental Studies of Human Robot Cooperation", "advisor": "Murray, Richard M.; Krause, R. Andreas; Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182013-191132413", "creators": [ { "name": { "family": "Trautman", "given": "Peter" }, "id": "Trautman-Peter", "display_name": "Trautman, Peter" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Krause", "given": "R. Andreas" }, "id": "Krause-R-A", "role": "advisor", "display_name": "Krause, R. Andreas" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Krause", "given": "R. Andreas" }, "id": "Krause-R-A", "role": "member", "display_name": "Krause, R. Andreas" } ], "option_major": [ "cds" ], "doi": "10.7907/BHGM-0C65", "abstract": "This thesis explores the problem of mobile robot navigation in dense human crowds. We begin by considering a fundamental impediment to classical motion planning algorithms called the freezing robot problem: once the environment surpasses a certain level of complexity, the planner decides that all forward paths are unsafe, and the robot freezes in place (or performs unnecessary maneuvers) to avoid collisions. Since a feasible path typically exists, this behavior is suboptimal. Existing approaches have focused on reducing predictive uncertainty by employing higher fidelity individual dynamics models or heuristically limiting the individual predictive covariance to prevent overcautious navigation. We demonstrate that both the individual prediction and the individual predictive uncertainty have little to do with this undesirable navigation behavior. Additionally, we provide evidence that dynamic agents are able to navigate in dense crowds by engaging in joint collision avoidance, cooperatively making room to create feasible trajectories. We accordingly develop interacting Gaussian processes, a prediction density that captures cooperative collision avoidance, and a \"multiple goal\" extension that models the goal driven nature of human decision making. Navigation naturally emerges as a statistic of this distribution.
\r\n\r\nMost importantly, we empirically validate our models in the Chandler dining hall at Caltech during peak hours, and in the process, carry out the first extensive quantitative study of robot navigation in dense human crowds (collecting data on 488 runs). The multiple goal interacting Gaussian processes algorithm performs comparably with human teleoperators in crowd densities nearing 1 person/m2, while a state of the art noncooperative planner exhibits unsafe behavior more than 3 times as often as the multiple goal extension, and twice as often as the basic interacting Gaussian process approach. Furthermore, a reactive planner based on the widely used dynamic window approach proves insufficient for crowd densities above 0.55 people/m2. We also show that our noncooperative planner or our reactive planner capture the salient characteristics of nearly any dynamic navigation algorithm. For inclusive validation purposes, we show that either our non-interacting planner or our reactive planner captures the salient characteristics of nearly any existing dynamic navigation algorithm. Based on these experimental results and theoretical observations, we conclude that a cooperation model is critical for safe and efficient robot navigation in dense human crowds.
\r\n\r\nFinally, we produce a large database of ground truth pedestrian crowd data. We make this ground truth database publicly available for further scientific study of crowd prediction models, learning from demonstration algorithms, and human robot interaction models in general.
\r\n" }, { "name": "Turner-Evans, Daniel B.", "degree": "PhD", "year": "2013", "title": "Wire Array Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292013-225612828", "creators": [ { "name": { "family": "Turner-Evans", "given": "Daniel B." }, "id": "Turner-Evans-Daniel-B", "display_name": "Turner-Evans, Daniel B." } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8E75-WH21", "abstract": "Over the past five years, the cost of solar panels has dropped drastically and, in concert, the number of installed modules has risen exponentially. However, solar electricity is still more than twice as expensive as electricity from a natural gas plant. Fortunately, wire array solar cells have emerged as a promising technology for further lowering the cost of solar.
\r\n\r\nSi wire array solar cells are formed with a unique, low cost growth method and use 100 times less material than conventional Si cells. The wires can be embedded in a transparent, flexible polymer to create a free-standing array that can be rolled up for easy installation in a variety of form factors. Furthermore, by incorporating multijunctions into the wire morphology, higher efficiencies can be achieved while taking advantage of the unique defect relaxation pathways afforded by the 3D wire geometry.
\r\n\r\nThe work in this thesis shepherded Si wires from undoped arrays to flexible, functional large area devices and laid the groundwork for multijunction wire array cells. Fabrication techniques were developed to turn intrinsic Si wires into full p-n junctions and the wires were passivated with a-Si:H and a-SiNx:H. Single wire devices yielded open circuit voltages of 600 mV and efficiencies of 9%. The arrays were then embedded in a polymer and contacted with a transparent, flexible, Ni nanoparticle and Ag nanowire top contact. The contact connected >99% of the wires in parallel and yielded flexible, substrate free solar cells featuring hundreds of thousands of wires.
\r\n\r\nBuilding on the success of the Si wire arrays, GaP was epitaxially grown on the material to create heterostructures for photoelectrochemistry. These cells were limited by low absorption in the GaP due to its indirect bandgap, and poor current collection due to a\r\ndiffusion length of only 80 nm. However, GaAsP on SiGe offers a superior combination of materials, and wire architectures based on these semiconductors were investigated for multijunction arrays. These devices offer potential efficiencies of 34%, as demonstrated through an analytical model and optoelectronic simulations. SiGe and Ge wires were fabricated via chemical-vapor deposition and reactive ion etching. GaAs was then grown on these substrates at the National Renewable Energy Lab and yielded ns lifetime components, as required for achieving high efficiency devices.
" }, { "name": "Varga, Aron", "degree": "PhD", "year": "2013", "title": "Advancing Electrocatalysis in Solid Acid Fuel Cells", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052013-080936057", "creators": [ { "name": { "family": "Varga", "given": "Aron" }, "id": "Varga-Aron", "display_name": "Varga, Aron" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Giapis", "given": "Konstantinos P." }, "id": "Giapis-K-P", "role": "member", "display_name": "Giapis, Konstantinos P." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9RX992C", "abstract": "Solid acid fuel cells are currently performance limited by the electrochemical reaction kinetics at the electrodes. For acceptable power output, precious metal catalysts such as platinum, are required, rendering the technology too expensive for commercialization in all but niche applications. This thesis explores new approaches to solid acid fuel cell electrodes with the aim of reducing the catalyst loading or even eliminating precious metals entirely, without sacrificing performance. Two broad approaches are pursued: nanostructuring for enhanced catalyst utilization and incorporation of carbon-based materials for enhanced electrical transport and even electrocatalysis.
\r\n\r\nElectrospray deposition is shown to be a viable technique to produce nanoparticles of the solid acid fuel cell electrolyte material CsH2PO4. In situ aerosol particle size measurements using a differential mobility analyzer and a condensation particle counter allowed the characterization of the electrospray parameter space, resulting in CsH2PO4 particle size control between 10 and 50 nm. Co-deposition of the CsH2PO4 nanoparticles together with a stabilizing surfactant polyvinylpyrrolidone (PVP) and platinum catalyst nanoparticles allows the creation of highly active, porous, interconnected electrode nanostructures. These nanostructures directly deposited onto fuel cell components, either the carbon paper current collector or the thin film electrolyte layer, serve as electrodes. A 30-fold reduction of platinum loading, without sacrificing electrode performance as compared to mixed powder-electrodes, is demonstrated.
\r\n\r\nThe direct deposition of CsH2PO4 nanoparticles with the stabilizing surfactant PVP onto a prefabricated CsH2PO4 electrolyte layer and subsequent magnetron sputtering of a nanometer thin platinum film lead to surprising catalyst-mass normalized electrode activities for solid acid fuel cell anodes. Specifically, a 25-fold increase in the mass normalized activity is shown as compared to the predicted values from analysis\r\nof platinum thin films with a controlled geometry.
\r\n\r\nThe second part of the thesis deals with the introduction of carbon nanotubes to the solid acid fuel cell electrodes. Three types of carbon nanotubes (CNTs) were grown directly onto the carbon paper current collector, in all cases using a chemical vapor deposition method and nickel catalyst nanoparticles.
\r\n\r\n(i) Conventional CNTs were shown to act as effective current collectors for electrosprayed composite electrode structures, containing platinum nanoparticles. Matching of scales between the current collector and the electrosprayed structure leads to improved interconnectivity of the platinum catalyst nanoparticles and a higher density of electrochemically active triple phase boundaries.
\r\n\r\n(ii) Nitrogen doped carbon nanotubes (NCNTs) were shown to actively catalyze oxygen electroreduction in solid acid fuel cells, with no platinum present.
\r\n\r\n(iii) Undoped but defective carbon nanotubes (dCNTs) were shown to be highly efficient catalysts of the oxygen electroreduction reaction, surpassing the activity of the state of the art, platinum containing electrodes. This is the first time undoped carbon nanotubes have been reported to be catalytically active for electroreduction of oxygen.
In addition, catalytically active carbon nanotubes show excellent catalysis of the water splitting reaction, creating the opportunity for new applications of these solid state electrochemical devices.
" }, { "name": "Vasilyev, Arseny", "degree": "PhD", "year": "2013", "title": "The Optoelectronic Swept-Frequency Laser and Its Applications in Ranging, Three-Dimensional Imaging, and Coherent Beam Combining of Chirped-Seed Amplifiers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032013-060508409", "creators": [ { "name": { "family": "Vasilyev", "given": "Arseny" }, "id": "Vasilyev-Arseny", "display_name": "Vasilyev, Arseny" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/YD38-BT07", "abstract": "This thesis explores the design, construction, and applications of the optoelectronic swept-frequency laser (SFL). The optoelectronic SFL is a feedback loop designed around a swept-frequency (chirped) semiconductor laser (SCL) to control its instantaneous optical frequency, such that the chirp characteristics are determined solely by a reference electronic oscillator. The resultant system generates precisely controlled optical frequency sweeps. In particular, we focus on linear chirps because of their numerous applications. We demonstrate optoelectronic SFLs based on vertical-cavity surface-emitting lasers (VCSELs) and distributed-feedback lasers (DFBs) at wavelengths of 1550 nm and 1060 nm. We develop an iterative bias current predistortion procedure that enables SFL operation at very high chirp rates, up to 10^16 Hz/sec. We describe commercialization efforts and implementation of the predistortion algorithm in a stand-alone embedded environment, undertaken as part of our collaboration with Telaris, Inc. We demonstrate frequency-modulated continuous-wave (FMCW) ranging and three-dimensional (3-D) imaging using a 1550 nm optoelectronic SFL.
\r\n\r\nWe develop the technique of multiple source FMCW (MS-FMCW) reflectometry, in which the frequency sweeps of multiple SFLs are \"stitched\" together in order to increase the optical bandwidth, and hence improve the axial resolution, of an FMCW ranging measurement. We demonstrate computer-aided stitching of DFB and VCSEL sweeps at 1550 nm. We also develop and demonstrate hardware stitching, which enables MS-FMCW ranging without additional signal processing. The culmination of this work is the hardware stitching of four VCSELs at 1550 nm for a total optical bandwidth of 2 THz, and a free-space axial resolution of 75 microns.
\r\n\r\nWe describe our work on the tomographic imaging camera (TomICam), a 3-D imaging system based on FMCW ranging that features non-mechanical acquisition of transverse pixels. Our approach uses a combination of electronically tuned optical sources and low-cost full-field detector arrays, completely eliminating the need for moving parts traditionally employed in 3-D imaging. We describe the basic TomICam principle, and demonstrate single-pixel TomICam ranging in a proof-of-concept experiment. We also discuss the application of compressive sensing (CS) to the TomICam platform, and perform a series of numerical simulations. These simulations show that tenfold compression is feasible in CS TomICam, which effectively improves the volume acquisition speed by a factor ten.
\r\n\r\nWe develop chirped-wave phase-locking techniques, and apply them to coherent beam combining (CBC) of chirped-seed amplifiers (CSAs) in a master oscillator power amplifier configuration. The precise chirp linearity of the optoelectronic SFL enables non-mechanical compensation of optical delays using acousto-optic frequency shifters, and its high chirp rate simultaneously increases the stimulated Brillouin scattering (SBS) threshold of the active fiber. We characterize a 1550 nm chirped-seed amplifier coherent-combining system. We use a chirp rate of 5*10^14 Hz/sec to increase the amplifier SBS threshold threefold, when compared to a single-frequency seed. We demonstrate efficient phase-locking and electronic beam steering of two 3 W erbium-doped fiber amplifier channels, achieving temporal phase noise levels corresponding to interferometric fringe visibilities exceeding 98%.
" }, { "name": "Wang, Ying Min", "degree": "PhD", "year": "2013", "title": "Deep Tissue Fluorescence Imaging with Time-Reversed Light", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:04282013-103938118", "creators": [ { "name": { "family": "Wang", "given": "Ying Min" }, "id": "Wang-Ying-Min", "display_name": "Wang, Ying Min" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "chair", "display_name": "Guo, Chin-Lin" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "co-chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Gradinaru", "given": "Viviana" }, "id": "Gradinaru-V", "role": "member", "display_name": "Gradinaru, Viviana" } ], "option_major": [ "bioeng" ], "doi": "10.7907/YNSN-8960", "abstract": "Advances in optical techniques have enabled many breakthroughs in biology and medicine. However, light scattering by biological tissues remains a great obstacle, restricting the use of optical methods to thin ex vivo sections or superficial layers in vivo. In this thesis, we present two related methods that overcome the optical depth limit\u2014digital time reversal of ultrasound encoded light (digital TRUE) and time reversal of variance-encoded light (TROVE). These two techniques share the same principle of using acousto-optic beacons for time reversal optical focusing within highly scattering media, like biological tissues. Ultrasound, unlike light, is not significantly scattered in soft biological tissues, allowing for ultrasound focusing. In addition, a fraction of the scattered optical wavefront that passes through the ultrasound focus gets frequency-shifted via the acousto-optic effect, essentially creating a virtual source of frequency-shifted light within the tissue. The scattered ultrasound-tagged wavefront can be selectively measured outside the tissue and time-reversed to converge at the location of the ultrasound focus, enabling optical focusing within deep tissues. In digital TRUE, we time reverse ultrasound-tagged light with an optoelectronic time reversal device (the digital optical phase conjugate mirror, DOPC). The use of the DOPC enables high optical gain, allowing for high intensity optical focusing and focal fluorescence imaging in thick tissues at a lateral resolution of 36 \u00b5m by 52 \u00b5m. The resolution of the TRUE approach is fundamentally limited to that of the wavelength of ultrasound. The ultrasound focus (~ tens of microns wide) usually contains hundreds to thousands of optical modes, such that the scattered wavefront measured is a linear combination of the contributions of all these optical modes. In TROVE, we make use of our ability to digitally record, analyze and manipulate the scattered wavefront to demix the contributions of these spatial modes using variance encoding. In essence, we encode each spatial mode inside the scattering sample with a unique variance, allowing us to computationally derive the time reversal wavefront that corresponds to a single optical mode. In doing so, we uncouple the system resolution from the size of the ultrasound focus, demonstrating optical focusing and imaging between highly diffusing samples at an unprecedented, speckle-scale lateral resolution of ~ 5 \u00b5m. Our methods open up the possibility of fully exploiting the prowess and versatility of biomedical optics in deep tissues." }, { "name": "Wang, Zhiying", "degree": "PhD", "year": "2013", "title": "Coding for Information Storage", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-123819501", "creators": [ { "name": { "family": "Wang", "given": "Zhiying" }, "id": "Wang-Zhiying", "display_name": "Wang, Zhiying" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "member", "display_name": "Winfree, Erik" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TFHZ-RW88", "abstract": "Storage systems are widely used and have played a crucial rule in both consumer and industrial products, for example, personal computers, data centers, and embedded systems. However, such system suffers from issues of cost, restricted-lifetime, and reliability with the emergence of new systems and devices, such as distributed storage and flash memory, respectively. Information theory, on the other hand, provides fundamental bounds and solutions to fully utilize resources such as data density, information I/O and network bandwidth. This thesis bridges these two topics, and proposes to solve challenges in data storage using a variety of coding techniques, so that storage becomes faster, more affordable, and more reliable.
\r\n\r\nWe consider the system level and study the integration of RAID schemes and distributed storage. Erasure-correcting codes are the basis of the ubiquitous RAID schemes for storage systems, where disks correspond to symbols in the code and are located in a (distributed) network. Specifically, RAID schemes are based on MDS (maximum distance separable) array codes that enable optimal storage and efficient encoding and decoding algorithms. With r redundancy symbols an MDS code can sustain r erasures. For example, consider an MDS code that can correct two erasures. It is clear that when two symbols are erased, one needs to access and transmit all the remaining information to rebuild the erasures. However, an interesting and practical question is: What is the smallest fraction of information that one needs to access and transmit in order to correct a single erasure? In Part I we will show that the lower bound of 1/2 is achievable and that the result can be generalized to codes with arbitrary number of parities and optimal rebuilding.
\r\n\r\nWe consider the device level and study coding and modulation techniques for emerging non-volatile memories such as flash memory. In particular, rank modulation is a novel data representation scheme proposed by Jiang et al. for multi-level flash memory cells, in which a set of n cells stores information in the permutation induced by the different charge levels of the individual cells. It eliminates the need for discrete cell levels, as well as overshoot errors, when programming cells. In order to decrease the decoding complexity, we propose two variations of this scheme in Part II: bounded rank modulation where only small sliding windows of cells are sorted to generated permutations, and partial rank modulation where only part of the n cells are used to represent data. We study limits on the capacity of bounded rank modulation and propose encoding and decoding algorithms. We show that overlaps between windows will increase capacity. We present Gray codes spanning all possible partial-rank states and using only ``push-to-the-top'' operations. These Gray codes turn out to solve an open combinatorial problem called universal cycle, which is a sequence of integers generating all possible partial permutations.
\r\n" }, { "name": "Weir, Peter Thomas", "degree": "PhD", "year": "2013", "title": "Polarization-Based Navigation in Drosophila", "advisor": "Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07242012-154851161", "creators": [ { "name": { "family": "Weir", "given": "Peter Thomas" }, "id": "Weir-Peter-Thomas", "orcid": "0000-0003-3111-7829", "display_name": "Weir, Peter Thomas" } ], "advisors": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "member", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "cns" ], "doi": "10.7907/3VXQ-TE73", "abstract": "Insects maintain a constant bearing across a wide range of spatial scales. Monarch butterflies and locusts traverse continents (Williams, 1957; Wehner, 1984), and foraging bees and ants travel hundreds of meters to return to their nests (Dyer, 1996; Wehner, 1984, 2003), whereas many other insects fly straight for only a few centimeters before changing direction. Despite this variation in spatial scale, the brain region thought to underlie long-distance navigation is remarkably conserved (Loesel et al., 2002; Homberg, 2008), suggesting that the use of a celestial compass is a general and perhaps ancient capability of insects. Laboratory studies of Drosophila have identified a local search mode in which short, straight segments are interspersed with rapid turns (Mayer et al., 1988; Bender and Dickinson, 2006). However, this flight mode is inconsistent with measured gene flow between geographically separated populations (Jones et al., 1981; Slatkin, 1985; Turelli and Hoffmann, 1991), and individual Drosophila can travel 10 km in a single night (Yerington, 1961; Jones et al., 1981; Coyne et al., 1982, 1987) -- a feat that would be impossible without prolonged periods of straight flight. One well-known cue relevant to orientation and navigation is the pattern of polarization of skylight. To study possible mechanisms of orientation to skylight polarization, we built an arena in which we could observe individual flight responses to rotating the angle of polarized light in the laboratory. We found that flies robustly steer in response to changes in the polarization angle of light. Individual flies also stabilize a particular polarization plane when they are given closed-loop control of such a stimulus. To directly examine orientation behavior under outdoor conditions, we built two portable flight arenas in which a fly viewed the natural sky through a clear aperture. In the first we examined the ability of flies to compensate for external rotations with or without the aid of skylight polarization. The second arena contained a liquid crystal device that could experimentally rotate the polarization angle of the skylight. In both outdoor arenas we tracked fly orientation using a digital video camera and custom computer vision system. Our findings indicate that Drosophila actively orient using the sky's natural polarization pattern.
" }, { "name": "Whittlesey, Robert Wells", "degree": "PhD", "year": "2013", "title": "Dynamics and Scaling of Self-Excited Passive Vortex Generators for Underwater Propulsion", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282013-114822808", "creators": [ { "name": { "family": "Whittlesey", "given": "Robert Wells" }, "id": "Whittlesey-Robert-Wells", "display_name": "Whittlesey, Robert Wells" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SC4M-8896", "abstract": "A series of experiments was conducted on the use of a device to passively generate vortex rings, henceforth a passive vortex generator (PVG). The device is intended as a means of propulsion for underwater vehicles, as the use of vortex rings has been shown to decrease the fuel consumption of a vehicle by up to 40% Ruiz (2010).
\r\n\r\nThe PVG was constructed out of a collapsible tube encased in a rigid, airtight box. By adjusting the pressure within the airtight box while fluid was flowing through the tube, it was possible to create a pulsed jet with vortex rings via self-excited oscillations of the collapsible tube.
\r\n\r\nA study of PVG integration into an existing autonomous underwater vehicle (AUV) system was conducted. A small AUV was used to retrofit a PVG with limited alterations to the original vehicle. The PVG-integrated AUV was used for self-propelled testing to measure the hydrodynamic (Froude) efficiency of the system. The results show that the PVG-integrated AUV had a 22% increase in the Froude efficiency using a pulsed jet over a steady jet. The maximum increase in the Froude efficiency was realized when the formation time of the pulsed jet, a nondimensional time to characterize vortex ring formation, was coincident with vortex ring pinch-off. This is consistent with previous studies that indicate that the maximization of efficiency for a pulsed jet vehicle is realized when the formation of vortex rings maximizes the vortex ring energy and size.
\r\n\r\nThe other study was a parameter study of the physical dimensions of a PVG. This study was conducted to determine the effect of the tube diameter and length on the oscillation characteristics such as the frequency. By changing the tube diameter and length by factors of 3, the frequency of self-excited oscillations was found to scale as f~D_0^{-1/2} L_0^0, where D_0 is the tube diameter and L_0 the tube length. The mechanism of operation is suggested to rely on traveling waves between the tube throat and the end of the tube. A model based on this mechanism yields oscillation frequencies that are within the range observed by the experiment.
" }, { "name": "Woo, Sungwook", "degree": "PhD", "year": "2013", "title": "Beyond Watson and Crick: Programming the Self-Assembly and Reconfiguration of DNA Nanostructures Based on Stacking Interactions", "advisor": "Rothemund, Paul W. K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-123041371", "creators": [ { "name": { "family": "Woo", "given": "Sungwook" }, "id": "Woo-Sungwook", "display_name": "Woo, Sungwook" } ], "advisors": [ { "name": { "family": "Rothemund", "given": "Paul W. K." }, "id": "Rothemund-P-W-K", "role": "advisor", "display_name": "Rothemund, Paul W. K." } ], "committee": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "chair", "display_name": "Winfree, Erik" }, { "name": { "family": "Rothemund", "given": "Paul W. K." }, "id": "Rothemund-P-W-K", "role": "member", "display_name": "Rothemund, Paul W. K." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "member", "display_name": "Tirrell, David A." }, { "name": { "family": "Fygenson", "given": "Deborah K." }, "id": "Fygenson-D-K", "role": "member", "display_name": "Fygenson, Deborah K." }, { "name": { "family": "Andersen", "given": "Ebbe S." }, "id": "Andersen-E-S", "role": "member", "display_name": "Andersen, Ebbe S." } ], "option_major": [ "bioeng" ], "doi": "10.7907/4NZK-XK58", "abstract": "Life is the result of the execution of molecular programs: like how an embryo is fated to become a human or a whale, or how a person\u2019s appearance is inherited from their parents, many biological phenomena are governed by genetic programs written in DNA molecules. At the core of such programs is the highly reliable base pairing interaction between nucleic acids. DNA nanotechnology exploits the programming power of DNA to build artificial nanostructures, molecular computers, and nanomachines. In particular, DNA origami\u2014which is a simple yet versatile technique that allows one to create various nanoscale shapes and patterns\u2014is at the heart of the technology. In this thesis, I describe the development of programmable self-assembly and reconfiguration of DNA origami nanostructures based on a unique strategy: rather than relying on Watson-Crick base pairing, we developed programmable bonds via the geometric arrangement of stacking interactions, which we termed stacking bonds. We further demonstrated that such bonds can be dynamically reconfigurable.
\r\n\r\nThe first part of this thesis describes the design and implementation of stacking bonds. Our work addresses the fundamental question of whether one can create diverse bond types out of a single kind of attractive interaction\u2014a question first posed implicitly by Francis Crick while seeking a deeper understanding of the origin of life and primitive genetic code. For the creation of multiple specific bonds, we used two different approaches: binary coding and shape coding of geometric arrangement of stacking interaction units, which are called blunt ends. To construct a bond space for each approach, we performed a systematic search using a computer algorithm. We used orthogonal bonds to experimentally implement the connection of five distinct DNA origami nanostructures. We also programmed the bonds to control cis/trans configuration between asymmetric nanostructures.
\r\n\r\nThe second part of this thesis describes the large-scale self-assembly of DNA origami into two-dimensional checkerboard-pattern crystals via surface diffusion. We developed a protocol where the diffusion of DNA origami occurs on a substrate and is dynamically controlled by changing the cationic condition of the system. We used stacking interactions to mediate connections between the origami, because of their potential for reconfiguring during the assembly process. Assembling DNA nanostructures directly on substrate surfaces can benefit nano/microfabrication processes by eliminating a pattern transfer step. At the same time, the use of DNA origami allows high complexity and unique addressability with six-nanometer resolution within each structural unit.
\r\n\r\nThe third part of this thesis describes the use of stacking bonds as dynamically breakable bonds. To break the bonds, we used biological machinery called the ParMRC system extracted from bacteria. The system ensures that, when a cell divides, each daughter cell gets one copy of the cell\u2019s DNA by actively pushing each copy to the opposite poles of the cell. We demonstrate dynamically expandable nanostructures, which makes stacking bonds a promising candidate for reconfigurable connectors for nanoscale machine parts.
" }, { "name": "Wu, Indira", "degree": "PhD", "year": "2013", "title": "Engineering Thermostable Fungal Cellobiohydrolases", "advisor": "Arnold, Frances Hamilton", "url": "https://resolver.caltech.edu/CaltechTHESIS:05022013-164749371", "creators": [ { "name": { "family": "Wu", "given": "Indira" }, "id": "Wu-Indira", "display_name": "Wu, Indira" } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" } ], "committee": [ { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "orcid": "0000-0003-4073-1185", "role": "chair", "display_name": "Rees, Douglas C." }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "orcid": "0000-0003-3175-4596", "role": "member", "display_name": "Tirrell, David A." }, { "name": { "family": "Mayo", "given": "Stephen L." }, "id": "Mayo-S-L", "orcid": "0000-0002-9785-5018", "role": "member", "display_name": "Mayo, Stephen L." } ], "option_major": [ "bioeng" ], "doi": "10.7907/V80F-X625", "abstract": "Meeting the world's growing energy demands while protecting our fragile environment is a challenging issue. Second generation biofuels are liquid fuels like long-chain alcohols produced from lignocellulosic biomass. To reduce the cost of biofuel production, we engineered fungal family 6 cellobiohydrolases (Cel6A) for enhanced thermostability using random mutagenesis and recombination of beneficial mutations. During long-time hydrolysis, engineered thermostable cellulases hydrolyze more sugars than wild-type Cel6A as single enzymes and binary mixtures at their respective optimum temperatures. Engineered thermostable cellulases exhibit synergy in binary mixtures similar to wild-type cellulases, demonstrating the utility of engineering individual cellulases to produce novel thermostable mixtures. Crystal structures of the engineered thermostable cellulases indicate that the stabilization comes from improved hydrophobic interactions and restricted loop conformations by proline substitutions. At high temperature, free cysteines contribute to irreversible thermal inactivation in engineered thermostable Cel6A and wild-type Cel6A. The mechanism of thermal inactivation in this cellulase family is consistent with disulfide bond degradation and thiol-disulfide exchange. Enhancing the thermostability of Cel6A also increases tolerance to pretreatment chemicals, demonstrated by the strong correlation between thermostability and tolerance to 1-ethyl-3-methylimidazolium acetate. Several semi-rational protein engineering approaches – on the basis of consensus sequence analysis, proline stabilization, FoldX energy calculation, and high B-factors – were evaluated to further enhance the thermostability of Cel6A." }, { "name": "Xu, Huan", "degree": "PhD", "year": "2013", "title": "Design, Specification, and Synthesis of Aircraft Electric Power Systems Control Logic", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312013-103940337", "creators": [ { "name": { "family": "Xu", "given": "Huan" }, "id": "Xu-Huan", "display_name": "Xu, Huan" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Holzmann", "given": "Gerard J." }, "id": "Holzmann-G-J", "role": "member", "display_name": "Holzmann, Gerard J." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/QDJN-BB72", "abstract": "Cyber-physical systems integrate computation, networking, and physical processes. Substantial research challenges exist in the design and verification of such large-scale, distributed sensing, ac- tuation, and control systems. Rapidly improving technology and recent advances in control theory, networked systems, and computer science give us the opportunity to drastically improve our approach to integrated flow of information and cooperative behavior. Current systems rely on text-based spec- ifications and manual design. Using new technology advances, we can create easier, more efficient, and cheaper ways of developing these control systems. This thesis will focus on design considera- tions for system topologies, ways to formally and automatically specify requirements, and methods to synthesize reactive control protocols, all within the context of an aircraft electric power system as a representative application area.
\r\n\r\nThis thesis consists of three complementary parts: synthesis, specification, and design. The first section focuses on the synthesis of central and distributed reactive controllers for an aircraft elec- tric power system. This approach incorporates methodologies from computer science and control. The resulting controllers are correct by construction with respect to system requirements, which are formulated using the specification language of linear temporal logic (LTL). The second section addresses how to formally specify requirements and introduces a domain-specific language for electric power systems. A software tool automatically converts high-level requirements into LTL and synthesizes a controller.
\r\n\r\nThe final sections focus on design space exploration. A design methodology is proposed that uses mixed-integer linear programming to obtain candidate topologies, which are then used to synthesize controllers. The discrete-time control logic is then verified in real-time by two methods: hardware and simulation. Finally, the problem of partial observability and dynamic state estimation is ex- plored. Given a set placement of sensors on an electric power system, measurements from these sensors can be used in conjunction with control logic to infer the state of the system.
" }, { "name": "Zheng, Guoan", "degree": "PhD", "year": "2013", "title": "Innovations in Imaging System Design: Gigapixel, Chip-Scale and MultiFunctional Microscopy", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:10102012-101657790", "creators": [ { "name": { "family": "Zheng", "given": "Guoan" }, "id": "Zheng-Guoan", "display_name": "Zheng, Guoan" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SF6E-S775", "abstract": "Microscopy imaging is of fundamental importance in diverse disciplines of science and technology. In a typical microscopy imaging platform, the light path can be generalized to the following steps: photons leave the light source, interact with the sample, and finally are detected by the image sensor. Based on such a light path, this thesis presents several new microscopy imaging techniques from three aspects: illumination design, sample manipulation, and imager modification.
\r\n \r\nThe first design strategy involves the active control of the illumination sources. Based on this strategy, we demonstrate a simple and cost-effective imaging method, termed Non-interferometric Aperture-synthesizing Microscopy (NAM), for breaking the spatial-bandwidth product barrier of a conventional microscope. We show that the NAM method is capable of providing two orders of magnitude higher throughput for most existing bright-field microscopes without involving any mechanical scanning. Based on NAM, we report the implementation of a 1.6 gigapixel microscope with a maximum numerical aperture of 0.5, a field-of-view of 120 mm2, and a resolution-invariant imaging depth of 0.3 mm. This platform is fast (acquisition time of ~ 3 minutes), free from chromatic aberration, capable for phase imaging, and, most importantly, compatible with most existing microscopes. High quality color images of histology slides were acquired by using such a platform for demonstration. The proposed NAM method provides a robust way to transform the problem of high-throughput microscopy from one that is tied to physical limitations of the optics to one that is computationally solvable. The active control of illumination sources can also be adapted for chip-scale microscopy imaging. To this end, we present a lensless microscopy solution termed ePetri-dish. This ePetri-dish platform can automatically perform high resolution (~ 0.66 micron) microscopy imaging over a large field-of-view (6 mm \u00d7 4 mm). This new approach is fully capable of working with cell cultures or any samples in which cells/bacteria may be contiguously connected, and thus, it can significantly improve Petri-dish-based cell/bacteria culture experiments. With this approach providing a low-cost and disposable microscopy solution, we can start to transit Petri-dish-based experiments from the traditionally labor-intensive process to an automated and streamlined process.
\r\n\r\nThe second strategy in design considerations is to manipulate the sample. We present a fully on-chip, lensless, sub-pixel resolving optofluidic microscope (SROFM). This device utilizes microfluidic flow to deliver specimens directly across an image sensor to generate a sequence of low-resolution projection images, where resolution is limited by the sensor\u2019s pixel size. This image sequence is then processed to reconstruct a single high-resolution image, where features beyond the Nyquist rate of the LR images are resolved. We demonstrate the device\u2019s capabilities by imaging microspheres, protist Euglena gracilis, and Entamoeba invadens cysts with sub-cellular resolution.
\r\n\r\nThe third accessing point in design considerations is the image sensor. Imager modification is an emerging technique that performs pre-detection light field manipulation. We present two novel optical structure designs: surface-wave-enabled darkfield aperture (SWEDA) and light field sensor. These structures can be directly incorporated onto optical sensors to accomplish pre-detection background suppression and wavefront sensing. We further demonstrate SWEDA\u2019s ability to boost the detection sensitivity, with a contrast enhancement of 27 dB.
\r\n" }, { "name": "Zhou, Hongchao", "degree": "PhD", "year": "2013", "title": "Randomness and Noise in Information Systems", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechTHESIS:07122012-141803264", "creators": [ { "name": { "family": "Zhou", "given": "Hongchao" }, "id": "Zhou-Hongchao", "display_name": "Zhou, Hongchao" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" } ], "option_major": [ "eleceng" ], "doi": "10.7907/82KV-2H11", "abstract": "This dissertation is devoted to the study of randomness and noise in a number of information systems including computation systems, storage systems, and natural paradigms like molecular systems, where randomness plays important and distinct roles. Motivated by applications in engineering and science we address a number of theoretical research questions.\r\nSome of the most appealing science targets for future exploration missions in our solar system lie in terrains that are inaccessible to state-of-the-art robotic rovers such as NASA's Opportunity, thereby precluding in situ analysis of these rich opportunities. Examples of potential high-yield science areas on Mars include young gullies on sloped terrains, exposed layers of bedrock in the Victoria Crater, sources of methane gas near Martian volcanic ranges, and stepped delta formations in heavily cratered regions. In addition, a recently discovered cryovolcano on Titan and frozen water near the south pole of our own Moon could provide a wealth of knowledge to any robotic explorer capable of accessing these regions.
\r\n\r\nTo address the challenge of extreme terrain exploration, this dissertation presents the Axel rover, a two-wheeled tethered robot capable of rappelling down steep slopes and traversing rocky terrain. Axel is part of a family of reconfigurable rovers, which, when docked, form a four-wheeled vehicle nicknamed DuAxel. DuAxel provides untethered mobility to regions of extreme terrain and serves as an anchor support for a single Axel when it undocks and rappels into low-ground.
\r\n\r\nAxel's performance on extreme terrain is primarily governed by three key system components: wheel design, tether control, and intelligent planning around obstacles. Investigations in wheel design and optimizing for extreme terrain resulted in the development of grouser wheels. Experiments demonstrated that these grouser wheels were very effective at surmounting obstacles, climbing rocks up to 90% of the wheel diameter. Terramechanics models supported by experiments showed that these wheels would not sink excessively or become trapped in deformable terrain.
\r\n\r\nPredicting tether forces in different configurations is also essential to the rover's mobility. Providing power, communication, and mobility forces, the tether is Axel's lifeline while it rappels steep slopes, and a cut, abraded, or ruptured tether would result in an untimely end to the rover's mission. Understanding tether forces are therefore paramount, and this thesis both models and measures tension forces to predict and avoid high-stress scenarios.
\r\n\r\nFinally, incorporating autonomy into Axel is a unique challenge due to the complications that arise during tether management. Without intelligent planning, rappelling systems can easily become entangled around obstacles and suffer catastrophic failures. This motivates the development of a novel tethered planning algorithm, presented in this thesis, which is unique for rappelling systems.
\r\n\r\nRecent field experiments in natural extreme terrains on Earth demonstrate the Axel rover's potential as a candidate for future space operations. Both DuAxel and its rappelling counterpart are rigorously tested on a 20 meter escarpment and in the Arizona desert. Through analysis and experiments, this thesis provides the framework for a new generation of robotic explorers capable of accessing extreme planetary regions and potentially providing clues for life beyond Earth.
" }, { "name": "An, Qi", "degree": "PhD", "year": "2012", "title": "Atomistic Simulations of Material Properties under Extreme Conditions", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182012-130227746", "creators": [ { "name": { "family": "An", "given": "Qi" }, "id": "An-Qi", "orcid": "0000-0003-4838-6232", "display_name": "An, Qi" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/E3Z0-1A27", "abstract": "Extreme conditions involve low or high temperatures (> 1500 K), high pressures (> 30 MPa), high strains or strain rates, high radiation fluxes (> 100 dpa), and high electromagnetic fields (> 15T). Material properties under extreme conditions can be extremely different from those under normal conditions. Understanding material properties and performance under extreme conditions, including their dynamic evolution over time, plays an essential role in improving material properties and developing novel materials with desired properties.
\r\n\r\nTo understand material properties under extreme conditions, we use molecular dynamics (MD) simulations with recently developed reactive force fields (ReaxFF) and traditional embedded atom methods (EAM) potentials to examine various materials (e.g., energetic materials and binary liquids) and processes. The key results from the simulations are summarized below.
\r\n\r\nAnisotropic sensitivity of RDX crystals: Based on the compress-and-shear reactive dynamics (CS-RD) simulations of cyclotrimethylene trinitramine (RDX) crystals, we predict that for mechanical shocks between 3 and 7 GPa, RDX is the most sensitive to shocks perpendicular to the (100) and (210) planes, while it is insensitive to those perpendicular to the (120), (111), and (110) planes. The simulations demonstrate that the molecular origin of anisotropic shock sensitivity is the steric hindrance to shearing of adjacent slip planes.
\r\n\r\nMechanisms of hotspot formation in polymer bonded explosives (PBXs): The simulations of a realistic model of PBXs reveal that hotspots may form at the nonplanar interfaces where shear relaxation leads to a dramatic temperature increase that persists long after the shock front has passed the interface. For energetic materials this temperature increase is coupled to chemical reactions that eventually lead to detonation. We show that decreasing the density of the binder eliminates the hotspots or reduces the sensitivity.
\r\n\r\nCavitation in binary metallic liquids: We demonstrate the stochastic nature of the cavitation process in binary metallic liquids, and that classical nucleation theory can predict the cavitation rate if we incorporate the Tolman length derived from the MD simulations.
\r\n\r\nSynthesis the single metallic glass on amorphous substrate: We show that single component metallic glasses (SCMGs) can be synthesized by thermal spray coating of nanodroplets onto an amorphous substrate (ND-AS). The key requirements to form the SCMGs are the rapid cooling rates and the amorphous substrates.
\r\n\r\nCarbon and hydrogen phases under extreme conditions: we report on the use of electron force fields (eFF) in characterizing the Hugoniot relationships of carbon, which includes consecutive phase transitions also captured by experiments, as well as the Hugonoit states of hydrogen centered at various initial densities compared to experiments and the predictions of other theories.
\r\n" }, { "name": "Bakshi, Mayank", "degree": "PhD", "year": "2012", "title": "Network Coding and Distributed Compression over Large Networks: Some Basic Principles", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082012-122324439", "creators": [ { "name": { "family": "Bakshi", "given": "Mayank" }, "id": "Bakshi-Mayank", "display_name": "Bakshi, Mayank" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GWDW-5H78", "abstract": "The fields of Network Coding and Distributed Compression have focused primarily on finding the capacity for families of problems defined by either a broad class of networks topologies (e.g., directed, acyclic networks) under a narrow class of demands (e.g., multicast), or a specific network topology (e.g. three-node networks) under different types of demands (e.g. Slepian-Wolf, Ahlswede-K\u00f6rner). Given the difficulty of the general problem, it is not surprising that the collection of networks that have been fully solved to date is still very small. This work investigates several new approaches to bounding the achievable rate region for general network source coding problems - reducing a network to an equivalent network or collection of networks, investigating the effect of feedback on achievable rates, and characterizing the role of side information.
\r\n\r\nWe describe two approaches aimed at simplifying the capacity calculations in a large network. First, we prove the optimality of separation between network coding and channel coding for networks of point-to-point channels with a Byzantine adversary. Next, we give a strategy for calculating the capacity of an error-free network by decomposing that network into smaller networks. We show that this strategy is optimal for a large class of networks and give a bound for other cases.
\r\n\r\nTo date, the role of feedback in network source coding has received very little attention. We present several examples of networks that demonstrate that feedback can increases the set of achievable rates in both lossy and lossless network source coding settings. We derive general upper and lower bounds on the rate regions for networks with limited feedback that demonstrate a fundamental tradeoff between the forward rate and the feedback rate. For zero error source coding with limited feedback and decoder side information, we derive the exact tradeoff between the forward rate and the feedback rate for several classes of sources. A surprising result is that even zero rate feedback can reduce the optimal forward rate by an arbitrary factor.
\r\n\r\nSide information can be used to reduce the rates required for reliable information. We precisely characterize the exact achievable region for multicast networks with side information at the sinks and find upper and lower bounds on the achievable rate region for other demand types.
" }, { "name": "Barmpoutis, Dionysios", "degree": "PhD", "year": "2012", "title": "Network Structure Optimization with Applications to Minimizing Variance and Crosstalk", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12102011-161913831", "creators": [ { "name": { "family": "Barmpoutis", "given": "Dionysios" }, "id": "Barmpoutis-Dionysios", "display_name": "Barmpoutis, Dionysios" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cns" ], "doi": "10.7907/ER8Y-ZK49", "abstract": "This thesis provides a unified methodology for analyzing structural properties of graphs, along with their applications. In the last several years, the field of complex networks has been extensively studied, and it is now well understood that the way a large network is built is closely intertwined with its function. Structural properties have an impact on the function of the network, and the form of many systems has been evolved in order to optimize for given functions. Despite the great progress, particularly in how structural attributes affect the various network functions, there is a significant gap in the quantitative study of how much these properties can change in a network without a significant impact on the functionality of the system, or what the bounds of these structural attributes are. Here, we find and analytically prove tight bounds of global graph properties, as well as the form of the graphs that achieve these bounds. The attributes studied include the network efficiency, radius, diameter, average distance, betweenness centrality, resistance distance, and average clustering. All of these qualities have a direct impact on the function of the network, and finding the graph that optimizes one or more of them is of interest when designing a large system. In addition, we measure how sensitive these properties are with respect to random rewirings or addition of new edges, since designing a network with a given set of constraints may include a lot of trade-offs. This thesis also studies properties that are of interest in both natural and engineered networks, such as maximum immunity to crosstalk interactions and random noise. We are primarily focused on networks where information is transmitted through a means that is accessible by all the individual units of the network and the interactions among the different entities that comprise it do not necessarily have a dedicated mechanism that facilitates information transmission, or isolates them from other parts of the network. Two examples of this class are biological and chemical reaction networks. Such networks suffer from unwanted crosstalk interactions when two or more units spuriously interact with each other. In addition, they are subject to random fluctuations in their output, both due to noisy inputs and because of the random variance of their parameters. These two types of randomness affect the behavior of the system in ways that are intrinsically different. We examine the network topologies that accentuate or alleviate the effect of random variance in the network for both directed and undirected graphs, and find that increasing the crosstalk among different parts reduces the output variance but also contributes to a slower response.\r\n" }, { "name": "Bodine-Baron, Elizabeth Anne", "degree": "PhD", "year": "2012", "title": "Peer Effects in Social Networks: Search, Matching Markets, and Epidemics", "advisor": "Hassibi, Babak; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222012-145639265", "creators": [ { "name": { "family": "Bodine-Baron", "given": "Elizabeth Anne" }, "id": "Bodine-Baron-Elizabeth-Anne", "display_name": "Bodine-Baron, Elizabeth Anne" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Yariv", "given": "Leeat" }, "id": "Yariv-L", "role": "member", "display_name": "Yariv, Leeat" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GDV2-YF12", "abstract": "Social network analysis emerged as an important area in sociology in the early 1930s, marking a shift from looking at individual attribute data to examining the relationships between people and groups. Surveying many different types of real-world networks, researchers quickly found that different types of social networks tend to share a common set of structural characteristics, including small diameter, high clustering, and heavy-tailed degree distributions. Moving beyond real networks, in the 1990s researchers began to propose random network models to explain these commonly observed social network structures. These models laid the foundation for investigation into problems where the underlying network plays a key role, from the spread of information and disease, to the design of distributed communication and search algorithms, to mechanism design and public policy. Here we focus on the role of peer effects in social networks. Through this lens, we develop a mathematically tractable random network model incorporating searchability, propose a novel way to model and analyze two-sided matching markets with externalities, model and calculate the cost of an epidemic spreading on a complex network, and examine the impact of conforming and non-conforming peer effects in vaccination decisions on public health policy.
\r\n\r\nThroughout this work, the goal is to bring together knowledge and techniques from diverse fields like sociology, engineering, and economics, exploiting our understanding of social network structure and generative models to understand deeper problems that \u2014 without this knowledge \u2014 could be intractable. Instead of crippling our analysis, social network characteristics allow us to reach deeper insights about the interaction between a particular problem and the network underlying it.
" }, { "name": "Boettcher, Philipp Andreas", "degree": "PhD", "year": "2012", "title": "Thermal Ignition", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162012-131336010", "creators": [ { "name": { "family": "Boettcher", "given": "Philipp Andreas" }, "id": "Boettcher-Philipp-Andreas", "display_name": "Boettcher, Philipp Andreas" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/H2W9-ZK95", "abstract": "Accidental ignition of flammable gases is a critical safety concern in many industrial applications. Particularly in the aviation industry, the main areas of concern on an aircraft are the fuel tank and adjoining regions, where spilled fuel has a high likelihood of creating a flammable mixture. To this end, a fundamental understanding of the ignition phenomenon is necessary in order to develop more accurate test methods and standards as a means of designing safer air vehicles. The focus of this work is thermal ignition, particularly auto-ignition with emphasis on the effect of heating rate, hot surface ignition and flame propagation, and puffing flames.
\r\n\r\nCombustion of hydrocarbon fuels is traditionally separated into slow reaction, cool flame, and ignition regimes based on pressure and temperature. Standard tests, such as the ASTM E659, are used to determine the lowest temperature required to ignite a specific fuel mixed with air at atmospheric pressure. It is expected that the initial pressure and the rate at which the mixture is heated also influences the limiting temperature and the type of combustion. This study investigates the effect of heating rate, between 4 and 15 K/min, and initial pressure, in the range of 25 to 100 kPa, on ignition of n-hexane air mixtures. Mixtures with equivalence ratio ranging from 0.6 to = 1.2 were investigated. The problem is also modeled computationally using an extension of Semenov's classical auto-ignition theory with a detailed chemical mechanism. Experiments and simulations both show that in the same reactor either a slow reaction or an ignition event can take place depending on the heating rate. Analysis of the detailed chemistry demonstrates that a mixture which approaches the ignition region slowly undergoes a significant modification of its composition. This change in composition induces a progressive shift of the explosion limit until the mixture is no longer flammable. A mixture that approaches the ignition region sufficiently rapidly undergoes only a moderate amount of thermal decomposition and explodes quite violently. This behavior can also be captured and analyzed using a one-step reaction model, where the heat release is in competition with the depletion of reactants.
\r\n\r\nHot surface ignition is examined using a glow plug or heated nickel element in a series of premixed n-hexane air mixtures. High-speed schlieren photography, a thermocouple, and a fast response pressure transducer are used to record flame characteristics such as ignition temperature, flame speed, pressure rises, and combustion mode. The ignition event is captured by considering the dominant balance of diffusion and chemical reaction that occurs near a hot surface. Experiments and models show a dependence of ignition temperature on mixture composition, initial pressure, and hot surface size. The mixtures exhibit the known lower flammability limit where the maximum temperature of the hot surface was insufficient at igniting the mixture. Away from the lower flammability limit, the ignition temperature drops to an almost constant value over a wide range of equivalence ratios (0.7 to 2.8) with large variations as the upper flammability limit is approached. Variations in the initial pressure and equivalence ratio also give rise to different modes of combustion: single flame, re-ignition, and puffing flames. These results are successfully compared to computational results obtained using a flamelet model and a detailed chemical mechanism for n-heptane. These different regimes can be delineated by considering the competition between inertia, i.e., flame propagation, and buoyancy, which can be expressed in the Richardson number.
\r\n\r\nIn experiments of hot surface ignition and subsequent flame propagation a 10 Hz puffing flame instability is visible in mixtures that are stagnant and premixed prior to the ignition sequence. By varying the size of the hot surface, power input, and combustion vessel volume, we determined that the instability is a function of the interaction of the flame with the fluid flow induced by the combustion products rather than the initial plume established by the hot surface. The phenomenon is accurately reproduced in numerical simulations and a detailed flow field analysis revealed a competition between the inflow velocity at the base of the flame and the flame propagation speed. The increasing inflow velocity, which exceeds the flame propagation speed, is ultimately responsible for creating a puff. The puff is then accelerated upward, allowing for the creation of the subsequent instabilities. The frequency of the puffing is proportional to the gravitational acceleration and inversely proportional to the flame speed. We propose a relation describing the dependence of the frequency on gravitational acceleration, hot surface diameter, and flame speed. This relation shows good agreement for lean and rich n-hexane-air as well as lean hydrogen-air flames.
" }, { "name": "Bohn, Florian", "degree": "PhD", "year": "2012", "title": "Integrated Circuit Signal Generation and Detection Techniques for Microwave and Sub-Millimeter Wave Signals", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:01082012-184435123", "creators": [ { "name": { "family": "Bohn", "given": "Florian" }, "id": "Bohn-Florian", "display_name": "Bohn, Florian" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Chattopadhyay", "given": "Goutam" }, "id": "Chattopadhyay-G", "role": "member", "display_name": "Chattopadhyay, Goutam" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Q018-QP18", "abstract": "The unabated reduction of device feature sizes in semiconductor processes, particularly in complementary metal-oxide semiconductor (CMOS) processes, has served as the enabling factor behind integrated electronic systems of ever increasing complexity and speeds. As a result, former niche market applications, such as the global-positioning system (GPS), cellular telephony or powerful general purpose computers, have expanded into the field of consumer electronics with tremendous impact on the daily lives of millions of people. It is, therefore, only logical that the future will bring new applications to the mass market that today only exist as niche applications.\r\nSystems operating in the millimeter wave frequency range are an example of a current niche market, with current research striving to fully integrate such systems using advanced semiconductor processing technology. Electromagnetic waves at these frequencies become comparable in size to the electronics circuits. This opens the possibility for novel design approaches that were traditionally not available to integrated circuit radio-frequency designers. On the other hand, the increase in the number of available devices also brings with it new challenges due to increasing variability in device performance. Self-correcting techniques for integrated circuits that offset this increased variability are therefore also highly desirable.
\r\n\r\nIn this dissertation, we explore the above issues on several fronts. We will first present a phase-locked loop synthesizer that auto-corrects its spurious output tones as an example of circuits that correct for a parasitic effect by leveraging the availability of many active devices to construct a digital feedback loop. We will then focus on the effort to operate CMOS integrated circuits in the terahertz regime by developing a solid design foundation for converting signals to frequencies beyond the maximum power gain frequency\u3016 f\u3017_max. We will use the insights gained to develop and explore two designs generating power at these high frequencies as proofs of concept. Finally, we will focus on the passive electromagnetic components of such high frequency systems and present a novel way of designing electromagnetic structures that are comparable to the wavelength size in integrated systems by introducing the third physical dimension into the design process for integrated electromagnetic structures.
\r\n" }, { "name": "Capece, Angela Maria", "degree": "PhD", "year": "2012", "title": "Plasma-Surface Interactions in Hollow Cathode Discharges for Electric Propulsion\r ", "advisor": "Shepherd, Joseph E.; Polk, James E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312012-113856351", "creators": [ { "name": { "family": "Capece", "given": "Angela Maria" }, "id": "Capece-Angela-Maria", "orcid": "0000-0003-4147-7174", "display_name": "Capece, Angela Maria" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "co-advisor", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "co-advisor", "display_name": "Polk, James E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Giapis", "given": "Konstantinos P." }, "id": "Giapis-K-P", "role": "member", "display_name": "Giapis, Konstantinos P." }, { "name": { "family": "Goebel", "given": "Dan M." }, "id": "Goebel-D-M", "role": "member", "display_name": "Goebel, Dan M." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7TDQ-DR81", "abstract": "Electric thrusters generate high exhaust velocities and can achieve specific impulses in excess of 1000 s. The low thrust generation and high specific impulse make electric propulsion ideal for interplanetary missions, spacecraft station keeping, and orbit raising maneuvers. Consequently, these devices have been used on a variety of space missions including Deep Space 1, Dawn, and hundreds of commercial spacecraft in Earth orbit. In order to provide the required total impulses, thruster burn time can often exceed 10,000 hours, making thruster lifetime essential.
\r\n\r\nOne of the main life-limiting components on ion engines is the hollow cathode, which serves as the electron source for ionization of the xenon propellant gas. Reactive contaminants such as oxygen can modify the cathode surface morphology and degrade the electron emission properties. Hollow cathodes that operate with reactive impurities in the propellant will experience higher operating temperatures, which increase evaporation of the emission materials and reduce cathode life. A deeper understanding of the mechanisms initiating cathode failure will improve thruster operation, increase lifetime, and ultimately reduce cost.
\r\n \r\nA significant amount of work has been done previously to understand the effects of oxygen poisoning on vacuum cathodes; however, the xenon plasma adds complexity, and its role during cathode poisoning is not completely understood. The work presented here represents the first attempt at understanding how oxygen impurities in the xenon discharge plasma alter the emitter surface and affect operation of a 4:1:1 BaO-CaO-Al2O3 hollow cathode.
\r\n \r\nA combination of experimentation and modeling was used to investigate how oxygen impurities in the discharge plasma alter the emitter surface and reduce the electron emission capability. The experimental effort involved operating a 4:1:1 hollow cathode at various conditions with oxygen impurities in the xenon flow. Since direct measurements of the emitter surface state cannot be obtained because of the cathode geometry and high particles fluxes, measurements of the emitter temperature using a two-color pyrometer were used to determine the oxygen surface coverage and characterize the rate processes that occur during poisoning.
\r\n \r\nA model describing the material transport in the plasma discharge was developed and is used to predict the barium and oxygen fluxes to the emitter surface during cathode operation by solving the species continuity and momentum equations. The dominant ionization process for molecular oxygen in the plasma gas is resonant charge exchange with xenon ions. Barium is effectively recycled in the plasma; however, BaO and O2 are not. The model shows that the oxygen flux to the surface is not diffusion limited.
\r\n\r\nExperimental results indicate that the oxygen poisoning rate is slow and that the oxygen poisoning coverage on the emitter surface is less than 3%. A time-dependent model of the reaction kinetics of oxygen and barium at the tungsten surface was developed using the experimental results.
\r\n \r\nThe experiments and kinetics model indicate that the dominant processes at the emitter surface are dissociative adsorption of O2, sputtering of the O2 precursor, and desorption of O. Ion sputtering of the weakly bound O2 precursor state limits the poisoning rate and yields low oxygen coverage. Removal of chemisorbed atomic oxygen is dominated by thermal processes. Based on the low oxygen coverage and long poisoning transients, plasma cathodes appear to be able to withstand higher oxygen concentrations than vacuum cathodes.
" }, { "name": "Chan, Man Nin", "degree": "PhD", "year": "2012", "title": "Mass Spectrometric Analysis of Organic Aerosol Composition: Laboratory and Ambient", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12152011-220323752", "creators": [ { "name": { "family": "Chan", "given": "Man Nin" }, "id": "Chan-Man-Nin", "orcid": "0000-0002-2384-2695", "display_name": "Chan, Man Nin" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/CGKH-EW24", "abstract": "Organic compounds contribute a significant mass fraction of ambient aerosol and play a role in determining the physiochemical properties of ambient aerosol. A significant fraction of organic aerosol is secondary organic aerosol (SOA), which is produced when the volatile organic compounds (VOCs) originated from various anthropogenic and biogenic sources react with atmospheric oxidants such as ozone, hydroxyl radicals, and nitrate radicals to form lower volatility organic compounds, which subsequently partition into the particle phase. Understanding the composition of ambient aerosol is crucial for identifying their sources and formation mechanisms and predicting their properties and effects on various ambient processes. This thesis focuses on investigating the composition of laboratory\u2013generated SOA formed from the oxidation of biogenic VOCs of atmospheric importance (isoprene and \u03b2\u2013caryophyllene) and ambient aerosol collected in the field campaigns using advanced mass spectrometric techniques. By comparing the mass spectrometric data collected for the both laboratory\u2013generated SOA and ambient aerosol, we propose reaction pathways and new chemical tracers for these biogenic VOCs, which enhance our knowledge of the composition, sources, and formation pathways of SOA in the atmosphere. With a better knowledge of the SOA composition, a product\u2013specific model is proposed to predict the composition and aerosol mass yields (mass of SOA formed per mass of hydrocarbon reacted) of laboratory\u2013generated \u03b1\u2013pinene SOA. " }, { "name": "Chang, Christopher SungWook", "degree": "PhD", "year": "2012", "title": "Applications of Coding in Network Communications", "advisor": "Ho, Tracey C.; Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312012-173613536", "creators": [ { "name": { "family": "Chang", "given": "Christopher SungWook" }, "id": "Chang-Christopher-SungWook", "display_name": "Chang, Christopher SungWook" } ], "advisors": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "advisor", "display_name": "Ho, Tracey C." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "chair", "display_name": "Ho, Tracey C." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "co-chair", "display_name": "Effros, Michelle" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Ligett", "given": "Katrina A." }, "id": "Ligett-K-A", "orcid": "0000-0003-2780-6656", "role": "member", "display_name": "Ligett, Katrina A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/3N60-MB49", "abstract": "This thesis uses the tool of network coding to investigate fast peer-to-peer file distribution, anonymous communication, robust network construction under uncertainty, and prioritized transmission.
\r\n\r\nIn a peer-to-peer file distribution system, we use a linear optimization approach to show that the network coding framework significantly simplifies analysis even in scenarios where the optimal solution does not require coding. We also study the effect of requiring reciprocity and the impact of dynamically changing network scenarios.
\r\n\r\nSecond, we investigate anonymous routing in peer-to-peer networks. The goal is to design and analyze a peer-to-peer system that hides the identities of source and sink pairs against adversarial nodes. We first propose a protocol for subgraph construction signaling. The protocol uses path diversity rather than cryptographic keys. We prove information theoretic security of the proposed protocol. We investigate a variety of deterministic and randomized subgraph designs. We also give a reverse path construction mechanism, with which a sink can reply to the source without knowing the source identity. We next investigate anonymous data transmission using network coding. Again, path diversity (with network coding) is used to hide the identities of source and sink pairs. We investigate the effect of subgraph shape on anonymity and congestion arising from traffic shaping constraints, demonstrating the tradeoff between the two through simulations.
\r\n\r\nThird, we study the problem of network construction under uncertainty about link-loss rates. We prove that both maximizing throughput and minimizing cost are coNP-hard problems. We find polynomial time-solvable solutions that outperform other deterministic approaches.
\r\n\r\nLastly, we investigate strategies for communication under a system that prioritizes data based on the worth of data and the probability of successful transmission. Only the highest priority data is transmitted when communication is very limited.
" }, { "name": "Cho, In Ho", "degree": "PhD", "year": "2012", "title": "Virtual Earthquake Engineering Laboratory with Physics-Based Degrading Materials on Parallel Computers", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01302012-081909374", "creators": [ { "name": { "family": "Cho", "given": "In Ho" }, "id": "Cho-In-Ho", "display_name": "Cho, In Ho" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "chair", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "role": "member", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Aivazis", "given": "Michael A. G." }, "id": "Aivazis-M-A-G", "role": "member", "display_name": "Aivazis, Michael A. G." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "civileng" ], "doi": "10.7907/49W9-PY43", "abstract": "For the last few decades, we have obtained tremendous insight into underlying microscopic mechanisms of degrading quasi-brittle materials from persistent and near-saintly efforts in laboratories, and at the same time we have seen unprecedented evolution in computational technology such as massively parallel computers. Thus, time is ripe to embark on a novel approach to settle unanswered questions, especially for the earthquake engineering community, by harmoniously combining the microphysics mechanisms with advanced parallel computing technology.
\r\n\r\nTo begin with, it should be stressed that we placed a great deal of emphasis on preserving clear meaning and physical counterparts of all the microscopic material models proposed herein, since it is directly tied to the belief that by doing so, the more physical mechanisms we incorporate, the better prediction we can obtain.
\r\n \r\nWe departed from reviewing representative microscopic analysis methodologies, selecting out \u201cfixed-type\u201d multidirectional smeared crack model as the base framework for nonlinear quasi-brittle materials, since it is widely believed to best retain the physical nature of actual cracks. Microscopic stress functions are proposed by integrating well-received existing models to update normal stresses on the crack surfaces (three orthogonal surfaces are allowed to initiate herein) under cyclic loading.
\r\n \r\nUnlike the normal stress update, special attention had to be paid to the shear stress update on the crack surfaces, due primarily to the well-known pathological nature of the fixed-type smeared crack model\u2013spurious large stress transfer over the open crack under nonproportional loading. In hopes of exploiting physical mechanism to resolve this deleterious nature of the fixed crack model, a tribology-inspired three-dimensional (3d) interlocking mechanism has been proposed. Following the main trend of tribology (i.e., the science and engineering of interacting surfaces), we introduced the base fabric of solid particle-soft matrix to explain realistic interlocking over rough crack surfaces, and the adopted Gaussian distribution feeds random particle sizes to the entire domain. Validation against a well-documented rough crack experiment reveals promising accuracy of the proposed 3d interlocking model.
\r\n \r\nA consumed energy-based damage model has been proposed for the weak correlation between the normal and shear stresses on the crack surfaces, and also for describing the nature of irrecoverable damage. Since the evaluation of the consumed energy is directly linked to the microscopic deformation, which can be efficiently tracked on the crack surfaces, the proposed damage model is believed to provide a more physical interpretation than existing damage mechanics, which fundamentally stem from mathematical derivation with few physical counterparts.
\r\n \r\nAnother novel point of the present work lies in the topological transition-based \u201csmart\u201d steel bar model, notably with evolving compressive buckling length. We presented a systematic framework of information flow between the key ingredients of composite materials (i.e., steel bar and its surrounding concrete elements). The smart steel model suggested can incorporate smooth transition during reversal loading, tensile rupture, early buckling after reversal from excessive tensile loading, and even compressive buckling. Especially, the buckling length is made to evolve according to the damage states of the surrounding elements of each bar, while all other dominant models leave the length unchanged.
\r\n \r\nWhat lies behind all the aforementioned novel attempts is, of course, the problem-optimized parallel platform. In fact, the parallel computing in our field has been restricted to monotonic shock or blast loading with explicit algorithm which is characteristically feasible to be parallelized. In the present study, efficient parallelization strategies for the highly demanding implicit nonlinear finite element analysis (FEA) program for real-scale reinforced concrete (RC) structures under cyclic loading are proposed. Quantitative comparison of state-of-the-art parallel strategies, in terms of factorization, had been carried out, leading to the problem-optimized solver, which is successfully embracing the penalty method and banded nature. Particularly, the penalty method employed imparts considerable smoothness to the global response, which yields a practical superiority of the parallel triangular system solver over other advanced solvers such as parallel preconditioned conjugate gradient method. Other salient issues on parallelization are also addressed.
\r\n \r\nThe parallel platform established offers unprecedented access to simulations of real-scale structures, giving new understanding about the physics-based mechanisms adopted and probabilistic randomness at the entire system level. Particularly, the platform enables bold simulations of real-scale RC structures exposed to cyclic loading\u2013H-shaped wall system and 4-story T-shaped wall system. The simulations show the desired capability of accurate prediction of global force-displacement responses, postpeak softening behavior, and compressive buckling of longitudinal steel bars. It is fascinating to see that intrinsic randomness of the 3d interlocking model appears to cause \u201clocalized\u201d damage of the real-scale structures, which is consistent with reported observations in different fields such as granular media.
\r\n \r\nEquipped with accuracy, stability and scalability as demonstrated so far, the parallel platform is believed to serve as a fertile ground for the introducing of further physical mechanisms into various research fields as well as the earthquake engineering community. In the near future, it can be further expanded to run in concert with reliable FEA programs such as FRAME3d or OPENSEES. Following the central notion of \u201cmultiscale\u201d analysis technique, actual infrastructures exposed to extreme natural hazard can be successfully tackled by this next generation analysis tool\u2013the harmonious union of the parallel platform and a general FEA program. At the same time, any type of experiments can be easily conducted by this \u201cvirtual laboratory.\u201d
\r\n" }, { "name": "DeBoer, Charles Meno Theodore", "degree": "PhD", "year": "2012", "title": "Biomimetic Accommodating Intraocular Lens", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042012-135440197", "creators": [ { "name": { "family": "DeBoer", "given": "Charles Meno Theodore" }, "id": "DeBoer-Charles-Meno-Theodore", "display_name": "DeBoer, Charles Meno Theodore" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Humayun", "given": "Mark" }, "id": "Humayun-M", "role": "member", "display_name": "Humayun, Mark" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9B56GQH", "abstract": "The crystalline lens allows the eye to focus on near and far objects. During the aging process, it loses its ability to focus and often becomes cloudy during cataract formation. At this point, traditional medical therapy replaces the lens with an artificial replacement lens. Although replacement lenses for the crystalline lens have been implanted since 1949 for cataract surgery, none of the FDA-approved lenses mimic the anatomy of the natural lens. Hence, they are not able to focus in a manner similar to the youthful lens. Instead, they function in a manner similar to the aged lens and only provide vision at a single distance or at a very limited range of focal distances. Patients with the newest implants are often obliged to use reading glasses when using near vision, or suffer from optical aberrations, halos, or glare. Therefore, there is a need to provide youthful vision after lens surgery in terms of focusing ability, accurate optical power, and sharp focus without distortion or optical aberrations.
\r\n\r\nThis thesis presents an approach to restoring youthful vision after lens replacement. An intraocular lens (IOL) that can provide accurate visual acuity along with focusing ability is proposed. This IOL relies on the natural anatomy and physiology of the eye, and therefore is actuated in a manner identical to the natural lens. In addition, the lens has the capability for adjustment during or after implantation to provide high-acuity vision throughout life.
\r\n\r\nThe natural anatomy and physiology of the eye is described, along with lens replacement surgery. A lens design is proposed to address the unmet need of lens-replacement patients. Specific care in the design is made for small surgical incisions, high visual acuity, adjustable acuity over years, and the ability to focus similar to the natural lens. Methods to test the IOL using human donor tissue are developed based upon prior experiments on the ex vivo natural lens. These tools are used to demonstrate efficacy of the newly developed accommodating intraocular lens.
\r\n\r\nTo further demonstrate implant feasibility, materials and processes for building the lens are evaluated for biocompatibility, endurance, repeatable manufacture, and stability. The lens biomechanics are determined after developing an artificial anatomy testing setup inspired by the natural anatomy of the human focusing mechanism. Finally, based upon a mechanical and optical knowledge of the lens, several improved lens concepts are proposed and demonstrated for efficacy.
" }, { "name": "Dempsey, William P.", "degree": "PhD", "year": "2012", "title": "Establishing a Genetic and Exogenous Toolbox for Studying Multiple Stages of Vertebrate Development in vivo", "advisor": "Fraser, Scott E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212012-132419705", "creators": [ { "name": { "family": "Dempsey", "given": "William P." }, "id": "Dempsey-William-P", "display_name": "Dempsey, William P." } ], "advisors": [ { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "advisor", "display_name": "Fraser, Scott E." } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "bioeng" ], "doi": "10.7907/Z98S4MVS", "abstract": "Understanding of cell behavior during vertebrate development and repair has been greatly facilitated by advances in biological imaging. Importantly, more powerful tools to generate contrast within the tissue make in vivo analyses of these processes in time and space more tractable. Here, I present my efforts to develop and refine an imaging toolbox to study in vivo cell shape, dynamics, structure, and behavior in the zebrafish vertebrate model system. Mosaic analysis and targeted photoconversion illuminate fine morphological details as cells migrate during gastrulation, revealing cell connections that span several cell diameters across the embryo. These intercellular bridges link cells between lineage boundaries and allow cells to share membrane components on a developmentally relevant time scale. The PhOTO zebrafish transgenic lines combine the strengths of sparse and global cell labeling to monitor cell dynamics and morphology at any stage in the lifetime of the zebrafish. I demonstrate targeted and instantaneous sparse cell tracking in the context of global cell behavior in the embryo, and I also isolate a subset of slowly dividing cells populating a regenerating adult tail fin. Combining fluorescence and endogenous second harmonic generation (SHG) imaging as a tool to study early muscle structure and organization within whole zebrafish muscle compartments uncovers the source of vernier-patterned signal in highly ordered myosin arrays. Instead of being physical distortions in muscle sarcomeres, these patterns may result from an optical artifact of SHG imaging, since comparable signal is not visible in both the SHG and fluorescence channels. To complement the aforementioned genetic labeling and endogenous contrast tools, barium titanate SHG nanoprobes \u2014 exogenous and nontoxic SHG-capable nanomaterial tags \u2014 are refined for cell labeling in the zebrafish. Silane functionalization acts as a platform for further surface modifications, including: multistep chemical additions, non-reactive surface coating modifications, and antibody linkages for cell targeting applications. The power of each of these tools lies in their compatibility with one another: combining the fluorescence and SHG contrast approaches described here may enable high-resolution imaging at a variety of developmental stages to appreciate the multifaceted cell behaviors governing vertebrate developmental programs more completely." }, { "name": "Deng, Xiaowei", "degree": "PhD", "year": "2012", "title": "Clefted Equilibrium Shapes of Superpressure Balloon Structures", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062012-202646378", "creators": [ { "name": { "family": "Deng", "given": "Xiaowei" }, "id": "Deng-Xiaowei", "display_name": "Deng, Xiaowei" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YYTP-2005", "abstract": "This thesis presents a numerical and analytical study of the clefted equilibrium shape of superpressure balloon structures. Lobed superpressure balloons have shown a tendency to deploy into unexpected asymmetric shapes, hence their design has to strike a balance between the lower stresses achieved by increasing lobing and the risk of incomplete deployment. Extensive clefting is a regular feature of balloons that are incompletely inflated, and is regularly seen during launch and ascent. Our particular interest in the research is in clefts that remain once a balloon has reached its float altitude and is fully pressurized.
\r\n\r\nA simplified simulation technique for orthotropic viscoelastic membranes is presented in the thesis. Wrinkling is detected by a combined stress-strain criterion and an iterative scheme searches for the wrinkle angle using a pseudoelastic material stiffness matrix based on a nonlinear viscoelastic constitutive model. This simplified model has been implemented in ABAQUS/Explicit and is able to compute the behavior of a membrane structure by superposition of a small number of response increments. The model has been tested against a published solution for a time-independent isotropic membrane under simple shear and also against experimental results on StratoFilm 420 under simple shear.
\r\n\r\n\r\nA fully three-dimensional finite element model of balloon structures incorporating wrinkling and frictionless contact, able to simulate the shapes taken up by lobed superpressure balloons during the final stages of their ascent has been established. Two different methods have been considered to predict the clefts: (i) deflation and\r\ninflation method and (ii) constraint shift method. In method (i), the starting configuration is obtained by deflating an initially symmetric balloon subject to uniform pressure. The deflation simulation is continued until the differential pressure at the bottom of the balloon has become negative, at which point the balloon is extensively clefted. The balloon is then inflated by increasing the bottom pressure while maintaining a uniform vertical ressure gradient, and the evolution of the shape and stress distribution of the balloon is studied. Two different designs of uperpressure balloons are investigated: a flat facet balloon and a ighly lobed balloon. It is found that the flat facet balloon follows essentially the same path during deflation and inflation, and hence will deploy into a unique, symmetric shape. For the lobed balloon it is found that it follows different paths during deflation and inflation, and deploys into an alternate, clefted equilibrium shape.
\r\n\r\nCompared to method (i), method (ii) is computationally a more efficient clefting test. The test consists in setting up the balloon in its symmetrically inflated configuration, then breaking the symmetry of this shape by artificially introducing a clefting imperfection, and finally determining the equilibrium shape of the balloon. The clefting imperfection is computed by shifting the constraint at the bottom of the balloon and removing the pressure in the bottom region, below the shifted constraint. The clefting test is applied successfully to three 27~m diameter superpressure balloons that have been tested indoors by NASA, of which one had remained clefted when it was inflated and the other two had deployed completely.
\r\n\r\nIn addition to numerical simulations, formulation of a new cleft factor, employed as an indicator of tendency to S-cleft for superpressure balloons based on constant-stress design has been established through dimensional analysis. The cleft factor, defined as the ratio of clefted volume to cyclically symmetrical volume, is expressed in the form of power law relation of the dimensionless groups. An example illustrates how to calculate the coefficients of the analytical formula and analyze sensitivity of design parameters to clefting.
" }, { "name": "Fitzmaurice, Arthur Gerald, III", "degree": "PhD", "year": "2012", "title": "The Role of Pesticide-Induced Aldehyde Dehydrogenase Inhibition in the Pathogenesis of Parkinson\u2019s Disease", "advisor": "Bronstein, Jeff M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042012-150150171", "creators": [ { "name": { "family": "Fitzmaurice", "given": "Arthur Gerald, III" }, "id": "Fitzmaurice-Arthur-Gerald-III", "display_name": "Fitzmaurice, Arthur Gerald, III" } ], "advisors": [ { "name": { "family": "Bronstein", "given": "Jeff M." }, "id": "Bronstein-J-M", "role": "advisor", "display_name": "Bronstein, Jeff M." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Bronstein", "given": "Jeff M." }, "id": "Bronstein-J-M", "role": "member", "display_name": "Bronstein, Jeff M." }, { "name": { "family": "Patterson", "given": "Paul H." }, "id": "Patterson-P-H", "role": "member", "display_name": "Patterson, Paul H." }, { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "role": "member", "display_name": "Leadbetter, Jared R." } ], "option_major": [ "envreng" ], "doi": "10.7907/FDAG-HH02", "abstract": "Parkinson\u2019s disease (PD) is a neurodegenerative disorder particularly characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. Its etiology is unknown but likely includes both genetic and environmental factors. Since pesticide use has been associated with PD occurrence, we conducted a screen to identify pesticides that impair the ubiquitin-proteasome system (UPS), a degradative process implicated in PD pathogenesis. Benomyl was identified as a UPS inhibitor in this screen and became the focus of this dissertation.
\r\n\r\nIn an epidemiologic study, we used state-mandated Pesticide Use Reports to estimate chronic exposures and observed 65-92% increased PD risk in a population exposed to the fungicide benomyl. In experimental models, we found that benomyl induced selective dopaminergic neuronal loss in vitro with primary mesencephalic cultures and selective aminergic neuronal loss in a novel in vivo zebrafish system. Benomyl is readily metabolized to S-methyl N-butylthiocarbamate and its sulfoxide, a potent aldehyde dehydrogenase (ALDH) inhibitor. These thiocarbamates inhibited ALDH activity in primary neurons at submicromolar concentrations leading to accumulation of the dopamine metabolite 3,4-dihydroxyphenylacetaldehyde, the proposed neurotoxicant. This model for PD etiology via ALDH inhibition may help explain the selective vulnerability of dopaminergic neurons in PD.
\r\n\r\nTo follow up on this finding, we developed a novel ex vivo neuronal assay to screen other pesticides for ALDH inhibitory activity. All dithiocarbamates tested (e.g., mancozeb, maneb, ziram), two dicarboxymides (captan, folpet), and two imidazoles (benomyl, triflumizole) inhibited ALDH activity, potentially via metabolic byproducts (e.g., carbon disulfide, thiophosgene). Exposures to ALDH-inhibiting pesticides (i.e., positive hits) applied in our study area were associated with dose-dependent twofold to fourfold increases in PD risk. Genetic variation in the ALDH2 gene potentiated this risk considerably (up to sixfold) for people working where these pesticides were sprayed liberally.
\r\n\r\nThis is the first report of a pesticide that damages dopaminergic neurons by inhibiting ALDH activity. The identification of multiple ALDH-inhibiting pesticides associated with increased PD risk supports the potential of ALDH as a novel therapeutic target and a subject for consideration by regulators and policymakers.
" }, { "name": "Ford, William Chastang", "degree": "PhD", "year": "2012", "title": "I. Quantal Effects in Biochemical Cooperativity and a Proposed Mechanism for the Differentiation of Calcium Signaling in Synaptic Plasticity. II. Evolutionary Algorithms for the Optimization of Methods in Computational Chemistry", "advisor": "Hoffmann, Michael R.; Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302012-122930768", "creators": [ { "name": { "family": "Ford", "given": "William Chastang" }, "id": "Ford-William-Chastang", "display_name": "Ford, William Chastang" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "co-advisor", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "co-advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "chair", "display_name": "Gray, Harry B." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Abrol", "given": "Ravinder" }, "id": "Abrol-R", "role": "member", "display_name": "Abrol, Ravinder" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "cns" ], "doi": "10.7907/Z9HH6H1Z", "abstract": "In Part 1 of this thesis, we propose that biochemical cooperativity is a fundamentally non-ideal process. We show quantal effects underlying biochemical cooperativity and highlight apparent ergodic breaking at small volumes. The apparent ergodic breaking manifests itself in a divergence of deterministic and stochastic models. We further predict that this divergence of deterministic and stochastic results is a failure of the deterministic methods rather than an issue of stochastic simulations.
\r\n\r\nErgodic breaking at small volumes may allow these molecular complexes to function as switches to a greater degree than has previously been shown. We propose that this ergodic breaking is a phenomenon that the synapse might exploit to differentiate Ca2+ signaling that would lead to either the strengthening or weakening of a synapse. Techniques such as lattice-based statistics and rule-based modeling are tools that allow us to directly confront this non-ideality. A natural next step to understanding the chemical physics that underlies these processes is to consider in silico specifically atomistic simulation methods that might augment our modeling efforts.
\r\n\r\nIn the second part of this thesis, we use evolutionary algorithms to optimize in silico methods that might be used to describe biochemical processes at the subcellular and molecular levels. While we have applied evolutionary algorithms to several methods, this thesis will focus on the optimization of charge equilibration methods. Accurate charges are essential to understanding the electrostatic interactions that are involved in ligand binding, as frequently discussed in the first part of this thesis.
" }, { "name": "Franco, Elisa", "degree": "PhD", "year": "2012", "title": "Analysis, Design, and in vitro Implementation of Robust Biochemical Networks", "advisor": "Murray, Richard M.; Winfree, Erik", "url": "https://resolver.caltech.edu/CaltechTHESIS:10192011-161454857", "creators": [ { "name": { "family": "Franco", "given": "Elisa" }, "id": "Franco-Elisa", "display_name": "Franco, Elisa" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "co-advisor", "display_name": "Winfree, Erik" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Rothemund", "given": "Paul W. K." }, "id": "Rothemund-P-W-K", "role": "member", "display_name": "Rothemund, Paul W. K." } ], "option_major": [ "cds" ], "doi": "10.7907/1C3S-FA59", "abstract": "The functionalities of every living organism are wired in the biochemical interactions among proteins, nucleic acids, and all the other molecules that constitute life's building blocks. Understanding the general design principles of this \"hardware of life\" is an exciting and challenging task for modern bioengineers. In this thesis, I focus on the topic of molecular network robustness: I investigate several design rules guaranteeing desired functionalities in specific systems, despite their components variability. Experimental verifications of such design schemes are carried out using \\emph{in vitro} transcriptional circuits, a minimal analogue of cellular genetic networks.
\r\n \r\nThe first problem I consider is flux control, which is a fundamental feature for the correct performance of biochemical systems. I describe a simple model problem where two reagents bind stoichiometrically to form an output product. In the absence of any regulation, imbalances in the reagent production rates can cause accumulation of unused molecules, and limit the output flow. To match the reagents' flux robustly with respect to the open loop rates, I propose the use of negative or positive feedback schemes that rely on competitive binding. Such schemes are modeled through ordinary differential equations and implemented using transcriptional circuits; data are presented showing the performance of the two approaches.
\r\n \r\nThe second topic I examine is the functional robustness of interconnected networks. Molecular devices characterized in isolation may lose their properties once interconnected. This challenge is illustrated with a case study: a synthetic transcriptional clock is used to time conformational changes in a molecular nanomachine called DNA tweezers. Mass conservation introduces parasitic interactions that perturb the oscillator trajectories proportionally to the total amount of tweezers \"load\". To overcome this problem, we can use a transcriptional switch that acts as a buffer amplifier, achieving signal propagation and at the same time reducing the perturbations on the source of signal.
\r\n\r\nFinally, I describe a general class of control-theoretic methods to analyze structural robustness in natural biological systems. Using Lyapunov theory and set invariance, the stability properties of several well-known case studies are analytically demonstrated. The key feature of this analysis is its reliance on parameter-independent models, which only capture essential dynamic interactions between molecular species.
\r\n \r\n" }, { "name": "Harel, Jonathan", "degree": "PhD", "year": "2012", "title": "Neural Pattern Similarity and Visual Perception", "advisor": "Koch, Christof; Adolphs, Ralph", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302012-200743814", "creators": [ { "name": { "family": "Harel", "given": "Jonathan" }, "id": "Harel-Jonathan", "display_name": "Harel, Jonathan" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "co-advisor", "display_name": "Adolphs, Ralph" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1BCV-MQ11", "abstract": "This thesis addresses the question of whether people actually see the same visual stimuli somehow differently, and under what conditions, if so. It is an experimental contribution to the basic understanding of visual and especially face perception, and its neural correlates, with an emphasis on comparing patterns of neural activity driven by visual stimuli across trials and across individuals. We make extensive use of functional magnetic resonance imaging (fMRI); all inferences about neural activity are made via this intermediary. The thesis is organized into two parts:
\r\n\r\nIn Part I, we investigate the nature of face familiarity and distinctiveness at perceptual and neural levels. We first address the question of how the faces of those people personally familiar to a viewer appear different than they would to an unfamiliar viewer. The main result is that they appear more distinctive, i.e., dissimilar to and distinguishable from other faces, and more so the higher the level of familiarity. Having established this connection between face familiarity and distinctiveness, we ask next what is different about the perception of such faces, as compared with indistinct and unfamiliar faces, at the level of brain activation. We find that familiar and distinctive faces are represented more consistently: compared with indistinct faces, which evoke slightly different patterns of activity with each new presentation, these faces evoke slightly similar patterns. Combined with the observation that consistency can enhance memory encoding (a result reported by Xue et al. [102]), this suggests a cyclic process for the learning of unfamiliar faces in which consistent representation and the presence of newly formed memories mutually feedback on each other.
\r\n\r\nWhereas in Part I we focus on individual differences in neural activity, principally by experimentally manipulating stimulus familiarity, in Part II, we shift our focus to similarities across individuals and extend our investigation beyond faces to the perception of visual objects in general and moving images. We begin with an experiment involving the perception of static images selected from 44 object categories, where we find that the distances between these categories, induced from activity in cortical visual object areas, correlate highly between subjects, and also to distances inferred from a behavioral clustering task, and that this correlation remains significant even among subsets of closely related categories. We also show that one subject's brain activity can be accurately modeled using another's, and that this allows us to predict which image a subject is viewing based on his/her brain activity. Then, in a different experiment investigating the perception of dynamic/video stimuli, we find evidence that when watching videos with sound, visual attention is likely blurred at times and transferred to audition; subjects relatively temporally decorrelate in visual areas compared to the muted case, in which the patterns of neural activity correlate across subjects at an average of 78% the level found with oneself later in time.
\r\n\r\nThe findings reported in this thesis thus offer quantitative lower bounds on how similarly different individuals neurally experience visual stimuli, and an explanation for how they perceptually and neurally diverge when familiarity with a (face) stimulus varies, suggesting a possible mechanism for the encoding of new visual objects into memory. We conclude with a discussion of some of the questions raised by this work and directions for future research.
" }, { "name": "Hu, Xin", "degree": "PhD", "year": "2012", "title": "Multiscale Modeling and Computation of 3D Incompressible Turbulent Flows", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302012-081356007", "creators": [ { "name": { "family": "Hu", "given": "Xin" }, "id": "Hu-Xin", "display_name": "Hu, Xin" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/K1RZ-1H07", "abstract": "In the first part, we present a mathematical derivation of a closure relating the Reynolds stress to the mean strain rate for incompressible turbulent flows. This derivation is based on a systematic multiscale analysis that expresses the Reynolds stress in terms of the solutions of local periodic cell problems. We reveal an asymptotic structure of the Reynolds stress by invoking the frame invariant property of the cell problems and an iterative dynamic homogenization of large- and small-scale solutions. The Smagorinsky model for homogeneous turbulence is recovered as an example to illustrate our mathematical derivation. Another example is turbulent channel flow, where we derive a simplified turbulence model based on the asymptotic flow structure near the wall. Additionally, we obtain a nonlinear model by using a second order approximation of the inverse flow map function. This nonlinear model captures the effects of the backscatter of kinetic energy and dispersion and is consistent with other models, such as a mixed model that combines the Smagorinsky and gradient models, and the generic nonlinear model of Lund and Novikov.
\r\n\r\nNumerical simulation results at two Reynolds numbers using our simplified turbulence model are in good agreement with both experiments and direct numerical simulations in turbulent channel flow. However, due to experimental and modeling errors, we do observe some noticeable differences, e.g. , root mean square velocity fluctuations at Re\u03c4 = 180.
\r\n\r\nIn the second part, we present a new perspective on calculating fully developed turbulent flows using a data-driven stochastic method. General polynomial chaos (gPC) bases are obtained based on the mean velocity profile of turbulent channel flow in the offline part. The velocity fields are projected onto the subspace spanned by these gPC bases and a coupled system of equations is solved to compute the velocity components in the Karhunen-Loeve expansion in the online part. Our numerical results have shown that the data-driven stochastic method for fully developed turbulence offers decent approximations of statistical quantities with a coarse grid and a relatively small number of gPC base elements.
" }, { "name": "Huang, Jinghao", "degree": "PhD", "year": "2012", "title": "Discrete Differential Form Subdivision and Vector Field Generation over Volumetric Domain", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082012-153445274", "creators": [ { "name": { "family": "Huang", "given": "Jinghao" }, "id": "Huang-Jinghao", "display_name": "Huang, Jinghao" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Aivazis", "given": "Michael A. G." }, "id": "Aivazis-M-A-G", "role": "member", "display_name": "Aivazis, Michael A. G." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/FXF2-4447", "abstract": "This thesis presents a new method to construct smooth l- and 2-form subdivision schemes over the 3D volumetric domain. Based on the subdivided 1- and 2-form coefficient field, smooth vector fields can be constructed using Whitney forms. To obtain stencils in the regular setting, classical 0-form subdivision and linear 1- and 2-form subdivision over the octet mesh are introduced. Then, convoluting with a smooth operator, smooth 1- and 2-form subdivision schemes in the regular case can be determined up to one free parameter. This parameter can be determined by a novel technique based on spectrum and momentum considerations. However, artifacts exist in boundary regions because of the incomplete regular support and the shrinking feature of the original 0-form subdivision scheme. To address these problems, the projection-scaling method and the expansion method are introduced and compared. The former method projects arbitrary discrete differential forms to a subspace spanned by low-order potential fields. The algorithm subdivides these potential fields and reconstructs the discrete form in the refined level using linear combinations. Scaling is included for elements near the boundary to offset the effect of mesh shrinkage. Alternatively, for the expansion method, a compatible nonshrinking 0-form subdivision scheme is constructed first. Based on the new 0-form subdivision method, extending 1- and 2-forms beyond the boundary becomes natural. In the experiment, no noticeable artifacts, including attenuation, enlarging or undesirable bend, are found in practice." }, { "name": "Huang, Jingqing", "degree": "PhD", "year": "2012", "title": "Wavelength-Scale Confinement of Light and Its Applications in On-Chip Photonic Devices", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062012-225422868", "creators": [ { "name": { "family": "Huang", "given": "Jingqing" }, "id": "Huang-Jingqing", "display_name": "Huang, Jingqing" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6F0A-TD74", "abstract": "We present design and experimental work toward building room temperature, continuous-wave (CW) lasers with a cavity that confines light to a volume of \u2264 (\u03bb/n)3. We begin with the mechanisms of strong optical confinement using dispersive metals and photonic crystals. Finite-difference time-domain methods (FDTD) are used to simulate the behavior of electromagnetic fields in the cavity; fast Fourier transform from FDTD-generated near-field data calculates the far-field radiation pattern from the microcavity laser.
\r\n\r\nWe then present our investigations into designs where metals are incorporated into microdisk and photonic crystal optical cavities to curb or redirect radiation loss. The significant effects of boundary conditions and substrate feedback on far-field radiation directionality are studied. We evaluate the threshold gain required to achieve room temperature lasing in these metallo-dielectric cavities.
\r\n\r\nWhile studying the confinement mechanism of photonic crystals on metal substrate, it became clear that room temperature lasing can be achieved in optically-thick photonic crystal cavities, where the thicker semiconductor layer would give us more freedom in designing the vertical p-i-n doping profile within, for a less resistive and leaky electrical path for current injection operation. We fabricate and demonstrate single-mode room temperature lasing by optical pumping in an optically- thick single-defect cavity.
\r\n\r\nWe move on to present our design and characterization of coupled-cavity photonic crystal lasers operating with CW, high output power, and directional emission. Single-mode stable emission with output power on the order of 10 \u03bcW and linear polarization was achieved. Moreover, we switched from the commonly used InGaAsP quantum well material to the lesser-known InAsP quantum wells in InP cladding, and found that the large band-edge offset between InAsP and InP made a world of difference in achieving high power operation despite the large thermal resistance in the device.
\r\nFor a microcavity laser with directional radiation, Purcell-enhanced spontaneous emission, and diminished effects due to feedback from surrounding structures such as the substrate, nanobeam photonic crystal lasers are analyzed, fabricated, and characterized. Despite thermal resistance an order of magnitude higher than their 2D counterparts, quasi-CW operation with a soft threshold turn-on was achieved.
\r\n\r\nMuch work was done to optimize fabrication techniques in order to realize the optical cavity designs with little fabrication error. We detail the high-contrast hydrogen silsesquioxane (HSQ) electron-beam lithography and deep vertical dry etch procedures especially developed for this work.
\r\n\r\nLastly, related projects on nonlinear silicon photonic devices are presented. Synthetic nonlinear polymer is integrated on to the silicon photonic platform to achieve low half-wave voltage electro-optic modulation. Causes and magnitude of the nonlinear loss particular to silicon waveguides with sub-\u03bcm2 cross-section are evaluated.
" }, { "name": "Huang, Ruo-Gu", "degree": "PhD", "year": "2012", "title": "High-Performance Silicon Nanowire Electronics", "advisor": "Heath, James R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12142011-124639130", "creators": [ { "name": { "family": "Huang", "given": "Ruo-Gu" }, "id": "Huang-Ruo-Gu", "display_name": "Huang, Ruo-Gu" } ], "advisors": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "advisor", "display_name": "Heath, James R." } ], "committee": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "chair", "display_name": "Heath, James R." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "eleceng" ], "doi": "10.7907/CG0M-QB27", "abstract": "This thesis explores 10-nm wide Si nanowire (SiNW) field-effect transistors (FETs) for logic applications via the fabrication and testing of SiNW-based ring oscillators. Both SiNW surface treatments and dielectric annealing are reported for producing SiNW FETs that exhibit high performance in terms of large on/off-state current ratio (~108), low drain-induced barrier lowering (~30 mV), high carrier mobilities (~269 cm2/V\u2022s), and low subthreshold swing (~80 mV/dec). The performance of inverter and ring-oscillator circuits fabricated from these nanowire FETs is explored as well. The inverter demonstrates the highest voltage gain (~148) reported for a SiNW-based NOT gate, and the ring oscillator exhibits near rail-to-rail oscillation centered at 13.4 MHz. The static and dynamic characteristics of these NW devices indicate that these SiNW-based FET circuits are excellent candidates for various high-performance nanoelectronic applications.
\r\n\r\nA set of novel charge-trap non-volatile memory devices based on high-performance SiNW FETs are well investigated. These memory devices integrate Fe2O3 quantum dots (FeO QDs) as charge storage elements. A template-assisted assembly technique is used to align FeO QDs into a close-packed, ordered matrix within the trenches that separate highly aligned SiNWs, and thus store injected charges. A Fowler-Nordheim tunneling mechanism describes both the program and erase operations. The memory prototype demonstrates promising characteristics in terms of large threshold voltage shift (~1.3 V) and long data retention time (~3 \u00d7 106 s), and also allows for key components to be systematically varied. For example, varying the size of the QDs indicates that larger diameter QDs exhibit a larger memory window, suggesting the QD charging energy plays an important role in the carrier transport. The device temperature characteristics reveal an optimal window for device performance between 275K and 350K.
\r\n\r\nThe flexibility of integrating the charge-trap memory devices with the SiNW logic devices offers a low-cost embedded non-volatile memory solution. A building block for a SiNW-based field-programmable gate array (FPGA) is proposed in the future work.
\r\n" }, { "name": "Inoue, Michio", "degree": "PhD", "year": "2012", "title": "Large-Eddy Simulation of the Flat-Plate Turbulent Boundary Layer at High Reynolds Numbers", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222012-183141047", "creators": [ { "name": { "family": "Inoue", "given": "Michio" }, "id": "Inoue-Michio", "display_name": "Inoue, Michio" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PXTM-W616", "abstract": "The near-wall, subgrid-scale (SGS) model [Chung and Pullin, \"Large-eddy simulation and wall-modeling of turbulent channel flow\", J. Fluid Mech. 631, 281--309 (2009)] is used to perform large-eddy simulations (LES) of the incompressible developing, smooth-wall, flat-plate turbulent boundary layer. In this model, the stretched-vortex, SGS closure is utilized in conjunction with a tailored, near-wall model designed to incorporate anisotropic vorticity scales in the presence of the wall. The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. This is then used to study several aspects of zero- and adverse-pressure gradient turbulent boundary layers.
\r\n\r\nFirst, LES of the zero-pressure gradient turbulent boundary layer are performed at Reynolds numbers Re\u03b8 based on the free-stream velocity and the momentum thickness in the range Re\u03b8 = 103 - 1012. Results include the inverse skin friction coefficient, \u221a2/Cf, velocity profiles, the shape factor H, the Karman \"constant\", and the Coles wake factor as functions of Re\u03b8. Comparisons with some direct numerical simulation (DNS) and experiment are made, including turbulent intensity data from atmospheric-layer measurements at Re\u03b8 = O(106. At extremely large Re\u03b8, the empirical Coles-Fernholz relation for skin-friction coefficient provides a reasonable representation of the LES predictions. While the present LES methodology cannot of itself probe the structure of the near-wall region, the present results show turbulence intensities that scale on the wall-friction velocity and on the Clauser length scale over almost all of the outer boundary layer. It is argued that the LES is suggestive of the asymptotic, infinite Reynolds-number limit for the smooth-wall turbulent boundary layer and different ways in which this limit can be approached are discussed. The maximum Re\u03b8 of the present simulations appears to be limited by machine precision and it is speculated, but not demonstrated, that even larger Re\u03b8 could be achieved with quad- or higher-precision arithmetic.
\r\n\r\nSecond, the time series velocity signals obtained from LES within the logarithmic region of the zero-pressure gradient turbulent boundary layer are used in combination with an empirical, predictive inner--outer wall model [Marusic et al., \"Predictive model for wall-bounded turbulent flow\", Science 329, 193 (2010)] to calculate the statistics of the fluctuating streamwise velocity in the inner region of the zero-pressure gradient turbulent boundary layer. Results, including spectra and moments up to fourth order, are compared with equivalent predictions using experimental time series, as well as with direct experimental measurements at Reynolds numbers Re\u03c4 based on the friction velocity and the boundary layer thickness, Re\u03c4 =7,300, 13,600 and 19,000. LES combined with the wall model are then used to extend the inner-layer predictions to Reynolds numbers Re\u03c4 =62,000, 100,000 and 200,000 that lie within a gap in log(Re\u03c4) space between laboratory measurements and surface-layer, atmospheric experiments. The present results support a log-like increase in the near-wall peak of the streamwise turbulence intensities with Re\u03c4 and also provide a means of extending LES results at large Reynolds numbers to the near-wall region of wall-bounded turbulent flows.
\r\n\r\nFinally, we apply the wall model to LES of a turbulent boundary layer subject to an adverse pressure gradient. Computed statistics are found to be consistent with recent experiments and some Reynolds number similarity is observed over a range of two orders of magnitude.
" }, { "name": "Jacobs, Henry Ochi", "degree": "PhD", "year": "2012", "title": "Geometric Descriptions of Couplings in Fluids and Circuits", "advisor": "Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:04302012-142612208", "creators": [ { "name": { "family": "Jacobs", "given": "Henry Ochi" }, "id": "Jacobs-Henry-Ochi", "display_name": "Jacobs, Henry Ochi" } ], "advisors": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "chair", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Kanso", "given": "Eva" }, "id": "Kanso-E", "role": "member", "display_name": "Kanso, Eva" } ], "option_major": [ "cds" ], "doi": "10.7907/AZXE-PH33", "abstract": "Geometric mechanics is often commended for its breadth (e.g., fluids, circuits, controls) and depth (e.g., identification of stability criteria, controllability criteria, conservation laws). However, on the interface between disciplines it is commonplace for the analysis previously done on each discipline in isolation to break down. For example, when a solid is immersed in a fluid, the particle relabeling symmetry is broken because particles in the fluid behave differently from particles in the solid. This breaks conservation laws, and even changes the configuration manifolds. A second example is that of the interconnection of circuits. It has been verified that LC-circuits satisfy a variational principle. However, when two circuits are soldered together this variational principle must transform to accommodate the interconnection.
\r\n\t\r\nMotivated by these difficulties, this thesis analyzes the following couplings: fluid-particle, fluid-structure, and circuit-circuit. For the case of fluid-particle interactions we understand the system as a Lagrangian system evolving on a Lagrange-Poincare bundle. We leverage this interpretation to propose a class of particle methods by \"ignoring\" the vertical Lagrange-Poincare equation. In a similar vein, we can analyze fluids interacting with a rigid body. We then generalize this analysis to view fluid-structure problems as Lagrangian systems on a Lie algebroid. The simplicity of the reduction process for Lie algebroids allows us to propose a mechanism in which swimming corresponds to a limit-cycle in a reduced Lie algebroid. In the final section we change gears and understand non-energetic interconnection as Dirac structures. In particular we find that any (linear) non-energetic interconnection is equivalent to some Dirac structure. We then explore what this insight has to say about variational principles, using interconnection of LC-circuits as a guiding example.
" }, { "name": "Jennings, Andrew Tynes", "degree": "PhD", "year": "2012", "title": "Deformation Mechanisms in Nanoscale Single Crystalline Electroplated Copper Pillars", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312012-162830014", "creators": [ { "name": { "family": "Jennings", "given": "Andrew Tynes" }, "id": "Jennings-Andrew-Tynes", "display_name": "Jennings, Andrew Tynes" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "role": "member", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/6128-HG61", "abstract": "Scientific research in nanotechnology has enabled advances in a diverse range of applications, such as: electronics, chemical sensing, and cancer treatment. In order to transition these nanotechnology-driven innovations out of the laboratory and into real-world applications, the resilience and mechanical reliability of nanoscale structures must be well understood in order to preserve functionality under real-world operating environments. Understanding the mechanical properties of nanoscale materials is especially important because several authors have shown that single crystalline metal pillars produced through focused-ion-beam milling have unique properties when the pillar diameter, D, approaches nanotechnology-relevant dimensions. The strength, \u03c3, of these pillars is size-dependent and is well described through a power-law relation showing that smaller is stronger: \u03c3\u221dD^(-n), where n is the exponent and is found to be 0.5\u2264n\u22641.0 in face-centered-cubic metals. In this work, the fundamental deformation mechanisms governing the size-dependent mechanical properties are investigated through uniaxial compression and tension tests of electroplated single crystalline copper pillars with diameters between 75 nm and 1000 nm. At larger pillar diameters, D >125 nm, these copper pillars are shown to obey a similar size-dependent regime, demonstrating that the \u201csmaller is stronger\u201d phenomenon is a function of the pillar microstructure, as opposed to the fabrication route. Furthermore, the dominant dislocation mechanism in this size-dependent regime is shown to be the result of single-arm, or spiral, sources. At smaller pillar diameters, D\u2264125 nm, a strain-rate-dependent mechanism transition is observed through both the size-strength relation and also quantitative, experimental measures of the activation volume. This new deformation regime is characterized by a size-independent strength and is governed by surface dislocation nucleation, a thermally activated mechanism sensitive to both temperature and strain-rate. Classical, analytical models of surface source-nucleation are shown to be insufficient to describe either the quantitative strength or the nucleation site preference. As a result, a combination of atomistic chain-of-states simulations and semi-analytical continuum models are developed in order to achieve a realistic, intuitive understanding of surface nucleation processes. " }, { "name": "Khajehnejad, M. Amin", "degree": "PhD", "year": "2012", "title": "Combinatorial Regression and Improved Basis Pursuit for Sparse Estimation", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072012-001523622", "creators": [ { "name": { "family": "Khajehnejad", "given": "M. Amin" }, "id": "Khajehnejad-M-Amin", "display_name": "Khajehnejad, M. Amin" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Dimakis", "given": "Alexandros G." }, "id": "Dimakis-A-G", "orcid": "0000-0002-4244-7033", "role": "member", "display_name": "Dimakis, Alexandros G." } ], "option_major": [ "eleceng" ], "doi": "10.7907/04J6-Y832", "abstract": "Sparse representations accurately model many real-world data sets. Some form of sparsity is conceivable in almost every practical application, from image and video processing, to spectral sensing in radar detection, to bio-computation and genomic signal processing. Modern statistics and estimation theory have come up with ways for efficiently accounting for sparsity in enhanced information retrieval systems. In particular, \\emph{compressed sensing} and \\emph{matrix rank minimization} are two newly born branches of dimensionality reduction techniques, with very promising horizons. Compressed sensing addresses the reconstruction of sparse signals from ill-conditioned linear measurements, a mathematical problem that arises in practical applications in one of the following forms: model fitting (regression), analog data compression, sub-Nyquist sampling, and data privacy. Low-rank matrix estimation addresses the reconstruction of multi-dimensional data (matrices) with strong coherence properties (low rank) under restricted sensing. This model is motivated by modern problems in machine learning, dynamic systems, and quantum computing.
\r\n\r\nThis thesis provides an in-depth study of recent developments in the fields of compressed sensing and matrix rank minimization, and sets forth new directions for improved sparse recovery techniques. The contributions are threefold: the design of combinatorial structures for sparse encoding, the development of improved recovery algorithms, and extension of sparse vector recovery techniques to other problems.
\r\n\r\nWe propose combinatorial structures for the measurement matrix that facilitate compressing sparse analog signal representations with better guarantees than any of the currently existing architectures. Our constructions are mostly deterministic and are based on ideas from expander graphs, LDPC error-correcting codes and combinatorial separators.
\r\n\r\nWe propose novel reconstruction algorithms that are amenable to the combinatorial structures we study, and have various advantages over the conventional convex optimization techniques for sparse recovery. In addition, we separately study the convex optimization Basis Pursuit method for compressed sensing, and propose regularization schemes that expand the success domain for such algorithms. Our studies contain rigorous analysis, numerical simulations, and examples from practical applications.
\r\n\r\nLastly, we extend some of our proposed techniques to low-rank matrix estimation and channel coding. These generalizations lead to the development of a novel and fast reconstruction algorithm for matrix rank minimization, and a modified regularized linear-programming-based decoding algorithm for detecting codewords of a linear LDPC code during an erroneous communication.
\r\n" }, { "name": "Khatri, Devvrath", "degree": "PhD", "year": "2012", "title": "Non-Destructive Evaluation of Material System Using Highly Nonlinear Acoustic Waves", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05102012-091402754", "creators": [ { "name": { "family": "Khatri", "given": "Devvrath" }, "id": "Khatri-Devvrath", "display_name": "Khatri, Devvrath" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Yang", "given": "Jinkyu" }, "id": "Yang-Jinkyu", "role": "member", "display_name": "Yang, Jinkyu" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P3VR-Q582", "abstract": "A chain of granular particles is one of the most studied examples of highly nonlinear systems deriving its response from the nonlinear Hertzian contact interaction between particles. Interest in these systems derives from their tunable dynamic response, encompassing linear, weakly nonlinear, and strongly nonlinear regimes, controlled by varying the static and dynamic load applied. In chains with a very weak (or zero) static precompression, the system supports the formation and propagation of highly nonlinear solitary waves (HNSWs). The dual-nonlinear interaction between particles (i.e., a power-law type contact potential in compression, and zero strength in tension) combined with discreteness of the system, makes the granular system highly tunable. The propagation properties of these waves, such as traveling pulse width, wave speed, number of separated pulses (single or train of pulses), etc., can be controlled by modifying one or many of the parameters, like the particle's dimension, material properties, static and dynamic force amplitude, the type and duration of the initial excitation applied to the system, and/or the periodicity of the chain. The ability to control the wave properties in such chains has been proposed for several different practical engineering applications.
\r\n\r\nThe dynamic properties of these granular chains have been conventionally studied using discrete particle models (DPMs) which consider the particles in the chains as point masses connected by nonlinear Hertzian springs with the neighboring particles. Although, this is a good approximation under proper circumstances, it does not capture many features of the three dimensional elastic particles such as the elastic wave propagation within the particles, the local deformation of the particles in the vicinity of the contact point, the corresponding changes in the contact area, and the collective vibrations of the particles among others. This thesis focuses on the development of a nite element model (FEM)using the commercially available software Abaqus, which takes into account many of these characteristic features. The nite element model discretizes particles by considering them as three-dimensional deformable bodies of revolution and describes the nonlinear dynamic response of one-dimensional granular chains composed of particles with various geometries and orientations. We showed that particles' geometries and orientations provide additional design parameters for controlling the dynamic response of the system, compared to chains composed of spherical particles. We also showed that the tunable and compact nature of these waves can be used to tailor the properties of HNSWs for specfic application, such as information carriers for actuation and sensing of mechanical properties and boundary effects of adjoining media in Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM). Using experiments and numerics, we characterized interface dynamics between granular media and adjoining linear elastic media, and found that the coupling produced temporary localization of the incident waves at the boundaries between the two media and their decomposition into reflected waves. We monitored the formation of reflected solitary waves propagating back from the interface and found that their properties are sensitive to the geometric and material properties of the adjoining media. The work done in this research enhances our understanding of the basic physics and tunability of nonlinear granular media, and further establishes a theoretical and numerical foundation\r\nin the applications of HNSWs as information carriers.
" }, { "name": "Langeland, Krista S.", "degree": "PhD", "year": "2012", "title": "Thin-Film Silicon Photovoltaics: Characterization of Thin-Film Deposition and Analysis of Enhanced Light Trapping from Scattering Nanoparticle Arrays", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:03072012-191033678", "creators": [ { "name": { "family": "Langeland", "given": "Krista S." }, "id": "Langeland-Krista-S", "display_name": "Langeland, Krista S." } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/ZS04-AH18", "abstract": "Thin-film solar cells have the potential to significantly decrease the cost of a finished device by cutting materials cost, and the characteristics of carrier transport through a thin film can concurrently increase the device performance over that of a wafer-based cell while tolerating a higher defect density in the absorbing material. However, while silicon is an attractive material for use in solar cells due to its nearly ideal band gap for single-junction cells and its relative abundance, its inefficient absorption of infrared light necessitates the development of light-trapping techniques to avoid losses in current generation. This thesis research has focused on two important goals: the development of a scalable thin-film silicon deposition method that produces high-quality material at minimal cost, and the evaluation of light-trapping mechanisms that will increase photon absorption in these films. Hot-wire chemical vapor deposition is used to fabricate silicon thin films with high crystalline fractions even on inexpensive substrates, and films grown with appropriate growth conditions exhibit initial open-circuit voltages above 450 mV, and while challenges in passivation still exist, this research illustrates the potential of this highly scalable and inexpensive deposition technique. Silver and silicon subwavelength structures were then both fabricated and simulated on ultra-thin silicon films on SiO2 to evaluate their potential for increasing light absorption through plasmonic and physical scattering mechanisms, and spectral response measurements demonstrate over a ten-fold increase in carrier generation with a metal nanoparticle surface array. Periodic dielectric structures exhibit Bloch modes in both measurement and simulation, with an increase in overall quantum efficiency of over 11% from both a flat silicon layer and one that is randomly textured. These results highlight the significant role of scattering particle distribution in determining the light trapping characteristics in these devices. Design guidelines have been explored for exploiting resonant modes in these structures, and this thesis demonstrates the potential for both metal and dielectric surface arrays to dramatically increase light absorption in silicon thin films.\r\n" }, { "name": "LeHew, Jeffrey Allen", "degree": "PhD", "year": "2012", "title": "Spatio-Temporal Analysis of the Turbulent Boundary Layer and An Investigation of the Effects of Periodic Disturbances", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232012-142127799", "creators": [ { "name": { "family": "LeHew", "given": "Jeffrey Allen" }, "id": "LeHew-Jeffrey-Allen", "display_name": "LeHew, Jeffrey Allen" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/20CM-EV70", "abstract": "The purpose of this study was to investigate the turbulent boundary layer to learn more about the dynamics of the flow and how it might be controlled through the input of spatially and/or temporally periodic disturbances. The first part of this work studies the structure of a zero-pressure-gradient turbulent boundary layer using time-resolved particle image velocimetry in both wall-normal and wall-parallel planes. Using data from wall-parallel measurements, a 3D spectrum over streamwise, spanwise, and temporal wavelengths was constructed for the first time, a major focus of this work. Among several uses, this spectrum allows the calculation of a scale-based convection velocity, that is, a convection velocity for each streamwise-spanwise scale pair present in the flow. This data set also provided a method for investigating the temporal evolution of coherent structures in the flow, of which, swirling coherent structures (SCS), indicative of vortices, and low-momentum regions were investigated thoroughly. The convection velocity and lifetime of the SCS were measured; using histograms of the SCS convection velocity in multiple wall-parallel planes, it was possible to statistically infer different SCS structures that could be categorized as ``attached'' or ``detached'' from the wall.
\r\n\t\r\nA study was also performed on the response of the turbulent boundary layer to a stationary periodic roughness inspired by the scale pattern on the sailfish. The roughness was relatively sparse with element spacing on the order of the boundary layer thickness allowing the measurement of turbulent statistics at different points along the roughness as well as below the crests of the roughness elements, a region not commonly accessible in rough-wall boundary layer studies. The streamwise turbulent statistics were studied using hotwire anemometry from which it was found that while the outer part of the flow remained similar, the near-wall region was perturbed by structures of size similar to the roughness spacing.
" }, { "name": "Lee, Lap Man", "degree": "PhD", "year": "2012", "title": "The Implementation of Optofluidic Microscopy on a Chip Scale and Its Potential Applications in Biology", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:10192011-190918785", "creators": [ { "name": { "family": "Lee", "given": "Lap Man" }, "id": "Lee-Lap-Man", "display_name": "Lee, Lap Man" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "co-chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" } ], "option_major": [ "bioeng" ], "doi": "10.7907/GKW9-QR51", "abstract": "This thesis presents an effort to miniaturize conventional optical microscopy to a chip level using microfluidic technology. Modern compound microscopes use a set of bulk glass lenses to form magnified images from biological objects. This limits the possibility of shrinking the size of a microscope system. The invention of micro/nanofabrication technology gives hope to engineers who want to rethink the way we build optical microscopes. This advancement can fundamentally reform the way clinicians and biologists conduct microscopy. Optofluidic microscopy (OFM) is a miniaturized optical imaging method which utilizes a microfluidic flow to deliver biological samples across a 1-D or 2-D array of sampling points defined in a microfluidic channel for optical scanning. The optical information of these sampling points is collected by a CMOS imaging sensor on the bottom of the microfluidic channel. Although the size of the OFM device is as small as a US dime, it can render high resolution images of less than 1 \u03bcm with quality comparable to that of a bulky, standard optical microscope. OFM has a good potential in various biological applications. For example, the integration of an OFM system with high-speed hydrodynamic focusing technology will allow very large scale imaging-based analysis of cells or microorganisms; the compactness and low cost nature of OFM systems can enable portable or even disposable biomedical diagnostic tools for future telemedicine and personalized health care. " }, { "name": "Levine, Joseph H.", "degree": "PhD", "year": "2012", "title": "Genetic Regulatory Circuit Dynamics: Analysis and Synthesis", "advisor": "Elowitz, Michael B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052012-121432503", "creators": [ { "name": { "family": "Levine", "given": "Joseph H." }, "id": "Levine-Joseph-H", "display_name": "Levine, Joseph H." } ], "advisors": [ { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "advisor", "display_name": "Elowitz, Michael B." } ], "committee": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "chair", "display_name": "Winfree, Erik" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "cns" ], "doi": "10.7907/35A7-K421", "abstract": "How can cells shape and utilize dynamic gene regulation to enable complex cellular behaviors? I study this question in natural and synthetic contexts.
\r\n\r\nThe first project studies how a natural genetic network can imbue cells with a sense of \u2018time\u2019. It has long been known that environmental signals induce diverse cellular differentiation programs. In certain systems, cells defer differentiation for extended time periods after the signal appears, proliferating through multiple rounds of cell division before committing to a new fate. How can cells set a deferral time much longer than the cell cycle? Here we study Bacillus subtilis cells that respond to sudden nutrient limitation with multiple rounds of growth and division before differentiating into spores. A well characterized genetic circuit controls the concentration and phosphorylation of the master regulator Spo0A, which rises to a critical concentration to initiate sporulation. However, it remains unclear how this circuit enables cells to defer sporulation for multiple cell cycles. Using quantitative time-lapse fluorescence microscopy of Spo0A dynamics in individual cells, we observed pulses of Spo0A phosphorylation at a characteristic cell cycle phase. Pulse amplitudes grew systematically and cell-autonomously over multiple cell cycles leading up to sporulation. This pulse growth required a key positive feedback loop involving the sporulation kinases, without which the deferral of sporulation became ultrasensitive to kinase expression. Thus, deferral is controlled by a pulsed positive feedback loop in which kinase expression is activated by pulses of Spo0A phosphorylation. This pulsed positive feedback architecture provides a more robust mechanism for setting deferral times than constitutive kinase expression. Finally, using mathematical modeling, we show how pulsing and time delays together enable \u2018polyphasic\u2019 positive feedback, in which different parts of a feedback loop are active at different times. Polyphasic feedback can enable more accurate tuning of long deferral times. Together, these results suggest that Bacillus subtilis uses a pulsed positive feedback loop to implement a timer that operates over time scales much longer than a cell cycle.
\r\n\r\nThe second project proposes a method to rapidly generate and test complex genetic network dynamics in living cells. Existing microorganisms have evolved genetic circuitry to meet diverse challenges and maximize their survival and fitness. These challenges arise from external environmental pressures, or internal evolved constraints. Furthermore, these challenges may be either static or dynamic in nature. While existing circuits have likely evolved to be \u2018good enough\u2019 to respond to historical challenges, it remains unclear if they can be improved upon, and whether they respond well to novel situations. Synthetic biology seeks to engineer organisms with complex novel phenotypes, both to harness these novel organisms for a function and to understand their underlying biology. Dynamic gene expression strategies may be necessary to successfully generate these phenotypes. Unfortunately, generating novel dynamic gene expression patterns with conventional genetic engineering remains a challenge. Here I propose and describe progress towards a computerized feedback control setup to enable the programming and rapid testing of dynamic gene regulatory patterns in living cells. Small sets of genes will be regulated optogenetically based on programmed control laws, and past and present cellular state. This setup will enable us to explore the functions and limits of engineered dynamic gene regulation, while hopefully, in the process, providing lessons about the underlying biology.
" }, { "name": "Li, Chen W.", "degree": "PhD", "year": "2012", "title": "Phonon Anharmonicity of Ionic Compounds and Metals", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05012012-155623422", "creators": [ { "name": { "family": "Li", "given": "Chen W." }, "id": "Li-Chen-W", "orcid": "0000-0002-0758-5334", "display_name": "Li, Chen W." } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/7VS5-0F52", "abstract": "Vibrational studies of materials at elevated temperatures are relatively rare, and most phonon work also has emphasized harmonic behavior. Non-harmonic effects are often unexplored. These non-harmonic effects can be important for many properties of the material, such as thermal transport and phase stability.
\r\n\r\nPhonon theory and computational methods are briefly reviewed, and the experimental techniques for phonon study, such as Raman spectroscopy and inelastic neutron scattering, are discussed. Several experiments on phonon anharmonicity were performed, and interpreted with these computational methods.
\r\n\r\nIn Raman spectroscopy studies on the phonon dynamics of hafnia and zirconia, Raman line positions, and shapes of temperatures to 1000 K were measured and the types of modes that exhibit the most anharmonicity were characterized and correlated to the vibrational displacements of individual atoms in the unit cell. It was found that anharmonicity in these systems is rich in information and strongly mode dependent.
\r\n\r\nUsing time-of-flight inelastic neutron scattering, we found purely quartic transverse modes with an anomalous mode stiffening with temperature, and related these modes to the enormous negative thermal expansion of the DO9 structure of scandium fluoride.
\r\n\r\nUsing second-order perturbation theory, phonon linewidths from the third-order anharmonicity were calculated from first-principles density functional theory with the supercell finite-displacement method. For face-centered cubic aluminum, the good agreement between calculations and the phonon density of states up to 750 K indicates that the third-order phonon-phonon interactions calculated can account for the lifetime broadenings of phonons in aluminum to at least 80% of its melting temperature.
" }, { "name": "Lin, Alice", "degree": "PhD", "year": "2012", "title": "Neural and Behavioral Investigations of Social Reward Processing", "advisor": "Rangel, Antonio; Adolphs, Ralph", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052012-163338072", "creators": [ { "name": { "family": "Lin", "given": "Alice" }, "id": "Lin-Alice", "display_name": "Lin, Alice" } ], "advisors": [ { "name": { "family": "Rangel", "given": "Antonio" }, "id": "Rangel-A", "role": "advisor", "display_name": "Rangel, Antonio" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "co-advisor", "display_name": "Adolphs, Ralph" } ], "committee": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "chair", "display_name": "O'Doherty, John P." }, { "name": { "family": "Bossaerts", "given": "Peter L." }, "id": "Bossaerts-P-L", "role": "member", "display_name": "Bossaerts, Peter L." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Rangel", "given": "Antonio" }, "id": "Rangel-A", "role": "member", "display_name": "Rangel, Antonio" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "member", "display_name": "Adolphs, Ralph" } ], "option_major": [ "cns" ], "doi": "10.7907/0XT9-2494", "abstract": "Despite an extensive literature on the neural substrates of reward, relatively little is known about how social interactions modify decision-making. Here I present three experiments that examine the neural basis of social reward processing both in neurotypicals and individuals with autism spectrum disorder (ASD), a neuropsychiatric syndrome associated with social cognition impairments. Using functional magnetic resonance imaging (fMRI), I recorded brain activity during a probabilistic reward learning task with either social (smiling/frowning faces) or monetary (gaining/losing money) rewards. I found substantial overlap in the neural circuitry associated with social and non-social reward processing, suggesting that social rewards are processed similarly to other types of rewards. In contrast, individuals with ASD showed behavioral impairments in social reward processing, both in probabilistic reward learning and in an ecologically valid charitable donation task. Exploratory neuroimaging in ASD showed hypoactivation of key reward areas during decision-making. Taken together, these findings support the idea of a \u201ccommon neural currency\u201d in decision-making but also suggest the construction of accurate social reward value signals relies on recruitment of additional regions known to process social information." }, { "name": "Lin, Jeffrey Chun-Hui", "degree": "PhD", "year": "2012", "title": "MEMS for Glaucoma", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192012-003206031", "creators": [ { "name": { "family": "Lin", "given": "Jeffrey Chun-Hui" }, "id": "Lin-Jeffrey-Chun-Hui", "display_name": "Lin, Jeffrey Chun-Hui" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4XD2-SP34", "abstract": "Glaucoma is an eye disease that gradually steals vision. Open angle glaucoma is one of the most common glaucoma forms, in which eye fluid (aqueous humor) produced by the ciliary body cannot be drained away normally by patients\u2019 eyes. The accumulated eye fluid inside the anterior chamber causes high intraocular pressure (IOP), which is transmitted onto the retina in the back of the eyeball (globe), continuously suppressing and damaging the patient\u2019s optic nerves; this may lead to total blindness if not treated properly.
\r\n\r\nThe current most-popular IOP monitoring technique is to use applanation tonometry, which applies applanation force onto the cornea and measures the resulting deformation in order to calculate the IOP. Even though applanation tonometry can provide quite useful information about patients\u2019 IOP, continuous monitoring of IOP is required for ophthalmologists to understand the IOP fluctuation of the patients, something which still cannot be achieved via current applanation approach. In addition, applanation tonometry requires skillful operation performed by well-trained professionals, such as ophthalmologists, making continuous IOP monitoring impractical. In this work, we have developed a telemetric IOP sensor that is capable of monitoring IOP wirelessly and continuously. As the quality factor drops when a telemetric IOP sensor is implanted in the anterior chamber, due to the high loss tangent of the saline-based aqueous humor (~ 0.2) compared to air (0.0), a modified IOP sensor is developed to monitor IOP with sensing coil that is left exposed after implantation in order to avoid interruption from the eye fluid. Another approach is also proposed and tested to demonstrate that the quality factor can also be recovered by covering the sensing coil with low loss tangent materials.
\r\n\r\nCurrently glaucoma is treated mostly by taking oral medications or applying eye drops. However, some glaucoma patients do not respond to those medications. Therefore, another physical approach, using a glaucoma drainage device (GDD), is necessary in order to drain out excessive eye fluid and serve as a long-term way to manage the increased IOP. Current commercially available glaucoma drainage devices do not have reliable valve systems to stop the drainage when the IOP falls into the normal range. Therefore, we have developed a dual-valved GDD to fulfill the \u201cband-pass\u201d flow regulation which drains out eye fluid only when IOP is higher than 20 mmHg, and stops drainage (closes the valve) when IOP is lower than 20 mmHg to prevent hypotony. The key component of GDD is a normally closed (NC) check-valve, which only opens to drain away the excess fluid when the pressure is higher than 20 mmHg. The proposed paradigm of our NC check-valve is to have a couple of parylene-C pre-stressed slanted tethers to provide the desired cracking pressure. The slanted tethers are achieved in this thesis by: 1) slanted photoresist generated by gray-scale photolithography, 2) pop-up mechanism, and 3) self-stiction bonding mechanism. The built-in residual tensile stress can be controlled by mechanical stretching or thermal annealing. The protecting mechanism preventing the unwanted drainage when the eyes experience sudden unpredicted high IOP is achieved by utilizing a normally open (NO) check-valve. A \"minimally invasive implantation\" procedure is proposed in the thesis to implant the GDD subconjunctivally. The small size of the device allows its insertion using a #19-gauge needle.
\r\n\r\nTo accurately design the desired cracking pressure and also predict the lifetime of the NC check-valve, parylene-C\u2019s mechanical, thermal, and polymer properties are investigated. The results show that the properties of parylene-C are highly process-temperature-dependent and therefore can be tailored by adjusting the thermal annealing process.
" }, { "name": "Lintner, St\u00e9phane Karl", "degree": "PhD", "year": "2012", "title": "High-Order Integral Equation Methods for Diffraction Problems Involving Screens and Apertures", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072012-004925615", "creators": [ { "name": { "family": "Lintner", "given": "St\u00e9phane Karl" }, "id": "Lintner-St\u00e9phane-Karl", "display_name": "Lintner, St\u00e9phane Karl" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/VP8P-DP74", "abstract": "This thesis presents a novel approach for the numerical solution of problems of diffraction by infinitely thin screens and apertures. The new methodology relies on combination of weighted versions of the classical operators associated with the Dirichlet and Neumann open-surface problems. In the two-dimensional case, a rigorous proof is presented, establishing that the new weighted formulations give rise to second-kind Fredholm integral equations, thus providing a generalization to open surfaces of the classical closed-surface Calderon formulae. High-order quadrature rules are introduced for the new weighted operators, both in the two-dimensional case as well as the scalar three-dimensional case. Used in conjunction with Krylov subspace iterative methods, these rules give rise to efficient and accurate numerical solvers which produce highly accurate solutions in small numbers of iterations, and whose performance is comparable to that arising from efficient high-order integral solvers recently introduced for closed-surface problems. Numerical results are presented for a wide range of frequencies and a variety of geometries in two- and three-dimensional space, including complex resonating structures as well as, for the first time, accurate numerical solutions of classical diffraction problems considered by the 19th-century pioneers: diffraction of high-frequency waves by the infinitely thin disc, the circular aperture, and the two-hole geometry inherent in Young's experiment.\r\n" }, { "name": "Liu, Hsi-Chun", "degree": "PhD", "year": "2012", "title": "Theory and Experiment of Slow-Light Coupled-Resonator Structures", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242012-174045229", "creators": [ { "name": { "family": "Liu", "given": "Hsi-Chun" }, "id": "Liu-Hsi-Chun", "display_name": "Liu, Hsi-Chun" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GVBF-4T29", "abstract": "Slow light has been an inter-disciplinary topic and a rapidly growing area, especially over the last decade with the improvement of fabrication technology. The ability to slow down and control the group velocity of light may find applications such as optical buffers, optical delay lines, and enhanced light-matter interaction in optical modulator, amplifier, detectors, lasers, and nonlinear optics. The spirit of slow light is to replace a bulky device with a much shorter, compact structure.
\r\n\r\nThis thesis explores the design and experiment of coupled-resonator optical waveguides (CROWs), which consist of arrays of optical resonators in which light propagates through the coupling between resonators. The group velocity of light is dictated by the inter-resonator coupling strength. Light can be significantly slowed down if the inter-resonator coupling is weak. CROWs can be realized with various types of resonators. This thesis focuses on grating resonators in silicon waveguides, including grating-defect resonators and bandgap-modulated resonators. With the strong gratings, the grating resonators are only a few microns long. We control the inter-resonator coupling via the number of holes between adjacent resonators.
\r\n\r\nThe major limitations in the realization of CROWs have been various kinds of transmission losses, including the resonator losses, the discontinuity between CROWs and the coupling waveguides, and the fabrication disorder. These transmission losses limit the achievable group velocity and the maximum number of resonators. We address these transmission losses throughout this thesis. The resonator losses are overcome with the design and optimized fabrication of tapered grating-defect resonators and bandgap-modulated resonators. The discontinuity between CROWs and waveguides is reduced by tailoring the coupling along the CROW for adiabatic conversion. The optimization of the CROW response leads to the study of filter design based on CROW. Filter design formalism based on coupled-mode theory is presented. The effect of fabrication disorder on CROWs is analyzed, and the Butterworth filters are shown to be more robust against fabrication disorder. The fabrication and measurement of grating CROWs are presented, featuring high-Q (Q=105) grating resonators, coupling of up to 50 resonators, control of group velocity between c/13 and c/49, and Butterworth filters.
\r\n\r\nFinally, an optical analog of electromagnetically induced transparency is presented. The structure consists of two co-spatial gratings imposed on a three-mode waveguide. One of the supermodes, the Dark mode, possesses a group velocity which depends on the ratio of the grating strengths. The group velocity can be nearly zero if the two grating strengths are nearly identical.
\r\n" }, { "name": "Lu, Bo", "degree": "PhD", "year": "2012", "title": "Parylene as a New Membrane Material for Biomems Applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:05022012-003225468", "creators": [ { "name": { "family": "Lu", "given": "Bo" }, "id": "Lu-Bo", "display_name": "Lu, Bo" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" } ], "option_major": [ "eleceng" ], "doi": "10.7907/DPDC-9E57", "abstract": "The work in this thesis aims to use MEMS and microfabrication technologies to develop two types of parylene membrane devices for biomedical applications. The first device is the parylene membrane filter for cancer detection. The presence of circulating tumor cells (CTC) in patient blood is an important sign of cancer metastasis. However, currently there are two big challenges for CTC detection. First, CTCs are extremely rare, especially at the early stage of cancer metastasis. Secondly, CTCs are very fragile, and are very likely to be damaged during the capturing process. By using size-based membrane filtration through the specially designed parylene filters, together with a constant-pressure filtration system, we are able to capture the CTCs from patient blood with high capture efficiency, high viability, moderate enrichment, and high throughput. Both immunofluorescence enumeration and telomerase activity detection have been used to detect and differentiate the captured CTCs. The feasibility of further cell culture of the captured CTCs has also been demonstrated, which could be a useful way to increase the number of CTCs for future studies. Models of the time-dependent cell membrane damage are developed to predict and prevent CTC damage during this detection process. The results of clinical trials further demonstrate that the parylene membrane filter is a promising device for cancer detection.
\r\n\r\nThe second device is the parylene artificial Bruch\u2019s membrane for age-related macular degeneration (AMD). AMD is usually characterized by an impaired Bruch\u2019s membrane with much lowered permeability, which impedes the transportation of nutrients from choroid vessels to nourish the retinal pigment epithelial (RPE) cells and photoreceptors. Parylene is selected as a substitute material because of its good mechanical properties, transparency, biocompatibility, and machinability. More importantly, it is found that the permeability of submicron parylene is very similar to that of healthy human Bruch\u2019s membrane. A mesh-supported submicron parylene membrane structure has been designed and its feasibility as an artificial Bruch\u2019s membrane has been demonstrated by diffusion experiments, cell perfusion culture, and pressure deflection tests. RPE cells are able to adhere, proliferate and develop into normal in vivo-like morphology and functions. Currently this artificial membrane is under clinical trials.
\r\n" }, { "name": "Mello, Michael", "degree": "PhD", "year": "2012", "title": "Identifying the Unique Ground Motion Signatures of Supershear Earthquakes: Theory and Experiments", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072012-032023169", "creators": [ { "name": { "family": "Mello", "given": "Michael" }, "id": "Mello-Michael", "orcid": "0000-0003-2129-9235", "display_name": "Mello, Michael" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DJDD-2487", "abstract": "The near-field ground motion signatures associated with sub-Rayleigh and supershear ruptures are investigated using the laboratory earthquake experiment originally developed by Rosakis and co-workers (Xia et al., 2004, 2005a; Lu et al., 2007; Rosakis et al., 2007). Heterodyne laser interferometers enable continuous, high-bandwidth measurements of fault-normal (FN), fault-parallel (FP), and vertical (V) particle velocity ``ground motion\" records at discrete locations on the surface of a Homalite-100 test specimen as a sub-Rayleigh or a supershear rupture sweeps along the frictional fault. Photoelastic interference fringes, acquired using high-speed digital photography, provide a synchronized, spatially resolved, whole field view of the advancing rupture tip and surrounding maximum shear stress field.
\r\n\r\nThe first phase of experimental investigations examine and verify the ground motion signatures of supershear ruptures. Experimental results demonstrate that a shear Mach front produced by a stable supershear rupture is characterized by a dominant FP velocity component. The situation is shown to reverse in the sub-Rayleigh rupture speed regime whereby the FN particle velocity component dominates the ground motion record. Additional distinguishing particle velocity signatures, consistent with theoretical and numerical predictions, and repeatedly observed in experimental records are, (1) a pronounced peak in the FP velocity record induced by the leading dilatational field, which sweeps the measurement station in advance of the shear Mach front, and (2) a pronounced velocity swing in the FN record associated with the arrival of a trailing Rayleigh sub-Rayleigh (secondary) rupture, which follows the arrival of the shear Mach front. Analysis of the particle velocity records also confirms 2D steady-state theoretical predictions pertaining to the separation, attenuation, and radiation partitioning of the shear and dilatational portions of the rupture velocity field components.
\r\n\r\nThe second phase of our experimental investigations re-examine the 2002, Mw7.9, Denali fault earthquake and the remarkable set of near-source ground motion records obtained at (PS10), located approximately 85 km east of the epicenter and just 3 km north of the fault along the Alaska pipeline. Motivated by the analysis and interpretation of these records by (Ellsworth et al., 2004; Dunham and Archuleta, 2004, 2005), we attempt to mimic the Denali strike-slip rupture scenario and replicate the PS10 ground motion signatures using a laboratory earthquake experiment. The experiments feature a left-to-right (west-to-east) propagating right lateral rupture within a Homalite-100 test specimen with particle velocity data collected at a near-field station situated just above (north of) the fault. Both sub-Rayleigh and supershear laboratory earthquake experiments are conducted using the Denali PS10 configuration in order to compare and contrast the resulting particle velocity signatures. Supershear laboratory records capture all of the prominent features displayed within the PS10 ground motion records. Noted velocity signatures are correlated to the location of the rupture fronts and their noted arrival times in the synchronized photoelastic image sequence. Scaling relationships are also presented which transform the laboratory records through six orders of magnitude in time, to match the scale of the PS10 ground motion records. The strong correlation between the scaled experimental records and the actual PS10 ground motion records support the hypothesis that the Denali strike-slip fault exhibited a supershear burst.
\r\n\r\nFinally, we present a 2D steady state, stress-velocity formulation that relates the FP and FN particle velocity records measured close to the fault, to the evolution of the stress tensor at the same location. A locally steady-state condition is assumed within a restricted time interval in order to invoke these relationships and estimate the dynamic stresses, \u03c3xx(t) and \u03c4(t), at the near-fault station. Dynamic stress measurements enable a new class of friction investigations using the laboratory earthquake configuration. Experimental findings are presented, which capture the temporal and spatial distributions of \u03c3xx and \u03c4, evolution of the dynamic friction coefficient, and velocity weakening behavior of a supershear slip-pulse.
" }, { "name": "Mendoza-Cortes, Jose Luis", "degree": "PhD", "year": "2012", "title": "Design of Molecules and Materials for Applications in Clean Energy, Catalysis and Molecular Machines Through Quantum Mechanics, Molecular Dynamics and Monte Carlo Simulations", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292012-220632933", "creators": [ { "name": { "family": "Mendoza-Cortes", "given": "Jose Luis" }, "id": "Mendoza-Cortes-Jose-Luis", "orcid": "0000-0001-5184-1406", "display_name": "Mendoza-Cortes, Jose Luis" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "orcid": "0000-0002-9692-7614", "role": "member", "display_name": "Agapie, Theodor" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/PQ74-HK88", "abstract": "We use a multiparadigm, multiscale strategy based on quantum mechanics (QM), first-principles QM-based molecular mechanics (MD) and grand canonical Monte Carlo (GCMC) to rationally design new molecules and materials for clean energy (H2 and CH4 storage), catalysis (O2 evolution, metal organic complexes) and molecular architectures (rotaxanes, hydrogels). This thesis is organized in seven chapters and shows that it is crucial to understand the scale of the system to be studied, the insight obtained can be used to rationally design new molecules and materials for desirable applications; as well as to guide and complement experimental studies. Chapter 1 discusses the specific details of the proposed methodology, including the theoretical underpinning of each modeling paradigm, potential limitations, and how we use these for in silico characterization and design optimization. Chapter 2 covers the structure prediction and characterization of metal-organic complex arrays (MOCA) through QM and force-field-based molecular mechanics. The methodology is inspired by the approach used for enzymatic systems, considering that experimentally determining their three-dimensional structure remains an open challenge. Chapter 3 describes the use of transition state theory for the calculation of reaction rates in polymer hydrogel network formation. This enables the determination of optimum concentrations for polymerization reactions and preparation of coarse-grained force elds. Chapter 4 describes the work performed on Stoddard's rotaxane dumbbells, where we explained origin for the template-directed synthesis through QM-derived free energies. We also give a consistent explanation for the role of the counter anion. Chapter 5 presents the simulation results for a tetranuclear cluster model for O2 evolution, based on CaMn304 and Mn4O4 clusters. We demonstrate how to calculate their oxidation potentials and propose new molecular designs that resemble the oxygen evolution complex (OEC) both structurally and electronically. Chapter 6 presents our findings for CH4 storage. Using a second-order Moller-Plesset perturbation theory force field and GCMC we propose a framework for optimal delivery. Chapter 7 presents our designed materials for hydrogen storage and the validation of our methodology against experimental results. We based our predictions in QM and GCMC calculations through the development of our own first-principles vdW force eld. Our results demonstrate novel frameworks capable of achieving the DOE energy density target for 2015. Finally, we show the generalization of adsorption phenomena for any porous material based on topological constraints." }, { "name": "Michener, Joshua Kieran", "degree": "PhD", "year": "2012", "title": "Combining Rational and Evolutionary Approaches to Optimize Enzyme Activity in Saccharomyces cerevisiae", "advisor": "Smolke, Christina D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05092012-121922995", "creators": [ { "name": { "family": "Michener", "given": "Joshua Kieran" }, "id": "Michener-Joshua-Kieran", "display_name": "Michener, Joshua Kieran" } ], "advisors": [ { "name": { "family": "Smolke", "given": "Christina D." }, "id": "Smolke-C-D", "role": "advisor", "display_name": "Smolke, Christina D." } ], "committee": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "chair", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "member", "display_name": "Leadbetter, Jared R." }, { "name": { "family": "Smolke", "given": "Christina D." }, "id": "Smolke-C-D", "role": "member", "display_name": "Smolke, Christina D." } ], "option_major": [ "bioeng" ], "doi": "10.7907/2KPP-DS46", "abstract": "Metabolic engineering has become an increasingly important tool for the production of bulk and fine chemicals. New biosynthetic pathways can be built in a tractable production host using enzymes from a wide variety of organisms. However, these enzymes did not evolve to function in their new host, and as a result their activity may be unacceptably low. Additionally, the host has not adapted to support this new pathway, and its response to any new stresses imposed by the pathway may further limit productivity. I describe two methods for optimizing the host-enzyme interface, using an evolutionary approach to adapt an enzyme to its new host and a rational approach to modify the host in response. Using a synthetic RNA switch to screen for improvements in enzymatic activity in vivo, I increased the activity of a model enzyme more than 30-fold. I then used a systems-level analysis of the host to identify a stress, heme depletion, that the enzyme placed on its host. Alleviating that stress increased the activity of an optimized enzyme by a further 2.3-fold. These results highlight the advantages of combining systems and synthetic biology during the construction of a metabolic pathway. I also consider options for extending the uses of synthetic RNA switches both earlier and later in the pathway development process. An RNA switch could first be used in a functional screen for enzyme discovery and then be used to adapt the newly discovered enzyme to its production host. Finally, a variant of that switch could be used to dynamically regulate a biosynthetic pathway and improve the pathway reliability." }, { "name": "Miller, Gerald Matthew", "degree": "PhD", "year": "2012", "title": "Electron Transport in Silicon Nanocrystal Devices: From Memory Applications to Silicon Photonics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062011-172253692", "creators": [ { "name": { "family": "Miller", "given": "Gerald Matthew" }, "id": "Miller-Gerald-Matthew", "display_name": "Miller, Gerald Matthew" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/FAZ1-XZ98", "abstract": "The push to integrate the realms of microelectronics and photonics on the silicon platform is currently lacking an efficient, electrically pumped silicon light source. One promising material system for photonics on the silicon platform is erbium-doped silicon nanoclusters (Er:Si-nc), which uses silicon nanoclusters to sensitize erbium ions in a SiO2 matrix. This medium can be pumped electrically, and this thesis focuses primarily on the electrical properties of Er:Si-nc films and their possible development as a silicon light source in the erbium emission band around 1.5 micrometers.
\r\n\r\nSilicon nanocrystals can also be used as the floating gate in a flash memory device, and work is also presented examining charge transport in novel systems for flash memory applications. To explore silicon nanocrystals as a potential replacement for metallic floating gates in flash memory, the charging dynamics in silicon nanocrystal films are first studied using UHV-AFM. This approach uses a non-contact AFM tip to locally charge a layer of nanocrystals. Subsequent imaging allows the injected charge to be observed in real time as it moves through the layer. Simulation of this interaction allows the quantication of the charge in the layer, where we find that each nanocrystal is only singly charged after injection, while holes are retained in the film for hours.
\r\n\r\nWork towards developing a dielectric stack with a voltage-tunable barrier is presented, with applications for flash memory and hyperspectral imaging. For hyperspectral imaging applications, film stacks containing various dielectrics are studied using I-V, TEM, and internal photoemission, with barrier tunability demonstrated in the Sc2O3/SiO2 system.
\r\n\r\nTo study Er:Si-nc as a potential lasing medium for silicon photonics, a theoretical approach is presented where Er:Si-nc is the gain medium in a silicon slot waveguide. By accounting for the local density of optical states effect on the emitters, and carrier absorption due to electrical pumping, it is shown that a pulsed excitation method is needed to achieve gain in this system. A gain of up to 2 db/cm is predicted for an electrically pumped gain medium 50 nm thick. To test these predictions Er:Si-nc LEDs were fabricated and studied. Reactive oxygen sputtering is found to produce more robust films, and the electrical excitation cross section found is two orders of magnitude larger than the optical cross section. The fabricated devices exhibited low lifetimes and low current densities which prevent observation of gain, and the modeling is used to predict how the films must be improved to achieve gain and lasing in this system.
" }, { "name": "Moser, Auna Louise", "degree": "PhD", "year": "2012", "title": "Dynamics of Magnetically Driven Plasma Jets: An Instability of an Instability, Gas Cloud Impacts, Shocks, and Other Deformations ", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:04132012-150652134", "creators": [ { "name": { "family": "Moser", "given": "Auna Louise" }, "id": "Moser-Auna-Louise", "display_name": "Moser, Auna Louise" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "role": "chair", "display_name": "Hillenbrand, Lynne A." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/V7P0-AW84", "abstract": "The Caltech experiment described here produces plasmas relevant to both astrophysical and fusion energy studies. A disk-shaped set of electrodes mounted on the inside of a meter-scale vacuum chamber provides the energy to break a neutral gas, provided at the electrodes only, down into a plasma. The plasma starts as eight loops, and then self-organizes into a single magnetically driven collimated plasma jet. This thesis explores the dynamic evolution of that plasma jet and how changes made to the jet power source or environment alter the evolution. The most significant finding is the discovery that a series of instabilities can lead to magnetic reconnection. The jet undergoes a first, primary instability, called the kink instability. The exponential growth of kink amplitude provides an acceleration that drives a smaller scale, secondary instability, called the Rayleigh\u2013Taylor instability. The Rayleigh\u2013Taylor instability can drop the diameter of the plasma to a small enough scale to allow magnetic reconnection. A second set of experiments explores the range of collision interactions between the plasma jet and a cloud of neutral gas in its path. A final set of experiments shows the dependence of jet radius on a time-changing current. A new power supply that led to the observation of some of these new dynamics is also described.\r\n" }, { "name": "Mullen, Patrick Gary", "degree": "PhD", "year": "2012", "title": "Eulerian Geometric Discretizations of Manifolds and Dynamics", "advisor": "Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:09092011-162631888", "creators": [ { "name": { "family": "Mullen", "given": "Patrick Gary" }, "id": "Mullen-Patrick-Gary", "display_name": "Mullen, Patrick Gary" } ], "advisors": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "chair", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Alliez", "given": "Pierre" }, "id": "Alliez-P", "role": "member", "display_name": "Alliez, Pierre" } ], "option_major": [ "compsci" ], "doi": "10.7907/5GSC-W341", "abstract": "This thesis explores new methods for geometric, structure-preserving Eulerian discretizations of dynamics, including Lie advection and incompressible fluids, and the manifolds in which these dynamics occur. The result is a novel method for discrete Lie advection of differential forms, a new family of structure-preserving fluid integrators, and a new set of energies for optimizing meshes appropriate for some discrete geometric operators. First, high-resolution nite volume methods are leveraged to introduce a new method for discretizing the Lie advection of discrete differential forms, along with the related contraction operator, on regular grids. Through its geometric approach, the method exactly preserves properties such as the closedness of Lie advected closed forms. This results in an extension of nite volume techniques applicable to forms of arbitrary degree. After this, attention is turned to simplicial meshes, where new meshing techniques are developed to give formal error bounds on the discrete diagonal Hodge star, an important operator for geometric computations. Utilizing weighted Delaunay triangulations, both the primal mesh and its dual are optimized simultaneously over the entire space of orthogonal primal/dual pairs. Improved accuracy of the solution of Poisson equations is demonstrated as a practical application, as well as an increase in percentage of well-centered elements. Finally, a new structure-preserving method for the incompressible Navier-Stokes equations on simplicial meshes is developed, offering in the inviscid case the exact conservation of either the discrete energy or symplectic form. This leads to capturing the correct energy decay when viscosity is added, resulting in dissipation independent of grid and time resolution." }, { "name": "Nair, Jayakrishnan U.", "degree": "PhD", "year": "2012", "title": "Scheduling for Heavy-Tailed and Light-Tailed Workloads in Queueing Systems", "advisor": "Low, Steven H.; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012012-134536732", "creators": [ { "name": { "family": "Nair", "given": "Jayakrishnan U." }, "id": "Nair-Jayakrishnan-U", "display_name": "Nair, Jayakrishnan U." } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/AAXJ-EX10", "abstract": "In much of classical queueing theory, workloads are assumed to be light-tailed, with job sizes being described using exponential or phase type distributions. However, over the past two decades, studies have shown that several real-world workloads exhibit heavy-tailed characteristics. As a result, there has been a strong interest in studying queues with heavy-tailed workloads. So at this stage, there is a large body of literature on queues with light-tailed workloads, and a large body of literature on queues with heavy-tailed workloads. However, heavy-tailed workloads and light-tailed workloads differ considerably in their behavior, and these two types of workloads are rarely studied jointly.
\r\n\r\nIn this thesis, we design scheduling policies for queueing systems, considering both heavy-tailed as well as light-tailed workloads. The motivation for this line of work is twofold. First, since real world workloads can be heavy-tailed or light-tailed, it is desirable to design schedulers that are robust in their performance to distributional assumptions on the workload. Second, there might be scenarios where a heavy-tailed and a light-tailed workload interact in a queueing system. In such cases, it is desirable to design schedulers that guarantee fairness in resource allocation for both workload types.
\r\n\r\nIn this thesis, we study three models involving the design of scheduling disciplines for both heavy-tailed as well as light-tailed workloads. In Chapters 3 and 4, we design schedulers that guarantee robust performance across heavy-tailed and light-tailed workloads. In Chapter 5, we consider a setting in which a heavy-tailed and a light-tailed workload complete for service. In this setting, we design scheduling policies that guarantee good response time tail performance for both workloads, while also maintaining throughput optimality.
" }, { "name": "Nelson, Matthew John", "degree": "PhD", "year": "2012", "title": "Understanding and Applying Extracellular Recordings in Awake, Behaving Animals", "advisor": "Shimojo, Shinsuke", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072012-131946481", "creators": [ { "name": { "family": "Nelson", "given": "Matthew John" }, "id": "Nelson-Matthew-John", "display_name": "Nelson, Matthew John" } ], "advisors": [ { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "advisor", "display_name": "Shimojo, Shinsuke" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Pouget", "given": "Pierre" }, "id": "Pouget-P", "role": "member", "display_name": "Pouget, Pierre" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Schall", "given": "Jeffrey D." }, "id": "Schall-J-D", "role": "member", "display_name": "Schall, Jeffrey D." } ], "option_major": [ "cns" ], "doi": "10.7907/1JYP-K183", "abstract": "Section I of this thesis presents specific projects applying extracellular recordings in macaques. The results demonstrate a novel relative position code employed by individual neurons in the dorsal premotor cortex during reaches and saccades, which may be important for hand-eye coordination. Another project suggests low-frequency coherence between dorsal premotor and posterior parietal cortices participates in making internally guided decisions of where to reach. Section II investigates analysis of data collected with this technique. One project compares methodologies for computing trial-by-trial coherence among neuron ensembles, and another documents how the innate nonstationarity of animal behavior can affect conclusions of certain analyses. Section III investigates the acquisition of extracellular electrophysiological data to understand how these recorded voltages relate to underlying neural activity. One project verifies a physical model of the microelectrode recording circuit using electrodes suspended in saline. Some lower-input impedance head stages used in the field are shown to result in electrode impedance and frequency-dependent amplitude attenuations and phase shifts of recorded signals. Other projects present a theoretical argument that local field potentials (LFPs) recorded from in-depth microelectrodes should be independent of electrode impedance within the range of impedances typically used. A simple physical model shows that if and only if gradients of LFP coherence exist at a scale finer than an electrode's recording site size, lower-impedance electrodes report higher coherence. However this is not expected to occur between different microelectrodes, but could explain differences between microelectrode and EEG recordings. The final project uses simultaneous extracellular and intracellular recordings in corticostriatal rat brain slices to show that frequency-dependent phase shifts and amplitude attenuations occur in neural tissue itself and characterize the transfer function between the intracellular and extracellular voltages. Inhomogenous microscale obstructions inherent in neural tissue are shown to differentially distort current flow depending on the severity of the obstructions. This challenges existing beliefs about the nature of current flow in the brain, and should be considered when interpreting electrophysiological data." }, { "name": "Noroozian, Omid", "degree": "PhD", "year": "2012", "title": "Superconducting Microwave Resonator Arrays for Submillimeter/Far-infrared Imaging", "advisor": "Zmuidzinas, Jonas", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122012-091920562", "creators": [ { "name": { "family": "Noroozian", "given": "Omid" }, "id": "Noroozian-Omid", "display_name": "Noroozian, Omid" } ], "advisors": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "advisor", "display_name": "Zmuidzinas, Jonas" } ], "committee": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "chair", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "role": "member", "display_name": "Golwala, Sunil" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8MG2-NB23", "abstract": "Superconducting microwave resonators have the potential to revolutionize submillimeter and far-infrared astronomy, and with it our understanding of the universe. The field of low-temperature detector technology has reached a point where extremely sensitive devices like transition-edge sensors are now capable of detecting radiation limited by the background noise of the universe. However, the size of these detector arrays are limited to only a few thousand pixels. This is because of the cost and complexity of fabricating large-scale arrays of these detectors that can reach up to 10 lithographic levels on chip, and the complicated SQUID-based multiplexing circuitry and wiring for readout of each detector. In order to make substantial progress, next- generation ground-based telescopes such as CCAT or future space telescopes require focal planes with large-scale detector arrays of 104\u2013106 pixels. Arrays using microwave kinetic inductance detectors (MKID) are a potential solution. These arrays can be easily made with a single layer of superconducting metal film deposited on a silicon substrate and pattered using conventional optical lithography. Furthermore, MKIDs are inherently multiplexable in the frequency domain, allowing \u223c 103 detectors to be read out using a single coaxial transmission line and cryogenic amplifier, drastically reducing cost and complexity.
\r\n\r\nAn MKID uses the change in the microwave surface impedance of a superconducting thin-film microresonator to detect photons. Absorption of photons in the superconductor breaks Cooper pairs into quasiparticles, changing the complex surface impedance, which results in a perturbation of resonator frequency and quality factor. For excitation and readout, the resonator is weakly coupled to a transmission line. The complex amplitude of a microwave probe signal tuned on-resonance and transmitted on the feedline past the resonator is perturbed as photons are absorbed in the superconductor. The perturbation can be detected using a cryogenic amplifier and subsequent homodyne mixing at room temperature. In an array of MKIDs, all the resonators are coupled to a shared feedline and are tuned to slightly different frequencies. They can be read out simultaneously using a comb of frequencies generated\r\nand measured using digital techniques.
\r\n\r\nThis thesis documents an effort to demonstrate the basic operation of \u223c 256 pixel arrays of lumped-element MKIDs made from superconducting TiNx on silicon. The resonators are designed and simulated for optimum operation. Various properties of the resonators and arrays are measured and compared to theoretical expectations. A particularly exciting observation is the extremely high quality factors (\u223c 3 \u00d7 107) of our TiNx resonators which is essential for ultra-high sensitivity. The arrays are tightly packed both in space and in frequency which is desirable for larger full-size arrays. However, this can cause a serious problem in terms of microwave crosstalk between neighboring pixels. We show that by properly designing the resonator geometry, crosstalk can be eliminated; this is supported by our measurement results. We also tackle the problem of excess frequency noise in MKIDs. Intrinsic noise in the form of an excess resonance frequency jitter exists in planar superconducting resonators that are made on dielectric substrates. We conclusively show that this noise is due to fluctuations of the resonator capacitance. In turn, the capacitance fluctuations are thought to be driven by two-level system (TLS) fluctuators in a thin layer on the surface of the device. With a modified resonator design we demonstrate with measurements that this noise can be substantially reduced. An optimized version of this resonator was designed for the multiwavelength submillimeter kinetic inductance camera (MUSIC) instrument for the Caltech Submillimeter Observatory.
" }, { "name": "Raney, Jordan Robert", "degree": "PhD", "year": "2012", "title": "Hierarchical Structures of Aligned Carbon Nanotubes as Low-Density Energy-Dissipative Materials", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05072012-134317580", "creators": [ { "name": { "family": "Raney", "given": "Jordan Robert" }, "id": "Raney-Jordan-Robert", "display_name": "Raney, Jordan Robert" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "chair", "display_name": "Daraio, Chiara" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "matsci" ], "doi": "10.7907/25R0-JT92", "abstract": "Carbon nanotubes (CNTs) are known to have remarkable properties, such as a specific strength two orders of magnitude higher than that of steel. It has remained a challenge, however, to achieve useful bulk properties from CNTs. Toward that goal, here we develop low-density bulk materials (0.1-0.4 g cm-3) entirely or nearly entirely from CNTs. These consist of nominally-aligned arrays of CNTs that display a dissipative compressive response, with a notable stress-strain hysteresis. The compressive properties of CNT arrays are examined in detail. This analysis reveals interesting features in the mechanical response, such as strain localization (resulting from a gradient in physical properties along the height), recovery after compression, non-linear viscoelasticity, and behavior under repeated compression that depends on the strain of previous cycles (similar to the Mullins effect in rubbers). We observe that in compression the energy dissipation of these materials is more than 200 times that of polymeric foams of comparable density.
\r\n\r\nNext, materials based on CNT arrays are studied as exemplary of hierarchical materials (materials with distinct structure at multiple length scales). Hierarchical materials have pushed the limits of traditional material tradeoffs (e.g., the typical trend that increased strength requires increased weight). Techniques are developed to separately vary the structure of CNT arrays at nanometer, micrometer, and millimeter length scales, and the effects on the bulk material response are examined. Structure can be modified during CNT synthesis, such as by varying the composition of the flow gas or by manipulating the input rate of chemical precursors; it can also be modified post-synthesis, e.g., by the in situ synthesis of nanoparticles in the interstices of the CNT arrays or by the assembly of multilayer structures of multiple CNT arrays connected by polymeric or metallic interlayers.
\r\n\r\nFinally, a mathematical model is applied to capture the complexities of the mechanical response. This one-dimensional, multiscale, bistable spring model is able to match the global stress-strain response as well as local effects such as strain localization and Mullins-like behavior. A technique is developed to reliably discern the model's material parameters based on in situ optical data from the experiments.
" }, { "name": "Rolfe, Jason Tyler", "degree": "PhD", "year": "2012", "title": "Intrinsic Gradient Networks", "advisor": "Cook, Matthew M.; Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:04202012-133210844", "creators": [ { "name": { "family": "Rolfe", "given": "Jason Tyler" }, "id": "Rolfe-Jason-Tyler", "display_name": "Rolfe, Jason Tyler" } ], "advisors": [ { "name": { "family": "Cook", "given": "Matthew M." }, "id": "Cook-M-M", "role": "advisor", "display_name": "Cook, Matthew M." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Cook", "given": "Matthew M." }, "id": "Cook-M-M", "role": "member", "display_name": "Cook, Matthew M." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" } ], "option_major": [ "cns" ], "doi": "10.7907/YCB7-7X24", "abstract": "Artificial neural networks are computationally powerful and exhibit brain-like dynamics. Unfortunately, the conventional gradient-dependent learning algorithms used to train them are biologically implausible. The calculation of the gradient in a traditional artificial neural network requires a complementary network of fast training signals that are dependent upon, but must not affect, the primary output-generating network activity. In contrast, the network of neurons in the cortex is highly recurrent; a network of gradient-calculating neurons in the brain would certainly project back to and influence the primary network. We address this biological implausibility by introducing a novel class of recurrent neural networks, intrinsic gradient networks, for which the gradient of an error function with respect to the parameters is a simple function of the network state. These networks can be trained using only their intrinsic signals, much like the network of neurons in the brain.
\r\n\r\nWe derive a simple equation that characterizes intrinsic gradient networks, and construct a broad set of networks that satisfy this characteristic equation. The resulting set of intrinsic gradient networks includes many highly recurrent instances for which the gradient can be calculated by a simple, local, pseudo-Hebbian function of the network state, thus resolving a long-standing contradiction between artificial and biological neural networks. We demonstrate that these networks can learn to perform nontrivial tasks like handwritten digit recognition using only their intrinsic signals. Finally, we show that a cortical implementation of an intrinsic gradient network would have a number of characteristic computational, anatomical, and electrophysiological properties, and review experimental evidence suggesting the manifestation of these properties in the cortex.
" }, { "name": "Sengupta, Kaushik", "degree": "PhD", "year": "2012", "title": "Silicon-Based Terahertz Circuits and Systems", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112012-145654043", "creators": [ { "name": { "family": "Sengupta", "given": "Kaushik" }, "id": "Sengupta-Kaushik", "display_name": "Sengupta, Kaushik" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Choo", "given": "Hyuck" }, "id": "Choo-Hyuck", "role": "member", "display_name": "Choo, Hyuck" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MBXB-6R29", "abstract": "The Terahertz frequency range, often referred to as the `Terahertz' gap, lies wedged between microwave at the lower end and infrared at the higher end of the spectrum, occupying frequencies between 0.3-3.0 THz. For a long time, applications in THz frequencies had been limited to astronomy and chemical sciences, but with advancement in THz technology in recent years, it has shown great promise in a wide range of applications ranging from disease diagnostics, non-invasive early skin cancer detection, label-free DNA sequencing to security screening for concealed weapons and contraband detection, global environmental monitoring, nondestructive quality control and ultra-fast wireless communication. Up until recently, the terahertz frequency range has been mostly addressed by high mobility compound III-V processes, expensive nonlinear optics, or cryogenically cooled quantum cascade lasers. A low cost, room temperature alternative can enable the development of such a wide array of applications, not currently accessible due to cost and size limitations. In this thesis, we will discuss our approach towards development of integrated terahertz technology in silicon-based processes. In the spirit of academic research, we will address frequencies close to 0.3 THz as 'Terahertz'.
\r\n\r\nIn this thesis, we address both fronts of integrated THz systems in silicon: THz power generation, radiation and transmitter systems, and THz signal detection and receiver systems. THz power generation in silicon-based integrated circuit technology is challenging due to lower carrier mobility, lower cut-o frequencies compared to compound III-V processes, lower breakdown voltages and lossy passives. Radiation from silicon chip is also challenging due to lossy substrates and high dielectric constant of silicon. In this work, we propose novel ways of combining circuit and electromagnetic techniques in a holistic design approach, which can overcome limitations of conventional block-by-block or partitioned design methodology, in order to generate high-frequency signals above the classical definition of cut-off frequencies (\u0192t/\u0192max). We demonstrate this design philosophy in an active electromagnetic structure, which we call Distributed Active Radiator. It is inspired by an Inverse\r\nMaxwellian approach, where instead of using classical circuit and electromagnetic blocks to generate and radiate THz frequencies, we formulate surface (metal) currents in silicon chip for a desired THz field prole and develop active means of controlling different harmonic\r\ncurrents to perform signal generation, frequency multiplication, radiation and lossless filtering, simultaneously in a compact footprint. By removing the articial boundaries between circuits, electromagnetics and antenna, we open ourselves to a broader design space. This\r\nenabled us to demonstrate the rst 1 mW Eective-isotropic-radiated-power(EIRP) THz (0.29 THz) source in CMOS with total radiated power being three orders of magnitude more than previously demonstrated. We also proposed a near-field synchronization mechanism, which is a scalable method of realizing large arrays of synchronized autonomous radiating sources in silicon. We also demonstrate the first THz CMOS array with digitally controlled beam-scanning in 2D space with radiated output EIRP of nearly 10 mW at 0.28 THz.
\r\n\r\nOn the receiver side, we use a similar electronics and electromagnetics co-design approach to realize a 4x4 pixel integrated silicon Terahertz camera demonstrating to the best of our knowledge, the most sensitive silicon THz detector array without using post-processing,\r\nsilicon lens or high-resistivity substrate options (NEP < 10 pW √ Hz at 0.26 THz). We put the 16 pixel silicon THz camera together with the CMOS DAR THz power generation arrays and demonstrated, for the first time, an all silicon THz imaging system with a CMOS source.
" }, { "name": "Standley, Brian Lawrence", "degree": "PhD", "year": "2012", "title": "Graphene as a Platform for Novel Nanoelectronic Devices", "advisor": "Bockrath, Marc William", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062012-025632521", "creators": [ { "name": { "family": "Standley", "given": "Brian Lawrence" }, "id": "Standley-Brian-Lawrence", "display_name": "Standley, Brian Lawrence" } ], "advisors": [ { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "advisor", "display_name": "Bockrath, Marc William" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "role": "member", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/6MMB-T165", "abstract": "Graphene's superlative electrical and mechanical properties, combined with its compatibility with existing planar silicon-based technology, make it an attractive platform for novel nanoelectronic devices. The development of two such devices is reported\u2014a nonvolatile memory element exploiting the nanoscale graphene edge and a field-effect transistor using graphene for both the conducting channel and, in oxidized form, the gate dielectric. These experiments were enabled by custom software written to fully utilize both instrument-based and computer-based data acquisition hardware and provide a simple measurement automation system.
\r\n\r\nGraphene break junctions were studied and found to exhibit switching behavior in response to an electric field. This switching allows the devices to act as nonvolatile memory elements which have demonstrated thousands of writing cycles and long retention times. A model for device operation is proposed based on the formation and breaking of carbon-atom chains that bridge the junctions. Information storage was demonstrated using the concept of rank coding, in which information is stored in the relative conductance of multiple graphene switches in a memory cell.
\r\n\r\nThe high mobility and two dimensional nature of graphene make it an attractive material for field-effect transistors. Another ultrathin layered material\u2014graphene's insulating analogue, graphite oxide\u2014was studied as an alternative to bulk gate dielectric materials such as Al2O3 or HfO2. Transistors were fabricated comprising single or bilayer graphene channels, graphite oxide gate insulators, and metal top-gates. Electron transport measurements reveal minimal leakage through the graphite oxide at room temperature. Its breakdown electric field was found to be comparable to SiO2, typically 1\u20133 \u00d7 108 V/m, while its dielectric constant is slightly higher, \u03ba \u2248 4.3.
\r\n\r\nAs nanoelectronics experiments and their associated instrumentation continue to grow in complexity the need for powerful data acquisition software has only increased. This role has traditionally been filled by semiconductor parameter analyzers or desktop computers running LabVIEW. Mezurit 2 represents a hybrid approach, providing basic virtual instruments which can be controlled in concert through a comprehensive scripting interface. Each virtual instrument's model of operation is described and an architectural overview is provided.
" }, { "name": "Stenson, Eve Virginia", "degree": "PhD", "year": "2012", "title": "Fields, Forces, and Flows: What Laboratory Experiments Reveal About the Dynamics of Arched Plasma Structures", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102012-025123301", "creators": [ { "name": { "family": "Stenson", "given": "Eve Virginia" }, "id": "Stenson-Eve-Virginia", "display_name": "Stenson, Eve Virginia" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "role": "member", "display_name": "Golwala, Sunil" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/24HR-J675", "abstract": "Magnetic flux tubes and, more generally, magnetic field structures that link a plasma volume to its boundary are prominent features in plasma systems of significant interest, such as the solar atmosphere and the interiors of magnetic fusion devices.
\r\n\r\nIn order to study the fundamental physics of these systems, experiments were conducted in the laboratory using a magnetized plasma gun to produce individual arched, plasma-filled magnetic flux tubes. More complex plasma topologies were also explored. The absence of confining walls allowed plasmas to evolve freely \u2014 which they did, very dynamically, over the course of several microseconds. The experiment setup featured excellent reproducibility, extensive diagnostic accessibility, and several tunable parameters. In particular, a plasma \"color coding\" technique and magnetic measurements provided new and interesting results.
\r\n\r\nThe single arches or \"loops\" of plasma exhibited sustained axial collimation, even during a dramatic evolution from a small, semicircular arch into a kinked structure up to seven times larger. The loops' magnetic structure was verified as consistent with that of a flux tube, and their evolution was found to be in quantitative agreement with two interrelated magnetohydrodynamic (MHD) theories: a simplified hoop force model for the axis expansion and a recently proposed MHD flow model for the collimation. More complex plasma structures were found to be similarly dominated by the effects of the magnetic field, exhibiting behavior that was highly repeatable but varied significantly from one magnetic structure to the next.
\r\n\r\nThese findings suggest that MHD-driven flows are an important mechanism for the transport of plasma in arched flux tubes and other magnetic plasma structures. Because MHD has no inherent length scale, the forces driving the evolution of these experiments are expected to similarly affect other systems with low plasma beta and a high Lundquist number.
" }, { "name": "Stetson, Robert Chess Abernathy", "degree": "PhD", "year": "2012", "title": "Interaction of Planning Regions in Cortex", "advisor": "Andersen, Richard A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262012-075609487", "creators": [ { "name": { "family": "Stetson", "given": "Robert Chess Abernathy" }, "id": "Stetson-Robert-Chess-Abernathy", "display_name": "Stetson, Robert Chess Abernathy" } ], "advisors": [ { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "advisor", "display_name": "Andersen, Richard A." } ], "committee": [ { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "chair", "display_name": "Andersen, Richard A." }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "co-chair", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" } ], "option_major": [ "cns" ], "doi": "10.7907/VGS7-PZ20", "abstract": "To what extent do parietal and frontal areas involved in action planning interact as a monkey plans a movement? This report seeks an answer using the timing relationships between action potentials, local field potentials (LFPs) and behavioral events as a monkey plans reaches and eye movements to remembered targets. Both parietal reach region (PRR) and dorsal premotor cortex (PMd) show similar profiles of activity characteristic of action planning. In some cases, both premotor and intraparietal areas show decision-making activity far earlier than previously anticipated, even before the onset of the trial. However, despite their similarities in action planning, PMd responds tens of milliseconds sooner to targets and movement instructions. These results suggest that PMd precedes PRR, apparently contrary to a common heuristic about the chain of processing from sensation to action. On the other hand, during periods of steady state, as the monkey anticipates information or plans a movement, the apparent directionality of fronto-parietal interaction may reverse. Coherent phase-locking between action potentials and local field potentials (LFPs), which has been implicated in directional influence between brain regions, is highly significant from PRR to PMd, but not vice-versa. Spikes in PRR cohere with LFPs in PMd between 15\u201325 Hz, whereas spikes in PMd do not cohere with LFPs in PRR at any frequency. This uni-directional spike-LFP coherence varies over the course of the trial, achieving a peak in magnitude and frequency, on average, during the planning period. The phase-locking component of the coherence shows weak but significant variation according to the particular action being planned. The cross-cortical coherence also varies significantly with cortical anatomy. Coherence is stronger between spikes in PRR and LFPs in its anatomical target PMd than between PRR and other recording areas within and beyond the arcuate sulcus (associated with saccades, and not known to be connected with PRR). The asymmetry of spike - LFP coherence, its task\u2013dependence, and variation over cortical territory add to a growing body of knowledge implicating the intraparietal sulcus as the center of a network of beta-band activity characteristic of action planning. This highly specific beta-band oscillation links frontal and parietal planning regions at the single cell level. Overall, these results suggest an interplay between premotor and parietal regions, with influence shifting back and forth according to the phase of behavior." }, { "name": "Sukhavasi, Ravi Teja", "degree": "PhD", "year": "2012", "title": "Distributed Control and Computing: Optimal Estimation, Error Correcting Codes, and Interactive Protocols", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302012-155108063", "creators": [ { "name": { "family": "Sukhavasi", "given": "Ravi Teja" }, "id": "Sukhavasi-Ravi-Teja", "display_name": "Sukhavasi, Ravi Teja" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/7431-FH32", "abstract": "Emerging applications of networked control and distributed computing are characterized by decentralization of information and the need to exchange it over potentially unreliable communication networks. This results in novel interactive communication scenarios that are incompatible with conventional information and coding theoretic approaches. To address this gap, through the early and late 1990's, a new information theoretic notion called anytime reliability and a new coding paradigm called tree codes were proposed. Although the central role of tree codes in several interactive communication problems such as distributed control and computing has been well understood, there have been no practical constructions till date. For the first time, we have an explicit ensemble of linear tree codes with efficient encoding and decoding for the class of erasure channels. In the process, we have developed novel non-asymptotic sufficient conditions on the kind of communication reliability required to stabilize control systems over noisy channels. We also study the application of tree codes to interactive protocols over erasure networks and illustrate their benefits through the example of average consensus." }, { "name": "Tan, Hongjin", "degree": "PhD", "year": "2012", "title": "A Study of the Thermodynamics and Kinetics of Li\u2093FePO\u2084 as a Cathode Material for Li Batteries", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11232011-221537072", "creators": [ { "name": { "family": "Tan", "given": "Hongjin" }, "id": "Tan-Hongjin", "display_name": "Tan, Hongjin" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Jackson", "given": "Jennifer M." }, "id": "Jackson-J-M", "orcid": "0000-0002-8256-6336", "role": "member", "display_name": "Jackson, Jennifer M." }, { "name": { "family": "Jones", "given": "Simon C." }, "id": "Jones-Simon-C", "role": "member", "display_name": "Jones, Simon C." } ], "option_major": [ "matsci" ], "doi": "10.7907/NQC1-J605", "abstract": "Olivine-type LiFePO4 has been recognized as one of the most promising cathode materials for rechargeable Li batteries. Its advantages include high capacity, high stability, nontoxicity, and low cost. Our methods for synthesizing nanocrystalline LixFePO4 with the olivine structure are described. Solid-state reactions and precipitation reactions were both successful, and ball milling was especially effective at reducing crystallite sizes. Diffractometry and microscopy were used to characterize these materials, and results of impurity phases, excess Fe3+, and internal stresses are reported for the different types of synthesis.
\r\n\r\nApplications of lithium-ion batteries, including automotive applications, require fast kinetics and high conductivity of ions and electrons. Unfortunately, LixFePO4 has the electronic structure of an insulator, an entirely unsatisfactory situation if it is to be used as a battery electrode. Electrical conductivity in LixFePO4 occurs by the motion of small polarons, which are valence electrons at Fe atoms plus their distorted local environments. Electrical conductivity of LixFePO4 is interpreted in terms of small polaron hopping. There are other factors of importance in these measurements, such as impurities or defects that block the one-dimensional conduction channels of the olivine structure of LixFePO4.
\r\n\r\nWe studied the polaron hopping directly, which allows us to understand the intrinsic electrical conductivity, and how it depends on microstructure and composition of LixFePO4. The experimental technique was Mossbauer spectrometry, which has been used for many years as a means for determining the fractions of Fe2+ and Fe3+ in a material. Usually the spectral signatures of Fe2+ and Fe3+ are distinct. When valence electrons hop between Fe2+ and Fe3+ at a frequency of 108 Hz or higher, however, the valence changes during the timescale of the Mossbauer measurement and the spectrum is blurred. By measuring Mossbauer spectra at elevated temperatures, we can determine the fractions of Fe atoms participating in polaron hopping, and determine the activation energy of the process. From this we estimate intrinsic electrical conductivities of 10-7S/cm at room temperature for nanocrystalline Li0.5FePO4, for example. We find a comparable conductivity for LixFePO4 prepared as a solid solution, but the conductivity of conventional LixFePO4 is much lower.
\r\n\r\nThere has been much discussion about how surface area might thermodynamically stabilize the solid solution phase of nanocrystalline LixFePO4. In a series of X-ray diffraction measurements, some at elevated temperatures, we found the solid solution phase of LixFePO4 to be especially robust at room temperature when the material was prepared in nanocrystalline form. Moreover, the consistent phase transition temperature around 200\u00b0C was observed, as evidence for the unchanged equilibrium phase diagram by crystallite size. This is consistent with our evaluation on the boundaries of the two-phase mixture of triphylite and heterosite during Li insertion and extraction. Profiles of entropy and enthalpy changes were evaluated by open-circuit voltage measurements. The boundaries were found at x=0.05 and 0.95 in the LixFePO4 with crystal size of 70 nm, similar to the reported values on bulk-LixFePO4. These are important in practice, because electrochemical lithiation and delithiation at room temperature should remain as a two-phase transformation, even if a solid solution of lithium is present in the initial electrode material.
" }, { "name": "Thomas, Vaughan Lamar", "degree": "PhD", "year": "2012", "title": "Particle-Based Modeling of Ni-YSZ Anodes", "advisor": "Shepherd, Joseph E.; Goodwin, David G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03302012-133547448", "creators": [ { "name": { "family": "Thomas", "given": "Vaughan Lamar" }, "id": "Thomas-Vaughan-Lamar", "display_name": "Thomas, Vaughan Lamar" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "advisor", "display_name": "Goodwin, David G." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/JF8P-5495", "abstract": "In this work we examine the performance of particle-based models with respect to the Ni-YSZ composite anode system. The conductivity and triple-phase boundary (tpb) of particle-based systems is estimated. The systems considered have mono-dispersed particle size distributions, bi-modal particle size distributions with a YSZ:Ni particle size ratio of 1:0.781, and particle size distributions based on experimental measurements. All three types of systems show qualitative behavioral agreement in terms of conductivity, with clear transition from non-conducting behavior to high conducting behavior over a small transition regime which varied from a nickel phase fraction of .22-.28 for the mono- dispersed cases, 0.19-.0.25 for the bimodal cases, and 0.19-0.30 for the experimentally based cases. Mono-dispersed and simple-polydispersed particle size distribution show very low variation from case to case, with \u03c3/\u03bc \u2264 0.04. Cases based on empirical particle size distribution data demonstrated significantly higher variances which varied over a very large range, 0.3 \u2264 \u03c3/\u03bc \u2264 1.1. With respect to the calculations of the TPB length, we find that the same pattern of variance in the measure of the triple-phase boundary length. The TPB length for the mono-dispersed and simple poly-dispersed systems was in the range of 3 \u00d7 1012 \u20134 \u00d7 1013 m/m3 . For empirical particle size distribution data the TPB length density was in the range of 8\u00d7109\u20132\u00d71011 m/m3. The variance of the TPB length density follows the same pattern as the conductivity measurements with very low variance for the mono-dispersed and simple poly-dispersed systems and much larger variance for the empirically-based systems. We also examine the association between the TPB length and the availability of conducting pathways for the participating particles xv of individual TPBs. The probability of a TPB having a conducting pathway in the gas phase is essentially 100% in all cases. The probability of an individual tpb section having conducting pathways in either of the solid phases is directly related to percolation condition of that phase.
\r\n\r\nWe also considered a particle-based composite electrode realization based on a three- dimensional reconstruction of an actual Ni-YSZ composite electrode. For this model we used particles which vary in nominal size from 85\u2013465 nm, with size increments of 42.5 nm. We paid particular attention to the coordination numbers between particles and the distribution of particle size interconnections. We found that homogeneous inter-particle connections were far more common than would occur using a random distribution of particles. In particular we found that for a random collection of particles of similar composition the likelihood Ni-Ni particle connections was between 0.18\u20130.30. For the reconstruction we found the likelihood of Ni-Ni particle connections to be greater than 0.56 in all cases. Similarly, the distribution of connections between particles, with respect to particle size of the participating particles, deviated from what would be expected using a random distribution of particles. Particles in the range of 85\u2013169 nm showed the highest coordination with particles of the same size. Particles in the range of 211\u2013338 nm have the highest coordination with particles of radius 169 nm with very similar distributions. Particles with radius greater than 338 nm represented only 7.2 \u00d7 10\u22123 % of the particles within the reconstruction, and showed the highest coordination with particles of radius of 211 nm, but the distributions vary widely.
\r\n\r\nIn the final chapter, we build a model which can account for mass transfer, hetero- geneous chemistry, surface chemistry, and electrochemistry within a porous electrode. The electric potential is calculated on a particle basis using a network model; gas phase concentrations and surface coverages are calculated with a one-dimensional porous me- dia model. Properties of the porous media are calculated via a TPMC method. TPB electrochemistry is calculated at individual triple phase boundaries within the particle xvi model, based on local gas phase concentrations, surface coverages and particle poten- tials, and then added to the porous media model. Using this tool we are able to calculate the spatial distribution of the Faradaic current within the electrode, and variation in gas phase concentrations within the porous media.
" }, { "name": "Tiwary, Pratyush", "degree": "PhD", "year": "2012", "title": "Atomistic Simulations of Materials: Methods for Accurate Potentials and Realistic Time-Scales", "advisor": "van de Walle, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302012-182258575", "creators": [ { "name": { "family": "Tiwary", "given": "Pratyush" }, "id": "Tiwary-Pratyush", "display_name": "Tiwary, Pratyush" } ], "advisors": [ { "name": { "family": "van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "advisor", "display_name": "van de Walle, Axel" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "member", "display_name": "van de Walle, Axel" } ], "option_major": [ "matsci" ], "doi": "10.7907/J8W9-XS70", "abstract": "This thesis deals with achieving more realistic atomistic simulations of materials, by developing accurate and robust force-fields, and algorithms for practical time scales.
\r\n\r\nI develop a formalism for generating interatomic potentials for simulating atomistic phenomena occurring at energy scales ranging from lattice vibrations to crystal defects to high-energy collisions. This is done by fitting against an extensive database of ab initio results, as well as to experimental measurements for mixed oxide nuclear fuels. The applicability of these interactions to a variety of mixed environments beyond the fitting domain is also assessed. The employed formalism makes these potentials applicable across all interatomic distances without the need for any ambiguous splining to the well-established short-range Ziegler-Biersack-Littmark universal pair potential. We expect these to be reliable potentials for carrying out damage simulations (and molecular dynamics simulations in general) in nuclear fuels of varying compositions for all relevant atomic collision energies.
\r\n\r\nA hybrid stochastic and deterministic algorithm is proposed that while maintaining fully atomistic resolution, allows one to achieve milliseconds and longer time scales for several thousands of atoms. The method exploits the rare event nature of the dynamics like other such methods, but goes beyond them by (i) not having to pick a scheme for biasing the energy landscape, (ii) providing control on the accuracy of the boosted time scale, (iii) not assuming any harmonic transition state theory (HTST), and (iv) not having to identify collective coordinates or interesting degrees of freedom. The method is validated by calculating diffusion constants for vacancy-mediated diffusion in iron metal at low temperatures, and comparing against brute-force high temperature molecular dynamics. We also calculate diffusion constants for vacancy diffusion in tantalum metal, where we compare against low-temperature HTST as well. The robustness of the algorithm with respect to the only free parameter it involves is ascertained.
\r\n\r\nThe method is then applied to perform tensile tests on gold nanopillars on strain rates as low as 100/s, bringing out the perils of high strain-rate molecular dynamics calculations. We also calculate temperature and stress dependence of activation free energy for surface nucleation of dislocations in pristine gold nanopillars under realistic loads. While maintaining fully atomistic resolution, we reach the fraction-of-a-second time scale regime. It is found that the activation free energy depends significantly and nonlinearly on the driving force (stress or strain) and temperature, leading to very high activation entropies for surface dislocation nucleation.
" }, { "name": "Welinder, Nils Peter Egon", "degree": "PhD", "year": "2012", "title": "Hybrid Human-Machine Vision Systems: Image Annotation using Crowds, Experts and Machines", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302012-110814322", "creators": [ { "name": { "family": "Welinder", "given": "Nils Peter Egon" }, "id": "Welinder-Nils-Peter-Egon", "display_name": "Welinder, Nils Peter Egon" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Krause", "given": "Andreas" }, "id": "Krause-A", "role": "member", "display_name": "Krause, Andreas" }, { "name": { "family": "Belongie", "given": "Serge J." }, "id": "Belongie-S-J", "role": "member", "display_name": "Belongie, Serge J." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "cns" ], "doi": "10.7907/N6A2-F347", "abstract": "The amount of digital image and video data keeps increasing at an ever-faster rate. While \"big data\" holds the promise of leading science to new discoveries, raw image data in itself is not of much use. In order to statistically analyze the data, it must be quantified and annotated. We argue that entirely automated methods are not accurate enough to annotate data in the short term. Crowdsourcing is an alternative that provides higher accuracy, but is too expensive to scale to millions of images. Instead, the solution is hybrid human-machine vision systems, where the work of both humans and machines is balanced to be as cost-effective and accurate as possible. With this goal in mind, we begin by categorizing different types of image annotations, and describe how nonexpert annotators can be trained to carry out challenging image annotation tasks. Having identified which types of annotations are appropriate for most tasks, including binary, confidence, pair-wise and continuous annotations, we present models for crowdsourcing annotations from hundreds of expert and nonexpert annotators (humans). By trading off the bias and expertise of multiple annotators, we show that it is possible to achieve high-quality annotations with very few labels. We show that the number of labels can be further reduced by actively choosing the best annotators to carry out most of the work. Finally, we study the problem of estimating the performance of automated classifiers (machines) used to annotate large datasets where few ground truth labels are available. Using a semisupervised model for classifier confidence scores, we show that it is possible to accurately estimate classifier performance with very few labels." }, { "name": "Yoo, Juhwan", "degree": "PhD", "year": "2012", "title": "Compressed Sensing Receivers: Theory, Design, and Performance Limits", "advisor": "Emami, Azita", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122012-144158047", "creators": [ { "name": { "family": "Yoo", "given": "Juhwan" }, "id": "Yoo-Juhwan", "display_name": "Yoo, Juhwan" } ], "advisors": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "advisor", "display_name": "Emami, Azita" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "chair", "display_name": "Emami, Azita" }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Y3FA-VB87", "abstract": "The past 50 years have seen tremendous developments in electronics due to the rise and rapid development of IC-fabrication technology [1]. In addition to the production of cheap and abundant computing resources, another area of rapid advancement has been wireless technologies. While the central focus of wireless research has been mobile communication, an area of increasing importance concerns the development of sensing/spectral applications over bandwidths exceeding multiple GHz. Such systems have many applications ranging from scientific to military. Although some solutions exist, their large size, weight, and power make more-efficient solutions desirable.
\r\n\r\nAt present, one of the principal bottlenecks in designing such systems is the power consumption of the back-end ADCs at the required digitization rate. ADCs are a dominant source of power consumption; it is also often the case that ADC block specifications are used to determine parameters for the rest of the signal chain, such as the RF front-end and the DSP-core which processes the digitized samples [2]. Historically, increases in system bandwidth have come from developing ADCs with superior performance.
\r\n\r\nIn contrast to improving ADC performance, this work presents a system-level approach with the goal of minimizing the required digitization rate for observation of a given effective instantaneous bandwidth (EIBW). The approach was inspired by the field of compressed sensing [3\u20135]. Loosely stated, CS asserts that samples which represent random projections can be used to recover sparse and/or compressible signals with what was previously thought to be insufficient information. The primary contributions of this thesis include: the establishment of physical feasibility of CS-based receivers through implementation of the first fully-integrated high speed CS-based front-end known as the random-modulation pre-integrator (RMPI) [6\u20139], and the development of a principled design methodology based on a rigorous analytical and empirical feasibility study of the system.
\r\n\r\nThe 8-channel RMPI was implemented in 90 nm CMOS and was validated by physical measurements of the fabricated chip. The implemented RMPI achieves an EIBW of 2 GHz, with > 54 dB of dynamic range. Most notably, the aggregate digitization rate is fs = 320 Msps, 12.5\u00d7 lower than the Nyquist rate.
\r\n\r\n" }, { "name": "Yu, Ted H.", "degree": "PhD", "year": "2012", "title": "Degradations and Improvements in PEM Fuel Cell Materials: A Computational Study\r ", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042012-095544878", "creators": [ { "name": { "family": "Yu", "given": "Ted H." }, "id": "Yu-Ted-H", "display_name": "Yu, Ted H." } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/0CYM-2B74", "abstract": "The advantages of Proton Exchange Membrane (PEM) fuel cells include lower operating temperature than other fuel cells and size small enough to fit into a car. Improving the cost and durability of PEM fuel cell materials is a hot topic of research today.
\r\n\r\nThe Nafion membrane and cathode catalysts are two areas where PEM fuel cells have issues of cost, durability, and efficiency. In order to improve these materials, researchers need a better understanding of the detailed mechanisms for basic operation and degradation. Computational quantum mechanics has improved in recent years to the point where it can provide accurate potential energy maps of reactions that are difficult to determine by laboratory experiments alone. With the basic understanding of mechanisms, experimentalists can make educated predictions of ways to improve fuel cell materials.
\r\n\r\nExperimental studies suggest that Nafion degradation is caused by generation of trace radical species (such as OH\u25cf, H\u25cf) when in the presence of H2, O2, and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H2 (or H+) and O2 in the presence of the Pt catalyst. We find that OH\u25cf can be generated in trace amounts on the Pt surface from HOOH and OOHad. Next, we look at various ways in which the OH\u25cf can attack the Nafion sidechains or endgroups on the backbone.
\r\n\r\nResearchers are looking for ways to replace the Pt cathode catalyst, due to the preciousness of Pt and the low efficiency of the oxygen reduction reaction (ORR) on Pt, among other things. Alloying Pt with non-precious Co greatly increases the ORR efficiency. However, Pt3Co was reported to not withstand long-cycle testing due to the migration of Co metals onto the catalyst surface and leaching of Co into the electrolyte. To overcome these challenges, we first study Pt3Co to find out what makes these alloys so special in improving fuel cell efficiency, as well as what causes degradation to occur. Then, we apply the principles we learned in proposing improved fuel cell alloy catalysts.
" }, { "name": "Ziegler, John Lewis (Jack)", "degree": "PhD", "year": "2012", "title": "Simulations of Compressible, Diffusive, Reactive Flows with Detailed Chemistry Using a High-Order Hybrid WENO-CD Scheme", "advisor": "Pullin, Dale Ian; Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12302011-185742249", "creators": [ { "name": { "family": "Ziegler", "given": "John Lewis (Jack)" }, "id": "Ziegler-John-Lewis-Jack", "orcid": "0000-0001-6127-5567", "display_name": "Ziegler, John Lewis (Jack)" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "co-advisor", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "co-advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZKW8-ES97", "abstract": "A hybrid weighted essentially non-oscillatory (WENO)/centered-difference (CD) numerical method, with low numerical dissipation, high-order shock-capturing, and structured adaptive mesh refinement (SAMR), has been developed for the direct numerical simulation (DNS) of the multicomponent, compressive, reactive Navier-Stokes equations. The method enables accurate resolution of diffusive processes within reaction zones. This numerical method is verified with a series of one- and two-dimensional test problems, including a convergence test of a two-dimensional unsteady reactive double Mach reflection problem. Validation of the method is conducted with experimental comparisons of three applications all of which model multi-dimensional, unsteady reactive flow: an irregular propane detonation, shock and detonation bifurcations, and spark ignition deflagrations.
\r\n\r\nThe numerical approach combines time-split reactive source terms with a high-order, shock-capturing scheme specifically designed for diffusive flows. A description of the order-optimized, symmetric, finite difference, flux-based, hybrid WENO / centered-difference scheme is given, along with its implementation in a high-order SAMR framework. The implementation of new techniques for discontinuity flagging, scheme-switching, and high-order prolongation and restriction is described. In particular, the refined methodology does not require upwinded WENO at grid refinement interfaces for stability, allowing high-order prolongation and thereby eliminating a significant source of numerical diffusion within the overall code performance.
\r\n\r\nA minimally reduced irregular detonation mixture mechanism (22 species and 53 reversible reactions) is developed and combined with the WENO-CD numerical method to accurately model two-dimensional hydrocarbon (propane) detonations with detailed chemistry and transport. First of its kind, resolved double Mach reflection (DMR) detonation simulations with a large hyrdocarbon mixture are presented. Detailed discussions and comparisons of the influence of grid resolution, lower-order numerical methods, and inviscid approximations are made in addition to the detailed presentation of fluid dynamics found in an unsteady, highly unstable, reactive DMR simulation. Also conducted are direct experimental comparisons to soot foils and schlieren images with an unresolved large-scale propane detonation channel simulation.
\r\n\r\nThe numerical method is also applied to the DNS of two other problems, detonation/shock bifurcations and spark ignited deflagrations. Through the resolution of viscous/diffusive scales, new insights into how a bifurcated foot develops after a detonation end wall reflection, and how geometry can influence the development of a flame kernel after spark ignition are found.
\r\n" }, { "name": "Aly, Mohamed Alaa El-Dien Mahmoud Hussein", "degree": "PhD", "year": "2011", "title": "Searching Large-Scale Image Collections", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:04252011-145432540", "creators": [ { "name": { "family": "Aly", "given": "Mohamed Alaa El-Dien Mahmoud Hussein" }, "id": "Aly-Mohamed-Alaa-El-Dien-Mahmoud-Hussein", "display_name": "Aly, Mohamed Alaa El-Dien Mahmoud Hussein" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Munich", "given": "Mario E." }, "id": "Munich-M-E", "role": "member", "display_name": "Munich, Mario E." } ], "option_major": [ "eleceng" ], "doi": "10.7907/VRGJ-4J54", "abstract": "Searching quickly and accurately in a large collection of images has become an increasingly important problem. The ultimate goal is to make visual search possible: allow users to search using images in addition to typing text. The typical approach is to index all the images of interest (e.g., images of landmarks, books, or DVDs) in a database and let users question the system with query images. Such a database can reach billions of images, and this poses challenges in terms of memory and computational requirements and recognition performance. In this work we provide an in depth study of systems used for searching large-scale image collections. \r\n\r\nSpecifically, we provide a thorough comparison of the two leading image search approaches: Full Representation (FR) vs. Bag of Words (BoW). We derive theoretical estimates of how the memory and computational cost scale with the number of images in the database, and empirically evaluate the performance and run time on four real-world datasets. Our experiments suggest that FR provides better recognition performance than BoW, though it requires more memory. Therefore, we address these shortcomings by presenting novel methods that increase the recognition performance of BoW and decrease the memory requirements of FR. Finally, we present a novel way to parallelize FR on multiple machines and scale up database sizes to 100 million images with interactive run time." }, { "name": "Andreetto, Marco", "degree": "PhD", "year": "2011", "title": "Unsupervised Learning of Categorical Segments in Image Collections", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:04262011-213152111", "creators": [ { "name": { "family": "Andreetto", "given": "Marco" }, "id": "Andreetto-Marco", "display_name": "Andreetto, Marco" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Welling", "given": "Max" }, "id": "Welling-M", "role": "member", "display_name": "Welling, Max" }, { "name": { "family": "Belongie", "given": "Serge J." }, "id": "Belongie-S-J", "role": "member", "display_name": "Belongie, Serge J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZH04-VT55", "abstract": "Which one comes first: segmentation or recognition? We propose a unified framework for carrying out the two simultaneously and without supervision. The framework combines a flexible probabilistic model for representing the shape and appearance of each segment, with the popular \"bag of visual words\" model for recognition. If applied to a collection of images, our framework can simultaneously discover the segments of each image, and the correspondence between such segments, without supervision. Such recurring segments may be thought of as the \"parts\" of corresponding objects that appear multiple times in the image collection. Thus, the model may be used for learning new categories, detecting/classifying objects, and segmenting images, without using expensive human annotation." }, { "name": "Becker, Stephen R.", "degree": "PhD", "year": "2011", "title": "Practical Compressed Sensing: Modern Data Acquisition and Signal Processing", "advisor": "Candes, Emmanuel J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022011-152525054", "creators": [ { "name": { "family": "Becker", "given": "Stephen R." }, "id": "Becker-Stephen-R", "orcid": "0000-0002-1932-8159", "display_name": "Becker, Stephen R." } ], "advisors": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "advisor", "display_name": "Candes, Emmanuel J." } ], "committee": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "chair", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Vandenberghe", "given": "Lieven" }, "id": "Vandenberghe-L", "role": "member", "display_name": "Vandenberghe, Lieven" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/DC16-K322", "abstract": "Since 2004, the field of compressed sensing has grown quickly and seen tremendous interest because it provides a theoretically sound and computationally tractable method to stably recover signals by sampling at the information rate. This thesis presents in detail the design of one of the world's first compressed sensing hardware devices, the random modulation pre-integrator (RMPI). The RMPI is an analog-to-digital converter (ADC) that bypasses a current limitation in ADC technology and achieves an unprecedented 8 effective number of bits over a bandwidth of 2.5 GHz. Subtle but important design considerations are discussed, and state-of-the-art reconstruction techniques are presented.
\r\n\r\nInspired by the need for a fast method to solve reconstruction problems for the RMPI, we develop two efficient large-scale optimization methods, NESTA and TFOCS, that are applicable to a wide range of other problems, such as image denoising and deblurring, MRI reconstruction, and matrix completion (including the famous Netflix problem). While many algorithms solve unconstrained l1 problems, NESTA and TFOCS can solve the constrained form of l1 minimization, and allow weighted norms. In addition to l1 minimization problems such as the LASSO, both NESTA and TFOCS solve total-variation minimization problem. TFOCS also solves the Dantzig selector and most variants of the nuclear norm minimization problem. A common theme in both NESTA and TFOCS is the use of smoothing techniques, which make the problem tractable, and the use of optimal first-order methods that have an accelerated convergence rate yet have the same cost per iteration as gradient descent. The conic dual methodology is introduced in TFOCS and proves to be extremely flexible, covering such generic problems as linear programming, quadratic programming, and semi-definite programming. A novel continuation scheme is presented, and it is shown that the Dantzig selector benefits from an exact-penalty property. Both NESTA and TFOCS are released as software packages available freely for academic use.
" }, { "name": "Beni, Catherine Elizabeth", "degree": "PhD", "year": "2011", "title": "Simulation Capabilities for Challenging Medical Imaging and Treatment Planning Problems", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272011-085600111", "creators": [ { "name": { "family": "Beni", "given": "Catherine Elizabeth" }, "id": "Beni-Catherine-Elizabeth", "display_name": "Beni, Catherine Elizabeth" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/8PBA-RN43", "abstract": "Advanced numerical solvers and associated simulation tools, such as, for example, numerical algorithms based on novel spectral methods, efficient time-stepping and domain meshing techniques for solution of Partial Differential Equations (PDEs) (enabling, in particular, effective resolution of extremely steep boundary layers in short computing times), can have a significant impact in the design of medical procedures. In this thesis we present three recently introduced numerical algorithms for medical problems whose performance improves significantly over those of earlier counterparts, and which can thereby provide solutions to a range of challenging computational problems for planning and design of medical treatments." }, { "name": "Boechler, Nicholas Sebastian", "degree": "PhD", "year": "2011", "title": "Granular Crystals: Controlling Mechanical Energy with Nonlinearity and Discreteness", "advisor": "Daraio, Chiara", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162011-131929134", "creators": [ { "name": { "family": "Boechler", "given": "Nicholas Sebastian" }, "id": "Boechler-Nicholas-Sebastian", "orcid": "0000-0001-9639-1533", "display_name": "Boechler, Nicholas Sebastian" } ], "advisors": [ { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "advisor", "display_name": "Daraio, Chiara" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Davis", "given": "Gregory L." }, "id": "Davis-G-L", "role": "member", "display_name": "Davis, Gregory L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BAHK-WD44", "abstract": "The presence of structural discreteness and periodicity can affect the propagation of phonons, sound, and other mechanical waves. A fundamental property of many of the periodic structures and materials designed for this purpose is the presence of complete band gaps in their dispersion relation. Waves with frequencies in the band gap cannot propagate and are reflected by the material. Like the concept of a band gap, the functionality of these periodic structures has historically been based on concepts from linear dynamics. Nonlinear systems can offer increased flexibility over linear systems including new ways to localize energy, convert energy between frequencies, and tune the response of the system. Granular crystals are arrays of elastic particles that interact nonlinearly via Hertzian contact, and are a type of nonlinear periodic structure whose response to dynamic excitations can be tuned to encompass linear, weakly nonlinear, and strongly nonlinear regimes. Drawing on ideas from condensed matter physics and nonlinear science, this thesis focuses on how the nonlinearity and structural discreteness of granular crystals can be used to control mechanical energy. The dynamic response of one-dimensional granular crystals composed of compressed elastic spheres (or cylinders) is studied using a combination of experimental, numerical, and analytical techniques. The discovery of fundamental physical phenomena occurring in the linear and weakly nonlinear regimes is described, along with how such phenomena can be used to create new ways to control the propagation of mechanical wave energy. The specific mechanisms investigated include tunable frequency band gaps, discrete breathers, nonlinear localized defect modes, and bifurcations. These mechanisms are utilized to create novel devices for tunable vibration filtering, energy harvesting and conversion, and tunable acoustic rectification." }, { "name": "Briggs, Ryan Morrow", "degree": "PhD", "year": "2011", "title": "Hybrid Silicon Nanophotonic Devices: Enhancing Light Emission, Modulation, and Confinement", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312011-175622776", "creators": [ { "name": { "family": "Briggs", "given": "Ryan Morrow" }, "id": "Briggs-Ryan-Morrow", "display_name": "Briggs, Ryan Morrow" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "matsci" ], "doi": "10.7907/G19Z-CY24", "abstract": "Silicon has become an increasingly important photonic material for communications, information processing, and sensing applications. Silicon is inexpensive compared to compound semiconductors, and it is well suited for confining and guiding light at standard telecommunication wavelengths due to its large refractive index and minimal intrinsic absorption. Furthermore, silicon-based optical devices can be fabricated alongside microelectronics while taking advantage of advanced silicon processing technologies. In order to realize complete chip-based photonic systems, certain critical components must continue to be developed and refined on the silicon platform, including compact light sources, modulators, routers, and sensing elements. However, bulk silicon is not necessarily an ideal material for many active devices because of its meager light emission characteristics, limited refractive index tunability, and fundamental limitations in confining light beyond the diffraction limit.
\r\n\r\nIn this thesis, we present three examples of hybrid devices that use different materials to bring additional optical functionality to silicon photonics. First, we analyze high-index-contrast silicon slot waveguides and their integration with light-emitting erbium-doped glass materials. Theoretical and experimental results show significant enhancement of spontaneous emission rates in slot structures. We then demonstrate the integration of vanadium dioxide, a thermochromic phase-change material, with silicon waveguides to form micron-scale absorption modulators. It is shown experimentally that a 2-\u00b5m long waveguide-integrated device exhibits broadband modulation of more than 6.5 dB at wavelengths near 1550 nm. Finally, we demonstrate polymer-on-gold dielectric-loaded surface-plasmon waveguides and ring resonators coupled to silicon waveguides with 1.0\u00b10.1 dB insertion loss. The plasmonic waveguides are shown to support a single surface mode at telecommunication wavelengths, with strong electromagnetic field confinement at the polymer-gold interface. These three device concepts show that diverse materials can be integrated with silicon waveguides to achieve enhanced light emission, broadband modulation, and strong confinement, all while retaining the advantages of the silicon photonics platform.
" }, { "name": "Brown, Evan Cornell", "degree": "PhD", "year": "2011", "title": "Electrochemically Deposited Ceria Structures for Advanced Solid Oxide Fuel Cells", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-123505549", "creators": [ { "name": { "family": "Brown", "given": "Evan Cornell" }, "id": "Brown-Evan-Cornell", "display_name": "Brown, Evan Cornell" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" } ], "option_major": [ "matsci" ], "doi": "10.7907/93NE-TG09", "abstract": "As the pursuit towards emissions reduction intensifies with growing interest and nascent technologies, solid oxide fuel cells (SOFCs) remain an illustrious candidate for achieving our goals. Despite myriad advantages, SOFCs are still too costly for widespread deployment, even as unprecedented materials developments have recently emerged. This suggests that, in addition to informed materials selection, the necessary power output\u2014and, thereby, cost-savings\u2014gains must come from the fuel cell architecture. The work presented in this manuscript primarily investigates cathodic electrochemical deposition (CELD) as a scalable micro-/nanoscale fabrication tool for engineering ceria-based components in a SOFC assembly. Also, polymer sphere lithography was utilized to deposit fully connected, yet fully porous anti-dot metal films on yttira-stabilized zirconia (YSZ) with specific and knowable geometries, useful for mechanistic studies. Particular attention was given to anode structures, for which anti-dot metal films on YSZ served as composite substrates for subsequent CELD of doped ceria. By tuning the applied potential, a wide range of microstructures from high surface area coatings to planar, thin films was possible. In addition, definitive deposition was shown to occur on the electronically insulating YSZ surfaces, producing quality YSZ|ceria interfaces. These CELD ceria deposits exhibited promising electrochemical activity, as probed by A.C. Impedance Spectroscopy. In an effort to extend its usefulness as a SOFC fabrication tool, the CELD of ceria directly onto common SOFC cathode materials without a metallic phase was developed, as well as templated deposition schemes producing ceria nanowires and inverse opals." }, { "name": "Brown, Justin Lee", "degree": "PhD", "year": "2011", "title": "High Pressure Hugoniot Measurements in Solids Using Mach Reflections", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242011-143955754", "creators": [ { "name": { "family": "Brown", "given": "Justin Lee" }, "id": "Brown-Justin-Lee", "display_name": "Brown, Justin Lee" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "mecheng" ], "doi": "10.7907/SC1V-PK42", "abstract": "Shock compression experiments provide access to high pressures in a laboratory setting. Matter at extreme pressures is often studied by utilizing a well controlled planar impact between two flat plates to generate a one dimensional shock wave. While these experiments are a powerful tool in equation of state (EOS) development, they are inherently limited by the velocity of the impacting plate. In an effort to dramatically increase the range of pressures which can be studied with available impact velocities, a new experimental technique is examined. The target plate is replaced by a composite assembly consisting of two concentric cylinders and is designed such that the initial shock velocity in a well characterized outer cylinder is higher than in the inner cylinder material of interest. After impact, conically converging shocks are generated at the interface due to the impedance mismatch between the two materials and the axisymmetric geometry. Upon convergence, an irregular reflection occurs and the conical analog of a Mach reflection develops. This Mach reflection grows until it reaches a steady state, for which an extremely high pressure state is concentrated behind the Mach stem. The reflection is studied using a combination of analytical, numerical, and experimental techniques. Ideas from gas dynamics, such as shock polars, are connected to the classic treatment of one-dimensional shocks in solids to form a simple method for treating the oblique reflections in the Mach lens configuration. Numerical simulations provide detailed full-field solutions and illustrate a methodology for extracting EOS information. The technique is validated experimentally by studying the shock response of copper and iron. Two different confining materials, 6061-T6 aluminum and molybdenum, are used to drive the converging shock waves for which the high pressure state is measured through a combination of velocity interferometry and impedance matching techniques." }, { "name": "Buchfuhrer, David Isaac", "degree": "PhD", "year": "2011", "title": "Limits on Computationally Efficient VCG-Based Mechanisms for Combinatorial Auctions and Public Projects", "advisor": "Umans, Christopher M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242011-112814785", "creators": [ { "name": { "family": "Buchfuhrer", "given": "David Isaac" }, "id": "Buchfuhrer-David-Isaac", "display_name": "Buchfuhrer, David Isaac" } ], "advisors": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "advisor", "display_name": "Umans, Christopher M." } ], "committee": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "chair", "display_name": "Umans, Christopher M." }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." } ], "option_major": [ "compsci" ], "doi": "10.7907/N0M7-C473", "abstract": "A natural goal in designing mechanisms for auctions and public projects is to maximize the social welfare while incentivizing players to bid truthfully. If these are the only concerns, the problem is easily solved by use of the VCG mechanism. Unfortunately, this mechanism is not computationally efficient in general and there are currently no other general methods for designing truthful mechanisms. However, it is possible to design computationally efficient VCG-based mechanisms which approximately maximize the social welfare.
\r\n \r\nWe explore the design space of computationally efficient VCG-based mechanisms under submodular valuations and show that the achievable approximation guarantees are poor, even compared to efficient non-truthful algorithms. Some of these approximation hardness results stem from an asymmetry in the information available to the players versus that available to the mechanism. We develop an alternative Instance Oracle model which reduces this asymmetry by allowing the mechanism to access some computational capabilities of the players. By building assumptions about player computation into the model, a more realistic study of mechanism design can be undertaken.
\r\n \r\nFinally, we give VCG-based mechanisms for some problems in the Instance Oracle model which achieve provably better approximations than the best VCG-based mechanism in the standard model. However, for other problems we give reductions in the Instance Oracle model which prove inapproximability results as strong as those shown in the standard model. These provide more robust hardness results that are not simply artifacts of the asymmetry in the standard model.
" }, { "name": "Choi, Jae-Woo", "degree": "PhD", "year": "2011", "title": "Surface Optofluidic Implementations towards the Development of a Biosensor", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:03242011-165209307", "creators": [ { "name": { "family": "Choi", "given": "Jae-Woo" }, "id": "Choi-Jae-Woo", "display_name": "Choi, Jae-Woo" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Willis", "given": "Peter" }, "id": "Willis-P", "role": "member", "display_name": "Willis, Peter" } ], "option_major": [ "eleceng" ], "doi": "10.7907/KYZG-3503", "abstract": "Microfluidics is a multidisciplinary field that uses minute volumes of liquids to attempt complex functionalities. These complicated functionalities often require manipulating interfaces through external forces. In addition, optics have become a fundamental necessity for most microfluidic devices. We combine these two concepts and call it surface optofluidics. Here, we focus on the advantages of surface optofluidics for the development of a biosensor, specifically focusing on the flexibility and adaptability offered by these techniques.
\r\n\r\nTo introduce the advantages presented by surface optofluidics, devices using droplet electrowetting techniques are discussed. We then discuss biosensing through structured electrodes on surfaces. The electrodes are used to align asymmetric bacteria. The aligned bacteria are detected optically. This method of detection is improved by incorporating two different surface optofluidic methods. Concentration and motion control of the bacterium is demonstrated with electric fields on three dimensionally structured electrodes and an optothermal nanoparticle carpet. Finally, we show preliminary work in the study of single bacterium behavior using nanoparticles as labels to detect its specific alignment in space.
\r\n" }, { "name": "Chueh, William C.", "degree": "PhD", "year": "2011", "title": "Electrochemical and Thermochemical Behavior of CeO\u2082-\u03b4", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11042010-235339265", "creators": [ { "name": { "family": "Chueh", "given": "William C." }, "id": "Chueh-William-C", "display_name": "Chueh, William C." } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" } ], "option_major": [ "matsci" ], "doi": "10.7907/EBKT-ET32", "abstract": "The mixed-valent nature of nonstoichiometric ceria (CeO2-\u03b4) gives rise to a wide range of intriguing properties, such as mixed ionic and electronic conduction and oxygen storage. Surface and transport behavior in rare-earth (samaria) doped and undoped ceria were investigated, with particular emphasis on applications in electrochemical and thermochemical energy conversion processes such as fuel cells and solar fuel production. The electrochemical responses of bulk- processed ceria with porous Pt and Au electrodes were analyzed using 1-D and 2-D transport models to decouple surface reactions, near-surface transport and bulk transport. Combined experimental and numerical results indicate that hydrogen electro-oxidation and hydrolysis near open-circuit conditions occur preferentially over the ceria | gas interface rather than over the ceria | gas | metal interface, with the rate-limiting step likely to be either surface reaction or transport through the surface oxygen vacancy depletion layer. In addition, epitaxial thin films of ceria were grown on zirconia substrates using pulsed-laser deposition to examine electrocatalysis over well-defined microstructures. Physical models were derived to analyze the electrochemical impedance response. By varying the film thickness, interfacial and chemical capacitance were decoupled, with the latter shown to be proportional to the small polaron densities. The geometry of microfabricated metal current collectors (metal = Pt, Ni) was also systematically varied to investigate the relative activity of the ceria | gas and the ceria | metal | gas interfaces. The data suggests that the electrochemical activity of the metal-ceria composite is only weakly dependent on the metal due to the relatively high activity of the ceria | gas interface. In addition to electrochemical experiments, thermochemical reduction-oxidation studies were performed on ceria. It was shown that thermally-reduced ceria, upon exposure to H2O and/or CO2, can be reoxidized to form H2, CO, and/or CH4. Analysis of gas evolution rates confirms that the kinetics of ceria oxidation by H2O and CO2 are dominated by surface reactions, rather than by ambipolar oxygen diffusion. Temperature-programmed oxidation experiments revealed that, even under thermodynamically favored conditions, carbonaceous species do not form on the surface of neat ceria, thereby giving a high CO selectivity when dissociating CO2. A scaled-up ceria-based solar reactor was designed and tested to demonstrate the feasibility of solar fuel production via thermochemical cycling." }, { "name": "Elbanna, Ahmed Ettaf", "degree": "PhD", "year": "2011", "title": "Pulselike Ruptures on Strong Velocity-Weakening Frictional Interfaces: Dynamics and Implications", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12122010-174517720", "creators": [ { "name": { "family": "Elbanna", "given": "Ahmed Ettaf" }, "id": "Elbanna-Ahmed-Ettaf", "display_name": "Elbanna, Ahmed Ettaf" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Ampuero", "given": "Jean-Paul" }, "id": "Ampuero-J-P", "role": "member", "display_name": "Ampuero, Jean-Paul" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/80MV-6Y66", "abstract": "Seismic inversion and computational models have shown that earthquake ruptures may propagate in one of two basic modes; the cracklike mode and the slip pulse mode. In this work we use analytical and numerical techniques to study the dynamics and implications of pulselike ruptures propagating on strong velocity-weakening frictional interfaces using both discrete and continuum models of fracture.
\r\n\r\nResults of the study of the discrete spring block slider model suggest that strong velocity-weakening friction might yield to the propagation of unsteady slip pulses and chaotic dynamics. The prestress in most of these systems evolves into very heterogeneous spatial distributions characterized, in general, by non-Gaussian statistics and power-law spectral properties. It is also shown that the combined effect of slip pulse propagation and strong velocity-weakening friction could yield to size effects in strength with the strength decreasing as a power law with increasing rupture length.
\r\n\r\nBy examining the energy budget of slip pulses in the discrete model, we show that it is possible to derive a nonlinear differential equation that could predict the final slip distribution in an event, given the prestress existing before that event and some information about friction and pulse dynamics. The equation is successful in replicating many of the macroscopic slip features, including the slip distribution and total rupture length, can also match many long-time statistics regarding the prestress evolution and the event size distribution.
\r\n\r\nResults from the continuum study suggest that the absence of steady pulses in previous studies could be attributed to the details of the nucleation procedure. We show that steady pulses could exist on strong velocity-weakening friction and uniform prestress if both the prestress and nucleation procedures are correctly tuned. We find that steady pulses are unstable to perturbations in the form of a step in the prestress and could arrest quickly in regions of low prestress. Steady pulses are also found to adapt well to local fluctuations in the prestress, leading to heterogeneous slip distributions. This result might have important implications for the problem of slip complexity in real earthquakes.
\r\n" }, { "name": "Farnsworth, Claire Elizabeth", "degree": "PhD", "year": "2011", "title": "Processes Controlling the Fate and Transport of Trace Metals in the Subsurface During Changing Redox Potential", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05132011-121157483", "creators": [ { "name": { "family": "Farnsworth", "given": "Claire Elizabeth" }, "id": "Farnsworth-Claire-Elizabeth", "display_name": "Farnsworth, Claire Elizabeth" } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "chair", "display_name": "Hering, Janet G." }, { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "member", "display_name": "Adkins, Jess F." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Orphan", "given": "Victoria J." }, "id": "Orphan-V-J", "role": "member", "display_name": "Orphan, Victoria J." } ], "option_major": [ "envreng" ], "doi": "10.7907/TB3A-Z569", "abstract": "This study investigated the cycling of Mn and Fe as oxic surface water entered shallow sediments and was reduced, and as reduced groundwater became exposed to oxygen and was oxidized. A Mn-oxide doped gel probe sampler was developed to study in situ rates of reductive dissolution and was validated with laboratory studies with ascorbic acid and Shewanella oneidensis MR-1 as model reductants. The sampler was deployed in the bank sediments of Lake Tegel, Berlin, Germany. Modeling of the diffusion-controlled reaction converted the mass loss from the gels in the sampler to a profile of pseudo-first-order rate constants as a function of depth. The rate constants were highest at depths with high dissolved Fe and low operationally defined fractions of reducible oxides of Fe and Mn in the sediments.
\r\n\r\nA laboratory column experiment showed that 1.3-m water table fluctuations, as observed in bank filtration sites around Berlin, were able to provide sufficient dissolved oxygen delivery for Pseudomonas putida GB-1, an obligate aerobe, to oxidize Mn(II) in situ. Accumulation of Mn on the quartz sand in the column at the end of the experiment was limited to the top 60 cm, as measured with X-ray fluorescence (XRF), and X-ray absorption spectroscopy (XAS) analysis confirmed that the solid formed was a Mn(IV) oxide characteristic of biogenic origin. After a period of \u201cfilter ripening\u201d in the column, rates of in situ oxidation were still lower than rates in engineered aerated sand filters.
\r\n\r\nAdjacent to a production well with a water table that fluctuates up to 7 m annually at Lake Tegel, however, sediments collected from a borehole did not show any significant accumulation of Mn or Fe with depth, as measured by XRF; analysis of the speciation of Mn and Fe in the solid phase by XAS suggested a slight increase in the proportions of total Mn as Mn(II) and of total Fe as Fe(II) with depth. At this location, vertical zonation of groundwater may preclude the co-occurrence of reduced Mn and Fe with dissolved oxygen entrapped by water table fluctuations. Whether groundwater changes from oxidizing to reducing conditions or vice versa, the behavior of Mn and Fe reflects a complex interaction between sediments, solutes, microbial activity, and hydrology.
" }, { "name": "Fuller, Sawyer Buckminster", "degree": "PhD", "year": "2011", "title": "Steady as She Goes: Visual Autocorrelators and Antenna-Mediated Airspeed Feedback in the Control of Flight Dynamics in Fruit Flies and Robotics ", "advisor": "Murray, Richard M.; Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechThesis:06082011-191034348", "creators": [ { "name": { "family": "Fuller", "given": "Sawyer Buckminster" }, "id": "Fuller-Sawyer-Buckminster", "display_name": "Fuller, Sawyer Buckminster" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "co-advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Straw", "given": "Andrew" }, "id": "Straw-A", "role": "member", "display_name": "Straw, Andrew" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "bioeng" ], "doi": "10.7907/Z3D0-GG27", "abstract": "Achieving agile autonomous flight by an insect-sized micro aerial vehicle (MAV) will require improved technology that is radically smaller, lighter, and more power-efficient. One animal that has solved the problem is the fly, a virtuoso among insect flyers whose nervous system can perform sophisticated aerial maneuvers under severe computational constraints. This thesis is concerned with understanding and emulating the dynamics of the fly's feedback control system. Because vision is noisy and information rich, processing time may a problem for a fast-moving MAV or fly. By tracking the fruit fly Drosophila melanogaster in free flight in gusts of wind, I found that they incorporate feedback from wind-sensing antennae in a fast feedback loop that dampens the forward-flight dynamics. The slower dynamics are easier to control for long-delay visual feedback, making the fly more robust to the limitations of its visual system. Using the fly as inspiration, I designed a minimal, visual autocorrelation based controller that used a small array of visual sensors to stabilize a fan-actuated hovercraft robot in a narrow corridor. Using a model for correlators developed for the robot, I showed that a uniform array of visual correlators was sufficient to explain the free-flight velocity regulation behavior of flies, rather than a different model. In addition to illustrating the benefits of concurrent scientific analysis and engineering synthesis, the results give new insight into how to control small biological and man-made flying vehicles using limited, noisy sensors." }, { "name": "Giacchino, Luca", "degree": "PhD", "year": "2011", "title": "MEMS Electrolytic Inchworms for Movable Neural Probe Applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:01102011-204907918", "creators": [ { "name": { "family": "Giacchino", "given": "Luca" }, "id": "Giacchino-Luca", "display_name": "Giacchino, Luca" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "role": "member", "display_name": "Kornfield, Julia A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GQYY-BM80", "abstract": "Over decades of cortical neural prosthesis, it was found that \"movable\" neural probes are important to track neurons for long-term, reliable prostheses. This is challenging because the ideal movable probes require low voltage, small power, bidirectional/latchable movement, and large total traveling distance. The device should also be small enough to entirely fit under the skull after implantation. Many different devices have been demonstrated to move neural probes, but none of them satisfies all the actuation and size requirements.
\r\n\r\nThis thesis presents our work on actuators for movable neural probes that combine MEMS technology with an electrolytic actuation mechanism. Each inchworm is based on two electrolytic balloon actuators. The actuators rely on gas generation by electrolysis inside a sealed balloon, which causes its expansion. When electrolysis is stopped, gas recombination and permeation across the balloon membrane cause the balloon to relax. Electrolytic actuation, although slow, has several advantages: low power, low voltage, and ability to provide large force and displacement. The balloons have been characterized and their behavior mathematically modeled. Innovative salt-shell-based and hydrogel-based processes have been developed to fabricate the balloons and to allow their replenishment by osmosis.
\r\n\r\nTwo balloons are combined into a bidirectional inchworm mechanism. Large traveling distance can be obtained in multiple cycles, the only constraint being the probe length. Displacement of a silicon probe and of a commercial metal probe have been demonstrated in both directions, with a displacement per cycle between 0.5 um and 75 um. The voltage required to drive electrolysis is typically around 3.5 V, with peak power per balloon around 100 uW. The devices were tested in air, water, and saline.
\r\n\r\nClosed-loop control of the inchworm may be needed for accurate positioning of the probe, and monitoring of the pressure inside the balloons represents a possible source of feedback from the inchworm. Parylene-membrane pressure sensors that are suitable for integration inside balloon actuators have been demonstrated.
" }, { "name": "Gomes, Ryan Geoffrey", "degree": "PhD", "year": "2011", "title": "Towards Open Ended Learning: Budgets, Model Selection, and Representation", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:02092011-171146758", "creators": [ { "name": { "family": "Gomes", "given": "Ryan Geoffrey" }, "id": "Gomes-Ryan-Geoffrey", "display_name": "Gomes, Ryan Geoffrey" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Krause", "given": "Andreas" }, "id": "Krause-A", "role": "member", "display_name": "Krause, Andreas" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Welling", "given": "Max" }, "id": "Welling-M", "role": "member", "display_name": "Welling, Max" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "cns" ], "doi": "10.7907/T92X-DQ05", "abstract": "Biological organisms learn to recognize visual categories continuously over the course of their lifetimes. This impressive capability allows them to adapt to new circumstances as they arise, and to flexibly incorporate new object categories as they are discovered. Inspired by this capability, we seek to create artificial recognition systems that can learn in a similar fashion.
\r\n\r\nWe identify a number of characteristics that define this Open Ended learning capability. Open Ended learning is unsupervised: object instances need not be explicitly labeled with a category indicator during training. Learning occurs incrementally as experience ensues; there is no training period that is distinct from operation and the categorization system must operate and update itself in a timely fashion with limited computational resources. Open Ended learning systems must flexibly adapt the number of categories as new evidence is uncovered.
\r\n\r\nHaving identified these requirements, we develop Open Ended categorization systems based on probabilistic graphical models and study their properties. From the perspective of building practical systems, the most challenging requirement of Open Ended learning is that it must be carried out in an unsupervised fashion. We then study the question of how best to represent data items and categories in unsupervised learning algorithms in order to extend their domain of application.
\r\n\r\nFinally, we conclude that continuously learning categorization systems are likely to require human intervention and supervision for some time to come, which suggests research in how best to structure machine-human interactions. We end this thesis by studying a system that reverses the typical role of human and machine in most learning systems. In Crowd Clustering, humans perform the fundamental image categorization tasks, and the machine learning system evaluates and aggregates the results of human workers.
" }, { "name": "Gonzalez, Marcial", "degree": "PhD", "year": "2011", "title": "Energy and Force Stepping Integrators in Lagrangian Mechanics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052010-230939247", "creators": [ { "name": { "family": "Gonzalez", "given": "Marcial" }, "id": "Gonzalez-Marcial", "display_name": "Gonzalez, Marcial" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SP10-A207", "abstract": "The overarching goal of this thesis is to develop new numerical time integration schemes for Lagrangian mechanics that better cope with the challenges of understanding the dynamic behavior of materials. We specifically address the formulation of convergent time integration schemes that exhibit good long-term behavior---such as conferred by symplecticity and exact conservation properties---and that have the ability to automatically and asynchronously modulate the time step in different regions of the domain. We achieve these properties in a progression of three developments: (i) energy-stepping, (ii) force-stepping, and (iii) asynchronous energy-stepping integrators. These developments are based on a new method of approximation for Lagrangian mechanics, proposed in this thesis, that consists of replacing the Lagrangian of the system by a sequence of approximate Lagrangians that can be solved exactly. Then, energy-stepping integrators result from replacing the potential energy by a piecewise constant approximation, force-stepping integrators result from replacing the potential energy by a piecewise affine approximation, and asynchronous energy-stepping integrators result from replacing localized potential energies by piecewise constant approximations. Throughout the dissertation, the properties of these time integrators are theoretically predicted and born out by a number of selected examples of application. Furthermore, we address the challenges of understanding the propagation of solitary waves in granular crystals at low impact velocity conditions by investigating the role of energy-trapping effects with the numerical time integration schemes developed in this work.\r\n" }, { "name": "Han, Si-ping", "degree": "PhD", "year": "2011", "title": "DNA Directed Self-Assembly of Carbon Nanotube Structures", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162010-142822030", "creators": [ { "name": { "family": "Han", "given": "Si-ping" }, "id": "Han-Si-ping", "orcid": "0000-0002-2213-4953", "display_name": "Han, Si-ping" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "matsci" ], "doi": "10.7907/3ZN9-T618", "abstract": "Production of pure carbon nanotube species and organization of nanoscale structure are two fundamental barriers to the utilization of CNTs in nanoelectronics. We have developed new methods to characterize double walled carbon nanotube (DWNT) structure by Raman spectroscopy and organize single walled carbon nanotube (SWNT) constructs using DNA.
\r\n\r\nFirst, using atomistic force fields calculations, we have shown that the radial breathing modes (RBM) of double walled carbon nanotubes can be accurately modeled as two uniform concentric cylindrical elastic shells coupled by a van der Waals interaction. This model leads to a simple equation which can be solved to give accurate RBMs (given diameters) or diameters (given RBMs).
\r\n\r\nSecondly, we have developed a method for using DNA origami to template the assembly of complex SWNT structures. In this process, SWNTs are modified with non-covalently attached DNA linkers that present duplex labeling domains for base pairing to complementary single stranded hooks on customized DNA origami. We show that the SWNTs attach at positions and in orientations specified by their labeling sequence, and that nanotube cross-junctions assembled from two different SWNTs in this manner can behave as field effect transistors.
\r\n\r\nFinally, we have devised a method for using DNA linkers to organize arrays of parallel SWNTs with uniform and selectable inter-nanotube separation of <20 nm. SWNTs are first dispersed in aqueous solution with DNA linkers-spacers that non-covalently anchor onto their sidewalls. When the modified SWNTs are then deposited on mica or polar lipid bilayers and allowed to diffuse on the surface, they form parallel arrays of SWNTs in which different domains of the DNA linker-spacers act to maintain array cohesion and enforce uniform separation. Thus, the use of 7 bp, 20 bp, and 60 bp DNA spacer domains result in ~3 nm, ~8.5 nm, and ~22 nm inter-nanotube separations. We further use the spacer domains as rigid scaffolds for the positioning of Streptavidin proteins between adjacent nanotubes, and give a simple method for transfer of intact arrays onto adhesive glass substrates. Further development of this technology could lead to wafer scale organization of dense parallel SWNT decorated with heterogeneous nanoscale objects.
" }, { "name": "Hariadi, Rizal Fajar", "degree": "PhD", "year": "2011", "title": "Non-Equilibrium Dynamics of DNA Nanotubes ", "advisor": "Winfree, Erik", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062011-122322347", "creators": [ { "name": { "family": "Hariadi", "given": "Rizal Fajar" }, "id": "Hariadi-Rizal-Fajar", "display_name": "Hariadi, Rizal Fajar" } ], "advisors": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "advisor", "display_name": "Winfree, Erik" } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Yurke", "given": "Bernard" }, "id": "Yurke-B", "role": "member", "display_name": "Yurke, Bernard" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "member", "display_name": "Winfree, Erik" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/6GQW-YG26", "abstract": "Can the fundamental processes that underlie molecular biology be understood and simulated by DNA nanotechnology? The early development of DNA nanotechnology by Ned Seeman was driven by the desire to find a solution to the protein crystallization problem. Much of the later development of the field was also driven by envisioned applications in computing and nanofabrication. While the DNA nanotechnology community has assembled a versatile tool kit with which DNA nanostructures of considerable complexity can be assembled, the application of this tool kit to other areas of science and technology is still in its infancy. This dissertation reports on the construction of non-equilibrium DNA nanotube dynamic to probe molecular processes in the areas of hydrodynamics and cytoskeletal behavior.
\r\n\r\nAs the first example, we used DNA nanotubes as a molecular probe for elongational flow measurement in different micro-scale flow settings. The hydrodynamic flow in the vicinity of simple geometrical objects, such as a rigid DNA nanotube, is amenable to rigorous theoretical investigation. We measured the distribution of elongational flows produced in progressively more complex settings, ranging from the vicinity of an orifice in a microfluidic chamber to within a bursting bubble of Pacific ocean water. This information can be used to constrain theories on the origin of life in which replication involves a hydrodynamically driven fission process, such as the coacervate fission proposed by Oparin.
\r\n\r\nA second theme of this dissertation is the bottom-up construction of a de novo artificial cytoskeleton with DNA nanotubes. The work reported here encompasses structural, locomotion, and control aspects of non-equilibrium cytoskeletal behavior. We first measured the kinetic parameters of DNA nanotube assembly and tested the accuracy of the existing polymerization models in the literature. Toward recapitulation of non-equilibrium cytoskeletal dynamics, we coupled the polymerization of DNA nanotubes with an irreversible energy consumption reaction, analogous to nucleotide hydrolysis in actin and microtubule polymerization. Finally, we integrated the DNA strand displacement circuits with DNA nanotube polymerization to achieve programmable kinetic control of behavior within artificial cytoskeleton. Our synthetic approach may provide insights into natural cytoskeleton dynamics, such as minimal architectural or reaction mechanism requirements for non-equilibrium behaviors including treadmilling and dynamic instability.
\r\n\r\nThe outgrowth of DNA nanotechnology beyond its own boundaries, serving as a general model system for biomolecular dynamics, can lead to an understanding of molecular processes that advances both basic and applied sciences.
" }, { "name": "Hersey, Scott Patrick", "degree": "PhD", "year": "2011", "title": "Studies of Aerosol Composition and Hygroscopicity", "advisor": "Seinfeld, John H.; Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-104023732", "creators": [ { "name": { "family": "Hersey", "given": "Scott Patrick" }, "id": "Hersey-Scott-Patrick", "display_name": "Hersey, Scott Patrick" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "co-advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Sorooshian", "given": "Armin" }, "id": "Sorooshian-A", "role": "member", "display_name": "Sorooshian, Armin" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/GZY7-P532", "abstract": "Atmospheric aerosols have significant impacts on human health, regional visibility, and the radiative energy balance of Earth, but there remain many uncertainties about their sources and evolution in the atmosphere, as well as the details and magnitude of their impact on climate. This thesis introduces a novel instrument for measuring aerosol hygroscopicity, an important factor in the overall climate impact of aerosols, and presents results from several field campaigns and laboratory experiments aimed at characterizing the chemical composition and hygroscopicity of atmospheric particles.
\r\n\r\nAerosol water uptake determines particle size, which thereby determines an aerosol's scattering properties and radiative forcing. The Differential Sizing and Hygroscopicity Spectrometer Probe (DASH-SP) was designed to make rapid measurements of hygroscopicity on timescales short enough for aircraft deployment. Combined with an iterative data processing algorithm, the DASH-SP is demonstrated to accurately measure particle size, growth, and ``effective\" refractive index for particles from 135 nm to over 1 \u03bcm on timescales as short as a few seconds.
\r\n\r\nThe DASH-SP was deployed off the coast of Central California to measure aerosol water uptake in a marine atmosphere impacted by aged anthropogenic emissions. Composition data from an Aerosol Mass Spectrometer (AMS) indicates that organics are uniformly highly oxidized (O:C ratio = 0.92 \u00b1 0.33), and aerosol growth data from the DASH-SP indicates that in such a highly-oxidized environment, growth factor GF = Dp,wet/Dp,dry) can be accurately predicted as a simple function of relative humidity (RH) and organic volume fraction.
\r\n\r\nA major ground-based sampling study was carried out in Pasadena, CA, a receptor site for transported Los Angeles pollution, and was dubbed the Pasadena Aerosol Characterization Observatory (PACO). Results indicate that organics dominate transported Los Angeles aerosols, and that they are overwhelmingly oxidized in nature. Aerosol species tend to reside in distinct size modes, with inorganics typically found in larger, accumulation-mode aerosol, while semivolatile secondary organic aerosol (SV-OOA) products appear to reside predominantly in a fine mode. Hygroscopicity was found to be a strong function of organic mass fraction (OMF).
\r\n\r\nThe end of PACO sampling coincided with a major forest fire in Los Angeles County. The impact of this fire on the sampling site is explored by comparing water soluble organic carbon (WSOC) and organic mass-to-charge (m/z) markers from the AMS. In the absence of fire influence, WSOC concentrations are primarily driven by concurrent photochemistry and sea breeze transport from source-rich areas. Fire periods are characterized by significant primary production of WSOC and overnight/early morning transport of fire emissions to the sampling site.
\r\n\r\nFinally, DASH-SP results from the May 2010 CalNex field experiment indicate that aerosol hygroscopicity is determined primarily by the mass fraction of organics and nitrate in the aerosol. Overall hygroscopicity is very similar to that measured during PACO, though organics appear to be less hygroscopic during CalNex - likely because PACO represented transported, aged aerosol, while CalNex flights covered the entirety of the LA basin, including more source-rich areas.
" }, { "name": "Hsieh, Chia-Lung", "degree": "PhD", "year": "2011", "title": "Imaging with Second-Harmonic Generation Nanoparticles", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082011-064907780", "creators": [ { "name": { "family": "Hsieh", "given": "Chia-Lung" }, "id": "Hsieh-Chia-Lung", "display_name": "Hsieh, Chia-Lung" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WCS2-FD82", "abstract": "Second-harmonic generation nanoparticles show promise as imaging probes due to their coherent and stable signal with a broad flexibility in the choice of excitation wavelength. In this thesis, we developed and demonstrated barium titanate nanoparticles as second-harmonic radiation imaging probes. We studied the absolute second-harmonic generation efficiency of the nanoparticles on single-particle level. The polarization dependent second-harmonic signal of single nanoparticles was studied in detail. From the measured polar response, we were able to find the orientation of the nanoparticle. We developed a biochemical interface for using the second-harmonic nanoprobes as biomarkers, including in vitro cellular imaging and in vivo live animal imaging. The nanoparticles were surface functionalized with primary amine groups for stable colloidal dispersion. We achieved specific labeling of the second-harmonic nanoprobes via immunostaining where the antibodies were covalently conjugated onto the nanoparticles. We observed no toxicity of the functionalized nanoparticles to biological cells. The coherent second-harmonic signal radiated from the nanoparticles offers opportunities for new imaging techniques. Using interferometric detection, namely harmonic holography, both amplitude and phase of the second-harmonic field can be captured. Through digital beam propagation, three-dimensional field distribution, reflecting three-dimensional distribution of the nanoparticles, can be reconstructed. We achieved a scan-free three-dimensional imaging of nanoparticles in biological cells with sub-micron spatial resolution by using the harmonic holographic microscope. We further exploited the coherent second-harmonic signal for imaging through scattering media by performing optical phase conjugation of the second-harmonic signal. We demonstrated an all-digital optical phase conjugation of the second-harmonic signal originated from a nanoparticle by combining harmonic holography and dynamic computer generated holography using a spatial light modulator. The phase-conjugated second-harmonic scattered field retraced the scattering trajectory and formed a clean focus on the nanoparticle placed inside a scattering medium. The nanoparticle acted as a beacon of light; it helped us find the tailored wavefront for concentrating light at the nanoparticle inside the scattering medium. We also demonstrated imaging through a thin scattering medium by raster-scanning the phase-conjugated focus in the vicinity of the beacon nanoparticle, in which a clear image of a target placed behind a ground glass diffuser was obtained." }, { "name": "Huang, Ray Kui-Jui", "degree": "PhD", "year": "2011", "title": "Flexible Neural Implants", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:07092010-104142755", "creators": [ { "name": { "family": "Huang", "given": "Ray Kui-Jui" }, "id": "Huang-Ray-Kui-Jui", "display_name": "Huang, Ray Kui-Jui" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/VMZB-0N20", "abstract": "Despite recent development in integration technologies for biomedical implantable devices, current state-of-the-art prosthetic platforms still lack a reliable and convenient packaging scheme to integrate high-density signal-driving chips, wireless telemetry circuitries and noise-canceling amplifiers, mainly due to the limitations in fabrication technology, material compatibility and interconnect reliability. In this dissertation, new packaging technologies are developed and presented to enable a new generation of flexible neural implants. These technologies can also house integrated circuit chips and provide high-density electrical connection to it.
\r\n\r\nThis packaging scheme utilizes the parylene-metal-parylene skin structure and can be totally integrated and be monolithically fabricated with existing functional devices. The size and the electrode patterns can be modified to suit different chips and applications. Integration with flexible cable integrated silicon probes for neural prosthesis, implantable muscle stimulators and implantable RFID tagging technology are all successfully demonstrated in this dissertation. Other discrete components can also be integrated to achieve high level functionality.
\r\n\r\nIn order to ensure the long-term stability of such packaging scheme, accelerated hot saline soaking test is conducted on the overall structure and its components. Detailed adhesion enhancement techniques are also presented to improve its performances. A physical model of the flexible retinal implant is then tested in vivo during the course of the experiment. Finally, the high-density squeegee bonding technique is introduced, which allows the integration of a 256-channel chip. Functionality of the chip has been demonstrated. As a result, this technology has the potential to achieve ultra high lead count connection and can facilitate future research in flexible implantable biodevices.
\r\n" }, { "name": "Hurtado Sepulveda, Daniel Esteban", "degree": "PhD", "year": "2011", "title": "Multiscale Modeling of Microcrystalline Materials", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:11222010-061455728", "creators": [ { "name": { "family": "Hurtado Sepulveda", "given": "Daniel Esteban" }, "id": "Hurtado-Sepulveda-Daniel-Esteban", "display_name": "Hurtado Sepulveda, Daniel Esteban" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/FHZT-3A33", "abstract": "Materials with micrometer dimensions and their distinct mechanical properties have generated a great interest in the material science community over the last couple of decades. There is strong experimental evidence showing that microcrystalline materials are capable of achieving much higher yield and fracture strength values than bulk mesoscopic samples as they decrease in size. Several theories have been proposed to explain the size effect found in micromaterials, but a predictive physics-based model suitable for numerical simulations remains an open avenue of research. Since the successful design of micro-electro-mechanical systems (MEMS) and novel engineered materials hinges upon the mechanical properties at the micrometer scale, there is a compelling need for a quantitative and accurate characterization of the size effects exhibited by metallic micromaterials.
\r\n\r\nThis work is concerned with the multiscale material modeling and simulation of strength in crystalline materials with micrometer dimensions. The elasto-viscoplastic response is modeled using a continuum crystal plasticity formulation suitable for large-deformation problems. Crystallographic dislocation motion is accounted for by stating the crystal kinematics within the framework of continuously distributed dislocation theory. The consideration of the dislocation self-energy and the step formation energy in the thermodynamic formulation of the constitutive relations renders the model non-local and introduces a length scale. Exploiting the concept of total variation we are able to recover an equivalent model that is local under a staggered approach, and therefore amenable to time integration using variational constitutive updates. Numerical simulations of compression tests in nickel micropillars using the proposed multiscale framework quantitatively capture the size dependence found in experimental results, showcasing the predictive capabilities of the model.
\r\n" }, { "name": "Kapre, Nachiket Ganesh", "degree": "PhD", "year": "2011", "title": "SPICE\u00b2: A Spatial, Parallel Architecture for Accelerating the Spice Circuit Simulator\r ", "advisor": "DeHon, Andre", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262010-082537998", "creators": [ { "name": { "family": "Kapre", "given": "Nachiket Ganesh" }, "id": "Kapre-Nachiket-Ganesh", "orcid": "0000-0002-2187-0406", "display_name": "Kapre, Nachiket Ganesh" } ], "advisors": [ { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "advisor", "display_name": "DeHon, Andre" } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Trimberger", "given": "Steven" }, "id": "Trimberger-S", "role": "member", "display_name": "Trimberger, Steven" }, { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "member", "display_name": "DeHon, Andre" } ], "option_major": [ "compsci" ], "doi": "10.7907/QVZR-VB52", "abstract": "Spatial processing of sparse, irregular floating-point computation using a single FPGA enables up to an order of magnitude speedup (mean 2.8X speedup) over a conventional microprocessor for the SPICE circuit simulator. We deliver this speedup using a hybrid parallel architecture that spatially implements the heterogeneous forms of parallelism available in SPICE. We decompose SPICE into its three constituent phases: Model-Evaluation, Sparse Matrix-Solve, and Iteration Control and parallelize each phase independently. We exploit data-parallel device evaluations in the Model-Evaluation phase, sparse dataflow parallelism in the Sparse Matrix-Solve phase and compose the complete design in streaming fashion. We name our parallel architecture SPICE\u00b2: Spatial Processors Interconnected for Concurrent Execution for accelerating the SPICE circuit simulator. We program the parallel architecture with a high-level, domain-specific framework that identifies, exposes and exploits parallelism available in the SPICE circuit simulator. This design is optimized with an auto-tuner that can scale the design to use larger FPGA capacities without expert intervention and can even target other parallel architectures with the assistance of automated code-generation. This FPGA architecture is able to outperform conventional processors due to a combination of factors including high utilization of statically-scheduled resources, low-overhead dataflow scheduling of fine-grained tasks, and overlapped processing of the control algorithms.
\r\n\r\nWe demonstrate that we can independently accelerate Model-Evaluation by a mean factor of 6.5X(1.4--23X) across a range of non-linear device models and Matrix-Solve by 2.4X(0.6--13X) across various benchmark matrices while delivering a mean combined speedup of 2.8X(0.2--11X) for the two together when comparing a Xilinx Virtex-6 LX760 (40nm) with an Intel Core i7 965 (45nm). With our high-level framework, we can also accelerate Single-Precision Model-Evaluation on NVIDIA GPUs, ATI GPUs, IBM Cell, and Sun Niagara 2 architectures.
\r\n\r\nWe expect approaches based on exploiting spatial parallelism to become important as frequency scaling slows down and modern processing architectures turn to parallelism (\\eg multi-core, GPUs) due to constraints of power consumption. This thesis shows how to express, exploit and optimize spatial parallelism for an important class of problems that are challenging to parallelize.
\r\n" }, { "name": "Keehr, Edward Arthur", "degree": "PhD", "year": "2011", "title": "Techniques for Mixed-Signal Linearization and Large Signal Handling in Radio-Frequency Receiver Circuits", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechTHESIS:08232010-071647727", "creators": [ { "name": { "family": "Keehr", "given": "Edward Arthur" }, "id": "Keehr-Edward-Arthur", "display_name": "Keehr, Edward Arthur" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "D'Addario", "given": "Larry R." }, "id": "D'Addario-L-R", "role": "member", "display_name": "D'Addario, Larry R." } ], "option_major": [ "eleceng" ], "doi": "10.7907/WFGT-4823", "abstract": "In this dissertation, two effective linearization schemes for radio-frequency receivers are introduced. The first of these comprises a mixed-signal feedforward path which regenerates third-order intermodulation (IM3) products at radio frequencies, downconverts these products, digitizes them, and then uses them to cancel corruptive IM3 products in the digital baseband portion of a nominally linear receiver path. The combined implemented receiver represents a SAW-less direct-conversion receiver for UMTS FDD Region 1 that achieves an uncorrected out-of-band IIP3 of -7.1dBm under worst-case blocking specifications. Under IM3 equalization, the receiver achieves an effective IIP3 of +5.3dBm and meets the UMTS BER sensitivity requirements with 3.7dB of margin. To enable this mixed-signal feedforward path, a multistage cubic term generator is introduced which uses cascaded nonlinear operations to generate reference IM3 products. The multistage nature of this circuit is considered in the context of the aforementioned linearization scheme and is shown to provide sufficient dynamic range for nearly complete IM3 cancellation while dissipating far less power than the original receiver front end. In particular, the effect of the group delay between stages is analyzed and shown to permit large IM3 cancellation ratios for interstage group delays less than 1ns.
\r\n\r\nExpanding upon the first effective linearization approach led to the development of a large signal handling receiver with an out-of-band 1-dB desensitization point of +12.5dBm. Enabling this large signal handling capability is a passive mixer downconverter preceded by a novel wide-swing LNTA. With a stacked push-pull class-AB common-gate architecture, the LNTA reduces the magnitude of input-referred distortion by up to 40dB beyond that predicted by an initial slope-of-3 characteristic while at the same time minimally impacting the effective small-signal gain of the receiver. To compensate for intermodulation distortion terms of order greater than 3, IM3 and IM2 products are processed down to digital baseband where they are successively multiplied to generate approximations to higher-order terms. In the case of a +12.4dBm QPSK-modulated signal and a -16.3dBm CW blocker, cancellation improves receiver input-referred error by over 24dB, resulting in an extrapolated IIP3 of +43.5dBm.
" }, { "name": "Keppel-Aleks, Gretchen", "degree": "PhD", "year": "2011", "title": "Constraints on the Global Carbon Budget from Variations in Total Column Carbon Dioxide", "advisor": "Wennberg, Paul O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312011-112642236", "creators": [ { "name": { "family": "Keppel-Aleks", "given": "Gretchen" }, "id": "Keppel-Aleks-Gretchen", "display_name": "Keppel-Aleks, Gretchen" } ], "advisors": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "advisor", "display_name": "Wennberg, Paul O." } ], "committee": [ { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "role": "chair", "display_name": "Schneider, Tapio" }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Toon", "given": "Geoffrey C." }, "id": "Toon-G-C", "role": "member", "display_name": "Toon, Geoffrey C." }, { "name": { "family": "Bordoni", "given": "Simona" }, "id": "Bordoni-S", "role": "member", "display_name": "Bordoni, Simona" }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/5BZZ-BW98", "abstract": "Diagnosing the patterns and trends in the flux of carbon dioxide, CO\u2082, between the land or ocean and the atmosphere is necessary to predict the response of the carbon cycle to climate change. Atmospheric observations of the vertically averaged mixing ratio of CO\u2082, (CO\u2082), provide a new tool that complements existing observations of boundary layer CO\u2082 in constraining surface fluxes of CO2. My dissertation explores how variations in (CO\u2082) arise and how these variations can be used to estimate surface fluxes.
\r\n\r\nThis thesis takes advantage of (CO\u2082) measurements from the Total Carbon Column Observing Network (TCCON). This global network uses ground-based Fourier transform spectrometers to obtain direct solar spectra in the near infrared, from which (CO\u2082) is retrieved. Because variations in atmospheric CO\u2082 are relatively small, it is essential that the data achieve high precision and accuracy to be useful for carbon cycle science. Using a retrieval algorithm I developed to remove transient interference from clouds and aerosols, precise measurements are achievable under a range\r\nof meteorological conditions, allowing the inclusion of data from partially cloudy days.
\r\n\r\nAt midlatitude TCCON sites, (CO\u2082) varies substantially on diurnal, synoptic, and seasonal timescales. A comparison of diurnal variations in (CO\u2082) with flux tower observations of net ecosystem exchange in northern Wisconsin suggests that local ecosystem fluxes account for only 10%\u201315% of variation in (CO\u2082) on hourly timescales. I use an atmospheric transport model with imposed surface fluxes of CO\u2082 to examine further the sensitivity of (CO\u2082) to surface fluxes and find that, as in the observations, simulated (CO\u2082) is relatively insensitive to local phenomena. Large variations in local fluxes and local physics (e.g., convection) produce only small changes in atmospheric (CO\u2082) patterns. Patterns in (CO\u2082) are most sensitive to the large-scale north\u2013south flux gradient, as zonal variations in fluxes are smoothed by transport and therefore have little impact on the total column.
\r\n\r\nRapid temporal variations in midlatitude (CO\u2082) arise due to transport across north-south gradients, and can be used to infer information about large-scale spatial patterns in CO\u2082. Here, I use the correlation between synoptic-scale variations in (CO\u2082) and dynamical tracers, such as potential\r\ntemperature, to infer spatial gradients in large-scale (CO\u2082) from sparse ground-based data. These estimated gradients, as well as the amplitude of the seasonal cycle in (CO\u2082), can be used as diagnostics to evaluate flux models. In simulations with one such model, the Carnegie Ames Stanford\r\nApproach (CASA) ecosystem fluxes, gradients inferred from TCCON data are 75% larger than simulated CO\u2082 gradients during summer, while the seasonal cycle amplitudes in (CO\u2082) at midlatitude TCCON sites are between 20% and 40% larger than in simulations. Given that (CO\u2082) is insensitive to local fluxes, the mismatch between observations and simulations points to an underestimation of northern hemisphere ecosystem fluxes. Simulated (CO\u2082) diagnostics are consistent with TCCON data if boreal net ecosystem exchange is increased by 40%, a finding that suggests boreal ecosystem parameterizations must be reevaluated.
\r\n\r\nThis work demonstrates that variability in (CO\u2082) is driven by large-scale phenomena rather than local fluxes, and has important implications for interpreting (CO\u2082) measurements from satellites such as GOSAT and OCO-2. These results suggest that total column measurements will provide a strong constraint on large-scale flux estimates. At the same time, extracting information about regional fluxes from (CO\u2082) observations alone will be challenging. Coupling column and surface CO\u2082 observations will yield improved flux estimates as surface CO\u2082 observations will constrain regional flux patterns, superimposed on top of the large-scale flux distribution revealed by total column observations.
\r\n\r\n" }, { "name": "Kovalchick, Christopher", "degree": "PhD", "year": "2011", "title": "Mechanics of Peeling: Cohesive Zone Law and Stability", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-172059575", "creators": [ { "name": { "family": "Kovalchick", "given": "Christopher" }, "id": "Kovalchick-Christopher", "display_name": "Kovalchick, Christopher" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/W2KT-CY70", "abstract": "The measurement of interface mechanical properties between an adhesive layer and a substrate is significant for optimization of a high-quality interface. A common method for measuring these properties is the peel test. While there are many interesting applications of peel in such areas as cell and gecko adhesion, the focus here is to obtain a better understanding of the fundamental mechanics underlying the problem.
\r\n\r\nThe mechanics of the peel test is examined through experiments, finite element simulations, and theoretical analysis with the aim of developing governing relations to describe the role of fracture in the peel test for elastic adhesive tapes. An inverse formulation is developed to extract a cohesive zone law from a set of experimental peel tests using a theoretical framework based upon non-linear beam theory. Through extracting a cohesive zone law, the adhesion energy during a peel test is determined along with the force distribution in the process zone. This local method of determining the adhesion energy is compared to a global method used by Rivlin in the context of finite deformations, showing good agreement.
\r\n\r\nThe effect of rate-dependency in the peel test is also examined experimentally, with the results used to derive a rate-dependent power-law for the adhesion energy in a peel test as a function of the peel rate. The effects of varying different geometrical parameters during the peel test and how they affect the force distribution and adhesion energy are also presented. Finally, a study of the stability in the peel test, including the role of compliance through several newly developed force-controlled experimental configurations is discussed. The stiffness of the system is varied by altering the magnitude and direction of the applied load during a test. This change in stiffness can be tuned in order to trigger or delay the onset of instability. Theoretical stability criteria are also presented to in order to develop insights of the role of parameters investigated experimentally.
" }, { "name": "Kwan, Alan Jake-Man", "degree": "PhD", "year": "2011", "title": "Investigating Sources and Sinks of Organic Aerosols: NO\u2083-initiated Oxidation of Isoprene and Heterogeneous Oxidation of Organic Aerosol\r ", "advisor": "Wennberg, Paul O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06222010-150731880", "creators": [ { "name": { "family": "Kwan", "given": "Alan Jake-Man" }, "id": "Kwan-Alan-Jake-Man", "display_name": "Kwan, Alan Jake-Man" } ], "advisors": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "advisor", "display_name": "Wennberg, Paul O." } ], "committee": [ { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "role": "chair", "display_name": "Sessions, Alex L." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "role": "member", "display_name": "Okumura, Mitchio" }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." } ], "option_major": [ "envreng" ], "doi": "10.7907/2ET7-0D89", "abstract": "Secondary organic aerosol (SOA) are important components in atmospheric processes and significantly impact human health. The complexity of SOA composition and formation processes has hampered efforts to fully characterize their impacts, and to predict how those impacts will be affected by changes in climate and human activity. Here, we explore SOA formation in the laboratory by coupling an environmental chamber with a suite of analytical tools, including a gas-phase mass spectrometry technique that is well suited for tracking the hydrocarbon oxidation processes that drive SOA formation. Focusing on the oxidation of isoprene by the nitrate radical, NO\u2083, we find that reactions of peroxy radicals (RO\u2082) to form ROOR dimers is an important process in SOA formation. The other gas-phase products of these RO\u2082 reactions differ from what is expected from studies of simpler radicals, indicating that more studies are necessary to fully constrain RO\u2082 chemistry. Finally, we examine the role of heterogeneous oxidation as a sink of organic aerosol and a source of oxygenated volatile organic compounds in the free troposphere." }, { "name": "Lamperski, Andrew G.", "degree": "PhD", "year": "2011", "title": "Hierarchies, Spikes, and Hybrid Systems: Physiologically Inspired Control Problems", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022011-110025485", "creators": [ { "name": { "family": "Lamperski", "given": "Andrew G." }, "id": "Lamperski-Andrew-G", "display_name": "Lamperski, Andrew G." } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Lall", "given": "Sanjay" }, "id": "Lall-S", "role": "member", "display_name": "Lall, Sanjay" } ], "option_major": [ "cds" ], "doi": "10.7907/0ANZ-8209", "abstract": "In animal motor control and locomotion, neurons process information, muscles are the actuators, and the body is the plant. Control theory is the standard mathematical language for describing motor control and locomotion, but many phenomena in physiological control remain outside of the scope of control theoretic reasoning. Unlike traditional engineering control systems, nearly all the components of physiological control systems have complex dynamics. Instead of a fast centralized computer, an animal implements controllers using a distributed network of slow, nonlinear, and noisy neurons. Rather than having linear plants and actuators, the animal must control limbs with nonlinear and hybrid dynamics.
\r\n\r\nThis dissertation develops basic control theory motivated by physiological systems. Dynamical phenomena that arise in physiology but remain outside the scope of mathematical methods are isolated and studied in general control theoretic frameworks. In particular, three problems are discussed: distributed linear quadratic Gaussian (LQG) control with communication delays, control over communication channels modeled after spiking neurons, and Zeno stability of hybrid systems.
\r\n\r\nMotivated by the presence of delays in the human motor system, Chapter 2 explores the architecture of distributed LQG controllers when communication between subsystems is limited by delays. Sensory and motor command information is processed in several different regions throughout the nervous system. Since processing speed in neurons is limited, information from different sensory and motor regions can only be integrated after a time delay. In spite of this difficulty, humans make efficient and reliable motions that are well-described by optimal feedback control. Optimal delay compensation is studied in a distributed LQG framework. The structure that emerges as the result of optimization resembles a management hierarchy, bearing similarities with the organization of the motor system.
\r\n\r\nNetworked control systems, in which communication between the controller and the plant occurs over a special neuron-inspired channel, are analyzed in Chapter 3. In addition to being the basic computing elements, neurons are the long-range communication channels of the body. Neurons transmit information in the form of short-lived voltage spikes, called action potentials. Sufficient conditions for stable control over the spiking channel are presented, along with bounds on tracking error and data rates.
\r\n\r\nThe final technical chapter studies the connections between Zeno behavior and Lyapunov stability. Zeno behavior occurs in a hybrid system when an infinite number of discrete transitions occurs in a finite amount of time. While Zeno behavior results from modeling abstractions, it is commonly observed in models of mechanical systems undergoing impacts, including models important for locomotion. Often, Zeno behavior is associated with dynamical mode transitions, such as knee locking and the transition between bouncing and sliding. To reason about such transitions without modifying the models, the chapter on hybrid systems gives Lyapunov-like sufficient conditions for Zeno behavior. A technique for constructing the Lyapunov-like certificates is presented for a general class of mechanical systems undergoing impacts.
\r\n" }, { "name": "Lavaei, Javad", "degree": "PhD", "year": "2011", "title": "Large-Scale Complex Systems: From Antenna Circuits to Power Grids", "advisor": "Doyle, John Comstock; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05132011-113642762", "creators": [ { "name": { "family": "Lavaei", "given": "Javad" }, "id": "Lavaeiyanesi-Javad", "display_name": "Lavaei, Javad" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "co-advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "co-chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "cds" ], "doi": "10.7907/CM46-5R54", "abstract": "This dissertation is motivated by the lack of scalable methods for the analysis and synthesis of different large-scale complex systems appearing in electrical and computer engineering. The systems of interest in this work are power networks, analog circuits, antenna systems, communication networks and distributed control systems. By combining theories from control and optimization, the high-level objective is to develop new design tools and algorithms that explicitly exploit the physical properties of these practical systems (e.g., passivity of electrical elements or sparsity of network topology). To this end, the aforementioned systems are categorized intro three classes of systems, and then studied in Parts I, II, and III of this dissertation, as explained below:
\r\n\r\nPower networks: In Part I of this work, the operation planning of power networks using efficient algorithms is studied. The primary focus is on the optimal power flow (OPF) problem, which has been studied by the operations research and power communities in the past 50 years with little success. In this part, it is shown that there exists an efficient method to solve a practical OPF problem along with many other energy-related optimization problems such as dynamic OPF or security-constrained OPF. The main reason for the successful convexification of these optimization problems is also identified to be the physical properties of a power circuit, especially the passivity of transmission lines.
\r\n\r\nCircuits and systems: Motivated by different applications in power networks, electromagnetics and optics, Part II of this work studies the fundamental limits associated with the synthesis of a particular type of linear circuit. It is shown that the optimal design of the parameters of this type of circuit can be performed in polynomial time if the circuit is passive and there are sufficient number of controllable (unknown) parameters. This result introduces a trade-off between the design simplicity and the implementation complexity for an important class of linear circuits. As an application of this methodology, the design of smart antennas is also studied; the goal is to devise an intelligent wireless communication device in order to avoid co-channel interference, power consumption in undesired directions and security issues. Since the existing smart antennas are either hard to program or hard to implement, a new type of smart antenna is synthesized by utilizing tools from algebraic geometry, control, communications, and circuits, which is both easy to program and easy to implement.
\r\n \r\nDistributed computation: The first problem tackled in Part III of this work is a very simple type of distributed computation, referred to as quantized consensus, which aims to compute the average of a set of numbers using a distributed algorithm subject to a quantization error. It is shown that quantized consensus is reached by means of a recently proposed gossip algorithm, and the convergence time of the algorithm is also derived. The second problem studied in Part III is a more advanced type of distributed computation, which is the distributed resource allocation problem for the Internet. The existing distributed resource allocation algorithms aim to maximize the utility of the network only at the equilibrium point and ignore the transient behavior of the network. To address this issue, it is shown that optimal control theory provides powerful tools for designing distributed resource allocation algorithms with a guaranteed real-time performance.
\r\n\r\nThe results of this work can all be integrated to address real-world interdisciplinary problems, such as the design of the next generation of the electrical power grid, named the Smart Grid.
\r\n\r\n" }, { "name": "Lopez Jimenez, Francisco", "degree": "PhD", "year": "2011", "title": "Mechanics of Thin Carbon Fiber Composites with a Silicone Matrix", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:03152011-154253229", "creators": [ { "name": { "family": "Lopez Jimenez", "given": "Francisco" }, "id": "Lopez-Jimenez-Francisco", "display_name": "Lopez Jimenez, Francisco" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A773-KF92", "abstract": "This thesis presents an experimental, numerical and analytical study of the behavior of thin fiber composites with a silicone matrix. The main difference with respect to traditional composites with epoxy matrix is the fact that the soft matrix allows the fibers to microbuckle without breaking. This process acts as a stress relief mechanism during folding, and allows the material to reach very high curvatures, which makes them particularly interesting as components of space deployable structures. The goal of this study is to characterize the behavior and understand the mechanics of this type of composite.
\r\n\r\nExperimental testing of the bending behavior of unidirectional composites with a silicone matrix shows a highly non-linear moment vs. curvature relationship, as well as strain softening under cyclic loading. These effects are not usually observed in composites with an epoxy matrix. In the case of tension in the direction transverse to the fibers, the behavior shows again non-linearity and strain softening, as well as an initial stiffness much higher than what would be expected based on the traditional estimates for fiber composites.
\r\n\r\nThe micro mechanics of the material have been studied with a finite element model. It uses solid elements and a random fiber arrangement produced with a reconstruction process based on micrographs of the material cross section. The simulations capture the macroscopic non-linear response, as well as the fiber microbuckling, and show how microbuckling reduces the strain in the fibers. The model shows good agreement for the bending stiffness of specimens with low fiber volume fraction, but it overestimates the effect of the matrix for more densely packed fibers. This is due to the high matrix strain that derives from the assumption of perfect bonding between fiber and matrix. In the case of tension transverse to the fibers, the model shows a much better agreement with experiments than traditional composite theory, and shows that the reason for the observed high stiffness is the incompressibility of the matrix. In order to capture the strain softening due to fiber debonding, cohesive elements have been introduced between the fibers and the matrix. This allows the model to capture quantitatively the non-linear behavior in the case of loading transverse to the fibers, and the damage due to cyclic loading. A single set of parameters for the cohesive elements produce good agreement with the experimental results for very different values of the fiber volume fraction, and could also be used in the analysis of more complicated loading cases, such as bending or biaxial tension.
\r\n\r\nIn addition to the simulations, a homogenized analytical model has also been created. It extends previous analysis of composites with a soft matrix to the case of very thin composites. It provides a good qualitative description of the material behavior, and it helps understand the mechanics that take place within the material, such as the equilibrium of energy terms leading to a finite wave length, as opposed to microbuckling under compression.
" }, { "name": "Meier, John Allen", "degree": "PhD", "year": "2011", "title": "A Novel Experimental Study of a Valveless Impedance Pump for Applications at Lab-On-Chip, Microfluidic, and Biomedical Device Size Scales", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-111659863", "creators": [ { "name": { "family": "Meier", "given": "John Allen" }, "id": "Meier-John-Allen", "display_name": "Meier, John Allen" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/DBKG-EJ21", "abstract": "In 1954, Gerhart Liebau demonstrated a simple valveless pumping phenomenon utilizing the periodic compression of a compliant tube and some systematic asymmetry to pump water out of a bucket. Liebau's goal was to explain peculiarities seen in the human circulatory system. In the years that have followed, the Liebau phenomenon has been studied in a variety of open and closed loop configurations, through experimental, computational, and analytical studies.
\r\n\r\nRecent advances in microfluidic and microelectromechanical systems (MEMS) technology have enabled a wide range of small scale engineering systems. The further development of many important systems is limited by the absence of an appropriate means of fluid transport. Valveless pumps based on the Liebau phenomenon show great promise, particularly in lab-on-chip (LOC), biological, and medical applications in which biocompatibility and the ability to move sensitive molecules without damage are key design requirements.
\r\n\r\nThe purpose of this thesis is to synthesize previous studies of the Liebau phenomenon and produce the first extensive experimental study of a novel valveless pump at size scales and geometries that are relevant to lab-on-chip, microfluidic, and biomedical device applications. For the first time, detailed, dynamic pressure and flow data have been recorded during the operation of these valveless pumps for a large range of operating parameters. This dynamic data allowed us to identify new flow regimes and observe previously undocumented pump behaviors and performance. Parameters investigated include pump material properties and geometry, working fluid density and viscosity, pump excitation properties (amplitude, offset, location, and frequency), and flow loop/system properties. A critical relationship between the relative volumetric compliance of the valveless pump to the system it acts upon is identified, and the implications for practical implementation of valveless pumps at small size scales are discussed.
" }, { "name": "Moore, Ashley", "degree": "PhD", "year": "2011", "title": "Discrete Mechanics and Optimal Control for Space Trajectory Design", "advisor": "Marsden, Jerrold E.; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252011-164957222", "creators": [ { "name": { "family": "Moore", "given": "Ashley" }, "id": "Moore-Ashley", "display_name": "Moore, Ashley" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ober-Blobaum", "given": "Sina" }, "id": "Ober-Blobaum-S", "role": "member", "display_name": "Ober-Blobaum, Sina" } ], "option_major": [ "cds" ], "doi": "10.7907/ZXTG-V056", "abstract": "Space trajectory design is often achieved through a combination of dynamical systems theory and optimal control. The union of trajectory design techniques utilizing invariant manifolds of the planar circular restricted three-body problem and the optimal control scheme Discrete Mechanics and Optimal Control (DMOC) facilitates the design of low-energy trajectories in the N-body problem. In particular, DMOC is used to optimize a trajectory from the Earth to the Moon in the 4-body problem, removing the mid-course change in velocity usually necessary for such a trajectory while still exploiting the structure from the invariant manifolds.
\r\n\r\nThis thesis also focuses on how to adapt DMOC, a method devised with a constant step size, for the highly nonlinear dynamics involved in trajectory design. Mesh refinement techniques that aim to reduce discretization errors in the solution and energy evolution and their effect on DMOC optimization are explored and compared with trajectories created using time adaptive variational integrators.
\r\n\r\nFurthermore, a time adaptive form of DMOC is developed that allows for a variable step size that is updated throughout the optimization process. Time adapted DMOC is based on a discretization of Hamilton's principle applied to the time adapted Lagrangian of the optimal control problem. Variations of the discrete action of the optimal control Lagrangian lead to discrete Euler-Lagrange equations that can be enforced as constraints for a boundary value problem. This new form of DMOC leads to the accurate and efficient solution of optimal control problems with highly nonlinear dynamics. Time adapted DMOC is tested on several space trajectory problems including the elliptical orbit transfer in the 2-body problem and the reconfiguration of a cubesat.
\r\n" }, { "name": "Nahmad Bensusan, Marcos", "degree": "PhD", "year": "2011", "title": "Interpretation and Scaling of Positional Information During Development", "advisor": "Stathopoulos, Angelike; Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:10212010-000757213", "creators": [ { "name": { "family": "Nahmad Bensusan", "given": "Marcos" }, "id": "Nahmad-Bensusan-Marcos", "display_name": "Nahmad Bensusan, Marcos" } ], "advisors": [ { "name": { "family": "Stathopoulos", "given": "Angelike" }, "id": "Stathopoulos-A", "role": "advisor", "display_name": "Stathopoulos, Angelike" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Stathopoulos", "given": "Angelike" }, "id": "Stathopoulos-A", "role": "chair", "display_name": "Stathopoulos, Angelike" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Rothenberg", "given": "Ellen V." }, "id": "Rothenberg-E-V", "role": "member", "display_name": "Rothenberg, Ellen V." }, { "name": { "family": "Lander", "given": "Arthur D." }, "id": "Lander-A-D", "role": "member", "display_name": "Lander, Arthur D." } ], "option_major": [ "cds" ], "doi": "10.7907/2ZYV-FF66", "abstract": "Cells in a developing animal require information about their relative position in order to function and differentiate appropriately. In the classical view, cellular positional information is interpreted from the concentration of chemical signals known as morphogens. However, recent studies have questioned the ability of morphogens to establish gene expression patterns in a concentration-dependent manner. Here we combine theoretical tools and experimental work in Drosophila melanogaster to investigate the mechanisms by which positional information is interpreted from a morphogen gradient and the ability of patterns to scale with respect to the size of the system.
\r\n\r\nFirst, we study how a concentration gradient of the signaling molecule Hedgehog establishes multiple patterns of gene expression along the anterior-posterior axis of the Drosophila wing disc. Using mathematical modeling as a hypotheses-generating tool, we predicted that positional information cannot be explained by different concentration thresholds from a static Hedgehog gradient. Instead, we propose that cells take into account their history of Hedgehog signaling exposure to determine patterns of gene expression. We provide experimental evidence that supports our model and conclude that gradient dynamics, resulting from the gene network architecture of the Hedgehog signaling pathway, determine pattern formation in the wing disc.
\r\n\r\nSecond, we introduce a theoretical formalism to study the role of morphogen gradient dynamics in developmental patterning. Given a mathematical model of pattern formation, we define and compute parameter perturbations that leave invariant the steady-state distribution of the relevant morphogen. We propose that this approach can be used as a tool to design genetic experiments that assay the function of morphogen dynamics.
\r\n\r\nLastly, we use dorsal-ventral patterning of the early Drosophila embryo as a model to study scaling of gene expression patterns with respect to natural variations in axis length, that is, the ability to establish positional information relative to the size of the system. We provide evidence that gene expression patterns that depend on the maternal factor Dorsal, scale along the dorsal-ventral axis. Our data suggest that scaling in this system is a gene-dependent rather than a position-dependent property. We propose that the mechanisms for scaling depend on feedback interactions downstream of Dorsal.
" }, { "name": "Paulot, Fabien Georges Andr\u00e9", "degree": "PhD", "year": "2011", "title": "Insights into the Isoprene Photochemical Cascade", "advisor": "Wennberg, Paul O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292011-155605494", "creators": [ { "name": { "family": "Paulot", "given": "Fabien Georges Andr\u00e9" }, "id": "Paulot-Fabien-Georges-Andr\u00e9", "display_name": "Paulot, Fabien Georges Andr\u00e9" } ], "advisors": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "advisor", "display_name": "Wennberg, Paul O." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Sander", "given": "Stanley P." }, "id": "Sander-S-P", "role": "member", "display_name": "Sander, Stanley P." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." } ], "option_major": [ "envreng" ], "doi": "10.7907/C11Q-E180", "abstract": "Isoprene emissions are the single largest source of non-methane reduced carbon to the atmosphere. Proper simulation of the effect of its photooxidation on regional air quality and secondary organic aerosol formation requires detailed multi-generation and multi-phase photochemical mechanisms. In this work, I first demonstrate that CF3O- chemical ionization mass spectrometry (CIMS) is a powerful method to probe isoprene photochemical oxidation. Under high NOx, isoprene nitrates and their photochemical products are directly observed and quantified. As isoprene nitrates are critical to the impact of isoprene photochemistry on ozone, these observations provide an important constraint on the effect of isoprene emissions on air quality in polluted and biogenic rich regions (e.g., Southeastern United States). The use of tandem CIMS in association with isotopically labelled hydroxy radicals is used to identify dihydroxyepoxides as major products of isoprene photooxidation in low NOx conditions. This class of compounds may provide an important precursor for secondary organic aerosols under acidic conditions. The chemical mechanism derived from these laboratory observations is then incorporated in a chemical transport model to assess the impact of isoprene photooxidation on atmospheric chemistry. I examine how the photooxidation of isoprene impacts the budget of formic and acetic acids, two ubiquitous trace gases whose sources are poorly constrained. Comparison with observations from satellite, ground and aircraft platforms, reveal a major missing source that may originate from the aging of secondary organic aerosols. Finally, the consequences of the multi-scale interplay between NOx and isoprene photochemistry on the tropical budget of ozone are examined using forward and adjoint sensitivity simulations." }, { "name": "Perotti, Luigi Emanuele", "degree": "PhD", "year": "2011", "title": "Modeling the Behavior of Fiber Reinforced Sandwich Structures Subjected to Underwater Explosions", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:11052010-113423550", "creators": [ { "name": { "family": "Perotti", "given": "Luigi Emanuele" }, "id": "Perotti-Luigi-Emanuele", "display_name": "Perotti, Luigi Emanuele" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "role": "member", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Pandolfi", "given": "Anna" }, "id": "Pandolfi-A", "role": "member", "display_name": "Pandolfi, Anna" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/83JD-HN76", "abstract": "Fiber composite material panels and sandwich panels possess both a high resistance to weight ratio and a high stiffness to weight ratio. Due to these features, fiber composite panels are used widely in aeronautic and marine structures, where the improvement of the structural performance while keeping a low weight is crucial. Sandwich structures, consisting of a foam core enclosed by two external layers of fiber reinforced material, seem to be promising in minimizing the total weight, maintaining structural rigidity and improving the resistance under exceptional loads, such as those due to explosions. Full scale experiments to test the performance of real fiber composite sandwich structures subjected to underwater explosions would be very complex and expensive. Therefore, the capability to numerically simulate the response of sandwich structures undergoing explosive loading will provide a powerful and unique tool to analyze and optimize their design by investigating the influence of different parameters. Obviously, small scale laboratory tests will still be essential to validate and calibrate the computational model before its use.
\r\n\r\nThe present research focuses on the development of a computational scheme to model the behavior of large sandwich panels subjected to underwater explosions. The description of the sandwich requires the definition of the material behavior of the components, i.e., the foam core and the external sheets, of the structural behavior of the thin shell structure, and of the interaction with the surrounding fluid. Several finite kinematics material models taken from the recent literature have been used, and a new simple model for fiber reinforced composites has been developed and validated. The thin shell structure is modeled with an existing in-house built non-local shell finite element code (SFC), equipped with fracturing capabilities. The coupling between the behavior of the shells and the action of the fluid as a consequence of an underwater explosion is modeled here with the aid of an existing fluid-solid interaction (FSI) code. In this study, the FSI code has been expanded in order to include the possibility of simulating fiber composite materials. New algorithms and new control indicators, such as global measures of energy dissipation, have also been developed. The new capabilities of the fluid-solid coupled solver have been verified and validated before applying the solver to realistic problems. In the applications part of the present research, two different methods for applying the pressure load due to an underwater explosion are compared. The first method is simpler, and consists in applying a prescribed pressure profile without considering FSI. In the second method, the explosive charge is modeled as a spherical energy deposition and the full FSI is considered. The simpler method is used to assess the role of different design parameters of the face sheets on the overall response of sandwich panels when subjected to impulsive loads. Subsequently, the best sandwich design obtained from these initial simulations is used for the evaluation of the mechanical performance of the hull section of an existing Argentinean navy vessel. The final application of the proposed computational scheme is a parametric analysis of the hull section, considering different weights of the explosive charge and different distances of the explosion location from the hull wall.
\r\n\r\nFinally, with awareness of the limits of the adopted approach, several alternative schemes to improve the dynamical analysis of sandwich panels impulsively loaded are presented and discussed. In particular, two different kinds of shell finite elements are introduced. The proposed shell elements are based on alternative approximation schemes, which may model in a more realistic way the behavior of sandwich structures under extreme loads.
\r\n" }, { "name": "Pilotto, Concetta", "degree": "PhD", "year": "2011", "title": "Systematic Design and Formal Verification of Multi-Agent Systems ", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232011-013046516", "creators": [ { "name": { "family": "Pilotto", "given": "Concetta" }, "id": "Pilotto-Concetta", "display_name": "Pilotto, Concetta" } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "compsci" ], "doi": "10.7907/SCQF-VP66", "abstract": "This thesis presents methodologies for verifying the correctness of multi-agent systems operating in hostile environments. Verification of these systems is challenging because of their inherent concurrency and unreliable communication medium. The problem is exacerbated if the model representing the multi-agent system includes infinite or uncountable data types.
\r\n\r\nWe first consider message-passing multi-agent systems operating over an unreliable communication medium. We assume that messages in transit may be lost, delayed or received out-of-order. We present conditions on the system that reduce the design and verification of a message-passing system to the design and verification of the corresponding shared-state system operating in a friendly environment. Our conditions can be applied both to discrete and continuous agent trajectories.
\r\n\r\nWe apply our results to verify a general class of multi-agent system whose goal is solving a system of linear equations. We discuss this class in detail and show that mobile robot linear pattern-formation schemes are instances of this class. In these protocols, the goal of the team of robots is to reach a given pattern formation.
\r\n\r\nWe present a framework that allows verification of message-passing systems operating over an unreliable communication medium. This framework is implemented as a library of PVS theorem prover meta-theories and is built on top of the timed automata framework. We discuss the applicability of this tool. As an example, we automatically check correctness of the mobile robot linear pattern formation protocols.
\r\n\r\nWe conclude with an analysis of the verification of multi-agent systems operating in hostile environments. Under these more general assumptions, we derive conditions on the agents' protocols and properties of the environment that ensure bounded steady-state system error. We apply these results to message-passing multi-agent systems that allow for lost, delayed, received out-of-order or forged messages, and to multi-agent systems whose goal is tracking time-varying quantities. We show that pattern formation schemes are robust to leaders dynamics, i.e., in these schemes, followers eventually form the pattern defined by the new positions of the leaders.
" }, { "name": "Plan, Yaniv", "degree": "PhD", "year": "2011", "title": "Compressed Sensing, Sparse Approximation, and Low-Rank Matrix Estimation\r ", "advisor": "Candes, Emmanuel J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02272011-233144146", "creators": [ { "name": { "family": "Plan", "given": "Yaniv" }, "id": "Plan-Yaniv", "display_name": "Plan, Yaniv" } ], "advisors": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "advisor", "display_name": "Candes, Emmanuel J." } ], "committee": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "chair", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/K8W9-RS71", "abstract": "The importance of sparse signal structures has been recognized in a plethora of applications ranging from medical imaging to group disease testing to radar technology. It has been shown in practice that various signals of interest may be (approximately) sparsely modeled, and that sparse modeling is often beneficial, or even indispensable to signal recovery. Alongside an increase in applications, a rich theory of sparse and compressible signal recovery has recently been developed under the names compressed sensing (CS) and sparse approximation (SA). This revolutionary research has demonstrated that many signals can be recovered from severely undersampled measurements by taking advantage of their inherent low-dimensional structure. More recently, an offshoot of CS and SA has been a focus of research on other low-dimensional signal structures such as matrices of low rank. Low-rank matrix recovery (LRMR) is demonstrating a rapidly growing array of important applications such as quantum state tomography, triangulation from incomplete distance measurements, recommender systems (e.g., the Netflix problem), and system identification and control.
\r\n\r\nIn this dissertation, we examine CS, SA, and LRMR from a theoretical perspective. We consider a variety of different measurement and signal models, both random and deterministic, and mainly ask two questions.
\r\n\r\nHow many measurements are necessary? How large is the recovery error?
\r\n\r\nWe give theoretical lower bounds for both of these questions, including oracle and minimax lower bounds for the error. However, the main emphasis of the thesis is to demonstrate the efficacy of convex optimization---in particular l1 and nuclear-norm minimization based programs---in CS, SA, and LRMR. We derive upper bounds for the number of measurements required and the error derived by convex optimization, which in many cases match the lower bounds up to constant or logarithmic factors. The majority of these results do not require the restricted isometry property (RIP), a ubiquitous condition in the literature.
" }, { "name": "Reina Romo, Celia", "degree": "PhD", "year": "2011", "title": "Multiscale Modeling and Simulation of Damage by Void Nucleation and Growth", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:11022010-080434454", "creators": [ { "name": { "family": "Reina Romo", "given": "Celia" }, "id": "Reina-Romo-Celua", "display_name": "Reina Romo, Celia" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Marian", "given": "Jaime" }, "id": "Marian-J", "role": "member", "display_name": "Marian, Jaime" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WFYW-AS22", "abstract": "Voids are observed to be generated under sufficient loading in many materials, ranging from polymers and metals to biological tissues. The presence of these voids can have drastic implications at the macroscopic level including strong material softening and more incipient fracture. Developing tools to appropriately account for these effects is therefore very desirable.
\r\n\r\nThis thesis is concerned with both, the appearance of voids (nucleation process) and the modeling and simulation of materials in the presence of voids. A particular nucleation mechanism based on vacancy aggregation in high purity metallic single crystals is analyzed. A multiscale model is developed in order to obtain an approximate value of the time required for vacancies to form sufficiently large clusters for further growth by plastic deformation. It is based on quantum mechanical results, kinetic Monte Carlo methods and continuum mechanics estimates calibrated with quasi-continuum results. The ultimate goal of these simulations is to determine the feasibility of this nucleation mechanism under shock loading conditions, where the temperature and tensions are high and vacancy diffusion is promoted.
\r\n\r\nOn the other hand, the effective behavior of materials with pre-existent voids is analyzed within the general framework of continuum mechanics and is therefore applicable to any material. The overall properties of the heterogeneous material are obtained through a two-level characterization: a representative volume element consisting of a hollow sphere is used to describe the \"microscopic\" fields, and an equivalent homogeneous material is used for the \"macroscopic\" behavior. A variational formulation of this two-scale model is presented. It provides a consistent definition of the macro-variables under general loading conditions, extending the well-known static averaging results so as to include microdynamic effects under finite deformations. This variational framework also provides a suitable starting point for time discretization and consistent definitions within discrete time. The spatial boundary value problem resulting from this multiscale model is solved with a particular spherical shell element specially developed for this problem. The approximation space is based on spherical harmonics, which respects the symmetries of the porous material and allows the representation of the fields on the sphere with very few degrees of freedom. Numerical tools, such as the exact representation of the boundary conditions and an exact quadrature rule, are also provided. The resulting numerical model is verified extensively, demonstrating good convergence results, and its applicability is shown through several material point calculations and a full two-scale finite element implementation.
" }, { "name": "Satyan, Naresh", "degree": "PhD", "year": "2011", "title": "Optoelectronic Control of the Phase and Frequency of Semiconductor Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292011-221312708", "creators": [ { "name": { "family": "Satyan", "given": "Naresh" }, "id": "Satyan-Naresh", "display_name": "Satyan, Naresh" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "eleceng" ], "doi": "10.7907/24DM-VW62", "abstract": "This thesis explores the precise control of the phase and frequency of the output of semiconductor lasers (SCLs), which are the basic building blocks of most modern optical communication networks. Phase and frequency control is achieved by purely electronic means, using SCLs in optoelectronic feedback systems, such as optical phase-locked loops (OPLLs) and optoelectronic swept-frequency laser (SFL) sources. Architectures and applications of these systems are studied.
\r\n\r\nOPLLs with single-section SCLs have limited bandwidths due to the nonuniform SCL frequency modulation (FM) response. To overcome this limitation, two novel OPLL architectures are designed and demonstrated, viz. (i) the sideband-locked OPLL, where the feedback into the SCL is shifted to a frequency range where the FM response is uniform, and (ii) composite OPLL systems, where an external optical phase modulator corrects excess phase noise. It is shown, theoretically and experimentally, and in the time and frequency domains, that the coherence of the master laser is \u201ccloned\u201d onto the slave SCL in an OPLL. An array of SCLs, phase-locked to a common master, therefore forms a coherent aperture, where the phase of each emitter is electronically controlled by the OPLL. Applications of phase-controlled apertures in coherent power-combining and all-electronic beam-steering are demonstrated.
\r\n\r\nAn optoelectronic SFL source that generates precisely linear, broadband, and rapid frequency chirps (several 100 GHz in 0.1 ms) is developed and demonstrated using a novel OPLL-like feedback system, where the frequency chirp characteristics are determined solely by a reference electronic oscillator. Results from high-sensitivity biomolecular sensing experiments utilizing the precise frequency control are reported. Techniques are developed to increase the tuning range of SFLs, which is the primary requirement in high-resolution three-dimensional imaging applications. These include (i) the synthesis of a larger effective bandwidth for imaging by \"stitching\" measurements taken using SFLs chirping over different regions of the optical spectrum; and (ii) the generation of a chirped wave with twice the chirp bandwidth and the same chirp characteristics by nonlinear four-wave mixing of the SFL output and a reference monochromatic wave. A quasi-phase-matching scheme to overcome dispersion in the nonlinear medium is described and implemented.
\r\n" }, { "name": "Sen, Shaunak", "degree": "PhD", "year": "2011", "title": "Regulatory Consequences of Bandpass Feedback in a Bacterial Phosphorelay", "advisor": "Elowitz, Michael B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252011-222115269", "creators": [ { "name": { "family": "Sen", "given": "Shaunak" }, "id": "Sen-Shaunak", "orcid": "0000-0002-1412-8633", "display_name": "Sen, Shaunak" } ], "advisors": [ { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "advisor", "display_name": "Elowitz, Michael B." } ], "committee": [ { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "chair", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Garcia-Ojalvo", "given": "Jordi" }, "id": "Garcia-Ojalvo-J", "role": "member", "display_name": "Garcia-Ojalvo, Jordi" } ], "option_major": [ "cds" ], "doi": "10.7907/NPZD-G382", "abstract": "Under conditions of nutrient limitation, Bacillus subtilis cells terminally differentiate into a dormant spore state. Progression to sporulation is controlled by a genetic circuit structured as a phosphorelay embedded in multiple transcriptional feedback loops, and which is used to activate the master regulator Spo0A by phosphorylation. These transcriptional regulatory interactions are 'bandpass'-like, in the sense that activation occurs within a limited band of Spo0A~P concentrations, and have recently been shown to pulse in a cell-cycle-dependent fashion. Additionally, the core phosphorelay is an architectural variant of the canonical two-component signaling system, which allows signal integration from a larger number of inputs, including two types of phosphatases that act on different protein components. However, the impact of these pulsed bandpass interactions on the circuit dynamics preceding sporulation and the utility of two types of phosphatases remains unclear. In order to address these questions, we measured key features of the bandpass interactions at the single-cell level and analyzed them in the context of a simple mathematical model. The model predicted the emergence of a delayed phase shift between the pulsing activity of the different sporulation genes, as well as the existence of a stable state, with elevated Spo0A activity but no sporulation, embedded within the dynamical structure of the system. To test the model, we used time-lapse fluorescence microscopy to measure dynamics of single cells initiating sporulation. We observed the delayed phase shift emerging during the progression to sporulation, while a re-engineering of the sporulation circuit revealed behavior resembling the predicted additional state. The core phosphorelay model also showed a post-translational bandpass response, and we find that the two types of phosphatases can independently tune the two bandpass thresholds. These results show that periodically-driven bandpass feedback loops can give rise to complex dynamics in the progression towards sporulation, and that similar inputs can tune different response features. " }, { "name": "Shadbakht, Sormeh", "degree": "PhD", "year": "2011", "title": "Entropy Region and Network Information Theory", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092011-140731576", "creators": [ { "name": { "family": "Shadbakht", "given": "Sormeh" }, "id": "Shadbakht-Sormeh", "display_name": "Shadbakht, Sormeh" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/P8ZB-4D40", "abstract": "This dissertation takes a step toward a general framework for solving network information theory problems by studying the capacity region of networks through the entropy region.
\r\n\r\nWe first show that the capacity of a large class of acyclic memoryless multiuser information theory problems can be formulated as convex optimization over the region of entropy vectors of the network random variables. This capacity characterization is universal, and is advantageous over previous formulations in that it is single letter. Besides, it is significant as it reveals the fundamental role of the entropy region in determining the capacity of network information theory problems.
\r\n\r\nWith this viewpoint, the rest of the thesis is dedicated to the study of the entropy region, and its consequences for networks. A full characterization of the entropy region has proven to be a very challenging problem, and thus, we mostly consider inner bound constructions. For discrete random variables, our approaches include characterization of entropy vectors with a lattice-derived probability distribution, the entropy region of binary random variables, and the linear representable region. Through these characterizations, and using matroid representability results, we study linear coding capacity of networks in different scenarios (e.g., binary operations in a network, or networks with two sources).
\r\n\r\nWe also consider continuous random variables by studying the entropy region of jointly Gaussian random variables. In particular, we determine the sufficiency of Gaussian random variables for characterizing the entropy region of 3 random variables in general. For more than 3 random variables, we point out the set of minimal necessary and sufficient conditions for a vector to be an entropy vector of jointly Gaussian random variables.
\r\n\r\nFinally, in the absence of a full analytical characterization of the entropy region, it is desirable to be able to perform numerical optimization over this space. In this regard, we propose a certain Monte Carlo method that enables one to numerically optimize entropy functions of discrete random variables, and also the achievable rates in wired networks. This method can be further adjusted for decentralized operation of networks. The promise of this technique is shown through various simulations of several interesting network problems.
\r\n" }, { "name": "Shin, Young Shik", "degree": "PhD", "year": "2011", "title": "Micro- and Nanotechnology-Based Platforms to Study Biology at Small Scale: From DNAs to Single Cells", "advisor": "Heath, James R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04012011-163924567", "creators": [ { "name": { "family": "Shin", "given": "Young Shik" }, "id": "Shin-Young-Shik", "display_name": "Shin, Young Shik" } ], "advisors": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "orcid": "0000-0001-5356-4385", "role": "advisor", "display_name": "Heath, James R." } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "orcid": "0000-0003-3175-4596", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Beauchamp", "given": "Jesse L." }, "id": "Beauchamp-J-L", "orcid": "0000-0001-8839-4822", "role": "member", "display_name": "Beauchamp, Jesse L." }, { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "orcid": "0000-0001-5356-4385", "role": "member", "display_name": "Heath, James R." } ], "option_major": [ "bioeng" ], "doi": "10.7907/T590-G472", "abstract": "This thesis describes technology platforms for various biological applications at nano- and microscale. The first platform is the silicon nanowire (SiNW) field-effect-transistor (FET)-based biosensor. SiNW FETs have unique features such as label-free, real-time, and electrical measurement, which will be demonstrated with DNA and protein sensing. We further demonstrate that using different surface chemistry can modulate the sensitivity and dynamic range of the sensor. Debye screening, one of the major bottlenecks of the technology, is shown to be circumvented by using electrostatically immobilized capture DNA for DNA sensing and a small synthetic capture agent, peptide, for protein sensing. A model for the detection of analyte by SiNW sensors is also developed and utilized to extract DNA binding kinetic parameters, which shows the potential of the platform as a more sensitive version of surface plasmon resonance (SPR).
\r\n\r\nThe second part of this thesis focuses on a more practical and easily expandable technology, the microfluidics-based platform, to perform a single-cell-based protein analysis. We develop a flow patterning technology to generate highly parallel DNA barcodes that can be further utilized as a handle to immobilize protein capture agents, such as antibodies. As a first step, a protocol to make high-quality DNA micro-barcodes with an excellent uniformity is introduced. The uniform DNA barcode patterns enable us to perform protein detection from single cells in a microfluidic device that spans the whole glass microscope slide. A data set from about thousand experiments can be collected from a single test with the developed microfluidic device, owing to the good quality of DNA barcodes and DNA Encoded Antibody Libraries (DEAL) technology. This platform further demonstrates that multi-parameter protein detection at the single-cell level presents cellular heterogeneity which leads to new findings in biology. A quantitative version of the Le Chatelier\u2019s principle, as derived using information theory, is applied to analyze a large amount of data from this platform. This principle provides a quantitative prediction of the role of perturbations and allows a characterization of a protein\u2013protein interaction network.
\r\n\r\nLastly, another application of microfluidics is demonstrated for studying interfacial chemistry on lung surfactant systems under oxidative stress, along with mass spectrometry (MS) and molecular dynamic (MD) simulation results. The findings from the MS and MD simulations provide mechanistic details for the reaction of ozone with unsaturated phospholipids, leading to possible damage of the pulmonary system by ROS or direct ozone exposure. These investigations focus on molecular transformations that occur as a result of oxidative stress. Such molecular transformations can have a strong influence on the physical properties of the pulmonary surfactant (PS) system (i.e., the surface tension and elasticity of the interface), and therefore understanding how chemical transformations influence such physical properties can provide key insights into how the PS system responds to environmental challenges. Thus, we also propose utilizing microbubbles as a model system for investigating the physical transformations of the PS system when exposed to environmental challenges. The chemical composition change, along with physical property change, is analyzed by altered bubble size and oscillatory behavior which can provide an improved understanding of the physics of a PS system when it is subjected to oxidative stress.
" }, { "name": "Silva, Michael Lee", "degree": "PhD", "year": "2011", "title": "Damage Evolution in Composite Materials and Sandwich Structures Under Impulse Loading", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05122011-154526450", "creators": [ { "name": { "family": "Silva", "given": "Michael Lee" }, "id": "Silva-Michael-Lee", "display_name": "Silva, Michael Lee" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Shukla", "given": "Arun" }, "id": "Shukla-A", "role": "member", "display_name": "Shukla, Arun" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CRX1-7D43", "abstract": "Damage evolution in composite materials is a rather complex phenomenon. There are numerous failure modes in composite materials stemming from the interaction of the various constituent materials and the particular loading conditions. This thesis is concerned with investigating damage evolution in sandwich structures under repeated transient loading conditions associated with impulse loading due to hull slamming of high-speed marine craft. To fully understand the complex stress interactions, a full field technique to reveal stress or strain is required. Several full field techniques exist but are limited to materials with particular optical properties. A full field technique applicable to most materials is known as thermoelastic stress analysis (TSA) and reveals the variation in sum of principal stresses of a cyclically loaded sample by correlating the stresses to a small temperature change occurring at the loading frequency. Digital image correlation (DIC) is another noncontact full field technique that reveals the deformation field by tracking the motion of subsets of a random speckle pattern during the loading cycles.
\r\n\r\nA novel experimental technique to aid in the study of damage progression that combines TSA and DIC simultaneously utilizing a single infrared camera is presented in this thesis. A technique to reliably perform DIC with an infrared (IR) camera is developed utilizing variable emissivity paint. The thermal data can then be corrected for rigid-body motion and deformation such that each pixel represents the same material point in all frames. TSA is then performed on this corrected data, reducing motion blur and increasing accuracy. This combined method with a single infrared camera has several advantages, including a straightforward experimental setup without the need to correct for geometric effects of two spatially separate cameras. Additionally, there is no need for external lighting in TSA as the measured electromagnetic radiation is emitted by the sample\u2019s thermal fields.
\r\n\r\nThe particular stress resolution of TSA will depend on properties of the material of interest but the noise floor for the temperature variation is universal to the camera utilized. For the camera system in this thesis, the noise floor was found to be fairly frequency independent with a magnitude of 0.01 oC, giving the minimum measurable stress for 2024 aluminum alloy of 3.6 MPa and for Nylon of 0.84 MPa. The average displacement range found during a static DIC test with IR images was 0.1 pixels. The maximum displacement variation at 1 Hz was 0.018 pixels. The average variation in strain at 1 Hz was 25 microstrain comparable to traditional DIC measurements in the visible optical regime.
\r\n\r\nThe combined TSA-DIC method in IR was validated with several benchmark example problems including plate structures with holes, cracks, and bimaterials. The validated technique was applied to foam-core sandwich composite beams under repeated simulated wave slamming loading. There are numerous failure modes in sandwich composite materials and the full field stress and strain from TSA and DIC, respectively, allow for improved failure analysis and prediction. Understanding damage in sandwich structures under impulse loading is a complex open area of research and the combined TSA-DIC method provides further insight into the failure process.
\r\n" }, { "name": "Spain, Merrielle Therese", "degree": "PhD", "year": "2011", "title": "Modeling and Predicting Object Attention in Natural Scenes", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-172742472", "creators": [ { "name": { "family": "Spain", "given": "Merrielle Therese" }, "id": "Spain-Merrielle-Therese", "display_name": "Spain, Merrielle Therese" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Belongie", "given": "Serge J." }, "id": "Belongie-S-J", "role": "member", "display_name": "Belongie, Serge J." } ], "option_major": [ "cns" ], "doi": "10.7907/JTEE-7367", "abstract": "Humans automatically attend to certain objects in a scene. Better understanding this process could improve a computer's ability to parse scene images and convey information about them to humans. This thesis is arranged in three parts. The first part explores how important a particular object is in a photograph of a complex scene. We propose a definition of importance and present two methods for measuring object importance from human observers. Using this ground truth, we fit a function for predicting the importance of each object directly from a segmented image; our function combines many object-related and image-related features. We validate our importance predictions on a large set of objects and find that the most important objects may be identified automatically. We find that object position and size are particularly informative, while a popular measure of saliency is not.
\r\n\r\nThe second part explores the relationship between object naming, eye movements, and saliency maps. Eye movements correlate with shifts in attention and are thought to be a consequence of optimal resource allocation for high-level tasks such as visual recognition. Saliency maps, are often built on the assumption that \"early\" features (e.g., color, contrast, orientation, and motion) as opposed to objects themselves drive attention. We measure the eye position of humans viewing scenes and then ask them to recall objects that they saw in each scene. Weighted with recall frequency or maximum saliency, these objects predict fixations in individual images better than early saliency, suggesting that early saliency may have an indirect effect on attention, acting through detected objects.
\r\n\r\nThe third part explores the problem of locating objects in a scene irrespective of category. We introduce the first benchmark for category-independent object detection. It is composed of a large public dataset of annotated high-resolution scene images and suitable metrics for performance evaluation. We demonstrate our benchmark by comparing three methods for generalized object detection against a baseline and an upper bound.
" }, { "name": "Stohlman, Olive Remington", "degree": "PhD", "year": "2011", "title": "Repeatability of Joint-Dominated Deployable Masts", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242011-022845109", "creators": [ { "name": { "family": "Stohlman", "given": "Olive Remington" }, "id": "Stohlman-Olive-Remington", "display_name": "Stohlman, Olive Remington" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Kim", "given": "Yunjin" }, "id": "Kim-Yunjin", "role": "member", "display_name": "Kim, Yunjin" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D3AR-G573", "abstract": "Deployable masts are a class of structure that can be stowed in a small volume and expanded into long, slender, and stable booms. Their greatest benefit as space structures is their packing ratio: masts can typically be packed to a fraction of their deployed length at a diameter only modestly wider than their deployed width. This thesis is concerned with precision deployable masts, which can be stowed and deployed with repeatability of the tip position of better than 1 mm over 60 m. The methods of investigation are experimental measurements of a sample mast and numerical modeling of the mast with specially attention to hysteretic joints.
\r\n\r\nA test article of an ADAM mast was used for the experimental work. Two categories of experi- ment were pursued: measurements of mast components as inputs to the model, and measurements of full bays as validation cases for the model. Measurements of the longeron ball end joint friction, cable preload, and latch behavior are of particular note, and were evaluated for their variability. Further measurements were made of a bay in torsion and a short two-bay mast in shear, showing that there is residual displacement in this mast after shear loading is applied and released.
\r\n\r\nThe modeling approach is described in detail, with attention to the treatment of the mast latches, which lock the structure in its deployed configuration. A user element subroutine was used within the framework of the Abaqus finite element analysis solver to model the behavior of the latches with high fidelity.
\r\n\r\nValidation cases for the model are presented in comparison with experimental observations of a two-bay mast. These cases show that the model captures a number of important and complex nonlinear effects of the hysteretic mast components. Parametric studies of the impacts of component behaviors and modeling practices are explored, emphasizing the impacts of part variability and the idealization of the mast latching mechanisms.
" }, { "name": "Suryanarayana, Phanish", "degree": "PhD", "year": "2011", "title": "Coarse-Graining Kohn-Sham Density Functional Theory", "advisor": "Bhattacharya, Kaushik; Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292011-200916324", "creators": [ { "name": { "family": "Suryanarayana", "given": "Phanish" }, "id": "Suryanarayana-Phanish", "display_name": "Suryanarayana, Phanish" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "co-advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GCKH-EX20", "abstract": "Defects, though present in relatively minute concentrations, play a significant role in determining macroscopic properties. Even vacancies, the simplest and most common type of defect, are fundamental to phenomena like creep, spall and radiation ageing. This necessitates an accurate characterization of defects at physically relevant concentrations, which is typically in parts per million. This represents a unique challenge since both the electronic structure of the defect core as well as the long range elastic field need to be resolved simultaneously. Unfortunately, accurate ab-initio electronic structure calculations are limited to a few hundred atoms, which is orders of magnitude smaller than that necessary for a complete description. Thus, defects represent a truly challenging multiscale problem.
\r\n\r\nDensity functional theory developed by Hohenberg, Kohn and Sham (DFT) is a widely accepted, reliable ab-initio method for computing a wide range of material properties. We present a real-space, non-periodic, finite-element and max-ent formulation for DFT. We transform the original variational problem into a local saddle-point problem, and show its well-posedness by proving the existence of minimizers. Further, we prove the convergence of finite-element approximations including numerical quadratures. Based on domain decomposition, we develop parallel finite-element and max-ent implementations of this formulation capable of performing both all-electron and pseudopotential calculations. We assess the accuracy of the formulation through selected test cases and demonstrate good agreement with the literature.
\r\n\r\nTraditional implementations of DFT solve for the wavefunctions, a procedure which has cubic-scaling with respect to the number of atoms. This places serious limitations on the size of the system which can be studied. Further, they are not amenable to coarse-graining since the wavefunctions need to be orthonormal, a global constraint. To overcome this, we develop a linear-scaling method for DFT where the key idea is to directly evaluate the electron density without solving for the individual wavefunctions. Based on this linear-scaling method, we develop a numerical scheme to coarse-grain DFT derived solely based on approximation theory, without the introduction of any new equations and resultant spurious physics. This allows us to study defects at a fraction of the original computational cost, without any significant loss of accuracy. We demonstrate the efficiency and efficacy of the proposed methods through examples. This work enables the study of defects like vacancies, dislocations, interfaces and crack tips using DFT to be computationally viable.
" }, { "name": "Tao, Molei", "degree": "PhD", "year": "2011", "title": "Multiscale Geometric Integration of Deterministic and Stochastic Systems", "advisor": "Owhadi, Houman; Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-171044915", "creators": [ { "name": { "family": "Tao", "given": "Molei" }, "id": "Tao-Molei", "display_name": "Tao, Molei" } ], "advisors": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "advisor", "display_name": "Owhadi, Houman" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "co-advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "cds" ], "doi": "10.7907/6J83-7C18", "abstract": "In order to accelerate computations and improve long time accuracy of numerical simulations, this thesis develops multiscale geometric integrators.
\r\n\r\nFor general multiscale stiff ODEs, SDEs, and PDEs, FLow AVeraging integratORs (FLAVORs) have been proposed for the coarse time-stepping without any identification of the slow or the fast variables. In the special case of deterministic and stochastic mechanical systems, symplectic, multisymplectic, and quasi-symplectic multiscale integrators are easily obtained using this strategy.
\r\n\r\nFor highly oscillatory mechanical systems (with quasi-quadratic stiff potentials and possibly high-dimensional), a specialized symplectic method has been devised to provide improved efficiency and accuracy. This method is based on the introduction of two highly nontrivial matrix exponentiation algorithms, which are generic, efficient, and symplectic (if the exact exponential is symplectic).
\r\n\r\nFor multiscale systems with Dirac-distributed fast processes, a family of symplectic, linearly-implicit and stable integrators has been designed for coarse step simulations. An application is the fast and accurate integration of constrained dynamics.
\r\n\r\nIn addition, if one cares about statistical properties of an ensemble of trajectories, but not the numerical accuracy of a single trajectory, we suggest tuning friction and annealing temperature in a Langevin process to accelerate its convergence.
\r\n\r\nOther works include variational integration of circuits, efficient simulation of a nonlinear wave, and finding optimal transition pathways in stochastic dynamical systems (with a demonstration of mass effects in molecular dynamics).
" }, { "name": "Tchieu, Andrew Allen", "degree": "PhD", "year": "2011", "title": "The Development of Low-Order Models for the Study of Fluid-Structure Interactions", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-133354529", "creators": [ { "name": { "family": "Tchieu", "given": "Andrew Allen" }, "id": "Tchieu-Andrew-Allen", "display_name": "Tchieu, Andrew Allen" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SYHX-8A77", "abstract": "In this work, several low-order models are derived to describe and simulate fluid-structure interaction problems with rigid bodies at a modest computational cost. The models are based on the inviscid flow assumption such that potential theory can be used with, in some cases, point vortices in the flow. Three general areas of application are considered. First, a thin airfoil undergoing small-scale unsteady motions in the presence of a freestream flow is investigated. The low-order model that is developed has only one ordinary differential equation for the fluid dynamic variables. This model is used to briefly investigate vortex-induced flutter in the attached-flow regime and control of a free-flying airfoil using synthetic jet actuators. Second, the vortex-induced vibrations of an arbitrary bluff body in the presence of vortices, with or without a freestream flow, are considered. Several examples of the canonical mass-spring-damper system for a circular cylinder and a flat plate are given to demonstrate the use of the vortex-based model for these applications. Finally, the two-body problem in a potential flow is addressed. A relatively simple solution specific to the doubly connected domain is determined and its resulting force and moment are coupled to the rigid bodies to investigate the mutual interactions between the two bodies. Aspects of drafting behind a forced body, the role of the fluid in elastic collision, and flapping flight are discussed in this context. Although a few specific examples and applications are given for each chapter, the main purpose of the thesis is to present low-order potential flow methods that are applicable to a variety of situations.\r\n" }, { "name": "Vakili, Ali", "degree": "PhD", "year": "2011", "title": "Random Matrix Recursions in Estimation, Control, and Adaptive Filtering", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022011-214438378", "creators": [ { "name": { "family": "Vakili", "given": "Ali" }, "id": "Vakili-Ali", "display_name": "Vakili, Ali" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/HCKN-7W53", "abstract": "This dissertation is devoted to the study of estimation and control over systems that can be described by linear time-varying state-space models. Examples of such systems are encountered frequently in systems theory, e.g., wireless sensor networks, adaptive filtering, distributed control, etc. Recent developments in distributed catastrophe surveillance, smart transportation, and power grid control systems further motivate such a study.
\r\n\r\nWhile linear time-invariant systems are well-understood, there is no general theory that captures various aspects of time-varying counterparts. With little exception, tackling these problems normally boils down to studying time-varying linear or non-linear recursive matrix equations, known as Lyapunov and Riccati recursions that are notoriously hard to analyze. We employ the theory of random matrices to elucidate different facets of these recursions and answer several important questions about the performance, stability, and convergence of estimation and control over such systems.
\r\n\r\nWe make two general assumptions. First, we assume that the coefficient matrices are drawn from jointly stationary matrix-valued random processes. The stationarity assumption hardly restricts the analysis since almost all cases of practical interest fall into this category. We further assume that the state vector size, n, is relatively large. The law of large numbers however guarantees fast convergence to the asymptotic results for n being as small as 10. Under these assumptions, we develop a framework capable of characterizing steady-state and transient behavior of adaptive filters and control and estimation over communication networks. This framework proves promising by successfully tackling several problems for the first time in the literature.
\r\n\r\nWe first study random Lyapunov recursions and characterize their transient and steady-state behavior. Lyapunov recursions appear in several classes of adaptive filters and also as lower bounds of random Riccati recursions in distributed Kalman filtering. We then look at random Riccati recursions whose nonlinearity makes them much more complicated to study. We investigate standard recursive-least-squares (RLS) filtering and extend our analysis beyond the standard case to filtering with multiple measurements, as well as the case of intermittent measurements. Finally, we study Kalman filtering with intermittent observations, which is frequently used to model wireless sensor networks. In all of these cases we obtain interesting universal laws that depend on the structure of the problem, rather than specific model parameters. We verify the accuracy of our results through various simulations for systems with as few as 10 states.
\r\n" }, { "name": "Van Valen, David Ashley", "degree": "PhD", "year": "2011", "title": "Case Studies in Quantitative Biology: Biochemistry on a Leash and a Single-Molecule Hershey-Chase Experiment", "advisor": "Phillips, Robert B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112011-144451576", "creators": [ { "name": { "family": "Van Valen", "given": "David Ashley" }, "id": "Van-Valen-David-Ashley", "orcid": "0000-0001-7534-7621", "display_name": "Van Valen, David Ashley" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "advisor", "display_name": "Phillips, Robert B." } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "orcid": "0009-0007-4566-8441", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "member", "display_name": "Roukes, Michael Lee" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/FJW3-G615", "abstract": "The last 50 years of biological research has seen a marked increase in the amount of quantitative data that describes living systems. This wealth of data provides a unique opportunity to recast the pictorial level descriptions of biological processes in the language of mathematics, with the hope that such an undertaking will lead to deeper insights into the behavior of living systems. To achieve this end, we have undertaken three case studies in physical biology. In the first case study, we used statistical mechanics and polymer physics to construct a simple model that describes how flexible chains of amino acids, referred to as tethers, influence the information processing properties of signaling proteins. In the second case study, we studied the DNA ejection process of phage lambda in vitro. In particular, we used bulk and single-molecule methods to study the control parameters that govern the force and kinematics of the ejection process in vitro. In the last case study, we studied the DNA ejection process of phage lambda in vivo. We developed an assay that allows real-time monitoring of DNA ejection in vivo at the single-molecule level. We also developed a parallel system that allows the simultaneous visualization of both phage capsids and phage DNA at the single-cell level, constituting a true single-molecule Hershey-Chase experiment. The work described in this thesis outlines new tools, both in theory and experiment, that can be used to study biological systems as well as a paradigm that can be employed to mathematicize the cartoons of biology.
" }, { "name": "Venturini, Gabriela Natalia", "degree": "PhD", "year": "2011", "title": "Topics in Multiscale Modeling of Metals and Metallic Alloys", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:11222010-114324484", "creators": [ { "name": { "family": "Venturini", "given": "Gabriela Natalia" }, "id": "Venturini-Gabriela-Natalia", "display_name": "Venturini, Gabriela Natalia" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "orcid": "0000-0001-6558-0323", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Marian", "given": "Jaime" }, "id": "Marian-J", "orcid": "0000-0001-9000-3405", "role": "member", "display_name": "Marian, Jaime" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D6YS-B365", "abstract": "In a number of areas of application, the behavior of systems depends sensitively on properties that pertain to the atomistic scale, i. e., the angstrom and femtosecond scales. However, generally the behaviors of interest are macroscopic and are characterized by slow evolution on the scale of meters and years. This broad disparity of length and time scales places extraordinary challenges in computational material science.
\r\n\r\nThe overarching objective of this dissertation is to address the problem of multiple space and time scales in atomistic systems undergoing slow macroscopic evolution while retaining full atomistic detail. Our approach may be summarized as follows:
\r\n\r\n(1) The issue of accounting for finite temperature in coarse grained systems has not been solved entirely. For finite temperature systems at equilibrium, constructing an effective free energy in terms of a reduced set of atomic degrees of freedom is still an open area of research. In particular, the thermal vibrations of the missing degrees of freedom need to be accounted for. This is specially important if the aim of the simulation is to determine the dynamic properties of a system, or to allow the transmission of dynamic information between regions of different spatial discretization. To this end, we introduce a framework to simulate (spatially) coarse dynamic systems using the Quasicontinuum method (QC). The equations of motion are strictly derived from dissipative Lagrangian mechanics, which provides a classical Langevin implementation where the characteristic time is governed by the vibrations of the finest length scale in the computational cell. In order to assess the framework's ability to transmit information across scales, we study the phonon impoverish spectra in coarse regions and the resulting underestimation of thermal equilibrium properties.
\r\n\r\n(2) Atomistic simulations have been employed for the past thirty years to determine structural and thermodynamic (equilibrium) properties of solids and their defects over a wide range of temperatures and pressures. The traditional Monte Carlo (MC) and Molecular Dynamics (MD) methods, while ideally suited to these calculations, require appreciable computational resources in order to calculate the long-time averages from which properties are obtained. In order to permit a reasonably quick, but accurate determination of the equilibrium properties of interest, we present an extension of the \u201cmaximum entropy\u201d method to build effective alloy potentials while avoiding the treatment of all the system's atomic degrees of freedom. We assess the validity of the model by testing its ability to reproduce experimental measurements.
\r\n\r\n(3) Based upon these effective potentials, we present a numerical framework capable of following the time evolution of atomistic systems over time windows currently beyond the scope of traditional atomistic methods such as Molecular Dynamics (MD) or Monte Carlo (MC). This is accomplished while retaining the underlying atomistic description of the material. We formulate a discrete variational setting in which the simulation of time-dependent phenomena is reduced to a sequence of incremental problems, each characterized by a variational principle. In this fashion we are able to study the interplay between deformation and diffusion using time steps or strain rates that are orders of magnitude larger or smaller than their MD|MC counterparts.
\r\n\r\n(4) We formulate a new class of \u201cReplica Time Integrators\u201d (RTIs) that allows for the two-way transmission of thermal phonons across mesh interfaces. This two-way transmission is accomplished by representing the state of the coarse region by a collection of identical copies or \u201creplicas\u201d of itself. Each replica runs at its own slow time step and is out-of-phase with respect to the others by one fast time step. Then, each replica is capable of absorbing from the fine region the elementary signal that is in phase with the replica. Conversely, each replica is capable of supporting --and transmitting to the fine region-- an elementary signal of a certain phase. Since fine and coarse regions evolve asynchronously in time, RTIs permit both spatial and temporal coarse graining of the system of interest. Using a combination of phase-error analysis and numerical testing we find that RTIs are convergent, and allow step waves and thermal phonons to cross mesh interfaces in both directions losslessly.
\r\n" }, { "name": "Vermesh, Udi Benjamin", "degree": "PhD", "year": "2011", "title": "Technologies for Protein Analysis and Tissue Engineering, with Applications in Cancer", "advisor": "Heath, James R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182010-040540249", "creators": [ { "name": { "family": "Vermesh", "given": "Udi Benjamin" }, "id": "Vermesh-Udi-Benjamin", "display_name": "Vermesh, Udi Benjamin" } ], "advisors": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "orcid": "0000-0001-5356-4385", "role": "advisor", "display_name": "Heath, James R." } ], "committee": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "orcid": "0000-0001-5356-4385", "role": "chair", "display_name": "Heath, James R." }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "orcid": "0000-0003-3175-4596", "role": "member", "display_name": "Tirrell, David A." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "orcid": "0000-0002-0057-7817", "role": "member", "display_name": "Grubbs, Robert H." } ], "option_major": [ "bioeng" ], "doi": "10.7907/21G2-0A20", "abstract": "The first part of this thesis describes electrolyte transport through an array of 20 nm wide, 20 \u03bcm long SiO2 nanofluidic transistors. At sufficiently low ionic strength, the Debye screening length exceeds the channel width, and ion transport is limited by the negatively charged channel surfaces. At source-drain biases > 5 V, the current exhibits a sharp, nonlinear increase, with a 20 \u2212 50-fold conductance enhancement. This behavior is attributed to a breakdown of the zero-slip condition. Implications for peptide sequencing as well as energy conversion devices are discussed.
\r\n\r\nThe next part describes a technology for the detection of the highly aggressive brain cancer glioblastoma multiforme (GBM). In this study, we used an antibody-based microarray to compare plasma samples from glioblastoma patients and healthy controls with respect to the plasma levels of 35 different proteins known to be generally associated with tumor growth, survival, invasion, migration, and immune regulation. Average-linkage hierarchical clustering of the patient data stratified the two groups effectively, permitting accurate assignment of test samples into either GBM or healthy control groups with a sensitivity and specificity as high as 90 % and 94 %, respectively. Using the same 35-protein panel, we then analyzed plasma samples from GBM patients who were treated with the chemotherapeutic drug Avastin (Bevacizumab) and were able to effectively stratify patients based on treatment-responsiveness.
\r\n\r\nFinally, single-cell resolution patterning of tissue engineered structures is demonstrated. The proper functioning of engineered constructs for tissue and organ transplantation requires positioning different cell types in anatomically precise arrangements that mimic their configurations in native tissues. Toward this end, we have developed a technique that involves two microfluidic-patterning steps run perpendicularly to each other using \u201canchor\u201d and \u201cbridge\u201d DNA oligomers to create dense arrays of DNA grids which can then be converted into cell arrays. As a proof-of-concept, both a neuron-astrocyte construct and a pancreatic islet construct containing 2 distinct islet cell types were patterned separately as a dense array of cell grids. Once fixed in a hydrogel matrix, layers of patterned cells were then stacked to form 3-D tissue engineered constructs.
\r\n" }, { "name": "Vyetrenko, Svitlana S.", "degree": "PhD", "year": "2011", "title": "Network Coding for Error Correction", "advisor": "Ho, Tracey C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032011-153909265", "creators": [ { "name": { "family": "Vyetrenko", "given": "Svitlana S." }, "id": "Vyetrenko-Svitlana-S", "display_name": "Vyetrenko, Svitlana S." } ], "advisors": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "advisor", "display_name": "Ho, Tracey C." } ], "committee": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "chair", "display_name": "Ho, Tracey C." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "orcid": "0000-0003-1024-1791", "role": "member", "display_name": "Tropp, Joel A." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/D2ZM-V541", "abstract": "In this thesis, network error correction is considered from both theoretical and practical viewpoints. Theoretical parameters such as network structure and type of connection (multicast vs. nonmulticast) have a profound effect on network error correction capability. This work is also dictated by the practical network issues that arise in wireless ad-hoc networks, networks with limited computational power (e.g., sensor networks) and real-time data streaming systems (e.g., video/audio conferencing or media streaming).
\r\n\r\nFirstly, multicast network scenarios with probabilistic error and erasure occurrence are considered. In particular, it is shown that in networks with both random packet erasures and errors, increasing the relative occurrence of erasures compared to errors favors network coding over forwarding at network nodes, and vice versa. Also, fountain-like error-correcting codes, for which redundancy is incrementally added until decoding succeeds, are constructed. These codes are appropriate for use in scenarios where the upper bound on the number of errors is unknown a priori.
\r\n\r\nSecondly, network error correction in multisource multicast and nonmulticast network scenarios is discussed. Capacity regions for multisource multicast network error correction with both known and unknown topologies (coherent and noncoherent network coding) are derived. Several approaches to lower- and upper-bounding error-correction capacity regions of general nonmulticast networks are given. For 3-layer two-sink and nested-demand nonmulticast network topologies some of the given lower and upper bounds match. For these network topologies, code constructions that employ only intrasession coding are designed. These designs can be applied to streaming erasure correction code constructions.
" }, { "name": "Walavalkar, Sameer Sudhir", "degree": "PhD", "year": "2011", "title": "Optical, Mechanical, and Electronic Properties of Etched Silicon Nanopillars ", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162011-142708481", "creators": [ { "name": { "family": "Walavalkar", "given": "Sameer Sudhir" }, "id": "Walavalkar-Sameer-Sudhir", "display_name": "Walavalkar, Sameer Sudhir" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Wong", "given": "Joyce Y." }, "id": "Wong-J-Y", "role": "member", "display_name": "Wong, Joyce Y." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/QCW6-0C39", "abstract": "This work focuses on the fabrication, characterization and applications of silicon nanopillars. We explain the techniques involved in creating sub 50 nm diameter pillars with aspect ratios of 60:1. Original work encompassed the use of a novel etch mask made of reactive ion sputtered aluminum oxide, 'pseudo-Bosch' inductively coupled reactive ion etching (ICP-RIE) to etch structures on the nanoscale. These methods demonstrate a unique approach to the largely 'bottom-up' technology used in nanowire fabrication.
\r\n\t\t\r\nWe also explored the self-terminating oxidation behavior of convex, two-dimension silicon structures. It was found that during the oxidation process, strain built up at the moving Si-SiO2 interface eventually led to a cessation of oxidation. This was used to predictably reduce the diameter of these pillars to 2 nm, making 'nanowhiskers.' We were able to characterize the results of this oxidation non-destructively by utilizing reflection mode transmission electron microscopy (R-TEM).
\r\n\t \t\t\r\nUsing spun-on PMMA and an electron beam to constrict it and bend the pillars, we were able to incorporate as much as 25% strain. More interestingly this deformation appeared to be elastic, as the pillars, once freed from the polymer, would snap back to their upright position.
\r\n\t\t\t\t\r\nA consequence of the creation of silicon nanowhiskers was that silicon, a normally poor light emitter due to its indirect bandgap, became photoluminescent. As we reduced the diameter we noticed that the bandgap became direct and the emission peak was blue-shifted. We were able to utilize a tight-binding model (TBM) that was modified by the oxidation induced strain. This modified model predicted the blue-shift in peak emission wavelength with decreasing pillar diameter. The strain induced in the pillar during the oxidation played a significant role in the peak emission wavelength and shape of the bandstructure. By corrugating the pillars with an oscillating etch technique we were able to turn our nanopillars into quantum dots which also proved to photoluminesce.
\r\n\t\r\nFinally we look at the possibilities of creating a silicon light emitting diode. By creating a double-gated structure it is possible to overcome the difficulties encountered with sub 5 nm diameter pillars. A possible fabrication process, and the current work done to implement it, is presented as well as a simulation explaining the behavior of this device in the future.
" }, { "name": "Ward, Geoffrey M.", "degree": "PhD", "year": "2011", "title": "The Simulation of Shock- and Impact-Driven Flows with Mie-Gr\u00fcneisen Equations of State", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162010-115725941", "creators": [ { "name": { "family": "Ward", "given": "Geoffrey M." }, "id": "Ward-Geoffrey-M", "display_name": "Ward, Geoffrey M." } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8Q2Q-GT29", "abstract": "An investigation of shock- and impact-driven flows with Mie-Gr\u00fcneisen equation of state derived from a linear shock-particle speed Hugoniot relationship is presented. Cartesian mesh methods using structured adaptive refinement are applied to simulate several flows of interest in an Eulerian frame of reference. The flows central to the investigation include planar Richtmyer-Meshkov instability, the impact of a sphere with a plate, and an impact-driven Mach stem.
\r\n\r\nFirst, for multicomponent shock-driven flows, a dimensionally unsplit, spatially high-order, hybrid, center-difference, limiter methodology is developed. Effective switching between center-difference and upwinding schemes is achieved by a set of robust tolerance and Lax-entropy-based criteria [49]. Oscillations that result from such a mixed stencil scheme are minimized by requiring that the upwinding method approaches the center-difference method in smooth regions. To attain this property a blending limiter is introduced based on the norm of the deviation of WENO reconstruction weights from ideal. The scheme is first demonstrated successfully for the linear advection equation in spatially fourth- and sixth-order forms. A spatially fourth-order version of the method that combines a skew-symmetric kinetic-energy preserving center-difference scheme with a Roe-Riemann solver is then developed and implemented in Caltech's Adaptive Mesh Refinement, Object-oriented C++ (AMROC) [16,17] framework for Euler flows.
\r\n\r\nThe solver is then applied to investigate planar Richtmyer-Meshkov instability in the context of an equation of state comparison. Comparisons of simulations with materials modeled by isotropic stress Mie-Gr\u00fcneisen equations of state derived from a linear shock-particle speed Hugoniot relationship [36,52] to those of perfect gases are made with the intention of exposing the role of the equation of state. First, results for single- and triple-mode planar Richtmyer-Meshkov instability between mid-ocean ridge basalt (MORB) and molybdenum modeled by Mie-Gr\u00fcneisen equations of state are presented for the case of a reflected shock. The single-mode case is explored for incident shock Mach numbers of 1.5 and 2.5. For the planar triple-mode case a single incident Mach number of 2.5 is examined with the initial corrugation wave numbers related by k\u2081=k\u2082+k\u2083. A comparison is drawn to Richtmyer-Meshkov instability in fluids with perfect gas equations of state utilizing matching of a nondimensional pressure jump across the incident shock, the post-shock Atwood ratio, post-shock amplitude-to-wavelength ratio, and time nondimensionalized by the Rcithmyer linear-growth rate time constant prediction. Result comparison demonstrates difference in start-up time and growth rate oscillations. Growth rate oscillation frequency is seen to correlate directly to the expected oscillation frequency of the transmitted and reflected shocks. For the single-mode cases, further comparison is given for vorticity distribution and corrugation centerline shortly after shock interaction that demonstrates only minor differences.
\r\n\r\nAdditionally, examined is single-mode Richtmyer-Meshkov instability when a reflected expansion wave is present for incident Mach numbers of 1.5 and 2.5. Comparison to perfect gas solutions in such cases yields a higher degree of similarity in start-up time and growth rate oscillations. Vorticity distribution and corrugation centerline shortly after shock interaction is also examined. The formation of incipient weak shock waves in the heavy fluid driven by waves emanating from the perturbed transmitted shock is observed when an expansion wave is reflected.
\r\n\r\nNext, the ghost fluid method [83] is explored for application to impact-driven flows with Mie-Gr\u00fcneisen equations of state in a vacuum. Free surfaces are defined utilizing a level-set approach. The level-set is reinitialized to the signed distance function periodically by solution to a Hamilton-Jacobi differential equation in artificial time. Flux reconstruction along each Cartesian direction of the domain is performed by subdividing in a way that allows for robust treatment of grid-scale sized voids. Ghost cells in voided regions near the material-vacuum interface are determined from surface-normal Riemann problem solution. The method is then applied to several impact problems of interest. First, a one-dimensional impact problem is examined in Mie-Gr\u00fcneisen aluminum with simple point erosion used to model separation by spallation under high tension. A similar three-dimensional axisymmetric simulation of two rods impacting is then performed without a model for spallation. Further results for three-dimensional axisymmetric simulation of a sphere hitting a plate are then presented.
\r\n\r\nFinally, a brief investigation of the assumptions utilized in modeling solids as isotropic fluids is undertaken. An Eulerian solver approach to handling elastic and elastic-plastic solids is utilized for comparison to the simple fluid model assumption. First, in one dimension an impact problem is examined for elastic, elastic-plastic, and fluid equations of state for aluminum. The results demonstrate that in one dimension the fluid models the plastic shock structure of the flow well. Further investigation is made using a three-dimensional axisymmetric simulation of an impact problem involving a copper cylinder surrounded by aluminum. An aluminum slab impact drives a faster shock in the outer aluminum region yielding a Mach reflection in the copper. The results demonstrate similar plastic shock structures. Several differences are also notable that include a lack of roll-up instability at the material interface and slip-line emanating from the Mach stem's triple point.
" }, { "name": "Weng, Ching-Chih", "degree": "PhD", "year": "2011", "title": "The Roles of Majorization and Generalized Triangular Decomposition in Communication and Signal Processing", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06032011-113200456", "creators": [ { "name": { "family": "Weng", "given": "Ching-Chih" }, "id": "Weng-Ching-Chih", "display_name": "Weng, Ching-Chih" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Tkacenko", "given": "Andre" }, "id": "Tkacenko-A", "role": "member", "display_name": "Tkacenko, Andre" }, { "name": { "family": "Quirk", "given": "Kevin J." }, "id": "Quirk-K-J", "role": "member", "display_name": "Quirk, Kevin J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/2R1B-QE65", "abstract": "Signal processing is an art that deals with the representation, transformation, and manipulation of the signals and the information they contain based on their specific features. The field of signal processing has always benefited from the interaction between theory, applications, and technologies for implementing the systems. The development of signal processing theory, in particular, relies heavily on mathematical tools including analysis, probability theory, matrix theory, and many others.
\r\n\r\nRecently, the theory of majorization, which is an extremely useful tool for deriving inequalities, was introduced to the signal processing society in the context of MIMO communication system design. This also led many researchers to develop a fundamental matrix decomposition called generalized triangular decomposition (GTD), which was general enough to include many existing matrix orthogonal decompositions as special cases.
\r\n\r\nThe main contribution of this thesis is toward the use of majorization and GTD to the theory and many applications of signal processing. In particular, the focus is on developing new signal processing methods based on these mathematical tools for digital communication, data compression, and filter bank design. We revisit some classical problems and show that the theories of majorization and GTD provide a general framework for solving these problems. For many important new problems not solved earlier, they also provide elegant solutions.
\r\n\r\nThe first part of the thesis focuses on transceiver design for multiple-input multiple-output (MIMO) communications. The first problem considered is the joint optimization of transceivers with linear precoders, decision feedback equalizers (DFEs), and bit allocation schemes for frequency flat MIMO channels. We show that the generalized triangular decomposition offers an optimal family of solutions to this problem. This general framework incorporates many existing designs, such as the optimal linear transceiver, the ZF-VBLAST system, and the geometric mean decomposition (GMD) transceiver, as special cases. It also predicts many novel optimal solutions that have not been observed before. We also discuss the use of each of these theoretical solutions under practical considerations. In addition to total power constraints, we also consider the transceiver optimization under individual power constraints and other linear constraints on the transmitting covariance matrix, which includes a more realistic individual power constraint on each antenna. We show the use of semi-definite programming (SDP), and the theory of majorization again provides a general framework for optimizing the linear transceivers as well as the DFE transceivers. The transceiver design for frequency selective MIMO channels is then considered. Block diagonal GMD (BD-GMD), which is a special instance of GTD with block diagonal structure in one of the semi-unitary matrices, is used to design transceivers that have many desirable properties in both performance and computation.
\r\n\r\nThe second part of the thesis focuses on signal processing algorithms for data compressions and filter bank designs. We revisit the classical transform coding problem (for optimizing the theoretical coding gain in the high bit rate regime) from the view point of GTD and majorization theory. A general family of optimal transform coders is introduced based on GTD. This family includes the Karhunen-Lo\\'{e}ve transform (KLT), and the prediction-based lower triangular transform (PLT) as special cases. The coding gain of the entire family, with optimal bit allocation, is maximized and equal to those of the KLT and the PLT. Other special cases of the GTD-TC are the GMD (geometric mean decomposition) and the BID (bidiagonal transform). The GMD in particular has the property that the optimum bit allocation is a uniform allocation. We also propose using dither quantization in the GMD transform coder. Under the uniform bit loading scheme, it is shown that the proposed dithered GMD transform coders perform significantly better than the original GMD coder in the low rate regime.
\r\n\r\nAnother important signal processing problem, namely the filter bank optimization based on the knowledge of input signal statistics, is then considered. GTD and the theory of majorization are again used to give a new look to this classical problem. We propose GTD filter banks as subband coders for optimizing the theoretical coding gain. The orthonormal GTD filter bank and the biorthogonal GTD filter bank are discussed in detail. We show that in both cases there are two fundamental properties in the optimal solutions, namely, {\\it total decorrelation} and {\\it spectrum equalization}. The optimal solutions can be obtained by performing the frequency dependent GTD on the Cholesky factor of the input power spectrum density matrices. We also show that in both theory and numerical simulations, the optimal GTD subband coders have superior performance than optimal traditional subband coders. In addition, the uniform bit loading scheme can be used in the optimal biorthogonal GTD coders with no loss of optimality. This solves the granularity problem in the conventional optimum bit loading formula. The use of the GTD filter banks in frequency selective MIMO communication systems is also discussed. Finally, the connection between the GTD filter bank and the traditional filter bank is clearly indicated.
\r\n" }, { "name": "White, Jerome S.", "degree": "PhD", "year": "2011", "title": "Applying Formal Methods to Distributed Algorithms Using Local-Global Relations ", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312011-123940546", "creators": [ { "name": { "family": "White", "given": "Jerome S." }, "id": "White-Jerome-S", "display_name": "White, Jerome S." } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Holzmann", "given": "Gerard J." }, "id": "Holzmann-G-J", "role": "member", "display_name": "Holzmann, Gerard J." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/8FRW-ZF17", "abstract": "This thesis deals with the design and analysis of distributed systems in which homogeneous, autonomous agents collaborate to achieve a common goal. The class of problems studied includes consensus algorithms in which all agents eventually come to an agreement about a specific action. The thesis proposes a framework, called local-global, for analyzing these systems. A local interaction is an interaction among subsets of agents, while a global interaction is one among all agents in the system. Global interactions, in practice, are rare, yet they are the basis by which correctness of a system is measured. For example, if the problem is to compute the average of a measurement made separately by each agent, and all the agents in the system could exchange values in a single action, then the solution is straightforward: each agent gets the values of all others and computes the average independently. However, if the system consists of a large number of agents with unreliable communication, this scenario is highly unlikely. Thus, the design challenge is to ensure that sequences of local interactions lead, or converge, to the same state as a global interaction.
\r\n\r\nThe local-global framework addresses this challenge by describing each local interaction as if were a global one, encompassing all agents within the system. This thesis outlines the concept in detail, using it to design algorithms, prove their correctness, and ultimately develop executable implementations that are reliable. To this end, the tools of formal methods are employed: algorithms are modeled, and mechanically checked, within the PVS theorem prover; programs are also verified using the Spin model checker; and interface specification languages are used to ensure local-global properties are still maintained within Java and C# implementations. The thesis presents example applications of the framework and discusses a class of problems to which the framework can be applied.
" }, { "name": "Winterrose, Michael Lon", "degree": "PhD", "year": "2011", "title": "Quantum Mechanical Simulation and X-Ray Scattering Applied to Pressure-Induced Invar Anomaly in Magnetic Iron Alloy", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08302010-215155302", "creators": [ { "name": { "family": "Winterrose", "given": "Michael Lon" }, "id": "Winterrose-Michael-Lon", "display_name": "Winterrose, Michael Lon" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Jackson", "given": "Jennifer M." }, "id": "Jackson-J-M", "role": "member", "display_name": "Jackson, Jennifer M." } ], "option_major": [ "matsci" ], "doi": "10.7907/2CBN-7H49", "abstract": "The Invar effect has remained at the forefront of materials research since Charles-\u00c9douard Guillaume discovered the vanishing thermal expansion of Fe-Ni alloys in 1897. More recently, a pressure-induced Invar effect was discovered in Fe-Ni alloys, and the relationship between classical and pressure induced Invar phenomena has added complexity to the century-old struggle to comprehend the microscopic origins of Invar behavior.
\r\n\r\nIn this thesis I present our recent discovery of pressure-induced Invar behavior in Pd\u2083Fe with the ordered L1\u2082 structure. Nuclear forward scattering measurements show that the ferromagnetic ground state in Pd\u2083Fe is destabilized with pressure, collapsing around 10GPa (V/V0=0.96) to a lowspin magnetic state. From high-pressure synchrotron x-ray diffraction measurements we find a large volume collapse at ambient temperature to accompany the collapse of ferromagnetism. After the volume collapse there is a significant increase in the bulk modulus. Using nuclear resonant inelastic x-ray scattering to study the 57Fe phonon partial density of states (PDOS) at high pressures, we find the pressure-induced magnetic transition to cause an anomalous relative softening of the average phonon frequency. Heating our sample to 650K in a furnace at a pressure of 7GPa, synchrotron xray diffraction measurements reveal negligible thermal expansion from 300 to 523 K, demonstrating pressure-induced Invar behavior in Pd\u2083Fe.
\r\n\r\nDensity functional theory calculations identify a ferromagnetic ground state in Pd\u2083Fe with large moments at the Fe sites. These calculations show that the application of pressure counteracts the band-filling effect of Pd. By tuning the position of the top of the 3d band with respect to the Fermi level, pressure-induced Invar behavior resembles classical Invar behavior that is controlled by chemical composition. This insight marks the first step towards a unification of our understanding vii of classical and pressure-induced Invar behavior. Pressure drives the majority-spin t2g antibonding electronic states closer to the Fermi level. The transition to the low-spin state occurs as these t2g states move across the Fermi level, transferring charge to the minority-spin eg nonbonding electronic states. This charge transfer reduces the internal electronic pressure in the material, giving a volume reduction in the low-spin state. The movement of the t2g states with increasing pressure results in a greater number of states at the Fermi level, increasing screening efficiency and softening the first nearest-neighbor Fe-Pd longitudinal force constants in the low-spin state. The measured and calculated magnetic transition pressures differ significantly, despite sharing similar elastic properties in both the ferromagnetic and low-spin states. The magnitude of the disagreement between theoretical and experimental magnetic transition pressures suggests a spin-disordered state exists at high pressures in Pd\u2083Fe. A shape discrepancy between the calculated and measured high-pressure Fe PDOS suggests significant short-range spin correlations exist in this spin-disordered state.
" }, { "name": "Yang, Yue", "degree": "PhD", "year": "2011", "title": "Lagrangian and Vortex-Surface Fields in Turbulence", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechTHESIS:02212011-233246689", "creators": [ { "name": { "family": "Yang", "given": "Yue" }, "id": "Yang-Yue", "display_name": "Yang, Yue" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DF3E-G629", "abstract": "In this thesis, we focus on Lagrangian investigations of isotropic turbulence, wall-bounded turbulence and vortex dynamics. In particular, the evolutionary multi-scale geometry of Lagrangian structures is quantified and analyzed. Additionally, we also study the dynamics of vortex-surface fields for some simple viscous flows with both Taylor--Green and Kida--Pelz initial conditions.
\r\n\r\nFirst, we study the non-local geometry of finite-sized Lagrangian structures in both stationary, evolving homogenous isotropic turbulence and also with a frozen turbulent velocity field. The multi-scale geometric analysis is applied on the evolution of Lagrangian fields, obtained by a particle-backward-tracking method, to extract Lagrangian structures at different length scales and to characterize their non-local geometry in a space of reduced geometrical parameters. Next, we report a geometric study of both evolving Lagrangian, and also instantaneous Eulerian structures in turbulent channel flow at low and moderate Reynolds numbers. A multi-scale and multi-directional analysis, based on the mirror-extended curvelet transform, is developed to quantify flow structure geometry including the averaged inclination and sweep angles of both classes of turbulent structures at multiple scales ranging from the half-height of the channel to several viscous length scales. Results for turbulent channel flow include the geometry of candidate quasi-streamwise vortices in the near-wall region, the structural evolution of near-wall vortices, and evidence for the existence and geometry of structure packets based on statistical inter-scale correlations.
\r\n\r\nIn order to explore the connection and corresponding representations between Lagrangian kinematics and vortex dynamics, we develop a theoretical formulation and numerical methods for computation of the evolution of a vortex-surface field. Iso-surfaces of the vortex-surface field define vortex surfaces. A systematic methodology is developed for constructing smooth vortex-surface fields for initial Taylor--Green and Kida--Pelz velocity fields by using an optimization approach. Equations describing the evolution of vortex-surface fields are then obtained for both inviscid and viscous incompressible flows. Numerical results on the evolution of vortex-surface fields clarify the continuous vortex dynamics in viscous Taylor--Green and Kida--Pelz flows including the vortex reconnection, rolling-up of vortex tubes, vorticity intensification between anti-parallel vortex tubes, and vortex stretching and twisting. This suggests a possible scenario for explaining the transition from a smooth laminar flow to turbulent flow in terms of topology and geometry of vortex surfaces.
\r\n" }, { "name": "Zia, Roseanna Nellie", "degree": "PhD", "year": "2011", "title": "Individual Particle Motion in Colloids: Microviscosity, Microdiffusivity, and Normal Stresses", "advisor": "Brady, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-141745737", "creators": [ { "name": { "family": "Zia", "given": "Roseanna Nellie" }, "id": "Zia-Roseanna-Nellie", "display_name": "Zia, Roseanna Nellie" } ], "advisors": [ { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "advisor", "display_name": "Brady, John F." } ], "committee": [ { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "chair", "display_name": "Brady, John F." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Lauga", "given": "Eric" }, "id": "Lauga-E", "orcid": "0000-0002-8916-2545", "role": "member", "display_name": "Lauga, Eric" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "mecheng" ], "doi": "10.7907/2743-8W26", "abstract": "Colloidal dispersions play an important role in nearly every aspect of life, from paint to biofuels to nano-therapeutics. In the study of these so-called complex \ufb02uids, a connection is sought between macroscopic material properties and the micromechanics of the suspended particles. Such properties include viscosity, diffusivity, and the osmotic pressure, for example. But many such systems are themselves only microns in size overall; recent years have thus seen a dramatic growth in demand for exploring microscale systems at a much smaller length scale than can be probed with conventional macroscopic techniques. Microrheology is one approach to such microscale interrogation, in which a Brownian \u201cprobe\u201d particle is driven through a complex \ufb02uid, and its motion tracked in order to infer the mechanical properties of the embedding material. With no external forcing the probe and background particles form an equilibrium microstructure that \ufb02uctuates thermally with the solvent. Probe motion through the dispersion distorts the microstructure; the character of this deformation, and hence its in\ufb02uence on probe motion, depends on the strength with which the probe is forced, F ext , compared to thermal forces, kT/b, defining a P\u00b4eclet number, P e = F ext /(kT /b), where kT is the thermal energy and b the bath-particle size. Both the mean and the \ufb02uctuating motion of the probe are of interest. Recent studies showed that the reduction in mean probe speed gives the e\ufb00ective material viscosity. But the velocity of the probe also \ufb02uctuates due to collisions with the suspended particles, causing the probe to undergo a random walk process. It is shown that the long-time mean-square \ufb02uctuational motion of the probe is diffusive and the effective diffusivity of the forced probe is determined for the full range of P\u00b4eclet number. At small Pe Brownian motion dominates and the diffusive behavior of the probe characteristic of passive microrheology is recovered, but with an incremental \ufb02ow-induced \u201cmicro-diffusivity\u201d that scales as Dmicro \u223c Da P e 2 \u03c6b , where viii \u03c6b is the volume fraction of bath particles and Da is the self-diffusivity of an isolated probe. At the other extreme of high P\u00b4eclet number the fuctuational motion is still diffusive, and the diffusivity becomes primarily force-induced , scaling as (F ext /\u03b7)\u03c6b , where \u03b7 is the viscosity of the solvent. The force-induced \u201cmicrodiffusivity\u201d is anisotropic, with diffusion longitudinal to the direction of forcing larger in both limits compared to transverse diffusion, but more strongly so in the high-P e limit.
\r\n\r\nPrevious work in microrheology defined a scalar viscosity; however, a tensorial expression for the suspension stress in microrheology was still lacking. The notion that diffusive \ufb02ux is driven by gradients in particle-phase stress leads to the idea that the microdiffusivity can be related directly to the suspension stress. In consequence, the anisotropy of the diffusion tensor may re\ufb02ect the presence of normal stress differences in non-linear microrheology. While the particle-phase stress tensor can be determined as the second moment of the deformed microstructure, in this study a connection is made between diffusion and stress gradients, and an analytical expression for particle-phase stress as a function of the microdiffusivity and microviscosity is obtained. The two approaches agree, suggesting that normal stresses and normal stress differences can be measured in active microrheological experiments if both the mean and mean-square motion of the probe are monitored. Owing to the axisymmetry of the motion about a spherical probe, the second normal stress difference is zero, while the \ufb01rst normal stress difference is linear in P e for P e \u226b 1 and vanishes as P e 3 for P e \u226a 1. An additional important outcome is that the analytical expression obtained for stress-induced migration can be viewed as a generalized non-equilibrium Stokes-Einstein relation.
\r\n\r\nStudies of steady-state dispersion behavior reveal the hydrodynamic and microstructural mechanisms that underlie non-Newtonian behaviors (e.g. shear-thinning, shear-thickening, and normal stress differences). But an understanding of how the microstructures evolve from the equilibrium state, and how non-equilibrium properties develop in time is much less well understood. Transient suspension behavior in the near-equilibrium, linear response regime has been studied via its connection to low-amplitude oscillatory probe forcing and the complex modulus; at very weak forcing, the microstructural response that drives viscosity is indistinguishable from equilibrium \ufb02uctuations. But important information about the basic physical aspects of structural development and relaxation ix in a medium are captured by start-up and cessation of the imposed deformation in the non-linear regime, where the structure is driven far from equilibrium. Here we study the evolution of stress and microstructure in a colloidal dispersion by tracking transient probe motion during start-up and cessation of a strong \ufb02ow. For large P e, steady state is reached when a boundary layer (in which advection balances diffusion) forms at particle contact on the timescale of the \ufb02ow, a/U , where a is the probe size and U its speed. On the other hand, relaxation following cessation occurs over several timescales corresponding to distinct physical processes. For very short times, the timescale for relaxation is set by the diffusion over the boundary-layer thickness. Nearly all stress relaxation occurs during this process, owing to the dependence of the bath-particle drag on the contact value of the microstructure. At longer times the collective diffusion of the bath particles acts to close the wake. In this long-time limit as structural isotropy is restored, the majority of the microstructural relaxation occurs with very little change in suspension stress. Theoretical results are presented and compared with Brownian dynamics simulation. Two regimes of probe motion are studied: an externally applied constant force and an imposed constant velocity. The microstructural evolution is qualitatively different for the two regimes, with a longer transient phase and a thinner boundary layer and longer wake at steady state in the latter case. The work is also compared to analogous results for sheared suspensions undergoing start-up and cessation.
\r\n\r\nThe study moves next to investigations of dual-probe microrheology. Motivated by the phenomenon of equilibrium depletion interactions, we study the interaction between a pair of probe particles translating with equal velocity through a dispersion with their line of centers transverse to the external forcing. The character of the microstructure surrounding the probes is determined both by the distance R by which the two probes are separated and by the strength of the external forcing, P e = U a/Db , where U is the constant probe velocity and Db the diffusivity of the bath particles. Osmotic pressure gradients develop as the microstructure is deformed, giving rise to an interactive force between the probes. This force is studied for a range of P e and R. For all separations R > 2a, the probes attract when P e is small. As the strength of the forcing increases, a qualitative change in the interactive force occurs: the probes repel each other. The probe separation R at which the x attraction-to-repulsion transition occurs decreases as P e increases, because the entropic depletion attraction becomes weak compared to the force-induced osmotic repulsion. The non-equilibrium interactive force is strictly repulsive for two separated probes.
\r\n\r\nBut non-linear microrheology provides far more than a microscale technique for interrogating complex \ufb02uids. In 1906, Einstein published the famous thought experiment in which he proposed that if a liquid were indeed composed of atoms, then the motion of a small particle suspended in the \ufb02uid would move with the same random trajectories as the solvent atoms. Combining the theories of kinetics, diffusion, and thermodynamics, he showed that the diffusive motion of a small particle is indeed evidence of the existence of the atom. Perrin con\ufb01rmed the theory with measurement in 1909. This is a profound conclusion, drawn by simply watching a particle move in a liquid. Here, we follow this example and watch a particle move in a complex \ufb02uid\u2014but now for a system that is not at equilibrium. In equilibrium systems, the relationship between \ufb02uctuation and dissipation is fundamental to our understanding of colloid physics. By studying \ufb02uctuations away from equilibrium, we have discovered an analogous non-equilibrium relation between \ufb02uctuation and dissipation\u2014and that the balance between the two is stored in the material stress. A \ufb01nal connection can be made between this stress and energy storage.
" }, { "name": "Ando, Keita", "degree": "PhD", "year": "2010", "title": "Effects of Polydispersity in Bubbly Flows", "advisor": "Colonius, Tim; Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-133830557", "creators": [ { "name": { "family": "Ando", "given": "Keita" }, "id": "Ando-Keita", "orcid": "0000-0002-9572-8242", "display_name": "Ando, Keita" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "mecheng" ], "doi": "10.7907/SW8K-Y135", "abstract": "This thesis concerns the dynamics of bubbly flows with a distribution of equilibrium bubble sizes. The main goal is to formulate the physical and numerical models of continuum bubbly flows that enable us to efficiently compute the average mixture dynamics. Numerical simulations are conducted to quantify the effects of bubble size distributions on the averaged dynamics for several model flows.
\r\n\r\nFirst, the ensemble-averaged conservation laws for polydisperse bubbly flows are derived. One-way-coupled flow computations are conducted to illustrate that the different-sized bubbles can oscillate with different frequencies. The resulting phase cancellations can be regarded as an apparent damping of the averaged dynamics of polydisperse flows. A high-order-accurate finite-volume method is then developed to compute the flow, paying special attention to issues of wave dispersion and stiffness.
\r\n\r\nNext, computations of one-dimensional shock propagation through bubbly liquids are performed. The numerical experiments reveal that the bubble size distribution has a profound impact on the averaged shock structure. If the distribution is sufficiently broad, the apparent damping due to the phase cancellations can dominate over the single-bubble-dynamic dissipation (due to thermal, viscous, and compressibility effects) and the averaged shock dynamics become insensitive to the individual bubble dynamics. One-dimensional cloud cavitation caused by fluid-structure interaction is also solved to investigate the collapse of cavitation clouds with both monodisperse and polydisperse nuclei. The phase cancellations among the cavitation bubbles with broad nuclei size distributions are found to eliminate violent cloud collapse in the averaged dynamics.
\r\n\r\nFinally, shock propagation through a bubbly liquid-filled, deformable tube is considered. The quasi-one-dimensional conservation law that takes into account structural deformation is formulated and steady shock relations are derived. The results are compared to water-hammer experiments; the present shock theory gives better agreement with the measured wave speeds than linear theory. This indicates that the gas-phase nonlinearity needs to be included to accurately predict the propagation speeds of finite-amplitude waves in a deformable tube filled with a bubbly liquid.
" }, { "name": "Bane, Sally Page Moffett", "degree": "PhD", "year": "2010", "title": "Spark Ignition: Experimental and Numerical Investigation With Application to Aviation Safety", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-173243262", "creators": [ { "name": { "family": "Bane", "given": "Sally Page Moffett" }, "id": "Bane-Sally-Page-Moffett", "orcid": "0000-0002-4764-3228", "display_name": "Bane, Sally Page Moffett" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W1NB-5W06", "abstract": "Determining the risk of accidental ignition of flammable mixtures is a topic of tremendous importance in industry and aviation safety. The concept of minimum ignition energy (MIE) has traditionally formed the basis for studying ignition hazards of fuels. However, in recent years, particularly in the aviation safety industry, the viewpoint has changed to one where ignition is statistical in nature. Approaching ignition as statistical rather than a threshold phenomenon appears to be more consistent with the inherent variability in the engineering test data.
\r\n\r\nIgnition tests were performed in lean hydrogen-based aviation test mixtures and in two hexane-air mixtures using low-energy capacitive spark ignition systems. Tests were carried out using both short, fixed sparks (1 to 2 mm) and variable length sparks up to 10 mm. The results were analyzed using statistical tools to obtain probability distributions for ignition versus spark energy and spark energy density (energy per unit spark length). Results show that a single threshold MIE value does not exist, and that the energy per unit length may be a more appropriate parameter for quantifying the risk of ignition than only the energy. The probability of ignition versus spark charge was also investigated, and the statistical results for the spark charge and spark energy density were compared. It was found that the test results were less variable with respect to the spark charge than the energy density. However, variability was still present due to phenomena such as plasma instabilities and cathode effects that are caused by the electrodynamics.
\r\n\r\nWork was also done to develop a two-dimensional numerical model of spark ignition that accurately simulates all physical scales of the fluid mechanics and chemistry. In this work a two-dimensional model of spark discharge in air and spark ignition was developed using the non-reactive and reactive Navier-Stokes equations. One-step chemistry models were used to allow for highly resolved simulations, and methods for calculating effective one-step parameters were developed using constant pressure explosion theory. The one-step model was tuned to accurately simulate the flame speed, temperature, and straining behavior using one-dimensional flame computations. The simulations were performed with three different electrode geometries to investigate the effect of the geometry on the fluid mechanics of the evolving spark kernel and on flame formation. The computational results were compared with high-speed schlieren visualization of spark and ignition kernels. It was found that the electrode geometry had a significant effect on the fluid motion following spark discharge and hence influences the ignition process.
\r\n" }, { "name": "Buzi, Gentian", "degree": "PhD", "year": "2010", "title": "Control Theoretic Analysis of Autocatalytic Networks in Biology with Applications to Glycolysis ", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:02262010-130618704", "creators": [ { "name": { "family": "Buzi", "given": "Gentian" }, "id": "Buzi-Gentian", "display_name": "Buzi, Gentian" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "El-Samad", "given": "Hana" }, "id": "El-Samad-H", "role": "member", "display_name": "El-Samad, Hana" } ], "option_major": [ "cds" ], "doi": "10.7907/MHMV-9M59", "abstract": "Metabolic networks in the cell break down food and resources to create useful energy and components. At the same time they use those same components and energy in the process, thus making autocatalysis an unavoidable part of core metabolism. The simplest and most widely studied autocatalytic network is the glycolytic pathway. It is common to every cell of living organisms, from bacteria to humans. Its special autocatalytic structure, like the structure of many similar autocatalytic networks, makes the pathway hard to control and can lead to instabilities.
\r\n\r\nIn this thesis, we study autocatalytic metabolic networks, specifically glycolysis, to investigate fundamental performance tradeoffs in these network topologies. We hypothesize that instabilities in glycolysis are a result of performance tradeoffs that stem from the structure of the pathways and a conservation law, mathematically described by a special form of the Bode Sensitivity Integral. We show that pathway size and intermediate metabolite consumption adversely affect the performance of the pathway, while reversibility of chemical reactions improves performance. We establish tight bounds for the feedback control gains that guarantee stability of pathways of arbitrary size and arbitrary parameter values for the intermediate reactions.
\r\n\r\nIn addition, we investigate effects of perturbations in metabolite concentrations through the estimation of invariant subsets of the region of attraction around nominal operating conditions. To this end we use a numerical procedure composed of system theoretic characterizations and optimization-based formulations. For large, computationally intractable systems we employ a different technique based on the underlying biological structure, which offers a natural decomposition of the system into a feedback interconnection of two input-output subsystems. This decomposition simplifies the analysis and leads to analytical construction of Lyapunov functions for a large family of autocatalytic pathways.
\r\n\r\nThe results of our analysis reveal fundamental tradeoffs between performance and robustness, energy efficiency, pathway evolvability and computational complexity in these networks.
" }, { "name": "Cheng, Jie", "degree": "PhD", "year": "2010", "title": "Chemical Fractionation at Environmental Interfaces", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212009-151636210", "creators": [ { "name": { "family": "Cheng", "given": "Jie" }, "id": "Cheng-Jie", "display_name": "Cheng, Jie" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/08FV-FP25", "abstract": "Chemical processes at the interfaces often differ kinetically and mechanistically from the bulk counterparts, partly due to the concentration inhomogeneity of different chemicals at the interfaces. The fractionation of chemicals at the interfaces not only determines their interfacial concentrations, but also affects the physicochemical properties of the interfaces. In this thesis, three sets of chemicals/interfaces with important environmental implications are studied: (1) anion fractionation at the gas\u2013liquid microdroplet interfaces, (2) fractionation of perfluoroalkyl surfactants and matrix components at the bubble\u2013water interface in ultrasonically irradiated solutions, and (3) ion fractionation across the ice\u2013water interface during the freeze\u2013thaw cycle of electrolyte solutions.
\r\n\r\nThe relative anion affinity for the air\u2013water interface, as measured by Electrospray Mass Spectrometry (ES\u2013MS), is exponentially correlated with ionic radius. The affinities respond differently to different additives, suggesting that specific anion effects are due to different energy levels of physical interactions. Relative anion affinities at the air\u2013methanol interfaces are almost identical to those at the air\u2013water interface, suggesting that surface structure is not the primary driving force for interfacial anion fractionation.
\r\n\r\nPerfluoroalkyl carboxylates and sulfonates can be transferred from the ocean to marine aerosols due to their high affinity for the air\u2013water interface, but transfer to gas phase is unlikely as they remain deprotonated in aqueous phase because of their low pKa. Organic matrix components may reduce the sonochemical kinetics of Perfluorooctanesulfonate (PFOS) and Perfluorooctanoate (PFOA) by competitive adsorption onto the bubble\u2013water interface or by lowering the interfacial temperatures. Inorganic anions, but not cations, may significantly enhance or reduce the sonochemical kinetics of PFOS and PFOA. The specific anion effects following the Hofmeister series are likely related to anions\u2019 partitioning to and interaction with the bubble\u2013water interface.
\r\n\r\nTime\u2013resolved confocal fluorescence microscopy of freezing electrolyte solutions reveals that the thickness of interstitial liquid films depends non\u2013monotonically on electrolyte concentration. It also confirms that selective incorporation of cations (anions) into the ice lattice decreases (increases) the pH of the interstitial liquid films. Since the magnitude of pH change during freezing is smaller than during the subsequent thawing process, it is likely to be limited by the seepage of proton or hydroxide slowly produced via water dissociation.
\r\n" }, { "name": "Choi, Harry Ming Tak", "degree": "PhD", "year": "2010", "title": "Programmable In Situ Amplification for Multiplexed Bioimaging", "advisor": "Pierce, Niles A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12292009-170615072", "creators": [ { "name": { "family": "Choi", "given": "Harry Ming Tak" }, "id": "Choi-Harry-Ming-Tak", "orcid": "0000-0002-1530-0773", "display_name": "Choi, Harry Ming Tak" } ], "advisors": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "advisor", "display_name": "Pierce, Niles A." } ], "committee": [ { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "chair", "display_name": "Fraser, Scott E." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." } ], "option_major": [ "bioeng" ], "doi": "10.7907/K4A3-1K41", "abstract": "In situ hybridization methods enable the mapping of mRNA expression within intact biological samples. With current approaches, it is challenging to simultaneously detect multiple target mRNAs in vertebrate embryos and tissue sections \u2013 a significant limitation in attempting to study interacting regulatory elements in systems most relevant to human development and disease. This thesis presents a multiplexed fluorescent in situ hybridization method based on orthogonal amplification with hybridization chain reaction (HCR). Using this approach, RNA probes complementary to mRNA targets trigger chain reactions in which fluorophore-labeled RNA hairpins self-assemble into tethered fluorescent amplification polymers. Robust performance and high signal-to-background are achieved when imaging five target mRNAs at the same time in fixed whole-mount zebrafish embryos. The programmability and sequence specificity of these amplification cascades enable all five amplifiers to operate orthogonally at the same time in the same sample. The fact that amplification polymers are triggered to self-assemble in situ results in excellent sample penetration and high signal-to-background. These properties suggest the broad applicability of fluorescent in situ HCR amplification to multiplexed imaging of mRNA expression in normal and pathological cells, embryos, and tissue sections.\r\n" }, { "name": "Choi, Jina", "degree": "PhD", "year": "2010", "title": "Development of Visible-Light-Active Photocatalyst for Hydrogen Production and Environmental Application", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03252010-121803765", "creators": [ { "name": { "family": "Choi", "given": "Jina" }, "id": "Choi-Jina", "display_name": "Choi, Jina" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "chair", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Davis", "given": "Mark E." }, "id": "Davis-M-E", "role": "member", "display_name": "Davis, Mark E." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/90AX-KS12", "abstract": "Semiconductor photocatalysis has been intensively studied in recent decades for a wide variety of application such as hydrogen production from water splitting and water and air treatment. The majority of photocatalysts are, however, wide band-gap semiconductors which are active only under UV irradiation. In order to effectively utilize visible solar radiation, this thesis investigates various types of visible-light active photocatalysts including metal ion-doped TiO\u2082, nanocomposites of potassium niobate (KNbO\u2083) and CdS with Ni co-catalyst, and a mixed-phase CdS matrix interlinked with elemental Pt deposits.
\r\n\r\nThirteen different metal ion-doped TiO\u2082 nanoparticles are synthesized. I compare the effects of individual dopants on the resulting physicochemical properties and corresponding photocatalytic activities with respect to the catalysis of several reactions under visible-light irradiation. I found several metal ion-doped Ti\u2082 nanoparticles such as Pt, Cr, and V had visible-light photocatalytic activities and the presence of rutile phase in these metal ion-doped TiO\u2082 may affect their photoreactivities. In addition, visible-light photocatalytic activities of TiO\u2082 are enhanced by co-doping with two metal ions.
\r\n \r\nHybrid nanocomposite photocatalysts based on CdS nanoparticles (e.g., Ni(0)/NiO/ KNbO\u2083/CdS, Zeolite/CdS, and nanocomposites of Q-sized cubic phase CdS and bulk-phase hexagonal CdS interlinked with elemental Pt deposits) are also studied. Different types of CdS nanocomposite photocatalysts are synthesized, optimized, and characterized using various analytical techniques. It is shown that these nanocomposites can enhance inherent photocatalytic activity of bulk-phase CdS for hydrogen production via effective charge separation of photogenerated electrons and holes in CdS under visible-light irradiation.
\r\n \r\nAdditionally, a sub-pilot size hybrid electrochemical system with Bi-doped TiO\u2082 anodes and SS cathodes for the degradation of organic pollutants and simultaneous hydrogen production has been developed to make the electrochemical system more economically viable. This system degrades a variety of organic pollutants and real wastewater with simultaneous production of hydrogen at the current efficiencies of 50~70%. Furthermore, it is demonstrated that this electrochemical system can be driven by a photovoltaic (PV) cell.
\r\n" }, { "name": "Chu, Chia-Chieh", "degree": "PhD", "year": "2010", "title": "Multiscale Methods for Elliptic Partial Differential Equations and Related Applications", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07312009-095021", "creators": [ { "name": { "family": "Chu", "given": "Chia-Chieh" }, "id": "Chu-Chia-Chieh", "display_name": "Chu, Chia-Chieh" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/PFGA-YY17", "abstract": "Multiscale problems arise in many scientific and engineering disciplines. A typical example is the modelling of flow in a porous medium containing a number of low and high permeability embedded in a matrix. Due to the high degrees of variability and the multiscale nature of formation properties, not only is a complete analysis of these problems extremely difficult, but also numerical solvers require an excessive amount of CPU time and storage. In this thesis, we study multiscale numerical methods for the elliptic equations arising in interface and two-phase flow problems. The model problems we consider are motivated by the multiscale computations of flow and transport of two-phase flow in strongly heterogeneous porous media. Although the analysis is carried out for simplified model problems, it does provide valuable insight in designing accurate multiscale methods for more realistic applications.
\r\n\r\nIn the first part, we introduce a new multiscale finite element method which is able to accurately capture solutions of elliptic interface problems with high contrast coefficients by using only coarse quasiuniform meshes, and without resolving the interfaces. The method is H\u00b9-conforming, and has an optimal convergence rate of O(h) in the energy norm and O(h\u00b2) in the L\u2082 norm, where h is the mesh diameter and the hidden constants in these estimates are independent of the \"contrast\" (i.e. ratio of largest to smallest value) of the PDE's coefficients. The new interior boundary conditions depend not only on the contrast of the coefficients, but also on the angles of intersection of the interface with the element edges. We conduct some numerical experiments to confirm the optimal rate of convergence of the proposed method and its independence from the aspect ratio of the coefficients.
\r\n\r\nIn the second part, we propose a flow-based oversampling method where the actual two-phase flow boundary conditions are used to construct oversampling auxiliary functions. Our numerical results show that the flow-based oversampling approach is several times more accurate than the standard oversampling method. A partial theoretical explanation is provided for these numerical observations.
\r\n\r\nIn the third part, we discuss \"metric-based upscaling\" for the pressure equation in two-phase flow problem. We show a compensation phenomenon and design a multiscale method for the pressure equation with highly oscillatory permeability.
\r\n" }, { "name": "Cui, Tao", "degree": "PhD", "year": "2010", "title": "Coding for Wireless Broadcast and Network Secrecy", "advisor": "Ho, Tracey C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062009-213639", "creators": [ { "name": { "family": "Cui", "given": "Tao" }, "id": "Cui-Tao", "display_name": "Cui, Tao" } ], "advisors": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "advisor", "display_name": "Ho, Tracey C." } ], "committee": [ { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "chair", "display_name": "Ho, Tracey C." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/JYV2-DM74", "abstract": "In the first part of this thesis, we exploit wireless broadcast across different layers in wireless networks. The wireless channel is distinguished by its broadcast nature. Wireless broadcast provides a fertile ground to improve the efficiency of existing wireless networks and design new ones.
\r\n\r\nSpecifically, we first consider relaying strategies for memoryless two-way relay channels at the physical layer. We generalize networking layer network coding operating on a finite field to physical layer network coding, which is a mapping from the relay's received signal to its transmitted signal. We analyze the symbol-error performance of several relay strategies, and optimize the relay function via functional analysis. Our results indicate that the interference caused by wireless broadcast can be exploited to improve the spectrum efficiency.
\r\n\r\nWe then develop a cross-layer framework with wireless broadcast, which integrates rate control, network coding and scheduling in transport, network and link layers. Under the primary interference model, we show that the link scheduling problem is the maximum weighted hypergraph matching problem, which is NP-complete. We propose several distributed approximation algorithms and bound their worst case performance.
\r\n\r\nNext, we describe a new class of medium access control (MAC) protocol, which uses successive interference cancelation to resolve packet collision due to wireless broadcast. Each user is allowed to transmit at different data rates chosen randomly from an appropriately determined set of rates. We characterize the throughput of the proposed protocol compared to that with a centralized controller. A game-theoretic framework along with the dynamic algorithms is proposed to achieve the desired throughput optimal equilibrium, which provides a valuable perspective to understand existing MAC protocols and a general framework to design new ones to improve the system performance.
\r\n\r\nIn the second part of this thesis, we consider the problem of secure transmission in the presence of a wiretapper. Due to wireless broadcast, wireless signals are particularly easy to jam and intercept. We derive the secrecy capacity region for the case when the location of the wiretapped links is known and propose several achievable strategies for the case when such information is unknown. We give an example to show that the secrecy capacities of the two cases are generally unequal and show that in both cases computing the secrecy capacity is NP-complete.
\r\n" }, { "name": "Cui, Xiquan", "degree": "PhD", "year": "2010", "title": "Optofluidic Microscopy and Wavefront Microscopy: Innovations in Biological Imaging", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:12032009-160213018", "creators": [ { "name": { "family": "Cui", "given": "Xiquan" }, "id": "Cui-Xiquan", "display_name": "Cui, Xiquan" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "eleceng" ], "doi": "10.7907/BJY0-NJ69", "abstract": "This thesis presents two new microscopic imaging techniques: the optofluidic microscopy (OFM) and the wavefront microscopy (WM). By integrating optical functionalities onto a single semiconductor chip, these inventions could reduce the cost and improve the efficiency and quality of microscopic imaging in biological research and clinical diagnostics. First, OFM utilizes a microfluidic flow to deliver cellular samples across array(s) of micron-sized apertures defined on a metal-coated CMOS image sensor to acquire direct projection images of the samples. Although the OFM prototype is as small as a dime, it can render high resolution images (~1 \u00b5m) with comparable quality to those of a bulky standard optical microscope. OFM has great potential in revolutionizing the way we use microscopes. For example, the availability of tens or even hundreds of microscopes on a single chip will allow massively paralleled imaging of large populations of cells or microorganisms; the compactness and low cost of the OFM can enable portable and even disposable biomedical diagnostic tools for future telemedicine and personalized health care. Second, we present a new microscopy concept - WM. Wavefront image sensor (WIS) is the enabling component of WM. By monitoring the tightly confined transmitted light spots through a 2D aperture grid (spacing = 11 \u00b5m, diameter = 6 \u00b5m) fabricated on a CMOS image sensor in a high Fresnel number regime, we can accurately measure both intensity and phase front variations (a measured normalized phase gradient sensitivity of 0.1 mrad under the typical working condition - 1.0 second total signal accumulation time and 9.2 \u00b5W/cm^2 light intensity on the sensor) of a wavefront separately and quantitatively. Therefore, researchers and clinicians can incorporate pure phase imaging into their current microscope systems by simply adding the WIS in place of the conventional camera. When combined with adaptive optics strategies, this technology will facilitate deep tissue imaging using multiphoton microscopy. " }, { "name": "Diest, Kenneth Alexander", "degree": "PhD", "year": "2010", "title": "Active Metal-Insulator-Metal Plasmonic Devices", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222009-133531", "creators": [ { "name": { "family": "Diest", "given": "Kenneth Alexander" }, "id": "Diest-Kenneth-Alexander", "display_name": "Diest, Kenneth Alexander" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "matsci" ], "doi": "10.7907/7J9Z-N927", "abstract": "As the field of photonics constantly strives for ever smaller devices, the diffraction limit of light emerges as a fundamental limitation in this pursuit. A growing number of applications for optical \"systems on a chip\" have inspired new ways of circumventing this issue. One such solution to this problem is active plasmonics. Active plasmonics is an emerging field that enables light compression into nano-structures based on plasmon resonances at a metal-dielectric interface and active modulation of these plasmons with an applied external field. One area of active plasmonics has focused on replacing the dielectric layer in these waveguides with an electro-optic material and designing the resulting structures in such a way that the transmitted light can be modulated. These structures can be utilized to design a wide range of devices including optical logic gates, modulators, and filters.
\r\n\r\nThis thesis focuses on replacing the dielectric layer within a metal-insulator-metal plasmonic waveguide with a range of electrically active materials. By applying an electric field between the metal layers, we take advantage of the electro-optic effect in lithium niobate, and modulating the carrier density distribution across the structure in n-type silicon and indium tin oxide.
\r\n\r\nThe first part of this thesis looks at fabricating metal-insulator-metal waveguides with ion-implantation induced layer transferred lithium niobate. The process is analyzed from a thermodynamic standpoint and the ion-implantation conditions required for layer transfer are determined. The possible failure mechanisms that can occur during this process are analyzed from a thin-film mechanics standpoint, and a metal-bonding method to improve successful layer transfer is proposed and analyzed. Finally, these devices are shown to naturally filter white light into individual colors based on the interference of the different optical modes within the dielectric layer. Full-field electromagnetic simulations show that these devices can preferentially couple to any of the primary colors and can tune the output color of the device with an applied field.
\r\n\r\nThe second part of this thesis looks at fabricating metal-insulator-metal waveguides with n-type silicon and indium tin oxide. With the silicon device, by tuning the thicknesses of the layers used in a metal-oxide semiconductor geometry, the device we call the \"plasMOStor\" can support plasmonic modes as well as exactly one photonic mode. With an applied field, this photonic mode is pushed into cutoff and modulation depths of 11.2 dB are achieved. With the indium tin oxide device, the doping density within the material is changed and as a result, the plasma frequency is shifted into the near-infrared and visible wavelengths. Using spectroscopic ellipsometry, the structure is characterized with and without an applied electric field, and measurements show that when an accumulation layer is formed within the structure, the index of refraction within that layer is significantly changed and as a result, will change the optical modes supported in such a structure.
\r\n" }, { "name": "Du Toit, Noel Eduard", "degree": "PhD", "year": "2010", "title": "Robot Motion Planning in Dynamic, Cluttered, and Uncertain Environments: the Partially Closed-Loop Receding Horizon Control Approach", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:02042010-152638957", "creators": [ { "name": { "family": "Du Toit", "given": "Noel Eduard" }, "id": "Du-Toit-Noel-Eduard", "display_name": "Du Toit, Noel Eduard" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Blackmore", "given": "James C." }, "id": "Blackmore-J-C", "role": "member", "display_name": "Blackmore, James C." } ], "option_major": [ "mecheng" ], "doi": "10.7907/SD3N-JR18", "abstract": "This thesis is concerned with robot motion planning in dynamic, cluttered, and uncertain environments. Successful and efficient robot operation in such environments requires reasoning about the future system evolution and the uncertainty associated with obstacles and moving agents in the environment. Current motion planning strategies ignore future information and are limited by the resulting growth of uncertainty as the system is evolved. This thesis presents an approach that accounts for future information gathering (and the quality of that information) in the planning process. The Partially Closed-Loop Receding Horizon Control approach, introduced in this thesis, is based on Dynamic Programming with imperfect state information. Probabilistic collision constraints, due to the need for obstacle avoidance between the robot and obstacles with uncertain locations and geometries, are developed and imposed. By accounting for the anticipated future information, the uncertainty associated with the system evolution is managed, allowing for greater numbers of moving agents and more complex agent behaviors to be handled. Simulation results demonstrate the benefit of the proposed approach over existing approaches in static and dynamic environments. Complex agent behaviors, including multimodal and interactive agent-robot models, are considered." }, { "name": "Du Toit, Philip Christopher", "degree": "PhD", "year": "2010", "title": "Transport and Separatrices in Time-Dependent Flows", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072009-165901284", "creators": [ { "name": { "family": "Du Toit", "given": "Philip Christopher" }, "id": "Du-Toit-Philip-Christopher", "display_name": "Du Toit, Philip Christopher" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "cds" ], "doi": "10.7907/X0Y5-N133", "abstract": "The method of using Finite Time Liapunov Exponents (FTLE) to extract Lagrangian Coherent Structures (LCS) in aperiodic flows, as originally developed by Haller, is applied to geophysical flows, and flows in the phase space of second order dynamical systems. In this approach, the LCS are identified as surfaces of greatest separation that parse the flow into regions with different dynamical behavior. In this way, the LCS reveal the underlying skeleton of turbulence. The time-dependence of the LCS provides insight into the mechanisms by which fluid is transported from one region to another. Of especial interest in this study, is the utility with which the FTLE-LCS method can be used to reveal homoclinic and horseshoe dynamics in aperiodic flows.
\r\n\r\nThe FTLE-LCS method is applied to turbulent flow in hurricanes and reveals LCS that delineate sharp boundaries to a storm. Moreover, intersections of the LCS define lobes that mediate transport into and out of a storm through the action of homoclinic lobe dynamics. Using FTLE-LCS, the same homoclinic structures are seen to be a dominant transport mechanism in the Global Ocean, and provide insights into the role of mesoscale eddies in enhancing lateral mixing.
\r\n\r\nBeyond geophysical flows, we also study transport in the phase space of a coupled oscillator model for biomolecules. Before we can analyze transport in this model, we first introduce an appropriate model reduction that captures the relevant statistics of the full system. In the reduced model, we see that transport is again mediated by the process of horseshoe dynamics in a perturbed homoclinic tangle.
\r\n\r\nWe also consider some theoretical aspects of FTLE-LCS, including the relationship between LCS and stable/unstable manifolds, the invariance of LCS, and the possibility of an evolution equation describing the motion of the LCS. A parallelized software for computing FTLE is also introduced.
" }, { "name": "Fong, Eileen", "degree": "PhD", "year": "2010", "title": "Wound Healing on Artificial Extracellular Matrix Proteins", "advisor": "Tirrell, David A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-151443763", "creators": [ { "name": { "family": "Fong", "given": "Eileen" }, "id": "Fong-Eileen", "display_name": "Fong, Eileen" } ], "advisors": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "advisor", "display_name": "Tirrell, David A." } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Bronner", "given": "Marianne E." }, "id": "Bronner-M-E", "role": "member", "display_name": "Bronner, Marianne E." }, { "name": { "family": "Asthagiri", "given": "Anand R." }, "id": "Asthagiri-A-R", "role": "member", "display_name": "Asthagiri, Anand R." }, { "name": { "family": "Davis", "given": "Mark E." }, "id": "Davis-M-E", "role": "member", "display_name": "Davis, Mark E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/8VQJ-DS58", "abstract": "Collective cell migration is a key process in tissue repair, and in drawing parallels from complex multi-cellular events such as tumor morphogenesis and embryogenesis. Mechanisms of wound healing have been studied extensively in vitro. Extracellular matrix (ECM) is required to support cell migration and ensure rapid coverage of the wound area. The main challenge in designing biomaterials for tissue repair is to provide cells with the appropriate biological and mechanical cues. Hence, understanding key cell-ECM interactions during wound healing is necessary for effective biomaterial design.
\r\n\r\nGenetic engineering provides a convenient avenue to customize materials for any given application. The artificial protein-based biomaterials discussed in this work were derived from fibronectin and elastin. These proteins have a modular design, and have material properties that can be fine-tuned according to specific applications. The artificial extracellular matrix (aECM) proteins prepared by previous members of our laboratory have been shown to promote attachment of endothelial cells. In this work, we studied extensively epithelial and fibroblast wound healing behavior on these aECM biomaterials.
\r\n\r\nCrosslinked aECM protein films of varying RGD densities have been prepared by mixing aECM proteins with the RGD cell binding domain with aECM proteins containing the scrambled RDG sequence. Corneal epithelial wound healing was observed on aECM films with 100% RGD but not on aECM films with 2.5% RGD. Surprisingly, we found a five fold difference between the wound closure rates between these surfaces, but individual cell speeds did not increase significantly. We proposed that the five fold increase in wound closure rate was determined by the rate of crossing the boundary between the wound area and the area underneath the cell sheet. Both simulation and experimental data verified that the rate of boundary-crossing was sufficient to account for five-fold difference in wound closure rates between 100% RGD and 2.5% RGD surfaces.
\r\n\r\nFull-length fibronectin domains have also been incorporated to improve the overall cell binding properties of the aECM proteins. The aECM proteins containing full-length fibronectin domains were shown to facilitate rapid spreading of Rat-1 fibroblasts. The aECM protein containing both fibronectin domains 9 and 10 exhibited an increased binding affinity to the \u03b15\u03b21 integrin. More importantly, these aECM proteins also promoted rapid wound closure, which was comparable to that on fibronectin. We showed that aECM proteins containing full-length fibronectin domains also promoted higher phosphorylated levels of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK), consistent with the faster cell migration and proliferation observed.
\r\n\r\nTo try to understand how cells select wound healing mechanisms, wound healing of Madin-Darby Canine Kidney (MDCK) epithelial cells were examined in vitro. On surfaces containing the aECM protein bearing the fibronectin domain 10, characteristic healing patterns were observed in MDCK wound healing. These patterns are defined by the formation of leader cells at regular intervals of actomyosin purse strings. The spacing between consecutive leader cell groups was also found to be independent of the wound diameter. This spacing however, was found to decrease with increasing myosin II inhibition. These observations could be explained using a simple force transmission mechanical model. Consistent with the model predictions, we demonstrated that wounds with a zigzag geometry biased the selection of the wound healing mechanism along the wound edge. These zigzag wounds also healed nearly eight fold faster than wounds with straight edges.
\r\n" }, { "name": "Gayme, Dennice F. Maynard", "degree": "PhD", "year": "2010", "title": "A Robust Control Approach to Understanding Nonlinear Mechanisms in Shear Flow Turbulence", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-195149679", "creators": [ { "name": { "family": "Gayme", "given": "Dennice F. Maynard" }, "id": "Gayme-Dennice-F-Maynard", "orcid": "0000-0003-0330-415X", "display_name": "Gayme, Dennice F. Maynard" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Bamieh", "given": "Bassam" }, "id": "Bassam-B", "role": "member", "display_name": "Bamieh, Bassam" } ], "option_major": [ "cds" ], "doi": "10.7907/P1DS-Q379", "abstract": "A robust control framework is used to investigate a streamwise constant projection of the Navier Stokes equations for plane Couette flow. Study of this streamwise constant model is motivated by both numerical and experimental observations that suggest the prevalence and importance of streamwise and quasi-streamwise elongated structures. Small-amplitude Gaussian noise forcing is applied to a two-dimensional, three-velocity component (2D/3C) model to describe its response in the presence of disturbances, uncertainty and modeling errors. A comparison of the results with Direct Numerical Simulation (DNS) data demonstrates that the simulations capture salient features of fully developed turbulence. In particular, the change in mean velocity profile from the nominal laminar to the characteristic \u201cS\u201d shaped turbulent profile. The application of Taylor\u2019s hypothesis shows that the model can also reproduce downstream information in the form of large-scale coherence resembling numerically and experimentally observed flow features. The 2D/3C model is able to generate \u201cturbulent-like\u201d behavior under small-amplitude stochastic noise. The laminar flow solution is globally stable, therefore transition to turbulence in this model is likely a consequence of the laminar flow solution\u2019s lack of robustness in the presence of disturbances and uncertainty. In fact, large disturbance amplification is common in both this model and the linearized Navier Stokes equations.
\r\n\r\nPeriodic spanwise/wall-normal (z\u2013y) plane stream functions are used as input to develop a forced 2D/3C streamwise velocity equation. The resulting steady-state solution is qualitatively similar to a fully turbulent spatial field of DNS data. Both numerical methods and a perturbation analysis confirm that the momentum transfer that produces a \u201cturbulent-like\u201d mean profile requires a nonlinear streamwise velocity equation.
\r\n\r\nA system theoretic approach is used to study the amplification mechanisms that develop through the 2D/3C nonlinear coupling in the streamwise velocity equation. The spanwise/wall-normal plane forcing required to produce each stream function is computedand used to define an induced norm from this forcing input to the streamwise velocity. This input-output response is used to determine the energy optimal spanwise wavelength (i.e.,the preferential spacing) over a range of Reynolds numbers and forcing amplitudes.
" }, { "name": "Gu, Ming", "degree": "PhD", "year": "2010", "title": "Interactions Between Hippocampal Areas CA3 and CA1 During Slow-Wave Sleep\r ", "advisor": "Siapas, Athanassios G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03102010-232405639", "creators": [ { "name": { "family": "Gu", "given": "Ming" }, "id": "Gu-Ming", "display_name": "Gu, Ming" } ], "advisors": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "orcid": "0000-0001-8837-678X", "role": "advisor", "display_name": "Siapas, Athanassios G." } ], "committee": [ { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "chair", "display_name": "Laurent, Gilles J." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "member", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "orcid": "0000-0001-8837-678X", "role": "member", "display_name": "Siapas, Athanassios G." } ], "option_major": [ "cns" ], "doi": "10.7907/Z9BV7DMM", "abstract": "Many lines of evidence suggest that the hippocampus plays a critical role in memory formation. The predominant hypothesis is that new memories are initially stored within hippocampal circuits during awake behavior, and are subsequently consolidated across neocortical networks under the influence of hippocampal activity during sleep. The hippocampal memory trace is conjectured to reside within the recurrent circuits of area CA3, which is believed to function as an autoassociative memory. Area CA3 projects almost exclusively to area CA1, one of the major output stages of the hippocampus. How is CA3 activity transformed in CA1, and what is the function of the CA1 subfield that intermediates between CA3 and the neocortex, the presumed long-term storage site of memories?
\r\n\r\nHere we characterize the relationships between CA3 and CA1 activity during slow-wave sleep (SWS), a stage of sleep conjectured to be important in memory consolidation. Activity in SWS is marked by the presence of short-lived (~100 ms) population bursts that are believed to be spontaneously generated within CA3 and that cooccur with high-frequency oscillations (~200 Hz ripples) in area CA1. We demonstrate that:
\r\n\r\n1. CA1 amplifies transient increases in CA3 activity levels, while attenuating background fluctuations.\r\n2. The fraction of co-active neurons is higher in CA1 than in CA3, while the firing intensity of active neurons is higher in CA3 than in CA1. \r\n3. The above dichotomy is particularly pronounced during the population bursts associated with ripples. \r\n4. In comparison to isolated spikes, bursts of action potentials by CA3 neurons are particularly effective at triggering large CA1 responses and predicting the onset of CA1 ripples.
\r\n\r\nThese results show that CA1 acts as a selective filter and amplifier of CA3 activity patterns, and that bursting of individual CA3 neurons plays a special role in this CA3-CA1 transformation. We hypothesize that coordinated bursts in CA3 reflect convergence to attractors, each representing a stored pattern in the auto-associative network. Our observations suggest that these stored patterns are preferentially amplified by CA1 and transmitted to downstream targets, while activity representing intermediate states in-between attractors are less likely to be transmitted.
\r\n" }, { "name": "Gu\u00f0mundsson, Kristj\u00e1n", "degree": "PhD", "year": "2010", "title": "Instability Wave Models of Turbulent Jets from Round and Serrated Nozzles", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:01242010-111852941", "creators": [ { "name": { "family": "Gu\u00f0mundsson", "given": "Kristj\u00e1n" }, "id": "Gu\u00f0mundsson-Kristj\u00e1n", "display_name": "Gu\u00f0mundsson, Kristj\u00e1n" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Hussain", "given": "Fazle" }, "id": "Hussain-F", "orcid": "0000-0002-2209-9270", "role": "member", "display_name": "Hussain, Fazle" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/BQH9-G487", "abstract": "In this thesis we study pressure fluctuations associated with large-scale coherent structures in turbulent round and serrated jets. Linear disturbances to the turbulent mean flow of the round jet are modeled via linear stability analysis and the Parabolized Stability Equations (PSE). We show that PSE provides better agreement with near-field microphone-array data at low frequencies than previous models based on linear stability theory. We examine the extent to which microphone data is contaminated by fluctuations uncorrelated with large-scale structures. By filtering out the uncorrelated fluctuations, via the proper orthogonal decomposition (POD), better agreement between data and theory is obtained. We next extend the linear stability analysis of round jets to include the effects of azimuthal inhomogeneities of serrated jets. We solve the resulting system of equations and find new modes, associated with the streamwise vorticity of the serrated-jet mean flow. All unstable modes of the serrated jet are stabilized, potentially explaining the noise reduction achieved by such jets. We also compare these predictions to POD-filtered microphone measurements, generally finding good agreement.\r\n" }, { "name": "Hanna, Jeffrey", "degree": "PhD", "year": "2010", "title": "Solid-Oxide Fuel Cell Electrode Microstructures: Making Sense of the Internal Framework Affecting Gas Transport", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-090420975", "creators": [ { "name": { "family": "Hanna", "given": "Jeffrey" }, "id": "Hanna-Jeffrey", "display_name": "Hanna, Jeffrey" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/NRY2-2K63", "abstract": "Optimal electrodes for solid-oxide fuel cells will combine high porosity for gas diffusion, high phase connectivity for ion and electron conduction, and high surface area for chemical and electrochemical reactions. Tracer-diffusion simulations are used to gain a better understanding of the interplay between microstructure and transport in porous materials. Results indicate that the coefficient of diffusion through a porous medium is a function of the details of the internal geometry (microscopic) and porosity (macroscopic). I report that current solid-oxide fuel cell electrodes produced from high-temperature sintering of ceramic powders severely hinder gas transport because the resulting structures are highly tortuous, complex three-dimensional networks. In addition, poor phase connectivities will assuredly limit ion and electron transport, as well as the density of active sites for power-producing reactions. With new access to a wide range of technologies, micro- and nano-fabrication capabilities, and high-performance materials, there is a new ability to engineer the fuel cell electrode architecture, optimizing the physical processes within, increasing performance, and greatly reducing cost per kilowatt. Even simple packed-sphere and inverse-opal architectures will increase gas diffusion by an order of magnitude, and provide a higher level of connectivity than traditional powder-based structures." }, { "name": "Henry, Michael David", "degree": "PhD", "year": "2010", "title": "ICP Etching of Silicon for Micro and Nanoscale Devices", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262010-152815609", "creators": [ { "name": { "family": "Henry", "given": "Michael David" }, "id": "Henry-Michael-David", "orcid": "0000-0002-5201-0644", "display_name": "Henry, Michael David" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9MW2FBC", "abstract": "The physical structuring of silicon is one of the cornerstones of modern microelectronics and integrated circuits. Typical structuring of silicon requires generating a plasma to chemically or physically etch silicon. Although many tools have been created to do this, the most finely honed tool is the Inductively Couple Plasma Reactive Ion Etcher. This tool has the ability to finesse structures from silicon unachievable on other machines. Extracting structures such as high aspect ratio silicon nanowires requires more than just this tool, however. It requires etch masks which can adequately protect the silicon without interacting with the etching plasma and highly tuned etch chemistry able to protect the silicon structures during the etching process.
\r\n \r\nIn the work presented here, three highly tuned etches for silicon, and its oxide, will be described in detail. The etches presented utilize a type of etch chemistry which provides passivation while simultaneously etching, thus permitting silicon structures previously unattainable. To cover the range of applications, one etch is tuned for deep reactive ion etching of high aspect ratio micro-structures in silicon, while another is tuned for high aspect ratio nanoscale structures. The third etch described is tuned for creating structures in silicon dioxide. Following the description of these etches, two etch masks for silicon will be described. The first mask will detail a highly selective etch mask uniquely capable of protecting silicon for both etches described while being compatible with mainstream semiconductor fabrication facilities. This mask is aluminum oxide. The second mask detailed permits for a completely dry lithography on the micro and nanoscale, FIB implanted Ga etch masks. The third chapter will describe the fabrication and in situ electrical testing of silicon nanowires and nanopillars created using the methods previously described. A unique method for contacting these nanowires is also described which has enabled investigation into the world of nanoelectronics. The fourth and final chapter will detail the design and construction of high magnetic fields and integrated planar microcoils, work which was enabled by the etching detailed here. This research was directed towards creation of a portable NMR machine.
\r\n" }, { "name": "Hofmann, Carrie Elizabeth", "degree": "PhD", "year": "2010", "title": "Optics at the Nanoscale: Light Emission in Plasmonic Nanocavities", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282010-101941747", "creators": [ { "name": { "family": "Hofmann", "given": "Carrie Elizabeth" }, "id": "Hofmann-Carrie-Elizabeth", "display_name": "Hofmann, Carrie Elizabeth" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "matsci" ], "doi": "10.7907/B774-EW86", "abstract": "Nanophotonics has greatly bene\ufb01ted from the unique ability of surface plasmons to confine optical modes to volumes well below the di\ufb00raction limit of light. Plasmonics is an emerging area of research that opens the path for controlling light-matter interactions on the subwavelength scale, enabling truly nanophotonic technologies that are unattainable with conventional di\ufb00raction-limited optical components. Novel surface plasmon devices exploit electromagnetic waves con\ufb01ned to the interface between a metal and a dielectric and permit the researcher to shrink light to dimensions previously inaccessible with optics. The extremely high and localized \ufb01elds in plasmonic nanocavities are \ufb01nding applications in research areas such as single-molecule sensing, nano-lasers, and photothermal tumor ablation, among others.
\r\n\r\nThis thesis explores, both experimentally and theoretically, light emission in a number of plasmonic nanostructures. We present cathodoluminescence imaging spectroscopy as a new method of characterizing surface plasmons on metal \ufb01lms and localized in nanocavity resonators, with experimental observations supported by analytical calculations and electromagnetic simulation. This technique enables extremely localized surface plasmon excitation, a feature we exploit in both planar metal geometries and plasmonic nanocavities. We also study a speci\ufb01c nanocavity geometry, the plasmonic core-shell nanowire resonator, investigating both passive and active semiconductor core materials. This geometry allows precise control of the local density of optical states (LDOS), exhibiting the highest LDOS and smallest mode volumes in structures with dimensions as small as \u03bb/50. Moreover, we discuss the Purcell effect as it applies to plasmonic nanocavities, and calculate enhancements in the radiative decay rate of more than 3000\u00d7 in the smallest structures. These results demonstrate the promise of plasmonics to enable truly nanophotonic technologies and to manipulate light at the nanoscale.
" }, { "name": "Joe, Won Tae", "degree": "PhD", "year": "2010", "title": "Optimized Feedback Control of Vortex Shedding on an Inclined Flat Plate", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-131025711", "creators": [ { "name": { "family": "Joe", "given": "Won Tae" }, "id": "Joe-Won-Tae", "display_name": "Joe, Won Tae" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Hussain", "given": "Fazle" }, "id": "Hussain-F", "orcid": "0000-0002-2209-9270", "role": "member", "display_name": "Hussain, Fazle" }, { "name": { "family": "MacMynowski", "given": "Douglas G." }, "id": "MacMynowski-D-G", "role": "member", "display_name": "MacMynowski, Douglas G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/6D11-2Y92", "abstract": "This thesis examines flow control and the potentially favorable effects of feedback, associated with unsteady actuation in separated flows over airfoils. The objective of the flow control is to enhance lift at post-stall angles of attack by changing the dynamics of the wake vortices. We present results from a numerical study of unsteady actuation on a two-dimensional flat plate at post-stall angles of attack at Reynolds number (Re) of 300 and 3000. At Re=300, the control waveform is optimized and a feedback strategy is developed to optimize the phase of the control relative to the lift with either a sinusoidal or the optimized waveform, resulting in a high-lift limit cycle of vortex shedding. Also at Re=3000, we show that certain frequencies and actuator waveforms lead to stable (high-lift) limit cycles, in which the flow is phase locked to the actuation.
\r\n\r\nFirst, a two-dimensional flat plate model at a high angle of attack at a Re of 300 is considered. We design the feedback to slightly adjust the frequency and/or phase of actuation to lock it to a particular phase of the lift, thus achieving a phase-locked flow with the maximal period-averaged lift over every cycle of actuation.
\r\n\r\nWith the sinusoidal forcing and feedback, we show that it is possible to optimize the phase of the control relative to the lift in order to achieve the highest possible period-averaged lift in a consistent fashion. However, continuous sinusoidal forcing could be adding circulation when it is unnecessary, or undesirable. Thus we employ an adjoint-based optimization in order to find the waveform (time history of the jet velocity) that maximizes the lift for a given actuation amplitude. The adjoint of the linearized perturbed equations is solved backwards in time to obtain the gradient of the lift to changes in actuation (the jet velocity), and this information is used to iteratively improve the controls.
\r\n\r\nOptimal control provides a periodic control waveform, resulting in high lift shedding cycle with minimal control input. However, if applied in open loop, the flow fails to phase lock onto the optimal waveform, degrading the lift performance. Thus, the optimized waveform is also implemented in a closed-loop controller where the control signal is shifted or deformed periodically to adjust to the (instantaneous) frequency of the lift fluctuations. The feedback utilizes a narrowband filter and an Extended Kalman Filter to robustly estimate the phase of vortex shedding and achieve phase-locked, high lift flow states. Feedback control of the optimized waveform is able to reproduce the high-lift limit cycle from the optimization, but starting from an arbitrary phase of the baseline limit cycle.
\r\n\r\nFinally, we apply the tools developed and knowledge gained at Re=300 to a Re of 3000 on a thin airfoil with a thickness-to-chord ratio of 4%, which were chosen to match the experimental studies of Greenblatt et al. (2008). We consider more detailed time-dependent aspects of the lift and corresponding flow fields, particularly the flow structures at the minimum and maximum lift, and the phase of pulses relative to the lift, in order to more precisely compare different actuated flow fields and distinguish the differences responsible for higher or lower instantaneous lift, along with identifying different vortex evolutions. We consider two representative angles of attack, 10 and 20 degrees, and investigate the lift enhancement and which combinations of forcing frequency and duty cycle lead to phase-locked flow. Finally, we show that for certain frequencies and actuator waveforms, there occur stable limit cycles in which the flow is phase locked to the actuation.
" }, { "name": "Jones, Glenn Evans", "degree": "PhD", "year": "2010", "title": "Instrumentation for Wide Bandwidth Radio Astronomy", "advisor": "Weinreb, Sander", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122009-094525715", "creators": [ { "name": { "family": "Jones", "given": "Glenn Evans" }, "id": "Jones-Glenn-Evans", "display_name": "Jones, Glenn Evans" } ], "advisors": [ { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "advisor", "display_name": "Weinreb, Sander" } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Kuiper", "given": "Thomas B. H." }, "id": "Kuiper-T-B-H", "role": "member", "display_name": "Kuiper, Thomas B. H." }, { "name": { "family": "Jarnot", "given": "Robert F." }, "id": "Jarnot-R-F", "role": "member", "display_name": "Jarnot, Robert F." } ], "option_major": [ "eleceng" ], "doi": "10.7907/BMZR-P813", "abstract": "Centimeter wavelength radio astronomy spans approximately two decades in frequency, from roughly 500 MHz to 50 GHz. In contrast, radio astronomy instruments have traditionally been limited to at most octave bandwidths, necessitating multiple instruments on a given telescope to cover a large fraction of the spectrum. This paradigm is infeasible for the next generation of telescopes, which will likely consist of hundreds to thousands of small dishes combined together in an array, because each receiver must be replicated for each element in the array. Therefore, wide bandwidth instrumentation must be developed for radio astronomy.
\r\n\r\nThis thesis presents a novel radio telescope with excellent system noise temperature and reasonable efficiency across an instantaneous fractional bandwidth greater than 4:1; amongst the widest ever demonstrated. This instrument illustrates that extremely wide bandwidth instruments are feasible, even in the presence of terrestrial interference. To make use of the enormous instantaneous bandwidth, a flexible, high performance, and cost effective digital signal processing system is also presented. Theory, design, and measurements of special purpose digital spectrometers built to minimize the effects of terrestrial interference are included.
\r\n\r\nAside from the practical advantages offered by wide bandwidth instrumentation, new scientific applications are also made possible. A special purpose system for performing detailed studies of giant radio pulses from rotating neutron stars (pulsars) is presented, along with demonstrations including some of the largest fractional bandwidth observations of these pulses made to date. This system includes a sensitive trigger which corrects for the dispersive effects of the interstellar medium in real time and a deep capture buffer optimized for observing repetitive transient phenomena. Measurements made using the trigger system at Arecibo Observatory are also presented to demonstrate the portability of the instrument.
" }, { "name": "Karnesky, James Alan", "degree": "PhD", "year": "2010", "title": "Detonation Induced Strain in Tubes", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142010-174001426", "creators": [ { "name": { "family": "Karnesky", "given": "James Alan" }, "id": "Karnesky-James-Alan", "display_name": "Karnesky, James Alan" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GTKC-FY91", "abstract": "When a detonation wave propagates through a piping system, it acts as a traveling pressure load to the pipe wall. The detonation wave must be followed by an expansion wave in order to bring the combustion products to zero velocity at the ignition end. When it reaches a closed end-wall, a reflected shock is formed which propagates back into the tube with a decaying pressure. The present study aims to develop predictive models for the stresses and strains produced in such a situation. To this end, two series of experiments are discussed. The first series used strain gauges and a laser vibrometer to measure the elastic response of the tube to the incident detonation in thin aluminum tubes. The second series used strain gauges and high speed video to measure the plastic response of steel tubes to incident detonations and reflected shocks. In these experiments a novel mode of plastic deformation was discovered in which the residual plastic deformation in the tube wall had a periodic sinusoidal pattern.
\r\n\r\nA semi-empirical model of the pressure history was developed for use as a boundary condition in models of the mechanical response of the tube. This model was tested against experiment, and it was found that the pressure and arrival time could not be simultaneously predicted from the simple model. This and the general form of the pressure traces in the experiment seem to suggest an interaction between the reflected shock and the boundary layer behind the detonation resulting in a possible bifurcation in the reflected shock wave.
\r\n\r\nWith these considerations in mind, the model was applied to single degree of freedom and finite element models of the tube wall. The ripples observed in the experiment were present in the 1-D single degree of freedom models, indicating that they are a result of the interaction of the reflected shock wave with the elastic oscillations set in motion by the detonation wave. Strain-rate hardening was found to be an important consideration under detonation loading conditions. With proper consideration of rate hardening, a single material model may be used to arrive at reasonable predictions the plastic strains resulting from detonations and reflections at initial pressures of 2 and 3 bar initial pressures.
" }, { "name": "Kelzenberg, Michael David", "degree": "PhD", "year": "2010", "title": "Silicon Microwire Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082010-074917811", "creators": [ { "name": { "family": "Kelzenberg", "given": "Michael David" }, "id": "Kelzenberg-Michael-David", "display_name": "Kelzenberg, Michael David" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "eleceng" ], "doi": "10.7907/99RA-7Z65", "abstract": "The favorable bandgap and natural abundance of Si, combined with the large expertise base for semiconductor wafer processing, have led to the use of wafer-based crystalline Si in the vast majority of photovoltaic cells and modules produced worldwide. However the high cost of purifying, crystallizing, and sawing Si wafers has inhibited these photovoltaic energy sources from approaching cost parity with fossil fuels. Crystalline Si microwires, grown by the catalytic vapor-liquid-solid (VLS) chemical vapor deposition process, have recently emerged as promising candidate materials for thin-film photovoltaics--combining low-cost Si deposition techniques with mechanically flexible, high-performance device geometries.
\r\n\r\nThis thesis presents several achievements that have helped to establish the viability of high-performance Si microwire photovoltaics. We begin by developing a comprehensive numerical model of Si microwire-array solar cells, combining finite-element device physics simulations with time-domain optical methods to predict that these devices can exceed 17% solar energy conversion efficiency. We then turn our attention to the optical properties of Si microwire arrays, concerned that the sparsely packed wires might not absorb enough sunlight. However our experiments reveal that simple light-trapping techniques can dramatically improve their absorption, not only permitting them to effectively absorb sunlight using 1/100th as much Si as a wafer, but also leading to an unexpected and fundamentally advantageous absorption enhancement over classical light trapping in planar materials. Techniques are then presented to characterize the material quality of VLS-grown Si wires. Although the growth of these wires is catalyzed by notoriously undesirable metal impurities for crystalline Si (e.g., Au, Ni, and Cu), we find it is nonetheless possible to synthesize high-quality material with remarkable diffusion lengths. By combining these materials with effective surface-passivation and a novel junction-fabrication technique, we realize single-wire solar cells that achieve open-circuit voltages of ~600 mV and with fill factors exceeding 80%. These observations suggest that Si microwires may offer a promising alternative to wafers for cost-effective crystalline Si photovoltaics.
" }, { "name": "Khankhoje, Uday Kiran", "degree": "PhD", "year": "2010", "title": "Photon Confinement in Photonic Crystal Cavities", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-215001543", "creators": [ { "name": { "family": "Khankhoje", "given": "Uday Kiran" }, "id": "Khankhoje-Uday-Kiran", "display_name": "Khankhoje, Uday Kiran" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "van Zyl", "given": "Jakob J." }, "id": "van-Zyl-J-J", "role": "member", "display_name": "van Zyl, Jakob J." }, { "name": { "family": "Kim", "given": "Se-Heon" }, "id": "Kim-S-H", "role": "member", "display_name": "Kim, Se-Heon" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CZBG-5917", "abstract": "In this thesis, the use of photonic crystal cavities for experiments in cavity quantum-electrodynamics is described. To this end, the propagation of light in photonic crystals, and the creation of cavities by making defects in the photonic crystal lattice, is discussed. By drawing an analogy with Fabry-Perot etalons, the mechanism of light confinement in these cavities is explained. It is shown that by engineering the immediate cavity neighborhood, the mirror reflectivities can be increased, resulting in a very high quality factor (Q) and low mode volume. Photonic crystal cavity designs used in this thesis are introduced, along with numerically computed data of their performance.
\r\n\r\nDevice fabrication in gallium arsenide wafers is described in detail, with special attention to address factors that lead to a lack of reproducibility. Over the course of this thesis effort, several thousand cavities were fabricated, and a wide range of Qs were recorded. Careful experiments were performed to determine the causes of low Qs, both at the wafer growth level, and at the fabrication level. Technological improvements in wafer growth are reported, as well as fabrication techniques to improve cavity Q.
\r\n\r\nThese cavities contain indium arsenide quantum dots (QDs) as internal light sources. Cavity-induced enhancement of QD light emission is discussed, along with interferometric measurements of photon correlations. It is found that light emission from coupled QD-cavity systems is highly non-classical, and this quantum nature is characterized by means of a second order correlation function.
\r\n\r\nTo conclude, a novel application of high-Q cavities is discussed, that of an electrically-pumped laser fabricated in a 1D nanobeam cavity. The salient feature of such a geometry is that a high Q is retained even with the introduction of gold in the cavity vicinity. Finally, approaches to improve cavity Q by material system optimizations are explored. In the first approach, QD growth in III-V material systems with light emission wavelengths in the telecommunications wavelength range (\u03bb \u2248 1.55 \u03bcm) is discussed, and in the second, the growth of III-V-based active media in silicon structures is considered.
" }, { "name": "Kharevych, Liliya", "degree": "PhD", "year": "2010", "title": "Geometric Interpretation of Physical Systems for Improved Elasticity Simulations", "advisor": "Schroeder, Peter; Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechTHESIS:11172009-224005473", "creators": [ { "name": { "family": "Kharevych", "given": "Liliya" }, "id": "Kharevych-Liliya", "display_name": "Kharevych, Liliya" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "co-advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "chair", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "compsci" ], "doi": "10.7907/8ZF3-XN72", "abstract": "The physics of most mechanical systems can be described from a geometric viewpoint; i.e., by defining variational principles that the system obeys and the properties that are being preserved (often referred to as invariants). The methods that arise from properly discretizing such principles preserve corresponding discrete invariants of the mechanical system, even at very coarse resolutions, yielding robust and efficient algorithms. In this thesis geometric interpretations of physical systems are used to develop algorithms for discretization of both space (including proper material discretization) and time. The effectiveness of these algorithms is demonstrated by their application to the simulation of elastic bodies.
\r\n\r\nTime discretization is performed using variational time integrators that, unlike many of the standard integrators (e.g., Explicit Euler, Implicit Euler, Runge-Kutta), do not introduce artificial numerical energy decrease (damping) or increase. A new physical damping model that does not depend on timestep size is proposed for finite viscoelasticity simulation. When used in conjunction with variational time integrators, this model yields simulations that physically damp the energy of the system, even when timesteps of different sizes are used. The usual root-finding procedure for time update is replaced with an energy minimization procedure, allowing for more precise step size control inside a non-linear solver. Additionally, a study of variational and time-reversible methods for adapting timestep size during the simulation is presented.
\r\n\r\nSpatial discretization is performed using a finite element approach for finite (non-linear) or linear elasticity. A new method for the coarsening of elastic properties of heterogeneous linear materials is proposed. The coarsening is accomplished through a precomputational procedure that converts the heterogeneous elastic coefficients of the very fine mesh into anisotropic elastic coefficients of the coarse mesh. This method does not depend on the material structure of objects, allowing for complex and non-uniform material structures. Simulation on the coarse mesh, equipped with the resulting elastic coefficients, can then be performed at interactive rates using existing linear elasticity solvers and, if desired, co-rotational methods. A time-reversible integrator is used to improve time integration of co-rotated linear elasticity.
\r\n" }, { "name": "Kim, Daegyoum", "degree": "PhD", "year": "2010", "title": "Characteristics of Three-dimensional Vortex Formation and Propulsive Performance in Flapping Locomotion", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-114858790", "creators": [ { "name": { "family": "Kim", "given": "Daegyoum" }, "id": "Kim-Daegyoum", "display_name": "Kim, Daegyoum" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8VZJ-7Z78", "abstract": "Three-dimensional vortex formation and propulsive performance were studied experimentally to identify some of the main characteristic mechanisms of flapping locomotion. Mechanical models with thin plates were used to simulate flapping and translating motions of animal propulsors. Three-dimensional flow fields were mapped quantitatively using defocusing digital particle image velocimetry.
\r\n\r\nFirst, vortex structures made by impulsively translating low aspect-ratio plates were studied. The investigation of translating plates with a 90 degree angle of attack is important since it is a fundamental model for a better understanding of drag-based propulsion systems. Rectangular flat-rigid, flexible, and curved-rigid thin plastic plates with the same aspect ratio were used to compare their vortex structures and hydrodynamic forces. The interaction of the tip flow and the nearby vortex is a critical flow phenomenon to distinguish vortex patterns among these three cases. In the flexible plate case, slow development of the vortex structure causes a small initial peak in hydrodynamic force during the acceleration phase. However, after the initial peak, the flexible plate generates large force magnitude comparable to that of the flat-rigid plate case.
\r\n \r\nDrag-based paddling propulsion was also studied to explain some of the fundamental differences in vortex formation of lift-based and drag-based propulsions. While the temporal change of the inner area enclosed by the vortex loop is an important factor in thrust generation of lift-based propulsion, the temporal change of the vortex strength becomes more important in drag-based propulsion. Spanwise flow behind the paddling plate plays an important role in tip vortex motion and thrust generation. The distribution of spanwise flow depends on the propulsor shape and the Reynolds number. A delta-shaped propulsor generates strong spanwise flow compared to a rectangular propulsor. For the low Reynolds number case, the spanwise flow is not as strong as that of the high Reynolds number case. The flexible propulsor can smooth out force peaks during impulsive motions without sacrificing total impulse, which is advantageous in avoiding structural failures and stabilizing body motion. The role of the stopping vortex was addressed in optimizing a stroke angle of paddling animals.
\r\n\r\nIn addition, vortex formation of clapping propulsion was investigated by varying aspect ratio and stroke angle. A low aspect-ratio propulsor produces larger total impulse than a high aspect-ratio propulsor. As the aspect ratio increases, circulation of the vortex is strengthened, and the inner area enclosed by the vortex structure tends to enlarge. Moreover, in terms of thrust, the advantage of a single plate over double clapping plates is larger for the lower aspect-ratio case. These results offer information to better understand the benefit of low aspect-ratio wings in force generation under specific locomotion modes. When a pair of plates claps, a vortex loop forms from two counter-rotating tip vortices by a reconnection process. The dynamics of wake structures are dependent on the aspect ratio and the stroke angle.
\r\n\r\nVortex formation and vorticity transport processes of translating and rotating plates with a 45 degree angle of attack were investigated as well. In both translating and rotating cases, the spanwise flow over the plate and the vorticity tilting process inside the leading-edge vortex were observed. The distribution of spanwise flow is a prominent distinction between the vortex structures of these two cases. While spanwise flow is confined inside the leading-edge vortex for the translating case, it is widely present over the plate and the wake region of the rotating case. As the Reynolds number decreases, due to the increase in viscosity, leading-edge and tip vortices tend to spread inside the area swept by the rotating plate, which results in lower lift force generation.
\r\n\r\nLastly, for translating motion, the dynamics of the vortex in corner regions was compared among three different corner shapes. For a large corner angle, the forward movement of the vortex tends to be uniform along the plate edges. However, for a small corner angle, the vortex close to the corner moves forward following the plate while the vortex away from the corner retards its forward movement.
" }, { "name": "Kim, Jin-Hong", "degree": "PhD", "year": "2010", "title": "State Diagram for Contact-Inhibition of Proliferation: A Quantitative Framework for Modulating Growth Patterns in Epithelial Cell Clusters", "advisor": "Asthagiri, Anand R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232010-172249275", "creators": [ { "name": { "family": "Kim", "given": "Jin-Hong" }, "id": "Kim-Jin-Hong", "orcid": "0000-0002-6480-1929", "display_name": "Kim, Jin-Hong" } ], "advisors": [ { "name": { "family": "Asthagiri", "given": "Anand R." }, "id": "Asthagiri-A-R", "role": "advisor", "display_name": "Asthagiri, Anand R." } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Meyerowitz", "given": "Elliot M." }, "id": "Meyerowitz-E-M", "role": "member", "display_name": "Meyerowitz, Elliot M." }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" }, { "name": { "family": "Asthagiri", "given": "Anand R." }, "id": "Asthagiri-A-R", "role": "member", "display_name": "Asthagiri, Anand R." } ], "option_major": [ "bioeng" ], "doi": "10.7907/JV13-YS19", "abstract": "Cell-cell contacts play a key role in the assembly and integrity of epithelial tissues. Cell-cell contact is not only a mere physical link between neighboring cells, but also a critical regulator of many cell behaviors including proliferation. Contact-inhibition of proliferation is a hallmark of normal epithelial tissues. Cancer development involves the loss of this key constraint. Both biochemical and physical mechanisms mediating contact-inhibition are emerging. A current, principal challenge is elucidating how the integrated performance of these mechanisms enforce or modulate contact-inhibition in a rich microenvironment that includes multiple, potentially conflicting cues such as soluble growth factors (GFs) and extracellular matrix (ECM).
\r\n\r\nHere, we propose a quantitative paradigm for contact-inhibition of proliferation. Our quantitative analysis of single cells within multicellular aggregates reveals that epithelial cells transition from a contact-inhibited to contact-independent mode of proliferation at a critical threshold EGF level. This transition point is a tunable property and can be modulated by varying the level of cell-cell contact. Furthermore, the proximity to this transition point is a quantitative gauge of \u201cdegree\u201d of contact-inhibition. Using this metric, we demonstrate that stiffening the adhesive matrix, a widely observed phenomenon during cancer development, leads to the quantitative, progressive reduction in the EGF threshold needed to induce contact-independent proliferation. Thus, stiffening the ECM moves an epithelial cell system closer to the transition to contact-independence, thereby quantitatively reducing the amount of EGF amplification needed to induce population-wide proliferation. Our results reveal that the potent effect of substratum compliance on contact-inhibition involves changes in contact-maturation and multicellular mechanics. The proposed quantitative model of contact-inhibition provides fundamental insights into our understanding of tissue morphogenesis and cancer progression in multicellular organisms. Furthermore, our findings provide design principles for engineering multicellular growth in applications such as tissue engineering.
\r\n" }, { "name": "Kim, Sukwon", "degree": "PhD", "year": "2010", "title": "Network Coding for Resource Optimization and Error Correction", "advisor": "Effros, Michelle; Ho, Tracey C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012010-161706139", "creators": [ { "name": { "family": "Kim", "given": "Sukwon" }, "id": "Kim-Sukwon", "display_name": "Kim, Sukwon" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "advisor", "display_name": "Effros, Michelle" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "advisor", "display_name": "Ho, Tracey C." } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "co-chair", "display_name": "Ho, Tracey C." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/9E6W-SN15", "abstract": "In the first part of this thesis, we demonstrate the benefits of network coding for optimizing the use of various network resources.
\r\n\r\nWe first study the problem of minimizing the power consumption for wireless multiple unicasts. A simple XOR-based coding strategy is considered for reducing the power consumption. We present a centralized polynomial time algorithm that approximately minimizes the number of transmissions for two unicast sessions. We extend it to a greedy algorithm for general problem of multiple unicasts.
\r\n\r\nPrevious results on network coding for low-power wireless transmissions of multiple unicasts rely on opportunistic coding or centralized optimization to reduce the power consumption. Thus we propose a distributed strategy for reducing the power consumption with wireless multiple unicasts. Our strategy attempts to increase network coding opportunities without the overhead required for centralized design or coordination. We present a polynomial time algorithm using our strategy that maximizes the expected power savings with respect to the random choice of sources and sinks on the wireless rectangular grid.
\r\n\r\nWe study the problem of minimum-energy multicast using network coding in mobile ad hoc networks (MANETs). The optimal subgraph can be obtained by solving a linear program every time slot, but it leads to high computational complexity. We present a low-complexity approach, network coding with periodic recomputation, which recomputes an approximate solution at fixed time intervals, and uses this solution during each time interval. We analyze the power consumption and the complexity of network with this approach.
\r\n\r\nRecently, several back-pressure type optimization algorithms with network coding are presented for multiple unicasts and multicast. Such algorithms are distributed since decisions are made locally at each node based on feedback about the size of queues at the destination node of each link. We develop a back-pressure based distributed optimization framework, which can be used for optimizing over any class of network codes. Our approach is to specify the class of coding operations by a set of generalized links, and to develop optimization tools that apply to any network composed of such generalized links.
\r\n\r\nIn the second part of this thesis, we study the capacity of single-source single-sink noiseless networks under adversarial attack on no more than z edges. Unlike prior papers, which assume equal capacities on all links, we allow arbitrary link capacities. Results include new upper bounds, general transmission strategies, and example networks where those bounds are tight. We introduce a new method for finding upper bounds on the linear coding capacities of arbitrary networks and show that there exists networks where the capacity is 50% greater than the best rate that can be achieved with linear coding. We also demonstrate examples where, unlike the equal link capacity case, it is necessary for intermediate nodes to do coding, nonlinear error detection or error correction in order to achieve the capacity. We introduce a new strategy called \"guess-and-forward\" and employ this strategy on a sequence of networks designed to provide increasingly complex generalizations of the cut-set bounds. The first is a two-node network with multiple feedback links. The second is a four-node acyclic network. The third is a family of 'zig-zag' networks. In the first two cases, the guess-and-forward strategy achieves the capacity. For zig-zag networks, we derive a achievable rate of guess-and-forward strategy.
" }, { "name": "Ko, Chih-Kai", "degree": "PhD", "year": "2010", "title": "On Matrix Factorization and Scheduling for Finite-Time Average-Consensus", "advisor": "Schulman, Leonard J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05022010-193157687", "creators": [ { "name": { "family": "Ko", "given": "Chih-Kai" }, "id": "Ko-Chih-Kai", "display_name": "Ko, Chih-Kai" } ], "advisors": [ { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "advisor", "display_name": "Schulman, Leonard J." } ], "committee": [ { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "chair", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GCT7-5Y66", "abstract": "We study the problem of communication scheduling for finite-time average-consensus in arbitrary connected networks. Viewing this consensus problem as a factorization of 1/n 11T by network-admissible families of matrices, we prove the existence of finite factorizations, provide scheduling algorithms for finite-time average consensus, and derive almost tight lower bounds on the size of the minimal factorization." }, { "name": "Krimmel, Jeffrey James", "degree": "PhD", "year": "2010", "title": "Numerical Simulation of Wave Focusing and Scattering in Shock Wave Lithotripsy", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282010-150032204", "creators": [ { "name": { "family": "Krimmel", "given": "Jeffrey James" }, "id": "Krimmel-Jeffrey-James", "display_name": "Krimmel, Jeffrey James" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/XWED-RZ95", "abstract": "In this work we simulate shock wave focusing and scattering that occurs during shock wave lithotripsy, a noninvasive medical treatment for kidney stone disease. Shock waves are generated outside the body of the patient and are focused at the kidney stone with the intention of pulverizing the stone while it remains inside the patient. The patient can then ostensibly pass the debris naturally. We use a multidimensional second-order method of the Godunov type with slope limiters and shock capturing capability to solve the inviscid Euler equations. Because we begin with the fundamental statements of conservation of mass, momentum, and energy, we simulate all the relevant acoustics occurring during a typical treatment.
\r\n\r\nLithotripters, the machines that generate and focus shock waves, can be classified according to the mechanism of shock generation. In this work, we simulate three different types of lithotripters: electrohydraulic, piezoelectric, and electromagnetic. We choose one representative of each lithotripter type: the Dornier HM3, a research piezoelectric lithotripter array, and the XX-Es, respectively. We first study a model of the in vitro setting for each lithotripter, where shock waves are generated and focus in a bath of pure water. Next, we introduce different heterogeneous materials near the focus of the lithotripter to model the effect of the body of an actual patient, i.e., the in vivo condition. We use two approaches in this modeling effort. One approach is to use simple geometrical models for the body cavity and kidney that we created ourselves. The other approach is to import real anatomical data made available from the VOXEL-MAN Group.
\r\n\r\nIn studying the focal region acoustics, we specifically examine the maximum calculated pressures. These pressures represent the forces that will ultimately cause the kidney stone to break. We also study the pulse intensity integral, i.e., the energy density carried by the focusing shock wave. In addition to these pressures and energy densities, we are interested in investigating how soft tissue in the focal region may potentially be damaged by the resulting wavefields. We isolate two mechanisms that are thought to be important in soft tissue injury: shearing and cavitation. We calculate estimates for the maximum principal normal and shear strains in the focal region in addition to the corresponding strain rates and use these as metrics for the potential for damage via shearing. We study the calculated negative pressure fields in this region as a surrogate for potential damage caused by cavitation.
\r\n\r\nWe find that our simple geometrical anatomical models cause little deviation from the acoustics observed in a water bath. However, when the real anatomical data of the VOXEL-MAN Group is used, the fields of the various relevant flow quantities become more highly oscillatory and produce secondary extrema that could produce damage not predicted from the water bath case. In addition to the conclusions from our own work, we discuss how our results motivate future studies that will hopefully help elucidate specific mechanisms by which kidney stones break and soft tissue becomes damaged.
" }, { "name": "Lamberson, Leslie Elise", "degree": "PhD", "year": "2010", "title": "Dynamic Optical Investigations of Hypervelocity Impact Damage", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282010-183132978", "creators": [ { "name": { "family": "Lamberson", "given": "Leslie Elise" }, "id": "Lamberson-Leslie-Elise", "orcid": "0000-0002-1340-4667", "display_name": "Lamberson, Leslie Elise" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AQJH-3D60", "abstract": "One of the prominent threats in the endeavor to develop next-generation space assets is the risk of space debris impact in earth\u2019s orbit and micrometeoroid impact damage in near-earth orbit and deep space. To date, there is no study available which concentrates on the analysis of dynamic crack growth from hypervelocity impacts on such structures, resulting in their eventual catastrophic degradation. Experiments conducted using a unique two-stage light-gas gun facility have examined the in situ dynamic fracture of brittle polymers subjected to this high-energy-density event. Optical techniques of caustics and photoelasticity, combined with high-speed photography up to 100 million frames per second, analyze crack growth behavior of Mylar and Homalite 100 thin plates after impact by a 1.8 mm diameter nylon 6-6 right cylindrical slug at velocities ranging from 3 to 7 km/s (7000\u201315500 mph). Crack speeds in both polymers averaged between 0.2 and 0.47 cR, the Rayleigh wave speed (450\u20131000 mph). Shadow spots and surrounding caustics reveal time histories of the dynamic stress intensity factor, as well as the energy release rate ahead of the mode-I, or opening, crack tips. Results indicate that even under extreme impact conditions of out of-plane loading, highly localized heating, and energetic impact phenomena involving plasma formation and ejecta, the dynamic fracture process occurs during a deformation regime dominated by in-plane loading. These findings imply that the reliability of impacted, thin-walled, plate and shell space structures, idealized by the experimental configuration investigated, can be predicted by the well defined principles of classical dynamic fracture mechanics." }, { "name": "Lee, Cheng-Chung", "degree": "PhD", "year": "2010", "title": "Chemical Synthesis in Elastomer-Based Integrated Microfluidics", "advisor": "Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04222010-082435622", "creators": [ { "name": { "family": "Lee", "given": "Cheng-Chung" }, "id": "Lee-Cheng-Chung", "display_name": "Lee, Cheng-Chung" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "member", "display_name": "Quake, Stephen R." }, { "name": { "family": "Stoltz", "given": "Brian M." }, "id": "Stoltz-B-M", "role": "member", "display_name": "Stoltz, Brian M." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "bioeng" ], "doi": "10.7907/8603-G150", "abstract": "There is wide interest in using the unique properties of microfluidic environments for the production of fine chemicals and pharmaceuticals. Compared to bench top synthesis, microfluidic systems engender the significant advantage of superior control of chemical state functions. The ability to tune reagent concentration, reaction temperature, mixing time, and residence time allows reactions to run more efficiently thus generating products of higher yield and purity. While several microfluidic platforms are actively developed in both academic and industrial laboratories, vast majority are based in rigid materials and have only demonstrated improvements in yield for single reaction steps.
\r\n\r\nMultilayer Soft Lithography has already found much use in the biological field. For example, several complex devices based upon functional modules have been developed for protein crystallography, nucleic acid processing, FACS, enzyme screening tools, and PCR. Because of the many similarities between operations in organic synthesis and biochemistry, there is widespread interest in extending these newfound successes in the realm of biology to the realm of automated chemical synthesis.
\r\n\r\nThis thesis focuses on the application of Multilayer Soft Lithography to the development and adaptation of microfluidic tools for chemical synthesis. The first successful demonstration of multistep organic synthesis in integrated microfluidics was the production of a molecular image probe, 2-deoxy-2-[18F]fluoro-d-glucose. The nanogram level dosage for imaging probes makes them attractive candidates for small scale synthesis of microfluidics. The reduced synthesis time achieved by using a microfluidic device is especially important because of the relatively short half-life of the radioactive fluoride.
\r\n\r\nWhile PDMS remains the material of choice for devices in biological applications, its incompatibility with many nonpolar organic solvents limits the types of reactions that can be performed with it. Through collaboration with Joseph DeSimone\u2019s group at the University of North Carolina at Chapel Hill, a suitable substitute for PDMS was found in perfluoropolyethers (PFPE). A solvent-resistant integrated microfluidic device was developed for solid-phase oligonucleotide synthesis using conventional phosphoramidite chemistry. To confirm that the microfluidic platform in development can indeed become a valuable tool in the field of synthetic biology, a 16 column parallel oligonucleotide synthesizer was manufactured that is capable of producing 16 distinct sequences up to 40 bases in length to be used in gene assembly. Successful construction of a gene fragment was completed from a mixture of unpurified and unamplified oligonucleotides synthesized on the device.
" }, { "name": "Li, Xiaobai", "degree": "PhD", "year": "2010", "title": "An Experimental and Numerical Study of Normal Particle Collisions in a Viscous Liquid", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-165618198", "creators": [ { "name": { "family": "Li", "given": "Xiaobai" }, "id": "Li-Xiaobai", "display_name": "Li, Xiaobai" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "mecheng" ], "doi": "10.7907/S5V0-3E25", "abstract": "When two solid bodies collide in a liquid environment, the collision process is influenced by viscous effects and the increased pressure in the interstitial liquid layer between the two solid boundaries. A normal collision process is investigated for a range of impact Stokes numbers using both experimental and numerical methods. Experiments of a steel sphere falling under gravity and colliding with a Zerodur wall with Stokes number ranging from 5 to 100 are performed, which complement previous investigations of immersed particle-wall collision processes. The incompressible Navier-Stokes equations are solved numerically to predict the coupled motion of the falling particle and the surrounding fluid as the particle impacts and rebounds from the planar wall. The numerical method is validated by comparing the numerical simulations of a settling sphere with experimental measurements of the sphere trajectory and the accompanying flow-field. A contact model of the liquid-solid and solid-solid interaction is developed that incorporates the elasticity of the solids to permit the rebound trajectory to be simulated accurately. The contact model is applied when the particle is sufficiently close to the wall that it becomes difficult to resolve the thin lubrication layer. The model is calibrated with measured particle trajectories and is found to represent well the observed coefficient of restitution over a range of impact Stokes numbers from 1 to 1000. In addition, the model is modified to simulate the normal collision of two spheres. The effective coefficient of restitution obtained from the simulation shows a strong dependence on the binary Stokes number accordant with other researcher\u2019s experimental results. The unique behaviors of the two spheres at low binary Stokes number including target motion prior to contact and group motion after collision are simulated by the current work." }, { "name": "Liu, Mike Chia-Chung", "degree": "PhD", "year": "2010", "title": "Integrated Microfluidic Devices for Cell Culture and Assay", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:10162009-053129363", "creators": [ { "name": { "family": "Liu", "given": "Mike Chia-Chung" }, "id": "Liu-Mike-Chia-Chung", "display_name": "Liu, Mike Chia-Chung" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" } ], "option_major": [ "bioeng" ], "doi": "10.7907/D43B-D825", "abstract": "This thesis presents the development of three-dimensional (3-D) microfluidic devices for cellular studies, with focus on applications for high-throughput cell culture and cell-based assay. Microfluidic devices provide potential inexpensive platforms for high-throughput screening with the advantages of precise liquid handling, ability to control cell culture microenvironment, and reduced reagents and cells.
\r\n \r\nBecause a mixture of drugs or chemical compounds can often treat diseases more effectively or act synergistically in certain cellular pathways, a device capable of screening the combinatorial effects of multiple compound exposures on cells is highly desirable. To this end, a novel method to monolithically fabricate 3-D microfluidic networks was developed, and based on this fabrication technology, the first cell culture device with an integrated combinatorial mixer was constructed. The proof-of-concept chip having a three-input combinatorial mixer and eight individually isolated micro culture chambers was fabricated on silicon utilizing the surface micromachining of Parylene C (poly(chloro-p-xylylene)). Unlike other 3-D microfluidic fabrications, multilayer bonding process was favorably obviated. By incorporating several microfluidic overpass structures to allow one microfluidic channel to cross over other microfluidic channels, the combinatorial mixer generated all the combinations of the input fluidic streams. Cell culturing on-chip was successful, and the ability to simultaneously treat arrays of cells with different combinations of compounds was demonstrated.
\r\n\r\nTo facilitate cell-based assay, another combinatorial cell array device was fabricated on glass with incorporated membrane. Characterization of the combined compound concentration profile at each chamber with a fluorescence method was developed. We demonstrated functionality of the quantitative cell-based assay by screening three different compounds\u2019 ability to reduce cytotoxicity of hydrogen peroxide on neuron cells and also assaying combinatorial exposures of three chemotherapeutic agents on breast cancer cells. The 3-D microfluidic fabrication process was extended to construct multilayer microfluidic device with integrated membrane. Applications of microfluidic devices for marine microbiology were demonstrated. Based on the capabilities demonstrated in this work, devices with high-density cell array and integrated high-input combinatorial mixer can be constructed. At the same time, the technology has general applicability for building complex 3-D microfluidic devices, which can broaden the applications for current lab-on-a-chip systems.
\r\n" }, { "name": "Ma, Jeremy Chee-Ming", "degree": "PhD", "year": "2010", "title": "Real-Time Applications of 3D Object Detection and Tracking", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:01152010-143831008", "creators": [ { "name": { "family": "Ma", "given": "Jeremy Chee-Ming" }, "id": "Ma-Jeremy-Chee-Ming", "display_name": "Ma, Jeremy Chee-Ming" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "mecheng" ], "doi": "10.7907/4N1K-GK74", "abstract": "Robot perception is a fundamental aspect of any autonomous system. It gives the robot the capacity to make sense of vast amounts of data and gain an understanding of the world around it. An active problem in the area of robot perception is real-time detection and pose estimation of 3D objects. This thesis presents an approach to 3D object detection and tracking utilizing a stereo-camera sensor. Geometric object models are learned in short order time via a training phase and real-time detection and tracking is made possible by performing sparse stereo calculations on the chosen features within an adaptive region of interest of the camera image. The experimental results obtained by using this method will show the effectiveness of the approach as compared against ground truth measures in real-time. Using that framework as a basis, extensions to two other problems in robot sensing are then considered: (1) sensor-planning for model identification, and (2) sensor-planning for object-search. In the former, a novel algorithm for determining the next-best-view for a mobile sensor to identify an unknown 3D object from among a database of known models is presented and tested across two experiments involving real robotic systems. An information theoretic approach is taken to quantify the utility of each potential sensing action and the validity of the algorithm is discussed. In the latter area, a novel approach is presented that allows an autonomous mobile robot to search for a 3D object using an onboard stereo camera sensor mounted on a pan-tilt head. Search efficiency is realized by the combination of a coarse-scale global search coupled with a fine-scale local search, guided by a grid-based probability map. Obstacle avoidance during the search is naturally integrated into the method with additional experimental results on a mobile robot presented to illustrate and validate the proposed search strategy. All presented experiments were carried out in real-time processing with modest computation done by a single laptop computer." }, { "name": "McDowell, Emily Jayne", "degree": "PhD", "year": "2010", "title": "Low Optical Signal Detection in Biological Materials: SNR Considerations and Novel Techniques", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechTHESIS:11012009-234712901", "creators": [ { "name": { "family": "McDowell", "given": "Emily Jayne" }, "id": "McDowell-Emily-Jayne", "display_name": "McDowell, Emily Jayne" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "bioeng" ], "doi": "10.7907/7Q7B-1E27", "abstract": "Light scattering poses significant challenges for biomedical optical imaging techniques. Diffuse scattering scrambles wavefront information, confounding easy analysis of signals reflected from or transmitted through biological tissues. For optical imaging techniques that employ only unscattered light components, the penetration depth is severely limited. In this thesis, we develop and discuss two general methods for dealing with large levels of light scattering in tissue. The first involves optimization of the signal-to-noise ratio (SNR) of coherence domain optical tomography techniques. The majority of the signal measured in these techniques is singly scattered. Thus, an improvement in SNR will improve the penetration depth of the system by picking out the weak signal contribution from increasing depths that would otherwise be buried in noise. We show that the SNR can be optimized in terms of image reconstruction algorithms, and in terms of detection parameters. An important detection parameter, the integration time, determines the dominant noise source of the measurement, and can be varied to obtain the maximal SNR. A second general method that will be discussed involves the time-reversal of scattered light components in tissues through the process of optical phase conjugation (OPC). OPC has long been used to remove optical aberrations and distortions, but has never before been applied to light scattering in tissues. We show that we are capable of time reversing light scattering in both chicken tissue sections and tissue phantoms, and characterize both the amplitude and resolution trends of the process. Finally, we provide the first successful results of OPC in living tissues." }, { "name": "Narayan, Anusha", "degree": "PhD", "year": "2010", "title": "Transfer at C. elegans Synapses", "advisor": "Sternberg, Paul W.; Laurent, Gilles J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262010-171937384", "creators": [ { "name": { "family": "Narayan", "given": "Anusha" }, "id": "Narayan-Anusha", "display_name": "Narayan, Anusha" } ], "advisors": [ { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "orcid": "0000-0002-7699-0173", "role": "co-advisor", "display_name": "Sternberg, Paul W." }, { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "co-advisor", "display_name": "Laurent, Gilles J." } ], "committee": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "orcid": "0000-0001-8837-678X", "role": "chair", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "member", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "orcid": "0000-0002-7699-0173", "role": "member", "display_name": "Sternberg, Paul W." }, { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "member", "display_name": "Laurent, Gilles J." } ], "option_major": [ "cns" ], "doi": "10.7907/CB9Q-MC14", "abstract": "The nematode C.elegans, with its 302 neurons and abundance of genetic, laser ablation, electrophysiological and imaging tools, is a compact and attractive system for neural circuit analysis. An understanding of the functional dynamics of neural computation requires physiological analyses. We undertook the \ufb01rst characterization of transfer at central synapses in C.elegans. To achieve this we employed optical stimulation techniques using channelrhodopsin-2, and combined this with whole-cell patch clamp electrophysiological recording techniques. We show that the synapse between AFD and AIY, the \ufb01rst stage in the thermotactic circuit, exhibits excitatory, tonic and graded release. The gain at the synapse was low (<0.1), and release was frequency independent, showing no signs of facilitation or depression. The AFD-AIY synapse thus seems designed for robust and reliable transmission of a scaled-down temperature signal from AFD to AIY, enabling AIY to continuously monitor temperature information and integrate it with other incoming sensory information. We also investigated the synapse between ASER, a chemosensory neuron, and AIY, and found that the synaptic response was small and inconsistent. The combination of optical stimulation tools with neural recording techniques is a powerful way to analyze neural circuitry, and will be a signi\ufb01cant aid in achieving the goal of understanding how information is processed in the compact yet densely interconnected nervous system of the worm." }, { "name": "Neumann, Dirk", "degree": "PhD", "year": "2010", "title": "Connectivity of the Brain from Magnetic Resonance Imaging", "advisor": "Adolphs, Ralph", "url": "https://resolver.caltech.edu/CaltechTHESIS:04282010-153942989", "creators": [ { "name": { "family": "Neumann", "given": "Dirk" }, "id": "Neumann-Dirk", "display_name": "Neumann, Dirk" } ], "advisors": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "advisor", "display_name": "Adolphs, Ralph" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "orcid": "0000-0003-0016-3531", "role": "member", "display_name": "O'Doherty, John P." }, { "name": { "family": "Tsao", "given": "Doris Y." }, "id": "Tsao-D-Y", "orcid": "0000-0003-1083-1919", "role": "member", "display_name": "Tsao, Doris Y." }, { "name": { "family": "Tyszka", "given": "Julian Michael" }, "id": "Tyszka-J-M", "role": "member", "display_name": "Tyszka, Julian Michael" } ], "option_major": [ "cns" ], "doi": "10.7907/1A5T-S275", "abstract": "How do different parts of the brain work? The naive and somewhat ill-posed question nonetheless admits of a serious answer. Different regions of the brain carry out their function principally through two components: the pattern of inputs and outputs that connect a region with the rest of the brain, and the computational transformations implemented by neurons within the region itself. Here we focus on the former problem and study the connectivity of the primate brain, with an emphasis on neocortex.
\r\n\r\nWe develop a novel set of algorithms for modeling anatomical connectivity based on diffusion-weighted magnetic resonance (MR) imaging. The approach is novel in several respects: it utilizes a new way of deriving a globally optimal solution from local message passing; it can be applied to the whole-brain level in a computationally tractable fashion; and it can flexibly incorporate much other information, such as constraints about the geometry of white-matter tracts and high-resolution anatomical MR images. The algorithm is first described as a hierarchical Bayesian model, and then applied to the diffusion MRI data obtained from two perfusion-fixed brains of macaque monkeys.
\r\n\r\nBased on the connectivity output provided from applying our novel algorithm to high-angular resolution MR data, we next derive several new insights about the connectivity of the macaque brain. We compare our results against those from published tracer studies, and we derive the relative weights of connections known from such prior studies. We also demonstrate the ability of the algorithm to generate entirely novel connectivity data, both at the level of specific anatomical regions that are queries, and also at the whole-brain level. The latter permits new insights into whole-brain connectivity and its architecture.
\r\n \r\nIn addition to this focus on the structural connectivity of the macaque brain, we also analyze an extant set of public data of BOLD-fMRI from the macaque brain. This data set yields information regarding the functional connectivity of the macaque brain that we put together with our new connectivity results in order to relate structural and functional connectivity, with several new discoveries about their relationship.
\r\n\r\nIn the final chapter, we apply these methods to MR data we collected from the live human brain. We provide an overview of structural and functional connectivity results obtained from this data set, and we apply the investigation to the brains of rare patients with agenesis of the corpus callosum, who lack the normal connection between the left and right hemispheres. We close by illustrating the power of the approach to ask questions that integrate functional questions with connectivity information on which function must ultimately be based: using connectivity profiles in order to segment cortical regions based on their pattern of inputs and outputs, with the aim of then querying these segmented regions using fMRI in cognitive activation studies. The description of our algorithm, the demonstration of its reliability, validity, and application to yield new data, together with the extensive software libraries on which the work is based, will provide cognitive neuroscientists with an array of new tools to investigate brain function in both health and disease.
" }, { "name": "Norman, Adam Keith", "degree": "PhD", "year": "2010", "title": "Effect of Surface Morphological Changes on Flow Over a Sphere", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212010-124044645", "creators": [ { "name": { "family": "Norman", "given": "Adam Keith" }, "id": "Norman-Adam-Keith", "display_name": "Norman, Adam Keith" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Hussain", "given": "Fazle" }, "id": "Hussain-F", "role": "member", "display_name": "Hussain, Fazle" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SED1-5250", "abstract": "An experimental investigation was undertaken to examine the effect of a morphing surface on the flow over a sphere in the Reynolds number range of 5x10\u2074 to 5x10\u2075. Here, a morphing surface is defined as a continuous surface that undergoes small amplitude changes in order to excite flow instabilities, rather than utilizing large mechanical changes to the overall shape as with traditional aerodynamic control surfaces. The sphere was chosen as an ideal geometry for testing morphing surfaces, because of the well-known sensitivity of the flow to small asymmetries on the surface. In this study, an approximation of a morphing surface was made by dynamically moving a small isolated roughness element along the sphere, thus producing small amplitude time-dependent changes to the surface shape. An experimental apparatus was designed that produced the actuation with an internal motor, which moved the roughness element via magnetic interaction. A three-component piezoelectric force sensor placed inside the sphere allowed for accurate, instantaneous measurements of the global effect of the actuator on the flow. It was found that the moving roughness could produce an instantaneous lateral force as large as the drag. Simultaneous force and particle image velocimetry measurements in the subcritical regime were used to show that there is a relatively long timescale associated with the instability growth, entrainment of fluid, and local change of the position of separation. This allowed the roughness to trip an extended region of the flow at once. It is shown that the three-dimensionality of the disturbance leads to the production of two helical counter-rotating vortices in the wake. In addition, it is demonstrated that a mean side force can be obtained by oscillating the roughness element about a point, producing a lateral force an order of magnitude larger than the force caused by a stationary roughness element. Finally, the results from the dynamic roughness were used to help interpret the underlying physical mechanisms that govern the forcing on a smooth sphere." }, { "name": "Pekarek, David N.", "degree": "PhD", "year": "2010", "title": "Variational Methods for Control and Design of Bipedal Robot Models", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282010-094801935", "creators": [ { "name": { "family": "Pekarek", "given": "David N." }, "id": "Pekarek-David-N", "display_name": "Pekarek, David N." } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "role": "member", "display_name": "Desbrun, Mathieu" } ], "option_major": [ "mecheng" ], "doi": "10.7907/KATX-3233", "abstract": "This thesis investigates nonsmooth mechanics using variational methods for the modeling, control, and design of bipedal robots.
\r\n\r\nThe theory of Lagrangian mechanics is extended to capture a variety of nonsmooth collision behaviors in rigid body systems. Notably, a variational impact model is presented for the transition of constraints behavior that describes a biped switching stance feet at the conclusion of a step.
\r\n\r\nNext, discretizations of the impact mechanics are developed using the framework of variational discrete mechanics. The resulting variational collision integrators are consistent with the continuous time theory and have an underlying symplectic structure.
\r\n\r\nIn addition to their role as integrators, the discrete equations of motion capturing nonsmooth dynamics enable a direct method for trajectory optimization. Upon specifically defining the optimal control problem for nonsmooth systems, examples demonstrate this optimization method in the task of determining periodic gaits for\r\ntwo rigid body biped models.
\r\n\r\nAn additional effort is made to optimize bipedal walking motions through modifications in system design. A method for determining optimal designs using a combination\r\nof trajectory optimization methods and surrogate function optimization methods is defined. This method is demonstrated in the task of determining knee joint placement\r\nin a given biped model.
" }, { "name": "Peng, Jifeng", "degree": "PhD", "year": "2010", "title": "A Lagrangian Approach to Transport of Momentum and Biomass in Aquatic Biological Systems", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07212009-132708", "creators": [ { "name": { "family": "Peng", "given": "Jifeng" }, "id": "Peng-Jifeng", "display_name": "Peng, Jifeng" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." } ], "option_major": [ "bioeng" ], "doi": "10.7907/3XEF-X568", "abstract": "In recent years, a Lagrangian Coherent Structures (LCS) method was developed to identify boundaries between distinct kinematic regions in unsteady flows. Many fluid transport processes can be described in terms of these kinematic boundaries in the flow. The method has since been applied to many engineering, biological, and geological fluid systems, but primarily on transport of homogenous fluid mass.
\r\n\r\nIn this thesis, with emphases on aquatic biological transport systems, the LCS analysis is further developed to study momentum transport in animal locomotion and biomass transport in animal predation. Three independent studies are included in this thesis.
\r\n\r\nIn the first study, LCS analysis is used to identify the boundary of the vortex attached to the fin in sunfish pectoral fin locomotion. A potential flow, deformable body theory is used to describe the dynamics of the vortex. The hydrodynamic forces acting on the fin are evaluated from the linear momentum of the vortex itself and its added-mass. The quantification of instantaneous locomotive forces provides necessary information for studying complicated locomotive behaviors such as motion control and maneuvers.
\r\n\r\nIn the second study, the LCS analysis is applied to a numerically simulated undulatory swimming and shows existence of 'upstream fluid structures' that are invisible in Eulerian velocity/vorticity fields. These structures indicate the exact portion of fluid that interacts with the swimmer. A mass flow rate and a momentum flux are then defined. A metric for propulsive efficiency is established using the momentum flux, which can be used to measure and compare the efficiency of other engineering and natural propulsion systems.
\r\n\r\nIn the third study, a framework is developed to study transport of zooplankton prey in the feeding currents generated by a predator jellyfish. An equation of motion is proposed to describe the dynamics of prey in the flow. Then the concept of particle Lagrangian Coherent Structures (pLCS) is introduced to separate prey encounter regions from prey escape regions. The framework provides a mechanical basis for evaluating the predatory role of medusae in marine planktonic ecosystems. It can also be used to study transport and mixing in multiphase and granular flows in general.
\r\n" }, { "name": "Pope, Melissa Davis", "degree": "PhD", "year": "2010", "title": "Dynamics of Multicellular Aggregation and Disaggregation: Implications for Tissue Engineering and Cancer Metastasis", "advisor": "Asthagiri, Anand R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242010-135950298", "creators": [ { "name": { "family": "Pope", "given": "Melissa Davis" }, "id": "Pope-Melissa-Davis", "display_name": "Pope, Melissa Davis" } ], "advisors": [ { "name": { "family": "Asthagiri", "given": "Anand R." }, "id": "Asthagiri-A-R", "role": "advisor", "display_name": "Asthagiri, Anand R." } ], "committee": [ { "name": { "family": "Asthagiri", "given": "Anand R." }, "id": "Asthagiri-A-R", "role": "chair", "display_name": "Asthagiri, Anand R." }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "member", "display_name": "Tirrell, David A." }, { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "role": "member", "display_name": "Sternberg, Paul W." }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" } ], "option_major": [ "bioeng" ], "doi": "10.7907/3Z4S-5676", "abstract": "Epithelial tissues play an important physiological role. Tightly cohesive epithelial sheets form protective barriers that line organs, and in addition, fold into a wide variety of complex 3D architectures with specialized functions. A key facet of tissue morphogenesis involves the aggregation of similar cells into cohesive groups. Here, we have analyzed the dynamics of aggregation using quantitative imaging techniques (Chapter II). We show that multicellular aggregation dynamics adhere to a transport-reaction model that is broadly appreciated for physicochemical systems. This model of aggregation dynamics differs from the classical equilibrium paradigm of cell aggregation based on differential adhesivity of cells to neighboring cells versus the underlying substratum. Our findings reveal a previously unrecognized role for cell motility during developmental aggregation processes and provide design principles for promoting cell aggregation dynamics in contexts such as tissue engineering that are distinct from the currently accepted paradigm.
\r\n\r\nMulticellular aggregation is reversible. In fact, the break-up of multicellular clusters (\u201ccell scatter\u201d) is not only important for developmental processes, but also contributes to metastasis. However, current molecular genetics studies of cell scatter are predominantly qualitative and do not provide a quantitative assessment of the relative strengths of molecular signals in inducing cell scatter. By developing and implementing an automated image processing algorithm, we quantify two aspects of cell scatter \u2013 the breakdown of cell-cell adhesions and the dispersion of detached cells \u2013 in mammary epithelial cells treated with different combinations of biochemical cues (Chapter III). We demonstrate that our metrics of cell scatter identify the effects of individual cues and detect synergies between them. We envision that this approach will be useful for mapping the relative potencies of regulators of cell scatter and may guide therapeutic strategies.
\r\n\r\nMulticellular processes such as aggregation and scatter involve molecular-level changes within cell-cell adhesions. To complement imaging-based strategies at the cellular and multicellular levels, we developed a quantitative microtiter assay for examining the expression of cell-cell adhesion proteins and associations between them (Chapter IV). Using two case studies related to cancer biology, we demonstrate that our assay provides a more detailed quantitative picture of molecular changes within epithelial adhesive structures, which can provide added insight into the regulation of morphogenetic events.
\r\n" }, { "name": "Purewal, Justin", "degree": "PhD", "year": "2010", "title": "Hydrogen Adsorption by Alkali Metal Graphite Intercalation Compounds", "advisor": "Fultz, Brent T.; Ahn, Channing C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03042010-183429960", "creators": [ { "name": { "family": "Purewal", "given": "Justin" }, "id": "Purewal-Justin", "display_name": "Purewal, Justin" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "co-advisor", "display_name": "Ahn, Channing C." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "member", "display_name": "Ahn, Channing C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" } ], "option_major": [ "matsci" ], "doi": "10.7907/20CE-T553", "abstract": "Adsorption occurs whenever a solid surface is exposed to a gas or liquid, and is characterized by an increase in fluid density near the interface. Adsorbents have drawn attention in the current effort to engineer materials that store hydrogen at high densities within moderate temperature and pressure regimes. Carbon adsorbents are a logical choice as a storage material due to their low costs and large surface areas. Unfortunately, carbon adsorbents suffer from a low binding enthalpy for H2 (about 5 kJ mol-1), well below the 15 to 18 kJ mol-1 that is considered optimal for hydrogen storage systems. Binding interactions can be increased by the following methods: (1) adjusting the graphite interplanar separation with a pillared structure, and (2) introducing dopant species that interact with H2 molecules by strong electrostatic forces. Graphite intercalation compounds are a class of materials that contain both pillared structures and chemical dopants, making them an excellent model system for studying the fundamentals of hydrogen adsorption in nanostructured carbons.
\r\n\r\nPressure-composition-temperature diagrams of the MC24(H2)x graphite intercalation compounds were measured for M = (K, Rb, Cs). Adsorption enthalpies were measured as a function of H2 concentration. Notably, CsC24 had an average adsorption enthalpy of 14.9 kJ mol-1, nearly three times larger than that of pristine graphite. The adsorption enthalpies were found to be positively correlated with the alkali metal size. Adsorption capacities were negatively correlated with the size of the alkali metal. The rate of adsorption is reduced at large H2 compositions, due to the effects of site-blocking and correlation on the H2 diffusion.
\r\n\r\nThe strong binding interaction and pronounced molecular-sieving behavior of KC24 is likely to obstruct the translational diffusion of adsorbed H2 molecules. In this work, the diffusion of H2 adsorbed in KC24 was studied by quasielastic neutron scattering measurements and molecular dynamics simulations. As predicted, the rate of diffusion in KC24 is over an order of magnitude slower than in other carbon adsorbents (e.g. carbon nanotubes, nanohorns and carbon blacks). It is similar in magnitude to the rate of H2 diffusion in zeolites with molecular-sized cavities. This suggests that H2 diffusion in adsorbents is influenced very strongly by the pore geometry. The H2 diffusion process in KC24 contains at least two distinct jump frequencies.
\r\n\r\nBound states of adsorbed H2 in KC24 were investigated by inelastic neutron scattering measurements and density functional theory calculations. Spectral peaks in the neutron energy loss range of 5 meV to 45 meV were observed for the first time. These peaks were interpreted as single- and multi-excitation transitions of the H2 phonon and rotational modes. The rotational barrier for H2 molecules is many times larger in KC24 than in other carbon adsorbents, apparently due to the confinement of the molecules between closely-spaced graphitic layers. Evidence was found for the existence of at least three H2 sorption sites in KC24, each with a distinctive rotational barrier.
\r\n" }, { "name": "Quach, Quoc Chan (Brandon)", "degree": "PhD", "year": "2010", "title": "A Parylene Real Time PCR Microdevice", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:12142009-145646250", "creators": [ { "name": { "family": "Quach", "given": "Quoc Chan (Brandon)" }, "id": "Quach-Quoc-Chan-Brandon", "display_name": "Quach, Quoc Chan (Brandon)" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "bioeng" ], "doi": "10.7907/YC9S-0R15", "abstract": "The polymerase chain reaction (PCR) is a powerful biochemical assay that is used in virtually all biochemical labs. By specifically amplifying a small sample of DNA, this technique is useful in the fields of paternity testing, forensics, and virus detection, just to name a few. A useful advancement of PCR involves monitoring the fluorescence generated by an increase in DNA during the amplification. This so called real time (RT)PCR allows quantification of the initial sample amount and allows for shorter assay times by stopping the reaction when enough fluorescence has been detected.
\r\n\r\nTechnology in the field of micro-electro-mechanical systems (MEMS) has advanced from the academic laboratory level to a handful of commercially successful devices. Work on adapting MEMS to biochemical applications, however, is still at the laboratory research stage. Recent breakthroughs in the use of more biocompatible materials in MEMS devices have helped to advance bio-MEMS. In particular, the polymer Parylene has superior properties that present a promising new platform for this field.
\r\n\r\nThis work presents the design, fabrication, and testing of a parylene-based MEMS RTPCR device. By combining advancements in both biology and MEMS engineering, this work demonstrates the feasibility of such a device along with quantitative analysis and data that serve as a guide for its future development.
\r\n" }, { "name": "Rosenberg, Jessie C.", "degree": "PhD", "year": "2010", "title": "Applications of Micro/Nanoscale Optical Resonators: Plasmonic Photodetectors and Double-Disk Cavity Optomechanics", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03072010-230109724", "creators": [ { "name": { "family": "Rosenberg", "given": "Jessie C." }, "id": "Rosenberg-Jessie-C", "display_name": "Rosenberg, Jessie C." } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Libbrecht", "given": "Kenneth George" }, "id": "Libbrecht-K-G", "role": "member", "display_name": "Libbrecht, Kenneth George" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/GA8B-F134", "abstract": "Optical resonators present the potential to serve vital purposes in many emergent technologies that require spectral filtering, high optical intensities, or optical delays. By scaling down the optical resonators to the micro or nanoscale, the relevant phenomena can increase significantly in magnitude, while the device geometries become suitable for chip-scale and integrated processing. In this thesis, research is presented on several valuable resonator geometries and implementations, beginning with a more standard all-optical design, and continuing on to investigate the novel phenomena and applications which are made possible when optical and mechanical structures can be synergistically combined.
\r\n\r\nFirst, the design and experimental implementation of a plasmonic photonic crystal spectral and polarization filtering element is presented. This resonator scheme, in addition to allowing for a tailorable frequency and polarization response for single detector pixels, also increases the absorption of a thin layer of detector material by utilizing the unique optical properties of metal to confine light more tightly within the detector active region. Demonstrated in the valuable mid-infrared regime, this method of producing pixel-integrated multispectral detectors could find application in biological sensing and spectroscopy, missile tracking and guidance, and night vision.
\r\n\r\nFollowing this discussion, progress is presented in the relatively new field of cavity optomechanics: utilizing mechanically compliant optical resonators to couple to, control, and read out mechanical motion via optical forces. The use of optical resonators allows the generally weak optical forces to be increased in strength by orders of magnitude due to the many passes light makes within the resonator, while miniaturizing optomechanical devices into a convenient form factor for on-chip applications. Using a fully silicon-compatible double-disk-geometry optomechanical resonator, extremely large optomechanical coupling and very high optical quality factors are shown, enabling the demonstration of regenerative mechanical amplification, high compression factor optomechanical cooling, coherent mechanical mode mixing, and wide-bandwidth all-optical wavelength routing. Applications to ground-state cooling of mesoscopic devices, tunable optical buffering, photonic-phononic quantum state transfer, channel routing/switching, pulse trapping/release, and tunable lasing are discussed.
" }, { "name": "Roumi, Farshid", "degree": "PhD", "year": "2010", "title": "Shape Changing Transformations: Interactions with Plasticity and Electrochemical Processes", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282010-141343271", "creators": [ { "name": { "family": "Roumi", "given": "Farshid" }, "id": "Roumi-Farshid", "display_name": "Roumi, Farshid" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "mecheng" ], "doi": "10.7907/P94H-4B23", "abstract": "Solids undergo phase transformations where the crystal structure changes with temperature, chemical potential, stress, applied electric fields, or other external parameters. These occur by either long-range diffusion of atoms (diffusional phase transformation) or by some form of cooperative, homogeneous movement of many atoms that results in changes in crystal structure (displacive phase transformation). In the latter case, these movements are usually less than the interatomic distances, and the atoms maintain their coordination. The most common example of displacive phase transformations is martensitic transformation. The martensitic transformation in steel is economically very important and can result in very different behavior in the product. Other examples of martensitic transformations are shape memory alloys which are lightweight, solid-state alternatives to conventional actuators such as hydraulic, pneumatic, and motor-based systems.
\r\n\r\nThe martensitic transformation usually only depends on temperature and stress and, in contrast to diffusion-based transformations, is not time dependent. In shape memory alloys the transformation is reversible. On the other hand in steel, the martensite formation from austenite by rapidly cooling carbon-steel is not reversible; so steel does not have shape memory properties.
\r\n\r\nIn Chapters 2 and 3, we study the interesting yet very complicated behavior of martensitic transformation interactions with plastic deformations. A good example here is steel, which has been known for thousands of years but still is believed to be a very complicated material. Steel can show different behavior depending on its complex microstructure. Thus understanding the formation mechanisms is crucial for the interpretation and optimization of its properties. As an example, low alloyed steels with transformation induced plasticity (TRIP), metastable austenite steels, are known for strong hardening and excellent elongation and strength. It is suggested that the strain-induced transformation of small amounts of untransformed (retained) austenite into martensite during plastic deformation is a key to this excellent behavior.
\r\n \r\nIn Chapters 4 and 5, we study the interactions of solid-solid phase transformations with electrochemical processes. It is suggested that electronic and ionic structures depends on lattice parameters, thus it is expected that structural transformations can lead to dramatic changes in material properties. These transformations can also change the energy barrier and hysteresis. It is known that compatible interfaces can reduce elastic energy and hysteresis, thus may extend the life of the system. Solid-solid transformations change the crystalline structure. These geometry changes can have long range effects and cause stresses in the whole material. The generated stress field itself changes the total free energy, due to the change in elastic energy, and thus, the electrochemical potential and processes are affected. An example is olivine phosphates which are candidates for cathode material in Li-ion batteries. These materials undergo an orthorhombic to orthorhombic phase transition. Experiments in the literature have suggested that elastic compatibility can affect rates of charge/discharge in the battery. Our theory provides some insight into this observation.
" }, { "name": "Roy, Anthony Mathew", "degree": "PhD", "year": "2010", "title": "Neuro-Evolution Using Recombinational Algorithms and Embryogenesis for Robotic Control", "advisor": "Antonsson, Erik K.; Shapiro, Andrew A.; Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092010-140839602", "creators": [ { "name": { "family": "Roy", "given": "Anthony Mathew" }, "id": "Roy-Anthony-Mathew", "display_name": "Roy, Anthony Mathew" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "co-advisor", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Shapiro", "given": "Andrew A." }, "id": "Shapiro-A-A", "role": "co-advisor", "display_name": "Shapiro, Andrew A." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Shapiro", "given": "Andrew A." }, "id": "Shapiro-A-A", "role": "member", "display_name": "Shapiro, Andrew A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/YNED-VN66", "abstract": "Control tasks involving dramatic nonlinearities, such as decision making, can be challenging for classical design methods. However, autonomous, stochastic design methods such as evolutionary computation have proved effective. In particular, genetic algorithms that create designs via the application of recombinational rules are robust and highly scalable. Neuro-Evolution Using Recombinational Algorithms and Embryogenesis (NEURAE) is a genetic algorithm that creates C++ programs that in turn create neural networks which can function as logic gates. The neural networks created are scalable and robust enough to feature redundancies that allow the network to function despite internal failures. An analysis of NEURAE evinces how biologically inspired phenomena apply to simulated evolution. This allows for an optimization of NEURAE that enables it to create controllers for a simulated swarm of Khepera-inspired robots." }, { "name": "Ruiz, Lydia Ann", "degree": "PhD", "year": "2010", "title": "The Role of Unsteady Hydrodynamics in the Propulsive Performance of a Self-Propelled Bioinspired Vehicle", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-122004587", "creators": [ { "name": { "family": "Ruiz", "given": "Lydia Ann" }, "id": "Ruiz-Lydia-Ann", "display_name": "Ruiz, Lydia Ann" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7JWD-TB88", "abstract": "Aquatic animals differ from typical engineering systems in their method of locomotion. In general, aquatic animals propel using unsteady dynamics producing vortex rings. Researchers have long shown interest in designing devices that resemble their shape and propulsive behavior. Traditional definitions of propulsive efficiency used to model these behaviors have not taken unsteady effects into account and are typically based on steady flow through propellers or rocket motors. Measurements of aquatic animals based on these quasi-steady metrics have suggested propulsive efficiencies over 80% when utilizing certain swimming kinematics. However, the mechanical efficiency of muscle-actuated biological propulsion has been found to be much lower, typically less than 20%. It is important to take into account the total efficiency of the system, the product of the mechanical and propulsive efficiency, when designing and implementing a biologically inspired propulsive device.
\r\n\r\nThe purpose of my research is to make a direct, experimental comparison between biological and engineering propulsion systems. For this study, I designed an underwater vehicle that has the capability of producing either a steady or unsteady jet for propulsion, akin to a squid and jellyfish, while utilizing the same mechanical efficiency. I show that it is unnecessary to take an approach that mimics animal shape and kinematics to achieve the associated propulsive performance. A bioinspired, propeller-based platform that mimics animal wake dynamics can be similarly effective.
\r\n\r\nA study on how vortex dynamics plays a key role in improving the propulsive efficiency of pulsed jet propulsion was conducted. Measurements of propulsive performance resulted in superior performance for the pulsed-jet configuration in comparison to the steady jet configuration particularly at higher motor speeds. The analysis demonstrated that vortex ring formation led to the acceleration of two classes of ambient fluid, entrained and added mass, and this consequently led to an increased total fluid impulse of the jet and propulsive performance. The first source of ambient fluid acceleration investigated was entrained mass. The magnitude of the entrainment ratio was measured and found to be smaller for the steady jet mode of propulsion in comparison to the pulsed jet mode of propulsion given comparable motor speeds. The role of the added mass effect was also investigated in increasing propulsive performance. A model developed by Krueger is used to determine the fraction of the total impulse imparted to the flow that was contributed by the added mass effect. Results demonstrated that the added mass effect associated with the acceleration of ambient fluid at the initiation of a starting jet provides an increase in the total impulse and is thus a source for increased propulsive performance. Last, a model was developed to investigate how an increase in the total fluid impulse due to vortex ring formation is related to the propulsive efficiency. Results obtained using the model are in agreement, within uncertainty, with previous experimental results for the measurement of propulsive efficiency. The results support that the additional force generated from the acceleration of two classes of ambient fluid are the source of increased propulsive efficiency for the pulsed jet configuration in comparison to the steady jet configuration. This model serves as an additional metric for determining the propulsive efficiency of a system utilizing pulsed jet propulsion.
\r\n" }, { "name": "Sasaki, Kenji Alexander", "degree": "PhD", "year": "2010", "title": "Electrochemical Characterization of Solid Acid Fuel Cell Electrodes", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05102010-184207288", "creators": [ { "name": { "family": "Sasaki", "given": "Kenji Alexander" }, "id": "Sasaki-Kenji-Alexander", "display_name": "Sasaki, Kenji Alexander" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Giapis", "given": "Konstantinos P." }, "id": "Giapis-K-P", "role": "member", "display_name": "Giapis, Konstantinos P." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "member", "display_name": "Ahn, Channing C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/BN8H-3F41", "abstract": "The quest for high-efficiency, high-power output fuel cells can be largely equated to the quest for high-performance components (anode, cathode, electrolyte). Solid Acid electrolytes, notably CsH2PO4, have been demonstrated to be affordable, stable, excellent ion conductors, and impermeable to parasitic fuel cross-over. Moreover, they operate at a temperature `sweet-spot' high enough to promote electrode kinetics and low enough to enable low-cost infrastructure. Fuel cell devices based on these materials are known to be limited, however, by electrode losses - even with high platinum loading. Improving the performance and lowering the cost of these components is necessary if such devices are to be considered viable alternatives.
\r\n\r\nIn this work, the primary focus was the development of electrochemical characterization approaches. In doing so, we investigated electrode losses through steady-state and time-dependent electrochemical characterization and identified the primary rate limiting process and mechanism as oxygen reduction at the cathode. To characterize anode kinetics, new testing approaches were implemented which employed robust, asymmetric electrode geometries to isolate electrode kinetics without the inclusion of a reference electrode. These geometries' isolation efficacy was assessed by numerical computation - the results of which were leveraged into an explicitly defined, material-agnostic tool to evaluate asymmetric electrode geometries.
\r\n\r\nWhile for platinum, the cathode mechanism was shown to be insensitive to the microstructures tested, the mechanism of hydrogen reduction/oxidation was seen to vary between nanoscale powder and microscale defined electrodes - reconfirming the importance of rigorous testing approaches. Asymmetric electrode geometries with defined microstructures allowed direct characterization and comparative evaluation of non-platinum candidates for both the anode and the cathode. On the anode, palladium was over an order of magnitude more active than platinum and nickel, which exhibited a comparable activity. Palladium and silver were shown to be stable cathode materials, though less active than platinum. As a demonstration of the developed methodology's flexibility, a palladium-silver alloy was synthesized and tested.
\r\n\r\nThe tools and methodologies developed in this work enable the rapid and flexible screening of electrodes for solid acid fuel cells.
" }, { "name": "Schramm, Joseph Paul", "degree": "PhD", "year": "2010", "title": "Mechanical Performance of Amorphous Metallic Cellular Structures", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechTHESIS:01292010-170058619", "creators": [ { "name": { "family": "Schramm", "given": "Joseph Paul" }, "id": "Schramm-Joseph-Paul", "display_name": "Schramm, Joseph Paul" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Conner", "given": "Robert Dale" }, "id": "Conner-R-D", "role": "member", "display_name": "Conner, Robert Dale" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "matsci" ], "doi": "10.7907/H56A-SA70", "abstract": "Metallic glass and metallic glass matrix composites are excellent candidates for application in cellular structures because of their outstanding plastic yield strengths and their ability to deform plastically prior to fracture. The mechanical performance of metallic-glass and metallic-glass-matrix-composite honeycomb structures are discussed, and their strength and energy absorption capabilities examined in quasi-static compression tests for both in-plane and out-of-plane loading. These structures exhibit strengths and energy absorption that well exceed the performance of similar structures made from crystalline metals. The strength and energy absorption capabilities of amorphous metal foams produced by a powder metallurgy process are also examined, showing that foams produced by this method can be highly porous and are able to inherit the strength of the parent metallic glass and absorb large amounts of energy. The mechanical properties of a highly stochastic set of foams are examined at low and high strain rates. It is observed that upon a drastic increase in strain rate, the dominant mechanism of yielding for these foams undergoes a change from elastic buckling to plastic yielding. This mechanism change is thought to be the result of the rate of the mechanical test approaching or even eclipsing the speed of elastic waves in the material." }, { "name": "Shearn, Michael Joseph, II", "degree": "PhD", "year": "2010", "title": "Silicon Integrated Optics: Fabrication and Characterization", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232010-110330796", "creators": [ { "name": { "family": "Shearn", "given": "Michael Joseph, II" }, "id": "Shearn-Michael-Joseph-II", "display_name": "Shearn, Michael Joseph, II" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/VKA1-B695", "abstract": "For decades, the microelectronics industry has sought integration and miniaturization as canonized in Moore's Law, and has continued doubling transistor density about every two years. However, further miniaturization of circuit elements is creating a bandwidth problem as chip interconnect wires shrink as well. A potential solution is the creation of an on-chip optical network with low delays that would be impossible to achieve using metal buses. However, this technology requires integrating optics with silicon microelectronics. The lack of efficient silicon optical sources has stymied efforts of an all-Si optical platform. Instead, the integration of efficient emitter materials, such as III-V semiconductors, with Si photonic structures is a low-cost, CMOS-compatible alternative platform.
\r\n\r\nThis thesis focuses on making and measuring on-chip photonic structures suitable for on-chip optical networking. The first part of the thesis assesses processing techniques of silicon and other semiconductor materials. Plasmas for etching and surface modification are described and used to make bonded, hybrid Si/III-V structures. Additionally, a novel masking method using gallium implantation into silicon for pattern definition is characterized. The second part of the thesis focuses on demonstrations of fabricated optical structures. A dense array of silicon devices is measured, consisting of fully-etched grating couplers, low-loss waveguides and ring resonators. Finally, recent progress in the Si/III-V hybrid system is discussed. Supermode control of devices is described, which uses changing Si waveguide width to control modal overlap with the gain material. Hybrid Si/III-V, Fabry-Perot evanescent lasers are demonstrated, utilizing a CMOS-compatible process suitable for integration on in electronics platforms. Future prospects and ultimate limits of Si devices and the hybrid Si/III-V system are also considered.
" }, { "name": "Shen, Kai", "degree": "PhD", "year": "2010", "title": "Neural Encoding of Mixtures and Stimulus Generation in the Insect Brain", "advisor": "Laurent, Gilles J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09122010-130333994", "creators": [ { "name": { "family": "Shen", "given": "Kai" }, "id": "Shen-Kai", "display_name": "Shen, Kai" } ], "advisors": [ { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "advisor", "display_name": "Laurent, Gilles J." } ], "committee": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "chair", "display_name": "Winfree, Erik" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "orcid": "0000-0001-8837-678X", "role": "member", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "member", "display_name": "Laurent, Gilles J." } ], "option_major": [ "cns" ], "doi": "10.7907/MDZC-0J48", "abstract": "Sensory object recognition is the most fundamental of operations performed by the brain. A key computational difficulty of object recognition is that it requires both selectivity to particular objects (e.g., exact odor mixture identification) and generalization across objects (identifying particular features or components common to different odors). Although previous results (1) suggest that odor identity and intensity are represented in the activity of both PNs and KCs, it is not clear how these representations generalize across complex odor mixtures. In particular, it is not clear what types of information are available in KC population (or if its even possible to decode across KC populations?) and how is this information represented? Using the locust olfactory system as a model system, we found that Kenyon cells (KCs), the principal neurons of the mushroom body, an area required for associative learning can identify the presence of components in mixtures and thus enable odor segmentation. As a population, small groups of KCs can both identify and categorize odors with high accuracy. We identified and tested simple circuit requirements for this computation, and propose that odor representations in mushroom bodies are optimized for odor memorization, identification and generalization. These rules may be relevant for pattern classifying circuits in general." }, { "name": "Sullivan, Regina Mariko", "degree": "PhD", "year": "2010", "title": "The Physics of High-Velocity Ions in the Hall Thruster Near-Field", "advisor": "Shepherd, Joseph E.; Johnson, Lee K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04022010-134100215", "creators": [ { "name": { "family": "Sullivan", "given": "Regina Mariko" }, "id": "Sullivan-Regina-Mariko", "display_name": "Sullivan, Regina Mariko" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Johnson", "given": "Lee K." }, "id": "Johnson-L-K", "role": "co-advisor", "display_name": "Johnson, Lee K." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Johnson", "given": "Lee K." }, "id": "Johnson-L-K", "role": "member", "display_name": "Johnson, Lee K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8F2Y-NM32", "abstract": "A study of the physics underlying high velocity ion trajectories within the near-field region of a Hall thruster plume is presented. In this context, \"high velocity\" ions are ions that have been accelerated through the full potential drop of the thruster (sometimes referred to as \"primary energy\" or \"primary beam energy\" ions). Results from an experimental survey of an SPT-70 thruster plume are shown, along with simulated data from a Hall thruster code and from a plasma sheath model. Two main features are examined: the central jet along the Hall thruster centerline, and the population of high velocity ions at high angles.
\r\n\r\nIn the experimental portion of the investigation, three diagnostic instruments were employed: (1) a Faraday probe for measuring ion current density, (2) an ExB velocity filter for mapping ions with the primary beam energy, and (3) a Retarding Potential Analyzer (RPA) for determining ion energy distributions. In the numerical portion, two codes were employed: (1) a hybrid-PIC Hall thruster code known as HPHall, and (2) a model of the plasma sheath near the exit plane of the thruster, which was developed by the author.
\r\n\r\nA comparison between the measured and simulated data sets is made, to analyze the degree to which different mechanisms are responsible for the evolution of the thruster\r\nplume in the near-field region. This analysis shows that the central jet is both a function of symmetric expansion of the ion beam as well as asymmetry in the internal potential field of the thruster. Additionally, it is suggested that high energy, high angle ions could be generated given a specific internal electric field configuration, while oscillations are ruled out as the cause of these ions. The results from the sheath model show that while the sheath can change trajectory angles by 10 to 20 degrees, it can not fully explain the presence of\r\nhigh angle ions with high energies.
" }, { "name": "Sun, Xiankai", "degree": "PhD", "year": "2010", "title": "Supermode Si/III-V Lasers and Circular Bragg Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:05072010-002329705", "creators": [ { "name": { "family": "Sun", "given": "Xiankai" }, "id": "Sun-Xiankai", "orcid": "0000-0002-9137-0298", "display_name": "Sun, Xiankai" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/6797-0136", "abstract": "Semiconductor lasers are arguably the most important component in optical communications. This thesis investigates two types of semiconductor lasers that are useful in integrated optics. Part I focuses on supermode Si/III\u2013V lasers and Part II discusses circular Bragg lasers for the application as surface-emitting lasers.
\r\n\r\nJust as optical fibers have largely replaced the traditional copper wires in long-distance applications, people started to consider incorporating optical communication onto chips, primarily because the increased ohmic heating and RC delay associated with the metal interconnection prevent further increase in the data-processing rate. Si is well known to be the integration platform for electronics, and III\u2013V materials (GaAs, InP, etc.) are efficient light emitters. It is natural to bring them together to realize the on-chip optical communication. Among various Si/III\u2013V integration schemes the most promising is the hybrid Si evanescent platform in which a wafer-bonding technique that is compatible with current CMOS processing is used to bring Si and III\u2013V materials together. Part I of this thesis focuses on the application of a novel mode-control method to such hybrid waveguide system to enhance the modal gain, which makes for more efficient and, most importantly, shorter devices that may hold the key to the photonics/electronics integration. The supermode theory is derived, the shortest adiabatic mode transformer is theoretically and numerically studied, and the device design and fabrication are presented, followed by the experimental demonstration of the performance enhancement in the mode-controlled Si/InGaAsP laser devices.
\r\n\r\nVertical cavity surface emitting lasers are a commercial light source for optical communications, but their single-modedness and good emission pattern are guaranteed only over a very small mode area (diameter of several microns) thus they have limitations in high-power applications. As an alternative, circular Bragg lasers can be designed as a superior surface emitting laser that produces high output power with good beam quality. Part II of this thesis presents a comprehensive and systematic theoretical study on the surface-emitting Hankel-phased circular Bragg lasers in various geometries. The analytical and numerical mode-solving methods will be described, followed by near- and above-threshold modal analyses.
" }, { "name": "Vriend, Nathalie Maria", "degree": "PhD", "year": "2010", "title": "Booming Sand Dunes", "advisor": "Hunt, Melany L.; Clayton, Robert W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312010-051551703", "creators": [ { "name": { "family": "Vriend", "given": "Nathalie Maria" }, "id": "Vriend-Nathalie-Maria", "orcid": "0000-0002-1456-2317", "display_name": "Vriend, Nathalie Maria" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "role": "co-advisor", "display_name": "Clayton, Robert W." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "role": "member", "display_name": "Clayton, Robert W." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Lamb", "given": "Michael P." }, "id": "Lamb-M-P", "role": "member", "display_name": "Lamb, Michael P." } ], "option_major": [ "mecheng" ], "doi": "10.7907/BFHE-0969", "abstract": "\"Booming\" sand dunes are able to produce low-frequency sound that resembles a pure note from a music instrument. The sound has a dominant audible frequency (70-105 Hz) and several higher harmonics and may be heard from far distances away. A natural or induced avalanche from a slip face of the booming dune triggers the emission that may last for several minutes. There are various references in travel literature to the phenomenon, but to date no scientific explanation covered all field observations.
\r\n\r\nThis thesis introduces a new physical model that describes the phenomenon of booming dunes. The waveguide model explains the selection of the booming frequency and the amplification of the sound in terms of constructive interference in a confined geometry. The frequency of the booming is a direct function of the dimensions and velocities in the waveguide. The higher harmonics are related to the higher modes of propagation in the waveguide.
\r\n\r\nThe experimental validation includes quantitative field research at the booming dunes of the Mojave Desert and Death Valley National Park. Microphone and geophone recordings of the acoustic and seismic emission show a variation of booming frequency in space and time. The analysis of the sensor data quantifies wave propagation characteristics such as speed, dispersion, and nonlinear effects and allows the distinction between the source mechanism of the booming and the booming itself.
\r\n\r\nThe migration of sand dunes results from a complicated interplay between dune building, wind regime, and precipitation. The morphological and morphodynamical characteristics of two field locations are analyzed with various geophysical techniques. Ground-penetrating radar images the subsurface structure of the dunes and reveal a natural, internal layering that is directly related to the history of dune migration. The seismic velocity increases abruptly with depth and gradually increases with downhill position due to compaction. Sand sampling shows local cementation of sand grains within the discrete layers that explains the increase in velocity and decrease in porosity. The subsurface layering may influence the speed of dune migration and therefore have important consequences on desertification.
\r\n\r\nThe positive qualitative and quantitative correlation between the subsurface layering in the dune and the manifestation of the booming sound implies a close relation between environmental factors and the booming emission. In this thesis, the frequency of booming is correlated with the depth of the waveguide and the seismic velocities. The variability on location and season suggests that the waveguide theory successfully unravels the phenomenon\r\nof booming sand dunes.
" }, { "name": "Walker, Christopher", "degree": "PhD", "year": "2010", "title": "Fabrication of Microfluidic Structures by Automated Laser Ablation and Automation of Optical Testing", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-060526366", "creators": [ { "name": { "family": "Walker", "given": "Christopher" }, "id": "Walker-Christopher", "display_name": "Walker, Christopher" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Kartalov", "given": "Emil P." }, "id": "Kartalov-E-P", "role": "member", "display_name": "Kartalov, Emil P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/PEET-AM61", "abstract": "A versatile, semi-automated instrument to fabricate embedded devices by laser ablation was designed, built, and tested. The expertise required for this came partially from the development of an optical testing system. This system and its utility in testing silicon on oxide waveguide structures are briefly explored. Processes for reproducibly fabricating microfluidic channels and vias were developed. Using one of these processes, design rules for more complex features were developed, and fully three dimensional structures realized. The phenomenon of nonlinear fluidic resistance in deformable channels was explored; a simple analytical model was designed, and compared favorably to measured data. Finally, using this effect, fully embedded valves were developed. With the combination of large scale accurate feature placement, a developed process for three dimensional features, and the development of valves, this instrument is capable of fabricating complex systems of devices, and should prove a useful tool in the future." }, { "name": "Wiest, Aaron", "degree": "PhD", "year": "2010", "title": "Thermoplastic Forming and Related Studies of the Supercooled Liquid Region of Metallic Glasses ", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechTHESIS:12222009-004407068", "creators": [ { "name": { "family": "Wiest", "given": "Aaron" }, "id": "Wiest-Aaron", "display_name": "Wiest, Aaron" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Conner", "given": "Robert Dale" }, "id": "Conner-R-D", "role": "member", "display_name": "Conner, Robert Dale" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "matsci" ], "doi": "10.7907/W2G5-1S16", "abstract": "The thermoplastic formability (TPF) of metallic glasses was found to be related to the calorimetrically measured crystallization temperature minus the glass transition temperature, Tg - Tx = \u0394T. Alloy development in the ZrTiBe system identified a composition with \u0394T = 120 \u00b0C. Many alloys with \u0394T > 150 \u00b0C and one alloy, Zr35Ti30Be27.5Cu7.5, with \u0394T = 165 \u00b0C were discovered by substituting Be with small amounts of fourth alloying elements. The viscosity as a function of temperature, \u03b7(T), and time temperature transformation (TTT) measurements for the new alloy are presented and combined to create \u03b7TT plots (viscosity time transformation) that are useful in determining what viscosities are available for a required processing time. \u03b7TT plots are created for many alloys used in TPF in the literature and it is found that for processes requiring 60 - 300 s, Zr35Ti30Be27.5Cu7.5 provides an order of magnitude lower viscosity for processing than the other metallic glasses. Injection molding is demonstrated with Zr35Ti30Be27.5Cu7.5 and the part shows improved mechanical properties over die cast specimens of the same geometry. Changes of slope in \u03b7(T) measurements were observed and investigated in some quaternary compositions and found to be present in ternary compositions as well. Traditionally metallic glasses show a single discontinuity in heat capacity at the glass transition temperature. Alloys with the changes in slope of \u03b7(T) were found to show two discontinuities in heat capacity with the changes in slope of \u03b7(T) roughly correlating with the observed Tg values. These two Tg values were assumed to arise from two glassy phases present in the alloy. Further heat capacity analysis found systematic trends in the magnitude of the heat capacity discontinuities with composition and the single phase compositions of a metastable miscibility gap were discovered. Microscopic evidence of the two phases is lacking so we must limit our claims to evidence of two relaxation phenomena existing and can\u2019t definitively claim two phases.
\r\n\r\nThe alloy development led to the discovery of alloys with densities near Ti that are among the highest strength to weight ratio materials known. Alloys with corrosion resistances in simulated sea water 10x greater than other Zr based glasses and commonly used marine metals were discovered. Glasses spanning 6 orders of magnitude in corrosion resistance to 37% w/w HCl were discovered. Corrosion fatigue in saline environments remains a problem for these compositions and prevents their utility as biomaterials despite good evidence of biocompatibility in in vitro and in vivo studies.
\r\n" }, { "name": "Wongpiromsarn, Tichakorn", "degree": "PhD", "year": "2010", "title": "Formal Methods for Design and Verification of Embedded Control Systems: Application to an Autonomous Vehicle", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272010-153304667", "creators": [ { "name": { "family": "Wongpiromsarn", "given": "Tichakorn" }, "id": "Wongpiromsarn-Tichakorn", "display_name": "Wongpiromsarn, Tichakorn" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Holzmann", "given": "Gerard J." }, "id": "Holzmann-G-J", "role": "member", "display_name": "Holzmann, Gerard J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/XZ3X-7V51", "abstract": "The design of reliable embedded control systems inherits the difficulties involved in designing both control systems and distributed (concurrent) computing systems. Design bugs in these systems may arise from the unforeseen interactions among the computing, communication and control subsystems. Motivated by the difficulties of finding this type of design bugs, this thesis develops mathematical frameworks, based on formal methods, to facilitate the design and analysis of such embedded systems. An expressive specification language of linear temporal logic (LTL) is used to specify the desired system properties. The practicality of the proposed frameworks is demonstrated through autonomous vehicle case studies and autonomous urban driving problems.
\r\n\r\nOur approach incorporates methodology from computer science and control, including model checking, theorem proving, synthesis of digital designs, reachability analysis, Lyapunov-type methods and receding horizon control. This thesis consists of two complementary parts, namely, verification and design. First, we introduce Periodically Controlled Hybrid Automata (PCHA), a subclass of hybrid automata that abstractly captures a common design pattern in embedded control systems. New sufficient conditions that exploit the structure of PCHAs in order to simplify their invariant verification are presented.
\r\n\r\nAlthough the aforementioned technique simplifies an invariant verification of PCHAs, finding a proper invariant remains a challenging problem. To complement the verification efforts, in the second part of the thesis, we present a methodology for automatic synthesis of embedded control software that provides a formal guarantee of system correctness, with respect to its desired properties expressed in linear temporal logic. The correctness of the system is guaranteed even in the presence of an adversary (typically arising from changes in the environments), disturbances and modeling errors. A receding horizon framework is proposed to alleviate the associated computational complexity of LTL synthesis. The effectiveness of this framework is demonstrated through the autonomous urban driving problems.
\r\n" }, { "name": "Wu, David Dah-wei", "degree": "PhD", "year": "2010", "title": "Biomechanical Information Transfer: Maximum Caliber, \u03bb Genome Ejection Dynamics, and the Formation of Otoliths in Zebrafish", "advisor": "Fraser, Scott E.; Phillips, Robert B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182010-213110299", "creators": [ { "name": { "family": "Wu", "given": "David Dah-wei" }, "id": "Wu-David-Dah-wei", "display_name": "Wu, David Dah-wei" } ], "advisors": [ { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "co-advisor", "display_name": "Fraser, Scott E." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "co-advisor", "display_name": "Phillips, Robert B." } ], "committee": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "chair", "display_name": "Pierce, Niles A." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "bioeng" ], "doi": "10.7907/X454-MV52", "abstract": "Biology is inherently a non-equilibrium process - constantly battling or co-opting the entropic enemy in order to achieve its sine qua non: growth, development, and reproduction. Involved in these processes is the formation of temporal and spatial order from disorder, and the transfer of information in genomic content but also in the form of physical principles.
\r\n\r\nFirst, I will describe a different way to analyze dynamics called Maximum Caliber, a model-free application of the Principle of Maximum Entropy to trajectories or processes, based purely on information theorya. We apply Maximum Caliber to analyze particles diffusing on a dual-minima energy landscape and attempt to describe and predict the probability distribution of trajectories. Next, I will discuss our efforts in analyzing the literal transfer of information from one organism to the next: specifically, how phage lambda's DNA gets inside Escherichia coli. The use of counterions as a parameter to tune the force of in vitro ejections is clarified before performing suggestive in vivo injection experiments. Last, the process of building and shaping the otolith of the zebrafish (the accelerometer and hearing organ) is analyzed, with the conclusion that it is possible to generate said organ through purely physical mechanisms, suggesting that biological information transfer is not exclusively genetic.
\r\n" }, { "name": "Wunderlich, Klaus", "degree": "PhD", "year": "2010", "title": "Multiple Forms of Valuation in the Human Brain", "advisor": "O'Doherty, John P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11112009-132836900", "creators": [ { "name": { "family": "Wunderlich", "given": "Klaus" }, "id": "Wunderlich-Klaus", "display_name": "Wunderlich, Klaus" } ], "advisors": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "advisor", "display_name": "O'Doherty, John P." } ], "committee": [ { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "chair", "display_name": "Andersen, Richard A." }, { "name": { "family": "Bossaerts", "given": "Peter L." }, "id": "Bossaerts-P-L", "role": "member", "display_name": "Bossaerts, Peter L." }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "member", "display_name": "O'Doherty, John P." } ], "option_major": [ "cns" ], "doi": "10.7907/90F2-1348", "abstract": "Our lives are defined by the decisions we make, often involving choices between different actions or goods. An important open problem in decision neuroscience is, what value signals are used in guiding the different types of choices, where are they stored in the brain, and how does the brain compare them to make a choice. We used fMRI in human subjects to address these questions in a variety of different choice settings: decisions between actions, economic choices, and more complex hierarchical decisions. We found evidence for a separate representation of two main forms of value signals in the human brain: precursors of choice, such as signals relating to the value of each available action or stimulus, and signals reflecting the consequence of the decision process by encoding the expected value of the option that is subsequently chosen. On the precursor side, we found action value signals in supplementary motor cortex and stimulus value signals in medial prefrontal cortex. Separate brain regions, most prominently ventromedial prefrontal cortex, were involved in encoding the value of the chosen action or stimulus. Importantly, we found value chosen signals in stimulus decisions even when no actions were associated with choosing the stimuli, providing evidence for the hypothesis that the brain doesn\u2019t need the motor system to make such decisions but is capable of making economic choices completely within an abstract representation of goods. Furthermore, in action decisions, we found that activity in dorsomedial frontal cortex resembles the output of a decision comparator, implicating this region in the computation of the decision itself. In a real world setting where multiple stimuli could potentially influence outcomes, an individual may consider a number of theories about which features are relevant for giving reward. We found that decision variables based on simultaneous integration of all evidences were better able to explain subjects\u2019 behavior and activity in prefrontal cortex than those generated by an attention-gated approach, i.e. by first picking the theory that is most likely correct and then choosing accordingly. These results demonstrate that the human brain is capable of optimally integrating information, similar to an ideal Bayesian observer." }, { "name": "Xu, Weiyu", "degree": "PhD", "year": "2010", "title": "Compressive Sensing for Sparse Approximations: Constructions, Algorithms, and Analysis", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262009-081233260", "creators": [ { "name": { "family": "Xu", "given": "Weiyu" }, "id": "Xu-Weiyu", "display_name": "Xu, Weiyu" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/F63K-GT12", "abstract": "Compressive sensing is an emerging research field that has applications in signal processing, error correction, medical imaging, seismology, and many more other areas. It promises to efficiently recover a sparse signal vector via a much smaller number of linear measurements than its dimension. Naturally, how to design these linear measurements, how to construct the original high-dimensional signals efficiently and accurately, and how to analyze the sparse signal recovery algorithms are important issues in the developments of compressive sensing. This thesis is devoted to addressing these fundamental issues in the field of compressive sensing.
\r\n\r\nIn compressive sensing, random measurement matrices are generally used and \u2113\u2081 minimization algorithms often use linear programming or other optimization methods to recover the sparse signal vectors. But explicitly constructible measurement matrices providing performance guarantees were elusive and \u2113\u2081 minimization algorithms are often very demanding in computational complexity for applications involving very large problem dimensions. In chapter 2, we propose and discuss a compressive sensing scheme with deterministic performance guarantees using deterministic explicitly constructible expander graph-based measurement matrices and show that the sparse signal recovery can be achieved with linear complexity. This is the first of such a kind of compressive sensing scheme with linear decoding complexity, deterministic performance guarantees of linear sparsity recovery, and deterministic explicitly constructible measurement matrices.
\r\n\r\nThe popular and powerful \u2113\u2081 minimization algorithms generally give better sparsity recovery performances than known greedy decoding algorithms. In chapter 3, starting from a necessary and sufficient null-space condition for achieving a certain signal recovery accuracy, using high-dimensional geometry, we give a unified null-space Grassmann angle-based analytical framework for compressive sensing. This new framework gives sharp quantitative trade-offs between the signal sparsity and the recovery accuracy of the \u2113\u2081 optimization for approximately sparse signal. Our results concern the fundamental \"balancedness\" properties of linear subspaces and so may be of independent mathematical interest.
\r\n\r\nThe conventional approach to compressed sensing assumes no prior information on the unknown signal other than the fact that it is sufficiently sparse over a particular basis. In many applications, however, additional prior information is available. In chapter 4, we will consider a particular model for the sparse signal that assigns a probability of being zero or nonzero to each entry of the unknown vector. The standard compressed sensing model is therefore a special case where these probabilities are all equal. Following the introduction of the null-space Grassmann angle-based analytical framework in this thesis, we are able to characterize the optimal recoverable sparsity thresholds using weighted \u2113\u2081 minimization algorithms with the prior information.
\r\n\r\nThe roles of \u2113\u2081 minimization algorithm in recovering sparse signals from incomplete measurements are now well understood, and sharp recoverable sparsity thresholds for \u2113\u2081 minimization have been obtained. The iterative reweighted \u2113\u2081 minimization algorithms or related algorithms have been empirically observed to boost the recoverable sparsity thresholds for certain types of signals, but no rigorous theoretical results have been established to prove this fact. In chapter 5, we try to provide a theoretical foundation for analyzing the iterative reweighted \u2113\u2081 algorithms. In particular, we show that for a nontrivial class of signals, the iterative reweighted \u2113\u2081 minimization can indeed deliver recoverable sparsity thresholds larger than the \u2113\u2081 minimization. Again, our results are based on the null-space Grassmann angle-based analytical framework.
\r\n\r\nEvolving from compressive sensing problems, where we are interested in recovering sparse vector signals from compressed linear measurements, we will turn our attention to recovering matrices of low rank from compressed linear measurements in chapter 6, which is a challenging problem that arises in many applications in machine learning, control theory, and discrete geometry. This class of optimization problems is NP-HARD, and for most practical problems there are no efficient algorithms that yield exact solutions. A popular heuristic replaces the rank function with the nuclear norm of the decision variable and has been shown to provide the optimal low rank solution in a variety of scenarios. We analytically assess the practical performance of this heuristic for finding the minimum rank matrix subject to linear constraints. We start from the characterization of a necessary and sufficient condition that determines when this heuristic finds the minimum rank solution. We then obtain probabilistic bounds on the matrix dimensions and rank and the number of constraints, such that our conditions for success are satisfied for almost all linear constraint sets as the matrix dimensions tend to infinity. Empirical evidence shows that these probabilistic bounds provide accurate predictions of the heuristic's performance in non-asymptotic scenarios.
" }, { "name": "Yang, Wanwan", "degree": "PhD", "year": "2010", "title": "Fast Viability Assessment of Clostridium Spores: Survival in Extreme Environments", "advisor": "Ponce, Adrian", "url": "https://resolver.caltech.edu/CaltechTHESIS:01072010-132355433", "creators": [ { "name": { "family": "Yang", "given": "Wanwan" }, "id": "Yang-Wanwan", "display_name": "Yang, Wanwan" } ], "advisors": [ { "name": { "family": "Ponce", "given": "Adrian" }, "id": "Ponce-A", "role": "advisor", "display_name": "Ponce, Adrian" } ], "committee": [ { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "role": "chair", "display_name": "Sessions, Alex L." }, { "name": { "family": "Orphan", "given": "Victoria J." }, "id": "Orphan-V-J", "role": "co-chair", "display_name": "Orphan, Victoria J." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Ponce", "given": "Adrian" }, "id": "Ponce-A", "role": "member", "display_name": "Ponce, Adrian" } ], "option_major": [ "envreng" ], "doi": "10.7907/8BBD-7Y02", "abstract": "Bacterial endospores are formed in genera such as Bacillus and Clostridium in response to adverse environmental changes. Endospores have remarkable resistance to various extreme conditions and can remain dormant for extended periods of time. Clostridium spores are of particular interest due to their significant importance in several industries, such as food processing, wastewater treatment, pharmaceuticals, and health care. They are also the ideal candidates to study Panspermia and potential extraterrestrial life. However, to date, most endospore research has been conducted on Bacillus, and study of the anaerobic spore former, Clostridium, is not adequate.
\r\n\r\nIn this study, we have developed a general protocol to produce and purify Clostridium spores. Spectroscopy and microscopy based Endospore Viability Assay (Spectro EVA and Micro EVA) were developed and validated to assess the viability of Clostridium spores. Germinability was used as an indicator for spore viability. The basic principle of the two EVAs is to measure the release of a unique biomarker, dipicolinic acid (DPA), via germination as a proxy for endospore viability. In particular, a luminescence time-gated microscopy technique (Micro EVA) has been developed to enumerate germinable Clostridium endospores within an hour. Micro EVA is based on energy transfer from DPA to terbium ions doped in a solid matrix upon UV excitation. The distinctive emission and millisecond lifetime enables time-resolved imaging to achieve single endospore sensitivity. Comparing to traditional CFU cultivation, EVA probes the early stage of germination, resulting in a much faster detection rate (within 60 minutes) than CFU measurement (more than 3 days incubation). Micro EVA has also been successfully applied to quantify Clostridium spores in an extreme cold biosphere, Greenland ice core, and a hyper-arid biosphere, Atacama Desert, two Mars analogs on earth.
\r\n\r\nThe development of EVA provides a faster way to assess viability of Clostridium spores, which has significant importance in various industries. It also enables the determination of the limit and longevity of life, and provides insight on the search of extinct or extant life on Mars and other celestial bodies.
\r\n\r\n" }, { "name": "Young, Kakani Katija", "degree": "PhD", "year": "2010", "title": "Effect of In Situ Animal-Fluid Interactions on Transport and Mixing", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252010-172302796", "creators": [ { "name": { "family": "Young", "given": "Kakani Katija" }, "id": "Young-Kakani-Katija", "display_name": "Young, Kakani Katija" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "chair", "display_name": "Schneider, Tapio" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "bioeng" ], "doi": "10.7907/QJAM-9228", "abstract": "Traditional studies of animal-fluid interactions have led to the understanding of factors that affect the distribution, ecology and energetics of swimming organisms. These interactions are commonly investigated by using quantitative flow measurement techniques, which include digital particle image velocimetry. Due to limitations in quantitative flow measurements in the natural environment, animal measurements are conducted in laboratories. Laboratory measurement techniques have been shown to have an altering impact on animal behavior and resulting flow fields. Hence, it is reasonable to question conclusions made about the impact of background flows in the natural environment from measurements conducted in the laboratory. Therefore, an apparatus that will enable the quantitative measurement of flows surrounding a swimming animal in the field is needed to accurately address the effect of background flows on animal swimming and fluid transport.
\r\n\r\nWe describe the development of a self-contained underwater velocimetry apparatus that achieves the goal of real-time, quantitative field measurements of aquatic animal-fluid interactions. Using this apparatus, we obtain measurements of flow fields surrounding animals in the field and analyze the effect of background flows on swimming animals. Using a dynamical systems technique called Lagrangian coherent structures to quantitatively compare laboratory and field-generated flows, we find that background flow structures alter fluid transport by swimming jellyfish. From these studies, we define a biologically-relevant metric for animal feeding that is based entirely on the volume of fluid that interacts with the swimming animal. The ability to quantify background flows and their influence on animal-fluid interactions will allow us to broaden our concept of animal-fluid interactions to include the effects swimming animals have on their surrounding environment. This represents a paradigm shift in the analysis of animal-fluid interactions.
\r\n\r\nRecent studies have provided heated debate about whether biologically-generated (or biogenic) mixing can have an impact in the ocean. Arguments for biogenic mixing lacked an efficient mechanism for fluid transport in viscous and stratified flow environments. We present an effective mechanism for biogenic mixing called drift, which is active during swimming, and results in permanent displacement of fluid in the direction of the animal's motion (in unstratified flow). We show that unlike mechanisms that rely on turbulent mixing generated by wake structures, drift is enhanced as viscous effects are increased. While drift has been observed in jellyfish and copepods, to understand its relevance in the global ocean, the effects of stratification need to be considered. By conducting simulations of moving bodies in stratified flow, we show that at buoyancy frequencies on the order of the mean ocean, fluid transport due to drift remains a powerful mechanism through which swimming animals may provide a significant contribution to mixing in the oceans.
" }, { "name": "Zadeh, Joseph N.", "degree": "PhD", "year": "2010", "title": "Algorithms for Nucleic Acid Sequence Design", "advisor": "Pierce, Niles A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05112010-205335518", "creators": [ { "name": { "family": "Zadeh", "given": "Joseph N." }, "id": "Zadeh-Joseph-N", "display_name": "Zadeh, Joseph N." } ], "advisors": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "advisor", "display_name": "Pierce, Niles A." } ], "committee": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "chair", "display_name": "Winfree, Erik" }, { "name": { "family": "Rothemund", "given": "Paul W. K." }, "id": "Rothemund-P-W-K", "orcid": "0000-0002-1653-3202", "role": "member", "display_name": "Rothemund, Paul W. K." }, { "name": { "family": "Mayo", "given": "Stephen L." }, "id": "Mayo-S-L", "orcid": "0000-0002-9785-5018", "role": "member", "display_name": "Mayo, Stephen L." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." } ], "option_major": [ "bioeng" ], "doi": "10.7907/20DG-NF39", "abstract": "Motivated by a growing field of research focused on programming function into biomolecules, we seek to decrease the cost of high-quality rational nucleic acid sequence design while increasing its versatility and availability. We begin by describing an algorithm for designing the sequence of one or more interacting nucleic acid strands intended to adopt a target secondary structure at equilibrium. Using ensemble defect optimization, we seek to minimize the average number of incorrectly paired nucleotides at equilibrium, calculated over the entire ensemble of unpseudoknotted secondary structures. Empirically, the algorithm exhibits asymptotic optimality and costs 4/3 the time of a single objective function evaluation for large structures. We then extend this algorithm to design multi-state systems with an arbitrary number of linked targets and demonstrate its efficacy on systems invented by molecular engineers. To improve the ease of use and availability of nucleic acid analysis and design tools, we present NUPACK, a web application already in wide use that allows the international research community to share a high-performance compute cluster for the analysis and design of systems of interacting nucleic acids. " }, { "name": "Zhang, David Yu", "degree": "PhD", "year": "2010", "title": "Dynamic DNA Strand Displacement Circuits", "advisor": "Winfree, Erik", "url": "https://resolver.caltech.edu/CaltechTHESIS:05262010-173410602", "creators": [ { "name": { "family": "Zhang", "given": "David Yu" }, "id": "Zhang-David-Yu", "display_name": "Zhang, David Yu" } ], "advisors": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "advisor", "display_name": "Winfree, Erik" } ], "committee": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "chair", "display_name": "Pierce, Niles A." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" } ], "option_major": [ "cns" ], "doi": "10.7907/Q4NR-CH87", "abstract": "Nucleic acids, the \"NA\" in DNA and RNA, have long been known to be vitally important molecules within biological cells and organisms. However, they are interesting for more than just their known roles in biology: their predictable Watson-Crick base pairing properties allow nucleic acids to be powerful nanoscale engineering tools. Additionally, nucleic acid-based devices are particularly attractive as biotechnological tools, because nucleic acids naturally exist within all life, and thus nucleic acid devices more easily function in cellular environments. It is for these reasons that nucleic acids have emerged as a frequent star in recent synthetic biology, biotechnology, and nanotechnology research papers.
\r\n\r\nThis thesis is a collection of 6 experimental papers, 3 theoretical papers, and 1 review paper that demonstrate and characterize novel nucleic acid-based devices such as catalysts, logic gates, and allosteric switches. Particular effort was placed in ensuring that all the designs are generalizable in sequence and that all the devices are modular in nature; this allows many different components to be integrated into higher-complexity devices.
\r\n\r\nThe works presented in this thesis were designed using only non-covalent changes to nucleic acid complexes and structures via Watson-Crick base pairing--i.e. hybridization, branch migration, and dissociation. These three primitives are sufficient to construct an endless variety of circuits and devices, much like how resistors, capacitors, and inductors allow complex electrical circuits. One advantage of devices, reactions, and circuits engineered using only Watson-Crick interactions is their robustness to their environmental conditions. While enzymatic reactions require specific temperatures, salt conditions, and co-factors, nucleic acid hybridization works reliably in a variety of different solutions.
\r\n\r\nThese works are not meant to be final, optimized designs for devices, but rather demonstrations of the wide range of possibilities afforded by nucleic acid engineering and of problems that can be practically solved with dynamic nucleic acid devices in the near future.
" }, { "name": "Zhang, Xinning", "degree": "PhD", "year": "2010", "title": "I. Formate Dehydrogenase Gene Diversity in Lignocellulose-Feeding Insect Gut Microbial Communities. II. Metabolic Impacts on the Hydrogen Isotope Content of Bacterial Lipids ", "advisor": "Leadbetter, Jared R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05072010-142709280", "creators": [ { "name": { "family": "Zhang", "given": "Xinning" }, "id": "Zhang-Xinning", "orcid": "0000-0003-2763-1526", "display_name": "Zhang, Xinning" } ], "advisors": [ { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "role": "advisor", "display_name": "Leadbetter, Jared R." } ], "committee": [ { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "role": "chair", "display_name": "Sessions, Alex L." }, { "name": { "family": "Orphan", "given": "Victoria J." }, "id": "Orphan-V-J", "role": "member", "display_name": "Orphan, Victoria J." }, { "name": { "family": "Mazmanian", "given": "Sarkis K." }, "id": "Mazmanian-S-K", "role": "member", "display_name": "Mazmanian, Sarkis K." }, { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "role": "member", "display_name": "Leadbetter, Jared R." } ], "option_major": [ "envreng" ], "doi": "10.7907/ETXQ-D671", "abstract": "I.) Symbiotic CO\u2082-reducing acetogens are important bacterial members of lignocellulose-feeding termite and roach gut communities. Acetogens are the major consumers of H\u2082 derived from lignocellulose fermentation and can contribute up to 1/3 of the acetate that serves as fuel for the insect host. Many acetogens in wood-feeding termites belong to a diverse group of relatively unstudied, uncultured spirochetes within the genus Treponema. Here, I use the gene sequence for hydrogenase-linked formate dehydrogenase, an enzyme utilized in sugar fermentation and the acetogenic metabolism of the spirochete isolate Treponema primitia, to investigate the diversity, evolution, and activity of uncultured acetogenic spirochetes in lignocellulose-feeding insect guts. The results suggest that (a) the trace element selenium has shaped the gene content of acetogenic spirochetes in gut communities over evolutionary time scales, (b) acetogenic spirochete populations have undergone extinctions and radiations associated with an evolutionary bottleneck, convergent evolutions, and possibly even invasion during termite evolution, and (c) termite gut acetogenesis is largely mediated by only a few spirochete species, which represent a small portion of total acetogenic spirochete diversity.
\r\n\r\nII.) The hydrogen-stable isotope compositions (D/H) of lipids in the environment vary greatly. All variations have been assumed to result from changes in the D/H of water, a source of lipid hydrogen. However, several studies suggest that water D/H may not be the only influential factor. In this study, I report that lipid D/H values can vary by 500\u2030 in bacterial cultures despite constant water D/H. This indicates variations in lipid/water fractionation need to be considered when interpreting environmental data. More significantly, I demonstrate that lipid D/H values are systematically related to the utilization of different central metabolic pathways in bacteria. The results suggest that different cellular mechanisms for NADPH synthesis result in lipids with characteristic D/H. Implications for the use of lipid D/H as an isotopic marker of energy metabolism are discussed.
" }, { "name": "Adleman, James Richard", "degree": "PhD", "year": "2009", "title": "Plasmonic Nanoparticles for Optofluidic Applications", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-05102009-103332", "creators": [ { "name": { "family": "Adleman", "given": "James Richard" }, "id": "Adleman-James-Richard", "display_name": "Adleman, James Richard" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Erickson", "given": "David" }, "id": "Erickson-D", "role": "member", "display_name": "Erickson, David" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." } ], "option_major": [ "eleceng" ], "doi": "10.7907/QB6E-2Q64", "abstract": "This thesis discusses the application of colloidal particles to optofluidic systems. Colloidal particles can be added as a \"dopant\" to the liquids in these devices to provide functionality that cannot be obtained with homogenous fluids. We examine electrooptic effects in liquid suspensions asymmetric metallic nanoparticles. The theoretical optical properties of gold nanorods and noble metal nanohalfshells are computed and compared with those of actual colloidal dispersions. We discuss the design and fabrication of electro-optic waveguides utilizing these suspensions as the active material. We also study the dynamics of photothermal holograms recorded by nanosecond laser pulses in suspensions of silver nanospheres. Unexpected transients in the grating diffraction efficiency correspond to the nanoscale inhomgeneity of the colloid. Longer timescale decay can be used to measure the thermal conductivity of the liquid as predicted by the established theory of heat conduction. This technique is extended to perform spatial imaging of the thermal diffusivity of immiscible binary liquids. Gold nanosphere coated substrates for microfluidic devices are employed to enable optical actuation of fluids. Nanoparticle absorption of continuous wave laser light was used to trap air bubbles inside partially filled microfluidic channels. Light focused on the array near one side of the trapped bubble will drive a mass flow across the bubble. This evaporative bubble assisted mass transport mechanism can be operated as a pump powered by a stationary laser beam. In addition, the process efficiently separates volatile and non-volatile materials and can concentrate and purify specimens in solution.
\r\n\r\nFinally, several schemes for storing and extracting data from subwavelength volumes using spectral multiplexing of semiconductor quantum dots are explored. We demonstrate microfluidic composition and delivery of cocktails of several colors of quantum dots to act as information packets for optical storage. In addition we analyze imaging at the subwavelength level using a patterned surface of quantum dots. The theoretical performance of such a surface is compared to imaging through nanoapertures as is currently implemented in optofluidic microscopy.
\r\n" }, { "name": "Arii, Motofumi", "degree": "PhD", "year": "2009", "title": "Retrieval of Soil Moisture under Vegetation Using Polarimetric Radar", "advisor": "Rutledge, David B.; van Zyl, Jakob J.; Kim, Yunjin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05082009-143935", "creators": [ { "name": { "family": "Arii", "given": "Motofumi" }, "id": "Arii-Motofumi", "orcid": "0000-0002-3242-7987", "display_name": "Arii, Motofumi" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." }, { "name": { "family": "van Zyl", "given": "Jakob J." }, "id": "van-Zyl-J-J", "role": "co-advisor", "display_name": "van Zyl, Jakob J." }, { "name": { "family": "Kim", "given": "Yunjin" }, "id": "Kim-Yunjin", "role": "co-advisor", "display_name": "Kim, Yunjin" } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "van Zyl", "given": "Jakob J." }, "id": "van-Zyl-J-J", "role": "member", "display_name": "van Zyl, Jakob J." }, { "name": { "family": "Kim", "given": "Yunjin" }, "id": "Kim-Yunjin", "role": "member", "display_name": "Kim, Yunjin" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SKJ9-KT40", "abstract": "The unique contributions of this thesis are: 1) a polarimetric classification algorithm that is a significant improvement over an existing algorithm and 2) introduction of a cube technique to retrieve soil moisture under vegetation.
\r\n\r\nThe most widely used classification algorithm is the three-component scattering technique. Even though it includes three dominant scattering mechanisms, the decomposition approach can cause a non-physical solution due to incorrect assumptions. The Adaptive Non Negative Eigenvalue Decomposition approach in this thesis produces correct solution. It appears that this new approach provides better classification results. It is a significant improvement over the existing technique.
\r\n\r\nA cube technique is introduced to retrieve soil moisture under vegetation. Using this approach, we have evaluated the retrieval accuracy of several polarimetric combinations. The effects of the incorrect vegetation model and data noise were investigated. In addition, the proposed cube algorithm can be improved by applying the classification result.
\r\n" }, { "name": "Axelrod, Blake Waters", "degree": "PhD", "year": "2009", "title": "Single Cell Pico Force Microscopy: A Novel Tool for High Resolution Measurement of Cell Forces", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechETD:etd-04082009-102110", "creators": [ { "name": { "family": "Axelrod", "given": "Blake Waters" }, "id": "Axelrod-Blake-Waters", "display_name": "Axelrod, Blake Waters" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ESGS-Z942", "abstract": "Nearly all eukaryotic cells exert forces on their surroundings to generate and maintain tension within their cytoskeleton which is critical for normal cell function. In addition, cells exert forces on their surroundings to orient themselves within an organism, thus gaining information that influences cell fate and behavior, a process called mechanotransduction. In order to study mechanotransduction, a tool is needed that can observe the molecular level sensing events that trigger a decision by a cell as well as the ultimate response that occurs on the whole cell level. There are a number of optical techniques that are used to measure forces from adherent cells at the single cell level; some are good for measuring whole cell forces and some for measuring single molecule level forces, but none have the dynamic range necessary to span both regimes, which is critical for understanding mechanotransduction. To address this need, I have developed a Nano-ElectroMechanical Systems (NEMS) based tool, Single-Cell-Pico-Force-Microscopy (SCPFM), that measures forces exerted by adherent cells with macro-molecular level force sensitivity and sufficient dynamic range to monitor whole cell responses to stimuli with macro-molecular resolution. I have used SCPFM to measure force versus time data from a NIH-3T3 fibroblast as it is perturbed with Cytochalasin D (CD) and allowed to recover in growth media. Within the data there are three excellent examples of previously inaccessible molecular-mechanical processes that illustrate the immense potential of SCPFM to significantly enhance resolution of cell biology at the single cell level: 1) an initial contraction upon exposure to CD followed by the expected force drop, 2) small force oscillations, roughly 400pN peak-to-peak, with frequency that is monotonically dependent on the force being exerted by the lamellipodia, and 3) large, stable, quantized force steps of order 1nN are manifested when a cell\u2019s cytoskeleton is perturbed with CD and allowed to recover in growth media. I propose two complimentary experimental efforts to undertake: a systematic effort to build a library of molecular-mechanical force signatures of various common cytoskeleton reactions and an effort to stimulate and observe compliance sensing and response in adherent cells.\r\n" }, { "name": "Bardin, Joseph Cheney", "degree": "PhD", "year": "2009", "title": "Silicon-Germanium Heterojunction Bipolar Transistors for Extremely Low-Noise Applications", "advisor": "Weinreb, Sander", "url": "https://resolver.caltech.edu/CaltechETD:etd-06092009-113849", "creators": [ { "name": { "family": "Bardin", "given": "Joseph Cheney" }, "id": "Bardin-Joseph-Cheney", "orcid": "0000-0002-6523-6730", "display_name": "Bardin, Joseph Cheney" } ], "advisors": [ { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "advisor", "display_name": "Weinreb, Sander" } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MCPE-4M30", "abstract": "Historically speaking, the world of extremely low-noise solid-state amplification has been dominated by exotic technologies such as InP and GaAs HEMTs. By cryogenically cooling these devices, it is possible to realize microwave amplifiers with noise temperatures as low as 5K over decades of bandwidth. Although HEMTs can provide very low noise amplification when cooled to cryogenic temperatures, their radiometer performance is limited by intrinsic transconductance fluctuations. It is believed that bipolar devices do not suffer from this problem. As industry has invested more and more money into silicon based technologies, silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) have continued to improve and are now at the point where they are beginning to become competitive with InP HEMTs for microwave cryogenic low-noise amplifiers. Although extremely high frequency device operation has been observed at cryogenic temperatures, little work has been done on modeling the noise of cooled SiGe HBTs.
\r\n\r\nIn this report, a thorough investigation into the theoretical and practical aspects of using silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) for extremely low-noise applications is presented. The dissertation is broken up into three sections:
\r\n\r\n1) Background information: The fundamentals of SiGe HBTs are presented along with a discussion of how the properties of semiconductors change at cryogenic temperatures, as well the impact that these changes have on the performance of the devices.
\r\n\r\n2) Modeling: A comprehensive study of seven state-of-the-art HBTs at temperatures ranging from 18 K to 300 K is presented. The devices are compared in terms of dc, small-signal, and noise performance, and small-signal noise models are extracted. The section concludes with a brief summary of the important conclusions regarding the performance of SiGe devices at cryogenic temperatures.
\r\n\r\n3) Applications: The models developed previously are applied to the design of several state-of-the-art LNAs in both MMIC and discrete form. Noise performance better than 2 K is achieved in the low-GHz range, which is comparable to the best InP results. The section concludes with a discussion of some high-impedance differential amplifiers which have recently been fabricated.
\r\n" }, { "name": "Bhattacharyya, Rajan", "degree": "PhD", "year": "2009", "title": "Egocentric Distance Encoding in the Posterior Parietal Cortex", "advisor": "Andersen, Richard A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062008-112215", "creators": [ { "name": { "family": "Bhattacharyya", "given": "Rajan" }, "id": "Bhattacharyya-Rajan", "display_name": "Bhattacharyya, Rajan" } ], "advisors": [ { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "advisor", "display_name": "Andersen, Richard A." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "co-chair", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." } ], "option_major": [ "cns" ], "doi": "10.7907/FBNQ-0P48", "abstract": "Previous studies have shown that the parietal reach region (PRR) encodes the two dimensional location of frontoparallel reach targets in an eye centered reference frame in early movement plans (Batista 1999; Snyder et al. 2000). Performing a visually guided reach initially requires the ability to perceive the depth of a target in three dimensional space. Beyond that initial perception, however, reach plans may represent the egocentric distance of the target in different ways. To investigate how a reach target is represented in three dimensions, recordings were made of the spiking activity of PRR neurons from two rhesus macaques trained to fixate and perform memory reaches to targets at different depths. Reach and fixation targets were configured to explore whether neural activity directly reflects egocentric distance as the amplitude of the required motor command, which is the absolute depth of the target, or rather the relative depth of the target with reference to fixation depth.
\r\n\r\nThis thesis shows that planning activity in PRR represents the depth of the reach target as a function of disparity and fixation depth, the spatial parameters important for encoding the egocentric distance of a reach goal in an eye centered reference frame. Most PRR neurons were found to be sensitive to the disparity of a reach target (82%), and vergence angle (74%) which determines fixation depth. Most PRR neurons carry both disparity and vergence angle signals, and comparisons of several modulation indices and the information carried in firing rates for each variable show a single homogenous PRR population encodes egocentric distance. The strength of modulation by disparity was maintained across vergence angle, where vergence angle gain modulates disparity tuning while preserving the location of peak tuning features in PRR neurons, which allows the absolute depth of the reach target to be decoded from the population activity. Neural activity in PRR shows a wide range of sensitivity to both target disparity and fixation depth that has never been previously tested in a reach task. The results demonstrate a specific role for PRR neurons in supporting eye-hand coordination when decoupling the effector from the point of gaze.
\r\n" }, { "name": "Braman, Julia Marie Badger", "degree": "PhD", "year": "2009", "title": "Safety Verification and Failure Analysis of Goal-Based Hybrid Control Systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292009-111937", "creators": [ { "name": { "family": "Braman", "given": "Julia Marie Badger" }, "id": "Braman-Julia-Marie-Badger", "display_name": "Braman, Julia Marie Badger" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "mecheng" ], "doi": "10.7907/3H42-BF56", "abstract": "The success of complex autonomous robotic systems depends on the quality and correctness of their fault tolerant control systems. A goal-based approach to fault tolerant control, which is modeled after a software architecture developed at the Jet Propulsion Laboratory, uses networks of goals to control autonomous systems. The complex conditional branching of the control program makes safety verification necessary. Three novel verification methods are presented. In the first, goal networks are converted to linear hybrid automata via a bisimulation. The converted automata can then be verified against an unsafe set of conditions using an existing symbolic model checker such as PHAVer. Due to the complexity issues that result from this method, a design for verification software tool, the SBT Checker, was developed to create goal networks that have state-based transitions. Goal networks that have state-based transitions can be converted to hybrid automata whose locations' invariants contain all information necessary to determine the transitions between the locations. An original verification software called InVeriant can then be used to find unsafe locations of linear hybrid systems based on the locations\u2019 invariants and rate conditions, which are compared to the unsafe set of conditions. The reachability of the unsafe locations depends only on the reachability of the states of the state variables constrained in the locations' invariants from those state variables' initial conditions. In cases where this reachability condition is not trivially true, the software efficiently searches for a path to the unsafe locations using properties of the system. The third verification method is the calculation of the failure probability of the verified hybrid control system due to state estimation uncertainty, which is extremely important in autonomous systems that rely heavily on the state estimates made from sensor measurements. Finally, two significant example goal network control programs, one for a complex rover and another for a proposed aerobot mission to Titan, a moon of Saturn, are verified using the three techniques presented." }, { "name": "Bray, Signe Lauren", "degree": "PhD", "year": "2009", "title": "Neural Mechanisms Underlying the Influence of Associative Learning on Valuation and Decision-Making in Humans", "advisor": "O'Doherty, John P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07052008-163103", "creators": [ { "name": { "family": "Bray", "given": "Signe Lauren" }, "id": "Bray-Signe-Lauren", "display_name": "Bray, Signe Lauren" } ], "advisors": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "advisor", "display_name": "O'Doherty, John P." } ], "committee": [ { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "chair", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Rangel", "given": "Antonio" }, "id": "Rangel-A", "role": "member", "display_name": "Rangel, Antonio" }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "member", "display_name": "O'Doherty, John P." }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/C5V1-RE97", "abstract": "Reward is a powerful modulator of behavior. Animals and humans are endowed with the ability to learn to associate events and actions with reinforcing stimuli, and flexibly adapt their behavior. The experiments described in this thesis use functional magnetic resonance imaging (fMRI) to study the neural mechanisms of reward learning in humans, the neural substrates by which reward associations influence behavior, and the neural plasticity that can be induced by provision of reward.
\r\n\r\nAttractive faces have been shown to be a form of visual reward, but their influence on behavior has yet to be characterized. We show that reward prediction errors in the nucleus accumbens are engaged when subjects learn associations between neutral cues and attractive faces, as has been shown with other reinforcers such as juice and money. This learning increases the subjective value of cues associated with attractive faces.
\r\n\r\nAnimal studies have shown that Pavlovian cues can influence response vigor and decision-making. We present the first investigation into the neural mechanisms by which Pavlovian cues influence human decision-making. We find that activity in the ventral striatum differentiates between decisions to act in a manner compatible or incompatible with a concurrently presented Pavlovian cue.
\r\n\r\nIn the next section we apply associative learning techniques to directly instrumentally condition neural activity, using reward feedback derived from fMRI images processed and analyzed in real time. This technique presents an alternative to standard bio/neurofeedback approaches and may prove useful in many clinical and research applications. We demonstrate that this method can be used to probe the causal influence of regional brain activity; specifically we test the impact of medial orbitofrontal cortex (mOFC) activity on affective judgments. Subjects learn to elevate mOFC activity on cue and elevated mOFC activity increases the propensity to make a positive subjective valuation judgment.
\r\n\r\nTaken together these studies advance our understanding of the functional contributions of ventral striatum and orbitofrontal cortex in influencing decision-making and valuation, and illustrate the utility of applying associative learning techniques in combination with real-time fMRI in order to evaluate the causal contribution of specific brain regions toward particular cognitive functions.
\r\n" }, { "name": "Brenner, Sarah Katherine", "degree": "PhD", "year": "2009", "title": "Engineering Synthetic Biofilm-Forming Microbial Consortia", "advisor": "Arnold, Frances Hamilton", "url": "https://resolver.caltech.edu/CaltechETD:etd-04212009-104756", "creators": [ { "name": { "family": "Brenner", "given": "Sarah Katherine" }, "id": "Brenner-Sarah-Katherine", "display_name": "Brenner, Sarah Katherine" } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" } ], "committee": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "chair", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "member", "display_name": "Newman, Dianne K." }, { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "member", "display_name": "Leadbetter, Jared R." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." } ], "option_major": [ "bioeng" ], "doi": "10.7907/PMZ3-4Z96", "abstract": "Most bacteria on earth live in heterogeneous surface-bound congregations called biofilms, and vast reaches of the earth are coated in these living films. In many cases, the microorganisms comprising this ubiquitous coating form complex, interactive communities called consortia. Microbial consortia are implicated in processes of great importance to humans, from environmental remediation and wastewater treatment to assistance in food digestion. Synthetic biologists are honing their ability to program the behavior of individual microbial populations, forcing the microbes to focus on specific applications, such as the production of drugs and fuels. Given that microbial consortia can perform even more complicated tasks and endure more changeable environments than monocultures can, they represent an important new frontier for synthetic biology. This thesis describes two engineered microbial consortia that live and perform their designed functions in biofilms. The biofilm consortium elucidated in Chapter 2 serves as a proof of concept for the development of the symbiotic biofilm consortium of Chapter 3. To provide a context for these two consortia, the first chapter highlights the salient features of microbial consortia that are of interest to synthetic biologists and reviews recent efforts to engineer synthetic microbial consortia, while the final chapter suggests challenges associated with and future directions for engineering microbial consortia.\r\n" }, { "name": "Capponi, Agostino", "degree": "PhD", "year": "2009", "title": "Credit Risk and Nonlinear Filtering: Computational Aspects and Empirical Evidence", "advisor": "Cvitani\u0107, Jak\u0161a", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272009-141742", "creators": [ { "name": { "family": "Capponi", "given": "Agostino" }, "id": "Capponi-Agostino", "orcid": "0000-0001-9735-7935", "display_name": "Capponi, Agostino" } ], "advisors": [ { "name": { "family": "Cvitani\u0107", "given": "Jak\u0161a" }, "id": "Cvitani\u0107-J", "orcid": "0000-0001-6651-3552", "role": "advisor", "display_name": "Cvitani\u0107, Jak\u0161a" } ], "committee": [ { "name": { "family": "Cvitani\u0107", "given": "Jak\u0161a" }, "id": "Cvitani\u0107-J", "orcid": "0000-0001-6651-3552", "role": "chair", "display_name": "Cvitani\u0107, Jak\u0161a" }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/7XV3-9Q45", "abstract": "This thesis proposes a novel credit risk model which deals with incomplete information on the firm's asset value. Such incompleteness is due to reporting bias deliberately introduced by insider managers and executives of the firm and unobserved by outsiders.
\r\n\r\nThe pricing of corporate securities and the evaluation of default measures in our credit risk framework requires the solution of a computationally unfeasible nonlinear filtering problem. The model introduces computational issues arising from the fact that the optimal probability density on the firm's asset value is the solution of a nonlinear filtering problem, which is computationally unfeasible. We propose a polynomial time-sequential Bayesian approximation scheme which employs convex optimization methods to iteratively approximate the optimal conditional density of the state on the basis of received market observations. We also provide an upper bound on the total variation distance between the actual filter density and our approximate estimator. We use the filter estimator to derive analytical expressions for the price of corporate securities (bond and equity) as well as for default measures (default probabilities, recovery rates, and credit spreads) under our credit risk framework. We propose a novel statistical calibration method to recover the parameters of our credit risk model from market price of equity and balance sheet indicators. We apply the method to the Parmalat case, a real case of misreporting and show that the model is able to successfully isolate the misreporting component. We also provide empirical evidence that the term structure of credit default swaps quotes exhibits special patterns in cases of misreporting by using three well known cases of accounting irregularities in US history: Tyco, Enron, and WorldCom.
\r\n\r\nWe conclude the thesis with a study of bilateral credit risk, which accommodates the case in which both parties of the financial contract may default on their payments. We introduce the general arbitrage-free valuation framework for counterparty risk adjustments in presence of bilateral default risk. We illustrate the symmetry in the valuation and show that the adjustment involves a long position in a put option plus a short position in a call option, both with zero strike and written on the residual net value of the contract at the relevant default times. We allow for correlation between the default times of each party of the contract and the underlying portfolio risk factors. We introduce stochastic intensity models and a trivariate copula function on the default times exponential variables to model default dependence. We provide evidence that both default correlation and credit spread volatilities have a relevant and structured impact on the adjustment. We also study a case involving British Airways, Lehman Brothers, and Royal Dutch Shell, illustrating the bilateral adjustments in concrete crisis situations.
\r\n" }, { "name": "Card, Gwyneth Megan", "degree": "PhD", "year": "2009", "title": "Neural Control and Biomechanics of Flight Initiation in Drosophila melanogaster", "advisor": "Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282009-215548", "creators": [ { "name": { "family": "Card", "given": "Gwyneth Megan" }, "id": "Card-Gwyneth-Megan", "orcid": "0000-0002-7679-3639", "display_name": "Card, Gwyneth Megan" } ], "advisors": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "bioeng" ], "doi": "10.7907/PR7S-Y618", "abstract": "In response to abrupt visual stimulation, the fruit fly, Drosophila melanogaster, quickly initiates flight. This rapid takeoff is believed to be a reflex coordinated by a pair of large descending interneurons (the \"giant fibers\"). However, it has been difficult to evoke escapes in wild-type flies, and thus flight initiation behavior in the unrestrained wild-type fly is poorly described. I have taken advantage of recent advances in high-speed videography to capture video sequences of Drosophila flight initiation at the temporal resolution of 6,000 frames per second. A three-dimensional kinematic analysis of takeoff sequences indicates that wing use during the jumping phase of flight initiation is essential for stabilizing flight. During voluntary takeoffs, flies raise their wings prior to leaving the ground, resulting in a stable, controlled takeoff. In contrast, during visually-elicited escapes flies pull their wings down close to their body during the takeoff jump, resulting in tumbling flights that are faster but less steady. The takeoff kinematics suggest that the power delivered by the legs is substantially greater during these escapes than during voluntary takeoffs. Thus, I show that the two types of Drosophila flight initiation result in different flight performances once the fly is airborne, and that these performances are distinguished by a trade-off between speed and stability. I also determined that flies can use visual information to plan a jump directly away from a looming threat. This is surprising, given the simple architecture of the giant fiber pathway thought to mediate escape. I found that approximately 200 ms before takeoff, flies begin a series of postural adjustments that determine the direction of their escape. These movements position their center of mass so that leg extension will push them away from the looming stimulus. These preflight movements are not the result of a simple feed-forward motor program because their magnitude and direction depend on the flies' initial postural state. Furthermore, flies plan a takeoff direction even in instances when they choose not to jump. This sophisticated motor program is evidence for a form of rapid, visually mediated motor planning in a genetically accessible model organism.\r\n" }, { "name": "Cerf, Moran", "degree": "PhD", "year": "2009", "title": "Competition and Attention in the Human Brain Eye-Tracking and Single-Neuron Recordings in Healthy Controls and Individuals with Neurological and Psychiatric Disorders", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:09022010-004952870", "creators": [ { "name": { "family": "Cerf", "given": "Moran" }, "id": "Cerf-Moran", "orcid": "0000-0002-2012-3177", "display_name": "Cerf, Moran" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "chair", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Tsao", "given": "Doris Y." }, "id": "Tsao-D-Y", "orcid": "0000-0003-1083-1919", "role": "member", "display_name": "Tsao, Doris Y." }, { "name": { "family": "Fried", "given": "Itzhak" }, "id": "Fried-I", "role": "member", "display_name": "Fried, Itzhak" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" } ], "option_major": [ "cns" ], "doi": "10.7907/BFNE-C518", "abstract": "At any given moment, our brains are bombarded with enormous amounts of information from the environment. External stimuli from the senses travel through our eyes, nose, or skin, and internal reflections and imagery travel from within. All these stimuli are processed in parallel and compete with each other toward one ultimate goal: becoming the single percept which we are aware of at this unique present moment.
\r\n\r\nThis work studies the way by which this competition occurs in our brains. The mechanisms and the methods which allow the brain to overcome this load of information by selecting one of many thoughts to reach the upper level of our consciousness.
\r\n\r\nWe studied healthy controls in eye-tracking experiments where they viewed sets of images in different tasks. In the first task, subjects freely viewed images with semantic high-level cues such as faces and social scenes. Subjects showed a significant tendency to rapidly attend to the faces in their first fixation. In a second task, subjects viewed similar images in a search task where they were instructed to find objects or faces in the scene. Subjects showed the same tendency to look at faces independent of the task. In a following study, subjects were looking at images with text and phones as control and were shown to look at text rapidly and early, but not as much as faces. Phones, as control, showed no increased rapid attentional attraction. In order to test the magnitude of the effect, we had subjects participate in a third experiment where they were instructed to refrain from looking at these objects, but were not able to do so as easily for faces as they were for text and phones. This suggests an innate mechanism that draws our attention to faces and social scenes early \u2014 even in situations where other stimuli compete for our attention. Faces win the competition for our attention regardless of the task. We used this striking result to modify an existing computer model for bottom-up attentional allocation to better predict human\u2019s fixation in images.
\r\n\r\nThe results were tested additionally in two groups of individuals with disorders that manifest themselves primarily in decreased social attention: autism and agenesis of the corpus callosum (AgCC; subjects who are missing the bridge between the left and right hemispheres in the brain). Individuals with these disorders were tested in the same paradigms and indeed showed decreased attention allocation to faces or social cues in the images. AgCC subjects showed an even lower level of interest in social cues. While the results suggested a competition for attention that has social cues win over alternative cues in healthy controls, the psychiatric disorder groups show no such effect. In order to test the competition in the brain even further we tested individuals with epilepsy undergoing brain surgery, who were implanted with electrodes to record from single neurons in their medial temporal lobe (MTL). These patients participated in a task where they were projecting their thoughts of one of various concepts onto a computer screen, in real-time, using a decoder that interpreted their thoughts and imagery. Patients performed a task in which they were instructed to think of one of four concepts, and by accurately doing so were fading into an image representation of that concept on the computer screen. Multiple images that were shown on the screen simultaneously while the patient tried to suppress one and maintain an imagery of the other allowed us to directly create a situation where competition between various external stimuli, and in turn multiple brain regions, is tested. Subjects were able to reach high level of control of their single MTL neurons after very little training. In this direct measure of the competition between brain regions and neurons in the brain, we show that attention can be modulated to direct the flow of information to one or the other area, even though the external stimuli from the environment is identical. We used the results from the fading experiment to construct a model of the mechanism by which competition between external stimuli and internal imagery modulates attention in the brain.
\r\n\r\nSubjects who were able to reach an even higher threshold of control of a single neuron played a computer game in which they were controlling an airplane on the screen using their thoughts alone. These subjects reached a high level of control suggesting an ability to use single neurons in the MTL for brain-machine interfaces with very high accuracy.
\r\n\r\nFinally, we report various case studies from experiments involving direct measures of attentional allocation by individuals with face blindness (Prosopagnosia) who performed poorly in tasks involving competition between facial and social attention attractors; a subject with no amygdalae who was unable to direct her attention to fearful entities including images of herself posing while displaying fearful emotions; identical twins who showed an extremely high correlation in their attentional allocation metrics \u2014 both eye-tracking and individual rating of interest in images; and a similar high correlation between a mother and her autistic son.
\r\n\r\nAltogether, these results shed light on the processes and the mechanisms undergoing in our brain, in the milliseconds between the moment information starts flowing in our brain from the environment, through the spotlight of attention that selects which of various inputs will be selected to reach our consciousness.
" }, { "name": "Chen, Po-Jui", "degree": "PhD", "year": "2009", "title": "Implantable Wireless Intraocular Pressure Sensors", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-09022008-113511", "creators": [ { "name": { "family": "Chen", "given": "Po-Jui" }, "id": "Chen-Po-Jui", "display_name": "Chen, Po-Jui" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Meng", "given": "Ellis" }, "id": "Meng E-F-C", "role": "member", "display_name": "Meng, Ellis" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "eleceng" ], "doi": "10.7907/46T7-0P24", "abstract": "The work in this thesis aims to develop a suite of biomedical microdevice implants, with an intense focus on pressure sensors, for glaucoma study and management featuring the enabling micro-electro-mechanical-system (MEMS) technologies and the use of parylene (poly-para-xylene) as a biocompatible MEMS material. The problems of the debilitating eye disease glaucoma threaten tens of millions of people worldwide with loss of vision, and are not completely resolved using the current non-optimal clinical procedures. Given the relation of neuropathy and the physiological parameter of intraocular pressure (IOP) in glaucoma from clinical findings, such parylene-based MEMS implants are investigated to realize physical IOP monitoring and regulation, and further to accomplish continuous, direct, accurate, reliable, and more effective glaucoma detection and treatment.
\r\n \r\nMiniaturized parylene-based passive pressure sensors are presented in this thesis for IOP monitoring. Complete design, fabrication, characterization, and analysis of such MEMS implants are described to demonstrate their feasibility, covering both engineering and surgical/biological aspects of the proposed applications. Their passive behaviors, based on the comprised micromechanical structures, facilitate unpowered device operations. In addition, such devices are microfabricated in suitable form factors so that minimally invasive suture-less implantation procedures are possible, minimizing time and complexity of the surgeries. Two types of micromachined wireless pressure sensors are developed utilizing optical and electrical sensing methodologies, respectively, to explore the possibility of the proposed implant approach. On-bench experimental results verify that wireless pressure sensing with 1 mmHg accuracy in the 0\u2013100 mmHg range can be achieved using both types of devices. Surgical studies, including ex vivo and in vivo animal tests, confirm the bioefficacy and biostability of the device implants in the intraocular environment. With the attempt of providing implementation concepts of the MEMS implant approaches for ultimate glaucoma study and management in practice, system-level designs and configurations involving such microdevice implants are briefly described as well. Micromachined passive-valved flow-control devices with designed surgical and engineering features are also developed (experimentally achieving 0\u2013100 mmHg and 0\u201310 uL/min pressure and flow rate regulation ranges) to investigate the feasibility and possibility of such implant approach for unpowered physical IOP regulation in glaucoma treatment.
\r\n" }, { "name": "Chen, Scott Chun-Yang", "degree": "PhD", "year": "2009", "title": "Signal Processing Algorithms for MIMO Radar", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06082009-131045", "creators": [ { "name": { "family": "Chen", "given": "Scott Chun-Yang" }, "id": "Chen-Scott-Chun-Yang", "display_name": "Chen, Scott Chun-Yang" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Tkacenko", "given": "Andre" }, "id": "Tkacenko-A", "role": "member", "display_name": "Tkacenko, Andre" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/TPT1-9V58", "abstract": "Radar is a system that uses electromagnetic waves to detect, locate and measure the speed of reflecting objects such as aircraft, ships, spacecraft, vehicles, people, weather formations, and terrain. It transmits the electromagnetic waves into space and receives the echo signal reflected from objects. By applying signal processing algorithms on the reflected waveform, the reflecting objects can be detected. Furthermore, the location and the speed of the objects can also be estimated. Radar was originally an acronym for \"RAdio Detection And Ranging\". Today radar has become a standard English noun. Early radar development was mostly driven by military and military is still the dominant user and developer of radar technology. Military applications include surveillance, navigation, and weapon guidance. However, radar now has a broader range of applications including meteorological detection of precipitation, measuring ocean surface waves, air traffic control, police detection of speeding traffic, sports radar speed guns, and preventing car or ship collisions.
\r\n\r\nRecently, the concept of MIMO radar has been proposed. The MIMO radar is a multiple antenna radar system which is capable of transmitting arbitrary waveform from each antenna element. In the traditional phased array radar, the transmitting antennas are limited to transmit scaled versions of the same waveform. However the MIMO radar allows the multiple antennas to transmit arbitrary waveforms. Like MIMO communications, MIMO radar offers a new paradigm for signal processing research. MIMO radar possesses significant potentials for fading mitigation, resolution enhancement, and interference and jamming suppression. Fully exploiting these potentials can result in significantly improved target detection, parameter estimation, target tracking and recognition performance. The MIMO radar technology has rapidly drawn considerable attention from many researchers. Several advantages of MIMO radar have been discovered by many different researchers such as increased diversity of the target information, excellent interference rejection capability, improved parameter identifiability, and enhanced flexibility for transmit beampattern design. The degrees of freedom introduced by MIMO radar improves the performance of the radar systems in many different aspects. However, it also generates some issues. It increases the number of dimensions of the received signals. Consequently, this increases the complexity of the receiver. Furthermore, the MIMO radar transmits an incoherent waveform on each of the transmitting antennas. This in general reduces the processing gain compared to the phased array radar. The multiple arbitrary waveforms also affects the range and Doppler resolution of the radar system.
\r\n\r\nThe main contribution of this thesis is to study the signal processing issues in MIMO radar and propose novel algorithms for improving the MIMO radar system. In the first part of this thesis, we focus on the MIMO radar receiver algorithms. We first study the robustness of the beamformer used in MIMO radar receiver. It is known that the adaptive beamformer is very sensitive to the DOA (direction-of-arrival) mismatch. In MIMO radar, the aperture of the virtual array can be much larger than the physical receiving array in the SIMO radar. This makes the performance of the beamformer more sensitive to the DOA errors in the MIMO radar case. In this thesis, we propose an adaptive beamformer that is robust against the DOA mismatch. This method imposes constraints such that the magnitude responses of two angles exceed unity. Then a diagonal loading method is used to force the magnitude responses at the arrival angles between these two angles to exceed unity. Therefore the proposed method can always force the gains at a desired interval of angles to exceed a constant level while suppressing the interferences and noise. A closed form solution to the proposed minimization problem is introduced, and the diagonal loading factor can be computed systematically by a proposed algorithm. Numerical examples show that this method has an excellent SINR (signal to noise-plus-interference ratio) performance and a complexity comparable to the standard adaptive beamformer. We also study the space-time adaptive processing (STAP) for MIMO radar systems. With a slight modification, STAP methods developed originally for the single-input multiple-output (SIMO) radar (phased array radar) can also be used in MIMO radar. However, in the MIMO radar, the rank of the jammer-and-clutter subspace becomes very large, especially the jammer subspace. It affects both the complexity and the convergence of the STAP algorithm. In this thesis, we explore the clutter space and its rank in the MIMO radar. By using the geometry of the problem rather than data, the clutter subspace can be represented using prolate spheroidal wave functions (PSWF). Using this representation, a new STAP algorithm is developed. It computes the clutter space using the PSWF and utilizes the block diagonal property of the jammer covariance matrix. Because of fully utilizing the geometry and the structure of the covariance matrix, the method has very good SINR performance and low computational complexity.
\r\n\r\nThe second half of the thesis focuses on the transmitted waveform design for MIMO radar systems. We first study the ambiguity function of the MIMO radar and the corresponding waveform design methods. In traditional (SIMO) radars, the ambiguity function of the transmitted pulse characterizes the compromise between range and Doppler resolutions. It is a major tool for studying and analyzing radar signals. The idea of ambiguity function has recently been extended to the case of MIMO radar. In this thesis, we derive several mathematical properties of the MIMO radar ambiguity function. These properties provide some insights into the MIMO radar waveform design. We also propose a new algorithm for designing the orthogonal frequency-hopping waveforms. This algorithm reduces the sidelobes in the corresponding MIMO radar ambiguity function and makes the energy of the ambiguity function spread evenly in the range and angular dimensions. Therefore the resolution of the MIMO radar system can be improved. In addition to designing the waveform for increasing the system resolution, we also consider the joint optimization of waveforms and receiving filters in the MIMO radar for the case of extended target in clutter. An extended target can be viewed as a collection of infinite number of point targets. The reflected waveform from a point target is just a delayed and scaled version of the transmitted waveform. However, the reflected waveform from an extended target is a convolved version of the transmitted waveform with a target spreading function. A novel iterative algorithm is proposed to optimize the waveforms and receiving filters such that the detection performance can be maximized. The corresponding iterative algorithms are also developed for the case where only the statistics or the uncertainty set of the target impulse response is available. These algorithms guarantee that the SINR performance improves in each iteration step. The numerical results show that the proposed iterative algorithms converge faster and also have significant better SINR performances than previously reported algorithms.
\r\n" }, { "name": "Chen, Wei-Ting", "degree": "PhD", "year": "2009", "title": "I. Global Simulations of Interactions between Aerosols and Future Climate and II. Sensitivity of Multiangle Imaging to the Optical and Microphysical Properties of Biomass Burning Aerosols", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182008-174607", "creators": [ { "name": { "family": "Chen", "given": "Wei-Ting" }, "id": "Chen-Wei-Ting", "orcid": "0000-0002-9292-0933", "display_name": "Chen, Wei-Ting" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "chair", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/0ZWE-9K94", "abstract": "To understand the interaction between aerosols and climate, equilibrium simulations with a general circulation model are carried out in Part I to study the effects of future climate change on aerosol distributions, as well as the climate responses to future aerosol changes. The predicted warmer climate induced by carbon dioxide modifies the climate-sensitive emissions, alters the thermodynamic partitioning, and enhances wet removal of the aerosols. The direct radiative perturbations of aerosols, and the modification of clouds by aerosols can potentially change the temperature distribution, the hydrological cycle, and the atmospheric circulation; the pattern of climatic impacts from aerosols are differentiated from those of anthropogenic greenhouse gases. In Part II, the aerosol retrieval algorithm of the remote sensing instrument, the Multi-angle Imaging SpectroRadiometer (MISR), is assessed for the retrieval of biomass burning aerosols. By comparisons with coincident ground measurements and theoretical sensitivity tests, specific refinements to particle and mixture properties assumed in the algorithm for biomass burning aerosols are proposed. Representative case studies confirm the theoretical results and underline the key role of surface characterization in the remote sensing of aerosols." }, { "name": "Chen, Yan", "degree": "PhD", "year": "2009", "title": "Integration of Dye Lasers and Microfluidics for Biochemical Analysis", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202008-164745", "creators": [ { "name": { "family": "Chen", "given": "Yan" }, "id": "Chen-Yan-Bioengineering", "display_name": "Chen, Yan" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "bioeng" ], "doi": "10.7907/2E06-0W63", "abstract": "This dissertation describes the study of two important aspects of integration in microfluidics: optics and biochemistry. In optics integration, two types of miniaturized dye lasers, namely the solid-state polymer dye lasers and optofluidic dye lasers were demonstrated. Both of the dye lasers possess a resonant cavity with circular grating geometry, and they are suitable to serve as low-threshold, surface-emitting coherent light source in microfluidic networks. The mass production and large scale fabrication of such low-cost dye laser arrays can be realized by the well developed nanoimprint and soft lithography, making this technology attractive for various biochemical applications. In biochemistry integration, a microfluidic system was developed to fully utilize the complexity of microfluidic circuits to process single cells and extract gene expression information in a parallel manner. The work presented here explored both the optics and biochemistry integration in microfluidics, which are the key issues for further development of complete \u201clab-on-a-chip\u201d systems. " }, { "name": "Cheung, Sai Hung", "degree": "PhD", "year": "2009", "title": "Stochastic Analysis, Model and Reliability Updating of Complex Systems with Applications to Structural Dynamics", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292009-102458", "creators": [ { "name": { "family": "Cheung", "given": "Sai Hung" }, "id": "Cheung-Sai-Hung", "orcid": "0000-0003-2324-3884", "display_name": "Cheung, Sai Hung" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "role": "member", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/K5T7-4B72", "abstract": "In many engineering applications, it is a formidable task to construct mathematical models that are expected to produce accurate predictions of the behavior of a system of interest. During the construction of such predictive models, errors due to imperfect modeling and uncertainties due to incomplete information about the system and its environment (e.g., input or excitation) always exist and can be accounted for appropriately by using probability logic. To assess the system performance subjected to dynamic excitations, a stochastic system analysis considering all the uncertainties involved has to be performed. In engineering, evaluating the robust failure probability (or its complement, robust reliability) of the system is a very important part of such stochastic system analysis. The word \u2018robust\u2019 is used because all uncertainties, including those due to modeling of the system, are taken into account during the system analysis, while the word \u2018failure\u2019 is used to refer to unacceptable behavior or unsatisfactory performance of the system output(s). Whenever possible, the system (or subsystem) output (or maybe input as well) should be measured to update models for the system so that a more robust evaluation of the system performance can be obtained. In this thesis, the focus is on stochastic system analysis, model and reliability updating of complex systems, with special attention to complex dynamic systems which can have high-dimensional uncertainties, which are known to be a very challenging problem. Here, full Bayesian model updating approach is adopted to provide a robust and rigorous framework for these applications due to its ability to characterize modeling uncertainties associated with the underlying system and to its exclusive foundation on the probability axioms.
\r\n\r\nFirst, model updating of a complex system which can have high-dimensional uncertainties within a stochastic system model class is considered. To solve the challenging computational problems, stochastic simulation methods, which are reliable and robust to problem complexity, are proposed. The Hybrid Monte Carlo method is investigated and it is shown how this method can be used to solve Bayesian model updating problems of complex dynamic systems involving high-dimensional uncertainties. New formulae for Markov Chain convergence assessment are derived. Advanced hybrid Markov Chain Monte Carlo simulation algorithms are also presented in the end.
\r\n\r\nNext, the problem of how to select the most plausible model class from a set of competing candidate model classes for the system and how to obtain robust predictions from these model classes rigorously, based on data, is considered. To tackle this problem, Bayesian model class selection and averaging may be used, which is based on the posterior probability of different candidate classes for a system. However, these require calculation of the evidence of the model class based on the system data, which requires the computation of a multi-dimensional integral involving the product of the likelihood and prior defined by the model class. Methods for solving the computationally challenging problem of evidence calculation are reviewed and new methods using posterior samples are presented.
\r\n\r\nMultiple stochastic model classes can be created even there is only one embedded deterministic model. These model classes can be viewed as a generalization of the stochastic models considered in Kalman filtering to include uncertainties in the parameters characterizing the stochastic models. State-of-the-art algorithms are used to solve the challenging computational problems resulting from these extended model classes. Bayesian model class selection is used to evaluate the posterior probability of an extended model classe and the original one to allow a data-based comparison. The problem of calculating robust system reliability is also addressed. The importance and effectiveness of the proposed method is illustrated with examples for robust reliability updating of structural systems. Another significance of this work is to show the sensitivity of the results of stochastic analysis, especially the robust system reliability, to how the uncertainties are handled, which is often ignored in past studies.
\r\n\r\nA model validation problem is then considered where a series of experiments are conducted that involve collecting data from successively more complex subsystems and these data are to be used to predict the response of a related more complex system. A novel methodology based on Bayesian updating of hierarchical stochastic system model classes using such experimental data is proposed for uncertainty quantification and propagation, model validation, and robust prediction of the response of the target system. Recently-developed stochastic simulation methods are used to solve the computational problems involved.
\r\n\r\nFinally, a novel approach based on stochastic simulation methods is developed using current system data, to update the robust failure probability of a dynamic system which will be subjected to future uncertain dynamic excitations. Another problem of interest is to calculate the robust failure probability of a dynamic system during the time when the system is subjected to dynamic excitation, based on real-time measurements of some output from the system (with or without corresponding input data) and allowing for modeling uncertainties; this generalizes Kalman filtering to uncertain nonlinear dynamic systems. For this purpose, a novel approach is introduced based on stochastic simulation methods to update the reliability of a nonlinear dynamic system, potentially in real time if the calculations can be performed fast enough.
" }, { "name": "Chiu, Hsin-Ying", "degree": "PhD", "year": "2009", "title": "Thermal Properties and Nanoelectromechanical System Based on Carbon Nanotubes", "advisor": "Bockrath, Marc William", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272009-033303", "creators": [ { "name": { "family": "Chiu", "given": "Hsin-Ying" }, "id": "Chiu-Hsin-Ying", "orcid": "0000-0002-6753-3261", "display_name": "Chiu, Hsin-Ying" } ], "advisors": [ { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "advisor", "display_name": "Bockrath, Marc William" } ], "committee": [ { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "role": "chair", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2T53-P806", "abstract": "In Chapter I, the fundamental electronic properties of two-dimensional (2D) graphene and one-dimensional (1D) carbon nanotubes are discussed, along with the carbon nanotube single-electron transistors (SETs). In addition to nanotubes' extraordinary electronic properties, the phenomena of phonon transport in carbon nanotubes are also notable. In Chapter II, we discuss our experiments probing the thermal properties of multi-walled carbon nanotubes. We exploit the specific breakdown temperature under a large current, which provides an effective thermometer, in conjunction with the known power input to measure the thermal conductivity of the nanotubes. Our results reveal the exceptional micron-scale phonon mean free path at temperatures approaching 900K, and we demonstrate the first evidence for ballistic phonon propagation in nanotubes, reaching a regime where the thermal conductance of nanotubes is limited only by fundamental quantum mechanical limits imposed by their 1D nature.
\r\n\r\nMoreover, the combination of remarkable electrical and mechanical properties makes carbon nanotubes a highly promising candidate for nanoelectromechanical systems (NEMS). In Chapter III, we investigate using doubly clamped suspended single-walled carbon nanotubes as nanomechanical resonators at cryogenic temperatures. Their intrinsic single-electron transistor behavior provides a mixing mechanism to self-detect their motion based on their capacitance to a nearby gate electrode. We exploit our devices to attain an ultrasensitive mass sensor, realizing atomic-scale mass sensing. Finally, in Chapter IV, nanoelectromechanical switches based on using multi-walled carbon nanotubes as nanoscale linear bearings are discussed. First we demonstrate the preparation of the initial OFF state by using electrical breakdown to create gaps in a free-standing MWNT device, while subsequently the ON state is actuated with electrical forces and undergoes linear bearing motion that telescopes the inner shells to bridge the gaps. The switching cycle can be performed in double-walled nanotube devices by restoring the insulating OFF state with a controllable gate voltage. These tubular switches can potentially serve as nonvolatile memory or logic gate elements.
\r\n" }, { "name": "Chung, Daniel", "degree": "PhD", "year": "2009", "title": "Numerical Simulation and Subgrid-Scale Modeling of Mixing and Wall-Bounded Turbulent Flows", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292009-123828", "creators": [ { "name": { "family": "Chung", "given": "Daniel" }, "id": "Chung-Daniel", "orcid": "0000-0003-3732-364X", "display_name": "Chung, Daniel" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NE1Y-M812", "abstract": "We extend the idea of multiscale large-eddy simulation (LES), the underresolved fluid dynamical simulation that is augmented with a physical description of subgrid-scale (SGS) dynamics. Using a vortex-based SGS model, we consider two areas of specialization: active (buoyant) scalar mixing and wall-bounded turbulence.
\r\n\r\nFirst, we develop a novel method to perform direct numerical simulation (DNS) of statistically stationary buoyancy-driven turbulence by using the fringe-region technique within a triply periodic domain, in which a mixing region is sandwiched between two fringes that supply the flow with unmixed fluids---heavy on top of light. Spectra exhibit small-scale universality, as evidenced by collapse in inner scales. A comparison with high-resolution DNS spectra from Rayleigh--Taylor turbulence reveals some similarities.
\r\n\r\nWe perform LES of this flow to show that a passive scalar SGS model can also be used in an unstably stratified environment. LES spectra, including subgrid extensions, show good agreement with DNS data. For stably stratified flows, we develop an active scalar SGS model by performing a perturbation expansion in small Richardson numbers of the passive scalar SGS model to obtain an expression for the SGS scalar flux that contains buoyancy corrections.
\r\n\r\nWe then develop a wall model for LES in which the near-wall region is unresolved. A special near-wall SGS model is constructed by averaging the streamwise momentum equation together with an assumption of local--inner scaling, giving an ordinary differential equation for the local wall shear stress that is coupled with the LES. An extended form of the stretched-vortex SGS model, which incorporates the production of near-wall Reynolds shear stresses due to the winding of streamwise momentum by near-wall attached SGS vortices, then provides a log relation for the off-wall LES boundary conditions. A Karman-like constant is calculated dynamically as part of the LES. With this closure we perform LES of turbulent channel flow for friction-velocity Reynolds numbers $Rey_\tau=2,\textrm{k}$--$20,\textrm{M}$. Results, including SGS-extended spectra, compare favorably with DNS at Rey_\tau=2,\textrm{k}$, and maintain an $O(1)$ grid dependence on $Rey_\tau$.
\r\n\r\nFinally, we apply the wall model to LES of long channels to capture effects of large-scale structures. Computed correlations are found to be consistent with recent experiments.
" }, { "name": "Ciucci, Francesco", "degree": "PhD", "year": "2009", "title": "Continuum Modeling of Mixed Conductors: A Study of Ceria", "advisor": "Goodwin, David G.; Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07212009-142144", "creators": [ { "name": { "family": "Ciucci", "given": "Francesco" }, "id": "Ciucci-Francesco", "orcid": "0000-0003-0614-5537", "display_name": "Ciucci, Francesco" } ], "advisors": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "advisor", "display_name": "Goodwin, David G." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "co-advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "co-chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/3TWK-W923", "abstract": "In this thesis we have derived a new way to analyze the impedance response of mixed conducting materials for use in solid oxide fuel cells (SOFCs), with the main focus on anodic materials, in particular cerium oxides.
\r\n\r\nFirst we have analyzed the impact of mixed conductivity coupled to electrocatalytic behavior in the linear time-independent domain for a thick ceria sample. We have derived that, for a promising fuel cell material, Samarium Doped Ceria, chemical reactions are the determining component of the polarization resistance.
\r\n\r\nAs a second step we have extended the previous model to the time-dependent case, where we focused on single harmonic excitation, the impedance spectroscopy conditions. We extended the model to the case where some input diffusivities are spatially nonuniform. For instance we considered the case where diffusivities change significantly in the vicinity of the electrocatalytic region.
\r\n \r\nAs a third and final step we use to model to capture the two dimensional behavior of mixed conducting thin films, where the electronic motion from one side of the sample to the other is impeded. Such conditions are similar to those encountered in fuel cells where an electrolyte conducting exclusively oxygen ions is placed between the anode and the cathode. The framework developed was also extended to study a popular cathodic material, Lanthanum Manganite.
\r\n\r\nThe model is used to give unprecedented insight in SOFC polarization resistance analysis of mixed conductors. It helps elucidate rigorously rate determining steps and to address the interplay of diffusion with diffusion losses. Electrochemical surface losses dominate for most experimental conditions of Samarium Doped Ceria and they are shown to be strongly dependent on geometry.
\r\n" }, { "name": "Deshpande, Vikram Vijay", "degree": "PhD", "year": "2009", "title": "One-Dimensional Physics of Interacting Electrons and Phonons in Carbon Nanotubes ", "advisor": "Bockrath, Marc William", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312008-123250", "creators": [ { "name": { "family": "Deshpande", "given": "Vikram Vijay" }, "id": "Deshpande-Vikram-Vijay", "display_name": "Deshpande, Vikram Vijay" } ], "advisors": [ { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "advisor", "display_name": "Bockrath, Marc William" } ], "committee": [ { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "chair", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Eisenstein", "given": "James P." }, "id": "Eisenstein-J-P", "role": "member", "display_name": "Eisenstein, James P." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/RTMF-SF53", "abstract": "The one-dimensional (1D) world is quite different from its higher dimensional counterparts. For example, the electronic ground state in 1D is not a Fermi liquid as in most solids, due to the role of electron-electron interactions. Most commonly, electrons in 1D are described as a Luttinger liquid, where the low-energy excitations are decoupled bosonic charge and spin waves. Carbon nanotubes are clean 1D systems which have been shown to behave like a Luttinger liquid at high electron density. However, at low electron density and in the absence of disorder, the ground state is predicted to be a 1D Wigner crystal\u2014an electron solid dominated by long-range Coulomb interaction. Moreover, short-range interaction mediated by the atomic lattice (umklapp scattering) is predicted to transform a nominal 1D metal into a Mott insulator.
\r\n\r\nIn this thesis, we develop techniques to make extremely clean nanotube single-electron transistors. We study them in the few-electron/hole regime using Coulomb blockade spectroscopy in a magnetic field. In semiconducting nanotubes, we map out the antiferromagnetic exchange coupling as a function of carrier number and find excellent agreement to a Wigner crystal model. In nominally metallic nanotubes, we observe a universal energy gap in addition to the single-particle bandgap, implying that nanotubes are never metallic. The magnitude, radius dependence and low-energy neutral excitations of this additional gap indicate a Mott insulating origin.
\r\n\r\nFurther, we use simultaneous electrical and Raman spectroscopy measurements to study the phonons scattered by an electric current. At high bias, suspended nanotubes show striking negative differential conductance, attributed to non-equilibrium phonons. We directly observe such \"hot\" phonon populations in the Raman response and also report preferential electron coupling to one of two optical phonon modes. In addition, using spatially-resolved Raman spectroscopy, we obtain a wealth of local information including the 1D temperature profile, a spatial map of the thermal conductivity and thermal contact resistances, which reveal the mechanism of thermal transport in nanotubes.
\r\n\r\nFinally, with multi-wall nanotubes (MWNTs), we use electrical breakdown as thermometry to provide evidence for ballistic phonon propagation and obtain an estimate for the quantum of thermal conductance. We also develop linear-bearing nanoswitches using the low-friction properties of MWNTs.
\r\n" }, { "name": "Dicken, Matthew James", "degree": "PhD", "year": "2009", "title": "Active Oxide Nanophotonics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-05032009-154839", "creators": [ { "name": { "family": "Dicken", "given": "Matthew James" }, "id": "Dicken-Matthew-James", "display_name": "Dicken, Matthew James" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/WPBT-C144", "abstract": "Materials that can be manipulated electrically or mechanically to induce a change in their intrinsic properties are highly relevant when suitably integrated with current technologies. These \"active\" materials, such as oxide-based ferroelectrics or materials with easily accessible changes of phase, find extensive use as mechanical resonators, solid-state memories, and optical modulators. Barium titanate, a tetragonal ferroelectric at room temperature, is a prime example of a material both mechanically and optically active. This thesis deals primarily with the deposition of active, oxide-based materials and their integration into device structures where either the mechanical or optical properties are exploited.
\r\n\r\nThe technologically interesting paradigms within which these active oxide materials have been investigated are microelectromechanical systems, plasmonics, and metamaterials. Microelectromechanical systems are devices that have been micromachined and rely on an applied voltage to induce a mechanical response. Mechanically active materials, such as piezoelectrics or ferroelectrics, can increase the response of these devices. Plasmonics deals with electromagnetic waves resonantly coupled into free electron oscillations at a metal-dielectric interface or metal nanoparticle. Coupling to these resonant modes allows surface plasmon polaritons to propagate along the metal with a nonlinear dispersion. Metamaterials are ordered, subwavelength, metal inclusions in a dielectric, which respond collectively to electromagnetic radiation. This response can yield a material permittivity or permeability not found in nature. The optical properties of metamaterials lead to effects such as negative index response and super lensing, and can be used to design optical cloaking structures. Here, devices utilizing these effects are investigated with an eye toward tuning or switching their resonant response using optically active oxide thin films.
\r\n\r\nThis manuscript follows the evolution of active oxide thin films from deposition, through design of plasmonic devices and active metamaterials, finite difference modeling of these structures, and finally experimental validation. First, deposition and material integration techniques for oxide-based thin films will be discussed. The role of molecular beam epitaxy, pulsed laser deposition, and ion beam assisted deposition as material growth techniques are investigated. Development of a multitude of oxide materials using these techniques including barium titanate, strontium ruthenate, vanadium oxide, and magnesium oxide will be covered. The following two sections deal with the mechanical and optical properties of barium titanate thin films as they are studied and utilized to design and fabricate active devices. Films were characterized mechanically, using nanoindentation and piezoresponse force microscopy, and optically with variable angle spectroscopic ellipsometry. The subsequent section deals with the design, fabrication, and experimental validation of an active optical device based on surface plasmon polariton wavevector modulation via electrooptic modulation of a barium titanate thin film. Interferometers based on pairs of parallel slits fabricated in silver films on barium titanate are used to investigate optical modulation due to both domain switching and the electrooptic effect. Finally, active metamaterials are discussed through the investigation of a new material, vanadium oxide, as it is deposited and characterized, and the results used to design and fabricate active, split-ring resonator metamaterial structures.
\r\n" }, { "name": "Dionne, Jennifer Anne", "degree": "PhD", "year": "2009", "title": "Flatland Photonics: Circumventing Diffraction with Planar Plasmonic Architectures", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302008-115303", "creators": [ { "name": { "family": "Dionne", "given": "Jennifer Anne" }, "id": "Dionne-Jennifer-Anne", "orcid": "0000-0001-5287-4357", "display_name": "Dionne, Jennifer Anne" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "role": "member", "display_name": "Preskill, John P." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3DCC-CZ57", "abstract": "On subwavelength scales, photon-matter interactions are limited by diffraction. The diffraction limit restricts the size of optical devices and the resolution of conventional microscopes to wavelength-scale dimensions, severely hampering our ability to control and probe subwavelength-scale optical phenomena. Circumventing diffraction is now a principle focus of integrated nanophotonics. Surface plasmons provide a particularly promising approach to sub-diffraction-limited photonics. Surface plasmons are hybrid electron-photon modes confined to the interface between conductors and transparent materials. Combining the high localization of electronic waves with the propagation properties of optical waves, plasmons can achieve extremely small mode wavelengths and large local electromagnetic field intensities. Through their unique dispersion, surface plasmons provide access to an enormous phase space of refractive indices and propagation constants that can be readily tuned with material or geometry.
\r\n\r\nIn this thesis, we explore both the theory and applications of dispersion in planar plasmonic architectures. Particular attention is given to the modes of metallic core and plasmon slot waveguides, which can span positive, near-zero, and even negative indices. We demonstrate how such basic plasmonic geometries can be used to develop a suite of passive and active plasmonic components, including subwavelength waveguides, color filters, negative index metamaterials, and optical MOS field effect modulators. Positive index modes are probed by near- and far-field techniques, revealing plasmon wavelengths as small as one-tenth of the excitation wavelength. Negative index modes are characterized through direct visualization of negative refraction. By fabricating prisms comprised of gold, silicon nitride, and silver multilayers, we achieve the first experimental demonstration of a negative index material at visible frequencies, with potential applications for sub-diffraction-limited microscopy and electromagnetic cloaking. We exploit this tunability of complex plasmon mode indices to create a compact metal-oxide-Si (MOS) field effect plasmonic modulator (or plasMOStor). By transforming the MOS gate oxide into an optical channel, amplitude modulation depths of 11.2 dB are achieved in device volumes as small as one one-fifth of a cubic wavelength. Our results indicate the accessibility of tunable refractive indices over a wide frequency band, facilitating design of a new materials class with extraordinary optical properties and applications.
\r\n" }, { "name": "Franck, Jennifer Ann", "degree": "PhD", "year": "2009", "title": "Large-Eddy Simulation of Flow Separation and Control on a Wall-Mounted Hump", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022009-183247", "creators": [ { "name": { "family": "Franck", "given": "Jennifer Ann" }, "id": "Franck-Jennifer-Ann", "display_name": "Franck, Jennifer Ann" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "mecheng" ], "doi": "10.7907/DH38-D592", "abstract": "Active flow control techniques such as synthetic jets have been successful in increasing the performance of naturally separating flows on post-stall airfoils, bluff body shedding, and internal flows such as wide-angle diffusers. However, in order to implement robust control techniques there is a need for accurate computational tools capable of predicting unsteady separation and control at high Reynolds numbers. This thesis developed a compressible large-eddy simulation (LES) and validated it by simulating the turbulent flow over a wall-mounted hump. The flow is characterized by an unsteady, turbulent recirculation region along the trailing edge of the geometry, and is simulated at a Reynolds number of 500,000. Active flow control is applied just before the natural separation point via steady suction and zero-net mass flux oscillatory forcing. The addition of control is shown to be effective in decreasing the size of the separation bubble and pressure drag. LES baseline and controlled results are validated against previously performed experiments by Seifert and Pack and those performed for the NASA Langley Workshop on Turbulent Flow Separation and Control. Three test cases are explored to determine the effect of explicit filtering and the Smagorinsky subgrid scale model on the average flow and turbulent statistics. The flow physics and the control effectiveness are investigated at two Mach numbers, M=0.25 and M=0.6. Compressibility is shown to increase the separation bubble length in the baseline case, but does not significantly change the effectiveness of the control. In terms of decreasing drag on the wall-mounted hump model, steady suction is more effective than oscillatory control, but both control techniques are effective in reducing the separation bubble length. Two-dimensional direct numerical simulations (DNS) of the wall-mounted hump flow are also presented, and the results show different baseline flow features than the 3D LES. However the controlled 2D flow gives an indication of the most receptive actuation frequencies around twice that of the natural shedding frequency. Two regimes of reduced actuation frequency are also explored with the 3D LES. It is found that the low frequency actuation is successful in reducing the separation bubble length, but high frequency actuation produces an average flow comparable to the baseline case, and does not result in drag or separation bubble length reduction.\r\n" }, { "name": "Glidden, Hilary K.", "degree": "PhD", "year": "2009", "title": "Tracker Effector-Specific and Motor Planning Signals in Human Frontal and Parietal Cortices: Relevance for Goal-Directed Action and Neural Prosthetics", "advisor": "Andersen, Richard A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302008-224422", "creators": [ { "name": { "family": "Glidden", "given": "Hilary K." }, "id": "Glidden-Hilary-K", "display_name": "Glidden, Hilary K." } ], "advisors": [ { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "advisor", "display_name": "Andersen, Richard A." } ], "committee": [ { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "chair", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Fineman", "given": "Igor" }, "id": "Fineman-I", "role": "member", "display_name": "Fineman, Igor" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "cns" ], "doi": "10.7907/CDC5-TK34", "abstract": "Delayed response tasks and functional magnetic resonance imaging were employed to map the neural architecture underlying goal-directed action planning in the human brain, examine interactions between motor planning and effector-specification (arm vs. eye), and explore other related processes and variables. Studies in healthy human subjects revealed a frontoparietal network of brain areas selectively involved in motor planning compared to control processes. Nodes within this network were characterized based on their functional properties, including effector-specificity. In frontal cortex, the dorsal premotor and supplementary motor areas preferentially encoded motor plans for arm reaches compared to saccadic eye movements, while the inferior frontal eye field was identified based on its selective involvement in eye movements. In parietal cortex, a similar dissociation of arm- and eye-specific brain areas was observed in the superior lobule. A medial branch of the intraparietal sulcus preferentially encoded eye movements, in contrast to more anterior medial, and posterior medial, portions of the intraparietal sulcus that preferentially encoded arm movements. Additionally, motor planning areas were engaged during voluntary shifts of spatial attention and during working memory for visual cues when these cues were relevant for upcoming movements. Many of these brain areas also encoded the type of arm movement (reach vs. point), arm posture, and limb contralaterality, a property that co-varied with increasing ties to motor execution. Also, a comparison of real vs. imagined arm movements revealed that the imagined arm could be used as a proxy for the real arm to drive activity in motor planning areas. Another study completed in healthy control and spinal cord-injured subjects demonstrated the preservation of a relatively normal pattern of brain activity after the brain is functionally disconnected from the limbs. The degree of preservation of healthy/normal BOLD activity levels, particularly in the medial parietal cortex, strongly correlated with clinical and behavioral variables and could predict functional motor improvements in spinal cord-injured subjects six months later. These studies contribute to our understanding of the representation of goal-directed action planning in the human brain, elucidate human-monkey interspecies functional homologies, and have implications for the design and implantation of cortical neural prosthetic devices.\r\n" }, { "name": "Gu, WeiHsin", "degree": "PhD", "year": "2009", "title": "On Achievable Rate Regions for Source Coding Over Networks", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262009-111455", "creators": [ { "name": { "family": "Gu", "given": "WeiHsin" }, "id": "Gu-WeiHsin", "display_name": "Gu, WeiHsin" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/J8JP-R695", "abstract": "In the field of source coding over networks, a central goal is to understand the best possible performance for compressing and transmitting dependent data distributed over a network. The achievable rate region for such a network describes all link capacities that suffice to satisfy the reproduction demands. Here all the links in the networks are error-free, the data dependency is given by a joint distribution of the source random variables, and the source sequences are drawn i.i.d. according to the given source distribution. In this thesis, I study the achievable rate regions for general networks, deriving new properties for the rate regions of general network source coding problems, developing approximation algorithms to calculate these regions for particular examples, and deriving bounds on the regions for basic multi-hop and multi-path examples.
\r\n\r\nIn the first part, I define a family of network source coding problems. That family contains all of the example networks in the literature as special cases. For the given family, I investigate abstract properties of the achievable rate regions for general networks. These properties include (1) continuity of the achievable rate regions with respect to both the source distribution and the distortion constraint vector and (2) a strong converse that implies the traditional strong converse. Those properties might be useful for studying a long-standing open question: whether a single-letter characterization of a given achievable rate region always exists.
\r\n\r\nIn the second part, I develop a family of algorithms to approximate the achievable rate regions for some example network source coding problems based on their single-letter characterizations by using linear programming tools. Those examples contain (1) the lossless coded side information problem by Ahlswede and Korner, (2) the Wyner-Ziv rate-distortion function, and (3) the Berger et al. bound for the lossy coded side information problem. The algorithms may apply more widely to other examples.
\r\n\r\nIn the third part, I study two basic networks of different types: the two-hop and the diamond networks. The two-hop network is a basic example of line networks with single relay node on the path from the source to the destination, and the diamond network is a basic example of multi-path networks that has two paths from the source to the destination, where each of the paths contains a relay node. I derive performance bounds for the achievable rate regions for these two networks.
\r\n" }, { "name": "Habbal, Feras", "degree": "PhD", "year": "2009", "title": "The Optimal Transportation Meshfree Method for General Fluid Flows and Strongly Coupled Fluid-Structure Interaction Problems", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012009-104937", "creators": [ { "name": { "family": "Habbal", "given": "Feras" }, "id": "Habbal-Feras", "display_name": "Habbal, Feras" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/MHQX-3Z52", "abstract": "This thesis develops a novel meshfree numerical method for simulating general fluid flows. Drawing from concepts in optimal mass transport theory and in combination with the notion of material point sampling and meshfree interpolation, the optimal transport meshfree (OTM) method provides a rigorous mathematical framework for numerically simulating three-dimensional general fluid flows with general, and possibly moving boundaries (as in fluid-structure interaction simulations). Specifically, the proposed OTM method generalizes the Benamou-Brenier differential formulation of optimal mass transportation problems which leads to a multi-field variational characterization of general fluid flows including viscosity, equations of state and general geometries and boundary conditions. With the use of material point sampling in conjunction with local max-entropy shape functions, the OTM method leads to a meshfree formulation bearing a number of salient features. Compared with other meshfree methods that face significant challenges to enforce essential boundary conditions as well as couple to other methods, such as the finite element method, the OTM method provides a new paradigm in meshfree methods. The OTM method is numerically validated by simulating the classical Riemann benchmark example for Euler flow. Furthermore, in order to highlight the ability of the OTM to simulate Navier-Stokes flows within general, moving three-dimensional domains, and naturally couple with finite elements, an illustrative strongly coupled FSI example is simulated. This illustrative FSI example, consisting of a gas-inflated sphere impacting the ground, is simulated as a toy model of the final phase of NASA's landing scheme devised for Mars missions, where a network of airbags are deployed to dissipate the energy of impact.\r\n\r\n" }, { "name": "Hansen, Benjamin Lee", "degree": "PhD", "year": "2009", "title": "Modeling Metallic Single Crystal Plastic Hardening Through the Evolution of Dislocation Subgrain Structures", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-03132009-154225", "creators": [ { "name": { "family": "Hansen", "given": "Benjamin Lee" }, "id": "Hansen-Benjamin-Lee", "display_name": "Hansen, Benjamin Lee" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bronkhorst", "given": "Curt" }, "id": "Bronkhorst-C", "role": "co-chair", "display_name": "Bronkhorst, Curt" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/C052-3119", "abstract": "A single crystal plasticity theory for insertion into finite element simulation is formulated using sequential laminates to model subgrain dislocation structures. It is known that local models do not adequately account for latent hardening, as latent hardening is not only a material property, but a nonlocal property (e.g., grain size and shape). The addition of the nonlocal energy from the formation of subgrain structure dislocation walls and the boundary layer misfits provide both latent and self hardening of crystal slip. Latent hardening occurs as the formation of new dislocation walls limit motion of new mobile dislocations, thus hardening future slip systems. Self hardening is accomplished by evolution of the subgrain structure length scale. No multiple slip hardening terms are included.
\r\n\r\nThe substructure length scale is computed by minimizing the nonlocal energy. The minimization of the nonlocal energy is a competition between the dislocation wall and boundary layer energy. The nonlocal terms are also directly minimized within the subgrain model as they impact deformation response. The geometrical relationship between the dislocation walls and slip planes affecting dislocation mean free path is accounted for giving a first-order approximation to shape effects. A coplanar slip model is developed due to requirements when modeling the subgrain structure. This subgrain structure plasticity model is noteworthy as all material parameters are experimentally determined rather than fit. The model also has an inherit path dependency due to the formation of the subgrain structures. Validation is accomplished by comparison to single crystal tension test results.
\r\n" }, { "name": "Hofmann, Douglas Clayton", "degree": "PhD", "year": "2009", "title": "Designing Bulk Metallic Glass Matrix Composites with High Toughness and Tensile Ductility", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102008-101837", "creators": [ { "name": { "family": "Hofmann", "given": "Douglas Clayton" }, "id": "Hofmann-Douglas-Clayton", "display_name": "Hofmann, Douglas Clayton" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Demetriou", "given": "Marios D." }, "id": "Demetriou-M-D", "role": "member", "display_name": "Demetriou, Marios D." } ], "option_major": [ "matsci" ], "doi": "10.7907/CJZ7-VV41", "abstract": "Metallic glasses have been the subject of intense scientific study since the 1960s, owing to their unique properties such as high strength, large elastic limit, high hardness, and amorphous microstructure. However, bulk metallic glasses have not been used in the high strength structural applications for which they have so much potential, owing to a highly localized failure mechanism that results in catastrophic failure during unconfined loading. In this thesis, bulk metallic glass matrix composites are designed with the combined benefits of high yield strengths and tensile ductility. This milestone is achieved by first investigating the length scale of the highly localized deformation, known as shear bands, that governs fracture in all metallic glasses. Under unconfined loading, a shear band grows to a certain length that is dependent on the fracture toughness of the glass before a crack nucleates and fracture occurs. Increasing the fracture toughness and ductility involves adding microstructural stabilization techniques that prevent shear bands from lengthening and promotes formation of multiple shear bands. To accomplish this, we develop in-situ formed bulk metallic glass matrix-composites with soft crystalline dendrites whose size and distribution are controlled through a novel semi-solid processing technique. The new alloys have a dramatically increased room-temperature ductility and a fracture toughness that appears to be similar to the toughest steels. Owing to their low modulus, the composites are therefore among the toughest known materials, a claim that has recently been confirmed independently by a fracture mechanics group. We extend our toughening strategy to a titanium-vanadium-based glass-dendrite composite system with density as low as 4.97 g/cm3. The new low-density composites rival the mechanical properties of the best structural crystalline Ti alloys. We demonstrate new processing techniques available in the highly toughened composites: room temperature cold rolling, work hardening, and thermoplastic forming. This thesis is a proven road map for developing metallic glass composites into real structural engineering materials.\r\n" }, { "name": "Hudson, Nicolas Henry", "degree": "PhD", "year": "2009", "title": "Inference in Hybrid Systems with Applications in Neural Prosthetics", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-12312008-184713", "creators": [ { "name": { "family": "Hudson", "given": "Nicolas Henry" }, "id": "Hudson-Nicolas-Henry", "display_name": "Hudson, Nicolas Henry" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/REB5-BB43", "abstract": "This thesis develops new hybrid system models and associated inference algorithms to create a ``supervisory decoder' for cortical neural prosthetic devices that aim to help the severely handicapped. These devices are a brain-machine interface, consisting of surgically implanted electrode arrays and associated computer decoding algorithms, that enable a human to control external electromechanical devices, such as artificial limbs, by thought alone.
\r\n\r\nHybrid systems are characterized by discrete switching between sets of continuous dynamical activity. New hybrid models, which are flexible enough to model neurological activity, are created that incorporate both duration and dynamical state based switching paradigms. Combining generalized linear models with nonstationary and semi-Markov chains gives rise to three new hybrid systems: generalized linear hidden Markov models (GLHMM), hidden semi-Markov models (HSMM) with generalized linear model dynamics, and hidden regressor dependent Markov models (HRDMM). Bayesian inference methods, including variational Bayes and Gibbs sampling, are derived for the identification of existing and developed hybrid models. The developed inference algorithms provide advances over the current hybrid system identification literature by providing a principled way to incorporate prior knowledge and select between alternative model classes and orders, including the number of discrete system states.
\r\n\r\nFuture neuroprostheses that seek to provide a facile interface for the paralyzed patient will require a supervisory decoder that classifies, in real time, the discrete cognitive, behavioral, or planning state of the brain. The developed hybrid models and inference algorithms provide a framework for supervisory decoding, where first, a hybrid-state neurological activity model is identified from data, and then used to estimate the discrete state in real time. The electrical activity of multiple neurons from a cortical area in the brain associated with motor planning (the parietal reach region), and multiple signal types, including both spike arrival times and local field potentials, are fused to give more accurate results. The model structure, including the number of discrete cognitive states, can also be estimated from the data, resulting in significantly improved decoding performance compared to existing methods.
\r\n\r\nAdditional demonstrated applications include the automated segmentation of honey bee motion into discrete primitives, and generating mechanical system models for a pick-and-place machine.
\r\n" }, { "name": "Johnson, Thomas James", "degree": "PhD", "year": "2009", "title": "Silicon Microdisk Resonators for Nonlinear Optics and Dynamics", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-120417", "creators": [ { "name": { "family": "Johnson", "given": "Thomas James" }, "id": "Johnson-Thomas-James", "display_name": "Johnson, Thomas James" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/SBDK-7J52", "abstract": "Silicon is incredibly well-studied as an electronic material. Since the out-migration of William Noyce, Gordon Moore, and the rest of the original Fairchild Semiconductor class from Shockley Semiconductor, silicon has only grown in prominence. Untold billions have been expended on research, development, and manufacture, and now silicon is perhaps the most well-controlled commercial material on Earth. For all that, the use of silicon as a mechanical material, though envisioned in the late 1950s, largely became viable only after the advent of large-scale silicon processing for microelectronics. As an optical material, silicon also has a long pedigree, with most of the positive focus on its excellent optical transparency and the enormous potential for improvement residing in its lack of effective emission.
\r\n\r\nThis thesis concerns an alternate route to the generation of light in silicon: the nonlinear route. Resonant elements play a critical role in making this viable. The ability to build up optical intensity in the confined volume of a microresonator reduces the input power required to achieve a given energy density. Silicon also has certain excellent nonlinear properties: a large Raman gain coefficient, for example, and an appreciable Kerr effect. Unfortunately, silicon also exhibits significant two-photon absorption (TPA) in the convenient telecommunications wavelength bands. As such, the build-up of optical energy in silion may also be accompanied by a build-up of TPA-induced free-carrier populations. These populations may serve to limit the efficiency of nonlinear processes or to generate additional nonlinear behavior in their interactions with optical fields.
\r\n\r\nThus two important stepping-stones on the way to the low-power,low-footprint use of silicon as an optical material are: the need to reduce optical losses in the optical elements, and to reduce or modify the populations of free carriers generated in the nonlinear optics regime. This thesis will present design considerations of, fabrication techniques developed for, and characterization techniques of high-Q silicon microresonators. In the course of this work, we have created silicon microdisk resonators with quality factors as high as 5\u00d710^6, and high-Q silicon microdisks with free-carrier lifetimes in the deep subnanosecond regime (Q=5\u20136\u00d710^5 and carrier lifetimes \u2264 240 ps). These results, with no indication that higher quality factors or shorter carrier lifetimes are not possible in similar structures, indicate that coherent, CW optical generation in passive silicon microresonators is approaching feasibility.
\r\n" }, { "name": "Kalyanaraman, Shankar", "degree": "PhD", "year": "2009", "title": "Limited Randomness in Games, and Computational Perspectives in Revealed Preference\r ", "advisor": "Umans, Christopher M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042009-233839", "creators": [ { "name": { "family": "Kalyanaraman", "given": "Shankar" }, "id": "Kalyanaraman-Shankar", "display_name": "Kalyanaraman, Shankar" } ], "advisors": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "advisor", "display_name": "Umans, Christopher M." } ], "committee": [ { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "chair", "display_name": "Umans, Christopher M." }, { "name": { "family": "Echenique", "given": "Federico" }, "id": "Echenique-F", "role": "member", "display_name": "Echenique, Federico" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/KH85-HJ73", "abstract": "In this dissertation, we explore two particular themes in connection with the study of games and general economic interactions: bounded resources and rationality. The rapidly maturing field of algorithmic game theory concerns itself with looking at the computational limits and effects when agents in such an interaction make choices in their \"self-interest.\" The solution concepts that have been studied in this regard, and which we shall focus on in this dissertation, assume that agents are capable of randomizing over their set of choices. We posit that agents are randomness-limited in addition to being computationally bounded, and determine how this affects their equilibrium strategies in different scenarios.
\r\n\r\nIn particular, we study three interpretations of what it means for agents to be randomness-limited, and offer results on finding (approximately) optimal strategies that are randomness-efficient:
\r\n\r\n1. One-shot games with access to the support of the optimal strategies: for this case, our results are obtained by sampling strategies from the optimal support by performing a random walk on an expander graph.
\r\n2. Multiple-round games where agents have no a priori knowledge of their payoffs: we significantly improve the randomness-efficiency of known online algorithms for such games by utilizing distributions based on almost pairwise independent random variables.
\r\n3. Low-rank games: for games in which agents' payoff matrices have low rank, we devise \"fixed-parameter\" algorithms that compute strategies yielding approximately optimal payoffs for agents, and are polynomial-time in the size of the input and the rank of the payoff tensors.
In regard to rationality, we look at some computational questions in a related line of work known as revealed preference theory, with the purpose of understanding the computational limits of inferring agents' payoffs and motives when they reveal their preferences by way of how they act. We investigate two problem settings as applications of this theory and obtain results about their intractability:
\r\n\r\n1. Rationalizability of matchings: we consider the problem of rationalizing a given collection of bipartite matchings and show that it is NP-hard to determine agent preferences for which matchings would be stable. Further, we show, assuming P \u2260 NP, that this problem does not admit polynomial-time approximation schemes under two suitably defined notions of optimization.
\r\n2. Rationalizability of network formation games: in the case of network formation games, we take up a particular model of connections known as the Jackson-Wolinsky model in which nodes in a graph have valuations for each other and take their valuations into consideration when they choose to build edges. We show that under a notion of stability, known as pairwise stability, the problem of finding valuations that rationalize a collection of networks as pairwise stable is NP-hard. More significantly, we show that this problem is hard even to approximate to within a factor 1/2 and that this is tight.
Our results on hardness and inapproximability of these problems use well-known techniques from complexity theory, and particularly in the case of the inapproximability of rationalizing network formation games, PCPs for the problem of satisfying the optimal number of linear equations in positive integers, building on recent results of Guruswami and Raghavendra.
\r\n" }, { "name": "Kayes, Brendan Melville", "degree": "PhD", "year": "2009", "title": "Radial pn Junction, Wire Array Solar Cells", "advisor": "Atwater, Harry Albert; Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222008-173738", "creators": [ { "name": { "family": "Kayes", "given": "Brendan Melville" }, "id": "Kayes-Brendan-Melville", "display_name": "Kayes, Brendan Melville" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "co-chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Yazami", "given": "Rachid" }, "id": "Yazami-R", "role": "member", "display_name": "Yazami, Rachid" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/X9WE-V642", "abstract": "Radial pn junctions are potentially of interest in photovoltaics as a way to decouple light absorption from minority carrier collection. In a traditional planar design these occur in the same dimension, and this sets a lower limit on absorber material quality, as cells must both be thick enough to effectively absorb the solar spectrum while also having minority-carrier diffusion lengths long enough to allow for efficient collection of the photo-generated carriers. Therefore, highly efficient photovoltaic devices currently require highly pure materials and expensive processing techniques, while low cost devices generally operate at relatively low efficiency.
\r\n\r\nThe radial pn junction design sets the direction of light absorption perpendicular to the direction of minority-carrier transport, allowing the cell to be thick enough for effective light absorption, while also providing a short pathway for carrier collection. This is achieved by increasing the junction area, in order to decrease the path length any photogenerated minority carrier must travel, to be less than its minority carrier diffusion length. Realizing this geometry in an array of semiconducting wires, by for example depositing a single-crystalline inorganic semiconducting absorber layer at high deposition rates from the gas phase by the vapor-liquid-solid (VLS) mechanism, allows for a \"bottom up\" approach to device fabrication, which can in principle dramatically reduce the materials costs associated with a cell.
\r\n\r\nThis thesis explores the potential of this design, first theoretically and computationally, and then by exploring the growth of structures with the proposed morphology via methods with the potential for low cost, and finally by the experimental characterization of cells.
\r\n" }, { "name": "Kelly, Alex", "degree": "PhD", "year": "2009", "title": "A Constitutive Relation for Shape-Memory Alloys", "advisor": "Bhattacharya, Kaushik; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09292008-204618", "creators": [ { "name": { "family": "Kelly", "given": "Alex" }, "id": "Kelly-Alex", "display_name": "Kelly, Alex" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "co-advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/YMT5-AX47", "abstract": "The novel nonlinear thermoelastic behavior of shape-memory alloys (SMAs) makes them increasingly desirable as components in many advanced technological applications. In order to incorporate these materials into engineering designs, it is important to develop an understanding of their constitutive response. The purpose of this thesis is to develop a constitutive model of shape-memory polycrystals that is faithful to the underlying micromechanics while remaining simple enough for utility in engineering analysis and design.
\r\n\r\nWe present a model in which the material microstructure is represented macroscopically as a recoverable transformation strain that is constrained by the texture of the polycrystal. The point of departure in this model is the recognition that the mechanics of the onset of martensitic transformation are fundamentally different from those of its saturation. Consequently, the constraint on the set of recoverable strains varies throughout the transformation process. The effects of constraint geometry on the constitutive response of SMAs are studied. Several well known properties of SMAs are demonstrated. Finally the model is simply implemented in a commercial finite-element package as a proof of the concept.
\r\n" }, { "name": "Kislitsyn, Mikhail N.", "degree": "PhD", "year": "2009", "title": "Materials Chemistry of Superprotonic Solid Acids", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282009-034846", "creators": [ { "name": { "family": "Kislitsyn", "given": "Mikhail N." }, "id": "Kislitsyn-Mikhail-N", "display_name": "Kislitsyn, Mikhail N." } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/4JCZ-BE49", "abstract": "Solid acid is a class of materials that shows potential as a fuel cell electrolyte. Understanding the phase and mechanical stability are required for further development of this technology. We addressed both issues in this work.
\r\n\r\nWe expanded the use of the crystallographic theory of the phase transformation to three major classes of solid acids. That allowed us to relate material properties hysteresis to fundamental crystallographic and thermodynamic parameters. The understanding of the mechanism of the transformation can guide the effort to create materials with desired hysteresis. Careful investigation of the thermal and phase behavior of CsHSO\u2084, CsH\u2082PO\u2084, Rb\u2083H(SeO\u2084)\u2082 and in Cs1-xRbxH\u2082PO\u2084 solid solution series for both low and high temperature phases was performed and crystal symmetry and lattice parameters for Cs0.75Rb0.25H\u2082PO\u2084, T=240\u00b0C phase were found for the first time. Consistency between predicted and measured properties was shown for all three different classes of solid acids as well as for the isostructural solid solution series.
\r\n\r\nNanocomposite materials based on cesium hydrogen sulfate and nanometer size silica were characterized. We observed 30-40 nm size surface stabilization of our material at the high temperature phase, otherwise metastable at room temperature. We developed methods to quantitatively study interface phases and its effect on ion mobility. The method allowed us to quantitatively find crystalline and amorphous amounts in the composites. We observed 3-4 order decrease in spin-lattice relaxation values of the metastable phase in the composite. Solid state NMR allowed surface interactions directly and suggest high ion mobility. Strong effect on superprotonic transition temperature in composites was observed. Superprotonic phase was stable in composites at temperatures up to 70\u00b0C below phase transition compared with pure phase CsHSO\u2084.
\r\n\r\nThe mechanism and activation energy of the creep plastic deformation in CsHSO4 were found. Based on that, a method to reduce creep by 1-2 orders of magnitude was developed and creep-resistant material was synthesized.
\r\n" }, { "name": "Kogan, Oleg Boris", "degree": "PhD", "year": "2009", "title": "Stochastic and Collective Properties of Nonlinear Oscillators", "advisor": "Cross, Michael Clifford", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012009-145134", "creators": [ { "name": { "family": "Kogan", "given": "Oleg Boris" }, "id": "Kogan-Oleg-Boris", "display_name": "Kogan, Oleg Boris" } ], "advisors": [ { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "advisor", "display_name": "Cross, Michael Clifford" } ], "committee": [ { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "chair", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/93R8-TJ70", "abstract": "Two systems of nonlinear oscillators are considered: (a) a single periodically driven nonlinear oscillator interacting with a heat bath, which may operate in the regime of bistability or monostability, and (b) a one-dimensional chain of self-sustaining phase oscillators with nearest-neighbor interaction.
\r\n\r\nFor a single oscillator we analyze the scaling crossovers in the thermal activation barrier between the two stable states. The rate of metastable decay in nonequilibrium systems is expected to display scaling behavior: the logarithm of the decay rate should scale as a power of the distance to a bifurcation point where the metastable state disappears. We establish the range where different scaling behavior is displayed and show how the crossover between different types of scaling occurs. Using the instanton method, we map numerically the entire parameter range of bistability and find the regions where the scaling exponents are 1 or 3/2, depending on the damping. The exponent 3/2 is found to extend much further from the bifurcation then where it would be expected to hold as a result of an overdamped soft mode. Additionally, we uncover a new scaling behavior with exponent of \u22481.3 that extends beyond the close vicinity of the bifurcation point.
\r\n\r\nWe also study the pattern of fluctuational trajectories in the monostable regime. For nonequilibrium systems, fluctuational and relaxational trajectories are not simply related by time-reversibility, as is the case in thermal equilibrium. One of the consequences of this is the onset of singularities in the pattern of fluctuational trajectories, where most probable paths to neighboring states are far away from each other. This also creates nonsmoothness in the probability distribution of the system in its phase space. We discover that the pattern of optimal paths in equilibrium systems is fragile with respect to the driving strength F, and investigate how the singularities occur as the system is driven away from equilibrium. As the strength of the driving F approaches zero, the cusp of the spiral caustic system recedes to larger radius R and the angle of the cusp also decreases. The dependence of R on F displays two scaling laws with crossovers, where the scaling exponents depend on the damping.
\r\n\r\nFor the one-dimensional chain of nearest-neighbor coupled phase oscillators, we develop a renormalization group method to investigate synchronization clusters. We apply it numerically to Lorentzian distributions of intrinsic frequencies and couplings and investigate the statistics of the resultant cluster sizes and frequencies. We find that the distributions of sizes of frequency clusters are exponential, with a characteristic length. The dependence of this length upon parameters of these Lorentzian distributions develops an asymptotic power law with an exponent of 0.48 \u00b1 0.02. The findings obtained with the renormalization group are compared with numerical simulations of the equations of motion of the chain, with an excellent agreement in all the aforementioned quantities.
\r\n" }, { "name": "Koos, Erin Crystal", "degree": "PhD", "year": "2009", "title": "Rheological Measurements in Liquid-Solid Flows", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03032009-092653", "creators": [ { "name": { "family": "Koos", "given": "Erin Crystal" }, "id": "Koos-Erin-Crystal", "orcid": "0000-0002-2468-2312", "display_name": "Koos, Erin Crystal" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Zenit Camacho", "given": "Jose Roberto" }, "id": "Zenit-Camacho-J-R", "role": "member", "display_name": "Zenit Camacho, Jose Roberto" } ], "option_major": [ "mecheng" ], "doi": "10.7907/KKTC-B990", "abstract": "This thesis presents experimental measurements of the shear stresses of a fluid-particulate flow at high Reynolds numbers as a function of the volume fraction of solids. From the shear stress measurements an effective viscosity, where the fluid-particulate flow is treated as a single fluid, is determined. This viscosity varies from the fluid viscosity when no solids are present to several orders of magnitude greater than fluid viscosity when the particles near their maximum packing state. It is the primary goal of this thesis to determine how the effective viscosity varies with the volume fraction of solids.
\r\n\r\nA variety of particle sizes, shapes, and densities were obtained through the use of polystyrene, nylon, polyester, styrene acrylonitrile, and glass particles, used in configurations where the fluid density was matched and where the particles were non-neutrally buoyant. The particle sizes and shapes ranged from 3 mm round glass beads to 6.4 mm nylon to polystyrene elliptical cylinders. To properly characterize the effect of volume fraction on the effective viscosity, the random loose- and random close-packed volume fractions were experimentally determined using a counter-top container that mimicked the in situ (concentric cylinder Couette flow rheometer) conditions. These volume fractions depend on the shape of the particles and their size relative to the container.
\r\n\r\nThe effective viscosity for neutrally buoyant particles increases exponentially with volume fraction at fractions less than the random loose-packing. Between the random loose- and random close-packed states, the effective viscosity increases more rapidly with volume fraction and asymptotes to very large values at the close-packed volume fraction. The effective viscosity does not depend on the size or shape of particles beyond the influence these parameters have on the random packing volume fractions.
\r\n\r\nFor non-neutrally buoyant particles, the difference in particle buoyancy requires an additional correction. The volume fraction at the time of the force measurement was recorded for several different ratios of particle-to-fluid density. This volume fraction increases with the shear rate of the Couette flow and decreases with the Archimedes number in a way that when plotted against the Reynolds number over the Archimedes number, these curves collapse onto one master curve. When the local volume fraction is used, the effective viscosity for non-neutrally buoyant particles shows the same dependence on volume fraction as the neutrally buoyant cases.
\r\n\r\nParticle velocities were also measured for both neutrally buoyant and non-neutrally buoyant particles. These particle velocities near the stationary inner wall show evidence for a small region near the walls with few particles. This particle depletion layer was measured directly using the velocity data and indirectly using the difference between the measured effective viscosities for the smooth- and rough-wall configurations. The slip in the smooth wall experiments can significantly affect the measured viscosity, but this deficiency can be corrected using the thickness of the depletion layer to find the actual value for the effective viscosity.
\r\n" }, { "name": "Kramer, Richard Michael Jack", "degree": "PhD", "year": "2009", "title": "Stable High-Order Finite-Difference Interface Schemes with Application to the Richtmyer-Meshkov Instability", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-03132009-095507", "creators": [ { "name": { "family": "Kramer", "given": "Richard Michael Jack" }, "id": "Kramer-Richard-Michael-Jack", "display_name": "Kramer, Richard Michael Jack" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HXGM-DC92", "abstract": "High-order adaptive mesh refinement offers the potential for accurate and efficient resolution of problems in fluid dynamics and other fields where a wide range of length scales is present. A critical requirement for the interface closures used with these methods is stability in the context of hyperbolic systems of partial differential equations.
\r\n\r\nIn this study, a class of energy-stable high-order finite-difference interface closures is presented for grids with step resolution changes in one dimension. Asymptotic stability in time for these schemes is achieved by imposing a summation-by-parts condition on the interface closure, which is thus also nondissipative. Interface closures compatible with interior fourth- and sixth-order explicit, and fourth-order implicit centered schemes are presented. Validation tests include linear and nonlinear problems in one and in two dimensions with tensor-product grid refinement.
\r\n\r\nA second class of stable high-order interface closures is presented for two-dimensional cell-centered grids with patch-refinement and step-changes in resolution. For these grids, coarse and fine nodes are not aligned at the mesh interfaces, resulting in hanging nodes. Stability is achieved by again imposing a summation-by-parts condition, resulting in nondissipative closures, at the cost of accuracy at corner interfaces. Interface stencils for an explicit fourth-order finite-difference scheme are presented for each geometry. Validation tests confirm the stability and accuracy of these closures for linear and nonlinear problems.
\r\n\r\nThe Richtmyer-Meshkov instability is investigated using a novel first-order perturbation of the two-dimensional Navier-Stokes equations about a shock-resolved base flow. The computational domain is efficiently resolved using the one-dimensional fourth-order interface scheme. Results are compared to analytic models of the instability, showing agreement with predicted asymptotic growth rates in the inviscid range, while significant discrepancies are noted in the transient growth phase. Viscous effects are found to be poorly predicted by existing models.
\r\n" }, { "name": "Kramer, Sharlotte Lorraine Bolyard", "degree": "PhD", "year": "2009", "title": "Phase-Shifting Full-Field Interferometric Methods for In-Plane Tensorial Stress Determination for Fracture Studies", "advisor": "Ravichandran, Guruswami; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272009-094456", "creators": [ { "name": { "family": "Kramer", "given": "Sharlotte Lorraine Bolyard" }, "id": "Kramer-Sharlotte-Lorraine-Bolyard", "orcid": "0000-0001-6015-8385", "display_name": "Kramer, Sharlotte Lorraine Bolyard" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M9NV-T722", "abstract": "Anisotropic fracture criteria can be established with understanding of full-field stresses near a crack. The anisotropy of the stresses implies that the full in-plane tensorial stress is required, but current experimental optical techniques only give the sum or difference of principal stresses, motivating development of experimental methods that combines two experimental techniques to determine all of the stress components, such as the proposed hybrid experimental method of phase-shifting photoelasticity and transmission Coherent Gradient Sensing (CGS). This thesis establishes this method for stress determination around cracks in photoelastic materials.
\r\n\r\nThis experimental method first requires a new theory for the use of CGS, a wavefront shearing interferometry technique, for photoelastic materials. The first analysis of transmission wavefront shearing interferometry for photoelastic materials is experimentally demonstrated using CGS in full field for a compressed polycarbonate plate with a side V-shaped notch with good agreement with theoretical data. For the hybrid experimental method, a six-step phase-shifting photoelasticity method determines principal stress directions and the difference of principal stresses, and the transmission CGS method utilizes a standard four-step phase-shifting method to measure the x and y first derivatives of the sum of principal stresses, which are numerically integrated for the sum of principal stresses. The full-field principal stresses may then be separated, followed by the Cartesian and polar coordinate stresses using the principal stress directions and the polar angle. The method is first demonstrated for in-plane tensorial stress determination for a compressed polycarbonate plate with a side V-shaped notch with good comparison to theoretical stress fields. The CGS-photoelasticity experimental method is then applied to determine stresses around Mode I-dominant cracks in Homalite-100. The experimental stress fields have excellent agreement with the full-field 2D asymptotic crack solution using the Mode I and Mode II stress intensity factor values calculated from the experimental data. With this foundation of stress determination around cracks in photoelastic materials and with some future analysis, this experimental method can be extended to determine stresses in anisotropic crystals for fracture studies.
\r\n" }, { "name": "Kresch, Max G.", "degree": "PhD", "year": "2009", "title": "Temperature Dependence of Phonons in Elemental Cubic Metals Studied by Inelastic Scattering of Neutrons and X-Rays", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082008-130722", "creators": [ { "name": { "family": "Kresch", "given": "Max G." }, "id": "Kresch-Max-G", "orcid": "0000-0002-6990-8979", "display_name": "Kresch, Max G." } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "member", "display_name": "Van de Walle, Axel" }, { "name": { "family": "Jackson", "given": "Jennifer M." }, "id": "Jackson-J-M", "role": "member", "display_name": "Jackson, Jennifer M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Sturhahn", "given": "Wolfgang" }, "id": "Sturhahn-W", "role": "member", "display_name": "Sturhahn, Wolfgang" } ], "option_major": [ "matsci" ], "doi": "10.7907/5FYM-3M24", "abstract": "The vibrations of atoms in a crystal (phonons) make up the majority of its entropy (or heat capacity), and these vibrations are typically modeled by simple harmonic oscillators. Deviations from this harmonic oscillator model are responsible for such well known effects as thermal expansion and temperature dependent elastic constants. Other anharmonic effects, such as the temperature dependence of phonon energies and their linewidths, may be less well known, but also significant. Changes in phonon energies can impact the phonon entropy.
\r\n\r\nMeasurements of the phonon spectra of aluminum, lead, nickel, and iron as a function of temperature are presented, and the anharmonic contributions to the entropies of these cubic metals are considered. These contributions are found to be of the same order of magnitude as those from independent electrons (discounting magnetic contributions). Trends in phonons and phonon-related properties of a wider array of face-centered- and body-centered-cubic (FCC & BCC) metals are also considered. The near-neighbor forces, spectral shapes, and anharmonic entropies of the BCC metals are shown to be far more varied than those of the FCC metals, and this is explained in terms of the crystal structures themselves. Finally, given the similarities in the FCC metals, experimental data and molecular dynamics simulations are used to investigate their phonon linewidths. Trends exist, and they imply similarities in the relative strengths of the harmonic and anharmonic forces in the FCC metals.
\r\n" }, { "name": "Kumar, Deepak", "degree": "PhD", "year": "2009", "title": "Experimental Investigations of Magnetohydrodynamic Plasma Jets", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-04092009-163047", "creators": [ { "name": { "family": "Kumar", "given": "Deepak" }, "id": "Kumar-Deepak", "display_name": "Kumar, Deepak" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "chair", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Meier", "given": "David L." }, "id": "Meier-D-L", "role": "member", "display_name": "Meier, David L." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ENZ7-QV92", "abstract": "This thesis primarily focuses on understanding the plasma behavior during the helicity injection stage of a pulsed spheromak experiment. Spheromak formation consists of a series of dynamic steps whereby highly localized plasma near the electrodes evolves toward a Taylor state equilibrium. The dynamical evolution stage has been modeled as a series of equilibrium states in the past. However, the experiments at the Caltech spheromak facility have revealed that unbalanced J x B forces drive non equilibrium Alfv\u00e9nic flows during these preliminary stages.
\r\n\r\nThe Caltech spheromak experiment uses coplanar electrodes to produce a collimated plasma jet flowing away from the electrodes. The jet formation stage precedes the spheromak formation and serves as a mechanism for feeding particles, magnetic helicity, energy, and toroidal flux into the system. Detailed density and flow velocity measurements of hydrogen and deuterium plasma jets have revealed that the jets are extremely dense with \u03b2 [subscript thermal] ~1. Furthermore, the flow velocity was found to be Alfv\u00e9nic with respect to the the toroidal magnetic field produced by the axial current within the plasma. An existing magnetohydrodynamics (MHD) model has been generalized to successfully predict the effect of plasma current on the jet's density and flow velocity. The behavior of these laboratory jets is in stark contrast to the often considered model for astrophysical jets describing them as equilibrium configurations with hollow density profiles.
\r\n\r\nOther contributions of this thesis include the following.
\r\n\r\n1. The thesis presents an analytical proof that resistive MHD equilibrium with closed flux tubes is not feasible. This implies that sustained spheromak experiments cannot maintain helicity while being in a strict equilibrium.
\r\n\r\n2. The thesis describes measurements to characterize the circuit parameters of the high voltage discharge circuit used in the Caltech spheromak experiment.
\r\n\r\n3. The thesis also describes the setup of novel He-Ne laser interferometers used to measure the density of plasma jets. The ease of alignment of these interferometers was greatly enhanced by having unequal path lengths of the scene and reference beams.
\r\n\r\n4. Finally, the thesis details the setup for a soft X-ray (SXR)/Vacuum ultra violet (VUV) imaging system. Some preliminary images of reconnecting flux tubes captured by the imaging setup are also presented.
\r\n" }, { "name": "Kwong, Gabriel Abner", "degree": "PhD", "year": "2009", "title": "DNA Encoded Biotechnologies for Informative Cancer Diagnostics", "advisor": "Heath, James R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022009-172223", "creators": [ { "name": { "family": "Kwong", "given": "Gabriel Abner" }, "id": "Kwong-Gabriel-Abner", "orcid": "0000-0002-6255-6755", "display_name": "Kwong, Gabriel Abner" } ], "advisors": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "advisor", "display_name": "Heath, James R." } ], "committee": [ { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "chair", "display_name": "Heath, James R." }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" }, { "name": { "family": "Bjorkman", "given": "Pamela J." }, "id": "Bjorkman-P-J", "role": "member", "display_name": "Bjorkman, Pamela J." }, { "name": { "family": "Mazmanian", "given": "Sarkis K." }, "id": "Mazmanian-S-K", "role": "member", "display_name": "Mazmanian, Sarkis K." } ], "option_major": [ "bioeng" ], "doi": "10.7907/AXMP-AM12", "abstract": "This thesis describes the development of DNA-encoded, multi-parametric, sensing platforms for informative cancer diagnostics. In the first part of this thesis, I will present a technology called \u201cDNA-encoded antibody library (DEAL).\u201d In this approach, computationally derived, orthogonal ssDNA sequences are conjugated to antibodies specific for protein targets and cell surface markers. The resulting collection of conjugates is applied to a biological sample of interest, binds to their cognate antigens, and is detected after the complexes are hybridized to a glass substrate printed with spatially distinct complementary DNA sequences. By using DNA assembly, the DEAL platform enables the simultaneous detection of the major classes of biological molecules, namely nucleic acids, proteins and cells.
\r\n\r\nThe second part of this thesis focuses on the development of a cell sorting platform that can detect antigen-specific T cells called \u201cNucleic Acid Cell Sorting (NACS).\u201d In NACS, ssDNA encoding is used to assemble peptide major histocompatability complexes (p/MHC) on glass substrates by hybridization to cDNA microarrays. These assembled peptide/MHC microarrays are then used to sort mixed populations of antigen-specific T cells. This spatially encoded scheme addresses the widespread desire for methods that allow the multiplexed detection of antigen-specific T cells. The sensitivity and selectivity of NACS is similar to flow cytometry, demonstrated in key experiments with T cells derived from multiple sources, including endogenous and TCR-engineered T cells collected from cancer patients. Finally, this platform is used to monitor the persistence of cancer-specific T cells in peripheral blood collected from a patient undergoing T cellular immunotherapy.
\r\n\r\nLastly, a scheme for the detection of cell surface markers is presented. In this approach, DEAL and NACS conjugates prepared with UV labile ssDNA oligonucleotides are allowed to bind to target cell samples in solution. The ssDNA tags are released in solution by UV-induced photocleavage. The presence and expression of the cognate antigen is determined by collecting the pool of reporter ssDNA tags followed by exponential amplification by PCR. A DEAL conjugate specific for the oncogene EGFR was used to determine the expression level of EGFR in a low-passage brain tumor primary cell line. The feasibility of using ssDNA-p/MHC complexes for detecting unique TCRs was also demonstrated. Finally an experimental flow is described for integration with second generational high-throughput sequencing platforms for global and quantitative surface-ome profiling.
\r\n" }, { "name": "Leong, Peter Anthony", "degree": "PhD", "year": "2009", "title": "Computational Challenges in High-Resolution Cryo-Electron Microscopy", "advisor": "Jensen, Grant J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08072008-171049", "creators": [ { "name": { "family": "Leong", "given": "Peter Anthony" }, "id": "Leong-Peter-Anthony", "display_name": "Leong, Peter Anthony" } ], "advisors": [ { "name": { "family": "Jensen", "given": "Grant J." }, "id": "Jensen-G-J", "orcid": "0000-0003-1556-4864", "role": "advisor", "display_name": "Jensen, Grant J." } ], "committee": [ { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "chair", "display_name": "Fraser, Scott E." }, { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "orcid": "0000-0003-4073-1185", "role": "member", "display_name": "Rees, Douglas C." }, { "name": { "family": "Jensen", "given": "Grant J." }, "id": "Jensen-G-J", "orcid": "0000-0003-1556-4864", "role": "member", "display_name": "Jensen, Grant J." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Zhou", "given": "Z. Hong" }, "id": "Zhou-Z-Hong", "role": "member", "display_name": "Zhou, Z. Hong" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/GJKS-2P80", "abstract": "To avoid the challenges of crystallization and the size limitations of NMR, it has long been hoped that single-particle cryo-electron microscopy (cryo-EM) would eventually yield atomically interpretable reconstructions. For the most favorable class of specimens (large icosahedral viruses), two of the key obstacles are the large computational requirements of high-resolution reconstructions and the curvature of the Ewald sphere, which leads to a breakdown of the projection theorem used by conventional 3D reconstruction programs. Here, two solutions to these obstacles are presented.
\r\n\r\nFirst, a simple distributed processing system named Peach was developed to meet the rising computational demands of modern structural biology (and other) laboratories without additional expense by using existing hardware resources more efficiently. A central server distributes jobs to idle workstations in such a way that each computer is used maximally, but without disturbing intermittent interactive users. As compared to other distributed systems, Peach is simple, easy to install, easy to administer, easy to use, scalable, and robust. While it was designed to queue and distribute large numbers of small tasks to participating computers, it can also be used to send single jobs automatically to the fastest currently available computer and/or survey the activity of an entire laboratory's computers. Tests of robustness and scalability are reported, as are three specific cryo-EM applications where Peach enabled projects that would not otherwise have been feasible without an expensive, dedicated cluster.
\r\n\r\nSecond, an iterative refinement reconstruction algorithm, Prec, is described that overcomes the curvature of the Ewald sphere resolution limitation by averaging information from images recorded from different points of view, as are present in typical micrographs. Prec was implemented in the popular software packages IMIRS, EMAN, and Bsoft. In preliminary tests with both simple and multi-slice simulated images, Prec overcame the curvature problem even in the presence of noise. Prec was then used to refine the three recently published, ~ 4 \u00c5 resolution, icosahedral virus reconstructions from experimental cryo-EM images, but unfortunately no significant improvements in resolution were realized. Further simulations showed that limitations other than the Ewald sphere curvature problem must still be dominant in these experimental studies.
\r\n" }, { "name": "Li, Bo", "degree": "PhD", "year": "2009", "title": "The Optimal Transportation Method in Solid Mechanics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212009-173044", "creators": [ { "name": { "family": "Li", "given": "Bo" }, "id": "Li-Bo", "orcid": "0000-0002-0127-8210", "display_name": "Li, Bo" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FAT3-0247", "abstract": "This dissertation is concerned with the development of a robust and efficient meshless method, the Optimal Transportation Method (OTM), for general solid flows involving extremely large deformation, fast, transient loading and hydrodynamic phenomena. This method is a Lagrangian particle method through an integration of optimal transportation theory with meshless interpolation and material point integrations. The theoretical framework developed in this thesis generalized the Benamou-Brenier differential formulation of optimal transportation problems and leads to a multi-field variational characterization of solid flows, including elasticity, inelasticity, equation of state, and general geometries and boundary conditions. To this end, the accuracy, robustness and versatility of OTM is assessed and demonstrated with convergence and stability test, Taylor anvil test and a series of full three-dimensional simulations of high/hyper-velocity impact examples with the aid of a novel meshless dynamic contact algorithm presented in this thesis.\r\n" }, { "name": "Li, John Jian-Zhong", "degree": "PhD", "year": "2009", "title": "Study of Liquid Metals by Electrostatic Levitation", "advisor": "Johnson, William Lewis; Rhim, Won-Kyu", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012009-162039", "creators": [ { "name": { "family": "Li", "given": "John Jian-Zhong" }, "id": "Li-John-Jian-Zhong", "display_name": "Li, John Jian-Zhong" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rhim", "given": "Won-Kyu" }, "id": "Rhim-W", "role": "co-advisor", "display_name": "Rhim, Won-Kyu" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "co-chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Rhim", "given": "Won-Kyu" }, "id": "Rhim-Won-Kyu", "role": "member", "display_name": "Rhim, Won-Kyu" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/JY7J-Q837", "abstract": "With the development of bulk metallic glasses (BMG) in recent years, more and more scientists in solid state physics are trying to understand the mechanism of glass-formation in terms of thermodynamics and kinetics, while engineers in metallurgy are trying different compositions and processes to improve the mechanical properties of BMGs and their composites.
\r\n\r\nGlasses are nothing but frozen liquids. So far most of the studies of metallic glasses have been below the glass transition temperature because molten metallic liquids are chemically reactive with the container walls. For this reason, we used the Electrostatic Levitation (ESL) method that was developed by Dr. Won-Kyu Rhim.
\r\n\r\nIn this thesis, the instrumentation of the ESL is described. Discussion on the advantages and disadvantages of ESL is given by comparing with the other levitation methods. Because of the advantage in sample position stability over all the other levitation methods, the ESL facility at Caltech is uniquely capable of measuring the viscosity and thermophysical properties of liquid metals in the undercooled temperature range. The ESL was further improved at Caltech to reduce temperature gradients on a sample and increase the stability of the sample positioning with a tetrahedral laser heating system.
\r\n\r\nUsing such an improved ESL, thermophysical properties of some evaporative metallic liquids such as Ti and silicon-germanium alloys have been successfully studied and mass loss as well as composition changes could be accounted for.
\r\n\r\nSeveral BMGs developed at Johnson group at Caltech have been studied using ESL. Among the liquid thermodynamics and kinetic properties of interest, special attention has been paid on to measurements of the TTT curve, viscosity, and volume changes with temperature. These data give useful insight on the glass-forming mechanism. Through these studies, guidelines in the search for good ductile metallic glass-formers have emerged. Discussing these guidelines is an important part of this thesis.
\r\n\r\nFinally, we discuss an investigation to understand observed hysteresis in the viscosity and the so-called threshold temperature that has been observed in some of the best glass-forming metallic liquids. We conclude this investigation with a hypothesis of a liquid-to-liquid phase transition that occurs above liquidus temperatures in several systems that we have studied.
\r\n" }, { "name": "Li, Wen", "degree": "PhD", "year": "2009", "title": "Integrated Retinal Implants", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-02162009-095558", "creators": [ { "name": { "family": "Li", "given": "Wen" }, "id": "Li-Wen", "display_name": "Li, Wen" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Weiland", "given": "James D." }, "id": "Weiland-J-D", "role": "member", "display_name": "Weiland, James D." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "eleceng" ], "doi": "10.7907/AMK6-TA42", "abstract": "Integrated wireless implants have always been the ultimate goal for neural prostheses. However, technologies are still in development and few have actually been transferred to clinical practice due to constraints in material biocompatibility, device miniaturization and flexibility. In this dissertation, emphasis is placed on the development of Parylene devices for neural prostheses, and particularly, for retinal prostheses that partially restore lost vision for patients suffering from outer retina degeneration.
\r\n\r\nA basic Parylene-metal-Parylene skin technology for making planar Parylene micro-electro-mechanical systems (MEMS) devices, such as electrode arrays and radio-frequency (RF) coil, is first discussed, followed by accelerated lifetime soaking tests to investigate the long term stability of such skins in hot saline under both passive and active electrical stressing. Discussion is further expanded on a detailed description of the design, fabrication, and testing procedure of two types of MEMS coils, which serve as receiver coils for wireless power and data transfer in a retinal implant system. After that, an embedded chip integration technology is presented, which allows the integration of complementary metal-oxide-semiconductor (CMOS) integrated circuit (IC) chips with other MEMS devices and discrete components so as to achieve high-level system functionality. Finally, an integrated wireless neural stimulator is designed and successfully fabricated using a test chip.
\r\n" }, { "name": "Li, Zhiyi", "degree": "PhD", "year": "2009", "title": "High-Order Solution of Elliptic Partial Differential Equations in Domains Containing Conical Singularities", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08042008-005339", "creators": [ { "name": { "family": "Li", "given": "Zhiyi" }, "id": "Li-Zhiyi", "display_name": "Li, Zhiyi" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/VEEB-AV75", "abstract": "In this thesis we introduce an algorithm, based on the boundary integral equation method, for the numerical evaluation of singular solutions of the Laplace equation in three dimensional space, with singularities induced by a conical point on an otherwise smooth boundary surface. This is a model version of a fundamental problem in science and engineering: accurate evaluation of solutions of Partial Differential Equations in domains whose boundaries contain geometric singularities. For simplicity we assume a small region near the conical point coincides with a straight cone of given cross section; otherwise the boundary surface is not restricted in any way. Our numerical results demonstrate excellent convergence as discretizations are refined, even at the singular point where the solutions tend to infinity." }, { "name": "Liu, Yi", "degree": "PhD", "year": "2009", "title": "Three-Dimensional Elastodynamic Modeling of Frictional Sliding with Application to Intersonic Transition", "advisor": "Lapusta, Nadia", "url": "https://resolver.caltech.edu/CaltechETD:etd-02142009-181805", "creators": [ { "name": { "family": "Liu", "given": "Yi" }, "id": "Liu-Yi", "display_name": "Liu, Yi" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "advisor", "display_name": "Lapusta, Nadia" } ], "committee": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "chair", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "role": "member", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/JWCV-8V74", "abstract": "Spontaneous slip on frictional interfaces involves both short-lived inertially-driven events and long-term quasi-static sliding. An example of considerable practical importance is the response of faults in the Earth's crust to tectonic loading. The response combines earthquakes that cause destructive ground motions and aseismic slip. Numerical models are needed to study the physics and mechanics of such complex behavior. In part, the models can help understand the observed slip patterns and interpret them in terms of constitutive properties of rocks determined in the lab.
\r\n\r\nThis thesis contains two main contributions. The first one is the development and implementation of a 3D methodology for simulations of spontaneous long-term interface slip punctuated by rapid inertially driven ruptures. Our approach is the first one to combine long-term deformation histories and the resulting stress redistribution on faults with full inclusion of inertial effects during simulated earthquakes in the context of 3D models. It reproduces all stages of earthquake cycles, from accelerating slip before dynamic instability, to rapid inertially driven propagation of earthquake rupture, to post-seismic slip, and to interseismic creep, including aseismic transients. The second main contribution is the discovery of the potentially dominating effect of favorable heterogeneity on intersonic transition in earthquakes, in both 2D models of single dynamic ruptures and 3D models of long-term fault slip. Studies of intersonic ruptures are practically important as they have the potential to cause strong ground motion farther from the fault than subsonic ruptures. Our conclusion that rheological boundaries promote transition to intersonic speeds in 3D rupture models is completely unexpected, as the neighboring stably slipping regions inhibit fast, inertially driven slip. The result could not be established in earlier studies, as it requires the computational methodology developed here that combines inertial effects, long-term slip histories, and 3D fault models. The thesis also develops test problems for dynamic rupture propagation and evaluates simplified quasi-dynamic approaches.
\r\n\r\nThe obtained results emphasize that dynamic ruptures should be considered in the context of the entire slip history of the fault, as such approach allows dynamic ruptures to occur under stress conditions established by prior slip, which leads to characteristic stress distributions that are not considered in single-event simulations. The developed 3D methodology can be applied to a number of problems in earthquake physics and mechanics that involve interaction of seismic and aseismic slip.
\r\n" }, { "name": "Lo, Hsi-Wen", "degree": "PhD", "year": "2009", "title": "Thin Film Silicon for Implantable Electronics", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-09242008-151715", "creators": [ { "name": { "family": "Lo", "given": "Hsi-Wen" }, "id": "Lo-Hsi-Wen", "display_name": "Lo, Hsi-Wen" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Meng", "given": "Ellis" }, "id": "Meng E-F-C", "role": "member", "display_name": "Meng, Ellis" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/DBDE-PQ14", "abstract": "The implantable electronic systems have changed our life greatly and provided crucial support for people who previously could not live an independent life otherwise. However, current implantable electronic systems are based on technologies more than 50 years old and more medical problems require advanced implantable electronic systems with small form factors and multiple electrodes. This work explores and evaluates possible alternatives of implantable electronic systems.
\r\n\r\nParylene, a widely used MEMS/CMOS process compatible material, is the cornerstone of this work. Parylene has been an ISO10933 and USP Class VI certi\ufb01ed biocompatible material. Parylene serves as the substrate and protective coating of the implantable electronic systems developed in this work.
\r\n\r\nThin \ufb01lm pentacene is studied in this work and thin \ufb01lm pentacene transistors are developed. The thin \ufb01lm pentacene transistor uses Parylene as the \ufb02exible substrate, the gate insulator and the protective coating. Studies of parylene surface are carried out. And based on this study, pentacene hole mobility is improved using spin-cast smoothing layers and top-contact con\ufb01gurations. To evaluate the long term reliability and stability of the thin \ufb01lm pentacene transistors, saline soaking tests are performed. The results are less than satisfactory.
\r\n\r\nIn addition, thin \ufb01lm amorphous silicon is studied and thin \ufb01lm amorphous silicon transistors are developed. This thin-\ufb01lm amorphous silicon uses Parylene HT\u00ae, a Parylene variant with high temperature stability, as the \ufb02exible substrate. To evaluate the long term reliability and stability of the thin \ufb01lm amorphous silicon transistor, room temperature saline soaking tests and 80\u25e6 C accelerated saline soaking tests are carried out. The thin \ufb01lm amorphous silicon transistors show excellent stability in saline soaking. The thin \ufb01lm amorphous silicon transitor shows no degradations after more than 90 days in 80\u25e6 C saline solution.
\r\n\r\nIn summary, thin \ufb01lm pentacene transistors and thin \ufb01lm amorphous silicon transistors are developed and their performances are optimized. The long-term stability and reliability of these transistors are evaluated via saline soaking tests. While thin \ufb01lm pentacene transistors show only less than satisfactory results, thin \ufb01lm amorphous silicon transistors exhibit stable and reliable performances.
" }, { "name": "Lu, Xiao", "degree": "PhD", "year": "2009", "title": "Combined Experimental and Numerical Study of Spontaneous Dynamic Rupture on Frictional Interfaces", "advisor": "Lapusta, Nadia; Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242008-070701", "creators": [ { "name": { "family": "Lu", "given": "Xiao" }, "id": "Lu-Xiao", "display_name": "Lu, Xiao" } ], "advisors": [ { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "advisor", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "role": "member", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BGGT-MC04", "abstract": "The process of spontaneous dynamic frictional sliding along the interface of two elastic solids is of great interest to a number of disciplines in engineering and sciences. Applications include frictional rupture processes in earthquakes, delamination of layered composite materials, and sliding between soft membranes in biological systems. The transient nature of rupture dynamics presents an array of fascinating yet challenging questions, including the nucleation process, the mechanism of interface failure, and the speed and mode of rupture propagation.
\r\n\r\nThis thesis presents such a combined experimental and theoretical study aimed at understanding the conditions for selecting pulse-like vs. crack-like rupture modes and subshear vs. supershear rupture speeds. There are two major contributions in this work. The first one is high-resolution experimental study of the rupture modes on a frictional interface. The study presents first experimental observations of spontaneous pulse-like ruptures in a homogeneous linear-elastic setting that mimics crustal earthquakes, reveals how different rupture modes are selected based on the level of fault prestress, demonstrates that both rupture modes can transition to supershear speeds, and advocates, based on comparison with theoretical studies, importance of velocity-weakening friction for earthquake dynamics. The second major contribution is the numerical modeling of the rupture experiments that reveal the importance of the rupture nucleation mechanism and friction formulations. The modeling of sub-Rayleigh to supershear transition has demonstrated the influence of rupture nucleation mechanism on supershear transition distance, as well as on the mechanism of supershear transition. The modeling of pulse-like to crack-like rupture mode transition has confirmed the necessity of velocity weakening friction for producing pulse-like rupture to match the experimental observations.
\r\n" }, { "name": "Lucas, Leonard Joseph", "degree": "PhD", "year": "2009", "title": "Uncertainty Quantification Using Concentration-of-Measure Inequalities", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292009-165215", "creators": [ { "name": { "family": "Lucas", "given": "Leonard Joseph" }, "id": "Lucas-Leonard-Joseph", "display_name": "Lucas, Leonard Joseph" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "mecheng" ], "doi": "10.7907/DRAM-H941", "abstract": "This work introduces a rigorous uncertainty quantification framework that exploits concentration\u2013of\u2013measure inequalities to bound failure probabilities using a well-defined certification campaign regarding the performance of engineering systems. The framework is constructed to be used as a tool for deciding whether a system is likely to perform safely and reliably within design specifications. Concentration-of-measure inequalities rigorously bound probabilities-of-failure and thus supply conservative certification criteria, in addition to supplying unambiguous quantitative definitions of terms such as margins, epistemic and aleatoric uncertainties, verification and validation measures, and confidence factors. This methodology unveils clear procedures for computing the latter quantities by means of concerted simulation and experimental campaigns. Extensions to the theory include hierarchical uncertainty quantification, and validation with experimentally uncontrollable random variables." }, { "name": "Lucas, Matthew Steven", "degree": "PhD", "year": "2009", "title": "Cluster Expansion Applied to Inelastic Scattering Experiments", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062008-221948", "creators": [ { "name": { "family": "Lucas", "given": "Matthew Steven" }, "id": "Lucas-Matthew-Steven", "display_name": "Lucas, Matthew Steven" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Halevy", "given": "Itzhak" }, "id": "Halevy-I", "role": "member", "display_name": "Halevy, Itzhak" }, { "name": { "family": "Jackson", "given": "Jennifer M." }, "id": "Jackson-J-M", "role": "member", "display_name": "Jackson, Jennifer M." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Sturhahn", "given": "Wolfgang" }, "id": "Sturhahn-W", "role": "member", "display_name": "Sturhahn, Wolfgang" } ], "option_major": [ "matsci" ], "doi": "10.7907/8SX7-KG02", "abstract": "In this thesis the cluster inversion method of Connolly and Williams is performed on measurements of properties of random solid solutions. This is possible when the number of terms required for the expansion is small. The interaction parameters are extended to interaction functions, which become physically significant when only a few terms are required. The focus of this thesis is on the phonon density of states (DOS), which is determined from the results of inelastic scattering experiments. Nuclear resonant inelastic X-ray scattering (NRIXS) is utilized to probe the phonon modes of 57Fe atoms in binary body-centered cubic alloys of Fe-V, Fe-Cr, and Fe-Co. Alloying with 3d series atoms causes a softening of the Fe phonon partial density of states (PDOS) curves with decreasing average atomic number.
\r\n\r\nFor Fe-Cr, the interaction phonon partial density of states (IPDOS) functions obtained from the disordered alloys up to a combined first- and second-nearest-neighbor triangle cluster were successful in reconstructing the 57Fe PDOS curves of thin-film multilayer samples. To obtain the phonon properties of the Cr atoms, inelastic neutron scattering spectra were measured on disordered solid solutions of BCC Fe-Cr alloys. These data were reduced from time-of-flight histograms to energy spectra that resemble the DOS, but were distorted by differences in efficiencies of the atom species for phonon scattering. Cluster expansion formalisms were developed to both correct for this neutron weighting problem, and to isolate the PDOS of Fe and Cr atoms. An asymmetry in the phonon entropy of mixing was identified, and attributed to the larger number of low-energy modes associated with like and unlike pairs in the first- and second-nearest-neighbor shells of Cr atoms, compared to Fe atoms.
\r\n\r\nThe results of inelastic neutron scattering on Cu-Au are re-analyzed with the cluster expansion technique. The neutron weight correction changes both the magnitude and sign of the phonon entropy of mixing. Although a low number of terms works very well for the low-energy modes, the optical modes are poorly treated. The failure of the cluster expansion to reproduce the optical phonon modes in the ordered Cu3Au sample indicates a much higher dependence on the local chemical arrangement.
\r\n" }, { "name": "Lyon, Mark Edward", "degree": "PhD", "year": "2009", "title": "High-Order Unconditionally-Stable FC-AD PDE Solvers for General Domains", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07312008-102751", "creators": [ { "name": { "family": "Lyon", "given": "Mark Edward" }, "id": "Lyon-Mark-Edward", "display_name": "Lyon, Mark Edward" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "orcid": "0009-0007-5991-2863", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/3FFW-GK56", "abstract": "A new methodology is introduced for the numerical solution of Partial Differential Equations in general spatial domains. The methodology is based on the use of the well-known Alternating Direction Implicit (ADI) approach of Peaceman and Rachford in conjunction with one-dimensional and high-order accurate Fourier representations of non-periodic data, obtained by way of a certain \"continuation method\" introduced recently for the resolution of the Gibbs phenomenon. We construct a number of high-order convergent PDE solvers on the basis of this strategy. Unlike previous alternating direction methods for general domains of order higher than one, the new algorithms possess the desirable property of unconditional stability for general spatial domains; the computational time required for these methods to advance one time-step, in turn, grows in an essentially linear manner with the number of spatial discretization points. In particular, the new methodology yields significant advantages over traditional low-order methods for computations involving wave propagation and \"large domains,\" as well as PDEs including diffusive terms. In all, we treat Dirichlet problems for the Heat Equation, the Poisson Equation, and the Wave Equation in two- and three-dimensional spatial domains with smooth boundaries. A stability analysis we present hinges upon the numerical evaluation of certain singular value decompositions. Numerical results arising from the implementations of two- and three-dimensional versions of the method for linear parabolic, hyperbolic and elliptic PDEs, exhibit unconditional stability and high-order convergence, in agreement with our theoretical results.\r\n" }, { "name": "Matsuda, Yuki", "degree": "PhD", "year": "2009", "title": "Ab Initio Quantum Mechanical Studies in Electronic and Structural Properties of Carbon Nanotubes and Silicon Nanowires", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-07222008-023323", "creators": [ { "name": { "family": "Matsuda", "given": "Yuki" }, "id": "Matsuda-Yuki", "display_name": "Matsuda, Yuki" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "role": "member", "display_name": "Heath, James R." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/7FXD-ZQ68", "abstract": "This dissertation focuses on ab-initio quantum mechanical calculations of nanoelectronics in three research topics: contact resistance properties of carbon nanotubes and graphenes (Chapters 1 through 3), electrical properties of carbon nanotubes (Chapter 4) and silicon nanowires (Chapter 5). Through all the chapters, the aim of the research is to provide useful guidelines for experimentalists.
\r\n\r\nChapter 1 presents the contact resistance of metal electrode\u2212carbon nanotube and metal electrode\u2212graphene interfaces for various deposited metals, based on first-principles quantum mechanical density functional and matrix Green\u2019s function methods. Chapters 2 and 3 describe inventive ways to enhance contact resistance properties as well as mechanical stabilities using \u201cmolecular anchors\u201d (Chapter 2) or using \"end-contacted\" (or end-on) electrodes (Chapter 3). Chapters 1 through 3 also provide useful guidelines for nanotube assembly process which is one of the main obstacles in nanoelectronics. Chapter 4 shows accurate and detailed band structure properties of single-walled carbon nanotubes using B3LYP hybrid functional, which are critical parameters in determining the electronic properties such as small band gaps (~0.1 eV) and effective masses. Chapter 5 details both structural and electronic properties of silicon nanowires. These results lead to the findings controlling the diameter and surface coverage by adsorbates (e.g., hydrogen) of silicon nanowires can be effectively used to optimize their properties for various applications.
\r\n\r\nAll the theoretical results are compared with other theoretical studies and experimental data. Notably, electronic studies using B3LYP show excellent agreement with experimental studies quantitatively, which previous quantum mechanical calculations had failed.
\r\n\r\nThese studies show how quantum mechanical predictions of complex phenomena can be effectively investigated computationally in nanomaterials and nanodevices. Given the difficulty, expense, and time required for experiments, theory may now be useful for high-throughout screening to identify the best conditions and materials before performing experiments.
\r\n" }, { "name": "Michael, Christopher Paul", "degree": "PhD", "year": "2009", "title": "Optical Material Characterization Using Microdisk Cavities", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282009-103510", "creators": [ { "name": { "family": "Michael", "given": "Christopher Paul" }, "id": "Michael-Christopher-Paul", "display_name": "Michael, Christopher Paul" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Eisenstein", "given": "James P." }, "id": "Eisenstein-J-P", "role": "member", "display_name": "Eisenstein, James P." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/G2P2-DY72", "abstract": "Since Jack Kilby recorded his \"Monolithic Idea\" for integrated circuits in 1958, microelectronics companies have invested billions of dollars in developing the silicon material system to increase performance and reduce cost. For decades, the industry has made Moore\u2019s Law, concerning cost and transistor density, a self-fulfilling prophecy by integrating technical and material requirements vertically down their supply chains and horizontally across competitors in the market. At recent technology nodes, the unacceptable scaling behavior of copper interconnects has become a major design constraint by increasing latency and power consumption\u2014more than 50% of the power consumed by high speed processors is dissipated by intrachip communications. Optical networks at the chip scale are a potential low-power high-bandwidth replacement for conventional global interconnects, but the lack of efficient on-chip optical sources has remained an outstanding problem despite significant advances in silicon optoelectronics. Many material systems are being researched, but there is no ideal candidate even though the established infrastructure strongly favors a CMOS-compatible solution.
\r\n\r\nThis thesis focuses on assessing the optical properties of materials using microdisk cavities with the intention to advance processing techniques and materials relevant to silicon photonics. Low-loss microdisk resonators are chosen because of their simplicity and long optical path lengths. A localized photonic probe is developed and characterized that employs a tapered optical-fiber waveguide, and it is utilized in practical demonstrations to test tightly arranged devices and to help prototype new fabrication methods. A case study in AlxGa1\u2212xAs illustrates how the optical scattering and absorption losses can be obtained from the cavity-waveguide transmission. Finally, single-crystal Er2O3 epitaxially grown on silicon is analyzed in detail as a potential CMOS-compatable gain medium due to its high Er3+ density and the control offered by the precise epitaxy. The growth and fabrication methods are discussed. Spectral measurements at cryogenic and room temperatures show negligible background losses and resonant Er3+ absorption strong enough to produce cavity-polaritons that persist to above 361 K. Cooperative relaxation and upconversion limit the optical performance in the telecommunications bands by transferring the excitations to quenching sites or by further exciting the ions up to visible transitions. Future prospects and alternative applications for Er2O3 and other epitaxial rare-earth oxides are also considered.
\r\n" }, { "name": "Mitchell, Marcus Quintana", "degree": "PhD", "year": "2009", "title": "Dynamic Simulation and Control of Articulated Limbs", "advisor": "Hopfield, John J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02162009-054828", "creators": [ { "name": { "family": "Mitchell", "given": "Marcus Quintana" }, "id": "Mitchell-Marcus-Quintana", "display_name": "Mitchell, Marcus Quintana" } ], "advisors": [ { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "advisor", "display_name": "Hopfield, John J." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." } ], "option_major": [ "cns" ], "doi": "10.7907/2FAM-6A26", "abstract": "Many useful mechanisms can be modelled as articulated systems: collections of rigid bodies linked together with joints that constrain relative movement. The two parts of this thesis study the complementary problems of simulation and control for such systems. In the first part, we describe an implementation and extension of a physically based modelling framework known as \"dynamic constraints\" in which forces of constraint linking bodies in an articulated system are explicitly calculated. In addition to identifying some important robustness and stability issues for these calculations, we extend the framework to systems whose internal degrees of freedom can be directly parameterized. This permits significant efficiency gains for mechanisms which model limbs. The second part of the thesis centers on the adaptive control of limb configuration through simulated actuators. In this problem, the nonlinear structure and parametric details of a limb are assumed to be unknown. We present and illustrate the performance of an adaptive scheme which performs considerably better than conventional nonadaptive techniques, and which is competitive with adaptive methods which use more a priori knowledge of limb dynamics. " }, { "name": "Ostby, Eric Paul", "degree": "PhD", "year": "2009", "title": "Photonic Whispering-Gallery Resonators in New Environments", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292009-172708", "creators": [ { "name": { "family": "Ostby", "given": "Eric Paul" }, "id": "Ostby-Eric-Paul", "display_name": "Ostby, Eric Paul" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ER2J-WT93", "abstract": "Optical whispering-gallery devices, like the microtoroid or microdisk, confine light at resonant frequencies and in ultra-small volumes for long periods of time. Such ultra-low loss resonators have been applied in diverse areas of scientific research, including low-threshold lasers on-chip, biological sensing, and quantum computing. In this thesis, novel ultra-low loss microstructures are studied for their unique characteristics and utility. The author investigates the interaction between microcavities and various environments in order to quantify the results and lay the foundation for future applications.
\r\n\r\nThe first optical cavity studied is the microtoroid, which possesses ultra-high quality factor (Q) on account of its nearly atomic smooth surface, produced by surface-tension induced laser reflow. Ytterbium-doped silica microtoroids are fabricated by a sol-gel technique. The ytterbium microtoroid laser achieves record-low laser threshold (2 \u00b5W) in air, and produces the first laser output for a solid-state laser in water. This laser in water can be developed as an ultra-sensitive biological sensor, with potentially record sensitivity enabled by gain-narrowed linewidth. Also, a novel CO2 laser reflow and microtoroid testing vacuum system is demonstrated. Fabrication and testing of microtoroids is performed in a vacuum chamber to study the effect of atmospheric water and upper limit of Q in microtoroids.
\r\n\r\nThe selective reflow of microtoroids presents difficulties for integration of on-chip optical waveguides. As an alternative, dimension-preserving low-loss optical structures are researched for their unique applications. A gold-coated silica microdisk is fabricated, and demonstrates record and nearly-ideal quality factor (1,376) as a surface-plasmon polariton resonator. The hybrid optical-plasmonic mode structure is studied in simulation and experiment. The plasmonic resonator has ultra-low mode volume and high field confinement, making it suitable for short-range optical communication or sensing. Finally, a novel whispering-gallery optical delay line in a spiral geometry is designed and experimentally demonstrated. The center transition region of the spiral is optimized for low transmission loss by beam propagation simulation. A 1.4 m long spiral waveguide within a 1 cm^2 area is presented. The spiral waveguide structure is being developed as a real-time optical delay line with fiber-like loss, important for optical communication and signal processing.
" }, { "name": "Othmer, Jonathan Andrew", "degree": "PhD", "year": "2009", "title": "Algorithms for Mapping Nucleic Acid Free Energy Landscapes", "advisor": "Pierce, Niles A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12312008-153810", "creators": [ { "name": { "family": "Othmer", "given": "Jonathan Andrew" }, "id": "Othmer-Jonathan-Andrew", "display_name": "Othmer, Jonathan Andrew" } ], "advisors": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "advisor", "display_name": "Pierce, Niles A." } ], "committee": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "chair", "display_name": "Pierce, Niles A." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/VJX1-6376", "abstract": "To complement the utility of thermodynamic calculations in the design and analysis of nucleic acid secondary structures, we seek to develop efficient and scalable algorithms for the analysis of secondary structure kinetics. Secondary structure kinetics are modeled by a first-order master equation, but the number of secondary structures for a sequence grows exponentially with the length of the sequence, meaning that for systems of interest, we cannot write down the rate matrix, much less solve the master equation. To address these difficulties, we develop a method to construct macrostate maps of nucleic acid free energy landscapes based on simulating the continuous-time Markov chain associated with the microstate master equation. The method relies on the careful combination of several elements: a novel procedure to explicitly identify transitions between macrostates in the simulation, a goodness-of-clustering test specific to secondary structures, an algorithm to find the centroid secondary structure for each macrostate, a method to compute macrostate partition functions from short simulations, and a framework for computing transition rates with confidence intervals. We use this method to study several experimental systems from our laboratory with system sizes in the hundreds of nucleotides, and develop a model problem, the d-cube, for which we can control all of the relevant parameters and analyze our method's error behavior. Our results and analysis suggest that this method will be useful not only in the analysis and design of nucleic acid mechanical devices, but also in wider applications of molecular simulation and simulation-based model reduction." }, { "name": "Perahia, Raviv", "degree": "PhD", "year": "2009", "title": "Investigation and Application of Microscale Semiconductor Lasers and Cavities", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06052009-131714", "creators": [ { "name": { "family": "Perahia", "given": "Raviv" }, "id": "Perahia-Raviv", "display_name": "Perahia, Raviv" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/TVHA-6D03", "abstract": "As optical, active, semiconductor devices are miniaturized to the wavelength scale, many applications of cavities, lasers, and detectors become possible. In order to make such devices useful in real-world applications one must first understand how these devices behave when they are reduced in size and what technological barriers must be overcome.
\r\n\r\nIn this dissertation several thrusts are presented toward the investigation and application of microscale active semiconductor cavities. Work is divided into four thrusts: fluid sensing based on surface sensitive quantum cascade lasers, hybridization of surface plasmon modes and waveguide modes as well as lasing in near-infrared subwavelength microdisks, quantum dot based cavities for strong coupling, and nascent work on optomechanical tuning of active cavities. In all four thrusts design and fabrication techniques are used to overcome challenges and capitalize on reduced scale.
\r\n\r\nProgress in fabrication, design, and testing of surface sensitive quantum cascade lasers is presented. Work focuses on increasing surface sensitivity by modifying the metal contacts on top of active material originally intended to be used with a surface plasmon waveguide. An experiment where isopropyl and ethyl alcohol is differentiated based on laser behavior is carried out. Work toward integration of semiconductor lasers with fluidic delivery systems is explored.
\r\n\r\nWork then turns to the intimate and advantageous inclusion of metal into subwavelength strained quantum well microdisk lasers in the near-infrared. Optical and thermal characteristics are simulated. Hybridization of surface plasmon mode and waveguide whispering-gallery modes is simulated and experimentally verified. Lasing behavior of such small devices is investigated.
\r\n\r\nIn parallel, work toward improving the probability of achieving a strongly coupled quantum dot microdisk cavity system is carried out. Improvements in fabrication techniques and potential metal integration makes this project a natural extension of the subwavelength microdisk laser project.
\r\n\r\nFinally, a new project is discussed where the above projects are combined with investigation of optomechanical systems currently ongoing in our lab. Work toward the combination of active optical cavities with optomechanical devices will lead to wide band wavelength tuning functionality.
\r\n" }, { "name": "Poon, Poh Chieh Benny", "degree": "PhD", "year": "2009", "title": "A Critical Appraisal of Nanoindentation with Application to Elastic-Plastic Solids and Soft Materials", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162008-023546", "creators": [ { "name": { "family": "Poon", "given": "Poh Chieh Benny" }, "id": "Poon-Poh-Chieh-Benny", "display_name": "Poon, Poh Chieh Benny" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Rittel", "given": "Daniel" }, "id": "Rittel-D", "role": "member", "display_name": "Rittel, Daniel" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/J1WM-BW36", "abstract": "This study examines the accuracy of the extracted elastic properties using nanoindentation. Since the conventional method to extract these properties utilizes Sneddon\u2019s elastic solution, this study first considers indentations of linearly elastic solids for direct comparison. The study proposes a criterion for a converged specimen\u2019s geometry and modifies Sneddon\u2019s equation to account for the finite tip radius and specimen compressibility effects. A composite correction factor is derived to account for the violations of the underlying assumptions behind Sneddon\u2019s derivation. This factor is a function of indentation depth, and a critical depth is derived beyond which the finite tip radius effect will be insignificant. Techniques to identify the radius of curvature of the indenter and to decouple the elastic constants for linear elastic materials are proposed. Experimental results on nanoindentation of natural latex are reported and discussed in light of the proposed modified relation and techniques.
\r\n\r\nThe second part of the study examines the accuracy of the extracted material properties in elastic-plastic nanoindentations. The study establishes that the accurate determination of the projected area of contact, A, is crucial. However, the conventional method to determine A is largely limited to elastic materials, hence a new electrical resistance method is proposed to measure A for elastic-plastic materials. With an accurate A, the error associated with the extracted elastic material properties is reduced by more than 50% in some cases. This error remains to be a function of the material\u2019s Poisson\u2019s ratio, which is identified to influence the amount of residual stresses at the plastic imprint.
\r\n\r\nFinally, this study examines the accuracy of the extracted material properties in the nanoindentation of soft materials using an Atomic Force Microscope (AFM). The effects of cantilever stiffness, preload, and surface interaction forces are observed to influence the measurements. Three set of experiments were performed to decouple these effects. The effect of a preload resembles a shift of nanoindentation load-displacement curve, while the cantilever stiffness is observed to have significant influence on the measurement of the surface forces. Lastly, a novel technique to account for these effects is proposed, in order to accurately extract the material properties of interest.
" }, { "name": "Rimoli, Julian Jose", "degree": "PhD", "year": "2009", "title": "A Computational Model for Intergranular Stress Corrosion Cracking", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142009-135909", "creators": [ { "name": { "family": "Rimoli", "given": "Julian Jose" }, "id": "Rimoli-Julian-Jose", "orcid": "0000-0002-8707-2968", "display_name": "Rimoli, Julian Jose" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "role": "member", "display_name": "Krishnan, Swaminathan" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K1HJ-DZ56", "abstract": "Stress corrosion cracking (SCC) is a very common failure mechanism characterized by a slow, environmentally induced crack propagation in structural components. Time-to-failure tests and crack-growth-rate tests are widespread practices for studying the response of various materials undergoing SCC. However, due to the large amount of factors affecting the phenomenon and the scattered data, they do not provide enough information for quantifying the effects of main SCC mechanisms. This thesis is concerned with the development of a novel 3-dimensional, multiphysics model for understanding the intergranular SCC of polycrystalline materials under the effect of impurity-enhanced decohesion. This new model is based upon: (i) a robust algorithm capable of generating the geometry of polycrystals for objects of arbitrary shape; (ii) a continuum finite element model of the crystals including crystal plasticity; (iii) a grain boundary diffusion model informed with first-principles computations of diffusion coefficients; and (iv) an intergranular cohesive model described by concentration-dependent constitutive relations also derived from first-principles. Results are validated and compared against crack-growth-rate and initiation time tests.\r\n" }, { "name": "Shi, Ling", "degree": "PhD", "year": "2009", "title": "Resource Optimization for Networked Estimator with Guaranteed Estimation Quality", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272008-121822", "creators": [ { "name": { "family": "Shi", "given": "Ling" }, "id": "Shi-Ling", "display_name": "Shi, Ling" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Johansson", "given": "Karl Henrik" }, "id": "Johansson-K-H", "role": "member", "display_name": "Johansson, Karl Henrik" } ], "option_major": [ "cds" ], "doi": "10.7907/DTCJ-BN07", "abstract": "Advances in fabrication, modern sensor and communication technologies, and computer architecture have enabled a variety of new networked sensing and control applications. However, many difficulties are inherent with these systems, for example, the constrained communication and computation capabilities, and limited energy resources, which are frequently seen in a wireless sensor network. As a consequence, the networks typically induce many new issues such as limited bandwidth, packet loss, and delay. Estimation and control over such networks thus require new design paradigms beyond traditional sampled-data control, as the aforementioned constraints undoubtedly affect system performance or even stability. In this thesis work, I consider the problem of state estimation over networks. As communication, computation, and energy are scarce resources in such networks, I focus on optimizing the use of them. When the state estimation is carried out over a sensor network, I consider the problem of minimizing the sensor energy usage and maximizing the network lifetime. When the state estimation is carried out over a packet-delaying network, I consider the problem of minimizing the buffer length at the remote state estimator. In each scenario, a certain desired level of estimation quality is guaranteed.\r\n" }, { "name": "Stern, Ari Joshua", "degree": "PhD", "year": "2009", "title": "Geometric Discretization of Lagrangian Mechanics and Field Theories", "advisor": "Marsden, Jerrold E.; Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechETD:etd-12312008-173851", "creators": [ { "name": { "family": "Stern", "given": "Ari Joshua" }, "id": "Stern-Ari-Joshua", "display_name": "Stern, Ari Joshua" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/K943-VJ44", "abstract": "This thesis presents a unified framework for geometric discretization of highly oscillatory mechanics and classical field theories, based on Lagrangian variational principles and discrete differential forms. For highly oscillatory problems in mechanics, we present a variational approach to two families of geometric numerical integrators: implicit-explicit (IMEX) and trigonometric methods. Next, we show how discrete differential forms in spacetime can be used to derive a structure-preserving discretization of Maxwell's equations, with applications to computational electromagnetics. Finally, we sketch out some future directions in discrete gauge theory, providing foundations based on fiber bundles and Lie groupoids, as well as discussing applications to discrete Riemannian geometry and numerical general relativity.\r\n" }, { "name": "Suh, Jin-Yoo", "degree": "PhD", "year": "2009", "title": "Fracture Toughness Study on Bulk Metallic Glasses and Novel Joining Method Using Bulk Metallic Glass Solder", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-01062009-001830", "creators": [ { "name": { "family": "Suh", "given": "Jin-Yoo" }, "id": "Suh-Jin-Yoo", "orcid": "0000-0003-3786-6652", "display_name": "Suh, Jin-Yoo" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Conner", "given": "Robert Dale" }, "id": "Conner-R-D", "role": "member", "display_name": "Conner, Robert Dale" } ], "option_major": [ "matsci" ], "doi": "10.7907/EQ77-D286", "abstract": "The fracture toughness of three new compositional variants of the Zr-Ti-Be-LTM (Late Transition Metal) family of bulk metallic glasses (BMG's) are studied in the as-cast and annealed condition. Quaternary Zr-Ti-Cu-Be alloys consistently had linear elastic fracture toughness values greater than 80 MPa\u2219m1/2, while Vitreloy 1, a Zr-Ti-Cu-Ni-Be alloy, had an average fracture toughness of 48.5 MPa\u2219m1/2 with a large amount of scatter. The addition of iron to Vitreloy 1 reduced the fracture toughness to 25 MPa\u2219m1/2. The Zr-Ti-Cu-Be alloy, having fracture toughness KQ = 85 MPa\u2219m1/2 as cast, was annealed at various time/temperature combinations. When the alloy was annealed 50C below Tg, the fracture toughness dropped to 6 MPa\u2219m1/2, while DSC and X-ray showed the alloy to still be amorphous. Fracture surfaces were analyzed using scanning electron microscopy. The tougher samples have shown evidence of highly jagged patterns at the beginning stage of crack propagation, and the length scale and roughness of this jagged pattern correlate well with the measured fracture toughness values. These jagged patterns, the main source of energy dissipation in the sample, are attributed to the formation of shear bands inside the sample. This observation provides a strong evidence of significant \u201cplastic zone\u201d screening at the crack tip.
\r\n\r\nUnlike the unstable fracture behavior of monolithic BMG's, ductile phase containing in-situ BMG composite shows stable crack growth behavior. Application of ductile BMG as a matrix for an in-situ composite with controlled microstructural characteristic length scales maximizes the toughening effect. In order to characterize this highly toughened BMG composite, the elastic-plastic fracture mechanics concept is introduced and the J-parameter is evaluated.
\r\n\r\nA novel thermoplastic bonding concept is demonstrated based on the unique rheological behavior and pattern-replication ability of bulk metallic glass forming liquids. In this approach, the bulk metallic glass is heated above Tg to the \u201csupercooled liquid\u201d region while a small normal force is applied to the joint. This results in liquid reflow, wetting and a strong bond. Complete wetting between copper substrates and a layer of platinum based bulk metallic glass leads to an atomistically intimate void-free interface.
\r\n" }, { "name": "Sutoyo, Daniel", "degree": "PhD", "year": "2009", "title": "Hysteretic Characteristics of Wood-Frame Structures Under Seismic Motions", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05172009-153304", "creators": [ { "name": { "family": "Sutoyo", "given": "Daniel" }, "id": "Sutoyo-Daniel", "display_name": "Sutoyo, Daniel" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "chair", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Duron", "given": "Ziyad H." }, "id": "Duron-Z-H", "role": "member", "display_name": "Duron, Ziyad H." } ], "option_major": [ "civileng" ], "doi": "10.7907/R92X-6R80", "abstract": "In order to develop seismic codes that can effectively mitigate damage to wood-frame construction under seismic activity, the dynamic characteristics of wood-frame buildings must be well understood. Funding of full-scale structure experimental tests can be costly and may not be a true replica of real life scenarios. Therefore, data interpretation projects focusing on dynamic behavior of low-rise wooden shearwall buildings under large seismic motions have become increasingly important. Procedures include determining the modal parameters and extracting hysteretic characteristics from the available records. The results help extend the understanding of wood-frame structures and update building codes. Furthermore, the amount of information extracted can help evaluate the effectiveness of the current instrumentation program.
\r\n\r\nThis work focuses on the seismic records from wood-frame structures during the 2004 Parkfield Earthquake. Studies involve verifying the amplitude dependence of modal parameters and retrieving pinching hysteresis curves that are common in wood-frame structures. Modal parameters are identified with a robust routine called MODE-ID. Equivalent viscous damping estimates in wood-frame buildings can range from 5% - 10% in largely linear behavior and 10% - 20% in significant nonlinear behavior. The discrepancies of damping estimates reported in the past are a result of inappropriate comparisons without understanding 1) the degree of nonlinear response and 2) the system identification methods used for the studies. By studying the hysteretic curves, insights can be obtained to reveal and to resolve the damping estimate discrepancies. Since displacement time histories of structures are not typically measured, the hysteretic curves are extracted from acceleration time histories. The proposed process accounts for inherent double integration errors and phase delay through filtering. It is still being debated that if the double integration can provide meaningful structural relative displacement time histories. In a laboratory setting with unilateral ground motion, the extraction process provides accurate hysteretic curves. However, this dissertation demonstrates that if the building experiences bi-directional ground motions, the nonlinear behavior of the diaphragm tampers with this process.
\r\n\r\nThe results from modal identification and hysteresis curves serve as a basis for creating numerical models. Direct and gradient search methods were used for model updating. Bayesian updating and model selection provided the best results for dealing with hysteretic structural models. This probabilistic framework demonstrates potential benefits in a seamless integration with a seismic database. The selected hysteretic model showed great resemblance to the measured responses and had evidence of pinching hysteresis. Insights on the structure\u2019s deformations and dissipation of energy can be inferred from the model.
\r\n" }, { "name": "Ursell, Tristan Scott", "degree": "PhD", "year": "2009", "title": "Stretching the Definition of a Lipid Bilayer: Elasticity's Role in Protein and Lipid Organization", "advisor": "Phillips, Robert B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062009-131454", "creators": [ { "name": { "family": "Ursell", "given": "Tristan Scott" }, "id": "Ursell-Tristan-Scott", "orcid": "0000-0001-9273-8413", "display_name": "Ursell, Tristan Scott" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "advisor", "display_name": "Phillips, Robert B." } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Klug", "given": "William" }, "id": "Klug-W", "role": "member", "display_name": "Klug, William" }, { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "orcid": "0000-0003-4073-1185", "role": "member", "display_name": "Rees, Douglas C." }, { "name": { "family": "Huang", "given": "Kerwyn" }, "id": "Huang-Kerwyn", "role": "member", "display_name": "Huang, Kerwyn" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Q0R5-K353", "abstract": "The Central Dogma forms the foundation of molecular biology couched in polymer language; all the key players are there \u2014 DNA, RNA, protein \u2014 or so it would seem. Yet one class of biologically synthesized molecules, crucial for life, is often over looked: lipids. These amphiphilic molecules exhibit a number of strange properties, integral to the cells ability to separate self from non-self in a chemically diverse environment. Lipids self-assemble into two-dimensional bi-layered fluids with aspect ratios of a thousand to one or more, capable of self-healing and bending into extraordinarily complex shapes. Within the cell, membranes allow for numerous chemically-distinct compartments, essential for metabolism, protein assembly, genome management, and cell division. With literally hundreds of different kinds of lipids and proteins interacting on a given membrane, we have much to learn about how membranes regulate the flow of materials into and out of cells. Clearly, molecular level detail is integral to our understanding of these systems, however, on the mesoscopic level membranes exhibit certain mechanical effects that serve to organize lipids and proteins, the study of which forms the bulk of this dissertation. We start by building an elastic model of bilayers, where embedded proteins deform the surrounding membrane and incur a free energy cost. This allows the mechanical attributes of the bilayer to influence the conformation of embedded proteins. We explore this connection in the context of mechanosensation in bacteria, as well as developing methods that allow bilayer mechanics to comment on the structure of classically voltage-gated ion channels. In addition to affecting conformational preferences, these same deformations have a finite length-scale that results in interactions between embedded proteins. Depending on the protein shape, these interactions can be attractive or repulsive, may exert torques on proteins, provide for a mechanism of shape-specific oligomerization, and importantly allow proteins to utilize the bilayer as a generic communicator of conformational information. The effects of these elastic interactions are discussed in the context of mean protein spacing, dimerization, conformational cooperativity, and likely pathways to multi-mer protein assembly, with the bacterial mechanosensitive channel MscL as a structural example. In subsequent chapters, bilayer elasticity is used to shed light on the large-scale organization of lipids themselves. Biological membranes likely have multiple fluid, lipid phases, where sequestration of saturated lipids and cholesterol form lipid domains. We found that formation of domains above a certain critical size induces morphological transitions to a \u2018dimpled\u2019 phase which turns on repulsive, elastic interactions that serve to spatially organize domains as well as severely inhibit domain coalescence. This provides a mechanism for the maintenance of lipid lateral heterogeneity on relatively short length-scales and long time scales. We further observed discrete transitions to a \u2018budded\u2019 domain morphology and developed a set of interpretive energetic transition rules between flat, dimpled and budded domains. We demonstrate that these morphologies and their attendant transitions lead to a unique form of domain-size-dependent transport in membranes. Further, we employ the mechanics of vesicles to model osmoregulation via channel proteins, and in the setting of conserved surface area and volume to develop a theoretical and experimental framework to study membrane adhesion in the context of the homophilic protein binding.\r\n" }, { "name": "Wang, Guangxi", "degree": "PhD", "year": "2009", "title": "Compact Nonlinear Optical Devices in Silicon-Polymer Hybrid Material System", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-014403", "creators": [ { "name": { "family": "Wang", "given": "Guangxi" }, "id": "Wang-Guangxi", "display_name": "Wang, Guangxi" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Inoue", "given": "Yoku" }, "id": "Inoue-Yoku", "role": "member", "display_name": "Inoue, Yoku" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/VJX4-5T05", "abstract": "Recently, integrated silicon photonics has become a topic of rising interests, due to its great potential to induce significant improvements in modern communication and computation systems. While optics is often viewed as a favorable solution to many issues faced by the rapidly evolving microelectronic technology, the high cost, large physical size, and discrete configuration of conventional optics have largely restricted its applications. The introduction of silicon nanophotonics permits a new look at the idea of incorporating optics with traditional electronic integrated circuits in a sensible and feasible fashion.
\r\n\r\nIn this dissertation, emphasis is placed on investigating nonlinear devices built in silicon but complemented by nonlinear polymer materials. Basic optical guiding and coupling components for silicon on insulator platform are first discussed, followed by a detailed description of the design, fabrication, and testing procedures of a Pockels effect electro-optic modulator based on nonlinear polymer-coated silicon nanostructures. Discussion is further expanded on other related devices that also make use of the second-order nonlinear effect, and designs to improve the speed and efficiency of existing devices are also elaborated. Finally, a third-order nonlinear all-optical modulation device is presented with a series of carefully designed experiments to verify its ultrafast operation.
\r\n" }, { "name": "Wang, Hua", "degree": "PhD", "year": "2009", "title": "Precision Frequency and Phase Synthesis Techniques in Integrated Circuits for Biosensing, Communication and Radar", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-06102009-164232", "creators": [ { "name": { "family": "Wang", "given": "Hua" }, "id": "Wang-Hua", "orcid": "0000-0003-4952-5505", "display_name": "Wang, Hua" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/T4EC-TX97", "abstract": "Today\u2019s CMOS technology provides circuit designers with a powerful implementation platform that supports innovation opportunities on both circuit-topology and system-architecture levels. Moreover, the versatility of CMOS implementation opens the door for a plethora of challenging and exciting interdisciplinary research.
\r\n\r\nThis dissertation focuses on investigating novel techniques and applications for precision frequency and phase synthesis in CMOS. It consists of two parts: a CMOS compatible molecular-level biosensor and a multiple-beam/multi-band scalable CMOS phased array receiver system.
\r\n\r\nIn the first part, a frequency shift based magnetic biosensing scheme is introduced to address the Point-of-Care (PoC) biomolecular diagnosis for high-sensitivity, portable and cost low applications. Compared with existing biosensing schemes, the proposed scheme achieves a competitive sensitivity without using optical devices, external biasing fields or expensive post-processing steps. A discrete implementation first verifies the sensing mechanism and reveals several design insights. An integrated implementation based on standard 130nm CMOS process is then designed with differential sensing and temperature controlling schemes. Overall, with a differential uncertainty of 0.13ppm for relative frequency shift, the sensor achieves reliable detection of one single micron-size magnetic particle (D=4.5um, 2.4um and 1um) as well as 1n-Molar real DNA samples labeled by magnetic nanoparticles (D=50nm).
\r\n\r\nIn the second part, a high-resolution compensation technique is proposed to address mismatch and offset issues encountered by practical phased array system. It employs a dense Cartesian interpolation scheme with an easily scalable architecture and a wide operation bandwidth. As an implementation example, a 6-to-18GHz dual-band quad-beam phased array CMOS receiver is presented, which is capable of forming four spatially independent beams at two different frequencies across the tritave bandwidth. With the mismatch compensation, the array element has achieved a maximum RMS phase error of 0.5\u02da with an RMS amplitude variation less than 1.5dB for the 360\u02da interpolation over the full operation bandwidth. For a 4-element phased array receiver system based on the designed CMOS chip, the electrical array pattern is measured at 6GHz, 10.4GHz and 18GHz, with the worst case peak-to-null ratio of 21.5dB. In addition, a broadband inductorless design methodology based on Cherry-Hooper topology is proposed for chip area saving. As implementation examples, we will show a DC-19GHz 10dB gain broadband buffer amplifier, a DC-12GHz broadband phase rotator with 10-bit resolution and a beam-forming network in a 10.4GHz to 18GHz phased array receiver chip with dual-beam capability.
" }, { "name": "Wang, Yu-Jiu", "degree": "PhD", "year": "2009", "title": "Circuits and Systems for Wireless Concurrent Communication", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-03292009-070752", "creators": [ { "name": { "family": "Wang", "given": "Yu-Jiu" }, "id": "Wang-Yu-Jiu", "orcid": "0000-0002-2534-1069", "display_name": "Wang, Yu-Jiu" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/FZ1R-MJ30", "abstract": "Concurrency is a special kind of analog circuit parallelism that uses a single circuit with necessary bandwidth to process multiple signals at the same time. Concurrent radios offer a higher data rate and improved system diversity. Our comprehensive treatment comprises proposals for potential transceiver architectures, invention of circuit blocks, and provisions of innovative analysis methods.
\r\n\r\nThe analysis of concurrent circuits are often complex. To simplify noise analysis, a R^(N^2 )-vector space is first proposed to re-formulate the N-port network noise modeling problem. Any internal physical source inside the noisy network contributes a small vector in the defined R^(N^2)-vector space, and the aggregate statistical behavior of this noisy network can be viewed as the vector sum of these vectors. Applying this concept to FET noise modeling leads to several modified FET noise models, in which three uncorrelated noise sources are sufficient to describe the statistical behavior of an intrinsic FET. The use of these new FET models can simplify the analysis, simulation, and optimization of low noise systems without sacrificing accuracy.
\r\n\r\nBroadband low-noise amplifier is a critical block in concurrent receiver systems. We propose a novel low-noise weighted distributed amplifier (WDA) topology, which uses the internal finite-impulse-response filtering inside a conventional distributed amplifier to partially suppress internal thermal noise. A distinct advantage of this topology is its tolerance to input parasitic capacitance which can be used to provide good electro-static discharge (ESD) protection without sacrificing its noise performance and power consumption. A compact 3.1\u250010.6 GHz WDA IC is built on a 130 nm CMOS process. Experimental results show 2.3\u25004.5 dB NF at 23 mW power consumption.
\r\n\r\nUsing concurrency in wireless link can boost communication data rate. As a proof-of concept, we propose dynamically scalable concurrent communication by dividing the 7.5 GHz bandwidth of the unlicensed 3.1\u250010.6 GHz spectrum into seven concurrent channels. A CMOS octa-core RF receiver is implemented to validate the idea. Based on the receiver measurement results, a wireless link can be built to achieve a 16 Gbps channel limit at five meter TX-RX distance at 400 mW power consumption.
\r\n\r\nTunable concurrency can improve the receiver diversity. A prototype 6\u250018 GHz concurrent tunable dual-band phased array receiver element IC is proposed and built on a 130 nm CMOS process. Experimental results demonstrate successful dual-band RF reception within a low band (6\u250010.4 GHz) and high band (10.4\u250018 GHz) with 300 MHz baseband bandwidth. A final four-element phased array receiver built from the prototyped ICs shows an array pattern with worst-case 21 dB peak-to-null ratio across all frequencies.
\r\n\r\nConcurrency can also be used to achieve multi-beam reception by providing multiple phase-shifts for each RF signals and combining them separately at baseband outputs. A 10.4\u250018 GHz concurrent dual-beam phased array receiver is proposed based on this concept, and is implemented on a 130 nm CMOS process. A final four-element phased array system shows successful concurrent dual-beam reception at the same RF frequency.
Yu-Jiu Wang (209\r\n" }, { "name": "Wierzynski, Casimir M.", "degree": "PhD", "year": "2009", "title": "Prefrontal-Hippocampal Interactions", "advisor": "Siapas, Athanassios G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262009-151920", "creators": [ { "name": { "family": "Wierzynski", "given": "Casimir M." }, "id": "Wierzynski-Casimir-M", "display_name": "Wierzynski, Casimir M." } ], "advisors": [ { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "orcid": "0000-0001-8837-678X", "role": "advisor", "display_name": "Siapas, Athanassios G." } ], "committee": [ { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "chair", "display_name": "Laurent, Gilles J." }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "orcid": "0000-0001-8837-678X", "role": "member", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "member", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" } ], "option_major": [ "cns" ], "doi": "10.7907/Z9833Q10", "abstract": "Long-term memories are established in the neocortex under the influence of hippocampal activity. The precise circuit mechanisms underlying this process, however, remain poorly understood. According to the dominant paradigm, memories are formed in two stages: first, neocortical activity during awake behavior embeds traces in hippocampal circuits; second, spontaneous hippocampal activity during offline periods, such as sleep, drives synaptic changes across cortical circuits so as to produce a stable, long-term memory trace. Evidence for this two-stage model at the level of neural activity, however, is incomplete. In this thesis we study interactions between the hippocampus and medial prefrontal cortex (mPFC) to elucidate the basic principles of how these brain circuits work in concert in support of long-term memory. Using recordings of single-unit actvity from multi-tetrode arrays in the hippocampus and mPFC of freely behaving rats, we performed two sets of experiments, each addressing one stage of the two-stage model. First, during awake behavior, we find a class of mPFC cells whose firing reflects the strength of a learned association and show that these tend to be strongly modulated by the hippocampus. Second, during sleep, we identify precise spike timing relationships between single mPFC and hippocampal cells that are consistent with information flow from the hippocampus to the prefrontal cortex, and show that these timing relationships are highly dependent on sleep stage. Taken together, these results provide key constraints on the circuit mechanisms of long-term memory formation.\r\n" }, { "name": "Wildman, Richard Alan", "degree": "PhD", "year": "2009", "title": "Biogeochemical Implications of Changing Groundwater and Surface Water Hydrology at Lake Powell, Utah and Arizona, and the Merced River, California, USA", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05182009-162828", "creators": [ { "name": { "family": "Wildman", "given": "Richard Alan" }, "id": "Wildman-Richard-Alan", "display_name": "Wildman, Richard Alan" } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "role": "chair", "display_name": "Sessions, Alex L." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "member", "display_name": "Hering, Janet G." }, { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "member", "display_name": "Adkins, Jess F." } ], "option_major": [ "envreng" ], "doi": "10.7907/2BQF-KR29", "abstract": "This thesis examines some effects of surface water and groundwater hydrology on the mobility of trace elements and phosphorus in natural environments. Three separate field sites are studied: 1) the shoreline of Lake Powell, a large reservoir on the Colorado River in Utah and Arizona where the surface elevation fluctuates on yearly and multi-yearly timescales, 2) the Colorado River inflow region to Lake Powell, where the sediment delta has been exposed due to low water levels, and 3) the lower Merced River, which is located in the San Joaquin Valley, California, amidst extensive agricultural development.
\r\n\r\nOn the shoreline of Lake Powell, depth profiles of manganese and uranium were used to estimate the redox state of sediment porewater. Samples were collected before and after a fluctuation in reservoir level exposed two sampling locations to air and then resubmerged them. Results indicate that reducing conditions are re-established at different rates in two nearby shoreline locations, and that manganese reduction occurs more rapidly than uranium reduction upon resubmergence.
\r\n\r\nIn the Colorado River inflow region of Lake Powell, sediment samples were collected from the lakebed and shoreline. Measurements indicate that particle size anticorrelates with the concentrations of most elements and clay minerals and explains much, but not all, of the variation in trace elements. Spatial trends of particle size imply that low reservoir levels may induce resuspension of fine sediment, a process that may lead to increased primary productivity observed in monitoring data. Sequential extractions performed on these sediment samples suggest that phosphorus, the limiting nutrient in Lake Powell, is primarily associated with calcite and biogenic apatite. Sorption experiments indicate that fine particles sorb much more phosphorus than coarse particles, and that only a small amount of the sediment-associated phosphorus is desorbed during sediment resuspension. When reservoir levels are low, measurements of dissolved phosphorus suggest that sediment resuspended by the Colorado River may supply phosphorus to the photic zone under specific hydrologic conditions.
\r\n\r\nSamples of groundwater collected from beneath the Merced River were analyzed for a suite of trace elements. Statistical analyses suggest that hydrologic processes generally influence the transport of trace solutes more than redox chemistry, and results vary between strontium, barium, uranium, and phosphorus.
\r\n" }, { "name": "Wu, Jigang", "degree": "PhD", "year": "2009", "title": "Coherence Domain Optical Imaging Techniques", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112008-102138", "creators": [ { "name": { "family": "Wu", "given": "Jigang" }, "id": "Wu-Jigang", "display_name": "Wu, Jigang" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6H07-PA44", "abstract": "Coherence domain optical imaging techniques have been developing quickly in the past few decades after the invention of laser. In this thesis, I will report the imaging methods that constitute my research projects during these years of graduate studies, including paired-angle-rotation scanning (PARS) forward-imaging probe for optical coherence tomography (OCT), full-field phase imaging technique based on harmonically matched diffraction grating (G1G2 grating), and Fresnel zone plate (FZP) based optifluidic microscopy (OFM). Compared with conventional optical microscopy, the coherence domain optical imaging has many advantages and greatly extends the application of imaging techniques.
\r\n\r\nOCT, based on low-coherence interferometry, is a high-resolution imaging technique that has been successfully applied to many biomedical applications. The development of various probes for OCT further made this technique applicable to endoscopic imaging. In the project of PARS-OCT probe, I have developed a forward-imaging probe based on two rotating angle-cut GRIN lenses. The diameter of the first prototype PARS-OCT probe that I made is 1.65 mm. My colleagues further built a probe with diameter of 0.82 mm. To our knowledge, this is the smallest forward-imaging probe that has been reported. The first prototype probe was characterized and successfully used to acquire OCT images of a Xenopus laevis tadpole.
\r\n\r\nFull-field phase imaging techniques are important for metrology and can also obtain high-resolution images for biological samples, especially transparent samples such as living cells. We have developed a novel full-field phase imaging technique based on the G1G2 grating. The G1G2 interferometry uses the G1G2 grating as a beam splitter/combiner and can confer nontrivial phase shift between output interference signals. Thus the phase and intensity information of the sample can be obtained by processing the two direct CCD images acquired at the output ports of the G1G2 grating. The details of this technique are explained in this thesis, and the phase imaging results for standard phase objects and biological samples are also shown.
\r\n\r\nOFM is a novel high-resolution and low-cost chip-level microscope developed by our group several years ago. Combining the unique imaging concept and microfluidic techniques, OFM system can be potentially useful to many biomedical applications, such as cytometry, blood parasite diagnosis, and water quality inspection. In the project of FZP-OFM, I applied the FZP to project the OFM aperture array onto an imaging sensor for OFM imaging. In this way, the sensor and the aperture array can be separated and will be useful for some situations. To demonstrate its capability, the FZP-OFM system was used to acquire OFM images of the protist Euglena gracilis.
\r\n\r\nThe studies in my research show the possibility of the application of various coherence domain optical imaging techniques in biomedical area, which is the primary objective of this thesis.
" }, { "name": "Yang, Jing", "degree": "PhD", "year": "2009", "title": "Nonlinear Responses of High-Rise Buildings in Giant Subduction Earthquakes", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04072009-042113", "creators": [ { "name": { "family": "Yang", "given": "Jing" }, "id": "Yang-Jing", "display_name": "Yang, Jing" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "role": "member", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/JDRP-HR74", "abstract": "With the exception of the 2003 Tokachi-Oki earthquake, strong ground recordings from large subduction earthquakes (Mw > 8.0) are meager. Furthermore there are no strong motion recordings of giant earthquakes. However, there is a growing set of high-quality broadband teleseismic recordings of large and giant earthquakes. In this thesis, we use recordings from the 2003 Tokachi-Oki (Mw 8.3) earthquake as empirical Green\u2019s functions to simulate the rock and soil ground motions from the 2004 Sumatra-Andaman earthquake and a scenario Mw 9.2 Cascadia subduction earthquake in the frequency band of interest to flexible and tall buildings (0.075 to 1 Hz). The effect of amplification by the Seattle basin is considered by using a basin response transfer function, which is derived from deconvolving the teleseismic waves recorded at rock sites from basin sites at the SHIP02 experiment. These strong ground motion time histories are used to simulate of the fully nonlinear response of 20-story and 6-story steel moment-frame buildings designed according to both the U.S. 1994 Uniform Building Code and the 1987 Japanese building code. We consider several realizations of the hypothetical subduction earthquake. The basin amplification and the down-dip limit of rupture are of particular importance to the simulated ground motions in Seattle. At rock sites, if slip is limited to offshore regions, the building model responses are mostly in the linear range. However, if rupture is extended beyond the Olympic Mountains, large deformations occur in the high-rise buildings models, especially those with brittle welds. At basin sites, our simulations indicate the collapse of all building models for a source model with rupture beyond the Olympic Mountains, whereas buildings with perfect welds avoid collapse for simulations based on a source model with rupture limited to offshore. The synthetic ground motions all have very long durations (more than 5 minutes at soil sites), and our building simulations should be considered as a low estimate since we the degradation model used in our simulation did not consider local flange buckling.\r\n" }, { "name": "Yogev, Or", "degree": "PhD", "year": "2009", "title": "Computational Evolutionary Embryogeny", "advisor": "Antonsson, Erik K.; Shapiro, Andrew A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162009-072031", "creators": [ { "name": { "family": "Yogev", "given": "Or" }, "id": "Yogev-Or", "display_name": "Yogev, Or" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Shapiro", "given": "Andrew A." }, "id": "Shapiro-A-A", "role": "co-advisor", "display_name": "Shapiro, Andrew A." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Shapiro", "given": "Andrew A." }, "id": "Shapiro-A-A", "role": "member", "display_name": "Shapiro, Andrew A." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/N4XG-F402", "abstract": "Evolution and development (Evo-Devo), are the two main processes which produce all of the different kinds of phenotypes we see in nature. Evolutionary process is responsible for eliminating the genetic information of weak phenotypes through natural selection, and also for exploring novel genotypes through genetic operations; crossover, mutation. The development process is the process of using the set of rules (codons) written in a genome, to turn a single set (zygote) into a mature phenotype. In this thesis, evolutionary and developmental processes are used to evolve the configurations of three-dimensional structures in silico to achieve desired performances. Although natural systems utilize the combination of both evolution and development processes to produce remarkable performance and diversity, this approach has not yet been applied extensively to the design of continuous three-dimensional load-supporting structures. Beginning with a single artificial cell containing information analogous to a DNA sequence, a structure is grown according to the rules encoded in the sequence. Each artificial cell in the structure contains the same sequence of growth and development rules, and each artificial cell is an element in a finite element mesh representing the structure of the mature individual. Rule sequences are evolved over many generations through selection and survival of individuals in a population.
\r\n\r\nModularity and symmetry are visible in nearly every natural and engineered structure. Understanding of the evolution and expression of symmetry and modularity is emerging from recent biological research. Initial evidence of these attributes is present in the phenotypes that are developed from the artificial evolution, although neither characteristic is imposed nor selected for directly.
\r\n\r\nThe computational evolutionary development approach presented here shows promise for synthesizing novel configurations of high-performance systems. The approach may advance system design to a new paradigm, where current design strategies have difficulty producing useful solutions. In addition to a new design approach perse, this model gives us the ability to explore the development process, from the standpoint of complex systems analysis. The phenotypes in our system have been grown under a highly stochastic environment, which serves as a triggered mechanism for gene expression. Still, evolution was able to find solutions which are robust to these stochastic elements, both at the phenotype level (the phenotype ability to function under the environment) and the growth process itself. In addition we have also explored the effects of symmetric and nonsymmetric environment over the topology of the phenotypes; we have found strong evidence that indicates a high correlation between the two. Finally we have also established a tool which enables us to understand the relationship between the environment and the degree of modularity of the phenotype.
\r\n" }, { "name": "Zheng, Ling", "degree": "PhD", "year": "2009", "title": "Wrinkling of Dielectric Elastomer Membranes", "advisor": "Ravichandran, Guruswami; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222008-161217", "creators": [ { "name": { "family": "Zheng", "given": "Ling" }, "id": "Zheng-Ling", "display_name": "Zheng, Ling" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "co-chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "role": "member", "display_name": "Pellegrino, Sergio" } ], "option_major": [ "mecheng" ], "doi": "10.7907/RTAB-GX13", "abstract": "Wrinkling of thin membranes due to different in-plane loading and boundary conditions has drawn attention of researchers in structural engineering since the development of thin webs for early aircraft structures. More recently, prestressed lightweight membrane structures have been proposed for future space missions, for example solar sails, the next generation space telescope sunshield and space-based radar systems. These structures are often partially wrinkled during operation. The formation of wrinkles alters the load paths and the structural stiffness of the membranes. More importantly its occurrence degrades the surface accuracy of these structures, which is a key design parameter.
\r\n\r\nThis dissertation focuses on wrinkling of thin rectangular membranes subjected to uniaxial tension and investigates the onset and profiles of wrinkles using both experimental and numerical approaches.
\r\n\r\nAn optical method, which integrates fringe projection method with four-frame phase-shifting technique, pre-conditioned conjugate gradient phase unwrapping algorithm and series-expansion carrier removal technique was developed in order to measure the full-field out-of-plane displacement of membranes, and an optical system was constructed including a uniaxial tension testbed, a LCD projector and a CCD camera. A series of uniaxial tensile tests were carried out on silicone rubber membranes of varying dimensions and aspect ratios in order to investigate the effect of geometric factors such as membrane dimension and aspect ratio on wrinkling onset; and a series of measurements were performed on each membrane at several desired strain levels to understand the evolution of the wrinkles, in particular wrinkle amplitude and wavelength.
\r\n\r\nA numerical study was carried out using the commercial finite element software ABAQUS to further understand the important characteristics of wrinkling of thin membranes observed in the physical model. Geometrically nonlinear finite element models of membrane structures were constructed with thin-shell elements. A series of simulations were carried out for different membrane dimensions. The critical buckling load and buckling modes was predicted for each dimension using a pre-buckling eigenvalue analysis. The desirable buckling mode was selected and introduced into the structure as a geometric imperfection. The formation and growth of wrinkles were simulated in the post-buckling analysis.
\r\n\r\nFinally, an idea of suppressing wrinkle instabilities of dielectric elastomer membranes using through-thickness electric field was proposed and verified in both experiment and numerical simulations.
" }, { "name": "Angelova, Anelia Nedelcheva", "degree": "PhD", "year": "2008", "title": "Visual Prediction of Rover Slip: Learning Algorithms and Field Experiments", "advisor": "Matthies, Larry H.; Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-10032007-121619", "creators": [ { "name": { "family": "Angelova", "given": "Anelia Nedelcheva" }, "id": "Angelova-Anelia-Nedelcheva", "orcid": "0000-0003-1822-7943", "display_name": "Angelova, Anelia Nedelcheva" } ], "advisors": [ { "name": { "family": "Matthies", "given": "Larry H." }, "id": "Matthies-L-H", "role": "advisor", "display_name": "Matthies, Larry H." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "co-advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Matthies", "given": "Larry H." }, "id": "Matthies-L-H", "role": "member", "display_name": "Matthies, Larry H." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/F7FY-5T13", "abstract": "Perception of the surrounding environment is an essential tool for intelligent navigation in any autonomous vehicle. In the context of Mars exploration, there is a strong motivation to enhance the perception of the rovers beyond geometry-based obstacle avoidance, so as to be able to predict potential interactions with the terrain. In this thesis we propose to remotely predict the amount of slip, which reflects the mobility of the vehicle on future terrain. The method is based on learning from experience and uses visual information from stereo imagery as input. We test the algorithm on several robot platforms and in different terrains. We also demonstrate its usefulness in an integrated system, onboard a Mars prototype rover in the JPL Mars Yard.
\r\n\r\nAnother desirable capability for an autonomous robot is to be able to learn about its interactions with the environment in a fully automatic fashion. We propose an algorithm which uses the robot's sensors as supervision for vision-based learning of different terrain types. This algorithm can work with noisy and ambiguous signals provided from onboard sensors. To be able to cope with rich, high-dimensional visual representations we propose a novel, nonlinear dimensionality reduction technique which exploits automatic supervision. The method is the first to consider supervised nonlinear dimensionality reduction in a probabilistic framework using supervision which can be noisy or ambiguous.
\r\n\r\nFinally, we consider the problem of learning to recognize different terrains, which addresses the time constraints of an onboard autonomous system. We propose a method which automatically learns a variable-length feature representation depending on the complexity of the classification task. The proposed approach achieves a good trade-off between decrease in computational time and recognition performance.
\r\n" }, { "name": "Ayalasomayajula, Meher Kiran Prakash", "degree": "PhD", "year": "2008", "title": "Theoretical Studies of Single Molecule Biophysical Systems and Photochemical Ensembles", "advisor": "Marcus, Rudolph A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062007-233423", "creators": [ { "name": { "family": "Ayalasomayajula", "given": "Meher Kiran Prakash" }, "id": "Ayalasomayajula-Meher-Kiran-Prakash", "display_name": "Ayalasomayajula, Meher Kiran Prakash" } ], "advisors": [ { "name": { "family": "Marcus", "given": "Rudolph A." }, "id": "Marcus-R-A", "orcid": "0000-0001-6547-1469", "role": "advisor", "display_name": "Marcus, Rudolph A." } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Marcus", "given": "Rudolph A." }, "id": "Marcus-R-A", "orcid": "0000-0001-6547-1469", "role": "member", "display_name": "Marcus, Rudolph A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/5D2K-7H81", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe focus of the present thesis is on theoretical analysis to understand the experimental results from three quite different systems - enzymes, RNA hairpins and nitrous oxide (N2O). Some experiments on single enzymes showed very unusual data: in separate experiments the fluctuations in catalysis rate ([...]) and fluorescence lifetime ([...]) of chromophore in single enzymes showed long-lasting autocorrelations, represented by a stretched exponential and power-law, respectively. With the aim of interpreting the origin of these fluctuations, we proposed a formulation based on fluctuations in electrostatic interaction energy ([...]) at the active site in the enzyme leading to the fluctuations in the various observables. We developed relations between the autocorrelation functions of [...], [...], spectral diffusion ([...]) and the radiative component of fluorescence lifetime ([...]). It was pointed out that the relation between [...] and [...], seen experimentally and modeled theoretically by using the relation noted above, is a dynamic analog of the solvatochromism concept used in the catalysis of organic reactions by solvent. The estimation of fluctuations in electrostatic interactions on the milliseconds to seconds time scale by computational methods is not possible, which are typically limited to tens of nanoseconds. To calculate the autocorrelation of electrostatic interactions and to compare them with experiments, we used the frequency dependent dielectric response of proteins and related it to the autocorrelation of [...]. Based on this formulation, we find a good agreement between the single molecule data on the enzyme candida antarctica lipase B and the calculation using dielectric response data on the enzyme. In single molecule data from other enzymes for which [...] is not yet available, we have predictions based on a commonly observed functional form of [...] for other proteins.\r\n\r\nSingle molecule experiments on RNA hairpins were used to test a nonequilibrium statistical physics result - Crooks' theorem. Crooks' theorem is about an exact equality relating the probability distributions of work done (W) on a system by varying an external parameter in the forward and reverse directions in a predetermined way. Usually in the single molecule experiments this predetermined variation is a constant rate ([...]) of increase or decrease of the external force for all runs of the experiment. Our study focuses on the relevance of the RNA hairpin unfolding experiments to the theorem. The unfolding of the molecule leads to a drop in the externally controlled force on the molecule, a condition which is not suited to the existing derivations of Crooks' theorem. An alternative interpretation of the experimental unfolding and refolding data using a phenomenological force-dependent distortion of activation barriers is provided to gain insight into the data on the probability distribution of work done during unfolding, refolding corresponding to different rates of change of force. This interpretation shows that the crossing of the unfolding and refolding work distributions which happens at the same value of W for all [... is a necessary but not sufficient condition to verify the theorem.\r\n\r\nThe experimental data on UV photodissociation of the greenhouse gas N2O and the associated isotope effects are important from the perspective of atmospheric interest. The calculations in the literature to model the photodissociation observations are of two kinds - some are computationally intensive quantum mechanical methods using wave packet propagation and the others are based on empirical calculations. The two different calculations we present, based on two different variants of the 'multidimensional reflection principle' maintain the simplicity of computation, while using the available ab initio data on the molecule for the potential energy surfaces and the transition dipole moments. In one of the calculations, the absorption cross section was broadened empirically to get agreement with the absorption data and the results were then used to make calculations of isotopologue fractionation. This broadening was also needed in a wave packet propagation calculation. In a later calculation, without introducing the broadening factor, the results were compared only on one side of the absorption cross section, where the isotopic fractionation measurements are available. Using these two methods, the fractionation of heavier isotopologues of N2O with respect to the most abundant isotopologue [...] were calculated and compared with the experiments. A simple relation between the fractionations of [...] and [...] was observed in the results from our calculations. A perturbation theoretical result was used to derive this relationship, which is independent of the detailed calculations required for each of the isotopologues individually." }, { "name": "Babakhani, Aydin", "degree": "PhD", "year": "2008", "title": "Direct Antenna Modulation (DAM) for On-Chip mm-Wave Transceivers", "advisor": "Hajimiri, Ali; Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06082008-174204", "creators": [ { "name": { "family": "Babakhani", "given": "Aydin" }, "id": "Babakhani-Aydin", "orcid": "0000-0001-8123-9061", "display_name": "Babakhani, Aydin" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "co-advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/BS6T-1S20", "abstract": "In the last few decades the puissant desire to miniaturize the digital circuits to achieve higher speed and larger density has shaped the evolution of the silicon-based technologies. This development opens a new era in the field of millimeter-wave electronics in which many low-cost high-yield silicon-based transistors can be used on a single chip to enable creation of novel architectures with unique properties not achievable with old processes. In addition to this high level of integration capability, the die size of comparable or even larger than the wave-length makes it possible to integrate antennas, transceivers, and digital circuitry all on a single silicon die.
\r\n\r\nIt is important to realize that although smaller parasitic capacitors and shorter transistor channels have improved fT and fmax of transistors, extremely thin metal layers, highly doped substrates, and low breakdown voltage transistors have severely affected the performance of analog and RF building blocks. For example, thin metal layers have increased the loss and lowered the quality factor of the building blocks such as capacitors and inductors and low breakdown voltage transistors have made the power generation quite challenging. Additionally, if not carefully designed, small wave-lengths in the millimeter-wave range may cause unintended radiation by on-chip components. In this dissertation, we address these issues in design of millimeter-wave silicon-based single-chip phased-array transceivers with integrated antennas. We also introduce the technique of Direct Antenna Modulation (DAM) and implement two proof-of-concept chips operating at 60 GHz.
\r\n\r\nWe will present the receiver and the on-chip antenna sections of a fully integrated 77 GHz four-element phased-array transceiver with on-chip antennas in silicon. The receiver section of the chip includes the complete down-conversion path comprising low-noise amplifier (LNA), frequency synthesizer, phase rotators, combining amplifiers, and on-chip dipole antennas. The signal combining is performed using a novel distributed active combining amplifier at an IF of 26 GHz. In the LO path, the output of the 52 GHz VCO is routed to different elements and can be phase shifted locally by the phase rotators. A silicon lens on the backside is used to reduce the loss due to the surface-wave power of the silicon substrate. Our measurements show a single-element LNA gain of 23 dB and a noise figure of 6.0 dB. Each of the four receive paths has a gain of 37 dB and a noise figure of 8.0 dB. Each on-chip antenna has a gain of +8 dBi.
\r\n\r\nA direct antenna modulation (DAM) technique is also introduced, where the radiated far-field signal is modulated by time-varying changes in the antenna near-field electromagnetic (EM) boundary conditions. This enables the transmitter to send data in a direction-dependent fashion producing a secure communication link. The transmitter architecture makes it possible to use narrow-band highly-efficient switching power amplifiers to transmit wideband constant and non-constant envelope modulated signals. Theoretically, these systems are capable of transmitting independent data in multiple directions at full-rate concurrently using a single transmitter. Direct antenna modulation (DAM) can be performed by using either switches or varactors. Two proof-of-concept DAM transmitters operating at 60GHz using switches and varactors are demonstrated in silicon proving the feasibility of this approach.
" }, { "name": "Bermejo-Moreno, Ivan", "degree": "PhD", "year": "2008", "title": "On the Non-Local Geometry of Turbulence", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092008-173614", "creators": [ { "name": { "family": "Bermejo-Moreno", "given": "Ivan" }, "id": "Bermejo-Moreno-Ivan", "display_name": "Bermejo-Moreno, Ivan" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DH9W-Y894", "abstract": "A multi-scale methodology for the study of the non-local geometry of eddy structures in turbulence is developed. Starting from a given three-dimensional field, this consists of three main steps: extraction, characterization and classification of structures. The extraction step is done in two stages. First, a multi-scale decomposition based on the curvelet transform is applied to the full three-dimensional field, resulting in a finite set of component fields, one per scale. Second, by iso-contouring each component field at one or more iso-contour levels, a set of closed iso-surfaces is obtained that represents the structures at that scale. For periodic domains, those structures intersecting boundaries are reconnected with their continuation in the opposite boundaries. The characterization stage is based on the joint probability density function (jpdf), in terms of area coverage on each individual iso-surface, of two differential-geometry properties, the shape index and curvedness, plus the stretching parameter, a dimensionless global invariant of the surface. Taken together, this defines the geometrical signature of the iso-surface. The classification step is based on the construction of a finite set of parameters, obtained from algebraic functions of moments of the jpdf of each structure, that specify its location as a point in a multi-dimensional 'feature space'. At each scale the set of points in feature space represents all structures at that scale, for the specified iso-contour value. This allows the application, to the set, of clustering techniques that search for groups of structures with a common geometry.
\r\n\r\nResults are presented of a first application of this technique to a passive scalar field obtained from 512\u00b3 direct numerical simulation of scalar mixing by forced, isotropic turbulence (Re\u03bb=265). These show transition, with decreasing scale, from blob-like structures in the larger scales to blob- and tube-like structures with small or moderate stretching in the inertial range of scales, and then toward tube and, predominantly, sheet-like structures with high level of stretching in the dissipation range of scales. Implications of these results for the dynamical behavior of passive scalar stirring and mixing by turbulence are discussed.
\r\n\r\nWe apply the same methodology to the enstrophy and kinetic energy dissipation rate instantaneous fields of a second numerical database of incompressible homogeneous isotropic turbulence decaying in time obtained by DNS in a periodic box. Three different resolutions are considered: 256\u00b3, 512\u00b3 and 1024\u00b3 grid points, with kmax\u03b7\u0305 approximately 1, 2, and 4, respectively, the same initial conditions and Re\u03bb \u2248 77. This allows a comparison of the geometry of the structures obtained for different resolutions. For the highest resolution, structures of enstrophy and dissipation evolve in a continuous distribution from blob-like and moderately stretched tube-like shapes at the large scales to highly stretched sheet-like structures at the small scales. The intermediate scales show a predominance of tube-like structures for both fields, much more pronounced for the enstrophy field. The dissipation field shows a tendency toward structures with lower curvedness than those of the enstrophy, for intermediate and small scales. The 256\u00b3 grid resolution case (kmax\u03b7\u0305 \u2248 1) was unable to detect the predominance of highly stretched sheet-like structures at the smaller scales.
\r\n\r\nThe same methodology, but without the multi-scale decomposition, is then applied to two scalar fields used by existing local criteria for the eduction of tube- and sheet-like structures in turbulence, Q and [Aij]+ respectively, obtained from invariants of the velocity gradient tensor and alike in the 1024\u00b3 case. This adds the non-local geometrical characterization and classification to those local criteria, assessing their validity in educing particular geometries.
\r\n\r\nFinally we introduce a new methodology for the study of proximity issues among different sets of structures, based also on geometrical and non-local analyses. We apply it to four of the fields previously studied. Tube-like structures of Q are mainly surrounded by sheets of [Aij]+, which appear at close distances. For the enstrophy, tube-like structures at an intermediate scale are primarily surrounded by sheets of smaller scales of the enstrophy and structures of dissipation at the same and smaller scales. A secondary contribution results from tubes of enstrophy at smaller scales appearing at farther distances. Different configurations of composite structures are presented.
\r\n" }, { "name": "Bruguier, Antoine Jean", "degree": "PhD", "year": "2008", "title": "Encoding of Financial Signals in the Human Brain", "advisor": "Bossaerts, Peter L.; Quartz, Steven R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10262007-140735", "creators": [ { "name": { "family": "Bruguier", "given": "Antoine Jean" }, "id": "Bruguier-Antoine-Jean", "orcid": "0000-0003-3668-7927", "display_name": "Bruguier, Antoine Jean" } ], "advisors": [ { "name": { "family": "Bossaerts", "given": "Peter L." }, "id": "Bossaerts-P-L", "role": "advisor", "display_name": "Bossaerts, Peter L." }, { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "co-advisor", "display_name": "Quartz, Steven R." } ], "committee": [ { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "chair", "display_name": "Quartz, Steven R." }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "member", "display_name": "O'Doherty, John P." }, { "name": { "family": "Bossaerts", "given": "Peter L." }, "id": "Bossaerts-P-L", "role": "member", "display_name": "Bossaerts, Peter L." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/76FW-PD72", "abstract": "Neuroeconomists investigate how the human brain analyzes and makes decisions about financial situations. They use functional magnetic resonance imaging (fMRI) of subjects who participate in economic games. Here we present three such experiments.
\r\n\r\nIn the first experiment, we investigate how the brain recombines expected reward (ER) and risk. Recent fMRI results show that the brain decomposes a gamble in terms of these two metrics. However, economic theory predicts that the brain must recombine them in order to obtain an effective evaluation of the gamble. It was not clear what biological mechanism directs such recombination. Here we show that the brain uses the correlation of noise to recombine signals. We implement a new technique based on canonical correlation analysis and we show that ER is added to risk to form a metric that activates the medial prefrontal cortex.
\r\n\r\nIn the second experiment, we investigate how the brain encodes two gambles instead of one. The brain is likely to encode the utility of each gamble in a common area but in separate groups of neurons. However, it is unknown how the brain indexes the gambles. Indeed, which group of neuron encodes which gamble can be decided in many ways. We hypothesized that the brain would use either the physical position of the gambles or an idiosyncratic parameter, such as ER or risk. Here we introduce a new analysis technique based on Hotelling T-squared statistics and we show that the brain uses risk as an index.
\r\n\r\nIn the third experiment, we investigate a much more complex situation: a stock market. Contrary to what standard finance theory predicts, we hypothesize that the brain does not use mathematical models but instead heuristically uses a social cognition approach. Specifically, we posit that humans understand stock markets by using Theory of Mind (ToM), the ability to attribute to others mental states different from one's own. Here we show that humans engage brain structures related to ToM (paracingulate cortex, anterior cingulate cortex, insula, and amygdala). Subsequent behavioral tests show that ToM, rather than mathematical, abilities are better predictors of success in forecasting stock markets.
" }, { "name": "Carson, John Maurice, III", "degree": "PhD", "year": "2008", "title": "Robust Model Predictive Control with a Reactive Safety Mode", "advisor": "Murray, Richard M.; MacMynowski, Douglas G.; Acikmese, Behcet", "url": "https://resolver.caltech.edu/CaltechETD:etd-05072008-131735", "creators": [ { "name": { "family": "Carson", "given": "John Maurice, III" }, "id": "Carson-John-Maurice-III", "display_name": "Carson, John Maurice, III" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "MacMynowski", "given": "Douglas G." }, "id": "MacMynowski-D-G", "role": "co-advisor", "display_name": "MacMynowski, Douglas G." }, { "name": { "family": "Acikmese", "given": "Behcet" }, "id": "Acikmese-B", "role": "co-advisor", "display_name": "Acikmese, Behcet" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Acikmese", "given": "Behcet" }, "id": "Acikmese-B", "role": "member", "display_name": "Acikmese, Behcet" }, { "name": { "family": "MacMynowski", "given": "Douglas G." }, "id": "MacMynowski-D-G", "role": "member", "display_name": "MacMynowski, Douglas G." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/S0VN-VE35", "abstract": "Control algorithms suitable for online implementation in engineering applications, such as aerospace and mechanical vehicles, often require adherence to physical state and control constraints. Additionally, the chosen algorithms must provide robustness to uncertainty affecting both the system dynamics and the constraints. As further autonomy is built into these systems, the algorithms must be capable of blending multiple operational modes without violating the intrinsic constraints. Further, for real-time applications, the implemented control algorithms must be computationally efficient and reliable. The research in this thesis approaches these application needs by building upon the framework of MPC (Model Predictive Control).
\r\n\r\nThe MPC algorithm makes use of a nominal dynamics model to predict and optimize the response of a system under the application of a feedforward control policy, which is computed online in a finite-horizon optimization problem. The MPC algorithm is quite general and can be applied to linear and nonlinear systems and include explicit state and control constraints. The finite-horizon optimization is advantageous given the finite online computational capabilities in practical applications. Further, recursively re-solving the finite-horizon optimization in a compressing- or receding-horizon manner provides a form of closed-loop control that updates the feedforward control policy by setting the nominal state at re-solve to the current actual state. However, uncertainty between the nominal model and the actual system dynamics, along with constraint uncertainty can cause feasibility, and hence, robustness issues with the traditional MPC algorithm.
\r\n\r\nIn this thesis, an R-MPC (Robust and re-solvable MPC) algorithm is developed for uncertain nonlinear systems to address uncertainty affecting the dynamics. The R-MPC control policy consists of two components: the feedforward component that is solved online as in traditional MPC; and a separate feedback component that is determined offline, based on a characterization of the uncertainty between the nominal model and actual system. The addition of the feedback policy generates an invariant tube that ensures the actual system trajectories remain in the proximity of the nominal feedforward trajectory for all time. Further, this tube provides a means to theoretically guarantee continued feasibility and thus re-solvability of the R-MPC algorithm, both of which are required to guarantee asymptotic stability.
\r\n\r\nTo address uncertainty affecting the state constraints, an SR-MPC (Safety-mode augmented R-MPC) algorithm is developed that blends a reactive safety mode with the R-MPC algorithm for uncertain nonlinear systems. The SR-MPC algorithm has two separate operational modes: standard mode implements a modified version of the R-MPC algorithm to ensure asymptotic convergence to the origin; safety mode, if activated, guarantees containment within an invariant set about a safety reference for all time. The standard mode modifies the R-MPC algorithm with a special constraint to ensure safety-mode availability at any time. The safety-mode control is provided by an offline designed control policy that can be activated at any time during standard mode. The separate, reactive safety mode provides robustness to unexpected state-constraint changes; e.g., other vehicles crossing/stopping in the feasible path, or unexpected ground proximity in landing scenarios.
\r\n\r\nExplicit design methods are provided for implementation of the R-MPC and SR-MPC algorithms on a class of systems with uncertain nonlinear terms that have norm-bounded derivatives. Further, a discrete SR-MPC algorithm is developed that is more broadly applicable to real engineering systems. The discrete algorithm is formulated as a second-order cone program that can be solved online in a computationally efficient manner by using interior-point algorithms, which provide convergence guarantees in finite time to a prescribed level of accuracy.
\r\n\r\nThis discrete SR-MPC algorithm is demonstrated in simulation of a spacecraft descent toward a small asteroid where there is an uncertain gravity model, as well as errors in the expected surface altitude. Further, realistic effects such as control-input uncertainty, sensor noise, and unknown disturbances are included to further demonstrate the applicability of the discrete SR-MPC algorithm in a realistic implementation.
" }, { "name": "Cassuto, Yuval", "degree": "PhD", "year": "2008", "title": "Coding Techniques for Data-Storage Systems", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-01242008-134459", "creators": [ { "name": { "family": "Cassuto", "given": "Yuval" }, "id": "Cassuto-Yuval", "orcid": "0000-0001-6369-6699", "display_name": "Cassuto, Yuval" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Xu", "given": "Lihao" }, "id": "Xu-Lihao", "role": "member", "display_name": "Xu, Lihao" }, { "name": { "family": "Blaum", "given": "Mario" }, "id": "Blaum-M", "role": "member", "display_name": "Blaum, Mario" }, { "name": { "family": "Farrell", "given": "Paddy" }, "id": "Farrell-P", "role": "member", "display_name": "Farrell, Paddy" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/38ZT-QT95", "abstract": "As information-bearing objects, data-storage systems are natural consumers of information-theoretic ideas. For many issues in data-storage systems, the best trade-off between cost, performance and reliability, passes through the application of error-correcting codes. Error-correcting codes that are specialized for data-storage systems is the subject studied by this thesis. On the practical side, central challenges of storage systems are addressed, both at the individual-device level and higher at the enterprise level for disk arrays. The results for individual devices include a new coding paradigm for Multi-Level Flash storage that benefits storage density and access speed, and also a higher-throughput algorithm for decoding Reed-Solomon codes with large decoding radii. The results for storage arrays address models and constructions to combat correlated device failures, and also introduce new highly-regular array-code constructions with optimal redundancy and updates. On the theoretical side, the research stretches across multiple layers of coding theory innovation: new codes for new error models, new codes for existing error models, and new decoding techniques for known codes. To bridge the properties and constraints of practical systems with the mathematical language of coding theory, new well-motivated models and abstractions are proposed. Among them are the models of t asymmetric limited-magnitude errors and clustered erasures. Later, after maximizing the theory's power in addressing the abstractions, the performance of storage systems that employ the new schemes is analytically validated." }, { "name": "Chow, Gang", "degree": "PhD", "year": "2008", "title": "Laser Tweezers for Moving Live Dissociated Neurons", "advisor": "Pine, Jerome", "url": "https://resolver.caltech.edu/CaltechETD:etd-10222007-134413", "creators": [ { "name": { "family": "Chow", "given": "Gang" }, "id": "Chow-Gang", "display_name": "Chow, Gang" } ], "advisors": [ { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "advisor", "display_name": "Pine, Jerome" } ], "committee": [ { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "chair", "display_name": "Pine, Jerome" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kasdan", "given": "Harvey L." }, "id": "Kasdan-H-L", "role": "member", "display_name": "Kasdan, Harvey L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "bioeng" ], "doi": "10.7907/9A72-G624", "abstract": "A laser tweezers system for transporting dissociated neurons into small \"cages\" on a culture dish was constructed, and it was studied extensively.
\r\n\r\nThe system consists of an inverted microscope, a 1064 nm or 980 nm laser module, a beam expander, a motorized mechanical stage, a CCD camera, and steering mirrors. A laser beam is generated by the IR laser module, and the beam is expanded by the beam expander to match the size of the back aperture of the objective. The beam is then steered into the objective where it is focused to a point. The system uses this single, tightly focused laser beam to trap a neuron. Once a neuron is trapped and lifted, the mechanical stage is moved to locate the neuron above its destination. The system will know the location of the neurocages and will automatically move neurons to their destination.
\r\n\r\nNewly dissociated neurons will attach to most substrate surfaces eagerly, and the lifting of a neuron is impossible when it is attached to the surface. Many possible surfaces were investigated, and it was discovered that the surface can best be made \"non-sticky\" for more than an hour, by coating the surface with Poly-2-hydroxyethyl methacrylate (PolyHEMA). The neural survival at different laser intensities, exposure times, and wavelengths were studied. The results show that neural survival depends strongly on laser wavelengths, and a 980 nm laser is less damaging than a 1064 nm laser. For 980 nm, perfect survival after irradiation is independent of laser power up to our maximum of 130 mW for exposure time up to 4 minutes. At 17 mW, almost all neurons can be lifted off a PolyHEMA substrate. The maximum speed for moving a neuron through the medium at different laser intensities was studied, and was 250 um/s at 100 mW for 980 nm. The studies have shown that a laser tweezers system is suitable for transporting live dissociated neurons over millimeter distance in less than a minute. The neural survival in neurocages on glass substrate was then studied. The survival and growth over time for neurons loaded into cages was found to be no different than for that of a control culture.
\r\n" }, { "name": "Donaldson, Roger David", "degree": "PhD", "year": "2008", "title": "Discrete Geometric Homogenisation and Inverse Homogenisation of an Elliptic Operator", "advisor": "Owhadi, Houman; Desbrun, Mathieu", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212008-164705", "creators": [ { "name": { "family": "Donaldson", "given": "Roger David" }, "id": "Donaldson-Roger-David", "display_name": "Donaldson, Roger David" } ], "advisors": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "advisor", "display_name": "Owhadi, Houman" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "advisor", "display_name": "Desbrun, Mathieu" } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/S4S7-8T31", "abstract": "We show how to parameterise a homogenised conductivity in R\u00b2 by a scalar function s(x), despite the fact that the conductivity parameter in the related up-scaled elliptic operator is typically tensor valued. Ellipticity of the operator is equivalent to strict convexity of s(x), and with consideration to mesh connectivity, this equivalence extends to discrete parameterisations over triangulated domains. We apply the parameterisation in three contexts: (i) sampling s(x) produces a family of stiffness matrices representing the elliptic operator over a hierarchy of scales; (ii) the curvature of s(x) directs the construction of meshes well-adapted to the anisotropy of the operator, improving the conditioning of the stiffness matrix and interpolation properties of the mesh; and (iii) using electric impedance tomography to reconstruct s(x) recovers the up-scaled conductivity, which while anisotropic, is unique. Extensions of the parameterisation to R\u00b3 are introduced." }, { "name": "Duan, Gang", "degree": "PhD", "year": "2008", "title": "Simulations, Modeling, and Designs of Bulk Metallic Glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-09252007-100851", "creators": [ { "name": { "family": "Duan", "given": "Gang" }, "id": "Duan-Gang", "display_name": "Duan, Gang" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "co-chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Samwer", "given": "Konrad" }, "id": "Samwer-K", "role": "member", "display_name": "Samwer, Konrad" } ], "option_major": [ "matsci" ], "doi": "10.7907/ZH3G-JF43", "abstract": "Bulk metallic glasses usually have very high yield strength, at least double that of ordinary commercially used crystalline materials, and high elastic strain limit, roughly 2% in tension or compression, due to their disordered atomic structure. Unfortunately, the Achilles heel of metallic glasses is their rather limited ductility and low resistance to the propagation of a crack especially in tension. Many research efforts have been devoted to understanding the deformation and fracture behavior of bulk metallic glasses. One interesting observation is that the properties of metallic glasses are well correlated with each other. The challenge is to understand these correlations, and to utilize such understanding to design novel glasses with good glass forming ability and mechanical toughness.
\r\n\r\nFollowing the Cooperative Shear Model, we investigated the temperature, volume, and configurational dependence of elastic properties by constructing an effective tight-binding force field for a Cu-Zr binary alloy system, and carrying out molecular dynamics simulations. We determined the isothermal Equation of State in a wide range of temperatures and pressures. Pressure-induced cavitation was observed and negative pressure is critical for triggering cavitation. The cavitation barrier height was estimated from the classical nucleation theory. The intrinsic origin of cavitation and its connection to Poisson\u2019s ratio or the ratio of G/B are investigated. The relationship to the deformation and fracture behavior of glasses is discussed.
\r\n\r\nWe designed several novel bulk metallic-glass-forming systems using the link between fragility, elastic properties, and glass forming ability as a guiding tool. The compositional dependence of thermal and elastic properties of Cu-Zr-Be ternary bulk-metallic-glass forming alloys was systematically studied. Lightweight Ti-based bulk amorphous structural metals with more than double the specific strength of conventional titanium alloys have been discovered. We report a novel class of bulk amorphous alloys with benchmark thermoplastic processability, having good glass forming ability, exceptional thermal stability, unexpectedly large Angell fragility number, and good mechanical toughness. Starting from the two binary bulk glass formers in the Cu-Zr system, we systematically investigated the compositional dependence of glass formation, thermal, elastic, and mechanical properties in the Cu-Zr-Ag ternary alloys.
\r\n" }, { "name": "Dunlop, Mary Julia", "degree": "PhD", "year": "2008", "title": "Dynamics and Correlated Noise in Gene Regulation", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302008-141602", "creators": [ { "name": { "family": "Dunlop", "given": "Mary Julia" }, "id": "Dunlop-Mary-Julia", "orcid": "0000-0002-9261-8216", "display_name": "Dunlop, Mary Julia" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "mecheng" ], "doi": "10.7907/AC8V-6S05", "abstract": "Gene regulatory interactions are context dependent, active in some cell types or cellular states but not in others. In this thesis we present a method for determining when a regulatory link is active given temporal measurements of gene expression. Correlations in time-series data are used to determine how genes influence each other and their causal relationships. Natural stochastic noise is shown to aid in the process of network identification by perturbing the expression of genes; the speed and direction at which the noisy signal propagates shows how the network is connected. Cross correlation functions are used to reveal time-delayed correlations.
\r\n\r\nWe develop a stochastic model of gene expression and show that by measuring correlations in cellular noise, it is possible to infer network activity and temporal properties of gene regulation. Using a linearized version of the model, we introduce a method for analytically deriving cross correlation functions for arbitrary networks. These results are validated experimentally using a synthetic gene circuit in E. coli bacteria. Single-cell time-lapse microscopy is used to measure noisy expression of multiple genes over time. Extending this work to natural systems, we study feed-forward loops and determine that certain classes of feed-forward loops are more robust to noise and parameter variations that others. Noise in two naturally occurring feed-forward loops involved in galactose utilization is measured experimentally and it is shown that neither is actively regulating its target in the conditions tested.
" }, { "name": "El Sayed, Tamer", "degree": "PhD", "year": "2008", "title": "Constitutive models for polymers and soft biological tissues", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242007-131150", "creators": [ { "name": { "family": "El Sayed", "given": "Tamer" }, "id": "ElSayed-Tamer", "display_name": "El Sayed, Tamer" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/KH16-4S81", "abstract": "Soft materials such as polymers and biological tissues have several engineering and biomechanical applications. These materials exhibit complex mechanical behavior, characterized by large strains, hysteresis, rate sensitivity, stress softening (Mullins effect), and deviatoric and volumetric plasticity. The need to accurately predict the behavior of such materials has been a tremendous challenge for scientists and engineers.
\r\n\r\nThis thesis presents a seamless, fully variational constitutive model capable of capturing all of the above complex characteristics. Also, this work describes a fitting procedure based on the use of Genetic Algorithms, which proves to be necessary for the multi-modal, non-convex optimization required to identify fitting material parameters.
\r\n\r\nThe capabilities of the presented model are demonstrated via several fits of experimental tests on a wide range of materials. These tests involve monotonic and cyclic loading of polyurea, high-density polyethylene, and brain tissue, and also involve cyclic hysteresis, softening, rate effects, shear, and cavitation plasticity.
\r\n\r\nApplication to ballistic impact on a polyurea retrofitted DH36 steel plate is simulated and validated, utilizing the soft material model presented in this thesis for the polymer and a porous plasticity model for the metal. Localization elements are also included in this application to capture adiabatic shear bands. Moreover, computational capability for assessing the blast performance of metal/elastomer composite shells utilizing the soft material model for the elastomer is also presented.
\r\n\r\nAnother implemented application is in the area of traumatic brain injuries under impact/acceleration loading. Clinically observed brain damage is reproduced utilizing the model presented in this work and a predictive capability of the distribution, intensity, and reversibility/irreversibility of brain tissue damage is demonstrated.
\r\n" }, { "name": "Emery, Teresa Holly", "degree": "PhD", "year": "2008", "title": "Fabrication of Nanowire-based Magnetic Structures for Magnetic Resonance Applications", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062008-115513", "creators": [ { "name": { "family": "Emery", "given": "Teresa Holly" }, "id": "Emery-Teresa-Holly", "display_name": "Emery, Teresa Holly" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Barbic", "given": "Mladen" }, "id": "Barbic-M", "role": "member", "display_name": "Barbic, Mladen" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/3XYZ-BW96", "abstract": "The development and fabrication of novel magnetic nanowire devices is presented. These devices are used both to explore the fundamental physics of single domain particles, and to provide signal amplification and increased resolution in magnetic resonance imaging. Fabrication protocols for the creation of nickel nanowires were developed using both electron beam lithography and electroplating into nanoporous templates. The templates for electroplating were created by anodizing aluminum in either oxalic or sulfuric acids. The templates are 15 to 25 $mu$m thick and composed of highly ordered pores of 40 nm and 20 nm in diameter respectively. Nanowire samples formed by each protocol are characterized using an alternating gradient magnetometer to measure magnetic hysteresis loops. The magnets formed by electroplating were found to be much closer to ideal single domain magnets than those written via electron beam. Coercivities over to 1000 Oe were observed.
\r\n\r\nIndividual cylindrical nanowires of 70 nm diameter were contacted using focused ion beam assisted platinum deposition. A contacted nanowire was tested in a cryostat to determine the temperature dependence of the magneto-resistive properties of the wire. Sections of plated nanowires still in the anodized aluminum template were examined for their reversible transverse susceptibility for applications in signal amplification in magnetic resonance imaging systems. A process of selectively plating into the aluminum templates to create shape magnets with interesting magnetic fields was developed for creating magnetic \"lenses' with focal points above the plane of the substrate. Finally, an inductive stripe loop array was fabricated for use in stripe sensor tomography. These developments will enable future work on magnetic resonance imaging using a background of patterned templates for amplification.
" }, { "name": "Epstein, Michael Steven", "degree": "PhD", "year": "2008", "title": "Managing Information in Networked and Multi-Agent Control Systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-153619", "creators": [ { "name": { "family": "Epstein", "given": "Michael Steven" }, "id": "Epstein-Michael-Steven", "display_name": "Epstein, Michael Steven" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "MacMynowski", "given": "Douglas G." }, "id": "MacMynowski-D-G", "role": "member", "display_name": "MacMynowski, Douglas G." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/84NT-9N46", "abstract": "Traditional feedback control systems give little attention to issues associated with the flow of information through the feedback loop. Typically implemented with dedicated communication links that deliver nearly precise, reliable and non-delayed information, researchers have not needed to concern themselves with issues related to quantized, delayed and even lost information. With the advent of newer technologies and application areas that pass information through non-reliable networks, these issues can not be ignored. In recent years the field of Networked Control Systems (NCS) has emerged to describe situations where these issues are present. The research in this field focuses on quantifying performance degradations in the presence of network effects and proposing algorithms for managing the information flow to counter those negative effects. In this thesis I propose and analyze algorithms for managing information flow for several NCS scenarios; state estimation with lossy measurement signals, using input buffers to reduce the frequency of communication with a remote plant, and performing state estimation when control signals are transmitted to a remote plant via a lossy communication link with no acknowledgement signal at the estimator. Multi-agent coordinated control systems serve as a prime example of an emerging area of feedback control systems that utilize feedback loops with information passed through possibly imperfect communication networks. In these systems, agents use a communication network to exchange information in order to achieve a desired global objective. Hence managing the information flow has a direct impact on the performance of the system. I also explore this area by focusing on the problem of multi-agent average consensus. I propose an algorithm based on a hierarchical decomposition of the communication topology to speed up the time to convergence. For all these topics I focus on designing intuitive algorithms that intelligently manage the information flow and provide analysis and simulations to illustrate their effectiveness.\r\n" }, { "name": "Erickson, Jonathan Christopher", "degree": "PhD", "year": "2008", "title": "The Neurochip: A Complete System for Long-Term Investigation of Cultured Neural Network Connectivity", "advisor": "Pine, Jerome", "url": "https://resolver.caltech.edu/CaltechETD:etd-04162008-113925", "creators": [ { "name": { "family": "Erickson", "given": "Jonathan Christopher" }, "id": "Erickson-Jonathan-Christopher", "display_name": "Erickson, Jonathan Christopher" } ], "advisors": [ { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "advisor", "display_name": "Pine, Jerome" } ], "committee": [ { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "chair", "display_name": "Pine, Jerome" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "bioeng" ], "doi": "10.7907/EAMA-EQ86", "abstract": "Traditional techniques for investigating cultured neural networks, such as the patch clamp and multi-electrode array, are limited by 1) the number of identified cells which can be in simultaneous electrical contact, 2) the length of time for which cells can be studied, and 3) the lack of 1:1 neuron-to-electrode specificity.
\r\n\r\nHere, I present a novel device --- dubbed the \"neurochip\" --- which overcomes these limitations. This micromachined device consists of 4x4 array of \"neurocages\" which mechanically trap a neuron near an extracellular electrode. While the cell body is trapped, the axon and dendrites can freely grow into the surrounding area to form a network. The electrode is bi-directional, capable of both stimulating and recording action potentials. This system is noninvasive, so that an entire network --- all constituent neurons --- can be studied over its lifetime with fixed 1:1 neuron-to-electrode correspondence. Proof-of-concept experiments have been completed to illustrate that functional networks do indeed form in the neurochip system, and that suprathreshold connectivity can be fully mapped over several weeks. The neurochip opens a new domain in neurobiology for studying small cultured neural networks.
\r\n" }, { "name": "Fanti, Claudio", "degree": "PhD", "year": "2008", "title": "Towards Automatic Discovery of Human Movemes", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-02262008-172531", "creators": [ { "name": { "family": "Fanti", "given": "Claudio" }, "id": "Fanti-Claudio", "display_name": "Fanti, Claudio" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Welling", "given": "Max" }, "id": "Welling-M", "role": "member", "display_name": "Welling, Max" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/M4PS-B302", "abstract": "Consider a number of moving points, each attached to a joint of the human body and projected onto an image. Johannson showed that humans can effortlessly detect and recognize the presence of other humans from such displays. This is true even when some of the body parts are missing (e.g., because of occlusion) and unrelated clutter points are added to the display. Furthermore, subtle aspects like age range and gender, as well as the ongoing activity, can be inferred with a surprising degree of accuracy from such a seemingly scarce amount of information. We are interested in replicating some of these abilities in a machine.
\r\n\r\nWe start by introducing a labeling and detection scheme in a Johannson-like display. Our method is based on a probabilistic representation of the positions and motion of body parts, which we use to calculate a likely interpretation of the scene by means of belief propagation techniques. We show how learning and inference can be done efficiently, and we provide an experimental validation of the method.
\r\n\r\nIn the second part of our work, we present our position on the analysis of human behaviors. We hypothesize a hierarchical description of motion, which provides a natural interpretation of actions and activities as stochastic sequences of \"atomic motions\" or movemes. We take an initial step in that direction by illustrating how to learn a dictionary of movemes from the trajectories of body parts, which can be used to concisely represent the video for further analysis.
\r\n" }, { "name": "Feldman, Daniel Robert", "degree": "PhD", "year": "2008", "title": "Remote Sensing of Radiative Fluxes and Heating Rates from Satellite Instrument Measurements", "advisor": "Yung, Yuk L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222008-234331", "creators": [ { "name": { "family": "Feldman", "given": "Daniel Robert" }, "id": "Feldman-Daniel-Robert", "orcid": "0000-0003-3365-5233", "display_name": "Feldman, Daniel Robert" } ], "advisors": [ { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "advisor", "display_name": "Yung, Yuk L." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Liou", "given": "Kuo-Nan" }, "id": "Liou-K", "role": "member", "display_name": "Liou, Kuo-Nan" }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/XMMC-F033", "abstract": "Weather and climate models are required to calculate radiative fluxes and shortwave heating and longwave cooling rate profiles on a large scale. Heating and cooling rates describe the effect that different configurations of temperature, radiatively active gases, and clouds have on the rates of interlayer energy exchange and affect circulation patterns. Meanwhile, a suite of satellite-based instruments from the NASA Earth Observing System\u2019s A-Train provide an unprecedented set of measurements that can be used to produce quantities that can also yield radiative fluxes and heating and cooling rates. This work explores the extent to which passive-infrared hyperspectral measurements such as those made by the Atmospheric Infrared Sounder impart information towards infrared cooling rates. Several novel methods are explored for interpreting and retrieving cooling rates using spectral measurements.
\r\n\r\nFor scenes with optically thick clouds, however, passive visible and infrared measurements will have limited power in describing heating and cooling rates. Vertical cloud information can be obtained from several A-Train instruments: the Microwave Limb Sounder Ice Water Content product provides data on the profiles of ice clouds in the upper troposphere and this work explores how this data can be used to describe the cloud radiative effect. Recently, active-sounding measurements from CloudSat have offered an unrivalled description of cloud profiles which can be used to compute fluxes and heating rates. Preliminary CloudSat products are evaluated and a case study of heating rate analysis is presented in which CloudSat products are used to determine Tropical Tropopause Layer radiation balance.
\r\n\r\nThe radiative processes that affect the far-infrared (wavelengths of 15\u2013100 \u03bcm) are described in a limited fashion by the current suite of A-Train measurements, and yet these spectral regions have a large impact on cooling rates in the troposphere. The extra information gained by the introduction of a set of spectrally resolved far-infrared measurements is discussed for clear and cloudy scenes.
\r\n\r\nFinally, this work discusses future directions for analyzing heating rates derived from remote sensing measurements, and challenges and opportunities for future research.
\r\n" }, { "name": "Flores Contreras, Melvin Estuardo", "degree": "PhD", "year": "2008", "title": "Real-Time Trajectory Generation for Constrained Nonlinear Dynamical Systems Using Non-Uniform Rational B-Spline Basis Functions", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02192008-153449", "creators": [ { "name": { "family": "Flores Contreras", "given": "Melvin Estuardo" }, "id": "Flores-Contreras-Melvin-Estuardo", "display_name": "Flores Contreras, Melvin Estuardo" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Milam", "given": "Mark B." }, "id": "Milam-M-B", "role": "member", "display_name": "Milam, Mark B." } ], "option_major": [ "cds" ], "doi": "10.7907/TK01-9X60", "abstract": "The thesis describes a new method for obtaining minimizers for optimal control problems whose minima serve as control policies for guiding nonlinear dynamical systems to achieve prescribed goals under imposed trajectory and actuator constraints. One of the major contributions of the present work resides in the approximation of such minimizers by piecewise polynomial functions expressed in terms of a linear combination of non-uniform rational B-spline (NURBS) basis functions and the judicious exploitation of the properties of the resulting NURBS curves to improve the computational effort often associated with solving optimal control problems for constrained dynamical systems.
\r\n\r\nIn particular, by exploiting the two structures combined in a NURBS curve, NURBS basis functions and an associated union of overlapping polytopes constructed from the coefficients of the linear combination, we are able to separate an optimal control problem into two subproblems | guidance and obstacle avoidance, making the original problem tractable. This is accomplished by laying out the union of overlapping polytopes in such a way that they delineate a section of space that avoids all obstacles and then manipulating the NURBS basis functions to obtain trajectories that are guaranteed to remain bounded by this section of space without explicitly including the conjunction of disjunctions naturally induced from obstacles into the guidance problem.
\r\n\r\nIn addition, we show how one can construct systematically a feasible region that corresponds to a NURBS parameterization starting from an ordered union of pairwise adjacently overlapping nonempty compact convex sets. Specifically, we show how to setup a nonlinear programming problem to solve for the feasible region in terms of an ordered union of pairwise adjacently overlapping polytopes with nonempty interiors by maximizing the sum of their volumes and starting from a feasible region described by an ordered union of pairwise adjacently overlapping nonempty convex compact simi-algebraic sets. Finally, we show how this strategy can be implemented practically for an autonomous system traversing an urban environment.
\r\n\r\nFinally, this work culminated in the filing of patent US20070179685 on behalf of Northrop Grumman for the Space Technology sector and in the development of the NURBS-based OTG software package. This C++ package contains the theoretical results of this thesis in the form of an object-oriented implementation optimized for real-time trajectory generation.
\r\n\r\n" }, { "name": "Fontaine, Ebraheem Ihsan", "degree": "PhD", "year": "2008", "title": "Automated Visual Tracking for Behavioral Analysis of Biological Model Organisms", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272008-161801", "creators": [ { "name": { "family": "Fontaine", "given": "Ebraheem Ihsan" }, "id": "Fontaine-Ebraheem-Ihsan", "display_name": "Fontaine, Ebraheem Ihsan" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/TSQ7-SN68", "abstract": "Capturing the detailed motion and behavior of biological organisms plays an important role in a wide variety of research disciplines. Many studies in biomechanics, neuroethology, and developmental biology rely on analysis of video sequences to understand the underlying behavior. However, the efficient and rapid quantification of these complex behavioral traits imposes a major bottleneck on the elucidation of many interesting scientific questions. The goal of this thesis is to develop a suite of model-based visual tracking algorithms that will apply across a variety of model organisms used in biology. These automated tracking algorithms operate in a high-throughput, high-resolution manner needed for a productive synthesis with modern genetic approaches. To this end, I demonstrate automated estimation of the detailed body posture of nematodes, zebrafish, and fruit flies from calibrated video.
\r\n\r\nThe current algorithm utilizes a generative geometric model to capture the organism's shape and appearance. To accurately predict the organism's motion between video frames, I incorporate a motion model that matches tracked motion patterns to patterns in a training set. This technique is invariant with respect to the organism's velocity and can easily incorporate training data from completely different motion patterns. The prediction of the motion model is refined using measurements from the image. In addition to high-contrast feature points, I introduce a region, segmentation model based on level sets that are formally integrated into the observation framework of an Iterated Kalman Filter (IKF). The prior knowledge provided by the geometric and motion models improves tracking accuracy in the presence of partial occlusions and misleading visual cues.
\r\n\r\nThe method is used to track the position and shape of multiple nematodes during mating behavior, zebrafish of different ages during escape response, and fruit flies during take off maneuvers. These applications demonstrate the modular design of this model-based visual tracking system, where the user can specify which components are appropriate to a given experiment. In contrast to other approaches, which are customized to a particular organism or experimental setup, my approach provides a foundation that requires little re-engineering whenever the experimental parameters are changed.
" }, { "name": "Franck, Christian", "degree": "PhD", "year": "2008", "title": "Quantitative Characterization of 3D Deformations of Cell Interactions with Soft Biomaterials", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-163638", "creators": [ { "name": { "family": "Franck", "given": "Christian" }, "id": "Franck-Christian", "display_name": "Franck, Christian" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "member", "display_name": "Tirrell, David A." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VMN5-SP86", "abstract": "In recent years, the importance of mechanical forces in directing cellular function has been recognized as a significant factor in biological and physiological processes. In fact, these physical forces are now viewed equally as important as biochemical stimuli in controlling cellular response. Not only do these cellular forces, or cell tractions, play an important role in cell migration, they are also significant to many other physiological and pathological processes, both at the tissue and organ level, including wound healing, inflammation, angiogenesis, and embryogenesis. A complete quantification of cell tractions during cell-material interactions can lead to a deeper understanding of the fundamental role these forces play in cell biology. Thus, understanding the function and role of a cell from a mechanical framework can have important implications towards the development of new implant materials and drug treatments.
\r\n\r\nPrevious research has contributed significant descriptions of cell-tissue interactions by quantifying cell tractions in two-dimensional environments; however, most physiological processes are three-dimensional in nature. Recent studies have shown morphological differences in cells cultured on two-dimensional substrates versus three-dimensional matrices, and that the intrinsic extracellular matrix interactions and migration behavior are different in three dimensions versus two dimensions. Hence, measurement techniques are needed to investigate cellular behavior in all three dimensions.
\r\n\r\nThis thesis presents a full-field imaging technique capable of quantitatively measuring cell traction forces in all three spatial dimensions, and hence addresses the need of a three-dimensional quantitative imaging technique to gain insight into the fundamental role of physical forces in biological processes. The technique combines laser scanning confocal microscopy (LSCM) with digital volume correlation (DVC) to track the motion of fluorescent particles during cell-induced or externally applied deformations. This method is validated by comparing experimentally measured non-uniform deformation fields near hard and soft spherical inclusions under uniaxial compression with the corresponding analytical solution. Utilization of a newly developed computationally efficient stretch-correlation and deconvolution algorithm is shown to improve the overall measurement accuracy, in particular under large deformations.
\r\n\r\nUsing this technique, the full three-dimensional substrate displacement fields are experimentally determined during the migration of individual fibroblast cells on polyacrylamide gels. This is the first study to show the highly three-dimensional structure of cell-induced displacement and traction fields. These new findings suggest a three-dimensional push-pull cell motility, which differs from the traditional theories based on two-dimensional data. These results provide new insight into the dynamic cell-matrix force exchange or mechanotransduction of migrating cells, and will aid in the development of new three-dimensional cell motility and adhesion models.
\r\n\r\nAs this study reveals, the mechanical interactions of cells and their extracellular matrix appear to be highly three-dimensional. It also shows that the LSCM-DVC technique is well suited for investigating the mechanics of cell-matrix interactions while providing a platform to access detailed information of the intricate biomechanical coupling for many cellular responses. Thus, this method has the capability to provide direct quantitative experimental data showing how cells interact with their surroundings in three dimensions and might stimulate new avenues of scientific thought in understanding the fundamental role physical forces play in regulating cell behavior.
" }, { "name": "Gao, Jiansong", "degree": "PhD", "year": "2008", "title": "The Physics of Superconducting Microwave Resonators", "advisor": "Zmuidzinas, Jonas", "url": "https://resolver.caltech.edu/CaltechETD:etd-06092008-235549", "creators": [ { "name": { "family": "Gao", "given": "Jiansong" }, "id": "Gao-Jiansong", "orcid": "0000-0001-9972-6220", "display_name": "Gao, Jiansong" } ], "advisors": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "advisor", "display_name": "Zmuidzinas, Jonas" } ], "committee": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "chair", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Eisenstein", "given": "James P." }, "id": "Eisenstein-J-P", "role": "member", "display_name": "Eisenstein, James P." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/RAT0-VM75", "abstract": "Over the past decade, low temperature detectors have brought astronomers revolutionary new observational capabilities and led to many great discoveries. Although a single low temperature detector has very impressive sensitivity, a large detector array would be much more powerful and are highly demanded for the study of more difficult and fundamental problems in astronomy. However, current detector technologies, such as transition edge sensors and superconducting tunnel junction detectors, are difficult to integrate into a large array.
\r\n\r\nThe microwave kinetic inductance detector (MKID)is a promising new detector technology invented at Caltech and JPL which provides both high sensitivity and an easy solution to the detector integration. It senses the change in the surface impedance of a superconductor as incoming photons break Cooper pairs, by using high-Q superconducting microwave resonators capacitively coupled to a common feedline. This architecture allows thousands of detectors to be easily integrated through passive frequency domain multiplexing.
\r\n\r\nIn this thesis, we explore the rich and interesting physics behind these superconducting microwave resonators. The first part of the thesis discusses the surface impedance of a superconductor, the kinetic inductance of a superconducting coplanar waveguide, and the circuit response of a resonator. These topics are related with the responsivity of MKIDs. The second part presents the study of the excess frequency noise that is universally observed in these resonators. The properties of the excess noise, including power, temperature, material, and geometry dependence, have been quantified. The noise source has been identified to be the two-level systems in the dielectric material on the surface of the resonator. A semi-empirical noise model has been developed to explain the power and geometry dependence of the noise, which is useful to predict the noise for a specified resonator geometry. The detailed physical noise mechanism, however, is still not clear.
\r\n\r\nWith the theoretical results of the responsivity and the semi-empirical noise model established in this thesis, a prediction of the detector sensitivity (noise equivalent power) and an optimization of the detector design are now possible.
\r\n" }, { "name": "Gao, Xiaojie", "degree": "PhD", "year": "2008", "title": "On A Capacitated Multivehicle Routing Problem", "advisor": "Schulman, Leonard J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292007-212511", "creators": [ { "name": { "family": "Gao", "given": "Xiaojie" }, "id": "Gao-Xiaojie", "display_name": "Gao, Xiaojie" } ], "advisors": [ { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "role": "advisor", "display_name": "Schulman, Leonard J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/3Y9X-EW47", "abstract": "The Vehicle Routing Problem (VRP) is a discrete optimization problem with high industrial relevance and high computational complexity. The problem has been extensively studied since it was introduced by Dantzig and Ramser. In a VRP, we are given a number of customers with known delivery requirements and locations (assumed to be vertices in a network). A fleet of vehicles with limited capacity is available. The objective is to design routes and customer assignments to minimize the total time or distance traveled to serve the demands. Because of its practical significance, this problem has been widely studied.
\r\n\r\nIn this thesis, we present a version of the VRP motivated by mobile sensor networks which we call the Capacitated Multivehicle Routing Problem (CMVRP). In our framework, there are multiple geographically disperse vehicles each equipped with a limited energy supply. The vehicle consumes energy as it moves around and it also consumes energy while serving jobs. This situation models a network of mobile sensors where locomotion and computation all drain the limited capacity battery onboard. Our objective is to determine the minimum amount of energy required to serve all jobs, which takes into account both the service requirement and the travel overhead. We present a constant factor approximation algorithm. Furthermore, we study the on-line problem where job demands arrive sequentially and present a distributed algorithm that serves all jobs using only a constant factor more energy than the off-line solution.
" }, { "name": "Grosberg, Anna", "degree": "PhD", "year": "2008", "title": "A Bioinspired Computational Model of Cardiac Mechanics: Pathology and Development", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-152117", "creators": [ { "name": { "family": "Grosberg", "given": "Anna" }, "id": "Grosberg-Anna", "orcid": "0000-0002-8878-0843", "display_name": "Grosberg, Anna" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/THMJ-C355", "abstract": "In this work we study the function and development of the myocardium by creating models that have been stripped down to essentials. The model for the adult myocardium is based on the double helical band formation of the heart muscle fibers, observed in both histological studies and advanced DTMRI images. The muscle fibers in the embryonic myocardium are modeled as a helical band wound around a tubular chamber. We model the myocardium as an elastic body, utilizing the finite element method for the computations. We show that when the spiral band architecture is combined with spatial wave excitations the structure is twisted, thus driving the development of the embryonic heart into an adult heart. The double helical band model of the adult heart allows us to gain insight into the long standing paradox between the modest, by only 15 %, ability of muscle fibers to contract, and the large left ventricular volume ejection fraction of 60 %. We show that the double helical band structure is the essential factor behind such efficiency. Additionally, when the double helical band model is excited following the path of the Purkinje nerve network, physiological twist behavior is reproduced. As an additional validation, we show that when the stripped down double helical band is placed inside a sack of soft collagen-like tissue it is capable of producing physiologically high pressures.
\r\n\r\nWe further develop the model to understand the different factors behind the loss of efficiency in heart with a common pathology such as dilated cardiomyopathy. Using the stripped down model we are able to show that the change to fiber angle is the much more important factor to heart function than the change in gross geometry. This finding has the potential to greatly impact the strategy used in certain surgical procedures.
" }, { "name": "Grubits, Katalin Anna", "degree": "PhD", "year": "2008", "title": "Low-Dimensional Representations of Transitions in Molecular Systems", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062008-171210", "creators": [ { "name": { "family": "Grubits", "given": "Katalin Anna" }, "id": "Grubits-Katalin-Anna", "display_name": "Grubits, Katalin Anna" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Kuppermann", "given": "Aron" }, "id": "Kuppermann-A", "role": "member", "display_name": "Kuppermann, Aron" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "cds" ], "doi": "10.7907/YMTC-WQ16", "abstract": "A major difficulty in modeling molecular systems is that the number of dimensions, even for a small system, is commonly too large for computation to be feasible. To overcome this challenge, a combination of lower-dimensional representations of the system and improved computational methods are required. In this thesis, we investigate techniques to achieve both of these aims via three model problems.
\r\n\r\nBy exploiting an understanding of the mechanism and dynamics of reaction in the systems considered, we attain a low-dimensional description of the transition that captures the essential dynamics. For the ionization of a Rydberg atom we utilize concepts from dynamical systems theory that reveal the geometric structures in phase space that mediate the reaction. The gyration radius formalism captures the kinematic effects of the secondary particles in a coarse variable that reduces the number of dimensions of the model, thereby providing a simple description of our methane and oxygen dissociation example. These methods are applicable more generally and provide a coarse model of chemical reactions that can be combined with efficient computational tools, such as the set-oriented method employed in our Rydberg example, to efficiently compute reaction rates of previously difficult problems.
\r\n\r\nThe third model problem considered is the self-assembly of particles into an ordered lattice configuration under the influence of an isotropic inter-particle potential. With the aim of characterizing the transition from a disordered to an ordered state, we develop metrics that assess the quality of the lattice with respect to the target lattice configuration. The five metrics presented use a single number to quantify the order within this large system of particles. We explore numerous applications of these quality assessment tools, in particular, finding the optimal potential for self-assembly. The very noisy, highly variable nature of our expensive-to-evaluate objective function prompted the development of a trend optimization algorithm that efficiently minimizes the objective function, using upper and lower envelopes that are responsible for the robustness of the method and the solution. This trend optimization scheme is widely applicable to problems in other fields.
" }, { "name": "Han, Lin", "degree": "PhD", "year": "2008", "title": "In vitro DNA Mechanics in Gene Regulation: One Molecule at a Time", "advisor": "Phillips, Robert B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282008-150852", "creators": [ { "name": { "family": "Han", "given": "Lin" }, "id": "Han-Lin", "display_name": "Han, Lin" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "advisor", "display_name": "Phillips, Robert B." } ], "committee": [ { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "chair", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7573-A922", "abstract": "The biological significance of DNA is primarily attributed to its sequence information. On the other hand, the mechanical properties of DNA can play a critical role in a wide variety of biological processes. One prime example is DNA looping in the context of transcriptional regulation. The emergence of single molecule tracking techniques in the last two decades presents an unprecedented opportunity for studying looping kinetics. One such powerful technique, tethered particle motion (TPM), harnesses the Brownian motion of a microsphere as a means of reporting on the excursion of its tethered molecule, such as DNA. The present work focuses on a looping system found in Escherichia coli, which is mediated by the Lac repressor (LacI) protein. TPM is used to measure individual, real-time looping/unlooping events in DNA of various length and sequence characteristics. By monitoring the magnitude, frequency, and time interval of these features while tuning different parameters, such as LacI concentration, DNA length and DNA sequence, one can survey a host of important information about looping kinetics. A measurement of the LacI concentration dependence of looping probability was found to be in quantitative agreement with a simple thermodynamic model, which also led to the measurement of free energy of LacI-mediated looping, the first such measurement in a single molecule, in vitro setting. A quantitative characterization of free energy was obtained under conditions of different inter-operator spacing, systematically varied from 300 to 310 base pairs in one-base-pair increments. An important conclusion from this study is that free energy is modulated by DNA\u2019s helical structure, yet the energy difference between the aligned and unaligned operator configurations is small compared to expectation from simple polymer physics. TPM measurements also revealed an additional looped state, lending support to the hypothesis that two distinct conformations of LacI, the closed and open forms, can coexist. This study also confirmed that the presence of certain DNA sequences, particularly TA pairs in the minor groove of the nucleosomal positioning sequence, makes DNA substantially softer than a corresponding random sequence. This provides direct support for the notion of sequence-dependent DNA elasticity. Finally, a surprising result is that loops as short as 100 base pairs-only two-thirds the persistence length of DNA-can form by LacI-DNA binding. Classical elasticity theory almost forbids this, suggesting that LacI itself plays a more direct role in the bending process, or classical understanding of DNA elasticity breaks down at length scales comparable to its persistence length." }, { "name": "Helgason, Hannes", "degree": "PhD", "year": "2008", "title": "Nonparametric Detection and Estimation of Highly Oscillatory Signals", "advisor": "Candes, Emmanuel J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05112008-152328", "creators": [ { "name": { "family": "Helgason", "given": "Hannes" }, "id": "Helgason-Hannes", "display_name": "Helgason, Hannes" } ], "advisors": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "advisor", "display_name": "Candes, Emmanuel J." } ], "committee": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "chair", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Weinstein", "given": "Alan Jay" }, "id": "Weinstein-Alan-J-Physics", "role": "member", "display_name": "Weinstein, Alan Jay" }, { "name": { "family": "Lorden", "given": "Gary A." }, "id": "Lorden-G-A", "role": "member", "display_name": "Lorden, Gary A." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/SAEK-MV13", "abstract": "This thesis considers the problem of detecting and estimating highly oscillatory signals from noisy measurements. These signals are often referred to as chirps in the literature; they are found everywhere in nature, and frequently arise in scientific and engineering problems. Mathematically, they can be written in the general form A(t) exp(ilambda varphi(t)), where lambda is a large constant base frequency, the phase varphi(t) is time-varying, and the envelope A(t) is slowly varying. Given a sequence of noisy measurements, we study two problems seperately: 1) the problem of testing whether or not there is a chirp hidden in the noisy data, and 2) the problem of estimating this chirp from the data.
\r\n\r\nThis thesis introduces novel, flexible and practical strategies for addressing these important nonparametric statistical problems. The main idea is to calculate correlations of the data with a rich family of local templates in a first step, the multiscale chirplets, and in a second step, search for meaningful aggregations or chains of chirplets which provide a good global fit to the data. From a physical viewpoint, these chains correspond to realistic signals since they model arbitrary chirps. From an algorithmic viewpoint, these chains are identified as paths in a convenient graph. The key point is that this important underlying graph structure allows to unleash very effective algorithms such as network flow algorithms for finding those chains which optimize a near optimal trade-off between goodness of fit and complexity.
\r\n\r\nOur estimation procedures provide provably near optimal performance over a wide range of chirps and numerical experiments show that both our detection and estimation procedures perform exceptionally well over a broad class of chirps. This thesis also introduces general strategies for extracting signals of unknown duration in long streams of data when we have no idea where these signals may be. The approach is leveraging testing methods designed to detect the presence of signals with known time support.
\r\n\r\nUnderlying our methods is a general abstraction which postulates an abstract statistical problem of detecting paths in graphs which have random variables attached to their vertices. The formulation of this problem was inspired by our chirp detection methods and is of great independent interest.
" }, { "name": "Heng, Xin", "degree": "PhD", "year": "2008", "title": "Optofluidic Microscopy: Technology Development and Its Applications in Biology", "advisor": "Yang, Changhuei", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182007-163333", "creators": [ { "name": { "family": "Heng", "given": "Xin" }, "id": "Heng-Xin", "display_name": "Heng, Xin" } ], "advisors": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "advisor", "display_name": "Yang, Changhuei" } ], "committee": [ { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "chair", "display_name": "Yang, Changhuei" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "co-chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "orcid": "0000-0002-6945-9958", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "orcid": "0000-0002-7699-0173", "role": "member", "display_name": "Sternberg, Paul W." }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JAYF-RX26", "abstract": "The Optofluidic Microscope (OFM) is a new imaging platform based upon nanoapertures that are fabricated on planar metallic film, whilst microfluidic delivery technology is used to transport the objects-of-interest. The planar nature of OFM makes it ideal to integrate with other micro total analysis systems, such as cell sorters or cell culturing chambers. Furthermore, a variety of imaging functionalities, such as differential phase contrast, fluorescence, and Raman spectroscopy can potentially fit into a single OFM device.
\r\n\r\nThis thesis reports on the early technology development of Optofluidic Microscopy. I have built a variety of off-chip prototypes of OFM that all possess different functionalities. These OFM prototypes include 1D array OFM, hydraulically pumped OFM, 2D nanoaperture grid OFM, super high-resolution OFM, OFM coupled with optical tweezer actuation, fluorescent OFM, electrokinetic enabled OFM, etc.
\r\n\r\nI applied the first OFM prototype in imaging Caenorhabditis elegans (C. elegans) larvae and characterizing different genotypes. Later on, the microscopy properties of OFM, such as the optical resolution and the depth of field, were thoroughly investigated both experimentally and theoretically. More recently, I successfully combined optical tweezers with a grid-based OFM prototype, which was then used in high-resolution imaging of microspheres and a few biological samples. In addition, preliminary results on fluorescence OFM imaging were also demonstrated.
\r\n\r\nI trust that these functionalities, after being demonstrated off-chip, can be readily fabricated and then assembled as a complete on-chip OFM. It will eventually enable a real \"microscale microscope on a chip\".
\r\n" }, { "name": "Heo, Jinseong", "degree": "PhD", "year": "2008", "title": "Probing Electronic Properties of Carbon Nanotubes", "advisor": "Bockrath, Marc William", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022008-222640", "creators": [ { "name": { "family": "Heo", "given": "Jinseong" }, "id": "Heo-Jinseong", "display_name": "Heo, Jinseong" } ], "advisors": [ { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "advisor", "display_name": "Bockrath, Marc William" } ], "committee": [ { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "chair", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Motrunich", "given": "Olexei I." }, "id": "Motrunich-Olexei", "orcid": "0000-0001-8031-0022", "role": "member", "display_name": "Motrunich, Olexei I." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/A83N-TN35", "abstract": "Carbon nanotubes are quasi-one-dimensional objects that have many remarkable electronic properties. In Chapter I, an electrostatic force microscopy technique to probe the local density of states of single-walled carbon nanotubes (SWCNTs) under ambient conditions is described. Coupling the atomic force microscope tip motion with the quantum capacitance of nanotubes enables the van Hove singularities in the one-dimensional density of states to be resolved. We utilized this technique to identify individual semiconducting and metallic tubes, and further to estimate the chiral angle of a nanotube. Moreover, in order to realize a SWCNT interferometer, nanotube loop devices where a self-crossing geometry yields two electron paths that is a possible analog of the optical Sagnac interferometer are fabricated and explored in Chapter II. Scanning gate microscopy reveals for semiconducting devices a 0\u201350% transmission probability into the loop segment at the junction, which can be controlled by applying back gate voltage, hence shifting the Fermi level of the nanotube. Metallic loop devices having low contact resistance showed a large- scale conductance peak with fast oscillations superposed on it. Possible theoretical explanations including Sagnac-type interference, which takes the velocity difference between left and right movers in to account, and Fabry-Perot-type interference are compared with the experimental observations. In Chapter III, in accordance with increasing demand for developing spin-electronic devices, cobalt-filled multi-walled carbon nanotubes (Co\u2013filled MWCNTs) are first synthesized and imaged by transmission electron microscopy, and also characterized by various spectroscopy tools like X\u2013ray diffraction and energy dispersive X\u2013ray spectrometry. Further, a Co\u2013filled MWCNT device having reproducible switching in magnetoresistance was demonstrated. The last topic, in Chapter IV, covers the effects of a transverse electric field in MWCNT devices, where conductance fluctuations as a function of the transverse electric field were observed. The electric field spacing between the peaks of the fluctuations is in agreement with the theoretical predictions of band structure modulation by transverse electric fields. Future work following our experimental studies is proposed and discussed at the end of each chapter." }, { "name": "Hoch, David", "degree": "PhD", "year": "2008", "title": "Nonreflecting Boundary Conditions Obtained from Equivalent Sources for Time-Dependent Scattering Problems", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202008-111349", "creators": [ { "name": { "family": "Hoch", "given": "David" }, "id": "Hoch-David", "display_name": "Hoch, David" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/5M0P-NR33", "abstract": "In many engineering applications, scattering of acoustic or electromagnetic waves from a body of arbitrary shape is considered in an infinite medium. Solving the underlying partial differential equations with a standard numerical method such as finite elements or finite differences requires truncating the unbounded domain of definition into a finite computational region. As a consequence, an appropriate boundary condition must be prescribed at the artificial boundary. Many approaches have been proposed for this fundamental problem in the field of wave scattering. All of them fall into one of three main categories.
\r\n\r\nThe first class of methods is based on mathematical approximations or physical heuristics. These boundary conditions are easy to implement and run in short computing times. However, these approaches give rise to spurious reflections at the artificial boundary, which travel back into the computational domain and corrupt the solution.
\r\n\r\nA second group consists of accurate and convergent methods. However, these formulations are usually harder to implement and often more expensive than the computation of the interior scheme itself.
\t\r\n\r\nFinally, there are methods which are accurate and fast. The drawback of these approaches lies in the fact that the outer boundary must be taken to be either a sphere, a plane, or a cylinder. For many applications of interest, this may require use of a computational domain much larger than actually needed, which leads to an expensive overall numerical scheme.
\r\n\r\nThis work introduces a new methodology in order to compute the fields at the artificial boundary. Like the second class of methods described above, the proposed algorithm is accurate and numerically convergent, yet its computational cost is less than the underlying portion of the volumetric calculation. And, unlike the third category, this new approach allows us to choose the artificial boundary to be arbitrarily close to the scatterer. This method is based on a novel concept of \"equivalent source' representations which allows a highly accurate and fast evaluation of the boundary condition.
" }, { "name": "Imoukhuede, Princess Ikhianosen Uerenikhosen", "degree": "PhD", "year": "2008", "title": "Visualizing the Membrane Confinement, Trafficking and Structure of the GABA Transporter, GAT1", "advisor": "Lester, Henry A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03142008-155402", "creators": [ { "name": { "family": "Imoukhuede", "given": "Princess Ikhianosen Uerenikhosen" }, "id": "Imoukhuede-Princess-Ikhianosen-Uerenikhosen", "orcid": "0000-0002-4257-1085", "display_name": "Imoukhuede, Princess Ikhianosen Uerenikhosen" } ], "advisors": [ { "name": { "family": "Lester", "given": "Henry A." }, "id": "Lester-H-A", "role": "advisor", "display_name": "Lester, Henry A." } ], "committee": [ { "name": { "family": "Lester", "given": "Henry A." }, "id": "Lester-H-A", "role": "chair", "display_name": "Lester, Henry A." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Chow", "given": "Robert" }, "id": "Chow-Robert", "role": "member", "display_name": "Chow, Robert" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/3Q8S-CV89", "abstract": "Transporter trafficking regulators can play an important role in maintaining the transporter density necessary for effective function. I determine interactions that confine GAT1 at the membrane by investigating GAT1 lateral mobility through fluorescence recovery after photobleaching (FRAP). I find that the mobility of GAT1 can be increased by depolymerizing actin or by blocking the GAT1 PDZ interacting domain. I also identify ezrin as the GAT1 adaptor to actin. Through fluorescence resonance energy transfer (FRET), the distance between GAT1-YFP and Ezrin-CFP is calculated as 64--68 \u00c5, and it can be significantly increased by disrupting the actin cytoskeleton. Altogether, my data reveals that actin confines GAT1 to the plasma membrane via ezrin, an interaction mediated through the GAT1-PDZ interaction domain.
\r\n\r\nDiscoveries in the field of vesicle fusion provide direct ties to translational research. While the study of vesicle fusion classically has been applied to neurotransmitter and neuropeptide containing vesicles; there is evidence that secretory vesicles physiologically differ from vesicles trafficking membrane protein. For instance, GAT1 resides on a vesicle lacking neurotransmitter but containing some v-SNARE proteins. These differences in the vesicle composition suggest inherent differences in trafficking mechanisms, which can only be confirmed through further study of membrane protein trafficking. To this end, I apply total internal reflection fluorescence microscopy (TIRFM) to quantify the number of GAT1 molecules on vesicles and to observe the movement of vesicles containing fluorescently tagged GAT1 into the plasma membrane. I determine that these vesicles contain 3--7 molecules of GAT1 and uncover a population of GAT1 vesicles with ATP-dependent lateral displacement.
\r\n\r\nThe protein-protein interactions, trafficking, and oligomerization of mouse GAT1 were studied using fourteen different fusions of mGAT1 with fluorescent protein. We determine that a natural PDZ-interacting motif is minimally required for wild-type GAT1 behavior. Fusions with wild-type function yielded up to 21% FRET efficiency, indicating efficient GAT1 oligomerization. Additionally, 45% FRET was observed between a GAT1 construct and YFP-syntaxin-1A. Inserting XFP between R565 and L566, resulted in 33% FRET but impaired function, which indicated the \"RL\" motif in the proximal C terminus governs export from the endoplasmic reticulum but not transporter oligomerization.
" }, { "name": "Jackson, Winston Paul", "degree": "PhD", "year": "2008", "title": "Characterization of Soft Polymers and Gels Using the Pressure-Bulge Technique", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302008-161653", "creators": [ { "name": { "family": "Jackson", "given": "Winston Paul" }, "id": "Jackson-Winston-Paul", "display_name": "Jackson, Winston Paul" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/DMZ9-RE14", "abstract": "A method to characterize the bulk hydrated properties of soft polymers and hydrogels, whose moduli are in the low MPa regime, using the pressure-bulge technique is presented. The pressure-bulge technique has been used extensively in the characterization of thin films, particularly for the case of metals. The extension of the plane-strain and circular bulge techniques to determine the Young's modulus and Poisson's ratio of bulk latex and silicone rubber sheets are shown here, in addition to the viscoelastic behavior of 5% agarose gels in the time domain using relaxation tests.
\r\n\r\nThe membranes are clamped between two stainless steel plates that are connected to a liquid pressure chamber. A syringe connected to a linear actuator causes changes in the pressure and displacement, and a pressure sensor and confocal displacement sensor are used to monitor these changes in real time. The theory presented converts the measured pressure and displacement data into stress and stretch data, using a geometrically nonlinear analysis, and the elastic/viscoelastic properties are then determined from this data.
\r\n\r\nThe results from the bulge tests are compared with data from uniaxial tension tests on hydrated specimens, and the data comparison with respect to each of the materials tested show good agreement between the two measurements. These results show promise regarding the use of pressure-displacement techniques to characterize other soft material systems, including biological polymers and tissues, as well as cell-to-matrix and cell-to-cell interactions under varying mechanical loading conditions of cell substrates.
\r\n" }, { "name": "Jang, Wonjin", "degree": "PhD", "year": "2008", "title": "Soft-Error Tolerant Quasi Delay-insensitive Circuits", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092007-180524", "creators": [ { "name": { "family": "Jang", "given": "Wonjin" }, "id": "Jang-Wonjin", "display_name": "Jang, Wonjin" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/ZVFF-WE07", "abstract": "A hard error is an error that damages a circuit irrevocably; a soft error flips the logic states without causing any physical damage to the circuit, resulting in transient corruption of data. They result in transient, inconsistent corruption of data.
\r\n\r\nThe soft-error tolerance of logic circuits is recently getting more attention, since the soft- error rate of advanced CMOS devices is higher than before. As a response to the concern on soft errors, we propose a new method for making asynchronous circuits tolerant to soft errors. Since it relies on a property unique to asynchronous circuits, the method is different from what is done in synchronous circuits with triple modular redundancy. Asynchronous circuits have been attractive to the designers of reliable systems, because of their clock-less design, which makes them more robust to variations on computation time of modules. The quasi delay-insensitive (QDI) design style is one of the most robust asynchronous design styles for general computation; it makes one minimal assumption on delays in gates and wires. QDI circuits are easy to verify, simple, and modular, because the correct operation of a QDI circuit is independent of delays in gates and wires.
\r\n\r\nHere, we shall overview how to design a QDI circuit, and what will happen if a soft error occurs on a QDI circuit. Then the crucial components of the method are shown: (1) a special kind of duplication for random logic (when each bit has to be corrected individually), (2) special protection circuitry for arbiter and synchronizer (as needed for example for external interrupts), (3) reconfigurable circuits using a special configuration unit, and (4) error correcting for memory arrays and other structures in which the data bits can be self- corrected. The solution of protecting random logic is compared with alternatives, which use other types of error correcting codes (e.g., parity code) in a QDI circuit. It turns out that the duplication generates efficient circuits more commonly than other possible constructions. Finally, the design of a soft-error tolerant asynchronous microprocessor is detailed and testing results of the soft-error tolerance of the microprocessor are shown.
\r\n\r\n" }, { "name": "Jiang, Hao", "degree": "PhD", "year": "2008", "title": "Adaptive Feature Selection in Pattern Recognition and Ultra-Wideband Radar Signal Analysis", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302008-134607", "creators": [ { "name": { "family": "Jiang", "given": "Hao" }, "id": "Jiang-Hao", "display_name": "Jiang, Hao" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "mecheng" ], "doi": "10.7907/7NR6-AR24", "abstract": "Feature selection from measured data aims to extract informative features to reveal the statistic or stochastic mechanism underlying the complicated or high dimensional original data. In this thesis, the feature selection problem is probed under two situations, one is pattern recognition and the other is ultra-wideband radar signal analysis.
\r\n\r\nClassical pattern recognition methods select features by their ability to separate the multiple classes with certain gauge measure. The deficiency in this general strategy is its lack of adaptation in specific situations. This deficiency may be overcome by viewing the selected features as a function of not only the training samples but also the unlabeled test data. From this perspective, this thesis proposes an adaptive sequential feature selection algorithm which utilizes an information-theoretic measure to reduce the classification task complexity sequentially, and finally outputs the probabilistic classification result and its variation level. To verify the potential advantage of this algorithm, this thesis applies it to one important problem of neural prosthesis, which concerns decoding a finite number of classes, intended reach directions, from recordings of neural activities in the Parietal Reach Region of one rhesus monkey. Experimental results show that the classification scheme of combining the adaptive sequential feature selection algorithm and the information fusion method outperforms some classical pattern recognition rules, such as the nearest neighbor rule and support vector machine, in decoding performance.
\r\n\r\nThe second scenario in this thesis targets developing a human presence and motion pattern detector through ultra-wideband radar signal analysis. To augment the detection robustness, both static and dynamic features should be utilized. The static features reflect the information of target geometry and its variability, while the dynamic features extract the temporal structure among radar scans. The problem of static feature selection is explored in this thesis, which utilizes the Procrustes shape analysis to generate the representative template for the target images, and makes statistical inference in the tangent space through the Hotelling one sample test. After that, the waveform shape variation structure is decomposed in the tangent space through the principal component analysis. The selected principal components not only accentuate the prominent dynamics of the target motion, but also generate another informative classification feature.
\r\n" }, { "name": "Johnsen, Eric", "degree": "PhD", "year": "2008", "title": "Numerical Simulations of Non-Spherical Bubble Collapse with Applications to Shockwave Lithotripsy", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092008-171346", "creators": [ { "name": { "family": "Johnsen", "given": "Eric" }, "id": "Johnsen-Eric", "orcid": "0000-0001-9530-408X", "display_name": "Johnsen, Eric" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/WPQB-2W24", "abstract": "Shockwave lithotripsy (SWL) is a non-invasive medical procedure in which shockwaves are focused on kidney stones in an attempt to break them. Because the stones are usually immersed in liquid, cavitation occurs during the process. However, the stone comminution mechanisms and the bubble dynamics of SWL are not fully understood. In the present thesis, numerical simulations are employed to study axisymmetric Rayleigh collapse and shock-induced collapse of a single gas bubble in a free field and near a wall. A high-order accurate, quasi-conservative, shock- and interface-capturing scheme is developed to solve the multicomponent Euler equations.
\r\n\r\nThe primary contributions of the present work are the development of a new numerical framework to study compressible multicomponent flows, the characterization of the dynamics of non-spherical bubble collapse, and quantitative measurements of wall pressures generated by bubble collapse. Because of asymmetries in the flow field, a re-entrant jet develops and generates a large water-hammer pressure upon impact onto the distal side. Jet properties are calculated and, as an indication of potential damage, wall pressures are measured; pressures on the order of 1 GPa are achieved locally. In shock-induced collapse, the wall pressure is amplified by the presence of bubbles within several initial radii from the wall. Thus, the pressure generated by the bubble collapse is larger than the incoming shock. The results extended to SWL show that shock-induced collapse has tremendous potential for damage along the stone surface. Furthermore, the simulations are coupled to an elastic wave propagation code to show that bubble collapse may cause damage within kidney stones as well.
\r\n" }, { "name": "Kao, Shannon Theresa", "degree": "PhD", "year": "2008", "title": "Detonation Stability with Reversible Kinetics", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022008-170629", "creators": [ { "name": { "family": "Kao", "given": "Shannon Theresa" }, "id": "Kao-Shannon-Theresa", "display_name": "Kao, Shannon Theresa" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/H8JN-VS03", "abstract": "Detonation propagation is unsteady due to the innate instability of the reaction zone structure. Up until the present, investigations of detonation stability have been exclusively concerned with model systems using the perfect gas equation of state and primarily single-step irreversible reaction mechanisms.
\r\n\r\nThis study investigates detonation stability characteristics with reversible chemical kinetics models. To allow for more general kinetics models, we generalize the perfect gas, one-step irreversible kinetics, linear stability equations to a set of equations using the ideal gas equation of state and a general reaction scheme. We linearly perturb the reactive Euler equations following the method of Lee and Stewart (1990) and Short and Stewart (1998). Our implementation uses Cantera (Goodwin, 2005) to evaluate all thermodynamic quantities and evaluate generalized analytic derivatives of quantities dependent on the kinetics model.
\r\n\r\nThe computational domain is the reaction zone in the shock-fixed frame such that the left boundary conditions are the perturbed shock jump conditions which we have derived for a general equation of state and implemented for an ideal gas equation of state. At the right boundary, the system must satisfy a radiation condition requiring that all waves travel out of the domain. Unlike the case of a single reversible reaction, in a truly multistep kinetics model, the radiation boundary condition cannot be solved analytically. In this work, we provide a general methodology for satisfying the appropriate boundary condition.
\r\n\r\nWe then investigate the effects of reversibility on the characteristics of the instability in one and two dimensions. These characteristics are quantified by the unstable eigenvalues as well as the shape of the base flow and eigenfunctions. We show that there is an exchange of stability as a function of reversibility. To confirm the results our work, we have performed unsteady calculations. We show that we can match the frequencies predicted by our linear stability calculations near the stability threshold.
" }, { "name": "Kumar, Shwetank", "degree": "PhD", "year": "2008", "title": "Submillimeter Wave Camera Using A Novel Photon Detector Technology", "advisor": "Zmuidzinas, Jonas", "url": "https://resolver.caltech.edu/CaltechETD:etd-05072008-075138", "creators": [ { "name": { "family": "Kumar", "given": "Shwetank" }, "id": "Kumar-Shwetank", "display_name": "Kumar, Shwetank" } ], "advisors": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "advisor", "display_name": "Zmuidzinas, Jonas" } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/F58T-SV45", "abstract": "Cryogenic photon detectors can be used to make extremely sensitive cameras for submillimeter astronomy. Current detector technologies already have sensitivities limited by the noise due to photon arrival statistics. To further improve the sensitivity and mapping speed of experiments for a wide field survey, focal planes containing tens of thousands of pixels are required. Unfortunately, the current technologies use discrete and massive components which are not easy to integrate into large arrays. This thesis presents a 16-pixel, two-color, submillimeter-wave, prototype camera developed at Caltech and the Jet Propulsion Laboratory using a novel photon detector technology. The camera also uses new designs for other constituent elements \u2013 the antenna, transmission line feednetwork, and bandpass filters \u2013 to implement the sub-millimeter pixels. These designs allow integration of the entire camera onto a single chip and conclusively address the problem of scalability while maintaining the sensitivity and noise performance of the current technologies. This thesis explains the design of each of these components and presents the results from experiments conducted to test their performance. Results from the 'first light', obtained by mounting the prototype camera onto the Caltech Submillimeter Observatory (CSO), are also presented.
\r\n\r\nWe have also studied the temperature and power dependence of the resonance frequency, quality factor, and frequency noise of the superconducting niobium thin-film coplanar waveguide (CPW) resonators in order to understand the factors affecting the noise performance of our photon detectors. These experiments were carried out at temperatures well below the superconducting transition (Tc = 9.2 K) in an attempt to understand the source of the excess frequency noise of superconducting resonators which form the sensing element of our photon detectors. The noise decreases by nearly two orders of magnitude as the temperature is increased from 120 to 1200 mK, while the variation of the resonance frequency with temperature over this range agrees well with the standard two-level systems (TLS) model for amorphous dielectrics. These results support the hypothesis that TLS are responsible for the noise in superconducting microresonators and have important implications for resonator applications such as qubits and photon detectors.
\r\n" }, { "name": "Lee, Wonhee", "degree": "PhD", "year": "2008", "title": "Microfluidic Chip Calorimeters for Biological Applications", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282008-103138", "creators": [ { "name": { "family": "Lee", "given": "Wonhee" }, "id": "Lee-Wonhee", "orcid": "0000-0003-0119-4372", "display_name": "Lee, Wonhee" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/W8E0-4W22", "abstract": "The usage of calorimeters is limited due to its long measurement time and large sample consumption, despite its many advantages including universal applicability and simple sample preparation. Miniaturization of calorimeters not only resolves these problems, it also enables high-throughput measurements with array operations. We have developed microfluidic chip calorimeters with high sensitivity and reliable microfluidics-based sample handling. Immense sensitivity improvements are attained through reduction of the thermal conductance via on-chip vacuum insulation. This is enabled by Parylene thin-film microfluidic systems. Polydimethylsiloxane microfluidic systems, combined with the Parylene microfluidic system, gives easy and accurate control of picoliter-scale sample volume in a manner that is easily scalable to large, complex systems. Two device classes have been realized.
\r\n\r\nHeat conduction calorimeters for biochemical reactions with 3.5 nL sample volume were built and validated by measurements of the heat of mixing and of enzyme activity. The thermal conductance of these devices was 15.5 \u00b5W/K and their power sensitivity was 4.2 nW. These devices can be built as calorimetric arrays to enable high-throughput heat of reaction measurements upon libraries of biomolecular interactions.
\r\n\r\nFlow calorimeters were designed for sensor applications and measurements of cellular metabolism. The thermal conductance of these devices was 4.7 \u00b5W/K and their power sensitivity was 1.5 nW. Further reduction of thermal conductance and optimal thermocouple materials will deliver sensitivity of order ~1 pW, which will enable real-time measurement of single cell metabolism.
" }, { "name": "Leprince, Sebastien", "degree": "PhD", "year": "2008", "title": "Monitoring Earth Surface Dynamics with Optical Imagery", "advisor": "Avouac, Jean-Philippe", "url": "https://resolver.caltech.edu/CaltechETD:etd-05192008-161405", "creators": [ { "name": { "family": "Leprince", "given": "Sebastien" }, "id": "Leprince-Sebastien", "orcid": "0000-0003-4555-8975", "display_name": "Leprince, Sebastien" } ], "advisors": [ { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "role": "advisor", "display_name": "Avouac, Jean-Philippe" } ], "committee": [ { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "role": "chair", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Simons", "given": "Mark" }, "id": "Simons-M", "role": "member", "display_name": "Simons, Mark" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZMTV-GV90", "abstract": "Despite the increasing availability of high-quality optical satellite images, continuous monitoring of Earth's surface changes is still of limited use due to technical limitations. To overcome these limitations, this thesis presents a processing chain to accurately orthorectify and co-register sets of satellite and aerial images, which, associated with a precise correlation technique, allow for the measurement of horizontal ground deformations with accuracy better than 1/10 of the pixel size. The irregular resampling problem is addressed to avoid introducing aliasing in the orthorectified images. Image registration and correlation is achieved with an iterative, unbiased processor that estimates the phase plane in the Fourier domain for sub-pixel shift detection. Errors due to the imaging system are calibrated and modeled, topography artifacts are characterized and solutions are proposed to compensate or to filter them.
\r\n\r\nA software package implementing these procedures, Co-registration of Optically Sensed Images and Correlation (COSI-Corr), is available from the Caltech Tectonics Observatory website. The procedure is validated in several different contexts, and applied to seismo-tectonics and glaciology studies.
\r\n\r\nAccurate measurements of horizontal co-seismic displacements in the near fault zone allow unambiguous imaging of surface ruptures. It is shown that measurements of surface ruptures from optical aerial and satellite images compare well with field measurements, and that in addition they have the potential of densely measuring the fault perpendicular component, and the off-fault distributed slip. When combined with seismic waveform modeling, fault geometry and surface offsets add crucial constraints to describe in details the seismic faulting process.
\r\n\r\nDense maps of glacier velocity are reported for several glaciers in Europe and in the Himalayas. Optical image correlation proves robust even in challenging mountainous areas, allowing accurate measurements of glacier flow velocity. Seasonal variations of glacier flow velocity are well identified, suggesting that such measurements can be used to better study the effects of climate change, and to refine the tuning of numerical glacier models.
" }, { "name": "Li, Zhenyu", "degree": "PhD", "year": "2008", "title": "Optofluidic Dye Lasers", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142007-143251", "creators": [ { "name": { "family": "Li", "given": "Zhenyu" }, "id": "Li-Zhenyu", "orcid": "0000-0002-7752-6225", "display_name": "Li, Zhenyu" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Libbrecht", "given": "Kenneth George" }, "id": "Libbrecht-K-G", "role": "member", "display_name": "Libbrecht, Kenneth George" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/AQQR-QG80", "abstract": "Optofluidic dye lasers refer to a class of liquid dye lasers, usually on a microfabricated device, in which the adaptive nature of the liquid gain medium allows the dynamical control of the laser properties. Miniaturizing liquid dye lasers onto a microfluidic device not only results in compact, easy-to-maintain and safe dye laser systems, but also provides unprecedented optical performances such as precise spatial mode control, low threshold, and automatic fluidic tuning. Equally important, such on-chip liquid laser sources represent an important component for \"lab-on-a-chip\" systems.
\r\n\r\nThis thesis studies the implementations of optofluidic dye lasers on polydimethylsiloxane (PDMS) based microfluidic devices. Replica molding soft lithography was used to fabricate monolithic PDMS devices which contain both wavelength-scale optical structures and large-sized microfluidic channels. We have demonstrated narrow linewidth single mode DFB lasers, simultaneous operation of integrated DFB laser arrays with a single pump, multiple color lasing from the same DFB cavity, continuous mechanical wavelength tuning over a 60nm range, microfluidic wavelength tuning, single mode liquid-core microring lasers using Vernier effect, liquid-cladding evanescent gain DFB lasers, and monolithic integration with PDMS microfluidic circuits. Typical laser thresholds achieved are well within the reach of commercial high power laser diodes, thus enabling the implementations of compact tunable laser sources for portable \u201clab-on-a-chip\u201d devices. The impressive performances, diverse geometries and applications clearly demonstrate the power of optofluidic integration and adaptation.
\r\n\r\n" }, { "name": "Liang, Wei", "degree": "PhD", "year": "2008", "title": "Study of Optical Phase Lock Loops and the Applications in Coherent Beam Combining and Coherence Cloning", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272008-143400", "creators": [ { "name": { "family": "Liang", "given": "Wei" }, "id": "Liang-Wei", "display_name": "Liang, Wei" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/YHBF-KW11", "abstract": "Optical Phase-Lock loops (OPLLs) have potential applications in phase coherent optics including frequency synthesis, clock distribution and recovery, jitter and noise reduction, etc. However, most implemented OPLLs are based on solid state lasers, fiber lasers, or specially designed semiconductor lasers, whose bulky size and high cost inhibit the applications of OPLLs.
\r\n\r\nSemiconductor lasers have the advantages of low cost, small size, and high efficiency. In this thesis, I report on a study of OPLLs using commercial SCLs, and explore their novel applications in coherent beam combining and coherence cloning.
\r\n\r\nIn chapter 1-3, I will first introduce the theory of OPLLs and presents the experimental study of OPLLs made of different commercial SCLs. To improve the performance of OPLLs, electronic compensations using filter designs are also discussed and studied.
\r\n\r\nIn chapter 4-5, I will study the application of OPLLs in coherent beam combining. Using OPLLs, an array of slave lasers can be phase locked to the same master laser at the same frequency, their outputs can then be coherently combined. The phase variations of the element beams due to the optical path-length variations in fibers can be further corrected for by using multi-level OPLLs. This approach eliminates the use of the optical phase/frequency shifters conventionally required in a coherent beam combining system. In the proof of principle experiment, we have combined two lasers with a combining efficiency of 94% using the filled-aperture combining configuration. Furthermore, I will discuss the scalability of a cascaded filled-aperture combining system for the combination of a large number of lasers.
\r\n\r\nOPLLs can also be used to reduce the phase noise of SCLs by locking them to a low noise master laser. In chapter 6, I will describe the theory of coherence cloning using OPLLs and present the experimental measurements of the linewidths and frequency noises of a low noise fiber laser, a free-running and locked slave lasers.
\r\n\r\nIn chapter 7, the thesis concludes by proposing a novel OPLL configuration of large loop bandwidth and identifying future works that need to be done to advance the development of this technology.
" }, { "name": "Liang, Yongqiang", "degree": "PhD", "year": "2008", "title": "Robotic Training for Motor Rehabilitation after Complete Spinal Cord Injury", "advisor": "Burdick, Joel Wakeman; Edgerton, V. Reggie", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202007-135027", "creators": [ { "name": { "family": "Liang", "given": "Yongqiang" }, "id": "Liang-Yongqiang", "display_name": "Liang, Yongqiang" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Edgerton", "given": "V. Reggie" }, "id": "Edgerton-V-R", "role": "advisor", "display_name": "Edgerton, V. Reggie" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Edgerton", "given": "V. Reggie" }, "id": "Edgerton-V-R", "role": "member", "display_name": "Edgerton, V. Reggie" } ], "option_major": [ "mecheng" ], "doi": "10.7907/T01R-P904", "abstract": "The spinal cord circuits have a great degree of automaticity and plasticity. They are able to generate complex locomotor patterns such as stepping and scratching even without input from supraspinal nervous systems. When provided with ensembles of afferent sensory information input associated with a specific motor task, e.g., stepping, the spinal cord can \"learn\" to perform that task even if it is isolated from the supraspinal nervous systems.
\r\n\r\nThe plasticity of the spinal cord led researchers to study the use of physical locomotor training, e.g., treadmill step training with body weight support, to rehabilitate locomotor function after spinal cord injury (SCI). With intensive training, the spinal-cord-injured subject can recover some level of stepping ability. Explorations were made in this thesis to find an optimal training paradigm. Novel assist-as-needed paradigms were developed to allow variability during training since it is an intrinsic feature of normal stepping. Comparative experiments were conducted against fixed-trajectory training. Results demonstrated that variability is an important factor to induce more improvement in step training.
\r\n\r\nStanding is another important function in one's daily life, though it received less research attention than stepping. A prototype stand platform with 6 degrees of freedom was developed as an experimental tool for stand and postural study. Analogous to step training, we tested the effect of daily training on extensor responses in the hind limbs of complete spinal rats. The results showed no significant effect of the training. This led to the conclusion that without tonic input, the spinal cord has very limited ability to generate enough extensor muscle tone and to respond to postural disturbance. Further studies in standing rehabilitation should combine other methods to provide tonic inputs to the spinal cord.
" }, { "name": "Lin, Hsuan-Tien", "degree": "PhD", "year": "2008", "title": "From Ordinal Ranking to Binary Classification", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302008-143505", "creators": [ { "name": { "family": "Lin", "given": "Hsuan-Tien" }, "id": "Lin-Hsuan-Tien", "orcid": "0000-0003-2968-0671", "display_name": "Lin, Hsuan-Tien" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "compsci" ], "doi": "10.7907/7B0F-E145", "abstract": "We study the ordinal ranking problem in machine learning. The problem can be viewed as a classification problem with additional ordinal information or as a regression problem without actual numerical information. From the classification perspective, we formalize the concept of ordinal information by a cost-sensitive setup, and propose some novel cost-sensitive classification algorithms. The algorithms are derived from a systematic cost-transformation technique, which carries a strong theoretical guarantee. Experimental results show that the novel algorithms perform well both in a general cost-sensitive setup and in the specific ordinal ranking setup.
\r\n\r\nFrom the regression perspective, we propose the threshold ensemble model for ordinal ranking, which allows the machines to estimate a real-valued score (like regression) before quantizing it to an ordinal rank. We study the generalization ability of threshold ensembles and derive novel large-margin bounds on its expected test performance. In addition, we improve an existing algorithm and propose a novel algorithm for constructing large-margin threshold ensembles. Our proposed algorithms are efficient in training and achieve decent out-of-sample performance when compared with the state-of-the-art algorithm on benchmark data sets.
\r\n\r\nWe then study how ordinal ranking can be reduced to weighted binary classification. The reduction framework is simpler than the cost-sensitive classification approach and includes the threshold ensemble model as a special case. The framework allows us to derive strong theoretical results that tightly connect ordinal ranking with binary classification. We demonstrate the algorithmic and theoretical use of the reduction framework by extending SVM and AdaBoost, two of the most popular binary classification algorithms, to the area of ordinal ranking. Coupling SVM with the reduction framework results in a novel and faster algorithm for ordinal ranking with superior performance on real-world data sets, as well as a new bound on the expected test performance for generalized linear ordinal rankers. Coupling AdaBoost with the reduction framework leads to a novel algorithm that boosts the training accuracy of any cost-sensitive ordinal ranking algorithms theoretically, and in turn improves their test performance empirically.
\r\n\r\nFrom the studies above, the key to improve ordinal ranking is to improve binary classification. In the final part of the thesis, we include two projects that aim at understanding binary classification better in the context of ensemble learning. First, we discuss how AdaBoost is restricted to combining only a finite number of hypotheses and remove the restriction by formulating a framework of infinite ensemble learning based on SVM. The framework can output an infinite ensemble through embedding infinitely many hypotheses into an~SVM kernel. Using the framework, we show that binary classification (and hence ordinal ranking) can be improved by going from a finite ensemble to an infinite one. Second, we discuss how AdaBoost carries the property of being resistant to overfitting. Then, we propose the SeedBoost algorithm, which uses the property as a machinery to prevent other learning algorithms from overfitting. Empirical results demonstrate that SeedBoost can indeed improve an overfitting algorithm on some data sets.
" }, { "name": "Lind, Mary Laura", "degree": "PhD", "year": "2008", "title": "Ultrasonic Investigation of the Elastic Properties and Liquid Fragility of Bulk Metallic Glasses in the Supercooled Liquid Region", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-10262007-104725", "creators": [ { "name": { "family": "Lind", "given": "Mary Laura" }, "id": "Lind-Mary-Laura", "orcid": "0000-0001-8585-8054", "display_name": "Lind, Mary Laura" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Conner", "given": "Robert Dale" }, "id": "Conner-R-D", "role": "member", "display_name": "Conner, Robert Dale" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/3B4B-ZV48", "abstract": "In this thesis new methods for accessing the ultrasonic properties of supercooled liquid region in bulk metallic glass forming liquids were developed. An extensive examination of the relationship between the elastic properties of metallic glasses and liquid fragility has been undertaken. Three experimental techniques were created/modified to access the Supercooled Liquid Region of the glass: annealing relaxation measurements, delay line measurements, and long notched-rod measurements. The methods as well as the limitations are discussed.
\r\n\r\nUltrasonic contact methods with measurement frequencies of 25MHz have been used for in situ and ex situ examination of the elastic properties of the supercooled liquid region (SCLR) in bulk metallic glasses (BMGs). Ex situ relaxation experiments in Vitreloy-4 (Zr46.75Ti8.25Cu7.5Ni10Be27.5) were performed that demonstrated that in the glassy state, the low-temperature dependence (from 78K to 298K) of the elastic modulii is linear as expected from Debye-Gruneisen theory. In the liquid state, the temperature dependence of the shear modulus was found to be stronger than that of the bulk modulus. The strong temperature dependence of G is found to be an important aspect of the recently developed Cooperative Shear Model. Additionally, this temperature dependence of the shear modulus in the liquid state was found to directly relate to the viscosity (or fragility) of the liquid. In situ experiments, utilizing delay lines and notched-rods, were performed on BMGs with a range of fragilities. Improvements to the model relating viscosity, shear modulus, and liquid fragility are presented. The results from both types of measurement (in and ex situ) compared favorably; thus supporting the claim that we are measuring the properties of the equilibrium supercooled liquid. Additionally, these results are used support the idea that the shear modulus relates to a unique potential energetic state of the glass.
\r\n" }, { "name": "Lombardini, Manuel", "degree": "PhD", "year": "2008", "title": "Richtmyer-Meshkov Instability in Converging Geometries", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302008-140331", "creators": [ { "name": { "family": "Lombardini", "given": "Manuel" }, "id": "Lombardini-Manuel", "display_name": "Lombardini, Manuel" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5SNE-4003", "abstract": "We investigate the Richtmyer-Meshkov instability (RMI) in converging geometries analytically and computationally. The linear, or small amplitude, regime is first covered as it is the onset to subsequent non-linear stages of the perturbation growth. While the plane interaction of a shock with a slightly perturbed density interface is classically viewed as a single interface evolving as baroclinic vorticity have been initially deposited on it, we propose a simple but more complete model characterizing the early interaction between the interface and the receding waves produced by the shock-interface interaction, in the case of a reflected shock. A universal time scale representing the time needed by the RMI to reach its asymptotic growth rate is found analytically and confirmed by ideal gas computations for various incident shock Mach numbers MI and Atwood ratios A, and could be useful especially for experimentalists in non-dimensionalizing their data.
\r\n\r\nConsidering again linear perturbations, we then obtain a general analytical model for the asymptotic growth rate reached by the instability during the concentric interaction of an imploding/exploding cylindrical shock with a cylindrical interface containing three-dimensional orthogonal perturbations, in the azimuthal and axial directions. Stable perturbations, typical of the converging geometry, are discovered. Comparisons are made with simulations where the effects of compressibility, wave reverberations, and flow convergence are isolated. Azimuthal and axial perturbation evolution are compared with results obtained for the plane RMI at comparable initial wavelengths.
\r\n\r\nA second interaction occurs when the transmitted shock, produced by the incident converging shock impacting the interface, converges to the axis and reflects to reshock the initially accelerated interface. This leads to highly non-linear perturbation growth. To isolate the complex wave interaction process, the interface is considered initially unperturbed so that the flow is radially symmetric. An accurate visualization procedure is performed to characterize the underlying physics behind the reshock event. We study extensively the cylindrical and spherical geometry, for various MI and for the air \u2192 SF6 (A=0.67) and SF6 \u2192 (A=-0.67) interactions, and draw important differences with the equivalent plane configuration.
\r\n\r\nA hybrid, low-numerical dissipation/shock-capturing method, embedded into an adaptive mesh refinement framework is optimized in order to achieve large-eddy simulations of the self-similar cylindrical converging shock-driven RMI and the turbulent mixing generated by the reshock. Computations are produced for MI=1.3 and 2.0, and for air -> SF6 SF6 -> air interfaces. We develop statistics tools to study extensively the growth of the turbulent mixing zone using cylindrical averages as well as various measures such as probability density functions of the mixing and turbulent power spectra, with the objectives of understanding the turbulent mixing in this particular geometry.
" }, { "name": "Lu, Jian", "degree": "PhD", "year": "2008", "title": "Quantitative Three-dimensional Imaging of Droplet Convection and Cardiac Cell Motions Based on Micro DDPIV", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012008-150234", "creators": [ { "name": { "family": "Lu", "given": "Jian" }, "id": "Lu-Jian", "display_name": "Lu, Jian" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Hove", "given": "Jay R." }, "id": "Hove-J-R", "role": "member", "display_name": "Hove, Jay R." }, { "name": { "family": "Lansford", "given": "Rusty" }, "id": "Lansford-R", "orcid": "0000-0002-2159-3699", "role": "member", "display_name": "Lansford, Rusty" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/4JFZ-AG10", "abstract": "Biomechanical forces such as blood flow induced shear stress as well as genetic programming are widely acknowledged as critical factors regulating vertebrate heart development. While mechanisms of genetic regulation have been well studied, effects of biomechanics are poorly understood due to the lack of proper imaging tools with sufficient spatial and temporal resolutions for quantitative analysis of the mechanical stimuli in complex three-dimensional (3D) living systems. 3D quantitative flow visualization by tracking microscale particles has become an invaluable tool in microfluid mechanics. Defocusing digital particle image velocimetry (DDPIV) can recover depth coordinates by calculating the separation between defocused images generated by an aperture mask with a plurality of pinholes forming an equilateral triangle. In this thesis, a novel high-speed 3D micro-PTV system was developed based on this technique with laser-induced fluorescence to achieve microscale velocity field measurements. Application of this technique to microscale imaging was validated by calibration of targets spread over the image field. A micro volume of 400x300 \u00b5m2 with 100 \u00b5m depth has been mapped using an inverted microscope equipped with a 20X objective lens. The proposed technique was successfully applied to 3D tracking of 2-\u00b5m fluorescent particles inside an evaporating water droplet, exhibiting convective flow induced by Marangoni effects.
\r\n\r\nThe microscopic imaging system was then utilized to acquire 3D time series data of highly dynamic cell motions in living embryonic zebrafish hearts. 1-\u00b5m and 500-nm fluorescent tracer particles were injected into the blood stream of developing zebrafish embryos at 32 hours post fertilization (hpf) to 59 hpf to help describe cardiac cell motions. Microinjection was delicately performed at the fish tail to minimize the influence to normal cardiovascular functions. The measurable depth in an embryonic heart is about 40 \u00b5m. 3D velocities of cardiovascular blood flow and trajectories of heart-wall motions were obtained, showing dynamic changes of the flow field and phase differences of wall movements between the atrium and the ventricle during heart beating. Endocardial ventricular strains were calculated based on the reconstructed coordinates of two particles adhered to the endocardium.
\r\n" }, { "name": "Maerkl, Sebastian Josef", "degree": "PhD", "year": "2008", "title": "Microfluidic Large Scale Integration and its Application to Systems Biology", "advisor": "Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222007-141119", "creators": [ { "name": { "family": "Maerkl", "given": "Sebastian Josef" }, "id": "Maerkl-Sebastian-Josef", "orcid": "0000-0003-1917-5268", "display_name": "Maerkl, Sebastian Josef" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "chair", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "co-chair", "display_name": "Fraser, Scott E." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "member", "display_name": "Quake, Stephen R." } ], "option_major": [ "biochem" ], "doi": "10.7907/5CMX-CV08", "abstract": "The goal of biology is to understand how complex systems such as cells and entire organisms function. Systems Biology attempts to quantitatively characterize all components comprising these systems. A considerable task. Microfluidics provides a powerful tool for undertaking this endeavor. This thesis describes the development of Microfluidic Large Scale Integration (MLSI) using devices fabricated by Multilayer Soft Lithography (MSL). MLSI and fluidic components, such as multiplexers and free-standing membranes, serve as the infrastructure for performing large-scale biophysical measurements of biological systems. Transcription factor binding energy landscapes were determined using MLSI and MITOMI, a novel method for measuring molecular interactions. The biophysical characterization of transcription factors described herein were the first comprehensive measurements of its kind, and answered basic questions regarding how transcription factors recognize DNA. Furthermore, it was possible to predict the in vivo function of transcription factors using only the measured binding topographies and a genome sequence, indicating that biological processes can be predicted with high accuracy. More generally, the methods described in this thesis are generally applicable to understanding the properties of any biological system and should find broad usage in the field of Systems Biology.\r\n" }, { "name": "Matheou, Georgios", "degree": "PhD", "year": "2008", "title": "Large-Eddy Simulations of Molecular Mixing in a Recirculating Shear Flow", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262008-152803", "creators": [ { "name": { "family": "Matheou", "given": "Georgios" }, "id": "Matheou-Georgios", "orcid": "0000-0003-4024-4571", "display_name": "Matheou, Georgios" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VFKF-SC30", "abstract": "The flow field and mixing in an expansion-ramp geometry is studied using large-eddy simulation (LES) with subgrid scale (SGS) modeling based on the stretched-vortex model. The expansionramp geometry was developed to provide enhanced mixing and flameholding characteristics while maintaining low total-pressure losses, elements that are important in the design and performance of combustors for hypersonic air-breathing propulsion applications. The mixing was studied by tracking a passive scalar without taking into account the effects of chemical reactions and heat release.
\r\n\r\nIn order to verify the solver and the boundary closure implementation, a method utilizing results from linear stability analysis (LSA) theory is developed. LSA can be used to compute unstable perturbations to a flow, subject to certain approximations. The perturbations computed from LSA are used as an inflow condition to the flow computed by the solver been assessed. A projection based metric is constructed that only assumes the shape of the solution and not the growth rate of the perturbations, thus also allowing the latter to be determined as part of the verification. The growth rate of the perturbations for an unbounded (effectively) incompressible shear layer and a confined compressible shear layer is found to be in agreement with the prediction of the LSA.
\r\n\r\nThe flow and mixing predictions of the LES are in good agreement with experimental measurements. Total (resolved and subgrid) probability density functions (PDFs) of the passive scalar are estimated using an assumed beta-distribution model for the subgrid scalar field. The improved mixing characteristics of the expansion-ramp geometry compared to free shear layers are illustrated by the shapes of the PDFs. Moreover, the temperature rise and the probability of mixed fluid profiles are in good agreement with the experimental measurements, indicating that the mixing on a molecular scale is correctly predicted by the LES\u2013SGS model. Finally, the predictions of the LES are shown to be resolution-independent. The mean fields and passive scalar PDFs have essentially converged at the two finer grid-resolutions used.
" }, { "name": "Mattson, Matthew Sanford", "degree": "PhD", "year": "2008", "title": "Understanding and Treating Eye Diseases: Mechanical Characterization and Photochemical Modification of the Cornea and Sclera", "advisor": "Kornfield, Julia A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282008-163501", "creators": [ { "name": { "family": "Mattson", "given": "Matthew Sanford" }, "id": "Mattson-Matthew-Sanford", "display_name": "Mattson, Matthew Sanford" } ], "advisors": [ { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "role": "advisor", "display_name": "Kornfield, Julia A." } ], "committee": [ { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "role": "chair", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Guo", "given": "Chin-Lin" }, "id": "Guo-Chin-Lin", "role": "member", "display_name": "Guo, Chin-Lin" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/DXGR-GV57", "abstract": "Proper vision depends on the physical properties of the eye tissues. Diseases that alter the chemical and mechanical states of the tissue can result in a loss of functionality. Degenerative myopia and keratoconus are diseases that exhibit such changes in the sclera and cornea, respectively. These diseases may be treatable by engineering the mechanical properties of the sclera and cornea.
\r\n\r\nWe have developed an intact globe expansion method for mechanical characterization of eyes in vitro, which provides reliable measurements, with relatively few samples, and mimics the type and distribution of stresses inherent in the natural boundary conditions of the eye. Furthermore, application of high intraocular pressures provides a way to study shape changes of the sclera and cornea which are similar to those exhibited in myopia and keratoconus. Potential treatments that show an ability to prevent ocular distension in this method have a chance of preventing the deformations that occur in vivo in the diseases.
\r\n\r\nOur studies in vitro indicate that crosslinking can improve tissue mechanical stability and resistance to deformation. Light activated crosslinking provides spatial and temporal control of treatments, and photoinitiator systems such as Eosin Y (EY) and triethanolamine (TEOA) allow this control with safe doses of visible light.
\r\n\r\nFor myopia treatment, we demonstrate in vitro stabilization of eyes using the intact globe method after drug is delivered to the sclera in vitro or in vivo on 2\u20133 week old rabbits. Biocompatibility studies of the scleral treatments indicate excellent tolerance to the light and drug in both rabbits and guinea pigs. Further, we have developed treatment protocols for use in a guinea pig form-deprivation model of myopia. In normally growing guinea pig eyes, treatments can create substantial changes to eye shape. These changes are manifested in shifts in the refractive error and ocular length that persist for the duration over which the animals are monitored.
\r\n\r\nFor keratoconus, treatment in vitro on rabbit eyes using EY/TEOA demonstrates similar capabilities of corneal stabilization as a treatment currently in clinical trials. The EY/TEOA treatment shows advantages of reduced treatment time and the possibility of treatment without removal of the epithelium.
" }, { "name": "McHale, Kevin L.", "degree": "PhD", "year": "2008", "title": "Feedback Tracking and Correlation Spectroscopy of Fluorescent Nanoparticles and Biomolecules", "advisor": "Mabuchi, Hideo", "url": "https://resolver.caltech.edu/CaltechETD:etd-05072008-204627", "creators": [ { "name": { "family": "McHale", "given": "Kevin L." }, "id": "McHale-Kevin-L", "display_name": "McHale, Kevin L." } ], "advisors": [ { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "advisor", "display_name": "Mabuchi, Hideo" } ], "committee": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "chair", "display_name": "Pierce, Niles A." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "bioeng" ], "doi": "10.7907/6YYA-9T10", "abstract": "The best way to study dynamic fluctuations in single molecules or nanoparticles is to look at only one particle at a time, and to look for as long as possible. Brownian motion makes this difficult, as molecules move along random trajectories that carry them out of any fixed field of view. We developed an instrument that tracks the Brownian motion of single fluorescent molecules in three dimensions and in real-time while measuring fluorescence with nanosecond time resolution and single-photon sensitivity. The apparatus increases observation times by approximately three orders of magnitude while improving data-collecting efficiency by locking tracked objects to a high-intensity region of the excitation laser.
\r\n\r\nAs a first application of our technique, we tracked and studied the fluorescence statistics of semiconductor quantum dots. Our measurements were well resolved at 10ns correlation times, allowing measurement of photon anti-bunching on single particles in solution for the first time. We observed variations of (34 \u00b1 16)% in the fluorescence lifetimes and (23 \u00b1 18)% in the absorption cross-sections within an aqueous quantum dot sample, confirming that these variations are real, not artifacts of the immobilization methods previously used to study them. Additionally, we studied quantum dot fluorescence intermittency and its dependence on 2-mercaptoethanol, finding evidence that the chemical suppresses blinking on short time-scales (<1s) by reducing the lifetime of the dark state.
\r\n\r\nFinally, we studied the translational and intramolecular Brownian motion of \u03bb-phage DNA molecules. Our apparatus decouples these motions almost completely, and yielded a translational diffusion coefficient estimate D=(0.71 \u00b1 0.05)\u03bcm\u00b2/s lying between previous measurements for this molecule under identical solution conditions but with less precise techniques. Our measurements show clear evidence of intramolecular motion of the polymer chain in the form of statistical correlations on time-scales up to 1s, but we have not yet been able to determine the influence of solvent interactions on these dynamics.
\r\n" }, { "name": "Mendez, Jeffrey Michael", "degree": "PhD", "year": "2008", "title": "Iron and Manganese in the Ocean: Investigation of Atmospheric Input by Dust and Coastal Ocean Time Series", "advisor": "Adkins, Jess F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05022008-220144", "creators": [ { "name": { "family": "Mendez", "given": "Jeffrey Michael" }, "id": "Mendez-Jeffrey-Michael", "display_name": "Mendez, Jeffrey Michael" } ], "advisors": [ { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "advisor", "display_name": "Adkins, Jess F." } ], "committee": [ { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "role": "chair", "display_name": "Sessions, Alex L." }, { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "member", "display_name": "Adkins, Jess F." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Orphan", "given": "Victoria J." }, "id": "Orphan-V-J", "role": "member", "display_name": "Orphan, Victoria J." } ], "option_major": [ "envreng" ], "doi": "10.7907/Q7JK-MV77", "abstract": "Trace metals such as iron (Fe) and manganese (Mn) are essential micronutrients in the biogeochemistry of the ocean (Turner and Hunter, 2001), and dry deposition is a substantial source of both Fe and Mn to the surface ocean (Duce and Tindale, 1991; Guieu et al., 1994). Kinetic and thermodynamic values for the release of metals from dust are needed for computer models which incorporate dust as part of their ocean system. Here we investigate the thermodynamic and kinetics parameters involved in the dissolution of metals from dust in seawater. We added dust from the Sahara and the Western United States to seawater in a variety of ways to investigate the dissolution patterns of Fe and Mn. Results show different apparent thermodynamic constants for manganese (Mn) and iron (Fe). The final Mn concentrations are proportional to the added dust concentration and light intensity, and independent of initial dissolution rate. Fe concentrations in fresh seawater reach a maximum concentration of less than 2 nM. However, depletion of organic ligands lead to the precipitation of Fe oxide from solution, and the addition of siderophores enhanced both the total Fe capacity of the seawater and the rate of Fe dissolution from dust. The first order rate constant for the dissolution of dust differed by dust source and was dependent on oxalate concentration and intensity of natural UV light. We conclude that final Mn concentrations are limited by available Mn on the dust surface, while Fe concentrations are limited by the ligand concentrations in the seawater, which ultimately are determined by the biological community. Because the coastal ocean plays a significant role in global biogeochemical cycles, (Smith and Hollibaugh, 1993; Tsunogai and Noriki, 1991), we conducted a coastal ocean time series to investigate the basic modes and cycles which characterize the ocean. We found that Mn is highly dependent on seasonal rain events, with surface water concentrations observed as high as 30 nM after rain events. Fe within the coastal ocean is highly variable and can be used as a tool to track water mass movements and mixing patterns.\r\n" }, { "name": "Monro, John Anderson", "degree": "PhD", "year": "2008", "title": "A Super-Algebraically Convergent, Windowing-Based Approach to the Evaluation of Scattering from Periodic Rough Surfaces", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01032008-222910", "creators": [ { "name": { "family": "Monro", "given": "John Anderson" }, "id": "Monro-John-Anderson", "display_name": "Monro, John Anderson" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/F9VM-JP39", "abstract": "We introduce a new second-kind integral equation method to solve direct rough surface scattering problems in two dimensions. This approach is based, in part, upon the bounded obstacle scattering method that was originally presented in Bruno et al. [2004] and is discussed in an appendix of this thesis. We restrict our attention to problems in which time-harmonic acoustic or electromagnetic plane waves scatter from rough surfaces that are perfectly reflecting, periodic and at least twice continuously differentiable; both sound-soft and sound-hard type acoustic scattering cases---correspondingly, transverse-electric and transverse-magnetic electromagnetic scattering cases---are treated. Key elements of our algorithm include the use of infinitely continuously differentiable windowing functions that comprise partitions of unity, analytical representations of the integral equation\u2019s solution (taking into account either the absence or presence of multiple scattering) and spectral quadrature formulas. Together, they provide an efficient alternative to the use of the periodic Green\u2019s function found in the kernel of most solvers\u2019 integral operators, and they strongly mitigate the rapidly increasing computational complexity that is typically borne as the frequency of the incident field increases.
\r\n\r\nAfter providing a complete description of our solver and illustrating its usefulness through some preliminary examples, we rigorously prove its convergence. In particular, the super-algebraic convergence of the method is established for problems with infinitely continuously differentiable scattering surfaces. We additionally show that accuracies within prescribed tolerances are achieved with fixed computational cost as the frequency increases without bound for cases in which no multiple reflections occur.
\r\n\r\nWe present extensive numerical data demonstrating the convergence, accuracy and efficiency of our computational approach for a wide range of scattering configurations (sinusoidal, multi-scale and simulated ocean surfaces are considered). These results include favorable comparisons with other leading integral equation methods as well as the non-convergent Kirchhoff approximation. They also contain analyses of sets of cases in which the major physical parameters associated with these problems (i.e., surface height, wavenumber and incidence angle) are systematically varied. As a result of these tests, we conclude that the proposed algorithm is highly competitive and robust: it significantly outperforms other leading numerical methods in many cases of scientific and practical relevance, and it facilitates rapid analyses of a wide variety of scattering configurations.
" }, { "name": "Moreels, Pierre", "degree": "PhD", "year": "2008", "title": "Probabilistic, Features-Based Object Recognition", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-11232007-213140", "creators": [ { "name": { "family": "Moreels", "given": "Pierre" }, "id": "Moreels-Pierre", "display_name": "Moreels, Pierre" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Moghaddam", "given": "Baback" }, "id": "Moghaddam-B", "role": "member", "display_name": "Moghaddam, Baback" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Matthies", "given": "Larry H." }, "id": "Matthies-L-H", "role": "member", "display_name": "Matthies, Larry H." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/YGYX-XX55", "abstract": "Object recognition is of fundamental importance in computer vision. In a few years, pedestrian detection, car detection, and more generally scene recognition will likely be reliable enough to allow fully-automated car navigation, and the human driver will be relegated to the back seat to sip his coffee.
\r\n\r\nIn this thesis we are interested in recognizing individual objects and categories. In order to reduce the volume of information one has to process, images are characterized by sets of features. These features, also called interest points, are targeted at image locations with high local information content. Various systems for detecting interest points and for describing the local image appearance near these points, have been proposed in the last two decades. We investigate which combinations from this plethora of detectors and descriptors, are most suited for object recognition tasks.
\r\n\r\nOn to the problem of object recognition, we are first interested in recognizing individual objects. In a few years, one can imagine that customers in shops, will take with their cell phone a picture of a product that looks interesting, send it to a remote server with a huge database of individual objects, and get back information about that specific product. We propose a system for individual object recognition, inspired from previous work on coarse-to-fine recognition. All steps of the recognition process are translated into principled probabilistic terms, which allows us to outperform a state-of-the-art commercial system for individual recognition.
\r\n\r\nRegarding categories, faces are probably the category that has received the most attention in computer vision literature. Here we propose a system to recognize images of the same individual in large databases of images. This can be of high interest when looking for images of a given person over the internet. Our method's advantage is that it works on real-world images, as opposed to the face databases from the literature, collected in laboratories with controlled lighting, pose and background conditions.
\r\n\r\nFinally, we are interested in recognition of object categories in general. Using support vector machines for the classification task, we propose a features-based kernel that improves recognition performance on object categories.
" }, { "name": "Mulliken, Grant Haverstock", "degree": "PhD", "year": "2008", "title": "Continuous Sensorimotor Control Mechanisms in Posterior Parietal Cortex: Forward Model Encoding and Trajectory Decoding", "advisor": "Andersen, Richard A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282008-192406", "creators": [ { "name": { "family": "Mulliken", "given": "Grant Haverstock" }, "id": "Mulliken-Grant-Haverstock", "display_name": "Mulliken, Grant Haverstock" } ], "advisors": [ { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "advisor", "display_name": "Andersen, Richard A." } ], "committee": [ { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "chair", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." } ], "option_major": [ "cns" ], "doi": "10.7907/VRHH-NT69", "abstract": "During goal-directed movements, primates are able to rapidly and accurately control a movement despite substantial delay times (more than 200 milliseconds) incurred in the sensorimotor control loop. To compensate for these large delays, it has been proposed that the brain uses an internal forward model of the arm to estimate current and upcoming states of a movement, which would be more useful for rapid online control. To study online control mechanisms in the posterior parietal cortex (PPC), we recorded from single neurons while monkeys performed a joystick task. Neurons encoded the static target direction and the dynamic heading direction of the cursor. The temporal encoding properties of many heading neurons reflected a forward estimate of the current state of the cursor that is neither directly available from passive sensory feedback nor compatible with outgoing motor commands, and is thus consistent with PPC serving as a forward model for online sensorimotor control. In addition, we found that the space-time tuning functions of these neurons mostly encode straight and approximately instantaneous trajectories.
\r\n\r\nRecent advances in cortical prosthetics have focused on recording neural activity in motor cortices and decoding these signals to control the trajectory of a cursor on a computer screen. Building on our encoding results, we demonstrate that joystick-controlled trajectories can also be decoded from PPC ensembles, presumably extracting the dynamic state of the cursor from a forward model. Remarkably, we found that we could accurately reconstruct a monkey\u2019s trajectories using only 5 simultaneously recorded PPC neurons. Furthermore, we tested whether we could decode trajectories during closed-loop brain control sessions, in which the real-time position of the cursor was determined solely by a monkey\u2019s thoughts. The monkey learned to perform brain control trajectories at 80% success rate (for 8 targets) after just 4\u20135 sessions. This improvement in behavioral performance was accompanied by a corresponding enhancement in neural tuning properties (i.e.,, increased tuning depth and coverage of 2D space) as well as an increase in offline decoding performance of the PPC ensemble. This work marks an important step forward in the development of a neural prosthesis using signals from PPC.
\r\n" }, { "name": "Naeimi, Helia", "degree": "PhD", "year": "2008", "title": "Reliable Integration of Terascale Systems with Nanoscale Devices", "advisor": "DeHon, Andre", "url": "https://resolver.caltech.edu/CaltechETD:etd-01242008-012650", "creators": [ { "name": { "family": "Naeimi", "given": "Helia" }, "id": "Naeimi-Helia", "display_name": "Naeimi, Helia" } ], "advisors": [ { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "orcid": "0000-0001-9177-7699", "role": "advisor", "display_name": "DeHon, Andre" } ], "committee": [ { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "orcid": "0000-0001-9177-7699", "role": "chair", "display_name": "DeHon, Andre" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Heath", "given": "James R." }, "id": "Heath-J-R", "orcid": "0000-0001-5356-4385", "role": "member", "display_name": "Heath, James R." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "compsci" ], "doi": "10.7907/P842-7B49", "abstract": "Nanotechnology design has attracted considerable attention in recent years and seems to be the technology for the future generation of the electronic devices, either as scaled and more restricted conventional lithographic technology, or as emerging sublithographic technologies, such as nanowires, carbon nanotubes, NDR (Negative Differential Resistance) devices, or other nanotechnology devices. Each of these technologies provides one or more design benefits including feature-size scaling, high on\u2013off ratios, and faster devices. However, all of these techniques share their most challenging design issue: reliability. Providing reliability is becoming constantly more challenging due to increases in both the device failure rate and system complexity. This work develops techniques that make achieving reliability in such systems feasible with practical area overhead and considerable improvement in area overhead and system reliability compared to related techniques.
\r\n\r\nConventional reliability techniques focus on low defect and fault rates, i.e., single event upset (SEU). These techniques cannot simply be scaled to larger systems with more unreliable devices. If these techniques are directly applied to the high defect and fault rate of the nanotechnology regime, they suffer impractically high overhead, or they may not achieve the desired reliability. Our approach in this thesis exploits the following design patterns to achieve a considerable area reduction compared to related works and achieve high reliability:
\r\n(1) Fine-grained reliability: In this technique, the system is partitioned into fine\u2013grained blocks, and the reliability is provided for each block. This technique is used to contain the area overhead and bound the impact on the throughput.
\r\n(2) Using alternative resources: This technique improves the design quality by sparing other resources when system is tight on one resource. In our work we replace some of the spacial redundancies with temporal redundancy to limit the area overhead. We further improve the system throughput to limit the throughput cost as well.
\r\n(3) Defect pattern matching: With this techniques, the defective resources are located and the design is reconfigured considering the defect pattern of the chip. Then the design configuration is mapped to the chip. This technique isolates the defective resources and make use of most of defect free resources.
\r\n(4) Global reliability: This technique is used to unify the reliability techniques used in different parts of the system. When using one unified technique to protect the system, the area overhead provided to protect one resource can be reused to protect other resources as well.
In the present work, we report considerable improvement in the area overhead using the above techniques. We show that using Fine-Grained Reliability, Alternative Resources, and Defect Pattern Matching, high permanent defect rates (e.g., 10%) which is the result of imperfect manufacturing can be tolerated with moderate area overhead (about 30% on average for typical designs). Again Using Alternative Resources and Fine-Grained Reliability improve the area overhead of the transient fault-tolerant designs by close to an order of magnitude compared to recent reliable works. Finally we report a fully reliable memory system that employs a Global Reliability scheme to tolerate permanent defects and transient faults, both in the memory and in the supporting logic and still achieves 100 Gbit/cm2 density for fault rate of 10\u221218 errors per bit per cycle and 10% junction defect rate.
" }, { "name": "Nicaise, Fabien", "degree": "PhD", "year": "2008", "title": "Automated Design Synthesis of Structures using Growth Enhanced Evolution", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06102008-153834", "creators": [ { "name": { "family": "Nicaise", "given": "Fabien" }, "id": "Nicaise-Fabien", "display_name": "Nicaise, Fabien" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "role": "member", "display_name": "Adami, Christoph Carl" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/28H7-E831", "abstract": "Engineering design is a complex problem on generating and evaluating a variety of options. In traditional methods, this typically involves evaluating up to a dozen different point designs. The limit on the process is the amount of time to generate, refine, and evaluate the various concepts. Using a computer helps to speed up the process, but human involvement still remains the weakest link.
\r\n\r\nThe natural extension of this process is to continually and rapid generate, refine, and evaluate concepts entirely automatically. Evolutionary Algorithms provide such a method, by emulating natural evolution. The computer maintains a population point design, each of which is represented by a gene string that is allowed to change (mutate) and combine with other genes (crossover). At each generation, every individual is modified then evaluated and the improved solutions proceed to the next generation.
\r\n\r\nThis thesis will extend the biological model by introducing a growth process to each individual. This is akin to the concept of a multi-cellular organism developing in the womb. An encoding for discrete truss structures is described that provides for such an extension. The truss grows from a few basic elements. After showing several examples demonstrating the growth process, the method is applied to a couple simple examples using evolutionary algorithms.
" }, { "name": "Oh, Chang Kook", "degree": "PhD", "year": "2008", "title": "Bayesian Learning for Earthquake Engineering Applications and Structural Health Monitoring", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052007-141434", "creators": [ { "name": { "family": "Oh", "given": "Chang Kook" }, "id": "Oh-Chang-Kook", "display_name": "Oh, Chang Kook" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Porter", "given": "Keith A." }, "id": "Porter-K-A", "role": "member", "display_name": "Porter, Keith A." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/RFD5-7Y72", "abstract": "Parallel to significant advances in sensor hardware, there have been recent developments of sophisticated methods for quantitative assessment of measured data that explicitly deal with all of the involved uncertainties, including inevitable measurement errors. The existence of these uncertainties often causes numerical instabilities in inverse problems that make them ill-conditioned.
\r\n\r\nThe Bayesian methodology is known to provide an efficient way to alleviate this ill-conditioning by incorporating the prior term for regularization of the inverse problem, and to provide probabilistic results which are meaningful for decision making.
\r\n\r\nIn this work, the Bayesian methodology is applied to inverse problems in earthquake engineering and especially to structural health monitoring. The proposed methodology of Bayesian earning using automatic relevance determination (ARD) prior, including its kernel version called the Relevance Vector Machine, is presented and applied to earthquake early warning, earthquake ground motion attenuation estimation, and structural health monitoring, using either a Bayesian classification or regression approach.
\r\n\r\nThe classification and regression are both performed in three phases: (1) Phase I (feature extraction phase): Determine which features from the data to use in a training dataset; (2) Phase II (training phase): Identify the unknown parameters defining a model by using a training dataset; and (3) Phase III (prediction phase): Predict the results based on the features from new data.
\r\n\r\nThis work focuses on the advantages of making probabilistic predictions obtained by Bayesian methods to deal with all uncertainties and the good characteristics of the proposed method in terms of computationally efficient training, and, especially, prediction that make it suitable for real-time operation. It is shown that sparseness (using only smaller number of basis function terms) is produced in the regression equations and classification separating boundary by using the ARD prior along with Bayesian model class selection to select the most probable (plausible) model class based on the data. This model class selection procedure automatically produces optimal regularization of the problem at hand, making it well-conditioned.
\r\n\r\nSeveral applications of the proposed Bayesian learning methodology are presented. First, automatic near-source and far-source classification of incoming ground motion signals is treated and the Bayesian learning method is used to determine which ground motion features are optimal for this classification. Second, a probabilistic earthquake attenuation model for peak ground acceleration is identified using selected optimal features, especially taking a non-linearly involved parameter into consideration. It is shown that the Bayesian learning method an be utilized to estimate not only linear coefficients but also a non-linearly involved parameter to provide an estimate for an unknown parameter in the kernel basis functions for elevance Vector Machine. Third, the proposed method is extended to a general case of regression problems with vector outputs and applied to structural health monitoring applications. It is concluded that the proposed vector output RVM shows promise for estimating damage locations and their severities from change of modal properties such as natural frequencies and mode shapes.
" }, { "name": "Olsen, Anna H.", "degree": "PhD", "year": "2008", "title": "Steel Moment-Resisting Frame Responses in Simulated Strong Ground Motions: or How I Learned to Stop Worrying and Love the Big One", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202008-201030", "creators": [ { "name": { "family": "Olsen", "given": "Anna H." }, "id": "Olsen-Anna-H", "display_name": "Olsen, Anna H." } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Jordan", "given": "Thomas H." }, "id": "Jordan-T-H", "role": "member", "display_name": "Jordan, Thomas H." }, { "name": { "family": "Duron", "given": "Ziyad H." }, "id": "Duron-Z-H", "role": "member", "display_name": "Duron, Ziyad H." } ], "option_major": [ "civileng" ], "doi": "10.7907/Y42R-V333", "abstract": "This thesis studies the response of steel moment-resisting frame buildings in simulated strong ground motions. I collect 37 simulations of crustal earthquakes in California. These ground motions are applied to nonlinear finite element models of four types of steel moment frame buildings: six- or twenty-stories with either a stiffer, higher-strength design or a more flexible, lower-strength design. I also consider the presence of fracture-prone welds in each design. Since these buildings experience large deformations in strong ground motions, the building states considered in this thesis are collapse, total structural loss (must be demolished), and if repairable, the peak inter-story drift. This thesis maps these building responses on the simulation domains which cover many sites in the San Francisco and Los Angeles regions. The building responses can also be understood as functions of ground motion intensity measures, such as pseudo-spectral acceleration (PSA), peak ground displacement (PGD), and peak ground velocity (PGV). This thesis develops building response prediction equations to describe probabilistically the state of a steel moment frame given a ground motion. The presence of fracture-prone welds increases the probability of collapse by a factor of 2--8. The probability of collapse of the more flexible design is 1--4 times that of the stiffer design. The six-story buildings are slightly less likely to collapse than the twenty-story buildings assuming sound welds, but the twenty-story buildings are 2--4 times more likely to collapse than the six-story buildings if both have fracture-prone welds. A vector intensity measure of PGD and PGV predicts collapse better than PSA. Models based on the vector of PGD and PGV predict total structural loss equally well as models using PSA. PSA alone best predicts the peak inter-story drift, assuming that the building is repairable. As \"rules of thumb,\" the twenty-story steel moment frames with sound welds collapse in ground motions with long-period PGD greater than 1 m and long-period PGV greater than 2 m/s, and they are a total structural loss for long-period PGD greater than 0.6 m and long-period PGV greater than 1 m/s." }, { "name": "Pang, Changlin", "degree": "PhD", "year": "2008", "title": "Parylene Technology for Neural Probes Applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-11262007-125539", "creators": [ { "name": { "family": "Pang", "given": "Changlin" }, "id": "Pang-Changlin", "display_name": "Pang, Changlin" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GH99-K875", "abstract": "Neural probes are important tools in detecting and studying neuron activities. Although people have been working on neural probe development for a long time, the current neural probes (including metal-wire probes and silicon neural probes) are still far from being satisfactory. An ideal neural probe array should have good biocompatibility, high-density electrodes with high signal-to-noise ratio, flexible cables for interconnections, integrated electronics, and even integrated actuators to track neuron movement.
\r\n\r\nThe work of this thesis focused on applying parylene technology to neural probes development to make a new generation of neural probes with better functions. With the properties of high electrical resistivity, mechanical flexibility, biocompatibility, low coefficient of friction, and an easy deposition/etching process, parylene is a good material for neural probe applications. In this thesis, we have designed, fabricated, and characterized a new parylene neural probe with a long, flexible parylene cable for a neural prosthesis system. Parylene layers are first used on the silicon probe shank with multiple electrodes as insulation and protective layers. And long parylene flexible cables are first monolithically integrated with silicon neural probes. A 96-electrode high-density, 3-D neural probe array for chronic implantation has been demonstrated. Different types of electrolysis actuators (including a silicon diaphragm actuator and a parylene balloon actuator) have been made and tested. The research on electrolysis-based actuators shows their great potential to be used for movable neural probes.
\r\n\r\nCompared with the traditional silicon neural probes (e.g., the Michigan probes, the Utah electrode arrays), our microfabricated neural probes have much longer and stronger probe shanks (8 or 12 mm long, able to penetrate the human pia) and much longer flexible parylene cable (about 7 or 12 cm, long enough to go through a percutaneous connector and the human skull). At the same time, our new probe arrays are shown to have better biocompatibility (being totally covered with parylene material), lower stress, better penetration ability, and greater flexibility for making high-density 3-D arrays and for use in chronic neural signal recording implantation.
\r\n" }, { "name": "Prakash, Piyush", "degree": "PhD", "year": "2008", "title": "Throughput Optimization of Quasi Delay Insensitive Circuits via Slack Matching", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262008-234258", "creators": [ { "name": { "family": "Prakash", "given": "Piyush" }, "id": "Prakash-Piyush", "display_name": "Prakash, Piyush" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "member", "display_name": "DeHon, Andre" }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/9HMY-RR92", "abstract": "Though the logical correctness of an asynchronous circuit is independent of implementation delays, the cycle time of an asynchronous circuit is of great importance to the designer. Oftentimes, the insertion of buffers to such circuits reduces the cycle time of the circuit without affecting the logical correctness of the circuit. This optimization is called slack matching. In this thesis the slack matching problem is formulated. I show that this problem is NP-complete via a reduction from subset sum. I describe two methods for expressing slack matching as a mixed integer linear program(MILP). The first method is applicable to any QDI circuit, while the second method produces a smaller MILP for circuits comprised solely of half buffers. These two formulations of slack matching were applied to the design of a fetch loop in an asynchronous micro-controller. Slack matching reduced the cycle time of the circuit by a factor of 3. For a circuit composed of 14 byte wide processes and a 8k instruction memory, 30s were required to generate the first MILP. It was solved in 2s. When the memory is modeled as a pipeline of half buffers, the second MILP could be formulated in 0.1s and solved in 0.6s. This MILP had half the number of integer variables as the first formulation." }, { "name": "Pratap, Amrit", "degree": "PhD", "year": "2008", "title": "Adaptive Learning Algorithms and Data Cloning", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-231048", "creators": [ { "name": { "family": "Pratap", "given": "Amrit" }, "id": "Pratap-Amrit", "display_name": "Pratap, Amrit" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "compsci" ], "doi": "10.7907/GV3D-AB69", "abstract": "This thesis is in the field of machine learning: the use of data to automatically learn a hypothesis to predict the future behavior of a system. It summarizes three of my research projects.
\r\n\r\nWe first investigate the role of margins in the phenomenal success of the Boosting Algorithms. AdaBoost (Adaptive Boosting) is an algorithm for generating an ensemble of hypotheses for classification. The superior out-of-sample performance of AdaBoost has been attributed to the fact that it can generate a classifier which classifies the points with a large margin of confidence. This led to the development of many new algorithms focusing on optimizing the margin of confidence. It was observed that directly optimizing the margins leads to a poor performance. This apparent contradiction has been the topic of a long unresolved debate in the machine-learning community. We introduce new algorithms which are expressly designed to test the margin hypothesis and provide concrete evidence which refutes the margin argument.
\r\n\r\nWe then propose a novel algorithm for Adaptive sampling under Monotonicity constraint. The typical learning problem takes examples of the target function as input information and produces a hypothesis that approximates the target as an output. We consider a generalization of this paradigm by taking different types of information as input, and producing only specific properties of the target as output. This is a very common setup which occurs in many different real-life settings where the samples are expensive to obtain. We show experimentally that our algorithm achieves better performance than the existing methods, such as Staircase procedure and PEST.
\r\n\r\nOne of the major pitfalls in machine learning research is that of selection bias. This is mostly introduced unconsciously due to the choices made during the learning process, which often lead to over-optimistic estimates of the performance. In the third project, we introduce a new methodology for systematically reducing selection bias. Experiments show that using cloned datasets for model selection can lead to better performance and reduce the selection bias.
" }, { "name": "Rinderknecht, Derek Gresham", "degree": "PhD", "year": "2008", "title": "Development of a Microimpedance Pump for Pulsatile Flow Transport - Part 1: Flow Characteristics of the Microimpedance Pump. Part 2: A Systematic Study of Steady and Pulsatile Transport in Microscale Cavities", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-115810", "creators": [ { "name": { "family": "Rinderknecht", "given": "Derek Gresham" }, "id": "Rinderknecht-Derek- Gresham", "orcid": "0000-0001-6387-8433", "display_name": "Rinderknecht, Derek Gresham" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "bioeng" ], "doi": "10.7907/0K4J-0548", "abstract": "Microfluidics offers an effective means to carry out a wide range of transport processes within a controlled microenvironment by drawing on the benefits imparted by increasing surface area to volume ratio at the microscale. Critical to the impact of microfluidics on integrated devices in the fields of bioengineering and biomedicine is the ability to transport fluids and biomolecules effectively particularly at the size scales involved. In this context a bio-inspired pumping mechanism, the valveless impedance pump, was explored for applications in microfluidics ranging from micro total analysis systems to microchannel cooling. Adhering to the basic principles of the impedance pump mechanism, pumps have been constructed at a variety of size scales from a few centimeters to a few hundred microns. The micro impedance pump is valveless, bidirectional, and can be constructed simply from a wide range of materials. Depending on the size of the pump flow rates range from nL/min to mL/min and pressures can be generated that exceed 20 kPa. Another benefit of the impedance pump is the pulsatile flow output which can be used in the context of microfluidic applications to enhance transport at low Reynolds numbers as well as metering in drug delivery.
\r\n\r\nPulsatile flow was therefore investigated as a method of augmenting transport in microfluidic systems. Micro PIV was used to study the affect of both steady and pulsatile flows on transport at low Reynolds number was examined in microscale rectangular cavities. Ventilation of the cavity contents was examined in terms of the residence time or average time a particle remains in the cavity region. Lagrangian coherent structures (LCS) were applied to empirical velocity fields to determine the impact of unsteadiness on time dependent boundaries to fluid transport present in the flow. Experimental results show that there are both frequencies which are beneficial and detrimental to cavity ventilation as well as certain frequencies which more evenly distribute particles originating in the cavity throughout the freestream.
\r\n" }, { "name": "Rodger, Damien Craig", "degree": "PhD", "year": "2008", "title": "Development of Flexible Parylene-based Microtechnologies for Retinal and Spinal Cord Stimulation and Recording", "advisor": "Weiland, James D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132007-223407", "creators": [ { "name": { "family": "Rodger", "given": "Damien Craig" }, "id": "Rodger-Damien-Craig", "orcid": "0000-0002-1583-5946", "display_name": "Rodger, Damien Craig" } ], "advisors": [ { "name": { "family": "Weiland", "given": "James D." }, "id": "Weiland-J-D", "role": "advisor", "display_name": "Weiland, James D." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Meng", "given": "Ellis" }, "id": "Meng E-F-C", "role": "member", "display_name": "Meng, Ellis" }, { "name": { "family": "Weiland", "given": "James D." }, "id": "Weiland-J-D", "role": "member", "display_name": "Weiland, James D." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "bioeng" ], "doi": "10.7907/ZCXK-8T38", "abstract": "The problems of outer retinal degeneration and spinal cord injury affect millions of people worldwide, often resulting in devastating blindness and para- or quadriplegia that strongly impair a person\u2019s activities of daily living and impact their level of happiness. To help thwart the effects of these diseases, novel flexible parylene-based microtechnologies have been developed for functional electrical stimulation and recording in retinal and spinal cord prosthetics. Microelectrode arrays have been microfabricated according to a single-metal-layer process and a revolutionary dual-metal-layer process that promises to meet the needs of extremely high-density stimulation applications. Arrays have been fabricated of thin-film platinum, electroplated platinum, and iridium, all on parylene substrates, some electrodes surviving for more than 430 million pulses without failing. In addition, a new annealing and heat-molding process has been implemented to improve parylene to parylene adhesion and conform electrode arrays to approximate the curvature of canine retinas. A chronic implantation study of the mechanical effects of parylene-based electrode arrays on the retina over a six month follow-up period has provided excellent results. Both retinal and spinal stimulation and recording from such arrays have been demonstrated.
\r\n\r\nThe first packaging technology for high lead-count prostheses capable of fully scalable interconnection of a high-density electrode array, radiofrequency telemetry coils, and other discrete components such as chip capacitors, with prefabricated, stand-alone driver circuitry is also presented, combining the best features of chip-level and wafer-level packaging technologies. This parylene-based drop-chip technology enables application-specific integrated circuits (ASICs) to be directly integrated into the fabrication process of the other system components, such that the resulting device is flexible, facilitating surgical implantation. The ASIC-to-electrode interconnects are patterned using standard photolithography and standard microfabrication techniques, enabling the density of interconnects to scale to the limits of the lithographic equipment used to define the etch holes over the on-chip pads. Electrical test results verify the efficacy of this cost-effective packaging scheme, and pave the way for a monolithic implantable parylene-based prosthesis system, which has been designed. Surgical tests of monolithic geometries for all-intraocular retinal prostheses have been conducted, and an exciting new configuration for such a device has been discovered.
\r\n" }, { "name": "Ruiz-Angulo, Angel", "degree": "PhD", "year": "2008", "title": "Surface Deformation in a Liquid Environment Resulting from Single Particle Collisions", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222008-090253", "creators": [ { "name": { "family": "Ruiz-Angulo", "given": "Angel" }, "id": "Ruiz-Angulo-Angel", "orcid": "0000-0002-7292-3002", "display_name": "Ruiz-Angulo, Angel" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/WVJT-TG10", "abstract": "Multiphase flows are fairly complex and they are usually studied as a bulk. In this thesis, these flows are approached by looking at single particle interactions (particle-particle and particle-wall). This work presents experimental measurements of the approach and rebound of a particle colliding with a ``deformable' surface in a viscous liquid. The complex interaction between the fluid and the solid phases is coupled through the dynamics of the flow as well as the deformation process. A simple pendulum experiment was used to produced single controlled collisions; steel particles were used to impact different aluminum alloy samples (Al-6061, Al-2024, and Al-7075) using different aqueous mixtures of glycerol and water as a viscous fluid. The velocity of the particle before and after the collision was estimated by post-processing the particle position recorded with a high speed camera. For the combination of materials proposed, the elastic limit is reached at relatively low velocities. The deformations produced by the collision were analyzed using an optical profilometer. The measurements showed that the size of the indentations is independent of the fluid media. It was found that the size of the indentations was the same for collisions in air than for the rest of the collisions using various viscous fluids. The results show that the plastic deformation is only a function of the impact velocity and the material properties. The normal coefficient of restitution and deformation parameters account for losses due to lubrication effect and inelasticity, identifying then, the dominant energy loss mechanism during the collision process.
\r\n\r\nAccording to the strain imposed in the samples due to the collision, the deformations were either elastic or elastic-plastic. The equivalent load due to the impact velocities used in this work did not reach the fully-plastic regime. For the collisions in air, different models were used to compare the experimental results showing that the elastic-plastic regime is not well characterized by only the material properties and the impact velocity. The time-resolved contact force was measured during the process of the indentation for the dry collision experiments using a quartz load transducer.
\r\n\r\nThe experiments clearly show four different regimes depending on the impact Stokes number: lubrication effect and elastic deformation, lubrication effect and elastic-plastic deformation, elastic deformation with no hydrodynamic effects, and elastic-plastic deformation with negligible lubrication effect. An analysis of the erosion of ductile materials during immersed collisions is presented. The size of the crater formed by the impact of a single particle against a ductile target can be estimated from theory, and these estimates agree well with experimental measurements.
" }, { "name": "Rutishauser, Ueli", "degree": "PhD", "year": "2008", "title": "Learning and Representation of Declarative Memories by Single Neurons in the Human Brain", "advisor": "Schuman, Erin Margaret; Koch, Christof; Mamelak, Adam N.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-112802", "creators": [ { "name": { "family": "Rutishauser", "given": "Ueli" }, "id": "Rutishauser-Ueli", "orcid": "0000-0002-9207-7069", "display_name": "Rutishauser, Ueli" } ], "advisors": [ { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "advisor", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "co-advisor", "display_name": "Koch, Christof" }, { "name": { "family": "Mamelak", "given": "Adam N." }, "id": "Mamelak-A-N", "role": "co-advisor", "display_name": "Mamelak, Adam N." } ], "committee": [ { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "chair", "display_name": "Laurent, Gilles J." }, { "name": { "family": "Mamelak", "given": "Adam N." }, "id": "Mamelak-A-N", "role": "member", "display_name": "Mamelak, Adam N." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "member", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "orcid": "0000-0003-0016-3531", "role": "member", "display_name": "O'Doherty, John P." } ], "option_major": [ "cns" ], "doi": "10.7907/GX3N-QD05", "abstract": "Episodic memories allow us to remember not only that we have seen an item before but also where and when we have seen it (context). Neurons in the medial temporal lobe (MTL) are critically involved in the acquisition of such memories. Since events happen only once, the ability to distinguish novel from familiar stimuli is crucial in order to rapidly encode such events after a single exposure. Theoretically, this is a hard learning problem (single-trial learning). Yet, successful detection of novelty is necessary for many types of learning. During retrieval, we can sometimes confidently report that we have seen something (familiarity) but cannot recollect where or when it was seen. Thus episodic memories have several components which can be recalled selectively. We recorded single neurons and local field potentials in the human hippocampus, amygdala, and anterior cingulate cortex while subjects remembered, and later retrieved, the identity and location of pictures shown. We describe two classes of neurons that exhibit such single-trial learning: novelty and familiarity detectors, which show a selective increase in firing for new and old stimuli, respectively. The neurons retain memory for the stimulus for at least 24 h. During retrieval, these neurons distinguish stimuli that will be successfully recollected from stimuli that will not be recollected. Similarly, they distinguish between failed and successful recognition. Pictures which were forgotten by the patient still evoked a non-zero response. Thus, their response can be different from the decision of the patient. Also, we demonstrate that listening to these neurons (during retrieval) enables a simple decoder to outperform the patient (i.e., it forgets fewer pictures). These data support a continuous strength of memory model of MTL function: the stronger the neuronal response, the better the memory (as opposed to a dual-process model). I also describe specific power increases in specific frequencies of the local field potential that are predictive of later retrieval success. These neural signatures, recorded during learning, thus indicate whether plasticity was successful or not." }, { "name": "Seitaridou, Effrosyni", "degree": "PhD", "year": "2008", "title": "Non-Equilibrium Dynamics: Diffusion in Small Numbers and Ribosomal Self-Assembly", "advisor": "Phillips, Robert B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142008-113003", "creators": [ { "name": { "family": "Seitaridou", "given": "Effrosyni" }, "id": "Seitaridou-Effrosyni", "orcid": "0000-0002-1668-6786", "display_name": "Seitaridou, Effrosyni" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "advisor", "display_name": "Phillips, Robert B." } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "orcid": "0000-0003-4073-1185", "role": "member", "display_name": "Rees, Douglas C." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/X12R-DA46", "abstract": "Biological systems are encountered in states that are far from equilibrium. A change in the cell's condition triggers the flow of energy and matter that causes the cell's transition from that non-equilibrium state to a different state. Our interest is on non-equilibrium systems and the way these relate to the cell's \"small numbers\" limit as well as to the mechanisms of self-assembly.
\r\n\r\nCells contain proteins and nucleotides in numbers smaller than Avogadro's. In addition, advances in single-molecule experiments, which are, by definition, a case of the \"small numbers\" problem, have emphasized the importance of fluctuations. Does the result we get from a single-molecule measurement agree with what we would get from a bulk measurement? Is it a fluctuation from the mean? It is, thus, of biological interest to see the behavior of non-equilibrium systems at the \"small numbers\" limit where fluctuations become important. Using microfluidics, we concentrate on the diffusion of a small number of submicron particles in a system that is away from equilibrium. Therefore, we study the \"small numbers\" limit of Fick's Law, with special reference to the fluctuations that attend diffusive dynamics in order to experimentally test the theoretical predictions obtained via the use of E. T. Jaynes' \"principle of maximum caliber.\"
\r\n\r\nThe process of macromolecular self-assembly is also highly dynamical. The system's components come together, defeating in this way entropic effects, to form the system. In the case of the ribosome, whose importance lies in its ability to synthesize proteins, understanding the mechanism of the highly dimensional process of self-assembly becomes relevant when designing, for example, new antibiotics. The second part of this thesis concentrates on the RNA-protein interactions which, in the case of the ribosome, determine the mechanism of self-assembly. With the use of microfluidic technology and a fluorescence assay we determine the thermodynamics and kinetics of RNA folding and RNA-protein binding for a fragment of the bacterial 30S ribosomal subunit, paving the way for the study of the complete assembly of the 30S subunit.
\r\n" }, { "name": "Shih, Jason J.", "degree": "PhD", "year": "2008", "title": "Microfabricated High-Performance Liquid Chromatography (HPLC) System with Closed-Loop Flow Control", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-05192008-132422", "creators": [ { "name": { "family": "Shih", "given": "Jason J." }, "id": "Shih-Jason-J", "display_name": "Shih, Jason J." } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Emami", "given": "Azita" }, "id": "Emami-A", "role": "member", "display_name": "Emami, Azita" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Lee", "given": "Terry D." }, "id": "Lee-T-D", "role": "member", "display_name": "Lee, Terry D." } ], "option_major": [ "eleceng" ], "doi": "10.7907/8A6W-2X34", "abstract": "This thesis presents the development of a microfabricated high-performance liquid chromatography (HPLC) system. The design, fabrication, and characterization of individual HPLC components such as high-pressure pumps, mixers, flow sensors, composition sensors, separation columns, filters, and detectors is presented. These individual components were then integrated to create robust, feedback-driven separation systems capable of performing gradient, reverse-phase, nanoscale HPLC. Two separate separation systems were created. The first integrated system was a microfluidic device for HPLC tandem mass spectrometry (HPLC-MS/MS) designed for proteomic applications. The second system was a portable HPLC conductivity detection (HPLC-CD) system designed for point-of-care applications such as biodetection. Both systems demonstrated good performance and repeatability. The performance of these systems is largely attributable to the development of HPLC-compatible sensors that could provide precise control over the elution profiles. These microfluidic closed-loop flow control systems represent an important advancement in the microfluidics field, where open-loop flow control is universally used, and risks becoming inadequate with the increasing complexity of microfluidic systems." }, { "name": "Soedarmadji, Edwin", "degree": "PhD", "year": "2008", "title": "Generalized Network Routing Metrics and Algorithms", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302008-002429", "creators": [ { "name": { "family": "Soedarmadji", "given": "Edwin" }, "id": "Soedarmadji-Edwin", "display_name": "Soedarmadji, Edwin" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z94B2ZJD", "abstract": "In this thesis, we introduce generalized network routing metrics that represent probability density parameters of the most popular communication channel models such as (a) the q-ary Symmetric Channel (q-SC) (b) the q-ary Erasure Channel (q-EC); (c) the Gilbert-Elliot Channel (GEC); and (d) the constrained Additive White Gaussian Noise (AWGN). The GEC is a very important for modelling correlated errors in channels such as the ubiquitous TCP/IP links and the wireless fading channels. In this thesis, we prove that channel models (a)--(d) can be used as inputs to the Generalized Dijkstra's Algorithm without resulting in any routing loop.
\r\n\r\nWe also define our own generalized Dijkstra's algorithm that can solve a modified standard shortest path problem that features: (1) a subset of network nodes that are capable of reducing the accumulated path cost down to zero, and (2) a constraint that the cumulative cost of any feasible path must never exceed a prespecified maximum value. We call this modified problem the Gas Station Problem, and its solution the Gas Station Algorithm. The algorithm can be applied in many different areas such as: vehicle routing, project management, and most importantly, network communication.
\r\n\r\nWe investigate various auxilliary synchronization algorithms used in popular routing protocols. Synchronization is used by routers to ensure that all routers operate on an identical routing table --- not a trivial task, considering network unreliabilities and possible malicious attacks. Our analysis produces a list of assumptions that guarantees synchronization. We also obtain the upper bounds to quantities such as transmission period, memory requirement, etc. In turn, these bounds can be used to rate network performance.
\r\n\r\nFinally, in a related contribution, we analyze message synchronization where a message is retransmitted only if the number of identical messages received exceeds a certain threshold. We define the Chinese Generals Problem as the problem of identifying the set of assumptions under which synchronization is guaranteed. This threshold-base message passing algorithm has the benefits of a tunable gain and a higher noise resistance.
\r\n" }, { "name": "Soloveichik, David", "degree": "PhD", "year": "2008", "title": "Molecules Computing: Self-Assembled Nanostructures, Molecular Automata,and Chemical Reaction Networks", "advisor": "Winfree, Erik", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-142339", "creators": [ { "name": { "family": "Soloveichik", "given": "David" }, "id": "Soloveichik-David", "orcid": "0000-0002-2585-4120", "display_name": "Soloveichik, David" } ], "advisors": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "advisor", "display_name": "Winfree, Erik" } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "cns" ], "doi": "10.7907/ZGE0-AF38", "abstract": "Many endeavors of molecular-level engineering either rely on biological material such as nucleic acids and restriction enzymes, or are inspired by biological processes such as self-assembly or cellular regulatory networks. This thesis develops theories on three such topics: self-assembled nanostructures, molecular automata, and chemical reaction networks. The abstractions and underlying methods of the theories presented herein are based on computer science and include Turing machines and circuits. Toward engineering self-assembled nanostructures, we create a theory of scale-free shapes in which the complexity of their self-assembly is connected to the shapes' descriptional complexity. Further, we study patterns in terms of whether they can be self-assembled robustly without an increase in scale to accommodate redundancy. We also describe a new method of ensuring resilience to more types of error simultaneously. Toward creating molecular automata we study the computational power of a restriction enzyme-based automaton. Toward designing chemical reaction networks, we develop a technique of storing and processing information in molecular counts, which is capable of achieving Turing universal computation. We also study the computational complexity of simulating stochastic chemical reaction networks and formally connect robustness and simulation efficiency. Lastly, we describe nucleic acid implementations of Boolean logic circuits and arbitrary mass-action kinetics. The three areas of this thesis are promising realizations of molecular-level engineering, and the theories presented here inform the range of possibility or delineate inherent difficulties in these areas. " }, { "name": "Stojnic, Mihailo", "degree": "PhD", "year": "2008", "title": "Optimization Algorithms in Wireless and Quantum Communications", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032007-113628", "creators": [ { "name": { "family": "Stojnic", "given": "Mihailo" }, "id": "Stojnic-Mihailo", "display_name": "Stojnic, Mihailo" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/D6RN-ZD88", "abstract": "Since the first communication systems were developed, the scientific community has been witnessing attempts to increase the amount of information that can be transmitted. In the last 10--15 years there has been a tremendous amount of research towards developing multi-antenna systems which would hopefully provide high-data-rate transmissions. However, increasing the overall amount of transmitted information increases the complexity of the necessary signal processing. A large portion of this thesis deals with several important issues in signal processing of multi-antenna systems. In almost every particular case the goal is to develop a technique/algorithm so that the overall complexity of the signal processing is significantly decreased.
\r\n\r\nIn the first part of the thesis a very important problem of signal detection in MIMO (multiple-input multiple-output) systems is considered. The problem is analyzed in two different scenarios: when the transmission medium (channel) 1) is known and 2) is unknown at the receiver. The former case is often called coherent and the later non-coherent MIMO detection. Both cases usually amount to solving highly complex NP-hard combinatorial optimization problems. For the coherent case we develop a significant improvement of the traditional sphere decoder algorithm commonly used for this type of detection. An interesting connection between the new improved algorithm and the H-infinity estimation theory is established, and the performance improvement over the standard sphere decoder is demonstrated. For the non-coherent case we develop a counterpart to the standard sphere decoder, the so-called out-sphere decoder. The complexity of the algorithm is viewed as a random variable; its expected value is analyzed and shown to be significantly smaller than the one of the overall exhaustive search. In the non-coherent case, in addition to the complexity analysis of the exact out-sphere decoder, we analyze the performance loss of a suboptimal technique. We show that only a moderate loss of a few dbs in power required at the transmitter will occur if a polynomial algorithm based on the semi-definite relaxation is used in place of any exact technique (which of course is not known to be polynomial).
\r\n\r\nIn the second part of the thesis we consider a few problems that arise in wireless broadcast channels. Namely, we consider the problem of the information symbol vector design at the transmitter. A polynomial linear precoding technique is constructed. It enables achieving data rates very close to the ones achieved with DPC (dirty paper coding) technique. Additionally, for another suboptimal polynomial scheme (the so-called nulling and cancelling), we show that it asymptotically achieves the same data rate as the optimal, exponentially complex, DPC.
\r\n\r\nIn the last part of the thesis we consider a quantum counterpart of the signal detection from classical communication. In quantum systems the signals are quantum states and the quantum detection problem amounts to designing measurement operators which have to satisfy certain quantum mechanics laws. A specific type of quantum detection called unambiguous detection, which has numerous applications including quantum filtering, has recently attracted a lot of attention in the research community. We develop a general framework for numerically solving this problem using the tools from the convex optimization theory. Furthermore, in the special case where the two quantum states are of rank 2, we construct an explicit analytical solution for the measurement operators.
\r\n\r\nAt the end we would like to emphasize that the contribution of this thesis goes beyond the specific problems mentioned here. Most algorithmic optimization techniques developed in this paper are generally applicable. While it is a fact that our results were originally motivated by wireless and quantum communications applications, we believe that the developed techniques will find applications in many different areas where similar optimization problems appear.
\r\n" }, { "name": "Su, Borching", "degree": "PhD", "year": "2008", "title": "Blind Channel Estimation Using Redundant Precoding: New Algorithms, Analysis, and Theory", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03102008-010821", "creators": [ { "name": { "family": "Su", "given": "Borching" }, "id": "Su-Borching", "orcid": "0000-0001-8617-2601", "display_name": "Su, Borching" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Tkacenko", "given": "Andre" }, "id": "Tkacenko-A", "role": "member", "display_name": "Tkacenko, Andre" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/R7MS-KQ06", "abstract": "Digital signal processing (DSP) techniques have played an important role in channel equalization and estimation in communication systems. While channel equalization and estimation are usually done by pilot-assisted methods in most systems, algorithms for blind channel estimation have also been largely studied due to high bandwidth efficiency. However, up to date, most blind methods possess disadvantages such as slow convergence speed, high complexity, poor performance, etc., compared to pilot-assisted methods. These drawbacks have made many consider blind methods as inapplicable in modern communication systems which feature fast-varying channels.
\r\n\r\nIn this thesis, we consider the blind channel estimation problem in block transmission systems with linear redundant precoding (LRP) which have been widely adopted in modern communication systems in recent years. The main contribution of this thesis is to considerably reduce the amount of received data required for blind estimation and suggest blind methods which are applicable even in fast-varying environments (e.g., in wireless channels). New algorithms are proposed, performance analysis derived, and theoretical issues studied.
\r\n\r\nThe first part of the thesis focuses on new algorithms for blind channel estimation and blind block synchronization in LRP systems. Two major types of linear redundant precoding, namely zero-padding (ZP) and cyclic prefixing (CP), are considered in this thesis. We first propose a generalized, subspace-based algorithm for blind channel estimation in ZP systems of which two previously reported algorithms are special cases. The generalization uses an integer parameter called {it repetition index} which represents the number of repeated uses of each received block. The number of received blocks required for subspace-based blind estimation is roughly inversely proportional to the repetition index. By choosing a larger repetition index, the amount of received data can be significantly reduced.
\r\n\r\nThe concept of repetition index is also applied in blind channel estimation in CP systems, which are more widely used than ZP systems in many current communication standards such as orthogonal frequency division multiplexing (OFDM) systems. The use of repetition index in CP systems is much less obvious and conceptually more complicated than in ZP systems. By choosing a repetition index larger than unity, the number of received blocks needed for blind estimation is significantly reduced compared to all previously reported methods. Theoretically, the proposed method can perform blind estimation using only three received blocks in absence of noise. In practice, the number of received blocks needed to yield a satisfactory bit error rate performance is usually on the order of half the block size. The proposed algorithm can be directly applied in OFDM systems without any modification of transmitter structure. A semiblind algorithm for channel estimation in OFDM systems is also proposed based on the extension of the blind algorithm.
\r\n\r\nAnother important problem, namely the blind block synchronization, is also studied. Most existing blind estimation methods in LRP systems assume the block boundaries of the received streams are perfectly known to the receiver, but this assumption is usually not true in practice since no extra known samples are transmitted. Two algorithms for blind block synchronization are proposed for ZP and CP systems, respectively. In particular, the block synchronization problem in CP systems is a broader version of the timing synchronization problem in the OFDM systems. The proposed algorithms exploit the concept of repetition index and both theoretical and simulation results suggest their advantages over all previously reported algorithms, especially when the amount of received data is limited.
\r\n\r\nThe second part of the thesis deals with theoretical issues related to blind channel estimation. Performance analysis of the generalized blind channel estimation algorithm in ZP systems is first given and shows that the system performance in terms of channel estimation mean square error (MSE) is very close to the Cramer-Rao bound (CRB), even when only two received blocks are available. Another important theoretical problem, namely the signal richness preservation problem, is also studied. Signal richness is an essential property for input signals in subspace-based blind channel estimation algorithms studied in this thesis. This property, however, may be altered by a linear precoder. Necessary and sufficient conditions for a linear precoder to preserve signal richness are explored. Several relevant interesting mathematical problems are also studied.
\r\n" }, { "name": "Sweatlock, Luke A.", "degree": "PhD", "year": "2008", "title": "Plasmonics: Numerical Methods and Device Applications", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-06112008-051943", "creators": [ { "name": { "family": "Sweatlock", "given": "Luke A." }, "id": "Sweatlock-Luke-A", "display_name": "Sweatlock, Luke A." } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8GPE-SB31", "abstract": "Plasmonics is a rapidly evolving subfield of nanophotonics that deals with the interaction of light with surface plasmons, which are the collective charge oscillations that occur at the interface between conductive and dielectric materials. Plasmonics meet a demand for optical interconnects which are small enough to coexist with nanoscale electronic circuits. Emerging technologies include very small, low-power active devices such as electrooptic or all-optical modulators. Passive plasmonic devices, or \"optical antennas\", are being used to enhance the performance of emitters and detectors, and to harvest sunlight for photovoltaics. This manuscript focuses on the process of developing novel plasmonic devices from concept to prototype, with specific emphasis on synthesizing data from numerical simulation and from empirical characterization into an accurate, predictive understanding of nanoscale optical phenomena.
\r\n\r\nThe first part of the thesis outlines the development of numerical methods. In the case of resonant nanostructures such as small metal particles, the principal technique employed is impulse excitation ringdown spectroscopy. This method allows the critical advantage of generating broadband spectra from a single time-domain simulation. For analysis of plasmonic waveguides, Fourier-space analysis is used to reveal the dispersion properties of supported modes, and to perform filtering in the wavevector domain or \"k-space\". The remainder of the thesis deals with the design and characterization of plasmonic devices, with the broad and general goal of creating a significant impact in the fields of optoelectronics and photovoltaics.
" }, { "name": "Sweatlock, Sarah Lynne", "degree": "PhD", "year": "2008", "title": "Asymptotic Weight Analysis of Low-Density Parity Check (LDPC) Code Ensembles", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202008-094714", "creators": [ { "name": { "family": "Sweatlock", "given": "Sarah Lynne" }, "id": "Sweatlock-Sarah-Lynne", "display_name": "Sweatlock, Sarah Lynne" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Tropp", "given": "Joel A." }, "id": "Tropp-J-A", "role": "member", "display_name": "Tropp, Joel A." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/86BY-MA30", "abstract": "With the invention of turbo codes in 1993 came increased interest in codes and iterative decoding schemes. Gallager's Regular codes were rediscovered, and irregular codes were introduced. Protograph codes were introduced and analyzed by NASA's Jet Propulsion Laboratory in the early years of this century. Part of this thesis continues that work, investigating the decoding of specific protograph codes and extending existing tools for analyzing codes to protograph codes.
\r\n\r\nThe rest of this work focuses on a previously unknown relationship between the binary entropy function and the asymptotic ensemble average weight enumerator, which we call the spectral shape of the ensemble. This result can be seen as an extension of the Pless power-moment identities based on the discovery that the convex hull of the spectral shape is the Legendre transform of a function closely related to the moment-generating function of a codeword's weight.
\r\n\r\nIn order to fully investigate this new relationship, tools needed to be designed to calculate the derivatives of the spectral shape as the equation describing an ensemble's spectral shape is rarely straightforward. For Gallager's regular ensembles, a formula for calculating derivatives of functions defined parametrically was required. For repeat-accumulate (RA) codes, a formula was needed for functions defined implicitly through a second function. Both formulas are similar to Faa di Bruno's formula for derivatives of compositions of functions.With the invention of turbo codes in 1993 came increased interest in codes and iterative decoding schemes. Gallager's Regular codes were rediscovered, and irregular codes were introduced. Protograph codes were introduced and analyzed by NASA's Jet Propulsion Laboratory in the early years of this century. Part of this thesis continues that work, investigating the decoding of specific protograph codes and extending existing tools for analyzing codes to protograph codes.
\r\n\r\nThe rest of this work focuses on a previously unknown relationship between the binary entropy function and the asymptotic ensemble average weight enumerator, which we call the spectral shape of the ensemble. This result can be seen as an extension of the Pless power-moment identities based on the discovery that the convex hull of the spectral shape is the Legendre transform of a function closely related to the moment-generating function of a codeword's weight.
\r\n\r\nIn order to fully investigate this new relationship, tools needed to be designed to calculate the derivatives of the spectral shape as the equation describing an ensemble's spectral shape is rarely straightforward. For Gallager's regular ensembles, a formula for calculating derivatives of functions defined parametrically was required. For repeat-accumulate (RA) codes, a formula was needed for functions defined implicitly through a second function. Both formulas are similar to Faa di Bruno's formula for derivatives of compositions of functions.
" }, { "name": "Taflanidis, Alexandros Angelos", "degree": "PhD", "year": "2008", "title": "Stochastic System Design and Applications to Stochastically Robust Structural Control", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062007-135604", "creators": [ { "name": { "family": "Taflanidis", "given": "Alexandros Angelos" }, "id": "Taflanidis-Alexandros-Angelos", "orcid": "0000-0002-9784-7480", "display_name": "Taflanidis, Alexandros Angelos" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Scruggs", "given": "Jeffrey" }, "id": "Scruggs-J", "role": "member", "display_name": "Scruggs, Jeffrey" }, { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-S", "role": "member", "display_name": "Krishnan, Swaminathan" }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." } ], "option_major": [ "civileng" ], "doi": "10.7907/6TRA-1C83", "abstract": "The knowledge about a planned system in engineering design applications is never complete. Often, a probabilistic quantification of the uncertainty arising from this missing information is warranted in order to efficiently incorporate our partial knowledge about the system and its environment into their respective models. In this framework, the design objective is typically related to the expected value of a system performance measure, such as reliability or expected life-cycle cost. This system design process is called stochastic system design and the associated design optimization problem stochastic optimization. In this thesis general stochastic system design problems are discussed. Application of this design approach to the specific field of structural control is considered for developing a robust-to-uncertainties nonlinear controller synthesis methodology.
\r\n\r\nInitially problems that involve relatively simple models are discussed. Analytical approximations, motivated by the simplicity of the models adopted, are discussed for evaluating the system performance and efficiently performing the stochastic optimization. Special focus is given in this setting on the design of control laws for linear structural systems with probabilistic model uncertainty, under stationary stochastic excitation. The analysis then shifts to complex systems, involving nonlinear models with high-dimensional uncertainties. To address this complexity in the model description stochastic simulation is suggested for evaluating the performance objectives. This simulation-based approach addresses adequately all important characteristics of the system but makes the associated design optimization challenging. A novel algorithm, called Stochastic Subset Optimization (SSO), is developed for efficiently exploring the sensitivity of the objective function to the design variables and iteratively identifying a subset of the original design space that has high plausibility of containing the optimal design variables. An efficient two-stage framework for the stochastic optimization is then discussed combining SSO with some other stochastic search algorithm. Topics related to the combination of the two different stages for overall enhanced efficiency of the optimization process are discussed.
\r\n\r\nApplications to general structural design problems as well as structural control problems are finally considered. The design objectives in these problems are the reliability of the system and the life-cycle cost. For the latter case, instead of approximating the damages from future earthquakes in terms of the reliability of the structure, as typically performed in past research efforts, an accurate methodology is presented for estimating this cost; this methodology uses the nonlinear response of the structure under a given excitation to estimate the damages in a detailed, component level.
\r\n" }, { "name": "Taira, Kunihiko (Sam)", "degree": "PhD", "year": "2008", "title": "The Immersed Boundary Projection Method and Its Application to Simulation and Control of Flows Around Low-Aspect-Ratio Wings", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232008-124342", "creators": [ { "name": { "family": "Taira", "given": "Kunihiko (Sam)" }, "id": "Taira-Kunihiko-Sam", "orcid": "0000-0002-3762-8075", "display_name": "Taira, Kunihiko (Sam)" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "mecheng" ], "doi": "10.7907/VSDD-P465", "abstract": "First, we present a new formulation of the immersed boundary method that is algebraically identical to the traditional fractional step algorithm. This method, called the immersed boundary projection method, allows for the simulations of incompressible flows over arbitrarily shaped bodies under motion and/or deformation in both two and three dimensions. The no-slip condition along the immersed boundary is enforced simultaneously with the incompressibility constraint through a single projection. The boundary force is determined implicitly without any constitutive relations for the rigid body formulation, which in turn allows the use of high CFL numbers in our simulations compared to past methods.
\r\n\r\nNext, the above immersed boundary projection method is used to analyze three-dimensional separated flows around low-aspect-ratio flat-plate wings. A number of simulations highlighting the unsteady nature of the separated flows are performed for Re = 300 and 500 with various aspect ratios, angles of attack, and planform geometries. The aspect ratio and angle of attack are found to have a large influence on the stability of the wake profile and the force experienced by the low-aspect-ratio wing. At early times, following an impulsive start, topologies of the wake vortices are found to be the same across different aspect ratios and angles of attack. Behind low-aspect-ratio rectangular plates, leading-edge vortices form and eventually separate as hairpin vortices following the start-up. This phenomenon is found to be similar to dynamic stall observed behind pitching plates. The detached structure would then interact with the tip vortices, reducing the downward velocity induced by the tip vortices acting upon the leading-edge vortex. At large time, depending on the aspect ratio and angles of attack, the wakes reach one of the three states: (i) a steady state, (ii) a periodic unsteady state, or (iii) an aperiodic unsteady state. We have observed that the tip effects in three-dimensional flows can stabilize the flow and also exhibit nonlinear interaction with the shedding vortices.
\r\n\r\nAt last, we apply steady blowing to separated flows behind the low-aspect-ratio rectangular wings. The objective of the flow control is to enhance lift at post-stall angles of attack by changing the dynamics of the wake vortices. This controller strengthens the tip vortices by engulfing the trailing-edge vortex sheet to increase the downward thrust and the downward induced velocity onto the leading-edge vortices. The tip vortices that are traditionally considered as an aerodynamic nuisance, have been used favorably to increase lift in post-stall flows for the considered low-aspect-ratio wings.
" }, { "name": "Tanabe, Katsuaki", "degree": "PhD", "year": "2008", "title": "Low-Cost High-Efficiency Solar Cells with Wafer Bonding and Plasmonic Technologies", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272008-123439", "creators": [ { "name": { "family": "Tanabe", "given": "Katsuaki" }, "id": "Tanabe-Katsuaki", "orcid": "0000-0002-0179-4872", "display_name": "Tanabe, Katsuaki" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "matsci" ], "doi": "10.7907/4W2B-RD63", "abstract": "III-V compound multijunction solar cells enable ultrahigh efficiency performance in designs where subcells with high material quality and high internal quantum efficiency can be employed. However the optimal multijunction cell bandgap sequence cannot be achieved using lattice-matched compound semiconductor materials. Most current compound semiconductor solar cell design approaches are focused on either lattice-matched designs or metamorphic growth (i.e., growth with dislocations to accommodate subcell lattice mismatch), which inevitably results in less design flexibility or lower material quality than is desirable. An alternative approach is to employ direct bonded interconnects between subcells of a multijunction cell, which enables dislocation-free active regions by confining the defect network needed for lattice mismatch accommodation to tunnel junction interfaces.
\r\n\r\nWe fabricated for the first time a direct-bond interconnected multijunction solar cell, a two-terminal monolithic GaAs/InGaAs dual-junction cell, to demonstrate a proof-of-principle for the viability of direct wafer bonding for solar cell applications. The bonded interface is a metal-free n\u207aGaAs/n\u207aInP tunnel junction with highly conductive Ohmic contact suitable for solar cell applications overcoming the 4% lattice mismatch. The quantum efficiency spectrum for the bonded cell was quite similar to that for each of unbonded GaAs and InGaAs subcells. The bonded dual-junction cell open-circuit voltage was equal to the sum of the unbonded subcell open-circuit voltages, which indicates that the bonding process does not degrade the cell material quality since any generated crystal defects that act as recombination centers would reduce the open-circuit voltage. Also, the bonded interface has no significant carrier recombination rate to reduce the open circuit voltage.
\r\n\r\nSuch a wafer bonding approach can also be applied to other photovoltaic heterojunctions where lattice mismatch accommodation is also a challenge, such as the InGaP/GaAs/InGaAsP/InGaAs four-junction tandem cell by bonding a GaAs-based lattice-matched InGaP/GaAs subcell to an InP-based lattice-matched InGaAsP/InGaAs subcell. Simple considerations suggest that for such a cell the currently-reported interfacial resistance of 0.12 Ohm-cm\u00b2 would result in a negligible decrease in overall cell efficiency of ~0.02%, under 1-sun illumination.
\r\n\r\nEngineered substrates consisting of thin films of InP on Si handle substrates (InP/Si substrates or epitaxial templates) have the potential to significantly reduce the cost and weight of compound semiconductor solar cells relative to those fabricated on bulk InP substrates. InGaAs solar cells on InP have superior performance to Ge cells at photon energies greater than 0.7 eV and the current record efficiency cell for 1 sun illumination was achieved using an InGaP/GaAs/InGaAs triple junction cell design with an InGaAs bottom cell. Thermophotovoltaic (TPV) cells from the InGaAsP-family of III-V materials grown epitaxially on InP substrates would also benefit from such an InP/Si substrate. Additionally, a proposed four-junction solar cell fabricated by joining subcells of InGaAs and InGaAsP grown on InP with subcells of GaAs and AlInGaP grown on GaAs through a wafer-bonded interconnect would enable the independent selection of the subcell band gaps from well developed materials grown on lattice matched substrates. Substitution of InP/Si substrates for bulk InP in the fabrication of such a four-junction solar cell could significantly reduce the substrate cost since the current prices for commercial InP substrates are much higher than those for Si substrates by two orders of magnitude. Direct heteroepitaxial growth of InP thin films on Si substrates has not produced the low dislocation-density high quality layers required for active InGaAs/InP in optoelectronic devices due to the ~8% lattice mismatch between InP and Si.
\r\n\r\nWe successfully fabricated InP/Si substrates by He implantation of InP prior to bonding to a thermally oxidized Si substrate and annealing to exfoliate an InP thin film. The thickness of the exfoliated InP films was only 900 nm, which means hundreds of the InP/Si substrates could be prepared from a single InP wafer in principle. The photovoltaic current-voltage characteristics of the In0.53Ga0.47As cells fabricated on the wafer-bonded InP/Si substrates were comparable to those synthesized on commercially available epi-ready InP substrates, and had a ~20% higher short-circuit current which we attribute to the high reflectivity of the InP/SiO\u00b2/Si bonding interface. This work provides an initial demonstration of wafer-bonded InP/Si substrates as an alternative to bulk InP substrates for solar cell applications.
\r\n\r\nMetallic nanostructures can manipulate light paths by surface plasmons and can dramatically increase the optical path length in thin active photovoltaic layers to enhance photon absorption. This effect has potential for cost and weight reduction with thinned layers and also for efficiency enhancement associated with increased carrier excitation level in the absorber layer.
\r\n\r\nWe have observed photocurrent enhancements up to 260% at 900 nm for a GaAs cell with a dense array of Ag nanoparticles with 150 nm diameter and 20 nm height deposited through porous alumina membranes by thermal evaporation on top of the cell, relative to reference GaAs cells with no metal nanoparticle array. This dramatic photocurrent enhancement is attributed to the effect of metal nanoparticles to scatter the incident light into photovoltaic layers with a wide range of angles to increase the optical path length in the absorber layer.
\r\n\r\nGaAs solar cells with metallic structures at the bottom of the photovoltaic active layers, not only at the top, using semiconductor-metal direct bonding have been fabricated. These metallic back structures could incouple the incident light into surface plasmon mode propagating at the semiconductor/metal interface to increase the optical path, as well as simply act as back reflector, and we have observed significantly increased short-circuit current relative to reference cells without these metal components.
" }, { "name": "Tian, Lixiu", "degree": "PhD", "year": "2008", "title": "Effective Behavior of Dielectric Elastomer Composites", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-145455", "creators": [ { "name": { "family": "Tian", "given": "Lixiu" }, "id": "Tian-Lixiu", "display_name": "Tian, Lixiu" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/CZNF-JB47", "abstract": "The class of electroactive polymers has been developed to a point where real life applications as ``artificial muscles\" are conceivable. These actuator materials provide attractive advantages: they are soft, lightweight, can undergo large deformation, possess fast response time and are resilient. However, widespread application has been hindered by their limitations: the need for a large electric field, relatively small forces and energy density. However, recent experimental work shows great promise that this limitation can be overcome by making composites of two materials with high contrast in their dielectric modulus. In this thesis, a theoretical framework is derived to describe the electrostatic effect of the dielectric elastomers. Numerical experiments are conducted to explain the reason for the promising experimental results and to explore better microstructures of the composites to enhance the favorable properties.
\r\n\r\nThe starting point of this thesis is a general variational principle, which characterizes the behavior of solids under combined mechanical and electrical loads. Based on this variational principle, we assume the electric field is small as of order \u03b5\u00bd, assume further the deformation is caused by the electrostatic effects; the deformation field is then of order \u03b5. Using the tool of \u0393-convergence, we derive a small-strain model in which the electric field and the deformation field are decoupled which results in a huge simplification of the problem.
\r\n\r\nBased on this small-strain model, employing the powerful tool of two-scale convergence, we derive the effective properties for dielectric composites conducting small strains. A formula of the effective electromechanical coupling coefficients is given in terms of the unit cell solutions.
\r\n\r\nArmed with these theoretical results, we carry out numerical experiments about the effective properties of different kind of composites. A very careful analysis of the numerical results provides a deep understanding of the mechanism of the enhancement in strain by making composites of different microstructures.
" }, { "name": "Tong, Chinghang", "degree": "PhD", "year": "2008", "title": "Thermodynamic Modeling of Organic Aerosol", "advisor": "Seinfeld, John H.; Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172007-160334", "creators": [ { "name": { "family": "Tong", "given": "Chinghang" }, "id": "Tong-Chinghang", "display_name": "Tong, Chinghang" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "co-advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Blanco", "given": "Mario" }, "id": "Blanco-M", "role": "member", "display_name": "Blanco, Mario" }, { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "role": "member", "display_name": "Okumura, Mitchio" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "envreng" ], "doi": "10.7907/3M7R-9620", "abstract": "Modeling atmospheric aerosols containing a large organic fraction with unknown chemical composition and properties has been a constant challenge. The dissertation focuses on the theoretical treatment of the thermodynamic equilibrium of atmospheric aerosol involving organic species.
\r\n\r\nWe present a vapor pressure estimation method, based on quantum chemistry methods, to predict the liquid vapor pressure, enthalpies of vaporization, and heats of sublimation of atmospheric organic compounds. Predictions are compared to literature data, and the overall accuracy is considered satisfactory given the simplicity of the equations. Quantum mechanical methods were also used to investigate the thermodynamic feasibility of various acid-catalyzed aerosol-phase heterogeneous chemical reactions. A stepwise procedure is presented to determine physical properties such as heats of formation, standard entropies, Gibbs free energies of formation, and solvation energies from quantum mechanics, for various short-chain aldehydes and ketones. Equilibrium constants of hydration reactions and aldol condensation are then reported; predictions are in qualitatively agreement with previous studies. We have shown that quantum methods can serve as useful tools for first approximation, especially for species with no available data, in determining the thermodynamic properties of multifunctional oxygenates.
\r\n\r\nWe also present an atmospheric aerosol phase equilibrium model to determine the aerosol phase equilibrium of aqueous systems. Phase diagrams for a number of organic/water systems characteristic of both primary and secondary organic aerosols are computed. Effects of organics on the deliquescence behavior of electrolytes are also shown in the inorganic/organic/water phase diagrams.
\r\n\r\nFinally, we evaluate the performance of four recent activity coefficient models developed for inorganic-organic-water mixtures typical of atmospheric aerosols. Based on the comparison on water activities, it is found that models that include ion-organic mixture parameters (referred to as coupled models) do not necessarily produce more accurate predictions than those models that utilizes additive approaches (referred to as decoupled models). Since the chemical composition and physical properties of the organic fraction is largely unknown, the additive approaches of the decoupled models are more feasible than the coupled model.
\r\n" }, { "name": "Wang, Ke", "degree": "PhD", "year": "2008", "title": "A Subdivision Approach to the Construction of Smooth Differential Forms", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282008-112022", "creators": [ { "name": { "family": "Wang", "given": "Ke" }, "id": "Wang-Ke", "display_name": "Wang, Ke" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/K0DE-9P44", "abstract": "Vertex- and face-based subdivision schemes are now routinely used in geometric modeling and computational science, and their primal/dual relationships are well studied. In this thesis we interpret these schemes as defining bases for discrete differential 0- resp. 2-forms, and present a novel subdivision-based method of constructing smooth differential forms on simplicial surfaces. It completes the picture of classic primal/dual subdivision by introducing a new concept named r-cochain subdivision. Such subdivision schemes map scalar coefficients on r-simplexes from the coarse to the refined mesh and converge to r-forms on the mesh. We perform convergence and smoothness analysis in an arbitrary topology setting by utilizing the techniques of matrix subdivision and the subdivision differential structure.
\r\n\r\nThe other significance of our method is its preserving exactness of differential forms. We prove that exactness preserving is equivalent to the commutative relations between the subdivision schemes and the topological exterior derivative. Our construction is based on treating r- and (r+1)-cochain subdivision schemes as a pair and enforcing the commutative relations. As a result, our low-order construction recovers classic Whitney forms, while the high-order construction yields a new class of high order Whitney forms. The 1-form bases are C^1, except at irregular vertices where they are C^0. We also demonstrate extensions to three-dimensional subdivision schemes and non-simplicial meshes as well, such as quadrilaterals and octahedra.
\r\n\r\nOur construction is seamlessly integrated with surface subdivision. Once a metric is supplied, the scalar 1-form coefficients define a smooth tangent vector filed on the underlying subdivision surface. Design of tangent vector fields is made particularly easy with this machinery as we demonstrate. The subdivision r-forms can also be used as finite element bases for physical simulations on curved surfaces. We demonstrate the optimal rate of convergence in solving the Laplace and bi-Laplace equations of 1-forms.
\r\n" }, { "name": "Waydo, Stephen J.", "degree": "PhD", "year": "2008", "title": "Explicit Object Representation by Sparse Neural Codes", "advisor": "Murray, Richard M.; Koch, Christof", "url": "https://resolver.caltech.edu/CaltechETD:etd-11022007-104734", "creators": [ { "name": { "family": "Waydo", "given": "Stephen J." }, "id": "Waydo-Stephen-J", "display_name": "Waydo, Stephen J." } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "co-advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "co-chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Olshausen", "given": "Bruno" }, "id": "Olshausen-B", "role": "member", "display_name": "Olshausen, Bruno" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cns" ], "doi": "10.7907/1XY7-2H19", "abstract": "Neurons have been identified in the human medial temporal lobe (MTL) that display a strong selectivity for only a few stimuli (such as familiar individuals or landmark buildings) out of perhaps 100 presented to the test subject. While highly selective for a particular object or category, these cells are remarkably insensitive to different presentations (i.e., different poses and views) of their preferred stimulus. This invariant, sparse, and explicit representation of the world may be crucial to the transformation of complex visual stimuli into more abstract memories. In this thesis I first discuss the issue of how best to quantify sparseness, particularly in very sparse systems where biases are significant, and show the results of this analysis applied to human MTL data. I also provide an overview of existing results from other investigators on measuring sparseness both elsewhere along the primate visual pathway and in selected other sensory processing systems. From there I move into the computational realm. Sparse coding as a computational constraint applied to the representation of natural images has been shown to produce receptive fields strikingly similar to those observed in mammalian primary visual cortex. I apply sparse coding as a model for processing further along the visual hierarchy: not directly to images but rather to an invariant feature-based representation of images analogous to that found in the inferotemporal cortex. This combination of sparseness and invariance naturally leads to explicit category representation. That is, by exposing the model to different images drawn from different categories, units develop that respond selectively to different categories. After extending an existing model of sparse coding and providing some mathematical analysis of its operation, I show results obtained by applying this method both to unsupervised category discovery in images and to differentiation between images of different individuals.\r\n" }, { "name": "Wolf, Julie Anne", "degree": "PhD", "year": "2008", "title": "A Plasticity Model to Predict the Effects of Confinement on Concrete", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212008-221749", "creators": [ { "name": { "family": "Wolf", "given": "Julie Anne" }, "id": "Wolf-Julie-Anne", "display_name": "Wolf, Julie Anne" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/XMA5-MK90", "abstract": "A plasticity model to predict the behavior of confined concrete is developed. The model is designed to implicitly account for the increase in strength and ductility due to confining a concrete member. The concrete model is implemented into a finite element (FE) model. By implicitly including the change in the strength and ductility in the material model, the confining material can be explicitly included in the FE model. Any confining material can be considered, and the effects on the concrete of failure in the confinement material can be modeled. Test data from a wide variety of different concretes utilizing different confinement methods are used to estimate the model parameters. This allows the FE model to capture the generalized behavior of concrete under multiaxial loading. The FE model is used to predict the results of tests on reinforced concrete members confined by steel hoops and fiber reinforced polymer (FRP) jackets. Loading includes pure axial load and axial load-moment combinations. Variability in the test data makes the model predictions difficult to compare but, overall, the FE model is able to capture the effects of confinement on concrete. Finally, the FE model is used to compare the performance of steel hoop to FRP confined sections, and of square to circular cross sections. As expected, circular sections are better able to engage the confining material, leading to higher strengths. However, higher strains are seen in the confining material for the circular sections. This leads to failure at lower axial strain levels in the case of the FRP confined sections. Significant differences are seen in the behavior of FRP confined members and steel hoop confined members. Failure in the FRP members is always determined by rupture in the composite jacket. As a result, the FRP members continue to take load up to failure. In contrast, the steel hoop confined sections exhibit extensive strain softening before failure. This comparison illustrates the usefulness of the concrete model as a tool for designers. Overall, the concrete model provides a flexible and powerful method to predict the performance of confined concrete." }, { "name": "Wolf, Michael Timothy", "degree": "PhD", "year": "2008", "title": "Target Tracking Using Clustered Measurements, with Applications to Autonomous Brain-Machine Interfaces", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-105504", "creators": [ { "name": { "family": "Wolf", "given": "Michael Timothy" }, "id": "Wolf-Michael-Timothy", "display_name": "Wolf, Michael Timothy" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/6Y3F-8M87", "abstract": "This thesis presents new methods for classifying and tracking the signals of targets that produce clusters of observations, measured in successive recording intervals or scans. This multitarget tracking problem arises, for instance, in extracellular neural recordings, in which an electrode is inserted into the brain to detect the spikes of individual neurons. Since multiple active neurons may lie near the electrode, each detected spike must be assigned to the neuron that produced it, a task known as spike sorting. In the scenario considered in this thesis, the electrode signal is sampled over many brief recording intervals. In each recording interval, all spikes must first be clustered according to their generating neurons, and then each cluster must be associated to clusters from previous recording intervals, thus tracking the signals of putative neuron \"targets.\"
\r\n\r\nThis thesis introduces a novel multitarget tracking solution for the above problem, called multiple hypothesis tracking for clusters (MHTC). The MHTC algorithm has two main parts: a Bayesian clustering algorithm for associating observations to clusters in each interval and a probabilistic supervisory system that manages association hypotheses across intervals. The clustering procedure provides significantly more consistent results than previously available methods, enabling more accurate tracking of targets over time. Such consistency is promoted by a maximum a posteriori (MAP) approach to optimizing a Gaussian mixture model via expectation-maximization (EM), in which information from the preceding intervals serves as a prior for the current interval while still allowing the number and locations of targets to change. MHTC's hypothesis management system, like that of traditional multiple hypothesis tracking (MHT) algorithms, propagates various possibilities for how to assign measurements to existing targets and uses a delayed decision-making logic to resolve data association ambiguities. It also, however, maintains several options, termed model hypotheses, for how to cluster the observations of each interval. This combination of clustering and tracking in a single solution enables MHTC to robustly maintain the identities of cluster-producing targets in challenging recording scenarios.
\r\n\r\nIn addition to these classification and tracking techniques, this thesis presents advances in a miniature robotic electrode microdrive capable of extracellular recordings lasting for days at a time. As a whole, these contributions can play an important role in enabling an autonomous neural interface, which, by frequent automatic repositioning of its recording electrodes, can optimize the recording quality of extracellular signals associated with individual neurons and maintain high quality recordings for long periods of time. Such autonomous movable electrodes may eventually overcome key barriers to engineering a practical neuroprosthetic device and, in the near term, can significantly improve state-of-the-art neuroscience experimental procedures.
\r\n" }, { "name": "Yun, Gunsu Soonshin", "degree": "PhD", "year": "2008", "title": "Dynamics of Plasma Structures Interacting with External and Self-Generated Magnetic Fields", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-07242007-162442", "creators": [ { "name": { "family": "Yun", "given": "Gunsu Soonshin" }, "id": "Yun-Gunsu-Soonshin", "orcid": "0000-0002-1880-5865", "display_name": "Yun, Gunsu Soonshin" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Meier", "given": "David L." }, "id": "Meier-D-L", "role": "member", "display_name": "Meier, David L." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/9CMD-C377", "abstract": "Plasmas interacting with external and self-generated magnetic fields often develop a long tubular structure of nearly uniform cross section. Such long collimated plasma tubes have been observed in a variety of contexts ranging from astrophysical plasma jets (1015\u20131022 m) to solar coronal loops (107\u2013108 m). Remarkably, much smaller-sized plasmas (0.1\u20131 m) produced by the Caltech planar spheromak gun develop collimated structures bearing a striking resemblance to these natural plasma tubes. This thesis presents experimental observations of gun-produced plasma tubes that support a recently-proposed magnetohydrodynamic (MHD) pumping model as a universal collimation mechanism. For any flared flux tube carrying a finite axial current, the model predicts (i) magnetic pumping of plasma particles from a constricted region into a bulged region and (ii) tube collimation if the flow slows down at the bulged region, leading to accumulation of mass and thus concentrating the azimuthal magnetic flux frozen in the mass flow (i.e., increasing the pinch force). Time- and space-resolved spectroscopic measurements of gun-produced plasmas show (i) suprathermal Alfvenic flow (30\u201350 km/s), (ii) large density amplification from ~1017 to ~1022 m-3 in an Alfvenic time scale (5\u201310 \u00b5s), and (iii) flow slowing down and mass accumulation at the flow front, the place where the tube collimation occurs according to high-speed camera imaging. These observations are consistent with the predictions of the MHD pumping model, and thus the model offers valuable insight into the formation mechanism of laboratory, solar, and astrophysical plasma structures." }, { "name": "Yung, Pun To (Douglas)", "degree": "PhD", "year": "2008", "title": "Detection of Aerobic Bacterial Endospores: From Air Sampling, Sterilization Validation to Astrobiology", "advisor": "Ponce, Adrian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292008-064614", "creators": [ { "name": { "family": "Yung", "given": "Pun To (Douglas)" }, "id": "Yung-Pun-To-Douglas", "orcid": "0000-0002-2005-9478", "display_name": "Yung, Pun To (Douglas)" } ], "advisors": [ { "name": { "family": "Ponce", "given": "Adrian" }, "id": "Ponce-A", "role": "advisor", "display_name": "Ponce, Adrian" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Ponce", "given": "Adrian" }, "id": "Ponce-A", "role": "member", "display_name": "Ponce, Adrian" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/9GJ2-FV58", "abstract": "Bacterial endospores are formed in genera such as Bacillus and Clostridium in times of incipient stresses. Derivative of their remarkable resistance and ubiquity, endospores are delivery vehicles for anthrax attack, biological indicators for checking sterilization efficacy, and candidates for Panspermia and potential extraterrestrial life, thereby underscoring the significance of their rapid detection. In this thesis project, spectroscopy and microscopy methods are studied to measure the release of a unique constituent, dipicolinic acid (DPA), via germination as a proxy for endospore viability. In particular, a luminescence time-gated microscopy technique (called microscopy endospore viability assay, acronym: \u03bcEVA) has been developed to enumerate germination-capable aerobic endospores rapidly based on energy transfer from DPA to terbium ions doped on a solid matrix upon UV excitation. The distinctive emission and millisecond lifetime enable \r\ntime-resolved imaging to achieve a sensitivity of one endospore.
\r\n\r\nEffective air sampling of endospores is crucial in view of the potential catastrophe caused by the dissemination of airborne anthrax endospores. Based on time-gated spectroscopy of terbium-DPA luminescence, the Anthrax Smoke Detector has been built to provide real-time surveillance of air quality for timely mitigation and decontamination. This technology also finds application in the monitoring of airborne endospore bioburden as an indicator of total biomass in a closed spacecraft system in order to safeguard the health of astronauts.
\r\n\r\nSterilization validation is of prime concern in the medical field and planetary protection to prevent cross-contaminations among patients and planets. \u03bcEVA has yielded faster and comparable results compared with the culture-based NASA standard assay in assessing surface endospore bioburden on spacecraft materials and clean rooms surfaces. The current analysis time has been expedited from 3 days to within an hour in compliance with planetary protection requirements imposed on landers and probes designed for life detection missions.
\r\n\r\nFrom the perspective of astrobiology, endospores are time capsules preserving geological history and may exist as dormant lives in analogous extraterrestrial environments. \u03bcEVA has successfully recovered ancient endospores in cold biospheres (Greenland ice core, Antarctic Lake Vida, polar permafrost) and hyper-arid biospheres (Atacama Desert) on Earth as templates for determining life longevity and the search of extinct or extant life on Mars and other icy celestial bodies. Result authenticity has been validated by a comprehensive suite of experiments encompassing culture-based and culture-independent techniques such as epifluorescence microscopy, flow cytometry, fluorometry, bioluminescence and 16s rRNA analysis. In conclusion, \u03bcEVA is a sensitive analytical tool that opens a new realm in microbiology to provide insights into air sampling, sterility assessment and exobiology.
\r\n" }, { "name": "Zhu, Lin", "degree": "PhD", "year": "2008", "title": "Photonic Crystal Bragg Lasers: Design, Fabrication, and Characterization", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282008-162123", "creators": [ { "name": { "family": "Zhu", "given": "Lin" }, "id": "Zhu-Lin", "display_name": "Zhu, Lin" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/7MMN-7Q15", "abstract": "On-chip, single mode semiconductor lasers are usually fabricated using conventional distributed feedback (DFB) structures. Due to the limitation of index guiding in the transverse direction, the width of these lasers has to be less than a few microns. Meanwhile, the laser output power is limited by catastrophic optical damage (COD) at the facets and thus large optical cavities are necessary for high power semiconductor lasers. Therefore, high power, single mode applications are challenging, due to the conflicting requirements for large modal volume (to prevent COD by reducing optical power density) and narrow width (to obtain the single mode operation). Increasing the width of single mode semiconductor lasers is fundamentally important for obtaining high spectral and spatial optical power densities.
\r\n\r\nThis thesis reports on achieving the single mode operation of large area, edge emitting semiconductor lasers, using the photonic crystal Bragg structure (two dimensional distributed feedback structure). Both theoretical and experimental results are presented. Two dimensional coupled mode approaches and transfer matrix methods are developed to analyze and design the photonic crystal Bragg structure. It is shown that the single mode lasing can be obtained by satisfying both the transverse and longitudinal Bragg conditions and a single lobe, diffraction limited far field can be obtained by optimizing the coupling coefficient of the photonic crystal.
\r\n\r\nElectrically pumped, large-area (100 um x 500 um), single mode semiconductor photonic crystal Bragg lasers are experimentally demonstrated in pulsed and continuous wave conditions with single lobe, diffraction limited far fields. Two dimensional lasing wavelength tuning is demonstrated, which proves that the lasing mode is truly defined by the photonic crystal lattice. Furthermore, a wavelength tuning sensitivity about 80 times smaller than a conventional DFB laser is also achieved, allowing for more accurate control of the lasing wavelength.
\r\n\r\nPhotonic crystal lasers based on effective index guiding are also studied. Single mode operation is achieved by combining the transverse confinement provided by an effective index guiding mechanism with the longitudinal mode selection provided by the Bragg reflection from the photonic crystal cladding. These devices represent an important first step toward using photonic crystals in a different way for the modal control of semiconductor lasers in planar optical circuits.
\r\n\r\n\r\n" }, { "name": "Afshari, Ehsan", "degree": "PhD", "year": "2007", "title": "Optotronics: Optically Inspired Electronics", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-08042006-144107", "creators": [ { "name": { "family": "Afshari", "given": "Ehsan" }, "id": "Afshari-Ehsan", "orcid": "0000-0002-4528-1788", "display_name": "Afshari, Ehsan" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z95M63XK", "abstract": "Waves are everywhere, from the distribution of cars on a highway to the wave patterns in the ocean. Intriguing phenomena in wave propagation, such as Soliton resonance, kink-antikink interaction, self-focusing, and Peakon generation can be used in many practical applications leading to novel architectures for signal processing and generation. These E/M based approaches could be particularly useful in the case of Extremely Wide Band (EWB) (DC to more than 100GHz) circuits and systems where the limited transistor cut-off frequency, maximum power efficiency, and breakdown voltage pose serious constraints on the use of conventional circuit techniques.
\r\n\r\nTo overcome the limitations of active devices in EWB signal processing and generation, we propose a general class of solutions based on novel circuit topologies inspired by commonly used structures in electromagnetics, and more specifically optics. The proposed methodology is based on nonlinear and/or inhomogeneous one-dimensional (1D) transmission lines which we have successfully extended to two-dimensional transmission lattices. The principles behind these designs stem from the mathematical theory of linear and nonlinear wave propagation. By analyzing the models for the transmission lines/lattices, we are able to exploit the large body of theory to design circuits, demonstrating the narrowest reported pulse on silicon (2.5ps), and for a single integrated-circuit silicon-based amplifier, the highest achieved center frequency of operation (85GHz) and the highest achieved power output (120mW) at this frequency. In addition, we have reported the first in-silicon transmission line system capable of sharpening both rising and falling edges of NRZ data by increasing the bandwidth. In the end, we will also present how the same approach can be applied to realize ultra-fast computation systems (such as a sub-nanosecond Fourier and Hankel transformers in silicon) and other structures, leading to a new design discipline we like to call \"Optotronics\".
\r\n" }, { "name": "Anen, C\u00e9dric Robert", "degree": "PhD", "year": "2007", "title": "Neural Correlates of Economic and Moral Decision-Making", "advisor": "Quartz, Steven R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05012007-133654", "creators": [ { "name": { "family": "Anen", "given": "C\u00e9dric Robert" }, "id": "Anen-C\u00e9dric-Robert", "display_name": "Anen, C\u00e9dric Robert" } ], "advisors": [ { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "advisor", "display_name": "Quartz, Steven R." } ], "committee": [ { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "chair", "display_name": "Quartz, Steven R." }, { "name": { "family": "Camerer", "given": "Colin F." }, "id": "Camerer-C-F", "role": "member", "display_name": "Camerer, Colin F." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/W3VS-MW78", "abstract": "Our daily lives are shaped by a series of decision processes, ranging from very unimportant choices to life-changing judgments. The complexity of the decision processes increases tremendously when the decision-making takes place in a social context, i.e., when other human beings are directly involved in the decision. In such conditions the decision-maker not only tries to maximize his own utility, but also needs to take into account the interdependent nature of the situation. Information about others' preferences, characteristics, and actions play an important role, and need to be thoroughly evaluated and predicted before making a decision. In this thesis we explore the neural correlates of two different types of social decision-making.
\r\n\r\nIn the first experiment we investigate economic decision-making in the context of a two-player social exchange game. In order to maximize their overall and personal earnings, players need to cooperate and build up a trust relationship with their partner. Synchronized neural data is recorded from the two interacting brains using functional magnetic resonance imaging. In this thesis we present four main findings: (i) the neural correlates of strategic uncertainty and how it can be used to predict a player's future strategic choice; (ii) the dynamic interaction of the brains of two interacting players; (iii) the neural correlates of trust and its development over the course of the game; and (iv) how the brain distinguishes between one's own actions and those of another person.
\r\n\r\nThe second experiment investigates the neural basis of moral decision-making and other- regarding preferences. Subjects have to make a morally difficult decision between helping two groups of children while trading off between efficiency and equity. By parametrically varying these variables, we show how two brain structures, the insula and the caudate, are actively involved in the decision-making process.
\r\n\r\nTaken together the results presented in this thesis shed some light on how our brain evaluates social situations, and how it uses social measures such as trust, agency, strategic interaction, and fairness to make decisions.
\r\n" }, { "name": "Au, John King-Tai", "degree": "PhD", "year": "2007", "title": "An Ab Initio Approach to the Inverse Problem-Based Design of Photonic Bandgap Devices", "advisor": "Mabuchi, Hideo", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242007-160527", "creators": [ { "name": { "family": "Au", "given": "John King-Tai" }, "id": "Au-John-King-Tai", "display_name": "Au, John King-Tai" } ], "advisors": [ { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "advisor", "display_name": "Mabuchi, Hideo" } ], "committee": [ { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "chair", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/TZG8-R064", "abstract": "We present an ab inito treatment of the inverse photonic bandgap (or photonic crystal) device design problem. Using first principles, we derive the two-dimensional inverse Helmholtz equation that solves for the dielectric function that supports a given electromagnetic field with the desired properties. We show that the problem is ill-posed, meaning a solution often does not exist for the design problem. Our work elucidates fundamental limits to any inverse problem based design approach for arbitrary and optimal design of photonic devices. Despite these severe limitations, we achieve remarkable success in two design problems of particular importance to atomic physics applications, but also of general importance to the rest of the photonic community. As the first demonstration of our technique, we arbitrarily design the full dispersion curve of a photonic crystal waveguide. Dispersion control is important for maintaining the shape of pulses as they propagate along the waveguide. For our second demonstration, we take a point defect photonic crystal cavity in the nominal acceptor configuration (where the central defect has a lower index of refraction than the bulk material) and force it into the donor configuration (where the defect has a higher index of refraction than the bulk material), while requiring that the electromagnetic field maintain the properties of the acceptor mode. We were able to cross over this threshold while retaining a 93.6 percent overlap with the original mode." }, { "name": "Babilo, Peter", "degree": "PhD", "year": "2007", "title": "Processing and Characterization of Proton Conducting Yttrium Doped Barium Zirconate for Solid Oxide Fuel Cell Applications", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242007-161826", "creators": [ { "name": { "family": "Babilo", "given": "Peter" }, "id": "Babilo-Peter", "display_name": "Babilo, Peter" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "member", "display_name": "Van de Walle, Axel" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/WE3X-GD14", "abstract": "To address the wide range of reported conductivities in literature and investigate the viability of yttrium-doped barium zirconate (BaZr1-xYxO3) as a membrane in electrochemical devices, the factors governing the protonic transport properties have been explored, with the aim of attaining reproducible proton conductivity in well-densified samples. It was found that a small initial particle size and high temperature sintering in the presence of excess barium were essential. By this procedure, BaZr0.8Y0.2O3 with 93\u201399% of theoretical density and high total (bulk plus grain boundary) conductivity could be reliably prepared. Samples sintered in the absence of excess barium displayed yttria precipitates and a bulk conductivity that was reduced by more than two orders of magnitude.
\r\n\r\nHydrogen transport across grain boundaries has been explored and the specific conductivity found to be two orders of magnitude lower than the bulk. Microstructural optimization of the total grain boundary conductivity included both decreasing total grain boundary density as well as improving intrinsic grain boundary properties.
\r\n\r\nTo investigate the influence of defect chemistry on stability, proton solubility, and proton mobility; samples with yttrium dopant concentration of 30 and 40 mol % were prepared in addition to the 20 Y mol %. Lattice parameters obtained suggests the solubility of yttrium in barium zirconate to be at least 40 mol %. Thermogravimetric analysis of the barium zirconate system showed excellent chemical stability under CO2 and protonic defects to be approaching theoretical hydrogen concentration for 20, 30, and 40 Y mol %. Significant hydroxyl-dopant associations were observed, especially at lower temperatures, which trap protons and impede transport.
\r\n\r\nTo simplify processing procedures, the influence of transitional metal oxides additives (especially zinc oxide) on the densification and electrical properties of doped barium zirconate have been examined. With the use of zinc oxide as a sintering aid, BaZr0.85Y0.15O3 was readily sintered to above 93% of theoretical density at 1300 \u00b0C. SEM investigations showed Zn accumulation in the intergranular regions.
\r\n\r\nElectromotive force measurements of BaZr0.8Y0.2O3 showed the ionic transference number under fuel cell conditions to be at least 0.92 at 600 \u00b0C. Fuel cells based on BYZ20 were prepared and characterized.
\r\n\r\n" }, { "name": "Balagadd\u00e9, Frederick Kiguli", "degree": "PhD", "year": "2007", "title": "Microfluidic Technologies for Continuous Culture and Genetic Circuit Characterization", "advisor": "Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06112007-102627", "creators": [ { "name": { "family": "Balagadd\u00e9", "given": "Frederick Kiguli" }, "id": "Balagadd\u00e9-Frederick-Kiguli", "orcid": "0000-0003-2796-8874", "display_name": "Balagadd\u00e9, Frederick Kiguli" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "member", "display_name": "Quake, Stephen R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/NJ5Z-XV43", "abstract": "In this thesis, I have used microfluidics--the science and technology of systems that manipulate small amounts of fluids (10-9 to 10-18 liters) in microsized channels--to invent and implement a miniaturized continuous culture device or microchemostat. It relies on a novel in silicone sterilization approach to circumventing biofilm formation. The microchemostat system has inbuilt automation, which allows it to run, unattended, indefinitely (for up to months at a time). With a working volume of ~10 nL, the microchemostat is capable of culturing extremely small populations of bacteria (100 to ~104 cells vs ~109 in macroscale cultures). The microsized population reduces the number of cell-division events per unit time and hence slows down microbial evolution. This aspect facilitates long-term monitoring of the behavior of genetically engineered microbes while preserving their genetic homogeneity. Unlike its conventional continuous-culture counterparts, the microchemostat allows simultaneous operation of fourteen (or more) independent microreactors which enjoy ultralow consumption of medium and biological reagents, allowing high-throughput research at low cost. It also facilitates automated, noninvasive monitoring of bacterial behavior in terms of bacterial count, cell morphology as well as single-cell resolved gene-expression dynamics reported by fluorescence or luminescence. The unprecedented temporal and single cell resolution readings allow the microchemostat to capture dynamics such as delicate oscillations that have eluded detection in conventional settings.
\r\n\r\nThanks to its unique capability for long-term culturing and suppression of microbial evolution, the microchemostat promises to become integrated as an ingredient of a multicomponent monolithic entity in future applications. The microchemostat would mainly be responsible for in silicone production and supply of genetically homogeneous bacteria for use in various capacities.
" }, { "name": "Bao, Xiaoyan Robert", "degree": "PhD", "year": "2007", "title": "Lost in a Crowd: Observations of Single DNA Knots and Single Mammalian Cells", "advisor": "Quake, Stephen R.; Simon, Melvin I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04062007-163445", "creators": [ { "name": { "family": "Bao", "given": "Xiaoyan Robert" }, "id": "Bao-Xiaoyan-Robert", "orcid": "0000-0001-7931-2944", "display_name": "Bao, Xiaoyan Robert" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "advisor", "display_name": "Quake, Stephen R." }, { "name": { "family": "Simon", "given": "Melvin I." }, "id": "Simon-M-I", "role": "co-advisor", "display_name": "Simon, Melvin I." } ], "committee": [ { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "chair", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Simon", "given": "Melvin I." }, "id": "Simon-M-I", "role": "member", "display_name": "Simon, Melvin I." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "member", "display_name": "Quake, Stephen R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/F2XV-MC44", "abstract": "The overarching theme for the two main experiments presented here is that standard biochemical and cell biological techniques, which need fairly large samples and hence average over large numbers of things, be they molecules or cells, tend to smear out interesting phenomena that occur to a small fraction of those things. Averaging also collapses the entire population distribution into one single value, and furthermore prevents tracking properties of individuals over the lifetime of the experiment. The first project described here involves mechanically tying knots into linear DNA molecules stretched out between optically trapped beads. Without mechanical intervention, the molecules we used contained knots only rarely, and those knots are expected to involve small portions of the DNA contour and hence give only small perturbations to the overall polymer dynamics. By tying and observing them singly, we were able to show that, while knots collapse and tighten under tension, even the most complex ones we tied retained mobility to quite a surprising degree. The observed knot sizes and diffusivities correlated well with theoretical predictions for knots in ideal ropes of finite thickness, indicating that even under high tension the different parts of the molecular knots are kept away from each other because of electrostatic repulsion. The differences between knots of different topologies, both in size and speed, open up the possibility that, with further refinement, this approach may allow us to observe the stepwise actions of single topoisomerases in chemically undoing complex knots. The second project was to develop a microfluidic system to perform many signaling experiments on cells simultaneously within a single field-of-view of a microscope. Single cell sensitivity has been pivotal both in verifying data quality and in understanding cell-to-cell variabilities in signaling strengths. In the course of these two projects I also had a few side ideas which, sadly, I wasn\u2019t able to develop to the degree that I would have liked. I've included them here as minor digressions, in the hopes that someone will see them and find them useful." }, { "name": "Barclay, Paul Edward", "degree": "PhD", "year": "2007", "title": "Fiber Coupled Nanophotonic Devices for Nonlinear Optics and Cavity QED", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042007-124631", "creators": [ { "name": { "family": "Barclay", "given": "Paul Edward" }, "id": "Barclay-Paul-Edward", "orcid": "0000-0002-9659-5883", "display_name": "Barclay, Paul Edward" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/JKP4-SC05", "abstract": "The sub-wavelength optical confinement and low optical loss of nanophotonic devices dramatically enhances the interaction between light and matter within these structures. When nanophotonic devices are combined with an efficient optical coupling channel, nonlinear optical behavior can be observed at low power levels in weakly-nonlinear materials. In a similar vein, when resonant atomic systems interact with nanophotonic devices, atom-photon coupling effects can be observed at a single quanta level. Crucially, the chip based nature of nanophotonics provides a scalable platform from which to study these effects.
\r\n\r\nThis thesis addresses the use of nanophotonic devices in nonlinear and quantum optics, including device design, optical coupling, fabrication and testing, modeling, and integration with more complex systems. We present a fiber taper coupling technique that allows efficient power transfer from an optical fiber into a photonic crystal waveguide. Greater than 97% power transfer into a silicon photonic crystal waveguide is demonstrated. This optical channel is then connected to a high-Q (> 40,000), ultra-small mode volume (V < (\u03bb/n)3) photonic crystal cavity, into which we couple > 44% of the photons input to a fiber. This permits the observation of optical bistability in silicon for sub-mW input powers at telecommunication wavelengths.
\r\n\r\nTo port this technology to cavity QED experiments at near-visible wavelengths, we also study silicon nitride microdisk cavities at wavelengths near 852 nm, and observe resonances with Q > 3 million and V < 15 (\u03bb/n)3). This Q/V ratio is sufficiently high to reach the strong coupling regime with cesium atoms. We then permanently align and mount a fiber taper within the near-field an array of microdisks, and integrate this device with an atom chip, creating an \"atom-cavity chip\" which can magnetically trap laser cooled atoms above the microcavity. Calculations of the microcavity single atom sensitivity as a function of Q/V are presented and compared with numerical simulations. Taking into account non-idealities, these cavities should allow detection of single laser cooled cesium atoms.
" }, { "name": "Basset, Christophe Jean-Michel", "degree": "PhD", "year": "2007", "title": "CMOS Imaging Technology with Embedded Early Image Processing", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-04262007-131214", "creators": [ { "name": { "family": "Basset", "given": "Christophe Jean-Michel" }, "id": "Basset-Christophe-Jean-Michel", "display_name": "Basset, Christophe Jean-Michel" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Pain", "given": "Bedabrata" }, "id": "Pain-B", "role": "member", "display_name": "Pain, Bedabrata" }, { "name": { "family": "Mathur", "given": "Bimal" }, "id": "Mathur-B", "role": "member", "display_name": "Mathur, Bimal" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/2GZN-T836", "abstract": "As imaging technology evolves, so does the need for accurate, low-power and high-data-rate low-level image processing in a variety of computationally intensive vision applications. These applications include optical-flow computation, autonomous navigation, object avoidance or intercept, real-time target tracking, and recognition. To reach this goal, a single chip was developed, which functions as a camera able to preprocess the image in real time. It processes images through a convolution filter with a user-chosen kernel.
\r\n\r\nOne of the particulars of this project is to combine the processing unit with an active pixel sensors (APS) pixel array. This complementary metal-oxide semiconductor (CMOS) technology for building imager chips allows on-focal plane signal processing, as opposed to their charge-coupled device (CCD) counterparts that need to serially output the flow of pixels to an external processing chip. The filtering can therefore be implemented as a fast, low-power analog circuit.
\r\n\r\nConvolution is achieved by matching a kernel to an image using a computation unit. The chip has an integrated imager array and a digital memory large enough to store a generic, up-loadable kernel. When recognizing or tracking a target, the uploaded kernel represents the template. Other convolution filters are implemented by setting the kernel to the set of parameters corresponding to the desired task. Filtering is performed through a column-parallel architecture of computing units, so real time computation can be achieved.
\r\n\r\nSeveral versions of the convolution circuit are investigated. They have been fabricated, fully tested and characterized. A number of important design changes have occurred, either to address issues that could be improved on or to experiment with alternative approaches. Timed and geometrical amplifier controls have also been investigated. By implementing image arrays of different sizes, we also demonstrate the scalability of the architecture in the spatial domain to an arbitrarily sized imager. Test results show the analog convolution chip is a viable solution for highly integrated embedded early image processing.
" }, { "name": "Bou-Rabee, Nawaf Mohammed", "degree": "PhD", "year": "2007", "title": "Hamilton-Pontryagin Integrators on Lie Groups", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06052007-153115", "creators": [ { "name": { "family": "Bou-Rabee", "given": "Nawaf Mohammed" }, "id": "Bou-Rabee-Nawaf-Mohammed", "orcid": "0000-0001-9280-9808", "display_name": "Bou-Rabee, Nawaf Mohammed" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/0EC4-2042", "abstract": "In this thesis structure-preserving time integrators for mechanical systems whose configuration space is a Lie group are derived from a Hamilton-Pontryagin (HP) variational principle. In addition to its attractive properties for degenerate mechanical systems, the HP viewpoint also affords a practical way to design discrete Lagrangians, which are the cornerstone of variational integration theory. The HP principle states that a mechanical system traverses a path that extremizes an HP action integral. The integrand of the HP action integral consists of two terms: the Lagrangian and a kinematic constraint paired with a Lagrange multiplier (the momentum). The kinematic constraint relates the velocity of the mechanical system to a curve on the tangent bundle. This form of the action integral makes it amenable to discretization.
\r\n\r\nIn particular, our strategy is to implement an s-stage Runge-Kutta-Munthe-Kaas (RKMK) discretization of the kinematic constraint. We are motivated by the fact that the theory, order conditions, and implementation of such methods are mature. In analogy with the continuous system, the discrete HP action sum consists of two parts: a weighted sum of the Lagrangian using the weights from the Butcher tableau of the RKMK scheme, and a pairing between a discrete Lagrange multiplier (the discrete momentum) and the discretized kinematic constraint. In the vector space context, it is shown that this strategy yields a well-known class of symplectic partitioned Runge-Kutta methods including the Lobatto IIIA-IIIB pair which generalize to higher-order accuracy.
\r\n\r\nIn the Lie group context, the strategy yields an interesting and novel family of variational partitioned Runge-Kutta methods. Specifically, for mechanical systems on Lie groups we analyze the ideal context of EP systems. For such systems the HP principle can be transformed from the Pontryagin bundle to a reduced space. To set up the discrete theory, a continuous reduced HP principle is also analyzed. It is this reduced HP principle that we apply our discretization strategy to. The resulting integrator describes an update scheme on the reduced space. As in RKMK we parametrize the Lie group using coordinate charts whose model space is the Lie algebra and that approximate the exponential map. Since the Lie group is non abelian, the structure of these integrators is not the same as in the vector space context.
\r\n\r\nWe carry out an in-depth study of the simplest integrators within this family that we call variational Euler integrators; specifically we analyze the integrator's efficiency, global error, and geometric properties. Because of their variational character, the variational Euler integrators preserve a discrete momentum map and symplectic form. Moreover, since the update on the configuration space is explicit, the configuration updates exhibit no drift from the Lie group. We also prove that the global error of these methods is second order. Numerical experiments on the free rigid body and the chaotic dynamics of an underwater vehicle reveal that these reduced variational integrators possess structure-preserving properties that methods designed to preserve momentum (using the coadjoint action of the Lie group) and energy (for example, by projection) lack.
\r\n\r\nIn addition we discuss how the HP integrators extend to a wider class of mechanical systems with, e.g., configuration dependent potentials and non trivial shape-space dynamics.
" }, { "name": "Bradford, Samuel Case, V", "degree": "PhD", "year": "2007", "title": "Time-Frequency Analysis of Systems with Changing Dynamic Properties", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292006-214839", "creators": [ { "name": { "family": "Bradford", "given": "Samuel Case, V" }, "id": "Bradford-Samuel-Case-V", "display_name": "Bradford, Samuel Case, V" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Kohler", "given": "Monica D." }, "id": "Kohler-M-D", "role": "member", "display_name": "Kohler, Monica D." }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "role": "member", "display_name": "Clayton, Robert W." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/HMK7-FJ81", "abstract": "The Wigner-Ville Distribution, and related refinements, represent a class of advanced time-frequency analysis tools that are distinguished from Fourier and wavelet methods by an increase in resolution in the time frequency plane. Time-frequency analysis provides a set of exploratory tools for analyzing changing frequency content in a signal, which can then be correlated with damage patterns in a structure.
\r\n\r\nFor systems of interest to engineers, investigating the changing properties of a system is typically performed by analyzing vibration data from the system, rather than direct inspection of each component. Nonlinear elastic behavior in the force-displacement relationship can decrease the apparent natural frequencies of the system - these changes typically occur over fractions of a second in moderate to strong excitation and the system gradually recovers to pre-event levels. Structures can also suffer permanent damage (e.g., plastic deformation or fracture), permanently decreasing the observed natural frequencies as the system loses stiffness. Advanced time-frequency representations provide a set of exploratory tools for analyzing changing frequency content in a signal, which can then be correlated with damage patterns in a structure. Modern building instrumentation allows for an unprecedented investigation into the changing dynamic properties of structures: a framework for using time-frequency analysis methods for instantaneous system identification is discussed.
" }, { "name": "Brown, Michal Amaris", "degree": "PhD", "year": "2007", "title": "Measuring Stress in Thin-Film - Substrate Systems Featuring Spatial Nonuniformities of Film Thickness and/or Misfit Strain", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042007-171342", "creators": [ { "name": { "family": "Brown", "given": "Michal Amaris" }, "id": "Brown-Michal-Amaris", "display_name": "Brown, Michal Amaris" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Streit", "given": "Dwight" }, "id": "Streit-D", "role": "member", "display_name": "Streit, Dwight" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/9GD9-A088", "abstract": "It is very important to be able to accurately determine the film stress distribution in a thin film structure, since stress can lead directly to failure and as such is intimately related to reliability and process yield. The most common way of inferring film stress caused by a given process is by measuring system curvature before and after the process; the change in curvature is directly related to the stress caused by that process, usually through the Stoney formula. This formula was derived based on a number of restrictive assumptions. Two of these are the assumptions of a spatially uniform film thickness and a spatially uniform misfit strain; taken together, these assumptions imply constant curvature and film stress over the entire wafer. In practice, these conditions are rarely met, and yet the Stoney formula is still the film stress measurement standard.
\r\nRecently, extensions to this formula were derived which allow for spatial non-uniformities in film thickness and misfit strain. The resulting Stoney-like relations which relate film stress and wafer curvature, known as the HR relations, require knowledge of not only the curvature at a single point, but also full-field curvature information. In this work, the HR relations are verified by comparison with X-ray microdiffraction. Two independent XRD measurements are used; one measures substrate curvature and the other determines film stress. Since these measurements are independent, the substrate curvature data are used as an input to the Stoney and HR stress/curvature relations. The resulting film stresses are then compared with XRD film stress data. From this, it is established that the HR relations result in substantially more accurate film stress predictions than does the Stoney analysis.
\r\n\r\nNext, a full-field curvature measurement technique, Coherent Gradient Sensing, is introduced as an ideally suited measurement tool for inferring film stress through the HR analysis. CGS measurements are taken of several progressively more interesting test wafers and the curvature is used through the HR relations to determine film stress.
" }, { "name": "Br\u00e8s, Guillaume Alain", "degree": "PhD", "year": "2007", "title": "Numerical Simulations of Three-Dimensional Instabilities in Cavity Flows", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-04262007-095945", "creators": [ { "name": { "family": "Br\u00e8s", "given": "Guillaume Alain" }, "id": "Br\u00e8s-Guillaume-Alain", "orcid": "0000-0003-2507-8659", "display_name": "Br\u00e8s, Guillaume Alain" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z96W988B", "abstract": "Direct numerical simulations are performed to investigate the stability of compressible flow over three-dimensional open cavities for future control applications.
\r\n\r\nFirst, the typical self-sustained oscillations, commonly referred as shear-layer (Rossiter) modes, are characterized for two-dimensional cavities over a range of flow conditions. A linear stability analysis is then conducted to search for three-dimensional global instabilities of the 2D mean flow for cavities that are homogeneous in the spanwise direction. The presence of such instabilities is reported for a range of cavity configurations. For cavities of aspect ratio (length to depth) of 2 and 4, the three-dimensional mode has a spanwise wavelength of approximately 1 cavity depth and oscillates with a frequency about an order-of-magnitude lower than two-dimensional Rossiter (flow/acoustics) instabilities. A steady mode of smaller spanwise wavelength is also identified for square cavities. The linear results indicate that the instability is hydrodynamic (rather than acoustic) in nature and arises from a generic centrifugal instability mechanism associated with the mean recirculating vortical flow in the downstream part of the cavity. These three-dimensional instabilities are related to centrifugal instabilities reported in flows over backward-facing steps, lid-driven cavity flows, and Couette flows.
\r\n\r\nResults from three-dimensional simulations of the nonlinear compressible Navier-Stokes equations are also reported. The formation of oscillating (and, in some cases, steady) spanwise structures is observed inside the cavity. The spanwise wavelength and oscillation frequency of these structures agree with the linear analysis predictions. When present, the shear-layer (Rossiter) oscillations experience a low-frequency modulation that arises from nonlinear interactions with the three-dimensional mode. These results are consistent with observations of low-frequency modulations and spanwise structures in previous experimental and numerical studies on open cavity flows.
" }, { "name": "Cai, Lance Lin-Lan", "degree": "PhD", "year": "2007", "title": "Robotics Training Algorithms for Optimizing Motor Learning in Spinal Cord Injured Subjects", "advisor": "Burdick, Joel Wakeman; Edgerton, V. Reggie", "url": "https://resolver.caltech.edu/CaltechETD:etd-08142006-165844", "creators": [ { "name": { "family": "Cai", "given": "Lance Lin-Lan" }, "id": "Cai-Lance-Lin-Lan", "display_name": "Cai, Lance Lin-Lan" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Edgerton", "given": "V. Reggie" }, "id": "Edgerton-V-R", "role": "co-advisor", "display_name": "Edgerton, V. Reggie" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Edgerton", "given": "V. Reggie" }, "id": "Edgerton-V-R", "role": "member", "display_name": "Edgerton, V. Reggie" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "bioeng" ], "doi": "10.7907/EH12-WD80", "abstract": "The circuitries within the spinal cord are remarkably robust and plastic. Even in the absence of supraspinal control, such circuitries are capable of generating functional movements and changing their level of excitability based on a specific combination of properceptive inputs going into the spinal cord. This has led to an increase in locomotor training, such as Body Weight Support Treadmill training (BWST) for spinal cord injured (SCI) patients. However, today, little is known about the underlying physiological mechanisms responsible for the locomotor recovery achieved with this type of rehabilitative training, and the optimal rehabilitative strategy is still unknown.
\r\n\r\nThis thesis describes a mouse model to study the effect of rehabilitative training on SCI. Using this model, the effects of locomotor recovery on adult spinal mice following complete spinal cord transaction is examined. Results that indicate adult spinal mice can be robotically trained to step, and when combined with the administration of quipazine (a broad serotonin agonist), there is an interaction and retention effect. Results also demonstrate that the training paradigm can be optimized in using \u201cAssisted-as-Needed\u201d (AAN) training. To find the optimal AAN training parameters, a learning model is developed to test the effect of various parameters of the AAN training algorithm. Simulation results from our model show that learning is training-dependent. In addition, the model predicts that improved motor learning can improve post-SCI by making the AAN training more adaptable.
\r\n\r\nThe primary contributions of this thesis are twofold, in biology and engineering. We develop a mouse model using novel robotic devices and controls that can be used to study SCI and other locomotor disorders in the future by taking advantage of the many different strains of transgenic mice that are commercially available. We also further confirm that sensory integration responsible for motor control is distributed throughout the hierarchy of the neuromuscular system and can be achieved within the isolated spinal cord. Lastly, by developing a learning model, we can start looking into how variability plays a role in motor learning, the understanding of which will have profound implications in neurophysiology, machine learning and adaptive optimal controls research.
" }, { "name": "Campbell, Kate Marie", "degree": "PhD", "year": "2007", "title": "Biogeochemical Mechanisms of Arsenic Mobilization in Haiwee Reservoir Sediments", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182006-102819", "creators": [ { "name": { "family": "Campbell", "given": "Kate Marie" }, "id": "Campbell-Kate-Marie", "orcid": "0000-0002-8715-5544", "display_name": "Campbell, Kate Marie" } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "orcid": "0000-0002-0865-1946", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "orcid": "0000-0002-0865-1946", "role": "chair", "display_name": "Hering, Janet G." }, { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "member", "display_name": "Newman, Dianne K." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/T3WC-DA42", "abstract": "Naturally-occurring arsenic (As) in the Los Angeles Aqueduct, a major drinking water source for the City of Los Angeles, is removed by precipitating an amorphous iron (Fe) oxyhydroxide floc in the aqueduct waters. The floc is removed via sedimentation at Haiwee Reservoir, where the Fe- and As-rich sediments provide a unique field site for studying the mechanisms of As mobilization to sediment porewater.
\r\n\r\nA gel probe equilibrium sampler was developed to measure the porewater concentrations and As sorption behavior in Haiwee Reservoir sediments. The gels consisted of a polyacrylamide polymer matrix and were 92% water. Undoped gels (clear gels) were used to determine porewater composition, and hydrous ferric oxide (HFO)-doped gels were used to measure in situ As adsorption chemistry. Gels were placed in a plastic holder, covered with a membrane filter, and allowed to equilibrate with the sediment porewaters. This study combined data from the gel probe samplers, gravity cores, and laboratory studies, to elucidate the biogeochemical processes governing As partitioning between the solid and aqueous phases. The gel probe device allowed for in situ observation of the effect of porewater chemistry on As adsorption.
\r\n\r\nArsenic was reduced from As(V) to As(III) in the upper layers of the sediment, but the change in redox state did not cause As to be mobilized into the porewaters. Arsenic mobilization occurred during reductive dissolution of Fe(III) oxides. Arsenate and Fe(III) reduction were probably microbially mediated. Arsenic sorption onto the HFO-doped gels was inhibited at intermediate depths, probably due to dissolved carbonate produced from organic carbon mineralization. The partitioning of As onto the sediment in this region may be primarily controlled by porewater chemistry, rather than sorption site availability. Deeper in the sediment column, the Fe(III) phase was partially transformed to carbonate green rust, possibly sequestering dissolved carbonate. In this region, As adsorption onto HFO-doped gels was controlled by dissolved phosphate. The accumulation of As in the porewater in this region may be due to lack of available surface adsorption sites on the sediment. Arsenic partitioning between solid and aqueous phases depends on microbially driven diagenetic processes, as well as porewater composition.
\r\n" }, { "name": "Chen, Lijun", "degree": "PhD", "year": "2007", "title": "Wireless Network Design and Control", "advisor": "Doyle, John Comstock; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282006-181735", "creators": [ { "name": { "family": "Chen", "given": "Lijun" }, "id": "Chen-Lijun", "orcid": "0000-0001-6694-4299", "display_name": "Chen, Lijun" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "co-chair", "display_name": "Low, Steven H." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "cds" ], "doi": "10.7907/TEVD-PK95", "abstract": "Optimization theory and game theory provide a suite of tools that are flexible in modelling various network systems, and a rich series of equilibrium solution concepts and convergent algorithms. In this thesis, we view network protocols as distributed algorithms achieving the corresponding network equilibria, and study wireless network design and control in optimization and game-theoretic frameworks.
\r\n\r\nSpecifically, we first take a holistic approach and design an overall framework for the protocol architecture in ad hoc wireless networks. The goal is to integrate various protocol layers into a unified framework, by regarding them as distributed computations over the network to solve some optimization problem. Our current theory integrates three functions--congestion control, routing and scheduling--in transport, network and link layers into a coherent framework. These three functions interact through and are regulated by congestion price so as to achieve a global optimality, even in a time-varying environment. This framework is promising to be extended to provide a mathematical theory for network architecture, and to allow us to systematically carry out cross-layer design.
\r\n\r\nWe then develop a general game-theoretic framework for contention control. We define a general game-theoretic model, called random access game, to study the contention/interaction among wireless nodes, and propose a novel medium access method derived from carrier sensing multiple access with collision avoidance in which each node estimates its conditional collision probability and adjusts its persistence probability or contention window, according to a distributed strategy update mechanism achieving the Nash equilibrium of random access game. This results in simple dynamics, controllable performance objectives, good short-term fairness, low collision, and high throughput. As wireless nodes can estimate conditional collision probabilities by observing consecutive idle slots between transmissions, we can decouple contention control from handling failed transmissions. This also opens up other opportunities such as rate adaptation to channel variations. In addition to providing a general and systematic design methodology for medium access control, the random access game model also provides an analytical framework to understand the equilibrium properties such as throughput, loss and fairness, and dynamic properties of different medium access protocols and their interactions.
\r\n\r\nFinally, we conclude this work with some suggestions for future research.
" }, { "name": "Choi, John Myun", "degree": "PhD", "year": "2007", "title": "Design, Fabrication, and Characterization of Semiconductor Transverse Bragg Resonance Lasers", "advisor": "Yariv, Amnon; Crosignani, Bruno", "url": "https://resolver.caltech.edu/CaltechETD:etd-02142007-151137", "creators": [ { "name": { "family": "Choi", "given": "John Myun" }, "id": "Choi-John-Myun", "display_name": "Choi, John Myun" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "co-advisor", "display_name": "Crosignani, Bruno" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "eleceng" ], "doi": "10.7907/NG25-BN55", "abstract": "Controlling the spatial modes of a laser cavity is fundamental for improving the beam quality of a laser and achieving highly efficient coupling of power into an optical system. High-power applications are particularly challenging due to the conflicting requirements for large modal volume, to prevent facet damage by reducing energy density, and narrow width, for single-mode operation of an index-guided waveguide. By replacing traditional index confinement with Bragg reflection in the transverse direction, single-mode operation can be achieved even for large modal volumes. These grating confined structures, transverse Bragg resonance (TBR) waveguides, have the unique ability to support localized modes above the light line. Such modes normally couple to radiation modes of the cladding when the confinement mechanism is total-internal-reflection and are too lossy to be considered guided modes. However, for Bragg resonance confined modes, the modal loss can be designed by careful optical mode engineering to introduce a large loss discrimination that can favor a single spatial, low-loss mode. Semiconductor TBR lasers in an InP/InGaAsP/InGaAs material system were designed, fabricated, and characterized to investigate this property. Two regions of operation are identified for TBR waveguides, and, while transverse mode selection is provided by a grating, longitudinal mode control is found to be also necessary to restrict operation to the region that supports modes above the light line." }, { "name": "Chung, Timothy Hahn Deut", "degree": "PhD", "year": "2007", "title": "Intelligent Information-Gathering: Using Control for Sensing and Decision-Making", "advisor": "Burdick, Joel Wakeman; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312007-024822", "creators": [ { "name": { "family": "Chung", "given": "Timothy Hahn Deut" }, "id": "Chung-Timothy-Hahn-Deut", "display_name": "Chung, Timothy Hahn Deut" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "co-advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "co-chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "mecheng" ], "doi": "10.7907/V5S4-4197", "abstract": "Information is everywhere and evolving, which necessitates both deliberate and efficient processing to acquire a good understanding of the dynamic situation, environment, or system of interest. Intelligent agents such as autonomous mobile sensors can control the way they gather information and thereby take advantage of feedback to improve the quality of that information. This approach reflects a shift from traditional \"sensing for control\" notions to \"control for sensing\" methods for addressing information-based objectives. This thesis presents several algorithms for distributed sensing tasks in the context of a team of mobile sensing agents. Applications of these types of mobile sensor networks include target tracking, dynamic environment monitoring, and distributed classification. These methods point beyond the use of sensory data for control and toward a framework for using control to improve information-based decisions made by intelligent agents. The sequential decision-theoretic framework presented herein has relevant applications in engineered systems such as search and rescue using a robotic team, as well as potential connections to natural systems including search strategies in the human vision system." }, { "name": "Cowan, Lisa", "degree": "PhD", "year": "2007", "title": "Superprotonic Solid Acid Phase Transitions and Stability", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232007-142037", "creators": [ { "name": { "family": "Cowan", "given": "Lisa" }, "id": "Cowan-Lisa", "display_name": "Cowan, Lisa" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/30RE-XG95", "abstract": "Solid acid proton conductors are viable alternatives to current fuel cell electrolytes. Incorporating solid acid electrolytes, next generation fuel cells would not require humidification of the electrolyte, as in proton exchange membrane fuel cells, and could operate at higher temperatures which would improve catalysis rates. Engineering the properties of these materials for fuel cell electrolyte applications requires an understanding of the structural and chemical parameters that support superprotonic phase transitions over melting or decomposition.
\r\n\r\nIn this thesis, the structures of three superprotonic solid acids are presented, and for the first time, a distinction is possible between local versus average structure. An adapted model for configurational entropy based on Pauling\u2019s entropy rules for ice is incorporated to describe the entropy of superprotonic solid acids. Insights from local structural information alleviate discrepancies between this model and experimentally determined entropy values. With clarifications from this work, the calculated configurational entropy of the superprotonic structures of CsD2PO4, RbDSeO4, and CsDSO4, agree well with experimentally determined entropy values.
\r\n\r\nA study of chemical intermediates, CsxRb1-xH2PO4, provides valuable insight into the nature of the cation size effect on superprotonic phase transitions within an isostructural system. For compounds in the series that do exhibit a superprotonic phase, CsH2PO4 \u2013 Cs0.3Rb0.7H2PO4, the magnitude of proton conductivity remains neutral to rubidium incorporation. Altering the effective cation size shows a profound impact on transition temperature for compounds with high rubidium content (x < 0.5) while preserving the overall conductivity of the high-temperature and low-temperature phases. X-ray diffraction, thermal analysis, Raman, IR, 133Cs, 87Rb and 1H-NMR spectroscopy all attest to the gradual variation in structural properties across the composition range.
\r\n\r\nThe complicated high-temperature properties of Rb3H(SO4)2 have been misinterpreted in earlier literature as a superprotonic phase transition. This work presents a careful analysis of a conglomeration of data from different techniques which definitively conclude that at ambient pressure, Rb3H(SO4)2 degrades via phase separation, Rb3H(SO4)2 \u2192 RbHSO4 + Rb2SO4.
" }, { "name": "Daly, Samantha Hayes", "degree": "PhD", "year": "2007", "title": "Deformation and Fracture of Thin Sheets of Nitinol", "advisor": "Bhattacharya, Kaushik; Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252007-000127", "creators": [ { "name": { "family": "Daly", "given": "Samantha Hayes" }, "id": "Daly-Samantha-Hayes", "orcid": "0000-0002-7297-1696", "display_name": "Daly, Samantha Hayes" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "co-chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Molinari", "given": "Alain" }, "id": "Molinari-A", "role": "member", "display_name": "Molinari, Alain" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Rittel", "given": "Daniel" }, "id": "Rittel-D", "role": "member", "display_name": "Rittel, Daniel" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "mecheng" ], "doi": "10.7907/RATX-WG46", "abstract": "Nickel-Titanium (Nitinol) is a Shape Memory Alloy (SMA) that exhibits superelasticity (pseudoelasticity) and shape memory by a solid-solid state diffusion-less phase transformation. Phase transformation and the resulting strain localization in Nitinol has long been a topic of study, both for its inherent scientific interest and also because of the large number of practical applications of this bimetallic alloy. Although Nitinol devices are extensively used in the medical industry, there is a fundamental gap in the amount of high-quality quantitative experimental data detailing strain localization. The numerous applications of shape memory alloys provide the motivation to understand the deformation and failure mechanisms of these materials, particularly their fatigue and fracture behavior. By using an in-situ optical technique called Digital Image Correlation (DIC), quantitative measures of strain localization in Nitinol are presented for the first time in both deformation and failure modes. In addition, a finite element small-scale transformation analysis near a crack tip in Nitinol subjected to mode-I loading under plane stress conditions is performed for the first time. The experimental results and finite element analysis provide new and detailed insights concerning the structure of phase transformation and crack tip fields in Nitinol." }, { "name": "Dayal, Kaushik", "degree": "PhD", "year": "2007", "title": "Nonlocal Microstructural Mechanics of Active Materials", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-06122006-161234", "creators": [ { "name": { "family": "Dayal", "given": "Kaushik" }, "id": "Dayal-Kaushik", "orcid": "0000-0002-0516-3066", "display_name": "Dayal, Kaushik" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "mecheng" ], "doi": "10.7907/YGR6-H428", "abstract": "This thesis deals with two aspects of the mechanics of symmetry-breaking defects such as phase boundaries, inclusions and free surfaces, and their role in the macroscopic response of active materials. We first examine the problem of kinetics using a nonlocal theory, and then study the role of geometry in active materials with fields that are not confined to the material.
\r\n\r\nClassical PDE continuum models of active materials are not closed, and require nucleation and kinetic information or regularization as additional constitutive input. We examine this problem in the peridynamic formulation, a nonlocal continuum model that uses integral equations to account for long-range forces that are important at small scales, and allows resolution of the structure of interfaces. Our analysis shows that kinetics is inherent to the theory. Viewing nucleation as a dynamic instability at small times, we obtain interesting scaling results and insight into nucleation in regularized theories. We also exploit the computational ease of this theory to study an unusual mechanism that allows a phase boundary to bypass an inclusion.
\r\n\r\nShifting focus to problems of an applied nature, we consider issues in the design of ferroelectric optical/electronic circuit elements. Free surfaces and electrodes on these devices generate electrical fields that must be resolved over all space, and not just within the body. These fields greatly enhance the importance of geometry in understanding the electromechanical response of these materials, and give rise to strong size and shape dependence. We describe a computational method that transforms this problem into a local setting in an accurate and efficient manner. We apply it to three examples: closure domains, a ferroelectric slab with segmented electrodes and a notch subjected to electro-mechanical loading.
" }, { "name": "Dodd, Joanna Lynn", "degree": "PhD", "year": "2007", "title": "Phase Composition and Dynamical Studies of Lithium Iron Phosphate", "advisor": "Fultz, Brent T.; Yazami, Rachid", "url": "https://resolver.caltech.edu/CaltechETD:etd-05072007-184544", "creators": [ { "name": { "family": "Dodd", "given": "Joanna Lynn" }, "id": "Dodd-Joanna-Lynn", "display_name": "Dodd, Joanna Lynn" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." }, { "name": { "family": "Yazami", "given": "Rachid" }, "id": "Yazami-R", "role": "co-advisor", "display_name": "Yazami, Rachid" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Yazami", "given": "Rachid" }, "id": "Yazami-R", "role": "member", "display_name": "Yazami, Rachid" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/0B7N-ZF63", "abstract": "The olivine phase of lithium iron phosphate (Li\u2093FePO\u2084) is a promising cathode material for lithium-ion batteries. Some of its advantages are that it is nontoxic, highly stable, and inexpensive, but its low intrinsic electrical conductivity is a major disadvantage. Li\u2093FePO\u2084 has generally been described as a two-phase system as lithium is removed from or inserted into the material. However, the mechanism of lithium removal and the system's phase composition is still not fully understood, and is an area of interest.
\r\n\r\nThe two low-temperature phases, heterosite and triphylite, have previously been shown to transform to a single-phase disordered solid solution at temperatures above 200\u00b0C. Here, the phase diagram for Li\u2093FePO\u2084 has been determined for different lithium concentrations and temperatures. This disordered phase is stable at relatively low temperatures. The proposed phase diagram resembles a eutectoid system, with eutectoid point at around x = 0.6 and 200\u00b0C. The kinetics of mixing and unmixing transformations, including the hysteresis between heating and cooling, will be shown. The enthalpy of this transition is at least 700 J/mol. Further thermostability studies of the material up to temperatures of 800\u00b0C will also be discussed.
\r\n\r\nSolid solution regions have also been indicated near the end compositions of x = 0 and 1 at room temperature. Measurements of the entropy (\u0394S(x)) and enthalpy (\u0394H(x)) of lithiation were performed, indicating the ranges of solid solution regions to be x < 0.05 and x > 0.85. In addition, the entropy of lithiation in between (0.05 < x < 0.85) changes gradually with x. This is unexpected, since \u0394S(x)) should be constant in a two-phase region. There are several alternatives which could be causing this result. Further clarification of this topic could give additional information about the phase transformation occurring as LiFePO4 is delithiated.
\r\n\r\nThe topic of dynamics in Li\u2093FePO\u2084 is also very relevant, especially since this material is now touted as an important high-rate capability cathode. The electronic and ionic conductivity of the new disordered solid-solution phase has generated widespread interest. The local electronic structure around iron ions in Li0.6FePO\u2084 was studied by 57Fe Mossbauer spectrometry at temperatures from 25 to 240\u00b0C. The equilibrium two-phase triphylite plus heterosite material was compared to a disordered solid solution that was obtained by quenching from a high temperature. Substantial electronic relaxations were found in the disordered solid solution compared to the two-phase material at temperatures of 130\u00b0C and above. Fluctuations in the electric field gradient and the isomer shift showed activation energies of 335 +- 25 meV and 600 +- 100 meV, respectively. It is suggested that these spectral relaxations are caused by the motions of Li\u207a ions. The activation energies from the isomer shift can be related to the material conductivity, giving values of 10-6 to 10-4 S/cm; 3 to 5 orders of magnitude higher than the measured value of 10-9 for fully lithiated LiFePO\u2084. A slight relaxation at 180\u00b0C in 10% of the two-phase material can be attributed to defects in the heterosite and triphylite phases. Overall, the disordered solid-solution phase shows faster electronic dynamics than the two-phase material.
\r\n\r\nAdditional studies on the dynamics of the disordered solid solution, along with attempts to stabilize this phase at lower temperatures, should be a topic of further work.
" }, { "name": "Dondl, Patrick Werner", "degree": "PhD", "year": "2007", "title": "Structure and Evolution of Martensitic Phase Boundaries", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292007-211950", "creators": [ { "name": { "family": "Dondl", "given": "Patrick Werner" }, "id": "Dondl-Patrick-Werner", "orcid": "0000-0003-3035-7230", "display_name": "Dondl, Patrick Werner" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/89AW-3S87", "abstract": "This work examines two major aspects of martensitic phase boundaries. The first part studies numerically the deformation of thin films of shape memory alloys by using subdivision surfaces for discretization. These films have gained interest for their possible use as actuators in microscale electro-mechanical systems, specifically in a pyramid-shaped configuration. The study of such configurations requires adequate resolution of the regions of high strain gradient that emerge from the interplay of the multi-well strain energy and the penalization of the strain gradient through a surface energy term. This surface energy term also requires the spatial numerical discretization to be of higher regularity, i.e., it needs to be continuously differentiable. This excludes the use of a piecewise linear approximation. It is shown in this thesis that subdivision surfaces provide an attractive tool for the numerical examination of thin phase transforming structures. We also provide insight in the properties of such tent-like structures.
\r\n\r\nThe second part of this thesis examines the question of how the rate-independent hysteresis that is observed in martensitic phase transformations can be reconciled with the linear kinetic relation linking the evolution of domains with the thermodynamic driving force on a microscopic scale. A sharp interface model for the evolution of martensitic phase boundaries, including full elasticity, is proposed. The existence of a solution for this coupled problem of a free discontinuity evolution to an elliptic equation is proved. Numerical studies using this model show the pinning of a phase boundary by precipitates of non-transforming material. This pinning is the first step in a stick-slip behavior and therefore a rate-independent hysteresis.
\r\n\r\nIn an approximate model, the existence of a critical pinning force as well as the existence of solutions traveling with an average velocity are proved rigorously. For this shallow phase boundary approximation, the depinning behavior is studied numerically. We find a universal power-law linking the driving force to the average velocity of the interface. For a smooth local force due to an inhomogeneous but periodic environment we find a critical exponent of 1/2.
\r\n" }, { "name": "El-Khamy, Mostafa Said", "degree": "PhD", "year": "2007", "title": "New Approaches to the Analysis and Design of Reed-Solomon Related Codes", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102006-120159", "creators": [ { "name": { "family": "El-Khamy", "given": "Mostafa Said" }, "id": "El-Khamy-Mostafa-Said", "display_name": "El-Khamy, Mostafa Said" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Fossorier", "given": "Marc" }, "id": "Fossorier-M", "role": "member", "display_name": "Fossorier, Marc" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/TQRJ-GM19", "abstract": "The research that led to this thesis was inspired by Sudan's breakthrough that demonstrated that Reed-Solomon codes can correct more errors than previously thought. This breakthrough can render the current state-of-the-art Reed-Solomon decoders obsolete. Much of the importance of Reed-Solomon codes stems from their ubiquity and utility. This thesis takes a few steps toward a deeper understanding of Reed-Solomon codes as well as toward the design of efficient algorithms for decoding them.
\r\n\r\nAfter studying the binary images of Reed-Solomon codes, we proceeded to analyze their performance under optimum decoding. Moreover, we investigated the performance of Reed-Solomon codes in network scenarios when the code is shared by many users or applications. We proved that Reed-Solomon codes have many more desirable properties. Algebraic soft decoding of Reed-Solomon codes is a class of algorithms that was stirred by Sudan's breakthrough. We developed a mathematical model for algebraic soft decoding. By designing Reed-Solomon decoding algorithms, we showed that algebraic soft decoding can indeed approach the ultimate performance limits of Reed-Solomon codes. We then shifted our attention to products of Reed-Solomon codes. We analyzed the performance of linear product codes in general and Reed-Solomon product codes in particular. Motivated by these results we designed a number of algorithms, based on Sudan's breakthrough, for decoding Reed-Solomon product codes. Lastly, we tackled the problem of analyzing the performance of sphere decoding of lattice codes and linear codes, e.g., Reed-Solomon codes, with an eye on the tradeoff between performance and complexity.
" }, { "name": "El-Naggar, Mohamed Y.", "degree": "PhD", "year": "2007", "title": "Textured Ferroelectric Thin Films: Synthesis, Characterization, and Influence of Compositional Grading on the Dielectric Behavior", "advisor": "Goodwin, David G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222006-131741", "creators": [ { "name": { "family": "El-Naggar", "given": "Mohamed Y." }, "id": "El-Naggar-Mohamed-Y", "display_name": "El-Naggar, Mohamed Y." } ], "advisors": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "display_name": "Goodwin, David G." } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/WMJW-H724", "abstract": "This dissertation focuses on two topics concerning the connections between structure and property in ferroelectric thin films. First, the synthesis of highly oriented ferroelectric thin films is addressed, where the texture is needed to generate high strains that rely on electromechanical domain switching. The ferroelectric films are integrated with oxide electrodes onto single crystal MgO and Si substrates using biaxially-textured MgO as buffer layers. The second topic focuses on modeling the dielectric behavior of compositionally graded ferroelectrics.
\r\n\r\nThe functional ferroelectric (Pb,Ba)TiO3 films are deposited by metalorganic chemical vapor deposition (MOCVD). SrRuO3, grown by pulsed laser deposition (PLD), is a lattice-matching electrode. Both the ferroelectric and oxide electrode layers are found to inherit the biaxial texture of the underlying MgO template, which can be deposited by ion beam assisted deposition (IBAD) directly on Si-based substrates. In addition, we demonstrated control of the ferroelectric film stoichiometry using a spectroscopic control loop that monitors the ultraviolet spectra of the gas-phase MOCVD precursors during growth. Detailed studies of the microstructural details of these films will be presented.
\r\n\r\nThe second topic of this thesis explores the dielectric behavior of functionally graded ferroelectric thin films. Homogenous ferroelectrics offer the possibility of engineering a tunable dielectric response for components in microwave circuits. However, this approach often leads to an undesired temperature sensitivity. Compositionally-graded (Ba,Sr)TiO3 ferroelectric films have been explored as a means of redressing this sensitivity, but experimental observations vary depending on geometry and other details. A continuum model is presented to calculate the capacitive response of graded ferroelectric films with realistic electrode geometries by accurately accounting for the polarization distribution and long-range electrostatic interactions. We show preferred designs that are extremely effective in obtaining high and temperature-stable dielectric properties.
" }, { "name": "Farajidana, Amir", "degree": "PhD", "year": "2007", "title": "Performance Limits and Design Issues in Wireless Networks", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechETD:etd-11052006-173021", "creators": [ { "name": { "family": "Farajidana", "given": "Amir" }, "id": "Farajidana-Amir", "display_name": "Farajidana, Amir" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/PRMQ-0644", "abstract": "The increasing utilization of networks, especially wireless networks, for different applications and in different aspects of modern life, has directed a great deal of attention towards the analysis and optimal design of networks. Distinguishing features of the wireless environment and the distributed nature of the network setup have raised many important challenges in finding the performance limits of different tasks such as communication, control, and computation over networks. There are also many design issues concerning the complexity and the robustness of wireless systems that should be addressed for a thorough understanding and an efficient operation of wireless networked systems. This thesis deals with a few of the challenges associated with the fundamental performance limits and optimal design of wireless networks.
\r\n\r\nIn the first part, we analyze performance limits of two applications for a special class of wireless networks called wireless erasure networks. These networks incorporate some of the essential features of the wireless environment. We look at the performance limits of two applications over these networks. The first application is data transmission with two different traffic patterns, namely multicast and broadcast. The capacity region and the optimal coding scheme for the multicast scenario are found, and outer and inner bounds on the capacity region for the broadcast scenario are provided. The second application considered in this thesis is estimation and control of a dynamical process at a remote location connected through a wireless erasure network to a sensor observing the process. In this case, we characterize the minimum steady-state error and its dependency on the parameters of the network. The final problem considered in the first part of the thesis concerns power consumption (as a performance measure) in wireless networks. We propose and analyze a simple scheme based on the idea of distributed beamforming that saves us in terms of power consumption for dense sensor and ad-hoc networks. We quantify this gain compared to the case when nodes have isolated communications without participating in the network.
\r\n\r\nThe second part of the thesis deals with two design issues in the downlink of cellular wireless networks. The first issue is related to quality of service provisioning in the downlink scenario. We investigate the problem of differentiated rate scheduling in which different users demand different sets of rates. We obtain explicit and practical scheduling schemes to achieve the rate constraints and at the same time maximize the throughput. These schemes are based on the idea of opportunistic beamforming, are simple, and require little amount of feedback to the transmitter. We further show that the throughput loss due to imposing the rate constraints is negligible for large systems.
\r\n\r\nThe next issue considered in this thesis is the robustness of the capacity region of multiple antenna Gaussian broadcast channels to the channel estimation error at the transmitter and the users. These channels are mathematical models for the downlink of cellular systems. We provide an inner bound on the capacity region of these channels and show that this inner bound is equivalent to the capacity region of a dual multiple access channel with a noise covariance that depends on the transmit powers. This duality is explored to show the effect of the estimation error on the sum-rate for a large number of users and in the large power regime. Finally, a training-based scheme for the block fading multiple antenna broadcast channels is proposed.
" }, { "name": "Feng, Philip Xiao-Li", "degree": "PhD", "year": "2007", "title": "Ultra-High Frequency Nanoelectromechanical Systems with Low-Noise Technologies for Single-Molecule Mass Sensing", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292007-002034", "creators": [ { "name": { "family": "Feng", "given": "Philip Xiao-Li" }, "id": "Feng-Philip-Xiao-Li", "orcid": "0000-0002-1083-2391", "display_name": "Feng, Philip Xiao-Li" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Hajimiri", "given": "S. Ali" }, "id": "Hajimiri-S-A", "role": "member", "display_name": "Hajimiri, S. Ali" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Bockrath", "given": "Marc W." }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc W." }, { "name": { "family": "Lifshitz", "given": "Ron" }, "id": "Lifshitz-R", "role": "member", "display_name": "Lifshitz, Ron" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9NC5Z62", "abstract": "Advancing today's very rudimentary nanodevices toward functional nanosystems with considerable complexity and advanced performance imposes enormous challenges. This thesis presents the research on ultra-high frequency (UHF) nanoelectromechanical systems (NEMS) in combination with low-noise technologies that enable single-molecule mass sensing and offer promises for NEMS-based mass spectrometry (MS) with single-Dalton sensitivity. The generic protocol for NEMS resonant mass sensing is based on real-time locking and tracking of the resonance frequency as it is shifted by the mass-loading effect. This has been implemented in two modes: (i) creating an active self-sustaining oscillator based on the NEMS resonator, and (ii) a higher-precision external oscillator phase-locking to and tracking the NEMS resonance.
\r\n\r\nThe first UHF low-noise self-sustaining NEMS oscillator has been demonstrated by using a 428MHz vibrating NEMS resonator as the frequency reference. This stable UHF NEMS oscillator exhibits ~0.3ppm frequency stability and ~50zg (1zg = 10-21 g) mass resolution with its excellent wideband-operation (~0.2MHz) capability. Given its promising phase noise performance, the active NEMS oscillator technology also offers important potentials for realizing NEMS-based radio-frequency (RF) local oscillators, voltage-controlled oscillators (VCOs), and synchronized oscillators and arrays that could lead to nanomechanical signal processing and communication. The demonstrated NEMS oscillator operates at much higher frequency than conventional crystal oscillators and their overtones do, which opens new possibilities for the ultimate miniaturization of advanced crystal oscillators.
\r\n\r\nLow-noise phase-locked loop (PLL) techniques have been developed and engineered to integrate with the resonance detection circuitry for the passive UHF NEMS resonators. Implementations of the NEMS-PLL mode with generations of low-loss UHF NEMS resonators demonstrate improving performance, namely, reduced noise and enhanced dynamic range. Very compelling frequency stability of ~0.02ppm and unprecedented mass sensitivity approaching 1zg has been achieved with a typical 500MHz device in the narrow-band NEMS-PLL operation.
\r\n\r\nRetaining high quality factors (Q's) while scaling up frequency has become crucial for UHF NEMS resonators. Extensive measurements, together with theoretical modeling, have been performed to investigate various energy loss mechanisms and their effects on UHF devices. This leads to important insights and guidelines for device Q-engineering.
\r\n\r\nThe first VHF/UHF silicon nanowire (NW) resonators have been demonstrated based on single-crystal Si NWs made by bottom-up chemical synthesis nanofabrication. Pristine Si NWs have well-faceted surfaces and exhibit high Q's (Q \u2248 13100 at 80MHz and Q \u2248 5750 at 215MHz). Given their ultra-small active mass and very high mass responsivity, these Si NWs also offer excellent mass sensitivity in the ~10?50zg range.
\r\n\r\nThese UHF NEMS and electronic control technologies have demonstrated promising mass sensitivity for kilo-Dalton-range single-biomolecule mass sensing. The achieved performance roadmap, and that extended by next generations of devices, clearly indicates realistic and viable paths toward the single-Dalton mass sensitivity. With further elaborate engineering, prototype NEMS-MS is optimistically within reach.
" }, { "name": "Fingler, Jeffrey Paul", "degree": "PhD", "year": "2007", "title": "Motion Contrast Using Optical Coherence Tomography", "advisor": "Fraser, Scott E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242007-121638", "creators": [ { "name": { "family": "Fingler", "given": "Jeffrey Paul" }, "id": "Fingler-Jeffrey-Paul", "display_name": "Fingler, Jeffrey Paul" } ], "advisors": [ { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "advisor", "display_name": "Fraser, Scott E." } ], "committee": [ { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "chair", "display_name": "Fraser, Scott E." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8W4X-Z041", "abstract": "Diagnosis of ophthalmic diseases like age-related macular degeneration is very important for treatment of the disease as well as the development of future treatments. Optical coherence tomography (OCT) is an optical interference technique which can measure the three-dimensional structural information of the reflecting layers within a sample. In retinal imaging, OCT is used as the primary diagnostic tool for structural abnormalities such as retinal holes and detachments. The contrast within the images of this technique is based upon reflectivity changes from different regions of the retina.
\r\n\r\nThis thesis demonstrates the developments of methods used to produce additional contrast to the structural OCT images based on the tiny fluctuations of motion experienced by the mobile scatterers within a sample. Motion contrast was observed for motions smaller than 50 nm in images of a variety of samples. Initial contrast method demonstrations used Brownian motion differences to separate regions of a mobile Intralipid solution from a static agarose gel, chosen in concentration to minimize reflectivity contrast.
\r\n\r\nZebrafish embryos in the range of 3-4 days post fertilization were imaged using several motion contrast methods to determine the capabilities of identifying regions of vascular flow. Vasculature identification was demonstrated in zebrafish for blood vessels of all orientations as small as 10 microns in diameter. Mouse retinal imaging utilized the same motion contrast methods to determine the contrast capabilities for motions associated with vasculature within the retina. Improved contrast imaging techniques demonstrated comparable images to fluorescein angiography, the gold standard of retinal vascular imaging. Future studies can improve the demonstrated contrast analysis techniques and apply them towards human retinal motion contrast imaging for ophthalmic diagnostic purposes.
" }, { "name": "Gavini, Vikram", "degree": "PhD", "year": "2007", "title": "Electronic Structure Calculations at Macroscopic Scales", "advisor": "Ortiz, Michael; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152007-121823", "creators": [ { "name": { "family": "Gavini", "given": "Vikram" }, "id": "Gavini-Vikram", "orcid": "0000-0002-9451-2300", "display_name": "Gavini, Vikram" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knap", "given": "Jaroslaw" }, "id": "Knap-J", "role": "member", "display_name": "Knap, Jaroslaw" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "mecheng" ], "doi": "10.7907/1R69-YY30", "abstract": "Electronic structure calculations, especially those using density-functional theory have provided many insights into various materials properties in the recent decade. However, the computational complexity associated with electronic structure calculations has restricted these investigations to periodic geometries with small cell-sizes (computational domains) consisting of few atoms (about 200 atoms). But material properties are influenced by defects---vacancies, dopants, dislocations, cracks, free surfaces---in small concentrations (parts per million). A complete description of such defects must include both the electronic structure of the core at the fine (sub-nanometer) scale and also elastic and electrostatic interactions at the coarse (micrometer and beyond) scale. This in turn requires electronic structure calculations at macroscopic scales, involving millions of atoms, well beyond the current capability. This thesis presents the development of a seamless multi-scale scheme, Quasi-Continuum Orbital-Free Density-Functional Theory (QC-OFDFT) to address this significant issue. This multi-scale scheme has enabled for the first time a calculation of the electronic structure of multi-million atom systems using orbital-free density-functional theory, thus, paving the way to an accurate electronic structure study of defects in materials.
\r\n\r\nThe key ideas in the development of QC-OFDFT are (i) a real-space variational formulation of orbital-free density-functional theory, (ii) a nested finite-element discretization of the formulation, and (iii) a systematic means of adaptive coarse-graining retaining full resolution where necessary, and coarsening elsewhere with no patches, assumptions, or structure. The real-space formulation and the finite-element discretization gives freedom from periodicity, which is important in the study of defects in materials. More importantly, the real-space formulation and its finite-element discretization support unstructured coarse-graining of the basis functions, which is exploited to advantage in developing the QC-OFDFT method. This method has enabled for the first time a calculation of the electronic structure of samples with millions of atoms subjected to arbitrary boundary conditions. Importantly, the method is completely seamless, does not require any ad hoc assumptions, uses orbital-free density-functional theory as its only input, and enables convergence studies of its accuracy. From the viewpoint of mathematical analysis, the convergence of the finite-element approximation is established rigorously using Gamma-convergence, thus adding strength and validity to the formulation.
\r\n\r\nThe accuracy of the proposed multi-scale method under modest computational cost, and the physical insights it offers into properties of materials with defects, have been demonstrated by the study of vacancies in aluminum. One of the important results of this study is the strong cell-size effect observed on the formation energies of vacancies, where cells as large as tens of thousands of atoms were required to obtain convergence. This indicates the prevalence of long-range physics in materials with defects, and the need to calculate the electronic structure of materials at macroscopic scales, thus underscoring the importance of QC-OFDFT.
\r\n\r\nFinally, QC-OFDFT was used to study a problem of great practical importance: the embrittlement of metals subjected to radiation. The brittle nature of metals exposed to radiation is associated with the formation of prismatic dislocation loops---dislocation loops whose Burgers vector has a component normal to their plane. QC-OFDFT provides an insight into the mechanism of prismatic dislocation loop nucleation, which has remained unclear to date. This study, for the first time using electronic structure calculations, establishes vacancy clustering as an energetically favorable process. Also, from direct numerical simulations, it is demonstrated that vacancy clusters collapse to form stable prismatic dislocation loops. This establishes vacancy clustering and collapse of these clusters as a possible mechanism for prismatic dislocation loop nucleation. The study also suggests that prismatic loops as small as those formed from a 7-vacancy cluster are stable, thus shedding new light on the nucleation size of these defects which was hitherto unknown.
\r\n" }, { "name": "Gowaikar, Radhika", "degree": "PhD", "year": "2007", "title": "Wireless Networks: New Models and Results", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechETD:etd-10032006-113124", "creators": [ { "name": { "family": "Gowaikar", "given": "Radhika" }, "id": "Gowaikar-Radhika", "display_name": "Gowaikar, Radhika" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/9652-QK53", "abstract": "Wireless communications have gained much currency in the last few decades. In this thesis we present results regarding several wireless communication systems, in particular, wireless networks.
\r\n\r\nFor some time now, it has been known that in an ad hoc network in which nodes share the wireless medium, and the connection strengths between nodes follow a distance-based decay law, the throughput scales like O(\u221an), where n is the number of nodes. In Chapter 2 we introduce randomness in the connection strengths and examine the effects of this on the throughput. We assume that all the channels are drawn independently from a common distribution and are not governed by a distance-decay law. It turns out that the aggregate information flow depends strongly on the distribution from which the channel strengths are drawn. For certain distributions, a throughput of n/(log n)d with d>0 is possible, which is a significant improvement over the O(\u221an) results known previously. In Chapter 3, we generalize the network model to two-scale networks. This model incorporates the distance-decay law for nodes that are separated by large distances, while maintaining randomness in close neighborhoods of a node. For certain networks, we show that a throughput of the form n1/t-1/log2n is achievable, where t>2 is a parameter that depends on the distribution of the connection at the local scale and is independent of the decay law that operates at a global scale.
\r\n\r\nIn Chapter 4, we consider a model of an erasure wireless network, in which every node is connected to certain other nodes by erasure links, on which packets or bits are lost with some probability and received accurately otherwise. Each node is constrained to send the same message on all outgoing channels, thus incorporating the broadcast feature, and we assume that there is no interference in the network, other than through the possible correlation of erasure occurrences. For such networks and in certain multicast scenarios, we obtain the precise capacity region. This region has a nice max-flow, min-cut interpretation and can be achieved using linear codes. We do require the side-information regarding erasure locations on all links to be available to the destinations. Thus, we have the capacity region for a non-trivial class of wireless networks.
\r\n\r\nRecent results for wireline networks show that in several scenarios, it is optimal to operate these networks by making each link error-free. In Chapter 5, we consider Gaussian networks with broadcast and interference, and erasure networks with broadcast, and show that in the presence of these wireless features, it is suboptimal to make each link or sub-network error-free. We then consider these networks with the constraint that each node is permitted to either retransmit the received information or decode it and retransmit the original source information. We propose a greedy algorithm that determines the optimal operation for each node, such that the rate achievable at the destination is maximized. Further, we present decentralized implementations of this algorithm that allow each node to determine for itself the optimal operation that it needs to perform.
\r\n\r\nIn Chapter 6, we consider a point-to-point communication system, involving multiple antennas at the transmitter and the receiver. These systems can give high data rates provided we can perform optimum, or maximum-likelihood, decoding of the received message. This problem typically reduces to that of finding the lattice point closest to a given point x in N-dimensional space. This is an integer least-squares problem and is NP-complete. The sphere decoder is an algorithm that performs decoding in an efficient manner by searching for the closest point only within a spherical region around x. In Chapter 6, we propose an algorithm that performs decoding in a sub-optimal manner by pruning the search region based on the statistics of the problem. This algorithm offers significant computational savings relative to the sphere decoder and allows us to tradeoff performance with computational complexity. Bounds on the error performance as well the complexity are presented.
" }, { "name": "Graff, Emilio Casta\u00f1o", "degree": "PhD", "year": "2007", "title": "On the Development of Defocusing Digital Particle Image Velocimetry with Full Characterization", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252007-140239", "creators": [ { "name": { "family": "Graff", "given": "Emilio Casta\u00f1o" }, "id": "Graff-Emilio-Casta\u00f1o", "display_name": "Graff, Emilio Casta\u00f1o" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9HM56F8", "abstract": "Defocusing Digital Particle Image Velocimetry is the first volumetric, three-dimensional PIV method ever put into practice. This manuscript contains the details of its development, a detailed analysis of its performance (both through simulation and real measurements), and a series of experimental demonstrations of the capability of the technique. The system is capable of resolving upwards of 7,000 vectors per pair with an absolute error on the order of 0.03% of the volume size." }, { "name": "Gupta, Vijay", "degree": "PhD", "year": "2007", "title": "Distributed Estimation and Control in Networked Systems", "advisor": "Murray, Richard M.; Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechETD:etd-08172006-130145", "creators": [ { "name": { "family": "Gupta", "given": "Vijay" }, "id": "Gupta-Vijay", "display_name": "Gupta, Vijay" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/KWN2-X741", "abstract": "Rapid advances in information processing, communication and sensing technologies have enabled more and more devices to be provided with embedded processors, networking capabilities and sensors. For the field of estimation and control, it is now possible to consider an architecture in which many simple components communicate and cooperate to achieve a joint team goal. This distributed (or networked) architecture promises much in terms of performance, reliability and simplicity of design; however, at the same time, it requires extending the traditional theories of control, communication and computation and, in fact, looking at a unified picture of the three fields. A systematic theory of how to design distributed systems is currently lacking.
\r\n\r\nThis dissertation takes the first steps towards understanding the effects of imperfect information flow in distributed systems from an estimation and control perspective and coming up with new design principles to counter these effects. Designing networked systems is difficult because such systems challenge two basic assumptions of traditional control theory - presence of a central node with access to all the information about the system and perfect transmission of information among components. We formulate and solve many problems that deal with the removal of one, or both, of these assumptions. The chief idea explored in this dissertation is the joint design of information flow and the control law. While traditional control design has concentrated on calculating the optimal control input by assuming a particular information flow between the components, our approach seeks to synthesize the optimal information flow along with the optimal control law that satisfies the constraints of the information flow. Thus besides the question of 'What should an agent do?', the questions of 'Whom should an agent talk to?', 'What should an agent communicate?', 'When should an agent communicate?' and so on also have to be answered. The design of the information flow represents an important degree of freedom available to the system designer that has hitherto largely been ignored. As we demonstrate in the dissertation, the joint design of information flow and the optimal control input satisfying the constraints of that information flow yields large improvements in performance over simply trying to fit traditional design theories on distributed systems.
\r\n\r\nWe begin by formulating a distributed control problem in which many agents in a formation need to cooperate to minimize a joint cost function. We provide numerical algorithms to synthesize the optimal constrained control law that involve solving linear equations only and hence are free from numerical issues plaguing the other approaches proposed in the literature. We then provide and analyze a model to understand the issue of designing the topology according to which the agents interact. The results are very surprising since there are cases when allowing communication to happen between two agents may, in fact, be detrimental to the performance.
\r\n\r\nWe then move on to consider the effects of communication channels on control performance. To counter such effects, we propose the idea of encoding information for the purpose of estimation and control prior to transmission. Although information theoretic techniques are not possible in our problem, we are able to solve for a recursive yet optimal encoder / decoder structure in many cases. This information flow design oriented approach has unique advantages such as being optimal for any packet drop pattern, being able to include the effect of known but random delays easily, letting us escape the limits set by reliability for transmission of data across a network by using intermediate nodes as 'repeaters' similar to a digital communication network and so on.
\r\n\r\nWe finally take a look at combining the effects of multiple sources of information and communication channels on estimation and control. We look at a distributed estimation problem in which, at every time step, only a subset out of many sensors can transmit information to the estimator. This is also a representative resource allocation problem. We propose the idea of stochastic communication patterns that allows us to include the effects of communication channels explicitly during system design. Thus, instead of tree-search based algorithms proposed in the literature, we provide stochastic scheduling algorithms that can take into account the random packet drop effect of the channels. We also consider a distributed control problem with switching topologies and solve for the optimal controller. The tools that we develop are applicable to many other scenarios and we demonstrate some of them in the dissertation.
\r\n\r\nAlong the way, we look at many other related problems in the dissertation. As an example, we provide initial results about the issue of robustness of a distributed system design to a malfunctioning agent. This notion is currently lacking in the control and estimation community, but has to be a part of any effective theory for designing networked or distributed systems.
" }, { "name": "Guzm\u00e1n, Marcelo Ioel", "degree": "PhD", "year": "2007", "title": "Photochemistry of Pyruvic Acid in Water and Ice", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292006-181629", "creators": [ { "name": { "family": "Guzm\u00e1n", "given": "Marcelo Ioel" }, "id": "Guzm\u00e1n-Marcelo-Ioel", "orcid": "0000-0002-6730-7766", "display_name": "Guzm\u00e1n, Marcelo Ioel" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/6CDJ-VD20", "abstract": "The 321 nm band photodecarboxylation of aqueous pyruvic acid, PA, solutions was studied in the range 5 \u2264 [PA] \u2264 100 mM. Prompt and delayed CO\u2082 production stages are detected using TEMPO as a scavenger. These two processes are resolved in the photolysis of frozen solutions: after simultaneous evolution during illumination, additional CO\u2082 is quantified in the dark (E\u2090 ~ 22 kJ mol\u207b\u00b9, T < 268 K). Photodecarboxylation rates of deareated aqueous PA solutions drop a two-fold in the frozen state at 253 K relative to the fluid at 293 K. Benzoylformic acid frozen solutions decarboxylate with no post-illumination CO\u2082 emissions.
\r\n\r\n\u00b9H-NMR studies of the hydration of aqueous PA between the carbonyl and its hydrated gem-diol species in the frozen state indicate that the fraction of the carbonyl-form of PA, approaches ~ 20% at temperatures below 263 K, regardless of the initial PA concentration in the range 0.1 M \u2264 [PA] \u2264 4.6 M. PA is cooperatively hydrated while dissolved in increasingly viscous aqueous microfluids often called quasi liquid layers (QLL) down to vitrification.
\r\n\r\nElectron magnetic resonance signals found in frozen aqueous PA solutions UV-irradiated at 77 K correspond to distant triplet radical pairs separated by ~ 0.9 nm. They originate by photoinduced electron transfer between a triplet excited state PA and ground state PA to produce \u00b3[PA\u207a\u22c5 PA\u207b\u22c5]. The subsequent deprotonation of PA\u207a\u22c5 into an acylcarbonyloxyl radical that undergoes ultrafast decarboxylation accounts for the unquenchable source of CO\u2082, even at cryogenic temperatures. Liquid chromatography with UV and ESI-MS detection in combination with \u00b9\u00b3C-isotope labeling experiments were used for products identification. The fate of the radical anion PA\u207b\u22c5 after protonation into a ketyl-radical is recombination into 2,3-dimethyltartaric acid or addition to a second PA molecule. The later process leads to an unstable 2-oxodicarboxylic acid that eliminates CO\u2082 to produce 2-(3-oxobutan-2-yloxy)-2-hydroxypropanoic.
\r\n\r\nIn conclusion, the possibility of photolysis in ice core records due to penetrating Cerenkov radiation derived from cosmic rays is explored. Potential impacts of the photolysis of organic matter trapped in ice with the subsequent release of CO and CO\u2082 over the last two millennia is analyzed.
" }, { "name": "Hampton, Alan Nicol\u00e1s", "degree": "PhD", "year": "2007", "title": "Model-Based Decision Making in the Human Brain", "advisor": "O'Doherty, John P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312007-113932", "creators": [ { "name": { "family": "Hampton", "given": "Alan Nicol\u00e1s" }, "id": "Hampton-Alan-Nicol\u00e1s", "display_name": "Hampton, Alan Nicol\u00e1s" } ], "advisors": [ { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "advisor", "display_name": "O'Doherty, John P." } ], "committee": [ { "name": { "family": "Bossaerts", "given": "Peter L." }, "id": "Bossaerts-P-L", "role": "chair", "display_name": "Bossaerts, Peter L." }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "role": "member", "display_name": "O'Doherty, John P." }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "member", "display_name": "Quartz, Steven R." } ], "option_major": [ "cns" ], "doi": "10.7907/K9Z8-E248", "abstract": "Many real-life decision making problems incorporate higher-order structure, involving interdependencies between different stimuli, actions, and subsequent rewards. It is not known whether brain regions implicated in decision making, such as ventromedial prefrontal cortex, employ a stored model of the task structure to guide choice (model-based decision making) or merely learn action or state values without assuming higher-order structure, as in standard reinforcement learning. To discriminate between these possibilities we scanned human subjects with fMRI while they performed two different decision making tasks with higher-order structure: probabilistic reversal learning, in which subjects had to infer which of two choices was the more rewarding and then flexibly switch their choice when contingencies changed; and the inspection game, in which subjects had to successfully compete against an intelligent adversary by mentalizing the opponent\u2019s state of mind in order to anticipate the opponent\u2019s behavior in future. For both tasks we found that neural activity in a key decision making region: ventromedial prefrontal cortex, was more consistent with computational models that exploit higher-order structure, than with simple reinforcement learning. Moreover, in the social interaction game, subjects were found to employ a sophisticated strategy whereby they used knowledge of how their actions would influence the actions of their opponent to guide their choices. Specific computational signals required for the implementation of such a strategy were present in medial prefrontal cortex and superior temporal sulcus, providing insight into the basic computations underlying competitive strategic interactions. These results suggest that brain regions such as ventromedial prefrontal cortex employ an abstract model of task structure to guide behavioral choice, computations that may underlie the human capacity for complex social interactions and abstract strategizing." }, { "name": "Hao, Yong", "degree": "PhD", "year": "2007", "title": "Numerical Study of Single-Chamber Solid Oxide Fuel Cells", "advisor": "Goodwin, David G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252007-110313", "creators": [ { "name": { "family": "Hao", "given": "Yong" }, "id": "Hao-Yong", "orcid": "0000-0001-7487-9327", "display_name": "Hao, Yong" } ], "advisors": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "advisor", "display_name": "Goodwin, David G." } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Ronney", "given": "Paul D." }, "id": "Ronney-P-D", "role": "member", "display_name": "Ronney, Paul D." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/H3E7-TY92", "abstract": "Single-chamber solid oxide fuel cells (SCFC) are ones in which the fuel and oxidizer are premixed, and selective electrode catalysts are used to generate the oxygen partial pressure gradient that in a conventional dual-chamber design is produced by physical separation of the fuel and oxidizer streams. The SCFC concept is a novel simplification of a conventional solid oxide fuel cell (SOFC), and SCFCs have been shown capable of generating power densities high enough to make them potentially useful in many applications where the simplicity of a single gas chamber and absence of seals offsets the expected lower efficiency of SCFCs compared to dual-chamber SOFCs.
\r\n\r\nSCFC performance is found to depend sensitively on cell microstructure, geometry, and flow conditions, and optimization of SCFC stacks requires considering complex, coupled chemical and transport processes. However, research activity in this area is far from sufficient and insights about SCFC systems are very limited. The understanding of many fundamental physical and chemical processes required for improving SCFC designs is often beyond the capability of modern experimental techniques, and efficient experimental studies are often held back by the lack of guidance from theoretical models due to the fact that modeling study about SCFC is very rare to date, and existing models about conventional SOFCs are not suitable for simulating SCFCs because of the inherent differences of single-chamber SOFCs from conventional ones. In order to systematically investigate these problems and optimize the electrical performance of SCFC systems, a 2D numerical model of a single-chamber solid oxide fuel cell (SCFC) operating on hydrocarbon fuels is developed and presented in this work.
\r\n\r\nThe model accounts for the coupled effects of gas channel fluid flow, heat transfer, porous media transport, catalytic reforming/shifting chemistry, electrochemistry, and mixed ionic-electronic conductivity. It solves for the velocity, temperature, and species distributions in the gas, profiles of gaseous species and coverages of surface species within the porous electrodes, and the current density profile in an SCFC stack for a specified electrical bias. The model is general, and can be used to simulate any electrode processes for which kinetics are known or may be estimated. A detailed elementary mechanism is used to describe the reactions over the anode catalyst surface. Different design alternatives including flow rates, flow geometry, temperature, optimal fuel to air ratio, anode thickness, YSZ vs. SDC electrolytes, and fuel cell efficiency and fuel utilization are explored. The reaction zones in the anode of an SOFC with hydrocarbon fuel and oxygen addition is also investigated and much deeper insights are obtained compared to the existing literature. Numerical techniques needed for such investigations are also introduced.
\r\n\r\nThe model is also expanded to simulate fuel cells in the commonly seen dual chamber configuration, including ones with either oxygen-ion conducting electrolytes (SOFCs) or proton conducting electrolytes (solid acid fuel cells). Good agreement with literature results and experimental measurements is obtained.
" }, { "name": "Harmon, John Shelby, III", "degree": "PhD", "year": "2007", "title": "Experimental Studies of Elasticity, Plastic Flow, and Anelasticity in Metallic-Glass-Forming-Liquids", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-05072007-150354", "creators": [ { "name": { "family": "Harmon", "given": "John Shelby, III" }, "id": "Harmon-John-Shelby-III", "display_name": "Harmon, John Shelby, III" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/53AD-3G15", "abstract": "A rheological law based on the concept of cooperatively-sheared flow zones is presented, in which the thermodynamic state variable controlling flow is identified to be the isoconfigurational shear modulus of the liquid. The law captures Newtonian as well as non-Newtonian viscosity data for glass-forming metallic liquids over a broad range of fragility. Acoustic measurements on specimens deformed at constant strain rates correlate with the measured steady-state viscosities, and define the relative effects of the \u201celastic\u201d and \u201ccooperative volume\u201d indices on the liquid fragility. The steady state deformation material properties are evaluated to obtain a relationship between the shear modulus and configurational enthalpy. Furthermore, the material properties are evaluated through steady state in an effort to probe the relaxation mechanisms governing flow." }, { "name": "Holub, Alex David", "degree": "PhD", "year": "2007", "title": "Discriminative vs. Generative Object Recognition: Objects, Faces, and the Web", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312007-204007", "creators": [ { "name": { "family": "Holub", "given": "Alex David" }, "id": "Holub-Alex-David", "display_name": "Holub, Alex David" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Welling", "given": "Max" }, "id": "Welling-M", "role": "member", "display_name": "Welling, Max" }, { "name": { "family": "Burl", "given": "Michael C." }, "id": "Burl-M-C", "role": "member", "display_name": "Burl, Michael C." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "cns" ], "doi": "10.7907/2HC2-K923", "abstract": "The ability to automatically identify and recognize objects in images remains one of the most challenging and potentially useful problems in computer vision. Despite significant progress over the past decade computers are not yet close to matching human performance. This thesis develops various machine learning approaches for improving the ability of computers to recognize object categories. In particular, it focuses on approaches which are able to distinguish between object categories which are visually similar to one another. Examples of similar visual object categories are motorcycles and bicycles, and lions and cougars. Distinguishing between similar object categories may require different algorithms than distinguishing between different categories. We explore two common machine learning paradigms, generative and discriminative learning, and analyze their respective abilities to distinguish between different sets of object categories. One set of object categories which we are exposed to on a daily basis are face images, and a significant portion of this thesis is spent analyzing different methods for accurately representing and discriminating between faces. We also address a key issue related to the discriminative learning paradigms, namely how to collect the large training set of images necessary to accurately learn discriminative models. In particular, we suggest a novel active learning which intelligently chooses the most informative image to label and thus drastically reduces (up to 10x) the time required to collect a training set. We validate and analyze our algorithms on large data-sets collected from the web and show how using hybrid generative-discriminative techniques can drastically outperform previous algorithms. In addition, we show how to use our techniques in practical applications such as finding similar-looking individuals within large data-sets of faces, discriminating between large sets of visual categories, and increasing the efficiency and speed of web-image searchi" }, { "name": "Jiang, Xun", "degree": "PhD", "year": "2007", "title": "I: Interannual Variability of Stratospheric Ozone and Temperature. II: Seasonal Cycle of N\u2082O", "advisor": "Yung, Yuk L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01032007-154646", "creators": [ { "name": { "family": "Jiang", "given": "Xun" }, "id": "Jiang-Xun", "orcid": "0000-0001-8932-3807", "display_name": "Jiang, Xun" } ], "advisors": [ { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "advisor", "display_name": "Yung, Yuk L." } ], "committee": [ { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "role": "chair", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/4022-0X13", "abstract": "This dissertation is a collection of empirical and modeling studies focusing on the interannual variability (IAV) of the stratospheric ozone and temperature. The IAV of O\u2083 in the high latitude is characterized by four main modes in both hemispheres. Similar spatial patterns and trends are simulated by the Goddard Earth Observation System, Version 4 (GEOS-4) chemistry-climate model (CCM). The El Ni\u00f1o-Southern Oscillation signal in column ozone is also simulated well by the GEOS-4 CCM in the tropics.
\r\n\r\nTo study the Quasi-biennial oscillation (QBO) and QBO-Annual Beat (QBO-AB) in column ozone, the Caltech/JPL two-dimensional (2-D) chemistry and transport model (CTM) has been used. The 2-D CTM provides realistic simulations of the seasonal and IAV of ozone in the tropics. The phase and amplitude of the QBO are well captured by the model. The QBO-AB found in the simulated ozone agrees well with that in the observed data. An idealized 2-D interactive chemistry, radiation, and dynamic model (CRDM) is used to investigate the spatial patterns of, and mechanism for, the QBO-AB signal in ozone in the tropics and subtropics. An extended EOF analysis reveals the characteristic pattern of the downward propagation of QBO and upward propagation of QBO-AB. The model results are compared to those from the Merged Ozone Data.
\r\n\r\nTo understand the IAV and trend in the stratospheric temperature, we apply principal component analysis to observations and global climate model simulations. The cooling trend in the stratosphere is associated with a spatially uniform pattern of stratospheric variability, which is isolated from more common modes of natural IAV such as the Northern Annular Mode. These results are supported by a number of coupled ocean-atmosphere climate model simulations.
\r\n\r\nFinally, a systematic study of the seasonal cycle and its latitudinal variation is carried out for the nitrous oxide data. In order to confirm the weak seasonal signal in the observations, we applied the multi-taper method for the spectrum analysis. The amplitude (peak to peak) of the seasonal cycle of N\u2082O varies from 0.29 ppb (parts-per-billion by mole fraction in dry air) at the South Pole to 1.15 ppb at Alert.
" }, { "name": "Jin, Zhipu", "degree": "PhD", "year": "2007", "title": "Coordinated Control for Networked Multi-Agent Systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182006-162259", "creators": [ { "name": { "family": "Jin", "given": "Zhipu" }, "id": "Jin-Zhipu", "display_name": "Jin, Zhipu" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZRAD-XN95", "abstract": "Coordination in networked multi-agent systems attracts significant interest in the realm of engineering. Typical examples include formations of unmanned aerial vehicles, automated highway systems, and sensor networks. One common feature for these systems is that coordinated behaviors are exhibited by interactions among agents where information exchange and manipulation are necessary. In this work, three relevant issues are investigated in detail: uniform strategy for multi-agent formation control, fast-converging consensus protocols, and packet-based state estimation over communication networks.
\r\n\r\nFormation control of multi-agent systems involves harmony among local controller design, interaction topology analysis, and objective agreement among networked agents. We propose a novel control strategy so that each agent responds to neighbors' behaviors as well as acts towards the global goal. Thus, information flows for local interactions and global objective synchronization are studied separately. Using the tools from signal flow graphs and algebraic graph theory, we show that this new strategy eases the design of local controllers by relaxing stabilizing conditions. Robustness against the link failure and scalable disturbance resistance are also discussed based on small-gain theory. Experimental results on the Caltech multi-vehicle wireless testbed are provided to verify the feasibility and efficiency of this control strategy.
\r\n\r\nConsensus protocols over communication networks are used to achieve agreement among agents. One important issue is the convergence speed. We propose multi-hop relay protocols for fast consensus seeking. Without physically changing the topology of the communication network, this type of distributed protocol increases the algebraic connectivity by employing multi-hop paths in the network. We also investigate the convergence behaviors of consensus protocols with communication delays. It is interesting that, the faster the protocol converges, the more sensitive it is to the delay. This tradeoff is identified when we investigate delay margins of multi-hop relay protocols using the frequency sweep method.
\r\n\r\nEfficiently estimating the states of other agents over communication links is also discussed in this work. When information flows in the network, packet-based data is normally not retransmitted in order to satisfy real-time requirements. Thus, packet drops and random delays are inevitable. In this context, observation data that the estimator can receive is intermittent. In order to decrease the chance of losing packets and efficiently using the limited bandwidth, we introduce multiple description source codes to manipulate the data before transmission. Using modified algebraic Riccati equations, we show that multiple description codes improve the performance of Kalman filters over a large set of packet-dropping scenarios. This problem is also generalized to the case where observation data has an independent and identical static distribution over a finite set of observation noise. Moreover, Kalman filtering with bursty packet drops is also discussed based on the two-state Markov chain model.
" }, { "name": "Kheradvar, Arash", "degree": "PhD", "year": "2007", "title": "The Role of Vortex Ring Formation and Pressure Drop on Dynamics of the Left Ventricle during Diastole", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132006-103720", "creators": [ { "name": { "family": "Kheradvar", "given": "Arash" }, "id": "Kheradvar-Arash", "orcid": "0000-0003-3864-1359", "display_name": "Kheradvar, Arash" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Vesely", "given": "Ivan" }, "id": "Vesely-I", "role": "member", "display_name": "Vesely, Ivan" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/M1QB-4Y59", "abstract": "In the field of cardiology, the current ability to accurately detect diastolic dysfunction is unsatisfactory due to the lack of an effective diagnostic index. Currently, assessments of diastolic dysfunction are based on echocardiographic measurements that are assumed to be correlated with progression from mild dysfunction to more severe disease. However, relying on existing ultrasonic indices for diagnosis of diastolic failure leads us to underestimate the progress of dysfunction. The presence of vortical flow that develops along with a strong propulsive trans-mitral jet during diastole in a normal left ventricle has been demonstrated by different imaging modalities. Thus, physical characteristics of these vortical structures may provide more effective indices of diastolic function than existing ones. In the first few chapters of this thesis, I fully describe the relationship between physical characteristics of these vortices and the dynamics of mitral valve during diastole. We found that regardless of the valve size and the pressure drop time-constant, the mitral annuls recoil computed would be maximized when the trans-mitral vortex ring pinches off in a range of formation time between three and five.
\r\n\r\nIn chapter five, I introduce a novel technique that can estimate the viscoelastic properties of the left ventricle based on harmonic behavior of the ventricular chamber. Elastic deformations resulting from the changes in the ventricular mechanical properties of myocardium are represented as a time-varying spring, while the viscous components of the model include a time-varying viscous damper, representing relaxation and the frictional energy loss.
\r\n\r\nIn the final chapter, I discussed about effect of isovolumic relaxation phase on diastolic rapid filling in the process of post-infarction cardiac remodeling in sheep. The results of this study confirmed that the post-infarction changes in isovolumic relaxation phase have direct influence on diastolic rapid filling phase, which leads to complex variations in end-diastolic lengthening and end-systolic shortening of the LV contractile elements.
" }, { "name": "Kidd, Theresa Hiromi", "degree": "PhD", "year": "2007", "title": "Mechanical Characterization of Damage and Failure in Polymeric Foams and Glass/Epoxy Composites", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102006-182329", "creators": [ { "name": { "family": "Kidd", "given": "Theresa Hiromi" }, "id": "Kidd-Theresa-Hiromi", "display_name": "Kidd, Theresa Hiromi" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G25Y-KE07", "abstract": "The mechanical characterization including evolution of damage and failure of foams and composites are becoming increasingly important, as they form the basic components of sandwich structures. Sandwich structures consist of two faceplates that surround a core material. In many modern applications, faceplates and cores are typically comprised of composite materials and polymeric foam, respectively. Knowledge of the failure behavior of these individual components is necessary for understanding the failure behavior and design of sandwich structures. A systematic investigation of the damage evolution and failure behavior of foams and composites was conducted using a variety of experimental techniques.
\r\n\r\nIn-situ ultrasonic measurements were used to track the damage behavior in PVC polymeric foams with densities ranging from 130 to 250 kg/m\u00b3. The wave speeds were measured by two quartz piezoelectric shear transducers with a resonant frequency of 5 MHz in the transmission mode. A fixture was developed and constructed to protect the transducers during compression, while allowing them to take sound speed measurements of the sample along the axis of the load train. This fixture was placed in a servo-hydraulic MTS (Materials Testing System) machine, where the load-displacement response of the foam was recorded. A digital image correlation (DIC) method was used to capture the progression of failure under compression. Two dominant failure modes, elastic buckling and plastic collapse, were identified \u2013 and their onsets corresponded to the change in elastic wave speeds in the material, measured by the in-situ ultrasonic technique.
\r\n\r\nThe transverse response of S-Glass/Epoxy unidirectional composites was investigated under varying degrees of confinement and strain rates. The experimental setup utilizes a fixture that allowed for independent measurement of the three principal stresses in a confined specimen. A servo-hydraulic materials testing system and a Kolsky (split Hopkinson) pressure bar generated strain rates between 10\u207b\u00b3 to 10\u2074 s\u207b\u00b9. Post-test scanning electron microscopy (SEM) observations suggest that under transverse loading at low-strain rates, confinement contributes to localized band formation. In addition, micrographs indicated that macroscopic transverse failure is dominated by shear stress, and occurs within these localized bands. These shear dominated failure bands were found inclined in a direction approximately 35\u00b0 to the direction of loading. Implications of this orientation deviation of failure bands from maximum shear trajectories at 45\u00b0 are discussed in reference to the state of confinement.
" }, { "name": "Klamo, Joseph Thomas", "degree": "PhD", "year": "2007", "title": "Effects of Damping and Reynolds Number on Vortex-Induced Vibrations", "advisor": "Leonard, Anthony; Gharib, Morteza; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292006-120631", "creators": [ { "name": { "family": "Klamo", "given": "Joseph Thomas" }, "id": "Klamo-Joseph-Thomas", "orcid": "0000-0003-1458-0379", "display_name": "Klamo, Joseph Thomas" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "co-advisor", "display_name": "Gharib, Morteza" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "co-advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "mecheng" ], "doi": "10.7907/S27Z-J533", "abstract": "Vortex-induced vibrations have been studied experimentally with emphasis on damping and Reynolds number effects. Our system was an elastically-mounted rigid circular cylinder, free to oscillate only transverse to the flow direction, with very low inherent damping. We were able to prescribe the mass, damping, and elasticity of the system over a wide range of values, with the damping controlled by a custom-made variable magnetic eddy-current damping system.
\r\n\r\nSpecial emphasis is put on a nontraditional parameter formulation. The advantages of this formulation are explained, and an important new parameter, effective stiffness, is introduced. Using this new formulation, the amplitude and frequency responses are only a function of damping, Reynolds number, and effective stiffness. We show the effects that damping and Reynolds number each have on the amplitude and frequency response profiles and make the interesting observation that changes in damping or Reynolds number have similar effects.
\r\n\r\nThe maximum amplitudes of our systems are studied in detail. We theoretically show that they should be functions of both damping and Reynolds number. This allows us to create constant-Reynolds-number curves of maximum amplitude over a large range of damping values, which we call a \"generalized\" Griffin plot. We also define maximum amplitudes in the case of zero damping as limiting amplitudes, and show that they are only a function of Reynolds number. We experimentally determine our limiting amplitude dependence on Reynolds number over the range 200 < Reynolds number < 5050.
\r\n\r\nDiscontinuities in the amplitude response profile are also investigated. The discontinuity between the initial branch and the large-amplitude, upper branch is studied in two ways. First, the time-averaged behavior is examined to understand what controls the discontinuity and look for damping and Reynolds number effects. Second, we track the cycle-by-cycle transient response through this discontinuous amplitude change, induced either by changes in the tunnel velocity or system damping. Finally, we also find a new discontinuity hysteresis region between the lower branch and the desynchronized region, which appears to be a low Reynolds number effect and is only seen in systems with Reynolds number < 1000.
" }, { "name": "Kolasinski, Robert David", "degree": "PhD", "year": "2007", "title": "Fundamental Ion-Surface Interactions in Plasma Thrusters", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11222006-105854", "creators": [ { "name": { "family": "Kolasinski", "given": "Robert David" }, "id": "Kolasinski-Robert-David", "orcid": "0000-0002-9633-1845", "display_name": "Kolasinski, Robert David" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "mecheng" ], "doi": "10.7907/XWSV-1E98", "abstract": "Ion thrusters offer the potential to enable many future interplanetary robotic missions presently under consideration by NASA. To realize the benefits offered by these low thrust devices, the sputtering mechanisms that are responsible for the degradation of thruster components over time must be well understood. Predictions of thruster life depend directly on the material removal rates from thruster electrodes such as the ion optics and hollow cathodes. To better understand the conditions encountered at these surfaces, this study includes an investigation of low energy sputtering at glancing incidence. Relevant ion\u2013target combinations that were considered included Xe\u207a incident on Mo, C, and Cu, as well as Ar\u207a incident on W, C, and Cu.\r\n\r\nTo characterize the sputtering yield angular dependence experimentally, an ion beam was used to etch a coated quartz crystal microbalance. This required the development of techniques to accurately measure the incident low energy ion flux to the target and the use of surface diagnostics to investigate the properties of target materials. Measurements of C and Mo sputtering yields were obtained for Xe\u207a incidence angles up to 80\u00b0 from the surface normal and for energies ranging from 80 eV\u20131 keV. In addition, existing transport theory models were used to examine projectile scattering within the different target media. The models also indicate that the sputtering behavior as a function of angle of incidence is not a strong function of energy, a conclusion that is supported by the experimental results. The surface roughness of the targets was investigated using atomic force microscopy to obtain local incidence angle distributions.\r\n\r\nA surface layer activation technique served as an alternate method of evaluating the sputtering rates of thruster components for situations where the ion bombardment conditions are not well known. In this study, a radioactive tracer was produced in the surfaces of a number of laboratory model ion thruster cathode assemblies by high energy proton bombardment. The cathodes were tested in a 30 cm diameter xenon ion thruster to provide insight into the relevant wear mechanisms at different thruster operating points. Methods for combating cathode degradation are proposed based on the experimental results." }, { "name": "Komijani, Abbas", "degree": "PhD", "year": "2007", "title": "Microwave Integrated Phased-Array Transmitters in Silicon", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282007-203227", "creators": [ { "name": { "family": "Komijani", "given": "Abbas" }, "id": "Komijani-Abbas", "display_name": "Komijani, Abbas" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "D'Addario", "given": "Larry R." }, "id": "D'Addario-L-R", "role": "member", "display_name": "D'Addario, Larry R." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/EW67-RX66", "abstract": "Phased-array systems, a special case of multiple-input-multiple-output (MIMO) systems, take advantage of spatial directivity and array gain to increase spectral efficiency. Implementing a phased-array system at high frequency in a commercial silicon process technology presents several challenges. This thesis focuses on the architectural and circuit-level trade-offs involved in the design of the silicon-based fully integrated phased-array transmitters.
\r\n \r\nAs the first implementation, a four-element 24GHz 0.18\u00b5m CMOS phased-array transmitter with integrated power amplifiers is presented. On-chip power amplifiers use substrate-shielded slow-wave transmission lines for impedance matching and can generate up to 14dBm of output power. The transmitter employs a two-step upconversion architecture with 4.8GHz as the intermediate frequency (IF) and uses a single 19.2GHz synthesizer serving as the local oscillator (LO) generator. The phased-array, employing the LO phase shifting architecture, achieves 23dB of peak to null-ratio when all four elements are used, demonstrates a beam steering range covering all signal incident angles, and can support a data rate of 500Mbps with a quadrature phase-shift keying (QPSK) baseband signal.
\r\n\r\nAs the second implementation with a modified phase shifting architecture, an integrated 4-element 77GHz Silicon-Germanium (SiGe) phased-array transceiver is presented. Two-step conversion, envisioning a dual-mode 77GHz/24GHz operation, is used at both the receiver and the transmitter paths. A differential phase of 52GHz is generated by the on-chip voltage-controlled oscillator (VCO) and is distributed to all radio frequency (RF) paths. The phase shifting is performed at the LO ports of the RF mixers with continuous analog phase shifters. The quadrature signal of the second LO, at the IF frequency of 26GHz, is generated by dividing the VCO frequency by a factor of 2 using a cross-coupled injection-locked frequency divider. The on-chip 77GHz power amplifier with an output power of 17.5dBm and peak power added efficiency (PAE) of 14% achieves the best performance demonstrated in silicon. A single transmitter path achieves a 40dB conversion gain at 77GHz with 2.5GHz of bandwidth and a maximum output power of 12.5 dBm.
\r\n\r\nThe measured results demonstrate the feasibility of using silicon-based integrated phased-arrays for wireless communication and vehicular radar applications.
" }, { "name": "Kulkarni, Yashashree", "degree": "PhD", "year": "2007", "title": "Coarse-Graining of Atomistic Description at Finite Temperature", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102006-152125", "creators": [ { "name": { "family": "Kulkarni", "given": "Yashashree" }, "id": "Kulkarni-Yashashree", "display_name": "Kulkarni, Yashashree" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knap", "given": "Jaroslaw" }, "id": "Knap-J", "role": "member", "display_name": "Knap, Jaroslaw" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/W9M0-HX47", "abstract": "This thesis presents a computational method for seamlessly bridging the atomistic and the continuum realms at finite temperature. The theoretical formulation is based on the static theory of the quasicontinuum and extends it to model non-equilibrium finite temperature material response.
\r\n\r\nAt non-zero temperature, the problem of coarse-graining is compounded by the presence of multiple time scales in addition to multiple spatial scales. We address this problem by first averaging over the thermal motion of atoms to obtain an effective temperature-dependent energy on the macroscopic scale. Two methods are proposed to this end. The first method is developed as a variational mean field approximation which yields local thermodynamic potentials such as the internal energy, the free energy, and the entropy as phase averages of appropriate phase functions. The chief advantage of this theory is that it accounts for the anharmonicity of the interaction potentials, albeit numerically, unlike many methods based on statistical mechanics which require the quasi-harmonic approximation for computational feasibility. Furthermore, the theory reduces to the classical canonical ensemble approach of Gibbs under the quasi-harmonic approximation for perfect, isotropic, infinite crystals subjected to uniform temperature. In the second method, based on perturbation analysis, the internal energy is derived as an effective Hamiltonian of the atomistic system by treating the thermal fluctuations as perturbations about an equilibrium configuration.
\r\n\r\nThese energy functionals are then introduced into the quasicontinuum theory, which facilitates spatial coarse-graining of the atomistic description. Finally, a variational formulation for simulating rate problems, such as heat conduction, using the quasicontinuum method is developed. This is achieved by constructing a joint incremental energy functional whose Euler-Lagrange equations yield the equilibrium equations as well as the time-discretized heat equation.
\r\n\r\nWe conclude by presenting the results for numerical validation tests for the thermal expansion coefficient and the specific heat for some materials and compare them with classical theory, molecular dynamics results, and experimental data. Some illustrative examples of thermo-mechanical coupled problems such as heat conduction in a deformable solid, adiabatic tension test, and finite temperature nanoindentation are also presented which show qualitative agreement with expected behavior and demonstrate the applicability of the method.
" }, { "name": "Lai, Wei", "degree": "PhD", "year": "2007", "title": "Impedance Spectroscopy as a Tool for the Electrochemical Study of Mixed Conducting Ceria", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072006-123745", "creators": [ { "name": { "family": "Lai", "given": "Wei" }, "id": "Lai-Wei", "display_name": "Lai, Wei" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Van de Walle", "given": "Axel" }, "id": "van-de-Walle-A", "role": "member", "display_name": "Van de Walle, Axel" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." } ], "option_major": [ "matsci" ], "doi": "10.7907/0SKX-1Z55", "abstract": "The A.C. impedance response of mixed ionic and electronic conductors (MIECs) is derived from first principles and quantitatively compared with experimental data of three model systems: pO2 |Pt|Sm0.15Ce0.85O2\u2212\u03b4(1350 \u25e6C)|Pt|pO2\r\n(system I), pO2|Pt|Sm0.15Ce0.85O2\u2212\u03b4(1550 -\u25e6C)|Pt|pO2\r\n(system II), and pO2\r\n(c)|Ba0.5Sr0.5Co0.8Fe0.2O3\u2212\u03b4|Sm0.15Ce0.85O2\u2212\u03b4(1350 \u25e6C)|Pt|-\r\npO2\r\n(a) (system III). For the equilibrium systems I and II, which differ in terms of the preparation of the electrolyte, a broad spectrum of electrical and thermodynamic properties is\r\nextracted solely from the measurement of impedance spectra over wide oxygen partial pressure (10\u221231\u20130.21 atm) and temperature ranges (500 to 650 \u25e6C). Electrolyte parameters\r\nderived from quantitative fitting of the impedance spectra include the concentration of\r\nfree electron carriers, the mobilities for both ion and electron transport, the entropy and\r\nenthalpy of reduction of Ce4+ to Ce3+, and, for system II, the space charge potential characterizing the grain boundary behavior. In addition, the electrochemical behavior of O2\r\nand H2 at the Pt|ceria interface has been characterized from these measurements. Under\r\noxidizing conditions, the data suggest an oxygen electro-reduction reaction that is rate limited by the dissociated adsorption/diffusion of oxygen species on the Pt electrode, similar\r\nto Pt|zirconia. Under reducing conditions, the inverse of the electrode polarization resistivity obeys a p\r\n\u22121/4\r\nO2\r\ndependence, with an activation energy that is similar to that measured\r\nfor the electronic conductivity. These results suggest that ceria is electrochemically active\r\nfor hydrogen electro-oxidation and that the reaction is limited by the rate of removal of\r\nelectrons from the ceria surface. For the nonequilibrium system III, examined from 550 to\r\n650 \u25e6C, the cathode oxygen partial pressure was fixed at 0.21 atm and the anode H2 was\r\nvaried from 0.2 to 1 atm. The combination of Open Circuit Voltage (OCV) measurement\r\nand quantitative fitting of the impedance spectra yields electrochemical information at the\r\ntwo interfaces. The results are consistent with the H2 electro-oxidation mechanism at the\r\nPt|ceria interface of systems I and II, whereas the resistance to the electro-reduction at the\r\nBa0.5Sr0.5Co0.8Fe0.2O3\u2212\u03b4|ceria is negligible." }, { "name": "Latini, Marco", "degree": "PhD", "year": "2007", "title": "Simulations and Analysis of Two- and Three-Dimensional Single-Mode Richtmyer-Meshkov Instability using Weighted Essentially Non-Oscillatory and Vortex Methods", "advisor": "Meiron, Daniel I.; Schilling, Oleg", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082006-124547", "creators": [ { "name": { "family": "Latini", "given": "Marco" }, "id": "Latini-Marco", "display_name": "Latini, Marco" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Schilling", "given": "Oleg" }, "id": "Schilling-O", "role": "advisor", "display_name": "Schilling, Oleg" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Schilling", "given": "Oleg" }, "id": "Schilling-O", "role": "member", "display_name": "Schilling, Oleg" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/1397-GZ04", "abstract": "An incompressible vorticity-streamfunction (VS) method is developed to investigate the single-mode Richtmyer-Meshkov instability in two and three dimensions. The initial vortex sheet (representing the initial shocked interface) is thickened to regularize the limit of classical Lagrangian vortex methods. In the limit of smaller thickness, the initial velocity converges to the velocity of a vortex sheet. The vorticity on the Cartesian grid follows the vorticity evolution equation augmented by the baroclinic vorticity production term (to capture the effects of the instability on the layer) and a viscous dissipation term. The equations are discretized using a fourth-order in space and third-order in time semi-implicit Adams-Bashforth backward differentiation scheme. The convergence properties of the method with respect to varying the diffuse interface thickness and viscosity are investigated. It is shown that the small-scale structures within the roll-up are more sensitive to the diffuse interface thickness than to the viscosity. By contrast, the large-scale quantities, including the perturbation, bubble, and spike amplitudes are less sensitive. Fourth-order point-wise convergence is achieved, provided that a sufficiently fine grid is used.
\r\n\r\nIn two dimensions, the VS method is applied to investigate late-time nonlinear effects of the single-mode Mach 1.3 air(acetone)/SF_6 shock tube experiment of Jacobs and Krivets. The results are also compared to those from compressible ninth-order weighted essentially non-oscillatory (WENO) simulations. The density fields from the WENO and VS methods agree with the experimental PLIF images in the large-scale structures but differ in the small-scale structures. The WENO method exhibits small-scale disordered structure similar to that in the experiment, while the VS method does not capture such structure, but shows a strong rotating core. The perturbation amplitudes from the two methods are in good agreement and match the experimental data points well. The WENO bubble amplitude is smaller than the VS amplitude and vice versa for the spike amplitude. Comparing amplitudes from simulations with varying Mach number shows that as the Mach number increases, the differences in the bubble and spike amplitudes increase due to intensifying pressure perturbations not present in the incompressible VS method. The perturbation amplitude from the WENO and VS methods is also compared to the predictions of nonlinear amplitude growth models in which the growth rate was reduced to account for the diffuse initial interface. In general, the model predictions agree with the simulation amplitudes at early-to-intermediate times and underpredict at later times, corresponding to the late nonlinear regime.
\r\n\r\nThe WENO simulation is used to investigate reshock, which occurs when the transmitted shock reflects from the end wall of the test section and interacts with the evolving layer. The post-reshock mixing layer width agrees well with the predictions of reshock models for short times until the interaction of the reflected rarefaction with the layer.
\r\n\r\nThe VS simulation was also compared to classical Lagrangian and vortex-in-cell simulations as the Atwood number was varied. For low Atwood numbers, all three simulations agree. As the Atwood number increases, the VS simulation shows differences in the bubble and spike amplitudes compared to the Lagrangian and VIC simulations, as the baroclinic vorticity production for a diffuse layer is different from that of a thin layer. The simulation amplitudes agree with the predictions of nonlinear amplitude growth models at early times. The growth models underpredict the amplitudes at later times.
\r\n\r\nThe investigation is extended to three dimensions, where the initial perturbation is a product of sinusoids and the initial vorticity deposition is given by linear instability analysis. The instability evolution and dynamics of vorticity are visualized using the mass fraction and enstrophy isosurface, respectively. For the WENO and VS methods, two roll-ups corresponding to the bubble and spike regions form, and the vorticity shows the formation of a ring-like structure. The perturbation amplitudes from the WENO and VS methods are in excellent agreement. The bubble and spike amplitude are in good agreement at early times. At later times, the WENO bubble amplitude is smaller than the VS amplitude and vice versa for the spike. The nonlinear three-dimensional Zhang-Sohn model agrees with the simulation amplitudes at early times, and underpredicts later. In three dimensions, the enstrophy iso-surface after reshock shows significant fragmentation and the formation of small, short, tubular structures. Simulations with different initial amplitudes show that the mixing layer width after reshock does not depend on the pre-shock amplitude. Finally, the effects of Atwood number are investigated using the VS method and the amplitudes are compared to the predictions of the Zhang-Sohn model. The simulation and the models are in agreement at early times, while the models underpredict later.
\r\n\r\nThe VS method constitutes a useful numerical approach to investigate the Richtmyer-Meshkov instability in two and three dimensions. The VS method and, more generally, vortex methods are valid tools for predicting the large-scale instability features, including the perturbation amplitudes, into the late nonlinear regime.
" }, { "name": "Li, Lun", "degree": "PhD", "year": "2007", "title": "Topologies of Complex Networks: Functions and Structures", "advisor": "Doyle, John Comstock; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282007-223415", "creators": [ { "name": { "family": "Li", "given": "Lun" }, "id": "Li-Lun", "display_name": "Li, Lun" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "co-advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Willinger", "given": "Walter" }, "id": "Willinger-W", "role": "member", "display_name": "Willinger, Walter" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9G3P-7F13", "abstract": "During the last decade, significant efforts have been made toward improving our understanding of the topological structures underlying complex networks and illuminating some of the intriguing large-scale properties exhibited by these systems. The dominant theme of these efforts has been on studying the graph-theoretic properties of the corresponding connectivity structures and on developing universal theories and models that transcend system-specific details and describe the different systems well in a statistical sense.
\r\n\r\nHowever, in this thesis we argue that these efforts have had limited success and are in need of substantial correction. Using a highly engineered system, the Internet, as a case study we demonstrate that networks are designed for a purpose, and ignoring that aspect or obscuring it with the use of some generic but random mechanism can result in models that misrepresent what matters for system functions. By accounting in a minimal manner for both the functional requirements and structural features inherent in the design of an engineered system, we propose an alternative, optimization-based modeling approach that highlights the necessary trade-offs between system performance and the technological and economic constraints that are crucial when designing the system. We show that our proposed approach yields network models that not only match the large-scale graph-theoretic properties of measured router-level topologies well but are also fully consistent with engineering intuition and networking reality, especially as far as their performance aspects and robustness properties are concerned. In fact, we show that our design-inspired network models can be easily distinguished from previously considered probabilistic network models and efficiently achieve the level of performance for which they were designed in the first place.
\r\n\r\nWhile this thesis focuses on the Internet, it has much broader implications for complex networks and graph theory generally. To better differentiate between different graphs that are identical in certain graph statistics, we introduce a structural metric, the s-metric, and demonstrate that it provides insights into the diversity of graphs constrained by certain common properties and sheds new light on many classic graph concepts such as the various notions of self-similarity, likelihood, and assortativity. Our s-metric clarifies much of the confusion surrounding the sensational qualitative claims in the current graph theory literature for complex networks and offers a rigorous and quantitative alternative.
\r\n\r\nMoreover, to examine the space of graphs that satisfy certain common properties, we propose a new approach that is based on establishing a link between two graphs if and only if one can be obtained from the other via a local transformation. Exploring the resulting connected space of graphs by dividing it into countable subspaces provides a much clearer picture on the whole space. We also show that this space of graphs has a rich and interesting structure and that some properties of the latter can be related to features of the individual graphs in this space (e.g., degree variability of a node $g$ in the space of graphs and the s-metric for g).
" }, { "name": "Li, Mo", "degree": "PhD", "year": "2007", "title": "Very High Frequency Nanoelectromechanical Resonators and their Chemical Sensing Applications", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212007-112803", "creators": [ { "name": { "family": "Li", "given": "Mo" }, "id": "Li-Mo-2007", "orcid": "0000-0002-5500-0900", "display_name": "Li, Mo" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/0KB4-H204", "abstract": "Nanoelectromechanical systems (NEMS) have been proven to be ultrasensitive sensors for a variety of physical variables with unprecedented sensitivity, including force, mass, electrical charge, magnetic field, pressure, and heat. This thesis is intended to discuss using NEMS devices as chemical gas sensors, in a portable and compact total chemical analysis system. An integrated transduction method using piezoresistive metallic thin film is described, which enables both fabrication and operation of nanoscale NEMS resonator devices with resonance frequency up to very high frequency (VHF). The advantages over using traditional doped semiconductor film as piezoresistive material is discussed. Performance and noise properties of the devices are carefully characterized. The dependence between quality factor, device dimension, and pressure is studied, and very high quality factor is obtained with devices at nanoscale dimensions, indicating advantages over their microscale counterparts. Subsequently, the resonator devices are employed as a mass sensor, demonstrating attogram scale mass sensitivity in ambient conditions. Application of these devices as detectors in a gas chromatographic (GC) system is then described, together with method of coating them with functional polymeric film. Detection of multiple analytes of nerve gas simulants with ultrahigh speed, superior sensitivity, and excellent selectivity is achieved. The replacement of conventional bulky detectors with an NEMS detector makes fully integrated microscale gas analysis system possible, which has promising potential applications in health care, medical science, and environmental science." }, { "name": "Liu, Xin", "degree": "PhD", "year": "2007", "title": "Robustness, Complexity, Validation and Risk", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272007-214755", "creators": [ { "name": { "family": "Liu", "given": "Xin" }, "id": "Liu-Xin", "display_name": "Liu, Xin" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Yi", "given": "Tau-Mu" }, "id": "Yi-Tau-Mu", "role": "member", "display_name": "Yi, Tau-Mu" } ], "option_major": [ "cds" ], "doi": "10.7907/JZX4-QN41", "abstract": "A robust design process starts with modeling of the physical system and the uncertainty it faces. Robust design tools are then applied to achieve specified performance criteria. Verification of system properties is crucial as improvements on the modeling and design practices can be made based on results of such verification. In this thesis, we discuss three aspects of this closed-loop process.
\r\n\r\nFirst and the most important aspect is the possibility of the feedback from verification to system modeling and design. When verification is hard, what does it tell us about our system? When the system is robust, would it be easy to verify so? We study the relation between robustness of a system property posed as a decision problem and the proof complexity of verifying such property. We examine this relation in two classes of problems: percolation lattices and linear programming problems, and show complexity is upper-bounded by the reciprocal of robustness, i.e. fragility.
\r\n\r\nThe second aspect we study is model validation. More precisely, when given a candidate model and experiment data, how do we rigorously refute the model or gain information about the consistent parameter set? Different methods for model invalidation and parameter inference are demonstrated with the G-protein signaling system in yeast to show the advantages and hurdles in their applications.
\r\n\r\nWhile quantification of robustness requirements has been well-studied in engineering, it is just emerging in the field of finance. Robustness specification in finance is closely related to the availability of proper risk measures. We study the estimation of a coherent risk measure, Expected Shortfall (ES). A consistent and asymptotically normal estimator for ES based on empirical likelihood is proposed. Although empirical likelihood based estimators usually involve numerically solving optimization problems that are not necessarily convex, computation of our estimator can be carried out in a sequential manner, avoiding solving non-convex optimization problems.
" }, { "name": "Lohwongwatana, Boonrat", "degree": "PhD", "year": "2007", "title": "Development, Characterization, and Applications of Gold and Platinum Bulk Metallic Glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212007-043942", "creators": [ { "name": { "family": "Lohwongwatana", "given": "Boonrat" }, "id": "Lohwongwatana-Boonrat", "orcid": "0000-0002-3131-8076", "display_name": "Lohwongwatana, Boonrat" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "matsci" ], "doi": "10.7907/F215-BD47", "abstract": "The development of bulk metallic glass alloys is presented with various elemental selection criteria, design strategies, and experimental techniques. The focus was later drawn towards the development of noble bulk metallic glasses based on gold and platinum. To formulate a good bulk glass forming composition, we found that the gold alloys had to be optimized using uncommon approaches. One strategy was to primarily increase the glass transition temperature of the alloy, instead of lowering the melting temperature. The resulting gold bulk metallic glass alloy could be cast fully amorphous up to 5 mm thick. However, the best gold glass former also exhibited many anomalous behaviors; for example, a very high strain rate could induce phase separation in the bulk glass forming liquid. A detail study on the strain rate induced crystallization was carried out systematically to pinpoint the exact conditions that would cause an anomaly.
\r\n\r\nAdditionally, a variety of comparative studies were conducted on the gold and platinum bulk metallic glass alloys, including elastic constants measurement, heat capacity measurement, viscosity measurement using three-point beam bending, and time to crystallization study in order to construct a Time-Temperature Transformation diagram.
\r\n\r\nThe last chapter switches gears to the engineering and technology aspect of gold and platinum bulk metallic glasses. The thermoplastic soldering technique is introduced as a novel method for joining any two materials at temperatures lower than that of brazing or welding processes. The proposed technique is a new alternative to the lead-free soldering process available to the electronic industry.
" }, { "name": "Loumes, Laurence", "degree": "PhD", "year": "2007", "title": "Multilayer Impedance Pump: A Bio-Inspired Valveless Pump with Medical Applications", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082007-103832", "creators": [ { "name": { "family": "Loumes", "given": "Laurence" }, "id": "Loumes-Laurence", "display_name": "Loumes, Laurence" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MT2J-AR81", "abstract": "This thesis introduces the concept of multilayer impedance pump, a novel pumping mechanism inspired from the embryonic heart structure.
\r\n\r\nThe multilayer impedance pump is a composite two-layer fluid-filled elastic tube featuring a thick, gelatin-like internal layer similar in nature to the embryonic cardiac jelly, and that is used to amplify longitudinal elastic waves. Pumping is based on the impedance pumping mechanism. Elastic waves are generated upon small external periodic compressions of the elastic tube. They propagate along the tube\u2019s walls, reflect at the tube\u2019s extremities and drive the flow in a preferential direction. This fully coupled fluid-structure interaction problem is solved for the flow and the structure using the finite element method over a relevant range of frequencies of excitation. Results show that the two-layer configuration can be an efficient wave propagation combination, and that it allows the pump to produce significant flow for small excitations. The multilayer impedance pump is a complex system in which flow and structure exhibit a resonant behavior. At resonance, a constructive elastic wave interaction coupled with a most efficient energy transmission between the elastic walls and the fluid is responsible for the maximum exit flow. The pump efficiency reaches its highest at resonance, highlighting furthermore the concept of resonance pumping.
\r\n\r\nUsing the proposed multilayer impedance pump model, we are able to bring an additional proof on the impedance nature of the embryonic heart by comparing a peristaltic and an impedance multilayer pump both excited in similar fashion to the one observed in the embryonic heart.
\r\n\r\nThe gelatin layer that models the embryonic cardiac jelly occupies most of the tube walls and is essential to the propagation of elastic waves. A comparison between the exact same impedance pump with and without the additional gelatin layer sheds light on the dynamic role of the cardiac jelly in the embryonic heart and on nature's optimized design.
\r\n\r\nFinally, several biomedical applications of multilayer impedance pumping are presented. A physiologically correct model of aorta is proposed to test the pump as an implantable cardiovascular assist device.
\r\n" }, { "name": "Maltezos, George Manuel", "degree": "PhD", "year": "2007", "title": "Microfluidic Devices for Accessible Medical Diagnostics", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282007-161248", "creators": [ { "name": { "family": "Maltezos", "given": "George Manuel" }, "id": "Maltezos-George-Manuel", "display_name": "Maltezos, George Manuel" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Baltimore", "given": "David L." }, "id": "Baltimore-D-L", "role": "member", "display_name": "Baltimore, David L." }, { "name": { "family": "Gomez", "given": "Frank" }, "id": "Gomez-F", "role": "member", "display_name": "Gomez, Frank" }, { "name": { "family": "Barbic", "given": "Mladen" }, "id": "Barbic-M", "role": "member", "display_name": "Barbic, Mladen" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/BWQC-RE07", "abstract": "This thesis covers devices exploring basic areas of physical and biological research including: surface plasmon enhanced InGaN light-emitting diode, analysis of using AlGaN emitters coupled with thin film heaters to cure onychomycosis infections, tunable organic transistors that use microfluidic source and drain electrodes, as well as an electrical microfluidic pressure gauge for PDMS MEMS. Also analyzed are devices created through the use of novel three-dimensional rapid prototyping techniques, such as: the replication of three-dimensional valves from printed wax molds, chemically robust three-dimensional monolithic SIFEL fluoropolymer microfluidics, microfluidic valves for customized radioactive positron emission dyes, reduction of microfluidic control inputs through the use of pressure multiplexing, bicuspid-inspired microfluidic check valves and microfluidic three-dimensional separation column. Devices created to analyze blood are also treated including: a microfluidic device to extract blood plasma from a fingerstick; inexpensive, portable immunoassay devices and their use in in small cell lung carcinoma and multiple sclerosis; as well as a device to screen metastasizing cancer cells. Devices created to perform polymerase chain reactions are also studied, including: an evaporative cooler for microfluidic channels, thermal management in microfluidics using micro-Peltier junctions in a microfluidic polymerase chain reaction system, and an accessible polymerase chain reaction system." }, { "name": "Martinez Estrada, Alfredo", "degree": "PhD", "year": "2007", "title": "A Treatise on Econometric Forecasting", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222007-101946", "creators": [ { "name": { "family": "Martinez Estrada", "given": "Alfredo" }, "id": "Martinez-Estrada-Alfredo", "display_name": "Martinez Estrada, Alfredo" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "cds" ], "doi": "10.7907/WXN5-9A47", "abstract": "We investigate the effects of model misspecification and stochastic dynamics in the problem of forecasting. In economics and many fields of engineering, many researchers are guilty of the dangerous practice of treating their mathematical models as the true data generating mechanisms responsible for the observed phenomena and downplaying or omitting all together the important step of model verification. In recent years, econometricians have acknowledged the need to account for model misspecification in the problems of estimation and forecasting. In particular, a large body of work has emerged to address properties of estimators under model misspecification, along with a plethora of misspecification testing methodologies. In this work, we investigate the combined effects of model misspecification and various types of stochastic dynamics on forecasts based on linear regression models. The data generating process (DGP) is assumed unknown to the forecaster except for the nature of process dependencies, i.e., independent identically distributed, covariance stationary, or nonstationary. Estimation is carried out by means of ordinary least squares, and forecasts are evaluated with the mean squared forecast error (MSFE) or mean square error of prediction. We investigate the sample size dependence of the MSFE. For this purpose, we develop an algorithm to approximate the MSFE by an expression depending only on the sample size n and moments of the processes. The approximation is constructed by Taylor series expansions of the squared forecast error which do not require knowledge of the functional form of the DGP. The approximation can be used to determine the existence of optimal observation windows which result in the minimum MSFE. We assess the accuracy of the approximating algorithm with Monte Carlo experiments.\r\n" }, { "name": "Masmanidis, Sotirios Konstantinos", "degree": "PhD", "year": "2007", "title": "Piezoelectric and Magnetoelastic Strain in the Transduction and Frequency Control of Nanomechanical Resonators", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechETD:etd-07282006-141724", "creators": [ { "name": { "family": "Masmanidis", "given": "Sotirios Konstantinos" }, "id": "Masmanidis-Sotirios-Konstantinos", "orcid": "0000-0002-8699-3335", "display_name": "Masmanidis, Sotirios Konstantinos" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "chair", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/85NX-A673", "abstract": "Stress and strain play a central role in semiconductors, and are strongly manifested at the nanometer-scale regime. Piezoelectricity and magnetostriction produce internal strains that are anisotropic and addressable via a remote electric or magnetic field. These properties could greatly benefit the nascent field of nanoelectromechanical systems (NEMS), which promises to impact a variety of sensor and actuator applications. The piezoelectric semiconductor GaAs is used as a platform for probing novel implementations of resonant nanomechanical actuation and frequency control. GaAs/AlGaAs heterostructures can be grown epitaxially, are easily amenable to suspended nanostructure fabrication, have a modest piezoelectric coefficient roughly twice that of quartz, and if appropriately doped with manganese, can form dilute magnetic compounds. In ordinary piezoelectric transducers there is a clear distinction between the metal electrodes and piezoelectric insulator. But this distinction is blurred in semiconductors. An integrated piezoelectric actuation mechanism is demonstrated in a series of suspended anisotype GaAs junctions, notably pin diodes. A dc bias was found to alter the resonance amplitude and frequency in such devices. The results are in good agreement with a model of strain based actuation encompassing the diode\u2019s voltage-dependent carrier depletion width and impedance. A bandstructure engineering approach is employed to control the actuation efficiency by appropriately designing the doping level and thickness of the GaAs structure. Actuation and frequency are also sensitively dependent on the device\u2019s crystallographic orientation. This combined tuning behavior represents a novel type of depletion-mediated electromechanical coupling in piezoelectric semiconductor nanostructures. All devices are actuated piezoelectrically, whereas three techniques are demonstrated for sensing: optical interferometry, piezoresistance and piezoelectricity. Finally, a nanoelectromechanical GaMnAs resonator is used to obtain the first measurement of magnetostriction in a dilute magnetic semiconductor. Resonance frequency shifts induced by field-dependent magnetoelastic stress are used to simultaneously map the magnetostriction and magnetic anisotropy constants over a wide range of temperatures. Owing to the central role of carriers in controlling ferromagnetic interactions in this material, the results appear to provide insight into a unique form of magnetoelastic behavior mediated by holes." }, { "name": "Mehyar, Mortada", "degree": "PhD", "year": "2007", "title": "Distributed Averaging and Efficient File Sharing on Peer-to-Peer Networks", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102007-010550", "creators": [ { "name": { "family": "Mehyar", "given": "Mortada" }, "id": "Mehyar-Mortada", "display_name": "Mehyar, Mortada" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Q9EV-S167", "abstract": "The work presented in this thesis is mainly divided in two parts. In the first part we study the problem of distributed averaging, which has attracted a lot of interest in the research community in recent years. Our work focuses on the issues of implementing distributed averaging algorithms on peer-to-peer networks such as the Internet. We present algorithms that eliminate the need for global coordination or synchronization, as many other algorithms require, and show mathematical analysis of their convergence.
\r\n\r\nDiscrete-event simulations that verify the theoretical results are presented. We show that the algorithms proposed converge rapidly in practical scenarios. Real-world experiments are also presented to further corroborate these results. We present experiments conducted on the PlanetLab research network. Finally, we present several promising applications of distributed averaging that can be implemented in a wide range of areas of interest.
\r\n\r\nThe second part of this thesis, also related to peer-to-peer networking, is about modelling and understanding peer-to-peer file sharing. The BitTorrent protocol has become one of the most popular peer-to-peer file sharing systems in recent years. Theoretical understanding of the global behavior of BitTorrent and similar peer-to-peer file sharing systems is however not very complete yet. We study a model that requires very simple assumptions yet exhibits a lot structure. We show that it is possible to consider a wide range of performance criteria within the framework, and that the model captures many of the important issues of peer-to-peer file sharing.
\r\n\r\nWe believe the results provide fundamental insights to practical peer-to-peer file sharing systems. We show that many optimization criteria can be studied within our framework. Many new directions of research are also opened up.
" }, { "name": "Miao, Shu", "degree": "PhD", "year": "2007", "title": "Electronic Structure and Bonding in Energy Storage Materials", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052007-090808", "creators": [ { "name": { "family": "Miao", "given": "Shu" }, "id": "Miao-Shu", "display_name": "Miao, Shu" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Yazami", "given": "Rachid" }, "id": "Yazami-R", "role": "member", "display_name": "Yazami, Rachid" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "matsci" ], "doi": "10.7907/FD8F-2H41", "abstract": "LixNi0.5Mn0.5O2 and LixNi1/3Mn1/3Co1/3O2 are cathode materials in Li-ion batteries. The changes in their electronic structure during charging/discharging processes were studied by using electron energy loss spectrometry (EELS) in a transmission electron microscope (TEM) and first-principles calculations. Significant growth was observed at O K-edge upon the removal of lithium, indicating a depletion of O 2p electrons. Only small changes were observed on Ni absorption edges. Our results indicate that the widely believed Ni2+ -> Ni4+ oxidation does not occur during delithiation, and O is mainly responsible for the charge compensation in these materials. Following similar procedure, the olivine phases of LixFePO4 were studied. It was found that about half electron was donated by Fe atoms during delithiation, while the rest of the charge was contributed by O atoms. We also studied the bonding in Mg2Si. The Mg-Si bond was found to be very ionic. An ionicity of 74% was found via Bader analysis." }, { "name": "Miserendino, Scott Brian", "degree": "PhD", "year": "2007", "title": "A Modular Microfluidic Approach to Nano High-Performance Liquid Chromatography with Electrochemical Detection", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142007-170140", "creators": [ { "name": { "family": "Miserendino", "given": "Scott Brian" }, "id": "Miserendino-Scott-Brian", "display_name": "Miserendino, Scott Brian" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Meng", "given": "Ellis" }, "id": "Meng E-F-C", "role": "member", "display_name": "Meng, Ellis" }, { "name": { "family": "Collier", "given": "C. Patrick" }, "id": "Collier-C-P", "role": "member", "display_name": "Collier, C. Patrick" }, { "name": { "family": "Lee", "given": "Terry D." }, "id": "Lee-T-D", "role": "member", "display_name": "Lee, Terry D." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GNV8-6M21", "abstract": "The field of microfluidics faces many challenges that must be overcome before wide-spread use of microfluidic devices can be achieved. Chief among these challenges are the need for reliable, user-friendly packaging and robust, reconfigurable, and reusable microfluidic systems. A modular microfluidic design approach to microfluidic systems is developed and a prototype modular nano high-performance liquid chromatography (nHPLC) system with electrochemical detection is demonstrated. The modular microfluidic system requires high operating pressure, low dead volume interconnects, and assembly into a simple, reliable package. The modular approach differs from the classic monolithic approach to microfluidic systems by offering increased system flexibility, reduced individual device fabrication complexity, and increased independence of component fabrication technologies at the cost of an additional microfluidic interconnect component.
\r\n\r\nMicrogaskets and MEMS O-rings based on a new, commercial, photodefinable silicone are developed and characterized to provide the necessary low dead volume interconnects. The microgaskets and MEMS O-rings are shown to work well at typical operating pressures and did not leak under operating pressures up to 250 psi. The modular nHPLC system is used to separate a nitrate/nitrite sample with efficiencies favorably comparable to commercial macro HPLC systems and other nano HPLC systems reported in the literature. Finally, new electrochemical working electrode materials are presented for use in electrochemical detectors. One material is a thin-film carbon based on pyrolyzed Parylene-C that can conformally coat high-aspect-ratio structures to achieve better than a ten-fold increase in effective electrode area relative to geometric surface area. The second material is a carbon nanotube (CNT) nanoarray that uses a Parylene-C stabilization and insulation matrix. The CNT nanoarray shows a bifurcated sensitivity profile that indicates possible application to trace analyte detection. The combination of trace analyte detection and high-efficiency analyte separation in modular microfluidic systems places applications, such as near real-time, single cell small molecule secretion monitoring, within reach.
" }, { "name": "Mitrani-Reiser, Judith", "degree": "PhD", "year": "2007", "title": "An Ounce of Prevention: Probabilistic Loss Estimation for Performance-Based Earthquake Engineering", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282007-233606", "creators": [ { "name": { "family": "Mitrani-Reiser", "given": "Judith" }, "id": "Mitrani-Reiser-Judith", "orcid": "0000-0002-3985-6848", "display_name": "Mitrani-Reiser, Judith" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Porter", "given": "Keith A." }, "id": "Porter-K-A", "role": "member", "display_name": "Porter, Keith A." }, { "name": { "family": "Comerio", "given": "Mary C." }, "id": "Comerio-M-C", "role": "member", "display_name": "Comerio, Mary C." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/JXPV-1Q19", "abstract": "Performance-based earthquake engineering (PBEE) is a methodology that incorporates desired performance levels into the design process. Performance in PBEE can be expressed in economic terms, or as elapsed downtime, or in terms of life and building safety objectives. These performance objectives are relevant to various types of stakeholders. They should be addressed in building loss estimation procedures because after an earthquake, the repair cost will not be the only \"loss\" suffered by building stakeholders. In a sizeable earthquake, there will likely also be some losses due to business interruption during the repair effort, building closure taken as a post-earthquake safety precaution, and human casualties caused by building failures during the seismic event.
\r\n\r\nAn analytical approach for PBEE is developed and implemented to evaluate the performance of a new reinforced-concrete moment-frame office building. The PBEE approach used is consistent with the Pacific Earthquake Engineering Research (PEER) center?s modular framework, which is divided into four core analytical stages: hazard analysis, structural analysis, damage analysis, and loss analysis. Future losses of the building are uncertain because they depend on uncertain quantities, such as the shaking intensity of the earthquake, the mechanical properties of the facility, and the uncertain damageability and unit repair costs of the facility. An analytical approach is developed to propagate these uncertainties. This work presents the mathematical foundation for the damage and loss analyses, and a description of its implementation into software. The results from running this software on multiple design variants of the building are presented, including seismic vulnerabilities as a function of shaking intensity and corresponding expected annual losses.
\r\n\r\nThe methodology developed and implemented in this work estimates the direct economic losses due to repair costs as well as two types of indirect economic losses, those produced by building downtime and by human fatalities. A procedure for a virtual inspection is used to assess the safety of buildings, based on current damage assessment guidelines. Additionally, a model is established to estimate human fatalities caused by the partial and global collapse of buildings, using probabilities of fatality based on relevant empirical data and the results of the virtual inspection process. A simplified methodology is presented for estimating building downtime after seismic events, including mobilization delays before construction begins and the elapsed time needed to repair damaged building components. The losses due to downtime and human fatalities are then added to the building repair cost in order to estimate the total building loss, which is then used to perform a benefit-cost analysis of the benchmark building. The work presented, is to our knowledge, the most faithful attempt to estimate the main decision variables (termed the 3 Ds?dollars, deaths, and downtime), proposed by PEER and the ATC-58 Project for performance assessment of structures.
\r\n" }, { "name": "Morris, Bradford S.", "degree": "PhD", "year": "2007", "title": "Charge-Exchange Collision Dynamics and Ion Engine Grid Geometry Optimization", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282007-154751", "creators": [ { "name": { "family": "Morris", "given": "Bradford S." }, "id": "Morris-Bradford-S", "display_name": "Morris, Bradford S." } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Johnson", "given": "Lee K." }, "id": "Johnson-L-K", "role": "member", "display_name": "Johnson, Lee K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W996-M220", "abstract": "The development of a new three-dimensional model for determining the absolute energy distribution of ions at points corresponding to spacecraft surfaces to the side of an ion engine is presented. The ions resulting from elastic collisions, both charge-exchange (CEX) and direct, between energetic primary ions and thermal neutral xenon atoms are accounted for. Highly resolved energy distributions of CEX ions are found by integration over contributions from all points in space within the main beam formed by the primary ions.
\r\n\r\nThe sputtering rate due to impingement of these ions on a surface is calculated. The CEX ions that obtain significant energy (10 eV or more) in the collision are responsible for the majority of the sputtering, though this can depend on the specific material being sputtered. In the case of a molybdenum surface located 60 cm to the side of a 30 cm diameter grid, nearly 90% of the sputtering is due to the 5% of ions with the highest collision exit energies. Previous models that do not model collision energetics cannot predict this. The present results agree with other models and predict that the majority of the ion density is due to collisions where little to no energy is transferred.
\r\n\r\nThe sputtering model is combined with a grid-structure model in an optimization procedure where the sputtering rate at specified locations is minimized by adjustment of parameters defining the physical shape of the engine grids. Constraints are imposed that require that the deflection of the grid under a specified load does not exceed a maximum value, in order to ensure survivability of the grids during launch. To faciliate faster execution of the calculations, simplifications based on the predicted behavior of the CEX ions are implemented. For diametrically opposed sputtering locations, a rounded barrel-vault shape reduces the expected sputtering rate by up to 30% in comparison to an NSTAR-shaped grid.
" }, { "name": "Motahari, Seyed-Maziar", "degree": "PhD", "year": "2007", "title": "Study of Constitutive Behavior of Ferroelectrics via Self-Consistent Modeling and Neutron Diffraction", "advisor": "Ustundag, Ersan; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252007-154233", "creators": [ { "name": { "family": "Motahari", "given": "Seyed-Maziar" }, "id": "Motahari-Seyed-Maziar", "display_name": "Motahari, Seyed-Maziar" } ], "advisors": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "advisor", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "co-advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "member", "display_name": "Ustundag, Ersan" } ], "option_major": [ "mecheng" ], "doi": "10.7907/55PX-GT55", "abstract": "The central goal of this study is to develop a reliable self-consistent model to describe the constitutive behavior of polycrystalline ferroelectrics and to predict their lattice strain and texture evolution. Starting with the model developed by Huber et al. formulations and refinements were added to increase both the functionality and the accuracy of the model\u2019s results. These refinements include methods for calculating lattice strain, tracking the number of domains contributing to diffraction patterns, locking the domain switching at a specified level, inputting initial grain orientation distribution, and a correction for a major flaw in the previous model: the phenomenon of reverse domain switching.
\r\n\r\nTo validate the model\u2019s predictions, in-situ neutron diffraction experiments were conducted on polycrystalline BaTiO\u2083 under uniaxial compression. It was found that the data analysis required a close inspection due to lattice strain anisotropy and leading to a systematic study of different analysis methods: the single peak method, the regular whole-pattern Rietveld method (with no strain anisotropy), and the improved Rietveld method which offers limited strain anisotropy analysis. The latter was judged to be the most appropriate for ferroelectrics and it was further improved by new formulations to permit lattice strain anisotropy analysis for tetragonal and hexagonal crystal structures.
\r\n\r\nThe comparison of model predictions and diffraction data from BaTiO\u2083 yielded the following observations: (i) domain switching starts at very low stresses (<\t 10 MPa) and proceeds gradually; (ii) domains with c-axes closer to the loading axis start switching earlier and experience more switching; (iii) lattice-plane-specific (hkl) strains, with the exception of (111), exhibit apparent hardening after switching starts. The level of agreement between the model and the experimental data was satisfactory, particularly considering the relative simplicity of the model. Keeping in mind the basic assumptions present in the model, it can be a useful analytical tool in the study of ferroelectric constitutive behavior when combined with diffraction experiments.
" }, { "name": "Mouton, Christopher Andre", "degree": "PhD", "year": "2007", "title": "Transition Between Regular Reflection and Mach Reflection in the Dual-Solution Domain", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01052007-125557", "creators": [ { "name": { "family": "Mouton", "given": "Christopher Andre" }, "id": "Mouton-Christopher-Andre", "display_name": "Mouton, Christopher Andre" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "role": "member", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TEA0-Q468", "abstract": "A study of the shock-reflection domain for steady flow is presented. Conditions defining boundaries between different possible shock-reflection solutions are given, and where possible, simple analytic expressions for these conditions are presented. A new, more accurate estimate of the steady-state Mach stem height is derived based on geometric considerations of the flow. In particular, the location of the sonic throat through which the subsonic convergent flow behind the Mach stem is accelerated to divergent supersonic flow is considered. Comparisons with previous computational and experimental work show that the theory presented in this thesis more accurately predicts the Mach stem height than previous theories. The Mach stem height theory is generalized to allow for a moving triple point. Based on this moving triple point theory, a Mach stem growth rate theory is developed. This theory agrees well with computational and experimental results. Numerical computations of the effects of water vapor disturbances are also presented. These disturbances are shown to be sufficient to cause transition from regular reflection to Mach reflection in the dual-solution domain. These disturbances are also modeled as a simple energy deposition on one of the wedges, and an estimate for the minimum energy required to cause transition is derived.
\r\n\r\nExperimental results using an asymmetric wedge configuration in the Ludwieg tube facility at the California institute of Technology are presented. A Mach 4.0 nozzle was designed and built for the Ludwieg tube facility. This Mach number is sufficient to provide a large dual-solution domain, while being small enough not to require preheating of the test gas. The test time of the facility is 100ms, which requires the use of high-speed cinematography and a fast motor to rotate one of the two wedges. Hysteresis in the transition between regular to Mach reflection was successfully demonstrated in the Ludwieg tube facility. The experiments show that regular reflection could be maintained up to a shock angle approximately halfway between the von Neumann condition and the detachment condition.
\r\n\r\nEnergy deposition studies were performed using an Nd:YAG laser. Triggering transition in this manner is found to depend on the location of the energy deposition. This finding is consistent with the numerical work presented in this thesis. Experiments were also performed to measure the Mach stem height and its growth rate. These results are compared with the theoretical estimates presented in this thesis. Excellent agreement between the steady-state Mach stem height and the theoretical estimates is seen. Comparisons of Mach stem growth rate with theoretical estimates show significant differences, but do show good agreement regarding the time required to reach the steady-state height.
" }, { "name": "Muto, Matthew Mokihana", "degree": "PhD", "year": "2007", "title": "Application of Stochastic Simulation Methods to System Identification", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222007-152843", "creators": [ { "name": { "family": "Muto", "given": "Matthew Mokihana" }, "id": "Muto-Matthew-Mokihana", "display_name": "Muto, Matthew Mokihana" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Duron", "given": "Ziyad H." }, "id": "Duron-Z-H", "role": "member", "display_name": "Duron, Ziyad H." } ], "option_major": [ "civileng" ], "doi": "10.7907/9JKZ-Z422", "abstract": "Reliable predictive models for the response of structures are a necessity for many branches of earthquake engineering. However, the process of choosing an appropriate class of models to describe a system, known as model-class selection, and identifying the specific predictive model based on available data, known as system identification, is difficult. Variability in material properties, complex constitutive behavior, uncertainties in the excitations caused by earthquakes, and limited constraining information make system identification an ill-conditioned problem. In addition, model-class selection is not trivial, as it involves balancing predictive power with simplicity.
\r\n\r\nThese problems of system identification and model-class selection may be addressed using a Bayesian probabilistic framework that provides a method for combining prior knowledge of a system with measured data and for choosing between competing model classes.
\r\n\r\nSimilar approaches have been used in the field of system identification, but these methods (referred to as asymptotic-approximation-based methods) often focus on the model defined by the set of most plausible parameter values and have difficulty dealing with ill-conditioned problems, where there may be many models with high plausibility. It is demonstrated here that ill-conditioned problems in system identification and model-class selection can be effectively addressed using stochastic simulation methods.
\r\n\r\nThis work focuses on the application of stochastic simulation to updating and comparing model classes in problems of: (1) development of empirical ground motion attenuation relations, (2) structural model updating using modal data for the purposes of structural health monitoring, and (3) identification of hysteretic structural models, including degrading models, from seismic structural response.
\r\n\r\nIn cases where asymptotic approximation-based methods are appropriate, the results obtained using stochastic simulation show good agreement with results from asymptotics. For cases involving ill-conditioned problems based on simulated data, stochastic simulation methods are successfully applied to obtain results in situations where the use of asymptotics is infeasible. Finally, preliminary studies using stochastic simulation to identify a deteriorating hysteretic model with sparse real data from a structure damaged in an earthquake show that the high-plausibility models demonstrate behavior consistent with the observed damage, indicating that there is promise in applying these methods to ill-conditioned problems in the real world.
" }, { "name": "Mysore, Shreesh Pranesh", "degree": "PhD", "year": "2007", "title": "Structural Plasticity in Neuronal Networks", "advisor": "Schuman, Erin Margaret; Quartz, Steven R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102006-021149", "creators": [ { "name": { "family": "Mysore", "given": "Shreesh Pranesh" }, "id": "Mysore-Shreesh-Pranesh", "orcid": "0000-0002-7781-8252", "display_name": "Mysore, Shreesh Pranesh" } ], "advisors": [ { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "advisor", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "co-advisor", "display_name": "Quartz, Steven R." } ], "committee": [ { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "chair", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "co-chair", "display_name": "Quartz, Steven R." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/EVYW-EY02", "abstract": "Neuronal networks are established during development by the formation of connections (synapses) between neurons. Once formed, these synapses undergo experience-dependent modifications throughout the lifespan of the animal (synaptic plasticity). Additionally, the connectivity pattern itself can be modified in an activity-dependent manner (architectural plasticity). Changes in the structure of synapses, neurons, and networks \u2013 collectively called structural plasticity \u2013 are the predominant mechanisms for changes in the network architecture in the brain. Structural plasticity forms the focus of this thesis and motivates both the experimental and the computational modeling work reported here. With experiments, we look in detail at one form of structural plasticity, namely dendritic spine dynamics. We develop a unified approach to characterize motility and use this both to detect subtle forms of structural dynamics and to uncover novel phenomena in it. We show that disruption of N-cadherin, a synaptic adhesion molecule, causes spines to first be more motile and to shrink in length, and then to be lost. Along with this, synapses are eliminated as well. For the first time, we show that early structural changes can predict later synapse elimination, suggesting that early dynamics may be readouts for future changes in the neural wiring diagram. We also address some of the related mechanistic questions. In our computational modeling work, we address structural plasticity at the next higher scale of complexity. We provide a novel, neurobiologically plausible, and experimentally consistent explanation for how changes in visual experience may produce axogenesis and the formation of new synaptic pathways in the barn owl auditory localization system. We discuss implications of architectural plasticity to the representational power of networks and explore links with statistical learning theory. Taken together, our work argues that architectural changes are a powerful and indispensable form of neural plasticity and sheds new light on the mechanisms of structural plasticity in the brain, thereby contributing to our understanding of learning and memory." }, { "name": "Nasiraei Moghaddam, Abbas", "degree": "PhD", "year": "2007", "title": "Measurement and Analysis of Structure and Function of Myocardium in Embryonic and Adult Heart", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012007-143736", "creators": [ { "name": { "family": "Nasiraei Moghaddam", "given": "Abbas" }, "id": "Nasiraei-Moghaddam-Abbas", "orcid": "0000-0002-6423-3458", "display_name": "Nasiraei Moghaddam, Abbas" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Wen", "given": "Han" }, "id": "Wen-Han", "role": "member", "display_name": "Wen, Han" }, { "name": { "family": "Tyszka", "given": "Julian Michael" }, "id": "Tyszka-J-M", "role": "member", "display_name": "Tyszka, Julian Michael" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/RQE4-MA23", "abstract": "Congestive heart failure is the most common and costly medical problem in the modern world. Current disease management procedures are mostly limited to treating the symptoms of this disease. The effective treatment, however, needs a deep understanding of the normal structure-function relationships of the myocardium.
\r\n\r\nThe research of this study is concerned with the relationship between the structure and function of the myocardium in both embryonic and adult hearts. This relationship was investigated through an in-depth analysis of the spatial distribution of the local contractile function in the myocardium. The analysis is based on the heart kinematics captured through the tissue tracking of the myocardium.
\r\n\r\nAdvanced imaging techniques, such as DENSE MRI and confocal microscopy, were used for tissue tracking in adult and embryonic myocardium, respectively. The acquired data, together with continuum mechanics concepts and computational methods, were exploited in a Lagrangian framework to measure appropriate characteristic parameters that describe local contribution of the myocardium in its global functionality.
\r\n\r\nThis method resulted in novel understandings of the local and global functions in each of these hearts. In particular, it was observed in the adult heart that the left ventricle functionality is not uniformly distributed. Instead, the regions with higher effect on the pumping process form a helical band which wraps around the heart. This is the first time that such a myocardium macro-structure, which is supported by the established histological evidence, is revealed from its function in a beating heart. It can be considered as a landmark in connecting the structure and function of the heart through imaging. Furthermore, the compatibility of this model with microscopic observations about the fiber direction is investigated.
\r\n \r\nA similar approach was applied to embryonic zebrafish heart with GFP labeled myocytes. It identified distribution of regions that play an active role in functionality of the heart tube. This new understanding has provided better insights into the pumping mechanism of the embryonic heart.
" }, { "name": "Natarajan, Arun Sridhar", "degree": "PhD", "year": "2007", "title": "Millimeter-Wave Phased Arrays in Silicon", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012007-130844", "creators": [ { "name": { "family": "Natarajan", "given": "Arun Sridhar" }, "id": "Natarajan-Arun-Sridhar", "display_name": "Natarajan, Arun Sridhar" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "D'Addario", "given": "Larry R." }, "id": "D'Addario-L-R", "role": "member", "display_name": "D'Addario, Larry R." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SGZC-FD54", "abstract": "Integration of mm-wave multiple-antenna systems on silicon-based processes enables complex, low-cost systems for high-frequency communication and sensing applications. While individual silicon devices struggle to achieve the same performance as III-V semiconductor-based transistors at mm-wave frequencies, the benefits of integration, such as good component matching and near-zero incremental device cost, can be leveraged to achieve good system performance. This dissertation presents different techniques and architectures for integrating mm-wave phased arrays on commercial silicon process technologies by demonstrating phased-array transmitters and receivers at 24GHz, 60GHz, and 77GHz, in CMOS and SiGe BiCMOS processes.
\r\n\r\nInitially, the tradeoffs of high-frequency systems are discussed in the context of Shannon capacity and the benefits of integrating phased arrays at such high frequencies are discussed in detail. An analysis of the output noise in a phased-array receiver in the presence of antenna coupling and input noise correlation is carried out and measurements on a discrete two-element array demonstrate the dependence of output noise on the phase-shift setting.
\r\n\r\nThe design of the first fully-integrated 24GHz phased-array transmitter using mainly 0.18[mu]m CMOS transistors is described. The four-element array adopts a centralized LO-path phase-shifting approach using a multi-phase VCO. The on-chip 19.2GHz VCO generates 16 equally spaced LO phases leading to 7 degree beam resolution for radiation normal to the array. The transmitter includes four on-chip CMOS power amplifiers, with outputs matched to 50 Ohms, that are each capable of generating up to 14.5dBm of output power at 24GHz. The array achieves a peak-to-null ratio of 23dB with four elements active and can support data rates of 500Mb/s on each channel (with BPSK modulation) while occupying 6.8mm x 2.1mm of die area.
\r\n\r\nA high-resolution local LO-path phase-shifting architecture is presented as part of the first fully-integrated 77GHz phased-array transceiver in a SiGe BiCMOS process. The SiGe transceiver includes four transmit and four receive elements (including 77GHz LNA and PA), along with the LO frequency generation and distribution circuitry. The local LO-path phase-shifting scheme enables a robust distribution network that scales well with increasing frequency and/or number of elements, while providing high-resolution phase shifts. Each transmit element of the heterodyne transmitter generates +12.5dBm of output power at 77GHz, with a bandwidth of 2.5GHz leading to a four-element EIRP of 24.5dBm. Each on-chip PA has a maximum saturated power of +17.5dBm at 77GHz while the on-chip VCO achieves a phase noise of -95dBc/Hz@1MHz offset at 54GHz. The phased-array performance is measured using an internal test option and achieves 12dB peak-to-null ratio with two transmit and receive elements active.
\r\n\r\nWhile the 24GHz and 77GHz array are multiple-input single-output systems, higher-order phase-shifting and combining techniques can be used to achieve arrays with multiple outputs, with beams focused on different directions concurrently. Toward this end, a 60GHz bidirectional RF-combined phased array front-end is implemented in SiGe BiCMOS, using a hybrid parallel/series phase-shift approach that reduces the requirements of the on-chip phase shifters, enabling RF signal combining. The four-element array enables simultaneous illumination of two angles of incidence and includes amplitude control, as well as continuous phase adjustment. The front-end has a noise figure lower than 6.9dB at 60GHz and the array achieves full spatial coverage with peak-to-null ratio higher than 25dB. The four-element front-end consumes 265mW and occupies 4.6mm2 of die area.
" }, { "name": "Polsenberg Thomas, AnnMarie", "degree": "PhD", "year": "2007", "title": "Exploration into the Feasibility of Underwater Synthetic Jet Propulsion", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-09252006-134742", "creators": [ { "name": { "family": "Polsenberg Thomas", "given": "AnnMarie" }, "id": "Polsenberg-Thomas-AnnMarie", "display_name": "Polsenberg Thomas, AnnMarie" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "role": "co-chair", "display_name": "Dabiri, John O." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." } ], "option_major": [ "mecheng" ], "doi": "10.7907/72SZ-T823", "abstract": "This thesis explores the feasibility of using synthetic jet actuators for the propulsion of small underwater vehicles. This work was inspired by the widespread use of pusatile jet propulsion by sea creatures such as squid, salp, and jellyfish. The jets created by these animals utilize vortex rings for thrust production. A method for creating similar vortex ring-based jets is the use of synthetic, or zero net mass flux, jets. These jets, which form a jet structure through the alternating sucking and blowing of fluid through a single orifice, have previously been investigated for the utility in air flow control.
\r\n\r\nThe design, construction, and testing of aquatic synthetic jet prototypes is presented. Force measurement and flow visualization experiments are performed on these jets to gain an understanding of the forces and flow structures produced. The flow visualizations confirm the outflow vortex ring observations reported previously in the literature and present the first images of vortex ring formation inside the synthetic jet chamber. A new phenomenon, that of self-induced coflow upstream of the jet orifice, is discussed. The force measurements present confirmation that a net thrust is produced by the jets and give insight to the relationship between jet forcing parameters (such as frequency) and the resulting thrust. An automated genetic algorithmic approach to optimizing the thrust for a given jet geometry is also presented and tested.
\r\n\r\nUsing the results of these experiments I propose a model for synthetic jet thrust. This model asserts that there are three force producing components to the flow: orifice inflow, orifice outflow, and a self-induced coflow. The contribution of each of these components is derived and compared with experimental results.
\r\n\r\nIncluded at the end of this thesis is a preliminary study into possible vehicle architecture for the utilization of synthetic jet thrusters.
" }, { "name": "Poon, Joyce Kai See", "degree": "PhD", "year": "2007", "title": "Active and Passive Coupled-Resonator Optical Waveguides", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242007-105741", "creators": [ { "name": { "family": "Poon", "given": "Joyce Kai See" }, "id": "Poon-Joyce-Kai-See", "display_name": "Poon, Joyce Kai See" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MX8K-9V82", "abstract": "Coupled-Resonator Optical Waveguides (CROWs) are chains of resonators in which light propagates by virtue of the coupling between the resonators. The dispersive properties of these waveguides are controllable by the inter-resonator coupling and the geometry of the resonators. If the inter-resonator coupling is weak, light can be engineered to propagate slowly in these structures. The small group velocities possible in CROWs may enable applications in and technologies for optical delay lines, interferometers, buffers, nonlinear optics, and lasers.
\r\n\r\nThis thesis reports on achieving and controlling the optical delay in passive and active CROWs. Both theoretical and experimental results are presented. Transfer matrices, tight-binding models, and coupled-mode approaches are developed to analyze and design a variety of coupled resonator systems in the space, frequency, and time domains. Although each analytical method is fundamentally different, in the limit of weak inter-resonator coupling these approaches are consistent with each other. From these formalisms, simple expressions for the delay, loss, bandwidth, and a figure of merit are derived to compare the performance of CROW delay lines. Using a time-domain tight-binding model, we examine the resonant gain enhancement and spontaneous emission noise in amplifying CROWs to find that the net amplification of a propagating wave does not always vary with the group velocity but instead depends on the termination and excitation of the CROW.
\r\n\r\nCROWs in the form of high-order (> 10) weakly coupled passive polymer microring resonators were fabricated and measured. The measured transmission, group delay, and dispersive properties of the CROWs agreed with the theoretical results. Delays in excess of 100 ps and slowing factors of about 25 over bandwidths of about 20 GHz were observed. The main limitation of the passive CROWs was the optical losses. To overcome the losses and to enable electrical integration, we demonstrated active CROWs in the form of current injection InP-InGaAsP Fabry-Perot laser arrays. Even though the losses could be completely compensated, the transmission spectra and signal-to-noise ratio depended strongly on the injection current and resonator position. The signal-to-noise ratio degraded rapidly away from the input. Our results highlight possible avenues to operate laser arrays as loss-compensated or amplifying CROWs.
" }, { "name": "Pracko, Steven Edmund", "degree": "PhD", "year": "2007", "title": "Laser Induced Fluorescence Measurements of Spheromak Plasmas", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312006-114659", "creators": [ { "name": { "family": "Pracko", "given": "Steven Edmund" }, "id": "Pracko-Steven-Edmund", "display_name": "Pracko, Steven Edmund" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/KHG6-DH51", "abstract": "This thesis reports the results of investigations intended to further the understanding of the formation and evolution of spheromak plasmas via the use of laser induced fluorescence (LIF) measurements of laboratory plasmas. LIF is a spectroscopic technique in which laser radiation induces atomic energy level transitions in a target species within a specified volume.
\r\n\r\nLIF experiments have been performed on Ar II plasmas produced in a spheromak confinement configuration. The term spheromak refers to a class of plasmas whose internal magnetic fields satisfy a particular topology, the details of which are presented as they relate to the formation and evolution of plasmas generated in this work. LIF measurements made on these spheromak plasmas suggest that 20 eV Ar II ions have been produced at densities of 10\u00b2\u00b9 m\u207b\u00b3.
\r\n\r\nLIF experiments studying plasmas generated by a second spheromak device are discussed. The planar electrodes in this new device produce spheromaks with a distinct central column of plasma whose evolution is related to [alpha], an important parameter in the theory of force-free Taylor states, where the internal magnetic field B of the plasma satisfies \u2207xB=\u03b1B. Experiments have been conducted with the probing laser oriented both parallel to and perpendicular to the axis of symmetry of the spheromak. Ion parameter estimates calculated from LIF measurements are found to agree with those obtained from other diagnostics, including passive spectroscopy and high speed photography.
\r\n\r\nDetails are presented concerning the design and operation of a portable device capable of generating plasma discharges. The motivation for the construction of this device is to provide a convenient plasma source that may be used to calibrate the laser and photodetection systems used in LIF experiments.
\r\n\r\nThe Ar II ion temperature and density values reported in this work are believed to be among the first such measurements performed on plasmas produced in a spheromak confinement configuration. Suggestions are offered for several modifications that could be made to the experiment that might serve to increase the amount of information that can be gained during each plasma discharge and thus augment the future value of the experiment.
" }, { "name": "Rao, Chaitanya Kumar", "degree": "PhD", "year": "2007", "title": "Asymptotic Analysis of Wireless Systems with Rayleigh Fading", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252007-122857", "creators": [ { "name": { "family": "Rao", "given": "Chaitanya Kumar" }, "id": "Rao-Chaitanya-Kumar", "display_name": "Rao, Chaitanya Kumar" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/YYD6-VP11", "abstract": "This thesis looks at ways to improve either the reliability or the rate at which we can successfully transmit information over Rayleigh-fading wireless communication channels.
\r\n\r\nWe study four wireless schemes, the first in the low signal-to-noise ratio (SNR) regime, the remaining three at high SNR. The analysis provides insights that apply to more general SNRs.
\r\n\r\nFirstly we investigate a point-to-point multiple antenna link at low SNR. At low SNR channel estimates can be unreliable, and therefore we assume the channel is unknown to both transmitter and receiver. Adopting a block-fading model we find the mutual information between transmitter and receiver up to second order in the SNR. The expression is valid for input distributions with regular behavior of fourth- and sixth-order moments, in particular most practical schemes. Subject to input-signal constraints, we determine the optimal signaling to maximize this mutual information.
\r\n\r\nWe undertake high SNR analysis by finding the diversity-multiplexing gain trade-off of three further wireless systems with fading. Using techniques from existing works we find the optimal diversity-multiplexing gain trade-off for an M by N multiple antenna system with R single antenna relays. This uses a two-stage protocol in which the source first transmits to relays, then the relays multiply their received signal by a unitary matrix, before forwarding the result to the receiver. The trade-off is found to be equal to that of a multiple-input multiple-output (MIMO) link with R transmit and min{M,N} receive antennas.
\r\n\r\nNext we consider a network with two source-destination pairs (an interference channel) and establish relationships between the rate and diversity achievable by certain schemes. We show through two more schemes how cooperation amongst the nodes achieves a higher diversity, but with a reduced rate of the system. These schemes can easily be generalized from two to m source-destination pairs.
\r\n\r\nA final scheme is considered where n relay nodes are added to the m source-destination pairs, which act to cancel interference in an aim to increase diversity. The outage behavior of this scheme is analyzed and it is shown that for sufficiently many relay nodes, a diversity linear in n can be obtained.
" }, { "name": "Reiser, Michael Bernard", "degree": "PhD", "year": "2007", "title": "Visually Mediated Control of Flight in Drosophila: Not Lost in Translation", "advisor": "Dickinson, Michael H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082007-033253", "creators": [ { "name": { "family": "Reiser", "given": "Michael Bernard" }, "id": "Reiser-Michael-Bernard", "orcid": "0000-0002-4108-4517", "display_name": "Reiser, Michael Bernard" } ], "advisors": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "advisor", "display_name": "Dickinson, Michael H." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cns" ], "doi": "10.7907/YYSN-7C82", "abstract": "Flying insects exhibit stunning behavioral repertoires that are largely mediated by the visual control of flight. For this reason, presenting a controlled visual environment to tethered insects has been and continues to be a powerful tool for studying the sensory control of complex behaviors. The work presented in this dissertation concerns several robust behavioral responses exhibited by Drosophila that shed light on some of the challenges of visual navigation. To address questions of visual flight control in Drosophila, a modular display system has been designed and has proven to be a robust experimental instrument. The display system has enabled the wide variety of experimental paradigms presented in the thesis.
\r\n\r\nMuch is known about the responses of tethered Drosophila to rotational stimuli. However, the processing of the more complex patterns of motion that occur during translatory flight is largely unknown. Recent experimental results have demonstrated that Drosophila turn away from visual patterns of expansion. However, the avoidance of expansion is so vigorous, that flies robustly orient towards the focus of contraction of a translating flow field. Much of the effort documented in this thesis has sought to explain this paradox.
\r\n\r\nThe paradox has been largely resolved by several significant findings. When undergoing flight directed towards a prominent object, Drosophila will tolerate a level of expansion that would otherwise induce avoidance. The expansion-avoidance behavior is also critically dependent on the speed of image motion; in response to reduced speeds of expansion, Drosophila exhibit a centering response in which they steer towards the focus of expansion by balancing the image motion seen by both eyes. Taken together, these behaviors contribute to a model of Drosophila's visual flight control as emerging from multiple behavioral modules that operate concurrently.
\r\n\r\nSimple computational models of Drosophila's visual system are used to demonstrate that the experimental results arrived at by doing psychophysics on tethered animals actually yield sensible navigation strategies. This final component of the thesis documents an effort to close the feedback loop around the experimenter, by using computational models of Drosophila behavior to constrain the design of future experiments.
" }, { "name": "Richardson, Christine Esber", "degree": "PhD", "year": "2007", "title": "Low-Temperature Hot-Wire Chemical Vapor Deposition of Epitaxial Films for Large-Grained Polycrystalline Photovoltaic Devices", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-07052006-123702", "creators": [ { "name": { "family": "Richardson", "given": "Christine Esber" }, "id": "Richardson-Christine-Esber", "display_name": "Richardson, Christine Esber" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/GG0F-1775", "abstract": "Large-grained polycrystalline silicon thin-films on low-cost substrates are an interesting area of research for photovoltaic devices. Such devices, with grain sizes larger than the thickness of the cell, have the potential to achieve multicrystalline-like efficiencies of 15%, but at a much lower cost by taking advantage of thin-film manufacturing techniques. In this thesis, low-temperature epitaxial growth, by hot-wire (or catalytic) chemical vapor deposition, is investigated for the epitaxial thickening of large-grained polycrystalline silicon templates formed by metal-induced crystallization on low-cost substrates. Low-temperature hot-wire chemical vapor deposition allows for the deposition of epitaxial silicon with polycrystalline breakdown and with open-circuit voltages close to that of monocrystalline silicon. This is possible due to the incorporation of hydrogen into the silicon lattice, at temperatures below 350\u00b0C, for internal surface and defect passivation. In addition with hot-wire chemical vapor deposition, the critical epitaxial thickness actually increases, with a decrease in the substrate temperature down to temperatures of 270\u00b0C. Epitaxial growth of 5.5 micron thick films at 300\u00b0C and twinned epitaxial silicon growth of 6.8 micron thick films at 230\u00b0C have been achieved, along with arbitrarily thick crystalline films at low temperatures. Since epitaxial and high-quality crystalline silicon can be deposited at such low deposition temperatures, low-cost substrates, such as ordinary soda lime glass and many polymers are possible. In order to work towards achieving an epitaxially-thickened large-grained polycrystalline device, this work studies the mechanisms that lead to epitaxial growth during hot-wire chemical vapor deposition on silicon (100) substrates under various growth regimes, examines the surface evolution of crystalline thin-films grown via hot-wire chemical vapor deposition and their growth mechanisms (including the unusual rough epitaxial growth and arbitrarily thick crystalline films at low temperatures), and concludes by presenting the optical and electrical characteristics of these films and their resultant devices. This thesis demonstrates that low-temperature epitaxial silicon growth by hot-wire chemical vapor deposition is a promising material for low-cost thin-film silicon photovoltaic devices." }, { "name": "Rubel, Michael Thomas", "degree": "PhD", "year": "2007", "title": "A Theory of Stationarity and Asymptotic Approach in Dissipative Systems", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122007-114557", "creators": [ { "name": { "family": "Rubel", "given": "Michael Thomas" }, "id": "Rubel-Michael-Thomas", "display_name": "Rubel, Michael Thomas" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VWDE-GB16", "abstract": "The approximate dynamics of many physical phenomena, including turbulence, can be represented by dissipative systems of ordinary differential equations. One often turns to numerical integration to solve them. There is an incompatibility, however, between the answers it can produce (i.e., specific solution trajectories) and the questions one might wish to ask (e.g., what behavior would be typical in the laboratory?) To determine its outcome, numerical integration requires more detailed initial conditions than a laboratory could normally provide. In place of initial conditions, experiments stipulate how tests should be carried out: only under statistically stationary conditions, for example, or only during asymptotic approach to a final state. Stipulations such as these, rather than initial conditions, are what determine outcomes in the laboratory.
\r\n\r\nThis theoretical study examines whether the points of view can be reconciled: What is the relationship between one's statistical stipulations for how an experiment should be carried out--stationarity or asymptotic approach--and the expected results? How might those results be determined without invoking initial conditions explicitly?
\r\n\r\nTo answer these questions, stationarity and asymptotic approach conditions are analyzed in detail. Each condition is treated as a statistical constraint on the system--a restriction on the probability density of states that might be occupied when measurements take place. For stationarity, this reasoning leads to a singular, invariant probability density which is already familiar from dynamical systems theory. For asymptotic approach, it leads to a new, more regular probability density field. A conjecture regarding what appears to be a limit relationship between the two densities is presented.
\r\n\r\nBy making use of the new probability densities, one can derive output statistics directly, avoiding the need to create or manipulate initial data, and thereby avoiding the conceptual incompatibility mentioned above. This approach also provides a clean way to derive reduced-order models, complete with local and global error estimates, as well as a way to compare existing reduced-order models objectively.
\r\n\r\nThe new approach is explored in the context of five separate test problems: a trivial one-dimensional linear system, a damped unforced linear oscillator in two dimensions, the isothermal Rayleigh-Plesset equation, Lorenz's equations, and the Stokes limit of Burgers' equation in one space dimension. In each case, various output statistics are deduced without recourse to initial conditions. Further, reduced-order models are constructed for asymptotic approach of the damped unforced linear oscillator, the isothermal Rayleigh-Plesset system, and Lorenz's equations, and for stationarity of Lorenz's equations.
" }, { "name": "Ruglovsky, Jennifer Lynn", "degree": "PhD", "year": "2007", "title": "Correlating Microscopic Ferroelectric Properties and Macroscopic Thin Film Device Performance", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-02252007-153131", "creators": [ { "name": { "family": "Ruglovsky", "given": "Jennifer Lynn" }, "id": "Ruglovsky-Jennifer-Lynn", "display_name": "Ruglovsky, Jennifer Lynn" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/K3BG-N315", "abstract": "The relationship between thin film device performance and crystallographic microstructure is one of fundamental importance in materials science. Ferroelectric materials that show an electromechanical response via domain switching, such as the perovskites BaTiO3 and PbTiO3, are discussed. In this work, we focus on thin film MEMS actuators fabricated from four different ferroelectric thin film microstructures: poorly oriented, fiber textured, biaxially textured, and single crystal. The microscale properties of these thin film materials are characterized and correlated to macroscale mechanical device behavior.
\r\n\r\nWe have modeled each of these four microstructures to determine the effect of grain-scale crystallographic texture on device-scale electromechanical constants. The method enables the effective electromechanical properties to be obtained for a polycrystalline film via a self-consistent approach. Using this model, we show that most electromechanical constants depend primarily on the out-of-plane texture of the ferroelectric thin film.
\r\n\r\nWe have used surface micromachining to create free-standing bridge geometries in ferroelectric thin films of polycrystalline and biaxially textured PbTiO3. The material properties of these thin films are characterized with various techniques to confirm the texture at the grain scale. We have utilized a custom experimental apparatus that can apply a loading force to a single microdevice via magnetostatic interaction while measuring the resulting displacement. The force-displacement curves that we measure provide insight into the initial stress and modulus of our composite beam devices and the role of the underlying crystalline microstructure.
\r\n\r\nIn order to study cantilever actuators, BaTiO3 active layers are grown monolithically on SrRuO3 electrodes and devices are patterned via focused ion beam (FIB) milling exclusively or with a subsequent XeF2 etch. Using this fabrication method, we study cantilevers consisting of fiber, biaxial, and single crystalline microtextures. The cantilevers are actuated by applying a voltage across the active layer and the resulting displacement is measured via inspection with optical microscopy. We are able to relate the macroscopic device performance to the microscopic piezoelectric constants via multimorph calculations.
\r\n\r\nOur experiments show that ferroelectric thin film device performance may be enhanced by improving the underlying grain scale crystalline microstructure - from fiber to biaxial to single crystal texture.
" }, { "name": "Sansom, Elijah Bodhi", "degree": "PhD", "year": "2007", "title": "Experimental Investigation on Patterning of Anchored and Unanchored Aligned Carbon Nanotube Mats by Fluid Immersion and Evaporation", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05072007-114349", "creators": [ { "name": { "family": "Sansom", "given": "Elijah Bodhi" }, "id": "Sansom-Elijah-Bodhi", "display_name": "Sansom, Elijah Bodhi" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Troian", "given": "Sandra M." }, "id": "Troian-S-M", "orcid": "0000-0003-1224-6377", "role": "member", "display_name": "Troian, Sandra M." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/TJ7E-PK42", "abstract": "Pattern formation by capillary forces in a nanoscale system was studied experimentally. Densely packed, vertically aligned mats of order 100 microns in height comprised of 20 nm diameter multi-walled carbon nanotubes were fabricated and treated with various liquids. The carbon nanotubes deflected and rearranged under the action of surface tension as the liquids evaporated, and remained fixed once dried. The size analysis of the resulting patterns in these experiments and in the literature showed they are distributed within one standard deviation from the mean, and there are, in general, many more small sizes than large ones within a pattern.
\r\n\r\nPreexisting defects in the mats were found to play a significant role in the pattern formation process, both in this work and in the literature, whereas the properties of the specific liquid used and the height of the mats did not.
\r\n\r\nA novel method for anchoring the aligned mats within another material using spin-coating was developed. An anchored mat made in this way was successfully held in place even under the application of a 5.5 m/s water jet.
\r\n\r\nThe anchoring method allowed the first known investigation of the role of boundary conditions in this pattern formation process. Under identical experimental conditions to cases where patterns are formed in the unanchored mats, it was found that no pattern formation occurs in the anchored mats.
\r\n\r\nA population balance model based on conservation of area was applied to the pattern formation process, but sufficient details are lacking to make predictions.
\r\n\r\nThe anchoring method and its prevention of pattern formation is a very important finding, and is relevant to applications of the aligned mats, such as field emission displays, supercapacitors, tissue culture scaffolds, and friction drag reducing surfaces.
" }, { "name": "Schulman, Rebecca Beth", "degree": "PhD", "year": "2007", "title": "The Self-Replication and Evolution of DNA Crystals", "advisor": "Winfree, Erik", "url": "https://resolver.caltech.edu/CaltechETD:etd-04302007-164103", "creators": [ { "name": { "family": "Schulman", "given": "Rebecca Beth" }, "id": "Schulman-Rebecca-Beth", "orcid": "0000-0003-4555-3162", "display_name": "Schulman, Rebecca Beth" } ], "advisors": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "advisor", "display_name": "Winfree, Erik" } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Yurke", "given": "Bernard" }, "id": "Yurke-B", "role": "member", "display_name": "Yurke, Bernard" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Joyce", "given": "Gerald" }, "id": "Joyce-G", "role": "member", "display_name": "Joyce, Gerald" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "cns" ], "doi": "10.7907/3F8C-9D50", "abstract": "How life began is still a mystery. While various theories suggest that life began in deep sea volcanic vents or that a world where life consisted predominantly of RNA molecules preceded us, there is no hard evidence to give shape to the chain of events that led to cellular life.
\r\n\r\nPerhaps the fundamental enigma of our origins is how life began to self-replicate in such a way that evolution could produce Earth's \"endless forms most beautiful.\" With the exception of biological organisms, we have no examples of self-replicating, evolving chemical systems, despite an extensive research program with the goal of identifying them.
\r\n\r\nIn this thesis, I construct a chemical system that is capable of the most basic self-replication and evolution. The system uses no enzymes or biological sequences, can support and replicate a combinatorial genome, and is completely autonomous. There are no fundamental obstacles to the replication by this system of much more complex sequences or to open-ended evolution.
\r\n\r\nThe design of the system is inspired by the work of Graham Cairns-Smith, who has proposed that life began with clay. Clays are tiny layered crystals; some clay crystals can contain one of several different patterns of atoms or molecules in each layer. The choice of patterns for the layers could be viewed as a sort of genome: it would be copied as the clay grew, and if the crystal broke, each new piece would inherit its pattern from the old piece and could replicate it in the same manner. If some patterns of layers could grow and reproduce faster than other patterns, crystals with faster-growing patterns would be selected for.
\r\n\r\nInstead of the atoms or small molecules of which clay consists, I use molecules consisting of 4-6 interwoven, synthetic DNA strands called DNA tiles to construct crystals that replicate and evolve as Cairns-Smith imagined. While the choice of construction material was influenced by ease of use -- in contrast to clay crystals, DNA tile crystals have been previously characterized and are easy to crystallize and image in the laboratory -- the choice was fundamentally made because DNA tile monomers are programmable, allowing us to create novel crystal morphologies rationally.
\r\n\r\nThe crystals I construct, termed \"zig-zag ribbons\", contain a sequence of information (\"a genome\") in each row. Growth of the ribbon adds rows, one at time, each of which contain an arrangement of DNA tiles that encode the same information sequence as the previous row. Altering the set of \"tiles\" used to assemble ribbons allows us to alter the alphabets for and the permitted lengths of sequences that can be copied.
\r\n\r\nI describe how to design tile sets that can replicate genomes with different alphabets and the kind of sequence evolution that is in theory possible with some simple tile sets. Altering the tile set can not only change the kinds of sequences that may be replicated, it can also make growth and splitting more robust. I show how to make changes to the crystals' design to prevent errors during growth and splitting and to reduce the rate of spontaneous generation of new crystals.
\r\n\r\nIt has been previously shown that DNA tile crystallization can be used to perform universal computation; I show that in theory crystals that can compute can undergo open-ended evolution as they try to produce more and more complex programs to take advantage of available growth resources. This mechanism is simple enough to potentially observe in the laboratory in the near future. In experiments, I demonstrate a much more basic kind of replication and evolution, in which zig-zag ribbons maintain a preference for a certain width into a second generation.
\r\n\r\nThis work suggests that the concept of a self-replicating chemistry is closely related to the concept of a chemistry that can store information and compute. It is only by clearly understanding how chemistry can perform these latter tasks that we can hope to understand how self-replication and evolution can occur, and by implication, understand how life might have begun.
" }, { "name": "Smith Downey, Nicole V.", "degree": "PhD", "year": "2007", "title": "Soil Uptake of Molecular Hydrogen and Remote Sensing of Soil Freeze and Thaw", "advisor": "Randerson, James T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08182006-105638", "creators": [ { "name": { "family": "Smith Downey", "given": "Nicole V." }, "id": "Smith-Downey-Nicole-V", "display_name": "Smith Downey, Nicole V." } ], "advisors": [ { "name": { "family": "Randerson", "given": "James T." }, "id": "Randerson-J-T", "role": "advisor", "display_name": "Randerson, James T." } ], "committee": [ { "name": { "family": "Eiler", "given": "John M." }, "id": "Eiler-J-M", "role": "chair", "display_name": "Eiler, John M." }, { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "role": "member", "display_name": "Sessions, Alex L." }, { "name": { "family": "Randerson", "given": "James T." }, "id": "Randerson-J-T", "role": "member", "display_name": "Randerson, James T." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." } ], "option_major": [ "envreng" ], "doi": "10.7907/BXV8-HH61", "abstract": "Soils play a large role in the cycling of atmospheric trace gases and are an important component of the climate system. The bulk of my thesis was directed at the role of soils in the global molecular hydrogen (H\u2082) cycle. I conducted field measurements of H\u2082 uptake in three Southern California ecosystems, and found that both the diffusion of H\u2082 into soils and the distribution of biological activity with depth controlled uptake rates at the surface. I then moved into the laboratory, where I mapped out the temperature and moisture controls on the biological uptake of H\u2082 in both desert and boreal forest soils. These experiments yielded simple relationships between moisture, temperature, and uptake rate, which I then used to constrain H\u2082 uptake by soils in a mechanistic model. The model is based on the 1D diffusion equation with a sink term, and is driven by a combination of remote sensing products and land surface modeling output. I calculated a mean annual soil H\u2082 sink of 67.3 \u00b1 5.5 Tg. The model was able to reproduce the seasonal cycle at high northern latitudes, and implies that seasonal variability in snow cover is a key process controlling H\u2082 uptake. I found that snow cover and soil moisture control the uptake of H\u2082 globally, which may have important implications for the hydrogen budget in future climate change scenarios.
\r\n\r\nMy second thesis topic involved the development of a remote sensing technique using passive microwave brightness temperatures to identify the freeze-thaw status of soils, which I applied to areas north of 45\u00b0N. I found a significant increase in the growing season length in North America by 3.8 days/decade, driven by both an earlier spring thaw and later fall freeze. The lengthening of the growing season may affect the carbon and hydrogen cycles at high northern latitudes, and is a new metric of global change.
" }, { "name": "Sone, Kazuo", "degree": "PhD", "year": "2007", "title": "Modeling and Simulation of Axisymmetric Stagnation Flames", "advisor": "Dimotakis, Paul E.; Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252007-170838", "creators": [ { "name": { "family": "Sone", "given": "Kazuo" }, "id": "Sone-Kazuo", "display_name": "Sone, Kazuo" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "co-chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DYGA-YJ20", "abstract": "Laminar flame modeling is an important element in turbulent combustion research. The accuracy of a turbulent combustion model is highly dependent upon our understanding of laminar flames and their behavior in many situations. How much we understand combustion can only be measured by how well the model describes and predicts combustion phenomena. One of the most commonly used methane combustion models is GRI-Mech 3.0. However, how well the model describes the reacting flow phenomena is still uncertain even after many attempts to validate the model or quantify uncertainties.
\r\n\r\nIn the present study, the behavior of laminar flames under different aerodynamic and thermodynamic conditions is studied numerically in a stagnation-flow configuration. In order to make such a numerical study possible, the spectral element method is reformulated to accommodate the large density variations in methane reacting flows. In addition, a new axisymmetric basis function set for the spectral element method that satisfies the correct behavior near the axis is developed, and efficient integration techniques are developed to accurately model axisymmetric reacting flow within a reasonable amount of computational time. The numerical method is implemented using an object-oriented programming technique, and the resulting computer program is verified with several different verification methods.
\r\n\r\nThe present study then shows variances with the commonly used GRI-Mech 3.0 chemical kinetics model through a direct simulation of laboratory flames that allows direct comparison to experimental data. It is shown that the methane combustion model based on GRI-Mech 3.0 works well for methane-air mixtures near stoichiometry. However, GRI-Mech 3.0 leads to an overprediction of laminar flame speed for lean mixtures and an underprediction for rich mixtures. This result is slightly different from conclusion drawn in previous work, in which experimental data are compared with a one-dimensional numerical solutions. Detailed analysis reveals that flame speed is sensitive to even slight flame front curvature as well as its finite extension in the radial direction. Neither of these can be incorporated in one-dimensional flow modeling.
" }, { "name": "Tiwari, Abhishek", "degree": "PhD", "year": "2007", "title": "Geometrical Analysis of Spatio-temporal Planning Problems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202007-135411", "creators": [ { "name": { "family": "Tiwari", "given": "Abhishek" }, "id": "Tiwari-Abhishek", "display_name": "Tiwari, Abhishek" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Jeffcoat", "given": "David E." }, "id": "Jeffcoat-D-E", "role": "member", "display_name": "Jeffcoat, David E." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "eleceng" ], "doi": "10.7907/917G-MJ20", "abstract": "In this thesis I represent and analyze spatially and temporally constrained multi-agent planning problems using tools from geometry and advanced calculus. The two problems considered in this thesis are multi-agent rendezvous and dynamic sensor coverage. Together, these problems encompass the cooperation, constraint representation,and task scheduling aspects of multi-agent planning problems. I have represented the constraint of the rendezvous problem on the phase space and shown that the fulfilment of rendezvous constraints is equivalent to certain conical regions being invariant. Alternatively, for the dynamic coverage problem, the constraints can be adequately represented on the uncertainty space and sensor motion laws can be obtained by partitioning the uncertainty space and making decisions based on which partition the uncertainty lies in. I have examined convergence behavior of sensor motion under such laws." }, { "name": "Tooker, Angela Colleen", "degree": "PhD", "year": "2007", "title": "Development of Biocompatible Parylene Neurocages for Action Potential Stimulation and Recording", "advisor": "Tai, Yu-Chong; Pine, Jerome", "url": "https://resolver.caltech.edu/CaltechETD:etd-05182007-171118", "creators": [ { "name": { "family": "Tooker", "given": "Angela Colleen" }, "id": "Tooker-Angela-Colleen", "display_name": "Tooker, Angela Colleen" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "advisor", "display_name": "Pine, Jerome" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Meng", "given": "Ellis" }, "id": "Meng E-F-C", "role": "member", "display_name": "Meng, Ellis" }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "member", "display_name": "Pine, Jerome" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9M7Q-ZM04", "abstract": "Neurons, and the neural networks they form, are at the heart of our biological and cognitive functions. Traditional in vitro techniques for studying neural networks use two-dimensional multi-electrode arrays. While furthering the study of neural networks, the inherent mobility of the neurons and the lack of specificity between neurons and electrodes can limit the use of these arrays. Initial work, the neuro-well, eliminated these problems by physically trapping individual neurons in wells. While neural networks were formed and action potentials recorded with arrays of neuro-wells, the bulk micromachining techniques required a complex fabrication process, with limited scalability and a low yield, thus inhibiting their further development.
\r\n\r\nParylene neurocages counteract these difficulties by using surface micromachined structures to trap neurons in close proximity to electrodes, without inhibiting their growth. The use of surface micromachining techniques minimizes the fabrication and scaling complexities, improving the device yield. The neurocages can be fabricated on either glass or silicon substrates, with a variety of electrical insulation materials, including Parylene and silicon-nitride. Parylene is a biocompatible polymer that is non-toxic, extremely inert, and resistant to moisture and most chemicals. Its conformal deposition makes it easy to fabricate 3D structures like the neurocage. Parylene is transparent, allowing the neurons to be easily seen.
\r\n\r\nIndividual neurons are placed into the neurocages, either manually with a pressure-driven micropipette or automatically with a laser tweezers system. The neurocages have openings to allow the neurites to extend out of the neurocages and form synaptic connections with their neighboring neurons. Each neurocage has its own electrode, which is platinized to increase its capacitance. Successful growth of neural networks has been achieved using arrays of neurocages with Parylene and silicon-nitride insulation on both silicon and glass substrates. These neurocages have a long-term cell survival rate of ~ 50% after 3 weeks and have proven 99% effective in trapping neurons. The neurons inside the neurocages have been successfully stimulated, with both current and voltage pulses. Action potentials, both spontaneous and resulting from a current stimulus, have been recorded from neurons comprising the neural networks.
" }, { "name": "Veazey, Christopher Thomas", "degree": "PhD", "year": "2007", "title": "Amorphous Metallic Foam: Synthesis and Mechanical Properties", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-01212007-235934", "creators": [ { "name": { "family": "Veazey", "given": "Christopher Thomas" }, "id": "Veazey-Christopher-Thomas", "display_name": "Veazey, Christopher Thomas" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "matsci" ], "doi": "10.7907/JXDW-9224", "abstract": "Bulk metallic glass alloys were processed into foam by several synthesis routes. These methods utilize the thermodynamic stability and thermoplastic formability of the supercooled liquid state to produce low-density homogeneous foams. The cellular structure is shown to evolve by growth of randomly distributed spherical bubbles towards polyhedral-like cells separated by microscopic intracellular membranes exhibiting random orientations and aspect ratios. The ability of amorphous metals to develop such random cellular morphologies is attributed primarily to the high ductility exhibited by their softened state, which enables large superplastic membrane elongations during foaming.
\r\n\r\nUpon loading, moderate porosity foams are known to deform plastically by recurring non-linear yielding transitions followed by non-catastrophic collapse events. The ability of these foams to yield non-catastrophically is a result of the plastic deformability of amorphous metals in sub-millimeter dimensions. Nonlinear yielding is found to be accommodated by clusters involving 4\u20136 cells, which yield by intracellular membrane buckling and ultimately collapse plastically to produce a localized plastic collapse band. By comparison, high-porosity foams deform plastically by multiple recurring non-catastrophic collapse events without undergoing macroscopic failure. The numerous minor collapse events are associated with localized ligament collapse, and the few major collapse events are associated with the cooperative collapse of several adjacent ligaments and the formation of a collapse band. On average, the serrated flow responses between major events appear to be self-similar and resemble the recurring nonlinear yielding responses exhibited by moderate porosity foams.
" }, { "name": "Walters, Robert Joseph", "degree": "PhD", "year": "2007", "title": "Silicon Nanocrystals for Silicon Photonics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042007-160130", "creators": [ { "name": { "family": "Walters", "given": "Robert Joseph" }, "id": "Walters-Robert-Joseph", "display_name": "Walters, Robert Joseph" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/TKXK-8930", "abstract": "In the absence of suitable methods for integrating traditional semiconductor optoelectronic materials in CMOS microelectronic fabrication processes, nanostructured silicon has been actively explored as an alternative light emitter for silicon photonics. This thesis presents new experimental results in silicon nanocrystal photophysics and optoelectronics, including novel device designs for optical memory elements and light-emitting structures.
\r\n\r\nAs quantum dots, silicon nanocrystals exhibit several interesting properties including size-tunable emission over visible and near-infrared wavelengths and improved oscillator strength for radiation. In contrast to bulk silicon, nanocrystals can emit light with quantum efficiencies approaching 100%. Through time-resolved photoluminescence measurements, we first quantitatively establish that the dense ensembles of nanocrystals that are attractive in device applications retain these advantages. We then describe the fabrication of fully CMOS compatible silicon nanocrystal optoelectronic test structures and show that such devices can function as room temperature optical memory elements.
\r\n\r\nWe further demonstrate that electroluminescence can be achieved in our devices through a previously unreported process we call field effect electroluminescence, in which sequential charge carrier injection is used to create excitons in silicon nanocrystals. This mechanism is a promising approach for overcoming the difficulty inherent in electrically exciting silicon nanocrystals, which are necessarily surrounded by an electrical insulator. Finally, we present electrically excited infrared light sources that combine carrier injection through the field effect electroluminescence mechanism with near field energy transfer from silicon nanocrystals to infrared emitters.
" }, { "name": "Wang, Bingwen", "degree": "PhD", "year": "2007", "title": "Information-Theoretic Methods for Modularity in Engineering Design", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282007-183612", "creators": [ { "name": { "family": "Wang", "given": "Bingwen" }, "id": "Wang-Bingwen", "display_name": "Wang, Bingwen" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/ZBBK-JM82", "abstract": "Due to their many advantages, modular structures commonly exist in artificial and natural systems, and the concept of modular product design has recently received extensive attention from the engineering research community. Although some work has been done on modularity, most of it is qualitative and exploratory in nature, and little is quantitative. One reason for this gap is the lack of a clear definition of modularity. This thesis begins with a detailed discussion on the concepts of \u201cmodularity\u201d and \u201cmodule.\u201d
\r\n\r\nBased on the background presented here, a mutual information-based method is proposed to quantify modularity. The method is based on the view that coupling is information flow instead of real physical interactions. Information flow can be quantified by mutual information, which is based on randomness (or uncertainty). Since most engineering products can be modeled as stochastic systems and therefore have randomness, the mutual information-based method can be applied in very general cases, and it is shown that the commonly existing linkage counting modularity measure is a special case of the mutual information-based modularity measure.
\r\n\r\nThe mutual information-based method is applicable to final design products. But at the early stage of the engineering design process, there are generally only function diagrams. To exploit the benefits of modularity as early as possible, a minimal description length principle-based modularity measure is proposed to determine the modularity of graph structures, which can represent function diagrams. The method is used as criteria to hierarchically decompose abstract graph structures and the real function structure of an HP printer by evolutionary computation. Due to the specialty of genome representations in evolutionary computation, new genetic operators are developed to determine optimal hierarchical decompositions.
\r\n\r\nThis quantitative modularity measure has been developed to synthesize modular engineering products, especially by evolutionary design. There are many factors affecting evolving modular structures, such as genome representation, fitness function, learning, and task structure. The thesis preliminarily studies the effects of the modularity of tasks on the modularity of products in evolutionary computation. Using feed-forward neural networks as examples, the results show that the effects are task-dependent and rely on the amount of resources available for the tasks.
" }, { "name": "Wang, Ya-Juan (Megan)", "degree": "PhD", "year": "2007", "title": "Studies on Environmental Relevance of Quorum Sensing Signal Decay", "advisor": "Leadbetter, Jared R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03212007-235559", "creators": [ { "name": { "family": "Wang", "given": "Ya-Juan (Megan)" }, "id": "Wang-Ya-Juan-Megan", "display_name": "Wang, Ya-Juan (Megan)" } ], "advisors": [ { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "advisor", "display_name": "Leadbetter, Jared R." } ], "committee": [ { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "chair", "display_name": "Leadbetter, Jared R." }, { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "member", "display_name": "Newman, Dianne K." }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "orcid": "0000-0002-0865-1946", "role": "member", "display_name": "Hering, Janet G." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/C00R-DG30", "abstract": "Signal degradation impacts all communications. Although acyl-homoserine lactone (acyl-HSL) quorum sensing signals are known to be degraded by defined laboratory cultures, little is known about their stability in nature. Here, we show for the first time that acyl-HSLs are biodegraded in soils sampled from diverse US sites. When amended to soil samples at physiologically relevant concentrations, \u00b9\u2074C-labeled acyl-HSLs were mineralized to \u00b9\u2074CO\u2082 rapidly and, at most sites examined, without lag. A lag-free turf soil activity was characterized in further detail. Heating or irradiation of the soil prior to the addition of radiolabel abolished mineralization, whereas protein synthesis inhibitors did not. Mineralization exhibited an apparent Km of 1.5 \u00b5M acyl-HSL, ca. 1000-fold lower than that reported for a purified acyl-HSL lactonase. Under optimal conditions, acyl-HSL degradation proceeded at a rate of 13.4 nmol . h\u207b\u00b9 . g of fresh weight soil\u207b\u00b9. An MPN of 4.6 \u00d7 105 cells . g of turf soil\u207b\u00b9 degraded physiologically relevant amounts of hexanoyl-[1-\u00b9\u2074C]HSL to \u00b9\u2074CO\u2082. The results implicate a real-world challenge for acyl-HSL-producing bacteria to outpace biological acyl-HSL degradation and thus to successfully engage in cell-cell communications in soils and other environments. Furthermore, high-affinity acyl-HSL degraders were enriched in oligotrophic biofilm reactors that were inoculated with the turf soil. When supplied at physiological concentration, acyl-HSL was observed to be >95% consumed through the reactors. Six bacterial strains were isolated belonging to Variovorax, Mesorhizobium, Bradyrhizobium and Labrys genera. Unambiguous growth of the six isolates on physiological amount of acyl-HSLs under oligotrophic condition was demonstrated. A Variovorax strain SOD31 exhibited acyl-HSL-limiting growth kinetics with a half-saturation constant of 1.7 \u00b5M, which is in high agreement with what we observed from the turf soil. The results suggest that strain SOD31 may be an active contributor to the soil\u2019s activity of degrading acyl-HSLs. This research reinforces the importance of signal decay as intrinsic to bacterial cell-cell communication, as well as providing bases for further studies towards how signal decay may influence community function and structure in naturally occurring microbial communities." }, { "name": "Wei, Xiaoliang (David)", "degree": "PhD", "year": "2007", "title": "Microscopic Behavior of Internet Congestion Control", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292007-223200", "creators": [ { "name": { "family": "Wei", "given": "Xiaoliang (David)" }, "id": "Wei-Xiaoliang-David", "display_name": "Wei, Xiaoliang (David)" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Cao", "given": "Pei" }, "id": "Cao-Pei", "role": "member", "display_name": "Cao, Pei" } ], "option_major": [ "compsci" ], "doi": "10.7907/W5E3-9N04", "abstract": "The Internet research community has focused on the macroscopic behavior of Transmission Control Protocol (TCP) and overlooked its microscopic behavior for years. This thesis studies the microscopic behavior of TCP and its effects on performance. We go into the packet-level details of TCP control algorithms and explore the behavior in short time scales within one round-trip time. We find that the burstiness effects in such small time scales have significant impacts on both delay-based TCP and loss-based TCP.
\r\n\r\nFor delay-based TCP algorithms, the micro-burst leads to much faster queue convergence than what the traditional macroscopic models predict. With such fast queue convergence, some delay-based congestion control algorithms are much more stable in reality than in the analytical results from existing macroscopic models. This observation allows us to design more responsive yet stable algorithm which would otherwise be impossible.
\r\n\r\nFor loss-based TCP algorithms, the sub-RTT burstiness in TCP packet transmission process has significant impacts on the loss synchronization rate, an important parameter which affects the efficiency, fairness and convergence of loss-based TCP congestion control algorithms.
\r\n\r\nOur findings explain several long-standing controversial problems and have inspired new algorithms that achieve better TCP performance.
" }, { "name": "Yamada, Masumi", "degree": "PhD", "year": "2007", "title": "Early Warning for Earthquakes with Large Rupture Dimension", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03152007-174624", "creators": [ { "name": { "family": "Yamada", "given": "Masumi" }, "id": "Yamada-Masumi", "display_name": "Yamada, Masumi" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Clayton", "given": "Robert W." }, "id": "Clayton-R-W", "role": "member", "display_name": "Clayton, Robert W." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Wu", "given": "Yih-Min" }, "id": "Wu-Yih-Min", "role": "member", "display_name": "Wu, Yih-Min" } ], "option_major": [ "civileng" ], "doi": "10.7907/RXHP-W788", "abstract": "Earthquake early warning systems have become popular these days, and many seismologists and engineers are making research efforts for their practical application. The existing earthquake early warning systems provide estimates of the location and size of earthquakes, and then ground motions at a site are estimated as a function of the epicentral distance and site soil properties. However, for large earthquakes, the energy is radiated from a large area surrounding the entire fault plane, and the epicenter indicates only where rupture starts.
\r\n\r\nIn this project, we focus on an earthquake early warning system considering fault finiteness. We provide a new methodology to estimate rupture geometry and slip size on a finite fault in real time for the purpose of earthquake early warning.
\r\n\r\nWe propose a new model to simulate high-frequency motions from earthquakes with large fault dimension: the envelope of high-frequency ground motion from a large earthquake can be expressed as a root-mean-squared combination of envelope functions from smaller earthquakes. We parameterize the fault geometry with an epicenter, a fault strike, and two along-strike rupture lengths, and find these parameters by minimizing the residual sum of squares of errors between ground motion models and observed ground motion envelopes.
\r\n\r\nTo provide the information on the spatial extent of rupture geometry, we present a methodology to estimate a fault dimension of an earthquake in real time by classifying seismic records into near-source or far-source records. We analyze peak ground motions and use Bayesian model class selection to find a function that best classifies near-source and far-source records based on these parameters. This discriminant function is useful to estimate the fault rupture dimension in real time, especially for large earthquakes.
\r\n\r\nIn order to characterize slip on the fault in real time, we construct an analytical function to estimate slip on the fault from near-source ground displacement observations. In real-time analysis, we back project the recorded displacement data onto the fault line to estimate the size of the slip on the fault. The simulation results show that the slip size estimation predicts the observed GPS static displacement on the fault quite well. This current slip size on the fault is used for a probabilistic prediction of additional rupture length in the near future. We characterize the distribution of additional rupture length conditioned on the current slip on the fault for the ongoing rupture from the simulation with a 1-D slip model. The probability density of additional rupture length can be approximated by a lognormal distribution conditioned on the current slip size.
" }, { "name": "Yoon, Byung-Jun", "degree": "PhD", "year": "2007", "title": "Signal Processing Methods for Genomic Sequence Analysis", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04092007-162353", "creators": [ { "name": { "family": "Yoon", "given": "Byung-Jun" }, "id": "Yoon-Byung-Jun", "display_name": "Yoon, Byung-Jun" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Smolke", "given": "Christina D." }, "id": "Smolke-C-D", "role": "member", "display_name": "Smolke, Christina D." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/48J3-G286", "abstract": "Signal processing is the art of representing, transforming, analyzing, and manipulating signals. It deals with a wide range of signals, from speech and audio signals to images and video signals, and many others. Signal processing techniques have been found very useful in diverse applications. Traditional applications include signal enhancement, denoising, speech recognition, audio and image compression, radar signal processing, and digital communications, just to name a few. In recent years, signal processing techniques have been also applied to the analysis of biological data with considerable success. For example, they have been used for predicting protein-coding genes, analyzing ECG signals and MRI data, enhancing and normalizing DNA microarray images, modeling gene regulatory networks, and so forth.
\r\n\r\nIn this thesis, we consider the application of signal processing methods to the analysis of biological sequences, especially, DNA and RNA molecules. We demonstrate how conventional signal processing techniques--such as digital filters and filter banks--can contribute to this end, and also show how we can extend the traditional models--such as the hidden Markov models (HMMs)--to better serve this purpose.
\r\n\r\nThe first part of the thesis focuses on signal processing methods that can be utilized for analyzing RNA sequences. The primary purposes of this part are to develop a statistical model that is suitable for representing RNA sequence profiles and to propose an effective framework that can be used for finding new homologues (i.e., similar RNAs that are biologically related) of known RNAs. Many functional RNAs have secondary structures that are well conserved among different species. The RNA secondary structure gives rise to long-range correlations between distant bases, which cannot be represented using traditional HMMs. In order to overcome this problem, we propose a new statistical model called the context-sensitive HMM (csHMM). The csHMM is an extension of the traditional HMM, where certain states have variable emission and transition probabilities that depend on the context. The context-sensitive property increases the descriptive power of the model significantly, making csHMMs capable of representing long-range correlations between distant symbols. Based on the proposed model, we present efficient algorithms that can be used for finding the optimal state sequence and computing the probability of an observed symbol string. We also present a training algorithm that can be used for optimizing the parameters of a csHMM. We give several examples that illustrate how csHMMs can be used for modeling various RNA secondary structures and recognizing them.
\r\n\r\nBased on the concept of csHMM, we introduce profile-csHMMs, which are specifically constructed csHMMs that have linear repetitive structures (i.e., state-transition diagrams). Profile-csHMMs are especially useful for building probabilistic representations of RNA sequence families, including pseudoknots. We also propose a dynamic programming algorithm called the sequential component adjoining (SCA) algorithm that can systematically find the optimal state sequence of an observed symbol string based on a profile-csHMM. In order to demonstrate the effectiveness of profile-csHMMs, we build a structural alignment tool for RNA sequences and show that the profile-csHMM approach can yield highly accurate predictions at a relatively low computational cost. At the end, we describe how the profile-csHMM can be used for finding homologous RNAs, and we propose a practical scheme for making the search significantly faster without affecting the prediction accuracy.
\r\n\r\nIn the second part of the thesis, we focus on the application of digital filters and filter banks in DNA sequence analysis. Firstly, we demonstrate how we can use digital filters for predicting protein-coding genes. Many coding regions in DNA molecules are known to display a period-3 behavior, which can be effectively detected using digital filters. Efficient schemes are proposed that can be used for designing such filters. Experimental results will show that the digital filtering approach can clearly identify the coding regions at a very low computational cost. Secondly, we propose a method based on a bank of IIR lowpass filters that can be used for predicting CpG islands, which are specific regions in DNA molecules that are abundant in the dinucleotide CpG. This filter bank is used to process the sequence of log-likelihood ratios obtained from two Markov chains, where the respective Markov chains model the base transition probabilities inside and outside the CpG islands. The locations of the CpG islands are predicted by analyzing the output signals of the filter bank. It will be shown that the filter bank approach can yield reliable prediction results without sacrificing the resolution of the predicted start/end positions of the CpG islands.
\r\n" }, { "name": "Yu, Xin", "degree": "PhD", "year": "2007", "title": "Reflection and Its Application to Mechanized MetaReasoning About Programming Languages", "advisor": "Hickey, Jason J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222007-211909", "creators": [ { "name": { "family": "Yu", "given": "Xin" }, "id": "Yu-Xin", "display_name": "Yu, Xin" } ], "advisors": [ { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "advisor", "display_name": "Hickey, Jason J." } ], "committee": [ { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "chair", "display_name": "Hickey, Jason J." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Joshi", "given": "Rajeev" }, "id": "Joshi-R", "role": "member", "display_name": "Joshi, Rajeev" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "compsci" ], "doi": "10.7907/S0HG-RT72", "abstract": "It is well known that adding reflective reasoning can tremendously increase the power of a proof assistant. In order for this theoretical increase of power to become accessible to users in practice, the proof assistant needs to provide a great deal of infrastructure to support reflective reasoning. In this thesis we explore the problem of creating a practical implementation of such a support layer.
\r\n\r\nOur implementation takes a specification of a logical theory (which is identical to how it would be specified if we simply intended to reason within this logical theory, instead of reflecting it) and automatically generates the necessary definitions, lemmas, and proofs that are needed to enable the reflected metareasoning in the provided theory.
\r\n\r\nOne of the key features of our approach is that the structure of a logic is preserved when it is reflected, including variables, meta variables, and binding structure. This allows the structure of proofs to be preserved as well, and there is a one-to-one map from proof steps in the original logic to proof steps in the reflected logic. The act of reflecting a language is automated; all definitions, theorems, and proofs are preserved by the transformation and all the key lemmas (such as proof and structural induction) are automatically derived.
\r\n\r\nThe principal representation used by the reflected logic is higher-order abstract syntax (HOAS). However, reasoning about terms in HOAS can be awkward in some cases, especially for variables. For this reason, we define a computationally equivalent variable-free de Bruijn representation that is interchangeable with the HOAS in all contexts. The de Bruijn representation inherits the properties of substitution and alpha-equality from the logical framework, and it is not complicated by administrative issues like variable renumbering.
\r\n\r\nWe further develop the concepts and principles of proofs, provability, and structural and proof induction. This work is fully implemented in the MetaPRL theorem prover. We illustrate with an application to [F...] as defined in the POPLmark challenge.
" }, { "name": "Zhang, Lei", "degree": "PhD", "year": "2007", "title": "Metric Based Upscaling for Partial Differential Equations with a Continuum of Scales", "advisor": "Owhadi, Houman", "url": "https://resolver.caltech.edu/CaltechETD:etd-05162007-172755", "creators": [ { "name": { "family": "Zhang", "given": "Lei" }, "id": "Zhang-Lei", "orcid": "0000-0002-2917-9652", "display_name": "Zhang, Lei" } ], "advisors": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "advisor", "display_name": "Owhadi, Houman" } ], "committee": [ { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "chair", "display_name": "Owhadi, Houman" }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/AZ06-4B54", "abstract": "Numerical upscaling of problems with multiple scale structures have attracted increasing attention in recent years. In particular, problems with non-separable scales pose a great challenge to mathematical analysis and simulation. Most existing methods are either based on the assumption of scale separation or heuristic arguments.
\r\n\r\nIn this thesis, we present rigorous results on homogenization of partial differential equations with L\u221e coefficients which allow for a continuum of spatial and temporal scales. We propose a new type of compensation phenomena for elliptic, parabolic, and hyperbolic equations. The main idea is the use of the so-called \"harmonic coordinates\" (\"caloric coordinates\" in the parabolic case). Under these coordinates, the solutions of these differential equations have one more degree of differentiability. It has been deduced from this compensation phenomenon that numerical homogenization methods formulated as oscillating finite elements can converge in the presence of a continuum of scales, if one uses global caloric coordinates to obtain the test functions instead of using solutions of a local cell problem.
" }, { "name": "Zhang, Zhaoyu", "degree": "PhD", "year": "2007", "title": "Towards Functional Miniaturized Lasers", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05162007-123028", "creators": [ { "name": { "family": "Zhang", "given": "Zhaoyu" }, "id": "Zhang-Zhaoyu", "display_name": "Zhang, Zhaoyu" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "eleceng" ], "doi": "10.7907/C2WY-TG62", "abstract": "In this thesis, nanometer scale semiconductor lasers and micrometer scale polymer based dye lasers are our focus in bringing the miniaturized lasers to applications in data transmission; ultra-small chemical / biological sensors; and ultra-compact spectroscopic sources. Combining the advantage of electrically driven semiconductor lasers and the advantage of a broad emission spectrum of dye molecules would utilize the highly dense multi-functional lab-on-a-chip by integrating microfluidic PCR, microfluidic fluorescent detection system, and compact visible and NIR detectors which are commercially available. On the other hand, in the meantime of pushing the size limit of the laser cavities, new phenomena with the nanoscale lasers enable further exploration and understanding in fundamental physics. \r\n\r\nIn the first part of this thesis, two sub-micron scale semiconductor lasers are presented. The smallest lasers utilizing the disk structures\u2014with diameters of approximately 600 nm\u2014were realized in the InGaP/InGaAlP quantum well material system at room temperature, featuring ultra-small mode volumes of approximately 0.03 cubic?microns, and exhibiting single-mode operation at low threshold powers. And the first visible photonic crystal ultra-small mode volume lasers, with cavity volumes of approximately 0.01 cubic?microns, are realized in the same material system. They are ideally suited for use as spectroscopic sources and both of them can be lithographically tuned from 650 \u2013 690 nm. \r\n\r\nIn the second part of this thesis, two sub-millimeter-scale polymer-based dye lasers\u2014a poly(dimethylsiloxane) (PDMS)-based mechanically tunable DFB dye laser and a poly(methylmethacrylate) (PMMA)-based second-order circular grating distributed feedback dye laser\u2014are presented. Both of them are compatible with microfluidic technology, which gives freedom in integrating the lasers with the microfluidic chips. Compared to the soft lithography used in the PDMS-based dye laser, the nanoimprint lithography used in the PMMA-based dye laser would be more useful for fabricating ultra-small dye lasers and enabling mass production in the near future. \r\n\r\nAt the end of the thesis, a nano-linewidth metal grating mask pattern transferred transient grating (MPT-TG) technique is described as a potential technique using the ultra-small lasers for molecular-dynamics study in solutions." }, { "name": "Zheng, Siyang", "degree": "PhD", "year": "2007", "title": "On-Chip Blood Count", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252007-220130", "creators": [ { "name": { "family": "Zheng", "given": "Siyang" }, "id": "Zheng-Siyang", "orcid": "0000-0002-0616-030X", "display_name": "Zheng, Siyang" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "orcid": "0000-0001-8791-0354", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Kasdan", "given": "Harvey L." }, "id": "Kasdan-H-L", "role": "member", "display_name": "Kasdan, Harvey L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SJ43-XM11", "abstract": "Blood count is one of the most common medical laboratory tests performed today. It provides information on patient\u2019s oxygen carrying capacity, immune system functionality, and the overall hemapoiesis process for disease diagnosis and drug side-effect monitoring. Traditionally blood count is performed either manually or by conventional automated blood analyzers. With the advance of microfabrication, on-chip blood count has become a target for miniaturization aiming at providing cost-effective, functional, capable point-of-care devices and systems that use less than 100 nL of blood sample and generate measurement results within minutes. The focus of this thesis is on investigation of erythrocyte/leukocyte counting and leukocyte differential, which are the two key components in blood count, in microdevices.
\r\n\r\nDue to the large number ratio of erythrocytes to leukocytes and their property overlap, conventional automated blood analyzers accomplish blood count in several different channels by measuring different parameters. Similarly, in microdevices, it is desirable that erythrocytes and leukocytes can be separated before further analysis. Two types of hydrodynamic separation devices were investigated to continuously separate erythrocytes and leukocytes based on size. The principle of the device exploits the laminar flow in microdevices and design of streamlines which particles follow. Pillar-shaped devices with single geometrical design demonstrate a binary separation profile. With proper design, separation efficiency over 90% can be achieved. Channel-shaped devices, an improved design, can achieve similar separation efficiency with the added benefits of a smaller footprint, fewer requirements on flow control, and easier integration with downstream components.
\r\n\r\nErythrocyte and leukocyte count is accomplished with electrical impedance sensing, which is one of the most accurate ways to measure particle volume. The well-known problem of small double-layer capacitance inherent to micro impedance sensors is solved by two methods: platinum black electroplating on the electrode surface and inductor-induced resonance sensing. In the first method, platinum black is electroplated in situ on the electrode surfaces, which increases the effective surface area by two orders of magnitude and thus increases the double-layer capacitance significantly. The other innovative way, inductor-induced resonance sensing, nullifies the capacitive components in the system at the resonance frequency by connecting a parallel inductor to the system. In this way the sensitivity can be greatly improved and the optimal sensing frequency can be chosen from the inductance value. For both methods, polystyrene beads of different diameters were used for validation, while diluted blood samples and leukocyte-rich plasma were used to successfully demonstrate the feasibility.
\r\n\r\nTwo-part leukocyte differential is demonstrated in microflow cytometers with fluorescence sensing. Unlike methods used in conventional blood analyzers, undiluted blood samples are stained with nucleic acid stain acridine orange. Lymphocytes and granulocytes emit fluorescent light at different peak frequency after interaction with the dye due to the difference in cellular composition. Using the undiluted sample greatly minimizes sample preparation procedure, and reduces the overall measurement time, the reagent, and the waste volume. These benefits make it a practical method for implementation in microdevices. A throughput of one thousand leukocytes per second was demonstrated, which means the leukocyte differential could be accomplished in a couple of seconds.
" }, { "name": "Analui, Behnam", "degree": "PhD", "year": "2006", "title": "Signal Integrity Issues in High-Speed Wireline Links: Analysis and Integrated System Solutions", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092005-100809", "creators": [ { "name": { "family": "Analui", "given": "Behnam" }, "id": "Analui-Behnam", "display_name": "Analui, Behnam" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/GGMB-0J23", "abstract": "This work focuses on the basic signal integrity issues of high-speed wireline links. It bridges the gap between optimum system design and circuit design for such links by: (1) understanding the effects of the system parameters on the bit error rate (BER), (2) introducing circuit architectures for the realization of systems that minimize the BER, and (3) demonstrating integrated circuit prototypes that verify the solutions.
\r\n\r\nFirst, we develop a theory that analytically relates the data link BER to the system characteristics, e.g., the channel response, the pre-amplifier bandwidth, and the transmitter clock jitter. We generate the BER contours to find the optimum receiver bandwidth as well as the optimum sampling point and its associated timing margin. We also develop the theory of the data-dependent jitter (DDJ), which is a significant component of the timing jitter in high-speed links. We provide an analytical distribution function for the DDJ of an arbitrary linear time-invariant system and include the impact of the DDJ on the BER.
\r\n\r\nSecond, we propose a bandwidth enhancement method for wideband amplifiers. This is useful for the realization of high-speed links in technologies that suffer from large parasitic components. The method leverages two-port broadband matching to enable amplifier stages to achieve their maximum gain-bandwidth product. We demonstrate a 10Gb/s CMOS 0.18um amplifier with this technique that has 2.4 times the bandwidth improvement over a design that does not apply the technique.
\r\n\r\nThird, we develop an eye-opening monitor (EOM) that enables full integration of adaptive equalizers. The EOM evaluates the signal eye diagram quality and reports a quantitative measure, which is correlated to the signal integrity. We demonstrate a prototype in 0.13um standard CMOS that operates up to 12.5Gb/s and has 68dB error dynamic range.
\r\n\r\nFinally, we introduce an instantaneous clockless demultiplexer for burst-mode communication applications. We propose a clockless finite state machine that recovers and demultiplexes the received burst of data instantaneously. The architecture consists of a combinational logic structure and a bit-period-delayed feedback loop. We demonstrate a 1:2 clockless demultiplexer based on this concept in SiGe BiCMOS technology that operates at 7.5Gb/s.
" }, { "name": "Baehr-Jones, Tom Wetteland", "degree": "PhD", "year": "2006", "title": "Novel Modulation and Detection Mechanisms in Silicon Nanophotonics", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05052006-225043", "creators": [ { "name": { "family": "Baehr-Jones", "given": "Tom Wetteland" }, "id": "Baehr-Jones-Tom-Wetteland", "display_name": "Baehr-Jones, Tom Wetteland" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/SRA3-F079", "abstract": "A number of nanophotonic integrated circuits are presented, which take advantage of the unique properties that light has when guided in very small waveguides to achieve novel functionality. The devices studied are designed to operate with light in the 1400-1600 nm range.
\r\n\r\nNanophotonic integrated circuits are tiny waveguides and other optical devices that are fabricated on the nanometer (10-9 meter) scale. These waveguides are often two orders of magnitude smaller than more conventional optical waveguides, such as a fiber optical cable. This reduction in size is interesting because it opens the possibility that expensive optical components might be integrated in very small areas on a chip, and also because the concentrated fields that result from this compression can be used to produce new optical functionality.
\r\n\r\nFirst, the techniques used to design passive optical structures, and the methods used to test them, are discussed. Most of the waveguides studied are fabricated from 110 nm thick layers of silicon from silicon-on-insulator wafers. The best waveguide loss achieved was -2.8 dB/cm. Also described are waveguides based on utilizing surface plasmon waves to guide light.
\r\n\r\nThe use of second order nonlinear optical polymers for modulation is also discussed. These polymers are integrated into Silicon slot waveguides, where the Silicon itself serves as the electrode. Modulation is achieved via the Pockels effect. The modulation figure of merit obtained for the device is superior to the contemporary state of the art, an improvement due to the nanoscale nature of the waveguide. Additionally, detectors based on these same polymers and waveguide geometry are presented. Though the detection efficiency is not very high, the detectors are interesting because they do not require any external power supply, and because they have virtually no speed ceiling.
\r\n\r\nFinally, the use of third order nonlinear optical polymers for all-optical modulation is discussed. When integrated with ridge waveguides, such polymers enable all-optical modulation. Several experiments are described that demonstrate that all-optical modulation has been achieved.
" }, { "name": "Borselli, Matthew Gregory", "degree": "PhD", "year": "2006", "title": "High-Q Microresonators as Lasing Elements for Silicon Photonics", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242006-085503", "creators": [ { "name": { "family": "Borselli", "given": "Matthew Gregory" }, "id": "Borselli-Matthew-Gregory", "display_name": "Borselli, Matthew Gregory" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Gyure", "given": "Mark F." }, "id": "Gyure-M-F", "role": "member", "display_name": "Gyure, Mark F." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2EF5-QD36", "abstract": "Although the concept of constructing active optical waveguides in crystalline silicon has existed for over twenty years, it is only in the past few years that silicon photonics has been given serious attention as a displacing technology. Fueled by the predicted saturation of \"Moore's Law\" within the next decade, universities and industries from all over the world are exploring the possibilities of creating truly integrated silicon opto-electronic devices in a cost effective manner. Some of the most promising silicon photonics technologies are chip-to-chip and intra-chip optical interconnects. Now that compact high-speed modulators in silicon have been achieved, the limiting factor in the widespread adoption of optical interconnects is the lack of practical on-chip optical sources. These sources are critical for the generation of the many wavelengths of light necessary for high-speed communication between the logical elements between and within microprocessors. Unfortunately, crystalline silicon is widely known as a poor emitter because of its indirect bandgap.
\r\n\r\nThis thesis focuses on the many challenges in generating silicon-based laser sources. As most CMOS compatible gain materials possess at most 1 dB/cm of gain, much of our work has been devoted to minimizing the optical losses in silicon optical microresonators. Silicon microdisk resonators fabricated from silicon-on-insulator wafers were employed to study and minimize the different sources of scattering and absorption present in high-index contrast Si microcavities. These microdisks supported whispering-gallery modes with quality factors as high as 5 x 10^6, close to the bulk limit of lightly doped silicon wafers. An external silica fiber taper probe was developed to test the microcavities in a rapid wafer-scale manner. Analytic theory and numerical simulation aided in the optimization of the cavity design and interpretation of experimental results. After successfully developing surface chemistry treatments and passivation layers, erbium-doped glasses were deposited over undercut microdisks and planar microrings. Single-mode laser oscillation was observed and carefully characterized for heavily oxidized silicon microdisks. Dropped power thresholds of 690 nW, corresponding to 170 nW of absorbed power, were measured from gain-spectra and Light in-Light out curves. In addition, quantum efficiencies for these lasers were as high as 24%, indicating that this technology may be ready for further development into real-world devices.
" }, { "name": "Branchaud, Edward Allan", "degree": "PhD", "year": "2006", "title": "A Control System for Positioning Recording Electrodes to Isolate Neurons in Extracellular Recordings", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042006-160620", "creators": [ { "name": { "family": "Branchaud", "given": "Edward Allan" }, "id": "Branchaud-Edward-Allan", "display_name": "Branchaud, Edward Allan" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/6HHC-5456", "abstract": "This thesis presents an algorithm that autonomously positions recording electrodes inside cortical tissue so as to isolate and then maintain optimal extracellular signal recording quality without human intervention. The algorithm is used to improve the quality and efficiency of acute (daily insertion) recordings that are needed for basic research in neurophysiology. It also offers the potential to increase the longevity and quality of chronic (long-term implant) recordings by controlling an emerging class of chronic arrays in which the electrodes can be continually repositioned after implantation.
\r\n\r\nThe challenges encountered in attempting to isolate neurons are studied. A solution is proposed in which a finite state machine oversees a number of signal processing steps, computes various metrics of the recording quality and issues commands to move the electrode close to neurons without causing them damage. A number of metrics of the quality of neuron isolation are compared.
\r\n\r\nThe algorithm has been used to control a number of commercial microdrive systems, including a single-electrode FHC microdrive and multielectrode microdrives from Thomas Recording and NAN, as well as a novel miniature microdrive. The autonomous positioning software is used by several neuroscientists to perform basic neurophysiology research. Analysis of the system's performance in isolating neurons is included.
" }, { "name": "Buckwalter, James Franklin", "degree": "PhD", "year": "2006", "title": "Deterministic Jitter in Broadband Communication", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-01302006-154842", "creators": [ { "name": { "family": "Buckwalter", "given": "James Franklin" }, "id": "Buckwalter-James-Franklin", "orcid": "0000-0002-9390-0897", "display_name": "Buckwalter, James Franklin" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Soyuer", "given": "Mehmet" }, "id": "Soyuer-M", "role": "member", "display_name": "Soyuer, Mehmet" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/EGRD-TZ84", "abstract": "The past decade has witnessed a drastic change in the design of high-speed serial links. While Silicon fabrication technology has produced smaller, faster transistors, transmission line interconnects between chips and through backplanes have not substantially improved and have a practical bandwidth of around 3GHz. As serial link speeds increase, new techniques must be introduced to overcome the bandwidth limitation and maintain digital signal integrity. This thesis studies timing issues pertaining to bandwidth-limited interconnects. Jitter is defined as the timing uncertainty at a threshold used to detect the digital signal. Reliable digital communication requires minimizing jitter.
\r\n\r\nThe analysis and modeling presented here focuses on two types of deterministic jitter. First, dispersion of the digital signal in a bandwidth-limited channel creates data-dependent jitter. Our analysis links data sequences to unique timing deviations through the channel response and is shown for general linear time-invariant systems. A Markov model is constructed to study the impact of jitter on the operation of the serial link and provide insight in circuit performance. Second, an analysis of bounded-uncorrected jitter resulting from crosstalk induced in parallel serial links is presented.
\r\n\r\nTiming equalization is introduced to improve the signal integrity of high-speed links. The analysis of deterministic jitter leads to novel techniques for compensating the timing ambiguity in the received data. Data-dependent jitter equalization is discussed at both the receiver, where it complements the operation of clock and data recovery circuits, and as a phase pre-emphasis technique. Crosstalk-induced, bounded-uncorrected jitter can also be compensated. By detecting electromagnetic modes between neighboring serial links, a transmitter or receiver anticipates the timing deviation that has occurred along the transmission line.
\r\n\r\nFinally, we discuss a new circuit technique for submillimeter integrated circuits. Demands of wireless communication and the high speed of Silicon Germanium transistors provide opportunities for unique radio architectures for submillimeter integrated circuits. Scalable, fully-integrated phased arrays control a radiated beam pattern electronically through tiling multiple chips. Coupled-oscillator arrays are used for the first time to subharmonically injection-lock across a chip or between multiple chips to provide phase coherence across an array.
" }, { "name": "Christianson, Gestur Bj\u00f6rn", "degree": "PhD", "year": "2006", "title": "Information Processing in the Interaural Time Difference Pathway of the Barn Owl", "advisor": "Konishi, Masakazu", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212005-110457", "creators": [ { "name": { "family": "Christianson", "given": "Gestur Bj\u00f6rn" }, "id": "Christianson-Gestur-Bj\u00f6rn", "display_name": "Christianson, Gestur Bj\u00f6rn" } ], "advisors": [ { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "advisor", "display_name": "Konishi, Masakazu" } ], "committee": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "chair", "display_name": "Winfree, Erik" }, { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "role": "member", "display_name": "Laurent, Gilles J." }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "member", "display_name": "Pine, Jerome" }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/3WJJ-7294", "abstract": "The interaural time difference (ITD) is one of two primary binaural cues used to compute the position of a sound source in space. In the barn owl, the ITD is processed in a dedicated neural pathway that terminates at the core area of the central nucleus of the inferior colliculus (ICcc). The actual locus of the computation of the ITD is prior to ICcc in the nucleus laminaris (NL), and ICcc receives no feed-forward inputs carrying information that did not originate in NL. Here, we compare single-unit responses in these two nuclei. The neurons of both nuclei encode spectrotemporal properties of the stimulus with high resolution in both frequency and time domains, and their response to ITD cues has a spectral profile given by the square of their spectral tuning, a relationship consistent with the prediction that these neurons behave as if computing the cross-correlation of the signals at the two ears. However, the ITD tuning curves of ICcc neurons develop more rapidly than those of the neurons of NL, requiring as little as a single stimulus presentation per ITD to show coherent ITD tuning. ICcc neurons also display a greater dynamic range, with a maximal difference in firing rates due to ITD cues approximately double that seen in NL. These results suggest that ICcc neurons sum across a population of similarly tuned NL neurons to produce an averaged response with greater single-unit reliability." }, { "name": "Cremean, Lars Br\u00f6r", "degree": "PhD", "year": "2006", "title": "System Architectures and Environment Modeling for High-Speed Autonomous Navigation", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242006-190748", "creators": [ { "name": { "family": "Cremean", "given": "Lars Br\u00f6r" }, "id": "Cremean-Lars-Br\u00f6r", "display_name": "Cremean, Lars Br\u00f6r" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "mecheng" ], "doi": "10.7907/8HT2-N165", "abstract": "Successful high-speed autonomous navigation requires integration of tools from robotics, control theory, computer vision, and systems engineering. This thesis presents work that develops and combines these tools in the context of navigating desert terrain.
\r\n\r\nA comparative analysis of reactive, behavior-based, and deliberative control architectures provides important guidelines for design of robotic systems. These guidelines depend on the particular task and environment of the vehicle. Two important factors are identified which guide an effective choice between these architectures: dynamic feasibility for the vehicle, and predictability of the environment. This is demonstrated by parallels to control theory, illustrative examples, simulations, and analysis of Bob and Alice---Caltech's full-scale autonomous ground vehicle entries in the 2004 and 2005 Grand Challenge races, respectively.
\r\n\r\nFurther, new model-based methods are developed for constructing and maintaining estimates of terrain elevation and road geometry. These are demonstrated in simulation and in fully autonomous operation of Alice, including accurate detection and tracking of the centerline of desert roads at speeds up to 5 m/s. Finally, Alice's navigation architecture is presented in full along with experimental results that demonstrate its capabilities.
" }, { "name": "Delaire, Olivier", "degree": "PhD", "year": "2006", "title": "The Phonon Entropy of Transition Metals and Alloys: Effects of Impurities and of a Martensitic Phase Transition", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262006-160244", "creators": [ { "name": { "family": "Delaire", "given": "Olivier" }, "id": "Delaire-Olivier", "orcid": "0000-0003-1230-2834", "display_name": "Delaire, Olivier" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Halevy", "given": "Itzhak" }, "id": "Halevy-I", "role": "member", "display_name": "Halevy, Itzhak" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/SDJF-E025", "abstract": "For a fixed configuration of ions on a given crystalline lattice, low energy excitations around the static average configuration can be thermally activated and will contribute to the entropy of the system. As such, phonons, spin-waves or electronic excitations have their own entropic contribution. This thesis investigates the entropic effects of lattice vibrations in transition metal alloys, both from experimental and computational points of view.
\r\n\r\nUsing inelastic neutron scattering, it is shown that a few percent of substitutional impurities from the transition metal series strongly affect the phonon density of states (DOS) of pure vanadium. Alloying with 6% Pt solutes produces a strong stiffening of the phonon DOS, inducing a large and negative vibrational entropy of mixing, which overcomes the increase in configurational entropy. A systematic study of chemical trends for different transition metal impurities was conducted. A previously unknown correlation is established between the vibrational entropy of alloying and the difference in electronegativity of the solute and the host. Density-functional theory calculations were conducted and confirmed the occurrence of systematic charge-transfers correlating with the electronegativity, which affect the interatomic force-constants and the phonons.
\r\n\r\nThe effect of impurities on the anomalous temperature-dependence of phonons in vanadium is investigated. It is found that the solutes which affect the phonon density of states most strongly at room temperature also suppress the anomalous temperature behavior. Electron-phonon and phonon-phonon couplings are examined as potential sources of this effect, through a careful accounting of their contributions to the heat capacity, based on inelastic neutron scattering experiments, calorimetry measurements and electronic structure calculations.
\r\n\r\nFinally, the changes in the phonon DOS and the vibrational entropy across the low-temperature martensitic phase transformation in Fe71Ni29 are investigated. The respective contributions of the phonons and magnetism to the entropy of the direct and reverse transformation are evaluated from neutron scattering and differential scanning calorimetry measurements. A significant magnetic entropy is found in the reverse transformation, which is not present in the direct transformation. This result stresses the necessity to account for the respective contributions of all microscopic degrees of freedom in evaluating entropy changes in solid-solid phase transitions.
" }, { "name": "Demanet, Laurent", "degree": "PhD", "year": "2006", "title": "Curvelets, Wave Atoms, and Wave Equations", "advisor": "Candes, Emmanuel J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262006-133555", "creators": [ { "name": { "family": "Demanet", "given": "Laurent" }, "id": "Demanet-Laurent", "orcid": "0000-0001-7052-5097", "display_name": "Demanet, Laurent" } ], "advisors": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "advisor", "display_name": "Candes, Emmanuel J." } ], "committee": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "chair", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/1TEF-RQ51", "abstract": "We argue that two specific wave packet families---curvelets and wave atoms---provide powerful tools for representing linear systems of hyperbolic differential equations with smooth, time-independent coefficients. In both cases, we prove that the matrix representation of the Green's function is sparse in the sense that the matrix entries decay nearly exponentially fast (i.e., faster than any negative polynomial), and well organized in the sense that the very few nonnegligible entries occur near a few shifted diagonals, whose location is predicted by geometrical optics.
\r\n\r\nThis result holds only when the basis elements obey a precise parabolic balance between oscillations and support size, shared by curvelets and wave atoms but not wavelets, Gabor atoms, or any other such transform.
\r\n\r\nA physical interpretation of this result is that curvelets may be viewed as coherent waveforms with enough frequency localization so that they behave like waves but at the same time, with enough spatial localization so that they simultaneously behave like particles.
\r\n \r\nWe also provide fast digital implementations of tight frames of curvelets and wave atoms in two dimensions. In both cases the complexity is O(N\u00b2 log N) flops for N-by-N Cartesian arrays, for forward as well as inverse transforms.
\r\n\r\nFinally, we present a geometric strategy based on wave atoms for the numerical solution of wave equations in smoothly varying, 2D time-independent periodic media. Our algorithm is based on sparsity of the matrix representation of Green's function, as above, and also exploits its low-rank block structure after separation of the spatial indices. As a result, it becomes realistic to accurately build the full matrix exponential using repeated squaring, up to some time which is much larger than the CFL timestep. Once available, the wave atom representation of the Green's function can be used to perform 'upscaled' timestepping.
\r\n\r\nWe show numerical examples and prove complexity results based on a priori estimates of sparsity and separation ranks. They beat the O(N^3) bottleneck on an N-by-N grid, for a wide range of physically relevant situations. In practice, the current wave atom solver can become competitive over a pseudospectral method in the regime when the wave equation should be solved several times with different initial conditions, as in reflection seismology.
" }, { "name": "Drummond, David Allan", "degree": "PhD", "year": "2006", "title": "Misfolding Dominates Protein Evolution", "advisor": "Arnold, Frances Hamilton", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022006-154329", "creators": [ { "name": { "family": "Drummond", "given": "David Allan" }, "id": "Drummond-David-Allan", "orcid": "0000-0001-7018-7059", "display_name": "Drummond, David Allan" } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" } ], "committee": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "chair", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "orcid": "0000-0002-2915-9504", "role": "member", "display_name": "Adami, Christoph Carl" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." } ], "option_major": [ "cns" ], "doi": "10.7907/DH8E-2N10", "abstract": "The diverse array of protein functions depends upon these molecules' reliable ability to fold into the native structures determined by their amino-acid sequences. Because mutations that alter a protein's sequence frequently disrupt its folding, protein evolution explores protein sequence space conservatively, either by point mutations or recombination between related sequences. Attempts to engineer proteins by co-opting the evolutionary algorithm have also largely proceeded by the stepwise accumulation of beneficial mutations. Other strategies for directed evolution have focused on introducing many mutations at once as a way to increase the likelihood of finding improved variants, attempting to balance higher mutational diversity with lower retention of folding. Using simple models, I explore this tradeoff and find that protein misfolding dominates whether increasing mutation levels increase the number of improved variants. I analyze results of a popular mutagenesis protocol, error-prone PCR, for evidence that coupling between mutations might favor higher mutation levels, as claimed by several groups. A comparison of high-mutation-rate mutagenesis to protein recombination between distantly related proteins reveals qualitative differences in protein tolerance for sequence changes introduced by each method. Mutational tolerance may also be reflected in the rate at which proteins accumulate sequence changes over evolutionary time; why proteins evolve at different rates remains a major open question in biology. An analysis of rate determinants suggests that one major variable, linked to how highly expressed the encoding gene is, dominates the rate of yeast protein evolution. To explain this trend, I hypothesize that proteins are selected to fold properly despite mistranslation, a property I call translational robustness, and test it using genomic data. To examine protein evolution at a higher level of detail, a large-scale simulation is constructed in which simulated organisms, with genomes containing genes expressing computationally foldable proteins at different levels, evolve over millions of generations with protein misfolding imposing the only fitness cost. The results suggest that protein misfolding suffices to explain many significant trends in genome evolution observed across taxa, predict a novel genomic trend which is then identified in yeast, and create insight into the causes of evolutionary rate variation in proteins." }, { "name": "Feng, Tao", "degree": "PhD", "year": "2006", "title": "Silicon Nanocrystal Charging Dynamics and Memory Device Applications", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-06052006-141803", "creators": [ { "name": { "family": "Feng", "given": "Tao" }, "id": "Feng-Tao", "display_name": "Feng, Tao" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Giapis", "given": "Konstantinos P." }, "id": "Giapis-K-P", "role": "member", "display_name": "Giapis, Konstantinos P." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/N8JK-ZQ70", "abstract": "The application of Si nanocrystals as floating gate in the metal oxide semiconductor field-effect transistor (MOSFET) based memory, which brings many advantages due to separated charge storage, attracted much attention in recent years. In this work, Si nanocrystal memory with nanocrystals synthesized by ion implantation was characterized to provide a better understanding of the relationship between structure and performance -- especially charge retention characteristics.
\r\n\r\nIn the structural characterization it was demonstrated that scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) enable much more accurate measurements of the ensemble size distribution and array density for small Si nanocrystals in SiO\u2082, estimated to be around 2-3 nm and 4 x 10\u00b9\u00b2 -3 x 10\u00b9\u00b3 cm\u207b\u00b2, respectively. The reflection high energy electron diffraction (RHEED) pattern further verified the existence of nanocrystals in SiO\u2082. Capacitance-voltage (C-V) measurements demonstrated the memory effects. The comparison between charge density and nanocrystal density suggests single charge storage on individual Si nanocrystals.
\r\n\r\nThe electronic property of tunnel oxide layer is a key factor influencing charge retention, and was characterized by conductive atomic force microscopy (C-AFM). An overall high conductance observed between the nanocrystal floating gate and the substrate is believed to be responsible for the relatively short retention time for electrons. A narrowed denuded zone contaminated with nanocrystals is suggested to be the reason for the high conductance, which is further supported by switching events and fluctuations in local current-voltage (I-V) curves. From the results of C-AFM, a better control of nanocrystal distribution close to the channel is shown to be critical for non-volatile nanocrystal memory made via Si ion implantation.
\r\n\r\nNanoscale charge retention characteristics of both electrons and holes were probed directly by ultrahigh vacuum (UHV) nc-AFM, in which a highly doped Si tip was applied to inject charges into the nanocrystal layer and monitor subsequent charge dissipation. The results reveal a much longer hole retention time (e.g., >1 day) than that for electrons (e.g., <1 hour), which is consistent with the charge retention characteristics from electrical characterization of nanocrystal floating gate MOS capacitors as well as time-resolved photoluminescence measurements. The large difference in charge retention times for electrons and holes is attributed to the difference in tunneling barrier heights: 3.1 eV and 4.7 eV for electrons and holes, respectively. Based on the charge injection and retention characteristics obtained from UHV nc-AFM and nanocrystal floating gate MOS devices, we suggest that hole programming in Si nanocrystal memory is an interesting choice in improving data retention or in further device scaling.
\r\n\r\nUHV nc-AFM guarantees high detection sensitivity and stability in charge imaging experiments due to a lack of air damping, so a three-dimensional (3D) electrostatic model can be developed to provide quantitative information regarding the distribution and evolution of the localized charges. For example, a transition from initial complementary error function distribution to Gaussian distribution was suggested in the simulation. In addition, charge detection sensitivity was found to increase with the scanning height, showing much room for further improvement of the sensitivity in UHV nc-AFM. The limitation of the electrostatic model is also discussed, and some knowledge regarding the charge distribution obtained from theoretical analysis and other experimental methods is suggested to be necessary supplements to the quantitative charge analysis by nc-AFM.
\r\n\r\nFinally, the approach used in the electrostatic simulation of nc-AFM was applied in 3D simulation of Si nanocrystal memory. The dependence of Coulomb charging energy on dielectric environment is analyzed. From the local variation of channel minority carrier density due to separated charge storage, the threshold number density of charged nanocrytals for 1D approximation to break down is shown to be 10\u00b9\u00b2 cm\u207b\u00b2 in the sample geometry investigated.
\r\n" }, { "name": "Ferguson, Megan Alameda", "degree": "PhD", "year": "2006", "title": "TiO\u2082-Photocatalyzed As(III) Oxidation and its Applicability to Water Treatment", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242006-105717", "creators": [ { "name": { "family": "Ferguson", "given": "Megan Alameda" }, "id": "Ferguson-Megan-Alameda", "display_name": "Ferguson, Megan Alameda" } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "chair", "display_name": "Hering, Janet G." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "envreng" ], "doi": "10.7907/093T-4643", "abstract": "Ingestion of arsenic (As) in drinking water can lead to several chronic illnesses, including bladder, lung, and skin cancers. Due to natural weathering reactions, As is present in many drinking water sources throughout the United States and other countries. The U.S. drinking water standard has recently been revised from 50 micrograms L-1 to 10 micrograms L-1, thus requiring thousands of water distribution facilities to implement new As removal procedures. However, most As removal technologies treat As(V) much more effectively than As(III), so a pre-oxidation step is recommended for source waters containing As(III) at significant concentrations. The photocatalyzed oxidation of As(III) on titanium dioxide (TiO\u2082) has been critically evaluated as a potential technology to achieve pre-oxidation.
\r\n\r\nBatch slurry studies showed that sorption of both As(III) and As(V) to TiO\u2082 occurs rapidly. Changes in As(III) concentration adsorbed to the TiO\u2082 surface, whether resulting from varying dissolved As(III) concentration or from the presence of competitive adsorbates, affected the rate of photooxidation. A transition from first-order to zero-order reaction kinetics was observed as the TiO\u2082 surface became saturated with As(III). Experiments targeting the reaction mechanism (which used hydroxyl radical quenchers, an alternate electron acceptor, and superoxide dismutase) suggested that superoxide plays a major role as an oxidizing agent in this system.
\r\n\r\nAs(III) was rapidly photooxidized in a fixed-bed, flow-through reactor. Catalyst poisoning or severe mass transport limitations were not observed for the conditions studied, although complete As(III) oxidation could not be achieved due to constraints of reactor geometry. With synthetic groundwater solutions, the reaction appeared to be inhibited by the presence of competitive adsorbates. Use of natural sunlight resulted in more rapid As(III) oxidation than that observed with irradiation from the 365 nm lamp used for other experiments.
\r\n\r\nAs arsenic detection methods improve, reporting levels and perhaps regulatory standards will be lowered, requiring more distribution systems to consider technologies for As treatment. In contrast to methods of pre-oxidation currently in use, TiO\u2082 photocatalysis involves no hazardous chemicals and generates no toxic reaction byproducts. Based on these findings, TiO\u2082-photocatalyzed As(III) oxidation could be a viable pre-oxidation technology for certain small water distribution facilities.
" }, { "name": "Forouhar, Arian Soroush", "degree": "PhD", "year": "2006", "title": "Dynamic Views of Structure and Function during Heart Morphogenesis", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-06282006-130509", "creators": [ { "name": { "family": "Forouhar", "given": "Arian Soroush" }, "id": "Forouhar-Arian-Soroush", "display_name": "Forouhar, Arian Soroush" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "chair", "display_name": "Fraser, Scott E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "co-chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Hove", "given": "Jay R." }, "id": "Hove-J-R", "role": "member", "display_name": "Hove, Jay R." }, { "name": { "family": "Dickinson", "given": "Mary E." }, "id": "Dickinson-Mary-E", "orcid": "0000-0003-4372-9638", "role": "member", "display_name": "Dickinson, Mary E." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "bioeng" ], "doi": "10.7907/Z0X2-HG40", "abstract": "Congenital heart defects remain the most common birth defect in humans, occurring in over 1% of live births. The high prevalence of cardiac malformations can be partially attributed to limited knowledge regarding the embryonic roots of the disease. A variety of congenital heart defects are thought to arise from combinations of genetic and epigenetic factors. In an effort to better understand this dynamic relationship, our study explores the structure and function of the developing heart and valves and examines hemodynamic factors influencing valvulogenesis. In order to study cardiac mechanics, we employed novel high-speed confocal microscopy and four-dimensional visualization techniques. A dynamic four-dimensional dataset describing heart and valve development along with blood flow patterns throughout cardiac morphogenesis is presented. Utilizing newly developed tools, we propose a novel pumping mechanism in the valveless embryonic heart tube via elastic wave propagation and reflection. We show that this form of pumping leads to oscillatory shear stresses in the developing atrio-ventricular canal, a phenomenon that had not previously been documented. An in vivo method to modulate trans-valvular oscillatory flows is described and used to test our hypothesis that oscillatory shear stress across the primitive valve cushions stimulates heart valve leaflet formation. Our results suggest hemodynamic forces contribute to valvulogenesis and enhance our understanding of normal and abnormal heart valve development.\r\n" }, { "name": "Goulet, David Michael", "degree": "PhD", "year": "2006", "title": "Mathematical Models of the Developing C. elegans Hermaphrodite Gonad\r ", "advisor": "Sternberg, Paul W.; Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092006-160328", "creators": [ { "name": { "family": "Goulet", "given": "David Michael" }, "id": "Goulet-David-Michael", "display_name": "Goulet, David Michael" } ], "advisors": [ { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "role": "advisor", "display_name": "Sternberg, Paul W." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "chair", "display_name": "Cohen, Donald S." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Petrasek", "given": "Danny" }, "id": "Petrasek-Danny", "role": "member", "display_name": "Petrasek, Danny" }, { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "role": "member", "display_name": "Sternberg, Paul W." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/D7C9-PA08", "abstract": "The study of growing and developing organisms is a fascinating branch of experimental biology. Once created, cells must exchange chemical and physical cues with neighboring cells in order to grow, divide, and differentiate properly. In this thesis we study portions of development of the C. elegans hermaphrodite gonad, building mathematical models of the development process. Using our models, we show that vulval precursor cells make fate decisions under a flexible program that takes advantage of inherent chemical oscillations. This flexibility allows the cells to react more sensitively to weak signaling gradients and to the actions of neighboring cells. With our mathematical models, we also show that the development of the anchor cell cannot proceed properly using the currently known decision mechanisms. We draw upon knowledge of homologous proteins in D. melanogaster to propose a modification to the current theory on anchor cell development. Our models suggest that this modified mechanism, though not yet identified in C. elegans, is sufficient to specify anchor cell fates in accordance with experimental observations. In studying our mathematical models, novel analytical techniques were developed to understand the asymptotic behavior of systems of delay differential equations." }, { "name": "Guan, Xiang", "degree": "PhD", "year": "2006", "title": "Microwave Integrated Phased Array Receivers in Silicon", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302005-024349", "creators": [ { "name": { "family": "Guan", "given": "Xiang" }, "id": "Guan-Xiang", "display_name": "Guan, Xiang" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "D'Addario", "given": "Larry R." }, "id": "D'Addario-L-R", "role": "member", "display_name": "D'Addario, Larry R." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/E5GE-EP91", "abstract": "Microwave integrated systems in silicon provide a low cost, low power and high yield solution for wideband data communication, radar, and many other applications. Phased-array systems are capable of steering the radiation beam by electronic means, emulating the behavior of a directional antenna. This dissertation is dedicated to presenting various techniques to implement microwave integrated phased-array receivers in silicon-based technologies in the context of three design examples.
\r\n\r\nA 24-GHz 0.18-\u00b5m complementary metal oxide semiconductor (CMOS) front-end was demonstrated. The front-end consists of a low noise amplifier (LNA) and a mixer. The LNA utilizes a novel topology common-gate with resistive feedthrough to obtain low-noise performance. The entire front-end achieves a 7.7dB noise figure and a 27.5dB power gain.
\r\n\r\nA fully integrated 8-element 24-GHz silicon germanium (SiGe) phased array receiver was implemented. The receiver uses two-step downconversion and local oscillator (LO) phase shifting with 4-bit resolution. The signal is combined at the 4.8-GHz intermediate frequency. The 16 phases of 19.2-GHz LO signal are generated with a voltage controlled oscillator (VCO) and symmetrically distributed to the phase selectors at all path. Appropriate phase sequence is applied to the phase distribution transmission lines to minimize mismatch. An integrated frequency synthesizer locks the 19.2-GHz VCO output to a 75-MHz external reference. Measured array patterns show a peak-to-null ratio of more than 20dB and a beam steering range covering all signal incident angles.
\r\n\r\nAn integrated 4-element 77-GHz SiGe wideband phased-array transceiver was implemented. Two-step conversion is used at both the receiver and the transmitter. A differential phase of 52 GHz is generated by the VCO and distributed to all RF paths at the transmitter and receiver. The phase shifting is performed at the LO ports of the RF mixers using continuous analog phase shifters. The quadrature signal of the second LO frequency is generated by dividing the VCO frequency by a factor of 2 using a cross-coupled injection-locked frequency divider. The signal combining is performed at IF with an active combining amplifier. The receiver achieves a 41dB gain at 80 GHz with 3 GHz of bandwidth. The 52-GHz-to-50MHz frequency divider chain obtains 7% locking range.
" }, { "name": "He, Qing", "degree": "PhD", "year": "2006", "title": "Integrated Nano Liquid Chromatography System On-a-Chip", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-07142005-013255", "creators": [ { "name": { "family": "He", "given": "Qing" }, "id": "He-Qing", "display_name": "He, Qing" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." }, { "name": { "family": "Lee", "given": "Terry D." }, "id": "Lee-T-D", "role": "member", "display_name": "Lee, Terry D." } ], "option_major": [ "eleceng" ], "doi": "10.7907/NQVA-F827", "abstract": "Integrated liquid chromatography (LC) chips are valued because of their significant advantages over conventional systems. However, they are very challenging to build due to the high complexity of LC systems and the need for high-level integration of many discrete microfluidic devices.
\r\n\r\nThe goal of this thesis is to develop technologies and devices towards a totally integrated LC system on-a-chip. Using parylene microfluidics technology, all of the devices are integrated on silicon wafers with CMOS-compatible batch processes. Due to the small size of the on-chip LC columns, the chips all perform nano LC, which means that the flow rates are on the scale of nano liters per minute.
\r\n\r\nThe thesis starts with the solution of the problem of bead integration, since most LC columns are packed with micro-beads. A wafer-scale batch process is developed to integrate beads into micromachined devices. The technology is applied to make an LC-ESI (Electro-Spray Ionization) chip with an integrated bead column packed with 5 \u00b5m diameter C18 silica beads. The integrated ESI nozzle allows direct coupling to a mass spectrometer (MS).
\r\n\r\nDue to the high-pressure nature of LC operations, a complete LC chip must be able to both withstand and generate high pressures on-chip. Therefore, an anchoring technique is developed to dramatically increase the pressure rating of parylene devices from about 30 psi to 1000 psi. In addition, on-chip high-pressure generation is achieved with electrolysis-based micro-actuators.
\r\n\r\nAn integrated ion liquid chromatography chip is demonstrated, which has on-chip column, filters, injection structure, and conductivity detector. The column is packed with 7 \u00b5m anion-exchange beads with a slurry packing technique. On-chip sample injection, separation, and detection of seven common anions are successfully demonstrated with a sensitivity of 1 ppm.
\r\n\r\nFinally, a microchip that demonstrates high-pressure LC with integrated ESI coupling to MS is presented. The capacity of the column, which is 6.5 cm long and packed with 5 \u00b5m C18 silica beads, is the highest of all the devices in the thesis. Gradient separation at a pressure of 450 psi and on-line MS detection of digested cytochrome c protein is successfully performed.
" }, { "name": "Hochberg, Michael", "degree": "PhD", "year": "2006", "title": "Integrated Ultrafast Nonlinear Optical Devices in Silicon", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252006-160420", "creators": [ { "name": { "family": "Hochberg", "given": "Michael" }, "id": "Hochberg-Michael", "display_name": "Hochberg, Michael" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Doll", "given": "Theodore" }, "id": "Doll-T", "role": "member", "display_name": "Doll, Theodore" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8124-DA56", "abstract": "Silicon-on-insulator (SOI) provides an intriguing system for developing massively integrated optics. By leveraging the processes and systems developed for electronics fabrication, it is possible to make highly repeatable devices where complexity can be scaled up through the use of wafer-scale batch fabrication. Because the mode concentration in silicon waveguides is two orders of magnitude higher than in fibers, it is possible to construct very compact nonlinear optical devices within this system, enabling the miniaturization and integration of ultrafast nonlinear devices. We have developed a library of devices, including both dielectric and plasmonic waveguides, as well as resonators, splitters, and a variety of other basic optical components.
\r\n\r\nUsing these components to construct integrated devices of moderate complexity, we have demonstrated Pockels\u2019 Effect-based ring modulators, optical rectification-based detectors, four-wave mixing devices, and ultrafast intensity modulators, which operate at speeds in excess of 2 Terahertz. By integrating optical polymers through evanescent coupling to high-mode-confinement silicon waveguides, the effective nonlinearity of the waveguides can be greatly increased. The combination of high mode confinement, multiple integrated optical components, and high nonlinearity produces all-optical ultrafast devices operating at power levels compatible with modern continuous-wave telecommunication systems. Although far from commercial modulator standards in terms of extinction, these modulator devices are a first step toward large scale integrated ultrafast optical logic in silicon, and are two orders of magnitude faster than existing free-carrier-based silicon devices.
\r\n" }, { "name": "Inamdar, Mandar Mukund", "degree": "PhD", "year": "2006", "title": "Dissipative Nanomechanics", "advisor": "Phillips, Robert B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272006-142956", "creators": [ { "name": { "family": "Inamdar", "given": "Mandar Mukund" }, "id": "Inamdar-Mandar-Mukund", "orcid": "0000-0001-8549-8490", "display_name": "Inamdar, Mandar Mukund" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "advisor", "display_name": "Phillips, Robert B." } ], "committee": [ { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "chair", "display_name": "Phillips, Robert B." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Dill", "given": "Ken A." }, "id": "Dill-K-A", "role": "member", "display_name": "Dill, Ken A." }, { "name": { "family": "Gelbart", "given": "William" }, "id": "Gelbart-W", "role": "member", "display_name": "Gelbart, William" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/P5K9-BD68", "abstract": "Due to thermal fluctuations, systems at small length scales are remarkably different than their large length scale counterparts. For example, bacterial viruses (phages) have thousands of nanometers of DNA packed inside a hollow capsid of tens of nanometers. This tight compaction leads to large forces on the phage DNA (tens of piconewtons). These forces can be subsequently utilized to instigate the DNA ejection during the infection phase. Developments in optics, biochemistry, microfluidics, etc., have enabled the experimental quantification of these forces, and the rate of DNA packing and ejection. Similarly, eukaryotic genome is compacted into nanometer size structures called nucleosomes. The conformational changes in the nucleosome due to the thermal fluctuations of the DNA are instrumental in making the DNA accessible for key genomic processes. Developments in FRET, gel electrophoresis, spectroscopy etc. have made it possible to quantify the equilibrium constant and the rates of these fluctuations. The first part of the thesis involves formulation of simple models for the phage and nucleosome to respond to the existing experimental data and predict results to stimulate further experimentation.
\r\n\r\nOne of the next frontiers in biology is to understand the \"small numbers\" problem: how does a biological cell function given that most of its proteins and nucleotide polymers are present in numbers much smaller than Avogadro's number? For example, one of the most important molecules, a cell's DNA, occurs in only a single copy. Also, it is the flow of matter and energy through cells that makes it possible for organisms to maintain a relatively stable form. Hence, cells must be in this stable state far from equilibrium to function. Many problems of current interest thus involve small systems that are out of equilibrium. Unfortunately, there is no general theoretical frame-work to model these dissipative systems. E. T. Jaynes suggested the use of dynamical microtrajectories to write down the trajectory entropy, or caliber, for such systems. Maximization of this trajectory entropy, subject to the external constraints, provides one with the probabilities of the underlying microtrajectories. Jaynes calls this the \"principle of maximum caliber.\" Advances in optics, video-microscopy, etc. have made it possible to experimentally measure these microtrajectories for various systems. In the second part of the thesis we develop simple microtrajectory models for small systems like molecular motors, ion-channels, etc., and apply the maximum caliber principle to obtain the probabilities of the underlying microtrajectories. Our goal is to respond to these experiments and make new predictions.
" }, { "name": "Jaggi, Sidharth", "degree": "PhD", "year": "2006", "title": "Design and Analysis of Network Codes", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302006-131149", "creators": [ { "name": { "family": "Jaggi", "given": "Sidharth" }, "id": "Jaggi-Sidharth", "orcid": "0000-0002-5522-7486", "display_name": "Jaggi, Sidharth" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Medard", "given": "Muriel" }, "id": "Medard-M", "orcid": "0000-0003-4059-407X", "role": "member", "display_name": "Medard, Muriel" }, { "name": { "family": "Koetter", "given": "Ralf" }, "id": "Koetter-R", "role": "member", "display_name": "Koetter, Ralf" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Ho", "given": "Tracey C." }, "id": "Ho-Tracey", "role": "member", "display_name": "Ho, Tracey C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/7ERZ-H253", "abstract": "The information theoretic aspects of large networks with many terminals present several interesting and non-intuitive phenomena. One such crucial phenomenon was first explored in a detailed manner in the excellent work by Ahlswede at al. It compared two paradigms for operating a network -- one in which interior nodes were restricted to only copying and forwarding incoming messages on outgoing links, and another in which internal nodes were allowed to perform non-trivial arithmetic operations on information on incoming links to generate information on outgoing links. It showed that the latter approach could substantially improve throughput compared to the more traditional scenario. Further work by various authors showed how to design codes (called network codes) to transmit under this new paradigm and also demonstrated exciting new phenomena for these codes such as robustness against network failures, distributed design, and increased security.
\r\n\r\nIn this work, we consider the low-complexity design and analysis of network codes, with a focus on codes for multicasting information. We examine both centralized and decentralized design of such codes, and also both randomized and deterministic design algorithms. We compare different notions of linearity and show the interplay between these notions in the design of linear network codes. We determine bounds on the complexity of network codes. We also consider the problem of error-correction and secrecy for network codes when a malicious adversary controls some subset of the network resources.
" }, { "name": "Jeon, Sanggeun", "degree": "PhD", "year": "2006", "title": "Design and Stability Analysis Techniques for Switching-Mode Nonlinear Circuits: Power Amplifiers and Oscillators", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242006-132815", "creators": [ { "name": { "family": "Jeon", "given": "Sanggeun" }, "id": "Jeon-Sanggeun", "orcid": "0000-0001-7453-2331", "display_name": "Jeon, Sanggeun" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Stancil", "given": "Daniel D." }, "id": "Stancil-D-D", "role": "member", "display_name": "Stancil, Daniel D." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/V4YT-YM88", "abstract": "A design technique for kW level switching mode power amplifiers is presented. Several push pull pairs, independently tuned to Class E/Fodd, are combined by a distributed active transformer. The zero voltage switching (ZVS) condition is investigated and modified for the Class-E/Fodd amplifier with a non-ideal output transformer. All lumped elements including the DAT, the transistor package, and the input power distribution network are modeled and optimized to achieve the ZVS condition and the high drain efficiency. Two power amplifiers are implemented at 29 MHz, following the technique. The amplifier with two push pull pairs combined exhibits 1.5 kW output power with 85 % drain efficiency and 18 dB gain. When four push pull pairs are combined, an output power of 2.7 kW is achieved with 79 % drain efficiency and 18 dB gain.
\r\n\r\nNonlinear stability analysis techniques, based on an auxiliary generator and pole zero identification, are introduced to predict and eliminate the instabilities of power amplifiers. The techniques are applied to two switching mode power amplifiers that exhibited different instabilities during the measurements. Self-oscillation, chaos, and hysteresis of a Class E/Fodd amplifier with a distributed active transformer are investigated by the stability and bifurcation analysis tools. An in-depth analysis of the oscillation mechanism is also carried out, which enables an efficient determination of the topology and location of the required global stabilization network. As the other application, the anomalous behavior observed in a Class-E power amplifier is analyzed in detail. It involves hysteresis in the power-transfer curve, self oscillation, harmonic synchronization, and noisy precursors. To correct the amplifier performance, a new technique for elimination of the hysteresis is proposed, based on bifurcation detection through a single simulation on harmonic-balance software. Also, investigated are the circuit characteristics that make the noisy precursors observable in practical circuits and a technique is derived for their elimination from the amplifier output spectrum. All of the stabilization and correction of the amplifiers are experimentally validated.
\r\n\r\nA simple nonlinear technique for the design of high efficiency and high-power switching-mode oscillators is presented. It combines existing quasi-nonlinear methods and the use of an auxiliary generator in harmonic balance. The auxiliary generator enables the oscillator optimization to achieve high output power and dc to rf conversion efficiency without affecting the oscillation frequency. It also imposes a sufficient drive on the transistor to enable the switching mode operation with high efficiency. The oscillation start-up condition and the steady state stability are analyzed with the pole-zero identification technique. The influence of the gate bias on the output power, efficiency, and stability is also investigated. A Class E oscillator is demonstrated using the proposed technique. The oscillator exhibits 75 W with 67 % efficiency at 410 MHz.
" }, { "name": "Kang, Dal Mo", "degree": "PhD", "year": "2006", "title": "Measurements of Combustion Dynamics with Laser-Based Diagnostic Techniques", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182005-164746", "creators": [ { "name": { "family": "Kang", "given": "Dal Mo" }, "id": "Kang-Dal-Mo", "display_name": "Kang, Dal Mo" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Ratner", "given": "Albert" }, "id": "Ratner-A", "role": "member", "display_name": "Ratner, Albert" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/6F5N-9G88", "abstract": "Since the early days of gas turbine engines, combustion/flow instability inside the combustor has been an issue in many engines, but little has been understood as to how the dynamics of the system involved contribute to the instability. The primary objective of this work is to provide general experimental procedures and to validate methods for examining the dynamic behaviors of combustion systems, and to provide accurate measurements of the combustion dynamics for use as a foundation for further theoretical and numerical research. Knowledge of the fundamental dynamics of combustion systems is crucial in understanding and modeling the flame behavior and enabling the use of insights in design process and for creating robust active control of combustors.
\r\n\r\nSince mixing plays significant roles in combustion processes, the dynamics of fuel/air mixing were studied. A non-premixed burner was examined with acoustic excitations at 22~55 Hz to assess the mixing and its relation to the thermo-acoustic coupling. Phase-resolved acetone-PLIF was used to image the mixing, and from this the unmixedness was calculated, which quantifies the degree of mixing. The results show that (1) the acoustic waves induce periodicity in the degree of mixing; (2) the way the unmixedness behaves coincides well with the behavior of the Rayleigh index, implying the degree of mixing is a major factor in determining the stability of the combustion system; (3) the two-dimensional measurements of temporal unmixedness effectively visualize the shear mixing zone.
\r\n\r\nA second low-swirl premixed burner was studied to examine the impact of acoustic waves on the combustion dynamics. Measurements were performed with OH-PLIF, with acoustic forcing up to 400 Hz. Swirl burners at higher pressure are industry standard, and this study examined the dynamics at elevated combustor pressure. The results show that (1) the thermo-acoustic coupling seems to be closely coupled to the vortices generated at the flame boundary; (2) high magnitude of flame response coincides with the high absolute value of Rayleigh index; (3) the way the thermo-acoustic coupling is distributed over the space is highly dependent on the excitation frequencies; (4) high pressure suppresses the sensitivity of combustions system to outside disturbances.
" }, { "name": "Kriechbaum, Kristopher Lars", "degree": "PhD", "year": "2006", "title": "Tools and Algorithms for Mobile Robot Navigation with Uncertain Localization", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012006-150109", "creators": [ { "name": { "family": "Kriechbaum", "given": "Kristopher Lars" }, "id": "Kriechbaum-Kristopher-Lars", "display_name": "Kriechbaum, Kristopher Lars" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Collins", "given": "Curtis L." }, "id": "Collins-C-L", "role": "member", "display_name": "Collins, Curtis L." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/R6YB-NQ21", "abstract": "The ability for a mobile robot to localize itself is a basic requirement for reliable long range autonomous navigation. This thesis introduces new tools and algorithms to aid in robot localization and navigation. I introduce a new range scan matching method that incorporates realistic sensor noise models. This method can be thought of as an improved form of odometry. Results show an order of magnitude of improvement over typical mobile robot odometry. In addition, I have created a new sensor-based planning algorithm where the robot follows the locally optimal path to the goal without exception, regardless of whether or not the path moves towards or temporarily away from the goal. The cost of a path is defined as the path length. This new algorithm, which I call \"Optim-Bug,\" is complete and correct. Finally, I developed a new on-line motion planning procedure that determines a path to a goal that optimally allows the robot to localize itself at the goal. This algorithm is called \"Uncertain Bug.\" In particular, the covariance of the robot's pose estimate at the goal is minimized. This characteristic increases the likelihood that the robot will actually be able to reach the desired goal, even when uncertainty corrupts its localization during movement along the path. The robot's path is chosen so that it can use known features in the environment to improve its localization. This thesis is a first step towards bringing the tools of mobile robot localization and mapping together with ideas from sensor-based motion planning." }, { "name": "Laurence, Stuart Jon", "degree": "PhD", "year": "2006", "title": "Proximal Bodies in Hypersonic Flow", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04242006-172719", "creators": [ { "name": { "family": "Laurence", "given": "Stuart Jon" }, "id": "Laurence-Stuart-Jon", "orcid": "0000-0001-8760-8366", "display_name": "Laurence, Stuart Jon" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Stevenson", "given": "David John" }, "id": "Stevenson-D-J", "orcid": "0000-0001-9432-7159", "role": "member", "display_name": "Stevenson, David John" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VZJV-KJ48", "abstract": "The problem of proximal bodies in hypersonic flow is encountered in several important situations, both natural and man-made. The present work seeks to investigate one aspect of this problem by exploring the forces experienced by a secondary body when some part of it is within the shocked region created by a primary body travelling at hypersonic speeds.
\r\n\r\nAn analytical methodology based on the blast wave analogy is developed and used to predict the secondary force coefficients for simple geometries in both two and three dimensions. When the secondary body is entirely inside the primary shocked region, the nature of the lateral coefficient is found to depend strongly on the relative size of the two bodies. For two spheres, the methodology predicts that the secondary body will experience an exclusively attractive lateral force if the secondary diameter is larger then one-sixth the primary diameter. The analytical results are compared with numerical simulations carried out using the AMROC software and good agreement is obtained if an appropriate normalization for the lateral displacement is used.
\r\n\r\nResults from a series of experiments in the T5 hypervelocity shock tunnel are also presented and compared with perfect-gas numerical simulations, again with good agreement. In order to model this situation experimentally, a new force-measurement technique for short-duration hypersonic facilities has been developed, and results from the validation experiments are included.
\r\n\r\nFinally, the analytical methodology is used to model two physical situations. First, the entry of a binary asteroid system into the Earth's atmosphere is simulated. Second, a model for a fragmenting meteoroid in a planetary atmosphere is developed, and simulations are carried out to determine whether the secondary scatter patterns in the Sikhote-Alin crater field may be attributed to aerodynamic interactions between fragments rather than to secondary fragmentation. It is found that while aerodynamic interactions lead to increased secondary crater grouping, these groups do not exhibit the typically elliptical shape that we would expect secondary fragmentation to produce.
" }, { "name": "Li, Ling", "degree": "PhD", "year": "2006", "title": "Data Complexity in Machine Learning and Novel Classification Algorithms", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04122006-114210", "creators": [ { "name": { "family": "Li", "given": "Ling" }, "id": "Li-Ling", "display_name": "Li, Ling" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "compsci" ], "doi": "10.7907/EW2G-9986", "abstract": "This thesis summarizes four of my research projects in machine learning. One of them is on a theoretical challenge of defining and exploring complexity measures for data sets; the others are about new and improved classification algorithms.
\r\n\r\nWe first investigate the role of data complexity in the context of binary classification problems. The universal data complexity is defined for a data set as the Kolmogorov complexity of the mapping enforced by that data set. It is closely related to several existing principles used in machine learning such as Occam's razor, the minimum description length, and the Bayesian approach. We demonstrate the application of the data complexity in two learning problems, data decomposition and data pruning. In data decomposition, we illustrate that a data set is best approximated by its principal subsets which are Pareto optimal with respect to the complexity and the set size. In data pruning, we show that outliers usually have high complexity contributions, and propose methods for estimating the complexity contribution. Experiments were carried out with a practical complexity measure on several toy problems.
\r\n\r\nWe then propose a family of novel learning algorithms to directly minimize the 0/1 loss for perceptrons. A perceptron is a linear threshold classifier that separates examples with a hyperplane. Unlike most perceptron learning algorithms, which require smooth cost functions, our algorithms directly minimize the 0/1 loss, and usually achieve the lowest training error compared with other algorithms. The algorithms are also computationally efficient. Such advantages make them favorable for both standalone use and ensemble learning, on problems that are not linearly separable. Experiments show that our algorithms work very well with AdaBoost.
\r\n\r\nWe also study ensemble methods that aggregate many base hypotheses in order to achieve better performance. AdaBoost is one such method for binary classification problems. The superior out-of-sample performance of AdaBoost has been attributed to the fact that it minimizes a cost function based on the margin, in that it can be viewed as a special case of AnyBoost, an abstract gradient descent algorithm. We provide a more sophisticated abstract boosting algorithm, CGBoost, based on conjugate gradient in function space. When the AdaBoost exponential cost function is optimized, CGBoost generally yields much lower cost and training error but higher test error, which implies that the exponential cost is vulnerable to overfitting. With the optimization power of CGBoost, we can adopt more \"regularized\" cost functions that have better out-of-sample performance but are difficult to optimize. Our experiments demonstrate that CGBoost generally outperforms AnyBoost in cost reduction. With suitable cost functions, CGBoost can have better out-of-sample performance.
\r\n\r\nA multiclass classification problem can be reduced to a collection of binary problems with the aid of a coding matrix. The quality of the final solution, which is an ensemble of base classifiers learned on the binary problems, is affected by both the performance of the base learner and the error-correcting ability of the coding matrix. A coding matrix with strong error-correcting ability may not be overall optimal if the binary problems are too hard for the base learner. Thus a trade-off between error-correcting and base learning should be sought. In this paper, we propose a new multiclass boosting algorithm that modifies the coding matrix according to the learning ability of the base learner. We show experimentally that our algorithm is very efficient in optimizing the multiclass margin cost, and outperforms existing multiclass algorithms such as AdaBoost.ECC and one-vs-one. The improvement is especially significant when the base learner is not very powerful.
" }, { "name": "Lieberman, Daniel Howard", "degree": "PhD", "year": "2006", "title": "Detonation Interaction with Sharp and Diffuse Interfaces", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11172005-092205", "creators": [ { "name": { "family": "Lieberman", "given": "Daniel Howard" }, "id": "Lieberman-Daniel-Howard", "display_name": "Lieberman, Daniel Howard" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9JZE-X524", "abstract": "Detonation interaction with an interface was investigated, where the interface separated a combustible from an oxidizing mixture. The ethylene-oxygen combustible mixture had a fuel-rich composition to promote secondary combustion with the oxidizer in the turbulent mixing zone that resulted from the interaction. Both sharp and diffuse interfaces were studied.
\r\n\r\nDiffuse interfaces were created by the formation of a gravity current using a sliding valve that initially separated the test gas and combustible mixture. Opening the valve allowed a gravity current to develop before the detonation was initiated. By varying the delay between opening the valve and initiating the detonation it was possible to achieve a wide range of interface conditions. Sharp interfaces were created by using a nitro-cellulose membrane to separate the two mixtures. The membrane was destroyed by the detonation wave.
\r\n\r\nThe interface orientation and thickness with respect to the detonation wave have a profound effect on the outcome of the interaction. Diffuse interfaces result in curved detonation waves with a transmitted shock and following turbulent mixing zone. Sharp interfaces result in an interaction occurring at a node point similar to regular shock refraction (Henderson, 1989). The impulse was measured to quantify the degree of secondary combustion accounting for 5-6% of the total impulse. A model was developed that estimated the volume expansion of a fluid element due to combustion in the turbulent mixing zone (Dimotakis, 1991) to predict the impulse in the limit of infinite Damkohler number.
" }, { "name": "Liger, Matthieu", "degree": "PhD", "year": "2006", "title": "Uncooled Carbon Microbolometer Imager", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302005-174955", "creators": [ { "name": { "family": "Liger", "given": "Matthieu" }, "id": "Liger-Matthieu", "display_name": "Liger, Matthieu" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Meng", "given": "Ellis" }, "id": "Meng E-F-C", "role": "member", "display_name": "Meng, Ellis" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/R7HB-GF96", "abstract": "The discovery of infrared radiation two centuries ago and the theory of blackbody radiation one century later have given birth to the field of thermal imaging. Since then, researchers have devised numerous ways to detect infrared radiation. From World War II to the 1980s, semiconductor-based cooled photon detector arrays have reigned over the field of thermal imaging. Albeit limited to expensive, bulky systems used for military applications due to their cooling requirement they have been . The emergence of micromachining techniques in the 1980s however, have allowed for the development of uncooled, thermal detector arrays. Uncooled systems are expected to find more and more applications, especially in the civilian world.
\r\n\r\nHere we present a novel and simple way to fabricate uncooled infrared detectors suitable for integration into large-area arrays. The design is based on carbon obtained by means of polymer pyrolysis. We demonstrate how some electrical and thermal properties can be adjusted by process parameters, and then present the first micromachined carbon uncooled bolometer made of two-layers of self-supporting pyrolyzed-parylene carbon having different process-tuned properties.
\r\n\r\nFinally, based on this unique design and fabrication process, we develop a carbon bolometer array and demonstrate the thermal imaging capability by taking thermal images. Measurements show that the sensitivity to target temperature can be as low as 31mK and 44mK for 100us and 12us electrical signal integration time, respectively. This matches the current state of the art which is very promising considering the fact that this is the first time pyrolytic carbon has been used to fabricate a microbolometer array.
\r\n" }, { "name": "Luo, Wuan", "degree": "PhD", "year": "2006", "title": "Wiener Chaos Expansion and Numerical Solutions of Stochastic Partial Differential Equations", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05182006-173710", "creators": [ { "name": { "family": "Luo", "given": "Wuan" }, "id": "Luo-Wuan", "display_name": "Luo, Wuan" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/RPKX-BN02", "abstract": "Stochastic partial differential equations (SPDEs) are important tools in modeling complex phenomena, and they arise in many physics and engineering applications. Developing efficient numerical methods for simulating SPDEs is a very important while challenging research topic. In this thesis, we study a numerical method based on the Wiener chaos expansion (WCE) for solving SPDEs driven by Brownian motion forcing. WCE represents a stochastic solution as a spectral expansion with respect to a set of random basis. By deriving a governing equation for the expansion coefficients, we can reduce a stochastic PDE into a system of deterministic PDEs and separate the randomness from the computation. All the statistical information of the solution can be recovered from the deterministic coefficients using very simple formulae.
\r\n\r\nWe apply the WCE-based method to solve stochastic Burgers equations, Navier-Stokes equations and nonlinear reaction-diffusion equations with either additive or multiplicative random forcing. Our numerical results demonstrate convincingly that the new method is much more efficient and accurate than MC simulations for solutions in short to moderate time. For a class of model equations, we prove the convergence rate of the WCE method. The analysis also reveals precisely how the convergence constants depend on the size of the time intervals and the variability of the random forcing. Based on the error analysis, we design a sparse truncation strategy for the Wiener chaos expansion. The sparse truncation can reduce the dimension of the resulting PDE system substantially while retaining the same asymptotic convergence rates.
\r\n\r\nFor long time solutions, we propose a new computational strategy where MC simulations are used to correct the unresolved small scales in the sparse Wiener chaos solutions. Numerical experiments demonstrate that the WCE-MC hybrid method can handle SPDEs in much longer time intervals than the direct WCE method can. The new method is shown to be much more efficient than the WCE method or the MC simulation alone in relatively long time intervals. However, the limitation of this method is also pointed out.
\r\n\r\nUsing the sparse WCE truncation, we can resolve the probability distributions of a stochastic Burgers equation numerically and provide direct evidence for the existence of a unique stationary measure. Using the WCE-MC hybrid method, we can simulate the long time front propagation for a reaction-diffusion equation in random shear flows. Our numerical results confirm the conjecture by Jack Xin that the front propagation speed obeys a quadratic enhancing law.
\r\n\r\nUsing the machinery we have developed for the Wiener chaos method, we resolve a few technical difficulties in solving stochastic elliptic equations by Karhunen-Loeve-based polynomial chaos method. We further derive an upscaling formulation for the elliptic system of the Wiener chaos coefficients. Eventually, we apply the upscaled Wiener chaos method for uncertainty quantification in subsurface modeling, combined with a two-stage Markov chain Monte Carlo sampling method we have developed recently.
" }, { "name": "Lykotrafitis, Georgios C.", "degree": "PhD", "year": "2006", "title": "Experimental Study of Dynamic Frictional Sliding Modes along Incoherent Interfaces", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162006-005552", "creators": [ { "name": { "family": "Lykotrafitis", "given": "Georgios C." }, "id": "Lykotrafitis-Georgios-C", "orcid": "0000-0003-2088-5478", "display_name": "Lykotrafitis, Georgios C." } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Tromp", "given": "Jeroen" }, "id": "Tromp-J", "role": "member", "display_name": "Tromp, Jeroen" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Huang", "given": "Yonggang" }, "id": "Huang-Yonggang", "role": "member", "display_name": "Huang, Yonggang" } ], "option_major": [ "mecheng" ], "doi": "10.7907/0CCJ-5S66", "abstract": "Dynamic sliding along incoherent (frictional) interfaces is investigated experimentally in a microsecond time scale. A bimaterial system comprised of Homalite and steel plates and a homogeneous system consisting of two Homalite plates are considered. The plates are held together by a uniform compressive stress while dynamic sliding is initiated by an impact-induced shear loading. The evolution of maximum shear stress contours is recorded by high-speed photography in conjunction with dynamic photoelasticity. Simultaneously with photoelasticity, a newly-developed technique based on laser interferometry is employed to locally measure the sliding speed at the interface.
\r\n\r\nThe response of the Homalite-steel bimaterial system differs according to whether the impact loading is applied to the Homalite plate or to the steel plate. In the first case, a disturbance traveling along the interface at a constant speed close to the Rayleigh wave speed of steel generates a shear Mach line crossing the P-wave front. Sliding initiates behind the P-wave front in the Homalite plate and it propagates at a supershear speed with respect to the shear wave speed of Homalite. A disturbance, traveling at constant speeds between the shear wave speed and the longitudinal wave speed of Homalite, appears behind the sliding tip. Wrinkle-like opening pulses, propagating along the bimaterial interface at a constant speed between the Rayleigh wave and the shear wave speed of Homalite, are also observed. When the impact loading is applied to the steel plate, sliding at a given point initiates with the arrival of the P-wave front there, so that the rupture is sonic with respect to steel and supersonic with respect to Homalite.
\r\n\r\nIn all the experiments performed on the bimaterial structure (Homalite-steel), sliding always occurred in a crack-like mode. In the case of a homogeneous system of Homalite plates however, direct physical evidence of different modes of sliding is recorded. Crack-like sliding, pulse-like sliding and mixed mode sliding in the form of pulses followed by a crack are discovered. Supersonic trailing pulses are also recorded. Behind the sliding tip, wrinkle-like opening pulses are developed for a wide range of impact speeds and confining stresses.
\r\n" }, { "name": "Maune, Brett Michael", "degree": "PhD", "year": "2006", "title": "Fluidic and Polymeric Integration and Functionalization of Optical Microresonators", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-11222005-163249", "creators": [ { "name": { "family": "Maune", "given": "Brett Michael" }, "id": "Maune-Brett-Michael", "display_name": "Maune, Brett Michael" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2746-3104", "abstract": "Optical resonators are structures that spatially confine and temporally store light. The use of such resonators continues to permeate throughout society as improvements in their design and fabrication qualify them to fulfill an ever-increasing array of technological and scientific applications. Traditionally, resonators have primarily been used in lasers and as filters, and more recently have been utilized in other areas including chemical sensing, spontaneous emission modulation, and quantum electrodynamics experiments. In many of these applications, the functionalities of the resonators are solely derived from the geometry and material composition of the resonators themselves. The central theme of this thesis is the investigation of further increasing a resonator's functionality through its integration with fluidic and polymeric materials.
\r\n\r\nThe thesis begins with an investigation of integrating silicon ring resonators with electro-optic polymer and liquid crystal in an effort to tune the resonators' resonant wavelengths. Although the electro-optic polymer efforts are a failure, we are able to electrically tune the rings' resonances using electrodes and the reorientation of liquid crystal surrounding the resonators. We then take the knowledge and experience acquired from these experiments and pursue the functionalization of photonic crystal laser resonators, a relatively new class of microresonators constructed from a thin slab of InGaAsP quantum well material with a periodic array of holes etched through the slab. To this end, we first infiltrate the porous resonators with liquid crystal and construct liquid crystal cells around the devices. We are then able to tune the lasing wavelengths by reorienting the liquid crystal with a voltage applied across the cell. Next, we devise a new photonic crystal cavity designed to optimally interact with infiltrated birefringent materials, by supporting two orthogonally polarized high-Q modes. Again, we infiltrate the cavity with liquid crystal, but this time optically control the liquid crystal orientation with a photoaddressable polymer film. By doing so we are able to realize a fundamentally new laser tuning method by reversibly Q-switching a resonator's lasing mode between the two cavity modes and thereby control the laser's emission wavelength and polarization. The successful fluidic and polymeric integration with optical resonators presented in this thesis demonstrates some of the possible synergies that can be obtained with such integration and suggests that further enhancements in resonator functionality is possible.
" }, { "name": "Min, Bumki", "degree": "PhD", "year": "2006", "title": "Ultrahigh\u2013Q Microtoroid On-Chip Resonators for Low Threshold Microlasers", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07062006-135109", "creators": [ { "name": { "family": "Min", "given": "Bumki" }, "id": "Min-Bumki", "orcid": "0000-0002-4639-3423", "display_name": "Min, Bumki" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/KGE9-J792", "abstract": "Recently demonstrated silica toroidal microcavities, as on-chip resonant cavities, become one of the most promising laser resonators due to their exceptional ability to confine optical energy temporarily and spatially (high Q-factor and small mode volume) while being integrated on a silicon substrate.
\r\n\r\nIn the first part of this thesis, semianalytic theory is presented for an in-depth understanding of the high-Q toroidal microcavity coupled to a tapered fiber waveguide. Basic properties of toroidal microcavities such as cavity mode field, resonance wavelength, cavity mode volume, radiative Q-factor, and phase-matching condition are described within the limit of an iterative perturbation expansion method. With this theoretical background, various laser systems with different gain media, utilizing the high-Q toroidal microcavity as a laser resonator, are demonstrated in the latter parts.
\r\n\r\nAs a first example, II-VI semiconductor nanocrystal, CdSe/ZnS (core/shell), quantum dots are coated on the surface of ultrahigh-Q toroidal microcavities. By pulsed excitation of quantum dots on the surface, either through tapered fiber waveguides or free-space, lasing is observed at both room and liquid nitrogen temperature. Use of a tapered fiber coupling substantially lowered the threshold energy when compared to the case of free-space excitation. Further threshold reduction down to 9.9 fJ was made possible by quantum dot density control.
\r\n\r\nLasing from an erbium-implanted high-Q silica toroidal microcavity is demonstrated and analyzed in the next chapter. A minimum threshold power as low as 4.5 uW and a maximum output lasing power as high as 39.4 uW are obtained. Control of lasing wavelength is demonstrated by changing the cavity loading. Analytic formulas predicting threshold power, differential slope efficiency are derived and their dependence on cavity loading, erbium ion concentration and Q-factor is found and compared with the experimental results.
\r\n\r\nThe nonlinear oscillation in an ultrahigh-Q silica toroidal microcavity is investigated in the last chapter. A controllable and reversible transition between parametric and Raman oscillation is experimentally demonstrated and theoretically analyzed. By direct change of cavity loading and indirect adjustment of frequency detuning, parametric and/or Raman oscillation can be accessed selectively without modification of cavity geometry in a toroidal microcavity with large enough aspect ratio. Based on an effective cavity gain theory, this transition is analyzed in terms of cavity loading and frequency detuning leading to a better understanding of the combined effects of parametric and Raman processes in silica microcavities.
" }, { "name": "Mitros, Ania Karolina", "degree": "PhD", "year": "2006", "title": "A Compact System for Self-Motion Estimation", "advisor": "Koch, Christof; Diorio, Christopher J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252006-145119", "creators": [ { "name": { "family": "Mitros", "given": "Ania Karolina" }, "id": "Mitros-Ania-Karolina", "display_name": "Mitros, Ania Karolina" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" }, { "name": { "family": "Diorio", "given": "Christopher J." }, "id": "Diorio-Christopher-J", "role": "advisor", "display_name": "Diorio, Christopher J." } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Diorio", "given": "Christopher J." }, "id": "Diorio-Christopher-J", "role": "member", "display_name": "Diorio, Christopher J." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cns" ], "doi": "10.7907/50B3-RW79", "abstract": "Self-motion estimation is a vital problem for autonomous robots, frequently and appropriately addressed by vision algorithms. Most approaches involve repeating some local calculation over the entire imaging array, such as detection of locally salient features. A simple and local calculation can be efficiently implemented on the same chip as the photo-sensing array, thus parallelizing a huge computational task and vastly reducing the amount of data to transmit off chip. Mismatch between devices has previously been a stumbling block to producing truly useful arrays of local processing elements. Floating gate technology is used here as a compact means of programming away offsets in subcircuits to remedy this problem. A custom analog chip performs the above functions. For each pixel, the chip outputs sensed light intensity, the values of the vertical and horizontal intensity gradients, and a binary value indicating whether a feature is centered on that pixel. These values can be used as inputs to a motion estimation algorithm implemented on a standard computer." }, { "name": "Mu\u00f1oz Fern\u00e1ndez, Michela", "degree": "PhD", "year": "2006", "title": "Coherent Optical Array Receiver for PPM Signals Under Atmospheric Turbulence", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252006-221314", "creators": [ { "name": { "family": "Mu\u00f1oz Fern\u00e1ndez", "given": "Michela" }, "id": "Mu\u00f1oz-Fern\u00e1ndez-M", "orcid": "0000-0001-8028-2156", "display_name": "Mu\u00f1oz Fern\u00e1ndez, Michela" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Mukai", "given": "Ryan" }, "id": "Mukai-R", "role": "member", "display_name": "Mukai, Ryan" }, { "name": { "family": "Vilnrotter", "given": "Victor" }, "id": "Vilnrotter-V", "role": "member", "display_name": "Vilnrotter, Victor" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/VDSA-SA42", "abstract": "The performance of a coherent free-space optical communications system operating in the presence of turbulence is investigated. Maximum Likelihood Detection techniques are employed to optimally detect Pulse Position Modulated signals with a focal-plane detector array and to reconstruct the turbulence-degraded signals.
\r\n\r\nLaboratory equipment and experimental setup used to carry out these experiments at the Jet Propulsion Laboratory are described. The key components include two lasers operating at 1064 nm wavelength for use with coherent detection, a 16 element (4 X 4) InGaAs focal-plane detector array, and a data-acquisition and signal-processing assembly needed to sample and collect the data and analyze the results. The detected signals are combined using the least-mean-square (LMS) algorithm. In the first part of the experimental results we show convergence of the algorithm for experimentally obtained signal tones in the presence of atmospheric turbulence. The second part of the experimental results shows adaptive combining of experimentally obtained heterodyned pulse position modulated (PPM) signals with pulse-to-pulse coherence in the presence of simulated spatial distortions resembling atmospheric turbulence. The adaptively combined PPM signals are phased up via an LMS algorithm suitably optimized to operate with PPM in the presence of additive shot noise. A convergence analysis of the algorithm is presented, and results with both computer-simulated and experimentally obtained PPM signals are analyzed.
\r\n\r\nThe third part of the experimental results, in which the main goal of this thesis is achieved, includes an investigation of the performance of the Coherent Optical Receiver Experiment (CORE) at JPL. Bit Error Rate (BER) results are presented for single and multichannel optical receivers where quasi shot noise-limited performance is achieved under simulated turbulence conditions using noncoherent postdetection processing techniques. Theoretical BER expressions are compared with experimentally obtained BER results, and array combining gains are presented. BER results are shown as a function of signal-to-noise ratio (SNR), photons per symbol, and photons per bit (PPB).
" }, { "name": "Neal, Terrell Demetris", "degree": "PhD", "year": "2006", "title": "Surface Plasmon Enhanced Light Emission from Organic Light Emitters", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222006-151349", "creators": [ { "name": { "family": "Neal", "given": "Terrell Demetris" }, "id": "Neal-Terrell-Demetris", "display_name": "Neal, Terrell Demetris" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/DH6C-2C59", "abstract": "We have experimentally verified that visible light emission for various organic light emitters can be enhanced through the use of surface plasmon coupling layers. By matching the plasmon frequency of a thin unpatterned silver film to the emission of a dye-doped polymer deposited onto this metal surface, we have observed an 11-fold enhancement of light emission. By patterning the silver layer, we estimate that the plasmon frequency can be tuned to match dye-doped polymer emission frequencies, and even larger emission enhancements as well as extraction efficiencies are expected. Carrier dynamics of such plasmon-enhanced organic light emitters were studied and a recombination rate increase due to surface plasmon polaritons was experimentally observed. Internal quantum efficiency data from the polyfluorenes studied follow the trend supported by the time-resolved photoluminescence measurements. Also, we have presented a way to extend the lifetime of organic light emitters by reducing the photodegredation effects from photo-oxidation using surface plasmon coupling." }, { "name": "Papadantonakis, Karl Spyros", "degree": "PhD", "year": "2006", "title": "Rigorous Analog Verification of Asynchronous Circuits", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01132006-152609", "creators": [ { "name": { "family": "Papadantonakis", "given": "Karl Spyros" }, "id": "Papadantonakis-Karl-Spyros", "display_name": "Papadantonakis, Karl Spyros" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "member", "display_name": "DeHon, Andre" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/4R8F-WF03", "abstract": "This thesis shows that rigorous verification of some analog implementation of any Quasi-Delay-Insensitive (QDI) asynchronous circuit is possible. That is, we show that in an accurate analog model, any behavior will adhere to the digital computation specifications under any possible noise and environment timing. Unlike a traditional simulation, we can analyze all of the infinitely many possible analog behaviors, in a time linear in the circuit size. A problem that arises in asynchronous circuit design is that the analog implementations of digital computations do not in general exhibit all properties demanded by the digital model assumed in circuit construction. For example, the digital model is atomic, in a sense we define. By contrast, analog models are non-atomic, and, as a result, we can give examples of real circuits with operational failures. There exist other attributes of analog models which can cause failures, and no complete classification exists. Ultimately there is only one way to solve this problem: we must show that all possible analog behaviors obey the atomic model. We focus on CMOS implementations, and the associated accepted bulk-scale model. Given any canonically-generated implementation of a general computation, we can rigorously verify it. The only exception to this rule is that restoring delay elements must be inserted into some implementations (fortunately, this change has no semantic effect on QDI circuits, by definition). Our theorem guarantees that when any possible analog behavior is properly observed, we obtain a valid, atomic digital execution. Several rigorous verifications have been produced, including one for an asynchronous pipeline circuit with dual-rail data." }, { "name": "Papandrew, Alexander Blair", "degree": "PhD", "year": "2006", "title": "The Effects of High Pressure on the Vibrational and Magnetic Properties of Iron-Based Materials", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03022006-151019", "creators": [ { "name": { "family": "Papandrew", "given": "Alexander Blair" }, "id": "Papandrew-Alexander-Blair", "display_name": "Papandrew, Alexander Blair" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Halevy", "given": "Itzhak" }, "id": "Halevy-I", "role": "member", "display_name": "Halevy, Itzhak" }, { "name": { "family": "Asimow", "given": "Paul David" }, "id": "Asimow-P-D", "role": "member", "display_name": "Asimow, Paul David" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/6VG5-GH55", "abstract": "High pressure experimental methods are demonstrated for studying pressure-dependent material properties and solid phases unattainable at ambient pressure with synchrotron nuclear resonance techniques.
\r\n\r\nThe phonon density of states (DOS) of nanocrystalline 57Fe was measured under pressures up to 28 gigapascals (2.8 x 10^5 atm) using the nuclear resonant inelastic x-ray scattering (NRIXS) technique. The nanocrystalline material exhibited an enhancement in its DOS at low energies by a factor of 2.2. This enhancement persisted throughout the entire pressure range, even across the pressure-induced bcc-to-hcp phase transformation at 13 GPa. At higher energies, the van Hove singularities in both samples were coincident in energy at all pressures, indicating that interatomic forces in nanocrystalline materials are similar to those in bulk crystals. Subsequent neutron inelastic scattering measurements at ultra-low energies (2 to 18 micro-eV) also observed enhancement in the vibrational spectrum of the nanocrystalline material. This enhancement is partly attributed to novel microstructural modes, characterized by cooperative dynamics of individual crystallites.
\r\n\r\nRecent density functional theory (DFT) investigations have identified a static antiferromagnetic structure with negligible hyperfine fields for the high-pressure hcp (epsilon) phase of iron. This structure exhibits a perfect cancellation of core electron polarization at the nucleus by an equally large and oppositely oriented conduction electron polarization. To test this hypothesis, an alloy of composition Fe92Ni8 was subjected to synchrotron Mossbauer spectrometry (SMS) measurements at 20 GPa and 11 K. The addition of nickel was expected to disrupt the precise balance of core and conduction electron polarization in the alloy, and to result in a measurable hyperfine field in the presence of significant magnetic moments. Full-potential DFT calculations in the generalized gradient approximation (GGA) verified this effect for a Fe7Ni1 hcp supercell, which exhibited calculated hyperfine fields of nearly 70 kG. However, SMS measurements were unable to detect a hyperfine field. This disparity may be a result of quantum spin fluctuations on the geometrically frustrated hcp lattice with a period much shorter than the lifetime of the nuclear excited state. Alternately, the result is evidence of a significant flaw in the handling of exchange coupling by the GGA exchange-correlation functional.
" }, { "name": "Parkin, Kevin L.G.", "degree": "PhD", "year": "2006", "title": "The Microwave Thermal Thruster and Its Application to the Launch Problem", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022006-160023", "creators": [ { "name": { "family": "Parkin", "given": "Kevin L.G." }, "id": "Parkin-Kevin-L-G", "orcid": "0000-0003-4521-8559", "display_name": "Parkin, Kevin L.G." } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Barmatz", "given": "Martin B." }, "id": "Barmatz-M-B", "role": "member", "display_name": "Barmatz, Martin B." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Worden", "given": "Simon P." }, "id": "Worden-S-P", "role": "member", "display_name": "Worden, Simon P." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T337-T709", "abstract": "Nuclear thermal thrusters long ago bypassed the 50-year-old specific impulse (Isp) limitation of conventional thrusters, using nuclear powered heat exchangers in place of conventional combustion to heat a hydrogen propellant. These heat exchanger thrusters experimentally achieved an Isp of 825 seconds, but with a thrust-to-weight ratio (T/W) of less than ten they have thus far been too heavy to propel rockets into orbit.
\r\n\r\nThis thesis proposes a new idea to achieve both high Isp and high T/W: The Microwave Thermal Thruster. This thruster covers the underside of a rocket aeroshell with a lightweight microwave absorbent heat exchange layer that may double as a re-entry heat shield. By illuminating the layer with microwaves directed from a ground-based phased array, an Isp of 700\u2013900 seconds and T/W of 50\u2013150 is possible using a hydrogen propellant. The single propellant simplifies vehicle design, and the high Isp increases payload fraction and structural margins. These factors combined could have a profound effect on the economics of building and reusing rockets.
\r\n\r\nA laboratory-scale microwave thermal heat exchanger is constructed using a single channel in a cylindrical microwave resonant cavity, and new type of coupled electromagnetic-conduction-convection model is developed to simulate it. The resonant cavity approach to small-scale testing reveals several drawbacks, including an unexpected oscillatory behavior. Stable operation of the laboratory-scale thruster is nevertheless successful, and the simulations are consistent with the experimental results.
\r\n\r\nIn addition to proposing a new type of propulsion and demonstrating it, this thesis provides three other principal contributions: The first is a new perspective on the launch problem, placing it in a wider economic context. The second is a new type of ascent trajectory that significantly reduces the diameter, and hence cost, of the ground-based phased array. The third is an eclectic collection of data, techniques, and ideas that constitute a Microwave Thermal Rocket as it is presently conceived, in turn selecting and motivating the particular experimental and computational analyses undertaken.
" }, { "name": "Pfister, Samuel Thomas", "degree": "PhD", "year": "2006", "title": "Algorithms for Mobile Robot Localization and Mapping, Incorporating Detailed Noise Modeling and Multi-scale Feature Extraction", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262006-130209", "creators": [ { "name": { "family": "Pfister", "given": "Samuel Thomas" }, "id": "Pfister-Samuel-Thomas", "display_name": "Pfister, Samuel Thomas" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/FN3J-M568", "abstract": "Mobile robot localization and mapping in unknown environments is a fundamental requirement for effective autonomous navigation. Three different approaches to localization and mapping are presented. Each is based on data collected from a robot using a dense range scanner to generate a planar representation of the surrounding environment. This externally sensed range data is then overlayed and correlated to estimate the robot's position and build a map.
\r\n\r\nThe three approaches differ in the choice of representation of the range data, but all achieve improvements over prior work using detailed sensor modeling and rigorous bookkeeping of the modeled uncertainty in the estimation processes. In the first approach, the raw range data points collected from two different positions are individually weighted and aligned to estimate the relative robot displacement. In the second approach, line segment features are extracted from the raw point data and are used as the basis for efficient and robust global map construction and localization. In the third approach, a new multi-scale data representation is introduced. New methods of localization and mapping are developed, taking advantage of this multi-scale representation to achieve significant improvements in computational complexity. A central focus of all three approaches is the determination of accurate and robust solutions to the data association problem, which is critical to the accuracy of any sensor-based localization and mapping method.
\r\n\r\nExperiments using data collected from a Sick LMS-200 laser scanner illustrate the effectiveness of the algorithms and improvements over prior work. All methods are capable of being run in real time on a mobile robot, and can be used to support fully autonomous navigation applications.
" }, { "name": "Rokhsari Azar, Hossein", "degree": "PhD", "year": "2006", "title": "High-Q Microcavities: Optomechanical Nonlinearities, Measurement Techniques and Applications", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082005-204747", "creators": [ { "name": { "family": "Rokhsari Azar", "given": "Hossein" }, "id": "Rokhsari-Azar-Hossein", "display_name": "Rokhsari Azar, Hossein" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Crosignani", "given": "Bruno" }, "id": "Crosignani-B", "role": "member", "display_name": "Crosignani, Bruno" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/CVT6-8J70", "abstract": "Optical microresonators have historically been perceived as structures that could efficiently confine optical energies. This is due to their exceedingly low losses at optical frequencies. This thesis has, for the first time, explored these structures in a starkly different frequency range. Optical microcavities like any other structure have mechanical eigenmodes or resonant modes of vibration with quality-factors representing the efficiency of energy storage at mechanical frequencies. It is shown here that micron size of these structures results in vibrations at radio frequencies (~1-100 MH), about seven orders of magnitude apart from the optical frequencies (~100 THz). Mechanical quality factors in excess of 5,000 are measured for toroidal microcavities revealing a heretofore unknown potential of these structures in storing energy at frequencies remarkably distant from their optical resonant modes. \r\n\r\nThis thesis describes how radiation-pressure or the force due to impact of photons could result in exceptionally strong couplings between the mechanical and optical resonators collocated within the same device. The discovered optomechanical coupling present in toroid microcavities is shown to reach such a high level that regenerative mechanical oscillations of the cavity structure are initiated with only micro-Watts of optical power. This is the first demonstration of radiation-pressure-induced mechanical oscillations in any type of optomechanical system. Embodied within a microscale, chip-based device, this mechanism can benefit both research into macroscale quantum mechanical phenomena and improve the understanding of the mechanism within the context of Laser interferometer gravitational-wave observatory (LIGO). It also suggests that new technologies are possible that will leverage the phenomenon within photonics.\r\n\r\nDifferent physical functionalities are also realized in this thesis by a combination of ultra-high-Q microtoroids and extremely low-loss tapered optical fibers for efficient delivery of optical power to these structures. Using these tools an almost ideal optical band-pass filter is designed with efficiencies solely limited by intrinsic losses of the optical resonator. These intrinsic loss mechanisms are experimentally studied and differentiated by a powerful technique based on thermal nonlinearities of the microcavity material. By taking advantage of slow response times of thermal effects, an innovative pump and probe technique is also developed to unveil and measure the Kerr nonlinearity in microcavities, for the first time, at room temperature." }, { "name": "Sadjadpour, Amir", "degree": "PhD", "year": "2006", "title": "A Micromechanics-Inspired Three-Dimensional Constitutive Model for the Thermomechanical Response of Shape-Memory Alloys", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-05112006-162948", "creators": [ { "name": { "family": "Sadjadpour", "given": "Amir" }, "id": "Sadjadpour-Amir", "display_name": "Sadjadpour, Amir" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/MB1W-1V17", "abstract": "The goal of this thesis is to develop a full dimensional micromechanics-inspired constitutive model for polycrystalline shape-memory alloys. The model is presented in two forms: (1) The one-dimensional framework where we picture the ability of the model in capturing main properties of shape memory alloys such as superelasticity and shape-memory effect; (2) The full dimensional model where micromechanics origins of the model, the concepts emerged from those analysis and their relation to macroscopic properties in both single and polycrystals are presented.
\r\n\r\nWe use this framework to study the effects of the texture and anisotropy in the material behavior. Since phase transformation often competes with plasticity in shape-memory alloys, we incorporate that phenomenon into our model. We also demonstrate the ability of the model to predict the response of the material and track the phase transformation process for multi-axial, proportional and non-proportional loading and unloading experiments. We consider both stress-controlled and strain-controlled experiments and develop the model for isothermal, adiabatic and non-adiabatic thermal conditions. Adiabatic heating and loading rate both lead to the apparent hardening at high rates. We also visit this problem and examine the relative role of these two factors.
\r\n\r\nFinally we extend our model to study the reversible \"bcc\" to \"hcp\" martensitic phase transformation in pure iron. We consider a wide range of loading rates ranging from quasistatic to high rate dynamic loading and use our model to describe the evolution of the microstructure along with the effects of the rate hardening and thermal softening.
" }, { "name": "Shadden, Shawn Christopher", "degree": "PhD", "year": "2006", "title": "A Dynamical Systems Approach to Unsteady Systems", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122006-083011", "creators": [ { "name": { "family": "Shadden", "given": "Shawn Christopher" }, "id": "Shadden-Shawn-Christopher", "orcid": "0000-0001-7561-1568", "display_name": "Shadden, Shawn Christopher" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "cds" ], "doi": "10.7907/BG86-YB12", "abstract": "For steady systems, interpreting the flow structure is typically straightforward because streamlines and trajectories coincide. Therefore the velocity field, or quantities derived from it, provide a clear description of the flow geometry. For unsteady flows, this is often not the case. A more natural choice is to understand the flow in terms of particle trajectories, i.e., the Lagrangian viewpoint. While the chaotic behavior of trajectories of unsteady systems makes direct interpretation difficult, more structured and frame-independent techniques have been developed. The method presented here uses finite-time Lyapunov exponent (FTLE) fields to locate Lagrangian Coherent Structures (LCS). LCS are co-dimension 1 separatrices that partition regions in phase space with dynamically different behavior. This method enables the detection of often non-obvious, time-dependent boundaries in complicated flows, which greatly elucidates the transport and mixing geometry.
\r\n\r\nThe first portion of this thesis deals with the theoretical development of LCS for two-, and then, n-dimensional systems, where n>2. Based on the definitions presented, some important properties of these structures are proven. It is shown that the flux across an LCS is typically very small and depends on the relative strength of the structure, the difference between the local rotation rate of the LCS with that of the Eulerian velocity field, and the integration time used to compute the FTLE field.
\r\n\r\nThe second portion of the thesis presents a series of numerical studies in which LCS are used to examine a range of interesting applications. This portion is bridged with the theoretical development presented in the first half by a brief chapter describing the numerical computation of FTLE fields and LCS. Applications presented in the second half of the thesis include the study of vortex rings in which LCS are used to define the unsteady vortex boundary to clarify the entrainment and detrainment processes; the computation of LCS in the ocean to provide mesoscale separatrices that help characterize the flow conditions and help navigate gliders or drifters used for sampling; flow over an airfoil where an LCS captures the unsteady separation profile; flow through a micro-mixing channel where LCS reveal the mechanism and geometry of chaotic mixing.
\r\n" }, { "name": "Sharif, Masoud", "degree": "PhD", "year": "2006", "title": "Broadband Wireless Broadcast Channels: Throughput, Performance, and PAPR Reduction", "advisor": "Hassibi, Babak", "url": "https://resolver.caltech.edu/CaltechETD:etd-08292005-100440", "creators": [ { "name": { "family": "Sharif", "given": "Masoud" }, "id": "Sharif-Masoud", "display_name": "Sharif, Masoud" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/25JK-Z952", "abstract": "The ever-growing demand for higher rates and better quality of service in cellular systems has attracted many researchers to study techniques to boost the capacity and improve the performance of cellular systems. The main candidates to increase the capacity are to use multiple antennas or to increase the bandwidth. This thesis attempts to solve a few challenges regarding scheduling schemes in the downlink of cellular networks, and the implementation of modulation schemes suited for wideband channels.
\r\n\r\nDownlink scheduling in cellular systems is known to be a bottleneck for future broadband wireless communications. Information theoretic results on broadcast channels provide the limits for the maximum achievable rates for each receiver and transmission schemes to achieve them. It turns out that the sum-rate capacity (sum-rate (or throughput) refers to the sum of the transmission rates to all users) of a multi-antenna broadcast channel heavily depends on the availability of channel state information (CSI) at the transmitter. Unfortunately, the dirty paper coding (DPC) scheme which achieves the capacity region is extremely computationally intensive especially in multiuser context. Furthermore, relying on the assumption that full CSI is available from all the n users may not be feasible in practice.
\r\n\r\nIn the first part of the thesis, we obtain the scaling law of the sum-rate capacity for large n and for a homogeneous fading MIMO (multiple input multiple output) broadcast channel, and then propose a simple scheme that only requires little (partial) CSI and yet achieves the same scaling law. Another important issue in downlink scheduling is to maintain fairness among users with different distances to the transmitter. Interestingly, we prove that our scheduling scheme becomes fair provided that the number of transmit antennas is large enough. We further analyze the impact of using a throughput optimal scheduling on the delay in sending information to the users. Finally, we look into the problem of differentiated rate scheduling in which different users demand for different sets of rates. We obtain explicit scheduling schemes to achieve the rate constraints.
\r\n\r\nIn the second part of the thesis, we focus on orthogonal frequency division multiplexing (OFDM), which is the most promising technique for broadband wireless channels (mainly due to its simplicity of channel equalization even in a severe multipath fading environment). The main disadvantage of this modulation, however, is its high peak to mean envelope power ratio (PMEPR). This is due to the fact that the OFDM signal consists of many (say n) harmonically related subcarriers which may, in the worst-case, add up constructively and lead to large peaks (of order n) in the signal.
\r\n\r\nDespite this worst-case performance, we show that when each subcarrier is chosen from some given constellation, the PMEPR behaves like log{n} almost surely, for large n. This implies that there exist almost full-rate codes with a PMEPR of log{n} for large n. We further prove that there exist codes with rate not vanishing to zero such that the PMEPR is less than a constant (independent of n). We also construct high rate codes with a guaranteed PMEPR of log{n}. Simulation results show that in a system with 128 subcarriers and using 16QAM, the PMEPR of a multicarrier signal can be reduced from 13.5 to 3.4 which is within 1.6dB of the PMEPR of a single carrier system.
" }, { "name": "Shih, Victor-Chi-Yuan", "degree": "PhD", "year": "2006", "title": "Temperature-Controlled Microchip Liquid Chromatography System", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-04182006-162552", "creators": [ { "name": { "family": "Shih", "given": "Victor-Chi-Yuan" }, "id": "Shih-Victor-Chi-Yuan", "display_name": "Shih, Victor-Chi-Yuan" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Lee", "given": "Terry D." }, "id": "Lee-T-D", "role": "member", "display_name": "Lee, Terry D." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZDK5-Q871", "abstract": "High-performance liquid chromatography (HPLC) is one of the most important analytical tools heavily used in the fields of chemistry, biotechnology, pharmaceutics, and the food industry. The power of liquid chromatography comes from its ability to achieve molecular separation with extremely high efficiency and its great flexibility of incorporating versatile sensors for detecting a broad range of analytes. In the past decades, great efforts have been put into liquid chromatography instrumentation and methods, aiming to further improve separation efficiency, sensitivity, repeatability, throughput, and costs. The contribution of this thesis is to illustrate with real examples the great potential of MEMS microchip liquid chromatography systems with on-chip temperature control for replacing and improving the conventional desktop HPLC systems.
\r\n\r\nThis thesis is composed of seven chapters. Chapter 1 gives an introduction to MEMS technology and its application in making lab-on-a-chip systems. Chapter 2 describes the theoretical background and the evolution of HPLC technology. Chapter 3 demonstrates how to use state-of-the-art MEMS technology to make high-pressure microfluidic channels, which will be used for constructing microchip HPLC systems later. Chapter 4 describes a temperature-controlled microchip HPLC system that uses a temporal temperature gradient to achieve analyte elution. Separation of amino acids and low density lipoproteins was successfully demonstrated using the proposed system. Chapter 5 describes a novel embedded HPLC system, which demonstrated a record high pressure capacity (> 1000 psi) among microchip HPLC systems. High quality separation results of trace-level daunorubicin and doxorubicin were obtained using the proposed system and laser-induced fluorescence detection. A novel C4D sensor together with the RISE sensitivity enhancement method was proposed and investigated for the first time for microchip HPLC analyte detection. Chapter 6 describes the first work to pack 30 nm gold nanoparticles into the HPLC separation column as the stationary phase with the assistance of in-situ molecular self-assembly between nanoparticles and thiolated molecules. Preliminary results demonstrated the possibility of building fully filled nanoparticle HPLC columns for extremely high separation efficiency application. Chapter 7 then gives the conclusions of this thesis.
" }, { "name": "Spanos, Demetri Polychronis", "degree": "PhD", "year": "2006", "title": "Distributed Gradient Systems and Dynamic Coordination", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06262006-171822", "creators": [ { "name": { "family": "Spanos", "given": "Demetri Polychronis" }, "id": "Spanos-Demetri-Polychronis", "display_name": "Spanos, Demetri Polychronis" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "cds" ], "doi": "10.7907/D1NJ-KF96", "abstract": "Many systems comprised of interconnected sub-units exhibit coordinated behaviors; social groups, networked computers, financial markets, and numerous biological systems come to mind. There has been long-standing interest in developing a scientific understanding of coordination, both for explanatory power in the natural and economic sciences, and also for constructive power in engineering and applied sciences. This thesis is an abstract study of coordination, focused on developing a systematic \"design theory\" for producing interconnected systems with specifiable coordinated behavior; this is in contrast to the bulk of previous work on this subject, in which any design component has been primarily ad-hoc.
\r\n\r\nThe main theoretical contribution of this work is a geometric formalism in which to cast distributed systems. This has numerous advantages and \"naturally\" parametrizes a wide class of distributed interaction mechanisms in a uniform way. We make use of this framework to present a model for distributed optimization, and we introduce the distributed gradient as a general design tool for synthesizing dynamics for distributed systems. The distributed optimization model is a useful abstraction in its own right and motivates a definition for a distributed extremum. As one might expect, the distributed gradient is zero at a distributed extremum, and the dynamics of a distributed gradient flow must converge to a distributed extremum. This forms the basis for a wide variety of designs, and we are in fact able to recover a widely studied distributed averaging algorithm as a very special case.
\r\n\r\nWe also make use of our geometric model to introduce the notion of coordination capacity; intuitively, this is an upper bound on the \"complexity\" of coordination that is feasible given a particular distributed interaction structure. This gives intuitive results for local, distributed, and global control architectures, and allows formal statements to be made regarding the possibility of \"solving\" certain optimization problems under a particular distributed interaction model.
\r\n\r\nFinally, we present a number of applications to illustrate the theoretical approach presented; these range from \"standard\" distributed systems tasks (leader election and clock synchronization) to more exotic tasks like graph coloring, distributed account balancing, and distributed statistical computations.
" }, { "name": "Srinivasan, Kartik", "degree": "PhD", "year": "2006", "title": "Semiconductor Optical Microcavities for Chip-Based Cavity QED", "advisor": "Painter, Oskar J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152006-102022", "creators": [ { "name": { "family": "Srinivasan", "given": "Kartik" }, "id": "Srinivasan-Kartik", "orcid": "0000-0003-2589-3688", "display_name": "Srinivasan, Kartik" } ], "advisors": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "advisor", "display_name": "Painter, Oskar J." } ], "committee": [ { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "chair", "display_name": "Painter, Oskar J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/0QW0-1R58", "abstract": "Optical microcavities can be characterized by two key quantities: an effective mode volume Veff, which describes the per photon electric field strength within the cavity, and a quality factor Q, which describes the photon lifetime within the cavity. Cavities with a small Veff and a high Q offer the promise for applications in nonlinear optics, sensing, and cavity quantum electrodynamics (cavity QED). Chip-based devices are particularly appealing, as planar fabrication technology can be used to make optical structures on a semiconductor chip that confine light to wavelength-scale dimensions, thereby creating strong enough electric fields that even a single photon can have an appreciable interaction with matter. When combined with the potential for integration and scalability inherent to microphotonic structures created by planar fabrication techniques, these devices have enormous potential for future generations of experiments in cavity QED and quantum networks.
\r\n\r\nThis thesis is largely focused on the development of ultrasmall Veff, high-Q semiconductor optical microcavities. In particular, we present work that addresses two major topics of relevance when trying to observe coherent quantum interactions within these semiconductor-based systems: (1) the demonstration of low optical losses in a wavelength-scale microcavity, and (2) the development of an efficient optical channel through which the sub-micron-scale optical field in the microcavity can be accessed. The two microcavities of specific interest are planar photonic crystal defect resonators and microdisk resonators.
\r\n\r\nThe first part of this thesis details the development of photonic crystal defect microcavities. A momentum space analysis is used to design structures in graded square and hexagonal lattice photonic crystals that not only sustain high Qs and small Veffs, but are also relatively robust to imperfections. These designs are then implemented in a number of experiments, starting with device fabrication in an InAsP/InGaAsP multi-quantum-well material to create low-threshold lasers with Qs of 1.3x10^4, and followed by fabrication in a silicon-on-insulator system to create passive resonators with Qs as high as 4.0x10^4. In the latter experiments, an optical fiber taper waveguide is used to couple light into and out of the cavities, and we demonstrate its utility as an optical probe that provides spectral and spatial information about the cavity modes. For a cavity mode with Q ~ 4x10^4, we demonstrate mode localization data consistent with Veff ~ 0.9(\u03bb/n)^3.
\r\n\r\nIn the second part of this thesis, we describe experiments in a GaAs/AlGaAs material containing self-assembled InAs quantum dots. Small diameter microdisk cavities are fabricated with Q ~ 3.6x10^5 and Veff ~ 6(\u03bb/n)^3, and with Q ~ 1.2x10^5 and Veff ~ 2(\u03bb/n)^3. These devices are used to create room-temperature, continuous-wave, optically pumped lasers with thresholds as low as 1\u03bcW of absorbed pump power. Optical fiber tapers are used to efficiently collect emitted light from the devices, and a laser differential efficiency as high as 16% is demonstrated. Furthermore, these microdisk cavities have the requisite combination of high Q and small Veff to enable strong coupling to a single InAs quantum dot, in that the achievable coupling rate between the quantum dot and a single photon in the cavity is predicted to exceed the decay rates within the system. Quantum master equation simulations of the expected behavior of such fiber-coupled devices are presented, and progress towards such cavity QED experiments is described.
\r\n" }, { "name": "Strinopoulos, Theofilos", "degree": "PhD", "year": "2006", "title": "Upscaling Immiscible Two-Phase Flows in an Adaptive Frame", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02192006-165348", "creators": [ { "name": { "family": "Strinopoulos", "given": "Theofilos" }, "id": "Strinopoulos-Theofilos", "display_name": "Strinopoulos, Theofilos" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/AP0P-8S11", "abstract": "We derive the two-scale limit of a linear or nonlinear saturation equation with a flow-based coordinate transformation. This transformation consists of the pressure and the streamfunction. In this framework the saturation equation is decoupled to a family of one-dimensional nonconservative transport equations along streamlines. This simplifies the derivation of the two-scale limit. Moreover it allows us to obtain the convergence independent of the assumptions of periodicity and scale separation. We provide a rigorous estimate on the convergence rate. We combine the two-scale limit with Tartar's method to complete the homogenization.
\r\n\r\nTo design an efficient numerical method, we use an averaging approach across the streamlines on the two-scale limit equations. The resulting numerical method for the saturation has all the advantages in terms of adaptivity that methods have. We couple it with a moving mesh along the streamlines to resolve the shock more efficiently. We use the multiscale finite element method to upscale the pressure equation because it gives access to the fine scale velocity, which enters in the saturation equation, through the basis functions. We propose to solve the pressure equation in the coordinate frame of the initial pressure and saturation, which is similar to the modified multiscale finite element method.
\r\n\r\nWe test our numerical method in realistic permeability fields, such as the Tenth SPE Comparative Solution Project permeabilities, for accuracy and computational cost.
" }, { "name": "Swan-Wood, Tabitha Liana", "degree": "PhD", "year": "2006", "title": "Vibrational Entropy Contributions to the Phase Stability of Iron- and Aluminum-Based Binary Alloys", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09012005-143247", "creators": [ { "name": { "family": "Swan-Wood", "given": "Tabitha Liana" }, "id": "Swan-Wood-Tabitha-Liana", "display_name": "Swan-Wood, Tabitha Liana" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/3PTA-J395", "abstract": "This work considers phonon entropy effects on phase stability of three binary alloys: Fe-Cr, FeAl, and Al-Ag. In all cases the vibrational entropy plays an interesting role.
\r\n\r\nThe phonon density of states was measured on body-centered cubic Fe0.50Cr0.50 prepared as a solid solution, and in increasingly un-mixed states induced by annealing the solid solution at 773 K. Mossbauer spectrometry was used to characterize the extent of decomposition after annealing. A neutron-weight correction was performed, using results from the Mossbauer spectra and recent data on inelastic nuclear resonant scattering from 57Fe-Cr. The vibrational entropy of decomposition was found to be 0.17 \u00b1 0.01 kB/atom, nearly equal to the change in configurational entropy after spinodal decomposition. Vibrational entropy has a large effect on the critical temperature for spinodal decomposition in equi-atomic Fe0.50Cr0.50.
\r\n\r\nThe vibrational entropy of formation of vacancies in FeAl is studied in detail. Born von Karman calculations show that the point defects due to vacancy formation have a strong stiffening effect on one of the transverse acoustic branches in the (1 1 0) direction. The vibrational entropy of vacancy formation is measured to be 0.75 kB/vacancy.
\r\n\r\nThe anharmonic vibrational entropy of FeAl is measured in the temperature range of 10 K to 1323 K. It is shown that there is an abnormally large softening between 10 K and 300 K, which is attributed to a local magnetic moment corresponding to Fe anti-site defects at 10 K. Also measured is an anomalously small anharmonic entropy between 300 K and 1323 K. This could be caused by thermal vacancies and point defects.
\r\n\r\nThe anharmonic entropy of Al0.40Ag0.60 have been measured to be extremely large between 20 C and 520 C. The origins of this anharmonicity are unclear. The origins of this anharmonic entropy of Al0.93Ag0.07 between 20\u00b0C and 520\u00b0C was found to be fully described by lattice expansion. A large Ag resonance peak was measured in Al0.93Ag0.07 at 20\u00b0C. The Mannheim method was used to show that this peak could make a large contribution to the increased solubility of Ag in Al at high temperatures.
" }, { "name": "Taghavi Larigani, Shervin", "degree": "PhD", "year": "2006", "title": "Theory, Fabrication and Applications of a Novel Archetype Semi-Ring Fabry-Perot (SRFP) Resonator and New Tiltmeters", "advisor": "Hoffmann, Michael R.; van Zyl, Jakob J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102006-175036", "creators": [ { "name": { "family": "Taghavi Larigani", "given": "Shervin" }, "id": "Taghavi-Larigani-Shervin", "orcid": "0000-0002-6599-7855", "display_name": "Taghavi Larigani, Shervin" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "van Zyl", "given": "Jakob J." }, "id": "van-Zyl-J-J", "role": "co-advisor", "display_name": "van Zyl, Jakob J." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "van Zyl", "given": "Jakob J." }, "id": "van-Zyl-J-J", "role": "member", "display_name": "van Zyl, Jakob J." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/KC5S-1T19", "abstract": "The first instinct of any animal (including human) is surviving, which implies security. It impacts how we perceive the whole universe. The best way of satisfying this need, consists of being able to control situations in which we are immersed. One way of doing so, consists of predicting future events. That is why we perceive and model our environment based on cyclic and periodic events, going back to the earliest civilizations.
\r\n\r\nFew examples of such periodic events are:
\r\nSo modeling any sort of event happening in our environment by repetitive events allows us to enforce a secure feeling, since (periodic, cyclic) events have the advantage of being able to be foreseen, which provides the advantage of being well understood. Most of the devices fabricated by human beings are inspired by the perception of its environment, and somehow in most cases we just copy nature. Few examples are:
\r\nThat is why basic tools of many applied and engineering sciences are resonators, which are engineered devices that generate or sustain periodic or cyclic events. One example of a resonator is a guitar. The string can just take a certain finite number of shapes since it is bounded on its two extremes. Any excitation of the string can be decomposed as the excitation of each one of these shapes, which would repeat itself after one round trip. These shapes are called the resonant mode of the string. Each note (the music coming out of it) of the guitar corresponds to one of its resonant modes. The same way that we use a basis to describe a vector (for example x and y in the case of two dimensional vector), we can use the resonant modes as a basis to describe any intensity within the resonator. Therefore in the case of the guitar, any vibration of the string can be decomposed on a set of vibrations of each resonator mode, where the intensity of vibration of each mode is independent of the others. What differentiates any vibration of the string from another is the intensity with which this vibration couple, to each resonant mode. The same way that the guitar is a mechanical resonator, we can think of an electromagnetic resonator. The same way an electromagnetic resonator has different resonant modes, and each intensity couple to the resonator can be decomposed on a set of intensity of each resonant mode. Another example is at the atomic scales, where the atoms within a molecule have specific repetitive vibration and rotation patterns, which are called the resonant modes.
\r\n\r\nThe overall concept of a resonator is the same whether it is mechanical or electromagnetic one. The basic concept of a resonator is based upon a feedback, which guarantees the repetition of an event. At the root there are no more than two ways of obtaining such feedback.
\r\n\r\n1. The first idea consists of forcing the feedback. Due to this feed back the same event would happen at the same time if it is a temporal event or at the same location if it is a spatial event.
\r\n\r\nBy confining the event within a (temporal or spatial) barrier, and by being sure that the event would bounce back at that barrier, we would have created such a feedback. Such a specific barrier is often called a reflector. In the case of a mechanical resonator, such a reflector could be a wall. As an example, when someone talks within a confined structure, their voice gets echoed or resonates and in some cases the voice generated by the speaker would get back to him. This is a resonant phenomenon. Another example is if someone who is confined in a medium separated by two walls throws a ball to one of the walls. In a specific case, where the trajectory of the ball repeats itself, we talk about resonance. The same structure is also used in an electromagnetic resonator where the two reflectors are now electromagnetic reflectors. In the case of optics, the reflectors would be mirrors. In that case, the feedback would be obtained by confining an optical medium (a waveguide) within two optical reflectors (mirrors). Such a structure is the most basic archetype resonator in optics and was invented 100 years ago, and was named after its inventors Fabry-Perot. Fundamentally, this structure is very similar to the mechanical resonator obtained with the help of two walls.
\r\n\r\n2. Another way of thinking of such a feedback is by assuring that either the temporal or spatial path used by the events would be repeated. This can be obtained if the path shape is closed. An example of such structure is a circular shape.
\r\n\r\nIn this thesis, we present a completely novel resonator that in addition to having both the advantages of the first and the second types of resonators, has its own specific features. We have called this resonator a Semi-Ring Fabry-Perot (SRFP) resonator. In order to better understand this resonator we will focus ourselves in the field of optics, which emphasizes the best on the wave particularity of resonators. As we will see almost all optical resonators could be modeled as combinations of Fabry-Perot and ring resonators. These devices are the most important letter of the alphabet of the optics, where any device behaves like a word obtained with the combinations of the letters composing the alphabet, similar to introducing a new letter to the alphabet. Thus, we can with the use of this new letter create new words, which are new devices and could be useful. The benefit of the novel resonator that we introduce is beyond the scope of this thesis, where mostly optical applications of the resonator have been introduced.
\r\n\r\nAt the end of the thesis, we will introduce a novel way of measuring the incidence tilt of a field using a resonator.
\r\n" }, { "name": "Tang, Ao (Kevin)", "degree": "PhD", "year": "2006", "title": "Heterogeneous Congestion Control Protocols", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242006-170918", "creators": [ { "name": { "family": "Tang", "given": "Ao (Kevin)" }, "id": "Tang-Ao-Kevin", "display_name": "Tang, Ao (Kevin)" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "eleceng" ], "doi": "10.7907/eh43-pa83", "abstract": "Homogeneity of price is an implicit yet fundamental assumption underlying price based resource allocation theory. In this thesis, we study the effects of relaxing this assumption by examining a concrete engineering system (network with heterogeneous congestion control protocols). The behavior of the system turns out to be very different from the homogeneous case and can potentially be much more complicated. A systematic theory is developed that includes all major properties of equilibrium of the system such as existence, uniqueness, optimality, and stability. In addition to analysis, we also present numerical examples, simulations, and experiments to illustrate the theory and verify its predictions.
\r\n\r\nWhen heterogeneous congestion control protocols that react to different pricing signals share the same network, the resulting equilibrium can no longer be interpreted as a solution to the standard utility maximization problem as the current theory suggests. After introducing a mathematical formulation of network equilibrium for multi-protocol networks, we prove the existence of equilibrium under mild assumptions. For almost all networks, the equilibria are locally unique. They are finite and odd in number. They cannot all be locally stable unless the equilibrium is globally unique. We also derive two conditions for global uniqueness. By identifying an optimization problem associated with every equilibrium, we show that every equilibrium is Pareto efficient and provide an upper bound on efficiency loss due to pricing heterogeneity. Both intra-protocol and inter-protocol fairness are then discussed. On dynamics, various stability results are provided. In particular it is shown that if the degree of pricing heterogeneity is small enough, the network equilibrium is not only unique but also locally stable. Finally, a distributed algorithm is proposed to steer a network to the unique equilibrium that maximizes the aggregate utility, by only updating a linear parameter in the sources' algorithms in a slow timescale.
" }, { "name": "Tao, Min", "degree": "PhD", "year": "2006", "title": "High Temperature Deformation of Vitreloy Bulk Metallic Glasses and Their Composite", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-03022006-005723", "creators": [ { "name": { "family": "Tao", "given": "Min" }, "id": "Tao-Min", "display_name": "Tao, Min" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Huang", "given": "Yonggang" }, "id": "Huang-Yonggang", "role": "member", "display_name": "Huang, Yonggang" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/27SN-R187", "abstract": "A complete understanding of the deformation mechanisms of BMGs and their composites requires investigation of the microstructural changes and their interplay with the mechanical behavior. In this dissertation, the deformation mechanisms of a series of Vitreloy glasses and their composites are experimentally investigated over a wide range of strain rates and temperatures, with focus on the supercooled liquid regime, by combining uniaxial mechanical testing with calorimetric and microscopic examinations. Various theories of deformation of metallic glasses and the composites are examined in light of the experimental data.
\r\n\r\nA comparative structural relaxation study was performed on two closely related Vitreloy alloys, Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit 1) and Zr46.7Ti8.3Cu7.5Ni10Be27.5 (Vit 4). Differential scanning calorimetric studies on the specimens deformed in compression at constant-strain-rate in supercooled liquid regime showed that mechanical loading accelerated the spinodal phase separation and nanocrystallization process in Vit 1, while the relaxation in Vit 4 featured local chemical composition fluctuation accompanied by annealing out of free volume. The effect of the structural relaxation on their mechanical behavior was further studied via single and multiple jump-in-strain-rate tests.
\r\n\r\nThe deformation and viscosity of a new Vitreloy alloy were characterized using uniaxial compression tests in its supercooled liquid regime. A new theoretical model named Cooperative Shear Model, which correlates the evolution of the macroscopic mechanical/thermal variables such as shear modulus and viscosity with the configurational energies of atom clusters in an amorphous alloy, was critically examined in this investigation. The model was successful in predicting the Newtonian and non-Newtonian viscosities of the material, as well as the shear moduli of the deformed specimens, in a self-consistent manner.
\r\n\r\nThe plastic flow of an in-situ metallic glass composite, beta-Vitreloy, was investigated under uniaxial compression in its supercooled liquid regime and at various strain rates. The composite, with ~0.25 volume fraction of crystalline beta-phase dendrites exhibited superplastic behavior similar to that of amorphous Vit 1. Significant strain hardening was observed when the material was deformed at high temperatures and low strain rates. A dual-phase composite model was employed in finite element simulations to understand the effect of the composite microstructure on its mechanical behavior.
" }, { "name": "Tsang, Mankei", "degree": "PhD", "year": "2006", "title": "Classical and Quantum Nonlinear Optical Information Processing", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-05032006-154541", "creators": [ { "name": { "family": "Tsang", "given": "Mankei" }, "id": "Tsang-Mankei", "orcid": "0000-0001-7173-1239", "display_name": "Tsang, Mankei" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Hong", "given": "John Hyunchul" }, "id": "Hong-J-H", "role": "member", "display_name": "Hong, John Hyunchul" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/BG6Y-VX33", "abstract": "This thesis is a theoretical investigation of the classical and quantum information processing enabled by the advent of modern ultrafast nonlinear optics.
\r\n\r\nChapter 2 and 3 study the propagation of ultrashort optical pulses in optical fibers, and propose two methods of compensating the linear and nonlinear distortions experienced by the pulses, namely, reverse propagation and spectral phase conjugation. Chapter 4 and 5 suggest different schemes that implement spectral phase conjugation.
\r\n\r\nChapter 6 and 7 establish the connection between classical spectral phase conjugation and quantum coincident frequency entanglement. Chapter 6 shows how a spectral phase conjugator can create coincident frequency entangled photon pairs, and Chapter 7 in turn demonstrates how a coincident frequency entanglement generator can perform spectral phase conjugation.
\r\n\r\nThe next three chapters, 8, 9, and 10, focus on quantum spatiotemporal information processing. Chapter 8 studies the temporal properties of entangled photon pair propagation and proposes the concept of quantum temporal imaging. Chapter 9 investigates how optical solitons can be used to perform quantum timing jitter reduction and temporal entanglement, while Chapter 10 applies the same idea to the spatial domain for quantum spatial information processing tasks, such as spatial beam displacement uncertainty reduction and quantum lithography.
\r\n\r\nThe final two chapters return to a couple of miscellaneous problems in classical optics. Chapter 11 shows how a pair of dielectric slabs can amplify the near field of an optical image. Chapter 12 explores the similarities between nonlinear optics and fluid dynamics, and speculates on the possibility of using nonlinear optics experiments to simulate fluid dynamics problems.
" }, { "name": "Tsuchiya, Naotsugu", "degree": "PhD", "year": "2006", "title": "Attention and Awareness: Visual Psychophysics and Aversive Conditioning in Humans", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-085914", "creators": [ { "name": { "family": "Tsuchiya", "given": "Naotsugu" }, "id": "Tsuchiya-Naotsugu", "orcid": "0000-0003-4216-8701", "display_name": "Tsuchiya, Naotsugu" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "O'Doherty", "given": "John P." }, "id": "O'Doherty-J-P", "orcid": "0000-0003-0016-3531", "role": "member", "display_name": "O'Doherty, John P." }, { "name": { "family": "Adolphs", "given": "Ralph" }, "id": "Adolphs-R", "orcid": "0000-0002-8053-9692", "role": "member", "display_name": "Adolphs, Ralph" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/JVP9-TA28", "abstract": "We studied the neuronal correlates of consciousness by characterizing the role of attention and awareness in three psychophysical experiments. First, we investigated the role of visual awareness in the formation of afterimages, phenomena believed to occur in the retina. Visibility of the afterimage-inducing stimuli was manipulated by a powerful dichoptic suppression technique, continuous flash suppression, which allows us to project visual stimuli onto the retina without subjects noticing them at all, sometimes longer than three minutes. We found that reliably suppressing the inducer weakens afterimage strength. Paradoxically, trial-to-trial variability in visibility did not correlate with the intensity of afterimage. As afterimages are enhanced when attention is withdrawn from the adaptor, the opposite effects between awareness and attention were demonstrated. Second, we examined visual motion processing outside the focus of spatial, top-down attention using a dual-task paradigm. Attentional effects in motion processing were characterized by our novel wavelet motion stimuli. Our stimuli effectively activate neurons in the first stage of motion processing, while they are poor stimuli for higher motion processing. Using a contrast-masking paradigm, we found that attention mainly affected the strength of inhibition for high-contrast motion stimuli in an orientation-specific, but not direction-specific manner, presumably reflecting the physiological properties for divisive inhibition within the primary visual cortex. Third, we characterized the role of awareness in classical aversive conditioning. Subjects associated previously neutral auditory stimuli (CS) with aversive mild electric shocks (US). We used skin conductance response, an index for autonomic arousal, as implicit measure for the conditioned response. In delay conditioning, CS was paired with delayed but overlapping US, while in trace conditioning CS was followed by US after a three-second temporal gap. We intermixed these two CSs with another control CS that never predicted US to examine whether awareness plays different roles depending on the temporal relationships between CS and US. Subjects expressed their shock expectancy using their gaze direction, from which we inferred the onset of awareness of CS-US contingency. By aligning the skin conductance response with the onset of awareness, we found that trace, but not delay, conditioning coincided with the onset of awareness." }, { "name": "Vyawahare, Saurabh", "degree": "PhD", "year": "2006", "title": "Manipulating Fluids: Advances in Micro-Fluidics, Opto-Fluidics and Fluidic Self-Assembly", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252006-223101", "creators": [ { "name": { "family": "Vyawahare", "given": "Saurabh" }, "id": "Vyawahare-Saurabh", "display_name": "Vyawahare, Saurabh" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/04XY-C430", "abstract": "This dissertation describes work in three inter-related areas \u2013 micro-fluidics, opto-fluidics and fluidic self-assembly. Micro-fluidics has gotten a boost in recent years with the development of multilayered elastomeric devices made of poly (dimethylsiloxane) (PDMS), allowing active elements like valves and pumps. However, while PDMS has many advantages, it is not resistant to organic solvents. New materials and/or new designs are needed for solvent resistance. I describe how novel fluorinated elastomers can replace PDMS when combined with three dimensional (3-D) solid printing. I also show how another 3-D fabrication method, multilayer photo-lithography, allows for fabrication of devices integrating filters. In general, 3-D fabrications allow new kinds of micro-fluidic devices to be made that would be impossible to emulate with two dimensional chips.
\r\n\r\nIn opto-fluidics, I describe a number of experiments with quantum dots both inside and outside chips. Inside chips, I manipulate quantum dots using hydrodynamic focusing to pattern fine lines, like a barcode. Outside chips, I describe our attempts to create quantum dot composites with micro-spheres. I also show how evaporated gold films and chemical passivation can then be used to enhance the emission of quantum dots.
\r\n\r\nFinally, within fluids, self-assembly is an attractive way to manipulate materials, and I provide two examples: first, a DNA-based energy transfer molecule that relies on quantum mechanics and self-assembles inside fluids. This kind of molecular photonics mimics parts of the photosynthetic apparatus of plants and bacteria. The second example of self-assembly in fluids describes a new phenomena - the surface tension mediated self assembly of particles like quantum dots and micro-spheres into fine lines. This self assembly by capillary flows can be combined with photo-lithography, and is expected to find use in future nano- and micro-fabrication schemes.
\r\n\r\nIn conclusion, advances in fluidics, integrating materials like quantum dots and solvent resistant elastomers along with 3-D fabrication and methods of self assembly, provide a new set of tools that significantly expand our control over fluids.
" }, { "name": "Walther, Dirk", "degree": "PhD", "year": "2006", "title": "Interactions of Visual Attention and Object Recognition: Computational Modeling, Algorithms, and Psychophysics", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechETD:etd-03072006-135433", "creators": [ { "name": { "family": "Walther", "given": "Dirk" }, "id": "Walther-Dirk", "orcid": "0000-0001-8585-9858", "display_name": "Walther, Dirk" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Itti", "given": "Laurent" }, "id": "Itti-L", "role": "member", "display_name": "Itti, Laurent" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/P5NY-VC91", "abstract": "Selective visual attention provides an effective mechanism to serialize perception of complex scenes in both biological and machine vision systems. In extension of previous models of saliency-based visual attention by Koch and Ullman (Human Neurobiology, 4:219-227, 1985) and Itti et al. (IEEE PAMI, 20(11):1254-1259, 1998), we have developed a new model of bottom-up salient region selection, which estimates the approximate extent of attended proto-objects in a biologically realistic manner.
\r\n\r\nBased on our model, we simulate the deployment of spatial attention in a biologically realistic model of object recognition in the cortex and find, in agreement with electrophysiology in macaque monkeys, that modulation of neural activity by as little as 20 % suffices to enable successive detection of multiple objects.
\r\n\r\nWe further show successful applications of the selective attention system to machine vision problems. We show that attentional grouping based on bottom-up processes enables successive learning and recognition of multiple objects in cluttered natural scenes. We also demonstrate that pre-selection of potential targets decreases the complexity of multiple target tracking in an application to detection and tracking of low-contrast marine animals in underwater video data.
\r\n\r\nA given task will affect visual perception through top-down attention processes. Frequently, a task implies attention to particular objects or object categories. Finding suitable features can be interpreted as an inversion of object detection. Where object detection entails mapping from a set of sufficiently complex features to an abstract object representation, finding features for top-down attention requires the reverse of this mapping. We demonstrate a computer simulation of this mechanism with the example of top-down attention to faces.
\r\n\r\nDeploying top-down attention to the visual hierarchy comes at a cost in reaction time in fast detection tasks. We use a task switching paradigm to compare task switches that do with those that do not require re-deployment of top-down attention and find a cost of 20-28 ms in reaction time for shifting attention from one stimulus attribute (image content) to another (color of frame).
" }, { "name": "Wang, Feiyu", "degree": "PhD", "year": "2006", "title": "Design and Analysis of High-Efficiency L-Band Power Amplifiers", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02182006-133932", "creators": [ { "name": { "family": "Wang", "given": "Feiyu" }, "id": "Wang-Feiyu", "display_name": "Wang, Feiyu" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Moussessian", "given": "Alina" }, "id": "Moussessian-A", "role": "member", "display_name": "Moussessian, Alina" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/CJGR-TF04", "abstract": "Discrete solid-state high-power amplifiers are among the important circuit components in today\u2019s wireless communications and remote-sensing applications. As the device technologies continue to improve, there are new opportunities and new challenges presented to power amplifier designers. This thesis presents novel techniques in the design and the analysis of L-band high-efficiency power amplifiers, which may be used in many communications and radar applications.
\r\n\r\nIn this work, high-efficiency power amplifier topologies are discussed and implemented. The goal is to push the boundary of output power, operating frequency, efficiency and bandwidth. Also, the design of a key passive component, a balanced-to-unbalanced transformer (balun) is discussed in detail. Some new designs of the baluns are shown, and the results show advantages of these baluns over some of the traditional work at L-band.
\r\n\r\nThe stability analysis of power amplifiers is one of the most critical and the most challenging aspects of power amplifier design. This work shows an analysis technique, which accurately predicts the oscillations in power amplifiers. Using the technique, different stabilization techniques and circuits are designed and implemented.
" }, { "name": "Wang, Jiantao", "degree": "PhD", "year": "2006", "title": "A Theoretical Study of Internet Congestion Control: Equilibrium and Dynamics", "advisor": "Doyle, John Comstock; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122005-082753", "creators": [ { "name": { "family": "Wang", "given": "Jiantao" }, "id": "Wang-Jianto", "display_name": "Wang, Jiantao" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "co-chair", "display_name": "Low, Steven H." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/4DQ0-GA49", "abstract": "In the last several years, significant progress has been made in modelling the Internet congestion control using theories from convex optimization and feedback control. In this dissertation, the equilibrium and dynamics of various congestion control schemes are rigorously studied using these mathematical frameworks.
\r\n\r\nFirst, we study the dynamics of TCP/AQM systems. We demonstrate that the dynamics of queue and average window in Reno/RED networks are determined predominantly by the protocol stability, not by AIMD probing nor noise traffic. Our study shows that Reno/RED becomes unstable when delay increases and more strikingly, when link capacity increases. Therefore, TCP Reno is ill suited for the future high-speed network, which has motivated the design of FAST TCP. Using a continuous-time model, we prove that FAST TCP is globally stable without feedback delays and provide a sufficient condition for local stability when feedback delays are present. We also introduce a discrete-time model for FAST TCP that fully captures the effect of self-clocking and derive the local stability condition for general networks with feedback delays.
\r\n\r\nSecond, the equilibrium properties (i.e., fairness, throughput, and capacity) of TCP/AQM systems are studied using the utility maximization framework. We quantitatively capture the variations in network throughput with changes in link capacity and allocation fairness. We clarify the open conjecture of whether a fairer allocation is always more efficient. The effects of changes in routing are studied using a joint optimization problem over both source rates and their routes. We investigate whether minimal-cost routing with proper link costs can solve this joint optimization problem in a distributed way. We also identify the tradeoff between achievable utility and routing stability.
\r\n\r\nAt the end, two other related projects are briefly described.
" }, { "name": "Washenfelder, Rebecca Ann", "degree": "PhD", "year": "2006", "title": "Column Abundances of Carbon Dioxide and Methane Retrieved from Ground-Based Near-Infrared Solar Spectra", "advisor": "Wennberg, Paul O.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022006-103523", "creators": [ { "name": { "family": "Washenfelder", "given": "Rebecca Ann" }, "id": "Washenfelder-Rebecca-Ann", "orcid": "0000-0002-8106-3702", "display_name": "Washenfelder, Rebecca Ann" } ], "advisors": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "advisor", "display_name": "Wennberg, Paul O." } ], "committee": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "chair", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Toon", "given": "Geoffrey C." }, "id": "Toon-G-C", "role": "member", "display_name": "Toon, Geoffrey C." }, { "name": { "family": "Randerson", "given": "James T." }, "id": "Randerson-J-T", "role": "member", "display_name": "Randerson, James T." }, { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "role": "member", "display_name": "Okumura, Mitchio" } ], "option_major": [ "envreng" ], "doi": "10.7907/7SPN-EY19", "abstract": "To predict future climate change, we must accurately predict future atmospheric concentrations of CO\u2082 and CH\u2084. The current budget has typically been inferred from top-down analyses of measurements from a global network of surface sites. These measurements are highly accurate, but have limited spatial coverage. In addition, accurate knowledge of local planetary boundary layer dynamics is necessary to determine fluxes.
\r\n\r\nColumn measurements, defined as the vertical integral of gas concentration, can complement the existing in situ network. Because column measurements sample a larger portion of the atmosphere, they exhibit less variability than surface data, while retaining information about surface fluxes. Column measurements are not influenced by planetary boundary layer dynamics, and do not suffer from the resulting correlation between exchange and transport.
\r\n\r\nAn automated observatory for measuring ground-based column abundances of CO\u2082, CH\u2084, and O\u2082 is described. Near-infrared spectra of the direct sun are obtained from 3,900\u201315,600 cm\u207b\u00b9 by a Bruker 125HR Fourier transform spectrometer. The observatory was assembled in Pasadena, California and then permanently deployed to Northern Wisconsin during May 2004. Under clear sky conditions, retrieved column CO\u2082 abundances demonstrate ~0.1% precision. Comparison of these column measurements with eight aircraft profiles of in situ CO\u2082 recorded during summer 2004 shows a small bias, but an excellent correlation.
\r\n\r\nThe observed secular increase and seasonal amplitude of column-average CO\u2082 observed during the period of May 2004 \u2013 March 2006 is 1.8 ppmv yr\u207b\u00b9 and 11 ppmv, consistent with theoretical predictions that the measurements will be representative of Northern Hemisphere CO\u2082 exchange over seasonal timescales. Comparisons with eddy covariance measurements show that the column measurements have potential for directly observing CO\u2082 exchange, but that this ability is constrained by the difficulty in accounting for atmospheric transport.
\r\n\r\nFinally, the use of near-infrared spectral analysis is extended to observations of tropospheric column-average CH\u2084 concentrations. By employing a stratospheric \"slope equilibrium\" relationship between CH\u2084 and HF, the varying contribution of stratospheric CH\u2084 to the total column is inferred. This method is used to determine tropospheric column-average CH\u2084 VMRs from near-infrared solar absorption spectra recorded at the Kitt Peak National Solar Observatory during 1977\u20131995.
" }, { "name": "Welp, Lisa Renee", "degree": "PhD", "year": "2006", "title": "Links Between Carbon and Water Cycles in Northern Ecosystems: Constraints from Stable Isotopes", "advisor": "Randerson, James T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022006-105702", "creators": [ { "name": { "family": "Welp", "given": "Lisa Renee" }, "id": "Welp-Lisa-Renee", "orcid": "0000-0001-7125-0478", "display_name": "Welp, Lisa Renee" } ], "advisors": [ { "name": { "family": "Randerson", "given": "James T." }, "id": "Randerson-J-T", "role": "advisor", "display_name": "Randerson, James T." } ], "committee": [ { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "chair", "display_name": "Adkins, Jess F." }, { "name": { "family": "Eiler", "given": "John M." }, "id": "Eiler-J-M", "role": "member", "display_name": "Eiler, John M." }, { "name": { "family": "Randerson", "given": "James T." }, "id": "Randerson-J-T", "role": "member", "display_name": "Randerson, James T." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." } ], "option_major": [ "envreng" ], "doi": "10.7907/KY54-DC47", "abstract": "High-latitude climate change will have an impact on the carbon and water cycles in northern ecosystems. Stable isotopes in these systems can serve as indicators of changes and feedbacks. Monitoring the stable isotopic composition of Arctic river discharge provides a means to investigate integrated basin-scale hydrologic changes in remote northern regions. I measured water \u03b4\u00b9\u2078O and \u03b4D from the Kolyma River in Siberia and local precipitation to partition the river flow into 60% snow and 40% rain inputs. Comparing this estimate with seasonal precipitation across the watershed showed a significant portion of snowmelt is retained in the soils of this permafrost dominated region, and contributes to ~40% of the growing season transpiration. The seasonal cycles of atmospheric CO\u2082 and \u03b4\u00b9\u2078O-CO\u2082 at high northern latitudes have the potential to serve as indicators of ecological change. Effective interpretation of atmospheric observations requires an understanding of how different species and ecosystems contribute to biosphere-atmosphere exchange. By combining isotopic signatures of ecosystem water pools with measured CO\u2082 fluxes in three stands of an Alaskan boreal fire chronosequence (recent burn, intermediate-aged deciduous and mature evergreen forests), I compared the relative effects of stand age on the phase and amplitude of the seasonal cycles of CO\u2082 and \u03b4\u00b9\u2078O-CO\u2082. Higher rates of mid-summer net carbon exchange and a shorter growing season at the deciduous stand resulted in the largest seasonal CO\u2082 amplitude and also delayed the drawdown of atmospheric CO\u2082 compared to the evergreen stand. Reduced levels of photosynthesis at the deciduous stand early in the growing season caused atmospheric \u03b4\u00b9\u2078O-CO\u2082 to increase more slowly compared to fluxes from the evergreen stand. The distribution of stand ages in northern boreal forests is likely to determine the response of net ecosystem exchange (NEE) to future climate changes. I used three years of NEE measurements from the Alaskan fire chronosequence to determine that the sensitivity of growing season NEE to spring air temperatures and summer drought was greater at the deciduous forest than the evergreen forest. As forest fire disturbance increases due to climate warming, the shift to younger forests should increase interannual variability in atmospheric CO\u2082 concentrations.
" }, { "name": "Williams, Kjerstin Irja", "degree": "PhD", "year": "2006", "title": "Multi-robot Systems: Modeling Swarm Dynamics and Designing Inspection Planning Algorithms", "advisor": "Burdick, Joel Wakeman; Martinoli, Alcherio", "url": "https://resolver.caltech.edu/CaltechETD:etd-05192006-063455", "creators": [ { "name": { "family": "Williams", "given": "Kjerstin Irja" }, "id": "Williams-Kjerstin-Irja", "display_name": "Williams, Kjerstin Irja" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Martinoli", "given": "Alcherio" }, "id": "Martinoli-A", "role": "advisor", "display_name": "Martinoli, Alcherio" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Martinoli", "given": "Alcherio" }, "id": "Martinoli-A", "role": "member", "display_name": "Martinoli, Alcherio" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/G1T2-FB74", "abstract": "For a variety of applications, the capability of simultaneous sensing and action in multiple locations that is inherent to multi-robot approaches offers potential advantages over single robot systems in robustness, efficiency, and application feasibility.
\r\n\r\nAt the fully distributed and reactive end of the multi-robot system spectrum, I present mathematical modeling methodologies developed to predict and optimize a self-organized robotic swarm\u2019s performance for several tasks. These models allow us to better understand the relationship between agent and group behavior by capturing the dynamics of these highly stochastic, nonlinear, asynchronous systems at various levels of abstraction, in some cases even achieving mathematical tractability. The models deliver qualitatively and quantitatively correct predictions several orders of magnitude more quickly than an embodied simulator can. Swarm modeling lays the foundation for more generalized SI system design methodology by saving time, enabling generalization to different robotic platforms, and estimating optimal design and control parameters.
\r\n\r\nIn considering more complex target tasks and behaviors, efficiency and completeness of execution may be of concern, and a swarm approach may not be appropriate. In such cases a more deliberative approach may be warranted. In that context, I introduce the multi-robot boundary coverage problem, in which a group of robots is required to completely inspect the boundary of all two-dimensional objects in a specified environment. To make such a guarantee, I present a centralized planning approach that constructs a two-component abstraction of the problem: a graph representing the particular instance of the inspection task and a graph problem whose solution represents a complete plan for inspection. Using the building blocks of this approach, related inspection tasks that require the robotic system to adapt to a changes in team size and task assignment are also explored. The application of these planning methods to the case of long-term deployment for surveillance applications that require repetitive coverage is also discussed.
\r\n\r\nThe recurring theme of this thesis is that we must look beyond implementation and validation of a particular system and ask how its design can contribute to the development of a more general design methodology.
" }, { "name": "Yang, Fu-Ling", "degree": "PhD", "year": "2006", "title": "Interaction Law for a Collision Between Two Solid Particles in a Viscous Liquid", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262006-120244", "creators": [ { "name": { "family": "Yang", "given": "Fu-Ling" }, "id": "Yang-Fu-Ling", "orcid": "0000-0002-6633-6311", "display_name": "Yang, Fu-Ling" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Zenit Camacho", "given": "Jose Roberto" }, "id": "Zenit-Camacho-J-R", "orcid": "0000-0002-2717-4954", "role": "member", "display_name": "Zenit Camacho, Jose Roberto" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/VFD0-C413", "abstract": "This thesis addresses the problem of inter-particle collisions in a viscous liquid. Experimental measurements were made on normal and oblique collisions between identical and dissimilar pairs of solid spheres. The experimental evidence supports the hypothesis that the normal and the tangential component of motions are decoupled during a rapid collision.
\r\n\r\nThe relative particle motion in the normal direction is crucial to an immersed collision process and can be characterized by an effective coefficient of restitution and a binary Stokes number. The effective coefficient of restitution monotonically decreases with a diminishing binary Stokes number, indicating a particle motion with less inertia and higher hindering fluid forces. The correlation between the two parameters exhibits a similar trend to what is observed in a sphere-wall collision, which motivates a theoretical modeling.
\r\n\r\nThe collision model developed in the current work includes a flow model and a revised rebound scheme. The flow model considers the steady viscous drag, the added mass force, and the history force. How the presence of a second nearby solid boundary affects these forces is investigated. A flow model is proposed with wall-correction terms and is used to predict an immersed pendulum motion toward a solid wall. General agreement with the available experimental data validates the model. The rebound scheme considers the magnitude of the surface roughness and the minimum distance of approach resuling from an elastohydrodynamic contact.
\r\n\r\nThe performance of the collision model in predicting the effective coefficient of restitution is evaluated through comparisons with experimental measurements and an existing elastohydrodynamic collision model that the current work is based on.
\r\n\r\nBased on the current experimental findings, the tangential component of motion can be described by a dry collision model, provided that the material parameters are properly modified for the interstitial liquid. Two pertinent parameters are the normal effective coefficient of restitution and an effective friction coefficient.
" }, { "name": "Yang, Ya-Tang", "degree": "PhD", "year": "2006", "title": "Phase Noise of Nanoelectromechanical Systems", "advisor": "Roukes, Michael L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10162006-124404", "creators": [ { "name": { "family": "Yang", "given": "Ya-Tang" }, "id": "Yang-Ya-Tang", "display_name": "Yang, Ya-Tang" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael L." }, "id": "Roukes-M-L", "role": "advisor", "display_name": "Roukes, Michael L." } ], "committee": [ { "name": { "family": "Roukes", "given": "Michael L." }, "id": "Roukes-M-L", "role": "chair", "display_name": "Roukes, Michael L." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/YDZP-3X10", "abstract": "Nanoelectromechanical systems (NEMS) are microelectromechanical systems (MEMS) scaled down to nanometer range. As the size of the NEMS resonators is scaled downward, some fundamental and nonfundamental noise processes will impose sensitivity limits to their performance. In this work, we first present theory of phase noise mechanism of NEMS to examine both fundamental and nonfundamental noise processes. Fundamental noise processes considered here include thermomechanical noise, momentum-exchange noise, adsorption-desorption noise, diffusion noise, and temperature-fluctuation noise. For nonfundamental noise processes, we develop a formalism to consider the Nyquist-Johnson noise from transducer-amplifier implementations.
\r\n\r\nAs an initial step to experimental exploration of these noise processes, we describe and analyze several phase-locked loop schemes based on NEMS at very high frequency and ultrahigh frequency bands. In particular, we measure diffusion noise of NEMS arising from xenon atoms adsorbed on the device surface using the frequency modulation phase-locked loop. The observed spectra of fractional frequency noise and Allan deviation agree well with the prediction from diffusion noise theory.
\r\n\r\nFinally, NEMS resonators also provide unprecedented sensitivity for inertial mass sensing. We demonstrate in situ measurement in real time with mass floor of ~20 zg. Our best mass sensitivity corresponds to ~7 zeptograms, equivalent to ~30 xenon atoms or the mass of an individual 4 kDa molecule. Detailed analysis of the ultimate sensitivity of such devices based on these experimental results indicates that NEMS can ultimately provide inertial mass sensing of individual intact, electrically neutral macromolecules with single-Dalton sensitivity.
" }, { "name": "Zhang, Rongjing", "degree": "PhD", "year": "2006", "title": "Mechanical Characterization of Thin Films with Application to Ferroelectrics", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-01312006-170959", "creators": [ { "name": { "family": "Zhang", "given": "Rongjing" }, "id": "Zhang-Rongjing", "display_name": "Zhang, Rongjing" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Molinari", "given": "Alain" }, "id": "Molinari-A", "role": "member", "display_name": "Molinari, Alain" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CJR5-DK94", "abstract": "One important part of the motivation for this research work comes from the microelectromechanical systems (MEMS) technology. Its basic concept of high volume production and low unit cost can only be achieved when the devices made by microelectronics technique are reliable. The success in this area largely depends on the understanding of materials. However, the mechanical characterization is lagged behind the theoretical work and designing software development. The standard characterization method is still not established. For MEMS actuators, especially for active materials, the desired characterization system for obtaining mechanical properties requires load control feature and the capability of doing dynamic tests. However, there is no such method among the currently available tools for mechanical characterization.
\r\n\r\nThe other part of the motivation comes from the comprehensive research work of Caltech ferroelectric group. This group, which consists of nine faculty members, is aiming to develop new devices, especially new actuators, by the aid of multi-scale theory tools and selected experimental methods. The work presented in this dissertation is an important and key step of this ambitious project: the electromechanical characterization of devices. This will provide validation for the multi-scale materials modeling framework and help to increase the reliability of the actuators and devices.
\r\n\r\nIn this work, two techniques were developed for mechanical characterization, which satisfy the challenging requirements for thin film structures and devices: being able to do dynamic study on fragile ceramic thin film samples with load control feature. The first technique is a new method to characterize mechanical properties of released thin films under concentrated load. This technique can be used to apply load in the ?N?mN range with displacement measured with high accuracy of 0.1 ?m. The successful characterization of Si3N4 free-standing membranes demonstrated the capability and reliability of this new technique. The elastic modulus and residual stress of Si3N4 free-standing thin film were measured to be around 250 GPa and 450 MPa, respectively. These values were in close agreement with values obtained using a different technique as well as those found in the literature. This technique has the potential application on elastic-plastic characterization and characterization of other functional thin film materials such as shape memory alloys.
\r\n\r\nPressure bulge test technique, which is another type of load control method suitable for dynamic test, was also developed. The apparatus was designed to be compact to fit into the x-ray diffractometer for in-situ XRD study and had additional compatibility for polarized light microscopy study. Characterization of free standing thin film of single layer amorphous silicon nitride (Si3N4) and multi-layered PBT/Si3N4, and thick film of single crystal barium titanate (BaTiO3) showed the capability and reliability of this technique. Excellent agreement of the Si3N4 Young\u2019s modulus between these two developed methods gave the confidence for using these techniques to understand new materials.
\r\n\r\nIn situ x-ray diffraction study was carried out on the single crystal thick films which were loaded with distributed mechanical loading by pressure bulge setup. Direct evidence of 90o domain switching was obtained from the in situ XRD results with the intensity changing in both (002) and (200) orientations. Obvious changes in domain patterns were observed by using the polarized light microscope. The Young\u2019s modulus of this barium titanate single crystal thick film with thickness of 100 ?m was characterized before the XRD exam. Using this information, in-plane stress can be analyzed, and the relation between the driving force (the stress) and the microstructural change (volume fraction change in a-domain or c-domain) can be determined.
" }, { "name": "Zhang, Yizhen", "degree": "PhD", "year": "2006", "title": "Engineering Design Synthesis of Sensor and Control Systems for Intelligent Vehicles", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252006-221412", "creators": [ { "name": { "family": "Zhang", "given": "Yizhen" }, "id": "Zhang-Yizhen", "display_name": "Zhang, Yizhen" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Martinoli", "given": "Alcherio" }, "id": "Martinoli-A", "role": "member", "display_name": "Martinoli, Alcherio" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/NB6H-S822", "abstract": "This thesis investigates the application of formal engineering design synthesis methodologies to the development of sensor and control systems for intelligent vehicles.
\r\n\r\nA formal engineering design synthesis methodology based on evolutionary computation is presented, with special emphasis on dealing with modern engineering design challenges, such as high or variable complexity of design solutions, multiple conflicting design objectives, and noisy evaluation results, etc. The efficacy of the evolutionary design synthesis method is validated through multiple different case studies, where a variety of novel design solutions are generated to represent different engineering design trade-offs, and they have achieved performances comparable to, if not better than, that of hand-coded solutions in the same simplified environment. More importantly, this automatic design synthesis method shows great potential to handle more complex design problems, where a good hand-coded solution may be very difficult or even impossible to obtain. Moreover, the evolutionary design synthesis methodology appears promising to deal with uncertainty in the problem efficiently and adapt to the collective task nature well.
\r\n\r\nIn addition, multiple levels of vehicle simulation models with different computational cost and fidelity as well as necessary driver behaviors are implemented for different types of simulation experiments conducted for different research purposes. Efforts are made to try to generate good candidate solutions efficiently with less computational time and human engineering effort.
\r\n\r\nFurthermore, a new threat assessment measure, time-to-last-second-braking (Tlsb), is proposed, which directly characterizes human natural judgment of the urgency and severity of threats in terms of time. Based on driver reaction time experimental results, new warning and overriding criteria are proposed in terms of the new Tlsb measure, and the performance is analyzed statistically in terms of two typical sample pre-crash traffic scenarios. Less affected by driver behavior variability, the new criteria characterize the current dynamic situations better than the previous ones, providing more appropriate warning and more effective overriding at the last moment. Finally, the possibility of frontal collision avoidance through steering (lane-changing) is discussed, and similarly the time-to-last-second-steering (Tlss) measure is proposed and compared with Tlsb.
" }, { "name": "Zielonka, Matias Gabriel", "degree": "PhD", "year": "2006", "title": "Configurational Forces and Variational Mesh Adaption in Solid Dynamics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05112006-162905", "creators": [ { "name": { "family": "Zielonka", "given": "Matias Gabriel" }, "id": "Zielonka-Matias-Gabriel", "display_name": "Zielonka, Matias Gabriel" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V6RB-FR94", "abstract": "This thesis is concerned with the exploration and development of a variational finite element mesh adaption framework for non-linear solid dynamics and its conceptual links with the theory of dynamic configurational forces. The distinctive attribute of this methodology is that the underlying variational principle of the problem under study is used to supply both the discretized fields and the mesh on which the discretization is supported. To this end a mixed-multifield version of Hamilton's principle of stationary action and Lagrange-d'Alembert principle is proposed, a fresh perspective on the theory of dynamic configurational forces is presented, and a unifying variational formulation that generalizes the framework to systems with general dissipative behavior is developed. A mixed finite element formulation with independent spatial interpolations for deformations and velocities and a mixed variational integrator with independent time interpolations for the resulting nodal parameters is constructed. This discretization is supported on a continuously deforming mesh that is not prescribed at the outset but computed as part of the solution. The resulting space-time discretization satisfies exact discrete configurational force balance and exhibits excellent long term global energy stability behavior. The robustness of the mesh adaption framework is assessed and demonstrated with a set of examples and convergence tests." }, { "name": "van Dam, Robert Michael", "degree": "PhD", "year": "2006", "title": "Solvent-Resistant Elastomeric Microfluidic Devices and Applications", "advisor": "Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052005-234258", "creators": [ { "name": { "family": "van Dam", "given": "Robert Michael" }, "id": "van-Dam-Robert-Michael", "orcid": "0000-0003-2316-0173", "display_name": "van Dam, Robert Michael" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "chair", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "orcid": "0000-0002-0057-7817", "role": "member", "display_name": "Grubbs, Robert H." }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "member", "display_name": "Quake, Stephen R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4EJF-1V78", "abstract": "Microfluidics is increasingly being used in many areas of biotechnology and chemistry to achieve reduced reagent volumes, improved performance, integration, and parallelism, among other advantages. Though early devices were based on rigid materials such as glass and silicon, elastomeric materials such as polydimethylsiloxane (PDMS) are rapidly emerging as a ubiquitous platform for applications in biotechnology. This is due, in part, to simpler fabrication procedures and to the ability to integrate mechanical microvalves at vastly greater densities. For many applications in the areas of chemical synthesis and analysis, however, PDMS cannot replace glass and silicon due to its incompatibility with many solvents and reagents.
\r\n\r\nSuch areas could benefit tremendously from the development of an elastomeric microfluidic device technology that combines the advantages of PDMS with the property of solvent resistance. Simplified fabrication could increase the accessibility of microfluidics, and the possibility of dense valve integration could lead to significant advances in device sophistication. Applications could be more rapidly developed by design re-use due to the independence of mechanical valves on fluid properties (unlike electrokinetic pumping), and the property of permeability could enable novel fluidic functions for accessing a broader range of reactions than is possible in glass and silicon.
\r\n\r\nThe first half of this thesis describes our strategies and efforts to develop this new enabling technology. Several approaches are presented in Chapter 3, and two particularly successful ones, based on new elastomers (FNB and PFPE), are described in Chapters 4 and 5. Chapter 6 describes a novel method of fabricating devices from 3D molds that could expand the range of useful elastomers.
\r\n\r\nThe second half of this thesis discusses microfluidic combinatorial synthesis and high throughput screening\u2014applications that take particular advantage of the ability to integrate thousands of individual valves and reaction chambers. Chapter 7 introduces several scalable device architectures and presents results of preliminary steps toward the synthesis of combinatorial DNA and peptide arrays. A novel method of performing universal gene expression analysis with combinatorial DNA arrays is described in Chapter 8 and an algorithm for predicting relationships among genes from gene expression array data is presented in Chapter 9.
\r\n" }, { "name": "\u021a\u0103pu\u0219, Cristian", "degree": "PhD", "year": "2006", "title": "Distributed Speculations: Providing Fault-Tolerance and Improving Performance", "advisor": "Hickey, Jason J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022006-140421", "creators": [ { "name": { "family": "\u021a\u0103pu\u0219", "given": "Cristian" }, "id": "\u021a\u0103pu\u0219-Cristian", "display_name": "\u021a\u0103pu\u0219, Cristian" } ], "advisors": [ { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "advisor", "display_name": "Hickey, Jason J." } ], "committee": [ { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "chair", "display_name": "Hickey, Jason J." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "compsci" ], "doi": "10.7907/YZCK-4T29", "abstract": "This thesis introduces a new programming model based on speculative execution and it examines the use of speculations, a form of distributed transactions, for improving the performance, reliability and fault tolerance of distributed systems. A speculation is defined as a computation that is based on an assumption that is not validated before the computation is started. If the assumption is later invalidated the computation is aborted and the state of the program is rolled back; if the assumption is validated, the results of the computation are committed. The primary difference between a speculation and a transaction is that a speculation is not isolated---for example, a speculative computation may send and receive messages, and it may modify shared objects. As a result, processes that share those objects may be absorbed into a speculation.
\r\n\r\nThe contributions presented in this thesis include:\r\n
A series of experiments were conducted on zebrafish (Danio rerio) in order to gain a better understanding of how blood flow and blood flow related forces, such as shear stress, affect vertebrate heart development. Zebrafish were used as a model due to their external fertilization and optical accessibility to the heart and vasculature. The flow field inside the 4.5 day post fertilization (dpf) embryo was analyzed using a combination of manual particle tracking and digital particle image velocimetry (DPIV) software. Our results present the first case of intracardiac microscale DPIV. Additionally, a minimally invasive and reversible technique of delivering and localizing magnetic microspheres inside the vasculature of the embryo was developed. The results of blocked flow induced with this method were compared with previous experiments and controls.
\r\n\r\nThe results of the flow field analysis showed the existence of an extremely dynamic flow environment containing jets with a velocity of 5 mm/s and regions of vorticity in a low Reynolds number environment. Calculations of the flow at the 4.5 dpf A-V resulted in wall shear stress levels of 70 dynes/cm2, levels much higher than needed for endothelial cell response.
\r\n\r\nWe also showed that injected magnetic microspheres can be delivered and localized within the embryonic vasculature to reversibly block blood flow in the dorsal artery and at the inflow to the heart. Blocked blood flow of 12 hours and longer resulted in lower blood velocity and a less developed heart, exhibiting edema, regurgitance, decreased contractile function, and delayed development. These findings are consistent with previous studies showing that blood flow is a necessary factor for heart development. Furthermore an unexpected result was observed. Exposure to a localized magnetic field eventually caused the absorption of magnetic microspheres into the surrounding tissue. It is theorized that this could be utilized in future studies modeling the effects of reduced cardiac contractility.
" }, { "name": "Alves, Steven Wayne", "degree": "PhD", "year": "2005", "title": "Nonlinear Analysis of Pacoima Dam with Spatially Nonuniform Ground Motion", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292004-155829", "creators": [ { "name": { "family": "Alves", "given": "Steven Wayne" }, "id": "Alves-Steven-Wayne", "display_name": "Alves, Steven Wayne" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Duron", "given": "Ziyad H." }, "id": "Duron-Z-H", "role": "member", "display_name": "Duron, Ziyad H." } ], "option_major": [ "civileng" ], "doi": "10.7907/QVFR-MV06", "abstract": "Spatially uniform ground motion is an assumption that has often been made for structural analysis of arch dams. However, it has been recognized for many years that the ground motion in a canyon during an earthquake is amplified at the top of the canyon relative to the base. Pacoima Dam has been strongly shaken by the 1971 San Fernando earthquake and the 1994 Northridge earthquake. The acceleration records from both of these events demonstrate the spatial nonuniformity of the ground motion, but the amount and quality of the data made it difficult to study in detail. An opportunity to do so arose on January 13, 2001, when a relatively small magnitude 4.3 earthquake was recorded by an upgraded accelerometer array at Pacoima Dam.
\r\n\r\nFrequency-dependent topographic amplification is apparent at locations along both abutments at 80% height of the dam relative to the base. Also, the ground motion is delayed at the abutment locations compared to the base. The delays are consistent with seismic waves traveling upward along the canyon, and the waves appear to be dispersive since the delays are frequency-dependent. Both of these effects are quantified in this thesis by several approaches that involve varying degrees of approximation. A method for generating nonuniform ground motion from a single 3-component ground motion specified for one location in the canyon, e.g., at the base, is developed using transfer functions that quantify the amplification and phase delay. The method is demonstrated for the 2001 earthquake and the Northridge earthquake with several variations in the transfer functions.
\r\n\r\nThe 2001 earthquake records were also used for system identification. These results do not agree with results from a forced vibration experiment, which indicate a stiffer system. The earthquake must induce nonlinear vibrations, even though the excitation is quite small. This observation has implications for applications of structural health monitoring.
\r\n\r\nThe generated nonuniform ground motions are supplied as input to a finite element model. The results indicate that the method for generating nonuniform input produces ground motion that yields reasonable modeled responses, but there is some evidence that the time delays may be larger for stronger ground motion. Comparisons of the responses from ground motions generated with various implementations of amplification and time delays were made. For modeling purposes, accuracy of the amplification appears to be more important than the delays, which can be dealt with using a simpler approximation. The nonuniform input produces a response that is substantially different than the response produced by uniform input. The major difference is that while the pseudostatic response is a rigid body motion for uniform input, it causes deformation of the dam, mostly close to the abutments, for nonuniform input. In order to refine the proposed method for generating nonuniform ground motion, more data is required from Pacoima Dam and other structures with instrumentation coverage along the abutments.
" }, { "name": "Armani, Deniz Karapetian", "degree": "PhD", "year": "2005", "title": "Ultra-High-Q Planar Microcavities and Applications", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-113247", "creators": [ { "name": { "family": "Armani", "given": "Deniz Karapetian" }, "id": "Armani-Deniz-Karapetian", "display_name": "Armani, Deniz Karapetian" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/EZHA-VY23", "abstract": "Ultra-high-Q (UHQ) silica microspheres have found research applications in diverse fields ranging from telecommunications to nonlinear optics to biological and chemical sensing. However, despite having quality factors greater than 108, the silica microsphere has not moved to an industrial setting because of several major drawbacks. The most hindering is the manual fabrication technique used that makes tight process control difficult and integration with other optical or electrical components impossible. Despite the strong desire to fabricate an integrated UHQ microresonator on a planar substrate, the highest quality factor achieved for any micro-fabricated planar micro-cavity (at the time of my first publication) was over 4 orders of magnitude lower than for silica microspheres. In this thesis, a process for creating planar micro-cavities with Q factors in excess of 400 million on silicon wafers is demonstrated. The advantage of these planar ultra-high-Q (UHQ) microtoroid resonators is that they successfully overcome the previously mentioned drawbacks of silica microsphere resonators while maintaining nearly identical, if not better, performance characteristics. Additionally, due to the planar nature of these new devices, functionality has been integrated in-situ while maintaining UHQ for the first time, such as active resonant frequency tuning, coupling control, and low-threshold lasing." }, { "name": "Bahreini, Roya", "degree": "PhD", "year": "2005", "title": "Studies with the Aerosol Mass Spectrometer", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05032005-180939", "creators": [ { "name": { "family": "Bahreini", "given": "Roya" }, "id": "Bahreini-Roya", "orcid": "0000-0001-8292-5338", "display_name": "Bahreini, Roya" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Beauchamp", "given": "Jesse L." }, "id": "Beauchamp-J-L", "orcid": "0000-0001-8839-4822", "role": "member", "display_name": "Beauchamp, Jesse L." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/1YNP-QQ95", "abstract": "Fast time-response of the Aerodyne Aerosol Mass Spectrometer (AMS) makes it a well-suited instrument for ambient field measurements. On the other hand, laboratory chamber experiments provide the opportunity to study a specific system in a more controlled environment. The goal of this thesis is to provide a summary of laboratory and field measurements using the AMS.
\r\n\r\nDuring laboratory chamber photooxidation experiments of diiodomethane (CH2I2), particle nucleation was observed at CH2I2 concentrations down to 15 ppt, which is comparable to the total gas-phase iodine species measured at coastal areas. Iodine oxides and oxyacids were observed in the aerosol mass spectra obtained by the AMS, consistent with the known gas-phase chemistry.
\r\n\r\nAirborne measurements by the AMS during the ACE-Asia field study revealed that the non-refractory submicron aerosols in the pollution layers of the boundary layer up to 3700 m were mainly composed of sulfate, ammonium, and organics. These pollution plumes originated primarily from urban and industrial areas of China and Korea.
\r\n\r\nThe laboratory chamber experiments of oxidation of cycloalkenes, terpenes, and m-xylene provided the opportunity to study the Secondary Organic Aerosol (SOA) forming potential, i.e., yield, and determine SOA effective density and chemical composition. Evidence of acid-catalyzed heterogeneous chemistry in the ozonolysis of a-pinene was observed since the total AMS organic mass during the experiments with acidic seed particles had a greater contribution of higher molecular weight fragments. The mixtures of SOA compounds produced from similar precursors studied resulted in broadly similar AMS mass spectra. Thus, fragmentation patterns observed for biogenic vs. anthropogenic SOA can be potentially useful in determining the sources of ambient SOA.
" }, { "name": "Bergthorson, Jeffrey Myles", "degree": "PhD", "year": "2005", "title": "Experiments and Modeling of Impinging Jets and Premixed Hydrocarbon Stagnation Flames", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-165713", "creators": [ { "name": { "family": "Bergthorson", "given": "Jeffrey Myles" }, "id": "Bergthorson-Jeffrey-Myles", "orcid": "0000-0003-2924-7317", "display_name": "Bergthorson, Jeffrey Myles" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Kuppermann", "given": "Aron" }, "id": "Kuppermann-A", "role": "member", "display_name": "Kuppermann, Aron" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7FQZ-EY88", "abstract": "To model the combustion of long-chain hydrocarbon fuels, an accurate kinetics mechanism must first be developed for the oxidation of small hydrocarbons, such as methane, ethane, and ethylene. Even for methane, a generally accepted mechanism is still elusive due to a lack of kinetically independent experimental data. In this work, a combined experimental and modeling technique is developed to validate and further optimize these mechanisms. This technique relies on detailed measurements of strained flames in a jet-wall stagnation flow using simultaneous Particle Streak Velocimetry (PSV) and CH Planar Laser Induced Fluorescence (PLIF). Stagnation flames are simulated using an axisymmetric, one-dimensional model with accurate specification of the requisite boundary conditions. Direct comparisons between experiment and simulation allow for an assessment of the various models employed, with an emphasis on the chemistry model performance.
\r\n\r\nThe flow field for a cold impinging laminar jet is found to be independent of the nozzle-to-plate separation distance if velocities are scaled by the Bernoulli velocity. The one-dimensional formulation is found to accurately model the stagnation flow if the velocity boundary conditions are appropriately specified. The boundary-layer-displacement-thickness corrected diameter is found to be an appropriate scale for axial distances and allows the identification of an empirical, analytical expression for the flow field of the impinging laminar jet.
\r\n\r\nStrained methane-air flame experiments confirm that the reacting flow is also independent of the nozzle-to-plate separation distance. Methane, ethane, and ethylene flames are studied as functions of the applied strain rate, mixture dilution, and mixture fraction. Mechanism performance is found to be relatively insensitive to both the mixture dilution and the imposed strain rate, while exhibiting a stronger dependence on the fuel type and flame stoichiometry. The approach and diagnostics presented here permit an assessment of the predictions of strained-hydrocarbon flames for several combustion chemistry mechanisms. The data presented in this thesis are made available to kineticists looking for optimization targets, with the goal of developing a predictive kinetics model for hydrocarbon fuels. The methodology described here can allow new optimization targets to be rapidly measured, reducing the experimental burden required to fully constrain the chemistry models.
" }, { "name": "Bhat, Harish Subrahmanya", "degree": "PhD", "year": "2005", "title": "Lagrangian Averaging, Nonlinear Waves, and Shock Regularization", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262005-100534", "creators": [ { "name": { "family": "Bhat", "given": "Harish Subrahmanya" }, "id": "Bhat-Harish-Subrahmanya", "orcid": "0000-0001-7631-1831", "display_name": "Bhat, Harish Subrahmanya" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Fetecau", "given": "Razvan Constantin" }, "id": "Fetecau-R-C", "role": "member", "display_name": "Fetecau, Razvan Constantin" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "role": "member", "display_name": "Schneider, Tapio" } ], "option_major": [ "cds" ], "doi": "10.7907/8DJ2-F672", "abstract": "In this thesis, we explore various models for the flow of a compressible fluid as well as model equations for shock formation, one of the main features of compressible fluid flows.
\r\n\r\nWe begin by reviewing the variational structure of compressible fluid mechanics. We derive the barotropic compressible Euler equations from a variational principle in both material and spatial frames. Writing the resulting equations of motion requires certain Lie-algebraic calculations that we carry out in detail for expository purposes.
\r\n\r\nNext, we extend the derivation of the Lagrangian averaged Euler (LAE-alpha) equations to the case of barotropic compressible flows. The derivation in this thesis involves averaging over a tube of trajectories centered around a given Lagrangian flow. With this tube framework, the LAE-alpha equations are derived by following a simple procedure: start with a given action, expand via Taylor series in terms of small-scale fluid fluctuations, truncate, average, and then model those terms that are nonlinear functions of the fluctuations.
\r\n\r\nWe then analyze a one-dimensional subcase of the general models derived above. We prove the existence of a large family of traveling wave solutions. Computing the dispersion relation for this model, we find it is nonlinear, implying that the equation is dispersive. We carry out numerical experiments that show that the model possesses smooth, bounded solutions that display interesting pattern formation.
\r\n\r\nFinally, we examine a Hamiltonian partial differential equation (PDE) that regularizes the inviscid Burgers equation without the addition of standard viscosity. Here alpha is a small parameter that controls a nonlinear smoothing term that we have added to the inviscid Burgers equation. We show the existence of a large family of traveling front solutions. We analyze the initial-value problem and prove well-posedness for a certain class of initial data. We prove that in the zero-alpha limit, without any standard viscosity, solutions of the PDE converge strongly to weak solutions of the inviscid Burgers equation. We provide numerical evidence that this limit satisfies an entropy inequality for the inviscid Burgers equation. We demonstrate a Hamiltonian structure for the PDE.
" }, { "name": "Boland, Justin Scott", "degree": "PhD", "year": "2005", "title": "Micro Electret Power Generators", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-06092005-112430", "creators": [ { "name": { "family": "Boland", "given": "Justin Scott" }, "id": "Boland-Justin-Scott", "display_name": "Boland, Justin Scott" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "eleceng" ], "doi": "10.7907/B16C-NT21", "abstract": "The taming of electricity and its widespread use allows people to see in the dark, to speak to one another instantaneously across the earth, and it allows retrieval of data from instruments sent out of the solar system. It is right to expect that the uses and demand for electricity will continue to grow, and to extend the ability to generate electricity; here two new micromachined devices for converting mechanical energy into electrical energy are presented. Aided by the wealth of micromachining process technology, generators that use an oscillatory motion to modify the physical structure of a capacitor with a built-in electric field provided by a permanent electret have been designed, built, and tested. The electret creates an electric field inside the capacitor structure, which induces mirror charge at some potential. The modification of the capacitor then generates an alternating displacement current through an external circuit, which provides useful electrical power. The electret microphone is a similar well known device for converting pressure waves into electrical signals by varying the distance between two charged capacitive plates. This work explores and proves feasible the ability to use mechanical forces to change the overlapping area of a charged capacitor structure and using mechanical forces to move a liquid into the gap of a charged capacitor structure, changing its permittivity to produce electricity. This work demonstrates 2.5mW of power from a 2cm diameter rotary generator at 12kRPM and 10[micro]w for a 0.1cm3 linear shaking generator at 60Hz.\r\n" }, { "name": "Boland, Stacey Walker", "degree": "PhD", "year": "2005", "title": "Sol-Gel Synthesis of Highly Oriented Lead Barium Titanate and Lanthanum Nickelate Thin Films for High Strain Sensor and Actuator Applications", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03282005-113506", "creators": [ { "name": { "family": "Boland", "given": "Stacey Walker" }, "id": "Boland-Stacey-Walker", "display_name": "Boland, Stacey Walker" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7H7R-6X26", "abstract": "Piezoelectric materials, capable of 0.1% strains, have been extensively used in sensor and actuator applications. Ferroelectric materials, a subset of the piezoelectric class, are capable of strains an order of magnitude larger. For a ferroelectric material with tetragonal crystal structure, large strains can be achieved through 90 degree domain switching between a and c domains. Bulk barium titanate has been shown to produce strains of 0.9% through such domain switching under combined electromechanical loading. Lead titanate has a larger c/a ratio and would be expected to produce 6% strains, though it is prone to brittle fracture. By examining the solid solution lead barium titanate, larger strains can be achieved while maintaining mechanical integrity. The work presented here covers the development of multiple sol-gel processes for producing powder and highly oriented thin film lead barium titanate, and a detailed discussion of their parametric optimization towards low temperature crystallization. Finally, results of early efforts toward integrating these films into useful structures and devices are discussed, including sol-gel synthesis of highly oriented conductive oxide electrodes. Thin film barium lead oxide and lanthanum nickelate electrodes were produced using sol-gel processing. (100)-oriented lanthanum nickelate electrodes were produced on a wide variety of amorphous and crystalline substrates, and subsequently deposited PBT showed excellent (100/001)-orientation regardless of substrate. The ability to produce highly oriented ferroelectric films on oxide electrodes deposited directly on Si promises to improve fatigue characteristics and greatly facilitate efforts to integrate ferroelectric thin films into MEMS process." }, { "name": "Boxe, Christopher Shawn", "degree": "PhD", "year": "2005", "title": "Nitrate Photochemistry and Interrelated Chemical Phenomena in Ice", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-143636", "creators": [ { "name": { "family": "Boxe", "given": "Christopher Shawn" }, "id": "Boxe-Christopher-Shawn", "orcid": "0000-0002-5288-961X", "display_name": "Boxe, Christopher Shawn" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "role": "member", "display_name": "Okumura, Mitchio" }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/NC6C-NA28", "abstract": "The detailed photochemistry of nitrate ions trapped within polycrystalline ice has been investigated. Using a variety of experimental techniques, the photolysis of NO3- within ice is shown to produce NO, HONO, NO2- and NO2 as stable and metastable products. The gaseous products are released to the overlying gas phase. Implications of these results for chemical transformations in polar regions are discussed.
\r\n\r\nThe isotopic composition of nitrate in polar ice cores exhibits mass-independent fractionation (?????~ 25 \u2030). However, in this study it is shown that nitrate photolysis is a mass-dependent process and that nitrate can be a conservative tracer for past atmospheric conditions.
\r\n\r\nPhotolysis of NO3- produces nitrite ion within ice and the rate of photolysis increases with increasing temperature. A linear Arrhenius temperature dependence for the measured quantum yield, , was found both above and below the normal melting point of water ice. These results indicate that nitrate photochemistry occurs primarily in the quasi-liquid layer (QLL), which is a disordered layer of ice that has chemical properties closer to water than solid crystalline ice.
\r\n\r\nThe photochemical production of gas-phase NO and NO2 from ice-phase nitrate was determined in real-time using laser-induced fluorescence, two-photon laser-induced fluorescence, and chemiluminescence. These results showed that NO and NO2, which was produced at lower temperatures is released in much larger quantities at ?7 \u00b1 2 oC from subsurface regions of the QLL or at the ice/vapor interface. These results highlight the importance of the QLL and sub-eutectic sub-surface solutions at grain boundaries in polycrystalline ice. In addition, it was shown that the total amount of NO2 that is photodesorbed scales nonlinearly with [NO3?]o or the heating rate. Evidence for extensive chemical and photochemical losses of NO2 before release into the gas-phase is presented. In the case of NO, photo-induced desportion occured at ~ ?20 oC, which suggests a preferential retention of NO2 over NO in the nanoporous water channels of the QLL domains.
\r\n\r\nThe impact of the specific nature of the chemical solutes in water on the nominal pH of the QLL was explored using the temperature dependence of 19F-NMR chemical shifts of 3-fluorobenzoic acid. The 19F-NMR measurements during the freezing of NaCl, NaNO2 and KNO3 solutions indicated that the QLL domains within the polycrystalline ice were shifted to higher pH values, while the freezing of NH4OH or Na2SO4 solutions produced QLL domains that showed a drop in pH (i.e., protons were released from the ice-phase to the QLL). These results help explain the release of HONO which is formed by protonation of NO2- within the QLL domains and are relevant to the observed release of nitrous acid to the atmospheric boundary layer in the Arctic and Antarctic.
" }, { "name": "Chatelain, Philippe", "degree": "PhD", "year": "2005", "title": "Contributions to the Three-Dimensional Vortex Element Method and Spinning Bluff Body Flows", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012005-061553", "creators": [ { "name": { "family": "Chatelain", "given": "Philippe" }, "id": "Chatelain-Philippe", "orcid": "0000-0001-9891-5265", "display_name": "Chatelain, Philippe" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YEDS-0V89", "abstract": "Several contributions to the three-dimensional vortex element method for incompressible flows are presented. We introduce redistribution schemes based on the hexagonal lattice in two dimensions, and the face-centered cubic lattice in three dimensions. Interpolation properties are studied in the frequency domain and are used to build high-order schemes that are more compact and isotropic than equivalent cubic schemes. We investigate the reconnection of vortex rings at small Reynolds numbers for a variety of configurations. In particular, we trace their dissipative nature to the formation of secondary structures.
\r\n\r\nA method for flows with moving boundaries is implemented. The contributions of rotating or deforming boundaries to the Biot-Savart law are derived in terms of surface integrals. They are implemented for rigid boundaries in a fast multipole algorithm. Near-wall vorticity is discretized with attached panels. The shape function and Biot-Savart contributions of these elements account for the presence of the boundary and its curvature. A conservative strength exchange scheme was designed to compute the viscous flux from these panels to free elements.
\r\n\r\nThe flow past a spinning sphere is studied for a Reynolds number of 300 and a wall velocity that is equal to half the free-stream velocity. Three directions of the angular velocity are considered. Good agreement with previous numerical and experimental measurements of the force coefficients is observed. Topological features such as the separation and critical points are investigated and compared amongst the configurations.
\r\n\r\nFinally, preliminary results for flapping motions are presented. Simple rigid geometries are used to model a fish swimming in a free-stream and a flapping plate.
" }, { "name": "Chow, Stephanie Sienyee", "degree": "PhD", "year": "2005", "title": "Speciation in Digital Organisms", "advisor": "Adami, Christoph Carl", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062005-171257", "creators": [ { "name": { "family": "Chow", "given": "Stephanie Sienyee" }, "id": "Chow-Stephanie-Sienyee", "display_name": "Chow, Stephanie Sienyee" } ], "advisors": [ { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "role": "advisor", "display_name": "Adami, Christoph Carl" } ], "committee": [ { "name": { "family": "Wold", "given": "Barbara J." }, "id": "Wold-B-J", "role": "chair", "display_name": "Wold, Barbara J." }, { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "role": "member", "display_name": "Adami, Christoph Carl" }, { "name": { "family": "Wilke", "given": "Claus O." }, "id": "Wilke-C-O", "role": "member", "display_name": "Wilke, Claus O." }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Quartz", "given": "Steven R." }, "id": "Quartz-S-R", "role": "member", "display_name": "Quartz, Steven R." } ], "option_major": [ "cns" ], "doi": "10.7907/X1PD-TN75", "abstract": "Current estimates of the number of species on Earth range from four to forty million total species. Why are there so many species? The answer must include both ecology and evolution. Ecology looks at the interactions between coexisting species, while evolution tracks them through time. Both are required to understand aspects of environments which promote speciation, and which promote species persistence in time.
\r\n\r\nThe explanation for this biodiversity is still not well understood. I argue that resource limitations are a major factor in the evolutionary origin of complex ecosystems with interacting and persistent species. Through experiments with digital organisms in environment with multiple limited resources, I show that these conditions alone can be sufficient to induce differentiation in a population. Moreover, the observed pattern of species number distributions match patterns observed in nature. I develop a simple metric for phenotypic distance for digital organisms, which permits quantitative analysis of similarities within, and differences between species. This enables a clear species concept for digital organisms that may also be applied to biological organisms, thus helping to clarify the biological species concept. Finally, I will use this measurement methodology to predict species and ecosystem stability.
" }, { "name": "Cook, Matthew M.", "degree": "PhD", "year": "2005", "title": "Networks of Relations", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032005-140944", "creators": [ { "name": { "family": "Cook", "given": "Matthew M." }, "id": "Cook-Matthew-M", "display_name": "Cook, Matthew M." } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "chair", "display_name": "Winfree, Erik" }, { "name": { "family": "Umans", "given": "Christopher M." }, "id": "Umans-C-M", "role": "member", "display_name": "Umans, Christopher M." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "cns" ], "doi": "10.7907/CVKM-D684", "abstract": "Relations are everywhere. In particular, we think and reason in terms of mathematical and English sentences that state relations. However, we teach our students much more about how to manipulate functions than about how to manipulate relations. Consider functions. We know how to combine functions to make new functions, how to evaluate functions efficiently, and how to think about compositions of functions. Especially in the area of boolean functions, we have become experts in the theory and art of designing combinations of functions to yield what we want, and this expertise has led to techniques that enable us to implement mind-bogglingly large yet efficient networks of such functions in hardware to help us with calculations. If we are to make progress in getting machines to be able to reason as well as they can calculate, we need to similarly develop our understanding of relations, especially their composition, so we can develop techniques to help us bridge between the large and small scales. There has been some important work in this area, ranging from practical applications such as relational databases to extremely theoretical work in universal algebra, and sometimes theory and practice manage to meet, such as in the programming language Prolog, or in the probabilistic reasoning methods of artificial intelligence. However, the real adventure is yet to come, as we learn to develop a better understanding of how relations can efficiently and reliably be composed to get from a low level representation to a high level representation, as this understanding will then allow the development of automated techniques to do this on a grand scale, finally enabling us to build machines that can reason as amazingly as our contemporary machines can calculate.
\r\n\r\nThis thesis explores new ground regarding the composition of relations into larger relational structures. First of all a foundation is laid by examining how networks of relations might be used for automated reasoning. We define exclusion networks, which have close connections with the areas of constraint satisfaction problems, belief propagation, and even boolean circuits. The foundation is laid somewhat deeper than usual, taking us inside the relations and inside the variables to see what is the simplest underlying structure that can satisfactorily represent the relationships contained in a relational network. This leads us to define zipper networks, an extremely low-level view in which the names of variables or even their values are no longer necessary, and relations and variables share a common substrate that does not distinguish between the two. A set of simple equivalence operations is found that allows one to transform a zipper network while retaining its solution structure, enabling a relation-variable duality as well as a canonical form on linear segments. Similarly simple operations allow automated deduction to take place, and these operations are simple and uniform enough that they are easy to imagine being implemented by biological neural structures.
\r\n\r\nThe canonical form for linear segments can be represented as a matrix, leading us to matrix networks. We study the question of how we can perform a change of basis in matrix networks, which brings us to a new understanding of Valiant's recent holographic algorithms, a new source of polynomial time algorithms for counting problems on graphs that would otherwise appear to take exponential time. We show how the holographic transformation can be understood as a collection of changes of basis on individual edges of the graph, thus providing a new level of freedom to the method, as each edge may now independently choose a basis so as to transform the matrices into the required form.
\r\n\r\nConsideration of zipper networks makes it clear that \"fan-out,\" i.e., the ability to duplicate information (for example allowing a variable to be used in many places), is most naturally itself represented as a relation along with everything else. This is a notable departure from the traditional lack of representation for this ability. This deconstruction of fan-out provides a more general model for combining relations than was provided by previous models, since we can examine both the traditional case where fan-out (the equality relation on three variables) is available and the more interesting case where its availability is sub ject to the same limitations as the availability of other relations. As we investigate the composition of relations in this model where fan-out is explicit, what we find is very different from what has been found in the past.
\r\n\r\nFirst of all we examine the relative expressive power of small relations: For each relation on three boolean variables, we examine which others can be implemented by networks built solely from that relation. (We also find, in each of these cases, the complexity of deciding whether such a network has a solution. We find that solutions can be found in polynomial time for all but one case, which is NP-complete.) For the question of which relations are able to implement which others, we provide an extensive and complete answer in the form of a hierarchy of relative expressive power for these relations. The hierarchy for relations is more complex than Post's well-known comparable hierarchy for functions, and parts of it are particularly difficult to prove. We find an explanation for this phenomenon by showing that in fact, the question of whether one relation can implement another (and thus should be located above it in the hierarchy) is undecidable. We show this by means of a complicated reduction from the halting problem for register machines. The hierarchy itself has a lot of structure, as it is rarely the case that two ternary boolean relations are equivalent. Often they are comparable, and often they are incomparable\u2014the hierarchy has quite a bit of width as well as depth. Notably, the fan-out relation is particularly difficult to implement; only a very few relations are capable of implementing it. This provides an additional ex post facto justification for considering the case where fan-out is absent: If you are not explicitly provided with fan-out, you are unlikely to be able to implement it.
\r\n\r\nThe undecidability of the hierarchy contrasts strongly with the traditional case, where the ubiquitous availability of fan-out causes all implementability questions to collapse into a finite decidable form. Thus we see that for implementability among relations, fan-out leads to undecidability. We then go on to examine whether this result might be taken back to the world of functions to find a similar difference there. As we study the implementability question among functions without fan-out, we are led directly to questions that are independently compelling, as our functional implementability question turns out to be equivalent to asking what can be computed by sets of chemical reactions acting on a finite number of species. In addition to these chemical reaction networks, several other nondeterministic systems are also found to be equivalent in this way to the implementability question, namely, Petri nets, unordered Fractran, vector addition systems, and \"broken\" register machines (whose decrement instruction may fail even on positive registers). We prove equivalences between these systems.
\r\n\r\nWe find several interesting results in particular for chemical reaction networks, where the standard model has reaction rates that depend on concentration. In this setting, we analyze questions of possibility as well as questions of probability. The question of the possibility of reaching a target state turns out to be equivalent to the reachability question for Petri nets and vector addition systems, which has been well studied. We provide a new proof that a form of this reachability question can be decided by primitive recursive functions. Ours is the first direct proof of this relationship, avoiding the traditional excursion to Diophantine equations, and thus providing a crisper picture of the relationship between Karp's coverability tree and primitive recursive functions.
\r\n\r\nIn contrast, the question of finding the probability (according to standard chemical kinetics) of reaching a given target state turns out to be undecidable. Another way of saying this is that if we wish to distinguish states with zero probability of occurring from states with positive probability of occurring, we can do so, but if we wish to distinguish low probability states from high probability states, there is no general way to do so. Thus, if we wish to use a chemical reaction network to perform a computation, then if we insist that the network must always get the right answer, we will only be able to use networks with limited computational power, but if we allow just the slightest probability of error, then we can use networks with Turing-universal computational ability. This power of probability is quite surprising, especially when contrasted with the conventional computational complexity belief that BPP = P.
\r\n\r\nExploring the source of this probabilistic power, we find that the probabilities guiding the network need to depend on the concentrations (or perhaps on time)\u2014fixed probabilities aren\u2019t enough on their own to achieve this power. In the language of Petri nets, if one first picks a transition at random, and then fires it if it is enabled, then the probability of reaching a particular target state can be calculated to arbitrary precision, but if one first picks a token at random, and then fires an enabled transition that will absorb that token, then the probability of reaching a particular target state cannot in general be calculated to any precision whatsoever.
\r\n\r\nIn short, what started as a simple thorough exploration of the power of composition of relations has led to many decidability and complexity questions that at first appear completely unrelated, but turn out to combine to paint a coherent picture of the relationship between relations and functions, implementability and reachability, possibility and probability, and decidability and undecidability.
" }, { "name": "Cua, Georgia B.", "degree": "PhD", "year": "2005", "title": "Creating the Virtual Seismologist: Developments in Ground Motion Characterization and Seismic Early Warning", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092005-125601", "creators": [ { "name": { "family": "Cua", "given": "Georgia B." }, "id": "Cua-Georgia-B", "display_name": "Cua, Georgia B." } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Hauksson", "given": "Egill" }, "id": "Hauksson-E", "role": "member", "display_name": "Hauksson, Egill" } ], "option_major": [ "civileng" ], "doi": "10.7907/M926-J956", "abstract": "The Virtual Seismologist method for earthquake early warning uses a Bayesian approach to find the most probable magnitude and location estimates given the incoming ground motions envelopes from a rupturing earthquake. Ground motion ratios and ground motion envelope attenuation relationships are used to estimate magnitude and epicentral location as early as 3 seconds after the initial P wave detection. The use of prior information distinguishes this method from other proposed methods for seismic early warning. The state of health of the seismic network, previously observed seismicity, fault locations, and the Gutenberg-Richter relationship are the types of prior information useful in resolving trade-offs in the initial source estimates which are unresolved by the limited data. Short-term earthquake forecasts are ideal priors for seismic early warning.
\r\n\r\nHaving a high density of stations with real-time telemetry reduces the complexity involved in finding the most probable source estimates and communicating these estimates to early warning subscribers. The benefits of prior information are most evident for regions with low station density. Most early warning studies are focused exclusively on either the source estimation problem, or how subscribers use the warning information. The inclusion of prior information ultimately requires a level of coordination and communication between the network broadcasting the early warning information and the subscribers that is not consistent with this divide. The need for a more integrated approach to seismic early warning which considers the source estimation and user response as interacting and interrelated parts of a single problem is discussed.
\r\n\r\nA parameterization that decomposes observed ground motion envelopes into P-wave, S-wave, and ambient noise envelopes is developed and applied to a large suite of observed ground motion envelopes recorded within 200 km of 2.0 < M < 7.3 Southern California earthquakes. Separate attenuation relationships are developed to describe the magnitude, distance, and site dependence of various channels of P- and S-wave envelopes. The P-wave relationships allow the early warning source estimates to be obtained from observed P-wave amplitudes. Aside from early warning applications, these envelope attenuation relationships are used to investigate the average properties of ground motions recorded by the Southern California Seismic Network. Station-specific amplification factors for 150 Southern California Seismic Network stations were obtained for horizontal and vertical acceleration, velocity, and displacement amplitudes, and are included (Excel format) as external multimedia objects.
" }, { "name": "Cummings, Uri Vaughan", "degree": "PhD", "year": "2005", "title": "Linearized and High Frequency Electrooptic Modulators", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312005-225644", "creators": [ { "name": { "family": "Cummings", "given": "Uri Vaughan" }, "id": "Cummings-Uri-Vaughan", "display_name": "Cummings, Uri Vaughan" } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "chair", "display_name": "Bridges, William B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Schaffner", "given": "James H." }, "id": "Schaffner-J-H", "role": "member", "display_name": "Schaffner, James H." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GTD7-V873", "abstract": "An analysis is performed of many standard and linearized electrooptic modulators known in the industry. The transfer functions of these modulators are evaluated under a consistent set of performance figures of merit, which are gain and spur-free dynamic range, using a canonical set of optical link parameters. The tolerance of the needed precision of the parameters of the linearization mechanisms of all of these modulators is compared over the entire interesting range of noise bandwidth.
\r\n\r\nA computer program was written to analyze the frequency dependence of any modulator transfer function under any set of functional inputs. The program is used to illustrate and compare the frequency dependence of the figures of merit of all of the modulators for which a d-c analysis was performed. Further analysis looks at the effect of greater noise-bandwidth and recovering the frequency-dependent degradation of gain and dynamic range through re-phasing techniques. The gain of directional couplers is analyzed in-depth.
\r\n\r\nTwo novel modulator schemes are produced. The first uses reflective wave techniques to retime the electrical and optical waves half way through the modulator. The second uses fabrication geometry and properties of the linearization technique to make a more robust modulator (applicable to three of the modulators analyzed).
\r\n\r\nA 94 GHz antenna-coupled directional coupler modulator was initially demonstrated using an old modulator chip from Finbar Sheehy. A peculiar bug with the chip was uncovered. And a new modulator experiment was constructed and many aspects of the experimental apparatus were optimized. Though the revised experiment ultimately did not yield modulation side bands, it did couple a 94 GHz microwave signal into the optical waveguide, and many interesting challenges of high frequency electrooptic modulator fabrication were evaluated and improved upon.
" }, { "name": "Dabiri, John Oluseun", "degree": "PhD", "year": "2005", "title": "Unsteady Fluid Mechanics of Starting-Flow Vortex Generators with Time-Dependent Boundary Conditions", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-04112005-151435", "creators": [ { "name": { "family": "Dabiri", "given": "John Oluseun" }, "id": "Dabiri-John-Oluseun", "orcid": "0000-0002-6722-9008", "display_name": "Dabiri, John Oluseun" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "bioeng" ], "doi": "10.7907/QV8Y-YZ12", "abstract": "Nature has repeatedly converged on the use of starting flows for mass, momentum, and energy transport. The vortex loops that form during flow initiation have been reproduced in the laboratory and have been shown to make a proportionally larger contribution to fluid transport than an equivalent steady jet. However, physical processes limit growth of the vortex loops, suggesting that these flows may be amenable to optimization. Although it has been speculated that optimal vortex formation might occur naturally in biological systems, previous efforts to quantify the biological mechanisms of vortex formation have been inconclusive. In addition, the unsteady fluid dynamical effects associated with starting flow vortex generators are poorly understood.
\r\n\r\nThis thesis describes a combination of new experimental techniques and in vivo animal measurements that determine the effects of fluid-structure interactions on vortex formation by starting flow propulsors. Results indicate that vortex formation across various biological systems is manipulated by these kinematics in order to maximize thrust and/or propulsive efficiency. An emphasis on observed vortex dynamics and transient boundary conditions facilitates quantitative comparisons across fluid transport schemes, irrespective of their individual biological functions and physical scales.
\r\n\r\nThe primary contributions of this thesis are the achievement of quantitative measures of unsteady vortex dynamics via fluid entrainment and added-mass effects, and the development of a robust framework to facilitate the discovery of general design principles for effective fluid transport in engineering technologies and biological therapies. The utility of this new research paradigm is demonstrated through a variety of examples.
" }, { "name": "Del Vecchio, Domitilla", "degree": "PhD", "year": "2005", "title": "State Estimation in Multi-Agent Decision and Control Systems", "advisor": "Murray, Richard M.; Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-113928", "creators": [ { "name": { "family": "Del Vecchio", "given": "Domitilla" }, "id": "Del-Vecchio-Domitilla", "display_name": "Del Vecchio, Domitilla" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "co-advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Klavins", "given": "Eric" }, "id": "Klavins-E", "role": "member", "display_name": "Klavins, Eric" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cds" ], "doi": "10.7907/SAX3-ED56", "abstract": "his thesis addresses the problem of estimating the state in multi-agent decision and control systems. In particular, a novel approach to state estimation is developed that uses partial order theory in order to overcome some of the severe computational complexity issues arising in multi-agent systems. Within this approach, state estimation algorithms are developed that enjoy provable convergence properties and are scalable with the number of agents.
\r\n\r\nThe dynamic evolution of the systems under study are characterized by the interplay of continuous and discrete variables. Continuous variables usually represent physical quantities such as position, velocity, voltage, and current, while the discrete variables usually represent quantities internal to the decision protocol that are used for coordination, communication, and control. Within the proposed state estimation approach, the estimation of continuous and discrete variables is developed in the same mathematical framework as a joint continuous-discrete space is considered for the estimator. This way, the dichotomy between the continuous and discrete world is overcome for the purpose of state estimation.
\r\n\r\nApplication examples are considered, which include the state estimation in competitive multi-robot systems and in multi-agent discrete event systems, and the monitoring of distributed environments.
" }, { "name": "Dooley, Bradley Scott", "degree": "PhD", "year": "2005", "title": "Stereo Digital Particle Image Velocimetry Investigation of a Free Surface Mixing Layer", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022005-180557", "creators": [ { "name": { "family": "Dooley", "given": "Bradley Scott" }, "id": "Dooley-Bradley-Scott", "display_name": "Dooley, Bradley Scott" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EH41-N436", "abstract": "Shear flows in the vicinity of a free surface are a problem with numerous applications, perhaps the most obvious being the wakes of seagoing surface vessels. The flow behind a full-scale ship is extremely complex \u2013 so much so that it is frequently more instructive to consider simpler cases highlighting particular elements of the larger problem. To that end, an experimental investigation has been conducted to study the behavior of a turbulent plane mixing layer intersecting a free surface at low Froude number. The local Reynolds number, based on the velocity differential across the layer and the momentum thickness, was approximately 10,000.
\r\n\r\nThe technique of Stereoscopic Digital Particle Image Velocimetry (SDPIV) was implemented to obtain instantaneous three-component velocity measurements within planar slices of the steady-state, spatially developing mixing layer flow. Guided by previous studies of the same flow conditions, specific depths were chosen at a single downstream station for investigation \u2013 specifically those in and around counter-rotating streamwise vortices known to exist in the mean flow very near the free surface. 3,000 consecutive SDPIV image pairs were recorded at a rate of 15 per second at each location, giving ample data for Reynolds decomposition and spectral analysis of the velocity fields.
\r\n\r\nThe present study has found that the anisotropy known to exist in some other free surface flows, such as surface-parallel submerged jets, is also present in the case of the mixing layer. Power spectra of all three velocity components are shown to capture part of the inertial subrange; the isotropic energy cascade seen to be present away from the free surface is also seen to disappear near the surface, as surface-normal velocity fluctuations are severely attenuated.
\r\n\r\nAdditionally, a low-frequency spanwise oscillation is deduced from the velocity power spectra and cospectra in the immediate vicinity of the mean streamwise vortices. Not present at all at significant depth, the motions at this frequency are also observed to markedly decrease \u2013 in all components \u2013 at locations closer to the surface. These observations appear to have both parallels and key differences compared to previously observed meandering of model boat wakes, and the possibility that the oscillation stems from the vortex-pair instability is discussed.
" }, { "name": "Dorn, Evan David", "degree": "PhD", "year": "2005", "title": "Universal Biosignatures for the Detection of Life", "advisor": "Adami, Christoph Carl; Nealson, Kenneth H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-071800", "creators": [ { "name": { "family": "Dorn", "given": "Evan David" }, "id": "Dorn-Evan-David", "display_name": "Dorn, Evan David" } ], "advisors": [ { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "orcid": "0000-0002-2915-9504", "role": "advisor", "display_name": "Adami, Christoph Carl" }, { "name": { "family": "Nealson", "given": "Kenneth H." }, "id": "Nealson-K-H", "role": "co-advisor", "display_name": "Nealson, Kenneth H." } ], "committee": [ { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "orcid": "0000-0002-2915-9504", "role": "chair", "display_name": "Adami, Christoph Carl" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Kirschvink", "given": "Joseph L." }, "id": "Kirschvink-J-L", "orcid": "0000-0001-9486-6689", "role": "member", "display_name": "Kirschvink, Joseph L." }, { "name": { "family": "Nealson", "given": "Kenneth H." }, "id": "Nealson-K-H", "orcid": "0000-0001-5189-3732", "role": "member", "display_name": "Nealson, Kenneth H." } ], "option_major": [ "cns" ], "doi": "10.7907/08B9-8Q96", "abstract": "My goal is to identify processes of life that leave measurable effects on an organism's environment, but which are not tied to any particular biochemistry, in order to build a conceptual framework for the search for extraterrestrial life. To this end, I test a pair of phenomena that appear in both terrestrial (biochemical) life and in digital life. Because these two life forms are different and unrelated, any phenomenon measurable in both is suggested to be universal.
\r\n\r\nThe Monomer Abundance Distribution Biosignature (MADB) is any measurement of the relative concentrations of related chemical compounds that cannot be explained by abiotic processes. I observe that living systems synthesize specific chemical compounds at rates that maximize their fitness. As a result, life-bearing environmental samples exhibit compounds in abundance ratios that are clearly not the result of abiotic synthesis because those ratios belie the formation kinetics and thermodynamics that would constrain abiotic synthesis. Often, biotic samples contain high concentrations of specific large, complex molecules that are never seen in abiotic synthesis and cannot be explained unless highly specific catalysts (i.e., enzymes) are present, and energy is expended to drive thermodynamically unfavorable reactions. I catalog this effect as it appears in terrestrial biochemical systems, including amino acids and carboxylic acids, and demonstrate the universality of selection's action on the monomeric composition of life forms by studying analogous examples in digital life. I suggest how this phenomenon provides a route to the detection of even unusual or unforeseen biochemistries, and give examples of detection methods using pattern-recognition techniques that may allow us to empower an autonomous system with the general ability to detect life forms.
\r\n\r\nThe Layered Trophic Residue Biosignature (LTRB) is any observation of stratification in solute chemistry that indicates metabolic activity by a sequence of diverse communities. When multiple chemical resources are available, natural selection drives adaptive radiation and the formation of specialist phenotypes. Competition ensures that specialists consume resources in decreasing order of energetic potential when resources diffuse through a medium near a boundary. The result is strata of chemicals appearing in order of redox potential, which is best explained by the presence of life.
\r\n" }, { "name": "Endelman, Jeffrey B.", "degree": "PhD", "year": "2005", "title": "Design and Analysis of Combinatorial Protein Libraries Created by Site-Directed Recombination", "advisor": "Arnold, Frances Hamilton", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022005-192548", "creators": [ { "name": { "family": "Endelman", "given": "Jeffrey B." }, "id": "Endelman-Jeffrey-B", "orcid": "0000-0003-0957-4337", "display_name": "Endelman, Jeffrey B." } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" } ], "committee": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "chair", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Mayo", "given": "Stephen L." }, "id": "Mayo-S-L", "orcid": "0000-0002-9785-5018", "role": "member", "display_name": "Mayo, Stephen L." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "bioeng" ], "doi": "10.7907/GF35-Q269", "abstract": "For many protein design problems, limited understanding of the relationship between sequence and function necessitates searching through a library of proteins to find the properties of interest. To accelerate this process, molecular models and optimization algorithms can be combined to design diverse libraries enriched in folded proteins. I apply this strategy to site-directed recombination, in which an alignment of p homologs is partitioned into f blocks, and the resulting gene fragments are combinatorially assembled to create a library with p^f chimeric sequences. To design the fragments, I present a dynamic programming algorithm that minimizes the average energy of the library, subject to constraints on fragment length. This algorithm works for any pairwise residue potential, several of which are compared for their ability to predict which chimeras retain the parental function and/or fold. The alignments of folded and unfolded chimeras are used to generate sequence-function relationships via logistic regression, a technique for fitting models to binary data. Compared to methods developed for alignments of naturally occurring proteins, logistic regression more readily distinguishes true interactions from correlations between strongly stabilizing but non-interacting residues." }, { "name": "Faddy, James Malcolm", "degree": "PhD", "year": "2005", "title": "Flow Structure in a Model of Aircraft Trailing Vortices", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-163801", "creators": [ { "name": { "family": "Faddy", "given": "James Malcolm" }, "id": "Faddy-James-Malcolm", "display_name": "Faddy, James Malcolm" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RC42-JY40", "abstract": "We consider a model of incompressible trailing vortices consisting of an array of counter-rotating structures in a doubly periodic domain, infinite in the vertical direction. The two-dimensional vortex array of Mallier and Maslowe is combined with an axial velocity profile chosen proportional to the initial axial vorticity to provide an initial condition for the vortex wake. This base flow is a weak solution of the three component steady Euler equations in two dimensions thus allowing its linear stability properties to be investigated. These are used to interpret several stages in the development of vortex structure observed in fully three-dimensional DNS at Reynolds numbers Gamma/(2 pi nu)=O(1000). For sufficiently high axial velocity, itseffect can be seen, in that each vortex in the linear array first develops helical structures before undergoing a period of relaminarization. At later times the more slowly growing co-operative elliptical instabilities become apparent; however, the helical structure persists and the observed vortical structures remain coherent for longer periods than in the absence of axial velocity. Using the stretched vortex subgrid model, large-eddy simulation runs are performed at higher Reynolds numbers and a mixing transition identified at about Re = 1-2 x 10\u2074. Similar phenomena are observed in these simulations as are seen in the DNS. Next the spatial nature of the true aircraft wake is compared to the temporal approximation commonly employed to simplify the computational complexity of the problem. A model is formulated to acount for the average axial pressure gradients that develops in the spatial wake but is absent from the temporal simulation. The model enables jet- and wake-like axial flows to be distinguished and the subtle differences in the ensuing turbulent states investigated. Finally, the model is used to investigate co-rotating vortex merger, the new thrust term providing a mechanism to enhance the axial flow further destabilizing the base flow." }, { "name": "Friedel, Ilja Heinrich", "degree": "PhD", "year": "2005", "title": "Approximation of Surfaces by Normal Meshes", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-164959", "creators": [ { "name": { "family": "Friedel", "given": "Ilja Heinrich" }, "id": "Friedel-Ilja-Heinrich", "display_name": "Friedel, Ilja Heinrich" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" } ], "option_major": [ "compsci" ], "doi": "10.7907/FVSZ-GF75", "abstract": "This thesis introduces a novel geometry processing pipeline based on unconstrained spherical parameterization and normal remeshing. We claim three main contributions:\r\n\r\nFirst we show how to increase the stability of Normal Mesh construction, while speeding it up by decomposing the process into two stages: parameterization and remeshing. We show that the remeshing step can be seen as resampling under a small perturbation of the given parameterization. Based on this observation we describe a novel algorithm for efficient and stable (interpolatory) normal mesh construction via parameterization perturbation.\r\n\r\nOur second contribution is the introduction of Variational Normal Meshes. We describe a novel algorithm for encoding these meshes, and use our implementation to argue that variational normal meshes have a higher approximation quality than interpolating normal meshes, as expected. In particular we demonstrate that interpolating normal meshes have about 60 percent higher Hausdorff approximation error for the same number of vertices than our novel variational normal meshes. We also show that variational normal meshes have less aliasing artifacts than interpolatory normal meshes.\r\n\r\nThe third contribution is on creating parameterizations for unstructured genus zero meshes. Previous approaches could only avoid collapses by introducing artificial constraints or continuous reprojections, which are avoided by our method. The key idea is to define upper bound energies that are still good approximations. We achieve this by dividing classical planar triangle energies by the minimum distance to the sphere center. We prove that these simple modifaction provides the desired upper bounds and are good approximations in the finite element sense.\r\n\r\nWe have implemented all algorithms and provide example results and statistical data supporting our theoretical observations." }, { "name": "Fung, Jimmy", "degree": "PhD", "year": "2005", "title": "Coarse Analysis of Multiscale Systems: Diffuser Flows, Charged Particle Motion, and Connections to Averaging Theory", "advisor": "Murray, Richard M.; Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-165938", "creators": [ { "name": { "family": "Fung", "given": "Jimmy" }, "id": "Fung-Jimmy", "orcid": "0000-0002-6612-2209", "display_name": "Fung, Jimmy" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wn0z-gn57", "abstract": "We describe a technique for the efficient computation of the dominant-scale dynamics of a fluid system when only a high-fidelity simulation is available. Such a technique is desirable when governing equations for the dominant scales are unavailable, when model reduction is impractical, or when the original high-fidelity computation is expensive. We adopt the coarse analysis framework proposed by I. G. Kevrekidis (Comm. Math. Sci. 2003), where a computational superstructure is designed to use short-time, high-fidelity simulations to extract the dominant features for a multiscale system. We apply this technique to compute the dominant features of the compressible flow through a planar diffuser. We apply the proper orthogonal decomposition to classify the dominant and subdominant scales of diffuser flows. We derive a suitable coarse projective Adams-Bashforth time integration routine and apply it to compute averaged diffuser flows. The results include accurate tracking of the dominant-scale dynamics for a range of parameter values for the computational superstructure. These results demonstrate that coarse analysis methods are useful for solving fluid flow problems of a multiscale nature.
\r\n\r\nIn order to elucidate the behavior of coarse analysis techniques, we make comparisons to averaging theory. To this end, we derive governing equations for the average motion of charged particles in a magnetic field in a number of different settings. First, we apply a novel procedure, inspired by WKB theory and Whitham averaging, to average the variational principle. The resulting equations are equivalent to the guiding center equations for charged particle motion; this marks an instance where averaging and variational principles commute. Secondly, we apply Lagrangian averaging techniques, previously applied in fluid mechanics, to derive averaged equations. Making comparisons to the WKB/Whitham-style derivation allows for the necessary closure of the Lagrangian averaging formulation. We also discuss the Hamiltonian setting and show that averaged Hamiltonian systems may be derivable using concepts from coarse analysis. Finally, we apply a prototypical coarse analysis procedure to the system of charged particles and generate trajectories that resemble guiding center trajectories. We make connections to perturbation theory to derive guidelines for the design of coarse analysis techniques and comment on the prototypical coarse analysis application.
" }, { "name": "Gavriliu, Marcel", "degree": "PhD", "year": "2005", "title": "Towards More Efficient Interval Analysis: Corner Forms and a Remainder Interval Newton Method", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022005-174844", "creators": [ { "name": { "family": "Gavriliu", "given": "Marcel" }, "id": "Gavriliu-Marcel", "display_name": "Gavriliu, Marcel" } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" } ], "option_major": [ "compsci" ], "doi": "10.7907/C196-9R88", "abstract": "In this thesis we present two new advancements in verified scientific computing using interval analysis:
\r\n\r\n1. The Corner Taylor Form (CTF) interval extension. The CTF is the first interval extension for multivariate polynomials that guarantees smaller excess width than the natural extension on any input interval, large or small. To help with the proofs we introduce the concept of Posynomial Decomposition (PD). Using PD we develop simple and elegant proofs showing the CTF is isotonic and has quadratic or better (local) inclusion convergence order. We provide methods for computing the exact local order of convergence as well as the magnitude of excess width reduction the CTF produces over the natural extension.
\r\n\r\n2. The Remainder Interval Newton (RIN) method. RIN methods use first order Taylor Models (instead of the mean value theorem) to linearize (systems of) equations. We show that this linearization has many advantages which make RIN methods significantly more efficient than conventional Interval Newton (IN). In particular, for single multivariate equations, we show that RIN requires only order of the square root as many solution regions as IN does for the same problem. Therefore, RIN realizes same order savings in both time and memory for a significant overall improvement.
\r\n\r\nWe also present a novel application of the two contributions to computer graphics: Beam Tracing Implicit Surfaces.
" }, { "name": "Green, William M. J.", "degree": "PhD", "year": "2005", "title": "InGaAsP-InP Semiconductor Microcavity Geometries for Annular Bragg Reflection, Optical Switching, and Sensing", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292005-111904", "creators": [ { "name": { "family": "Green", "given": "William M. J." }, "id": "Green-William-M-J", "display_name": "Green, William M. J." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GGH2-AQ53", "abstract": "One of the key mandates of modern optoelectronic research is the development of compact photonic integrated circuits, capable of performing many diverse functions for the generation, manipulation, and detection of light, all on a single chip. A key practical requirement for such circuits is the development of optical devices for the localization and processing of light within extremely small dimensions. In recent years, planar microring and microdisk resonators, in which light is confined by total internal reflection, have emerged as versatile photonic elements for filling this role. The high quality factors and long photon storage times associated with the whispering-gallery modes supported by these microcavities result in several technologically useful characteristics, including narrow-band filter response, and large resonant enhancement of the circulating electric field. These properties have been exploited in numerous passive and active device applications, including optical add/drop multiplexers, all-optical switches, and tunable lasers.
\r\n\r\nThis thesis describes the study of several unique ring-based optical microcavity geometries based upon the indium gallium arsenide phosphide/indium phosphide alloy semiconductor material system, undertaken in an effort to explore new optoelectronic architectures for confining and manipulating light.
\r\n\r\nThe first portion of this work involves the analysis and demonstration of a new microcavity geometry, in which cylindrical Bragg reflection is used for radial optical confinement, as an alternative to total internal reflection. In this class of structures, collectively known as annular Bragg resonators, light can be guided within a ring or pillar defect layer surrounded by cylindrical Bragg mirrors. Several microcavities based upon this configuration are designed and fabricated using a thin InGaAsP quantum well membrane. Using pulsed optical excitation, the characteristics of these structures as low threshold vertically emitting lasers is explored.
\r\n\r\nSecond, a total internal reflection-based coupled waveguide-resonator geometry, having applications to low power optical switching and modulation, is analyzed. This geometry makes use of the hybrid integration of a Mach-Zehnder interferometer with a racetrack resonator. Switching takes place using the Mach-Zehnder to control the coupling parameters in the vicinity of the critical coupling condition. Characterization of the static and dynamic output response of a thermooptically actuated InGaAsP-InP hybrid switch device demonstrates good ON-OFF switching contrast, microsecond response time, and reduced switching power in comparison with a conventional Mach-Zehnder configuration.
\r\n\r\nFinally, this work concludes by examining both the annular Bragg resonator and hybrid switch geometries in application to chemical and biological sensing. Both microcavity devices are shown to possess unique characteristics making them ideal for sensitive monitoring of small changes in the refractive index of a chemical or biological analyte.
" }, { "name": "Gregory, Irene Michelle", "degree": "PhD", "year": "2005", "title": "Design and Stability Analysis of an Integrated Controller for Highly Flexible Advanced Aircraft Utilizing the Novel Nonlinear Dynamic Inversion", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-07232004-075729", "creators": [ { "name": { "family": "Gregory", "given": "Irene Michelle" }, "id": "Gregory-Irene-Michelle", "display_name": "Gregory, Irene Michelle" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Davidson", "given": "John B." }, "id": "Davidson-J-B", "role": "member", "display_name": "Davidson, John B." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/Y6B1-ZZ55", "abstract": "High performance aircraft of the future will be designed to be lighter, more maneuverable, and operate over an ever expanding flight envelope. This set of conditions will necessarily mean highly flexible vehicles operating in nonlinear regimes. A methodology proposed to better optimize their responses to both pilot input and external disturbances, as well as to decrease the cost of vehicle design is the novel dynamic inversion. The attractiveness of this methodology lies in the fact that the inherent nonlinearities of the problem and the coupled nature of flexible dynamics are explicitly considered.
\r\n\r\nThe contribution of this work to the state of the art is predicated on the development and application of the novel dynamic inversion methodology to handle highly flexible aircraft in an integrated flight/structural mode control manner. The unprecedented small separation between rigid body and flexible dynamics as well as the reciprocal interaction between them due to flight control action are the key elements of the aircraft model. The novel approach to the nonlinear dynamic inversion allows the methodology to more intelligently handle flexible dynamics in the context of the dual objectives of integrated flight/SMC control by altering flexible mode damping without cancellation; thus, improving disturbance response and avoiding the potentially destabilizing effect of pole cancellation close to the j-omega-axis in case of modeling uncertainty. The necessary level of model complexity for design has been established with particular attention given to understanding physics. The effect of uncertainty in the structural mode dynamics has been addressed.
\r\n\r\nFurther contribution of this work addresses the issue of stability of the dynamic systems driven by nonlinear controllers. One result shows how assessing stability of an n-dimensional system can be reduced to checking stability of a two-dimensional one using algebraic expressions that are based on the vehicle characteristics such as aerodynamic coefficients. This reduces a complicated dynamical problem to something purely algebraic and manageably complex. Another approach is based on algorithmically finding a local Lyapunov function using sum of squares. The presented results are the first to address the question of stability for the nonlinear dynamic inversion in the presence of flexible dynamics.
\r\n" }, { "name": "Gunn, Lawrence Cary, III", "degree": "PhD", "year": "2005", "title": "Integration of Complex Optical Functionality in a Production CMOS Process", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012005-091623", "creators": [ { "name": { "family": "Gunn", "given": "Lawrence Cary, III" }, "id": "Gunn-Lawrence-Cary-III", "display_name": "Gunn, Lawrence Cary, III" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yablonovitch", "given": "Eli" }, "id": "Yablonovitch-E", "role": "member", "display_name": "Yablonovitch, Eli" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/HKW9-4K53", "abstract": "Optical functionality has been developed within the confines of an existing CMOS process. As of this writing, 10Gigabit modulators, electrically tunable optical filters, waveguides, and grating coupler technology have been successfully implemented alongside the existing transistors in the Freescale Hip7SOI process. This technology will be used to manufacture high bandwidth optical interconnections directly on silicon chips, allowing a new type of network and computing infrastructure to be developed.
\r\n\r\nThis work is covered in two distinct phases. First, the exploratory work done to gain experience with high index contrast silicon waveguides primarily served to uncover challenges related with simulation of these devices, and with the practical limitations of efficiently coupling the resulting waveguide devices with the outside world.
\r\n\r\nThe second phase began as the grating coupler emerged to address the coupling challenge. It became feasible to conceive of a commercially viable technology based on silicon photonics. The coupler has been evolved to a high level, currently achieving coupling loss of less than 1dB. Once the light is on chip, filtering and modulation technology are implemented. The reverse-biased plasma dispersion modulator has a 3dB roll-off of 10GHz, and an insertion loss less than 5dB. Optical filters based on ring resonators, arrayed waveguide gratings, and interleavers have all been implemented, often with world record performance, and many of the devices have been made electronically tunable to compensate for manufacturing variations and environmental excursions.
\r\n\r\nFinally, circuitry has been designed and constructed on the same die with the optical functionality, fully demonstrating the ability to achieve monolithic integration of these devices.
" }, { "name": "Hickerson, Anna Iwaniec", "degree": "PhD", "year": "2005", "title": "An Experimental Analysis of the Characteristic Behaviors of an Impedance Pump", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232005-141405", "creators": [ { "name": { "family": "Hickerson", "given": "Anna Iwaniec" }, "id": "Hickerson-Anna-Iwaniec", "orcid": "0000-0001-5223-6531", "display_name": "Hickerson, Anna Iwaniec" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "bioeng" ], "doi": "10.7907/SQQK-FD11", "abstract": "When a fluid-filled pliant tube is connected to tubing of a different impedance, a net flow in either direction can be induced by periodically compressing the pliant section asymmetrically from the ends. An experimental analysis of the characteristic behaviors of such a pump has been done demonstrating interesting results not predicted by prior analytical and computational results. Measurements show a complex non-linear behavior in response to the compression frequency, including distinct resonance peaks and reversals in flow direction. Ultrasound imaging provided a unique view of the tube wall and flow within, allowing us to visualize the wave propagation and reflection. Measurements include transient responses, resonant responses, and bulk flow behaviors for a variety of configurations. Net flow rates can exceed the volumetric displacement done by active compression demonstrating that, as a first approximation, this pump can have a higher efficiency than peristaltic pumping. Elasticity has been shown not to be a necessary factor in stimulating net forward flow.
\r\n\r\nResults from this study have helped show that a zebrafish (a model for human cardiac development) may utilize impedance pumping to drive circulation in early embryonic stages prior to valve formation as opposed to peristaltic pumping as was once thought. Additional research is being conducted to develop a micro-scaled version with applications in medicine, heat transfer, lab-on-chip technology, and micro-mixing.
" }, { "name": "Hostler, Stephen Richard", "degree": "PhD", "year": "2005", "title": "Wave Propagation in Granular Materials", "advisor": "Brennen, Christopher E.; Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072005-120514", "creators": [ { "name": { "family": "Hostler", "given": "Stephen Richard" }, "id": "Hostler-Stephen-Richard", "orcid": "0000-0002-3160-1269", "display_name": "Hostler, Stephen Richard" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/NQ1S-5E45", "abstract": "Wave propagation is a fundamental property of all physical systems. The wave speed is directly related to the compressibility of the system and determines the rate at which local disturbances are propagated into the bulk of the material. The wave propagation characteristics of conventional forms of matter are well understood and well documented. In contrast, waves in granular materials are more complex due to the heterogeneous nature of these systems. The key element of the mechanics of a granular system is the force chain. It is along these preferentially stressed chains of particles that waves are transmitted. These nonlinear chains are heavily dependent on the geometry of the bed and are prone to rearrangement even by the slightest of forces.
\r\n\r\nResults from both experiments and simulations on wave propagation in granular materials are presented in the current study. The experiments measure the pressures at two points within the granular bed that result from the motion of a piston at one end of the bed. The simulations are a two-dimensional version of the experiments and use a discrete, soft-particle method to detect the wave at both the output of the simulated bed and at any point within it. In addition to examining wave propagation in a granular bed at rest, simulations and experiments are also performed for a granular bed undergoing agitation perpendicular to the direction of the wave input. Imposed agitation increases the granular temperature of the bed and allows for the exploration of the effect of granular state changes on the wave propagation characteristics. Such information may provide a means to diagnose the state of a flowing granular material.
\r\n\r\nMeasurements of the wave speed and attenuation in the bed reveal the unique properties of waves in granular systems that result from the nonlinearity of the bed and the heterogeneity of the force chains. Sinusoidal waves demonstrate the nondispersive nature of a granular bed and show the transient effects of force chain rearrangement. Pulsed waves display a semi-permanent shape qualitatively similar to predictions from nonlinear wave theory. In an agitated granular bed, measurements of the wave characteristics were found to be possible even in the presence of significant agitation. The prevailing confining pressure, which changes throughout the agitation cycle, was determined to be the system parameter that correlates best with changes to the wave speed.
" }, { "name": "Hsieh, Hung-Te", "degree": "PhD", "year": "2005", "title": "Operation of Holographic Elements with Broadband Light Sources", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-05052005-131822", "creators": [ { "name": { "family": "Hsieh", "given": "Hung-Te" }, "id": "Hsieh-Hung-Te", "display_name": "Hsieh, Hung-Te" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Hong", "given": "John Hyunchul" }, "id": "Hong-J-H", "role": "member", "display_name": "Hong, John Hyunchul" }, { "name": { "family": "Buse", "given": "Karsten" }, "id": "Buse-K", "role": "member", "display_name": "Buse, Karsten" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9R5R-JT19", "abstract": "This thesis presents the theoretical and experimental investigation of volume holography operated with broadband/polychromatic light sources, i.e., in both continuous-wave (linear) and femtosecond-pulse (nonlinear) regimes.
\r\n\r\nThe first chapter reviews the concept of volume holography and provides a tacit introduction to some basic properties of volume holograms and compares the operation of holograms in the spatial and temporal domains, preparing the readers for later chapters.
\r\n\r\nThe second chapter introduces a powerful theoretical tool for the analysis of volume holograms in the reflection geometry: the matrix formulation, laying the foundation for the application of holographic gratings utilized as WDM filters.
\r\n\r\nThe third chapter takes into consideration the effects of the practically inevitable finite beam-widths. By means of Fourier decomposition, the deviation of the filtering properties of volume holographic gratings from the ideal plane-wave case can be satisfactorily explained and predicted. Experiments and simulations are performed and compared to confirm the validity of the theory.
\r\n\r\nVolume holographic gratings in the reflection geometry serve as excellent WDM filters for telecommunication purposes thanks to their low cross-talk and readily engineered filtering properties. The theoretical design and experimental realization of athermal holographic filters are presented in the fourth chapter. By incorporating a passive, thermally actuated MEMS mirror, the temperature dependence of the Bragg wavelength of a holographic filter can be compensated.
\r\n\r\nThe analysis of holographic gratings in the 90 degree geometry requires a two dimensional theory. The relevant boundary conditions give rise to some peculiar behaviors in this configuration. Theory, simulations and some experimental results of the 90-degree holography are presented in chapter five.
\r\n\r\nThe sixth chapter delves into the subject of instantaneous Kerr index grating established by two intense, interfering femtosecond (pump) pulses at 388 nm owing to the omnipresent third-order nonlinearity. The coupled-mode equations describing the incident and diffracted (probe) pulses at 776 nm are written down; the solution is experimentally corroborated. It is further demonstrated that the temporal resolution in such a holographic pump-probe configuration does not degrade appreciably as the angular separation between pump pulses increases.
\r\n\r\nChapter seven investigates the nonlinear absorption processes in lithium niobate crystals with femtosecond pulses. The model of two-photon absorption well explains and anticipates the transmission coefficients of single pulses over a wide range of intensity. Collinear pump-probe transmission experiments are then carried out to look into the nonlinear absorption suffered by the probe pulse at 776 nm owing to the pump pulse at 388 nm; the dependence of the probe pulse transmission coefficient on the time delay between pump and probe pulses is characterized by a dip and a long-lasting plateau, which are attributed, respectively, to direct two-photon transitions involving pump and probe photons and the existence of free carriers.
\r\n\r\nBuilding on the experimental experience and theoretical understanding of the previous two chapters, the results of holographic pump-probe experiments in lithium niobate crystals are presented in the final chapter. The behavior is much more complicated because it encompasses all phenomena explored in the two preceding chapters, i.e., both the real and imaginary parts of the third-order susceptibility come into play in the instantaneous material response; furthermore, another mixed grating due to excited charge carriers exists long after the pump pulses pass through. Valuable information on the grating formation process is obtained thanks to the sub-picosecond temporal resolution of such configurations.
" }, { "name": "Humbert, James Sean", "degree": "PhD", "year": "2005", "title": "Bio-Inspired Visuomotor Convergence in Navigation and Flight Control Systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06072005-163739", "creators": [ { "name": { "family": "Humbert", "given": "James Sean" }, "id": "Humbert-James-Sean", "orcid": "0000-0002-0863-875X", "display_name": "Humbert, James Sean" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "MacMynowski", "given": "Douglas G." }, "id": "MacMynowski-D-G", "role": "member", "display_name": "MacMynowski, Douglas G." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/T5QZ-QS18", "abstract": "Insects exhibit incredibly robust closed loop flight dynamics in the face of uncertainties. A fundamental principle contributing to this unparalleled behavior is rapid processing and convergence of visual sensory information to flight motor commands via spatial wide-field integration, accomplished by retinal motion pattern sensitive interneurons (LPTCs) in the lobula plate portion of the visual ganglia. Within a control-theoretic framework, an inner product model for wide-field integration of retinal image flow is developed, representing the spatial decompositions performed by LPTCs in the insect visuomotor system. A rigorous characterization of the information available from this visuomotor convergence technique for motion within environments exhibiting non-homogeneous spatial distributions is performed, establishing the connection between retinal motion sensitivity shape and closed loop behavior. The proposed output feedback methodology is shown to be sufficient to give rise to experimentally observed insect navigational heuristics, including forward speed regulation, obstacle avoidance, hovering, and terrain following behaviors. Hence, extraction of global retinal motion cues through computationally efficient wide-field integration processing provides a novel and promising methodology for utilizing visual sensory information in autonomous robotic navigation and flight control applications.\r\n" }, { "name": "Jackson, Scott Irving", "degree": "PhD", "year": "2005", "title": "Gaseous Detonation Initiation Via Wave Implosion", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-151253", "creators": [ { "name": { "family": "Jackson", "given": "Scott Irving" }, "id": "Jackson-Scott-Irving", "orcid": "0000-0002-6814-3468", "display_name": "Jackson, Scott Irving" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "co-chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "co-chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MKP3-VC84", "abstract": "Efficient detonation initiation is a topic of intense interest to designers of pulse detonation engines. This experimental work is the first to detonate propane-air mixtures with an imploding detonation wave and to detonate a gas mixture with a non-reflected, imploding shock. In order to do this, a unique device has been developed that is capable of generating an imploding toroidal detonation wave inside of a tube from a single ignition point without any obstruction to the tube flow path. As part of this study, an initiator that creates a large-aspect-ratio planar detonation wave in gas-phase explosive from a single ignition point has also been developed.
\r\n\r\nThe effectiveness of our initiation devices has been evaluated. The minimum energy required by the imploding shock for initiation was determined to scale linearly with the induction zone length, indicating the presence of a planar initiation mode. The imploding toroidal detonation initiator was found to be more effective at detonation initiation than the imploding shock initiator, using a comparable energy input to that of current initiator tubes.
" }, { "name": "Jing, Yindi", "degree": "PhD", "year": "2005", "title": "Space-Time Code Design and Its Applications in Wireless Networks", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-09072004-204814", "creators": [ { "name": { "family": "Jing", "given": "Yindi" }, "id": "Jing-Yindi", "display_name": "Jing, Yindi" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "co-chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/QYN9-0Z55", "abstract": "This thesis has two main contributions: the designs of differential/non-differential unitary space-time codes for multiple-antenna systems and the analysis of the diversity gain when using space-time coding among nodes in wireless networks.
\r\n\r\nCapacity has long been a bottleneck in wireless communications. Recently, multiple-antenna techniques have been used in wireless communications to combat the fading effect, which improves both the channel capacity and performance greatly. A recently proposed method for communicating with multiple antennas over block-fading channels is unitary space-time modulation, which can achieve the channel capacity at high SNR. However, it is not clear how to generate well performing unitary space-time codes that lend themselves to efficient encoding and decoding. In this thesis, the design of unitary space-time codes using Cayley transform is proposed. The codes are designed based on an information-theoretic criterion and have a polynomial-time near-maximum-likelihood decoding algorithm. Simulations suggest that the resulting codes allow for effective high-rate data transmissions in multiple-antenna communication systems without knowing the channel. Another well-known transmission scheme for multiple-antenna systems with unknown channel information at both the transmitter and the receiver is differential unitary space-time modulation. It can be regarded as a generalization of DPSK and is suitable for continuous fading. In differential unitary space-time modulation, fully diverse constellations, i.e., sets of unitary matrices whose pairwise differences are non-singular, are wanted for their good pairwise error properties. In this thesis, Lie groups and their representations are used in solving the design problem. Fully diverse differential unitary space-time codes for systems with four and three transmit antennas are constructed based on the Lie groups Sp(2) and SU(3). The designed codes have high diversity products, lend themselves to a fast maximum-likelihood decoding algorithm, and simulation results show that they outperform other existing codes, especially at high SNR.
\r\n\r\nThen the idea of space-time coding devised for multiple-antenna systems is applied to communications over wireless networks. In wireless relay networks, the relay nodes encode the signals they receive from the transmit node into a distributed space-time code and transmit the encoded signals to the receive node. It is shown in this thesis that at very high SNR, the diversity gain achieved by this scheme is almost the same as that of a multiple-antenna system whose number of transmit antennas is the same as the number of relay nodes in the network, which means that the relay nodes work as if they can cooperate fully and have full knowledge of the message. However, at moderate SNR, the diversity gain of the wireless network is inferior to that of the multiple-antenna system. It is further shown that for a fixed total power consumed in the network, the optimal power allocation is that the transmitter uses half the power and the relays share the other half fairly. This result addresses the question of what performance a relay network can achieve. Both it and its extensions have many applications to wireless ad hoc and sensory network communications.
" }, { "name": "Kowalewsky, Olga", "degree": "PhD", "year": "2005", "title": "Theory of Complex Lattice Quasicontinuum and Its Application to Ferroelectrics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-12202004-182638", "creators": [ { "name": { "family": "Kowalewsky", "given": "Olga" }, "id": "Kowalewsky-Olga", "display_name": "Kowalewsky, Olga" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rb0c-9534", "abstract": "Complex lattice Quasicontinuum theory is developed and applied to the description of ferroelectric phenomena. Quasicontinuum theory is a multiscale theory that provides a unified description of materials by combining atomistic and continuum approaches. It provides a seamless transition between atomistics and continuum, but the description of the material is derived directly from the underlying atomic structure, using the computationally expensive atomistics only where needed, at the location of phenomena of atomistic origin.
\r\n\r\nComplex Lattice Quasicontinuum theory can be applied to complex lattice crystals consisting of many kinds of atoms. One highlight of it is treatment of each component lattice as separately and independently as possible. The component Quasicontinua are coupled through the microscopic forces within nodal clusters, making the complex atomistics of the heterogeneous lattice the basis of the description.
\r\n\r\nFerroelectrics are especially suited to the application of Quasicontinuum theory. The nature of defects in ferroelectric materials is atomistic, but their influence over the material is long ranged due to induced elastic fields. Many different ferroelectric phenomena involving the perovskite ferroelectrics Barium Titanate and Lead Titanate are investigated and simulated. For Barium Titanate: the 180 degree domain wall structure and quasistatic crack under load. For Lead Titanate: the 180 degree domain wall structure and a domain wall step.
\r\n\r\nThe results for the domain walls show that the domain wall thickness is atomistically small, of the order of few lattice constants, which is in agreement with recent ab initio molecular dynamics simulations, but we also observe long range effects resulting from the presence of the wall. During crack loading in the sample of Barium Titanate we observe polarization changes around the crack tip which are consistent with experimental observations of an increase of fracture toughness. The quasicontinuum study of a domain wall step gives an atomistical view into the equilibrium structure of the step.
\r\n\r\nQuasicontinuum is able to model these phenomena with atomistic precision around the defects and non-homogeneities, and also capture the influence of long-ranging effects in the samples. These studies could also give valuable modeling input for larger scale continuum approaches.
" }, { "name": "Lee, Seung-Yub", "degree": "PhD", "year": "2005", "title": "Deformation Mechanisms of Bulk Metallic Glass Matrix Composites", "advisor": "Ustundag, Ersan; Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-131120", "creators": [ { "name": { "family": "Lee", "given": "Seung-Yub" }, "id": "Lee-Seung-Yub", "display_name": "Lee, Seung-Yub" } ], "advisors": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "advisor", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "co-advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Conner", "given": "Robert Dale" }, "id": "Conner-R-D", "role": "member", "display_name": "Conner, Robert Dale" }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "matsci" ], "doi": "10.7907/X74S-3H47", "abstract": "Bulk metallic glasses (BMGs) possess a unique set of mechanical properties that make them attractive structural materials: yield strength > 2 GPa, fracture toughness ~20 MPa.m1/2 and elastic strain limit ~2%. BMGs can also be cast into intricate shapes which retain their dimensional integrity and require no further machining. Unfortunately, monolithic BMGs fail catastrophically under unconstrained loading by forming shear bands. To overcome this problem, BMG matrix composites with fiber and dendritic reinforcements were proposed. The former type includes metallic fibers of Ta, Mo and stainless steel. The latter composites develop precipitates during casting and are thus called in-situ composites. Here, the reinforcements form an interpenetrating dendritic structure and enhance the ductility of the composite.
\r\n\r\nThis study investigated the deformation behavior of these two types of BMG composites. Loading measurements were performed during neutron or high-energy X-ray diffraction to determine lattice strains in the crystalline reinforcements. The diffraction data were then combined with finite element and self-consistent modeling to deduce the behavior of the amorphous matrix, as well as to understand the effective deformation mechanisms in the composite.
\r\n\r\nThe deformation of the wire composites was studied using an integrated neutron diffraction and finite element (FE) approach. The FE model yielded a reasonable version of in-situ stress-strain plots for both reinforcements and the matrix. It was found that the reinforcements yielded first and started transferring load to the matrix which remained elastic throughout the whole loading experiment. The reinforcements were seen to possess yield strengths lower than their monolithic forms, likely due to annealing during processing. After optimizing material properties to fit experimental data, the FE model developed was reasonably successful in describing both the macroscopic composite deformation and the lattice strain evolution in the reinforcements.
\r\n\r\nIn the case of the in-situ composites, a detailed neutron and high energy X-ray diffraction study was conducted combined with a self-consistent deformation model. The compressive behavior of the composite and the second phase (in its monolithic form) were investigated. It was shown that the ductile second phase yields first upon loading the composite followed by multiple shear band formation in the BMG matrix, a process which enhances the ductility of the composite. It was also discovered that the mechanical properties of the reinforcements, and indirectly the composite, are highly variable and quite sensitive to processing conditions. This resulted from the unstable nature of the BCC beta phase reinforcements which tend to transform into an ordered phase leading to significant stiffening, but also loss of ductility. An additional heat treatment study confirmed this phase evolution.
\r\n\r\nThe overall conclusion of this study is that BMG composites with high ductility require reinforcements that yield first and induce multiple shear bands in the amorphous matrix, which in turn enhances the latter\u2019s ductility. To also retain a high yield point, the reinforcements need to be stiff. These two properties can best be optimized in beta phase composites via a judicious combination of microstructure control and heat treatment.
" }, { "name": "Li, Fei-Fei", "degree": "PhD", "year": "2005", "title": "Visual Recognition: Computational Models and Human Psychophysics", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022005-150332", "creators": [ { "name": { "family": "Li", "given": "Fei-Fei" }, "id": "Li-Fei-Fei", "orcid": "0000-0002-7481-0810", "display_name": "Li, Fei-Fei" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Biederman", "given": "Irving" }, "id": "Biederman-I", "role": "member", "display_name": "Biederman, Irving" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/G5NP-KH67", "abstract": "Object and scene recognition is one of the most essential functionalities of human vision. It is also of fundamental importance for machines to be able to learn and recognize meaningful objects and scenes. In this thesis, we explore the following four aspects of object and scene recognition.
\r\n\r\nIt is well known that humans can be \"blind\" even to major aspects of natural scenes when we attend elsewhere. The only tasks that do not need attention appear to be carried out in the early stages of the visual system. Contrary to this common belief, we show that subjects can rapidly detect animals or vehicles in briefly presented novel natural scenes while simultaneously performing another attentionally demanding task. By comparison, they are unable to discriminate large T\u2019s from L\u2019s, or bisected two-color disks from their mirror images under the same conditions. We explore this phenonmenon further by removing color from the natural scenes, or increasing the number of images peripherally. We find evidence that suggests that familiarity and meaningfulness might be among the factors that determine attentional requirements for both natural and synthetic stimuli.
\r\n\r\nSo what exactly do we see when we glance at a natural scene? And does what we see change as the glance becomes longer? We asked naive subjects to report what they saw in nearly a hundred briefly presented photographs. After each presentation subjects reported what they had just seen as completely as possible. Afterward, another group of sophisticated individuals who were not aware of the goals of the experiment were instructed to score each of the descriptions produced by the subjects in the first stage. Individual scores were assigned to more than a hundred different attributes. Given the evaluation of the responses, we show that within a single glance, much object and scene level information is perceived by human subjects. But the richness of our perception seems asymmetrical. Subjects tend to have a bias to natural scenes being perceived as outdoor rather than indoor.
\r\n\r\nIn computer vision, it is commonly known that learning visual models of object categories notoriously requires thousands of training examples. We show that it is possible to learn much information about a category from just one image, or a handful of images. The key insight is that, rather than learning from scratch, one can take advantage of knowledge coming from previously learnt categories, no matter how different these categories might be. We explore a Bayesian implementation of this idea. Object categories are represented by probabilistic models. Prior knowledge is represented as a probability density function on the parameters of these models. The posterior model for an object category is obtained by updating the prior in the light of one or more observations. We test a simple implementation of our algorithm on a database of 101 diverse object categories. We compare category models learnt by a simple implementation of our Bayesian approach to models learnt from maximum likelihood (ML) and maximum a posteriori (MAP) methods. We find that in a database of more than 100 categories the Bayesian approach produces informative models when the number of training examples is too small for other methods to operate successfully.
\r\n\r\nWe also propose a novel approach to learn and recognize natural scene categories. Unlike previous work, it does not require experts to annotate the training set. We represent the image of a scene by a collection of local regions, denoted as codewords obtained by unsupervised learning. Each region is represented as part of a \"theme.\" In previous work, such themes were learnt from hand-annotations of experts, while our method learns the theme distributions as well as the codewords distribution over the themes without supervision. We report satisfactory categorization performances on a large set of 13 categories of complex scenes.
" }, { "name": "Litke, Nathan Jacob", "degree": "PhD", "year": "2005", "title": "Variational Methods in Surface Parameterization", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312005-224704", "creators": [ { "name": { "family": "Litke", "given": "Nathan Jacob" }, "id": "Litke-Nathan-Jacob", "display_name": "Litke, Nathan Jacob" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Rumpf", "given": "Martin" }, "id": "Rumpf-M", "role": "member", "display_name": "Rumpf, Martin" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" } ], "option_major": [ "compsci" ], "doi": "10.7907/EW4Q-0727", "abstract": "A surface parameterization is a function that maps coordinates in a 2-dimensional parameter space to points on a surface. This thesis investigates two kinds of parameterizations for surfaces that are disc-like in shape. The first is a map from a region of the plane to the surface. The second is a mapping from one surface to another, which defines a correspondence between them. The main challenge in both cases is the construction of a smooth map with low distortion. In this thesis we present a variational approach to surface parameterization that addresses these challenges.
\r\n\r\nThe first contribution of this thesis is the development of a variational framework for parameterizations. This framework encompasses the mapping of a region of the plane to a surface that is isomorphic to a disc, and the mapping between such surfaces. It is based on the rich mathematical theory built up over decades in the study of rational mechanics. Because of its roots in mechanics, our parameterizations are guaranteed to be smooth and locally bijective, and optimal parameterizations which minimize a variational energy are known to exist. A proof of existence is given for the case of optimal parameterizations in the plane.
\r\n\r\nOur second contribution is a set of algorithms to construct parameterizations for surface triangulations. We describe in detail free-boundary methods that use standard numerical optimization algorithms for the computation of optimal parameterizations. A flexible set of parameters is offered to the user to formulate preferences for the trade-off between angle, area and length distortion in parameterizations in the plane. In the specification of a correspondence between surfaces, we provide user control through feature lines which are mapped as sets onto corresponding feature lines. Additionally we allow for a partial correspondence of the surfaces which is particularly important for correlating surfaces with boundaries.
\r\n\r\nOur third contribution is an analysis of the performance of the algorithms based on our implementations. Our testing focuses on parameterizations of physically-acquired triangle mesh data. The efficiency of our methods is measured by analyzing the rate of convergence of the energy minimization, and execution times are shown to be quite reasonable. Robustness is established in the presence of large deformations in the parameterizations and the stability of our parameterizations is demonstrated under different discretizations of the surfaces.
\r\n\r\nOur fourth contribution is a set of concrete, compelling applications of surface parameterization. Non-trivial examples which draw from texture mapping, morphing and facial animation provide further evidence and insight into the versatility of our parameterization framework.
" }, { "name": "Lu, Miao-Ling", "degree": "PhD", "year": "2005", "title": "Large-Eddy Simulations of Marine Cumulus and Stratocumulus and Study of Humidity Halos and Aerosol Indirect Radiative Effects", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172005-152448", "creators": [ { "name": { "family": "Lu", "given": "Miao-Ling" }, "id": "Lu-Miao-Ling", "display_name": "Lu, Miao-Ling" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/H3BE-W731", "abstract": "The first part of the thesis focuses on understanding the characteristics of the cloud humidity halos, the significant enhancements in humidity around cumulus clouds, and their radiative impacts. The simulated cloud and halo properties were compared with the measurement data from the aircraft campaign \u2013 \"Cloud Halo\" conducted in Hawaii, 2001. The cloud halo spatial distribution, the relationship with the vertical wind shear, and the temporal variation with cloud lifetime are explored by the 3D numerical simulations. Results suggest that halos are formed as a result of evaporation of cloudy air or detrainment of high humidity by the turbulent mixing in the cloud lateral boundary regions, or simply due to cloud dissipation. Humidity halos absorb the incoming sunlight, warm the atmosphere, and cool the surface. The 3D radiative transfer model results show that the SW column absorption (surface - 3.4 km) enhanced by the halo is 1.32 W m-2 averaged over the cloud mature and dissipating stages, a 1.3% change in the absence of the halo, for the cloud of the Cloud Halo experiment.
\r\n\r\nThe second part of the thesis is to understand the first and second aerosol indirect effects by conducting 98 3D LES simulations of the marine stratocumulus clouds - under various conditions of nighttime and daytime, SST (sea surface temperature), aerosol number concentration, and large-scale subsidence rate. Based on the statistical analysis, the cloud optical depth is found to be positively correlated with the cloud liquid water path, which is mainly regulated by large-scale subsidence and SST. The regression analysis shows that the second aerosol indirect effect is more pronounced in clean than polluted clouds and that it increases (reduces) the cloud optical depth for the same relative change in aerosol number concentration than considering the Twomey (first indirect) effect alone. Introducing a small amount of giant sea salt aerosols into the simulation lowers the number of cloud droplets activated and initiates precipitation for non-drizzling clouds. It also results in a reduction of cloud optical depth by 3% - 77% for heavily drizzling cases.
" }, { "name": "Mazor, Ofer", "degree": "PhD", "year": "2005", "title": "Neural Dynamics and Population Coding in the Insect Brain", "advisor": "Laurent, Gilles J.; Meister, Markus", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062005-113150", "creators": [ { "name": { "family": "Mazor", "given": "Ofer" }, "id": "Mazor-Ofer", "display_name": "Mazor, Ofer" } ], "advisors": [ { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "role": "advisor", "display_name": "Laurent, Gilles J." }, { "name": { "family": "Meister", "given": "Markus" }, "id": "Meister-M", "role": "co-advisor", "display_name": "Meister, Markus" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Siapas", "given": "Athanassios G." }, "id": "Siapas-A-G", "role": "member", "display_name": "Siapas, Athanassios G." }, { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "role": "member", "display_name": "Laurent, Gilles J." }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "cns" ], "doi": "10.7907/PANC-K035", "abstract": "Sensory information is represented in the brain through the activity of populations of neurons. How this information is encoded and how it is processed and read out are crucial questions in neuroscience. The work presented here examines these issues using an insect brain model system. Specifically, this work addresses how odor information is represented across a population of neurons in this relatively simple nervous system. It asks how the dynamics of a population of neurons contribute to the encoding of information.
\r\n\r\nTo address these questions, simultaneous multi-unit extracellular recordings were made in vivo in the locust brain. The first part of the dissertation describes several advances in spike-sorting methods that were necessary for analyzing such recordings. These advances include quantitative tests of sorting quality, and they allow for automated spike-sorting. Using these techniques, data sampled from tens of neurons over hours of recording can be analyzed with relative ease.
\r\n\r\nThe remainder of the dissertation examines the encoding of olfactory information by a population of neurons called projection neurons (PNs), located in the first olfactory relay of the brain. Odor information is shown to be represented by a subpopulation of responsive PNs. The composition of this population changes over time in an odor-specific manner, thus forming a distributed, dynamical representation. The statistics of this response and its dynamics are quantified.
\r\n\r\nFurthermore, the mechanism by which odor information is extracted from the PN population response is examined. A second set of recordings were made from Kenyon cells (KCs), which receive direct excitatory synaptic input from PNs. The dynamic response of the PN population appears to be decoded by KCs through a mechanism based on several underlying components, including oscillatory dynamics, feed-forward inhibition, and intrinsic properties of the KCs. This decoding process is shown to drastically change the odor representations, from dense to sparse.
\r\n\r\nTaken together, the results presented in this dissertation establish that the complex spatial and temporal dynamics of the PN population do encode odor information, and that this information is decoded by other neurons (KCs) in a very precise way, resulting in a drastic transformation of representation. The basic mechanisms underlying this transformation exist in many brain areas and across phyla, suggesting that many of the principles described here could be of general relevance.
" }, { "name": "Meeker, Daniella Elena Patricia", "degree": "PhD", "year": "2005", "title": "Cognitive Neural Prosthetics: Brain Machine Interfaces Based in Parietal Cortex", "advisor": "Andersen, Richard A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032005-170438", "creators": [ { "name": { "family": "Meeker", "given": "Daniella Elena Patricia" }, "id": "Meeker-Daniella-Elena-Patricia", "orcid": "0000-0002-1034-7628", "display_name": "Meeker, Daniella Elena Patricia" } ], "advisors": [ { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "advisor", "display_name": "Andersen, Richard A." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/V2BZ-EG30", "abstract": "Systems neuroscience has recently emerged as an applied field in the form of neural prosthetic development. This integration of empirical systems neuroscience with engineering in order to develop functional interfaces between external devices and the brain has not only been beneficial in its applied goal, but has resulted in observations of scientific interest. The body of work presented here demonstrates the efficacy of two varieties of brain machine interfaces (BMIs) based in Parietal Cortex. The first using information about intended reaches present in action potentials, the second using local field potentials (LFPs). Both studies were predicated and succeeded with offline analyses demonstrating feasibility and novel insight to the function and neural coding properties of Parietal Cortex. We found that using BMIs resulted in adaptive change which tended to improve performance. LFPs, though less successful than spikes for BMI control under these experimental conditions, appear to have a multiplexing of different types of information that might aid in BMIs as well as providing a different way of looking at the neural processing. A preliminary exploration of relative timing of spikes and LFPs might result in some of the adaptive properties observed during BMI use via spike timing dependent plasticity concludes the research presented here." }, { "name": "Mukherjee, Sundeep", "degree": "PhD", "year": "2005", "title": "Study of Crystallization Behavior, Kinetics and Thermodynamics of Bulk Metallic Glasses Using Noncontact Electrostatic Levitation Technique", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282005-111916", "creators": [ { "name": { "family": "Mukherjee", "given": "Sundeep" }, "id": "Mukherjee-Sundeep", "orcid": "0000-0002-1954-0045", "display_name": "Mukherjee, Sundeep" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Rhim", "given": "Won-Kyu" }, "id": "Rhim-Won-Kyu", "role": "member", "display_name": "Rhim, Won-Kyu" } ], "option_major": [ "matsci" ], "doi": "10.7907/33FY-8482", "abstract": "The exceptional stability against crystallization of recently developed bulk metallic glasses, together with the non-contact measurement techniques to investigate their thermophysical properties, have opened the doors for detailed studies of these systems in the deep undercooled liquid state. The primary objective of this thesis is identification of reliable predictive indicators of glass-forming ability based on the measured thermophysical properties and intrinsic crystallization behavior of bulk metallic glasses. A number of bulk metallic glass-forming alloys having widely different glass-forming abilities are chosen for this investigation. All of the measurements are carried out using the noncontact high vacuum electrostatic levitation technique to avoid any heterogeneous nucleation effects from container walls or environment.
\r\n\r\nThe measured kinetic properties, viscosity, and free volume are found to have the most pronounced influence on glass-forming ability, while the thermodynamics show weak correlation with the trends in glass-formation. The glass-forming melts show orders of magnitude higher viscosity compared to pure metals. Among the glass-forming alloys, better glass formers have higher melting temperature viscosity, higher fragility, and show a smaller change in volume upon crystallization compared to poor glass formers. The melting temperature viscosity is correlated with volume change upon crystallization in accordance with Cohen-Grest free-volume theory for a wide variety of alloys.
\r\n\r\nTo quantify the glass-forming ability, Time-Temperature-Transformation (TTT) curves of a number of glass-forming melts are measured over a wide temperature range between their glass-transition and melting temperatures. A pronounced effect of overheating is observed on the undercooling levels and crystallization time scales. This is attributed to oxide particles acting as heterogeneous nucleation sites unless dissolved by overheating above their melting points. The TTT curves, obtained after eliminating the heterogeneous influences, are found to scale with their respective glass transition temperatures. The TTT curves are analyzed within the framework of nucleation theory to obtain a quantitative correlation between crystal-melt interfacial tension, melt viscosity, and glass forming ability.
\r\n\r\nFinally, the crystallization behavior, microstructure, and melt viscosity of an in situ ductile phase reinforced amorphous matrix composite is investigated as a function of the processing temperature. The results for the in situ composite are compared with those of the monolithic bulk metallic glasses.
" }, { "name": "Mukhtar, Saleem", "degree": "PhD", "year": "2005", "title": "Interval Modulation: A New Paradigm for the Design of High Speed Communication Systems", "advisor": "Hajimiri, Ali; Bruck, Jehoshua; Sternberg, Paul W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07072004-154316", "creators": [ { "name": { "family": "Mukhtar", "given": "Saleem" }, "id": "Mukhtar-Saleem", "display_name": "Mukhtar, Saleem" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "advisor", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Sternberg", "given": "Paul W." }, "id": "Sternberg-P-W", "orcid": "0000-0002-7699-0173", "role": "advisor", "display_name": "Sternberg, Paul W." } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "cns" ], "doi": "10.7907/6F03-MP11", "abstract": "In this thesis we propose a new, biologically inspired, paradigm for the design of high speed communication systems. The paradigm consists of a new modulation format referred to as Interval Modulation (IM). In order to transmit data in an efficient manner using this format, new coding techniques are needed. In this thesis we propose a coding technique based on variable length to variable length prefix trees and code construction algorithms are outlined. These codes are referred to as Interval Modulation Codes (IMC). Furthermore, data encoded with this modulation format cannot be transmitted or received using conventional synchronous CDR based receivers. In this thesis we outline a new asynchronous circuit architecture for both the transmitter and receiver. The architecture is based on active delay lines and eliminates the need for clock recovery." }, { "name": "Paloczi, George T.", "degree": "PhD", "year": "2005", "title": "Polymer Integrated Optics: Device Architectures and Fabrication Methods", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-05102005-112605", "creators": [ { "name": { "family": "Paloczi", "given": "George T." }, "id": "Paloczi-George-T", "display_name": "Paloczi, George T." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/W41G-2374", "abstract": "Polymer materials are becoming increasingly important for integrated photonic circuits in optical communications networks. The optical and mechanical properties of polymers for integrated optics are explored in this thesis and it is shown that the manipulation of these properties leads to developments that in other optical materials could not be achieved as quickly or as easily, or not achieved at all.
\r\n\r\nSo that the benefits of a large range of operating wavelengths due to low material dispersion in polymers, are not lost to the wavelength dependence of optical couplers, we design wavelength-invariant couplers using a geometrical representation of coupled mode theory. Simulations of the resulting couplers confirm a virtually constant response over a large range of input wavelengths.
\r\n\r\nThe direct-write ability of electron beam sensitive polymers enables rapid fabrication of high-precision optical devices. Microring resonator optical filters and a compact microring-based inline reflector are fabricated by this method and characterized. Chaining multiple rings together results in the coupled resonator optical waveguide (CROW). A CROW-Mach-Zehnder interferometer is fabricated and the measured response corresponds well with the predictions based on the matrix theory.
\r\n\r\nPolymer materials can be patterned by a variety of methods not possible with traditional optical materials. Soft-stamp replica molding presents a means to further reduce the costs of implementing polymer materials. Demonstrating the potential of the method, microring resonators are fabricated, with excellent agreement between the responses of the original and the replica. To further demonstrate the effectiveness of the process, it is applied in the fabrication of Mach-Zehnder modulators. The modulators exhibit excellent properties, with single-arm modulation voltages of 8 V and extinction ratios better than 19 dB. Successive repetition of the molding process allows for multilayer polymer optical devices. Finally, the flexible properties of polymers are exploited for pliable, all-polymer freestanding optical circuits.
" }, { "name": "Papachristodoulou, Antonis", "degree": "PhD", "year": "2005", "title": "Scalable Analysis of Nonlinear Systems Using Convex Optimization", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-05082005-100243", "creators": [ { "name": { "family": "Papachristodoulou", "given": "Antonis" }, "id": "Papachristodoulou-Antonis", "orcid": "0000-0002-3565-8967", "display_name": "Papachristodoulou, Antonis" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Rantzer", "given": "Anders" }, "id": "Rantzer-A", "role": "member", "display_name": "Rantzer, Anders" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "cds" ], "doi": "10.7907/5YG6-JG32", "abstract": "In this thesis, we investigate how convex optimization can be used to analyze different classes of nonlinear systems at various scales algorithmically. The methodology is based on the construction of appropriate Lyapunov-type certificates using sum of squares techniques.
\r\n\r\nAfter a brief introduction on the mathematical tools that we will be using, we turn our attention to robust stability and performance analysis of systems described by Ordinary Differential Equations. A general framework for constrained systems analysis is developed, under which stability of systems with polynomial, non polynomial vector fields and switching systems, as well as estimating the region of attraction and the L2 gain can be treated in a unified manner. Examples from biology and aerospace illustrate our methodology.
\r\n\r\nWe then consider systems described by Functional Differential Equations (FDEs), i.e., time-delay systems. Their main characteristic is that they are infinite dimensional, which complicates their analysis. We first show how the complete Lyapunov-Krasovskii functional can be constructed algorithmically for linear time delay systems. Then, we concentrate on delay-independent and delay-dependent stability analysis of nonlinear FDEs using sum of squares techniques. An example from ecology is given.
\r\n\r\nThe scalable stability analysis of congestion control algorithms for the Internet is investigated next. The models we use result in an arbitrary interconnection of FDE subsystems, for which we require that stability holds for arbitrary delays, network topologies and link capacities. Through a constructive proof, we develop a Lyapunov functional for FAST - a recently developed network congestion control scheme - so that the Lyapunov stability properties scale with the system size. We also show how other network congestion control schemes can be analyzed in the same way.
\r\n\r\nFinally, we concentrate on systems described by Partial Differential Equations. We show that axially constant perturbations of the Navier-Stokes equations for Hagen-Poiseuille flow are globally stable, even though the background noise is amplified as R3 where R is the Reynolds number, giving a 'robust yet fragile' interpretation. We also propose a sum of squares methodology for the analysis of systems described by parabolic PDEs.
\r\n\r\nWe conclude this work with an account for future research.
" }, { "name": "Pintgen, Florian Peter", "degree": "PhD", "year": "2005", "title": "Detonation Diffraction in Mixtures with Various Degrees of Instability", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072005-173741", "creators": [ { "name": { "family": "Pintgen", "given": "Florian Peter" }, "id": "Pintgen-Florian-Peter", "display_name": "Pintgen, Florian Peter" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Kuppermann", "given": "Aron" }, "id": "Kuppermann-A", "role": "member", "display_name": "Kuppermann, Aron" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/YSG0-TH85", "abstract": "Planar laser induced fluorescence (PLIF) is widely used in combustion diagnostics but has only recently been successfully applied to detonation. The strong spatial variations in temperature, pressure, and background composition under these conditions influence the quantitative link between OH-number density and fluorescence intensity seen on images. Up to now, this has lead to uncertainties in interpreting the features seen on PLIF images obtained in detonations. A one-dimensional fluorescence model has been developed, which takes into account light sheet attenuation by absorption, collisional quenching, and changing absorption line shape. The model predicts the fluorescence profile based on a one-dimensional distribution in pressure, temperature, and mixture composition. The fluorescence profiles based on a calculated ZND detonation profile were found to be in good agreement with experiments.
\r\n\r\nThe PLIF technique is used to study the diffraction process of a self-sustained detonation wave into an unconfined space through an abrupt area change. Simultaneous schlieren images enable direct comparison of shock and reaction fronts. Two mixture types of different effective activation energy [theta] are studied in detail, these represent extreme cases in the classification of detonation front instability and cellular regularity. Striking differences are seen in the failure mechanisms for the very regular H2-O2-Ar mixture ([theta] ~ 4.5) and the highly irregular H2-N2O mixture ([theta] ~ 9.4). Detailed image analysis quantifies the observed differences. Stereoscopic imaging reveals the complex three-dimensional structure of the transverse detonation and its location with respect to the shock front. The study is concluded by using the experimentally-obtained shock and reaction front profiles in a simplified model to examine the decoupling of the shock from the chemical reaction. The rapid increase in activation energy for the H2-O2-Ar mixtures with decreasing shock velocity is proposed as an important new element in the analysis of diffraction for these mixture.
" }, { "name": "Ponchaut, Nicolas Frederic", "degree": "PhD", "year": "2005", "title": "Part I: 3DPTV: Advances and Error Analysis. Part II: Extension of Guderley's Solution for Converging Shock Waves", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312005-111401", "creators": [ { "name": { "family": "Ponchaut", "given": "Nicolas Frederic" }, "id": "Ponchaut-Nicolas-Frederic", "display_name": "Ponchaut, Nicolas Frederic" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/09ZH-9M66", "abstract": "This work is divided into two unrelated parts. In the first part, a full three-dimensional particle tracking system was developed and tested. Three images, from three separate CCDs placed at the vertices of an equilateral triangle, permit the three-dimensional location of particles to be determined by triangulation. Particle locations measured at two different times can then be used to create a three-component, three-dimensional velocity field. Key developments are the ability to accurately process overlapping particle images, offset CCDs to significantly improve effective resolution, treatment of dim particle images, and a hybrid particle tracking technique ideal for three-dimensional flows when only two sets of images exist. An in-depth theoretical error analysis was performed, which gives the important sources of error and their effect on the overall system. This error analysis was verified through a series of experiments, and a vortex flow measurement was performed.\r\n\r\nIn the second part, the problem of a cylindrically or spherically imploding and reflecting shock wave in a flow initially at rest was examined. Guderley's strong shock solution around the origin was improved by adding two more terms in the series expansion solution for both the incoming and the reflected shock waves. A series expansion was also constructed for the case where the shock is still very far from the origin. In addition, a program based on the characteristics method was written. Thanks to an appropriate change of variables, the shock motion could be computed from virtually infinity to very close to the reflection point. Comparisons were made between the series expansions, the characteristics program, and the results obtained using an Euler solver. These comparisons showed that the addition of two terms to the Guderley solution significantly increases the accuracy of the series expansion." }, { "name": "Prajna, Stephen", "degree": "PhD", "year": "2005", "title": "Optimization-Based Methods for Nonlinear and Hybrid Systems Verification", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-144358", "creators": [ { "name": { "family": "Prajna", "given": "Stephen" }, "id": "Prajna-Stephen", "display_name": "Prajna, Stephen" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Rantzer", "given": "Anders" }, "id": "Rantzer-A", "role": "member", "display_name": "Rantzer, Anders" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/S3BJ-4M47", "abstract": "Complex behaviors that can be exhibited by hybrid systems make the verification of such systems both important and challenging. Due to the infinite number of possibilities taken by the continuous state and the uncertainties in the system, exhaustive simulation is impossible, and also computing the set of reachable states is generally intractable. Nevertheless, the ever-increasing presence of hybrid systems in safety critical applications makes it evident that verification is an issue that has to be addressed.
\r\n\r\nIn this thesis, we develop a unified methodology for verifying temporal properties of continuous and hybrid systems. Our framework does not require explicit computation of reachable states. Instead, functions of state termed barrier certificates and density functions are used in conjunction with deductive inference to prove properties such as safety, reachability, eventuality, and their combinations. As a consequence, the proposed methods are directly applicable to systems with nonlinearity, uncertainty, and constraints. Moreover, it is possible to treat safety verification of stochastic systems in a similar fashion, by computing an upper-bound on the probability of reaching the unsafe states.
\r\n\r\nWe formulate verification using barrier certificates and density functions as convex programming problems. For systems with polynomial descriptions, sum of squares optimization can be used to construct polynomial barrier certificates and density functions in a computationally scalable manner. Some examples are presented to illustrate the use of the methods. At the end, the convexity of the problem formulation is also exploited to prove a converse theorem in safety verification using barrier certificates.
" }, { "name": "Romero-Talam\u00e1s, Carlos Alejandro", "degree": "PhD", "year": "2005", "title": "Investigations of Spheromak Plasma Dynamics: High-Speed Imaging at the Sustained Spheromak Physics Experiment and Magnetic Diagnostics at the Caltech Spheromak Experiment", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02042005-150634", "creators": [ { "name": { "family": "Romero-Talam\u00e1s", "given": "Carlos Alejandro" }, "id": "Romero-Talam\u00e1s-Carlos-Alejandro", "orcid": "0000-0002-6830-3126", "display_name": "Romero-Talam\u00e1s, Carlos Alejandro" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Hill", "given": "David" }, "id": "Hill-D", "role": "member", "display_name": "Hill, David" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z21H-6A46", "abstract": "This thesis consists of two parts. The first part describes a specially designed high-speed imaging system installed at the Sustained Spheromak Physics Experiment (SSPX). Thousands of images have been obtained at SSPX using a high-speed, 1280 x 1024 pixel, cooled and intensified CCD camera with double frame capability, and show unprecedented details of the SSPX plasma. From these images, three different stages were identified according to distinct plasma features. These stages are breakdown and ejection, sustainment, and decay.
\r\n\r\nDuring the breakdown and ejection stage, JxB forces push the plasma and stretches the initial vacuum field into the flux conserver. As the plasma enters the field of view of the camera, undulations in the expansion front are visible. These undulations are caused by filaments formed in the gun region, and merge as they travel towards the flux conserver and rotate around the chamber axis. In less than 100 microseconds after breakdown, a transient plasma column is formed. Just microseconds after this, the column bends impulsively and seemingly merges in the toroidal direction (around the axis of the chamber). It is conjectured that the bending precedes a reconnection event that leads to magnetic flux amplification.
\r\n\r\nImages taken during the sustainment stage show the presence of a central column which is very stable. Some images suggest nested current channels in this column. Comparisons of column diameter measurements versus numerical modeling (using the CORSICA code) are presented here. Bright and distinct patterns were observed on the surface of the source cathode, and appear to be related to the sustainment column and open flux surfaces. These patterns elongate toroidally in a constant direction which depends on the bias field polarity. It is conjectured that the pattern motion is caused by E x B drifts, or J x B effects near the cathode surface.
\r\n\r\nMost of the hardware was specially designed for the high-speed imaging system, including a double-branch fiber bundle that was used to produce rough tomography (at midplane) of the transient central column. The algorithm used for tomographical reconstruction is based on a maximum entropy restoration method that was also used to improve noisy and blurry images.
\r\n\r\nThe second part of this thesis describes a 60-element magnetic probe array that was constructed using miniature commercial chip inductors. The coils are oriented in orthogonal directions to yield three-dimensional information. The probe has been used to investigate magnetic evolution at the Caltech Spheromak Experiment.
" }, { "name": "Savarese, Silvio", "degree": "PhD", "year": "2005", "title": "Shape Reconstruction from Shadows and Reflections", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-162056", "creators": [ { "name": { "family": "Savarese", "given": "Silvio" }, "id": "Savarese-Silvio", "display_name": "Savarese, Silvio" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "eleceng" ], "doi": "10.7907/FH0V-3M10", "abstract": "Measuring automatically the shape of physical objects in order to obtain corresponding digital models has become a useful, often indispensable, tool in design, engineering, art conservation, computer graphics, medicine and science. Machine vision has proven to be more appealing than competing technologies. Ideally, we would like to be able to acquire digital models of generic objects by simply walking around the scene, while filming with a handheld camcorder. Thus, one of the main challenges in modern machine vision is to develop algorithms that: i) are inexpensive, fast and accurate; ii) can handle objects with arbitrary appearance properties and shape; and iii) need little or no user intervention.
\r\n\r\nIn this thesis, we address both issues. In the first part, we present a novel 3D reconstruction technique which makes use of minimal and inexpensive equipment. We call this technique \"shadow carving\". We explore the information contained in the shadows that an object casts upon itself. An algorithm is provided that makes use of this information. The algorithm iteratively recovers an estimate of the object which i) approximates the object\u2019s shape more and more closely; and ii) is provably an upper bound to the object's shape. Shadow carving is the first technique to incorporate \"shadow\" information in a multi-view shape recovery framework. We have implemented our approach in a simple table-top system and validated our algorithm by recovering the shape of real objects.
\r\n\r\nIt is well known that vision-based 3D scanning systems handle specular or highly reflective surfaces only poorly. The cause of this deficiency is most likely not intrinsic, but rather due to our lack of understanding of the relevant cues. In the second part of this thesis, we focus on how to promote mirror reflections from \"noise\" to \"signal\". We first present a geometrical and algebraic characterization of how a patch of the scene is mapped into an image by a mirror surface of given shape. We then develop solutions to the inverse problem of deriving surface shape from mirror reflections in a single image. We validate our theoretical results with both numerical simulations and experiments with real surfaces.
\r\n\r\nA third goal of this thesis is advancing our understanding of human perception of shape from reflections. Although the idea of perception of shape from different visual cues (e.g., shading, texture, etc.) has been extensively discussed in the past, little is known to what extent highlights and specular reflections carry useful information for shape perception. We use psychophysics to study this capability. Our goal is to provide a benchmark, as well as inspire possible technical approaches, for our computational work. We find that surprisingly, humans are very poor at judging the shape of mirror surfaces when additional visual cues (i.e., contour, shading, stereo, texture) are not visible.
" }, { "name": "Staneff, Geoffrey D.", "degree": "PhD", "year": "2005", "title": "High-Pressure Synthesis of Thermoelectric Materials", "advisor": "Asimow, Paul David", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262005-004951", "creators": [ { "name": { "family": "Staneff", "given": "Geoffrey D." }, "id": "Staneff-Geoffrey-D", "display_name": "Staneff, Geoffrey D." } ], "advisors": [ { "name": { "family": "Asimow", "given": "Paul David" }, "id": "Asimow-P-D", "orcid": "0000-0001-6025-8925", "role": "advisor", "display_name": "Asimow, Paul David" } ], "committee": [ { "name": { "family": "Asimow", "given": "Paul David" }, "id": "Asimow-P-D", "orcid": "0000-0001-6025-8925", "role": "chair", "display_name": "Asimow, Paul David" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/HWWN-NS80", "abstract": "New thermoelectric materials were synthesized using high-pressure techniques. The synthetic limits of cerium filling in cobalt triantimonide were explored and a model for successful synthesis conditions was generated. The high-pressure technique expanded the practical filling limit from x=0.07 to x=0.5 in the CexCo4Sb12 system. Explorations of cerium filled ruthenium-rhodium triantimonide were also undertaken, using our previous work to guide the synthesis attempt. This material was predicted to have outstanding thermoelectric properties, but our investigations did not confirm this result. The filled skutterudite, Ce(Ru0.67Rh0.33)4Sb12, exhibited the low thermal conductivity anticipated, approximately half the total thermal conductivity of a binary CoSb3 skutterudite over a wide range in temperatures. The electrical properties were insufficient to produce a high efficiency thermoelectric, but these results did suggest incorporated rare earth filling atoms do not fully ionize when incorporated into the skutterudite structure. Modification of the carrier type should therefore be investigated by solid solution on the transition metal or pnictide sites and not the filling ion.
\r\n\r\nThe high-pressure synthesis techniques developed for skutterudite synthesis were then employed to sinter nano-scale silicon-germanium compounds. A sintering figure of merit was created to justify the use of high-pressure synthesis, which later proved to be a useful tool for planning subsequent experiments. Sintered silicon, germanium, and silicon-germanium composites were obtained, with the nano-scale grain structure and chemical heterogeneity of the starting powder aggregate intact.
\r\n\r\nFuture work in high-pressure synthesis should be undertaken to quantify the sintering figure of merit presented in this work. The ability to produce a dense multiphase material with a controlled nano-structure should provide a great boon to thermoelectrics research. The high-pressure synthesis technique provides an method to mix two thermoelectric materials without homogenizing them. Both the two-phased solid and the network of nano-scale grains provide powerful tools for minimizing the thermal conductivity of a thermoelectric device component.
" }, { "name": "Stredie, Valentin Gabriel", "degree": "PhD", "year": "2005", "title": "Mathematical Modeling and Simulation of Aquatic and Aerial Animal Locomotion", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-004852", "creators": [ { "name": { "family": "Stredie", "given": "Valentin Gabriel" }, "id": "Stredie-Valentin-Gabriel", "display_name": "Stredie, Valentin Gabriel" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "co-chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/8PWE-RK28", "abstract": "In this thesis we investigate the locomotion of fish and birds by applying both new and well known mathematical techniques.
\r\n\r\nThe two-dimensional model is first studied using Krasny's vortex blob method, and then a new numerical method based on Wu's theory is developed. To begin with, we will implement Krasny's ideas for a couple of examples and then switch to the numerical implementation of the nonlinear analytical mathematical model presented by Wu. We will demonstrate the superiority of this latter method both by applying it to some specific cases and by comparing with the experiments. The nonlinear effects are very well observed and this will be shown by analyzing Wagner's result for a wing abruptly undergoing an increase in incidence angle, and also by analyzing the vorticity generated by a wing in heaving, pitching and bending motion. The ultimate goal of the thesis is to accurately represent the vortex structure behind a flying wing and its influence on the bound vortex sheet.
\r\n\r\nIn the second part of this work we will introduce a three-dimensional method for a flat plate advancing perpendicular to the flow. The accuracy of the method will be shown both by comparing its results with the two-dimensional ones and by validating them versus the experimental results obtained by Ringuette in the towing tank of the Aeronautics Department at Caltech.
" }, { "name": "Thorpe, Jeremy Christopher", "degree": "PhD", "year": "2005", "title": "Analysis and Design of Protograph Based LDPC Codes and Ensembles", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02102006-144149", "creators": [ { "name": { "family": "Thorpe", "given": "Jeremy Christopher" }, "id": "Thorpe-Jeremy-Christopher", "display_name": "Thorpe, Jeremy Christopher" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/dyfb-2z28", "abstract": "Channel coding is a key component of artificial communication systems, allowing reliable communication using unreliable channels. In the last decade, iteratively decoded channel codes have become or clearly will become standards in a wide range of applications where large amounts of information must be communicated using unreliable media. Of the class of iteratively decoded codes, Low-density parity check (LDPC) codes are arguably the simplest class to describe, and indeed were described more than four decades ago in 1963 by Robert Gallager.
\r\n\r\nThe current understanding of LDPC codes has progressed in several significant ways beyond what had been expressed by 1963 by Gallager. Importantly, irregular LDPC codes, whose parity check matrices do not have constant row and column sums, have been shown to significantly outperform their regular counterparts explicitly considered by Gallager.
\r\n\r\nBy 1999, researchers had defined a class of irregular ensembles, each characterized by a pair of polynomials. Along with this new class of ensemble, they defined an analytical technique, density evolution, that accurately predicted the channel coding performance of a typical code under iterative message-passing decoding. The pair of polynomials could be effectively be designed by optimizing the coefficients of the polynomial for density evolution threshold threshold.
\r\n\r\nThis thesis concerns a different class of ensembles, namely protograph ensembles. Protograph ensembles are characterized by a template graph called, intuitively, a protograph. The Tanner-graph representation of a code in the ensemble is a random lift of the protograph.
\r\n\r\nProtograph-based codes have significant advantages over unstructured irregular codes in regard to implementation of their encoders and decoders. In the decoder, this structure can be used in at least two distinct ways to organize the computations defined by any message-passing algorithm. If, in addition to the protograph structure, circulant structure is imposed on each \"section\" of the matrix then a quasi-cyclic code results, bestowing even mores advantages, especially in the possible implementation of the encoder.
\r\n\r\nA central difficulty in using protograph ensembles is finding a suitable protograph. Since graphs are discrete objects, there is no obvious correspondence to any optimization model using vectors of real numbers. Instead, the technique of simulated annealing has been applied with a remarkable degree of success. For example, on the AWGN channel, given a constraint on the node degrees, protograph ensembles can be found that achieve a threshold only half as far (measured in dB) from the Shannon limit as unstructured irregular ensembles. This simultaneously illustrates an inherent performance advantage of protograph codes over unstructured codes as well as the efficacy of simulated annealing as an optimization technique.
\r\n\r\nA persistent problem which appears to be common in all codes optimized for density evolution threshold is that of error floors. On a superficial level, this is explained by the maxim that \"There's no such thing as a free lunch.\" In some contexts, such as in codes designed for the erasure channel, the phenomenon can be explained on a much deeper level, though it is not clear why the phenomenon should persist so universally.
\r\n\r\nStill, even without a detailed understanding the cause of this problem, there are techniques that can mitigate error floors. An important tool toward this end is weight enumerators, which are discussed in chapter 3. Codeword and stopping set enumerators can be efficiently computed if a certain (non-concave) function can be efficiently maximized. Protographs that are selected on the basis of their enumerators have shown some success in reducing error floors.
" }, { "name": "Thunnissen, Daniel Pierre", "degree": "PhD", "year": "2005", "title": "Propagating and Mitigating Uncertainty in the Design of Complex Multidisciplinary Systems", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072005-162147", "creators": [ { "name": { "family": "Thunnissen", "given": "Daniel Pierre" }, "id": "Thunnissen-Daniel-Pierre", "display_name": "Thunnissen, Daniel Pierre" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." } ], "option_major": [ "mecheng" ], "doi": "10.7907/0FX2-AM50", "abstract": "As humanity has developed increasingly ingenious and complicated systems, it has not been able to accurately predict the performance, development time, reliability, or cost of such systems. This inability to accurately predict parameters of interest in the design of complex multidisciplinary systems such as automobiles, aircraft, or spacecraft is due in great part to uncertainty. Uncertainty in complex multidisciplinary system design is currently mitigated through the use of heuristic margins. The use of these heuristic margins can result in a system being overdesigned during development or failing during operation.
\r\n\r\nThis thesis proposes a formal method to propagate and mitigate uncertainty in the design of complex multidisciplinary systems. Specifically, applying the proposed method produces a rigorous foundation for determining design margins. The method comprises five distinct steps: identifying tradable parameters; generating analysis models; classifying and addressing uncertainties; quantifying interaction uncertainty; and determining margins, analyzing the design, and trading parameters. The five steps of the proposed method are defined in detail. Margins are now a function of risk tolerance and are measured relative to mean expected system performance, not variations in design parameters measured relative to heuristic values.
\r\n\r\nAs an example, the proposed method is applied to the preliminary design of a spacecraft attitude determination and control system. In particular, the design of the attitude control system on the Mars Exploration Rover spacecraft cruise stage is used. Use of the proposed method for the example presented yields significant differences between the calculated design margins and the values assumed by the Mars Exploration Rover project.
\r\n\r\nIn addition to providing a formal and rigorous method for determining design margins, this thesis provides three other principal contributions. The first is an uncertainty taxonomy for use in the design of complex multidisciplinary systems with detailed definitions for each uncertainty type. The second is the modification of two simulation techniques, the mean value method and subset simulation, that can significantly reduce the computational burden in applying the proposed method. The third is a set of diverse application examples and various simulation techniques that demonstrate the generality and benefit of the proposed method.
" }, { "name": "Westhead, Andrew Neil", "degree": "PhD", "year": "2005", "title": "Upscaling for Two-Phase Flows in Porous Media", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252005-085744", "creators": [ { "name": { "family": "Westhead", "given": "Andrew Neil" }, "id": "Westhead-Andrew-Neil", "display_name": "Westhead, Andrew Neil" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Owhadi", "given": "Houman" }, "id": "Owhadi-H", "orcid": "0000-0002-5677-1600", "role": "member", "display_name": "Owhadi, Houman" }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/T7Q0-FG76", "abstract": "The understanding and modeling of flow through porous media is an important issue in several branches of engineering. In petroleum engineering, for instance, one wishes to model the \"enhanced oil recovery\" process, whereby water or steam is injected into an oil saturated porous media in an attempt to displace the oil so that it can be collected. In groundwater contaminant studies the transport of dissolved material, such as toxic metals or radioactive waste, and how it affects drinking water supplies, is of interest.
\r\n\r\nNumerical simulation of these flow are generally difficult. The principal reason for this is the presence of many different length scales in the physical problem, and resolving all these is computationally expensive. To circumvent these difficulties a class of methods known as upscaling methods has been developed where one attempts to solve only for large scale features of interest and model the effect of the small scale features.
\r\n\r\nIn this thesis, we review some of the previous efforts in upscaling and introduce a new scheme that attempts to overcome some of the existing shortcomings of these methods. In our analysis, we consider the flow problem in two distinct stages: the first is the determination of the velocity field which gives rise to an elliptic partial differential equation (PDE) and the second is a transport problem which gives rise to a hyperbolic PDE.
\r\n\r\nFor the elliptic part, we make use of existing upscaling methods for elliptic equations. In particular, we use the multi-scale finite element method of Hou et al. to solve for the velocity field on a coarse grid, and yet still be able to obtain fine scale information through a special means of interpolation.
\r\n\r\nThe analysis of the hyperbolic part forms the main contribution of this thesis. We first analyze the problem by restricting ourselves to the case where the small scales have a periodic structure. With this assumption, we are able to derive a coupled set of equations for the large scale average and the small scale fluctuations about this average. This is done by means of a special averaging, which is done along the fine scale streamlines. This coupled set of equations provides better starting point for both the modeling of the largescale small-scale interactions and the numerical implementation of any scheme. We derive an upscaling scheme from this by tracking only a sub-set of the fluctuations, which are used to approximate the scale interactions. Once this model has been derived, we discuss and present a means to extend it to the case where the fluctuations are more general than periodic.
\r\n\r\nIn the sections that follow we provide the details of the numerical implementation, which is a very significant part of any practical method. Finally, we present numerical results using the new scheme and compare this with both resolved computations and some existing upscaling schemes.
" }, { "name": "Wheatley, Vincent", "degree": "PhD", "year": "2005", "title": "On the Richtmyer-Meshkov Instability in Magnetohydrodynamics", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-145538", "creators": [ { "name": { "family": "Wheatley", "given": "Vincent" }, "id": "Wheatley-Vincent", "orcid": "0000-0002-7287-7659", "display_name": "Wheatley, Vincent" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/N407-2B54", "abstract": "The Richtmyer-Meshkov instability is important in a wide variety of applications including inertial confinement fusion and astrophysical phenomena. In some of these applications, the fluids involved may be plasmas and hence be affected by magnetic fields. For one configuration, it has been numerically demonstrated that the growth of the instability in magnetohydrodynamics is suppressed in the presence of a magnetic field. Here, the nature of this suppression is theoretically and numerically investigated.
\r\n\r\nIn the framework of ideal incompressible magnetohydrodynamics, we examine the stability of an impulsively accelerated, sinusoidally perturbed density interface in the presence of a magnetic field that is parallel to the acceleration. This is accomplished by analytically solving the linearized initial value problem, which is a model for the Richtmyer-Meshkov instability. We find that the initial growth rate of the interface is unaffected by the presence of a magnetic field, but for a finite magnetic field the interface amplitude asymptotes to a constant value. Thus the instability of the interface is suppressed. The interface behavior from the analytical solution is compared to the results of both linearized and non-linear compressible numerical simulations for a wide variety of conditions.
\r\n\r\nWe then consider the problem of the regular refraction of a shock at an oblique, planar contact discontinuity separating conducting fluids of different densities in the presence of a magnetic field aligned with the incident shock velocity. Planar ideal MHD simulations indicate that the presence of a magnetic field inhibits the deposition of vorticity on the shocked contact, which leads to the suppression of the Richtmyer-Meshkov instability. We show that the shock refraction process produces a system of five to seven plane waves that may include fast, intermediate, and slow MHD shocks, slow compound waves, 180\u00b0 rotational discontinuities, and slow-mode expansion fans that intersect at a point. In all solutions, the shocked contact is vorticity free and hence stable. These solutions are not unique, but differ in the type of waves that participate. The set of equations governing the structure of these multiple-wave solutions is obtained in which fluid property variation is allowed only in the azimuthal direction about the wave-intersection point. Corresponding solutions are referred to as either quintuple-points, sextuple-points, or septuple-points, depending on the number of participating waves. A numerical method of solution is described and examples are compared to the results of numerical simulations for moderate magnetic field strengths. The limit of vanishing magnetic field at fixed permeability and pressure is studied for two solution types. The relevant solutions correspond to the hydrodynamic triple-point with the shocked contact replaced by a singular structure consisting of a wedge, whose angle scales with the applied field magnitude, bounded by either two slow compound waves or two 180\u00b0 rotational discontinuities, each followed by a slow-mode expansion fan. These bracket the MHD contact which itself cannot support a tangential velocity jump in the presence of a non-parallel magnetic field. The magnetic field within the singular wedge is finite and the shock-induced change in tangential velocity across the wedge is supported by the expansion fans that form part of the compound waves or follow the rotational discontinuities. To verify these findings, an approximate leading order asymptotic solution appropriate for both flow structures was computed. The full and asymptotic solutions are compared quantitatively and there is shown to be excellent agreement between the two.
" }, { "name": "White, Christopher John", "degree": "PhD", "year": "2005", "title": "A Solid-state Atomic Frequency Standard", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-172142", "creators": [ { "name": { "family": "White", "given": "Christopher John" }, "id": "White-Christopher-John", "display_name": "White, Christopher John" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Weitekamp", "given": "Daniel P." }, "id": "Weitekamp-D-P", "role": "member", "display_name": "Weitekamp, Daniel P." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ATKE-YX40", "abstract": "The thesis describes a new class of frequency reference. The frequency source uses the same operating principle as a passive atomic frequency standard; however, the device is entirely solid-state, removing many cost and reliability issues associated with gas-phase atomic clocks. More specifically, the \"atomic resonance\" is derived from zero-field magnetic resonance transitions of the vanadium ion in a cubic crystal lattice. The characteristics of these resonances will be described in detail. The apparatus for measuring the \"atomic\" resonances uses a radio-frequency resonant cavity and frequency discriminator circuit. Using integrated circuits, the radio-frequency signal processing functions can be implemented at very low cost in a reliable manufacturing process. We discuss the system design and the measurement sensitivity. Advantages of the new frequency reference may include immunity to vibration and reduced aging compared to crystal oscillators." }, { "name": "Wirz, Richard Edward", "degree": "PhD", "year": "2005", "title": "Discharge Plasma Processes of Ring-Cusp Ion Thrusters", "advisor": "Culick, Fred E. C.; Polk, James E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232005-162628", "creators": [ { "name": { "family": "Wirz", "given": "Richard Edward" }, "id": "Wirz-Richard-Edward", "orcid": "0000-0001-5309-3659", "display_name": "Wirz, Richard Edward" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "co-advisor", "display_name": "Polk, James E." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VKKE-PC20", "abstract": "This study has increased the viability of miniature ion thruster technology, advanced state-of-the-art discharge modeling, and revealed important aspects of discharge plasma processes. These extensions of existing ion thruster technology and understanding are necessary to fulfill the needs of future space missions. Experimental comparisons of the discharge performance of an array of miniature (3cm diameter) ion thruster discharge configurations were conducted and showed that a 3-ring configuration with length-to-diameter of 1.0 exhibited the best performance. A compact and lightweight version of this configuration, using small accelerator grid holes, exhibited discharge losses of 250-550eV/ion and propellant efficiency of as much as 87%. This performance represents a significant advancement in miniature (less than 5cm diameter) ion thruster technology and demonstrates that a miniature ion thruster of low magnet and thruster weight can yield desirable performance.
\r\n\r\nA multi-component hybrid 2-D computational Discharge Model was developed to help identify important ion thruster discharge processes and investigate miniaturization issues. Combining experimental and computational results reveals that magnetic field optimization for a miniature ion thruster is bracketed by considerations of primary electron utilization and discharge stability. Discharge Model analysis of the larger (30cm diameter) NSTAR thruster revealed that the peak observed in the NSTAR beam profile is due to double ions that are created by over-confinement of primary electrons on the thruster axis. Design sensitivity results show that, at the NSTAR thruster scale, efficient confinement of primary electrons is relatively easy to achieve; therefore, efforts to improve thruster performance should focus on effectively utilizing the primary electrons to minimize double ion production and maximize the number of single ions extracted to the beam.
\r\n\r\nThe observations from this study have furthered the understanding of discharge processes and should improve future ion thruster design and modeling efforts. The Discharge Model advances state-of-the-art ion thruster modeling and provides a framework for a complete thruster model that can be used for long-life performance assessment and life validation.
" }, { "name": "Witzens, Jeremy", "degree": "PhD", "year": "2005", "title": "Dispersion in Photonic Crystals", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-094353", "creators": [ { "name": { "family": "Witzens", "given": "Jeremy" }, "id": "Witzens-Jeremy", "orcid": "0000-0002-2896-7243", "display_name": "Witzens, Jeremy" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yablonovitch", "given": "Eli" }, "id": "Yablonovitch-E", "role": "member", "display_name": "Yablonovitch, Eli" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/NV9T-SC75", "abstract": "Investigations on the dispersive properties of photonic crystals, modified scattering in ring-resonators, monolithic integration of vertical-cavity surface-emitting lasers and advanced data processing techniques for the finite-difference time-domain method are presented.
\r\n\r\nPhotonic crystals are periodic mesoscopic arrays of scatterers that modify the propagation properties of electromagnetic waves in a similar way as \"natural\" crystals modify the properties of electrons in solid-state physics. In this thesis photonic crystals are implemented as planar photonic crystals, i.e., optically thin semiconductor films with periodic arrays of holes etched into them, with a hole-to-hole spacing of the order of the wavelength of light in the dielectric media. Photonic crystals can feature forbidden frequency ranges (the band-gaps) in which light cannot propagate. Even though most work on photonic crystals has focused on these band-gaps for application such as confinement and guiding of light, this thesis focuses on the allowed frequency regions (the photonic bands) and investigates how the propagation of light is modified by the crystal lattice. In particular the guiding of light in bulk photonic crystals in the absence of lattice defects (the self-collimation effect) and the angular steering of light in photonic crystals (the superprism effect) are investigated. The latter is used to design a planar lightwave circuit for frequency domain demultiplexion. Difficulties such as efficient insertion of light into the crystal are resolved and previously predicted limitations on the resolution are circumvented. The demultiplexer is also fabricated and characterized.
\r\n\r\nMonolithic integration of vertical-cavity surface-emitting lasers by means of resonantly enhanced grating couplers is investigated. The grating coupler is designed to bend light through a ninety-degree angle and is characterized with the finite-difference time-domain method. The vertical-cavity surface-emitting lasers are fabricated and characterized.
\r\n\r\nA purely theoretical section of the thesis investigates advanced data processing techniques for the finite-difference time-domain method. In particular it is shown that an inner product can be used to filter out specific photonic crystal modes or photonic crystal waveguide modes (Bloch-modes). However it is also shown that the numerical accuracy of this inner product severely worsens for Bloch modes with very low group velocities.
" }, { "name": "Wu, Jian", "degree": "PhD", "year": "2005", "title": "Defect Chemistry and Proton Conductivity in Ba-based Perovskites", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062004-232639", "creators": [ { "name": { "family": "Wu", "given": "Jian" }, "id": "Wu-Jian", "display_name": "Wu, Jian" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/VTCG-T978", "abstract": "The site incorporation mechanism of M\u00b3\u207a dopants into A\u00b2\u207aB\u2074\u207aO\u2083 perovskites controls the overall defect chemistry and thus their transport properties. For charge balance reasons, incorporation onto the A\u00b2\u207a site would require the creation of negatively charged point defects, such as cation vacancies, whereas incorporation onto the B\u2074\u207a site is accompanied by the generation of positively charged defects, typically oxygen vacancies. Oxygen vacancy content, in turn, is relevant to proton conducting oxides in which protons are introduced via the dissolution of hydroxyl ions at vacant oxygen sites.
\r\n\r\nThis work proposes that, on the basis of X-ray powder diffraction studies, electron microscopy, chemical analysis, thermal gravimetric analysis, AC impedance spectroscopy, extended X-ray fine structure (EXAFS) and atomistic simulation, that nominally B-site doped barium cerate can exhibit dopant partitioning partially as a consequence of barium evaporation at elevated temperatures. Such partitioning and the presence of significant dopant concentrations on the A-site negatively impact proton conductivity. As a consequence of the greater ability of larger cations to exist on the Ba site, the H\u2082O adsorption and proton conductivities of large-cation doped barium cerates are lower than those of small-cation doped analogs.
\r\n\r\nA series of dopants, La, Nd, Sm, Gd and Yb are adopted in doped BaCeO\u2083 with the composition BaCe0.85M0.15O3-\u03b4. Yb doped BaCeO\u2083 yields the highest proton conductivity among all the doped samples. Compositional non-stoichiometry, which is closely tied to sample processing, is studied in a Bax0.85M0.15O3\u00b1\u03b4 series. It is indicated that low temperature synthesis is beneficial to reduce barium evaporation at elevated temperatures and in turn increase the proton conductivity. The chemical stability of BaCeO\u2083 is investigated and Zr is used to stabilize BaCeO\u2083 in CO\u2082-rich atmosphere effectively. This result helps to commercialize doped BaCeO\u2083 as the electrolyte material for SOFCs.
" }, { "name": "Xia, Kaiwen", "degree": "PhD", "year": "2005", "title": "Laboratory Investigations of Earthquake Dynamics", "advisor": "Rosakis, Ares J.; Kanamori, Hiroo", "url": "https://resolver.caltech.edu/CaltechETD:etd-02262005-161824", "creators": [ { "name": { "family": "Xia", "given": "Kaiwen" }, "id": "Xia-Kaiwen", "display_name": "Xia, Kaiwen" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "advisor", "display_name": "Kanamori, Hiroo" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "co-chair", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Tromp", "given": "Jeroen" }, "id": "Tromp-J", "role": "member", "display_name": "Tromp, Jeroen" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "mecheng" ], "doi": "10.7907/WQQX-6Q19", "abstract": "Earthquake represents one of most destructive geological hazards. In this thesis I will attempt to understand it through controlled laboratory experiments. The earthquake dynamic rupturing process itself is a complicated phenomenon, involving dynamic friction, wave propagation, and heat production. Because controlled experiments can produce results without assumptions needed in theoretical and numerical analysis, the experimental method is thus advantageous over theoretical and numerical methods.
\r\n\r\nOur laboratory fault is composed of carefully cut photoelastic polymer plates (Homalite-100, Polycarbonate) held together by uniaxial compression. As a unique unit of the experimental design, a controlled exploding wire technique provides the triggering mechanism of laboratory earthquakes. Three important components of real earthquakes (i.e., pre-existing fault, tectonic loading, and triggering mechanism) correspond to and are simulated by frictional contact, uniaxial compression, and the exploding wire technique. Dynamic rupturing processes are visualized using the photoelastic method and are recorded via a high-speed camera. Our experimental methodology, which is full-field, in situ, and non-intrusive, has better control and diagnostic capacity compared to other existing experimental methods.
\r\n\r\nUsing this experimental approach, we have investigated several problems: dynamics of earthquake faulting occurring along homogeneous faults separating identical materials, earthquake faulting along inhomogeneous faults separating materials with different wave speeds, and earthquake faulting along faults with a finite low wave speed fault core. We have observed supershear ruptures, rupture speed transition, directionality of rupture in faults with a material contrast, self-healing slip pulses in faults with a finite core, crack-like to pulse-like rupture transition in faults with a finite core.
" }, { "name": "Xiao, Yu", "degree": "PhD", "year": "2005", "title": "The Influence of Oxygen Vacancies on Domain Patterns in Ferroelectric Perovskites", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-01032005-140446", "creators": [ { "name": { "family": "Xiao", "given": "Yu" }, "id": "Xiao-Yu", "display_name": "Xiao, Yu" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "mecheng" ], "doi": "10.7907/5QSX-9Y68", "abstract": "This thesis investigates the role of oxygen vacancies in determining ferroelectric properties and domain patterns of ferroelectric perovskites. Being non-polar (paraelectric) above their Curie temperature but spontaneously polarized (ferroelectric) below it, ferroelectric perovskites offer a tantalizing potential for applications: large actuation through domain switching and memory storage via switchable electric polarization. Oxygen vacancies, commonly present and mobile at high temperature, are the primary defects and thus play a central role in these applications.
\r\n\r\nWe develop a model that combines the ferroelectric and semiconducting nature of ferroelectric perovskites. Oxygen vacancies act as n-type dopants and thus affect the semiconducting properties. We show that the ferroelectric and semiconducting features interact and lead to the formation of depletion layers near the electrodes and double layers at the 90\u00b0 domain walls. We find a potential drop across 90\u00b0 domain walls even in a perfect crystal. This potential drop marks the essential difference between a 90\u00b0 and an 180\u00b0 domain wall, drives the formation of a space charge double layer in a doped crystal, promotes electronic charge injection and trapping, and leads to the redistribution of oxygen vacancies at 90\u00b0 domain walls. The rearrangement of oxygen vacancies near 90\u00b0 domain walls may form a basis for domain memory and provides a potentially new mechanism for large electrostriction.
\r\n\r\nWe also rigorously justify the continuum theory by calculating the Coulomb energy of a spontaneously polarized solid starting from a periodic distribution of charges based on the classical interpretation of ferroelectrics and with a definite choice of polarization per unit cell. We prove that in the limit where the size of the body is large compared to the unit cell, the energy of Coulombic interactions may be approximated by a sum of a local part and a nonlocal part. The local part depends on the lattice structure, but is different from the Lorentz formula for a lattice of dipoles. The nonlocal part is identical to the Lorentz formula.
" }, { "name": "Xie, Jun", "degree": "PhD", "year": "2005", "title": "Integrated Parylene LC-ESI on a Chip", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-03032005-135900", "creators": [ { "name": { "family": "Xie", "given": "Jun" }, "id": "Xie-Jun", "display_name": "Xie, Jun" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Lee", "given": "Terry D." }, "id": "Lee-T-D", "role": "member", "display_name": "Lee, Terry D." } ], "option_major": [ "eleceng" ], "doi": "10.7907/00KQ-V723", "abstract": "In this thesis, several microfluidic devices will be introduced to demonstrate the integration capability of a multilayer parylene surface micromachining technology. Due to its flexibility and versatility, various devices have been developed and integrated onto a single ship. Based on the technology, on-chip LC-ESI was successfully demonstrated.
\r\n\r\nBased on the technology, an electrostatically actuated micro peristaltic pump has been developed. An AC actuation voltage combined with a peristaltic actuation was used to demonstrate fluid pumping. A reasonable flow rate and pumping pressure were achieved. The pump dynamics and performance were then addressed further by an analysis based on a lumped-parameter model of the system.
\r\n\r\nBased on the same technology, an entirely surface micromachined electrostatically actuated valve has been demonstrated. A thermal flow sensor was integrated with the valve to be used for feedback control. Two modes, actuation voltage adjustment and PWM were investigated in characterizing the valve to control air flow. The testing results show that PWM has better linearity and performance.
\r\n\r\nThree types of capacitive fluidic sensors were demonstrated in several microfluidic applications. These include sensors for fluid pressure, flow rate, volume, and composition measurement. The sensors showed great promise for microfluidic applications because of their high sensitivity and easy integration capabilities. The integration of these sensors with abovementioned devices was achieved.
\r\n\r\nA novel electrochemical pumping system for on-chip LC gradient generation was demonstrated. This pump was able to deliver significant flow rates under high back pressures that are sufficient for many LC applications. On-chip gradient formation with integrated electrospray ionization was demonstrated.
\r\n\r\nFinally, a complete LC-ESI system was integrated in a chip format. Typical nano-LC reversed-phase gradient elution was demonstrated using on-chip electrolysis pump. Separated analytes from on-chip column were then sprayed into MS for analysis through an integrated ESI-nozzle. Separation results are comparable to those of commercial system. Peptide identification performance using the LC-ESI chip with MS was also very close to those achieved by the commercial system.
" }, { "name": "Xu, Donghua", "degree": "PhD", "year": "2005", "title": "Development of Novel Binary and Multi-Component Bulk Metallic Glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272005-160315", "creators": [ { "name": { "family": "Xu", "given": "Donghua" }, "id": "Xu-Donghua", "orcid": "0000-0001-5018-5603", "display_name": "Xu, Donghua" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Conner", "given": "Robert Dale" }, "id": "Conner-R-D", "role": "member", "display_name": "Conner, Robert Dale" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "matsci" ], "doi": "10.7907/XD2M-WW51", "abstract": "Bulk Metallic Glasses (BMGs) have been drawing increasing attention in recent years due to their scientific and engineering significance. A great deal of effort in this area has been devoted to developing BMGs in different alloy systems. BMGs based on certain late transition metals (e.g. Fe, Co, Ni, Cu) have many potential advantages over those based on early transition metals. These include even higher strength and elastic modulii, and lower materials cost, to name a few, which are highly preferable for a broad application of BMGs as engineering materials. Nevertheless, these ordinary-late-transition-metal-based BMGs generally have quite limited glass-forming ability (GFA). In particular, for the Ni-based and Cu-based alloys reported prior to this research, the maximum casting thickness allowed to retain their amorphous structures is only ~2 mm (or lower) and ~5 mm (or lower), respectively.
\r\n\r\nDuring this research it was first found that certain quinary Ni-based alloys in the Ni-Cu-Ti-Zr-Al system can be cast into 5 mm diameter amorphous rods. This critical casting thickness is the highest for any reported Ni-based BMG\u2019s indicating that these alloys are the easiest metallic glass formers based on Ni discovered to date. Secondly, certain binary alloys in the Cu-Zr and Cu-Hf systems were found to form bulk glasses with casting thickness as high as 2 mm. The discovery of these binary BMGs was very surprising since it had been widely considered that only multi-component (containing at least three elements) alloys could form bulk metallic glasses. These new binary BMGs provide interesting subjects for future theoretical studies such as molecular dynamics simulations since they possess both the simplicity of binary alloys and the good GFA of multi-component BMGs. In fact, these binary BMGs have led to the third but perhaps the most significant progress during this research, i.e., the discovery of a family of Cu-based BMGs in the Cu-Zr-Al-Y system which possess a critical casting thickness up to 1 cm. These quaternary Cu-based alloys, together with some complicated Fe-based alloys reported by two other groups during the course of this research, are the first centimeter level BMGs based on the ordinary late transition metals.
\r\n\r\nThis thesis first reviews the fundamentals related to BMG development, then reports in detail the formation and properties of the above-mentioned binary and multi-component BMGs based on Ni and Cu. A generalized geometric model for the critical-value problem of nucleation developed in this research is also presented.
" }, { "name": "Yang, Lan", "degree": "PhD", "year": "2005", "title": "Fabrication and Characterization of Microlasers by the Sol-Gel Method", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032005-115306", "creators": [ { "name": { "family": "Yang", "given": "Lan" }, "id": "Yang-Lan", "orcid": "0000-0002-9052-0450", "display_name": "Yang, Lan" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yang", "given": "Changhuei" }, "id": "Yang-Changhuei", "role": "member", "display_name": "Yang, Changhuei" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/HHQ8-VC25", "abstract": "The present study explores the application of new materials systems for low threshold microlasers, and characterization of the microcavities. The sol-gel method is used for gain functionalization of high-Q microcavities. A detailed procedure for preparation of the sol-gel films by the spin-on or dip-coating method is presented. The effect of different process conditions on the properties and microstructure of the thin films is investigated through Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), and etching rate test.
\r\n\r\nSurface gain functionalization of microsphere cavities is fabricated by coating the microsphere with a thin layer of Er\u00b3\u207a-doped sol-gel films. The optical gain is due to the population inversion of rare earth ions in the sol-gel films. A fiber taper is used to both couple the pump power into and extract the laser power out of the microsphere laser. The laser dynamics change between continuous-wave and pulsating operation by varying the doping concentration and the thickness of the sol-gel films outside the microsphere.
\r\n\r\nSurface functionalization is also achieved on the microtoroid on a single silicon chip, which can be fabricated in parallel using wafer-scale processing and has characteristics that are more easily controlled than microsphere. The microtoroid can be selectively coated only at the periphery by making use of the variation of etching rate (in buffered HF) of sol-gel films with different degrees of densification. The laser performance of the gain functionalized microtoroids is investigated. Highly confined whispering gallery modes make possible single-mode microlasers. This work also shows that the high Q microtoroid laser has a linewidth much lower than 300 kHz.
\r\n\r\nThe thesis explores fabrication of high Q microcavities directly from the sol-gel silica films deposited on a single silicon wafer. Quality factor as high as 2.5 x 10\u2077 at 1561 nm is obtained in toroidal microcavities formed of silica sol-gel, which allows Raman lasing at absorbed pump power below 1 mW. Additionally, Er\u00b3\u207a-doped microlasers are fabricated from Er\u00b3\u207a-doped sol-gel layers with control of the laser dynamics possible by varying the erbium concentration of the starting sol-gel material. Continuous lasing with a record threshold of 660 nW for erbium-doped microlaser on a silicon wafer is also obtained.
\r\n\r\nAnalytic formulas are derived to predict the laser performance, such as the laser output power, the threshold power, and the differential quantum efficiency, under different loading condition, i.e. the air gap between the fiber-taper coupler and the cavities. The effect of Er3+ concentration on the minimum threshold is also investigated. In addition, we present a theoretical model in which we include paired ions as the saturable absorber. It shows that self-pulsing operation can be expected with paired-ions-induced quenching in the system. The pulsation frequency increases linearly with the square root of the pumping level, which is consistent with the experimental observation.
" }, { "name": "Yavari, Arash", "degree": "PhD", "year": "2005", "title": "Atomic Structure of Ferroelectric Domain Walls, Free Surfaces and Steps", "advisor": "Ortiz, Michael; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-12142004-121255", "creators": [ { "name": { "family": "Yavari", "given": "Arash" }, "id": "Yavari-Arash", "orcid": "0000-0002-7088-7984", "display_name": "Yavari, Arash" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/jdy3-1m77", "abstract": "The goal of this thesis is to develop a general framework for lattice statics analysis of defects in ferroelectric Perovskites. The techniques presented here are general and can be easily applied to other systems as well. We present all the calculations and numerical examples for two technologically important ferroelectric materials, namely, PbTiO3 and BaTiO3. We use shell potentials, that are derived using quantum mechanics calculations, and analyze three types of defects: (i) 180\u00b0 and 90\u00b0 domain walls, (ii) free surfaces and (iii) steps in 180\u00b0 domain walls. Our formulation assumes that an interatomic potential is given. In other words, there is no need to have the force constants or restrict the number of nearest neighbor interactions a priori. Depending on the defect and symmetry, the discrete governing equations are reduced to those for representatives of some equivalence classes. The idea of symmetry reduction in lattice statics calculations is one of the contributions of this thesis. We call our formulation of lattice statics 'inhomogeneous lattice statics' as we consider the fact that close to defects force constants (stiffness matrices) change. For defects with one-dimensional symmetry reduction we solve the discrete governing equations directly using a novel method in the setting of the theory of difference equations. This will be compared with the solutions obtained using discrete Fourier transform. For defects with two-dimensional symmetry reduction we solve the discrete governing equations using discrete Fourier transform. We calculate the fully nonlinear solutions using modified Newton-Raphson iterations and call the method 'inhomogeneous anharmonic lattice statics'. This work is aimed to fill the gap between quantum mechanics ab initio calculations and continuum models (based on Landau-Ginzberg-Devonshire theory) of ferroelectric domain walls." }, { "name": "Yu, Xinwei", "degree": "PhD", "year": "2005", "title": "Localized Non-bBlowup Conditions for 3D Incompressible Euler Flows and Related Equations", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302005-161405", "creators": [ { "name": { "family": "Yu", "given": "Xinwei" }, "id": "Yu-Xinwei", "display_name": "Yu, Xinwei" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/K5E1-W938", "abstract": "In this thesis, new results excluding finite time singularities with localized assumptions/conditions are obtained for the 3D incompressible Euler equations.
\r\n\r\nThe 3D incompressible Euler equations are some of the most important nonlinear equations in mathematics. They govern the motion of ideal fluids. After hundreds of years of study, they are still far from being well-understood. In particular, a long-outstanding open problem asks whether finite time singularities would develop for smooth initial values. Much theoretical and numerical study on this problem has been carried out, but no conclusion can be drawn so far.
\r\n\r\nIn recent years, several numerical experiments have been carried out by various authors, with results indicating possible breakdowns of smooth solutions in finite time. In these numerical experiments, certain properties of the velocity and vorticity field are observed in near-singular flows. These properties violate the assumptions of existing theoretical theorems which exclude finite time singularities. Thus there is a gap between current theoretical and numerical results. To narrow this gap is the main purpose of the work presented in this thesis.
\r\n\r\nIn this thesis, a new framework of investigating flows carried by divergence-free velocity fields is developed. Using this new framework, new, localized sufficient conditions for the flow to remain smooth are obtained rigorously. These new results can deal with fast shrinking large vorticity regions and are applicable to recent numerical experiments. The application of the theorems in this thesis reveals new subtleties, and yields new understandings of the 3D incompressible Euler flow.
\r\n\r\nThis new framework is then further applied to a two-dimensional model equation, the 2D quasi-geostrophic equation, for which global existence is still unproved. Under certain assumptions, we obtain new non-blowup results for the 2D quasi-geostrophic equation.
\r\n\r\nFinally, future plans of applying this new framework to some other PDEs as well as other possibilities of attacking the 3D Euler and 2D quasi-geostrophic singularity problems are discussed.
" }, { "name": "Zhang, Qingsong", "degree": "PhD", "year": "2005", "title": "Atomistic Simulation of Barium Titanate", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292004-152709", "creators": [ { "name": { "family": "Zhang", "given": "Qingsong" }, "id": "Zhang-Qingsong", "display_name": "Zhang, Qingsong" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Cagin", "given": "Tahir" }, "id": "Cagin-Tahir", "role": "member", "display_name": "Cagin, Tahir" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "matsci" ], "doi": "10.7907/SQ9J-4H73", "abstract": "We present the Polarizable Charge Equilibration (P-QEq) force field to include self-consistent atomic polarization and charge transfer in molecular dynamics of materials. The short-range Pauli repulsion effects are described by two body potentials without exclusions. A linear self-consistent field solution to the charge transfer is proposed for charge transfer in large systems. The P-QEq is parameterized for BaTiO\u2083 based on quantum mechanics calculations (DFT with GGA) and applied to the study of the phase transitions, domain walls and oxygen vacancies.
\r\n\r\nFrozen phonon analysis reveals that the three high-temperature BaTiO\u2083 phases in the displacive model are unstable. Within their corresponding macroscopic phase symmetries, the smallest stable phase structures are achieved by antiferroelectric distortions from unstable phonons at the Brillouin zone boundaries. The antiferroelectric distortions soften phonons, reduce zero point energies and increase vibrational entropies. A correct BaTiO\u2083 phase transition sequence and comparable transition temperatures are obtained by free energy calculations. The inelastic coherent scattering functions of these phases agree with X-ray diffraction experiments.
\r\n\r\nBaTiO\u2083 180\u00b0 domain wall is Ba-centered with abrupt polarization switching across the wall. The center of BaTiO\u2083 90\u00b0 domain wall is close to its orthogonal phase. There are transition layers from the wall centers to the internal domains in the types of domain walls. Polarization variation in these transition layers induces polarization charge and free charge transfer. This effect causes a strong bipolar electric field in BaTiO\u2083 90\u00b0 domain wall.
\r\n\r\nOxygen vacancies are frozen at room temperature, and mobile near the Curie temperature. In the tetragonal phase, the broken Ti-O chains are frozen, reducing switchable polarization. Due to charge redistribution and local relaxation, oxygen vacancy interaction is short-range and anisotropic. Two oxygen vacancies can form a stable pair state, where two broken Ti-O chains are aligned parallel. Oxygen vacancy clusters can form dendritic structures as a result of local relaxation and charge interaction.
" }, { "name": "Zhou, Jijie", "degree": "PhD", "year": "2005", "title": "Nanowicking: Multi-scale Flow Interaction with Nanofabric Structures", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-04202005-172426", "creators": [ { "name": { "family": "Zhou", "given": "Jijie" }, "id": "Zhou-Jijie", "display_name": "Zhou, Jijie" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Noca", "given": "Flavio" }, "id": "Noca-F", "role": "member", "display_name": "Noca, Flavio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "bioeng" ], "doi": "10.7907/XMW0-DJ25", "abstract": "Dense arrays of aligned carbon nanotubes are designed into strips \u2014 nanowicks \u2014 as a miniature wicking element for liquid delivery and potential microfluidic chemical analysis devices. The delivery function of nanowicks enables novel fluid transport devices to run without any power input, moving parts or external pump. The intrinsically nanofibrous structure of nanowicks provides a sieving matrix for molecular separations, and a high surface-to-volume ratio porous bed to carry catalysts or reactive agents.
\r\n\r\nThis work also experimentally studies the spontaneous fluid transport along nanowicks. Liquid is conveyed through corner flow, surface flow, and interstitial flow through capillary force and the Marangoni effect. The main course for corner flow and surface flow follows Washburn behavior, and can deliver liquid centimeters away from the input blob with a speed on the order of millimeters per second depending on the nanowick configuration and the amount of input liquid. Corner flow can be minimized and even eliminated through proper nanowick and input design. Otherwise, corner flow interacts with surface flow in the first 2mm of the pathway closest to the input point. Interstitial flow dominates the late stage. It is driven by both capillary force and concentration-gradient-induced Marangoni force. The concentration gradient is determined by two competing rates: surfactant diffusion in solution and adsorption onto nanotube surfaces. The flow inside nanowicks may wick hundreds of microns in seconds or tens of seconds. A non-conventional advancing front may develop in the flow around nanowicks. They are seen as (i) Rayleigh instability-induced fingering in surface flow on millimeter-wide nanowicks, (ii) viscous instability-induced branching near almost-stagnant surface film at low surfactant concentration, and (iii) disjointed wetting domains at very low concentration.
" }, { "name": "Adams, Mark Lee", "degree": "PhD", "year": "2004", "title": "Integration of Optoelectronics and Microfluidics for Biological and Chemical Sensing", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162003-151751", "creators": [ { "name": { "family": "Adams", "given": "Mark Lee" }, "id": "Adams-Mark-Lee", "orcid": "0000-0003-0536-8325", "display_name": "Adams, Mark Lee" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "member", "display_name": "Quake, Stephen R." }, { "name": { "family": "Anderson", "given": "W. French" }, "id": "Anderson-W-F", "role": "member", "display_name": "Anderson, W. French" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JVSC-D109", "abstract": "Over the past decade, rapid advances in microfluidics have led to the creation of valves, pumps, mixers, multiplexers, along with a large variety of other devices. This technology has allowed for many fluidics applications to be performed on a chip that is approximately an inch square in area. Such applications include cell sorting, PCR on chip, crystal growth, combinatorial mixing and many others. Although the complexity of these devices may seem overwhelming, they are based on simple process called multilayer soft lithography, which uses a silicone-based elastomer to create these amazing devices. However, with the current state of technology, the applications are somewhat limited. New devices need to be created to further such fields as fluidic logic and biomimetics.
\r\n\r\nAnother major issue that challenges true acceptance of microfluidics is the need for a typically large interrogation setup to determine what is actually happening in the flow cell. In general, a microfluidic chip is placed under a bench top optical microscope in order to perform either colorimetric, absorption, or luminescence spectroscopy. Through these methods everything from cells to chemicals can be identified; however, a true lab-on-a-chip must not rely on something as cumbersome as a microscope. Integrated sensors must be developed to truly make lab-on-a-chip reasonable.
\r\n\r\nThrough this thesis, several approaches for realization of integrated optoelectronic microfluidic systems are presented. The systems are capable of performing optical interrogation of analyte, from both outside of the flow cell as well as directly inside a flow channel. Also, some novel microfluidic devices which should pave the way for greater advancement in the field of microfluidics are discussed. Through the technologies presented, true lab-on-a-chip systems should be even closer to realization.
" }, { "name": "Aparicio Joo, Roberto", "degree": "PhD", "year": "2004", "title": "Frequency Generation Techniques for Integrated Applications", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-06052004-180113", "creators": [ { "name": { "family": "Aparicio Joo", "given": "Roberto" }, "id": "Aparicio-Joo-Roberto", "orcid": "0000-0003-2910-9969", "display_name": "Aparicio Joo, Roberto" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/S2EP-3A93", "abstract": "This thesis presents novel oscillator topologies and passive structures that demonstrate improvements in performance compared to existing devices in CMOS. The contributions of this work include the development of original topologies and concepts together with practical implications in the area of integrated frequency generation.
\r\n\r\nA noise-shifting differential Colpitts oscillator topology is proposed. It is less sensitive to noise generated by the active devices than commonly used integrated oscillator topologies such as NMOS- or PMOS-only, and complementary cross-coupled. This is achieved through cyclostationary noise alignment while providing a fully differential output and large loop gain for reliable start up. An optimization strategy is derived for this oscillator that is used in the implementation of a CMOS prototype. The performance of this oscillator is compared to traditional topologies and previously published integrated oscillators achieving lower phase noise and some of the highest figures of merit, respectively.
\r\n\r\nA new circular-geometry oscillator topology is introduced. It allows the implementation of slab inductors for high-frequency and low-phase noise oscillator applications. Slab inductors present an attractive alternative for monolitic applications where low loss, low impedance, and high self-resonance integrated inductors are required. A general methodology to ensure the proper oscillation mode when several oscillator cores are coupled in a circular-geometry as well as to achieve a stable dc bias point is offered. Several circular-geometry CMOS integrated oscillator prototypes are presented as a proof of concept and their performances are compared to previously published high frequency oscillators achieving some of the best figures of merit.
\r\n\r\nTheoretical limits for the capacitance density of integrated capacitors with combined lateral and vertical field components are derived. These limits are used to investigate the efficiency of various capacitive structures such as lateral flux and quasi-fractal capacitors. This study leads to two new capacitor structures with high lateral-field efficiencies. These new capacitors demonstrate larger capacities, superior matching properties, tighter tolerances, and higher self-resonance frequencies than the standard horizontal parallel plate and previously reported lateral-field capacitors, while maintaining comparable quality factors. These superior qualities are verified by simulation and experimental results.
\r\n\r\nFinally, three phase-locked-loops (PLL) are presented. A 6.6GHz PLL for applications in a concurrent dual-band CMOS receiver is described. Careful frequency planning allows the generation of the three local oscillator signals required by the entire receiver using only one PLL, reducing power consumption and chip area considerably. The design issues of an ultra-low-power PLL prototype implemented in a sub-micron CMOS process are also discussed. The design of a low-power 3.2GHz PLL implementing a phase-compensation technique for fractional-N frequency synthesis is described. It uses an on-chip delay-locked-loop tuning scheme that attenuates the fractional spur independent of the output frequency and process variations.
" }, { "name": "Aydiner, Cahit Can", "degree": "PhD", "year": "2004", "title": "Investigation of Thermal Tempering in Bulk Metallic Glasses", "advisor": "Ustundag, Ersan", "url": "https://resolver.caltech.edu/CaltechETD:etd-04192004-120604", "creators": [ { "name": { "family": "Aydiner", "given": "Cahit Can" }, "id": "Aydiner-Cahit-Can", "orcid": "0000-0001-8256-6742", "display_name": "Aydiner, Cahit Can" } ], "advisors": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "advisor", "display_name": "Ustundag, Ersan" } ], "committee": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "chair", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ZC9Z-5Y06", "abstract": "Bulk metallic glasses are recent advanced materials which generate residual stresses due to rapid cooling from their surfaces during processing. These stresses arise from the thermal gradients that form within the sample at and above the glass transition region. A typical processing of BMGs involves feeding the alloy melt into a mold followed by severe quenching. The formation and nature of these stresses are analogous to the residual stresses due to the thermal tempering of silicate glasses. This analytical-experimental study investigates the thermal tempering phenomenon in BMGs for the first time.
\r\n\r\nOne of the best glass forming metallic alloys, Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vitreloy 1TM), is employed in this study. First, the best technique for the high-resolution measurement of residual stresses in BMGs is determined to be the crack compliance method. Second, the formation of the stresses is modeled with three different levels of viscoelastic phenomenology, namely, an instant freezing model, a viscoelastic model and a structural model. The first is a simplistic analytical model to estimate residual stresses whereas the structural model accounts for the temperature history dependence of the glassy structure. The constitutive laws for the viscoelastic and structural models are incorporated into the finite element method (ABAQUSTM software package) allowing the application of these models to complex geometries. To increase the accuracy of the analysis, the 'correct' temperature evolution in the sample during processing has to be input to these 'mechanical' models. Therefore, the heat transfer problem during the casting process of the BMG is analyzed in detail. Accuracy also requires a detailed knowledge of the thermal parameters of the material as a function of temperature; thus, some attention is also devoted to their measurement.
\r\n \r\nAt the end, calculated and measured stresses are compared and good agreement is achieved. BMGs are demonstrated to be capable of generating very high (around 400 MPa) compression on their surfaces. The study also yielded valuable physical insight into the thermal tempering process itself. It is seen that this process exhibits significant discrepancies in BMGs compared to its analogy in silicate glasses. For instance, the transient tensile stresses that develop in the latter are shown to be lacking in the BMGs. Another discrepancy between the two materials is that the density of BMGs is uniform across the sample cross section in contrast to that found in silicate glasses. Overall, this investigation developed sufficient understanding of the thermal tempering phenomenon in BMGs to establish it as a viable process to manipulate properties.
\r\n" }, { "name": "Barba, Lorena A.", "degree": "PhD", "year": "2004", "title": "Vortex Method for Computing High-Reynolds Number Flows: Increased Accuracy with a Fully Mesh-Less Formulation", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-030854", "creators": [ { "name": { "family": "Barba", "given": "Lorena A." }, "id": "Barba-Lorena-A", "orcid": "0000-0001-5812-2711", "display_name": "Barba, Lorena A." } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TSR5-DE67", "abstract": "For the applications of high Reynolds number flows, the vortex method presents the advantage of being free from numerically dissipative truncation error. In practice, however, many vortex methods introduce some numerical dissipation in mesh-based spatial adaption stages, or schemes such as vortex particle splitting. The need for spatial adaption in vortex methods arises from the Lagrangian framework, which results in an increase of discretization error over time. Presently, a vortex method is devised that incorporates radial basis function (RBF) interpolation to provide spatial adaption in a fully mesh-less formulation. Numerical experiments show that there is a potential for higher accuracy in comparison with the standard remeshing techniques. The rate of convergence of the new spatial adaption method is exponential, however convection error limits the vortex method to second order convergence. Avenues for future research involve decreasing convection error, for example by means of deformable basis functions. Nevertheless, the RBF-based spatial adaption scheme has various advantages, in addition to a demonstrated higher accuracy and the obvious benefit of not requiring a regular arrangement of particles or mesh. One presently demonstrated advantage is automatic core size control for the core spreading viscous method, without the need for vortex particle splitting.
\r\n\r\nThree applications have been successfully treated with the presently developed vortex method. The relaxation of monopoles under non-linear perturbations has been computed, resulting in noticeable improvements compared to previously published results. The existence of a quasi-steady state consisting of a rotating tripole has been corroborated, for the case of large amplitude perturbations. The second application consists of the early adaptation of two co-rotating vortices at high Reynolds number, characterized by elliptical deformation of the cores, as well as small scale deformation in the weak areas of vorticity. This is considered to pose a severe test on the present method, or indeed any method. Comparison with results using spectral methods demonstrate in practice the potential for high accuracy computations using a mesh-less method, and in addition show that the naturally adaptive vortex method can result in considerably reduced problem sizes. Finally, for the calculation of non-symmetric Burgers vortices, a correction to the core spreading method for out-of-plane strain was developed. The results establish the capability of the vortex method for the computation of vortices under three-dimensional strain.
" }, { "name": "Barsic, David Nicholas", "degree": "PhD", "year": "2004", "title": "Small-Scale Liquid-State Dynamics in Nanometer Size Devices", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-110405", "creators": [ { "name": { "family": "Barsic", "given": "David Nicholas" }, "id": "Barsic-David-Nicholas", "display_name": "Barsic, David Nicholas" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "George", "given": "Thomas" }, "id": "George-T", "role": "member", "display_name": "George, Thomas" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/BWJB-7K61", "abstract": "This dissertation will present research on state-of-the-art micrometer- and nanometer-scale machining techniques to fabricate fluid channels with integral sensing electrodes. The motivation for this project is to create new instruments for investigating the behavior and properties of particles or molecules in solution and confined in a fluid channel with cross-sectional dimensions ranging from less than 50 nanometers to one micron.
\r\n\r\nThe objective of this research is to develop techniques for building fluid analysis systems which combine fluid channels with sensing electrodes. Design of physical devices and the measurement circuit are both important steps in accomplishing this task. The design issues necessary for optimizing these aspects are investigated in detail. The size scale of these systems is at the lower limit achievable with current technology. Such devices require critical dimensions of less than 100 nanometers in order to perform measurements on small-scale fluid systems. Applications of this type of system include detection of both the presence and the motion of particles and molecules suspended in the small volume of fluid confined within the fluid channel. The motion of particles in the fluid channel is detected by measuring the change in electrode capacitance as particles move past the electrodes. Typical fluid volumes used in this type of system range from 50 femtoliters to less than one femtoliter.
\r\n\r\nAccomplishing this task required a careful look at the machining techniques for making microscopic devices. The approach is to use lithographic and circuit manufacturing techniques to make small fluid channels on either side of which are sets of electrodes. Existing techniques for making small-scale devices were modified to provide the required performance. In some cases the development of entirely new techniques was necessary.
" }, { "name": "Bobba, Kumar Manoj", "degree": "PhD", "year": "2004", "title": "Robust Flow Stability: Theory, Computations and Experiments in Near Wall Turbulence", "advisor": "Doyle, John Comstock; Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-143324", "creators": [ { "name": { "family": "Bobba", "given": "Kumar Manoj" }, "id": "Bobba-Kumar-Manoj", "display_name": "Bobba, Kumar Manoj" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "co-chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0J1D-1B18", "abstract": "Helmholtz established the field of hydrodynamic stability with his pioneering work in 1868. From then on, hydrodynamic stability became an important tool in understanding various fundamental fluid flow phenomena in engineering (mechanical, aeronautics, chemical, materials, civil, etc.) and science (astrophysics, geophysics, biophysics, etc.), and turbulence in particular. However, there are many discrepancies between classical hydrodynamic stability theory and experiments. In this thesis, the limitations of traditional hydrodynamic stability theory are shown and a framework for robust flow stability theory is formulated. A host of new techniques like gramians, singular values, operator norms, etc. are introduced to understand the role of various kinds of uncertainty. An interesting feature of this framework is the close interplay between theory and computations. It is shown that a subset of Navier-Stokes equations are globally, non-nonlinearly stable for all Reynolds number. Yet, invoking this new theory, it is shown that these equations produce structures (vortices and streaks) as seen in the experiments. The experiments are done in zero pressure gradient transiting boundary layer on a flat plate in free surface tunnel. Digital particle image velocimetry, and MEMS based laser Doppler velocimeter and shear stress sensors have been used to make quantitative measurements of the flow. Various theoretical and computational predictions are in excellent agreement with the experimental data. A closely related topic of modeling, simulation and complexity reduction of large mechanics problems with multiple spatial and temporal scales is also studied. A nice method that rigorously quantifies the important scales and automatically gives models of the problem to various levels of accuracy is introduced. Computations done using spectral methods are presented.\r\n" }, { "name": "Boysen, Dane Andrew", "degree": "PhD", "year": "2004", "title": "Superprotonic Solid Acids: Structure, Properties, and Applications", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-155105", "creators": [ { "name": { "family": "Boysen", "given": "Dane Andrew" }, "id": "Boysen-Dane-Andrew", "display_name": "Boysen, Dane Andrew" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Asimow", "given": "Paul David" }, "id": "Asimow-P-D", "role": "member", "display_name": "Asimow, Paul David" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/41BQ-3R07", "abstract": "In this work, the structure and properties of superprotonic MH\u2099XO\u2084-type solid acids (where M = monovalent cation, X = S, Se, P, As, and n = 1, 2) have been investigated and, for the first time, applied in fuel cell devices. Several MH\u2099XO\u2084-type solid acids are known to undergo a \"superprotonic\" solid-state phase transition upon heating, in which the proton conductivity increases by several orders of magnitude and takes on values of ~ 0.01 S/cm. The presence of superprotonic conductivity in fully hydrogen bonded solid acids, such as CsH\u2082PO\u2084, has long been disputed. In these investigations, through the use of pressure, the unequivocal identification of superprotonic behavior in both RbH\u2082PO\u2084 and CsH\u2082PO\u2084 has been demonstrated, whereas for chemically analogous compounds with smaller cations, such as KH\u2082PO\u2084 and NaH\u2082PO\u2084, superprotonic conductivity was notably absent. Such observations have led to the adoption of radius ratio rules, in an attempt to identify a critical ion size effect on the presence of superprotonic conductivity in solid acids. It has been found that, while ionic size does play a prominent role in the presence of superprotonic behavior in solid acids, equally important are the effects of ionic and hydrogen bonding. Next, the properties of superprotonic phase transition have been investigated from a thermodynamic standpoint. With contributions from this work, a formulation has been developed that accounts for the entropy resulting from both the disordering of both hydrogen bonds and oxy-anion librations in the superprotonic phase of solid acids. This formulation, fundamentally derived from Linus Pauling's entropy rules for ice, accurately accounts for the change in entropy through a superprotonic phase transition. Lastly, the first proof-of-principle fuel cells based upon solid acid electrolytes have been demonstrated. Initial results based upon a sulfate electrolyte, CsHSO\u2084, demonstrated the viability of solid acids, but poor chemical stability under the highly reducing H\u2082 gas environment of the fuel cell anode. Later experiments employing a CsH\u2082PO\u2084 electrolyte proved quite successful. The results of these solid acid-based fuel cell measurements suggest solid acids could serve as an alternative to current state-of-the-art fuel cell electrolytes." }, { "name": "Camp, Charles David", "degree": "PhD", "year": "2004", "title": "Temporal and Spatial Patterns of the Interannual Variability of Stratospheric Ozone and Dynamics", "advisor": "Yung, Yuk L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042004-131001", "creators": [ { "name": { "family": "Camp", "given": "Charles David" }, "id": "Camp-Charles-David", "orcid": "0000-0003-0295-7861", "display_name": "Camp, Charles David" } ], "advisors": [ { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "display_name": "Yung, Yuk L." } ], "committee": [ { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "chair", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "role": "member", "display_name": "Schneider, Tapio" }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/A4EC-6M08", "abstract": "This dissertation is a collection of empirical and modeling studies focusing on the interannual variability (IAV) of stratospheric ozone and the dynamics associated with that variability. Empirical analyses of the IAV of total column ozone in the tropics and midlatitudes are performed using the Merged Ozone Data (MOD) set. MOD combines the monthly mean column abundances collected by the Total Ozone Mapping Spectrometer and the Solar Backscatter Ultraviolet instruments, provides a nearly continuous record from late 1978 to present on a 2D grid. The first four EOFs from principal component analyses of MOD capture over 93% (82%) of the variance of the tropical (midlatitude) IAV. These analyses display structures attributable to the quasi-biennial oscillation (QBO), with influence from a decadal oscillation, an interaction between the QBO and an annual cycle (QBO-AB), and ENSO. Similar decompositions occur for dynamical fields from the NCEP/NCAR reanalysis. Using these analyses, we found possible connections between the deduced patterns in ozone and the climate variables. For comparison to the observations, a 2D chemistry and transport model (CTM) was used to simulate the ozone IAV. The NCEP/Department of Energy (DOE) Reanalysis 2 data are used to derive a monthly mean meridional circulation from 1979 to 2002 which is then used to drive the Caltech/JPL 2D CTM, allowing for an investigation of the impact of dynamics on the interannual variability (IAV) of the total column ozone for all years for which the MOD is available. The 2D CTM provides realistic simulations of the seasonal and IAV of ozone in the tropics, reasonable agreement in the NH midlatitudes but poor agreement in the SH midlatitudes. The influence of the QBO and QBO-AB are well represented in the simulation. A 71-year record of column ozone from Arosa, Switzerland is analyzed using singular spectrum analysis (SSA). The SSA decomposition separates the signals from the seasonal cycle, QBO, QBO-AB, and decadal oscillations. A 3.5-year oscillation is also discovered. A nonlinear trend is extracted and nonstationary behavior of some of the oscillations is found. Finally, a connection between fluctuations in stratospheric ozone and in tropospheric methane is observed and modeled." }, { "name": "Cao, Shiyan", "degree": "PhD", "year": "2004", "title": "Spike Train Characterization and Decoding for Neural Prosthetic Devices", "advisor": "Burdick, Joel Wakeman; Andersen, Richard A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07232003-012018", "creators": [ { "name": { "family": "Cao", "given": "Shiyan" }, "id": "Cao-Shiyan", "display_name": "Cao, Shiyan" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "co-advisor", "display_name": "Andersen, Richard A." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/GK20-5W75", "abstract": "Neural prosthetic device has the potential of benefiting millions of lock-in and spinal cord injury survivors. One branch of the ongoing research is to construct reach movement based prosthetic devices. This thesis proposes statistical methods based on applying the Haar wavelet packets to spike trains in order to answer some of the questions in this field.
\r\n\r\nAlthough spike train is the most frequently used data in the neural science community, its stochastic properties are not fully understood or characterized. This thesis suggests a formal spike train characterization method using the Haar wavelet packet. Because of the multi-scale property of the wavelet packet, Poisson characteristics at different scales can be assessed. Moreover, Poisson Scale-gram is proposed to help visualize the characteristics of the spike train at different scales.
\r\n\r\nBecause some neurons display non-Poisson characteristics, it is necessary to extract the relevant features from spike trains in the context of decoding. The thesis suggests a feature extraction method that searches all the wavelet packet coefficients for the ones with the largest discriminability, quantified by mutual information. This technique returns the most informative feature(s) in the context of the Bayesian classifier. Decoding performance of this proposed method is compared against the one using mean firing rate only on both surrogate data and the actual data from PRR.
\r\n\r\nIt is also crucial to decode cognitive states because they provide the extra control signals necessary for practical implementation of the prosthetic devices. This thesis proposes a simple finite state machine approach along with an interpreter that interprets the decoding results and to regulate when the transition should occur. It demonstrates that the finite state machine framework, when coupled with the interpreter, offers a simple autonomous control scheme for the neuron prosthetic system envisioned.
\r\n\r\nWhile the neural prosthetic system is in its infancy, many theoretical and experimental works lay the foundation for a bright future in this field. This thesis answers the spike train characterization and decoding questions in a theoretical manner while offering several novel techniques that bring new ideas and insights into the research field.
" }, { "name": "Chao, Tong Wa", "degree": "PhD", "year": "2004", "title": "Gaseous Detonation-Driven Fracture of Tubes", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04062004-165940", "creators": [ { "name": { "family": "Chao", "given": "Tong Wa" }, "id": "Chao-Tong-Wa", "display_name": "Chao, Tong Wa" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TEZP-YC46", "abstract": "An experimental investigation of fracture response of aluminum 6061-T6 tubes under internal gaseous detonation loading has been carried out. The pressure load, with speeds exceeding 2 km/s, can be characterized as a pressure peak (ranging from 2 to 6 MPa) followed by an expansion wave. The unique combination of this particular traveling load and tube geometry produced fracture data not available before in the open literature. Experimental data of this type are useful for studying the fluid-structure-fracture interaction and various crack curving and branching phenomena, and also for validation for multi-physics and multi-scale modeling.
\r\n\r\nAxial surface flaws were introduced to control the crack initiation site. Fracture threshold models were developed by combining a static fracture model and an extensively studied dynamic amplification factor for tubes under internal traveling loads. Experiments were also performed on hydrostatically loaded preflawed aluminum 6061-T6 tubes for comparison. Significantly different fracture behavior was observed and the difference was explained by fluid dynamics and energy considerations. The experiments yielded comparison on crack speeds, strain, and pressure histories.
\r\n\r\nIn other experiments, the specimens were also pre-torqued to control the propagation direction of the cracks. Measurements were made on the detonation velocity, strain history, blast pressure from the crack opening, and crack speeds. The curved crack paths were digitized. The Chapman-Jouguet pressure, initial axial flaw length, and torsion level were varied to obtain different crack patterns. The incipient crack kinking angle was found to be consistent with fracture under mixed-mode loading. High-speed movies of the fracture events and blast wave were taken and these were used in interpreting the quantitative data.
\r\n\r\nNumerical simulations were performed using the commercial explicit finite-element software LS-Dyna. The detonation wave was modeled as a traveling boundary load. Both non-fracturing linear elastic simulations and elastoplastic simulations with fracture were conducted on three-dimensional models. The simulated fracture was compared directly with an experiment with the same conditions. The overall qualitative fracture behavior was captured by the simulation. The forward and backward cracks were observed to branch in both the experiment and simulation.
" }, { "name": "Chaubell, Mario Juli\u00e1n", "degree": "PhD", "year": "2004", "title": "Low-Coherence Interferometric Imaging: Solution of the One-Dimensional Inverse Scattering Problem", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09092003-212358", "creators": [ { "name": { "family": "Chaubell", "given": "Mario Juli\u00e1n" }, "id": "Chaubell-Mario-Juli\u00e1n", "orcid": "0000-0002-8067-6988", "display_name": "Chaubell, Mario Juli\u00e1n" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/ED7Y-Q436", "abstract": "Optical coherence tomography (OCT) is a non-invasive imaging technique based on the use of light sources exhibiting a low degree of coherence. Low coherence interferometric microscopes have been successful in producing internal images of thin pieces of biological tissue; typically samples of the order of 1 milimeter in depth have been imaged, with a resolution of the order of 10 to 20 microns in some portions of the sample. In this thesis, I deal with the imaging problem of determining the internal structure of a body from backscattered laser light and low-coherence interferometry. In detail, I formulate and solve an inverse problem which, using the interference fringes that result as the back-scattering of low-coherence light is made to interfere with a reference beam, produces maps detailing the values of the refractive index within the imaged sample. Unlike previous approaches to this imaging problem, the solver I introduce does not require processing at data collection time, and it can therefore produce solutions for inverse problems of multi-layered structures containing thousands of layers from back-scattering interference fringes only. We expect that the approach presented in this work, which accounts fully for the statistical nature of the coherence phenomenon, should prove of interest in the fields of medicine, biology and materials science." }, { "name": "Chenchiah, Isaac Vikram", "degree": "PhD", "year": "2004", "title": "Energy-Minimizing Microstructures in Multiphase Elastic Solids", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252004-131315", "creators": [ { "name": { "family": "Chenchiah", "given": "Isaac Vikram" }, "id": "Chenchiah-Isaac-Vikram", "orcid": "0000-0002-8618-620X", "display_name": "Chenchiah, Isaac Vikram" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/RXE5-9A33", "abstract": "This thesis concerns problems of microstructure and its macroscopic consequences in multiphase elastic solids, both single crystals and polycrystals.
\r\n\r\nThe elastic energy of a two-phase solid is a function of its microstructure. Determining the infimum of the energy of such a solid and characterizing the associated extremal microstructures is an important problem that arises in the modeling of the shape memory effect, microstructure evolution (precipitation, coarsening, etc.), homogenization of composites and optimal design. Mathematically, the problem is to determine the relaxation under fixed volume fraction of a two-well energy.
\r\n\r\nWe compute the relaxation under fixed volume fraction for a two-well linearized elastic energy in two dimensions with no restrictions on the elastic moduli and transformation strains; and show that there always exist rank-I or rank-II laminates that are extremal. By minimizing over the volume fraction we obtain the quasiconvex envelope of the energy. We relate these results to experimental observations on the equilibrium morphology and behavior under external loads of precipitates in Nickel superalloys. We also compute the relaxation under fixed volume fraction for a two-well linearized elastic energy in three dimensions when the elastic moduli are isotropic (with no restrictions on the transformation strains) and show that there always exist rank-I, rank-II or rank-III laminates that are extremal.
\r\n\r\nShape memory effect is the ability of a solid to recover on heating apparently plastic deformation sustained below a critical temperature. Since utility of shape memory alloys critically depends on their polycrystalline behavior, understanding and predicting the recoverable strains of shape memory polycrystals is a central open problem in the study of shape memory alloys. Our contributions to the solution of this problem are twofold:
\r\n\r\nWe prove a dual variational characterization of the recoverable strains of shape memory polycrystals and show that dual (stress) fields could be signed Radon measures with finite mass supported on sets with Lebesgue measure zero. We also show that for polycrystals made of materials undergoing cubic-tetragonal transformations the strains fields associated with macroscopic recoverable strains are related to the solutions of hyperbolic partial differential equations.
" }, { "name": "Clinton, John Francis", "degree": "PhD", "year": "2004", "title": "Modern Digital Seismology: Instrumentation, and Small Amplitude Studies in the Engineering World", "advisor": "Heaton, Thomas H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202004-225044", "creators": [ { "name": { "family": "Clinton", "given": "John Francis" }, "id": "Clinton-John-Francis", "orcid": "0000-0001-8626-2703", "display_name": "Clinton, John Francis" } ], "advisors": [ { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "advisor", "display_name": "Heaton, Thomas H." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Tromp", "given": "Jeroen" }, "id": "Tromp-J", "role": "member", "display_name": "Tromp, Jeroen" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/DVSS-2290", "abstract": "The recording of ground motions is a fundamental part of both seismology and earthquake engineering. The current state-of-the-art 24-bit continuously recording seismic station is described, with particular attention to the frequency range and dynamic range of the seismic sensors typically installed. An alternative method of recording the strong-motions would be to deploy a velocity sensor rather than an accelerometer. This instrument has the required ability to measure the strongest earth motions, with enhanced long period sensitivity.
\r\n\r\nAn existing strong motion velocity sensor from Japan was tested for potential use in US seismic networks. It was found to be incapable of recording strong motions typically observed in the near source of even moderate earthquakes. The instrument was widely deployed near the M8.3 Sept 2003 Tokachi-Oki earthquake. The dataset corroborated our laboratory observations of low velocity saturations. The dataset also served to show all inertial sensors are equally sensitive to tilting, which is widespread in large earthquakes. High rate GPS data is also recorded during the event. Co-locating high-rate GPS with strong motion sensors is suggested to be currently the optimal method by which the complete and unambiguous deformation field at a station can be recorded.
\r\n\r\nA new application of the modern seismic station is to locate them inside structures. A test station on the 9th floor of Millikan Library is analysed. The continuous data-stream facilitates analysis of the building response to ambient weather, forced vibration tests, and small earthquakes that have occurred during its lifetime. The structure's natural frequencies are shown to be sensitive not only to earthquake excitation, but rainfall, temperature and wind. This has important implications on structural health monitoring, which assumes the natural frequencies of a structure do not vary significantly unless there is structural damage.
\r\n\r\nModerate to small earthquakes are now regularly recorded by dense, high dynamic range networks. This enhanced recording of the earthquake and its aftershock sequences makes possible the development of a Green's Function deconvolution approach for determining rupture parameters.
" }, { "name": "Cooper, Marcia Ann", "degree": "PhD", "year": "2004", "title": "Impulse Generation by Detonation Tubes", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252004-164627", "creators": [ { "name": { "family": "Cooper", "given": "Marcia Ann" }, "id": "Cooper-Marcia-Ann", "orcid": "0000-0003-0831-6109", "display_name": "Cooper, Marcia Ann" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/97GS-4N79", "abstract": "Impulse generation with gaseous detonation requires conversion of chemical energy into mechanical energy. This conversion process is well understood in rocket engines where the high pressure combustion products expand through a nozzle generating high velocity exhaust gases. The propulsion community is now focusing on advanced concepts that utilize non-traditional forms of combustion like detonation. Such a device is called a pulse detonation engine in which laboratory tests have proven that thrust can be achieved through continuous cyclic operation. Because of poor performance of straight detonation tubes compared to conventional propulsion systems and the success of using nozzles on rocket engines, the effect of nozzles on detonation tubes is being investigated. Although previous studies of detonation tube nozzles have suggested substantial benefits, up to now there has been no systematic investigations over a range of operating conditions and nozzle configurations. As a result, no models predicting the impulse when nozzles are used exist. This lack of data has severely limited the development and evaluation of models and simulations of nozzles on pulse detonation engines.
\r\n\r\nThe first experimental investigation measuring impulse by gaseous detonation in plain tubes and tubes with nozzles operating in varying environment pressures is presented. Converging, diverging, and converging-diverging nozzles were tested to determine the effect of divergence angle, nozzle length, and volumetric fill fraction on impulse. The largest increases in specific impulse, 72% at an environment pressure of 100 kPa and 43% at an environment pressure of 1.4 kPa, were measured with the largest diverging nozzle tested that had a 12 degree half angle and was 0.6 m long. Two regimes of nozzle operation that depend on the environment pressure are responsible for these increases and were first observed from these data. To augment this experimental investigation, all data in the literature regarding partially filled detonation tubes was compiled and analyzed with models investigating concepts of energy conservation and unsteady gas dynamics. A model to predict the specific impulse was developed partially filled tubes. The role of finite chemical kinetics in detonation products was examined through numerical simulations of the flow in nonsteady expansion waves.
" }, { "name": "Dugatkin, Diego G.", "degree": "PhD", "year": "2004", "title": "Optimization of Multi-Resolution Source Codes", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022004-013457", "creators": [ { "name": { "family": "Dugatkin", "given": "Diego G." }, "id": "Dugatkin-Diego-G", "display_name": "Dugatkin, Diego G." } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Chan", "given": "Tony F-C" }, "id": "Chan-T-F", "role": "member", "display_name": "Chan, Tony F-C" } ], "option_major": [ "eleceng" ], "doi": "10.7907/RZ2Y-1Z78", "abstract": "This thesis studies the optimization of multi-resolution source codes. A multi-resolution source code is a data compression algorithm that generates a bit-stream that can be truncated at any point to reconstruct low-resolution representations of the original data. By progressively refining the description, these codes allow the receiver to get representations of progressively increasing quality from a single file.
\r\n\r\nThe optimization methods presented here are based on the minimization of a Lagrangian performance measure, which is a weighted sum of rates and distortions at the different resolutions of the multi-resolution code. The Lagrangian coefficients are the weights that parameterize the priorities assigned to the resolutions. The relative value of these parameters can be set according to the user's preferences regarding which rates are more important, the probability of decoding the file at each possible rate, or any other prioritization rationale. We present a method for converting design constraints into the corresponding Lagrangian parameters.
\r\n\r\nWe also use a Lagrangian analysis to investigate optimality properties of multi-resolution codes. Specifically, we explore the characterization of the theoretically optimal output density functions of a two-resolution source code for any arbitrary set of priorities over the resolutions.
\r\n\r\nOnce the priority function has been identified, the goal is to design the multi-resolution code that yields the best rate-distortion trade-off for those priorities. The minimization of the multi-resolution Lagrangian is somewhat specific to the framework and type of multi-resolution code. We pursue this goal in several coding frameworks.
\r\n\r\nThe first framework is the multi-resolution vector quantizer (MRVQ) framework. Prior work on the topic described optimal MRVQ design for both fixed- and variable-rate systems but implemented only fixed-rate codes. The earliest portion of this thesis began with the implementation of the earlier described algorithm for variable-rate MRVQ for use as a testbed for understanding the important question of how to choose the Lagrangian parameters for multi-resolution codes to meet a collection of desired constraints.
\r\n\r\nArmed with a new understanding of parameter choice in the MRVQ framework, we moved next to the more sophisticated coding framework of wavelet-based embedded bit-plane coders. New results in this framework include improvements on the Set Partitioning in Hierarchical Trees (SPIHT) and the Group Testing for Wavelets (GTW) algorithms that apply the lessons learned from MRVQ theory in these more sophisticated wavelet coding frameworks. Experimental results demonstrate the performance benefits associated with this approach.
" }, { "name": "Dunbar, William Bruce", "degree": "PhD", "year": "2004", "title": "Distributed Receding Horizon Control of Multiagent Systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-170123", "creators": [ { "name": { "family": "Dunbar", "given": "William Bruce" }, "id": "Dunbar-William-Bruce", "orcid": "0000-0002-0913-318X", "display_name": "Dunbar, William Bruce" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Shamma", "given": "Jeff" }, "id": "Shamma-J", "role": "member", "display_name": "Shamma, Jeff" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." } ], "option_major": [ "cds" ], "doi": "10.7907/1N74-MZ62", "abstract": "Multiagent systems arise in several domains of engineering. Examples include arrays of mobile sensor networks for aggregate imagery, autonomous highways, and formations of unmanned aerial vehicles. In these contexts, agents are governed by vehicle dynamics and often constraints, and the control objective is achieved by cooperation. Cooperation refers to the agreement of the agents to 1) have a common objective with neighboring agents, with the objective typically decided offline, and 2) share information online to realize the objective. To be viable, the control approach for multiagent systems should be distributed, for autonomy of the individual agents and for scalability and improved tractability over centralized approaches.
\r\n\r\nOptimization-based techniques are suited to multiagent problems, in that such techniques can admit very general objectives. Receding horizon control is an optimization-based approach that is applicable when dynamics and constraints on the system are present. Several researchers have recently explored the use of receding horizon control to achieve multi-vehicle objectives. In most cases, the common objective is formulated, and the resulting control law implemented, in a centralized way.
\r\n\r\nThis dissertation provides a distributed implementation of receding horizon control with guaranteed convergence and performance comparable to a centralized implementation. To begin with, agents are presumed to be individually governed by heterogeneous dynamics, modelled by a nonlinear ordinary differential equation. Coupling between agents occurs in a generic quadratic cost function of a single optimal control problem. The distributed implementation is generated by decomposition of the single optimal control problem into local problems, and the inclusion of local compatibility constraints in each local problem. The coordination requirements are globally synchronous timing and local information exchanges between neighboring agents. For sufficiently fast update times, the distributed implementation is proven to be asymptotically stabilizing. Extensions for handling inter-agent coupling constraints and partially synchronous timing are also explored. The venue of multi-vehicle formation stabilization demonstrates the efficacy of the implementation in numerical experiments. Given the generality of the receding horizon control mechanism, there is great potential for the implementation presented here in dynamic and constrained distributed systems.
" }, { "name": "Fago, Matthew Justin", "degree": "PhD", "year": "2004", "title": "Constrained Sequential Lamination: Nonconvex Optimization and Material Microstructure", "advisor": "Ortiz, Michael; Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142004-144712", "creators": [ { "name": { "family": "Fago", "given": "Matthew Justin" }, "id": "Fago-Matthew-Justin", "display_name": "Fago, Matthew Justin" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "co-advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Lapusta", "given": "Nadia" }, "id": "Lapusta-N", "role": "member", "display_name": "Lapusta, Nadia" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P1PK-E179", "abstract": "A practical algorithm has been developed to construct, through sequential lamination, the partial relaxation of multiwell energy densities such as those characteristic of shape memory alloys. The resulting microstructures are in static and configurational equilibrium, and admit arbitrary deformations. The laminate topology evolves during deformation through branching and pruning operations, while a continuity constraint provides a simple model of metastability and hysteresis. In cases with strict separation of length scales, the method may be integrated into a finite element calculation at the subgrid level. This capability is demonstrated with a calculation of the indentation of a Cu-Al-Ni shape memory alloy by a spherical indenter.
\r\n\r\nIn verification tests the algorithm attained the analytic solution in the computation of three benchmark problems. In the fourth case, the four-well problem (of, e.g., Tartar), results indicate that the method for microstructural evolution imposes an energy barrier for branching, hindering microstructural development in some cases. Although this effect is undesirable for purely mathematical problems, it is reflective of the activation energies and metastabilities present in applications involving natural processes.
\r\n\r\nThe method was further used to model Shield's tension test experiment, with initial calculations generating reasonable transformation strains and microstructures that compared well with the sequential laminates obtained experimentally.
" }, { "name": "Fleming, Michael Ian James", "degree": "PhD", "year": "2004", "title": "On Source Coding for Networks", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-170744", "creators": [ { "name": { "family": "Fleming", "given": "Michael Ian James" }, "id": "Fleming-Michael-Ian-James", "display_name": "Fleming, Michael Ian James" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/CY48-QJ71", "abstract": "In this thesis, I examine both applied and theoretical issues in network source coding.
\r\n\r\nThe applied results focus on the construction of locally rate-distortion-optimal vector quantizers for networks. I extend an existing vector quantizer design algorithm for arbitrary network topologies [1] to allow for the use of side information at the decoder and for the presence of channel errors. I show how to implement the algorithm and use it to design codes for several different systems. The implementation treats both fixed-rate and variable-rate quantizer design and includes a discussion of convergence and complexity. Experimental results for several different systems demonstrate in practice some of the potential performance benefits (in terms of rate, distortion, and functionality) of incorporating a network's topology into the design of its data compression system.
\r\n\r\nThe theoretical work covers several topics. Firstly, for a system with some side information known at both the encoder and the decoder, and some known only at the decoder, I derive the rate-distortion function and evaluate it for binary symmetric and Gaussian sources. I then apply the results for binary sources in evaluating the binary symmetric rate-distortion function for a system where the presence of side information at the decoder is unreliable. Previously, only upper and lower bounds were known for that problem. Secondly, I address with an example the question of whether feedback from a decoder to an encoder ever enlarges the achievable rate region for lossless network source coding of memoryless sources. Thirdly, I show how cutset methods can yield quick and simple rate-distortion converses for any source coding network. Finally, I present rate-distortion results for two different broadcast source coding systems.
" }, { "name": "Florens, C\u00e9dric Jean Paul", "degree": "PhD", "year": "2004", "title": "Data Collection and Distribution in Sensory Networks", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312004-205111", "creators": [ { "name": { "family": "Florens", "given": "C\u00e9dric Jean Paul" }, "id": "Florens-C\u00e9dric-Jean-Paul", "display_name": "Florens, C\u00e9dric Jean Paul" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Estabrook", "given": "Polly" }, "id": "Estabrook-P", "role": "member", "display_name": "Estabrook, Polly" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZK3J-VB92", "abstract": "The deployment of large-scale, low-cost, low-power, multifunctional sensory networks brings forward numerous and diverse research challenges. Critical to the design of systems that must operate under extreme resource constraints, the understanding of the fundamental performance limits of sensory networks is a research topic of particular importance. This thesis examines, in this respect, an essential function of sensory networks, viz., data collection, that is, the aggregation at the user location of information gathered by sensor nodes.
\r\n\r\nIn the first part of this dissertation we study, via simple discrete mathematical models, the time performance of the data collection and data distribution tasks in sensory networks. Specifically, we derive the minimum delay in collecting sensor data for networks of various topologies such as line, multi-line, tree and give corresponding optimal scheduling strategies assuming that the amount of data observed at each node is finite and known at the beginning of the data collection phase. Furthermore, we bound the data collection time on general graph networks.
\r\n\r\nIn the second part of this dissertation we take the view that the amount of data collected at a node is random and study the statistics of the data collection time. Specifically, we analyze the average minimum delay in collecting randomly located/distributed sensor data for networks of various topologies when the number of nodes becomes large. Furthermore, we analyze the impact of various parameters such as lack of synchronization, size of packet, transmission range, and channel packet erasure probability on the optimal time performance. Our analysis applies to directional antenna systems as well as omnidirectional ones. We conclude our study with a simple comparative analysis showing the respective advantages of the two systems.
\r\n" }, { "name": "Fon, Warren Chung Wah", "degree": "PhD", "year": "2004", "title": "Thermal Properties of Nano- and Microstructures", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262004-123035", "creators": [ { "name": { "family": "Fon", "given": "Warren Chung Wah" }, "id": "Fon-Warren-Chung-Wah", "orcid": "0000-0002-5447-2324", "display_name": "Fon, Warren Chung Wah" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "chair", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "orcid": "0000-0002-2916-6026", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/FK4H-CV52", "abstract": "My work is on the experimental study of thermal conduction in nano and microscale structures. The work is divided into two parts. In the first part, we measure the thermal conductance of a suspended device from 4 to 40 K. The thermal conduction of a suspended, free-standing beam is analyzed to study the effect of phonon scattering on thermal conduction. We conclude that phonon scattering is much more severe in a nanoscale beam than bulk material.
\r\n\r\nIn the second part of the work, we proceed to dynamic measurement to measure the heat capacity of a suspended device. From that we study the origin of heat capacity of a silicon nitride membrane. We conclude that much of the heat capacity comes from the motional tunneling states of the ions. We use the device to demonstrate an ultrasensitive calorimeter with a very high resolution of 0.5 aJ/K. We conclude the work by applying the calorimeter to study the heat capacity of a thin adsorbed film of helium gas.
\r\n" }, { "name": "Hansen, Carl Lars Genghis", "degree": "PhD", "year": "2004", "title": "Microfluidic Technologies for Structural Biology", "advisor": "Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012004-144201", "creators": [ { "name": { "family": "Hansen", "given": "Carl Lars Genghis" }, "id": "Hansen-Carl-Lars-Genghis", "display_name": "Hansen, Carl Lars Genghis" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "chair", "display_name": "Quake, Stephen R." }, { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "orcid": "0000-0003-4073-1185", "role": "member", "display_name": "Rees, Douglas C." }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "orcid": "0000-0002-1221-0967", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "orcid": "0000-0002-1581-9209", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Bjorkman", "given": "Pamela J." }, "id": "Bjorkman-P-J", "orcid": "0000-0002-2277-3990", "role": "member", "display_name": "Bjorkman, Pamela J." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/N9T3-7114", "abstract": "In the post-genomic era, X-ray crystallography has emerged as the workhorse of large-scale structural biology initiatives that seek to understand protein function and interaction at the atomic scale. Despite impressive technological advances in X-ray sources, phasing techniques, and computing power, the determination of protein structure has been severely hampered by the difficulties in obtaining high-quality protein crystals. Emergent technologies utilizing microfluidics now have the potential to solve these problems on several levels, both by allowing researchers to conduct efficient assays in nanoliter reaction volumes, and by exploiting the properties of mass-transport at the micron scale to improve the crystallization process. The technique of Multilayer Soft Lithography (MSL) has been used to developed a set of microfluidic tools suitable for all stages of protein crystallogenesis, including protein solubility phase-space mapping, crystallization screening, harvesting, and in silicone diffraction studies. These tools represent the state of the art in on-chip fluid handling functionality and have been demonstrated to dramatically improve protein crystallization.\r\n" }, { "name": "Hashemi, Hossein", "degree": "PhD", "year": "2004", "title": "Integrated Concurrent Multi-Band Radios and Multiple-Antenna Systems", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302003-125128", "creators": [ { "name": { "family": "Hashemi", "given": "Hossein" }, "id": "Hashemi-Hossein", "orcid": "0000-0002-3329-7061", "display_name": "Hashemi, Hossein" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "co-chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/3R2B-8A25", "abstract": "This thesis presents a unique view on radio systems that can simultaneously function at multiple frequency bands. These radios offer a higher data-rate and robustness in addition to the added functionality in the performance of wireless systems. Our treatment includes the definition of such novel radios, formulation of their singular characteristics, proposition for transceiver architectures, and invention of circuit blocks.
\r\n\r\nVarious transceiver architectures for this new class of concurrent multi-band radios are proposed. The results for an integrated concurrent dual-band receiver operating at 2.4 GHz and 5.2 GHz frequency bands for wireless networking applications are presented. Meticulous frequency-planning results in a high level of integration and a low power design for the concurrent receiver. Several new circuit concepts including the concurrent multi-band low-noise amplifier are demonstrated in this design. A general class of these concurrent multi-band amplifiers is investigated with numerous implementations of integrated concurrent dual-band and triple-band amplifiers.
\r\n\r\nA theoretical treatment of nonlinear oscillators with multi-band resonator structures is also offered. It is shown that given certain nonlinearities these oscillators can generate multi-frequency outputs. The phase-noise of such negative-resistance oscillators with general resonator structure is addressed. By providing a link between the stored and dissipated energies of a network and its associated circuit parameters, useful interpretations of resonator quality factor are derived. With the aid of this analysis and the previously developed phase-noise models, dependencies of phase-noise on the resonator structure are derived. Based on our theoretical results, enhanced resonators with higher quality factor providing a superior oscillator phase-noise are proposed.
\r\n\r\nFinally, in order to enhance the performance of wireless systems by exploiting the spatial properties of the electromagnetic wave, multiple-antenna radios in phased-array configuration are investigated. The phased-array technology results in higher immunity to unwanted interference and therefore achieves a superior overall system capacity in a shared environment. The first fully integrated multiple-antenna receiver targeting the 24 GHz ISM band using silicon technology is presented. The phased-array radio at 24 GHz is a cheap solution for high data-rate WLAN, as well as for fixed wireless broadband access applications.
" }, { "name": "Hern\u00e1ndez, Maria Eugenia", "degree": "PhD", "year": "2004", "title": "Mechanisms of Indirect Mineral Reduction by Bacteria", "advisor": "Newman, Dianne K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042004-011242", "creators": [ { "name": { "family": "Hern\u00e1ndez", "given": "Maria Eugenia" }, "id": "Hern\u00e1ndez-Maria-Eugenia", "display_name": "Hern\u00e1ndez, Maria Eugenia" } ], "advisors": [ { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "advisor", "display_name": "Newman, Dianne K." } ], "committee": [ { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "chair", "display_name": "Newman, Dianne K." }, { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "member", "display_name": "Leadbetter, Jared R." }, { "name": { "family": "Simon", "given": "Melvin I." }, "id": "Simon-M-I", "role": "member", "display_name": "Simon, Melvin I." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/G5P3-ER69", "abstract": "This thesis concerns the biological process of iron reduction mediated by microbially produced extracellular redox-active organic molecules. Two different iron reducing bacteria were studied: Shewanella oneidensis and Pseudomonas chlororaphis. S. oneidensis can grow by reducing ferric iron [Fe(III)] as a terminal electron acceptor in anaerobic respiration (i.e. dissimilatory iron reduction). Previous studies had suggested that it produces extracellular electron shuttles as a strategy for reducing poorly crystalline iron (hydr)oxides, however this had not been shown. To investigate this, a new method was developed to measure iron reduction at a distance using Fe-coated porous glass beads. Given this assay, it was shown that Fe(III) reduction at a distance is an active process that requires anaerobic conditions and coincides with biofilm formation. The possibility that S. oneidensis excretes a soluble quinone derived from the menaquinone biosynthetic pathway as a mediator was ruled out, but it was shown that such molecules are present in culture fluids and can be used by the cells to make menaquinone. Regardless of the nature of the mediator, it appears to act locally within the biofilm-bead environment for S. oneidensis. P. chlororaphis is a plant root isolate that cannot respire iron but produces redox active secondary metabolites (e.g. phenazine carboxamide, PCN) that promote microbial mineral reduction. P. chlororaphis can reductively dissolve poorly crystalline iron and manganese oxides whereas a mutant in one of the phenazine biosynthetic genes (phzB) cannot. PCN functions as an electron shuttle rather than an iron chelator. Multiple phenazines and the glycopeptidic antibiotic, bleomycin, can also stimulate mineral reduction by S. oneidensis MR-1. Because diverse bacterial strains that cannot grow on iron can reduce phenazines, and thermodynamic calculations suggest that phenazines have lower redox potentials than poorly crystalline iron (hydr)oxides in a range of relevant environmental pH (5 to 9), it seems likely that natural products like phenazines promote microbial mineral reduction in the environment. Whether cycling of microbially produced extracellular redox-active organic molecules serves a physiological function remains to be determined." }, { "name": "Hunt, Cynthia Lee", "degree": "PhD", "year": "2004", "title": "Transition-Edge Superconducting Antenna-Coupled Bolometer", "advisor": "Lange, Andrew E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-131005", "creators": [ { "name": { "family": "Hunt", "given": "Cynthia Lee" }, "id": "Hunt-Cynthia-Lee", "display_name": "Hunt, Cynthia Lee" } ], "advisors": [ { "name": { "family": "Lange", "given": "Andrew E." }, "id": "Lange-A-E", "role": "advisor", "display_name": "Lange, Andrew E." } ], "committee": [ { "name": { "family": "Lange", "given": "Andrew E." }, "id": "Lange-A-E", "role": "chair", "display_name": "Lange, Andrew E." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "role": "member", "display_name": "Golwala, Sunil" } ], "option_major": [ "matsci" ], "doi": "10.7907/RG6K-C898", "abstract": "The temperature anisotropy of the cosmic microwave background (CMB) is now being probed with unprecedented accuracy and sky coverage by the Wilkinson Microwave Anisotropy Probe (WMAP), and will be definitively mapped by the Planck Surveyor after its launch in 2007. However, the polarization of the CMB will not be mapped with sufficient accuracy. In particular, the measurement of the curl-polarization, which may be used to probe the energy scale of the inflationary epoch, requires a large advance in the format of millimeter-wave bolometer arrays. SAMBA (Superconducting Antenna-coupled Multi frequency Bolometric Array) is being developed to address these needs for the next generation of submillimeter astronomical detectors. SAMBA consists of a focal plane populated with microstrip-coupled slot antennas, whose signals are coherently added and sent to transition-edge superconducting (TES) bolometers via microstrip lines. SAMBA eliminates the need for the feedhorns and optical filters currently used on CMB observational instruments, such as Planck and Boomerang. The SAMBA architecture allows for a high density of pixels in the focal plane with minimal sub-Kelvin mass. As a precursor to a full monolithic high-density antenna array, we are developing a single-band antenna-coupled bolometric detector.
\r\n\r\nIn this thesis, I report test results for a single-pixel antenna-coupled bolometric detector. Our device consists of a dual slot microstrip-coupled slot antenna coupled to an Al/Ti/Au voltage-biased TES. The coupling architecture involves propagating the signal along superconducting microstrip lines and terminating the lines at a normal metal resistor collocated with a TES on a thermally isolated island. The device, which is inherently polarization sensitive, is optimized for 140 GHz measurements. In the thermal bandwidth of the TES, we measure a noise equivalent power (NEP) of 2.0x10-17 W/\u221a Hz in dark tests which agrees with the calculated NEP including only contributions from phonon, Johnson and amplifier noise. We do not measure any excess noise above this expectation at frequencies between 1 and 200 Hz. We measure a thermal conductance G=55 pW/K. We measure a thermal time constant as low as 437 \u00b5s at 3 \u00b5V bias when stimulating the TES directly using a light emitting diode.
" }, { "name": "Husain, Ali", "degree": "PhD", "year": "2004", "title": "Nanotube and Nanowire Devices", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252004-113507", "creators": [ { "name": { "family": "Husain", "given": "Ali" }, "id": "Husain-Ali", "display_name": "Husain, Ali" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Barbic", "given": "Mladen" }, "id": "Barbic-M", "role": "member", "display_name": "Barbic, Mladen" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1MNR-PW32", "abstract": "The microelectronic revolution has spawned many fields that take advantage of the incredibly small size devices that can be made. However, the limits of photolithography and even electron beam lithography are fast approaching. Future progress in miniaturization of electronics, mechanical devices and optical structures will require new processes and materials.
\r\n\r\nThe work presented in this thesis is an investigation into the possibilities of using new nanomaterials to fabricate simple devices. It is a challenge to integrate these materials with traditional microfabrication techniques. The processes commonly used to make electronics can damage or destroy some nanomaterials. Also, it is difficult to place and orient these novel substances. Finally, at the nanometer scale, different physical properties emerge due to confinement effects and the large surface-area-to-volume ratio.
\r\n\r\nWe have fabricated devices out of carbon nanotubes and electrodeposited nanowires. The nanowires have been fabricated in gold, platinum, silver and nickel. For all the nanowires except silver we have measured the temperature dependence of the resistance and found that it is consistent with bulk metals. We have created and tested crossed nickel nanowires for magnetoresistive effects and found none.
\r\n\r\nFrom the platinum wires we have fabricated and tested the first doubly clamped resonator fabricated out of \"bottom-up\" materials. This resonator has much lower Q than comparable devices made by traditional techniques. The resonator also exhibits non-linear behavior well described by the Duffing oscillator.
\r\n\r\nFrom carbon nanotubes we have created a doubly-clamped beam. In addition, we have created a novel carbon nanotube field emission device with integrated grid. Work is ongoing to achieve experimental results from these devices.
\r\n\r\nThe appendix describes photonic crystal defect cavity lasers, which offers interesting potential for integration with nanotubes and nanowires.
" }, { "name": "Jiang, Anxiao (Andrew)", "degree": "PhD", "year": "2004", "title": "Optimized Network Data Storage and Topology Control", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-163315", "creators": [ { "name": { "family": "Jiang", "given": "Anxiao (Andrew)" }, "id": "Jiang-Anxiao-Andrew", "orcid": "0000-0002-0120-7930", "display_name": "Jiang, Anxiao (Andrew)" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Blaum", "given": "Mario" }, "id": "Blaum-M", "role": "member", "display_name": "Blaum, Mario" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/91R7-MH71", "abstract": "This thesis addresses two key challenges for network data-storage systems: optimizing data placement for highly efficient and robust data access, and constructing network topologies that facilitate data transmission scalable to both network sizes and network dynamics. It focuses on two new topics \u2014 data placement using erasure-correcting codes, and topology control for nodes in normed spaces. The first topic generalizes traditional file-assignment problems, and has the distinct feature of interleavingly placing data in networks. The second topic emphasizes the construction of network topologies that achieve excellent global performance in comprehensive measurements, through purely local decisions on connectivity. The results of the thesis deepen the current understanding on these important and intriguing topics, and follow a mathematically rigorous approach.
\r\n" }, { "name": "Kartalov, Emil Paskalev", "degree": "PhD", "year": "2004", "title": "Single-Molecule Detection and DNA Sequencing-by-Synthesis", "advisor": "Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142004-100932", "creators": [ { "name": { "family": "Kartalov", "given": "Emil Paskalev" }, "id": "Kartalov-Emil-Paskalev", "orcid": "0000-0003-0521-9194", "display_name": "Kartalov, Emil Paskalev" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "chair", "display_name": "Quake, Stephen R." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Elowitz", "given": "Michael B." }, "id": "Elowitz-M-B", "role": "member", "display_name": "Elowitz, Michael B." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Anderson", "given": "W. French" }, "id": "Anderson-W-F", "role": "member", "display_name": "Anderson, W. French" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/50YQ-0S81", "abstract": "Fluorescence detection has established itself as one of the main techniques of interrogation of biological systems. Extending those techniques to decrease the sample size to single molecules provides an absolute standard for bulk sample calibrations, as well as better insights since individual behavior is observed instead of population averages. We observed a number of fluorophores, including GFP, at the single-molecule level at room temperature. Calibrations gave a correct estimate of bulk surface densities over four orders of magnitude, through an optical, non-invasive, non-destructive means. Novel surface chemistry enabled visualization of single tagged nucleotide incorporations inside DNA immobilized on a glass surface at the single-molecule level. This technology was later extended to successful single-molecule DNA sequencing.\r\n\r\nAt the same time, PDMS microfluidics was developed to provide the plumbing control, speed, and economy of scale for a broad range of applications. Novel surface chemistry anchored DNA to the PDMS microchannels, which allowed sequencing-by-synthesis to be conducted in the microfluidic environment using optical techniques. Materials, device, and architecture problems were also solved. Finally, all technology was put together and successful microfluidic bulk-fluorescence DNA sequencing was demonstrated. The same technology is applicable to any DNA studies in microfluidic environments and can eventually be extended to close the circle to single-molecule detection." }, { "name": "Kippenberg, Tobias Jan August", "degree": "PhD", "year": "2004", "title": "Nonlinear Optics in Ultra-High-Q Whispering-Gallery Optical Microcavities", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06072004-085555", "creators": [ { "name": { "family": "Kippenberg", "given": "Tobias Jan August" }, "id": "Kippenberg-Tobias-Jan-August", "orcid": "0000-0002-3408-886X", "display_name": "Kippenberg, Tobias Jan August" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/T5B6-9R14", "abstract": "Optical microcavities confine light at resonant frequencies for extended periods of time and fundamentally alter the interaction of light with matter. They are the basis of numerous applied and fundamental studies, such as cavity QED, photonics and sensing. Of all resonant geometries, surface tension-induced microcavities, such as silica micro-spheres, exhibit the highest Q-factor to date of nearly 9 billion. Despite these high Q-factor and the intense interest in these structures, the nonlinear optical properties of silica micro-spheres have remained nearly entirely unexplored. In this thesis the nonlinear optical phenomena which can occur in ultra-high-Q microcavities are investigated. To efficiently excite the whispering-gallery modes, tapered optical fibers are used and the coupling to ultra-high-Q modes studied. It is found, that microcavities with ultra-high enter a regime where scattering of light into the degenerate pair of clockwise and counter-clockwise mode is the dominant scattering process. In this regime the coupling properties are significantly altered, but the cavities still retain their ability to achieve significant cavity build-up fields. This allowed exceeding the threshold for all common nonlinearities encountered in silica. In particular, stimulated Raman scattering is observed in taper fiber coupled silica micro-spheres at threshold levels typically in the micro-Watt range, which usually is considered the regime of linear optics. Cascaded Raman lasing is also observed in these structures. The tapered optical fiber in these experiments functions to both pump WGMs as well as to extract the nonlinear Raman fields. In addition, the tapered-fiber coupling junction is highly ideal, making it possible to strongly over-couple ultra-high-Q cavities with negligible junction loss. This feature allows for the observation of very high internal differential photon conversion efficiencies approaching unity. Whereas micro-spheres are both compact and efficient nonlinear oscillators, their fabrication properties lack the control and parallelism typical of micro-fabrication techniques. A synergistic approach of micro-fabrication and a laser assisted reflow process, allows to create toroidally silica microcavities on a chip. In this thesis it is demonstrated, that these cavities can exhibit ultra-high-Q whispering-gallery modes, allowing to achieve ultra-high-Q modes on a chip. This results is a nearly four-order of magnitude improvement with respect to other wafer-scale microcavities. In addition their azimuthal mode-spectrum is strongly reduced. Nonlinear oscillation in these cavities has also been studied, and stimulated Raman scattering observed, allowing to achieve the first Raman laser on a chip. The devices show improved performance compared to micro-spheres due to a strongly reduced azimuthal mode spectrum, which allowed to observe single mode emission. The enhanced geometric control of these cavities is also studied and found to profoundly alter the nonlinear optical processes the toroid microcavities. Reduction of toroidal cross section is observed to cause a transition from stimulated Raman to parametric oscillation regime. This allowed to observe Kerr nonlinearity induced parametric oscillation in a microcavity for the first time. The parametrically generated \"twin beams\" exhibit high conversion efficiency and show near unity signal-to-idler ratio.
\r\n" }, { "name": "Klug, William Scott", "degree": "PhD", "year": "2004", "title": "A Director-Field Theory of DNA Packaging in Bacteriophage Viruses", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132003-150122", "creators": [ { "name": { "family": "Klug", "given": "William Scott" }, "id": "Klug-William-Scott", "display_name": "Klug, William Scott" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/E0V6-4Y97", "abstract": "This thesis is concerned with the formulation of a continuum theory of packaging of DNA in bacterial viruses based on a director-field representation of the encapsidated DNA. The point values of the director field give the local direction and density of the DNA. The continuity of the DNA strand requires that the director field be divergence-free and tangent to the capsid wall. The energy of the DNA is defined as a functional of the director field which accounts for bending, torsion, and for electrostatic interactions through a density-dependent interaction energy. The operative principle which determines the encapsidated DNA conformation is assumed to be energy minimization.
\r\n\r\nThe director-field theory is used for the direct formulation and study of two low-energy DNA conformations: the inverse spool and torsionless toroidal solenoids. Analysis of the inverse spool configuration yields predictions of the interaxial spacing and the dependence of the packing force on the packed genome fraction which are found to be in agreement with experiments. Further analysis shows that torsionless toroidal solenoids can achieve lower energy than the inverse spool configuration.
\r\n\r\nAlso, the theory is adapted to a framework of numerical optimization, wherein all fields are discretized on a computational lattice, and energy minimizing configurations are sought via simulated annealing and the nonlinear conjugate gradient method. It is shown that the inverse spool conformation is stable in all regions of the virus capsid except in a central core, where the DNA tends to buckle out of the spooling plane.
" }, { "name": "Krishnan, Swaminathan", "degree": "PhD", "year": "2004", "title": "Three-Dimensional Nonlinear Analysis of Tall Irregular Steel Buildings Subject to Strong Ground Motion", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02252004-181515", "creators": [ { "name": { "family": "Krishnan", "given": "Swaminathan" }, "id": "Krishnan-Swaminathan", "orcid": "0000-0002-2594-1523", "display_name": "Krishnan, Swaminathan" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." } ], "option_major": [ "civileng" ], "doi": "10.7907/A00K-RQ42", "abstract": "Strong ground motion from a nearby fault has frequency content in the same range as the natural frequencies of tall buildings. This may have serious repercussions and is the topic of this dissertation.Buildings are designed per building code standards. But, are the code provisions adequate? Strong motion from large earthquakes has been recorded only in recent times in the near-source region. Have the current codes used this information to update tall structure design guidelines? Considerable damage has been observed in tall buildings from the Northridge, Kobe, Turkey, and Taiwan earthquakes. How will tall buildings designed per the latest code regulations perform if they were to be shaken by any of these earthquakes? This thesis attempts to answer these questions.
\r\n\r\nTall buildings by their nature are computationally intensive to analyze. They consist of thousands of degrees of freedom and when subjected to strong ground motion from a nearby source, exhibit inelastic response. Modeling this inelastic response requires an iterative approach that is computationally expensive. Furthermore, a large class of buildings, classified as irregular, exhibits complex behavior that can be studied only when the structures are modeled in their entirety. To this end, a three-dimensional analysis program, FRAME3D, has been developed incorporating two special beam-column elements -- the plastic hinge element and the elastofiber element that can model beams and columns in buildings accurately and efficiently, a beam-column joint element that can model inelastic joint deformation, and 4-noded elastic plane-stress elements to model floor slabs acting as diaphragms forcing the lateral force resisting frames in a building to act as one unit. The program is capable of performing time-history analyses of buildings in their entirety.
\r\n\r\nSix 19-story irregular steel moment frame buildings (with buildings 2A and 3A being variants of buildings 2 and 3, respectively) have been designed per the latest code (Uniform Building Code, 1997). Two of these buildings have reentrant corners and the other two have torsional irregularity. Their strength and ductility are assessed by performing pushover analyses on them. To assess their performance under strong shaking, FRAME3D models of these buildings are subjected to near-source strong motion records from the Iran earthquake (Mw = 7.3, Tabas Station) of 1978, the Northridge earthquake (Mw = 6.7, Sylmar Station) of 1994 and the Kobe earthquake (Mw = 6.9, Takatori Station) of 1995. None of the buildings collapsed under these strong events in the computer analyses. However, when compared against the acceptable limits for various performance levels in FEMA 356 document, the damage in terms of plastic deformation at the ends of beams and columns and at joints would render the buildings inadequate in terms f life safety in quite a few cases and would even indicate possible collapse in a couple of cases. Thus, in these terms, the code falls short of achieving its life safety objective, and the near-source factors introduced in the code in 1997 in recognition of the special features of near-source ground motion seem to be inadequate.
\r\n\r\nThe ductility demand, in terms of plastic rotation at the ends of beams and columns and in joints, on these buildings during this class of earthquakes is up to 6% of a radian, which is far greater than a typical limiting plastic rotation of 3% associated with fracture and consequent failure of large wide-flanged steel sections during experiments. Thus, if strength degradation due to fractures, local buckling, etc., were to be included in the analysis, then the results would likely to be worse, as far as the ability of these buildings to withstand these earthquakes without collapse is concerned.
\r\n\r\nDue to damage localization, the peak drifts observed in the structure far exceeded the inelastic drift limit in the code of 0.02 (in some cases up to 3 times). This points to serious non-structural damage to facades, interior dry wall, etc. Furthermore, large roof permanent offsets after the events indicate significant post-earthquake repair requiring considerable disruption and building closure.
\r\n\r\nColumn yielding was minimal thus validating the strong-column weak-beam criterion in the code. Redundancy factors used to assess the redundancy in the system need to take into account the case of torsionally sensitive structures where frames in both principal directions are simultaneously activated. Stress concentration was not observed at the reentrant corners in L-shaped buildings.
\r\n\r\nFinally, the data catalogued in this work could be useful for future code development and tall structure design guidelines.
" }, { "name": "Leok, Melvin", "degree": "PhD", "year": "2004", "title": "Foundations of Computational Geometric Mechanics", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03022004-000251", "creators": [ { "name": { "family": "Leok", "given": "Melvin" }, "id": "Leok-Melvin", "orcid": "0000-0002-8326-0830", "display_name": "Leok, Melvin" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Weinstein", "given": "Alan Jay" }, "id": "Weinstein-Alan-J-Physics", "role": "member", "display_name": "Weinstein, Alan Jay" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "cds" ], "doi": "10.7907/KDV0-WR34", "abstract": "Geometric mechanics involves the study of Lagrangian and Hamiltonian mechanics using geometric and symmetry techniques. Computational algorithms obtained from a discrete Hamilton's principle yield a discrete analogue of Lagrangian mechanics, and they exhibit excellent structure-preserving properties that can be ascribed to their variational derivation.
\r\n\r\nWe construct discrete analogues of the geometric and symmetry methods underlying geometric mechanics to enable the systematic development of computational geometric mechanics. In particular, we develop discrete theories of reduction by symmetry, exterior calculus, connections on principal bundles, as well as generalizations of variational integrators.
\r\n\r\nDiscrete Routh reduction is developed for abelian symmetries, and extended to systems with constraints and forcing. Variational Runge-Kutta discretizations are considered in detail, including the extent to which symmetry reduction and discretization commute. In addition, we obtain the Reduced Symplectic Runge-Kutta algorithm, which is a discrete analogue of cotangent bundle reduction.
\r\n\r\nDiscrete exterior calculus is modeled on a primal simplicial complex, and a dual circumcentric cell complex. Discrete notions of differential forms, exterior derivatives, Hodge stars, codifferentials, sharps, flats, wedge products, contraction, Lie derivative, and the Poincar?emma are introduced, and their discrete properties are analyzed. In examples such as harmonic maps and electromagnetism, discretizations arising from discrete exterior calculus commute with taking variations in Hamilton's principle, which implies that directly discretizing these equations yield numerical schemes that have the structure-preserving properties associated with variational schemes.
\r\n\r\nDiscrete connections on principal bundles are obtained by introducing the discrete Atiyah sequence, and considering splittings of the sequence. Equivalent representations of a discrete connection are considered, and an extension of the pair groupoid composition that takes into account the principal bundle structure is introduced. Discrete connections provide an intrinsic coordinatization of the reduced discrete space, and the necessary discrete geometry to develop more general discrete symmetry reduction techniques.
\r\n\r\nGeneralized Galerkin variational integrators are obtained by discretizing the action integral through appropriate choices of finite-dimensional function space and numerical quadrature. Explicit expressions for Lie group, higher-order Poincar\u00e9, higher-order symplectic-energy-momentum, and pseudospectral variational integrators are presented, and extensions such as spatio-temporally adaptive and multiscale variational integrators are briefly described.
" }, { "name": "Lin, Jiao", "degree": "PhD", "year": "2004", "title": "M\u00f6ssbauer Diffractometry: Principles, Practice, and an Application to a Study of Chemical Order in \u2075\u2077Fe\u2083Al", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05192004-092347", "creators": [ { "name": { "family": "Lin", "given": "Jiao" }, "id": "Lin-Jiao", "display_name": "Lin, Jiao" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "role": "member", "display_name": "Rees, Douglas C." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/JSZ7-BC77", "abstract": "For the first time, M\u00f6ssbauer powder diffractometry went beyond the proof-of-principal stage and was used to study unknown periodicities of defect-related chemical environments of Fe atoms in a partially-ordered \u2075\u2077Fe\u2083Al polycrystalline sample.
\r\n\r\nM\u00f6ssbauer powder diffractometry is based on two phenomena, the M\u00f6ssbauer effect and the Bragg diffraction. The M\u00f6ssbauer effect is sensitive to short-range order whereas diffractometry is sensitive to long-range order. Together, they enable M\u00f6ssbauer powder diffractometry to provide information on long-range periodicities of target atoms having specific short-range order.
\r\n\r\nBoth experimental and theoretical efforts are necessary for this novel technique to become practical. In this research, hardware and software for M\u00f6ssbauer powder diffractometry were improved. A kinematical diffraction theory for M\u00f6ssbauer powder diffractometry incorporating effects of interference between electronic and nuclear resonant scattering was developed. The applicability of the theory was verified by computer calculations that accounted for dynamical diffraction effects. A thorough analysis of polarization effects, including a polycrystalline average of polarization factors, was done systematically using spherical harmonic expansions.
\r\n\r\nMultiple diffraction patterns were measured at Doppler velocities across all nuclear resonances of \u2075\u2077Fe\u2083Al. On the basis of the theory developed, the superlattice diffractions were analyzed to provide data on the long-range order of Fe atoms having different numbers of Al neighbors. Comparing experimental data to calculations showed that Fe atoms having three Al atoms as first-nearest neighbors (1nn) have partial simple cubic long-range order, similar to that of Fe atoms with four Al 1nn. The simple cubic periodicity of Fe atoms with three Al 1nn was significantly lower than expected for homogeneous antisite disorder, however. Monte-Carlo simulations and transmission electron microscopy suggest that a significant fraction of aperiodic Fe atoms with three Al 1nn are near antiphase domain boundaries.
" }, { "name": "Lu, Dai", "degree": "PhD", "year": "2004", "title": "Active Patch Array Design and Indoor Channel Modeling for Future Wireless Communications", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212004-015508", "creators": [ { "name": { "family": "Lu", "given": "Dai" }, "id": "Lu-Dai", "display_name": "Lu, Dai" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Pogorzelski", "given": "Ronald" }, "id": "Pogorzelski-R", "role": "member", "display_name": "Pogorzelski, Ronald" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PVB9-TH19", "abstract": "Indoor wireless LAN systems currently operate at ranges of up to 30 meters, with practical data rates of 10 Mbps. In order to achieve higher data rates, higher frequencies are under consideration. Smaller antennas are required at these frequencies, but path loss increases. To combat the large path loss and multipath, 24 GHz phased arrays are being considered. The advantage of a phased array is that it can form narrow beams to favored directions, and nulls to combat interference. A 24 GHz active antenna with a 5-element patch array is demonstrated that includes an integrated GaAs MMIC power amplifier and low noise amplifier chip. Bias switching is used for changing from transmit to receive. The measured active gain is 31 dB in receive and 35 dB in transmit. The measured noise figure in receive is 3.5 dB and the maximum output power in transmit is 22 dBm (158 mW). Indoor wireless channels are investigated at five different frequency bands. The understanding of the channel will help link budgeting and system planning for future wireless communication. An automatic testing system has been developed using remote control by LABVIEW. This increases testing efficiency and reduces near field interference from the operator. A combined E/H plane 2-D ray-tracing method is proposed to predict the channel performance. This approach accurately predicts path loss for both line-of-sight and non-line-of-sight paths. It predicts the delay spread in line-of-sight paths well but fails for non-line-of-sight paths. This could be due to the ignorance of some higher order paths with small amplitudes but near random phases. In addition, a 3-D simplified ray-tracing code is developed to for access point optimization and to predict human shadow effects.\r\n" }, { "name": "Malhotra, Sanjeev", "degree": "PhD", "year": "2004", "title": "On Combustion Instability in Solid Rocket Motors", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05062004-130913", "creators": [ { "name": { "family": "Malhotra", "given": "Sanjeev" }, "id": "Malhotra-Sanjeev", "display_name": "Malhotra, Sanjeev" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Flandro", "given": "G. A." }, "id": "Flandro-G-A", "role": "member", "display_name": "Flandro, G. A." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V1WS-S833", "abstract": "An investigation of combustion instability in solid rocket motors was conducted using perturbation techniques, with particular emphasis placed upon understanding the fluid dynamics of the chamber environment. It was shown that although the phenomena generally manifests itself as oscillations of pressure, with the frequencies measured in tests well predicted by classical acoustic formulas, important aspects of the behavior cannot be explained without due recognition of the two basic processes of fluid dynamics\u2014i.e., the compressing/expanding process and the shearing process.
\r\n\r\nThus, a new framework for studying these instabilities that accommodated both linear and nonlinear behavior was developed. The approach differed from previous work in its use of linear stability eigenfunctions\u2014that satisfy the no-slip boundary condition\u2014as a basis for the expansion, with adjoints used to effect a spatial averaging. Among other things, this allowed for the self-consistent inclusion of vortical flow effects.
\r\n\r\nWith respect to the linear behavior, two dominant vorticity-related pathways were shown to exist: one because of sound creating vorticity, and the other, because of that vorticity, in turn, creating more sound. These effects cancel however and thus to leading order no net contribution exists. Though this finding had been reported in an earlier study, restrictive assumptions were introduced. In contrast, we establish that the result is independent of grain geometry and holds for any fluid motion, turbulent or otherwise.
\r\n\r\nA nonlinear coupling to the flame zone owing to vorticity creation was also identified. The term was left unevaluated however, since no satisfactory model of the flame response presently exists. To help circumvent this difficulty, i.e., that much remains to be done on modeling nonlinear processes, the amplitude equations were studied in a general way using perturbation techniques based on ideas of resonance. The advantage of such an approach is that the nonlinear coefficients need not be specified a priori\u2014only conditions on the linear behavior of the system need to be placed. Closed form results were derived for the limiting periodic behavior when the first mode is unstable and compared against results from numerical integration. Striking agreement was shown.
" }, { "name": "Mason, Maribeth Swiatek", "degree": "PhD", "year": "2004", "title": "Synthesis of Large-Grained Polycrystalline Silicon by Hot-Wire Chemical Vapor Deposition for Thin Film Photovoltaic Applications", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182004-221215", "creators": [ { "name": { "family": "Mason", "given": "Maribeth Swiatek" }, "id": "Mason-Maribeth-Swiatek", "display_name": "Mason, Maribeth Swiatek" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7K9R-VX22", "abstract": "In this study, we investigate the fabrication of large-grained polycrystalline silicon by hot-wire chemical vapor deposition (HWCVD) and its suitability for thin-film photovoltaic applications. We have devised two strategies for the fast, low-temperature growth of thin polycrystalline silicon films on glass substrates. The first is the direct growth of polycrystalline silicon on SiO\u2082 by HWCVD. We use atomic force microscopy (AFM) to characterize fully continuous polycrystalline silicon films grown by HWCVD on SiO\u2082, as well as the nucleation density of silicon islands formed in the early stages of HWCVD growth, as a function of temperature and hydrogen dilution (H\u2082:SiH\u2084). Our observations of the nucleation kinetics of Si on SiO\u2082 can be explained by a rate-equation pair-binding model, from which we derive an estimate for the prefactor and activation energy for surface diffusion of Si on SiO\u2082 during HWCVD growth and assess the viability of this method for the rapid growth of large-grained polycrystalline silicon on SiO\u2082.
\r\n\r\nThe second strategy uses large-grained (~100 \u00b5m) polycrystalline silicon layers fabricated by selective nucleation and solid-phase epitaxy (SNSPE) on SiO\u2082 substrates as templates for epitaxial growth by HWCVD. Using reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM), we have derived a phase diagram for Si on Si(100) consisting of epitaxial, twinned epitaxial, mixed epitaxial/polycrystalline, and polycrystalline phases of growth on Si(100) in the 50 nm-2 \u00b5m thickness regime. Evidence is also presented for epitaxial growth on SNSPE templates, which use nickel nanoparticles as nucleation sites for the solid-phase crystallization of phosphorus-doped amorphous silicon on SiO\u2082. Minority carrier lifetimes for films on Si(100), as measured by resonant-coupled photoconductive decay experiments, range from 5.7 to 14.8 microseconds while those for films on SNSPE templates range from 5.9 to 19.3 microseconds. Residual nickel present in the SNSPE templates does not significantly affect the lifetime of films grown on SNSPE templates, making the growth of epitaxial layers by HWCVD on SNSPE templates a possible strategy for the fabrication of thin-film photovoltaics.
" }, { "name": "Meyer, Mark", "degree": "PhD", "year": "2004", "title": "Discrete Differential Operators for Computer Graphics", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-085345", "creators": [ { "name": { "family": "Meyer", "given": "Mark" }, "id": "Meyer-Mark", "display_name": "Meyer, Mark" } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "compsci" ], "doi": "10.7907/M3NP-4G18", "abstract": "This thesis presents a family of discrete differential operators. Since these operators are derived taking into account the continuous notions of differential geometry, they possess many similar properties. This family consists of first- and second-order properties, both geometric and parametric. These operators are then analyzed and their practical use is tested in several example applications.
\r\n\r\nFirst, the operators are used in a smoothing application. Due to the properties of the operators, the resulting smoothing algorithm is general, efficient and robust to sampling problems. The smoothing can be applied to many different inputs ranging from images to surfaces to volume data.
\r\n\r\nSecond, a surface remeshing technique using the operators is presented. Given the operators, we present an algorithm that resamples a surface mesh according to several geometric criteria (integrated curvature, directional curvature, geometric distortion). The resulting algorithm is efficient, general and user-tunable.
\r\n\r\nNext, a surface mesh parameterization technique is presented. Using geometric invariants associated with the discrete operators, we present an efficient, tunable parameterization algorithm that is robust to sampling irregularities in the input model. Using the properties of the differential operators allows us to make a parameterization algorithm that relies only on geometric information and not the original parameterization of the input model.
\r\n\r\nFinally, we conclude and present future work including physical simulation and sampling theory.
" }, { "name": "O'Gorman, Paul Ambrose", "degree": "PhD", "year": "2004", "title": "Theory and Simulation of Passive Scalar Mixing in the Presence of a Mean Scalar Gradient", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-150652", "creators": [ { "name": { "family": "O'Gorman", "given": "Paul Ambrose" }, "id": "O'Gorman-Paul-Ambrose", "display_name": "O'Gorman, Paul Ambrose" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K02H-HK48", "abstract": "The turbulent mixing of a passive scalar in the presence of a mean scalar gradient was investigated using theory and simulation. The velocity-scalar cospectrum measures the distribution of the mean scalar flux across scales. An inequality is shown to bound the magnitude of the cospectrum in terms of the shell-summed energy and scalar spectra. At high Schmidt number this bound limits the possible contribution of the sub-Kolmogorov scales to the scalar flux. At low Schmidt number we use an argument of Batchelor, Howells, and Townsend (1959) to derive a new asymptotic result for the cospectrum in the inertial-diffusive range, with a -11/3 power law wavenumber dependence. A comparison is made with results from large-eddy simulation at low Schmidt number.
\r\n\r\nThe sparse direct-interaction perturbation (SDIP) was used to calculate the cospectrum for a range of Schmidt numbers. The Kolmogorov type scaling result is recovered in the inertial-convective range, and the constant of proportionality was calculated. At high Schmidt numbers, the cospectrum is found to decay exponentially in the viscous-convective range, and at low Schmidt numbers the -11/3 power law is observed in the inertial-diffusive range. The stretched-spiral vortex model was used to calculate the cospectrum, and asymptotic expressions were found for the contribution to the cospectrum from the axial velocity in the vortex structures. Results are reported for the cospectrum from a direct numerical simulation at a Taylor Reynolds number of 265, and a comparison is made of results for the cospectrum from the SDIP, the stretched-spiral vortex model, simulation, and experiment.
\r\n\r\nThe stretched-spiral vortex model was also used to derive expressions for the modal time correlation functions of the velocity and scalar fields. These expressions were evaluated numerically and asymptotically. Winding by the vortex core is shown to lead to an inertial timescale, and movement of the vortex structures by the large scale flow leads to a sweeping timescale. The velocity and scalar modal time correlation functions were calculated in the direct numerical simulation. They coincide for large enough wavenumber, and are found to collapse to universal forms when a sweeping timescale is used.
" }, { "name": "O'Reilly, Gerard Kieran", "degree": "PhD", "year": "2004", "title": "Compressible Vortices and Shock-Vortex Interactions", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262004-145030", "creators": [ { "name": { "family": "O'Reilly", "given": "Gerard Kieran" }, "id": "O'Reilly-Gerard-Kieran", "display_name": "O'Reilly, Gerard Kieran" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FGJD-0Z31", "abstract": "Secondary instabilities on the organized, spanwise, vortical structures in incompressible shear layers, play an important role in generating the onset of three-dimensional turbulence in such flows. The effect of increasing compressibility on these instabilities is examined by using the compressible Stuart vortex as a model for a compressible shear layer. It is found that both two- and three-dimensional subharmonic instabilities cease to promote pairing events even at moderate free stream Mach numbers. The fundamental mode becomes dominant as the free stream Mach number is increased, and a new instability corresponding to an instability on a parallel shear layer is observed. The interaction of a shock with a compressible vortex may be viewed as a simplified model of the general interaction of a shock with the coherent structures in a turbulent flow field. An approximate theory for computing shock-compressible-vortex interactions is developed, based on Ribner (1954). The problem of convection of a frozen patern of vorticity, dilatation, temperature and entropy through a planar shock wave is considered. The refraction and modification of the upstream disturbances into the three basis modes permitted by the linear Euler equations is derived, as well as the perturbation to the shock wave. This theory is used to compute approximate post-shock states corresponding to shock-CSV interactions, a model for shock shear layer interactions. The method is verified by comparing its approximate post-shock fields with those computed explicitly using AMROC, a finite difference, AMR-WENO code. Finally, numerical solutions corresponding to a compressible analogue of the Mallier and Maslowe vortex (a periodic array of counter-rotating vortices) are presented. These solutions admit the existence of large regions of smooth supersonic flow, and could potentially be used to model the counter-rotating vortices arising from the single- and multi-mode Richtmyer-Meshkov instability." }, { "name": "Oldham, Neal Curtis", "degree": "PhD", "year": "2004", "title": "Investigation of Spintronic Materials Systems: Deposition and Characterization", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-013645", "creators": [ { "name": { "family": "Oldham", "given": "Neal Curtis" }, "id": "Oldham-Neal-Curtis", "display_name": "Oldham, Neal Curtis" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Picus", "given": "Gerry" }, "id": "Picus-G", "role": "member", "display_name": "Picus, Gerry" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/ZAV0-8X28", "abstract": "Continuing initiatives to deploy radical new computing schemes impel the study of new materials systems appropriate for realization of these schemes. One contemporary idea for a basis for new computing architectures is spintronics, the manipulation of electron or nuclear spin for the construction of physical quantum logic and other devices. In this work basic materials development for spintronics will be discussed. The growth and characterization of materials systems proposed as means of injecting spin-polarized electron populations into nonmagnetic semiconductors is examined. Specific materials systems analyzed include magnetite (Fe3O4), cobalt-chromium alloys, and gallia (Ga\u2082O\u2083). Deposition of these materials in thin film form with a suite of techniques including pulsed laser deposition (PLD) and electron-beam evaporation (EBE) is analyzed. Particular attention is given to the chemistry and magnetic properties of these films. Magnetic thin films of magnetite are observed upon silicon, gallium arsenide, and magnesium oxide; the epitaxy of magnetite upon indium arsenide is addressed. Additionally out-of-plane magnetization of Co-Cr alloys is demonstrated and several metallurgical issues with their deposition are discussed. Finally aspects of EBE deposition of gallium oxide for ultrathin tunnel barriers are discussed." }, { "name": "Palanki, Ravi", "degree": "PhD", "year": "2004", "title": "Iterative Decoding for Wireless Networks", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212004-153855", "creators": [ { "name": { "family": "Palanki", "given": "Ravi" }, "id": "Palanki-Ravi", "display_name": "Palanki, Ravi" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Yedidia", "given": "Jonathan S." }, "id": "Yedidia-J-S", "role": "member", "display_name": "Yedidia, Jonathan S." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Dolinar", "given": "Samuel J." }, "id": "Dolinar-S-J", "role": "member", "display_name": "Dolinar, Samuel J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/05AN-ME34", "abstract": "The invention of turbo codes and low density parity check (LDPC) codes has made it possible for us for design error correcting codes with low decoding complexity and rates close to channel capacity. However, such codes have been studied in detail only for the most basic communication system, in which a single transmitter sends data to a single receiver over a channel whose statistics are known to both the transmitter and the receiver. Such a simplistic model is not valid in the case of a wireless network, where multiple transmitters might want to communicate with multiple receivers at the same time over a channel which can vary rapidly.
\r\n \r\nWhile the design of efficient error correction codes for a general wireless network is an extremely hard problem, it should be possible to design such codes for several important special cases. This thesis takes a few steps in that direction. We analyze the performance of low density parity check codes under iterative decoding in certain simple networks and prove Shannon-theoretic results for more complex networks.
\r\n \r\nMore specifically, we analyze the iterative decoding algorithm in two very important special cases: (a) when the transmitter and receiver have no prior knowledge of the channel and (b) when the channel is a multiple access channel. We also apply iterative decoding to some non-LDPC codes on the binary symmetric channel and the additive white Gaussian noise channel. Finally, we derive capacity results for a class of wireless multicast networks and a class of fading channels.
" }, { "name": "Preston, Alastair Thomas", "degree": "PhD", "year": "2004", "title": "Modeling Heat and Mass Transfer in Bubbly Cavitating Flows and Shock Waves in Cavitating Nozzles", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182003-150738", "creators": [ { "name": { "family": "Preston", "given": "Alastair Thomas" }, "id": "Preston-Alastair-Thomas", "display_name": "Preston, Alastair Thomas" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/ZHSN-D849", "abstract": "Two problems are considered in this thesis: the modeling of heat and mass diffusion effects on the dynamics of spherical bubbles, and the computation of unsteady, bubbly cavitating flows in nozzles. The goal of Part I is to develop a reduced-order model that is able to accurately and efficiently capture the effect of heat and mass transfer on the dynamics of bubbles. Detailed computations of forced and oscillating bubbles including heat and mass diffusion show that the assumptions of polytropic behavior, constant vapor pressure, and an effective liquid viscosity do not accurately account for diffusive damping and thus do not accurately capture bubble dynamics. While the full bubble computations are readily performed for single bubbles, they are too expensive to implement into continuum models of complex bubbly flows where the radial diffusion equations would have to be solved at each grid point. Therefore reduced-order models that accurately capture diffusive effects are needed.
\r\n\r\nWe first develop a full bubble computation, where the full set of radial conservation equations are solved in the bubble interior and surrounding liquid. This provides insight as to which equations, or terms in equations, may be able to be neglected while still accurately capturing the bubble dynamics. Motivated by results of the full computations, we use constant heat and mass transfer coefficients to model the transfer at the bubble wall. In the resulting reduced-order model the heat and mass diffusion equations are each replaced by a single ordinary differential equation. The model is therefore efficient enough to implement into continuum computations. Comparisons of the reduced-order model to the full computations over a wide range of parameters indicate agreement that is superior to existing models.
\r\n\r\nIn Part II we investigate the effects of unsteady bubble dynamics on cavitating flow through a converging-diverging nozzle. A continuum model that couples the Rayleigh-Plesset equation with the continuity and momentum equations is used to formulate unsteady, quasi-one-dimensional partial differential equations. Flow regimes studied include those where steady state solutions exist, and those where steady state solutions diverge at the so-called flashing instability. These latter flows consist of unsteady bubbly shock waves traveling downstream in the diverging section of the nozzle. An approximate analytical expression is developed to predict the critical back pressure for choked flow. The results agree with previous barotropic models for those flows where bubble dynamics are not important, but show that in many instances the neglect of bubble dynamics cannot be justified. Finally the computations show reasonable agreement with an experiment that measures the spatial variation of pressure, velocity and void fraction for steady shock free flows, and good agreement with an experiment that measures the throat pressure and shock position for flows with bubbly shocks. In the model, damping of the bubble radial motion is restricted to a simple \"effective\" viscosity to account for diffusive effects. However, many features of the nozzle flow are shown to be independent of the specific damping mechanism. This is confirmed by the implementation of the more sophisticated diffusive modeling developed in Part I.
" }, { "name": "Ran, Hongyu", "degree": "PhD", "year": "2004", "title": "Numerical Study of the Dynamics and Sound Generation of a Turbulent Vortex Ring", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-06082004-151101", "creators": [ { "name": { "family": "Ran", "given": "Hongyu" }, "id": "Ran-Hongyu", "display_name": "Ran, Hongyu" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ASHK-JV07", "abstract": "In the present study, Direct Numerical Simulations (DNS) of the fully compressible, three-dimensional Navier-Stokes equations are used to generate an axisymmetric vortex ring to which three-dimensional stochastic disturbances are added. The radiated acoustic field is computed directly in the near field, and by solving the wave equation in a spherical coordinate system in the far field.
\r\n\r\nAt high Reynolds number, a vortex ring will undergo an instability to azimuthal waves. The instability produces higher azimuthal modes and induces nonlinear interaction between the modes, and will cause the vortex ring to break down and transition to turbulence. The early stages of the simulation agree well with the linear instability theory. Nonlinear stage of instability, transition, formation of axial flow and streamwise vorticity are analyzed and compared with experimental results. After turbulent transition, the evolution of statistical quantities becomes independent of viscosity and the initial geometry, and the flow become self-similar. The temporal evolution of quantities including total circulation, axial velocity profile, vortex ring displacement and vorticity profile agrees well with the self-similarity law. Turbulent energy spectrum, Reynolds stresses and turbulence production are also presented.
\r\n\r\nThe unsteady vorticity field generates acoustic waves with higher azimuthal modes, each mode with a distinctive spectrum and directivity. The ensemble averaged peak frequency, bandwidth, and the sound pressure level agrees qualitatively with reported experimental results. The directivity of each azimuthal mode is compared with predictions of vortex sound theory. The sound generation consists of three stages. The first is a deterministic stage when linear instability waves emerge and grow and generate relatively weak sound. The second stage is nonlinear interaction and vortex breakdown; at this stage the sound pressure level reaches a peak value. The third stage is the turbulent asymptotic decay of the acoustic field. Based on the self-similar decay of the turbulent near field, the self-similar decay of the sound field is investigated. Connection between the acoustic field and the vortex ring oscillations is also studied with vortex sound theory. Finally, we note some similarities between the sound radiated by a train of de-correlated vortex rings and turbulent jet noise. The sound pressure level, spectrum, and directivity of the train of vortex rings is similar to the sound field from a jet with similar Reynolds number and Mach number.
" }, { "name": "Riedel, Marcus D.", "degree": "PhD", "year": "2004", "title": "Cyclic Combinational Circuits", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-05032004-153842", "creators": [ { "name": { "family": "Riedel", "given": "Marcus D." }, "id": "Riedel-Marcus-D", "orcid": "0000-0002-3318-346X", "display_name": "Riedel, Marcus D." } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Viterbi", "given": "Andrew" }, "id": "Viterbi-A", "role": "member", "display_name": "Viterbi, Andrew" }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/410B-XR25", "abstract": "A collection of logic gates forms a combinational circuit if the outputs can be described as Boolean functions of the current input values only. Optimizing combinational circuitry, for instance, by reducing the number of gates (the area) or by reducing the length of the signal paths (the delay), is an overriding concern in the design of digital integrated circuits.
\r\n\r\nThe accepted wisdom is that combinational circuits must have acyclic (i.e., loop-free or feed-forward) topologies. In fact, the idea that \"combinational\" and \"acyclic\" are synonymous terms is so thoroughly ingrained that many textbooks provide the latter as a definition of the former. And yet simple examples suggest that this is incorrect. In this dissertation, we advocate the design of cyclic combinational circuits (i.e., circuits with loops or feedback paths). We demonstrate that circuits can be optimized effectively for area and for delay by introducing cycles.
\r\n\r\nOn the theoretical front, we discuss lower bounds and we show that certain cyclic circuits are one-half the size of the best possible equivalent acyclic implementations. On the practical front, we describe an efficient approach for analyzing cyclic circuits, and we provide a general framework for synthesizing such circuits. On trials with industry-accepted benchmark circuits, we obtained significant improvements in area and delay in nearly all cases. Based on these results, we suggest that it is time to re-write the definition: combinational might well mean cyclic.
" }, { "name": "Ringuette, Matthew James", "degree": "PhD", "year": "2004", "title": "Vortex Formation and Drag on Low Aspect Ratio, Normal Flat Plates", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292004-183807", "creators": [ { "name": { "family": "Ringuette", "given": "Matthew James" }, "id": "Ringuette-Matthew-James", "orcid": "0000-0002-8998-9489", "display_name": "Ringuette, Matthew James" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "orcid": "0000-0002-8587-9936", "role": "member", "display_name": "Dickinson, Michael H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/907K-2F28", "abstract": "Experiments were done to investigate the role of vortex formation in the drag force generation of low aspect ratio, normal flat plates starting from rest. This very simplified case is a first, fundamental step toward understanding the more complicated flow of hovering flight, which relies primarily on drag for propulsion. The relative importance of the plate's free end, or tip, with varying aspect ratio was also studied.
\r\n\r\nIdentifying the relationship among aspect ratio, vortex formation, and drag force can provide insight into the wing aspect ratios and kinematics found nature, with the eventual goal of designing man-made flapping wing micro air vehicles.
\r\n\r\nThe experiments were carried out using flat plate models in a towing tank at a moderate Reynolds number of 3000. Two aspect ratios, 6 and 2, were considered, the latter in order to have a highly tip-dominated case. A force balance measured the time-varying drag, and multiple, perpendicular sections of the flow velocity were measured quantitatively using digital particle image velocimetry. Vorticity fields were calculated from the velocity data, and features in the drag force for different aspect ratios were related to the vortex dynamics. Finally, since the flow is highly three-dimensional, dye flow visualization was done to characterize its structure and to augment the two-dimensional digital particle image velocimetry data.
" }, { "name": "Rogan, Robert Cashman", "degree": "PhD", "year": "2004", "title": "Investigation of the Multiscale Constitutive Behavior of Ferroelectric Materials Using Advanced Diffraction Techniques", "advisor": "Ustundag, Ersan", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-105848", "creators": [ { "name": { "family": "Rogan", "given": "Robert Cashman" }, "id": "Rogan-Robert-Cashman", "display_name": "Rogan, Robert Cashman" } ], "advisors": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "advisor", "display_name": "Ustundag, Ersan" } ], "committee": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "chair", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "matsci" ], "doi": "10.7907/BT3T-F608", "abstract": "Ferroelectric ceramics are widely used in a diverse set of devices including sensors, actuators, and transducers. The technological importance of ferroelectrics originates from their large electromechanical coupling. Ferroelectric materials exhibit a complicated behavior in response to both electrical and mechanical loads which produce large internal stresses that eventually lead to failure. Efforts to model and predict the behavior of ferroelectrics have been hindered by the lack of suitable constitutive relations that accurately describe the electromechanical response of these materials. While many measurements have been conducted on the macroscopic response of single-crystals or polycrystals, multiaxial (and multiscale) data about the in situ internal strain and texture response of these materials is lacking; this information is critical to the development of accurate models, and diffraction techniques which directly measure internal crystal strains and material texture are aptly suited to supply it.
\r\n\r\nA neutron diffraction technique was employed which allowed for the simultaneous measurement of material texture and lattice strains in directions parallel and transverse to an applied mechanical load. By comparing the behaviors of single-phase tetragonal, single-phase rhombohedral, and dual-phase morphotropic compositions, information concerning mechanics of average macroscopic behavior was inferred. In an effort to probe more of the multiaxial constitutive behavior, a high-energy X-ray diffraction technique was employed. Using transmission geometry and a 2-D image plate detector, 36 different directions of sample behavior were measured simultaneously. Polychromatic scanning X-ray microdiffraction was used to investigate the microscale three-dimensional strain tensor in single-crystals. One investigation yielded the first ever direct measurement of the tri-axial strain fields associated with single domain walls in ferroelectrics. The second investigation recorded the domain switching mechanisms activated to accommodate indentation-induced fracture stresses. Finally, 3-D XRD was used to probe the mesoscale constitutive behavior of single, embedded grains of BaTiO3 within a polycrystalline matrix.
\r\n\r\nThe experimental methods described in this thesis provide access to two-dimensional and three-dimensional multiaxial constitutive strain behavior in ferroelectrics for each of the microscopic, mesoscopic, and macroscopic length scales. Results from each of these length scales will provide critical data for models attempting to accurately describe the behavior of ferroelectric materials.
\r\n" }, { "name": "Ross, Shane David", "degree": "PhD", "year": "2004", "title": "Cylindrical Manifolds and Tube Dynamics in the Restricted Three-Body Problem", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05182004-154045", "creators": [ { "name": { "family": "Ross", "given": "Shane David" }, "id": "Ross-Shane-David", "orcid": "0000-0001-5523-2376", "display_name": "Ross, Shane David" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Scheeres", "given": "Daniel" }, "id": "Scheeres-D", "role": "member", "display_name": "Scheeres, Daniel" }, { "name": { "family": "Lo", "given": "Martin" }, "id": "Lo-Martin", "role": "member", "display_name": "Lo, Martin" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/KHYT-A428", "abstract": "Within the phase space of the planar circular restricted three-body problem, stable and unstable manifolds of periodic orbits with a S x R (cylindrical) geometry are shown to exist. The periodic orbits considered reside in bottleneck regions of the energy manifold, separating large zones associated with motion about one mass, the other mass, or both masses.
\r\n\r\nThe cylinders have the physical property that all motion through the bottleneck in which the periodic orbit resides must occur through the interior of these surfaces. The cylinders thus mediate the global transport of test particles between large zones of the energy surface which are separated by the bottlenecks.
\r\n\r\nBy elucidating the structuring role of the cylinders, we provide a new language for discussing some important problems in celestial mechanics. Furthermore, we propose that these cylindrical structures are the natural objects of study for the design of space mission trajectories which take advantage of three-body effects.
" }, { "name": "Sankaran, Ramanathan Mohan", "degree": "PhD", "year": "2004", "title": "High-Pressure Microdischarges as Microreactors for Materials Applications", "advisor": "Giapis, Konstantinos P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012004-152711", "creators": [ { "name": { "family": "Sankaran", "given": "Ramanathan Mohan" }, "id": "Sankaran-Ramanathan-Mohan", "orcid": "0000-0002-9399-4790", "display_name": "Sankaran, Ramanathan Mohan" } ], "advisors": [ { "name": { "family": "Giapis", "given": "Konstantinos P." }, "id": "Giapis-K-P", "role": "advisor", "display_name": "Giapis, Konstantinos P." } ], "committee": [ { "name": { "family": "Giapis", "given": "Konstantinos P." }, "id": "Giapis-K-P", "role": "chair", "display_name": "Giapis, Konstantinos P." }, { "name": { "family": "Collier", "given": "C. Patrick" }, "id": "Collier-C-P", "role": "member", "display_name": "Collier, C. Patrick" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "member", "display_name": "Gavalas, George R." } ], "option_major": [ "chemeng" ], "doi": "10.7907/DP21-7606", "abstract": "This thesis describes a novel \"microplasma\" source that is suitable for microreactor applications. The high-pressure \"microplasma\" is a direct current microdischarge, formed between two metal electrodes: a cathode with a pin-hole (diameter~100 \u00b5m) and an anode of unspecified shape. Strong radial electric fields are produced in the microhollow cathode geometry, causing electrons to oscillate (Pendel effect). As a result of enhanced ionization processes, it is possible to produce a stable high-intensity discharge at pressures of 1 atmosphere or higher. We have utilized these microdischarges for several applications including pattern transfer, diamond deposition, excimer emission, and nanoparticle synthesis.
\r\n\r\nMaskless etching of structures for MEMS and microfluidic applications is achieved by forming microplasmas in complex patterns within a stencil mask in contact with the surface to be patterned. In one application, CF4/Ar microdischarges are formed inside planar copper-polyimide stencil masks that permit direct etching of silicon wafers. To deposit films, microdischarges are formed inside metal capillaries that accommodate flow. A plasma microjet is created and directed towards a heated substrate that enables deposition of polycrystalline diamond films over small spatial scales. Simultaneous operation of multiple micodischarges could form the basis of a combinatorial tool for rapid materials development.
\r\n\r\nMicrodischarges in capillary tubes can serve as sources of intense UV radiation. Excimer emission in argon (Ar2*) at 128 nm has been studied by vacuum UV spectroscopy. A method to increase the on-axis excimer radiation is demonstrated by adding discharges in a linear array. Building of emitting volume shows potential for intensifying excimer emission.
\r\n\r\nThe properties of microdischarges are especially conducive to applications as short-residence time reactors. For example, microdischarges are attractive for nanoparticle synthesis since the residence time of particle nucleation can be limited in the reactor to time scales on the order of milliseconds. This methodology has been used to produce silicon particles with mean sizes of 1-5 nm and narrow size distributions. The silicon nanoparticles exhibit blue photoluminescence at room temperature suggesting quantum confinement. The pristine nature of the nanoparticles enables fundamental studies of surface functionalization.
" }, { "name": "Schkolne, Steven", "degree": "PhD", "year": "2004", "title": "3-D Interfaces for Spatial Construction", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-003252", "creators": [ { "name": { "family": "Schkolne", "given": "Steven" }, "id": "Schkolne-Steven", "display_name": "Schkolne, Steven" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-E", "orcid": "0000-0002-5899-7523", "role": "member", "display_name": "Winfree, Erik" }, { "name": { "family": "Ishii", "given": "Hiroshi" }, "id": "Iishii-H", "role": "member", "display_name": "Ishii, Hiroshi" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "compsci" ], "doi": "10.7907/8VWJ-TX38", "abstract": "It is becoming increasingly easy to bring the body directly to digital form via stereoscopic immersive displays and tracked input devices. Is this space a viable one in which to construct 3d objects? Interfaces built upon two-dimensional displays and 2d input devices are the current standard for spatial construction, yet 3d interfaces, where the dimensionality of the interactive space matches that of the design space, have something unique to offer.
\r\n\r\nThis work increases the richness of 3d interfaces by bringing several new tools into the picture: the hand is used directly to trace surfaces; tangible tongs grab, stretch, and rotate shapes; a handle becomes a lightsaber and a tool for dropping simple objects; and a raygun, analagous to the mouse, is used to select distant things. With these tools, a richer 3d interface is constructed in which a variety of objects are created by novice users with relative ease. What we see is a space, not exactly like the traditional 2d computer, but rather one in which a distinct and different set of operations is easy and natural.
\r\n\r\nDesign studies, complemented by user studies, explore the larger space of three-dimensional input possibilities. The target applications are spatial arrangement, freeform shape construction, and molecular design. New possibilities for spatial construction develop alongside particular nuances of input devices and the interactions they support. Task-specific tangible controllers provide a cultural affordance which links input devices to deep histories of tool use, enhancing intuition and affective connection within an interface. On a more practical, but still emotional level, these input devices frame kinesthetic space, resulting in high-bandwidth interactions where large amounts of data can be comfortably and quickly communicated.
\r\n\r\nA crucial issue with this interface approach is the tension between specific and generic input devices. Generic devices are the tradition in computing -- versatile, remappable, frequently bereft of culture or relevance to the task at hand. Specific interfaces are an emerging trend -- customized, culturally rich, to date these systems have been tightly linked to a single application, limiting their widespread use. The theoretical heart of this thesis, and its chief contribution to interface research at large is an approach to customization. Instead of matching an application domain's data, each new input device supports a functional class. The spatial construction task is split into four types of manipulation: grabbing, pointing, holding, and rubbing. Each of these action classes spans the space of spatial construction, allowing a single tool to be used in many settings without losing the unique strengths of its specific form. Outside of 3d interface, outside of spatial construction, this approach strikes a balance between generic and specific suitable for many interface scenarios.
\r\n\r\nIn practice, these specific function groups are given versatility via a quick remapping technique which allows one physical tool to perform many digital tasks. For example, the handle can be quickly remapped from a lightsaber that cuts shapes to tools that place simple platonic solids, erase portions of objects, and draw double-helices in space.
\r\n\r\nThe contributions of this work lie both in a theoretical model of spatial interaction, and input devices (combined with new interactions) which illustrate the efficacy of this philosophy. This research brings the new results of Tangible User Interface to the field of Virtual Reality. We find a space, in and around the hand, where full-fledged haptics are not necessary for users physically connect with digital form.
" }, { "name": "Scruggs, Jeffrey Thomas", "degree": "PhD", "year": "2004", "title": "Structural Control Using Regenerative Force Actuation Networks", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012004-063432", "creators": [ { "name": { "family": "Scruggs", "given": "Jeffrey Thomas" }, "id": "Scruggs-Jeffrey-Thomas", "orcid": "0000-0002-1560-6211", "display_name": "Scruggs, Jeffrey Thomas" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/W3M9-ZW72", "abstract": "A Regenerative Force Actuation (RFA) Network consists of multiple electromechanical forcing devices distributed throughout a structural system and actuated in such a way as to reduce the response of the structure when subject to an excitation. The associated electronics of the devices are connected together such that they are capable of sharing electrical power with each other. This makes it possible for some devices to extract mechanical energy from the structure, while others re-inject a portion of that energy back into the structure at other locations. The forcing capability of an RFA network is constrained only by the requirement that in the aggregate the total network must always dissipate energy.
\r\n\r\nThe electromechanical currents generated by RFA networks must be controlled to create the desired structural forces. This control is facilitated by the alternation of a multitude of power-electronic transistor switches in the electrical network. In this study, a sliding-mode switching controller is proposed for realizing zero-error force command tracking. It is shown that parameter uncertainty is a critical issue for force commands which require the network to operate near its optimum transmissive efficiency.
\r\n\r\nRFA networks can be used to create velocity-proportional damping forces in structures. However, unlike traditional structural damping, RFA networks have the ability to create non-local and asymmetric damping forces. It is shown that this more generalized damping capability can lead to significant improvements in the forced response of a structure, as compared with traditional linear damping.
\r\n\r\nRFA networks may also be used for feedback control. In this context, the forcing capability of the RFA network is constrained by its physical limitations. In this study, a systematic method of nonlinear control design called \"Damping-Reference\" control is proposed, which guarantees a certain level of quadratic performance for the structural response. Variants of the control law synthesis are proposed for quadratic regulation, stochastic control, and H[infinity] control contexts.
\r\n\r\nThese ideas are illustrated in the context of earthquake engineering through a simulation example, involving a three-story structure with a two-actuator RFA network installed. In this example, it is shown that the \"power sharing\" nature of the RFA network has a significant influence on the response.
" }, { "name": "Shaikhutdinov, Rustem Vil", "degree": "PhD", "year": "2004", "title": "Structural Damage Evaluation: Theory and Applications to Earthquake Engineering", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05172004-101516", "creators": [ { "name": { "family": "Shaikhutdinov", "given": "Rustem Vil" }, "id": "Shaikhutdinov-Rustem-Vil", "orcid": "Shaikhutdinov", "display_name": "Shaikhutdinov, Rustem Vil" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Porter", "given": "Keith A." }, "id": "Porter-K-A", "role": "member", "display_name": "Porter, Keith A." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/5SA6-4414", "abstract": "The further development of performance-based earthquake engineering (PBEE) is on the current agenda of the earthquake engineering community. A part of assessing the seismic performance of civil engineering structures involves estimation of seismic damage. The conventional approach to damage estimation is based on fragility functions that relate some chosen parameters of structural response to incurred damage. Therefore, damage prediction is based exclusively on the knowledge of the chosen structural response parameters, meaning that damage analysis is uncoupled from the structural analysis. The structural response parameters selected for use in damage analysis are usually referred to as engineering demand parameters (EDP). In the present study, it is shown that for structural damage estimation, the uncoupled damage analysis has deficiencies that lead to less accurate damage prediction. These shortcomings originate from two sources: first, dependence of practically all EDPs on structural damage and second, inexact damage description. To overcome these deficiencies, another approach to structural damage estimation is proposed. The proposed approach, besides using an EDP, uses all information available from structural analysis that is relevant to the damage to be assessed, implying that damage analysis is coupled with structural analysis. It is shown that utilization of this additional information provides more accurate damage prediction. The difference between the two approaches is studied by comparison of results of damage estimation performed for a 2-D structural model of a reinforced-concrete frame. The results show that difference between uncoupled and coupled damage analysis estimates could be significant and that it depends on specific characteristics of the chosen structural model and the damage model in a complex way, preventing the possibility of estimating this error in a general form that is applicable to all practically possible cases. Damage estimation is performed for various damage models that include both single and multiple damage states. Since the final goal of seismic performance evaluation is estimation of decision variables such as repair cost, downtime, etc., the two approaches to damage estimation are also compared in terms of repair cost that is calculated for the reinforced-concrete frame. A case where structural damage prediction is based on observation of EDP alone, without a structural model available, is also studied. It is shown that incorporating site-specific information can significantly change the damage estimates and, therefore, may be worth doing." }, { "name": "Spillane, Sean Michael", "degree": "PhD", "year": "2004", "title": "Fiber-Coupled Ultra-High-Q Microresonators for Nonlinear and Quantum Optics", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012004-104250", "creators": [ { "name": { "family": "Spillane", "given": "Sean Michael" }, "id": "Spillane-Sean-Michael", "display_name": "Spillane, Sean Michael" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "member", "display_name": "Kimble, H. Jeff" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/MKYH-WV47", "abstract": "The ability to confine optical energy in small volumes for long periods of time is desirable for a number of applications, ranging from photonics and nonlinear optics, to fundamental studies in quantum electrodynamics. Whispering-gallery-mode microresonators are a promising cavity to study, due to the ability to obtain quality factors exceeding 100 million in micron-scale volumes. This thesis investigates the suitability of ultra-high-quality factor silica microresonators (both silica microspheres and silica toroidal microresonators) for nonlinear and quantum optics. Crucial to the actual use of these structures is the ability to efficiently excite and extract optical energy. The first part of this thesis investigates the ability to achieve near lossless coupling between a fiber-taper waveguide and a silica microresonator. It is shown that a coupling ideality (which is the fraction of energy coupled into the desired fiber mode) in excess of 99.97% is possible, meaning that optical energy can be coupled both to and from the optical resonator with near perfect efficiency.
\r\n\r\nUsing tapered fibers, low threshold stimulated Raman scattering is observed in both silica microspheres and silica microtoroids at record low incident pump powers below 100 microwatts, much lower than previous devices. High conversion efficiencies (>35%) are also realized. Furthermore, the conditions for optimized performance of both stimulated Raman scattering and parametric oscillation in a microcavity are described.
\r\n\r\nLastly, the suitability of toroidal microcavities for strong coupling cavity quantum electrodynamics is investigated. Numerical modeling of the optical modes demonstrates a significant reduction of modal volume with respect to spherical cavities, while retaining high quality factors. The extra degree of freedom of toroid microcavities can be used to achieve improved strong-coupling characteristics, and numerical results for atom-cavity coupling strength, critical atom number and critical photon numbers for cesium are calculated and shown to exceed values currently possible using Fabry-Perot cavities. Modeling predicts atom-cavity coupling rates exceeding 700 MHz and critical atom numbers approaching 10\u207b\u2077.
" }, { "name": "Swift, Geoffrey Allen", "degree": "PhD", "year": "2004", "title": "Neutron Diffraction Study of In Situ-Reinforced Silicon Nitride during Creep", "advisor": "Ustundag, Ersan", "url": "https://resolver.caltech.edu/CaltechETD:etd-03122004-105618", "creators": [ { "name": { "family": "Swift", "given": "Geoffrey Allen" }, "id": "Swift-Geoffrey-Allen", "display_name": "Swift, Geoffrey Allen" } ], "advisors": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "advisor", "display_name": "Ustundag, Ersan" } ], "committee": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "chair", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "member", "display_name": "Ahn, Channing C." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "matsci" ], "doi": "10.7907/A3PQ-FC67", "abstract": "Neutron diffraction was used to study the high temperature creep of in situ-reinforced silicon nitride (ISR Si3N4). Full pattern and single peak fitting methods were used to calculate the average and hkl-specific mechanical properties, including thermal expansion coefficient, creep exponent, Young?s modulus, and Poisson?s ratio. This is both the first in-depth study using time-of-flight neutron diffraction to examine materials at such temperatures (1473 and 1648 K) and the first in situ microstructural study of creeping silicon nitride. Two commercial grades of ISR Si3N4 were tested, AS800 and GS44.
\r\n\r\nThe refractory grain boundary phase of AS800 prevented the onset of creep in the vacuum environment of the SMARTS furnace. However, the high temperature stress-strain data allowed determination of the 1648 K single crystal elastic stiffness tensor, the first such calculation from neutron diffraction strain data. Also determined was the coefficient of thermal expansion (CTE) tensor. The 1648 K stiffness tensor indicated a less stiff C33 component compared to a room temperature stiffness tensor. This lesser value is due either to microstructural or thermal effects.
\r\n\r\nCreep was observed for GS44. A stress step-up test and four constant stress creep tests were performed. Large strains were measured by an extensometer, though of much less magnitude than literature creep studies, with the difference attributed to the vacuum environment protecting the grain boundary phase from suffering reduced viscosity. This is supportive evidence of the long-held notion that the grain boundary phase is the primary determinate of creep behavior. The diffraction strains, though of significantly lower magnitude than the extensometer strains, were measured as non-constant, though the silicon nitride lattice parameters behaved in an unexpected manner. The two lattice parameters were seen to fork from a nearly common initial strain, with the c lattice parameter indicating tensile strain and the a lattice parameter compressive. The relative changes, however, corresponded to an essentially constant unit cell volume, as computed from simple geometry. None of the potential inelastic strain effects on diffraction peaks, such as peak broadening, were observed, further supporting the notion that the grain boundary phase is the source of strain. Neither was there any measured preferred orientation evolution due to creep. The creep exponent of GS44 was calculated as 3.18, a greater value than in literature, likely due to the same creep inhibition of the vacuum furnace.
\r\n\r\nThe classic Norton Equation for creep matched well with the steady state creep rates as a function of applied stress, while a newer model by Luecke and Wiederhorn, incorporating multiple facets specific to Si3N4, matched the data comparably, though with an additional empirical stress dependence incorporated. The effect of performing these experiments in a vacuum rather than in air likely prevented as accurate prediction by their model as with Norton?s. This result is based on the much-reduced creep strain measured compared to literature measurements of the same material at like temperature and stress. However, given the large disparity between the extensometer creep strain and the diffraction creep strain, it is clear that the grain boundary phase experiences the bulk of the deformation. Subsequent SEM observations of tested samples indicated no microstructural change due to the short duration of creep experiments. As with AS800, the GS44 CTE tensor was found, while the stiffness tensor was incalculable due to extreme non-linearity of single peak data.
" }, { "name": "Tanguay, Michel", "degree": "PhD", "year": "2004", "title": "Computation of Bubbly Cavitating Flow in Shock Wave Lithotripsy", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-130028", "creators": [ { "name": { "family": "Tanguay", "given": "Michel" }, "id": "Tanguay-Michel", "display_name": "Tanguay, Michel" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "orcid": "0000-0001-5817-9128", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Crum", "given": "Lawrence A." }, "id": "Crum-L-A", "role": "member", "display_name": "Crum, Lawrence A." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/VQXV-Y948", "abstract": "Lithotripsy is at the forefront of treatment of kidney stones. By firing shock waves at the stone, it can be broken down into small fragments. Although the treatment is non-invasive, both short- and long-term side effects occur. In order to understand and rectify these shortcomings, lithotripsy has been the subject of ongoing research. Based on in vitro experiments, it has been ascertained that the cloud of cavitating bubble produced in the wake of the shock wave is a crucial element in the stone comminution process.
\r\n\r\nVarious solutions designed to maximize stone comminution and/or decrease tissue damage have been proposed over the years. However, the particulars of the comminution mechanism(s) are still undetermined. In this work, a numerical model of the two-phase flow inside an electrohydraulic lithotripter was used to provide additional insight in the behavior of the bubble cloud. The numerical model is based on an ensemble averaged two-phase flow model for a compressible liquid. The differential equations were discretized following the WENO shock capturing scheme in prolate spheroidal and cylindrical coordinate systems. The initial conditions for the flow field are estimated based on empirical observations and then validated by comparing the predicted pressure measurements and bubble cloud behavior against experimental values.
\r\n\r\nIn order to gain additional insight in the mechanism for stone comminution, a variety of relevant initial conditions were modeled. The following lithotripter configurations were analyzed: free-field, dual-pulse and single-pulse with an artificial stone at the focus. The impact of parameters such as the intensity of the initial shock wave and the pulse rate frequency (PRF) has been investigated. Based on an energy argument, conclusions regarding the efficiency of stone comminution are presented. In addition, based on these conclusions, avenues for improvement of the numerical model are highlighted.
" }, { "name": "Tkacenko, Andre", "degree": "PhD", "year": "2004", "title": "Optimization Algorithms for Realizable Signal-Adapted Filter Banks", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142004-214312", "creators": [ { "name": { "family": "Tkacenko", "given": "Andre" }, "id": "Tkacenko-Andre", "display_name": "Tkacenko, Andre" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Vrcelj", "given": "Bojan" }, "id": "Vrcelj-B", "role": "member", "display_name": "Vrcelj, Bojan" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/QZYN-ND12", "abstract": "Multirate filter banks are fundamental systems commonly used in digital signal processing (DSP). Typically, they are used to decompose a discrete-time signal into a set of frequency selective components called subband signals. Filter banks have been found to be useful for lossy data compression schemes such as MP3 and JPEG 2000, denoising, and signal estimation. In the last decade, transmultiplexers, the dual structures of multirate filter banks, have been shown to be useful in digital communications systems such as discrete multitone (DMT) systems for channel equalization and inter/intra-symbol interference cancellation in the presence of noise.
\r\n\r\nRecently, a special type of filter bank adapted to its input known as the principal component filter bank (PCFB) has been shown to be simultaneously optimal for a wide variety of objectives. Such filter banks are not only optimal for relevant data compression type objectives such as coding gain and multiresolution, but also for digital communications type objectives such as power minimization, when the filter bank is implemented in its transmultiplexer form. The only problem is that PCFBs, which are defined over classes of paraunitary (PU) filter banks, are only known to exist for certain classes. In particular, PCFBs are in general known to exist only in the extremal cases where the analysis/synthesis polyphase matrix has zero memory and doubly infinite memory, respectively. Furthermore, for many practical cases of inputs, the filters corresponding to the infinite-order PCFB have ideal bandpass response and are as such unrealizable. When the polyphase matrix has finite memory or a finite impulse response (FIR), it is believed that PCFBs do not exist, although this has not yet been formally proven in the literature.
\r\n\r\nThe main contribution of this thesis is to bridge the gap between the zero memory PCFB and the infinite-order one. To that end, a variety of methods for the design of realizable signal-adapted FIR filter banks is presented. It is shown that a popular conventional method for designing signal-adapted FIR PU filter banks, which only requires the design of an optimal FIR compaction filter, is in fact not well suited for designing good filter banks due to the exponential complexity caused by the nonuniqueness of the FIR compaction filter. To avoid this dilemma, we propose a method by which all of the filters are obtained together. In particular, the method consists of finding an FIR PU least-squares approximant to the infinite-order PCFB polyphase matrix. Using an elegant complete parameterization of FIR PU systems in terms of canonical building blocks, an iterative greedy algorithm for solving the least-squares problem is presented. Simulation results provided here show that as the order or memory of the signal-adapted FIR PU filter bank increases, the filter bank behaves more and more like the infinite-order PCFB in terms of a variety of objectives including coding gain, multiresolution, and power minimization. This serves to bridge the gap between the zero memory and infinite memory PCFBs, which previously has not been done in the literature.
\r\n\r\nIn addition to being useful for the design of PCFB-like FIR filter banks, the proposed iterative algorithm can also be used for a variety of other design problems including the FIR PU interpolation problem. Unlike the traditional FIR interpolation problem, whose solution is known in closed form, the FIR PU interpolation problem is far more difficult and is in fact still open. Despite this, the proposed algorithm can be used to find an approximant to an interpolant and sometimes even find an interpolant, as we show here through simulations.
\r\n\r\nIn the second part of the thesis, we focus on the design of realizable signal-adapted quantized filter banks in which the filters are FIR but otherwise unconstrained. The filters are chosen to minimize the mean-squared error of the output, which is shown to be equivalent to maximizing the coding gain of the system. By alternately optimizing the analysis and synthesis filters, an iterative greedy algorithm, different from that mentioned above, is proposed for the design of such filter banks. Simulation results provided show that the filter banks designed exhibit performance close to the information theoretic rate-distortion bound.
\r\n\r\nFinally, we show how some of the techniques used in the above iterative algorithms can be used for the design of a channel shortening equalizer. Channel shortening equalizers, which arise in the context of digital communications, have been found to be necessary for DMT systems such as the digital subscriber loop (DSL) in which the channel impulse response must be shortened to the length of the cyclic prefix. In particular, we show how the eigenfilter technique which is used in the above-mentioned FIR PU iterative greedy algorithm, can be used for the design of a noise optimized channel shortening equalizer. As opposed to other techniques, which require a Cholesky decomposition of a certain matrix for every delay parameter considered, the proposed method is lower in complexity in that it only requires a single such decomposition for all delay values. Despite this significant decrease in complexity, it is shown through simulations that the equalizers designed using this technique perform nearly optimally in terms of observed bit rate.
" }, { "name": "Vrcelj, Bojan", "degree": "PhD", "year": "2004", "title": "Multirate Signal Processing Concepts in Digital Communications", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06252003-115639", "creators": [ { "name": { "family": "Vrcelj", "given": "Bojan" }, "id": "Vrcelj-Bojan", "display_name": "Vrcelj, Bojan" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Mese", "given": "Murat" }, "id": "Mese-M", "role": "member", "display_name": "Mese, Murat" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ABS2-4505", "abstract": "Multirate systems are building blocks commonly used in digital signal processing (DSP). Their function is to alter the rate of the discrete-time signals, by adding or deleting a portion of the signal samples. They are essential in various standard signal processing techniques such as signal analysis, denoising, compression and so forth. During the last decade, however, they have increasingly found applications in new and emerging areas of signal processing, as well as in several neighboring disciplines such as digital communications.
\r\n\r\nThe main contribution of this thesis is aimed towards a better understanding of multirate systems and their use in modern communication systems. To this end, we first study a property of linear systems appearing in certain multirate structures. This property is called biorthogonal partnership and represents a terminology introduced recently to address a need for a descriptive term for such class of filters. In the thesis we especially focus on the extensions of this simple idea to the case of vector signals (MIMO biorthogonal partners) and to accommodate for nonintegral decimation ratios (fractional biorthogonal partners).
\r\n\r\nThe main results developed here study the properties of biorthogonal partners, e.g., the conditions for the existence of stable and of finite impulse response (FIR) partners. In this context we develop the parameterization of FIR solutions, which makes the search for the best partner in a given application analytically tractable. This proves very useful in their central application, namely, channel equalization in digital communications with signal oversampling at the receiver. A good channel equalizer in this context is one that helps neutralize the distortion on the signal introduced by the channel propagation but not at the expense of amplifying the channel noise.
\r\n\r\nIn the second part of the thesis, we focus on another class of multirate systems, used at the transmitter side in order to introduce redundancy in the data stream. This redundancy generally serves to facilitate the equalization process by forcing certain structure on the transmitted signal. We first consider the transmission systems that introduce the redundancy in the form of a cyclic prefix. The examples of such systems include the discrete multitone (DMT) and the orthogonal frequency division multiplexing (OFDM) systems. We study the signal precoding in such systems, aimed at improving the performance by minimizing the noise power at the receiver.
\r\n\r\nWe also consider a different class of communication systems with signal redundancy, namely, the multiuser systems based on code division multiple access (CDMA). We specifically focus on the special class of CDMA systems called 'a mutually orthogonal usercode receiver' (AMOUR). We show how to find the best equalizer from the class of zero-forcing solutions in such systems, and then increase the size of this class by employing alternative sampling strategies at the receiver.
" }, { "name": "Waniuk, Theodore Andrew", "degree": "PhD", "year": "2004", "title": "Viscosity and Crystallization in a Series of Zr-based Bulk Amorphous Alloys", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-06102004-214551", "creators": [ { "name": { "family": "Waniuk", "given": "Theodore Andrew" }, "id": "Waniuk-Theodore-Andrew", "display_name": "Waniuk, Theodore Andrew" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Schroers", "given": "Jan" }, "id": "Schroers-J", "role": "member", "display_name": "Schroers, Jan" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "matsci" ], "doi": "10.7907/8z8r-yw55", "abstract": "The various influences on glass-forming ability and crystallization in a series of alloy compositions ranging along a tie-line from Zr41.2Ti13.8Cu12.5Ni10Be22.5 to Zr46.75Ti8.25Cu7.5Ni10Be27.5 are studied using multiple techniques. Both the kinetic and thermodynamic aspects of crystallization are examined experimentally and used to explain why, in this series, thermal stability is greatest in those alloys with the poorest glass-forming ability. Overall, the investigations reveal that a single criterion like thermal stability or high viscosity is an insufficient indicator of the glass-forming ability in certain complex bulk glass-forming systems. Instead, in these complex systems, multiple criteria must be combined to get a complete picture.
\r\n\r\nThe equilibrium viscosity of Zr41.2Ti13.8Cu12.5Ni10Be22.5 and three other alloys was determined for temperatures near the glass transition using three-point beam bending. The results of these measurements indicate that the alloys in this system are moderately strong liquids, and relaxation behavior is directly influenced by a chemical decomposition process which occurs in the supercooled liquid.
\r\n\r\nThis decomposition process also appears to affect the crystallization behavior in the same series of alloys. Critical cooling rates were determined by observing crystallization upon cooling from the molten state with different rates, and these were compared to thermal analysis performed under constant heating conditions. The latter measurements show that the supercooled liquid region is largest for compositions midway between the two endpoints; in contrast, the critical cooling rate increases continuously from 1.4 K/s to 28 K/s for each successive alloy in this series.
\r\n\r\nIn order to examine the crystallization process more closely, low temperature time-temperature-transformation diagrams for the alloy series were measured during isothermal annealing of initially amorphous specimens. For all investigated alloys, a primary quasicrystalline phase forms at a rate which varies substantially with alloy composition. Describing the complicated influences on crystallization required not only the previous thermal analysis but also constant heating measurements and x-ray diffraction data obtained after various states of annealing.
" }, { "name": "West, Matthew", "degree": "PhD", "year": "2004", "title": "Variational Integrators", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06072004-161416", "creators": [ { "name": { "family": "West", "given": "Matthew" }, "id": "West-Matthew", "orcid": "0000-0002-7605-0050", "display_name": "West, Matthew" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" } ], "option_major": [ "cds" ], "doi": "10.7907/CMZ1-RQ16", "abstract": "Variational integrators are a class of discretizations for mechanical systems which are derived by discretizing Hamilton's principle of stationary action. They are applicable to both ordinary and partial differential equations, and to both conservative and forced problems. In the absence of forcing they conserve (multi-)symplectic structures, momenta arising from symmetries, and energy up to a bounded error.
\r\n\r\nIn this thesis the basic theory of discrete variational mechanics for ordinary differential equations is developed in depth, and is used as the basis for constructing variational integrators and analyzing their numerical properties. This is then taken as the starting point for the development of a new class of asynchronous time stepping methods for solid mechanics, known as Asynchronous Variational Integrators (AVIs). These explicit methods time step different elements in a finite element mesh with fully independent and decoupled time steps, allowing the simulation to proceed locally at the fastest rate allowed by local stability restrictions. Numerical examples of AVIs are provided, demonstrating the excellent properties they posess by virtue of their variational derivation.
" }, { "name": "Wintenberger, Eric", "degree": "PhD", "year": "2004", "title": "Application of Steady and Unsteady Detonation Waves to Propulsion", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04222004-121013", "creators": [ { "name": { "family": "Wintenberger", "given": "Eric" }, "id": "Wintenberger-Eric", "display_name": "Wintenberger, Eric" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2NXT-SE76", "abstract": "The present work investigates the applications of steady and unsteady detonation waves to air-breathing propulsion systems. The efficiency of ideal detonation-based propulsion systems is first investigated based on thermodynamics. We reformulate the Hugoniot analysis of steady combustion waves for a fixed initial stagnation state to conclude that steady detonation waves are less desirable than deflagrations for propulsion. However, a thermostatic approach shows that unsteady detonations have the potential for generating more work than constant-pressure combustion. The subsequent work focuses on specific engine concepts. A flow path analysis of ideal steady detonation engines is conducted and shows that their performance is limited and poorer than that of the ideal ramjet or turbojet engines. The limitations associated with the use of a steady detonation in the combustor are drastic and such engines do not appear to be practical. This leads us to focus on unsteady detonation engines, i.e., pulse detonation engnes. The unsteady generation of thrust in the simple configuration of a detonation tube is first analyzed using gas dynamics. We develop one of the first models to quickly and reliably estimate the impulse of a pulse detonation tube. The impulse is found to scale directly with the mass of explosive in the tube and the square root of the energy release per unit mass of the mixture. Impulse values for typical fuel-oxidizer mixtures are found to be on the order of 160 s for hydrocarbon-oxygen mixtures and 120 s for fuel-air mixtures at standard conditions. These results are then used as a basis to develop the first complete system-level performance analysis of a supersonic, single-tube, air-breathing pulse detonation engine. We show that hydrogen- and JP10-fueled pulse detonation engines generate thrust up to a Mach number of 4, and that the specific impulse decreases quasi-linearly with increasing flight Mach number. Finally, we find that the performance of our pulse detonation engine exceeds that of the ramjet below a Mach number of 1.35." }, { "name": "Wong, Catherine Grace", "degree": "PhD", "year": "2004", "title": "High-Level Synthesis and Rapid Prototyping of Asynchronous VLSI Systems", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11192009-161338958", "creators": [ { "name": { "family": "Wong", "given": "Catherine Grace" }, "id": "Wong-Catherine-Grace", "display_name": "Wong, Catherine Grace" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "member", "display_name": "DeHon, Andre" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." } ], "option_major": [ "compsci" ], "doi": "10.7907/5N2N-0W58", "abstract": "This thesis introduces data-driven decomposition (DDD), a new method for the high-level synthesis of asynchronous VLSI systems and the first method to target high-performance asynchronous circuits. Given a sequential description of circuit behavior, DDD produces an equivalent network of communicating processes that can each be directly implemented as fine-grained asynchronous pipeline stages. Control and datapath are integrated within each pipeline stage of the final system.
\r\n\r\nWe present many aspects of the synthesis of asynchronous VLSI systems, including general circuit templates that DDD uses to estimate low-level performance and energy metrics while optimizing the concurrent system. We also introduce a new circuit model and new techniques for slack matching, a performance optimization that inserts pipelining into a system to modify asynchronous handshake dynamics and increase throughput. The entire method is then applied to a complex control unit from an asynchronous 8051 microcontroller, as an example.
\r\n\r\nThis thesis also introduces a new architecture for an asynchronous field-programmable gate array (FPGA). The architecture is cluster-based and, unlike most FPGA designs, contains an entirely delay-insensitive interconnect. The basic reconfigurable cells of this FPGA fit the asynchronous pipeline-stage circuit-template used by DDD, and the reconfigurable clusters include circuitry that implements features assumed by an optimization phase of DDD, which reduces the energy consumption of the system.
" }, { "name": "Yang, Qiang", "degree": "PhD", "year": "2004", "title": "Thermomechanical Variational Principles for Dissipative Materials with Application to Strain Localization in Bulk Metallic Glasses", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-152537", "creators": [ { "name": { "family": "Yang", "given": "Qiang" }, "id": "Yang-Qiang", "display_name": "Yang, Qiang" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6FV2-KV63", "abstract": "This thesis is concerned with variational principles for general coupled thermomechanical problems in dissipative materials including finite elastic and plastic deformation, non-Newtonian viscosity, rate sensitivity, arbitrary flow and hardening rule, as well as heat conduction. It is shown that there exists a potential function such that both the conservation of energy and balance of linear momentum are the Euler-Lagrange equations of its first variation. Inspired from the time-discretized version of the variational formulation, we present a procedure for variational thermomechanical update, which generalizes the isothermal approach under a variational thermodynamic framework. This variational formulation then serves as a basis for temperature change as well as constitutive updates.
\r\n\r\nAn important application of the variational formulation is to optimize the shear band thickness in strain localization processes. We show that this optimization takes the form of a configurational-force equilibrium and results in a well-defined band thickness. We further implement displacement discontinuities into a class of strain-localization finite elements. These elements consist of two surfaces, attached to the abutting volume elements, which can separate and slip relative to each other, and thus enable the accurate and efficient simulation of the dynamical formation of stain localization.
\r\n\r\nThe variational formulation also leads to a finite-deformation continuum modeling of bulk metallic glasses. It is shown that the strain softening of bulk metallic glasses is due to the increase of free volume (and thus the decrease of viscosity), while temperature rise accelerates the localization of the deformation. The model reproduces the constitutive behavior of Vitreloy 1 bulk metallic glass at various strain rates and temperatures.
" }, { "name": "Yoshie, Tomoyuki", "degree": "PhD", "year": "2004", "title": "Planar Photonic Crystal Nanocavities with Active Quantum Nanostructures", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-095431", "creators": [ { "name": { "family": "Yoshie", "given": "Tomoyuki" }, "id": "Yoshie-Tomoyuki", "display_name": "Yoshie, Tomoyuki" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WD4W-XQ37", "abstract": "Extreme photon localization is applicable to constructing building blocks in photonic systems and quantum information systems. A finding fact that photon localization in small space modifies the radiation process was reported in 1944 by Purcell, and advances in fabrication technology enable such structures to be constructed at optical frequencies. Many demands of building compact photonic systems and quantum information systems have enhanced activities in this field. The photonic crystal cavity has potential in providing a cavity that supports only the fundamental mode of (lambda/2n)^3 together with good confinement of light within a resonator. This thesis addresses experimental and theoretical aspects of building such photon localization blocks embedding active quantum nanostructures in a planar photonic crystal platform. Examples given in this thesis are (1) quantum dot photonic crystal nanolasers, (2) high-speed photonic crystal nanolasers, and (3) light-matter coupling in a single quantum dot photonic crystal cavity system.
\r\n\r\n(1) A combination of quantum dots and photonic crystal nanocavities provides chirpless high-speed nanolasers. Room temperature low-threshold lasing action was demonstrated from a coupled cavity design (0.7 - 1.2(lambda/n)^3) embedding InAs/GaAs self-assembled quantum dots. The nanolasers showed small (absorbed) pumping power threshold as sub-20 microW and high spontaneous coupling factors of 0.1. Single quantum dot lasing is likely to occur both by proper alignment of the single quantum dot relative to geometries of photonic crystals and by a narrow QD emission line in the high-Q localized mode.
\r\n\r\n(2) Enhancement of radiation process in a small cavity was used to demonstrate high frequency relaxation oscillation up to 130 GHz. Built-in quantum well saturable absorbers enable us to probe the relaxation oscillation of such small lasers.
\r\n\r\n(3) Onset of intermediate light-matter coupling was demonstrated in a single quantum dot photonic crystal cavity system. A tripling in Q/V (quality factor divided by mode volume) is found to enable photons to start a strong interaction with a single quantum dot.
" }, { "name": "Agassounon, William B. G.", "degree": "PhD", "year": "2003", "title": "Modeling Artificial, Mobile Swarm Systems", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282003-205506", "creators": [ { "name": { "family": "Agassounon", "given": "William B. G." }, "id": "Agassounon-William-B-G", "display_name": "Agassounon, William B. G." } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Martinoli", "given": "Alcherio" }, "id": "Martinoli-A", "role": "member", "display_name": "Martinoli, Alcherio" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Behrens", "given": "Wilhelm" }, "id": "Behrens-W", "role": "member", "display_name": "Behrens, Wilhelm" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/EJYZ-3Y55", "abstract": "Swarm intelligence is a new research paradigm that offers novel approaches for studying and solving distributed problems using solutions inspired by social insects and other natural behaviors of vertebrates. In this thesis, we present methodologies for modeling artificial, mobile systems within the swarm intelligence framework. The proposed methodologies provide guidelines in the study and design of artificial swarm systems for the following two classes of experiments: distributed sensing and distributed manipulation.
\r\n\r\nEvent discovery and information dissemination through local communication in artificial swarm systems present similar characteristics as natural phenomena such as foraging and food discovery in insect colonies and the spread of infectious diseases in animal populations, respectively. We show that the artificial systems can be described in similar mathematical terms as those used to describe the natural systems. The proposed models can be classified in two main categories: non-embodied and embodied models. In the first category agents are modeled as mobile bodiless points, whereas the other models take into account the physical interference between agents resulting from embodiment. Furthermore, within each category, we distinguish two subcategories: spatial and nonspatial models. In the spatial models we keep track of the trajectory of each agent, the correlation between the positions occupied by the agents over consecutive time steps, or make use of the spatial distribution resulting from the movement pattern of the agents. In the nonspatial models we assume that agents hop around randomly and occupy independent positions over consecutive time steps.
\r\n\r\nIn our description of distributed manipulation in swarm robotic systems we present two case studies of non-collaborative and collaborative manipulations, respectively. The general approach proposed here consists of first representing the group behavior of the active agents with a Finite State Machine (FSM) then describing mathematically the dynamics of the group. The first case study is the aggregation experiment that consists of collecting and gathering objects scattered around an enclosed arena. We present a macroscopic model that accurately captures the dynamics of the experiment and a suite of threshold-based, scalable, and fully distributed algorithms for allocating the workers to the task optimally. The second case study is that of the stick-pulling experiment in which a group of robots is used to pull sticks from the ground. This task requires the collaborative effort of two robots to be successful. Here, we present a discrete-time macroscopic model that helps us uncover counter-intuitive behaviors that result from collaboration between the agents.
\r\n\r\nWe complete each proposed modeling methodology by showing how the parameters of the models can be calculated using solely the characteristics of the environment and those of the agents and by analyzing the constraints and limitations of the different models. Finally, we use different tools (simulations and real robots) to validate the proposed models.
\r\n" }, { "name": "Arienti, Marco", "degree": "PhD", "year": "2003", "title": "A Numerical and Analytical Study of Detonation Diffraction", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122003-152525", "creators": [ { "name": { "family": "Arienti", "given": "Marco" }, "id": "Arienti-Marco", "orcid": "0000-0001-8166-0016", "display_name": "Arienti, Marco" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MAGN-R628", "abstract": "An investigation of detonation diffraction through an abrupt area change has been carried out via two-dimensional, parallel simulations. The existence of critical conditions for successful diffraction is closely related to the occurrence of localized re-initiation mechanisms, and is relevant to propulsion and safety concepts concerning detonation transmission. Our analysis is specialized to a reactive mixture with perfect gas equation of state and a single-step reaction in the Arrhenius form. The concept of shock decoupling from the reaction zone is the simplest idea used to explain the behavior of a diffracting detonation front. Lagrangian particles are injected into the flow in order to identify the dominant terms in the equation that describes the temperature rate of change of a fluid element, expressed in a shock-based reference system. Conveniently simplified, this equation provides an insight into the competition between the energy release rate and the expansion rate behind the diffracting front. We also examine the mechanism of spontaneous generation of transverse waves along the front. This mechanism is related to the sensitivity of the reaction rate to temperature, and it is investigated in the form of a parametric study for the activation energy. We study in detail three highly resolved cases of detonation diffraction that illustrate different types of behavior, super-, sub-, and near-critical diffraction. We review the applicability of existing shock dynamics models to the corner-turning problem. Numerical results from the parametric study are compared with predictions from these theories in the attempt to find a formula for shock decay in a quenching detonation. This estimate is then used in the simplified temperature rate of change equation to provide a relation between critical channel width and activation energy. We conclude this study by examining the spontaneous formation of transverse waves along the wavefront of a successfully transmitted detonation. The problem is simplified to a planar CJ detonation moving in a channel over a small obstacle to investigate how acoustic waves propagate within the reaction zone. Depending on the reaction kinetics, we show that such waves may be amplified due to feedback between the chemical reaction and fluid motion. The amplification can lead to shock steepening and formation of transverse detonation waves.\r\n" }, { "name": "Austin, Joanna Maria Karol", "degree": "PhD", "year": "2003", "title": "The Role of Instability in Gaseous Detonation", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292003-150534", "creators": [ { "name": { "family": "Austin", "given": "Joanna Maria Karol" }, "id": "Austin-Joanna-Maria-Karol", "orcid": "0000-0003-3129-5035", "display_name": "Austin, Joanna Maria Karol" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X7YH-T687", "abstract": "In detonation, the coupling between fluid dynamics and chemical energy release is critical. The reaction rate behind the shock front is extremely sensitive to temperature perturbations and, as a result, detonation waves in gases are always unstable. A broad spectrum of behavior has been reported for which no comprehensive theory has been developed. The problem is extremely challenging due to the nonlinearity of the chemistry-fluid mechanics coupling and extraordinary range of length and time scales exhibited in these flows. Past work has shown that the strength of the leading shock front oscillates and secondary shock waves propagate transversely to the main front. A key unresolved issue has emerged from the past 50 years of research on this problem: What is the precise nature of the flow within the reaction zone and how do the instabilities of the shock front influence the combustion mechanism?
\r\n\r\nThis issue has been examined through dynamic experimentation in two facilities. Key diagnostic tools include unique visualizations of superimposed shock and reaction fronts, as well as short but informative high-speed movies. We study a range of fuel-oxidizer systems, including hydrocarbons, and broadly categorize these mixtures by considering the hydrodynamic stability of the reaction zone. From these observations and calculations, we show that transverse shock waves do not essentially alter the classic detonation structure of Zeldovich-von Neumann-Doring (ZND) in weakly unstable detonations, there is one length scale in the instability, and the combustion mechanism is simply shock-induced chemical-thermal explosion behind a piecewise-smooth leading shock front. In contrast, we observe that highly unstable detonations have substantially different behavior involving large excursions in the lead shock strength, a rough leading shock front, and localized explosions within the reaction zone. The critical decay rate model of Eckett et al. (JFM 2000) is combined with experimental observations to show that one essential difference in highly unstable waves is that the shock and reaction front may decouple locally. It is not clear how the ZND model can be effectively applied in highly unstable waves. There is a spectrum of length scales and it may be possible that a type of \"turbulent\" combustion occurs. We consider how the coupling between chemistry and fluid dynamics can produce a large range of length scales and how possible combustion regimes within the front may be bounded.
" }, { "name": "Bhave, Prakash Viththal", "degree": "PhD", "year": "2003", "title": "Air Pollution at the Single-Particle Level: Integrating Atmospheric Measurements with Mathematical Models", "advisor": "Seinfeld, John H.; Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252003-091827", "creators": [ { "name": { "family": "Bhave", "given": "Prakash Viththal" }, "id": "Bhave-Prakash-Viththal", "orcid": "0000-0002-2573-951X", "display_name": "Bhave, Prakash Viththal" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Kleeman", "given": "Micheal J." }, "id": "Kleeman-M-J", "role": "member", "display_name": "Kleeman, Micheal J." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/ZA39-HJ32", "abstract": "Particulate air pollution is of growing concern in the United States and around the world. Elevated concentrations of aerosols (solid particles and liquid droplets suspended in air) are correlated with increased cases of lung cancer, cardiopulmonary disorders, and human mortality. A detailed understanding of the size, chemical composition, and concentration of atmospheric particles is needed to assess their effects on human health, as well as on regional visibility and global climate. One can acquire such knowledge through direct measurements, or by utilizing mathematical air quality models. New and innovative instruments allow us to measure the size and composition of individual particles, rather than to infer aerosol chemical properties from bulk particulate matter samples. Concurrently, air quality models have been developed to numerically simulate the emissions of discrete particles, and their transport and chemical evolution in the atmosphere. This thesis focuses on how to integrate and compare measurements taken by state-of-the-science single-particle instruments with the air pollutant properties calculated using state-of-the-science mathematical models. A 1996 field experiment conducted in the Los Angeles air basin serves as the case study for this thesis research.
\r\n\r\nComparisons of model calculations against single-particle observations identify specific areas where model improvements are needed, and also identify important areas for future instrumental development. These comparisons contribute to our understanding of atmospheric pollution at the single-particle level, and ultimately, may provide tremendous value to policy makers who are seeking least-cost solutions to urban and regional air quality problems. After presenting initial comparisons of single-particle measurements and model results, efforts to quantify and categorize the single-particle chemical composition data are described. The quantitatively reconstructed single-particle measurements are compared with mathematical model calculations of the atmospheric aerosol mixing characteristics. Finally, an example is presented of how the model and measurement combination enhance our ability to reduce particulate pollution in the air we breathe.
" }, { "name": "Camelo, Vanessa Sabrina", "degree": "PhD", "year": "2003", "title": "Dynamic Characteristics of Woodframe Buildings", "advisor": "Beck, James L.; Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06092003-150851", "creators": [ { "name": { "family": "Camelo", "given": "Vanessa Sabrina" }, "id": "Camelo-Vanessa-Sabrina", "display_name": "Camelo, Vanessa Sabrina" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Porter", "given": "Keith A." }, "id": "Porter-K-A", "role": "member", "display_name": "Porter, Keith A." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Duron", "given": "Ziyad H." }, "id": "Duron-Z-H", "role": "member", "display_name": "Duron, Ziyad H." } ], "option_major": [ "civileng" ], "doi": "10.7907/GPHK-KA52", "abstract": "A database of dynamic characteristics of woodframe buildings was developed through analysis of recorded earthquake response and by forced vibration and shake-table testing. Modal identification was performed on eight sets of strong-motion records obtained from five buildings, and forced vibration tests were performed on five other buildings. The periods identified were sensitive to the amplitude of shaking, due to the reduction in lateral stiffness at stronger shaking levels. The equivalent viscous damping ratios were usually more than 10% of critical during earthquake shaking. A regression analysis was performed on the earthquake and forced vibration test data to obtain a simple, but reasonably accurate, period formula for woodframe buildings at low drift levels (less than 0.1%). Data obtained from the UC San Diego and UC Berkeley full-scale shake-table tests illustrate the shift in periods due to increasing shaking amplitude. Forced vibration tests of the UC Berkeley 3-story building before and after the shake-table tests showed how the periods and modeshapes shift due to damage. A simple analytical model of masses and springs was used to model the UC Berkeley test structure. The effects of diaphragm stiffness and mass distribution assumptions were evaluated and found to have a significant effect on the model torsional response. This model was used to find the equivalent wall stiffnesses giving frequency-response curves that best-fit the experimental data. These spring values were used to quantify the stiffness loss resulting from severe shaking of the structure, and the observed damage corresponded to stiffness losses of over 75%. The correlation between stiffness loss and damage to woodframe buildings has potential structural health monitoring implications." }, { "name": "Cartoix\u00e0 Soler, Xavier", "degree": "PhD", "year": "2003", "title": "Theoretical Methods for Spintronics in Semiconductors with Applications", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232003-104331", "creators": [ { "name": { "family": "Cartoix\u00e0 Soler", "given": "Xavier" }, "id": "Cartoix\u00e0-Soler-Xavier", "orcid": "0000-0003-1905-5979", "display_name": "Cartoix\u00e0 Soler, Xavier" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Hunter", "given": "A." }, "id": "Hunter-A", "role": "member", "display_name": "Hunter, A." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Ting", "given": "David Z." }, "id": "Ting-D-Z", "role": "member", "display_name": "Ting, David Z." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/0YTD-VC11", "abstract": "Theoretical studies of the role of structural inversion symmetry (SIA) and bulk inversion symmetry (BIA) in the band structure and tunneling properties of zincblende heterostructures have been carried out.
\r\n\r\nThe effective bond orbital model (EBOM) method is used to examine the spin splitting due to SIA in AlSb/InAs/GaSb asymmetric heterostructures. It is found for the resulting two-dimensional electron gas (2DEG) that large theoretical values of the Rashba coefficient in the range of 50E-10 eV.cm can be achieved for optimized structures. Structures presenting anticrossing of the conduction and valence bands show an appreciable reduction in the value of the Rashba coefficient. The possibility of extracting the Rashba coefficient from magnetization measurements is explored. An expression is derived, valid in the diffusive limit, for the spin polarization of the current resulting from a bias parallel to the plane of the quantum well.
\r\n\r\nThe EBOM method is expanded to include BIA effects. The resulting formalism is then used to compute the band structure of an AlSb/GaSb superlattice, where the BIA-induced splitting is observed. The results agree with k.p calculations.
\r\n\r\nThe first implementation of an 8-band Envelope Function Approximation method faithful to the Td symmetry of bulk zincblendes has been made. It has been used to compute the bands for quantum wells with and without BIA effects included, and demonstrates that the BIA effects can be of the same order of magnitude as SIA (i.e., Rashba) effects. A 2-band Hamiltonian describing BIA effects is proposed. The origin of spurious solutions for certain values of the input parameters is determined and a condition for its absence is derived. Modest modifications to the superlattice method allow the computation of spin-dependent transmission coefficients with the multiband quantum transmitting boundary method (MQTBM). The effect of BIA on the transmitted states and the spin filtering action of an asymmetric resonant interband tunneling diode are investigated.
\r\n\r\nFinally, a Monte Carlo single photon generation algorithm is devised. The photons generated are satisfactory for simulation of light emitted from band-to-band spontaneous transitions in crystals. The polarization is determined taking into account the electron spin, making the algorithm suitable for the analysis of optical detection of spin injection experiments.
" }, { "name": "Cheung, Chun Tung", "degree": "PhD", "year": "2003", "title": "Waveguide Packaging of Quasi-Optical Grid Amplifiers", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05192003-161134", "creators": [ { "name": { "family": "Cheung", "given": "Chun Tung" }, "id": "Cheung-Chun-Tung", "display_name": "Cheung, Chun Tung" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rosenberg", "given": "Jim" }, "id": "Rosenberg-J", "role": "member", "display_name": "Rosenberg, Jim" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/KSGC-3G92", "abstract": "Quasi-optical amplifiers combining the output powers of hundreds of transistors have demonstrated the capability to deliver more than 10 Watts of power at millimeter wave frequencies. However, these amplifiers are large and expensive to manufacture. In this work, we attempt to find a compact, low-cost approach using metallic waveguide to package a grid amplifier. This thesis details the design and implementation of a grid amplifier packaged in waveguide. Frequency and time-domain simulation methods are used to calculate the field flatness and the small signal gain of the amplifier. Four different active grids packaged in waveguide will be reported. The first grid, operating at Ka-band, is fed with a waveguide and radiates its output into free space. The amplifier chip design was previously measured in free-space. This work demonstrates a small signal gain of 7 dB with output power of 5.5 W at 3-dB compression. The performance is similar to the same grid design measured in free-space. A second Ka-band grid amplifier packaged in waveguide for both input and output gives a small signal gain of 6 dB. The 3-dB compressed output power is 670 mW while the same amplifier measured in free-space gave 1.2 W output power. In order to further verify our active grid and packaging design methods, a V-band single-stage monolithic grid amplifier was designed and fabricated. A transmission grid amplifier and a reflection grid amplifier using this chip were fabricated. Both amplifiers have 2 dB small-signal gain at 58 GHz. In order to increase small-signal gain, a two-stage monolithic grid amplifier was designed and fabricated. A reflection approach was used to package this chip. Measured small-signal gain was 2.7 dB at 82 GHz." }, { "name": "Chisholm, Calum Ronald Inneas", "degree": "PhD", "year": "2003", "title": "Superprotonic Phase Transitions in Solid Acids: Parameters Affecting the Presence and Stability of Superprotonic Transitions in the MH\u2099XO\u2084 Family of Compounds (X=S,Se,P,As; M=Li,Na,K,NH\u2084,Rb,Cs)", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01292003-150309", "creators": [ { "name": { "family": "Chisholm", "given": "Calum Ronald Inneas" }, "id": "Chisholm-Calum-Ronald-Inneas", "display_name": "Chisholm, Calum Ronald Inneas" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/FYTW-7G64", "abstract": "The present work attempted to uncover the structural and chemical parameters that favor superprotonic phase transitions over melting or decomposition in the MHXO\u2084, MH\u2082ZO\u2084, and mixed MHXO\u2084-MH\u2082ZO\u2084 classes of compounds (X=S, Se; Z=P, As; M=Li, Na, K, NH\u2084, Rb, Cs) and to thereby gain some ability to \"engineer\" the properties of solid acids for applications. Three approaches are described. First, the general observation that larger cations enable superprotonic transitions was investigated in both the isostructural M\u2082(HSO\u2084)(H\u2082PO\u2084) and non-isostructural MHSO\u2084 family of compounds. The results of these studies confirmed and explained such a cation size effect, and also supplied a crystal-chemical measure for determining the likelihood of a compound undergoing a phase transition. Second, the entropic driving force behind the transitions was explored in the mixed CsHSO\u2084-CsH\u2082PO\u2084 system of compounds. From these investigations, a general set of rules for calculating the entropy change of a superprotonic transition was established and the role of entropy in the transitions illuminated. Finally, the superprotonic phase transition of CsHSO4 was simulated by molecular dynamics, with which means the transition was probed in ways not possible through experimental methods. A sufficiently general approach was utilized so as to be applicable to other (as yet un-synthesized) compounds, thereby speeding up the process of discovering novel superprotonic solid acids. All three approaches increase the fundamental understanding of which chemical/structural features facilitate superprotonic transitions and should aid attempts to create new solid acids with properties ideal for application." }, { "name": "Fetecau, Razvan Constantin", "degree": "PhD", "year": "2003", "title": "Variational Methods for Nonsmooth Mechanics", "advisor": "Marsden, Jerrold E.; Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222003-110241", "creators": [ { "name": { "family": "Fetecau", "given": "Razvan Constantin" }, "id": "Fetecau-Razvan-Constantin", "orcid": "0000-0001-9059-0283", "display_name": "Fetecau, Razvan Constantin" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "co-advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/VXBJ-R447", "abstract": "In this thesis we investigate nonsmooth classical and continuum mechanics and its discretizations by means of variational numerical and geometric methods.
\r\n\r\nThe theory of smooth Lagrangian mechanics is extended to a nonsmooth context appropriate for collisions and it is shown in what sense the system is symplectic and satisfies a Noether-style momentum conservation theorem.
\r\n\r\nNext, we develop the foundations of a multisymplectic treatment of nonsmooth classical and continuum mechanics. This work may be regarded as a PDE generalization of the previous formulation of a variational approach to collision problems. The multisymplectic formulation includes a wide collection of nonsmooth dynamical models such as rigid-body collisions, material interfaces, elastic collisions, fluid-solid interactions and lays the groundwork for a treatment of shocks.
\r\n\r\nDiscretizations of this nonsmooth mechanics are developed by using the methodology of variational discrete mechanics. This leads to variational integrators which are symplectic-momentum preserving and are consistent with the jump conditions given in the continuous theory. Specific examples of these methods are tested numerically and the longtime stable energy behavior typical of variational methods is demonstrated.
" }, { "name": "Franceschetti, Massimo", "degree": "PhD", "year": "2003", "title": "Wireless Networks, from Collective Behavior to the Physics of Propagation", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202003-154451", "creators": [ { "name": { "family": "Franceschetti", "given": "Massimo" }, "id": "Franceschetti-Massimo", "orcid": "0000-0002-4057-8152", "display_name": "Franceschetti, Massimo" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/SCTG-FN57", "abstract": "This thesis addresses some of the key challenges in the emerging wireless scenario. It focuses on the problems of connectivity, coverage, and wave propagation, following a mathematically rigorous approach. The questions addressed are very basic and extremely easy to state. Their solution, however, can be difficult and leads to the development of a new kind of percolation theory, to a new theorem in geometry, and to a new model of wave propagation in urban environments. The problems are connected together to provide guidelines in the design of wireless networks.\r\n" }, { "name": "Gallivan, Martha Anne", "degree": "PhD", "year": "2003", "title": "Modeling and Control of Epitaxial Thin Film Growth", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10222002-115711", "creators": [ { "name": { "family": "Gallivan", "given": "Martha Anne" }, "id": "Gallivan-Martha-Anne", "orcid": "0000-0002-7036-776X", "display_name": "Gallivan, Martha Anne" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Christofides", "given": "Panagiotis D." }, "id": "Christofides-P-D", "role": "member", "display_name": "Christofides, Panagiotis D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/FXZB-XT91", "abstract": "Thin film deposition is a manufacturing process in which tolerances may approach the size of individual atoms. The final film is highly sensitive to the processing conditions, which can be intentionally manipulated to control film properties. A lattice model of surface evolution during thin film growth captures many important features, including the nucleation and growth of clusters of atoms and the propagation of atomic-height steps. The dimension of this probabilistic master equation is too large to directly simulate for any physically realistic domain, and instead stochastic realizations of the lattice model are obtained with kinetic Monte Carlo simulations.
\r\n\r\nIn this thesis simpler representations of the master equation are developed for use in analysis and control. The static map between macroscopic process conditions and microscopic transition rates is first analyzed. In the limit of fast periodic process parameters, the surface responds only to the mean transition rates, and, since the map between process parameters and transition rates is nonlinear, new effective combinations of transition rates may be generated. These effective rates are the convex hull of the set of instantaneous rates.
\r\n\r\nThe map between transition rates and expected film properties is also studied. The dimension of a master equation can be reduced by eliminating or grouping configurations, yielding a reduced-order master equation that approximates the original one. A linear method for identifying the coefficients in a master equation is then developed, using only simulation data. These concepts are extended to generate low-order master equations that approximate the dynamic behavior seen in large Monte Carlo simulations. The models are then used to compute optimal time-varying process parameters.
\r\n\r\nThe thesis concludes with an experimental and modeling study of germanium film growth, using molecular beam epitaxy and reflection high-energy electron diffraction. Growth under continuous and pulsed flux is compared in experiment, and physical parameters for the lattice model are extracted. The pulsing accessible in the experiment does not trigger a change in growth mode, which is consistent with the Monte Carlo simulations. The simulations are then used to suggest other growth strategies to produce rougher or smoother surfaces.
" }, { "name": "Graetz, Jason Allan", "degree": "PhD", "year": "2003", "title": "Electronic Environments and Electrochemical Properties in Lithium Storage Materials", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05162003-142018", "creators": [ { "name": { "family": "Graetz", "given": "Jason Allan" }, "id": "Graetz-Jason-Allan", "orcid": "0000-0002-2584-2357", "display_name": "Graetz, Jason Allan" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rez", "given": "Peter" }, "id": "Rez-P", "role": "member", "display_name": "Rez, Peter" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/CS3R-RW08", "abstract": "The local electronic environments and energy storage properties of lithium electrodes are investigated through inelastic electron scattering and electrochemical measurements. Experimental and computational methods are developed to characterize the electronic structure of lithiated compounds during electrochemical cycling. An electrochemical investigation of new lithium alloys has led to a better understanding of the thermodynamics, kinetics, and mechanical properties of nanostructured materials. These studies have also inspired the development of new anode materials for rechargeable lithium batteries.
\r\n\r\nOne of the large controversies regarding lithium cathodes concerns the arrangement of the local electronic environments in the host material and how these environments are affected by lithium intercalation. To investigate this issue, the core edges of the 3d transition-metal oxides were studied using electron energy-loss spectrometry. A number of techniques were developed to better understand how characteristics of the electronic structure are reflected in the core edge and near-edge structure of metal oxides. An empirical relationship is established between the transition-metal L23 white line intensity and the transition-metal 3d occupancy. In addition, the near-edge structure of the oxygen K-edge was used to investigate the 2p electron density about the oxygen ions. The results of these investigations were used to study charge compensation in lithiated transition-metal oxides (e.g., LiCoO2 and LiNi0.8Co0.2O2) during electrochemical cycling. These results show a large increase in state occupancy of the oxygen 2p band during lithiation, suggesting that much of the lithium 2s electron is accommodated by the anion. Ab initio calculations of the oxygen 2p partial density of states curves confirm the increase in unoccupied states that accompany lithium extraction. In contrast with the large changes observed in the oxygen K-edge, much smaller changes were observed in the transition-metal L23 white lines. Surprisingly, for layered LiCoO2 and Li(Ni, Co)O2, the transition-metal valence changes little during the charge compensation accompanying lithiation. These results have led to a better understanding of intercalation hosts and the role of oxygen in these layered structures.
\r\n\r\nRecent demand for alternatives to graphitic carbon for lithium anodes motivated an investigation into novel binary lithium alloys. The large volume expansions associated with lithium insertion is known to generate tremendous microstructural damage, making most alloys unsuitable for rechargeable lithium batteries. Electrodes of nanostructured lithium alloys were prepared in an attempt to mitigate the particle decrepitation that occurs during cycling and to shorten diffusion times for lithium. Anodes of silicon and germanium were prepared in thin film form as nanocrystalline particles (10 nm mean diameter) and as continuous amorphous thin films (60-250 nm thick). These nanostructured materials exhibited stable capacities up to six times larger than what is found in graphitic carbons, which are currently the industry standard. In addition, these electrodes do not suffer from particle decrepitation and therefore exhibit excellent cycle life. Nanocrystalline electrodes of silicon and germanium were found to transform into a glassy phase via an electrochemically driven solid-state amorphization during the initial alloying. The disordered structure is believed to assuage strains of intercalation by bypassing multiple crystallographic phases. However, the primary reason for the improved reversibility in these electrodes is attributed to the nanoscale dimensions, which circumvent conventional mechanisms of mechanical deterioration. Nanostructured Li-Si and Li-Ge exhibit the highest reversible electrochemical capacities yet reported for an alloy electrode.
\r\n\r\nFuture investigations of the local electronic environments in cathodes could be extended to include more complicated systems such as Li(Ni, Mn)O2 and Li(Fe, X)PO4. Our results suggest that the electronic stability of the metal ion is necessary to maintain a prolonged cycle life. Therefore, an understanding of charge compensation in these complex oxides will be important for understanding new cathode materials. The electronic environments will also be a critical component in the development of alternative anodes, such as binary and ternary lithium alloys. Chemical and valence maps will be used to determine how the lithium is distributed and how its chemical potential varies throughout the electrode. In addition, a better understanding of the thermodynamics, kinetics, and mechanical properties of lithium hosts will be necessary for the development of lithium electrodes with high capacities and high rate capabilities.
" }, { "name": "Greenberg, Andrei Yakovlevich", "degree": "PhD", "year": "2003", "title": "Chebyshev Spectral Method for Singular Moving Boundary Problems with Application to Finance", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042002-131120", "creators": [ { "name": { "family": "Greenberg", "given": "Andrei Yakovlevich" }, "id": "Greenberg-Andrei-Yakovlevich", "display_name": "Greenberg, Andrei Yakovlevich" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Bossaerts", "given": "Peter L." }, "id": "Bossaerts-P-L", "role": "member", "display_name": "Bossaerts, Peter L." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/J383-YX41", "abstract": "Accurate results for the inherently nonlinear models involving moving boundaries can only be produced by sophisticated, high-quality numerical algorithms. However the most general approaches are usually not very accurate, while those producing accurate results for certain cases are hard to generalize. In an attempt to bridge this gap, we propose a general method, based on a unified framework for arbitrary parabolic operators, which, in particular, can accurately treat singular problems.
\r\n\r\nOur method consists of front-fixing and a Chebyshev series solution of the resulting nonlinear partial differential equation. An appropriate set of convergent smooth approximations is used in singular cases. For smooth problems, our method is very competitive in both speed and accuracy. At the same time, our method is able to produce accurate solutions in the most general setting, whenever existence theorems for moving boundary problems hold. We establish convergence of numerical solutions to the true solution for a large class of possibly singular initial conditions.
\r\n\r\nIn addition to the general method, we introduce computational techniques which enhance its performance for singular problems. These include derivative evaluations with Pad\u00e9 approximations; prior integration in time; and domain decomposition.
\r\n\r\nWe demonstrate the performance of our method with several regular and singular problems. A comparison with other methods shows that our algorithms produce more accurate results. The additional techniques, which do not use smoothing approximations, significantly shorten computing times while retaining reasonable accuracy.
\r\n\r\nWe present a systematic study of the mathematical finance problem of pricing American options on a dividend-paying asset from the point of view of partial differential equations. A symmetry result, obtained via a simple change of variables, allows to reduce any American option problem to one of the two canonical cases, depending on the relation between the interest rate and the dividend yield. Each of these cases is equivalent to a singular Stefan problem, which can be solved by our method. We present calculations for the classical problems of options written on a single stock and the more complicated examples, such as index options and foreign currency options, thus demonstrating the remarkable practical scope of the proposed approach.
" }, { "name": "Grinspun, Eitan", "degree": "PhD", "year": "2003", "title": "The Basis Refinement Method", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechETD:etd-05312003-133558", "creators": [ { "name": { "family": "Grinspun", "given": "Eitan" }, "id": "Grinspun-Eitan", "orcid": "0000-0003-4460-7747", "display_name": "Grinspun, Eitan" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Krysl", "given": "Petr" }, "id": "Krysl-Petr", "role": "member", "display_name": "Krysl, Petr" } ], "option_major": [ "compsci" ], "doi": "10.7907/QH6Z-0276", "abstract": "Finite element solvers are critical in computer graphics, engineering, medical and biological application areas. For large problems, the use of adaptive refinement methods can tame otherwise intractable computational costs. Current formulations of adaptive finite element mesh refinement seem straightforward, but their implementations prove to be a formidable task. We offer an alternative point of departure which yields equivalent adapted approximation spaces wherever the traditional mesh refinement is applicable, but proves to be significantly simpler to implement. At the same time it is much more powerful in that it is general (no special tricks are required for different types of finite elements), and applicable to novel discretizations where traditional mesh refinement concepts are not of much help, for instance on subdivision surfaces.
\r\n\r\nFor classical finite-elements, adaptive refinement is typically carried out by splitting mesh elements in isolation. While so-called mesh refinement is well-understood, it is considered cumbersome to implement for unstructured three-dimensional meshes, among other settings, in particular because mesh compatibility must be explicitly maintained. Furthermore, element-splitting does not apply to problems that benefit from higher-order B-spline discretizations and their more general counterparts, so-called subdivision elements. We introduce a simple, general method for adaptive refinement which applies uniformly in all these settings and others. The basic principle of our approach is to refine basis functions, not elements. Our method is naturally compatible: unlike mesh refinement, basis refinement never creates incompatible meshes. Our contributions are (a) a minimal mathematical framework, with (b) associated algorithms for basis refinement; furthermore, we (c) describe the mapping of popular methods (finite-elements, wavelets, splines and subdivision) onto this framework, and (d) demonstrate working implementations of basis refinement with applications in graphics, engineering, and medicine.
\r\n\r\nOur approach is based on compactly supported refinable functions. We refine by augmenting the basis with narrowly-supported functions, not by splitting mesh elements in isolation. This removes a number of implementation headaches associated with element-splitting and is a general technique independent of domain dimension, element type (eg, triangle, quad, tetrahedron, hexahedron), and basis function order (piecewise linear, quadratic, cubic, etc.). The (un-)refinement algorithms are simple and require little in terms of data structure support. Many popular discretizations, including classical finite-elements, wavelets and multi-wavelets, splines and subdivision schemes may be viewed as refinable function spaces, thus they are encompassed by our approach.
\r\n \r\nOur first contribution is the specification of a minimal mathematical framework, at its heart a sequence of nested approximation spaces. By construction, the bases for these spaces consist of refinable functions. From an approximation theory point of view this is a rather trivial statement; however it has a number of very important and highly practical consequences. Our adaptive solver framework requires only that the basis functions used be refinable. It makes no assumptions as to (a) the dimension of the domain; (b) the tesselation of the domain, i.e., the domain elements be they triangles, quadrilaterals, tetrahedra, hexahedra, or more general domains; (c) the approximation smoothness or accuracy; and (d) the support diameter of the basis functions. The specification of the nested spaces structure is sufficiently weak to accomodate many practical settings, while strong enough to satisfy the necessary conditions of our theorems and algorithms.
\r\n\r\nOur second contribution is to show that basis refinement can be implemented by a small set of simple algorithms. Our method requires efficient data structures and algorithms to (a) keep track of interactions between basis functions (i.e., to find the non-zero entries in the stiffness matrix), and (b) manage a tesselation of the domain suitable for evaluation of the associated integrals (i.e., to evaluate the entries of the stiffness matrix). We provide a specification for these requirements, develop the relevant theorems and proofs, and invoke these theorems to produce concrete, provably-correct pseudo-code. The resulting algorithms, while capturing the full generality (in dimension, tesselation, smoothness, etc.) of our method, are surprisingly simple.
\r\n\r\nOur third contribution is the mapping of finite-elements, wavelets and multi-wavelets, splines and subdivision schemes onto our nested spaces framework. No single discretization fits all applications. In our survey of classical and recently-popularized discretizations we demonstrate that our unifying algorithms for basis refinement encompass a very broad range of problems.
\r\n\r\nOur fourth contribution is a set of concrete, compelling examples based on our implementation of basis refinement. Adaptive basis refinement may be profitably applied in solving partial differential equations (PDEs) useful in many application domains, including simulation, animation, modeling, rendering, surgery, biomechanics, and computer vision. Our examples span thin shells (fourth order elliptic PDE using a Loop subdivision discretization), volume deformation and stress analysis using linear elasticity (second order PDE using linear-tetrahedral and trilinear-hexahedral finite elements respectively) and a subproblem of electrocardiography (the generalized Laplace equation using linear tetrahedral finite elements).
" }, { "name": "Guyader, Andrew Charles", "degree": "PhD", "year": "2003", "title": "A Statistical Approach to Equivalent Linearization with Application to Performance-Based Engineering", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06012003-123539", "creators": [ { "name": { "family": "Guyader", "given": "Andrew Charles" }, "id": "Guyader-Andrew-Charles", "display_name": "Guyader, Andrew Charles" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Wallace", "given": "J. W." }, "id": "Wallace-J-W", "role": "member", "display_name": "Wallace, J. W." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9HZ-9M41", "abstract": "A new methodology for calculating optimal effective linear parameters for use in predicting the earthquake response of structures is developed. The methodology is applied to several single-degree-of-freedom inelastic structural models subjected to a suite of earthquake acceleration time histories. Separately, far-field and near-field earthquakes are analyzed. Error distributions over a two-dimensional parameter space of period and damping are analyzed through a statistical approach with optimization criterion most applicable to structural design. Four hysteretic models are analyzed: bilinear, stiffness degrading, strength degrading and pinching. Initial structural periods are analyzed in groups for several second slope ratios (alpha) at different levels of ductility. It was discovered that as ductility increases, the accuracy of the effective parameters decrease but the consequences of bad parameter selection become less severe.
\r\n\r\nThe new effective parameters are intended for use in displacement-based structural analysis procedures as used in Performance-Based Engineering. Of the several procedures available, Nonlinear Static Procedures, such as the Capacity Spectrum Method, are widely used by structural engineers because the nonlinear characteristics of both structural components and the global structure are utilized without running a nonlinear time history analysis. Effective linear parameters are used in the Capacity Spectrum Method to calculate the expected displacement demand, or Performance Point, for a structure. Because several sources of error exist within the Capacity Spectrum Method, an analysis that isolates the error from the effective linear parameters is performed. The new effective linear parameters show considerable improvement over the existing effective linear equations. The existing linear parameters are extremely unconservative at the lower ductilities and conservative at the higher ductilities. The new parameters lead to a significant improvement in both cases.
\r\n\r\nA modification to the Capacity Spectrum Method is introduced to account for the new effective linear period. Currently, the Capacity Spectrum Method uses the secant period as the effective linear period. The modification preserves the basic Performance Point calculation. Finally, a new, entirely graphical solution procedure using a Locus of Performance Points provides crucial insight into the effects of strengthening, stiffening and increasing building ductility not available in the current procedure.
" }, { "name": "Hanan, Jay Clarke", "degree": "PhD", "year": "2003", "title": "Damage Evolution in Uniaxial SiC Fiber Reinforced Ti Matrix Composites", "advisor": "Ustundag, Ersan", "url": "https://resolver.caltech.edu/CaltechETD:etd-05062003-123650", "creators": [ { "name": { "family": "Hanan", "given": "Jay Clarke" }, "id": "Hanan-Jay-Clarke", "orcid": "0000-0002-2583-2079", "display_name": "Hanan, Jay Clarke" } ], "advisors": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "orcid": "0000-0002-0812-7028", "role": "advisor", "display_name": "Ustundag, Ersan" } ], "committee": [ { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "orcid": "0000-0002-0812-7028", "role": "chair", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Noyan", "given": "I. Cev" }, "id": "Noyan-I-Cev", "role": "member", "display_name": "Noyan, I. Cev" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/C5GW-WV41", "abstract": "Fiber fractures initiate damage zones ultimately determining the strength and lifetime of metal matrix composites (MMCs). The evolution of damage in a MMC comprising a row of unidirectional SiC fibers (32 vol.%) surrounded by a Ti matrix was examined using X-ray microdiffraction (?m beam size) and macrodiffraction (mm beam size). A comparison of high-energy X-ray diffraction (XRD) techniques including a powerful two-dimensional XRD method capable of obtaining powder averaged strains from a small number of grains is presented (HE?XRD?).
\r\n\r\nUsing macrodiffraction, the bulk residual strain in the composite was determined against a true strain-free reference. In addition, the bulk in situ response of both the fiber reinforcement and the matrix to tensile stress was observed and compared to a three-dimensional finite element model. Using microdiffraction, multiple strain maps including both phases were collected in situ before, during, and after the application of tensile stress, providing an unprecedented detailed picture of the micromechanical behavior in the laminate metal matrix composite.
\r\n\r\nFinally, the elastic axial strains were compared to predictions from a modified shear lag model, which unlike other shear lag models, considers the elastic response of both constituents. The strains showed excellent correlation with the model. The results confirmed, for the first time, both the need and validity of this new model specifically developed for large scale multifracture and damage evolution simulations of metal matrix composites. The results also provided unprecedented insight for the model, revealing the necessity of incorporating such factors as plasticity of the matrix, residual stress in the composite, and selection of the load sharing parameter.
\r\n\r\nThe irradiation of a small number of grains provided strain measurements comparable to a continuum mechanical state in the material. Along the fiber axes, thermal residual stresses of 740 MPa (fibers) and +350 MPa (matrix) were found. Local yielding was observed by 500 MPa in the bulk matrix of the composite. Plastic anisotropy was observed in the matrix. The intergranular strains in the Ti matrix varied as much as 50%. In spite of this variation, the HE?XRD? technique powerfully provided reliable information from the matrix as well as the fibers.
" }, { "name": "Hirani, Anil Nirmal", "degree": "PhD", "year": "2003", "title": "Discrete Exterior Calculus", "advisor": "Marsden, Jerrold E.; Arvo, James R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202003-095403", "creators": [ { "name": { "family": "Hirani", "given": "Anil Nirmal" }, "id": "Hirani-Anil-Nirmal", "orcid": "0000-0003-3506-1703", "display_name": "Hirani, Anil Nirmal" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "co-advisor", "display_name": "Arvo, James R." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" } ], "option_major": [ "compsci" ], "doi": "10.7907/ZHY8-V329", "abstract": "This thesis presents the beginnings of a theory of discrete exterior calculus (DEC). Our approach is to develop DEC using only discrete combinatorial and geometric operations on a simplicial complex and its geometric dual. The derivation of these may require that the objects on the discrete mesh, but not the mesh itself, are interpolated.
\r\n\r\nOur theory includes not only discrete equivalents of differential forms, but also discrete vector fields and the operators acting on these objects. Definitions are given for discrete versions of all the usual operators of exterior calculus. The presence of forms and vector fields allows us to address their various interactions, which are important in applications. In many examples we find that the formulas derived from DEC are identitical to the existing formulas in the literature. We also show that the circumcentric dual of a simplicial complex plays a useful role in the metric dependent part of this theory. The appearance of dual complexes leads to a proliferation of the operators in the discrete theory.
\r\n\r\nOne potential application of DEC is to variational problems which come equipped with a rich exterior calculus structure. On the discrete level, such structures will be enhanced by the availability of DEC. One of the objectives of this thesis is to fill this gap. There are many constraints in numerical algorithms that naturally involve differential forms. Preserving such features directly on the discrete level is another goal, overlapping with our goals for variational problems.
\r\n\r\nIn this thesis we have tried to push a purely discrete point of view as far as possible. We argue that this can only be pushed so far, and that interpolation is a useful device. For example, we found that interpolation of functions and vector fields is a very convenient. In future work we intend to continue this interpolation point of view, extending it to higher degree forms, especially in the context of the sharp, Lie derivative and interior product operators. Some preliminary ideas on this point of view are presented in the thesis. We also present some preliminary calculations of formulas on regular nonsimplicial complexes
" }, { "name": "Howard, Elizabeth Anne", "degree": "PhD", "year": "2003", "title": "A Front Tracking Method for Modelling Thermal Growth", "advisor": "Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042003-115138", "creators": [ { "name": { "family": "Howard", "given": "Elizabeth Anne" }, "id": "Howard-Elizabeth-Anne", "display_name": "Howard, Elizabeth Anne" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/HRNV-DA03", "abstract": "Several important thermal growth problems involve a solid growing into an undercooled liquid. The heat that is released at the interface diffuses into both the solid and the liquid phases. This is a free boundary problem where the position of the interface is an unknown which must be found as part of the solution. The problem can conveniently be represented as an integral equation for the unknown interface. However, a history integral must be evaluated at each time step which requires information about the boundary position at all previous times. The time and memory required to perform this calculation quickly becomes unreasonable. We develop an alternative way to deal with the problems that the history integral presents. By taking advantage of properties of the diffusion equation, we can use a method with a constant operation count and amount of memory required for each time step. We show that a numerical algorithm can be implemented for a two-dimensional, symmetric problem with equal physical parameters in both phases. The results agree well with the exact solution for the expanding circle case and microscopic solvability theory. We also extend the method to the nonsymmetric case. Additionally, a stability analysis is done of a simple, parabolic moving front to perturbations on the surface. As the eigenvalues of our problem increase, the interface becomes more increasingly oscillatory. " }, { "name": "Hung, Patrick Hin Fun", "degree": "PhD", "year": "2003", "title": "Algorithms for Reaction Mechanism Reduction and Numerical Simulation of Detonations Initiated by Projectiles", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-142744", "creators": [ { "name": { "family": "Hung", "given": "Patrick Hin Fun" }, "id": "Hung-Patrick-Hin-Fun", "display_name": "Hung, Patrick Hin Fun" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/H5GV-PV33", "abstract": "The evolution of a homogeneous, chemically reactive system with n species forms a dynamical system in chemical state-space. Under suitable constraints, unique and stable equilibrium exists and can be interpreted as zeroth-dimensional (point like) attractors in this n-dimensional space. At these equilibrium compositions, the rates of all reversible reactions vanish and can, in fact, be determined from thermodynamics independent of chemical kinetics.
\r\n\r\nGeneralizing this concept, an m-dimensional Intrinsic Low Dimensional Manifold (ILDM) represents an m-dimensional subspace in chemical state-space where all but the m-slowest aggregate reactions are in equilibrium, and these aggregate reactions are determined by eigenvalue considerations of the chemical kinetics. In this context, a certain composition is said to be m-dimensional if it is on an m-, but not an (m-1)-, dimensional ILDM.
\r\n\r\nTwo new algorithms are proposed that allow the dimensionality of chemical compositions be determined simply. The first method is based on recasting the Maas and Pope algorithm. The second, and more efficient, method is inspired by the mathematical structure of the Maas and Pope algorithm and makes use of the technique known as arc-length reparameterization. In addition, a new algorithm for the construction of ILDM, and the application of these ideas to detonation simulations, is discussed.
\r\n\r\nIn the second part of the thesis, numerical simulations of detonation waves initiated by hypervelocity projectiles are presented. Using detailed kinetics, only the shock-induced combustion regime is realized as simulating the conditions required for a stabilized detonation is beyond the reach of our current computational resources. Resorting to a one-step irreversible reaction model, the transition from shock-induced combustion to stabilized oblique detonation is observed, and an analysis of this transition based on the critical decay-rate model of Kaneshige (1999) is presented.
" }, { "name": "Hyde, Edward McKay", "degree": "PhD", "year": "2003", "title": "Fast, High-Order Methods for Scattering by Inhomogeneous Media", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08142002-182101", "creators": [ { "name": { "family": "Hyde", "given": "Edward McKay" }, "id": "Hyde-Edward-McKay", "display_name": "Hyde, Edward McKay" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "chair", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/Z0V0-KM52", "abstract": "In this thesis, we introduce a new, fast, high-order method for scattering by inhomogeneous media in three dimensions. As in previously existing methods, the low (O(N log N)) complexity of our integral equation method is obtained through extensive use of the fast Fourier transform (FFT) in evaluating the required convolutions. Unlike previous FFT-based methods, however, this method yields high-order accuracy, even for scatterers containing geometric singularities such as discontinuities, corners, and cusps.
\r\n\r\nWe begin our discussion with a thorough theoretical analysis of an efficient, high-order method recently introduced by Bruno and Sei (IEEE Trans. in Antenn. Propag., 2000), which motivated the present work. This two-dimensional method is based on a Fourier approximation of the integral equation in polar coordinates and a related, generally low-order, Fourier smoothing of the scatterer. The claim that use of this low-order approximation of the scatterer leads to a high-order accurate numerical method generated considerable controversy. Our proofs establish that this method indeed yields high-order accurate solutions. We also introduce several substantial improvements to the numerical implementation of this two-dimensional algorithm, which lead to increased numerical stability with decreased computational cost.
\r\n\r\nWe then present our new, fast, high-order method in three dimensions. An immediate generalization of the polar coordinate approach in two dimensions to a spherical coordinate approach in three dimensions appears less advantageous than our chosen approach: Fourier approximation and integration in Cartesian coordinates. To obtain smooth and periodic functons (which are approximated to high-order via Fourier series), we 1) decompose the Green's function into a smooth part with infinite support and a singular part with compact support; and 2) replace, as in the two-dimensional approach, the (possibly discontinuous) scatterer with its truncated Cartesian Fourier series.
\r\n\r\nThe accuracy of our three-dimensional method is approximately equal to that of the two-dimensional method mentioned above and, interestingly, is actually much simpler than the two-dimensional approach. In addition to our theoretical discussion of these high-order methods, we present a parallel implementation of our three-dimensional Cartesian approach. The efficiency, high-order accuracy, and overall performance of both the polar and Cartesian methods are demonstrated through several computational examples.
" }, { "name": "Joseph Gonzalez, Gustavo", "degree": "PhD", "year": "2003", "title": "Collisional Dynamics of Macroscopic Particles in a Viscous Fluid", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-171943", "creators": [ { "name": { "family": "Joseph Gonzalez", "given": "Gustavo" }, "id": "Joseph-Gonzalez-Gustavo", "display_name": "Joseph Gonzalez, Gustavo" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Zenit Camacho", "given": "Jose Roberto" }, "id": "Zenit-Camacho-J-R", "role": "member", "display_name": "Zenit Camacho, Jose Roberto" } ], "option_major": [ "mecheng" ], "doi": "10.7907/FFFC-X753", "abstract": "This thesis presents experimental measurements of the approach and rebound of a particle colliding with a wall in a viscous fluid. Steel, glass, nylon, and Delrin particles were used, with diameters ranging from 3 to 12 mm. The experiments were performed using a thick Zerodur or Lucite wall with various mixtures of glycerol and water. Normal and tangential coefficients of restitution were defined from the ratios of the respective velocity components at the point of contact just prior to and after impact. These coefficients account for losses due to lubrication effects and inelasticity.
\r\n\r\nThe experiments clearly show that the rebound velocity depends strongly on the impact Stokes number and weakly on the elastic properties of the materials. Below a Stokes number of approximately 10, no rebound of the particle occurs. Above a Stokes number of approximately 500, the normal coefficient of restitution asymptotically approaches the value for a dry collision. The data collapse onto a single curve of restitution coefficient as a function of Stokes number when normalized by the dry coefficient of restitution.
\r\n\r\nOblique collisions in a fluid are qualitatively similar to oblique collisions in a dry system, with a lowered friction coefficient dependent on surface roughness. For smooth surfaces the friction coefficient is drastically reduced due to lubrication effects. Values for the friction coefficient are predicted based on elastohydrodynamic lubrication theory. The particle surface roughness was found to affect the repeatability of some measurements, especially for low impact velocities.
\r\n\r\nA significant retardation of a particle approaching a target at a low Stokes number was observed and quantified. The distance at which the particle's trajectory varies due to the presence of the wall is dependent on the impact Stokes number. The observed slowdown can be predicted from hydrodynamic theory to a good approximation.
\r\n\r\nAn analysis of the erosion of ductile materials during immersed collisions is presented. The size of the crater formed by the impact of a single particle against a ductile target can be estimated from theory, and these estimates agree well with experimental measurements.
" }, { "name": "Kastner, Jason Christopher", "degree": "PhD", "year": "2003", "title": "Modeling a Hox Gene Network: Stochastic Simulation with Experimental Perturbation", "advisor": "Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-200303", "creators": [ { "name": { "family": "Kastner", "given": "Jason Christopher" }, "id": "Kastner-Jason-Christopher", "display_name": "Kastner, Jason Christopher" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Solomon", "given": "Jerry" }, "id": "Solomon-J", "role": "member", "display_name": "Solomon, Jerry" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/2TWD-EK72", "abstract": "The Hox genes show a striking segment specific pattern of expression in a variety of vertebrate embryos, and have been the topic of many experimental analyses. There are now sufficient data to construct a higher-level model for the interaction and regulation of the Hox genes. This thesis presents the results of an investigation into a regulatory network for the early Hox genes. Instead of using conventional differential equation approaches for analyzing the system, a stochastic simulation algorithm has been employed to model the network. The model can track the behavior of each component of a biochemical pathway and produce computerized movies of the time evolution of the system that is a result of the dynamic interplay of these various components. The simulation is able to reproduce key features of the wild-type pattern of gene expression, and in silico experiments yield results similar to their corresponding in vivo experiments. This work shows the utility of using stochastic methods to model biochemical networks and expands the stochastic simulation algorithm methodology to work in multi-cellular systems. In addition, the model has suggested several predictions that can be tested in vivo.
\r\n\r\nA tight connection was also created between the modeling and laboratory experiments. To investigate a connection between two components of the network, retinoic acid (RA) and Hoxa1, a novel laboratory experiment was performed to perturb the system. An RA soaked bead was implanted into the neural tube of a developing chick embryo and the effect of the exogenous RA was assayed with an in situ hybridization for the gene Hoxa1. The resulting expression patterns suggested that one aspect of the model design was not accurate, and based on these results the model was modified to encompass the new data, without losing the fit to the original data sets. The thesis work was therefore brought full circle, thus showing the utility of an interconnected effort: the act of constructing and using the model identified interesting biology questions, and the answer to one of those questions was used to enhance the model.
" }, { "name": "Khandekar, Aamod Dinkar", "degree": "PhD", "year": "2003", "title": "Graph-Based Codes and Iterative Decoding", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06202002-170522", "creators": [ { "name": { "family": "Khandekar", "given": "Aamod Dinkar" }, "id": "Khandekar-Aamod-Dinkar", "display_name": "Khandekar, Aamod Dinkar" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Preskill", "given": "John P." }, "id": "Preskill-J", "orcid": "0000-0002-2421-4762", "role": "member", "display_name": "Preskill, John P." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/Q06G-MW38", "abstract": "The field of error correcting codes was revolutionized by the introduction of turbo codes in 1993. These codes demonstrated dramatic performance improvements over any previously known codes, with significantly lower complexity. Since then, much progress has been made towards understanding the performance of these codes, as well as in using this understanding to design even better codes.
\r\n\r\nThis thesis takes a few more steps in both these directions. We develop a new technique, called the typical set bound, for analyzing the asymptotic performance of code ensembles based on their weight enumerators. This technique yields very tight bounds on the maximum-likelihood decoding threshold of code ensembles, and is powerful enough to reproduce Shannon's noisy coding theorem for the class of binary-input symmetric channels.
\r\n\r\nWe also introduce a new class of codes called irregular repeat-accumulate (IRA) codes, which are adapted from the previously known class of repeat-accumulate (RA) codes. These codes are competitive in terms of decoding performance with the class of irregular low-density parity-check (LDPC) codes, which are arguably the best class of codes known today, at least for long block lengths. In addition, IRA codes have a significant advantage over irregular LDPC codes in terms of encoding complexity.
\r\n\r\nWe also derive an analytical bound regarding iterative decoding thresholds of code ensembles on general binary-input symmetric channels, an area in which theoretical results are currently lacking.
" }, { "name": "Koslowski, Marisol", "degree": "PhD", "year": "2003", "title": "A Phase-Field Model of Dislocations in Ductile Single Crystals", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-094155", "creators": [ { "name": { "family": "Koslowski", "given": "Marisol" }, "id": "Koslowski-Marisol", "orcid": "0000-0001-9650-2168", "display_name": "Koslowski, Marisol" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Molinari", "given": "Alain" }, "id": "Molinari-A", "role": "member", "display_name": "Molinari, Alain" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SFMJ-1B50", "abstract": "A phase-field theory of dislocations, strain hardening and hysteresis in ductile single crystals is developed. The theory accounts for an arbitrary number and arrangement of dislocation lines over a slip plane; the long-range elastic interactions between dislocation lines; the core structure of the dislocations; the interaction between the dislocations and an applied resolved shear stress field; and the irreversible interactions with short-range obstacles, resulting in hardening, path dependency and hysteresis.
\r\n\r\nWe introduce a variational formulation for the statistical mechanics of dissipative systems. The influence of finite temperature as well as the mechanics in the phase-field theory are modeled with a Metropolis Monte Carlo algorithm and a mean field approximation.
\r\n\r\nA chief advantage of the present theory is that at zero temperature it is analytically tractable, in the sense that the complexity of the calculations may be reduced, with the aid of closed form analytical solutions, to the determination of the value of the phase field at point-obstacle sites. The theory predicts a range of behaviors which are in qualitative agreement with observation, including hardening and dislocation multiplication in single slip under monotonic loading; the Bauschinger effect under reverse loading; the fading memory effect; the evolution of the dislocation density under cycling loading; temperature softening; strain rate dependence; and others.
\r\n\r\nThe model also reproduces the formation of dislocation networks observed in grain boundaries for different crystal structures and orientations. Simultaneously with the stable configurations the theory naturally predicts the equilibrium dislocation density independently of initial values or sources.
" }, { "name": "Kumar, Sanjay", "degree": "PhD", "year": "2003", "title": "An Experimental Investigation of Richtmyer-Meshkov Instability", "advisor": "Hornung, Hans G.; Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212003-140109", "creators": [ { "name": { "family": "Kumar", "given": "Sanjay" }, "id": "Kumar-Sanjay", "display_name": "Kumar, Sanjay" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NKDR-TT39", "abstract": "In this study, the interaction of a shock wave with an interface between two gases is studied experimentally. The basic mechanism for the initial growth of perturbations on the interface is the baroclinic generation of vorticity which results from the misalignment of the pressure gradient in the shock and the density gradient at the interface. The growth of perturbations soon enters into a nonlinear regime with the appearance of bubbles of light fluid rising into heavy fluid and spikes of heavy fluid falling into light fluid. In the nonlinear regime, interaction between various scales and the appearance of other instabilities, such as Kelvin-Helmholtz instability, along the boundaries of the spikes occur, which results in the breakup of the interface. These processes lead to a turbulent mixing zone (TMZ) which grows with time. The main focus of this study is to understand the growth of TMZ with time in a cylindrical geometry with square cross section and for the the first time study the effect of area convergence in a conical geometry on its growth rate. The present set of experiments is done in the GALCIT 17 in. shock tube with air and sulfur hexafluoride as light and heavy gases. The growth of the TMZ is studied in a straight test section for single-mode initial perturbation consisting of two different wavelength and amplitude combinations at incident shock Mach number of 1.55. The multimode initial perturbation growth at late times is studied in a conical geometry to study the effect of area convergence at incident Mach numbers of 1.55 and 1.39. The results are compared with the experiments of Vetter which were done in the same shock tube with a straight test section with no area convergence and at the same Mach number.
\r\n\r\nIn the study of the Richtmyer-Meshkov (RM) instability of single-scale perturbations on air/sulfur-hexafluoride interface in a straight test section, the initially sinusoidal interface is formed by a polymeric membrane of thickness 1.5 micron and the flow visualization is done using schlieren imaging technique. The interface thickness is measured visually from the photographs. It is found that the growth rate decreases rapidly with time with a small dependence on the initial wavelength persisting until late times.
\r\n\r\nIn the case of the RM instability, growth of multimode initial perturbations in a conical geometry, it is found from the schlieren flow visualization images that the interface thickness grows about 40-50 % more rapidly than in Vetter's experiments. Experimental results for laser-induced scattering at late times are presented for air/He gas combinations at the interface. In situations when the rear of the interface is not clearly demarcated, the thickness is determined by an image processing technique. This technique is also used to determine the possible dominant eddy/blob size in the TMZ from the schlieren images. Some inviscid computational studies, with a planar or spherical shock interacting with a planar or spherical initial interface in light-heavy (air/sulfur-hexafluoride) and heavy-light (air/He) configurations, are also presented. In the conical geometry there is a reflected shock originating from the triple point. This reflection is a consequence of the transition from the cylindrical shock tube to the converging cone. Due to the vorticity created by the interaction of reflected shock from the cone wall with the interface in initial stage, it is found that the interface curves toward or away from the apex of the cone, depending on the sign of density gradient. This curving of the interface could have a role to play in the diffuse rear boundary of the interface in schlieren flow visualization images but the laser-induced scattering image shows that the mixing zone indeed does not have a well-defined rear boundary. Rather, small blobs of fluids on the right are scattered in the mixing zone. An inviscid computational study is also done on cylindrical and conical test section geometries to study the effect of transverse reflected waves on the growth of small sinusoidal initial perturbations. It is found by comparison with cylindrical geometry (where reflected waves do not exist) that the transverse reflected waves do not affect the growth of perturbations on the interface.
" }, { "name": "Lee, Hyon-Jee", "degree": "PhD", "year": "2003", "title": "Molecular Dynamics Studies of Metallic Glasses", "advisor": "Johnson, William Lewis; Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292003-165018", "creators": [ { "name": { "family": "Lee", "given": "Hyon-Jee" }, "id": "Lee-Hyon-Jee", "display_name": "Lee, Hyon-Jee" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "co-chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" } ], "option_major": [ "matsci" ], "doi": "10.7907/ZE5V-VZ33", "abstract": "The thermodynamic, structural, and mechanical properties of metallic glasses are studied using molecular dynamics simulations. Molecular dynamics provides a computational framework to simulate the movement of interacting atoms in response to external perturbations, such as changes in temperature or pressure. In this thesis, a Sutton-Chen potential was chosen to describe the many-body interactions in metals and alloys. Our first application for this approach is to develop a simple model to derive the thermodynamic properties of metallic alloys (Chapter 2). Based on this model, we demonstrate that the glass transition is thermodynamically sensitive to differences between atomic radii and that there is an optimal difference for glass formation. Next, we extend these simulations to elucidate the details of structural organization in the glass (Chapter 3). We find that the liquid phase is characterized by a local five-fold symmetry, which becomes more prominent as the glass phase forms. This five-fold symmetry is related to the formation of icosahedral structures. The mechanical properties of glasses are also investigated and it is found that shear localization, which accompanies a sharp drop in the stress-strain curve, occurs at 45 degree with respect to the loading axis (Chapter 4). The generation of free volume is found to be the dominant mechanism that leads to shear localization, rather than adiabatic heating. Finally, generic first principle potentials are constructed to guide the experimental development of AlTiNi based metallic glasses (Chapter 5). Together, the results from these simulations improve our understanding of the thermodynamic, structural, and mechanical properties of metallic glasses and will aid computer-driven materials design.\r\n" }, { "name": "Lekien, Francois Paul", "degree": "PhD", "year": "2003", "title": "Time-Dependent Dynamical Systems and Geophysical Flows", "advisor": "Marsden, Jerrold E.; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04082003-180353", "creators": [ { "name": { "family": "Lekien", "given": "Francois Paul" }, "id": "Lekien-Francois-Paul", "display_name": "Lekien, Francois Paul" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Haller", "given": "George" }, "id": "Haller-G", "role": "member", "display_name": "Haller, George" }, { "name": { "family": "Mezic", "given": "Igor" }, "id": "Mezic-I", "role": "member", "display_name": "Mezic, Igor" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/A83E-VZ73", "abstract": "This thesis presents a dynamical systems approach to transport and mixing in geophysical flows. First, new algorithms are developed that allow one to study a dynamical system that is described in a variety of ways such as by means of observational data or numerical simulations of differential equations.
\r\n\r\nNext, methods available to study non-autonomous systems, such as hyperbolic trajectories and Lagrangian coherent structures, are developed. These concepts are applied to examples of interests: Monterey Bay, the coast of Florida and the circulation in the North Atlantic. Combining accurate current measurements and recent developments in dynamical systems theory provides new and original answers to many problems, such as the minimization of the impact of released contaminants in a coastal area or the optimization of the coverage by a group of drifters.
\r\n\r\nThe appendices give details about MANGEN, a software package developed to produce the numerical results of this thesis. Some projects that make use of its algorithms, such as the dissociation rate of a molecule and efficient space mission design, are also described.
" }, { "name": "Lessard, Guillaume", "degree": "PhD", "year": "2003", "title": "Apertureless Near-Field Optical Microscopy for Fluorescence Imaging", "advisor": "Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-145931", "creators": [ { "name": { "family": "Lessard", "given": "Guillaume" }, "id": "Lessard-Guillaume", "orcid": "0000-0003-4275-3556", "display_name": "Lessard, Guillaume" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "chair", "display_name": "Quake, Stephen R." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Collier", "given": "C. Patrick" }, "id": "Collier-C-P", "role": "member", "display_name": "Collier, C. Patrick" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Y704-ER28", "abstract": "This thesis describes the development of a new type of optical microscope, an apertureless near-field microscope for fluorescence imaging (FANSOM). We have demonstrated that it is possible to use the probe of an atomic force microscope (AFM) to create a detectable modulation of the fluorescence of a nanometer-scale fluorescent object, and that it is possible to use that modulation to produce images by raster-scanning. Our results show that such a microscope is capable of a lateral resolution better than 20 nm.
\r\n\r\nThe processes that cause this modulation act for very small probe-sample separations, smaller than 20 nm. We have demonstrated FANSOM contrast using two completely different effects, one being a fluorescence inhibition, the other being a fluorescence enhancement generated by electric field enhancement. We have obtained contrast ratios of 1.90:1 using the fluorescence inhibition effect, and 5:1 using the fluorescence enhancement effect.
\r\n\r\nFluorescence can be inhibited by the proximity of a metallic probe. We have mapped the vertical profile of this phenomenon, and have shown that its shape is dependent upon the method of illumination. With evanescent illumination, the closest range of the interaction can exhibit some fluorescence enhancement that partially cancels the fluorescence inhibition effect.
\r\n\r\nWhen a metallic or dielectric probe approaches a sample illuminated by an evanescent illumination field polarized parallel to the probe (i.e., vertically with respect to the surface), field enhancement occurs. A local fluorescence enhancement is detected as a result of the field enhancement. The range of this effect is less than 10 nm, located mostly under the AFM probe; the optical images acquired using this contrast mechanism exhibit a lateral resolution equal to or higher than the topographic resolution measured by AFM.
\r\n\r\nThe design of the data acquisition system allows us to obtain precise mappings of signal intensity to probe--sample separation, more precise than have previously been achieved in an apertureless near-field microscopy system. It has allowed us to obtain repeatable approach curves that differ clearly from one another when the type of illumination or probe is changed.
" }, { "name": "Leung, Fok-Yan Thomas", "degree": "PhD", "year": "2003", "title": "Elucidation of the Origins of Stratospheric Sulfate Aerosols by Isotopic Methods", "advisor": "Hoffmann, Michael R.; Yung, Yuk L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292003-144531", "creators": [ { "name": { "family": "Leung", "given": "Fok-Yan Thomas" }, "id": "Leung-Fok-Yan-Thomas", "display_name": "Leung, Fok-Yan Thomas" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "co-advisor", "display_name": "Yung, Yuk L." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Randerson", "given": "James T." }, "id": "Randerson-J-T", "role": "member", "display_name": "Randerson, James T." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/CPWV-0307", "abstract": "Stratospheric sulfate aerosols (SSA) play an important part in regulating the climate of the earth and in the maintenance of important stratospheric species, including stratospheric ozone. The sources of stratospheric sulfate aerosol sulfur remain an unresolved issue because of uncertainties in the global sulfur budget and model limitations. The origins of SSA particles should be reflected in their isotopic composition. In this thesis project, the sulfur isotopic fractionation factors of processes that produce stratospheric sulfate aerosols (SSA) were quantified using a variety of theoretical and experimental techniques. RRKM (unimolecular dissociation) theory was applied to compute the isotopic fractionation of the homogeneous oxidation of SO2 via OH radicals. The overall isotopic enrichment associated with the total OCS loss pathways in the stratosphere was determined by analyzing high resolution FT-IR data from balloon flights. The isotopic fractionation of the photolytic decomposition of OCS was estimated by measuring the absorption spectra of OCS sulfur isotopologues. We also measured the isotopic composition of stratospheric aerosols sampled during the period 1973-1974, in the course of the Department of Energy?s AIRSTREAM campaign. Combining our results with literature values of the sulfur isotopic composition of SSA precursors, we modeled the steady-state isotopic composition of sulfur compounds in the atmosphere using the JPL/Caltech 1-D chemical transport model. Our data supports the view that OCS and SO2 are both important in the maintenance of the background stratospheric sulfate aerosol layer." }, { "name": "Lew, Adri\u00e1n Jos\u00e9", "degree": "PhD", "year": "2003", "title": "Variational Time Integrators in Computational Solid Mechanics", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262003-200254", "creators": [ { "name": { "family": "Lew", "given": "Adri\u00e1n Jos\u00e9" }, "id": "Lew-Adri\u00e1n-Jos\u00e9", "display_name": "Lew, Adri\u00e1n Jos\u00e9" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Sulsky", "given": "Deborah" }, "id": "Sulsky-D", "role": "member", "display_name": "Sulsky, Deborah" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6C74-GC16", "abstract": "This thesis develops the theory and implementation of variational integrators for computational solid mechanics problems, and to some extent, for fluid mechanics problems as well. Variational integrators for finite dimensional mechanical systems are succinctly reviewed, and used as the foundations for the extension to continuum systems. The latter is accomplished by way of a space-time formulation for Lagrangian continuum mechanics that unifies the derivation of the balance of linear momentum, energy and configurational forces, all of them as Euler-Lagrange equations of an extended Hamilton's principle. In this formulation, energy conservation and the path independence of the J- and L-integrals are conserved quantities emanating from Noether's theorem. Variational integrators for continuum mechanics are constructed by mimicking this variational structure, and a discrete Noether's theorem for rather general space-time discretizations is presented. Additionally, the algorithms are automatically (multi)symplectic, and the (multi)symplectic form is uniquely defined by the theory. For instance, in nonlinear elastodynamics the algorithms exactly preserve linear and angular momenta, whenever the continuous system does.
\r\n\r\nA class of variational algorithms is constructed, termed asynchronous variational integrators (AVI), which permit the selection of independent time steps in each element of a finite element mesh, and the local time steps need not bear an integral relation to each other. The conservation properties of both synchronous and asynchronous variational integrators are discussed in detail. In particular, AVI are found to nearly conserve energy both locally and globally, a distinguishing feature of variational integrators. The possibility of adapting the elemental time step to exactly satisfy the local energy balance equation, obtained from the extended variational principle, is analyzed. The AVI are also extended to include dissipative systems. The excellent accuracy, conservation and convergence characteristics of AVI are demonstrated via selected numerical examples, both for conservative and dissipative systems. In these tests AVI are found to result in substantial speedups, at equal accuracy, relative to explicit Newmark.
\r\n\r\nIn elastostatics, the variational structure leads to the formulation of discrete path-independent integrals and a characterization of the configurational forces acting in discrete systems. A notable example is a discrete, path-independent J-integral at the tip of a crack in a finite element mesh.
" }, { "name": "Lon\u010dar, Marko", "degree": "PhD", "year": "2003", "title": "Nanophotonic Devices Based on Planar Photonic Crystals", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022003-042444", "creators": [ { "name": { "family": "Lon\u010dar", "given": "Marko" }, "id": "Lon\u010dar-Marko", "orcid": "0000-0002-5029-5017", "display_name": "Lon\u010dar, Marko" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "member", "display_name": "Quake, Stephen R." } ], "option_major": [ "eleceng" ], "doi": "10.7907/SB3Y-8Z20", "abstract": "Photonic Crystals, man-made periodic structures with a high refractive index contrast modulation, have recently become very interesting platform for the manipulation of light. The existence of a photonic bandgap, a frequency range in which propagation of light is prevented in all directions, makes photonic crystals very useful in applications where spatial localization of light is required. Ideally, by making a three-dimensional photonic crystal, propagation of light in all three dimensions can be controlled. Since fabrication of 3-D structures is still a difficult process, a more appealing approach is based on the use of lower dimensional photonic crystals. A concept that has recently attracted a lot of attention is a planar photonic crystal based on a dielectric membrane, suspended in the air, and perforated with a two-dimensional lattice of holes.
\r\n\r\nIn this thesis theoretical and experimental study of planar photonic crystal nanolasers, waveguides and super-dispersive elements is presented. Room temperature operation of low-threshold nanolaser is demonstrated, both in air and in different chemical solutions. For the first time, we have demonstrated that photonic crystal nanocavity lasers can be used to perform spectroscopic tests on ultra-small volumes of analyte. Our porous cavity design permits the introduction of analyte directly into the high optical field of the laser cavity, and therefore it is ideally suited for the investigation of interaction between light and matter on a nanoscale level. We showed that small changes in refractive index of the ambient surrounding the laser can be detected by observing the shifts in emission wavelengths of the laser. Our lasers can be integrated into large arrays to permit the analysis of many reagents at the same time. The nanolasers can also be integrated with photonic crystal waveguides to form the integrated systems of higher complexities. Theoretical and experimental investigation of various photonic crystal waveguide designs is discussed. Details of the fabrication procedure used to realize nanophotonic devices in silicon on insulator as well as InGaAsP materials are presented.
" }, { "name": "Maier, Stefan Alexander", "degree": "PhD", "year": "2003", "title": "Guiding of Electromagnetic Energy in Subwavelength Periodic Metal Structures", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062003-155401", "creators": [ { "name": { "family": "Maier", "given": "Stefan Alexander" }, "id": "Maier-Stefan-Alexander", "orcid": "0000-0001-9704-7902", "display_name": "Maier, Stefan Alexander" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "member", "display_name": "Quake, Stephen R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/TKPX-3H40", "abstract": "The ultimate miniaturization of optical devices requires structures that guide electromagnetic energy with a lateral confinement below the diffraction limit of light. In this thesis, the possibility of employing plasmon-polariton excitations in plasmon waveguides consisting of closely spaced metal nanoclusters for this purpose is examined. The feasibility of energy transport with mode sizes below the diffraction limit of visible light over distances of several hundred nanometers is demonstrated.
\r\n\r\nAs a macroscopic analogue to plasmon waveguides, the transport of electromagnetic energy in the microwave regime along closely spaced centimeter-scale metal rods is examined. Full-field electrodynamic simulations show that information transport occurs at a group velocity of 0.65c for fabricated structures consisting of copper rods excited at 8 GHz. A variety of passive routing structures and an all-optical modulator are demonstrated.
\r\n\r\nThe possibility of guiding electromagnetic energy at visible frequencies with mode sizes below the diffraction limit using plasmon waveguides is analyzed using a point-dipole model and finite-difference time-domain simulations. It is shown that energy transport occurs via near-field coupling between metal nanoparticles, which leads to coherent propagation of energy. For spherical gold particles in air, group velocities up to 0.06c are demonstrated, and a change in particle shape to spheroidal particles shows up to a threefold increase in group velocity. Pulses with transverse polarization are shown to propagate with negative phase velocities antiparallel to the energy flow.
\r\n\r\nPlasmon waveguides consisting of gold and silver nanoparticles were fabricated using electron beam lithography. The key parameters that govern the energy transport are determined for various interparticle spacings and particle chain lengths using far-field measurements of the collective plasmon modes. Spherical gold nanoparticles with a diameter of 50 nm and an interparticle spacing of 75 nm show an energy attenuation of 6 dB/30 nm. This loss can be reduced by one order of magnitude by a geometry change to spheroidal particles. Using the tip of a near-field optical microscope as a local excitation source and fluorescent nanospheres as detectors, experimental evidence for energy transport over a distance of 0.5 micron is presented for plasmon waveguides consisting of silver rods with a 3:1 aspect ratio.
" }, { "name": "Mason, Richard James", "degree": "PhD", "year": "2003", "title": "Fluid Locomotion and Trajectory Planning for Shape-Changing Robots", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292003-160843", "creators": [ { "name": { "family": "Mason", "given": "Richard James" }, "id": "Mason-Richard-James", "display_name": "Mason, Richard James" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "mecheng" ], "doi": "10.7907/MFM1-0866", "abstract": "Motivated by considerations of shape changing propulsion of underwater robotic vehicles, I analyze the mechanics of deformable bodies operating in an ideal fluid. I give particular attention to fishlike robots which may be considered as one or more flexing or oscillating hydrofoils. I then describe methods of planning trajectories for a fishlike robot or any other sort of robot whose locomotion has a periodic or quasi-periodic nature." }, { "name": "Matveev, Konstantin Ivanovich", "degree": "PhD", "year": "2003", "title": "Thermoacoustic Instabilities in the Rijke Tube: Experiments and Modeling", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042003-102221", "creators": [ { "name": { "family": "Matveev", "given": "Konstantin Ivanovich" }, "id": "Matveev-Konstantin-Ivanovich", "display_name": "Matveev, Konstantin Ivanovich" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/3X6A-6D11", "abstract": "Thermoacoustic instability can appear in thermal devices when unsteady heat release is coupled with pressure perturbations. This effect results in excitation of eigen acoustic modes of the system. These instabilities are important in various technical applications, for instance, in rocket motors and thermoacoustic engines.
\r\n\r\nA Rijke tube, representing a resonator with a mean flow and a concentrated heat source, is a convenient system for studying the fundamental physics of thermoacoustic instabilities. At certain values of the main system parameters, a loud sound is generated through a process similar to that in real-world devices prone to thermoacoustic instability. Rijke devices have been extensively employed for research purposes. The current work is intended to overcome the serious deficiencies of previous investigations with regard to estimating experimental errors and the influence of parameter variation on the results. Also, part of the objective here is to account for temperature field non-uniformity and to interpret nonlinear phenomena. The major goals of this study are to deliver accurate experimental results for the transition to instability and the scope and nature of the excited regimes, and to develop a theory that explains and predicts the effects observed.
\r\n\r\nAn electrically heated, horizontally oriented, Rijke tube is used for the experimental study of transition to instability. The stability boundary is quantified as a function of major system parameters with measured uncertainties for the data collected. Hysteresis in the stability boundary is observed for certain operating regimes of the Rijke tube.
\r\n\r\nAn innovative theory is developed for modeling the Rijke oscillations. First, linear theory, incorporating thermal analysis that accurately determines the properties of the modes responsible for the transition to instability, is used to predict the stability boundary. Then, a nonlinear extension of the theory is derived by introducing a hypothesis for a special form of the nonlinear heat transfer function. This nonlinear modeling is shown to predict the hysteresis phenomenon and the limit cycles observed during the tests.
\r\n\r\nA new, reduced-order modeling approach for combustion instabilities in systems with vortex shedding is derived using the developed analytical framework. A hypothesis for the vortex detachment criterion is introduced, and a kicked oscillator model is applied to produce nonlinear results characteristic for unstable combustion systems.
\r\n\r\nThe experimental system and the mathematical model, developed in this work for the Rijke tube, are recommended for preliminary design and analysis of real-world thermal devices, where thermoacoustic instability is a concern.
" }, { "name": "Mauch, Sean Patrick", "degree": "PhD", "year": "2003", "title": "Efficient Algorithms for Solving Static Hamilton-Jacobi Equations", "advisor": "Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202003-170423", "creators": [ { "name": { "family": "Mauch", "given": "Sean Patrick" }, "id": "Mauch-Sean-Patrick", "display_name": "Mauch, Sean Patrick" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/5R5P-Y603", "abstract": "We present an algorithm for computing the closest point transform to an explicitly described manifold on a rectilinear grid in low dimensional spaces. The closest point transform finds the closest point on a manifold and the Euclidean distance to a manifold for the points in a grid. We consider manifolds composed of simple geometric shapes, such as, a set of points, piecewise linear curves or triangle meshes. The algorithm solves the eikonal equation |grad u| = 1 with the method of characteristics. For many problems, the computational complexity of the algorithm is linear in both the number of grid points and the complexity of the manifold.
\r\n\r\nMany query problems can be aided by using orthogonal range queries (ORQ). There are several standard data structures for performing ORQ's in 3-D, including kd-trees, octrees, and cell arrays. We develop additional data structures based on cell arrays. We study the characteristics of each data structure and compare their performance.
\r\n\r\nWe present a new algorithm for solving the single-source, non-negative weight, shortest-paths problem. Dijkstra's algorithm solves this problem with computational complexity O((E + V) log V) where E is the number of edges and V is the number of vertices. The new algorithm, called Marching with a Correctness Criterion (MCC), has computational complexity O(E + R V), where R is the ratio of the largest to smallest edge weight.
\r\n\r\nSethian's Fast Marching Method (FMM) may be used to solve static Hamilton-Jacobi equations. It has computational complexity O(N log N), where N is the number of grid points. The FMM has been regarded as an optimal algorithm because it is closely related to Dijkstra's algorithm. The new shortest-paths algorithm discussed above can be used to develop an ordered, upwind, finite difference algorithm for solving static Hamilton-Jacobi equations. This algorithm requires difference schemes that difference not only in coordinate directions, but in diagonal directions as well. It has computational complexity O(R N), where R is the ratio of the largest to smallest propagation speed and N is the number of grid points.
" }, { "name": "Meng, Ellis Fan-Chuin", "degree": "PhD", "year": "2003", "title": "MEMS Technology and Devices for a Micro Fluid Dosing System", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-05182003-163704", "creators": [ { "name": { "family": "Meng", "given": "Ellis Fan-Chuin" }, "id": "Meng-Ellis-Fan-Chuin", "orcid": "0000-0003-0981-9197", "display_name": "Meng, Ellis Fan-Chuin" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "member", "display_name": "Pine, Jerome" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/MRDS-FC06", "abstract": "Microelectromechanical systems (MEMS) technology has matured to the point where practical biological and chemical applications are possible. One particularly active research area is in the development of lab-on-a-chip type systems. In order to create successful lab-on-a-chip and other microfluidic systems, it is necessary to have the capability of controlling and directing fluid flow. Such functionality can be found on the front end of a microfluidic system and is known as a fluid delivery or dosing subsystem. For a MEMS micro fluid dosing system to be realized, several components are necessary. The essential components include a fluid actuator, a fluidic control device, and micro plumbing. A prototype fluid delivery system is demonstrated here using a micropump as the fluid actuator, a thermal flow sensor as the fluidic control device, and micromachined couplers as plumbing. The technology to build these components has been developed and each of these components have been fabricated and tested. A prototype constructed of discrete components has also been demonstrated. A truly integrated, channel-based fluid dosing system can be achieved through device scaling." }, { "name": "Milam, Mark Bradley", "degree": "PhD", "year": "2003", "title": "Real-Time Optimal Trajectory Generation for Constrained Dynamical Systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022003-114340", "creators": [ { "name": { "family": "Milam", "given": "Mark Bradley" }, "id": "Milam-Mark-Bradley", "display_name": "Milam, Mark Bradley" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Hauser", "given": "John" }, "id": "Hauser-J", "role": "member", "display_name": "Hauser, John" } ], "option_major": [ "cds" ], "doi": "10.7907/1X68-E370", "abstract": "With the advent of powerful computing and efficient computational algorithms, real-time solutions to constrained optimal control problems are nearing a reality. In this thesis, we develop a computationally efficient Nonlinear Trajectory Generation (NTG) algorithm and describe its software implementation to solve, in real-time, nonlinear optimal trajectory generation problems for constrained systems. NTG is a nonlinear trajectory generation software package that combines nonlinear control theory, B-spline basis functions, and nonlinear programming. We compare NTG with other numerical optimal control problem solution techniques, such as direct collocation, shooting, adjoints, and differential inclusions.
\r\n\r\nWe demonstrate the performance of NTG on the Caltech Ducted Fan testbed. Aggressive, constrained optimal control problems are solved in real-time for hover-to-hover, forward flight, and terrain avoidance test cases. Real-time trajectory generation results are shown for both the two-degree of freedom and receding horizon control designs. Further experimental demonstration is provided with the station-keeping, reconfiguration, and deconfiguration of micro-satellite formation with complex nonlinear constraints. Successful application of NTG in these cases demonstrates reliable real-time trajectory generation, even for highly nonlinear and non-convex systems. The results are among the first to apply receding horizon control techniques for agile flight in an experimental setting, using representative dynamics and computation.
" }, { "name": "Mookherjea, Shayan", "degree": "PhD", "year": "2003", "title": "Coupled-Resonator Optical Waveguides and Multiplexed Solitons", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152003-144457", "creators": [ { "name": { "family": "Mookherjea", "given": "Shayan" }, "id": "Mookherjea-Shayan", "orcid": "0000-0001-9864-2367", "display_name": "Mookherjea, Shayan" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "eleceng" ], "doi": "10.7907/9BYR-7J64", "abstract": "Whether over micron-long or kilometer-long distances, periodic phenomena can strongly affect both the propagation and the confinement of optical pulses. Periodicities can be engineered through the structural design of optical waveguides, or they may manifest self-consistently from induced nonlinear polarizations. In light of recent developments in fabrication technologies for semiconductor waveguides, polymeric materials, and optical fiber, we show that both strongly- and weakly-nonlinear channels are promising for new devices and systems in optical communications. This thesis proposes and discusses applications of guided wave periodicities in the framework of photonic crystals (coupled-resonator optical waveguides as well as transverse Bragg resonance waveguides and amplifiers), nonlinear phenomena in photorefractive semiconductors, and the nonlinear evolution of temporal solitons in dispersion-managed fibers.
\r\n\r\nCoupled-resonator optical waveguides (CROWs) are composed of a periodic array of electromagnetic resonators, typically on the micron or sub-micron length scales. A photon in such a waveguide sees a periodic potential, and according to the Floquet-Bloch theorems, has a wavefunction that reflects this periodicity. CROWs have a unique dispersion relationship compared to other semiconductor waveguides, and can be used to slow down the speed of propagation, enhance nonlinear interactions such as second-harmonic generation and four-wave mixing, and form frozen soliton-type field distributions that use the optical Kerr nonlinearity to stabilize themselves against decay via adjacent-resonator or waveguide-resonator coupling.
\r\n\r\nIn optical fibers that possess the optical Kerr nonlinearity in addition to group-velocity dispersion, it is possible to propagate pulses with envelopes that \"breathe\" with distance, typically at kilometer or longer length scales. Such waveforms are characterized by a set of parameters, e.g., amplitude, chirp, etc., that vary in a periodic manner as the pulse propagates. Borrowing an idea from field theory, e.g., of classical pendulums, or quantum-mechanical elementary particles, the pulse envelope may be viewed as a particle traversing a trajectory in a phase space defined by its characteristic parameters. Distinct, non-overlapping trajectories are assigned as symbols of a multilevel communication code. Since it is the periodicity, arising from the Kerr nonlinearity, that generates this diversity in phase-space, there is no analog of this multiplexed system in linear optical transmission links. The overall bit-rate can be improved several fold above the current limits.
" }, { "name": "Morgan, Matthew Alexander", "degree": "PhD", "year": "2003", "title": "Millimeter-Wave MMICs and Applications", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04082003-150009", "creators": [ { "name": { "family": "Morgan", "given": "Matthew Alexander" }, "id": "Morgan-Matthew-Alexander", "display_name": "Morgan, Matthew Alexander" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "chair", "display_name": "Weinreb, Sander" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Pogorzelski", "given": "Ronald" }, "id": "Pogorzelski-R", "role": "member", "display_name": "Pogorzelski, Ronald" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MW4Z-2Q79", "abstract": "As device technology improves, interest in the millimeter-wave band grows. Wireless communication systems migrate to higher frequencies, millimeter-wave radars and passive sensors find new solid-state implementations that promise improved performance, and entirely new applications in the millimeter-wave band become feasible. The circuit or system designer is faced with a new and unique set of challenges and constraints to deal with in order to use this portion of the spectrum successfully. In particular, the advantages of monolithic integration become increasingly important.
\r\n\r\nThis thesis presents many new developments in Monolithic Millimeter-Wave Integrated Circuits (MMICs), both the chips themselves and systems that use them. It begins with an overview of the various applications of millimeter waves, including a discussion of specific projects that the author is involved in and why many of them demand a MMIC implementation. In the subsequent chapters, new MMIC chips are described in detail, as is the role they play in real-world projects. Multi-chip modules are also presented with specific attention given to the practical details of MMIC packaging and multi-chip integration. The thesis concludes with a summary of the works presented thus far and their overall impact on the field of millimeter-wave engineering.
" }, { "name": "Panotopoulos, Georgios", "degree": "PhD", "year": "2003", "title": "Holographic Information Systems", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-04282003-142947", "creators": [ { "name": { "family": "Panotopoulos", "given": "Georgios" }, "id": "Panotopoulos-Georgios", "display_name": "Panotopoulos, Georgios" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Buse", "given": "Karsten" }, "id": "Buse-K", "role": "member", "display_name": "Buse, Karsten" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/P6B7-VR22", "abstract": "The goal of this work is to investigate the use of holographic techniques for information processing and transmission systems. Until recently information has been processed and transmitted mainly electronically. With the advent of optical fiber communications the monopoly of electronics has receded in the telecommunications field, but the domain of information processing is still dominated by electronic processors.
\r\n\r\nThis thesis follows a top-down approach to the design of processors that integrate both electronic and optical components. It begins with the design considerations of a compact, rapidly reconfigurable opto-electronic processor, which possesses an optical bus in addition to the traditional electronic bus. The optical bus takes advantage of the massive parallelism that is afforded by optics and can be coupled to a holographic digital memory, allowing rapid reconfiguration of the device. The capability of rapid reconfiguration gives rise to a new computational paradigm, where the reprogramming of the device can become part of the computation. We suggest additional applications of this processor, namely as a smart reading head for large scale holographic disk memories. Finally we present novel algorithms that were developed specifically to take advantage of the additional capabilities of our processor.
\r\n\r\nThe next section is concerned with the wavelength and angular tuning of strong volume holograms, both in the reflection and 90-degree geometries. Since photons have no charge, we need to rely on their wave properties to manipulate them, both for long-range transmission, such as telecommunications, and short-range transmission, such as on chip interconnects. In this section we investigate how volume holograms can be used to selectively redirect information bearing light beams.
\r\n\r\nThe final part of this thesis is concerned with material issues. Holographic recording of strong volume gratings is one of the most commonly used approaches, and photorefractive materials have a strong bearing on the overall performance of the final system. Two properties of iron doped lithium niobate are investigated, namely the dependence of absorption on temperature and the quadratic electro-optic coefficient. The former is crucial for the commonly used technique of thermal fixing, and the latter can become significant should we choose to use applied continuous fields to tune our gratings.
" }, { "name": "Pottebaum, Tait Sherman", "degree": "PhD", "year": "2003", "title": "The Relationship Between Near-Wake Structure and Heat Transfer for an Oscillating Circular Cylinder in Cross-Flow", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-05202003-145011", "creators": [ { "name": { "family": "Pottebaum", "given": "Tait Sherman" }, "id": "Pottebaum-Tait-Sherman", "display_name": "Pottebaum, Tait Sherman" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Richardson", "given": "Mark I." }, "id": "Richardson-M-I", "role": "member", "display_name": "Richardson, Mark I." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C9NQ-N832", "abstract": "A series of experiments were carried out in order to understand the relationship between wake structure and heat transfer for a transversely oscillating circular cylinder in cross-flow and to explore the dynamics of the vortex formation process in the wake. The cylinder's heat transfer coefficient was determined over a range of oscillation amplitudes up to 1.5 cylinder diameters and oscillation frequencies up to 5 times the stationary cylinder natural shedding frequency. The results were compared to established relationships between oscillation conditions and wake structure. Digital particle image thermometry/velocimetry (DPIT/V) was used to measure the temperature and velocity fields in the near-wake for a set of cases chosen to be representative of the variety of wake structures that exist for this type of flow. The experiments were carried out in a water tunnel at a Reynolds number of 690.
\r\n\r\nIt was found that wake structure and heat transfer both significantly affect one another. The wake mode, a label indicating the number and type of vortices shed in each oscillation period, is directly related to the observed heat transfer enhancement. The dynamics of the vortex formation process, including the trajectories of the vortices during roll-up, explain this relationship. The streamwise spacing between shed vortices was also shown to affect heat transfer coefficient for the 2S mode, which consists of two single vortices shed per cycle. The streamwise spacing is believed to influence entrainment of freestream temperature fluid by the forming vortices, thereby affecting the temperature gradient at the cylinder base. This effect may exist for other wake modes, as well.
\r\n\r\nThe cylinder's transverse velocity was shown to influence the heat transfer by affecting the circulation of the wake vortices. For a fixed wake structure, the effectiveness of the wake vortices at enhancing heat transfer depends on their circulation. Also, the cylinder's transverse velocity continually changes the orientation of the wake with respect to the freestream flow, thereby spreading the main source of heat transfer enhancement--the vortices near the cylinder base--over a larger portion of the cylinder surface.
\r\n\r\nPreviously observed heat transfer enhancement associated with oscillations at frequencies near the natural shedding frequency and its harmonics were shown to be limited to amplitudes of less than about 0.5 cylinder diameters.
\r\n\r\nA new phenomenon was discovered in which the wake structure switches back and forth between distinct wake modes. Temperature induced variations in the fluid viscosity are believed to be the cause of this mode-switching. It is hypothesized that the viscosity variations change the vorticity and kinetic energy fluxes into the wake, thereby changing the wake mode and the heat transfer coefficient. This discovery underscores the role of viscosity and shear layer fluxes in determining wake mode, potentially leading to improved understanding of wake vortex formation and pinch-off processes in general.
\r\n\r\nAspect ratio appears to play a role in determining the heat transfer coefficient mainly for non-oscillating cylinders. The heat transfer is also affected by aspect ratio for oscillation conditions characterized by weak synchronization of the wake to the oscillation frequency.
" }, { "name": "Preisler, Edward James", "degree": "PhD", "year": "2003", "title": "Investigation of Novel Semiconductor Heterostructure Systems: I. Cerium Oxide/Silicon Heterostructures. II. 6.1 \u00c5 Semiconductor-Based Avalanche Photodiodes", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022003-071834", "creators": [ { "name": { "family": "Preisler", "given": "Edward James" }, "id": "Preisler-Edward-James", "display_name": "Preisler, Edward James" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "role": "member", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Painter", "given": "Oskar J." }, "id": "Painter-O", "role": "member", "display_name": "Painter, Oskar J." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/59X1-WQ68", "abstract": "The work presented in this thesis concerns the development of two different semiconductor heterostructure technologies.
\r\n\r\nPart I describes research in the CeO2/silicon heterostructure system. Details are presented concerning the growth of CeO2 on silicon and the reactions that take place at the CeO2/silicon interface. The evolution of this interface as a function of annealing temperature and annealing ambient are studied via in situ x-ray photoelectron spectroscopy (XPS). Studies of metal-CeO2-silicon capacitors are also presented which help to determine the usefulness of this oxide as an alternative gate dielectric for silicon-based device applications.
\r\n\r\nPart II involves research into the fabrication of avalanche photodiodes (APD's) utilizing the 6.1 A semiconductor system. Certain alloys of Al_xGa_(1-x)Sb are shown to greatly favor hole multiplication which is beneficial for both noise characteristics and gain-bandwidth product. Further, details are presented on the current investigation into using 6.1 A superlattices to acheive even more desirable detector performance.
" }, { "name": "Radford, James Edward", "degree": "PhD", "year": "2003", "title": "Symmetry, Reduction and Swimming in a Perfect Fluid", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042003-181857", "creators": [ { "name": { "family": "Radford", "given": "James Edward" }, "id": "Radford-James-Edward", "display_name": "Radford, James Edward" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/CE65-XM80", "abstract": "This thesis presents a geometric picture of a deformable body in a perfect fluid and a way to approximate its dynamics and the motion, resulting from cyclic shape deformations, of the body and, interestingly, the fluid as well. Emphasis is placed on the group structure of the configuration space of the body fluid system and the resulting symmetry in their equations of motion. Symmetry is also used to reduce a series expansion for the flow of a time dependent vector field in order to obtain a novel expansion for the path-ordered exponential. This can be used to approximate holonomy, or geometric phase, in a principal bundle when its evolution is governed by a connection on the bundle and it is subject to periodic shape inputs. Simple models for swimming in and the stirring of a perfect fluid are proposed and examined." }, { "name": "Santamore, Deborah Hannah", "degree": "PhD", "year": "2003", "title": "Quantum Transport and Dynamics of Phonons in Mesoscopic Systems", "advisor": "Cross, Michael Clifford", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272003-152136", "creators": [ { "name": { "family": "Santamore", "given": "Deborah Hannah" }, "id": "Santamore-Deborah-Hannah", "orcid": "0000-0001-6305-7096", "display_name": "Santamore, Deborah Hannah" } ], "advisors": [ { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "advisor", "display_name": "Cross, Michael Clifford" } ], "committee": [ { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "chair", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Milburn", "given": "Gerard" }, "id": "Milburn-G", "role": "member", "display_name": "Milburn, Gerard" }, { "name": { "family": "Thorne", "given": "Kip S." }, "id": "Thorne-K-S", "role": "member", "display_name": "Thorne, Kip S." }, { "name": { "family": "Bockrath", "given": "Marc William" }, "id": "Bockrath-M-W", "role": "member", "display_name": "Bockrath, Marc William" }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Leggett", "given": "Tony" }, "id": "Leggett-T", "role": "member", "display_name": "Leggett, Tony" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/E62V-PR26", "abstract": "Recent advances in nanotechnology have shrunk the size of mesoscopic structures. This allows us to investigate the quantum mechanics of mechanical oscillators. In this thesis we focus on two aspects.
\r\n\r\nIn Part I, an individual discrete mode structure of an oscillator and its effect to thermal conductance have been thoroughly examined: Specifically, we investigated the reduction in the thermal conductance in the quantum limit due to phonon scattering by surface roughness, first using scalar waves, then using full three dimensional elasticity theory for an elastic beam with a rectangular cross section. At low frequencies, we find power laws for the scattering coefficients that are strongly mode dependent, and different from the results deriving from Rayleigh scattering of scalar waves, that is often assumed. The scattering gives temperature dependent contributions to the reduction in thermal conductance with the same power laws. At higher frequencies, the scattering coefficient becomes large at the onset frequency of each mode due to the flat dispersion. We use our results to attempt a quantitative understanding of the suppression of the thermal conductance from the universal value observed in experiment.
\r\n\r\nAs individual phonon energy becomes comparable to or greater than the thermal energy, the individual phonon dynamics within each mode can be resolved. In Part II, we examine a possibility of detecting individual quanta of a system: We investigate a scheme that makes a quantum non-demolition measurement of the excitation level of a mesoscopic mechanical oscillator by utilizing the anharmonic coupling between two bending modes of an elastic beam. The non-linear coupling between the two modes shifts the resonant frequency of the readout oscillator proportionate to the excitation of the system oscillator. This frequency shift may be detected as a phase shift of the readout oscillation when driven on resonance. We show that in an appropriate regime this measurement approaches a quantum non-demolition measurement of the phonon number of the system oscillator. As a result it should be possible to monitor jumps between Fock states caused by the coupling of the system to the thermal reservoirs.
" }, { "name": "Song, Yang", "degree": "PhD", "year": "2003", "title": "A Probabilistic Approach to Human Motion Detection and Labeling", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102002-113833", "creators": [ { "name": { "family": "Song", "given": "Yang" }, "id": "Song-Yang", "display_name": "Song, Yang" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Soatto", "given": "Stefano" }, "id": "Soatto-Stefano", "role": "member", "display_name": "Soatto, Stefano" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/945J-QX86", "abstract": "Human motion analysis is a very important task for computer vision with many potential applications. There are several problems in human motion analysis: detection, tracking, and activity interpretation. Detection is the most fundamental problem of the three, but remains untackled due to its inherent difficulty. This thesis develops a solution to the problem. It is based on a learned probabilistic model of the joint positions and velocities of the body parts, where detection and labeling are performed by hypothesis testing on the maximum a posterior estimate of the pose and motion of the body. To achieve efficiency in learning and testing, a graphical model is used to approximate the conditional independence of human motion. This model is also shown to provide a natural way to deal with clutter and occlusion.
\r\n\r\nOne key factor in the proposed method is the probabilistic model of human motion. In this thesis, an unsupervised learning algorithm that can obtain the probabilistic model automatically from unlabeled training data is presented. The training data include useful foreground features as well as features that arise from irrelevant background clutter. The correspondence between parts and detected features is also unknown in the training data. To learn the best model structure as well as model parameters, a variant of the EM algorithm is developed where the labeling of the data (part assignments) is treated as hidden variables. We explore two classes of graphical models: trees and decomposable triangulated graphs and find that the later are superior for our application. To better model human motion, we also consider the case when the model consists of mixtures of decomposable triangulated graphs.
\r\n \r\nThe efficiency and effectiveness of the algorithm have been demonstrated by applying it to generate models of human motion automatically from unlabeled image sequences, and testing the learned models on a variety of sequences. We find detection rates of over 95% on pairs of frames. This is very promising for building a real-life system, for example, a pedestrian detector.
" }, { "name": "Thoutireddy, Pururav", "degree": "PhD", "year": "2003", "title": "Variational Arbitrary Lagrangian-Eulerian Method", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292003-113845", "creators": [ { "name": { "family": "Thoutireddy", "given": "Pururav" }, "id": "Thoutireddy-Pururav", "display_name": "Thoutireddy, Pururav" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "chair", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DQT0-5104", "abstract": "This thesis is concerned with the development of Variational Arbitrary Lagrangian-Eulerian method (VALE) method. VALE is essentially finite element method generalized to account for horizontal variations, in particular, variations in nodal coordinates. The distinguishing characteristic of the method is that the variational principle simultaneously supplies the solution, the optimal mesh and, in case problems of shape optimization, optimal shape. This is accomplished by rendering the functional associated with the variational principle stationary with respect to nodal field values as well as with respect to the nodal positions of triangulation of the domain of analysis. Stationarity with respect to the nodal positions has the effect of the equilibriating the energetic or configurational forces acting in the nodes. Further, configurational force equilibrium provides precise criterion for mesh optimality. The solution so obtained corresponds to minimum of energy functional (minimum principle) in static case and to the stationarity of action sum (discrete Hamilton's stationarity principle) in dynamic case, with respect to both nodal variables and nodal positions. Further, the resulting mesh adaption scheme is devoid of error estimates and mesh-to-mesh transfer interpolation errors. We illustrate the versatility and convergence characteristics of the method by way of selected numerical tests and applications, including the problem of semi-infinite crack, the shape optimization of elastic inclusions and free vibration of 1-d rod." }, { "name": "Vela, Patricio Antonio", "degree": "PhD", "year": "2003", "title": "Averaging and Control of Nonlinear Systems", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282003-094253", "creators": [ { "name": { "family": "Vela", "given": "Patricio Antonio" }, "id": "Vela-Patricio-Antonio", "orcid": "0000-0002-6888-7002", "display_name": "Vela, Patricio Antonio" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Ostrowski", "given": "James P." }, "id": "Ostrowski-J-P", "role": "member", "display_name": "Ostrowski, James P." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/N7HH-PM67", "abstract": "This dissertation investigates three principal areas regarding the dynamics and control of nonlinear systems: averaging theory, controllability of mechanical systems, and control of underactuated nonlinear systems. The most effective stabilizing controllers for underactuated nonlinear systems are time-periodic, which leads to the study of averaging theory for understanding the nonlinear effect generated by resonant oscillatory inputs.
\r\n\r\nThe research on averaging theory generalizes averaging theory to arbitrary order by synthesizing series expansion methods for nonlinear time-varying vector fields and their flows with nonlinear Floquet theory. It is shown that classical averaging theory is the application of perturbation methods in conjunction with nonlinear Floquet theory. Many known properties and consequences of averaging theory are placed within a single framework.
\r\n\r\nThe generalized averaging theory is merged with controllability analysis of underactuated nonlinear systems to derive exponentially stabilizing controllers. Although small-time local controllability (STLC) is easily demonstrated for driftless systems via the Lie algebra rank condition, STLC for systems with drift is more complicated. Furthermore, there exists a variety of techniques and canonical forms for determining STLC. This thesis exploits notions of geometric homogeneity to show that STLC results for a large class of mechanical systems with drift can be recovered by considering a class of nonlinear dynamical systems satisfying certain homogeneity conditions. These theorems generalize the controllability results for simple mechanical control systems found in Lewis and Murray [85]. Most nonlinear controllability results for classes of mechanical systems may be obtained using these methods.
\r\n\r\nThe stabilizing controllers derived using the generalized averaging theory and STLC analysis can be used to stabilize both systems with and without drift. Furthermore, they result in a set of tunable gains and oscillatory parameters for modification and improvement of the feedback strategy. The procedure can not only derive known controllers from the literature, but can also be used to improve them. Examples demonstrate the diversity of controllers constructed using the generalized averaging theory.
\r\n\r\nThis dissertation concludes with a chapter devoted to biomimetic and biomechanical locomotive control systems that have been stabilized using the generalized averaging theory and the controller construction procedure. The locomotive control systems roll, wriggle, swim, and walk, demonstrating the universal nature of the control strategy proposed.
" }, { "name": "Wang, Xiaoou", "degree": "PhD", "year": "2003", "title": "Set Mapping in the Method of Imprecision", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10032002-214953", "creators": [ { "name": { "family": "Wang", "given": "Xiaoou" }, "id": "Wang-Xiaoou", "display_name": "Wang, Xiaoou" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/J0JH-M190", "abstract": "The Method of Imprecision, or MoI, is a semi-automated set-based approach which uses mathematics of fuzzy sets to aid the designer making decisions with imprecise information in the preliminary design stage.
\r\n\r\nThe Method of Imprecision uses preference to represent the imprecision in engineering design. The preferences are specified both in the design variable space (DVS) and the performance variable space (PVS). To reach the overall preference which is needed to evaluate designs, the mapping between the DVS and the PVS should be explored. Many engineering design tools can only produce precise results with precise specifications, and usually the cost is high. In the preliminary stage, the specifications are imprecise and resources are limited. Hence, it is not cost-effective nor necessary to use these engineering design tools directly to study the mapping between the DVS and the PVS. An interpolation model is introduced to the MoI to construct metamodels for the actual mapping function between the DVS and the PVS. Due to the nature of engineering design, multistage metamodels are needed. Experimental design is used to choose design points for the first metamodel. In order to find an efficient way to choose design points when a priori information is available, many sampling criteria are discussed and tested on two specific examples. The difference between different sampling criteria when the number of added design points is small, while more design points do improve the accuracy of the metamodel substantially.
\r\n\r\nThe metamodels can be used to induce preferences in the DVS or the PVS according to the extension principle. The Level Interval Algorithm (LIA) is a discrete approximate implementation of the extension principle. The resulting preference by the LIA is presented as an alpha-cut, which is the set of designs or performances with a certain level of preference. There are some limitations of the LIA, especially for multidimensional DVS and PVS. A new extension of the LIA is proposed to compute alpha-cuts with more accuracy and less limitations. The designers have more control over the trade-off between the cost and accuracy of the computation with the new extension of the LIA.
\r\n\r\nThe results of the Method of Imprecision should be the set of alternative designs in the DVS at a certain preference level, and the set of achievable performances in the PVS. The information about preferences in the DVS and the PVS is needed to transfer back and forth. Usually the mapping from the PVS to the DVS is unavailable, while it is needed to induce preference in the DVS from the PVS. A new method is constructed to compute the alpha-cuts in both spaces from preferences specified in the DVS and the PVS.
\r\n\r\nFinally, a new measure is proposed to find the most cost-effective sampling region of new design points for a metamodel. Also, the full implementation of the Method of Imprecision is listed in detail. Then it is applied to an example of the structure design of a passenger vehicle, and comparisons are made between the new results and previous results.
" }, { "name": "Wood, Zo\u00eb Justine", "degree": "PhD", "year": "2003", "title": "Computational Topology Algorithms for Discrete 2-Manifolds", "advisor": "Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-161403", "creators": [ { "name": { "family": "Wood", "given": "Zo\u00eb Justine" }, "id": "Wood-Zo\u00eb-Justine", "display_name": "Wood, Zo\u00eb Justine" } ], "advisors": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "chair", "display_name": "Schroeder, Peter" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Hoppe", "given": "Hugues" }, "id": "Hoppe-H", "role": "member", "display_name": "Hoppe, Hugues" }, { "name": { "family": "Desbrun", "given": "Mathieu" }, "id": "Desbrun-M", "orcid": "0000-0003-3424-6079", "role": "member", "display_name": "Desbrun, Mathieu" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "compsci" ], "doi": "10.7907/BQT9-SS34", "abstract": "This thesis presents computational topology algorithms for discrete 2-manifolds. Although it is straightforward to compute the genus of a discrete 2-manifold, this topological invariant does not tell us enough for most computer graphics applications where we would like to know: what does the topology look like? Genus is a scalar value with no associated geometric appearance. We can, however, isolate geometric regions of the surface that are topologically interesting. The simplest topologically interesting, and perhaps most intuitive, regions to consider are those with genus equal to one. By isolating and examining such regions we can compute measures to better describe the appearance of relevant surface topology. Thus, this work focuses on isolating handles, regions with genus equal to one, in discrete 2-manifolds.
\r\n\r\nIn this thesis, we present novel algorithms guaranteed to identify and isolate handles for various discrete surface representations. Additionally, we present robust techniques to measure the geometric extent of handles by identifying two locally minimal-length non-separating cycles for each handle. We also present algorithms to retain or simplify the topology of a reconstructed surface as desired. Finally, the value of these algorithms is demonstrated through specific applications to computer graphics. For example, we demonstrate how geometric models can be greatly improved through topology simplification both for models represented by volume data or by triangle meshes.
\r\n\r\nThe contributions of this work include:\r\n
High-frequency/high-speed integrated circuits become increasingly important because of the strong demand for higher data rate and lower power consumption, and they rely more on silicon-based technologies, which has the advantages of low cost, fast technological development and system-on-a-chip (SoC) capabilities. However, silicon technologies also present great challenges in high-frequency/high-speed integrated circuits. This work demonstrated that distributed circuit and injection locking are two enabling circuit techniques that can help overcome silicon limitations.
\r\n\r\nDistributed voltage-controlled oscillators (DVCO's) demonstrated the high-frequency capabilities of distributed circuits. The operation of distributed oscillators is analyzed and the general oscillation condition is derived, resulting in analytical expressions for the oscillation frequency and amplitude. Two tuning techniques are developed, namely, the inherent-varactor tuning and delay-balanced current-steering tuning. A complete analysis of the tuning techniques is also presented. CMOS and bipolar DVCO prototypes have been designed and fabricated in a commercial 0.35\u00b5m BiCMOS process. A 10-GHz CMOS DVCO achieves a tuning range of 12\\% and a phase noise of -103 dBc/Hz at 600 kHz frequency offset. A 12-GHz bipolar DVCO achieves a tuning range of 26% and a phase noise of -99 dBc/Hz at 600 kHz frequency offset. New DVCO architectures are also proposed to improve the performance.
\r\n\r\nThe distributed circuit technique is also used for equalization in high-speed fiber-optic systems, in which inter-symbol interference (ISI) caused by fibre dispersion imposes a major limitation. Compared to optical-domain methods and other electrical-domain methods, equalization with distributed transversal filters (DTF's) presents the most cost-effective and SoC-compatible solution. Prototype DTF's have been implemented in a commercial 0.18\u00b5m SiGe BiCMOS process for 10 Gpbs fiber-optic systems. A 7-tap DTF reduces the ISI of a 10 Gbps signal after 800m 50\u00b5m multi-mode fiber from 5 dB to 1.38 dB, and improves the BER from 10\u207b\u2075 to 10\u207b\u00b9\u00b2.
\r\n\r\nThe injection locking technique is applied in high-speed, low-power frequency dividers, namely, injection-locked frequency dividers (ILFD's). Based on the detailed analysis, shunt-peaking and oscillation-suppression techniques are developed to enhance the locking range. Prototypes are implemented in a commercial 0.35\u00b5m BiCMOS process using only CMOS transistors. A 19 GHz ILFD achieves a locking range of 1350 MHz with the power consumption of 1 mW. A 9 GHz ILFD achieves a locking range of 1490 MHz with the power consumption of 1.3 mW. Self-dividing oscillators are proposed to generate accurate low-phase-noise quadrature signals.
" }, { "name": "Yang, Yunping", "degree": "PhD", "year": "2003", "title": "Holographic Recording and Dynamic Range Improvement in Lithium Niobate Crystals", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252003-104132", "creators": [ { "name": { "family": "Yang", "given": "Yunping" }, "id": "Yang-Yunping", "display_name": "Yang, Yunping" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Adibi", "given": "Ali" }, "id": "Adibi-A", "role": "member", "display_name": "Adibi, Ali" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Chao", "given": "Tien-hsin" }, "id": "Chao-Tien-hsin", "role": "member", "display_name": "Chao, Tien-hsin" } ], "option_major": [ "eleceng" ], "doi": "10.7907/V631-NJ22", "abstract": "This thesis presents the results of research centered on the topic of improvement of dynamic range and sensitivity in volume holographic recording using photorefractive lithium niobate crystals. In general, there are two approaches to improving the dynamic range. One is at system level, the other approach is at material level. The second chapter compares the system performances of two holographic recording geometries (the 90-degree and transmission geometries) using iron-doped lithium niobate. The comparison is based on dynamic range, sensitivity, scattering noise, inter-pixel noise, and storage capacity. The third chapter investigates dark decay mechanisms in lithium niobate crystals. Two mechanisms of the dark decay, proton compensation and electron tunneling with activation energies of 1.0 eV and 0.28 eV, respectively, are identified. In crystals with low doping levels, proton compensation dominates the dark decay and extrapolation of lifetimes by an Arrhenius law to room temperature is valid. The time constant of this type of dark decay is inversely proportional to the proton concentration. For crystals with high doping levels, electron tunneling dominates the dark decay. This type of dark decay also limits the highest practical doping level in LiNbO3 crystals. For crystals with medium doping levels, both proton compensation and electron tunneling contribute significantly to the dark decay, and the single Arrhenius law does not hold with a single activation energy. In the fourth chapter, holographic data storage experiments are performed using manganese-doped lithium niobate crystals. The idea to use manganese-doped lithium niobate crystals for holographic storage is the direct result of the understanding of dark decay mechanisms discussed in Chapter 3. The experimental results of dark decay, M/#, sensitivity, multiplexing, thermal fixing, and holographic scattering for LiNbO3 : 0.2 atomic% Mn and LiNbO3 : 0.5 wt% MnCO3 are presented. The experimental results show that manganese-doped lithium niobate crystals are well suited for holographic storage. In the final chapter attention is focused on photorefractive properties of manganese-doped lithium niobate crystals. Material parameters, such as the distribution coefficient, are determined. Absorption measurements are used to obtain some information about several charge transport parameters. The dynamic range (M/#) and sensitivity for crystals of different doping levels, different oxidation states, and for different light polarizations have been measured.\r\n" }, { "name": "Zhao, Qian", "degree": "PhD", "year": "2003", "title": "Network Source Coding: Theory and Code Design for Broadcast and Multiple Access Networks", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechETD:etd-05302003-125004", "creators": [ { "name": { "family": "Zhao", "given": "Qian" }, "id": "Zhao-Qian", "display_name": "Zhao, Qian" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/61XN-MV62", "abstract": "In the information age, network systems and applications have been growing rapidly to provide us with more versatile and high bit rate services. However, the limited bandwidth restricts the amount of information that can be sent through the networks. Thus efficient data representation or source coding is imperative for future network development. Distinct from the traditional source coding strategy, network source codes take advantage of the network topology and are able to maximally compress data before transmission.
\r\n\r\nIn this thesis, I present a variety of source coding techniques for use in network environments and demonstrate the benefits of network source codes over traditional source codes from both theoretical and practical perspectives.
\r\n\r\nFirst, I address source coding for broadcast systems. The results I obtain include derivation of the theoretical limits of broadcast system source codes, algorithm design for optimal broadcast system vector quantizers, implementation of the optimal code, and experimental results.
\r\n\r\nThen, I focus on multiple access systems which are the dual systems of broadcast systems. I present the properties of multiple access source codes and generalize traditional entropy code design algorithms to attain the corresponding optimal multiple access source codes for arbitrary joint source statistics. I further introduce a family of polynomial complexity code design algorithms that approximates the optimal solutions. Application to universal coding for multiple access networks when the joint source statistics are unknown a priori is briefly discussed. Finally, I demonstrate algorithmic performance by showing experimental results on a variety of data sets.
\r\n\r\ninally, in seeking a simple lossy source coding method for general networks, I apply entropy constrained dithered quantization in network source code design and present the coding results for multi-resolution source codes and multiple access source codes. Multi-resolution and multiple access dithered quantizers are low complexity codes that achieve performance very close to the theoretical rate-distortion bound.
" }, { "name": "Anderson, David Deloyd", "degree": "PhD", "year": "2002", "title": "Experimental Investigation of Quasistatic and Dynamic Fracture Properties of Titanium Alloys", "advisor": "Rosakis, Ares J.; Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-02112002-153745", "creators": [ { "name": { "family": "Anderson", "given": "David Deloyd" }, "id": "Anderson-David-Deloyd", "display_name": "Anderson, David Deloyd" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "co-chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "orcid": "0000-0002-0812-7028", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/NHZS-D271", "abstract": "The goal of this work is to investigate the quasistatic and dynamic fracture properties of three titanium alloys: 6Al-4V titanium, 6Al-4V titanium ELI, and Timetal 5111. While standard tests exist for measuring quasistatic fracture toughness, the dynamic investigation requires that several measurement techniques are employed including Coherent Gradient Sensing (CGS), Crack Opening Displacement (COD), and the use of strain gages. The use of these methods with difficult engineering materials in the dynamic loading regime requires methodologies to be advanced beyond that previously required with model materials having properties ideal for experimental measurements techniques.
\r\n\r\nAfter a description of each measurement technique is given, stress intensity factor measurements made on 12.7 mm thick pre-cracked 6Al-4V titanium specimens are compared. These specimens were dynamically impacted in three point bend in a drop weight tower. Specimens with and without side-grooves were tested as each measurement technique allows. Side-grooves are useful to increase the degree of plane strain experienced in proximity of the crack tip, allowing plane strain (geometry independent) fracture toughnesses to be obtained from specimens that may be otherwise too thin in cross section. Resulting stress intensity factor-time histories from the different techniques are compared to verify that their results mutually agree.
\r\n\r\nAdvancements in employing CGS, a shearing interferometric technique, are described in more detail. First, the analysis of CGS interferograms is extended to allow experimental fringe data to be fit to very general analytical asymptotic crack tip solution to determine mixed mode stress intensity factors. As formulated in this work, the CGS technique can be used to measure stress intensity factors for non-uniformly propagating dynamic mixed mode cracks moving along arbitrary paths in homogeneous linear elastic isotropic materials. Other advancements are also detailed which improve analysis accuracy, objectivity, and efficiency.
\r\n\r\nFinally, with the equivalence of the three measurement technique results established, tests were performed on 8--17 mm thick pre-cracked three point bend specimens of the three materials to measure critical stress intensity values for crack initiation. Side-grooves are necessary for the more ductile 6Al-4V titanium ELI and Timetal 5111 materials to obtain plane strain fracture toughness values. It is found that both the 6Al-4V titanium ELI and Timetal 5111 alloys are 50-70% tougher than the 6Al-4V titanium, and for all three materials their initiation toughness does not vary significantly with loading rate over the domain tested.
" }, { "name": "Aoki, Ichiro", "degree": "PhD", "year": "2002", "title": "Distributed Active Transformer for Integrated Power Amplification", "advisor": "Janda, Kenneth C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-094928", "creators": [ { "name": { "family": "Aoki", "given": "Ichiro" }, "id": "Aoki-Ichiro", "display_name": "Aoki, Ichiro" } ], "advisors": [ { "name": { "family": "Janda", "given": "Kenneth C." }, "id": "Janda-K-C", "role": "advisor", "display_name": "Janda, Kenneth C." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Janda", "given": "Kenneth C." }, "id": "Janda-K-C", "role": "member", "display_name": "Janda, Kenneth C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/6XMD-MR86", "abstract": "A novel on-chip impedance transformation and power-combining technique, the distributed active transformer (DAT) is introduced. It overcomes the fundamental difficulties presented by silicon technology in the design of integrated rf power amplifiers. This technique efficiently combines several low-voltage push-pull amplifiers and simultaneously performs an impedance transformation to produce a larger output power while maintaining a 50\u03a9 match. It also uses virtual ac grounds and magnetic couplings extensively to eliminate the need for any off-chip component, such as tuned bonding wires or external inductors. Furthermore, it desensitizes the operation of the amplifier to the inductance of bonding wires making the design more repeatable.
\r\n\r\nIn this work, the performance of the introduced DAT structure is compared to that of conventional on-chip impedance transformation methods. Their fundamental power-efficiency limitations in the design of high-power fully-integrated amplifiers in standard silicon process technologies are analyzed and the DAT is demonstrated to be more efficient. Furthermore, different classes of power amplification operations and their use in DAT power amplifiers are studied.
\r\n\r\nTo demonstrate the feasibility of this concept several silicon integrated power amplifiers have been fabricated and measured including a 2.4-GHz, 2-W, 2-V truly fully-integrated power amplifier with 50\u03a9 on-chip input and output matching using 0.35\u00b5m CMOS transistors. It achieves a power added efficiency (PAE) of 41 % at this power level, demonstrating for the first time a truly fully-integrated watt-level GHz range CMOS power amplifier. It can also produce 450mW using a 1 V supply. A two stage DAT prototype, also at 2.4GHz using the same technology, operates with higher gain and lower supply voltage achieving 1-W output power, 30% PAE, and 14-dB gain with 1.15-V supply.
" }, { "name": "Bogdanoff, Peter David", "degree": "PhD", "year": "2002", "title": "The Phonon Entropy of Metals and Alloys: The Effects of Thermal and Chemical Disorder", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12272005-154952", "creators": [ { "name": { "family": "Bogdanoff", "given": "Peter David" }, "id": "Bogdanoff-Peter-David", "display_name": "Bogdanoff, Peter David" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "display_name": "Phillips, Robert B." } ], "option_major": [ "matsci" ], "doi": "10.7907/045G-6426", "abstract": "Vibrational entropy is important for the thermodynamics of alloying, alloy formation, phase transitions and phase stability at high temperature. Vibrational entropies of alloying and alloy formation were calculated for 32 binary alloys and intermetallic compounds using phonon DOS curves taken from the literature. The vibrational entropies of formation span a wide range from -0.64 to +0.55 kB/atom, and the vibrational entropies of alloying ranged from -0.39 to +1.0 kB/atom. This range exceeds the range of configurational entropy of a binary alloy, which reaches a maximum value of +0.69 kB/atom and a minimum value of 0 kB/atom.
\r\n\r\nThe vibrational entropy of the NiTi martensitic transition was measured using low-temperature calorimetry and inelastic neutron-scattering. The high-temperature B2 phase of NiTi has a vibrational entropy 0.5 kB/atom larger than the low-temperature martensitic phase. The difference in vibrational entropy accounts for the total entropy of the austenitic-martensitic phase transition.
\r\n\r\nInelastic neutron scattering was used to show that the phonon DOS of V is unchanged between 20 and 1000\u00b0C, inconsistent with the phonon softening expected from thermal expansion. It is found that the effects of volume expansion and rising temperature exert equal and opposite shifts on the phonon DOS. The pure temperature dependence of the phonon DOS is due to strong phonon-phonon scattering, which in turn leads to a large anharmonic vibrational entropy contribution at high temperature.
\r\n\r\nThe vibrational entropy of eight chemically disordered Cu-Au alloys was measured using inelastic neutron scattering. The analysis of the phonon entropy of a disordered alloy was performed in a novel way by modeling the partial vibrational entropies of Cu and Au. The partial vibrational entropies of Cu and Au were shown to be slowly varying and smooth functions of composition. The vibrational entropy of disordering in Cu3Au is calculated as 0.24 \u00b1 0.02 kB/atom, substantially larger than results predicted from recent theoretical work.
" }, { "name": "Chang, Dong Eui", "degree": "PhD", "year": "2002", "title": "Controlled Lagrangian and Hamiltonian Systems", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112010-161816245", "creators": [ { "name": { "family": "Chang", "given": "Dong Eui" }, "id": "Chang-Dong-Eui", "display_name": "Chang, Dong Eui" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/3DRR-ZV53", "abstract": "any control systems are mechanical systems. The unique feature of mechanical systems is the notion of energy, which gives much information on the stability of equilibria. Two kinds of forces are associated with the energy: dissipative force and gyroscopic force. A dissipative force is, by definition, a force which decreases the energy, and a gyroscopic force is, by definition, a force that does not change the energy. Gyroscopic forces add couplings to the dynamics. In this thesis, we develop a control design methodology which makes full use of these three physical notions: energy, dissipation, and coupling.
\r\n\r\nFirst, we develop the method of controlled Lagrangian systems. It is a systematic procedure for designing stabilizing controllers for mechanical systems by making use of energy, dissipative forces, and gyroscopic forces. The basic idea is as follows: Suppose that we are given a mechanical system and want to design a controller to asymptotically stabilize an equilibrium of interest. We look for a feedback control law such that the closed-loop dynamics can be also described by a new Lagrangian with a dissipative force and a gyroscopic force where the energy of the new Lagrangian has a minimum at the equilibrium. Then we check for asymptotic stability by applying the Lyapunov stability theory with the new energy as a Lyapunov function.
\r\n\r\nNext, we show that the method of controlled Lagrangian systems and its Hamiltonian counterpart, the method of controlled Hamiltonian systems, are equivalent for simple mechanical systems where the underlying Lagrangian is of the form kinetic minus potential energy. In addition, we extend both the Lagrangian and Hamiltonian sides of this theory to include systems with symmetry and discuss the relevant reduction theory.
" }, { "name": "Chasiotis, Ioannis", "degree": "PhD", "year": "2002", "title": "The Strength of Polycrystalline Silicon at the Micro- and Nano-Scales with Applications to MEMS", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142005-105805", "creators": [ { "name": { "family": "Chasiotis", "given": "Ioannis" }, "id": "Chasiotis-Ioannis", "display_name": "Chasiotis, Ioannis" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "orcid": "0000-0002-0812-7028", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JPRZ-P277", "abstract": "Three aspects concerning the reliability of MicroElectroMechanical Systems (MEMS) are discussed in this work. These aspects are: (1) the development of a new tensile testing technique for measuring the elastic modulus and rupture strengths of thin films, (2) an assessment of stress concentration and specimen size effects in failure of micron-sized specimens and (3) the consequences of Hydrofluoric Acid (HF) chemical treatment on the microstructural integrity and the tensile strength of polycrystalline silicon.
\r\n\r\nA new method for tensile testing of thin films by means of an improved apparatus has been developed to measure the elastic properties (Young's modulus, tensile strength) of surface micromachined polycrystalline silicon specimens. The newly designed tensile tester makes use of an Ultraviolet (UV) light curable adhesive to clamp micron-sized specimens. It permits for the first time the testing of thin film materials possessing high failure strength. The properties determination utilizes surface topologies of deforming specimens, acquired with an Atomic Force Microscope (AFM), for determining strain fields by means of Digital Image Correlation (DIC). This full-field, direct and local measurements technique provides the capability of testing any type of thin film materials with nanometer resolution. The gage section of the specimens tested in this study varied between 200 and 1000 \u00b5m in length, 6 and 50 \u00b5m in width, all for a nominal thickness of 2 \u00b5m.
\r\n\r\nThe dependence of fracture strength on micron and sub-micron sized geometries was studied by means of specimens containing various degrees of stress concentrations. A systematic study of small-scale size effects was thus performed by tensioning elliptically perforated specimens (minimum radius of curvature of 1 gm) so as to: (a) vary the stress concentration with constant radius of curvature, (b) increasing radius of curvature of micronotches relative to the grain size. The results demonstrate a strong influence of the size of the highly strained domain (decreasing notch radii) on the failure strength of MEMS scale specimens, while the effect of varying the stress concentration factor is rather insignificant. In addition, tests performed on unnotched tensile specimens of varying dimensions revealed a specimen size effect by which the values of strength scaled with the specimen length. The Young's modulus, however, is found to be rather insensitive to the specimen dimensions at the scale of microns.
\r\n\r\nIn an effort to assess the unexplained and puzzling large variation in properties reported for very small polysilicon specimens a study was conducted to search for a cause. Contrary to the common belief that 49% HF wet release represents a safe post-process for manufacturing polycrystalline silicon, this study has clearly identified the release process as a key item in determining thin film failure properties. It is found that surface roughness as characterized by groove formation at the grain boundaries depends distinctly on the HF release time. In addition, while the actual failure mechanism in polysilicon follows a transgranular fracture, moderate exposure in HF results in partial intergranular fracture at the film surface that is responsible for complete failure. Long exposures yield films of low mechanical strength that demonstrate clear intergranular failure.
" }, { "name": "Chen, Min", "degree": "PhD", "year": "2002", "title": "Mathematical Methods for Image Synthesis", "advisor": "Arvo, James R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08272010-091235772", "creators": [ { "name": { "family": "Chen", "given": "Min" }, "id": "Chen-Min-Computer-Science", "display_name": "Chen, Min" } ], "advisors": [ { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "advisor", "display_name": "Arvo, James R." } ], "committee": [ { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "chair", "display_name": "Arvo, James R." }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "compsci" ], "doi": "10.7907/WDPH-N912", "abstract": "This thesis presents the application of some advanced mathematical methods to image synthesis. The mainstream of our work is to formulate and analyze some rendering problems in terms of mathematical concepts, and develop some new mathematical machineries to pursue analytical solutions or nearly analytical approximations to them. An enhanced Taylor expansion formula is derived for the perturbation of a general ray-traced path and new theoretical results are presented for spatially-varying luminaires. On top of them, new deterministic algorithms are presented for simulating direct lighting and other scattering effects involving a wide range of non-diffuse surfaces and spatially-varying luminaires. Our work greatly extends the repertoire of non-Lambertian effects that can be handled in a deterministic fashion.
\r\n\r\nFirst, my previous work on \"Perturbation Methods for Image Synthesis\u201d is extended here in several ways: 1) I propose a coherent framework using closed-form path Jacobians and path Hessians to perturb a general ray-traced path involving both specular reflections and refractionsi and an algorithm similar to that used for interactive specular reflections is employed to simulate lens effects. 2) The original path Jacobian formula is simplified by means of matrix manipulations. 3) Path Jacobians and Hessians are extended to parametric surfaces which may not have an implicit definition. 4) Theoretical comparisons and connections are made with related work including pencil tracing and ray differentials. 5) Identify potential applications of perturbation methods of this nature in rendering and computer vision.
\r\n\r\nNext, a closed-form solution is derived for the irradiance at a point on a surface due to an arbitrary polygonal Lambertian luminaire with linearly-varying radiant exitance. The solution consists of elementary functions and a single well-behaved special function known as the Clausen integral. The expression is derived from the Taylor expansion and a recurrence formula derived for an extension of double-axis moments, and then verified by Stokes' theorem and Monte Carlo simulation. The study of linearly-varying luminaires introduces much of the machinery needed to derive closed-form solutions for the general case of luminaires with radiance distributions that vary polynomially in both position and direction.
\r\n\r\nFinally, the concept of irradiance tensors is generalized to account for inhomogeneous radiant exitance distributions from luminaires. These tensors are comprised of scalar elements that consist of constrained rational polynomials integrated over regions of the sphere, which arise frequently in simulating some rendering effects due to polynomially-varying luminaires. Several recurrence relations are derived for generalized irradiance tensors and their scalar elements, which reduce the surface integrals associated with spatially-varying luminaires to one-dimensional boundary integrals, leading to closed-form solutions in polyhedral environments. These formulas extend the range of illumination and non-Lambertian effects that can be computed deterministically, which includes illumination from polynomially-varying luminaires, reflections from and transmissions through glossy surfaces due to these emitters. Particularly, we have derived a general tensor formula for the irradiance due to a luminaire whose radiant exitance varies according to a monomial of any order, which subsumes Lambert's formula and expresses the solution for higher order monomials in terms of those for lower-order cases.
" }, { "name": "Cornu, Catherine J. G.", "degree": "PhD", "year": "2002", "title": "Photocatalysis Under Periodic Illumination", "advisor": "Readhead, Anthony C. S.; Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05082006-143046", "creators": [ { "name": { "family": "Cornu", "given": "Catherine J. G." }, "id": "Cornu-Catherine-J-G", "display_name": "Cornu, Catherine J. G." } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "orcid": "0000-0003-0787-1610", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "member", "display_name": "Hering, Janet G." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." } ], "option_major": [ "envreng" ], "doi": "10.7907/ZDAH-V967", "abstract": "In the first part of this work, the use of periodic illumination is investigated as a means to improve the quantum yield of aqueous phase photocatalysis. We find that quantum yield enhancements are obtained under periodic illumination compared to those under continuous illumination with the same maximum photon absorption rate. This result is in agreement with previous literature reports. However, no enhancements are obtained when compared to those under continuous illumination with the same average photon absorption rate. Ways in which the use of periodic illumination in remediation systems might nevertheless be more cost-effective than continuous operation are discussed. In the second part of this work, periodic illumination is applied as a tool to investigate the kinetic behavior of the intermediates involved in photocatalysis. Two transitions are observed in the quantum yield as a function of the active light period, corresponding to separate lifetimes of two intermediates. These lifetimes are found to be relatively insensitive to the physical properties of the TiO2 photocatalyst particles, the compound being photocatalytically oxidized, or the oxygen concentration. However, a strong correlation with the pH of the solution is observed. For example, one intermediate's lifetime increases exponentially with pH, while the other one's decreases exponentially. Principles from electrochemistry, namely Nernst's law and the Butler-Volmer equation, allow us to conclude that the intermediate with a decreasing lifetime with pH is a reducing species, while the other one is an oxidizing species. The intermediates' lifetimes are equal at a pH ~ 8, concurrent with a minimum in quantum yield. Below pH 8 the reducing species has a longer lifetime, indicating that interfacial electron transfer to oxygen is the slowest step under these conditions.
\r\n\r\nThe observed lifetimes are compatible with those previously measured for superoxide radicals (reducing species), and hydroxyl radicals, surface trapped holes, or surface bound hydroxyl radicals (oxidizing species).
" }, { "name": "Craciun, Bogdan", "degree": "PhD", "year": "2002", "title": "Phase Boundary Propagation in Heterogeneous Media", "advisor": "Meiron, Daniel I.; Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:10082010-142653040", "creators": [ { "name": { "family": "Craciun", "given": "Bogdan" }, "id": "Craciun-Bogdan", "display_name": "Craciun, Bogdan" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "advisor", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/JXG6-W865", "abstract": "There has been much recent progress in the study of free boundary problems motivated by phase transformations in materials science. Much of this literature considers fronts propagating in homogeneous media. However, usual materials are heterogeneous due to the presence of defects, grains and precipitates. This thesis addresses the propagation of phase boundaries in heterogeneous media.
\r\n\r\nA particular motivation is a material undergoing martensitic phase transformation. Given a martensitic material with many non-transforming inclusions, there are well established microscopic laws that give the complex evolution of a particular twin or phase boundary as it encounters the many inclusions. The issue of interest is the overall evolution of this interface and the effect of defects and impurities on this evolution. In particular, if the defects are small, it is desirable to find the effective macroscopic law that governs the overall motion, without having to follow all the microscopic details but implicitly taking them into account. Using a theory of phase transformations based on linear elasticity, we show that the normal velocity of the martensitic phase or twin boundary may be written as a sum of several terms: first a homogeneous (but non-local) term that one would obtain for the propagation of the boundary in a homogeneous medium, second a heterogeneous term describing the effects of the inclusions but completely independent of the phase or twin boundary and third an interfacial energy term proportional to the mean curvature of the boundary.
\r\n\r\nAs a guide to understanding this problem, we begin with two simplified settings which are also of independent interest. First, we consider the homogenization for the case when the normal velocity depends only on position (the heterogeneous term only). This is equivalent to the homogenization of a Hamilton-Jacobi equation. We establish several variational principles which give useful formulas to characterize the effective Hamiltonian. We illustrate the usefulness of these results through examples and we also provide a qualitative study of the effective normal velocity.
\r\n\r\nSecond, we address the case when the interfacial energy is not negligible, so we keep the heterogeneous and curvature terms. This leads to a problem of homogenization of a degenerate parabolic initial value problem. We prove a homogenization theorem and obtain a characterization for the effective normal velocity, which however proves not to be too useful a tool for actual calculations. We therefore study some interesting examples and limiting cases and provide explicit formula in these situations. We also provide some numerical examples.
\r\n\r\nWe finally address the problem in full generality in the setting of anti-plane shear. We explicitly evaluate the term induced by the presence of the inclusions and we propose a numerical method that allows us to trace the evolution of the phase boundary. We use this numerical method to evaluate the effect of the inclusions and show that their effect is quite localized. We use it to explain some experimental observations in NiTi.
" }, { "name": "Eldredge, Jeffrey D.", "degree": "PhD", "year": "2002", "title": "A Dilating Vortex Particle Method for Compressible Flow with Applications to Aeroacoustics", "advisor": "Colonius, Tim; Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282004-113953", "creators": [ { "name": { "family": "Eldredge", "given": "Jeffrey D." }, "id": "Eldredge-Jeffrey-D", "orcid": "0000-0002-2672-706X", "display_name": "Eldredge, Jeffrey D." } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "co-chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "co-chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/7EYY-0S65", "abstract": "Vortex methods have become useful tools for the computation of incompressible fluid flow. In the present work, a vortex particle method for the simulation of unsteady two-dimensional compressible flow is developed and applied to several problems. The method is the first Langrangian simulation method for the full compressible Navier-Stokes equations. By decomposing the velocity into irrotational and solenoidal parts, and using particles that are able to change volume and that carry vorticity, dilation, enthalpy, entropy, and density, the equations of motion are satisfied. A general deterministic treatment of spatial derivatives in particle methods is developed by extending the method of particle strength exchange through the construction of higher-order-accurate, non-dissipative kernels for use in approximating arbitrary differential operators. The application of this technique to wave propagation problems is thoroughly explored. A one-sided operator is developed for approximating derivatives near the periphery of particle coverage; the operator is used to enforce a non-reflecting boundary condition for the absorption of acoustic waves at this periphery. Remeshing of the particles and the smooth interpolation of their strengths are addressed, and a criterion for the frequency of remeshing is developed on the principle axes of the rate-of-strain tensor. The fast multipole method for the fast summation of the velocity field is adapted for use with compressible particles. The new vortex method is applied to co-rotating and leapfrogging vortices in compressible flow, with the acoustic field computed using a two-dimensional Kirchoff surface, and the results agree will with those of previous work or analytical prediction. The method is also applied to the baroclinic generation of vorticity, and to the steepening of waves in the one-dimensional Burgers\u2019 equation, with favorable results in both cases.
" }, { "name": "Fax, Joseph Alexander", "degree": "PhD", "year": "2002", "title": "Optimal and Cooperative Control of Vehicle Formations", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242005-105000", "creators": [ { "name": { "family": "Fax", "given": "Joseph Alexander" }, "id": "Fax-Joseph-Alexander", "display_name": "Fax, Joseph Alexander" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "cds" ], "doi": "10.7907/M4N7-AK02", "abstract": "Control of vehicle formations has emerged as a topic of significant interest to the controls community. In applications such as microsatellites and underwater vehicles, formations have the potential for greater functionality and versatility than individual vehicles. In this thesis, we investigate two topics relevant to control of vehicle formations: optimal vehicle control and cooperative control.\r\n\r\nThe framework of optimal control is often employed to generate vehicle trajectories. We use tools from geometric mechanics to specialize the two classical approaches to optimal control, namely the calculus of variations and the Hamilton-Jacobi-Bellman (HJB) equation, to the case of vehicle dynamics. We employ the formalism of the covariant derivative, useful in geometric representations of vehicle dynamics, to relate variations of position to variations of velocity. When variations are computed in this setting, the evolution of the adjoint variables is shown to be governed by the covariant derivative, thus inheriting the geometric structure of the vehicle dynamics. To simplify the HJB equation, we develop the concept of time scalability enjoyed by many vehicle systems. We employ this property to eliminate time from the HJB equation, yielding a purely spatial PDE whose solution supplies both finite-time optimal trajectories and a time-invariant stabilizing control law.\r\n\r\nCooperation among vehicles in formation depends on intervehicle communication. However, vehicle communication is often subject to disruption, especially in an adversarial setting. We apply tools from graph theory to relate the topology of the communication network to formation stability. We prove a Nyquist criterionthat uses the eigenvalues of the graph Laplacian matrix to determine the effect of the graph on formation stability. We also propose a method for decentralized information exchange between vehicles. This approach realizes a dynamical system that supplies each vehicle with a common reference to be used for cooperative motion. We prove a separation principle that states that formation stability is achieved if the information flow is stable for the given graph and if the local controller stabilizes the vehicle. The information flow can be rendered highly robust to changes in the graph, thus enabling tight formation control despite limitations in intervehicle communication capability." }, { "name": "Feng, Hanying", "degree": "PhD", "year": "2002", "title": "Rate Loss of Network Source Codes", "advisor": "Effros, Michelle", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232002-173821", "creators": [ { "name": { "family": "Feng", "given": "Hanying" }, "id": "Feng-Hanying", "display_name": "Feng, Hanying" } ], "advisors": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "advisor", "display_name": "Effros, Michelle" } ], "committee": [ { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "chair", "display_name": "Effros, Michelle" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/GVDP-7248", "abstract": "In this thesis, I present bounds on the performance of a variety of network source codes. These rate loss bounds compare the rates achievable by each network code to the rate-distortion bound R(D) at the corresponding distortions. The result is a collection of optimal performance bounds that are easy to calculate. \r\n\r\nI first present new bounds for the rate loss of multi-resolution source codes (MRSCs). Considering an M-resolution code with M>=2, the rate loss at the ith resolution with distortion D_i is defined as L_i=R_i-R(D_i), where R_i is the rate achievable by the MRSC at stage i. For 2-resolution codes, there are three scenarios of particular interest: (i) when both resolutions are equally important; (ii) when the rate loss at the first resolution is 0 (L_1=0); (iii) when the rate loss at the second resolution is 0 (L_2=0). The work of Lastras and Berger gives constant upper bounds for the rate loss in scenarios (i) and (ii) and an asymptotic bound for scenario (iii). In this thesis, I show a constant bound for scenario (iii), tighten the bounds for scenario (i) and (ii), and generalize the bound for scenario (ii) to M-resolution greedy codes. \r\n\r\nI also present upper bounds for the rate losses of additive MRSCs (AMRSCs), a special MRSC. I obtain two bounds on the rate loss of AMRSCs: one primarily good for low rate coding and another which depends on the source entropy. \r\n\r\nI then generalize the rate loss definition and present upper bounds for the rate losses of multiple description source codes. I divide the distortion region into three sub-regions and bound the rate losses by small constants in two sub-regions and by the joint rate losses of a normal source with the same variance in the other sub-region. \r\n\r\nFinally, I present bounds for the rate loss of multiple access source codes (MASCs). I show that lossy MASCs can be almost as good as codes based on joint source encoding." }, { "name": "Feng, Xiaolin", "degree": "PhD", "year": "2002", "title": "Methods for the Analysis of Visual Motion", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072010-140426638", "creators": [ { "name": { "family": "Feng", "given": "Xiaolin" }, "id": "Feng-Xiaolin", "display_name": "Feng, Xiaolin" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SAVS-VJ68", "abstract": "Vision is a primary sense that allows human beings to interact with their environment and motion is one of the most important cues that vision can explore and utilize.\r\nIn this thesis, we present computational approaches to the problems of inferring three-dimensional motion information and perceiving two-dimensional human motions from a sequence of images captured by a camera.\r\nThe three-dimensional structure of world can be represented by distinguishable features, such as points. Assume all the features move under the same rigid motion in space, this motion can be recovered from the projections of the features in three views by solving a set of trilinear constraints. The trilinear constraints have been considered only as algebraic equations so that their satisfactory performance in motion estimation is not easy to understand. This thesis solves this puzzle by discovering a geometrical interpretation of trilinear constraints. It is showed that those algebraic equations correspond to depth errors appropriately weighted by a function of the relative reliability of the corresponding measurements. When the assumption is relaxed to allowing features to move under different rigid motions, this thesis proposes a three-dimensional motion based expectation-maximization algorithm combined with the modified separation matrix scheme to cluster the features undergoing the same motion into a group and estimate the motion for every group at the same time.\r\nThe problem of detecting and recognizing human motions arises from many applications in computer vision. This thesis describes an algorithm to detect human body from their motion patterns in a pair of frames which is based on learning an approximate probabilistic model of the positions and velocities of body joints. It then presents a scheme to recognize human actions in a sequence of frames assuming the human body is detected. This scheme enables us to simultaneously recognize both the action and the body poses in the observed sequence.\r\nAll our theoretical work is supported by experimental results.\r\n" }, { "name": "Fine, Philip Malcolm", "degree": "PhD", "year": "2002", "title": "The Contribution of Biomass Combustion to Ambient Fine Particle Concentrations in the United States", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112010-091412647", "creators": [ { "name": { "family": "Fine", "given": "Philip Malcolm" }, "id": "Fine-Philip-Malcolm", "display_name": "Fine, Philip Malcolm" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Simoneit", "given": "Bernd R. T." }, "id": "Simoneit-B-R-T", "role": "member", "display_name": "Simoneit, Bernd R. T." } ], "option_major": [ "envreng" ], "doi": "10.7907/B4VY-AS20", "abstract": "Biomass combustion is an important source of fine particle emissions to the atmosphere. According to USEPA emissions inventories for the year 1995, approximately 20% of total primary PM_(2.5) emissions come from biomass combustion sources. As an alternative to inventory data such as this, source apportionment with chemical mass balance receptor models can determine the contribution of different fine particle source types to a particular ambient fine particle sample. The identification of individual organic compounds in the fine particle emissions from biomass combustion and other fine particle sources provides a rich source of potential molecular tracers that can be used in apportionment calculations.\r\n\r\nA series of experiments were conducted to characterize the fine particle emissions from the following biomass combustion sources: residential wood combustion in fireplaces, non-catalytic wood stoves, and catalytic wood stoves; the prescribed burning of foliar fuels; and the open burning of agricultural waste. Results include emission factors for particle mass, organic and elemental carbon, ionic species, selected elements, and over 200 individual organic compounds as determined by GC/MS analysis. The cellulose pyrolysis product, levoglucosan, was emitted from all of the biomass combustion sources and serves as a unique tracer for biomass combustion in general. Substituted syringols were emitted primarily from hardwood combustion, and resin acids were emitted exclusively from the burning of softwoods. Fine particle emission factors are lower and elemental carbon and PAH emissions are higher from wood stoves than from fireplaces. The burning of foliar fuels produces more alkanoic acids than wood combustion due to the higher concentration of plant waxes in the foliage.\r\n\r\nThe data from the residential wood combustion source tests were used in a chemical mass balance receptor model to determine the contribution of biomass combustion to ambient fine particle concentrations throughout the United States. Ambient samples collected as part of the IMPROVE and other sampling networks were combined into seasonal composite samples and analyzed for important molecular markers of biomass combustion and other fine particle sources. The resulting national map provides seasonal and geographical information on the significance of biomass combustion as a fine particle source in the United States." }, { "name": "Foltz, Kevin E.", "degree": "PhD", "year": "2002", "title": "Periodic Broadcast Scheduling for Data Distribution", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-05132005-151145", "creators": [ { "name": { "family": "Foltz", "given": "Kevin E." }, "id": "Foltz-Kevin-E", "display_name": "Foltz, Kevin E." } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/980Q-RQ20", "abstract": "As wireless computer networks grow in size and complexity, we are faced with the problem of providing scalable, high-bandwidth service to their users. Wired networks typically use \"data pull,\" where users send requests to a server and the server responds with the desired information. In the wireless domain, \"data push\" promises to provide better performance for many applications [1]. The broadcast domain that is typical of wireless communication is very effective in distributing information to large audiences.\r\n\r\nThe idea of broadcast disks has been around since the Teletext system [3]. There is now an interest in applying these ideas to wireless computer networks. There are some interesting research questions about scheduling for data distribution. Computing optimal schedules has been shown to be difficult [18]. The optimal schedules themselves, however, seem to be less complex, and often periodic [4]. Xu [24] looks at the scheduling of streaming data, which involves splitting the data into smaller pieces. The idea of error correction is also important for wireless transmission due to the noisy nature of the channel [6].\r\n\r\nWe look at scheduling data for broadcast. We compare time-division scheduling and frequency-division scheduling for data items of equal length. We show that time-division is better for sending dynamic data. We then find optimal time-division schedules for two items. We show how the freedom to split items into smaller pieces can give improvements in performance. With a single split, where each of two items is split in half, we find the optimal schedules for items of equal length.\r\n\r\nWe continue with the idea of splitting items, and show what happens when the number of splits is very large. Then, we examine what happens when we add streaming data to our broadcast. We compare time-division and frequency-division as before, and now also look at a mix of the two. We prove bounds on where the mix is the best broadcast method." }, { "name": "Ginis, Roman", "degree": "PhD", "year": "2002", "title": "Automating Resource Management for Distributed Business Processes", "advisor": "Chandy, K. Mani; Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012005-093745", "creators": [ { "name": { "family": "Ginis", "given": "Roman" }, "id": "Ginis-Roman", "display_name": "Ginis, Roman" } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "co-advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Schulman", "given": "Leonard J." }, "id": "Schulman-L-J", "orcid": "0000-0001-9901-2797", "role": "member", "display_name": "Schulman, Leonard J." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." } ], "option_major": [ "compsci" ], "doi": "10.7907/9GXT-BD03", "abstract": "A distributed business process is a set of related activities performed by independent resources offering services for lease. For instance, constructing an office building involves hundreds of activities such as excavating, plumbing and carpentry performed by machines and subcontractors, whose activities are related in time, space, cost and other dimensions. In the last decade Internet-based middleware has linked consumers with resources and services enabling the consumers to more efficiently locate, select and reserve the resources for use in business processes. This recent capability creates an opportunity for a new automation of resource management that can assign the optimal resources to the activities of a business process to maximize its utility to the consumer and yield substantial gains in operational efficiency.\r\n\r\nThis thesis explores two basic problems towards automating the management of distributed business processes: 1. How to choose the best resources for the activities of a process (the Activity Resource Assignment - ARA - optimization problem); and 2. How to reserve the resources chosen for a process as an atomic operation when time has value, i.e., commit all resources or no resources (the Distributed Service Commit problem - DSC). I believe these will become the typical optimization and agreement problems between consumers and producers in a networked service economy.\r\n\r\nI propose a solution to the ARA optimization problem by modeling it as a special type of Integer Programming and I give a method for solving it efficiently for a large class of practical cases. Given a problem instance the method extracts the structure of the problem and using a new concept of variable independence recursively simplifies it while retaining at least one optimal solution. The reduction operation is guided by a novel procedure that makes use of the recent advances in tree-decomposition of graphs from the graph complexity theory.\r\n\r\nThe solution to the DSC problem is an algorithm based on financial instruments and the two-phase commit protocol adapted for services. The method achieves an economically sensible atomic reservation agreement between multiple distributed resources and consumers in a free market environment.\r\n\r\nI expect the automation of resource management addressed in my thesis and elsewhere will pave the way for more efficient business operations in the networked economy." }, { "name": "Gonz\u00e1lez Li\u00f1ero, Luis", "degree": "PhD", "year": "2002", "title": "Global Fracture Analysis of Laminated Composite Materials for Aerospace Structures", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032011-085654224", "creators": [ { "name": { "family": "Gonz\u00e1lez Li\u00f1ero", "given": "Luis" }, "id": "Gonz\u00e1lez-Li\u00f1ero-Luis", "display_name": "Gonz\u00e1lez Li\u00f1ero, Luis" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FCJ8-EW63", "abstract": "The failure process of laminated composite materials originating from precut sharp cracks, as well as their propagation, is studied from a \"global\" perspective,\r\nappropriate for structural analysis. The size effect in the damage development is explored and the question of \"scaling\" of the results is addressed.\r\n\r\nTwo globally orthotropic sets of panels with the notches aligned along the axes of orthrotopy are studied. The internally evolving damage in the crack tip region is\r\nexamined through enhanced x-ray radiographic inspection and surface strain fields are measured by means of the Digital Image Correlation method (the applicability and limitations of which are analyzed and discussed). The results obtained from these two experimental techniques are joined to assess the feasibility of identifying internal damage solely from surface measurements.\r\n\r\nThe shape of the region of influence of the crack is described and its extension measured. A simplified model for damage progression analysis is proposed.\r\n\r\nThe process of initiation of the damage propagation is described in detail and the different responses for the two different layups are discussed. The maximum stress/strain and the Tsai-Hill failure criteria are compared with the experimental results on the laminates, and their reliability and limitations are addressed.\r\n\r\nThe effective properties of the two sets of laminates are measured at three different loading rates and compared to theory, and the relevance of the time dependence of the material is studied.\r\n" }, { "name": "Halverson, Nils William", "degree": "PhD", "year": "2002", "title": "A Measurement of the Cosmic Microwave Background Angular Power Spectrum with DASI", "advisor": "Carlstrom, John E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05022011-085219561", "creators": [ { "name": { "family": "Halverson", "given": "Nils William" }, "id": "Halverson-Nils-William", "display_name": "Halverson, Nils William" } ], "advisors": [ { "name": { "family": "Carlstrom", "given": "John E." }, "id": "Carlstrom-J-E", "role": "advisor", "display_name": "Carlstrom, John E." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Carlstrom", "given": "John E." }, "id": "Carlstrom-J-E", "role": "member", "display_name": "Carlstrom, John E." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Lange", "given": "Andrew E." }, "id": "Lange-A-E", "role": "member", "display_name": "Lange, Andrew E." }, { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "member", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/BEJN-HQ49", "abstract": "The Cosmic Microwave Background (CMB) has long been recognized as an astounding source of information about the early Universe. In this thesis we describe the design,\r\nimplementation, and first-year results of the Degree Angular Scale Interferometer (DASI), a compact interferometer designed to measure the angular power spectrum of the CMB. We discuss details of the optics, receivers, and power spectrum analysis, including the use of constraint matrices to project out contaminants and test for correlations with diffuse foreground templates.\r\n\r\nWe present a measurement of the CMB angular power spectrum in the multipole range l \u2248 100- 900 in nine bands. The measured fluctuations have a temperature spectral index of \u03b2 = -0.1 \u00b1 0.2 (1\u03c3) consistent with CMB. We find no evidence of foregrounds other than point sources in the data. We detect a first peak in the power spectrum at l ~ 200, a second peak in the power spectrum at l ~ 550, and a rise in the power spectrum at l ~ 800 which is indicative of a third, consistent with inflationary theories. \r\n\r\nUsing the DASI measurement along with COBE DMR data, and adopting conservative priors on the Hubble parameter h > 0.45 and an optical depth due to reionization 0.0 \u2264 \u03c4_c \u2264 0.4, we constrain the total density of the Universe \u03a9_(tot) = 1.04 \u00b1 0.06, the spectral index of the primordial density fluctuations n_s = 1.01^(+0.08)_(-0.06), and the physical baryon density \u03a9_bh^2 = 0.022^(+0.004)_(-0.003) among others (all 68% confidence limits). These constraints are consistent with inflation and estimates of \u03a9_bh^2 from Big Bang Nucleosynthesis. With prior h = 0.72 \u00b1 0.08, we constrain the matter density \u03a9_m = 0.40 \u00b1 0.15, and the vacuum energy density \u03a9_\u039b = 0.60 \u00b1 0.15, indicating from CMB data the presence of dark matter and dark energy in the Universe." }, { "name": "Ham, Donhee", "degree": "PhD", "year": "2002", "title": "Statistical Electronics: Noise Processes in Integrated Communication Systems", "advisor": "Hajimiri, Ali", "url": "https://resolver.caltech.edu/CaltechETD:etd-03162005-141416", "creators": [ { "name": { "family": "Ham", "given": "Donhee" }, "id": "Ham-Donhee", "display_name": "Ham, Donhee" } ], "advisors": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "advisor", "display_name": "Hajimiri, Ali" } ], "committee": [ { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "chair", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/tgja-7y11", "abstract": "This thesis presents a comprehensive investigation of noise and thermodynamics in electronic circuits and systems. This study of \"statistical electronics\" spans two disciplines, statistical thermodynamics and electronic circuit engineering, and leads to a general picture that bridges electronics and statistical thermodynamics.
\r\n\r\nOur work on statistical electronics has both scientific and engineering implications. Scientifically, this work is an extensive study of statistical thermodynamics in the context of electrical circuits, which has made several significant contributions to the understanding of noise processes in electrical circuits. The technological importance is a demonstration of how the fundamental physical considerations evolve to practical high-performance novel circuit design. The power of our fundamental approach is demonstrated through several practical circuit examples.
\r\n\r\nFirst, our investigation of fluctuations in nonlinear electrical circuits provides deep insight into the nonlinear fluctuation phenomena. Especially, the study of fluctuations in nonlinear active devices constitutes an important sector in this investigation; verifying the physical soundness of the contemporary active device noise modeling and leading to clear understanding of fluctuation-dissipation relations in nonlinear devices.
\r\n\r\nSecond, we apply statistical electronics to noise problems involved in frequency conversion, an essential function in modern RF and microwave receivers. This study leads to two novel observations of noise figure degradation due to cyclostationary noise and conversion gain enhancement, both dependent on the size of energy storing elements. This novel behavior is experimentally verified with a direct measurement of integrated switching mixers. The results provide new insight into cyclostationary noise processes in frequency conversion and optimum deisgn for switching mixers.
\r\n\r\nThird, application of statistical electronics to noise in frequency generation by self-sustained oscillators leads to a new theory of oscillator noise. This study demonstrates the direct correspondence between the phase noise and the Einstein relation; revealing the underlying physics of oscillator noise. Our approach clarifies the fluctuation-dissipation relation in oscillator noise generation, establishing a link between currently available fluctuation-based and dissipation-based phase noise. models and leading to a clear definition of loaded quality factor of ail oscillator. The novel concepts of virtual damping and linewidth compression put resonators and oscillators in a unified framework, providing immediate design optimization insight. The power of this theoretical development is demonstrated through experimental measurements of various integrated oscillators.
\r\n\r\nOur work on statistical electronics combining circuit engineering and physical science has also resulted in other useful engineering methods, such as graphical optimization, noise simulations for computer-aided design (CAD), and time-varying filter theory.
" }, { "name": "Hayes, Adam Thomas", "degree": "PhD", "year": "2002", "title": "Self-Organized Robotic System Design and Autonomous Odor Localization", "advisor": "Murray, Richard M.; Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06112002-132034", "creators": [ { "name": { "family": "Hayes", "given": "Adam Thomas" }, "id": "Hayes-Adam-Thomas", "display_name": "Hayes, Adam Thomas" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "co-advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." } ], "option_major": [ "cns" ], "doi": "10.7907/KH16-XH33", "abstract": "This thesis presents a methodology for designing self-organized autonomous robotic systems and demonstrates how this process can be applied to the problem of finding the source of an airborne odor plume. The design methodology is applicable to other task domains and the resulting odor localization system extends the state of the art.\r\n\r\nThe design procedure centers on the ability to define a specific task performance metric, systematically evaluate performance in a realistic environment, and define abstract relationships between system parameters and system performance. Once such relationships have been experimentally validated in a test environment, they can be used to guide the design of a deployable system. Because this process relies heavily on evaluative feedback, this work emphasizes the development of tools that allow the collection of accurate performance data. It presents a reliable multiple robot test-bed and some task-enabling sensory hardware, as well as validation of the sensory and kinematic models used in simulation. Also, a reinforcement learning methodology is described that provides consistent optimization performance while minimizing the amount of required evaluation.\r\n\r\nThe design methodology is applied to the task of odor localization. Specifically, this thesis analyzes a basic collective search task and derives the optimal group size and expected performance bounds for random and coordinated search. It also investigates a set of biologically inspired behaviors that permit an agent to traverse an odor plume to its source and describes the common characteristics of successful algorithms. One of these algorithms is implemented on the real test-bed and in simulation to verify that plume traversal is taking place and that the use of multiple collaborating robots can expand the reachable performance space. Collective search and plume traversal are then combined (along with egocentric source declaration) into the full odor localization task which is optimized in simulation. Then, following the design methodology, a model is presented which can aid in the prediction of performance and choice of algorithm parameters in more complex environments. Finally, a flocking behavior is designed, and the addition of this flocking behavior to the plume tracing algorithm is shown to produce a more capable system" }, { "name": "Kee, Scott David", "degree": "PhD", "year": "2002", "title": "The Class E/F Family of Harmonic-Tuned Switching Power Amplifiers", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04262005-152703", "creators": [ { "name": { "family": "Kee", "given": "Scott David" }, "id": "Kee-Scott-David", "display_name": "Kee, Scott David" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "orcid": "0000-0002-9353-6204", "role": "member", "display_name": "Weinreb, Sander" }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/MD86-FX51", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA new family of harmonic-tuned switching amplifiers is introduced having the beneficial features of the class-E tuning while allowing improved performance to be achieved through additional harmonic tuning. This E/F family may be tuned to achieve the ZVS/ZdVS switching features characteristic of the class-E amplifier and, like the class-E tuning, accounts and compensates for the effect of the switch parallel capacitance. By tuning one or more overtones to the [...] tuning, however, the switching waveforms may be improved, lowering the peak voltage and reducing the RMS current. Additionally, the tolerance to large switch parallel capacitance is generally improved so that a larger switching device may be used, allowing reduction of the on-resistance. Due to these factors, the efficiency of E/F amplifiers is expected to exceed that of class E.\r\n\r\nTo demonstrate these advantages, methods of estimating the optimal efficiency of switching amplifiers using waveform properties are given. A general solution technique is then presented which allows the calculation of the ZVS tuning requirements and the resulting switching waveforms for an arbitrary harmonic tuning. Using these two tools, switching waveforms and resulting efficiency estimates are calculated for E/F amplifier tunings, which are then compared to class E.\r\n\r\nFinally, potential application areas of the E/F technique are explored, and measured results of several first-generation E/F amplifiers are presented. Aside from efficiency benefits, E/F amplifiers also may achieve load-invariance, dual- and multi-band operation, high volumetric power densities, and efficient integrated circuit implementation using the Aoki distributed active transformer power combining structure.\r\n" }, { "name": "Kiniry, Joseph Roland", "degree": "PhD", "year": "2002", "title": "Kind Theory", "advisor": "Hickey, Jason J.; Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062002-164914", "creators": [ { "name": { "family": "Kiniry", "given": "Joseph Roland" }, "id": "Kiniry-Joseph Roland", "orcid": "0000-0002-3589-2454", "display_name": "Kiniry, Joseph Roland" } ], "advisors": [ { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "advisor", "display_name": "Hickey, Jason J." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "chair", "display_name": "Hickey, Jason J." }, { "name": { "family": "Lea", "given": "Doug" }, "id": "Lea-Doug", "role": "member", "display_name": "Lea, Doug" }, { "name": { "family": "Klavins", "given": "Eric" }, "id": "Klavins-E", "role": "member", "display_name": "Klavins, Eric" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/TVTD-E826", "abstract": "My contribution, described in this thesis, is a theory that is meant to assist in the construction of complex software systems. I propose a notion of structure that is independent of language, formalism, or problem domain. I call this new abstraction a kind, and its related formal system, kind theory. I define a type system that models the structural aspects of kind theory. I also define an algebra that models this type system and provides a logic in which one can specify and execute computations.
\r\n \r\nA reflective definition of kind theory is reviewed. This reflective specification depends upon a basic ontology for mathematics. By specifying the theory in itself, I provide an example of how one can use kind theory to reason about reuse in general formal systems.
\r\n \r\nI provide examples of the use of kind theory in reasoning about software constructs in several domains of software engineering. I also discuss a set of software tools that I have constructed that realize or use kind theory.
\r\n \r\nA logical framework is used to specify a type theoretic and algebraic model for the theory. Using this basic theorem prover one can reason about software systems using kind theory. Also, I have constructed a reuse repository that supports online collaboration, houses software assets, helps search for components that match specifications, and more. This repository is designed to use kind theory (via the logical framework) for the representation of, and reasoning about, software assets.
\r\n \r\nFinally, I propose a set of language-independent specification constructs called semantic properties which have a semantics specified in kind theory. I show several uses of these constructs, all of which center on reasoning about reusable component-based software, by giving examples of how these constructs are applied to programming and specification languages. I discuss how the availability of these constructs and the associated theory impact the software development process.
" }, { "name": "Lee, Cin-Young", "degree": "PhD", "year": "2002", "title": "Efficient Automatic Engineering Design Synthesis Via Evolutionary Exploration", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032011-082523919", "creators": [ { "name": { "family": "Lee", "given": "Cin-Young" }, "id": "Lee-Cin-Young", "display_name": "Lee, Cin-Young" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "orcid": "0009-0009-4668-8289", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "orcid": "0009-0009-4668-8289", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Martinoli", "given": "Alcherio" }, "id": "Martinoli-A", "role": "member", "display_name": "Martinoli, Alcherio" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/5HRP-ND58", "abstract": "The evolution of designs in nature has been the inspiration for this thesis, which seeks to develop a framework for efficient automatic engineering design synthesis based on evolutionary methods.\r\n\r\nThe design synthesis process is equated to an evolutionary process. Because of this, the same formalization for evolution, the evolution algorithm, is used as a design synthesis formalism. Implementation of the evolution algorithm on a computer allows evolution of non-biological systems, and, hence, automatic engineering design synthesis. The early and canonical versions of such evolutionary computation are bare bones evolution tools that neglect several key aspects of evolutionary systems. Some universal aspects of good designs are identified, three of which are dealt with in this thesis. These are variable complexity, modularity, and speciation.\r\n\r\nFramed in an evolutionary context, each of these characteristics are requisites for being able to evolve in correspondence with a dynamic environment. Those that are most evolvable will survive. After all, if a species cannot evolve quickly enough with changes in the environment, it will perish. In a design context, this indicates that the characteristics are vital for efficiency and shorter design cycles.\r\n\r\nAn integrated framework is developed to address all three aspects individually or in any combination thereof, which has not been done heretofore. Because of the poor theoretical foundations of evolutionary computation, the effectiveness of the developed approach is determined through computer experimentation on several test and design problems. Results are promising as all three\r\naspects were successfully achieved in comparison to canonical evolutionary computation.\r\n" }, { "name": "Liao, Hong", "degree": "PhD", "year": "2002", "title": "Interactions between Tropospheric Chemistry and Aerosols in a Unified GCM Simulation", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032011-083245119", "creators": [ { "name": { "family": "Liao", "given": "Hong" }, "id": "Liao-Hong", "display_name": "Liao, Hong" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "orcid": "0000-0002-4263-2562", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/E2SZ-YX06", "abstract": "Anthropogenic changes in the atmospheric abundances of tropospheric ozone and aerosols make significant contributions to climate change. In turn, climate change\r\naffects the abundances of ozone and aerosols, resulting in complicated feedbacks. To move toward understanding interactions and feedbacks among tropospheric chemistry,\r\naerosol formation, and climate change, a unified tropospheric chemistry-aerosol model is developed within the Goddard Institute for Space Studies general circulation model. The model includes a detailed simulation of tropospheric ozone-NO_x-hydrocarbon chemistry and a thermodynamic representation of sulfate/nitrate/ammonium aerosols. Two-way coupling between aerosols and chemistry provides consistent chemical fields for aerosol dynamics and aerosol mass for heterogeneous processes and calculations of gas-phase photolysis rates. Although the current version of the unified model does not include\r\nprognostic treatments of black carbon, organic carbon, and mineral dust aerosols, we include effects of these particles on photolysis and heterogeneous processes by using three-dimensional off-line fields. The unified model is applied to examine interactions between tropospheric chemistry and aerosols. This dissertation is the first step in the development of a fully-coupled climate/chemistry/aerosol model.\r\n" }, { "name": "Liu, Zhiwen", "degree": "PhD", "year": "2002", "title": "Optical Information Storage and Processing", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:04272011-110550070", "creators": [ { "name": { "family": "Liu", "given": "Zhiwen" }, "id": "Liu-Zhiwen", "display_name": "Liu, Zhiwen" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "member", "display_name": "Quake, Stephen R." }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/EVK8-H316", "abstract": "Optical information storage and optical information processing are the two themes of this thesis. Chapter two and three discuss the issue of storage while the final two chapters investigate the topic of optical computing.\r\n\r\nIn the second chapter, we demonstrate a holographic system which is able to record phenomena in nanosecond speed. Laser induced shock wave propagation is recorded by\r\nangularly multiplexing pulsed holograms. Five frames can be recorded with frame interval of 12ns and time resolution of 5.9ns. We also demonstrate a system which can record fast\r\nevents holographically on a CCD camera. Carrier multiplexing is used to store 3 frames in a single CCD frame with frame interval of 12ns. This technique can be extended to record femtosecond events.\r\n\r\nInformation storage in subwavelength structures is discussed in the third chapter. A 2D simulation tool using the FDTD algorithm is developed and applied to calculate the far field scattering from subwavelength trenches. The simulation agrees with the experimental data very well. Width, depth and angle multiplexing is investigated to encode information in subwavelength features. An eigenfunction approach is adopted to analyze how much\r\ninformation can be stored given the length of the feature. Finally we study the effect of nonlinear buffer layer.\r\n\r\nWe switch gear to holographic correlators in the fourth chapter. We study various properties of the defocused correlator which can control the shift invariance conveniently. An approximate expression of the shift selectivity is derived. We demonstrate a real time\r\ncorrelator with 480 templates. The cross talk of the correlators is also analyzed.\r\n\r\nFinally, in the fifth chapter we apply the optical correlator to fingerprint identification and study the performance of the correlation based algorithms. The windowed correlation can improve the rotation and distortion tolerance." }, { "name": "Lu, Jun", "degree": "PhD", "year": "2002", "title": "Mechanical Behavior of a Bulk Metallic Glass and Its Composite Over a Wide Range of Strain Rates and Temperatures", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-06082005-151713", "creators": [ { "name": { "family": "Lu", "given": "Jun" }, "id": "Lu-Jun", "display_name": "Lu, Jun" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "orcid": "0000-0002-0812-7028", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "mecheng" ], "doi": "10.7907/3SZ8-Y947", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe development of bulk metallic glasses (BMG), which have exceptional mechanical properties such as high strength, high hardness and corrosion resistance, as well as good glass forming and shaping abilities, using relatively expensive materials and processing techniques, offers great opportunities to use this class of solids as structural amorphous materials (SAM). In this thesis, the mechanical behavior of a bulk metallic glass [...] (Vitreloy 1) and its composite [beta]-phase Vitreloy 1 composite, i.e., [...]) is investigated.\r\n\r\nThe stress-strain relations for Vitreloy 1 over a broad range of temperatures (from room temperature up to the crystallization temperature) and strain rates [...] were established in uniaxial compression using both quasi-static and dynamic Kolsky pressure bar loading systems. The effect of strain rate and temperature on steady state flow stress, viscosity and peak stress, as well as the effect of jump-in-strain-rate on the stress-strain behavior, were investigated. Based on the experimental results, boundaries between three main deformation modes are proposed, namely, Newtonian flow and nonlinear flow resulting in homogeneous deformation and shear-localized failure constituting inhomogeneous deformation. To characterize the constitutive behavior of the bulk metallic glass, a free volume based model as well as a fictive stress model are utilized to analyze the stress-strain behavior and a mechanism for shear band formation.\r\n\r\nA unique deformation characteristic of a bulk metallic glass is the shear localization of the material in response to external mechanical loading, which may lead to catastrophic shear failure immediately after yielding under uniaxial loading and at low temperatures. A dynamic indentation experimental setup was developed to evaluate the high-strain-rate inelastic post yield deformation behavior of Vitreloy 1 and its [beta]-phase composite. Time-resolved depth and load responses during the process of indentation on the materials were obtained. Both materials are found to be strain rate insensitive up to 2,000 [...]. Numerical simulations of the indentation experiments, using both pressure insensitive (J2 von Mises) and pressure dependent (Drucker-Prager) flow models, reveal that both materials are pressure (or normal stress) dependent. Intense multiple shear bands are observed in the indentation craters and are responsible for the observed overall inelastic deformation.\r\n\r\nTo further examine the inelastic deformation and as well as whether a pressure sensitive or normal stress is more appropriate for Vitreloy 1, multiaxial compression experiments using a confining sleeve technique were performed. In contrast to the catastrophic shear failure behavior in uniaxial compression, Vitreloy 1 exhibits large inelastic deformation of more than 10 percent under confinement, indicating the nature of ductile deformation under constrained conditions. It is found that the metallic glass follows a pressure dependent Tresca criterion, [...], and the coefficient of the pressure dependence, [beta], is 0.17. Multiple parallel shear bands are observed on the outer surfaces of the deformed specimens.\r\n\r\nMotivated by potential use of Vitreloy 1 in impact related applications, the shock compression characteristics of both Vitreloy 1 and [beta]-Vitreloy composite were studied using planar impact loading. A surprisingly low amplitude elastic precursor bulk wave, corresponding to the elastic response of the 'frozen structure' of the intact metallic glasses, was observed to precede the rate-dependent large deformation shock wave. A concave downward curvature after the initial increase of the [...] shock Hugoniots suggests that a phase-change-like transition occurred during shock compression. In addition, compression damage occurred due to the shear localization. The spalling inside Vitreloy 1 was induced by shear localization, while in [beta]-Vitreloy 1, it was due to debonding of the [beta]-phase boundary from the matrix. The spall strengths at strain rate of [...] were 2.35 GPa and 2.11 GPa for Vitreloy I and [beta]-Vitreloy 1, respectively." }, { "name": "Mumbr\u00fa, Jos\u00e9", "degree": "PhD", "year": "2002", "title": "Optoelectronic Circuits Using Holographic Elements", "advisor": "Psaltis, Demetri; Bossaerts, Peter L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05042011-091003477", "creators": [ { "name": { "family": "Mumbr\u00fa", "given": "Jos\u00e9" }, "id": "Mumbr\u00fa-Jos\u00e9", "display_name": "Mumbr\u00fa, Jos\u00e9" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bossaerts", "given": "Peter L." }, "id": "Bossaerts-P-L", "role": "co-advisor", "display_name": "Bossaerts, Peter L." } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "co-chair", "display_name": "Bridges, William B." }, { "name": { "family": "Mok", "given": "Fai H." }, "id": "Mok-Fai-H", "role": "member", "display_name": "Mok, Fai H." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "eleceng" ], "doi": "10.7907/GM6Y-TE35", "abstract": "This thesis presents the results of research in the use of holographic modules in optoelectronic systems, their applications, and the characterization of polymer materials on which to record volume holograms, for these modules. The first chapter makes the case that a direct interface between an optical memory and a chip integrating detectors and logic circuitry can better utilize the high parallelism inherent in holographic modules.\r\n\r\nThe second chapter introduces the idea of reconfigurable computing and Field Programmable Gate Arrays (FPGAs) as the framework in which to design a hybrid system, the\r\nOptically Programmable Gate Array (OPGA), that outperforms its electronic counterpart by reducing its reconfiguration time by three orders of magnitude. \r\n\r\nThe OPGA is the combination of three elements: an addressing device to selectively recall holographic data pages, an optical memory, and an optoelectronic chip. The third chapter investigates the issues related to each one of these elements and their integration in a compact module. Operation of the system is demonstrated by holographically programming the OPGA chip.\r\n\r\nIn the fourth chapter, experiments are performed to characterize the Aprilis ULSH500-7A photopolymer and study quantitatively its ability to store high-bandwidth\r\nholographic data pages. A method for hologram mastering and copying using Aprilis films is also demonstrated.\r\n\r\nChapter five investigates the recording and diffusional-amplification dynamics of the PQ-doped PMMA polymer. Different strategies to optimize the material by reducing\r\nthe duration of its post-exposure are examined, and the corresponding experimental results presented. The recording of strong gratings in samples of PQ-PMMA is tested to determine the suitability of this material for components in optical fiber networks.\r\n\r\nThe final chapter deals with applications and systems that can benefit from a direct interface with a holographic module. The use of optically programmable processors in the\r\nfield of neural prosthetics is explored. The design of a holographic 4-D microscope is presented and tested experimentally.\r\n" }, { "name": "Murphey, Todd David", "degree": "PhD", "year": "2002", "title": "Control of Multiple Model Systems", "advisor": "Burdick, Joel Wakeman; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07312002-091923", "creators": [ { "name": { "family": "Murphey", "given": "Todd David" }, "id": "Murphey-Todd-David", "display_name": "Murphey, Todd David" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "co-advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/17Q7-Y019", "abstract": "This thesis considers the control of multiple model systems. These are systems for which only one model out of some finite set of models gives the system dynamics at any given time. In particular, the model that gives the system dynamics can change over time. This thesis covers some of the theoretical aspects of these systems, including controllability and stabilizability. As an application, ``overconstrained' mechanical systems are modeled as multiple model systems. Examples of such systems include distributed manipulation problems such as microelectromechanical systems and many wheeled vehicles such as the Sojourner vehicle of the Mars Pathfinder mission. Such systems are typified by having more Pfaffian constraints than degrees of freedom. Conventional classical motion planning and control theories do not directly apply to overconstrained systems. Control issues for two examples are specifically addressed. The first example is distributed manipulation. Distributed manipulation systems control an object's motion through contact with a high number of actuators. Stability results are shown for such systems and control schemes based on these results are implemented on a distributed manipulation test-bed. The second example is that of overconstrained vehicles, of which the Mars rover is an example. The nonlinear controllability test for multiple model systems is used to answer whether a kinematic model of the rover is or is not controllable." }, { "name": "Nguyen, Olivier Thanh", "degree": "PhD", "year": "2002", "title": "Cohesive Models of Fatigue Crack Growth and Stress-Corrosion Cracking", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032004-161201", "creators": [ { "name": { "family": "Nguyen", "given": "Olivier Thanh" }, "id": "Nguyen-Olivier-Thanh", "display_name": "Nguyen, Olivier Thanh" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Pandolfi", "given": "Anna" }, "id": "Pandolfi-A", "role": "member", "display_name": "Pandolfi, Anna" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C3KP-4M44", "abstract": "The aim of this dissertation was to develop models of fatigue crack growth and stress-corrosion cracking by investigating cohesive theories of fracture. These models were integrated in a finite-element framework embedding a contact algorithm and techniques of remeshing and adaptive meshing.\r\n\r\nFor the fatigue model, we developed a phenomenological cohesive law which exhibits unloading-reloading hysteresis. This model qualitatively predicts fatigue crack growth rates in metals under constant amplitude regime for short and long cracks, as well as growth retardation due to overload. Quantitative predictions were obtained in the case of long cracks.\r\n\r\nWe developed a chemistry-dependent cohesive law which serves as a basis for the stress-corrosion cracking model. In order to determine this cohesive law, two approaches, based on energy relaxation and the renormalization group, were used for coarse-graining interplanar potentials. We analyzed the cohesive behavior of a large--but finite--number of interatomic planes and found that the macroscopic cohesive law adopts a universal asymptotic form. The resulting stress-corrosion crack growth rates agreed well with those observed experimentally in 'static' fatigue tests given in the literature.\r\n" }, { "name": "Nicholson, Alexander Marshall", "degree": "PhD", "year": "2002", "title": "Generalization Error Estimates and Training Data Valuation", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062005-083717", "creators": [ { "name": { "family": "Nicholson", "given": "Alexander Marshall" }, "id": "Nicholson-Alexander-Marshall", "display_name": "Nicholson, Alexander Marshall" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Magdon-Ismail", "given": "Malik" }, "id": "Magdon-Ismail", "role": "member", "display_name": "Magdon-Ismail, Malik" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "compsci" ], "doi": "10.7907/1H16-VX81", "abstract": "This thesis addresses several problems related to generalization in machine learning systems. We introduce a theoretical framework for studying learning and generalization. Within this framework, a closed form is derived for the expected generalization error that estimates the out-of-sample performance in terms of the in-sample performance. We consider the problem of overfitting and show that, using a simple exhaustive learning algorithm, overfitting does not occur. These results do not assume a particular form of the target function, input distribution or learning model, and hold even with noisy data sets. We apply our analysis to practical learning systems, illustrate how it may be used to estimate out-of-sample errors in practice, and demonstrate that the resulting estimates improve upon errors estimated with a validation set for real world problems.\r\n\r\nBased on this study of generalization, we develop a technique for quantitative valuation of training data. We demonstrate that this valuation may be used to select training sets that improve generalization performance. With a reasonable prior over target functions, it further allows us to estimate the level of noise in a data set and provides for detection and correction of noise in individual examples. Finally, this data valuation can be used to classify new examples, yielding a new learning algorithm that is shown to be relatively robust to noise.\r\n" }, { "name": "Noelte, Jeff Lee", "degree": "PhD", "year": "2002", "title": "Effects of Surface Chemistry on Deposition Kinetics of Colloidal Hematite (\u03b1-Fe2O3) in Packed Beds of Silica Sand", "advisor": "Hoffmann, Michael R.; Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03072011-155440857", "creators": [ { "name": { "family": "Noelte", "given": "Jeff Lee" }, "id": "Noelte-Jeff-Lee", "display_name": "Noelte, Jeff Lee" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Davis", "given": "Mark E." }, "id": "Davis-M-E", "orcid": "0000-0001-8294-1477", "role": "member", "display_name": "Davis, Mark E." }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "orcid": "0000-0003-0787-1610", "role": "member", "display_name": "Blake, Geoffrey A." } ], "option_major": [ "envreng" ], "doi": "10.7907/KSZB-2238", "abstract": "The removal of colloidal (sub-micrometer) particles from flowing suspensions by deposition on surfaces is important in many natural and industrial processes (e.g., the fate\r\nof colloids and associated pollutants in groundwater systems and water treatment involving separation processes). In deposition, colloidal particles are transported to the vicinity of the collector surface by advection and diffusion. Colloidal interactions at\r\nshort distances determine whether a particle will attach to a collector. Deposition rates are reduced by the presence of repuls4e colloidal interactions. Van der Waals attraction\r\nand electric double layer repulsion are combined in DLVO theory to describe the total interaction energy between two surfaces. The total interaction energy depends on the\r\nsolution chemistry and the electric charge and potential of the interacting surfaces. To understand the attachment step of particle deposition, an understanding of the role of\r\nsimple chemical changes in the water altering the electrostatic interaction is critical.\r\n\r\nDeposition experiments using hematite particles and a silica sand were conducted to investigate the influence of specific adsorption to hematite on deposition kinetics. A\r\nvariety of electrolytes, both inorganic and organic, were studied (e.g., phosphate, small organic acids, and polymeric organic compounds including fulvic and humic acid). Electrokinetic measurements were carried out, under chemical conditions similar to those in the deposition experiments, to provide information about the sign and magnitude of the surface charge on hematite particles.\r\n\r\nExperimental results show that the deposition rate is influenced primarily by electrostatic interactions, which are determined by the adsorption of potential\r\ndetennining ions. In the absence of specifically adsorbed species, hematite deposition is transport limited (favorable deposition) at pH 6.5 and 1 millimolar NaCl. The addition of 100 micromolar total phosphate results in unfavorable deposition in which the deposition\r\nrate is reduced by approximately two orders of magnitude. Polymeric organic compounds produce unfavorable deposition at total concentrations around 10^(-5) g/L. It was observed that electrokinetic measurements in the presence of polymeric organic compounds are influenced by the particle concentration when hematite mobility is measured as a function of the total solute concentration. Experimental results indicated that adjusting the total polyelectrolyte concentration by the same factor relating the particle concentrations in the mobility measurements and deposition experiments resulted in matching the hematite surface properties in the mobility measurements to the\r\ndeposition experiments.\r\n\r\nThe experimental collision efficiency for hematite deposition was consistent with deposition under conditions of surface heterogeneity (i.e., the collision efficiency\r\ndecreased gradually as electrostatic repulsion increased). The natural silica sand used (Ottawa 30) has a high degree of surface roughness and is expected to be chemically\r\nheterogeneous.\r\n" }, { "name": "Pesavento, Alberto", "degree": "PhD", "year": "2002", "title": "Visual Sensors for Focal Plane Computation of Image Features", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:03022011-094512699", "creators": [ { "name": { "family": "Pesavento", "given": "Alberto" }, "id": "Pesavento-Alberto", "display_name": "Pesavento, Alberto" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Diorio", "given": "Christopher J." }, "id": "Diorio-Christopher-J", "role": "member", "display_name": "Diorio, Christopher J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/BS04-5817", "abstract": "Feature detection and tracking is a fundamental problem in computer vision research. By detecting and tracking features in an image sequence it is possible to recover\r\ninformation about both the motion of the viewer and the structure of the environment. The selection of features is a computationally intensive task. We derived two low-complexity algorithms that are suitable for integration in a CMOS sensor with focal-plane processing. We review the two algorithms and the circuits that implement them. We present results from accurate simulations and experimental results from the testing of these CMOS sensors.\r\n" }, { "name": "Petrasek, Danny", "degree": "PhD", "year": "2002", "title": "Diffusion-Mediated Regulation Endocrine Networks", "advisor": "Bruno, Oscar P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052003-095049", "creators": [ { "name": { "family": "Petrasek", "given": "Danny" }, "id": "Petrasek-Danny", "orcid": "0000-0003-4178-4844", "display_name": "Petrasek, Danny" } ], "advisors": [ { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "advisor", "display_name": "Bruno, Oscar P." } ], "committee": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "chair", "display_name": "Cohen, Donald S." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/776t-vs55", "abstract": "In endocrine glands, vigorous and coordinated responses are often elicited by modest changes in the concentration of the organist molecule. The mammalian parathyroid gland is a representative case. Small (5%) changes in serum calcium result in tenfold (1000%) changes in glandular parathyroid hormone (PTH) release. In vitro, single isolated cells are observed to secrete fewer hormones than cells residing within a connected group, suggesting that a network has emergent regulatory properties. In PTH secreting tumors however, the ability to quickly respond to changes in calcium is strongly damped. A unifying hypothesis that accounts for these phenomena is realized by extra-cellular modulation of calcium diffusivity. A theoretical model and computational experiments demonstrate qualitative agreement with published experimental results. Our results suggest that in addition to the cellular mechanisms, endocrine glandular networks may have regulatory prowess at the level of interstitial transport. The extra-cellular diffusional mechanism proposed provides a consistent argument for 1) higher secretion of single cells in a connected network compared to isolated cells, 2) the rapid nonlinear response seen in healthy glands as well as 3) the pathological responses seen in hyperplasia and adenoma. Since the proposed diffusional regulation strongly depends on the existence of a connected cell network (gland), it also suggests a rationale for the advantages of cell networks as organs versus a dispersed system of isolated cells (in the case of the parathyroid gland)." }, { "name": "Pornsinsirirak, Teerachai Nicholas", "degree": "PhD", "year": "2002", "title": "Parylene MEMS Technology for Adaptive Flow Control of Flapping Flight", "advisor": "Neugebauer, Gerry", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162005-110430", "creators": [ { "name": { "family": "Pornsinsirirak", "given": "Teerachai Nicholas" }, "id": "Pornsinsirirak-Teerachai-Nicholas", "display_name": "Pornsinsirirak, Teerachai Nicholas" } ], "advisors": [ { "name": { "family": "Neugebauer", "given": "Gerry" }, "id": "Neugebauer-G", "role": "advisor", "display_name": "Neugebauer, Gerry" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Neugebauer", "given": "Gerry" }, "id": "Neugebauer-G", "role": "member", "display_name": "Neugebauer, Gerry" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Ho", "given": "C-M" }, "id": "Ho-C-M", "role": "member", "display_name": "Ho, C-M" } ], "option_major": [ "eleceng" ], "doi": "10.7907/jtjd-dd33", "abstract": "This thesis is the culmination of research work in developing a parylene MEMS technology to fabricate MEMS wings and large-area parylene actuator skins for real-time adaptive flow control for flapping flight applications.\r\n\r\nIn this thesis, the novel MEMS-based wing technology is presented using titanium-alloy metal (Ti-6A1-4V) as wingframe and parylene-C as wing membrane. With this technology, the ability to produce light, yet robust, 3-D wings can be achieved. The use of MEMS technology enables systematic research in terms of repeatability, size control, weight minimization, and mass production of the wings. By fabricating the wing with the photolithography and etching techniques, fast turnaround time of various wing designs can be easily obtained. The wings are optimized to utilize the flow separation to achieve a high lift coefficient, C(L), as large as five times that of the fixed-wing aircraft. The aerodynamic tests are performed in a high quality low-speed wind tunnel with velocity uniformity of 0.5% and speeds range from 1 to 10 m/s. The wind-tunnel test results are presented and discussed.\r\n\r\nAs part of the investigation to integrate MEMS actuators onto the wings for realtime adaptive flow control, the MEMS technology is developed to fabricate the first large-area wafer-sized, flexible parylene MEMS electrostatic actuator skins. The technology is first developed to fabricate parylene actuator diaphragm on a silicon chip. The actuator diaphragm is made of two metallized layers of parylene membranes with offset vent holes. Without electrostatic actuation, air can move freely from one side of the skin to the other side through the vent holes. With actuation, these vent holes are sealed and the airflow is controlled. The membrane behaves as a complete diaphragm. This function is successfully demonstrated using a 2-mm x 2-mm parylene diaphragm electrostatic actuator valves.\r\n\r\nFinally, this technology is applied to fabricate large area wafer-sized actuator skins. The skins contain only parylene and metalized electrodes and have no bulk silicon as a structural component. Plate and check-valved skin types are fabricated and both are integrated onto the MEMS wings for aerodynamic flow control. The integration of micro-valved actuators has shown significant effect on the aerodynamic performance of the flapping flight. The wind-tunnel test results are analyzed and discussed in detail in this thesis.\r\n" }, { "name": "Purohit, Prashant Kishore", "degree": "PhD", "year": "2002", "title": "Dynamics of Phase Transitions in Strings, Beams and Atomic Chains", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072006-100058", "creators": [ { "name": { "family": "Purohit", "given": "Prashant Kishore" }, "id": "Purohit-Prashant-Kishore", "display_name": "Purohit, Prashant Kishore" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/DP97-XH80", "abstract": "This thesis presents a theory for dynamical martensitic phase transitions in strings and beams. Shape memory alloys that rely on such phase transitions for their unique properties are often used in slender configurations like beams and rods. Yet most studies of phase transformations are in one dimension and consider only extension. The theory presented in this thesis to model these slender structures is based on the general continuum mechanical framework of thermoelasticity with a non-convex Helmholtz free energy. This non-convexity allows for the simultaneous existence of several metastable phases in a material; in particular, it leads to the formation of phase boundaries. The study of the laws governing the propagation of phase boundaries is the object of this thesis.\r\n\r\nPhase boundaries in strings are studied first. It is demonstrated that the motion of phase boundaries is not fully described by the usual balance laws of mass, momentum and energy. Additional constitutive information must be furnished from outside, and this additional information is referred to as the kinetic relation. While this notion is well-accepted in continuum theory, there is no definitive experiment or theoretical framework to determine the kinetic relation. This study of strings proposes a simple experiment to determine the kinetic relation. It also proposes a numerical method that accurately describes the complex behaviour of strings with phase boundaries.\r\n\r\nThe kinetic relation can also be viewed from the atomic scale. Phase transformations involve a complex rearrangement of the atoms the explicit details of which are averaged in a continuum theory. The kinetic relation may be viewed as an aggregate of those aspects of the atomistic rearrangement that have a bearing on macroscopic phenomena. This view is explored using a simple one dimensional model of an atomic chain with non-convex interaction potentials. A kinetic relation is obtained from dynamic simulations of impact experiments on the chain.\r\n\r\nThe latter part of this thesis studies beams made of materials capable of phase transitions. It develops a conceptual framework that accounts for extension, shear and flexure in such beams using a non-convex stored energy function. Specific constitutive assumptions that relate to the underlying crystallography are developed. The theory is applied to design a simple experiment on single crystals of martensitic materials with the objective of measuring the kinetic relation.\r\n\r\nFinally, propulsion at small scales is discussed as an application of beams made of phase transforming material. The goal is to mimic the flagellum of a micro-organism by propagating phase boundaries through a shearbale rod." }, { "name": "P\u00e9nzes, Paul Ivan", "degree": "PhD", "year": "2002", "title": "Energy-Delay Complexity of Asynchronous Circuits", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03022011-131111881", "creators": [ { "name": { "family": "P\u00e9nzes", "given": "Paul Ivan" }, "id": "P\u00e9nzes-Paul-Ivan", "display_name": "P\u00e9nzes, Paul Ivan" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "member", "display_name": "DeHon, Andre" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Nystr\u00f6em", "given": "Mika" }, "id": "Nystr\u00f6em-M", "role": "member", "display_name": "Nystr\u00f6em, Mika" } ], "option_major": [ "compsci" ], "doi": "10.7907/9jpj-5s67", "abstract": "In this thesis, a circuit-level theory of energy-delay complexity is developed for asynchronous circuits. The energy-delay efficiency of a circuit is characterized using the metric Et^n , where E is the energy consumed by the computation, t is the delay of the computation, and n is a positive number that reflects a chosen trade-off between\r\nenergy and delay. Based on theoretical and experimental evidence, it is argued that for a circuit optimized for minimal Et^n, the consumed energy is independent, in first\r\napproximation, of the types of gates (NAND, NOR, etc.) used by the circuit and is solely dependent on n and the total amount of wiring capacitance switched during computation. Conversely, the circuit speed is independent, in first approximation, of the wiring capacitance and depends only on n and the types of gates used.\r\n\r\nThe complexity model allows us to compare the energy-delay efficiency of two circuits implementing the same computation. On the other hand, the complexity model itself does not say much about the actual transistor sizes that achieve the optimum. For this reason, the problem of transistor sizing of circuits optimized for Et^n is investigated, as well. A set of analytical formulas that closely approximate the optimal transistor sizes are explored. An efficient iteration procedure that can further\r\nimprove the original analytical solution is then studied. Based on these results, a novel transistor-sizing algorithm for energy-delay efficiency is introduced.\r\n\r\nIt is shown that the Et^n metric for the energy-delay efficiency index n \u2265 0 characterizes any optimal trade-off between the energy and the delay of a computation. For\r\nexample, any problem of minimizing the energy of a system for a given target delay can be restated as minimizing Et^n for a certain n. The notion of minimum-energy function is developed and applied to the parallel and sequential composition of circuits in general and, in particular, to circuits optimized through transistor sizing and\r\nvoltage scaling. Bounds on the energy and delay of the optimized circuits are computed, and necessary and sufficient conditions are given under which these bounds are\r\nreached. Necessary and sufficient conditions are also given under which components of a design can be optimized independently so as to yield a global optimum when\r\ncomposed. Through these applications, the utility of the minimum-energy function is demonstrated. The use of this minimum-energy function yields practical insight into\r\nways of improving the overall energy-delay efficiency of circuits.\r\n" }, { "name": "Ragan, Regina", "degree": "PhD", "year": "2002", "title": "Direct Energy Bandgap Group IV Alloys and Nanostructures", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-02142002-211940", "creators": [ { "name": { "family": "Ragan", "given": "Regina" }, "id": "Ragan-Regina", "orcid": "0000-0002-8694-5683", "display_name": "Ragan, Regina" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "member", "display_name": "Quake, Stephen R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/1WKJ-RZ66", "abstract": "Novel group IV nanostructures were fabricated and the optical properties\r\nof such nanostructures were investigated for monolithic integration of optically\r\nactive materials with silicon. The SnxGe1-x alloy system was studied due to the\r\nprevious demonstration of an indirect to direct energy bandgap transition for\r\nstrain-relieved SnxGe1-x films on Si(001). In addition, quantum confined\r\nstructures of Sn were fabricated and the optical properties were investigated.\r\nDue to the small electron effective mass of \u03b1-Sn, quantum confinement effects are\r\nexpected at relatively large radii.
\r\n\r\nCoherently strained, epitaxial SnxGe1-x films on Ge(001) substrates were\r\nsynthesized with film thickness exceeding 100 nm for the first time. The\r\ndemonstration of dislocation-free SnxGe1-x films is a step toward the fabrication\r\nof silicon-based integrated infrared optoelectronic devices. The optical\r\nproperties of coherently strained SnxGe1-x/Ge(001) alloys were investigated both\r\ntheoretically and experimentally. Deformation potential theory calculations\r\nwere performed to predict the effect of coherency strain on the extrema points of\r\nthe conduction band and the valence band. The energy bandgap of\r\nSnxGe1-x/Ge(001) alloys was measured via Fourier transform infrared\r\nspectroscopy. Coherency strain did not change the SnxGe1-x energy bandgap\r\nwhen the strain axis was along [001] but deformation potential theory predicted \r\nthe absence of an indirect to direct energy bandgap transition when the strain\r\naxis was along [111].
\r\n\r\nIn addition to being the only group IV alloy exhibiting a direct energy\r\nbandgap, when grown beyond a critical thickness, SnxGe1-x/Ge(001) exhibits an\r\ninteresting phenomenon during MBE growth. Sn segregates via surface\r\ndiffusion to the crest of a surface undulation during growth and forms ordered\r\nSn-enriched SnxGe1-x rods oriented along [001]. The SnxGe1-x alloy system was\r\nused as a model system to gain insight to the physical mechanisms governing\r\nself-assembly and ordering during molecular beam epitaxy.
\r\n\r\nSn nanowires were fabricated in anodic alumina templates with lengths\r\nexceeding 1 \u03bcm and diameters on the order of 40 nm. Anodic alumina templates\r\ncan be fabricated non-lithographically with ordered domains of hexagonally\r\npacked pores greater than 1 \u03bcm and pore densities on the order of 1011 cm-2. The\r\nachievement of single crystal Sn nanowires fabricated using pressure injection in\r\nporous alumina templates was demonstrated.
\r\n\r\nThe fabrication of \u03b1-Sn quantum dots embedded in Ge was achieved by\r\nannealing 1 \u03bcm thick SnxGe1-x films at 750\u00b0C. The measured diameter of the\r\nquantum dots was 32 nm and a 10% size variation was observed. Quantum size\r\neffects were observed in \u03b1-Sn quantum dots. Optical transmittance\r\nmeasurements yield a value of 0.45 eV for the direct energy bandgap as a result\r\nof quantum confinement. A high degree of tunability of the bandgap energy\r\nwith the quantum dot radius is expected for \u03b1-Sn. Thus quantum-confined\r\nstructures of \u03b1-Sn are promising for optoelectronic device applications.
" }, { "name": "Rowley, Clarence Worth, III", "degree": "PhD", "year": "2002", "title": "Modeling, Simulation, and Control of Cavity Flow Oscillations", "advisor": "Colonius, Tim", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032004-075012", "creators": [ { "name": { "family": "Rowley", "given": "Clarence Worth, III" }, "id": "Rowley-Clarence-Worth-III", "display_name": "Rowley, Clarence Worth, III" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/G4ZX-KH73", "abstract": "This thesis involves the modeling of self-sustained oscillations in the flow past a rectangular cavity. The emphasis is on developing low-dimensional models that are suitable for analysis using tools from dynamical systems and control theory. Two-dimensional direct numerical simulations are performed, and indicate the presence of a \u201cwake mode,\u201d which has been observed previously in experiments, but which is much less well understood than the \u201cshear-layer mode\u201d usually observed. We characterize the flow in both shear-layer mode and wake mode, and provide a criterion for predicting the onset of wake mode, as a function of the various geometrical and flow-related parameters. We focus on the modeling of shear-layer mode, and employ two distinct modeling approaches: first, we use the method of Proper Orthogonal Decomposition (POD) and Galerkin projection to reduce the Navier-Stokes equations to a lowdimensional system of ordinary differential equations (ODEs). We extend the method to compressible flows, using approximations that are valid for cold flows at moderate Mach number. In a compressible flow, both the kinematic and thermodynamic variables contribute to the total energy, and an inner product is introduced which respects this, and allows one to use vector-valued POD modes for the Galerkin projection. We obtain models in the form of ODEs with between 2 and 60 states, and compare models based on scalar-valued and vector-valued POD modes. All of the models work well for short times (a few periods of oscillation), but the models based on scalar-valued modes deviate for longer times, while in general the models based on vector-valued modes retain qualitatively correct dynamical behavior. In the second modeling approach, we model the underlying physical mechanisms separately (shear-layer amplification, acoustic scattering, acoustic propagation), and obtain linear models that are suitable for control design and analysis. We design a controller which stabilizes the model, and implement a similar control law on an experiment, demonstrating significant reduction in the amplitude of the oscillations, but revealing some limitations of feedback control." }, { "name": "Spence, Charles Frederick", "degree": "PhD", "year": "2002", "title": "Nanobiology: Halting Steps into a Portion of Richard Feynman 's Vision", "advisor": "Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10082002-182045", "creators": [ { "name": { "family": "Spence", "given": "Charles Frederick" }, "id": "Spence-Charles-Frederick", "display_name": "Spence, Charles Frederick" } ], "advisors": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "chair", "display_name": "Quake, Stephen R." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Anderson", "given": "W. French" }, "id": "Anderson-W-F", "role": "member", "display_name": "Anderson, W. French" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/a3g1-x447", "abstract": "The advancement of nanotechnology has slightly opened the door for significant applications in biology. These technologies offer the potential to analyze and manipulate biological systems on the single cell and single molecule scales. The ability to analyze biological systems on these scales provides a direct means to reverse engineer multicellular organisms by following gene regulation and protein expression from the point of embryo fertilization onward. The need for amplification for standard bulk assays would be eliminated. Significant diagnostic applications would also be possible especially for genetic disorders and viral based diseases. Unfortunately there are still significant hurdles to overcome so that this potential can be realized and the technology can be used in a more robust manner. This thesis describes a significant effort for advancing the state of the nanoscale art. Specifically: the design and development of microfluidic devices for manipulating and analyzing DNA and E. coli cells, and the design and development of a modular DSP based feedback controller for scanned probe microscope (SPM) and nanomanipulator applications. In addition two significant applications of the DSP controller are presented: controlling the Q of an SPM microcantilever and sculpting the force potential of optical tweezers on the nanometer scale. With the microfluidic devices described here single DNA molecules from 2-200 kbp were sized and sorted with equivalent or better resolution than gel electrophoresis methods and in less time. Using similar techniques a disposable fluorescent cell sorter was developed and demonstrated by sorting green fluorescent protein E. coli cells from wild type cells. Using the DSP electronics the Q of an SPM microcantilever was controlled over three orders of magnitude using force feedback techniques. The Q can be lowered to one, enabling high speed tapping mode scanning ten times faster than possible with the natural Q. Using the same basic DSP electronics the potential of optical tweezers was arbitrarily shaped with 10 nm edge resolution. Advisor: Prof. Stephen Quake." }, { "name": "Stephens, Jennie Catherine", "degree": "PhD", "year": "2002", "title": "Response of Soil Mineral Weathering to Elevated Carbon Dioxide", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05162002-135325", "creators": [ { "name": { "family": "Stephens", "given": "Jennie Catherine" }, "id": "Stephens-Jennie-Catherine", "display_name": "Stephens, Jennie Catherine" } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "chair", "display_name": "Hering, Janet G." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Randerson", "given": "James T." }, "id": "Randerson-J-T", "role": "member", "display_name": "Randerson, James T." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/9ET7-QX09", "abstract": "Understanding the rates of weathering of soil minerals and the factors that may either enhance or inhibit these rates is a crucial part of understanding many processes from the watershed to the global scale. One potentially important factor in mineral weathering that is not yet well understood is the effect of elevated CO2 concentrations on weathering rates. Here, the direct and indirect effects of elevated soil CO2 are examined in field and laboratory-based studies, and the incorporation of the relationship between CO2 and mineral weathering in soil chemistry models is critically evaluated. \r\nAt Mammoth Mountain, California, volcanic ash soil is exposed to naturally occurring high levels of CO2 from a magmatic source. Comparative analyses of chemical and mineralogical characteristics of exposed and control soils suggest that decade-long exposure to elevated CO2 concentrations has altered soil dissolution rates. Indirect effects of elevated soil CO2 at this site, including vegetation mortality and a decrease in pH, have significant potential to alter weathering rates. Laboratory dissolution studies on whole soils under varying conditions of pH, PCO2, and concentrations of oxalate (chosen as a proxy for low-molecular-weight organic acids associated with vegetation in soils) were designed to assess both the direct and indirect effects of CO2. The results of these experiments provide confirming evidence that CO2 does not directly influence soil dissolution rates under acidic conditions. However, soil dissolution rates are sensitive to indirect effects of elevated CO2, including changes in pH and organic acid concentration. The inclusion of a direct CO2 dependence in a widely used soil chemistry model, PROFILE, may be perpetuating confusion on this issue. Erroneous conclusions in future model applications could result if this relationship is not removed from the PROFILE model. \r\nA significant and striking decrease in the specific surface area of the soil material was observed during all soil dissolution experiments. These observations call into question the informal convention of normalizing reported dissolution rates to the initial surface area. For effective comparison of weathering rates and identification of the factors influencing them, changes in surface area must be accounted for in reporting dissolution rates." }, { "name": "Sverdrup, Lawrence Henry", "degree": "PhD", "year": "2002", "title": "Lower Hybrid Current Drive Experiments on the Encore Tokamak", "advisor": "Vreeland, Thad; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:10212009-105023039", "creators": [ { "name": { "family": "Sverdrup", "given": "Lawrence Henry" }, "id": "Sverdrup-Lawrence-Henry", "display_name": "Sverdrup, Lawrence Henry" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "co-chair", "display_name": "Bridges, William B." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "co-chair", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/27RZ-SM06", "abstract": "The work of this thesis concerns a technological aspect of a tokamak fusion power reactor. A toroidal current in tokamaks is necessary for plasma equilibrium. Ohmic heated tokamaks are inherently pulsed devices since the toroidal plasma current is essentially a single turn secondary of a transformer. A pulsed power reactor is undesirable for a number of reasons including thermal fatigue to material structures and other mechanical cycling effects. Various means to drive a continuous current have been studied. One of the more successful schemes has been to inject unidirectional lower hybrid plasma waves into a tokamak. The plasma waves Landau damp on the high velocity tail of the electron distribution, delivering wave momentum to electrons and generating plasma current.
\r\n\r\nThe results of early experiments produced two plasma physics problems. First, the current drive effect disappeared above a certain plasma density that depended in some way on the particulars of the experiment. This effect became known as the 'density limit' problem. Secondly, the phase velocities of the launched lower hybrid plasma waves in most experiments turned out to be so high that essentially no electrons in the high velocity tail of the electron distribution were available to interact with the plasma waves. Despite this, large currents were indeed driven in most of the experiments. Somehow the 'spectral gap' between the launch phase velocity of the wave and the Landau damping phase velocity was being bridged.
\r\n\r\nExperiments at Caltech on the Encore tokamak failed to produce the large driven currents seen in other experiments. The reason for this and simultaneously the cause of the density limit seen in the other experiments was explained by a relatively simple and appealing theory.
\r\n\r\nSmall driven currents were observed. Initially puzzling was the result that currents could be driven in the same toroidal direction regardless of the directionality of the launched lower hybrid waves. The Encore tokamak had a handedness. The cause of this handedness turned out to be a radial, horizontal, magnetic error field associated with the toroidal magnetic field which led to a horizontal spiraling of the toroidal field lines.
" }, { "name": "Vela-Arevalo, Luz Vianey", "degree": "PhD", "year": "2002", "title": "Time-Frequency Analysis Based on Wavelets for Hamiltonian Systems", "advisor": "Wiggins, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302004-115559", "creators": [ { "name": { "family": "Vela-Arevalo", "given": "Luz Vianey" }, "id": "Vela-Arevalo-Luz-Vianey", "display_name": "Vela-Arevalo, Luz Vianey" } ], "advisors": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "advisor", "display_name": "Wiggins, Stephen R." } ], "committee": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Candes", "given": "Emmanuel J." }, "id": "Candes-E-J", "role": "member", "display_name": "Candes, Emmanuel J." }, { "name": { "family": "Haller", "given": "George" }, "id": "Haller-G", "role": "member", "display_name": "Haller, George" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/8MBB-3Z60", "abstract": "In this work, we present the method of time-frequency analysis based on wavelets for Hamiltonian systems and demonstrate its applications and consequences in the general dynamics of higher dimensional systems.\r\n\r\nBy extracting instantaneous frequencies from the wavelet transform of numerical solutions, we can distinguish regular from chaotic motions, and characterize the global structure of the phase space. The method allows us to determine resonance areas that persists even for high energy levels. We can also show how the existence of resonant motion affects the dynamics of the chaotic motion: we detect when chaotic trajectories are temporarily trapped around resonance areas, or undergo transitions between different resonances. This process is a good indicator of intrinsic transport in the phase space.\r\n\r\nThe method can be applied to a large class of systems, since it is not restricted to nearly integrable systems expressed in action-angle variables, which is the traditional framework for the definition of frequencies.\r\n\r\nThe main contribution of this method is that we have included the time variable in the analysis. We can determine exactly when the trajectories exchange between different regions by keeping records of resonance trappings. This allows us to analyze chaotic trajectories and not only quasiperiodic trajectories. And, we do not require any assumption about the regularity of chaotic trajectories.\r\n\r\nWe present three different applications of the method.\r\n\r\nThe first application consists of the analysis of dynamics and global phase space structure of the classical version of a quantum Hamiltonian for the water molecule. In the second application, we study the planar circular restricted three body problem, and show how resonance transitions of chaotic orbits are related to transport between different regions of the Solar system. Finally, we applied our method to a vibrational three-degrees-of-freedom Hamiltonian of the planar OCS molecule. We study the global dynamics at an energy level close to dissociation, which corresponds to a highly excited state of the molecule." }, { "name": "Vu\u010dkovi\u0107, Jelena", "degree": "PhD", "year": "2002", "title": "Photonic Crystal Structures for Efficient Localization or Extraction of Light", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-08252004-130544", "creators": [ { "name": { "family": "Vu\u010dkovi\u0107", "given": "Jelena" }, "id": "Vu\u010dkovi\u0107-Jelena", "orcid": "0000-0002-4603-9686", "display_name": "Vu\u010dkovi\u0107, Jelena" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Mabuchi", "given": "Hideo" }, "id": "Mabuchi-H", "role": "member", "display_name": "Mabuchi, Hideo" }, { "name": { "family": "Yamamoto", "given": "Yoshihisa" }, "id": "Yamamoto-Y", "role": "member", "display_name": "Yamamoto, Yoshihisa" } ], "option_major": [ "eleceng" ], "doi": "10.7907/VDXC-S449", "abstract": "Three-dimensional (3D) photonic crystals offer the opportunity of light manipulation in all directions in space, but they are very difficult to fabricate. On the other hand, planar photonic crystals are much simpler to make, but they exhibit only a \"quasi-3D\" confinement, resulting from the combined action of 2D photonic crystal and internal reflection. The imperfect confinement in the third dimension produces some unwanted out-of-plane loss, which is usually a limiting factor in performance of these structures. This thesis proposes how to fully take advantage of the relatively simple fabrication of planar photonic crystals, by addressing a problem of loss-reduction.
\r\n\r\nOne of the greatest challenges in photonics is a construction of optical microcavities with small mode volumes and large quality factors, for efficient localization of light. Beside standard applications of these structures (such as lasers or filters), they can potentially be used for cavity QED experiments, or as building blocks for quantum networks. This work also presents the design and fabrication of optical microcavities based on planar photonic crystals, with mode volumes of the order of one half of cubic wavelength of light (measured in material) and with Q factors predicted to be even larger than 10000.
\r\n\r\nIn addition to photonic crystals fabricated in semiconductors, we also address interesting properties of metallic photonic crystals and present our theoretical and experimental work on using them to improve the output of light emissive devices.
\r\n\r\nFeature sizes of structures presented here are below those achievable by photolithography. Therefore, a high resolution lithography is necessary for their fabrication. The presently used e-beam writing techniques suffer from limitations in speed and wafer throughput, and they represent a huge obstacle to commercialization of photonic crystals. Our preliminary work on electron beam projection lithography, the technique that could provide us with the speed of photolithography and the resolution of e-beam writing, is also discussed in this thesis.
" }, { "name": "Wang, Guofeng", "degree": "PhD", "year": "2002", "title": "First Principles Based Multiscale Modeling of Single Crystal Plasticity: Application to BCC Tantalum", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:11132009-112545862", "creators": [ { "name": { "family": "Wang", "given": "Guofeng" }, "id": "Wang-Guofeng", "orcid": "0000-0001-8249-4101", "display_name": "Wang, Guofeng" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Cagin", "given": "Tahir" }, "id": "Cagin-Tahir", "role": "member", "display_name": "Cagin, Tahir" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "matsci" ], "doi": "10.7907/5nyn-ct36", "abstract": "In principle, the macroscopic plasticity properties of crystalline materials are derivable from the physical processes involving dislocations and interactions between dislocations with other defects. However, a quantitative theory of plasticity based on the dislocation mechanism requires crossing multiple length and time scales. To accommodate these requirements, we developed a multiscale approach for modeling crystalline solids. In this thesis, to establish the connections between simulations in different length and time scales, I mainly focus on identifying and determining the importance and influence of various unit processes involving the dislocations through atomic level simulations. These unit processes in turn play a major role in modeling the single crystal plasticity.
\r\n\r\nKey Results from Atomistic Simulations
\r\n\r\nDislocation core structure and core energy: Using the first-principles qEAM force field (FF), we determine the core energy for 1/2a<111> screw dislocation and 1/2a<111> edge dislocation in bcc Ta. We find that the core energy of edge dislocation is 1.77 times higher than that of screw dislocation. This ratio (1.77) is a fundamental material property used as input to the macroscopic model. Furthermore, we find that the central 12 atoms closest to the 1/2a<111> screw dislocation line have distinguishably higher atomistic strain energy than the other atoms. Thus, we arrive at a physical definition of dislocation core.
\r\n\r\nScrew dislocation mobility: In this thesis, we proposed a new method to investigate dislocation mobility by analyzing the process of migration of a screw dislocation dipole. The new method is based on the energy distribution at the atomistic scale and is used to calculate the Peierls potential barrier and Peierls stress for dislocation continuous motion. The calculated Peierls stress is in good agreement with results obtained using other method. Simulating dislocation motion at finite temperatures (from 20 K to 300 K), we find that the activation energy for dislocation motion is about 6 times lower than computed at 0.001 K. Our results suggest that the decrease in the correlation between neighboring segments in the dislocation line accounts for the decrease of activation energy. We observe that the formation of kink pair along the dislocation line enhances the dislocation mobility. This verifies the traditional belief that the screw dislocation in bcc metals moves by first kink pair nucleation and subsequently lateral movements of kinks along the dislocation.
\r\n\r\nKinks in screw dislocations: To bridge the atomistic process of dislocation motion with continuum model, we accurately calculate the material properties, such as kink pair formation energy and effective kink pair length, using atomic level simulations. In detailed structural analysis, we discover the substructures of different kinks when the screw dislocation core is asymmetric. There are only two kinds of elementary kinks in the dislocation and the others are the composite kinks consisting of an elementary kink and one or two flips. Based on these findings, we further explain the observed trend of the formation energy and mobility of different classes of kinks. (Note: Similar trend and conclusion could have been found in earlier studies but not mentioned by the authors of those papers.)
\r\n\r\nIn summary, we have used quantum mechanics based interaction potentials to investigate the unit processes that play important role in single crystal plasticity and verified the findings using the quantitative results obtained from the atomic level simulation in a macroscopic model for single crystal plasticity.
" }, { "name": "Xu, Luoyu Roy", "degree": "PhD", "year": "2002", "title": "Dynamic Failure Characteristics in Layered Materials and Structures", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04252011-111825843", "creators": [ { "name": { "family": "Xu", "given": "Luoyu Roy" }, "id": "Xu-Luoyu-Roy", "display_name": "Xu, Luoyu Roy" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "orcid": "0000-0003-3363-2197", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wver-8342", "abstract": "Systematic investigations were carried out to understand the general nature of dynamic failure mechanisms in layered materials and structures such as composite and\r\nsandwich structures, thin films, layered armors and layered rock. A series of impact experiments on model-layered specimens were conducted using high-speed photography\r\nand dynamic photoelasticity.\r\n\r\nFor the first time, the sequence and interaction of two major dynamic failure modes in layered materials-inter-layer cracking and intra-layer cracking were revealed\r\nin real time. For heterogeneous three-layer systems, shear-dominated inter-layer cracking was always the first failure event for specimens subjected to low-speed impact. Interlayer cracking generally nucleated from interfacial locations where the inter-layer shear stress acquired a local maximum. Depending on impact speed and bond strength\r\ncharacteristics, inter-layer cracks were very transient and often became intersonic even under moderate impact speeds. Intra-layer cracking always initiated after the development of inter-layer cracks as a result of inter-layer crack kinking into the adjacent layer. The resulting intra-layer mode I cracks often accelerated and branched as they\r\nattained high speeds, causing core layer fragmentation. For homogenous-layered systems composed of bonded layers of Homalite, intra-layer cracks appeared in the form of cracks\r\nradiating from the impact site. As soon as these cracks approached an interface, interlayer cracks were often induced depending on the angle between the crack path and the interface. Direct experimental evidence of the dynamic equivalent of \"Cook-Gordon mechanism\" was recorded, i.e., two intersonic interfacial cracks nucleated and propagated along the interface before a fan of mode I incident cracks was ever able to reach the interface. Also, significant dependence of the failure characteristics on impact speeds and interfacial strengths was found. For the heterogeneous three-layer system subjected to a high impact speed, two clear shear shock waves associated with the intersonic inter-layer cracks were observed at the specimen center. Shock waves were also observed along the interface in heterogeneous three-layer systems featuring weak and ductile bonds. The impact momentum and loading duration were identified as two important parameters in damage spreading for a given impact energy.\r\n\r\nMotivated by the experimental observations of crack deflection/penetration at an interface, a novel wedge-loaded impact specimen was designed to explore the basic\r\nmechanics nature of this phenomenon. The deflection/penetration behavior of an incoming dynamic crack at an interface was found to depend on the interfacial angle and the interfacial fracture toughness. A dynamic fracture model, together with an energy criterion, were proposed and were found to agree reasonably well with the experimental observations." }, { "name": "Xu, Yong", "degree": "PhD", "year": "2002", "title": "Flexible MEMS Skin Technology for Distributed Fluidic Sensing", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-12302004-144248", "creators": [ { "name": { "family": "Xu", "given": "Yong" }, "id": "Xu-Yong-EE", "display_name": "Xu, Yong" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Martinoli", "given": "Alcherio" }, "id": "Martinoli-A", "role": "member", "display_name": "Martinoli, Alcherio" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." } ], "option_major": [ "eleceng" ], "doi": "10.7907/V3KW-SV35", "abstract": "Inherently, most MEMS devices are fabricated on rigid substrates. However, for a wide variety of applications, it has long been desirable that sensors, actuators, or circuits can be fabricated on flexible substrates so as to be mounted on nonplanar surfaces or even on flexible objects such as a human body. A novel flexible skin technology, which is compatible with MEMS and ICs processes, was developed in the Caltech Micromachining Lab for the distributed fluidic sensing.\r\n\r\nWith this technology, a flexible shear-stress sensor skin was fabricated and successfully implemented on an Unmanned Aerial Vehicle (UAV). The flow separation detection along the leading edge of UAV was demonstrated in both wind tunnel and the real flight test. The complete UAV sensing/computing/controlling system, including microsensors, microelectronics, and microactuators, was also demonstrated in wind tunnel and ready for the flight test.\r\n\r\nThis technology was further explored by making an underwater shear-stress sensor skin for applications such as flow pattern measurement of radio controlled submarines, and the study of the safety and arming mechanisms of next generation smart torpedoes. Underwater shear-stress sensor was developed, addressing the challenges of minimization of the pressure crosstalk and waterproof coating. A selective Parylene deposition method was investigated as well to achieve high shear-stress sensitivity and excellent waterproof simultaneously. With the skin structure, the packaging was significantly simplified and improved.\r\n\r\nAdditionally, MEMS-IC integration is highly desirable since this integration promises to bring very important benefits such as operational improvement, packaging simplification, and cost reduction. For the first time, an IC-integrated flexible shearstress sensor skin, which has bias and signal conditioning circuitry on-chip, was developed by using post-CMOS MEMS processes. The fluidic sensing on a semicylindrical surface with the IC-integrated shearstress sensor skin was demonstrated in the wind tunnel.\r\n\r\nIn addition to distributed fluidic sensing, the MEMS skin technology, with the demonstrated capability to be integrated with ICs, can enable many other important applications in biomedicine, wearable microsystems, RF systems, and robotics." }, { "name": "Yao, Tze-Jung", "degree": "PhD", "year": "2002", "title": "Parylene for MEMS Applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202004-135306", "creators": [ { "name": { "family": "Yao", "given": "Tze-Jung" }, "id": "Yao-Tze-Jung", "display_name": "Yao, Tze-Jung" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "member", "display_name": "Pine, Jerome" }, { "name": { "family": "Shumate", "given": "M." }, "id": "Shumate-M", "role": "member", "display_name": "Shumate, M." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "eleceng" ], "doi": "10.7907/caxb-sr18", "abstract": "The goal of this thesis is to utilize Parylene, a room-temperature chemical-vapor-deposited (CVD) polymer, for MicroElectroMechanical Systems (MEMS) applications. The identified unique properties of Parylene are used to fabricate various micromachining devices such as thermopneumatic microvalve, in-channel microflow restrictor, and electret microphones.\r\n\r\nFirst, the properties of Parylene as a MEMS material are reviewed. The electrical, thermal, surface, and mechanical properties are first compared with that of other materials and further studied specifically for MEMS applications. The high dielectric strength (determined as 250V/pm) of Parylene makes it suitable for use as an electrical insulation material. However, its high resistivity causes un-desired charging effects first described in polymer-based electrostatic devices. The undesired high pull-in voltage, \"bounce-back,\" and \"snap-down\" effects caused by dielectric charging are studied.\r\n\r\nSecond, to make Parylene as a surface-micromachined material, a process that overcomes the stiction problem has to be developed. Thus, a new technique that combines wet-acetone dissolution and dry BrF3 dry etching has developed to overcome the stiction problem, which prevents Parylene microstructures from freestanding. The devices of mm*mm size with high yield are demonstrated using this technology.\r\n\r\nA thermopneumatic microvalve with a corrugated silicone/Parylene composite membrane is designed, fabricated, and tested for gas flows of several slpm and inlet pressures of tens of psi. The lowest power consumption to turn off the gas flow is determined to be 73mW. A silicone-based microfluidic coupler, initially designed for microvalve packaging, is also demonstrated for its ability to connect the external macrofluidic world to microfluidic devices. The demonstrated \"quick-connect\" microfluidic coupler has low leakage, is reusable, and can maintain good seal up to 60 psi.\r\n\r\nAn in-channel microflow restrictor is also demonstrated with freestanding Parylene integration technology. The demonstrated restrictor can modulate flow at several tens of nl/min range with inlet pressures of several psi. The restrictor, although AC-actuated, can modulate the flow up to 50%.\r\n\r\nFinally, an electret microphone with thin-film Teflon AF is demonstrated. Parylene is shown to enhance the rigidity and yield of the microphone back plate. The demonstrated electret microphone has an open sensitivity of up to 45mV/Pa with a bandwidth of up to 10KHz.\r\n" }, { "name": "Yuen, Ka-Veng", "degree": "PhD", "year": "2002", "title": "Model Selection, Identification and Robust Control for Dynamical Systems", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02082012-113016272", "creators": [ { "name": { "family": "Yuen", "given": "Ka-Veng" }, "id": "Yuen-Ka-Veng", "orcid": "0000-0002-1755-6668", "display_name": "Yuen, Ka-Veng" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Johnson", "given": "Erik A." }, "id": "Johnson-E-A", "role": "member", "display_name": "Johnson, Erik A." } ], "option_major": [ "civileng" ], "doi": "10.7907/YEV9-8X44", "abstract": "To fully exploit new technologies for response mitigation and structural health monitoring, improved system identification and controller design methodologies are desirable that explicitly treat all the inherent uncertainties. In this thesis, a probabilistic framework is presented for model selection, identification and robust control of smart structural systems under dynamical loads, such as those induced by wind or earthquakes. First, a probabilistic based approach is introduced for selecting the most plausible class of models for a dynamical system using its response measurements. The proposed approach allows for quantitatively comparing the plausibility of different classes of models among a specified set of classes.
\r\n\r\nThen, two probabilistic identification techniques are presented. The first one is for modal identification using nonstationary response measurements and the second one is for updating nonlinear models using incomplete noisy measurements only. These methods allow for updating of the uncertainties associated with the values of the parameters controlling the dynamic behavior of the structure by using noisy response measurements only. The probabilistic framework is very well-suited for solving this nonunique problem and the updated probabilistic description of the system can be used to design a robust controller of the system. It can also be used for structural health monitoring.
\r\n\r\nFinally, a reliability-based stochastic robust control approach is used to design the controller for an active control system. Feedback of the incomplete response at earlier time steps is used, without any state estimation. The optimal controller is chosen by minimizing the robust failure probability over a set of possible models for the system. Here, failure means excessive levels of one or more response quantities representative of the performance of the structure and the control devices. When calculating the robust failure probability, the plausibility of each model as a representation of the system's dynamic behavior is quantified by a probability distribution over the set of possible models; this distribution is initially based on engineering judgement, but it can be updated using the aforementioned system identification approaches if dynamic data become available from the structure. Examples are presented to illustrate the proposed controller design procedure, which includes the procedure of model selection, identification and robust control for smart structures.
" }, { "name": "Zhu, Weidong", "degree": "PhD", "year": "2002", "title": "Nonlinearly Viscoelastic Response of Glassy Polymers", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:04212011-132230527", "creators": [ { "name": { "family": "Zhu", "given": "Weidong" }, "id": "Zhu-Weidong", "display_name": "Zhu, Weidong" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Emri", "given": "Igor" }, "id": "Emri-Igor", "orcid": "0000-0003-3329-9312", "role": "member", "display_name": "Emri, Igor" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "mecheng" ], "doi": "10.7907/V7GW-0342", "abstract": "This thesis consists of three chapters. After a brief introduction on the general aspects of polymer characterization and viscoelasticity in the first chapter, all major features of this research project are described in the following two chapters.\r\n\r\nThe second chapter deals exclusively with the nonlinearly thermo-mechanical creep behavior of (bisphenol A) polycarbonate under pure shear loading at different\r\ntemperatures (0 \u00b0C to 140 \u00b0C). The shear creep in the linearly viscoelastic range was measured with a torsiometer for reference purposes and a master curve, along with a shift factor curve, were deduced. While the master curve is well defined with no detectable deviation, the shift factor can be represented by two straight line segments interrupted at the \u03b2 transition temperature of polycarbonate. The shear creep tests in the nonlinearly\r\nviscoelastic range were conducted on an Arcan specimen geometry at different temperatures and under different stress levels, utilizing digital image correlation for the\r\nrecording of the creep strains. The difference between the nominal stress and the actual stress distribution in the Arcan specimen was explored via numerical simulations\r\n(ABAQUS) by assuming linear quasi-elastic and quasi-plastic analysis in place of the as yet uncertain material characterization. Isochronal plots were created from the creep data. Nonlinearly viscoelastic behavior starts to take effect near 1% strain at the temperatures considered. The applicability of the stress-clock representation for material characterization has been explored and is found to be dubious, at best, for this material. The \"yield-like\" behavior of polycarbonate has been examined in terms of the isochronal stress-strain response and a corresponding \"yield-like shear stress\" has been determined\r\nto be a monotonically decreasing function of the temperature, but again with an interruption at the \u03b2 transition temperature. Time-temperature trade-off as practiced for \"time-temperature shifting\" at small strains does not apply in the nonlinear domain. The results are generally in agreement with those found for Poly(Methyl Methacrylate), thus fostering the idea that the present results can be generalized -with additional work- to other amorphous polymers.\r\n\r\nThe third chapter focuses on the role of volumetric strain in nonlinearly viscoelastic behavior of polycarbonate. The creep responses of (bisphenol A) polycarbonate at 80 \u00b0C under combined two-dimensional shear and tensile/compressive\r\nstress states were measured on Arcan specimens in the nonlinearly viscoelastic regime. Of particular interest is the influence of the dilatational deformation component on the nonlinearly viscoelastic creep behavior. Because the nonlinear material response determines the stress distribution under fixed deformation or load, but is not known a priori, a re-estimation of the latter is essential to verify or adjust the stress state(s). This is\r\naccomplished by approximating isochronal stress-strain relations derived from shear creep behavior, encompassing the nonlinear domain, by a classical incremental elastoplastic\r\nmaterial description at appropriate times. Inasmuch as the two-dimensional character of the test configuration places limits on accessing three-dimensional information, a coherent representation of the results in terms of maximum shear and/or octahedral representation is examined. It is found that the creep behavior under shear and normal stress or deformation imposition differ significantly: when viewed as a response in terms of a maximum shear description, there are material responses under combined loading when either one or the other dominates. Once the response is formulated in terms of an octahedral description the representation becomes less sensitive to normal vs. shear\r\nbehavior. Within the precision underlying the measurements it is found that the shear and normal strain components accumulate under creep in nearly constant ratios. However,\r\nunder this scenario it is demonstrated quite clearly that the addition of negative dilatational stress (or deformation) to pure shear leads to distinctly lower creep rates. The converse is true, if positive dilatational stresses are added, though not monotonically so.\r\n" }, { "name": "Zhuang, Shiming", "degree": "PhD", "year": "2002", "title": "Shock Wave Propagation in Periodically Layered Composites", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:05102011-141326530", "creators": [ { "name": { "family": "Zhuang", "given": "Shiming" }, "id": "Zhuang-Shiming", "display_name": "Zhuang, Shiming" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Grady", "given": "Dennis E." }, "id": "Grady-D-E", "role": "member", "display_name": "Grady, Dennis E." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/988X-1V27", "abstract": "Mathematically, a shock wave is treated as a discontinuity in a medium. In reality, however, a shock wave is always structured, i.e., its front takes a finite time to rise from an initial material state to the final shocked state. The structuring of a shock front is due to the competition between the nonlinearity of material behavior and the dissipation processes occurring during the wave propagation. There are many mechanisms which may be responsible for the dissipation and/or dispersion of shock wave energy. In homogeneous media, such as metals, one common interpretation for the structuring of a shock wave is that the viscoplasticity processes (dislocation, twinning, etc.) are responsible for the dissipation of energy. While in heterogeneous composites, besides the viscous dissipative processes existing in each of its constituents, due to the existence of internal interfaces, the scattering induced by the interface during shock compression could be another important mechanism.\r\n\r\nIn this study, the interface scattering effects on shock wave propagation in heterogeneous media were investigated by subjecting periodically layered composites to planar impact loading with a flyer plate. The flyer plate was accelerated to a desired velocity using a powder gun loading system. In order to measure shock particle velocity time history at an internal or the free surface of the specimen, the so-called VISAR (Velocity Interferometry System for Any Reflector) diagnostic system was constructed and used during shock compression experiments. Manganin stress gages were embedded inside the specimen at selected internal interfaces to measure shock stress time history. To study the scattering mechanisms of the interface to waves, two-component composite specimens with different interface mechanical properties and heterogeneity were prepared and tested. Different types of composites were prepared with differing mechanical impedance. Specimens with different heterogeneity were obtained by changing the geometrical configuration (length scale) of the layered stack. Two-dimensional numerical simulations were also carried out to understand the process of shock wave evolution in the layered composites.\r\n\r\nExperimental and numerical studies show that periodically layered composites support steady structured shock waves. The influence of internal interfaces on the shock wave propagation is through the scattering mechanism, i.e., multiple reflection of waves in the layers and their interaction with the shock wave. The interface scattering affects both the bulk and the deviatoric response of the composite to shock compression. The influence of scattering on the bulk behavior is to slow down the velocity of the shock wave in the composites, while its influence on the deviatoric response is to structure the shock wave profile. If all the dissipative and dispersive effects are collectively termed as viscosity, which causes the shock front structuring, i.e., the shock front rise-time increasing, then the effective shock viscosity increases with the increase of interface impedance mismatch and decreases with the increase of interface density (interface area per unit volume) and shock loading strength. The existing mixture model for constructing the constitutive relation for composites based on the known properties of its component materials can only, at best, reasonably predict the response of the composites under strong shock loading conditions. In order to fully describe the response of a heterogeneous composite to shock compression loading, accurate physics-based constitutive relations need to be formulated to take into account the scattering effects induced by the heterogeneous microstructure.\r\n" }, { "name": "Zimmerman, Daniel Marc", "degree": "PhD", "year": "2002", "title": "Dynamic UNITY", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072001-160019", "creators": [ { "name": { "family": "Zimmerman", "given": "Daniel Marc" }, "id": "Zimmerman-Daniel-Marc", "display_name": "Zimmerman, Daniel Marc" } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "compsci" ], "doi": "10.7907/AC6E-WE21", "abstract": "Dynamic distributed systems, where a changing set of communicating processes must interoperate to accomplish particular computational tasks, are becoming extremely important. Designing and implementing these systems, and verifying the correctness of the designs and implementations, are difficult tasks. The goal of this thesis is to make these tasks easier.\r\n\r\nThis thesis presents a specification language for dynamic distributed systems, based on Chandy and Misra's UNITY language. It extends the UNITY language to enable process creation, process deletion, and dynamic communication patterns.\r\n\r\nThe thesis defines an execution model for systems specified in this language, which leads to a proof logic similar to that of UNITY. While extending UNITY logic to correctly handle systems with dynamic behavior, this logic retains the familiar UNITY operators and most of the proof rules associated with them. \r\n\r\nThe thesis presents specifications for three example dynamic distributed systems to demonstrate the use of the specification language, and full correctness proofs for two of these systems and a partial correctness proof for the third to demonstrate the use of the proof logic. \r\n\r\nThe thesis details a method for determining whether a system in the specification language can be transformed into an implementation in a standard programming language, as well as a method for performing this transformation on those specifications that can. This guarantees a correct implementation for any specification that can be so transformed. \r\n" }, { "name": "Akkarakaran, Sony John", "degree": "PhD", "year": "2001", "title": "Filter Bank Optimization with Applications in Noise Suppression and Communications", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072010-095516188", "creators": [ { "name": { "family": "Akkarakaran", "given": "Sony John" }, "id": "Akkarakaran-Sony-John", "display_name": "Akkarakaran, Sony John" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "orcid": "0000-0001-9176-3078", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Djokovic", "given": "Igor" }, "id": "Djokovic-I", "role": "member", "display_name": "Djokovic, Igor" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4712-9414", "abstract": "A filter bank (FB) is used to analyze or decompose a signal into several frequency bands, which are processed separately and then combined. This allows us to allocate processing resources in a manner tailored to the distribution of the relevant signal features among the bands. A judicious allocation leads to improved system performance over direct processing of the input signal (without using an FB). FBs have found applications in almost every area of modern digital signal processing, including audio, image and video compression and communications.
\r\n\r\nThe main thrust of this thesis is towards the optimization of FBs based on the statistical properties of their input. We establish the optimality of a type of FB called the principal component filter bank (PCFB) for numerous signal processing problems. The PCFB depends on the input power spectrum and on the class of M channel orthonormal FBs over which we seek to optimize the FB. PCFB optimality for compression and progressive transmission has been observed to varying degrees in the past. Our work provides a unified framework for orthonormal FB optimization, that includes these earlier results as special cases. It also covers many other problems not observed earlier, notably in noise suppression and communications.
\r\n\r\nA central result that we establish is that the PCFB is the optimum orthonormal FB whenever the minimization objective is a concave function of the vector of subband variances of the FB. Many signal processing problems result in such objectives. The earlier results on PCFB optimality for compression can be explained by this framework. Another example not noticed earlier is FBbased white noise reduction using zeroth order Wiener filters or hard thresholds in the subbands. Yet another case involves the discrete multitone modulation (DMT) communication system, used in ADSL (asymmetric digital subscriber line) and wireless OFDM (orthogonal frequency division multiplexing) technologies. These systems use the transmultiplexer configuration of an FB, which is usually chosen as a DFT or cosine-modulated FB for efficiency of implementation. We show that at increased implementation cost, we can minimize the transmission power requirement (for a given bitrate and error probability) by using the PCFB associated with a certain normalized noise spectrum. We present simulation examples with realistic channel and noise models for the ADSL system to compare the performance of the PCFB against other types of FBs, such as the DFT.
\r\n\r\nWe study various extensions of the basic PCFB optimality result. The noise suppression problem becomes more involved when the noise is colored, because the objective then depends on both signal and noise subband variances. For a specific FB class, namely the orthogonal transform coder class, we show that a simultaneous PCFB for the signal and noise is optimal (if it exists). For the class of unconstrained FBs, this does not hold in general; we develop an algorithm that computes the best FB for piecewise constant spectra. In some cases, PCFB optimality extends to classes of biorthogonal FBs too, although there are many open problems in this area, as we point out. We study the effect of nonexistence of a PCFB on the FB optimizations and show how they usually become analytically intractable. We show that PCFBs do not exist for the classes of DFT and cosine-modulated FBs. We also study nonuniform FB optimization: We establish the definition of nonuniform PCFBs and study their existence and optimality, which are shown to be much more restricted when compared with uniform PCFBs.
\r\n\r\nLastly, we study a related open problem on the parameterization of nonuniform perfect reconstruction (PR) FBs of various classes, such as the rational and FIR classes. Not all nonuniform PRFBs can be built by the common method of using tree structures of uniform PRFBs. Given a set of decimators, is there a rational PRFB using them? If so, what are all the PRFBs possible? When are they necessarily derivable from a tree structure? Very little is known about the answers to many such questions. For example, for existence of rational PRFBs with a given set of decimators, certain conditions on the decimators are known to be necessary, while certain others are sufficient. However, conditions that are both necessary and sufficient are unknown. One of our contributions is to strengthen considerably the known conditions. This is an important step towards a complete PR theory for nonuniform filter banks.
" }, { "name": "Au, Siu-Kui", "degree": "PhD", "year": "2001", "title": "On the Solution of First Excursion Problems by Simulation with Applications to Probabilistic Seismic Performance Assessment", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03062014-085528325", "creators": [ { "name": { "family": "Au", "given": "Siu-Kui" }, "id": "Au-Siu-Kui", "orcid": "0000-0002-0228-1796", "display_name": "Au, Siu-Kui" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Conte", "given": "Joel P." }, "id": "Conte-Joel-P", "orcid": "0000-0003-2068-7965", "role": "member", "display_name": "Conte, Joel P." }, { "name": { "family": "Katafygiotis", "given": "Lambros" }, "id": "Katafygiotis-Lambros", "orcid": "0000-0001-9275-9687", "role": "member", "display_name": "Katafygiotis, Lambros" } ], "option_major": [ "civileng" ], "doi": "10.7907/C0JQ-G051", "abstract": "In a probabilistic assessment of the performance of structures subjected to uncertain environmental\r\nloads such as earthquakes, an important problem is to determine the probability that the structural response exceeds some specified limits within a given duration of interest. This problem is known as the first excursion problem, and it has been a challenging problem in the theory of stochastic dynamics and reliability analysis. In spite of the enormous amount of attention the problem\r\nhas received, there is no procedure available for its general solution, especially for engineering\r\nproblems of interest where the complexity of the system is large and the failure probability is small.
\r\n\r\nThe application of simulation methods to solving the first excursion problem is investigated in this dissertation, with the objective of assessing the probabilistic performance of structures subjected to uncertain earthquake excitations modeled by stochastic processes. From a simulation perspective, the major difficulty in the first excursion problem comes from the large number of uncertain parameters\r\noften encountered in the stochastic description of the excitation. Existing simulation tools are examined, with special regard to their applicability in problems with a large number of uncertain parameters. Two efficient simulation methods are developed to solve the first excursion problem. The first method is developed specifically for linear dynamical systems, and it is found to be extremely efficient compared to existing techniques. The second method is more robust to the type of\r\nproblem, and it is applicable to general dynamical systems. It is efficient for estimating small failure probabilities because the computational effort grows at a much slower rate with decreasing failure probability than standard Monte Carlo simulation. The simulation methods are applied to assess the probabilistic performance of structures subjected to uncertain earthquake excitation. Failure\r\nanalysis is also carried out using the samples generated during simulation, which provide insight into the probable scenarios that will occur given that a structure fails.
\r\n" }, { "name": "Bhardwaj, Ashish Ishwar Singh", "degree": "PhD", "year": "2001", "title": "All-Optical Logic Circuits Based on the Polarization Properties of Non-Degenerate Four-Wave Mixing", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07132001-112041", "creators": [ { "name": { "family": "Bhardwaj", "given": "Ashish Ishwar Singh" }, "id": "Bhardwaj-Ashish-Ishwar-Singh", "display_name": "Bhardwaj, Ashish Ishwar Singh" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/CMAB-WF06", "abstract": "This thesis investigates a new class of all-optical logic circuits that are based on the polarization properties of non-degenerate Four-Wave Mixing. Such circuits would be used in conjunction with a data modulation format where the information is coded on the states of polarization of the electric field. Schemes to perform multiple triple-product logic functions are discussed and it is shown that higher-level Boolean operations involving several bits can be implemented without resorting to the standard 2-input gates that are based on some form of switching. Instead, an entire hierarchy of more complex Boolean functions can be derived based on the selection rules of multi-photon scattering processes that can form a new class of primitive building blocks for digital circuits.
\r\n \r\nPossible applications of these circuits could involve some front-end signal processing to be performed all-optically in shared computer back-planes. As a simple illustration of this idea, a circuit performing error correction on a (3,1) Hamming Code is demonstrated. Error-free performance (Bit Error Rate of < 10\u207b\u2079) at 2.5 Gbit/s is achieved after single-error correction on the Hamming word with 50 percent errors. The bit-rate is only limited by the bandwidth of available resources. Since Four-Wave Mixing is an ultrafast nonlinearity, these circuits offer the potential of computing at several terabits per second. Furthermore, it is shown that several Boolean functions can be performed in parallel in the same set of devices using different multi-photon scattering processes. The main objective of this thesis is to motivate a new paradigm of thought in digital circuit design. Challenges pertaining to the feasibility of these ideas are discussed.
" }, { "name": "Billock, Joseph Gregory", "degree": "PhD", "year": "2001", "title": "Attentional Control of Complex Systems", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:01032013-152450777", "creators": [ { "name": { "family": "Billock", "given": "Joseph Gregory" }, "id": "Billock-Joseph-Gregory", "display_name": "Billock, Joseph Gregory" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Barbastathis", "given": "G." }, "id": "Barbastathis-G", "role": "member", "display_name": "Barbastathis, G." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "eleceng" ], "doi": "10.7907/132r-jm11", "abstract": "This thesis reports on work done in applying some of the concepts and architectures found in biological computation to computer algorithms. Biology has long inspired computer technology at the level of processing elements. This thesis explores the application of biologically inspired algorithms at a higher level-that of functional structures of the nervous system. The first chapter gives background on the attentional/awareness model of the brain, why it is important to biology and the advantages in real-time performance and in learning facilitation which we expect from applying it in computer algorithms.
\r\n\r\nThe second chapter examines the application of this model to a canonical computer science problem-the bin packing problem. Approaching this NP-complete problem when limited by computational resources and time constraints means that algorithms which throwaway large amounts of the information about the problem perform better than those which attempt to consider everything. The existence of an optimum in the size of a working memory needed to find the best solution under time pressure is shown. The transition between the regime of strict time constraints and more forgiving time constraints is quite sudden. Chapter 3 presents an analytical model for better understanding the performance of various bin packing algorithms.
\r\n\r\nChapter 4 examines the application of the attentional model to a real-time computer game testbed. This testbed is explained, and results are shown which illustrate that in a complex, unpredictable environment with tight time and resource constraints conditions, an algorithm which examines only that information which falls into a relatively small part of the playing area can win against player which addresses it all.
\r\n\r\nChapter 5 turns to an examination of the role of reduced informational representations upon learning. Solving of various logical-kinetic puzzles by a simulated segmented arm is done by a learning system. A logic supervisory subsystem utilizes attentional/awareness methods to train, and pass control of the different control levels of the articulate arm over to, the neural networks, adaptive resonance theory networks, and declarative computer memory which it trains. Finally, chapter 6 presents an overview and evaluation of the work.
" }, { "name": "Blandino, John Joseph", "degree": "PhD", "year": "2001", "title": "Application of Diamond Films to Electric Propulsion: Low Energy Sputter Yield Measurement and MPD Plasma Assisted Chemical Vapor Deposition", "advisor": "Goodwin, David G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252005-143838", "creators": [ { "name": { "family": "Blandino", "given": "John Joseph" }, "id": "Blandino-John-Joseph", "display_name": "Blandino, John Joseph" } ], "advisors": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "display_name": "Goodwin, David G." } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Capelli", "given": "Mark" }, "id": "Capelli-M", "role": "member", "display_name": "Capelli, Mark" }, { "name": { "family": "Brophy", "given": "John R." }, "id": "Brophy-J-R", "role": "member", "display_name": "Brophy, John R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/270K-TR61", "abstract": "Progress made in the area of chemically vapor deposited (CVD) diamond films has led to its consideration for a number of novel applications. One potential application under evaluation at the Jet Propulsion Laboratory involves the use of diamond films as coatings for ion thruster electrodes which are subject to sputter erosion. In order to assess their benefit in mitigating sputter erosion as a failure mode it was necessary to first measure the erosion rate compared with molybdenum and carbon-carbon when subjected to ion bombardment.
\r\n\r\nSputter yields were measured for polycrystalline diamond, single crystal diamond, a carbon-carbon composite, and molybdenum subject to xenon ion bombardment. The tests were performed using a 3 cm Kaufman ion source to produce incident ions with energy in the range of 150 - 750 eV and a profilometry-based technique to measure the amount of sputtered material. The yields increased monotonically with energy with values ranging from 0.16 atoms/ion at 150 eV to 0.80 at 750 eV for the molybdenum and 0.06 to 0.14 for the carbon-carbon. At 150 eV the yield for both diamond samples was 0.07 and at 750 eV, 0.19 and 0.17 for the CVD and single crystal diamond respectively. In terms of erosion rate, this translates into a factor of 7 - 12 lower erosion rate for diamond compared to molybdenum and at least a factor of 1.5 compared to carbon-carbon.
\r\n\r\nWith the erosion rates established, the remaining effort concentrated on the experimental and analytical investigation of an electromagnetic (magnetoplasmadynamic or NIPD) plasma source for diamond CVD using a mixture of methane and hydrogen. Specific questions to be addressed included identifying the implications of higher velocity, dissociation, and ionization levels than those expected in an electrothermal (arcjet) plasma source. An experimental facility was used in which the process conditions produced were representative of the high temperature, ionization, and dissociation levels one would expect from an MPD in an actual reactor although not the high velocity. Numerous trials were conducted using methane to hydrogen mixture ratios of 1.5 - 3.5 percent by volume, four different methane injector configurations, and substrate biasing at potentials of 25 - 75 V positive with respect to facility ground. These tests were performed at discharge currents of 700 - 950 A at approximately 18 V (12 - 17 kW).
\r\n\r\nCrystalline films were produced with predominantly (110) oriented facets. X-ray diffraction spectroscopy was used to identify at least one unambiguous diamond peak in each sample with numerous films containing metal or metallic carbide impurities. Growth rates of 0.8 to 6.3 [micrometers]/hr were measured. The films all exhibited poor Raman spectra with no well defined peak at 1332 cm\u207b\u00b9 and a broad background possibly due to high background levels of nitrogen, defects, and contamination.
\r\n\r\nThe question of high velocity and high ionization level was investigated analytically using estimated hydrogen MPD plume data from the literature. For conditions expected with an MPD source, Knudsen numbers in the plume are calculated to be approximately 0.1 in the free stream and less than 0.01 (i.e., transition-continuum boundary) in the stagnation boundary layer. The heavy particle static temperature in the plume is expected to be on the order of 10000 K in the core. For Mach numbers in the range 1.0 - 2.0, the stagnation temperature can be expected to reach peak values of over 20000 K. This temperature far exceeds the range of available thermodynamic and transport databases for hydrocarbon mixtures needed to model stagnation boundary layer chemistry and growth rates, so a scaling relation was used to obtain a relative comparison of the atomic hydrogen mole fraction at the substrate for an electrothermal and electromagnetic accelerated plasma source. Because of its higher jet velocity and lower operating pressure, the electromagnetic: source operates in more of a convection dominated regime resulting in a calculated hydrogen mole fraction at the substrate approximately 40 percent higher than that predicted for an electrothermal accelerator.
\r\n\r\nAn energy balance was used to determine an upper bound on the level of electron heating obtainable for a given bias current density. Results show that even for pressures of a few Torr and ionization fractions of 5 - 25 percent, the required current for a few thousand degree increase in electron temperature over the heavy particle gas temperature is on the order of several tens of A/cm\u00b2. From this analysis it is concluded that high plasma conductivity in an MPD plume and electron energy losses through inelastic molecular collisions will preclude the effective use of ohmic heating of the electrons as a means of enhancing electron catalyzed dissociation in the boundary layer.
\r\n\r\nEstimates were made of the optimal residence time for methane decomposition in the plume in order to maximize the flux of methyl radicals and atomic hydrogen to the substrate; two species which have been identified as having a significant role in high rate, high quality diamond synthesis. At pressures of 100 Pa and 333 Pa, which approximate the pressure in the plume and stagnation regions, there is little recombination of the hydrogen even at a temperature of 5000 K which one could expect well into the thermal boundary layer for an MPD stagnation flow. The methyl mole fraction reaches a maximum at a residence time of 1 - 3 [millisec]. Achieving adequate entrainment and mixing of the methane in the hydrogen jet oil such a short time scale is a very difficult challenge.
\r\n\r\nTwo major conclusions of this thesis are: 1) The lower erosion rate measured for CVD diamond as compared with molybdenum makes coating of grid electrodes with CVD diamond a possible option for extending the lifetime of ion thrusters worth further investigation. 2) Based on both the experimental and analytical investigation of the MPD source for diamond deposition, the potential for higher growth rates than those obtainable with more conventional plasma sources is not significant enough to offset the disadvantages associated with contamination of the film due to metal vapor from the high current electrodes and poor entrainment of the carbon precursor gas due to the short, residence time in the plume.
" }, { "name": "Boer, Elizabeth A.", "degree": "PhD", "year": "2001", "title": "Synthesis, Passivation and Charging of Silicon Nanocrystals", "advisor": "Libbrecht, Kenneth George", "url": "https://resolver.caltech.edu/CaltechETD:etd-01132002-032219", "creators": [ { "name": { "family": "Boer", "given": "Elizabeth A." }, "id": "Boer-Elizabeth-A", "display_name": "Boer, Elizabeth A." } ], "advisors": [ { "name": { "family": "Libbrecht", "given": "Kenneth George" }, "id": "Libbrecht-K-G", "orcid": "0000-0002-8744-3298", "role": "advisor", "display_name": "Libbrecht, Kenneth George" } ], "committee": [ { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "chair", "display_name": "Quake, Stephen R." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Libbrecht", "given": "Kenneth George" }, "id": "Libbrecht-K-G", "orcid": "0000-0002-8744-3298", "role": "member", "display_name": "Libbrecht, Kenneth George" }, { "name": { "family": "Crocker", "given": "John C." }, "id": "Crocker-J-C", "role": "member", "display_name": "Crocker, John C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ZB66-SN79", "abstract": "Silicon nanocrystals are intriguing from both a fundamental and an applied physics point of view. The efficient room temperature luminescence exhibited by Si nanocrystals (as compared to bulk silicon) and the apparent size-dependent bandgap of Si nanocrystals are two incompletely explained phenomena. Meanwhile, the applied physicist may take advantage of the optical and electronic properties of small Si structures to build devices not possible with only bulk silicon.
\r\n\r\nIn this thesis, nanocrystal samples produced by aerosol techniques were investigated. The aerosol samples were size-classified in the size range of 2-50 nm with a size variation of 15-20%. Conducting tip atomic force microscopy (AFM) was used to manipulate and investigate the samples' charging characteristics. The AFM was used to inject charge into single Si nanocrystals and to observe the dissipation.
\r\n\r\nThe charging characteristics of samples made by ion implantation and annealing were also explored. An atomic force microscope was used to locally inject, detect and quantify the amount and location of charge in SiO2 films containing Si nanocrystals (size 2-6 nm). By comparison with control samples, charge trapping was shown to be due to nanocrystals and not ion implantation-induced defects in these samples.
\r\n\r\nTwo models were developed for quantitative charge imaging with an atomic force microscope, one appropriate for non-contact mode and the other for intermittent contact (tapping) mode imaging. From the models, estimates of the best charge sensitivity of an unbiased standard AFM cantilever were found to be on the order of a few electrons. The models were used to estimate the amount of charge injected in the charging experiments: in typical experiments, on the order of 60 electrons were injected in an isolated Si nanoparticle, and a few hundred electrons were injected in SiO2 films containing Si nanocrystals.
\r\n\r\nFinally, for optical studies, nanocrystal passivation with hydrogen and SiO2 were briefly investigated using photoluminescence and X-ray photoelectron spectroscopy.
" }, { "name": "Bossuyt, Sven Cecile Rene", "degree": "PhD", "year": "2001", "title": "Microstructure and Crystallization Behavior in Bulk Glass Forming Alloys", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-07022001-164944", "creators": [ { "name": { "family": "Bossuyt", "given": "Sven Cecile Rene" }, "id": "Bossuyt-Sven-Cecile-Rene", "orcid": "0000-0002-9223-735X", "display_name": "Bossuyt, Sven Cecile Rene" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "orcid": "0000-0002-0812-7028", "role": "member", "display_name": "Ustundag, Ersan" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/MHKM-QR74", "abstract": "The solidification microstructure in wedge-shaped castings of Cu-Ni-Ti-Zr glass forming alloys is investigated, while the composition was systematically varied. Near the critical thickness for glass formation, a spatially inhomogeneous dispersion of nanocrystals is observed, where spherical regions contain a much higher density of nanocrystals than the surrounding material. This microstructure is inconsistent with the prevalent theories for crystallization in metallic glasses, which predict a spatially uniform distribution of crystals.
\r\n\r\nThe spatial localization of the nucleation density is attributed to a recalescence instability. Linear stability analysis of the equations for heat flow coupled with crystal nucleation and growth reveals that at low temperature recalescence can occur locally, triggered by a small fluctuation in the early stages of the crystallization process, because in deeply undercooled liquids the nucleation rate increases with temperature. The localized recalescence events and their interaction accelerate crystallization; consequently they are important in determining the glass forming ability as well as the microstructure of these alloys.
\r\n\r\nThe composition dependence of the critical thickness for glass formation, determined from the observed microstructures, and in situ small angle scattering results indicate that the crystallization occurs in several steps, involving competing crystalline phases.
" }, { "name": "Burcsu, Eric Noboru", "degree": "PhD", "year": "2001", "title": "Investigation of Large Strain Actuation in Barium Titanate", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-10232001-192042", "creators": [ { "name": { "family": "Burcsu", "given": "Eric Noboru" }, "id": "Burcsu-Eric-Noboru", "display_name": "Burcsu, Eric Noboru" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "co-chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XT3Y-Z860", "abstract": "Sensors and actuators based on ferroelectric materials have become indispensable in the fields of aerospace, high technology, and medical instruments. Most devices rely on the linear piezoelectric behavior of formulations of PZT which offer high bandwidth, linear actuation but very low strains of around 0.1%. The nonlinear electromechanical behavior of these materials is largely governed by the motion of domains and is highly affected by stress as well as electric field. The recent theories of Shu and Bhattacharya have sought to address some of the issues related to the structure and behavior of these materials at the mesoscale. One result of the theories is the prediction of another mode of actuation in ferroelectric crystals based on a combined electrical and mechanical loading that could result in strains of up to 6%.
\r\n\r\nDescriptions of the phenomenological theories of ferroelectrics are presented including the classical Landau-Ginsburg-Devonshire theory and the more recent theory of Shu and Bhattacharya. Predictions are made, based on the theory, of the electromechanical behavior of ferroelectric crystals that are addressed by the experiments. An experimental setup has been designed to investigate large strain actuation in single crystal ferroelectrics based on combined electrical and mechanical loading. An investigation of the stress dependence of the electrostrictive response has been carried out with in situ observations of the domain patterns under constant compressive stress and variable electric field. Experiments have been performed on initially single domain crystals of barium titanate with (100) and (001) orientation at compressive stresses between 0 and 5 MPa. Global strain and polarization histories have been recorded. The electrostrictive response is shown to be highly dependent on the level of applied stress with a maximum strain of 0.9% measured at a compressive stress of about 2 MPa. An unusual secondary hysteresis has been observed in the polarization signal at high levels of stress that indicates an intermediate structural configuration, possibly the orthorhombic state. Polarized light microscopy has been used to observe the evolution of the domain pattern simultaneously with the strain and polarization measurement. These results are discussed and suggestions for future work are proposed.
" }, { "name": "Cai, Ming", "degree": "PhD", "year": "2001", "title": "Optical Fiber Taper Coupled Glass Microsphere Resonators", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10212010-100027618", "creators": [ { "name": { "family": "Cai", "given": "Ming" }, "id": "Cai-Ming", "display_name": "Cai, Ming" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JB4C-VR78", "abstract": "This thesis studies optical fiber taper coupled dielectric microsphere resonators and their applications. Fundamental properties including ideal coupling and critical coupling in an optical fiber taper to fused silica glass microsphere coupling system is investigated both theoretically and experimentally. A symmetrical dual-taper coupling configuration is proposed to obtain highly efficient power transfer from the taper coupler to the microsphere resonator. Applications as channel add/drop filters and microsphere lasers are also demonstrated.
\r\n\r\nThe physical essence of the fiber taper to silica microsphere is analyzed using a two-dimensional model. The relationship between the coupling strength and the cavity loss is unveiled. Adiabatic tapers and high-quality microspheres are fabricated and used to demonstrate actual coupling systems. Perfect agreement between the experimental results and the theoretical prediction is presented.
\r\n\r\nPower transfer from the taper to a microsphere resonator has been significantly improved by employing a dual-taper symmetrically coupling configuration. Up to -28 dB extinction at the central resonant wavelength has been measured.
\r\n\r\nWe then propose a device application of the taper-sphere-taper structure as a channel add/drop filter in the wavelength division multiplexing systems. For a filter with a bandwidth of 3.8 GHz and a dropping channel isolation of 26 dB, the bit-error-rate measurement shows no power penalty at 2.5 Gbit/s.
\r\n\r\nA 1.5 \u00b5m wavelength single-frequency fiber laser is also demonstrated using a single tapered fiber coupling to a highly doped erbium:ytterbium phosphate glass microsphere. The fiber taper serves the dual purpose of transporting optical pump power into the sphere and extracting the resulting laser emission. As low as 60 \u00b5W pump threshold and fiber-coupled output power as high as 3 \u00b5W with single mode operation are obtained. Imaging of photoluminescence from the sphere at visible wavelengths reveals the pump power is resonantly coupled into semiclassical orbits due to the strong absorption damping in the phosphate glass. A bi-sphere laser system consisting of two microspheres attached to a single fiber taper is also demonstrated.
\r\n\r\nFinally, a novel hybrid fiber taper, made from a combination of a 980 nm single mode fiber and a 1550 nm single mode fiber, is proposed and demonstrated as the microsphere laser coupler. Both the pump wave and laser emission are found to be more efficiently coupled to and from, respectively, the sphere modes. As high as 112 \u00b5W single-frequency laser output power is measured with a differential quantum efficiency of 12%.
" }, { "name": "Chen, Claudine Minnie", "degree": "PhD", "year": "2001", "title": "Polycrystalline Silicon Thin Films for Photovoltaics", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162010-081444511", "creators": [ { "name": { "family": "Chen", "given": "Claudine Minnie" }, "id": "Chen-Claudine-Minnie", "display_name": "Chen, Claudine Minnie" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "orcid": "0000-0002-5293-6252", "role": "member", "display_name": "Haile, Sossina M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/fgh9-ze28", "abstract": "Selective nucleation and solid phase epitaxy offers a low temperature method to fabricate large grain, polycrystalline silicon on foreign substrates. Undoped and highly doped silicon films were nucleated with nickel or indium and annealed at 600\u00b0C. Indium nucleated crystallization proceeded by conventional solid phase epitaxy. Undoped silicon had grain sizes of 1-2 \u00b5m. With doping, although there was enhancement of the growth rate, the grain size did not increase, since the incubation time correspondingly decreased. The exception was the phosphorus-doped silicon that had a maximum grain size of 10 \u00b5m. In nickel-nucleated samples, the amorphous silicon layer fully crystallized before the onset of random nucleation, achieving grain sizes on order of tens of microns. Within each grain, however, were many low angle, sub-grain boundaries that came from the needle-like crystal growth. Epitaxy on these\r\nlayers resulted in strained columnar crystals with dislocations.
\r\n\r\nPositron annihilation spectroscopy (PAS) was used to study vacancies in solid phase crystallized silicon in four doping cases: undoped, B-doped, P-doped, and P and B-doped. Oxygen-vacancy complexes were seen in all samples and phosphorus-vacancy complexes in the P- and P and B-doped samples. Progressive etchback of a subset of the samples was achieved, and a defect concentration on order of 10\u00b9\u2075 cm\u207b\u00b3 was estimated for all samples.
" }, { "name": "Ching, Weng Ki", "degree": "PhD", "year": "2001", "title": "Disinfection by Pulsed Power Discharges", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07252005-142630", "creators": [ { "name": { "family": "Ching", "given": "Weng Ki" }, "id": "Ching-Weng-Ki", "display_name": "Ching, Weng Ki" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Nealson", "given": "Kenneth H." }, "id": "Nealson-K-H", "orcid": "0000-0001-5189-3732", "role": "member", "display_name": "Nealson, Kenneth H." }, { "name": { "family": "Newman", "given": "Dianne K." }, "id": "Newman-D-K", "orcid": "0000-0003-1647-1918", "role": "member", "display_name": "Newman, Dianne K." }, { "name": { "family": "Leadbetter", "given": "Jared R." }, "id": "Leadbetter-J-R", "orcid": "0000-0002-7033-0844", "role": "member", "display_name": "Leadbetter, Jared R." } ], "option_major": [ "envreng" ], "doi": "10.7907/RV3M-0849", "abstract": "We study the disinfection of Escherichia coli in a pulsed power discharge reactor. The pulsed power discharge process is an electrohydraulic phenomenon characterized by a rapid release of electrical energy across a submerged electrode pair.
\r\n\t\r\nThe survival kinetics of pure strains of E. coli suspensions exposed to 5.5 kV, 90 kA electrohydraulic discharges (EHD) is investigated. The probability of survival Pn of a 2 x 10\u2077 E. coli CFU mL\u207b\u00b9 population after 50 consecutive EHD's follows a logit distribution that corresponds to lethal doses of LD\u2085\u2080 = 2.2 and L:D\u2089\u2080 = 10.8 EHDs. Variation of the initial cell concentration produced nearly constant values of LD\u2085\u2080 = 0.9\u00b10.1 in the range 2 x 10\u00b3 \u2264 E. coli/CFU mL\u207b\u00b9 \u2264 2 x 10\u2076. Beyond 10\u2076 CFU mL\u207b\u00b9, the LD\u2085\u2080 values increase exponentially due to nonlinear light absorbance with increasing E. coli concentrations. Qualitatively similar initial cell concentration dependence is observed for survival under low intensity 254 nm irradiation, in contrast with lower values of LD\u2085\u2080 obtained in denser colonies to 20 kHz power ultrasound exposure.
\r\n\r\nThe high intensity (3.3 x 10\u00b9\u2070 W m\u207b\u00b2) ultraviolet radiation emitted by the electrohydraulic discharge is completely suppressed in the presence of less than 100 mg L\u207b\u00b9 2,2'-dihydroxy-4,4'-dimethoxybenzophenone-5,5'-disulfonic acid (BP9), a well-known sunscreen agent. Concentrations of BP9, in the range (0 - 100) mg L\u207b\u00b9, are varied to measure the sterilization kinetics of ~3 x 10\u2077 CFU mL\u207b\u00b9 suspensions to varying degrees of high intensity UV exposure. The slope of the logit plots of E. coli as function of BP9 concentration is consistent with the screening of radiation as the sole lethal agent. Computed values of biologically available light fluences are 5.0 x 10\u00b9\u00b9 photons CFU\u207b\u00b9 for high intensity, high power, pulsed EHD experiments and 6.6 x 10\u2078 photons CFU\u207b\u00b9 for separate low power continuous UV experiments. The net availability of 3 orders of magnitude more photons during high intensity UV exposure suggests the possibility of a multiphotonic disinfection mechanism at play in the EHD process relative to low intensity case.
\r\n\r\nThe overall resistance to long term exposure to EHD is also investigated. Selective pressure experiments with E. coli exposed to 11 cycles of 50 consecutive EHDs each show a weak kinetic change in the dose-response curves reflected in the nearly constant values of LD\u2085\u2080 - 0.24 \u00b1 0.03. A greater than 98% metabolic similarity in carbon source consumption between initial and final E. coli populations are enzymatically related. In addition, the results indicate that no bacterial contaminants are propagated throughout the experiment.
" }, { "name": "Chow, Benjamin Bin", "degree": "PhD", "year": "2001", "title": "Application of dynamic fracture mechanics to the investigation of catastrophic failure in aircraft structures", "advisor": "Rosakis, Ares J.; Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-08112005-103246", "creators": [ { "name": { "family": "Chow", "given": "Benjamin Bin" }, "id": "Chow-B-B", "display_name": "Chow, Benjamin Bin" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/745f-mb29", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA dynamic fracture mechanics approach to the estimation of the residual strength of aircraft structures is presented. The dependence of the dynamic crack initiation toughness of aluminum 2024-T3 on loading rate is first studied experimentally. A drop of up to 40% in the value of dynamic initiation toughness, [...], is discovered for loading rates in the range of [...]. This range of loading rate corresponds to the typical rates found in an aircraft fuselage experiencing explosive loading conditions. A dramatic increase in the value of dynamic crack initiation toughness is also found for loading rates above [...]. Based on these results and on established dynamic fracture mechanic concepts, a fracture mechanics based failure model is established and is used to estimate the residual strength of aircraft structures.\r\n\r\nA methodology to determine residual strength of dynamically loaded structures based on global structural analysis coupled with local finite element analysis is introduced. Local finite element calculations were performed for different loading rates, [...], ranging from [...] to [...], to simulate the conditions encountered in an explosively loaded aircraft fuselage. Simulations were conducted at a number of loading rates for the following cases of relevance to aircraft fuselage: (i) center cracked panels, (ii) rivet holes with wing cracks, (iii) biaxially loaded panels and (iv) panels prestressed to simulate pressurization. The results from the analyses were then used in conjunction with the experimental results for the dynamic fracture toughness of a 2024-T3 aluminum alloy as a function of loading rate, [...], to determine the time to failure, [...], for a given loading rate. A failure envelope, [...], based on the failure model and finite element analysis, is presented for the different cases and the implications for the residual strength of aircraft structures is discussed.\r\n\r\nMixed mode dynamic crack initiation in aluminum 2024-T3 alloy is investigated by combining experiments with numerical simulations. Pre-fatigued single edge notched specimens and three point bend specimens are subjected to dynamic symmetric and asymmetric loading to generate a range of mode mixity at the cracktip. The optical technique of coherent gradient sensing (CGS) and a strain gage method are employed to study the evolution of the mixed mode stress intensity factors. The dynamic mixed mode failure envelope is obtained using the crack initiation data from the experiments at a nominal loading rate of [...] and is compared with the static counterpart for 2024-T3 aluminum alloy. The fracture surfaces near the crack initiation site are investigated using a scanning electron microscope and reveal ductile void growth and coalescence. Numerical simulations of the experiments are conducted to both help in designing the experiments and to validate the results of the experiments. The numerical simulations show good correlation with the experimental results." }, { "name": "Cocker, David Rea", "degree": "PhD", "year": "2001", "title": "Chamber investigations of secondary organic aerosol formation", "advisor": "Seinfeld, John H.; Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232007-072920", "creators": [ { "name": { "family": "Cocker", "given": "David Rea" }, "id": "Cocker-D-R", "orcid": "0000-0002-0586-0769", "display_name": "Cocker, David Rea" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/22w2-vk68", "abstract": "Hydrocarbons in the atmosphere undergo oxidation that can lead to the formation of semi-volatile products. These products undergo gas-to-particle conversion to form secondary organic aerosol (SOA). Reaction chambers provide a controlled environment which gas-to-particle conversion is investigated. First, an extensive investigation into the aerosol forming potential of 14 biogenic hydrocarbons is reported.\r\n\r\nTraditionally, chamber experiments have been performed at relative humidity levels such that the aerosol investigated is water-free. However, atmospheric conditions are typically such that ambient aerosol contains water. A new facility to improve measurement of SOA formation under humid conditions is described. A comprehensive study on how the presence of water affects gas-to-particle partitioning in the alpha-pinene ozonolysis and m-xylene and mesitylene photooxidation systems is reported.\r\n\r\nThe diurnal trends in the hygroscopic nature of Pasadena, CA, aerosol is reported for late summer, 1999. Presented are additional investigations into the identification of products resulting from ozonolysis of alpha-pinene, beta-pinene, sabinene, Delta^3-carene, and cyclohexene. A field campaign to identify similar monoterpene oxidation products in a forest environment is presented. Finally, an estimate of the global aerosol burden from biogenic hydrocarbons is provided." }, { "name": "Coker, Demirkan", "degree": "PhD", "year": "2001", "title": "Dynamic Initiation and Propagation of Cracks in Unidirectional Composite Plates", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112010-152127073", "creators": [ { "name": { "family": "Coker", "given": "Demirkan" }, "id": "Coker-Demirkan", "orcid": "0000-0001-7385-7089", "display_name": "Coker, Demirkan" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/yrm2-4b88", "abstract": "Dynamic crack growth along weak planes is a significant mode of failure in composites and other layered/sandwiched structures and is also the principal mechanism of shallow crustal earthquakes. In order to shed light on this phenomenon dynamic crack initiation and propagation characteristics of a model fiber-reinforced unidirectional graphite/epoxy composite plate was investigated experimentally. Dynamic fracture experiments were conducted by subjecting the composite plates to in-plane, symmetric and asymmetric, impact loading. The lateral shearing interferometric technique of coherent gradient sensing (CGS) in conjunction with high-speed photography was used to visualize the failure process in real time. It was found that mode-I cracks propagated subsonically with crack speeds increasing to the neighborhood of the Rayleigh wave speed of the composite. Also in mode-I, the dependence of the dynamic initiation fracture toughness on the loading rate was determined and was found to be constant for low loading rates and to increase rapidly above K̇dI > 10\u2075. The dynamic crack propagation toughness, KID, was observed to decrease with crack tip speed up to the Rayleigh wave speed of the composite.
\r\n\r\nFor asymmetric, mode-II, types of loading the results revealed highly unstable and intersonic shear-dominated crack growth along the fibers. These cracks propagated with unprecedented speeds reaching 7400 m/s which is the dilatational wave speed of the composite along the fibers. For intersonic crack growth, the interferograms featured a shock wave structure typical of disturbances traveling with speeds higher than one of the characteristic wave speeds in the solid. In addition high speed thermographic measurements are conducted that show concentrated hot spots behind the crack tip indicating non-uniform crack face frictional contact. In addition, shear dominated dynamic crack growth is investigated along composite/Homalite interfaces subjected to impact loading. The crack growth phenomenon was observed usivvvvng dynamic photoelasticity in conjunction with high-speed photography. Three quantized intersonic and supersonic crack tip speed regimes were identified. First conclusive evidence of crack growth at supersonic speeds with respect to lower speed material and sonic speeds with respect to the unidirectional composite was obtained. Furthermore, this investigation documents the first experimental observation of a mother/daughter crack mechanism allowing a subsonic crack to evolve into an intersonic crack.
\r\n\r\n" }, { "name": "Dubowski, Yael", "degree": "PhD", "year": "2001", "title": "Photochemical transformations in ice: implications for the fate of chemical species", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262010-092147677", "creators": [ { "name": { "family": "Dubowski", "given": "Yael" }, "id": "Dubowski-Y", "display_name": "Dubowski, Yael" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/e57f-dj36", "abstract": "Post-depositional photochemical alterations in snowpacks and sea ice may affect the chemical records in polar caps and the chemistry of the polar atmospheric boundary layer. Although it is known that UV-induced photochemistry actually occurs in ice matrices, quantitative information on such processes is still lacking. With new methods for determining the light absorption by chromophores embedded in packed ice, this study investigates the rates and products of the photodegradation of 4-nitrophenol and nitrate in ice. \r\n\r\nA quantum yield (\u03a6_(ice)) of (2.3 \u00b1 0.4) x 10^(-4) was obtained for the photochemical degradation of 4-nitrophenol over the wavelength range of 300 to 370 nm in ice pellets (pH 5.6). Five reaction products were positively identified: hydroquinone, benzoquinone, 4-nitrosophenol, nitrate, and nitrite. Indirect evidence suggests the formation of organic polymers. These results are similar to those found for 4-nitrophenol photolysis in aqueous solutions, indicating that comparable mechanisms operate in both phases. \r\n\r\nUpon irradiation (\u03bb = 313 \u00b1 15 nm) of NO_3^- doped ice layers, the formation of NO_2(g) and NO_2^- was observed. The yield for both products increased with temperature over the range 248 - 268 K; with values of \u03a6_(NO_2-) ~ (4.8 \u00b1 1.5) x 10^(-3) and \u03a6'(NO_2) (1.2 \u00b1 0.9) x 10^(-3) at 263 K, 10 mM KNO_3. The formation of NO_2^- during the photolysis of NO_3^- in ice pellets has apparent activation energy, E_a, of 5.8 kcal mole^(-1). This E_a is similar to the water cage-effect for supercooled water. \u03a6_(NO_2) showed a much stronger temperature dependence (E_a ~ 10 kcal mole^(-1)); This can be interpreted as the probability of the product NO_2 escaping into the gas-phase, before it is photolyzed into NO. \r\n\r\nThese results suggest that, under our experimental conditions, the photochemical transformations occur within the quasi-liquid layer, which behaves as a supercooled solution. \r\n\r\nThe experimental data for \u03a6'_(NO_2), coupled with snow absorptivity data, lead to a predicted NO_2 fluxes in reasonable agreement with recent measurements in Antarctic snow under solar illumination. NO_3^- photolysis within snowpacks may also be a significant source for OH radicals, which may further react and cause chemical changes in important species, such as H_2O_2 and H_2CO and CH_3CHO.\r\n" }, { "name": "Duchemin, Olivier Bernard", "degree": "PhD", "year": "2001", "title": "An investigation of ion engine erosion by low energy sputtering", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242002-122344", "creators": [ { "name": { "family": "Duchemin", "given": "Olivier Bernard" }, "id": "Duchemin-O-B", "display_name": "Duchemin, Olivier Bernard" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "co-chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Polk", "given": "James E." }, "id": "Polk-J-E", "role": "member", "display_name": "Polk, James E." }, { "name": { "family": "Brophy", "given": "John R." }, "id": "Brophy-J-R", "role": "member", "display_name": "Brophy, John R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K408-J123", "abstract": "Unlike chemical propulsion systems, which are fundamentally limited in performance by propellant energy density, electric propulsion devices, such as ion engines, are limited in iotal deliverable impulse by maximum propellant throughput due to engine wear.\r\n\r\nIn order to perform realistic modeling of engine lifetime, the erosion mechanisms involved must be understood. In particular, the damage---or sputtering---caused by slow ions on solid surfaces is extremely difficult to quantify. We first review the engine failure modes in which sputtering of molybdenum by slow xenon ions plays a critical role. We then present the relevant physical mechanisms, and describe a model for estimating the minimum kinetic energy necessary to dislodge a surface atom.\r\n\r\nOver seventeen analytical approaches to the energy dependence of sputtering have been published in the literature. We implement the four that are most relevant to ion engine erosion processes. In addition, we use the Monte-Carlo simulation program TRIM to calculate sputtering yields. We find, in particular, that the relative sensitivity of sputtering yield to surface binding energy increases dramatically near the sputtering threshold energy. Although the surface binding energy is a (weak) function of temperature, we show that the sputtering yield should not increase significantly at temperatures typical of ion engine operation.\r\n\r\nAn experimental approach to the measurement of low energy sputtering yields is implemented and validated. Based on the Quartz Crystal Microbalance (QCM) technique, this method takes advantage of the differential mass sensitivity exhibited by the piezoelectric quartz resonator used in this study. Because of the importance of surface contamination in low energy sputtering, a surface kinetics model is presented to describe a surface under the simultaneous cleaning effect of ion bombardment, and background gas flow contamination.\r\n\r\nA special case of simultaneous surface contamination and erosion occurs during engine ground testing, where carbon is backsputtered on the accelerator grid from the facility. We describe experiments to measure ion-induced desorption cross-sections for carbon on molybdenum, before concluding that the protective effect of the carbon contamination is unlikely to significantly affect engine erosion, so that ground testing results are applicable to space operations" }, { "name": "Duttweiler, Mark Edward", "degree": "PhD", "year": "2001", "title": "Surge Instability on a Cavitating Propeller", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-112838", "creators": [ { "name": { "family": "Duttweiler", "given": "Mark Edward" }, "id": "Duttweiler-Mark-Edward", "display_name": "Duttweiler, Mark Edward" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/07RB-NX02", "abstract": "The present study details results from experiments investigating a surge instability on a cavitating propeller. Initially, the stable behavior of the propeller is explored, and the nature and extent of the cavitation is documented at various experimental conditions, including propeller yaw. The cavitation surge instability is first explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Particular note is made of similarities between the behavior of the re-entrant jets and that noted by other investigators. It is also observed that the nature of the instability is closely related to the partial cavity instability observed on single, two-dimensional hydrofoils.
\r\n\r\nThe flow conditions that lead to instability are determined and it is shown that onset corresponds to a specific configuration of attached cavity lengths on an individual propeller blade. Pressure measurements are obtained from transducers within the experimental facility, and the acoustic signature of the instability is identified. The magnitude of the fluctuating pressures is very large, presumably capable of producing severe hull vibration. A simple model is developed based on cavity volume estimates obtained from high speed video footage, and the predictions of the model are compared with the experimentally obtained pressures.
\r\n\r\nTo assess the significance of the surrounding facility in initiating and sustaining the instability, a model is developed for the experimental facility dynamics. The predictions of this model are then compared with an experimentally determined facility response to a volumetric excitation imposed by an oscillating piston. To quantify the response of the cavitation to fluctuations in test section conditions, quasistatic estimates are obtained for the cavitation compliance and mass flow gain factor of the propeller. These parameters have previously been employed in developing system transfer functions for cavitating pumps.
\r\n\r\nFinally, a model is developed for the complete system, incorporating both the cavitation and facility dynamics. The model predicts active system dynamics and therefore potentially unstable behavior for two distinct frequency ranges, and one such range is hypothesized to correspond to the observed instability. The ability of the model to predict the observed characteristics of the instability is then evaluated.
" }, { "name": "Eckett, Christopher Adam", "degree": "PhD", "year": "2001", "title": "Numerical and Analytical Studies of the Dynamics of Gaseous Detonations", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-143255", "creators": [ { "name": { "family": "Eckett", "given": "Christopher Adam" }, "id": "Eckett-Christopher-Adam", "display_name": "Eckett, Christopher Adam" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/83ME-8076", "abstract": "This thesis examines two dynamic parameters of gaseous detonations, critical energy and cell size. The first part is concerned with the direct initiation of gaseous detonations by a blast wave and the associated critical energy. Numerical simulations of the spherically symmetric direct initiation event with a simple chemical reaction model are presented. Local analysis of the computed unsteady reaction zone structure identities a competition between heat release rate, front curvature and unsteadiness. The primary failure mechanism is found to be unsteadiness in the induction zone arising from the deceleration of the shock front. On this basis, simplifying assumptions are applied to the governing equations, permitting solution of an analytical model for the critical shock decay rate. The local analysis is validated by integration of reaction zone structure equations with detailed chemical kinetics and prescribed unsteadiness. The model is then applied to the global initiation problem to produce an analytical equation for the critical energy. Unlike previous phenomenological models, this equation is not dependent on other experimentally determined parameters. For different fuel-oxidizer mixtures, it is found to give agreement with experimental data to within an order of magnitude. The second part of the thesis is concerned with the development of improved reaction models for accurate quantitative simulations of detonation cell size and cellular structure. The mechanism reduction method of Intrinsic Low-Dimensional Manifolds, originally developed for flame calculations, is shown to be a viable option for detonation simulations when coupled with a separate model in the induction zone. The agreement with detailed chemistry calculations of constant volume reactions and one-dimensional steady detonations is almost perfect, a substantial improvement on previous models. The method is applied to a two-dimensional simulation of a cellular detonation in hydrogen-oxygen-argon. The results agree well with an earlier detailed chemistry calculation and experimental data. The computational time is reduced by a factor of 15 compared with a detailed chemistry simulation." }, { "name": "Fain, Daniel Cark", "degree": "PhD", "year": "2001", "title": "Kinematic Measurement and Feature Sets for Automatic Speech Recognition", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11192010-074900476", "creators": [ { "name": { "family": "Fain", "given": "Daniel Cark" }, "id": "Fain-D-C", "display_name": "Fain, Daniel Cark" } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cns" ], "doi": "10.7907/9vse-8c78", "abstract": "This thesis examines the use of measured and inferred kinematic information in automatic speech recognition and lipreading, and investigates the relative information content and recognition performance of vowels and consonants. The kinematic information describes the motions of the organs of speech-the articulators. The contributions of this thesis include a new device and set of algorithms\r\nfor lipreading (their design, construction, implementation, and testing); incorporation of direct articulator-position measurements into a speech recognizer; and reevaluation of some assumptions regarding vowels and consonants.\r\nThe motivation for including articulatory information is to improve modeling of coarticulation\r\nand reconcile multiple input modalities for lipreading. Coarticulation, a ubiquitous phenomenon, is the process by which speech sounds are modified by preceding and following sounds.\r\nTo be useful in practice, a recognizer will have to infer articulatory information from sound, video, or both. Previous work made progress towards recovery of articulation from sound. The present project assumes that such recovery is possible; it examines the advantage of joint acousticarticulatory representations over acoustic-only. Also reported is an approach to recovery from video in which camera placement (side view, head-mounted) and lighting are chosen to robustly obtain\r\nlip-motion information.\r\nJoint acoustic-articulatory recognition experiments were performed using the University of Wisconsin X-ray Microbeam Speech Production Database. Speaker-dependent monophone recognizers, based on hidden Markov models, were tested on paragraphs each lasting about 20 seconds. Results\r\nwere evaluated at the phone level and tabulated by several classes (vowel, stop, and fricative). Measured articulator coordinates were transformed by principal components analysis, and velocity and acceleration were appended. Concatenating the transformed articulatory information to a standard acoustic (cepstral) representation reduced the error rate by 7.4 %), demonstrating across-speaker\r\nstatistical significance (p = 0.018). Articulation improved recognition of male speakers more than female, and recognition of vowels more than fricatives or stops.\r\nThe analysis of vowels, stops, and fricatives included both the articulatory recognizer of chapter 3 and other recognizers for comparison. The information content of the different classes was also estimated. Previous assumptions about recognition performance are false, and findings of information content require consonants to be defined to include vowel-like sounds." }, { "name": "Fan, Chenggong Charles", "degree": "PhD", "year": "2001", "title": "Fault-tolerant cluster of networking elements", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152001-144501", "creators": [ { "name": { "family": "Fan", "given": "Chenggong Charles" }, "id": "Fan-C-C", "display_name": "Fan, Chenggong Charles" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "member", "display_name": "DeHon, Andre" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/R15B-VD58", "abstract": "The explosive growth of the Internet demands higher reliability and performance than what the current networking infrastructure can provide. This dissertation explores novel architectures and protocols that provide a methodology for grouping together multiple networking elements, such as routers, gateways, and switches, to create a more reliable and performant distributed networking system. Clustering of networking elements is a novel concept that requires the invention of distributed computing protocols that facilitate efficient and robust support of networking protocols. We introduce the Raincore protocol architecture that achieves these goals by bridging the fields of computer networks and distributed systems.\nIn designing Raincore, we paid special attention to the unique requirements from the networking environment. First, networking clusters need to scale up the networking throughput in addition to the scaling up of computing power. Second, task switching between the different services supported by a networking element has a major negative impact on performance. Third, fast fail-over time is critical for maintaining network connections in the event of failures. We discuss in depth the design of Raincore Group Communication Manager that addresses the forgoing requirements and provides group membership management and reliable multicast transport. It is based on a novel token-ring protocol. We prove that this protocol is formally correct, namely, it satisfies the set of formal specifications that defines the Group Membership problem. \nThe creation of Raincore has already made a substantial impact both at Caltech and the academic community as well as in the industry. The first application is SNOW, a scalable web server cluster that is part of RAIN, a collaborative project between Caltech and JPL/NASA. The second application is RainWall, a commercial solution created by Rainfinity, a Caltech spin-off company, that provides the first fault-tolerant and scalable firewall cluster. These applications exhibit the fast fail-over response, low overhead, and near-linear scalability of the Raincore protocols.\nIn addition, we studied fault-tolerant networking architectures. In particular, we considered efficient constructions of extra-stage fault-tolerant Multistage Interconnection Networks. Multistage Interconnection Networks provide a way to construct a larger switching network using smaller switching elements. We discovered an optimal family of constructions, in the sense that it requires the least number of extra components to tolerate multiple switching element failures. We prove that this is the only family of constructions that has this optimal fault-tolerance property. \n" }, { "name": "Giammar, Daniel", "degree": "PhD", "year": "2001", "title": "Geochemistry of uranium at mineral-water interfaces: rates of sorption-desorption and dissolution-precipitation reactions", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212002-125705", "creators": [ { "name": { "family": "Giammar", "given": "Daniel" }, "id": "Giammar-D", "display_name": "Giammar, Daniel" } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "chair", "display_name": "Hering, Janet G." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/EJ9E-XW58", "abstract": "The extraction and processing of uranium for use in the nuclear weapons program and in commercial nuclear energy has led to extensive contamination of the environment. Migration of uranium is also a concern for the proposed long-term nuclear waste disposal in geologic repositories. Reactions occurring at mineral surfaces significantly affect the mobility of uranium in the environment. Both the equilibrium and kinetics of reactions at mineral surfaces must be understood in order to predict the extent of reactions on time scales pertinent to human exposure. Such information is needed to establish input parameters for reactive transport models and to design remediation technologies.\n\nRates of uranium sorption on mineral surfaces and the dissolution of uranium-containing minerals have been investigated. Rates of sorption onto and desorption from goethite, an important environmental sorbent, were determined by measuring the responses of goethite suspensions (pre-equilibrated with or without uranium) to perturbations of the solution chemistry. Dissolution rates were measured for a set of laboratory-synthesized minerals: the uranyl oxide hydrate schoepite, the uranyl silicate soddyite, and a uranyl phosphate phase. These minerals have been observed in contaminated environments and are produced during the corrosion of spent nuclear fuel. Mineral dissolution and transformation were monitored in batch reactors, while dissolution rates were quantified in flow-through reactors. In both sorption and dissolution-precipitation studies, measurements of bulk solution chemistry were integrated with solid phase characterization.\n\nWhile sorption processes were rapid, dissolution and surface-precipitation reactions occurred more slowly. Adsorption and desorption reactions of uranium onto or from goethite reached greater than 50% completion within minutes and completion on a time-scale of hours. In some uranium-goethite suspensions, a meta-stable sorption state persisted for as long as three weeks before a schoepite-like phase precipitated. Dissolution reactions proceeded at time-scales of hours for schoepite and days to weeks for soddyite and the uranyl phosphate. Common groundwater cations affected dissolution rates and, in several cases, resulted in the precipitation of uranium in secondary phases. In several schoepite and soddyite batch dissolution experiments, uranium ultimately reprecipitated in sodium or cesium uranyl oxide hydrate phases which subsequently controlled the dissolved uranium concentration." }, { "name": "Glade, Stephen Clarke", "degree": "PhD", "year": "2001", "title": "The Cu47Ti34Zr11Ni8 glass-forming alloy : thermophysical properties, crystallization, and the effect of small alloying additions on the thermal stability", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242005-084824", "creators": [ { "name": { "family": "Glade", "given": "Stephen Clarke" }, "id": "Glade-Stephen-Clarke", "display_name": "Glade, Stephen Clarke" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "matsci" ], "doi": "10.7907/4ZJQ-RP66", "abstract": "The thermophysical properties, crystallization, and the effect of small alloying additions on the thermal stability of Cu47Ti34Zr11Ni8 were investigated. The thermophysical properties studied were specific heat capacity and viscosity. From the specific heat capacity data, the differences in the thermodynamic functions between the liquid and the crystalline states of Cu47Ti34Zr11Ni8 were calculated. A lower Gibbs free energy difference between the liquid and the crystalline states generally indicates a better glass-forming ability of an alloy. A lower entropy of fusion indicates a better glass-forming ability as well. The viscosity data, using the strong/fragile classification of glasses, also give a measure of the glass-forming ability of the alloy.\r\n\r\nThe crystallization of amorphous Cu47Ti34Zr11Ni8 was studied with many experimental techniques. Similar to other metallic glass-forming alloys, Cu47Ti34Zr11Ni8 phase separates prior to crystallization. Cu47Ti34Zr11Ni8 decomposes to copper-enriched and titanium-enriched regions (the copper-enriched regions are low in titanium and vice versa). Primary crystallization of Cu47Ti34Zr11Ni8 consists of face centered cubic nanocrystals growing in an amorphous matrix.\r\n\r\nThe glass-forming ability of certain metallic glass-forming alloys has been improved with small silicon additions, which has been attributed to silicon destabilizing oxide nucleation sites. To investigate this further, a study of the effect of silicon on the crystallization of Cu47Ti34Zr11Ni8 was performed. Prior to crystallization, both Cu47Ti34Zr11Ni8 and Cu47Ti33Zr11Ni8Si1 phase separate to copper-enriched and titanium-enriched regions. A face centered cubic phase then nucleates and grows in both alloys. No change in the local composition around a silicon atom in Cu47Ti33Zr11Ni8Si1 was detected.\r\n\r\nSmall additions of magnesium and germanium were added to Cu47Ti34Zr11Ni8 to observe the effect on the thermal stability of the alloy. In contrast to the results observed with silicon, no improvement in the glass-forming ability was observed. However, there was an improvement in the thermal stability of the alloy against crystallization in the supercooled liquid regime with both the magnesium and germanium additions." }, { "name": "Good, Nathan Ray", "degree": "PhD", "year": "2001", "title": "The Influence of Texture on the Magnetoelastic Properties of Polycrystalline TbDy Alloys", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10152010-111044693", "creators": [ { "name": { "family": "Good", "given": "Nathan Ray" }, "id": "Good-Nathan-Ray", "display_name": "Good, Nathan Ray" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Crocker", "given": "John C." }, "id": "Crocker-J-C", "role": "member", "display_name": "Crocker, John C." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/nh91-2f05", "abstract": "An investigation into the influence of texture on the magneto elastic properties of cold-rolled polycrystalline terbium-dysprosium alloys has been performed. Significant influence of grain orientations on the thermal expansion, magnetostrictive and magnetomechanical damping properties of TbDy were observed.
\r\n\r\nDrop cast ingots of TbDy alloys were deformed by cold-rolling and annealing with the aim of reorienting grains for large magnetostrictive strains and damping capacities. Thermal expansion coefficients of single crystal and polycrystalline samples of TbDy were measured from 77 - 570 K. These measurements confirmed the expected strong reorientation of the c-axes of grains toward the direction of applied force during deformation. The anisotropy of thermal expansion between the rolling and applied stress directions provided a measure of the effectiveness of various sample preparations for maximizing magnetocrystalline anisotropy. Furthermore, the effects of magnetic phase transitions on thermal expansion through the Curie and N eel points of TbDy revealed thermal expansion anisotropy between grain orientations in the rolling and transverse directions of deformation.\r\nMagnetostrictive strains along the rolling direction of polycrystalline TbDy alloys were measured at 77 K. Saturation magnetostriction of up to 55% of previous single crystal results were observed. Minimal applied stress was required to obtain near maximum magnetostrictions for all of the samples tested. This suggests a preloading mechanism within the grain structure of polycrystalline TbDy not present in single crystals. Also in contrast with single crystal measurements, the performance of more economical commercial purity (99.7%) samples was seen to be somewhat higher than similarly prepared high purity (99.94%) samples. Resistance to deterioration of performance over multiple cycles was observed, as changes in magnetostriction over 150 cycles at 0.1 Hz were within measurement errors. By comparing thermal expansion anisotropy of TbDy samples with peak magnetostrictive strain, a clear proportionality between texture and magnetostrictive performance was established. Deviations from this pattern by samples with more deformation and annealing suggest microstructural mechanisms beyond average grain orientation impacting magnetostriction.
\r\n\r\nMagnetomechanical damping effects were observed for polycrystalline TbDy samples through compression stress-strain curves. Elastic moduli at 77 K was measured to be up to 80% less than at 300 K, with a large hysteresis present in the stress-strain curves of all samples tested below the Curie point. Damping capacity was measured as the stress-strain hysteresis loop divided by the total area under the stress-strain curve. Damping capacities up to 23% were measured for polycrystalline TbDy alloys. Larger magnetomechanical damping was observed at lower strains, with higher strains corresponded to saturation of magnetic domain realignment, smaller damping capacities and larger elastic moduli. Samples with larger magnetostrictions displayed larger damping capacities over a wide range of applied stresses, and also had consistently lower elastic moduli at 77K.
\r\n\r\nMechanisms of damping were investigated by fitting magnetostriction, elastic modulus and estimated strain of damping saturation of TbDy alloys to a model of magnetomechanical energy dissipation. This model relates magnetomechanical damping to magnetic hysteresis, neglecting microstructural influences not present in magnetostriction data. The damping capacities predicted by this model were approximately an order of magnitude higher than experimental results. This result suggests a prominent role of microstructural interactions in the domain realignments responsible for magnetoelastic damping.
" }, { "name": "Grosjean, Charles", "degree": "PhD", "year": "2001", "title": "Silicone MEMS for fluidics", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162005-105347", "creators": [ { "name": { "family": "Grosjean", "given": "Charles" }, "id": "Grosjean-C", "display_name": "Grosjean, Charles" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/j98f-v013", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn this thesis, silicone rubber was integrated with standard silicon based micromachining processes to allow fabrication of large deflection actuators. Taking advantage of the low Young's modulus and resulting flexibility of silicone rubber, several different devices for fluidic control were demonstrated.\r\n\r\nA novel self-releasing process for defining large actuators on silicon substrates irrespective of backside opening size was developed and used to generate micro balloon actuators used for delta wing control. When deployed near the separation line on the rounded leading edge of a delta wing, significant aerodynamic moments were generated allowing flight control at high angle of attack. To allow more flexibility in spatial actuation, a flexible metal substrate actuator \"skin\" was also developed and tested on flight models. With vertical actuations of 2 mm, rolling moment coefficients up to 0.012 were obtained at high angle of attack, comparable to conventional flaps.\r\n\r\nThe low durometer and flexibility of silicone rubber membranes were exploited to fabricate a peristaltic pump. Taking advantage of the low dead volume and good sealing afforded by membranes combined with form-fitting chambers, a self-priming pump capable of pumping gas and liquid with high particle immunity was demonstrated. Due to the planar nature of the device, it is straightforward to construct integrated systems of reservoirs, channels, valves, and pumps. Standalone operation without an external pneumatic source was achieved using thermopneumatic actuation with air as the working fluid. To achieve low power consumption and reasonable operational frequency, a suspended silicon island heater process was also developed. Flow rates up to 6.3 [...]/min at 291 mW power consumption were achieved with thermopneumatic actuation and flow rates above 100 [...]/min can be easily obtained with external pneumatic operation.\r\n\r\nUsing technology developed for the peristaltic pump, a diaphragm pump topology suitable for complex fluidic systems was developed. By using a plurality of active valves and a single pumping chamber, fluids can be pumped from any input to any output. This can significantly reduce the number of pumps necessary for anything other than the simplest flow system. Using an improved thermopneumatic actuator, integrated flow systems can be constructed." }, { "name": "Guduru, Pradeep Reddy", "degree": "PhD", "year": "2001", "title": "An investigation of dynamic failure events in steels using full field high-speed infrared thermography and high-speed photography", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11052003-085740", "creators": [ { "name": { "family": "Guduru", "given": "Pradeep Reddy" }, "id": "Guduru-P-R", "display_name": "Guduru, Pradeep Reddy" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3w5m-qb27", "abstract": "An infrared (IR) imaging system has been developed recently at Caltech for measuring the temperature increase during the dynamic deformation of materials. The system consists of an 8x8 HgCdTe focal plane array, with 64 parallel preamplifiers. Outputs from the 64 detector/preamplifiers are digitized using a row-parallel scheme. In this approach, all 64 signals are simultaneously acquired and held using a bank of track and hold amplifiers. An array of eight 8:1 multiplexers then routes the signals to eight 10MHz digitizers, acquiring data from each row of detectors in parallel. The maximum rate is one million frames per second.\r\n\r\nCrack tip temperature rise during dynamic deformation is known to alter the fracture mechanisms and consequently the fracture toughness of a material. However, no direct experimental measurements have ever been made to determine the same because of limited diagnostic tools. Further, the temperature rise in the vicinity of the crack tip could potentially be used as a direct measure of loading and could serve as a diagnostic tool in order to extract appropriate fracture parameters. By transcending the existing experimental limitations, this investigation presents detailed, real time evolution of the transient crack tip temperature fields in two different steels (C300 and HY100 steels), using the 2-D high speed IR camera. The crack tip temperature rise at initiation in C300 steel was found to be about 55K. In case of HY100, the crack tip temperature rise was above 90K and was seen to be a strong function of loading rate. HRR elastic-plastic singular field has been used to extract J integral evolution from the measured temperature field. Critical value of J integral at initiation was seen to increase with loading rate.\r\n\r\nAn experimental investigation has been conducted to study the initiation and propagation characteristics of dynamic shear bands in C300 maraging steel. Pre-fatigued single edge notched specimens were impacted on the edge under the notch to produce shear dominated mixed mode stress fields. The optical technique of coherent gradient sensing (CGS) was employed to study the evolution of the mixed mode stress intensity factors. Simultaneously, the newly developed 2-D high speed infrared (IR) camera was employed to obtain the temperature field evolution during the initiation and propagation of the shear bands. A criterion for shear band initiation is proposed in terms of a critical mode II stress intensity factor. The IR images, for the first time, revealed the transition of crack tip plastic zone into a shear band and also captured the structure of the tip of a propagating shear band. These thermographs support the notion of a diffuse shear band tip and reveal \"hot spots\" distributed along the length of a well developed shear band." }, { "name": "Hansen, John Freddy", "degree": "PhD", "year": "2001", "title": "Laboratory simulations of solar prominences", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-08192008-160303", "creators": [ { "name": { "family": "Hansen", "given": "John Freddy" }, "id": "Hansen-J-F", "display_name": "Hansen, John Freddy" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/SACS-CK16", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA solar prominence is a large, arch-shaped structure of magnetized hydrogen plasma protruding from the surface of the sun. From shifts in spectral lines, observers estimate typical prominence temperatures of 4300-8500 K, densities of 10[superscript 16]-10[superscript 17]m[superscript -3], and magnetic fields of 0.4-2 mT. The typical length scale is 10[superscript 7]-10[superscript 8]m. Through careful scaling of terms in the two-fluid electron equation of motion, we have designed an experiment that should reproduce the essential physics of solar prominences. Our experiment has typical temperatures of about 50000 K, densities on the order of 10[superscript 19]m[superscript -3], magnetic fields of 100-500 mT, and a length scale of about 0.1 m. The advantages of having a prominence-like plasma conveniently located in a laboratory, rather than over 100 million kilometers away, include the following:\r\n\r\n\u2022 Observations of the prominence from a vantage point of choice.\r\n\r\n\u2022 Stereographic observation to better discern the three-dimensional shape of the prominence.\r\n\r\n\u2022 In situ measurements of physical properties such as magnetic fields, electric potentials, densities and temperatures.\r\n\r\n\u2022 Control of parameters that govern the creation and evolution of the prominence.\r\n\r\nThe topology and dynamics of solar prominences have been of great interest for several decades. While intrinsically interesting, solar prominences are also believed to produce magnetic clouds which can destroy sensitive spacecraft electronics or cause costly damage to power-grid components when passing by Earth. Thus, it is important to better understand the physical phenomena behind these events.\r\n\r\nOur experimental solar device is mounted on a large vacuum chamber. The solar device consists of a horseshoe magnet that provides a bias magnetic field from one prominence footpoint to the other. A gas valve injects hydrogen at the footpoints. As the hydrogen expands into the vacuum chamber, a high-voltage capacitor is connected between the two footpoints. The high voltage breaks down the hydrogen gas. The plasma forms along the arching magnetic field lines of the horseshoe magnet. The laboratory prominence is much smaller (footpoint distance 0.1 m) than the vacuum chamber (1.4 m diameter, 2 m long) so that one vacuum chamber wall acts as the solar surface while the other walls are too far away to influence the experiment.\r\n\r\nStill photographs obtained from two high-speed cameras in a stereographic configuration have been combined to make three-dimensional movies of the evolution of the plasma. The plasmas resemble actual solar prominences, and evolve in a reproducible sequence through three stages. First, initial breakdown forms a main current channel consisting of several bright and dark strands of plasma. Second, as helicity is injected by ramping up the current flowing through the plasma from one footpoint to the other, the strands twist around each other. Third, the entire plasma takes on a helical structure and expands outward. The three-dimensional structure of the plasma has a handedness consistent with the sign of the injected helicity. Photographs taken from a top view show S-shaped and reverse S-shaped plasmas for the two different polarities of the horseshoe magnetic field, in accordance with observations of sigmoids on the southern and northern hemispheres of the Sun.\r\n \r\nWe have investigated plasma behavior using various boundary conditions and demonstrated several phenomena of importance to solar prominences. First, prominence eruption has been slowed or completely inhibited by a vacuum arcade field, or strapping field. It has been conjectured that the eruption of a solar prominence can be inhibited if a much larger scale, arched magnetic field straddles the prominence and effectively straps it down. We found that it is neither magnetic pressure nor magnetic field line tension in the strapping field that inhibits prominence eruption, as predicted in earlier models. Rather it is a J x B- force between the current in the prominence and the strapping field. The strapping field magnitude required to completely inhibit prominence eruption is in good agreement with a theoretical model which takes into account the full three-dimensional magnetic topology.\r\n\r\nSecond, the interaction between two side-by-side prominences of equal or opposite helicity has been studied. In the co-helicity case, helicity is transferred from one prominence to the other, increasing the instability of the receiving prominence. In the counterhelicity case, there is evidence of reconnection and magnetic flux destruction causing increased instability in both prominences. X-ray production is larger by an order of magnitude in the counter-helicity case than in the co-helicity case.\r\n\r\nThird, aspects of prominence shapes are explained by the force-free state equation [...]. This supports the suggestion that solar prominences are in Woltjer-Taylor states.\r\n" }, { "name": "Hightower, Adrian", "degree": "PhD", "year": "2001", "title": "Lithium electronic environments in rechargeable battery electrodes", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11192010-080258624", "creators": [ { "name": { "family": "Hightower", "given": "Adrian" }, "id": "Hightower-A", "display_name": "Hightower, Adrian" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/tb89-6g55", "abstract": "This work investigates the electronic environments of lithium in the electrodes of rechargeable batteries. The use of electron energy-loss spectroscopy (EELS) in conjunction with transmission electron microscopy (TEM) is a novel approach, which when coupled with conventional electrochemical experiments, yield a thorough picture of\r\nthe electrode interior.\r\nRelatively few EELS experiments have been preformed on lithium compounds owing to their reactivity. Experimental techniques were established to minimize sample contamination and control electron beam damage to studied compounds. Lithium hydroxide was found to be the most common product of beam damaged lithium alloys. Under an intense electron beam, halogen atoms desorbed by radiolysis in lithium halides. EELS spectra from a number of standard lithium compounds were obtained in order to identify the variety of spectra encountered in lithium rechargeable battery electrodes. Lithium alloys all displayed characteristically broad Li K-edge spectra, consistent with\r\ntransitions to continuum states. Transitions to bound states were observed in the Li K and oxygen K-edge spectra of lithium oxides. Lithium halides were distinguished by\r\ntheir systematic chemical shift proportional to the anion electronegativity. Good agreement was found with measured lithium halide spectra and electron structure calculations using a selfconsistant multiscattering code.\r\nThe specific electrode environments of LiC_6, LiCoO_2, and Li-SnO were investigated. Contrary to published XPS predictions, lithium in intercalated graphite was determined to be in more metallic than ionic. We present the first experimental evidence of charge compensation by oxygen ions in deintercalated LiCoO_2. Mossbauer studies on cycled Li-SnO reveal severely defective structures on an atomic scale.\r\nMetal hydride systems are presented in the appendices of this thesis. The mechanical alloying of immiscible Fe and Mg powders resulted in single-phase bcc alloys of less than 20 at% Mg. Kinetic studies on LaNi_(5-x)Sn_x alloys proved that the mass transfer of hydrogen through these alloys was not hindered with increasing Sn substitutions for Ni. Collaborations with Energizer\u00a9 found LanNi_(4.7)Sn_(0.3) alloys to possess limited utility in rechargeable nickel-metal-hydride sealed-cell batteries." }, { "name": "Hill, Cory James", "degree": "PhD", "year": "2001", "title": "Investigation of spin injection and optical imaging with scanning probe microscopy techniques", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12172004-153816", "creators": [ { "name": { "family": "Hill", "given": "Cory James" }, "id": "Hill-C-J", "display_name": "Hill, Cory James" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/bvj9-jv02", "abstract": "The work presented in thesis focuses on two important applications of scanning probe microscopy. The first is the attempt at measuring spin-polarized current injection from a ferromagnet into a semiconductor in an ex-situ environment at room temperature. The interface current-voltage characteristics in scanning tunneling microscopy (STM) offer one of the few viable methods that can produce the current densities and contact resistances necessary to surmount the theoretical barriers to this type of spin injection. Surface passivation techniques for the semiconductors used in these experiments are also discussed. Experimental data with different ferromagnetic tips on two types of semiconductors are presented. The results obtained in this and other spin injection experiments are explained with an interfacial equilibrium drift-diffusion theory.\r\n\r\nThe second part focuses on the theory of the generally accepted contrast mechanism in scanning apertureless microscopy (SAM). Simulations are presented of a dipole-dipole interaction model between the tip and sample. These simulations show that the dipole coupling model does indeed predict optical discrimination on the nanometer scale. Simulated images are contrasted with experiment in order to test the validity of the model.\r\n" }, { "name": "Hsieh, Wen Hsuan", "degree": "PhD", "year": "2001", "title": "MEMS thin film teflon electret condenser microphones", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302005-135533", "creators": [ { "name": { "family": "Hsieh", "given": "Wen Hsuan" }, "id": "Hsieh-Wen-Hsuan", "display_name": "Hsieh, Wen Hsuan" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/sk4y-ws65", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe goal of this thesis is to develop miniature, inexpensive, high-quality, self-biasing electret condenser microphones that are fabricated using Micro Electro Mechanical Systems (MEMS) technology. These MEMS electret microphones are to be used in any application where a conventional electret microphone can be used (such as in cell phones, and hearing aids) and in new acoustic sensing applications where current microphone technology cannot be applied (such as in smart cards of the future or in new applications where it is advantageous to integrate microelectronics with the microphone).\r\n\r\nTo accomplish this, a MEMS-compatible Teflon electret technology has been developed. The electret material used is thin film spin-on Teflon AF. A custom-built pulsed electron gun, called the Back-Lighted Thyratron (BLT), is used for charge implantation. Thermal annealing is used to stabilize (age) the implanted charge. An electric field compensation method is used to measure the charge density of the electrets. The electrets obtained have stable charge densities on the order of [...] to [...].\r\n\r\nTwo main types of MEMS thin film Teflon electret condenser microphones have been successfully fabricated and tested. Both microphones use silicon substrates and are fabricated using bulk-micromachining techniques. Each microphone is manufactured as a two piece structure, comprising a microphone membrane unit having an extremely thin diaphragm and a perforated microphone backplate unit. When one is placed on top of the other, the two units form a highly reliable, inexpensive microphone that can produce a signal without the need for external biasing. This reduces system volume and complexity. One type of microphone uses a silicon nitride/Teflon AF composite diaphragm, while the other type uses a Parylene C/Teflon AF composite diaphragm. Both microphones use the same perforated silicon nitride/Parylene C composite backplate.\r\n\r\nBoth types of millimeter-scale electret microphones have very low stray capacitance, are self-biasing, mass producible, arrayable, integratable with on-chip electronics, structurally simple and extremely stable over time in the ordinary environment. The dynamic range is from less than 30 dB to above 110 dB SPL (re. 20 [...]) and the open-circuit sensitivities obtained range from 3.5 - 44 mV/Pa over the frequency range 100 Hz - 13 kHz. The total harmonic distortion of both devices is less than 2% at 110 dB SPL, 1 kHz." }, { "name": "Hsu, Yun", "degree": "PhD", "year": "2001", "title": "Rotordynamic Forces Generated by Annular Leakage Flows in Centrifugal Pumps", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12022010-081219787", "creators": [ { "name": { "family": "Hsu", "given": "Yun" }, "id": "Hsu-Yun", "display_name": "Hsu, Yun" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/fr51-ft92", "abstract": "Fluid-induced rotordynamic forces in pumping machinery are well documented but poorly understood. The present research focuses on the rotordynamics due to fluid flow in annuli, in particular, the discharge-to-suction leakage flow in centrifugal pumps. There are indications that the contribution of the front shroud leakage flow can be of the same order of magnitude as contributions from the nonuniform pressure acting on the impeller discharge. Previous investigations have established some of\r\nthe basic traits of these flows. This work furthers the experimental and computational approach to quantify and predict the shroud contribution to the rotordynamic\r\nstability of pumping machinery.\r\nChilds' bulk flow model for leakage paths is carefully examined, and convective relations for vorticity and total pressure are deduced. This analysis leads to a new\r\nsolution procedure for the bulk flow equations which does not resort to linearization or assumed harmonic forms of the flow variables.\r\nExperimental results presented show the contributions of the inlet swirl velocities\r\nto the rotordynamic forces. Antiswirl devices are evaluated for their effectiveness in reducing instability. Additional tests measuring the pressure distributions and the inlet swirl velocities of the leakage flow confirm some of the predictions by numerical analysis." }, { "name": "Hu, Gang", "degree": "PhD", "year": "2001", "title": "Singularity formation in three-dimensional vortex sheets", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02232011-105921767", "creators": [ { "name": { "family": "Hu", "given": "Gang" }, "id": "Hu-G", "display_name": "Hu, Gang" } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/5mw5-d871", "abstract": "In this thesis, we investigate both theoretically and numerically the singularity formation and long time existence of three-dimensional vortex sheets.\r\n\r\nFor the theoretical work, we divide it into two parts. In the first part, we study the early time singularity formation and the local form of the vortex sheet in the neighborhood of a singularity near the singularity time. We show that under a special set of coordinates, the three-dimensional vortex sheet can be viewed as a two-dimensional vortex sheet along certain space curves. As a result, the study of singularity formation of a three-dimensional vortex sheet can be related to that of the corresponding two-dimensional vortex sheet. And the singular behavior of these two problems is very similar. Moreover, by performing a transformation in the interface variables and deriving leading order asymptotic approximations for the evolution of these transformed variables, we show that the Kelvin-Helmholtz instability is a result of the coupling of two of these three variables to the leading order. This observation simplifies significantly our singularity analysis for three-dimensional vortex sheets and allows us to reveal clearly the nature of the curvature singularity in the three-dimensional vortex sheet equation. In the second part of our theoretical work, we prove the long time existence of the three-dimensional vortex sheet problem for analytic initial conditions near equilibrium. Moreover, the existence time is almost optimal if the initial perturbation over the equilibrium is sufficiently small.\r\n\r\nWe have performed careful numerical study to validate our theoretical results. Well-resolved numerical study of the three-dimensional vortex sheet equation is difficult due to the complexity in evaluating the interface velocity. To alleviate this difficulty, we introduce two model equations. An important feature of these models equations is that they can be expressed in terms of convolution operators and consequently they can be computed efficiently by Fast Fourier Transform. Moreover, we show by asymptotic analysis that these model equations preserve the singularity type of the full equations. Our analysis also suggests that the model equations generate the same local form of curvature singularity near the physical singularity time as that of the full equations. Our detailed numerical computations on the two-dimensional problem show that the model equation captures all the essential singularity behavior of the full vortex sheet equation. Our calculations based on the three-dimensional model equation provide convincing evidences that a curvature singularity develops in finite time in the three-dimensional vortex sheet. And the type of the singularity is of order -1/2 in the mean curvature." }, { "name": "Huang, Ying", "degree": "PhD", "year": "2001", "title": "Scanning Tunneling Microscopy and Digital Image Correlation in Nanomechanics Investigations", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212010-112400412", "creators": [ { "name": { "family": "Huang", "given": "Ying" }, "id": "Huang-Ying", "display_name": "Huang, Ying" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/exy7-5z58", "abstract": "Probe microscopy (scanning tunneling microscopy and atomic force microscopy) and digital image correlation together serve as a potentially powerful tool for experimentally\r\ninvestigating the mechanical behaviors of materials at the sub-micron and nanometer scales. Based on the tunneling effect in quantum physics, the scanning tunneling\r\nmicroscope (STM) records surface topography quantitatively and can achieve angstrom resolution. The digital image correlation (DIC) extracts the displacements and gradients\r\nfrom the undeformed and deformed topographical images.\r\nIn this work, a calibration has been performed on the existing STM built \"in-house\" and the coefficients used in the STM system were confirmed. Major improvements on several\r\ncomponents of the system have been made, including constructing a new actuator probe to decouple its in-plane and out-of-plane movements, designing and implementing a new\r\nfirst-stage amplifier to reduce the noise output by a factor of 10 and modeling of the controller in the STM feedback loop.\r\nFurther, systematic study of the digital image correlation has been conducted. In the simple case of one-dimensional correlation, key parameters involved are the subset size,\r\nvariables in the displacement representation, frequency content of the signal and noise. The one-dimensional study was then extended to two dimensions. In addition to those\r\nkey parameters identified in the one-dimensional study, the sampling rate poses substantial influence on the correlation accuracy. Low amplitude, high frequency noise\r\nstill increases the correlation error significantly." }, { "name": "Hughes, Lara Shane", "degree": "PhD", "year": "2001", "title": "Evolution of atmospheric aerosols along trajectories crossing the Los Angeles basin", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechTHESIS:12022010-095908059", "creators": [ { "name": { "family": "Hughes", "given": "Lara Shane" }, "id": "Hughes-L-S", "display_name": "Hughes, Lara Shane" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/r80f-v702", "abstract": "A primary concern in the regulation, control and monitoring of particulate air pollution is its detrimental effect on human health. One objective of this thesis is to determine the concentration and chemical composition of urban atmospheric fine (diameter < 2.2 \u00b5m) and ultrafine (diameter < 0.1 \u00b5m) particulate matter (PM). Laboratory research into ultrafine particles suggests that these particles may be especially damaging to health. Size-segregated fine PM was collected in Pasadena, California, using micro orifice impactors. Ultrafine particle mass concentrations ranged from 0.88-1.58 \u00b5g m^(-3), small in comparison to fine PM, but ultrafine particle number concentrations in the size range 0.017-0.1 \u00b5m particle diameter were relatively large at 1.3x10^4 \u00b1 8.9x10^3 cm^(-3). This study provides the first detailed data published on urban ultrafine particle chemical composition including organics and elemental carbon, trace metals, and ionic species. Organic compounds were the largest component of ultrafine particle mass.\r\nDevelopment of effective particulate control policies requires a thorough understanding of the chemical and physical processes affecting primary particle emissions as they are transported downwind from emissions sources. Mathematical models which calculate the chemical evolution of airborne particles as they are affected by gas-to-particle conversion processes can provide the needed insight when combined with experimental data on particle evolution at the single particle level. Three field studies were conducted in the Los Angeles area for the purpose of gathering the necessary experimental data by sampling single\r\nair parcels at multiple points along an air parcel trajectory. Cascade impactors, particle size distribution monitors, filter-based PM samplers, and aerosol time-of-\r\nflight mass spectrometry instruments capable of making single-particle size and composition measurements were employed at three urban monitoring sites chosen along typical wind trajectories. The three studies focused on different aspects of particle evolution: particle transformation during transport inland over urban areas from the ocean; evolution of particle populations dominated by motor vehicle emissions from Central Los Angeles; and formation of particulate ammonium nitrate during transport over large ammonia sources. Particle populations\r\ntransported over the Los Angeles area showed depletion and chemical alteration of sea salt particles, addition of fine carbon-containing particles, and secondary aerosol nitrate formation. Measurements made at the single particle\r\nlevel show that particles of the same size can differ substantially in chemical composition and that single particle composition becomes more complex over\r\ntime as particles are transformed through a chemically reactive atmosphere." }, { "name": "Isella, Giorgio Carlo", "degree": "PhD", "year": "2001", "title": "Modeling and Simulation of Combustion Chamber and Propellant Dynamics and Issues in Active Control of Combustion Instabilities", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012006-093758", "creators": [ { "name": { "family": "Isella", "given": "Giorgio Carlo" }, "id": "Isella-Giorgio-Carlo", "display_name": "Isella, Giorgio Carlo" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/k1rf-a525", "abstract": "A method for a comprehensive approach to analysis of the dynamics of an actively controlled combustion chamber, with detailed analysis of the combustion models for the case of a solid rocket propellant, is presented here. The objective is to model the system as interconnected blocks describing the dynamics of the chamber, combustion and control (including sensors and actuators).
\r\n\r\nThe analytical framework for the analysis of the dynamics of a combustion chamber is based on spatial averaging, as introduced by Culick. This method results in the determination of a set of coupled oscillator equations that are then integrated with the appropriate forcing terms deriving from combustion and control.
\r\n\r\nCombustion dynamics are analyzed for the case of a solid propellant. Considerable data exists suggesting that the response functions for many solid propellants tend to have higher values, in some ranges of frequencies, than predicted by the conventional quasi-steady theory. Hence, quasi-steady theory is extended to include the dynamics of the gas-phase and also of a surface layer interposed between the gaseous flame zone and the heated solid phase of the propellant. The models are constructed so that they produce a combustion response function for the solid propellant that can be immediately introduced in the our analytical framework. The principal objective of this analysis is to determine which characteristics of the solid propellant are responsible for the large sensitivity, observed experimentally, of propellant burning response to small variations in the conditions. We show that velocity coupling, and not pressure coupling, has the potential to be the mechanism responsible for that high sensitivity. Some issues related to the modeling of solid propellant are also discussed, namely the importance of particulate modeling and its effect on the global dynamics of the chamber and a revisited interpretation of the intrinsic stability limit for burning of solid propellants.
\r\n\r\nActive control is also considered in the analysis. A critical discussion about the most commonly used control strategies used in combustion allows us to define which are the most promising algorithms to use on future experiments. Particular attention is devoted to the effect of time delay (between sensing and actuation) on the control strategy; several methods to compensate for it are presented and discussed, with numerical examples based on the approximate analysis produced by our framework.
\r\n\r\nExperimental results are presented for the case of a Dump Combustor. The combustor exhibits an unstable burning mode, defined through the measurement of the pressure trace and shadowgraph imaging. The transition between stable and unstable modes of operation is characterized by the presence of hysteresis, also observed in other experimental works, and hence not a special characteristic of this combustor. Control is introduced in the form of pulsed secondary fuel. We show the capability of forcing the transition from unstable to stable burning, hence extending the stable operating regime of the combustor. The transition, characterized by the use of a shadowgraph movie sequence, is attributed to a combined fluid-mechanic and combustion mechanism.
" }, { "name": "Jadbabaie, Ali", "degree": "PhD", "year": "2001", "title": "Receding horizon control of nonlinear systems: a control Lyapunov function approach", "advisor": "Doyle, John Comstock; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262010-112027161", "creators": [ { "name": { "family": "Jadbabaie", "given": "Ali" }, "id": "Jadbabaie-A", "display_name": "Jadbabaie, Ali" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." } ], "option_major": [ "cds" ], "doi": "10.7907/CRHD-3202", "abstract": "With the advent of faster and cheaper computers, optimization based control methodologies have become a viable candidate for control of nonlinear systems. Over the past twenty years, a group of such control schemes have been successfully used in the process control industry where the processes are either intrinsically stable or have very large time constants.
\r\n\r\nThe purpose of this thesis is to provide a theoretical framework for synthesis of a class of optimization based control schemes, known as receding horizon control techniques for nonlinear systems such as unmanned aerial vehicles.
\r\n\r\nIt is well known that unconstrained infinite horizon optimal control may be used to construct a stabilizing controller for a nonlinear system. In this thesis, we show that similar stabilization results may be achieved using unconstrained finite horizon optimal control. The key idea is to approximate the tail of the infinite horizon cost-to-go using, as terminal cost, an appropriate control Lyapunov function (CLF). A CLF can be thought of as generalization of the concept of a Lyapunov function to systems with inputs.
\r\n\r\nRoughly speaking, the terminal CLF should provide an (incremental) upper bound on the cost. In this fashion, important stability characteristics may be retained without the use of terminal constraints such as those employed by a number of other researchers. The absence of constraints allows a significant speedup in computation.
\r\n\r\nFurthermore, it is shown that in order to guarantee stability, it suffices to satisfy an improvement property, thereby relaxing the requirement that truly optimal trajectories be found.
\r\n\r\nWe provide a complete analysis of the stability and region of attraction/operation properties of receding horizon control strategies that utilize finite horizon approximations in the proposed class. It is shown that the guaranteed region of operation contains that of the CLF controller and may be made as large as desired by increasing the optimization horizon (restricted, of course, to the infinite horizon domain). Moreover, it is easily seen that both CLF and infinite horizon optimal control approaches are limiting cases of our receding horizon strategy. The key results are illustrated using a familiar example, the inverted pendulum, as well as models of the Caltech ducted fan at hover and forward flight, where significant improvements in guaranteed region of operation and cost are noted.
\r\n\r\nWe also develop an optimization based scheme for generation of aggressive trajectories for hover and forward flight models of the Caltech ducted fan experiment, using a technique known as trajectory morphing. The main idea behind trajectory morphing is to develop a simplified model of the nonlinear system and solve the trajectory generation problem for that model. The resulting trajectory is then used as a reference in a receding horizon optimization scheme to generate trajectories of the original nonlinear system. Several aggressive trajectories are obtained in this fashion for the forward flight model of the Caltech ducted fan experiment.
" }, { "name": "Jin, Hui", "degree": "PhD", "year": "2001", "title": "Analysis and design of turbo-like codes", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08222001-151244", "creators": [ { "name": { "family": "Jin", "given": "Hui" }, "id": "Jin-Hui", "display_name": "Jin, Hui" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Dolinar", "given": "Samuel J." }, "id": "Dolinar-S-J", "role": "member", "display_name": "Dolinar, Samuel J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/VC95-2C74", "abstract": "50 years after Shannon determined the capacity of memoryless channels, we finally know of practical encoding and decoding algorithms that closely approach this limit. This remarkable feat was first achieved by the invention of turbo codes by Berrou, Glavieux, and Thitimajshima in 1993 cite{BGT93}. Since then turbo codes have essentially revolutionized the coding field and became one of the central research problems in recent years. While there has been a great deal of excellent theoretical work on turbo codes, it is fair to say practice still leads theory by a considerable margin.\r\n \r\nThis thesis endeavors to fill some of that gap. The main body of the thesis concerns coding theorems for general turbo codes. We first prove coding theorems for some simple (yet interesting) serial turbo code ensembles on the AWGN channel. Then we generalize the results for a broader class of turbo-like codes on any memoryless channel. To closely estimate the noise threshold when calculate is feasible, we develop a method based on ``typical pairs decoding'. This method is powerful enough to reproduce Shannon's original coding theorems on any memoryless binary-input symmetric channels. Last we introduce a linearly encodable and decodable code, after carefule design, with performance provably close to Shannon's limit.\r\n \r\nOne main contribution here of both theoretical and practical interests is the introduction of \"repeat-accumulate\" (RA) codes. RA codes are structurally simple enough that a rigorous theoretical analysis is possible, yet random enough that powerful performance under iterative decoding can be obtained. The generalization, irregular RA codes, are shown to be a serious competitor against turbo codes and LDPC codes." }, { "name": "Kim, Choongnyun Paul", "degree": "PhD", "year": "2001", "title": "Ductile phase reinforced bulk metallic glass composites formed by chemical partitioning", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-06022005-144138", "creators": [ { "name": { "family": "Kim", "given": "Choongnyun Paul" }, "id": "Kim-C-P", "display_name": "Kim, Choongnyun Paul" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/fe9w-sc46", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nA new class of ductile metal reinforced bulk metallic glass matrix composite material has been prepared that demonstrates improved mechanical properties. This newly designed material exhibits both improved toughness and large plastic strain to failure. Primary dendrite growth accompanied by solute partitioning in the molten state yields an equilibrium microstructure consisting of a ductile crystalline Ti-Zr-Nb [beta] phase, with the bcc-structure, in a Zr-Ti-Nb-Cu-Ni-Be bulk metallic glass matrix processed via in situ processing. Under mechanical loading, the microstructure imposes constraints on the glassy matrix that leads to the generation of highly organized shear band patterns throughout the sample. This results in a dramatic increase in the plastic strain to failure, impact resistance, and toughness of the metallic glass. This thesis shows how microstructural inhomogeneity can be used to control the initiation and propagation of localized shear bands in metallic glasses under a variety of unconstrained loading conditions. A series of mechanical property tests were conducted on composite materials. These include quasi-static tensile and compression tests, Charpy impact, and three point bend tests on specimens prepared according to ASTM standards. Also, in situ straining transmission electron microscopy (TEM) experiments were performed to study the propagation of the shear bands in the bulk metallic glass based composite.\n" }, { "name": "Koosh, Vincent Frank", "degree": "PhD", "year": "2001", "title": "Analog Computation and Learning in VLSI", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10022001-201911", "creators": [ { "name": { "family": "Koosh", "given": "Vincent Frank" }, "id": "Koosh-Vincent-Frank", "display_name": "Koosh, Vincent Frank" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Diorio", "given": "Christopher J." }, "id": "Diorio-Christopher-J", "role": "member", "display_name": "Diorio, Christopher J." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9B65-TB43", "abstract": "Nature has evolved highly advanced systems capable of performing complex computations, adaptation, and learning using analog components. Although digital systems have significantly surpassed analog systems in terms of performing precise, high speed, mathematical computations, digital systems cannot outperform analog systems in terms of power. Furthermore, nature has evolved techniques to deal with imprecise analog components by using redundancy and massive connectivity. In this thesis, analog VLSI circuits are presented for performing arithmetic functions and for implementing neural networks. These circuits draw on the power of the analog building blocks to perform low power and parallel computations.
\r\n\r\nThe arithmetic function circuits presented are based on MOS transistors operating in the subthreshold region with capacitive dividers as inputs to the gates. Because the inputs to the gates of the transistors are floating, digital switches are used to dynamically reset the charges on the floating gates to perform the computations. Circuits for performing squaring, square root, and multiplication/division are shown. A circuit that performs a vector normalization, based on cascading the preceding circuits, is shown to display the ease with which simpler circuits may be combined to obtain more complicated functions. Test results are shown for all of the circuits.
\r\n\r\nTwo feedforward neural network implementations are also presented. The first uses analog synapses and neurons with a digital serial weight bus. The chip is trained in loop with the computer performing control and weight updates. By training with the chip in the loop, it is possible to learn around circuit offsets. The second neural network also uses a computer for the global control operations, but all of the local operations are performed on chip. The weights are implemented digitally, and counters are used to adjust them. A parallel perturbative weight update algorithm is used. The chip uses multiple, locally generated, pseudorandom bit streams to perturb all of the weights in parallel. If the perturbation causes the error function to decrease, the weight change is kept, otherwise it is discarded. Test results are shown of both networks successfully learning digital functions such as AND and XOR.
" }, { "name": "Koumans, Roger Gerard Matthias", "degree": "PhD", "year": "2001", "title": "Semiconductor mode-locked lasers : modeling, characterization and applications", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-06092005-103556", "creators": [ { "name": { "family": "Koumans", "given": "Roger Gerard Matthias" }, "id": "Koumans-R-G-M", "display_name": "Koumans, Roger Gerard Matthias" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/wx7b-6286", "abstract": "This thesis describes the modeling and characterization of mode-locked semiconductor lasers. An enhanced dynamic model is developed to describe the startup and steadystate behavior of mode-locked lasers. Two new applications for mode-locked lasers are given and their potential is discussed. A new technique to characterize the optical pulses emitted from a mode-locked laser is analyzed and demonstrated.\n\nA combined time and frequency-domain dynamic model is introduced for semiconductor mode-locked lasers. The model includes both linear mode-coupling effects through carrier density modulation at harmonics of the mode-spacing as well as nonlinear effects like gain saturation and additional mode-coupling through four wave mixing. The model is used to study the behavior of a 2 mm long mode-locked semiconductor laser with a gain section of 1900 \u00b5m and an absorber section of 100 \u00b5m. Without the inclusion of spontaneous emission, steady state mode-locking is achieved after a few tens of nanoseconds producing chirped picosecond pulses. The inclusion of spontaneous emission disturbs the steady state mode-locking solution into a quasi-steady state which causes timing and amplitude jitter of the pulse train.\n\nThe potential of a semiconductor mode-locked laser with a dense mode spacing (~25 GHz) as an optical source for wavelength division multiplexing is studied. One of the locked modes is filtered out by a narrow band fiber Bragg grating and its use as a single wavelength source is examined. The bit error rate (BER) performance of the source is measured but no \"error free\" transmission is achieved due to mode competition noise. The laser is next used in an external feedback configuration where the feedback is provided by a fiber Bragg grating. Lasing only occurs when the fiber Bragg grating is tuned to one of the monolithic cavity modes leading to a discretely tunable single wavelength source whose channel spacing is determined by the mode spacing of the semiconductor laser. Single mode operation of the laser with more than 40 dB side mode suppression is obtained. The BER performance of several channels is examined by stretching the fiber Bragg grating. \"Error free\" performance is obtained for all channels.\n\nAs another new application, the use of semiconductor mode-locked lasers in a photonic analog to digital (A/D) converter is proposed. The method uses wavelength multiplicity to increase the sampling rate of A/D converters. The optical output of a number of semiconductor lasers each mode-locked at a different center wavelength is spectrally stitched and time-interleaved into a high repetition rate multi-wavelength sampling pulse train (MW-SPT) which can be used in a photonic A/D converter to sample a high-end microwave signal. The amplitude modulated high repetition rate MW-SPT is next wavelength demultiplexed into parallel pulse streams with a lower sampling rate which can be processed by conventional electronic state-of-the-art A/D converters in a parallel fashion.\n\nFinally, a new method for the characterization of ultrashort pulses called time resolved optical gating based on dispersive propagation (DP-TROG) is introduced and demonstrated. The DP-TROG technique is a new non-interferometric method for characterizing ultra-short optical pulses in amplitude and phase without the need for a short optical gating pulse. An algorithm is developed for the reconstruction of the pulse amplitude and phase from the measurements. The pulse train emitted from a mode-locked semiconductor laser at 1.5\u00b5m is characterized using this new technique and excellent pulse retrieval is achieved.\n" }, { "name": "Krueger, Paul Samuel", "degree": "PhD", "year": "2001", "title": "The Significance of Vortex Ring Formation and Nozzle Exit Over-Pressure to Pulsatile Jet Propulsion", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142005-111030", "creators": [ { "name": { "family": "Krueger", "given": "Paul Samuel" }, "id": "Krueger-Paul-Samuel", "display_name": "Krueger, Paul Samuel" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3QWF-8G05", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPulsatile jet propulsion can be accomplished using a fully-pulsed jet (i.e., a periodic series of starting jets or pulses), the unsteady nature of which engenders vortex ring formation. The significance of vortex ring formation for this type of propulsion is studied experimentally using a piston-cylinder mechanism to generate starting and fully-pulsed, round jets of water into water at a maximum jet Reynolds number of 13,000. Starting jets are considered separately since they are the limiting case of a fully-pulsed jet at zero pulsing frequency. Direct measurements of the total impulse per pulse (starting jets) and time-averaged thrust (fully-pulsed jets) are made using a force balance. Hotfilm anemometry is used to measure the jet velocity and Digital Particle Image Velocimetry (DPIV) is used to measure vortex ring position, vorticity, energy, circulation, and impulse.\r\n\r\nThe pulses for both types of jets are generated using piston stroke to diameter ratios (L/D) in the range 2 to 8 for piston velocity programs in a generally positive-sloping (PS) or negative-sloping (NS) family. The range of L/D considered brackets the transition between the case where an individual vortex ring is produced with each pulse (small L/D) and the case where the vortex ring stops growing and pinches off from its generating jet, producing a trailing jet (large L/D). This transition occurs at a higher L/D for the PS ramps, allowing the effects of vortex ring formation and pinch off to be illuminated by comparison of the results for the NS and PS ramps.\r\n\r\nThe significance of vortex ring formation is first analyzed for starting jets. Measurements of the total impulse per pulse as a function of L/D show that a leading vortex ring adds more impulse per unit L/D than a trailing jet. This leads to a maximum in the average thrust during a pulse at the L/Ds just before vortex ring pinch off is observed for both the PS and NS ramps. The propulsive benefit provided by a leading vortex ring over a trailing jet is connected to over-pressure at the nozzle exit plane during vortex ring formation. DPIV measurements demonstrate that nozzle exit over-pressure also makes an important contribution to energy and circulation. It is shown that this over-pressure can be related to the momentum that must be supplied by the forming vortex ring to ambient fluid in the form of added and entrained mass. A model is proposed for nozzle exit over-pressure near the initiation of an impulsive velocity program where entrainment can be ignored. The model readily accounts for the pressure contribution to circulation in the NS ramps, but modeling of entrainment is required to properly determine impulse and energy.\r\n\r\nFor the fully-pulsed jet experiments, a normalized thrust, [...], is introduced to characterize the pressure effects associated with vortex ring formation. The pulsing frequency is expressed in dimensionless form as [...], which is between 0 and 1 for all fully-pulsed jets. A propulsive benefit from pressure ([...]) is observed for all L/D and [...] considered. At low [...], the results are similar to those for the starting jets. At higher [...], [...] decreases with L/D as with the starting jets, which is related to the existence of vortex ring pinch off for all observed [...]. At a fixed L/D, two dominant decreasing trends in [...] with [...] appear and seem to be related to the effects of previously ejected pulses on forming vortex rings. No dramatic increase in [...] with [...] (associated with the increased convective velocity of multiple coaxial vortex rings over that of individual vortex rings) is observed since (a) the ring separation is never reduced low enough to see an increase in the ring velocity (even for [...]), and (b) the vortex rings don't remain coaxial or coherent as [...]." }, { "name": "Lindal, John", "degree": "PhD", "year": "2001", "title": "An investigation of several document classification algorithms leading to the design of an autonomous software agent for locating specific, relevant information on the World Wide Web", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12162010-110439957", "creators": [ { "name": { "family": "Lindal", "given": "John" }, "id": "Lindal-J", "display_name": "Lindal, John" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/k937-cy67", "abstract": "The goal of the research described in this thesis was to design an autonomous software agent that can locate specific, relevant information on the World Wide Web. The first chapter provides the motivation behind this project\r\nand a brief overview of the challenges associated with it. The next chapter presents the analysis which led to the development of a new, improved version of the computer program called ITRule. The improvements consist\r\nof a new algorithm for classifying documents that outperforms the previous one, significantly enhanced support for data exploration, i.e., the process of\r\nextracting information from raw data, and a new algorithm for quantizing numeric variables so they can be used by ITRule. The third part of this thesis compares the performances of three versions of ITRule, two versions of the Naive Bayes classifier, several neural networks, the decision tree algorithm called CART, and a linear support vector machine, in order to determine which one is best suited for selecting relevant web pages. An analysis of the\r\ntest results shows that a new ITRule classification algorithm, based on cross validation combined with the J-measure, performs best. The fourth and final part of the thesis describes how some of these results were used in the design of a user friendly, autonomous software agent called Poirot that can help World Wide Web users stay up to date on new developments in topics of interest." }, { "name": "Liu, Wenhai", "degree": "PhD", "year": "2001", "title": "Holographic resolution and its application in memory and imaging", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:10152010-092145939", "creators": [ { "name": { "family": "Liu", "given": "Wenhai" }, "id": "Liu-W", "display_name": "Liu, Wenhai" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/BDB0-VJ12", "abstract": "Optical information storage and optical information processing are two major applications of holography, with significantly different holographic philosophies. For a\r\nholographic memory system, a complex holographic pattern encoded with the storage data is recorded first, and is read out later by a simple pre-designed reference beam.\r\nFor a holographic information processing system, a pre-designed holographic pattern is stored in the medium first, and is probed by complex incident signal wave fronts.\r\nThe pre-designed hologram extracts certain components from the complex input and diffract them as specific reference wave fronts. Holographic resolution, or Bragg phase\r\nselectivity in spatial and spectral dimensions, plays a key role in both applications. It determines the information capacity to be stored in and reconstructed from the\r\nhologram memory, or the information capacity to be extracted and processed by a hologram from the complex signal input. In this thesis, we investigate the holographic\r\nresolution in volume holograms and its specific issues in both applications.\r\nIn a phase conjugate holographic memory system, we demonstrate the recording and reconstruction of a submicron pixel resolution, leading to the potential of storing 1 Gbit in 1 cm^3 volume holographically. Phase conjugate reconstruction eliminates the optical resolution limit by the imaging optics and reduces the system volume and\r\ncost. Phase conjugate reconstruction and its multiplexing in a compact holographic module are investigated.\r\nIn general, a volume hologram has two degenerate Bragg phase-matching dimensions besides the spatial and spectral selectivity, in which significant diffraction is\r\npresent. They provide a potential ability for optically sectioning a two-dimensional slice from the spatial plus spectral hyperspace and for linearly transferring the information onto a two-dimensional sensor array by a single hologram. The resolution of optical sectioning and information transformation is not only determined by the volume hologram diffraction intensity selectivity but also by the holographic architecture and the transformation aberration.\r\nWe study two holographic architectures theoretically and experimentally, on issues of optical sectioning and linear transformation for imaging application. By designing\r\na transmission geometry system, we have achieved a linear 2-D optical sectioning and imaging from a 4-D object hyperspace (3-D spatial plus spectral dimension). By optical sectioning of multiplexed holograms, the ability of imaging 3-D spatial information from an object without a scanning mechanism is demonstrated by a holographic imaging system." }, { "name": "Lokhandwalla, Murtuza", "degree": "PhD", "year": "2001", "title": "Damage Mechanisms in Shock Wave Lithotripsy (SWL)", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-03162005-130412", "creators": [ { "name": { "family": "Lokhandwalla", "given": "Murtuza" }, "id": "Lokhandwalla-Murtuza", "display_name": "Lokhandwalla, Murtuza" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VZWS-7Z85", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nShock wave lithotripsy is a 'non-invasive' therapy for treating kidney stones. Focused shock waves fragment stones to a size that can be passed naturally. There is, however, considerable tissue injury associated with this treatment, and the mechanisms of stone fragmentation and tissue injury are not well understood. This work investigates potential tissue damage mechanisms, with an aim towards modifying the wave-field parameters, so as to enhance stone fragmentation and minimize tissue damage.\r\n\r\nLysis of red blood cells (RBC's) due to in vitro exposure to shock waves was considered as a model of cellular level damage. Fluid flow-fields induced by a non-uniform shock wave, as well as radial expansion/implosion of a bubble was hypothesized to cause lysis of cells. Both the above flow-fields constitute an unsteady, extensional flow exerting inertial as well as viscous forces on the RBC membrane. The resultant membrane tension and the membrane areal strain ([Delta]A/A) due to the above flow-fields were estimated. Both were found to exert a significantly higher inertial force (50 - 100 mN/m) than the critical membrane tension (10 mN/m). Bubble-induced flow-field was estimated to last for a longer duration ([...]) compared to the shock-induced flow ([...]) and hence, was predicted to be lytically more effective, in typical in vitro experimental conditions. However, in vivo conditions severely constrain bubble growth, and cell lysis due to shock-induced shear could be dominant.\r\n\r\nHemolysis due to shock-induced shear, in absence of cavitation, was experimentally investigated. The lithotripter-generated shock wave was refocused by a parabolic reflector. This refocused wave-field had a tighter focus (smaller beam-width and a higher amplitude) than the lithotripter wave-field. Cavitation was eliminated by applying overpressure to the fluid. A novel passive cavitation detector (HP-PCD) operating at high overpressure (upto 7 MPa) was used to measure acoustic emission due to bubble activity. Aluminum foils were also used to differentiate cavitational from non-cavitational mode of damage. RBC's suspended in phosphate-buffered saline PBS) were exposed to the reflected wave-field from the parabolic reflector and also from a flat reflector, the latter serving as a control experiment. Exposure to the wave-field from the parabolic reflector increased hemolysis four-fold compared to untreated controls and was twice that of cell lysis with the flat reflector. This result corroborated the hypothesis of shock-induced shear as a cell damage mechanism in the absence of cavitation.\r\n" }, { "name": "Louie, Michael", "degree": "PhD", "year": "2001", "title": "Numerical study of pattern forming processes in models of rotating Rayleigh-B\u00e9nard convection", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10132010-082113565", "creators": [ { "name": { "family": "Louie", "given": "Michael" }, "id": "Louie-M", "display_name": "Louie, Michael" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/v9dx-9b55", "abstract": "In this thesis we numerically study two unique pattern forming processes observed in Rayleigh-B\u00e9nard convection. Using variants of the Swift-Hohenberg equation, we study the K\u00fcppers-Lortz instability and a spiral chaos state in a large cylindrical cell. For the K\u00fcppers-Lortz instability, we show that the theoretical scaling of the correlation length and domain switching frequency hold in the case of our model equations. We find, however, that it is necessary to account for finite size effects by scaling the correlation length appropriately. We find then that the correlation length scales linearly with the size of the cell when the cell is small and/or when the control parameter is small. Scaling of the domain switching frequency for finite size effects is not necessary as domain switching appears to be enhanced by sidewall processes. Our results provide strong evidence that finite size effects are responsible for the observed discrepancies between theoretical and experimental scalings.\r\n\r\nWe also study the effect of rotation on the spiral state which occurs in a Swift-Hohenberg equation through a coupling with mean flow effects. We find that rotation and mean flow are competing processes. Mean flow shifts the pattern wave number so that the usual K\u00fcppers-Lortz instability is only observed at higher rotation rates. A parameter search is performed and a consistent trend of patterns is observed as the rotation rate is increased.\r\n" }, { "name": "Ma, Lin", "degree": "PhD", "year": "2001", "title": "Robust mask-layout and process synthesis in micro-electro-mechanical-systems (MEMS) using genetic algorithms", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302005-131428", "creators": [ { "name": { "family": "Ma", "given": "Lin" }, "id": "Ma-L", "display_name": "Ma, Lin" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Pickar", "given": "Kenneth A." }, "id": "Pickar-K-A", "role": "member", "display_name": "Pickar, Kenneth A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/e8hm-z754", "abstract": "This thesis reports a Genetic Algorithm approach for the mask-layout and process flow synthesis problem. For a given desired target shape, an optimal mask-layout and process flow can be automatically generated using the Genetic Algorithm synthesis approach. The Genetic Algorithm manipulates and evolves a population of candidate solutions (mask-layouts and process parameters) by utilizing a process simulation tool to evaluate the performance of the candidate solutions. For the mask-layout and process flow synthesis problem, encoding schemes, selection schemes, and genetic operations have been developed to effectively explore the solution space and control the evolution and convergence of the solutions.\n\nThe synthesis approach is tested for mask-layout and process synthesis for bulk wet etching. By integrating a bulk wet etching simulation tool into the Genetic Algorithm iterations, the algorithm can automatically generate proper mask-layout and process flow which can fabricate 3-D geometry close to the desired 3-D target shape. For structures with convex corners, complex compensation structures can be synthesized by the algorithm. More importantly, the process flow can also be synthesized. For multi-step wet etching processes, proper etchant sequence and etch times for each etch step can be synthesized automatically by the algorithm. When the choice of different process flows exists, the enlarged solution space makes the design problem more challenging. The ability to synthesize process flows makes the automatic design method more complete and more valuable.\n\nThe algorithm is further extended to achieve robust design. Since fabrication variations and modeling inaccuracy always exist, the synthesized solutions without considering these variations may not generate satisfactory results in actual fabrication. Robust design methods are developed to synthesize robust mask-layouts and process flows in \"noisy\" environment. Since the synthesis procedure considers the effect of variations in the fabrication procedures, the final synthesized solution will have high robustness to the variations, and will generate satisfactory results under a variety of fabrication conditions. The robust design approaches are implemented and tested for robust mask-layout design for mask misalignment and etch rate variations. Mask-layouts robust to mask misalignment noise and etch rate variations during the fabrication can be synthesized. The synthesized mask-layouts generally improve the yield significantly by exhibiting consistent performance under a variety of fabrication conditions." }, { "name": "Manley, Michael Edward", "degree": "PhD", "year": "2001", "title": "From Elementary Excitations to Microstructures: the Thermodynamics of Metals and Alloys Across Length Scales", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12142010-083329053", "creators": [ { "name": { "family": "Manley", "given": "Michael Edward" }, "id": "Manley-Michael-Edward", "display_name": "Manley, Michael Edward" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." } ], "option_major": [ "matsci" ], "doi": "10.7907/WECC-4662", "abstract": "An experimental investigation has been made into the components that determine the phase stability of metals and alloys. Contributions were found to be important across many length scales from electronic excitations to atomic vibrations and finally microstructural strains at the continuum level. The metals and alloy that have been studied are U, Ce, and Pd3V.
\r\n\r\nTime-of-flight (TOF) inelastic neutron scattering spectra were measured on the three crystalline phases of uranium at temperatures from 50 K to 1213 K. Phonon density of states (DOS) curves were obtained from these spectra. For the \u03b1-phase, a large decrease in phonon energies with increasing temperature was observed over the entire temperature range. Analysis of the vibrational power spectrum showed that the phonon softening originates with continuous softening of a harmonic solid, as opposed to vibrations in anharmonic potentials. Without anharmonicty, it must be that thermal excitations of the electronic structure are changing the interatomic forces. State-of-the-art electronic band structure calculations are based on the assumption that temperature effects on the electronic structure can be neglected when compared to volume effects (where the volume effects are just a manifestation of anharmonicity). The present results turn that problem upside down by showing that temperature effects are actually more important than volume effects. Vibrational entropies of the phase transitions were (S\u03b2-S\u03b1)vib = (0.15\u00b10.1) kB/atom and (S\u03b3 -S\u03b2)vib = (0.36\u00b10.1) kB/atom.The former accounts for about 35% and the latter 65% of the total entropy of the phase transition. The remaining entropy must be electronic.
\r\n\r\nTOF inelastic neutron scattering spectra were measured on cerium at temperatures near the fcc (\u03b3) to bcc (\u03b4) transition temperature. Phonon DOS curves were extracted from data acquired over a wide range of momentum transfers. A large softening of the phonon DOS was found in going from \u03b3-cerium to \u03b4-cerium, and this accounts for an increase in vibrational entropy of (0.71 \u00b1 0.05) kB/atom. To be consistent with the latent heat of the \u03b3-\u03b4 transition, this increase in vibrational entropy must be accompanied by a large decrease in electronic entropy. The results not only confirm the recent discovery of a significant electronic contribution to the \u03b3-\u03b4 transition but also suggest that it may be twice as large as previously reported.
\r\n\r\nTOF inelastic neutron scattering spectra were measured on \u03b2-cerium (dhcp) and \u03b3-cerium (fcc) near the phase transition temperature. Phonon densities of states (DOS) were extracted from the TOF spectra. A softening of the phonon DOS occurs in the transition from \u03b2-cerium to \u03b3-cerium, accounting for an increase in vibrational entropy of \u0394S\u03b3-\u03b2vib = (0.09 \u00b10.05) kB/atom. Crystal field levels were extracted from the magnetic scattering for both\r\nphases. The entropy calculated from the crystal field levels and a fit to calorimetry data from the literature was significantly larger in \u03b2-cerium than \u03b3-cerium below room temperature. The difference was found to be negligible at the experimental phase transition temperature. There was a contribution to the specific heat from Kondo spin fluctuations that was consistent with the quasielastic magnetic scattering, but the difference between phases was negligible. To be consistent with the latent heat of the \u03b2-\u03b3 transition, the increase in vibrational entropy at the phase transition may be accompanied by a decrease in electronic entropy not associated with the crystal field splitting or spin fluctuations. At least three sources of entropy need to be considered for the \u03b2-\u03b3 transition in cerium.
\r\n\r\nDifferences in the heat capacity and thermal expansion of cubic (fcc-disordered) and tetragonal (DO22-ordered) Pd3V were measured from 40 K to 315 K. Below 100 K the heatcapacity difference was consistent with harmonic vibrations. At higher temperatures, however, the data show significant anharmonic effects. Measurements of elastic constants, densities, and thermal expansion showed that the anharmonic volume expansion contribution (Cp \u2013 Cv) could account for only about one-third of this anharmonic heat capacity difference. The remainder may originate with elastic and plastic deformation of the polycrystalline microstructure. Strain energy from anisotropic thermal contractions of grains in the tetragonal ordered phase contributes to the heat capacity, but some of this strain energy is eliminated by plastic deformation. The vibrational entropy difference of disordered and ordered Pd3V was estimated to be Sdis \u2013 Sord = (+0.035\u00b1 0.001) kB//atom at 300 K, with 70% of this coming from anharmonic effects.
\r\n\r\nThe microstructural contribution to the heat capacity of \u03b1-uranium was determined bymeasuring the heat capacity difference between polycrystalline and single crystal samples from 77 K to 320 K. When cooled to 77 K and then heated to about 280 K, the uranium microstructure released (3\u00b12) J/mol of strain energy. On further heating to 300 K the microstructure absorbed energy as the microstructure began to redevelop microstrains. Neutron diffraction measurements on polycrystals predicted the total strain energy stored in the microstructure to be (3.7\u00b10.5) J/mol at 77 K and (1\u00b10.5) J/mol at room temperature in good agreement with the calorimetry.
" }, { "name": "Mehta, Neelesh B.", "degree": "PhD", "year": "2001", "title": "Impact of User Mobility on Resource Allocation Schemes in Cellular Radio Systems", "advisor": "Goldsmith, Andrea Jo", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302010-111553894", "creators": [ { "name": { "family": "Mehta", "given": "Neelesh B." }, "id": "Mehta-Neelesh-B", "orcid": "0000-0002-3614-049X", "display_name": "Mehta, Neelesh B." } ], "advisors": [ { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "orcid": "0000-0001-5686-800X", "role": "advisor", "display_name": "Goldsmith, Andrea Jo" } ], "committee": [ { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "orcid": "0000-0001-5686-800X", "role": "chair", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "orcid": "0000-0001-9176-3078", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Kiely", "given": "Aaron B." }, "id": "Kiely-A-B", "role": "member", "display_name": "Kiely, Aaron B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/9fje-n644", "abstract": "Next generation wireless cellular radio systems are being designed to provide anytime, anywhere communication capabilities to serve a range of applications. The ability to support mobility is a key reason for the increasing demand for such systems. To accommodate this demand, efficient resource allocation schemes that can operate over the harsh wireless channel environment need to be devised. User mobility has a significant influence on the design and performance of these schemes. The focus of this dissertation is the analysis of the impact of mobility on such resource allocation schemes.\r\nWhat impact mobility has depends on the scheme under consideration. We first analyze the impact of user mobility on the performance of a link adaptation scheme that employs\r\nthe recently proposed no-transmission mode. In this scheme, users adapt their modulation and coding for transmitting data packets based on their estimates of the link condition\r\nand suspend transmissions when link quality is very poor. Based on a simplified system model, we derive expressions for the system performance as a function of the basic, system-defining parameters. We show that for a stable system, the channel correlation, a function of user speed and feed-back delay of estimates, is an important factor that determines the optimal link adaptation thresholds. We then study a packet based multiple access scheme called Packet Reservation Multiple Access (PRMA), which can simultaneously handle the different traffic requirements of periodic, delay intolerant (voice) and bursty, delay tolerant (data) users. An approximate technique is developed to analyze the impact of user mobility\r\nas well as channel fading and interference-induced packet errors on PRMA. Both these effects lead to a premature loss of reservation and, consequently, more dropped packets\r\nfor voice users. Finally, we look at dedicated channel assignment schemes that assign an entire channel to a user for the duration of his conversation. We investigate heuristic prediction based techniques that take into account mobility traffic statistics to modify the\r\nnew call access criteria. This is done so as to introduce prioritization for hand-off requests in hitherto unprioritized channel assignment schemes." }, { "name": "Me\u015fe, Murat", "degree": "PhD", "year": "2001", "title": "Image halftoning and inverse reconstruction problems with considerations to image watermarking", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02222011-105108216", "creators": [ { "name": { "family": "Me\u015fe", "given": "Murat" }, "id": "Me\u015fe-M", "display_name": "Me\u015fe, Murat" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Djokovic", "given": "Igor" }, "id": "Djokovic-I", "role": "member", "display_name": "Djokovic, Igor" } ], "option_major": [ "eleceng" ], "doi": "10.7907/561b-d051", "abstract": "In this work, we first discuss the image halftoning problem. Halftoning is the rendition of\r\ncontinuous-tone pictures on displays that are capable of producing only two levels. There\r\nare several well-known algorithms for half toning. The dot diffusion method for digital\r\nhalf toning has the advantage of pixel-level parallelism unlike the error diffusion method,\r\nwhich is a popular half toning method. The image quality offered by error diffusion is\r\nstill regarded as superior to most of the other known methods. We show how the image\r\nquality obtained using the dot diffusion method can be improved by optimization of the\r\nso-called class matrix. By taking the human visual characteristics into account we show\r\nthat such optimization consistently results in images comparable to error diffusion, without\r\nsacrificing the pixel-level parallelism. The dot diffusion algorithm will be discussed and\r\nby modifying the algorithm, embedded multiresolution property will be added. Later,\r\nwe introduce LUT (Look Up Table) based half toning and tree-structured LUT (TLUT)\r\nhalftoning. We demonstrate how error diffusion characteristics can be achieved with this\r\nmethod. Afterwards, our algorithm will be trained on halftones obtained by Direct Binary\r\nSearch (DBS) which is an algorithm with high computational complexity. The complexity\r\nof TLUT halftoning is higher than that of error diffusion but much lower than that of the\r\nDBS algorithm. Thus, halftone image quality between that of error diffusion and DBS will\r\nbe achieved depending on the size of tree structure in TLUT algorithm.\r\nWe also discuss the inverse halftoning problem. Inverse halftoning is the reconstruction\r\nof a continuous tone image from its halftoned version. We propose two methods for\r\ninverse half toning of dot diffused images. The first one uses Projection Onto Convex Sets\r\n(POCS) and the second one uses wavelets. We then propose a novel and fast method for\r\ninverse halftoning called the Look Up Table (LUT) Method. The LUT for inverse halftoning\r\nis obtained from the histogram gathered from a few sample halftone images and the\r\ncorresponding original images. For each pixel, the algorithm looks at the pixel's neighborhood\r\n(template) and depending upon the distribution of pixels in the template, it assigns\r\na contone value from a precomputed LUT. The method is extremely fast (no filtering is\r\nrequired) and the image quality achieved is comparable to the best methods known for inverse halftoning. The LUT inverse half toning method does not depend on the specific\r\nproperties of the half toning method, and can be applied to any method. An algorithm for\r\ntemplate selection for LUT inverse half toning is introduced. We also extend LUT inverse\r\nhalftoning to color halftones.\r\nThe next topic is image watermarking and effects of halftoning on watermarked images.\r\nWatermarking is the process of embedding a secret signal into a host signal in order to\r\nverify ownership or authenticity. We discuss the effects of applying inverse half toning before\r\ndetection of watermark in half toned images and offer methods to improve watermark\r\ndetection from halftoned images.\r\nFinally, we consider the optimal histogram modification with MSE metric and optimal\r\ncodebook selection problem. Watermarking with histogram modification is one of the few\r\nwatermarking methods which is robust to rotation and scaling. We formulate histogram\r\nmodification problem as finding a transformation such that the error between the input and\r\nthe output signal is minimized and the output signal has the desired histogram. It turns\r\nout that this problem is equivalent to the integer linear programming problem. Then, we\r\nformulate the problem of finding the optimal code book where the codewords can come from\r\na finite set. The equivalent problem again turns out to be a linear integer programming\r\nproblem and the solution is guaranteed to be globally optimal." }, { "name": "Molinari, Jean-Francois Roland", "degree": "PhD", "year": "2001", "title": "Three dimensional finite element analysis of impact damage and erosion of metallic targets", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-102656", "creators": [ { "name": { "family": "Molinari", "given": "Jean-Francois Roland" }, "id": "Molinari-J-R", "display_name": "Molinari, Jean-Francois Roland" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6ZJV-B162", "abstract": "This dissertation is concerned with the development of a robust three-dimensional finite-element framework for the simulation of complex problems in mechanics and physics of solids. This approach is intended to shine light on impact and erosion mechanisms among other multiscale, multiphysics problems. The components of the computational framework are a contact algorithm including friction, wear, finite deformation plasticity, heat generation, heat transfer, and adaptive meshing coupled with error estimation. The adaptive meshing is a key development that enhances the efficiency and robustness of the method. We demonstrate the ability of the methodology to simulate diverse problems such as shear banding, impact, and wear.\r\n" }, { "name": "Moser, Christophe", "degree": "PhD", "year": "2001", "title": "Optical Information Processing", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:10222010-101901467", "creators": [ { "name": { "family": "Moser", "given": "Christophe" }, "id": "Moser-C", "display_name": "Moser, Christophe" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/3mvn-0f95", "abstract": "The title of this work Optical Information Processing reflects the multi-facets of this thesis.\r\nIn the first three chapters, I look at specific aspects of optical data storage. Enabled by new recording materials, a read-write holographic memory is explored. The memory combines a two-dimensional layered architecture and holography. Recording dynamics are analyzed and compared with conventional memories. A novel multiplexing\r\nmethod, based on the confinement of spherical waves in waveguides, allows the implementation of fiat read-only memories with no moving parts. Novel polymer films at low temperatures show extremely selective frequency absorption which yields up to hundred thousands of independent frequency channels. This radically different multiplexing scheme is combined with Bragg multiplexing to increase the\r\nstorage density. Femtosecond pulses can be stored and retrieved in these materials. For further processing, a pulse shaper and an all-optical logic capable of processing\r\nTerahertz pulse streams are experimentally demonstrated.\r\nThe last two chapters look at three-dimensional surface measurements. A profilometer and a wavefront sensor based on the propagation of light in birefringent crystals are investigated. The performance of both sensors is theoretically modeled and experimentally verified. A third sensor is designed for an ophthalmic application." }, { "name": "Nolte, Christopher Glenn", "degree": "PhD", "year": "2001", "title": "Polar organic compounds in fine particulate matter sources and in the urban atmosphere", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechTHESIS:10222010-075111918", "creators": [ { "name": { "family": "Nolte", "given": "Christopher Glenn" }, "id": "Nolte-C-G", "display_name": "Nolte, Christopher Glenn" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/nxc3-re40", "abstract": "Polar organic compounds are quantified in fine particulate matter emitted from major urban air pollution sources. Fine particulate matter emissions from meat cooking, hardwood and softwood combustion, motor vehicle exhaust, and cigarette smoking, along with leaf particulate abrasion products, tire dust, brake dust, and paved road dust, are converted to trimethylsilyl derivatives and analyzed by gas chromatography/mass spectrometry. Silylation enables or improves the quantification of a number of compounds,\r\nincluding cholesterol and other sterols, monoglycerides, levoglucosan and related sugar anhydrides, normal alkanols, triterpenoids, and compounds derived from wood lignin, which may be suitable tracers for specific emission\r\nsources of fine particulate matter. In addition, gas phase formic and acetic acids concentrations are reported over an 8-month period at 9 sites in the Los Angeles air basin. A comparison of these concentration profiles with concentrations of other pollutants and with meteorological variables shows that both direct emissions and atmospheric chemical formation contribute to observed levels of formic and acetic acids. Finally, longer chain gas phase organic\r\nacids (from C_2 up to C_(10)) are measured during a severe photochemical smog episode in the Los Angeles area." }, { "name": "Nystr\u00f6m, Mika", "degree": "PhD", "year": "2001", "title": "Asynchronous Pulse Logic", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10152010-145548970", "creators": [ { "name": { "family": "Nystr\u00f6m", "given": "Mika" }, "id": "Nystr\u00f6m-Mika", "display_name": "Nystr\u00f6m, Mika" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "DeHon", "given": "Andre" }, "id": "DeHon-A", "role": "member", "display_name": "DeHon, Andre" }, { "name": { "family": "Manohar", "given": "Rajit" }, "id": "Manohar-R", "role": "member", "display_name": "Manohar, Rajit" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "compsci" ], "doi": "10.7907/B107-MW15", "abstract": "This thesis explores a new way of computing with CMOS digital circuits, single-track\u2014handshake asynchronous pulse-logic (STAPL). These circuits are similar to quasi delay-insensitive (QDI) circuits, but the normal four-phase QDI handshake is replaced with a simpler two-phase pulsed handshake. While a delay-insensitive two-phase handshake requires complicated decoding circuits, the pulsed handshake maintains the simpler, electrically beneficial signaling senses of four-phase handshaking by using timing assumptions that are easy to meet.
\r\n\r\nWe cover many aspects of designing moderately large digital systems out of STAPL circuits, from the communicating-process level to the production-rule and transistor level.
\r\n\r\nWe study the theory of operation of pulsed asynchronous circuits, starting with simple pulse repeaters; hence we progress to a general theory of operation for pulsed asynchronous circuits. This theory is a generalization of the theory of operation of synchronous digital circuits.
\r\n\r\nWe then develop the family of STAPL circuits. This is a complete family of dataflow processes: the presented circuits can compute unconditionally as well as conditionally; they can also store state and arbitrate.
\r\n\r\nNext, we present some aspects of automatic design-tools for compiling from a higher-level description to STAPL circuits. Many of these aspects apply equally well to tools for QDI circuits; in particular, we study boolean-simplification operations that may be used for improving the performance of slack-elastic asynchronous systems.
\r\n\r\nFinally, a simple 32-bit microprocessor is presented as a demonstration that the circuits and design methods work as described. Comparisons are made, mainly with QDI asynchronous design-styles: SPICE simulations in 0.6-\u00b5m CMOS suggest that a system built out of automatically compiled STAPL circuits performs at about three times higher throughput (650-700 MHz in 0.6-\u00b5m CMOS) compared with a similar system built out of carefully hand-compiled QDI circuits; the STAPL system uses about twice the energy per operation and twice the area; in other words, the STAPL system improves on the QDI system by four to five times as measured by the Et^2 and At^2 metrics.
" }, { "name": "Ol, Michael Volf", "degree": "PhD", "year": "2001", "title": "The Passage Toward Stall of Nonslender Delta Wings at Low Reynolds Number", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:11192010-085724406", "creators": [ { "name": { "family": "Ol", "given": "Michael Volf" }, "id": "Ol-Michael-Volf", "display_name": "Ol, Michael Volf" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/016w-2332", "abstract": "Separated flow over the leeside of relatively nonslender delta wings was studied experimentally. Such flowfields are more complex than those of the slender delta wing\r\nof very low aspect ratio. A version of Stereo Digital Particle Image Velocimetry was applied to measurements in a low speed water tunnel, at Reynolds numbers below 20,000, for delta wing models of 50\u00b0 and 65\u00b0 leading edge sweep angles and 30\u00b0 windward-side leading edge bevels. Since the objective was to draw comparisons to the stall of classical high aspect ratio wings, low angles of attack were emphasized, with most data points taken in the 5\u00b0-20\u00b0 angle of attack range. Measurements were taken over the starboard portion of the wing planform in crossflow planar slices near the apex region, yielding all three components of the velocity field, albeit restricted to planar cuts.\r\nVorticity and circulation were calculated from these measurements. All three components of vorticity were obtained in select cases, by central-differencing velocity\r\ndata across triplets of adjacent interrogation planes. In addition, flow visualization by dye injection into the windward apex stagnation region was used to confirm the presence of primary and secondary leading edge vortices, to qualitatively verify the locations of vortex breakdown, and to verify the stereo digital particle image velocimetry results.\r\nBoth delta wings exhibit stable, coherent leading edge vortices at very low angles of attack, down to 2.5\u00b0. Results for the 65\u00b0 wing were in accordance with the literature. The 50\u00b0 wing, however, exhibited flow characteristics akin to both slender delta wings, and wings of high aspect ratio, and generally exhibited stronger and more robust leading edge vortices than usually observed. For the 50\u00b0 wing, the primary leading edge vortices were stable below 10\u00b0 angle of attack, with gradual and steady upstream progression of the vortex breakdown region with increasing angles of attack, from aft of the trailing\r\nedge to approximately the midchord. Secondary leading edge vortices were found to decay more abruptly, and at lower angle of attack than the primaries, all but disappearing\r\nby 10\u00b0 angle of attack. This fact has the potential of serving as the basis for a predictive criterion for breakdown of the primary vortices.\r\nThe entire vortex system undergoes large-scale instabilities in the 12\u00b0-20\u00b0 angle of attack range. While the flow visualization was inconclusive, particle image\r\nvelocimetry confirmed that breakdown sweeps over the entire forward third of the wing planform in going from 12.5\u00b0 to 15\u00b0 angle of attack. This change is characterized by a\r\nsharp drop in axial velocity in the primary leading edge vortex core region, along with a loss of coherent vortical structure normally associated with this region. The leading edge shear layer, however, remains in an organized rolled-up state. By 20\u00b0, the flow over the leeward side of the wing is at the threshold of complete separation, with flow along the wing centerline stalling as the left and right separated regions grow and merge.\r\nBoth wings exhibited a largely stagnant region outboard of the primary LEV and inboard of the leading edge shear layer, especially at angles of attack beyond 10\u00b0. This\r\nphenomenon is consistent with some prior observations at Reynolds numbers on the order of 20,000 and below, and differs sharply from that at higher Reynolds numbers. Further experiments are necessary to elucidate the cause and extent of Reynolds number influence on separation near the leeward surface. Also, the 50\u00b0 wing is probably of too\r\nhigh sweep to be a true limiting case for the existence of coherent leading edge vortices, for the conditions of the present experiment. But the abruptness of its stall and the close relationship between the leading edge vortex flow and the leeward surface boundary layer are qualitatively indicative of such a transitional case from slender delta wing separation to classical airfoil stall." }, { "name": "Painter, Oskar Jon", "degree": "PhD", "year": "2001", "title": "Optical Nanocavities in Two-Dimensional Photonic Crystal Planar Waveguides", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-111605", "creators": [ { "name": { "family": "Painter", "given": "Oskar Jon" }, "id": "Painter-Oskar-Jon", "orcid": "0000-0002-1581-9209", "display_name": "Painter, Oskar Jon" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/y7hm-zq23", "abstract": "One of the most fundamental properties of a physical system is its energy-momentum dispersion. The electronic dispersion present in semiconductor crystals results in energy gaps which play an extremely important role in the physics of many of the electronic and optical devices we use today. A similar dispersion for electromagnetic waves can be found in periodic dielectric structures. Owing to their strong dispersion, these \"photonic crystals\" can be used to manipulate light at sub-wavelength scales. The majority of this thesis is concerned with the design and implementation of optical resonant cavities formed by introducing small local imperfections into a periodically perforated slab waveguide. Light becomes localized to these \"defect\" regions, forming optical cavities with modal volumes approaching the theoretical limit of a cubic half-wavelength.
\r\n\r\nThe resonant cavities studied in this thesis are fabricated using electron-beam lithography, anisotropic dry etching, and selective wet etching. These methods are used to create a two-dimensional array of cylindrical air holes in a free-standing waveguide structure. A multi-quantum-well Indium Gallium Arsenide Phosphide (InGaAsP) active region is epitaxially grown within the waveguide in order to provide light emission in the 1.5 \u00b5m band. Optical pumping of the active region is then used to probe the resonant structure of the photonic crystal cavities.
\r\n\r\nNumerical finite-difference time-domain simulations and qualitative predictions based on symmetry arguments are used to label the different resonant modes present in the cavity photoluminescence spectra. It is found that both donor and acceptor type modes are localized within the defect cavities. Pulsed lasing action is observed in cavity modes with modal volumes as small as 2(\u03bb/2n)\u00b3. Lithographic adjustments in the scale and symmetry of the cavity geometry are also used to tune the resonant mode wavelength, split mode degeneracies, and adjust the emission pattern and polarization of the defect modes.
" }, { "name": "Piatina, Tatiana Borisovna", "degree": "PhD", "year": "2001", "title": "Studies of metal-organic interactions with model synthetic and natural ligands applicable to natural waters", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-103734735", "creators": [ { "name": { "family": "Piatina", "given": "Tatiana Borisovna" }, "id": "Piatina-T-B", "display_name": "Piatina, Tatiana Borisovna" } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/57TJ-PE22", "abstract": "Metal speciation significantly influences the geochemical cycling of trace metals and can control metal bioavailability and toxicity. This study addressed some unresolved questions concerning metal speciation in natural waters in several complementary ways.\r\n\r\nMetal competition for model and natural organic ligands was examined by coupling size-exclusion chromatography (SEC) with inductively-coupled plasma mass spectrometry.\r\nThe method was validated with well-defined organic ligands in ligandcompetition studies with a single metal and a binary metal mixture. The measured concentrations\r\nof metal-ligand species corresponded to the calculated equilibrium speciation. However, the method is subject to kinetic limitations. For metal complexes that are partially\r\nlabile during chromatographic separation, the rate constant for complex dissociation and the concentration of the (initial) complex were estimated based on a mathematical\r\nmodel.\r\n\r\nApplication of this method to studies of copper complexation by Suwannee River humic acid demonstrated that copper complexes are kinetically labile on the SEC column\r\nfor copper additions comparable to the background concentrations in the humic acid samples. This suggests that the copper-binding sites that form complexes detectable by this method are present in humic acids at very low concentrations and are not available to\r\nbind added copper.\r\n\r\nInvestigation of copper complexation with a synthetic analog of the natural metalbinding peptide phytochelatin has demonstrated that Cu(II) is not stable in the presence of phytochelatin but that the peptide fonns strong complexes with Cu(I). Complexation of Cu(I) by phytochelatin was studied using a spectroscopic technique in which bathocuproine was added as a competing ligand. The method was validated in experiments with glutathione.\r\n\r\nTitrations of bathocuproine and phytochelatin with Cu(I) and of Cu(I) and bathocuproine with phytochelatin were explained by formation of 1:1 and 1:2 Cu(I)phytochelatin\r\ncomplexes. To account for the experimental observations, a polynuclear (1:2:1) phytochelatin-Cu(I)-bathocuproine complex was introduced in modeling the titration\r\ndata. Consistent values of conditional stability constants were obtained in Cu(I) and phytochelatin titrations. However these results were not consistent with those obtained in titrations of Cu(I) and phytochelatin with bathocuproine possibly due to the slow ligand\r\nexchange kinetics of the pre-formed Cu(I)-phytochelatin complexes.\r\n" }, { "name": "Provenzano, Dan Raymond", "degree": "PhD", "year": "2001", "title": "From semiconductor lasers to fiber Bragg grating lasers in optical communications", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-06132005-083934", "creators": [ { "name": { "family": "Provenzano", "given": "Dan Raymond" }, "id": "Provenzano-D-R", "display_name": "Provenzano, Dan Raymond" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/setx-7j50", "abstract": "This thesis describes the semiconductor laser signal and noise propagation effects in single mode fiber and fiber Bragg gratings. The capability to fabricate custom fiber Bragg gratings was developed, which enabled the design and fabrication of gratings for a number of applications. Finally, gratings were developed and specialized for use in a single mode fiber ring laser.\r\n\r\nA quantum mechanical description of laser noise is presented in order to discuss pump-noise suppressed semiconductor lasers capable of sub-shot noise, also known as \"squeezing.\" Experimental results for an 850 nm Fabry-Perot semiconductor laser are presented showing squeezing at room temperature of 29% below the shot noise limit measured using a balanced homodyne detector, corresponding to 41% below the standard quantum limit at the output facet of the laser. The side mode suppression ratio was varied with slight temperature tunings and correlated with the laser noise. It was found that the higher the sidemode suppression ratio, the lower the noise.\r\n\r\nNoise analysis was continued with 1540 nm distributed feedback semiconductor lasers. Laser parameters such as noise, chirp, and resonance frequency were characterized by propagation in dispersive fiber,and fitting the parameters to a model for the fiber. Again, a correlation was found between side mode suppression and laser noise, especially after several kilometers of propagation in fiber. The principles of signal and noise propagation were applied to fiber Bragg gratings. Theory and experiment indicated direct laser modulation enhancement by a uniform fiber Bragg grating by 7 dB at modulation frequencies, of up to 25 GHz, and also noise reduction of 2 dB at frequencies up to 15 GHz.\r\n\r\nFacilities were established to write and produce customized fiber Bragg gratings of various strengths in various fiber types as well as in ion-exchanged waveguides in bulk glasses. Analyses of writing times and strengths were performed and optimized for various applications. Uses for these gratings include dispersion compensation, noise reduction, beam or pulse shaping, and spectral filtering for dense wavelength division multiplexed (DWDM) optical networks. Amplitude and phase masks were developed and shown to produce arbitrarily apodized and chirped gratings.\r\n\r\nFiber gratings were next refined for use as key elements in a new type of single mode fiber ring laser. Some of the beneficial characteristics of this fiber laser include long cavity size (80 cm), 80 dB signal-to-noise ratio, high side mode suppression ratio, and white noise linewidth as narrow as 2 kHz. The laser noise was also nearly shot noise limited. This combination of low amplitude and low phase noise allowed the observation of extremely low noise enhancement after 50 km of standard, dispersive fiber up to 20 GHz frequency. A comparison was made between our fiber ring laser and a standard high grade distributed feedback semiconductor laser in transmitting 10 Gbits/sec data. Over a 50 km fiber, the fiber ring laser achieved the same signal to noise ratio with half the power as the semiconductor laser.\r\n" }, { "name": "Pun, Winston", "degree": "PhD", "year": "2001", "title": "Measurements of Thermo-Acoustic Coupling", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08222001-170336", "creators": [ { "name": { "family": "Pun", "given": "Winston" }, "id": "Pun-Winston", "display_name": "Pun, Winston" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/SPSR-VD18", "abstract": "The problem of combustion instabilities has existed since the early 1940s, when they were observed during the development of solid and liquid rocket engines. While various engineering solutions have served well in these fields, the problem is revisited in modern gas-turbine engines. The purpose of this work is to provide experimental measurements of laboratory devices that exhibit thermo-acoustic coupling, similar to the interaction observed during combustion instabilities, which will aid in the design and development of stable systems.\r\n\r\nPossibly the simplest device which exhibits these characteristics is a Rijke tube. An electrical, horizontally mounted, 1 m long version of the original Rijke tube is presented, with measurements taken during unstable and stable operation. An accurate stability boundary with uncertainty is determined for a heater position of x/L = ?, as a function of mass flow rate and heater power. Hysteresis, not previously reported, is observed at flow rates above 3 g/s. A one-dimensional model of the stability boundary with linear acoustics is shown to have qualitative agreement with experimental data.\r\n\r\nA novel technique has also been devised which can provide insight into the local dynamic response of a flame to an acoustic field. In the experiments, a test chamber is acoustically excited by a pair of low-frequency drivers. The response of the flame is visualized by two techniques; chemiluminescence and planar laser-induced fluorescence (PLIF) of the hydroxyl (OH) radical, both of which are well-known indicators for heat release in flames. The resulting images are phase-resolved and averaged to yield a qualitative picture of the fluctuation of the heat release. The images are correlated with a pressure transducer near the flame, which allows stability to be evaluated using Rayleigh?s criterion and a combustion response function. This is the first known measurement of the combustion dynamics of a flame over a range of frequencies. Results indicate that the drive frequency and burner configuration have a pronounced effect on the response of the flame. Drive frequencies ranging from 22 Hz to 55 Hz are applied to the jet mixed burner, supplied with a premixed 50/50 mixture of methane and carbon dioxide at a Reynolds number of 20,000. The burner is operated in two configurations; with an aerodynamically stabilized flame and with a flame stabilized by two protruding bluff-bodies. Results indicate that in general the bluff-body stabilized flame is less sensitive to chamber acoustic excitation." }, { "name": "Qi, Yue", "degree": "PhD", "year": "2001", "title": "Molecular dynamics (MD) studies on phase transformation and deformation behaviors in FCC metals and alloys", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172008-112120", "creators": [ { "name": { "family": "Qi", "given": "Yue" }, "id": "Qi-Yue", "display_name": "Qi, Yue" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/9NXP-E603", "abstract": "This thesis focused on the phase transformation and deformation in face center cubic (FCC) metals and alloys. These studies use the new quantum modified Sutton-Chen (QMSC) many-body potentials for Cu, Ni, Ag, and Au and for their alloys through simple combination rules. Various systems and processes are simulated by standard equilibrium molecular dynamics (MD), quasi-static equilibrium MD and non-equilibrium MD (NEMD), cooperated with different periodic boundary conditions. The main topics and their outlines are listed as the following:\r\n\r\n1) Melting, glass formation, and crystallization processes in bulk alloys: Using cooling rates in the range of 2*10[superscript 12] to 4*10[superscript 14]K/s, we find that CuNi and pure Cu always form an FCC crystal while Cu[subscript 4]Ag[subscript 6] always forms a glass (with Tg decreasing as the quench rate increases), which confirms the role of size mismatch in glass formability and validates the accuracy of the force field.\r\n\r\n2) The size effects in melting and crystallization in Ni nano clusters, ranging 100 to 8007 atoms: We find a transition from cluster or molecular behavior below ~500 atoms to a mesoscale nanocrystal regime (with well-defined bulk and surface properties and surface melting processes, which leads to T[subscript m,N] = T[subscript m,bulk] - \u03b1 N[superscript -1/3]) above ~750 atoms. Cooling from the melt leads first to supercooled clusters with icosahedral local structure, then for N>500 the supercooled clusters transform to FCC grains, while clusters with N<500 form icosahedral structures.\r\n\r\n3) The deformation behavior of metallic nanowires of pure Ni, NiCu and NiAu alloys, under high rates of uniaxial tensile strain, ranging from 5*10[superscript 8]/s to 5*10[superscript 10]/s: These nanowires are too small to sustain dislocations; instead we find that deformation proceeds through twinning and coherent slipping mechanisms at low strain rate, and amorphization at high strain rate. We find that critical strain rate, beyond which the crystal transformed into glassy state, for NiAu (13% size mismatch) is 100 times slower than that for NiCu (2.5% size mismatch). Thus the critical strain rate also depends on the glass formability.\r\n\r\n4) The calculation of the 1/2<110> screw dislocation in nickel (Ni): From a quadrupolar dislocation system with 3-D periodic boundary conditions, we found the screw dislocation dissociated into two partials on {111} planes, and the core energy is 0.5 eV/b. We also studied motion and annihilation process of opposite signed dislocations with different configurations of dissociation planes. On two intersecting or parallel dissociation planes, a cross-slip process is captured and the energy barriers is 0.1eV/b in our simulations.\r\n\r\n5) Friction Anisotropy at Ni(100)/(100) interface: We carried out a series of NEMD simulations for sliding of Ni(100) interfaces under a constant force. We found that the clean, flat, and incommensurate interface has a very small static friction coefficient, as analytical theory predicted. However surface roughness can increase the static friction on the incommensurate interfaces dramatically, and increase the friction on the commensurate interfaces to a lesser extent. The dynamic frictional coefficients are comparable to the experimental values and show the same anisotropic behavior, thus explaining the difference between theory and experiment.\r\n" }, { "name": "Rasheed, Adam", "degree": "PhD", "year": "2001", "title": "Passive Hypervelocity Boundary Layer Control Using an Ultrasonically Absorptive Surface", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08192001-143746", "creators": [ { "name": { "family": "Rasheed", "given": "Adam" }, "id": "Rasheed-Adam", "display_name": "Rasheed, Adam" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "chair", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "busecon" ], "doi": "10.7907/EFZZ-X764", "abstract": "A series of exploratory boundary layer transition experiments was performed on a sharp 5.06 degree half-angle round cone at zero angle-of-attack in the T5 Hypervelocity Shock Tunnel in order to test a novel hypersonic boundary layer control scheme. Recently performed linear stability analyses suggested that transition could be delayed in hypersonic boundary layers by using an ultrasonically absorptive surface that would damp the second mode (Mack mode). The cone used in the experiments was constructed with a smooth surface on half the cone (to serve as a control) and an acoustically absorptive porous surface on the other half. It was instrumented with flush-mounted thermocouples to detect the transition location. Test gases investigated included nitrogen and carbon dioxide at M = 5 with specific reservoir enthalpy ranging from 1.3 MJ/kg to 13.0 MJ/kg and reservoir pressure ranging from 9.0 MPa to 50.0 MPa. Detailed comparisons were performed to insure that previous results obtained in similar boundary layer transition experiments (on a regular smooth surface) were reproduced and the results were extended to examine the effects of the porous surface. These experiments indicated that the porous surface was highly effective in delaying transition provided that the hole size was significantly smaller than the viscous length scale." }, { "name": "Roberts, Gregory Charles", "degree": "PhD", "year": "2001", "title": "Cloud condensation nuclei in the Amazon Basin : their role in a tropical rainforest", "advisor": "Hoffmann, Michael R.; Andreae, Meinrat O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-122520361", "creators": [ { "name": { "family": "Roberts", "given": "Gregory Charles" }, "id": "Roberts-G-C", "display_name": "Roberts, Gregory Charles" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Andreae", "given": "Meinrat O." }, "id": "Andreae-M-O", "role": "advisor", "display_name": "Andreae, Meinrat O." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/ebt1-np17", "abstract": "Cloud condensation nuclei (CCN) are closely linked to cloud structure and precipitation; yet, their role in tropical climates remains largely unknown. CCN measurements were performed during several field campaigns during 1998 and 1999 as part of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) in the states of Amazonas and Rond\u00f4nia. An airborne experiment transected the Amazon Basin and allowed for sampling of different airmasses ranging from clean maritime aerosol along the eastern coast to the smoke plumes and regional haze of the biomass burning. CCN concentrations between 0.15% and 1.5% supersaturation were measured using static thermal-gradient CCN chambers.\r\n\r\nThe wet-season CCN concentrations measured in the unpolluted Amazon Basin were surprisingly low and resembled conditions more typical of marine locations than of other continental sites. It is remarkable that very similar CCN concentrations prevail in pristine marine and continental regions, in spite of the different aerosol production mechanisms and particle compositions. Physical and chemical properties responsible for CCN activation were estimated using a number and mass size distribution closure. In spite of the large organic fraction in Amazonian aerosol, the results suggest that the soluble, inorganic component accounts for most of the CCN activity during the wet season.\r\n\r\nBiomass burning smoke aerosol dramatically increased CCN concentrations during the dry season, which likely increases colloidal stability and cloud lifetime, resulting in the observed non-precipitating clouds. Because of the low natural CCN abundance in Amazonia, climatic effects related to the enhanced aerosol emissions due to human activity may have a stronger impact on climate change than in other continental regions.\r\n\r\nAn early part of my research also included measuring the air-to-sea flux of biogenic trace gases on the Black Sea and the characterization of aerosol composition and their sources in the central African rainforest.\r\n" }, { "name": "Salmassi, Tina Megerdichian", "degree": "PhD", "year": "2001", "title": "Bacterial oxidation of arsenite at Hot Creek: characterization of biofilm communities and isolation of novel bacteria associated with aquatic macrophytes", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222004-091308", "creators": [ { "name": { "family": "Salmassi", "given": "Tina Megerdichian" }, "id": "Salmassi-T-M", "display_name": "Salmassi, Tina Megerdichian" } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/J3TC-QJ66", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nHot Creek, a tributary of the Owens River in the Long Valley Caldera in California, contains naturally elevated concentrations of arsenic as a result of geothermal activity. This site is of particular interest because of its substantial impact on the quality of the drinking water supply for the City of Los Angeles.\r\n\r\nPrevious studies revealed a rapid in situ oxidation of arsenite in Hot Creek. In this work, bacterial oxidation of arsenite is viewed from the perspective of cultivation-based studies (focusing on pure cultures of arsenite oxidizers) and molecular technique-based studies (surveying the community under ambient conditions).\r\n\r\nThe cultivation-based techniques yielded four new arsenite oxidizers. One isolate, Agrobacterium albertimagni strain AOL15, is an [alpha]-proteobacterium that was isolated using an enrichment-based isolation technique with arsenite concentrations much higher than ambient levels. Values of the kinetic parameters [...] and [...] were determined for AOL15. The [...] is near the ambient concentration of arsenite in Hot Creek. However, molecular-based techniques suggested that AOL15 is not a significant member of the biofilm associated with submerged macrophytes.\r\n\r\nThe other three oxidizers, YED1-18, YED6-4, and YED6-21, all [beta]-proteobacteria of the genus Hydrogenophaga, were isolated from solid media. Molecular techniques suggested that [beta]-proteobacteria are important members of the macrophyte surface community. In the molecular survey, one sequence from Clone #44 (partial) was found to be 99.6% identical to YED6-21. This result, coupled with the isolation of the Hydrogenophaga oxidizers from a million-fold dilution of a suspension of cells from the macrophyte surface, suggests that the Hydrogenophaga are significant members of this community and may be the dominant arsenite oxidizers.\r\n\r\nThe densities of total and oxidizer cells associated with the submerged macrophytes in Hot Creek were estimated using most probable number (MPN) analysis. The normalized MPN values were [...] total cells/g dry wt. plant and [...] oxidizer cells/g dry wt. plant. These estimates suggest that the oxidizers constitute a significant fraction (on average 24%) of the overall biofilm community." }, { "name": "Samudrala, Omprakash", "degree": "PhD", "year": "2001", "title": "Subsonic and intersonic crack growth along weak planes and bimaterial interfaces", "advisor": "Knauss, Wolfgang Gustav; Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-134248309", "creators": [ { "name": { "family": "Samudrala", "given": "Omprakash" }, "id": "Samudrala-Omprakash", "display_name": "Samudrala, Omprakash" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/51b0-1c87", "abstract": "A combined experimental and analytical study has been conducted to investigate the phenomena of intersonic crack propagation along weak planes in homogeneous solids and dissimilar material interfaces. A single edge notch/crack oriented along a weak plane in a brittle polymer or along a polymer/metal interface was loaded in shear by impacting the specimen with a high velocity projectile fired from a gas gun. Homalite-100 or PMMA was chosen for the polymer and 6061 Aluminum or 4340 steel was chosen for the metal. The stress field information around the propagating crack tip was recorded in real time by two different optical techniques which provide complimentary information - photoelasticity and coherent gradient sensing (CGS), in conjunction with high speed photography. Along weak planes in Homalite-100, dynamic shear cracks were observed to initiate and propagate at speeds exceeding the shear wave speed (c_s) of the polymer. The isochromatic fringe patterns reveal two distinct lines of strong stress field discontinuity (Mach waves) emanating from the crack tip. Intersonic cracks were observed to initially accelerate up to the longitudinal wave speed (c_l) of Homalite and thereafter slow down to propagate at a near constant velocity slightly above \u221a2c_s . A series of short secondary opening cracks parallel to each other and at a steep angle to the weak plane (\u2248 80\u00b0) were also observed to initiate behind the main intersonic crack tip. Motivated by the experimental observations, an asymptotic analysis was performed to obtain the near tip fields for an intersonically propagating steady state mode II crack with a finite sized shear cohesive zone in front of it. The cohesive shear stress was chosen to be either a constant or to depend linearly on the magnitude of the local slip rate. Decohesion was chosen to occur when the relative slip between the two cohesive surfaces reaches a material/interface specific critical value. Unlike the case of a point sized dissipative region, it is shown that with a finite cohesive zone, the dynamic energy release rate is finite through out the intersonic regime. The influence of crack plane shear strength and of the rate parameter on the crack propagation behavior is investigated. Isochromatic fringe patterns were constructed using the cohesive crack tip fields, which compare favorably with the experimentally observed fringe patterns, and an attempt is made to extract the relevant analytical parameters. Unlike for a mode-I crack, a cohesive stress distribution that decreases with the local slip rate is found to match the experimental observations. The rate parameter was extracted by fitting the secondary crack angle observed in the experiments to that predicted by the analytical solution based on a maximum principal stress fracture criterion. Edge notches/cracks on polymer/metal interfaces were loaded under different impact configurations and the conditions governing the attainment of intersonic crack growth along a bimaterial interface were investigated. High resolution isochromatic fringe patterns were obtained to study the nature of the crack tip fields during subsonic/intersonic transition. Careful observations of the transition of an interface crack into the intersonic regime showed the formation of crack face contact at speeds beyond c_R of the polymer. Subsequently, the contact zone is observed to expand in size, detach from the intersonic crack tip and finally vanish. The recorded isochromatic fringe patterns showed multiple Mach wave formation associated with such a scenario. Along PMMA/ Al and PMMA/steel bimaterial interfaces, dynamic cracks initiating from edge notches were observed to accelerate to speeds higher than c_l of PMMA (supersonic), almost reaching c_R of aluminum. The resulting crack growth was observed to be highly transient and the gradients of in-plane normal stress components were recorded using CGS interferometry. Motivated by the aforementioned experimental observations, an asymptotic analysis was performed to obtain the stress and deformation fields around a steadily propagating intersonic crack on an elastic-rigid interface with a finite zone of crack face frictional sliding contact located a finite distance behind the tip. A linear frictional contact model is adopted, wherein the shear stress is proportional to the normal stress through a constant, the coefficient of dynamic friction. Isochromatic fringe patterns predicted by the near-tip fields exhibit the essential features observed during the experiments. Frictional sliding contact is shown to be possible only for velocities between c_s and \u221a2c_s of the polymer. The relevant analytical parameters were predicted by comparing the model to the experimental isochromatic fringe patterns and comments are made on the merits of the model presented." }, { "name": "Sane, Sandeep Bhalchandra", "degree": "PhD", "year": "2001", "title": "Time-dependent compressibility of poly (methyl methacrylate) (PMMA) : an experimental and molecular dynamics investigation", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:04262011-100757709", "creators": [ { "name": { "family": "Sane", "given": "Sandeep Bhalchandra" }, "id": "Sane-S-B", "display_name": "Sane, Sandeep Bhalchandra" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/saw5-7p32", "abstract": "This thesis contains three chapters, which describe different aspects of an investigation of the bulk response of Poly(Methyl Methacrylate) (PMMA). The first chapter describes the physical measurements by means of a Belcher/McKinney-type apparatus. Used earlier for the measurement of the bulk response of Poly(Vinyl Acetate), it was now adapted for making measurements at higher temperatures commensurate with the glass transition\r\ntemperature of PMMA. The dynamic bulk compliance of PMMA was measured at atmospheric pressure over a wide range of temperatures and frequencies, from which the master curves for the bulk compliance were generated by means of the time-temperature superposition principle. It was found that the extent of the transition ranges for the bulk and shear response were comparable. Comparison of the shift factors for bulk and shear responses supports the idea that different molecular mechanisms contribute to shear and\r\nbulk deformations.\r\n\r\nThe second chapter delineates molecular dynamics computations for the bulk response for a range of pressures and temperatures. The model(s) consisted of 2256 atoms\r\nformed into three polymer chains with fifty monomer units per chain per unit cell. The time scales accessed were limited to tens of pico seconds. It was found that, in addition to the typical energy minimization and temperature annealing cycles for establishing equilibrium models, it is advantageous to subject the model samples to a cycle of\r\nrelatively large pressures (GPa-range) for improving the equilibrium state. On comparing the computations with the experimentally determined \"glassy\" behavior, one finds that,\r\nalthough the computations were limited to small samples in a physical sense, the primary limitation rests in the very short times (pico seconds). The molecular dynamics computations do not model the physically observed temperature sensitivity of PMMA, even if one employs a hypothetical time-temperature shift to account for the large\r\ndifference in time scales between experiment and computation. The values computed by the molecular dynamics method do agree with the values measured at the coldest\r\ntemperature and at the highest frequency of one kiloHertz.\r\n\r\nThe third chapter draws on measurements of uniaxial, shear and Poisson response conducted previously in our laboratory. With the availability of four time or frequency-dependent material functions for the same material, the process of interconversion between different material functions was investigated. Computed material functions were\r\nevaluated against the direct experimental measurements and the limitations imposed on successful interconversion due to the experimental errors in the underlying physical data\r\nwere explored. Differences were observed that are larger than the experimental errors would suggest.\r\n" }, { "name": "Santamaria-Perez, Fidel", "degree": "PhD", "year": "2001", "title": "Processing of Mossy Fiber Activity in the Cerebellar Cortex: a Combination of Computer Modeling and Electrophysiological Experiments", "advisor": "Bower, James M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10082010-103716987", "creators": [ { "name": { "family": "Santamaria-Perez", "given": "Fidel" }, "id": "Santamaria-Perez-Fidel", "display_name": "Santamaria-Perez, Fidel" } ], "advisors": [ { "name": { "family": "Bower", "given": "James M." }, "id": "Bower-J-M", "role": "advisor", "display_name": "Bower, James M." } ], "committee": [ { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "chair", "display_name": "Allman, John Morgan" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Schuman", "given": "Erin Margaret" }, "id": "Schuman-E-M", "orcid": "0000-0002-7053-1005", "role": "member", "display_name": "Schuman, Erin Margaret" }, { "name": { "family": "Bower", "given": "James M." }, "id": "Bower-J-M", "role": "member", "display_name": "Bower, James M." } ], "option_major": [ "cns" ], "doi": "10.7907/r9zp-5814", "abstract": "A combination of computer modeling and experimental approaches were\r\ntaken to study tactile sensory processing in the cerebellar cortex. First, a\r\ndetailed computer simulation of the cerebellar cortex was built. This model\r\nincluded the physiological properties of the different cells involved and their\r\nsynaptic distributions. The model was used to study how a single tactile\r\nstimulus, arriving in the granule cell layer, is translated into Purkinje cell\r\nactivity, the output of the cerebellar cortex. The model was also used to\r\nstudy the lack of beam-like Purkinje cell activation after a focal stimulation\r\nof the granule cell layer in opposition to the most accepted theory of cerebellar\r\ncortical function: The beam hypothesis. The model predicts that the fast\r\ncoupling between the axons of granule cells with a small number of inhibitory\r\ncells generates a compensatory driving force on the Purkinje cell's dendritic\r\ntree that cancels the beam activation. The main prediction of the model is\r\nthat when supressing the inhibitory influence on Purkinje cells a beam would\r\nbe observed.
\r\n\r\nSecond, simultaneous recordings of Purkinje cells sharing the same granule\r\ncell input were collected while the receptive field of one of them was stimulated.\r\nThe cortex was bathed with bicuculline to block inhibitory input to Purkinje cells and the stimulation repeated. In the control case, only one of the Purkinje cells responded to the stimulus; the others showed inhibition or\r\ndid not respond at all. After bicuculline application, beams of Purkinje cell\r\nactivity were observed, thus confirming our simulation predictions.\r\nThird, using a detailed Purkinje cell model the effects of different levels of\r\ngranule cell and molecular interneuron input on the output of this cell were\r\nexplored. The results suggest that the granule cell input is divided in two\r\nfunctional synaptic systems. The first one drives the Purkinje cell to fire and\r\ncomes from the ascending segment part of the granule cell axon. The second\r\none, combined with molecular interneuron activity, modulates the response\r\nof the Purkinje cell to ascending segment input.\r\nBased on the computational and experimental results of this work, we\r\npropose that parallel fibers and molecular interneurons have a modulatory\r\neffect on the response of the Purkinje cell to the more direct and strong\r\nascending segment input.
" }, { "name": "Schooler, Eve Meryl", "degree": "PhD", "year": "2001", "title": "Why multicast protocols (don't) scale: an analysis of multipoint algorithms for scalable group communication", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272001-155016", "creators": [ { "name": { "family": "Schooler", "given": "Eve Meryl" }, "id": "Schooler-Eve-Meryl", "display_name": "Schooler, Eve Meryl" } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Estrin", "given": "Deborah" }, "id": "Estrin-D", "role": "member", "display_name": "Estrin, Deborah" }, { "name": { "family": "Hickey", "given": "Jason J." }, "id": "Hickey-J-J", "role": "member", "display_name": "Hickey, Jason J." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" } ], "option_major": [ "compsci" ], "doi": "10.7907/44QZ-R465", "abstract": "With the exponential growth of the Internet, there is a critical need to design efficient, scalable and robust protocols to support the network infrastructure. A new class of protocols has emerged to address these challenges, and these protocols rely on a few key techniques, or micro-algorithms, to achieve scalability. By scalability, we mean the ability of groups of communicating processes to grow very large in size. We study the behavior of several of these fundamental techniques that appear in many deployed and emerging Internet standards: Suppression, Announce-Listen, and Leader Election.\r\n\r\nThese algorithms are based on the principle of efficient multipoint communication, often in combination with periodic messaging. We assume a loosely-coupled communication model, where acknowledged messaging among groups of processes is not required. Thus, processes infer information from the periodic receipt or loss of messages from other processes.\r\n\r\nWe present an analysis, validated by simulation, of the performance tradeoffs of each of these techniques. Toward this end, we derive a series of performance metrics that help us to evaluate these algorithms under lossy conditions: expected response time, network usage, memory overhead, consistency attainable, and convergence time. In addition, we study the impact of both correlated and uncorrelated loss on groups of communicating processes.\r\n\r\nAs a result, this thesis provides insights into the scalability of multicast protocols that rely upon these techniques. We provide a systematic framework for calibrating as well as predicting protocol behavior over a range of operating conditions. In the process, we establish a general methodology for the analysis of these and other scalability techniques. Finally, we explore a theory of composition; if we understand the behavior of these micro-algorithms, then we can bound analytically the performance of the more complex algorithms that rely upon them." }, { "name": "Seywert, Claude", "degree": "PhD", "year": "2001", "title": "Combustion Instabilities: Issues in Modeling and Control", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252007-135242", "creators": [ { "name": { "family": "Seywert", "given": "Claude" }, "id": "Seywert-Claude", "display_name": "Seywert, Claude" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JKFD-7W43", "abstract": "This study deals with various aspects in the development of active control of combustion instabilities.\r\n\r\nA low-order model is developed, reconciling along the way two different approaches taken by researchers to attack the description of combustion instabilities. The model is demonstrated with application to a Rijke tube and compared to experiments. The Rijke burner experiments suggest two major discrepancies with the model: the presence of a hysteresis loop is unaccounted for and the model does not describe the seemingly random fluctuations in the amplitude of the pressure oscillations in the 'unstable' regime. So far no explanation for the hysteresis can be given; however, this phenomenon is successfully exploited by using a novel nonlinear control technique to expand the stable operating range of the burner. The origin of the 'noise' in the pressure trace is explained by considering entropy and vorticity waves in the combustor. Their presence leads to a slight modification of the original model, introducing stochastic source terms into the oscillator equations. The consequences of the presence of these terms is analyzed by means of simulations. One interesting result is that they allow for the identification of model parameters from a single experimental run of a stable combustion system.\r\n\r\nFinally, a unified approach to controlling combustion instabilities is presented. The formulation and analysis account for truncation to a few modes; uncertainties in the description of the system (including uncertain sensing and actuating); external disturbances; and intrinsic noise sources. An explicit expression is derived against which any controller can be checked for stability." }, { "name": "Shan, Wei-Jen Jerry", "degree": "PhD", "year": "2001", "title": "Mixing and Isosurface Geometry in Turbulent Transverse Jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082002-152648", "creators": [ { "name": { "family": "Shan", "given": "Wei-Jen Jerry" }, "id": "Shan-Wei-Jen-Jerry", "display_name": "Shan, Wei-Jen Jerry" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0R6S-DY34", "abstract": "Mixing and the geometry of jet-fluid-concentration level sets in turbulent transverse jets were experimentally studied. Jet-fluid concentration fields were measured with laser-induced fluorescence and digital imaging techniques for Reynolds numbers between 1000 and 20000. The scalar field is assessed in terms of classical measures, such as two-dimensional power spectra, as well as probability-density functions (PDFs). Enhanced scalar mixing with increasing Reynolds number is found in the evolution of PDFs of jet-fluid concentration. In the far field of the transverse jet, the scalar PDF is seen to evolve from a monotonically-decreasing function to a strongly-peaked distribution with increasing Reynolds number. Turbulent mixing is found to be flow dependent, based on differences between PDFs of scalar fields in transverse jets and axisymmetric, turbulent jets. The distribution of scalar increments is also studied for separations of varying distance and direction. A novel technique for whole-field measurement of scalar increments is introduced. Probability-density functions of scalar increments are found to trend toward exponential-tailed distributions with decreasing separation distances. The scalar field is anisotropic with decreasing scale, as seen in the two-dimensional power spectra, directional scalar microscales, and in directional PDFs of scalar increments.\r\n\r\nThe geometric complexity of level-sets (iso-concentration contours) in turbulent mixing is assessed within the framework of fractal geometry.\r\nGeneralized coverage statistics are introduced for anisotropic, non-self-similar geometries. This generalized coverage counting involves covering with parallelepipeds of varying size and aspect ratio. A scale-dependent measure of the anisotropy of a set is also introduced. It is shown that this scale-dependent measure transforms the generalized coverage count to isotropy through a scale-dependent normalization of the coordinates. Level sets of jet-fluid concentration in the transverse jet are found to be anisotropic at both large and small scales. The small-scale anisotropy is explained by vertically-oriented extensional strain caused by a counter-rotating vortex pair, while the large-scale anisotropy is associated with the horizontally-elongated shape of the cross-section of the transverse jet. For the special case of isotropic box-counting, the scale-dependent coverage dimension is found to vary from unity, at the smallest length scales, to 2, at the largest length scales, indicating that the isosurfaces produced by turbulent mixing are more complex than can be described by power-law fractals" }, { "name": "Steckman, Gregory Joseph", "degree": "PhD", "year": "2001", "title": "Holographic recording in polymeric materials with applications", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232009-094031", "creators": [ { "name": { "family": "Steckman", "given": "Gregory Joseph" }, "id": "Steckman-G-J", "display_name": "Steckman, Gregory Joseph" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/m10t-n277", "abstract": "This thesis presents the results of research in volume holographic recording in several polymeric recording materials and their use in selected applications. The first chapter discusses the key properties of holographic recording materials. The second chapter develops a technique for calculating exposure schedules for photorefractive polymers which do not exhibit mono-exponential recording dynamics. It is determined that these materials require performance improvements before they can be successfully applied to many interesting applications of volume holography, such as holographic data storage and optical correlators which are described in later chapters.\r\n\r\nThe third chapter investigates recording in diffusion amplification based polymer materials. This class of materials overcomes many limitations of other polymer types, such as limited thicknesses and volume shrinkage. A new material based on the diffusion amplification principle is developed with the goal of increasing dynamic range. The new material, a naphtoquinone and PMMA based co-polymer, is demonstrated in holographic recording experiments.\r\n\r\nIn the fourth chapter, holographic data storage experiments are performed and a storage density of 7 bits/\u03bcm[superscript 2] is achieved. A holographic data storage system which utilizes shift multiplexing is modeled and simulated to determine optimal system parameters and material characteristics. It is discovered that the dynamic range of the material used, phenanthrenequinone doped poly(methyl methacrylate), is insufficient to provide very high data storage densities.\r\n\r\nIn the fifth chapter attention is focused on the development and characterization of an optical holographic correlator system using the DuPont HRF-150 photopolymer. The system is used for image recognition and tracking. The performance of the system is characterized with multiple 2-d and 3-d objects with respect to camera resolution, magnification, rotation, and other transformations. The system is demonstrated to be capable of simultaneously recognizing and tracking multiple targets, even in the presence of extraneous objects and partial obscuring of the targets.\r\n\r\nThe final chapter describes the development of a high-speed holographic movie camera. Utilizing a Q-switched Nd:YAG pulse laser and Aprilis ULSHSO0-7A recording material, multi-frame holographic exposures with a 80 MHz frame rate are recorded.\r\n" }, { "name": "Tang, Kea-Tiong", "degree": "PhD", "year": "2001", "title": "Neuromorphic VLSI circuits for an electronic nose chip", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-085150166", "creators": [ { "name": { "family": "Tang", "given": "Kea-Tiong" }, "id": "Tang-K-T", "display_name": "Tang, Kea-Tiong" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/sdb6-3c88", "abstract": "Human olfaction is still the primary instrument used in many industries to classify the smell or flavor of products. This is a costly process since trained experts are required who can only work for relatively short periods of time. Therefore using machine olfaction to perform the task would be a significant advance. Many researchers have investigated electronic noses, but currently only relatively large \"instrument\" electronic noses have been built. We have designed an electronic nose on a single silicon chip, including adaption, signal processing, and classification.\r\n\r\nThe electronic nose chip is composed of four different stages: Sensor stage, Signal Processing stage, Database stage, and Classifier stage.\r\n\r\nThe sensor stage, as its name suggests, deals with the sensor directly. The sensor we use is a carbon black-organic polymer whose relative resistance change is proportional to the given odor concentration. The function of the sensor stage is to adapt this resistive sensor to a preset baseline value, take the AC signal voltage, then output a current proportional to the signal voltage. So the sensor stage outputs a signal current which contains information about the odor concentration. An adaptive electronics stage, a peak detector, and a transconductance amplifier are designed to complete the sensor stage. Adaptive electronics are implemented to adapt the sensor to be within a proper working range of the circuit while tuning out the environment background. Adaption is done by constructing an adjustable current source. After adaption is done, the bias current value is held, so the sensor voltage at this time contains two different types of information: baseline value and signal value. The peak detector traces the input signal to its maximum value, then holds the value for further signal processing. This is needed because the signal voltage is defined as the difference between the maximum sensor voltage and the baseline sensor voltage. The transconductance amplifier converts voltage to current linearly while functioning as high pass filter. The output current is equal to the difference between the two input voltages multiplied by some gain (called transconductance). The output of the peak detector, the maximum sensor voltage, is used as the noninverting input, while the baseline sensor voltage is used as the inverting input. By the differential input characteristic of the transconductance amplifier, the baseline information is cancelled, and only the signal information remains. Thus, the output current from the transconductance amplifier contains the signal information, i.e., odor concentration.\r\n\r\nThe signal processing stage performs two important tasks for further signal processing. First, normalization throughout the signal array is realized. Then the Euclidean distance between the signal vector and the data vector is calculated. A normalizer using city-blocks distance is designed and an Euclidean distance calculation circuit is built. A normalization circuit using city-blocks distance is implemented to generate a normalized signal vector. This normalized signal vector is stored in a SRAM through an A/D in the LEARNING State. On the other hand, in the CLASSIFYING state, Euclidean distance between the normalized signal vector and the data vector is calculated. Euclidean distance circuit is implemented to calculate the Euclidean distance between signal vector and data vector. The Euclidean distance is output in the form of a current. This distance measure is utilized for classification.\r\n\r\nThe database stage stores the signal vector in the data storage device (LEARNING state) or outputs the data vector from the data storage device (CLASSIFYING state). This stage also takes care of the interface between the electronic nose chip and the outside world. A central control unit is designed to generate all the control signals and arrange the time sequence. Eight-bit Static Random-Access Memory (SRAM) is used for data storage. A/D converter is used to convert the signal vector into a digital word. This happens during the LEARNING process. A D/A converter is used to convert the data from SRAM into the data vector. This happens during the CLASSIFYING process. A current copier cell is designed to maintain the value of the data current. Several current copier cells are used to form a data vector. The central control unit is designed to generate all the control signals needed and their time sequence.\r\n\r\nThe classifier stage receives all the Euclidean distances between signal vector and data vectors, and generates the output corresponding to the shortest Euclidean distance, while inhibiting all the other outputs. The generated output is denoted as the answer to the pattern recognition problem. The current copier cell in the database stage is used to maintain the value of the Euclidean distance current. Several current copier cells are used to generate inputs for the LTA circuit. The Loser-Take-All (LTA) is used for parallel classification. Global inhibition can be done by using an LTA circuit." }, { "name": "Tokman, Mayya", "degree": "PhD", "year": "2001", "title": "Magnetohydrodynamic modeling of solar magnetic arcades using exponential propagation methods", "advisor": "Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062006-154529", "creators": [ { "name": { "family": "Tokman", "given": "Mayya" }, "id": "Tokman-M", "display_name": "Tokman, Mayya" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/PDCS-GX15", "abstract": "Advanced numerical methods based on exponential propagation have been applied to magnetohydrodynamic (MHD) simulations. This recently developed numerical technique evolves the system of nonlinear equations using exponential propagation of the Jacobian matrix. The exponential of the matrix is approximated by projecting it onto the Krylov subspace using the Arnoldi algorithm. The primary advantage of the exponential propagation method is that it allows time steps exceeding the Courant-Friedrichs-Lewy (CFL) limit. Another important aspect is faster convergence of the iteration computing the Krylov subspace projection compared to solving an implicit formulation of the system with similar iterative methods. Since the time scales in the resistive MHD equations are widely separated, the exponential propagation methods are especially advantageous for computing the long term evolution of a low-beta plasma. We analyze several types of exponential propagation methods and highlight important issues in the development of such techniques. Our analysis also suggests new ways to construct schemes of this type. Implementation issues, including scalability properties of exponential propagation methods, and performance are also discussed.\r\n\r\nIn the second part of this work we present numerical MHD models which are constructed using exponential propagation methods and which describe the evolution of the magnetic arcades in the solar corona. Since these numerical methods have not been used before for large evolutionary systems like resistive MHD, we first validate our approach by demonstrating application of the exponential schemes to two existing magnetohydrodynamic models. We simulate the reconnection process resulting from shearing the footpoints of two-dimensional magnetic arcades and compute the three-dimensional linear force-free states of plasma configurations. Analysis of these calculations leads us to new insights about the topology of the solutions. The final chapter of this work is dedicated to a new three-dimensional numerical model of the dynamics of coronal plasma configurations. The model is motivated by observations and laboratory experiments simulating the evolution of solar arcades. We analyze the results of numerical simulations and demonstrate that our numerical approach provides an accurate and stable way to compute the solution to the zero-resistive MHD system. Based on comparisons of the simulation results and the observational data, we offer an explanation for the observed structure of eruptive events in the corona called coronal mass ejections (CME). We argue that the diversity of the images of CMEs obtained by the observational instruments can be explained as two-dimensional projections of a unique three-dimensional plasma configuration and suggest an eruption mechanism." }, { "name": "Tripathi, Ashok Burton", "degree": "PhD", "year": "2001", "title": "In-Situ Diagnostics for Metalorganic Chemical Vapor Deposition of YBCO", "advisor": "Goodwin, David G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262005-143545", "creators": [ { "name": { "family": "Tripathi", "given": "Ashok Burton" }, "id": "Tripathi-Ashok-Burton", "display_name": "Tripathi, Ashok Burton" } ], "advisors": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "advisor", "display_name": "Goodwin, David G." } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Raja", "given": "L." }, "id": "Raja-L", "role": "member", "display_name": "Raja, L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/3ZJS-BE38", "abstract": "A new stagnation flow MOCVD research reactor is described that is designed to serve as a testbed to develop tools for \"intelligent\" thin film deposition, such as in-situ sensors and diagnostics, control algorithms, and thin film growth models. The reactor is designed in particular for the deposition of epitaxial YBa2Cu3O7-\u03b4 on MgO, although with minor modifications it would be suitable for deposition of any metal-oxide thin films.
\r\n\r\nThe reactor is specifically designed to permit closed-loop thermal and stoichiometric control of the film growth process. Closed-loop control of precursor flow rates is accomplished by using ultraviolet absorption spectroscopy on each precursor line. Also integrated into the design is a Fourier Transform Infrared (FTIR) spectroscopy system which collects real-time, in-situ infrared polarized reflectance spectra of the film as it grows. Numerical simulation was used extensively to optimize the fluid dynamics and heat transfer to provide uniform fluxes to the substrate. As a result, thickness uniformity across the substrate is typically within 3% from the center to the edge of the substrate.
\r\n\r\nExperimental studies of thin films grown in the Y/Ba/Cu/O system have been carried out. The films have been characterized by Rutherford Backscattering Spectrometry and X-ray Diffraction. Results indicate c-axis oriented grains with pure 1:2:3 phase YBCO, good spatial uniformity, and a low degree of c-axis wobble. Experimental growth data is used in a gas phase and surface chemistry model to calculate sticking coefficients for yttrium oxide, barium oxide, and copper oxide on YBCO.
\r\n\r\nIn-situ FTIR and Coherent Gradient Sensing (CGS) analysis of growing films has been performed, yielding accurate substrate temperature, film thickness monitoring, and full-field, real-time curvature maps of the films. In addition, we have implemented CGS to obtain full-field in-situ images of local curvature during oxygenation and deoxygenation of YBCO films. An analysis of the oxygen diffusion is performed, and diffusivity constants are presented for a variety of temperature and film conditions.
" }, { "name": "Watanabe, Katsumi", "degree": "PhD", "year": "2001", "title": "Crossmodal Interaction in Humans", "advisor": "Shimojo, Shinsuke", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-090303102", "creators": [ { "name": { "family": "Watanabe", "given": "Katsumi" }, "id": "Watanabe-Katsumi", "display_name": "Watanabe, Katsumi" } ], "advisors": [ { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "advisor", "display_name": "Shimojo, Shinsuke" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" } ], "option_major": [ "cns" ], "doi": "10.7907/66cn-aq26", "abstract": "Since different senses are attuned to the different aspects of the environment, crossmodal interactions can reduce perceptual ambiguity which may result from relying on a single sensory modality. While many studies have shown that visual information affects perception in the other modalities, little is known about how auditory and tactile information affect visual perception. The present thesis explores how the human perceptual system synthesizes visual event perception by using an ambiguous visual motion display: Two identical visual targets moving across each other can be perceived either to bounce off or to stream through each other. A brief sound at the moment the targets coincide biases perception toward bouncing. Extensive psychophysical investigations on this bounce-inducing effect show that: (1) A salient sensory transient biases visual perception toward bouncing, irrespective of the modality in which such a transient is presented. (2) The magnitude of the bounce-inducing effect depends on both the saliency of a sensory transient and the timing of a sensory transient relative to the visual coincidence. (3) The magnitude of the bounce-inducing effect increases as the sensory saliency of bounce-inducing transients increases. (4) The interaction window during which a sensory transient can bias visual perception is fixed in time. (5) Auditory and tactile transients have much larger temporal interaction windows than visual transients. (6) Auditory and tactile transients presented before the visual coincidence tend to have a stronger bounce-inducing effect than those presented after the visual coincidence; visual transients do not show this asymmetry. (7) The lack of attention to the visual moving targets in the streaming/bouncing motion display increases the likelihood of the bouncing percept. Based on these results, I conclude that the streaming percept arises when amodal attentional resource is available for moving stimuli around the moment of the visual coincidence and that the bouncing percept results from the lack of attentional resource. The role of salient sensory transients in the bounce-inducing effect is to distract attention from the coinciding moving stimuli. Thus, this thesis shows that dynamics of attentional resource allocation, not simply associative learning, can be the cause of amodal event perception in humans.\r\n" }, { "name": "Ye, Yun", "degree": "PhD", "year": "2001", "title": "Interaction of Hydrogen with Novel Carbon Materials", "advisor": "Cass, Glen Rowan; Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-083542958", "creators": [ { "name": { "family": "Ye", "given": "Yun" }, "id": "Ye-Yun", "display_name": "Ye, Yun" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "co-advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "member", "display_name": "Ahn, Channing C." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "orcid": "0000-0003-1468-6835", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bowman", "given": "Robert Clark, Jr." }, "id": "Bowman-Robert-Clark-Jr", "role": "member", "display_name": "Bowman, Robert Clark, Jr." } ], "option_major": [ "matsci" ], "doi": "10.7907/z8wn-gs34", "abstract": "The hydrogen storage properties of sonic carbon materials were studied. Graphite nanofibers (GNF) were synthesized by catalytic decomposion of ethylene and hydrogen. Catalyst supported carbon materials were prepared by impregnation process. Hydrogen desorption and adsorption properties of graphite nanofibers, single-walled carbon nanotubes (SWNT), fullerene materials and catalysts supported carbon materials were measured volumetrically using a Sievert's apparatus. The hydrogen desorption capacity of GNF was typically less than 0.2 wt.%. A phase transition between crystal SWNT and a new hydride phase was found at high pressures at 80K. The phase transition was of first order, and involved the separation of the individual tubes within a rope, exposing a high surface area for hydrogen adsorption. From the change in chemical potential of the hydrogen gas upon adsorption, we were able to calculate the cohesive van der Waals energy between the tubes as 5 mcV/C atom. This is much smaller than expected from previous theoretical work, and shows that defects in the crystal structure cause large suppressions of the cohesive energy. We were able to alter this cohesive energy by changing the state of the material. Over several cycles of isotherm measurements at 77 K, the hydrogen storage capacities of one of the fullerite samples increased from an initial value of 0.4 wt% for the first cycle to a capacity of 4.2 wt% for the fourth cycle. Correspondingly, the surface area increased from 0.9 m^2/gm to 11 m^2/gm and showed a phase transformation, characterized by X-ray powder diffraction. By adding Ni particles onto the sample, the hydrogen storage capacity of fullerite and activated carbon sample was increased. The adsorption of hydrogen on Ni particle can not account for the total increased capacity even by assuming complete coverage of hydrogen molecules on the Ni particle surface." }, { "name": "Yu, Chengxiang Rena", "degree": "PhD", "year": "2001", "title": "Three-Dimensional Cohesive Modeling of Impact Damage of Composites", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112010-130530819", "creators": [ { "name": { "family": "Yu", "given": "Chengxiang Rena" }, "id": "Yu-Chengxiang-Rena", "orcid": "0000-0003-4176-0324", "display_name": "Yu, Chengxiang Rena" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Pandolfi", "given": "Anna" }, "id": "Pandolfi-A", "role": "member", "display_name": "Pandolfi, Anna" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/nd8e-tc84", "abstract": "The objective of this work is to establish the applicability of cohesive theories of fracture in situations involving material interface, material heterogeneity (e.g., layered composites), material anisotropy(e.g., fiber-reinforced composites), shear cracks, intersonic dynamic crack growth and dynamic crack branching. The widely used cohesive model is extended to orthotropic range. The so-developed computational tool, completed by a self-adaptive fracture procedure and a frictional contact algorithm, is capable of following the evolution of three-dimensional damage processes, modeling the progressive decohesion of interfaces and anisotropic materials. The material parameters required by cohesive laws are directly obtained from static experiments. The ability of the methodology to simulate diverse problems such as delamination between fibers of graphite/epoxy composites, as well as sandwich structures and branching within brittle bulk materials has been demonstrated.
" }, { "name": "Zhang, Yunfeng", "degree": "PhD", "year": "2001", "title": "Semi-Active Control of Dynamically Excited Structures Using Active Interaction Control", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechThesis:10242017-093657605", "creators": [ { "name": { "family": "Zhang", "given": "Yunfeng" }, "id": "Zhang-Yunfeng", "display_name": "Zhang, Yunfeng" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/N9QZ-ZP30", "abstract": "This thesis presents a family of semi-active control algorithms termed Active Interaction Control (AIC) used for response control of dynamically excited structures. The AIC approach has been developed as a semiactive means of protecting building structures against large earthquakes. The AIC algorithms include the Active Interface Damping (AID), Optimal Connection Strategy (OCS), and newly developed Tuned Interaction Damping (TID) algorithms. All of the AIC algorithms are founded upon the same basic instantaneous optimal control strategy that involves minimization of an energybased performance index at every time instant.
\r\n\r\nA typical AIC system consists of a primary structure targeted for vibration control, a number of auxiliary structures, and interaction elements that connect the auxiliary structures to the primary structure. Through actively modulating the operating states of the interaction elements according to pre-specified control logic, control forces favorable to the control strategy are reactively developed within the interaction elements and the vibration of the primary structure is thus restrained. The merits of this structural control approach include both high control performance and minimal external power requirement for the operation of the control devices. The latter is important during large earthquakes when power blackouts are likely to occur. Most encouraging is that with currently available technology this control approach can be readily implemented in real structures.
\r\n\r\nIn this thesis, the cause for an overattachment problem in the original OCS system is clarified and corresponding counter-measures are proposed. The OCS algorithm is reformulated within an energy framework and therefore all of the AIC control algorithms are unified under the same instantaneous optimal control strategy.
\r\n\r\nTo implement the AIC algorithms into multi-degree-of-freedom systems, two approaches are formulated in this thesis: the Modal Control and Nodal Control approaches. The Modal Control approach directs the control effort to certain dominant response modes, and the Nodal Control approach directly controls the response quantities in physical space. It is found that the Modal Control approach is more efficient than the Nodal Control approach. The effectiveness of the AIC control algorithms is verified through numerical simulation results for three-story, nine-story and twenty-story steel-framed buildings. The statistical behavior of the AIC system is evaluated based on a Monte Carlo simulation.
" }, { "name": "Zuhal, Lavi Rizki", "degree": "PhD", "year": "2001", "title": "Formation and Near-Field Dynamics of a Wing Tip Vortex", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072013-122723580", "creators": [ { "name": { "family": "Zuhal", "given": "Lavi Rizki" }, "id": "Zuhal-Lavi-Rizki", "display_name": "Zuhal, Lavi Rizki" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VNJW-6592", "abstract": "The search for a more efficient method to destroy aircraft trailing vortices requires\r\na good understanding of the early development of the vortices. For that purpose, an\r\nexperimental investigation has been conducted to study the formation and near-field\r\ndynamics of a wing tip vortex.
\r\n\r\nTwo versions of the Digital Particle Image Velocimetry (DPIV) technique were\r\nused in the studies. Planar DPIV was used to obtain velocity fields adjacent to the wing\r\nsurface. Stereoscopic DPIV, which allows instantaneous measurements of all three\r\ncomponents of velocity within a planar slice, was used to measure velocity fields behind\r\nthe wing. The trailing vortex was produced by a rectangular half-wing model with an\r\nNACA 0012 profile. All measurements were made at Reynolds number, based on chord\r\nlength, of 9040.
\r\n\r\nThe present study has found that the wing sheds multiple vortices. A structure\r\nthat closely resembles a wing tip vortex is first observed on the suction side of the wing\r\nnear the tip at the mid-chord section of the wing. At the trailing edge of the wing, a\r\nsmaller vortex with an opposite sense of rotation is observed next to the tip vortex. In\r\naddition to the two vortices, two vortex layers with opposite sense of rotation, one on the\r\npressure side and one on the suction side, are apparent at the trailing edge. Farther\r\ndownstream, most of the vorticity in the vortex layer, with the same sense of rotation as\r\nthe tip vortex, rolls up into the wing tip vortex. The vortices, with opposite sense of\r\nrotation, break up into smaller vortices which orbit around the tip vortex. At least one\r\nrelatively strong satellite vortex appears in some of the instantaneous fields. The studies\r\nfound that the interaction of the tip vortex and satellite vortices give rise to the unsteady\r\nmotion of the wing tip vortex. In addition, the studies also examined the effects of the\r\nboundary layer and the tip geometry to the strength and motion of the trailing vortex.
" }, { "name": "Aagaard, Brad Thomas", "degree": "PhD", "year": "2000", "title": "Finite-Element Simulations of Earthquakes", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechThesis:04292016-090209111", "creators": [ { "name": { "family": "Aagaard", "given": "Brad Thomas" }, "id": "Aagard-Brad-Thomas", "display_name": "Aagaard, Brad Thomas" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." } ], "option_major": [ "civileng" ], "doi": "10.7907/T65C-9C94", "abstract": "This thesis discusses simulations of earthquake ground motions using prescribed ruptures and dynamic failure. Introducing sliding degrees of freedom led to an innovative technique for numerical modeling of earthquake sources. This technique allows efficient implementation of both prescribed ruptures and dynamic failure on an arbitrarily oriented fault surface. Off the fault surface the solution of the three-dimensional, dynamic elasticity equation uses well known finite-element techniques. We employ parallel processing to efficiently compute the ground motions in domains containing millions of degrees of freedom.
\r\n\r\nUsing prescribed ruptures we study the sensitivity of long-period near-source ground motions to five earthquake source parameters for hypothetical events on a strike-slip fault (Mw 7.0 to 7.1) and a thrust fault (Mw 6.6 to 7.0). The directivity of the ruptures creates large displacement and\r\nvelocity pulses in the ground motions in the forward direction. We found a good match between the severity of the shaking and the shape of the near-source factor from the 1997 Uniform Building Code for strike-slip faults and thrust faults with surface rupture. However, for blind thrust faults the peak displacement and velocities occur up-dip from the region with the peak near-source factor. We assert that a simple modification to the formulation of the near-source factor improves the match between the severity of the ground motion and the shape of the near-source factor.
\r\n\r\nFor simulations with dynamic failure on a strike-slip fault or a thrust fault, we examine what constraints must be imposed on the coefficient of friction to produce realistic ruptures under the application of reasonable shear and normal stress distributions with depth. We found that variation of the coefficient of friction with the shear modulus and the depth produces realistic rupture behavior in both homogeneous and layered half-spaces. Furthermore, we observed a dependence of the rupture speed on the direction of propagation and fluctuations in the rupture speed and slip rate as the rupture encountered changes in the stress field. Including such behavior in prescribed ruptures would yield more realistic ground motions.
" }, { "name": "Adibi, Ali", "degree": "PhD", "year": "2000", "title": "Persistent holographic storage in photorefractive crystals", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092010-094455249", "creators": [ { "name": { "family": "Adibi", "given": "Ali" }, "id": "Adibi-Ali", "display_name": "Adibi, Ali" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ESSK-6B14", "abstract": "The work presented in this thesis has been focused on solving the most important and long-lasting problem of destructive read-out in holographic recording in photorefractive crystals. Several interesting methods for solving this problem were proposed and demonstrated by researchers for more than two decades. However, none of them\r\nwere practical for read / write applications. The most promising all-optical method, which is still being pursued by some researchers, was two-step recording. However,\r\nthe method suffers from low sensitivity and dynamic range, even in the optimized conditions. Furthermore, several experimental results were not explained due to the\r\nlack of a complete understanding of the dominant phenomena that were involved. Our strategy in solving the problem of destructive read-out of holograms was to first provide a complete understanding of the physics of the two-step recording method by appropriate modeling, and to explain the experimental results that had not been explained before. Such an understanding gave us a good idea about the major problem of the method, and we were able to find a solution to that problem by adding one dopand to the recording crystal. The method we developed both theoretically and experimentally in this thesis is called two-center holographic recording. The initial results of the method (without any optimization) offer more than one order of magnitude (and for some parameters, two orders of magnitude) improvement over the optimized two-step recording method.\r\nIn this thesis, we provide a complete modeling for two-center recording that agrees\r\nvery well with the experimental results, provides us with the understanding of the\r\nmain physical phenomena that are involved, and helps us in optimizing the method.\r\nThe next step is to relate the material and system parameters for the system design.\r\nWe present in this thesis a standard framework for such a relation, and outline the\r\nmain general steps in the system design using two-center recording. The idea developed\r\nin this thesis opens us several avenues for further thinking and research, and\r\nsome of them are already being investigated by different research groups." }, { "name": "Aji, Srinivas Mandayam", "degree": "PhD", "year": "2000", "title": "Graphical Models and Iterative Decoding", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04112003-162805", "creators": [ { "name": { "family": "Aji", "given": "Srinivas Mandayam" }, "id": "Aji-Srinivas-Mandayanl", "display_name": "Aji, Srinivas Mandayam" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/79XC-5C54", "abstract": "Since the invention of turbo codes, there has been a lot of interest in iterative decoding schemes.It is also known that the turbo decoding algorithm and several other previously known iterative algorithms are instances of Pearl's belief propagation algorithm applied to a graph with cycles, while the algorithm is known to work only for graphs without cycles. We describe a marginalization algorithm which works on junction trees, which is based on some newer developments in Bayesian networks. This is sufficiently general that Pearl's belief propagation and decoding on Tanner graphs may be regarded as special cases. An attempt to compute the discrete Fourier transform as a marginalization problem in this framework gives the fast Fourier transform algorithm, thus showing that this framework has applications apart from probabilistic computations. Junction graphs with cycles lead to an iterative algorithm. The case of junction graphs with a single cycle is analyzed, with specific results in the case of the sum-product algorithm. We also have some experimental results for small turbo code-like junction graphs.\r\n\r\nOn a different topic, we consider the typical set decoder, which can be used to obtain bounds on the noise threshold for asymptotically error free decoding, for given code ensembles. Some choices of the typical set for AWGN channel are considered and the resulting bounds on the threshold obtained.\r\n" }, { "name": "Babcock, David S.", "degree": "PhD", "year": "2000", "title": "Intelligent control using generalizing case-based reasoning with neural networks", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09302010-142626064", "creators": [ { "name": { "family": "Babcock", "given": "David S." }, "id": "Babcock-D-S", "display_name": "Babcock, David S." } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/HBTD-WE62", "abstract": "One model of human learning involves choosing an action based on past experiences in similar situations. The chosen action is typically modified to compensate for any discrepancies with the current situation. After sufficient experience has been obtained, at least in a particular regime, the experiences are conceptualized into a general\r\nresponse mechanism. This thesis presents an algorithm that formalizes this hybrid reasoning process and applies it to control of a nonlinear physical system. Experiences\r\nare stored as vectors of variables known as cases in a set called a casebase. Vector norms are used to select an appropriate case from the case base which is then modified\r\nusing an adaptation routine. Once the modified action is applied to the system and the resulting outcome is observed, the casebase is augmented to include the new experience for improved future performance. A gated expert neural network is eventually trained on subsets of the case base to create local inverse model approximations for\r\nregions of the input space where sufficient data is available to support generalization. The gate network selects one of the experts if appropriate or otherwise defaults back to case-based reasoning. The applicability of the hybrid algorithm is demonstrated on a nonlinear control problem, setpoint regulation in a ball and beam system.\r\n" }, { "name": "Bandi\u0107, Zvonimir Z.", "degree": "PhD", "year": "2000", "title": "Novel devices employing epitaxial wide bandgap semiconductors : physics, electronics and materials characterization", "advisor": "McGill, T. C.; McCaldin, James Oeland", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052010-115649444", "creators": [ { "name": { "family": "Bandi\u0107", "given": "Zvonimir Z." }, "id": "Bandi\u0107-Z-Z", "display_name": "Bandi\u0107, Zvonimir Z." } ], "advisors": [ { "name": { "family": "McGill", "given": "T. C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, T. C." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "advisor", "display_name": "McCaldin, James Oeland" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/cnyb-cq58", "abstract": "This thesis describes the developments of novel semiconductor devices based on epitaxial wide bandgap semiconductors GaN and ZnS. The number of interesting and exciting results in physics, electronics and materials science of these systems were found in studies motivated by these devices. This thesis consists of three major topics, structural characterization and kinetic growth modeling of the GaNAs/GaAs superlattices, structural and optical characterization and solid phase recrystallization of ZnS thin films grown on GaN and sapphire substrates, and design and fabrication of GaN high power devices as well as measurement of fundamental electronic properties of GaN, such as minority carrier diffusion lengths and lifetimes and critical field for electric breakdown.\r\n\r\nThe set of GaNAs/GaAs superlattices grown by molecular beam epitaxy was analyzed by high resolution X-ray diffraction and cross\u2014sectional transmission electron microscopy. The nitrogen incorporation and GaNAs/GaAs interface sharpness were experimentally found to strongly depend on growth temperature. The activation energies for nitrogen desorption and nitrogen to arsenic segregation were found through simple kinetic model, which is in fine agreement with experimentally obtained results. These fundamental studies provide important insights into growth of GaN on GaAs substrates, which is of significant practical importance for all electronic GaN devices.\r\n\r\nZinc sulfide/Gallium nitride heterostructures are potentially interesting system for light emitters in blue and green part of visible spectrum, with DC low power consumption electroluminescent displays being one attractive application of these diodes. Zinc sulfide thin films grown on GaN (0001), GaAs (001) and sapphire (0001) substrates by MBE were characterized by variable temperature photoluminescence and high resolution X-ray diffraction. The structural properties of the films suffered from the large lattice mismatch between ZnS and various substrates which were used. The optical properties of the ZnS films were found to be in direct correlation with structural properties of the films. The ZnS films doped with Al and Ag grown on n and p-type GaN, and sapphire were characterized by low temperature photoluminescence and displayed bright blue luminescence. Fabricated N-ZnS/p-GaN heterostructures were characterized by current-voltage and electroluminescence. Electroluminescence was found to be centered around 390 nm, corresponding to high energy silver band, and it shifted to higher energies with increase in device voltage. Since as grown films suffered from crystalline imperfections, the ZnS thin films on sapphire were recrystallized, by annealing at temperatures above 900 \u00b0C at sulfur overpressure of 10 atm. The structural properties of samples significantly improved, indicating more than 10-fold reduction in tilting and excellent crystallinity. The role of sulfur was discussed, and it was found that sulfur is important in preventing film evaporation, increasing boundary migration and providing compliancy to sapphire substrate.\r\n\r\nThe minority carrier diffusion lengths and lifetimes were measured for electrons and holes in unintentionally doped, n and p-type GaN samples grown by several different growth techniques. The experimentally observed diffusion lengths were in the 0.2 \u2014 0.3 \u00b5m range for Metal-Organic Chemical Vapor Deposition (MOCVD) and Molecular Beam Epitaxy (MBE) grown samples, and 1 \u2014 2 \u00b5m in the case of Halide Vapor Phase Epitaxy (HVPE) grown sample. In the case of MOCVD grown samples, the hole lifetime was estimated to approximately 7 ns, and electron lifetime to approximately 0.1 ns. The same samples were structurally characterized by AFM, and the size of the defect-free regions surrounded by linear dislocations is found to be of the order of measured diffusion length, in qualitative agreement with minority carrier recombination at linear dislocations. A simple model is presented which explains an increase in minority carrier lifetime and diffusion length with a decrease in the dislocation density or increase in the size of defect-free grains. A model which explains why linear dislocations might act as recombination sites is also presented.\r\n\r\nThe important advantage of nitrides and other wide band gap materials for high power devices is a smaller standoff layer thickness for the same standoff voltage, giving smaller ON-state voltage and resistance, smaller power dissipation and larger maximum current density, allowing physically smaller devices for the same power rating. The design rules for nitride based Schottky rectifiers and thyristors are presented. The critical field for electric breakdown and minority carrier recombination lifetimes are found to be important design parameters. Using modeling parameters which are well in the range currently available with GaN, and measured from fabricated devices, design results indicate the possibility of 18 \u00b5m thick GaN Schottky rectifiers and 12 \u00b5m thick A1GaN thyristors supporting 5 kV standoff voltage. The critical field for electric breakdown was found to be 5 MV/cm from the theoretical studies. The maximum current density for 5 kV thyristors is in the 200 \u2014 400 A/cm^2 range depending on the hole lifetime, and is limited by thermal breakdown. The maximum operating frequency of 5 kV thyristors is in the 1-2 MHz range and also depends on the hole lifetime.\r\n\r\nTwo-terminal GaN Schottky rectifiers were fabricated. The Schottky rectifiers were fabricated on thick GaN layers grown by HVPE and had a standoff voltages in the 450 V to 750 V range, depending on the thickness of the GaN film and contact geometry. Best devices were characterized with reverse current density of 10^(-5)A/cm^2 at reverse bias of 100 V, and 4.2 V ON-state voltage at a forward current density of 100 A/cm^2. Various contact geometries were investigated. It was found that mesa geometry improves ON-state voltage, but causes increase in reverse current density, while that metal field plate geometry significantly reduces reverse current density. The measured critical field for electric breakdown in GaN was found to be (2.5 \u00b1 0.5) MV/cm and it approaches the theoretical estimate of 5 MV/cm. The measured values of critical field are only a lower limit since the reverse breakdown voltage was limited by premature corner and edge breakdown." }, { "name": "Brady, Mark A.", "degree": "PhD", "year": "2000", "title": "Regularized vortex sheet evolution in three dimensions", "advisor": "Pozrikidis, Constantine; Pullin, Dale Ian; Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-145525634", "creators": [ { "name": { "family": "Brady", "given": "Mark A." }, "id": "Brady-M-A", "display_name": "Brady, Mark A." } ], "advisors": [ { "name": { "family": "Pozrikidis", "given": "Constantine" }, "id": "Pozrikidis-C", "role": "advisor", "display_name": "Pozrikidis, Constantine" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/pbyj-k986", "abstract": "A computational method is presented to follow the evolution of regularized three-dimensional (3D) vortex sheets through an otherwise irrotational, inviscid, constant-density fluid. The sheet surface is represented by a triangulated mesh with interpolating functions locally defined inside each triangle. C^1 continuity is maintained between triangles via combinations of cubic B\u00e9zier triangular interpolants. The self-induced sheet motion generally results in a highly deformed surface which is adaptively refined as needed to capture regions of increasing curvature and to avoid severe Lagrangian deformation. Automatic mesh refinement is implemented with an advancing front technique. Sheet motion is regularized by adding a length scale cut-off to the BiotSavart kernel. Velocity evaluation takes less time than the standard O(N^2) scaling, due to utilization of multi-pole expansions of the kernel. Zero, singly, and doubly periodic vortex sheets are simulated, modeling vortex rings, vortex/jet combinations and standard shear layers. Comparisons with previous two-dimensional (2D) results are favorable and 3D simulations are presented. The perturbed 3D planar shear layer is simulated and compared with a similar experiment revealing qualitatively similar results and agreement on the mechanism by which streamwise vorticity is created. We find the ratio of spanwise to streamwise vorticity to vary between 7 and 9 during early stages of roll-up.\r\n\r\nA new technique for estimating the curvature singularity time of true vortex sheets (i.e., non-regularized motion) is presented. The motion and singularity time of a planar, doubly periodic sheet, evolving from a 3D normal mode perturbation, is found to reduce to that of a well known singly periodic (and only two-dimensional) problem, an unexpected extension of Moore's [38] non-linear analysis for 2D vortex sheets." }, { "name": "Chattopadhyay, Goutam", "degree": "PhD", "year": "2000", "title": "Dual polarized and balanced receivers at millimeter and submillimeter wavelengths", "advisor": "Zmuidzinas, Jonas", "url": "https://resolver.caltech.edu/CaltechETD:etd-02032004-163517", "creators": [ { "name": { "family": "Chattopadhyay", "given": "Goutam" }, "id": "Chattopadhyay-Goutam", "orcid": "0000-0001-7942-5025", "display_name": "Chattopadhyay, Goutam" } ], "advisors": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "advisor", "display_name": "Zmuidzinas, Jonas" } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "co-chair", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Carlstrom", "given": "John E." }, "id": "Carlstrom-J-E", "role": "member", "display_name": "Carlstrom, John E." }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/RMVX-0619", "abstract": "Dramatic advances in millimeter and submillimeter wave receivers in recent years have resulted from the development of superconductor insulator superconductor (SIS) mixers, which now offer unsurpassed performance from 70 GHz to 1 THz. To increase the sensitivity of the receivers further at these frequencies, one needs to use dual-polarized and balanced receivers. When both the polarizations are received simultaneously, there is a square root of two improvement in the signal to noise ratio (SNR). Balanced mixers improve the sensitivity of receivers by suppressing local oscillator (LO) amplitude modulation (AM) noise and rejecting LO thermal noise. This thesis describes the design, fabrication and performance of mixers and components for low noise dual-polarized and balanced receivers at millimeter and submillimeter wavelengths both in quasi-optical and waveguide configurations. The quasi-optical receiver utilizes a novel cross-slot antenna on a silicon hyperhemispherical lens, two junction tuning circuits, niobium trilayer junctions, and an IF circuit containing a lumped element 180 degree hybrid. The antenna has four feed points, two for each polarization; and each feed point is coupled to a two-junction SIS mixer. For dual polarization operation, the mixer is mounted in such a way that a single LO can pump the junctions for both the polarizations. For the balanced receiver, the LO and the RF signals are coupled to the mixer in orthogonal polarizations using a wire-grid polarizer. For waveguide dual polarization receivers, a moderately broadband septum ortho-mode transducer (OMT) is designed and experimental results are presented at millimeter wavelengths. Broadband finline OMTs are investigated for possible use at millimeter wavelengths, and experimental results of a finline OMT is presented at X-band." }, { "name": "Chou, Hou-Pu", "degree": "PhD", "year": "2000", "title": "Microfabricated devices for rapid DNA diagnostics", "advisor": "Scherer, Axel; Quake, Stephen R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-091302341", "creators": [ { "name": { "family": "Chou", "given": "Hou-Pu" }, "id": "Chou-Hou-Pu", "display_name": "Chou, Hou-Pu" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "advisor", "display_name": "Scherer, Axel" }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "advisor", "display_name": "Quake, Stephen R." } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "co-chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "co-chair", "display_name": "Quake, Stephen R." }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Crocker", "given": "John C." }, "id": "Crocker-J-C", "role": "member", "display_name": "Crocker, John C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/0D20-Y875", "abstract": "Science makes new technology and technology pushes science forward. For biological studies and hospital diagnoses, knowledge and techniques accumulated from other fields, such as semiconductors, optics, electronics, and chemistry, are generating huge impacts in almost every aspect and for almost everyone involved. Among these, tools for DNA diagnostics play a very important role. They are also essential to many genetic studies, drug discovery, and even forensic identifications.
\r\n\r\nWorking with Professor Stephen Quake, Professor Axel Scherer, and my colleagues in Caltech, I have developed several building blocks for rapid DNA sizing, cell sorting, molecular fingerprinting, and hybridization assays, based on those newly available technologies. First, a microfabricated flow-cell device was developed using 'soft lithography'. It offers a small, cheap, robust, and contamination-free alternative to the complicated glass-capillary structure used in a conventional flow cytometer. Based on this device, a highly sensitive single-molecule DNA sizing system was demonstrated. It is 100 times faster and requires a million times less sample than pulsed-field gel electrophoresis. For DNA molecules of 1-200 kbp, it has comparable resolution, which improves with increasing DNA length. To serve as a real substitute for a conventional flow cytometry, DNA and cell sorting has also been demonstrated under this system. Simple enclosed actuation schemes are implemented and system downtime due to capillary cleaning is totally eliminated because the device costs only pennies to make and thus becomes disposable. Therefore, there is no cross-contamination issue for both DNA sizing and cell sorting applications. Using this system, prototype work for rapid DNA molecular fingerprinting was devised as an alternative to the widely used Southern blot fingerprinting protocol. Molecular evolution, VNTR fingerprinting of human forensic samples, disease diagnosis based on restriction fragment length polymorphism (RFLP), and simple DNA genomic mapping can all be accomplished with this system. Because of the great flexibility of microfabrication, more complicated functions can also be designed and incorporated into these flow-cell devices. Therefore, this single-molecule sizing system can become a key component in the family of lab-on-a-chip devices.
\r\n\r\nIn addition, a multilayer soft lithography technique was invented, allowing monolithic microvalves and micropumps to be built into these flow-channel devices. Active microfluidic systems containing on-off valves, switching valves and pumps were made, entirely out of elastomer. The softness of these materials allows the device area to be reduced by more than two orders of magnitude compared with silicon-based devices. An actuation volume as small as about one picoliter is demonstrated. The other advantages of soft lithography, such as rapid prototyping, ease of fabrication, and biocompatibility, are retained. Based on these active components, an integrated diagnostic chip was built. More than two orders of magnitude improvement in terms of binding speed and efficiency over passive devices was shown. Selective surface patterning of DNA molecules, biotin, and avidin within the chips by elastomeric flow channels was also shown. With active pumping, we are able to make a rotary motion in these microfluidic devices and show fast inline mixing which overcomes the limitation of laminar flow in this low-Reynolds number regime. Moreover, the problem of buffer depletion due to electrolysis in electroosmotic or electrophoretic flow control does not exist in these devices.
\r\n\r\nAll of these serve as fast, cheap, and robust alternatives to many conventional techniques used widely in biological studies and hospital pathogenic diagnosis. They are all very simple to fabricate and easy to use. If desired, more complicated flow patterns and functions can also be incorporated with much less effort than their silicon counterparts. We anticipate that more applications and devices based on these systems and techniques will be developed rapidly in the near future.
" }, { "name": "Collins, Donald R.", "degree": "PhD", "year": "2000", "title": "Characterization of the Physical Properties of Atmospheric Aerosols through Airborne Sampling", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:08032010-152440690", "creators": [ { "name": { "family": "Collins", "given": "Donald R." }, "id": "Collins-Donald-R", "display_name": "Collins, Donald R." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/3XTD-ZV06", "abstract": "Atmospheric aerosols are highly variable both in their characteristics and their concentration. Aircraft-based sampling provides a means of characterizing such a complex and variable constituent. To maximize the potential of aircraft sampling, improvements in existing aerosol instrumentation and development of new instruments is necessary.
\r\n\r\nA new approach to inversion of differential mobility analyzer (DMA) data has been developed that improves the accuracy with which accelerated size distribution\r\nmeasurements can be made. Extensive testing of this inversion has demonstrated that it accurately recovers initial distributions of actual aerosols sampled directly\r\nby a commonly used detector, actual aerosols analyzed with a scanning DMA, and test-case aerosols.
\r\n\r\nTo expand upon the measurable size range of the DMA, a new technique has been employed in which the associated flow rates are varied in conjunction with the applied\r\nvoltage. The performance of the instrument was evaluated theoretically through detailed flow and trajectory modeling, and experimentally through comparison with\r\na constant flow instrument. By varying the flow rates by an order of magnitude, it was shown that measurable size range could be increased by a factor of four.
\r\n\r\nDuring the Second Aerosol Characterization Experiment (ACE-2), aerosol size distributions were measured using a DMA and two optical particle counters (OPCs) during 21 missions flown on the CIRPAS Pelican. These data were combined with chemical composition measurements to derive a range of associated optical properties, which were compared with simultaneous direct measurements by a sunphotometer and three nephelometers. Agreement between derived and measured quantities varied, but was generally within calculated uncertainties.
\r\n\r\nA similar payload to that used during ACE-2 was employed for the Southern California Ozone Study (SCOS). Physical and chemical aerosol properties were analyzed to provide a three-dimensional description of the Los Angeles aerosol. Pronounced aerosol layers aloft were found to exist over the majority of the study area, and over a range of altitudes. In addition to the complex vertical structure of the aerosol observed, horizontal gradients were found to be sufficient to cause more than 50% variability in aerosol concentration over 5 km. The sampled aerosol was estimated to enhance photolysis rates of important gas-phase species by up to 5%.
\r\n" }, { "name": "Daniell, Cynthia Evors", "degree": "PhD", "year": "2000", "title": "Object Recognition in Compressed Imagery.", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052010-135012445", "creators": [ { "name": { "family": "Daniell", "given": "Cynthia Evors" }, "id": "Daniell-Cynthia-Evors", "display_name": "Daniell, Cynthia Evors" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/6z3z-ar86", "abstract": "It is often necessary to search for objects in large databases of compressed imagery. In the past, object recognition and image compression have generally been treated as separate problems, resulting in inefficient suboptimal performance. Moreover, computational and storage issues make it fundamentally prohibitive to uncompress large images prior to object recognition. We provide two complementary solutions to the problem of object recognition in compressed imagery, each of which integrates subband and correlation filtering in a unique manner.
\r\n\r\nOne key benefit of correlation filters is that, as linear systems, they are highly compatible with the subband filtering process. This enables us to provide a seamless operation in which object recognition and data compression are viewed as continuations of the same process. The public MSTAR data set illustrates our results on a three class problem of 79 Synthetic Aperture Radar images at one foot resolution.
\r\n\r\nOur general framework, the Pattern Recognition Subband Coder (PRSC), provides simultaneous synthesis and recognition at full resolution in a computationally efficient architecture. Its parallelism enables a result 1.6 times faster, in the limit, than correlation on uncompressed imagery. Furthermore, by jointly optimizing the synthesis and recognition filters, the PRSC achieves 100% recognition accuracy on our compressed data set, improving performance over that produced from the original (uncompressed) data set, by 3.7%. We maintain this success for compression ratios up to 6:1.
\r\n\r\nAddressing the issue of reduced resolution recognition, our Subband Domain Correlation Filters operate directly on the subband coefficients at multiple resolution levels. For compression ratios of at least 20:1, we achieve recognition performance of at least 90%, 85%, and 75%, respectively, on two, four, and eight foot resolution data.
\r\n\r\nThus, through our solutions with compressed imagery, we outperform correlation results on the equivalent original imagery in terms of both speed and accuracy, as well as provide success at reduced resolutions of the data.
" }, { "name": "Davis, John F.", "degree": "PhD", "year": "2000", "title": "Low-cost, industrial class-E power amplifiers with sine-wave drive", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-115944627", "creators": [ { "name": { "family": "Davis", "given": "John F." }, "id": "Davis-J-F", "display_name": "Davis, John F." } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/j5vk-kx77", "abstract": "The Class-E amplifier is a switching-mode amplifier in which the transistor operates as a switch with a passive, resonant load network. Losses are minimized by having the transistor switch on when both the voltage and current are small. These amplifiers are extremely efficient with about 90% of the DC input power converted to RF output power. This thesis will present two high-power Class-E amplifiers designed for the Industrial, Scientific, and Medical (ISM) frequency of 13.56 MHz. The first is a 200-W amplifier that incorporates the inexpensive International Rectifier IRFP440 MOSFET. With a drive level of 10 W, a drain efficiency of 91% and an overall efficiency of 87% are achieved. The second is a 400-W, air-cooled design that uses a new International Rectifier low-charge MOSFET, the IRFP450LC. This device features improved switching speed and reduced gate drive requirements. A drive level of 12 W is used to attain a drain efficiency of 86% and an overall efficiency of 84%. In both amplifiers, all harmonics are more than 40 dB below the carrier. Design procedures, modelling techniques, and extensive experimental results will be presented for each. In addition, results from a thermal study of a 400-W Class-E amplifier will be discussed. Component and junction temperature data are obtained by a direct measurement technique, Infrared Thermographic Imaging or Thermography and compared with simulated results. Particular attention is paid to the MOSFET and load network capacitors." }, { "name": "Deckman, Blythe Chadwick", "degree": "PhD", "year": "2000", "title": "Active quasi-optics and measurements", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052010-090202496", "creators": [ { "name": { "family": "Deckman", "given": "Blythe Chadwick" }, "id": "Deckman-B-C", "display_name": "Deckman, Blythe Chadwick" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/a6x5-z643", "abstract": "Quasi-optical grid amplifiers and oscillators have been limited in power to less than a watt at Ka-band until recently. Additionally, measurements of grid structures have been done with far-field techniques, making reflection measurements difficult. Some focused techniques have been used as well. Here are presented a 5-watt grid amplifier at 37.2 GHz, and a grid oscillator, after Moonil\r\nKim, that shows 1 watt of effective transmitter power at 38 GHz. Focused beam measurement techniques are also discussed, introducing a new method to calibrate a network analyzer for reflection measurements. Measurements are\r\npresented on passive structures to validate the calibration technique, and then measurements of the active structures are presented.\r\n\r\nFollowing the presentation of the 5-watt amplifier and l-watt oscillator, a design technique for a l0-watt grid amplifier is presented, along with a mode converter that allows the grid to be fed from a standard waveguide port.\r\n" }, { "name": "Desai, Amish S.", "degree": "PhD", "year": "2000", "title": "Micromachined Devices for an Airborne Bio-Particle Analysis System", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-095709235", "creators": [ { "name": { "family": "Desai", "given": "Amish S." }, "id": "Desai-Amish-S", "display_name": "Desai, Amish S." } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" }, { "name": { "family": "Rosenberg", "given": "Jim" }, "id": "Rosenberg-J", "orcid": "0009-0006-8388-7437", "role": "member", "display_name": "Rosenberg, Jim" }, { "name": { "family": "Sovero", "given": "Emilio Andres" }, "id": "Sovero-Emilio-Andres", "role": "member", "display_name": "Sovero, Emilio Andres" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ge1w-t045", "abstract": "The goal of this thesis is to develop micromachined devices for an automated miniaturized airborne bio-particle analysis system. The realization of such a system is complex requiring a particle capture, transport, collection, sample preparation, and analysis. Accordingly, microelectromechanical systems (MEMS) teams have studied and developed micro-pumps, valves, channels as building blocks for a miniature chemical analysis system. In this thesis, novel micromachined solutions to some of these tasks are presented. Specifically, the development of: 1) a low voltage, air-based electrostatic particle transportation system, 2) an air-to-liquid interface design for transport of airborne particles into a liquid environment 3) a micro-chip electrospray (ES) mass spectrometer interface for small volume(nL) mass spectrometry, 4) and fast mixers (<100\u03bcs) for the study of chemical reaction kinetics. The particle transport system consists of 3-phase electrode arrays covered by photoresist and Teflon. Extensive testing of this system has been done using a variety of insulation materials, thicknesses (0-12\u03bcm), particle sizes (1-10\u03bcm), particle materials (metal, glass, polystyrene, spores, etc.), waveforms, frequencies, and voltages. Although previous literature claimed it impractical to electrostatically transport particles with sizes of 5-10\u03bcm due to complex surface forces, this effort actually demonstrates 90% transportation efficiencies with the optimal combination of insulation thickness, electrode geometry, and insulation material. As the second step, this particle transportation technology has also been integrated with an active micromachined filter and an air-to-liquid silicone rubber interface. Two methods of air to liquid particle transport were explored \u2014 moving particles across a stationary fluid meniscus and the other, moving meniscus across stationary particles. Third, the development of a micron-sized MEMS nozzle (1-3 \u03bcm orifice diameters) is presented with successful demonstration of its application for electrospray ionization mass spectroscopy. MEMS scaling issues were verified with the flow visualization of the Taylor Cone on this nozzle. Fourth, a 1 cm x 1 cm x 1 mm DRIE silicon mixer capable of initiating and quenching (starting and stopping) chemical reactions in intervals as short as 100 \u03bcs was characterized by employing two carefully chosen chemical reactions with reaction time constants of 3 ms and 9 ms along with visualization techniques using dyes and acid-base indicators." }, { "name": "Djeki\u0107, Ognjen", "degree": "PhD", "year": "2000", "title": "Optimization and miniaturization of microprocessor power supplies", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112010-125157508", "creators": [ { "name": { "family": "Djeki\u0107", "given": "Ognjen" }, "id": "Djeki\u0107-O", "display_name": "Djeki\u0107, Ognjen" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/afba-8b98", "abstract": "This thesis is motivated by the power demands of the modern Intel microprocessors. These microprocessors require a very stable and tightly controlled core supply voltage in order to reliably operate at their correct clock frequency. The core supply voltage has to remain within the prescribed window during normal operation, as well as during power-up and power-down when the processor current can change from almost zero to 16A or more in 200-300ns. Maintaining tight processor voltage regulation during these current transients can be difficult. In addition to stringent load transient specifications, a microprocessor power supply has to meet efficiency requirements, as well as size and cost requirements. Size requirements become especially important in portable computer systems where space is at a premium.\r\n\r\nThe work presented in this thesis deals with the optimization of the microprocessor power supply for performance, size and cost, with the emphasis on size. Every aspect of the power supply is carefully analyzed and optimized through the size prism: the topology, the control algorithm, and the components. Design and optimization tools are developed, and the theoretical calculations are verified in hardware. The result of the optimization is a microprocessor power supply that meets Intel Pentium III electrical performance specs in approximately one-fifth of the specified volume, resulting in a power density of roughly 40W/in^3." }, { "name": "Gibson, Michael Andrew", "degree": "PhD", "year": "2000", "title": "Computational methods for stochastic biological systems", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-05132005-154222", "creators": [ { "name": { "family": "Gibson", "given": "Michael Andrew" }, "id": "Gibson-M-A", "display_name": "Gibson, Michael Andrew" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "cns" ], "doi": "10.7907/G4X0-D149", "abstract": "The virtual completion of the genome project and prodigious amounts of work by different biologists throughout the world have elucidated many of the components of biological systems. The genes (and hence proteins) are largely known, and the tools of molecular biology allows one to manufacture and express them, so as to understand their function. Given this increased understanding of components, the next step in understanding complex biology will be understanding systems, which will almost certainly involve formal, detailed, and quantitative models.\n\nOne of the great challenges of modeling biological systems is that they tend to \"break the math.\" Biological systems have small numbers of molecules, operate far from equilibrium, change shape and size, etc. This thesis develops mathematical and computational tools for biological systems with few molecules. Such systems are particularly problematic because the usual macroscopic view of chemistry, in which concentrations of molecules vary continuously, continually, and deterministically, does not work. Rather, one needs to use the mesoscopic view of chemistry: molecules undergo discrete reaction events, and the timing of these events is probabilistic. There are many standard numerical computational techniques for the macroscopic view, but far fewer for the mesoscopic view.\n\nThis thesis develops (1) an efficient, exact stochastic simulation algorithm, to generate trajectories of mesoscopic biological systems, (2) a sensitivity analysis algorithm, to quantify how a model\u2019s predictions depend on the exact values of parameters (e.g., rate constants) used, and (3) a parameter estimation algorithm, to estimate the values of model parameters from observed trajectories." }, { "name": "Goncalves, Luis", "degree": "PhD", "year": "2000", "title": "Automatic observation and synthesis of human motion", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-11022006-104150", "creators": [ { "name": { "family": "Goncalves", "given": "Luis" }, "id": "Goncalves-L", "display_name": "Goncalves, Luis" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." } ], "option_major": [ "cns" ], "doi": "10.7907/n3fn-jd79", "abstract": "Over the past few decades Computer Vision and Computer Graphics have experienced a rapid evolution, thanks in part to the continual improvement in computer hardware, which enables the investigation of increasingly complex problems.\r\n\r\nIn Computer Graphics this evolution is visible on a nearly day-by-day basis. For instance, computer-generated special effects in feature films have evolved to such a level of sophistication that it is often impossible to distinguish what is real from what is not. However, one challenging problem that still stands, considered by many experts in the field to be a Holy-Grail of Computer Graphics, is the automatic synthesis of life-like human character animation. Although rendering and modeling techniques have reached a stage where a computer generated image of a person is nearly indistinguishable from the real thing, as soon as that model begins to move the illusion is broken. The problem is difficult because no-one yet knows how to model human motion in all it's intricacy and subtlety, and also because humans are so well tuned to perceive these subtleties that they can only be fooled if the modeling is done with complete perfection.\r\n\r\nIn this thesis, we explore a novel method of automatic synthesis of human motion that brings us one step closer to the ultimate goal. The method is based on decomposing human motion into elemental, nameable actions such as walking, running, and throwing, and using observations of people performing these actions to create mathematical models of the actions. Various samples of an action are acquired, and each sample is labeled according to state (initial body configuration), goal (desired outcome of the motion, such as direction of a throw or placement of a foot for a step), and mood and style parameters. Then established and novel techniques of machine learning are applied to derive a function that can synthesis a motion given some desired parameters. We explore the use of polynomial interpolants, radial basis function networks (RBFs), feed-forward neural networks (FFNNs) with sigmoidal activation functions, as well as a new method with local linear models. We find that a linear model more often that not works quite well, whereas higher order polynomial interpolants, RBFs and FFNNs are unable to extrapolate robustly when the motion parameters lie outside of the convex hull of the parameters of the available sample motions. The method with local linear models successfully improves the fidelity of the synthetic motions compared to the linear model, and also provides robust extrapolation. We also investigate the use of a recursive, probabilitic model where motions are specified by defining the initial and final body poses of the motion, and synthesis is done by computing the most likely motion to satisfy the boundary constraints. Although the results with this method are not yet completely satisfactory, it holds promise, and under certain types of conditions can re-synthesize the sample motions more accurately than any of the other methods.\r\n\r\nWith the additional development of methods to smoothly concatenate actions together and to interactively map synthesized motions to a 3-D polygonal character model, a realtime interactive demo was created that successfully demonstrates the level of realism and interactivity achievable by our method of human motion synthesis.\r\n\r\nOur interest in the problem of realistic human motion synthesis arose from an initial study of the (in some sense) inverse problem in Computer Vision of the automatic observation (rather than synthesis) of human motion. Although progress in Computer Vision has not yet reached a level enabling it's widespread use in daily life, this state will most likely be achieved within the next decade. One large class of problems for which this is the case is the endowment of computers with visual perceptual skills similar to those of humans. Among the vast set of visual tasks imagineable, the automatic detection, recognition, and estimation of humans and human motion is a particularly interesting set of problems since there are many possible applications of such a technology in modern life, ranging from security and monitoring systems, to systems for biometric analysis, to novel human-machine interfaces.\r\n\r\nIn this thesis we describe a method of robustly estimating the motion of a human body from a monocular view. The method is based on the use of a 3-D model of the body, and comparing the actual image to an expected image based on the 3-D model to update the estimate of the body pose at each time step. The method was implemented in realtime as a human-machine interface. This system demonstrated that the method can be used to robustly track a human arm with a hand-tip positioning resolution of 2cm under close viewing conditions (where perspective projection causes significant changes in the appearance of the arm in the camera view).\r\n" }, { "name": "Harrison, Reid R.", "degree": "PhD", "year": "2000", "title": "An analog VLSI motion sensor based on the fly visual system", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292010-141342517", "creators": [ { "name": { "family": "Harrison", "given": "Reid R." }, "id": "Harrison-Reid-R", "display_name": "Harrison, Reid R." } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Dickinson", "given": "Michael H." }, "id": "Dickinson-M-H", "role": "member", "display_name": "Dickinson, Michael H." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "role": "member", "display_name": "Laurent, Gilles J." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cns" ], "doi": "10.7907/TSDS-SJ16", "abstract": "Vision is a vitally important sense for flying insects. Over half of the 350,000 neurons in the housefly's brain are believed to have some role in visual processing. Flies use visual motion cues to navigate through turbulent air, avoid obstacles, chase other flies, and land safely. Much is known about the neural circuitry that extracts motion information from retinal light intensity signals. This\r\ndissertation describes the development and testing of integrated silicon sensors that estimate visual\r\nmotion using architectures derived from the neurophysiology of the fly optic lobe. We built VLSI systems incorporating light sensors and information processing circuits side by side on the same chip. These continuous-time analog CMOS circuits operate in the weak inversion (subthreshold)\r\nregime to match biological time constants and achieve sub-milliwatt power dissipation. Detailed characterization showed our sensor to be an accurate implementation of the Hassenstein-Reichardt motion detector model, originally developed to describe insect visual responses. We developed a novel test paradigm using stimuli with natural image statistics and spatiotemporal noise to evaluate the\r\nsensor's robustness. Our sensors were able to discriminate motion direction using naturalistic stimuli in noisy conditions (SNR < 1). Information theoretic techniques were used to measure the ability of our sensor to encode time-varying image velocity. Coding efficiency was quantified and compared with results from motion-sensitive neurons in the fly. The silicon system was tested in the context of a visually guided behavior-the optomotor stabilization response. Direct comparisons with the\r\nfly were made in real-time, closed-loop control experiments. A circuit architecture was developed to\r\nmodel the biophysical properties of wide-field motion-sensitive neurons in greater detail. This gave\r\nour sensor array nonlinear spatial integration properties that decreased sensitivity to gaps in the optic flow field. Finally, we investigated the issue of sensory fusion and explored a circuit that could assist in the integration of visual motion sensors with other sensors, such as angular rate gyroscopes.\r\n" }, { "name": "Ho, Ching Elizabeth", "degree": "PhD", "year": "2000", "title": "Multiple mechanisms of apparent motion perception", "advisor": "Sperling, George; Shimojo, Shinsuke", "url": "https://resolver.caltech.edu/CaltechETD:etd-04072005-145953", "creators": [ { "name": { "family": "Ho", "given": "Ching Elizabeth" }, "id": "Ho-C-E", "display_name": "Ho, Ching Elizabeth" } ], "advisors": [ { "name": { "family": "Sperling", "given": "George" }, "id": "Sperling-G", "role": "advisor", "display_name": "Sperling, George" }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "role": "advisor", "display_name": "Shimojo, Shinsuke" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "cns" ], "doi": "10.7907/gmqp-sx69", "abstract": "Motion perception is a complex phenomenon. Recently, multiple categories of motion perception have been defined through properties of the stimulus: e.g., short-range and long-range motion (Braddick, 1980), or first-order (luminance-defined), second-order (texture-defined) (Chubb and Sperling, 1988; Chubb and Sperling, 1989; Cavanagh and Mather, 1989), and third-order (pattern-tracking) (Lu and Sperling, 1995a; Lu and Sperling, 1995b) motion. This thesis elucidates the mechanisms of motion perception for a class of ambiguous motion stimuli. In particular, two competing motion systems were found to be involved in the perception of nominal second-order motion stimuli. These systems were hypothesized to explain the inter-observer differences in the perceived direction of motion, and to explain the differences in performance under a dual task paradigm. The interference effects seen in the dual task performances implied the involvement of multiple forms of/distributed attention. Choice of systems could be influenced by attentional instructions and training in addition to stimulus conditions.\r\n\r\nIn viewing an ambiguous texture-defined motion stimulus first devised by Werkhoven et al (1993), the observers fell into two distinct groups based on the direction of perceived motion. The differences were interpreted in terms of the algorithms used to extract motion: one group using a second-order motion process, the other, a third-order motion process. This was investigated fuither using a dual-task paradigm in which the interference between two tasks indicated the nature of processing involved. Observers who used third-order motion processing experienced interference with a letter-recognition task, and a more severe interference in dual third-order motion tasks. Observers who used second-order motion processing experienced interference with another second-order motion detection task, but not with the letter-recognition task.\r\n\r\nThese observations suggest that two systems, a second-order system and a third-order system, are involved in the perception of the nominal second-order motion stimuli. The performance of observers can be interpreted in terms of a simple architecture of motion processing and attentional resource. Insofar as task interference implies competition for attentional resource, the complex and apparently paradoxical interference effects of second-order motion perception suggest that there are multiple attentional resources, or in another word, attention is distributed. Whether two tasks interfere or not depends on whether they require the same attentional resource. A quantitative method, Structure-Attention-Mapping (SAM) was formulated, and a model architecture for the motion pathways was proposed using this method. It was found to be able to explain the data in the experiment.\r\n\r\nWhile different observers have different innate tendencies to use one pathway over the other, the selection of pathway is not fixed but can be induced by attentional instructions, training, temporal frequency, and viewing conditions. High temporal frequencies and monocular displays favored the second-order system, low temporal frequencies and interocular displays favor the third-order system. In addition, stimuli composed of patches with orthogonal slant patterns (one slant could be selectively attended) favored the third-order direction; same-slant stimuli favored the second-order direction. A study of luminance-defined motion showed that it can also be perceived by a third-order motion system as well as a first-order motion system. The competition between first- and third-order systems qualitatively resembles that between second- and third-order motion systems.\r\n" }, { "name": "Ikriannikov, Alexandr", "degree": "PhD", "year": "2000", "title": "New Developments in Single Phase Power Factor Correction", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-085940604", "creators": [ { "name": { "family": "Ikriannikov", "given": "Alexandr" }, "id": "Ikriannikov-Alexandr", "display_name": "Ikriannikov, Alexandr" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/c1b0-qk33", "abstract": "Power Factor Correction (PFC) is a necessary feature of many AC/DC Power Electronics products. The issues of increasing the value of the Power Factor (PF) and increasing efficiency of transferring the power in such applications motivated this thesis.
\r\n\r\nInput rectification is needed for the most topologies in AC/DC applications for these topologies to perform however, it is pretty much one of the main causes of distortions and power losses. Diode bridge is also one the hottest components of PFC, which is an important issue in terms of thermal management.
\r\n\r\nNew approach for Power Factor Correction is introduced in the first part. Topologies with bipolar gain characteristics are proposed to be used, naturally providing constant DC output from non-rectified AC input. Practical design of such converter is presented and analyzed, theoretical predictions are confirmed by experimental data; proposed idea of Power Factor Correction is verified.
\r\n\r\nAnother new general approach of Power Factor Correction improvement is introduced in second part. Idea of shifting input line rectification to switching elements of the power stage is proposed for certain topologies and verified on practical example. Key features are analyzed and illustrated by experimental data. This class of converters presents an opportunity for accurate comparison with related conventional topologies, which is included to show the advantages of the new approach.
\r\n\r\nGeneral advantages and improvements of Power Factor value in bridge-less topologies in comparison to conventional converters are analyzed and illustrated experimentally in the third part of the thesis.
\r\n" }, { "name": "Irfanoglu, Ayhan", "degree": "PhD", "year": "2000", "title": "Structural Design under Seismic Risk Using Multiple Performance Objectives", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechThesis:05052016-115652196", "creators": [ { "name": { "family": "Irfanoglu", "given": "Ayhan" }, "id": "Irfanoglu-Ayhan", "orcid": "0000-0001-8334-6717", "display_name": "Irfanoglu, Ayhan" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "civileng" ], "doi": "10.7907/W5WE-TD86", "abstract": "Structural design is a decision-making process in which a wide spectrum of requirements, expectations, and concerns needs to be properly addressed. Engineering design criteria are considered together with societal and client preferences, and most of these design objectives are affected by the uncertainties surrounding a design. Therefore, realistic design frameworks must be able to handle multiple performance objectives and incorporate uncertainties from numerous sources into the process.
\r\n\r\nIn this study, a multi-criteria based design framework for structural design under seismic risk is explored. The emphasis is on reliability-based performance objectives and their interaction with economic objectives. The framework has analysis, evaluation, and revision stages. In the probabilistic response analysis, seismic loading uncertainties as well as modeling uncertainties are incorporated. For evaluation, two approaches are suggested: one based on preference aggregation and the other based on socio-economics. Both implementations of the general framework are illustrated\r\nwith simple but informative design examples to explore the basic features of the framework.
\r\n\r\nThe first approach uses concepts similar to those found in multi-criteria decision theory, and directly combines reliability-based objectives with others. This approach is implemented in a single-stage design procedure. In the socio-economics based approach, a two-stage design procedure is recommended in which societal preferences are treated through reliability-based engineering performance measures, but emphasis is also given to economic objectives because these are especially important to the structural designer's client. A rational net asset value formulation including losses from uncertain future earthquakes is used to assess the economic performance of a design. A recently developed assembly-based vulnerability analysis is incorporated into the loss estimation.
\r\n\r\nThe presented performance-based design framework allows investigation of various design issues and their impact on a structural design. It is a flexible one that readily allows incorporation of new methods and concepts in seismic hazard specification, structural analysis, and loss estimation.
\r\n\r\n" }, { "name": "Jabbour, Michel E.", "degree": "PhD", "year": "2000", "title": "Modeling chemical vapor deposition of thin solid films", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:10042010-153504863", "creators": [ { "name": { "family": "Jabbour", "given": "Michel E." }, "id": "Jabbour-Michel-E", "display_name": "Jabbour, Michel E." } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/pa2d-3n29", "abstract": "Chemical vapor deposition (CVD) is a process by which thin solid films are deposited on solid substrates for various technological applications. Roughly speaking, a multispecies chemically reacting gas flows past a heated substrate on top of which the deposition and subsequent formation of the alloy or compound of interest take place via a series of heterogeneous chemical reactions. The growth rate of the thin film is determined by the competition between the diffusive and convective transports of species in the gas phase, the homogeneous and heterogeneous chemical kinetics, and the morphology of the gas-film interface.\r\nIn chapter 2, a thermomechanical macroscopic model is proposed that couples the multicomponent chemically reactive gaseous flow to the bulk of the growing thin solid film via the equations that govern the morphological evolution of the film-gas interface. The surface is modeled as a separate anisotropic elastic phase, and such phenomena as surface species diffusion, heat conduction and chemistry are accounted for. In particular, the driving force at the surface is identified, and a thermodynamically consistent kinetic relation linking it to the growth velocity is proposed. A specialization of this general framework to the case of a multicomponent ideal gas and a linearly elastic solid film separated by an isotropic surface is considered.\r\nIn chapter 3, we examine a multicomponent gas flow in a vertical axisymmetric MOCVD reactor whose geometry is characterized by a small aspect ratio (defined as the ratio of the height of the reactor channel to the radius of the substrate) and operating under conditions insuring a small Mach number. A two-parameter asymptotic analysis yields, in the limit of vanishingly small aspect ratio and Mach number, a set of approximate equations governing the gas phase, combined with approximate boundary conditions at the showerhead and the gas-film interface. A specialization to the steady-state approximation is then proposed, and an analytical solution to the approximate problem is derived. It is found that this solution is of the similarity type, thus insuring a uniform temperature and chemical composition profiles along the film surface.\r\nFinally, in chapter 4, the growth of a generic thin film via a ledge-and-terrace mechanism is examined. Of particular interest is the interaction between the microstructure of the surface and the chemical kinetics by which the adsorption/desorption of species along the terraces and the formation of the compound at the steps occur. A simple step-flow model is proposed and its specialization to the case of a binary compound is used to illustrate the complex dependence of the averaged growth rate on the chemical composition of the gas phase as well as on the morphology of the evolving surface.\r\n" }, { "name": "Jeon, David S.", "degree": "PhD", "year": "2000", "title": "On Cylinders Undergoing One- and Two-Degree of Freedom Forced Vibrations in a Steady Flow", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:09302010-151500998", "creators": [ { "name": { "family": "Jeon", "given": "David S." }, "id": "Jeon-David-S", "display_name": "Jeon, David S." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ky58-en52", "abstract": " Formation of vortices in the near wake of circular cylinders is discussed. Two different cases are compared: starting flow around an initially stationary cylinder and flow around an oscillating cylinder in a steady freestream. The effects of formation time on the morphology of the vortices are shown, as well as some consequences thereof.\r\n\r\n For starting flows, the critical formation time defines the point where the wake transitions from the initially symmetrical state to the intermediate asymmetrical state. The asymmetrical state breaks down into the periodic shedding state normally associated with cylinder flows. It appears that the wake reaches a critical level of vorticity annihilation at the critical time. This triggers an exponential growth of asymmetry in the near wake. Evidence of this process can also be seen in the early time force data.\r\n\r\n For oscillating flows, the critical time defines the transition from vortex to vortex-and-tail morphology. First, phase averaged vorticity fields are presented showing the changes in the wake with forcing frequency and streamwise motion. These changes are related to the formation time, and related to similar effects seen in other flows. In addition, prolonged formation is related to the observed switch in the phase of the vortex shedding. The effects of streamwise motion are also shown, including the increased phase coherence of the shedding via coordination of the shedding process and the ability to adjust formation time via streamwise acceleration. The latter was used to demonstrate a plausible explanation for the vortex pair formation process observed by some researchers by showing how the formation process affects the number of vortices generated per cycle." }, { "name": "Karion, Anna", "degree": "PhD", "year": "2000", "title": "Couette Flows of Granular Materials: Mixing, Rheology, and Energy Dissipation", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-093837", "creators": [ { "name": { "family": "Karion", "given": "Anna" }, "id": "Karion-Anna", "display_name": "Karion, Anna" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Campbell", "given": "Charles S." }, "id": "Campbell-C-S", "role": "member", "display_name": "Campbell, Charles S." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/HX15-PC72", "abstract": "This thesis examines the behavior of a granular material sheared in a gap between two moving boundaries. In fluid mechanics, this type of flow is known as a Couette flow. Two different kinds of granular Couette flows were studied. First, gravity-free flow between two infinite plates moving in opposite directions was investigated using computer simulations. Second, flow between a stationary outer cylinder and an inner rotating cylinder was studied using both experiments and computer simulations.
\r\n\r\nTwo-dimensional discrete element computer simulations of infinite planar Couette flows were used to study the rheology, energy dissipation, and other flow properties in flows of particles of uniform size for three different gap widths. The energy dissipation rate was measured and a thermal analysis was conducted to determine the thermodynamic temperature rise and heat flux of such flows. Given a constant wall velocity, all of the properties in flows of identical particles were found to depend on the value of the solid fraction at the walls, which in turn depended on both the average solid fraction and the gap width. When the average solid fraction reached a critical threshold, the amount of work done on the flow drastically increased, increasing the average strain rate, granular temperature, wall stresses, and energy dissipation in the flow. This solid fraction threshold occurred after the center region of the flow had reached a dense limit and any further increase in solid fraction necessarily occurred in the wall regions. Various results from computer simulations were found to compare reasonably well with past results derived using kinetic theory.
\r\n\r\nMixing and other flow properties were also investigated in planar Couette flows of two different particle sizes, as functions of the size ratio and solid fraction ratio of the two species. Larger particles were found to migrate away from the regions of high fluctuation energy near the two moving boundaries in all cases. Mixture flows were found to behave very similarly to flows of mono-sized particles at high ratios of the solid fraction of small to large particles. As the solid fraction ratio decreased and the number of large particles increased, results deviated from the corresponding flow of identical particles. Flows with large size ratios of large to small particles deviated the most from the result of mono-sized particles, because stresses and energy dissipation rates are both mass-dependent.
\r\n\r\nThe second type of Couette flow, between two concentric cylinders, was investigated in a horizontal orientation (with the axis of rotation perpendicular to the direction of gravity) and in a vertical orientation (with the axis parallel to the direction of gravity), using both experiments and computer simulations. In the horizontal geometry, high-speed imaging was used to calculate experimental mean and fluctuation velocity profiles that were compared to results from three-dimensional discrete element simulations. Segregation of binary particle mixtures was also investigated in this geometry. Segregation in this flow was driven by a percolation mechanism acting at the free surface, causing large particles to migrate to the top. Computer simulations compared well qualitatively with experiments, successfully predicting the velocity profiles and the segregation pattern at the surface. When compared quantitatively, however, fluctuation velocities in the simulations were considerably greater than those found in the experiment, and the radial segregation observed in experiments did not occur to the same extent in simulations.
\r\n\r\nThe vertically-oriented cylindrical Couette flow experiment was used to measure the shear stress on the outer cylinder wall as a function of different variables. The shear stress was found to be independent of the inner cylinder rotation rate, because the material was unconfined and allowed to dilate. The measured stress showed a linear dependence on the height of material in the apparatus, indicating a hydrostatic variation of the normal stress. The shear stress also varied significantly with the ratio of the gap width to the particle diameter.
" }, { "name": "Kazadi, Sanza Nkashama Tsilobo", "degree": "PhD", "year": "2000", "title": "Swarm Engineering", "advisor": "Goodman, Rodney M.; Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-090510798", "creators": [ { "name": { "family": "Kazadi", "given": "Sanza Nkashama Tsilobo" }, "id": "Kazadi-Sanza-Nkashama-Tsilobo", "display_name": "Kazadi, Sanza Nkashama Tsilobo" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "co-advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Mataric", "given": "Maja" }, "id": "Mataric-M", "role": "member", "display_name": "Mataric, Maja" }, { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "orcid": "0000-0002-2915-9504", "role": "member", "display_name": "Adami, Christoph Carl" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cns" ], "doi": "10.7907/YR44-KF67", "abstract": "Swarm engineering is the natural evolution of the use of swarm-based techniques in the accomplishment of high level tasks using a number of simple robots. In this approach, one seeks not to generate a class of behaviors designed to accomplish a given global goal, as is the approach typically found in mainstream robotics. Once the class of behaviors has been understood and decided upon, specific behaviors designed to accomplish this goal may be generated that will complete the desired task without any concern about whether or not the final goal will actually be completed. As long as the generated behaviors satisfy a set of conditions generated in the initial investigation, the desired goal will be accomplished.\r\n\r\nThis approach is investigated in terms of three specific practical problems. First we apply swarm engineering to plume tracking, utilizing both real and simulated experiments. We initially decide whether or not this is a problem that swarm engineering should be applied to at all, A careful investigation of two plume-tracking algorithms yields the weakness of single-robot plume tracking \u2014 the tracking of low density plumes. Application of swarm engineering to this sub-problem yields performance that is capable of tracking plumes that are significantly more diffuse than those which can be tracked by single plume trackers.\r\n\r\nThe second problem is position-independent clustering, in which a cluster of objects is constructed from many initial clusters, without predetermination of the final cluster's location. Although we have completed a robotic instantiation of this type of system, the bulk of our work is theoretical and verification with simulation. A minimal condition is derived which guarantees this final global outcome, in both an unrealistic case and a case that is more realistic for real robots. Methods of generating efficiency improvements are derived. The application of this formalism to real robots is discussed. Finally, conditions are derived and demonstrated leading to stable arrangements of multiple clusters, a precursor of distributed construction.\r\n\r\nThe third and last problem is the traveling salesman problem (TSP). Marco Dorigo (see, for instance, Dorigo 1996) generated much interest in the use of \"ants\" on the problem. We theoretically demonstrate that Dorigo's ants satisfy a swarm engineering condition generated for this problem. However, the result of Dorigo's work is also demonstrably fragile under random fluctuations. A second more robust ant-based method is generated and tested on a small number of standard test problems taken from TSPLIB, a source of many well-known TSP instantiations. In all cases, the new algorithm is capable of reliably finding the minimum distance path.\r\n\r\nThis thesis makes a number of contributions to the literature. First, we study two systems that take advantage of the embodiment and interaction dynamics of the robot to accomplish the single robot goal. We then extend this work to answer two questions:\r\n\r\n1. Is it possible to apply swarm engineering to plume tracking?\r\n\r\n2. How can one apply swarm engineering to plume tracking?\r\n\r\nWe demonstrate that is indeed possible to extend one of the two previous plume tracking systems to a swarm. We demonstrate that the swarm is capable of successfully tracking plumes that are significantly more diffuse than those capable of being tracked by individual agents.\r\n\r\nNext, we derive a formal condition which must be satisfied in order for a system made up of many clusters and robots to become a system of one cluster and many robots, if the robots do not have global information. We extend this work by deriving ways of generating more efficient paradigms, and demonstrate how to use the theory in the design of individual robots. Finally, we modify our theory to include systems generating multiple clusters, and demonstrate how to generate clusters of predefined relative sizes.\r\n\r\nOur third contribution is a formalism for ant-based TSP algorithms. This allows us to understand why Dorigo's algorithms are relatively unstable. We create a completely new system of traveling agents that also solve TSP by having the ability to \"die along the way\" and to self replicate in a specific fashion.\r\n\r\nPerhaps the most important contribution here is an alternative approach to the design of swarm systems. This allows us to explore the three problems of interest here by first determining a condition that allows the completion of the task, and then allows the generation of behaviors satisfying the minimal condition. This view to system design has the advantage of allowing the design of systems that will generate the desired behavior, concommittantly reducing the danger of generating unwanted emergent behavior.\r\n" }, { "name": "Kneebone, Penelope E.", "degree": "PhD", "year": "2000", "title": "Arsenic geochemistry in a geothermally impacted system : the Los Angeles Aqueduct", "advisor": "Hering, Janet G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08042006-091727", "creators": [ { "name": { "family": "Kneebone", "given": "Penelope E." }, "id": "Kneebone-P-E", "display_name": "Kneebone, Penelope E." } ], "advisors": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "advisor", "display_name": "Hering, Janet G." } ], "committee": [ { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "chair", "display_name": "Hering, Janet G." }, { "name": { "family": "List", "given": "John" }, "id": "List-J", "role": "member", "display_name": "List, John" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Bercaw", "given": "John E." }, "id": "Bercaw-J-E", "role": "member", "display_name": "Bercaw, John E." } ], "option_major": [ "envreng" ], "doi": "10.7907/83BV-0B62", "abstract": "Elevated arsenic concentrations in the Los Angeles Aqueduct (LAA) derive from geothermal inputs in Hot Creek. This study examines arsenic geochemistry in three sections of the LAA system: Hot Creek, Crowley Lake and Haiwee Reservoir.
\r\n\r\nAt Hot Creek, the accumulation of arsenic in the sediments is strongly influenced by hot springs and plants. Solid-phase arsenic is present as As(III) throughout the sediment column with an identifiable organic phase in the surface sediment and a sulfide phase in the deep sediment. Sediments carry only a small fraction of the arsenic load in Hot Creek. Concentration profiles obtained with a novel, high resolution pore water sampler reveal a net flux of arsenic out of the sediments. Sediment-water exchange of arsenic in Hot Creek depends on initial arsenic concentrations and the presence of other ions in solution; this latter effect may be partly due to colloid aggregation and peptization.
\r\n\r\nIn Crowley Lake, water column profiles obtained during stratified and well-mixed conditions provide no evidence for sediment-water exchange of arsenic. Algal uptake and transformation of arsenic is not sufficient to perturb the distribution of arsenic species in the water column or to accumulate substantial arsenic concentrations in the sediment. Arsenic is associated, and immobilized, with sulfide in the sediments, which are permanently anoxic. Sediment arsenic concentrations are modestly elevated; release of arsenic from the sediments driven by decreased water column arsenic concentrations would be gradual and would not threaten the water quality of the LAA.
\r\n\r\nIn Haiwee Reservoir, arsenic is deposited in the sediments as a result of the Los Angeles Department of Water and Power's interim arsenic management plan. This solid-phase arsenic is unstable with respect to reductive dissolution of the iron oxyhydroxide with which it is associated. A strong redox gradient exists below the sediment water interface and solid-phase arsenic speciation evolves rapidly with depth from an As(V) to an As(III) phase. The potential for release of this arsenic to the overlying water poses a threat to the LAA water supply.
\r\n" }, { "name": "Lee, Reginald K.", "degree": "PhD", "year": "2000", "title": "Lasing and modified spontaneous emission in photonic crystal structures and microcavities", "advisor": "Yariv, Amnon; Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-06102005-082207", "creators": [ { "name": { "family": "Lee", "given": "Reginald K." }, "id": "Lee-R-K", "display_name": "Lee, Reginald K." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "co-advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/kvvd-em02", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nSemiconductor light-emitting devices in the near-infrared (1.55 \u00b5m) based on microfabricated photonic crystal structures are demonstrated. The photonic structures consist of two-dimensional arrays of air holes patterned into an optically thin, airsuspended InGaAsP slab by high-resolution electron beam lithography and various dry etching techniques.\n\nTwo types of microcavities are examined. The first are larger hexagonally shaped cavities in the range of 10 to 20 \u00b5m in size and bounded by the photonic crystal structure. Cavity mode spontaneous emission at room temperature under optical pumping is used to demonstrate mode confinement due to the in-plane bandgap. No cavity mode peaks in the emission spectrum are seen if the in-plane bandgap is not spectrally aligned with the material emission. Pulsed lasing is also demonstrated with the lasing threshold at 66 mW peak incident optical pump power at a duty cycle of less than 1% in order to minimize membrane heating. Changes in the pump geometry is shown to result in controllable lasing mode switching. This behaviour is explained in terms of mode Q, lasing threshold and enhanced spontaneous emission into the mode.\n\nThe second type of microcavity consists of a single point defect into photonic lattice with a modal volume of [...]. Cavity quality factors up to 250 are demonstrated and suppressed spontaneous emission due to the bandgap except at the mode frequency is shown. Pulsed lasing at 143 K under optical pumping is demonstrated.\n\nThe fundamental modification of the spontaneous emission rate due to the in-plane bandgap in a photonic crystal slab structure with no microcavity is experimentally and numerically examined. Incomplete bandgaps are theoretically shown to be able to strongly inhibit spontaneous emission. High density of states points in the band-structure are seen to greatly enhance the spontaneous emission rate. Measurements using phase sensitive spectroscopy of the spontaneous emission rate from quantum wells in the photonic crystal slab show a greater than 10 times inhibition of the emission rate in the in-plane bandgap. Experimental evidence for saturation of the surface recombination at relatively low pumping levels is found.\n" }, { "name": "Li, Lifang", "degree": "PhD", "year": "2000", "title": "Adaptive Receiver Design and Optimal Resource Allocation Strategies for Fading Channels", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-101242368", "creators": [ { "name": { "family": "Li", "given": "Lifang" }, "id": "Li-Lifang", "display_name": "Li, Lifang" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "orcid": "0000-0001-5686-800X", "role": "chair", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "orcid": "0000-0001-9176-3078", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Hajimiri", "given": "Ali" }, "id": "Hajimiri-A", "orcid": "0000-0001-6736-8019", "role": "member", "display_name": "Hajimiri, Ali" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ata8-3r29", "abstract": "The mobile wireless environment has been a challenge to reliable communications because of the time-varying nature of the channel. Detrimental effects such as path loss, shadowing, and multipath fading can greatly attenuate the transmitted signal. Therefore, adaptive channel estimation and data detecting algorithms must be designed for such channels. Moreover, in a multi-user system, dynamic resource allocation is an important means to transmit information efficiently through the varying channel.
\r\n\r\nIn this thesis we first propose two adaptive feedback maximum-likelihood detection techniques, a decision-feedback decoder and an output-feedback decoder, for coded signals transmitted over channels with correlated fading. Both analysis and simulation results demonstrate that they have far better performance than the conventional decoder. We also propose a simple improvement to conventional decoders by using a weighted metric. The BER performance of all these decoders is analyzed through a sliding window decoding method.
\r\n\r\nNext we derive the ergodic (Shannon) capacity region and optimal dynamic resource allocation for an M-user fading broadcast channel under code-division with and without successive decoding, time-division, and frequency-division. For this channel we also derive the outage and zero-outage capacity regions and the corresponding optimal resource allocation strategies under different spectrum-sharing techniques. We obtain the outage capacity region implicitly by deriving the minimum common outage probability or the outage probability region for a given rate vector. The corresponding optimal power allocation scheme is a multi-user generalization of the single-user threshold-decision rule.
\r\n\r\nFinally, we obtain the outage capacity region and optimal power allocation for fading multiple access channels. Successive decoding is proved to be optimal and iterative algorithms are proposed to obtain the optimal decoding order and power allocation in each fading state under the average power and outage probability constraints of each user. We also obtain the average power regions that can support a rate vector with the given average outage probability of each user satisfied.
\r\n" }, { "name": "Li, Ying", "degree": "PhD", "year": "2000", "title": "Tsunamis: Non-Breaking and Breaking Solitary Wave Run-Up", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-112425905", "creators": [ { "name": { "family": "Li", "given": "Ying" }, "id": "Li-Ying", "display_name": "Li, Ying" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" } ], "option_major": [ "mecheng" ], "doi": "10.7907/kake-7p89", "abstract": "This study considers the run-up of non-breaking and breaking solitary waves on a smooth sloping beach. A non-linear theory and a numerical model solving the non-linear shallow water equations (NLSW) were developed to model this physical process. Various experiments to obtain wave amplitude time-histories, water particle velocities, wave free-surface profiles, and maximum run-up were conducted and the results were compared with the analytical and numerical models.\r\nA higher order theoretical solution to the non-linear shallow water equations, which describes the non-breaking wave characteristics on the beach, was sought and presented in this study. The solution was obtained analytically by using the Carrier and Greenspan (1958) hodograph transformation. It was found that the non-linear theory agreed well with experimental results. The maximum run-up predicted by the non-linear theory is larger than that predicted by Synolakis (1986) at the order of the offshore relative wave height for a given slope. This correction for non-breaking waves on beach decreases as the beach slope steepens, and increases as the relative incident solitary wave height increases.\r\nA unique run-up gage that consists of a laser and a photodiode camera was developed in connection with this study to measure the time-history of the tip of the run-up tongue of a non-breaking solitary wave as it progresses up the slope. The results obtained with this run-up gage agree well with other measurements and provides a simple and reliable way of measuring run-up time histories.\r\nThe run-up of breaking solitary waves was studied experimentally and numerically since no fully theoretical approach is possible. The wave characteristics such as wave shape and shoaling characteristics, and, for plunging breakers, the shape of the jet produced are presented. The experimental results show that wave breaking is such a complicated process that even sophisticated numerical models cannot adequately model its details.\r\nTwo different plunging wave breaking and resultant run-up were found from the experiments. The point, where the tip of the incident jet produced by the plunging breaking wave impinges determines the characteristics of the resulting splash-up. If the jet impinges on a dry slope, no splash-up occurs and the plunging breaker simply collapses. If the impingement point is located on the free-surface, splash-up including a reflected jet is formed, which further increases the turbulence and energy dissipation associated with wave breaking. It is hypothesized that both clockwise and counter clockwise vortices may be generated by the impinging plunging jet and the reflected jet associated with the splash-up when the jet impinges on the front face of a breaking wave or on the still water surface in front of the wave.\r\nIf only the run-up process and maximum run-up are of interest, the wave and the water flow produced after breaking can be simplified as a propagating bore, which is analogous to a shock wave in gas dynamics. A numerical model using this bore structure to treat the process of wave breaking and propagation was developed. The non-linear shallow water equations were solved using the weighted essentially non-oscillatory (WENO) shock capturing scheme employed in gas dynamics. Wave breaking and propagation is handled automatically 1w this scheme and no ad-hoc term is required. A computational domain mapping technique proposed by Zhang (1996) is used in the numerical scheme to model the shoreline movement. This numerical scheme is found to provide a somewhat simple and reasonably good prediction of various aspects of the run-up process. The numerical results agree well with the experiments corresponding to the run-up on a. relatively steep slope (1:2.08) as well as on a more gentle slope (1:19.85).\r\nA simple empirical estimate of maximum run-up based on energy conservation considerations is also presented where the energy dissipation associated with wave breaking was estimated using the results from the numerical model. This approach appears to be useful and the maximum run-up predicted agrees reasonably well with the experimental results.\r\nThe splash-up of a solitary wave on a vertical wall positioned at different locations on a gentle slope was also investigated in this study to understand the degree of protection from tsunamis afforded by seawalls. It was found that the effect of breaking wave kinematics offshore of the vertical wall on the splash-up is of critical importance to the maximum splash-up. The maximum slope of the front face of the wave upon impingement of the wave on the wall, which represents the maximum water particle acceleration, was important in defining the maximum sheet splash-up as well as the trend for splash-up composed of drops and spray.\r\n" }, { "name": "Lu, Daqi", "degree": "PhD", "year": "2000", "title": "Theoretical Studies of the Nonlinear Optical Properties of Organic Materials", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-103544088", "creators": [ { "name": { "family": "Lu", "given": "Daqi" }, "id": "Lu-Daqi", "display_name": "Lu, Daqi" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "co-chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/myx9-7278", "abstract": "No abstract." }, { "name": "Manwani, Amit", "degree": "PhD", "year": "2000", "title": "Information-theoretic analysis of neuronal communication", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-093222400", "creators": [ { "name": { "family": "Manwani", "given": "Amit" }, "id": "Manwani-A", "display_name": "Manwani, Amit" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "cns" ], "doi": "10.7907/q9c5-f606", "abstract": "One of the most fundamental functions of brains is to process information. Whether we are engaged in tasks like reading a book, listening to our favorite music station on radio, smelling a flower in bloom or relishing our favorite gourmet cuisine, we invariably employ our brains to process the information received through our senses and create a perception of the world around us. The physical signals incident on our sensory organs, either in the form of photon fluxes, acoustic vibrations, or plumes of chemical concentrations, are transduced, represented and processed as electrical signals within our brains. One of the essential inquiries in neuroscience is the nature of this representation of information in the brain. This is often referred to as the \"neural coding\" problem which has been and continues to be the object of a lot of theoretical and experimental scientific effort.\r\n\r\nIn most theoretical approaches that address the problem, nerve cells are characterized empirically by collection of their input-output responses. The knowledge of constraints imposed on information processing due to biophysics of the underlying biological hardware is generally ignored. This thesis reports the outcome of our efforts to combine techniques from stochastic processes, information theory and single neuron biophysics to unravel the neural coding problem. We believe that a systematic reductionist analysis which takes into account the extant noise due to biological processes specific to neuronal processing will provide fundamental insights overlooked in earlier approaches. We analytically characterize the sources of biological noise associated with different stages in the neuronal information pathway, namely the synapse, the dendritic tree and the spike-initiation zone and employ information-theoretical measures to compute the ability of these components to transmit information in specific signal processing tasks. For analytical tractability, we demonstrate our results using abstract and simplified mathematical models. However, our approach can be readily applied to realistic and complicated descriptions of single neurons to provide a greater understanding of the role of noise in neuronal communication." }, { "name": "Min, Kyu Sung", "degree": "PhD", "year": "2000", "title": "Synthesis and properties of light-emitting Si-based nanostructures", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122010-100418753", "creators": [ { "name": { "family": "Min", "given": "Kyu Sung" }, "id": "Min-Kyu-Sung", "display_name": "Min, Kyu Sung" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." } ], "option_major": [ "matsci" ], "doi": "10.7907/tjep-v350", "abstract": "The concept of silicon-based optoelectronics has attracted much scientific and technological interests over the past decade. The vision of Si-based optoelectronics is based on integration of Si-based photonic components, in which light can be generated, waveguided, modulated, amplified, and detected, with the advanced Si electronics onto the same Si substrate to make monolithically integrated Si-based optoelectronic circuits. The main driving force for development of Si-based optical components comes from unsurpassed qualities of Si as the substrate material on which the electronic components rest: superior native oxide as well as excellent thermal, mechanical, and economic properties. Despite superior substrate properties, the field still remains a frontier at large. The main technological limitation comes from the lack of materials for efficient Si-based light sources such as Si-based lasers and light-emitting devices. \r\n\r\nTwo novel Si-based nanostructures are studied for potential application as visible and infrared light sources: ion-beam synthesized Ge and Si nanocrystals in SiO_2 and coherently strained quantum well and quantum dots based on the Si-Sn system grown by molecular beam epitaxy. \r\n\r\nThe study of Ge and Si nanocrystals is motivated by the prediction that quantum confinement of carriers leads to efficient luminescence despite the indirect nature of the energy gaps. Ge and Si nanocrystals in thermal SiO_2 films are synthesized via precipitation from a supersaturated solid solution of Ge and Si in SiO_2 made by Ge^+ and Si^+ ion implantation. The precipitation of nanocrystals occurs upon thermal annealing in vacuum. It is demonstrated that the SiO_2films containing Ge nanocrystals only exhibit defect-related luminescence and that the Ge nanocrystals do not exhibit luminescence from quantum-confined excitons due to the poor nanocrystal/SiO_2 interface. The visible luminescence from SiO_2 films containing Si nanocrystals, on the other hand, is unambiguously demonstrated to be originating from quantum-confined excitons in Si nanocrystals, based on systematic photoluminescence and photoluminescence decay rate measurements. In agreement with the predictions of the theory of quantum confinement, the peak energy of visible photoluminescence from Si nanocrystals can be continuously tuned throughout most of the visible spectrum by controlling the size distribution of the nanocrystals. \r\n\r\nThe growth of nanostructures based on the Si-Sn system by molecular beam epitaxy is motivated by the fact that diamond cubic \u03b1-Sn is a zero band gap semiconductor and that band structure calculations predict a direct and tunable energy gap for Sn-rich Sn_(x)Si_(1-x) alloy system. However, the large lattice mismatch (19%) and severe segregation of Sn to the surface during growth prevent growth of Sn-rich Sn_(x)Si_(1-x) films by ordinary thermal molecular beam epitaxy. The growth of pseudomorphic Sn/Si and Sn_(x)Si_(1-x)/Si heterostructures is demonstrated via a modified molecular beam epitaxy technique employing temperature and growth rate modulations. The growth of pseudomorphic single quantum well structures as well as superlatttice structures is demonstrated. In addition, a novel route for synthesis of coherent Sn-rich Sn_(x)Si_(1-x) quantum dots in Si matrix is presented. Due to chemical instability of the Si-Sn mixture, Stranski-Krastonow growth of coherently strained Sn-rich Sn_(x)Si_(1-x) quantum dot structures using conventional molecular beam epitaxy techniques is very difficult. The novel technique involves phase separation of Sn-rich Sn_(x)Si_(1-x) quantum dots at elevated temperatures from an epitaxially stabilized homogeneous Sn_(x)Si_(1-x)/Si metastable solid solution grown by low temperature molecular beam epitaxy. The dots have been verified to be completely coherent with the surrounding Si matrix by high-resolution transmission electron microscopy.\r\n" }, { "name": "Moeleker, Piet", "degree": "PhD", "year": "2000", "title": "The filtered advection-diffusion equation : Lagrangian methods and modeling", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-114741410", "creators": [ { "name": { "family": "Moeleker", "given": "Piet" }, "id": "Moeleker-P", "display_name": "Moeleker, Piet" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2q17-4g27", "abstract": "This research focuses on the incompressible scalar advection-diffusion equation. After applying a Gaussian filter, an infinite series expansion is found for the advection term to obtain a closed equation. Only the first two terms in this expansion are retained yielding the tensor-diffusivity subgrid model. This model can be interpreted as a tensor-diffusivity term which is proportional to the rate-of-strain tensor of the large-scale\r\nfiltered velocity field. Due to the negative diffusion in the stretching directions, care needs to be taken in the choice of a numerical method.\r\n\r\nThe scalar field is decomposed in a collection of anisotropic or axisymmetric Gaussian particles. Equations of motion for the location and the shape/size of the particles are derived using an expansion in Hermite polynomials. A novel, accurate remeshing scheme was found resulting in explicit expressions for the amplitudes of the new set of particles.\r\n\r\nA stagnation flow was used for illustrative purposes and validation. Using a 2D time-dependent velocity field yielding chaotic advection, both axisymmetric and\r\nanisotropic particles yield good agreement with filtered direct numerical simulations and compare favorably with the Smagorinsky subgrid model. Computational efficiency\r\nmakes axisymmetric particles the preferred choice.\r\n\r\nA literature study using a 3D stationary one-parameter chaotic velocity field was used to validate model and particle-method in 3D. For highly chaotic fields good\r\nagreement was obtained with this study. Computations have been performed for 3D forced isotropic periodic turbulence to study scalar mixing. Comparisons with literature are made.\r\n\r\nIt was shown that when the unfiltered velocity field is known, the most accurate results are obtained by moving particles using this field. It was concluded that a good\r\nsubgrid model modifies the equation of motion to get a good approximation to the unfiltered velocity field.\r\n" }, { "name": "Mohseni, Kamran", "degree": "PhD", "year": "2000", "title": "A: Universality in Vortex Formation. B: Evaluation of Mach Wave Radiation Mechanisms in a Supersonic Jet", "advisor": "Colonius, Tim; Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:10082010-114955709", "creators": [ { "name": { "family": "Mohseni", "given": "Kamran" }, "id": "Mohseni-Kamran", "display_name": "Mohseni, Kamran" } ], "advisors": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "advisor", "display_name": "Colonius, Tim" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "chair", "display_name": "Colonius, Tim" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/MB7E-7950", "abstract": "In this thesis two distinct features of coherent structures are investigated. In Part I a model for the pinch-off process in vortex ring formation is developed. The predicted nondimensional stroke length L/D (referred to as \"formation number\") satisfactorily matches experimental observations. The model introduces two nondimensional parameters that govern the limiting value of the formation number: a nondimensional energy and circulation, E_(nd) and \u0393_(nd), respectively. The predicted value of E_(nd) also matches well with the experimental data. The limiting value for the new nondimensional circulation is predicted to be in the range 1.77 \u2272 \u0393_(nd) \u2272 2.07. We perform detailed computations of vortex ring formation by nonconservative forcing. The validity of the assumptions in our model is verified in these computations. Some techniques for generating fat rings are successfully investigated, resulting in generation of vortex rings with Hill's like properties. We consider thermodynamics of the vorticity density field (w/r), and we develop a statistical equilibrium theory for axisymmetric flows. It is shown that the statistical equilibrium of an axisymmetric flow is the state that maximizes an entropy functional constrained to the invariants of motion. Furthermore, it is shown that the final equilibrium state satisfies a variational principle similar to Kelvin's variational principle. In Part II Mach wave radiation mechanisms in a fully expanded supersonic jet is studied. We compare a direct numerical simulation (DNS) of a 1.92 Mach number jet with a linearized Navier-Stokes (LNS) simulation. The numerical integration technique, inflow boundary conditions, and grid distributions are the same in both simulations. We found that the generated noise in the DNS calculation is dominated by the first two azimuthal modes, and contributions from all other azimuthal modes were limited to less than 1.5 dB in the acoustic field. The total directivity of the sound field in the LNS matches reasonably well with the sound field of the DNS data. At the peak Strouhal frequency, particularly for the azimuthal mode n = 1, the amplification of flow variables in the LNS closely matches that of the DNS data. However, for frequencies away from the peak Strouhal number the DNS data shows amplification rates comparable to those of the peak Strouhal number, while in the LNS data any disturbances away from the peak Strouhal number are highly damped. These extra noise sources in the DNS data have the characteristics of a nonlinear interaction among various modes. The noise generated by the first two modes in the linearized computation is substantially weaker than in the DNS. For example, in the near acoustic field, at a distance of 6 jet diameters from the jet centerline, the sound pressure level in the linearized computation is as much as 8 db smaller than the DNS results. We observed that the maximum amplification rate for the DNS data occurs at an axial location further downstream than for the LNS data, which corresponds to regions around and beyond the end of the potential core. Our results indicate that the missing sound generation mechanisms in the LNS computation at the frequencies considered in this study can be attributed to the non-linear sound generation mechanisms, that are not captured in linear theories." }, { "name": "Munich, Mario Enrique", "degree": "PhD", "year": "2000", "title": "Visual input for pen-based computers", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-03152006-094551", "creators": [ { "name": { "family": "Munich", "given": "Mario Enrique" }, "id": "Munich-M-E", "orcid": "0000-0002-6665-7473", "display_name": "Munich, Mario Enrique" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Burl", "given": "Michael C." }, "id": "Burl-M-C", "role": "member", "display_name": "Burl, Michael C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/1VW0-ZG46", "abstract": "The development of computer technology has had a parallel evolution of the interface between humans and machines, giving rise to interface systems inspired by human communication. Vision has been demonstrated to be the sense of choice for face recognition, gesture recognition, lip reading, etc. This thesis presents the design and implementation of a camera-based, human-computer interface for acquisition of handwriting. The camera focuses on the sheet of paper and images the hand writing; computer analysis of the resulting sequence of images enables the trajectory of the pen to be tracked and the times when the pen is in contact with the paper to be detected. The recovered trajectory is shown to have sufficient spatio-temporal resolution and accuracy to enable handwritten character recognition.\r\n\r\nSignatures can be acquired with the camera-based interface with enough resolution to perform verification. This thesis describes the performance of a visual-acquisition signature verification system, emphasizing the importance of the parameterization of the signature to achieving good classification results. The generalization error of the verification algorithm is estimated using a technique that overcomes the small number of example signatures and forgeries provided by the subjects.\r\n\r\nThe problem of establishing correspondence and measuring the similarity of a pair of planar curves, in our case a pair of signatures, arises in many application in computer vision and pattern recognition. This thesis presents a new method for comparing planar curves and for performing matching at sub-sampling resolution. The analysis of the algorithm as well as its structural properties are described. The performance of the new technique is evaluated for the problem of signature verification and compared to the performance of the well-known Dynamic Programming Matching algorithm." }, { "name": "Oguni, Kenji", "degree": "PhD", "year": "2000", "title": "Micromechanical Aspects of Failure in Unidirectional Fiber Reinforced Composites", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechTHESIS:10082010-091323238", "creators": [ { "name": { "family": "Oguni", "given": "Kenji" }, "id": "Oguni-Kenji", "orcid": "0000-0003-0425-9784", "display_name": "Oguni, Kenji" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "role": "member", "display_name": "Ustundag, Ersan" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/3VSA-QN96", "abstract": "Micromechanical aspects of failure in unidirectional fiber reinforced composites are investigated using combined experimental and analytical methods. Results from an experimental investigation on mechanical behavior of a unidirectional fiber reinforced polymer composite (E-glass/vinylester) with 50% fiber volume fraction under quasi-static uniaxial and proportional multiaxial compression are presented. Detailed examination of the specimen during and after the test reveals the failure mode transition from axial splitting to kink band formation as the loading condition changes from uniaxial to multiaxial compression.
\r\n\r\nMotivated by the experimental observations, an energy-based model is developed to provide an analytical estimate of the critical stress for axial splitting observed in unidirectional fiber reinforced composites under uniaxial compression in the fiber direction (also with weak lateral confinement). The analytic estimate for the compressive strength is used to illustrate its dependence on material properties, surface energy, fiber volume fraction, fiber diameter and lateral confining pressure.
\r\n\r\nTo understand the effect of flaws on the strength of unidirectional fiber reinforced composites, a fracture mechanics based model for failure is developed. Based on this model, failure envelope, dominant initial flaw orientation and failure mode for the composites under a wide range of stress states are predicted. Parametric study provides quantitative evaluation of the effect of various mechanical and physical properties on failure behavior and identifies their influence on strength.
\r\n\r\nFinally, results from an experimental investigation on the dynamic mechanical behavior of unidirectional E-glass/vinylester composites with 30%, 50% fiber volume fraction under uniaxial compression are presented. Limited experimental results are also presented for the 50% fiber volume fraction composite under dynamic proportional lateral confinement. Specimens are loaded in the fiber direction using a modified Kolsky (split Hopkinson) pressure bar. The results indicate that the compressive strength of the composite increases with increasing strain rate and confinement. Post-test scanning electron microscopy reveals that axial splitting is the dominant failure mechanism in the composites under uniaxial compression in the entire range of strain rates. Based on the experimental results and observations, the energy-based analytic model is extended to predict the compressive strength of these composites under dynamic uniaxial loading conditions.
" }, { "name": "Park, Peter J.", "degree": "PhD", "year": "2000", "title": "Multiscale numerical methods for the singularly perturbed convection-diffusion equation", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272006-094856", "creators": [ { "name": { "family": "Park", "given": "Peter J." }, "id": "Park-P-J", "display_name": "Park, Peter J." } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/4C7T-3440", "abstract": "We develop efficient and robust numerical methods in the finite element framework for numerical solutions of the singularly perturbed convection-diffusion equation and of a degenerate elliptic equation. The standard methods for purely elliptic or hyperbolic problems perform poorly when there are sharp boundary and internal layers in the solution caused by the dominant convective effect. We offer a new approach in which we design the finite element basis functions that capture the local behavior correctly.\n\nWhen the structure of the layers can be determined locally, we apply the multiscale finite element method in which we solve the corresponding homogeneous equation on each element to capture the small scale features of the differential operator. We demonstrate the effectiveness of this method by computing the enhanced diffusivity scaling for a passive scalar in the cellular flow. We carry out the asymptotic error analysis for its convergence rate and perform numerical experiments for verification. When the layer structure is nonlocal, we use a variational principle to gain additional information. For a random velocity field, this variational principle provides correct scaling results. This allows us to design asymptotic basis functions that can capture the global layers correctly.\n\nThe same approach is also extended to elliptic problems with high contrast coefficients. When an asymptotic result is available, it is incorporated naturally into the finite element setting developed earlier. When there is a strong singularity due to a discontinuous coefficient, we construct the basis functions using the infinite element method. Our methods can handle singularities efficiently and are not sensitive to the large contrast.\n" }, { "name": "Parrilo, Pablo A.", "degree": "PhD", "year": "2000", "title": "Structured semidefinite programs and semialgebraic geometry methods in robustness and optimization", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-05062004-055516", "creators": [ { "name": { "family": "Parrilo", "given": "Pablo A." }, "id": "Parrilo-P-A", "display_name": "Parrilo, Pablo A." } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/2K6Y-CH43", "abstract": "In the first part of this thesis, we introduce a specific class of Linear Matrix Inequalities (LMI) whose optimal solution can be characterized exactly. This family corresponds to the case where the associated linear operator maps the cone of positive semidefinite matrices onto itself. In this case, the optimal value equals the spectral radius of the operator. It is shown that some rank minimization problems, as well as generalizations of the structured singular value ($mu$) LMIs, have exactly this property.\n\nIn the same spirit of exploiting structure to achieve computational efficiency, an algorithm for the numerical solution of a special class of frequency-dependent LMIs is presented. These optimization problems arise from robustness analysis questions, via the Kalman-Yakubovich-Popov lemma. The procedure is an outer approximation method based on the algorithms used in the computation of hinf norms for linear, time invariant systems. The result is especially useful for systems with large state dimension.\n\nThe other main contribution in this thesis is the formulation of a convex optimization framework for semialgebraic problems, i.e., those that can be expressed by polynomial equalities and inequalities. The key element is the interaction of concepts in real algebraic geometry (Positivstellensatz) and semidefinite programming.\n\nTo this end, an LMI formulation for the sums of squares decomposition for multivariable polynomials is presented. Based on this, it is shown how to construct sufficient Positivstellensatz-based convex tests to prove that certain sets are empty. Among other applications, this leads to a nonlinear extension of many LMI based results in uncertain linear system analysis.\n\nWithin the same framework, we develop stronger criteria for matrix copositivity, and generalizations of the well-known standard semidefinite relaxations for quadratic programming.\n\nSome applications to new and previously studied problems are presented. A few examples are Lyapunov function computation, robust bifurcation analysis, structured singular values, etc. It is shown that the proposed methods allow for improved solutions for very diverse questions in continuous and combinatorial optimization.\n" }, { "name": "Pekarsky, Sergey", "degree": "PhD", "year": "2000", "title": "Discrete reduction of mechanical systems and multisymplectic geometry of continuum mechanics", "advisor": "Marsden, Jerrold E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-115304008", "creators": [ { "name": { "family": "Pekarsky", "given": "Sergey" }, "id": "Pekarsky-S", "display_name": "Pekarsky, Sergey" } ], "advisors": [ { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "advisor", "display_name": "Marsden, Jerrold E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "cds" ], "doi": "10.7907/1y6f-7w97", "abstract": "This thesis develops discrete reduction techniques for mechanical systems defined on Lie groups and also presents multisymplectic formulation of both compressible and incompressible models of continuum mechanics on general Riemannian manifolds. While the former synthesizes ideas of Euler-Poincar\u00e9 and Lie-Poisson reduction for mechanical systems with the Veselov type discretization of such systems, the latter sets the stage for multisymplectic reduction and for further development of Veselov type multisymplectic discretizations.\r\n\r\nFor systems defined on finite dimensional Lie groups G with Lagrangians L : TG \u2192 R that are G-invariant, the reduced discrete equations provide \"reduced\" numerical algorithms which manifestly preserve the underlying (symplectic) structure. The manifold G x G is used as an approximation of TG, and a discrete Lagrangian L : G x G \u2192 R is constructed in such a way that the G-invariance property is preserved. Reduction by G results in new \"variational\" principle for the reduced Lagrangian \u2113 : G \u2192 R, and provides the discrete Euler-Poincar\u00e9 (DEP) equations. The solution of the DEP algorithm immediately leads to a discrete Lie-Poisson (DLP) algorithm.\r\n\r\nIt is also shown that the reduced Lagrangian \u2113 : G \u2192 R defines a Poisson structure on (a subset) of one copy of the Lie group G. This structure governs the corresponding discrete reduced dynamics. The symplectic leaves of this structure become dynamically invariant manifolds which are manifestly preserved under the structure preserving discrete Euler-Poincar\u00e9 algorithm.\r\n\r\nA variational multisymplectic formulation of non-relativistic continuum mechanics on general Riemannian manifolds is developed. Two main applications of our theory are considered \u2014 fluid dynamics and elasticity \u2014 each specified by a particular choice of the Lagrangian density. The non-relativistic character of the theory enables applications to such important cases as incompressible hydrodynamics and constrained director models of elastic rods and shells. These are applications of a general formalism developed here for treating non-relativistic first-order multisymplectic field theories with constraints.\r\n\r\nThe results obtained in this thesis also set the stage for multisymplectic reduction and for the further development of Veselov-type multisymplectic discretizations and numerical algorithms Combined with the ideas on discretizing systems with symmetries, this approach would results in so called multisymplectic integrators which preserve the discrete analogues of the conservation laws.\r\n" }, { "name": "Peral, Eva M.", "degree": "PhD", "year": "2000", "title": "Some issues relevant to propagation of lightwave signals in optical fibers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052010-144834578", "creators": [ { "name": { "family": "Peral", "given": "Eva M." }, "id": "Peral-E-M", "display_name": "Peral, Eva M." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PVBN-KY66", "abstract": "Fiber optics is a promising technology that can enable the high bit rates and long spans that are on increasing demand. Although the fiber bandwidth is as large as several terahertz, there are several phenomena, related to both intrinsic fiber properties and characteristics of the state-of-the-art transmitters and receivers, which seriously degrade the performance of fiber communication systems, imposing limits on the transmission bandwidths and distances that can be achieved.\r\n\r\nIn this thesis, some of the issues affecting linear and nonlinear propagation in optical fiber will be theoretically and experimentally studied. Schemes for compensation of some of these phenomena or amelioration of their effects will be presented." }, { "name": "Qu, Wendong", "degree": "PhD", "year": "2000", "title": "Studies on Nonlinear Dispersive Water Waves", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152006-140314", "creators": [ { "name": { "family": "Qu", "given": "Wendong" }, "id": "Qu-Wendong", "display_name": "Qu, Wendong" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "eng" ], "doi": "10.7907/19B4-2N21", "abstract": "This study investigates the phenomena of evolution of two-dimensional, fully nonlinear, fully dispersive, incompressible and irrotational waves in water of uniform depth in single and in double layers. The study is based on an exact fully nonlinear and fully dispersive (FNFD) wave model developed by Wu (1997, 1999a). This FNFD wave model is first based on two exact equations involving three variables all pertaining to their values at the water surface. Closure of the system of model equations is accomplished either in differential form, by attaining a series expansion of the velocity potential, or in integral form by adopting a boundary integral equation for the velocity field.\r\n\r\nA reductive perturbation method for deriving asymptotic theory for higher-order solitary waves is developed using the differential closure equation of the FNFD wave theory. Using this method, we have found the leading 15th-order solitary wave solutions. The solution is found to be an asymptotic solution which starts to diverge from the 12th-order so that the 11th-order solution appears to provide the best approximation to the fully nonlinear solitary waves, with a great accuracy for waves of small to moderately large amplitudes.\r\n\r\nTwo numerical methods for calculating unsteady fully nonlinear waves, namely, the FNFD method and the Point-vortex method, are developed and applied to compute evolutions of fully nonlinear solitary waves. The FNFD method, which is based on the integral closure equation of Wu's theory, can provide good performance on computation of solitary waves of very large amplitude. The Point-vortex method using the Lagrange markers is very efficient for computation of waves of small to moderate amplitudes, but has intrinsic difficulties in computing waves of large amplitudes. These two numerical methods are applied to carry out a comparative study of interactions between solitary waves.\r\n\r\nCapillary-gravity solitary waves are investigated both theoretically and numerically. The theoretical study based on the reductive perturbation method provides asymptotic theories for higher-order capillary-gravity solitary waves. A stable numerical method (FNFD) for computing exact solutions for unsteady capillary-gravity solitary waves is developed based on the FNFD wave theory. The results of the higher-order asymptotic theories compare extremely well with those given by the FNFD method for waves of small to moderate amplitudes.\r\n\r\nA numerical method for computing unsteady fully nonlinear interfacial waves in two-layer fluid systems is developed based on the FNFD model. The subcritical and supercritical cases can be clearly distinguished by this method, especially for waves of amplitudes approaching the maximum attainable for the fully nonlinear theory." }, { "name": "Schlamp, Stefan", "degree": "PhD", "year": "2000", "title": "Laser-induced thermal acoustic velocimetry", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-130705165", "creators": [ { "name": { "family": "Schlamp", "given": "Stefan" }, "id": "Schlamp-S", "display_name": "Schlamp, Stefan" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/skm0-tk82", "abstract": "Laser-Induced Thermal Acoustics (LITA) is a non-intrusive, remote, four-wave mixing laser diagnostic technique for measurements of the speed of sound and of the thermal diffusivity in gases. If the gas composition is known, then its temperature and density can be inferred. Beam misalignments and bulk fluid velocities can influence the time history and intensity of LITA signals. A closed-form analytic expression for LITA signals incorporating these effects is derived. The magnitude of beam misalignment and the flow velocity can be inferred from the signal shape using a least-squares fit of this model to the experimental data. High-speed velocimetry using homo dyne detection is demonstrated with NO_2-seeded air in a supersonic blow-down nozzle. The measured speed of sound deviates less than 2% from the theoretical value assuming isentropic quasi-1D flow. Boundary layer effects degrade the velocity measurements to errors of 20%. Heterodyne detection is used for low-speed velocimetry up to Mach number M = 0.1. The uncertainty of the velocity measurements was ~ 0.2 m/s. The sound speed measurements were repeatable to 0.5%. The agreement between theory and experiments is very good. A one-hidden-layer feed-forward neural network is trained using back-propagation learning and a steepest descent learning rule to extract the speed of sound and flow velocity from a heterodyne LITA signal. The effect of the network size on the performance is demonstrated. The accuracy is determined with a second set of LITA signals that were not used during the training phase. The accuracy is found to be better than that of a conventional frequency decomposition technique while being computationally as efficient. This data analysis method is robust with respect to noise, numerically stable, and fast enough for real-time data analysis. The accuracy and uncertainty of non-resonant LITA measurements is investigated. The error in measurements of the speed of sound and of the thermal diffusivity initially decreases with increasing signal intensity (excitation beam pulse energy) and increases again after passing a minimum. The location of the minimum error for the speed of sound and for the thermal diffusivity coincide. The errors at the minimum are 0.03% and 1%, respectively. The uncertainties for the speed of sound and the thermal diffusivity decrease monotonically to 0.25% and 5%, respectively. The increased error for high excitation beam pulse energies results from finite-strength waves that cannot be treated using the linearized equations of motion." }, { "name": "Schultz, Eric", "degree": "PhD", "year": "2000", "title": "Detonation Diffraction Through an Abrupt Area Expansion", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-180459", "creators": [ { "name": { "family": "Schultz", "given": "Eric" }, "id": "Schultz-Eric", "display_name": "Schultz, Eric" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/96F1-QR61", "abstract": "The problem of a self-sustaining detonation wave diffracting from confinement into an unconfined space through an abrupt area change is characterized by the geometric scale of the confinement and the reaction scale of the detonation. Previous investigations have shown that this expansion associated with a detonation transitioning from planar to spherical geometry can result in two possible outcomes depending upon the combustible mixture composition, initial thermodynamic state, and confining geometry. Competition between the energy release rate and expansion rate behind the diffracting wave is crucial. The sub-critical case is characterized by the rate of expansion exceeding the energy release rate. As the chemical reactions are quenched, the shock wave decouples from the reaction zone and rapidly decays. The energy release rate dominates the expansion rate in the super-critical case, maintaining the coupling between the shock and reaction zone which permits successful transition across the area change. A critical diffraction model has been developed in the present research effort from which the initial conditions separating the sub-critical and super-critical cases can be analytically determined. Chemical equilibrium calculations and detonation simulations with validated detailed reaction mechanisms provide the model input parameters. Experiments over a wide range of initial conditions with single- and multi-sequence shadowgraphy and digital chemiluminescence imaging support the model derivation and numerical calculations. Good agreement has been obtained between the critical diffraction model and experimental results." }, { "name": "Smith, James N.", "degree": "PhD", "year": "2000", "title": "A. Computational chemistry applied to the analysis of air pollution reaction mechanisms ; B. Fundamental studies of droplet evaporation and discharge dynamics in electrospray ionization", "advisor": "Flagan, Richard C.; Beauchamp, Jesse L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202007-080810", "creators": [ { "name": { "family": "Smith", "given": "James N." }, "id": "Smith-J-N", "display_name": "Smith, James N." } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." }, { "name": { "family": "Beauchamp", "given": "Jesse L." }, "id": "Beauchamp-J-L", "role": "advisor", "display_name": "Beauchamp, Jesse L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/M9MM-6Z40", "abstract": "The first part of the thesis investigates the use of theoretical quantum chemical calculations for the study of the reaction pathways of the atmospheric aromatic-OH reaction. The computational model is comprised of a semi-empirical PM3 geometry optimization followed by a single point calculation performed using the Becke3LYP hybrid density functional and a 6-31G(d,p) basis. Zero-point energies were calculated using PM3, and transition states barrier heights estimated by a constrained optimization procedure developed for this study. Full mechanisms for the OH-initiated photooxidation of toluene, m-xylene, p-xylene, 1,2,4-trimethylbenzene and m-ethyltoluene are developed. The lowest energy intermediates have been determined and predicted products from these structures are compared to available experimental product data. These studies serve to refine proposed mechanisms currently available for toluene, mxylene and p-xylene, while providing new information on the 1,2,4-trimethylbenzene and m-ethyltoluene reaction pathways.\r\n\r\nIn the second part of the thesis, an experimental technique is described for probing the mechanism and dynamics of charged droplet breakup in electrospray ionization. At its core is an instrument that can perform simultaneous, in situ measurements of size and charge on individual droplets. Charged droplets are sampled directly from the spray source into a drift cell with a uniform electric field. A simultaneous diameter and charge measurement is made on individual droplets at the center of the cell using phase Doppler anemometry. By reversing the field in the drift chamber once the initial size and charge measurement is made, the droplet can be made to pass again through the measurement region of the phase Doppler anemometer. In this way, repeated measurements of the size and charge can be made on a single droplet. This technique has been applied to a variety of solutions used commonly in electrospray ionization and lead to the following generalizations. (1) The discharge dynamics of droplets with the same initial diameter and charge are highly reproducible for all solvents and analyte/solvent combinations studied to date. (2) Published over a hundred years ago, Lord Rayleigh's analysis of charged droplet instabilities resulting from solvent evaporation is remarkably accurate in predicting observed discharge events for all three solvents. (3) Droplet discharge events are characterized by loss of 15-20% of the charge from methanol and acetonitrile droplets, and 20-40% from water droplets, with little accompanying loss of solvent. (4) Discharge events occur in a reproducible temporal pattern, with decreasing time intervals between successive events, dictated by solvent evaporation and the approach to the Rayleigh limit. The droplet size decrease agrees well with a model of solvent evaporation. (5) The addition of biomolecules or salt (up to 10[superscript -3] M to the solution does not significantly alter discharge dynamics. The size-charge correlation and discharge dynamics of negatively charged droplets formed in electrospray ionization of 10[superscript -4] M NaCl in methanol are similar to those observed for positively charged droplets. (6) The life history of a single electrosprayed droplet can be followed through numerous discharge events (sequences with up to 50 measurements and 6 discharges have been observed) in the absence of radial confinement. This implies that no significant displacement of the droplet arises from discharge events and is inconsistent with any notion of high energy chaotic fission processes. (7) Droplet size-charge correlations show that, in certain instances, droplets from an electrospray fall into discrete groupings that can be attributed to fission events.\r\n" }, { "name": "Swenson, Grant Douglas", "degree": "PhD", "year": "2000", "title": "Numerical simulations of combustion instabilities in gas turbine combustors, with applications", "advisor": "Culick, Fred E. C.; Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-140810", "creators": [ { "name": { "family": "Swenson", "given": "Grant Douglas" }, "id": "Swenson-G-D", "display_name": "Swenson, Grant Douglas" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "co-advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3QG6-JN34", "abstract": "Recent advances in technology have opened up a potential market for small gas turbine power systems in the 50-100 MW range. In an effort to improve their systems, the gas-turbine industry is interested in understanding and controlling combustion instabilities as well as reducing pollutant production. To understand the dynamics inherent in a combustion system, information about the flow field behavior is required. Because of a scarcity of available experimental or numerical results for full-scale gas-turbine combustors, we decided to use numerical simulations to provide the required information about the flow field dynamics. The ability of the numerical simulations to reproduce unstable behavior in combustion environments will be presented. The investigation of the flow field dynamics has been conducted for three test cases; a planar heat source in a tube, premixed flow in a dump combustor, and premixed and diffusion flames in a full-scale gas turbine combustor. The numerically determined unsteady acoustic modes will be shown to compare well with theory and experiments. An investigation of the local heat release response to an unsteady flow field is conducted for incorporation into an approximate analysis method. The results of including a Helmholtz resonator in a dump combustor as a passive control mechanism will be presented. The production of NOx and CO will be compared between stable and unstable flow configurations. The pollutant results indicate that for the planar flame in a tube and the dump combustor, the NOx levels at the exit plane are reduced when the system is unstable.\n" }, { "name": "Voelkl, Tobias", "degree": "PhD", "year": "2000", "title": "A physical-space version of the stretched-vortex subgrid-stress model for large-eddy simulation of incompressible flow", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-07092007-154618", "creators": [ { "name": { "family": "Voelkl", "given": "Tobias" }, "id": "Voelkl-T", "display_name": "Voelkl, Tobias" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/d900-mk74", "abstract": "In large-eddy simulations of turbulence, the large scales of the flow are resolved by a numerical solution of the equations of motion for these scales, but the contribution of the fine-scale turbulence must be modeled. The stretched-vortex model estimates the influence of these unresolved subgrid-scale turbulence fluctuations on the resolved-scale velocities by using kinematic results for homogeneous, anisotropic turbulence consisting of locally straight, unidirectional vortex structures [D. I. Pullin and P. G. Saffman, Phys. Fluids 6 (5), 1994]. A new method is presented to dynamically determine the value of model constants related to the subgrid kinetic energy. For this purpose, a relation between the resolved-scale velocity structure function of second order and the energy spectrum is derived based on the kinematics of the model vortex structures, and therefore without the assumption of isotropy. Implementation of this relation using a local, circular average allows application of the model to wallbounded turbulent flows without special modifications. The resulting algebraic model is completely localized, i.e., no global flow quantities like the resolved-scale spectrum are required. This facilitates the application of the model in physical-space numerical methods using, for example, finite differences or Lagrangian-interpolation polynomials. The model includes an estimate of the subgrid kinetic energy, which is used to compute subgrid contributions to low-order turbulence statistics of the full flowfield. Results will be shown for the decay of kinetic energy and energy spectra of decaying, isotropic turbulence, for mean velocities, root-mean-square velocity fluctuations and turbulence-kinetic-energy budgets of channel flow up to a Reynolds number of approximately 23 000 (based on channel halfwidth and centerline velocity), and for mean velocities and turbulence kinetic energy of channel flow under spanwise rotation. The results are compared to unfiltered data from direct numerical simulations and experiment." }, { "name": "Wang, Xu", "degree": "PhD", "year": "2000", "title": "Optoelectric devices for optical memory systems", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052010-160806470", "creators": [ { "name": { "family": "Wang", "given": "Xu" }, "id": "Wang-Xu", "display_name": "Wang, Xu" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/kf9g-xq27", "abstract": "This thesis describes several optoelectronic devices developed for the optical memory system. It consists of three parts, which are liquid crystal beam steering devices,\r\nmodeling and measurement of optical diffraction from subwavelength structure at focused spot, and CMOS detector design.\r\n\r\nIn liquid crystal beam steering devices, two types of liquid crystal beam deflectors have been successfully demonstrated. The essential working idea of those two deflectors is the same, which is utilizing a blazed grating (either permanently fabricated or virtually built up) to deflect the incident beam and the liquid crystal is used as an electrically controllable birefringent medium. The reflective type deflector exploits the liquid crystal on silicon (LCOS) technology to build up a virtual blazed grating (dynamic grating) and vary this virtual grating's period to achieve multiple steering angels. Seven addressable angles with as high as 93% steering efficiency have been demonstrated. A numerical modeling tool is also developed to analyze liquid crystal molecule director's distribution under nonuniform electrical field (fringe-field-effect). The transmission type deflector is based on a custom-fabricated PMMA blazed grating (fixed grating) and dynamically address multiple angles by stacking several layers of PMMA/LC composite gratings. 16 steering angles are obtained with the contrast ratio of 18. A fabrication-compensation trick is proposed to greatly improve the\r\ndevice's performance.\r\n\r\nIn modeling and measurement of optical diffraction from subwavelength structure at focused spot, we describe a technique for studying scattering from subwavelength\r\nfeatures that used a focused ion beam system to generate subwavelength, submicron features and a simple scatterometer to measure the scattering from single subwavelength scatterers. A two-dimensional model that handles arbitrary profiles is described. The model is shown to agree quite well with the experimental measurements.\r\nThe model is then used to demonstrate ways in which the aspect ratios of subwavelength ridges and trenches can be obtained from scattering data and how ridges can be distinguished from trenches over a wide range of aspect ratios. We show that some earlier results on distinguishing pits from particles do not extend to low aspect ratio features.\r\n\r\nFinally, in CMOS detector, we have designed a CMOS detector to be used in the compact memory module. The chip features 64 x 64 array of 17\u00b5m x 17\u00b5m pixel with 23% filling factor within a 2mm x 2mm die, correlated double sampling (CDS) signalconditioning circuit in each column, as well as the software-controlled window-of-interest readout. Even more, two pixel designs (active photodiode and direct readout photo diode) are incorporated with the same chip for performance comparison.\r\n" }, { "name": "Wang, Xuan-Qi", "degree": "PhD", "year": "2000", "title": "Integrated parylene micro electro mechanical systems (MEMS)", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062005-112235", "creators": [ { "name": { "family": "Wang", "given": "Xuan-Qi" }, "id": "Wang-Xuan-Qi", "display_name": "Wang, Xuan-Qi" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/qe8x-ca65", "abstract": "One important goal of micro electro-mechanical systems (MEMS) development is to seamlessly interface microelectronics with the non-electronic world in an integrated manner. In the mean time, integrated micro fluidic devices and systems are expected to extract biomedical information in ways similar to how IC-chips process electrical current. Therefore, functional integration and fabrication process integration are the keys and challenges to MEMS development.\r\n\r\nThis work is first devoted to developing novel low-temperature MEMS fabrication technologies that use Parylene as a micro-structural material. A bromine trifluoride (BrF3) gas phase silicon etching method for micromachining is then developed. Combining with the Parylene processes, BrF3 etching method plays important roles in bulk silicon etching, the release of Parylene freestanding structures and silicon surface treatment.\r\n\r\nThe developed technology facilitates wafer scale post-CMOS integration and integrated micro fluidic systems. Using this technology, a Parylene-based electro-spray chip for protein mass spectrometry, a single chip micro check valve, an in-channel normally closed check valve, and a fully integrated shear stress sensor are successfully designed, fabricated, and tested.\r\n" }, { "name": "Wang, Yong", "degree": "PhD", "year": "2000", "title": "Effects of actuator limits in bifurcation control with applications to active control of fluid instabilities in turbomachinery", "advisor": "Murray, Richard M.; Paduano, James D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06282005-103901", "creators": [ { "name": { "family": "Wang", "given": "Yong" }, "id": "Wang-Yong", "display_name": "Wang, Yong" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Paduano", "given": "James D." }, "id": "Paduano-J-D", "role": "co-advisor", "display_name": "Paduano, James D." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." } ], "option_major": [ "cds" ], "doi": "10.7907/229f-f376", "abstract": "Feedback stabilization is one of the most dominant issues in modern control theory. The validity of linear control design is based on the assumption that the system is stabilizable. With rapid broadening of control applications to complex systems during the past two decades, the attainability of linear stabilizability sometimes has to compromise with system constraints and affordability of distributed actuation. The goal of this thesis is to tackle some of the problems in control of nonequilibrium behavior and to apply the theory to active control of fluid instabilities in gas turbine engines.\r\n\r\nWe consider two of the simplest nontrivial scenarios in local smooth feedback stabilization: the steady-state case, when the linearly unstabilizable eigenvalue is zero; and the Hopf case, when the unstabilizable eigenvalues are a pair of pure imaginary numbers. Under certain nondegeneracy conditions, we give explicit algebraic conditions for stabilizability. And when the system is stabilizable, the stabilizing feedback can be explicitly constructed.\r\n\r\nThe problem of local smooth feedback stabilization for systems with critical unstabilizable modes is closely related to bifurcation control. Under certain nondegeneracy conditions, a steady-state/Hopf bifurcation can be turned into a supercritical pitchfork/Hopf bifurcation if and only if the system is locally stabilizable at the bifurcation point. Algebraic necessary and sufficient conditions are derived under which the criticality of a simple steady-state or Hopf bifurcation can be changed to supercritical by a smooth feedback. The effects of magnitude saturation, bandwidth, and rate limits are important issues in control engineering. We give qualitative estimates of the region of attraction to the stabilized bifurcating equilibrium/periodic orbits under these constraints.\r\n\r\nWe apply the above theoretical results to the Moore-Greitzer model in active control of rotating stall and surge in gas turbine engines. Though linear stabilizability can be achieved using distributed actuation, it limits the practical usefulness due to considerations of affordability and reliability. On the other hand, simple but practically promising actuation schemes such as outlet bleed valves, a couple of air injectors, and magnetic bearings will make the system loss of linear stabilizability, thus the control design becomes a challenging task. The above mentioned results in bifurcation stabilization can be applied to these cases. We analyze the effects of magnitude and rate saturations in active stall and surge control using bleed valves and magnetic bearings using the Moore-Greitzer model. The analytical formulas for bleed valve actuation give good qualitative predictions when compared with experiments. Our conclusion is that these constraints are serious limiting factors in stall control and must be addressed in practical implementation to the aircraft engines." }, { "name": "Weber, Markus", "degree": "PhD", "year": "2000", "title": "Unsupervised learning of models for object recognition", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:10052010-115540388", "creators": [ { "name": { "family": "Weber", "given": "Markus" }, "id": "Weber-M", "display_name": "Weber, Markus" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "cns" ], "doi": "10.7907/ec32-c786", "abstract": "A method is presented to learn object class models from unlabeled and unsegmented cluttered scenes for the purpose of visual object recognition. The variability across a class of objects is modeled in a principled way, treating objects as flexible constellations of rigid parts (features). Variability is represented by a joint probability density function (pdf) on the shape of the constellation and the output of part detectors. Corresponding \"constellation models\" can be learned in a completely unsupervised fashion. In a first stage, the learning method automatically identifies distinctive parts in the training set by applying a clustering algorithm to patterns selected by an interest operator. It then learns the statistical shape model using expectation maximization. Mixtures of constellation models can be defined and applied to \"discover\" object categories in an unsupervised manner. The method achieves very good classification results on human faces, cars, leaves, handwritten letters, and cartoon characters." }, { "name": "Wen, Jiajun", "degree": "PhD", "year": "2000", "title": "What you can see outside the focus of attention", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-144224980", "creators": [ { "name": { "family": "Wen", "given": "Jiajun" }, "id": "Wen-J", "display_name": "Wen, Jiajun" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "cns" ], "doi": "10.7907/9z53-3157", "abstract": "Visual attention is widely considered to be first and foremost a means of controlling the flow of information between different levels of processing. Stimuli selected by attention are thought to gain access to higher levels of processing, including awareness, recognition, memory, and the generation of voluntary responses, while stimuli rejected by attention are deemed to be denied such access. However, visual attention remains poorly understood in\r\nmany aspects. In this study, we try to investigate some part of the problem.\r\n\r\nSeveral behavioral methods have been devised for the study of visual attention, one of them - the concurrent task paradigm - has gained more and more recognition and is widely used in different studies. In the first part of the thesis, we use this paradigm to investigate an important question: whether attentional capacity is differentiated or not. In non-human primates, neuronal sensitivities to stimulus dimensions such as form, color, or motion are concentrated in different visual cortical areas (Felleman and Van Essen, 1991; Van Essen and Gallant 1994), and functional imaging studies show similar functional specializations in the visual cortex of humans (Corbetta et al., 1990, 1995; Van Essen and Drury, 1997). It has been proposed that attentional capacity is \"differentiated\" (Sperling and Dosher, 1986; Pashler, 1997) in that discriminations concerning different dimensions draw at least in part on different attentional capacities and are thus less liable to interfere than discriminations concerning the same stimulus dimension. However, Duncan and colleagues have argued at length for a contrary point of view (Desimone and Duncan, 1995; Duncan et al., 1997). In their view, due\r\nto the strong interdependence of the subsystems that process different stimulus dimensions attentional capacity is \"undifferentiated\". By conducting experiments on the concurrent discrimination of form, color and motion attributes, we test which hypothesis is true. We quantify interference between concurrent discriminations by establishing the attention-operating characteristic. Interference is indistinguishable for similar and dissimilar task combinations (form-form, color-color, motion-motion, and color-form, color-motion, motion-color, motionform, respectively) for both demanding and less-demanding tasks. These results suggest\r\nstrongly that different visual discriminations draw on the same attentional capacity, in other words, that the capacity of visual attention is undifferentiated.\r\n\r\n\r\nAfter establishing that a task is equally attentional demanding no matter what the stimulus\r\ndimension the second task is based on, we use the concurrent task paradigm to investigate how attention affects spatial vision. We measure thresholds for discriminating the contrast, orientation, and spatial frequency of simple patterns that are either fully or poorly attended. We observe differences of about 20% in contrast detection thresholds, 40-50% in contrast discrimination thresholds (and appearance of the \u201cdipper\u201d), 60-70% in orientation and spatial frequency discrimination thresholds, and up to 50% in contrast masking thresholds. These observations tightly constrain any effect attention may have on the visual filters and/or the interactions amongst filters that are thought to underlie basic spatial vision. Comparison with a computational model due to Laurent Itti shows that the observed effects of attention\r\nare consistent with stronger interactions amongst filters, but not with a change in noise parameters, as is sometimes thought (Bonnel and Miller, 1994; Lu and Dosher, 1998. Essentially, the effects of attention on different thresholds are too disparate to be accommodated\r\nby a single change in noise parameters. In the framework of our model, the strength of the interaction amongst filters is controlled by the exponents of a power law, \u03b3\r\nand \u03b4. The larger exponents activate what is best described as a winner-take-all competition amongst visual filters. Attention accentuates existing differences between filter responses, boosting filters that respond relatively well to a given stimulus, while suppressing filters that respond\r\nrelatively poorly. This explains the perceptual advantage conferred by attention: attention enhances the sensory representation by restricting responses to the filters tuned best to the stimulus at hand. Our experimental and modeling results show that the activation of a winner-take-all competition amongst overlapping visual filters explains many basic perceptual consequences of attention.\r\n" }, { "name": "Witham, Charles Kincaid", "degree": "PhD", "year": "2000", "title": "The effects of alloy chemistry on the electrochemical and hydriding properties of NI-substituted LaNi5", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12272004-145717", "creators": [ { "name": { "family": "Witham", "given": "Charles Kincaid" }, "id": "Witham-C-K", "display_name": "Witham, Charles Kincaid" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/w3e0-5779", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe primary goal of this work was to verify the hypothesis that alloying LaNi5 with ternary elements that have a large heat of formation with La (and secondarily, with Ni) would slow the kinetics of metal (La) atom diffusion. This would have the effect of stabilizing the Haucke phase crystal structure of LaNi5 during electrochemical and gasphase hydrogen absorption/desorption cycling, and extending the material's useful lifetime.\r\n\r\nTo test this hypothesis, I prepared a variety of single-phase alloys of composition [...]. Each alloy was annealed to insure equilibrium starting conditions. The lifetimes of these alloys were tested by charge-discharge cycling as the anode of an alkaline Ni-MH rechargeable cell. By characterizing the lifetimes of the alloys as an exponential capacity decay, I was able to determine a trend between the capacity decay and the heat of formation of an average 'B' element with La.\r\n\r\nThe alloys were further characterized by obtaining gas-phase isotherms and, in the case of the [...] alloys, the thermodynamics of metal hydride formation and decomposition. X-ray diffraction was used to measure the effect of substitution on the alloy and its hydride phase. By examining the data obtained at Caltech as well as data published in the literature, several trends were noted. There is a fairly linear relationship between the solute's expansion of the LaNi5 unit cell and its radius. The total volume expansion an alloy experienced upon absorption of hydrogen was found to decrease with substituted composition. The discrete lattice expansion of [...] alloys was found to to decrease substantially for 0 < x < 0.2, but subsequent substitution had little effect on the volume expansion.\r\n\r\nThe electrode electrochemical kinetice of charge transfer were investigated for each MH alloy. Measurements of the charge transfer exchange current by micropolarization and AC impedance were similar, while those measured by Tafel polarization did not have a clear relationship." }, { "name": "Wong, Joyce Y.", "degree": "PhD", "year": "2000", "title": "Perpendicular patterned media for high density magnetic storage", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05032007-080831", "creators": [ { "name": { "family": "Wong", "given": "Joyce Y." }, "id": "Wong-J-Y", "display_name": "Wong, Joyce Y." } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Doll", "given": "Theodore" }, "id": "Doll-T", "role": "member", "display_name": "Doll, Theodore" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/WEP6-MN90", "abstract": "Current longitudinal thin-film media in magnetic hard-disk drives are facing an oncoming limit caused by the superparamagnetic effect, in which the individual grains in the medium become so small that they are no longer stable against thermal fluctuation. This situation is undesirable as the stored information may be lost within an unexpectedly short time frame. There have been several proposed solutions in addressing the superparamagnetic limit, and one of them is perpendicular patterned media. In this approach, a periodic array of magnetic pillars is defined lithographically on a non-magnetic substrate. Binary data of \"1\" or \"0\" can be stored in each of these elements, which have two possible magnetization directions perpendicular to the plane of the medium.\n\nIn our perpendicular patterned media design, Ni columns of 150-230nm diameter with a 6:1 aspect ratio are embedded in an (AlGa)2O3/GaAs substrate. The fabrication procedure uses a combination of high resolution electron beam lithography, dry etching, and electroplating. The high aspect ratio in the column is achieved by taking advantage of the high etching rate and selectivity of AlGaAs/GaAs over (AlGa)203 in the Cl2 chemically assisted ion beam etching process. In addition to being a robust etching mask, the (AlGa)2O3 layer also plays an important role in the chemical mechanical polishing procedure to remove the overplated Ni mushrooms.\n\nOnce the Ni columns are fabricated, magnetic characterization is performed using magnetic force microscopy and scanning magnetoresistance microscopy. The former measurement confirms that the electroplated Ni columns are magnetic while the latter determines whether the individual columns are stable enough to retain the recorded information. We have successfully demonstrated recording in our 170nm diameter Ni column array arranged in a square format using a commercial read/write head. This is the first demonstration of single magnetic column per bit data storage in a prototype perpendicular patterned medium. Furthermore, we have recorded in higher density Ni column arrays in the form of tracks, corresponding to 1.3 and 2.6Gbits/in.2. Even though we are limited by the spatial resolution of the magnetoresistive read sensor, we have continued to pursue higher density structures up to an areal density of 350Gbits/in.2. Consideration of the issues in high resolution patterning and the magnetic stability of the individual columns have prompted researchers in the magnetic recording industry to anticipate the ultimate storage limit of perpendicular patterned media to be around 1Tbits/in.2" }, { "name": "Wu, Shuyun", "degree": "PhD", "year": "2000", "title": "Integrated polysilicon thermistors for microfluidic sensing", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062010-112439245", "creators": [ { "name": { "family": "Wu", "given": "Shuyun" }, "id": "Wu-Shuyun", "display_name": "Wu, Shuyun" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/w1yy-ne91", "abstract": "This thesis documents results related to the design, fabrication, and testing of integrated polysilicon thermistors for microfluidic sensing in experimental investigations of micro impinging jet cooling and microchannel flow. Such experimental study has yielded fundamental understanding and practical design guidelines of these two microfluidic applications. Novel MEMS devices fabricated include temperature imagers, MEMS nozzles and nozzle arrays, and micro fluidic couplers. A technology for suspended microchannels with integrated polysilicon thermistors has been developed and used for microchannel flow study and flow-rate sensing. Theoretical models have been developed to analyze such micro thermal and fluidic phenomena.\r\n\r\nIn the micro impinging jet cooling study, a MEMS-based heat transfer measurement paradigm has been successfully developed for the first time. This includes technology for MEMS device fabrication, an experimental setup well suited for microscale thermal study, and accurate and efficient data processing techniques. Sensing and heating are integrated into a single thermal imager chip, which allows temperature measurement over a large area at very high spatial resolution. The heat transfer data demonstrate the excellent promise of micro-impinging-jet heat transfer, and provide useful rules for designing impinging-jet-based micro heat exchangers for IC packages.\r\n\r\nIn the investigation of micro channel flow, suspended microchannels with integrated thermistors have successfully been designed and fabricated to study the basic science of micro-scale channel flow. Considerable discrepancies between existing theory and experimental data have been observed, and an improved flow model that accounts for the effects of compressibility, boundary slip, fluid acceleration, non-parabolic fluid velocity profile and channel-wall bulging has been proposed to address such discrepancies.\r\n\r\nIn addition, micro fluidic couplers have been designed and fabricated as the fluidic interface connection between micro fluidic systems and the external macro environment. The experiments show that MEMS couplers are capable of handling pressures as high as 1200 psig.\r\n\r\nFinally, this thesis presents the development of liquid flow sensors. Resolution of 0.4 nL/min and a capability of bubble detecting have been demonstrated. A numerical model is developed to understand device operation and to guide the design process. Excellent agreement has been found between numerical and experimental results." }, { "name": "Yee, Jimmy", "degree": "PhD", "year": "2000", "title": "Experimental investigations in spheromaks : injection into a tokamak and formation in an unbounded environment", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302005-134459", "creators": [ { "name": { "family": "Yee", "given": "Jimmy" }, "id": "Yee-Jimmy", "display_name": "Yee, Jimmy" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Y45X-9C19", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nSpheromaks are investigated in two separate experiments. In the first, the CT Injector experiment, spheromaks are accelerated by a coaxial rail gun for injection into a medium-sized tokamak ([...] = 10 kG). Speeds of 3 x 10[...] m/s and densities in the high 10[...] m[...] range are achieved upon implementation of impurity reduction techniques and high bias flux. Tokamak injection experiments indicate anomalous stopping of the spheromak within the injector at toroidal filed (TF) levels well below previous theoretical predictions. Modifications of the electrode geometry were found to substantially improve performance.\r\n\r\nAn extension of the previously accepted theory is proposed which takes into account the effect of TF flux trapping within the electrodes. A 2-D magnetostatic analysis indicates that this phenomenon increases the spheromak kinetic energy density required for penetration by a factor dependent on spheromak size. A numerical analysis extends these results to finite length spheromaks. These calculations also show that the spheromak shape has an effect on penetration levels. The proposed theory indicates that a realistic assessment of spheromak injection requirements must take into account magnetic field interaction with the injector walls as well as the spheromak itself.\r\n\r\nThe second part of this thesis describes an experiment examining the formation and decay of spheromaks in unbounded environments; i.e., without the influence of flux-conserving walls. A coaxial gun is discharged into a much larger vacuum chamber and the subsequent evolution of the plasma is observed, mainly using high speed cameras and a magnetic probe array. Photographic results suggest four distinct regimes of operation, labeled I-IV, each possessing qualitatively different dynamics, with the parameter [...] determining the operative regime.\r\n\r\nPlasmas produced in Regime II are identified as detached spheromak configurations. Images depict a roughly donut-like shape, while magnetic data, when interpreted using a propagation inference method, suggest that a closed toroidal flux-surface topology is present. Poloidal flux amplification shows that Taylor relaxation mechanisms are at work. Calculations of the spatial and temporal variation of [...] indicated that the spheromak is decaying and expanding in a manner consistent with the self-similar expansion model proposed for magnetic clouds. This implies that magnetic heating may be operative.\r\n\r\nRegime III is associated with stuffed coaxial gun operation. Images show several complex helical and twisted features, which are shown to be magnetic in nature through field line tracing of the magnetic data. Toroidal and poloidal flux and [...] calculations clearly demonstrate the stuffed nature of this regime." }, { "name": "Zhu, Xiaoyun", "degree": "PhD", "year": "2000", "title": "Hard vs. soft bounds in probablilistic robustness analysis and generalized source coding and optimal web layout design", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-05042006-131410", "creators": [ { "name": { "family": "Zhu", "given": "Xiaoyun" }, "id": "Zhu-Xiaoy", "display_name": "Zhu, Xiaoyun" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "eleceng" ], "doi": "10.7907/1f3r-va82", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I:\r\n\r\nThe relationship between hard vs. soft bounds and probabilistic vs. worst-case problem formulations for robustness analysis has been a source of some apparent confusion in the control community, and this thesis attempts to clarify some of these issues. Essentially, worst-case analysis involves computing the maximum of a function which measures performance over some set of uncertainty. Probabilistic analysis assumes some distribution on the uncertainty and computes the resulting probability measure on performance. Exact computation in each case is intractable in general. In the past most research focused on computing hard bounds on worst-case performance. This thesis explores the use of both hard and soft bounds in probabilistic robustness analysis, and investigates the computational complexity of the problems through extensive numerical experimentation. We focus on the simplest possible problem formulations that we believe reveal the difficulties associated with more general probabilistic analysis.\r\n\r\nBy extending the standard structured singular value [...] framework to allow for probabilistic descriptions of uncertainty, probabilistic [...] is defined, which characterizes the probability distribution of some performance function. The computation of probabilistic [...] involves approximating the level surface of the function in the parameter space, which is even more complex than the worst-case [...] computation, a well-known NP-hard problem. In particular, providing sufficiently tight bounds in the tail of the distribution is extremely difficult. This thesis proposes three different methods for computing a hard upper bound on probabilistic [...] whose tightness can be tested by comparison with the soft bound provided by Monte-Carlo simulations. At the same time, the efficiency of the soft bounds can be significantly improved with the information from the hard bound computation. Among the three algorithms proposed, the LC-BNB algorithm is proven by numerical experiments to provide the best average performance on random examples. One particular example is shown in the end to demonstrate the effectiveness of the method.\r\n\r\nPart II: \r\n\r\nThe design of robust and reliable networks and network services has become an increasingly challenging task in today's Internet world. To achieve this goal, understanding the characteristics of Internet traffic plays a more and more critical role. Empirical studies of measured traffic traces have led to the wide recognition of self-similarity in network traffic. Moreover, a direct link has been established between the self-similar nature of measured aggregate network traffic and the underlying heavy-tailed distributions of the Web traffic at the source level.\r\n\r\nThis thesis provides a natural and plausible explanation for the origin of heavy tails in Web traffic by introducing a series of simplified models for optimal Web layout design with varying levels of realism and analytic tractability. The basic approach is to view the minimization of the average file download time as a generalization of standard source coding for data compression, but with the design of the Web layout rather than the codewords. The results, however, are quite different from standard source coding, as all assumptions produce power law distributions for a wide variety of user behavior models.\r\n\r\nIn addition, a simulation model of more complex Web site layouts is proposed, with more detailed hyperlinks and user behavior. The throughput of a Web site can be maximized by taking advantage of information on user access patterns and rearranging (splitting or merging) files on the Web site accordingly, with a constraint on available resources. A heuristic optimization on random graphs is formulated, with user navigation modeled as Markov Chains. Simulations on different classes of graphs as well as more realistic models with simple geometries in individual Web pages all produce power law tails in the resulting size distributions of the files transferred from the Web sites. This again verifies our conjecture that heavy-tailed distributions result naturally from the tradeoff between the design objective and limited resources, and suggests a methodology for aiding in the design of high-throughput Web sites." }, { "name": "Aivazis, Keri Ann", "degree": "PhD", "year": "1999", "title": "A Spherical Vortex Model for Homogeneous Turbulence", "advisor": "Saffman, Philip G.; Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152006-081730", "creators": [ { "name": { "family": "Aivazis", "given": "Keri Ann" }, "id": "Aivazis-Keri-Ann", "display_name": "Aivazis, Keri Ann" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/3acm-yj36", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nWe investigate a stochastic model for homogeneous, isotropic turbulence based on Hill's spherical vortex. This is an extension of the original work done by Synge and Lin in the early 1940's. The spherical vortex is an inviscid, steady, rotational solution to Euler's equation and its structure makes it a natural candidate for a model of a turbulent eddy. The model assumes that a field of locally isotropic turbulence is generated by a homogeneous distribution of Hill's vortices. The cascade process of eddy breakdown is incorporated into the statistical model through an average over vortex size. Dissipation field characteristics are assumed for the vortex size distribution. We are interested in the statistical properties of the model, in particular order-n structure functions defined by rank-n tensors for the ensemble average of a set of incremental differences in a given field property. We are primarily concerned with the second order pressure structure function, [...], and the velocity structure functions, orders 2-6, where [...] and [...] denotes the ensemble average.\r\n\r\nSpecifically [...], and the longitudinal component of [...] are calculated. Comparing [...] and [...] with experimental curves fixes the two independent model parameters while the sixth-order longitudinal velocity structure function is a predicted result. The pressure structure function is calculated both from first principles and directly from its integral relation with the fourth-order velocity structure function and compared with direct numerical simulation." }, { "name": "Alonzo, Alicia Cristina", "degree": "PhD", "year": "1999", "title": "Effects of geometry on the wet thermal oxidation of aluminum arsenide", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082008-165325", "creators": [ { "name": { "family": "Alonzo", "given": "Alicia Cristina" }, "id": "Alonzo-Alicia-Cristina", "display_name": "Alonzo, Alicia Cristina" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Q286-WB43", "abstract": "In recent years, the wet thermal oxidation of high aluminum-content III-V semiconductors has provided significant device improvements, most notably in vertical cavity surface emitting lasers (VCSELs). Although circles and squares are the most efficient geometries for VCSELs, most studies of the oxidation process to date have been conducted exclusively with stripes, rather than these two-dimensional mesa structures. The studies presented in this thesis examine the effect of geometry on the wet thermal oxidation process, focusing primarily on those mesa geometries with direct applicability to VCSELs. However, many of the results can be applied to more exotic mesa shapes as well.
\r\n\r\nA model is presented for the time-dependence of oxide formation in two-dimensional mesa structures. This work represents the first attempt to model the oxidation of square mesas. Although other researchers have recently proposed models for the oxidation of circular mesas, these models do not adequately account for the effect of geometry on the oxidation process. As compared to the one-dimensional oxidation of stripes, the oxidation of circular and square mesas exhibits an increased oxidation rate as the process proceeds. This is a direct effect of the geometry of the mesas. Extensive data is presented in support of our model, and a comparison is made to other models for the oxidation of circular mesas.
\r\n\r\nThe two-dimensional mesa geometry, coupled with anisotropies in the oxidation process itself, is shown to produce variations in the strain induced in the overlying GaAs layer by the oxidation process. Using micro-Raman spectroscopy, this strain has been spatially mapped and shown to correspond to color variations observed in the mesas with an optical microscope. A crystallographic-dependence for the oxidation is documented and used to explain the spatial variations in the strain as well as the shape of apertures formed in circular and square mesas by the wet thermal oxidation process.
\r\n\r\n" }, { "name": "Benedict, Noel Lakshman", "degree": "PhD", "year": "1999", "title": "Buoyant flows in vertical channels relating to smoke movement in high-rise building fires", "advisor": "Hunt, Melany L.; Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072008-074758", "creators": [ { "name": { "family": "Benedict", "given": "Noel Lakshman" }, "id": "Benedict-N-L", "display_name": "Benedict, Noel Lakshman" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "co-advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ynbt-qn25", "abstract": "This experimental study is motivated by the widespread loss of life and property due to accidental fires in high rise buildings, and investigates the progress of hot, toxic, products during such fires. The Stack Effect and Turbulent Mixing, two of the primary factors responsible for smoke movement within tall buildings are the focus of this study. The results of this investigation could be used for the development of fire modeling codes that simulate high-rise building fires.\n\nThe experiments involve a 2.6 m tall square shaft with various cross sections and openings. The shaft was situated above a large temperature controlled hot air reservoir, and the two chambers were initially separated by a partition. At the start of the experiment the partition was removed in a rapid horizontal motion and the hot and cold gases were allowed to mix. For the shafts with openings, the gases were withdrawn from the apertures at different rates with the Reynolds number varying between 600 and 7200. The temperature of the gas and wall, and the heat transfer to the wall were measured as functions of time at various locations in the shaft. Additionally, hot wire anemometry techniques were used to obtain velocity data in the channel. Some experiments involved monitoring a tracer gas in the vertical channel. Simple one-dimensional analytical modeling was performed to validate the experimental results.\n\nThe experiments indicated an initial transient period followed by a \"pseudo steady state.\" At each elevation measured the cross-section averaged gas temperature, reached and fluctuated about a steady state value soon after the initial front of hot gas arrived at that location. For the closed channel experiments, the front arrival time was a function of the initial density ratio, the shaft width, and the gravitational constant.\n\nThe tracer gas trials suggested that the molecular diffusion was insignificant in comparison to the turbulent mixing. For the closed channels the observed velocity fluctuations were the same order of magnitude as the mean velocities. The time averaged heat transfer coefficient was weakly dependent on the initial reservoir temperature.\n\nThe vented shaft experiments indicated that the front propagation times are significantly affected by openings in the shaft and that the effect is more pronounced the higher the vents are located. The venting caused a significant rise in the steady state temperatures, and a reduction in both the temperature and velocity fluctuations. The local Nusselt number was independent of the Reynolds number and a function only of the Rayleigh number, indicating that the heat transfer was dominated by free convection effects.\n\nThe predictions made by the one dimensional analytical model agreed reasonably well with the experiments, particularly in the case of the closed channel." }, { "name": "Bond, Christopher Llewellyn", "degree": "PhD", "year": "1999", "title": "Reynolds number effects on mixing in the turbulent shear layer", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242005-162912", "creators": [ { "name": { "family": "Bond", "given": "Christopher Llewellyn" }, "id": "Bond-C-L", "display_name": "Bond, Christopher Llewellyn" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3KKM-HB66", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperiments have been performed in turbulent shear layers to assess the effects of Reynolds number on mixing. The experiments extend the upper range of incompressible, chemically-reacting flow data from [...] to [...] and, in a subsequent collaboration with M. Slessor and others, to 7 x 10[...]. The experiments address an ambiguity in recent measurements of mixing in compressible shear layers, whose differences from measurements in incompressible shear layers could have been due either to compressibility or Reynolds number effects. The current results, collectively with previous results, show that the decrease of mixing with increasing Reynolds number first seen by Mungal et al. (1985) continues to the Reynolds numbers studied, but do not show a further decrease in mixing. The conclusions must be tempered by the presence of changes in the initial boundary layers and acoustic environment, and by the compressibility ([...] = 0.25) of the highest Reynolds number (Re = 7 x 10[...]) case.\r\n" }, { "name": "Bouguet, Jean-Yves", "degree": "PhD", "year": "1999", "title": "Visual methods for three-dimensional modeling", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072008-115723", "creators": [ { "name": { "family": "Bouguet", "given": "Jean-Yves" }, "id": "Bouguet-J", "display_name": "Bouguet, Jean-Yves" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." } ], "option_major": [ "eleceng" ], "doi": "10.7907/hc2c-sp47", "abstract": "Most animals use vision as a primary sensor to interact with their environment. Navigation or manipulation of objects are among the tasks that can be better achieved while understanding the three-dimensional structure of the scene.\n\nIn this thesis, we present a variety of computational techniques for estimating 3D shape from 2D images, based on both passive and active technologies.\n\nThe first proposed method is purely passive. In this technique, a single camera is moved in an unconstrained manner around the scene to model as it acquires a sequence of images. The reconstruction process consists then of retrieving the trajectory of the camera, as well as the 3D structure of the scene using only the information contained in the images.\n\nThe second method is based on active lighting technology. In the philosophy of standard 3D scanning methods, a projector is used to project light patterns in the scene. The shape of the scene is then inferred from the way the patterns deform on the objects. The main novelty of our scheme compared to traditional methods is in the nature of the patterns, and the type of image processing associated to them. Instead of using standard binary patterns made out of black and white stripes, our scheme uses a sequence of grayscale patterns with a sinusoidal profile in brightness intensity. This choice allows us to establish correspondence (between camera image, and projector image) in a dense fashion, leading to depth computation at (almost) \nevery pixel in the image.\n\nThe last reconstruction method that we propose in this thesis is an alternative 3D scanning scheme that does not require any other device besides a camera. The main idea is to substitute the projector by a standard light source (such as a desk lamp), and use a pencil (or any other object with a straight edge) to cast planar shadows in the scene. The 3D geometry of the scene is then inferred from the way the shadow naturally deforms on the objects in the scene. Since this technology is largely inspired from structured lighting techniques, we call it 'weakly structured lighting.'\n" }, { "name": "Bridger, Paul Martin", "degree": "PhD", "year": "1999", "title": "Development of Apertureless Microscopy and Force Microscopy of GaN and CeO\u2082", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10122007-132811", "creators": [ { "name": { "family": "Bridger", "given": "Paul Martin" }, "id": "Bridger-Paul-Martin", "display_name": "Bridger, Paul Martin" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Baldeschwieler", "given": "John D." }, "id": "Baldeschwieler-J-D", "role": "member", "display_name": "Baldeschwieler, John D." }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "orcid": "0000-0002-1613-0809", "role": "member", "display_name": "Quake, Stephen R." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8ybw-sh03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis concentrates on the development of both novel scanning probes as well as \r\nnovel applications of existing ones in three major areas. The first area is our development of apertureless microscopy and progress toward our goal of 1nm optical imaging \r\nand spectroscopy. Fundamental experiments and simulations of the apertureless imaging mechanism were conducted using nanosphere size standards. Fifteen nanometer \r\nresolution as well as optical property discrimination was demonstrated. The apertureless microscope was then used to investigate the near field optical structure of \r\nchromosomes and anti-reflective polymer thin films. The second area is the investigation of the electronic properties of the wide bandgap semiconductor GaN by atomic \r\nforce microscopy. Defects in GaN were correlated to diffusion lengths as measured by \r\nelectron beam induced current. Electric force microscopy (EFM), a varient of atomic \r\nforce microscopy, was subsequently used to investigate sub [...] electric field gradient \r\nand surface potential variation associated with these defects. A novel application of \r\nEFM to measure the surface state density was also demonstrated. The third area \r\nis another novel application of EFM for localized charge storage in double barrier \r\nCe02/Si/Ce02/Si structures which may have relevance for data storage and charge \r\ndirected lithography." }, { "name": "Bullo, Francesco", "degree": "PhD", "year": "1999", "title": "Nonlinear control of mechanical systems : a Riemannian geometry approach", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072008-100242", "creators": [ { "name": { "family": "Bullo", "given": "Francesco" }, "id": "Bullo-F", "display_name": "Bullo, Francesco" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cds" ], "doi": "10.7907/xrak-3409", "abstract": "Nonlinear control of mechanical systems is a challenging discipline that lies at the intersection between control theory and geometric mechanics. This thesis sheds new light on this interplay while investigating motion control problems for Lagrangian systems. Both stability and motion planning aspects are treated within a unified framework that accounts for a large class of devices such as robotic manipulators, autonomous vehicles and locomotion systems.\n\nOne distinguishing feature of mechanical systems is the number of control forces. For systems with as many input forces as degrees of freedom, many control problems are tractable. One contribution of this thesis is a set of trajectory tracking controllers designed via the notions of configuration and velocity error. The proposed approach includes as special cases a variety of results on joint and workspace control of manipulators as well as on attitude and position control of vehicles.\n\nWhenever fewer input forces are available than degrees of freedom, various control questions arise. The main contribution of this thesis is the design of motion algorithms for vehicles, i.e., rigid bodies moving in Euclidean space. First, an algebraic controllability analysis characterizes the set of reachable configurations and velocities for a system starting at rest. Then, provided a certain controllability condition is satisfied, various motion algorithms are proposed to perform tasks such as short range reconfiguration and hovering.\n\nFinally, stabilization techniques for underactuated systems are investigated. The emphasis is on relative equilibria, i.e., steady motions for systems that have a conserved momentum. Local exponential stabilization is achieved via an appropriate splitting of the control authority." }, { "name": "Carlson, Anders Elof", "degree": "PhD", "year": "1999", "title": "Three-Dimensional Nonlinear Inelastic Analysis of Steel Moment-Frame Buildings Damaged by Earthquake Excitations", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192014-110246738", "creators": [ { "name": { "family": "Carlson", "given": "Anders Elof" }, "id": "Carlson-Anders-Elof", "display_name": "Carlson, Anders Elof" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/7s2s-9r50", "abstract": "The Northridge earthquake of January 17, 1994, highlighted the two previously known problems of premature fracturing of connections and the damaging capabilities of near-source ground motion pulses. Large ground motions had not been experienced in a city with tall steel moment-frame buildings before. Some steel buildings exhibited fracture of welded connections or other types of structural degradation.
\r\n\r\nA sophisticated three-dimensional nonlinear inelastic program is developed that can accurately model many nonlinear properties commonly ignored or approximated in other programs. The program can assess and predict severely inelastic response of steel buildings due to strong ground motions, including collapse.
\r\n\r\nThree-dimensional fiber and segment discretization of elements is presented in this work. This element and its two-dimensional counterpart are capable of modeling various geometric and material nonlinearities such as moment amplification, spread of plasticity and connection fracture. In addition to introducing a three-dimensional element discretization, this work presents three-dimensional constraints that limit the number of equations required to solve various three-dimensional problems consisting of intersecting planar frames.
\r\n\r\nTwo buildings damaged in the Northridge earthquake are investigated to verify the ability of the program to match the level of response and the extent and location of damage measured. The program is used to predict response of larger near-source ground motions using the properties determined from the matched response.
\r\n\r\nA third building is studied to assess three-dimensional effects on a realistic irregular building in the inelastic range of response considering earthquake directivity. Damage levels are observed to be significantly affected by directivity and torsional response.
\r\n\r\nSeveral strong recorded ground motions clearly exceed code-based levels. Properly designed buildings can have drifts exceeding code specified levels due to these ground motions. The strongest ground motions caused collapse if fracture was included in the model. Near-source ground displacement pulses can cause columns to yield prior to weaker-designed beams. Damage in tall buildings correlates better with peak-to-peak displacements than with peak-to-peak accelerations.
\r\n\r\nDynamic response of tall buildings shows that higher mode response can cause more damage than first mode response. Leaking of energy between modes in conjunction with damage can cause torsional behavior that is not anticipated.
\r\n\r\nVarious response parameters are used for all three buildings to determine what correlations can be made for inelastic building response. Damage levels can be dramatically different based on the inelastic model used. Damage does not correlate well with several common response parameters.
\r\n\r\nRealistic modeling of material properties and structural behavior is of great value for understanding the performance of tall buildings due to earthquake excitations.
\r\n" }, { "name": "Cheng, Xiao-chang", "degree": "PhD", "year": "1999", "title": "Investigation of New Devices and Characterization Techniques in the III-V Semiconductor System", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122007-134645", "creators": [ { "name": { "family": "Cheng", "given": "Xiao-chang" }, "id": "Cheng-Xiao-chang", "display_name": "Cheng, Xiao-chang" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Baldeschwieler", "given": "John D." }, "id": "Baldeschwieler-J-D", "role": "member", "display_name": "Baldeschwieler, John D." }, { "name": { "family": "Hunter", "given": "A." }, "id": "Hunter-A", "role": "member", "display_name": "Hunter, A." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4pmy-xb16", "abstract": "This thesis concerns the investigation of novel devices and material characterization techniques in the III-V semiconductor system. In the first part of the thesis, we demonstrate that novel devices, such as avalanche photodiodes and tunnel switch diodes, can be fabricated from InAs/GaSb/A1Sb heterostructures by molecular beam epitaxy (MBE). In the second part of the thesis, ballistic electron emission microscopy (BEEM) is employed to examine the local band offset in these heterostructures, which is often found to be crucial in device design.\r\n\r\nIn the avalanche photodiode study, devices with near infrared response out to 1.74 [mu]m were demonstrated. Two types of devices were investigated: those with a bulk Al0.04Ga0.96Sb multiplication region and those with a GaSb/A1Sb superlattice multiplication region. Both types of devices were implemented in a MBE grown p[superscript -]n[superscript +] structure that uses a selectively doped InAs/AlSb superlattice as the n-type layer. This particular structure was optimized through several design, fabrication, characterization cycles. It was found that the photodiode dark current depended critically on the InAs/A1Sb superlattice period and the resulting band offset at the p[superscript -]n[superscript +] heterojunction. The InAs/AlSb superlattice was henceforth optimized by using a three stage design. The ionization rates in bulk multiplication layer devices were measured and found to be consistent with hole impact ionization enhancement in Al0.04Ga0.96Sb. However, direct comparison with superlattice multiplication layer devices revealed the latter to be more promising due to more effective dark current suppression from the larger band gap of the superlattice multiplication layer.\r\n \r\nThe second device studied is the tunnel switch diode. We have fabricated the first such device in the antimonide material system and obtained characteristic \"S\" shaped I-V curves from these devices. The epilayer and barrier dependence of tunnel diode switching were studied and found to deviate significantly from the punch-through model of operation. In addition, the device I-V curve was observed to \"hop\" between two branches when subjected to high levels of stress. We speculate that this was due to instability associated with mobile charges in the A1Sb tunnel barrier. A computer model was used to simulate the device behavior and generated results consistent with the observed dependence of switching on tunnel barrier thickness.\r\n\r\nIn the second part of the thesis, III-V heterostructures were characterized by using ballistic electron emission microscopy (BEEM). BEEM images were shown to reveal sub surface features in AlxGal-xAs. epilayers, whereas BEEM spectroscopy was used to map out the shift in [capital gamma], X, and L band edges with material composition in AlxGal-xAs. BEEM spectroscopy was also applied to device relevant antimonide heterostructures such as A1Sb barriers and InAs/AlSb superlattices. It was found that electron transport in A1Sb was dictated by the conduction band minium near the X point, and there is large local variation in the AlSb Schottky barrier height. These results were in good correlation with the observed barrier characteristics of A1Sb. Due to the small bandgap of InAs/A1Sb superlattice and the associated high level of noise current, only the shortest period superlattice was examined by BEEM. The resulting band offset agreed with the calculated value and demonstrated that BEEM spectroscopy can be applied to structures with a large number of hetero-interfaces." }, { "name": "Choi-Yim, Haein", "degree": "PhD", "year": "1999", "title": "Synthesis and characterization of bulk metallic glass matrix composities", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072008-141021", "creators": [ { "name": { "family": "Choi-Yim", "given": "Haein" }, "id": "Choi-Yim-H", "display_name": "Choi-Yim, Haein" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/NZS0-9N89", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nComposites with a bulk metallic glass matrix are synthesized and characterized. This was made possible by the recent development of bulk metallic glasses that exhibit high resistance to crystallization in the undercooled liquid state. In this thesis, experimental methods for processing metallic glass composites are introduced. Three different bulk metallic glass (BMG) forming alloys were used as the matrix materials. Ceramics such as SiC, WC, or TiC, and metals W or Ta were introduced as reinforcement into the metallic glass.\r\n\r\nStructure, microstructure and thermal stability of the composites are studied by X-ray diffraction, optical microscopy and differential scanning calorimetry. The metallic glass matrix remained amorphous after adding up to 30 percent volume fraction of particles or short wires. X-ray diffraction patterns of the composites show only peaks from the second phase particles superimposed on the broad diffuse maxima from the amorphous phase. Optical micrographs reveal uniformly distributed particles in the matrix. The thermal stability of the matrix did not deteriorate after adding the particles. In the case of SiC, the matrix becomes even more robust with respect to crystallization.\r\n\r\nThe reactions at the interfaces between the matrix and the different reinforcing materials are investigated with scanning electron microscopy, transmission electron microscopy, and electron microprobe. At the interfaces between the matrix and the WC or SiC particles, ZrC layers foiled. W and Si diffused into the matrix, repectively. At the interface between W and the matrix, a thin layer of nanocrystals is observed after cooling the liquid/particulate mixture.\r\n\r\nThe mechanical properties of the composites are studied in compression and tension. Compressive strain to failure increased by over 300% compared to the unreinforced [...] and the energy to fracture of the tensile samples increased by over 50% adding 15 vol. % W.\r\n\r\nThe effect of silicon on the glass forming ability of [...] bulk metallic glass during composite processing is studied. Composites of the [...] bulk metallic glass, reinforced with up to 30 vol. % SiC particles are synthesized. During processing of the composites, a TiC layer forms around the SiC particles and Si diffuses into the [...] matrix stabilizing the supercooled liquid against crystallization. The small Si addition between 0.5 and 1 at. % increases the attainable maximum thickness of glassy ingots from 4mm for Cu-Ti-Zr-Ni alloy to 7mm for Cu-Ti-Zr-Ni-Si alloys. DSC analyses show that neither the thermodynamics nor the kinetics of the alloy is significantly affected by the Si addition. This suggests that Si enhances the glass forming ability by chemically passivating impurities such as oxygen and carbon that cause heterogeneous nucleation in the melt." }, { "name": "Chuang, Patrick Yung-Shie", "degree": "PhD", "year": "1999", "title": "Experimental and theoretical studies of cloud condensation nuclei", "advisor": "Seinfeld, John H.; Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082008-164553", "creators": [ { "name": { "family": "Chuang", "given": "Patrick Yung-Shie" }, "id": "Chuang-Patrick-Yung-Shie", "display_name": "Chuang, Patrick Yung-Shie" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Charlson", "given": "Robert" }, "id": "Charlson-R", "role": "member", "display_name": "Charlson, Robert" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/RY6B-CY09", "abstract": "Cloud condensation nuclei (CCN), the subset of atmospheric aerosol that nucleate cloud droplet formation, are a key component in cloud formation, and are an important factor in controlling climatically-relevant cloud properties such as cloud albedo, cloud lifetime, and precipitation rate.
\r\n\r\nA CCN instrument that satisfies the constraints for small aircraft operation \u2014 minimum weight, volume, and power consumption, good robustness, and high frequency measurement \u2014 was constructed. The measurement technique was based on that of Hudson (1989) because it reportedly offered the ability to make measurements of CCN at all supersaturations simultaneously at high frequency and with good counting statistics. Modelling studies, and laboratory and field measurements, subsequently showed that this technique exhibits poor sensitivity. The CCN instrument was also studied in fixed supersaturation mode, where it is able to accurately measure CCN concentration at a fixed supersaturation, whose value ranges from 0.1 and 2%.
\r\n\r\nThe CCN instrument was flown during the 2nd Aerosol Characterization Experiment (ACE-2). The data were reported at a fixed supersaturation of 0.1%. Intercomparison of these measurements with those on two other aircraft shows good agreement. A sublinear relationship between measured CCN concentration and that predicted from aerosol size distribution and chemical composition measurements, Nmeas ~ N0.72pred. In-situ measurements of below-cloud CCN concentration and cloud droplet number concentration are compared. The results are in agreement with model predictions and with previous studies. Cloud droplet concentration is predicted to depend on the CCN spectrum and updraft velocity.
\r\n\r\nCloud droplet activation has often been assumed to be reasonably described by an equilibrium model. The error in calculated cloud droplet number concentration due to the influence of condensational growth kinetics was shown to be significant for some conditions. Such errors are estimated to lead to overestimates of indirect radiative climate forcing on the order of Wm-2. Accurate interpretation of measured CCN concentration may require consideration of activation kinetics associated with CCN instruments.
\r\n" }, { "name": "Davis, Jean-Paul", "degree": "PhD", "year": "1999", "title": "High-enthalpy shock/boundary-layer interaction on a double wedge", "advisor": "Sturtevant, Bradford; Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272008-125333", "creators": [ { "name": { "family": "Davis", "given": "Jean-Paul" }, "id": "Davis-J", "display_name": "Davis, Jean-Paul" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4C98-MN23", "abstract": "Interaction between a shock wave and a boundary layer at a compression corner can produce a region of separated flow. The length of separation is important in determining aerodynamic forces, and the heat transfer at reattachment is important for the design of thermal protection systems. The effects of high-enthalpy flow on these phenomenon, particularly separation length, are not well known. Experiments to measure separation length and reattachment heating are performed in the T5 Hypervelocity Shock Tunnel using nitrogen test gas and a double-wedge geometry which allows greater control over local flow conditions at separation and, at high incidence angle, may produce real-gas effects due to dissociation behind the leading shock. Local external flow conditions were found by computational reconstruction of the inviscid nonequilibrium flow field.\n\nApplication of results from asymptotic theory to a simple model for separation leads to a new scaling parameter which approximately accounts for wall temperature effects on separation length for a laminar nonreacting boundary layer and extends previous results to arbitrary viscosity law. A. classification is introduced which divides mechanisms for real-gas effects into those acting internal and external to viscous regions of the flow, with internal mechanisms further subdivided into those arising upstream and downstream of separation. Application of the ideal dissociating gas model to a scaling law based on local external flow parameters and a nonreacting boundary layer shows that external mechanisms due to dissociation decrease separation length at low incidence but depend on the free-stream dissociation at high incidence, and have only a small effect on peak heating. A limited numerical study of reacting boundary layers shows that internal mechanisms due to recombination in the upstream boundary layer cause a slight decrease in separation length and a large increase in heat flux relative to a nonreacting boundary layer with the same external conditions.\n\nCorrelations are presented of experimentally measured separation length using local external flow parameters computed for reacting flow, which scales out external mechanisms but not internal mechanisms. These show the importance of the new scaling parameter in high-enthalpy flows, a linear relationship between separation length and reattachment pressure ratio as found previously for supersonic interactions, and a Reynolds-number effect for transitional interactions. A significant increase in scaled separation length is observed for high-enthalpy data in the laminar regime, and this is attributed to an internal recombination mechanism occurring in the separated shear layer. Experimental data for reattachment heat flux are found to agree roughly with existing correlations and to exhibit an increase due to an internal recombination mechanism, but cannot provide further insight due to large scatter." }, { "name": "Dickson, Jeffrey Allen", "degree": "PhD", "year": "1999", "title": "Integration of analog VLSI and thin films for chemical sensing arrays", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062008-131420", "creators": [ { "name": { "family": "Dickson", "given": "Jeffrey Allen" }, "id": "Dickson-J-A", "display_name": "Dickson, Jeffrey Allen" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9rg8-4a38", "abstract": "Chemical sensors are typically discrete elements, each sensitive to a particular odor. Current chemical sensing systems are unable to detect a wide range of chemicals. Moreover, the lack of an integrated sensor technology prevents the fabrication large arrays of chemical sensors.\n\nA sensing technology is presented that integrates chemical sensors based on conducting carbon black particles and polymers with standard integrated circuit technology. An integrated circuit for array sensing is presented. The necessary post processing steps, consisting of and electroless gold deposition and subsequent polymer deposition, are discussed. The system is demonstrated to function as an array of individually addressable chemical sensors.\n\nIn addition, a novel nonvolatile analog storage element based on floating gates is presented. The application of this circuit and floating gate adaptation to ratiometric sensing is demonstrated.\n" }, { "name": "Efendiev, Yalchin R.", "degree": "PhD", "year": "1999", "title": "The Multiscale Finite Element Method (MsFEM) and Its Applications", "advisor": "Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-090314", "creators": [ { "name": { "family": "Efendiev", "given": "Yalchin R." }, "id": "Efendiev-Yalchin-R", "orcid": "0000-0001-9626-303X", "display_name": "Efendiev, Yalchin R." } ], "advisors": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "chair", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "role": "member", "display_name": "Bruno, Oscar P." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/2QJN-2S06", "abstract": "Multiscale problems occur in many scientific and engineering disciplines, in petroleum engineering, material science, etc. These problems are characterized by the great deal of spatial and time scales which make it difficult to analyze theoretically or solve numerically. On the other hand, the large scale features of the solutions are often of main interest. Thus, it is desirable to have a numerical method that can capture the effect of small scales on large scales without resolving the small scale details.
\r\n\r\nIn the first part of this work we analyze the multiscale finite element method (MsFEM) introduced in [28] for elliptic problems with oscillatory coefficients. The idea behind MsFEM is to capture the small scale information through the base functions constructed in elements that are larger than the small scale of the problem. This is achieved by solving for the finite element base functions from the leading order of homogeneous elliptic equation. We analyze MsFEM for different situations both analytically and numerically. We also investigate the origin of the resonance errors associated with the method and discuss the ways to improve them.
\r\n\r\nIn the second part we discuss flow based upscaling of absolute permeability which is an important step in the practical simulations of flow through heterogeneous formations. The central idea is to compute the upscaled, grid-block permeability from fine scale solutions of the flow equation. It is well known that the grid block permeability may be strongly influenced by the boundary conditions imposed on the flow equations and the size of grid blocks. We analyze the effects of the boundary conditions and grid block sizes on the computed grid block absolute permeabilities. Moreover, we employ the ideas developed in the analysis of MsFEM to improve the computed values of absolute permeability.
\r\n\r\nThe last part of the work is the application of MsFEM as well as upscaling of absolute permeability on upscaling of two-phase flow. In this part we consider coarse models using MsFEM. We demonstrate the efficiency of these models for practical problems. Moreover, we show that these models improve the existing approaches.
" }, { "name": "Gallagher, Donal A.", "degree": "PhD", "year": "1999", "title": "Saffman-Taylor fingers in deformed Hele-Shaw cells", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062008-103933", "creators": [ { "name": { "family": "Gallagher", "given": "Donal A." }, "id": "Gallagher-D-A", "display_name": "Gallagher, Donal A." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/32e1-fp41", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nViscous fingering occurs when an essentially inviscid fluid is used to displace a viscous fluid in a porous medium or a Hele-Shaw cell. Long finger-shaped protrusions of the non-viscous fluid are found to advance into the viscous fluid. The importance of viscous fingering was first realised when attempts were made to retrieve oil from underground reservoirs by water injection.\n\nWhen one displaces oil in a Hele-Shaw cell of width a with air, an initially plane interface between the two fluids becomes unstable. This interface eventually develops into a finger shaped protrusion of width [...] moving at constant speed. Experimentally, in the presence of small surface tension at the air-oil interface the constant [...] is found to be near 1/2. An exact solution of the model equations was found by Saffman and Taylor in the absence of surface tension.\n\nUntil now the fingering problem has only been studied in Hele-Shaw of constant gap corresponding to a porous medium with constant permeability. In order to understand the effect of non-homogenous permeability we look at the problem of fingering in a Hele-Shaw cell of varying gap. We consider variations in the direction perpendicular to the motion of the finger allowing steady fingers to exist.\n\nWe extend previous work on the constant gap case to show how the presence of surface tension interacts with variations in the gap to change the solution structure in a non-trivial way. For example values of [...] less than a half are possible. It is even found that solutions cease to exist for small surface tension in some cases. We solve the problem using both numerical methods based on conformal mapping and analytical methods involving asymptotics beyond all orders." }, { "name": "Gleeson, James P.", "degree": "PhD", "year": "1999", "title": "Random advection of a passive scalar", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062008-095449", "creators": [ { "name": { "family": "Gleeson", "given": "James P." }, "id": "Gleeson-J-P", "display_name": "Gleeson, James P." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/1k1x-z678", "abstract": "A novel functional method is applied to calculate the statistics of a passive scalar in a turbulent velocity field. The method yields asymptotic series expansions for small velocity correlation time, from which approximate closure equations are derived. Analytical and numerical solutions of the equations accurately predict effective diffusivities and give new results for the scalar spectrum. Formulas expressing the Lagrangian correlation of the velocity in the terms of the Eulerian correlation are given.\r\n" }, { "name": "Horn, Gavin B.", "degree": "PhD", "year": "1999", "title": "Iterative decoding and pseudo-codewords", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062008-130016", "creators": [ { "name": { "family": "Horn", "given": "Gavin B." }, "id": "Horn-G-B", "display_name": "Horn, Gavin B." } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/RS6G-C640", "abstract": "In the last six years, we have witnessed an explosion of interest in the coding theory community, in iterative decoding and graphical models, due primarily to the invention of turbo codes. While the structural properties of turbo codes and low density parity check codes have now been put on a firm theoretical footing, what is still lacking is a satisfactory theoretical explanation as to why iterative decoding algorithms perform as well as they do. In this thesis we make a first step by discussing the behavior of various iterative decoders for the graphs of tail-biting codes and cycle codes. By increasing our understanding of the behavior of the iterative min-sum (MSA) and sum-product (SPA) algorithms on graphs with cycles, we can design codes which achieve better performance.\n\nMuch of this thesis is devoted to the analysis of the performance of the MSA and SPA on the graphs for tail-biting codes and cycle codes. We give sufficient conditions for the MSA to converge to the maximum likelihood codeword after a finite number of iterations. We also use the familiar union bound argument to characterize the performance of the MSA after many iterations. For a cycle code, we show that the performance of the MSA decoder is asymptotically as good as maximum likelihood. For tail-biting codes this will depend on our choice of trellis.\n" }, { "name": "Huang, Yun", "degree": "PhD", "year": "1999", "title": "Nonlinear optimal control: an enhanced quasi-LPV approach", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212007-082553", "creators": [ { "name": { "family": "Huang", "given": "Yun" }, "id": "Huang-Yun", "display_name": "Huang, Yun" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/5VNR-GF60", "abstract": "Realistic models of physical systems are often nonlinear. Our objective is to synthesize controllers for nonlinear systems that not only provide stability, but also deliver good closed-loop performance.\r\n\r\nThe frozen Riccati equation approach is thoroughly examined. Although it suffers fundamental deficiencies due to its pointwise nature, it is proven that optimality is always possible under a certain assumption on the optimal value of the performance index. This is a consequence of the non-uniqueness of the pointwise linear model of the nonlinear dynamics. However, one cannot assess a priori the guaranteed global performance for a particular model choice.\r\n\r\nAn alternative to the pointwise design is to treat nonlinear plants as linear parameter varying systems with the underlying parameters being functions of the state variables. By exploiting the variation rate bounds of the parameters, a controller that smoothly schedules on the parameters can be synthesized by solving a convex optimization problem. Depending upon the choice of the variation rate bounds, the resulting controller can range from replicating the pointwise design result, which comes with no guarantee on performance, to providing quadratic stability, in which case it can withstand arbitrarily fast parameter variation.\r\n\r\nUnder the above quasi-LPV framework, we present a new scheme that incorporates the freedom of choosing the state-dependent linear representation into the control design process. It is shown that the L2-gain analysis can be reformulated as an infinite dimensional convex optimization problem, and an approximate solution can be obtained by solving a collection of linear matrix inequalities. The synthesis problem is cast as a minimization over an infinite dimensional bilinear matrix inequality constraint. An iterative algorithm, similar to the \"D - K iteration\" for \u00b5 synthesis, is proposed to compute the best achievable performance. It is demonstrated through several examples that this approach can effectively reduce conservatism of the overall design." }, { "name": "Johansen, Anne Marie Jorunn", "degree": "PhD", "year": "1999", "title": "Aerosol chemistry over remote oceanic regions", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272008-111006", "creators": [ { "name": { "family": "Johansen", "given": "Anne Marie Jorunn" }, "id": "Johansen-A-J", "display_name": "Johansen, Anne Marie Jorunn" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "member", "display_name": "Hering, Janet G." } ], "option_major": [ "envreng" ], "doi": "10.7907/P5HP-F516", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAtmospheric sampling of aerosol was carried out from ships during four separate month-long research cruises over remote oceanic regions. Three cruises took place in the Arabian Sea, during the inter-, SW- and NE-monsoons. An additional cruise was focused on the tropical North Atlantic Ocean. Identical sampling techniques were employed for all cruises. One high volume dichotomous virtual impactor and two low volume collectors were used to collect aerosol particles for the quantification of trace metals, anions and major cations. Ferrous iron concentrations were determined immediately after sample collection on board the ship using a ferrozine extraction technique. Data were analyzed by principal component, enrichment factor and weighted multiple linear regression analyses.\r\n\r\nThe mineralogical composition of aerosol collected over the Arabian Sea reflected that of an average of the earth's crust, while over the Atlantic Ocean, shale appeared to best represent the sampled mineral dust. With exception of the SW-monsoon samples, which were characterized by weak continental influences, the aerosol samples contained excess water-soluble non-sea-salt calcium that appeared to be of crustal origin, in the form of CaCO[...] or CaSO[...].\r\n\r\nFerrous iron concentrations accounted for 0.3, 1.3, and 0.5% of the total observed Fe during the inter- and NE-monsoons over the Arabian Sea, and over the Atlantic Ocean, respectively. Absolute Fe(II) concentrations were determined at 5.2, 9.8, and 3.1 [...]g [...] for the corresponding seasons, with most of the Fe(II) (> 80%) present in the fine fraction. Fe(II) did not exhibit a simple relationship with any of the sources indicating the complexity of iron redox reactions is this system.\r\n\r\nNon-sea-salt sulfate (NSS-SO[...]) sources were identified and quantified with the use of multiple linear regression analyses. Biogenically-derived [...] contributed significant amounts of NSS-SO42-, especially during the SW-monsoon, when anthropogenic sources were small. Biogenic SO[...]/methansulfonic acid (MSA) weight ratios were determined and found to be in agreement with reported literature values from pristine oceanic regions, varying from 6.8 at 24\u00b0C to 17.7 at 28.9\u00b0C." }, { "name": "Kaneshige, Michael Jiro", "degree": "PhD", "year": "1999", "title": "Gaseous Detonation Initiation and Stabilization by Hypervelocity Projectiles", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-144510", "creators": [ { "name": { "family": "Kaneshige", "given": "Michael Jiro" }, "id": "Kaneshige-Michael-Jiro", "display_name": "Kaneshige, Michael Jiro" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/GBE9-FG37", "abstract": "An experimental investigation of gaseous detonations initiated and stabilized by high-speed spherical projectiles has been carried out. Detonation initiation by projectiles is closely related to propulsion concepts such as the ram accelerator and the oblique detonation wave engine, in which, theoretically, rapid combustion occurs in detonation waves stabilized on solid objects. The criteria for initiation and stabilization by projectiles are also related to other initiation and propagation criteria such as blast initiation and failure of diffracting detonations. Experimental data of this type are useful for identifying relevant assumptions and important processes, and for providing validation for computational and analytical models.
\r\n\r\nExperiments were performed in the Caltech T5 shock tunnel laboratory. T5 was used in a shock-compression light gas gun mode, with 25.4-mm diameter nylon spheres and velocities around 2300 m/s. Gaseous mixtures studied included 2H\u2082+O\u2082+\u03b2N\u2082 (1 \u2264 \u03b2 \u2264 3.76), C\u2082H4+3O\u2082+5N\u2082, and C\u2082H\u2082+2.5O\u2082+9.4N\u2082 at initial pressures of 0.08 - 2.56 bar. Flow visualization results obtained by differential interferometry, shadowgraphy, and intensified CCD imaging were augmented by wall pressure records.
\r\n\r\nA wide variety of results were observed, including non-detonative shock-induced combustion, unstably initiated detonations, stabilized prompt initiations, and stabilized delayed initiations. These results can be roughly correlated in terms of the ratio of projectile velocity to mixture Chapman-Jouguet detonation speed, and the ratio of projectile diameter to detonation cell size or reaction zone thickness, although the effects of confinement and unsteadiness complicate this categorization.
\r\n\r\nTwo basic approaches to modeling the results have been attempted. In the first, a global model for initiation is based on an existing blast-initiation model using the hypersonic blast-wave analogy. This model is simple, and roughly predicts the experimental results, but suffers from a number of assumptions and approximations that restrict its usefulness and accuracy. The second approach, based on the local shock curvature, is not directly capable of predicting global initiation and failure, but illustrates the mechanism responsible for decoupling of the reaction zone from the shock front in cases of detonation failure. Coupled with a separate model for the shock shape, shock-curvature theory can be used for quantitative global predictions.
" }, { "name": "Khatri, Sven H.", "degree": "PhD", "year": "1999", "title": "Extensions to the structured singular value", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082008-161357", "creators": [ { "name": { "family": "Khatri", "given": "Sven H." }, "id": "Khatri-S-H", "display_name": "Khatri, Sven H." } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/aw0t-7881", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThere are two basic approaches to robustness analysis. The first is Monte Carlo analysis which randomly samples parameter space to generate a profile for the typical behavior of the system. The other approach is fundamentally worst case, where the objective is to determine the worst behavior in a set of models. The structured singular value, [...], is a powerful frame work for worst case analysis. Where [...] is a measure of the distance to singularity using the co-norm.\n\nUnder the appropriate projection, the uncertainty sets in the standard [...] framework that admit analysis are hypercubes. In this work, [...] and the computation of the bounds is extended to spherical sets or equivalently measuring the distance to singularity using the 2-norm. The upper bound is constructed by converting the spherical set of operators into a quadratic form relating the input and output vectors. Using a separating hyperplane or the S-procedure, a linear matrix inequality (LMI) upper bound can be constructed which is tighter than and consistent with the standard p upper bound. This new upper bound has special structure that can be exploited for efficient computation and the standard power algorithm is extended to compute lower bounds for spherical [...]. The upper bound construction is further generalized to more exotic regions like arbitrary ellipsoids, the Cartesian product of ellipsoids, and the intersection of ellipsoids. These generalizations are unified with the standard structures. These new tools enable the analysis of more exotic descriptions of uncertain models.\n\nFor many real world problems, the worst case paradigm leads to overly pessimistic answers and Monte Carlo methods are computationally expensive to obtain reasonable probabilistic descriptions for rare events.\n\nA few natural probabilistic robustness analysis questions are posed within the [...] framework. The proper formulation is as a mixed probabilistic and worst case uncertainty structure. Using branch and bound algorithms, an upper bound can be computed for probabilistic robustness. Motivated by this approach, a purely probabilistic [...] problem is posed and bounds are computed. Using the existing machinery, the branch and bound computation cost grows exponentially in the average case for questions of probabilistic robustness. This growth is due to gridding an n-dimensional surface with hypercubes.\n\nA motivation for the extensions of [...] to other uncertainty descriptions which admit analysis is to enable more efficient gridding techniques than just hypercubes. The desired fundamental region is a hypercube with a linear constraint. The motivation for this choice is the rank one problem. For rank one, the boundary of singularity is a hyperplane, but the conventional branch and bound tools still result in exponential gridding growth.\n\nThe generalization of the [...] framework is used to formulate an LMI upper bound for [...] with the linear constraint on uncertainty space. This is done by constructing the upper bound for the intersection of an eccentric ellipsoid with the standard uncertainty set. A more promising approach to this computation is the construction of an implicit [...] problem where the linear constraints on the uncertainty can be generically rewritten as an algebraic constraint on signals. This may lead to improvements on average to the branch and bound algorithms for probabilistic robustness analysis." }, { "name": "Kirac, Ahmet", "degree": "PhD", "year": "1999", "title": "Optimal orthonormal subband coding and lattice quantization with vector dithering", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02202008-104935", "creators": [ { "name": { "family": "Kirac", "given": "Ahmet" }, "id": "Kirac-A", "display_name": "Kirac, Ahmet" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Fadavi", "given": "Jalil" }, "id": "Fadavi-J", "role": "member", "display_name": "Fadavi, Jalil" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ec82-t391", "abstract": "In the digital era that we live in, efficient coding of signals is an unquestionable need. This thesis is about one of the most useful and popular technique of digital coding: subband coding. Subband coding and its cousin wavelet-based coding are now the preferred methods for not only speech, but also audio, image, and video signals. Subband coding involves a linear part which is a filter bank, and a nonlinear part which is usually a uniform scalar quantization of each of the subbands. Subband coders are classified according to the type of filter bank used for its transform. This thesis is mainly about orthonormal subband coding. The ability of an orthonormal filter bank to decompose the signal into components that have a diverse set of signal energies is an indicator of its efficiency for subband coding. Such a diversity in the set of the subband energies is fully utilized by a process called bit allocation. The traditional results on the optimality of a filter bank for given input statistics assume that the quantizers operate at high bit rates.\n\nThis thesis presents optimality results under more general quantizer models without assuming high bit rates. This is accomplished by revealing the relationship between the problems of optimal orthonormal subband coding and principal component representation of signals. The latter is done using what is called a principal component filter bank (PCFB). A PCFB is one that compacts most of the energy of a signal into smaller subsets of subbands. To date, there has not been significant theoretical developments in the field of optimal nonuniform subband coding, although the successful techniques of wavelet-based coding are among the state of the art in practice. Such techniques utilize a form of a nonuniform filter bank with a certain structure which makes it efficient for its implementation. In this thesis, we provide optimality results for the nonuniform orthonormal subband coding as well. As in the uniform case, the principal component representation of signals continues to play the key role. We introduce nonuniform PCFB's and link them to the optimal subband coding problem. A PCFB, in particular, contains a filter that compacts most of the signal energy into one single channel: energy compaction filter. The thesis goes into details of designing such filters optimally. In particular, we propose an analytical method in the two-channel case and a very efficient window method in the arbitrary M\u2014channel case. Multistage design of compaction filters has also been worked out.\n\nFinally we extend the analysis of uniform scalar quantization to multiple dimensions. We provide an exact statistical relationship between a lattice quantizer noise and its input vector. We then extend the idea of dithering to the vector case. Dithering is a means of statistically rendering the quantization noise independent of the input. We address the optimal choice of a lattice for a given dimension and also optimal pre- and post-filtering of a dithered lattice quantizer.\n" }, { "name": "Laubach, Sharon Lynn", "degree": "PhD", "year": "1999", "title": "Theory and experiments in autonomous sensor-based motion planning with applications for flight planetary microrovers", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-02202008-130626", "creators": [ { "name": { "family": "Laubach", "given": "Sharon Lynn" }, "id": "Laubach-S-L", "display_name": "Laubach, Sharon Lynn" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/b1wv-hc78", "abstract": "With the success of Mars Pathfinder's Sojourner rover, a new era of planetary exploration has opened, with demand for highly capable mobile robots. These robots must be able to traverse long distances over rough, unknown terrain autonomously, under severe resource constraints. Much prior work in mobile robot path planning has been based on assumptions that are not truly applicable to navigation through planetary terrains. Based on the author's firsthand experience with the Mars Pathfinder mission, this work reviews issues which are critical for successful autonomous navigation of planetary rovers. No current methodology addresses all of these constraints. We next develop the sensor-based \"Wedgebug\" motion- planning algorithm. This algorithm is complete, correct, requires minimal memory for storage of its world model, and uses only on-board sensors, which are guided by the algorithm to efficiently sense only the data needed for motion planning, while avoiding unnecessary robot motion. The planner has the additional advantage of producing locally-optimal paths, and is suitable for robots with a field-of-view limited in both downrange and angular scope, for a variety of applications including planetary navigation. This work includes the proof of completeness and correctness of the Wedgebug algorithm, and in particular provides a corrected, detailed proof of a key result required for the proof of completeness of the Wedgebug algorithm (and for the TangentBug algorithm which inspired this approach). In addition, we extend this result to a broader class of environments. The implementation of a version of Wedgebug, called \"RoverBug,\" on the Rocky7 Mars Rover prototype at the Jet Propulsion Laboratory (JPL) is described, and experimental results from operation in simulated martian terrain are presented.\n" }, { "name": "Lemieux, Patrick", "degree": "PhD", "year": "1999", "title": "The instability of shear layers produced by curved shocks", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212008-090557", "creators": [ { "name": { "family": "Lemieux", "given": "Patrick" }, "id": "Lemieux-P", "display_name": "Lemieux, Patrick" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/V9R0-JD15", "abstract": "A curved shock of general shape in hypersonic flow generates vorticity, so that a shear layer is formed in the flow downstream of the shock. The parameters affecting the distribution of vorticity in the shear layer are identified. Experiments aimed at determining the preferred wavelength of structures that develop in these flows are carried out in the T5 Hypervelocity Shock Tunnel. To visualize these structures, a new technique using streaklines is developed. The results are compared with numerical simulations of perfect-gas flows.\n\nThe numerical study also points to a flow regime, as the Newtonian limit is approached, where the instability of the shear layer is such that the shock becomes distorted. A series of experiments aimed at investigating flows approaching this limit is performed, using the T5 Light Gas Gun facility, and confirms the existence of this new regime.\n" }, { "name": "Leyva, Ivett A.", "degree": "PhD", "year": "1999", "title": "Shock detachment process on cones in hypervelocity flows", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082008-162753", "creators": [ { "name": { "family": "Leyva", "given": "Ivett A." }, "id": "Leyva-I-A", "display_name": "Leyva, Ivett A." } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/62TN-GA26", "abstract": "The shock detachment process on cones in hypervelocity flows is one of the most sensitive flows to relaxation effects. The critical angle for shock detachment under frozen conditions can be very different from the critical angle under chemical and thermal equilibrium. The rate of increase of the detachment distance with cone angle is also affected by the relaxation rate.
\r\n\r\nThe purpose of this study is to explain the effects of nonequilibrium on the shock detachment distance and its growth rate on cones in hypervelocity flows. The study consists of an experimental and a computational program. The experimental part has been carried out at Caltech's hypervelocity reflected shock tunnel (T5). Six different free-stream conditions have been chosen, four using N2 as the test gas and two using CO2. About 170 shots were performed on 24 cones. The cones range in diameter from 2 cm to 16 cm with half-angles varying from 55\u00b0 to 75\u00b0. The experimental data obtained are holographic interferograms of every shot, and surface temperature and pressure measurements for the bigger cones. Extensive numerical simulations were made for the N2 flows and some were also made for the CO2 flows. The code employed is a Navier-Stokes solver that can account for thermal and chemical nonequilibrium in axisymmetric flows.
\r\n\r\nThe experimental and computational data obtained for the shock detachment distance confirms a previous theoretical model that predicts the detachment distance will grow more slowly for relaxing flows than for frozen or equilibrium flows. This difference is explained in terms of the behavior of the sonic line inside the shock layer. Different growth rates result when the detachment distance is controlled by the diameter of the cone (frozen and equilibrium cases) than when it is controlled by the extent of the relaxation zone inside the shock layer (nonequilibrium flows). The experimental data are also complemented with computational data to observe the behavior of the detachment distance from the frozen to equilibrium limits for a given cone half-angle and free-stream condition. As deduced by a previous simple scaling argument, the ratio of the detachment distance to the diameter of the cone is constant in the two extremes and rapidly switches from one value to the other for cone diameters of about 2 cm to 16 cm. The experimental interferograms are also compared with numerical ones in terms of the detachment distance, the number of fringes in the shock layer, and the shape of the fringes.
\r\n\r\nThe heat flux traces obtained from the temperature measurements show different behaviors for the attached and detached cases, but these effects can be related to the conditions at the edge of and inside the boundary layer and to the Reynolds number of the flow rather than to nonequilibrium effects. The pressure measurements were insensitive to the degree of nonequilibrium.
\r\n" }, { "name": "Li, Shijie", "degree": "PhD", "year": "1999", "title": "UHF and X-Band Class-E amplifiers", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082008-163454", "creators": [ { "name": { "family": "Li", "given": "Shijie" }, "id": "Li-S", "display_name": "Li, Shijie" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/wrwt-7a21", "abstract": "A Class-E amplifier consists of a single transistor which is driven as a switch and a passive output load network. The output load network is a tuned resonant circuit and is designed to minimize the voltage and current waveforms overlapping, thus minimize the power dissipation in the transistor. The Class-E amplifier is for high efficiency operation with a theoretical maximum efficiency of 100%, and in practice about 80%-90%. Design approaches for Class-E amplifiers are described. Designs and experimental results for one 440 MHz and two X-band Class-E amplifiers are presented in detail. The 440 MHz Class-E amplifier is implemented using lumped components and the active transistor is the Motorola MRF183 n-channel lateral MOSFET. It delivers an output power of 15 W, drain efficiency of 77%, power-added efficiency (PAE) of 70% with an input power of 1.4 W. For the two X-band Class-E amplifiers, one uses Fujitsu FHX35X HEMT as the active device and has an output power of 30 mW, drain efficiency of 80% and PAE of t 11.2 GHz. The other one uses Fujitsu FLR056XV MESFET and achieves an output power of 190 mW, drain efficiency of 72% and PAE of 56% at 9 GHz. The two X-band Class-E amplifiers are implemented using microstrip transmission lines.\n" }, { "name": "Lloyd, Thomas", "degree": "PhD", "year": "1999", "title": "Dissolution of Fe(III)- and Mn(III,IV)- (hydr)oxides by deferrioxamine B", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082008-163932", "creators": [ { "name": { "family": "Lloyd", "given": "Thomas" }, "id": "Lloyd-T", "display_name": "Lloyd, Thomas" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "member", "display_name": "Hering, Janet G." }, { "name": { "family": "Bercaw", "given": "John E." }, "id": "Bercaw-J-E", "role": "member", "display_name": "Bercaw, John E." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/dxzk-z221", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nMicrobially produced siderophores are thought to have evolved to increase the availability of iron in oxic aqueous systems. Historically, it has been assumed that siderophores interact with iron found in Fe(III)-(hydr)oxides, removing iron from the solid to form ferrated aqueous species of the siderophore available for uptake by the microorganism. However, this proposed interaction of siderophore with the solid phase has not been examined in detail.\n\nThe work presented in this thesis examines the interaction of a model trihydroxamic acid siderophore (deferrioxamine B) with synthetic Fe(III)-, Mn(III), Mn(IV)- (hydr)oxide particles. The experiments were designed to characterize the mineral dissolution process mediated by deferrioxamine B (DFA). DFA was found to dissolve all the solid particles used in the study. The Fe(III)- (hydr)oxides dissolved exclusively by a nonreductive mechanism. The dissolution is a surface-mediated process. Dissolution of manganite was found to be analogous to the Fe(III)-(hydr)oxide dissolution process, while the dissolution of pyrolusite was found to follow a complicated mechanism that involves reductive processes. The interactions between DFA and the solid surface are examined experimentally and theoretically.\n\nUnder the conditions in which (i) the concentration of DFA in solution remains essentially constant over the course of the reaction, i.e., the concentration of the ferrated form of DFA (FA) is much less than [DFA][...] over the whole time of the reaction, and (ii) the concentration of available surface sites remains constant, the dissolution rate can be modeled as a pseudo-zero [...] order reaction, where\n\n \t\tR = k'.\n\nUnder the same conditions and where the concentration of adsorbed DFA is measured, the dissolution rate can be modeled as a pseudo-first order process, where\n\n\t\tR = k [[...]Fe \u2014 DFA],\n\nwhere [[...]Fe \u2014 DFA] is defined as the concentration of adsorbed DFA. Conditions (i) and (ii) imply that a necessary condition for observation of a pseudo-zero [...] order process is that [[...]Fe \u2014 DFA] remains constant over the course of the reaction. Where these conditions fail, the dissolution process becomes more complicated, and the experiments presented here do not address these cases in detail.\n" }, { "name": "Long, Mark K.", "degree": "PhD", "year": "1999", "title": "Computer aided mask layout synthesis for anisotrophic etch photolithography", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02142008-130713", "creators": [ { "name": { "family": "Long", "given": "Mark K." }, "id": "Long-M-K", "display_name": "Long, Mark K." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/pt5c-d720", "abstract": "The increasing penetration of MEMS technology into new application domains suggests the need for sophisticated engineering tools that can automate routine MEMS engineering design functions. This thesis discusses the development of algorithms and automated software tools that are intended to automate the mask-layout process for bulk etch micro-machining.\n\nAt present, a designer conceives of a MEMS function, then (informally) creates a mask-layout that the designer believes will process into a shape that will exhibit the desired function. Because of the highly anisotropic nature of the bulk etching process, the mask design process relies heavily upon the designer's intuitive understanding of the etching process. A prototype device is created from the candidate mask, and its actual function is tested. This process can result in many iterations, and many prototypes.\n\nThis dissertation presents a method to automatically synthesize the mask layout for a bulk etching process. That is, given a desired part geometry and process parameters, the algorithm determines a candidate mask geometry that will etch to the final desired shape even in the case of highly anisotropic etchants. It will also compute compensation structures for difficult to etch features. Conceptually, the algorithm is based on the use of a forward etch simulation in reverse time. Since the forward etch process is a many-to-one map, the reverse time simulation is augmented to include a choice of valid preimages. Timing models are introduced to develop mask layouts that have appearing crystal planes during the etch and shown to allow more complex compensation structures.\n\nFinally, calibration masks are developed that allow the experimental determination of etch rate parameters without painstaking measurements.\n" }, { "name": "Love, Philip", "degree": "PhD", "year": "1999", "title": "Bifurcations in Kolmogorov and Taylor-vortex flows", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122008-090309", "creators": [ { "name": { "family": "Love", "given": "Philip" }, "id": "Love-P", "display_name": "Love, Philip" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "chair", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/g2f3-s507", "abstract": "The bifurcation structure of Kolmogorov and Taylor-Vortex flows was computed with the aid of the Recursive Projection Method; see Schroff and Keller [32]. It was shown that RPM significantly improves the convergence of our numerical method while calculating steady state solutions. Moreover we use RPM to detect bifurcation points while continuing along solution branches, and to provide the required augmentation when continuing around a fold, or along a traveling wave branch.\n\nThe bifurcations to two and three-dimensional solutions from the shear flow solution of Kolmogorov flow are calculated both numerically, by solving an ordinary differential equation, and analytically, using an approximation method. Our results for the two-dimensional bifurcations agree with the work of Meshalkin and Sinai [26].\n\nWe also explain how the branches of Kolmogorov flows observed by Platt and Sirovich [29] are connected together, and observe that our solutions have worm like structures even at relatively low Reynolds numbers. Various statistics of our flows are calculated and compare with those from isotropic turbulence calculations.\n\nAdditionally various solution branches of the Taylor Vortex flow were computed, including spiral vortices. Furthermore, it was discovered that the Wavy Taylor Vortex branches arise from sub-critical Hopf bifurcations, and they undergo a fold close to their bifurcation point.\n" }, { "name": "Maheo, Patrice Michel", "degree": "PhD", "year": "1999", "title": "Free-Surface Turbulent Shear Flows", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212008-104541", "creators": [ { "name": { "family": "Maheo", "given": "Patrice Michel" }, "id": "Maheo-Patrice-Michel", "display_name": "Maheo, Patrice Michel" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TCTV-BM26", "abstract": "The structure and dynamics of turbulent wakes and shear layers in the presence of a clean free surface have been investigated experimentally using digital particle image velocimetry (DPIV). The purpose of this study was to determine the extent and characteristics of the influence, if any, of the free surface on these underlying turbulent shear flows.
\r\n\r\nThe free surface was found to affect the dynamics of turbulence within a surface layer on the order of one half-width of the submerged wake and one half of the local vorticity thickness of the submerged shear layer. Within this layer, the vertical velocity fluctuations are inhibited and the turbulence kinetic energy is redistributed to the horizontal components. The self-induced motion of surface-parallel vortical structures under the influence of their images was shown to lead to large-scale mean streamwise secondary flows and associated outward surface currents-symmetric for the wake and asymmetric for the shear layer. This motion was the origin of the significantly higher lateral spreading rates of these surface shear flows compared to the spreading rates of their fully-submerged counterparts \u2014 20% and 25% for the wake and shear layer respectively. In addition, the evolution of the streamwise and surface-normal enstrophy components within the surface layer was consistent with the normal connection of vortical structures required at a free surface.
\r\n\r\nThe influence of the secondary flows was tracked back to the splitter plate's turbulent boundary layers where they were hence deduced to originate. A simple analysis of the mixed-boundary corner flows of the splitter plate made using the mean streamwise vorticity equation coupled with the evolution of the values of the transverse velocity confirmed the latter. In this picture of the mean flow, the secondary flows present in the near-surface edges of these shear flows were related to the pair of outer secondary vortices generated thereby. Furthermore, using a simplified equation for the surface-normal Reynolds stress, it was shown that the mutual interaction of the surface-parallel vortical structures with their images yielded a decrease in vertical velocity fluctuations as the free surface was approached. This equation shed further light on the redistribution of the vertical kinetic energy of turbulence into the other two Reynolds normal stresses. The resulting free-surface Reynolds-stress anisotropy in turn gave birth to the two streamwise secondary flows.
\r\n\r\n\r\n" }, { "name": "Manohar, Rajit", "degree": "PhD", "year": "1999", "title": "The impact of asynchrony on computer architecture", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08112005-114144", "creators": [ { "name": { "family": "Manohar", "given": "Rajit" }, "id": "Manohar-R", "display_name": "Manohar, Rajit" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/xzwa-p598", "abstract": "The performance characteristics of asynchronous circuits are quite different from those of their synchronous counterparts. As a result, the best asynchronous design of a particular system does not necessarily correspond to the best synchronous design, even at the algorithmic level. The goal of this thesis is to examine certain aspects of computer architecture and design in the context of an asynchronous VLSI implementation.\n\nWe present necessary and sufficient conditions under which the degree of pipelining of a component can be modified without affecting the correctness of an asynchronous computation.\n\nAs an instance of the improvements possible using an asynchronous architecture, we present circuits to solve the prefix problem with average-case behavior better than that possible by any synchronous solution in the case when the prefix operator has a right zero. We show that our circuit implementations are area-optimal given their performance characteristics, and have the best possible average-case latency.\n\nAt the level of processor design, we present a mechanism for the implementation of precise exceptions in asynchronous processors. The novel feature of this mechanism is that it permits the presence of a data-dependent number of instructions in the execution pipeline of the processor.\n\nFinally, at the level of processor architecture, we present the architecture of a processor with an independent instruction stream for branches. The instruction set permits loops and function calls to be executed with minimal control-flow overhead." }, { "name": "Maric, Dragan S.", "degree": "PhD", "year": "1999", "title": "Advanced flux weakening techniques for surface-mounted permanent-magnet machine drives", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212008-112258", "creators": [ { "name": { "family": "Maric", "given": "Dragan S." }, "id": "Maric-D-S", "display_name": "Maric, Dragan S." } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/fy8g-pm69", "abstract": "Surface-Mounted Permanent-Magnet Synchronous (SMPMS) machine drives have been considered thus far unsuitable for an efficient, wide-range flux weakening operation. This thesis will detail two novel schemes that provide stable and reliable operation over a wide range above the machine base speed, without dependence on machine parameters, usage of look-up tables or DC bus voltage measurements. Both techniques employ space vector modulation (SVM) with the option of smooth transition into six-step mode through the over-modulation range, maximizing the torque available. The first scheme ensures exact torque command tracking, whereas the second one intrinsically gives a steady state error in the flux weakening area. The second method, on the other hand, is computationally simpler, offers better transient response and the steady state torque error is not a critical feature if the torque control loop is an inner loop. The first method uses closed loop control of the phase voltage magnitude to generate magnetizing current reference for the flux-weakening operation. The second approach detects the steady-state error in the torque current component regulation, and then uses the error to generate the magnetizing current reference. However, when the over-modulation and six-step modes are utilized, the fifth and seventh stator current harmonics of the fundamental frequency propagate through the current control loops, resulting in the sixth harmonic in the current error signals and, henceforth, in the reference voltage duty cycles for the flux weakening control section. This deteriorates drive performance. To filter the sixth harmonic, a constrained lattice-structure all-pass-based notch filter is used here, providing minimal phase delay and complete attenuation of the sixth harmonic. Similar filter solutions have been used so far only in certain communications and sonar applications, but this work sets a path for a broader utilization in electrical drive systems. Modeling and simulation techniques, design procedure, and experimental results will be presented. The results of this work proved that SMPMS machines are suitable for applications when the extended speed range was required, e.g., in electric propulsion." }, { "name": "Masuhr, Andreas", "degree": "PhD", "year": "1999", "title": "Viscous flow and crystallization of bulk metallic glass forming liquids", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-06242005-094416", "creators": [ { "name": { "family": "Masuhr", "given": "Andreas" }, "id": "Masuhr-A", "display_name": "Masuhr, Andreas" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/S22B-5C59", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental setup was designed and implemented to measure the flow behavior of liquids in the viscosity range from [...] Pa s to [...] Pa s. The viscosity of the [...] (V1) bulk metallic glass forming alloy was measured over a temperature range from 927 K to 1173 K. At the liquidus temperature, the viscosity is 2.3 Pa s, which is about three orders of magnitude larger than the viscosity of a pure metallic liquid. The free volume theory as formulated by Cohen and Grest describes the temperature dependence of the viscosity of V1 over 14 orders in magnitude.\r\n\r\nThe high viscosity of V1 above the liquidus temperature stabilizes the liquid against convective flow due to temperature gradients and allows for diffusion experiments in the equilibrium liquid. The temperature dependence of the diffusivity of large atoms like A1 or Au scales with the viscosity. The time scales obtained from the viscosity measurements suggest that above the calorimetric glass transition region the diffusion of small and medium sized atoms is governed by thermally activated jumps.\r\n\r\nLiquid V1 could be successfully supercooled inside high purity graphite crucibles without changing the stability of the supercooled liquid with respect to crystallization compared to levitated samples. The sluggish kinetics that are reflected in the high viscosity in the supercooled liquid state contribute significantly to the good glass forming ability of the alloy. The critical cooling rate is about 1 K/s.\r\n\r\nThe onset of crystallization under isothermal conditions as well as upon heating from the amorphous state was studied in detail. The critical heating rate to bypass crystallization was measured to be 200 K/s and the difference between the critical cooling and critical heating rate can be qualitatively understood in the framework of nucleation and growth.\r\n\r\nHowever, the observed deviations from classical steady state nucleation behavior indicate a more complex crystallization mechanism. Rheological and crystallization studies at constant shear rate suggest that changes in the morphology of the supercooled liquid of V1 occur as a precursor of crystallization." }, { "name": "Monzon, Franklin Gregory", "degree": "PhD", "year": "1999", "title": "Semiconductor magnetoelectronics and prospects for a spin transistor", "advisor": "Roukes, Michael Lee", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242008-091431", "creators": [ { "name": { "family": "Monzon", "given": "Franklin Gregory" }, "id": "Monzon-F-G", "display_name": "Monzon, Franklin Gregory" } ], "advisors": [ { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "advisor", "display_name": "Roukes, Michael Lee" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/gccy-3j80", "abstract": "The first demonstration of spin-coupled electronic transport, in all-metallic devices, occurred over ten years ago. Although the development of similar ferromagnet/semiconductor structures poses unique difficulties, these devices are exciting because they afford the possibility of constructing active circuit elements based upon the manipulation of spin rather than charge.\n\nIn this thesis we clearly delineate the requirements that must be met in order to successfully implement a semiconductor spin transistor. We present extensive 4.2 K measurements of NiFe/InAs quantum well spin devices fabricated both by photolithography and electron beam lithography, both wet-etched and dry-etched. These measurements often exhibit strong magnetoelectronic phenomena, not based on spin transport, that complicate the demonstration of spin injection/detection. We use local Hall voltages to carefully characterize submicron ferromagnetic thin films in order to improve the switching behavior of our ferromagnetic contacts and to minimize stray field effects. We describe theoretical calculations for ballistic spin-coupled transport, along with careful on-chip electrical characterization, that reveal our InAs conduction channels to be adequate spin-preserving wires. We conclude that inefficient spin transfer across the NiFe/InAs interface severely degrades the spin polarization of the injected current. Though we therefore do not obtain a conclusive demonstration of spin transport even in our smallest devices, with injector/detector spacings of less than 1 mm, we make firm suggestions for future spin devices, including expectations for what consitutes a definitive demonstration of spin transport in a high mobility two-dimensional electron gas (2DEG).\n\nFrom a physics standpoint, such a demonstration is very interesting because control of a semiconductor spin-polarized current offers possibilities both for experiments in spin dynamics without the use of high magnetic fields or optical-polarization schemes, and for the investigation of spin-scattering mechanisms in tunable-density (gated) devices. From an engineering standpoint, these same transistor-like devices are intriguing as novel memories or switches. Despite this, the development of semiconductor spin devices has lagged behind the advance of metallic multilayer (GMR) spin devices. This thesis addresses the difficulties inherent in implementing semiconductor spin devices, with the aim of enabling the successful manufacture of a spin transistor in the near future." }, { "name": "Ofria, Charles A.", "degree": "PhD", "year": "1999", "title": "Evolution of genetic codes", "advisor": "Adami, Christoph Carl", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042007-091804", "creators": [ { "name": { "family": "Ofria", "given": "Charles A." }, "id": "Ofria-C-A", "orcid": "0000-0003-2924-1732", "display_name": "Ofria, Charles A." } ], "advisors": [ { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "role": "advisor", "display_name": "Adami, Christoph Carl" } ], "committee": [ { "name": { "family": "Adami", "given": "Christoph Carl" }, "id": "Adami-C-C", "role": "chair", "display_name": "Adami, Christoph Carl" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Allman", "given": "John M." }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "cns" ], "doi": "10.7907/2z40-1m97", "abstract": "In this thesis, I use analytical and computational techniques to study the development of codes in evolutionary systems. We only know of one instance of such a genetic code in the natural world: our own DNA. However, the results from my work are expected to be universally true for all evolving systems. I use mathematical models and conduct experiments with avida, a software-based research platform for the study of evolution in \"digital organisms.\" This allows me to collect statistically powerful data over evolutionary timescales infeasible in a biological system.\r\n\r\nIn the avida system, Darwinian evolution is implemented on populations of self-replicating computer programs. A typical experiment is seeded with a single ancestor program capable only of reproduction. This ancestor gives rise to an entire population of programs, which adapt to interact with a complex environment, while developing entirely new computational capabilities. I study the process of evolution in this system, taking exact measurements on the underlying genetic codes, and performing tests that would be prohibitively difficult in biological systems.\r\n\r\nI have focused on the following areas in studying the evolution of genetic codes: \r\n\r\nInformation Theory: I treat the process of reproduction as a noisy channel in which codes are transmitted from the parent's genome to the child. Unlike most channels, however, evolution actively selects for codes received with a higher information content, even if this increased information was introduced via noise. A genetic code consists of information about the environment surrounding the organism. As a population adapts, this information increases, and can be approximated through measuring the reduction of per-nucleotide entropy - in effect sites freeze in place as they code for useful functionality. In the avida system, we know the sequence of all genomes in the population, and new computational genes can be identified as they are formed.\r\n\r\nThe Evolution of Genetic Organization: Organisms incapable of error correction (such as viruses) develop strong code compaction techniques to minimize their target area for mutations, the most prominent of which is overlapping genes. Higher organisms, however, are capable of reducing their mutational load and will explicitly spread out their code, cleanly segregating their genes. I investigate the pressures behind overlapping or segregation of genes, and demonstrate that overlaps have a side effect of drastically reducing the probability of neutral mutations within a gene, and hence hindering continued adaptation. Further, in a changing environment, overlapping genes have a significantly reduced ability to adapt independently. I compare overlapping and singly expressed sections of code in avida, and show a significant (two-fold) difference in the average per-site variation. I also demonstrate the evolutionary pressure for organisms to segregate their genes in a fluctuating environment to improve their adaptive abilities.\r\n\r\nEvolving Computer Programs: I explore evolution in digital genetic codes, and isolate some of those features of a programming language that promote continuous adaptation. In the biological world evolution gives rise to complex organisms robust to changing situations in their environment. This increase in complexity and \"functionality\" of the organisms typically generates more stable systems. On the other hand, as computer programs gain complexity, they only become more fragile. If two programs interact in a way not explicitly designed, the results are neither predictable nor reliable. In fact, computer programs often fail even when put to the use for which they were explicitly intended. Computational organisms, however, have a level of robustness more akin to their biological counterparts, not only performing computations, but often doing so in a manner beyond the efficiency that a human programmer could produce.\r\n\r\nFinally, all of this work is tied together, and future directions for its continuation are explored." }, { "name": "Paiella, Roberto", "degree": "PhD", "year": "1999", "title": "Physics and application of four-wave mixing in semiconductor optical amplifiers", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242008-091907", "creators": [ { "name": { "family": "Paiella", "given": "Roberto" }, "id": "Paiella-R", "display_name": "Paiella, Roberto" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/r9qa-0n27", "abstract": "This thesis investigates the physical mechanisms responsible for four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs), and their application to quantum-well spectroscopy and all-optical signal processing. A microscopic theory of polarization-resolved FWM is developed, and the corresponding polarization selection rules are derived. It is then shown how these results can be used to study basic carrier dynamics in semiconductor active layers. Finally, a wavelength conversion device and a new class of all-optical logic gates, based on FWM in SOAs, are presented and characterized.\n\nThe first part of the thesis is devoted to several experimental and theoretical investigations of carrier transport dynamics in multiquantum-well SOAs, and of their relation to the FWM nonlinearity of these devices. A polarization-resolved FWM configuration is used to study interwell carrier transport in a SOA consisting of alternating pairs of tensile and compressively strained quantum wells. A similar structure with interwell coupling provided by resonant tunneling is then investigated theoretically; it is shown how FWM can be used to excite coherent electric-dipole oscillations in this device, leading to efficient generation of TeraHertz radiation. Finally, a novel wavelength-resolved FWM technique is demonstrated to directly study the capture of carriers in quantum wells.\n\nThe second part of the thesis focuses on the application of FWM to all-optical signal processing for WDM communication systems. A wavelength conversion device based on FWM in a long (1.5 mm) SOA is developed, and used to demonstrate error-free conversion of 10 Gbit/sec data over a record 30 nm wavelength span. Other configurations for wavelength conversion by FWM are then proposed and demonstrated, including: a dual-pump configuration for polarization insensitive operation; a self-pumped FWM converter, based on a fiber-Bragg-grating coupled diode laser; and a device based on injection-locked FWM in this same laser, characterized by a large resonance peak in its conversion efficiency. Finally, the last chapter is devoted to a novel class of all-optical logic gates, based on FWM, designed to operate on bytes of information encoded in wavelength (\"byte-wide WDM\").\n" }, { "name": "Phares, Denis Joseph", "degree": "PhD", "year": "1999", "title": "Particle resuspension from surfaces", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012008-135507", "creators": [ { "name": { "family": "Phares", "given": "Denis Joseph" }, "id": "Phares-D-J", "display_name": "Phares, Denis Joseph" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/63FG-BC19", "abstract": "A series of experiments were performed in order to investigate how fine particles are resuspended from a surface once they are adhered to the surface through van der Waals interactions. Model spherical particles were generated, deposited on well- characterized substrates, and exposed to various types of forces. Impulsive forces were applied to the particles using impacting particles and impinging shock waves, and steady shearing forces were applied by impinging gas jets and a laminar channel flow. In each case, the threshold conditions to resuspension were determined by optically monitoring particle removal from the substrate. Particles of various size and material properties were considered. Resuspension thresholds were reproducible and unambiguous in the model experiments.\r\n\r\nThe threshold to resuspension of the model spheres exposed to impinging gas jets was evidenced by abrupt changes in removal efficiency at specific locations. An analytical method to solve the flow field produced by an impinging jet was developed in order to calculate the shear stress experienced by the particles at the threshold locations. An inviscid model of normal jet impingement provided the free stream conditions for the ensuing boundary layer analysis. Calculated shear stress distributions using the model agree with previous measurements.\r\n\r\nTheoretical descriptions of the resuspension mechanisms were inferred from the observed resuspension thresholds. Such an undertaking involves the combination of existing equilibrium adhesion models and the kinetics of aerodynamic or particle collisional interactions. Resuspension models based on equilibrium adhesion theories did not accurately describe the observed size dependence of threshold applied shear stress, or the effect on resuspension of force duration. A kinetic model was developed to qualitatively describe these observed trends.\r\n\r\nThe particle removal techniques were applied to a study of particle sampling from explosive fingerprint transfer deposits and fingerprint simulations. A crude sampling system consisting of an impinging gas jet and a suction tube/filter assembly was calibrated with model composite spheres made from a mixture of polystyrene and 2,4,6-trinitrotoluene. Observed removal and collection efficiencies were related to the results of the model experiments. It was found that calibrated sampling systems could be used effectively to test the accuracy of fingerprint simulations.\r\n" }, { "name": "Piquette, Eric C.", "degree": "PhD", "year": "1999", "title": "Molecular beam heteroepitaxial growth and characterization of wide band gap semiconductor films and devices", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292006-152956", "creators": [ { "name": { "family": "Piquette", "given": "Eric C." }, "id": "Piquette-E-C", "display_name": "Piquette, Eric C." } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/by67-nr24", "abstract": "The thesis consists of two parts. Part I describes work on the molecular beam epitaxial (MBE) growth of GaN, AlN, and Al(x)Ga(1-x)N alloys, as well as efforts in the initial technical development and demonstration of nitride-based high power electronic devices. The major issues pertaining to MBE growth are discussed, including special requirements of the growth system, substrates, film nucleation, n- and p-type doping, and the dependence of film quality on growth parameters. The GaN films were characterized by a variety of methods, including high resolution x-ray diffraction, photoluminescence, and Hall effect measurement. It is found that the film polarity and extended defect density as well as quality of photoluminescence and electrical transport properties depend crucially on how the nitride layer is nucleated on the substrate and how the subsequent film surface morphology evolves, which can be controlled by the growth conditions. A technique is proposed and demonstrated that utilizes the control of morphology evolution to reduce defect density and improve the structural quality of MBE GaN films.\n\nIn addition to growth, the design and processing of high voltage GaN Schottky diodes is presented, as well as an experimental study of sputter-deposited ohmic and rectifying metal contacts to GaN. Simple models for high power devices, based on materials properties such as minority carrier diffusion length and critical electric breakdown field, are used to estimate the voltage standoff capability, current carrying capacity, and maximum operating frequency of unipolar and bipolar GaN power devices. The materials and transport properties of GaN pertinent to high power device design were measured experimentally. High voltage Schottky rectifiers were fabricated which verify the impressive electric breakdown field of GaN (2-5 MV/cm). Electron beam induced current (EBIC) experiments were also conducted to measure the minority carrier diffusion length for both electrons and holes in GaN.\n\nPart II of the thesis describes studies of the MBE growth of ZnS and investigations of ZnS/GaN light emitting heterojunctions which show promise for application as blue and green light emitters. Zinc sulfide layers doped with Ag and Al were grown by MBE on sapphire, GaAs, and GaN substrates and characterized by x-ray diffraction and photoluminescence. Preliminary current-voltage and electroluminescence results are presented for a processed ZnS:Al,Ag/GaN:Mg prototype blue light emitting device.\n" }, { "name": "Preventza, Polly", "degree": "PhD", "year": "1999", "title": "Analysis and design for quasi-optical structures", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242008-093525", "creators": [ { "name": { "family": "Preventza", "given": "Polly" }, "id": "Preventza-P", "display_name": "Preventza, Polly" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/t7ve-td81", "abstract": "Quasi-optical power combiners such as quasi-optical grids provide an efficient means of combining the output power of many solid-state devices in free space. Unlike traditional power combiners no transmission lines are used, therefore, high output powers with less loss can be achieved at higher frequencies. This thesis will detail three quasi-optical grids and their modeling. Two new models for analyzing quasi-optical grid amplifiers based on a finite-element simulator (HFSS) are presented and their validity is tested. A 36-element Ka-band grid amplifier is also described. The grid uses Flip-Chip InP HEMT's and has a peak gain of 4.8 dB at 36 GHz. A beam-steering method which includes microelectromechanical (MEM) switches on an insulating membrane is presented. The arrays are fabricated monolithically on highly- doped silicon by Rockwell Science Center. Processing challenges in fabricating the structures will be discussed. Measurements of s-parameters of capacitive arrays (Off state) are made and give promising results for the beam-steering grid. The design, construction and performance of a 36-element hybrid gid oscillator is also presented. The active devices are InP-based HEMT's. A locked frequency spectrum was achieved, with a Peak Effective Radiated Power (ERP) of 200 mW at 43 GHz. The grid is designed to minimize the substrate-mode power and produce an E-field with low side-lobes.\n" }, { "name": "Primbs, James A.", "degree": "PhD", "year": "1999", "title": "Nonlinear optimal control: a receding horizon appoach", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-103315", "creators": [ { "name": { "family": "Primbs", "given": "James A." }, "id": "Primbs-J-A", "display_name": "Primbs, James A." } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Krener", "given": "Arthur" }, "id": "Krener-A", "role": "member", "display_name": "Krener, Arthur" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/4AD2-0T48", "abstract": "As advances in computing power forge ahead at an unparalleled rate, an increasingly compelling question that spans nearly every discipline is how best to exploit these advances. At one extreme, a tempting approach is to throw as much computational power at a problem as possible. Unfortunately, this is rarely a justifiable approach unless one has some theoretical guarantee of the efficacy of the computations. At the other extreme, not taking advantage of available computing power is unnecessarily limiting. In general, it is only through a careful inspection of the strengths and weaknesses of all available approaches that an optimal balance between analysis and computation is achieved. This thesis addresses the delicate interaction between theory and computation in the context of optimal control.\n\nAn exact solution to the nonlinear optimal control problem is known to be prohibitively difficult, both analytically and computationally. Nevertheless, a number of alternative (suboptimal) approaches have been developed. Many of these techniques approach the problem from an off-line, analytical point of view, designing a controller based on a detailed analysis of the system dynamics. A concept particularly amenable to this point of view is that of a control Lyapunov function. These techniques extend the Lyapunov methodology to control systems. In contrast, so-called receding horizon techniques rely purely on on-line computation to determine a control law. While offering an alternative method of attacking the optimal control problem, receding horizon implementations often lack solid theoretical stability guarantees.\n\nIn this thesis, we uncover a synergistic relationship that holds between control Lyapunov function based schemes and on-line receding horizon style computation. These connections derive from the classical Hamilton-Jacobi-Bellman and Euler-Lagrange approaches to optimal control. By returning to these roots, a broad class of control Lyapunov schemes are shown to admit natural extensions to receding horizon schemes, benefiting from the performance advantages of on-line computation. From the receding horizon point of view, the use of a control Lyapunov function is a convenient solution to not only the theoretical properties that receding horizon control typically lacks, but also unexpectedly eases many of the difficult implementation requirements associated with on-line computation. After developing these schemes for the unconstrained nonlinear optimal control problem, the entire design methodology is illustrated on a simple model of a longitudinal flight control system. They are then extended to time-varying and input constrained nonlinear systems, offering a promising new paradigm for nonlinear optimal control design." }, { "name": "Roweis, Sam T.", "degree": "PhD", "year": "1999", "title": "Data driven production models for speech processing", "advisor": "Abu-Mostafa, Yaser S.; Hopfield, John J.; Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272008-093303", "creators": [ { "name": { "family": "Roweis", "given": "Sam T." }, "id": "Roweis-S-T", "display_name": "Roweis, Sam T." } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "advisor", "display_name": "Hopfield, John J." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "cns" ], "doi": "10.7907/DP55-8897", "abstract": "When difficult computations are to be performed on sensory data it is often advantageous to employ a model of the underlying process which produced the observations. Because such generative models capture information about the set of possible observations, they can help to explain complex variability naturally present in the data and are useful in separating signal from noise. In the case of neural and artificial sensory processing systems generative models are learned directly from environmental input although they are often rooted in the underlying physics of the modality involved. One effective use of learned models is made by performing model inversion or state inference on incoming observation sequences to discover the underlying state or control parameter trajectories which could have produced them. These inferred states can then be used as inputs to a pattern recognition or pattern completion module.\r\n\r\nIn the case of human speech perception and production, the models in question are called articulatory models and relate the movements of a talker's mouth to the sequence of sounds produced. Linguistic theories and substantial psychophysical evidence argue strongly that articulatory model inversion plays an important role in speech perception and recognition in the brain. Unfortunately, despite potential engineering advantages and evidence for being part of the human strategy, such inversion of speech production models is absent in almost all artificial speech processing systems.\r\nThis dissertation presents a series of experiments which investigate articulatory speech processing using real speech production data from a database containing simultaneous audio and mouth movement recordings. I show that it is possible to learn simple low dimensionality models which accurately capture the structure observed in such real production data. I discuss how these models can be used to learn a forward synthesis system which generates spectral sequences from articulatory movements. I also describe an inversion algorithm which estimates movements from an acoustic signal Finally, I demonstrate the use of articulatory movements, both true and recovered, in a simple speech recognition task, showing the possibility of doing true articulatory speech recognition in artificial systems." }, { "name": "Schenk, Kurt", "degree": "PhD", "year": "1999", "title": "Power factor correction topologies and small-signal modeling. I: Single-phase and three-phase power factor correction. II: Small-signal analysis of converters in discontinuous conduction mode", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechTHESIS:08302010-162310049", "creators": [ { "name": { "family": "Schenk", "given": "Kurt" }, "id": "Schenk-K", "display_name": "Schenk, Kurt" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/EXCX-Z103", "abstract": "Part I: This thesis is motivated by the increasing demand for power quality improvement. Power factor correction topologies for both single- and the three-phase utility lines are\r\ninvestigated and new modes of operation are introduced. The discussed topologies are so-called automatic power factor correctors. The current shaping function is a natural\r\nproperty of these circuits, and no extra current control loop is necessary.\r\n\r\n\r\nIn both the single- and three-phase cases, a control method is introduced which provides full output regulation and simultaneously reduces the distortion of the input\r\ncurrent at no extra cost.\r\n\r\nWhereas in the single-phase topology, galvanic isolation is easily obtained, in the three-phase topology, some obstacles have to be overcome. The isolated three-phase\r\nconverter has an inherent output voltage ripple. This problem is analyzed and a solution is presented.\r\n\r\n\r\nResults obtained on experimental circuits agree well with the prediction and therefore confirm the validity of the analysis.\r\n\r\nPart II:\r\n\r\nThe small-signal behavior of converters in discontinuous conduction mode (DCM) is investigated using an alternative approach. Transfer functions obtained by state-space\r\naveraging in DCM do not provide accurate results at higher frequencies. A correction term is introduced that can be added to the transfer function. This greatly enhances the\r\naccuracy.\r\n\r\nFor converters operating in DCM, the state-space averaging method as originally introduced is relatively complicated if more than one element operates in discontinuous\r\nconduction mode. In this thesis, a standardized procedure is introduced to perform state-space averaging. Also, the complexity of this procedure does not increase as the\r\nnumber of discontinuous states increases.\r\n" }, { "name": "Shapiro, Benjamin", "degree": "PhD", "year": "1999", "title": "Passive control of flutter and forced response in bladed disks via mistuning", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272008-083040", "creators": [ { "name": { "family": "Shapiro", "given": "Benjamin" }, "id": "Shapiro-B", "display_name": "Shapiro, Benjamin" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "cds" ], "doi": "10.7907/1xae-bn33", "abstract": "Mistuning or blade to blade variation in jet-engine bladed-disks can lead to large changes in engine performance. Even the small random mistuning associated with manufacturing tolerances can significantly change both stability boundaries and forced response. This thesis addresses two questions. Analysis: given any mistuning (random or intentional), what is the resulting change in performance? And passive control: can intentional mistuning be used to improve stability and forced response in a robust manner? \n\nA general framework based on symmetry arguments and eigenvalue/vector perturbations is presented to answer both questions. Symmetry constrains all facets of mistuning behaviour and provides simplifications for both the analysis and control problems. This is combined with the eigenvalue/vector perturbation which captures the nonlinear mistuning dependence and solves the analysis problem. It is shown that intentional mistuning can provide robust damping and so guarantee improved stability and forced response under fixed manufacturing tolerances. Results are demonstrated on a high-fidelity low-order model derived from computational-fluid-dynamic data." }, { "name": "Shariff, Shaun", "degree": "PhD", "year": "1999", "title": "Numerical simulation of viscous reacting hypersonic flow past cones", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212008-155520", "creators": [ { "name": { "family": "Shariff", "given": "Shaun" }, "id": "Shariff-S", "display_name": "Shariff, Shaun" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D6TR-5Z18", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nThe stepback and partial grid techniques were used in the numerical simulation of laminar viscous reacting flows past cones at incidence. The stepback technique is a method for computing exactly flows which are truly conical, and can be an effective approximate method for nearly conical flows such as viscous flow past cones. The partial grid technique uses a stepback solution as the upstream boundary condition for a time-marching calculation, and is more accurate than the stepback method. Both frozen and chemically active equilibrium flow were considered, using the Ideal Dissociating Gas model. Computations were performed for frozen hypersonic flow past a 10[...] half-angle cone inclined at 24[...] incidence, and for hypervelocity flow past a 15[...] half-angle cone at 30[...] incidence with active dissociation and recombination chemistry. These computations were compared with experiments, and the effects of equilibrium and non-equilibrium chemistry were observed. These calculations also show that the effects of chemistry on heat transfer and separation location are small and of the same order as the errors associated with the stepback method. Therefore, for high accuracy in computing reacting flows, the partial grid method should be used.\r\n" }, { "name": "Shu, Yi-Chung", "degree": "PhD", "year": "1999", "title": "Shape-Memory Effect in Bulk and Thin-Film Polycrystals", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212008-114547", "creators": [ { "name": { "family": "Shu", "given": "Yi-Chung" }, "id": "Shu-Yi-Chung", "display_name": "Shu, Yi-Chung" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Bruno", "given": "Oscar P." }, "id": "Bruno-O-P", "orcid": "0000-0001-8369-3014", "role": "member", "display_name": "Bruno, Oscar P." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/4NW5-3Q89", "abstract": "Shape-memory effect (SME) is a phenomenon where deformation suffered below a critical temperature can be recovered on heating. About 20-30 alloys are known to exhibit SME in single crystals. However, the degree to which they retain their shape-memory behavior in polycrystals is widely varied. In particular, Ti-Ni and Cu-Zn-Al undergo cubic to monoclinic transformation and recover similar strains as single crystals; yet, the observed shape-memory behavior in the former is much better than that in the latter. We develop a model based on energy minimization to understand this difference. Using this model, we establish that texture is the very important reason why the strains recoverable in Ti-Ni are so much larger than those in Cu-based shape-memory alloys in rolled, extruded and drawn specimens. We find that even the qualitative behavior of combined tension-torsion can critically depend on the texture. The results are in good agreement with experimental observations.\r\n\r\nWe extend our analysis to the behavior of very thin films with three competing length scales: the film thickness, the length scales of heterogeneity and material microstructure. We start with three-dimensional nonhomogeneous nonlinear elasticity enhanced with an interfacial energy of the van der Waals type, and derive the effective energy density as all length scales tend to zero with given limiting ratios. We do not require any priori selection of asymptotic expansion or ansatz in deriving our results. Depending on the dominating length scale, the effective energy density can be identified by three procedures: averaging, homogenization and thin-film limit. We apply our theory to martensitic thin films and use a model example to show that the shape-memory behavior can crucially depend on the relative magnitudes of these length scales. Using this theory, we show that sputtering textures in both Ti-Ni and Cu-based shape-memory thin films are not favorable for large recoverable strain. We comment on multilayers made of shape-memory and elastic materials.\r\n\r\nFinally, we suggest textures for improved SME in bulk and thin-film polycrystals." }, { "name": "Slatkin, Andrew Brett", "degree": "PhD", "year": "1999", "title": "Modeling and Experiments for a Class of Robotic Endoscopes", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-10112006-154843", "creators": [ { "name": { "family": "Slatkin", "given": "Andrew Brett" }, "id": "Slatkin-Andrew-Brett", "display_name": "Slatkin, Andrew Brett" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Grundfest", "given": "W." }, "id": "Grundfest-W", "role": "member", "display_name": "Grundfest, W." } ], "option_major": [ "mecheng" ], "doi": "10.7907/NG6V-TD44", "abstract": "Current developments in minimally invasive medical practice motivated this study of self-propelled, robotic endoscopes for deep penetration into curved physiological lumens. The conceptual design of such devices is applicable to endoscopy within a variety of lumens in the human body, e.g., blood vessels, but the initial objective of this technology is to provide access to the interior of the entire small intestine without surgical incisions. The small intestine presents several challenges to endoscopic penetration: it is extremely compliant to applied loading, internally lubricated, easily injured, and contains many tight curves along its length of approximately eighteen feet.
\r\n\r\nThis thesis reports the basic design and locomotion concepts for one class of endoscopic robots that are intended to provide safe and reliable traversal of the small intestine via worm-like actuation. Five generations of proof-of-concept prototype robots have been built to validate the fundamental concepts. Furthermore, these miniaturized robots have incorporated the following features: redundant actuation with computer control, tool-free modular assembly, and on-board videoimaging capability. The prototypes have been tested in rubber tubing, the small intestines of deceased pigs, and in the small intestines of live, anaesthetized pigs.
\r\n\r\nAt the onset of this research, little regarding the elastic properties of small intestine existed in the biomechanics literature that would be applicable to the design of these mechanisms. However, accurate prediction of the small intestine's response to robotic loadings would dramatically improve the research and development process of these machines. Thus, an investigation of the elastic behavior of the small intestine commenced. Finite deformation, nonlinear, anisotropic, incompressible, viscoelastic behavior of the small intestine was studied. This soft tissue biomechanical analysis and experimentation (on living and dissected intestinal specimens) culminated with a numerical model that simulates intestinal response to the actions of a prototypical robotic component. Experiments on living specimens were performed to determine the levels of applied loadings and internal stresses that are likely to injure these fragile tissues, and the biomechanics computer modeling incorporates three distinct measures for injury potential.
" }, { "name": "Song, Xubo", "degree": "PhD", "year": "1999", "title": "Contextual pattern recognition with applications to biomedical image identification", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222005-111015", "creators": [ { "name": { "family": "Song", "given": "Xubo" }, "id": "Song-Xubo", "display_name": "Song, Xubo" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Kasdan", "given": "Harvey L." }, "id": "Kasdan-H-L", "role": "member", "display_name": "Kasdan, Harvey L." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "eleceng" ], "doi": "10.7907/F5YK-HM52", "abstract": "This thesis studies two rather distinct topics: one is the incorporation of contextual information in pattern recognition, with applications to biomedical image identification; and the other is the theoretical modeling of learning and generalization in the regime of machine learning.\r\n\r\nIn Part I of the thesis, we propose techniques to incorporate contextual information into object classification. In the real world there are cases where the identity of an object is ambiguous due to the noise in the measurements based on which the classification should be made. It is helpful to reduce the ambiguity by utilizing extra information referred to as context, which in our case is the identities of the accompanying objects. We investigate the incorporation of both full and partial context. Their error probabilities, in terms of both set-by-set error and element-by-element error, are established and compared to context-free approach. The computational cost is studied in detail for full context, partial context and context-free cases. The techniques are applied to toy problems as well as real world problems such as white blood cell image classification and microscopic urinalysis. It is demonstrated that superior classification performance is achieved by using context. In our particular application, it reduces overall classification error, as well as false positive and false negative diagnosis rates.\r\n\r\nIn Part II of the thesis, we propose a novel theoretical framework, called the Bin Model, for learning and generalization. Using the Bin Model, a closed form is derived for generalization that estimates the out-of-sample performance in terms of the in-sample performance. We address the problems of overfitting, and characterize conditions under which it does not appear. The effect of noise on generalization is studied, and the generalization of the Bin Model framework from classification problems to regression problems is discussed.\r\n" }, { "name": "Waniewski, Tricia Ann", "degree": "PhD", "year": "1999", "title": "Air entrainment by bow waves", "advisor": "Brennen, Christopher E.; Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-05012003-121103", "creators": [ { "name": { "family": "Waniewski", "given": "Tricia Ann" }, "id": "Waniewski-T-A", "display_name": "Waniewski, Tricia Ann" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "co-advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/JAY3-M016", "abstract": "Experimental studies of air entrainment by breaking waves are essential for advancing the understanding of these flows and creating valid models. The present study used three-dimensional simulations of a bow wave to examine its air entrainment process. The simulated waves were created by a deflecting plate mounted at an angle in a super-critical free surface flow. Since the air entrainment process is closely coupled with breaking wave dynamics, the present study included both air entrainment and free surface measurements.\n\nMeasurements of the free surface wave were obtained from the simulated bow waves at two scales, and also from the bow wave created a towed wedge model. Contact line and bow wave profile measurements for the different experiments were compared, demonstrating the similarity of the experimental simulations to the towed model experiments. The plunging wave jet shape was measured in the larger scale stationary model and towed model experiments and used to calculate the jet thickness, velocity, and impingement angle. The bow wave profile data from the towed model experiments were used to investigate the scaling on the plunging wave face, and their wavelength, frequency, and velocity were measured.\n\nThe primary mechanisms for air entrainment were the impact of the plunging wave jet and individual droplets in the splash region on the free surface. The air entrainment process was observed in the larger scale stationary model experiments, and the air bubbles were entrained in spatially periodic bubble clouds. Due to the shallow depth in these experiments, measurements of only the larger bubbles in the initial stages of air entrainment were obtained. An impedance based void fraction meter, developed specifically for the purpose, was used to measure the void fractions and bubble size distributions beneath the wave. The bubble cloud size and void fraction increased with downstream distance.\n\nThere were indications that the surface disturbances control the periodicity of the bubble clouds. Namely, the surface disturbances divide the plunging liquid jet sheet into a series of plunging wave jets, each entraining air into a separate bubble cloud beneath the free surface.\n" }, { "name": "Winfree, Nancy A.", "degree": "PhD", "year": "1999", "title": "Impact-Induced Phase Transformations in Elastic Solids: A Continuum Study Including Numerical Simulations for GeO\u2082", "advisor": "Knowles, James K.; Ahrens, Thomas J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02262008-153435", "creators": [ { "name": { "family": "Winfree", "given": "Nancy A." }, "id": "Winfree-Nancy-A", "display_name": "Winfree, Nancy A." } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "co-advisor", "display_name": "Ahrens, Thomas J." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "member", "display_name": "Ahrens, Thomas J." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/4dhf-fj83", "abstract": "This thesis applies recently developed continuum theories of diffusionless phase transformations in solids to the study of impact problems involving materials which can experience such phase changes. Our objective is to compare the theoretical predictions against certain experimental results.
\r\n\r\nIn the experiments of interest, a face-to-face impact occurs between a disk of amorphous germanium dioxide and another material, either tungsten or an aluminum alloy. The GeO\u2082 is believed to transform to another phase if sufficient compressive stress is achieved.
\r\n\r\nWe model these experiments using one-dimensional finite elasticity. Phase-changing materials are represented by non-convex potential energy functions. This can produce phase boundaries that propagate subsonically or supersonically with respect to the slower longitudinal wave speed of the two phases. When a subsonic phase boundary is possible, it is not uniquely determined by the fundamental field equations and jump conditions. Uniqueness is obtained by invoking a nucleation criterion to control the initiation of the new phase, and a kinetic relation to govern its evolution.
\r\n\r\nThe experiments considered here are sufficiently long in duration (\u2248 3 \u00b5s) that several reflections and wave interactions occur, and the analysis becomes analytically intractable. Accordingly, a finite-difference method of Godunov type is employed to analyze these experiments numerically. Methods of Godunov type treat adjoining discretized spatial elements as the two sides of a Riemann problem, which is typically solved approximately by linearizing around the initial conditions on each side. Fortuitously, all constitutive models employed in this thesis are such that the required Riemann problems can be solved exactly without too much effort.
\r\n\r\nSimulations utilizing the numerical method demonstrate that the impact response of a material is sensitive to the kinetic relation that enters the model. It appears the theory may offer a plausible description of the experiments, though the restrictions placed on the constitutive models herein seem too severe to provide a good quantitative match to the experimental results.
" }, { "name": "Wright, John A.", "degree": "PhD", "year": "1999", "title": "Through-wafer 3-D micromachining and its applications for neural interfaces and microrelays", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092006-110012", "creators": [ { "name": { "family": "Wright", "given": "John A." }, "id": "Wright-J-A", "display_name": "Wright, John A." } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/g4sj-2q41", "abstract": "The relatively new field of Micro Electro Mechanical Systems (MEMS) is proving to be a very powerful technology capable of producing devices beneficial to a wide range of disciplines. Instruments once impossible to fabricate can now made with relative ease opening up new possibilities in experimental research as well as commercial applications. Through-wafer, 3-D micromachining techniques used to produce two families of such devices are presented.\r\n\r\nA functional silicon micromachined device that permits non-invasive, bi-directional, highly specific communication with cultured mammalian neurons is discussed. The mechanical and electrical nature of the system is reported and experimental data presented. In arriving at the present design, an iterative approach was used to create a structure that allows normal growth of neurons and permits the formation of functional neural networks while preventing cell body escape.\r\n\r\nThe set of low-temperature (< 400\u00b0C) fabrication steps that have been used to develop two types of magnetically actuated MEMS relays are presented. Designed to be potentially compatible with CMOS substrates, the fabrication uses thick electroplated metal films (> 10 \u00b5m) including Au, Cu and Ni80Fe20, and insulating material deposited at low temperatures. Millinewton force, variable-reluctance actuators have been realized with this technology and used as the basis of a miniature electromagnetic relay. Prototypes utilize > 5 \u00b5m contact gaps and produce 200 \u00b5N of force with a coil power of only 320 mW. Initial electrical tests show contact resistances of less than 1\u00b0. For a second application, magnetostatic relays have been designed to commutate miniature DC brushless motors. Large contact closure forces (> 5 mN) are generated to produce contact resistance of less than 35 milliohms. Commutation of a three-phase, four-pole DC brushless motor by three of the MEMS relays has been successfully demonstrated.\r\n" }, { "name": "Xu, Lihao", "degree": "PhD", "year": "1999", "title": "Highly available distributed storage systems", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-05162005-084223", "creators": [ { "name": { "family": "Xu", "given": "Lihao" }, "id": "Xu-Lihao", "display_name": "Xu, Lihao" } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "van Tilborg", "given": "Henk C.A." }, "id": "van-Tilborg-H-C-A", "role": "member", "display_name": "van Tilborg, Henk C.A." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/EQK9-8C84", "abstract": "As the need for data explodes with the passage of time and the increase of computing power, data storage becomes more and more important. Distributed storage, as distributed computing before it, is coming of age as a good solution to make systems highly available, i.e., highly scalable, reliable and efficient. The focus of this thesis is how to achieve data reliability and efficiency in distributed storage systems. This thesis consists of two parts. The first part deals with the reliability of distributed storage systems. Reliability is achieved by computationally efficient MDS array codes that eliminate single points of failure in the systems, thus providing more reliability and flexibility to the systems. Such codes can be used as general MDS error-correcting codes. They are particularly suitable for use in distributed storage systems. The second part deals with the efficiency of distributed storage systems. Methods are proposed to improve the performance of data server and storage systems significantly through the proper use of data redundancy. These methods are based on error-correcting codes, particularly the MDS array codes developed in the first part.\r\n\r\nTwo new classes of MDS array codes are presented: the X-Code and the B-Code. The encoding operations of both codes are optimal, i.e., their update complexity achieves the theoretical lower bound. They distribute parity bits over all columns rather than concentrating them on some parity columns. As with other array codes, the error model for both codes is that errors or erasures are columns of the array, i.e., if at least one bit of a column is an error or erasure, then the whole column is considered to be an error or erasure. Both codes are of distance 3, i.e., they can either: correct two erasures, detect two errors or correct one error. In addition to encoding algorithms, efficient decoding algorithms are proposed, both for erasure-correcting and for error-correcting. In fact, the erasure-correcting algorithms are also optimal in terms of computation complexity.\r\n\r\nThe X-Code has a very simple geometrical structure: the parity bits are constructed along two groups of parallel parity lines of slopes 1 and -1. This is the origin of the name X-Code. This simple geometrical structure allows simple erasure-decoding and error-decoding algorithms, using only XORs and vector cyclic-shift operations.\r\n\r\nThe significance of the B-code not only includes all its optimality properties: MDS, optimal encoding and optimal decoding, but also its relation with a 3-decade old graph theory problem. It is proven in this thesis that constructing a B-Code of odd length is exactly equivalent to constructing a perfect one-factorization (or P1F) of a complete graph. Constructing a P1F of an arbitrary complete graph has remained a conjecture since the early 1960's. Though the P1F conjecture remains unsolved, the B-code as the first real application of the P1F problem will hopefully spur more research on it. It is also conjectured in this thesis that constructing a B-Code of any length, even or odd, is equivalent to constructing a P1F of a complete graph. An efficient error-correcting algorithm for the B-Code is also presented, which is based on the relations between the B-Code and its dual. The algorithm might give a hint of how to develop efficient decoding algorithms for other codes.\r\n\r\nWhile it is intuitive that redundancy can bring reliability to a system, this thesis gives another direction: using redundancy actively to improve performance (efficiency) of distributed data systems. The results in this direction are both theoretical and experimental. System models are extracted from experiments in real practical systems; analytical results are derived using these and are then fed back to experiments for verification.\r\n\r\nIn this thesis, a novel deterministic voting scheme that uses error-correcting codes is proposed. The voting scheme generalizes all known simple deterministic voting algorithms. It can be tuned to various application environments with different error rates to drastically reduce average communication complexity, i.e., the amount of information that must be transmitted in order to get correct voting results.\r\n\r\nTwo problems are identified to improve the performance of general data server systems, namely the data distribution problem and the data acquisition problem. Solutions to these are proposed, as are general analytical results on performance of (n, k) systems. A simple service time model of a practical disk-based distributed server system is given. This model, which is based on experimental results, is a starting point for data distribution and data acquisition schemes. These results, both experimental and analytical, can be further used for more sophisticated scheduling schemes to optimize or improve the performance of data server systems that serve multiple clients simultaneously.\r\n\r\nFinally, some research problems related to storage systems are proposed as future directions." }, { "name": "Xu, Meina", "degree": "PhD", "year": "1999", "title": "Iterative decoding and graphical code representations", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02262008-093428", "creators": [ { "name": { "family": "Xu", "given": "Meina" }, "id": "Xu-Meina", "display_name": "Xu, Meina" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Kaleh", "given": "Ghassan Kawas" }, "id": "Kaleh-G-K", "role": "member", "display_name": "Kaleh, Ghassan Kawas" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Tanner", "given": "Michael" }, "id": "Tanner-M", "role": "member", "display_name": "Tanner, Michael" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/q731-9q50", "abstract": "Since the invention of turbo codes, there has been an explosion of interest in iterative decoding and graphical representation of codes. This thesis examines the iterative decoding of codes defined on graphs with cycles, which appears to be an efficient means of achieving the Shannon limit. Much of this analysis is on the iterative min-sum decoding of tail-biting codes and cycle codes. We have identified the pseudocodeword as the cause of the suboptimal performance of the iterative decoder, and we have obtained a union bound for the performance of the iterative decoder on both AWGN and BSC channels. Using the union bound argument, for cycle codes, we have shown that the performance of the iterative decoder is asymptotically as good as that of the ML decoder. As for tail-biting codes, the same thing is true if the lowest weight pseudocodeword is at least the minimum weight of the code. Unfortunately, the analysis of tail-biting codes and cycle codes does not extend to turbo codes and low density parity check codes in general. Our next approach is to determine the average behavior of message passing algorithms by studying the evolution of their \"message\" densities. For the class of \"repeat and accumulate\" serially concatenated turbo-like codes, we have devised an algorithm for determining their \"threshold\" values. When the signal-to-noise ratio is larger than the threshold value, the error probabilities of message passing algorithms approach zero, whereas if the signal-to-noise ratio is less than the threshold value, the error probability stays bounded away from zero. Some message passing algorithms and graphical representation of codes are efficient means of devising ML or MAP decoding algorithms. We have proposed a junction tree representation for linear block codes, and we have shown that the minimum junction tree can be less complex than the minimal trellis." }, { "name": "Yang, Xing", "degree": "PhD", "year": "1999", "title": "Micromachined Silicone Rubber Membrane Valves for Fluidic applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-02262008-140740", "creators": [ { "name": { "family": "Yang", "given": "Xing" }, "id": "Yang-Xing", "display_name": "Yang, Xing" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/k8hw-ph10", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe goal of this thesis is to develop high flow rate, low power consumption valves for micromachined fluid handling systems. It has been identified that large actuation deflection and force are the key. In this thesis, several technologies have been developed to achieve large deflection in micromechanical structures.\r\n\r\nFirst, a surface micromachined multi-layer structure, microbellows, has been successfully developed. With polysilicon as the sacrificial layer, the structure of the microbellows has been optimized to achieve large deflection and high strength. It has been shown that the microbellow can deliver more than three times the deflection of a flat membrane of the same size. Thermopneumatic actuators using the microbellows have been demonstrated.\r\n\r\nSecond, silicone rubber has been explored as the valve membrane material. Several methods for fabricating silicone membranes and integrating them with micromachined components to make actuators and valves have been developed. The silicone has been characterized and has been found to have many desirable properties including high elongation, low modulus, and good sealing. A thermopneumatically actuated valve has been successfully demonstrated.\r\n\r\nThird, a normally open, low power thermopneumatic MEMS valve utilizing a composite silicone/Parylene membrane has been developed. A novel suspended silicon nitride membrane heater has been developed to reduce heat loss. By using a \"soft\" membrane with a large gap and thermopneumatic actuation, high flow rates are achievable while still keeping power consumption low. The steady state and transient response of the thermopneumatic action with various working liquids have been studied. Valves with various constructions have been tested extensively with nitrogen and water flow. As low as 35.5 mW of power is sufficient to control a nitrogen flow of 1.04 1pm with an inlet pressure of 32 psi.\r\n\r\nAlso, to prevent particles from clogging the microfluidic system, membrane filters (8 x 8 mm[...]) with various shapes of filtering holes have been developed. By varying hole dimensions from 6 to 12 [...], opening factors from 4% to 45% are achieved. A composite silicon nitride/Parylene membrane technology is developed to enhance filter strength. Fluid dynamic performance of the filters has been studied extensively through experiments and numerical simulations." }, { "name": "Yeung, Chung-hei (Simon)", "degree": "PhD", "year": "1999", "title": "Nonlinear control of rotating stall and surge with axisymmetric bleed and air injection on axial flow compressors", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272008-083453", "creators": [ { "name": { "family": "Yeung", "given": "Chung-hei (Simon)" }, "id": "Yeung-C-S", "display_name": "Yeung, Chung-hei (Simon)" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "chemeng" ], "doi": "10.7907/1wef-gp10", "abstract": "The study of compressor instabilities in gas turbine engines has received much attention in recent ears. In particular, rotating stall and surge are major causes of problems ranging from component stress and lifespan reduction to engine explosion. In this thesis, modeling and control of rotating stall and surge using bleed valve and air injection is studied and validated on a low speed, single stage, axial compressor at Caltech.\n\nBleed valve control of stall is achieved only when the compressor characteristic is actuated, due to the fast growth rate of the stall cell compared to the rate limit of the valve. Furthermore, experimental results show that the actuator rate requirement for stall control is reduced by a factor of fourteen via compressor characteristic actuation. Analytical expressions based on low order models (2-3 states) and a high fidelity simulation (37 states) tool are developed to estimate the minimum rate requirement of a bleed valve for control of stall. A comparison of the tools to experiments show a good qualitative agreement, with increasing quantitative accuracy as the complexity of the underlying model increases.\n\nAir injection control of stall and surge is also investigated. Simultaneous control of stall and surge is achieved using axisymmetric air injection. Three cases with different injector back pressure are studied. Surge control via binary air injection is achieved in all three cases. Simultaneous stall and surge control is achieved for two of the cases, but is not achieved for the lowest authority case. This is consistent with previous results for control of stall with axisymmetric air injection without a plenum attached.\n\nNon\u2014axisymmetric air injection control of stall and surge is also studied. Three existing control algorithms found in literature are modeled and analyzed. A three\u2014state model is obtained for each algorithm. For two cases, conditions for linear stability and bifurcation criticality on control of rotating stall are derived and expressed in terms of implementation\u2014oriented variables such as number of injectors. For the third case, bifurcation criticality conditions are not obtained due to complexity, though linear stability property is derived. A theoretical comparison between the three algorithms is made, via the use of low\u2014order models, to investigate pros and cons of the algorithms in the context of operability.\n\nThe effects of static distortion on the compressor facility at Caltech is characterized experimentally. Results consistent with literature are obtained. Simulations via a high fidelity model (34 states) are also performed and show good qualitative as well as quantitative agreement to experiments. A non\u2014axisymmetric pulsed air injection controller for stall is shown to be robust to static distortion." }, { "name": "Alouini, Mohamed-Slim", "degree": "PhD", "year": "1998", "title": "Adaptive and Diversity Techniques for Wireless Digital Communications Over Fading Channels", "advisor": "Goldsmith, Andrea Jo; Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102004-143535", "creators": [ { "name": { "family": "Alouini", "given": "Mohamed-Slim" }, "id": "Alouini-Mohamed-Slim", "display_name": "Alouini, Mohamed-Slim" } ], "advisors": [ { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "orcid": "0000-0001-5686-800X", "role": "advisor", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "co-advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "orcid": "0000-0001-5686-800X", "role": "chair", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "orcid": "0000-0001-9176-3078", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "orcid": "0000-0003-3757-0675", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/SDZ9-8G93", "abstract": "Demand for mobile and personal communications is growing at a rapid pace, both in terms of the number of potential users and the introduction of new high-speed services. Meeting this demand is challenging since wireless communications are subject to three major constraints: a complex and harsh fading channel, a scarce usable radio spectrum, and limitations on the power and size of handheld terminals. Therefore, effective spectral and power efficient fading mitigation techniques are required. In this thesis we discuss two particular techniques to overcome fading: diversity combining and adaptive transmission. We first present a new approach for the performance evaluation of digital communications over fading channels. This approach, which is based on alternate representations of classic functions arising in the error probability analysis such as the Gaussian Q-function and the Marcum Q-function, leads to a unified analytical framework to determine the exact error rate of digital communications with multichannel reception. The unified approach gives new analytical expressions for average bit error rate under very general channel conditions, in addition to simplifying previously-known results both analytically and computationally. We next present methods of adapting to random channel variations in order to increase the spectral efficiency of wireless systems. As a first step we determine the theoretical spectral efficiency limits of wireless communication systems subject to the underlying severe multipath fading. We then propose an adaptive M-QAM modulation technique and analyze its performance over Nakagami-[...] fading channels. We also propose an adaptive modulation technique which combines voice and data, and study its performance. Finally, we consider adaptive modulation in cellular systems, and compute the resulting area spectral efficiency, defined as the maximum bit/sec/Hz/Km\u00b2, which can be supported in the system." }, { "name": "Bachman, David Alan", "degree": "PhD", "year": "1998", "title": "Nonlinear Phenomena in a Pure Electron Plasma Studied with a 2-D Fluid Code", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232008-081243", "creators": [ { "name": { "family": "Bachman", "given": "David Alan" }, "id": "Bachman-David-Alan", "display_name": "Bachman, David Alan" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "chair", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/72z8-gm50", "abstract": "This thesis presents a new computational tool for studying cylindrical pure electron plasmas. Previous research used linear methods to describe the evolution of small plasma perturbations. This new tool numerically solves the nonlinear two- dimensional (2-D) fluid equations in cylindrical coordinates, allowing the exploration of many phenomena that have been observed experimentally in these plasmas. Most experimentally observed phenomena are large in amplitude and follow nonlinear dynamics. Clearly, codes based on the linearized equations can not reproduce these nonlinear phenomena.\r\n\r\nThe plasma was first studied for small amplitude perturbations using the nonlinear fluid code, producing results that agree with linearized calculations. The perturbed electric field decays in time, due to shear in the flow of density perturbations at different radii, which results in the total contribution to the perturbed electric field phase mixing away.\r\n\r\nAt higher amplitudes, the decay envelope becomes modulated, which is a result that has been observed experimentally and is also reproduced by this fluid code. The modulation is caused by nonlinear trapping of fluid elements within the wave, which is illustrated in images of the perturbed density.\r\n\r\nFor two applied pulses separated in time, a third echo response is observed after the responses to the two applied pulses have decayed away. Echoes have been observed experimentally in neutral plasmas, but have not yet been observed experimentally in non-neutral plasmas.\r\n\r\nAt very high amplitudes, a nonlinear decay instability occurs. A high amplitude wave decays into a wave with lower azimuthal symmetry number due to an interaction occurring at the beat frequency between the two waves. The beat-wave decay instability has been observed experimentally, and is also observed using the 2-D nonlinear fluid code.\r\n\r\nThe 2-D cylindrical nonlinear fluid code is capable of reproducing a wide range of non-neutral plasma phenomena, and is an important new tool for future research on non-neutral plasmas. This research is also relevant to ordinary fluids, since the equations describing a non-neutral plasma are analogous to the 2-D Euler equations for an inviscid fluid." }, { "name": "Barbastathis, George", "degree": "PhD", "year": "1998", "title": "Intelligent holographic databases", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172008-142604", "creators": [ { "name": { "family": "Barbastathis", "given": "George" }, "id": "Barbastathis-George", "display_name": "Barbastathis, George" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/1R63-9H50", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nMemory is a key component of intelligence. In the human brain, physical structure and functionality jointly provide diverse memory modalities at multiple time scales. How could we engineer artificial memories with similar faculties? In this thesis, we attack both hardware and algorithmic aspects of this problem.\r\n\r\nA good part is devoted to holographic memory architectures, because they meet high capacity and parallelism requirements. We develop and fully characterize shift multiplexing, a novel storage method that simplifies disk head design for holographic disks. We develop and optimize the design of compact refreshable holographic random access memories, showing several ways that 1 Tbit can be stored holographically in volume less than 1 [...], with surface density more than 20 times higher than conventional silicon DRAM integrated circuits. To address the issue of photorefractive volatility, we further develop the two-lambda (dual wavelength) method for shift multiplexing, and combine electrical fixing with angle multiplexing to demonstrate 1,000 multiplexed fixed holograms. Finally, we propose a noise model and an information theoretic metric to optimize the imaging system of a holographic memory, in terms of storage density and error rate.\r\n\r\nMotivated by the problem of interfacing sensors and memories to a complex system with limited computational resources, we construct a computer game of Desert Survival, built as a high-dimensional non-stationary virtual environment in a competitive setting. The efficacy of episodic learning, implemented as a reinforced Nearest Neighbor scheme, and the probability of winning against a control opponent improve significantly by concentrating the algorithmic effort to the virtual desert neighborhood that emerges as most significant at any time. The generalized computational model combines the autonomous neural network and von Neumann paradigms through a compact, dynamic central representation, which contains the most salient features of the sensory inputs, fused with relevant recollections, reminiscent of the hypothesized cognitive function of awareness. The Declarative Memory is searched both by content and address, suggesting a holographic implementation. The proposed computer architecture may lead to a novel paradigm that solves \"hard\" cognitive problems at low cost.\r\n" }, { "name": "Blackwell, Veronica R.", "degree": "PhD", "year": "1998", "title": "Formation processes of clathrate hydrates of carbon dioxide and methane", "advisor": "Morgan, James J.; North, Wheeler J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232008-100246", "creators": [ { "name": { "family": "Blackwell", "given": "Veronica R." }, "id": "Blackwell-V-R", "display_name": "Blackwell, Veronica R." } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." }, { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "advisor", "display_name": "North, Wheeler J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/XR79-CF85", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis explores the formation kinetics and mechanisms of clathrate hydrates of carbon dioxide and methane, focusing on the nucleation and early growth of hydrates. Homogenous and heterogeneous systems were studied. The catalysis of hydrate nucleation was accomplished by the addition of certain particles to the hydrate forming solution. Copper (II) oxide, calcium carbonate and some [...] and [...] aluminum oxide particles were found to be effective nucleators while a-iron oxide, magnesium hydroxide, silica and some other [...] and [...] aluminum oxide particles were found ineffective. The induction period for hydrate formation was reduced by as much as 85% with copper oxide particles. The important requisites of a nucleation catalyst included a satisfactory match between the crystal structure faces of ice and catalyst particle. The nature of the surface hydroxyl groups on the particle was also important. Particles nucleated hydrate by encouraging hydrogen bonding between the surface hydroxyl groups on the particles and water molecules near the surface, forming a layer of structured water. These structures then built up into clathrate cages when stabilized by guest molecules. Methane hydrate only formed at the interface between gas and water, because only there were there enough methane molecules to stabilize the structures. Carbon dioxide hydrate formed in the bulk solution because the higher solubility of carbon dioxide in water ensures enough carbon dioxide molecules to stabilize cages and allow them to grow into full hydrate structures.\r\n" }, { "name": "Bohossian, Vasken Z.", "degree": "PhD", "year": "1998", "title": "Neural logic : theory and implementation", "advisor": "Bruck, Jehoshua", "url": "https://resolver.caltech.edu/CaltechETD:etd-05132005-143440", "creators": [ { "name": { "family": "Bohossian", "given": "Vasken Z." }, "id": "Bohossian-Vasken-Z", "display_name": "Bohossian, Vasken Z." } ], "advisors": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "advisor", "display_name": "Bruck, Jehoshua" } ], "committee": [ { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "chair", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "cns" ], "doi": "10.7907/N0T5-7J92", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nHuman brains are by far superior to computers in solving hard problems like combinatorial optimization and image and speech recognition, although their basic building blocks are several orders of magnitude slower. This observation has boosted interest in the field of artificial networks [20], [37]. The latter are built by interconnecting artificial neurons whose behavior is inspired by that of biological neurons. In this thesis we consider the Boolean version of an artificial neuron, namely, a Linear Threshold (LT) element, which computes a neural-like Boolean function of n binary inputs [32]. An LT element outputs the sign of a weighted sum of its Boolean inputs. The main issues in the study of networks (circuits) consisting of LT elements, called LT circuits, include the estimation of their computational capabilities and limitations and the comparison of their properties with those of traditional Boolean logic circuits based on AND, OR and NOT gates (called AON circuits). For example, there is a strong evidence that LT circuits are more efficient than AON circuits in implementing a number of important functions including the addition, product and division of integers [44], [45].\r\n\r\nIt is easy to see that an LT element is more powerful than an AON gate, simply because of the freedom one has in selecting the weights. Indeed, different choices of weights produce different Boolean functions. As a matter of fact, the number of n-input Boolean functions that can be implemented by a single LT element is of the order of [\u2026], [42], [22]. That additional power comes at the cost of added complexity. Some LT functions require weights that are very different in magnitude, potentially rendering difficult hardware or software implementations of the corresponding LT elements. For that reason, theoretical research in the field of LT circuits has focused on the weights, in particular the power of LT elements with restricted weights. As early as 1971, Muroga, [32], proved that any linear threshold element can be implemented with integer weights. That is, by restricting the magnitudes of the weights to natural numbers, one does not lose any power of the original LT element. We generalize this result to arbitrary subsets of the set of real numbers. For example, we show that one can restrict the weights to be the square of integers, and still be able to realize all LT functions. We ask the following question. What are the conditions on the subset [\u2026] which guarantee that all LT functions can be implemented with weights drawn from it?\r\n\r\nAnother aspect of the complexity of the weights is their growth as the number of inputs increases. It has been shown [17], [33], [38], [43] that there exist linear threshold functions that can be implemented by a single threshold element with exponentially growing weights, but cannot be implemented by a threshold element with smaller polynomialy growing weights. In light of that result the above question was dealt with by defining a class, called [\u2026], within the set of linear threshold functions: the class of functions with \"small\" (i.e. polynomialy growing) weights [43]. We focus on a single LT element. Our contribution consists in two novel methods for constructing threshold functions with minimal weights, which allow us to fill up the gap between polynomial and exponential weight growth by further refining the separation. Namely, we prove that the class of linear threshold functions with polynomial-size weights can be divided into subclasses [\u2026], according to the degree, d, of the polynomial. In fact, we prove a more general result-\u2014that there exists a linear threshold function for any arbitrary number of inputs and any weight size.\r\n\r\nEven though some LT functions require weights that grow exponentially with the number of input variables, it has been shown recently, in [13], [18], that such functions can be replaced by a two-layer circuit composed of LT gates with polynomially growing, i.e., small weights. We improve the best known bound on the size of that circuit, presented in [18] by focusing on a particular function with large coefficients. We also derive explicit two-layer circuits. Two layer LT circuits are in general composed of different linear threshold elements, but for some useful Boolean functions, such as parity, addition and product, the gates of the first layer are almost identical. To take advantage of this fact we introduce a new Boolean computing element. Instead of the sign function, it computes an arbitrary (with polynomialy many transitions) Boolean function of the weighted sum of its inputs. We call the new computing element an LTM element, which stands for Linear Threshold with Multiple transitions. The advantages of LTM become apparent in the context of VLSI implementation. Indeed, this new model reduces the layout area of the corresponding symmetric function from [\u2026] to O(n). We present a VLSI implementations of both LT and LTM elements. Two kinds of elements were fabricated, programmable and hardwired. The programmable elements use the charge on a floating gate in order to store the values of the weights.\r\n\r\nFor many years, the topic of linear threshold logic, has been approached in two different ways, theory, i.e. computational circuit complexity, [38], [56], and hardware implementation, [48], [40]. Surprisingly, there has been very little interaction between those two approaches. As a whole, the present thesis is one step towards establishing a connection between the theory and implementation of threshold circuits. Its contributions are at three levels. At the theoretical level, new classes of functions such as [\u2026] and LTM are defined and their computational power is estimated. At the algorithmic level, we show how to convert real weights to weights drawn from arbitrary subset of the real numbers, e.g., integer weights, we also show how to construct LT functions with minimal weights, and finally we present an algorithm that produces an [\u2026] circuit (circuit composed of gates with small weights), that computes the comparison function, COMP. We also present LTM circuits computing useful functions, such as XOR, ADD, PRODUCT. At the implementation level, we show the design, layout and testing of the VLSI implementation of LT and LTM. Establishing a connection between the theoretical and practical aspects of threshold logic will profit both domains by providing solutions for practical problems and by defining new theoretical questions inspired by implementation issues.\r\n" }, { "name": "Camata, Renato Penha", "degree": "PhD", "year": "1998", "title": "Aerosol synthesis and characterization of silicon nanocrystals", "advisor": "Atwater, Harry Albert; Vahala, Kerry J.; Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01182008-131457", "creators": [ { "name": { "family": "Camata", "given": "Renato Penha" }, "id": "Camata-Renato-Penha", "display_name": "Camata, Renato Penha" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/n9df-zc75", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nSynthesis and processing of optically active silicon nanocrystals are explored from an aerosol science perspective.\r\n\r\nSpark ablation, laser ablation and thermal evaporation in inert atmospheres are employed alternatively as vapor phase sources of nanocrystals. Nanocrystals generated employing these techniques comprise a highly polydisperse and morphologically diverse aerosol. After collection on a solid substrate, samples of these nanocrystals exhibit wide-band visible photoluminescence. A system for size classification of the initial polydisperse nanocrystal aerosol is demonstrated employing differential mobility analysis. Working at low nanocrystal concentrations (around [...]) size control within 15% to 20% is achieved in the 2 to 10 nm size regime with a radial differential mobility analyzer at the expense, however, of low throughputs which make optical studies challenging.\r\n\r\nSeeking higher throughputs, the physics of aerosol size classification by this technique is investigated in detail by self-consistent numerical simulations of the particle transport inside the differential mobility analyzer. Our results lead to the identification of critical design characteristics required to maximize the analyzer performance from the viewpoint of semiconductor nanocrystal synthesis. With the guidance of these theoretical predictions, an optimized differential mobility analyzer design is suggested. This instrument has its parameters chosen to perform high resolution, high throughput size classification of nanocrystals in the 0.5 to 10 nm range.\r\n\r\nOptical characterization studies on polydisperse and size-classified silicon nanocrystal samples are performed. Results suggest that at least two mechanisms for light emission are at work in aerosol synthesized silicon nanocrystals.\r\n\r\nX-ray photoelectron measurements on size-classified silicon nanocrystals reveal that an oxide layer with thickness in excess of several nanometers forms on the silicon nanocrystals within a few minutes of air exposure. In order to preserve and control the surface chemistry of the nanocrystals, a system for anaerobic transfer of the size- classified silicon nanocrystals is designed and built. The system couples the nanocrystal synthesis experiment with the ultra high vacuum chamber of a surface analysis system via a load lock high vacuum chamber. Optical characterization capabilities are also installed. Preliminary results on nanocrystal synthesis and characterization using this in situ setup are presented and discussed.\r\n" }, { "name": "Cheng, Chuan-cheng", "degree": "PhD", "year": "1998", "title": "Nanofabrication and Characterization of Photonic Crystals", "advisor": "Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-01182008-132046", "creators": [ { "name": { "family": "Cheng", "given": "Chuan-cheng" }, "id": "Cheng-Chuan-cheng", "display_name": "Cheng, Chuan-cheng" } ], "advisors": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "chair", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/sjy2-r565", "abstract": "Both techniques and applications of nanofabrication have been explored in the field of periodic dielectric nanostructures. These periodic dielectric structures are expected to exhibit interesting properties in both fields of physics and engineering. These artificial nanostructures are named \"photonic crystals\" because photons demonstrate similar behavior in these structures as electrons in natural semiconductor crystals. In order to construct these crystals in the optical regime, suitable nanofabrication techniques have to be developed and demonstrated, including high resolution electron beam lithography and anisotropic chemically assisted ion beam etching. In this work, both 2D and 3D photonic crystals are fabricated and characterized in the near-infrared range.
\r\n\r\nIn the first part of this thesis, exploration of resolution limit of nanofabrication will be demonstrated and discussed. 15nm structures with 30nm period dot arrays and 20nm line width with 40mn period gratings are presented. Along with high resolution lithography, anisotropic pattern transfer is also developed. These powerful fabrication techniques enable us to miniaturize the dimension of both electronic and optical devices into the nanometer regime.
\r\n\r\nIn the second and third part of this thesis, detailed experiments and characterization of 2D and 3D photonic crystals are discussed. A brief introduction and a theoretical simulation are also presented. In the second part, computer generated form-birefringent nanostructures are first discussed and their performance demonstrated to agree well with design using rigorous coupled wave analysis (RCWA). In-plane 2D photonic crystals used as beam splitting micropolarizers are introduced and fabricated. High extinction ratios (>820:1) between transmitted TE and TM modes are measured. These in-plane photonic crystals are the first working devices using the idea of 2D photonic crystals. Three-dimensional artificial photonic crystals with a complete 3D bandgap represent a more attractive idea.
\r\n\r\nIn the third part of this thesis, we challenge the nanofabrication limits encountered when fabricating a 3D photonic crystal. The first three-dimensional photonic crystals with a forbidden photonic bandgap lying in the near infrared region of the electromagnetic spectrum, 1.1 \u03bcm < \u03bb < 1.5 \u03bc, just beyond the electronic band-edge of Gallium Arsenide (GaAs) are demonstrated in the world. These 3D photonic crystals were originally proposed by E. Yablonovitch and can now be fabricated using anisotropic angle etching at three directions through a hexagonal hole array mask. The field distribution using filtered finite-difference time-domain (FFDTD) calculation is briefly discussed. Development of the fabrication techniques and the optical transmission characterization are shown. Photonic crystals with up to six repeating layers are obtained and presented 90% attenuation of transmission measurement in the bandgap region. We also show the spectral shift in the transmission measurement corresponding with 2D lithographic control of microfabrication. Those artificial photonic crystals are expected to be useful in the study of inhibition of spontaneous emission and single-mode light-emitting diodes.
\r\n" }, { "name": "Conner, Robert Dale", "degree": "PhD", "year": "1998", "title": "Mechanical properties of bulk metallic glass matrix composites", "advisor": "Rosakis, Ares J.; Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282006-161438", "creators": [ { "name": { "family": "Conner", "given": "Robert Dale" }, "id": "Conner-R-D", "display_name": "Conner, Robert Dale" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/xvhx-px15", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis report discusses two aspects of research on bulk metallic glasses. The first is an effort to increase their toughness by combining them with reinforcement to form a composite. The second is the first direct measurement of plane strain fracture toughness of bulk metallic glass.\n\nParticulate and continuous fiber reinforced composite materials were fabricated using bulk metallic glass as the matrix. The particulate composites combined W, WC, SiC and Ta reinforcements in a matrix with the composition Zr57Nb5Al10Cu15.4Ni12.6. Continuous fiber composites were fabricated using W and 1080 carbon steel (music) wire reinforcement in a Zr41.25Ti13.75Cu12.5Ni10Be22.5 matrix. In both cases the metallic glass remained amorphous during processing.\n\nCompressive strain to failure was greatly enhanced in both particulate and continuous fiber composites by the formation of multiple shear bands. Tungsten reinforcement provided the greatest improvement. The tungsten is wet well by the metallic glass, and forms a strong interface.\n\nBoth particulate and fiber reinforced composite showed improved tensile properties. Energy (per unit volume) to break increased 52% for 5% Vf, 150 [...] W reinforced Zr57Nb5Al10Cu15.4Ni12.6 and 18% for 60% Vf music wire reinforced Zr41.25Ti13.75Cu12.5Ni10Be22.5. Tightly bonded ductile particles and weakly bonded continuous fibers proved best for enhancing the tensile properties of bulk metallic glass.\n\nFracture toughness of the unreinforced Zr41.25Ti13.75Cu12.5Ni10Be22.5 bulk metallic glass was determined using 3-point bend measurements and coherent gradient sensing (CGS). The measured fracture toughness is nominally 55 [...]. Once initiated, cracks in the unreinforced metallic glass propagated in an unstable manner. Continuous fiber reinforcement was demonstrated to arrest crack propagation in 3-point bend fracture tests of bulk metallic glass matrix composites." }, { "name": "Crowdy, Darren G.", "degree": "PhD", "year": "1998", "title": "Exact solutions for two-dimensional Stokes flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01182008-133427", "creators": [ { "name": { "family": "Crowdy", "given": "Darren G." }, "id": "Crowdy-D-G", "display_name": "Crowdy, Darren G." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/3jys-vr33", "abstract": "This thesis comprises three parts. The principal topic is presented in Part I and concerns the problem of the free-boundary evolution of two dimensional, slow, viscous (Stokes) fluid driven by capillarity. A new theory of exact solutions is presented using a novel global approach involving complex line integrals around the fluid boundaries. It is demonstrated how the consideration of appropriate sets of geometrical line integral quantities leads to a concise theoretical reformulation of the problem. All previously known results for simply-connected regions are retrieved and the analytical form of the exact solutions formally justified. For appropriate initial conditions, an infinite number of conserved quantities is identified. An important new general result (herein called the theorem of invariants) is also demonstrated.\n\nFurther, using the new theoretical reformulation, an extension to the case of doubly-connected fluid regions with surface tension is made. A large class of exact solutions for doubly-connected fluid regions is found. The method combines the new theoretical approach with elements of loxodromic function theory. To the best of the author's knowledge, this thesis provides the first known examples of exact solutions for Stokes flow in a doubly-connected topology. The theorem of invariants is extended to the doubly-connected case.\n\nFinally analytical arguments are presented to demonstrate the existence, in principle, of a class of exact solutions for geometrically symmetrical four-bubble configurations.\n\nIn Part II, the most general representation for local solutions to the two dimensional elliptic and hyperbolic Liouville equations is formally derived.\n\nIn Part III, some analytical observations are presented on solutions to the linearized equations for small disturbances to the axisymmetric Burgers vortex. The relevance to the (as yet unsolved and little studied) problem of the linear stability of Burgers vortex to axially-dependent perturbations is argued and discussed.\n" }, { "name": "Dandliker, Richard B.", "degree": "PhD", "year": "1998", "title": "Bulk metallic glass matrix composites : processing, microstructure, and application as a kinetic energy penetrator", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-01242008-074925", "creators": [ { "name": { "family": "Dandliker", "given": "Richard B." }, "id": "Dandliker-R-B", "display_name": "Dandliker, Richard B." } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/HTJS-N846", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe development of alloys with high glass forming ability allows fabrication of bulk samples of amorphous metal. This capability makes these materials available for applications which require significant material thickness in all three dimensions. Superior mechanical properties and advantages in processing make metallic glass a choice candidate as a matrix material for composites.\r\n\r\nThis study reports techniques for making composites by melt-infiltration casting using the alloy [...] ([...]) as a matrix material. Composite rods 5 cm in length and 7 mm in diameter were made and found to have a nearly fully amorphous matrix; there was less than 3 volume percent crystallized matrix material. The samples were reinforced by continuous metal wires, tungsten powder, or silicon carbide particulate preforms. The most easily processed samples were made with uniaxially aligned tungsten and carbon steel continuous wire reinforcement; the majority of the analysis presented is of these samples. The measured porosity was typically less than 3%. The results also indicate necessary guidelines for developing processing techniques for large scale production, new reinforcement materials, and other metallic glass compositions.\r\n\r\nAnalysis of the microstructure of the tungsten wire and steel wire reinforced composites was performed by x-ray diffraction, scanning electron microscopy, scanning Auger microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy. The most common phase in the crystallized matrix is most likely a Laves phase with the approximate formula [...]. In tungsten-reinforced composites, a crystalline reaction layer 240 nm thick of tungsten nanocrystals in anamorphous matrix formed. In the steel reinforced composites, the reaction layer was primarily composed of a mixed metal carbide, mainly [...].\r\n\r\nOne promising application of the metallic glass mat composite is as a kinetic energy penetrator material. Ballistic tests show that a composite of 80 volume percent uniaxially aligned tungsten wires and a [...] 1 matrix has self-sharpening behavior, which is a necessary characteristic of superior penetrator materials. Small-scale tests with both aluminum and steel targets show that this composite performs better than tungsten heavy alloys typically used for penetrator applications, and comparably with depleted uranium.\r\n" }, { "name": "Engin, Doruk", "degree": "PhD", "year": "1998", "title": "Nonlinear spatial dynamics of double phase conjugation in photorefractive crystals and holographic dynamics of photopolymerization", "advisor": "Yariv, Amnon; Cross, Michael Clifford", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232008-110449", "creators": [ { "name": { "family": "Engin", "given": "Doruk" }, "id": "Engin-D", "display_name": "Engin, Doruk" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "co-advisor", "display_name": "Cross, Michael Clifford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/78gp-sz41", "abstract": "This thesis explores spatial nonlinear optical effects in photorefractive crystals and photopolymers. In these materials upon exposure with spatially varying light, large refractive index changes occur. In the first part of the thesis Double Phase Conjugation in photorefractive crystals is studied both theoretically and experimentally. Various processes effecting the conjugation fidelity, such as fanning are quantified through a coupled multiple mode model which is an extension of the coupled mode theory. Predictions of the model such as phase conjugation is confirmed experimentally. Critical slowing down near the threshold is also predicted and experimentally confirmed. Lastly the amplitude equation formalism is carried out for the wave mixing phenomenon. This approach unifies the optical phenomenon with a large class of other physical phenomena referred to as pattern formation outside of equilibrium. Through this formalism the instability is identified as a convective instability and the possibility of a transition to absolute instability is studied.\n\nIn the second part of the thesis, photopolymerization dynamics is studied with holography. A theoretical model is developed for the holographic configuration starting from a standard chain polymerization model. A holographic characterization method is developed. The method is especially powerful in measuring diffusion constants. Various multifunctional polymers is characterized using the novel technique.\n" }, { "name": "Forman, Selena M.", "degree": "PhD", "year": "1998", "title": "The transport of nonlinearly adsorbing compounds between stream water and sediment bed in a laboratory flume", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02042008-085125", "creators": [ { "name": { "family": "Forman", "given": "Selena M." }, "id": "Forman-S-M", "display_name": "Forman, Selena M." } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/vj00-a140", "abstract": "The exchange of nonlinearly adsorbing compounds between stream water and sediment beds covered with stationary bedforms was investigated in laboratory experiments. The dominant physical exchange process is advective pumping caused by dynamic pressure variations over dunes on the bed. Observations of net mass exchange of cationic surfactants in a 5-meter long recirculating flume were used to validate the exchange model, which is based on the hydraulics of advective pumping and nonlinear adsorption isotherms derived from batch experiments.\n\nThe flume experiments were conducted under steady, uniform flow conditions. The pH and ionic strength of the flume water was controlled by adding sodium chloride and sodium bicarbonate to deionized water. The sand was washed prior to every experiment. The mass exchange of cationic surfactants and bromide was determined by measuring the depletion of these compounds in the overlying water column as it mixed with the clean porewater from the bed. Porewater concentration profiles were acquired to monitor the penetration depth of the compounds in the bed. Bromide was used as a conservative tracer to observe the hydraulics of water exchange between the bed and the overlying water. Garnet sand was used as the model sediment because it had heterogeneous properties similar to natural sediments.\n\nThe net mass exchange with a bed covered with stationary bedforms was greater than the exchange with a flat bed. The mass exchange of the cationic surfactants versus time observed in the flume experiments could not be modeled using linear adsorption; however, linear approximations provided upper and lower limits on the exchange. The total mass transfer of the cationic surfactants to the bed increased with their hydrocarbon chain lengths.\n\nThe model for the exchange of nonlinearly adsorbing compounds solves the advection equation to track the transport of the compounds within the bed and computes the net mass flux through the bed surface. Nonlinear adsorption was modeled by the means of four different isotherm equations fitted to the batch adsorption data. The effect of the choice of isotherm on the exchange models for the flume experiments was found to be very small. The model generally predicted the flume results well without calibration. Additional model simulations were performed to provide a sensitivity analysis for the model inputs.\n" }, { "name": "Frank, Timothy S.", "degree": "PhD", "year": "1998", "title": "Computing with spiking neurons", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-02042008-110206", "creators": [ { "name": { "family": "Frank", "given": "Timothy S." }, "id": "Frank-T-S", "display_name": "Frank, Timothy S." } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/vf21-gw62", "abstract": "This thesis explores methods for computing with spikes. A spiking neuron model (SNM) is developed, which uses relatively few variables. A neuron's state is completely determined by the amount of neurotransmitter at its input synapses and the time since it last produced a spike. A spike is treated as a discrete event, which triggers the release of neurotransmitter at the neuron's output synapses. Neurotransmitter affects the voltage potentials of postsynaptic neurons.\n\nThe SNM is able to duplicate many of the properties of biological neurons, including: latency, efractory periods, and oscillatory spiking behavior, thus indicating that it is sufficiently complex for duplicating many of the computations performed by real neurons. Although the inspiration for the SNM comes from biology, the purpose of this research is to develop better computational devices.\n\nSeveral single neuron building blocks are designed to perform useful functions, such as: a high gain response, a memory oscillator, a bounded threshold response, and an identity or inverse response. These single neuron building blocks are then used in larger networks to accomplish more complex tasks including: synchronizing input stimuli, recognizing spiking patterns, evaluating Boolean logic expressions, memorizing spike patterns, counting input spikes, multiplexing signals, comparing spike patterns, and recalling an associative memory.\n\nWhen using the SNM, there are several possible methods for encoding information within a spike train. With synchronous spike patterns, each spike can encode a single bit. The strength of an input stimulus may be retained within the output phase of a spike or logarithmically encoded in the neurotransmitter released at a synapse. And when two sensory neurons receive the same input signal, the time duration of the stimulus can be linearly encoded within their phase differences, while the strength of the input signal is logarithmically encoded in their firing rates.\n\nLearning may also be incorporated into an SNM network. A special feedforward network architecture is presented, in which each neuron has either an inhibitory or excitatory effect on all of the neurons to which it connects. A new learning rule is developed to train this network to respond to any combinations of input spike patterns.\n" }, { "name": "Frase, Heather N.", "degree": "PhD", "year": "1998", "title": "Vibrational and magnetic properties of mechanically attrited Ni3Fe nanocrystals", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232008-095308", "creators": [ { "name": { "family": "Frase", "given": "Heather N." }, "id": "Frase-H-N", "display_name": "Frase, Heather N." } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/7fy9-h825", "abstract": "The vibrational and magnetic properties of mechanically attrited nanocrystalline Ni3Fe powders were studied. The as-milled Ni3Fe powders were annealed to create nanocrystalline samples with different grain sizes, RMS strains, and grain boundary atomic structures. The average grain size and RMS strain of the samples were measured using x-ray diffractometry and transmission electron microscopy. From inelastic neutron scattering experiments, the phonon density of states (DOS) of various as-milled and annealed Ni3Fe nanocrystalline powders were determined. At low energies (<15 meV), nanocrystalline samples compared to bulk Ni3Fe showed an enhancement in the phonon DOS that was proportional to the density of grain boundaries in the powders. A broadening of features in the phonon DOS was also observed for the smallest nanocrystals. The room temperature phonon DOS of nanocrystals with an average grain size of 6 nm and a large grain boundary volume fraction of 20%, was different from the phonon DOS of the same powder after it had been exposed to 10 K. It is believed that upon exposure to 10 K the grain boundary local atomic structure changed affecting the vibrational properties of the sample.\n\nThe magnetic properties of nanocrystalline Ni3Fe were studied using Mossbauer spectroscopy, M-H magnetization curves, complex permeability measurements using microwave cavity perturbation technique, and small angle neutron scattering. M-H magnetization curves and cavity perturbation measurements showed that the coercivity and magnetic saturation are related to nanocrystal grain size and RMS strain while the complex permeability is intricately related to grain size and frequency. Both Mossbauer spectroscopy and small angle neutron scattering showed that the grain boundary magnetic moment density of as-milled Ni3Fe nancrystalline powder was smaller than that of powder annealed at low temperature. This indicates that local atomic structure in the grain boundary affects the magnetic moment density.\n" }, { "name": "Glavaski, Sonja", "degree": "PhD", "year": "1998", "title": "Robust system analysis and nonlinear system model reduction", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-08122005-094404", "creators": [ { "name": { "family": "Glavaski", "given": "Sonja" }, "id": "Glavaski-S", "display_name": "Glavaski, Sonja" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Tierno", "given": "Jorge E." }, "id": "Tierno-J-E", "role": "member", "display_name": "Tierno, Jorge E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/jh14-eg48", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe aim of the first part of this thesis is to broaden the classes of linear systems and performance measures that numerical tools for robustness analysis can be used for. First, we consider robustness problems involving uncertain real parameters and present several new approaches to computing an improved structured singular value [...] lower bound. We combine these algorithms to yield a substantially improved power algorithm.\n\nThen, we show that both the worst case [...] performance and the worst case [...] performance of uncertain systems subject to norm bounded structured LTI perturbations can be written exactly in terms of the skewed [...]. The algorithm for the structured singular value lower bound computation, can be extended to computing skewed [...] lower bound without significant loss of performance or accuracy.\n\nWe also demonstrate how a power algorithm can be used to compute a necessary condition for disturbance rejection of both discrete and continuous time nonlinear systems. For the general case of a system with a non-optimal controller this algorithm can provide us with knowledge of the worst case disturbance.\n\nIn the second part of this thesis we explore different approaches to the model reduction of systems. First, we show that the balancing transforma and Galerkin projection commute. We also demonstrate that if the balancing transformation matrix is orthogonal, balanced truncation and Galerkin projection commute.\n\nNext, we pursue model reduction of nonlinear systems with rotational symmetry. We separate the movement of the wave from the evolution of the wave shape using the \"centering procedure,\" and accurately approximate the shape of the wave with just few modes. The method may be viewed as a way of implementing the Karhunen-Loeve expansion on the space of solutions of the given PDE modulo a given symmetry group. The methodology is quite general and therefore should be useful in a variety of problems." }, { "name": "Goodwine, John William", "degree": "PhD", "year": "1998", "title": "Control of stratified systems with robotic applications", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232008-144001", "creators": [ { "name": { "family": "Goodwine", "given": "John William" }, "id": "Goodwine-J-W", "display_name": "Goodwine, John William" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/49h9-q898", "abstract": "Many interesting and important control systems evolve on stratified configuration spaces. Roughly speaking, a configuration manifold is called \"stratified\" if it contains subspaces (submanifolds) upon which the system had different equations of motion. Robotic systems, in particular, are of this nature. For example, a legged robot has discontinuous equations of motion near points in the configuration space where each of its \"feet\" comes into contact with the ground. In such a case, when the system moves from one submanifold to another, the equations of motion change in a non-smooth, or even discontinuous manner. In such cases, traditional nonlinear control methodologies are inapplicable because they generally rely upon some form of differentiation. Yet, it is precisely the discontinuous nature of such systems that is often their most important characteristic.\n\nThis dissertation presents methods which consider the intrinsic physical geometric structure present in such problems to address nonlinear controllability and motion planning for stratified systems. For both problems, by exploiting this geometric structure of stratified systems, we can extend standard nonlinear control results and methodologies to the stratified case. A related problem addressed by this dissertation is that of controllability of systems where some control inputs are constrained to be non-negative. This problem arises in stratified systems which arise by way of physical contact because the normal force between contacting systems must be nonnegative. For all the results, a basic goal is to generate results which are general. For example, for robotics applications, these results are independent of a particular robot's number of legs, fingers or morphology.\n" }, { "name": "Heirich, Alan Bryant", "degree": "PhD", "year": "1998", "title": "Analysis of scalable algorithms for dynamic load balancing and mapping with application to photo-realistic rendering", "advisor": "Arvo, James R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232008-111520", "creators": [ { "name": { "family": "Heirich", "given": "Alan Bryant" }, "id": "Heirich-Alan-Bryant", "display_name": "Heirich, Alan Bryant" } ], "advisors": [ { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "advisor", "display_name": "Arvo, James R." } ], "committee": [ { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "chair", "display_name": "Arvo, James R." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Kesselman", "given": "Carl" }, "id": "Kesselman-C", "role": "member", "display_name": "Kesselman, Carl" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "orcid": "0000-0002-0780-0911", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "compsci" ], "doi": "10.7907/ZVYW-H876", "abstract": "This thesis presents and analyzes scalable algorithms for dynamic load balancing and mapping in distributed computer systems. The algorithms are distributed and concurrent, have no central thread of control, and require no centralized communication. They are derived using spectral properties of graphs: graphs of physical network links among computers in the load balancing problem, and graphs of logical communication channels among processes in the mapping problem. A distinguishing characteristic of these algorithms is that they are scalable: the expected cost of execution does not increase with problem scale. This is proven in a scalability theorem which shows that, for several simple disturbance models, the rate of convergence to a solution is independent of scale. This property is extended through simulated examples and informal argument to general and random disturbances. A worst case disturbance is presented and shown to occur with vanishing probability as the problem scale increases. To verify these conclusions the load balancing algorithm is deployed in support of a photo-realistic rendering application on a parallel computer system based on Monte Carlo path tracing. The performance and scaling of this application, and of the dynamic load balancing algorithm, are measured on different numbers of computers. The results are consistent with the predictions of scalability, and the cost of load balancing is seen to be non-increasing for increasing numbers of computers. The quality of load balancing is evaluated and compared with the quality of solutions produced by competing approaches for up to 1,024 computers. This comparison shows that the algorithm presented here is as good as or better than the most popular competing approaches for this application. The thesis then presents the dynamic mapping algorithm, with simulations of a model problem, and suggests that the pair of algorithms presented here may be an ideal complement to more expensive algorithms such as the well-known recursive spectral bisection.\r\n" }, { "name": "Hill, David J.", "degree": "PhD", "year": "1998", "title": "Part I. Vortex dynamics in wake models. Part II. Wave generation", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04052007-141032", "creators": [ { "name": { "family": "Hill", "given": "David J." }, "id": "Hill-D-J", "display_name": "Hill, David J." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/81N1-6X49", "abstract": "In Part I, steady wakes in inviscid fluid are constructed and investigated using the techniques of vortex dynamics. As a generalization of Foppl's flow past a circular cylinder [5], a steady solution is given for flow past an elliptical cylinder of arbitrary aspect ratio (perpendicular or parallel to the flow at infinity) with a bound wake of two symmetric recirculating eddies in the form of a point vortex pair. Linear stability analysis predicts an asymmetric instability and the symmetric nonlinear evolution is discussed in terms of a Kirchhoff-Routh path function. The wake behind a sphere is represented by a thin cored vortex ring of arbitrary internal structure. Steady configurations are obtained and long-wavelength perturbations to the ring centerline identify a tilting instability. A generalization of the Kirchhoff Routh function to an axisymmetric flow consisting of vortex rings and a body is presented. Using conformal maps and point vortices, translating symmetric two-dimensional bubbles with a vortex pair wake are constructed. An instability in which the bubble and vortex pair tilt away from each other is found as well as a symmetric oscillatory instability. The cross-section of a trailing vortex pair immersed in a cross stream shear is represented by two counter-rotating vortex patches. Numerical and analytical analyses are provided. The method of Schwarz functions as introduced by Meiron, Saffman and Schatzman [13] is used in the computation and stability analysis of steady patch shapes. Excellent agreement is obtained using an elliptical patch model. An instability essentially isolated to a single patch is identified, the nonlinear evolution of the elliptical patch model suggests that the patch whose fluid elements rotate against the shear will be destroyed.\n\nPart II examines a possible mechanism for the generation of water waves which arises from the instability of an initially planar free surface in the presence of a parallel, sheared, inviscid flow. A two-dimensional steady flow comprised of exponential profiles representing both wind and a drift layer in the water is infinitesimally perturbed. The resulting Rayleigh equation is analytically solved by mean of Hyper-geometric functions and the dispersion relation is implicitly defined as solutions of a transcendental equation; stability boundaries are determined and growth rates are calculated. Comparisons are made with the simpler model of Caponi et al. [2] which uses piecewise linear profiles." }, { "name": "Hunziker, Guido H.", "degree": "PhD", "year": "1998", "title": "Spectroscopy and wavelength conversion by four-wave mixing in semiconductor optical amplifers", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232008-143421", "creators": [ { "name": { "family": "Hunziker", "given": "Guido H." }, "id": "Hunziker-G-H", "display_name": "Hunziker, Guido H." } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/fcfk-7n73", "abstract": "The first part of this thesis is dedicated to the study of the physics of the four-wave mixing (FWM) optical non-linearity in semiconductor optical amplifiers (SOAs). We focus our attention on the polarization properties of FWM and spectroscopic measurements of ultrafast carrier dynamics in these amplifiers. The second part presents investigations of FWM applications in the context of high-speed optical communication systems.\n\nThe detuning and polarization dependence of the third-order non-linear susceptibility is presented with a model based on the density matrix formalism. Experimental verifications of the model for the polarization properties of the four-wave mixing are presented using an alternating compressive and tensile strained multiquantum-well semiconductor optical amplifier. The polarization selection rules are then used for spectroscopic measurements of the carrier dynamics in quantum well SOAs. In particular, we present new techniques to measure the stimulated carrier lifetime, the inter quantum-well transport lifetime as well as the intrinsic escape and capture time constants for quantum wells. The capture lifetime is further studied in a separate experiment involving wavelength resolved spectroscopy.\n\nWe then demonstrate that strongly saturated and long SOAs (1.5 mm) are very effective wide span wavelength converters. We present bit error rate measurements for 30 nm wavelength down-conversion and 15 nm wavelength up-conversion at 10 Gb/s. We also present an application of the polarization selection rules to generate a polarization independent conversion at 2.5 Gb/s. Then, we introduce two different configurations where we use a lasing optical amplifier with a fiber Bragg grating to enhance the conversion efficiency and simplify the converter design. In the first case, we used the laser mode as pump wave and in the second case the lasing mode is injection locked to the FWM signal generated within the cavity. Finally, we present a new paradigm to perform wavelength encoded logic operations on a byte-wide WDM bus. Again, we use the polarization properties of the FWM to perform the logic operations.\n" }, { "name": "Jiang, Fukang", "degree": "PhD", "year": "1998", "title": "Silicon-micromachined flow sensors", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-08172005-081926", "creators": [ { "name": { "family": "Jiang", "given": "Fukang" }, "id": "Jiang-Fukang", "display_name": "Jiang, Fukang" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/R2QN-SC72", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA new generation of silicon-micromachined or micro-electro-mechanical-system (MEMS) sensors for the general purpose of microflow measurement and control is presented here. The first one is a polysilicon hot-wire anemometer made by a combined bulk and surface micromachining process. The new devices feature batch-fabricated freestanding micro polysilicon hot wires that are similar to conventional metal hot wires. Both the theoretical analysis and experimental (steady-state and dynamic) results show that MEMS hot wires have order-of-magnitude better frequency response, finer spatial resolution, and higher sensitivity over conventional hot-wire anemometers.\r\n\r\nA novel MEMS thermal shear-stress sensor featuring vacuum-cavity insulation has been developed. The device is a polysilicon wire thermistor embedded in a silicon-nitride diaphragm which sits on top of a vacuum cavity. The vacuum cavity is to improve the thermal isolation between the polysilicon wire and substrate. To characterize the devices, both steady-state and transient heat-transfer theories have been established and used to calibrate wind-tunnel results, temperature sensitivities and frequency responses. Shear-stress sensor array chips have also been developed. Each of the shear-stress imagers has more than 100 sensors integrated on a 1x2.85 [...] chip. Our measurement results from a fully developed 2-D channel flow are well agreeable with previously published results. For the first time, real-time 2-D wall shear-stress images in a turbulent flow have been experimentally obtained.\r\n\r\nA new technology for the integration of micro-sensors, micro-actuators and microelectronics (M3) on a single chip has been explored. Prototype M3 chips including shear-stress sensors, magnetic actuators and CMOS circuits have been fabricated. This technology sets a base for the future development of a fully functional M3 chip drag reduction.\r\n\r\nFinally, a novel flexible MEMS skin technology fully compatible with IC process has been developed. Mechanically, the skin is made of metal leads sandwiched between polyimide layers that connect a number of silicon islands together. The skin can be applied conformablly on non-planar surfaces. The first application of this technology is a flexible shear-stress sensor skin that has been successfully used for the real-time measurement of shear-stress distribution on the leading edge of a delta wing model.\r\n" }, { "name": "Kao, John", "degree": "PhD", "year": "1998", "title": "Two-Dimensional Steady Bow Waves in Water of Finite Depth", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222008-091958", "creators": [ { "name": { "family": "Kao", "given": "John" }, "id": "Kao-John", "display_name": "Kao, John" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "eng" ], "doi": "10.7907/tp0w-sd61", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn this study, the two-dimensional steady bow flow in water of arbitrary finite depth has been investigated. The two-dimensional bow is assumed to consist of an inclined flat plate connected downstream to a horizontal semi-infinite draft plate. The bottom of the channel is assumed to be a horizontal plate; the fluid is assumed to be invicid , incompressible; and the flow irrotational. For the angle of incidence \u03b1 (held by the bow plate) lying between 0\u00b0 and 60\u00b0, the local flow analysis near the stagnation point shows that the angle lying between the free surface and the inclined plate, \u03b2, must always be equal to 120\u00b0, otherwise no solution can exist. Moreover, we further find that the local flow solution does not exist if \u03b1 > 60\u00b0, and that on the inclined plate there exists a negative pressure region adjacent to the stagnation point for \u03b1 < 30\u00b0. Singularities at the stagnation point and the upstream infinity are found to have multiple branch-point singularities of irrational orders.
\r\n\r\nA fully nonlinear theoretical model has been developed in this study for evaluating the incompressible irrotational flow satisfying the free-surface conditions and two constraint equations. To solve the bow flow problem, successive conformal mappings are first used to transform the flow domain into the interior of a unit semi-circle in which the unknowns can be represented as the coefficients of an infinite series. A total error function equivalent to satisfying the Bernoulli equation is defined and solved by minimizing the error function and applying the method of Lagrange's multiplier. Smooth solutions with monotonic free surface profiles have been found and presented here for the range of 35\u00b0 < \u03b1 < 60\u00b0, a draft Froude number Frd less then 0.5, and a water-depth Froude number Frh less than 0.4.
\r\n\r\nThe dependence of the solution on these key parameters is examined. As \u03b1 decreases for fixed Frd and Frh, the free surface falls off more steeply from the stagnation point. Similarly, as Frd increases, the free surface falls off quickly from the stagnation point, but for decreasing Frh it descends rather slowly towards the upstream level. As Frh decreases further, difficulties cannot be surmounted in finding an exact asymptotic water level at upstream infinity, which may imply difficulties in finding solutions for water of infinite depth. Our results may be useful in designing the optimum bow shape.
" }, { "name": "Kelly, Scott D.", "degree": "PhD", "year": "1998", "title": "The mechanics and control of robotic locomotion with applications to aquatic vehicles", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08122005-152639", "creators": [ { "name": { "family": "Kelly", "given": "Scott D." }, "id": "Kelly-S-D", "display_name": "Kelly, Scott D." } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "mecheng" ], "doi": "10.7907/50M3-1529", "abstract": "This work illuminates the utility of a theory of locomotion rooted in geometric mechanics and nonlinear control. We regard the internal configuration of a deformable body, together with its position and orientation in ambient space, as a point in a trivial principal fiber bundle over the manifold of body deformations. We obtain connections on such bundles which describe the nonholonomic constraints, conservation laws, and force balances to which certain propulsors are subject, and contruct and analyze control-affine normal forms for different classes of systems. We examine the applicability of results involving geometric phases to the practical computation of trajectories for systems described by single connections. We propose a model for planar carangiform swimming based on reduced Euler-Lagrange equations for the interaction of a rigid body and an incompressible fluid, accounting for the generation of thrust due to vortex shedding through controlled coupling terms. We investigate the correct form of this coupling experimentally with a robotic propulsor, comparing its observed behavior with that predicted numerically.\r\n" }, { "name": "Lee, Sangwook", "degree": "PhD", "year": "1998", "title": "Failure of laminated composites at thickness discontinuities under complex loading and elevated temperatures", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222008-140642", "creators": [ { "name": { "family": "Lee", "given": "Sangwook" }, "id": "Lee-Sang", "display_name": "Lee, Sangwook" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9p36-ht49", "abstract": "Failure initiation of laminated composites with discontinuous thickness is examined in terms of typical structural load description (tension, shear force and bending moment) rather than in terms of micromechanics considerations. Because transverse shear produced relatively small effects in failure initiation, results are presented as tension-bending interactions. Two loading frames were designed to apply moments and tension simultaneously. Four types of specimens of different stacking sequence were examined to determine failure initiation, and analyzed subsequently via a finite element analysis (ABAQUS). Depending on the stacking sequence across the interface of the step, two different failure modes are identified: For uni-directional fiber orientation across the interface in the tension direction, failure occurs through cracking and delamination which is governed by a fracture mechanics criterion. While the initiation strength for this failure mode is higher than for the cross-ply configurations, the residual strength after initiation is only marginally higher, providing virtually no margin of safety (10%). For cases involving cross-plies on either side of the interface, failure initiation occurs by matrix cracking, with a critical strain across the fibers providing a universal failure criterion. In these cases the residual load bearing capability was 30 to 45% higher than the failure initiation loads. The interaction between moment and tension at failure initiation is linear, an observation that does not hold for the delamination failure driven by crack propagation. It is found that all failures can be described in terms of a common fracture principle; the stress or strain criteria are interchangeable with the fracture energy computations, provided one allows for a range of values of associated fracture energies. Assuming that time dependent aspects of the failure process are not dominant, elevated temperatures did not change the general results of how bending and tension loads interact, provided one accounts for residual thermal stresses; however, the stress magnitude at which the failure initiation occurs decreases with increasing temperature.\r\n" }, { "name": "Levene, Michael", "degree": "PhD", "year": "1998", "title": "Optics in neural computation", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-08132004-133148", "creators": [ { "name": { "family": "Levene", "given": "Michael" }, "id": "Levene-M", "display_name": "Levene, Michael" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Tanguay", "given": "Armand" }, "id": "Tanguay-A", "role": "member", "display_name": "Tanguay, Armand" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "cns" ], "doi": "10.7907/XQVE-SA13", "abstract": "In all attempts to emulate the considerable powers of the brain, one is struck by both its immense size, parallelism, and complexity. While the fields of neural networks, artificial intelligence, and neuromorphic engineering have all attempted oversimplifications on the considerable complexity, all three can benefit from the inherent scalability and parallelism of optics. This thesis looks at specific aspects of three modes in which optics, and particularly volume holography, can play a part in neural computation.\n\nFirst, holography serves as the basis of highly-parallel correlators, which are the foundation of optical neural networks. The huge input capability of optical neural networks make them most useful for image processing and image recognition and tracking. These tasks benefit from the shift-invariance of optical correlators. In this thesis, I analyze the capacity of correlators, and then present several techniques for controling the amount of shift invariance. Of particular interest is the Fresnel correlator, in which the hologram is displaced from the Fourier plane. In this case, the amount of shift invariance is limited not just by the thickness of the hologram, but by the distance of the hologram from the Fourier plane.\n\nSecond, volume holography can provide the huge storage capacity and high speed, parallel read-out necessary to support large artificial intelligence systems. However, previous methods for storing data in volume holograms have relied on awkward beamsteering or on as-yet non-existent cheap, wide-bandwidth, tunable laser sources. This thesis presents a new technique, shift multiplexing, which is capable of very high densities, but which has the advantage of a very simple implementation. In shift multiplexing, the reference wave consists of a focused spot a few millimeters in front of the hologram. Multiplexing is achieved by simply translating the hologram a few tens of microns or less. This thesis describes the theory for how shift multiplexing works based on an unconventional, but very intuitive, analysis of the optical far-field. A more detailed analysis based on a path-integral interpretation of the Born approximation is also derived. The capacity of shift multiplexing is compared with that of angle and wavelength multiplexing.\n\nThe last part of this thesis deals with the role of optics in neuromorphic engineering. Up until now, most neuromorphic engineering has involved one or a few VLSI circuits emulating early sensory systems. However, optical interconnects will be required in order to push towards more ambitious goals, such as the simulation of early visual cortex. I describe a preliminary approach to designing such a system, and show how shift multiplexing can be used to simultaneously store and implement the immense interconnections required by such a project.\n" }, { "name": "Lin, Qiao", "degree": "PhD", "year": "1998", "title": "Mechanics and Planning of Workpiece Fixturing and Robotic Grasping", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-01302008-111854", "creators": [ { "name": { "family": "Lin", "given": "Qiao" }, "id": "Lin-Qiao", "display_name": "Lin, Qiao" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Collins", "given": "Curtis L." }, "id": "Collins-C-L", "role": "member", "display_name": "Collins, Curtis L." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "mecheng" ], "doi": "10.7907/1d4m-j065", "abstract": "This thesis addresses several key issues in mechanics and automated planning of workpiece fixturing and robotic grasping, including accurate and efficient modelling of compliance, well-defined and practically useful quality measures, and well-defined kinematic metric functions for rigid bodies.
\r\n\r\nThe accurate and efficient modelling of compliant fixtures and grasps is considered. A stiffness matrix formula is derived using the overlap compliance representation for quasi-rigid bodies. In contrast to existing approaches using the linear contact model, this formula is well-suited to automated planning algorithms since it can incorporate realistic nonlinear contact models (e.g., the classical Hertz model), and can be directly computed from CAD data on basic geometric and material properties of the bodies. The formula is then used as a basis for a systematic analysis of local curvature effects on fixture stability. This analysis shows that destabilizing effects of local curvatures are practically negligible, and that curvature effects can be used to stabilize, sometimes significantly, an otherwise unstable fixture. The stiffness matrix formula is also used to show that stability analysis in general depends on the choice of contact models, which offers additional evidence for the importance of using realistic contact models.
\r\n\r\nThe stiffness and deflection quality measures are defined for compliant fixtures and grasps, and are applied to optimal planning. Unlike existing quality measures that rely on heuristic rules or depend on reference frame choices, the stiffness and deflection quality measures are theoretically sound. Equally important is that these quality measures accurately characterize functional performances which are important to practical fixturing applications, such as fixture stiffness and workpiece deflections. The stiffness and deflection quality measures are applied to optimal fixture and grasp planning, resulting in maximum-stiffness and minimum-deflection fixtures and grasps. The qualitative properties of optimal fixtures are characterized with respect to each quality measure, and efficient techniques are developed for finding such optimal fixtures.
\r\n\r\nThe final key issue is concerned with formal well-definedness conditions and practical development methods for rigid body kinematic metric functions, such as norms, inner products, and distance metrics. Based on an intrinsic definition of the configuration space of a rigid body, the notion of objectivity is proposed to formalize the natural requirement that metric measurements be indifferent to the observers who perform the measurements. This notion is then used to clarify the fundamental physical implications of left, right and bi-invariant functions on SE(3), and is further shown to be equivalent to the notion of frame-invariance. Based on these clarifications, several frame-invariant norms of rigid body velocities and wrenches, which have interesting physical interpretations, are defined.
" }, { "name": "Magdon-Ismail, Malik", "degree": "PhD", "year": "1998", "title": "Supervised learning in probabilistic environments", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232005-143548", "creators": [ { "name": { "family": "Magdon-Ismail", "given": "Malik" }, "id": "Magdon-Ismail-M", "display_name": "Magdon-Ismail, Malik" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6Y8S-4442", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nFor a wide class of learning systems and different noise models, we bound the test performance in terms of the noise level and number of data points. We obtain O(1/N) convergence to the best hypothesis, the rate of convergence depending on the noise level and target complexity with respect to the learning model. Our results can be applied to estimate the model limitation, which we illustrate in the financial markets. Changes in model limitation can be used to track changes in volatility.\r\n\r\nWe analyze regularization in generalized linear models, focusing on weight decay. For a well specified linear model, the optimal regularization parameter decreases as [...]. When the data is noiseless, regularization is harmful. For a misspecified linear model, the \"degree\" of misspecification has an effect analogous to noise. For more general learning systems we develop EXPLOVA (explanation of variance) which also enables us to derive a condition on the learning model for regularization to help. We emphasize the necessity of prior information for effective regularization.\r\n\r\nBy counting functions on a discretized grid, we develop a framework for incorporating prior knowledge about the target function into the learning process. Using this framework, we derive a direct connection between smoothness priors and Tikhonov regularization, in addition to the regularization terms implied by other priors.\r\n\r\nWe prove a No Free Lunch result for noise prediction: when the prior over target functions is uniform, the data set conveys no information about the noise distribution. We then consider using maximum likelihood to predict non-stationary noise variance in time series. Maximum likelihood leads to systematic errors that favor lower variance. We discuss the systematic correction of these errors.\r\n\r\nWe develop stochastic and deterministic techniques for density estimation based on approximating the distribution function, thus placing density estimation within the supervised learning framework. We prove consistency of the estimators and obtain convergence rates in L1 and L2. We also develop approaches to random variate generation based on \"inverting\" the density estimation procedure and based on a control formulation.\r\n\r\nIn general, we use multilayer neural networks to illustrate our methods.\r\n" }, { "name": "Massingill, Berna Linda", "degree": "PhD", "year": "1998", "title": "A structured approach to parallel programming", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechETD:etd-01242008-074143", "creators": [ { "name": { "family": "Massingill", "given": "Berna Linda" }, "id": "Massingill-B-L", "display_name": "Massingill, Berna Linda" } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Van de Velde", "given": "Eric" }, "id": "van-de-Velde-E", "role": "member", "display_name": "Van de Velde, Eric" }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/5ma9-h225", "abstract": "Parallel programs are more difficult to develop and reason about than sequential programs. There are two broad classes of parallel programs: (1) programs whose specifications describe ongoing behavior and interaction with an environment, and (2) programs whose specifications describe the relation between initial and final states. This thesis presents a simple, structured approach to developing parallel programs of the latter class that allows much of the work of development and reasoning to be done using the same techniques and tools used for sequential programs. In this approach, programs are initially developed in a primary programming model that combines the standard sequential model with a restricted form of parallel composition that is semantically equivalent to sequential composition. Such programs can be reasoned about using sequential techniques and executed sequentially for testing. They are then transformed for execution on typical parallel architectures via a sequence of semantics-preserving transformations, making use of two secondary programming models, both based on parallel composition with barrier synchronization and one incorporating data partitioning. The transformation process for a particular program is typically guided and assisted by a parallel programming archetype, an abstraction that captures the commonality of a class of programs with similar computational features and provides a class-specific strategy for producing efficient parallel programs. Transformations may be applied manually or via a parallelizing compiler. Correctness of transformations within the primary programming model is proved using standard sequential techniques. Correctness of transformations between the programming models and between the models and practical programming languages is proved using a state-transition-based operational model.\n\nThis thesis presents: (1) the primary and secondary programming models, (2) an operational model that provides a common framework for reasoning about programs in all three models, (3) a collection of example program transformations with arguments for their correctness, and (4) two groups of experiments in which our overall approach was used to develop example applications. The specific contribution of this work is to present a unified theory/practice framework for this approach to parallel program development, tying together the underlying theory, the program transformations, and the program-development methodology.\n" }, { "name": "May, Bennett Scott", "degree": "PhD", "year": "1998", "title": "Probabilistic Robust Control: Theory and Applications", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03042014-093439011", "creators": [ { "name": { "family": "May", "given": "Bennett Scott" }, "id": "May-Bennett-Scott", "display_name": "May, Bennett Scott" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" } ], "option_major": [ "civileng" ], "doi": "10.7907/19jn-c337", "abstract": "In this work, the development of a probabilistic approach to robust control is motivated by structural control applications in civil engineering. Often in civil structural applications, a system's performance is specified in terms of its reliability. In addition, the model and input uncertainty for the system may be described most appropriately using probabilistic or \"soft\" bounds on the model and input sets. The probabilistic robust control methodology contrasts with existing H\u221e/\u03bc robust control methodologies that do not use probability information for the model and input uncertainty sets, yielding only the guaranteed (i.e., \"worst-case\") system performance, and no information about the system's probable performance which would be of interest to civil engineers.
\r\n\r\nThe design objective for the probabilistic robust controller is to maximize the reliability of the uncertain structure/controller system for a probabilistically-described uncertain excitation. The robust performance is computed for a set of possible models by weighting the conditional performance probability for a particular model by the probability of that model, then integrating over the set of possible models. This integration is accomplished efficiently using an asymptotic approximation. The probable performance can be optimized numerically over the class of allowable controllers to find the optimal controller. Also, if structural response data becomes available from a controlled structure, its probable performance can easily be updated using Bayes's Theorem to update the probability distribution over the set of possible models. An updated optimal controller can then be produced, if desired, by following the original procedure. Thus, the probabilistic framework integrates system identification and robust control in a natural manner.
\r\n\r\nThe probabilistic robust control methodology is applied to two systems in this thesis. The first is a high-fidelity computer model of a benchmark structural control laboratory experiment. For this application, uncertainty in the input model only is considered. The probabilistic control design minimizes the failure probability of the benchmark system while remaining robust with respect to the input model uncertainty. The performance of an optimal low-order controller compares favorably with higher-order controllers for the same benchmark system which are based on other approaches. The second application is to the Caltech Flexible Structure, which is a light-weight aluminum truss structure actuated by three voice coil actuators. A controller is designed to minimize the failure probability for a nominal model of this system. Furthermore, the method for updating the model-based performance calculation given new response data from the system is illustrated.
" }, { "name": "Misra, Ashish", "degree": "PhD", "year": "1998", "title": "Large-eddy simulation using a vortex-based subgrid stress model", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-08102005-134328", "creators": [ { "name": { "family": "Misra", "given": "Ashish" }, "id": "Misra-A", "display_name": "Misra, Ashish" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/0J91-NE77", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA class of subgrid-stress (SGS) models for large-eddy simulation (LES) are presented based on the idea of structure-based subgrid-stress closure. The subgrid structure of the turbulence is assumed to consist of stretched vortices whose orientations are determined by the resolved velocity field. An equation which relates the subgrid stress to the structure orientation and the subgrid kinetic energy, together with an assumed Kolmogorov energy spectrum for the subgrid vortices, gives a closed coupling of the SGS model dynamics to the filtered Navier-Stokes equations for the resolved flow quantities. The subgrid energy is calculated directly by use of a local balance between the total dissipation and the sum of the resolved-scale dissipation and production by the resolved scales. Simple one- and two-vortex models are proposed and tested in which the subgrid vortex orientations are either fixed by the local resolved velocity gradients, or rotate in response to the evolution of the gradient field. These models are not of the eddy viscosity type. The choice of the energy spectrum introduces the Kolmogorov prefactor as a parameter. In the simplest case we make an a priori choice of the Kolmogorov prefactor which we refer to as the fixed [...] scheme. Alternatively, one can compute the Kolmogorov prefactor dynamically by enforcing continuity of the resolved energy spectrum with the subgrid spectrum. This introduces an additional equation for the Kolmogorov prefactor which is solved in conjunction with the equation relating the dissipation. This is referred to as the coupled [...] scheme. LES calculations with the present models are described for [...] decaying turbulence and also for forced [...] box turbulence at Taylor Reynolds numbers, [...], in the range [...] (fully resolved) to [...], = [...]. The models give good agreement with experiment for decaying turbulence and produce negligible SGS dissipation for forced turbulence in the limit of fully resolved flow.\r\n\r\nUsing the coupled [...] scheme, we present LES results for a three-dimensional channel flow. The coupled [...] scheme is implemented in planes of constant height and the Kolmogorov prefactor is calculated as a function of the wall-normal direction by computing a two-dimensional energy spectrum. Results are presented for the alignment models in an open channel of dimensions [...] at a Reynolds number (based on the friction velocity and the channel half width), [...] = 180 and a grid resolution of 32 x 32 x 65, where the last index refers to the wall-normal direction. Results compare favorably with direct numerical simulation (DNS).\r\n" }, { "name": "Montilla Edmonds, Karina Luciel", "degree": "PhD", "year": "1998", "title": "Shock Wave Processing of Transitional Metal Silicides", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202002-154801", "creators": [ { "name": { "family": "Montilla Edmonds", "given": "Karina Luciel" }, "id": "Montilla-Edmonds-Karina-Luciel", "display_name": "Montilla Edmonds, Karina Luciel" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Ustundag", "given": "Ersan" }, "id": "Ustundag-E", "orcid": "0000-0002-0812-7028", "role": "member", "display_name": "Ustundag, Ersan" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9g63-5c59", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nShock wave consolidation is an innovative processing technique for the densification of initially porous media. A compressive shock wave is introduced in the material by the impact of a high velocity flyer plate. Densification is achieved via intense inhomogeneous plastic deformation, pore collapse, and localized melting around particle surface. The passage of the shock wave may also induce chemical reactions within the material. The chemical reactivity of the powders are enhanced through dislocation nucleation, plastic flow, grain fracture and mass mixing as a result of the shock wave.\r\n\r\nA systematic investigation is performed to examine the effects of particle size and porosity on the initiation of the Ti[subscript 5]Si[subscript 3] reaction from the elemental powder mixture (i.e., 5 Ti + 3 Si). The initial powder porosity is varied from 40% to 49% of the theoretical density for two different size powders. The threshold shock energy necessary for complete silicide reaction is established. The powders are consolidated with shock energies up to 671 J/g and shock pressures up to 7.3 GPa. The threshold shock energy for the large powder mixture is found to be approximately 80% higher than that for the smaller powder mixture. For both sized powders, an increase in the threshold shock energy of 75% is observed in decreasing the initial porosity of the powders from 49% to 40%. Evidence for the reaction of solid Ti and liquid Si is observed in isolated regions at shock energies slightly below the threshold energy.\r\n\r\nMechanical alloying and shock wave consolidation are examined as viable alternatives for the synthesis and consolidation of MoSi [subscript 2]. Mechanic alalloying of Mo + 2Si is monitored with X-ray diffraction and differential scanning calorimetry (DSC). The milling time is varied from two hours to one hundred forty-four hours. Nanocrystalline MoSi [subscript 2] is observed after sixteen hours of ball milling. X-ray diffraction is used to follow the extent of alloying and average grain size as a function of ball milling time. DSC is utilized to determine the onset endothermic and exothermic reactions in the ball milled powder. MoSi [subscript 2] is produced from the elemental powder mixture by shock wave consolidation." }, { "name": "Nairn, Bruce James", "degree": "PhD", "year": "1998", "title": "Incipient transport of silt-sized sediments", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10202005-130933", "creators": [ { "name": { "family": "Nairn", "given": "Bruce James" }, "id": "Nairn-B-J", "display_name": "Nairn, Bruce James" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Werner", "given": "Brad" }, "id": "Werner-B", "role": "member", "display_name": "Werner, Brad" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Morgan", "given": "James. J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James. J." } ], "option_major": [ "envreng" ], "doi": "10.7907/E67A-3484", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nLaboratory experiments were conducted to determine the influence of stream bed shear stress and water chemistry on the sediment transport rate for silt-sized particles near the critical threshold for motion. Experiments were conducted in two large recirculating laboratory flumes, 40 m and 12 m long, with a small sediment bed 40 cm long. The sediment transport rate was determined from the volume of sediment eroded from this sediment bed per unit time. The smaller flume was filled with deionized water, to which specific electrolytes were added to vary the water chemistry.\n\nDimensional analysis predicted the sediment transport rate of non-cohesive material can be described by two dimensionless groups, one for transport and one for bed shear stress. A new transport model was developed on physical considerations for particles smaller than the thickness of the viscous sublayer, and supported this conclusion.\n\nSediment transport rates were measured in experiments using carefully cleaned glass beads (15 \u00b5m to 69 \u00b5m) in low ionic strength [...] solution by measuring the elevation of the sediment bed along transects with a laser displacement meter every 10 to 30 minutes. The results supported the prediction that the dimensionless shear stress (Shields parameter) and the water composition, and not of the bed Reynolds number, when the latter is less than one.\n\nExperiments were conducted with NaCI and CaCI2 electrolytes at differing concentrations up to [...]M, which reduced the transport rate by up to 2 to 3 orders of magnitude for the finest particles. Calcium was more effective at reducing the sediment transport rate than sodium. These trends were captured by the transport model, but additional work is required in estimating the inter-particle forces.\n\nA new criterion for initiation of motion is proposed based on a small dimensionless transport rate [...] = 0.01, corresponding to about 2% of the surface grains in motion. For bed Reynolds numbers u*d/v < 1, the equivalent Shields parameter for critical shear becomes [...] = 0.075 for non-cohesive sediment. With cohesion, a new model is used to predict the change in the Shields curve for various dimensionless interparticle forces.\n" }, { "name": "Odum, Jay Russell", "degree": "PhD", "year": "1998", "title": "Secondary Organic Aerosol Formation and Gas/Aerosol Partitioning", "advisor": "Seinfeld, John H.; Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252008-155400", "creators": [ { "name": { "family": "Odum", "given": "Jay Russell" }, "id": "Odum-Jay-Russell", "display_name": "Odum, Jay Russell" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "co-advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/R5WB-VW19", "abstract": "An intensive smog chamber study has revealed that secondary organic aerosol (SOA) formation follows Raoult's Law type gas/aerosol absorption thermodynamics. SOA formation was shown to occur via the gas/aerosol partitioning of semi-volatile, oxidation products rather than through the condensation of saturated, non-volatile products. The major consequence of this finding is that SOA yields are not constant, but rather are a function of the organic aerosol mass concentration. The theory has been used to successfully describe the aerosol formation potential of seventeen individual aromatic species, eight biogenic compounds, two different simple hydrocarbon precursor mixtures, and twelve different blends of whole gasoline vapor, in hundreds of smog chamber experiments. These results have been included in a 3-dimensional size- and chemically-resolved atmospheric chemical-transport model and used to simulate SOA formation in the South Coast Air Basin. The inherent dependence of SOA concentrations on primary organic aerosol (POA) concentrations, places strict constraints on organic and elemental carbon aerosol emissions inventories.\r\n" }, { "name": "Park, Han G.", "degree": "PhD", "year": "1998", "title": "A Study of Heat Transport Processes in the Wake of a Stationary and Oscillating Circular Cylinder Using Digital Particle Image Velocimetry/Thermometry", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132004-150955", "creators": [ { "name": { "family": "Park", "given": "Han G." }, "id": "Park-Han-G", "display_name": "Park, Han G." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C9KN-RQ12", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\t\t\t\t\t\r\nAn experimental investigation is carried out on the processes of heat transfer associated with a heated circular cylinder in crossflow. Two studies are made. First, a study of the transport of heat in the near wake (x/D<5) of a stationary and transversely oscillated cylinder is made at Reynolds number of 610. Second, a study is made of the surface heat transfer from a cylinder which is undergoing forced oscillations in the transverse direction.\r\n\r\nThe studies are made using the technique of Digital Particle Image Velocimetry/Thermometry (DPIV/T) which allows simultaneous measurements of both the velocity and temperature fields of the flow. The temperature is measured by seeding the flow with thermochromic liquid crystal (TLC) particles which change their reflected wavelength as function of temperature. By calibrating reflected wavelength versus temperature using a color multi-CCD camera, the local temperature of the flow may be deduced. The velocity is measured by using the same particles as Lagrangian flow tracers, and local velocity or displacement of the flow may be measured by cross-correlating two sequential images. A limitation of DPIV/T, which is the low level of precision (5% - 20% of the temperature span of TLC particles), may be overcome by a process in which the temperature at a given location is computed by averaging the temperatures of the particles within a specified sampling window. This process increases the precision to 2% - 10%.\r\n\r\nIn the study of the heat transport in the near wake, the velocity and temperature measurements obtained from DPIV/T are decomposed into their mean, coherent, and incoherent components using the triple decomposition. It is found that the heat from the cylinder is transported down the wake mostly by the mean heat flux and is laterally transported out of the wake by the coherent and the incoherent heat fluxes. In examining the direction of the turbulent heat flux vectors, the vectors are found not to be co-linear with the gradient of mean temperature. This misalignment implies that the gradient transport models are inappropriate for modeling the turbulent heat transport in the near wake of a circular cylinder. In examining the production of turbulence, it is found that that kinetic energy fluctuations are produced in the saddle regions (regions where the fluid is being stretched in one direction and compressed in another) while the temperature fluctuations are produced at the edges of center regions (regions where the fluid is rotating), i.e., the edges of the vortex cores.\r\n\r\nFrom the study of the heat convection from a cylinder as function of forced oscillation frequency [...] and amplitudes (A/D=0.1, 0.2), it is found that besides the previously known increase near the natural vortex shedding frequency, there also exists a large increase in the heat transfer at approximately three times this frequency for A/D=0.1. For A/D=0.2, there exist large increases at roughly two and three times the natural vortex shedding frequency. From a DPIV/T study, it is found that the wake pattern becomes synchronized with the mechanical oscillation of the cylinder at these frequencies where the heat transfer increases significantly. At the frequencies corresponding to roughly two and three times the unforced vortex shedding frequency, the wake pattern may become synchronized by processes of period doubling and tripling with respect to the cylinder oscillation period, respectively. The increase in the heat transfer rate is found to correlate with the distance at which vortices roll-up behind the cylinder. The distance is observed to decrease sharply at the frequencies corresponding to a sharp increase in the heat transfer. Therefore, the near wake is found to play a critical role in the heat transfer from the surface of a circular cylinder, and the cause of the increase in heat transfer is believed to the removal of the stagnant and low heat convecting fluid at the base of the cylinder during the roll-up of the vortices." }, { "name": "Polidori, David Charles", "degree": "PhD", "year": "1998", "title": "A probabilistic treatment of uncertainty in nonlinear dynamical systems", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechThesis:03112014-113438332", "creators": [ { "name": { "family": "Polidori", "given": "David Charles" }, "id": "Polidori-D-C", "display_name": "Polidori, David Charles" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Papadimitriou", "given": "Costas" }, "id": "Papadimitriou-Costas", "role": "member", "display_name": "Papadimitriou, Costas" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/axk4-vz45", "abstract": "In this work, computationally efficient approximate methods are developed for analyzing uncertain dynamical systems. Uncertainties in both the excitation and the modeling are considered and examples are presented illustrating the accuracy of the proposed approximations.
\r\n\r\nFor nonlinear systems under uncertain excitation, methods are developed to approximate the stationary probability density function and statistical quantities of interest. The methods are based on approximating solutions to the Fokker-Planck equation for the system and differ from traditional methods in which approximate solutions to stochastic differential equations are found. The new methods require little computational effort and examples are presented for which the accuracy of the proposed approximations compare favorably to results obtained by existing methods. The most significant improvements are made in approximating quantities related to the extreme values of the response, such as expected outcrossing rates, which are crucial for evaluating the reliability of the system.
\r\n\r\nLaplace's method of asymptotic approximation is applied to approximate the probability integrals which arise when analyzing systems with modeling uncertainty. The asymptotic approximation reduces the problem of evaluating a multidimensional integral to solving a minimization problem and the results become asymptotically exact as the uncertainty in the modeling goes to zero. The method is found to provide good approximations for the moments and outcrossing rates for systems with uncertain parameters under stochastic excitation, even when there is a large amount of uncertainty in the parameters. The method is also applied to classical reliability integrals, providing approximations in both the transformed (independently, normally distributed) variables and the original variables. In the transformed variables, the asymptotic approximation yields a very simple formula for approximating the value of SORM integrals. In many cases, it may be computationally expensive to transform the variables, and an approximation is also developed in the original variables. Examples are presented illustrating the accuracy of the approximations and results are compared with existing approximations.
\r\n" }, { "name": "Press, William Alan", "degree": "PhD", "year": "1998", "title": "Effects of Spatial Attention on Macaque Primary Visual Cortex", "advisor": "Van Essen, David C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012008-111851", "creators": [ { "name": { "family": "Press", "given": "William Alan" }, "id": "Press-William-Alan", "display_name": "Press, William Alan" } ], "advisors": [ { "name": { "family": "Van Essen", "given": "David C." }, "id": "Van-Essen-D-C", "orcid": "0000-0001-7044-4721", "role": "advisor", "display_name": "Van Essen, David C." } ], "committee": [ { "name": { "family": "Van Essen", "given": "David C." }, "id": "Van-Essen-D-C", "orcid": "0000-0001-7044-4721", "role": "chair", "display_name": "Van Essen, David C." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Shimojo", "given": "Shinsuke" }, "id": "Shimojo-S", "orcid": "0000-0002-1290-5232", "role": "member", "display_name": "Shimojo, Shinsuke" } ], "option_major": [ "cns" ], "doi": "10.7907/jt9f-av51", "abstract": "Does spatial attention affect neuronal responses in primary visual cortex? This question has been addressed in several previous studies, either with negative results or with modest positive results that do not rule out the possibility of experimental artifacts. The present study addressed three critical facets of this question: are responses in V1 affected by whether spatial attention is engaged, are they affected by where attention is directed, and does attention influence the modulatory effects of stimuli shown in the non-classical surround? Answering these questions requires establishing the following: whether V1 responses vary with attentional condition; whether any response changes are attributable to systematic offsets in eye position; and whether any responses changes are due to direct modulation of visually evoked responses or whether they are indirectly due to changes in baseline activity.
\r\n\r\nResponses from isolated single cells in V1 were recorded in two awake behaving monkeys. The monkeys were trained to perform a same-different orientation discrimination task while maintaining fixation. There were three attentional conditions, as determined by a cue: attending to the cell's classical receptive field (CRF); attending away from the CRF; and a passive condition, where no cue was shown and the animals had to maintain fixation throughout the trial's duration. In all three conditions, stimuli were presented both in the CRF and in the opposite hemifield. These stimuli were shown either alone, surrounded by parallel-oriented bars, or surrounded by orthogonal oriented bars.
\r\n\r\n59 cells were recorded under all three attentional conditions. 11/59 (19%) cells showed a significant effect of attentional condition on responses; no cells showed a significant effect of attentional condition on surround modulation. This was evident over the population of mean responses, as well, and could not be attributed to systematic biases in eye position. Compared to passive fixation, responses were suppressed, on average, by 7% when attention was engaged away from the CRF; compared to when attention was directed away from the CRF, moving attention to the CRF facilitated responses by 15%, back to passive fixation levels (similar results were obtained for the set of all 99 cells recorded with attending-away and attending-to conditions). Analyzing baseline activity showed that these response differences were modulations of the stimulus-evoked responses themselves and not of the baseline firing rates. This was confirmed by analyzing the time course of these attentional effects; modulations began about 80 ms after stimulus onset, 30-50 ms beyond the onset times for the responses. In addition, the response onset times were unchanged between attentional conditions. These results are discussed both in the context of previous studies that have investigated attentional modulation in V1 and in the context of computational models that attempt to describe the neurobiological underpinnings of spatial attention.
" }, { "name": "Radovitzky, Raul A", "degree": "PhD", "year": "1998", "title": "Error estimation and adaptive meshing in strongly nonlinear dynamic problems", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-113427", "creators": [ { "name": { "family": "Radovitzky", "given": "Raul A" }, "id": "Radovitzky-R-A", "display_name": "Radovitzky, Raul A" } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MF7F-YK03", "abstract": "This dissertation is concerned with the development of a general computational framework for mesh adaption such as is required in the three-dimensional lagrangian finite element simulation of strongly nonlinear, possibly dynamic, problems. It is shown that, for a very general constitutive framework, the solutions of the incremental boundary value problem obey a minimum principle, provided that the constitutive updates are formulated appropriately. This minimum principle is taken as a basis for asymptotic error estimation. In particular, we chose to monitor the error of a lower-order projection of the finite element solution. The optimal mesh size distribution then follows from a posteriori error indicators which are purely local, i. e., can be computed element-by-element.\n\nA sine qua non condition for the successful accomplishment of the kind of analysis envisioned in this work is the possibility to mesh the deforming domains of analysis. In the first section of this thesis a method is presented for mesh generation in complex geometries and general--possibly non-manifold--topologies.\n\nThe robustness and versatility of the computational framework is demonstrated with the aid of convergence studies and selected examples of application and the results contrasted with previous approaches" }, { "name": "Repetto, Eduardo A.", "degree": "PhD", "year": "1998", "title": "On the fatigue behavior of ductile F.C.C. metals", "advisor": "Ortiz, Michael", "url": "https://resolver.caltech.edu/CaltechETD:etd-01242008-133649", "creators": [ { "name": { "family": "Repetto", "given": "Eduardo A." }, "id": "Repetto-E-A", "display_name": "Repetto, Eduardo A." } ], "advisors": [ { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "advisor", "display_name": "Ortiz, Michael" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/zkfb-sr87", "abstract": "A micromechanically based model for fatigue crack nucleation in ductile F.C.C. metals is developed. The theory includes a model of F.C.C. crystal-plasticity in finite deformations that takes into account the Bauschinger effect, dipole annihilation in the persistent slip bands (PSBs), with vacancy generation and PSB elongation as a byproduct, as well as coupled vacancy diffusion and the attendant surface motion due to the flux of vacancies out of the body.\r\n\r\nFinite element simulations are performed in order to establish the predictive capability of the theory. Detailed modelling of the intersection of the PSB with a free surface, enhanced by the use of remeshing and surface evolution techniques, enable the prediction of nucleation sites, life expectancy, surface profile, alternate slip between the sides of the PSB and strain localization at the grooves.\r\n\r\nIn an attempt to resolve the dislocation structures experimentally observed during cyclic loading, a theory based on the non-convexity of a pseudo-energy density is developed. Non-homogeneous minimizers are found containing variants oriented in coincidence with the dislocation walls observed experimentally. Due to the latent hardening and geometrical softening, the minimizing structures are found to consist of regions of single slip which is in accordance with the observed \"patchy slip.\"" }, { "name": "Rieffel, Marc A.", "degree": "PhD", "year": "1998", "title": "Performance modeling for concurrent particle simulations", "advisor": "Taylor, Stephen", "url": "https://resolver.caltech.edu/CaltechETD:etd-01242008-132610", "creators": [ { "name": { "family": "Rieffel", "given": "Marc A." }, "id": "Rieffel-M-A", "display_name": "Rieffel, Marc A." } ], "advisors": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "advisor", "display_name": "Taylor, Stephen" } ], "committee": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "chair", "display_name": "Taylor, Stephen" }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "McKoy", "given": "Basil Vincent" }, "id": "McKoy-B-V", "role": "member", "display_name": "McKoy, Basil Vincent" } ], "option_major": [ "compsci" ], "doi": "10.7907/sx57-5d89", "abstract": "This thesis develops an application- and architecture-independent framework for predicting the runtime and memory requirements of particle simulations in complex three-dimensional geometries. Both sequential and concurrent simulations are addressed, on a variety of homogeneous and heterogeneous architectures. The models are considered in the context of neutral flow Direct Simulation Monte Carlo (DSMC) simulations for semiconductor manufacturing and aerospace applications.\n\nComplex physical and chemical processes render algorithmic analysis alone insufficient for understanding the performance characteristics of particle simulations. For this reason, detailed knowledge of the interaction between the physics and chemistry of a problem and the numerical method used to solve it is required.\n\nPrediction of runtime and storage requirements of sequential and concurrent particle simulations is possible with the use of these models. The feasibility of simulations for given physical systems can also be determined. While the present work focuses on the concurrent DSMC method, the same modeling techniques can be applied to other numerical methods, such as Particle-In-Cell (PIC) and Navier-Stokes (NS).\n" }, { "name": "Rudnev, Mikhail K.", "degree": "PhD", "year": "1998", "title": "Exponentially small splitting of separatrices and the Arnold's diffusion problem", "advisor": "Wiggins, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252008-161610", "creators": [ { "name": { "family": "Rudnev", "given": "Mikhail K." }, "id": "Rudnev-M-K", "display_name": "Rudnev, Mikhail K." } ], "advisors": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "advisor", "display_name": "Wiggins, Stephen R." } ], "committee": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "chair", "display_name": "Wiggins, Stephen R." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/mxyg-3c49", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis dissertation is concerned with the generalization of Arnold's original example in which he discussed the existence of a mechanism for instability caused by the splitting of the homoclinic manifolds of the weakly hyperbolic tori, that has subsequently been referred to as \"Arnold diffusion\" in case when the number of degrees of freedom n [...] 3. Namely, we consider a widely studied model of a pendulum weakly coupled with n -1 rotors with the degeneracies in the unperturbed Hamiltonian, corresponding to different time-scales, existing in the problem.\n\nUsing an alloy of the iterative and direct methods developed within the last years we give exponentially small upper bounds for the splitting measure of transversality for the case of an even, analytic perturbation, thus improving the estimate of Gallavotti [1994], which he calls quasiflat, and generalizing the analogous recent estimate of Delshams et al. [1996] for the rapidly quasiperiodically forced pendulum to a much larger class of Hamiltonian systems. In particular, the exponentially small upper bound for the transversality measure of the splitting applies when the Hamiltonian has extra degeneracies, namely when the frequencies on a torus become near-resonant. In fact, we show that in such a case the quantity in question becomes smaller, which is the incarnation of the general fact that resonant regions in the action space are in fact more stable in the sense that they have larger Nekhoroshev exponent. Nevertheless, we emphasize that getting uniform estimates for an arbitrary n [...] 3 is very hard unless one makes some additional assumptions on the approximation properties of the frequency vector.\n\nAlthough recent developments show that the first order of canonical perturbation theory, given by Melnikov integrals, generally cannot be accepted as the leading order answer for the splitting distance for the case of more than two degrees of freedom, including the rapidly quasiperiodically forced pendulum problem, we suggest an analytic perturbation, the majority of whose Fourier components are strictly non-zero, for which Melnikov integrals can be vindicated as the leading order approximation for the components of the splitting distance in different directions if the frequencies on the invariant tori satisfy certain arithmetic conditions. This allows us to bound the splitting distance from below.\n\nFurthermore, having such a perturbation, for the case of three degrees of freedom, we use a simple number-theoretical argument to find the asymptotics of the Fourier series with exponentially small coefficients involved. This enables us to compute the numerous homoclinic orbits for the whiskered tori of asymptotically full measure, and by proving the domineering contribution of the first order of perturbation theory for the transversality measure, to suggest a leading order answer for this quantity, thus proving the existence of an infinite number of heteroclinic connections between tori with close diophantine frequencies.\n\nWe elucidate the numerous arithmetic issues that obstruct getting a compact leading-order approximation for the splitting size, most of which can be overcome in the case of three degrees of freedom, as our example shows. These obstacles can be also possibly avoided in the same fashion for an arbitrary n [...] 3 if one treats the case when the frequencies of the rotors are near a resonance of multiplicity n - 3 or n - 2." }, { "name": "Sanders, Steven Jay", "degree": "PhD", "year": "1998", "title": "Plasma ion dynamics in large-amplitude drift waves : stochasticity, collisions, orbit loss, and recycling", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252008-115408", "creators": [ { "name": { "family": "Sanders", "given": "Steven Jay" }, "id": "Sanders-S-J", "display_name": "Sanders, Steven Jay" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/11sj-hm29", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe dynamics of plasma ions in the presence of large-amplitude electrostatic waves are investigated experimentally. The work was conducted in Caltech's Encore research tokamak. The toroidal plasma current excites coherent, poloidally propagating drift waves which stochastically heat ions in the poloidal plane. Ion distribution functions f (x, v ,t) are probed via Laser-Induced Fluorescence along three orthogonal velocity directions. Wave phase resolution is provided by the narrow laser pulse width and by a novel data-acquisition system which ensures synchronization between laser trigger and drift wave.\n\nTime-resolved measurements show a multi-step heating process during each wave period: (i) The wave electric field excites stochastic ion orbits in the poloidal [...] plane, resulting in [...] heating. (ii) ion-ion collisions impart energy to the toroidal [...] direction, raising [...] to relax the [...] temperature anisotropy. (iii) Hot ions with large gyroradius escape confinement, reaching the chamber wall and cooling the distribution. (iv) Cold ions from the plasma edge are convected back into the plasma (recycled), significantly replenishing the density depleted by orbit losses.\n\nThe ion-ion collision period [...] is highly time-dependent due to intense ([...]50%) fluctuations in both n and T. The anisotropic temperature relaxation rate is found to be consistent with Fokker-Planck theory when the time-dependence of the collision period is properly taken into account. Thus, classical Fokker-Planck correctly describes the evolution of f (vil), despite the intrinsic single-particle stochasticity in the [...] direction.\n\nEvidence for ion recycling is given by observations of significantly non-Maxwellian (NM) ion velocity distributions near the plasma edge. These appear periodically, synchronous with the drift wave phase at which, simultaneously, ion fluid flow from the wall toward the plasma center peaks, ion density is a local minimum, and ion temperature is high. The appearance of NM features at this phase is consistent with the intantaneously low ion collision rate which allows non-equilibrium features to be long-lived. The observed NM distributions are bimodal and indicate the presence of a group of cold ions (0.4 eV) superimposed on a hot background plasma (8 eV) of roughly equal density." }, { "name": "Schauer, James Jay", "degree": "PhD", "year": "1998", "title": "Source contributions to atmospheric organic compound concentrations : emissions measurements and model predictions", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282008-110050", "creators": [ { "name": { "family": "Schauer", "given": "James Jay" }, "id": "Schauer-J-J", "display_name": "Schauer, James Jay" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Simoneit", "given": "Bernd R. T." }, "id": "Simoneit-B-R-T", "role": "member", "display_name": "Simoneit, Bernd R. T." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/3FPH-HY50", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA dilution source sampling system is used to quantify the air pollutant emissions from major urban air pollution sources. The emissions from catalyst-equipped gasoline-powered motor vehicles, noncatalyst gasoline-powered motor vehicles, diesel trucks, meat charbroiling, the cooking of vegetables with seed oils, fireplace combustion of softwood and hardwood, cigarette combustion, and paint spray coating operations are characterized. Semi-volatile and particle-phase organic compounds in the diluted source emissions are collected simultaneously by both a traditional filter/PUF (polyurethane foam) sampling train and by an advanced organic compound-based denuder/filter/PUF sampling train to provide information on the gas/particle phase distribution of the semi-volatile organic compounds. Emission rates of hundreds of organic compounds, spanning carbon numbers from [...] to [...] are determined by gas chromatography/mass spectrometry and gas chromatography with flame ionization detection including n-alkanes, isoprenoids and other branched alkanes, cycloalkanes, aromatics, polycylic aromatic hydrocarbons, olefins, n-alkanoic acids, n-alkenoic acids, carbonyls, lactones, petroleum biomarkers, levoglucosan and other wood smoke markers, steroids, and synthetic chemicals. Fine particle mass emission rates and fine particle elemental chemical composition are measured as well.\r\n\r\nThe emissions profiles collected by use of the dilution source sampler are used to develop receptor-based air quality models that use organic compounds as tracers to determine source contributions to gas-phase and particle-phase air pollutant concentrations in the atmosphere. These models are applied to study source contributions to the existing particulate and gas-phase organic air pollution problems in Southern California and in California's San Joaquin Valley. In the Los Angeles area, diesel engine exhaust, fine particle paved road dust, food cooking operations and wood smoke are the largest contributors to annual average fine particle concentrations in the atmosphere, accompanied by smaller amounts of gasoline-powered vehicle exhaust aerosol, cigarette smoke, tire dust, plant fragments and natural gas combustion aerosol. In the San Joaquin Valley, wood smoke, background aerosol are found to be major contributors to the elevated fine particle concentrations experienced during the winter months." }, { "name": "Shiels, Douglas G.", "degree": "PhD", "year": "1998", "title": "Simulation of Controlled Bluff Body Flow with a Viscous Vortex Method", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-03162004-133652", "creators": [ { "name": { "family": "Shiels", "given": "Douglas G." }, "id": "Shiels-Dpouglas-G", "display_name": "Shiels, Douglas G." } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/49A0-VA12", "abstract": "Bluff body flows controlled in various manners are simulated with a high-resolution, gridless vortex method. Two-dimensional, unsteady, viscous simulations are utilized to illuminate the physical phenomenon underpinning certain flows of this class. Flows past a rotationally oscillating circular cylinder and flows past an elastically mounted circular cylinder are studied, providing a variety of new insights about these systems. A computational method facilitating longtime, high-resolution vortex simulations is developed whose grid-free nature enables future extension to complex geometries.\r\n\r\nThe significant fluid forces experienced by bluff bodies are of much practical concern and are induced by flowfields that are often complex. The studies in this thesis aim to contribute to the understanding of the relation between wake development and forces and how to exploit this relationship to achieve flow control. A circular cylinder undergoing rotational oscillation is known to experience a significant deviation in forces from unforced flow. Computations from Re=150-15000 verify past experimental observation of significant drag reduction for certain forcing parameters. These simulations also illuminate the mechanism which renders this control effective - a forced boundary layer instability triggering premature shedding of multipole vortex structures.\r\n\r\nNew insights were also provided by studies of flow over a model of an elastically mounted cylinder. A two-dimensional cylinder modeled as a damped oscillator can serve as an approximation to three-dimensional situations such as a cable under tension. Simulations clarified the behavior of such a two-dimensional system and, contrary to a line of classical thinking, revealed an unexpected adaptivity in wake evolution. New scaling is also suggested which better classifies these systems under certain conditions.\r\n\r\nVortex methods are well-suited for incompressible bluff body flow in many ways. However, the handling of viscous diffusion causes complications for such simulations. A relatively unexplored approach, the core expansion method, is studied, extended, and implemented in this work in order to balance accuracy with preservation of the gridless foundation of vortex methods. This viscous technique is found to enable long-time calculations that are prohibitive with other techniques while preserving a high level of accuracy." }, { "name": "Sill, Joseph", "degree": "PhD", "year": "1998", "title": "Monotonicity and connectedness in learning systems", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222005-110351", "creators": [ { "name": { "family": "Sill", "given": "Joseph" }, "id": "Sill-J", "display_name": "Sill, Joseph" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "cns" ], "doi": "10.7907/GQWN-1H71", "abstract": "This thesis studies two properties- monotonicity and connectedness- in the context of machine learning. The first part of the thesis examines the role of monotonicity constraints in machine learning from both practical and theoretical perspectives. Two techniques for enforcing monotonicity in machine learning models are proposed. The first method adds to the objective function a penalty term measuring the degree to which the model violates monotonicity. The penalty term can be interpreted as a Bayesian prior favoring functions which obey monotonicity. This method has the potential to enforce monotonicity only approximately, making it appropriate for situations where strict monotonicity may not hold. The second approach consists of a model which is monotonic by virtue of functional form. This model is shown to have universal approximation capabilities with respect to the class M of monotonic functions. A variety of theoretical results are also presented regarding M. The generalization behavior of this class is shown to depend heavily on the probability distribution over the input space. Although the VC dimension of M is [infinity], the VC entropy (i.e., the expected number of dichotomies) is modest for many distributions, allowing us to obtain bounds on the generalization error. Monte Carlo techniques for estimating the capacity and VC entropy of M are presented.\n\nThe second part of the thesis considers broader issues in learning theory. Generalization error bounds based on the VC dimension describe a function class by counting the number of dichotomies it induces. In this thesis, a more detailed characterization is presented which takes into account the diversity of a set of dichotomies in addition to its cardinality. Many function classes in common usage are shown to possess a property called connectedness. Models with this property induce dichotomy sets which are highly clustered and have little diversity. We derive an improvement to the VC bound which applies to function classes with the connectedness property.\n" }, { "name": "Sivilotti, Paolo A. G.", "degree": "PhD", "year": "1998", "title": "A method for the specification, composition, and testing of distributed object systems", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252008-095244", "creators": [ { "name": { "family": "Sivilotti", "given": "Paolo A. G." }, "id": "Sivilotti-P-A-G", "display_name": "Sivilotti, Paolo A. G." } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Bagrodia", "given": "Rajive" }, "id": "Bagrodia-R", "role": "member", "display_name": "Bagrodia, Rajive" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/z89g-gm27", "abstract": "The formation of a distributed system from a collection of individual components requires the ability for components to exchange syntactically well-formed messages. Several technologies exist that provide this fundamental functionality, as well as the ability to locate components dynamically based on syntactic requirements. The formation of a correct distributed system requires, in addition, that these interactions between components be semantically well-formed. The method presented in this thesis is intended to assist in the development of correct distributed systems.\n\nWe present a specification methodology based on three fundamental operators from temporal logic: initially, next, and transient. From these operators we derive a collection of higher-level operators that are used for component specification. The novel aspect of our specification methodology is that we require that these operators be used in the following restricted manner:\n\n\u2022A specification statement can refer only to properties that are local to a single component.\n\u2022A single component must be able to guarantee unilaterally the validity of the specification statement for any distributed system of which it is a part. Specification statements that conform to these two restrictions we call certificates.\n\nThe first restriction is motivated by our desire for these component specifications to be testable in a relatively efficient manner. In fact, we describe a set of simplified certificates that can be translated into a testing harness by a simple parser with very little programmer intervention. The second restriction is motivated by our desire for a simple theory of composition: If a certificate is a property of a component, that certificate is also a property of any system containing that component.\n\nAnother novel aspect of our methodology is the introduction of a new temporal operator that combines both safety and progress properties. The concept underlying this operator has been used implicitly before; but by extracting this concept into a first-class operator, we are able to prove several new theorems about such properties. We demonstrate the utility of this operator and of our theorems by using them to simplify several proofs.\n\nThe restrictions imposed on certificates are severe. Although they have pleasing consequences as described above, they can also lead to lengthy proofs of system properties that are not simple conjunctions. To compensate for this difficulty, we introduce collections of certificates that we call services. Services facilitate proof reuse by encapsulating common component interactions used to establish various system properties.\n\nWe experiment with our methodology by applying it to several extended examples. These experiments illustrate the utility of our approach and convince us of the practicality of component-based distributed system development. This thesis addresses three parts of the development cycle for distributed object systems: (i) the specification of systems and components, (ii) the compositional reasoning used to verify that a collection of components satisfy a system specification, and (iii) the validation of component implementations.\n" }, { "name": "Slessor, Michael David", "degree": "PhD", "year": "1998", "title": "Aspects of turbulent-shear-layer dynamics and mixing", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03292005-085835", "creators": [ { "name": { "family": "Slessor", "given": "Michael David" }, "id": "Slessor-M-D", "display_name": "Slessor, Michael David" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K55F-8589", "abstract": "Experiments have been conducted in the GALCIT Supersonic Shear Layer Facility to investigate some aspects of high-Reynolds-number, turbulent, shearlayer flows in both incompressible- and compressible-flow regimes. Experiments designed to address several issues were performed; effects of inflow boundary conditions, freestream conditions (supersonic/subsonic flow), and compressibility, on both large-scale dynamics and small-scale mixing, are described.\r\n\r\nChemically-reacting and non-reacting flows were investigated, the former relying on the (H2 + NO/F2) chemical system, in the fast-kinetic regime, to infer the structure and amount of molecular-scale mixing through use of \"flip\" experiments. A variety of experimental techniques, including a color-schlieren visualization system developed as part of this work, were used to study the flows.\r\n\r\nBoth inflow conditions and compressibility are found to have significant effects on the flow. In particular, inflow conditions are \"remembered\" for long distances downstream, a sensitivity similar to that observed in low-dimensionality, non-linear (chaotic) systems. The global flowfields (freestreams coupled by the shear layer) of transonic flows exhibit a sensitivity to imposed boundary conditions, i. e., local area ratios. A previously-proposed mode-selection rule for turbulent-structure convection speeds, based on the presence of a lab-frame subsonic freestream, was experimentally demonstrated to be incorrect. Compressibility, when decoupled from all other parameters, e.g., Reynolds number, velocity and density ratios, etc., reduces laxge-scale entrainment and turbulent growth, but slightly enhances smallscale mixing, with an associated change in the structure of the molecularly-mixed fluid. This reduction in shear-layer growth rate is examined and a new parameter that interprets compressibility as an energy-exchange mechanism is proposed. The parameter reconciles and collapses experimentally-observed growth rates.\r\n" }, { "name": "Springfield, Christopher D.", "degree": "PhD", "year": "1998", "title": "Development of an object-oriented infrared imaging system simulator and its application to multi-spectral infrared imaging", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01312008-150151", "creators": [ { "name": { "family": "Springfield", "given": "Christopher D." }, "id": "Springfield-C-D", "display_name": "Springfield, Christopher D." } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/jcn5-z151", "abstract": "This thesis describes research efforts undertaken to investigate passive, multi-spectral infrared imaging. Although many applications of multi-spectral infrared imaging may exist, the high cost of developing viable multi-spectral technologies has limited research into, and subsequent exploitation of, these applications. Our efforts attempt to find a way to minimize the cost of this research while concurrently investigating one of the possible applications of multi-spectral infrared imaging using current infrared imaging technology. The outcome is an object-oriented, infrared imaging system simulator, called IRIMAGE, and a series of experiments and simulations that confirm the viability of gaseous pollution detection using passive, multi-spectral infrared imaging.\n\nIRIMAGE is a flexible tool capable of applications research and basic infrared system design. This combination makes it a cost effective tool for researching the applications of multi-spectral IR imaging and the technological requirements they require. We present the physical and computational concepts that underly the simulation as well as certain computational advances made during IRIMAGE's development. A comprehensive discussion of the primary objects that make up IRIMAGE and how the simulation works is also provided. Since the reliability of a simulation depends on experimental verification of its output, we also present the results of this verification.\n\nBesides verifying IRIMAGE, these experiments investigated detecting gaseous pollutants using passive, multi-spectral IR imaging. The thesis describes the imaging system we used and the theoretical background of these experiments. For each experiment, we describe the experimental setup and how IRIMAGE simulated the experiment. Finally, we compare the experimental and simulation results. Although these experiments verify IRIMAGE and demonstrate how gaseous pollutants can be detected using passive, multi-spectral IR imaging, further research is necessary and certain technological advances must be made before this application can be exploited. More information about IRIMAGE is available on the web at www.ssdp.caltech.edu.\n" }, { "name": "Taylor, Maggie Elizabeth", "degree": "PhD", "year": "1998", "title": "Pulsed laser deposition : energetic growth effects in group iv semiconductor materials", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062008-104635", "creators": [ { "name": { "family": "Taylor", "given": "Maggie Elizabeth" }, "id": "Taylor-Maggie-Elizabeth", "display_name": "Taylor, Maggie Elizabeth" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "display_name": "McGill, Thomas C." } ], "option_major": [ "matsci" ], "doi": "10.7907/1vfn-ax53", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPulsed laser deposition is characterized by a broad deposition energy distribution with a mean energy of a few eV or a few tens of eV. The research that comprises this thesis was motivated by a desire to characterize energetic growth effects in pulsed laser deposition of Group IV semiconductor materials in order to understand and manipulate fundamental growth kinetics. This research specifically focuses on energetic effects in growth morphology, in growth on hydrogen-terminated surfaces, and in alloy growth.\r\n\r\nIn Chapter 1, pulsed laser deposition is introduced. In Chapter 2, simulated growth morphologies for Si growth by molecular beam deposition, sputter deposition, and pulsed laser deposition are compared. Feature atom displacement, an energetic effect, was found to significantly decrease roughness at low substrate temperatures. Pulsed roughening, a temporal effect, was found to slightly increase roughness at high substrate temperatures. In Chapter 3, crystalline Si grown by pulsed laser deposition on dihydride-terminated Si (001) surfaces and by molecular beam deposition and sputter deposition on clean Si (001) surfaces are compared. H transfer and Si subplantation, two energetic effects, were found to enable crystalline growth on dihydride-terminated Si (001) surfaces. In Chapter 4, crystalline [...] grown by solid phase epitaxy and pulsed laser deposition are compared. Solid phase epitaxy was found to produce alloys with compositions no larger than approximately 0.05. Pulsed laser deposition was found to produce alloys with compositions as large as approximately 0.38. Composition was found to increase with ablation energy density. In Appendix A, actual and simulated growth morphologies for Si growth by molecular beam deposition and pulsed laser deposition are compared. In Appendix B, the simulation code is listed.\r\n" }, { "name": "Tong, Xiaolin", "degree": "PhD", "year": "1998", "title": "Properties and applications of potassium lithium tantalate niobate", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052008-083834", "creators": [ { "name": { "family": "Tong", "given": "Xiaolin" }, "id": "Tong-Xiaolin", "display_name": "Tong, Xiaolin" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Y1N1-2V86", "abstract": "This thesis describes the physical and photorefractive properties of potassium lithium tantalate niobate (KLTN) single crystal material.\r\n\r\nThe top seeded solution growth method is reviewed. The phase transition temperatures and dielectric properties are related to the compositions of the KLTN crystals. A liquid/solid interface dynamics model is introduced to explain the experimental results which is that hydrogen ion concentration in KLTN crystals can be reduced dramatically by doping copper in the absence of titanium.\r\n\r\nDark conductivity of KLTN crystals are contributed by two species when the temperature is in the range of 250 K and 350 K. Two species are hydrogen ions and shallow trapped electrons (holes). These results have been confirmed by direct dc conductivity measurements and holograms fixing experiments. Hydrogen ion has two types of motion in the crystals: O-H vibration and O-H libration. We established a model to describe hydrogen ions motions and hopping in KLTN crystals. The theoretical prediction is in agreement with experimental results. Hologram thermal fixing for optical data storage is discussed. Hydrogen ions are identified as the mobile ion which is responsible for thermal fixing.\r\n\r\nIn ferroelectric phase KLTN crystals, spontaneous polarization of individual microdomains can be aligned throughout the entire crystal by the poling process. Photorefractive space charge fields play a role deploing the microdomains wherever space charge field opposing to spontaneous polarization. This may cause microdomain switching and lead to the generation of index grating. Experimental observation of Barkhausen current jumps is the signature of domain inversion.\r\n\r\nHolograms thermal fixing in potassium niobate crystals are also investigated. Because potassium niobate crystal has an orthognal structure with space group mm2, 3D polarization dependence of OH bands are observed. A special cut of iron doped potassium niobate crystal was designed to achieve the maximum exponential gain coefficient for thermal fixing of volume holograms. A significant enhancement of diffraction efficiency of the fixed grating 43% is measured.\r\n\r\nThe last part of this thesis discussed topological distribution of phase matching of three-wave mixing in biaxial crystals. Thirty possible distributions are illustrated. The optimum operating directions under phase matching condition in biaxial crystal can be obtained from the calculation of the effective nonlinear coefficients. A set of analytical expressions of effective nonlinear optical coefficient for the crystals with mm2 point group is given. The phase matching directions are in either x, y, or z plane in order to obtain maximum coefficient." }, { "name": "Tsao, Thomas Rocco", "degree": "PhD", "year": "1998", "title": "Silicon micromachined magnetic actuators for aerodynamic flow control applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052008-112354", "creators": [ { "name": { "family": "Tsao", "given": "Thomas Rocco" }, "id": "Tsao-Thomas-Rocco", "display_name": "Tsao, Thomas Rocco" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/z29s-kt20", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nActive micro-scale flow control has been a long sought-after goal of fluid mechanists. One of the primary desires within this field is to control macroscopic events with microscopic forces. Recent research has provided shear stress sensors capable of detecting micro-scale structures present in aerodynamic flows. In this work, the results (fabrication, device testing, fluidic testing) of developing magnetic actuators to interact with and affect the flow are reported. A first attempt at [...] (microsensor, mielodetuator, and microelectronic) integration is also presented.\r\n\r\nOne of the primary aerodynamic motivations is the control of the rolling moment of delta wing aircraft. For the demonstration of such an application, a line of flaps on a leading edge of the wing should be activated simultaneously. Therefore, arrays of passive magnetic flaps were fabricated and successfully used to create significant rolling moments in wind tunnel testing of delta wings.\r\n\r\nThe other motivation in the development of magnetic flaps is the reduction of drag in turbulent boundary layers. To succeed in this effort, the actuators must interact with, and negate the effects of, millimeter sized turbulent structures. Due to the unpredictable nature of such structures, each flap across a control surface should be individually addressable. Many designs of actively controlled magnetic flaps were fabricated and tested. The various generations were designed not only with device performance in mind, but also eventual integration with sensors and electronics. To this end, several fabrication issues, most notably dealing with the sacrificial layer, are presented.\r\n\r\nFinally, a first attempt at integrating sensors, actuators, and electronics on one substrate is presented. Such an effort is crucial both for the eventual use in flow control applications as well as in other generic MEMS/electronics integration efforts.\r\n" }, { "name": "Tuqan, Jamal", "degree": "PhD", "year": "1998", "title": "Statistical optimization of multirate systems and orthonormal filter banks", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02042008-081232", "creators": [ { "name": { "family": "Tuqan", "given": "Jamal" }, "id": "Tuqan-J", "display_name": "Tuqan, Jamal" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/vx5t-w383", "abstract": "The design of multirate systems and/or filter banks adapted to the input signal statistics is a generic problem that arises naturally in variety of communications and signal processing applications. The two main applications we have in mind are the statistical optimization of subband coders for signal compression and the multirate modeling of WSS random processes. These two applications lead naturally to the important concepts of energy compaction filters and principal component filter banks. In this thesis, we study three problems that are directly related to the above mentioned applications. The first problem is motivated by the observation that in the presence of subband quantizers, it is a loss of generality to assume that the synthesis section in a filter bank is the inverse of the analysis section. We therefore consider the statistical optimization of linear time invariant (LTI) pre- and postfilters surrounding a quantization system. Unlike in previous work, the postfilter is not restricted to be the inverse of the prefilter. Closed form expressions for the optimum filters as well as the resulting minimum mean square error (m.m.s.e.) are derived. The importance of the m.m.s.e. expression is that it clearly quantifies the additional gain obtained by relaxing the perfect reconstruction assumption. In the second problem, we study the quantization of a certain class of non bandlimited signals, modeled as the output of L < M interpolation filters where M is the interpolation factor. Using the fact that these signals are oversampled, we show how to decrease substantially the quantization noise variance using appropriate multirate reconstruction schemes. We also optimize a variety of noise shapers, indicating the corresponding additional reduction in the average mean square error for each case. The results of this chapter extend, using multirate signal processing theory, some well known techniques of efficient A/D converters (e.g. sigma-delta modulators) that usually apply only to bandlimited signals. In the last problem, a novel procedure to design globally optimal FIR energy compaction filters is presented. Energy compaction filters are important due to their close connection to orthonormal filter banks adapted to the input signal statistics. In fact, for the two channel case, the problems are equivalent. A special case of compaction filters arise also in applications such as echo cancelation, time varying systems identification, standard subband filter design and optimal transmitter and receiver design in digital communications. The new proposed approach guarantees theoretical optimality which previous methods could not achieve. Furthermore, the new algorithm is:\ni) extremely general in the sense that it can be tailored to cover any of the above applications.\nii) numerically robust.\niii) can be solved efficiently using interior point methods.\nThe design of a special class of two channel IIR compaction filters is also considered. We show that, in general, this class of optimum IIR compaction filters, parameterized by a single coefficient, are competitive with very high order optimum FIR filters.\n" }, { "name": "Uy, Robert Vincent", "degree": "PhD", "year": "1998", "title": "Studies of Rotordynamic Forces Generated by Annular Flows", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-111205", "creators": [ { "name": { "family": "Uy", "given": "Robert Vincent" }, "id": "Uy-Robert-Vincent", "display_name": "Uy, Robert Vincent" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9nq0-qp03", "abstract": "Fluid-induced rotordynamic forces in pumping machinery are well documented but poorly understood. The present research focuses on the rotordynamics due to fluid flow in annuli, in particular, the discharge-to-suction leakage flow in centrifugal pumps. There are indications that the contribution of the front shroud leakage flow can be of the same order of magnitude as contributions from the nonuniform pressure acting on the impeller discharge. Previous investigations have established some of the basic traits of these flows. This work further elaborates both the experimental and computational approach to quantify and predict the shroud contribution to the rotordynamic stability of pumping machinery.\t\r\n\r\nExperimental results presented show the contributions of the curvature of the leakage path to the rotordynamics both with and without inlet swirl. The effect of different inlet swirl rates at constant flow rate is examined. Anti-swirl devices are evaluated for their effectiveness in reducing instability. Geometrical changes to the high-pressure and low-pressure seals for the leakage path are quantified. All results are in good agreement with other reported measurements.\r\n\r\nChilds' bulk flow model for leakage paths is carefully examined, and convective relations for vorticity and total pressure are deduced. This analysis suggests a new solution procedure of the bulk flow equations which does not resort to linearization or assumed harmonic forms of the flow variables." }, { "name": "Wang, Chun-Ming", "degree": "PhD", "year": "1998", "title": "Image enhancement with two-photon laser scanning microscopy", "advisor": "Fraser, Scott E.; Wayland, J. Harold", "url": "https://resolver.caltech.edu/CaltechETD:etd-01312008-153939", "creators": [ { "name": { "family": "Wang", "given": "Chun-Ming" }, "id": "Wang-C-M", "display_name": "Wang, Chun-Ming" } ], "advisors": [ { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "advisor", "display_name": "Fraser, Scott E." }, { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "co-advisor", "display_name": "Wayland, J. Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/nrrt-dr18", "abstract": "Although confocal microscopy provides an efficient means of fluorescence imaging, many obstacles including extensive photobleaching and limited penetration depths limit its application. Emergence of two-photon laser scanning microscopy (TPLSM), with limited excitation volume, successfully overcomes those difficulties. Not only is TPLSM shown to have much less photobleaching and better penetration depths than CLSM, but also it is capable of doing UV imaging without using special UV optical elements.\r\n\r\nSeveral different aspects of TPLSM are discussed in the dissertation. The progress of 3-D fluorescence microscopy, a historical retrospective of two-photon excitation, the physics of two-photon excitation and our instrument setupare is discussed in the first chapter. In chapter II, a qualitative and quantitative confirmation of two-photon excitation, optical transfer efficiency, point spread function and resolution, signal-to-noise ratio, and two-photon excitation spectrum are presented. Chapter III shows the comparison between TPLSM and CLSM. Although CLSM has slightly better resolution than TPLSM, TPLSM has much less photobleaching and toxicity, greater penetration depth, less signal cross talk, and better signal collecting efficiency.\r\n\r\nImage deconvolution techniques with CLSM and TPLSM are discussed in chapter IV. Using this image processing methods and acquired PSF, we improved the resolution of CLSM and TPLSM dramatically. These deblurring techniques were applied to study the positions of proteins in the pre- and postsynaptic compartments of rat hippocampal culture cells. The improved resolution enabled us to distinguish the positions of Synapsin I, CaM Kinase U, and PSD-95, which could only be done with electron microscopy before.\r\n\r\nIn chapter V, image degradation due to brain tissue scattering is discussed. Emission signals with long wavelengths were shown to have better resolution and image contrast because of less tissue scattering. This result shows the necessity of designing fluorophores with low emission wavelengths for deep tissue imaging.\r\n\r\nTPLSM already provides many insightful images to the study of the dynamics and structures of biological systems. With the advance of technology, applications of TPLSM will be further developed to help understand biological or physical mechanism.\r\n" }, { "name": "Watts, Jerrell R.", "degree": "PhD", "year": "1998", "title": "Dynamic load balancing and granularity control on heterogeneous and hybrid architectures", "advisor": "Taylor, Stephen", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072008-075916", "creators": [ { "name": { "family": "Watts", "given": "Jerrell R." }, "id": "Watts-J-R", "display_name": "Watts, Jerrell R." } ], "advisors": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "advisor", "display_name": "Taylor, Stephen" } ], "committee": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "chair", "display_name": "Taylor, Stephen" }, { "name": { "family": "Arvo", "given": "James R." }, "id": "Arvo-J-R", "role": "member", "display_name": "Arvo, James R." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "van de Geijn", "given": "Robert A." }, "id": "van-de-Geijn-R-A", "role": "member", "display_name": "van de Geijn, Robert A." } ], "option_major": [ "compsci" ], "doi": "10.7907/gvgq-3d11", "abstract": "The past several years have seen concurrent applications grow increasingly complex, as the most advanced techniques from academia find their way into production parallel applications. Moreover, the platforms on which these concurrent computations now execute are frequently heterogeneous networks of workstations and shared-memory multiprocessors, because of their low cost relative to traditional large-scale multicomputers. The combination of sophisticated algorithms and more complex computing environments has made existing load balancing techniques obsolete. Current methods characterize the loads of tasks in very simple terms, often fail to account for the communication costs of an application, and typically consider computational resources to be homogeneous. The complexity of current applications coupled with the fact that they are running in heterogeneous environments has also made partitioning a problem for concurrent execution an ordeal. It is no longer adequate to simply divide the problem into some number of pieces per computer and hope for the best. In a complex application, the workloads of the pieces, which may be equal initially, may diverge over time. On a heterogeneous network, the varying capabilities of the computers will widen this disparity in resource usage even further. Thus, there is a need to dynamically manage the granularity of an application, repartitioning the problem at runtime to correct inadequacies in the original partitioning and to make more effective use of computational resources.\n\nThis thesis presents techniques for dynamic load balancing in complex irregular applications. Advances over previous work are three-fold: First, these techniques are applicable to networks comprised of heterogeneous machines, including both single- processor workstations and personal computers, and multiprocessor compute servers. Second, the use of load vectors more accurately characterizes the resource requirements of tasks, including the computational demands of different algorithmic phases as well as the needs for other resources, such as memory. Finally, runtime repartitioning adjusts the granularity of the problem so that the available resources are more fully utilized. Two other improvements over earlier techniques include improved algorithms for determining the ideal redistribution of work as well as advanced techniques for selecting which tasks to transfer to satisfy those ideals. The latter algorithms incorporate the notion of task migration costs, including the impact on an application's communications locality. The improvements listed above are demonstrated on both industrial applications and small parametric problems on networks of heterogeneous computers as well as traditional large-scale multicomputers.\n" }, { "name": "Weavers, Linda K.", "degree": "PhD", "year": "1998", "title": "Enhancement of ultrasonic and ultraviolet irradiation with chemical oxidants", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052008-100328", "creators": [ { "name": { "family": "Weavers", "given": "Linda K." }, "id": "Weavers-L-K", "display_name": "Weavers, Linda K." } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "member", "display_name": "Hering, Janet G." } ], "option_major": [ "envreng" ], "doi": "10.7907/WPCP-PA50", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe combination of ultrasound and ozone was used to study the degradation of nitrobenzene, 4-nitrophenol, 4-chlorophenol, cyclohexene, and pentachlorophenol in aqueous solutions. Using ultrasonic frequencies of 20 and 500 kHz revealed apparent enhancement at 20 kHz and antagonism at 500 kHz for the combined system although the first-order degradation rate constants in the absence of 03 (ozone) was typically a factor of 10 larger at 500 kHz. A comparison of the first-order degradation rate constants for nitrobenzene, 4-nitrophenol, and 4-chlorophenol by sonication, ozonation, and the combination of sonication and ozonation revealed that the observed enhancement upon the combination of ultrasound and ozone is mainly the result of thermolytic decomposition of ozone in a collapsing cavitation bubble. A continuous flow reactor closed to the atmosphere, open to the atmosphere, and open to the atmosphere with gas bubbling was used to probe the effects of ultrasound on [...] mass transfer. Enhanced mass transfer of [...] appeared to be the result of rapid decomposition of [...] in a cavitation bubble. The degradation of pentachlorophenol and observation of intermediates showed OH attack of the aromatic ring. A chemical kinetic model was developed to gain insight into the formation of radicals in various bubbles at 20 and 500 kHz with and without [...] present. The model revealed [...] pyrolysis slightly before the end of collapse followed rapid free- radical formation in the last nanoseconds due to [...] and [...] decomposition.\r\n\r\nIn addition, a new advanced oxidation process, photoactivated periodate, was developed to investigate the decomposition of triethanolamine, its associated chemical oxygen demand, and the oxidation of an industrial wastewater. The optimal [...] for COD degradation was determined to be pH 7.6 due to the combined effects of pH on the speciation of TEA and [...]. Increasing the [...] ratio increased the degradation rate up to an apparent saturation value. Irradiation with a 1000 W Hg(Xe) lamp increased the pseudo first-order degradation rate constant of COD by a factor of 5.5 for synthetic TEA solutions and 2.3 for the industrial wastewater as compared to irradiation with a 1000 W Xe lamp.\r\n" }, { "name": "Winfree, Erik", "degree": "PhD", "year": "1998", "title": "Algorithmic Self-Assembly of DNA", "advisor": "Hopfield, John J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05192003-110022", "creators": [ { "name": { "family": "Winfree", "given": "Erik" }, "id": "Winfree-Erik", "orcid": "0000-0002-5899-7523", "display_name": "Winfree, Erik" } ], "advisors": [ { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "advisor", "display_name": "Hopfield, John J." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Abelson", "given": "John N." }, "id": "Abelson-J-N", "role": "member", "display_name": "Abelson, John N." }, { "name": { "family": "Adleman", "given": "Leonard M." }, "id": "Adleman-Leonard-M", "role": "member", "display_name": "Adleman, Leonard M." }, { "name": { "family": "Baldeschwieler", "given": "John D." }, "id": "Baldeschwieler-J-D", "role": "member", "display_name": "Baldeschwieler, John D." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." } ], "option_major": [ "cns" ], "doi": "10.7907/HBBV-PF79", "abstract": "How can molecules compute? In his early studies of reversible computation, Bennett imagined an enzymatic Turing Machine which modified a hetero-polymer (such as DNA) to perform computation with asymptotically low energy expenditures. Adleman's recent experimental demonstration of a DNA computation, using an entirely different approach, has led to a wealth of ideas for how to build DNA-based computers in the laboratory, whose energy efficiency, information density, and parallelism may have potential to surpass conventional electronic computers for some purposes. In this thesis, I examine one mechanism used in all designs for DNA-based computer -- the self-assembly of DNA by hybridization and formation of the double helix -- and show that this mechanism alone in theory can perform universal computation. To do so, I borrow an important result in the mathematical theory of tiling: Wang showed how jigsaw-shaped tiles can be designed to simulate the operation of any Turing Machine. I propose constructing molecular Wang tiles using the branched DNA constructions of Seeman, thereby producing self-assembled and algorithmically patterned two-dimensional lattices of DNA. Simulations of plausible self-assembly kinetics suggest that low error rates can be obtained near the melting temperature of the lattice; under these conditions, self-assembly is performing reversible computation with asymptotically low energy expenditures. Thus encouraged, I have begun an experimental investigation of algorithmic self-assembly. A competition experiment suggests that an individual logical step can proceed correctly by self-assembly, while a companion experiment demonstrates that unpatterned two dimensional lattices of DNA will self-assemble and can be visualized. We have reason to hope, therefore, that this experimental system will prove fruitful for investigating issues in the physics of computation by self-assembly. It may also lead to interesting new materials.
\r\n" }, { "name": "Winner, Darrell Alan", "degree": "PhD", "year": "1998", "title": "Long-term modeling of regional ozone concentrations and control strategies", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052008-131756", "creators": [ { "name": { "family": "Winner", "given": "Darrell Alan" }, "id": "Winner-D-A", "display_name": "Winner, Darrell Alan" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/WAJM-9058", "abstract": "The capability to accurately model the long-term frequency of occurrence of high and low ozone concentrations in the urban and regional atmosphere is developed. A full year of hourly ozone concentration predictions is generated throughout Southern California using a photochemical airshed model driven by automated assimilation of routine meteorological observations. Statistical measures of airshed model performance for the full year are comparable to results achieved by episodic models for 2-3 days of simulation that are driven by data from expensive special field measurement programs.
\r\n\r\nThe effect of alternative emission control strategies on the long-term frequency distribution of daily peak ozone concentrations in Southern California is determined. Ozone isopleth diagrams are constructed in terms of the number of days per year that the current U.S. Federal 8 h average and former 1 h average ozone standards will be exceeded at all feasible combinations of air basin-wide reactive organic gases and oxides of nitrogen emissions. It is found that the frequency of violation of the former 1 h average ozone standard set at 0.12 ppm ozone could be reduced to approximately 25 days per year through stringent emissions controls under 1987 meteorological conditions. No practical way is evident to even come close to meeting the new 8 h average standard set at 0.08 ppm ozone. It is shown that the days with the highest historically observed ozone concentrations are not necessarily the hardest days to bring below the air quality standard.
\r\n\r\nUse of synthetic meteorological data is explored as an efficient means to meet the input data requirements of airshed models that must operate over long periods of tine. A semi-Markov process is used to generate a time series of synoptic weather conditions that statistically resembles the occurrence and persistence of historically observed weather. Local weather variables then are drawn for each day that are representative of the meteorological potential for ozone formation. These values are used as the initial conditions for a prognostic mesoscale meteorological model that generates the meteorological fields needed by a photochemical airshed model. The procedure produces daily peak 8 h average ozone concentration predictions that compare well with historical observations.
\r\n" }, { "name": "Zaremba, Slawomir M.", "degree": "PhD", "year": "1998", "title": "Dynamical signatures of gearbox vibrations", "advisor": "Caughey, Thomas Kirk; Beck, James L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082008-160817", "creators": [ { "name": { "family": "Zaremba", "given": "Slawomir M." }, "id": "Zaremba-S-M", "display_name": "Zaremba, Slawomir M." } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ab9t-b513", "abstract": "The applicability of a dynamical systems approach to the analysis of gearbox vibration signatures is investigated. The signal acquired from a standard one-step helical gearbox is analyzed and the existence of the low-dimensional nonlinear and chaotic behavior is examined. For this purpose, the criteria of broadband spectrum, sensitivity to initial conditions, positive Lyapunov exponents, and short-term dynamical predictability are applied. The largest Lyapunov exponent is also used to quantify the predictability of the measured time series and a surrogate data test is performed to confirm that the analyzed signal is unlikely to correspond to a linear stochastic time-invariant model. To confirm the applicability of a dynamical systems approach, forecasts of the gearbox time series are produced, using various predictors in the state space. Several methods of dynamical signal separation are also discussed. Finally, a family of statistics is proposed, on the basis of geometric features of the system dynamics in the state space, to serve as dynamical monitoring tools for observing changes in the operating conditions. These are tested using several models of dynamical systems which exhibit behavior similar to that observed in the actual gearbox. The most promising monitoring statistics are recommended for additional studies of gearboxes.\n" }, { "name": "Zenit Camacho, Jose Roberto", "degree": "PhD", "year": "1998", "title": "Collisional mechanics in solid-liquid flows", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08122005-140811", "creators": [ { "name": { "family": "Zenit Camacho", "given": "Jose Roberto" }, "id": "Zenit-Camacho-J-R", "display_name": "Zenit Camacho, Jose Roberto" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." } ], "option_major": [ "mecheng" ], "doi": "10.7907/E0D9-C117", "abstract": "Experimental measurements of the particle pressure were obtained for a liquid fluidized bed and for a vertical gravity driven liquid-solid flow. The particle, or granular, pressure is defined as the extra pressure generated by the action of particles in a particulate multi-phase flow. Using a high-frequency-response pressure transducer, individual collisions of particles were collected and measured to obtain a time-averaged particle pressure. Results were obtained for a number of different particles and for two different test section diameters. Results show that the particle pressure experiences a maximum at intermediate concentrations, and that its magnitude is scaled with the particle density and the square of the terminal velocity of the particles. The particle pressure was found to be composed of two main contributions: one from pressure pulses generated by direct collisions of particles against the containing walls (direct component), and a second one from pressure pulses due to collisions between individual particles that are transmitted through the liquid (radiated component).\r\n\r\nThe direct component of the particle pressure was studied by an analysis of particle collisions submerged in a liquid. A simple pendulum experiment provides controlled impacts in which measurements are made of the particle trajectories for different particles immersed in water. The velocity of the approaching particle is measured using a high speed digital camera; the magnitude of the collision is quantified using a high frequency response pressure transducer at the colliding surface. The measurements show that most of the particle deceleration occurs at less than half a particle diameter away from the wall. The measured collision pressure appears to increase with the impact velocity. Comparisons are drawn between the measured pressures and the predictions by Hertzian theory. A simple control-volume model is proposed to account for the effects of fluid inertia and viscosity. The pressure profile is estimated, and then integrated over the surface of the particle to obtain a force. The model predicts a critical Reynolds number at which the particle reaches the wall with zero velocity. Comparisons between the proposed model and the experimental measurements show qualitative agreement.\r\n\r\nExperiments involving binary collisions of particles were performed to investigate the radiated component of the particle pressure. This component results from the pressure front generated by the impulsive motion of a fluid resulting from a collision of particles in a liquid. When the two particles come into contact, the impulsive acceleration due to the elastic rebound produces a pressure pulse, which is transmitted through the fluid. A simple dual pendulum experiment was set up to generate controlled collisions. Measurements were obtained for a range of impact velocities, angles of incidence, and distances away from the wall for different pairs of particles. The magnitude of the impulse pressure appears to scale with the particle impact velocity and the density of the fluid. Based on the impulse pressure theory, a prediction for pressure generated due to the collision can be obtained. The model appears to agree well with the experimental measurements.\r\n\r\nThe fluctuating component of the solid fraction was studied, as one of the sources of the particle pressure. The instantaneous cross-sectional averaged solid fraction was measured using an impedance meter. The root-mean square fluctuation of the solid fraction signal was measured in a liquid fluidized bed and a vertical gravity-driven flow, for different particle sizes and densities. Two types of fluctuations were identified: low-frequency large-scale fluctuations which dominate at high concentrations, and high-frequency small-scale fluctuations which are dominant at intermediate solid fractions. The effect of each type was isolated by filtering. When the large-scale fluctuations were present, the magnitude of the rms fluctuation was found to scale with particle diameter, but when eliminated the mean fluctuation appeared to scale with the particle mass instead.\r\n" }, { "name": "Zorin, Denis N.", "degree": "PhD", "year": "1998", "title": "Stationary Subdivision and Multiresolution Surface Representations", "advisor": "Barr, Alan H.; Schroeder, Peter", "url": "https://resolver.caltech.edu/CaltechETD:etd-08102005-152703", "creators": [ { "name": { "family": "Zorin", "given": "Denis N." }, "id": "Zorin-Denis-N", "display_name": "Zorin, Denis N." } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "advisor", "display_name": "Schroeder, Peter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/EKMR-0233", "abstract": "Stationary subdivision is an important tool for generating smooth free-form surfaces used in CAGD and computer graphics. One of the challenges in the construction of subdivision schemes for arbitrary meshes is to guarantee that the surfaces produced by the algorithm are C1-continuous. First results in this direction were obtained only recently. In this thesis we derive necessary and sufficient criteria for Ck-continuity that generalize and extend most known conditions.
\r\n\r\nWe present a new method for analysis of smoothness of subdivision which allows us to analyze subdivision schemes which do not generate surfaces admitting closed-form parameterization on regular meshes, such as the Butterfly scheme and schemes with modified rules for tagged edges.
\r\n\r\nThe theoretical basis for analysis of subdivision that we develop allows us to suggest methods for constructing new subdivision schemes with improved behavior. We present a new interpolating subdivision scheme based on the Butterfly scheme, which generates C1-continuous surfaces from arbitrary meshes.
\r\n\r\nWe describe a multiresolution representation for meshes based on subdivision. Combining subdivision and the smoothing algorithms of Taubin [61] allows us to construct a set of algorithms for interactive multiresolution editing of complex hierarchical meshes of arbitrary topology.
" }, { "name": "\u00c7ataltepe, Zehra K\u00f6k", "degree": "PhD", "year": "1998", "title": "Incorporating Input Information into Learning and Augmented Objective Functions", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042005-104636", "creators": [ { "name": { "family": "\u00c7ataltepe", "given": "Zehra K\u00f6k" }, "id": "\u00c7ataltepe-Zehra-K\u00f6k", "orcid": "0000-0002-9742-5907", "display_name": "\u00c7ataltepe, Zehra K\u00f6k" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/82JV-3D67", "abstract": "In many applications, some form of input information, such as test inputs or extra inputs, is available. We incorporate input information into learning by an augmented error function, which is an estimator of the out-of-sample error. The augmented error consists of the training error plus an additional term scaled by the augmentation parameter. For general linear models, we analytically show that the augmented solution has smaller out-of-sample error than the least squares solution. For nonlinear models, we devise an algorithm to minimize the augmented error by gradient descent, determining the augmentation parameter using cross validation.
\r\n\r\nAugmented objective functions also arise when hints are incorporated into learning. We first show that using the invariance hints to estimate the test error, and early stopping on this estimator, results in better solutions than the minimization of the training error. We also extend our algorithm for incorporating input information to the case of learning from hints.
\r\n\r\nInput information or hints are additional information about the target function. When the only available information is the training set, all the models with the same training error are equally likely to be the target. In that case, we show that early stopping of training at any training error level above the minimum can not decrease the out-of-sample error. Our results are nonasymptotic for general linear models and the bin model, and asymptotic for nonlinear models. When additional information is available, early stopping can help.
" }, { "name": "Adam, Philippe H.", "degree": "PhD", "year": "1997", "title": "Enthalpy Effects on Hypervelocity Boundary Layers", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072008-111636", "creators": [ { "name": { "family": "Adam", "given": "Philippe H." }, "id": "Adam-Philippe-H", "display_name": "Adam, Philippe H." } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YF0K-HK91", "abstract": "More than 50 shots with air and 35 shots with carbon dioxide were carried out in the T5 shock tunnel at GALCIT to study enthalpy effects on hypervelocity boundary layers. The model tested was a 5\u00b0 half-angle cone measuring approximately 1 meter in length. It was instrumented with 51 chromel-constantan coaxial thermocouples and the surface heat transfer rate was computed to deduce the state of the boundary layer and, when applicable, the transition location.\r\n\r\nTransitional boundary layers obtained confirm the stabilizing effect of enthalpy. As the reservoir enthalpy is increased, the transition Reynolds number evaluated at the reference conditions increases as well. The stabilizing effect is more rapid in gases with lower dissociation energy and it seems to level off when no further dissociation can be achieved. These effects do not appear when the transition location is normalized with the edge conditions. Further normalizing the reservoir enthalpy with the edge enthalpy appears to collapse the data for all gases onto a single curve. A similar collapse is obtained when normalizing both the transition location and the reservoir enthalpy with maximum temperature conditions obtained with BLIMPK, a nonequilibrium boundary layer code.\r\n\r\nThe observation that the reference conditions seem more appropriate to normalize high enthalpy transition data was taken a step further by comparing the tunnel data with results from a reentry experiment. When the edge conditions are used, the tunnel data are around an order of magnitude below the flight data. This is commonly attributed to the fact that disturbance levels in tunnels are high, causing the boundary layer to transition prematurely. However, when the conditions at the reference temperature are used instead, the data come within striking distance of one another although the trend with enthalpy seems to be a destabilizing one for the flight data. This difference could be due to the cone bending and blunting observed during the reentry.\r\n\r\nExperimental laminar heat transfer levels were compared to numerical results obtained with BLIMPK. Results for air indicate that the reactions are probably in nonequilibrium and that the wall is catalytic. The catalycity is seen to yield higher surface heat transfer rates than the noncatalytic and frozen chemistry models. The results for carbon dioxide, however, are inconclusive. This is, perhaps, because of inadequate modeling of the actual reactions. Experimentally, an anomalous yet repeatable, rise in the laminar heat transfer level can be seen at medium enthalpies in carbon dioxide boundary layers.\r\n" }, { "name": "Assad, Christopher", "degree": "PhD", "year": "1997", "title": "Electric field maps and boundary element simulations of electrolocation in weakly electric fish", "advisor": "Bower, James M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-112132", "creators": [ { "name": { "family": "Assad", "given": "Christopher" }, "id": "Assad-C", "display_name": "Assad, Christopher" } ], "advisors": [ { "name": { "family": "Bower", "given": "James M." }, "id": "Bower-J-M", "role": "advisor", "display_name": "Bower, James M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2xh4-jv86", "abstract": "Weakly electric fish use electroreception - the generation and detection of electric currents - to explore the world around them. Neurophysiological studies of these fish have greatly increased our understanding of central electrosensory processing, and have significant implications for sensory processing in the cerebellum and cerebellar-like neural structures.\n\nThis thesis addresses a particular deficiency in our understanding of electrosensory systems: the input pattern of currents stimulating the fish's electroreceptors has not yet been well defined. My goals were to quantitatively reconstruct the electric organ discharge (EOD) and electrosensory images detected by weakly electric fish. These were accomplished by mapping the EODs of six gymnotiform species, simulating the EODs in two (Eigenmannia and Apteronotus), and predicting the electrosensory input during exploratory behaviors.\n\nThe EOD maps display a wide diversity of species-specific patterns, implying significant differences in field generation, sensory input patterns, possible behavioral strategies, and processing algorithms. Each fish must interpret electrosensory images which are highly dependent upon its own particular EOD pattern.\n\nTo study electrolocation noninvasively during natural behaviors, I developed a 3-d electric fish simulator based on the boundary element method. The simulator solves Poisson's equation for the electric potential in and around the fish, modeled as an electrostatic boundary value problem. Models of two species were built and optimized to match the measured maps. By varying only a few parameters, I explored how the electric organ structure and activation generate a particular EOD pattern: Eigenmannia has a synchronous electric organ and dipolar EOD, while Apteronotus is better described as a propagating multipole.\n\nThe simulator was used to reconstruct the EOD during a previously published tailprobing behavior of Eigenmannia, and from my own videotapes of Apteronotus exploring objects under infrared light. Simulations of selected exploratory behaviors revealed the EOD fields, modulations from body orientation and objects, and the resulting electrosensory patterns. The results (1) imply the fish control their body positions to regulate particular features of the electrosensory image, (2) predict features of the electrosensory input reaching the brain, and (3) suggest algorithms needed to extract useful signals from the electrosensory stream.\n" }, { "name": "Bakke, Eric", "degree": "PhD", "year": "1997", "title": "Viscosity measurements of bulk metallic glass forming alloys", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-01042008-090419", "creators": [ { "name": { "family": "Bakke", "given": "Eric" }, "id": "Bakke-E", "display_name": "Bakke, Eric" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/5161-9m27", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe viscosity of the [...] bulk metallic glass forming alloy in both the supercooled liquid and the equilibrium molten state was measured. Parallel plate rheometry and three-point beam-bending were used to measure the viscosity as a function of temperature in the supercooled liquid, and the technique of capillary flow was used in the molten state. The high thermal stability above the glass transition of this bulk metallic glass former with respect to crystallization allows measuring viscosities 120 K into the supercooled liquid region. Viscosity in the range from [...] to [...] poise has been measured using parallel plate rheometry, a region of viscosities that has not been previously accessible for supercooled metallic melts. The measurements were carried out with different heating rates between 0.0167 K/s and 1.167 K/s as well as isothermally. Using three-point beam bending, viscosity in the range from [...] to [...] poise has also been measured. These two methods, which involve completely different geometries for the measurement of flow, yielded consistent values for viscosity where their applicable regions overlap. The viscosity of the supercooled liquid of this bulk glass former, above the glass transition temperature, can be fit by a Vogel-Fulcher relation which exhibits a small Vogel-Fulcher temperature relative to the glass transition temperature. The values of viscosity measured by capillary flow above the liquidus temperature agree with the extrapolation of the Vogel-Fulcher relation to these temperatures. This bulk metallic glass former exhibits strong glass behavior, similar to silicate glasses. The relatively high viscosity in the supercooled liquid and smaller Gibbs free energy difference compared to the crystal both favor bulk glass formation. This glass forming ability is directly related to the fragility index and the relaxation kinetics as measured by viscosity, as well as the critical cooling rate. Knowledge of the viscosity as a function of temperature is essential for shaping and molding, and has led to possible extended commercial applications of these novel materials which exhibit unique mechanical properties.\n" }, { "name": "Baumstein, Anatoly I.", "degree": "PhD", "year": "1997", "title": "Nonlinear water waves with shear", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01042008-093737", "creators": [ { "name": { "family": "Baumstein", "given": "Anatoly I." }, "id": "Baumstein-A-I", "display_name": "Baumstein, Anatoly I." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/1QTM-MP39", "abstract": "Various aspects of nonlinear inviscid gravity waves in the presence of shear in the air and water are investigated. The shear, which appears due to the presence of wind in the air and current in the water, is modeled by a piecewise linear velocity profile.
\r\n\r\nThe interaction of short and long gravity waves is studied numerically, using spectral methods, and analytically, using perturbation methods. Special attention is paid to the verification of observations and experimental results. It is confirmed that finite amplitude waves propagating in the same direction as the wind or current are more stable with respect to superharmonic infinitesimal perturbations than the waves moving against the wind or current.
\r\n\r\nInfinitesimal perturbations in the form of side bands are also investigated both numerically and analytically. The nonlinear cubic Schrodinger equation for the wave envelope of a slowly varying wave train is derived. It is shown that depending on the direction of propagation (along or against the shear) of the finite amplitude waves, the effect of the shear on the stability is substantially different. In most cases, however, the shear strength increase first enhances the instability, but later suppresses it.
\r\n\r\nThree-wave interactions of gravity waves with shear in the water are considered. The interaction equations are derived with the help of two different perturbation approaches. The question of stability is addressed for both resonant and near-resonant interactions. The regions of explosive and \"pump-wave\" instability are identified for various types of three-wave interactions.
\r\n\r\nA new type of steady two-dimensional gravity waves with water shear is computed numerically. These waves appear at relatively low amplitudes and lack symmetry with respect to any crest or trough. A boundary integral formulation is used to obtain a one-parameter family of non-symmetric solutions through a symmetry-breaking bifurcation.
" }, { "name": "Beck, Carolyn Louise", "degree": "PhD", "year": "1997", "title": "Model Reduction and Minimality for Uncertain Systems", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-01042008-091550", "creators": [ { "name": { "family": "Beck", "given": "Carolyn Louise" }, "id": "Beck-Carolyn-Louise", "orcid": "0000-0003-4880-6380", "display_name": "Beck, Carolyn Louise" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/MPV7-2Q79", "abstract": "The emphasis of this thesis is on the development of systematic methods for reducing the size and complexity of uncertain system models. Given a model for a large complex system, the objective of these methods is to find a simplified model which accurately describes the physical system, thus facilitating subsequent control design and analysis.
\r\n\r\nModel reduction methods and realization theory are presented for uncertain systems represented by Linear Fractional Transformations (LFTs) on a block diagonal uncertainty structure. A complete generalization of balanced realizations, balanced Gramians and balanced truncation model reduction with guaranteed error bounds is given, which is based on computing solutions to a pair of Linear Matrix Inequalities (LMIs). A necessary and sufficient condition for exact reducibility of uncertain systems, the converse of minimality, is also presented. This condition further generalizes the role of controllability and observability Gramians, and is expressed in terms of singular solutions to the same LMIs. These reduction methods provide a systematic means for both uncertainty simplification and state order reduction in the case of uncertain systems, but also may be interpreted as state order reduction for multi-dimensional systems.
\r\n\r\nLFTs also provide a convenient way of obtaining realizations for systems described by rational functions of several noncommuting indeterminates. Such functions arise naturally in robust control when studying systems with structured uncertainty, but also may be viewed as a particular type of description for a formal power series. This thesis establishes connections between minimal LFT realizations and minimal linear representations of formal power series, which have been studied extensively in a variety of disciplines, including nonlinear system realization theory. The result is a fairly complete development of minimal realization theory for LFT systems.
\r\n\r\nGeneral LMI problems and solutions are discussed with the aim of providing sufficient background and references for the construction of computational procedures to reduce uncertain systems. A simple algorithm for computing balanced reduced models of uncertain systems is presented, followed by a discussion of the application of this procedure to a pressurized water reactor for a nuclear power plant.
\r\n" }, { "name": "Behnken, Robert Louis", "degree": "PhD", "year": "1997", "title": "Nonlinear Control and Modeling of Rotating Stall in an Axial Flow Compressor", "advisor": "Brennen, Christopher E.; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07102006-085216", "creators": [ { "name": { "family": "Behnken", "given": "Robert Louis" }, "id": "Behnken-Robert-Louis", "display_name": "Behnken, Robert Louis" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "co-advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ke8m-n471", "abstract": "This thesis focuses on understanding the use of air injection as a means of controlling rotating stall in an axial flow compressor, involving modeling, dynamical systems analysis, and experimental investigations.
\r\n\r\nThe first step towards this understanding was the development of a low order model for air injection control, the starting point of which was the Moore and Greitzer model for axial flow compressors. The Moore and Greitzer model was extended to include the effects of air injection and bifurcation analysis was performed to determine how the closed loop system dynamics are different from those of the open loop system. This low order model was then used to determine the optimal placement of the air injection actuators.
\r\n\r\nExperimental work focused on verifying that the low order model, developed for air injection actuation, qualitatively captured the behavior of the Caltech compressor rig. Open loop tests were performed to determine how the placement of the air injectors on the rig affected the performance of the compressor. The positioning of the air injectors that provided the greatest control authority were used in the development of air injection controllers for rotating stall. The controllers resulted in complete elimination of the hysteresis associated with rotating stall. The use of a throttle actuator for the control of the surge dynamics was investigated, and then combined with an air injection controller for rotating stall; the resulting controller performed quite well in throttle disturbance rejection tests.
\r\n\r\nA higher order model was developed to qualitatively match the experimental results with a simulation. The results of this modeling effort compared quite well with the experimental results for the open loop behavior of the Caltech rig. The details of how the air injection actuators affect the compressor flow were included in this model, and the simulation predicted the same optimal controller that was developed through experimentation.
\r\n\r\nThe development of the higher order model also included the investigation of systematic methods for determining the simulation parameters. Based on experimental measurements of compression system transients, the open loop simulation parameters were identified, including values for the compressor performance characteristic in regions where direct measurements were not possible. These methods also provided information on parameters used in the modeling of the pressure rise delivered by the compressor under unsteady flow conditions.
" }, { "name": "Boahen, Kwabena Adu", "degree": "PhD", "year": "1997", "title": "Retinomorphic vision systems : reverse engineering the vertebrate retina", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092008-085128", "creators": [ { "name": { "family": "Boahen", "given": "Kwabena Adu" }, "id": "Boahen-Kwabena-Adu", "display_name": "Boahen, Kwabena Adu" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Sterling", "given": "P." }, "id": "Sterling-P", "role": "member", "display_name": "Sterling, P." } ], "option_major": [ "cns" ], "doi": "10.7907/96W6-N605", "abstract": "This thesis seeks to explain how the retina satisfies both top-down constraints (functional) and the bottom-up constraints (structural) by analyzing simple physical models of the retina and mimicking its structure and function in silicon. In particular, I examine spatiotemporal filtering in the outer plexiform layer of the vertebrate retina, and show how outer retina processing is augmented by further processing in the inner plexiform layer, creating an efficient implementation that encodes moving stimuli efficiently over a wide range of speeds.\r\n\r\nMy working hypothesis is that biological sensory systems seek to optimize both functional and structural constraints. On the functional side, they must maximize information uptake from the environment while they minimize redundancy in their outputs. On the structural side, they must maximize resolving power in space and time, by making the processing elements small and fast, while they minimize wiring and energy consumption. If structure and function did indeed coevolve, as I assume, studying how structural and functional constraints are optimized simultaneously is our only hope of understanding why nature picks the solutions that we observe.\r\n\r\nAddressing both structural and functional constraints requires combining science and engineering. Scientists study an existing structure, and seek to understand how it functions in an optimal or near-optimal fashion, based on theoretical grounds. Rarely does a scientist ask: Will the structure be more cost effective, more reliable, or more reproducible if a less-than-optimum function is chosen? Engineers, on the other hand, design an optimal implementation for some desired function, based on an existing set of standard primitives. Rarely does an engineer ask: Is this the most natural set of primitives to use for this particular function? Thus, neither discipline attempts to optimize both function and structure globally. In contrast, evolution, operating in a purely opportunistic fashion, continuously seeks increasingly elegant solutions that meet these constraints.\r\n\r\nFor these reasons, I have adopted a multidisciplinary engineering-science approach that combines analysis with synthesis. When tailored synergestically, this approach can shed light on questions about which neurobiologists care, while advancing the state of the art in sensory-system design." }, { "name": "Burl, Michael C.", "degree": "PhD", "year": "1997", "title": "Recognition of visual object classes", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092008-094943", "creators": [ { "name": { "family": "Burl", "given": "Michael C." }, "id": "Burl-M-C", "display_name": "Burl, Michael C." } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "Smyth", "given": "Padhraic" }, "id": "Smyth-P", "role": "member", "display_name": "Smyth, Padhraic" }, { "name": { "family": "Fayyad", "given": "Usama M." }, "id": "Fayyad-U-M", "role": "member", "display_name": "Fayyad, Usama M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/96P7-6E62", "abstract": "Humans can look at a scene or a photograph and easily recognize objects. Outside my window I can see cars, people walking a dog on a brick pathway, trees, buildings, etc. This perception is so effortless that it belies the difficulty of the task. Visual perception begins with light that is reflected from the scene into the eye. The light impinges upon the retina and is transduced by a two-dimensional array of photoreceptors into noisy electrical signals. The brain must then accomplish the difficult task of transforming from this low-level representation to a higher-level understanding of the scene in terms of regions, surfaces, textures, and objects.
\r\n\r\nFor computer vision the problem is the same, but the hardware is different. A camera approximates the function of the eye and retina; that is, the camera produces a two-dimensional array of numbers (pixel values) representing the intensity of light reflected from the scene. The fundamental question addressed in this thesis is the following: what mathematical processing should be applied to the pixel values in order for a computer to recognize objects? The methods we propose are not intended as a model of human brain function, although they may provide some insight. We are simply trying to solve the same visual recognition problems as the brain without concern for whether (or how) our algorithms could be realized in neuronal \"hardware.\"
\r\n\r\nWe have developed a new framework for recognizing visual object classes in which the class members consist of characteristic parts in a deformable spatial configuration. Human faces are an object class of this type, since faces consist of eyes, nose, and mouth arranged in a configuration that varies depending on expression and pose and also from one person to another. A second object class is cursive handwriting, which consists of loops, cusps, crossings, etc. arranged in a deformable pattern. In our approach, the allowed object deformations are represented through shape statistics, which are learned from examples. Instances of an object in an image are detected by finding the appropriate features in the correct spatial configuration. Our algorithm is robust with respect to partial occlusion, detector false alarms, and missed features.
\r\n\r\nPotential applications include intelligent tools for finding objects in image data-bases, human-machine interfaces, user authentication, intelligent data gathering and compression, signature verification, and keyword spotting. Experimental results will be presented for two problems: (1) locating quasi-frontal views of human faces in cluttered scenes and with occlusions and (2) spotting keywords in on-line cursive handwriting data.
" }, { "name": "Capewell, Dale L.", "degree": "PhD", "year": "1997", "title": "Planar Laser Induced Fluorescence Imaging and Monte Carlo Simulations of Pulsed Laser Ablation", "advisor": "Goodwin, David G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-095243", "creators": [ { "name": { "family": "Capewell", "given": "Dale L." }, "id": "Capewell-Dale-L", "display_name": "Capewell, Dale L." } ], "advisors": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "advisor", "display_name": "Goodwin, David G." } ], "committee": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "chair", "display_name": "Goodwin, David G." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/1bah-m913", "abstract": "The first reported planar laser-induced fluorescence (PLIF) images depicting the relative ground-state, neutral density of Si within a pulsed laser ablation (PLA) plume as it expands into vacuum and 10 mTorr Ar are presented. Because of the high flow speeds in PLA plumes and the narrow bandwidth of typical lasers, several images acquired with the laser detuned incrementally must be superimposed to produce images which compensate for Doppler shifts. Density profiles of Si along the axis of symmetry as a plume expands into Ar at pressures of 0-150 mTorr demonstrate the influence of a background gas and substrate on the expanding plume in the interval 0 < t < 5\u03bcs. In-flight production of SiO along the contact as an Si plume expands into 1.0 Torr air is demonstrated in the first reported images of a reactive intermediate species produced during PLA.
\r\n\r\nThe expansion of Si into both 10 mTorr and 100 mTorr Ar is investigated using the technique of Direct Simulation Monte Carlo (DSMC), with a simple ablation model used to generate the Si plume. As a consequence of the rapid displacement of background gas, i.e. the snowplow effect, the plume divides into two components, one which travels nearly collisionlessly toward the substrate and one which interacts more strongly with the gas. At 10 mTorr, collisions between fast component Si atoms and Ar atoms during the period t < 250 ns are responsible for most of the energy transfer from Si to Ar. This results in the creation of a fast (15 eV), collisionless Ar component which impacts the substrate shortly after the fast Si component arrives, but does not result in thermal heating. At 100 mTorr, the energy transfer from the plume to the Ar gas occurs on a \u03bcs time scale and is attributed primarily to thermal heating. The energy of the fast Ar component decreases to about 5 eV.
\r\n\r\nFinally, the DSMC technique is employed to study the expansion of Si into both 10 mTorr and 100 mTorr O2. The chemical reaction Si + O2 \u2192 SiO + O is investigated, including rotational and vibrational excitation the diatomic molecules O2 and SiO. At both pressures, SiO first appears along the sides of the expanding plume and, at 100 mTorr, appears only along the contact front between the Si and O2. This result compares well will PLIF data. An examination of the O2 rotational temperature indicates that the background gas is heated along a conical surface whose tip is located at the ablation spot as the plume expands.
\r\n\r\nCollectively, these simulations demonstrate the potential of the DSMC method to provide quantitative information about the reactive expansion of a wide variety of PLA plumes into rarified background gas mixtures, and study the particle flux onto a substrate when parameters such as background gas pressure and composition are varied.
\r\n" }, { "name": "Chan, Eduardo", "degree": "PhD", "year": "1997", "title": "Optimal Design of Building Structures Using Genetic Algorithms", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechThesis:03132014-152131012", "creators": [ { "name": { "family": "Chan", "given": "Eduardo" }, "id": "Chan-Eduardo", "display_name": "Chan, Eduardo" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/4jea-yw44", "abstract": "A general framework for multi-criteria optimal design is presented which is well-suited for automated design of structural systems. A systematic computer-aided optimal design decision process is developed which allows the designer to rapidly evaluate and improve a proposed design by taking into account the major factors of interest related to different aspects such as design, construction, and operation.
\r\n\r\nThe proposed optimal design process requires the selection of the most promising choice of design parameters taken from a large design space, based on an evaluation using specified criteria. The design parameters specify a particular design, and so they relate to member sizes, structural configuration, etc. The evaluation of the design uses performance parameters which may include structural response parameters, risks due to uncertain loads and modeling errors, construction and operating costs, etc. Preference functions are used to implement the design criteria in a \"soft\" form. These preference functions give a measure of the degree of satisfaction of each design criterion. The overall evaluation measure for a design is built up from the individual measures for each criterion through a preference combination rule. The goal of the optimal design process is to obtain a design that has the highest overall evaluation measure - an optimization problem.
\r\n\r\nGenetic algorithms are stochastic optimization methods that are based on evolutionary theory. They provide the exploration power necessary to explore high-dimensional search spaces to seek these optimal solutions. Two special genetic algorithms, hGA and vGA, are presented here for continuous and discrete optimization problems, respectively.
\r\n\r\nThe methodology is demonstrated with several examples involving the design of truss and frame systems. These examples are solved by using the proposed hGA and vGA.
" }, { "name": "Cheng, Jung-Fu", "degree": "PhD", "year": "1997", "title": "Iterative decoding", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092008-082210", "creators": [ { "name": { "family": "Cheng", "given": "Jung-Fu" }, "id": "Cheng-Jung-Fu", "display_name": "Cheng, Jung-Fu" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "role": "member", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "Divsalar", "given": "Dariush" }, "id": "Divsalar-D", "role": "member", "display_name": "Divsalar, Dariush" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ydj9-zq05", "abstract": "Though coding theory suggests long error correcting codes chosen at random perform close to the optimum, the problem of designing good codes has traditionally been attacked by developing codes with a lot of structure, which lends itself to feasible decoders. The challenge to find practical decoders for long random codes has not been seriously considered until the recent introduction of turbo codes in 1993. This methodology of multi-stage iterative decoding with exchange of soft information, applied to codes with pseudo-random structure, has provided a whole new approach to construct good codes and to decode them with low complexity. This thesis examines the theoretical ground as well as the design and implementation details of these iterative decoding techniques. The methodology is first applied to parallel concatenated unit-memory convolutional codes and generalized concatenated convolutional codes to demonstrate its power and the general design principle. We then show that, by representing these coding systems with appropriate Bayesian belief networks, all the ad hoc algorithms can be derived from a general statistical inference belief propagation algorithm A class of new binary codes based on low-density generator matrices is proposed to eliminate the arbitrariness and unnecessary constraints in turbo coding we have recognized from this Bayesian network viewpoint. Contrary to the turbo decoding paradigm where sequential processing is accomplished by very powerful central units, the decoding algorithm for the new code is highly parallel and distributive. We also apply these codes to M-ary modulations using multilevel coding techniques to achieve higher spectral efficiency. In all cases, we have constructed systems with flexible error protection capability and performance within 1 dB of the channel capacity.\r\n" }, { "name": "D'Andrea, Raffaello", "degree": "PhD", "year": "1997", "title": "Generalizations of H-infinity optimization. Control of rotating stall", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092008-110959", "creators": [ { "name": { "family": "D'Andrea", "given": "Raffaello" }, "id": "D'Andrea-Raffaello", "display_name": "D'Andrea, Raffaello" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Smith", "given": "Roy" }, "id": "Smith-Roy", "role": "member", "display_name": "Smith, Roy" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4R8P-RR02", "abstract": "Arguably one of the most significant contributions to the field of optimal control has been the formulation and eventual solution of the H\u221e design problem. Armed with this mathematical tool, designs which are robust to plant uncertainty and insensitive to plant parameters can be performed in a systematic and rigorous fashion.
\r\n\r\nThe H\u221e methodology, however, typically leads to conservative designs. The reasons are twofold. The first is that the plant uncertainty can only be accounted for in an approximate manner, with the result that designs are performed for a set of allowable systems which is larger than what is being modeled; thus the resulting control strategy is forced to guard against non-realizable situations, potentially sacrificing system performance. The second has to do with the physical interpretation of H\u221e optimization: the minimization of a system's power to power gain. Thus it is implicitly assumed in the design process that the worst case disturbance is allowed to be an arbitrary power signal, such as a sinusoid. This is clearly a poor modeling choice for many types of physical disturbances, such as sensor or thermal noise, wind gusts, and impulsive forces.
\r\n\r\nThe main contribution of this dissertation is the extension of H\u221e optimization to allow for general closed loop design objectives which address the two limitations outlined above. In particular, non-conservative, computationally tractable, linear matrix inequality based methods for control design are developed for a certain class of physically motivated uncertain systems. In addition, these new techniques can accommodate constraints on the allowable disturbances, excluding unrealistic disturbances from the design process.
\r\n\r\nAnother contribution of this dissertation is an attempt to view control in the broader context of system design. Typically, a control algorithm is only sought after the system to be controlled has already been designed, and the type and location of the actuators and sensors has been determined. For most applications, however, the level of performance which can be attained by any control strategy is dictated by the dynamics of the plant. Thus from a system level, the above methodology is not optimal, since the control design process is decoupled from the design of the rest of the system. By adopting the behavioral framework for systems, an optimization problem where the given system is not treated as an input-output operator, a natural assumption when considering first principles models, is formulated and solved. The interpretation of the above extension of H\u221e optimization is that of designing optimal systems.
\r\n\r\nIn contrast to the general purpose tools developed in the first part of the dissertation and summarized above, the second part deals with an actual experimental problem, that of controlling rotating stall using pulsed air injection in a low-speed, axial flow compressor. By modeling the injection of air as an unsteady shift in the compressor characteristic, the viability of various air injection orientations are established. A control strategy is developed which controls the pulsing of air in front of the rotor face based on unsteady pressure measurements near the rotor face. Experimental results show that this technique eliminates the hysteresis loop normally associated with rotating stall. A parametric study is used to determine the optimal control parameters for suppression of stall. The resulting control strategy is also shown to suppress surge when a plenum is present. Using a high fidelity model, the main features of the experimental results are duplicated via simulations. The main contributions of this part of the dissertation are a simple control scheme which has the potential of greatly increasing the operability of compressors, and a low-order modeling mechanism which captures the essential features of air injection, facilitating subsequent analyses and control designs which make use of air injectors.
\r\n" }, { "name": "Deng, Tony H.", "degree": "PhD", "year": "1997", "title": "Measurement of the dynamic bulk compliance of polymers", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082008-112920", "creators": [ { "name": { "family": "Deng", "given": "Tony H." }, "id": "Deng-T-H", "display_name": "Deng, Tony H." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "mecheng" ], "doi": "10.7907/vxb1-4950", "abstract": "Measurements are described and analyzed for the determination of the dynamic bulk compliance for polyvinyl acetate) [PVAc] as a function of frequency and temperature. The real and imaginary parts of the dynamic bulk compliance over the frequency range from 10 Hz to 1,000 Hz have been measured at different temperatures by determining the compressibility of a specimen confined to an oil-filled cavity via pressurization by a piezoelectric driver and response of a piezoelectric sensor. The wavelength of the compressional wave generated by the piezoelectric transducer over the frequency range used is much larger than the size of the cavity so that the pressure can be considered uniform inside the cavity. The complex compliances of the specimen, confining liquid, and the cavity, are additive upon the pressure variations due to the piezoelectric transducer expansion and contraction. All deformations are considered to be purely dilitational.\n\nA master compliance curve over a total frequency range of about 12 decades is generated by the method of time-temperature superposition. Experimental problems addressing limitations in resolution capability are discussed. The results are compared with the classical measurements obtained by McKinney and Belcher over thirty years ago. Further comparison of the bulk with shear compliance data shows that the extent of the transition ranges for the shear and for the bulk functions are comparable, but the two transitions belong to different time scales: That of the bulk response falls mostly into the glassy domain of the shear behavior. One concludes thus that for linearly viscoelastic response the molecular mechanisms contributing to shear and bulk deformations have different conformational sources.\n" }, { "name": "Diorio, Christopher J.", "degree": "PhD", "year": "1997", "title": "Neurally Inspired Silicon Learning : from Synapse Transistors to Learning Arrays", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092008-080326", "creators": [ { "name": { "family": "Diorio", "given": "Christopher J." }, "id": "Diorio-Christopher-J", "display_name": "Diorio, Christopher J." } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/vbyq-fy15", "abstract": "A computation is an operation that can be performed by a physical machine. We are familiar with digital computers: Machines based on a simple logic function (the binary NOR) and optimized for manipulating numeric variables with high precision. Other computing machines exist: The neurocomputer, the analog computer, the quantum computer, and the DNA computer all are known. Neurocomputers-defined colloquially as computing machines comprising nervous tissue-exist; that they are computers also is certain. Nervous tissue solves ill-posed problems in real time. The principles underlying neural computation, however, remain for now a mystery.\r\n\r\nI believe that there are fundamental principles of computation that we can learn by studying neurobiology. If we can understand how biological information-processing systems operate, then we can learn how to build circuits and systems that deal naturally with real-world data. My goal is to investigate the organizational and adaptive principles on which neural systems operate, and to build silicon integrated circuits that compute using these principles. I call my approach silicon neuroscience: the development of neurally inspired silicon-learning systems.\r\n\r\nI have developed, in a standard CMOS process, a family of single-transistor devices that I call synapse transistors. Like neural synapses, synapse transistors provide nonvolatile analog memory, compute the product of this stored memory and the applied input, allow bidirectional memory updates, and simultaneously perform an analog computation and determine locally their own memory updates. I have fabricated a synaptic array that affords a high synapse-transistor density, mimics the low power consumption of nervous tissue, and performs both fast, parallel computation and slow, local adaptation. Like nervous tissue, my array simultaneously and in parallel performs an analog computation and updates the nonvolatile analog memory.\r\n\r\nAlthough I do not believe that a single transistor can model the complex behavior of a neural synapse completely, my synapse transistors do implement a local learning function. I consider their development to be a first step toward achieving my goal of a silicon learning system.\r\n" }, { "name": "Drolet, Jean-Jacques P.", "degree": "PhD", "year": "1997", "title": "Optoelectronic devices for information storage and processing", "advisor": "Psaltis, Demetri; Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-090916", "creators": [ { "name": { "family": "Drolet", "given": "Jean-Jacques P." }, "id": "Drolet-J-P", "display_name": "Drolet, Jean-Jacques P." } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "co-advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/80x4-rf73", "abstract": "Optoelectronic information storage and processing systems offer many important advantages compared to their electronic and magnetic counterparts: speed, massive parallelism and insensitivity to interference. Optoelectronic devices are a pivotal technology in the implementation of such systems. Devices consisting of optical inputs and outputs and information processing circuits are needed to interface optoelectronic components and modules to electronic systems, and to perform operations that are more difficult to reliably implement using optics alone. The main thrust of our research is to develop and evaluate optoelectronic technologies conducive to highly integrated optoelectronic components and systems for cost-effective information storage and processing. \n\nAt the device level, we describe a simple and inexpensive method for fabricating liquid crystal modulators on silicon integrated circuits. The modulators provide analog amplitude or phase modulation at low voltages. They are compatible with mainstream very-large-scale-integration processes and require only a minimal amount of post-processing performed on conventionally fabricated die. Experimental data are presented and compared to theoretical predictions.\n\nAt the chip level, we present an innovative optoelectronic integrated circuit functioning as an optically or electrically addressed spatial light modulator. The device merges the functions of a spatial light modulator and a detector array in a holographic memory system. Moreover, it helps refresh dynamic holograms which slowly decay in a read/write photorefractive memory as a result of their exposure to the reference beam. When combined with the technique of conjugate readout, this device allows a lens-less data path and a very compact, self-aligning integration of the memory module. We also describe two neural arrays, using self-electro-optic-effect devices bonded to a silicon integrated circuit, and light-emitting diodes grown on a commercially processed gallium arsenide integrated circuit.\n\nFinally, at the system level, we describe several integrated system architectures for holographic information storage and processing based on conjugate readout and the aforementioned device. We formulate storage density and cost projections. We report on laboratory prototypes of integrated modular holographic memory. Dynamic holograms were sustained over 50 refresh/decay cycles. Experimental data is presented.\n" }, { "name": "Feng, Jing", "degree": "PhD", "year": "1997", "title": "Frequency chirp and spectral dynamics in semiconductor lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032005-160031", "creators": [ { "name": { "family": "Feng", "given": "Jing" }, "id": "Feng-J", "display_name": "Feng, Jing" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/mahd-9t42", "abstract": "A study of the effects of the longitudinal distribution of optical intensity and carrier density on the static and dynamic characteristics of semiconductor lasers has been performed. Through a self-consistent way, a static model for above threshold operation of a single mode distributed feedback (DFB) laser is developed by calculating the longitudinal optical intensity and carrier density distribution. A dynamic model for large signal modulation of the DFB laser is also presented based on time-dependent coupled-mode equation for electric traveling waves in the laser. The spatial hole burning (SHB) has been analyzed in a quarter wavelength shifted DFB laser and a conventional DFB laser.\n\nA small-signal model is developed by including the optical intensity and carrier density distributions. Expressions are derived for the intensity modulation and resonance frequency, the frequency chirp and FM modulation, and the linewidth enhancement factor. Theoretical analysis of the frequency chirp in the DFB lasers has been used to support our experimental results. The model has led us to a new understanding of frequency chirp in DFB lasers and discovery of the ultra small chirp lasers.\n\nThe spectral dynamics and high speed response of uncooled DFB lasers have been studied. The most distinguished element differentiating the uncooled DFB lasers from uncooled FP lasers is that in uncooled DFB lasers; the wavelength detuning plays an important role in determining their spectral and high speed characteristics at high temperatures. Comparing with lasers lasing at gain peak, the DFB lasers with large negative wavelength detune could have better high speed performance at room temperature, but they might have higher threshold current. We can achieve optimum performance of uncooled DFB lasers by choosing wavelength detuning properly based on the laser applications." }, { "name": "Gan, Wenshui", "degree": "PhD", "year": "1997", "title": "Earthquake Response of Steel Braces and Braced Steel Frames", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechThesis:03142014-103017013", "creators": [ { "name": { "family": "Gan", "given": "Wenshui" }, "id": "Gan-Wenshui", "display_name": "Gan, Wenshui" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "civileng" ], "doi": "10.7907/6zt3-2k51", "abstract": "This thesis consists of three parts. Chapter 2 deals with the dynamic buckling behavior of steel braces under cyclic axial end displacement. Braces under such a loading condition belong to a class of \"acceleration magnifying\" structural components, in which a small motion at the loading points can cause large internal acceleration and inertia. This member-level inertia is frequently ignored in current studies of braces and braced structures. This chapter shows that, under certain conditions, the inclusion of the member-level inertia can lead to brace behavior fundamentally different from that predicted by the quasi-static method. This result is to have significance in the correct use of the quasi-static, pseudo-dynamic and static condensation methods in the simulation of braces or braced structures under dynamic loading. The strain magnitude and distribution in the braces are also studied in this chapter.
\r\n\r\nChapter 3 examines the effect of column uplift on the earthquake response of braced steel frames and explores the feasibility of flexible column-base anchoring. It is found that fully anchored braced-bay columns can induce extremely large internal forces in the braced-bay members and their connections, thus increasing the risk of failures observed in recent earthquakes. Flexible braced-bay column anchoring can significantly reduce the braced bay member force, but at the same time also introduces large story drift and column uplift. The pounding of an uplifting column with its support can result in very high compressive axial force.
\r\n\r\nChapter 4 conducts a comparative study on the effectiveness of a proposed non-buckling bracing system and several conventional bracing systems. The non-buckling bracing system eliminates buckling and thus can be composed of small individual braces distributed widely in a structure to reduce bracing force concentration and increase redundancy. The elimination of buckling results in a significantly more effective bracing system compared with the conventional bracing systems. Among the conventional bracing systems, bracing configurations and end conditions for the bracing members affect the effectiveness.
\r\n\r\nThe studies in Chapter 3 and Chapter 4 also indicate that code-designed conventionally braced steel frames can experience unacceptably severe response under the strong ground motions recorded during the recent Northridge and Kobe earthquakes.
" }, { "name": "Geraghty, David Francis", "degree": "PhD", "year": "1997", "title": "Investigation of wavelength conversion by four-wave mixing in semiconductor optical amplifiers", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092008-081143", "creators": [ { "name": { "family": "Geraghty", "given": "David Francis" }, "id": "Geraghty-D-F", "display_name": "Geraghty, David Francis" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/rqrk-zs39", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nFour-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is investigated for wavelength conversion in high-speed, all-optical networks. The design of the wavelength converter is optimized and the system performance limitations imposed by the fundamental physical principles involved in the SOA FWM process are characterized.\n\nSingle channel conversion performance is evaluated. The FWM efficiency ultimately determines many systems-level characteristics of the wavelength converter. The spectral range of our wavelength converter is characterized. Wide wavelength conversions of up to 18 nm and complete coverage of a 10 nm spectral range are demonstrated, while maintaining a BER performance of better than [...] at 10 Gb/s. \nThe converter also demonstrates a large dynamic input range of over 10 dB at 2.5 Gb/s. And the first characterization of cascaded FWM SOA wavelength converters, cascading conversion of up to 10 nm at 10 Gb/s, is performed.\n\nWith a simple modification of the converter design to a dual-pump configuration, the wavelength converter is able to provide nearly polarization insensitive performance. The converted signal's magnitude varies by less than 1.5 dB and its sensitivity varies by less than 2 dB for 2.5 Gb/s signals over the entire range of input polarizations.\n\nTime resolved spectral analysis is performed to evaluate the spectral properties of the wavelength converter. A pattern-dependent additional chirp is measured on the signal, primarily resulting from fluctuations in the gain saturation of the SOA. This degradation to the optical phase conjugation, intrinsic to the SOA FWM process, is minimal enough to allow dispersion compensation by mid-span spectral inversion. Error-free detection of a directly modulated 10 Gb/s signal is achieved over 120 km.\n\nAdditional demonstrations are also presented. Multi-channel wavelength conversion and dynamic routing are successfully performed. Finally, some work on a microcavity erbium-doped fiber laser, initially designed and developed for use as a tunable source for wavelength-division multiplexed networks, is presented.\n" }, { "name": "Gibson, Andrew Douglas", "degree": "PhD", "year": "1997", "title": "Physical scale modeling of geotechnical structures at one-G", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-140908", "creators": [ { "name": { "family": "Gibson", "given": "Andrew Douglas" }, "id": "Gibson-A-D", "display_name": "Gibson, Andrew Douglas" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/97V4-YE48", "abstract": "The use of physical scale modeling techniques for geotechnical applications is investigated. The scaling laws to relate a prototype structure to a model are developed for the centrifuge modeling technique and for the laboratory (or one-g) environment. A theory based on critical or steady state concepts for the constitutive scaling of the behavior of the soil in a one-g model is investigated. A series of one-g models of varying configurations was constructed in a laminar box and subjected to earthquake like motions on a shake table. A total of 73 tests was performed. Most tests were constructed of saturated Nevada sand placed in a loose and dense state in adjacent halves of a laminar box, and the results of these tests were compared with a similar centrifuge test (Model 3) which was performed as part of the VELACS study. Some of the one-g models were constructed with an alternate model sand and an alternate pore fluid to investigate these modeling variations. One-g models were also constructed with the sand at a uniform density throughout the laminar box.\r\n\r\nThe research indicates that there is a significant conflict between the time scaling for dynamic processes and dissipation processes in both the centrifuge and one-g techniques, which means that excess pore pressures generated in the model saturated sand by a simulated earthquake will be less than what would occur in the same sand in the real prototype. This effect is generally more severe in the centrifuge. This implies that model tests performed to investigate liquefaction, flow failure problems, and/or deformation problems in saturated sands may significantly underestimate the potential behavior of the prototype. In addition to the above, the research provides insight into the behavior of adjacent loose and dense sands and indicates the potential for high excess pore pressures to develop in the dense sand. Current practice ignores the potential for liquefaction in dense sands or the development of cyclic mobility in the assessment of the seismic performance of geotechnical structures.\r\n" }, { "name": "Gupta, Vidyabhusan", "degree": "PhD", "year": "1997", "title": "Analog VLSI for active drag reduction", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-132037", "creators": [ { "name": { "family": "Gupta", "given": "Vidyabhusan" }, "id": "Gupta-V", "display_name": "Gupta, Vidyabhusan" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/3zas-5z34", "abstract": "In today's cost conscious air transportation industry, fuel costs are a substantial economic concern. Drag reduction is an important way to increase fuel efficiency which reduces these costs. Even 1% reduction in drag can translate into estimated savings of tens of millions of dollars in annual fuel costs.\r\n\r\nFluid mechanicists believe that microscopic vortex pairs impinging on the surface play an important role in turbulent transport that may cause large skin friction drag. The microscopic nature and unpredictable appearance of these structures has limited practical approaches to their control. With the advent of micromachining technology providing the ability to build mechanical structures with microscopic dimensions, the tools finally exist with which to detect and control the vortex structures. These sensors and actuators require control circuitry between them in order to build a complete system.\r\n\r\nWe propose an analog VLSI system that can process information along a surface in a moving fluid with the goal of controlling actuators to minimize the surface shear stress. We obtain the information from the surface by using microsensors which measure the surface shear stress. The actuators interact with the fluid by moving up and down in an attempt to diminish the impact of the drag-inducing structures in the fluid.\r\n\r\nWe have designed and fabricated an analog control system. We have tested the system in several different experiments to verify its effectiveness in providing a control signal that energizes an actuator. We also have studied the methodology for creating a completely integrated wafer-scale system.\r\n" }, { "name": "Haroldsen, David John", "degree": "PhD", "year": "1997", "title": "The numerical calculation of three-dimensional water waves using a boundary integral method", "advisor": "Meiron, Daniel I.; Hou, Thomas Y.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-153911", "creators": [ { "name": { "family": "Haroldsen", "given": "David John" }, "id": "Haroldsen-D-J", "display_name": "Haroldsen, David John" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "co-advisor", "display_name": "Hou, Thomas Y." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/etyh-8140", "abstract": "In this work, we consider the numerical calculation of water waves in three dimensions. One well accepted method for studying surface waves is the boundary integral method, which defines the fluid velocities at the interface in terms of integrals over the boundary of the domain in which the problem is posed. There exists a considerable body of work on the numerical study of surface waves in two dimensions. However, until recently the numerical study of surface waves was considered intractable because of the high computational cost of approximating the defining integrals.\n\nWe discuss the boundary integral formulation for the three-dimensional water wave problem and present the point vortex approximation to the singular integrals which define the particle velocities. We consider three aspects of the point vortex approximation: accuracy of the approximation, efficient means of computing solutions, and numerical stability of the scheme.\n\nConcerning the accuracy of the point vortex method, we analyze the error associated with the approximation and show that it can be expressed as a series in odd powers of the discretization parameter h. We present quadrature rules which are highly accurate.\n\nThe efficient computation of the point vortex approximation is achieved through the use of the fast multipole algorithm, which combines long distance particle inter-actions into multipole expansions which can be efficiently evaluated. The underlying periodicity of the problem is reduced to a lattice sum which can be rapidly evaluated. We discuss the implementation of the numerical schemes in both serial and parallel computing environments.\n\nThe point vortex method is shown to be highly unstable for straightforward discretizations of the surface. We analyze the stability of the method about equilibrium and discuss methods for stabilizing the numerical schemes for both the linear and nonlinear regimes. We present numerical results which show that the method can be effectively stabilized.\n\nIn the final chapter, we present numerical results from several calculations of three-dimensional waves using the methods developed in the previous chapters." }, { "name": "Hasler, Paul Edward", "degree": "PhD", "year": "1997", "title": "Foundations of learning in analog VLSI", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062005-155140", "creators": [ { "name": { "family": "Hasler", "given": "Paul Edward" }, "id": "Hasler-Paul-Edward", "display_name": "Hasler, Paul Edward" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Andreou", "given": "Andreas G." }, "id": "Andreou-Andreas-G", "orcid": "0000-0003-3826-600X", "role": "member", "display_name": "Andreou, Andreas G." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "cns" ], "doi": "10.7907/2J7M-GE02", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nFloating-gate technology can be used to build silicon systems that adapt and learn. This technology is well suited to implement adaptation and learning because we are not building analog EEPROMS, but rather circuit elements with important time domain dynamics. These floating-gate circuits use the hot-electron-injection, electron-tunneling, and drain-induced-barrier-lowering phenomena in a standard submicron CMOS process. This technology works with the constraints of the silicon medium, and is similar to biological systems that turned potential liabilities into features.\r\n\r\nI develop the first analytical model of the impact-ionization and hot-electron processes in MOS devices by solving for a self-consistent distribution function from the spatially varying Boltzmann transport equation. From this electron distribution function, the probabilities of impact ionization and hot-electron injection are calculated as functions of channel current, drain voltage, and floating-gate voltage. The analytical model simultaneously fits both the hot-electron-injection and impact-ionization data. These analytical results yield measurements of the energy-dependent impactionization collision rate that is consistent with numerically calculated collision rates reported in the literature.\r\n\r\nI describe the design, fabrication, characterization, and modeling of an array of single-transistor synapses that simultaneously store the weight value, compute the product of the input and floating gate value, and update the weight value according to a hebbian or backpropagation learning rule. Circuits with one floating-gate synapse exhibit a range of possible stabilizing and destabilizing behaviors, and circuits with multiple-synapses show examples of competitive and cooperative behavior. By providing feedback to the source, we get a [...]FET synapse where voltage changes in both the floating gate and drain stabilize the floating gate.\r\n\r\nI present a bandpass floating gate amplifier that uses tunneling and [...]FET hot-electron injection to adaptively set its DC operating point. Because the gate currents are small, the circuit exhibits a high-pass characteristic with a cutoff frequency less than 1 Hz. The high frequency cutoff is controlled electronically, as is done in continuous-time filters. I have derived analytical models that completely characterize the amplifier and that are in good agreement with experimental data for a wide range of operating conditions and input waveforms. This autozeroing floating-gate amplifier demonstrates how to use continuous-time, floating-gate adaptation." }, { "name": "Hodowany, Jon", "degree": "PhD", "year": "1997", "title": "On the conversion of plastic work into heat", "advisor": "Ravichandran, Guruswami; Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-074409", "creators": [ { "name": { "family": "Hodowany", "given": "Jon" }, "id": "Hodowany-J", "display_name": "Hodowany, Jon" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FENH-ZK36", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe present study investigated heat evolution in metal plasticity. Specifically, experiments were designed to measure the partition of plastic work into heat and stored energy during dynamic deformations. The fraction of plastic work converted into heat has implications in a wide range of thermomechanical phenomena, including shear bands, dynamic fracture, ballistic penetration and high speed machining.\r\n\r\nKolsky bars, in compression and torsion, were used to determine mechanical properties at strain rates between [...] and [...]. For dynamic loading, in-situ temperature changes were measured using a high-speed HgCdTe photoconductive detector. Specially designed infrared optics, configured in tandem with the HgCdTe detector and the Kolsky bar constituted a novel experimental configuration for determining the fraction of plastic work converted into heat, and thus, the amount of energy stored in metals. The temperature detection system was ideally suited for small temperature excursions from ambient conditions, and was sensitive to temperature changes as little as 0.5 \u00b0C. The emissivity of metals was found to increase above certain high levels of plastic strain due to changes in surface roughness, which can affect the validity of temperature calibration. A technique of sample recovery, rough surface layer removal, and reloading was employed to obtain large plastic strains in the Kolsky bar. A Materials Testing System (MTS) servo-hydraulic load frame was used to measure mechanical properties at lower strain rates, [...] to [...] When temperature measurement was needed within this range of strain rates, a fast E-type thin wire thermocouple, with a time response of 1 ms, was employed.\r\n\r\nThe fraction of plastic work converted into heat, [beta], was treated as a constitutive function of strain and strain rate in the heat conduction equation. 2024 aluminum alloy and commercially pure [alpha]-titanium were the metal systems used in the current study to determine the functional dependence of [beta] on strain and strain rate. The T351, T4 and T6 tempers of 2024 aluminum did not exhibit strain rate dependence in flow stress over the entire range of strain rates tested. At low levels of plastic strain, all tempers of 2024 aluminum stored more than 50% of the input plastic work. At some level of plastic strain, depending on temper, 2024 aluminum could no longer store plastic work. After this point, [beta] increased to a value near 1.0 and remained nearly constant during subsequent plastic deformation. When averaged over all strains, [beta] was 0.85-0.95 depending on the particular heat treatment. The fraction of plastic work dissipated as heat was not found to be sensitive to strain rate over a wide range of strain rates. In contrast, the flow stress of [alpha]-titanium was strongly dependent on strain rate. The initial flow stress increased by more than 15% between strain rates of [...] and [...]. In addition, the strain hardening was also observed to be rate dependent. For fixed plastic strain, the tangent modulus increased as strain rate increased. Titanium dissipated a greater proportion of energy as heat at low strains than all tempers of 2024 aluminum. The ability to store energy in titanium decreased with increasing plastic strain. For plastic strains above 0.3, titanium dissipated nearly all input plastic work as heat. The proportion of energy dissipated as heat at fixed strain increased as strain rate increased.\r\n" }, { "name": "Horiuchi, Timothy Ken", "degree": "PhD", "year": "1997", "title": "Analog VLSI-Based, Neuromorphic Sensorimotor Systems: Modeling the Primate Oculomotor System", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechTHESIS:04092013-113114781", "creators": [ { "name": { "family": "Horiuchi", "given": "Timothy Ken" }, "id": "Horiuchi-Timothy-Ken", "display_name": "Horiuchi, Timothy Ken" } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "DeWeerth", "given": "Steve" }, "id": "DeWeerth-S", "role": "member", "display_name": "DeWeerth, Steve" }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." } ], "option_major": [ "cns" ], "doi": "10.7907/nbm7-1361", "abstract": "Using neuromorphic analog VLSI techniques for modeling large neural systems has several advantages\r\nover software techniques. By designing massively-parallel analog circuit arrays which are\r\nubiquitous in neural systems, analog VLSI models are extremely fast, particularly when local interactions\r\nare important in the computation. While analog VLSI circuits are not as flexible as software\r\nmethods, the constraints posed by this approach are often very similar to the constraints faced by\r\nbiological systems. As a result, these constraints can offer many insights into the solutions found by\r\nevolution. This dissertation describes a hardware modeling effort to mimic the primate oculomotor\r\nsystem which requires both fast sensory processing and fast motor control. A one-dimensional hardware\r\nmodel of the primate eye has been built which simulates the physical dynamics of the biological\r\nsystem. It is driven by analog VLSI circuits mimicking brainstem and cortical circuits that control\r\neye movements. In this framework, a visually-triggered saccadic system is demonstrated which\r\ngenerates averaging saccades. In addition, an auditory localization system, based on the neural \r\ncircuits of the barn owl, is used to trigger saccades to acoustic targets in parallel with visual targets.\r\nTwo different types of learning are also demonstrated on the saccadic system using floating-gate\r\ntechnology allowing the non-volatile storage of analog parameters directly on the chip. Finally, a\r\nmodel of visual attention is used to select and track moving targets against textured backgrounds,\r\ndriving both saccadic and smooth pursuit eye movements to maintain the image of the target in the\r\ncenter of the field of view. This system represents one of the few efforts in this field to integrate\r\nboth neuromorphic sensory processing and motor control in a closed-loop fashion." }, { "name": "Jonscher, Karen Rae", "degree": "PhD", "year": "1997", "title": "Quadrupole Ion Trap Mass Spectrometry of Peptides", "advisor": "Hood, Leroy E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142008-075423", "creators": [ { "name": { "family": "Jonscher", "given": "Karen Rae" }, "id": "Jonscher-Karen-Rae", "orcid": "0000-0002-7929-4886", "display_name": "Jonscher, Karen Rae" } ], "advisors": [ { "name": { "family": "Hood", "given": "Leroy E." }, "id": "Hood-L-E", "orcid": "0000-0001-7158-3678", "role": "advisor", "display_name": "Hood, Leroy E." } ], "committee": [ { "name": { "family": "Hood", "given": "Leroy E." }, "id": "Hood-L-E", "orcid": "0000-0001-7158-3678", "role": "chair", "display_name": "Hood, Leroy E." }, { "name": { "family": "Beauchamp", "given": "Jesse L." }, "id": "Beauchamp-J-L", "orcid": "0000-0001-8839-4822", "role": "member", "display_name": "Beauchamp, Jesse L." }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "orcid": "0000-0003-0787-1610", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/9btc-bk47", "abstract": "Biological mass spectrometry addresses the challenging unsolved structural issues surrounding biopolymers of fundamental importance to the biomedical sciences. Key to this discipline is the ability to extract useful information from complex peptide mixtures. Several approaches were developed to analyze peptides utilizing the unique capabilities of the quadrupole ion trap mass spectrometer. An external matrix-assisted laser desorption ionization source was constructed. Detection of peptides in the mid-femtomole range and of proteins in the low-femtomole range was reported. Singly-charged molecules with molecular weights in excess of 34,000 u were observed. Peptides generated by enzymatic digestion of the P protein of Sendai virus were separated by HPLC and the technique was successfully applied to locate phosphorylation sites.\r\n\r\nA hybrid quadrupole mass filter/quadrupole ion trap mass spectrometer was assembled. Peptide mixtures were separated by sequentially transmitting one value of m/z into the ion trap for mass analysis. The sequential injection technique served to significantly reduce space charge-induced suppression effects and improved resolution and fragmentation efficiency when compared to results obtained using an ion trap. A novel method of scanning afforded the ability to perform neutral loss experiments for the identification of phosphopeptides in a mixture. A long duty cycle, due to acquisition hardware, limited the utility of this approach for continuous ionization techniques.\r\n\r\nA low flowrate ionization source was constructed and interfaced to the hybrid and to an ion trap. A unique needle configuration provided a detection limit of 75 attomole of a peptide mixture infused into the source. A new type of liquid junction was developed to apply voltage to the sample consisting of a platinum wire inserted into the sidewall of a length of Teflon tubing. The junction was versatile, robust, and easy to use and performance compared well with other types of junctions. Capillary electrophoresis and hydrophobic membranes were used to separate peptide mixtures. Detection limits of the techniques were 1 femtomole and 10 femtomoles, respectively, for angiotensin. Differential release of peptides using step elutions from the hydrophobic membrane was demonstrated, providing a sensitive, high throughput means of mixture simplification prior to separation by capillary electrophoresis." }, { "name": "Kantner, Michael James", "degree": "PhD", "year": "1997", "title": "Robust simulation and analysis of nonlinear systems", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-080147", "creators": [ { "name": { "family": "Kantner", "given": "Michael James" }, "id": "Kantner-M-J", "display_name": "Kantner, Michael James" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/BDXE-V419", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nFor linear systems, robust analysis techniques are well developed. For non-linear systems, they are not. Most nonlinear analysis techniques use extensive simulation to examine system performance. However, these simulations do not give guarantees, they only describe local performance.\r\n\r\nThis thesis presents a simulation technique, called robust simulation, that answers the nonlinear robust analysis question. For an uncertain nonlinear system and a set of initial conditions, robust simulation calculates the set of all possible trajectories. By applying a measure to the set of all trajectories, a performance guarantee is obtained. To allow efficient robust simulation, only discrete time piecewise linear systems are considered. This class of systems admits a wide variety of nonlinearities and can approximate generic nonlinear systems to any degree of accuracy. To measure performance, a generalized [...] norm is used. As in the linear case, the robust nonlinear analysis question cannot be answered exactly. Instead, upper and lower bounds are calculated. Many techniques, including traditional simulation, exist for finding lower bounds. Robust simulation provides efficient methods for calculating an upper bound.\r\n\r\nRobust simulation also supports simulation when multiple models exist for a single system. When modeling a physical system, any amount of complexity is possible. Traditional simulation of these models with different levels of detail yields different individual trajectories. Which is correct? By explicitly quantifying the uncertainty as noise, robust simulation calculates sets of possible trajectories. For each model the result is guaranteed to contain the true output. More detailed models yield smaller sets of possible trajectories.\r\n\r\nTo test the algorithms, robust simulation is applied to a variety of examples. Algorithm performance is generally very good. Three other applications of robust simulation are also presented. In addition to measuring robust non-linear performance, robust simulation also generates lower bounds for model predictive control optimizations, verifies the stability of piecewise linear systems, and analyzes gain scheduled systems.\r\n" }, { "name": "Kedia, Rajesh", "degree": "PhD", "year": "1997", "title": "An Investigation of Velocity and Temperature Fields in Taylor-Couette Flows", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-131126", "creators": [ { "name": { "family": "Kedia", "given": "Rajesh" }, "id": "Kedia-Rajesh", "display_name": "Kedia, Rajesh" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Moser", "given": "Robert" }, "id": "Moser-R", "role": "member", "display_name": "Moser, Robert" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/0AAS-AW20", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn many experiments, especially those investigating aspects of fluid flow, it is common to observe time series data exhibiting chaos. Chaos lies in the realm of nonlinear dynamics, and specialized methods are available for the analysis of nonlinear time series. One particular method, called time delay analysis, is particularly useful for extracting information from time series representing measurements at a single point in space. In this thesis, hot-wire anemometry is used to obtain velocity time series from experiments on isothermal Taylor-Couette flow. For R/R[subscript c]=1.6, a simple limit cycle is observed, yielding an attractor of dimension of 1. For R/R[subscript c]=11.1, the attractor dimension increases, and the reconstructed attractor exhibits features characteristic of a transition to turbulence. In addition, various other states and transitions of the Taylor-Couette system are studied as well.\r\n\r\nDirect numerical simulations (DNS) have also been performed to study the effects of the gravitational and the centrifugal potentials on the stability of heated, incompressible Taylor-Couette flow. The flow is confined between two differentially heated, concentric cylinders and the inner cylinder is allowed to rotate. The Navier-Stokes equations and the coupled energy equation are solved using a spectral method. To validate the code, comparisons are made with existing linear stability analysis and with experiments. The code is used to calculate the local and average heat transfer coefficients for a fixed Reynolds number (R=100) and a range of Grashof numbers. The variation of the local coefficients of heat transfer on the cylinder surface is investigated, and maps showing different stable states of the flow are presented. Calculations of the time and space averaged equivalent conductivity show that the heat transfer decreases with Grashof number in axisymmetric Taylor vortex flow regime and increases with Grashof number after the flow becomes non-axisymmetric.\r\n\r\nThe numerical simulations also demonstrate the existence of a hysteresis loop in heated Taylor-Couette flow, obtained by slowly varying the Grashof number. Two different stable states with same heat transfer are found to exist at the same Grashof number. The validity of Colburn's correlation is investigated as well; the Prandtl number dependence is found to be slightly different from Pr[...] for the range of Reynolds number investigated. Finally, a time delay analysis of the radial velocity and the local heat transfer coefficient time series obtained from the numerical simulation of the radially heated Taylor-Couette flow is performed. The two-dimensional projection of the reconstructed attractor shows a limit cycle for Gr[...]-1700. The limit cycle behavior disappears at Gr[...]-2100, and the reconstructed attractor becomes irregular. The attractor dimension increases to about 3.2 from a value of 1 for the limit cycle case.\r\n" }, { "name": "Krok, James Christopher", "degree": "PhD", "year": "1997", "title": "Jet Initiation of Deflagration and Detonation", "advisor": "Shepherd, Joseph E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-181337", "creators": [ { "name": { "family": "Krok", "given": "James Christopher" }, "id": "Krok-James-Christopher", "display_name": "Krok, James Christopher" } ], "advisors": [ { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "advisor", "display_name": "Shepherd, Joseph E." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Kirschvink", "given": "Joseph L." }, "id": "Kirschvink-J-L", "orcid": "0000-0001-9486-6689", "role": "member", "display_name": "Kirschvink, Joseph L." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PSTR-T717", "abstract": "We have constructed a facility for the study of jet-initiated deflagration and detonation in hydrogen-air-steam mixtures. The facility is built around two pressure vessels. Mixtures of hydrogen, oxygen and nitrogen are spark-ignited in the driver vessel, generating a hot mixture of combustion products. The pressure rise ruptures a diaphragm, venting the products into the receiver vessel through nozzles of 12.7-92 mm diameter. The receiver is filled with hydrogen-air and hydrogen-oxygen mixtures diluted with either nitrogen or steam.
\r\n\r\nThe deflagration tests studied the lean and maximum-dilution limits of hydrogen-air mixtures ignited by a hydrogen-steam jet. The lean limit of 6% hydrogen was comparable to other studies. The maximum dilution limit for steam was 60%. This is higher than the limit found in spark/glow plug ignition experiments. Shock oscillations in the receiver increased with nozzle size.
\r\n\r\nFurther tests studied the initiation of detonation in both hydrogen-air and stoichiometric hydrogen-oxygen-diluent mixtures. In terms of jet diameter, D, and receiver detonation cell size, \u03bb, we found initiation limits of 2 < D/\u03bb < 7, where other experiments required a D/\u03bb of 11 or more. We propose that the D/\u03bb model does not adequately characterize jet initiation, as it does not reflect the conditions in the driver.
\r\n\r\nThe tests indicated that shock focusing plays an important role, promoting strong secondary explosions with or without prompt initiation of detonation. Mixtures with steam dilution were prone to DDT near the detonation limit, as the slower flame speed allows shock reflection and pressurization to occur before the reactants are consumed. Tests with nitrogen dilution had no DDT regime. Because of DDT and shock focusing, peak pressures were highest in mixtures that were slightly less sensitive than the detonation threshold. Schlieren movies confirmed the formation of a detonation near the nozzle exit.
" }, { "name": "Lazar, James Frederick", "degree": "PhD", "year": "1997", "title": "Analysis of single phase rectifier circuits", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142008-080504", "creators": [ { "name": { "family": "Lazar", "given": "James Frederick" }, "id": "Lazar-J-F", "display_name": "Lazar, James Frederick" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "co-advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZWBE-EV76", "abstract": "The preponderant application of rectifier circuits is the powering of dc loads from the ac utility line. Ordinary rectifier circuits present a nonlinear load impedance to the utility line, thereby generating harmonic currents, and contributing to the harmonic current problem. There are many active and passive rectifier circuits offering reduced harmonic currents, and in this work a methodology is developed by which these circuits may be analyzed and compared.\n\nRectifier circuits can be classified as either active or passive. A passive rectifier circuit contains passive components (inductors, capacitors, saturable reactors, etc.), and passive switches (rectifier diodes) only. Active rectifier circuits use at least one controllable active switch (power transistor), in addition to passive switches and passive components. The performance characteristics of these circuits can be assessed with respect to a fictional device called the ideal rectifier. This assessment allows direct comparison of various approaches, passive or active, using the ideal rectifier as the common reference. Rectifier circuit performance may also be compared against specified requirements.\n\nThe next topic considered is the analysis of active rectifier circuits employing a pwm (pulse width modulation) converter as a means to control power flow within the rectifier circuit. The pwm converter is modeled using the pwm switch method. A large-signal nonlinear pwm switch model is used for modeling large-signal rectifier circuit behavior, and models are developed for operation in either the continuous or discontinuous conduction mode. Similarly, a small-signal model is developed for small-signal considerations. In addition, for pwm converters operating in the continuous conduction mode, the effect of lossy resistive elements inside the converter are accounted for in the pwm switch model, and this modeling technique is shown to give results identical to those obtained via the state-space averaging method.\n\nThe methods developed are then applied to the analysis of the boost rectifier operating in the discontinuous conduction mode. Three control schemes are compared, each offering a different compromise between circuit complexity and performance. Finally, a design example is given, and experimental results are provided.\n" }, { "name": "Lee, Robert Bumju", "degree": "PhD", "year": "1997", "title": "All-Optical Wavelength Conversion by Four-Wave Mixing in a Semiconductor Optical Amplifier", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-142830", "creators": [ { "name": { "family": "Lee", "given": "Robert Bumju" }, "id": "Lee-Robert-Bumju", "display_name": "Lee, Robert Bumju" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "chair", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "member", "display_name": "Quake, Stephen R." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4yye-5f58", "abstract": "Wavelength division multiplexed optical communication systems will soon become an integral part of commercial optical networks. A crucial new function required in WDM networks is wavelength conversion, the spectral translation of information-laden optical carriers, which enhances wavelength routing options and greatly improves network reconfigurability. One of several techniques for implementing this function is four-wave mixing utilizing ultra-fast intraband nonlinearities in semicondutor optical amplifiers.
\r\n\r\nThe effects of input power, noise prefiltering and semiconductor optical amplifier length on the conversion efficiency and optical signal-to-noise ratio were examined. Systems experiments have been conducted in which several important performance characteristics of the wavelength converter were studied. A bit-error-rate performance of < 10-9 at 10 Gb/s was achieved for a record shift of 18 nm down in wavelength and 10 nm up in wavelength. Two cascaded conversions spanning a 40 km fiber link at 10 Gb/s are also demonstrated for conversions of up to 9 nm down and up in wavelength. The dynamic range of input signal power and its impact on the BER performance were studied at 2.5 Gb/s for both a single-channel conversion and a simultaneous 2-channel conversion. The crosstalk penalty induced by parasitic cross-gain modulation in 2-channel conversion is quantified. The spectral inversion which results from the conversion process is studied by time-resolved spectral analysis, and its application as a technique for dispersion compensation is demonstrated.
\r\n\r\nFinally, the application of selective organometallic vapor-phase epitaxy for the formation of highly-uniform and densely-packed arrays of GaAs quantum dots is demonstrated. GaAs dots of 15-20 nm in base diameter and 8-10 nm in height terminated by slow-growth crystallographic planes were grown within dielectric-mask openings and characterized by atomic force microscopy.
\r\n" }, { "name": "Lin, Wei", "degree": "PhD", "year": "1997", "title": "The trellis complexity of block and convolutional codes", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142008-075936", "creators": [ { "name": { "family": "Lin", "given": "Wei" }, "id": "Lin-Wei", "display_name": "Lin, Wei" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Kiely", "given": "Aaron B." }, "id": "Kiely-A-B", "role": "member", "display_name": "Kiely, Aaron B." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Wilson", "given": "Richard M." }, "id": "Wilson-R-M", "role": "member", "display_name": "Wilson, Richard M." }, { "name": { "family": "Dolinar", "given": "Samuel J." }, "id": "Dolinar-S-J", "role": "member", "display_name": "Dolinar, Samuel J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/5130-4858", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis concerns the computational complexity of high performance decoding algorithms. The primary objective is to design the most efficient maximum-likelihood (ML) decoders for both block codes and convolutional codes. By efficient, we mean an implementation of ML decoding algorithms on trellises that minimize the computational complexity (the total number of additions and comparisons). Trellises are graph representations of codes. Since decoding complexity is completely determined by the particular trellis employed, the problem is equivalent to constructing the minimal trellis (one that has the minimum number of edges, vertices and bifurcations) for a given code.\r\n\r\nThere are four parts to this research. The first problem we attacked was to construct the minimal trellises for block codes over the coordinate permutations. The related problem of finding a coordinate permutation that minimizes the number of vertices at a given depth in the minimal trellis for a binary linear block code [36] has been proven to be NP-complete. Our approach was based on the concept of span of the generator matrices, which connects the code parameters and the trellis complexity. New bounds on measures of trellis complexity such as [E] (the total number of edges) and [V] (the total number of vertices) were obtained from the analysis of the span distribution. Aiming to minimize the total span in a generator matrix, an efficient, effective \"divide-and-conquer\" algorithm and variants were proposed to search for the optimal or a good trellis structure for any block code. For example, it took about 12 minutes on a Sun Sparc Station 20 to find one optimal permutation for the [48,24,12] QR code from 48! candidates.\r\n\r\nBy introducing the concept of trellis-canonical generator matrices and a simple algorithm to compute one, we developed a general theory of minimal trellises for convolutional codes. In this theory, punctured convolutional codes no longer have to be treated as special cases. By then, the minimal trellises for block and convolutional codes were both well-defined. This allowed one to make a direct performance-complexity comparison between block codes and convolutional codes.\r\n\r\nThe ratio of performance (measured by the asymptotic coding gain-ACG) and complexity (measured by the logarithm trellis edge complexity-LTC) defines the coding efficiency. By means of the span analysis, we also proved a universal lower bound on the complexity to performance ratio. It implies that [...] can never be smaller than 1 for any code, block or convolutional. In some cases, the bound is optimal or asymptotically optimal. The study suggests that optimal codes in terms of minimum distance or free distance do not necessarily offer the best coding efficiency.\r\n\r\nThe last problem addressed in this dissertation is the implementation of maximum-likelihood decoding and the computational complexity for convolutional codes. By combining the optimal sectionalization technique [45] with minimal trellis theory, a low complexity hybrid decoding algorithm was developed. For some partial unit memory convolutional codes, its decoding complexity is significantly superior to other known algorithms. There are two components of the computational complexity. One is the edge metric computation cost [...]. We proved a lower bound on [...] which is independent of the computation mechanism (sequential or parallel). This bound is optimal in some cases. The other is the cost of the state metric updating which is inferable from the trellis structure. This sets a lower bound on the computational complexity for any implementation.\r\n\r\nFinally we give a general review of research activities on this subject and present a list of open problems.\r\n" }, { "name": "Lin, Xianghong", "degree": "PhD", "year": "1997", "title": "Bulk Glass Formation and Crystallization of Zr-Ti Based Alloys", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042004-160010", "creators": [ { "name": { "family": "Lin", "given": "Xianghong" }, "id": "Lin-Xianghong", "display_name": "Lin, Xianghong" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/dwm0-yq34", "abstract": "The first metallic glass was discovered by Pol Duwez and his colleagues at Caltech in 1960. Shortly after that, Turnbull pointed out that a high ratio of melting temperature over glass transition temperature favors glass formation based on classical nucleation theory. Using Turnbull's theory as a guideline, many alloy systems were found forming glasses. As a new state of metallic alloys, metallic glass is of scientific interest by itself as well as attractive for practical applications due to unique properties. However, since the critical cooling rates for glass formation of conventional alloys are relatively high, at least one dimension of the metallic glass is limited to a few tenths of milimeter. This severely limited the application of metallic glasses.
\r\n\r\nRecently, several multicomponent alloy systems were discovered that form bulk metallic glasses with the smallest dimension of several mm up to several cm. Two of these alloy systems are the Ti-Zr-Cu-Ni and the Zr-Ti-(Nb)-Cu-Ni-Al alloys, which were discovered during this thesis research.
\r\n\r\nIn this thesis homogeneous and heterogeneous nucleation theories and their influence on glass formation are reviewed. Experimental methods for metallic glass processing are introduced. The formation of Ti-Zr-Cu-Ni and Zr-Ti-(Nb)-Cu-Ni-Al bulk metallic alloys are reported. The glass transition, crystallization behavior, and mechanical properties of these glassy alloys are presented. The optimized combinations of four or five elements in these alloys leads to very deep eutetic multicomponent alloys, in which nucleation of crystals upon undercooling becomes increasingly improbable. Thermodynamic, kinetic and topological factors are discussed that contribute the exceptional glass forming ability of these alloys.
\r\n\r\nThe very high stability of the undercooled liquids of bulk glass forming alloys makes it possible to perform studies on undercooled liquids in a time and temperature window that was not accessible thus far. In this thesis the time temperature transformation diagrams were measured for the crystallization of undercooled Zr-Ti-(Nb)-Cu-Ni-Al liquids. It has been discovered that the crystallization of the undercooled liquid is caused by heterogeneous nucleation induced by oxide particles, even when the oxygen concentration is as low as 250 atomic ppm. Overheating the melts above the liquidus temperature of the oxide particle results in maximum undercooling. Strong oxygen concentration dependence of the overheating, undercooling, and TTT diagrams was found. These results suggest that impurities play a key role in the crystallization of undercooled liquid. This first systematic study of impurity effect on crystallization of undercooled liquid will have many important implications on making bulk glasses and any study of undercooled liquids.
\r\n\r\nTo summarize this thesis, important factors which affect the crystallization are revealed and discussed. Strategies on how to find new bulk metallic glasses are suggested.
" }, { "name": "Lin, Yuan-Pei", "degree": "PhD", "year": "1997", "title": "One- and Two-Dimensional Cosine Modulated Filter Banks", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-145701", "creators": [ { "name": { "family": "Lin", "given": "Yuan-Pei" }, "id": "Lin-Yuan-Pei", "display_name": "Lin, Yuan-Pei" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/n255-7g92", "abstract": "Subband coding as a lossy data compression technique was first introduced for speech coding. It has been demonstrated to be a very competitive coding method for general audio signals as well as images. Subband coding has been incorporated in various popular coding standards. Essential to the implementation of subband coding is an M-channel filter bank that partitions the input signal into M subbands. In the context of 1D (one-dimensional) filter bank design, the CMFB (cosine modulated filter bank) is well-known for design and implementation efficiency. All the filters in the filter bank are cosine modulated versions of a prototype filter. As a result the cost of design as well as complexity is reduced dramatically by a factor of M. In this thesis we study the design of CMFB in 1D case and 2D (two-dimensional) case.
\r\n\r\nIn previous works on 1D CMFB, the filters in the filter bank do not have linear phase, which is considered an important feature in image coding applications. The design of cosine modulated filter banks with linear-phase filters is the first topic to be presented in this thesis. Design examples will be given to show that filter banks with filters having good frequency selectivity can be obtained in spite of the linear phase constraint.
\r\n\r\nFor the design of 2D cosine modulated filter banks, the simplest approach is to cascade 1D filter banks in the form of a tree. This type of 2D filter banks are referred to as separable. The frequency support of the filters in a separable filter bank are restricted to rectangular shapes. Nonseparable filter banks allow more flexible partitions of the frequency plane and achieve better performance. Almost all the existing design techniques for 2D nonseparable filter banks are developed exclusively for the two-channel case. We will consider two types of 2D M-channel nonseparable filter banks, the two-parallelogram type and the four-parallelogram type. These are respectively the classes of filter banks in which the passbands of the filters consist of two and four parallelograms. In these designs additional cosine modulated constraints will be incorporated for design and implementation economy.
" }, { "name": "Lu, Hongbing", "degree": "PhD", "year": "1997", "title": "Nonlinear thermo-mechanical behavior of polymers under multiaxial loading", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072003-103136", "creators": [ { "name": { "family": "Lu", "given": "Hongbing" }, "id": "Lu-H", "display_name": "Lu, Hongbing" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SH42-W153", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [?]. Abstract is included in .pdf document.\n\nIn order to better understand phenomena related to \"yield-like\" behavior of polymers, the nonlinear thermo-mechanical behavior of Polymethyl Methacrylate (PMMA) under combined axial (tension, compression) and shear stress states (torsion) is investigated on thin walled cylindrical specimens at temperatures between 22[degrees] and 100[degrees]C. A non-contact measurement technique based on digital image correlation method is developed to determine the surface deformations on curved cylindrical specimens at various temperatures, including temperatures close to the glass transition when the specimens become soft. The study indicates that in contrast to tile mutual independence of shear and dilatational response under conditions appropriate for linearized viscoelasticity, one observes an increasingly strong coupling between all deformation or stress invariants as assessed in creep experiments for strains in excess of' 0.4%. While shear stresses alone elicit nonlinear response in creep (rates) as \"intrinsically\" nonlinear shear response, the superposition of small positive dilatation accelerates shear deformations while negative dilatation retards it in quantitative agreement with free volume arguments. Passing below the glass transition still produces greater creep acceleration from positive dilatation than from a decrease in specific volume, but the dominance of the intrinsic shear nonlinearity vis-a-vis the dilatational ilifluence increases below [...] as the temperature drops. A constitutive model based oil free volume consideration is modified from the models proposed by Losi and Knauss (1992). Comparison of experimental results with model prediction indicates a good qualitative agreement, and reasonably good quantitative agreement." }, { "name": "Marshall, William K.", "degree": "PhD", "year": "1997", "title": "Dynamics of Amplitude and Phase in Semiconductor Lasers and Effects of Propagation in Dispersive Optical Fibers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-06072005-131657", "creators": [ { "name": { "family": "Marshall", "given": "William K." }, "id": "Marshall-William-K", "display_name": "Marshall, William K." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Libbrecht", "given": "Kenneth George" }, "id": "Libbrecht-K-G", "role": "member", "display_name": "Libbrecht, Kenneth George" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/amwv-x166", "abstract": "The work described in this thesis occupies the region of overlap between the modulation, chirp, and noise properties of semiconductor lasers on one hand and dispersive propagation in optical fiber on the other. It is shown herein that simple relationships exist between the amplitude and phase variations of different kinds and that these relations lead to consequences of dispersive propagation which are different for the noise from semiconductor lasers than for the modulation. A range of topics related to the main theme of the interplay between laser chirp, amplitude-phase correlation, and dispersive propagation is considered. That there is much to be gained by understanding them together, as inter-related issues, is the overall conclusion.
\r\n\r\nFirst, changes in intensity variations which occur during dispersive propagation are described compactly in terms of a transfer function involving the relationship between amplitude and phase variations of the source. Then, the main dynamic characteristics of semiconductor lasers are described including the relationships between amplitude and phase variations produced by modulation and noise in semiconductor lasers. For an appropriate combination of laser and fiber parameters, it is demonstrated that the laser intensity noise can be reduced over a wide range of frequencies. It is also demonstrated that the change in relative intensity noise with propagation has a different dependence on laser and fiber parameters than does the change in modulation response. Next, the phenomenon of adiabatic compression of the gain and index of refraction in a semiconductor due to spectral hole burning is considered, clarifying some aspects of the commonly-used spectral hole burning model. Finally, the problem of the semiconductor laser and dispersive propagation of the output is re-examined within a quantum mechanical context and the input-output relations for the laser are explored.
" }, { "name": "Maskit, Daniel", "degree": "PhD", "year": "1997", "title": "Software register synchronization for super-scalar processors with partitioned register files", "advisor": "Taylor, Stephen", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102008-153402", "creators": [ { "name": { "family": "Maskit", "given": "Daniel" }, "id": "Maskit-D", "display_name": "Maskit, Daniel" } ], "advisors": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "advisor", "display_name": "Taylor, Stephen" } ], "committee": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "chair", "display_name": "Taylor, Stephen" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/tyap-ea69", "abstract": "Increases in high-end microprocessor performance are becoming increasingly reliant on simultaneous issuing of instructions to multiple functional units on a single chip. As the number of functional units increases, the chip area, wire lengths, and delays required for a monolithic register file become unreasonable. Future microprocessors will have partitioned register files. The correctness of contemporary super-scalar processors relies on synchronized accesses to registers. This issue will be critical in systems with partitioned register files. Current techniques for managing register access ordering, such as register score boarding and register renaming, are inadequate for architectures with partitioned register files. This thesis demonstrates the difficulties of implementing these techniques with a partitioned register file, and introduces a novel compiler algorithm which addresses this issue.\n\nWhenever a processor using register scoreboarding or register renaming issues an instruction, either the scoreboard or the register name table must be accessed to check the instruction's sources and destination. If the register file is partitioned, checking the scoreboard or name table for a remote register is difficult. One functional unit cannot determine at runtime when it is safe to write to a register in another functional unit's register file. While these techniques can be supported through use of a global or partitioned scoreboard, such an implementation would be complex, and have latency problems similar to those of a monolithic register file.\n\nThis work discusses the organization of multiple functional units into loosely-coupled groups of functional units that can communicate via direct register writes, but with purely local hardware interlocks to force synchronization. A novel compiler algorithm, Software Register Synchronization (SRS), is introduced. A comparison between SRS and existing hardware mechanisms is conducted using the Multiflow compiler modified to generate code for the MIT M-Machine, Experiments to evaluate the SRS algorithm are run on the M-Machine simulator being used for architectural verification. In order to support partitioned register file architectures, an alternative to traditional hardware methods for managing register synchronization needs to be developed. This thesis presents a novel compiler algorithm to address this need. The SRS algorithm is described, demonstrated to be correct, and evaluated. Details of the implementation of the SRS algorithm within the Multiflow compiler for the MIT M-Machine are provided." }, { "name": "Melnik, M. Susan", "degree": "PhD", "year": "1997", "title": "Diamond surfaces : interactions with hydrogen and halogens", "advisor": "Goddard, William A., III; Goodwin, David G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-075117", "creators": [ { "name": { "family": "Melnik", "given": "M. Susan" }, "id": "Melnik-M-Susan", "display_name": "Melnik, M. Susan" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "co-advisor", "display_name": "Goodwin, David G." } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/gdrt-7n92", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAbsolute deuterium coverage on the diamond C(100) surface has been measured under a variety of dosing conditions by nuclear reaction analysis (NRA) using [...]. The (2x1) surface with ~1.0 D per surface C is produced under typical dosing conditions. However, at unusually high filament temperatures circa 2000\u00b0C, coverages up to 1.34 \u00b1 0.09 D per surface C are observed. Coverage is calibrated by comparing to a standard containing 1.5x[...] D/[...]. Signal from subsurface deuterium is estimated to be negligible by comparison to previous scattering experiments and by secondary-ion mass spectroscopy of a homoepitaxial CVD (100) sample. D breakage of surface dimer bonds at high filament temperature is proposed as a mechanism to generate surface dideuterides. The relevance of dimer breakage and dihydride formation to recent experiments on surface degradation is briefly discussed.\r\n\r\nPrevious models of hydrogen reactions with C(100) are substantially revised to include all types of sites on the reconstructed terrace, and it is shown that saturation coverage determines the ratio of site-averaged abstraction rate to site-averaged recombination rate, [...]. NRA coverage measurements of 0.95 \u00b1 0.04 D per surface C imply a [...] of 0.06 \u00b1 0.04 at 1800\u00b0C gas temperature and 360\u00b0C surface temperature. Results indicate that thermochemical kinetic models overpredict by a factor of ~20 the fraction of sites available for growth during diamond CVD.\r\n\r\nIn a separate issue, C(110) surface mobility is demonstrated by calculating activation energies for the migrations of H, F, and Cl with quantum chemical methods using hydrocarbon cluster models. The calculations included extensive basis sets with many-body effects at the level of single and double excitations from Hartree-Fock and Complete-Active-Space wavefunctions. Intra-chain migrations of H along [...] carbon chains and nearest-neighbor F migration are found to be too slow to compete with thermal desorption. However, inter-chain migrations of H and Cl are calculated to be sufficiently fast to compete with thermal desorption under ultrahigh vacuum conditions and with gas-surface reactions under typical diamond growth conditions. This was the first study to consider migration rates as well as barriers, establishing mobility's competitiveness during diamond growth. [...]/[...] is estimated to be [...]. Finally, a kinetic Monte-Carlo algorithm is presented to directly combine mobility with gas-surface reactions in the same iteration step when simulating hydrogen processing of diamond.\r\n" }, { "name": "Meng, Zhaoyue", "degree": "PhD", "year": "1997", "title": "Thermodynamic and dynamic modeling of atmospheric aerosols", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-085509", "creators": [ { "name": { "family": "Meng", "given": "Zhaoyue" }, "id": "Meng-Z", "display_name": "Meng, Zhaoyue" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/0jjb-5n70", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis dissertation investigates thermodynamic and dynamic modeling of urban and regional atmospheric aerosols. A rigorous and efficient aerosol thermodynamic model, SCAPE2, is developed. The model considers the inorganic aerosol system of sulfate, nitrate, ammonium, chloride, sodium, potassium, calcium, magnesium, carbonate, and water. SCAPE2 can be used to predict either the equilibrium gas/aerosol partition of volatile inorganic species or the particle surface vapor concentrations if applied to the aerosol phase only. It has also the option of predicting the equilibrium or metastable aerosol water content.\r\n\r\nA three-dimensional, size- and chemically-resolved aerosol dynamic model is developed by incorporating the aerosol thermodynamic model, SCAPE2, into an urban airshed model (CIT model). The model includes advection, turbulent diffusion, condensation/evaporation, nucleation, emissions, and dry deposition. Gas-to-particle conversion is represented by dynamic mass transfer between the gas and aerosol phases. The model employs an absorption approach in dynamically modeling production of secondary organic aerosols. A calculation method for dry deposition of aerosol particles is proposed.\r\n\r\nThe aerosol model is applied to simulate gas and aerosol behavior in the 27-29 August episode in the 1987 Southern California Air Quality Study (SCAQS). Simulation results are compared systematically against SCAQS measurements, and general good agreement is observed. The assumption that volatile inorganic species such as [...] are at instantaneous, local equilibrium is examined and it is found that, in many instances, gas/aerosol mass transfer limits the rate of gas-to-particle conversion.\r\n" }, { "name": "Miller, Raanan Ariel", "degree": "PhD", "year": "1997", "title": "Microfabricated electromagnetic flap actuators and their applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142008-081338", "creators": [ { "name": { "family": "Miller", "given": "Raanan Ariel" }, "id": "Miller-R-A", "display_name": "Miller, Raanan Ariel" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1m4s-8d50", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn this thesis, a new technology which successfully combines silicon bulk micromachining with the electroplating of metal conductors and magnetic materials is presented. This technology has enabled the fabrication of the first bulk micromachined electromagnetic flap actuators. The demonstrated characteristics of these actuators are large size (> 16 mm [...]), large forces (> 100 [...]N), and large (> 60 degrees ) deflections. In this technology, silicon bulk micromachining is used to form the mechanical structures of the actuators, and the electroplating of copper and ferromagnetic permalloy provides the electromagnetic actuating components.\r\n\r\nThe developed actuators are configured in the shape of a flap, consisting of a single crystal silicon plate and on-plate electromagnetic components. The silicon plate, 4 mm x 4 mm x 40 [...]m, is connected to a substrate via several silicon springs. When the electromagnetic components are activated the silicon plate flaps up and down similar to a butterfly wing. Three types of actuators have been examined and they differ in electromagnetic components. Type-1 actuators have a permalloy layer, the type-2 actuators have copper coils, and the type-3 actuators have both the permalloy and copper coils. The actuators are operated in the presence of an externally applied magnetic field, and the deflections of the flap actuators can be controlled either by varying the external magnetic field strength or by changing the current to the copper coils.\r\n\r\nThe electromagnetically induced deflections of the actuators are measured and agree well with the design using a combined electromagnetic/mechanical model. Achieved deflection angles of the type-1 actuators exceed 60 \u00b0 at an applied field of around 80 KA/m (1000 gauss). Additional deflection angles of about \u00b1 20 degrees (type-3 actuator) can also be obtained by coil currents of \u00b1 100 mA. As a result, large deflections up to 80\u00b0, together with a large force exceeding 100 [...]N, have been achieved in the micro devices. Moreover, we have successfully demonstrated these actuators in two applications for scanning mirrors for holographic data storage systems and fiber optic bypass switches. Using the actuators as scanning mirrors, we have demonstrated initial storage of several hundred holograms in a photosensitive crystal. The fiber optic bypass switches using the MEMS flap actuator have much better mechanical performance and lower power consumption when compared to a commercial (Di-Con) fiber optic bypass switch.\r\n" }, { "name": "Minch, Bradley Arthur", "degree": "PhD", "year": "1997", "title": "Analysis, synthesis, and implementation of networks of multiple-input translinear elements", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-075623", "creators": [ { "name": { "family": "Minch", "given": "Bradley Arthur" }, "id": "Minch-B-A", "display_name": "Minch, Bradley Arthur" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "co-chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" } ], "option_major": [ "cns" ], "doi": "10.7907/rh58-rz05", "abstract": "At the time of its invention in the seventeenth century, the logarithmic slide rule literally revolutionized the way calculation was done. From then until the advent of the pocket calculator, this analog computational device was widely used to perform multiplications and divisions, to raise numbers to fixed powers and extract fixed roots of numbers. Today, the slide rule may be gone, but it is not forgotten. In this thesis, I present a class of simple translinear network circuits which essentially function as electronic slide rules, accurately computing products, quotients, powers, and roots. I describe two different analysis procedures that allow us to determine the steady-state relationship between input and output currents. I also describe systematic techniques for synthesizing such circuits whereby we can produce a circuit whose steady-state transfer characteristics embody some desired product-of-power-law relationship between input and output currents. These circuits are made from multiple-input translinear elements; such elements produce output currents that are proportional to the exponential of a weighted sum of their input voltages. We can implement the weighted voltage summations with either resistive or capacitive voltage dividers. We can obtain the required exponential voltage-to-current transformations from either bipolar transistors or subthreshold MOS transistors. The subthreshold floating-gate MOS transistor naturally implements the exponential-of-a-weighted-sum operation in a single device. I will present experimental results from several of these translinear network circuits breadboarded from subthreshold floating-gate MOS transistors. I will also describe and present experimental data from a variety of other implementations of the multiple-input translinear element." }, { "name": "Moussessian, Alina", "degree": "PhD", "year": "1997", "title": "Quasi-optical active antennas", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292010-105455980", "creators": [ { "name": { "family": "Moussessian", "given": "Alina" }, "id": "Moussessian-A", "display_name": "Moussessian, Alina" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0nah-v928", "abstract": " Quasi-optical power combiners such as quasi-optical grids provide an efficient means of combining the output power of many solid-state devices in free space. Unlike traditional power combiners no transmission lines are used, therefore, high output powers with less loss can be achieved at higher frequencies.\r\n\r\n This thesis investigates four different active antenna grids. The first investigation is into X-band High Electron Mobility Transistor (HEMT) grid amplifiers. Modelling and stability issues of these grids are discussed, and gain and power measurements are presented. A grid amplifier with a maximum efficiency of 22.5% at 10 GHz and a peak gain of 11 dB is presented. The second grid is a varactor grid used as a positive feedback network for a grid amplifier to construct a tunable grid oscillator. Reflection measurements for the varactor grid show a tuning range of 1.2 GHz. The third grid is a self-complementary grid amplifier. The goal is to design a new amplifier with a unit cell structure that can be directly modelled using CAD tools. The properties of self-complementary structures are studied and used in the design of this new amplifier grid. The fourth grid is a 12 x 12 terahertz Schottky grid frequency doubler with a measured output power of 24 mW at 1 THz for 3.1- \u00b5s 500-GHz input pulses with a peak power of 47 W.\r\n\r\n A passive millimeter-wave travelling-wave antenna built on a dielectric substrate is also presented. Calculations indicate that the antenna has a gain of 15 dB with 3-dB beamwidths of 10\u00b0 in the H-plane and 64\u00b0 in the E-plane. Pattern measurements at 90 GHz support the theory. The antenna is expected to have an impedance in the range of 505\u03a9 to 80\u03a9." }, { "name": "Nagel, Laura Jeanne", "degree": "PhD", "year": "1997", "title": "Vibrational entropy differences in materials", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-094133", "creators": [ { "name": { "family": "Nagel", "given": "Laura Jeanne" }, "id": "Nagel-L-J", "display_name": "Nagel, Laura Jeanne" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/bwwk-w256", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nAn investigation has been made into the differences in vibrational entropy between two states of a material. These vibrational entropy differences have been measured experimentally by low-temperature calorimetry for several alloy systems. The results from the calorimetry experiments have been compared with phonon densities of states (DOS) for the two states of the material obtained from inelastic neutron scattering data. The systems which have been examined are [...], and nanophase [...].\n\nThe difference in vibrational entropy between chemically disordered and [...]-ordered [...] was measured by calorimetry to be [...] /atom at high temperatures, with the ordered alloy having the lower vibrational entropy. Analysis of the vibrational modes of the ordered and disordered alloys with a Born-von Karman model showed that the lower vibrational entropy of the ordered alloy originates from high-frequency optical modes involving large-amplitude vibrations of the aluminum-rich sublattice.\n\nInelastic neutron scattering measurements were performed on powdered [...]. The alloy was prepared in two states of chemical order: 1) with equilibrium [...] order, and 2) an fcc solid solution prepared by high- energy ball milling. The main difference in the phonon DOS of the ordered and disordered alloys occurs near 39 meV, the energy of a peak arising from optical modes in the ordered alloy. These high-frequency optical modes involve primarily the vibrations of the aluminum-rich sublattice. The difference in vibrational entropy of disordered and ordered [...] kB/atom at high temperatures.\n\nThe difference in heat capacity of chemically disordered and [...] ordered [...] was measured by calorimetry from 70 K - 300 K. By comparing these measured results to a harmonic heat capacity calculated with a Born-von Karman model, we estimate the difference in vibrational entropy between disordered and ordered Cu3Au to be [...] kg/atom at high temperatures.\n\nSamples of [...] were prepared with two microstructures: 1) with equilibrium [...] order, and 2) with partial disorder (having a large [...] chemical order parameter, but without the tetragonality of the unit cell). We measured the difference in their heat capacities from 60 K to 325 K and inelastic neutron scattering spectra at four values of Q at 11 K and at 300 K. We describe a microstructural contribution to the anharmonic heat capacity that originates with the anisotropy of the [...] structure. We estimate the difference in vibrational entropy between partially-disordered and ordered [...] to be [...] kg/atom at high temperature. The elastic energy stored in the microstructure is about 60 J/mole at low temperatures.\n\nThe difference in vibrational entropy between fcc disordered and hexagonal ordered [...] was measured by calorimetry to be [...] /atom at high temperatures, with the ordered alloy having the lower vibrational entropy. Neutron diffraction data revealed that the observed L12 region of the phase diagram does not exist, but is a state that can be obtained in quenched alloys.\n\nNeutron energy loss spectra were measured for two states of nanophase Fe: 1) as-milled, with a characteristic nanocrystallite size of 12 nm, and 2) annealed, with a characteristic crystallite size of 28 nm. The longitudinal peak in the phonon DOS of the nanophase Fe was broadened compared to that of\nthe annealed material. We attribute this broadening to short phonon lifetimes in nanocrystals. The nanophase material also showed an enhanced density of states at low energies below 15 meV, which may indicate the presence of inter-crystallite vibrations. These differences in phonon DOS should have only a small effect on the difference in vibrational entropy of n.anocrystalline and larger-grained [...].\n\nThe vibrational entropy differences that have been measured are large enough in comparison to 0.56 [...]/atom, the maximum possible difference in configurational entropy for a 3:1 atomic ratio, to make a significant contribution to the alloy thermodynamic" }, { "name": "Natarajan, Venkata V. R.", "degree": "PhD", "year": "1997", "title": "Material and thermal transport in vertical granular flows", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01182008-091551", "creators": [ { "name": { "family": "Natarajan", "given": "Venkata V. R." }, "id": "Natarajan-V-V-R", "display_name": "Natarajan, Venkata V. R." } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." } ], "option_major": [ "mecheng" ], "doi": "10.7907/wze4-p323", "abstract": "The term \"granular material flow\" is applied in the literature to particulate flows such as the flow of coal down an inclined chute, the discharge of grains from a hopper or the motion of debris in a landslide. In these flows, the material has an overall bulk motion; however, individual particles may collide, roll or slide against each other, and may interact with the bounding surfaces. Hence, the individual particle motions are composed of a mean velocity component and a fluctuating, or random, velocity component. An analogy is drawn between this random motion and the random motion of molecules. As a result, much of the theoretical analysis of these flows has developed from concepts derived from dense-gas kinetic theory. Although this random velocity component is a key property in analytical studies, there have been few attempts to measure its magnitude in experimental studies. In the current work, measurements were made of two components of the average and fluctuating velocities in the flow of granular material in a vertical chute for flows with different particle and boundary properties. The fluctuation velocities were highly anisotropic, with the streamwise components being 2 to 2.5 times the magnitude of the transverse components. Increasing the surface roughness of the particles reduced the fluctuation velocities significantly.\n\nAnother area of considerable industrial interest is particle mixing in monodisperse and polydisperse particle flows. Because of the random component of particle motion, the particles can exhibit a diffusive motion similar to that found in gases and liquids. In the second part of this work, local self diffusion coefficients were measured in the granular flow using image processing techniques to track individual particles. The influence of flow shear rates and fluctuation velocities on the self diffusion coefficients was investigated. The self-diffusion coeffecients were found to increase with the shear rate and the fluctuation velocity, with the coefficients in the streamwise direction being an order-of-magnitude higher than those for the transverse direction. The surface roughness of the particles led to a decrease in the self-diffusion coefficients.\n\nThe effect of shearing on the convective heat transfer from a heater immersed in a granular flow was investigated experimentally. Comparisons were made with previous experiments and with results obtained for unsheared plug flows. The results indicated that the medium density close to the wall played a critical role in determining the overall heat transfer.\n\nFinally, theoretical solutions, based on a combination of the dense-gas kinetic theory and an empirical friction model, were generated to study and compare experimental and theoretical results for velocity profiles and heat transfer characteristics in vertical, fully developed granular flows. The results indicated good agreement between theoretical and experimentally measured mean velocity proflies but the fluctuation velocity magnitudes were usually underpredicted by the theoretical solutions. There was qualitative agreement between experimental and theoretical results for convective heat transfer.\n" }, { "name": "Noca, Flavio", "degree": "PhD", "year": "1997", "title": "On the Evaluation of Time-Dependent Fluid-Dynamic Forces on Bluff Bodies", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08102005-132659", "creators": [ { "name": { "family": "Noca", "given": "Flavio" }, "id": "Noca-Flavio", "display_name": "Noca, Flavio" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K2Z0-9016", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nWe present some exact expressions for the evaluation of time-dependent forces on a body in an incompressible and viscous cross-flow which only require the knowledge of the velocity field (and its derivatives) in a finite and arbitrarily chosen region enclosing the body.\r\n\r\nGiven a control volume V with external surface S which encloses an arbitrary body, the fluid-dynamic force F on the body can be evaluated from one of the following three expressions (in abbreviated form):\r\n\r\nF = [...] + body motion terms,\r\n\r\nF = [...] + body motion terms,\r\n\r\nF = no volume integral terms + [...] + body motion terms,\r\n \r\nwhere N is the space dimension, u is the flow velocity, [...] is the vorticity, x is the position vector, and the tensors [...], [...], [...] depend only on the velocity field u and its (spatial and temporal) derivatives.\r\n\r\nThe first equation is already known for either simply connected domains or inviscid flows. We re-derive it here for viscous flows in doubly connected domains (i.e. domains which include a body). We then obtain the second and third equation through a simple algebraic manipulation of the first equation.\r\n\r\nThese expressions are particularly useful for experimental techniques like Digital particle Image Velocimetry (DPIV) which provide time sequences of 2D velocity fields but not pressure fields.\r\n\r\nThey are tested experimentally with DPIV on two-dimensional, low Reynolds number circular cylinder flows. Both steady and unsteady motions are studied." }, { "name": "Packman, Aaron Ian", "degree": "PhD", "year": "1997", "title": "Exchange of colloidal kaolinite between stream and sand bed in a laboratory flume", "advisor": "Brooks, Norman H.; Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01152008-142257", "creators": [ { "name": { "family": "Packman", "given": "Aaron Ian" }, "id": "Packman-A-I", "display_name": "Packman, Aaron Ian" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "co-advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "member", "display_name": "Hering, Janet G." }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Murray", "given": "Bruce C." }, "id": "Murray-B-C", "role": "member", "display_name": "Murray, Bruce C." } ], "option_major": [ "envreng" ], "doi": "10.7907/FYMP-BR13", "abstract": "Experiments were conducted in a recirculating flume to study the exchange of colloids between a stream and sand bed. Observations of the net transport of kaolinite clay from the stream to the bed were used to validate models for colloid exchange which include the hydraulics of water exchange along with the particle-specific effects of filtration and settling.\r\n\r\nThe flume allowed extensive control of the stream conditions (slope, depth, velocity) and bed parameters (bed depth, bedform height, wavelength, and velocity). All experiments had steady, uniform stream flow and well-developed bedforms. To define the chemistry of the system, the composition of the flume water was controlled, the clay was reproducibly prepared, and the sand was cleaned prior to every experiment.\r\n\r\nExperiments involved observing the exchange of both a conservative lithium chloride tracer and the kaolinite tracer. Net exchange was determined by measuring the change of tracer concentration in the stream water. Vertical profiles of the tracer distribution in the bed were also measured.\r\n\r\nColumn experiments were performed to measure kaolinite filtration by the bed sediment. The pH and ionic strength of both the flume and column water were controlled to vary the extent of filtration.\r\n\r\nTwo mechanisms are responsible for exchange between the stream and stream bed--an advective pore-water flow driven by bedform-induced pressure variations at the surface of the bed (pumping), and the burial and release of water due to bedform motion (turnover). Pumping causes kaolinite to be carried deep in the bed where it is trapped due to filtration and settling. Turnover causes continuous mixing of the uppermost portion of the bed which hinders penetration of clay to the deeper bed.\r\n\r\nModels incorporating the relevant physical and chemical processes controlling colloid transport were developed to predict the net exchange of kaolinite between the stream and sand bed. Model parameters were nondimensionalized so the models can be applied to problems of any scale. Models for conservative solutes were developed to predict the exchange with a finite bed and exchange due to fast-moving bedforms. Models for colloid transport were developed which are based on the solute transport models, but include the impact of settling on particle flow paths and filtration along path lines. When input data were taken from laboratory experiments, the models generally predicted the flume results well with no calibration. In all flume experiments, filtration and settling of colloids in the bed were sufficiently high so that it could be assumed that all colloid which entered the bed was irreversibly trapped.\r\n\r\nAdditional model simulations were performed to demonstrate the effect of major input variables on exchange. These simulations cover cases not examined in experiments and provide a sensitivity analysis for the model inputs.\r\n" }, { "name": "Palmer, Michael Edward", "degree": "PhD", "year": "1997", "title": "Exploiting parallel memory hierarchies for ray casting volumes", "advisor": "Taylor, Stephen", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-080520", "creators": [ { "name": { "family": "Palmer", "given": "Michael Edward" }, "id": "Palmer-M-E", "display_name": "Palmer, Michael Edward" } ], "advisors": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "advisor", "display_name": "Taylor, Stephen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/mbmg-ne39", "abstract": "Previous work in single-processor ray casting methods for volume rendering has concentrated on algorithmic optimizations to reduce computational work. This approach leaves untapped the performance gains which are possible through efficient exploitation of the memory hierarchy.\n\nPrevious work in parallel volume rendering has concentrated on parallel partitioning, with the goals of maximizing load balance and minimizing communication between distributed nodes. This implies a simplified view of the memory hierarchy of a parallel machine, ignoring the relationship between parallel partitioning and memory hierarchy effects at all but the top level.\n\nIn this thesis, we progressively develop methods to optimize memory hierarchy performance for ray casting: 1) on a uniprocessor, using algorithmic modifications to isolate cache miss costs, specialized hardware to monitor cache misses on the bus, and a software cache simulator; 2) on the a shared-memory Power Challenge multiprocessor, examining the fundamental dependence of algorithmic design decisions regarding parallel partitioning upon memory hierarchy effects at several levels; and 3) on a distributed array of interconnected Power Challenge multiprocessors, on which we implement a logical global address space for volume blocks, and investigate the tradeoff between replication (caching) and communication of data.\n\t\nThe methods we develop permit us to exploit the coherence found in volume rendering to increase memory locality, and thereby increase memory system performance. This focus on the optimal exploitation of the entire memory hierarchy, from the processor cache, to the interconnection network between distributed nodes, yields faster frame rates for large (357 MB to 1 GB) datasets than have been previously cited in the literature, and allows us to efficiently render a 7.1 GB dataset, the largest ever rendered.\n\nOur results have implications for the parallel solution of other problems which, likeray casting, require a global gather operation, use an associative operator to combine partial results, and contain coherence. We discuss implications for the design of a parallel architecture suited to solving this class of problems, specifically, that these algorithms are best served by a deep memory hierarchy." }, { "name": "Papalexandris, Miltiadis Vassilios", "degree": "PhD", "year": "1997", "title": "Unsplit Numerical Schemes for Hyperbolic Systems of Conservation Laws with Source Terms", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032005-161139", "creators": [ { "name": { "family": "Papalexandris", "given": "Miltiadis Vassilios" }, "id": "Papalexandris-Miltiadis-Vassilios", "display_name": "Papalexandris, Miltiadis Vassilios" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HW7S-AR36", "abstract": "In this thesis, a new method for the design of unsplit numerical schemes for hyperbolic systems of conservation laws with source terms is developed. Appropriate curves in space-time are introduced, along which the conservation equations decouple to the characteristic equations of the corresponding one-dimensional homogeneous system. The local geometry of these curves depends on the source terms and the spatial derivatives of the solution vector. Numerical integration of the characteristic equations is performed on these curves.\r\n\r\nIn the first chapter, a scalar conservation law with a stiff, nonlinear source term is studied using the proposed unsplit scheme. Various tests are made, and the results are compared with the ones obtained by conventional schemes. The effect of the stiffness of the source term is also examined.\r\n\r\nIn the second chapter, the scheme is extended to the one-dimensional, unsteady Euler equations for compressible, chemically-reacting flows. A numerical study of unstable detonations is performed. Detonations in the regime of low overdrive factors are also studied. The numerical simulations verify that the dynamics of the flow-field exhibit chaotic behavior in this regime.\r\n\r\nThe third chapter deals with the development and implementation of the unsplit scheme, for the two-dimensional, reactive Euler equations. In systems with more than two independent variables there are one-parameter families of curves, forming manifolds in space-time, along which the one-dimensional characteristic equations hold. The local geometry of these manifolds and their position relative to the classical characteristic rays are studied. These manifolds might be space-like or time-like, depending on the local flow gradients and the source terms.\r\n\r\nIn the fourth chapter a numerical study of two-dimensional detonations in performed. These flows are intrinsically unstable and produce very complicated patterns, such as cellular structures and vortex sheets. The proposed scheme appears to be capable of capturing many of the the important details of the flow-fields. Unlike traditional schemes, no explicit artificial-viscosity mechanisms need to be used with the proposed scheme." }, { "name": "Paulsen, Susan Catherine", "degree": "PhD", "year": "1997", "title": "A Study of the Mixing of Natural Flows Using ICP-MS and the Elemental Composition of Waters", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012008-080000", "creators": [ { "name": { "family": "Paulsen", "given": "Susan Catherine" }, "id": "Paulsen-Susan-Catherine", "display_name": "Paulsen, Susan Catherine" } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "chair", "display_name": "List, E. John" }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/mx81-8e29", "abstract": "Determining flow patterns and the distribution of chemical constituents in the environment is critical to understanding and solving problems in freshwater, estuarine, and coastal environments. Computer models describing flows in the environment usually use empirical estimates of key parameters and are difficult to validate. The objective of this research was to develop a method to trace flows in surface waters by directly measuring existing conditions. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to establish elemental \"fingerprints\" for water sources, and fractions of \"fingerprinted\" waters in a sample containing these source waters were estimated. Two different, complex systems were studied: the Sacramento-San Joaquin Delta and the near-coastal environment of Oahu, Hawaii. If the method could be successfully used in these highly complicated environments, it should be applicable in almost any other natural environment. Successful application in three smaller, simpler systems supports this conclusion.
\r\n\r\nWithin the Delta, source \"fingerprints\" were established, and their variation both temporally and spatially was determined. Elemental behavior was determined by laboratory work and field studies, and a simple mathematical model was used to calculate the fraction of source water in samples collected throughout the system. Mixing was consistently determined for most flow conditions using the tracer elements sodium, magnesium, calcium, and strontium. The method was used to establish the sources of water pumped from the Delta into major aqueducts and the effects of various operational changes.
\r\n\r\nBecause of Hawaii's uniform geology and difficulties measuring trace elements in saline waters, the method was significantly less successful in Hawaii. Concentrations of major ions were used to estimate dilution for stream and wastewater flows to 25:1 in receiving waters; rare earth elements (lanthanum, praseodymium, and neodymium) were added to a wastewater flow to qualitatively determine mixing at dilution levels of about 300:1.
\r\n\r\nThe procedures for ICP-MS analysis developed for this study are presented, as are the criteria for selecting and using elemental tracers in freshwater, estuarine, and certain saltwater environments. The method can be used to directly determine mixing levels and the distribution of chemical constituents, to validate computer models, and to address a variety of specific environmental issues.
" }, { "name": "Peill, Nicola Joy", "degree": "PhD", "year": "1997", "title": "Fiber-optic bundled array cable reactors for heterogeneous photocatalysis and waste stream remediation", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142008-082303", "creators": [ { "name": { "family": "Peill", "given": "Nicola Joy" }, "id": "Peill-N-J", "display_name": "Peill, Nicola Joy" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/4x4b-8w92", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nApplication of semiconductor photocatalysis in a fixed-bed fiber-optic bundled array cable reactor (OFR) for the purification of contaminated water is investigated in this thesis. An optical fiber cable is employed as a means of light transmission and distribution to solid-supported TiO2. The system is designed for remote delivery of light to the photocatalyst, to allow for measurement of light fluxes for direct determination of quantum yields and for reuse of the reactor to test various coatings and light input angles, and to minimize possible heat build-up and delamination problems.\n\nExperiments are carried out to determine the operational factors affecting the chemical efficiency of the OFR system. The uniformity and extent of light propagation down the fiber, the degree of light absorption by the TiO2 coating, the fiber diameter, the input light intensity, and the ability of the chemical substrates to diffuse into the TiO2 coating are determined to be important parameters. In addition, a TiO2 coating that minimizes the interfacial surface area of the quartz core and TiO2 particles and operation with incident irradiation angles near 90\u00b0 enhance light propagation down the fibers. Relative quantum efficiencies in the OFR are found to be comparable to slurry-phase photochemical reaction systems.\n\nThe OFR is shown to effectively degrade several model chemical contaminants such as pentachlorophenol (PCP), 4-chlorophenol (4CP), dichloroacetate (DCA), and oxalate (OX) under varying reaction conditions. Relatively high quantum efficiencies of [...] = 0.010, 0.015, 0.08, and 0.17, respectively, and complete mineralization to CO2, H2O and HCl are observed.\n\nWhen iron(III)-doped quantum-sized (Q) TiO2 (Fe/Q-TiO2) is used as a photocatalytic coating, the extent of linear light transmission in a single fiber is doubled relative to Degussa P25. However, the Fe/Q-TiO2 coating is found to have inferior light absorption properties and chemical reactivity leading to lower relative quantum efficiencies.\n\nA concentrating, solar powered prototype OFR is designed and tested. Photoefficiencies with sunlight were comparable to that achieved with a Xe-arc source. Lower light intensity-to-photocatalytic surface area ratios result in increased relative quantum efficiencies.\n\nA mathematical model of a fiber-optic bundled array reactor system is developed using Langmuir-Hinshelwood kinetics and compared to experimental data. A global quantum efficiency, [...], is defined and used as a model fitting parameter. It incorporates reaction parameters such as the absorbed light intensity, the intrinsic rate constant, and the effects of other adsorbed reactants and reaction intermediates. An empirical term to describe the radiation field within the coated fiber is derived and normalized by the coating photocatalyst particle concentration to account for the inverse relationship between the absorbed light intensity and the reaction quantum efficiency. The [...] is determined to be independent of the absorbed light intensity and calculated values are in excellent agreement with experimental values.\n\nAn analysis of conventional and advanced remediation technologies is performed (Appendix). The chemistry and engineering behind advanced oxidation systems is reviewed, and a means of technical evaluation and comparison is presented. The \"electrical energy per order,\" or EEO is defined as the electrical energy required to reduce the concentration of a given pollutant by one order of magnitude in 1000 gal of water. The EEO can be used to compare the efficacy of remediation technologies with other AOT's and conventional systems for a particular cleanup application.\n" }, { "name": "Prochazka, Aurelius", "degree": "PhD", "year": "1997", "title": "Stability and structure of stretched vortices", "advisor": "Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142008-091416", "creators": [ { "name": { "family": "Prochazka", "given": "Aurelius" }, "id": "Prochazka-A", "display_name": "Prochazka, Aurelius" } ], "advisors": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "chair", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Grether", "given": "David M." }, "id": "Grether-D-M", "role": "member", "display_name": "Grether, David M." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/sc0x-1g40", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nWe investigate, numerically and analytically, the structure and stability of steady and quasi-steady solutions of the Navier-Stokes equations corresponding to steady stretched vortices embedded in a uniform nonsymmetric straining field, [...], [...], one principal axis of extensional strain of which is aligned with the vorticity. These are known as nonsymmetric Burgers vortices studied first by Robinson and Saffman (1984). We consider vortex Reynolds numbers [...] where [...] is the vortex circulation and [...] the kinematic vorticity, in the range [...], and a broad range of strain ratios [...] including [...], and in some cases [...]. A pseudo-spectral method is used to obtain numerical solutions corresponding to steady vortex states over our whole ([...] parameter space including [...], where arguments proposed by Moffatt, Kida, and Ohkitani (1994) suggest the nonexistence of steady solutions. When [...] and [...], we find an accurate asymptotic form for the vorticity in a region [...], giving, in some cases, near machine-precision agreement with our numerical solutions. This suggests the existence of an extended region where the exponentially small vorticity is confined to a near cat's-eye shaped region of the almost two-dimensional flow, and takes a constant value nearly equal to [...] on bounding streamlines. This allows an estimate of the leakage rate of circulation to infinity as [...] = [...] with corresponding exponentially slow decay of the vortex when [...]. This leakage rate differs substantially from that estimated by Moffatt, Kida, and Ohkitani. The normal-mode linear stability of the axisymmetric Burgers vortex [...] to two-dimensional disturbances is calculated in detail and the vortex is found to be stable at all Reynolds numbers. An iterative technique based on the Power method is used to estimate the largest eigenvalues for the nonsymmetric case [...]. Stability is found for [...], and a neutrally convective mode of instability is found and analyzed analytically for [...]. Our general conclusion is that the generalized nonsymmetric Burgers vortex is unconditionally stable to two-dimensional disturbances for all [...], and that the vortex will tend to move with the background strain when [...], but maintain its structure which will change only through exponentially slow leakage of vorticity, indicating extreme robustness in this case.\n" }, { "name": "Rathinam, Muruhan", "degree": "PhD", "year": "1997", "title": "Differentially flat nonlinear control systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01152008-082733", "creators": [ { "name": { "family": "Rathinam", "given": "Muruhan" }, "id": "Rathinam-M", "display_name": "Rathinam, Muruhan" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/k7pm-hs13", "abstract": "Differentially flat systems are underdetermined systems of (nonlinear) ordinary differential equations (ODEs) whose solution curves are in smooth one-one correspondence with arbitrary curves in a space whose dimension equals the number of equations by which the system is underdetermined. For control systems this is the same as the number of inputs. The components of the map from the system space to the smaller dimensional space are referred to as the flat outputs. Flatness allows one to systematically generate feasible trajectories in a relatively simple way. Typically the flat outputs may depend on the original independent and dependent variablesterms of which the ODEs are written as well as finitely many derivatives of the dependent variables. Flatness of systems underdetermined by one equation is completely characterised by Elie Cartan's work. But for general underdetermined systems no complete characterisation of flatness exists.\n\nIn this dissertation we describe two different geometric frameworks for studying flatness and provide constructive methods for deciding the flatness of certain classes of nonlinear systems and for finding these flat outputs if they exist. We first introduce the concept of \"absolute equivalence\" due to Cartan and define flatness in this frame work. We provide a method of testing for the flatness of systems, which involves making a guess for all but one of the flat outputs after which the problem is reduced to the case solved by Cartan. Secondly we present an alternative geometric approach to flatness which uses \"jet bundles\" and present a theorem which partially characterises flat outputs that depend only on the original variables but not on their derivatives, for the case of systems described by two independent one-forms in arbitrary number of variables. Finally, for the class of Lagrangian mechanical systems whose number of control inputs is one less than the number of degrees of freedom, we provide a characterisation of flat outputs that depend only on the configuration variables, but not on their derivatives. This characterisation makes use of the Riemannian metric provided by the kinetic energy of the system.\n" }, { "name": "Reisman, Garrett Erin", "degree": "PhD", "year": "1997", "title": "Dynamics, acoustics and control of cloud cavitation on hydrofoils", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302004-140539", "creators": [ { "name": { "family": "Reisman", "given": "Garrett Erin" }, "id": "Reisman-G-E", "display_name": "Reisman, Garrett Erin" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/48X3-7X08", "abstract": "Cloud-cavitation, often formed by the breakdown and collapse of a sheet or vortex cavity, is responsible for severe cavitation noise and erosion damage. This thesis describes an experimental investigation of the dynamics and acoustics of cloud cavitation on a three dimensional hydrofoil and examines the injection of air as a means of noise suppression.\n\nPart one of this work examines the large amplitude impulsive pressures which were measured on the suction surface of an oscillating hydrofoil experiencing cloud cavitation and these pressure pulses are correlated with the observation of shock waves propagating through the bubbly mixture. Recess mounted transducers were used to measure unsteady pressures at four locations along the chord of the suction surface of a hydrofoil. By examining the transducer output, two distinct types of pressure pulses were identified. Local pulses occurred at a single transducer location and were randomly distributed in position and time. Conversely, global pulses were registered by all the transducers almost simultaneously. The location of the global pulses relative to the foil oscillation was quite repeatable and these events produced substantial far-field noise. Correlation of the transducer output with high speed movies of the cavitation revealed that the global pulses were produced by a large scale collapse of the bubble cloud. Conversely, local pulses were generated by local disturbances in the bubbly mixture characterized by large changes in void fraction.\n\nThe large pressure pulse associated with the local and global cavitation structures, the geometric coherence of their boundaries and the nearly discrete change in void fraction across the boundaries of these structures indicate that these structures consist of bubbly shock waves. Qualitative and quantitative comparisons between the current experiments and the numerical, analytic and experimental bubbly shock wave analysis of other investigators support this conclusion.\n\nPart two of this work examines the dramatic reduction in cloud cavitation noise due to both continuous and pulsed injection of air into the cavitating region of the foil. At sufficient air flow rates, the radiated noise could be reduced by a factor greater than 200 relative to the noise produced without air injection. Unsteady surface pressure measurements also showed a reduction in the acoustic impulse with air injection by a factor of up to two orders of magnitude. An explanation for this noise reduction can be found by examining the high speed motion pictures. The presence of the non-condensible gas in the cavitation cloud is shown to prevent any rapid or coherent collapse process. Although the formation of local structures is still observed, the presence of air in the bubbles diminishes both the magnitude and the frequency of occurrence of local pressure pulses. Finally, pulsed air injection results in a lower acoustic impulse than the impulse obtained by injecting the same mass of air continuously over the entire oscillation cycle." }, { "name": "Salik, Boaz", "degree": "PhD", "year": "1997", "title": "Spatio-temporal beam synthesis and applications to photolithography", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-01172008-101729", "creators": [ { "name": { "family": "Salik", "given": "Boaz" }, "id": "Salik-B", "display_name": "Salik, Boaz" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ws8q-mt53", "abstract": "This thesis explores techniques for and applications of free-space beam shaping. After reviewing the basic principles of scalar diffraction theory, I discuss and experimentally demonstrate several approaches to two- and three-dimensional transverse beam synthesis; these include analytical solutions of varying complexity as well as methods for computer optimization of beams with arbitrary constraints. Analytical solutions are also presented for the temporal analogy of nondiffracting beams, i.e., nondispersing pulses, and repercussions to time-dependent diffraction theory are discussed.\n\nNext these beam shaping methods are applied to imaging photolithography, addressing ways to improve both resolution and focal depth therein with the use and proper design of phase masks. In this work it is evident that computation time plays a critical role in the applicability of phase masks to photolithography, because phase mask design algorithms tend to scale unfavorably with mask size. I therefore introduce an approximation to the Hopkins equation which reduces the computation time for partially coherent imaging by one to two orders of magnitude. Following this the question of spatial coherence in phase mask-assisted photolithography becomes interesting, and the optimal coherence for such systems is investigated both theoretically and experimentally. The properties of incoherent imaging are next applied to a slightly different problem--imaging through random media. A new technique for ballistic imaging is presented, discussed theoretically, simulated, and demonstrated experimentally, and its advantages and drawbacks are analyzed. Finally, a theoretical overview of the fundamental limits to space-time beam shaping is presented, several results of which are demonstrated.\n\nDue to the diversity of the subjects discussed, introductions and brief histories are given at the beginning of relevant chapters." }, { "name": "Sarpeshkar, Rahul", "degree": "PhD", "year": "1997", "title": "Efficient precise computation with noisy components : extrapolating from an electronic cochlea to the brain", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092005-104717", "creators": [ { "name": { "family": "Sarpeshkar", "given": "Rahul" }, "id": "Sarpeshkar-Rahul", "display_name": "Sarpeshkar, Rahul" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "orcid": "0000-0002-7947-0472", "role": "member", "display_name": "Andersen, Richard A." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Lyon", "given": "Richard F." }, "id": "Lyon-Richard-F", "role": "member", "display_name": "Lyon, Richard F." } ], "option_major": [ "cns" ], "doi": "10.7907/FSBH-QA93", "abstract": "Low-power wide-dynamic-range systems are extremely hard to build. The cochlea is one of the most awesome examples of such a system: It can sense sounds over 12 orders of magnitude in intensity, with an estimated power dissipation of only a few tens of microwatts.\r\n\r\nWe describe an analog electronic cochlea that processes sounds over 6 orders of magnitude in intensity, while dissipating less than 0.5mW. This 117-stage, 100Hz-10Khz cochlea has the widest dynamic range of any artificial cochlea built to date. This design, using frequency-selective gain adaptation in a low-noise traveling-wave amplifier architecture, yields insight into why the human cochlea uses a traveling-wave mechanism to sense sounds, instead of using bandpass filters.\r\n\r\nWe propose that, more generally, the computation that is most efficient in its use of resources is an intimate hybrid of analog and digital computation. For maximum efficiency, the information and information-processing resources of the hybrid form of computation must be distributed over many wires, with an optimal signal-to-noise ratio per wire. These results suggest that it is likely that the brain computes in a hybrid fashion, and that an underappreciated and important reason for the efficiency of the human brain, which only consumes 12W, is the hybrid and distributed nature of its architecture." }, { "name": "Shcheglov, Kirill Vadim", "degree": "PhD", "year": "1997", "title": "Synthesis, optical and electronic properties of group IV semiconductor nanocrystals", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-01172008-081522", "creators": [ { "name": { "family": "Shcheglov", "given": "Kirill Vadim" }, "id": "Shcheglov-Kirill-Vadim", "display_name": "Shcheglov, Kirill Vadim" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Quake", "given": "Stephen R." }, "id": "Quake-S-R", "role": "member", "display_name": "Quake, Stephen R." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/59ar-ek67", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nEvery operating control system must deal with constraints. On the one hand, the range and rate of change of the input or manipulated variable is limited by the physical nature of the actuator (saturation limits). On the other hand, process state variables or outputs (pressures, temperatures, voltages) may not be allowed to exceed certain bounds arising from equipment limitation, safety considerations, or environmental regulations.\r\n\r\nA rich theory exists for designing controllers - both linear ([...],LQG, LTR, pole-placement) and nonlinear (nonlinear [...], control, feedback linearization, sliding mode control, gain scheduling). However, none of these popular and fashionable controller design techniques account for the presence of input or output constraints. Although occasionally these constraints may be neglected, in general, they lead to design and operating problems unless they are accounted for properly.\r\n\r\nIn traditional control practice, overrides or mode selection schemes are used to deal with output constraints: they switch between a \"bank\" of controllers, each of which is designed to achieve a specific objective. In both cases (saturation limit and mode selection), a control input nonlinearity is introduced into the operating system.\r\n\r\nDespite its significance, the study of the constrained control problem has received far less attention than the traditional unconstrained (linear and nonlinear) control theory. With few exceptions, most of the controller design techniques for constrained systems are by-and-large ad-hoc, with very little guarantees of stability, performance and robustness to plant model uncertainty.\r\n\r\nThe objective of this thesis is to take a broad approach towards the constrained control problem. One part of the thesis is devoted to the development of a systematic and unifying theory for studying the so-called Anti-Windup Bumpless Transfer (AWBT) problem. The other part aims towards the development of a general novel approach for the synthesis of a robust model predictive control (MPC) algorithm.\r\n\r\n\r\nNOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nGroup IV semiconductor (Si, Ge and Sn) nanocrystals were synthesized in dielectric matrixes by ion implantation of the respective species into the matrix to form a supersaturated solid solution and subsequent precipitation by thermal annealing. The resulting structure was characterized by Transmission Electron Microscopy and Raman spectroscopy. It was found that nanocrystals of these materials can be effectively synthesized with diameters in the nanometer range. Ge nanocrystals in SiO[...] were extensively characterized, particle size distributions were counted from TEM results and were used to compare experimental photoluminescence spectra with theoretical predictions. Unusual nanostructures were formed in samples co-implanted with Ge and Sn and annealed at 600\u00b0C. Raman spectroscopy indicated a possibility of significant alloying of Ge and Sn in these nanostructures. Optical properties of Si nanocrystals in silicon dioxide were investigated by photoluminescence spectroscopy as well. It was found that while Ge nanocrystal system luminescence is mostly due to defects in the matrix produced by ion implantation, Si nanocrystal sample luminescence is due to the Si nanocrystals themselves. The luminescence is above the bulk Si bandgap and supports the quantum confined excitonic luminescence theory. Light emitting devices were fabricated using both systems. Electroluminescence was observed for both Si and Ge, albeit with rather low efficiency, in the 10[...] - 10[...] range. Electroluminescence from Si nanocrystal containing devices was spectrally similar to photoluminescence from that system, with a band about 800 nm, consistent with electronic excitation of radiative transitions in Si nanocrystals. Cubic nonlinearities were measured for both Ge and Si nanocrystals and found to be 10[...] - 10[...] esu range. Finally, an interesting interferometric arrangement which has a potential to be useful for investigating nanoscale structures was theoretically described.\r\n" }, { "name": "Siefert, Ronald Lyn", "degree": "PhD", "year": "1997", "title": "Speciation of Fe in ambient aerosol and cloudwater", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01172008-110632", "creators": [ { "name": { "family": "Siefert", "given": "Ronald Lyn" }, "id": "Siefert-R-L", "display_name": "Siefert, Ronald Lyn" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/fssg-ew75", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nAtmospheric iron (Fe) is thought to play an important role in cloudwater chemistry (e.g., S(IV) oxidation, oxidant production, etc.), and is also an important source of Fe to certain regions of the worlds oceans where Fe is believed to be a rate-limiting nutrient for primary productivity. This thesis focuses on understanding the chemistry, speciation and abundance of Fe in cloudwater and aerosol in the troposphere, through observations of Fe speciation in the cloudwater and aerosol samples collected over the continental United States and the Arabian Sea. Different chemical species of atmospheric Fe were measured in aerosol and cloudwater samples to help assess the role of Fe in cloudwater chemistry. Chapter 2 presents a set of experiments which used ambient aerosol samples suspended in aqueous solution and then irradiated with uv-light to simulate cloudwater conditions. These experiments found Fe to be a critical component for the production of [...]. Chapter 3 discusses the development and application of a novel photochemical extraction method for the determination of photochemically-available Fe in ambient aerosol samples. Photochemically-available Fe ranged from < 4 ng [...] to 308 ng [...], and accounted for 2.8% to 100% of the total Fe in aerosol samples collected in California and New York. Calculations based on the results of these experiments predicted that redox reactions of Fe in cloudwater could be an important in situ source of oxidants ([...], [...]/[...]). Chapter 4 presents results of several field studies which measured the redox states of Fe and other transition metals (Mn, Cu and Cr) in cloudwater. These measurements were then used in thennodynamic models which predicted Fe(III) to be either as Fe(III)-hydroxy species or Fe(III)-oxalate species. However, an un-identified strong chelating ligand with Fe(III) was also suggested by the thermodynamic model results. Chapter 5 presents results of a field study conducted on the Arabian Sea. Total atmospheric labile-Fe(II) ranged between < 0.09 ng [...] to 7.5 ng [...] during the inter-monsoon period, and was consistently below the detection limit during the southwest-monsoon period. The labile-Fe(II) measured during the inter-monsoon period was predominantly found in the fine fraction of the aerosol. Principal component analysis revealed a significant source of Fe and Mn which was not associated with the main aeolian dust component.\n" }, { "name": "Sivo, Joseph Michael", "degree": "PhD", "year": "1997", "title": "Rotordynamic Forces Due to Annular Leakage Flows in Shrouded Centrifugal Pumps", "advisor": "Hunt, Melany L.; Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-103727", "creators": [ { "name": { "family": "Sivo", "given": "Joseph Michael" }, "id": "Sivo-Joseph-Michael", "display_name": "Sivo, Joseph Michael" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "advisor", "display_name": "Hunt, Melany L." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "co-advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/bpfm-0a24", "abstract": "Previous experimental and analytical results have shown that discharge-to-suction leakage flows in the annulus of a shrouded centrifugal pump contribute substantially to the fluid induced rotordynamic forces (Adkins, 1988). Experiments conducted in the Rotor Force Test Facility (RFTF) at Caltech on an impeller undergoing a prescribed circular whirl have indicated that the leakage flow contribution to the normal and tangential forces can be as much as 70% and 30% of the total, respectively (Jery, 1986). Recent experiments at Caltech have examined the rotordynamic consequences of leakage flows and have shown that the rotordynamic forces are functions not only of the whirl ratio but also of the leakage flow rate and the impeller shroud to pump housing clearance. The forces were found to be inversely proportional to the clearance and a region of forward subsynchronous whirl was found for which the average tangential force was destabilizing. This region decreased with flow coefficient (Guinzburg, 1992).
\r\n\r\nThe present research is a continuation of the previous experimental work and has been motivated by the rotordynamic stability problems with the recently developed Alternate Turbopump Design (ATD) of the Space Shuttle High Pressure Oxygen Turbopump. The present study investigates the influence of swirl brakes, installed in the annular leakage path, as a means of reducing the undesirable rotordynamic forces over a range of flow rates. Also, the present study evaluates the effect on the rotordynamic forces of tip leakage restrictions at discharge used by the ATD for establishing axial thrust balance. As a first step to understanding the flow field in the leakage annulus, the region is probed with a laser velocimeter to provide basic information on these unsteady turbulent three-dimensional leakage flows and to serve as a standard of comparison for approximate theoretical models as well as applications of computational fluid dynamics.
" }, { "name": "Sur, Sudipto", "degree": "PhD", "year": "1997", "title": "Robotic manipulation with flexible link fingers", "advisor": "Burdick, Joel Wakeman; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01172008-092801", "creators": [ { "name": { "family": "Sur", "given": "Sudipto" }, "id": "Sur-S", "display_name": "Sur, Sudipto" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/RVP5-Q254", "abstract": "Robots with structural flexibility provide an attractive alternative to rigid robots for many of the new and evolving applications in robotics. In certain applications their use is unavoidable. The increased complexity in modeling and control of such robots is offset by desirable performance enhancements in some respects. In this thesis we present a singular perturbation approach for modeling, analysis and control of robots with flexibility. As our singular perturbation approach does not treat the flexible manipulator as a perturbation of the rigid manipulator, it can treat significant flexibility, beyond the linear range. Analysis based on this approach leads to some provably stable control laws for the hybrid position and force control of flexible-link manipulators. The analysis is done in the framework of a single robot manipulator in a constrained motion task. Simulations and experimental results are presented for this case. To show applicability of the results to more general and complex systems with flexibilities we also present experimental data from a planar, two-fingered, reconfigurable grasping setup which allows rigid and flexible configurations. The aim of the experimentation is to show the applicability of the control laws and analysis developed, and to determine the performance enhancements resulting from the introduction of flexibility. Experimental data is analysed to show the tradeoffs between controller complexity and performance enhancement as we deal with greater flexibility. Various performance criteria are set up and experimental results are discussed within their framework. We conclude that large flexibility can be controlled without too much additional effort, has performance comparable to that of rigid robots, and possesses enhancing properties which make it appealing for use in certain types of applications." }, { "name": "Turteltaub, Sergio Ricardo", "degree": "PhD", "year": "1997", "title": "Dynamics of phase transformations in thermoelastic solids", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02042008-151022", "creators": [ { "name": { "family": "Turteltaub", "given": "Sergio Ricardo" }, "id": "Turteltaub-S-R", "display_name": "Turteltaub, Sergio Ricardo" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/gk0c-8r75", "abstract": "The dynamical aspects of solid-solid phase transformations are studied within the framework of the theory of thermoelasticity. The main purpose is to analyze the role of temperature in the theory of phase transitions. This investigation consists of two parts: first, it is shown that by imposing a kinetic relation and a nucleation criterion it is possible to single out a unique solution to the Riemann problem for an adiabatic process. This extends to the thermomechanical case results previously found in a purely mechanical context. Secondly, based on an admissibility criterion for traveling wave solutions within the context of an augmented theory that includes viscosity, strain gradient and heat conduction effects, a special kinetic relation is derived using singular perturbation techniques.\n" }, { "name": "Van Nieuwstadt, Michiel Jacques", "degree": "PhD", "year": "1997", "title": "Trajectory generation for nonlinear control systems", "advisor": "Murray, Richard M.; Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-01172008-085534", "creators": [ { "name": { "family": "Van Nieuwstadt", "given": "Michiel Jacques" }, "id": "Van-Nieuwstadt-M-J", "display_name": "Van Nieuwstadt, Michiel Jacques" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9X7P-A431", "abstract": "This thesis explores the paradigm of two degree of freedom design for nonlinear control systems. In two degree of freedom design one generates an explicit trajectory for state and input around which the system is linearized. Linear techniques are then used to stabilize the system around the nominal trajectory and to deal with uncertainty. This approach allows the use of the wealth of tools in linear control theory to stabilize a system in the face of uncertainty, while exploiting the non-linearities to increase performance. Indeed, this thesis shows through simulations and experiments that the generation of a nominal trajectory allows more aggressive tracking in mechanical systems.\r\n\r\nThe generation of trajectories for general systems involves the solution of two point boundary value problems which are hard to solve numerically. For the special class of differentially flat systems there exists a unique correspondence between trajectories in the output space and the full state and input space. This allows us to generate trajectories in the lower dimensional output, space where we don't have differential constraints, and subsequently map these to the full state and input space through an algebraic procedure. No differential equations have to be solved in this process. This thesis gives a definition of differential flatness in terms of differential geometry, and proves some properties of flat systems. In particular, it is shown that differential flatness is equivalent to dynamic feedback linearizability in an open and dense set.\r\n\r\nThis dissertation focuses on differentially flat systems. We describe some interesting trajectory generation problems for these systems, and present software to solve them. We also present algorithms and software for real time trajectory generation, that allow a computational tradeoff between stability and performance. We prove convergence for a rather general class of desired trajectories. If a system is not differentially flat we can approximate it with a differentially flat system, and extend the techniques for flat systems. The various extensions for approximately flat systems are validated in simulation and experiments on a thrust vectored aircraft. A system may exhibit a two layer structure where the outer layer is a flat system, and the inner system is not. We call this structure outer flatness. We investigate trajectory generation for these systems and present theorems on the type of tracking we can achieve. We validate the outer flatness approach on a model helicopter in simulations and experiment.\r\n" }, { "name": "Vanik, Michael William", "degree": "PhD", "year": "1997", "title": "A bayesian probabilistic approach to structural health monitoring", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechThesis:03142014-104500651", "creators": [ { "name": { "family": "Vanik", "given": "Michael William" }, "id": "Vanik-M-W", "display_name": "Vanik, Michael William" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ve6c-w550", "abstract": "A Bayesian probabilistic methodology for on-line structural health monitoring which addresses the issue of parameter uncertainty inherent in problem is presented. The method uses modal parameters for a limited number of modes identified from measurements taken at a restricted number of degrees of freedom of a structure as the measured structural data. The application presented uses a linear structural model whose stiffness matrix is parameterized to develop a class of possible models. Within the Bayesian framework, a joint probability density function (PDF) for the model stiffness parameters given the measured modal data is determined. Using this PDF, the marginal PDF of the stiffness parameter for each substructure given the data can be calculated.
\r\n\r\nMonitoring the health of a structure using these marginal PDFs involves two steps. First, the marginal PDF for each model parameter given modal data from the undamaged structure is found. The structure is then periodically monitored and updated marginal PDFs are determined. A measure of the difference between the calibrated and current marginal PDFs is used as a means to characterize the health of the structure. A procedure for interpreting the measure for use by an expert system in on-line monitoring is also introduced.
\r\n\r\nThe probabilistic framework is developed in order to address the model parameter uncertainty issue inherent in the health monitoring problem. To illustrate this issue, consider a very simplified deterministic structural health monitoring method. In such an approach, the model parameters which minimize an error measure between the measured and model modal values would be used as the \"best\" model of the structure. Changes between the model parameters identified using modal data from the undamaged structure and subsequent modal data would be used to find the existence, location and degree of damage. Due to measurement noise, limited modal information, and model error, the \"best\" model parameters might vary from one modal dataset to the next without any damage present in the structure. Thus, difficulties would arise in separating normal variations in the identified model parameters based on limitations of the identification method and variations due to true change in the structure. The Bayesian framework described in this work provides a means to handle this parametric uncertainty.
\r\n\r\nThe probabilistic health monitoring method is applied to simulated data and laboratory data. The results of these tests are presented.
" }, { "name": "Wang, Luo-Jia", "degree": "PhD", "year": "1997", "title": "Active interaction control for civil structures", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechThesis:03142014-105804007", "creators": [ { "name": { "family": "Wang", "given": "Luo-Jia" }, "id": "Wang-L-J", "display_name": "Wang, Luo-Jia" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." } ], "option_major": [ "civileng" ], "doi": "10.7907/zsgm-ve62", "abstract": "This thesis presents a civil engineering approach to active control for civil structures. The proposed control technique, termed Active Interaction Control (AIC), utilizes dynamic interactions between different structures, or components of the same structure, to reduce the resonance response of the controlled or primary structure under earthquake excitations. The primary control objective of AIC is to minimize the maximum story drift of the primary structure. This is accomplished by timing the controlled interactions so as to withdraw the maximum possible vibrational energy from the primary structure to an auxiliary structure, where the energy is stored and eventually dissipated as the external excitation decreases. One of the important advantages of AIC over most conventional active control approaches is the very low external power required.
\r\n\r\nIn this thesis, the AIC concept is introduced and a new AIC algorithm, termed Optimal Connection Strategy (OCS) algorithm, is proposed. The efficiency of the OCS algorithm is demonstrated and compared with two previously existing AIC algorithms, the Active Interface Damping (AID) and Active Variable Stiffness (AVS) algorithms, through idealized examples and numerical simulations of Single- and Multi-Degree-of Freedom systems under earthquake excitations. It is found that the OCS algorithm is capable of significantly reducing the story drift response of the primary structure. The effects of the mass, damping, and stiffness of the auxiliary structure on the system performance are investigated in parametric studies. Practical issues such as the sampling interval and time delay are also examined. A simple but effective predictive time delay compensation scheme is developed.
" }, { "name": "Warncke, Amy E.", "degree": "PhD", "year": "1997", "title": "The Effects of Surfactants on Free-Surface Flows", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-01172008-092233", "creators": [ { "name": { "family": "Warncke", "given": "Amy E." }, "id": "Warncke-Amy-E", "display_name": "Warncke, Amy E." } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1xg2-yy62", "abstract": "This experimental investigation into the nature of free surface flows is to study the effects of surfactants on the boundary condition at the free surface and the resulting flow field. In particular, the flow field associated with a stationary Reynolds ridge was investigated as well as the wake behind a surface-piercing cylinder, where experimental techniques such as Digital Particle Image Velocimetry and a new surface slope measurement technique were utilized.\r\n\r\nResults show a large change in the flow field in the free-surface vicinity depending on the presence of surface tension gradients and thus shear stresses at the free surface. In particular, the boundary layer beneath a Reynolds ridge was measured and it is shown that the primary source of vorticity at the free surface can be attributed to the free surface deceleration at the ridge. Also, in the wake of the cylinder, depending on the surface condition, the connection of the shedding vortex filaments was found to be greatly altered with the propensity of surface tension gradients to redirect the vorticity near the free surface to that of the surface-parallel component. Thus it is shown that surfactants can dramatically alter the flow field due to the change in the free-surface boundary condition and resulting vorticity generation and conversion in the vicinity of the free surface." }, { "name": "Wassgren, Carl R.", "degree": "PhD", "year": "1997", "title": "Vibration of granular materials", "advisor": "Brennen, Christopher E.; Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11112004-104123", "creators": [ { "name": { "family": "Wassgren", "given": "Carl R." }, "id": "Wassgren-C-R", "display_name": "Wassgren, Carl R." } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/QMSQ-QJ88", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis thesis examines the fundamental behavior of a granular material subject to external vibrations. Experiments were designed to investigate the phenomena that appear in a container filled with glass spheres subject to vertical, sinusoidal oscillations. In addition, a discrete element computer simulation code was written to supplement the experimental program.\n\nExperiments and simulations reveal that the behavior of the particle bed can be classified into two regimes known as shallow and deep beds. For example, when a shallow bed consisting of less than six layers of glass spheres is subjected to oscillations with acceleration amplitudes greater than approximately 2.Og where g is the acceleration due to gravity, the particles in the container are fluidized and do not display coordinated movement. However, when more than six particle layers are used, the particles move coherently and the deep bed behaves as a single, completely inelastic mass.\n\nIn the shallow bed regime three distinct sub-states are observed that differ in the degree of coherency in the particle motions. Each appears depending upon the number of particle layers in the bed and on the acceleration amplitude of the oscillations. The transitions between the states are gradual and not well-defined.\n\nThe transition from the deep bed to the shallow bed state is characterized by a sudden expansion of the bed that occurs at a critical acceleration amplitude for a fixed bed depth and particle type. Simulations indicate that when the particle fluctuating kinetic energy is dissipated completely each oscillation cycle, the bed remains in the deep bed state. If the energy is not completely dissipated, a shallow bed state results. A simple model consisting of an inelastic ball bouncing on a sinusoidally oscillating table reproduces the sudden expansion.\n\nIn the deep bed regime, phenomena such as side wall convection, surface waves, kinks, and kink convection cells appear depending primarily on the acceleration amplitude of the oscillations and, to a lesser degree, the number of particle layers in the bed. Phase maps of when these behaviors occur were constructed using both experimental and simulation data.\n\nWhen the acceleration amplitude is greater than approximately lg, side wall convection cells appear at the vertical wall boundaries of the container. Particles move down along the vertical walls of the container and up within the bulk of the bed. Simulations indicate that the convection cells are the result of the frictional contact between particles and the walls and the asymmetry of the particle/wall collision rate over an oscillation cycle. Using the simulations, the width of the boundary layer next to the walls, the height of the convection cell center from the container base, and the particle flux in the boundary layer were measured as functions of the vibration parameters and particle properties. The results from the simulation compare well with experimental measurements. The simulation indicates that the boundary layer width is proportional to the container width when the bed aspect ratio, defined as the bed depth to the bed width, is greater than approximately 0.2. For beds with aspect ratios less than 0.2, however, the boundary layer width remains constant. Simulation results also demonstrate that the convection cell height is proportional to the bed depth and that the flux of particles in the boundary layer increases with increasing particle/wall friction and decreases for coefficients of restitution near one.\n\nAt acceleration amplitudes between approximately 2.Og and 3.5g, standing waves appear on the top free surface of the bed. These waves form at half the forcing oscillation frequency and are referred to as [...]/2 waves. A second set of standing waves appears when the acceleration amplitude is greater than approximately 5.Og and persist up to at least 7.0g. These waves form at one-quarter the forcing frequency and are known as [...]/4 waves. Experimental measurements indicate that the wave amplitude expressed as a Froude number increases with increasing acceleration amplitude for the [...]/2 waves but remains constant for the [...]/4 waves. Additionally, measurements of the wavelength suggest that the waves have a dispersion relation similar to that for deep fluid gravity waves where the wavelength is proportional to the square of the inverse frequency.\n\nKinks and kink convection cells appear in the particle bed after a period doubling bifurcation occurs in the flight dynamics of the bed. The formation of kinks can be explained using a simple model consisting of a completely inelastic ball on a sinusoidally oscillating table. Experimental measurements indicate a minimum allowable distance between nodes that is a function of the bed depth and acceleration amplitude. The convection cells bracketing each kink are shown to be the result of the out-of-phase motion of the bed sections and the interaction between fluidized and solidified regions of the bed.\n\nThe effect of vertical, sinusoidal vibrations on a discharging wedge-shaped hopper was also investigated. When the hopper exit is closed, side wall convection cells appear with particles moving up at the inclined container boundaries and down at the centerline of the bed. The same mechanism that causes downward convection at vertical walls can also explain the upward motion at inclined walls. Experimental measurements also indicate that the discharge rate from the vibrating hopper scales with the oscillation velocity amplitude. At low velocity amplitudes, the discharge rate from the hopper is slightly greater than the non-vibrating hopper discharge rate. At high velocity amplitudes, however, the discharge rate decreases significantly. A simple model accounting for the change in the effective gravity acting on the particle bed throughout the oscillation cycle and the impact velocity of the bed with the hopper predicts the observed trend.\n\nThe experiments and simulations conducted in the present work suggest that the boundary conditions and the fluid- and solid-like nature of granular materials are significant factors affecting the response of a granular bed. Additionally, this work demonstrates the value of discrete element computer simulations as a tool for complementing experimental observations." }, { "name": "Watts, Philip", "degree": "PhD", "year": "1997", "title": "Water waves generated by underwater landslides", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132005-133022", "creators": [ { "name": { "family": "Watts", "given": "Philip" }, "id": "Watts-P", "display_name": "Watts, Philip" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/S3NH-RA23", "abstract": "Water waves generated by underwater landslides threaten coastal communities near heads of fjords, near heads of underwater canyons, near river deltas, and on volcanic islands. This work provides a thorough analysis of water waves generated by two-dimensional underwater landslides using experimental, theoretical, and computational means. Water wave amplitudes generated by an underwater landslide are a function of the landslide length, the initial landslide submergence, the incline angle measured from horizontal, the characteristic distance of landslide motion, the characteristic duration of landslide motion, and the landslide rate of deformation. Nondimensional wavemaker curves constructed from the aforementioned parameters allow water wave amplitudes to be predicted. These wavemaker curves apply broadly to water waves generated by unsteady motion of a submerged object provided the motion is governed by only one characteristic distance scale and one characteristic time scale. Water wave amplitude predictions can be used for hazard mitigation studies.\r\n\r\nAn analytical solution of underwater landslide center of mass position in time provides the characteristic distance and time scales of landslide motion. Two-dimensional experimental results on a 45 degree incline confirm the existence of wavemaker curves for solid block landslides as a function of nondimensional geometrical quantities and what is called the Hammack number. The Hammack number is the correct nondimensional time for water wave generation problems. Water wave amplitudes generated by solid block landslides can be predicted from the wavemaker curves if the center of mass motion is known. The analytical solution reproduces the center of mass motion of solid block and granular material landslides. Experimental results of granular material landslides on a 45 degree incline show that landslide deformation reduces water wave amplitudes. Therefore, water waves generated by solid block landslides provide an upper bound on water waves generated by geometrically and kinematically similar deforming landslides. A criterion for the generation of linear water waves is given along with criteria for deep (or long) wave propagation down a constant depth channel. Simulations of water waves generated by underwater landslides were conducted with an inviscid fluid dynamics code. The waves simulated by the code agree reasonably well with experimental results." }, { "name": "Xu, Yuanjian", "degree": "PhD", "year": "1997", "title": "Quantum well intersubband transition detection and modulation", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-05112005-153655", "creators": [ { "name": { "family": "Xu", "given": "Yuanjian" }, "id": "Xu-Yuanjian", "display_name": "Xu, Yuanjian" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/pbpa-dx11", "abstract": "This thesis is a theoretical and experimental investigation of the intersubband transitions in quantum well structures. The I-V characteristics, infrared absorption spectra, and photoresponse spectra of superlattices are used to characterize multiple quantum well structure properties in unipolar devices.\r\n\r\nAn important numerical method for solving the problem of bound-to-continuum transitions, the transfer matrix method, is presented for the self-consistent calculations. Although the boundary conditions are relaxed due to the calculation self-consistentcy, inappropriate boundary conditions were previously included in the literature.\r\n\r\nThe first observation of the quantum interference effect in the photocurrent spectra is described using a weakly coupled bound-to-continuum transition quantum well structure and electric field domain formation in the device. This effect persists even at high biases where Kronig-Penny minibands of periodic superlattice potential in the continuum are destroyed. Using this observation, the electric field domain formation and the electron coherence length in superlattices were analyzed. A large off-resonant energy level alignment between two neighboring wells in the high field domain was observed. The effect of temperature on the transport properties was also discussed. As a further study of electric field domain formation in superlattices, an optical experiment using Stark effect is suggested.\r\n\r\nThe dependence of the absorption spectral linewidth of quantum well intersubband transitions on the electron population in the well is experimentally demonstrated using field-induced charge transfer and thermal-induced charge transfer in an asymmetric coupled quantum well structure. We show that this population-induced broadening is very important in the broadening of intersubband transitions in quantum well structures and that previously reported linewidth values for the contribution from donor scattering were overestimated. Many body effects and single-particle band non-parabolicity are the likely causes. An electronic light chopper based on population modulation was fabricated using the asymmetric coupled quantum well structure. A modulation depth of 45% has been demonstrated using 50 periods of the coupled well structure.\r\n" }, { "name": "Yang, Chih Meng", "degree": "PhD", "year": "1997", "title": "Manipulation of Si and Ge Crystallization", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162008-112621", "creators": [ { "name": { "family": "Yang", "given": "Chih Meng" }, "id": "Yang-Chih-Meng", "display_name": "Yang, Chih Meng" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "member", "display_name": "Haile, Sossina M." } ], "option_major": [ "matsci" ], "doi": "10.7907/3693-9p48", "abstract": "This thesis discusses methods for altering the crystallization kinetics of Si and Ge in order to obtain large-grained polycrystalline semiconductor thin films or size-selected semiconductor nanocrystals in silicon dioxide. Reduction of grain boundaries in polycrystalline semiconductor thin films is important for improving the performance of microelectronic devices because grain boundaries act as traps for charge carriers. Control of nanocrystal size and concentration in silicon dioxide is important in controlling the nanocrystal photoluminescence and electroluminescence characteristics. Results of modification of crystal nucleation and growth rate via ion beam irradiation, thermal annealing, metal-induced crystallization, and dopant enhanced solid phase epitaxy are presented.
\r\n\r\nIon beam irradiation was used to induce amorphization of 1-50 nm Si crystals in amorphous Si. A size-dependent amorphization rate was calculated from the temporal evolution of the crystal size distribution under ion irradiation. A model for irradiation- induced, size-dependent crystal growth/amorphization is developed and it shows good quantitative agreement with the present experiment as well as other experiments.
\r\n\r\nPrecipitation of 1-10 nm Ge nanocrystals and 1-2 nm Si nanocrystals in silicon dioxide was accomplished by ion implantation followed by thermal annealing. Nucleation of 1-2 nm Ge nanocrystals occurred during implantation, and annealing at temperatures higher than 600\u00b0C induced coarsening. Increasing the Ge implantation dose resulted in increased nanocrystal concentration but not size. In contrast, no Si nanocrystals were observed in as-implanted samples or samples annealed at less than 1000\u00b0C. Samples annealed at 1000\u00b0C for 40 min contained 1-2 nm Si nanocrystals.
\r\n\r\nLarge grained polycrystalline Ge thin films, with controlled grain location and size, were synthesized at low temperatures. Grain sizes of 10-20 \u00b5m in 50-nm-thick amorphous Ge were obtained at temperatures less than 475\u00b0C, which represents a two-orders-of-magnitude improvement over previous efforts. Selective nucleation was achieved by deposition of an array of 5-micron-diameter metal islands on top of amorphous Ge and annealing at low temperatures. During subsequent anneal at higher temperatures crystals that selectively nucleated underneath the metal islands grew tens of microns before random nucleation impeded their growth. The crystal growth rate was enhanced by doping Ge with B or P, resulting in even larger crystal sizes.
" }, { "name": "Yu, Zhong", "degree": "PhD", "year": "1997", "title": "Design Issues in Communications Networks: Reliability and Traffic Analysis", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-090303", "creators": [ { "name": { "family": "Yu", "given": "Zhong" }, "id": "Yu-Zhong", "display_name": "Yu, Zhong" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "orcid": "0000-0001-5686-800X", "role": "member", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "orcid": "0000-0001-8474-0812", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Wilson", "given": "Richard M." }, "id": "Wilson-R-M", "role": "member", "display_name": "Wilson, Richard M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/pa8m-ay72", "abstract": "This thesis aims to investigate two rather separate issues: network reliability and traffic analysis. The first concerns the reliability for unreliable systems, including communications networks with possible link failures, and more general fault-tolerant systems. The second concerns the traffic characteristics specifically in ATM networks with respect to the performance of statistical multiplexers.\r\n\r\nOne way in which we studied the reliability issue is via mean time to failure (MTTF) which considers systems that have component failures and repairs with exponential distributions. Such systems can be modeled by continuous-time discrete- state Markov chains. We investigated the MTTF from a more general framework of fault-tolerant systems (FTS), and developed two systematic approaches, the allpath-weight approach and the signal-flow-graph approach, to compute the MTTF. We also derived a simple asymptotic formula for estimating the MTTF, and obtained asymptotically the optimal networks in terms of the MTTF.\r\n\r\nThe other way in which we studied the reliability issue is via reliability polynomials for a system with component failures with certain fixed probability that is independent of time, but a function of the size of the system. No repair is allowed. We modeled such systems by random graphs, and analyzed reliability polynomials in a framework of random graph theory. We specifically focused on certain regular random graphs and analyzed the evolution of the regular random graphs, by showing a transition phenomenon when such a regular random graph evolves from edge probability zero to probability one because of the expansion of graph size, and identified its threshold function. Our work extends the study of the evolution of random graphs to regular random graphs which do not appear in the literature of random graphs, and our results are generalizations of some famous previously known results in random graph theory.\r\n\r\nAs for the second issue of traffic analysis in ATM networks, we first studied, via the approach of generating functions, Markov on-off traffic and the performance behavior of a statistical multiplexer with such traffic. We developed a heuristic procedure which allowed us to compute the expected buffer occupancy of a statistical multiplexer with Markov on-off traffic, and obtained closed form formulas showing that the expected buffer occupancy under such traffic not only depends on the incoming traffic intensity, but also largely on the burstiness of incoming traffic. The expected buffer occupancy becomes unbounded with large enough traffic burstiness, even though the traffic intensity is small. These results showed that burstiness control of traffic was very critical in designing ATM networks.\r\n\r\nWe then introduced a class of burst-constrained traffic sources, the periodic interchangeable (PI) traffic, and applied generalized Ballot theorems to analyze the buffer occupancy in a statistical multiplexer with PI traffic. We derived closed form formulas for survivor functions, expected buffer occupancy, and simple asymptotic formula that can be used as a rule of thumb for dimensioning buffer size in designing a statistical multiplexer. The results obtained could shed light on the study of worst case performance of statistical multiplexers for burst-constrained traffic sources in ATM networks." }, { "name": "Ambrose, Barry E.", "degree": "PhD", "year": "1996", "title": "Dynamic routing of telephone traffic using network management tools", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192006-170430", "creators": [ { "name": { "family": "Ambrose", "given": "Barry E." }, "id": "Ambrose-B-E", "display_name": "Ambrose, Barry E." } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "role": "member", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "Smyth", "given": "Padhraic" }, "id": "Smyth-P", "role": "member", "display_name": "Smyth, Padhraic" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/cky0-6y06", "abstract": "In this thesis, the consequences of automating network management of telephone networks are examined. The role of network managers is to monitor the network for exceptional conditions and place controls into the network if necessary to deal with these network exceptions. One potential consequence of automating network management is a network which is capable of adjusting itself quickly to changing traffic conditions, also known as a network with dynamic routing. Simulations are used to show that there are benefits to be gained from implementing dynamic routing by automating the actions of the network managers.\r\n\r\nIn this thesis, the application of learning techniques such as neural networks and linear predictors to the tasks of network traffic management is also examined. Three network management tasks considered are: (i) recognition of traffic patterns in the network (ii) learning suitable thresholds for network congestion control and (iii) time series prediction of trunk group occupancy. It is found that non-linear learning techniques such as neural networks can give small gains over the more standard technique of linear predictors." }, { "name": "Ardalan, Kayvan", "degree": "PhD", "year": "1996", "title": "Compressible vortex arrays", "advisor": "Meiron, Daniel I.; Pullin, Dale Ian", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062008-091358", "creators": [ { "name": { "family": "Ardalan", "given": "Kayvan" }, "id": "Ardalan-K", "display_name": "Ardalan, Kayvan" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "advisor", "display_name": "Pullin, Dale Ian" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/s4n5-1v32", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nWe construct steady, two dimensional, compressible vortex arrays with specified vorticity distributions. We begin by examining the effects of compressiblity on the structure of a single row of hollow-core, constant pressure vortices. The problem is formulated and solved in the hodograph plane. The transformation from the physical plane to the hodograph plane results in a linear problem that is solved numerically. The numerical solution is checked via a Rayleigh-Janzen expansion. It is observed that for an appropriate choice of the parameters [...], the Mach number at infinity, and the speed ratio, a, transonic shock-free flow exists. Also, for a given fixed speed ratio, a, the vortices shrink in size and get closer as the Mach number at infinity, [...], is increased. In the limit of an evacuated vortex core, we find that all such solutions exhibit cuspidal behaviour corresponding to the onset of limit lines.\n\nThe hollow core vortex array corresponds to a vorticity distribution wherein the vorticity is concentrated on the vortex boundary. In the second part of this thesis, we examine vortex arrays with continuous vorticity distributions. In particular, we construct Stuart-type vortices in a channel by requiring the vorticity distribution to be an exponential func-tion of the stream function of the flow. The problem is formulated and solved in the physical plane. The numerical solution is checked via a Rayleigh-Janzen expansion of the unbounded Stuart vortex solution. It is shown that, in the limit of infinite speed of sound (incompressible flow), as the channel walls tend to infinity, [...] , the Stuart vortex solutions are recovered. Furthermore, it is shown that unbounded, compressible Stuart vortices exist and that a generalized Stuart vortex solution is the proper incompressible limit. For a given fixed circulation, [...], Mach number, [...], and [...], (a measure of the compactness of the vorticity distribution) it is shown that the limit of a very narrow channel, [...]0, is a parallel shear flow. Exact analytical solutions for the compressible parallel shear flow are also found in implicit form.\n" }, { "name": "Berson, Olga", "degree": "PhD", "year": "1996", "title": "The study of copper bioavailability and mechanism of uptake in the type I methanotroph Methylomicrobium albus BG8", "advisor": "Lidstrom, Mary E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062008-105513", "creators": [ { "name": { "family": "Berson", "given": "Olga" }, "id": "Berson-O", "display_name": "Berson, Olga" } ], "advisors": [ { "name": { "family": "Lidstrom", "given": "Mary E." }, "id": "Lidstrom-M-E", "role": "advisor", "display_name": "Lidstrom, Mary E." } ], "committee": [ { "name": { "family": "Lidstrom", "given": "Mary E." }, "id": "Lidstrom-M-E", "role": "chair", "display_name": "Lidstrom, Mary E." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Chan", "given": "Sunney I." }, "id": "Chan-S-I", "role": "member", "display_name": "Chan, Sunney I." } ], "option_major": [ "envreng" ], "doi": "10.7907/X6N0-JR80", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nTwo aspects of copper uptake by the type I methanotroph Methylomicrobium albus BG8 were investigated \u2014 the effect of copper speciation in the growth medium on copper accumulation and mechanisms of copper transport in this microorganism.\r\n\r\nCopper accumulation in M. albus BG8 consisted of nonspecific sorption of copper to outer cell layers and copper internalization. Most of the copper accumulated by the cells was nonspecifically sorbed to the cellular surface and was removable by EDTA. This phenomenon was especially prominent when cultures were grown at high total copper concentrations in the growth medium. This reversible binding of copper to external sites (e.g., amino acid, carboxylic, hydroxy groups, etc.) was described by a hyperbolic model with a mean maximum binding capacity of [...] moles/cell and an apparent half saturation constant of [...] moles/l. Copper availability to M. albus BG8 was related to the cupric ion concentration rather than to that of total copper added to the growth medium. Total internalized copper (total copper not removable by EDTA) was relatively constant at [...] moles of copper per cell despite a 100\u2014fold variation in medium total copper and cupric ion concentrations, indicating the presence of a specific homeostasis mechanism for copper.\r\n\r\nA specific copper uptake system is expected to be copper-regulated. Several copper-regulated polypeptides were identified in both soluble and membrane cellular fractions. The corresponding gene of one copper-repressible polypeptide, corA, was cloned and sequenced. CorA appeared to be vital for M. albus BG8 since an insertion mutant defective in the gene grew very poorly on plates or in liquid culture. It was suggested that CorA might be a divalent metal porin.\r\n\r\nThree putative copper ATPase genes, atpA, atpB, atpC, were cloned and the complete sequence of atpA was obtained. The gene product of atpA contained a copper-binding signature motif, suggesting that AtpA does play a role in copper transport in M. albus BG8.\r\n\r\nA hypothesis for copper uptake in M. albus BG8 was suggested by this research. A copper-repressible protein (CorA) described in Chapter Three may be an outer membrane porin that works in tandem with the putative copper ATPase(s) (Chapter Four). Such a porin would not necessarily be specific for copper, and might be overexpressed under conditions of any divalent metal limitation to facilitate the metal diffusion into periplasm.\r\n" }, { "name": "Burnley, Victor Scott", "degree": "PhD", "year": "1996", "title": "Nonlinear Combustion Instabilities and Stochastic Sources", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012005-140017", "creators": [ { "name": { "family": "Burnley", "given": "Victor Scott" }, "id": "Burnley-Victor-Scott", "display_name": "Burnley, Victor Scott" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Levine", "given": "Jay" }, "id": "Levine-J", "role": "member", "display_name": "Levine, Jay" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/013z-q287", "abstract": "An investigation of combustion instabilities was conducted using an approximate analysis which allows any relevant physical processes to be included. The resulting system of coupled nonlinear oscillator equations was studied using the methods of dynamical systems theory. Previous investigations have further simplified the system using the method of time-averaging and truncation to a small number of modes. We have investigated the consequences of using these additional approximations, a case which had not been addressed completely in the literature. It was determined that application of the method of time-averaging introduces a stability boundary which limits the range in which the averaged equations are valid.
\r\n\r\nTransverse oscillations in a cylindrical chamber were also treated. It was established that in addition to its role in energy transfer between modes, nonlinear gasdynamics also provides a means of shifting the frequencies of oscillations to integral multiples of the fundamental. This additional role can reduce the efficiency of energy transfer, thus increasing the acoustic amplitudes. An example of a low amplitude transverse oscillation was produced suggesting a means by which the amplitudes of transverse modes, as well as nonintegral longitudinal modes, may be reduced.
\r\n\r\nThe coupling between combustion processes and acoustic oscillations was studied as a possible explanation of the phenomenon known as triggering. Using several ad hoc models, the effects of nonlinear pressure coupling and velocity coupling on the behavior of the system were investigated. Substantial regions of possible triggering were produced when using a model of velocity coupling with a threshold, but only if nonlinear gas dynamics was also included.
\r\n\r\nThe interaction between combustion noise and acoustic instabilities has received relatively little attention. The sources of noise in a combustion chamber are associated with vorticity and entropy waves. By including these contributions in the approximate analysis, the general forms of the stochastic excitations were obtained. Subsequently, the efects of these excitations on the amplitudes of acoustic modes were studied. When only nonlinear gasdynamics was included, no cases of bimodal probability density functions, characteristic of triggering, were found. However, when the model of velocity coupling with a threshold is added, bimodal probability densities can occur.
" }, { "name": "Catrakis, Haris J.", "degree": "PhD", "year": "1996", "title": "Mixing and the Geometry of Isosurfaces in Turbulent Jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312005-152819", "creators": [ { "name": { "family": "Catrakis", "given": "Haris J." }, "id": "Catrakis-Haris-J", "display_name": "Catrakis, Haris J." } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GPS6-DW08", "abstract": "Experiments have been conducted to investigate mixing and the geometry of scalar isosurfaces in turbulent jets. Specifically, images of the jet-fluid concentration in the far-field of round, liquid-phase, turbulent jets have been recorded at high resolution and signal-to-noise ratio using laser-induced-fluorescence digital-imaging techniques, in the Reynolds number range 4.5 x 10\u00b3 \u2264 Re \u2264 18 x 10\u00b3. Analysis of these data indicates that this Reynolds-number range spans a mixing transition in the far field of turbulent jets. This is manifested in the probability-density function of the scalar field, as well as in other scalar-field and scalar-isosurface measures. Classical as well as fractal measures of the isosurfaces have been computed, from small to large spatial scales, and are found to be functions of both scalar threshold and Reynolds number. The coverage of level sets of jet-fluid concentration in the two-dimensional images is found to possess a scale-dependent-fractal dimension that increases continuously with increasing scale, from near unity, at the smallest scales, to 2, at the largest scales. The geometry of the scalar isosurfaces is, therefore, more complex than power-law fractal, exhibiting an increasing complexity with increasing scale. This behavior necessitates a scale-dependent generalization of power-law-fractal geometry. A connection between scale-dependent-fractal geometry and the distribution of scales is established and used to compute the distribution of spatial scales in the flow. A lognormal model of scales is proposed. The data also indicate a lognormal distribution of size of the isoscalar islands and lakes, and a powerlaw distribution of shape complexity, with values of the latter that increase with increasing size.
" }, { "name": "Chiao, Jung-Chih", "degree": "PhD", "year": "1996", "title": "Quasi-optical components for millimeter and submillimeter waves", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182007-105428", "creators": [ { "name": { "family": "Chiao", "given": "Jung-Chih" }, "id": "Chiao-J", "display_name": "Chiao, Jung-Chih" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/qr6b-zk66", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nPower-combining schemes involving planar grids of solid-state devices or passive elements quasi-optically coupled in free space are an efficient means of combining power that makes them ideal for millimeter/submillimeter-wave applications by eliminating waveguide sidewall losses and machining difficulties. Three quasi-optical components including grid frequency multipliers, microswitch beam-steering grids and evanescent-wave couplers are presented.\n\nA terahertz grid frequency doubler using a 6x6 diode-grid periodically loaded with planar Schottky diodes has been developed. A peak output power of 330[...] was measured at 1.00 THz for 2.42-[...] 500-GHz input pulses with a peak power of 3.3 W.\n\nThe microswitch beam-steering grid has potential advantages over mechanical-scanning devices or active beam-steering reflectors based on diodegrids such as lower losses and simple control circuits at submillimeter wavelengths. Micromechanical electrostatically-controlled [...]-membrane switches have been fabricated on silicon wafers to provide binary reactance control. Simulations predict that a 4-bit controlled 10-layer microswitch beam-steering grid can have a phase-shift resolution of 22.5[...] over 360[...] with a maximum loss of 1.6 dB and a maximum phase error of 5[...] at 240 GHz.\n\nThe metal-mesh evanescent-wave couplers have been demonstrated to have wider bandwidths and larger modulations than Fabry-Perot couplers. The evanescent-wave coupling effect has been studied and used to increase the efficiency of an optically-controlled amplitude-modulator at 56.5 GHz.\n" }, { "name": "Choset, Howard Marc", "degree": "PhD", "year": "1996", "title": "Sensor Based Motion Planning: The Hierarchical Generalized Voronoi Graph", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182007-090504", "creators": [ { "name": { "family": "Choset", "given": "Howard Marc" }, "id": "Choset-Howard-Marc", "orcid": "0000-0002-2266-8744", "display_name": "Choset, Howard Marc" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Lewis", "given": "Andrew D." }, "id": "Lewis-A-D", "role": "member", "display_name": "Lewis, Andrew D." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/49ee-a204", "abstract": "Sensor based motion planning incorporates sensor information reflecting the state of a robot's environment into its planning process, whereas traditional approaches assume complete prior knowledge of the robot's environment. Recent research has focused on the development and incremental construction of the hierarchical generalized Voronoi graph (HGVG), which is a concise representation of a robot's environment. The HGVG is advantageous in that it lends itself to sensor based construction in a rigorous and provably correct manner. With this approach, a robot can enter an unknown environment, incrementally construct the HGVG, and then use the HGVG for future excursions in the environment. Simulations and experiments validate this approach." }, { "name": "De Lisio, Michael Peter", "degree": "PhD", "year": "1996", "title": "Hybrid and monolithic active quasi-optical grids", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132007-090419", "creators": [ { "name": { "family": "De Lisio", "given": "Michael Peter" }, "id": "DeLisio-M-P", "display_name": "De Lisio, Michael Peter" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/knb4-j089", "abstract": "Quasi-optical grids combine the output powers of many solid-state sources in free space, eliminating the conductor losses associated with traditional waveguide or transmission-line combiners. This approach shows most promise at millimeterwave frequencies, where the outputs of thousands of devices could potentially be combined through wafer-scale integration. This thesis will detail three separate active quasi-optical grids. The first grid is a 16-element hybrid tunnel diode oscillator. This grid achieved a locked output frequency spectrum, with a peak Effective Radiated Power (ERP) of 1.3 mW at 1.9 GHz. This grid is a prototype for monolithic Resonant Tunneling Diode (RTD) grid oscillators, designed to operate from 200 to 500 GHz. The second grid is a 100-element hybrid pseudomorphic High Electron Mobility Transistor (pHEMT) amplifier. Modelling techniques, design procedure, and experimental results will be presented. This grid has a peak gain of 12 dB at 9 GHz, with a 15% 3-dB bandwidth. The output power, 3. W, increases with the number of devices, while the noise figure, 3 dB, is similar to that of a single device. The third grid is a 36-element monolithic pHEMT amplifier. This grid has a peak gain of 6.5 dB at 44 GHz. By changing the positions of external polarizers and slabs, the grid can be tuned to operate up to 60 GHz with 2.5 dB gain. In addition, theoretical discussions of two topics relevant to active grids will be discussed. The first is a technique employing the method of moments and the induced emf technique to determine the electromagnetic properties of periodic grating structures. The second explores some thermal properties of quasi-optical grids.\n" }, { "name": "Demiralp, Ersan", "degree": "PhD", "year": "1996", "title": "Prediction of structures and properties for organic superconductors", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-09082006-140314", "creators": [ { "name": { "family": "Demiralp", "given": "Ersan" }, "id": "Demiralp-E", "display_name": "Demiralp, Ersan" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7p7g-sm17", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe main contributions of this thesis to the field of organic superconductors are basically (a) the band structure calculations for the investigations of the conduction properties of [...] using 2-D Hubbard Model with Unrestricted Hartree-Fock (UHF) theory, (b) ab initio quantum mechanical calculations for the structural characterizations and the properties of the donors of the organic superconductors, (c) electron-transfer boat-vibration (ET-BV) mechanism for the superconductivity of these materials, (d) developing force fields for BEDT-TTF and BEDT-TTF+.\n\nTo provide a basis for understanding the puzzling electronic properties of the organic superconductor [...] (with Tc=10.4K), we carried out band calculations using the 2-D Hubbard Model with Unrestricted Hartree-Fock (UHF) theory. The electron transfer hopping interactions are from ab initio calculations and the Hubbard parameter (Uopt=0.678950 eV) is adjusted to fit Shubnikov-de Haas and magnetic breakdown experiments. The calculations lead to a two-band semi-metal with a momentum gap separating the electron and the hole bands. The anomalous experimental observations are explained in terms of BEDT-TTF related phonons coupling these two bands (lower temperature) and by anion related phonons (higher temperature). These results also provide a framework for describing the conduction properties of other such complexes.\n\nThe donors of all known one- or two-dimensional organic superconductors, X, are based on a core organic molecule that is either tetrathiafulvalene (denoted as TTF) or tetraselenafulvalene (denoted as TSeF) or some mixture of these two molecules. Coupling X, with appropriate acceptors, Y, leads to superconductivity. The oxidized form of X may be X+ or X2+ species in the crystal. Using ab initio Hartree-Fock (HF) calculations (6-31G** basis set), we show that BEDT-TTF deforms to a boat structure (C2 symmetry) with an energy 28 meV (0.65 kcal/mol) lower than planar BEDT-TTF (D2 Symmetry). On the other hand BEDT-TTF+ is planar. Performing ab initio quantum mechanical calculations (HF/6-31G**) also on the other donors of organic superconductors, we find that all known organic superconductors involve an X that deforms to a boat structure while X+ is planar. This leads to a coupling between charge transfer and the boat deformation phonon modes. We propose that this electron-phonon coupling is responsible for the superconductivity and predict the isotope shifts [...] for experimental tests of the electron-transfer boat-vibration (ET-BV) mechanism. We suggest that new higher temperature organic donors can be sought by finding modifications that change the frequency and stability of this boat distortion mode. Based on this idea we have developed similar organic donors having the same properties and have suggested that with appropriate electron acceptors they will also lead to superconductivity.\n\nThe highest transition temperature Tc organic superconductors all involve molecule BEDT-TTF coupled with an appropriate acceptor. The experimental structures exhibit considerable disorder in the outer rings and concomitant uncertainty in the structures of BEDT-TTF. We find that Hartree-Fock (6-31G** basis set) calculations leads to results within 0.01\u00c5 and 1\u00b0 of experiment for the ordered regions allowing us to predict to composite structures expected to have this accuracy. We report optimized geometries and atomic charges for BEDT-TTF, BEDT-TTF+, and BEDT-TTF+1/2 that should be useful for atomistic simulations.\n\nThe vibrational levels of BEDT-TTF and BEDT-TTF+ have been only partially observed and assigned. In order to provide a complete consistent description of all levels, we carried out HF calculations for all fundamental vibrational frequencies of BEDT-TTF and BEDT-TTF+ and obtained the Hessians for these structures. With these Hessians and available experimental frequencies, we developed the force fields for the neutral and cation BEDT-TTF molecules by using Hessian-biased method.\n" }, { "name": "Deng, Edward E.", "degree": "PhD", "year": "1996", "title": "I. Negative incremental impedance of fluorescent lamps. II. Simple high power factor lamp ballasts", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-12272004-164134", "creators": [ { "name": { "family": "Deng", "given": "Edward E." }, "id": "Deng-E-E", "display_name": "Deng, Edward E." } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "co-advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SCBW-QZ94", "abstract": "Two important subjects in high frequency fluorescent lighting are investigated. Part I. presents a fundamental understanding of the negative incremental impedance of flourescent lamps. Search for simple, high power factor, lamp ballast topologies, a more practical aspect of lighting electronics, is presented in Part II.\n\nPart I.\n\nFlourescent lamps have a special v-i characteristic. Their incremental or small-signal impedance is defined and studied in the frequency domain. It is found that the negative incremental impedance of a fluorescent lamp can be characterized by a right half plane zero. The existence of such a result is explained by the modified Francis equation. Two approaches are proposed in order to set up a stable operating point for the lamp. First, a resonant matching network, which provides impedance transformation, is placed between a voltage source and the lamp. Second, a feedback loop is closed from the lamp current to control the magnitude of the voltage source. Stability criteria based on the Nyquist criterion are developed for the impedance of the resonant matching network and for the loop gain in the above two cases, respectively.\n\nIt is found that the input impedance of a switching dc-to-dc regulator, which is another case with the negative incremental impedance, and the fluorescent lamp impedance, are two dual cases and thus can be analyzed in a unified manner based on the stability of one-port circuit.\n\nThe small-signal lamp impedance is measured in the most practical case of a sinusoidal carrier, and it is fit by a real rational function with a right half plane zero. The small signal models describing low frequency variations of sinusoidal magnitude are developed and are experimentally verified for the three major resonant matching networks. Stability analysis for resonant matching networks at parallel resonance are performed. It shows that the LCC network is the simplest resonant matching network that a fluorescent lamp needs. It is also predicted, and experimentally verified, that the resonant matching networks at series resonance are feasible as ballasts when the lamp current feedback loop is closed.\n\nPart II.\n\nUnlike conventional high power factor ballasts requiring two cascaded power conversion stages, the proposed new lamp ballasts achieve near unity input power factor and high frequency sinusoidal lamp current in a single power conversion stage.\n\nA single-stage, high power factor lamp ballast is proposed, which is derived from the Cuk converter. A new discontinuous inductor current mode of its input inductor makes this possible by separating the input current-shaping from the output high frequency inversion. The desirable mode of operation is presented with major waveforms. The high efficiency is further enhanced by the soft-switching improvement, which is provided naturally through the lagging current of the resonant matching network. Design equations are given. The performances of the proposed single-stage, high power factor lamp ballast are verified by the experimental results.\n\nSingle-switch, unity power factor ac-to-ac converter topologies based on proper integrations of automatic current shapers and single-switch inverters, such as the Class E converter, are presented, which are suitable for lamp ballast applications. Descriptions of the desirable mode of operations and a first order analysis are given. The ballasts have the compact structure of single active switch, high input power factor and low crest factor lamp current as well as soft-switching. Experimental results confirm all the performance advantages.\n" }, { "name": "Fey, Kate Elizabeth", "degree": "PhD", "year": "1996", "title": "Experimental and theoretical aspects of dynamic crack growth along bimaterial interfaces", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132007-082556", "creators": [ { "name": { "family": "Fey", "given": "Kate Elizabeth" }, "id": "Fey-K-E", "display_name": "Fey, Kate Elizabeth" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ehea-x787", "abstract": "This work presents findings of an experimental and theoretical study of dynamic bimaterial crack growth. Bimaterial systems composed of constituents with large material mismatch were investigated under dynamic loading conditions. The materials used in this study consisted of Poly-Methylmethacrylate (PMMA) and AISI 4340 Steel, bonded together using a Methylmethacrylate monomer. One point bend loading was achieved using a drop weight tower. Dynamic crack growth, with velocities up to eighty percent of the Rayleigh wave speed of PMMA, was observed using the lateral shearing interferometric technique of Coherent Gradient Sensing (CGS) in conjunction with high speed photography. The results of these experiments are first discussed within the realm of the validity of the linear, elastodynamic asymptotic stress fields. The complex interdependency of stress intensity and mode mixity with crack tip speed is also discussed. The interpretation of |K[superscript d]| and [phi superscript d] in a dynamic bimaterial crack is clarified through the experimental observation of crack growth.\r\n\r\nComplications in analysis arising from this interdependency between the dynamic K[superscript d]-field and velocity are examined for experimentally obtained CGS fringe patterns. Improvements of existing analyzing procedures are made, resulting in increased confidence in data obtained utilizing the method of CGS in dynamic bimaterial fracture. Special attention is given to the interaction of loading and velocity in the behavior of these crack tip fields.\r\n\r\nPrevious methods of investigation have used an elastodynamic, asymptotic K[superscript d]-field to describe the deformations near a bimaterial crack tip. Attempts to develop a fracture criterion based on these results have suffered from the lack of natural length scale as the major criticism. Motivated by experimental observations, a cohesive zone model is presented in this thesis that allows an investigation of dynamic crack growth. The length of the cohesive zone is given by a combination of stress intensity and mixity, bimaterial behavior, and velocity, and emerges as a natural, time evolving length scale with which to examine the bimaterial crack problem. A fracture criterion based on critical cohesive displacements at the trailing edge of the cohesive zone is presented.\r\n\r\nThis cohesive zone model is subsequently used to examine data obtained from experiment. The model enhances our ability to extrapolate our experimental measurements to the near tip region, and to thus study the neighborhood close to the propagating crack tip. Within experimental error, predictions of the proposed fracture criterion are shown to correspond to the experimentally observed dependence of |K[superscript d]| and [phi superscript d] on the instantaneous crack tip velocity. The fracture criterion based on the cohesive model presented in this paper provides the natural next step in understanding dynamic bimaterial crack growth. It provides a criterion based on physically motivated parameters, introduces a natural length scale into the problem, and increases our understanding of dynamic bimaterial fracture mechanics.\r\n" }, { "name": "Forstner, Hali J. L.", "degree": "PhD", "year": "1996", "title": "Aerosol formation from atmospheric hydrocarbon photooxidation", "advisor": "Seinfeld, John H.; Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182007-114559", "creators": [ { "name": { "family": "Forstner", "given": "Hali J. L." }, "id": "Forstner-H-J-L", "display_name": "Forstner, Hali J. L." } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/khpq-7188", "abstract": "Outdoor smog chamber experiments have been performed to determine the secondary organic aerosol (SOA) formation potential of various C7, C8, and C9 aromatics in sunlight-irradiated hydrocarbon- NO[subscript x] mixtures. Measured aerosol yields from toluene,m-xylene, p -xylene, ethylbenzene, m -ethyltoluene, p-ethyltoluene, and 1 ,2,4-trimethylbenzene were found to correlate with organic mass concentration according to semi-volatile gas/particle partitioning theory. Aerosol yields of the C9 aromatics were greater than those of the C8 aromatics, with m-ethyltoluene resulting in the greatest yields. Toluene and ethylbenzene demonstrated some aerosol-forming potential, but the other aromatics produced significantly more SOA.\n\nFilter samples were also collected during the experiments to determine the molecular composition of the SOA from these aromatics Gas-phase mechanisms leading to these products have been proposed. Unsaturated anhydrides (2,5-furandione, 3-methyl-2,5-furandione, 3-ethyl-2,5-furandione) are predominant components of aerosol from all the aromatics, an observation that is consistent with gas-phase aromatic mechanisms involving ring-fragmentation. Saturated anhydrides were also detected in significant quantities, which could result from the hydrogenation of furandiones in sunlight in the particle phase. A new organic aerosol extraction procedure utilizing supercritical CO2 extraction is outlined.\n\nOutdoor smog chamber experiments were also performed to characterize aerosol from 1-octene and 1-decene photooxidation. The dominant aerosol species were heptanal, heptanoic acid, and dihydro-5-propyl-2(3H)-furanone from 1-octene, and nonanal, nonanoic acid, and dihydro-5-pentyl-2(3H)-furanone from 1-decene. Gas-phase oxidation mechanisms of 1-octene and 1-decene with OH and O3 account for the aerosol products.\n" }, { "name": "Hayen, Jeffrey Clyde", "degree": "PhD", "year": "1996", "title": "Response Control of Structural Systems Using Semi-Actively Controlled Interactions", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01032013-113224489", "creators": [ { "name": { "family": "Hayen", "given": "Jeffrey Clyde" }, "id": "Hayen-Jeffrey-Clyde", "display_name": "Hayen, Jeffrey Clyde" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/2c70-e383", "abstract": "The objective of the research described herein is to demonstrate conditions under which controlled interactions between two structures or structural components can be made effective in reducing the response of structures that are subjected to seismic excitation. It is shown that the effectiveness depends upon such factors as the control\r\nstrategy implementation, the interaction element mechanical properties, and the parameters which characterize the dynamic behavior of the structural systems.
\r\n\r\nA study is conducted to examine the performance of a structural response control approach referred to as Active Interface Damping (AID). This control approach utilizes\r\ncontrolled interactions between two distinct structural systems or different components of a single structural system to reduce the resonance buildup that develops\r\nduring an external excitation. Control devices or elements may be employed to physically produce the interactions between the systems. The proposed control approach\r\ndiffers from some other control approaches in that the sensors, processors, and switching components all operate actively, whereas the interaction elements function passively. The major advantage of this semi-active control technology is that relatively large control forces can be generated with minimal power requirements, which is of prime importance for the control of relatively massive systems, such as structures.
\r\n\r\nIn the most simple form, the strategy of the control approach is to remove energy associated with vibration from only one system (the primary system). This process is\r\naccomplished through the transfer of energy to another system (the auxiliary system) by means of interaction elements, the dissipation of energy directly in the interaction elements, or a combination of both these methods. In a more complex form, the control strategy may be to minimize some composite response measure of the combined primary-auxiliary system. Only the most simple form of the control strategy is considered in the present study.
\r\n\r\nSeveral physical interpretations of the control approach are possible: one is that the systems represent two adjacent multi-story buildings; another is that the primary system represents a single multi-story building, while the auxiliary system could represent either an externally- situated resilient frame or a relatively small, unrestrained mass - or even be completely absent (in this latter scenario, the interaction elements are internally-mounted control devices). The interactions consist of reaction forces that are developed within and transmitted through the elements which are located between the two systems (or different points of a single system). The mechanical properties of these elements can be altered in real time by control signals, so the reaction forces applied to the systems may be changed, and the response control objective is achieved by actively changing the\r\ninteractions at the interface of the two systems (or different points of a single system).
\r\n\r\nInitially, a preliminary study of the proposed control approach is conducted within the specialized setting of linear single-degree-of-freedom (SDOF) primary and auxiliary\r\nsystems. Numerical simulations are performed for a series of control cases using horizontal ground accelerations from an ensemble of earthquake time histories as excitation input. Subsequently, a follow-on study of the proposed control approach is conducted for linear multiple-degree-of-freedom (MDOF) primary and auxiliary systems intended to represent actual structural systems. Based upon the investigation and insight obtained from the preliminary study, a limited number of control cases are considered\r\nwhich include those deemed most effective and implementable. Numerical simulations are again performed using the same excitation input as for the SDOF systems. The\r\ncontrol approach is targeted at reducing the response contribution from the fundamental or dominant mode of vibration associated with the primary system. Uniformly-discretized models of a 6-story primary structural system capable of only lateral deformations are considered in most cases. A few cases involving models of a 3-story primary\r\nstructural system are also examined.
\r\n\r\n" }, { "name": "Heikal, Ahmed Abdou", "degree": "PhD", "year": "1996", "title": "Ultrafast molecular dynamics in complexed trans-stilbene", "advisor": "Zewail, Ahmed H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-150129", "creators": [ { "name": { "family": "Heikal", "given": "Ahmed Abdou" }, "id": "Heikal-A-A", "display_name": "Heikal, Ahmed Abdou" } ], "advisors": [ { "name": { "family": "Zewail", "given": "Ahmed H." }, "id": "Zewail-A-H", "role": "advisor", "display_name": "Zewail, Ahmed H." } ], "committee": [ { "name": { "family": "Zewail", "given": "Ahmed H." }, "id": "Zewail-A-H", "role": "chair", "display_name": "Zewail, Ahmed H." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Marcus", "given": "Rudolph A." }, "id": "Marcus-R-A", "role": "member", "display_name": "Marcus, Rudolph A." }, { "name": { "family": "McKoy", "given": "Basil Vincent" }, "id": "McKoy-B-V", "role": "member", "display_name": "McKoy, Basil Vincent" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/p3gz-kj57", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nUltrafast molecular dynamics in large molecular systems have been studied using either pump/probe time-of-flight mass spectrometry, or laser-induced fluorescence with time-correlated single photon counting technique. Intramolecular vibrational energy redistribution (IVR) and photoisomerization reaction in alkane-solvated and substituted trans-stilbenes are presented. Absent, restricted, and dissipative IVR were identified in stilbene-hexane[...] van der Waals complex. The dramatic increase of the density of states upon hexane solvation shifts the threshold for an efficient IVR to much lower excess-energy (~300 [...] for the dissipative regime) in comparison with the bare molecule (~1170 [...]). The effects of symmetry, density of states, and number of atoms on IVR were studied by using 4-methoxystilbene, 4,4'-dimethoxystilbene, and 2-phenylindene as model systems. The solvation and structural effects on the isomerization reaction in trans-stilbene is even more dramatic. For the first time, the lowering of the isomerization barrier (~700\u00b1100 [...]) in trans-stilbene upon one-hexane complexation is observed experimentally upon and compared with that in the bare molecule (~1250\u00b1100 [...]). Furthermore, the isomerization rate above the barrier in stilbene-(hexane)[...] complex is slightly slower than that in bare trans-stilbene. As the excess-vibrational energy exceeds the calculated binding energy of the (1:1) complex, the vibrational predissociation channel become open and was accounted for by using a simple kinetic model. Further decrease in the isomerization rate in stilbene-hexane[...] clusters was observed as the number of solvent molecules [...] increases. As the cluster size increases, the rate becomes less dependent on the excess energy in the [...]-state and the separation of the barrier must await theoretical calculations. The solvent polarity (in stilbene-hexanenitrile[...] complexes) and isotope effects (in stilbene-hexane-[...] complex) on the overall isomerization reaction were also examined. Similar studies were carried out on stilbene-(ethane)[...] clusters which has a lower binding energy than stilbene-(hexane)[...] clusters which, in turn, make the fragmentation of the cluster more severe. On the other hand, interesting observations were made on the reaction dynamics in a designed set of substituted stilbenes. 4-Methoxystilbene, 4,4'-dimethoxystilbene, 4,4'-dihydroxystilbene, trans-[beta]-1-cyclohexene-styrene and 2-phenylindene were used as model systems to study the role of electron conjugation and the torsional motion around [...]-[...] single bond in the isomerization reaction in trans-stilbene.\n" }, { "name": "Hong, Liubo", "degree": "PhD", "year": "1996", "title": "Structures and stabilities of nanocrystalline materials synthesized by mechanical alloying and modeled as driven alloys", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12172007-114124", "creators": [ { "name": { "family": "Hong", "given": "Liubo" }, "id": "Hong-L", "display_name": "Hong, Liubo" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/shrg-rd86", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nNanocrystalline materials (NCM) are single-phase or multi-phase polycrystalline materials with crystal sizes in the nanometer range (2-20 nm). Owing to their very small grain size, NCM have enhanced or novel physical and mechanical properties compared to conventional materials, making NCM attractive for various technical applications. Mechanical alloying (MA) is now one of the most commonly used methods to synthesize NCM, among other far-from-equilibrium materials. During mechanical alloying, nanocrystalline materials are sustained in nonequilibrium states by continuous external driving (e.g., collisions, shearing, fracturing, welding, etc.), and can be studied as driven alloys -- a simplified model that grasps the essentials of external driving in a general way. In this thesis study, the structures and thermal stabilities of nanocrystalline materials synthesized by mechanical alloying were studied by experimental techniques, and were modeled as driven systems by Monte Carlo simulations.\n\nA general introduction to nanocrystalline materials is given in Chapter 1 and discusses their structures, synthesis methods, characterization techniques, properties and technical applications. In parallel, introductions on phase transformations, driven alloys, and Monte Carlo simulations are given in Chapter 2. Our theoretical and simulational work on critical temperature of ordering transformations of driven square alloys is presented in Chapter 3, while the study on the ordering kinetics and low temperature phase diagrams of driven bcc alloys is presented in Chapter 4. We found that the ballistic (random) atom movements, caused by external driving, suppressed the critical temperature of ordering on square lattices. The decrease in critical temperature was linear only at small driving intensity. The ballistic atom movements also changed both the transient states and the steady states of ordering of bcc alloys. The stability of B32 order was increased with respect to the stabilities of B2 order and an unmixed state because of the smaller defect enthalpy sustained in B32 phase. In steady state, the B32 phase region encroached into adjacent B2 or unmixed phase regions, and regions of two-phase coexistence were formed. The changes were significant and nonintuitive, and provided useful guidance to the experimental studies presented in Chapter 5, 6, and 7.\n\nIn the experimental studies described in Chapters 5, 6, and 7, we studied how the microstructures of NCM prepared by MA depended on milling intensity, temperature, and composition (I, T, c). We found: (1) I -- The intensity of MA had little effect on the average grain size or strain, but changed the phase boundaries of Fe-Ni nanocrystalline materials drastically and in nonintuitive ways. Similar to what was found in Monte Carlo simulations, a region of bcc plus fcc two-phase coexistence occurred from MA, and shifted asymmetrically to the bcc side with increased milling intensity. This was attributed to the larger heterogeneities in free energy density in the alloy at higher MA intensity. (2) T -- Mechanical alloying of Ni3Fe and Fe3X (X=Si, Zn, Sn) at temperatures from 23 [...] to 300 [...] showed that the effect of milling temperature was little different from the role of temperature itself on the microstructure of NCM. (3) c -- The same Hume-Rothery rules for 5% solubility in equilibrium alloys translated to a 25% solubility in nanocrystalline materials Fe3X (X=Al, As, Ge, In, Sb, Si, Sn, Zn) prepared by MA. Also observed was the transient DO3 ordering of NCM Fe3Ge prepared by MA upon annealing at high temperature.\n" }, { "name": "Howard, Danny Dwayne", "degree": "PhD", "year": "1996", "title": "Part I. Mechanisms of injury associated with extracorporeal shock wave lithotripsy; Part II. Exsolution of volatiles", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242005-083544", "creators": [ { "name": { "family": "Howard", "given": "Danny Dwayne" }, "id": "Howard-D-D", "display_name": "Howard, Danny Dwayne" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "role": "member", "display_name": "Shepherd, Joseph E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/995X-8517", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nPart I - Shock waves are focused in extracorporeal shock wave lithotripsy (ESWL) machines to strengths sufficient to fracture kidney stones. Substantial side effects-most of them acute-have resulted from this procedure, including injury to soft tissue. The focusing of shock waves through various layers of tissue is a complex process which stimulates many bio-mechano-chemical responses.\n\nThis thesis presents results of an in vitro study of the initial mechanical stimulus. Planar nitrocellulose membranes of order 10 um thick were used as models of thin tissue structures. Two modes of failure were recorded: Failure due to cavitation collapsing on or near the membranes, and failure induced by altering the structure of shock waves. Tests were done in water at and around F2 to characterize the extent of cavitation damage, and was found to be confined within the focal region, 1.2 cm along the axis of focus.\n\nScattering media were used to simulate the effects of acoustic nonuniformity of tissue and to alter the structure of focusing shock waves. 40 um diameter (average) hollow glass spheres were added to ethylene glycol, glycerine and castor oil to vary the properties of the scattering media. Multiple layer samples of various types of phantom tissue were tested in degassed castor oil to gauge the validity of the scattering media. The scattering media and tissue samples increased the rise time decreased strain rate in a similar fashion. Membranes were damaged by the decreased strain rate and accumulated effects of the altered structure: After about 20 or so shocks immersed in the scattering media and after about 100 shocks behind the tissue samples. The mode of failure was tearing with multiple tears in some cases from about .1 cm to about 3 cm depending of the number of shocks and membrane thickness.\n\nPart II - This work examines the exsolution of volatiles-carbon dioxide from water-in a cylindrical test cell under different pressure conditions. Water was supersaturated with carbon dioxide under various pressures (620 to 1062 kPa), and depressurized rapidly to investigate how carbon dioxide is undissolved, exsolution, and its effects on the surrounding environment. Cavities grow as a result of convective diffusion: They move before depleting carbon dioxide in a given region. The radius of a cavity in this environment grows at a faster rate [...] than that of a cavity at rest [...]. Bubble growth rates were inferred by measuring the bulk liquid using high speed motion pictures. Water in the test-cell is accelerated as a result of buoyancy induced by cavity growth. Cavities are elliptical in shape and grow until mutual interaction causes them to fragment. Accelerations range from 10 to 100 g were measured with velocities ranging from 7 to 13 m/s.\n" }, { "name": "Hua, Inez", "degree": "PhD", "year": "1996", "title": "The sonochemistry of aqueous solutions", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182007-084901", "creators": [ { "name": { "family": "Hua", "given": "Inez" }, "id": "Hua-I", "display_name": "Hua, Inez" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "member", "display_name": "Hering, Janet G." } ], "option_major": [ "envreng" ], "doi": "10.7907/YWAK-2730", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe ultrasonic irradiation of organic compounds in aqueous solution is studied under various physical conditions. The observed sonochemical rate constants can be analyzed to yield information about the nature of the bubbles which exist during acoustic cavitation and to determine which parameters are significant for enhancing cavitation chemistry. Aqueous solutions of p-nitrophenylacetate (PNPA), p-nitrophenol (PNP), and carbon tetrachloride (CCl4) were sonicated in various reactor configurations and with different saturating gases. The production of hydroxyl radical ([...]) and hydrogen peroxide (H2O2) was quantified at four different ultrasonic frequencies.\r\n\r\nThe most significant features of the sonolytic hydrolysis of PNPA at 20 kHz are that the observed first order rate constants are independent of pH in the range of 3 to 8, but significantly influenced by the saturating gas (Kr, Ar, or He). Furthermore, the apparent activation parameters for hydrolysis of PNPA ([...], [...], [...]) are significantly different in sonicated systems than in solutions under ambient conditions. These changes are attributed to changes in the physical nature of the solvent when a layer of transient supercritical water is formed around the cavitation bubbles.\r\n\r\nThe psuedo-first order degradation rate constants for the transformation of PNP in a near-field acoustical processor (NAP) increases with increasing power-to-volume ratio over the range of 0.98-7.27 W/[...]. An increase in the power-to-area ratio results in an increasingly fast degradation rate up to 1.2 W/[...] and a slight decrease thereafter. The nature of the background gas influences the degradation rate constant and product distribution. The fastest rate is observed when a mixture of Ar and O2 is used to saturate the solution.\r\n\r\nThe sonolytic degradation of CCl4 is investigated in Ar- and O3-saturated aqueous solutions. The chlorine mass balance is typically >70%, mostly in the form of chloride ion (Cl-). The reactive intermediate, dichlorocarbene, is identified and quantified by means of trapping with 2,3-dimethyl-2-butene. Low concentrations (0.01-0.1 [...]) of hexachloroethane and tetrachloroethylene are detected. Ultrasonic irradiation of a mixture of PNP and CCl4 results in the acceleration of the sonochemical degradation rate of p-NP.\r\n\r\nBoth the ultrasonic frequency and the saturating gas influence the production of [...] and H2O2 during sonolysis of buffered, aqueous solutions. Ultrasonic frequencies of 20,40,80 and 500 kHz are used, and the background gas in solution are Kr, Ar, He or O2. Both species are found at the highest rates during sonolysis of a Kr-saturated solution at 500 kHz, whereas the lowest rates of production are observed during sonolysis of a He-saturated solution at 20 kHz. A range of rate constants for the production of [...] and H2O2 are observed at each frequency because each of the four saturating gases has different physical properties (e.g., thermal conductivity.) However, the range narrows at the higher ultrasonic frequencies (80 and 500 kHz) compared to that observed at the lower frequencies (20 and 40 kHz).\r\n" }, { "name": "Hua, Xinlei", "degree": "PhD", "year": "1996", "title": "First principles simulations : development of new density functionals and pseudopotentials and formation mechanism of fullerenes", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072008-115130", "creators": [ { "name": { "family": "Hua", "given": "Xinlei" }, "id": "Hua-X", "display_name": "Hua, Xinlei" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/r7qa-wt76", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis thesis consists of two parts. Part I deals with the development of first principles methodologies. Part II deals with applications of atomistic simulations, i.e. quantum mechanics and molecular dynamics simulations.\n\nPart I includes two topics. One is generalized gradient correction for the density functional theory which constitutes Chapter 2. The other is first principle pseudopotentials which is covered in Chapter 3 and 4. Chapter 3 develops the density functional theory version used mostly in solid state physics, while Chapter 4 develops the Ab initio version used mostly in chemistry. Part II also includes two topics. One is the fullerenes formation mechanism which is covered in Chapter 5 and 6. Chapter 5 deals with their thermodynamical properties and Chapter 6 discusses their formation processes. The other is the lattice properties for the [...], superconductor which is covered by Chapter 7. Also, in Chapter 1 we summarize the hierarchy models for materials simulations and review the state-of-the-art tools at various levels of that hierarchy.\n\nPredicting the band gap from first principles has been hindered by the complexity of the systems and the flaws in the simplified theories. The most successful first principle theory, i.e. DFT, gives a value about the 2/3 of the measured one. [...] This is partly due to the approximate nature of the functionals used in DFT calculations. It has long been known that HOMOs calculated with LDA, the most commonly used DFT, is far from ionization potential. [...] In Chapter 2, after analyzing the nature of gradient corrected functional for DFT, we proposed a new exchange energy functional. The new functional is tested on several atoms and molecules and found to reproduce the Hartree-Fock eigenvalues to a good accuracy. With the incorporation of correlation energy in DFT, we can hope that the new functional would lead to a new and efficient way of predicting energy band gaps for all the materials from first principles.\n\nAll chemistries involve mainly valence electrons. The effect of inner shells, shielding the nucleus Coulomb potential and providing Pauli repulsions to support the valence electrons, can be implemented by a potential called effective core potential (ECP). Since valence electrons of different angular momentum would experience different Pauli repulsion of the core electrons, this ECP is angular momentum dependent. This leads to a nonlocal potential and requires three-center integrals, which scales quadratically with the size of the system. On the other hand, the wave nature of electrons allows us to lower the resolution in describing the potential. By using a set of Gaussian functions to replace real-space grid in representing the ECP, we factorized the three-center integral into a sum of products of two-center integrals. We have found a set of Gaussian functions that gives accuracy of better than [...] for all the elements in the periodic table, sufficient for all ECP calculations. The new method scales linearly with the system size. At 128 atoms, the cost is 1/15 of the old ECP method. This cleared a bottleneck for first principle programs that use ECP to study heavy elements.\n\nWhy [...] fullerenes are so stable and how this highly symmetric molecule is formed in the super-heated vapor is the two most fundamental questions in fullerene research. Prompted by the recent observations of the monocyclic ring and bycyclic rings as intermediates, we performed DFT calculations on the ring isomers and fullerene isomers of carbon clusters of various sizes. From it we extracted a force field (FF) for molecular dynamics simulations. This FF is used to calculate the free-energies at different temperatures. Based on our analysis of the physical forces that drive the carbon clustering and isomerization, we describe an evolution process for fullerene formation that is consistent with all the observations so far. With a combined DFT/MD method we are able to provide the energetics for a complete path of fullerene formation. Hint for synthesis improvement are suggested.\n\nHigh-Tc superconductors are ceramics. To improve their mechanical and electrical properties, we conducted a molecular dynamics simulation for the [...] superconductor. We derived a ionic-covalent force field from fitting the experimental data. Our FF is able to reproduce the structure and Raman modes accurately. The FF predictions of isotope shifts of Raman frequencies, phonon dispersion spectra, phonon density of states, elastic stiffness constants, and volume thermal expansion are all in fairly good agreement with experiments." }, { "name": "Huang, Ching-Tung", "degree": "PhD", "year": "1996", "title": "On the Dynamic Response of Nonlinear Uncertain Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10282019-124732191", "creators": [ { "name": { "family": "Huang", "given": "Ching-Tung" }, "id": "Huang-Ching-Tung", "display_name": "Huang, Ching-Tung" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "civileng" ], "doi": "10.7907/2xpp-3s50", "abstract": "This thesis presents an approach for performing second moment analyses of nonlinear dynamic systems with parameter uncertainty. The uncertain parameters are modeled as time-independent random variables. The set of orthogonal polynomials associated with the probability density function is used as the solution basis. When a deterministic excitation source is considered, the response variables are expanded in terms of a finite sum of these polynomials with time-dependent coefficients. The weighted residual method is employed to derive a set of deterministic nonlinear differential equations that can be solved numerically for evaluations of response statistics.
\r\n\r\nThis solution approach is further extended to nonlinear continuous systems involving inhomogeneous random media. A discrete representation is obtained via a spatial discretization procedure for the continuous response variables as well as the random continuum. Thus, the continuous random system can then be treated as in the case of the discrete random systems. The solution approach is applied to a study of a nonlinear random shear-beam model subjected to a near-field earthquake ground motion.
\r\n\r\nThe response uncertainty for nonlinear uncertain systems subjected to external stochastic excitation is also investigated. A general solution procedure based on equivalent linearization is presented. In this solution methodology, the instantaneous equivalent stiffness and damping matrices are approximated as quadratic random functions. The resulting Liapunov system with explicit random coefficients can then be solved using the newly developed solution approach. Applications to single-degree-of-freedom uncertain systems are given and the accuracy of the results is validated.
" }, { "name": "Jaegle, Lyatt", "degree": "PhD", "year": "1996", "title": "Stratospheric chlorine and nitrogen chemistry: observations and modeling", "advisor": "Webster, Chris; Yung, Yuk L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-120002", "creators": [ { "name": { "family": "Jaegle", "given": "Lyatt" }, "id": "Jaegle-L", "display_name": "Jaegle, Lyatt" } ], "advisors": [ { "name": { "family": "Webster", "given": "Chris" }, "id": "Webster-C", "role": "advisor", "display_name": "Webster, Chris" }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "role": "advisor", "display_name": "Yung, Yuk L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/fk0v-h242", "abstract": "In order to predict the effects of anthropogenic perturbations (such as the increase of chlorine) and natural events (such as volcanic eruptions) on the chemical composition of the stratosphere, it is essential to quantitatively test our knowledge of the photochemistry by conducting detailed comparisons between stratospheric observations and models. Through such comparisons, this thesis focuses on explaining sets of simultaneous measurements obtained from balloon (Chapters 3, 4, 5) and ER-2 aircraft (Chapters 2, 6) platforms, with particular emphasis on the basic chemical processes underlying the partitioning of the chlorine and nitrogen families in the stratosphere. Following an introductory first chapter, Chapter 2 tests our knowledge of the photochemical balance between NO2 and NO. Chapter 3 examines the effects of enhanced heterogeneous chemistry resulting from the eruption of Mt. Pinatubo on the partitioning between NO2 and HNO3. Chapter 4 discusses the factors controlling the distribution of chlorine between its main reservoirs (HCl, ClON2) and more reactive (HOCl and ClO) forms. Chapter 5 questions the completeness of our understanding of chlorine chemistry and proposes the existence of a new atmospheric species perchloric acid, HClO4. Finally, Chapter 6 focuses on the heterogeneous processes taking place during the Antarctic winter and their effect on the evolution of reactive chlorine and nitrogen species within and outside of the polar vortex.\n" }, { "name": "Klewicki, J. Kenneth", "degree": "PhD", "year": "1996", "title": "The Kinetics of Redox Reactions of Mn(II) and Mn(III) in Aqueous Systems: Homogenous Autoxidation of Mn(II) and the Formation and Disappearance of Mn(III) Complexes", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-155028", "creators": [ { "name": { "family": "Klewicki", "given": "J. Kenneth" }, "id": "Klewicki-J-Kenneth", "display_name": "Klewicki, J. Kenneth" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Hering", "given": "Janet G." }, "id": "Hering-J-G", "role": "member", "display_name": "Hering, Janet G." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/40pv-rq92", "abstract": "The kinetics of manganese redox reactions are important for understanding redox cycles in natural waters. This study examined the kinetics of the homogenous oxidation of Mn(II) and formation and disappearance of Mn(III) complexes.
\r\n\r\nThe oxidation of Mn(II) was studied to determine the homogenous oxidation rate in the absence of solid surfaces and biological activity. Experiments were conducted at 35, 45, 50, and 60\u00b0C. The pH was 8.0. The reaction solution was prepared so that at no time during the experiment was the solubility product of any solid phase exceeded. Oxidized Mn was measured using leuco crystal violet dye reagent. Measurable rates were observed for the 45, 50, and 60\u00b0C experiments. An Arrhenius expression was fitted to the rates in order to extrapolate to 25\u00b0C. The second order rate constant for the rate expression
\r\n\r\n-d[Mn(II)]/dt = k\u22c5[Mn(II)\u22c5[O2]
\r\n\r\nwas calculated to be 6.9 \u00b1 1.6 x 10-7 M-1s-1.
\r\n\r\nThe kinetics of disappearance of Mn(III) complexes from aqueous solution were studied. Complexes of pyrophosphate (P2O74-), ethylenediaminetetracetate (EDTA), and citrate (CIT) were synthesized from MnO4- and a Mn(II) salt in a 1:4 ratio in the presence of excess ligand. Concentrations of Mn(III) complex were monitored spectrophotometrically. Experiments were conducted in the pH range of 6 to 9 for pyrophosphate and citrate and 3 to 9 for EDTA. The total manganese concentration was varied between 0.5 and 1.0 mM. Ligand concentrations were varied from 0.5mM to 200mM. Experiments were also conducted to examine the effects of oxygen, light, and ionic strength. Oxygen had a significant effect on only the citrate complex; ionic strength affected only the EDTA complex. Light was found to be insignificant in all cases.
\r\n\r\nThe Mn(III)P2O7 complex was found to disappear from solution relatively slowly providing the ligand was in at least ten-fold excess. Disappearance time scales were on the order of 107 s. The Mn(III)EDTA complex reacted rather rapidly with time scales on the order of 104 s. There were at least two Mn(III)EDTA complexes, a protonated one more stable at low pH and an unprotonated one more stable at high pH. The pKa of the complex appeared to be approximately 5.3. The rate of disappearance of the Mn(III)EDTA had a fractional dependence on pH, probably indicative of an unknown pH dependent intermediate in the decomposition of the complex. The rate was found to increase with increased EDTA, indicating that the rate limiting step was an outer sphere electron transfer from Mn(III)EDTA to an excess EDTA. The rate law for the reaction above pH 6 was found to be
\r\n\r\n-d[Mn(III)EDTA]/dt = k\u22c5[H+]0.31\u22c5[EDTA]1.35\u22c5[Mn(III)EDTA]
\r\n\r\nThe Mn(III)CIT complex was found to undergo a redox cycle. The Mn(III)CIT complex was reduced, forming Mn(II). The Mn(II) was then oxidized in the presence of oxygen to re-form the Mn(III) complex. Both pH and ligand concentration were found to have fractional orders in the rate expression, largely due to the competition between the reduction and the oxidation and possibly complicated by radicals formed by the reaction.
\r\n\r\nThe dissolution of MnOOH by pyrophosphate, EDTA, and citrate was studied. A MnOOH solid was synthesized by oxidizing Mn(II) with hydrogen peroxide at elevated temperatures and high pH. The solid was identified by X-ray diffraction to be \u03b2-MnOOH, with some contamination by Mn3O4. Throughout the dissolution process samples were removed by pipette and filtered. The filtrate was analyzed spectrophotometrically for the presence of Mn(III) complexes and total Mn. The solids captured on the filter were analyzed by an iodine titration technique, coupled with formaldoxime measurements to determine the average oxidation state of the solids. The effects of pH and ligand concentration on rates were examined.
\r\n\r\nPyrophosphate was found to dissolve the Mn(III) solids nonreductively, producing the Mn(III) complex in solution. The dissolution reaction rate was dependent on approximately the half power of [H+], possibly indicative of a surface binding ligand binding on the surface. No dependence on the ligand concentration was found down to a ligand:Mn ratio of 10:1, probably indicative of surface site saturation by ligand.
\r\n\r\nEDTA was found to dissolve the solids reductively with no Mn(III) solution species being observed. The dependence on [H+] was approximately one half order, possibly indicative of a surface binding.
\r\n\r\nCitrate dissolved the MnOOH solids in what appeared to be two steps. There seemed to be an initial stage of nonreductive dissolution, followed by a reductive dissolution. The rate and duration of the two different stages depended on pH. The dependence was slightly greater than first order in [H+], possibly indicating the reaction becomes controlled by reactions of the radicals produced by oxidation of the citrate.
\r\n\r\nThis study has shown that Mn(III) complexes can be formed in pH conditions relevant to natural waters. These complexes can be formed either through oxidation of Mn(II) by strong oxidants in the presence of stabilizing ligands or by dissolution of Mn(III)-containing solids by stabilizing ligands. Once formed, the lifetime of these complexes will depend on the nature of the ligand and chemical characteristics of the aquatic environment. If the ligand does not rapidly reduce Mn(III) these complexes can be powerful mobile oxidants which could significantly affect the local redox environment.
\r\n" }, { "name": "Kolb, F. Christopher", "degree": "PhD", "year": "1996", "title": "Two themes in perceptual ecology : visual attention and awareness", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-12202007-110933", "creators": [ { "name": { "family": "Kolb", "given": "F. Christopher" }, "id": "Kolb-F-C", "display_name": "Kolb, F. Christopher" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Andersen", "given": "Richard A." }, "id": "Andersen-R-A", "role": "member", "display_name": "Andersen, Richard A." } ], "option_major": [ "cns" ], "doi": "10.7907/tv8e-g179", "abstract": "The nature of consciousness poses the central problem for both neuroscience and philosophy of mind: how is the brain constructed to enable the mind, a collection of perceptual, emotional, and intentional functions that evolve around a fleeting stream of subjective (sensory) experience? This thesis is about how to approach mental processes, such as mindfulness (attention) and minding (awareness), for the primary human sense, vision, with reductionist tools. Neurobiological studies of consciousness have proven elusive in the past for the neural structures, by which visual attention and awareness operate, are difficult to observe. Although cellular studies of visual attention have come a long way to explain a specific instance of conscious awareness, where certain aspects of the world stand out in consciousness at the expense of others, there is no indication that cognitive neuroscience may soon stride the \"anatomical path\" to self-understanding.\r\n\r\nThe difficulty lies in anatomically isolating one component of consciousness from the other in sensory interactions that are the product of complex neural mechanisms. It is here we make our prevalent contribution by experimentally unfolding the ecological range of sensory interactions that (potentially) reveal the cortical specificity of visual attention and awareness. Each chapter of this thesis delivers possible neural mechanisms and/or sites that pertain to component operations of visual awareness: \"seeing\", without looking (Chapter 2, perception outside the focus of attention), \"looking\" without seeing (Chapter 3, unconscious visual perception), \"reading\" without seeing the letters (Chapter 4, visual interpretation devoid cognition), \"sensing\" which eye sees (Chapter 5, unmasking the visual origin of eye), \"learning\" what the other eye sees (Chapter 6, dichoptic collaboration in \"filling-in\").\r\n\r\nThis thesis provides a conceptual framework that draws together results from visual neuroscience and psychophysics. It describes new approaches to determine the neural correlates and events responsible for imparting sense-data to the level of abstract thought and planned action. The central theme. however, is the discovery of \"blindsight\" in normals (Chapters 3 and 4). Visual behavior in the absence of visual awareness (blindsight) has been established unequivocally in patients with lesions in area V1, but remains controversial for normal observers (\"subliminal perception\"). We describe two visual displays that induce blindsight in normal observers, using an objective measure to distinguish conscious and unconscious performance. Both displays are designed to stimulate area V1 strongly and extrastriate areas poorly. In each display, one quadrant differs from the other three, and this \"odd\" quadrant is consciously perceived in one form of the display (C-form) but not another (NC-form) (100-200ms presentation time).\r\n\r\nThe first display consists of paired dots moving on orthogonal trajectories (different directions in odd and other quadrants), either within 0.2\u00b0 of each pair (NC-form) or separated by several deg (C-form), so that the two forms differentially stimulate units in area MT but not area V1 (Qian and Andersen 1994). The second display dichoptically presents arrays of oriented Gabor-elements (different orientations in odd and other quadrants), producing either binocular rivalry (NC-form) or fusion (C-form), so the two forms differentially stimulate binocular but not monocular units. To objectively demonstrate unconscious performance, we randomly interleave two forms of each display in a block of trials. Observers perform a forced-choice task (locating the odd quadrant), and rate their confidence in the choice of quadrant (scale of 1 to 10). Performance is comparable (and far above chance) for C- and NC-forms, but performance and confidence are correlated only for C-forms and essentially uncorrelated for NC-forms, confirming that performance in NC-forms is not accompanied by visual awareness. We surmise that performance may be based on stimulation of area V1 while conscious experience may result from stimulation of extrastriate areas.\r\n" }, { "name": "Kuzo, David Matthew", "degree": "PhD", "year": "1996", "title": "An experimental study of the turbulent transverse jet", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02232005-160358", "creators": [ { "name": { "family": "Kuzo", "given": "David Matthew" }, "id": "Kuzo-D-M", "display_name": "Kuzo, David Matthew" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/xa4v-qb95", "abstract": "An experimental study that examines the mean flow properties of the turbulent transverse jet using Digital Particle Image Velocimetry (DPIV) is reported.
\r\n\r\nThis study examines various jet flows over a range of Reynolds numbers based upon jet velocity and diameter. Within this range it is documented that mean flow fields, identified as alternate mean flow states, other than the symmetric vortex pair exist. These alternate flow states are characterized by unsteadiness, asymmetry, and multiple streamwise vortices. Flow visualization shows that these alternate flow states are formed during initial jet roll-up, and persist far downstream without developing into the (expected) vortex pair. A map of the domain of existence, in velocity ratio - Reynolds number space, of these alternate states is provided, and a discussion of the underlying physics is included.
\r\n\r\nWith this new understanding, selected symmetric jet flows at velocity ratios of 5, 10, and 20 are generated and studied using DPIV. The mean flow is quantified through measurements of vortex circulation, size, and impulse, and the relationship of these properties to the (initial) jet momentum flux is examined.
" }, { "name": "Lie, Yu-Chun Donald", "degree": "PhD", "year": "1996", "title": "Ion implantation in epitaxial GexSi1-x on Si(100)", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-083658", "creators": [ { "name": { "family": "Lie", "given": "Yu-Chun Donald" }, "id": "Lie-Yu-Chun-Donald", "display_name": "Lie, Yu-Chun Donald" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "chair", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "member", "display_name": "Tai, Yu-Chong" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6GA1-F433", "abstract": "The question of whether one can effectively dope or process epitaxial Si(100)/GeSi heterostructures by ion implantation is experimentally investigated. Results that cover several different ion species (Si, P, and As), doses (1.0x10[superscript 13]/cm[superscript 2] to 1.5x10[superscript 15]/cm [superscript 2]), implantation temperatures (RT to 150\u00b0C), as well as annealing techniques (steady-state and rapid thermal annealing) are included in this thesis. Implantation-induced damage and strain and their annealing behavior for both strained and relaxed GeSi are measured and compared with those in Si and Ge. The damage and strain generated in pseudomorphic GeSi by room-temperature implantation are considerably higher than the values interpolated from those of Si and Ge. Implantation at slightly elevated substrate temperatures (e.g., 100\u00b0C) can very effectively suppress the implantation-induced damage and strain in GeSi. The fractions of electrically active dopants in both Si and GeSi are measured and compared for several doses and under various annealing conditions. Solid-phase epitaxial regrowth of GeSi amorphized by implantation has also been studied and compared with regrowth in Si and Ge. For the case of metastable epi-GeSi amorphized by implantation, the pseudomorphic strain in the regrown GeSi is always lost and the layer contains a high density of defects, which is very different from the clean regrowth of Si(100). Solid-phase epitaxy, however, facilitates the activation of dopants in both GeSi and Si, irrespective of the annealing techniques used. For metastable GeSi films that are not amorphized by implantation, rapid thermal annealing is shown to outperform steady-state annealing for the preservation of pseudomorphic strain and the activation of dopants. In general, defects generated by ion implantation can enhance the strain relaxation process of strained GeSi during post-implantation annealing. The processing window that is optimized for ion-implanted Si therefore has to be modified considerably for ion-implanted GeSi.\r\n" }, { "name": "Lin, Duo-min", "degree": "PhD", "year": "1996", "title": "Run-Up and Nonlinear Propagation of Oceanic Internal Waves and Their Interactions", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-084353", "creators": [ { "name": { "family": "Lin", "given": "Duo-min" }, "id": "Lin-Duo-min", "display_name": "Lin, Duo-min" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" } ], "option_major": [ "eng" ], "doi": "10.7907/rgkn-4g56", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA weakly nonlinear and weakly dispersive oceanic internal long wave (ILW) model, in analogy with the generalized Boussinesq's (gB) model, is developed to investigate generation and propagation of internal waves (IWs) in a system of two-layer fluids. The ILW model can be further derived to give a bidirectional ILW model for facilitating calculations of head-on collisions of nonlinear internal solitary waves (ISWs). The important nonlinear features, such as phase shift of ISWs resulting from nonlinear collision encounters, are presented. The nonlinear processes of reflection and transmission of waves in channels with a slowly varying bottom are studied.
\r\n\r\nThe terminal effects of IWs running up submerged sloping seabed are studied by the ILW model in considerable detail. Explicit solution of the nonlinear equations are obtained for several classes of wave forms, which are taken as the inner solutions and matched, when necessary for achieving uniformly valid results, with the outer solution based on linear theory for the outer region with waves in deep water. Based on the nonlinear analytic solution, two kinds of initial run-up problems can be solved analytically, and the breaking criteria and run-up law for IWs are obtained. The run-up of ISWs along the uniform beach is simulated by numerical computations using a moving boundary technique. The numerical results based on the ILW model are found in good agreement with the run-up law of ISWs when the amplitudes of the ISWs are small.
\r\n\r\nThe ILW model differs from the corresponding KdV model in admitting bidirectional waves simultaneously and conserving mass. This model is applied to analyze the so-called critical depth problem of ISWs propagating across a critical station at which the depths of the two fluid layers are about equal so as to give rise to a critical point of the KdV equation. As the critical point is passed, the KdV model may predict a new upward facing ISW relative to a local mean interface is about to emerge from the effects of disintegrating original downward ISW. This phenomenon has never been observed in our laboratory. Numerical results are presented based on the present ILW model for ISWs climbing up a curved shelf and a sloping plane seabed. It is shown that in the transcritical region, the behaviour of the ISWs predicted by the ILW model depends on the relative importance of two dimensionless parameters, sw, the order of ISW wave slope, and s, the beach slope. For s >> sw, the wave profile of ISWs exhibits a smooth transition across the transcritical region; for s <sw, ISWs emerge with an oscillatory tail after passing across the critical point. Numerical simulations based on the ILW model are found in good agreement with laboratory observations.
\r\n\r\nFinally, conclusions are drawn from the results obtained in the present study based on the ILW model.
" }, { "name": "Liu, Chang", "degree": "PhD", "year": "1996", "title": "Silicon Micromachined Sensors and Actuators for Fluid Mechanics Applications", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072008-151023", "creators": [ { "name": { "family": "Liu", "given": "Chang" }, "id": "Liu-Chang", "display_name": "Liu, Chang" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "eleceng" ], "doi": "10.7907/k8pm-8g13", "abstract": "The major contributions of this thesis are the developments of silicon micromachined flow shear-stress sensors and magnetic actuators, together with original studies on two fundamental issues of micro fabrication. Sensors and actuators applications in two fluid-mechanics projects have been successfully demonstrated.
\r\n\r\nMicro shear-stress sensors utilize boundary-layer thermal transfer principles. For the proposed fluid-mechanics applications these sensors must have higher sensitive compared with conventional sensors, among other requirements. This has been realized by implementing a unique vacuum-sealed cavity which greatly reduces heat loss to the substrate silicon.
\r\n\r\nFluid applications present unique challenges to micromachined actuators: they must achieve large out-of-plane motion and withstand large forces. We have developed two types of magnetic actuators that fit these requirements. The first type is based on interaction between the magnetic dipole moment of a current-carrying coil and an external magnetic field. A second-type uses the torque generated by an electroplated Permalloy (Ni[subscript 80]Fe[subscript 20] plate inside an external magnetic field.
\r\n\r\nThe two fundamental micro-fabrication issues are the reactive sealing of cavities and the magnetic-levitation assisted release of surface structures. We have conducted systematic experiments to determine the dependance of sealing performance on the test- structure geometric parameters, sealing materials and other factors. Release/drying of micro actuators, with their large surface areas, is especially challenging. The idea for magnetic-levitation assisted release is obtained while we were developing the Permalloy magnetic actuator. Magnetic forces counteract the surface tension forces during the drying to avoid structure stiction to the substrate. Original results from these fundamental studies add to the general micromachining knowledge base.
\r\n\r\nThe applications of developed sensors and actuators are demonstrated in two fluid- mechanics projects. In the first, we explore a unique scheme for active drag reduction, which is possible only by using a Micro Electro Mechanical System (MEMS). The MEMS consists of an array of shear-stress sensors, actuators and embedded neural-network (NN) circuitry. The goal of the second project is to achieve enhanced maneuverability of delta-wings using MEMS devices. Shear-stress sensors are successfully applied to identify the flow separation lines along the delta-wing's leading edges. Permalloy magnetic actuators interact with the leading-edge flow for controlling the wing motion.
" }, { "name": "Liu, Cheh-Ming Jeff", "degree": "PhD", "year": "1996", "title": "Monolithic grid amplifiers", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12202007-141824", "creators": [ { "name": { "family": "Liu", "given": "Cheh-Ming Jeff" }, "id": "Liu-C-J", "display_name": "Liu, Cheh-Ming Jeff" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9c1y-j677", "abstract": "A grid amplifier is a quasi-optical power-combining device which amplifies a microwave beam and spatially combines the outputs of many transistors, making it possible to greatly increase power. This thesis will discuss gain and stability models for Heterojunction-Bipolar-Transistor (HBT) grid amplifiers. A transmission-line equivalent-circuit model for gain analysis will be discussed. Hybrid HBT grid amplifiers, fabricated with high-dielectric substrates, have been demonstrated with gains of 11 dB at 10 GHz and 6 dB at 16 GHz. A stability model for common-mode oscillations will be presented and stabilizing techniques will be discussed. With stabilizing capacitors, a highly stable grid amplifier has been achieved at 10 GHz. Based on the models, a 36-element monolithic HBT grid amplifier is designed, fabricated and tested. The result is a highly stable monolithic grid amplifier with a peak gain of 5 dB and 3-dB bandwidth of 1.8 GHz. This monolithic HBT grid amplifier has a maximum saturated output power of 670 mW at 40 GHz. The far-field approach was employed to measure the gain and power of the grid amplifiers. Theoretical discussions on aperture efficiencies of grids and thermal modelling for a two-layer structure of a grid with a carrier will be discussed.\n" }, { "name": "Lubecke, Victor Manuel", "degree": "PhD", "year": "1996", "title": "Micromechanical tuning elements for submillimeter wave integrated circuits", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182007-135252", "creators": [ { "name": { "family": "Lubecke", "given": "Victor Manuel" }, "id": "Lubecke-V-M", "display_name": "Lubecke, Victor Manuel" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/g8rb-ds84", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nMonolithic integrated circuit technology promises a practical means for realizing reliable and reproducible planar millimeter and submillimeter wave circuits. Planar circuits are fabricated through photolithographic techniques, which allow for the cost-effective production of intricate designs not possible with waveguide technology. Such circuits however, do not typically allow for post-fabrication optimization of performance. This can be a critical problem for the millimeter and submillimeter band, where device parasitics and fabrication tolerances are difficult to control and characterize. In this thesis, a micromechanical tuning element suitable for integration in a variety of monolithic millimeter and submillimeter wave circuits is presented. It is called a sliding planar backshort (SPB) and it can be fabricated as an integral part of a dielectric-coated coplanar transmission line. The SPB forms a movable short-circuit over a useful bandwidth, which allows for the variation of the transmission line's electrical length. A semiempirical approach was employed in its design. Measurements of [...] for the SPB at 2 GHz, were better than -0.5 dB over a bandwidth of at least 50% on both coplanar strip and coplanar waveguide transmission lines. A frequency-scaled version of the SPB was photolithographically fabricated and tested in a planar quasi-optical 100 GHz detector circuit. The response of a Schottky diode was successfully varied over a range of almost 14 dB, creating a 3 dB improvement over the untuned response. A technique for fabricating a micromechanical version of the SPB was developed. Two of these SPB's were fabricated as integral parts of a quasi-optical 620 GHz monolithic integrated detector circuit, where they were used to vary the measured response over a range of almost 15 dB. Such tuning elements can be used for characterizing developmental circuits, and for optimizing the in-use performance of various millimeter and submillimeter wave integrated circuits.\n" }, { "name": "Luo, Jiafu", "degree": "PhD", "year": "1996", "title": "Monolithic GaAs VLSI optoelectronic neuron arrays", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-05012006-124513", "creators": [ { "name": { "family": "Luo", "given": "Jiafu" }, "id": "Luo-Jiafu", "display_name": "Luo, Jiafu" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/F7DG-YM82", "abstract": "This thesis focuses on the design and fabrication of GaAs monolithic optoelectronic integrated circuits (OEIC's) for use in optical neural networks. The basic circuit in a neuron array consists of GaAs MESFET (Metal-Semiconductor Field Effect Transistor) circuits and optical input/output (I/O) devices. By implementing the I/O process optically, we can greatly increase the neuron density for a 2-dimensional array and thus achieve highly parallel computation.\r\n\r\nBecause of the high loss involved in optical interconnections, high density neuron arrays require high gain photodetectors and high efficiency output devices. With responsivities up to 10(4)A/W and structure compatibility with MESFET circuits, optical FET detectors (OPFET's) are an excellent choice as photodetectors. Several techniques have been investigated in order to fabricate high efficiency LED's (light-emitting-diodes) at low current levels. Low power consumption neurons based on OPFET's and GaAs/A1GaAs double-Zn-diffusion double-heterojunction LED's are fabricated using in-house facilities.\r\n\r\nIndustrial foundries provide the most convenient answer to the challenge of fabricating high density 2-D neuron arrays. Two approaches will be described. The first approach utilizes the FET-SEED (self-electrooptic effect device) process from AT&T Bell labs. It provides monolithically integrated circuits with optical I/O devices and depletion mode FET's. In the other approach, GaAs/AlGaAs multiple quantum well modulators are grown on MOSIS GaAs MESFET circuits by MBE regrowth. It is found that in both approaches, the FET's can be used as high gain photodetectors even though the mechanisms are different, thus making it possible to achieve low power consumption high density neuron arrays. Various kinds of complex optoelectronic circuits can be fabricated through these two approaches." }, { "name": "Moore, Cyrille Dennis", "degree": "PhD", "year": "1996", "title": "Experiments in axisymmetric supersonic jets", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-151911", "creators": [ { "name": { "family": "Moore", "given": "Cyrille Dennis" }, "id": "Moore-C-D", "display_name": "Moore, Cyrille Dennis" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1g15-nz55", "abstract": "An experimental study of the effects of exit Mach number and density ratio on the development of axisymmetric jets is described in this thesis. Jet exit Mach numbers of 1.41, 2.0, and 3.0, were studied for jets of helium, argon, and nitrogen. The jets exit into a gas at rest (velocity ratio = 0), in order to better isolate the effects of compressibility and density ratio. Density ratios vary from 0.23 to 5.5.\n\nIn order to generate shock free-jets, unique nozzles were designed and constructed for each gas and Mach number combination. A plating method for the construction of the nozzles was developed to ensure high-accuracy and a good surface finish at a cost significantly less than direct-machining techniques.\n\nThe spreading rate of the jet for several downstream locations is measured with a pitot probe. Centerline data are used to characterise the length of the potential core of the jet, which correlates well with the relative spreading rates. Limited frequency data is obtained through the use of piezo-resistive pressure probes. This method is promising for flows that are not conducive to hot-wire probes.\n\nSpark shadography is used to visualize both the mean and instantaneous flow, with the minimum spark time being 20 nanoseconds. The convection velocity of large-scale disturbances is estimated from the visible Mach-type acoustic waves emanating from the jet.\n\nFor a wide range of jet Mach and Reynolds numbers, the convection velocity of the large scale disturbances in the potential core region of the jet is approximately 0.8 times the jet velocity, the approximate velocity of the first helical instability mode of the jet.\n\nThe main objectives of the present work were to investigate the effects of compressibility and density on the initial development of the axisymmetric jet. Although the data are not sufficient to determine if the convective Mach number concept used in 2-d shear layer research will work in the case of an axisymmetric jet, it is clear that the axisymmetric data do not collapse onto the 2-d curve. However, the density ratio scaling used for the 2-d shear layer appears to work well for the axisymmetric jet, based on the available data.\n\nThe data appear to indicate that the initial development of the jet is dominated by instability modes of the jet as a whole, rather than the shear layers.\n\nOne anomaly noted was that there were long period variations in the centerline total pressure, with times on the order of 3000 jet time scales. The fluctuations did not appear to be experimental artifacts." }, { "name": "Moore, Kevin C.", "degree": "PhD", "year": "1996", "title": "Experiments on the interaction of a coflowing light gas jet with a weak oblique shock wave", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072013-095344022", "creators": [ { "name": { "family": "Moore", "given": "Kevin C." }, "id": "Moore-K-C", "display_name": "Moore, Kevin C." } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/qgz4-en52", "abstract": "Results of experiments performed in the GALCIT Supersonic Wind Tunnel involving\r\na coflowing helium jet in a Mach 2.4 air freestream are presented. Measurements\r\nof the undisturbed jet arc compared with those made after the jet interacts with\r\ndifferent weak oblique shock waves. Data collected using stagnation temperature\r\nand pitot pressure probes is used to form time averaged cross sectional views of the\r\nflow for different downstream stations. These views show that the baroclinic vorticity\r\ngenerated when the jet passes through the shock wave causes the jet to develop\r\ninto a pair of counter-rotating vortices whose axes are aligned with the flow. Previously\r\nproposed models for the circulation deposited on the jet-freestream interface\r\nand characteristic time of an analogous unsteady two-dimensional flow are adapted\r\nto this flow. Comparison of the jet cross sections for corresponding characteristic\r\ntimes shows agreement with experiments and analysis previously performed on the\r\nuustcady two-dimensional analogy. Shear between the jet and the freestream is not\r\nseen to materially affect the development of the flow, but the development of the\r\njet is seen to strongly depend on the strength of the oblique shock. Scattering of\r\na laser light sheet off of ice crystals present in the air but absent from the helium\r\nprovides time-resolved flow visualization pictures which show large departures from\r\nthe mean as the flow moves downstream. This demonstrates the need to consider\r\nturbulence effects which were not considered in previous two-dimensional studies.\r\nThey also show that the presence of the shock wave increases the apparent randomness\r\nof the flow as well as the spreading rate of the jet, likely increasing mixing.\r\nA jet cross section extracted from the average of several Rayleigh scattered images\r\nagrees well with the general size and shape of the jet cross section taken from the\r\ncorresponding time averaged temperature data. The design and construction of the\r\nactive feedback control loop in a gas blending system used to independently control\r\nthe mass flowrate and temperature of the jet is described.\r\n" }, { "name": "Morris, John Christopher", "degree": "PhD", "year": "1996", "title": "Experimental Control: a Helicopter Case Study", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-12202007-115753", "creators": [ { "name": { "family": "Morris", "given": "John Christopher" }, "id": "Morris-John-Christopher", "display_name": "Morris, John Christopher" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/sdad-de68", "abstract": "Robust control has not been used as widely as it could because modelling tools have not advanced as far as analysis and synthesis tools. This becomes readily apparent when applying robust control theory to real problems. With this in mind, an experimental platform was designed and built to study the application of robust control. This platform consists of a real-time computer and a radio-controlled model helicopter mounted on a six degree-of-freedom stand. Experimental systems provide the opportunity not only to verify the applicability of new control theory but also to highlight potential deficiencies.
\r\n\r\nTraditional system identification and control techniques were used to construct hover controllers for the model helicopter. These techniques are not suitable for the construction of robust models for a system of this complexity. In particular, there was no systematic way to augment nominal identified models with uncertainty suitable for the construction of robust controllers.
\r\n\r\nTo address this issue, frequency-domain model validation algorithms and software were developed. These algorithms provide a methodology for verifying the applicability and consistency between experimental data and robust models. Additionally, they provide a method whereby nominal model parameters can be tuned in a robust setting. This is the first set of software tools which provide this capability for general linear uncertain systems.
\r\n\r\nUsing these new software tools, a systematic design process was developed which incorporated frequency-domain model validation analysis, \u00b5-analysis and \u00b5-synthesis, simulation, and implementation. This design process proved to be a valuable new tool for constructing robust models and designing robust control systems. In particular, by applying this design process to the helicopter, the size of uncertainty in the robust model was substantially reduced without sacrificing the ability of the model to \"cover\" experimental data and the first controller implemented performed well. This was strikingly different from the results obtained when using standard robust control techniques, where several controllers destabilized the helicopter when implemented, even though they performed well under simulation.
\r\n\r\nThe model validation software and design process provide a consistent methodology and systematic framework which connects system identification, the construction of robust models, and controller synthesis with experimental data. For the first time the control engineer can compute measures on the validity of a robust model, with respect to all observed data on the actual physical system, which are directly related to the robustness measures resulting from \u00b5-analysis and \u00b5-synthesis.
\r\n" }, { "name": "Newlin, Matthew Philip", "degree": "PhD", "year": "1996", "title": "Model Validation, Control, and Computation", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-01032008-090000", "creators": [ { "name": { "family": "Newlin", "given": "Matthew Philip" }, "id": "Newlin-Matthew- Philip", "display_name": "Newlin, Matthew Philip" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Smith", "given": "Roy" }, "id": "Smith-Roy", "role": "member", "display_name": "Smith, Roy" } ], "option_major": [ "mecheng" ], "doi": "10.7907/nvwd-hw47", "abstract": "Engineering in general is concerned with controlling and predicting future behavior with some certainty despite having only imperfect information. Although feedback can be an exceptionally effective engineering tool and is often easy to apply, the behavior of a system under feedback can be extremely sensitive to model mismatch, which is always present. The potential for unpredictable behavior is a major drawback to the engineering application of feedback. Robust control theory addresses this difficulty by parametrizing a family of feedback controllers that are less sensitive to model mismatch.
\r\n\r\nDespite encouraging early applications, robust control theory has so far been deficient in analysis of systems, synthesis of controllers, connection to real problems, and applicability to nonlinear problems. Further, results on the computational complexity of robust control problems that necessitate either bounds computation or a restricted class of problems have cast doubts about the potential utility of the area.
\r\n\r\nInitial work in robust control focused on complex uncertainty in the frequency domain. A perceived deficiency is that such model sets are unrealistic: uncertainty in mass, stiffness, aero-coefficients, and the like are naturally modeled as real variations. This thesis includes initial work on practical upper bound computation and substantially improved lower bound computation for moderately large robust control analysis problems that include such real parametric uncertainty, despite the computational complexity of the problems. Although better upper bound computation than that described here is now available for small problems, such is not the case for large problems. The improved lower bound computation chronicled here is desirable because the initial lower bound computation for problems with real parametric uncertainty is not as reliable as in the complex case. Additionally, this thesis shows that branch and bound is a limited but critical tool for better computation, a fact that previously has gone unrecognized.
\r\n\r\nTogether, these contributions allow for the practical computation of robust control problems of engineering interest and provide the basis not only for applications that may ultimately determine the utility of the robust control paradigm but also for the computation of various outgrowths of the [mu] framework, which is the basis for computational robust control.
\r\n\r\nOne such outgrowth is the model validation problem. Model validation tests whether a robust control model in the [mu] framework is consistent with experimentally determined time histories quite a different problem than standard system identification. This thesis shows that the model validation problem is indeed closely related to the standard [mu] problem and its computation.
\r\n\r\nThe practical computation of the model validation problem, which should follow naturally from the work presented here, provides the basis for the connection between robust control theory and practical applications. Future work along these lines should elevate the application of robust control theory from chance and intuition to a standard engineering tool.
\r\n\r\nFurther, the techniques that render the model validation problem similar to the standard [mu] problem are applicable to a great variety of systems analysis and design problems. This newly perceived generality of the [mu] paradigm may ultimately provide a unifying framework for the many seemingly disparate aspects of systems and control design.
" }, { "name": "O'Brien, John David", "degree": "PhD", "year": "1996", "title": "Design, growth, and characterization of vertical cavity surface emitting lasers", "advisor": "Yariv, Amnon; Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252005-084438", "creators": [ { "name": { "family": "O'Brien", "given": "John David" }, "id": "O'Brien-J-D", "display_name": "O'Brien, John David" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "co-advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/79nd-7w93", "abstract": "Vertical cavity surface emitting laser design, growth, and characterization is discussed. Theoretical models for gain in semiconductors as well as for the threshold gain in vertical cavity lasers is presented. The distributed Bragg mirrors used in these lasers are treated theoretically using the coupled-mode approach and with a matrix method that is generalized to include gain and loss.\r\n\r\nThe growth by molecular beam epitaxy of these structures is also discussed including steps taken to obtain precise, reproducible growth rates. Specific problems and tradeoffs encountered in the growth include greater oxygen incorporation at the lower substrate temperatures needed to ensure precise thickness control. Beryllium diffusion is also discussed and SIMS measurements are presented.\r\n\r\nTwo types of vertical cavity lasers are demonstrated. The first is a hybrid semiconductor/dielectric structure. In this design, the n-doped mirror and the optical cavity are epitaxially grown semiconductors and the top mirror is a SiO2/Si3/N4 distributed Bragg reflector added to the structure by reactive sputter deposition. These lasers have InGaAs quantum wells and are top-emitting near 980 nm. This design has the advantage of removing the top mirrors from the current path which reduces the series resistance. Threshold voltages of 1.8-1.9 V were obtained from 18 \u00b5m diameter lasers. In addition, the hybrid structure allows characterization before the deposition of the top mirror. Measurements of the carrier distribution and the temperature of the devices operating without the top mirrors are presented. A minimum lasers threshold current of 2.5 mA was obtained from a 6 \u00b5m diameter laser, and a maximum peak power of 1.67 mW was obtained from a 12 \u00b5m diameter laser. The lasers exhibit strongly index-guided transverse modes and are multi-moded above threshold." }, { "name": "Orlov, Sergei S.", "degree": "PhD", "year": "1996", "title": "Holographic storage dynamics, phase conjugation, and nonlinear optics in photorefractive materials", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-06082005-110714", "creators": [ { "name": { "family": "Orlov", "given": "Sergei S." }, "id": "Orlov-S-S", "display_name": "Orlov, Sergei S." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/RYVB-3254", "abstract": "This thesis explores the application of photorefractive materials in two distinct areas: the holographic data storage and the dynamic nonlinear optical interactions. First, we have established that partial ferroelectric domain reversal in certain ferroelectric materials can be used to permanently fix the dynamic holographic gratings, and analyzed the interaction between the fixed and the dynamic components of a hologram. A comprehensive analysis of the storage temporal dynamics in photorefractive materials is further developed for the case of thermal ionic fixing. An experimental study of holographic storage dynamics in photorefractive lithium niobate revealed new features related to the ionic conductivity in this and similar materials. We established and developed techniques for long-lifetime and high-efficiency hologram fixing in the holographic data storage applications. We further analyze theoretically the impact of the recording response properties of different storage media (including photorefractive materials and photopolymers) and optical detection noise on the ultimate storage capacity of holographic memories.\n\nSecond, the transverse properties of the photorefractive double phase conjugate mirror (DPCM) have been studied. We have established that the DPCM exhibits a sharp conjugation fidelity gain threshold which increases with image resolution, while the reflectivity is a smoothly varying function of nonlinear gain. The conjugation fidelity was found to degrade dramatically for unequal intensities ratio. The DPCM exhibits critical slowing down in the vicinity of the oscillation threshold. A two-dimensional coupled-modes perturbation analysis of the DPCM is introduced and its basic predictions are in a good qualitative agreement with the results of the experimental study.\n\nFinally, we analyze the nonlinear optical second harmonic generation in materials with strong photorefractivity. In the presence of strong self-phase modulation the phase matching conditions are modified and we found that in some cases this leads to a unique effect, namely, the nonlinear self-phase matching of optical nonlinear interaction. Strong photorefractive response manifests itself in two characteristic and very apparent manners; a large change in the conversion efficiency and self-defocusing of the generated second harmonic beam. We introduced a two-dimensional model of photorefractive effect and found its predictions to be in a good qualitative agreement with the observed transverse dynamics.\n" }, { "name": "Ostrowski, James Patrick", "degree": "PhD", "year": "1996", "title": "The mechanics and control of undulatory robotic locomotion", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-10202005-153514", "creators": [ { "name": { "family": "Ostrowski", "given": "James Patrick" }, "id": "Ostrowski-J-P", "display_name": "Ostrowski, James Patrick" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Chirikjian", "given": "Gregory S." }, "id": "Chirikjian-G-S", "role": "member", "display_name": "Chirikjian, Gregory S." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Y1TF-RF86", "abstract": "In this dissertation, we examine a formulation of problems of undulatory robotic locomotion within the context of mechanical systems with nonholonomic constraints and symmetries. Using tools from geometric mechanics, we study the underlying structure found in general problems of locomotion. In doing so, we decompose locomotion into two basic components: internal shape changes and net changes in position and orientation. This decomposition has a natural mathematical interpretation in which the relationship between shape changes and locomotion can be described using a connection on a trivial principal fiber bundle.\n\nWe begin by reviewing the processes of Lagrangian reduction and reconstruction for unconstrained mechanical systems with Lie group symmetries, and present new formulations of this process which are easily adapted to accommodate external constraints. Additionally, important physical quantities such as the mechanical connection and reduced mass-inertia matrix can be trivially determined using this formulation. The presence of symmetries then allows us to reduce the necessary calculations to simple matrix manipulations.\n\nThe addition of constraints significantly complicates the reduction process; however, we show that for invariant constraints, a meaningful connection can be synthesized by defining a generalized momentum representing the momentum of the system in directions allowed by the constraints. We then prove that the generalized momentum and its governing equation possess certain invariances which allows for a reduction process similar to that found in the unconstrained case. The form of the reduced equations highlights the synthesized connection and the matrix quantities used to calculate these equations.\n\nThe use of connections naturally leads to methods for testing controllability and aids in developing intuition regarding the generation of various locomotive gaits. We present accessibility and controllability tests based on taking derivatives of the connection, and relate these tests to taking Lie brackets of the input vector fields.\n\nThe theory is illustrated using several examples, in particular the examples of the snakeboard and Hirose snake robot. We interpret each of these examples in light of the theory developed in this thesis, and examine the generation of locomotive gaits using sinusoidal inputs and their relationship to the controllability tests based on Lie brackets.\n" }, { "name": "Paganini-Herrera, Fernando", "degree": "PhD", "year": "1996", "title": "Sets and Constraints in the Analysis of Uncertain Systems", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172007-080812", "creators": [ { "name": { "family": "Paganini-Herrera", "given": "Fernando" }, "id": "Paganini-Herrera-Fernando", "display_name": "Paganini-Herrera, Fernando" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "role": "member", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/3X73-5F28", "abstract": "This thesis is concerned with the analysis of dynamical systems in the presence of model uncertainty. The approach of robust control theory has been to describe uncertainty in terms of a structured set of models, and has proven successful for questions, like stability, which call for a worst-case evaluation over this set. In this respect, a first contribution of this thesis is to provide robust stability tests for the situation of combined time varying, time invariant and parametric uncertainties.
\r\n\r\nThe worst-case setting has not been so attractive for questions of disturbance rejection, since the resulting performance criteria (e.g., H\u221e) treat the disturbance as an adversary and ignore important spectral structure, usually better characterized by the theory of stochastic processes. The main contribution of this thesis is to show that the set-based methodology can indeed be extended to the modeling of white noise, by employing standard statistical tests in order to identify a typical set, and performing subsequent analysis in a worst-case setting. Particularly attractive sets are those described by quadratic signal constraints, which have proven to be very powerful for the characterization of unmodeled dynamics. The combination of white noise and unmodeled dynamics constitutes the Robust H2 performance problem, which is rooted in the origins of robust control theory. By extending the scope of the quadratic constraint methodology we obtain a solution to this problem in terms of a convex condition for robustness analysis, which for the first time places it on an equal footing with the H\u221e performance measure.
\r\n\r\nA separate contribution of this thesis is the development of a framework for analysis of uncertain systems in implicit form, in terms of equations rather than input-output maps. This formulation is motivated from first principles modeling, and provides an extension of the standard input-output robustness theory. In particular, we obtain in this way a standard form for robustness analysis problems with constraints, which also provides a common setting for robustness analysis and questions of model validation and system identification.
" }, { "name": "Pettersson, Per-Olov", "degree": "PhD", "year": "1996", "title": "Silicon heterojunctions", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112006-145849", "creators": [ { "name": { "family": "Pettersson", "given": "Per-Olov" }, "id": "Pettersson-P", "display_name": "Pettersson, Per-Olov" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/pvjr-8w50", "abstract": "The three topics presented in this thesis all concern silicon heterojunction growth and device applications. We developed growth techniques for two relatively immature material systems, silicon/calciumfluoride (Si/CaF2) and silicon/silicon-carbon (Si/Si1-yCy), and fabricated devices which take the mature silicon/silicon dioxides (Si/SiO2) material system to new limits in terms of oxide thickness.\n\nWe applied novel growth techniques in the undeveloped material systems with the ultimate goal of producing device quality material suitable for quantum device fabrication. In the Si/CaF2 material system, we used a new technique known as Electron Beam Assisted Molecular Beam Epitaxy to improve the morphology of silicon grown on calciumfluoride. The result was a decrease in roughness of the silicon overlayer. In the silicon/silicon-carbon material system, we employed Surfactant Assisted Molecular Beam Epitaxy to grow smooth high carbon content silicon-carbon on silicon. Here, the result was a greatly improved surface morhology and the technique looks promising for applications requiring high carbon concentrations.\n\nIn the mature and extremely important (from a technological and commercial point of view) Si/SiO2 material system, we fabricated Metal Insulator Semiconductor Switches devices in a study of the dependence of the I/V curve on the insulator thickness. While the primary objective of this study was to optimize the I/V curve, we learned that this material system is not very well understood, neither from a theoretical nor experimental standpoint, when the oxide is extremely thin." }, { "name": "Phoong, See-May", "degree": "PhD", "year": "1996", "title": "Time-varying and finite field filter banks", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222007-114654", "creators": [ { "name": { "family": "Phoong", "given": "See-May" }, "id": "Phoong-See-May", "display_name": "Phoong, See-May" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Bruck", "given": "Jehoshua" }, "id": "Bruck-J", "role": "member", "display_name": "Bruck, Jehoshua" }, { "name": { "family": "Effros", "given": "Michelle" }, "id": "Effros-M", "role": "member", "display_name": "Effros, Michelle" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Xia", "given": "Xiang-Gen" }, "id": "Xia-Xiang-Gen", "role": "member", "display_name": "Xia, Xiang-Gen" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1bzz-ba31", "abstract": "Filter banks find many applications in signal processing. This thesis deals with four different problems in filter banks.\r\n\r\nFirst we find a new application of filter banks: Filter bank convolver. We prove two filter bank convolution theorems which tell us how to do the convolution in the subbands. Applying the multirate technique to the problem of convolution, we obtain a significant improvement in the accuracy of the convolutional result when the computation is done with finite precision. The derivation also leads to a low sensitivity robust structure for FIR filters.\r\n\r\nIn the second part, a new class of two-channel biorthogonal filter banks is proposed. We successfully design IIR filter banks which achieve the following desired properties simultaneously: (i) Perfect reconstruction (PR); (ii) causality and stability; (iii) near linear-phase; (iv) frequency selectivity. Two classes of causal stable maximally flat IIR wavelets are derived and closed form formulas are given. We also provide a novel mapping of the proposed 1D framework into 2D. The mapping preserves: (i) PR; (ii) stability in the IIR case and linear phase in the FIR case; (iii) frequency selectivity; (iv) low complexity.\r\n\r\nIn the third part, the theory of paraunitary (PU) filter banks is extended to the case of GF(q) with prime q. We show that finite field PU filter banks are very different from real or complex PU filter banks. Despite all the differences, we are able to prove a number of factorization theorems. All unitary matrices in GF(q) are factorizable in terms of Householder-like matrices. The class of first-order PU matrices, the lapped orthogonal transform in finite fields, can always be expressed as a product of degree-one or degree-two building blocks.\r\n\r\nFinally the theory of conventional LTI filter banks is extended to the time-varying case. We develop a polyphase representation method for time-varying filter bank (TVFB). Using the proposed polyphase approach, we are able to show some unusual properties which are not exhibited by the conventional LTI filter banks. For example, we can show that for a PR TVFB, the losslessness of analysis bank does not always imply that of the synthesis bank, and a PR TVFB in general will only generate a discrete-time frame, rather than a basis, for the class of finite energy signals. The class of lossless TVFB is studied in detail. We show that all lossless linear time-varying systems are invertible and provide explicit construction of the inverse. The interplay between invertibility, uniqueness and losslessness of the inverse is investigated. The factorizability of lossless TVFB is addressed and we show that there are factorizable and unfactorizable examples." }, { "name": "Salvatore, Randal A.", "degree": "PhD", "year": "1996", "title": "Ultrashort and ultrahigh-repetition-rate pulses from passively mode-locked semiconductor lasers", "advisor": "Yariv, Amnon; Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072008-092000", "creators": [ { "name": { "family": "Salvatore", "given": "Randal A." }, "id": "Salvatore-R-A", "display_name": "Salvatore, Randal A." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "co-advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1f05-ek48", "abstract": "This thesis is an investigation into both the fundamental and experimental aspects of using semiconductor lasers to generate extremely short (100's of fs) and very high repetition frequency (> 50 GHz) optical pulses. The pulses are produced through modelocking, a technique of forcing a laser to operate in a number of optical modes simultaneously and to hold a constant phase relationship between these modes. Both the shortest and highest repetition rate pulses have been obtained from passive modelocking. An inherently nonlinear technique which does not use any active external timing source. Two structures, ridge-waveguide stripe lasers and liquid phase epitaxy (LPE) regrown lasers, were used to directly generate picosecond width pulses. Using cross-correlation techniques, pulse shape and phase measurements are made. Linear dispersion compensation is shown to achieve nearly a factor of 20 in pulse compression. Stable pulses down to 260 fs are generated.\n\nShowing that exitonic effects are not essential in these devices, wavelength tunability was combined with dispersion compensation to create the first broadly tunable subpicosecond semiconductor source. The device is found to give tunability ranges and mode-locked spectral widths that are comparable to the best results achieved in dye lasers in terms of fractions of the operating gain spectral width. Results for different regimes in the tuning range are examined, and pulses directly from the laser are found to have about a 2 to 1 fall-time to rise-time ratio. A significant nonlinear chirp is found only when the laser is tuned to the short wavelength side of its tuning range and was determined to cause long tails in the autocorrelations of compressed pulses. Additionally, spread-resistant pulses are described and experimentally analyzed.\n\nThe case of high-repetition-rate modelocking, which more likely involves about 5 modes instead of 5000 modes, is examined. Approximations in the leading theory of passive modelocking are shown to be inadequate in this case. A steady-state model for high-repetition-rate modelocking is developed including phase effects and is tailored to parameters of semiconductor lasers. Self-consistent solutions show that a lower threshold gain can exist for a supermode than for single mode operation. Predictions of the laser's behavior upon modifying key material, geometric, and bias parameters are made. Experimental results show that through adjustment of the gain current, \"chirp-controlled\" modelocking is obtained with operation in any of the three chirp regimes (up-chirped, chirp-free, or down-chirped). This pulse chirp and resulting broadening are due to the algebraic addition of opposite-signed chirps from saturation of the absorber and gain sections. Theoretical modelling from the supermode analysis also traverses the same chirp regimes when the photon intensity is increased.\n" }, { "name": "Shakouri, Ali", "degree": "PhD", "year": "1996", "title": "Electron transport in quantum well infrared photodetectors", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-05172005-084805", "creators": [ { "name": { "family": "Shakouri", "given": "Ali" }, "id": "Shakouri-A", "display_name": "Shakouri, Ali" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/aqq2-yj56", "abstract": "In this work the technique of molecular beam epitaxy is used to grow GaAs/AlGaAs multiquantum well structures. The material composition and thicknesses are chosen in a way that the electrons in the device interact resonantly with infrared radiation. This interaction originates from quantized energy states (subbands) in the conduction band of the material. The infrared absorption and photocurrent spectroscopies, in conjunction with standard DC-characterizations, are used to investigate electron transport in these structures.\n\nAfter a brief description of electronic energy states based on the multi-band k.p approximation, the optical properties of intersubband transitions are theoretically and experimentally investigated. Evidence for the above-the-barrier energy states (continuum minibands) affecting the absorption and photocurrent spectra is presented.\n\nStudying electron transport perpendicular to the multiquantum well layers, different regimes of miniband and hopping conduction are distinguished. It is shown that sequential resonant tunneling and electric field domain formation occur even in very weekly coupled quantum wells (separated by 44 nm barriers), its application to the design of voltage-controlled multi-color infrared detectors is discussed and demonstrated. Finally, the low bias behavior of quantum well detectors is analyzed and evidence for photocurrent flowing in the opposite direction to the applied bias is presented." }, { "name": "Soatto, Stefano", "degree": "PhD", "year": "1996", "title": "A geometric framework for dynamic vision", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082008-103705", "creators": [ { "name": { "family": "Soatto", "given": "Stefano" }, "id": "Soatto-Stefano", "display_name": "Soatto, Stefano" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "chair", "display_name": "Perona, Pietro" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Ponce", "given": "Jean" }, "id": "Ponce-J", "role": "member", "display_name": "Ponce, Jean" }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "orcid": "0000-0002-7696-5058", "role": "member", "display_name": "Morari, Manfred" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "cds" ], "doi": "10.7907/x87w-t943", "abstract": "This thesis explores the problem of inferring information about the three-dimensional world from its projections onto a camera (images). Among all visual cues, we do not address \"pictorial\" ones, such as texture or shading. Instead, we concentrate on \"dynamic\" cues, which are associated with variations of the image over time.\r\n\r\nIn order to eliminate pictorial cues, one may represent the world as a collection of geometric primitives, such as points, curves or surfaces in three-dimensional space. Then, from the two-dimensional motion of the projection of such primitives onto the image, one can infer the three-dimensional structure of the world and its motion relative to the viewer.\r\n\"Three-dimensional structure from two-dimensional images\" has now been a central theme in Computer Vision for over two decades, and tools from Linear Algebra and Projective Geometry have been widely employed to attack the problem as a \"static\" task. It is only in recent years that the role of time has started to be recognized, after the influential work of Dickmanns and his coworkers on vehicle guidance on freeways.\r\n\r\nWe do not impose restrictions on the structure of the environment, and we cast the problem of general three-dimensional structure and motion estimation within the framework of Dynamical Systems. We show how different algebraic constraints on the image projections can be interpreted as nonlinear and implicit dynamical models whose (unknown) parameters live in peculiar differentiable manifolds that encode three-dimensional information. Recovering such three-dimensional information then amounts to identifying dynamical models while taking into account the geometry of the parameter manifolds." }, { "name": "Stephens, Tab Allen", "degree": "PhD", "year": "1996", "title": "Chemical environment selectivity in Mossbauer diffraction", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06172005-081511", "creators": [ { "name": { "family": "Stephens", "given": "Tab Allen" }, "id": "Stephens-T-A", "display_name": "Stephens, Tab Allen" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/q4tq-7k23", "abstract": "We demonstrate a new feature of Mossbauer diffraction that is useful for studies of atomic arrangements in materials - that Mossbauer diffraction can measure the autocorrelation function of 57Fe atoms as a function of their chemical environment. To acquire the experimental data, we built a Debye-Scherrer type powder diffractometer with a 57Co radiation source and a large angle position sensitive detector. By working with polycrystalline materials near the kinematical limit of diffraction, the broadening of nuclear energy levels is not severe, so the spectroscopic capabilities of Mossbauer scattering are preserved. The sample was polycrystalline 57Fe3Al with the ordered DO3 structure. The two sites for the 57Fe atoms, the Wyckoff 4(b) and 8(c) sites, differ in both their chemical environment (0Al versus 4Al 1nn) and in their spatial arrangement (face-centered cubic, fcc, with lattice parameter 2a0 versus simple cubic, sc, with lattice parameter a0). Diffraction peaks from the fcc structure were detected when the incident radiation was tuned to the Mossbauer resonance of the Wyckoff 4(b) Fe site, but not for tuning to the 8(c) site, thereby distinguishing the spatial arrangements of these two Fe sites. Thus, the validity of chemical environment selectivity was proven.\r\n\r\nThe phase change of the Mossbauer scattering near resonance affects the interference of diffracted waves from different chemical environments. Interference effects between x-ray Rayleigh scattering and Mossbauer scattering from the 57Fe3Al sample were observed, as were interference effects involving the different components of the Mossbauer spectra. A simple oscillator model was used successfully to calculate the interference effects seen in the experimental data.\r\n" }, { "name": "Thornley, John William", "degree": "PhD", "year": "1996", "title": "A Parallel Programming Model with Sequential Semantics", "advisor": "Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechETD:etd-01042008-085720", "creators": [ { "name": { "family": "Thornley", "given": "John William" }, "id": "Thornley-John-William", "display_name": "Thornley, John William" } ], "advisors": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "chair", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Kesselman", "given": "Carl" }, "id": "Kesselman-C", "orcid": "0000-0003-0917-1562", "role": "member", "display_name": "Kesselman, Carl" }, { "name": { "family": "Van de Velde", "given": "Eric" }, "id": "van-de-Velde-E", "role": "member", "display_name": "Van de Velde, Eric" }, { "name": { "family": "Hall", "given": "Mary" }, "id": "Hall-Mary", "orcid": "0000-0002-3058-7573", "role": "member", "display_name": "Hall, Mary" }, { "name": { "family": "Schroeder", "given": "Peter" }, "id": "Schr\u00f6der-P", "orcid": "0000-0002-0323-7674", "role": "member", "display_name": "Schroeder, Peter" } ], "option_major": [ "compsci" ], "doi": "10.7907/mytw-er77", "abstract": "Parallel programming is more difficult than sequential programming in part because of the complexity of reasoning, testing, and debugging in the context of concurrency. In this thesis, we present and investigate a parallel programming model that provides direct control of parallelism in a notation with sequential semantics. Our model consists of a standard sequential imperative programming notation extended with the following three pragmas:\r\n\r\n1. The parallelizable sequence of statements pragma indicates that a sequence of statements can be executed as parallel threads.\r\n\r\n2. The parallelizable for-loop statement pragma indicates that the iterations of a for-loop statement can be executed as parallel threads.\r\n\r\n3. The single-assignment type pragma indicates that variables of a given type are assigned at most once and that ordinary assignment and evaluation operations can be used as implicit communication and synchronization operations between parallel threads.\r\n\r\nIn our model, a parallel program is simply an equivalent sequential program with added pragmas. The placement of the pragmas is subject to a small set of restrictions that ensure the equivalence of the parallel and sequential semantics. We prove that if standard sequential execution of a program (by ignoring the pragmas) satisfies a given specification and the pragmas are used correctly, parallel execution of the program (as directed by the pragmas) is guaranteed to satisfy the same specification.\r\n\r\nOur model allows parallel programs to be developed using sequential reasoning, testing, and debugging techniques, prior to parallel execution for performance. Since parallelism is specified directly, sophisticated analysis and compilation techniques are not required to extract parallelism from programs. However, it is important that parallel performance issues such as granularity, load balancing, and locality be considered throughout algorithm and program development.\r\n\r\nWe describe a series of programming experiments performed on up to 32 processors of a shared-memory multiprocessor system. These experiments indicate that for a wide range of problems:\r\n\r\n1. Our model can express sophisticated parallel algorithms with significantly less complication than traditional explicit parallel programming models.\r\n\r\n2. Parallel programs in our model execute as efficiently as sequential programs on one processor and deliver good speedups on multiple processors.\r\n\r\n3. Program development with our model is less difficult than with traditional explicit parallel programming models because reasoning, testing, and debugging are performed using sequential methods.\r\n\r\nWe believe that our model provides the basis of the method of choice for a large number of moderate-scale, medium-grained parallel programming applications." }, { "name": "Tierno, Jorge E.", "degree": "PhD", "year": "1996", "title": "A computational approach to nonlinear system analysis", "advisor": "Doyle, John Comstock; Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072008-082023", "creators": [ { "name": { "family": "Tierno", "given": "Jorge E." }, "id": "Tierno-J-E", "display_name": "Tierno, Jorge E." } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "co-advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4txk-p492", "abstract": "Most practical control systems have significant nonlinear components. However, these systems are typically analyzed either through robustness analysis of their linearizations, or through extensive simulation of their nonlinear models. Other forms of analysis of nonlinear systems have not as yet led to computationally tractable solutions. The aim of this thesis is to extend the analysis methodology for linear systems given by the structured singular value framework to nonlinear systems. We study the question: Given an uncertain nonlinear system, driven by a nominal command signal over a finite time horizon, and subject to bounded noise, norm bounded feedback components, and uncertain parameters, how far from the nominal trajectory will the actual trajectory be? In order to inherit the properties of the structured singular value, we will use the 2-norm as measure for noise signals and undermodeled feedback components. As is the case for robustness analysis of linear systems, we can only find efficient computation algorithms for upper and lower bounds to the answer to this question.\n\nTo compute the lower bound we develop a power algorithm similar to the one developed for the structured singular value. Since, as was the case for linear systems, the algorithm is not guaranteed to converge in general, its analysis has to be done empirically. We test this algorithm by applying it to simulations of real systems and show that it performs better than other available optimization methods. To develop an upper bound, we study a class of rational nonlinear systems. We show that for problems in this class, an uncertain, constrained linear system can be constructed that achieves the same performance level. Upper bounds on the performance of these systems can be computed by solving linear matrix inequalities. Finally, we study extensions that can be obtained to these analysis methods when the system is linear but time varying.\n" }, { "name": "Tsai, Charles Su-Chang", "degree": "PhD", "year": "1996", "title": "Optoelectronic structure fabrication by organometallic vapor-phase epitaxy and selective epitaxy", "advisor": "Vahala, Kerry J.; Scherer, Axel", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222007-114128", "creators": [ { "name": { "family": "Tsai", "given": "Charles Su-Chang" }, "id": "Tsai-C-S", "display_name": "Tsai, Charles Su-Chang" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "co-advisor", "display_name": "Scherer, Axel" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/vrda-c377", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe internal configuration and external supports of OMVPE reactors are examined. The quality of epitaxial layers deposited by an OMVPE reactor is strongly influenced by its internal configuration. The quality of the external supports determines the safety, the environmental impact, and the operating efficiency of the OMVPE reactor.\n\nOptoelectronic structures are fabricated by selective epitaxy. The morphology and growth behavior of GaAs, AlGaAs, and InGaAs using selective epitaxy are presented. Highly selective growth can be achieved through the use of organometallic compounds which contain halogens. The selective growth of nanometer-scale GaAs wire and dot structures is demonstrated. Spectrally-resolved cathodoluminescence images as well as pectra from single dots and wires, passivated by an additional AIGaAs layer, are presented. A blue shifting of the GaAs luminescence peak is observed as the size scale of the wires and dots decreases. Formation of highly-uniform and densely-packed arrays of GaAs dots by selective epitaxy is described. The smallest GaAs dots formed are 15-20 nm in base diameter and 8-10 nm in height with slow-growth crystallographic planes limiting growths of individual dots. Completely selective GaAs growth within dielectric-mask openings at these small size-scales is also demonstrated. The technique of facet-modulation selective epitaxy and its application to quantum-well wire doublet fabrication are described. The smallest wire fabricated has a crescent cross-section less than 140 [...] thick and less than 1400 [...] wide.\n\nThe development of OMVPE epitaxial layers for a visible-wavelength vertical-cavity surface-emitting laser (VCSEL) is presented. The defect density of the mirror layers was reduced to a negligible level by optimizing gas switching. Electroluminescence spectrum of an InGaP heterostructure p-n diode is presented. The defect density of the active region was also reduced to a negligible level by optimizing the gas-switching sequences.\n" }, { "name": "Valluri, Siddhartha", "degree": "PhD", "year": "1996", "title": "Bluff Body Flows in the Presence of a Free Surface", "advisor": "Roshko, Anatol; Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechETD:etd-06082007-075443", "creators": [ { "name": { "family": "Valluri", "given": "Siddhartha" }, "id": "Valluri-Siddhartha", "display_name": "Valluri, Siddhartha" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "co-chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2wbk-9k81", "abstract": "An experimental study is performed in a water tunnel (Re = 40,000 to Re = 60,000) to study the interaction between the wake of a circular disk and the free surface. The deformation of the free surface is correlated with the behavior of the wake by utilizing surface pictures, wake flow visualization, drag measurement and Digital Particle Image Velocimetry techniques. It is observed that the wake can exist in two modes with different stabilities. The flow can switch between these two modes and the switching process exhibits hysteresis. The topological differences between these modes and their relation to the observed surface patterns are discussed. The changes in the wake are reflected by an increase in Cd which reaches a maximum value when the upper edge of the disk is 0.125 diameters from the surface. Comparison is also made with a disk approaching a solid boundary." }, { "name": "Walter, Mark E.", "degree": "PhD", "year": "1996", "title": "The evolution of damage in ceramic matrix composites", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072008-112449", "creators": [ { "name": { "family": "Walter", "given": "Mark E." }, "id": "Walter-M-E", "display_name": "Walter, Mark E." } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/w4b4-dx66", "abstract": "In an effort to better understand the evolution of damage in brittle matrix composites, the mechanical behavior of a ceramic matrix composite, unidirectional SiC/CAS (SiC fibers reinforcing a calcium aluminosilicate matrix), was studied. The presented results are based on uniaxial tension experiments for specimens with the fibers aligned in the loading direction. Post-test optical and scanning electron microscopy was also used to identify the various micromechanisms of damage; axial and transverse strain gauges on all four gage section surfaces and in situ acoustic emission and ultrasonic wave speed measurements were used to monitor the evolution of damage. The experimental results demonstrate the existence of \"zones of deformation\" which are associated with the onset of different damage mechanisms. The energy dissipated in each of these zones was calculated. It is shown that the observed stress-strain behavior can be qualitatively explained in terms of the material properties of the matrix and the fiber, the material processing, and the postulated zones of deformation.\r\n\r\nThe experimental results for SiC/CAS were compared with an existing shear-lag model, and the shortcomings of the model are discussed. By approximating matrix cracks as penny shaped cracks, a micromechanical model was used to estimate the change in the axial modulus of the composite. These results also present another way to interpret the acoustic emission data.\r\n\r\nThe evolution of damage in the SiC/CAS experiments was found to be strain rate dependent even within the quasi-static strain rate regime. For higher rate experiments, the transition from elastic to matrix cracked occurred at a stress level that was nearly twice that of the same transition in the lower rate experiments. This phenomenon and the mechanisms which cause it was further investigated with a model material system (a brittle epoxy resin sandwiched between aluminum strips). In situ quantification of the stress during damage initiation and propagation was realized by the optical method of Coherent Gradient Sensing. Based on these results, the reasons for strain rate dependence of the composite are postulated.\r\n\r\nDetailed understanding of aspects of the evolution of in brittle matrix composites was achieved with finite element simulations. This modeling was based on an axisymmetric unit cell composed of a fiber and its surrounding matrix. The unit cell was discretized into linearly elastic elements for the fiber and the matrix and cohesive elements which allow cracking in the matrix, fiber-matrix interface, and fiber. The cohesive elements failed according to critical stress and critical energy release rate criteria (in shear and/or in tension). After failing, the cohesive elements could slide with Coulomb friction. The tension and shear aspects of failure were uncoupled. The cohesive elements were used to simulate a Dugdale penny shaped crack in a homogeneous cylinder; results compared well to the analytical solution. In order to solve the composite axisymmetric unit cell problem, inertia and viscous damping were added to the formulation. The resulting dynamic problem was solved implicitly using the Newmark Method. Results were compared to the experiment by assuming that only a given number of unit cells were active at any point during the simulation. The effects of changing material properties (e.g., interface strength and toughness and matrix toughness) and loading rate are discussed. Several aspects of the experimentally observed material response of SiC/CAS composite were reproduced by the numerical simulations.\r\n" }, { "name": "Wang, Yi-Chun", "degree": "PhD", "year": "1996", "title": "Shock waves in bubbly cavitating flows. Part I. Shock waves in cloud cavitation. Part II. Bubbly cavitating flows through a converging-diverging nozzle", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282006-144334", "creators": [ { "name": { "family": "Wang", "given": "Yi-Chun" }, "id": "Wang-Yi-Chun", "display_name": "Wang, Yi-Chun" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/82EP-4P53", "abstract": "Two problems are considered in this thesis: the nonlinear dynamics of a cloud of cavitation bubbles, and bubbly cavitating flows in a converging-diverging nozzle. The focus of the first problem is to explore the characteristics of the growth and collapse of a spherical cloud of bubbles. The prototypical problem solved considers a finite cloud of nuclei that is exposed to a decrease in the ambient pressure which causes the cloud to cavitate. A subsequent pressure recovery then causes the cloud to collapse. This is typical of the transient behaviour exhibited by a bubble cloud as it passes a body or the blade of a ship propeller. The simulations employ the fully nonlinear, non-barotropic, homogeneous two-phase flow equations coupled with the Rayleigh-Plesset equation for the dynamics of individual bubbles. A Lagrangian integral method is developed to solve this set of equations. The computational results confirm the idea put forward by Morch and his co-workers (Morch [1980], [1981], [1982]; Hanson et al. [1981]) who speculated that the collapse of the cloud involved the formation of a shock wave on the surface of the cloud and that inward propagation and geometric focusing of this shock would lead to very large localized pressure pulses. The effects of varying the bubble population density, the cavitation number, and the ratio of the cloud size to the bubble size are examined. The theoretical results are shown to provide a satisfactory explanation for dynamic structures and acoustic signature observed in recently conducted experiments of cloud cavitation at California Institute of Technology (Reisman and Brennen [1996]; Brennen et al. [1996]). It is concluded that the formation and focusing of bubbly shock waves are responsible for the severe noise and damage potential in cloud cavitation.\r\n\r\nThe second problem investigates the nonlinear behavior of a bubbly cavitating flow, both steady and unsteady, through a converging-diverging nozzle. Two different flow regimes are found from steady state solutions: quasi-steady and quasi-unsteady. The former is characterized by the large spatial fluctuations in the downstream of the flow. Bifurcation occurs as the flow transitions from one regime to the other. An analytical expression for the critical bubble size at bifurcation is obtained. Finally, unsteady solutions in a period of consecutive times are presented. These solutions are characterized by the downstream spatial fluctuations coupled with large pressure pulses changing in both magnitude and location with time. The characteristics of these pulses are similar to the shock pulses of Part I and are produced by the local violent collapse of the bubbles in the flow.\r\n" }, { "name": "Zhang, Jin E.", "degree": "PhD", "year": "1996", "title": "I. Run-Up of Ocean Waves on Beaches II. Nonlinear Waves in a Fluid-Filled Elastic Tube", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072008-105605", "creators": [ { "name": { "family": "Zhang", "given": "Jin E." }, "id": "Zhang-Jin-E", "display_name": "Zhang, Jin E." } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." } ], "option_major": [ "eng" ], "doi": "10.7907/TGA4-F552", "abstract": "Part I.
\r\n \r\nThis study considers the three-dimensional run-up of long waves on a horizontally uniform beach of vertically constant or variable slope which is connected to an open ocean of uniform depth. An inviscid linear long-wave theory is first applied to obtain the fundamental solution for a uniform train of sinusoidal waves obliquely incident upon a uniform beach of variable downward slope without wave breaking. The linearly superposable solutions provide a basis for subsequent comparative studies when the nonlinear and dispersive effects are taken into account, both separately and jointly, thus providing a comprehensive prospect of the extents of influences due to these physical effects. These comparative results seem to be new.
\r\n\r\nBy linear theory for waves at nearly grazing incidence, run-up is significant only for the waves in a set of eigenmodes being trapped within the beach at resonance with the exterior ocean waves. Fourier synthesis is employed to analyze a solitary wave and a train of cnoidal waves obliquely incident upon a sloping beach, with the nonlinear and dispersive effects neglected at this stage. Comparison is made between the present theory and the ray theory to ascertain a criterion of validity for the classical ray theory. The wave-induced longshore current is evaluated by finding the Stokes drift of the fluid particles carried by the momentum of the waves obliquely incident upon a sloping beach. Currents of significant velocities are produced by waves at incidence angles about 45\u00b0 and by grazing waves trapped on the beach. Also explored are the effects of the variable downward slope and curvature of a uniform beach on three-dimensional run-up and reflection of long waves.
\r\n\r\nWhen the nonlinear effects are taken into account, the exact governing equations for determining a moving inviscid waterline are introduced here based on the local Lagrangian coordinates. A special numerical scheme has been developed for efficient evaluation of these governing equations. The scheme is shown to have a very high accuracy by comparison with some exact solutions of the shallow water equations. The maximum run-up of a solitary wave predicted by the shallow water equations depends on the initial location of the solitary wave and is not unique in value because the wave becomes increasingly more steepened given longer time to travel in the absence of the dispersive effects; it is in general larger than that predicted by the linear long-wave theory. The farther the initial solitary wave of the KdV form is imposed from the beach, the larger the maximum run-up it will reach.
\r\n\r\nThe dispersive effects are also very important in two-dimensional run-ups in its role of keeping the nonlinear effects balanced at equilibrium, so that the run-ups predicted by the generalized Boussinesq model (Wu 1979) always yield unique values for run-up of a given initial solitary wave, regardless of its initial position. The result for the gB model is slightly larger than the wave run-up predicted by linear long-wave theory. The dispersive effects tend to reduce the wave run-up either for linear system or for nonlinear system.
\r\n\r\nA three-dimensional process of wave run-up upon a vertical wall has also been studied.
\r\n\r\nPart II.
\r\n\r\nThis part is a study of nonlinear waves in a fluid-filled elastic tube, whose wall material satisfies the stress-strain law given by the kinetic theory of rubber. The results of this study have extended the scope of this subject, which has been limited to dealing with unidirectional solitary waves only (Olsen and Shapiro 1967), by establishing an exact theory for bidirectional solitons of arbitrary shape. This class of solitons has several remarkable characteristics. These solitons may have arbitrary shape and arbitrary polarity (upward or downward), and all propagate with the same phase velocity. The last feature of wave velocity renders the interactions impossible between unidirectional waves. However, the present new theory shows that bidirectional waves can have head-on collision through which our exact solution leaves each wave a specific phase shift as a permanent mark of the waves having made the nonlinear encounter. The system is at least tri-Hamiltonian and integrable. An iteration scheme has been developed to integrate the system. The system is distinguished by the fact that any local initial disturbance released from a state of rest will become two solitons traveling to the opposite direction, and shocks do not form if initial value is continuous.
" }, { "name": "Zhou, Dongyan", "degree": "PhD", "year": "1996", "title": "Synthesis of PWM Dc-to-Dc Power Converters", "advisor": "Middlebrook, Robert David; Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-01312005-163350", "creators": [ { "name": { "family": "Zhou", "given": "Dongyan" }, "id": "Zhou-Dongyan", "display_name": "Zhou, Dongyan" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "co-advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JEK6-1P40", "abstract": "A novel systematical synthesis method of PWM dc-to-dc converters is established in this thesis. The new method can generate converters in an efficient way, with clear circuit insight.
\r\n\r\nThe family of PWM dc-to-dc converters is defined to include converters with multiple-input and/or multiple-output; converters with arbitrary switched networks in each switching period; and converters with loops consisting only of capacitors and possibly a voltage source or cut-sets consisting only of inductors and possibly a current source in the individual switched networks.
\r\n\r\nThis method is based on the equivalent ac and dc circuits of a PWM dc-to-dc converter, which consist only of switches in the converter.
\r\n\r\nThe first part of the synthesis procedure is carried out without the participation of reactive elements. For a given number of switches and other requirements, the ac topology and its control sequence can be decided. Basic properties of ac and dc circuits are derived. Moreover, the topological relation between an ac circuit and its associated dc circuits is discovered. Based on the volt-second and ampere-second balance equations of the ac circuit and the matrix representation of dc circuits, a formalized dc model in terms of average switch voltages and currents is first developed. Consequently, the dc conversion ratio and switch implementation can be derived for each pair of ac and dc circuits. The associated dc circuits of the given ac circuit can be formally generated and sorted out according to the required dc conversion ratio, the types of switches, the order of the dc circuit, and other properties.
\r\n\r\nThe insertion procedure for reactive elements is also formalized. The basic procedure generates the converters with the minimum number of inductors and capacitors. A modification of the basic procedure is given to generate converters with continuous input and output currents.
\r\n\r\nDifferent classes of converters are generated by the new synthesis approach. A class of three-switch converters are discovered, each of which has a loop of capacitors and possibly the voltage source. Some of these three-switch converters are of special practical interests. Also, a class of three-switch, and two-output converters are discovered that can provide opposite polarity output voltages without using a transformer.
\r\n\r\nMost importantly, this systematic synthesis method provides an analytic and circuit-oriented approach to develop new converter topologies in order to meet new requirements introduced by ever growing number of applications.
" }, { "name": "Almogy, Gilad", "degree": "PhD", "year": "1995", "title": "Quantum Well Intersubband Transitions: Nonlinear Optics, Refractive Index and Infrared Modulation", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192007-110145", "creators": [ { "name": { "family": "Almogy", "given": "Gilad" }, "id": "Almogy-Gilad", "display_name": "Almogy, Gilad" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3qj9-9777", "abstract": "The nonperturbative theory for the nonlinear optical interaction of quantum well intersubband transitions is developed. The nonlinear optical response of intersubband transitions in quantum wells is rigorously derived and the implications of their resonantly-enhanced nature are examined. Limitations on the use of the standard expansion of the induced polarization in terms of perturbative nonlinear coefficients are presented and it is shown that an alternative nonperturbative formalism is necessary for analyzing intersubband device applications. Upper limits are derived on the magnitudes of several key intersubband transition-induced nonlinear processes. It is shown that for both electrooptic and all-optic modulation, resonantly-enhanced absorption modulation is inherently preferable to phase modulation. A limit on the second-harmonic intensity that may be generated in a given propagation length and modified design criteria for optimizing second-harmonic generation in quantum wells are also obtained from the nonperturbative formalism.
\r\n\r\nThe large and highly dispersive refractive index contribution of intersubband transitions was observed for the first time through the birefringence induced in a GaAs/AlGaAs multi-quantum well stack. It is shown that this index, rather than the absorption induced by intersubband transitions, may become the dominant limitation on frequency conversion efficiencies. Potential applications of this controllable refractive index for a novel phase-matching technique of second-harmonic generation and for improved waveguiding in semiconductors is suggested and analyzed.
\r\n\r\nRemoval of charge integration limitations upon the performance of thermal imagers through the 'ac'-coupling of infrared focal-plane arrays is suggested. This is achieved by the monolithic integration of an intersubband infrared absorption modulator and detector leading to a modulation depth of 45% at a wavelength of 10.6\u00b5m. The uniquely accurate design of the coupled quantum well infrared modulator was based on a self-consistent computer model of the Schrodinger and Poisson equations in quantum wells, taking into account many body effects, band nonparabolicity and flat band boundary conditions. Monolithic integration of the modulator and detector also turns out to be a simple and accurate method of studying the optical properties of quantum wells under bias. This technique led to the first observation of the exchange-interaction's contribution to the charge transfer between coupled quantum wells.
" }, { "name": "Bodenheimer, Robert Edward", "degree": "PhD", "year": "1995", "title": "The Whirling Blade and the Steaming Cauldron", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112007-080755", "creators": [ { "name": { "family": "Bodenheimer", "given": "Robert Edward" }, "id": "Bodenheimer-Robert-Edward", "orcid": "0000-0002-0616-5936", "display_name": "Bodenheimer, Robert Edward" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Packard", "given": "Andrew K." }, "id": "Packard-A-K", "role": "member", "display_name": "Packard, Andrew K." } ], "option_major": [ "eleceng" ], "doi": "10.7907/fmwm-mm97", "abstract": "This dissertation applies recent theoretical developments in control to two practical examples. The first example is control of the primary circuit of a pressurized water nuclear reactor. This is an interesting example because the plant is complex and its dynamics vary greatly over the operating range of interest. The second example is a thrust-vectored ducted fan engine, a nonlinear flight control experiment at Caltech.
\r\n\r\nThe main part of this dissertation is the application of linear parameter-dependent control techniques to the examples. The synthesis technique is based on the solution of linear matrix inequalities (LMIs) and produces a controller which achieves specified performance against the worst-case time variation of measurable parameters entering the plant in a linear fractional manner. Thus the plant can have widely varying dynamics over the operating range, a quality possessed by both examples. The controllers designed with these methods perform extremely well and are compared to H\u221e, gain-scheduled, and nonlinear controllers.
\r\n\r\nAdditionally, an in-depth examination of the model of the ducted fan is performed, including system identification. From this work, we proceed to apply various techniques to examine what they can tell us in the context of a practical example. The primary technique is LMI-based model validation.
\r\n\r\nThe contribution this dissertation makes is to show that parameter-dependent control techniques can be applied with great effectiveness to practical applications. Moreover, the trade-off between modelling and controller performance is examined in some detail. Finally, we demonstrate the applicability of recent model validation techniques in practice, and discuss stabilizability issues.
" }, { "name": "Bruck, Hugh Alan", "degree": "PhD", "year": "1995", "title": "Quasi-static and dynamic constitutive characterization of beryllium bearing bulk metallic glasses", "advisor": "Rosakis, Ares J.; Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112007-130646", "creators": [ { "name": { "family": "Bruck", "given": "Hugh Alan" }, "id": "Bruck-H-A", "display_name": "Bruck, Hugh Alan" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/jd42-3s83", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nMetallic glasses were first discovered by Pol Duwez in 1960 using the fabrication technique of splat quenching. The mechanical behavior of metallic glasses were first characterized in 1969 from tensile tests conducted on thin ribbons. From these tests it was apparent that metallic glasses possessed tensile fracture strengths of approximately [...], which approach theoretical limits. Compressive mechanical data became available in 1974 with the fabrication of small cylindrical rods of [...]. This data indicated that the quasi-static yield behavior of metallic glasses may obey a pressure insensitive von Mises yield criterion. In 1983, Mechanical tests were conducted on [...] in multi-axial stress states which further confirmed the von Mises yield behavior. However, in 1988, mechanical tests performed on [...] indicated that metallic glasses may instead obey a pressure sensitive Mohr-Coulomb criterion.\n\nThere is some ambiguity in interpreting the results of mechanical tests performed on metallic glasses. The data from these tests were obtained by testing specimens whose sizes do not guarantee a well-defined stress state. Furthermore, the mechanical behavior of metallic glasses may depend on composition. In order to properly determine the yield behavior of metallic glasses in multi-axial stress states, it was necessary to fabricate specimens with geometries suitable for generating well-defined stress states.\n\nIn 1993, a new beryllium bearing bulk metallic glass with the nominal composition of [...] was discovered at Caltech. This metallic glass can be cast as cylindrical rods as large as 16 mm in diameter. Specimens could then be fabricated with geometries that conformed to ASTM testing standards. These specimens were then tested in quasi-static compressive, tensile, and torsional stress states at strain rates of [...] to [...] in order to properly characterize the yield behavior of the metallic glass. From these tests it was determined that the beryllium bearing bulk metallic glass obeys a von Mises yield criterion. In addition it was discovered that the ductility of this metallic glass could be altered by adding Boron and varying the quench rate.\n\nFor the first time, the dynamic compressive yield behavior of a metallic glass could be characterized at strain rates of [...] to [...] by using the split Hopkinson pressure bar. High-speed infrared thermal detectors were also used to determine if adiabatic heating occurred during dynamic deformation of the metallic glass. From these tests it appears that the yield stress of the metallic glass is insensitive to strain rate and no adiabatic heating occurs before yielding." }, { "name": "Chen, Jen-Sue", "degree": "PhD", "year": "1995", "title": "Ohmic contacts to beta silicon carbide : electrical and metallurgical characterizations", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172007-133201", "creators": [ { "name": { "family": "Chen", "given": "Jen-Sue" }, "id": "Chen-Jen-Sue", "display_name": "Chen, Jen-Sue" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/yk40-pj23", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThermally induced reactions between a sputter-deposited Re, Pt or Ta film and a single crystalline (001) [beta]-SiC substrate in vacuum at temperatures from 300 to 1200\u00b0C for 30 min or 1 h are investigated by MeV [...] backscattering spectrometry, x-ray diffraction, secondary ion mass spectrometry, transmission and scanning electron microscopies. The contact resistivities of the as-deposited and the annealed Pt, Re, and Ta contacts to [beta]-SiC are characterized using circular transmission line.\r\n\r\nNo reaction between Re and SiC is observed for all annealing conditions. The average grain size of the as-deposited Re film is 220 nm and increases to 280 nm after annealing at 1100\u00b0C for 30 min. A strong {0001}[...] fiber texture is also observed after annealing. The chemical stability of Re thin films on SiC is consistent with an earlier study in the ternary Re-Si-C system which shows that Re and its silicides have tie lines with SiC at 1600\u00b0C. This finding also coincides with our calculations of the free energy of reactions from critically assessed thermodynamic data for rhenium silicides and SiC.\r\n\r\nBackscattering spectrometry shows that Pt reacts with SiC at 500\u00b0C. The product phase identified by x-ray diffraction is Pt3Si. At 600-900\u00b0C, the main reaction product is Pt2Si but the depth distribution of the Pt atoms changes with annealing temperature. Samples annealed at 500-900\u00b0C have a double-layer structure with a silicide surface layer and a carbon-silicide mixed layer below. At 900\u00b0C, the phases in the mixed layer become stratified, with a continuous carbon layer in direct contact with the substrate. When the sample is annealed at 1000\u00b0C, the surface morphology deteriorates with the formation of some dendrite-like hillocks; both Pt2Si and PtSi are detected by x-ray diffraction.\r\n\r\nThe SiC-Pt interaction is resolved at an atomic scale with high-resolution electron microscopy. It is found that the grains of the sputtered Pt film first align themselves preferentially along an orientation of {111}[...]//{001}[...] without reaction between Pt and SiC. A thin amorphous interlayer then forms at 400\u00b0C. At 450\u00b0C, a new crystalline phase nucleates discretely at the Pt-interlayer interface and projects into or across the amorphous interlayer towards the SiC, while the undisturbed amorphous interlayer between the newly-formed crystallites maintains its thickness. These nuclei grow extensively down into the substrate region at 500\u00b0C and the rest of the Pt film is converted to Pt3Si.\r\n\r\nNo significant reaction between Ta and SiC is observed at 800\u00b0C or below. At 900\u00b0C, the main product phases are Ta2C and carbon-stabilized Ta5Si3. A minor amount of unreacted Ta is also present. After annealing at 1000\u00b0C, all the tantalum has reacted; the reaction zone possesses a multilayered structure of [beta]-SiC/TaC/carbon-stabilized Ta5Si3/[alpha]-Ta5Si3/Ta2/C. At 1100\u00b0C, the reacted layer has an interface with the SiC substrate that is still quite flat, but has a rough surface due to the formation of macroscopic voids within the reacted layer. The equilibrium products predicted by the phase diagram are TaC and [TaSi2. This final state is reached upon annealing at 1200\u00b0C for 1 h. At that point, the reacted layer has a laterally very uneven structure and morphology.\r\n\r\nContact resistivities of the as-deposited and annealed Pt, Re, and Ta films on n-type, single-crystalline (001) [beta]-SiC are determined using a circular contact pattern and the method of the circular transmission line. The [beta]-SiC substrates used in the experiment are n-type doped either non-intentionally to a carrier concentration of [...], or by nitrogen implantation and annealing to a concentration of [...]. A resistance-network model is developed to derive an analytic expression for the angular dependence of the voltage distribution along the rings when they have a non-negligible resistance. By applying this model, the resistance between two concentric contacts can be extracted and will yield the correct contact resistivity when one uses the formulae of the circular transmission line model that ignores the finite resistance of the rings.\r\n\r\nOn the non-intentionally doped [beta]-SiC substrates, Pt contacts are non-ohmic regardless of the heat treatment. The as-deposited Ta and Re contacts are ohmic with contact resistivities of [...] and [...], respectively. Upon annealing at 500\u00b0C for 30 min, the resistivity of Ta increases slightly while that of Re decreases slightly. Both Ta and Re contacts become non-ohmic by annealing at 900\u00b0C for 30 min.\r\n\r\nThe as-deposited Ta, Pt, and Re contacts are all ohmic on the nitrogen-implanted [beta]-SiC substrate. The contact resistivity of the as-deposited Ta contact is the lowest and in the order of high [...], stays about the same at 500\u00b0C and degrades to [...] at 1000\u00b0C. The as-deposited Re contact has the highest contact resistivity of [...] but it improves to [...] upon annealing at 900\u00b0C. The contact resistivity of the as-deposited Pt contacts is [...] and increases to [...] at 500\u00b0C. After annealing at 900\u00b0C for 30 min, the Pt contact on the nitrogen-implanted [beta]-SiC is no longer ohmic. The results are compared with the reactions that take place in those systems.\r\n" }, { "name": "Chen, Weinong", "degree": "PhD", "year": "1995", "title": "Dynamic failure behavior of ceramics under multiaxial compression", "advisor": "Ravichandran, Guruswami", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-101839", "creators": [ { "name": { "family": "Chen", "given": "Weinong" }, "id": "Chen-Weinong", "display_name": "Chen, Weinong" } ], "advisors": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "advisor", "display_name": "Ravichandran, Guruswami" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "member", "display_name": "Ahrens, Thomas J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0NNE-JD20", "abstract": "An experimental technique has been developed that is capable of (1) dynamically loading the specimen in multiaxial compression; (2) controlling the stress state in the specimen in the range from uniaxial stress to uniaxial strain; and (3) allowing the recovery of the sample after loaded by a single, well defined pulse for the characterization of the failure mode. In this technique, cylindrical ceramic specimens were loaded in the axial direction using a split Hopkinson pressure bar modified to apply a single loading pulse, and were confined laterally either by shrink fit sleeves, or by eletro-magnetic force.\r\n\r\nQuasi-static and dynamic multiaxial compression experiments have been performed on a machinable glass ceramic, Macor, and a monolithic engineering ceramic, sintered aluminum nitride (A1N). The cylindrical ceramic specimens were confned laterally by shrink fit sleeves: the amount of confining pressure (0-230 MPa) was varied by using different sleeve materials. The quasi-static axial load was applied by a hydraulic driven Material Test System (MTS), whereas the dynamic axial load was provided by a modified split Hopkinson (Kolsky) pressure bar (SHPB). Under both quasi-static and dynamic loading conditions, the experimental results for both materials showed that the failure mode changed from fragmentation by axial splitting under conditions of uniaxial stress (without lateral confinement) to localized deformation on faults under moderate lateral confinement. The fault initiation process was studied experimentally in detail. Based on the experimental results, a compressive brittle failure process was summarized. A transition from brittle to ductile behavior was observed in Macor under high confinement pressure which was achieved using a second sleeve around the inner sleeve. The compressive failure strengths of both materials increased with increasing confinement pressure under both quasi-static and dynamic loading conditions. The highest dynamic compressive strengths of Macor and A1N measured in the experiments were 1.35 GPa and 5.40 GPa, respectively, whereas their quasi-static compressive strength were measured to be 0.43 GPa and 2.5 GPa, respectively.\r\n\r\nBased on the experimental results on A1N together with available data in the literature, a failure/flow criterion was developed for ceramic materials under multiaxial loading. A Mohr-Coulomb criterion and an improved Johnson-Holmquist model were found to fit the experimental data for brittle failure, whereas the materials exhibited pressure insensitive plastic flow at high pressures. Observations made in other types of dynamic experiments (e.g., shock wave loading) were rationalized based on the postulated failure mechanisms and the possibility of plastic flow beyond the Hugoniot elastic limit (HEL). The effect of various material properties on the failure behavior was investigated using the proposed failure criterion. The applicability of the present model to a range of ceramics was also explored and the limitations of the model were outlined.\r\n" }, { "name": "Cortese, John Anthony", "degree": "PhD", "year": "1995", "title": "Stochastic Computation", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02202004-150303", "creators": [ { "name": { "family": "Cortese", "given": "John Anthony" }, "id": "Cortese-John-Anthony", "display_name": "Cortese, John Anthony" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/W627-YA05", "abstract": "This thesis approaches computation from a communication theory perspective. Data is given to a computer, which is asked to arrive at a binary hypothesis decision. The computation task is viewed as a signal drawn from an ensemble, corrupted by noise, and passed to a receiver which is asked to make a binary signal detection decision.
\r\n\r\nTo illustrate the approach, learning in a neural network is studied. An algorithm based on statistical communication techniques is developed which allows the determination of the neural network size, architecture, and system parameters. The computation, as interpreted in the communication framework, is assigned an equivalent channel capacity which measures the effectiveness with which the computing system extracts information in the Shannon sense from the input data. Numerical simulations of a neural network recognizing handwritten digits are used to illustrate key points.
" }, { "name": "Cummings, Eric Bryant", "degree": "PhD", "year": "1995", "title": "Laser-Induced Thermal Ccoustics", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182007-085047", "creators": [ { "name": { "family": "Cummings", "given": "Eric Bryant" }, "id": "Cummings-Eric-Bryant", "display_name": "Cummings, Eric Bryant" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Shepherd", "given": "Joseph E." }, "id": "Shepherd-J-E", "orcid": "0000-0003-3181-9310", "role": "member", "display_name": "Shepherd, Joseph E." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/p7mb-d967", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nLaser-induced thermal acoustics (LITA) is a new technique for remote nonintrusive measurement of thermophysical gas properties. LITA involves forming, via opto-acoustic effects, grating-shaped perturbations of gas properties using intersecting beams from a short-pulse laser. A third beam scatters coherently into a signal beam off the perturbation grating via acousto-optical effects. The evolution of the gas perturbations modulates the scattered signal beam. Accurate values of the sound speed, transport properties, and composition of the gas can be extracted by analyzing the signal beam.\r\n\r\nAn analytical expression for the spectrum, absolute magnitude, and time history of the LITA signal is derived. The optoacoustic effects of thermalization and electrostriction are treated. Finite beam-diameter, beam-duration, and thermalization-rate effects are included in the analysis. The expression accurately models experimental signals over a wide range of gas conditions.\r\n\r\nExperimental tests using LITA have been conducted on pure and [...]-seeded air and helium at pressures ranging from ~0.1 kPa-14 MPa. Carbon dioxide has been explored near its liquid-vapor critical point. Accuracies of 0.1% in sound speed measurements have been achieved in these tests. Accuracies of ~1% have been achieved in measurements of thermal diffusivity, although beam misalignment effects have typically degraded this accuracy by a factor of ~10-20. Using LITA, susceptibility spectra have been taken of approximately a femtogram of [...]. The effects of fluid motion and turbulence have been explored. LITA velocimetry has been demonstrated, in which the Doppler shift of light scattered from a flowing fluid is measured. LITA velocimetry requires no particle seeding, has a coherent signal beam, and can be applied to pulsed flows. LITA has also been applied to measure single-shot [...] or \"Rayleigh scattering\" spectra of a gas using a technique of wavelength-division multiplexing, called multiplex LITA. The LITA apparatus used in these tests costs about one-tenth that of many conventional laser diagnostics. Narrowband LITA measurements of the sound speed and transport properties and multiplex LITA measurements of the spectral properties of gases may be taken in a single laser shot.\r\n" }, { "name": "Deora, Sanjeev K.", "degree": "PhD", "year": "1995", "title": "Channel assignment algorithms in cellular radio networks", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172007-153727", "creators": [ { "name": { "family": "Deora", "given": "Sanjeev K." }, "id": "Deora-S-K", "display_name": "Deora, Sanjeev K." } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Goldsmith", "given": "Andrea Jo" }, "id": "Goldsmith-A-J", "role": "member", "display_name": "Goldsmith, Andrea Jo" }, { "name": { "family": "Blanchard", "given": "John" }, "id": "Blanchard-J", "role": "member", "display_name": "Blanchard, John" }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/1nxh-ak43", "abstract": "In this thesis, we study and compare the performance of several distributed channel assignment algorithms (CAAs) in a cellular system. The CAA which is used to assign a channel to a new call greatly influences the amount of traffic the system can support. We are interested in the design and analysis of algorithms which perform well, but at the same time are relatively easy to implement. In this thesis, we have analyzed the performance of a very simple CAA which we call the Timid Algorithm, in the limiting case of a large number of channels. We have been able to show that, under a plausible mathematical hypothesis, the algorithm is asymptotically optimal, where \"asymptotically\" refers to a system with a large number of channels. This is very surprising as there are algorithms of much higher complexity which provably do not have this property.\n\nThe Timid Algorithm is asymptotically optimal, but it requires a large number of channels for a satisfactory performance. We looked at some algorithms which retain the simplicity of the Timid algorithm but which can be expected to give a good performance even with a smaller number of channels. We called one such algorithm the Modified DCAA. We present some simulation results which show that this algorithm gives a reasonably good performance even when the number of channels is small. One of the ways to increase the capacity of a cellular system is through the use of micro-cells. The Modified DCAA, because of its distributed nature and low complexity, is particularly suitable for such microcellular systems.\n\nWe also present a method for computing the upper bound on the performance of any CAA in a cellular system with adjacent channel constraints. The method, although computationally intensive, may be useful for determining how close an algorithm's performance is to the optimal performance.\n\nFinally, we discuss ways of obtaining the set of \"allowable\" states for a system. We also present some \"measurement-based\" algorithms and compare their performance with \"prediction-based\" algorithms.\n" }, { "name": "Djokovic, Igor", "degree": "PhD", "year": "1995", "title": "Optimization issues in wavelets and filter banks", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172007-152709", "creators": [ { "name": { "family": "Djokovic", "given": "Igor" }, "id": "Djokovic-I", "display_name": "Djokovic, Igor" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" } ], "option_major": [ "eleceng" ], "doi": "10.7907/pyy4-dt15", "abstract": "In the last decade or so, we have witnessed a rapid development of the wavelet and filter bank theory. Wavelets find applications in signal compression, computer vision, geophysics, pattern recognition, numerical analysis, and function theory, just to name a few. Filter banks, on the other hand, offer very efficient implementation of different algorithms in connection with wavelets. The thesis deals with three problems in filter banks and wavelets.\r\n\r\nIn the first part, we show that perfect reconstruction is equivalent to biorthogonality of the filters. Using this, we examine existence issues in nonuniform filter banks. We show that whenever there exists a rational biorthogonal filter bank, then there is a rational orthonormal filter bank as well. We also derive a number of necessary conditions for the existence of perfect reconstruction nonuniform filter banks. We show how the tools developed in the first part can be used for decorrelation of subband signals.\r\n\r\nThe second problem deals with optimality issues in wavelet and filter bank theory. We tune scaling function for the analysis of WSS random processes, so that the energy is concentrated in as few transform coefficients as possible. The corresponding problem in the filter bank theory is that of adapting filter responses to a given (discrete time) WSS random process so as to achieve a better energy compaction.\r\n\r\nFinally, the last part is devoted to developing sampling theory for multiresolution subspaces. More precisely, we extend existing uniform sampling theory to periodically nonuniform sampling. This extension offers one very important advantage over the existing sampling theory. By allowing for periodically nonuniform sampling grid, it is possible to have compactly supported synthesis functions, which was not the case before. Several variations on the basic theme are considered. Also, an application of the developed techniques to efficient computation of inner products in multiresolution subspaces is presented." }, { "name": "Flanagan, Michael J.", "degree": "PhD", "year": "1995", "title": "Reduced-complexity digital sinusoid generators and oversampled data converters", "advisor": "Posner, Edward C.; McEliece, Robert J.; Zimmerman, G. A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10022007-131456", "creators": [ { "name": { "family": "Flanagan", "given": "Michael J." }, "id": "Flanagan-M-J", "display_name": "Flanagan, Michael J." } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." }, { "name": { "family": "Zimmerman", "given": "G. A." }, "id": "Zimmerman-G-A", "role": "advisor", "display_name": "Zimmerman, G. A." } ], "committee": [ { "name": { "family": "Zimmerman", "given": "G. A." }, "id": "Zimmerman-G-A", "role": "chair", "display_name": "Zimmerman, G. A." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "co-chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Satorius", "given": "Edgar H." }, "id": "Satorius-E-H", "role": "member", "display_name": "Satorius, Edgar H." }, { "name": { "family": "Galton", "given": "I." }, "id": "Galton-I", "role": "member", "display_name": "Galton, I." } ], "option_major": [ "eleceng" ], "doi": "10.7907/SP61-8895", "abstract": "This thesis separately addresses two important issues in signal processing: digital sinusoid generators and oversampled data converters. The first part of the thesis addresses noise additive, or dithering, techniques that exponentially reduce the complexity of digital sinusoid generators for a given level of spur performance. With the appropriate dither signals the quantization noise can be rendered nearly white and free of large spurs, or periodic error components, without recourse to large look-up tables. New analysis shows that when the phase dither signal is the sum of M uniform white variates, the phase spurs are at a level of -6(M + 1) dBc per look-up phase bit instead of the usual -6 dBc per phase bit in a non-dithered system. This exponentially reduces the complexity of the digital sinusoid generator for a given spur requirement at the expense of linearly increasing the nearly-white quantization noise.
\r\n\r\nThe second part of the thesis presents two metric-based approaches to the design of over-sampled data converters (ODCs). The first approach leads to an architecture which is derived based on the minimization of a causal, constrained-memory, power-spectral-distortion metric. This architecture is compared to standard ΔΣ modulators and shown to have superior noise performance under some conditions.
\r\n\r\nAnother metric-based approach to the design of ODCs uses a more general distortion metric and incorporates elements of vector quantization, eigensystems and analysis of the discrete prolate spheroidal wave functions. This enables the application of vector quantization theory to oversampled data converters. A vector-quantizer-based ODC architecture called the eigenmodulator is motivated and analyzed. Rate-distortion results are presented for the important case of a band-limited Gaussian input. When both the complexity of the eigenmodulator and the oversampling ratio become large, it is shown that the distribution of the output vectors in an important transform space becomes joint Gaussian. This is shown to be important in light of the centroid condition for an optimal vector quantizer. The implication of this result on the choice of output scaling for the single-bit data converter is addressed.
\r\n" }, { "name": "Fleischer, Kurt W.", "degree": "PhD", "year": "1995", "title": "A multiple-mechanism developmental model for defining self-organizing geometric structures", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10022007-150221", "creators": [ { "name": { "family": "Fleischer", "given": "Kurt W." }, "id": "Fleischer-K-W", "display_name": "Fleischer, Kurt W." } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." }, { "name": { "family": "Prusinkiewicz", "given": "Przemyslaw" }, "id": "Prusinkiewicz-P", "role": "member", "display_name": "Prusinkiewicz, Przemyslaw" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "role": "member", "display_name": "Fraser, Scott E." } ], "option_major": [ "cns" ], "doi": "10.7907/sz7n-ad32", "abstract": "This thesis introduces a model of multicellular development. The model combines elements of the chemical, cell lineage, and mechanical models of morphogenesis pioneered by Turing, Lindenmayer, and Odell, respectively. The internal state of each cell in the model is represented by a time-varying state vector that is updated by a differential equation. The differential equation is formulated as a sum of contributions from different sources, describing gene transcription, kinetics, and cell metabolism. Each term in the differential equation is multiplied by a conditional expression that models regulatory processes specific to the process described by that term.\n\nThe resulting model has a broader range of fundamental mechanisms than other developmental models. Since gene transcription is included, the model can represent the genetic orchestration of a developmental process involving multiple mechanisms.\n\nWe show that a computational implementation of the model represents a wide range of biologically relevant phenomena in two and three dimensions. This is illustrated by a diverse collection of simulation experiments exhibiting phenomena such as lateral inhibition, differentiation, segment formation, size regulation, and regeneration of damaged structures.\n\nWe have explored several application areas with the model:\n\nSynthetic biology. We advocate the use of mathematical modeling and simulation for generating intuitions about complex biological systems, in addition to the usual application of mathematical biology to perform analysis on a simplified model. The breadth of our model makes it useful as a tool for exploring biological questions about pattern formation and morphogenesis. We show that simulated experiments to address a particular question can be done quickly and can generate useful biological intuitions. As an example, we document a simulation experiment exploring inhibition via surface chemicals. This experiment suggests that the final pattern depends strongly on the temporal sequence of events. This intuition was obtained quickly using the simulator as an aid to understanding the general behavior of the developmental system.\n\nArtificial evolution of neural networks. Neural networks can be represented using a developmental model. We investigate the use of artificial evolution to select equations and parameters that cause the model to create desired structures. We compare our approach to other work in evolutionary neural networks, and discuss the difficulties involved.\n\nComputer graphics modeling. We extend the model to allow cells to sense the presence of a 3D surface model, and then use the multicellular simulator to grow cells on the surface. This database amplification technique enables the creation of cellular textures to represent detailed geometry on a surface (e.g., scales, feathers, thorns).\n\nIn the process of writing many developmental programs, we have gained some experience in the construction of self-organizing cellular structures. We identify some critical issues (size regulation and scalability), and suggest biologically-plausible strategies for addressing them.\n" }, { "name": "Halling, Marvin Wilford", "degree": "PhD", "year": "1995", "title": "Investigation of Base-Isolated Structures During Recent Earthquakes and Computer Simulations Utilizing Near-Source Long-Period Ground Motions", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10152007-141910", "creators": [ { "name": { "family": "Halling", "given": "Marvin Wilford" }, "id": "Halling-Marvin-Wilford", "display_name": "Halling, Marvin Wilford" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Wald", "given": "David J." }, "id": "Wald-D-J", "role": "member", "display_name": "Wald, David J." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/HWVH-DM02", "abstract": "Base isolation is a recently applied technology for building structures in the United States. To date, the three base-isolated buildings considered in this study have been subjected to earthquakes of varying magnitudes and epicentral distances. The records obtained from these instrumented buildings demonstrate low levels of excitation and small structural responses. In all cases, the maximum relative displacement of the roof to the foundation is less than 3 cm. However, an increasing quantity of near-source strong-motion records produces large spectral displacements of up to approximately 50-55 cm in the 2 to 2.5 sec period range for 15% damping. This suggests that long-period structures such as base-isolated structures would be vulnerable to these near-source ground motions.
\r\n\r\nThe current study contains two major parts. Part One consists of the identification and analysis of three existing base-isolated buildings in Southern California. The identification and analysis utilize the recorded motions of these structures from past earthquakes. System identification is useful for understanding the extent to which the structures enter the nonlinear realm and how much their properties change.
\r\n\r\nModels are constructed assuming completely elastic three-dimensional superstructures, with idealized bi-linear hysteretic elements for the isolating bearings. The properties used in the bearing models were taken from tests of the actual bearings before installation. The models were then verified by comparing their responses computed using the various recorded foundation ground motions, with the recorded responses of the actual structures. The models were adjusted to minimize the error of several response quantities.
\r\n\r\nPart Two contains computer simulations for the three structural models developed in Part One subjected to large-amplitude near-source ground motions. These structural models were subjected to two classes of ground motions. The first is a sampling of near-source recorded motion from past moderate-to-large earthquakes. The second is a group of synthetic near-source motions generated for a hypothetical M 7.0 earthquake. In some cases, the lateral response of the models exceeds the isolation gap, indicating that the displacement barrier would be impacted.
\r\n\r\nIn order to further study base-isolated buildings when the isolation bearings undergo large displacements, a typical base-isolated building (TBIB) model is used and the computer program 2D-BUMP is developed. This program includes the effects of a fully nonlinear superstructure, nonlinear springs acting as displacement barriers which engage at specified distances, and a tri-linear model for the elastomeric bearings. Using this model, several conclusions are drawn regarding the probable areal extent of damaging near-source ground motions from the M 7.0 event, as well as the behavior of base-isolated structures due to these near-source long-period ground motions.
" }, { "name": "Hattori, Masayuki", "degree": "PhD", "year": "1995", "title": "Subspace Subcodes of Reed-Solomon Codes", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-105811", "creators": [ { "name": { "family": "Hattori", "given": "Masayuki" }, "id": "Hattori-Masayuki", "display_name": "Hattori, Masayuki" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/m50j-xx64", "abstract": "In this paper we introduce a new class of non-linear cyclic error-correcting codes, which we call subspace subcodes of Reed-Solomon (SSRS) codes. An SSRS code is a subset of a parent Reed-Solomon (RS) code consisting of codewords whose components all lie in a fixed v-dimensional vector subspace S of GF(2\u1d50).
\r\n\r\nStarting from a (n, k\u2080, d\u2080) RS code over GF(2\u1d50), with any positive integer 0 \u2264 v \u2264 m, there is an SSRS code of length n and designed minimum distance d\u2080 over the symbol alphabet S, the vector space of binary v-tuples. SSRS codes are constructed using properties of the Galois field GF(2\u1d50). SSRS codes are not linear over GF(2\u1d5b) but are Abelian group codes over S. However, they are linear over GF(2), and the symbol-wise cyclic shift of any codeword is also a codeword.
\r\n\r\nOur first main result is an explicit formula for the dimension of an SSRS code. It is followed by a corollary which gives a simple lower bound, which gives the true value for \"most\" subspaces. We also prove several important duality properties.
\r\n\r\nNext, we give a classification of the v-dimensional subspaces of GF(2\u1d50) into categories, such that two subspaces in the same category always produce isometric SSRS codes. Then, we give an efficient means to find the \"exceptional\" subspaces among the huge number of subspaces. We also present a reasonably simple encoding algorithm that works for systematic shortened linear codes in general.
\r\n\r\nFinally, we present some numerical examples, which show, among other things, that (1) SSRS codes can have a higher dimension than comparable GBCH codes, so that even if GF(2\u1d5b) is a subfield of GF(2\u1d50), it may not be the \"best\" v-dimensional subspace for constructing SSRS codes; and (2) many high-rate SSRS codes have larger dimension than any previously known code with the same values of n, d and q, including algebraic-geometry codes. These examples suggest that high-rate SSRS codes are likely candidates to replace Reed-Solomon codes in high-performance transmission and storage systems.
" }, { "name": "Hofstee, H. Peter", "degree": "PhD", "year": "1995", "title": "Synchronizing processes", "advisor": "Van de Snepscheut, Jan L. A.; Chandy, K. Mani", "url": "https://resolver.caltech.edu/CaltechETD:etd-10112007-083903", "creators": [ { "name": { "family": "Hofstee", "given": "H. Peter" }, "id": "Hofstee-H.-Peter", "display_name": "Hofstee, H. Peter" } ], "advisors": [ { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "advisor", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" } ], "committee": [ { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "chair", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Bagrodia", "given": "Rajive" }, "id": "Bagrodia-R", "role": "member", "display_name": "Bagrodia, Rajive" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/G620-GG65", "abstract": "In this monograph we develop a mathematical theory for a concurrent language based on angelic and demonic nondeterminism. An underlying model is defined with sets of sets of sequences of synchronization actions. A refinement relation is defined for the model, and equivalence classes under this relation are identified with processes. Processes, together with the refinement relation, form a complete distributive lattice.\r\n\r\n\tWe define a language with parallel composition, sequential composition, angelic and demonic nondeterminism, and an operator that connects pairs of synchronization actions into synchronization statements and hides these actions from observation. Also, angelic and demonic iteration are defined. All operators are monotonic with respect to the refinement ordering. Many algebraic properties are proven from these definitions. We study duals of processes and prove that they can be related to the most demonic environment in which a process will not deadlock. We give a simple example to illustrate the use of duals.\r\n\r\n\tWe study classes of programs for which angelic choice can be implemented by probing the environment for its next action. To this end specifications of processes are extended with simple conditions on the environment. We give a more elaborate example to illustrate the use of these conditions and the compositionality of the method.\r\n\r\n\tFinally we briefly introduce an operational model that describes implementable processes only. This model mentions probes explicitly. Such a model may form a basis for a language that is less restrictive than ours, but that will also have less attractive algebraic properties.\r\n" }, { "name": "Huang, Liping", "degree": "PhD", "year": "1995", "title": "Mode-Like Properties and Identification of Nonlinear Vibrating Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12012011-113838877", "creators": [ { "name": { "family": "Huang", "given": "Liping" }, "id": "Huang-Liping", "display_name": "Huang, Liping" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Papadimitriou", "given": "Konstantinos" }, "id": "Papadimitriou-Konstantinos", "role": "member", "display_name": "Papadimitriou, Konstantinos" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/707b-jf67", "abstract": "A study is made of mode-like properties and identification of nonlinear systems and their applications in structural seismic analysis.
\r\n\r\nIn the thesis, mode-like behavior of nonlinear systems is examined. The modal frequencies and mode shapes of nonlinear systems are found to be dependent on the\r\nresponse. Based on approximation, amplitude-dependent mode shape is defined and approximate methods for calculation of modal frequencies and mode shapes (instantaneous and amplitude-dependent) are presented. Based on amplitude-dependent modal relationship, amplitude-dependent models of modal equations which are valid in large range of response\r\nand suitable for unique identification are proposed and the corresponding modal identification procedures are developed. The applicability of the new models and\r\nidentification algorithms is tested through the analysis of an ideal 3DOF nonlinear system.
\r\n\r\nAs applications, the seismic responses of a 47-story building and a 4-story building are investigated using the presented methods. The modal parameters and modal equations\r\nof the structures are identified.
" }, { "name": "Iannelli, John M.", "degree": "PhD", "year": "1995", "title": "Coherence and spectral properties of composite-cavity semiconductor lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012007-104414", "creators": [ { "name": { "family": "Iannelli", "given": "John M." }, "id": "Iannelli-J-M", "display_name": "Iannelli, John M." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/y55j-f079", "abstract": "This thesis addresses many current issues in the theoretical and experimental aspects of coherence and spectral properties of semiconductor lasers. It begins with a brief overview of the theory of fluctuations in semiconductor lasers. This includes a study of relative intensity noise, frequency/phase noise, and frequency chirp. A method of spectral linewidth reduction and stabilization is then proposed and analyzed. This method utilizes an atomic resonance in cesium to which a semiconductor laser can be frequency locked. A Van der Pol analysis as well as a rate equation analysis are carried out and predict reductions in the spectral linewidth, frequency chirp, and enhanced frequency stability. Experimental results confirm several aspects of the theory and also introduce the effects of 1/f noise in semiconductor lasers. Spectral linewidth reductions by a factor of 2000 below the solitary laser linewidth are presented.\n\nInvestigations are then made into the spectral characteristics of multielectrode distributed feedback (DFB) lasers. A novel measurement technique is introduced which utilizes the phase angle between the FM and AM responses for the determination of adiabatic chirp and linewidth enhancement factors. The mode switching properties of these devices are then studied within the context of bistable operation. Bistability in output power and output wavelength is shown and is applied to experiments in stochastic resonance. Using bistable DFB and Fabry-Perot semiconductor lasers, stochastic resonance is demonstrated experimentally in different laser systems as well as in electronic circuits. The effect is analyzed from a rate equation approach as well as a Kramer's escape approach. Results predict a noise suppression at higher even harmonic frequencies which are then experimentally verified.\n" }, { "name": "Jain, Mohit Kumar", "degree": "PhD", "year": "1995", "title": "Processing and mechanical behavior of ultrafine grain materials", "advisor": "Christman, Tom", "url": "https://resolver.caltech.edu/CaltechETD:etd-10112007-090033", "creators": [ { "name": { "family": "Jain", "given": "Mohit Kumar" }, "id": "Jain-M-K", "display_name": "Jain, Mohit Kumar" } ], "advisors": [ { "name": { "family": "Christman", "given": "Tom" }, "id": "Christman-T", "role": "advisor", "display_name": "Christman, Tom" } ], "committee": [ { "name": { "family": "Christman", "given": "Tom" }, "id": "Christman-T", "role": "chair", "display_name": "Christman, Tom" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" } ], "option_major": [ "matsci" ], "doi": "10.7907/8fty-t229", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe mechanical behavior of ultrafine grain Fe-28A1-2Cr and 304 stainless steel was \nexamined by conducting conventional mechanical testing and pre- and post-deformation \nmicrostructural characterization on bulk samples.\n\nShock wave consolidation was used to produce a fully-dense nanophase Fe-28A1-2Cr \n(grain size = 80 nm) intermetallic compound. In tension, the nanophase intermetallic \nfailed in a brittle fashion with failure strength comparable to the coarse grain intermetallic \nof similar composition. However, the nanophase intermetallic yielded at 2.1 GPa during \nquasi-static compressive deformation and deformed to true strains greater than 1.4 without \nwork hardening. The elastic-perfectly plastic behavior of nanophase Fe-28A1-2Cr is \nsignificantly different from that of coarse-grained intermetallic of the same composition, \nwhich yielded at 0.25 GPa and works hardened to 1.5 GPa before failure (at true strain \nof about 0.37). Microstructural examination before and after compressive deformation \nrevealed that a significant portion of the microstructure refined to 10 nm grains surrounded \nby amorphous material. A similar grain refinement process was observed in 80 urn Fe-\n28A1-2Cr produced by ingot metallurgical technique.\n\nA novel thermo-mechanical processing technique was developed for the production of a \nultrafine grain 304 stainless steel (grain size = 200 nm). The key steps to this processing \ntechnique involved (1) formation of ultrafine dislocation cell structure, and (2) the conversion of dislocation cells into grains with medium to high misorientation by initiating \ngrain boundary sliding in the microstructure. The ultrafine grain steel (grain size = 200\nnm) was about six times stronger ([...] = 1700 MPa) than coarse-grained steel of the same \ncomposition. Grain size hardening behavior of 304 stainless steel was also investigated \nover a broad range of grain sizes (200 nm to 200[...]).\n" }, { "name": "Kendrick, Donald William", "degree": "PhD", "year": "1995", "title": "An experimental and numerical investigation into reacting vortex structures associated with unstable combustion", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10122007-131523", "creators": [ { "name": { "family": "Kendrick", "given": "Donald William" }, "id": "Kendrick-D-W", "display_name": "Kendrick, Donald William" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." } ], "option_major": [ "mecheng" ], "doi": "10.7907/9QDG-AP23", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental and numerical investigation into reacting vortex structures shed from a rearward facing step flameholder was performed to gain insight into the fundamental reasons why certain acoustic modes of the laboratory dump combustor were excited for a given set of flow parameters. Cases examined used premixed [...] air mixtures [...], various duct heights (2.54, 5.08 and 7.62 cm) and dump plane speeds (21, 30 and 35 m/s). The above parameters permitted observing instabilities having either one or both of the longitudinal acoustic modes present (188 or 234 Hz) in their respective pressure and velocity spectra.\r\n\r\n\tIgnition of the vortex structures was found to be heavily dependent on geometry (i.e., duct height) and invariant to stoichiometric variations. This fact indicated the dominance of turbulent exchange processes over chemical effects for the pulsating flowfield. The coherent structures which typically convected at the local dump plane speed and exhibited high initial strain rates, were found to exhibit shorter burning times and more intense combustion for decreasing duct heights. Use of high-speed shadowgraph and chemiluminescent (CCD) imagery permitted a complete description of the typically nonuniform, reacting flowfield. Time-resolved vortex and floor temperature measurements as well as time-averaged floor heat flux measurements completed the quantitative description of the vortex structures.\r\n\r\n\tCulick's technique of expanding the acoustic filed into orthogonal modes was employed to confirm mode selection theories and suggest the importance of the shape of the average burner distribution. A nonlinear heat release model was formulated whereby the vortices were characterized as gaussian envelopes convecting at the local dump plane speed. The system of equations formulated was a set of two coupled oscillators with a nonlinear driving term. A final discussion was also undertaken to infer the geometrical implications into the mode selection process (what system acoustic mode was excited).\r\n" }, { "name": "Kewitsch, Anthony S.", "degree": "PhD", "year": "1995", "title": "Part I. Optically induced, ferroelectric domain gratings in photorefractive crystals and applications to nonlinear optics. Part II. Self-focusing and self-trapping of optical beams upon photopolymerization and applications to microfabrication", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-10152007-130350", "creators": [ { "name": { "family": "Kewitsch", "given": "Anthony S." }, "id": "Kewitsch-A-S", "display_name": "Kewitsch, Anthony S." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Cross", "given": "Eric" }, "id": "Cross-E", "role": "member", "display_name": "Cross, Eric" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "member", "display_name": "Grubbs, Robert H." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ngzk-1s10", "abstract": "This thesis explores the application of two distinct nonlinear optical phenomena, the \nphotorefractive effect and photopolymerization, to optically generate microstructures \nwith feature sizes on the order of optical wavelengths. First, we have found that in \ncertain photorefractive crystals, the photogenerated space charge field dynamically aligns \nferroelectric domains. This is demonstrated by the observation of Barkhausen noise \nlinked to the formation of domain gratings. Domain gratings are recorded with spatial \nperiods on the order of optical wavelengths, which we use for quasi-phase matched \nsecond harmonic generation and holographic data storage.\n\nThe second part of this thesis explores the nonlinear optical response accompanying \nphotopolymerization. In some photopolymers, the crosslinking of polymer chains \ninduces a significant increase in the index of refraction in the exposed region. This index \nperturbation acts as a lens which subsequently focuses down the input light wave. We \nobserve self-focused and self-trapped optical beams upon photo-induced crosslinking of a \nliquid monomer. In the case of self-trapping, the inherent diffraction of the optical beam \nis exactly balanced by self-focusing, so the diameter of the beam does not change as it \npropagates through the medium. Most importantly, this waveguiding generates solid \npolymer microstructures in the illuminated region, which can be used to fabricate micro-electromechanical systems and optical interconnects.\n" }, { "name": "Kitching, John E.", "degree": "PhD", "year": "1995", "title": "Quantum noise reduction in semiconductor lasers using dispersive optical feedback", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-10162007-131138", "creators": [ { "name": { "family": "Kitching", "given": "John E." }, "id": "Kitching-J-E", "display_name": "Kitching, John E." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ANGH-BY42", "abstract": "This thesis describes the phase and amplitude noise properties of semiconductor lasers subjected to weak, dispersive optical feedback. In the first half, experiments demonstrating reductions in the laser frequency noise power spectrum and spectral linewidth by several orders of magnitude are presented. Weak optical feedback is applied to the laser by an external cavity containing an atomic vapor. The presence of the vapor adds to the dispersion of the cavity and simultaneously locks the laser to a fixed frequency reference. The role of 1/f frequency noise in limiting the effectiveness of this linewidth reduction technique is investigated and 1/f noise is found to be the dominant contribution to the linewidth under strong optical feedback conditions.\r\n\r\nAn electronic feedback scheme utilizing FM sideband locking is then implemented alongside the optical feedback, and an additional reduction in the low frequency 1/f frequency noise power spectrum by over two orders of magnitude is obtained. With both systems operating simultaneously, the spectral linewidth is narrowed from its free-running value of about 20 MHz to 1.4 kHz. Excellent absolute frequency stability is also achieved.\r\n\r\nIn the second half, the effects of optical feedback on the quantum mechanical amplitude noise properties of the laser are examined. A fully quantum mechanical theory of amplitude and phase noise for a semiconductor laser with weak optical feedback is developed, and the nature and limits of the noise reduction using this technique are established. Particular attention is given to the feedback-induced enhancement of the amplitude squeezing which can be obtained in a pump-suppressed semiconductor laser: an improvement in the squeezing by 3 dB is predicted under moderate pumping. Somewhat larger noise reductions are expected when the laser is operating closer to threshold. Measurements performed on a laser biased close to threshold are then described and a reduction in the low frequency amplitude noise power spectrum by 7 dB is obtained.\r\n\r\nAn experimental investigation of the effects of optical feedback on the amplitude squeezing in a semiconductor laser is then discussed. The low frequency squeezing in a room temperature device is increased from 3% below the standard quantum limit (SQL) under free-running conditions to 19% below the SQL with optimal feedback. The experimental results are found to agree poorly with the single-mode model and a multi-mode model including the effects of asymmetrical cross-mode non-linear gain is developed to explain the discrepancy. Finally, further experimental investigation into the generation of amplitude squeezed light is presented using a commercial laser with no intentional external modifications. Squeezing as large as 29% below the SQL is measured using a balanced homodyne detector with the laser operating near room temperature, corresponding to 41% below the SQL at the output facet of the laser.\r\n" }, { "name": "Laidlaw, David H.", "degree": "PhD", "year": "1995", "title": "Geometric model extraction from magnetic resonance volume data", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10152007-132141", "creators": [ { "name": { "family": "Laidlaw", "given": "David H." }, "id": "Laidlaw-D-H", "display_name": "Laidlaw, David H." } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/1spw-fx17", "abstract": "This thesis presents a computational framework and new algorithms for creating geometric models and images of physical objects. Our framework combines magnetic resonance imaging (MRI) research with image processing and volume visualization. One focus is feedback of requirements from later stages of the framework to earlier ones.\n\nWithin the framework we measure physical objects yielding vector-valued MRI volume datasets. We process these datasets to identify different materials, and from the classified data we create images and geometric models. New algorithms developed within the framework include a goal-based technique for choosing MRI collection protocols and parameters and a family of Bayesian tissue-classification methods.\n\nThe goal-based data-collection technique chooses MRI protocols and parameters subject to specific goals for the collected data. Our goals are to make identification of different tissues possible with data collected in the shortest possible time. Our method compares results across different collection protocols, and is fast enough to use for steering the data-collection process.\n\nOur new tissue-classification methods operate on small regions within a volume dataset, not directly on the sample points. We term these regions voxels and assume that each can contain a mixture of materials. The results of the classification step are tailored to make extraction of surface boundaries between solid object parts more accurate.\n\nAnother new algorithm directly renders deformed volume data produced, for example, by simulating the movement of a flexible body. The computational framework for building geometric models allows computer graphics users to more easily create models with internal structure and with a high level of detail. Applications exist in a variety of fields including computer graphics modeling, biological modeling, anatomical studies, medical diagnosis, CAD/CAM, robotics, and computer animation. We demonstrate the utility of the computational framework with a set of computer graphics images and models created from data.\n" }, { "name": "Lee, Tak Kwan", "degree": "PhD", "year": "1995", "title": "A General Approach to Performance Analysis and Optimization of Asynchronous Circuits", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172007-090528", "creators": [ { "name": { "family": "Lee", "given": "Tak Kwan" }, "id": "Lee-Tak-Kwan", "display_name": "Lee, Tak Kwan" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Burns", "given": "Steven" }, "id": "Burns-S", "role": "member", "display_name": "Burns, Steven" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/ehzs-y537", "abstract": "A systematic approach for evaluating and optimizing the performance of asynchronous VLSI circuits is presented. Index-priority simulation is introduced to efficiently find minimal cycles in the state graph of a given circuit. These minimal cycles are used to determine the causality relationships between all signal transitions in the circuit. Once these relationships are known, the circuit is then modeled as an extended event-rule system, which can be used to describe many circuits, including ones that are inherently disjunctive. An accurate indication of the performance of the circuit is obtained by analytically computing the period of the corresponding extended event-rule system.\r\n" }, { "name": "Leifer, Stephanie D.", "degree": "PhD", "year": "1995", "title": "Characterization of fullerenes for electrostatic propulsion applications", "advisor": "Goodwin, David G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10152007-152404", "creators": [ { "name": { "family": "Leifer", "given": "Stephanie D." }, "id": "Leifer-S-D", "display_name": "Leifer, Stephanie D." } ], "advisors": [ { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "advisor", "display_name": "Goodwin, David G." } ], "committee": [ { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2GRP-X396", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n[...], also known as Buckminsterfullerene, possesses a remarkable resilience, high mass, and low ionization potential which indicate that it could make an excellent ion engine propellant. The development of an efficient, reliable [...] ion thruster for space flight requires a knowledge of many of the properties of this new molecule. The research described here focusses on the determination of some of these properties and their effects on the behavior of [...] in a plasma environment. Investigations of fullerene thermal stability, polarizability, electron-impact ionization and fragmentation phenomena, vibrational spectra, and plasma discharges are reported.\r\n\r\nThe electron-impact ionization and fragmentation experiments were conducted using a time-of-flight mass spectrometer. Ionization efficiency curves for the production of both [...] and [...] ions were obtained, and appearance potentials of [...] eV for [...] and [...]eV for [...] and [...], respectively were identifed. Fullerene cracking patterns showed only even-numbered fragments, and only at electron energies above 70 eV. Multiply charged fullerene ions through [...] were observed, revealing the remarkable resistance of [...] to coulomb explosion.\r\n\r\nExperiments to determine the polarizability of [...] using a Mach-Zehnder interferometer and the Clausius-Mossotti relation were performed. The data yielded a polarizability value near [...].\r\n\r\nAlthough previous experiments performed by other researchers with filament cathode discharge chambers successfully demonstrated the production of [...] plasma at a minimum discharge voltage of 22 V, difficulty with severe erosion of the tungsten filament cathode was encountered. Also, decomposition of the fullerenes at temperatures above 1073 K was observed.\r\n\r\nIn light of these observations, the thermal stability of a fullerene mix was examined. Decay constants were obtained and used to find an Arrhenius plot for the thermal decomposition. The Arrhenius activation energy was found to be [...] kJ/mol. The disintegration of [...] occurs at significantly lower temperatures than those predicted by molecular dynamics simulations. A mechanism for fullerene disintegration different than [...] elimination, possibly involving ring-rearrangement in the fullerene cage, may be responsible.\r\n\r\nBecause the determination of the purity of fullerene samples is vital when investigating their degradation at elevated temperatures, a study of fullerene contaminants and adsorbates using Fourier Transform Infrared (FTIR) spectroscopy was conducted. For solid fullerene samples, Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy was employed. Features in the 2350, 2330, and 1540 [...] region of the spectrum were found to be intrinisic to [...] and did not result from CO2 or O2 contamination. By increasing the CO2 content of solid [...], new features could be observed at 2377, 2330 and 2316 [...]. The peak observed at 1539 [...] in the solid vanished when fullerenes were placed in solution, but reappeared when the sample was dried under N2. The strength of this peak may be due to a Fermi resonance or crystal field effect, both of which could be destroyed by solvent interactions in solution.\r\n\r\nTo avoid the presence of high temperature metal surfaces, a RF discharge chamber was constructed to maintain a fullerene plasma inductively, eliminating the presence of hot electrode surfaces. A xenon plasma was successfully generated in the thruster. The maximum extractable beam current was approximately 45 mA. Ion production cost for a pure xenon plasma was 1400 eV/ion. When [...] vapor was added to the xenon plasma, the discharge quenched when the ratio of [...] molecules to xenon atoms exceeded 1:16. A pure fullerene RF discharge could not be initiated.\r\n\r\nThe cause of this phenomenon can be found in the electron attachment cross section of [...] this cross section is very large for electron energies up to 14 eV. It would be necessary to maintain an electron temperature of 10 eV or greater for positive fullerene ion production rates to exceed that of negative ion production rates.\r\n\r\nIn summary, this research has been an investigation of some fundamental properties of [...] relevant to fullerene ion thruster development. It was found that although fragmentation by electron impact of [...] does not pose a significant problem, the thermal stability of fullerenes is not as great as had been anticipated. As a result, use of conventional hollow cathode configurations in fullerene ion thrusters is precluded. A RF fullerene ion thruster configuration was pursued instead, but proved difficult to operate because electron attachment cross sections for [...] remain large up to 14 eV electron energy. Therefore, the use of other ionization mechanisms may prove more successful for fullerene ion thruster development, and should be pursued in future work.\r\n" }, { "name": "Leino, K. Rustan M.", "degree": "PhD", "year": "1995", "title": "Toward reliable modular programs", "advisor": "Van de Snepscheut, Jan L. A.; Chandy, K. Mani; Nelson, Greg", "url": "https://resolver.caltech.edu/CaltechETD:etd-10162007-111256", "creators": [ { "name": { "family": "Leino", "given": "K. Rustan M." }, "id": "Leino-K-M", "display_name": "Leino, K. Rustan M." } ], "advisors": [ { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "advisor", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "advisor", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Nelson", "given": "Greg" }, "id": "Nelson-G", "role": "advisor", "display_name": "Nelson, Greg" } ], "committee": [ { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "chair", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Sanders", "given": "Beverly" }, "id": "Sanders-B", "role": "member", "display_name": "Sanders, Beverly" }, { "name": { "family": "Nelson", "given": "Greg" }, "id": "Nelson-G", "role": "member", "display_name": "Nelson, Greg" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Wilson", "given": "Richard M." }, "id": "Wilson-R-M", "role": "member", "display_name": "Wilson, Richard M." } ], "option_major": [ "compsci" ], "doi": "10.7907/ynt2-nn65", "abstract": "Software is being applied in an ever-increasing number of areas. Computer programs and systems are becoming more complex and consisting of more delicately interconnected components. Errors surfacing in programs are still a conspicuous and costly problem. It's about time we employ some techniques that guide us toward higher reliability of practical programs. The goal of this thesis is just that.\n\nThis thesis presents a theory for verifying programs based on Dijkstra's weakest-precondition calculus. A variety of program paradigms used in practice, such as exceptions, procedures, object orientation, and modularity, are dealt with.\n\nThe thesis sheds new light on the theory behind programs with exceptions. It develops an elegant algebra, and shows it to be the foundation on which the semantics of exceptions rests. It develops a trace semantics for programs with exceptions, from which the weakest-precondition semantics is derived. It also proves a theorem on programming methodology relating to exceptions, and applies this theorem in the novel derivation of a simple program.\n\nThe thesis presents a simple model for object-oriented data types, in which concerns have been separated, resulting in the simplicity of the model.\n\nTo deal with large programs, this thesis takes a practical look at modularity and abstraction. It reveals a problem that arises in writing specifications for modular programs where previous techniques fail. The thesis introduces a new specification construct that solves that problem, and gives a formal proof of soundness for modular verification using that construct. The model is a generalization of Hoare's classical data refinement. However, there are more problems to be solved. The thesis reports on some of these problems and suggests some future directions toward more reliable modular programs.\n" }, { "name": "Levy, Harold", "degree": "PhD", "year": "1995", "title": "Application and integration of quantum-effect devices for cellular VLSI", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10152007-133745", "creators": [ { "name": { "family": "Levy", "given": "Harold" }, "id": "Levy-H", "display_name": "Levy, Harold" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/qtd4-5r46", "abstract": "Cellular VLSI is that subclass of electronic systems for which small perturbations in a repeated cell design can dramatically influence the cost and performance of the entire system. This thesis presents examples of how the room-temperature quantum effects of tunneling and resonance may be used to condense the functionality of many conventional VLSI devices into a smaller and more efficient subunit, thus yielding tremendous benefits for the system as a whole. In particular, two and three-terminal applications of a complimentary pair of quantum-effect devices, the resonant-tunneling diode and the tunneling-switch diode, are presented.\r\n\r\nThe first example is an image-segmentation network for machine vision, implemented by using resonant-tunneling diodes in one and two-dimensional networks to extract boundaries between regions of constant spatial texture. In this case a single quantum-effect device may replace up to thirty-three CMOS transistors per pixel.\r\n\r\nThe second example is an artificial neural-network processor based on multistate resistors for synaptic conductances. These programmable resistors were produced by combining a vertically-integrated stack of resonant-tunneling diodes with a resistive load and a single MOSFET driven in its ohmic region. This macrostructure has the potential to provide synaptic changes on the picosecond time scale at length scales well below one micron.\r\n\r\nThe third example is a current-mode transistorless memory array based on a two-dimensional network of cells containing only a single tunneling-switch diode and a resistive load. The resulting system has the potential for reaching more than an order-of-magnitude more cell density than state-of-the-art DRAM arrays, while operating at state-of-the-art SRAM speeds and reasonable power consumption." }, { "name": "Lewis, Andrew David", "degree": "PhD", "year": "1995", "title": "Aspects of geometric mechanics and control of mechanical systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07132006-143133", "creators": [ { "name": { "family": "Lewis", "given": "Andrew David" }, "id": "Lewis-A-D", "display_name": "Lewis, Andrew David" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "member", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/CHWF-M421", "abstract": "Many interesting control systems are mechanical control systems. In spite of this, there has not been much effort to develop methods which use the special structure of mechanical systems to obtain analysis tools which are suitable for these systems. In this dissertation we take the first steps towards a methodical treatment of mechanical control systems.\n\nFirst we develop a framework for analysis of certain classes of mechanical control systems. In the Lagrangian formulation we study \"simple mechanical control systems\" whose Lagrangian is \"kinetic energy minus potential energy.\" We propose a new and useful definition of controllability for these systems and obtain a computable set of conditions for this new version of controllability. We also obtain decompositions of simple mechanical systems in the case when they are not controllable. In the Hamiltonian formulation we study systems whose control vector fields are Hamiltonian. We obtain decompositions which describe the controllable and uncontrollable dynamics. In each case, the dynamics are shown to be Hamiltonian in a suitably general sense.\n\nNext we develop intrinsic descriptions of Lagrangian and Hamiltonian mechanics in the presence of external inputs. This development is a first step towards a control theory for general Lagrangian and Hamiltonian control systems. Systems with constraints are also studied. We first give a thorough overview of variational methods including a comparison of the \"nonholonomic\" and \"vakonomic\" methods. We also give a generalised definition for a constraint and, with this more general definition, we are able to give some preliminary controllability results for constrained systems.\n" }, { "name": "Liu, Jianqiang", "degree": "PhD", "year": "1995", "title": "Integrated micro devices for small scale gaseous flow study", "advisor": "Tai, Yu-Chong", "url": "https://resolver.caltech.edu/CaltechETD:etd-10162007-133943", "creators": [ { "name": { "family": "Liu", "given": "Jianqiang" }, "id": "Liu-Jianqiang", "display_name": "Liu, Jianqiang" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/sra1-0d58", "abstract": "Microfluidics has been an active research field for several years. Numerous micro devices such as pumps, valves, flow sensors and integrated systems for chemical analysis and medical applications have been developed. However, experimental studies of fluid flow in those micro devices are rare to find. As a result, design and analysis of microfluidic devices are mostly based upon continuous flow theory which is subjected to serious suspection as dimensions of the device become smaller and smaller. Several experimental studies have actually shown their results can not be explained with continuous flow model.\r\n\r\nSo far, almost all the experimental studies of microflow are limited to the two-point pressure (inlet and outlet) and flow rate measurements using either conventional capillaries or micromachined channels. In order to measure the microflow with more details, several integrated microflow systems are presented in the thesis. These systems include microchannels (with either uniform or non-uniform cross-sections) and pressure sensors (which are distributed along the channels). Using the integrated microflow systems, some preliminary gas flow experiments have been conducted. For the first time, the gaseous pressure distribution inside microchannels are measured experimentally. The pressure distribution inside a microchannel with uniform cross-sectional area is found to be nonlinear. The experimental results can be explained with an isothermal viscous flow model with slip-flow boundary conditions. Furthermore, it is found that a channel with non-uniform cross-sections can cause a non-trivial pressure change.\r\n\r\nDuring the developments of the integrated microflow systems, several related problems has been studied and solved, for example, a universal model has been found which can be used to simulate PSG or oxide sacrificial layer etching process in HF based solutions, a surface micromachined pressure sensor has been designed and modeled. Many technical difficulties such as, thin film stress, etching and sealing of the microchannels and chambers, process integration for microchannels and pressure sensors, etc., have been overcome. All the details related to the design and fabrication have been discussed in the thesis.\r\n" }, { "name": "Liu, Yixin", "degree": "PhD", "year": "1995", "title": "Quantum tunneling, field induced injecting contact, and excitons", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10232007-143854", "creators": [ { "name": { "family": "Liu", "given": "Yixin" }, "id": "Liu-Yixin", "display_name": "Liu, Yixin" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/JKFM-1G06", "abstract": "This thesis consists of three parts: Quantum tunneling simulation, Schottky barrier induced injecting contact on wide band gap II-VI materials, and excitons in semiconductor heterostructures.
\r\n\r\nPart I (chapter 2, 3) deals with quantum transport and electronic band structure in semiconductor heterostructures. In chapter 2, we present a new method for quantum transport calculations in tunnel structures employing multiband k.p theory. This method circumvents the numerical instability problems that arise in the standard transfer-matrix method. In addition to being numerically stable, efficient, and easy to implement, this method can also be easily generalized to include the magnetic field and strain effects. The development of this technique mainly consists of two parts, the discretization of effective-mass Schrodinger's equation using finite-difference method, and the formulation of boundary conditions. The treatment of boundary condition in quantum transport is similar to the Multiband Quantum Transmitting Boundary Method (MQTBM) for use with multiband tight-binding models. The calculations of transmission coefficients reduce to a set of linear equations, which can be solved very easily. With appropriate formulation of boundary conditions, this technique can be readily extended to the calculations of electronic band structures in quantum confinement and superlattice structures. We have applied this new technique to magnetotunneling in interband tunnel structures in chapter 3, and studied two prototypical device structures: Resonant Interband Tunneling (RIT) devices and Barrierless Resonant Interband Tunneling (BRIT) devices. Effects of transverse magnetic field on the band structures, transmission spectrum, and I - V characteristics are investigated. Evidence of heavy-hole resonance contribution can be identified in the change of I - V characteristics under applied magnetic field. The technique has also been illustrated for hole tunneling in p-type GaAs/AlAs double barrier tunnel structures, and calculations of electronic band structures in lattice-matched InAs/GaSb superlattices, and strained InAs/Ga1-xInxSb superlattices.
\r\n\r\nPart II describes a novel approach to achieve ohmic injecting contact on wide bandgap II-VI semiconductors. The problem of making good ohmic contact to wide bandgap II-VI materials has been a major challenge in the effort of making visible light emitting diodes. The method we propose consists of forming the device structure in an electric field at elevated temperatures in the Schottky barrier region, to spatially separate the ionized dopants from the compensating centers. In this way, the ratio of dopants to compensating centers can be greatly increased at the semiconductor surface. Upon cooling, the dopant concentrations are frozen to retain a large net concentration of dopants in a thin surface layer, resulting in a depletion layer that is sufficiently thin to allow tunneling injection. Calculations of band profiles, distributions of dopant concentrations, and current-voltage characteristics were performed. We have selected the case of Al doped ZnTe in our study, in which two Al donors complex with a doubly negatively ionized Zn vacancy to produce total compensation. The results show that the bulk doping concentration and the total band bending during the forming process are the crucial factors for achieving injecting contacts. For Schottky barrier heights above 1 eV, doping concentrations as high as 1020cm-3 are needed.
\r\n\r\nIn part III, we studied excitons in semiconductor heterostructures, consisting of two subjects: excitons in II-VI heterostructures, and exciton coherent transfer process in quantum structures. Calculations of exciton binding energies and oscillator strengths are performed in both Type-I strained CdTe/ZnTe superlattices with very small valence-band offset and Type-II strained ZnTe/ZnSe superlattices. A special variational approach was employed to take into account the effects of unusual band alignment, strain, and image charges at the heterojunction interface. It is found that the large enhancements of exciton binding energy and oscillator strength in the CdTe/ZnTe system are similar to what one finds in systems with a much larger valence band offset. For small CdTe layer thickness, however, the confinement of holes in the CdTe layer is weak, resulting in a lowering of the exciton binding energy. The oscillator strength in CdTe/ZnTe superlattice system shows the expected enhancement over the oscillator strengths in the bulk.
\r\n\r\nFor the ZnTe/ZnSe system, the Type-II character of the heterojunction results in the confinement of the electrons and holes in different layers. It is found that strong confinement of electrons and holes by the large band offsets can give rise to a fairly large exciton binding energy for thin heterojunction layers. Also, the mismatch in dielectric constants induces an image charge at the interface, which modifies significantly the exciton Hamiltonian in an asymmetric superlattice structure and plays an important role in determining the degree of localization of the electron and hole at the interface.
\r\n\r\nWe have investigated exciton coherent transfer in semiconductor quantum structures. In systems where the typical dimensions of the semiconductor quantum structures and the spacings between them are significantly smaller than the photon wavelength, the resonant transfer of excitons between two identical quantum structures is accomplished through the interaction of near field dipole-dipole transitions (exchange of virtual photons). The transfer matrix elements are calculated for three different geometries: quantum wells, quantum wires and quantum dots, respectively. The results show that the exciton transfer matrix element is proportional to exciton oscillator strength, and depends on exciton polarization. The transfer matrix element between quantum wells depends on the exciton wave vector in the plane of the wells, k\u2225, and vanishes when k\u2225 = 0. For quantum wire and quantum dot structures, the transfer matrix elements between two units separated by R vary as R-2 and R-3, respectively. For quantum structures with typical characteristic size of 50 \u00c5 with separation about 100 \u00c5, the transfer matrix element is on the order of 10-3 meV. It corresponds to a resonant transfer time of 1 ns, comparable with the exciton lifetime. However, it is significantly smaller than the inhomogeneous broadening due to phonons and structural imperfection in most synthesized semiconductor quantum structures achievable today, which is typically on the order of a few meV, making the realization of experimental observation difficult. The study is to explore new ideas and potential technological applications based on excitonic devices.
" }, { "name": "Liu, Zhenhuan", "degree": "PhD", "year": "1995", "title": "Nuclei population dynamics and cavitation", "advisor": "Brennen, Christopher E.; Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10222007-152116", "creators": [ { "name": { "family": "Liu", "given": "Zhenhuan" }, "id": "Liu-Zhenhuan", "display_name": "Liu, Zhenhuan" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "co-advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/eq2r-9z75", "abstract": "The effect of the nuclei population in water on cavitation has not been investigated thoroughly due to the difficulties of measuring the microbubbles in water. In this thesis, a Phase Doppler Anemometer (PDA) was calibrated by a holographic method and used to measure the micro-bubble distribution in water. Substantial agreement was achieved between the PDA and the holographic method. After the calibration, the PDA was used to study the nuclei population dynamics in two water tunnels. It was also employed in a study of cavitation on an axisymmetric Schiebe body in which the cavitation on the headform and the upstream nuclei population were simultaneously observed.\r\n\r\nSubstantial changes in the nuclei number density distributions were found in these two water tunnels. The nuclei population in each water tunnel can also vary significantly, sometimes by as much as an order of magnitude. The nuclei population dynamics are complicated and are affected by the tunnel design, the tunnel operating condition and the air content. The cavitation event rate on the Schiebe headform is mainly determined by the cavitation number. It increases dramatically as the cavitation number is decreased. It also varies with the magnitude and the shape of the nuclei number distribution. As the upstream nuclei population increases, the cavitation event rate increases. During the experiments, cavitation acoustic emissions were also measured and analyzed.\r\n\r\nAn analytical model based on the spherical bubble assumption and the Rayleigh-Plesset theory is developed to relate the free stream nuclei population to the cavitation event rate and the acoustic noise on an axisymmetric body. Complications, such as the effect of the boundary layer flow rate, of the bubble screening, of the bubble/bubble interactions and of the observable bubble size are examined and included in the model. The predicted cavitation event rate and acoustic impulse are compared with the experimental observations. It is shown that the predicted event rates agree with the observations when the population is small, but that increasing discrepancies occur at lower cavitation numbers when the bubble density becomes larger. The predicted noise qualitatively agrees with the observations, but is generally larger than the observations, mainly due to the fact that the spherical bubble assumption usually departs from the observed bubble shape." }, { "name": "Lough, Michael F.", "degree": "PhD", "year": "1995", "title": "The motion of thin-cored vortex filaments : the equations of motion and their solution for some special cases", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172007-093152", "creators": [ { "name": { "family": "Lough", "given": "Michael F." }, "id": "Lough-M-F", "display_name": "Lough, Michael F." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/gbak-q488", "abstract": "This thesis looks at the motion of vortex filaments, which are regions in a fluid flow where the vorticity field, equal to the curl of the velocity field, is negligible outside a cylindrical type tube -- the filament. The vortex filament is said to be thin-cored if the radius of the tube is much smaller than any axial length scale along the filament. This thin core assumption allows the motion of the filament to be described by the motion of the centerline of the tube, when it is coupled to the internal core dynamics via an asymptotic matching procedure. Our studies of the motion and dynamics of such structures can be grouped into three topics: (1) analyses of equations of motion for thin-cored vortex filaments, (2) an analysis of the linear stability of a vortex ring moving along the axis of a pipe and (3) the construction of finite amplitude wave solutions for the shape of the centerline of planar vortex filament.\n\nOur main thrust in the first topic is to show that the \"new\" equations derived by Klein and Majda (1991) are merely a reformulation of some of the more well known equations for vortex filament motion; in particular we show that their equations can be obtained by a linearization of the well known cut-off equation. The cut-off equation has been used by a number of authors (e.g., Crow (1970), Widnall and Sullivan (1973), etc.) to analyse problems in vortex motion, and a systematic justification for the equation was provided by Moore and Saffman (1972), who showed the equation was asymptotically correct.\n\nWith regard to the second topic, questions of stability naturally arise when one considers coherent structures, such as vortex rings. The stability of a vortex ring in an unbounded fluid was first examined by Thomson (1883) who found that the ring was stable to infinitesimal perturbations (the vortex ring being a model for the so-called indestructible atom). Widnall and Sullivan (1973) reconsidered the stability problem, but retained terms of higher order in the small parameter (i.e., the ratio of core radius to ring radius). Their results indicated a spurious instability where theonly unstable perturbations were those with wavelengths that were comparable with the core radius (a situation for which the cut-off equation is inapplicable). For the case where the ring moves inside a cylindrical pipe, along its axis, only the effect of the wall on the speed of the ring had been computed to date (Raja Gopal (1963) and Brasseur (1979)). From the theoretical point of view, the effect of the wall on the stability of the ring has, until now, been unknown. We show that the wall induces an instability on the vortex ring characterized by a tendancy for the ring to tilt out of its original plane.\n\nThe so-called local induction equation, for vortex filament motion, corresponds to the zero core radius limit of the cut-off equation. Hasimoto (1972) showed that there was a direct relationship between the local induction equation and the cubic Schrodinger equation, a completely integrable equation. He also computed the corresponding soliton solution of the equation. Kida (1981) computed a general solution of the equation having periodic shape parameters. Both of these solutions are finite amplitude wave solutions for vortex filaments whose motion is governed by the local induction equation. Unfortunately, the local induction equation is known to admit some solutions that are unphysical, a fact which lends credence to the belief that the general solutions are also unphysical. Accordingly, it is important to see whether equations containing more physics also admit finite amplitude wave solutions. Kelvin (1880) obtained a solution of the linearized problem for periodic waves of infinitesimal amplitude that lay in a rotating plane. (In fact, Kelvin's solutions described infinitesimal filament waves having a general three-dimensional structure.) We numerically compute such plane wave solutions to the full nonlinear equations and continue the solution to finite amplitude.\n" }, { "name": "Lu, Wei-Min", "degree": "PhD", "year": "1995", "title": "Control of Uncertain Systems: State-Space Characterizations", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-03022006-131646", "creators": [ { "name": { "family": "Lu", "given": "Wei-Min" }, "id": "Lu-Wei-Min", "display_name": "Lu, Wei-Min" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "orcid": "0000-0001-6287-1133", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "orcid": "0000-0002-0780-0911", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "eleceng" ], "doi": "10.7907/dnxg-nz58", "abstract": "A central issue in control system design has been to deal with uncertainty and nonlinearity in the systems. In this dissertation, an integrated treatment for both uncertainty and nonlinearity is proposed. This dissertation consists of two relatively independent parts. The first part deals with uncertain linear systems, while the second part treats uncertain nonlinear systems.
\r\n\r\nIn the first part, the problem of control synthesis of uncertain linear systems is considered. A linear fractional transformation (LFT) framework is proposed for robust control design of uncertain linear control systems with structured uncertainty. Linear parameter-varying systems whose coefficients depend on some time-invariant unknown parameters are treated in a general algebraic framework; both the stabilization and the H\u221e-control problems are considered. For uncertain linear systems under structured perturbations, robustness synthesis problems are characterized in terms of linear matrix inequalities (LMIs) in the LFT framework. A generalized PBH test is also used to characterize the robustness synthesis problems. Moreover, a separation principle for the control synthesis of uncertain linear systems is revealed. The machinery also streamlines a number of results concerning the analysis and synthesis of multidimensional systems.
\r\n\r\nIn the second part, the problem of control synthesis for nonlinear systems is addressed; stabilization, L1-control, H\u221e-control, robustness analysis, and robustness synthesis problems for nonlinear systems are examined in detail. In particular, locally and globally stabilizing controller parameterizations for nonlinear systems are derived; the formulae generalize the celebrated Youla-parameterization for linear systems. Both nonlinear L1-control and nonlinear H\u221e-control are also considered for dealing with disturbance attenuation problems for nonlinear systems. The L1-performance and L1-control of nonlinear systems are characterized in terms of certain invariance sets of the state space; in addition, the relation between the L1-control of a continuous-time system and the \u21131-control of the related Euler approximated discrete-time systems is established. A systematic treatment for H\u221e-control synthesis of nonlinear systems is provided; the nonlinear H\u221e-control problem is characterized in terms of Hamilton-Jacobi Inequalities (HJIs) and nonlinear matrix inequalities (NLMIs); a class of H\u221e-controllers are parameterized as a fractional transformation of contractive stable parameters. Finally, the problems of stability and performance robustness analysis and synthesis for uncertain nonlinear systems subject to structured perturbations with bounded L2-gains are introduced; they are characterized in terms of HJIs and NLMIs as well. Computational issues are also addressed; it is confirmed that the computation needed for robustness analysis and synthesis of nonlinear systems is of equivalent difficulty to that for checking Lyapunov stability.
" }, { "name": "Lunden, Melissa Mae", "degree": "PhD", "year": "1995", "title": "Sintering of aerosol agglomerates", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06182004-103836", "creators": [ { "name": { "family": "Lunden", "given": "Melissa Mae" }, "id": "Lunden-M-M", "display_name": "Lunden, Melissa Mae" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/R12F-E147", "abstract": "Fundamental studies of the sintering of aerosol agglomerates have been undertaken. A model has been developed that closely follows the sintering kinetics of the two-sphere system. The model solves a detailed description of the evolving geometry as the particles sinter, allowing neck growth to be calculated beyond the small neck limit. Contributions due to multiple mechanisms are calculated by integrating the sum of the individual sintering mechanism fluxes. It has been demonstrated that the relative contributions of individual mechanisms can change as the neck grows. Moreover, changes in sintering temperature can drastically alter which of the sintering mechanisms is predominant.\n\nExperiments performed on model bisphere show that neck formation occurs quickly, until the difference between the surface free energy and the grain boundary energy of the aggregate becomes small. This metastable configuration depends upon the equilibrium, or dihedral, angle of the particle. Following neck growth, coalescence proceeds slowly.\n\nThe projected area and hence, the mobility-equivalent diameter of an agglomerate will generally decrease as coalescence occurs. However, experimental observations of larger model agglomerates reveal some unexpected behavior, including apparent increases in the mobility-equivalent size. These effects may be caused by particle orientation in the mobility classifier. It is postulated that the rotation of individual particles to preferred grain boundary orientations leads to an increase in the projected area of the particle during sintering.\n" }, { "name": "M'Closkey, Robert Thomas", "degree": "PhD", "year": "1995", "title": "Exponential stabilization of driftless nonlinear control systems", "advisor": "Murray, Richard M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172007-104556", "creators": [ { "name": { "family": "M'Closkey", "given": "Robert Thomas" }, "id": "M-Closkey-R-R", "display_name": "M'Closkey, Robert Thomas" } ], "advisors": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "advisor", "display_name": "Murray, Richard M." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "member", "display_name": "Wiggins, Stephen R." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7myb-h217", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis dissertation lays the foundation for practical exponential stabilization of driftless control systems. Driftless systems have the form,\n\n[...].\n\nSuch systems arise when modeling mechanical systems with nonholonomic constraints. In engineering applications it is often required to maintain the mechanical system around a desired configuration. This task is treated as a stabilization problem where the desired configuration is made an asymptotically stable equilibrium point. The control design is carried out on an approximate system. The approximation process yields a nilpotent set of input vector fields which, in a special coordinate system, are homogeneous with respect to a non-standard dilation. Even though the approximation can be given a coordinate-free interpretation, the homogeneous structure is useful to exploit. Since implementing a controller requires choosing a coordinate system, there are extra benefits to be gained by choosing coordinates in which the approximation is homogeneous. The feedbacks are required to be homogeneous functions and thus preserve the homogeneous structure in the closed-loop system. The stability achieved is called p-exponential stability. This extended notion of exponential stability is required since the feedback, and hence the closed-loop system, is not Lipschitz. However, it is shown that the convergence rate of a Lipschitz closed-loop driftless system cannot be bounded by an exponential envelope.\n\nThe synthesis methods generate feedbacks which are not smooth on [...]. The solutions of the closed-loop system are proven to be unique in this case. In addition, for many driftless systems the control inputs are often velocities. A more appropriate formulation of the stabilization problem has the control law specifying forces instead of velocities. We have extended the kinematic velocity controllers to controllers which command forces and still p-exponentially stabilize the system. \n\nPerhaps the ultimate justification of the methods proposed in this thesis are the experimental results. The experiments demonstrate the superior convergence performance of the p-exponential stabilizers versus traditional smooth feedbacks. The experiments also highlight the importance of transformation conditioning in the feedbacks. Other design issues, such as scaling the measured states to eliminate hunting, are discussed. The methods and problems in this thesis bring the practical control of strongly nonlinear systems one step closer.\n" }, { "name": "Marquardt, Ronald R.", "degree": "PhD", "year": "1995", "title": "Quantum magnetotransport studies of semiconductor heterostructure devices", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172007-111750", "creators": [ { "name": { "family": "Marquardt", "given": "Ronald R." }, "id": "Marquardt-R-R", "display_name": "Marquardt, Ronald R." } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/P7Z1-T478", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nResonant interband tunneling is perhaps the most generalized example of quantum transport in semiconductor heterosystems, and yet few studies of interband magnetotunneling have been reported. This thesis presents the results of the first in-depth study of quantum magnetotransport through valence band-like well states in broken-gap semiconductor heterostructures. The transport characteristics of a series of InAs/AlSb/GaSb/AlSb/InAs resonant interband tunneling (RIT) diodes were investigated in magnetic fields as great as 8 tesla oriented both parallel and perpendicular to the tunnel current density. The resulting observations advance the understanding of interband transport and reveal interesting and complex phenomena previously unseen in magnetotunneling investigations.\r\n\r\nIn magnetic fields perpendicular to the tunnel current density, evidence of both low-mass, negative dispersion, and high-mass, positive dispersion states in the GaSb well is shown. The magnetic field in this geometry has no discernible effect on the RIT transport characteristics at low fields, however, and the transition between this low-field regime, and the expected response at higher field strengths is extremely abrupt. Associated with this marked change in behavior is an additional, narrow peak present in the negative differential resistance (NDR) region of the device at the threshold, or critical, magnetic field. This anomalous discontinuity in device transport violates semi-classical theory and is suggestive of a dramatic and fundamental change in resonant quantum transport.\r\n\r\nWith the field applied normal to the epitaxial layers, Landau levels form and resonant tunneling through them is observed indirectly via Shubnikov-de Haas-like oscillations of the tunneling conductance. The non-conservation of Landau level index in interband magnetotunneling is first proposed theoretically, and subsequently verified experimentally. Evidence for this effect is asserted from the discontinuous changes in the Shubnikov-de Haas oscillatory phase as a function of applied bias. These phase shifts result from bias-dependent changes in the resonant current path through well hole states of differing longitudinal angular momentum. The data are the first observation of Landau level mixing in interband tunnel devices, and only the second report for magnetotunneling in general. The lack of separate Shubnikov-de Haas oscillations for coupling to spin-up and spin-down states is interpreted to be evidence that the well masses are significantly less than the electrode mass, such that the reduced mass [...] of the two is approximately equal to the well mass, [...].\r\n" }, { "name": "McKenney, Elizabeth Anne", "degree": "PhD", "year": "1995", "title": "A Study of Tip Vortices and Cavitation on a Propeller in a Non-Uniform Flow Field", "advisor": "Brennen, Christopher E.; Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-131335", "creators": [ { "name": { "family": "McKenney", "given": "Elizabeth Anne" }, "id": "McKenney-Elizabeth-Anne", "display_name": "McKenney, Elizabeth Anne" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "co-advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7THC-NG74", "abstract": "Unsteady lifting surface flows are important subjects for study, both for the purposes of improving propulsive or lifting efficiency and also for mitigating the destructive effects and noise caused by cavitation. Some progress may be made by selecting a simple type of unsteadiness for closer study. In the present work, this tactic was implemented in two ways: the operation of a propeller at an angle of yaw to the freestream and the pitching oscillation of a finite-span hydrofoil.\r\n\r\nA new facility was designed and constructed to set a propeller at an angle of yaw to the freestream, creating a fairly simple non-uniformity in the propeller inflow. Tip vortex cavitation inception measurements were made for a range of yaw angles and freestream velocities, and photographs of the cavitation were taken to illustrate the effects of the yaw angle.\r\n\r\nThe unsteady tip vortex flow field was measured on an oscillating finite aspect ratio hydrofoil using Particle Image Velocimetry (PIV), revealing how the circulation varied during a typical oscillation cycle. The results were compared with unsteady infinite-span theory, and also with recent measurements using LDV techniques on the same foil.\r\n\r\nThe hydrofoil was also the focus of a study of surface cavitation. High-speed motion pictures of the cavitation cycle helped to separate the process into its component stages, and variations with cavitation number and reduced frequency of oscillation were observed. The acoustic signals generated by the cavity collapse were correlated with the motion pictures, providing insights into the correspondence between the flow structures involved in the cavity collapse process and the sound generated by them.\r\n\r\nThe results from these studies provide valuable insights into the effects of unsteadiness in lifting surface flows.\r\n" }, { "name": "Miles, Robert J.", "degree": "PhD", "year": "1995", "title": "Microprobe investigations of semiconductor structures", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172007-144050", "creators": [ { "name": { "family": "Miles", "given": "Robert J." }, "id": "Miles-R-J", "display_name": "Miles, Robert J." } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7bk3-4486", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis thesis describes the results of experimental studies of semiconductor structures using local microprobe techniques. The studies primarily concern two questions: the detection of local variations in material quality and transport properties, and the control of material preparation and growth to minimize these variations.\n\nIn chapter 2 we investigate the source of defects in nitrogen-doped ZnTe grown on ZnTe and GaSb substrates. Through the use of atomic force microscopy (AFM) and transmission electron microscopy (TEM), we find that defect generation is minimized on GaSb substrates with nitrogen delta-doping. Using selective etching techniques, we also show that the Zn {111} fault planes tend to originate at the doping layers while Te {111} fault planes tend to originate at the substrate/epilayer interface. A simple doping model from Chadi et al., explains the observed effect.\n\nIn chapter 3 we studied the effects of electron-beam-assisted molecular beam epitaxy (EB MBE) on the growth of Si on [...]/Si(111). By irradiating the surface of [...] with low energy electrons, the surface free energy of the [...] is raised and the subsequent Si layer is smoother. By using AFM, X-ray diffraction, and XPS, we find that an optimal range of exposures exist that minimizes surface roughness and we present a simple thermodynamic model to explain this. We further show that for temperatures below the epitaxial growth temperature of Si (500\u00b0C), the irradiation causes a transition in the Si grown from amorphous to ordered.\n\nIn chapter 4 we investigate the electrical properties of the intrinsic ZnTe(110) surface. Using scanning tunneling microscopy (STM) and spectroscopy, we find a new criterion for determining the extent of Fermi level pinning. This criterion involves observing the enhancement of reverse bias current with increasing tip-sample separation. The mechanism is an increase in the tunneling transmission of carriers through the semiconductor's space charge region that more than compensates for the reduced tunneling transmission through the tip-sample gap as the tip retracts from the surface. We also find that upon subsequent exposure of the surface to contaminates, the surface becomes pinned.\n\nChapter 5 describes our ballistic electron emission microscopy (BEEM) investigations of semiconductor structures. We describe our studies of Au/Si(100) interfaces and show that the barrier height extracted from the spectroscopy using a simple model agrees well with the known Au/Si Schottky barrier height. We also present preliminary studies of InAs/AlAs/GaAs single barrier structures. Through frequency plots we feel we can confidently identify transport associated with specific local band structure, particularly the GaAs and AlAs [...]-pt.\n\nFinally, in Appendix A we discuss the contemporary STM theories along with the theory we used for our calculations in chapter 4. In Appendix B, we discuss in detail the construction of BEEM equipment along with its operation.\n" }, { "name": "Min, Inki A.", "degree": "PhD", "year": "1995", "title": "Transport, stirring and mixing in two-dimensional vortex flows", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182007-132306", "creators": [ { "name": { "family": "Min", "given": "Inki A." }, "id": "Min-I-A", "display_name": "Min, Inki A." } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8y2c-8203", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nTo understand the basic contribution of vortex motion in the transport and mixing of passive fluid, we study a system of N discrete vortices. With variation of N and [...] (a vorticity distribution parameter), we are able to experiment with a range of vortex dynamics sufficient to capture many of the features of two-dimensional turbulence in their elementary form - such as vortex merging (inverse cascade of energy), filamentation (enstrophy cascade), etc. With this model the mixing of the fluid is numerically studied via stretch statistics and the spatial distribution of a non-diffusive scalar interface. The spectrum of spatial distribution of scalars as a result of the stirring motion of the N vortices is particularly important in view of the recent (as well as historical) interest in the characterization of the scalar distribution in turbulence. We also examine the velocity field statistics and the Lagrangian motion of fluid particles. It is also instructive to look at the kinematic causes behind the types of statistics that are obtained for the velocity structure functions. A 'building block' approach to understanding these effects in turbulence may lie in building up from a collection of discrete vortices, as done in this thesis, to adding vortices of different scales and the three-dimensional effects. It is in the context of these wider issues that we study the N-vortex problem.\n\nIn the final part of this thesis we investigate the two-dimensional mixing produced by large scale vortical structures during the evolution of a spatially developing mixing layer. Although the advent of three-dimensionality and fully developed turbulence are essential features of mixing layers, it is still dominated by the large scale two-dimensional structures and its effect on the mixing is illustrated here.\n" }, { "name": "Murty, M. V. Ramana", "degree": "PhD", "year": "1995", "title": "Ion-surface interactions and limits to silicon epitaxy at low temperatures", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-10262007-111208", "creators": [ { "name": { "family": "Murty", "given": "M. V. Ramana" }, "id": "Murty-M-V-Ramana", "display_name": "Murty, M. V. Ramana" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/1vkn-xh33", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nLow temperature (T [...] 400\u00b0C) deposition of Si on Si(001) proceeds epitaxially up to a finite thickness followed by a crystal-state-amorphous-state transition. An atomistic model, the twin-boundary/facet (TBF) mechanism, has been proposed for this transition. The increase in surface roughness during film growth has been directly tied to the breakdown of epitaxy. The mechanism involves the nucleation of a twin boundary on a {111} facet (produced by roughening). When the twinned region meets a different part of the perfect crystal, it inevitably leads to the formation of five- and seven-member rings. These act as nucleation sites for amorphous silicon. Adsorbates such as carbon and oxygen can dramatically increase the surface roughness even at small coverages ([...] 0.01 ML). They thus play an indirect role by accelerating the surface roughening rate.\r\n\r\nFilms with improved crystalline quality were deposited by ion beam-assisted molecular beam epitaxy. Atomic force microscopy revealed that the main effect of low energy [...] ion irradiation was surface smoothing.\r\n\r\nMolecular dynamics simulations suggest that epitaxy on hydrogen-terminated silicon surfaces (at high hydrogen coverage) proceeds by subplantation of the incident Si atom and segregation of [...] units. The remarkable success of sputter deposition in growing epitaxial films on a dihydride-terminated Si(001) surface is explained by the very rapid rise in the subplantation probability with the incident Si atom energy.\r\n\r\nAn empirical interatomic potential has been developed to describe Si-H interactions. This can be used, with caution, for classical molecular dynamics investigations of hydrogen-terminated silicon surfaces, chemical vapor deposition of silicon and hydrogenated amorphous silicon.\r\n\r\nA technique for low temperature Si(001)-2x1 substrate preparation was developed to complement the various low temperature processes that are being developed for device fabrication. This was achieved by low energy noble gas ion ([...] or [...]) irradiation of a nominally dihydride-terminated Si(001)-1x1 surface. Reconstructed Si(001)-2x1 surfaces were prepared at temperatures as low as 100\u00b0C. Silicon films deposited on such surfaces were epitaxial." }, { "name": "Musgrave, Charles Bruce", "degree": "PhD", "year": "1995", "title": "Molecular Mechanics and Ab Initio Simulations of Silicon (111) Surface Reconstructions, Semiconductors and Semiconductor Superlattices, H Abstraction for Nanotechnology, Polysilane, and Growth of CVD Diamond", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192007-104223", "creators": [ { "name": { "family": "Musgrave", "given": "Charles Bruce" }, "id": "Musgrave-Charles-Bruce", "orcid": "0000-0002-5732-3180", "display_name": "Musgrave, Charles Bruce" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "role": "member", "display_name": "Okumura, Mitchio" } ], "option_major": [ "matsci" ], "doi": "10.7907/7khv-pb17", "abstract": "This thesis describes the application of ab initio and molecular mechanics quantum chemical methods to several problems in the materials and surface sciences. Chapter 1 reviews these methods. Chapter 2 details the application of these methods to study the reaction rate of a proposed mechanism for growth of CVD diamond. Chapter 3 uses high level ab initio methods to study the feasibility of a hydrogen abstraction tool for nanotechnology. Chapter 4 uses ab initio methods together with experimental data to develop a force field potential to model polysilane polymers. Chapter 5 is comprised of the development of atomistic potentials to describe semiconductors and their superlattices and interfaces. The approach of Chapter 5 is extended in Chaper 6 by combining the bulk force field with force field parameters developed from the Biased Hessian Method applied to unique clusters to model the reconstructions of the Si (111) surface. Chapter 7 concludes this thesis with a description of the Generalized London Potential which was developed to accurately model chemical reactions at the accuracy of high level configuration interaction methods, but with the practicality of molecular mechanics.
" }, { "name": "Pedroni, Volnei Antonio", "degree": "PhD", "year": "1995", "title": "VLSI Systems for Analog and Hamming Parallel Computation", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172007-153538", "creators": [ { "name": { "family": "Pedroni", "given": "Volnei Antonio" }, "id": "Pedroni-Volnei-Antonio", "display_name": "Pedroni, Volnei Antonio" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Scherer", "given": "Axel" }, "id": "Scherer-A", "orcid": "0000-0002-2160-9064", "role": "member", "display_name": "Scherer, Axel" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/DC5Z-3Q89", "abstract": "This thesis explores the vast field of physically implementing parallel-computing algorithms. In this research, we introduce a series of new circuit architectures and new technology applications, which implement multi-dimensional functions that are at the heart of many parallel signal processing systems, e.g., neural and Hamming networks, vector quantizers, and median filters. The functions are realized using low-cost, low-power, high-density technologies (CMOS and CCD), fully compatible with current industrial processes. The systems are either analog or hybrid, allowing lower time and/or storage complexities in many types of applications when compared to fully digital systems. Special emphasis is placed on circuit modeling, with the purpose of thoroughly understanding the potentialities - and limitations - of each alternative. The models are verified experimentally on most occasions. As a consequence, the results presented in this dissertation are expected not only to provide new technological alternatives, but also new means of evaluating the technologies themselves.
\r\n\r\nChapter 1 presents an introductory discussion on parallel systems. It has three main purposes. One is to describe some of the parallel functions whose implementations we are interested in. Another is to present a graphical discussion on how certain multidimensional systems work, which is probably the best way of describing - and appreciating - systems of this kind. And finally to describe basic guidelines concerning this research.
\r\n\r\nChapter 2 discusses a function that is inherent to most analog parallel processors, the winner-take-all function. The reason for it to be developed first is that this function is part of many other function realizations. A global discussion is presented, which provides an overview on the potentialities of most implementations available in CMOS technology, followed by high-resolution alternatives. The use of this function to implement other functions and systems is also illustrated.
\r\n\r\nChapter 3 presents a detailed discussion on charge-coupled device (CCD) technology and its applications to parallel signal processing systems. This technology, compatible with conventional double-poly CMOS, is of interest due to its low power consumption and very high integration density, allowing the construction of very efficient vector-matrix multipliers and Hamming networks. To overcome its main limitation (i.e., charge-transfer inefficiency), a locally-controlled architecture is introduced. Several chips and extensive measurements are shown, with the purpose of concretely evaluating the performance of this technology when performing signal processing tasks.
\r\n\r\nFinally, Chapter 4 describes further research on CMOS cells that compute distance-based functions. These circuits allow the construction of LMS and other distance-based parallel processors, and provide additional valuable means of further examining the use of MOS technology for analog computation. Once again experimental results are presented, and the systems are illustrated through vector quantizers, Hamming networks, vector multipliers, and median filters. This chapter also provides further applications of the winner-take-all function to the construction of more complex functions.
" }, { "name": "Perez, Frank Allen", "degree": "PhD", "year": "1995", "title": "Hue Segmentation, Color Circuitry, and the Mantis Shrimp", "advisor": "Antonsson, Erik K.; Koch, Christof", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182007-093223", "creators": [ { "name": { "family": "Perez", "given": "Frank Allen" }, "id": "Perez-Frank-Allen", "display_name": "Perez, Frank Allen" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "orcid": "0009-0009-4668-8289", "role": "advisor", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "co-advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "orcid": "0009-0009-4668-8289", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "mecheng" ], "doi": "10.7907/zev6-6330", "abstract": "The focus of this thesis is on engineering effective color vision subsystems for object segmentation based on hue and discontinuities in hue. Hue, which encodes color, is a psychophysical scalar variable defined on the ring [0, [pi]]. A computational theory justifying the use of hue for distinguishing material differences is established and novel algorithms are developed to detect its discontinuity. Although the focus of this thesis has been on anthropocentrically based trichromatic systems, some effort is placed in exploring the multi-dimensional spaces of more than three primary colors. A hypothetical explanation is proposed of the 11 spectral sensors of the Mantis shrimp, which performs functionally as a biological spectrum analyzer. The importance of the opponency calculation is emphasized. Its role in optimum filter design offers hyperacuity in the spectral domain.
\r\n\r\nThis work encompasses spectral filter design, color space evaluation, computer vision algorithm development, and hardware implementation in custom analog VLSI circuitry. A one pixel (zero dimension) \"intensity/normalized-color/hue\" sensor is built based on a trichromatic system. For the basic analog circuit element required in hue segmentation, the current-fuse is developed. Guidelines for building higher dimensional sensors in both spatial and spectral domains are presented. Practical offshoots from this research range from color quality sensors for inexpensive printing to vision systems for robotics and autonomous vehicles.
" }, { "name": "Pich, Peter", "degree": "PhD", "year": "1995", "title": "Nonlinear rigid block dynamics", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12012011-112223883", "creators": [ { "name": { "family": "Pich", "given": "Peter" }, "id": "Pich-P", "display_name": "Pich, Peter" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/2gsn-6v23", "abstract": "Motion of a block on flat ground under the influence of gravity is studied.
\r\n\r\nA general model is introduced for the free motion of a rectangular, rigid block on a continuous, perfectly elastic foundation. The model includes friction forces between the block and foundation and allows for sliding, rocking and flight of the block. Solutions are obtained through numerical integration. A three parameter study is carried out, namely as a function of aspect ratio, r, coefficient of friction, \u00b5 and non-dimensional stiffness, k_, for various initial conditions.
\r\n\r\nDominant types of response are identified and the stability of the block against overturning and its tendency to fly are studied. For initial conditions with sufficient energy, critical curves are found in the (k_, r) parameter space which define a transition between a flight and no flight region. For initial conditions with sufficient energy there also exists a critical curve in the same parameter space which separates a region of overturning from a region where the block does not overturn.
\r\n\r\nChaos is found in the flight region of the (k_,r) parameter space for sufficiently high r. Poincare maps and Liapunov exponents are computed to document the existence of chaos.
" }, { "name": "Pillai, N. Sateesh", "degree": "PhD", "year": "1995", "title": "Non-Dissipative Decay of Linear Quasimodes in a Pure Electron Plasma", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-10122007-090003", "creators": [ { "name": { "family": "Pillai", "given": "N. Sateesh" }, "id": "Pillai-N-Sateesh", "display_name": "Pillai, N. Sateesh" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "chair", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" } ], "option_major": [ "eleceng" ], "doi": "10.7907/GHGX-Z547", "abstract": "This thesis describes the first experimental observations of linear collisionless damping of perturbations in a pure electron plasma and provides the theoretical proof for collisionless damping in two dimensional inviscid incompressible fluids. Observations in the non-linear regime provide evidence for fluid trapping in the potential well of the perturbation.
\r\n\r\nThe perturbations are in the form of diocotron waves which possess azimuthal symmetries described by the eigen number m = 2. The plasma is a cylindrical column of electrons confined in a Penning trap. Diocotron waves are excited by applying azimuthally propagating electric fields to the electrode structures forming the wall of the Penning trap.
\r\n\r\nExperiment shows that the damping of diocotron waves is not caused by dissipation at the electrode wall, and that the presence of such a dissipation decreases the decay rate of these waves, confirming that the m = 2 diocotron wave is a negative energy wave.
\r\n\r\nA self consistent set of equations for the perturbed potential is derived using the cold two dimensional fluid model. This results in the diocotron equation, which is the cylindrical plasma analog of Rayleigh's equation for shear flow of an inviscid incompressible fluid between parallel sheets. The complex form of the diocotron equation is solved, with homogeneous boundary conditions, for a particularly simple radial density profile showing that the diocotron resonances are quasimodes of the 2-D fluid. The solution reveals a complex eigenvalue which is consistent with the observed collisionless exponential damping of the diocotron wave in the linear regime.
\r\n\r\nSolution of the diocotron equation with more complicated density profiles is carried out numerically using the Runge-Kutta method on a computer.
\r\n" }, { "name": "Regehr, Martin W.", "degree": "PhD", "year": "1995", "title": "Signal extraction and control for an interferometric gravitational wave detector", "advisor": "Drever, Ronald W. P.; Raab, Frederick J.; Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192007-092215", "creators": [ { "name": { "family": "Regehr", "given": "Martin W." }, "id": "Regehr-M-W", "display_name": "Regehr, Martin W." } ], "advisors": [ { "name": { "family": "Drever", "given": "Ronald W. P." }, "id": "Drever-R-W-P", "role": "advisor", "display_name": "Drever, Ronald W. P." }, { "name": { "family": "Raab", "given": "Frederick J." }, "id": "Raab-F-J", "role": "advisor", "display_name": "Raab, Frederick J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5EYV-5813", "abstract": "Large interferometers are currently under construction for the detection of gravitational radiation. These will contain a number of optical surfaces at each of which the relative phase of incident beams must be kept strictly controlled in order to achieve high sensitivity.\n\nThe type of interferometer considered here consists of two Fabry-Perot cavities illuminated by a laser beam which is split in half by a beam splitter, together with a recycling mirror between the laser and the beam splitter, which reflects light returning from the beam splitter toward the laser back into the interferometer. A scheme for sensing deviations from proper interference has been analyzed and the adequacy of this method for incorporation in a control system has been evaluated. The sensing scheme involves phase modulating the laser light incident on the interferometer, introducing an asymmetry in the distances between the Fabry-Perot cavities and the beam splitter, and demodulating the signals from photodetectors monitoring three optical outputs of the interferometer. These optical outputs are light returning to the laser, light extracted by a pick-off from between the recycling mirror and the beam splitter, and light leaving the interferometer at the beam splitter.\n\nThe analysis has shown that the matrix of transfer functions from mirror displacement to demodulated signal is ill-conditioned, that as many as three of the transfer functions may contain right half plane zeros, and that one of these transfer functions can be affected by the modulation depth. The performance of the closed-loop system, however, need not be significantly affected, provided that certain constraints are observed in the optical and electronic design.\n\nA table-top interferometer has been constructed, to demonstrate the feasibility of constructing a control system using this sensing scheme and to compare the response of the interferometer with that predicted by calculations. Good agreement between the experiment and the calculation has been obtained.\n" }, { "name": "Reid, Jason S.", "degree": "PhD", "year": "1995", "title": "Amorphous ternary diffusion barriers for silicon metallizations", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192007-131842", "creators": [ { "name": { "family": "Reid", "given": "Jason S." }, "id": "Reid-Jason-S", "display_name": "Reid, Jason S." } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4TFH-VM05", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nReactively sputtered from transition-metal silicide or boride targets in [...] discharges, thin amorphous films of TM-Si-N (TM = Mo, Ta, Ti, or W) and W-B-N are investigated. Resistivity, density, stress, and structure are given as functions of composition, and in some cases, temperature. As-deposited films typically contain 100 to 900 MPa of compressive stress, which can be fully relaxed on 'Si' substrates through annealing at 400 to 500[...]. Transmission electron microscopy shows that most of the films are marginally amorphous with the scale of local order ranging from 0.5 to 1.5 nm. Small-angle scattering experiments reveal local chemically dissimilar regions within the films. When fully nitrided, Si appears to be preferentially bonded to nitrogen in the form of Si3N4 in the TM-Si-N films, according to extended energy loss fine structure (EXELFS) measurements.\r\n\r\nAccording to tests on shallow junction diodes, 100-nm thick TM-Si-N barriers are able to prevent aluminum overlayers from spiking the Si substrate at temperatures above aluminum's melting point, 660[...]. The exceptional degree of stability is partly attributable to a 3 nm, self-sealing AlN layer which grows at the TM-Si-N/Al interface. By virtue of the self-sealing layer, secondary ion mass spectrometry (SIMS) measurements of [...]/[...] trilayers after a 700[...]/10 h vacuum anneal reveal no diffusivity of Al in [...] films.\r\n\r\nThe performance of the TM-Si-N and W-B-N barriers with copper overlayers is equally impressive. At the proper compositions, 100-nm barriers prevent copper from diffusing into the junction at 800[...] or higher for a 30-min vacuum annealing. Diode failure typically corresponds to the crystallization temperature of the barrier, which can be reduced by the presence of copper. Once the barrier crystallizes, well-defined grain boundaries are introduced that provide fast diffusion paths for Cu. Paring the barriers' thickness down to 10 nm lowers the barriers' effectiveness to approximately 650[...]. Bias stress testing of 10-nm TM-Si-N barriers with Cu overlayers on MOS capacitors reveals no penetration of Cu into SiO2 during an 80 h treatment at 300[...] and 1 MV/cm applied field. Preliminary diffusion measurements of Cu in [...] films by SIMS yield an approximate diffusivity constant of [...].\r\n\r\nThrough a microscopic four-point probe lithographically defined on a Cu/barrier/Cu trilayer stack, the specific contact resistances of barrier/Cu interfaces are determined for TM-Si-N, TiN, and W barriers. In all instances, the contact resistance is approximately [...] for as-deposited samples. The lack of difference among the barriers may be attributable to inadequate vacuum leading to interfacial impurities.\r\n" }, { "name": "Sanderson, Simon Ralph", "degree": "PhD", "year": "1995", "title": "Shock wave interaction in hypervelocity flow", "advisor": "Sturtevant, Bradford; Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092004-094744", "creators": [ { "name": { "family": "Sanderson", "given": "Simon Ralph" }, "id": "Sanderson-S-R", "display_name": "Sanderson, Simon Ralph" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3GPK-5G29", "abstract": "The interaction of a weak oblique shock with the strong bow shock ahead of a blunt body in supersonic flow produces extreme heat transfer rates and surface pressures. Although the problem has been studied extensively in low enthalpy flows, the influences of high enthalpy real gas effects are poorly understood. Existing perfect gas models predict greatly increased heating with increasing Mach number and decreasing ratio of specific heats.\r\n\r\nExperiments are conducted in a free piston shock tunnel to determine the effects of thermochemistry on the problem at high enthalpy. The flow topology is simplified by studying the nominally two-dimensional flow about a cylinder with a coplanar impinging shock wave. High resolution holographic interferometry is used to investigate changes in the flow structure as the location of the impinging shock wave is varied. Fast response heat transfer gauges provide time resolved measurements of the model surface temperature. The data that are obtained do not support the existing predictions of greatly increased heat transfer at high enthalpy.\r\n\r\nA model is developed to study the thermochemical processes occurring in the interaction region. The phenomenon arises because the stagnation streamline is forced to pass through a system of oblique shock waves that produce less entropy than the undisturbed bow shock. Peak heating is shown to result from a balancing of the strengths of the oblique shock waves. This condition is demonstrated to simultaneously minimize the influence of thermochemistry on the flow. Real gas effects are shown to become important at lower Mach numbers (< 7.5) and for shock angles weaker or stronger than that which produces maximum heating. The model accurately reproduces the experimental observations.\r\n\r\nA nonequilibrium approximation is introduced that applies when the oblique waves are weak with respect to the undisturbed bow shock. Within the scope of the approximation, non-monotonic behavior with the reaction rate is predicted. The reaction rate is not varied as an independent parameter in the current experiments.\r\n" }, { "name": "Semrau, Jeremy D.", "degree": "PhD", "year": "1995", "title": "Kinetic, biochemical, and genetic analysis of the particulate methane monooxygenase", "advisor": "Lidstrom, Mary E.; Chan, Sunney I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192007-132819", "creators": [ { "name": { "family": "Semrau", "given": "Jeremy D." }, "id": "Semrau-J-D", "display_name": "Semrau, Jeremy D." } ], "advisors": [ { "name": { "family": "Lidstrom", "given": "Mary E." }, "id": "Lidstrom-M-E", "role": "advisor", "display_name": "Lidstrom, Mary E." }, { "name": { "family": "Chan", "given": "Sunney I." }, "id": "Chan-S-I", "role": "co-advisor", "display_name": "Chan, Sunney I." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/jvdy-gy47", "abstract": "The partiuculate methane monooxygenase (pMMO) is expressed by all known methanotrophs and may be very useful for the degradation of small halogenated hydrocarbons such as trichloroethylene (TCE). The pMMO, however, is poorly understood and much work is needed to determine the usefulness of this enzyme for the degradation of wastes both in-situ and in above-ground treatment reactors. In this thesis, the kinetics, biochemistry, and genetics of the pMMO are examined. The research indicates that copper plays a major role in the kinetics of both TCE and methane oxidation by the pMMO. Furthermore, by correlating activity assays, metal analysis, and electron paramagnetic resonance spectroscopy, we have concluded that copper makes up the active site of the pMMO, and that multiple active sites may exist on the pMMO. Finally, genetic analysis of chromosomal DNA from several methanotrophs indicates that two copies of the pMMO exist. Data suggest the products of these gene copies may be different, and that they might be affected by the amount of bioavailable copper.\n" }, { "name": "Stevanovic, Ljubisa D.", "degree": "PhD", "year": "1995", "title": "Switching converters for input current shaping and regulation of multiple outputs", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-10122007-083417", "creators": [ { "name": { "family": "Stevanovic", "given": "Ljubisa D." }, "id": "Stevanovic-L-D", "display_name": "Stevanovic, Ljubisa D." } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7tyd-1d21", "abstract": "A novel class of isolated Capacitive Idling switching power converters featuring decoupled primary and secondary side feedback loops is presented. While preserving the cost, size and simplicity of the conventional multiple output dc-to-dc converters, this new class of isolated converters possesses the following advantages: no need to cross isolation barrier in the feedback, full regulation of all outputs from no-load to full-load, faster transient response, and independent short circuit protection of each output.\r\n\r\nOperation of the Capacitive Idling converters in single-phase ac-to-dc power conversion systems is also analyzed. It is found that these converters perform input current shaping automatically, i.e., without an input current feedback loop. This is achieved by operating primary side inductance(s) in discontinuous inductor current mode (DICM). Consequently, the high power factor performance is obtained without any penalty in complexity, cost and size of the converter.\r\nInput current shaping and full regulation of multiple outputs is made possible by the internal energy storage and presence of one secondary-side active switch for each output. When compared to conventional current shaper-regulator configurations involving up to three cascaded power stages, the new converter class represents a very attractive alternative. The main advantages of the Capacitive Idling shapers are:\r\n- current shaping and regulation in a single power stage,\r\n- simplified control implementation with no feedback isolation, - wide bandwidth loop gain on all outputs, - independent short-circuit protection of each output.\r\nAnalysis of the Capacitive Idling converters reveals that the input current shaping mode of operation involves a trade-off between the high power factor and the increased switch voltage stress. Boundary of the DICM of operation is determined, resulting in a design equation for the primary side inductance(s). Experimental results verify the analysis and confirm that these converters represent a viable and attractive approach for input current shaping and multiple output regulation.\r\n" }, { "name": "Suarez, Humbert H.", "degree": "PhD", "year": "1995", "title": "Modeling motion detection in striate visual cortex using massive excitatory feedback", "advisor": "Koch, Christof", "url": "https://resolver.caltech.edu/CaltechETD:etd-10252006-092222", "creators": [ { "name": { "family": "Suarez", "given": "Humbert H." }, "id": "Suarez-Humbert-H", "display_name": "Suarez, Humbert H." } ], "advisors": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "advisor", "display_name": "Koch, Christof" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Laurent", "given": "Gilles J." }, "id": "Laurent-G-J", "orcid": "0000-0002-2296-114X", "role": "member", "display_name": "Laurent, Gilles J." }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cns" ], "doi": "10.7907/78a8-3m56", "abstract": "This thesis is a detailed description and analysis of a model of direction-selective simple cells in cat striate visual cortex. There are three main defining features of our modeling effort compared to previous ones. (1) Local excitatory intracortical connections, known to be very numerous, are taken into account. (2) The model is very detailed: compartmental models of neurons are used and spiking is modeled using Hodgkin and Huxley-like active ionic currents. (3) Model responses are analyzed through standard electrophysiological methods and are compared in detail to physiology. Two separate operating modes are described. When the model acts as a proportional amplifier, contrast-response curves are relatively linear. In the hysteretic amplifier mode, contrast-response curves are much steeper initially, including an early portion with expansivity nonlinearity, but saturate abruptly at high contrasts. These features of the second mode are very similar to cortical contrast-response curves, but very different from the thalamus'. The second mode also predicts that hysteresis is latent in cortex, but that because of resetting through inhibition, cortical neurons do not fire in the absence of stimulation. In both modes, the model achieves strong amplification of the input through the excitatory cortical feedback. Amplification results in small changes in conductance for stimuli moving in the null direction, long a puzzling experimental finding; direction selectivity also persists during blockade of all inhibition in a single cell, as observed in recent experiments. Due to the nonlinearity of this amplification, bandpass velocity-response curves of thalamic neurons can be transformed into velocity low-pass cortical curves. Direction selectivity is invariant over a wide range of contrasts and velocities, a prominent feature of direction-selective cells in cortex. The model also makes specific predictions concerning the effects of selective blockade of cortical inhibition on direction selectivity at different velocities. Finally, we address the important issue of testing experimentally the linearity of cortical neurons. The same intracellular linearity test that has been used for cortical neurons is performed on the model. Although the model has substantial nonlinearities, it appears quite linear according to the linearity test. We explain these surprising observations in detail, and conclude that such tests are much more limited in usefulness than apparent at first." }, { "name": "Swenberg, Johanes F. N.", "degree": "PhD", "year": "1995", "title": "Development of wide-bandgap II-VI semiconductor light-emitting device technology based on the graded injector design", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10122007-142152", "creators": [ { "name": { "family": "Swenberg", "given": "Johanes F. N." }, "id": "Swenberg-J-F-N", "display_name": "Swenberg, Johanes F. N." } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/p2ey-5557", "abstract": "This thesis describes the technical development of a novel semiconductor device design aimed at realizing short wavelength visible light emitters. The device structure, called the graded injector, achieves minority carrier injection in a heterojunction system with unfavorable type-II band alignment. Band edge engineering with an alloy graded intermediary layer effectively reduces the conduction band offset and allows for efficient minority carrier injection. The basic device structure consists of a n-CdSe/Mg[subscript x]Cd[subscript 1-x]Se/p-ZnTe heterojunction, where the Mg[subscript x]Cd[subscript 1-x]Se region is graded.\n\nThe device design, materials growth, and characterization of II-VI green LEDs based on this structure are presented. Simulations demonstrate the operating principle of the graded injector. Early device development had been hindered by the lack of a p-type dopant for MBE ZnTe and the unavailability of high quality substrates. These restrictions have been overcome with the development of efficient nitrogen p-type doping of ZnTe and the growth capability of high quality heteroepitaxy on GaSb substrates. The materials characterization of the Mg-chalcogenides has enabled more accurate band edge engineering necessary for an operating device.\n\nThe advances in growth technology and materials characterization have been incorporated to grow and fabricate working graded injector LEDs. The operating characteristics of these devices unequivocally demonstrate the diode-like operation and efficient minority carrier injection. The electrical and optical performance of these devices will be presented and analyzed.\n" }, { "name": "Tatic-Lucic, Svetlana", "degree": "PhD", "year": "1995", "title": "Silicon micromachined devices for in vitro and in vivo studies of neural networks", "advisor": "Tai, Yu-Chong; Pine, Jerome", "url": "https://resolver.caltech.edu/CaltechETD:etd-10262007-104017", "creators": [ { "name": { "family": "Tatic-Lucic", "given": "Svetlana" }, "id": "Tatic-Lucic-S", "display_name": "Tatic-Lucic, Svetlana" } ], "advisors": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "role": "advisor", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "co-advisor", "display_name": "Pine, Jerome" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6jhx-9889", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe design, fabrication and mechanical testing of two new kinds of silicon-micromachined devices for both in vitro and in vivo extracellular stimulation and recording are investigated. The novelty of these devices is a neuron well structure fabricated in a 16-20 [...] thick silicon membrane using a double-sided micromachining technique. The neuron well is a trapezoidal cavity with a gold electrode at the bottom and a mechanical grillwork on the top. Through the grillwork, live embryonic neurons can be implanted, cultured, and then electro-physiologically studied inside the wells. This approach can tremendously improve the reliability and signal-to-noise ratio of extracellular recording of the cultured neurons compared to previous approaches.\r\n\r\nFirst, a silicon-micromachined microchip for in vitro studies of cultured neural networks has been developed. The bottom of the neurochip has two different designs. One has a circular silicon-dioxide rim ([...] step height) at the bottom (called dimpled bottom), and the other has only a flat bottom. The dimpled bottom is expected to provide a better mechanical seal between the cultured cell and the gold electrode, which would result in a better signal-to-noise ratio. Physiologically, it has been confirmed that the neuron growth inside the well is independent of the kind of bottom. So far, the neurochips' biocompatibility for up to a week has been demonstrated using both rat hippocampal and superior cervical ganglion (SCG) neuron cells. Next, silicon neuroprobes for in vivo studies of central nervous systems have also been successfully developed. These probes are developed using a modified neurochip technology. The mechanical properties of the neuroprobes are satisfactory, proven in bending, buckling, and even in vivo animal tests. Recently, the neuroprobes have been physiologically tested in rat hippocampus. For the first time, outgrowth of neurites from the cultured neurons inside the wells into the host hippocampus has been observed, which represents the very important evidence for the success of using neuroprobes.\r\n\r\nIn the future, although beyond the scope of this work, a lot more exciting electrophysiological research using these devices should be done. This should lead to further improvement over the prototypes, and finally produce a new generation of working neural prosthetic devices.\r\n" }, { "name": "Tierno, Jose Andres", "degree": "PhD", "year": "1995", "title": "An energy-complexity model for VLSI computations", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10252007-094408", "creators": [ { "name": { "family": "Tierno", "given": "Jose Andres" }, "id": "Tierno-Jose-Andres", "display_name": "Tierno, Jose Andres" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/PP38-4935", "abstract": "An energy complexity model for CSP programs to be implemented in CMOS VLSI is developed. This model predicts with some accuracy the energy dissipation of the \"standard\" asynchronous VLSI implementation of a CSP program, associated to a given trace of that program. This energy complexity is used in the analysis of CSP programs, in order to optimize this high level representation of asynchronous circuits for energy efficiency. A lower bound to the energy complexity of a CSP program is derived, based on the information theoretical entropy per symbol of the input/output behavior of the CSP program. This lower bound abstracts the specification of the circuit (that is, its input/output behavior), from the implementation of the specification (that is, the text of the program), and therefore applies to any program that meets the specification. A number of techniques are presented to write programs of low energy complexity, and are applied to several examples.\r\n\r\nTo link the high level representation of circuits to the CMOS representation, several circuits are analyzed to provide standard translations for basic CSP operators into CMOS. In particular, a method for pipelining bus transfers using the sense-amplifier of the bus as a register is proposed.\r\n" }, { "name": "Van der Goot, Marcel Rene", "degree": "PhD", "year": "1995", "title": "Semantics of VLSI synthesis", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10162007-093427", "creators": [ { "name": { "family": "Van der Goot", "given": "Marcel Rene" }, "id": "Van-der-Goot-M-R", "display_name": "Van der Goot, Marcel Rene" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Sanders", "given": "Beverly" }, "id": "Sanders-B", "role": "member", "display_name": "Sanders, Beverly" }, { "name": { "family": "Hofstee", "given": "H. Peter" }, "id": "Hofstee-H-P", "role": "member", "display_name": "Hofstee, H. Peter" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/SR5V-KT18", "abstract": "We develop a new form of formal operational semantics, suitable for concurrent programming languages. The semantics directly supports sequential and parallel composition, rendezvous synchronization, shared variables, and non-determinism. Based on an abstract notion of program execution, a refinement relation is defined. We show how the refinement relation can be used to prove that one program implements another.\r\n\r\nWe use the operational semantics as a semantic framework for a synthesis method for asynchronous VLSI circuits. We define the semantics of the programming notations that are used, and use the refinement relation to prove the correctness of the program transformations that form the basis of the synthesis method. Among other transformations, we proof the correctness of the replacement of atomic synchronization actions by handshake protocols, and the transformation of a sequence of actions into a network of concurrently executing gates.\r\n" }, { "name": "Wang, Michael Wei-Ching", "degree": "PhD", "year": "1995", "title": "Graded injector, wide bandgap light emitters and XPS studies of the InAs/GaSb heterointerface", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10262007-091414", "creators": [ { "name": { "family": "Wang", "given": "Michael Wei-Ching" }, "id": "Wang-M-W", "display_name": "Wang, Michael Wei-Ching" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/653J-FX31", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis consists of two parts: research performed towards the development of \r\na II-VI graded electron injector wide bandgap light emitter and characterization \r\nof the InAs/GaSb heterointerface, for application to InAs/[...] infrared \r\nsuperlattice detectors. Background and motivation for both projects are presented.\r\n\r\n Investigations of the II-VI graded electron injector light emitter consist of simulations to test the feasibility of a number of LED designs, band alignment measurements, materials characterization and device performance studies. The simulations, based on the Drift-Diffusion model with modifications to account for heterojunctions, demonstrate that the graded electron injector LED design is feasible. \r\nImprovements to the basic design can be implemented by incorporating confining \r\nlayers and active layers with wider bandgaps using ternaries and quaternaries. The \r\nXPS measurements of the MgSe/[...] and MgTe/[...] valence \r\nband offsets show a deviation from the common anion rule with the valence band \r\nedge of the Mg-based semiconductor lower in both cases. The significance of these \r\nresults is discussed. XRD, TEM and SIMS characterization of the graded injector \r\ndevices reveal potential problems in material quality. Device performance characterization show good current-voltage and electroluminescence properties, but poor \r\nexternal quantum efficiency and device lifetimes.\r\n\r\n Characterization of the InAs/GaSb heterointerface consists of surface exchange \r\nreaction studies, band alignment measurements and interface abruptness studies. \r\nThe XPS/RHEED investigation of surface exchange reactions shows monolayer\r\nexchange and Sb island formation for the Sb soaks of InAs surfaces, and As exchange with Sb past the terminating monolayer of Sb into the underlying GaSb \r\nfor the As soaks of GaSb surfaces. The XPS band alignment studies show that \r\nthe InAs/GaSb valence band offset is independent of interface composition, but \r\nchanges with growth direction. Possible mechanisms for this behavior are discussed. Finally, the XPS, RHEED, cross-sectional STM and SIMS studies of the \r\nabruptness of the InAs/GaSb interface show that the GaSb-on-InAs growth direction is more abrupt than the InAs-on-GaSb growth direction. Mechanisms for this \r\nasymmetry in the interface abruptness are presented.\r\n" }, { "name": "Witelski, Thomas P.", "degree": "PhD", "year": "1995", "title": "Problems in nonlinear diffusion", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10252007-112314", "creators": [ { "name": { "family": "Witelski", "given": "Thomas P." }, "id": "Witelski-T-P", "display_name": "Witelski, Thomas P." } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/SC6N-KK20", "abstract": "A variety of effects can occur from different forms of nonlinear diffusion or from coupling of diffusion to other physical processes. I consider two such classes of problems; first, the analysis of behavior of diffusive solutions of the generalized porous media equation, and second, the study of stress-driven diffusion in solids. The porous media equation is a nonlinear diffusion equation that has applications to numerous physical problems. By combining classical techniques for the study of similarity solutions with perturbation methods, I have examined some new initial-boundary value problems for the porous media equation, including \"stopping\" and \"merging\" problems. Using matched asymptotic expansions and boundary layer analysis, I have shown that the initial deviations from similarity solution form in these problems are asymptotic beyond all orders. Applications of these studies to the Cahn-Hilliard and Fisher's equations are also considered. In my examination of stress-driven diffusion, I consider models for the behavior of systems in the emerging technological field of viscoelastic diffusion in polymer materials. Using asymptotic analysis, I studied some of the non-traditional effects, shock formation in particular, that occur in initial-boundary value problems for these models. Phase-interface traveling waves for \"Case II\" diffusive transport were also studied, using phase plane techniques.\r\n" }, { "name": "Zhong, Xiaoguang Allan", "degree": "PhD", "year": "1995", "title": "Continuum dynamics of solid-solid phase transitions", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10222007-135103", "creators": [ { "name": { "family": "Zhong", "given": "Xiaoguang Allan" }, "id": "Zhong-Xiaoguang-Allan", "display_name": "Zhong, Xiaoguang Allan" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Hou", "given": "Thomas Y." }, "id": "Hou-T-Y", "role": "member", "display_name": "Hou, Thomas Y." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/PW4M-9B73", "abstract": "This work focuses on the applications in dynamics of recently developed continuum-mechanical models of solid-solid phase transitions. The dynamical problems considered here involve only one space coordinate, and attention is limited to hyperelastic materials that involve two phases. This investigation has two purposes. The first is to determine the predictions of the models in complicated situations. Secondly, the present study attempts to develop analytical and numerical approaches to problems that may be relevant to the interpretation and understanding of experiments involving phase transitions under dynamical conditions.
\r\n\r\nThe first problem studied involves the study of a semi-infinite bar initially in an equilibrium state that involves two material phases separated by a phase boundary at a given location. The end of the bar is suddenly subject to a constant impact velocity that persists for a finite time and is then removed. Interaction between the phase boundary and the elastic waves generated by the impact and subsequent reflections are studied in detail, and the trajectory of the phase boundary is determined exactly. The second task addressed involves the development of a Riemann solver to be applied to the numerical solution of Riemann problems for two-phase elastic materials. Riemann problems for such materials involve complications not present in the corresponding problems that arise, for example, in classical gas dynamics. Finally, a finite-difference method of Godunov type is developed for the numerical treatment of boundary-initial-value problems arising in the model of Abeyaratne and Knowles. The method is applied to specific problems.
" }, { "name": "Zhou, Jianhui", "degree": "PhD", "year": "1995", "title": "Four-wave mixing in semiconductor optical amplifiers for terahertz spectroscopy and wavelength conversion", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09082005-105846", "creators": [ { "name": { "family": "Zhou", "given": "Jianhui" }, "id": "Zhou-Jian", "display_name": "Zhou, Jianhui" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/vmke-sz45", "abstract": "Four-wave mixing in semiconductor gain media from GHz to THz detuning rates was used as a frequency-domain technique for analysis of carrier relaxation mechanisms having relaxation times extending from nanosecond to femtosecond time scales. Measurements of four-wave mixing in various semiconductor traveling-wave amplifiers were performed for detuning frequencies as large as 1.7 THz. Ultrafast intraband mechanisms having relaxation time constants of 650 fs, in agreement with dynamic carrier heating, and of less than 100 fs, in agreement with intraband carrier-carrier scattering, were determined in the measurements.\r\n\r\nA novel cross-polarized four-wave mixing technique was also developed to study the inter quantum well carrier transport process in quantum well amplifiers. A semiconductor optical amplifier having a structure of alternating tensile and compressively strained quantum wells was used. Polarization selection rule of the strained quantum wells enables selective excitation and probing of adjacent quantum wells according to polarization, thereby enabling study of inter-well carrier transport. A one-dimensional diffusion model was developed to illustrate the different transport efficiencies for carrier number and temperature modulations, thereby qualitatively explaining the experimental data. The inter-well carrier number transport rate in the device measured was determined to be greater than 100 GHz.\r\n\r\nFour-wave mixing in semiconductor optical amplifiers was also studied as a wavelength conversion technique. Conversion efficiency over spans up to 65 nm was measured, and wavelength conversion with gain was also demonstrated. It was found theoretically and confirmed experimentally that the conversion efficiency varies with the cube of the saturated amplifier gain. Noise characteristics of four-wave mixing wavelength converters and their dependence on various device and operational parameters were also studied. Noise reduction by introducing a filter between the preamplifier and the mixer was demonstrated and significant noise reduction was achieved. Finally, wavelength conversion of modulated signals at data rates of 2.5 Gb/s and 10 Gb/s was demonstrated." }, { "name": "Al Juhany, Khalid Ahmed Bin Talal", "degree": "PhD", "year": "1994", "title": "Supersonic Film Cooling Including the Effect of Shock Wave Interaction", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112007-084103", "creators": [ { "name": { "family": "Al Juhany", "given": "Khalid Ahmed Bin Talal" }, "id": "Al-Juhany-Khalid-Ahmed-Bin-Talal", "display_name": "Al Juhany, Khalid Ahmed Bin Talal" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7ry6-fy87", "abstract": "The current work is an investigation of supersonic film cooling effectiveness including interactions with a two-dimensional shock wave. Air and helium, which are either heated or cooled, are injected at Mach numbers between 1.2 and 2.2 into a Mach 2.4 air freestream. The adiabatic wall temperature is measured directly. The injection velocity and mass flux are varied by changing the total temperature and Mach number while maintaining matched pressure conditions.
\r\n\r\nHeated injection, with the injectant to freestream velocity ratios greater than 1, exhibit a rise in wall temperature downstream of the slot yielding effectiveness values greater than one. The temperature rise, which also occurs for cooled injection, is attributed to the merging of the injectant boundary layer and the lip-wake. As a result comparisons between heated and cooled injection may not be valid. With the exception of heated helium runs, larger injection Mach numbers slightly increase the effective cooling length per mass injection rate. The results for helium injection indicate an increase in effectiveness as compared to that for air injection. The experimental results are compared with studies in the literature.
\r\n\r\nFlow profiles at several axial locations, up to 90 slot heights, indicate that for the same Mach number the helium injections induce a larger wake and a thicker boundary layer than air injection.
\r\n\r\nThe influence of the shock impingement on the recovery temperature is not large if the flow remains attached. Once separation occurs the temperature changes drastically with downstream distance. The shock strength for incipient separation is smaller when helium is injected than when no film coolant is present. However, the converse is true with air injection even though, for the same Mach number, the momentum flux for the air injection is less than that for the helium injection. The induced separation in the case of helium is attributed to the reduced fullness of its momentum flux profile prior to interaction. This research demonstrates how the performance of supersonic film cooling for thermal control is undermined by the susceptibility to shock induced separation, and raises concerns about hydrogen film cooling for N.A.S.P.
" }, { "name": "Antsos, Dimitrios", "degree": "PhD", "year": "1994", "title": "Computer-aided modeling and analysis of passive microwave and millimeter-wave high-temperature superconductor circuits and components", "advisor": "Posner, Edward C.; McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122007-135636", "creators": [ { "name": { "family": "Antsos", "given": "Dimitrios" }, "id": "Antsos-D", "display_name": "Antsos, Dimitrios" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "chair", "display_name": "Posner, Edward C." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/fb3q-7f74", "abstract": "As their critical temperatures continue to rise, high-temperature superconductors (HTS) promise applications in microwave, and to some extent in millimeter-wave circuits, because they should exhibit lower loss, in these frequencies, than their normal metal counterparts. However, in the case of passive circuits, fundamental performance limits (finite insertion loss) still exist and apply, as explored in this thesis.\n\nCommercial computer-aided design (CAD) and analysis software tools exist, that permit design and analysis of normal metal microwave and millimeter-wave circuits. These tools minimize design and manufacturing errors and the need for costly re-work and design iterations. In the case of HTS circuits these tools are insufficient because of three effects present in HTS circuits that do not exist in normal metal circuits. First, because of manufacturing practices, the HTS layers on substrates are usually very thin; of the order of the magnetic field penetration depth. Second, there is an additional internal inductance, the kinetic inductance, which is due to the inertia of the superelectrons. Third, high input power induces high magnetic fields and current densities which drive the superconductor into its normal state, in which it is an insulator.\n\nThis thesis is a study of these phenomena and their effects on quasi-TEM transmission line circuit performance. Methods for accounting for these effects and introducing them into currently available CAD tools are presented. These methods are applied to three example circuits for which modeled and measured performance is compared.\n\nThe viability and advantages of HTS waveguides are also studied and analyzed. A finite difference analysis program is presented." }, { "name": "Bhattacharyya, Abhijit", "degree": "PhD", "year": "1994", "title": "Internal flows and force matrices in axial flow inducers", "advisor": "Acosta, Allan J.; Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012005-141633", "creators": [ { "name": { "family": "Bhattacharyya", "given": "Abhijit" }, "id": "Bhattacharyya-A", "display_name": "Bhattacharyya, Abhijit" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Q4ST-4X32", "abstract": "Axial flow pump runners known as inducers are subject to complex internal flows and fluid-induced lateral and rotordynamic forces. The internal flows in inducers are three dimensional and are characterized by complicated secondary flows. The current research investigates the boundary layer flows on the blades, hub and housing of unshrouded and shrouded axial flow inducers using flow visualization techniques. Rotordynamic and lateral force data on unshrouded inducers were also obtained under varying conditions of flow and whirl.\n\nStudies on the internal flows showed that the blade boundary layer flow had strong radial components at off-design conditions. The flow remains attached to the blade surface of unshrouded inducers at all flow coefficients tested. The origin of the upstream swirling backflow was found to be at the discharge plane of the inducer. In addition, flow reversal was observed at the suction side blade tip near the leading edge in a shrouded inducer. Re-entry of the hub boundary layer flow (a downstream backflow) into the blade passage area was observed at flow coefficients below design. For unshrouded inducers the radially outward flow near the blade tip mixed with the tip clearance leakage flow to form the upstream backflow. These observations provide a better understanding of the internal flows and the occurrence of upstream backflows in inducers.\n\nThe rotordynamic forces acting on an inducer due to an imposed whirl motion was also investigated. It was found that the rotordynamic force data at various whirl frequency ratios does not allow a normal quadratic fit; consequently the conventional inertial, stiffness and damping coefficients cannot be obtained and a definite whirl ratio describing the instability region does not result. Rotordynamic forces were found to be significantly dependent on the flow coefficient. At flow coefficients below design, these forces are characterized by multiple zero crossings at various whirl frequencies and large destabilizing peeks. Theoretical estimates of the tangential rotordynamic force on a non-whirling inducer using actuator disk theory were significantly different, both in magnitude and direction, from the experimentally measured forces.\n\nThe effect of upstream and downstream flow distortions on the rotordynamic and lateral forces on an inducer were studied. It was found that at flow coefficients below design, large lateral forces occurred in the presence of a downstream asymmetry. The reverse flows occurring downstream which consist of high energy fluid are the possible cause of these large forces. The imposition of a uniform downstream condition reduced these forces to near zero values. Results of inlet distortion experiments show that a strong inlet shear causes a significant increase in the lateral force. However, weak inlet shear flows and the flow asymmetry due to a 180\u00b0 upstream bend did not cause a significant lateral force. It was found that flow distortions upstream or downstream did not cause any significant effect on the rotordynamic forces. Cavitation was found to have important consequences for fluid-induced rotordynamic forces. These forces become destabilizing for both forward and reverse whirl. The magnitudes of the destabilizing forces were found to increase with decreasing cavitation numbers.\n" }, { "name": "Brkovic, Milivoje Slobodan", "degree": "PhD", "year": "1994", "title": "Switching converters with magnetic amplifiers as controllable switches : I: Soft-switching converters. II: Input current shaping", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042007-133110", "creators": [ { "name": { "family": "Brkovic", "given": "Milivoje Slobodan" }, "id": "Brkovic-M-S", "display_name": "Brkovic, Milivoje Slobodan" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "co-advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/y716-bs43", "abstract": "Part I:\nNovel soft-switching converters combine the functions of loss-less soft-switching for all switches and secondary side output voltage regulation at constant switching frequency. This was made possible by using magnetic amplifiers in series with the rectifier diodes in \nthe symmetrical topologies. The primary side switches are driven at constant frequency and near 50% duty ratio with small dead-time and the output voltage is regulated by pulse width modulation (PWM) control on the secondary side.\n\nAll three soft-switching topologies, half-bridge, full-bridge and push-pull, are analyzed. It was found that the multiple-output extension of these converter do not have some serious adverse effects inherent to their parent PWM converters with magnetic amplifier post-regulators.\n\nExperimental results obtained on two different prototypes confirm the key advantages of the proposed soft-switching converters.\n\nPart II:\n\nTwo classes of automatic current shapers are analyzed, with external and internal capacitive energy storage.\n\nThe Cuk converter with Integrated Magnetics when operated in DICM with external energy storage exhibits advantages over other automatic current shaper topologies. Unity power factor is provided automatically and by using \"ripple steering\" mechanism essentially zero input and output current ripples are obtained for all operating conditions. Consequently, the size of the magnetics can be significantly reduced even at very modest switching frequencies.\n\nThe requirement for fast output regulation implies that low-frequency energy is stored internally in the input current shaper. A new AC-to-DC converter which combines the functions of automatic current shaping, fast output voltage regulation, and loss-less soft-switching in a single converter is proposed. This was made possible through internal energy storage and discovery of the new modes of operation, which together, effectively decoupled the input boost-like part of the Cuk converter from its buck-like output. In order to keep the voltage stress on the switches low, the variable frequency control is required in addition to PWM control.\n\nAnother novel class of single stage AC-to-DC converters with unity power factor and fast output regulation is also proposed. These converters use a magnetic amplifier for the input current shaping, while the active switch is used for fast output regulation. By using \ncore material for magnetic amplifiers with high saturated permeability, and operating the input stage of the converter in DICM, the linear input inductance can be replaced by the saturated inductance of the magnetic amplifier. Thus, the magnetic amplifier combines the functions of a controllable switch and a linear inductor into a single device.\n\nThe proposed method of current shaping with magnetic amplifiers is extended to the full-bridge topologies with their input, boost-like stage operated in continuous conduction mode. \n\nExperimental results obtained on different prototypes confirm advantages of the proposed topologies." }, { "name": "Buntine, James D.", "degree": "PhD", "year": "1994", "title": "Part I: Inviscid, swirling flows and vortex breakdown. Part II: A numerical investigation of the Lundgren turbulence model", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-082716", "creators": [ { "name": { "family": "Buntine", "given": "James D." }, "id": "Buntine-J-D", "display_name": "Buntine, James D." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/5rah-r125", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAbstract for part I\r\n\r\nA study of the behaviour of an inviscid, swirling fluid is performed. This flow can be described by the Squire-Long equation if the constraints of time-independence and axisymmetry are invoked. The particular case of flow through a diverging pipe is selected and a study is conducted to determine over what range of parameters (both pipe inlet conditions and geometry) does a (unique) solution exist. The work is performed with a view to understanding how the phenomenon of vortex breakdown develops. Experiments and previous numerical studies have indicated that the flow is sensitive to boundary conditions particularly at the pipe inlet. A \"quasi-cylindrical\" simplification of the Squire-Long equation is compared with the more complete model and shown to be able to account for most of its behaviour. An advantage of this latter representation is the relatively undetailed description of the flow geometry it requires in order to calculate a solution.\r\n\r\n\"Criticality\" or the ability of small disturbances to propagate upstream is related to results of the quasi-cylindrical and axisymmetric flow models. This leads to an examination of claims made by researchers such as Benjamin and Hall concerning the interrelationship between \"failure\" of the quasi-cylindrical model and the occurrence of a \"critical\" flow state. Other criteria for predicting the onset of vortex breakdown are considered in the context of the model employed, particularly those of Brown & Lopez and Spall, Gatski & Grosch.\r\n\r\nAbstract for part II\r\n\r\nLundgren (1982) developed an analytical model for homogeneous turbulence based on a collection of contracting spiral vortices each embedded in an axisymmetric strain field. Using asymptotic approximations he was able to deduce the Kolmogorov [...] behaviour for inertial scales in the turbulence energy spectrum. Pullin & Saffman have enlarged upon his work to make a number of predictions about the behaviour of turbulence described by the model. This work investigates the model numerically. The first part considers how the flow description compares with numerical simulations using the Navier-Stokes equations. Integration of the full expressions proposed by Lundgren for the energy spectrum is also performed to determine how the various parameters available affect the behaviour and validity of the result." }, { "name": "Cauwenberghs, Gert", "degree": "PhD", "year": "1994", "title": "Analog VLSI Autonomous Systems for Learning and Optimization", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192005-081338", "creators": [ { "name": { "family": "Cauwenberghs", "given": "Gert" }, "id": "Cauwenberghs-Gert", "display_name": "Cauwenberghs, Gert" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Baldi", "given": "Pierre" }, "id": "Baldi-Pierre", "role": "member", "display_name": "Baldi, Pierre" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CW78-8H63", "abstract": "The integration of adaptive functions within analog neural hardware, while certainly promising to enhance system performance, has for long been hindered by technological difficulties due to the complexity and sensitivity of standard adaptive algorithms. We present a general framework for self-contained adaptation in analog VLSI supporting a broad class of supervised learning and optimization tasks, which largely alleviates the implementation problems by virtue of a robust system approach exploiting statistics and redundancy in stochastic processes. Specifically, the framework includes: i) a perturbative algorithm based on stochastic approximation to optimize a set of parameters in an arbitrary deterministic system, these parameters being adjusted according to global performance evaluations rather than using explicit knowledge about the internal structure of the system; and ii) a scalable and modular CMOS architecture that implements this algorithm, and that additionally provides for embedded long-term dynamic storage of the volatile analog parameter values, quantized locally and refreshed autonomously on capacitors with direct external access in both digital and analog formats. We analyze the convergence and scaling properties of the stochastic algorithm, present on-line versions of the algorithm for supervised learning in dynamical systems, and provide experimental results demonstrating real-time trajectory learning on an analog CMOS chip containing a network of six fully recurrent dynamical neurons. We also include results demonstrating robust long-term retention of locally stored volatile information in analog VLSI using the autonomous refresh technique." }, { "name": "Cetin, Bedri Cag", "degree": "PhD", "year": "1994", "title": "TRUST : a new global optimization methodology, application to artificial neural networks, and analog VLSI implementation", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192005-153248", "creators": [ { "name": { "family": "Cetin", "given": "Bedri Cag" }, "id": "Cetin-B-C", "display_name": "Cetin, Bedri Cag" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/gf87-7y12", "abstract": "A new method for unconstrained global function optimization, acronymed TRUST, is introduced. This method formulates optimization as the solution of a deterministic dynamical system incorporating terminal repellers and a novel subenergy tunneling function. Benchmark tests comparing this method to other global optimization procedures are presented, and the TRUST algorithm is shown to be substantially faster.\n\nThis algorithm is provably convergent to the global minimum for objective functions of one variable. Theoretically, convergence to a global solution is not guaranteed in the multi-dimensional case. However, in practical applications, TRUST has found the global minimum in all multi-dimensional benchmark functions as a result of its global descent property. The TRUST formulation leads to a simple stopping criterion.\n\nThe algorithm is also applied to Backpropagation learning in artificial neural networks in order to overcome the susceptibility to local minima during training, which is associated with gradient descent. TRUST (or Global Descent in this context) was proposed as a candidate for replacing gradient descent in order to eliminate the local minima problem. We test the ability of the new dynamical system to overcome local minima with common benchmark examples and a pattern recognition example. The results demonstrate that the new method does indeed escape encountered local minima, and in most cases converges to the globally optimal solution of a specific problem.\n\nThe structure of the TRUST's equations enables an implementation of the algorithm in analog VLSI hardware for further substantial speed enhancement. We have designed, fabricated and tested a terminal repeller circuit and a gradient descent circuit, which constitute the main components of the TRUST's dynamics. Measured chip data, which confirmed the efficient performance of these circuits, are presented. We have also designed a novel global optimization circuit which incorporates the above circuits with additional control logic. This circuit implements the TRUST algorithm, and thus locates the global minimum of arbitrary one-dimensional objective functions. Simulated experiments of this circuit are thoroughly discussed. The convergence time required for the circuit to converge to the global minimum is remarkably at the order of micro-seconds." }, { "name": "Chen, I-Ming", "degree": "PhD", "year": "1994", "title": "Theory and Applications of Modular Reconfigurable Robotic Systems", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-10202005-090745", "creators": [ { "name": { "family": "Chen", "given": "I-Ming" }, "id": "Chen-I-Ming", "orcid": "0000-0002-4831-3781", "display_name": "Chen, I-Ming" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Rodriguez", "given": "Guillermo" }, "id": "Rodriguez-G", "role": "member", "display_name": "Rodriguez, Guillermo" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "mecheng" ], "doi": "10.7907/2AAA-RY45", "abstract": "A modular reconfigurable robotic system consists of various link and joint units with standardized connecting interfaces that can be easily separated and reassembled into different configurations. Compared to a fixed configuration robot, which is usually a compromised design for a limited set of tasks, a modular robot can accomplish a large class of tasks through reconfiguration of a small inventory of modules. This thesis studies how to find an optimal module assembly configuration constructed from a given inventory of module components for a specific task. A set of generalized module models that bear features found in many real implementations is introduced. The modular robot assembly configuration is represented by a novel Assembly Incidence Matrix (AIM). Equivalence relations based on module geometry symmetries and graph isomorphisms are defined on the AIMs. An enumeration algorithm to generate non-isomorphic assembly configurations based on this equivalence relation is proposed. Examples demonstrate that this method is a significant improvement over a brute force enumeration process. Configuration independent kinematic models for modular robots are developed, and they are essential for solving the task-optimal configuration problem. A task-oriented objective function is defined on the set of non-isomorphic module assembly configurations. Task requirements and kinematic constraints on the robot assembly are treated as parameters to this objective function. The task-optimal configuration problem is formulated as a combinatorial optimization problem to which genetic algorithms are employed for solutions. Examples of finding task-optimal serial revolute-jointed robot configurations are demonstrated. In addition, the applications of modular robots to planning multifinger grasping and manipulation are developed. Planning two-finger grasps is done through finding antipodal point grasps on smooth shaped objects. Planning n-finger grasps is achieved by defining a qualitative force-closure test function on the n-finger grasps on an object. Applications of this test function to manipulation task and finger gaiting are illustrated." }, { "name": "Conley, Andrew", "degree": "PhD", "year": "1994", "title": "New plane shear flows", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-102648", "creators": [ { "name": { "family": "Conley", "given": "Andrew" }, "id": "Conley-A", "display_name": "Conley, Andrew" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "chair", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/T34K-J848", "abstract": "A classical problem in fluid dynamics is the study of the stability of plane Couette flow. This flow experimentally sustains turbulence for Reynolds numbers greater than 1440\u00b140 (see [10],[5]). (The Reynolds number is based on channel width and wall velocity difference). Since plane Couette flow is linearly stable for all Reynolds numbers, obtaining non-trivial mathematical solutions to the plane Couette flow equations is difficult. However, M. Nagata [6] finds a non-trivial numerical solution of the plane Couette flow equations at low Reynolds number. We confirm these solutions. We compute the minimum Reynolds number at which they exist. We study their stability. We also study the effect of a Coriolis force on plane Poiseuille flow.\n" }, { "name": "Curtis, Kevin R.", "degree": "PhD", "year": "1994", "title": "3-D photopolymer disks for correlation and data storage, and cross-talk in volume holographic memories", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-155528", "creators": [ { "name": { "family": "Curtis", "given": "Kevin R." }, "id": "Curtis-K-R", "display_name": "Curtis, Kevin R." } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "member", "display_name": "Grubbs, Robert H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/6FK7-Z369", "abstract": "This thesis considers the optical storage and processing of data using volume holography. First, cross-talk noise due to geometrical considerations is calculated for volume holographic memories. Cross-talk is due to energy diffracted from non-Bragg matched gratings. The SNR (signal-to-noise-ratio) of holographic memories due to cross-talk noise is calculated for Fourier transform holograms stored by angle, wavelength, phase-coded, and rotational multiplexing methods. Considerations include page size, geometry, angular bandwidth of the optical system, wavelength of the light used, material size, spatial light modulator (SLM) contrast, and the phase of the image plane. The SNR for angle multiplexed image plane holograms is also calculated and compared to the results for Fourier transformed angle multiplexed holograms. A comparison of the various multiplexing methods based on cross-talk is presented, and then the effect of geometry and material dynamic range is included to determine when cross-talk will be the dominant noise source. The use of photopolymers as a holographic element is then presented. The recording characteristics of the DuPont photopolymer are described and a method of multiplexing multiple holograms in the photopolymer is given. A new method for multiplexing holograms (called peristrophic multiplexing) is described. This method significantly increases the storage capacity of thin films. After this, a 3-D disk-based correlator and storage device using the photopolymer is described and demonstrated. In this device, holograms are multiplexed at a given spot and then disk rotation/head motion are used to access multiple spots on the disk. Theoretical correlation speed, read-out rates, and the storage capacity of the 3-D disk as limited by geometry and laser power are given.\n" }, { "name": "Duong, Cong N.", "degree": "PhD", "year": "1994", "title": "A nonlinear thermoviscoelastic stress and fracture analysis of an adhesive bond", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-153006", "creators": [ { "name": { "family": "Duong", "given": "Cong N." }, "id": "Duong-C-N", "display_name": "Duong, Cong N." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/3HF2-K703", "abstract": "The evolution of residual stresses resulting from cooling an adhesive bond configuration on its lateral surfaces at a constant rate through the glass transition of the polymer are considered. A nonlinear, viscoelastic (free-volume) model serves for the thermoviscoelastic characterization of the polymer. The simultaneous solution to the heat diffusion and the transient thermoviscoelatic problems are addressed. Both an infinite (one-dimensional) and a finite (two-dimensional) domain are studied. A \"critical\" cooling time exists, in the present case on the order of a few seconds, which separates the control of the solidification process according to whether the relaxation or thermal diffusion time scale governs. The short time \"quenching process,\" i.e., when the time scale is governed by thermal diffusion, leads to essentially constant residual stresses. Slower cooling increasingly invokes the time and rate sensitive properties of the polymer and leads to monotically decreasing residual stresses with longer cooling times. To reduce residual stresses by a factor of two from their maximal values requires cooling times on the order of one or two days. These results are not drastically altered by changes in the thicknesses of the bond components. Apart from singular behavior of the stress components in the two-dimensionally finite domain \"quenching\" has the effect of producing significantly different stress distributions (including stress \"spikes\") than slow or thermoelastic analyses would suggest. This observation is attributed to the interaction of the bending response of the metal components early in the cooling history under the high thermal gradients, which deformations are then partially frozen in during the subsequent cooling of the polymer. Implications of these results for systems possessing geometric and material differences subjected to various thermal cooling ranges are also discussed. The results demonstrate the importance of knowing the bulk relaxation or creep spectrum for the polymer.\n\nIn the second part of the thesis the effect of the residual stresses on fracture behavior of an adhesive bond are addressed within the context of linear fracture mechanics for dissimilar materials. The crack faces are found to be in contact at the fractured end during the (residually stress) unloading process. A significantly error results if this contact zone is not taken into account. The combined effect of the mechanical loads and the residual stresses on the energy release rate is also studied. The total energy release rate from the combined effect is not necessarily higher or equal to the sum of the individual contribution from external loads and from residual stresses separately.\n" }, { "name": "Edwards, David A.", "degree": "PhD", "year": "1994", "title": "A model for nonlinear diffusion in polymers", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09092005-155000", "creators": [ { "name": { "family": "Edwards", "given": "David A." }, "id": "Edwards-D-A", "display_name": "Edwards, David A." } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/45KS-DN62", "abstract": "In certain polymer-penetrant sytems, the effects of Fickian diffusion are augmented by nonlinear viscoelastic behavior. Consequently, such systems often exhibit concentration fronts unlike those seen in classical Fickian systems. These fronts not only are sharper than in standard systems, but also they propagate at speeds other than that typical of Fickian diffusion. A model is presented which replicates such behavior. This model is reduced to a moving boundary-value problem where the boundary separates the polymer into two distinct states: glassy and rubbery, in each of which different physical processes dominate. An unusual condition at the moving interface, which arises from the inclusion of a viscoelastic memory term, is not solvable by similarity solutions, but can be solved by integral equation techniques. Perturbation methods are used to obtain asymptotic solutions for differing strengths of molecular diffusion and viscoelastic stress. These solutions are characterized by sharp fronts which move with constant speed; the asymptotic solutions mimic those found experimentally in polymer-penetrant systems." }, { "name": "Eldering, Annmarie", "degree": "PhD", "year": "1994", "title": "Alternative Models for Air Pollutant Effects on Visibility", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092004-141937", "creators": [ { "name": { "family": "Eldering", "given": "Annmarie" }, "id": "Eldering-Annmarie", "orcid": "0000-0003-1080-9922", "display_name": "Eldering, Annmarie" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Palfrey", "given": "Thomas R." }, "id": "Palfrey-T-R", "role": "member", "display_name": "Palfrey, Thomas R." } ], "option_major": [ "envreng" ], "doi": "10.7907/502K-HY92", "abstract": "Air pollution causes visibility reduction in urban areas such as Los Angeles as well as in national parks and wilderness areas. In this work, alternative mathematical models are formulated that relate air pollutant emissions or ambient air pollutant concentrations to visual range or to changes in the appearance of a scenic vista.
\r\n\r\nThe first model examined connects continuous measurements of airborne particle size distributions to resulting effects on visibility via Mie scattering calculations. The model is tested by application to data taken during the 1987 Southern California Air Quality study. The time series of measured light scattering coefficient values is reproduced well when redundant nephelometer measurements are available to assure that the measured light scattering coefficient values are not in doubt.
\r\n\r\nA source-oriented model for air pollutant effects on visibility next is assembled that computes light scattering directly from data on gas-phase and primary particle-phase air pollutant emissions from sources. Airborne particle mass concentrations are predicted accurately. The model predictions generally match the measured aerosol size distribution and chemical composition. Good agreement is attained between model predictions and measurements of atmospheric light scattering coefficient values.
\r\n\r\nAn image processing-based visibility model is presented that displays model calculations as synthetic color photographs having the appearance of a smog event. Beginning with a digitized clear day photograph of the scene of interest, a theoretically based model for light scattering and absorption is used to recalculate sky color and skylight addition between the observer and objects in the field of view in order to predict the appearance of the scene in the presence of heavy smog. Model verification data are collected experimentally, including photographs of chosen vistas and measurements of the atmospheric aerosol chemical composition and size distribution. The model performs well, producing representations of the sky color and objects in the field of view that are close to those seen in actual photographs. This model also is adapted to begin with data on landscape features taken from earth-orbiting satellites combined with digital terrain elevation data, such that the model could be applied on a global scale.
" }, { "name": "Eylers, Hinrich", "degree": "PhD", "year": "1994", "title": "Transport of adsorbing metal ions between stream water and sediment bed in a laboratory flume", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-135501", "creators": [ { "name": { "family": "Eylers", "given": "Hinrich" }, "id": "Eylers-H", "display_name": "Eylers, Hinrich" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "List", "given": "John A." }, "id": "List-J-A", "role": "member", "display_name": "List, John A." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/ZATX-S424", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe transport of adsorbing metal ions (copper, zinc, calcium and magnesium) between the water column and the sand bed in a 5 meter long recirculating laboratory flume with bottom bedforms has been investigated. A non-adsorbing tracer, lithium, was used simultaneously to observe the exchange of water between bed and water column. The presence of bedforms and associated pumping increases the exchange rate by several orders of magnitude over molecular processes.\r\n\r\nThe concentrations of initially added metal ions were monitored both in the circulating overlying water and in the pore-water of the sediment bed. The sand used for the bed was composed of over 99% silica, with geometric means of 500 [...] and 195 [...]. Before each run, the sand was acid-washed at pH 3.5 to provide reproducible experimental conditions. The chemical composition of the recirculating water was controlled and steady flow conditions were maintained in the experiments.\r\n\r\nBatch experiments were performed to investigate the chemical partitioning of the selected metal ions to the sand grain surfaces. The adsorption of zinc onto silica was modeled in detail and binding constants were determined. The observed adsorption of the metal ions in the flume experiments compared well with batch adsorption data.\r\n\r\nThe transfer of metal ions into and out of a bed covered with stationary bedforms is dominated by advective pumping caused by pressure fluctuations over the bed. A residence-time model based on pressure-driven advective flow and linear equilibrium partitioning of the pollutant to the sediment was developed and describes the observed metal ion exchange between sediment and water column well. Increased partitioning of the metal ion onto the sediment leads to an increase of the amount of tracer stored within the sediment bed. Furthermore, the concentrations of metal ions released from the bed after passing of an initial pulse in the overlying water will be lower, but longer lasting for stronger partitioning, leading to tailing in the water column for long times.\r\n\r\nFor a bed with moving bedforms, the main mechanism for mass exchange is the trapping and release of overlying water by the traveling bedform. The transport of metal ions can be approximately described for the initial phase of the experiment, but large deviations from the model occur for long times.\r\n\r\nThe models do not require calibration since the parameters for transport into and out of the bed can be derived from flow conditions, sediment parameters, bedform dimensions and adsorption characteristics of the tracer on the sand. Criteria for the applicability of the models and appropriate scaling variables are identified. The experimental results are presented in nondimensional form." }, { "name": "Gao, Zheng-Quiang", "degree": "PhD", "year": "1994", "title": "The kinetics of ordering, grain growth and chemical segregation in nonequilibrium Fe3X alloys (X=Al, Si and Ge)", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092005-084814", "creators": [ { "name": { "family": "Gao", "given": "Zheng-Quiang" }, "id": "Gao-Zheng-Quiang", "display_name": "Gao, Zheng-Quiang" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/d93x-xn03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperimental studies on the kinetics of microstructural evolution in highly nonequilibrium Fe3X based alloys (X = Al, Si and Ge) are the topic of this dissertation research. The kinetics of ordering especially, and other processes of microstructural evolution including grain growth and chemical segregation, were studied.\r\n \r\nMaterials far from their states of thermodynamic equilibrium were first prepared by rapid quenching and ball milling methods. Heat treatments at relatively low temperatures were used to allow the alloy microstructure to evolve towards equilibrium. Mossbauer spectroscopy was used heavily for measuring short range ordering, but X-ray diffractometry and transmission electron microscopy were also used extensively for microstructural characterization.\r\n \r\nThe initial states of the Fe3X (X = Al, Si and Ge) binary alloys were chemically disordered bcc polycrystals (nearly random solid solution). Kinetics of disorder -> order transformations were studied by plotting the kinetic paths through the space spanned by two order parameters. The kinetic paths for Fe3Al showed a strong temperature dependence, but no temperature dependence was observed for kinetic paths of Fe3Si and Fe3Ge. A thermodynamically unexpected transient B32 ordered structure was observed in the early stages of ordering in Fe3Al annealed at 300[degrees]C.\r\n\r\nThe kinetics of microstructural evolution, especially grain growth was also studied on nanocrystalline [...] alloys. The Nb atoms were first forced into solid solution in bcc Fe-Si by ball milling. Upon annealing, Nb atoms segregated to grain boundaries, and impeded grain growth. The inter-dependence of grain growth, chemical segregation and chemical ordering was studied. A better understanding of such kinetics, we believe, can be an important step towards the controlled synthesis of new nonequilibrium materials." }, { "name": "Germain, Patrick", "degree": "PhD", "year": "1994", "title": "The boundary layer on a sharp cone in high-enthalpy flow", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-112714", "creators": [ { "name": { "family": "Germain", "given": "Patrick" }, "id": "Germain-P", "display_name": "Germain, Patrick" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/hfje-z896", "abstract": "An exploratory study of the laminar, transitional and turbulent boundary layer on a 5 deg. half-angle cone in hypervelocity flow was conducted in the high-enthalpy shock tunnel T5 by measurement of the heat flux distribution and by qualitative flow visualization. A novel flow visualization technique using sodium seeding to increase the sensitivity of conventional interferometric techniques by resonant enhancement of the refractivity of the medium was developed to study the boundary layer structure. The experiments were designed to cover a large range of specific reservoir enthalpy, ranging from the perfect-gas regime to the range where significant oxygen and some nitrogen dissociation and recombination effects may be expected in the boundary layer. The presence of atomic species is due to the combined effect of nozzle freezing and frictional heating in the boundary layer. In the laminar regime and in the latter range, the following effects were found to be present: At the same nominal conditions, heat flux levels are higher in air than in nitrogen because of a larger heat release from oxygen recombination at the wall. By varying the reservoir specific enthalpy in air and nitrogen, and from measurements in carbon dioxide, it was found that real-gas effects stabilize the boundary layer. If the transition Reynolds number is renormalized by evaluating it at the reference temperature, the data for a given gas becomes correlated in a plot against reservoir enthalpy. Increasing enthalpy stabilizes the flow. The stabilizing effect is stronger with gases whose lowest activation energy is low. This behavior is opposite to the prediction made by the linear stability theory regarding the second linear mode of instability. The linear stability theory predicts, however, that real-gas effects stabilize the Tollmien-Schlichting mode. Flow visualization results suggest that the dominant instability mode in the present experiments was the Tollmien-Schlichting mode. Finally, the flow visualization pictures show structures that are not qualitatively different from those of an incompressible turbulent boundary layer, but they do not indicate if real-gas effects change significantly the structure of the turbulent boundary layer. The heat transfer measurements compare well with semi-empirical predictions." }, { "name": "Greenspan, Hayit", "degree": "PhD", "year": "1994", "title": "Multi-resolution image processing and learning for texture recognition and image enhancement", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192005-104013", "creators": [ { "name": { "family": "Greenspan", "given": "Hayit" }, "id": "Greenspan-Hayit", "display_name": "Greenspan, Hayit" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Anderson", "given": "Charles Hammond" }, "id": "Anderson-C-H", "role": "member", "display_name": "Anderson, Charles Hammond" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "eleceng" ], "doi": "10.7907/KR83-J714", "abstract": "A general recognition framework is presented that consists of multi-resolution pyramidal feature-extraction and learning paradigms for classification. The system is presented in the context of the texture recognition task.\r\n\r\nIn the feature extraction part of the system, an oriented Laplacian pyramid is used as an efficient filtering scheme to transform the input image to a more robust representation in the frequency and orientation space. An optimal technique is presented for computing a steerable representation of the pyramid. Steerability is used to generate a rotation-invariant input representation.\r\n\r\nIn the learning stage of the system we focus on a rule-based probabilistic learning scheme. This information-theoretic technique is utilized to find the most informative correlations between the attributes and the output classes while producing probability estimates for the outputs. Both unsupervised and supervised learning are utilized. Apart from the rule-based approach we experiment with other non-parametric classifiers, such as the k-nearest neighbor classifier and the Backprop neural-network.\r\n\r\nWe demonstrate experimentally that our scheme improves significantly upon the state-of-the-art both in rotation-invariant classification and in orientation estimation. A variety of applications are presented, including autonomous navigation scenarios and remote-sensing, as possible extensions for the texture recognition system. A generalization of the system to face-recognition is discussed.\r\n\r\nIn the latter part of the thesis, a procedure for creating images with higher resolution than the sampling rate would allow is described. The enhancement algorithm augments the frequency content of the image by using a non-linearity that generates phase-coherent higher harmonics. The procedure utilizes the Laplacian pyramid image representation. Results are presented depicting the power-spectra augmentation and the visual enhancement of several images. Simplicity of computations and ease of implementation allow for real-time applications such as high-definition television (HDTV). An initial investigation is pursued to combine the enhancement scheme with pyramid coding schemes." }, { "name": "Hacker, Jonathan Bruce", "degree": "PhD", "year": "1994", "title": "Grid mixers and power grid oscillators", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302007-145419", "creators": [ { "name": { "family": "Hacker", "given": "Jonathan Bruce" }, "id": "Hacker-J-B", "display_name": "Hacker, Jonathan Bruce" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/fekf-qz14", "abstract": "Power-combining schemes involving planar grids of solid-state devices quasi-optically coupled in free space are an efficient means of combining power at microwave and millimeter-wave frequencies. The quasi-optical coupling of these grid circuits makes them ideal for millimeter-wave and submillimeter-wave applications by eliminating waveguide sidewall losses and machining difficulties. The planar property of the grids potentially allows thousands of devices to be integrated monolithically. In this thesis, a grid mixer suitable for mixing or detecting quasi-optical signals is presented. The mixer is a planar grid structure periodically loaded with diodes. The grid mixer power handling and dynamic range scales as the number of devices in the grid. The conversion loss and noise figure of the grid are equal to that of a conventional mixer. A variation of the grid mixer, the sideband generator grid, is shown to be an efficient package for increasing the theoretical operating frequency and output power of monolithic planar diodes at terahertz frequencies. Techniques for designing power grid oscillators to produce Watt-level output powers are described. Designs and experimental results for MESFET grid oscillators operating in X-band with output powers of 0.9 W to 10.3 W are presented in detail. Methods that make use of finite-element electromagnetic solvers for analyzing grid structures of arbitrary shape are discussed." }, { "name": "Haller, Gyorgy", "degree": "PhD", "year": "1994", "title": "Multi-pulse homoclinic phenomena in resonant Hamiltonian systems", "advisor": "Wiggins, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302007-152315", "creators": [ { "name": { "family": "Haller", "given": "Gyorgy" }, "id": "Haller-G", "display_name": "Haller, Gyorgy" } ], "advisors": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "advisor", "display_name": "Wiggins, Stephen R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/dx2n-8q82", "abstract": "In this thesis we develop a global perturbation method to detect homoclinic orbits which arise in perturbations of manifolds of equilibria with a homoclinic structure in two degree-of-freedom Hamiltonian systems. Our energy-phase method gives conditions for the existence of multiple-pulse and \"jumping\" orbits asymptotic to different invariant sets within a slow manifold of the perturbed system. The perturbations we consider are either Hamiltonian or weakly dissipative, and the orbits created by these perturbations are generic in both cases. The geometric criterion we derive requires simple algebraic manipulations and detects orbits which are not amenable to Melnikov-type methods, even if those methods are combined with geometric singular perturbation theory. We apply the energy-phase method to the analysis of three-degree-of-freedom resonant Hamiltonian normal forms and prove the existence of non-exponentially small splittings of separatrices connecting invariant tori. These structures, together with double-pulse homoclinic tori, exist arbitrarily close to resonant elliptic equilibria in a class of Hamiltonian systems. As another application, we consider a two-mode truncation of the driven nonlinear Schrodinger equation and establish the existence of chaotic multiple-pulse \"jumping orbits\" which can be arranged in a fractal structure. We confirm the predictions of the energy-phase method by numerical simulation and visualization of intersecting multipulse orbit cylinders.\n" }, { "name": "Hashim, Imran", "degree": "PhD", "year": "1994", "title": "Microstructural and magnetic properties of polycrystalline and epitaxial permalloy (Ni80Fe20) multilayered thin films", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302007-112544", "creators": [ { "name": { "family": "Hashim", "given": "Imran" }, "id": "Hashim-Imran", "display_name": "Hashim, Imran" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "matsci" ], "doi": "10.7907/X1XA-W810", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPermalloy ([...]) thin films are of great scientific and technological interest because of their unique soft magnetic properties, and applications to magnetic recording. Chapter 1 provides an introduction to magnetic and magnetotransport properties of [...] thin films, and how the film microstructure affects these properties. Chapter 2 discusses the instrumentation used for thin film fabrication, and for magnetic and structural characterization. Further details of instrumentation are discussed in Appendix A.\r\n\r\nTypically, the [...] films for magnetoresistive applications are capped with a refractory metal thin film such as Ta to prevent its oxidation and corrosion. We investigated the interdiffusion kinetics of polycrystalline Ta/[...] thin films and found that for 400 [...] T [...] 600'C, there was significant grain-boundary interdiffusion which drastically affected soft magnetic properties of [...]. In Chapter 3, we present details of the microstructural evolution of these multilayers and the subsequent effects on their magnetic properties.\r\n\r\nAn alternate method for reducing grain-boundary scattering would be to fabricate grain-boundary free epitaxial [...] films. The epitaxy of [...] on MgO, NaCl and Cu had been demonstrated by investigators as early as the 60s. However, none of these substrates are available with as good atomic flatness as Si wafers. Following reports of epitaxial growth of Cu on Si[1], we proposed using it as a seed layer for growing [...] epitaxially on Si. However, there were conflicting reports of Cu epitaxy on Si, as some investigators claimed that Cu epitaxy on Si in UHV was not possible[2]. We were able to resolve some of these controversies (see Chapter 4 for details) and thus fabricate epitaxial Ni80Fe20 films on Cu/Si.\r\n\r\nChapter 5 examines the effect of the lattice mismatch between Cu and [...] and the subsequent strain, on the soft magnetic properties of [...]. To explain these experimentally observed magnetic properties, a micromagnetic model was developed taking into account domain wall interaction with misfit dislocations and film surface roughness especially during the initial stages of epitaxial growth. Finally, epitaxial growth of [...]/Cu on Si suggests the possibility of growing grain-boundary free atomically sharp [...]/Cu multilayers which exhibit recently-discovered \"giant\" magnetoresistance.\r\n\r\n[1] C.A. Chang, Appl. Phys. Lett. 55, 2754 (1989).\r\n[2] B.P. Tonner, J. Zhang, X. Chen, Z-L. Han, G.R. Harp, and D.K. Saldin, \r\nJ. Vac. Sci. Technol. B10, 2082 (1992)." }, { "name": "Huang, Mei-Jiau", "degree": "PhD", "year": "1994", "title": "Theoretical and computational studies of isotropic homogeneous turbulence", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-06222005-133921", "creators": [ { "name": { "family": "Huang", "given": "Mei-Jiau" }, "id": "Huang-M", "display_name": "Huang, Mei-Jiau" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/CQ2T-Z242", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nNumerical simulations are presented for viscous incompressible homogeneous turbulent flows with periodic boundary conditions. Our numerical method is based on the spectral Fourier method. Rogallo's code is modified and extended to trace fluid particles and simulate the evolution of material line elements.\n\nThe first part of the thesis is about modifying and applying the code to simulate a passive vector field convected and stretched by the so-called ABC flows in the presence of viscosity. The correlation of the geometry of the physical structures of the passive vector with the external straining is investigated. It is observed that most amplifications either occur in the neighborhoods of local unstable manifolds of the stagnation points of the ABC flows, if they exist, especially those with only one positive eigenvalue, or they are confined within the chaotic regions of the ABC flows if there is no stagnation point. Tube-like structures in all simulations are observed.\n\nThe second part of the thesis is an investigation of the power-law energy decay of turbulence. Two decay exponents, 1.24 and 1.54, are measured from simulations. A new similarity form for the double and triple velocity autocorrelation functions using the Taylor microscale as the scaling, consistent with the Karman-Howarth equation and a power-law, energy decay, is proposed and compared with numerical results. The proposed similarity form seems applicable at small to intermediate Reynolds number. For flows with very large Reynolds number, an expansion form of energy spectrum is proposed instead. Two lengthscales are used to express the energy spectrum in the energy-containing range and in the dissipation range of wave numbers. The uniform expansion is obtained by matching spectra in the inertial subrange to the famous Kolmogorov's [...] spectrum.\n\nThe third part of the thesis is a presentation of the Lagrangian data collected by tracking fluid particles in decaying turbulent flows. The mean growth rates of the magnitudes of material line elements, that of the vorticity due to nonlinear forces, and the mean principal rates of strain tensors are found to be proportional to the square root of the mean enstrophy. The proportional coefficients remain constant during the decay. The mean angles between material line elements and the principal directions of the strain tensors corresponding to the most stretching and the intermediate principal rates are about the same which is probably caused by the averaging process and by the possible switch of principal directions. The evolution of these angles under the action of one Burger's vortex is examined and the results support the conjecture. Following fluid particles which suffer substantial stretching in their history, we, through use of flow visualization tools, observe the evolution of nearby vorticity structures. It is observed that vortex sheets are created first by the nonlinear stretching which gradually become tubes at later times by diffusion.\n" }, { "name": "Hubbard, Ted J.", "degree": "PhD", "year": "1994", "title": "MEMS design : the geometry of silicon micromachining", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162005-134646", "creators": [ { "name": { "family": "Hubbard", "given": "Ted J." }, "id": "Hubbard-T-J", "display_name": "Hubbard, Ted J." } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." } ], "option_major": [ "mecheng" ], "doi": "10.7907/TK4C-M144", "abstract": "The design of MEMS (Micro Electro Mechanical Systems) on the millimeter to micron length scales will be examined in this thesis.\n\nA very broad base of knowledge has been developed concerning the etching processes commonly used in MEMS fabrication. The fundamental problem we have sent out to study is how to model the shape transformations that occur in MEMS fabrication. The ultimate goal is to determine the required input mask geometry for a desired output etched shape.\n\nThe body of work begins with the crystal structure of silicon and ends with etched shapes. The underlying crystal structure causes different rates for different directions; this behavior has been modeled to obtain rate models. The information in these rate models has then been used in a number of shape modelers. High level models like the Eshape model provide not only simulation but a framework for true design. Other models such as the Cellular Automata model take a different approach and provide flexible and robust simulators. The tools were used to develop real world MEMS applications such as compensation structures.\n\nAs important as the individual models, is the ability to integrate them together to a coherent design tool and allow information to flow between different parts. This synthesis allows a fuller understanding of the etching process from start to finish.\n\nIt is important to note that while this thesis deals with etching, the methods developed are very general and are applicable to many shape transformation processes.\n" }, { "name": "Kuhn de Chizelle, Yan P.", "degree": "PhD", "year": "1994", "title": "Hydrodynamics, acoustics and scaling of traveling bubble cavitation", "advisor": "Acosta, Allan J.; Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10202005-152545", "creators": [ { "name": { "family": "Kuhn de Chizelle", "given": "Yan P." }, "id": "KuhndeChizelle-Y-P", "display_name": "Kuhn de Chizelle, Yan P." } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/E92Q-C197", "abstract": "Recent observations of the geometries of growing and collapsing bubbles over axisymmetric headforms have revealed the complexity of the \"microfluidmechanics\" associated with these flows (Hamilton et al., 1982, Briancon Marjollet and Franc, 1990, Ceccio and Brennen, 1991). Among the complex features observed were bubble to bubble interaction, cavitation noise generation and bubble interaction with the boundary layer which leads to the shearing of the underside of the bubble and alters the collapsing process. All of these previous tests were performed on small headform sizes. The focus of this research is to determine the dynamics governing the growth and collapse of traveling bubbles and to analyze the scaling effects due to variations in geometry size, Reynolds number and cavitation number. For this effect, cavitating flows over Schiebe headforms of different sizes (5.08cm, 25.4cm and 50.8cm in diameter) were studied in the David Taylor Large Cavitation Channel (LCC). This thesis presents the scaling effects captured on high-speed film and electrode sensors as well the noise signals generated during the collapse of the cavities. The influence of each of these parameters on the dynamics involved in the growth and collapse phases of the traveling bubble are presented, along with the acoustical impulse produced during the collapse of the bubble.\n\nIn order to model and analyze the dynamics of the three-dimensional bubble deformation in the presence of the pressure field around the Schiebe headform, an unsteady numerical code using traveling sources has been developed. This thesis presents calculations of the interaction between the irrotational flow outside the boundary layer of the headform and individual traveling bubbles. An error estimation of the method and comparisons with the LCC experiments are presented. This method is shown to predict some of the features of three-dimensional bubble growth and collapse dynamics remarkably well. Furthermore, analysis of these computations allow a better understanding bubble interaction and event rate prediction.\n" }, { "name": "Lambros, John", "degree": "PhD", "year": "1994", "title": "Dynamic decohesion of bimaterial interfaces", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042007-075432", "creators": [ { "name": { "family": "Lambros", "given": "John" }, "id": "Lambros-J", "display_name": "Lambros, John" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/36hw-c185", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nIn the present work, findings of an experimental study of dynamic decohesion of bimaterial systems composed of constituents with a large material property mismatch are presented. PMMA/steel or PMMA/aluminum bimaterial fracture specimens are used. Dynamic one point bend loading is accomplished with a drop weight tower device (for low and intermediate loading rates) or a high speed gas gun (for high loading rates). High speed interferometric measurements are made using the lateral shearing interferometer of Coherent Gradient Sensing in conjunction with high speed photography. Very high crack propagation speeds (terminal crack tip speeds up to [...], where [...] is the shear wave speed of PMMA) and high accelerations ([...], where g is the acceleration of gravity) are observed and reported. Issues regarding data analysis of the high speed interferograms are discussed. The effects of near tip three dimensionality are also analyzed. In crack propagation regions governed by large crack tip accelerations it is found that for accurate analysis of the optical data use of a transient elastodynamic crack tip field is necessary. Otherwise use of a Kd-dominant analysis is sufficient. Using the dynamic complex stress factor histories obtained by fitting the experimental data, a dynamic crack growth criterion is proposed. In the subsonic regime of crack growth it is seen that the opening and shearing displacements behind the propagating crack tip remain constant, i.e., the crack retains a self-similar profile during crack growth at any speed. This forms the basis of the proposed dynamic interfacial fracture criterion. It is also found that the process of dynamic interfacial fracture is highly unstable. This is corroborated by both the very large measured values of crack tip speed and acceleration and by the observation that the energy release rate at the propagating crack tip decreases with increasing crack tip speed. A mechanism of energy transfer from the metal to the PMMA side of the specimen is believed to be responsible for the high transient and transonic effects. An analysis and discussion of this phenomenon is also presented in this work.\n" }, { "name": "Langlois, Jean-Marc", "degree": "PhD", "year": "1994", "title": "New methods for ab initio quantum mechanical calculations in molecular and crystalline systems", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042007-081615", "creators": [ { "name": { "family": "Langlois", "given": "Jean-Marc" }, "id": "Langlois-J", "display_name": "Langlois, Jean-Marc" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/j75s-5f43", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis thesis deals with the development of new methods for doing ab initio quantum mechanical calculations of electronic wavefunctions of large molecules and crystalline systems with the emphasis on inclusion of electronic correlation or many body effects using generalized valence-bond (GVB) wavefunctions.\n\nChapters 1 and 2 describe two necessary steps for using the generalized valence-bond (GVB) formalism in large molecular systems. In Chapter 1 a fast method for generating GVB trial wavefunctions is described. The method is based on piecewise atomic and diatomic localization and makes possible calculations with large numbers of GVB pairs. The efficacy of the method is illustrated by application to several cases including GVB wavefunctions with up to 26 pairs. In Chapter 2 the pseudospectral (PS) method for self-consistent-field calculations is applied to the GVB formalism. In the GVB perfect pairing approximation, the PS method is shown to reduce the scaling cost of the calculation from [...] to [...], where N is the number of basis functions. This makes possible the calculation of GVB wavefunctions for large molecular systems.\n\nChapter 3 describes a density-functional method for calculations on crystalline systems using Gaussian type orbitals. Accurate and efficient strategies were developed for computing both the Hamiltonian matrix elements and the Coulomb field. The Hamiltonian matrix elements are computed by decomposing the multicenter numerical integrations into single-center integrations via a projection technique and the Coulomb field is evaluated analytically using a dual-space approach based on the Ewald method. The self-consistent field is obtained by a fast conjugate gradient method which uses both first and second derivative information and an efficient preconditioning strategy. Illustrative calculations are performed on two allotropes of carbon: diamond and [...] crystals.\n" }, { "name": "Lee, Ming-Chieh", "degree": "PhD", "year": "1994", "title": "Still and Moving Image Compression Systems Using Multiscale Techniques", "advisor": "Posner, Edward C.; McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042007-132203", "creators": [ { "name": { "family": "Lee", "given": "Ming-Chieh" }, "id": "Lee-Ming-Chieh", "display_name": "Lee, Ming-Chieh" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "chair", "display_name": "Posner, Edward C." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Cheung", "given": "Kar-Ming" }, "id": "Cheung-Kar-Ming", "role": "member", "display_name": "Cheung, Kar-Ming" }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/02w7-rg28", "abstract": "Multi-scale techniques have been popular methods for image and video compression. The basic idea behind these techniques is to decompose the original signals into several components of different scales, however the scale is defined, of different sizes. One then applies appropriate encoding strategies to different components to achieve compression by taking advantage of various properties. In this thesis, we review and present several new schemes of multi-scale techniques using linear and nonlinear systems. Linear techniques, which use linear filters for decomposition, have been thoroughly investigated and widely applied because of their simplicity in implementation and analysis. Herein we describe how to appropriately combine these techniques in order to process the signals more efficiently and advantageously; moreover, the picture quality of the quantized images can be improved. The sub-band coding technique is used as the basis for these combinations. As for the nonlinear technique, we would like to take advantage of the nonlinear features of images (such as edges) in compression to achieve compressing and enhancing of the images. Herein we design several nonlinear multi-resolution systems, using various nonlinear filters, to decompose the signals in a proper form. We show that, in terms of rate-distortion performance, where mean squared error is used as the distortion criterion, these schemes are close to, or even better than, JPEG standard, whereas the encoding and, especially, decoding complexity is lower than that of JPEG. We can obtain much better image quality (in the perceptual sense), however, by applying suitable simple and fast lossless compression schemes to sub-images. Simulation results are demonstrated to show the advantages and feasibility of the proposed scheme. In summary, we mention the current status and future trends of compression technologies." }, { "name": "Li, Mo", "degree": "PhD", "year": "1994", "title": "Crystal to Glass Transition and its Relation to Melting", "advisor": "Goddard, William A., III; Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-10052004-121305", "creators": [ { "name": { "family": "Li", "given": "Mo" }, "id": "Li-Mo-1994", "orcid": "0000-0002-0139-5839", "display_name": "Li, Mo" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "co-advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "co-chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "co-chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/a2hw-gm49", "abstract": "This work contributes to the understanding of thermodynamic aspects and microscopic mechanisms of the crystal to glass transition and its relationship to melting. The topological order to disorder transition was investigated primarily in a model system consisting of Lennard-Jones binary solid solutions via molecular dynamics simulations. Under constant temperature and pressure, thermodynamic properties and structures of the solid solutions are mainly determined by solute/solvent atomic size difference and solute concentration. At a critical atomic size difference and/or concentration, the transition was found to occur with extremely small latent heat and density change, but large softening of shear elastic constants. Microscopic details such as atomic configuration show that the transition is induced by collective topological defects created by differences in atomic sizes of the solute and solvent atoms. The inhomogeneity in atomic displacements caused by these defects was shown to be directly responsible for crossover of the transition from a first order transition to a continuous one. The fundamental difference between melting and the crystal to glass transition was demonstrated by their thermodynamic, dynamic, and structural behavior under different kinetic environments. It was shown that melting is intrinsically a first order transition, whereas crystal to glass transition can occur in a variety of forms that are crucially dependent on the kinetic constraints imposed on the solid phases.\r\n" }, { "name": "Liu, Cheng", "degree": "PhD", "year": "1994", "title": "Dynamic fracture problems involving highly transient crack growth histories : an investigation of dynamic failure in homgeneous and bimaterial systems", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122007-141145", "creators": [ { "name": { "family": "Liu", "given": "Cheng" }, "id": "Liu-C", "display_name": "Liu, Cheng" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "member", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/k32y-0450", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nHighly transient elastodynamic fracture processes in both homogeneous and bimaterial systems have been investigated. It is found that due to the wave character of the mechanical fields during transient and dynamic crack growth, the customarily assumptions of steady state and K[superscript d]-dominance may be violated. This may be particularly true during crack growth in laboratory size specimens where crack growth seldom reaches steady state conditions due to the persistence of the initiation transients and the influence of reflected stress waves from the specimen boundaries. By relaxing both restrictions of steady state and of K[superscript d]-dominance, and by permitting the crack-tip speed and the dynamic stress intensity factor to be arbitrary functions of time, the transient asymptotic elastodynamic field near the moving crack-tip was established in the form of higher order expansion for both homogeneous solids and bimaterial systems. In homogeneous solids, we considered cracks that propagated along arbitrary smooth paths, while in bimaterial systems, we only considered crack growth along a straight interface. The higher order coefficients of the asymptotic expansion were found to depend on the time derivative of crack-tip speed, the time derivative of the dynamic stress intensity factors, and for crack propagating along curved paths, on the instantaneous value of the local curvature of the crack path.\n\nThe issue of K[superscript d]-dominance during dynamic crack initiation and transient crack growth was further investigated by solving a particular transient initial/boundary value problem. This corresponds to a planar dilatational wave impinging on a semi-infinite crack in an unbounded elastic solid. The crack initiates under the influence of the wave, and then propagates dynamically. Through comparison of this full field solution and the equivalent K[superscript d]-dominant field or the field represented by the higher order transient terms, it is found that even for points which are relatively far away from the crack-tip, or for times very close to the crack initiation, the higher order transient representation provides a very good description of the actual stress field. \nThe K[superscript d]-dominant field, however, is incapable of approximating the complete stress field with any accuracy (lack of K[superscript d]-dominance).\n\nThe implications of the above observations (possible lack of K[superscript d]-dominance) on the interpretability of dynamic fracture experiments are also explored. The interpretation of experimental data in past laboratory investigations of dynamic fracture events is based on the assumption of K[superscript d]-dominance. However, as we have seen theoretically this assumption may often fail in laboratory situations. As a result, experimental measurements must be analyzed by techniques that allow for the possibility of the existence of transient higher order term effects. Several types of experiments are considered as examples. Plate impact experiments involving very high rates of loading are first analyzed by both a K[...]-dominant and a high order transient approach. The results clearly show the strong effects of transients on the interpretation of the data. As a second example, the optical method of caustics is reanalyzed. A new way of extracting the instantaneous value of the dynamic stress intensity factor K[...](t), which takes transients into account, is proposed and verified theoretically. For the bimaterial system, the issues are equivalent but much more complicated analytically. Here transient effects are found to be magnified by the material property mismatch between the constituent solids. It is shown however, that the higher order transient analysis can predict accurately the fringe patterns from actual experiment performed by means of the CGS (Coherent Gradient Sensing) technique and high speed photography.\n\nThe observations of this thesis suggest that a variety of conclusions made in the literature based on interpretations of experimental data on the basis of steady state or K[superscript d]-dominance may be suspect." }, { "name": "Liu, Wen-Shu", "degree": "PhD", "year": "1994", "title": "Oxidation of GeSi and applications", "advisor": "Nicolet, Marc-Aurele; Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302007-084825", "creators": [ { "name": { "family": "Liu", "given": "Wen-Shu" }, "id": "Liu-Wen-Shu", "display_name": "Liu, Wen-Shu" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "co-advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/pv5t-qy03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe thermal oxidation of epitaxial and polycrystalline [...] has been studied in a dry or wet ambient at various temperatures. It is found that the composition of the resulting oxide depends on temperature, ambient, Ge content, structure of the [...] alloy, and the oxidation procedure. While in a wet ambient, and following the preheating procedure, a uniform [...] oxide is observed for a high Ge content at low oxidation temperatures, a [...] oxide is obtained for a low Ge content at high temperatures. A [...] oxide with reduced Ge content (y < x) is found in between. Ge piles up behind the oxide when [...] or [...] forms. When a uniform [...] grows, its thickness is proportional to the square root of the oxidation duration, which indicates that the rate-limiting process is the diffusive transport across the oxide of, most probably, the oxidant. The rate increases with the Ge content in the alloys. It is proposed that, in general, the oxidation behavior is determined by the competition between the speed of the diffusive process in the unoxidized GeSi alloy and the velocity at which the oxidation front progresses. The controlling factors are the oxidation temperature, the composition, and the structure of the [...] alloy. A model is proposed that is based on these three factors.\r\n\r\nThe stability of an amorphous [...] in contact with an epitaxial (100)[...] layer obtained by partially oxidizing an epitaxial [...] layer on a (100)Si substrate in a wet ambient at 700\u00b0C has been investigated. It is noticed that [...] is thermodynamically unstable in contact with Si or GeSi, or in the presence of hydrogen and [...] will be reduced to elemental Ge.\r\n\r\nWhen [...] films are exposed to hydrogen, germanium nucleates homogeneously and the result is a suspension of nanocrystalline Ge grains embedded in a film of [...]. This nanocrystalline Ge is photoluminescent, as would be surmised by analogy with porous Si. When some parameters of the reduction experiment just described are altered, the outcome is radically different. This is accomplished by annealing\r\na [...] bilayer on a Si substrate in a 5% [...] ambient. A heterogeneous nucleation occurs on the interface between the epitaxial [...] and the oxide, with the consequence that Ge grows in the form of an epitaxial layer there as it precipitates out of the oxide. Surprisingly, this Ge layer is of a superior crystalline quality than that of [...] seed layer on which it grows.\r\n\r\nFinally, we oxidized amorphous Ge/Si bilayers on Si substartes. Epitaxial [...] layers can be produced this way. Vacuum annealing of these samples only results in polycrystalline [...] layers." }, { "name": "Mezic, Igor", "degree": "PhD", "year": "1994", "title": "On the geometrical and statistical properties of dynamical systems : theory and applications", "advisor": "Wiggins, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07212005-131406", "creators": [ { "name": { "family": "Mezic", "given": "Igor" }, "id": "Mezic-I", "display_name": "Mezic, Igor" } ], "advisors": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "advisor", "display_name": "Wiggins, Stephen R." } ], "committee": [ { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "co-chair", "display_name": "Brady, John F." }, { "name": { "family": "Marsden", "given": "Jerrold E." }, "id": "Marsden-J-E", "role": "co-chair", "display_name": "Marsden, Jerrold E." }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/SM03-1C46", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nWe develop analytical methods for studying particle paths in a class of three-dimensional incompressible fluid flows. We study three-dimensional volume preserving vector fields that are invariant under the action of a one-parameter symmetry group whose infinitesimal generator is autonomous and volume preserving. We show that there exists a coordinate system in which the vector field assumes a simple form. In particular, the evolution of two of the coordinates is governed by a time-dependent, one-degree-of-freedom Hamiltonian system with the evolution of the remaining coordinate being governed by a first-order differential equation that depends only on the other two coordinates and time. The new coordinates depend only on the symmetry group of the vector field. Therefore they are field independent. The coordinate transformation is constructive. If the vector field is time independent, then it posseses an integral of motion. Moreover, we show that the system can be further reduced to action-angle-angle coordinates. These are analogous to the familiar action-angle variables from Hamiltonian mechanics and are quite useful for perturbative studies of the class of sytems we consider. All of the above is useful in framing a perturbative setting for analyses of chaotic, volume-preserving vector fields. In particular, explicit expressions for the transformation to action-angle-angle coordinates is given. This leads to the proof of a KAM-type theorem for volume-preserving vector fields admitting a volume-preserving group of symmetries using the KAM-type result for three-dimensional maps. The proof of the persistence of finite cylinders, relevant in fluid dynamical applications is provided. Also, a Melnikov-type theory is developed, allowing for the prediction of parameter values for which the vector field possesses chaotic behavior.We discuss the integrability of the class of flows considered, and draw an analogy with Clebsch variables in fluid mechanics.\r\n\r\nRecently there has been a lot of numerical and experimental work on three dimensional, volume-preserving, chaotic fluid flows. The above theory can explain qualitative, geometric, features observed in these flows. But, the quantities of interest in those investigations are often of statistical nature. Furthermore, in most of these investigations, the flows considered are non-ergodic, with a rich structure of the phase space.\r\n\r\nThe theory of statistical properties of dynamical systems developed in this thesis is based on the Birkhoff's ergodic theorem, ergodic partition, and methods of probability theory. It is shown that, in the case when the system is not ergodic, the only quantities necessary to describe the limiting behavior (when the time or the number of iterations [approaching infinity] behavior of these systems are the time averages. Using this observation, necessary and sufficient condition are derived for the ubiquitous [...] asymptotic behavior of the dispersion. A link is obtained between probability distributions of sum functions and the ergodic partition, which is used to explain the phenomenon of patchiness in fluid flows. The problem of first passage times is analyzed, and some conjectures inspired by numerical experiments proved. The theory is developed for both maps and flows, and has applications in a variety of problems related to the statistical description of chaotic motion in physical systems. Two specific applications are diffusion in two-dimensional, area-preserving maps, and shear dispersion in fluid flows. An obvious question arising from this part of the work was: how can one calculate the ergodic partition, which is an important ingredient of the statistical part of the theory. In ergodic theory, two ways of presentation of the ergodic partition exist. These two approaches can be successfully joined to provide a simple constructive algorithm for the construction of the ergodic partition. The ergodic partition of the compact metric space A, under the dynamics of a continuous automorphism T, is shown to be the product of measurable partitions of the space induced by the time averages of a dense, countable subset of the set of all continuous functions on A. As a consequence of this, closed ergodic components are shown to be uniquely ergodic. Also, a connection can be made between the ergodic partitions induced by the time averages of measurable, bounded functions, and the ergodic partition. Besides giving a method of constructing the ergodic partition, this work might give rise to numerical algorithms for computation of the ergodic partition.\r\n\r\nAll of the above theory is applied to the ideal, incompressible fluid flow induced by a helical vortex filament in an axisymmetric time-dependent strain field. It is shown that the helical filament stays helical for all times. Using symmetry concepts we transform the velocity field to a particularly simple form that is convenient for the use of perturbation methods. We analyze bifurcations and the structure of particle paths in the unperturbed velocity field (no strain). The underlying geometrical structures in the unperturbed problem are cylinders and two dimensional separatrices. Away from separatrices we transform the system into coordinates that enable us to use KAM theory to show the persistence of infinite cylinders in the perturbed flow. Further, we analyze the unperturbed motion on separating manifolds, and present a three-dimensional Melnikov theory for the analysis of the motion near the separatrices under perturbation. We use this analysis to propose that chaoticity of the motion provides a physical mechanism for the Ranque effect for swirling flows in pipes. Finally, we analyse the problem of shear dispersion of passive scalars in our flow. A natural question related to the above considerations of statistics of deterministic dynamical systems is how do they affect the statistical properties of the system when noise is added. This leads to a study of the convection-diffusion equation. We establish conditions for the maximal, [...] behavior of the effective diffusivity in time periodic incompressible velocity fields for both the [...] 0 limits. Using ergodic theory, these conditions can be interpreted in terms of the Lagrangian time averages of the velocity. We reinterpret the maximal effective diffusivity conditions in terms of a Poincare map of a velocity field. The connection between the [...] asymptotic behavior of the effective diffusivity and [...] asymptotic dispersion of the nondiffusive tracer is established. Several examples are analyzed: we relate the existence of the accelerator modes in a flow with [...] effective diffusivity, and show how maximal effective diffusivity can appear as a result of a time-dependent perturbation of a steady cellular velocity field. Also, three-dimensional, symmetric, time-dependent duct velocity fields are analyzed, and the mechanism for effective diffusivity with Peclet number dependence different from [...] in time-dependent flows is established, thus generalizing the Taylor-Aris dispersion theory." }, { "name": "Park, Namkyoo", "degree": "PhD", "year": "1994", "title": "Application of fiber amplifiers to fiber lasers and terahertz spectroscopy", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212006-102347", "creators": [ { "name": { "family": "Park", "given": "Namkyoo" }, "id": "Park-N", "display_name": "Park, Namkyoo" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ZK03-KN91", "abstract": "Starting with a review of the Erbium doped fiber amplifier, this thesis will describe the construction, intensity noise, linewidth, stabilization techniques, and spectroscopic applications of the Erbium doped fiber ring laser developed as a part of the thesis research activity. This laser, which uses the Erbium doped fiber amplifier as its gain module within fiber based ring resonator, exhibits excellent sidemode suppression (>70dB) and intensity noise properties (shot noise limited beyond GHz regime) with ultranarrow linewidth (<4kHz).\n\nTo measure and improve these performance, several new techniques were developed. A new interferometer based on a loss-compensated recirculating delayed self heterodyne technique, for the measurement of ultranarrow linewidth. A novel intracavity filtering technique to make the laser operate at the shot noise floor of intensity noise. Extension of Pound-Drever locking technique into the laser cavity, to enable the laser be stabilized and locked to an external reference at the same time.\n\nThe laser was also applied as a spectroscopic tool to study the four wave mixing process in semiconductor optical amplifiers. Because of the ultranarrow linewidth and intensity noise characteristics of fiber laser, it was possible to resolve THz intraband dynamics in a quantum well amplifier.\n\nThis thesis will also cover mode locked operation of the fiber laser and related issues briefly in the appendix.\n" }, { "name": "Peker, Atakan", "degree": "PhD", "year": "1994", "title": "Formation and characterization of bulk metallic glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-10252005-074557", "creators": [ { "name": { "family": "Peker", "given": "Atakan" }, "id": "Peker-A", "display_name": "Peker, Atakan" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/KBSB-JM25", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nSince the discovery of metallic glass formation by ultra-rapid melt quenching at Caltech in 1959, it was thought that metallic glasses can be processed only as very thin ribbons or fine powders, due to the required high cooling rate, and that they are not stable above the glass transition temperature. This has severely limited the technological applications of metallic glasses which combine unique and desirable properties. Also, bulk glass forming metallic alloys have long been desired to improve our scientific knowledge of nucleation, crystal growth and other properties of undercooled metallic melts.\r\n\r\nAfter the discovery of solid state amorphization in early eighties, there were several years of paused research on metallic glass formation by melt quenching. At the end of the last decade, a Japanese group in Sendai discovered new metallic systems, which require substantially lower cooling rates for glass formation than previous systems and which have high thermal stability above their glass transition temperature.\r\n\r\nAs a major contribution to a new era of metallic glasses, this thesis extended the formation and the thermal stability of metallic glasses to the extent that many potential uses of metallic glasses have come to the brink of reality. For the first time, the art of metallic glass making has become as easy as a single step alloy preparation using conventional metallurgical processing. The production of the larger bulk metallic glass specimens is limited only by the scale of equipment in our laboratory and not by limitations arising from the glass forming ability of the particular alloy. These new developments presented throughout this thesis may not only extend the applications of metallic glasses but they also allow us to study the properties of highly undercooled metallic melts which are very important in phenomena such as nucleation and crystal growth.\r\n\r\nThe thesis starts with an introductory chapter describing the art and science of metallic glasses prior to this work. Then, a critical review of the current knowledge of thermodynamics and kinetics of glass formation is given in chapter 2. In chapter 3, an example of a highly processable metallic glass alloy, [...], is presented along with its preparation methods. Its general characteristics which distinguish it from conventional metallic glasses are emphasized. This particular glassy alloy, [...], belongs to an exceptionally large family of excellent glass forming metallic systems, which were developed in the course of this thesis research. In chapter 4, various forms of heterogeneous nucleation,--an important phenomena in glass formation--are discussed with reference to several glass forming alloys. Finally, conditions for bulk glass formation are proposed in view of our current theoretical knowledge and experimental observations. Difficulties in attaining these conditions are also discussed and suggestions are made for finding other bulk glass forming alloys.\r\n" }, { "name": "Raphaeli, Dan", "degree": "PhD", "year": "1994", "title": "Noncoherent Coded Modulation", "advisor": "McEliece, Robert J.; Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112007-082807", "creators": [ { "name": { "family": "Raphaeli", "given": "Dan" }, "id": "Raphaeli-Dan", "display_name": "Raphaeli, Dan" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/fexw-ex94", "abstract": "In this thesis, we are concerned with the transmission of data over noncoherent channels (the carrier phase is random). We consider a receiving system which does not attempt to estimate the carrier phase from the received data. Instead, the transmitter and receiver will be designed so that the data transmission is robust with respect to the unknown phase variations of the channel. For the transmitter, we propose new combined coding and modulation, specifically designed to match the noncoherent channel. For the receiver, efficient decoders to noncoherently decode the coded modulation are developed. As a result, we are able to show, both analytically and by computer simulations, that Noncoherent Coded Modulation (NCM) approaches the performance of coded coherent modulation. NCM achieves almost the same power efficiency without bandwidth expansion or an extensive increase in complexity.
\r\n\r\nWe consider the problem of the Uniform Error Property (UEP) for a broad class of transmitters and receivers. A sufficient condition for a general linear code to satisfy the UEP is presented and a structure of a trellis-coded modulation that satisfies this condition is offered. We call these codes \"linear noncoherent trellis-coded modulation\" since they apply to noncoherent detection. The problem of noncoherently catastrophic codes, which can result in noncoherent detection of trellis codes, is discussed and a general solution which does not rely on differential encoding of the code output is offered.
\r\n\r\nHigh performance noncoherent detection is achieved using multiple symbol observations. Unlike previous approaches, a sliding window is used for the observations, with each observation covering several branches of the trellis, so that the observations are time-overlapped. We define a new type of noncoherent maximum likelihood sequence estimator, and analyze its performance over the Additive White Gaussian Noise (AWGN) channel by numerical calculation of the union bound. We perform a computerized search and present new high performance coded M-ary Phase Shift Keying (PSK) modulations for noncoherent detection and their performance. The new codes cover many useful rates and complexities and achieve higher performance than existing codes for noncoherent detection. We evaluate the performance of NCM in the presence of phase jitter in the channel. The method can also be used for multiple symbol demodulation of M-ary Differential PSK (MDPSK) and of Continuous Phase Modulation (CPM). We provide results for both, full and partial response CPM schemes as well as convolutionally coded CPM. The complexity and power efficiency of this new method is superior to all past schemes known to the author for noncoherent detection.
\r\n\r\nThe optimal implementation of the decoder, using the Viterbi Algorithm (VA), is given. For L-symbols observation, it requires a number of states that grows exponentially with L. Three novel sub-optimal algorithms are presented, whose number of states is the same as the original code so their complexity has a relatively weak dependence on L. For practical values of L, these algorithms are substantially less complex than the optimal algorithm.
\r\n\r\nThe first suboptimal algorithm to be described is called the Basic Decision Feedback Algorithm (BDFA). In this algorithm, the symbols from the decisions are fed back to be used in the subsequent decisions. This algorithm suffers from increased error event probability and from error propagation. However, by a small modification of the BDFA, we obtain another improved algorithm, which will be called Modified Decision Feedback Algorithm (MDFA).
\r\n\r\nTo obtain close to optimal performance, the third algorithm, the Estimated Future Decision Feedback Algorithm (EFDFA) is offered. This sophisticated algorithm, which uses the BDFA as a basic building block, is based on a novel concept called \"estimated future.\" Performance analysis and simulation results are given.
" }, { "name": "Salam, Gamze Erten", "degree": "PhD", "year": "1994", "title": "An analog VLSI architecture for stereo correspondence", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072007-084843", "creators": [ { "name": { "family": "Salam", "given": "Gamze Erten" }, "id": "Salam-G-E", "display_name": "Salam, Gamze Erten" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/H61K-0Q06", "abstract": "My goal in engaging in this project was to design a hardware system to solve the stereo correspondence problem in real-time.\r\n\r\nConsequently, this work describes and analyzes an algorithm for stereo correspondence, its extension to an analog VLSI architecture, and the results obtained from its hardware implementation as a chip.\r\n\r\nThe first chapter, titled Introduction, describes the stereo correspondence problem. Therein, I discuss biological and psychophysical mechanisms of stereo vision, and include a brief history of ideas to date on the subject. I wrote this chapter to introduce the problem to the reader without assuming any previous knowledge about vision. I believe that reading it with the aid of definitions in the glossary can equip most any reader with information regarding the basics of stereo vision.\r\n\r\nThe second chapter, titled In Search of the Correct Similarity Measure, expands, first by a simple example, later in mathematical terms, the issues involved in the selection of a similarity measure. The similarity measure is a key component in the solution of the stereo correspondence problem. My main approach is a statistical one, using probability distributions and Bayesian analysis. The chapter motivates the two-sided approach of the algorithm, by using a disparity and a confidence metric for each image region.\r\n\r\nThe third chapter, titled Simulating the Hardware Algorithm, describes my stereo correspondance algorithm in detail. Simulation results that include both disparity and confidence values obtained with a variety of images are presented. Experiments are conducted to demonstrate the effect of parameter adjustments. In addition, the algorithm is compared with other correspondence schemes which use various different similarity measures.\r\n\r\nThe fourth chapter, titled Analog VLSI Implementation, is devoted fully to the hardware implementation. First, the details of the hardware architecture are described. Then, results are presented with two unique implementations. As in the previous chapter, experiments are conducted, this time using the chips themselves. Their results are compared with simulation. Again a variety of images are used.\r\n\r\nThe fifth chapter, titled Conclusions and Future Work, summarizes the work and explores future expansions." }, { "name": "Sanouillet, Remy D.", "degree": "PhD", "year": "1994", "title": "Computer mediated communication", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072007-090605", "creators": [ { "name": { "family": "Sanouillet", "given": "Remy D." }, "id": "Sanouillet-R-D", "display_name": "Sanouillet, Remy D." } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "member", "display_name": "Taylor, Stephen" }, { "name": { "family": "Thompson", "given": "Bozena H." }, "id": "Thompson-B-H", "role": "member", "display_name": "Thompson, Bozena H." }, { "name": { "family": "Tschoegl", "given": "Nicholas W." }, "id": "Tschoegl-N-W", "role": "member", "display_name": "Tschoegl, Nicholas W." }, { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "member", "display_name": "Thompson, Frederick B." } ], "option_major": [ "compsci" ], "doi": "10.7907/THJT-R127", "abstract": "What will the age of the telephone-computer be like? In this thesis we present an answer to this question. We will base this answer on a conceptual framework being developed by the research group in which this work has been done, namely the Caltech/NCR Project; the work of this Project is embodied in the New World of Computing System. This framework will be stated as a paradigm for human information activities.
\r\n\r\nThe main contributions of this thesis are, first, an examination of the implications of this framework for the communication aspects of information processing. The second is the design of the communication aspects of the New World of Computing System, reflecting the results of this examination. The System, in its totality, provides a computer environment for the telephone-computer age.
\r\n" }, { "name": "Santi, Enrico", "degree": "PhD", "year": "1994", "title": "Magnetics and control in power electronics : I. Modeling of coupled inductors. II. One-cycle control of switching converters", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072007-140529", "creators": [ { "name": { "family": "Santi", "given": "Enrico" }, "id": "Santi-E", "display_name": "Santi, Enrico" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "co-advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/QR7V-XF60", "abstract": "Part 1:\r\n\r\nFor coupled-inductor and integrated-magnetics design it is of paramount importance to accurately model leakages. Air gap position has a dramatic effect on coupled-inductor characteristics. Improved reluctance models that capture this effect are proposed.\r\n\r\nFor the most common coupled-inductor structures, i.e., UU and UI cores with windings on different legs, a simple model valid for any gap arrangement is proposed. The model has a single leakage reluctance that is constant for a given core geometry and can be determined from a single set of measurements.\r\n\r\nA method to estimate this reluctance from core geometry is also suggested.\r\n\r\nA new coupled-inductor structure that achieves quasi-zero current ripple without need for turns ratio adjustment is introduced.\r\n\r\nClosed-form design equations for coupled-inductors are given.\r\n\r\nPart 2:\r\n\r\nThe concept of One-Cycle control has recently been proposed. The generality of this control technique is demonstrated through description of its implementation for different DC-DC switching converters. It is a nonlinear control technique with significant advantages in terms of rejection of line perturbation, speed of response and insensitivity to circuit parameters. Until now, no stability analysis was available and, under certain conditions, instability was observed. In this paper a stability analysis of a One-Cycle controlled Cuk converter (a fourth order system) is performed, which shows that stability depends on the value of parasitic elements. A modification of the control to eliminate steady-state output voltage error is proposed. Finally, a modification of the control that ensures stability independently of the value of parasitic elements is suggested. All theoretical results are experimentally verified.\r\n" }, { "name": "Schrans, Thomas", "degree": "PhD", "year": "1994", "title": "Part 1: Longitudinal static and dynamic effects in semiconductor lasers. Part II: Spectral characteristics of passively mode-locked quantum well lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:04192013-141541657", "creators": [ { "name": { "family": "Schrans", "given": "Thomas" }, "id": "Schrans-T", "display_name": "Schrans, Thomas" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6fvd-ez10", "abstract": "In the first part of this thesis a study of the effect of the longitudinal distribution of optical intensity and electron density on the static and dynamic behavior of semiconductor lasers is performed. A static model for above threshold operation of a single mode laser, consisting of multiple active and passive sections, is developed by calculating the longitudinal optical intensity distribution and electron density distribution in a self-consistent manner. Feedback from an index and gain Bragg grating is included, as well as feedback from discrete reflections at interfaces and facets. Longitudinal spatial holeburning is analyzed by including the dependence of the gain and the refractive index on the electron density. The mechanisms of spatial holeburning in quarter wave shifted DFB lasers are analyzed. A new laser structure with a uniform optical intensity distribution is introduced and an implementation is simulated, resulting in a large reduction of the longitudinal spatial holeburning effect.
\r\n\r\nA dynamic small-signal model is then developed by including the optical intensity and electron density distribution, as well as the dependence of the grating coupling coefficients on the electron density. Expressions are derived for the intensity and frequency noise spectrum, the spontaneous emission rate into the lasing mode, the linewidth enhancement factor, and the AM and FM modulation response. Different chirp components are identified in the FM response, and a new adiabatic chirp component is discovered. This new adiabatic chirp component is caused by the nonuniform longitudinal distributions, and is found to dominate at low frequencies. Distributed feedback lasers with partial gain coupling are analyzed, and it is shown how the dependence of the grating coupling coefficients on the electron density can result in an enhancement of the differential gain with an associated enhancement in modulation bandwidth and a reduction in chirp.
\r\n\r\nIn the second part, spectral characteristics of passively mode-locked two-section multiple quantum well laser coupled to an external cavity are studied. Broad-band wavelength tuning using an external grating is demonstrated for the first time in passively mode-locked semiconductor lasers. A record tuning range of 26 nm is measured, with pulse widths of typically a few picosecond and time-bandwidth products of more than 10 times the transform limit. It is then demonstrated that these large time-bandwidth products are due to a strong linear upchirp, by performing pulse compression by a factor of 15 to a record pulse widths as low 320 fs.
\r\n\r\nA model for pulse propagation through a saturable medium with self-phase-modulation, due to the a-parameter, is developed for quantum well material, including the frequency dependence of the gain medium. This model is used to simulate two-section devices coupled to an external cavity. When no self-phase-modulation is present, it is found that the pulses are asymmetric with a sharper rising edge, that the pulse tails have an exponential behavior, and that the transform limit is 0.3. Inclusion of self-phase-modulation results in a linear upchirp imprinted on the pulse after each round-trip. This linear upchirp is due to a combination of self-phase-modulation in a gain section and absorption of the leading edge of the pulse in the saturable absorber.
\r\n" }, { "name": "Seizovic, Jakov N.", "degree": "PhD", "year": "1994", "title": "The architecture and programming of a fine-grain multicomputer", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072007-131639", "creators": [ { "name": { "family": "Seizovic", "given": "Jakov N." }, "id": "Seizovic-Jakov-N", "display_name": "Seizovic, Jakov N." } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "chair", "display_name": "Seitz, Charles L." }, { "name": { "family": "Van de Velde", "given": "Eric" }, "id": "van-de-Velde-E", "role": "member", "display_name": "Van de Velde, Eric" }, { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "member", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/53vc-hs15", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe research presented in this thesis was conducted in the context of the Mosaic C, an experimental, fine-grain multicomputer. The objective of the Mosaic experiment was to develop a concurrent-computing system with maximum performance per unit cost, while still retaining a general-purpose application span. A stipulation of the Mosaic project was that the complexity of a Mosaic node be limited by the silicon complexity available on a single VLSI chip.\r\n\r\nThe two most important original results reported in the thesis are:\r\n\r\n\u2022 The design and implementation of C+-, a concurrent, object-oriented programming system.\r\n\r\nSyntactically, C+- is an extension of C++. The concurrent semantics of C+- are contained within the process concept. A C+- process is analogous to a C++ object, but it is also an autonomous computing agent, and a unit of potential concurrency. Atomic single-process updates that can be individually enabled and disabled are the execution units of the concurrent computation. The limited set of primitives that C+- provides is shown to be sufficient to express a variety of concurrent-programming problems concisely and efficiently.\r\n\r\nAn important design requirement for C+- was that efficient implementations should exist on a variety of concurrent architectures, and, in particular, on the simple and inexpensive hardware of the Mosaic node. The Mosaic runtime system was written entirely in C+-.\r\n\r\n\u2022 Pipeline synchronization, a novel, generally-applicable technique for hardware synchronization.\r\n\r\nThis technique is a simple, low-cost, high-bandwidth, high-reliability solution to interfaces between synchronous and asynchronous systems, or between synchronous systems operating from different clocks.\r\n\r\nThe technique can sustain the full communication bandwidth and achieve an arbitrarily low, non-zero probability of synchronization failure, P[subscript f], with the price in both latency and chip area being [...].\r\n\r\nPipeline synchronization has been successfully applied to the high-performance inter-computer communication in Mosaic node ensembles." }, { "name": "Shih, Angela Chao-Hsuan", "degree": "PhD", "year": "1994", "title": "The study of Taylor-Couette flows with superimposed isothermal and heated axial flows at high Taylor numbers", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112007-104052", "creators": [ { "name": { "family": "Shih", "given": "Angela Chao-Hsuan" }, "id": "Shih-A-C", "display_name": "Shih, Angela Chao-Hsuan" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/3r06-hm27", "abstract": "This experimental study investigates the effect of an isothermal or heated superimposed axial flow on a Taylor-Couette flow in an open, vertical annulus with the inner cylinder rotating. The tangential component of the velocity is measured using a hot-wire anemometer, and the velocity power spectra are calculated. The flows studied are for Taylor numbers ranging from 1.2 x 10[superscript 7] to 2.4 x 10 [superscript 7], and the axial Reynolds number from 0 to 2500. At a low axial Reynolds number, the power spectrum of the velocity measurements shows a single dominant frequency. The frequency is indicative of the uniformly-spaced vortices passing through the anemometer, and roughly corresponds with the axial velocity divided by the vortex spacing. As the rotational speed is increased at a fixed axial flow rate, the dominant frequency decreases, indicating a change in the size of the vortices. As the axial Reynolds number is increased at a fixed rotational speed, the power spectra first indicate a decrease in the dominant frequency, and then a subsequent increase in the other frequencies. For very large axial flow rates, the power spectra indicate a broad distribution in frequencies.\n\nThe experiment also include the measurements of the transient and the local fluid temperatures, and the corresponding temperature spectra are calculated. Heating of the axial flow also changes the characteristic of the velocity spectra, where peaks at higher frequencies emerge in the spectra. In heated flows, the peaks of the greatest spectral strength in the velocity and temperature spectra are different, possibly indicating that the largest temperature and velocity fluctuations occur in different directions. The average temperature measurements indicate that as the axial flow rate is increased, the mean temperature distribution curves shift upward. The temperature ratio, (T[subscript max] - T[subscript min])/(T[subscript in] - T[subscript out]), also increases with an increasing in the axial Reynolds numbers.\n" }, { "name": "Shin, Jung Hoon", "degree": "PhD", "year": "1994", "title": "Defects in amorphous silicon : dynamics and role on crystallization", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052007-131414", "creators": [ { "name": { "family": "Shin", "given": "Jung Hoon" }, "id": "Shin-Jung-Hoon", "display_name": "Shin, Jung Hoon" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/TW9D-5657", "abstract": "Defects play a crucial role in determining the properties of many materials of scientific and technological interest. With ion irradiation, it is possible to controllably inject defects, and thus carefully study the dynamics of defect creation and annihilation, as well as the effects such defect injection has on materials properties and phase transformations. Amorphous silicon is a model system for the study of amorphous solids characterized as continuous random networks. In hydrogenated form, it is an important material for semiconductor devices such as solar cells and thin film transistors. It is the aim of this thesis to elucidate the dynamics of defects in an amorphous silicon matrix, and the role such defects can play on crystallization of amorphous silicon.\r\n\r\nIn the first chapter, the concept of a continuous random network that characterizes amorphous silicon is presented as an introduction to amorphous silicon. Structural relaxation, or annihilation of non-equilibrium defects in an amorphous matrix, is introduced. Also developed are the concept of the activation energy spectrum theory for structural relaxation of amorphous solids and the density of relaxation states. In the second chapter, the density of relaxation states for the structural relaxation of amorphous silicon is measured by measuring changes in electrical conductivity, using ion irradiation and thermal anneal to create and annihilate defects, respectively. A new quantitative model for defect creation and annihilation, termed the generalized activation energy spectrum theory, is developed in Chapter 3, and is found to be superior to previous models in describing defect dynamics in amorphous silicon. In Chapter 4, the effect of irradiation on the crystallization of amorphous silicon is investigated. It is found that irradiation affects crystallization even when the growth kinetics of crystal grains is unaffected, and that defects injected into amorphous matrix by irradiation probably play a role in affecting the thermodynamic quantities that control nucleation. The role of defect injection in affecting the thermodynamic quantities is investigated in Chapter 5, where we estimate the change in the free energy of amorphous silicon under the irradiation conditions of Chapter 4, using the generalized activation energy theory of Chapter 3. The experimental data and its interpretation are consistent with predictions of generalized activation energy spectrum theory.\r\n" }, { "name": "Suzuki, Hideyuki", "degree": "PhD", "year": "1994", "title": "Scintillation mechanisms of cerium-doped rare earth oxyorthosilicates", "advisor": "Tombrello, Thomas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182005-130418", "creators": [ { "name": { "family": "Suzuki", "given": "Hideyuki" }, "id": "Suzuki-H", "display_name": "Suzuki, Hideyuki" } ], "advisors": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "advisor", "display_name": "Tombrello, Thomas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/3a2x-nk63", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nRare earth oxyorthosilicates (RE)2(SiO4)O (RE = rare earth) have high densities and effective atomic numbers for efficient gamma-ray detection. Among these, Gd2(SiO4)O, Y2(SiO4)O and Lu2(SiO4)O have no absorption lines at visible wavelengths and thus were examined as potential single crystal scintillators by doping with cerium (Ce).\n\nThe light emission mechanism of the activator Ce3+ ion in (RE)2(SiO4)O was investigated with UV light, by selectively exciting absorption bands of Ce3+ at low temperature (~11 K). It was found that all three compounds have two types of excitation and emission spectra and decay constants, and they were attributed to two Ce3+ centers (Ce1 and Ce2) occupying two different host rare earth sites.\n\nThe origins of two decay constants in the gamma-ray excited decay of Gd2(SiO4)O:Ce (GSO) were investigated. We focused on GSO since the gamma-ray excited decay times of GSO are much slower than the intrinsic Ce3+ decay, in contrast with Y2(SiO4)O:Ce and Lu2(SiO4)O:Ce. Since Gd3+ emission bands overlap Ce3+ absorption bands, the energy transfer from Gd3+ to Ce3+ was analyzed for a possible explanation for the slow Ce3+ decays. The Gd3+ absorption bands in the UV region were excited by a synchrotron light source and the Ce3+ decay was monitored. With excitation into the [...] and [...] states of Gd3+, a slow decay component and a build-up were observed in the Ce3+ decay, consistent with energy transfer from [...] and [...] states of Gd3+ to Ce3+.\n\nThe energy migration through the Gd sublattice in GSO was investigated. The Gd was diluted by optically inactive rare earths, Y and Lu, and the macroscopic energy transfer rate from Gd3+ to Ce3+ was measured as a function of Gd concentration. The results show that the macroscopic transfer rate from Gd3+ to Ce3+ increases as Gd concentration increases, indicating that the energy of the excited Gd3+ can migrate through the Gd sublattice before one of the Gd3+ near a Ce3+ can transfer its energy to the Ce3+.\n" }, { "name": "Tan, Fang Dong", "degree": "PhD", "year": "1994", "title": "Modeling and control of switching converters : I. Unified modeling and measurement of current-programmed converters. II. A generic averaged model for switches in dc-to-dc converters", "advisor": "Middlebrook, Robert David; Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072007-113216", "creators": [ { "name": { "family": "Tan", "given": "Fang Dong" }, "id": "Tan-F-D", "display_name": "Tan, Fang Dong" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "co-advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TGBG-N220", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I\r\n\r\nA unified model is established for a current-programmed converter, which unifies and extends previous models.\r\n\r\nA low-frequency modification leads to a unified duty-ratio control law for the buck, the boost, and the buck/boost converters, which results in improved predictions for several essential quantities of the current-loop gain.\r\n\r\nInclusion of the sampling effect allows the presence of an additional pole [...] in the current-loop gain to be derived. The resulting final double-slope asymptote is fixed in position, and the crossover frequency cannot exceed half the switching frequency.\r\n\r\nTwo parameters are found to be central quantities of interest. A parameter [...] represents the minimum value of D', the complementary duty ratio, to maintain stability of the current loop, and shows explicitly the stabilizing effect of a compensating ramp. A \"stability parameter\" [...] determines the additional pole [...] and describes the degree of peaking in the closed-loop transfer functions.\r\n\r\nExperimental verification employs an analog signal injection technique, which is easier to use, and contains more information about high-frequency dynamics than a conventional digital signal injection technique.\r\n\r\nPart II\r\n\r\nA generic averaged model for switches in dc-to-dc converters is established for the first time by using, in addition to averaging, volt-second and amp-second balance equations.\r\n\r\nThe generic model inherits advantages of previous models and extend then to a new height: switches in dc-to-dc converters can now be handled as linear-time-invariant two-terminal circuit elements for their low-frequency characterizations.\r\n\t\r\nIt is shown that the generic model is equivalent to the canonical circuit model from state-space averaging when it is substituted into a particular converter. It is also shown that the model for PWM switches is a special case of the generic model.\r\n\r\nA theoretical discussion about the equivalent duty ratio [...] reveals that averaging can retain low-frequency information contained in the original quantity regardless of its ripple content. The conditions are that the dc value of the original quantity is not vanishingly small, and the perturbation frequency is limited to half the switching frequency for amplitude perturbation or to a quarter of the switching frequency for frequency perturbation.\r\n\r\nExtensions of the generic model to converters with isolations, in discontinuous conduction mode, in current programming, and in other modes of operation are obtained. The concept of equivalent duty ratio is found useful.\r\n\r\nOne salient feature of the extended generic model, which distinguishes it from similar previous models, is that different versions of the model have exactly the same form. The invariance of the form of the model is extremely useful for computer simulations of the averaged large- and small-signal dynamics in dc-to-dc converters under various modes of operation.\r\n\r\nOne important feature of the approach, which separates it from all previous modeling approaches, is that its application is not limited by the number of switches in a converter. A three-switch converter is analyzed to show key steps in the derivation of a generic model for converters with multiple switches. Experimental results support the predictions from the generic model for the three-switch converter.\r\n" }, { "name": "Vendroux, Guillaume", "degree": "PhD", "year": "1994", "title": "Scanning tunneling microscopy in micromechanics investigations", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-06162005-104436", "creators": [ { "name": { "family": "Vendroux", "given": "Guillaume" }, "id": "Vendroux-G", "display_name": "Vendroux, Guillaume" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KVSX-Q863", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nA new experimental method is proposed for studying deformations of micromechanical material systems at the submicron scale. To that end, a Scanning Tunneling Microscope (STM) was designed and built to allow placement on a mechanically deforming specimen. Operating in constant current mode, this digitally controlled STM records detailed topographies of specimen surfaces with a resolution of 10.15 nm in-plane and [...] out-of-plane, over a [...] area.\n\nA pattern recognition type algorithm was written to extract the 3-D displacement field from topographies of a given specimen area but under different loading conditions. This Digital Image Correlation (DIC) scheme was found to have very robust convergence characteristics and a higher resolution than that of the images it compares. The accuracy of the DIC code on STM scans was assessed by measuring displacement fields resulting from a translation of the specimen under the microscope. Two major causes of noise were identified, namely drifting of the specimen during scan acquisition and hysteresis distortion of the scan grid. An experimental procedure was devised to limit the occurrence of such perturbations and under these guidelines the resolution of the DIC scheme was found to be 4.8 nm for in-plane displacement measurements and 1.5 nm for out-of plane's.\n\nA micromechanical study of the deformation mechanism of PolyVinylChloride (PVC) was undertaken. Analysis of STM scans revealed that, upon first loading the surface of PVC specimens is deformed irreversibly even at low strain levels. The size of the strain induced topographic changes suggests that, at the scale of [...], a continuum type constitutive modeling of PVC may not be appropriate. This investigation also uncovered the present limitations of the STM-DIC scheme in measuring displacement fields consistently at the nanometer scale." }, { "name": "Vollin, Jeffrey Lance", "degree": "PhD", "year": "1994", "title": "Resonant power processing at a fixed frequency using a controllable inductance", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-06212005-102928", "creators": [ { "name": { "family": "Vollin", "given": "Jeffrey Lance" }, "id": "Vollin-J-L", "display_name": "Vollin, Jeffrey Lance" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "co-advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WRR4-7B68", "abstract": "Power processing at high frequencies often involves the use of resonant conversion techniques. Most of these techniques require the use of a variable switching frequency to provide control over the output voltage or current. In many applications this variable switching frequency is not tolerable and another method of regulation is required. A novel device called a magnetic regulator can be used in conjunction with a resonant DC-to-DC converter to provide regulation of the output voltage or current at a fixed switching frequency. This device resembles an ordinary transformer except with an additional winding which provides control over the input-output conversion ratio.
\r\n\r\nPrior to the use of the magnetic regulator, suitable resonant DC-to-DC converters are identified and partitioned into a resonant inverter which converts the incoming DC energy into high frequency AC energy and into a rectifier circuit which converts the AC back to DC. The candidate inverters used include the Class E and Class D Zero-Voltage-Switched circuits. Since the rectifier circuit must be compatible with the choice of the inverter, the design details of such a rectifier are presented.
\r\n\r\nThe magnetic regulator is modeled using the reluctance concept exposing the true nature of the regulation mechanism. The control current changes the permeability of a portion of the core of the device which results in a current-controlled leakage inductance.
\r\n\r\nThe magnetic regulator may be inserted into the forward power path of a resonant DC-to-DC converter. In the process, it is possible to integrate the resonant inductor and a matching inductor into the basic structure of the magnetic regulator. The result is a high frequency, resonant converter with only one or two magnetic components which can be controlled by a low-level control signal without resorting to a variable switching frequency.
\r\n\r\nThe inclusion of a variable inductance poses special problems in the design and modeling of the control loop which regulates this family of converters. The small-signal model of the magnetic regulator is derived and verified with experimental results. This model is then incorporated into a model for the DC-to-DC converter. The converter model is presented with three levels of complexity beginning with a very simple model which exposes the contribution of the magnetic regulator to the overall response of the converter. The model is further refined to include a bilateral model for a resonant rectifier with a final bilateral model for the inverter.
\r\n\r\nThe model of the complete DC-to-DC converter is compared against simulated data from the computer program SPICE and also against measured data on a typical converter. The model is shown to contain low frequency dynamics dominated by the input and output filters on the converter, and high frequency dynamics associated with the resonant circuit elements. The models developed are continuous-time average models which are conveniently represented using equivalent circuits.
" }, { "name": "Von Sosen, Harald", "degree": "PhD", "year": "1994", "title": "Part I: Folds and bifurcations in the solutions of semi-explicit differential-algebraic equations. Part II: The recursive projection method applied to differential-algebraic equations and incompressible fluid mechanics", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechETD:etd-07282005-161146", "creators": [ { "name": { "family": "Von Sosen", "given": "Harald" }, "id": "VonSosen-H", "display_name": "Von Sosen, Harald" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/JP6Q-ED69", "abstract": "Part I: Folds and Bifurcations in the Solutions of Semi-Explicit Differential-Algebraic Equations\n\nA general existence theory for the solutions of semi-explicit differential-algebraic equations (DAEs) is given. Theorems on the form and number of solutions in a neighborhood of an initial value are presented. A set of bifurcation equations is derived, from which the tangents of these solutions can be computed. The phenomena of folds and bifurcation are studied. It is shown that solutions near fold points and pitchfork bifurcation points can be represented smoothly if an appropriate parametrization is introduced. Moreover, it is shown that the complex analytic extension of a real DAE often has complex solutions near a real initial value, and existence theorems on these complex solutions are given. Examples from electrical engineering are presented in support of the theory. Methods for adapting existing numerical DAE solvers to handle fold and bifurcation points are introduced. These methods are tested on a nonlinear electric circuit problem.\n\n\nPart II: The Recursive Projection Method Applied to Differential-Algebraic Equations and Incompressible Fluid Mechanics\n\nThe Recursive Projection Method (RPM) was originally invented by Schroff and Keller for the stabilization of unstable fixed point iterations. A direct application of RPM lies in the computation of unstable steady states of nonlinear ordinary differential equations (ODEs) via time integration. Here, the method is generalized to handle algebraic constraints so that it can be applied to certain differential-algebraic equations (DAEs). This is accomplished by reformulating the DAE as an ODE. In particular, this approach applies to DAEs obtained by semi-discretization of the incompressible Navier-Stokes equations by use of the method of lines. The method is applied to compute unstable steady states of the flow between concentric rotating cylinders." }, { "name": "Wen, Chihyung", "degree": "PhD", "year": "1994", "title": "Hypervelocity flow over spheres", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212004-092435", "creators": [ { "name": { "family": "Wen", "given": "Chihyung" }, "id": "Wen-C", "display_name": "Wen, Chihyung" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5DDV-GW34", "abstract": "The nature of the nonequilibrium flow of dissociating gases over spheres was investigated experimentally, numerically and theoretically. A series of experiments with three different gases, nitrogen, air and carbon dioxide, was performed in the shock tunnel T5 at GALCIT. Five spheres of different radii equipped with thermocouples for surface heat flux measurements were used. The state-of-the-art numerical method by Candler (1988) was used to conduct a parallel study which strongly complemented the experimental and theoretical efforts.\n\nExperimental heat flux measurements are presented. Good agreement was observed among the measured stagnation point heat transfer rates, computational results and Fay and Riddell\u2019s theoretical predictions. For nitrogen and air, the measured heat flux distributions were also in good agreement with numerical computation results and Lees\u2019 theory. For carbon dioxide, large deviations were observed. Early transition tripped by surface roughness is a possible cause for the deviation of heat flux distribution from the theory. The experimental differential interferograms were compared with the images constructed from computational flowfields. Good agreement of fringe pattern and shock shape was observed.\n\nAn analytical solution is obtained for inviscid hypervelocity dissociating flow over spheres. The solution explains the correlation between the dimensionless stand-off distance and the dimensionless reaction rate parameter previously observed by Hornung (1972) for nitrogen. The physics of the correlation can be shown as the binary scaling. Based on the solution, a new dimensionless reaction rate parameter is defined to generalize Hornung\u2019s correlation for more complex gases than nitrogen. Experimental and numerical results confirm the new correlation.\n\nThe effect of nonequilibrium recombination downstream of a curved two-dimensional shock was also addressed. An analytical solution for an ideal dissociating gas was obtained, giving an expression for dissociation fraction as a function of temperature on a streamline. The solution agrees well with the numerical result and provides a rule of thumb to check the validity of binary scaling for the experimental conditions. The effects upon the binary scaling of the large difference in freestream temperature between flight and free-piston shock tunnel conditions are discussed." }, { "name": "Willette, Gregory Thomas", "degree": "PhD", "year": "1994", "title": "Stochastic excitation of the solar oscillations by turbulent convection", "advisor": "Goldreich, Peter Martin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072007-081017", "creators": [ { "name": { "family": "Willette", "given": "Gregory Thomas" }, "id": "Willette-G-T", "display_name": "Willette, Gregory Thomas" } ], "advisors": [ { "name": { "family": "Goldreich", "given": "Peter Martin" }, "id": "Goldreich-P-M", "role": "advisor", "display_name": "Goldreich, Peter Martin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7nmq-8a04", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nThe thesis topic is the stochastic excitation of the solar p-modes by turbulent convection, and the work consists of four parts: three theoretical sections and one observational. In the first section of the thesis, an explicit calculation of the acoustic radiation of a buoyant oscillating bubble is presented as a model for the excitation of the solar p-modes. The central scientific issue addressed in this work is the cancellation of monopole and dipole radiation fields in an anisotropic medium, first pointed out by Goldreich and Kumar (1990). When the bubble oscillation frequency is small compared to the acoustic cutoff, the monopole and dipole disturbances cancel to the quadrupole order in the far field. The second section deals with the role of convective structures in a wide number of problems, including the creation of acoustic disturbances, the transport of heat and magnetic fields, and the penetration of flows into stable layers of the atmosphere (overshoot). A model of plume convection is developed to discuss these issues. It is argued that the scaleheight-sized flows (the only energetically significant ones) are properly characterized as coherent, entropy-preserving plumes, in contradistinction to the picture of amorphous parcels of fluid suggested by the Mixing Length Theory, and in spite of the large Reynolds numbers typical in astrophysical convection. The third section of the thesis is an analysis of high-resolution surface velocity data taken with a magneto-optical filter on the 10 inch telescope at Big Bear Solar Observatory. Estimates are obtained for the frequencies and amplitudes of the solar oscillations of high spherical harmonic degree ([...] 2000). The observed mode energies follow a Boltzmann distribution [...], as is predicted in the stochastic excitation model. In the final section of the thesis, a derivation of the variational principle for an incompressible fluid is presented. The Lagrange and Hamiltonian densities are calculated to third order in the displacement field, and these results suitable to study the non-linear interactions among incompressible modes.\r\n" }, { "name": "Yvon, Pascal", "degree": "PhD", "year": "1994", "title": "Metastable phases in the aluminum-germanium alloy system. Synthesis by mechanical alloying and pressure induced transformations", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122007-111950", "creators": [ { "name": { "family": "Yvon", "given": "Pascal" }, "id": "Yvon-P", "display_name": "Yvon, Pascal" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/a9ct-na12", "abstract": "Amorphous alloys have been prepared by a variety of techniques from rapid solidification to solid state crystal-to-glass transformations. In this work we report the use of pressure to obtain amorphous alloys in the aluminum-germanium alloy system. Aluminum and germanium form a simple equilibrium eutectic with limited mutual solubility and no intermetallic intermediate phases. We used a regular solution approach to model the effects of pressure on the Al-Ge binary phase diagram. The main effects of pressure are to extend the solubility of germanium in aluminum, to displace the eutectic composition towards the germanium-rich side, and to slightly decrease the eutectic temperature. Using this modeled phase diagram, we designed thermobaric treatments to induce crystal-to-glass transformations in fine grain mixtures of aluminum and germanium.\n\nWe used Merrill-Bassett diamond anvil cells to perform experiments at high pressures. We designed and built an x-ray apparatus to enable us to determine the structure of the alloys at pressure and from cryogenic temperatures to 4000C. Two-phase A1-Ge samples with fine microstructures were prepared by splat-quenching and mechanical alloying. We observed a crystal-to-glass transformation at about 80 kbar. The amorphous phase formed was metastable at ambient temperature after the pressure was released. This result was confirmed by transmission electron microscopy (TEM) studies. The amorphous phase obtained by pressurization was found to have a liquid-like structure and was metallic. This is the first time such an amorphous phase is reported in the aluminum-germanium alloy system. In the TEM samples we also observed the presence of a second amorphous phase that was formed upon release of the pressure. This second phase had a tetrahedrally-bonded continuous random network structure, similar to that of semi-conductig amorphous germanium." }, { "name": "Zeng, Zheng", "degree": "PhD", "year": "1994", "title": "Recurrent neural networks for grammatical inference", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112007-090004", "creators": [ { "name": { "family": "Zeng", "given": "Zheng" }, "id": "Zeng-Z", "display_name": "Zeng, Zheng" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Smyth", "given": "Padhraic" }, "id": "Smyth-P", "role": "member", "display_name": "Smyth, Padhraic" }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/BQBV-GE18", "abstract": "In this thesis, various artificial recurrent neural network models are investigated for the problem of deriving grammar rules from a finite set of example \"sentences.\" A general discrete network framework and its corresponding learning algorithm are presented and studied in detail in learning three different types of grammars.
\r\n\r\nThe first type of grammars considered is regular grammars. Experiments with conventional analog recurrent networks in learning regular grammars are presented to demonstrate the unstable behavior of such networks in processing very long strings after training. A new network structure to force recurrent networks to learn stable states by discretizing the internal feedback signals is constructed. For training such discrete networks a \"pseudo-gradient\" learning rule is applied.
\r\n\r\nAs an extension to the discrete network model, an external discrete stack is added to accommodate the inference of context-free grammars. A composite error function is devised to deal with various situations during learning. The pseudo-gradient method is also extended to train such a network to learn context-free grammars with the added option of operating on the external stack.
\r\n\r\nAnother extension to the discrete network structure is made for the purpose of learning probabilistic finite state grammars. The network consists of a discrete portion which is intended to represent the structure of the grammar, and an analog portion which is intended to represent the transition probabilities. Two criteria for the network to verify the correctness of its solution during training are proposed. Theoretical analysis of the necessary and sufficient conditions for the correct solution is presented.
\r\n\r\nExperimental results show that the discrete network models have similar capabilities in learning various grammars as their analog counterparts, and have the advantage of being provably stable.
" }, { "name": "Zhao, Bin", "degree": "PhD", "year": "1994", "title": "Threshold and Dynamics in Semiconductor Quantum Well Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112007-133429", "creators": [ { "name": { "family": "Zhao", "given": "Bin" }, "id": "Zhao-Bin", "display_name": "Zhao, Bin" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/5ZK1-TC36", "abstract": "The application of semiconductor lasers to optical communications and interconnects requires low threshold current, high-frequency modulation, and low-noise characteristics. Quantum well (QW) lasers have received considerable attention due to the demonstrated low threshold current, predicted superior modulation and spectral dynamics due to the reduction of active layer thickness and corresponding modification of density of states for the injected carriers in the extremely thin active region. However, in comparison with their bulk counterparts - double heterostructure (DH) lasers, quantum well lasers have not experimentally demonstrated significant improvement in the modulation bandwidth especially in the case of single quantum well (SQW) lasers.
\r\n\r\nIn a practical quantum well structure, the separate confinement heterostructure (SCH) is usually used to confine the optical field in the waveguide and the injected carriers in the quantum well region. The fundamental Fermi-Dirac statistics results in that, in addition to the carrier population in the quantum well region, there is also a significant carrier population in the optical confining region. In the previous differential gain evaluations, the carrier population in the energy states in the optical confining region of the separate confinement heterostructure (referred as the state/band filling effects in QW lasers) was omitted.
\r\n\r\nThe state filling effects are, in principle, inherent in any QW structure due to the Fermi distribution of the injected carriers. A re-evaluation of differential gain for typical GaAs/AIGaAs QW and DH bulk lasers with consideration of state filling shows that (i) there is no differential gain enhancement in SQW lasers in comparison to the bulk lasers; (ii) there is an additional differential gain enhancement in multiple quantum well (MQW) lasers stemming from the reduction of state filling. These conclusions are consistent with the experimental results of high speed modulation bandwidth in semiconductor lasers.
\r\n\r\nThese theoretical and experimental investigations provide useful guides in design of QW lasers of ultra-high performance. Using these design criteria, strained InGaAs MQW buried heterostructure (DH) lasers have been fabricated. These lasers have demonstrated record low lasing threshold currents (0.25 mA) and high speed at low operation current (3dB bandwidth of 5 GHz at 2.1 mA). These lasers are potentially important for optical interconnects and local area network communication systems.
" }, { "name": "Abe, Yoshio", "degree": "PhD", "year": "1993", "title": "Formation and stability of nanocrystalline alloys synthesized by mechanical milling", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-08222007-085631", "creators": [ { "name": { "family": "Abe", "given": "Yoshio" }, "id": "Abe-Yoshio", "display_name": "Abe, Yoshio" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/td6t-jp61", "abstract": "Nanocrystalline materials are expected to have quite different physical properties from both conventional polycrystalline materials and amorphous materials, particularly due to high fraction of grain boundaries. For their application, to improve the stability is of great concern. In this study, nanocrystalline Ti - Cu, Ti - Zr - Cu and Nb - Cu alloys were synthesized by the mechanical alloying technique. Macroscopically, supersaturated single-phase solid solutions were obtained in the form of powder after certain duration of ball milling. The powders obtained were characterized by X-ray diffraction, differential scanning calorimetry, transmission electron microscopy and small angle X-ray scattering. In Ti - Cu and Ti - Zr - Cu systems, crystal grains do not grow by heating until the intermetallic Cu(Ti, Zr)2 phase nucleates, while in Nb - Cu system, grain growth follows the clustering of elemental Cu. These result lead to the hypothesis that grain growth is suppressed due to the segregation of Cu atoms in grain boundaries. Furthermore, the mechanisms of solute segregation in grain boundaries and the stability of the nanocrystalline structure are discussed in terms of the hypothesis that grain boundaries consist of a liquid-like disordered phase. Finally, based on the above argument, we have proposed a new technology, high temperature ball milling, to synthesize nanocrystalline alloys with finer grain size and more stability and to control grain size as desired.\r\n" }, { "name": "Anthony, Lawrence", "degree": "PhD", "year": "1993", "title": "Kinetics of disorder -> order transformations in highly nonequilibrium materials", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092005-083533", "creators": [ { "name": { "family": "Anthony", "given": "Lawrence" }, "id": "Anthony-L", "display_name": "Anthony, Lawrence" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/5e9h-nh03", "abstract": "Of late, there has been need for rigorous first-principles theoretical considerations of materials that are far removed from equilibrium. This is especially true as nonequilibrium materials of all shapes (e.g., thin film structures) and sizes (e.g., nanocrystalline composites) gain ever-increasing technological importance. To this end, the main contribution of this dissertation is to the study of the kinetics of disorder -> order transformations in highly nonequilibrium binary alloys, specifically body-centered cubic alloys exhibiting B2, D0_3, and/or B32 order at equilibrium. This study takes several independent approaches. Chapter 2 presents two analytical methods. The first of these, a master equation method, is formulated in the Bragg-Williams or point approximation. The second analytical technique employs the path probability method of Kikuchi in the Bethe or pair approximation. Chapter 3 employs kinetic Monte Carlo simulations instead. Apart from the presentation of individual results using these three different techniques, the thermodynamic and kinetic trends exhibited by these different approaches are compared and discussed. One of the more compelling features exhibited by all three of these diverse approaches is the appearance, during ordering, of certain well-developed transient states, which do not persist at equilibrium, e.g., the transient appearance of B2 order during ordering in an alloy that exhibits equilibrium B32 order. These transient states are discussed within the context of pseudostability. Central to the notion of pseudostability is the concept of a free energy surface or manifold in order parameter space. While it is quite straightforward to obtain a closed-form, analytical (albeit approximate) expression for the configurational entropy and free energy in the master equation method and the path probability method, there is no simple, direct means of obtaining the same in the kinetic Monte Carlo simulations. Chapter 4 seeks to remedy this limitation of the Monte Carlo method and introducs a hybrid Monte Carlo-cluster variation method approach to order-disorder kinetics. This method is used to reexamine some of the results of Chapter 3 in the context of the time evolution of the free energy. Chapter 5 summarizes the results of the preceeding chapters and suggests avenues for further investigation.\r\n" }, { "name": "Bailey, Andrew Dewey", "degree": "PhD", "year": "1993", "title": "Drift wave ion fluid velocity field measured by planar laser induced fluorescence", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-08222007-091624", "creators": [ { "name": { "family": "Bailey", "given": "Andrew Dewey" }, "id": "Bailey-A-D", "display_name": "Bailey, Andrew Dewey" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/0437-H138", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe first plasma planar laser induced fluorescence (PLIF) diagnostic has been developed and used to study Ar plasma discharges in Caltech's Encore tokamak. The first two-dimensional time resolved measurements of the ion fluid velocity have been made with this diagnostic. PLIF excited in a poloidal cross section by a narrow linewidth laser sheet is imaged onto a 10x10 anode microchannel plate photomultiplier. Both the ion temperature and one component of the fluid velocity of metastable ArII ions are measured by scanning the laser wavelength through the Doppler broadened and shifted PLIF absorption line. The maximum measured wavelength shifts correspond to velocities [...] (1.5 [...] 0.08) x 10[...]cm/s. A periodic spatial structure in the fluid velocity field is observed to oscillate in phase with a coherent, large amplitude, mostly electrostatic drift-Alfven wave with poloidal and toroidal mode numbers m = 2, n = 1. Previous work (McChesney '87) indicates that the anomalously hot ion temperatures measured ([...] 6eV) are due to stochastic ion motion in the drift waves. Using PLIF, oscillations in the temperature ([...] 3eV) out of phase with the drift wave potential have been observed for the first time.\r\n\r\nTo provide an interpretation of the PLIF fluid velocity data, Langmuir probe measurements were made in a nearby poloidal cross section. The calculated ion fluid flow pattern in the drift approximation agreed qualitatively with the measured velocity field, but the calculations predict much larger velocities than are measured. The general agreement, despite the stochastic dynamics, emphasizes the robust nature of the two-fluid description of the plasma. The discrepancies with the PLIF measurements also highlight the need for a better understanding of the relationship between stochastic particle dynamics and macroscopic plasma parameters.\r\n\r\nAn explicit connection is made between the ion distribution and Poincare maps of the single particle dynamics in prescribed mean fields by considering the characteristics of the collisionless Vlasov equation. A self-consistent distribution function is restricted to being constant in stochastic regions of phase space where one particle orbit comes arbitrarily close to any point in the region. The implications of this viewpoint are explored for a simplified model of the drift wave. When the bulk of the ions are stochastic, the center of the distribution function is flattened leading to higher ion 'temperatures' derived from Maxwellian fits, but the envelope of the stochastic region and thus the fluid velocity and temperature continue to oscillate periodically with the wave despite the nonperiodicity of the individual particle orbits." }, { "name": "Belanger, Jacques", "degree": "PhD", "year": "1993", "title": "Studies of Mixing and Combustion in Hypervelocity Flows with Hot hydrogen injection", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08222007-092852", "creators": [ { "name": { "family": "Belanger", "given": "Jacques" }, "id": "Belanger-Jacques", "display_name": "Belanger, Jacques" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/012K-GE91", "abstract": "The ability to build an air-breathing single-stage-to-orbit propulsion system requires examination of key elements such as turbulent mixing rates, especially at the \"zero shear\" fuel-air mixing condition, and combustion efficiency. The required data can only be obtained in experiments which simultaneously match the flight total pressure and total enthalpy as well as the fuel conditions. GALCIT, with its new free piston shock tunnel T5, has the capability to do some of these combustion experiments. But prior to these tests, it was felt that there was a need to simulate the gas dynamical processes in the free piston shock tunnel and also in a new combustion driven shock tunnel built for these experiments so that both systems could be used as efficiently as possible. The numerical code helped explain the piston motion in the free piston shock tunnel. The code was also very useful for the design of the combustion driven shock tunnel.
\r\n\r\nBecause hydrogen has to be injected into the combustion chamber of the propulsion system after being used as a cooling fluid, a combustion driven shock tunnel was built to reproduce this \"hot\" hydrogen fuel. The system has been used successfully to supply hydrogen at up to 1500 K for the experiments. To reduce the complexity of the problem, a very basic configuration for the hydrogen injection system was tested. This was first done with an injection system mounted flush with the surface of a flat plate in the test section of T5. Different test conditions as well as Mach 2 and 5 nozzle injectors at angles of 15\u00b0 or 30\u00b0 were tested to determine criteria for significant combustion. Lower limits in pressure and enthalpy were found where hydrogen combustion becomes very limited using this \"hot\" hydrogen fuel. The second set of experiments still used an injection system mounted flush with the surface but involved a small combustor model previously tested in the hypervelocity HYPULSE facility. Low pressure experiments were performed to reproduce some of the HYPULSE tests and excellent agreement was found. Experiments at high pressure were also performed to better match the real flight total pressure and some hydrogen combustion was detected in these tests.
" }, { "name": "Boden, Nanette Jackson", "degree": "PhD", "year": "1993", "title": "Runtime systems for fine-grain multicomputers", "advisor": "Van de Snepscheut, Jan L. A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08222007-103344", "creators": [ { "name": { "family": "Boden", "given": "Nanette Jackson" }, "id": "Boden-Nanette-Jackson", "display_name": "Boden, Nanette Jackson" } ], "advisors": [ { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "advisor", "display_name": "Van de Snepscheut, Jan L. A." } ], "committee": [ { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "chair", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Van de Velde", "given": "Eric" }, "id": "van-de-Velde-E", "role": "member", "display_name": "Van de Velde, Eric" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "member", "display_name": "Taylor, Stephen" } ], "option_major": [ "compsci" ], "doi": "10.7907/2c3a-k589", "abstract": "During the past decade, our research group has been engaged in experiments in the architecture and programming of multicomputers. This research has progressed steadily toward the ideal of small granularity, both of the computing nodes within a multicomputer, and of the execution units within concurrent programs. The context for the runtime-system and program-behavior experiments reported in this thesis are: (1) the reactive-process, message passing computational model, (2)C+-, a C++ -based, concurrent-programming notation, and (3) the Mosaic C, an experimental, fine-grain multicomputer.\r\n\r\nWe present first a long-sought solution to the formulation of an unbounded queue of elements within the reactive-process model. This result is applied to allow messages to be received selectively using purely reactive semantics.\r\n\r\nThe primary contributions of this thesis are distributed algorithms and a design method for runtime systems for fine-grain multicomputers. To evaluate the algorithms and design, a prototype runtime system called MADRE was developed, C+- programs whose behaviors are typical of a variety of applications were written, these programs were executed on the Mosaic C under MADRE, and the program behavior was instrumented.\r\n\r\nIn addition to conventional operating- and runtime-system functions such as local memory management and quiescence detection, MADRE automatically manages userprocess placement and naming. MADRE can also be configured to include capabilities for distributing resource demands across the nodes of the multicomputer. Buffered messages can be exported from congested nodes so that incoming messages can continue to be received. The code of user programs can be distributed across the ensemble, and accessed automatically. Each of these capabilities depends upon the formulation of selective receive demonstrated in the solution to the unbounded queue.\r\n\r\nOur experiments evaluate various automatic process-placement strategies. We show that one algorithm, called k-biased placement, distributes loads nearly as well as random placement, while providing a tunable degree of locality between parent and child processes. Other experiments demonstrate that the message-exportation capability is crucial to finegrain multicomputers; unless messages can be exported, computations fail due to receive queue overflow when only a fraction of the multicomputer's memory resources are being used.\r\n" }, { "name": "Bourzutschky, Marc S.", "degree": "PhD", "year": "1993", "title": "Complex dynamics in systems with many degrees of freedom", "advisor": "Cross, Michael Clifford", "url": "https://resolver.caltech.edu/CaltechETD:etd-08232007-131927", "creators": [ { "name": { "family": "Bourzutschky", "given": "Marc S." }, "id": "Bourzutschky-M-S", "display_name": "Bourzutschky, Marc S." } ], "advisors": [ { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "advisor", "display_name": "Cross, Michael Clifford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/s944-8d11", "abstract": "Complex dynamics in systems with many degrees of freedom are investigated with two classes of computational models. The models in the first class are motivated by the experimental observation of spatiotemporal chaos in strongly driven convection cells, and are designed to display chaotic evolution in discrete space and time. A local conservation law is incorporated into the equations of motion, and its importance is discussed. The central limit theorem is applied to characterize fluctuations over large uncorrelated regions, and a simple theory predicting the long wavelength properties of the models is developed and verified numerically. The applicability of the fluctuation-dissipation theorem and the maximum entropy principle to nonequilibrium systems is tested extensively. A possible application to an experimental situation is outlined.\n\nThe models in the second class are motivated by the concept of self organized criticality, which predicts that driven dynamical systems naturally evolve to a statistically stationary state displaying scale invariance. Several scenarios of how scaling behavior can occur in dynamical systems are discussed, using ideas from dimensional analysis. A simple mean field theory for a large class of cellular automata models is developed. Extensive numerical simulations are described which test the validity of scaling forms and demonstrate possible errors resulting from finite size effects." }, { "name": "Bridges, David Henry", "degree": "PhD", "year": "1993", "title": "Tip effects on the vortex wake of an axisymmetric body at angle of attack", "advisor": "Hornung, Hans G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08232007-081713", "creators": [ { "name": { "family": "Bridges", "given": "David Henry" }, "id": "Bridges-D-H", "display_name": "Bridges, David Henry" } ], "advisors": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "advisor", "display_name": "Hornung, Hans G." } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Peck", "given": "Charles W." }, "id": "Peck-C-W", "role": "member", "display_name": "Peck, Charles W." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DZ4H-M010", "abstract": "Experiments on the effects of conditions at the tip of an axisymmetric body on the vortex wake of the body at large angle of attack in incompressible flow have been performed. The separation patterns that occur at the nose of a cone with a hemispherical tip have been documented for ranges of Reynolds number based on tip radius and of relative angle of attack. Tips with cross sections that vary smoothly from elliptic to circular have been designed and tested on a cone. The effectiveness of the tips in varying the cone side force coefficient as the tip is rotated has been demonstrated. The relation between tip roll angle and side force coefficient has been shown to be essentially independent of Reynolds number, for the range of Reynolds number tested, as well as cone base conditions and roll direction. The relation between tip roll angle and side force coefficient has been shown to be a strong function of angle of attack. The reasons for nonsmooth variation of side force coefficient with tip roll angle at higher angles of attack have been determined by examinations of the vortex wake geometry. Peaks in the magnitude of the side force coefficient after zero crossings have been shown to be caused by a rapid shift in the wake vortices away from a symmetric configuration as the tip rotates away from a symmetry condition. Reductions in magnitude of the side force coefficient between magnitude peaks have been demonstrated to be a result of the near vortex crossing over the cone centerline. This vortex crossover has been shown to occur near and after the breakaway from the cone of the far vortex. The ability of one of the elliptic cross section tips to produce smooth variations of side force coefficient with roll angle ahead of vortex breakaway has been demonstrated, suggesting that the tip might be an effective yaw control device for aircraft at high angle of attack." }, { "name": "Cardell, Gregory Scott", "degree": "PhD", "year": "1993", "title": "Flow past a circular cylinder with a permeable wake splitter plate", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012005-092116", "creators": [ { "name": { "family": "Cardell", "given": "Gregory Scott" }, "id": "Cardell-G-S", "display_name": "Cardell, Gregory Scott" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/25C5-1150", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nMeasurements in the near wake region of a circular cylinder in a uniform flow in the Reynolds number range [...] with permeable splitter plates spanning the wake center plane are presented. Permeability is defined by the pressure drop across the plates, and the relationship between permeability and plate solidity is determined for a set of plates constructed from woven wire mesh, permitting unambiguous characterization of the splitter plates by the solidity. The effects of different solidities on the flow in the near wake are investigated using smoke wire flow visualization, hot-wire anemometry, and measurements of the mean pressure at the cylinder surface, and the results are related to cylinder flow without a splitter plate.\n\nFlow visualization results demonstrate that the introduction of low solidity splitter plates does not change the basic near wake structure, and that sufficiently high solidity uncouples the large-scale wake instability from the body, with the primary vortex formation occurring downstream of the separation bubble due to instability of the wake profile. Hotwire and surface pressure measurements confirm and quantify the flow visualization results, showing that the permeable splitter plates reduce the drag and modify the primary wake frequency. When the solidity is high enough that the wake is convectively unstable, the base pressure is independent of the Reynolds number and solidity. For a wide range of solidities, the same asymptotic value of the Strouhal number is reached at high Reynolds numbers. The relationship between the Strouhal number and the base pressure is discussed.\n\nDetailed measurements in the separating shear layers with splitter plates moderating the primary vortex formation show that in the mean the development of the separating shear layers is similar to that of the plane mixing layer. The presence of the splitter plates enhances shear layer development, and it is found that for all solidities the instability amplifies a broad frequency band without discrete spectral features. Turbulent transition in the shear layer and its role in the pronounced Reynolds number dependency of the flow in this Reynolds number range is discussed. Acoustic excitation of the separated shear layers confirms the broad band frequency response of the shear layer instability, and the effect of the driven shear layers on the near wake is investigated." }, { "name": "Chan, Wingsiu Richard", "degree": "PhD", "year": "1993", "title": "Experimental and numerical studies on two-dimensional gravity currents in a horizontal channel", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08232007-094513", "creators": [ { "name": { "family": "Chan", "given": "Wingsiu Richard" }, "id": "Chan-Wingsiu-Richard", "display_name": "Chan, Wingsiu Richard" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "mecheng" ], "doi": "10.7907/d44w-pm14", "abstract": "The objective of this investigation is to examine the behavior of two-dimensional gravity currents, especially as applied to the spreading of smoke, generated from a room fire, along a long corridor. Both experimental and numerical techniques were used to provide a model that can adequately explain and predict the behavior of a gravity current under certain boundary conditions.\r\n\r\nA series of experiments was carried out to study the effects of Reynolds number on gravity currents in a horizontal water channel. Measurements of the time varying front position, velocity profile of the following current, and the depth of a gravity current were made using either dyed liquids or hydrogen bubble technique. Quantitative results were shown to agree with previously published results. A model was put forth to bridge the gap between the existing models for an inertia-buoyancy dominated gravity current and a viscous-buoyancy dominated one. Comparison between the experimental results and numerical results obtained from the model proved that the model can adequately explain the behavior of the phenomenon.\r\n\r\nA second series of experiments was conducted to investigate the behavior of gravity currents in an inclined channel. The quantitative results obtained were less scattered than those obtained in previous research. The gravity current was found to be unsteady in a horizontal channel, while a channel with an angle of inclination of one degree was found to produce a steady flow behind the front of the gravity current. The change of the gravity currents from an unsteady to a steady nature due to the change in the inclination of the channel was found to be gradual and much less abrupt than assumed in previous studies." }, { "name": "Chen, Tsuhan", "degree": "PhD", "year": "1993", "title": "Multidimensional multirate filters and filter banks : theory, design, and implementation", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08232007-095226", "creators": [ { "name": { "family": "Chen", "given": "Tsuhan" }, "id": "Chen-Tsuhan", "display_name": "Chen, Tsuhan" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/XHE8-RB96", "abstract": "Multidimensional (MD) multirate systems, which find applications in the coding and compression of image and video data, and in high definition television (HDTV) systems, have recently attracted much attention. Central to these systems is the idea of sampling lattices. The basic building blocks in an MD multirate system are the decimation matrix M, the expansion matrix L, and MD digital filters. When M and L are diagonal, most of the one-dimensional (1D) multirate results can be extended automatically, using separable approaches (i.e., separate operations in each dimension). Separable approaches are commonly used in practice due to their low complexity in implementation. However, nonseparable operations, with respect to nondiagonal decimation and expansion matrices, often provide more flexibility and better performance. Several applications, such as the conversion between progressive and interlaced video signals, actually require the use of nonseparable operations. For the nonseparable case, extensions of 1D results to the MD case are nontrivial. In this thesis, we will introduce some developments in these extensions. The three main results are: the design of nonseparable MD filters and filter banks derived from 1D filters, the commutativity of MD decimators and expanders and its applications to the efficient polyphase implementation of MD rational decimation systems, and the vector space framework for unifying MD filter bank and wavelet theory. In particular, properties of integer matrices like matrix fraction descriptions, coprimeness, the Bezout identity, etc., of which the polynomial versions are known in system theory, are used for the first time in the area of multirate signal processing.\r\n" }, { "name": "Chiang, Dar-Yun", "degree": "PhD", "year": "1993", "title": "Parsimonious modeling of inelastic systems", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11192012-102847690", "creators": [ { "name": { "family": "Chiang", "given": "Dar-Yun" }, "id": "Chiang-D-Y", "display_name": "Chiang, Dar-Yun" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "co-chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/75ZY-2K10", "abstract": "Analytical modeling of one-dimensional hysteresis and general multi-axial cyclic plasticity is studied, with particular emphasis on the parsimony of model parameters and the physical consistency of model behavior. General criteria for good models are proposed to provide guidelines to the modeling studies conducted in this research.
\r\n\r\nVarious one-dimensional hysteretic models are examined in detail, including both deteriorating and non-deteriorating models. A general formulation for modeling of degrading systems is presented based on the formulation of the Distributed-Element Model (DEM) and the introduction of a damage index function. A new class of deteriorating Masing models, whose behavior can be completely described by a few simple mathematical rules and the extended Masing rules, is also developed to substitute for a special class of deteriorating DEMs, so that their applicabilty to system identification studies is improved.
\r\n\r\nThe one-dimensional DEMs are extended to the multi-dimensional case for constitutive modeling of cyclic plasticity, while preserving the concept of modeling plasticity by an assemblage of simple ideal elasto-plastic elements. In the generalization, a new invariant-yield-surface theory is proposed, in which no kinematic hardening rule is needed to account for the subsequent yielding and strain hardening behavior. A general theory is also developed to elucidate some important properties of material behavior based on the proposed multi-dimensional DEMs. The establishment of the theory provides instructive insight into the elastic-plastic response mechanisms of real materials under complicated loading conditions. Based on the insight, the Masing rules for one-dimensional hysteresis are extended to the multi-dimensional case by introducing a composition of plane-geometry transformations to a response formula developed for initial loading. This transformation method serves as an efficient way of implementing the classical multi-yield-surface theory with the Mroz kinematic hardening rule. Validity of the new formulations are confirmed by comparison with experimental results from the literature.
" }, { "name": "Choi, Wooyoung", "degree": "PhD", "year": "1993", "title": "Forced Generation of Solitary Waves in a Rotating Fluid and Their Stability", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-08242007-075146", "creators": [ { "name": { "family": "Choi", "given": "Wooyoung" }, "id": "Choi-Wooyoung", "display_name": "Choi, Wooyoung" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "eng" ], "doi": "10.7907/v6v3-v763", "abstract": "The primary objective of this graduate research is to study forced generation of solitary waves in a rotating fluid and their stability properties. For axisymmetric flow of a non-uniformly rotating fluid within a long cylindrical tube, an analysis is presented to predict the periodic generation of upstream-advancing vortex solitons by axisymmetric disturbance steadily moving with a transcritical velocity as a forcing agent. The phenomenon is simulated using the forced Korteweg-de Vries (fKdV) equation to model the amplitude function of the Stokes stream function for describing this family of rotating flows of an inviscid and incompressible fluid. The numerical results for the weakly nonlinear and weakly dispersive wave motion show that a sequence of well-defined axisymmetrical recirculating eddies is periodically produced and emitted to radiate upstream of the disturbance, soon becoming permanent in the form as a procession of vortex solitons, which we call vortons. Two primary flows, the Rankine vortex and the Burgers vortex, are adopted to exhibit in detail the process of producing the upstream vortons by the critical motion of a slender body moving along the central axis, with the Burgers vortex being found the more effective of the two in the generation of vortons. To investigate the evolution of free or forced waves within a tube of non-uniform radius, a new forced KdV equation is derived which models the variable geometry with variable coefficients. A set of section-mean conservation laws is derived specially for this class of rotational tube flows of an inviscid and incompressible fluid, in both differential and integral forms. A new aspect of stability theory is analyzed for possible instabilities of the axisymmetric solitary waves subject to non-axisymmetric disturbances. The present linear analysis based on the model equation involving the bending mode shows that the axisymmetric solitary wave is neutrally stable with respect to small bending mode disturbances. To study nonlinear interactions between the axisymmetric mode and bending mode, a new model is derived which consists of two coupled equations for disturbances of the two modes. The numerical results of the coupled equations show that the primary axisymmetric soliton appears to maintain its own entity, with some oscillations of its amplitude and an undular tail, inferring an interchange of energy between the two modes, when subject to small non-axisymmetric perturbations." }, { "name": "Cortelezzi, Luca", "degree": "PhD", "year": "1993", "title": "A Theoretical and Computational Study on Active Wake Control", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302005-111117", "creators": [ { "name": { "family": "Cortelezzi", "given": "Luca" }, "id": "Cortelezzi-Luca", "display_name": "Cortelezzi, Luca" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "eng" ], "doi": "10.7907/ZMMS-XA57", "abstract": "In the first part of this dissertation a two-dimensional unsteady separated flow past a semi-infinite plate with transverse motion is considered. The flow is assumed incompressible and at high Reynolds number. The rolling-up of the separated shear-layer is modelled by a point vortex whose time dependent circulation is predicted by an unsteady Kutta condition. A power-law starting flow is assumed along with a power-law for the transverse motion. The effects of the motion of the plate on the starting vortex circulation and trajectory are presented. A suitable vortex shedding mechanism is introduced and a class of flows involving several vortices is presented. Subsequently, a control strategy able to maintain constant circulation when a vortex is present is derived. An exact solution for the non-linear controller is then obtained. Dynamical system analysis is used to explore the performance of the controlled system. Finally, the control strategy is applied to a class of flows and the results are discussed.\r\n\r\nIn the second part of this dissertation the previous results are extended to the case of a two-dimensional unsteady separated flow past a plate of variable length. Again the rolling-up of the separated shear-layer is modelled by a vortex pair whose time dependent circulation is predicted by an unsteady Kutta condition. A power-law starting flow is assumed while the plate length is kept constant. The results of the simulations are presented and the model validated. A time-dependent scaling which unveils the universality of the phenomenon is discussed. The previous vortex shedding mechanism is implemented and a vortex merging scheme is tested in a class of flows involving several vortices and is shown to be highly accurate. Subsequently, a control strategy able to maintain constant circulation when a vortex pair is present is derived. An exact solution for the non-linear controller is obtained in the form of an ordinary differential equation. Dynamical system analysis is used to explore the performance of the controlled system and the existence of a controllability region is discussed. Finally, the control strategy is applied to two classes of flows and the results are presented." }, { "name": "Dawson, Jay W.", "degree": "PhD", "year": "1993", "title": "Single and multiple frequency fiber lasers", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-084804", "creators": [ { "name": { "family": "Dawson", "given": "Jay W." }, "id": "Dawson-J-W", "display_name": "Dawson, Jay W." } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/65s0-wf19", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nSingle frequency, low intensity noise, widely tunable lasers operating in the 1.5 [...]m region have potential applications in future wavelength division multiplexed optical communications systems, fiber sensor arrays and high resolution spectroscopic measurements. A single frequency fiber laser having these characteristics will be described in detail. The laser cavity contains an erbium doped fiber gain module, fiber isolators to ensure unidirectional travelling wave operation and two fiber Fabry-Perot filters acting in tandem, which provide broadband tunability (1530 nm -1560 nm) combined with stable single frequency operation. Shot noise limited operation of this laser has been observed at frequencies greater than 300 MHz. At lower frequencies (1-300 MHz) the intensity noise has been characterized in terms of sidemode suppression (> 60 dB of minimum sidemode suppression has been realized). Lower still (10 kHz - 1 MHz) the intensity noise is dominated by the laser's relaxation resonance (30 kHz @ 1 mW output, -105 dBc/Hz). The linewidth of this laser has been measured to be less than 4 kHz using a loss compensated recirculating delayed self-heterodyne interferometer (RDSHI). The RDSHI is an improvement over the standard delayed self-heterodyne interferometer in that the effective delay line can be increased by a factor of 30 over the standard method, increasing the resolution by a corresponding amount. The RDSHI also allows measurement of the short term frequency jitter of a laser. In order to reduce laser frequency jitter, the Pound-Drever technique was employed to lock the laser frequency to an external fiber Fabry-Perot. The same technique also permitted the internal mode selection filter to track the laser frequency, completely eliminating residual mode hopping due to thermal length changes of the laser cavity. Finally, fiber laser configurations that allow multiple frequencies to be simultaneously produced in one laser cavity will be described." }, { "name": "Delbruck, Tobias", "degree": "PhD", "year": "1993", "title": "Investigations of analog VLSI visual transduction and motion processing", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-07022004-144710", "creators": [ { "name": { "family": "Delbruck", "given": "Tobias" }, "id": "Delbruck-Tobias", "display_name": "Delbruck, Tobias" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "chair", "display_name": "Koch, Christof" }, { "name": { "family": "Fraser", "given": "Scott E." }, "id": "Fraser-S-E", "orcid": "0000-0002-5377-0223", "role": "member", "display_name": "Fraser, Scott E." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cns" ], "doi": "10.7907/N5TD-G224", "abstract": "This thesis is a detailed description of a neuromorphic visual-motion processing chip and its component parts. The chip is the first two-dimensional silicon retina with a full set of direction-selective, velocity-tuned pixels. The architecture for the chip is based on the biological correlation-type motion detector, with the addition of a novel spatiotemporal aggregation. All the processing on the chip is analog and occurs in parallel. Novel, on-chip, continuous-time, adaptive, logarithmic photoreceptor circuits are used to couple temporal image signals into the motion processing network. These continuous-time photoreceptor circuits have also been used in a wide variety of other vision chips. The photoreceptor circuits center their operating point around the history of the illumination, simultaneously achieving high sensitivity and wide dynamic range. The receptor circuits are characterized and analyzed carefully for their temporal bandwidth and detection performance. Noise properties are analyzed, resulting in a simple and intuitive understanding of the limiting parameters. Novel adaptive elements are described that are insensitive to light-generated minority carriers. Novel measurements are presented of the spectral response properties of phototransducers that can be built in ordinary CMOS or BiCMOS processes. A novel nonlinear circuit that measures similarity and dissimilarity of signals is described and characterized. These bump circuits are used on the motion chip to extract the motion energy signal, and have also been used in other chips in numerous ways." }, { "name": "Dugan, Regina E.", "degree": "PhD", "year": "1993", "title": "Axisymmetric Buoyant Jets in a Cross Flow with Shear: Transition and Mixing", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-090225", "creators": [ { "name": { "family": "Dugan", "given": "Regina E." }, "id": "Dugan-Regina-E", "display_name": "Dugan, Regina E." } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "chair", "display_name": "List, E. John" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/1jmz-kj71", "abstract": "It has been proposed that axisymmetric buoyant jets discharged vertically into a horizontal turbulent boundary layer flow undergo a transition from self-induced mixing to an ultimate state where mixing is dominated by the shear-flow turbulence. Both plume mixing and ambient shear-flow mixing have been separately well characterized by many previous studies and can be thought of as asymptotic mixing regimes. This investigation focuses on the transition between the two asymptotic regimes that is not well understood and that is often of particular engineering interest.
\r\n\r\nIn this work, we present the results of a detailed experimental analysis of buoyant jet mixing in a turbulent shear flow. Our purpose is to obtain a detailed picture of the turbulent velocity field and the concentration distributions throughout the various mixing regimes in order to discern the effects of changes in various flow parameters on the predominant mixing mechanisms. The experimental technique employs buoyant jets whose fluid is optically homogeneous with that of the ambient shear flow. This enables the combined use of laser-Doppler velocimetry and laser-induced fluorescence to measure the velocity and concentration profiles, respectively.
\r\n\r\nDimensional analysis indicates that the cross-flow shear velocity and the plume specific buoyancy flux are the parameters controlling the transition from plume mixing to diffusion mixing. Quantitative analysis of the experimental results indicates that the mixing is dominated entirely by diffusion, or shear-flow mixing, even close to the point of discharge. Further, we observe that within the diffusive mixing regime, a transition occurs from a region where the turbulent mixing coefficient is proportional to the local elevation to a region where the turbulent mixing coefficient is proportional to the boundary layer thickness. Detailed instantaneous spatial concentration distributions indicate that regions of dilution far below mean values persist well into the mixing regime dominated by shear-flow turbulence. This indicates that both plume mixing and diffusion-type mixing models may provide a false sense of security with regard to the absolute minimum dilutions observed in actual flow situations since both methods focus on the minimum average dilution.
" }, { "name": "Eng, Lars E.", "degree": "PhD", "year": "1993", "title": "Low threshold current strained InGaAs/AlGaAs quantum well lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-091655", "creators": [ { "name": { "family": "Eng", "given": "Lars E." }, "id": "Eng-L-E", "display_name": "Eng, Lars E." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/wxtc-4x91", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nStrained InGaAs quantum well lasers offer the prospect of lower threshold currents, higher modulation speed, and lower linewidths than lattice matched GaAs quantum well lasers. In addition, the useful wavelength region of the GaAs material system is extended from 0.87[...] to beyond 1[...] with the addition of indium to the quantum well.\n\nThe lasers are fabricated using Molecular Beam Epitaxy (MBE) for the semiconductor layer structure. Liquid Phase Epitaxy (LPE) is then used to provide lateral optical mode and current confinement. Broad area threshold current densities of [...] is the first demonstration of high quality MBE grown strained InGaAs laser material. Measured transparency currents of 25[...] are a factor of two lower than in GaAs, which is consistent with a lower valence band density of states in the strained material. Buried heterostructure lasers made from this material with 2[...] wide stripe widths lase with a minimum threshold of 1.0mA (CW), the lowest value for a single quantum well laser with as-cleaved mirrors in any material system. With high reflectivity coatings (R=0.9) the first sub milliampere strained InGaAS lasers are obtained, with [...]. Details of the material growth, device fabrication, and device optimization are presented.\n\nThe broad gain bandwidth of single quantum well lasers is used to tune the lasing wavelength of optimized GaAs lasers over 125 nm and InGaAs lasers over 170 nm in an external cavity configuration. The measured tuning curves obtained for the InGaAs lasers are qualitatively different, and the difference can be attributed to the modified strained valence band strucure.\n\nLow temperature (5\u00b0K) performance of low threshold lasers is investigated. The decrease in threshold with temperature is found to be linear over a range of 200\u00b0K for both GaAs and InGaAs with a larger decrease in threshold for the GaAs case. This result agrees well with a lowered valence band effective mass in the strained laser." }, { "name": "Fu, Zezhong", "degree": "PhD", "year": "1993", "title": "The mechanical alloying of aluminum and zirconium", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-103954", "creators": [ { "name": { "family": "Fu", "given": "Zezhong" }, "id": "Fu-Z", "display_name": "Fu, Zezhong" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/wfgh-ej06", "abstract": "Over the last several years, mechanical alloying/milling (MA/MM) process has been applied to produce different types of metastable or non-equilibrium materials such as metallic glasses, quasi-crystalline materials, nanocrystalline metals, compounds and supersaturated solid solutions. It appears that MA offers greater latitude in controlling the microstructure than other non-equilibrium processing methods such as rapid solidification. Despite a considerable number of experiments using MA/MM, many questions regarding the mechanisms of phase transformations induced by MA, especially the mechanism of amorphization, remain to be answered. In this thesis, the sequence of phase transformations induced by the mechanical alloying of aluminum and zirconium has been studied. The structural analysis indicated that none of the thermodynamically stable intermetallic compounds found in the phase diagram are formed during MA of the Al-Zr system. Instead, the nanocrystalline supersaturated [alpha]-Zr solid solution and amorphous phase are synthesized depending on the initial composition of the powder mixture. The thermodynamic and structural properties of these ball-milled materials have been characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC).\n\nAs we know, one of the crucial aspects of nanophase and amorphous phase materials is the stability against grain growth and crystallization. In Chapter 4, the metastability of nanocrystalline materials based on the thermodynamics and grain boundary segregation arguments proposed by Johnson has been discussed. The thermal stabilities of the nanostructured [alpha]-Zr solid solutions and amorphous materials have also been studied. The experiments found that the grain size of nanocrystalline supersaturated solid solution is stable under heat treatment until reaching a temperature where the crystallization of an equilibrium compound phase occurs.\n\nIn Chapter 5, the temperature effects on the mechanical alloying of Al and Zr have been studied by milling at different ambient temperatures. The experiments reveal that the ultimate grain size of nanostructured materials prepared by ball milling is determined by two main factors. One is densities of structural defects which depends on the competition between the severe plastic deformation induced by MA and the recovery behavior of the materials. Another is chemical effects which are related to the composition of the sample and the interactions among the components. Obviously, the recovery or relaxation behavior is temperature dependent, so the milling temperature could influence the average grain size. The chemical effects on grain size may also change with the milling temperature. The experimental results suggest that the steady state obtained by ball milling at higher temperature is much closer to a chemical equilibrium state compared with the state formed by milling at room temperature. A faster alloying rate is obtained at higher temperature milling. This is consistent with the solid state reaction mechanism by MA.\n\nThe mechanisms of amorphizations by MA of aluminum and zirconium under different experimental conditions have been discussed in Chapter 6. The emphasis is to argue the possibility of polymorphic amorphization.\n" }, { "name": "Geubelle, Philippe H.", "degree": "PhD", "year": "1993", "title": "Nonlinear effects in interfacial fracture", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-104817", "creators": [ { "name": { "family": "Geubelle", "given": "Philippe H." }, "id": "Geubelle-P-H", "display_name": "Geubelle, Philippe H." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/rkt0-7k90", "abstract": "The issue of the non-coplanar quasi-static propagation of a crack in homogeneous and bimaterial sheets is investigated. Through a preliminary linear analysis, it is shown that the interface crack kinking problem is confronted, in most practical cases, with difficulties which do not arise in the homogeneous situation: the crack path as predicted by the maximum energy release rate criterion cannot be determined uniquely and an additional length parameter, absent in the homogeneous case, needs to be specified to assure uniqueness. Following that development, the assumption of small deformations is relinquished and it is shown how the size of the nonlinear zone imparts possibly the physical significance of the additional length parameter. The analysis is performed numerically in the homogeneous and bimaterial cases within the framework of the nonlinearly elastic theory of plane stress and using a \"boundary-layer\" approach. Material and geometrical nonlinearities are combined through the use of the Generalized Neo-Hookean (GNH) model. As the length of the crack extension becomes comparable to the size of the nonlinear zone, a transition is observed between the value of the energetically most favorable kink angle predicted by the linear theory and a unique \"nonlinear\" value which is found to be independent of the crack extension length and the far-field loading conditions.\n\nThe results of the crack propagation analysis are related to those of a detailed asymptotic analysis of the structure of the near-tip stress and deformation fields for the GNU class of hyperelastic materials. The investigation addresses a) the symmetric (mode I) and non-symmetric (mixed-mode) homogeneous situations, b) the rigid substrate case and c) the general bimaterial problem which allows for an arbitrary choice, on both sides of the interface, of the three material parameters characterizing the GNH model. The asymptotic analysis allows to quantify the effect of the \"hardening\" characteristics on the blunting of the crack and the associated stress and strain singularities, and shows that the near-tip fields corresponding to a general nonsymmetric loading are, in the homogeneous situation, related to those of the symmetric (mode I) case through a rotation which depends on the material characteristics and the far-field loading conditions. A somewhat similar property is obtained in the bimaterial problem, where the existence of a non-oscillatory and \"contact-free\" solution is confirmed for all material combinations." }, { "name": "Grave, Ilan", "degree": "PhD", "year": "1993", "title": "GaAs quantum well devices for detection and nonlinear optics in the mid-infrared", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-111424", "creators": [ { "name": { "family": "Grave", "given": "Ilan" }, "id": "Grave-I", "display_name": "Grave, Ilan" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/mjwc-4k88", "abstract": "The basic physical limits for infrared detection based on intersubband processes in semiconductor quantum wells are presented. An evaluation of the potential of GaAs intersubband detectors and a comparison with other systems is attempted. It is shown that the performances of the single GaAs detector falls short with respect to the single HgCdTe detector. Still, the performances of GaAs intersubband detectors answer the needs of many conceivable applications; this fact, together with the maturity, integrability and uniformity of the cheaper GaAs technology might make these detectors the choice for many future applications and systems.\n\nOptimization of parameters in the design and epitaxial growth of these structures yield standard intersubband detectors with very respectable performances at reasonable cooling costs.\n\nThe narrow bandwidth and the lack of post-growth tunability limit the capability and versatility of intersubband detection. A new kind of intersubband detector, the multistack integrated detector, is conceived in an attempt to address these issues. This detector can operate in a number of modes; it can have a narrow or wide bandwidth of detection, and even a voltage-controlled expandable bandwidth. Among its features a multi-color option and a switching-peak option for combined or alternate color detection. The underlying physics involves the formation, expansion and readjustment of electric field high and low domains along the multi-quantum well region.\n\nAdditional topics in the physics and applications of intersubband processes for detection of infrared light are explored: a band-gap design involving a variably-spaced superlattice barrier, is investigated by photocurrent spectroscopy. The experiments reveal the subtle breaking of the parity selection rules, and also the possibility of detecting infrared light at shorter wavelengths than previously thought possible in the GaAs/AlGaAs system.\n\nThe second part of this thesis deals with the study and observation of enhanced nonlinear optical effects at the mid infrared, close to intersubband resonances. Second harmonic generation is obtained around 5 \u00b5m. Third-order effects are then investigated in different experimental configurations, including the first observation of phase conjugation based on these nonlinearities. Very large third-order susceptibilities and intensity-dependent refractive indices are deduced from the experimental results." }, { "name": "Hammer, Jay A.", "degree": "PhD", "year": "1993", "title": "Lifted turbulent jet flames", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-131353", "creators": [ { "name": { "family": "Hammer", "given": "Jay A." }, "id": "Hammer-J-A", "display_name": "Hammer, Jay A." } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/fn1k-za85", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nExperiments were conducted on lifted, turbulent jet diffusion flames. An automated technique using a linear photodiode array was implemented to measure the temporal history of the liftoff height h. The measurements enabled accurate determination of the mean liftoff height [...] under a wide range of flow conditions, including several fuels, nozzle diameters, and exit velocities [...]. The results showed an approximately linear relationship between [...] and [...], with a slight dependence on Reynolds number. A strain-rate model for liftoff, based on far-field scaling of turbulent jets, provides an explanation for the linear dependence of [...] on [...]. Measurements were also made in which the nozzle fluid contained varying amounts of air, where it was found that the slope of the [...] vs. [...] line increases faster than predicted by far-field scaling of turbulent jets. The discrepancy is attributed to near-field effects.\n\nThe amplitudes of the fluctuations in h were found to be of the order of the local large scale of the jet. There is a slight increase in normalized fluctuation level [...] with [...], and there is some variation of [...] with fuel type. The time scales of the fluctuations of h were found to be considerably longer than the local large-scale time of the turbulence [...]. By using fuels of different chemical times to vary [...], the measured correlation time [...] normalized by [...] was found to collapse with Richardson number [...]. Experiments in which the nozzles were oriented horizontally showed no change in [...], however. Additional experiments were conducted to investigate alternative explanations for the variation of [...] with [...]. These experiments included measuring the flame length L simultaneously with h, and measuring the visible radiation I simultaneously with h. L(t) was found to be nearly uncorrelated with h(t), dismissing the possibility that a feedback mechanism from L to h controls the fluctuations of h. Although I(t) is highly correlated with h(t) for the most sooting fuel, acetylene, it is not deemed responsible for the longer correlation times of that fuel. This was deduced from experiments using mixtures of hydrogen with other fuels, which produce very little radiation, but which have values of [...] comparable to those of acetylene flames.\n\nAnother experiment was conducted in which two-dimensional images of fuel concentration (CH4) and reaction zones (indicated by CH) were obtained. The images showed a wide variety of structure types, indicating that there is no universal description of the flow field at the flame base. The flame stabilization position showed large fluctuations in both the axial and radial directions. The shot to shot variation in methane number density at the flame base was also large." }, { "name": "Harley, Robert Adam", "degree": "PhD", "year": "1993", "title": "Mathematical Modeling of Gas-Phase Organic Air Pollutants", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-08282007-080127", "creators": [ { "name": { "family": "Harley", "given": "Robert Adam" }, "id": "Harley-Robert-Adam", "display_name": "Harley, Robert Adam" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "orcid": "0000-0002-4263-2562", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/va0x-2331", "abstract": "Volatile organic compounds (VOCs) play a significant role in the production of ozone in urban atmospheres. In addition, VOCs are of concern because some of them are toxic, and because the atmospheric oxidation of directly emitted VOCs can form condensable products which contribute to airborne particulate matter concentrations. In this study, a general model that relates pollutant emissions to ambient VOC concentrations is described. Model performance is evaluated both for ozone and VOCs for the August 27-29, 1987 period in the Los Angeles area using data from the Southern California Air Quality Study (SCAQS).\r\n\r\nImproved chemical composition profiles for major VOC emission sources are presented, and use of these profiles results in significant changes to previous emissions estimates for many individual VCs. Reconciliation of emission data with speciated ambient VOC concentration data from the Los Angeles area indicates that there is much more unburned gasoline in the atmosphere than the emission inventory suggests.\r\n\r\nThree photochemical airshed models are presented that predict the ambient concentrations of VOCs. The first model predicts concentrations of lumped VOC classes (e.g. lumped canes, monoalkyl benzenes). Satisfactory model performance is obtained only after the VOC emission estimates prepared by the government are scaled up to match emission rates measured in the Van Nuys tunnel. An enhanced airshed model with 53 individual VOCs represented explicitly also is described and tested. The best performance is obtained for aromatic hydrocarbons which are predicted to within \u00b120% by the model in most cases; concentrations of most other species are predicted to better than \u00b150%. Finally, a model for gas-phase toxic organic air pollutants is described and tested for species including aromatics, aldehydes, ketones, and 1,3-butadiene among others. Significant contributions to total ambient concentrations from atmospheric photochemical formation are found for formaldehyde, acetaldehyde, propionaldehyde, acrolein and methyl ethyl ketone. Therefore, control programs for some toxic air pollutants must consider photochemical formation pathways in addition to direct emissions.\r\n\r\nThe novel aspects of this study include the analysis and improvement of speciated VOC emission estimates, and the development and testing of airs hed models for lumped and individual VOCs using data from SCAQS." }, { "name": "Hart, Douglas P.", "degree": "PhD", "year": "1993", "title": "Cavitation and wake structure of unsteady tip vortex flows", "advisor": "Acosta, Allan J.; Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-131947", "creators": [ { "name": { "family": "Hart", "given": "Douglas P." }, "id": "Hart-D-P", "display_name": "Hart, Douglas P." } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "co-advisor", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "co-advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ANNN-VC25", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nUnsteady flows are prevalent in virtually every fluid application yet, because of their intrinsic complexity, few attempts have been made to measure them or explain their behavior. This thesis presents an experimental study of one of the simplest unsteady flow induced effects, the periodic change in angle of attack of a lifting surface. Of particular interest is the influence this effect has on the tip vortex structure of a finite aspect ratio hydrofoil and the part it plays in the inception of cavitation.\r\n\r\nAn aspect ratio 2.3 hydrofoil was reflection-plane mounted to the test section floor of the Caltech Low Turbulence Water Tunnel and harmonically oscillated in pitch near its center of pressure. Observations of the growth and collapse of surface and tip vortex cavitation were made along with detailed observations of the interaction of the tip vortex formation with the spanwise wake structure. Measurements of the cavitation inception number for surface cavitation and tip vortex cavitation were made relative to the phase of the hydrofoil and the reduced frequency, k=[low-case omega]c/2U[...], of oscillation. Studies of the oscillation-induced spanwise trailing vortex structures and the Karman vortex street generated by the boundary layer were made of a two-dimensional hydrofoil. Laser Doppler Velocimetry (LDV) measurements were taken of the tip vortex velocity profile and the flow at the trailing edge of both the two-and the three-dimensional hydrofoils at reduced frequencies ranging from 0.5 to 2.0. Dynamic changes in bound circulaion and shed vorticity in the streamwise and spanwise directions relative to the freestream were calculated from these measurements at three locations along the span of the foil. The results of these measurements are compared to theoretical flow calculations and related to measurements of the cavitation inception number in the tip vortex region of the three-dimensional foil" }, { "name": "Higgins, Charles Marion", "degree": "PhD", "year": "1993", "title": "Classification and Approximation with Rule-Based Networks", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-132407", "creators": [ { "name": { "family": "Higgins", "given": "Charles Marion" }, "id": "Higgins-Charles-Marion", "display_name": "Higgins, Charles Marion" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/4r7r-w573", "abstract": "This thesis describes the architecture of learning systems which can explain their decisions through a rule-based knowledge representation. Two problems in learning are addressed: pattern classification and function approximation.
\r\n\r\nIn Part I, a pattern classifier for discrete-valued problems is presented. The system utilizes an information-theoretic algorithm for constructing informative rules from example data. These rules are then used to construct a computational network to perform parallel inference and posterior probability estimation. The network can be extended incrementally; that is, new data can be incorporated without repeating the training on previous data. It is shown that this technique performs comparably with other techniques including the backpropagation network while having unique advantages in incremental learning capability, training efficiency, and knowledge representation. Examples are shown of rule-based classification and explanation.
\r\n\r\nIn Part II, we present a method for the learning of fuzzy logic membership functions and rules to predict a numerical function from examples of the function and its independent variables. This method uses a three-step approach to building a complete function approximation system: first, learning the membership functions and creating a cell-based rule representation; second, simplifying the cell-based rules using an information-theoretic approach for induction of rules from discrete-valued data; and finally, constructing a computational network to compute the function value given its independent variables. Applications of the system to adaptive control are suggested, including a method for learning a complete control system for an unknown plant. Experimental validation of the suggested methods using a ball-and-beam system is shown.
" }, { "name": "Hofmeister, Rudolf", "degree": "PhD", "year": "1993", "title": "Growth and applications of photorefractive potassium lithium tantalate niobate (KLTN)", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272007-134313", "creators": [ { "name": { "family": "Hofmeister", "given": "Rudolf" }, "id": "Hofmeister-R", "display_name": "Hofmeister, Rudolf" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/zm1c-8w92", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis thesis describes the growth of photorefractive potassium lithium tantalate niobate (KLTN) single crystal material and characterization of its physical and photorefractive properties. The band transport model is used to discuss the conventional photorefractive effect. The coupled mode formalism is introduced to determine the interaction of interfering light beams in a photorefractive material. Solutions for intensity coupling and phase coupling between two beams, as well as diffraction off a dynamic index grating, are presented for both the copropagating and counterpropagating experimental geometries. These solutions are obtained for arbitrary photorefractive phase, [...]. The linear- and quadratic electro-optic effects are discussed. The influence of electric field application on the electro-optic tensor is described.\n\nThe top seeded solution growth method is reviewed. The design and construction of a crystal growth system is described. The growth procedures of KLTN are enumerated for several compositions and dopant types. Phase diagrams of the KLTN system are determined. Structural properties of the grown crystals are presented. Certain material characteristics of KLTN are discussed. These include the phase transition temperatures, dielectric properties, and the optical absorption properties.\n\nElectric field control of the photorefractive effect, beam coupling and diffraction, is demonstrated for paraelectric KLTN. A theory is developed to describe the diffraction of beams off photorefractive index gratings in paraelectric KLTN. The solutions of the coupled mode equations are used to develop methods of determining the photorefractive phase [...] in a photorefractive material. These methods are experimentally demonstrated for several types of photorefractive material. In addition, they are used to corroborate a theory describing the magnitude and phase of the net holographic grating in paraelectric KLTN under applied electric field.\n\nA new effect, the Zero External Field Photorefractive (ZEFPR) effect is studied, as well as the application of its unique zero phase ([...] = 0) photorefractive gratings. The ZEFPR effect is forbidden by the conventional photorefractive theory; its origin is shown to be due to the creation of strain gratings under spatially periodic illumination. A theory of coordination of microscopic strains by a macroscopic (growth induced) strain is presented. The ZEFPR gratings are shown to possess identically zero phase when no external electric field is applied. This property is employed in the implementation of various new linear phase-to-intensity transduction devices. In particular, an all-optical phase modulation/vibration sensor (microphone) is described. This device is expected to have numerous applications in environments where electric fields cannot be permitted. The possible implementation of ZEFPR gratings in high speed self aligning interferometric data links is discussed, as well as implementation of a novel self aligning holographic image subtraction device.\n\nThe final chapter is devoted to the solution of beam coupling and diffraction off of a \"fixed\" photorefractively written holographic plane grating. The solutions and mathematical tools developed in this chapter are used extensively throughout the thesis: in chapters two and five to describe diffraction off a photorefractive grating, in chapters seven and eight to solve for the beam coupling off a grating when one beam is phase modulated, and in chapter nine to study the spectral response of fixed holographic interference filters. The techniques are presented with sufficient generality to allow application to numerous other problems, not limited to the ones described here.\n" }, { "name": "Hsiau, Shu-San", "degree": "PhD", "year": "1993", "title": "Shear-induced transport properties of granular material flows", "advisor": "Hunt, Melany L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08292007-090134", "creators": [ { "name": { "family": "Hsiau", "given": "Shu-San" }, "id": "Hsiau-S", "display_name": "Hsiau, Shu-San" } ], "advisors": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "advisor", "display_name": "Hunt, Melany L." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/yj3a-tm14", "abstract": "A granular flow is a two-component flow with an assembly of discrete solid particles dispersed in a fluid. Because of the similarity between the random motion of particles in a granular flow and the motion of molecules in a gas, the dense-gas kinetic theory has been broadly employed to analyze granular flows. However, most research only discusses aspects of momentum transport; three issues have received less attention: the diffusion process, the heat transfer problem, and the behavior of binary mixtures. The current research emphasizes these aspects.\n\nA granular flow diffusion experiment was conducted in a vertical channel to investigate the effects that result in mixing of the material. The mean velocities, the longitudinal fluctuating velocities, and the mixing-layer thickness were measured. A simple analysis based on the diffusion equation shows that the thickness of the mixing layer increases with the square-root of downstream distance and depends on the magnitude of the velocity fluctuations relative to the mean velocity. The experimental velocity profiles were also compared with profiles calculated from theoretical analysis based on kinetic theory.\n\nThe analytical relations were developed for the flow-induced particle diffusivity and the thermal conductivity based on dense-gas kinetic theory. The two coefficients were found to increase with the square-root of the granular temperature, a term that quantifies the specific kinetic energy of the flow. The theoretical particle diffusivity was used to compare with the current experimental measurements involving the granular flow mixing layer. The analytical expression for the effective thermal conductivity was also compared with experimental measurements. The differences between the predictions and the measurements suggest limitations in some of the underlying kinetic-theory assumptions.\n\nThe constitutive relations were presented for a binary-mixture of granular materials as derived from the revised Enskog theory. The current research focuses on the process of granular thermal diffusion - a diffusion process resulting from the granular temperature gradient. A granular flow of binary-mixtures in an oscillatory no-flow system, in a sheared system, and in a vertical channel were examined, and indicated a complete segregation when granular thermal diffusion effect was sufficiently large." }, { "name": "Hsueh, Wen-Jean", "degree": "PhD", "year": "1993", "title": "High-resolution optoelectronic and photogrammetic 3-D surface geometry acquisition and analysis", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08292007-091850", "creators": [ { "name": { "family": "Hsueh", "given": "Wen-Jean" }, "id": "Hsueh-W", "display_name": "Hsueh, Wen-Jean" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/wn0s-6y22", "abstract": "A high-resolution, high-speed, automatic, and non-contact 3-D surface geometry measuring system has been developed. It is based on a photogrammetric and optoelectronic technique that adopts lateral-photoeffect diode detectors sensitive in the near-infrared range. Two cameras in stereo positions are both equipped with the large 2-axis analog detectors. A light beam is focused and scanned onto the surface of an object as a very small light spot. Excitations on detectors generated by the reflected light from the spot create photocurrents that are transformed into 2-D position signals in a very short time. A simple set of calculations is done to photogrammetrically triangulate two sets of 2-D coordinates from the detectors into the 3-D coordinates of the light spot. Because only one small light spot in the scene is illuminated at a time, the stereo-correspondence problem is solved in real time. The detectors are able to collect data at 10 KHz with 4,096x4,096 resolution based on a 12-bit A/D converter. The resolution and precision can be improved up to eight times by oversampling. The system is able to resolve, for example, less than 10 \u00b5m from 47 cm away with a nominal viewing volume of (22 cm)[superscript 3]. Its performance is better than contemporary coordinate measuring, range finding, shape digitizing, and machine vision systems, and is comparable to the best aspects of each existing system. The irregular 3-D data it generates can be regularized so that data processing algorithms designed for image systems may be applied. The system is designed for the acquisitions of general surface geometries, such as fabricated parts, machined surfaces, biological surfaces, and deformed parts. The system will be useful in solving a variety of 3-D surface geometry measuring problems in engineering design, manufacturing, inspection, robot kinematics measurement, and vision.\n" }, { "name": "Iinoya, Fujio", "degree": "PhD", "year": "1993", "title": "Pulsed expansion of plasma in a magnetic thruster", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-143404379", "creators": [ { "name": { "family": "Iinoya", "given": "Fujio" }, "id": "Iinoya-F", "display_name": "Iinoya, Fujio" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/j09c-vb03", "abstract": "The inertial confinement fusion (ICF) pulse rocket is an advanced space propulsion system, which, through intermittent nuclear fusion energy production isolated from the vehicle structure, is capable of both extremely high specific impulses and high thrust-to-weight ratios. Such rockets, if realized, should revolutionize space travel by making possible very robust interplanetary missions as well as interstellar flight. The thruster of the rocket, which converts an initially isotropically expanding ICF debris plasma into a directed pulse jet exhaust, is to be fabricated out of magnetic fields created by current coils attached to the vehicle. The proper operation of such a thruster therefore rests upon the successful redirection of an initially spherical plasma of high conductivity by a suitably configured vacuum magnetic field against which the plasma expands. But to date, there have been no detailed analyses to guarantee that the concept in the present form will function satisfactorily as envisioned to yield reasonable propulsive efficiencies.\r\nBecause of the highly dynamic behavior of the flow, which is bounded by an interface whose motion is unknown a priori, the first problem which must be investigated is that of the bulk flow under idealized conditions. In the work contained in this thesis, the plasma was assumed to be impermeable to the external fields, and the fields entered the debris dynamics only by way of applying a magnetic pressure force at the plasma-vacuum interface. The interface motion, bulk fluid profiles (when applicable), and resultant efficiencies were investigated for various parameter ratios and geometries. Such idealized bulk flow analyses are intended to serve as a basis for more detailed studies of how the flow will behave with a real plasma.\r\nNumerical simulations of the bulk flow process were conducted under both the thin-shell and the classical hydrodynamic approximations. The thin-shell calculation has been pioneered by other authors, but the present work is more complete, and as for the hydrodynamical calculations, application to the type of flows to be found in the magnetic thrusters of proposed ICF pulse rockets may be unique to this work, despite earlier claims. In the former approach, all of the plasma is assumed to be collected into an azimuthally symmetric perfectly conducting shell at the interface by virtue of the finite applied pressure at the interface. No fluid dynamics is considered under this approximation. These simulations showed that promising propulsive efficiencies could be obtained for a range of field-to-plasma energy ratios and thruster geometries, and the efficiencies reached a well-defined maximum for particular values of these parameters. However, because of the approximations used in this model, the efficiencies obtained do overestimate the real efficiencies. The thin-shell code is simpler to implement, and allows faster calculations and requires far less memory, than the more realistic hydrodynamic code, but the approximation made is not entirely accurate nor physical. In the second approach, the plasma is approximated by an unmagnetized perfectly conducting fluid obeying the laws of classical hydrodynamics. Here, we have a novel problem of a fluid expanding against a region of zero density, which nevertheless exerts a finite pressure on the fluid interface.\r\nIn both the two-dimensional thin-shell and hydrodynamic calculations, the vacuum magnetic pressure applying at the plasma-vacuum interface was calculated from the quasi-static Maxwell Equations. By assuming the plasma and field coil structures to be perfectly conducting, the magnetic field in the vacuum region, from which the magnetic pressure at the interface was computed, was calculated by prescribing the initial flux through the field coils to remain trapped between the expanding plasma surface and the surfaces of the field coil structures. Such a prescription, which can be explained through the presence of surface currents, is valid as long as we have ideal perfect conductors.\r\nThe hydrodynamic codes (both 1-D and 2-D) employed an advanced Classical Particle-In-Cell (PIC) scheme, and were successful at capturing the interface motion self-consistently (with pressure matching across the interface), and without iterations, via appropriate application of boundary conditions. The shock arising from the interface\r\ndeceleration was also captured correctly. The formation of a shell-like structure originating close to the interface was observed in simulations of flows with large expansion ratios that were carried out in two dimensions employing realistic thruster fields. But depending upon the pressure history at the interface, these \"shells\" did not necessarily stay at the interfacial region. When tested on such processes as free expansion into a vacuum or shock-tube problems, for which well-known theoretical solutions exist, the one-dimensional planar-geometry simulations gave results that matched well with the analytical calculations.\r\nThe qualitative features of the interface and its motion as found by the hydrodynamic simulations were similar to those obtained by the thin-shell simulations. Nevertheless, the physics of the internal flow was found to affect the performance of the thruster in ways not accountable by the thin-shell model. There were also implications that not all of the debris plasma may leave the thruster in one reflection. The substantial shock heating observed in the interfacial regions downstream of the inward-facing shock would help contribute towards maintaining high temperatures there for (possibly) achieving sufficient conductivities, provided the plasma stayed highly ionized. But because of the large expansion ratio experienced, the bulk temperature of an ICF debris plasma will fall below the ionization temperature from relatively early stages of expansion in the magnetic thrusters of currently proposed ICF pulse rockets, and the design parameters of these thrusters do not appear that promising.\r\nBecause of memory limitations imposed by computers, the maximum expansion ratio treatable by the two-dimensional hydrodynamic codes was limited, and initial plasma states rather far removed from those typical of situations in proposed thrusters had to be employed. This also lowered the efficiency values quite notably. The ignorance of real plasma properties such as finite conductivities further rendered the results of this work very optimistic. However, the primary goal of this work, which was to acquire intuition for the bulk flow and performance under idealized conditions, was accomplished. Furthermore, techniques for handling this type of problem were developed. Future work should concentrate on treating more realistic parameters and on incorporating more precise plasma physics into the analysis, based on bulk flow results heretofore obtained.\r\n" }, { "name": "Kerns, Douglas A.", "degree": "PhD", "year": "1993", "title": "Experiments in Very Large-Scale Analog Computation", "advisor": "Hopfield, John J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08292007-100152", "creators": [ { "name": { "family": "Kerns", "given": "Douglas A." }, "id": "Kerns-Douglas-A", "display_name": "Kerns, Douglas A." } ], "advisors": [ { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "advisor", "display_name": "Hopfield, John J." } ], "committee": [ { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "chair", "display_name": "Hopfield, John J." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "co-chair", "display_name": "Mead, Carver" }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "member", "display_name": "Pine, Jerome" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5ph3-1w81", "abstract": "The easy and inexpensive availability of microelectronic prototype fabrication allows us to perform many kinds of experiments in the construction of electronic computational machinery. There has been a recent resurgence in analog computation in various guises: electronic implementations of neural networks, other kinds of neuromorphic circuits, and electronic simulations of various physical systems.\r\n\r\nThis text documents a set of experiments in analog computation in silicon, and includes a short discussion of the relative advantages of analog vs digital computation. The most generally useful result of the work is the development of a set of techniques that allow analog circuits to automatically trim themselves, turning marginal components into devices of good precision." }, { "name": "Kim, Moonil", "degree": "PhD", "year": "1993", "title": "Grid amplifiers", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08292007-104142", "creators": [ { "name": { "family": "Kim", "given": "Moonil" }, "id": "Kim-M", "display_name": "Kim, Moonil" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/19xw-he51", "abstract": "Presented in this thesis are two grid amplifiers for operation in the microwave range. The first 5 x 5 MESFET amplifier grid verified the design approach by showing a gain of 11 dB at 3.3GHz. The second 10 x 10 amplifier grid, which has a metal layout pattern suitable for future monolithic integration, has shown a gain of 10 dB at 10 GHz with a 3 dB bandwidth of 1 GHz. The active devices in the grid were custom-designed HBT differential-pairs with a self-biasing resistor network for the base. This amplifier grid has produced a saturated output power of 450 mW while exhibiting a noise figure of 6.5 dB. The amplifier grid was also converted into an oscillator with smooth frequency-tuning between 8 and 11 GHz by using external feedback. A grid-array system of an oscillator and the amplifier was built to show the conservation of propagation angle for an rf beam through the amplifier grid. Amplitude modulation of the grid amplifier gain was demonstrated by applying a modulating signal to the grid's dc bias lines." }, { "name": "Kirk, David B.", "degree": "PhD", "year": "1993", "title": "Accurate and Precise Computation Using Analog VLSI, with Applications to Computer Graphics and Neural Networks", "advisor": "Barr, Alan H.; Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-08292007-104823", "creators": [ { "name": { "family": "Kirk", "given": "David B." }, "id": "Kirk-David-B", "display_name": "Kirk, David B." } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Barr, Alan H." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "co-advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "compsci" ], "doi": "10.7907/1ykm-yq27", "abstract": "This thesis develops an engineering practice and design methodology to enable us to use CMOS analog VLSI chips to perform more accurate and precise computation. These techniques form the basis of an approach that permits us to build computer graphics and neural network applications using analog VLSI. The nature of the design methodology focuses on defining goals for circuit behavior to be met as part of the design process.\r\n\r\nTo increase the accuracy of analog computation, we develop techniques for creating compensated circuit building blocks, where compensation implies the cancellation of device variations, offsets, and nonlinearities. These compensated building blocks can be used as components in larger and more complex circuits, which can then also be compensated. To this end, we develop techniques for automatically determining appropriate parameters for circuits, using constrained optimization. We also fabricate circuits that implement multi-dimensional gradient estimation for a gradient descent optimization technique. The parameter-setting and optimization tools allow us to automatically choose values for compensating our circuit building blocks, based on our goals for the circuit performance. We can also use the techniques to optimize parameters for larger systems, applying the goal-based techniques hierarchically. We also describe a set of thought experiments involving circuit techniques for increasing the precision of analog computation.\r\n\r\nOur engineering design methodology is a step toward easier use of analog VLSI to solve problems in computer graphics and neural networks. We provide data measured from compensated multipliers built using these design techniques. To demonstrate the feasibility of using analog VLSI for more quantitative computation, we develop small applications using the goal-based design approach and compensated components. Finally, we conclude by discussing the expected significance of this work for the wider use of analog VLSI for quantitative computation, as well as qualitative." }, { "name": "Ko, Tsz-Mei", "degree": "PhD", "year": "1993", "title": "On the VLSI decompositions for complete graphs, DeBruijn graphs, hypercubes, hyperplanes, meshes, and shuffle-exchange graphs", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302007-094049", "creators": [ { "name": { "family": "Ko", "given": "Tsz-Mei" }, "id": "Ko-T", "display_name": "Ko, Tsz-Mei" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/s7w7-a995", "abstract": "A C-chip VLSI decomposition of a graph G is a collection of C vertex-disjoint subgraphs of G which together contain all of G's vertices and a subset of its edges. If the vertex-disjoint subgraphs are isomorphic to each other, we call one of these isomorphic subgraphs a building block. The efficiency of a VLSI decomposition is defined to be the fraction of edges of G that are in the subgraphs. In this thesis, motivated by the need to construct large Viterbi decoders, we study VLSI decompositions for deBruijn graphs. We obtain some strong necessary conditions for a graph to be a building block for a deBruijn graph, and some slightly more restrictive sufficient conditions which allow us to construct some efficient building blocks for deBruijn graphs. By using the methods described in this thesis, we have found a 64-chip VLSI decomposition of the deBruijn graph B13 with efficiency 0.754. This decomposition is being used by JPL design engineers to build a single-board Viterbi decoder for the K = 15, rate 1/4 convolutional code which will be used on NASA's Galileo mission.\n\nFurthermore, we study VLSI decompositions for the families of complete graphs, hypercubes, hyperplanes, meshes, and shuffle-exchange graphs. In each of these cases, we obtain very efficient or even optimal decompositions. We also prove several general theorems that can be applied to obtain bounds on the efficiencies for VLSI decompositions of other complex graphs. In general, the results presented in this thesis are useful for implementing massively parallel computers.\n" }, { "name": "Koumoutsakos, Petros D.", "degree": "PhD", "year": "1993", "title": "Direct numerical simulations of unsteady separated flows using vortex methods", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-082957", "creators": [ { "name": { "family": "Koumoutsakos", "given": "Petros D." }, "id": "Koumoutsakos-P-D", "display_name": "Koumoutsakos, Petros D." } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TCQ9-9C86", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nNumerical simulations are presented for viscous incompressible flows with and without solid wall boundaries. Our numerical method is based on vortex methods. The classical inviscid scheme is enhanced to account for viscous effects via the method of particle strength exchange. The method is extended to account for the enforcement of the no-slip boundary condition as well by appropriately modifying the strength of the particles. Computations are possible for extended times by periodically remeshing the vorticity field.\n\nThe particles are advanced using the Blot-Savart law for the evaluation of the velocity. Computations are made using up to [...](10[superscript 6]) vortex particles by efficiently implementing the method of multipole expansions for vector computer architectures to obtain an [...](N) algorithm.\n\nThe method is used to simulate the inviscid evolution of an elliptical vortex in an unbounded fluid as well as unsteady separated flows around circular cylinders for a wide range of Reynolds numbers (40 - 9500). Direct comparisons are made of the results of the present method with those from a variety of theoretical, computational and experimental studies. The results exhibit the robustness and validity of the present method and allow to gain physical insight as to vorticity formation and its relation to the forces experienced by the body." }, { "name": "Lappas, Tasso", "degree": "PhD", "year": "1993", "title": "An adaptive Lagrangian method for computing 1-D reacting flows, and, The theory of Riemann invariant manifolds for the compressible Euler equations", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192007-130342", "creators": [ { "name": { "family": "Lappas", "given": "Tasso" }, "id": "Lappas-T", "display_name": "Lappas, Tasso" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/bw0e-2789", "abstract": "In the first part of this thesis, a method for computing one-dimensional, unsteady compressible flows, with and without chemical reactions, is presented. This work has focused on accurate computation of the discontinuous waves that arise in such flows. The main feature of the method is the use of an adaptive Lagrangian grid. This allows the computation of discontinuous waves and their interactions with the accuracy of front-tracking algorithms. This is done without the use of additional grid points representing shocks, in contrast to conventional, front-tracking schemes. The Lagrangian character of the present scheme also allows contact discontinuities to be captured easily. The algorithm avoids interpolation across discontinuities in a natural and efficient way. The method has been used on a variety of reacting and non-reacting flows in order to test its ability to compute complicated wave interactions accurately and in a robust way.\r\n\r\nIn the second part of this thesis, a new approach is presented for computing multidimensional flows of an inviscid gas. The goal is to use the knowledge of the one-dimensional, characteristic problem for gas dynamics to compute genuinely multidimensional flows in a mathematically consistent way. A family of spacetime manifolds is found on which an equivalent 1-D problem holds. These manifolds are referred to as Riemann Invariant Manifolds. Their geometry depends on the local, spatial gradients of the flow, and they provide locally a convenient system of coordinate surfaces for spacetime. In the case of zero entropy gradients, functions analogous to the Riemann invariants of 1-D gas dynamics can be introduced. These generalized Riemann Invariants are constant on the Riemann Invariant Manifolds. The equations of motion are integrable on these manifolds, and the problem of computing the solution becomes that of determining the geometry of these manifolds locally in spacetime.\r\n\r\nThe geometry of these manifolds is examined, and in particular, their relation to the characteristic surfaces. It turns out that they can be space-like or time-like, depending on the flow gradients. An important parameter is introduced, which plays the role of a Mach number for the wave fronts that these manifolds represent. Finally, the issue of determining the solution at points in spacetime, using information that propagates along space-like surfaces is discussed. The question of whether it is possible to use information outside the domain of dependence of a point in spacetime to determine the solution is discussed in relation to the existence and uniqueness theorems, which introduce the concept of domain of dependence.\r\n\r\nThis theory can be viewed as an extension of the method of characteristics to multidimensional, unsteady flows. There are many ways of using the theory to develop practical, numerical schemes. It is shown how it is possible to correct a conventional, second-order Godunov scheme for multidimensional effects, using this theory. A family of second-order, conservative Godunov schemes is derived, using the theory of Riemann Invariant Manifolds, for the case of two-dimensional flow. The extension to three dimensions is straightforward. One of these schemes is used to compute two standard test cases and a two-dimensional, inviscid, shear layer.\r\n" }, { "name": "Lee, David Soong-Hua", "degree": "PhD", "year": "1993", "title": "Thermodynamic and structural aspects of equilibrium and mechanically milled YBa2Cu3O6+delta powder", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302007-095221", "creators": [ { "name": { "family": "Lee", "given": "David Soong-Hua" }, "id": "Lee-D-S", "display_name": "Lee, David Soong-Hua" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/xzfk-gw94", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe equilibrium relationships between partial pressure of oxygen, temperature, lattice parameters and oxygen content in the YBa2Cu3O6+[delta] superconductor were examined by differential scanning calorimetry, high-temperature x-ray diffraction, thermogravimetric analysis and measurement of pressure versus concentration isotherms. Oxygen pressures ranged from 1 mbar to 1013 mbar and temperatures ranged from 400\u00b0C to 750\u00b0C. Lattice parameters as a function of temperature and partial pressure of oxygen were measured. P(c) isotherms and TGA were used to measure oxygen content as a function of temperature. A phase line separating the low temperature orthorhombic phase and the high temperature tetragonal phase was determined. No evidence of a miscibility gap between the two phases was found in the range of temperatures and oxygen pressures explored. From the data, the excess enthalpy and entropy through the orthorhombic to tetragonal phase transition was calculated. It was found that the excess entropy is less than the entropy of mixing for an ideal solution. DSC was used to measure enthalpies for the transition and to calculate activation energies for the process. The enthalpy for the evolution of oxygen from the solid was found to be 5.2 kJ/mol in Argon, 2.0 kJ/mol in 16% oxygen and 1.7 kJ/mol in pure oxygen. Activation energies for the transition were 1.2 eV/atom in Argon, 1.8 eV/atom in 16% oxygen, and 2.9 eV/atom in 100% oxygen. DSC using a sealed sample pan (to maintain a constant concentration of oxygen in the solid during heating) was done and no signal arising from the order-disorder transition was seen.\n\nHigh temperature x-ray diffraction and differential scanning calorimetry were used to study the effect of high energy mechanical deformation on the structural and thermal characteristics of YBa2Cu3O6+[delta] powder. A Warren-Auerbach analysis was done on the x-ray peaks to determine the grain size of the material as a function of milling time. A Phillips 430 transmission electron microscope equipped with an EDX detector was used to determine chemical composition and grain size of the ball-milled material.\n\nBroadening of Bragg peaks due to the reduction of grain size makes the distinction between orthorhombic and tetragonal phases of YBa2Cu3O6+[delta] difficult after only one hour of ball milling. The equilibrium orthorhombic to tetragonal phase transition may occur within the first hour of ball-milling. Longer milling times (>5hrs) produce a cationic disorder on the yttrium and barium sites. A metastable cubic (Y1/3Ba2/3)CuO2+[delta] structure with a= 3.86[...] is formed. Further mechanical deformation does not induce the formation of an amorphous phase; rather, an eventual decomposition into the constituent oxides Y2O3 and BaCuO2 is observed. Annealing of the metastable cubic (Y1/3Ba2/3)CuO2+[delta] phase in relatively low pressures of oxygen ([...]100mbar) and at moderate temperatures (~400-600\u00b0C) produces an as yet unidentified cubic phase which is unstable in air and has a lattice constant of a= 5.47[...]." }, { "name": "Lisoski, Derek Lee Ashton", "degree": "PhD", "year": "1993", "title": "Nominally 2-Dimensional Flow About a Normal Flat Plate", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-04042005-105646", "creators": [ { "name": { "family": "Lisoski", "given": "Derek Lee Ashton" }, "id": "Lisoski-Derek-Lee-Ashton", "display_name": "Lisoski, Derek Lee Ashton" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AZEG-2T16", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nTowing tank and water channel experiments and a two-dimensional vortex element numerical model were used to study the forces experienced by a bluff flat plate set normal to a nominally two-dimensional flow. Intrinsic (small scale) and extrinsic (large scale) three-dimensional motions in the experimental flow were isolated and their separate and combined effects on forces and overall wake development were studied. Transient flow development starting from rest, as well as steady flow conditions, were investigated.\r\n\r\nA force balance was used to measure the unsteady lift and drag of vertically oriented models projecting through a free surface with various lower end conditions; simultaneous LIF flow visualizations imaged the structure of the vortices in the wake. Plate aspect ratio, lower end condition and angle of attack were varied to effect changes in large scale three-dimensional motions, while changes in Reynolds number and Richardson number (flow stratification) modified the small scale three dimensionality intrinsic to the flow.\r\n\r\nTowing tank experiments indicated that normal plates required sixty to one hundred chord lengths of travel to establish steady vortex shedding. An initial drag peak during acceleration was followed by a drag minimum of [...] reached while the wake was confined to a symmetric vortex bubble. Subsequent to the breakdown of this bubble, a region of symmetric flow with [...] and no vortex shedding was apparent for twenty to thirty chord lengths, followed by the final onset of vortex shedding which occurred exponentially. During this onset forces overshot their final steady-state values [...]. Flows with less large scale extrinsic three dimensionality (higher aspect ratio, \"more two-dimensional\" end conditions, and stratified flow) had longer development times and higher subsequent overshoot levels.\r\n\r\nSmall geometric asymmetries (angle of attack variations) increased the minimum drag level seen after the acceleration and resulted in an earlier breakdown of the closed wake, followed by an immediate transition to steady shedding. The breakdown of the initial bubble in this case was more coherent spanwise and did not result in a long-lasting symmetric nonshedding flow.\r\n\r\nDuring \"steady-state\" shedding, modulation in the vortex shedding amplitude at a time scale of five to ten Strouhal periods resulted in a twenty percent fluctuation in mean drag level, with a corresponding increase in rms lift. This modulation accompanied a slow oscillation in the formation distance of the shed vorticity, the period of which was Reynolds number independent but decreased with increasing aspect ratio, reaching a minimum value of six Strouhal periods for aspect ratios greater than ten.\r\n\r\nAgreement between three-dimensional experimental and two-dimensional numerical-model results was good at early times, indicating the experiments were two-dimensional until the breakdown of the closed wake bubble following the initial acceleration. Prior to this breakdown the numerical model of a normal plate gave a drag coefficient [...], similar to that given by the Kirchhoff-Rayleigh free-streamline prediction but lower than experiments. Small asymmetries of the 2d model resulted in an increase in the minimum drag level to [...] . Subsequent to the closed wake breakdown, drag levels of [...] are 65% higher than steady-state experimental values.\r\n\r\nAlthough no region corresponding to the post-acceleration non-vortex-shedding seen experimentally was found in the basic numerical results, the addition of circulation decay to the numerical-model resulted in a region which appeared qualitatively similar. This circulation decay also decreased mean drag levels [...] and gave an exponential shedding onset with subsequent long period shedding modulation.\r\n\r\nStabilizing spanwise stratification of the experimental flow had little effect for Richardson numbers [...] (based on chord). For [...] and [...] a longer lasting post-acceleration closed wake was followed by strong initial shedding and a large drag overshoot, with a subsequent decrease in shedding amplitude and increase in formation distance to the levels seen in the unstratified [...] case, which exhibited considerable Reynolds number dependence. For plates at [...] angle of attack the symmetric nonvortex shedding region was reduced in duration and subsequent \"steady-state\" drag levels were increased ten to fifteen percent [...] from the unstratified case." }, { "name": "Mandell, Michael I.", "degree": "PhD", "year": "1993", "title": "A comparison of CDMA and frequency hopping in a cellular environment", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302007-154436", "creators": [ { "name": { "family": "Mandell", "given": "Michael I." }, "id": "Mandell-M-I", "display_name": "Mandell, Michael I." } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Simon", "given": "Marvin K." }, "id": "Simon-M-K", "role": "member", "display_name": "Simon, Marvin K." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/xsbz-qt92", "abstract": "This paper compares the performances of Direct Sequence Code Division Multiple Access (CDMA) and Frequency Hopping (FH) schemes in a cellular multiuser environment. Our multiuser channel model incorporates the effects of propagation, frequency selective fading, and interference among users in the presence of a constrained system bandwidth. This channel model is applicable for cellular mobile communications, as well as other forms of personal communications. The CDMA and FH systems are compared using BPSK modulation. The main point of contrast between these systems is that the orthogonal hopping patterns in a FH system result in a decreased additive interference power, however, the frequency spreading nature of CDMA results in both the ability to combat fading, and the ability to effectively use low rate codes. An information-theoretic analysis is presented, and shows that the system capacity is larger for CDMA than for FH. Hence, with sufficient coding the CDMA system can achieve a higher level of performance than the FH system. However, it is unclear what level of complexity would be required to achieve such performance, and what effect such complexity would have on the practicality of the system. Finally, through the use of simulation, the performances of several simple coding schemes are measured and compared to the theoretical limits. These simple coding schemes perform far below the theoretical limits and also display a tradeoff in performance where the FH system performs better at high levels of traffic, and the CDMA system performs better at low levels of traffic." }, { "name": "Mason, James Joseph", "degree": "PhD", "year": "1993", "title": "Mechanisms and effects of heat generation at the tips of dynamic cracks and notches in metals", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312007-094213", "creators": [ { "name": { "family": "Mason", "given": "James Joseph" }, "id": "Mason-J-J", "display_name": "Mason, James Joseph" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/FAB4-5056", "abstract": "A high-speed InSb infrared detector array and the method of Coherent Gradient Sensing (CGS) are used in several experimental configurations to explore the mechanisms and effects of heat generation in dynamic fracture and deformation.\r\n\r\nFirst, the dependence of the measured dynamic crack tip temperature upon crack tip speed is investigated for cracks propagating dynamically in AISI 4340 carbon steel. Then, the dynamic crack tip temperature in a titanium alloy (Ti-l0V-2Fe-3Al) is measured in order to examine the role of material parameters in determining the crack tip temperature at different crack growth speeds. It is seen that the crack tip temperature increases when crack tip velocities are increased from 600 m/s to 900 m/s in 4340 steel. The extent of the active plastic zone at the surface of the specimen, however, decreases with increasing crack velocity. When the results for temperature measurements in steel are compared with those for titanium, it is seen that the material parameters that are most important are the dynamic yield strength, which determines the amount of plasticity, and the heat capacity of the material. Conductivity has little effect.\r\n\r\nNext, the nature of hyperbolic heat conduction at the tip of a dynamic crack is investigated. A mathematical model is developed to predict the temperature field around a dynamically propagating crack tip for a material that follows a hyperbolic heat conduction law. A Green's function for the governing partial differential equation is derived. The model is solved for a variety of experimental conditions by numerical integration of the Green's function. Various possible effects of hyperbolic heat conduction around a crack tip are explored. The model is then used to simulate the experimental conditions typically observed in dynamic fracture. Because conduction is minimal around the dynamically propagating crack tip, no effects of hyperbolic heat conduction are observed. It is also observed that the temperature field around the dynamic crack tip is adiabatic.\r\n\r\nSince adiabatic conditions are observed around a propagating crack tip, an important parameter which governs the distribution and intensity of crack tip heating is the fraction of plastic work rate converted to heat, [beta]. For this investigation [beta] is not treated as a mere parameter, the possibility of the existence of a constitutive relationship between this parameter and strain at high strain-rates is investigated using the Kolsky bar as a loading apparatus. It is found that the conversion of plastic work to heat at high strain-rates is similar to that at low strain rates for aluminum and for steel and that [beta] remains a constant independent of strain at high strains for both these materials. For rate sensitive titanium, [beta] is observed to be a function of strain possibly due to twinning deformation.\r\n\r\nIt is known that heat generation can lead to the formation of shear bands especially in dynamic fracture experiments. The formation of a shear band at the tip of a notch or crack in C-300 steel is examined using the method of CGS. First, the CGS method is used to verify a model of the notch tip stress intensity factor, K[subscript II], as a function of time. Good agreement is found between the experimental measurement of K[subscript II] and the predicted value for PMMA impacted at 5 m/s. Then the method is used to investigate the formation of shear bands at the tip of a notch under the same conditions. A Dugdale crack model is used to interpret the results, and it is seen that the shear stress decreases from 1.6 GPa to 1.3 GPa as the shear band propagates. This result is in good agreement with measurements made using the Kolsky bar.\r\n" }, { "name": "Miller, John W.", "degree": "PhD", "year": "1993", "title": "Building probalistic models from databases", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302007-155345", "creators": [ { "name": { "family": "Miller", "given": "John W." }, "id": "Miller-J-W", "display_name": "Miller, John W." } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "eleceng" ], "doi": "10.7907/mm98-d904", "abstract": "The problem of creating a probabilistic model using a database is analyzed in this thesis. Two independent results in probabilistic modeling are presented. The first result is a method for creating a model which produces accurate probability estimates. The model is a Gibbs probability distribution representation of the database. This model is created by a new transformation relating the joint probabilities of attributes in the database to Gibbs potentials. The theory of this transformation is presented together with a specific algorithm for efficiently collecting and using the Gibbs potentials. A hash table scheme is used to collect the important potentials without iterative error minimization or repeated searches through a database. The Gibbs modeling scheme allows flexible control of the tradeoffs involving modeling error and sampling error as well as the tradeoffs involved in using the resources of computation time and memory. The performance of the probabilistic modeling algorithm is tested and analyzed. Used as a classifier with a variety of datasets, the Gibbs modeling algorithm was found to equal or surpass the classification results of other models such as neural networks trained with backwards error propagation and the nearest neighbor classification algorithm.\n\nThe second independent result is the analysis of systems that use error minimization to estimate probabilities. Minimization to a probability has been a known property of the squared error and cross entropy objective functions. Here the necessary and sufficient conditions for minimization to a probability are developed. It is found that the squared error and cross entropy functions are two of the simplist functions from a family of objective functions which minimize to a probability. If the system is incapable of producing the outputs consistent with the probability estimates, it is shown the minimum error is achieved when the system produces outputs closest to the correct probability estimate outputs. The measure of closeness is described here in terms of the objective function." }, { "name": "Mouchtaris, Petros N.", "degree": "PhD", "year": "1993", "title": "Analysis of an interactive video architecture", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022005-162907", "creators": [ { "name": { "family": "Mouchtaris", "given": "Petros N." }, "id": "Mouchtaris-P-N", "display_name": "Mouchtaris, Petros N." } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "chair", "display_name": "Posner, Edward C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/A9Z4-N267", "abstract": "A new residential application for interactive video is proposed. There is a service provider that prepares and distributes daily news programs customized to subscriber interest. The provider assembles the programs from short news clips and uses a profile data base of subscribers for selecting the appropriate clips. The time of viewing the program can be selected by the customers in near-real-time. We model this service and propose a network architecture that can support it. There is a main node that contains most of the storage and sourcing facilities, and an intermediate node to which all customers are connected. Multicasting is used as much as possible for reducing the traffic load on the network. In addition to that, popular material is stored in the intermediate node which is closer to the customers, which further decreases the traffic load.\n\nOur main concern is the time that a customer has to wait until he starts getting his program. This time is a function of the capacity of the link that connects the main node to the intermediate node, the so-called main link. The case that the main link can only transport a single video connection is considered first. We propose a recurrent algorithm that calculates the probabilities of the states and uses them for evaluating the expected wait, and prove that there is a very simple relationship between the expected wait and the probabilities of the states. A simplified analysis that directly computes the expected wait is proposed next. This approach is computationally more efficient but does not give us any information about the probabilities of the states.\n\t\nFor the general case that the main link can transport more than one video connection, we generalize the recurrent algorithm that calculates the probabilities of the states and the simple relationship between the expected wait and the probabilities of the states. For the cases that the complexity of our algorithm is too large, we propose and evaluate three approximate techniques for estimating the expected wait. In the first technique we use the results for the case that a main link can only transport a single connection for estimating the results for the general case. In the second technique we use the idea of rescaling time. In the third, motivated by the fluid-flow theory, we solve a deterministic problem and use the results of that problem for estimating the expected wait for the problem we are interested in. We show that these approximate techniques compare well with simulations. Thus, we can now decide what the capacity of the main link should be so that our system has the desired performance, and we can do that even if the number of customers is very large.\n" }, { "name": "Neugebauer, Charles F.", "degree": "PhD", "year": "1993", "title": "Parallel Analog Computation with Charge Coupled Devices", "advisor": "Yariv, Amnon; Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312007-094832", "creators": [ { "name": { "family": "Neugebauer", "given": "Charles F." }, "id": "Neugebauer-Charles-F", "display_name": "Neugebauer, Charles F." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "co-advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3e7h-9p50", "abstract": "Many signal processing and neural network algorithms can be mathematically described in terms of vector matrix multiplication. This thesis introduces two new architectures for computing high-speed vector matrix multiplication using charge coupled devices. These integrated circuits have been designed to accept optical matrix input as well as direct electrical matrix input. In both architectures, the matrix elements are stored as analog charge packets in CCD wells while the vectors are communicated to and from the integrated circuits by electrical means.\r\n\r\nThe first architecture accomplishes the vector matrix product using a semiparallel computation scheme that requires N clock cycles of the device to complete one vector matrix multiplication where N is the length of the input vector. An analysis of the linearity and charge transfer induced errors is given. The circuit represents an advance over other analog signal processors in density and speed but has serious shortcomings in accuracy, particularly the limited precision of the input vectors.\r\n\r\nThe second architecture is based on charge injection device (CID) imager arrays and addresses many of the inadequacies of the semiparallel architecture. A fully parallel circuit, the CID has similar density and much higher computation speed and accuracy. A novel digital input method is introduced that extends the input vector precision significantly. In addition, accuracy issues related to charge transfer efficiency are resolved. An analysis of linearity and accuracy is provided showing the advantages of the architecture over previous implementations." }, { "name": "Okamoto, James Kozo", "degree": "PhD", "year": "1993", "title": "Temperature-dependent extended electron energy loss fine structure measurements from K, L23, and M45 edges in metals, intermetallic alloys, and nanocrystalline materials", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112006-073855", "creators": [ { "name": { "family": "Okamoto", "given": "James Kozo" }, "id": "Okamoto-J-K", "display_name": "Okamoto, James Kozo" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/kk1d-wm17", "abstract": "This dissertation developed the extended energy loss fine structure (EXELFS) technique. EXELFS experiments using the Al K, Fe L23 and Pd M45 edges in the elemental metals gave nearest-neighbor distances which were accurate to within \u00b1 0.1 A. In addition, vibrational mean-square relative displacements (MSRD) derived from the temperature dependence of the EXELFS compared favorably with predictions from published force constant models derived from inelastic neutron scattering data. Thus, information about \"local\" atomic environments can be obtained not only from K edges, but from L23 and M45 edges as well. This opens up most of the periodic table to possible EXELFS experiments.\r\n\r\nThe EXELFS technique was used to study the local atomic structure and vibrations in intermetallic alloys and nanocrystalline materials. EXELFS measurements were performed on Fe3Al and Ni3Al alloys which were chemically disordered by piston-anvil quenching and high-vacuum evaporation, respectively. Chemical short-range order was observed to increase as the as-quenched Fe3Al and as-evaporated Ni3Al samples were annealed in-situ at 300 C and 150 C respectively. Temperature-dependent measurements indicated that local Einstein temperatures of ordered samples of Fe3Al and Ni3Al were higher than those of the corresponding disordered samples. Within a \"pair\" approximation, these increases in local Einstein temperatures for the ordered alloys corresponded to decreases in vibrational entropy per atom of 0.48 \u00b1 0.25 kB for Fe3Al and 0.71 \u00b1 0.38 kB for Ni3Al. In comparison, the decrease in configurational entropy per atom between perfectly disordered and ordered A3B alloys is 0.56 kB in the mean-field approximation. These results suggest that including vibrational entropy in theoretical treatments of phase transformations would lower significantly the critical temperature of ordering for these alloys.\r\n\r\nEXELFS investigations were also performed on nanocrystalline Pd and TiO2. At 105 K, the MSRD in nanocrystalline Pd and TiO2 were found to be greater than that in the corresponding large-grained materials by 1.8 \u00b1 0.3 x 10(-3) A2 and 1.8 \u00b1 0.4 x 10(-3) A2, respectively. Temperature-dependent measurements were inconclusive in measuring differences in local atomic vibrations between the nanocrystalline and large-grained materials." }, { "name": "Ouyang, Hao", "degree": "PhD", "year": "1993", "title": "Grain boundaries of nanophase materials", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312007-095729", "creators": [ { "name": { "family": "Ouyang", "given": "Hao" }, "id": "Ouyang-H", "display_name": "Ouyang, Hao" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/8d25-6574", "abstract": "Several iron alloys with nanometer-scale grain sizes were prepared by mechanical attrition in a high energy ball mill. Mossbauer spectrometry was used to measure the internal hyperfine magnetic fields. X-ray diffractometry (XRD) and transmission electron microscopy (TEM) were used to measure the grain size. The proposed structures of nanophase materials consist of two components of comparable volume fractions: a crystalline component and an interfacial component. By correlating features in the Mossbauer spectra to the structural results of XRD and TEM, we identified the hyperfine magnetic fields of 57Fe atoms at grain boundaries. Once identified, the fractions of 57Fe atoms at grain boundaries were determined by the intensities of their magnetic signatures seen in Mossbauer spectra. With data on the fraction of 57Fe atoms at grain boundaries versus grain size, a model of the microstructure can be used to obtain the average width of the grain boundaries. Data from the model were obtained by Monte Carlo simulations. The average grain boundary widths of the fcc alloys Fe-Mn and Ni-Fe are approximately 0.5 nm, but the average widths of grain boundaries in the bcc alloys Cr-Fe and Fe-Ti are larger, approximately 1 nm.\n\nThe Debye temperature is a physical parameter of the vibrational spectrum of the solid. The difference in the Debye temperatures between the grain boundaries and the crystalline regions was found. The Debye temperature of the crystallites in nanophase Cr-Fe is 470 K, which is larger than that of grain boundary component, 370 K." }, { "name": "Petroff, Catherine M.", "degree": "PhD", "year": "1993", "title": "The interaction of breaking solitary waves with an armored bed", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-07182007-103459", "creators": [ { "name": { "family": "Petroff", "given": "Catherine M." }, "id": "Petroff-C-M", "display_name": "Petroff, Catherine M." } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "chair", "display_name": "Raichlen, Fredric" }, { "name": { "family": "List", "given": "John A." }, "id": "List-J-A", "role": "member", "display_name": "List, John A." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "member", "display_name": "Vanoni, Vito A." } ], "option_major": [ "civileng" ], "doi": "10.7907/65xx-xn79", "abstract": "This study investigates the interaction of breaking waves with a bed of loose angular material with a median grain size of 4.8 mm. It is motivated by the engineering problem of determining rock sizes for revetments used as protection for structures in the coastal zone and by the need for an understanding of the mechanics of material movement under waves. Both the effect of the bed on the velocities and accelerations in breaking and non-breaking waves, and the effect of breaking waves on the movement of bed material is measured.\n\nVelocities in breaking waves are measured at elevations approaching the bottom boundary, both for the case of a level bed of graded angular material and for a flat plate at the same location. By changing the water depth and the initial conditions of the incident wave, the relative size of the rock with respect to the breaking wave height is varied. Material movement resulting from the wave passage is measured and compared to the breaking wave height and to the turbulent shear determined near the bed. Using velocity and acceleration records near the rock bed together with observations of rock motion, the mechanics of material movement under waves are investigated.\n\nThe roughness elements in the bed are found to have a large effect on both the mean and fluctuating velocities in the wave near the bottom. Evidence is shown of the existence of an inner layer where individual pieces of bed material influence the flow over the bed. A method for determining the maximum mean shear under a single wave is presented. Mean vertical velocities are measured to be not negligible near the bed and are shown to produce convective accelerations of the same order as the accelerations due to turbulent fluctuations.\n\nThe movement of bed material is compared with the calculated shear on the bed and with local velocities and accelerations measured very close to the individual rocks. The mean size of the material moved in the bed is found to vary with the amount of shear on the bed. When adjusted for the mean size of the moved material, the calculated shears correspond well with the criterion for critical shear from the Shields curve used in steady flow. From the observed movement of particles during the passage of a wave and the measured velocities and accelerations in the wave, inertial forces are found to contribute to particle movement, especially in the regions before and after wave crest passage." }, { "name": "Pulos, Guillermo C.", "degree": "PhD", "year": "1993", "title": "Nonsteady crack propagation and craze behavior in PMMA", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312007-104217", "creators": [ { "name": { "family": "Pulos", "given": "Guillermo C." }, "id": "Pulos-G-C", "display_name": "Pulos, Guillermo C." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4kqe-ec90", "abstract": "This work is devoted to the study of nonsteady crack propagation under cyclic loading in polymers, specifically PMMA. The first part deals with the delineation of a precision loading facility allowing ultra-precise load or displacement control commensurate with the high resolution measurements of crack tip material response.\r\n\r\nA method of determining the advance of crack tip through combined microscope and computer-analyzed observation is presented. In particular, the experimental set up and software development is described by which these measurements are achieved. It is shown that automated crack tip location is possible with a precision of one to two microns, which is amply sufficient for present purposes to make definitive statements about the smoothness or discontinuity of crack propagation.\r\n\r\nThe craze and crack opening displacements are measured near the free surface of the specimen both under quasi-static step loading and cyclic loading. Eleven craze opening profiles for equal load increments are acquired during a single cycle under fatigue loading. A multi-linear craze stress model is used to match the opening displacements to the measurements. While the primordial thickness can be defined from the Lorentz-Lorenz equation and from the assumption of a constant index of refraction for the quasi-static loading, the effect of load history may prevent such determinations for cyclic loading. The damage accumulated through cyclic deformation reduces the strength of the fibrils in the middle of the craze and produces a drop in the middle of the stress distribution. The craze and crack opening displacement are monitored in connection with a jump-like crack/craze advance constituting 50% of the craze length. The newly-drawn craze fibrils after the jump show mechanical behavior that is different from their behavior before the jump and exhibit no deterioration in their stress-displacement relation." }, { "name": "Ramsden, Jerald Day", "degree": "PhD", "year": "1993", "title": "Tsunamis : forces on a vertical wall caused by long waves, bores, and surges on a dry bed", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242005-150131", "creators": [ { "name": { "family": "Ramsden", "given": "Jerald Day" }, "id": "Ramsden-Jerald-Day", "display_name": "Ramsden, Jerald Day" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "chair", "display_name": "Raichlen, Fredric" }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "civileng" ], "doi": "10.7907/HVQR-ZH55", "abstract": "The major objective of this study has been to investigate experimentally the forces and overturning moments produced by tsunamis on vertical walls. The experimental results are compared with several analytical and numerical models. Several types of waves were used in a horizontal tank including solitary waves, undular bores, turbulent bores, and surges on a dry bed. Bores produced from breaking solitary waves in a tilting wave tank were also investigated. Various measurements were made, including the incident wave celerity, the wave profile, the runup, force, overturning moment, and pressure time histories. The impact process of the bores in the tilting wave tank were recorded with high-speed movies.\r\n\r\nThe wave profiles in the horizontal tank were defined using a laser induced-fluorescence system (LIF) which allows the free surface on a two-dimensional plane in the center of the wave tank to be recorded. This method was developed to measure accurately the surface elevation profile of turbulent high-speed flows which is difficult to measure reliably either with conventional flow visualization techniques or intrusive devices such as wave gages. The LIF method was also used to determine the runup on the wall.\r\n\r\nStrong vertical accelerations were shown to occur during the reflection of bores and steep solitary waves at a vertical wall. These reduced the force on the wall relative to a hydrostatic force computed from the maximum runup height on the wall. The accelerations also cause the maximum force to occur before and after the maximum runup for steep solitary waves and bores, respectively. For these cases, the maximum measured force and overturning moment were always less than computed from the maximum measured runup on the wall using hydrostatic considerations. The maximum force due to surges on a dry bed was also less than the hydrostatic force calculated from the maximum runup height on the wall. For all the dry bed cases studied, the maximum runup height on the wall was between 1.46 and 1.62 times the velocity head computed from the celerity of the incident surge. For the entire range of wave conditions of this study, the maximum relative runup occurred for a bore with a relative wave height of 1.23, and produced a runup equal to 3.8 times the velocity head computed from the wave celerity.\r\n\r\nThe maximum measured water surface slopes along the front of long waves, bores, and dry bed surges were computed from the measured wave profiles. At the transition from undular bores to turbulent bores, there was a discontinuity in the maximum water surface slope where the slope increased by a factor of 2.5 to three for turbulent bores. This discontinuity corresponded with a rapid increase in the measured runup, force, and moment on the wall.\r\n\r\nThe properly normalized force on a vertical wall due to the impingement of a bore on a mildly sloping beach is shown to be equivalent to the force produced by a bore of constant volume on a horizontal bed. This implies the results from the horizontal wave tank experiments can be used to estimate the loads expected from bores propagating on mild beaches with slopes ranging up to 0.02m/m.\r\n\r\nTwo numerical models were compared with the experimental results. A boundary integral element model, which solves the potential flow problem subject to the full nonlinear free surface boundary conditions, predicted the loads imposed on the wall due to steep solitary waves quite well. A finite difference model of the Navier-Stokes equations was also used to simulate the reflection of solitary waves and mild turbulent bores at a vertical wall. This finite difference model predicted the solitary wave loads quite well; however, it over-predicted the steepness of the incident bore profiles and produced a force-time history with a high amplitude and short-duration peak, which was not observed in the measurements. Except for this sharp peak, the agreement of the finite difference model with the experimental results was quite reasonable." }, { "name": "Restuccio, Jim M.", "degree": "PhD", "year": "1993", "title": "Continuum modeling of materials that can undergo martensitic phase transformations", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192005-160834", "creators": [ { "name": { "family": "Restuccio", "given": "Jim M." }, "id": "Restuccio-J-M", "display_name": "Restuccio, Jim M." } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/YB1M-0R23", "abstract": "A continuum model for materials that can undergo martensitic phase transformations is developed and applied to the study of several problems that involve such transformations. One of the several advantages of using this continuum model is that the corresponding boundary value problem is in a form that permits direct linearization, while retaining finite shape deformations for the martensite phases. The continuum model is used to study several problems dealing with which variant of martensite is preferred during the application of a loading. Among these problems is the case of a uniaxial tensile traction applied to a two-phase cylindrical body, and the case of a hydrostatic pressure applied to a two-phase body that has a finite shape deformation with an infinitesimal dilatation. The results that are obtained correspond with those that have been observed from experiments and with those that might be expected from physical considerations. The next problem that is considered involves the temperature at the interface and quasi-static motions of a two-phase thermoelastic bar. The bar is subject to different temperatures at each boundary and to a mechanical end-loading. The last problem that is considered involves the longitudinal free vibrations of a fixed-free, two-phase bar. The main focus in this problem is the damping behavior of the two-phase bar that is due to the motions of the interface during the free vibrations. A finite-difference numerical routine is used to approximate the displacement solutions for this problem. The damping of the bar is studied as the material coefficients are varied, and the values of the material coefficients that produce the maximum damping are investigated." }, { "name": "Rotstein, Hector P.", "degree": "PhD", "year": "1993", "title": "Constrained H[infinity]-optimization for discrete-time control systems", "advisor": "Sideris, Athanasios", "url": "https://resolver.caltech.edu/CaltechETD:etd-11282007-130457", "creators": [ { "name": { "family": "Rotstein", "given": "Hector P." }, "id": "Rotstein-H-P", "display_name": "Rotstein, Hector P." } ], "advisors": [ { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "advisor", "display_name": "Sideris, Athanasios" } ], "committee": [ { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "chair", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "role": "member", "display_name": "Morari, Manfred" } ], "option_major": [ "eleceng" ], "doi": "10.7907/51VE-9H34", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn order to formulate a problem in the [...]-optimal control framework, all specifications have to be combined in a single [...]-norm objective, by an appropriate selection of weighting functions. If some of the specifications have the form of hard time domain constraints, the task of finding weighting functions that achieve a satisfactory design can become arduous. In this thesis, a theory for constrained [...]-control is presented, that can deal with the standard [...] objective and time domain constraints. Specifically, the following time domain constrained problem is solved: given a number [...], and a set of fixed inputs [...], find a controller such that the closed loop transfer matrix has an [...]-norm less than [...], and the time response [...] to the signal [...] belongs to some pre-specified set [...] for each [...]. Constraints are only imposed over a finite horizon, and this allows the formulation of a two step procedure. In the first step, the optimal way of clearing the constraints is found by computing a solution to a convex non differentiable problem. In the second, a standard unconstrained [...]-problem is solved. The final controller results from putting together the solution to both subproblems.\r\n\r\nThe objective function for the minimization, and the solution to the whole problem are constructed using state-space formulas. The ellipsoid algorithm is argued to be a convenient procedure for performing the optimization since, if carefully implemented, it can deal with the two main characteristics of the problem, i.e., nondifferentiability and large-scale. The validity of assuming constraints over a finite horizon is justified by presenting a procedure for computing a solution that gives an overall satisfactory behavior. For clarity of exposition, this thesis starts by discussing a very special instance of the problem, and then proceeds to give the solution to the general case. Also, a benchmark problem for robust control is solved to illustrate the applicability of the theory.\r\n" }, { "name": "Ruoff, Carl F.", "degree": "PhD", "year": "1993", "title": "Robotic hand-eye motor learning", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052007-130729", "creators": [ { "name": { "family": "Ruoff", "given": "Carl F." }, "id": "Ruoff-Carl-F", "display_name": "Ruoff, Carl F." } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "mecheng" ], "doi": "10.7907/47t1-2f31", "abstract": "This thesis investigates the use of neural networks and nonlinear estimation in robotic motor learning. It presents a detailed experimental investigation of the performance and parametric sensitivity of resource-allocating neural networks along with a new learning algorithm that offers rapid adaptation and excellent accuracy. It also includes an appendix that relates feed-forward neural networks to familiar mathematical ideas.\r\n\r\nIn addition, it presents two learning hand-eye calibration systems, one based on neural networks and the other on nonlinear estimation. The network-based system learns to correct robot positioning errors arising from the use of nominal system kinematics, while the estimation-based system identifies the robot's kinematic parameters. Both systems employ the same two-link robot with stereo vision, and include noise and various other error sources. The network-based system is robust to all error sources considered, though noise naturally limits performance. The estimation-based system has significantly better performance when the robot and vision systems are well modeled, but is extremely sensitive to unmodeled error sources and noise.\r\n\r\nFinally, it presents a robot control system based on neural networks that learns to catch balls perfectly without requiring explicit programming or conventional controllers. It uses only feed-forward pursuit motions learned through practice, and is initially incapable of even moving its arm in response to external stimuli. It learns to identify and control its pursuit movements, to identify and predict ball behavior, and, with the aid of advice from a critic, to modify its movement commands to improve catching success. The system, which incorporates information from visual, arm state, and drive force sensors, characterizes control situations using input/response pairs. This allows it to learn and respond to plant variations without requiring parametric models or parameter identification. It achieves robust execution by comparing predicted and observed behavior, using inconsistencies to trigger learning and behavioral change. The architectural approach, which involves both declarative and analog knowledge as well as short- and long-term memory, can be extended to learning other sensor-motor skills like mechanical assembly and synchronizing motor actions with external processes." }, { "name": "Ryan, Barry James", "degree": "PhD", "year": "1993", "title": "Lie-Poisson integrators in Hamiltonian fluid mechanics", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242005-152235", "creators": [ { "name": { "family": "Ryan", "given": "Barry James" }, "id": "Ryan-B-J", "display_name": "Ryan, Barry James" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/n4ds-zz40", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis thesis explores the application of geometric mechanics to problems in 2D, incompressible, inviscid fluid mechanics. The main motivation is to try to develop symplectic integration algorithms to model the Hamiltonian structure of inviscid fluid flow. The main manifestation of this Hamiltonian or conservative nature is the preservation of the infinite family of Casimirs parametrized by the body integrals of vorticity in the 2D case. The main difficulties encountered in trying to model the Hamiltonian structure of a fluid mechanical system are that the configuration space for the Hamiltonian flow is an infinite dimensional Frechet space and that the phase space is not symplectic but Lie-Poisson. Therefore, an appropriate finite mode truncation must be constructed under the constraint that it too remains Poisson and in some sense converges to the infinite dimensional parent manifold. With such a truncation in hand, there still remains the obstacle of non-symplectic structure. This geometry invalidates the application of traditional symplectic integrators and requires a more sophisticated algorithm.\n\nWe develop a Lie-Poisson truncation on the Lie group SU(N) for the Euler equations on the special geometry of a twice periodic domain in [...]. We show that this finite dimensional analog is compatible with the Arnold[5] formulation of Hamiltonian mechanics on Lie groups with a left or right invariant metric. We then proceed to review the Lie-Poisson integration literature and to develop Hamilton-Jacobi type symplectic algorithms for a broad class of Lie groups. For this same class of groups, we also succeed in constructing an explicit Lie-Poisson algorithm which radically improves computational speed over the current implicit schema. We test this new algorithm against a Hamilton-Jacobi implicit technique with favorable results." }, { "name": "Sercel, Joel Christopher", "degree": "PhD", "year": "1993", "title": "An experimental and theoretical study of the ECR plasma engine", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10192005-142203", "creators": [ { "name": { "family": "Sercel", "given": "Joel Christopher" }, "id": "Sercel-J-C", "display_name": "Sercel, Joel Christopher" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/PDWR-J354", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe process of Electron-Cyclotron-Resonance (ECR) plasma acceleration has several potential applications including use as a new type of electric space propulsion device designated the ECR plasma engine. The ECR plasma engine is interesting due to its theoretical promise to deliver a combination of improved efficiency, specific impulse, power-handling capability, length of life, or operational flexibility relative to other electric propulsion devices now being developed. Besides its possible application in electric propulsion, the ECR plasma engine might be useful for beamed-energy propulsion or fusion propulsion. Related devices are used in the semiconductors field for plasma etching.\n\nThis study includes theoretical modeling and a series of experimental measurements. The theoretical work was focused in two areas. The first area involved the development of a collisionless, steady-state, axisymmetric model of a cold flowing plasma separating from a diverging magnetic field. This model suggests that beam divergence can be an important loss mechanism for plasma propulsion devices that use magnetic nozzles, but that the use of optimized field geometries can reduce divergence losses to acceptable levels. We suggest that future research be directed at confirming theoretical predictions made using the axisymmetric model of beam separation.\n\nThe second area of theoretical investigation involved the development of a steady-state, quasi-one-dimensional model that provides theoretical predictions of plasma density, electron temperature, plasma potential, ion energy, engine specific impulse, efficiency, and thrust. The quasi-one-dimensional model consists of a system of five first-order, nonlinear, ordinary differential equations. The boundary conditions required to solve the system of equations are relationships between the ambient neutral gas density, the plasma density, the two components of the electron temperature, and the position at which the plasma passes through the ion-acoustic Mach number 1. The model was used to solve two classes of problems that are thought to bound the conditions under which the ECR plasma accelerator operates. The first class of problem is based on the assumption of negligible conductive heat flow within the plasma. The second class of problem is based on the assumption that electron thermal transport along magnetic field lines is so large that the component of the electron temperature along magnetic field lines is isothermal. The model can be used to simulate accelerator operation in space or in the presence of a vacuum system with finite tank pressure. Measurements of plasma conditions in a working research device confirm the general features of the quasi-one-dimensional theory.\n\nThe experimental apparatus constructed to study ECR plasma acceleration consists of a vacuum facility, a 20-kW microwave power supply, and an ECR plasma accelerator. In tests of the facility we have measured microwave input power, reflected power, propellant flow rate, and vacuum-tank static pressure. The working ECR plasma research device uses argon propellant gas with 2.12-GHz microwave radiation at power levels of up to a few kilowatts. Among the plasma diagnostics employed in this research are a gridded energy analyzer, a Faraday cup beam-density analyzer, Langmuir probes, emissive probes, and a diamagnetic loop. With these diagnostics, we have measured plasma potentials of up to 70 eV and electron temperatures of up to 35 eV. Measurements of accelerated-ion kinetic energy show a direct relationship between ion energy and peak plasma potential, as predicted by theory. Indirect measurements indicate that the plasma density in the existing accelerator is on the order of [...].\n\nWe now understand previously unexplained losses in converting microwave power to jet power by ECR plasma acceleration as the result of diffusion of energized plasma to the metallic walls of the accelerator. Our theory suggests that future researchers should attempt to reduce the influence of these diffusion losses by increasing the cross-sectional area of the accelerator. It may be possible to reduce line radiation losses due to electron-ion and electron-atom inelastic collisions below levels estimated by past researchers through careful accelerator design. Minimizing inelastic collision losses will place a limit on the maximum thrust density that can be achieved using argon and other non-hydrogenic propellant materials. High thrust density may be achievable using propellants that are isotopes of hydrogen because once ionized, these species exhibit negligible inelastic collision effects. Deuterium is arguably the best candidate for achieving both high efficiency and high thrust, but will only be effective at specific impulses of over about 10,000 lbf s/lbm.\n\nWe expect that efficient ECR plasma engines can be designed for use in high specific impulse spacecraft propulsion at power levels ranging from a few kilowatts to tens of megawatts. The maximum theoretical efficiency of converting applied microwave power to directed jet power in this device can be more than 60 percent. The achievable total efficiency of converting direct-current electric power to jet power in a propulsion system based on the ECR plasma engine will probably be considerably less." }, { "name": "Sheehy, Finbar T.", "degree": "PhD", "year": "1993", "title": "Antenna-coupled mm-wave electro-optic modulators and linearized electro-optic modulators", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242005-151449", "creators": [ { "name": { "family": "Sheehy", "given": "Finbar T." }, "id": "Sheehy-F-T", "display_name": "Sheehy, Finbar T." } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MSTR-SC86", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nWe have demonstrated antenna-coupled electro-optic modulators at frequencies up to 98 GHz. The antenna-coupled design allows the modulator to overcome the velocity-mismatch problem which limits the maximum operating frequency of more conventional designs. Several modulators have been demonstrated, including a prototype narrowband phase modulator (optical wavelength 0.633 [...]) at 10 GHz, a narrowband phase modulator (0.633 [...]) at 60 GHz, a broadband Mach-Zehnder modulator operated as a phase modulator at 60 GHz, and a broadband Mach-Zehnder amplitude modulator at 94 GHz (optical wavelength 1.3 [...]). The performance of the prototype modulator at 10 GHz is not quite as good as that of conventional modulators at this frequency, but is comparable. The performance of the mm-wave modulators cannot be directly compared to conventional modulators, as none exist at these frequencies. However, we have established that the relative performance of the mm-wave modulators is consistent with a simple scaling law.\r\n\r\nLinearized [...] modulators have been demonstrated recently by other workers. These linearized modulators consist of conventional [...] coupler-modulators cascaded with additional couplers. We have considered the general case of cascade-linearized [...] modulators, and have shown that it is possible to provide up to four degrees of freedom which can be used to modify the modulator transfer function. We have shown that these degrees of freedom can be identified and separated for design purposes, and have shown how to implement a given design.\r\n" }, { "name": "Sheiman, Arthur E.", "degree": "PhD", "year": "1993", "title": "A new method for solving irises in waveguides", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02282011-111234950", "creators": [ { "name": { "family": "Sheiman", "given": "Arthur E." }, "id": "Sheiman-A-E", "display_name": "Sheiman, Arthur E." } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6ptc-ac45", "abstract": "A new boundary residual mode-matching method is developed to find scattering solutions for an infinitely thin transverse iris (diaphragm) mounted in a waveguide (i.e., junction discontinuities). Differing dielectric constants are allowed on the two sides of the iris, and an\r\noptional transverse short placed behind the iris is also treated, allowing solutions useful in understanding planar grids used in microwave/millimeter wave power combining. The new method treats the edge-singularity of the iris (edge-condition) in both the electric and magnetic\r\nfields, and at each edge of a multi-edge iris, all simultaneously. This results in a rapidly-converging\r\nnumerical solution, and oscillation-free transverse (electromagnetic) field plots (not available with methods that ignore singularity extraction). The solution is also free from relative convergence problems. Furthermore, the method when used without singularity extraction\r\nresults in a formulation that is up to eight times faster than the standard boundary residual method, yet requires only one-fourth the memory, and is simpler to program. Singularity extraction further improves the speed and reduces memory requirements.\r\n\r\nIn addition, extensions are made to Schwinger's variational formulas, resulting in formulas that produce highly-accurate answers for certain problems, even with multi-moding.\r\n\r\nA new type of problem is introduced, that of a triangular shaped iris, and the complicated inner product integrals are solved analytically in closed rational form. Theory and\r\nexperiment are compared.\r\n\r\nA group of computer programs are developed to apply this new method, and the source code is listed and declared as \"public domain.\"" }, { "name": "Soman, Anand", "degree": "PhD", "year": "1993", "title": "New results on paraunitary filter banks : energy compaction properties, linear phase factorizations and relation to wavelets", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10202005-094027", "creators": [ { "name": { "family": "Soman", "given": "Anand" }, "id": "Soman-A", "display_name": "Soman, Anand" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/tkk3-a559", "abstract": "Subband coding schemes have been widely used to encode signals from speech, high quality audio, and image sources. The theory of perfect reconstruction filter banks has also been studied extensively. The purpose of this thesis is to study the properties of the so-called paraunitary systems, and issues pertaining to their applications and implementations.\n\nWe will begin by proving several properties of paraunitary filter banks. For example, we will prove that all orthonormal discrete-time wavelets can be generated using paraunitary binary trees. We will also extend this result to arbitrary tree-structures and wavelet packets. Next, we will address the two issues involved in the design of a paraunitary subband coding system. 1) the problem of optimal bit allocation among various channels given a fixed bit-rate, and 2) the problem of finding the optimal filter bank (by optimization) to encode a given signal. We will prove several interesting results in this regard. We will then show how generalized polyphase representations can be used to enhance the coding gain of transform coding systems.\n\nIn practical applications, one often imposes several other conditions on the individual filters in a filter bank. For example, the linear phase property is found to be important for encoding image signals, whereas the 'pairwise mirror-image' property generally yields filters with better responses and, therefore, better frequency selectivity. The final part of the thesis deals with the implementions of paraunitary systems having such additional properties. We will obtain factorizations for such systems which will be proved to be minimal as well as complete. These factorizations yield structures which are robust, i.e., all the desired properties are retained in spite of coefficient quantization." }, { "name": "Watts, Donald Lloyd", "degree": "PhD", "year": "1993", "title": "Cochlear Mechanics: Analysis and Analog VLSI", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-07022004-115127", "creators": [ { "name": { "family": "Watts", "given": "Donald Lloyd" }, "id": "Watts-Donald-Lloyd", "display_name": "Watts, Donald Lloyd" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Lyon", "given": "Richard F." }, "id": "Lyon-Richard-F", "role": "member", "display_name": "Lyon, Richard F." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "eleceng" ], "doi": "10.7907/19EW-YM12", "abstract": "The cochlea separates sounds based on their frequency content and on their fine time structure, using an active and nonlinear fluid-mechanical traveling-wave mechanism. This dissertation describes a simplified model of the cochlear mechanics problem, and techniques for solving the problem.
\r\n\r\nThe Liouville-Green (LG) method has been used to obtain analytical solutions for the cochlear mechanics problem; however, the failure of the method to agree quantitatively with numerical methods has left doubts about its validity. In this dissertation, it is shown that the LG method fails to solve the problem, and that an additional degree of freedom is required for a consistent solution. The additional degree of freedom corresponds to a second wave mode, which has been observed experimentally in the cochleas of living animals. The new mode-coupling LG solution agrees quantitatively with numerical solutions. This problem has been outstanding since 1971.
\r\n\r\nIn addition to analytical techniques, this dissertation also presents analog circuit techniques, specifically for the medium of analog very-large-scale-integration (VLSI) complementary metal-oxide-semiconductor (CMOS) technology. A silicon cochlea that models the behavior of the passive cochlea has been fabricated and tested. The silicon cochlea operates in real time with 8 mW of power dissipation.
\r\n\r\nThe active and nonlinear behavior of the cochlea is a subject of intense research interest at the present time, and many issues are still unresolved. A preliminary model of active elements in the cochlea is described and characterized, and shown to be consistent with the prevailing views of active cochlear function.
" }, { "name": "Young, Peter Michael", "degree": "PhD", "year": "1993", "title": "Robustness with Parametric and Dynamic Uncertainty", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302007-075425", "creators": [ { "name": { "family": "Young", "given": "Peter Michael" }, "id": "Young-Peter-Michael", "display_name": "Young, Peter Michael" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "orcid": "0000-0002-7696-5058", "role": "member", "display_name": "Morari, Manfred" }, { "name": { "family": "Dahleh", "given": "Munther A." }, "id": "Dahleh-Munther-A", "orcid": "0000-0002-1470-2148", "role": "member", "display_name": "Dahleh, Munther A." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/HJF8-J281", "abstract": "In many disciplines of engineering it is often convenient, for analysis and design purposes, to approximate the real behavior of physical systems by mathematical models. For some applications however, and in particular when one wishes to design a high performance controller, the differences between the behavior of the mathematical model and the physical system can be crucial to the performance of the final design. The theory of robust control attempts to take into account these inherent inaccuracies in the model, and provide systematic analysis and design techniques in the face of this \"uncertainty.\"
\r\n\r\nThese goals can be restated as formal mathematical problems. In order to handle more realistic descriptions of physical systems, one has to allow more sophisticated models, and this leads to more difficult mathematical problems. In this thesis we will consider both the theoretical and computational aspects of such problems. In particular we will consider robustness in the presence of both real (e. g., parametric) and complex (e. g., dynamic) structured uncertainty.
\r\n\r\nThis leads to a consideration of the general mixed \u00b5 analysis and synthesis problems. Some special cases of the analysis problem can be solved exactly, but the general problem is in fact NP hard, so that in order to develop solutions for large problems with reasonable computational requirements, we will adopt a scheme of computing and refining upper and lower bounds. By exploiting the theoretical properties of the problem, we are able to develop practical algorithms, capable of handling mixed \u00b5 analysis problems with tens of parameters, in computation times that are typically of the order of minutes. This is despite the fact that the mixed \u00b5 problem appears to have inherently combinatoric worst-case behavior.
\r\n\r\nFor the synthesis problem a new \"D,G-K iteration\" procedure is developed to design a stabilizing controller which attempts to minimize the peak value across frequency of mixed \u00b5. The scheme utilizes a combination of some new results from the mixed \u00b5 upper bound problem with the H\u221e optimal control solution. The theoretical results developed here have already been successfully applied to a number of real engineering problems, and some of these applications are briefly reviewed, to illustrate the advantages offered by the new analysis and synthesis techniques.
" }, { "name": "Zhang, Yongfang", "degree": "PhD", "year": "1993", "title": "Coupled array of CO2 waveguide lasers", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212007-125547", "creators": [ { "name": { "family": "Zhang", "given": "Yongfang" }, "id": "Zhang-Yong", "display_name": "Zhang, Yongfang" } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/zajm-ra61", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn this thesis, arrays of coupled waveguide [...] lasers and some aspects of coupled laser arrays in general are studied. The in-phase coupled supermode is desirable in almost all laser applications, but it is not always obtained in laser arrays. An analytical method is used to investigate the spatial overlap between the distributions of laser mode intensity and the medium gain and cavity loss, and its effect on mode. The result shows that the gain/loss in the inter-element regions of an array determines which supermode to oscillate: for a fixed gain level a high loss favors the out-of-phase supermode while a low loss, the in-phase supermode. Several waveguide [...] lasers, including wall-slot coupled ceramic and metal arrays, uncoupled arrays, single slab waveguide lasers, and slab waveguide lasers with unstable resonators were tested for their modal properties and power output. A new structure, the groove-coupled strip waveguide [...] laser array, that favors the in-phase coupled supermode was proposed and tested in two, three and five-element arrays. The experimental results showed that this new structure yields robust, pure in-phase coupled mode operation with a reasonable amount of output power.\r\n\r\nAlso discussed in this thesis are the coupling of Gaussian waves in active media, the experiments in an all-metal, ridge-waveguide [...] laser pumped by microwaves, a new type of optical switching based on the unique properties of a coupled twin-element laser, and two-dimensional array of gas discharge lasers." }, { "name": "Zsak, Thomas William", "degree": "PhD", "year": "1993", "title": "An investigation of the reacting vortex structures associated with pulse combustion", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212007-105308", "creators": [ { "name": { "family": "Zsak", "given": "Thomas William" }, "id": "Zsak-T-W", "display_name": "Zsak, Thomas William" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "mecheng" ], "doi": "10.7907/aja3-z307", "abstract": "An investigation of the reacting vortex structures associated with pulsating combustion is performed using a laboratory dump combustor in order to gain an understanding of the controlling physical and chemical processes present during the burning of the vortex structures. Stabilized on the lip of a rearward-facing step flame holder, the vortices are shed at acoustic longitudinal modes of the apparatus. In all cases examined, a fuel-rich mixture of methane and air is used, 30% greater than stoichiometric, and the velocity at the dump plane is 21 m/sec. Results are presented for the expansion ratios of 4.0 and 12.0.\n\nA linearized one-dimensional acoustic model is developed to predict the resonant acoustic modes and mode shapes of the system for the two configurations. Heat addition is modeled as a sinusoidally varying volumetric mass source which can be placed at any location within the combustion chamber. Good agreement is found between the natural frequencies predicted by the model and those obtained experimentally under both hot- and cold-flow conditions. The effects of different combustion chamber temperatures on the pressure and velocity responses are revealed as are the effects of placing the heat addition at different axial locations downstream of the dump plane. It is shown that the pressure amplitude spectra for each expansion ratio can be successfully predicted given the relationship between heat release in the chamber and frequency.\n\nThe ignition mechanisms of the vortex structures are found to be different for the two chamber configurations, and the bulk of the heat release is shown to occur much closer to the dump plane for the chamber with the smaller expansion ratio. The influence of the lower wall of the combustor on the burning of the structures is shown to be weaker for the chamber with the larger expansion ratio.\nThe additions of ionization probes and an intensified, charge-injection-device (CID) camera to the experimental program have allowed the burning histories of the shed vortex structures to be recorded. Capturing an image of the chemiluminescence from the burning of the vortices at nearly the same instant as a shadowgraph image of the density gradients within the chamber completely describes the reacting flow field. Temperature measurements made with fine-wire thermocouples complete the experimental investigation and complement the results obtained above.\n" }, { "name": "Ammons, Richard Lewis Martin", "degree": "PhD", "year": "1992", "title": "Mathematical control theory for liquid chromatography", "advisor": "Lorenz, Jens; Kreiss, Heinz-Otto", "url": "https://resolver.caltech.edu/CaltechTHESIS:09082011-113722649", "creators": [ { "name": { "family": "Ammons", "given": "Richard Lewis Martin" }, "id": "Ammons-R-L-M", "display_name": "Ammons, Richard Lewis Martin" } ], "advisors": [ { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-J", "role": "advisor", "display_name": "Lorenz, Jens" }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "co-advisor", "display_name": "Kreiss, Heinz-Otto" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/bneq-qh86", "abstract": "A more comprehensive mathematical theory for liquid\r\nchromatography is set forth, incorporating dynamical models for mixed solvents and solutes, and new mathematical models for adsorption, including adsorbent and exchange processes.\r\nThe equations for solvent and solute are shown to possess unique solutions, using so-called energy methods. The solvent modulation of local velocity is found theoretically, as is solvent control of solute adsorption, diffusivity, and dispersion. The theory for solvent control of solute adsorption is found to be very accurate against experiment, and offers a useful method of treating normal phase, reversed phase, ion exchange, and ion pair liquid chromatography in a unified mathematical framework, under the name catalyzed adsorption. The long-recognised problem\r\nof solvent localization is modelled, and the model shown to be consistent with experiment. Another classical problem, solvent demixing, is explained in terms of the nonlinear multicomponent solvent model, wherein solvent gradients steepen according to the adsorption and shock formation. Perturbation theory, based on a small packing number d_p/L \u00ab 1 (where d_p is substrate particle diameter, L is column length), is applied to the solvent-controlled pulsed solute dynamical equations. When moment techniques are used in conjunction with perturbation theory, very useful and simplified system control equations are obtained. These control equations are used in some model problems to discuss HETP (Height Equivalent to a Theoretical Plate) variations with Peclet number, with relative solvent concentration, and between solutes. Finally, numerical methods for the solvent and solute equations are discussed.
\r\n" }, { "name": "Askenazy, Philip Douglas", "degree": "PhD", "year": "1992", "title": "Deformation-induced amorphization of Cu-Ti intermetallics", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-07192007-131937", "creators": [ { "name": { "family": "Askenazy", "given": "Philip Douglas" }, "id": "Askenazy-P-D", "display_name": "Askenazy, Philip Douglas" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/qssf-8m12", "abstract": "Two methods of inducing amorphization in Cu-Ti intermetallic compounds by mechanical means have been investigated. Ingots of compositions Cu35Ti65 and Cu33.3Ti66.7 were rapidly quenched into ribbons. The microstrucure consisted largely of microcrystals in an amorphous matrix, which were either quenched in or grown by annealing. The ribbons were cold-rolled, which reduced their effective thickness by a factor of about 8. The status of the intermetallic compound CuTi2 was monitored by x-ray diffraction and transmission electron microscopy (TEM). The crystals were found to amorphize as rolling progressed. This behavior was not reproduced in polycrystalline samples that had no amorphous matrix present initially. The presence of the amorphous phase is thus necessary for amorphization of the crystal: it eliminates the need to nucleate the new glass, and it prevents the ribbon from disintegrating at high deformation stages. It may also change the deformation mechanism that occurs in the crystals, retarding the onset of amorphization. Diffuse scattering in close-packed directions is similar to that seen in electron irradiation experiments. It is postulated that the chemical disorder present in antiphase boundaries caused by deformation raises the free energy of the crystal higher than that of the amorphous phase.\n\nIngots of the same compound were worn against each other in a custom-built wear apparatus. The design eliminates iron contamination of the wear sample and requires relatively small quantities of material. Alteration of the surface structure was monitored by plane-view and cross-sectional TEM. Larger subsurface crystals exhibit diffuse scattering, similar to that found in the rolled samples. A wide range of grain sizes was observed, due to the inhomogeneous nature of the wear process. An unusual phase was observed at the surface, consisting of a nanometer-scale mixture of aligned nanocrystalline regions and disordered areas. Some amorphous phase is possibly present as well. It is postulated a combination of high unidirectional strain rates and small grain sizes forces the nanocrystals to accommodate deformation by disordering in one direction. Deformation in additional directions might presumably cause the structure to go completely amorphous." }, { "name": "Barzel, Ronen", "degree": "PhD", "year": "1992", "title": "A structured approach to physically-based modeling for computer graphics", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282011-075406850", "creators": [ { "name": { "family": "Barzel", "given": "Ronen" }, "id": "Barzel-R", "display_name": "Barzel, Ronen" } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "orcid": "0000-0001-9190-1290", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "compsci" ], "doi": "10.7907/tbgd-g285", "abstract": "This thesis presents a framework for the design of physically-based computer graphics models. The framework includes a paradigm for the structure of physically-based models, techniques for \"structured\" mathematical modeling, and a specification of a computer program structure in which to implement the models. The framework is based on known principles and methodologies of structured programming and mathematical modeling. Because the framework emphasizes the structure and organization of models, we refer to it as \"Structured Modeling.\"
\r\n\r\nThe Structured Modeling framework focuses on clarity and \"correctness\" of models, emphasizing explicit statement of assumptions, goals, and techniques. In particular, we partition physically-based models, separating them into conceptual and mathematical models, and posed problems. We control complexity of models by designing in a modular manner, piecing models together from smaller components.
\r\n\r\nThe framework places a particular emphasis on defining a complete formal statement of a model's mathematical equations, before attempting to simulate the model. To manage the complexity of these equations, we define a collection of mathematical constructs, notation, and terminology, that allow mathematical models to be created in a structured and modular manner.
\r\n\r\nWe construct a computer programming environment that directly supports the implementation of models designed using the above techniques. The environment is geared to a tool-oriented approach, in which models are built from an extensible collection of software objects, that correspond to elements and tasks of a \"blackboard\" design of models.
\r\n\r\nA substantial portion of this thesis is devoted to developing a library of physically-based model \"modules,\" including rigid-body kinematics, rigid-body dynamics, and dynamic constraints, all built with the Structured Modeling framework. These modules are intended to serve both as examples of the framework, and as potentially useful tools for the computer graphics community. Each module includes statements of goals and assumptions, explicit mathematical models and problem statements, and descriptions of software objects that support them. We illustrate the use of the library to build some sample models, and include discussion of various possible additions and extensions to the library.
\r\n\r\nStructured Modeling is an experiment in modeling: an exploration of designing via strict adherence to a dogma of structure, modularity, and mathematical formality. It does not stress issues such as particular numerical simulation techniques or efficiency of computer execution time or memory usage, all of which are important practical considerations in modeling. However, at least so far as the work carried on in this thesis, Structured Modeling has proven to be a useful aid in the design and understanding of complex physically based models.
" }, { "name": "Bonazza, Riccardo", "degree": "PhD", "year": "1992", "title": "X-ray measurements of shock-induced mixing at an air/xenon interface", "advisor": "Sturtevant, Bradford; Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232005-111112", "creators": [ { "name": { "family": "Bonazza", "given": "Riccardo" }, "id": "Bonazza-R", "display_name": "Bonazza, Riccardo" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "co-advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3h5j-yb71", "abstract": "A new experimental technique to measure the density of a high atomic number gas at an interface has been developed and demonstrated. It is based on the absorption of X-rays by the high atomic number gas, and it was implemented in a vertical square shock tube for the study of shock-accelerated air/xenon interfaces. These were prepared by retracting a metal plate initially separating the two gases, prior to the release of the shock wave. Thus the interfaces were all of initial finite thickness. Interfaces of two types, quasi-sinusoidal and nominally flat, were examined. Object of study were the amplitude of large wavelength (25 - 100 mm) perturbations on the interface, and the thickness of the interface. An integral definition for the interface mean line (proposed in a previous numerical work at GALCIT) was adopted; a new integral definition for the interface thickness was proposed, making it feasible to study for the first time the thickness of quasi sinusoidal interfaces. Experiments were performed to image interfaces having interacted with the incident shock, the incident and the reflected shock, or a series of weak waves reverberating between the interface and the shock tube end wall. The results for the growth rates of the amplitudes were compared against a model based on the linear theory: The measured values are larger than the predicted ones in the case when the interface only interacts with the incident and the first reflected shocks. They are smaller than the theoretical ones in the case of multiple reverberations. The interface thickness exhibits essentially no growth upon interaction with the incident shock. The interaction of the reflected shock with the turbulent boundary layer behind the incident one generates random acoustical disturbances which reach the interface and cause the subsequent thickness growth. The thickness growth rates of nominally flat interfaces are larger than those previously found at GALCIT in a schlieren visualization experiment, in the case of two shock interactions. They are smaller in the case of multiple interactions. In the case of two shock interactions, wall vortices generated by the interaction of the reflected shock with the boundary layer behind the incident one severely affected the measurements. A correction was proposed to account for this effect in the measurements of the interface thickness. The need remains for a different experimental technique, capable of eliminating these adverse effects altogether." }, { "name": "Budzinski, John Michael", "degree": "PhD", "year": "1992", "title": "Planar Rayleigh Scattering Measurements of Shock Enhanced Mixing", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202007-130628", "creators": [ { "name": { "family": "Budzinski", "given": "John Michael" }, "id": "Budzinski-John-Michael", "display_name": "Budzinski, John Michael" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/pwj0-h036", "abstract": "This investigation was concerned with the mixing which occurs after the unsteady interaction of a shock wave with a laminar jet of helium. The jet of helium was injected normal to the direction of the propagation of the shock. The vorticity created at the boundaries of the jet during the shock interaction generates a stream of air which divides the initial circular cross section of the jet into two lobes. Each lobe is further divided into a tail region and a vortex core. The vortex cores from each lobe form a vortex pair that pulls ahead of the tail regions. In the present investigation the primary diagnostic, planar Rayleigh scattering, had sufficient spatial and temporal resolution to resolve the smallest diffusion scales present and allowed helium mole fractions to be measured in two-dimensional planes normal to the original jet flow direction. The amount of molecular mixing was evaluated with a mass distribution function at increasing times after the shock interaction. The total masses of helium contained in regions where the molar concentration of helium was at least 30% and 50% were also calculated. The shock Mach number was varied, and the effect of a reflected shock was studied. The velocity and spacing of the vortex pairs was measured. It was found that shock interactions can significantly increase the mixing between the air and helium. As the Mach number increases, better mixing occurs as the stream of air divides the jet. However, less mixing occurs at the later times when the vortex pairs are moving ahead of the tails. A rough collapse of the mixing data occurs when time is normalized with the change in velocity of the air behind the shock. The measured velocities and estimated values of the circulation agree very well with previous computational results. An increase in the enhancement of mixing occurred after the interaction with the reflected shock." }, { "name": "Challa, Venkata Ramana Murty", "degree": "PhD", "year": "1992", "title": "Nonlinear seismic behaviour of steel planar moment-resisting frames", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062011-075420910", "creators": [ { "name": { "family": "Challa", "given": "Venkata Ramana Murty" }, "id": "Challa-Venkata-Ramana-Murty", "display_name": "Challa, Venkata Ramana Murty" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Heaton", "given": "Thomas H." }, "id": "Heaton-T-H", "role": "member", "display_name": "Heaton, Thomas H." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." } ], "option_major": [ "civileng" ], "doi": "10.7907/jk1f-2d70", "abstract": "The nonlinear response of steel planar moment-resisting frames during strong earthquakes poses a strong need for accurately modelling inelastic behaviour and large displacements. This thesis attempts to provide realistic and efficient analytical tools to aid this study.
\r\n\r\nTwo large-displacement small-strain beam-column models are employed to include material and geometric nonlinearities. The first model assumes lumped plasticity, and discretises an element into segments. Axial force-Bending Moment strength interaction and flexural bowing are considered. Ten characteristic segment states are identified. An efficient numerical scheme is suggested to solve the nonlinear governing equations. This model only approximately represents the strength and stiffness of beam-columns.
\r\n\r\nA comprehensive finite element beam-column model is developed to more accurately model the strength and stiffness. A beam-column is discretised into segments, and further, each segment into one-dimensional fibres. A uniaxial cyclic constitutive law valid under arbitrary transient loading is proposed for structural steel. This physically motivated law incorporates the initial yield plateau, and provides explicit expressions for stress in terms of strain throughout the hysteretic path. This law is used to control the hysteretic loading of fibres.
\r\n\r\nA simple semi-empirical model is employed to analytically describe the highly nonlinear hysteretic behaviour of flexible joint panel zones in steel planar frames. Some modelling assumptions that may be made in frame analyses are evaluated. Numerical study of a building frame with flexible joints indicates that its collapse is sensitive to the joint panel zone design in addition to the ground motion.
\r\n" }, { "name": "Chirikjian, Gregory Scott", "degree": "PhD", "year": "1992", "title": "Theory and Applications of Hyper-Redundant Robotic Manipulators", "advisor": "Burdick, Joel Wakeman", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082006-132210", "creators": [ { "name": { "family": "Chirikjian", "given": "Gregory Scott" }, "id": "Chirikjian-Gregory-Scott", "display_name": "Chirikjian, Gregory Scott" } ], "advisors": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "advisor", "display_name": "Burdick, Joel Wakeman" } ], "committee": [ { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "chair", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Hayati", "given": "S." }, "id": "Hayati-S", "role": "member", "display_name": "Hayati, S." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/F12D-0X25", "abstract": "The term \"hyper-redundant\" refers to robotic manipulators and mobile robots with a very large, possibly infinite, number of actuatable degrees of freedom. These robots are analogous in morphology and operation to snakes, worms, elephant trunks, and tentacles. This thesis presents a novel kinematic framework for hyper-redundant manipulator motion planning and task implementation. The basis of this formulation is the use of a \"backbone reference set\" which captures the essential macroscopic geometric features of hyper-redundant robots. In the analytical part of this work, the backbone representation is developed and used to solve problems in obstacle avoidance, locomotion, grasping, and \"optimal\" end effector placement. The latter part of this thesis deals with the design and implementation of a thirty-degree-of-freedom planar hyper-redundant manipulator which is used to demonstrate these novel kinematic and motion planning techniques. Design issues such as robustness with respect to mechanical failure, and design for easy assembly and repair are also addressed. The analytical and design concepts are combined to illustrate tasks for which hyper-redundant robotic mechanisms are well suited.\r\n" }, { "name": "Frieler, Clifford Eugene", "degree": "PhD", "year": "1992", "title": "Mixing and reaction in the subsonic 2-D turbulent free shear layer", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03292005-135259", "creators": [ { "name": { "family": "Frieler", "given": "Clifford Eugene" }, "id": "Frieler-C-E", "display_name": "Frieler, Clifford Eugene" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/fsen-at31", "abstract": "Several aspects of mixing and reaction in a turbulent two-dimensional shear layer have been studied. Experiments have been performed with reacting H2, F2, and NO in inert diluent gases. Sensing the heat release by these reactions, several aspects of the mixing process can be examined without the usual resolution limitations. For example, in contrast with direct measurements of composition, the amount of mixed fluid can be conservatively estimated with the results of the \"flip\" experiments. These have been performed over a range of density ratios, Reynolds numbers and heat release.\r\n\r\nThe effects of initial conditions are of primary importance when comparisons to other studies are undertaken. Aspects as fundamental as growth rate of the turbulent region, or as obscure as the mixed fluid flux ratio depend strongly on the boundary conditions of this flow. These effects are examined in conjunction with those of Reynolds number and density ratio. For most cases studied here, tripping of the high speed boundary layer led to growth rate decreases. An exception was found for the case of high density ratio where the opposite effect was observed. This anomalous result occurred at conditions under which a new mode of instability has been shown to exist. Parallels exist between this unusual result and those of Batt in the uniform density case.\r\n\r\nAn extensive study of the effects of density ratio on the mixing and reaction in the 2-D shear layer has been performed. Results indicate that several aspects of the mixing process are remarkably similar. Profiles of mixed fluid change little as the density ratio varies by a factor of 30. The integral amount of mixed fluid varies less than 6% for all density ratios examined. This insensitivity contrasts with that of the profiles of mixed fluid composition. While having very similar shapes the profiles are offset by an amount which depends very strongly upon the density ratio. The entrainment into the mixing layer has also been examined. Power spectral densities of the temperature time series were calculated and found to collapse upon normalization with the adiabatic flame temperature and large structure passage frequency. Least squares fits of the probability density functions were also examined.\r\n\r\nThe initial work of Mungal and Frieler (1988) on the effects of chemical kinetics on the formation of product in the 2-D mixing layer have been greatly expanded. Measurements have been extended to include a wider range of NO concentrations and have been performed for two other stoichiometries. Results indicate that the simple model envisioned in Mungal and Frieler may only be suited for cases with extreme stoichiometry (very high or very low). Further investigations have turned up a serious discrepancy reflecting both on the experimental technique and on theory and modeling of this reacting flow. Experiments run under otherwise identical conditions demonstrate that more product is formed when F2 is the rich reactant than when H2 is the rich reactant. This dependence upon molecular character is counter intuitive and stems from a coupling of the effects of differing diffusivity and chemical kinetics. Numerical calculations based on simplified flow models are reported which demonstrate this coupling. These results indicate that even subtle diffusion effects can measurably effect reacting flows and imply that assumptions common among current modeling efforts must be re-examined.\r\n\r\nThe effects of Reynolds number on mixing and reaction in the 2-D turbulent mixing layer have been examined. Evidence of the remnants of the initial roll up and mixing transition are seen for Reynolds numbers as large as 30,000. Indications of a resonance with the acoustic mode of the apparatus exist which affect results for Reynolds numbers up to 60,000. Natural transition of the high and low speed boundary layer on the splitter plate complicate comparisons of the high Reynolds number data with the remainder. In spite of all of these qualifications, the amount of mixed fluid is nearly constant. Over the range of Reynolds numbers 10,000 to 200,000, it varies by less than 12%. No evidence of an asymptotic decline in the amount of mixed fluid is observed.\r\n" }, { "name": "Fyfe, William John Andrew", "degree": "PhD", "year": "1992", "title": "Invariance hints and the VC dimension", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202007-075240", "creators": [ { "name": { "family": "Fyfe", "given": "William John Andrew" }, "id": "Fyfe-W-J-A", "display_name": "Fyfe, William John Andrew" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Wilson", "given": "Richard M." }, "id": "Wilson-R-M", "role": "member", "display_name": "Wilson, Richard M." } ], "option_major": [ "compsci" ], "doi": "10.7907/ft2z-te28", "abstract": "We are interested in having a neural network learn an unknown function f. If the function satisfies an invariant of some sort, such as f is an odd function, then we want to be able to take advantage of this information and not have the network deduce the invariant based on an example of f.\r\n\r\nThe invariant might be defined in terms of an explicit transformation of the input space under which f is constant. In this case it is possible to build a network that necessarily satisfies the invariant.\r\n\r\nIn general, we define the invariant in terms of a partition of the input space such that if x, x' are in the same partition element then f(x) = f(x'). An example of the invariant would be a a pair (x, x') taken from a single partition element. We can combine examples of the invariant with examples of the function in the learning process. The goal is to substitute examples of the invariant for examples of the function; the extent to which we can actually do this depends on the appropriate VC dimensions. Simulations verify, at least in simple cases, that examples of the invariant do aid the learning process." }, { "name": "Galton, Ian", "degree": "PhD", "year": "1992", "title": "An analysis of quantization noise in delta sigma modulation and its application to parallel delta sigma modulation", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202007-150751", "creators": [ { "name": { "family": "Galton", "given": "Ian" }, "id": "Galton-I", "display_name": "Galton, Ian" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "chair", "display_name": "Posner, Edward C." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/BF7F-6D40", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe trend toward digital signal processing in communication systems has resulted in a large demand for fast, accurate analog-to-digital (A/D) converters, and advances in VLSI technology have made [...] modulator based A/D converters attractive solutions. However, because they are non-linear systems, they have proven difficult to analyze. Rigorous analyses have been previously performed only for a small number of artificial input sequences and then only for the simplest of [...] modulator architectures. This thesis consists of three self-contained papers addressing these and related problems. The first two papers extend the repertoire of tractable input sequences for most of the known DE modulator architectures. The third paper applies the results from the first two papers to develop a scalable architecture for parallel [...] Modulation.\r\n\r\nThe first paper concentrates on the first-order [...] modulator and develops rigorous results for a large class of input sequences. Under the assumptions that some circuit noise is present and that the input sequence does not cause overload, a simple autocorrelation expression is developed that is only locally dependent upon the input sequence. Ergodic properties are derived and various examples are presented.\r\n\r\nIn the second paper, a rigorous analysis of the granular quantization noise in a general class of DE modulators is developed. Again under the assumption that some circuit noise is present, the joint statistics of the granular quantization noise sequences are determined and the sequences are shown to be correlation ergodic. The exact results developed for the granular quantization noise are shown to approximately hold for the overall quantization noise if the quantizers in the [...] modulator overload occasionally.\r\n\r\nThe third paper develops a scalable A/D converter architecture consisting of multiple [...] modulators. By combining [...] modulator based A/D converters, each with an oversampling ratio of N, an effective oversampling ratio of approximately NM is achieved with only an M-fold increase in the quantization noise power. In particular, the special case of N = 1 allows for full-rate analog to digital conversion. Unlike most other approaches to trading modulator complexity for accuracy, the system retains the robustness of the individual [...] modulators to circuit imperfections.\r\n" }, { "name": "Grant, Stanley Clement Baugh", "degree": "PhD", "year": "1992", "title": "Detection and partitioning of bacteriophage in fluid/solid systems: application to the ecology and mobility of viruses in the environment", "advisor": "Lidstrom, Mary E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062007-095236", "creators": [ { "name": { "family": "Grant", "given": "Stanley Clement Baugh" }, "id": "Grant-Stanley-Clement-Baugh", "display_name": "Grant, Stanley Clement Baugh" } ], "advisors": [ { "name": { "family": "Lidstrom", "given": "Mary E." }, "id": "Lidstrom-M-E", "role": "advisor", "display_name": "Lidstrom, Mary E." } ], "committee": [ { "name": { "family": "Lidstrom", "given": "Mary E." }, "id": "Lidstrom-M-E", "role": "chair", "display_name": "Lidstrom, Mary E." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Stolzenbach", "given": "Keith D." }, "id": "Stolzenbach-K-D", "role": "member", "display_name": "Stolzenbach, Keith D." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." } ], "option_major": [ "envreng" ], "doi": "10.7907/91MJ-XK16", "abstract": "Viruses are ubiquitous in natural environments where they can exist as natural inhabitants or as contaminants from the disposal of human and animal wastes. Studies of viruses in nature are hampered because currently available methods for detection are not ideally suited to environmental applications. In the first part of this thesis, a modified hybridization assay is presented which employs DNase protection and slot blot methods to measure quantitatively the concentration of soluble and bacteriophage-encapsulated DNA in fluid samples. The potential use of this assay for estimating virus viability was tested with a model system consisting of inactivating bacteriophage lambda particles. These experiments show that the new hybridization assay provides upper-limit estimates of bacteriophage viability when inactivation results in the release of DNA.\r\n\r\nThe mobility and ecology of viruses in natural environments is strongly influenced by the adsorption of virus particles to solid surfaces. In the second part of this thesis, a kinetic theory for virus adsorption and inactivation in batch experiments is presented. Based on the results of this theory, a new experimental approach is proposed for studying the effects of solid surfaces on virus partitioning and survival over long time scales.\r\n\r\nIn the third part of the thesis, this new experimental approach was used to investigate the interactions between bacteriophage lambda particles and Ottawa sand over the course of days. Virus/surface interactions on these time scales were strongly dependent on solution pH and electrolyte composition. Sand stabilized the virus at high pH (10) and reduced fluid-phase virus infectivity at intermediate to low pH (5 and 7). The observed reduction in virus infectivity at pH 7 was attributed to virus adsorption to the sand surface, based on data from elution experiments. Viruses adsorbed to the sand at pH 7 desorbed when the sand was resuspended in nutrient broth, but not when the sand was resuspended in a virus-free pH 7 buffer. When model simulations were compared to elution data, virus adsorption did not follow the predictions of quasi-equilibrium adsorption models. On the basis of these results, several alternative kinetic mechanisms for virus adsorption are proposed." }, { "name": "Guinzburg, Adiel", "degree": "PhD", "year": "1992", "title": "Rotordynamic forces generated by discharge-to-suction leakage flows in centrifugal pumps", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-091813", "creators": [ { "name": { "family": "Guinzburg", "given": "Adiel" }, "id": "Guinzburg-A", "display_name": "Guinzburg, Adiel" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "member", "display_name": "Wiggins, Stephen R." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "mecheng" ], "doi": "10.7907/dv7v-hy83", "abstract": "In recent years, increasing attention has been given to fluid-structure interaction problems in turbomachines. The present research focuses on just one such fluid-structure interaction problem, namely the role played by fluid forces in determining the rotordynamic stability and characteristics of a centrifugal pump. While the geometry of the impeller shroud/pump casing annulus varies considerably, previous studies indicate that the contributions from the leakage flow can be of the same order as the contributions from the nonuniform pressure acting on the impeller discharge. Thus, the emphasis of this study is to investigate the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating impeller and the stationary pump casing. An experiment was designed to measure the rotordynamic shroud forces due to simulated leakage flows for different parameters such as flow rate, shroud clearance, face-seal clearance and eccentricity. The data demonstrates substantial rotordynamic effects and a destabilizing tangential force for small positive whirl ratios; this force decreased with increasing flow rate. The rotordynamic forces appear to be inversely proportional to the clearance and change significantly with the flow rate. Two sets of data taken at different eccentricities yielded quite similar nondimensional rotordynamic forces indicating that the experiments lie within the linear regime of eccentricity.\n\nLike earlier measurements of the total fluid induced rotordynamic forces on impellers [Chamieh et al. (1985), Jery et al. (1985), Adkins et al. (1988)], the forces measured in these experiments scaled with the square of the rotor speed. The functional dependence on the ratio of whirl frequency to rotating frequency (termed the whirl ratio) is very similar to that measured in experiments and similar to that predicted by the theoretical work of Childs. Childs' bulk flow model yielded some unusual results including peaks in the rotordynamic forces at particular positive whirl ratios, a phenomenon which Childs tentatively described as a \"resonance\" of the leakage flow. This unexpected phenomenon developed at small positive whirl ratios when the inlet swirl velocity ratio exceeded about 0.5. Childs points out that a typical swirl velocity ratio at inlet (pump discharge) would be about 0.5 and may not therefore be large enough for the resonance to be manifest. To explore whether this effect occurs, an inlet guide vane was constructed which introduced a known amount of swirl into the flow upstream of the leakage flow inlet. A detailed comparison of model predictions with the present experimental program is presented. The experimental results showed no evidence of the \"resonances\", even at much larger swirl inlet velocities than explored by Childs.\n" }, { "name": "Guo, Yong", "degree": "PhD", "year": "1992", "title": "Millimeter-wave integrated-circuit horn-antenna imaging arrays", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07242007-092924", "creators": [ { "name": { "family": "Guo", "given": "Yong" }, "id": "Guo-Y", "display_name": "Guo, Yong" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ewa6-ey43", "abstract": "A new millimeter-wave, integrated-circuit, back-to-back, horn-antennamixer array is presented. The configuration of the array is one called \"displaced back-to-back horn-antenna array,\" which consists of a set of forward- and backward-looking horns made with a set of silicon wafers. The front side is used to receive the incoming signal, and the back side is used to feed the local oscillator. IF is led out from the side of the array. Pyramidal-shaped horns in silicon bounded by (111) crystal planes were formed by anisotropic etching of the silicon wafers. The power received by the horns is picked up by antenna probes suspended on thin silicon-oxynitride membranes inside the horns. The array is fully two-dimensional, and the horns are made simultaneously by integrated-circuit processing techniques. Aperture efficiency of the horn-antenna array has been improved up to 72 %, and system coupling efficiency is 36 %. In the efficiency measurements, a new thin-film, power-density meter is developed for measuring the asolute power densities. The main applications of the array include imaging, remote sensing and plasma diagnostics.\n" }, { "name": "Guthart, Gary Steven", "degree": "PhD", "year": "1992", "title": "On the Existence and Stability of Standing Solitary Waves in Faraday Resonance", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182011-080621226", "creators": [ { "name": { "family": "Guthart", "given": "Gary Steven" }, "id": "Guthart-Gary-Steven", "display_name": "Guthart, Gary Steven" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "eng" ], "doi": "10.7907/fp2g-ds59", "abstract": "A rectangular tank of high-aspect ratio contains a liquid of moderate depth. The tank is subjected to vertical, sinusoidal oscillations. When the frequency of forcing is nearly twice the first natural frequency of the short side of the tank, waves are observed on the free surface of the liquid that slosh across the tank at a frequency equal to one half of the forcing frequency. These sloshing waves are modulated by a slowly varying envelope along the length of the tank. The envelope of the sloshing wave possesses two solitary-wave solutions, the standing soliton corresponding to a hyperbolic-secant solution and the standing kink wave corresponding to a hyperbolic-tangent solution. The depth and width of the tank determine which soliton is present. In the present work, we derive an analytical model for the envelope solitons by direct perturbation of the governing equations. This derivation is an extension of a previous perturbation approach to include forcing and dissipation. The envelope equation is the parametrically forced, damped, nonlinear Schrodinger equation. Solutions of the envelope equations are found that represent the solitary waves, and regions of formal existence are discussed. Next, we investigate the stability of these solitary-wave solutions. A linear-stability analysis is constructed for both the kink soliton and the standing soliton. In both cases, the linear-stability analysis leads to a fourth-order, nonself-adjoint, singular eigenvalue problem. For the hyperbolic-secant envelope, we find eigenvalues that correspond to the continuous and discrete spectrum of the linear operator. The dependence of the continuous-spectrum eigenvalues on the system parameters is found explicitly. By using local perturbations about known solutions and numerically continuing the branches, we find the bound-mode eigenvalues. For the kink soliton, continuous-spectrum branches are also found, and their dependence on the system parameters is determined. Bound-mode branches are found as well. In the case of the kink soliton, we extend the linear analysis by providing a nonlinear proof of stability when dissipation is neglected. We compute numerical solutions of the nonlinear Schrodinger equation directly and compare the results to the previous local analysis to verify the predicted behavior. Lastly, laboratory experiments were performed, examining the stability of the solitary waves, and comparisons are made with the foregoing work. In general, the agreement between the local analysis, the numerical simulations and the experiments is good. However, experiments and direct simulations show the existence of periodic solutions of the envelope equation when bound-mode instabilities are present." }, { "name": "Hazewindus, Pieter Johannes", "degree": "PhD", "year": "1992", "title": "Testing delay-insensitive circuits", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202007-132706", "creators": [ { "name": { "family": "Hazewindus", "given": "Pieter Johannes" }, "id": "Hazewindus-P-J", "display_name": "Hazewindus, Pieter Johannes" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "member", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "compsci" ], "doi": "10.7907/0d7v-9d09", "abstract": "A method is developed to test delay-insensitive circuits, using the single stuck-at fault model. These circuits are synthesized from a high-level specification. Since the circuits are hazard-free by construction, there is no test for hazards in the circuit. Most faults cause the circuit to halt during test, since they cause an acknowledgement not to occur when it should. There are stuck-at faults that do not cause the circuit to halt under any condition. These are stimulating faults; they cause a premature firing of a production rule. For such a stimulating fault to be testable, the premature firing has to be propagated to a primary output. If this is not guaranteed to occur, then one or more test points have to be added to the circuit. Any stuck-at fault is testable, with the possible addition of test points. For combinational delay-insensitive circuits, finding test vectors is reduced to the same problem as for synchronous combinational logic. For sequential circuits, the synthesis method is used to find a test for each fault efficiently, to find the location of the test points, and to find a test that detects all faults in a circuit.\r\n\r\nThe number of test points needed to fully test the circuit is very low, and the size of the additional testing circuitry is small. A test derived with a simple transformation of the handshaking expansion yields high fault coverage. Adding tests for the remaining faults results in a small complete test for the circuit." }, { "name": "Ji, Chuanyi", "degree": "PhD", "year": "1992", "title": "Generalization capability of neural networks", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202007-143215", "creators": [ { "name": { "family": "Ji", "given": "Chuanyi" }, "id": "Ji-Chuanyi", "display_name": "Ji, Chuanyi" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/HR3F-0410", "abstract": "The generalization capability of feedforward multilayer neural networks is investigated from two aspects: the theoretical aspect and the algorithmic aspect.
\r\n\r\nIn the theoretical part, a general relation is derived between the so-called VC-dimension and the statistical lower epsilon-capacity, and then applied to two cases. First, as a general constructive approach, it is used to evaluate a lower bound of the VC-dimension of two layer networks with binary weights and integer thresholds. Second, how the sample complexity may vary with respect to distributions is investigated through analyzing a particular network which separates two binary clusters. Bounds for the capacity of two layer networks with binary weights and integer thresholds are also obtained.
\r\n\r\nIn the algorithmic part, a network reduction algorithm is developed to study generalization in learning analog mappings. It is applied to control a two-link manipulator to draw characters. The network addition-deletion algorithm is described to find an appropriate network structure during learning. It is used to study the effect of sizes of networks on generalization, and applied to various classification problems including hand written digits recognition.
" }, { "name": "Kaper, Tasso J.", "degree": "PhD", "year": "1992", "title": "Part I. On the structure in separatrix-swept regions of slowly-modulated Hamiltonian systems. Part II. On the quantification of mixing in chaotic Stokes' flows : the eccentric journal bearing", "advisor": "Wiggins, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062007-100540", "creators": [ { "name": { "family": "Kaper", "given": "Tasso J." }, "id": "Kaper-T-J", "display_name": "Kaper, Tasso J." } ], "advisors": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "advisor", "display_name": "Wiggins, Stephen R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/MDD9-3Z11", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPART I:\r\n\r\nIn this work, we establish the structure of the large [...]-sized separatrix-swept regions in Hamiltonian systems which depend on a slow-varying parameter z: H = H(p,q,z = [...]), where 0 < [...] 1. These regions are complementary to those in which the theory of adiabatic invariance and Arnold's extension of the KAM Theorem to adiabatic systems apply. We prove the following theorem about the structure of lobes, which, being regions of phase space bounded by segments of intersecting stable and unstable manifolds terminating on principal homoclinic points, are the fundamental building blocks of homoclinic tangles. Theorem: The area of a lobe in (1.1) is: A = [...], where Z0 and Z1 are two adjacent simple zeroes of MA(z), the adiabatic Melnikov function of the system. We also derive a corollary: The area of a lobe in these systems is given to leading order by the difference between the areas enclosed by two sequential extremal instantaneous separatrices, [...] and [...]. The remaining terms are [...]. Theorem 1 and the corollary establish several important results: First, the area occupied by the homoclinic tangles formed by the intersection of the stable and unstable manifolds is [...] to leading order. Second, Theorem 1 implies that the flux between regions separated by instantaneous separatrices is [...] asymptotically, see Part II for an application. Third, for systems in which H depends periodically or quasiperiodically on z, Theorem 1 states that the region in which orbits evolve chaotically is [...] in the limit of [...]. This result stands in marked contrast to the known examples of chaotic systems in which the \"stochastic\" regions are either of [...] or [...] and vanish as [...]. Finally, since islands must lie outside of the lobes, Theorem 1 shows that the phase space area in which islands must lie vanishes with [...] as [...]. We remark that we lower the upper bounds on island size presented in Elskens and Escande [1991] using asymptotic expansions of the exact resonance-zone area formula of MacKay and Meiss [1986]. We also derive an exact lobe area formula for general time-dependent Hamiltonian systems, which eliminates the need for the existence of a recurrent p - q section in the extended phase space assumed in the previous work. A direct measurement of the type used on weakly-perturbed Hamiltonian systems is not possible in adiabatic systems since the pieces of stable and unstable manifold defining the boundary of the lobe cannot be expressed as graphs over the unperturbed separatrix. Therefore, the shape-independence of this exact formula is needed. We illustrate our results on the adiabatic pendulum: H = [...] cos q and on a model due to Hastings and McLeod. Finally, for z-periodic H, we show for the first time in an example that a Smale horseshoe map can be created in one iteration of the Poincare map.\r\n\r\nPART II:\r\n\r\nWe study the transport of tracer dye in a low Reynolds number flow in the two-dimensional eccentric journal bearing. Modulation of the angular velocities of the cylinders continuously, slowly, and periodically in time causes the integrable steady-state flow to become nonintegrable. In stark contrast to the flows usually studied with dynamical systems, however, these slowly-varying systems are singular-perturbation problems in which the nonintegrability is due to the slow [...] modulation of the position of the saddle stagnation point and the two streamlines stagnating on it. We establish an analytical technique to determine the location and size of the region in which mixing occurs. This technique gives us explicit control over the mixing process. We also develop a transport theory based on the lobes formed by the segments of stable and unstable manifolds of the fixed points of the Poincare map, which are responsible for the transport of tracer in the mixing zone. In particular, we show that the radically different shape of these lobes, as compared to the shape of the lobes studied in the usual flows, readily makes them identifiable as the mechanism by which the modulation causes the patches of tracer to develop into elaborately striated and folded lamellar structures. When the modulation frequency is small we apply the tools developed in Part I to analytically predict several important quantities associated with the lobes and transport theory for the first time. From the measurement of these quantities, we determine the combination of the flow parameters with which one achieves the most efficient mixing possible. Furthermore, we use an extension of the KAM theory to explain the highly-regular appearance of islands in quasi-steady Stokes' flows for the first time. Finally, we we show that diffusion enhances stretching, discuss the robustness of our model by analyzing the influence of the inertial terms, and compare our results to those obtained experimentally using so-called blinking protocols." }, { "name": "Karasawa, Naoki", "degree": "PhD", "year": "1992", "title": "Simulations of polymer crystals : new methods and applications", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062007-104316", "creators": [ { "name": { "family": "Karasawa", "given": "Naoki" }, "id": "Karasawa-N", "display_name": "Karasawa, Naoki" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/mjj7-qt65", "abstract": "The most important applications for simulations of polymers involve composites or blends with extensive, amorphous regions. To simulate such materials we use a very large unit cell, so that the polymer can have random behavior within the cell, but periodic boundary conditions to keep the problem tractable. The major difficulties in carrying out such calculations are: (a) accurate calculation of the lattice sums for the nonbond interactions (electrostatic and dispersion), which converge very slowly; (b) computational time for systems large enough to simulate real materials (1 million atoms); (c) procedures for calculating the properties of interest (energy, force, stress, curvature, phonons, elastic constants, dielectric constants, and piezoelectric constants).\n\nWe describe herein significant progress on each of these three issues. Concerning (a) we developed the Accuracy-Bounded Convergence Acceleration (ABCA) procedure, which finds the optimal Ewald parameters to achieve a given accuracy in minimum computation time. Concerning (b) the critical bottleneck in atomic-level simulations of the structure and dynamics of very large molecules is the calculation of N2 nonbond interactions. Here a major advance is the development of the Cell Multipole Method (CMM), which involves no steps scaling a higher order than N. CMM treats the interactions in terms of a far field (which is evaluated in terms of multipole expansions) and a near field (which involves only approximately 50 near neighbors). The far field can be evaluated infrequently so that the full calculation for a million-atom system involves only the effort of calculation to interactions of each atom with about 50 near neighbors. This leads to a dramatic increase in efficiency, and systematic calculations have been carried out in realistic polymers with up to 1 million atoms (on a workstation). The CMM is 1500 times faster than the exact method for 1 million atoms. For periodic systems the cell multipole method is extended, using a reduced set that reproduces low-order multipoles of an original unit cell (CMMX). For a polymer with 1 million atoms, the C calculation is 1000 times faster than either the Ewald or Minimum Image Methods (the standards currently in use).\n\nA major issue in carrying out simulations for materials is the force field. We have developed general procedures for obtaining empirical force fields and have applied this to systematic development of force-field parameters for polyethylene and poly (vinylidene fluoride) crystals. Van der Waals parameters for carbon and hydrogen are empirically determined from experimental lattice constants, elastic constants and lattice frequencies utilizing Ewald/ABCA procedures. Various mechanical properties are calculated and compared with experimental data. For polyethylene, valence terms are determined by a biased- Hessian method for n-butane, and yield stress and surface energy are obtained from calculations of stress-strain relations in directions perpendicular to polymer chains. For poly (vinylidene fluoride) crystals, a shell model is introduced to include atomic polarizabilities into the simulation. Properties of five different forms (including a new form suggested by Lovinger) are computed using the same parameter sets. We find that using the shell model leads to significant improvement in the agreement between calculated and experimental piezoelectric and dielectric constants. In addition we find that the new form (not yet observed form) is mechanically stable with comparable energy with other forms." }, { "name": "Kay, Timothy L.", "degree": "PhD", "year": "1992", "title": "From geometry to texture : experiments towards realism in computer graphics", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062007-110815", "creators": [ { "name": { "family": "Kay", "given": "Timothy L." }, "id": "Kay-T-L", "display_name": "Kay, Timothy L." } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Blinn", "given": "Jim" }, "id": "Blinn-J", "role": "member", "display_name": "Blinn, Jim" }, { "name": { "family": "Osher", "given": "Stanley" }, "id": "Osher-S", "role": "member", "display_name": "Osher, Stanley" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "compsci" ], "doi": "10.7907/XCAM-R775", "abstract": "This thesis presents a new computer graphics texture element called a texel as well as an associated rendering algorithm, which together produce an appearance never before achieved in computer graphics. Unlike previous modeling primitives, which are limited to solid, crisp appearances (e.g., metal, plastics, and glass), texels have a soft, fuzzy appearance, and thus can be used to create models and images of soft objects.\n\nThis thesis presents a solution to the problem of creating fur. As an example, a Teddy bear is modeled and rendered. As part of the process, a new BDRF is developed for texels which can produce back lighting effects. A model deformation technique using trilinear solids is developed.\n\nThis thesis then addresses a more complex example, that of creating a microscopic swatch of cloth by computationally \"weaving\" threads. The process of converting the resulting geometric model into texels is presented. The swatch of cloth is then replicated to cover the infinite plane seamlessly.\n\nA new phenomenon, the texture threshold effect is presented. It is the point at which geometry turns into texture. When viewed from beyond a certain distance threshold, the appearance of a microscopic model will converge to a macroscopic model. The position of the texture threshold is calculated. The infinite cloth model is then rendered from beyond the texture threshold, and its cloth BDRF is extracted computationally. This BDRF is then used to render a cloth-covered car seat.\n\nThe BDRF extraction process involves sampling an image which contains spectral energy above the Nyquist limit. Hence, the use of point sampling in computer graphics is analyzed to verify that aliasing energy is controlled. The process of jittered subsampling is analyzed, correcting and completing previous attempts. The results confirm that it is possible to render complex computer graphics imagery avoiding artifacts from aliased energy.\n" }, { "name": "Kotronarou, Anastassia", "degree": "PhD", "year": "1992", "title": "Ultrasonic irradiation of chemical compounds in aqueous solutions", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062007-152346", "creators": [ { "name": { "family": "Kotronarou", "given": "Anastassia" }, "id": "Kotronarou-A", "display_name": "Kotronarou, Anastassia" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Lidstrom", "given": "Mary E." }, "id": "Lidstrom-M-E", "role": "member", "display_name": "Lidstrom, Mary E." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." } ], "option_major": [ "envreng" ], "doi": "10.7907/RR28-5R10", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe ultrasonic irradiation of para-nitrophenol, S(-II), and parathion is studied in aqueous solutions at 20 kHz and [...] 75 [...]. Para-nitrophenol was degraded primarily by denitration and secondarily by [...] radical attack to yield [...], [...], benzoquinone, hydroquinone, 4-nitrocatechol, formate and oxalate. These reaction products and the kinetic observations are consistent with a model involving high-temperature reactions of p-nitrophenol in the interfacial region of cavitation bubbles. The average effective temperature of the interfacial region surrounding the cavitation bubbles was estimated to be T [...] 800 K.\r\n\r\nUltrasonic irradiation of S(-II) is studied in aqueous solutions over the pH range 7 - 12. The reaction of HS- with [...] is the principal pathway for the oxidation of S(-II) at pH [...] 10; the oxidation products are [...], [...], and [...]. Upon prolonged sonication, [...] is the only observed product. At pH [...] 8.5, thermal decomposition of H2S within or near collapsing cavitation bubbles becomes the important pathway and elemental sulfur is found as an additional product of the sonolysis of S(-II). The sonolytic oxidation of H2S at pH [...] 10 was successfully modeled with an aqueous-phase free-radical chemistry mechanism and assuming continuous and uniform [...] input into solution from the imploding cavitation bubbles.\r\n\r\nParathion degradation occurred primarily by enhanced hydrolysis and secondarily by direct [...] radical attack.\r\n\r\nThe effect of various physical and chemical parameters on sonolytic yields is examined. The observed effects are in qualitative agreement with the sonolysis mechanisms proposed for the chemicals of interest and the existing hydrodynamic theories of acoustic cavitation.\r\n\r\nThe formation of iodine upon ultrasonic irradiation of potassium iodide solutions and the sonolysis of S(-II) are used as probes to compare the sonochemical efficiency of different experimental set-ups.\r\n\r\nThis work elucidates the mechanisms of the ultrasonic decomposition of typical organic and inorganic pollutants. It is shown that ultrasound has the potential to become a viable alternative for the destruction of chemical contaminants in water and wastewater. The current limitation of sonolysis is its low energy utilization efficiency, but there is room for improvement by optimizing reactor design and physical/chemical operation conditions. This work offers some recommendations and insight in that respect." }, { "name": "Kumar, Sanjay", "degree": "PhD", "year": "1992", "title": "Some theoretical and experimental studies of cavitation noise", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01052006-142036", "creators": [ { "name": { "family": "Kumar", "given": "Sanjay" }, "id": "Kumar-S", "display_name": "Kumar, Sanjay" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/zr24-gn41", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis work investigates two aspects of cavitation noise. The first part models some nonlinear interactive effects in bubbly mixtures generated in cavitating flows, and the second part focuses on an acoustical study of the collapse process of a single bubble in travelling bubble cavitation.\n\nThe nonlinear interactive effects in a bubbly cloud have been studied by investigating the frequency response of a bubble layer bounded by a wall oscillating normal to itself. First, a Fourier analysis of the Rayleigh-Plesset equation is used to obtain an approximate solution for the nonlinear response of a single bubble in an infinite fluid. This is used in an approximate solution of the oscillating wall problem for bubble layers of finite and infinite thickness in which all the bubbles have the same equilibrium size and a semi-infinite layer containing bubbles with a distribution of size. Particular attention is paid to the generation of harmonics that is due to nonlinear effects.\n\nThe finite thickness of the layer results in characteristic natural frequencies of the bubble mixture, all of which are less than bubble natural frequency. These characteristic natural frequencies are functions of the void fraction and the ratio of layer thickness to the bubble radius. In general, the lowest characteristic natural frequency is found to dominate the response. The amplitude of the response increases as the excitation frequency, [...], is reduced from [...] to around 0.5[...] and decreases with further decrease in excitation frequency. The characteristic frequencies disappear in the limit of a semi-infinite layer. The bubble size oscillation in a semi-infinite layer is maximum at the excitation frequency of [...]. The pressure oscillation is minimum at the excitation frequency of [...] with equally significant first and second harmonic components.\n\nFor sub-resonant and trans-resonant excitation [...], the response consists of standing wave patterns with an amplitude that decays slowly with distance from the oscillating wall. This decay is different from that found in spherical bubble clouds (d'Agostino and Brennen 1988a) because of the geometric effects of propagating disturbance. However, for super-resonant excitation the amplitude of oscillation rapidly decays with distance from the source of excitation.\n\nA phenomenon termed harmonic cascading is seen to take place when the bubble layer consists of bubbles with a distribution of bubble sizes. In this phenomenon a large response is observed at twice the excitation frequency when the layer contains bubbles with a natural frequency equal to twice the excitation frequency. The effect is manifest as an increase in the ratio of the second harmonic to the first harmonic as the number of bubbles with small radii gets larger relative to the number of bubbles with large radii. Also, a similar change in the bubble size distribution, while holding the equilibrium void fraction constant, results in a weaker response. This reduction in amplitude of pressure oscillation may be due to the increased number of bubbles. Larger void fraction and smaller amplitudes of wall oscillation are observed to produce a weaker response. Reduced effects of viscocity and surface tension that are due to changes in ambient conditions result in a larger response.\n\nIn the second part the collapse processes of single bubbles in the travelling bubble cavitation around two axisymmetric headforms have been studied acoustically to understand the collapse process of a cavitation bubble and to characterize the sound emission in travelling bubble cavitation. The bubbles were observed to collapse and then sometimes to rebound and collapse again, resulting in one or two pulses in the acoustic signal from a cavitation event. It was observed that each of the pulses could contain more than one peak. This phenomenon is called multipeaking and is clearly distinct from rebounding. The occurrence of rebounding and multipeaking and their effects on some characteristic measures of the acoustic signal such as power spectra are examined in this chapter. Two particular head-forms (I.T.T.C. headform and Schiebe headform) with distinct flow characteristics were investigated.\n\nBoth rebounding and multipeaking increased with reduction in cavitation number in case of the I.T.T.C. headform. However, multipeaking decreased and rebounding increased with the reduction in cavitation number for the Schiebe headform. Smaller flow velocity, smaller cavitation number and multipeaking delay the rebound. The peak amplitude of the sound emitted from the first collapse was seen to be twice as large as the peak amplitude of sound from the second collapse suggesting a repeatable process of bubble fission during the collapse process. The multipeaking and rebounding increased the characteristic measures of the acoustic signal. These characteristic measures have larger magnitudes for smaller flow velocity. Also, the values of these characteristics are larger for the I.T.T.C. headform than for the Schiebe headform.\n\nTheoretical calculations based on the Rayleigh-Plesset equation were seen to predict correctly the order of magnitude for most of these characteristic measures. However, the distribution of spectral energy is not properly predicted by the model based on the Rayleigh-Plesset equation; bubble fission during the collapse is thought to account for this discrepancy. Reduction in the cavitation number and multipeaking are observed to decrease the fraction of spectral energy contained in the high frequency range (30 kHz-80kHz)." }, { "name": "Lee, Ho-Hoon", "degree": "PhD", "year": "1992", "title": "Robust adaptive control of manipulators with application to joint flexibility", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08072007-073507", "creators": [ { "name": { "family": "Lee", "given": "Ho-Hoon" }, "id": "Lee-H-H", "display_name": "Lee, Ho-Hoon" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ks5z-8e20", "abstract": "This thesis discusses the model-based adaptive trajectory control of commercial manipulators whose dynamics are well known with uncertainties confined to parameters.\r\n\r\nThis thesis emphasizes the importance of the transient behavior as well as robust stability of a system and takes it into account in the design of adaptive control laws. The basic idea is to search for compensators in the direction of minimizing a quadratic performance index, and then analyze the stability and robustness of the selected compensators in the presence of bounded disturbances, sensor noises, and unmodelled dynamics. With this idea, centralized and decentralized adaptive control schemes are proposed for rigid-joint manipulators. Stability bounds for disturbances, control and adaptation gains, and desired trajectories and their time-derivatives are derived for the proposed schemes. These bounds are sufficient conditions for robust stability of the proposed schemes in the presence of unmodelled dynamics such as feedback delays in the digital control systems and the coupled dynamics in the decentralized scheme.\r\n\r\nA flexibility compensator is designed to treat the problem of joint flexibility. With the flexibility compensator, a manipulator having flexible joints is transformed to that having rigid joints with high-frequency dynamics of joint couplings representing unmodelled dynamics. In this way, control of flexible-joint manipulators is converted to that of the corresponding rigid-joint manipulators. Accordingly, the robust adaptive control schemes proposed for rigid-joint manipulators are applied. Then, through stability analysis, stability bounds for disturbances, control and adaptation gains, and desired trajectories and their time-derivatives are derived for the scheme with the flexibility compensator, in the presence of the unmodelled dynamics. Under the constraint of these bounds, the proposed adaptive scheme is not only almost independent of the gear-reduction ratios, flexibilities of joint couplings, and characteristics of actuators, but also free from the requirements of measuring angular accelerations and jerks of links." }, { "name": "Li, Xiaoming", "degree": "PhD", "year": "1992", "title": "Experimental Studies of Char Oxidation and Fume Formation from Pyrite", "advisor": "Flagan, Richard C.; Gavalas, George R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08072007-075230", "creators": [ { "name": { "family": "Li", "given": "Xiaoming" }, "id": "Li-Xiaoming", "display_name": "Li, Xiaoming" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "co-advisor", "display_name": "Gavalas, George R." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/3kmh-j058", "abstract": "Pulverized coal combustion is nowadays the most commonly used technology for power generation from coal. The detailed understanding of the coal combustion process is of fundamental importance to the design of more economic and efficient combustion devices and to the control of gaseous and particulate pollutant emission. This thesis presents an experimental study of (a) thermally induced changes of char structure and their effect on its combustion reactivity and (b) the mechanism of ash formation under conditions pertinent to pulverized coal combustion.
\r\n\r\nPyrolyzed or partially oxidized coal char was generated in a drop-tube furnace from a Pittsburgh seam hvA bituminous coal (PSOC 1451). The char was characterized by elemental analysis and N2 adsorption for specific surface area and pore volume distribution to better understand the influence of oxygen and residence time on the char structure. The reactivities of chars produced under different oxygen contents and residence times were examined by oxidation in a thermogravimetric analyzer. The conversion of the combustible material at high temperature was measured using ash as a tracer.
\r\n\r\nThe pyrolysis and combustion of pyrite particles were studied with an electrodynamic balance and a drop-tube reactor. Two types of pyrite were examined, a natural pyrite (85% purity) and a synthetic pyrite (99.9% purity). Fume particles formed from individual pyrite particles were observed directly in electrodynamic balance experiments. The drop tube reactor experiments allow measurements of the fume particle concentration and size distribution. The nature of the fume was characterized using a Transmission Electron Microscope equipped with energy dispersive X-ray analysis. Physical mechanisms that might lead to the release of iron rich fragments were investigated.
" }, { "name": "Lin, Steven H.", "degree": "PhD", "year": "1992", "title": "GaAs optoelectronic integrated circuits for optical neural network applications", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-08072007-133843", "creators": [ { "name": { "family": "Lin", "given": "Steven H." }, "id": "Lin-S-H", "display_name": "Lin, Steven H." } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/tqm4-en29", "abstract": "Optoelectronic integrated circuits (OEIC's) have emerged as a viable method in the implementation of optical neurons required for a neural network. This is due to the increased capability in both the material and the device engineering in GaAs technology, which has proliferated incredibly fast during the last decade. In this thesis, two different approaches to monolithically integrate various electronic and optical devices are explored for the implementation of optical neurons. The first approach utilizes the technology from double heterojunction bipolar transistor for its potentially high current gain and its structural compatibility with optical devices. In achieving the current gain required for optical neurons, modeling of the base leakage current, effect of surface passivation and diffusion characteristics is performed for Zn-diffused bipolar transistors. The second approach employs metal semiconductor field-effect transistors as the driver for the optical devices. It is found that, by properly designing the circuit, high optical gain, low electrical power dissipation and low optical switching energy thresholding devices can be accomplished in this approach with large input-output isolation. Such performance is required if large arrays of optoelectronic neurons are to be inserted into a neural network to perform tasks that make neural computation a unique approach in solving a certain class of problems. In this thesis, an optical gain of 80 is demonstrated along with an electrical power dissipation of 1.6 mW and an optical switching energy of 10 pJ. These results generate high promises and optimism for the realization of a physical neural computer in the near future." }, { "name": "Lu, Lingyun", "degree": "PhD", "year": "1992", "title": "On the development and application of a modified boundary element method for the analysis of three-dimensional elastostatic problems in thick plates", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08072007-131209", "creators": [ { "name": { "family": "Lu", "given": "Lingyun" }, "id": "Lu-L", "display_name": "Lu, Lingyun" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/tkxp-f839", "abstract": "A modified three-dimensional Boundary Element Method (BEM) is developed. This method is specially tailored towards applications in three-dimensional elasticity, involving regions containing two parallel planar surfaces. Typical structures are the three-dimensional plate structures. The formulation makes use of the three-dimensional fundamental solution of a concentrated load applied in an infinite three-dimensional plate of uniform finite thickness (obtained by Benitez and Rosakis in 1985). The most attractive feature of this modified BEM is that, for the class of problems involving structures described above subjected to traction-free boundary conditions on the planar surfaces, discretization is only required on the lateral surfaces of the plate and the surfaces of the cavities, holes, and cracks in the plate. No discretization is needed on the planar surfaces of the plate. In this initial study, three problems involving a pressurized hole in an infinite three-dimensional plate are analyzed. The shapes of the holes include a circular hole and two elliptical holes with the aspect ratios of 4 and 10, respectively. In all the cases, the accuracy of the modified BEM is established by direct comparison of its results with those of finite element calculations. The results of the modified BEM are also compared with the plane-stress and plane-strain approximations of the problems under consideration. This comparison make it possible to access the important three-dimensional effects near the surface of the elliptical hole." }, { "name": "Lui, Shiu-Hong", "degree": "PhD", "year": "1992", "title": "Part I: Multiple bifurcations. Part II: Parallel homotopy method for the real nonsymmetric eigenvalue problem", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechETD:etd-06152005-084230", "creators": [ { "name": { "family": "Lui", "given": "Shiu-Hong" }, "id": "Lui-S", "display_name": "Lui, Shiu-Hong" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/b79y-vb23", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nPART I\n\nConsider an analytic operator equation [...] = 0 where [...] is a real parameter. Suppose 0 is a \"simple\" eigenvalue of the Frechet derivative [...] at [...]. We give a hierarchy of conditions which completely determine the solution structure of the operator equation. It will be shown that multiple bifurcation as well as simple bifurcation can occur. This extends the standard bifurcation theory from a \"simple\" eigenvalue in which only one branch bifurcates. When 0 is a multiple eigenvalue, we give some sufficient conditions for multiple bifurcations with a lower bound on the multiplicity of the bifurcation. This theory is applied to some semilinear elliptic partial differential equations on a cylinder with a constant cross-section.\n\nPART II\n\nWe present a homotopy method to compute the eigenvectors and eigenvalues, i.e., the eigenpairs of a given real matrix [...]. From the eigenpairs of some real matrix [...], we follow the eigenpairs of [...] at successive times from t = 0 to t = 1 using continuation. At t = 1, we have the eigenpairs of the desired matrix [...]. The following phenomena are present for a general nonsymmetric matrix:\n\n- complex eigenpairs\n\n- ill-conditioned problems due to non-orthogonal eigenvectors\n\n- bifurcation (i.e., crossing of eigenpaths)\n\nThese can present computational difficulties if not handled properly. Since each eigenpair can be followed independently, this algorithm is ideal for concurrent computers. We will see that the homotopy method is extremely slow for full matrices but has the potential to compete with other algorithms for sparse matrices as well as matrices with defective eigenvalues.\n" }, { "name": "Lusk, Mark T.", "degree": "PhD", "year": "1992", "title": "Martensitic phase transitions with surface effects", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11052004-161432", "creators": [ { "name": { "family": "Lusk", "given": "Mark T." }, "id": "Lusk-M-T", "display_name": "Lusk, Mark T." } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/NBES-9M76", "abstract": "Continuum treatments of martensitic phase transformations are capable of accounting for a variety of important surface effects attributable to the spatially localized interaction of coexisting material phases. Such phenomena are thought to play a critical role in determining the size, shape, and stability of nucleated embryos as well as to affect the conditions under which nucleation events occur. These issues are examined within a purely mechanical context wherein the special properties are modeled as traction and energy fields defined on a two-dimensional abstraction of the interface region. Materials that undergo martensitic phase changes are modeled as having a hyperelastic character in both the bulk and interface. The characterization of such bodies is examined in detail and a representation theorem is presented for describing the interfaces of isotropic, hyperelastic media. A class of isotropic, nonlinearly hyperelastic bulk material is introduced that is capable of modeling the dilatative component of martensitic phase transformations. Such materials are considered within a noninertial setting referred to as The Cylinder Problem. This problem provides a means of exploring a variety of surface effects, and a criterion for nucleation based on energy is presented towards this end. Here nucleation events are modeled as deterministic, temporal shocks that are global in spatial extent. The fundamental development presented does more than capture the desired surface effects. It shows how they are related to specific assumptions regarding interface and bulk constitution. Four different interface characterizations are presented that serve to illustrate this.\n" }, { "name": "Lysek, Mark Joseph", "degree": "PhD", "year": "1992", "title": "A thermodynamic study of layering and capillary condensation of methane adsorbed on graphite foam", "advisor": "Goodstein, David L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08142007-090035", "creators": [ { "name": { "family": "Lysek", "given": "Mark Joseph" }, "id": "Lysek-M-J", "display_name": "Lysek, Mark Joseph" } ], "advisors": [ { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "advisor", "display_name": "Goodstein, David L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/1tad-9z23", "abstract": "Multilayer films of methane adsorbed on graphite foam have been studied using heat capacity and vapor pressure measurements. An automated, high resolution differential calorimeter was designed and constructed that yielded far better data in much less time. It was found that capillary condensate in the pores of the graphite foam coexists with uniform films as thin as 1.1 layers. Heat capacity features near the triple point previously thought to be the melting of the uniform film are identified as the melting of the capillary condensate. The latent heat of melting of the capillary condensate was measured to be as small as half the bulk value when it was confined inside the smallest pores. The melting temperature of the capillary condensate confirms a simple model for the melting of bulk matter in cylindrical pores. This model explains why the melting temperature is the same for systems with the same chemical potential but on different branches of the hysteresis curve. The model indicates that the capillary condensate may undergo surface melting if the solid does not wet graphite and the condensate undergoes substrate freezing. The phase diagram of the layer closest to the substrate is altered slightly by the finding that this layer melts from the commensurate phase when the uniform film is thicker than 1.1 layers. Heat capacity signals from phase transitions in the uniform films map out complicated phase diagrams in the second, third and fourth layers, including a 2-D triple point and liquid vapor coexistence region for each layer. The layering critical temperatures indicate that the bulk solid-vapor interface may roughen at about 81 K." }, { "name": "Mau, Russell Edgar", "degree": "PhD", "year": "1992", "title": "Particle transport in flow through porous media : advection, longitudinal dispersion, and filtration", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08202007-142809", "creators": [ { "name": { "family": "Mau", "given": "Russell Edgar" }, "id": "Mau-R-E", "display_name": "Mau, Russell Edgar" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "List", "given": "John A." }, "id": "List-J-A", "role": "chair", "display_name": "List, John A." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." } ], "option_major": [ "civileng" ], "doi": "10.7907/4JBE-GH29", "abstract": "A theoretical and experimental investigation of the transport parameters of particles flowing through porous media has been made. These parameters are the particle advective velocity, longitudinal dispersion coefficient, and filter coefficient. Both theoretical and experimental results are limited to flows with low Reynolds number (linear, laminar flow) and high Peclet number (advection dominates diffusion). The theoretical development used dimensionless numbers to define the transport parameters and incorporated them into an advective-dispersion equation describing particle transport. A relationship for unfavorable filtration due to repulsive double layer interactions is proposed.\r\n\r\nA solution to the complete advective-dispersion equation for particle transport was derived for the case of a constant filter coefficient. This solution when compared to a similar solution previously derived for solute transport, showed that for small filtration the solutions were identical except for the exponential decay factor due to filtration. A numerical model was developed for the case of a variable filter coefficient.\r\n\r\nFlow experiments were conducted in a 1.5 m vertical column with sand (geo. mean diameter = 381 micron), with suspensions of polystyrene latex particles (three cases, mean diameter = 0.1, 1.0, and 2.8 micron), and with NaCl as the electrolyte (0.4 mM < Ionic strength < 2.1 mM). The range of Peclet number studied was 1.26 x 10(4) to 2.00 x 10(6). The measurement of the particle concentrations during passage of a displacement front provided the necessary data to determine the particle transport parameters.\r\n\r\nThe particle advective velocities for the three different sized particles was found to range approximately from 0 to 5.4% greater than the solute velocity, and these values were within a few percent of predictions based on particle and pore radii.\r\n\r\nThe longitudinal dispersion coefficient for the three different sized particles was found to be a function of only the advective velocity of the particles and grain diameter of the porous bed which confirmed the dimensional analysis argument and closely matched previous solute work.\r\n\r\nA dimensional analysis argument for the relationship between the favorable and unfavorable filter coefficient was proposed to be a function of the ratio of the particle diffusion length of an advecting particle and the double layer thickness (which in turn depends on the ionic strength of the water). A wide range of filtration data (Brownian to advective particles) was empirically fitted using this dimensionless number.\r\n\r\nThe effects of ionic strength on particle transport were found to be either minimal or separable from the hydraulic variables. For advection, effects of changing ionic strength were analyzed as changes in the effective particle radius and calculations made using this apparent particle radius matched experimental results. For dispersion, an increase of a factor of 6 in the ionic strength increased the longitudinal dispersion by a factor of 1.2.\r\n" }, { "name": "Melman, Aharon", "degree": "PhD", "year": "1992", "title": "Complexity analysis for the Newton modified barrier function method", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechETD:etd-08082007-143657", "creators": [ { "name": { "family": "Melman", "given": "Aharon" }, "id": "Melman-A", "display_name": "Melman, Aharon" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/yrr2-5a17", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThe modified barrier function (MBF) is examined for linear, convex quadratic and other convex nonlinear constrained optimization problems. This new method of transforming a constrained problem into a sequence of unconstrained ones has elements of both Lagrangian function and barrier function methods. At each step, the method updates multipliers, which converge to the optimal Lagrange multipliers. Each such update entails a minimization using Newton's method.\n\nWe show that there is a ball around the primal-dual solution of the optimization problem, a so-called \"hot start\" ball, such that starting from any point in this ball, Newton's method converges quadratically and continues to do so after each subsequent update. We characterize the \"hot start\" ball in terms of the primal-dual solution of the optimization problem.\n\nThis means that from the \"hot start\" on, only [...] Newton steps are necessary after each update in order to reach the next update ([...] > 0 is the desired accuracy for the solution). Taking into account the basic MBF convergence properties, one obtains that the number of Newton steps from a \"hot start\" to the solution is [...].\n\nTo reach the \"hot start\" one has to spend [...], where [...] > 0 is defined by the condition number of the constrained optimization problem, which in turn can be characterized explicitly in terms of quantities defined at the solution." }, { "name": "Minahen, Timothy M.", "degree": "PhD", "year": "1992", "title": "Structural instabilities involving time dependent materials : theory and experiment", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-08082007-100442", "creators": [ { "name": { "family": "Minahen", "given": "Timothy M." }, "id": "Minahen-T-M", "display_name": "Minahen, Timothy M." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Christman", "given": "Tom" }, "id": "Christman-T", "role": "member", "display_name": "Christman, Tom" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7h70-2p51", "abstract": "The creep buckling of viscoelastic structures is studied analytically and experimentally to investigate structural stability in the presence of time dependent materials. The theory of linear viscoelasticity is used to model polymeric column specimens subjected to constant compressive end loads. A strength of materials approach (Euler-Bernoulli beam theory) is employed to model the moment-curvature relation for the column. The growth of initial imperfections is calculated using the hereditary integral formulation. Solution techniques are developed for small displacements and then generalized to include the effects of large displacements and rotations. A failure criterion based on maximum deformation allows the column life to be estimated directly from the material relaxation modulus. A discussion generalizing the results to include plates and shells is presented.\n\nRectangular cross-section polymethylmethacrylate (PMMA) specimens with hinged boundary conditions are used to study viscoelastic buckling experimentally. Constant compressive end loads are applied using a servo-controlled load frame while the specimens are kept in a temperature cabinet at elevated temperatures (accelerating the creep behavior). Specimen shortening and out-of-plane deflections are monitored during the tests. The relaxation modulus of PMMA is approximated by a Prony-Dirichlet series and the model is used to simulate the laboratory experiments. Model and experimental results show good agreement during the \"glassy\" and slow growth phases of the column response. As the growth rate increases some deviations between theory and experiment are seen. It is shown that the deviations are not a result of geometric nonlinearities, but may, in part, be explained by material nonlinearities not accounted for in the model.\n" }, { "name": "Nadiga, Balasubramanya T.", "degree": "PhD", "year": "1992", "title": "A study of multi-speed discrete-velocity gases", "advisor": "Sturtevant, Bradford; Broadwell, James E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092007-090234", "creators": [ { "name": { "family": "Nadiga", "given": "Balasubramanya T." }, "id": "Nadiga-B-T", "display_name": "Nadiga, Balasubramanya T." } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "advisor", "display_name": "Broadwell, James E." } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/tz85-x511", "abstract": "The applicability of multi-speed discrete-velocity gases to compressible flow situations is considered. First, the equation of state, the anisotropies and the advection velocities for any multi-speed model on the square and triangular lattices are derived. The dependence on the model of any of these to leading order in the flow velocity is shown to be only through a fourth moment of the stationary equilibrium speed distribution. Next, a computation scheme is introduced, wherein adjacent cells in a cell network interact through an exchange of particles, commensurate with the equilibrium fluxes of mass, momentum, and energy. This corresponds to the infinite collision rate limit of the model gas, resulting in very low viscosities. Finally, a simple multi-speed model, the nine-velocity model is studied in detail: Solving the shock tube flow with the model yields almost all phenomenology associated with a perfect gas. An exact shock profile is computed for the model and is compared to a Navier-Stokes shock profile. An adiabatic channel flow is simulated with the model and the results compared to an integral solution of the Navier-Stokes equation. The comparisons in both the cases are excellent. It is also shown that the nine-velocity gas does not permit steady supersonic flow." }, { "name": "Pearson, Douglas Harvey", "degree": "PhD", "year": "1992", "title": "Measurements of white lines in transition metals and alloys using electron energy loss spectrometry", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05262005-095151", "creators": [ { "name": { "family": "Pearson", "given": "Douglas Harvey" }, "id": "Pearson-D-H", "display_name": "Pearson, Douglas Harvey" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "member", "display_name": "Ahn, Channing C." }, { "name": { "family": "Kojoian", "given": "Gabriel" }, "id": "Kojoian-G", "role": "member", "display_name": "Kojoian, Gabriel" }, { "name": { "family": "Seal", "given": "James" }, "id": "Seal-J", "role": "member", "display_name": "Seal, James" }, { "name": { "family": "Rez", "given": "Peter" }, "id": "Rez-P", "role": "member", "display_name": "Rez, Peter" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Q7FW-HP21", "abstract": "This thesis addresses the interpretation of the peaks known as \"white lines\" found at the onsets of the L2 and L3 absorption spectra of 3d and 4d transition metals and alloys. These peaks arise from excitations of 2p core electrons to unoccupied outer d states at transition metal atoms. Recent work has suggested that differences in white line intensities observed between pure transition metals and associated compounds may be used to infer changes in the occupancies of the corresponding d states local to a given atom species. These prior studies, however, have focused on compounds of only a few transition metals. A systematic investigation of the relationship between white line intensity and d-state occupancy for 3d and 4d transition metals had not yet been done.\n \nIn this work an experimental analysis of the white lines for the 3d and 4d transition metals was carried out using electron energy loss spectrometry (EELS), and a linear decrease in white line intensity with increasing d state occupancy was found for both transition series. These results suggest that the intensities of the white lines reflect the occupancies of the outer d states in 3d and 4d transition metals, which are known to increase linearly with atomic number. In addition, these empirical correlations provide a straightforward method for measuring changes in 3d or 4d state occupancy.\n \nIn an application of this work, L2,3 spectra were measured for a number of binary copper alloys, Fe-Co alloys of varying composition, and several binary nickel alloys. Significant changes in the intensities of the white lines were observed in some cases. Changes in 3d occupancies inferred from these measurements were in agreement with other measurements and density-of-states calculations from the literature where available.\n" }, { "name": "Ramesh, Rajaram", "degree": "PhD", "year": "1992", "title": "Efficient multichannel methods for high-rate data transmission with application to ISDN (or) pouring water to get more out of copper", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08082007-081649", "creators": [ { "name": { "family": "Ramesh", "given": "Rajaram" }, "id": "Ramesh-R", "display_name": "Ramesh, Rajaram" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "chair", "display_name": "Posner, Edward C." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/s4r5-wm48", "abstract": "In this thesis, we are concerned with the transmission of data over channels with intersymbol interference. We consider input signals which are multiplexed versions of several parallel input signals, with the aim of splitting the input signal spectrum into disparate frequency bands and shaping the input spectrum by adjusting the power on each of the frequency bands. We introduce a multirate signal processing framework for the representation of the channel under these conditions and derive simple equivalents for the channel and the associated processors.\n\nUsing the equivalent circuits, we derive simple equalization schemes for the channel by drawing from the theory of polynomial matrices. We show that vector equalization can be reduced to a combination of prefiltering, postfiltering and scalar equalization of a few of the parallel input signals. We also discuss several interesting properties of this decomposition.\n\nIn the case when the channel is corrupted by colored noise, we derive expressions for the optimum prefilters and postfilters with decision feedback equalization that minimize the mean-squared error between the input and the output, given a constraint on the input power. For uncorrelated inputs, the scheme leads to a set of parallel independent scalar channels with the optimum postfilter whitening the noise, which permits the optimal use of trellis codes for data transmission.\n\nWe apply the scheme to a special channel, viz., the ISDN digital subscriber loop. The main impairments on this channel are intersymbol interference and crosstalk due to adjacent loops in the same binder group. Crosstalk is an especially interesting case of noise since it depends on the signal being transmitted; we assume that all loops in a binder group transmit using the same scheme. We consider two cases of crosstalk noise: when transmission between different loops in a binder group is synchronized, the crosstalk noise is wide-sense cyclostationary, and with a lack of synchronization between loops, the crosstalk noise is wide-sense stationary. We present methods to determine the optimum filters for data transmission and the optimum input power distributions for both these cases. We demonstrate the possibility of data transmission at the T1 rate, i.e., 1.544 Mb/s over most loops in the local loop plant. We also find that synchronizing transmission between different loops in a binder group does not get us much; the difference in the throughputs for the cases of cyclostationary crosstalk and wide-sense stationary crosstalk does not seem to justify the effort involved in synchronization." }, { "name": "Rulison, Aaron John", "degree": "PhD", "year": "1992", "title": "Part 1. Synthesis of ceramic powders by electrospray pyrolysis. Part 2. An approach to interplanetary particle sampling", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08202007-130850", "creators": [ { "name": { "family": "Rulison", "given": "Aaron John" }, "id": "Rulison-A-J", "display_name": "Rulison, Aaron John" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "member", "display_name": "Ahrens, Thomas J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/5tcw-c634", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nIn Part 1, the application of electrospray atomization for the production of ceramic powders is described. A model of the Taylor cone was developed which predicts the droplet size, volumetric flow rate, and electrical current for atomization of electrolytic solutions as functions of the liquid's specific electrical conductivity, surface tension, absolute viscosity, and density, as well as the applied electrical potential and atomizer geometry. Experimental verification was obtained for atomization of sodium iodide in n-propyl alcohol. The knowledge gleaned from the sodium iodide experiments was used to apply electrospray atomization to the production of submicron, spheroidal, and yttria particles by atomization of yttrium nitrate in n-propyl alcohol and thermal decomposition of the resulting aerosol droplets. This process is named \"electrospray pyrolysis.\" A means of increasing the ceramic powder production rate for industrial and more extensive laboratory use via arrays of Taylor cones was experimentally tested.\n\nIn Part 2, a method of sampling interplanetary dust particles (IDPs) is described. IDPs move at speeds [...]10 km/s relative to an interplanetary probe. A gas-filled balloon stops the particles by drag and ablation after they penetrate the balloon's skin. A model for ablation and deceleration of particles in the continuum and transition regimes was developed and experimentally tested using 7 [...] diameter glass spheres moving with an initial speed of 5 km/s through xenon gas at 0.1 and 0.2 atm. To analyze stopped IDPs by mass spectrometry, microscopy, etc., they must be deposited on a small sample substrate. To this end, a method of inward electrostatic precipitation was devised, modelled, and experimentally tested for [...] carbon soot particles in a cylindrical chamber. By this method, [...] IDPs can be intercepted by a [...] m noble gas-filled balloon, and deposited on a [...] mm centrally located sample substrate for subsequent analysis." }, { "name": "Sanders, Steven", "degree": "PhD", "year": "1992", "title": "Passive mode-locking and millimeter-wave modulation of quantum well lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-08132007-085419", "creators": [ { "name": { "family": "Sanders", "given": "Steven" }, "id": "Sanders-S", "display_name": "Sanders, Steven" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/z29s-kq29", "abstract": "Quantum well lasers with their optical cavities electrically divided into regions of saturable absorption and gain are passively mode-locked to generate picosecond pulse trains. Current is injected into the gain region, and the absorber is biased below the p-n junction turn-on voltage to control the absorption level and the rate of extraction of photogenerated carriers. Using only DC or low frequency electrical bias on monolithic devices, pulse trains at repetition rates above 100 GHz are generated for the first time.\n\nTheoretical considerations show that quantum well laser properties including the reduction of differential gain with increasing carrier density and the fast recovery time of the absorber allow passive mode-locking to occur at repetition rates far beyond the direct modulation bandwidth of a semiconductor laser, at frequencies above 100 GHz. The saturable absorption in the cavity, however, also induces self-sustained pulsations at a few gigahertz that can interfere with the higher frequency mode-locking process. However, it is shown that increasing the photon lifetime in the cavity can inhibit self-sustained pulsations while extending the range of conditions for high-frequency passive mode-locking.\n\nMultisection stripe lasers are fabricated from quantum well materials by etching through the highly conductive cap layer to electrically isolate regions along the stripes. A two-section monolithic triple quantum well GaAs/AlGaAs stripe laser is passively mode-locked at a 108 GHz repetition rate, with pulsewidths averaging 2.4 ps. More stable mode-locking is observed in a three-section passively mode-locked InGaAs/AlGaAs double quantum well laser emitting 5.9 ps pulses at a 42 GHz repetition rate.\n\nBy coupling a two-section quantum well buried heterostructure laser to an external cavity, the pulse train period becomes comparable to the gain and absorber recovery times and compatible with conventional optical detectors and electronics. It is shown that the laser can operate at six different harmonics of the 1.17 GHz repetition rate, by adjustment of the gain section current only. Both small and large-signal saturation models for passive mode-locking are described and applied to determine the conditions where the laser should operate at the different harmonics and are in reasonable agreement with the experimental results. From power spectrum measurements of a laser mode-locked at 546 MHz, the timing jitter is determined to be 5.5 ps above 50 Hz, and the pulse energy fluctuations less than 0.52% above 200 Hz. While it is expected that stable pulse trains can be generated at these lower repetition rates, as is demonstrated, the stability of the millimeter-wave mode-locked lasers remains a critical problem for future research.\n" }, { "name": "Sayano, Masahiro", "degree": "PhD", "year": "1992", "title": "Analyses of coding and compression strategies for data storage and transmission", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08132007-084323", "creators": [ { "name": { "family": "Sayano", "given": "Masahiro" }, "id": "Sayano-M", "display_name": "Sayano, Masahiro" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/xxh5-v758", "abstract": "Selected topics in error correction coding and data compression for data storage and transmission will be analyzed here. In particular, a model for the mean time to failure for computer memories protected by error correction coding, characteristics and applications of phased burst error correcting array codes, and locally adaptive vector quantization for image and data compression will be examined.\n\nA model of the mean time to failure (MTTF) of semiconductor random access memories protected by single error correcting-double error detecting (SEC-DED) codes on the chip and with soft error scrubbing and multiple types of hard failures will be presented. Only a few assumptions and approximations will be made. This model will provide a more complete picture of the expected failure modes, reliability, and the mean time to failure of memory systems protected by on-chip error correction coding. Special cases will also be addressed, such as slow or fast scrubbing and dominance of hard or soft errors.\n\nCharacteristics of a family of phased burst error correcting array codes will be addressed. In particular, allowable and optimal code sizes will be examined. When used in non-binary applications, these codes retain their characteristics and can correct \"approximate\" errors with even higher rate: If the amount any q-ary symbol can be in error is bounded by some value, these codes can be designed to address this type of error with even fewer check symbols.\n\nImprovements to a locally adaptive vector quantization compression strategy will be discussed. The basic strategy involves reorganization of the code book after each use so that the most recent codewords are moved to the front. With the various improvements covered in this work, the algorithm is capable of matching the performance of other more computationally intensive algorithms at a fraction of the computational complexity.\n" }, { "name": "Schlautman, Mark A.", "degree": "PhD", "year": "1992", "title": "Mineral Surfaces and Humic Substances: Partitioning of Hydrophobic Organic Pollutants", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08132007-085939", "creators": [ { "name": { "family": "Schlautman", "given": "Mark A." }, "id": "Schlautman-Mark-A", "orcid": "0000-0001-6522-4345", "display_name": "Schlautman, Mark A." } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." } ], "option_major": [ "envreng" ], "doi": "10.7907/pdy0-wk35", "abstract": "The influence of aqueous chemistry on the sorption reactions of three polycyclic aromatic hydrocarbons (PAHs) with Suwannee River humic substances and with an inorganic fused silica surface was examined using fluorescence techniques. By varying the pH, ionic strength and composition of the background electrolyte, the influence of solution chemistry on carbon-normalized partition coefficients and surface area-normalized reaction quotients and adsorption constants was observed. The humic substances examined in this study were present as freely dissolved species and as organic coatings on colloidal-sized aluminum oxide particles.
\r\n\r\nBinding of the PAHs by dissolved and adsorbed humic material was complete within 3 minutes for all samples; several reactions with dissolved humic substances appeared to be equilibrated within 20 seconds. The association of a PAH compound with Suwannee River humic material appeared to depend on the size of the solute molecule and its ability to fit into hydrophobic cavities in the humic structure. The adsorption of humic and fulvic acid onto alumina decreased their ability to bind perylene. The ability of adsorbed humic substances to bind perylene was dependent on the type of surface complex which was formed between the alumina surface and the humic material. A major effect of solution chemistry was to alter the adsorption mechanisms of the humic substances, which in turn dictated the types of surface complexes formed.
\r\n\r\nThe adsorption of perylene to a nonporous silica surface required 2\u00bd to 4 hours to reach equilibrium. An apparent equilibrium was attained in 60 to 90 minutes for desorption reactions. Quantitative recovery of adsorbed perylene was observed after a 5- to 10-minute methanol extraction. The observed adsorption rates were correlated with the fugacity of perylene and the surface speciation of fused silica. From long-term adsorption data it appears that two different processes are operative in the adsorption of perylene to the fused silica surface. The nature of these processes is not clear, but may relate to the structure of water at the solid-liquid interface.
" }, { "name": "Sercel, Peter C.", "degree": "PhD", "year": "1992", "title": "Semiconductor structures in the quantum size regime", "advisor": "Vahala, Kerry J.; Atwater, Harry Albert; Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08202007-132916", "creators": [ { "name": { "family": "Sercel", "given": "Peter C." }, "id": "Sercel-Peter-C", "display_name": "Sercel, Peter C." } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "co-advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "co-advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/cmqv-p871", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe physics of quantum wires and quantum dots is investigated theoretically. We develop an analytical formalism for determining the energy eigenstates and bandstructure of spherical quantum dots and cylindrical quantum wires. The technique is based upon a reformulation of second order [...] theory in a basis of eigenstates of total angular momentum. We are led by analysis of quantum wires and dots based upon the InAs-GaSb material system to propose a novel class of self-doping nanostructures for carrier transport experiments and possible future application. The polarization dependence of linear optical absorption and gain spectra in cylindrical quantum wires is calculated. Applicability of the results derived for cylindrical quantum wires to the case of wires with lower symmetry is addressed using symmetry group theory.\r\n\r\nFabrication of quantum wires and dots is attempted by several techniques. A method for fabricating nanometer-scale GaAs wire structures from quantum well material by selective impurity induced disordering is demonstrated. The technique produces lateral bandgap modifications on a 100 nm scale, as verified by cathodoluminescence imaging and spectroscopy. We demonstrate vapor phase synthesis of nanometer-scale III-V semiconductor clusters in the 5 to 20 nm diameter regime. Clusters form by homogeneous nucleation from a non-equilibrium vapor created by the explosive vaporization of a bulk semiconductor filament in an inert atmosphere. The clusters produced have zincblende crystal structure and are faceted. The optical absorption spectra of the clusters are suggestive of quantum confinement effects. A second method of cluster formation utilizes homogeneous nucleation from volatile metal-organic and hydride precursors to produce nanometer-scale, zincblende GaAs clusters." }, { "name": "Steele, Craig Stanley", "degree": "PhD", "year": "1992", "title": "Affinity : a Concurrent Programming System for Multicomputers", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152007-074128", "creators": [ { "name": { "family": "Steele", "given": "Craig Stanley" }, "id": "Steele-Craig-Stanley", "display_name": "Steele, Craig Stanley" } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "chair", "display_name": "Seitz, Charles L." }, { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "role": "member", "display_name": "Rees, Douglas C." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-S", "role": "member", "display_name": "Taylor, Stephen" } ], "option_major": [ "compsci" ], "doi": "10.7907/syrm-sx30", "abstract": "Affinity is an experiment to explore a simple, convenient, and expressive programming model that provides adequate power for complex programming tasks while setting few constraints on potential concurrency. Although the programmer is required to formulate a computational problem explicitly into medium-sized pieces of data and code, most of the additional functions necessary for concurrent execution are implicit. The execution of the light-weight, reactive processes, called actions, implicitly induces atomicity and consistency of data modifications. The programmer accesses shared data structures in a shared-memory fashion, but without the need for explicit locking to manage the problems of concurrent access and mutual exclusion. Program control flow is distributed and implicit.\r\n\r\nThe name given to the programming model, Affinity, has a definition, \"causal connection or relationship,\" that is fitting to the way programs are structured and scheduled.\r\n\r\nAffinity consistency and coherence properties provide a tractable discipline for the dangerous power of a concurrent, shared-memory programming style. Existing programming complexity-management techniques such as object-oriented languages can be used in this multicomputer environment. Affinity programs can compute consistent and correct results despite staleness of data, and asynchrony and nondeterminism in execution of code. Program correctness is invariant under replication, or cloning, of actions. This aspect of the model yields a simple and robust mechanism for fault-tolerance.\r\n\r\nThe practicality of the Affinity programming model has been demonstrated by an implementation on a second-generation multicomputer, the Ametek S/2010. The implementation is distributed, scalable, and relatively insensitive to network latency. Affinity has demonstrated reasonable efficiency and performance for computations with tens of processing nodes, hundreds of actions, and thousands of shared data structures." }, { "name": "Sullivan, Gregory Daniel", "degree": "PhD", "year": "1992", "title": "An investigation of mixing and transport at a sheared density interface", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152007-082818", "creators": [ { "name": { "family": "Sullivan", "given": "Gregory Daniel" }, "id": "Sullivan-G-D", "display_name": "Sullivan, Gregory Daniel" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/931s-r394", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nScalar transport is investigated at a density interface imbedded in a turbulent shear flow. This problem is investigated first experimentally, and based on the experimental findings, a physical model for entrainment is developed.\n\nSteady-state interfacial shear flows are generated in a laboratory water channel for layer Richardson numbers, Ri, between about 1 and 10. The flow field is made optically homogeneous, enabling the combined use of laser-Doppler velocimetry and laser-induced fluorescence with photodiode array imaging to measure the velocity and concentration fields at high resolution.\n\nFalse-color images of the concentration field provide valuable insight into mixing and transport at the interface. The dominant interfacial mixing mechanism is found to depend on the local mean shear Richardson number, [...] for [...] less than about 0.40 to 0.45, local mixing is dominated by Kelvin-Helmholtz (K-H) instabilities; for somewhat larger values of [...], mixing is dominated by interfacial wave breaking. In both cases, vertical transport of mixed fluid into adjacent turbulent layers is accomplished by large-scale turbulent eddies which impinge on the interface and scour fluid from its outer edges.\n\nBased on the experimental results, a model for interfacial mixing and entrainment is developed. A local equilibrium is assumed in which the rate of loss of interfacial fluid by eddy scouring is balanced by the rate of production (local mixing) by interfacial instabilities and molecular diffusion. In the case of one-sided entrainment, the model results are as follows: when interfacial mixing is diffusion dominated, [...] and [...], where [...] is the interface thickness, h is the boundary layer thickness, Pe is the Peclet number, and E is the normalized entrainment velocity; when mixing is wave breaking dominated, [...] and [...]; and when mixing is K-H dominated, [...] and [...]. In all cases the maximum concentration anomaly is [...]. The model for single-sided entrainment is simply extended to the case in which both layers are entraining. In the latter case it is found that entrainment depends on combinations of parameters from both layers.\n\nThe proposed entrainment model is supported by experimental results from this and previous studies. The data from this study are in agreement with [...] and are consistent with model results for [...]; results from previous studies support model predictions for E and [...]." }, { "name": "Tsai, Cho-Jen", "degree": "PhD", "year": "1992", "title": "Low energy ion-surface interaction and epitaxial growth in the SiGe system", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152007-092600", "creators": [ { "name": { "family": "Tsai", "given": "Cho-Jen" }, "id": "Tsai-Cho-Jen", "display_name": "Tsai, Cho-Jen" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "matsci" ], "doi": "10.7907/886t-t311", "abstract": "The structure of a growing epitaxial film is controlled by the relative rate of different surface processes. Low energy ion beams (50-500 eV) can be used to provide energy to adatoms on the surface and atoms in the near-surface region of a growing film. Thus, a low energy ion beam can be employed as a tool to modify surface kinetics. The study of the effects of the beam-induced defects on the epitaxial growth can also provide valuable insights into intrinsic growth processes by altering the relative rate of various surface kinetics. The work contained in this thesis is focused on the role of defects produced by low energy ion bombardment in modification of epitaxial growth of Si, Ge, and SiGe alloy films.\r\n\r\nIn the first two chapters, theoretical and technical aspects of X-ray rocking curve diffractometry which is one of the principal analytic methods used in this thesis is discussed. The high-resolution X-ray diffractometer built at Caltech and the dynamical theory of X-ray diffraction are briefly discussed. The last four chapters are focused on the manner in which low energy ion beam bombardment affect the structural properties and growth kinetics of epitaxial films. One of the most important factors determining the changes that occur in ion-assisted epitaxy is the ion energy used to stimulate the growth processes, which determines the relative number of surface displacements and bulk displacements. The effect of bulk displacement defects on an epitaxial film structure is discussed in Chapter 3. In Chapter 4, a simple moving boundary diffusion model in conjunction with thermal spike activated kinetics is presented to describe the bulk defect incorporation process. The moving boundary diffusion model has also been used to describe the adatom concentration on the vicinal Si surface and the low energy dopant incorporation processes. Surface displacements produced by low energy ion bombardment has a dramatic effect on the growth mode of epitaxial Ge films on Si(100); this is the main theme of Chapter 5. In the initial stages of Ge growth on Si, a layer-by-layer growth followed by island growth was observed in conventional (thermal) molecular beam epitaxial growth. Island formation is inhibited by low energy ion bombardment during epitaxial growth which can prolong the layer-by-layer growth mode to greater thicknesses than for thermal growth. In Chapter 6, the effect of the low energy ion bombardment on the misfit accommodation of the lattice mismatched system is discussed. The point defects injected by the low energy ion bombardment impede dislocation motion in the growing epitaxial film and cause misfit strain to be accommodated by the threading dislocations which greatly enhances the misorientation between a film and its substrate." }, { "name": "Wissler, John B.", "degree": "PhD", "year": "1992", "title": "Transmission of thin light beams through turbulent mixing layers", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08162007-133929", "creators": [ { "name": { "family": "Wissler", "given": "John B." }, "id": "Wissler-J-B", "display_name": "Wissler, John B." } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/pw33-qc68", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nLight transmission through incompressible gaseous turbulent mixing layers is investigated with the objective of understanding the effects of large-scale coherent structures and mixing transition on the optical quality of the mixing layer. Experiments are done in a vertically flowing mixing layer which is enclosed inside a pressure tank and fed by two banks of high-pressure gas bottles. The study considers both the unequal density (high-speed [...] and low-speed [...]) and equal density (high-speed [...] and low-speed [...]) cases; the mixing of dissimilar gases is the source of the optical aberrations. Large-scale Reynolds numbers range between 3500 and 80000 over pressures from 2 to 6 bar. Light transmission characteristics are first studied qualitatively using a network of thin sheets of short-exposure ([...]) white light which are aberrated by the mixing layer and then image directly onto photographic film. Light transmission characteristics are then studied quantitatively using a lateral effect detector to dynamically track a thin He-Ne laser beam as it wanders under the influence of the passing coherent structures.\n\nThe study finds that the spanwise coherent structures generate systematic deflections of the light beam in the streamwise direction; the greatest deflections occur near the trailing edges of the structures at a formation called the cusp, where the high-speed fluid and low-speed fluid are entrained into the vortex core. The streamwise coherent structures, which form later in the mixing layer's development than the spanwise structures, generate substantial beam deflections in the span-wise direction which are closely associated with the streamwise streaks in plan-view shadowgraphs. The rms fluctuations of the streamwise and spanwise deflection angles increase rapidly during mixing transition, peaking at 380 high-speed-side momentum thicknesses downstream from the splitter plate, then decrease far down-stream to asymptotic values of 0.6 to 0.8 as scaled by the static pressure and the Gladstone-Dale constant shift across the mixing layer. The data suggest that a possible mechanism for the deflections is the interaction of the beam with the thin interfaces which bound relatively uniform bodies of fluid inside the structures." }, { "name": "Wong, Yiu-fai Isaac", "degree": "PhD", "year": "1992", "title": "Towards a simple and fast learning and classification system", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172006-104502", "creators": [ { "name": { "family": "Wong", "given": "Yiu-fai Isaac" }, "id": "Wong-Yiu-fai-Isaac", "display_name": "Wong, Yiu-fai Isaac" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "chair", "display_name": "Posner, Edward C." }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Bower", "given": "James M." }, "id": "Bower-J-M", "role": "member", "display_name": "Bower, James M." }, { "name": { "family": "Fox", "given": "Geoffrey C." }, "id": "Fox-G-C", "role": "member", "display_name": "Fox, Geoffrey C." }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" } ], "option_major": [ "eleceng" ], "doi": "10.7907/531t-v696", "abstract": "This work consists of two parts which can be read independently.\r\n\r\nThe first part contains a novel proof of the learning convergence in the Cerebral Model Articulation Controller (CMAC) proposed by Albus in 1976. That CMAC can learn any discrete input-output mapping was not known. Our work presents two ways of looking at the learning algorithm in CMAC. The learning algorithm is formulated as a matrix iteration scheme, the convergence of which can be proved by a) standard matrix theory and b) Fourier analysis. Each approach offers unique insights about the nature of the learning mechanism in CMAC. The analysis provides mathematical rigor and structure for a neural network learning model with simple and intuitive mechanisms.\r\n\r\nThe second part presents a new clustering algorithm derived from an interdisciplinary approach. The original motivation came from studies in Part I. The new algorithm departs from traditional approaches in many ways. It is the only algorithm which incorporates scale, though scale has been recognized by other researchers. It also introduces a new concept into clustering: cluster independence, which proves essential. The new framework allows us to derive a formulation based on information theory and statistical mechanics. The cluster centers correspond to the local minima of the thermodynamical free energy, which are identified as the fixed points of a one-parameter nonlinear map. Bifurcation techniques are used to obtain a complete picture of the dynamics of the map. A new clustering algorithm based on the melting process is obtained, which is hierarchical and unsupervised. Melting produces a tree of clusters in the scale space, analogous to a dendrogram. A characterization of \"cluster\" is given. Robustness considerations in scale space lead to a natural way of determining the optimal number of clusters. The algorithm is also insensitive to variability in cluster densities, cluster sizes and ellipsoidal shapes and orientations. We tested the algorithm successfully on both simulated data and a multi-dimensional Synthetic Aperture Radar image of an agricultural site for crop identification, and found that it beat the competition. Our clustering algorithm may also provide new and important insights for neural network research and optimization theory." }, { "name": "Workman, Thomas Wilson", "degree": "PhD", "year": "1992", "title": "Analysis of collision cascades in titanium deuteride by D-D fusion", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-08172007-080314", "creators": [ { "name": { "family": "Workman", "given": "Thomas Wilson" }, "id": "Workman-Thomas-Wilson", "display_name": "Workman, Thomas Wilson" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/fa6m-mh68", "abstract": "As a test of the linear binary collision cascade model for ion-solid interaction, theoretical models of D-D fusion induced by heavy ion irradiation of titanium deuteride are compared with experimental results. Thin-film titanium deuteride samples of composition TiD1.7 were prepared by heating 320 nm titanium films on silicon dioxide in a static pressure of deuterium. The deuterium content of these films was inferred from changes in the titanium and oxygen contaminant signals measured by 3.05 MeV oxygen-resonance backscattering spectrometry.
\r\n\r\nThe titanium deuteride samples were irradiated with beams of argon and xenon ions with energies ranging from 140 to 600 keV. The energy of the incident ion was transferred to atoms in the sample through a series of nuclear collisions, resulting in deuteron-deuteron collisions with energies up to tens of keV. The cross sections for D-D fusion at these energies are large enough for fusion events to be detected for doses above 1014 ions. A silicon surface-barrier detector placed at an angle of 130\u00b0 with respect to the incident ion beam was used to monitor the 3.02 MeV protons and 1.01 MeV tritons from the D(d,p)T reaction and 0.82 MeV 3He ions from the D(d,n)3He reaction. Fusion yields (fusion events per incident ion) ranging from 10-14 to 10-10 were measured.
\r\n\r\nA linear binary collision cascade model is presented which predicts fusion yields which are in excellent agreement with the measured yields for all cases studied. The model predicts a distribution of deuteron-deuteron center-of-mass velocities which causes a distribution of Doppler shifts in the spectrum of the fusion products. The shape of the theoretical proton signals based on the model is a reasonably good fit to the experimental proton signals.
\r\n\r\nThe use of D-D fusion induced by heavy-ion irradiation for measuring deuterium concentrations is compared with currently used methods and is found to be somewhat less sensitive than nuclear reaction analysis, but suitable for measuring deuterium concentrations as low as 2 atomic percent with ion beams producible by ion implanters with an energy range of a few hundred kV.
" }, { "name": "Yamamura, Alan Akihiro", "degree": "PhD", "year": "1992", "title": "Neural network control and an optoelectronic implementation of a multilayer feedforward neural network", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-08202007-091426", "creators": [ { "name": { "family": "Yamamura", "given": "Alan Akihiro" }, "id": "Yamamura-Alan-Akihiro", "display_name": "Yamamura, Alan Akihiro" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4dbn-z991", "abstract": "Artificial neural networks are a computational paradigm inspired by biological neural systems. By modeling neural networks to a certain degree after their counterparts in nature, it is hoped that they can capture those aspects of biological neural systems that allow them to outperform more conventional processing systems in tasks such as motor control and pattern recognition. A brief overview of neural networks is provided in Item 1, concentrating on those aspects pertinent to the remainder of this thesis.\r\n\r\nThe application of neural networks to control is examined in Item 2. A general control system can be divided into feedforward and feedback components. Specifically, the use of neural networks in learning to generate the feedforward control signal for unknown, potentially nonlinear, plants is examined. A class of learning algorithms applicable to feedforward networks is developed, and their use in learning to control a simulated two-link robotic manipulator is studied.\r\n\r\nAn optoelectronic implementation of a multilayer feedforward neural network, with binary weights and connections, is described in the final part of this thesis. The neurons and connections are implemented electronically on a custom VLSI chip. The pattern and strength of the connections is controlled, through photodetectors placed in the connections, by a pattern of light illuminating the chip. This pattern is read out, in parallel, from an optical disk. Issues concerning parallel readout of information from optical disks are discussed in Item 3, while Item 4 contains a descriptionn of both the design of the Optoelectronic Neural Network Chip (ONNC) and experiments involving the optical disk and neural network chip.\r\n" }, { "name": "van Putten, Maurice H. P. M.", "degree": "PhD", "year": "1992", "title": "MHD in divergence form : a computational method for astrophysical flow", "advisor": "Phinney, E. Sterl", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152007-144037", "creators": [ { "name": { "family": "van Putten", "given": "Maurice H. P. M." }, "id": "van-Putten-M-H-P-M", "orcid": "0000-0002-9212-411X", "display_name": "van Putten, Maurice H. P. M." } ], "advisors": [ { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "role": "advisor", "display_name": "Phinney, E. Sterl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/263j-a556", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe equations of MHD in curved space-time are presented in divergence form for the purpose of numerical implementation. This result follows from a covariant divergence form of the single fluid theory of electro-magneto-hydrodynamics in curved space-time with general constitutive relations.\r\n\r\nSome one- and two-dimensional shock computations are given. A pseudospectral method with weak smoothing is used in all of our computations. The pseudo-spectral method is constructed by consideration of Riemann problems in one dimension. The power of MHD in divergence form is brought about by using uniform grid-spacing and explicit time-stepping. The problems considered are shock-tube problems in transverse MHD with analytical comparison solution and a coplanar Riemann problem as discussed for nonrelativistic MHD in Brio and Wu [37]. In a limit of nonrelativistic velocities comparison is made of the results of the latter with those in [37]. In two dimensions cylindrically symmetric problems are considered for test of isotropy, independence of coordinate system and convergence (using comparison results in polar coordinates). We conclude with a computation of a shock induced vortex in jet flow with [...] 2.35, a relativistic jet computation with [...] 3.25 and, finally, computations on magnetic pressure dominated stagnation points in a 2D shock problem in nontransverse MHD.\r\n\r\nThis work is proposed for numerical study of astrophysical flows, and in particular as a \"vehicle\" towards the origin of jets." }, { "name": "Atiya, Amir", "degree": "PhD", "year": "1991", "title": "Learning algorithms for neural networks", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232005-083502", "creators": [ { "name": { "family": "Atiya", "given": "Amir" }, "id": "Atiya-Amir", "display_name": "Atiya, Amir" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/F46C-3V67", "abstract": "This thesis deals mainly with the development of new learning algorithms and the study of the dynamics of neural networks. We develop a method for training feedback neural networks. Appropriate stability conditions are derived, and learning is performed by the gradient descent technique. We develop a new associative memory model using Hopfield's continuous feedback network. We demonstrate some of the storage limitations of the Hopfield network, and develop alternative architectures and an algorithm for designing the associative memory. We propose a new unsupervised learning method for neural networks. The method is based on applying repeatedly the gradient ascent technique on a defined criterion function. We study some of the dynamical aspects of Hopfield networks. New stability results are derived. Oscillations and synchronizations in several architectures are studied, and related to recent findings in biology. The problem of recording the outputs of real neural networks is considered. A new method for the detection and the recognition of the recorded neural signals is proposed.\r\n" }, { "name": "Bai, Gang", "degree": "PhD", "year": "1991", "title": "I. Heteroepitaxy on Si. II. Ion implantation in Si and heterostructures", "advisor": "Nicolet, Marc-Aurele; Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-06282007-105319", "creators": [ { "name": { "family": "Bai", "given": "Gang" }, "id": "Bai-Gang", "display_name": "Bai, Gang" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "co-advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/v8kr-gm23", "abstract": "The themes of this thesis, heteroepitaxy and ion implantation, are two areas that have been very actively researched in the last two decades.\r\n\r\nHeterostructures made of III-V compound semiconductors by MBE and OMVPE have been used extensively in the fabrication of optoelectronics devices such as high-speed transistors and semiconductor lasers. Heterostructures on Si, which is the focus of part I of this thesis, have the advantage of compatibility with Si-based VLSI and promise to have impact on the microelectronics industry. Studies on the structural, elastic, thermal, and electrical properties of heteroepitaxial CoSi2, ReSi2, and GeSi films grown on Si constitute the backbone of this thesis. Some new characteristics of heterostructures were discovered as a result of this investigation. Among them are the observation and modeling of misorientation effects on an epitaxial film grown on a vicinal substrate; the misorientation induced by interfacial misfit dislocation arrays; the experimental measurements and phenomenological analysis of thermal strain, dislocation generation, and strain relaxation; and illustrative measurements of elastic, thermal, and structural properties of epitaxial films.\r\n\r\nIon implantation is an important process in the fabrication of integrated circuits. The second part of this thesis deals with the production and annealing of damage produced by ion implantation in semiconductors. The defect production, stability, microstructure, and the induced strain in implanted bulk Si crystals were quantitatively investigated as a function of ion species, dose, and implantation temperature. Many new features, such as the rapid rise of damage near the amorphization threshold, the correlation between the strain and defect concentration, and the scaling behavior of the damage with ion species and implantation temperature, are revealed.\r\n\r\nThe last chapter concerns the effects of ion implantation in CoSi2, ReSi2, and GeSi/Si heterostrcutures which is a marriage of heteroepitaxial and of ion implantation studies. Some interesting phenomena, such as the selective damage of the film and the substrate, the superposition of the intrinsic and the induced strain, are observed, and some preliminary results are obtained. Many interesting questions remain, and there are great research opportunities in this relatively unexplored area." }, { "name": "Beck, Robert Teran", "degree": "PhD", "year": "1991", "title": "Fundamental Problems in the Application of Structural Identification Procedures to Damage Detection", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04112011-152332381", "creators": [ { "name": { "family": "Beck", "given": "Robert Teran" }, "id": "Beck-Robert-Teran", "display_name": "Beck, Robert Teran" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/ty3h-hz53", "abstract": "There are fundamental problems in the application of structural identification procedures to damage detection which still need to be resolved. The present study investigates the underlying issues and then provides a number of techniques which solve a series of unresolved problems. The techniques developed range from extensions and refinements of previous methods to the adaptation of novel homotopy methods.
\r\n\r\nThe results from simulated data show that ill-conditioning, non-uniqueness and temporal synchronization of the data are the most serious problems encountered. Criteria to resolve these are then put forth. From the experimental studies, however it becomes evident that modeling error is the most serious issue. The experimental results show, nonetheless, that even with large model errors, it is possible to localize the area of damage to within a sub-structure.
\r\n\r\nThe techniques are then applied to data obtained from a ten-story steel frame building. Previous studies on such structures have indicated large changes in the natural frequencies, especially during the San Fernando earthquake of February 9, 1971. The present study shows how changes in the natural frequencies and in the modeshapes are related to the degradation of the inter-story stiffness along the height of the building. Low amplitude forced vibration and ambient vibration test data yield one set of results: at these levels of motion the structure seems to retain much of its original uniform stiffness. This is true even after strong motion, leading to the notion that the building \"has healed\" with time. It is clear from the studies how this apparent stiffness is lost immediately once the strong motion of even moderate earthquakes has begun and it is thought t hat this is due to a combinations of effects. Results show that for the 1971 San Fernando earthquake, stiffness losses in the order of 50% occurred in the middle stories towards the end of the strong motion part of the seismic motion.
" }, { "name": "Brown, Timothy X.", "degree": "PhD", "year": "1991", "title": "Neural network design for switching network control", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03142014-142621814", "creators": [ { "name": { "family": "Brown", "given": "Timothy X." }, "id": "Brown-T-X", "display_name": "Brown, Timothy X." } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ABJA-5B60", "abstract": "A neural network is a highly interconnected set of simple processors. The many connections allow information to travel rapidly through the network, and due to their simplicity, many processors in one network are feasible. Together these properties imply that we can build efficient massively parallel machines using neural networks. The primary problem is how do we specify the interconnections in a neural network. The various approaches developed so far such as outer product, learning algorithm, or energy function suffer from the following deficiencies: long training/ specification times; not guaranteed to work on all inputs; requires full connectivity.
\r\n\r\nAlternatively we discuss methods of using the topology and constraints of the problems themselves to design the topology and connections of the neural solution. We define several useful circuits-generalizations of the Winner-Take-All circuitthat allows us to incorporate constraints using feedback in a controlled manner. These circuits are proven to be stable, and to only converge on valid states. We use the Hopfield electronic model since this is close to an actual implementation. We also discuss methods for incorporating these circuits into larger systems, neural and nonneural. By exploiting regularities in our definition, we can construct efficient networks. To demonstrate the methods, we look to three problems from communications. We first discuss two applications to problems from circuit switching; finding routes in large multistage switches, and the call rearrangement problem. These show both, how we can use many neurons to build massively parallel machines, and how the Winner-Take-All circuits can simplify our designs.
\r\n\r\nNext we develop a solution to the contention arbitration problem of high-speed packet switches. We define a useful class of switching networks and then design a neural network to solve the contention arbitration problem for this class. Various aspects of the neural network/switch system are analyzed to measure the queueing performance of this method. Using the basic design, a feasible architecture for a large (1024-input) ATM packet switch is presented. Using the massive parallelism of neural networks, we can consider algorithms that were previously computationally unattainable. These now viable algorithms lead us to new perspectives on switch design.
\r\n" }, { "name": "Burns, Steven Morgan", "degree": "PhD", "year": "1991", "title": "Performance analysis and optimization of asynchronous circuits", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07092007-072640", "creators": [ { "name": { "family": "Burns", "given": "Steven Morgan" }, "id": "Burns-Steven-Morgan", "display_name": "Burns, Steven Morgan" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "member", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/kez1-7q52", "abstract": "Analytical techniques are developed to determine the performance of asynchronous digital circuits. These techniques can be used to guide the designer during the synthesis of such a circuit, leading to a high-performance, efficient implementation. Optimization techniques are also developed that further improve this implementation by determining the optimal sizes of the low-level devices (CMOS transistors) that compose the circuit.\r\n" }, { "name": "Croke, Edward Timothy, III", "degree": "PhD", "year": "1991", "title": "Growth and Characterization of Si-Based Electronic Materials for Novel Device Applications", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06292007-075639", "creators": [ { "name": { "family": "Croke", "given": "Edward Timothy, III" }, "id": "Croke-Edward-Timothy-III", "display_name": "Croke, Edward Timothy, III" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/yc74-1m24", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe material presented in this thesis concerns the growth and characterization of Si-based electronic materials through the use of molecular beam epitaxy (MBE). In particular, the Si1-xGex/Si and V1-xSix/Si material systems are studied because of their potential application in novel, heteroepitaxial device structures grown on crystalline Si substrates. Our work with the Si1-xGex/Si material system involves a study of the kinetics of strain relaxation for coherently strained Si1-xGex alloys grown on (100) Si at extremely low temperatures. In addition, we measure the strain dependence of the (100) Si/Ge valence band offset through the use of x-ray photoelectron spectroscopy (XPS). Further study of Si1-xGex alloys reveals a previously unreported (2 x 8) surface reconstruction, and for highly metastable alloys, the occurrence of chemical segregation during growth. We also report the successful nucleation and growth of superconducting V3Si on (111) Si, the first step toward the realization of epitaxial superconductor/semiconductor heterostructures. Finally, we make use of the knowledge gained in our preliminary studies and present the first electrical characterization of p-Si1-xGex/n-Si heterojunction interband-tunnel (HIT) diodes, demonstrating an enhancement of negative differential resistance (NDR) as a function of Ge concentration in the p-type Si1-xGex layer.
\r\n\r\nIn Chapter 2, we present a study of strain relaxation in metastable Si1-xGex/Si superlattices and Si1-xGex alloys. The samples prepared for this study are grown at unusually low growth temperatures (~ 365\u00b0C) to thicknesses significantly in excess of previously established critical thicknesses for growth at higher temperatures. 0-20 x-ray diffraction (0-20 XRD) is used to study the relaxation process as the samples are annealed in a sequence of isochronal anneal steps. Significant relaxation is observed at anneal temperatures as low as 370\u00b0C. In addition, we compare the relaxation behavior of Si1-xGex/Si superlattices and Si1-xGex alloys designed to possess the same average properties and report that the superlattices relax to a lesser extent than the corresponding alloys. Finally, alloy relaxation is described as a thermally activated, first-order kinetic process described by a single activation energy of approximately 2.0 eV.
\r\n\r\nIn Chapter 3, the strain dependence of the (100) Si/Ge valence band offset is measured through the use of XPS. Coherently strained Si, strained Ge, and symmetrically strained Si/Ge superlattices are grown on relaxed Si1-xGex buffer layers and transferred in ultrahigh vacuum (UHV) to the XPS chamber. Si 2p and Ge 3d core level to valence-band edge, and core level to core-level energy separations are measured as a function of in-plane lattice constant. High resolution x-ray diffraction (HRXRD) is used to measure the strain in these samples. For the valence band offset, we measure 0.83 \u00b1 0.11 eV for Ge strained to (100) Si and 0.22 \u00b1 0.13 eV for Si strained to (100) Ge.
\r\n\r\nHigh-quality, coherently strained Si1-xGex alloy layers are studied in Chapter 4 using HRXRD and ex situ transmission electron diffraction (TEM). Several samples are grown at extremely low temperatures (310-330\u00b0C) by MBE. Sample thicknesses and alloy concentrations are chosen to span a range beginning just below to significantly above critical thicknesses previously reported for this system. HRXRD observations demonstrate a high degree of coherency in the as-grown structures, since measurements of the lattice constant parallel to the sample surface (a\u2225) consistently yield the value for the (100) Si substrate. HRXRD from (004) planes used to measure a\u22a5 typically yield a spectrum with several peaks for growths in excess of the critical thickness and single peaks for those below the critical thickness. The high degree of coherency observed in these samples suggests that chemical segregation is responsible for the observed x-ray peaks.
\r\n\r\nIn Chapter 5, the surfaces of Si1-xGex alloys are studied using reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED) techniques. Si1-xGex films are grown on Si (100) substrates by MBE at temperatures between approximately 230 and 550\u00b0C, with alloy compositions ranging from x = 0.11-0.30. RHEED and LEED patterns from samples within this compositional range and at temperatures between 350\u00b0C and 550\u00b0C exhibit the usual Si-like (2 x 1) surface reconstruction patterns modified by the appearance of new, n/8-order diffracted beams. The n/8-order beams are observed for both coherently strained and unstrained films. Upon annealing and recooling, they appear to degrade reversibly within the temperature range 600-700\u00b0C. The additional fractional orders are interpreted as an 8-fold-periodic modulation in electron scattering factor, which is due to spatial correlation (ordering) of Ge atoms along the dimer chains of a (2 x 1) surface reconstruction. Possible physical origins of the Ge odering are discussed.
\r\n\r\nA study of the growth parameters governing the nucleation of metastable superconducting A15 V3Si on Si and Al2O3 is presented in Chapter 6. Nominally, 500\u00c5 films of V1-xSix are produced through codeposition of V and Si onto heated (111) Si and 1102 Al2O3 substrates. Samples are prepared in a custom-built UHV chamber containing dual a-beam evaporation sources and a high-temperature substrate heater. V and Si fluxes are adjusted to result in the desired average film composition. V0.75Si0.25 films prepared at temperatures in excess of 550\u00b0C on Si show significant reaction with the substrate and are nonsuperconducting, while similar films grown on l2O3 exhibit superconducting transition temperatures (Tc) approaching bulk values for V3Si (16.6 - 17.1 K). Codeposition at temperatures between 350 and 550\u00b0C results in superconducting films on Si substrates, while growth at lower temperatures results in nonsuper-conducting films. Lowering the growth temperature to 400\u00b0C is shown through ex situ TEM and Auger compositional profiling to minimize the reaction with the Si substrate while still activating the surface-migration processes needed to nucleate A15 V3Si. Variation of film composition about x = 0.25 is shown to result in nonsuperconducting films for high x and superconducting films with Tc approaching the bulk V value (5.4K) for low x. Finally, lowering the V0.75Si0.25 deposition rate is shown to raise Tc.
\r\n\r\nIn Chapter 7, we present an electrical characterization of the first p-Si1-xGex/n-Si HIT diodes. Equilibrium band-bending calculations are used to predict qualitatively an enhancement of NDR as a function of Ge concentration in the Si1-xGex alloy layers. Experimentally, measurements of I-V curves from HIT diodes compared with a Si interband-tunnel diode confirm the enhancement effect. Finally, differentiation of the current-voltage relationship through the use of inelastic electron tunnelling spectroscopy (LETS) reveals previously unobserved phonon peaks in the HIT diodes. The possible origin of these features is discussed.
\r\n" }, { "name": "DeWeerth, Stephen Paul", "degree": "PhD", "year": "1991", "title": "Analog VLSI Circuits for Sensorimotor Feedback", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-06212007-074949", "creators": [ { "name": { "family": "DeWeerth", "given": "Stephen Paul" }, "id": "DeWeerth-Stephen-Paul", "display_name": "DeWeerth, Stephen Paul" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Bower", "given": "James M." }, "id": "Bower-J-M", "role": "member", "display_name": "Bower, James M." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "cns" ], "doi": "10.7907/vvye-b883", "abstract": "This thesis presents a design framework and circuit implementations for integrating sensory and motor processing onto very large-scale integrated (VLSI) chips. The designs consist of analog circuits that are composed of bipolar and subthreshold MOS transistors. The primary emphasis in this work is the transformation from the spatially-encoded representation found in sensory images to a scalar representation that is useful for controlling motor systems.\r\n\r\nThe thesis begins with a discussion of the aggregation of sensory signals and the resulting extraction of high-level features from sensory images. An integrated circuit that computes the centroid of a visual image is presented. A theoretical analysis of the function of this circuit in stimulus localization and a detailed error analysis are also presented. Next, the control of motors using pulse trains is discussed. Pulse-generating circuits for use in bidirectional motor control and the implementation of traditional control schemes are presented. A method for analyzing the operation of these controllers is also discussed. Finally, a framework for the combination of sensory aggregation and pulse-encoded outputs is presented. The need for signal normalization and circuits to perform this task are discussed. Two complete sensorimotor feedback systems are presented." }, { "name": "Dumas, Guy", "degree": "PhD", "year": "1991", "title": "Study of spherical couette flow via 3-D spectral simulations: large and narrow-gap flows and their transitions", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-04162004-103555", "creators": [ { "name": { "family": "Dumas", "given": "Guy" }, "id": "Dumas-G", "display_name": "Dumas, Guy" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z6DW-4T51", "abstract": "Incompressible, viscous flows in the spherical gap between a rotating inner-sphere and a stationary outer-shell, Spherical Couette Flows (SCF), are studied via direct numerical simulations. The investigation covers both \"small-gap\" and \"large-gap\" geometries, and is concerned primarily with the first occurrence of transition in those flows. Strong emphasis is put on the physical understanding of the basic flows and their transition mechanisms.\n\nAn alias-free spectral method, based on divergence-free vector expansions for the 3-D velocity field in spherical coordinates, is developed. The vector expansions are constructed with Chebyshev polynomials in the radial direction and Vector Spherical Harmonics for the two angular directions. Accuracy and spectral convergence of the resulting initial-value code are thoroughly tested. Three-dimensional transitional flows in both narrow-gaps and large-gaps as well as axisymmetric transitions in moderate-gaps are simulated.\n\nFor small-gap SCF's, this study shows that the formation of Taylor-vortices at transition is a deterministic process and not the result of the instability of initial perturbations. The formation process involves the sub-critical appearance of a saddle-stagnation point within the meridional circulation cell in each hemisphere. A minimum length-scale ratio is shown necessary, and for a given inner-sphere radius, this leads to a theoretical prediction of the largest gap-width in which Taylor-vortices may form.\n\nThis investigation confirms that the first transition in large-gap SCF's is caused by a 3-D instability of a linear nature. It is found that the process is characterized by very small growth-rates of the disturbance and by the absence of a \"jump\" in the friction torque. The supercritical flow is a complex-structured, laminar, time-periodic flow that exhibits traveling azimuthal-waves. The physical mechanism responsible for the large-gap transition is shown to be related to a shear instability of the \"radial-azimuthal jet\" that develops at the equator of the basic flow. A physical model is proposed in which that jet is viewed as a sequence of adjacent \"fan-spreading quasi-2-D plane jets\". Predictions from the model are presented and verified from the computed unstable disturbance field. Extension of the model to the transition toward waviness in the Taylor-Couette flow, the Gortler-vortex flow and the Dean-vortex flow is proposed." }, { "name": "Dyer, Lounette M.", "degree": "PhD", "year": "1991", "title": "An Object-Oriented Real-Time Simulation of Music Performance Using Interactive Control", "advisor": "Barr, Alan H.; Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-08102006-081706", "creators": [ { "name": { "family": "Dyer", "given": "Lounette M." }, "id": "Dyer-LLounette-M", "display_name": "Dyer, Lounette M." } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Mathews", "given": "Jon" }, "id": "Mathews-J", "role": "member", "display_name": "Mathews, Jon" } ], "option_major": [ "compsci" ], "doi": "10.7907/cy26-vp85", "abstract": "This thesis presents a software architecture for interactive control of real-time music performance by sound synthesizers. The architecture is based on a model of a real world orchestra performance. An object-oriented paradigm is used to define objects that are one-to-one with the real world entities: a conductor, performers, instruments, a score, and parts. Methods are defined for the objects to simulate some of the dynamic behavior of the conductor and performers during the performance. A detailed design of each of the objects is presented, and the objects and their real world counterparts are compared. An abstract digital music representation is defined to represent the musical composition that is to be performed by the system. The device independence of the representation is highlighted. A real-time control mechanism is described that allows a human user to control various aspects of the performance in musically expressive ways. The model is implemented in a system called ZED, which has been shown to simulate some of the dynamic behavior of a live orchestra. Issues concerning the trade-off between runtime efficiency and runtime flexibility are addressed in detail, as well as how these issues affect real-time scheduling. Optimization techniques are presented that help insure timeliness. ZED provides two levels of programmability: the orchestration of a score and the interpretation of real-time inputs can be defined in a configuration file; and new methods and subclasses can be added to the system to provide new functionality. The architecture, coupled with the object-oriented features of inheritance and encapsulation, are shown to provide the system with flexibility and extensibility, making ZED an ideal platform for developing and evolving real-time interactive control applications." }, { "name": "Elliott, Alexander H.", "degree": "PhD", "year": "1991", "title": "Transfer of solutes into and out of streambeds", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07092007-074127", "creators": [ { "name": { "family": "Elliott", "given": "Alexander H." }, "id": "Elliott-A-H", "display_name": "Elliott, Alexander H." } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Koh", "given": "Robert C. Y." }, "id": "Koh-R-C-Y", "role": "member", "display_name": "Koh, Robert C. Y." }, { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "member", "display_name": "Vanoni, Vito A." } ], "option_major": [ "envreng" ], "doi": "10.7907/JBTC-ZX91", "abstract": "Laboratory experiments were conducted to determine the mechanisms and rates of bed/stream exchange of non-reactive solutes for beds of medium and fine sand. Experiments were conducted under steady flow conditions with and without sediment transport in a recirculating flume. Flat beds and beds covered with ripples or triangular bedforms were studied. The net mass exchange was determined by measuring concentration changes in the main flow. The penetration of the solute (fluorescent dye) into the bed was also observed visually.\r\n\r\nTwo key exchange mechanisms, 'pumping' and 'turnover', were identified. Pumping is the movement of pore water into and out of the bed due to flows induced by pressure variations over bedforms (ripples and dunes). Turnover occurs as moving bedforms trap and release interstitial fluid.\r\n\r\nPredictive models based on the details of the exchange processes were developed. A residence time distribution approach was used. The models do not require calibration. Appropriate scaling variables were identified.\r\n\r\nWith stationary bedforms the exchange is strongly influenced by pumping. The predictions of net mass exchange based on models of pumping with periodic bedforms show good agreement with the measured exchange in the initial stages of the experiments (hours to days). The models under-predict the exchange later in the experiments. The deviation is associated with the large-scale and somewhat random features in the penetration of the dye cloud. Such features are expected to influence the net exchange for large time in natural streams.\r\n\r\nWhen the bedforms move slowly in relation to the characteristic pore water velocity, turnover can be neglected and pumping dominates. A model based on a random distribution of bedform sizes provides a good prediction of the mass exchange with slowly-moving bedforms.\r\n\r\nWith rapidly-moving bedforms, turnover dominates the exchange at the start of the experiments, when the solute penetration is limited to the maximum bedform scour depth. The scour depth can be predicted well. Later the depth of penetration is greater than the scour depth and the model predictions." }, { "name": "Erlanson, Ruth A.", "degree": "PhD", "year": "1991", "title": "Soft-decision decoding of a family of nonlinear codes using a neural network", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06252007-080630", "creators": [ { "name": { "family": "Erlanson", "given": "Ruth A." }, "id": "Erlanson-R-A", "display_name": "Erlanson, Ruth A." } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "chair", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/c855-aj24", "abstract": "We demonstrate the use of a continuous Hopfield neural network as a K-WinnerTake-All (KWTA) network. We prove that, given an input of N real numbers, such a network will converge to a vector of K positive one components and (N-K) negative one components, with the positive positions indicating the K largest input components. In addition, we show that the [(N K)] such vectors are the only stable states of the system. \n\nOne application of the KWTA network is the analog decoding of error-correcting codes. We prove that the KWTA network performs optimal decoding.\n\nWe consider decoders that are networks with nodes in overlapping, randomly placed KWTA constraints and discuss characteristics of the resulting codes.\n\nWe present two families of decoders constructed by overlapping KWTA constraints in a structured fashion on the nodes of a neural network. We analyze the performance of these decoders in terms of error rate, and discuss code minimum distance and information rate. We observe that these decoders perform near-optimal, soft-decision decoding on a class of nonlinear codes. We present a gain schedule that results in improved decoder performance in terms of error rate.\n\nWe present a general algorithm for determining the minimum distance of codes defined by the stable states of neural networks with nodes in overlapping KWTA constraints.\n\nWe consider the feasibility of embedding these neural network decoders in VLSI technologies and show that decoders of reasonable size could be implemented on a single integrated circuit. We also analyze the scaling of such implementations with decoder size and complexity.\n\nFinally, we present an algorithm, based on the random coding theorem, to communicate an array of bits over a distributed communication network of simple processors connected by a common noisy bus." }, { "name": "Fried, Eliot", "degree": "PhD", "year": "1991", "title": "Aspects of the morphological character and stability of two-phase states in non-elliptic solids", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01302007-160351", "creators": [ { "name": { "family": "Fried", "given": "Eliot" }, "id": "Fried-E", "display_name": "Fried, Eliot" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Christman", "given": "Tom" }, "id": "Christman-T", "role": "member", "display_name": "Christman, Tom" } ], "option_major": [ "mecheng" ], "doi": "10.7907/WJKM-GB39", "abstract": "Part I. This work focuses on the construction of equilibrated two-phase antiplane shear deformations of a non-elliptic isotropic and incompressible hyperelastic material. It is shown that this material can sustain metastable two-phase equilibria which are neither piecewise homogeneous nor axisymmetric, but, rather, involve non-planar interfaces which completely segregate inhomogeneously deformed material in distinct elliptic phases. These results are obtained by studying a constrained boundary value problem involving an interface across which the deformation gradient jumps. The boundary value problem is recast as an integral equation and conditions on the interface sufficient to guarantee the existence of a solution to this equation are obtained. The contraints, which enforce the segregation of material in the two elliptic phases, are then studied. Sufficient conditions for their satisfaction are also secured. These involve additional restrictions on the interface across which the deformation gradient jumps-which, with all restrictions satisfied, constitutes a phase boundary. An uncountably infinite number of such phase boundaries are shown to exist. It is demonstrated that, for each of these, there exists a solution - unique up to an additive constant - for the constrained boundary value problem. As an illustration, approximate solutions which correspond to a particular class of phase boundaries are then constructed. Finally, the kinetics and stability of an arbitrary element within this class of phase boundaries are analyzed in the context of a quasistatic motion.\n\nPart II. This work investigates the linear stability of an antiplane shear motion which involves a planar phase boundary in an arbitrary element of a wide class of non-elliptic generalized neo-Hookean materials which have two distinct elliptic phases. It is shown, via a normal mode analysis, that, in the absence of inertial effects, such a process is linearly unstable with respect to a large class of disturbances if and only if the kinetic response function - a constitutively supplied entity which gives the normal velocity of a phase boundary in terms of the driving traction which acts on it or vice versa - is locally decreasing as a function of the appropriate argument. An alternate analysis, in which the linear stability problem is recast as a functional equation for the interface position, allows the interface to be tracked subsequent to perturbation. A particular choice of the initial disturbance is used to show that, in the case of an unstable response, the morphological character of the phase boundary evolves to qualitatively resemble the plate-like structures which are found in displacive solid-solid phase transformations. In the presence of inertial effects a combination of normal mode and energy analyses are used to show that the condition which is necessary and sufficient for instability with respect to the relevant class of perturbations in the absence of inertia remains necessary for the entire class of perturbations and sufficient for all but a very special, and physically unrealistic, subclass of these perturbations. The linear stability of the relevant process depends, therefore, entirely upon the transformation kinetics intrinsic to the kinetic response function.\n\nPart III. This investigation is directed toward understanding the role of coupled mechanical and thermal effects in the linear stability of an isothermal antiplane shear motion which involves a single planar phase boundary in a non-elliptic thermoelastic material which has multiple elliptic phases. When the relevant process is static - so that the phase boundary does not move prior to the imposition of the disturbance - it is shown to be linearly stable. However, when the process involves a steadily propagating phase boundary it may be linearly unstable. Various conditions sufficient to guarantee the linear instability of the process are obtained. These conditions depend on the monotonicity of the kinetic response function - a constitutively supplied entity which relates the driving traction acting on a phase boundary to the local absolute temperature and the normal velocity of the phase boundary - and, in certain cases, on the spectrum of wave-numbers associated with the perturbation to which the process is subjected. Inertia is found to play an insignificant role in the qualitative features of the aforementioned sufficient conditions. It is shown, in particular, that instability can arise even when the normal velocity of the phase boundary is an increasing function of the driving traction if the temperature dependence in the kinetic response function is of a suitable nature. Significantly, the instability which is present in this setting occurs only in the long waves of the Fourier decomposition of the moving phase boundary, implying that the interface prefers to be highly wrinkled." }, { "name": "Gilbrech, Richard Joseph", "degree": "PhD", "year": "1991", "title": "An experimental investigation of chemically-reacting, gas-phase turbulent jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06272007-091419", "creators": [ { "name": { "family": "Gilbrech", "given": "Richard Joseph" }, "id": "Gilbrech-R-J", "display_name": "Gilbrech, Richard Joseph" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/p80s-h321", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nA new high pressure combustion facility was built to investigate mixing in axisymmetric, turbulent jets exiting into quiescent reservoirs. The facility uses fluorine and nitric oxide, diluted with nitrogen, for chemical product formation that is accompanied by heat release. The average temperature was measured by a set of long, thin, resistance wire thermometers stretched across the jet centerline at 16 downstream locations from x/d[subscript 0] = 30 to 240. Runs at several stoichiometric mixture ratios [phi], for Reynolds numbers ranging from 10,000 [...] Re [...] 150,000, were performed to determine any dependence of flame length on Reynolds number. The Reynolds number was varied through density, i.e., pressure, while the jet exit velocity and exit diameter were held constant. The time-averaged line integral of temperature, measured along the transverse axis of the jet by the wires, displays a logarithmic dependence on x/d* within the flame zone, and asymptotes to a constant value beyond the flame tip, as predicted from scaling and similarity arguments for a momentum-dominated, turbulent jet. The main result of the work is that the flame length, as estimated from the temperature measurements, varies with changes in Reynolds number, suggesting that the mixing process is not Reynolds number independent up to Re = 150,000. Specifically, the normalized flame length Lf/d* displays a linear dependence on [phi], with a slope that decreases from Re = 10,000 to 20,000, and then remains constant for Re > 20,000. Additionally, the measurements revealed a \"mixing virtual origin,\" defined as the far-field flame length extrapolated to [phi] = 0, that increases with increasing Re for Re [...]20,000 and then decreases with increasing Re for Re > 20, 000. A separate set of experiments indicated that the runs described above were momentum dominated to the farthest measuring station and that the kinetics of the chemical reactions were fast compared to the characteristic mixing time. The transition of the jet flow from a momentum- dominated to a buoyancy-dominated regime was identified in another set of experiments." }, { "name": "Gupta, Rajiv", "degree": "PhD", "year": "1991", "title": "Compiler Optimization of Data Storage", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-06272007-081805", "creators": [ { "name": { "family": "Gupta", "given": "Rajiv" }, "id": "Gupta-Rajiv", "display_name": "Gupta, Rajiv" } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/E8DD-VG68", "abstract": "The system efficiency and throughput of most architectures are critically dependent on the ability of the memory subsystem to satisfy data operand accesses. This ability is in turn dependent on the distribution or layout of the data relative to the access of the data by the executing code. Page faults, cache misses, truncated vectors, global communication, for example, are expensive but common symptoms of data and access misalignment.
\r\n\r\nCompiler optimization, traditionally synonymous with code optimization, has addressed the issue of efficient data access by manipulating the code to better access the data under a fixed, default distribution. This approach is restrictive, and often suboptimal. Data optimization, or data-layout optimization, is presented as an integral part of compiler optimization.
\r\n\r\nFor scalar data, a good compile-time approximation of the \"reference string,\" or sequence of data accesses, is advanced for the purpose of distributing the data. However, the optimal distribution of the scalar data for such, or any, reference string is proved NP-complete. A methodology and a polynomial algorithm for an approximate solution are developed. Experiments with representative, but scaled, scientific programs and execution environments display a reduction in cache misses up to two orders in magnitude.
\r\n\r\nFor array data, compile-time predictions of the patterns in which the data is accessed by programs in scalar and array languages are examined. For arbitrary computations in an array language, the determination of the optimal layout of the data is proved to be NP-complete. Polynomial techniques for the approximate solutions to the optimal layout of arrays in both languages, scalar and array, are outlined.
\r\n\r\nThe general applicability of the techniques, in terms of environments other than hierarchical memories, and in terms of interdependence with code manipulations, is discussed. New code optimizations inspired by the data distribution techniques are motivated. The prudence of compiler- over user-optimized data distribution is argued.
" }, { "name": "Hall, Jeffery Lawrence", "degree": "PhD", "year": "1991", "title": "An experimental investigation of structure, mixing and combustion in compressible turbulent shear layers", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232005-141544", "creators": [ { "name": { "family": "Hall", "given": "Jeffery Lawrence" }, "id": "Hall-J-L", "display_name": "Hall, Jeffery Lawrence" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T0MN-J472", "abstract": "Two-dimensional, compressible, turbulent shear layers are studied in a new wind tunnel facility. Both reacting and non-reacting flows are investigated, with one free stream velocity supersonic and the other subsonic. The combustion experiments are based on the use of low concentrations of hydrogen, nitric oxide and fluorine gases. Side-view Schlieren photographs of these reacting and non-reacting flows appear devoid of the two-dimensional, large-scale structures seen in incompressible flows. Comparison with all-subsonic flows produced in the same facility suggests that this lack of two-dimensional structure is due to the presence of the supersonic high-speed free stream velocity. Travelling shock and expansion waves are observed in the high compressibility flows, evidently created by turbulent structures convecting at supersonic velocities. Such waves are seen only in the low-speed fluid, with apparent convection velocities much higher than those predicted on the basis of isentropic pressure-matching arguments. The measured shear layer growth rates agree with previous results by other experimenters, except for a few cases at low compressibility and low density ratio. The fast chemistry regime is attained in some of the high compressibility flows tested. \"Flip\" experiments conducted in this regime indicate that the volume fraction of mixed fluid in the layer is substantially reduced as compared to previous incompressible results. These same flip experiments also reveal that compressibility significantly alters the entrainment ratio. Finally, it is observed that the shear layer growth rate is relatively insensitive to incident shock /expansion waves and significant heat release inside the shear layer." }, { "name": "Hobson, Dana Daniel", "degree": "PhD", "year": "1991", "title": "Point Vortex Models for Modon Dynamics", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06222007-142041", "creators": [ { "name": { "family": "Hobson", "given": "Dana Daniel" }, "id": "Hobson-Dana-Daniel", "display_name": "Hobson, Dana Daniel" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/69f0-gs44", "abstract": "We study the dynamics of modons in the Charney-Hasegawa-Mima equation using a point vortex model introduced by Zabusky and McWilliams. This model reduces the equation to a system of ordinary differential equations which facilitate systematic studies of several problems involving modons. These problems are relevant to the study of large-scale motions in the Earth's atmosphere as well as the study of microturbulence in tokamak plasmas. We study the possible motions of an isolated modon using the model and show by direct numerical simulation that these motions compare very well with those of actual modons. As a by-product, we discover that the path of a left-moving (westward) modon is actually unstable to small perturbations in its position or orientation. This points out that a modon may be unstable in the path sense even if it is stable in the Lyapunov sense, as was shown for left-moving modons by Laedke and Spatschek. We use the flow field generated by the model to study the flow of fluid around an isolated modom. We show that the separatrices enclosing a modon in uniform motion break and tangle in the fashion described by Poincare when the motion is nonuniform. This is established analytically by computation of a Melnikov integral and numerically by plotting invariant manifolds of stagnation points in the flow. In contrast to past assumption, we find that significant mixing occurs between the modon and the external flow when the modon is not in uniform motion. So, at least on long timescales, modons do not serve as complete atmospheric blocks. Finally, we apply the model to the study of coaxial collisions between two modons. This results in a problem for the motion of four point vortices similar to that considered by Love for point vortices in the Euler equations. The relative behavior of the two modons is described completely by a planar Hamiltonian system which we study in detail. We find a wide variety of possible interactions between the two modons and note several behaviors not previously observed in numerical simulations. An effort is made to relate these results to the fluid inside a tokamak which may contain many such modons with frequent collisions.\r\n" }, { "name": "Hudson, Raymond Scott", "degree": "PhD", "year": "1991", "title": "Radar imaging for aircraft identification and planetary astronomy", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-06242005-160651", "creators": [ { "name": { "family": "Hudson", "given": "Raymond Scott" }, "id": "Hudson-R-S", "display_name": "Hudson, Raymond Scott" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/cf3k-sv32", "abstract": "The potential for identifying aircraft using one-dimensional radar range profiles in conjunction with a bank of correlation filters is investigated. Filters which maximize the expected value of the correlation with a target's profiles are derived, and an algorithm for computing them is presented. The algorithm is used on an extensive set of real aircraft profiles, and target identification experiments are performed. It is found that an averaging of identifications of several profiles is required to achieve reliable identification.\n \nThe use of multiple radar range profiles to form two-dimensional images through the techniques of inverse synthetic aperture radar (ISAR) is explored. Particular attention is given to the blurring which can arise when the target aspect does not vary linearly with time. An iterative algorithm for estimating target motion is developed which allows well-focused images to be formed in these cases. It is applied to simulated data and to an acoustic imaging experiment.\n\nA technique for forming two-dimensional radar images of a spherical planetary surface using one-dimensional Doppler spectra is developed. Simulations are used to explore the technique's effectiveness and robustness. It is then applied to real data from Jupiter's moons Ganymede and Callisto, and to Mars.\n" }, { "name": "Jackson, Michael Kevin", "degree": "PhD", "year": "1991", "title": "Optical studies of semiconductor heterostructures: measurements of tunneling times, and studies of strained superlattices", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07022007-134108", "creators": [ { "name": { "family": "Jackson", "given": "Michael Kevin" }, "id": "Jackson-Michael-Kevin", "display_name": "Jackson, Michael Kevin" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Miles", "given": "Richard Henry" }, "id": "Miles-R-H", "role": "member", "display_name": "Miles, Richard Henry" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/2c3x-qn71", "abstract": "This thesis describes experimental studies of semiconductor heterostructures, using optical techniques. The work presented concerns two topics in the study of semiconductor heterostructures: the escape of confined electrons and holes by tunneling, and the accommodation of lattice mismatch by strain. Time-resolved photoluminescence techniques have been used to measure the times required for electrons and holes to escape by tunneling through the A1As barriers of GaAs/A1As/GaAs/A1As/GaAs double barrier heterostructures. The effect of the indirect (X-point) levels in the AlAs barriers upon escape of confined electrons has been investigated using continuous (CW) photoluminescence. Time-resolved studies of electrically biased double-barrier heterostructures have been made, using both photoluminescence and photocurrent techniques. Finally, the accommodation of the large (6%) lattice mismatch in CdTe/ZnTe superlattices has been studied using Raman scattering.\r\n\r\nIn Chapter 2 we describe the measurement of tunneling escape times for electrons and holes confined in the quantum well of undoped GaAs/A1As/GaAs/A1As/GaAs double-barrier heterostructures. Photoluminescence from carriers photoexcited in the quantum well by short optical pulses was used to study escape from the quantum well. By using the two-beam technique of photoluminescence excitation correlation spectroscopy (PECS), the first experimental measurements of the tunneling escape times for both the electrons and the holes were obtained. The tunneling escape times were seen to be exponentially dependent upon the barrier thickness for barriers between 16 and 34 A. Escape times for both electrons and holes were found to be fast, and were as short as 12 ps in structures with 16 A (6 monolayer) A1As barriers. The rapid escape of heavy holes that was observed experimentally was in disagreement with simple calculations of the heavy-hole tunneling escape times, which indicated that the heavy holes should escape on a time scale many orders of magnitude longer than the times observed experimentally. This drastic difference can be explained theoretically by considering a four-band model for holes in confined systems. For finite carrier densities and temperatures, mixing of the quantum well heavy hole levels with light hole levels, due to dispersion perpendicular to the growth direction, can explain the experimental observations. This observation that heavy holes can escape rapidly by tunneling is quite general, and is applicable to a wide variety of problems involving tunneling of holes in semiconductor heterostructures.\r\n\r\nChapter 3 describes a study of the effect of indirect (X-point) levels in the A1As barriers on the tunneling escape of electrons in undoped GaAs/AlAs/GaAs/AlAs/GaAs double-barrier heterostructures. The X-point levels, thought to be important in the electrical characteristics of double-barrier heterostructures, were found to affect the escape of photoexcited electrons in devices where the energy of the electron state confined in the GaAs quantum well is nearly equal to, or higher than, that of the X-point levels in the AlAs barriers.\r\n\r\nIn Chapter 4, we present time-resolved photoluminescence and photocurrent studies of tunneling in doped devices under electrical bias, in which current is flowing. Studies of the photoluminescence decay indicate that significant transport of photoexcited carriers from the electrodes into the quantum well occurs. This transport of photoexcited carriers constitutes a photocurrent, and the two-beam PECS technique for photoluminescence has been extended to a study of photocurrents in these devices. This technique may be useful for the study of tunneling in devices not amenable to photoluminescence techniques.\r\n\r\nChapter 5 describes a study of the accommodation of lattice mismatch in CdTe/ZnTe strained layer superlattices. Using resonance Raman scattering, the energies of the ZnTe-like phonons were determined in a series of superlattices of varying average CdTe content. The ZnTe-like phonon energies decrease with increasing average CdTe content, indicative of the increasing strain of the ZnTe layers. The observed energies agree well with calculations of the strain shift of the phonons. The results indicate that the superlattice layers adopt a lattice constant independent of the buffer layer on which they are grown, and are coherently strained to a lattice constant that minimizes the strain energy of the superlattice.\r\n\r\nFinally, the Appendix describes operation of the colliding pulse mode-locked (CPM) dye laser used in the time-resolved photoluminescence and photocurrent experiments. Alignment of the laser, and routine operation are documented.\r\n" }, { "name": "Katafygiotis, Lambros Solon", "degree": "PhD", "year": "1991", "title": "Treatment of Model Uncertainties in Structural Dynamics", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04252011-102457629", "creators": [ { "name": { "family": "Katafygiotis", "given": "Lambros Solon" }, "id": "Katafygiotis-Lambros-Solon", "display_name": "Katafygiotis, Lambros Solon" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/6s88-dn31", "abstract": "The uncertainties related to the modeling of the dynamic behavior of a structure are analyzed using a probabilistic approach.
\r\n\r\nFirst, the case of preliminary design is addressed, where the structure has not yet been built. A new efficient and accurate numerical method is proposed to investigate the resulting uncertainties in the structural response due to uncertainties in the modeling process, where engineering judgement is used to quantify the latter uncertainties.
\r\n\r\nSecond, the case where records of measured structural response are available to reduce the uncertainties in the structural models is addressed. The posterior probability distribution of the uncertain parameters is found to be very peaked at the values of some optimal parameters. These optimal parameters can be obtained by minimizing a positive-definite measure-of-fit function. A new efficient minimization algorithm is proposed to resolve difficulties in convergence of existing methods. The identifiability of the optimal parameters is also addressed. The problem of finding the whole set of the optimal models that have the same output at the observed degrees of freedom is resolved for the first time, by presenting an algorithm which methodically and efficiently searches the parameter space.
" }, { "name": "Kittl, Jorge A.", "degree": "PhD", "year": "1991", "title": "Growth and characterization of Y-BA-CU-O high-Tc superconductor thin films", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-06222007-150332", "creators": [ { "name": { "family": "Kittl", "given": "Jorge A." }, "id": "Kittl-J-A", "display_name": "Kittl, Jorge A." } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/918E-BJ98", "abstract": "Two types of growth processes of Y-Ba-Cu-O thin films were investigated: three step processes involving post deposition high temperature anneals, and in situ growth processes. Films were deposited by sequential ion beam sputtering from elemental Y, Ba and Cu targets, and characterized by x-ray diffraction, transmission and scanning electron microscopy, energy dispersive x-ray analysis, Rutherford backscattering spectrometry, and low temperature resistivity measurements. In the three step process, multilayers of ~60 \u00c5 periodicity were deposited on (001) SrTiO3, annealed in oxygen at 850-900\u00b0C, and subsequently at 400-500\u00b0C, to obtain the superconducting YBa2Cu3O7-\u03b4 phase. The films were epitaxial, predominantly single phase YBa2Cu3O7-\u03b4, with different orientations. The nucleation and growth of Y-Ba-Cu-O films deposited on (001) SrTiO3 by magnetron sputtering from separate Y, BaF2 and Cu sources and grown by a three step process, was investigated by transmission electron microscopy. The in situ growth of YBa2Cu3O7-\u03b4 films by sequential ion beam sputtering was investigated. The films were deposited following the stacking sequence of YBa2Cu3O7-\u03b4, with the individual layer thicknesses nominally equal to one monolayer, at temperatures between 550 and 750\u00b0C. O2 was supplied during growth. Epitaxial, c-axis oriented YBa2Cu3O7-\u03b4 films were obtained on MgO and SrTiO3. The correlations between deposition parameters, and structural and electrical properties were investigated. The films had expanded c-axis lattice parameters. The superconducting transition temperatures decreased with the enlargement of the c-lattice parameter. The deposition temperature was the main parameter controlling the lattice expansion. This was later interpreted in terms of the thermally activated dissociation of O2 at the film surface. We proposed that the expansion of the c-lattice parameter was a consequence of kinetic limitations to the incorporation of oxygen into the films during growth. This led to a consistent description of the results obtained in this work, and results reported in the literature for other in situ growth techniques. The films also presented inhomogeneous lattice distortions along the c-direction, that were larger for films with large lattice parameters. The superconducting transitions were broader for films with large inhomogeneous strains. The microstructure of films grown on several substrates (SrTiO3, MgO, SiO2/Si) under different growth conditions was investigated.\r\n" }, { "name": "Koilpillai, Ravinder David", "degree": "PhD", "year": "1991", "title": "Design issues in multirate digital filter banks, including transmultiplexers", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06272007-082624", "creators": [ { "name": { "family": "Koilpillai", "given": "Ravinder David" }, "id": "Koilpillai-R-D", "display_name": "Koilpillai, Ravinder David" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/C6MF-3A43", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nSeveral aspects of the theory and design of FIR digital filter banks for analysis/synthesis systems are studied in this thesis. In particular, we focus on filter banks satisfying the perfect reconstruction (PR) property. We present a new approach to design PR filter banks wherein the filter bank is obtained by cosine-modulation of a linear-phase prototype filter of length N = 2mM, m [...] 1 (where M is the number of channels). The PR property is satisfied because the polyphase component matrix of the modulated filter bank is lossless. This is achieved by satisfying the necessary and sufficient condition - a pairwise power complementary property between the 2M polyphase components of the prototype. In this approach, regardless of the number of channels, we still design only the prototype. The design procedure involves the two-channel lossless lattice. This approach compares favorably (in terms of the number of parameters to be optimized and the ease of design) with other design techniques. Design examples and detailed comparisons are presented.\r\n\r\nThe existing approaches for designing PR filter banks include the lattice based methods, which structurally force the polyphase component matrix to be lossless. New initialization procedures, which can be used to initialize the values of all the lattice parameters (prior to optimization), are presented. The main advantage is that we can get 'good' initializations by using conventional Quadrature Mirror Filter (QMF) banks and pseudo-QMF banks (which can be readily designed, but do not satisfy PR). It is shown that these filter banks have polyphase component matrices that are 'approximately' lossless. The initialization also enables the design of a family of PR filter banks.\r\n\r\nIn conventional approaches to pseudo-QMF design, the prototype filter is obtained by optimization, wherein lies the main computational effort. We present a new approach in which the prototype of a M-channel filter bank is obtained by spectral factorization (of a 2Mth band filter), thereby eliminating the need for optimization. The overall transfer function T(z) has linear-phase and an approximate 'flat' magnitude response in the region [epsilon][...][omega][...] ([pi] - [epsilon] where [epsilon] depends on the transition bandwidth of the prototype [...]. A new spectral factorization algorithm (non-iterative) which is based on the Inverse Linear Predictive Coding (LPC) technique is presented. Design examples for the above method are obtained by using this algorithm.\r\n\r\nFinally, we consider a dual of the QMF circuit - the transmultiplexer (TMUX). Traditional TMUX designs suppress the undesirable crosstalk. The crosstalk-free transmultiplexer (CF-TMUX) focuses on crosstalk cancellation, rather that suppression. It is shown that the filters of a CF-TMUX are the same as the filters of a 1-skewed AF-QMF bank. In addition, if the QMF bank satisfies PR, then the TMUX also achieves PR." }, { "name": "Kramer, Kathleen A.", "degree": "PhD", "year": "1991", "title": "Large operand division and an asynchrous approach to fault detection", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06212007-143920", "creators": [ { "name": { "family": "Kramer", "given": "Kathleen A." }, "id": "Kramer-K-A", "display_name": "Kramer, Kathleen A." } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/pt8p-9g83", "abstract": "Larger, faster ICs are creating a rash of new problems for the system designer. Designers faced with building larger and larger systems base their architectures on smaller systems that may scale poorly. As a result of VLSI, many new architectures are coming into favor, either because of the changing importance of design factors or because it is now possible to design bigger chips.\n\nEfficient VLSI methods for implementing the basic arithmetic operations can push back many system-performance limitations. There is continued need for re-evaluation of arithmetic architectures, as the efficiency of implementation is related to both implementation technology and size of the operands. A new binary divider for n-bit integer operands, which produces the quotient and remainder in O(n) time using O(n) area, is presented. For very large operands, such as those required in Public Key Cryptography, the new divider is faster than comparable carry-save dividers and is more area-efficient than implementations using more redundant arithmetic.\n\nA further problem faced by the designer of very large systems is their susceptibility to error. The system must be efficiently designed to function in the presence of errors, which become more likely as the size of the system increases. Qualities inherent in many asynchronous designs can be used to provide fault detection and therefore, fault tolerance. An approach to fault tolerance, one not possible with conventional, clocked, systolic arrays, is presented. This method of fault detection/correction exploits the inherent redundancy of architectures using four-state coding, a data-driven technique for implementing bit-level wave-front arrays." }, { "name": "Krueger, Barry Robert", "degree": "PhD", "year": "1991", "title": "Shock-wave processing of powder mixtures", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-06222007-081112", "creators": [ { "name": { "family": "Krueger", "given": "Barry Robert" }, "id": "Krueger-B-R", "display_name": "Krueger, Barry Robert" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/f01e-9k60", "abstract": "The effects of shock waves on the initiation of exothermic chemical reactions in mixtures of powders is explored experimentally and compared to thermal initiation at atmospheric pressure in this thesis. A full understanding of shock initiated chemical reactions and shock compaction of composites requires knowledge of the Hugoniot of the mixture. A model for calculation of the shock Hugoniot of non-reacting solid or powder mixtures up to moderate pressures using only thermodynamic properties of the components is presented. In addition, conditions for the production of dense, bulk samples of a metallic glass from the metastable powder are determined.\r\n\r\nPrevious models for the Hugoniot of a mixture assume the components in the shock front are in mutual thermal equilibrium, and use measured or calculated Hugoniot data for the components. The model proposed in this thesis does not presuppose either the relative magnitude of the thermal and elastic energies or temperature equilibrium between the components. It assumes the components are at equal pressures and have equal particle velocities. For a mixture, it is shown that the conservation equations define a Hugoniot surface, and that the ratio of the thermal energy of the components determines where on that surface the shocked state of the mixture lies. This ratio, which may strongly affect shock initiated chemical reactions and the properties of consolidated mixtures, is found to have only a minor effect on the Hugoniot. It is also found that the Hugoniots of solids and solid mixtures are sensitive to the pressure derivative of the isentropic bulk modulii of the components at constant entropy.\r\n\r\nThe initiation of the reaction forming the compound NiSi from elemental powders by shock waves of varying energy and pressure and by thermal initiation at atmospheric pressure was investigated. Using plane wave shock geometry with well-defined shock pressure and energy, it was determined that a sharp energy threshold, between 384 and 396 J/g, exists for the initiation of the reaction (with 20 \u00b5m to 45 \u00b5m Ni and -325 mesh Si). The threshold energy range heats the powder mixture to a temperature between 631 and 648\u00b0 C (with no chemical reaction) after local thermal equilibration is achieved. The reaction goes to completion when the shock energy is above the threshold energy, and melting of the compound is indicated. Differential thermal analyses (DTA) of powder mixtures of Ni and Si (1:1 atomic ratio) at atmospheric pressure show the reaction starts at a temperature which depends upon the porosity of the mixture. Higher porosities give higher initiation temperatures. Reaction starts at about 900\u00b0 C in a mixture with 50% porosity and at about 650\u00b0 C in a sample statically pressed to 23% porosity. The sharp energy threshold for the initiation of the reaction, and the correlation with the shock temperature and the reaction initiation temperature in the DTA indicates that the homogeneous temperature determines whether or not the reaction occurs rather than local particle conditions of temperature or pressure as has been proposed in the literature.\r\n\r\nThe conditions for initiation and propagation of the reaction forming Ti5Si3 from elemental powders (5:3 atomic ratio) of varying porosity have been investigated using shock waves of different pressure in vacuum, and using hot wire ignition in an argon atmosphere. In powders with a high initial porosity, evacuated to 0.1 torr, a low energy regime (producing low shock pressures) triggers the reaction in the presence of residual oxygen while no reaction is observed with a 128% higher shock energy and a lower initial porosity (producing a higher shock pressure) in an inert residual gas. Hot wire ignition of porous powder at room temperature initiates a self-propagating high temperature reaction (SHS) in air or (less readily) in an Ar atmosphere, while the Ni/Si powder must be heated to allow the reaction to propagate in high or low porosity mixtures. These observations are compared to published work on self-sustaining reactions in multilayer films.\r\n" }, { "name": "Leyva, Victor", "degree": "PhD", "year": "1991", "title": "Investigations of the photorefractive effect in potassium tantalum niobate", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-081932", "creators": [ { "name": { "family": "Leyva", "given": "Victor" }, "id": "Leyva-Victor", "display_name": "Leyva, Victor" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/cayt-6896", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis describes results of investigations of the photorefractive effect in potassium tantalum niobate ([...]) crystals. A band transport model is used to describe the photorefractive effect. The coupled mode equations are then introduced and used to solve self-consistently for the interaction of the light and space charge fields in a photorefractive material. The design and construction of a high temperature crystal growth system is discussed. The growth of photorefractive KTN crystals doped with a variety of transition metal dopants using the top seeded solution growth method is described. Two applications in the areas of volume holography are described which take advantage of the unique ferroelectric properties of KTN. The first makes use of the quadratic electrooptic effect in paraelectric KTN to control the magnitude of a diffracted wave with an externally applied field. Full amplitude modulation at speeds much faster than the grating formation time demonstrated. The second application described is a procedure used to fix a holographic diffraction grating in KTN. It invovles the writing of a photorefractive grating in the paraelectric phase of KTN and cooling the sample under an applied field through successive phase transitions into the rhombohedral phase.\r\n\r\nMaterials investigations of the photorefractive effect are described. Investigations focused on the optimization of the photorefractive properties of IKTN by the control of the concentration and the valence state of the photorefractive donor ions both during and after the growth stage. Absorption, photoconductivity, and electron microprobe measurements are used to identify the photorefractive species and to determine all relevant parameters which enter into the band transport model in a KTN:CuV sample after a series of thermal oxidation and reduction treatments. Holographic diffraction measurements are compared with those expected from theory. The oxidation and reduction process is modelled. Approaches to optimize the photorefractive sensitivity are discussed. The photorefractive properties of Fe and Ti doped KTN samples are investigated. Absorption and photoconductivity measurements indicate that the double dopant combination of Fe and Ti leads to an increased [...] and total Fe concentrations as compared to single doped samples. A corresponding increase in photorefractive sensitivity is measured. The dependence of the photorefractive properties of Fe and Ti doped KTN on electric field, grating period, and temperature is characterized." }, { "name": "Miller, Paul Lewis", "degree": "PhD", "year": "1991", "title": "Mixing in high Schmidt number turbulent jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142005-152828", "creators": [ { "name": { "family": "Miller", "given": "Paul Lewis" }, "id": "Miller-P-L", "display_name": "Miller, Paul Lewis" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/PN2P-RK49", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis is an experimental investigation of the passive scalar (species concentration) field in the far-field of round, axisymmetric, high Schmidt number (liquid phase), turbulent jets issuing into a quiescent reservoir, by means of a quantitative laser-induced fluorescence technique. Single-point concentration measurements are made on the jet centerline, at axial locations from 100 to 305 nozzle diameters downstream, and Reynolds numbers of 3,000 to 102,000, yielding data with a resolved temporal dynamic range up to [...], and capturing as many as 504 large-scale structure passages. Long-time statistics of the jet concentration are found to converge slowly. Between 100 and 300 large-scale structure passages are required to reduce the uncertainty in the mean to 1%, or so. The behavior of the jet varies with Reynolds number. The centerline concentration pdf's become taller and narrower with increasing Re, and the normalized concentration variances correspondingly decrease with Re. The concentration power spectra also evolve with Re. The behavior of the spectral slopes is examined. No constant -1 (Batchelor) spectral slope range is present. Rather, in the viscous region, the power spectra exhibit log-normal behavior, over a range of scales exceeding a factor of 40, in some cases. The frequency of the beginning of this log-normal range scales like [...] (Kolmogorov scaling). Mixing in the far-field is found to be susceptible to initial conditions. Disturbances in the jet plenum fluid and near the nozzle exit strongly influence the scalar variance, with larger disturbances causing larger variances, i.e., less homogeneous mixing. The plenum/nozzle geometry also influences the variance. These effects of initial conditions persist for hundreds of diameters from the nozzle exit, over hundreds of large scales. Mixing in these jets differs from gas-phase, order unity Sc, jet mixing. At low to moderate Re, the higher Sc jet is less well mixed. The difference is less pronounced at higher Re. Flame length estimates imply either an increase in entrainment and/or an increase in molecular mixing, with increasing Re. Experimental considerations such as buoyancy and resolution are shown not to influence these results.\r\n" }, { "name": "Morehart, James Henry", "degree": "PhD", "year": "1991", "title": "Species Produced in Fires Burning in Two-Layered and Homogenous Vitiated Environments", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07032007-142951", "creators": [ { "name": { "family": "Morehart", "given": "James Henry" }, "id": "Morehart-James-Henry", "orcid": "0009-0007-3814-5159", "display_name": "Morehart, James Henry" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Serdengecti", "given": "Sedat" }, "id": "Serdengecti-Sedat", "role": "member", "display_name": "Serdengecti, Sedat" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9xja-9n92", "abstract": "The chemical species produced in a buoyant, turbulent diffusion flame exposed initially to a supply of fresh air and extending into a reduced-oxygen environment containing products of combustion are investigated. The stably stratified, vitiated region is formed by placing a hood above a burner so that it accumulates the gases of the fire plume, while the direct injection of air into the upper portion of the hood allows conditions to be studied where the stoichiometry of the collected gases is different than that of the plume flow crossing the interface between these two regions.\r\n\r\nMeasurements of the composition show that the species produced in the flame depend primarily on the stoichiometry of the gases in the vitiated region, but are independent of the fuel-air ratio of the mass transported across the interface by the plume. A weak dependence of species concentrations on the temperature of the product gas layer was observed over the range 500 to 900 K. Using a detailed chemical kinetics model, the composition of the product gases is found to be stable for the temperatures measured in the experiments, but reactions do occur at temperatures above 700 K.\r\n\r\nThe effects of varying the fuel's molecular structure on the product gas composition are also considered. Experiments were conducted with natural gas, ethylene, and propylene fuels. The presence of a double bond between carbon atoms appears to assist the combustion process towards further completion. As expected, the behavior of the propylene fuel (which contains both single and double carbon-carbon bonds) fell between that of the other fuels.\r\n\r\nAdditionally, the minimum oxygen concentration necessary to support a diffusion flame in a homogeneous, vitiated environment is investigated. By submerging the entire flame into the interior volume of the hood, the oxygen content of the supporting atmosphere is controlled. As conditions approach the limit of flammability, radiation from soot in the reaction zone becomes imperceptible, leaving only a weakly-luminous blue flame. Even with significant reductions in both the flame height and luminosity, these fires near the limiting conditions completely consume the fuel and generate no measurable amounts of incomplete combustion products." }, { "name": "Mudkavi, Vidyadhar Yogeshwar", "degree": "PhD", "year": "1991", "title": "Numerical studies of nonlinear axisymmetric waves on vortex filaments", "advisor": "Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07092007-105408", "creators": [ { "name": { "family": "Mudkavi", "given": "Vidyadhar Yogeshwar" }, "id": "Mudkavi-V-Y", "display_name": "Mudkavi, Vidyadhar Yogeshwar" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/TMK2-ME89", "abstract": "The equations of Moore and Saffman (1971) are examined and are shown to contain the fast time scale equations governing the core waves on a straight vortex filament. The equations so derived are the same as those reported by Lundgren and Ashurst (1989) except for a correction term that allows for variation of the axial velocity structure within the vortex core. Numerical solutions of the Moore and Saffman equations are presented for various initial conditions consisting of wave-like perturbations on a cylindrical vortex, and they all show development of a jump in the core area. This has been advanced to be a mechanism for vortex breakdown by Lundgren and Ashurst. A comparison of the solutions of the Moore and Saffman equations with the solutions of the Navier-Stokes equations at high Reynolds number is presented for three different cases. In the first case a vortex with a very small perturbation is considered. The Moore and Saffman solution shows steepening of the initial wave resulting in the development of jump in the core area (shock). The Navier-Stokes solution shows bulging of the core. But, there is no indication of formation of a shock. In the second case a vortex with moderate perturbation is considered. The Moore and Saffman solution leads to a shock similar to the weak perturbation case. As before, the Navier-Stokes solution does not develop jump in the core area. However, development of a bubble of reversed flow is seen. In the third case, a jump in the core area in the solutions of the Navier-Stokes equations is seen for a strongly perturbed vortex. But the location and the sense of jump disagrees with jump that develops in the Moore-Saffman solution. Thus, the solutions of the Navier-Stokes equations and the Moore-Saffman equations show qualitative disagreement.\r\n\r\nNext, an extension of steady Kelvin waves for two different types of vorticity profiles is considered. In the first case, steady nonlinear waves are constructed via a perturbation method. In this case, the vorticity is nonzero inside the core and sharply drops to zero across the boundary. The shape of the core boundary is determined as part of the problem. The dependence of the Bernoulli function and the circulation function on the streamfunction are specified. This serves as the additional constraint necessary to determine the solution uniquely. The solutions are free of any vortex sheets. In the second case, nonlinear steady Kelvin waves on smooth vorticity distributions are constructed by means of a direct Newton method and a large order perturbation method. Instead of specifying the dependence of the Bernoulli function and the circulation function on the stream function as in the previous case, the solutions are restricted such that they have the same axial mean as the base flow. In both the approaches, regions of reversed flow are observed. This is the structure of bubble type of vortex breakdown.\r\n\r\nNext, an analysis of the weakly nonlinear stability of a columnar vortex is presented. It is shown that the amplitude, assumed to vary slowly in time and space, satisfies a cubic-nonlinear Schrodinger equation. Solutions are found to be unstable in the sense that the perturbations grow slowly in time. Solitary wave solutions are possible in this unstable case.\r\n" }, { "name": "Mutz, Andrew Howard", "degree": "PhD", "year": "1991", "title": "Heterogeneous shock energy deposition in shock wave consolidation of metal powders", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-06282007-091349", "creators": [ { "name": { "family": "Mutz", "given": "Andrew Howard" }, "id": "Mutz-A-H", "display_name": "Mutz, Andrew Howard" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/makt-d357", "abstract": "Shock wave consolidation of powder is a high deformation rate process in which a shock wave generated by an explosive or a colliding projectile rapidly densifies and bonds together the powder particles into a solid compact. The deposition of the shock energy during this process is highly inhomogeneous on the powder particle scale. Evidence of the extent and pattern of the energy deposition was provided by recovery experiments performed using an initially crystalline alloy which solidifies to a metallic glass upon rapid quenching from the liquid state. The amount of metallic glass was measured and analyzed using a heat flow model. The energy deposited during the shock wave passage was best modeled as deposited partly into the particle bulk and partly onto particle surfaces. To investigate this inhomogeneity, and the powder parameters which influence it, a propellant driven gas gun was designed, built and utilized. The planarity of the shock waves produced using the targets designed for the gun was established. Powder-powder thermocouples were impacted with powders of varying sizes to establish the effect of particle size on energy deposition. Small particles in contact with large ones were inferred to absorb the greater fraction of shock energy. Hardened and unhardened steel powder was shocked to investigate the effect of particle hardness on energy distribution. The recovered compacts were not measurably affected by the initial hardness. Compaction experiments were performed on a Ni based super-alloy and on a SiC reinforced Ti matrix composite to test some of the practical applications of the process and the target designs developed. Superior tensile properties were observed in the shock consolidated and heat treated Ni based 718 alloy. The SiC reinforced composite was recovered in the intended net shape with no macro-cracks in the compact body, but with fractured SiC particles." }, { "name": "Neifeld, Mark A.", "degree": "PhD", "year": "1991", "title": "Optical memory disks in optical pattern recognition systems", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-073524", "creators": [ { "name": { "family": "Neifeld", "given": "Mark A." }, "id": "Neifeld-M-A", "display_name": "Neifeld, Mark A." } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5bbq-0q27", "abstract": "We describe the use of optical memory disks in optical pattern recognition systems. Algorithmic and architectural issues associated with the realization of such systems are discussed. Experimental demonstrations of several optical disk-based architectures are included to aid in the understanding of system limitations and performance issues. First we discuss correlation-based pattern recognition and describe the relationship between this approach and the neural paradigm. The need for invariances in image recognition leads to the notion of the reference image library. This approach is shown to be attractive in the case of limited processor and spatial light modulator dynamic range. We characterize the optical disk as a parallel readout device. An overview of optical storage media is included. Parallel readout of data from Sony sampled format media is characterized. We identify a match between the characteristics of the optical disk and the requirements for pattern recognition systems. Four optical disk-based image correlators which may serve as building blocks in disk-based pattern recognition systems are introduced. These image correlators are experimentally demonstrated and compared in terms of speed, efficiency, and sensitivity to noise sources and disk imperfections. We discuss advantages and limitations of these systems.\n\nWe include a discussion of learning and generalization in neural networks. We present a new learning algorithm and discuss its generalization characteristics. Three disk-based systems for pattern recognition are proposed. The first is a correlation-based architecture. The performance of this system as compared with theoretical expectations is encouraging; however, data rate constraints suggest the investigation of an alternate approach. The next two systems are more neurally inspired and realize the k-nearest neighbor and radial basis function algorithms. An evaluation of the performance of these two systems is presented with respect to the handwritten digit recognition problem.\n\nLastly, we present two candidates for future optoelectronic computing and pattern recognition systems. We detail the operation of these architectures and discuss the need for a better understanding of the relationship between mass memory and a general parallel processing environment." }, { "name": "Newkirk, Michael Avery", "degree": "PhD", "year": "1991", "title": "Investigations of semiconductor laser modulation dynamics and field fluctuations", "advisor": "Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07102007-112900", "creators": [ { "name": { "family": "Newkirk", "given": "Michael Avery" }, "id": "Newkirk-M-A", "display_name": "Newkirk, Michael Avery" } ], "advisors": [ { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/98ma-fx75", "abstract": "Active-layer photomixing is an optical modulation technique to probe the fundamental modulation response of a semiconductor laser. By heterodyning two laser sources with a tunable frequency difference in the device's active region, the gain, and hence the optical output, is modulated at the beat frequency of the sources. Using an equivalent circuit model for the laser diode, the optical modulation is shown to be decoupled from the electrical parasitics of the laser structure. The fundamental modulation response of the laser can thereby be studied independently of the parasitic response, which would otherwise mask the fundamental response. The photomixing technique is used on GaAs/GaAlAs lasers at room temperature, liquid nitrogen and liquid helium temperature, and it is verified that the modulation response appears ideal to millimeter-wave frequencies.\n\nApplication of the active-layer photomixing technique led to the discovery and explanation of a new effect called the \"gain lever.\" It enhances the modulation efficiency of a semiconductor laser with a quantum well active layer. By inhomogeneously pumping the device, regions with unequal differential gain are created. If the laser is above threshold, then the overall modal gain is clamped, and by modulating the section with larger differential gain, the output power can be modulated with greater than unity quantum efficiency.\n\nThe fundamental coupling between intensity noise and phase noise in semiconductor laser light is investigated. This coupling, described by the [alpha] parameter, causes the well-known linewidth enhancement, but also implies the fluctuations are correlated. By the technique of \"amplitude-phase decorrelation,\" the intensity noise can be passively reduced by the ratio 1/(1 + [alpha](2)). Using a Michelson interferometer as a frequency discriminator, intensity noise from a DFB laser is reduced below its intrinsic level up to a factor of 28.\n\nA balanced homodyne detection scheme is used to study the noise reduction in relation to the photon shot noise floor. The decorrelated intensity noise can be reduced to within a dB of the shot noise level. Reduction below shot noise may be inhibited by uncorrelated phase noise in the lasing mode." }, { "name": "Papadimitriou, Konstantinos", "degree": "PhD", "year": "1991", "title": "Stochastic Characterization of Strong Ground Motion and Applications to Structural Response", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04142011-154846507", "creators": [ { "name": { "family": "Papadimitriou", "given": "Konstantinos" }, "id": "Papadimitriou-Konstantinos", "orcid": "0000-0002-9792-0481", "display_name": "Papadimitriou, Konstantinos" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/Y124-M904", "abstract": "This study addresses the problem of characterizing strong ground motion for the purpose of computing the dynamic response of structures to earthquakes. A new probabilistic ground motion model is proposed which can act as an interface between ground motion prediction studies and structural response studies. The model is capable of capturing, with at most nine parameters, all those features of the ground acceleration history which have an important influence on the dynamic response of linear and nonlinear structures, including the amplitude and frequency content nonstationarities of the shaking. Using a Bayesian probabilistic framework, a simple and effective statistical method is developed for extracting the \"optimal\" model from an actual accelerogram. The proposed ground motion model can be efficiently applied in simulations as well as analytical response and reliability studies of linear and inelastic structures.
\r\n\r\nThe random response of linear and nonlinear oscillators subjected to the proposed stochastic excitation is considered. The nonlinearity of the oscillator is accounted for by equivalent linearization. A formulation is developed which approximates the original lengthy expressions for the second-moment statistics of the transient response by much simpler expressions. The results provide insight into the characteristics of the nonstationary response and the effect of the ground motion nonstationarities. It is found that the temporal nonstationarity in the frequency content of the ground motion significantly influences the response of both linear and nonlinear structural models. Simulations are also used to study the sensitivity of inelastic structural response parameters to the details of the ground motion which are left \"random\" by the model. The results can also be used to provide a quantitative assessment of the expected structural damage associated with the ground motion described by the model.
\r\n" }, { "name": "Paulson, Suzanne Elizabeth", "degree": "PhD", "year": "1991", "title": "Contributions of biogenic and anthropogenic hydrocarbons to photochemical smog formation", "advisor": "Seinfeld, John H.; Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-150535", "creators": [ { "name": { "family": "Paulson", "given": "Suzanne Elizabeth" }, "id": "Paulson-S-E", "display_name": "Paulson, Suzanne Elizabeth" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "co-advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/3cyt-0315", "abstract": "Photochemical oxidation of biogenic (Isoprene) and anthropogenic (1-octene) hydrocarbons are examined. Experiments studied the individual daylight reactions of both isoprene and 1-octene, including those of OH, O3, and O([superscript 3]P). Results from both the smog chamber experiments and computer kinetic modeling were then used to develop photochemical oxidation mechanisms for each hydrocarbon. Aerosols formed by isoprene and another biogenic, beta-pinene, are characterized.\n\nThe OH reaction with isoprene is studied. Methyl nitrite photolysis experiments were carried out in an outdoor smog chamber in an attempt to identify as completely as possible OH-isoprene product spectrum. Emphasis was placed on identification and quantification of oxygenated products. The design of a Tenax-based cryo-trap thermal desorber used to trap, concentrate, and dry chamber samples for identification on a GC/MS is described. Analysis of the products revealed that O([superscript 3]P) can form in reaction systems designed to study OH reactions that include high concentrations of NO, and consequently NO2, hence this reaction is also examined. The yields of methacrolein and methyl vinyl ketone are determined as 25\u00b13 and 35.5\u00b14%, respectively, with an additional 5.1\u00b13% as 3-methyl furan, totaling 66\u00b13%. These results, combined with those of previous studies-allow 80% of isoprene's products to be explicitly identified, and the general structure of the remaining products to be ascertained. The O([superscript 3]P) reaction produces 84\u00b18% epoxides, and 8\u00b13% species which result in production of HO2, and subsequently OH. A heretofore unidentified product of the O([superscript 3]P) reaction, 2,2 methyl butenal, is identified. The rate constant of the NO2-isoprene reaction is measured.\n\nA series of experiments have been carried out to study the ozone-isoprene reaction in a smog chamber using externally produced O3, added to the hydrocarbon in the dark. A chemical tracer, methyl cyclohexane, was added to probe the OH formation in the system. O([superscript 3]P) formation was also examined using the known distribution of products that are unique to the O([superscript 3]P)-isoprene reaction (part 1). The results provide clear evidence that both OH and O([superscript 3]P) are produced from the O3-isoprene reaction directly in large quantities; about 0.68\u00b10.15 and 0.45\u00b10.15 per O3 -isoprene reaction, respectively. These additional radicals severely complicate the analysis of the O3 reaction, hence computer kinetic modeling was necessary to ascertain the products of the O3 reaction itself. The product spectrum, which differs dramatically from that published previously, is: 67\u00b19% methacrolein, 26\u00b16% methyl vinyl ketone, and 7\u00b13% propene, accounting for 100\u00b110% of the reacted isoprene. Applicability of these results to the gas-phase O3 reaction with other unsaturated hydrocarbons is briefly discussed.\n\nThe photooxidation chemistry of 1-octene is examined in detail. Formation of OH from the O3 reaction was examined with the use of a tracer/absorber, methyl cyclohexane. The O3 - 1-octene reaction is found to produce, apparently directly, significant quantities of OH, 0.55+0.2 on a per molecule reacted 1-octene basis. Almost 100% of the reacted 1-octene could be accounted for as 80\u00b110% heptanal, 11\u00b16% thermally stabilized Criegee biradical, and about 1% hexane. The OH - 1-octene reaction was found to produce only 15\u00b15% heptanal. The remainder is assumed to result in the formation of alkyl nitrates (32%), and isomerization and eventual formation of multisubstituted products (52%). A separate experiment examining the O([superscript 3]P)-1-octene reaction, showed that 1-octyl oxide accounted for about 80% of the reacted 1-octene. A photochemical model was developed for 1-octene oxidation, and is compared with smog chamber results from NO/NO2-octene experiments. The most crucial factor in the performance of the model is the quantity of assumed alkyl nitrate formation.\n\nA mechanism for the oxidation of isoprene is developed and includes the recent developments on each of isoprene's atmospherically important reactions: O3, OH, O([superscript 3]P), and NO3. The mechanism is tested against chamber data that includes a range of mixtures of these reactions. While it performs reasonably well under conditions where the OH and O([superscript 3]P) reactions dominate, it tends to over predict O3 formation, as well as the speed of development of O3 under conditions where the O3 and NO3 reactions are important. The NO3 reaction is the most uncertain aspect of the isoprene mechanism, and may be responsible for a large part of this discrepancy. The discrepancy may also arise from the difficulty in extrapolating the results of O3 experimental results, necessarily carried out in the absence of NOx, to conditions that include significant concentrations of NOx.\n\nAn extensive set of outdoor smog chamber experiments was carried out to study aerosol formation by two representative biogenic hydrocarbons: isoprene and beta-pinene. The hydrocarbons, at concentrations ranging from a few ppb to a few ppm, were photooxidized in the presence of NOx. Isoprene was found to produce negligible aerosol at ambient conditions, whereas beta-pinene aerosol carbon yields were as high as 8%, depending strongly on the hydrocarbon to NOx ratio. Aerosol samples subjected to infrared absorption spectroscopy revealed that the dominant aerosol products for both isoprene and beta-pinene are organic nitrates, organic acids, as well as other carbonyls and hydroxy compounds. GCMS of the neutral fraction of the beta-pinene aerosol revealed nopinone and several other compounds with molecular weights ranging from 138-200 amu, indicating mainly mono- and dioxygenated products. The average vapor pressure of the 13-pinene aerosol was estimated to be 37 \u00b1 24 ppt at 31 C. Scanning electron micrographs showed that the particles consist of both liquid droplets and agglomerates of small (40-60 nm) solid particles.\n" }, { "name": "Pfaff, Richard D.", "degree": "PhD", "year": "1991", "title": "Three-dimensional effects in nonlinear fracture explored with interferometry", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-07102007-104514", "creators": [ { "name": { "family": "Pfaff", "given": "Richard D." }, "id": "Pfaff-R-D", "display_name": "Pfaff, Richard D." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "role": "member", "display_name": "Ravichandran, Guruswami" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6jnw-kh62", "abstract": "The prospects for understanding fracture mechanics in terms of a general material constitutive description are explored. The effort consists of three distinct components.\n\nFirst, optical interferometry, in its various forms (Twyman-Green, diffraction moire, etc.), can potentially be used under a wide range of conditions to very accurately measure the displacement and strain fields associated with the deformation surrounding a cracktip. To broaden the range of fracture problems to which interferometry may be applied, certain of the necessary experimental improvements have been developed:\n\n1. High speed camera designs capable of extremely high (> 10(9) frames/second) framing rates with large array sizes, (> 4000 x 4000 pixels per frame) so that the application of optical techniques to solid mechanics may be considered without limitation on the rate of deformation.\n\n2. An accurate and adaptable device for dynamic loading of fracture specimens to high load levels utilizing electromagnetic (Lorentz force) loading with ultrahigh (> 2,000,000 Amp/cm(2)) current flux densities.\n\n3. Implementation of high sensitivity (2 nm), large range (2 nm x 3,200,000) interferometry achieved with wide field array sizes of 50,000 x 50,000 and 8 bit gray scale (error restricted to 1 bit) for surface deformation measurements on fracture specimens.\n\nSecond, functional descriptions for certain aspects of the displacement fields associated with fracture specimens are developed. It is found that the fully three-dimensional crack tip field surrounding a through-thickness crack in a plate of elastic-plastic material shows a hierarchical structure of organization and that the primary aspects of the deformation field would seem to have a relatively simple form of expression if the deformation is viewed in a properly normalized form.\n\nThird, a comparison is made between interferometrically measured surface displacements for a notched 3-point-bend speciemn of a ductile heat treatment of 4340 steel and a numerical simulation of the specimen based on a material constitutive description determined from uniaxial tests performed on the same material. The small but finite notch tip radius (0.15 mm) fabricated by a wire-cutting electrical discharge machine allows one to explore the limits of applicability of standard continuum plasticity theories without involving a process zone model for the very near tip region extent in a cracked specimen geometry.\n" }, { "name": "Pham, Thu", "degree": "PhD", "year": "1991", "title": "Numerical studies of incompressible Richtmyer-Meshkov instability in a stratified fluid", "advisor": "Meiron, Daniel I.; Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-143228", "creators": [ { "name": { "family": "Pham", "given": "Thu" }, "id": "Pham-T", "display_name": "Pham, Thu" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "advisor", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "co-advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Leal", "given": "L. Gary" }, "id": "Leal-L-G", "role": "member", "display_name": "Leal, L. Gary" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appliedmath" ], "doi": "10.7907/ryrb-cg53", "abstract": "Theory and calculations are presented for the evolution of Richtmyer-Meshkov instability in continuously stratified fluid layers. The initial acceleration and subsequent instability of the fluid layer are induced by means of an impulsive pressure distribution. It is shown that such an initial condition is an adequate approximation of the effect of a weak shock impinging on a stratified layer of fluid. We then calculate the subsequent dynamics of the fluid layer numerically using the incompressible equations of motion.\n\nBoth initial conditions having single scale perturbations and multiple scale random perturbations are considered. It is found that the growth rates for Richtmyer-Meshkov instability of stratified fluid layers are substantially lower than those predicted by Richtmyer for a sharp fluid interface with an equivalent jump in density. The initial behavior is linear over a time equivalent to the traversal of several layer thicknesses. It is observed that the nonlinear development of the instability results in the formation of plumes of penetrating fluid. Late in the process, the initial momentum deposited by the shock is primarily used in the internal mixing of the layer rather than in the overall growth of the stratified layer.\n\nAt intermediate time, the existence of a weak scaling behavior in the width of the mixing layer of the instability is observed for the multiple scale random perturbations, but not for the single scale perturbations. The time variation of the layer thickness differs from the scaling hypothesized by Barenblatt even at low Atwood ratio, presumably because of the inhomogeneity and anisotropy due to the excitation of vortical plumes. The emergence of these plumes at the boundaries of the density layer is characterized by the elongation of the internal spikes which have weak interactions and grow proportionally to their intial perturbed amplitudes. It is conjectured that the formations of the plumes may correspond to weakly interacting single scale modes." }, { "name": "Rajakarunanayake, Yasantha Nirmal", "degree": "PhD", "year": "1991", "title": "Optical properties of Si-Ge superlattices and wide band gap II-VI superlattices", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-074702", "creators": [ { "name": { "family": "Rajakarunanayake", "given": "Yasantha Nirmal" }, "id": "Rajakarunanayake-Y-N", "display_name": "Rajakarunanayake, Yasantha Nirmal" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/b43v-6930", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis thesis presents the investigation of semiconductor heterostructures for optoelectronic applications, with particular emphasis on band alignment considerations, strain effects, band structure calculations and characterization by optical spectroscopy. The purpose of the work described here is two-fold. The first part of this thesis is concerned with the study of novel optoelectronic properties exhibited by Si/Ge superlattices both in the near infrared (interband transitions) and far infrared (intersubband transitions) energy ranges. The second part of this thesis is concerned with establishing the merits of II-VI semiconductor heterostructures for producing visible light emitters, and investigating techniques to improve the dopability of II-VI semiconductors.\n\nIn the first part of this thesis we investigate the merits of Si/Ge superlattices for optical applications. Although Si and Ge are indirect band gap materials, Si/Ge superlattices can exhibit a direct band gap for certain layer thickness combinations. In Chapter 2, we show that the optical absorption/emission strengths for interband transitions in Si/Ge superlattices can be enhanced by six orders of magnitude over pure Si or Ge. However, these numbers are still three to four orders of magnitude lower than the optical absorption/emission strengths of direct band gap materials such as GaAs. These results are based on a full zone [...] formalism that we developed specifically to study the band structure of Si/Ge superlattices. In Chapter 3, we investigate the intersubband absorption coefficients in doped Si/Ge superlattices. Intersubband transitions in these superlattices make them interesting candidates for long-wavelength infrared detectors. Such infrared detectors are analogous to extrinsic Si detectors, with the additional advantage of tunability of the peak absorption wavelength. The intersubband absorption strengths of Si/Ge superlattices reported in this thesis are comparable to those for AlxGa1-xAs/GaAs superlattices, with the additional benefits of the ability to detect normally incident light, and compatibility with the fabrication and processing technology of Si electronics.\n\nIn the second part of this thesis, we describe investigations of II-VI semiconductor heterostructures for visible light emitter applications. The wide band gap II-VI semiconductors are ideally suited for visible optoelectronics by virtue of their direct band gaps in the blue/green region of the spectrum. However, difficulties associated with doping these materials have severely limited their applications. Low-temperature, epitaxial-growth techniques such as molecular beam epitaxy have opened up new approaches for II-VI materials that show potential for overcoming some of these problems. In Chapter 4, we investigate minority carrier injection in II-VI semiconductors using heterojunctions. We also perform band structure calculations on II-VI strained layer superlattices to investigate the role of strain on the heterojunction band alignments. We experimentally determine the band offsets for CdTe/ZnTe and ZnSe/ZnTe heterojunctions using optical techniques, and remark on the merits of these heterojunctions for carrier injection. We theoretically extended our conclusions to II-VI quaternary alloys and show that there is great promise for visible light-emitter applications within quaternary heterostructures. In Chapter 5, we analyze the role of external electric fields applied during growth in suppressing self-compensation in II-VI semiconductors. This is a novel approach to achieve and control metastability in semiconductors. Our results indicate that II-VI doping efficiencies can be dramatically improved if substantial electric fields are applied during growth.\n" }, { "name": "Rogak, Steven Nicholas", "degree": "PhD", "year": "1991", "title": "Aerosol dynamics of agglomerates", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-131336", "creators": [ { "name": { "family": "Rogak", "given": "Steven Nicholas" }, "id": "Rogak-S-N", "display_name": "Rogak, Steven Nicholas" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." } ], "option_major": [ "envreng" ], "doi": "10.7907/PVDQ-PN74", "abstract": "The mobility, charging, coagulation and mass-transfer properties of aerosol agglomerates were related to the particle and the background gas mean free path \u03bb. The mobility-equivalent diameter dm of a self-similar cluster of spheres in the continuum regime \u03bb<<dm was calculated to be proportional to the radius of gyration Rg of the cluster for fractal dimension Df>1.3. Slender-body behavior is approached for Df<1.3. In the free-molecule regime dm<<\u03bb, dm is nearly equal to the projected-area diameter dA. In the transition regime dm~\u03bb, dm depends on both dA and Rg. In general, there is a divergence of dA and Rg as the agglomerate size increases, but it is very gradual for typical aerosol agglomerates, for which dm~dA in the transition regime.
\r\n\r\nThe mass transfer of nanometer-sized 211Pb clusters to TiO2 agglomerates was investigated with an Epiphaniometer. The measured mass-transfer-equivalent diameters of the agglomerates were within 10% of dm. The lead cluster mean free path was nearly the same as \u03bb. For an analogous phenomenon, the bipolar diffusion charging of agglomerates, it was found that the charging-equivalent diameter of the agglomerates was ~10% larger than dm.
\r\n\r\nThese measurements were incorporated into a model describing the coagulation of agglomerates in the transition regime. Particles smaller than the primary particle diameter d1 were assumed to coalesce rapidly, while large particles were assumed to be solid with a fractal structure. In the transition regime, the agglomerate mean free paths are much smaller than dm even when dm<\t\u03bb. This leads to distinctly different dynamic behavior than predicted by previous models developed for the continuum or free-molecule regimes. The enhancement of coagulation over that of dense spheres is large for aerosols with median diameters slightly greater than d1 but smaller for aerosols consisting of much larger particles.
\r\n" }, { "name": "Rose, Kenneth", "degree": "PhD", "year": "1991", "title": "Deterministic annealing, clustering, and optimization", "advisor": "Fox, Geoffrey C.; Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-085228", "creators": [ { "name": { "family": "Rose", "given": "Kenneth" }, "id": "Rose-K", "display_name": "Rose, Kenneth" } ], "advisors": [ { "name": { "family": "Fox", "given": "Geoffrey C." }, "id": "Fox-G-C", "role": "advisor", "display_name": "Fox, Geoffrey C." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "co-advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Fox", "given": "Geoffrey C." }, "id": "Fox-G-C", "role": "chair", "display_name": "Fox, Geoffrey C." }, { "name": { "family": "Kechris", "given": "Alexander S." }, "id": "Kechris-A-S", "role": "member", "display_name": "Kechris, Alexander S." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/8N1R-3G60", "abstract": "This work introduces the concept of deterministic annealing (DA) as a useful approach to clustering and other related optimization problems. It is strongly motivated by analogies to statistical physics, but is formally derived within information theory and probability theory. This approach enables escaping local optima that plague traditional techniques, without the extremely slow schedules typically required by stochastic methods. The clustering solutions obtained by DA are totally independent of the choice of initial configuration.\n\nA probabilistic framework is constructed, which is based on the principle of maximum entropy. The association probabilities at a given average distortion are Gibbs distributions parametrized by the corresponding Lagrange multiplier [beta], which is inversely proportional to the temperature in the physical analogy. By computing marginal probabilities within the framework, an effective cost is obtained, which is minimized to find the most probable set of cluster representatives at a given temperature. This effective cost is the free energy in statistical mechanics, which is indeed optimized at isothermal, stochastic equilibrium.\n\nWithin the probabilistic framework, annealing is introduced by controlling the Lagrange multiplier [beta]. This annealing is interpreted as gradually reducing the \"fuzziness\" of the associations. Phase transitions are identified in the process, which are, in fact, cluster splits. A sequence of phase transitions produces a hierarchy of fuzzy-clustering solutions. Critical [beta] are computed exactly for the first phase transition and approximately for the following ones.\n\nSpecific algorithms are derivable from the general approach, to address different aspects of clustering in the large variety of application fields. Here, algorithms are derived, and simulation results are presented for the three major classes, namely, hard clustering, fuzzy clustering, and hierarchical clustering. From the experimental results it appears that DA is substantially superior to traditional techniques.\n\nThe last part of the work extends the approach to deal with a larger family of optimization problems that can be reformulated as constrained clustering. A probabilistic framework for constrained clustering is derived based on the principle of maximum entropy. It is shown that for our annealing purpose, the constraint can be directly applied to the free energy. Three examples of constrained clustering are discussed. Mass-constrained clustering is formulated and yields an improvement of the clustering procedure. The process is now independent of the number of representatives and their multiplicity in the clusters. Secondly, the travelling salesman problem (TSP) is reformulated as constrained clustering, yielding the elastic net approach. A second Lagrange multiplier is identified, which is used to obtain a more powerful annealing method. Finally, self-organization of neural networks is shown to be closely related to TSP, and a similar annealing method is suggested. A fuzzy solution is sought to obtain the optimal net for a given training data set.\n" }, { "name": "Sathe, Vinay Padmakar", "degree": "PhD", "year": "1991", "title": "Multirate adaptive filtering algorithms : analysis and applications", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-103754", "creators": [ { "name": { "family": "Sathe", "given": "Vinay Padmakar" }, "id": "Sathe-V-P", "display_name": "Sathe, Vinay Padmakar" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/ec5w-7460", "abstract": "In this thesis, we discuss the application of multirate signal processing concepts to adaptive filtering to achieve low computational complexity and speed. To be able to analyze systems involving multirate building blocks, we have studied effects of multirate filters on the statistics of random inputs. As an example of the multirate adaptive filtering concepts, we study the problem of adaptive identification of an unknown bandlimited channel. We show that the bandlimited property can be very efficiently exploited to reduce both the speed and number of computations. The new method embeds an adaptive filter into multirate filters to reduce complexity and speed of computation.\n\nWe have applied the theoretical results obtained for the effects of multirate building blocks on stationary inputs to the adaptive identification scheme above and shown that the optimal filter is a matrix filter. We have shown through simulations that for a practical setup, a scalar adaptive filter performs almost as well if the fixed filters in the scheme are designed to have good stopband attenuation.\n\nIn a practical implementation of adaptive algorithms, computational noise is of concern. Most of the current analysis focuses on deriving the worst case upper bound on the roundoff errors. We analyze some basic signal processing steps by introducing a statistical flavor to it. This analysis answers questions such as \"what is a typical value of the roundoff error?\" In particular, for the case of dot product computation, we obtain expressions for the roundoff noise variance for the floating point case, and compare the results with the fixed point noise roundoff noise analysis. We also perform error variance analysis of Givens rotation and Householder transformation. These two algorithms are used in the upper triangularization of matrices. We have compared the results obtained for these cases and shown that error variance for the Householder case is lower, meaning that the Householder transformation adds lower roundoff error \"on an average\".\n\nWe also address the problem of bandlimited extrapolation of discrete-time signals. We have explained why the term \"best solution\" does not have a unique answer. Several new techniques for bandlimited extrapolation of discrete-time segments are explored. These methods apply to a wide range of situations (including multiple-burst interpolation of multiband signals). A closed form expression for the optimal solution (for a given value of the energy of extrapolated sequence) has been obtained and evaluated for various values of the final energy. The various methods are compared on the basis of out-of-band energy of the extrapolated signal, total energy of the extrapolated signal (in relation to that of the given segment), and numerical robustness." }, { "name": "Schultheisz, Carl R.", "degree": "PhD", "year": "1991", "title": "Comparison of experimental and computational crack-tip deformations using Moire interferometry and finite elements", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-132245", "creators": [ { "name": { "family": "Schultheisz", "given": "Carl R." }, "id": "Schultheisz-C-R", "display_name": "Schultheisz, Carl R." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/etqv-z784", "abstract": "The large plastic deformations at the tip of a crack in a ductile heat treatment of 4340 steel are studied experimentally and numerically to investigate the details of the deformation in a tough material. The specimen is loaded in a three-point-bend arrangement. The finite-element model of the experiment uses a small-strain, incremental plasticity law, with a power-law hardening behavior. Both the in-plane and out-of-plane deformations were measured on the same specimen at the same time.\n\nThe experimental technique of moire interferometry is used to measure the in-plane displacements. This technique is described in detail, including an analysis of the effect of out-of-plane rotations on the use of the technique. A four-beam interferometer for measuring orthogonal displacement components is described, and its performance analyzed.\n\nThe three-dimensional, finite-element model has 11913 degrees of freedom, and provides data for comparison with the experiment between 4000 N (linear behavior) up to 73.5 kN (continuous fracture of the steel specimen). The model material properties are determined from a uniaxial test on specimens taken from the same bar as the fracture specimens and with identical heat treatment. This model characterizes the crack as a rounded notch to match the notch in the steel fracture specimen. The effects of tunneling of the crack are introduced through the release of nodes along the crack plane corresponding to measured crack profiles.\n\nResults indicate that the numerical model matches the experiment quite well up to a load of 52.3 kN; mismatch at higher loads may be caused by a lack of finite-strain formulation in the code. The finite notch tip negates the singularity in either the stress or strain fields; the HRR field seems to have no region of dominance. However, the function of the J-integral appropriate to the HRR field does normalize the stresses and strains well, indicating that the J-integral is still a good fracture criterion. The effects of the added tunnel indicate that failure of the material depends on both the plastic strain and the hydrostatic stress." }, { "name": "Schweizer, David Lawrence", "degree": "PhD", "year": "1991", "title": "Combinatorial design of fault-tolerant communication structures, with applications to non-blocking switches", "advisor": "Abu-Mostafa, Yaser S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-092015", "creators": [ { "name": { "family": "Schweizer", "given": "David Lawrence" }, "id": "Schweizer-David-Lawrence", "display_name": "Schweizer, David Lawrence" } ], "advisors": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "advisor", "display_name": "Abu-Mostafa, Yaser S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/92k2-w943", "abstract": "This thesis is an investigation into structures and strategies for fault-tolerant communication. We assume the existence of some set of nodes--people, telephones, processors--with a need to pass messages--telephone calls, signals on a wire, data packets--amongst themselves.\r\n\r\nIn Part I, our goal is to create a structure, that is, a pattern of interconnection, in which a designated source node can broadcast a message to (and through) a group of recipient nodes. We seek a structure in which every node has tightly limited fan-out, but which is nonetheless able to function reliably even when challenged with significant numbers of node failures. The structures are described only in terms of their connectivity, and we therefore use the language of graph theory.\r\n\r\nPart II is based on the observation that certain transformations of the graphs in Part I produce graphs that look like previously studied structures called non-blocking switches. We show that these transformations, when applied to other graphs, yield new, easier approaches to, and proofs of, some known theorems.\r\n\r\nPart III is an independent body of work describing some investigations into possible extensions of the theory of Kolmogorov-Chaitin complexity into the foundations of pattern recognition. We prove the existence of an information theoretic metric on strings in which the distance between two strings is a measure of the amount of specification required for a universal computer to interconvert the strings. We also prove two topological theorems about this metric." }, { "name": "Scott, Michael James", "degree": "PhD", "year": "1991", "title": "Kinetics of adsorption and redox processes on iron and manganese oxides : reactions of As(III) and Se(IV) at goethite and birnessite surfaces", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062006-131627", "creators": [ { "name": { "family": "Scott", "given": "Michael James" }, "id": "Scott-Michael-James", "display_name": "Scott, Michael James" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Patterson", "given": "Clair C." }, "id": "Patterson-C-C", "role": "member", "display_name": "Patterson, Clair C." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." } ], "option_major": [ "envreng" ], "doi": "10.7907/3617-qj61", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nSelenium and arsenic are naturally-occurring, non-metallic elements with complex chemical and biological behavior in aquatic environments. In this study, rates and mechanisms of adsorption, desorption, and electron transfer reactions involving selenium and arsenic oxyanions and two naturally occurring metal oxides, goethite ([...]-FeOOH) and birnessite ([...]-MnO2), have been investigated. Adsorption of Se(IV), As(III), and As(V) on goethite and of Se(IV) and As(III) on birnessite occurs within a time scale of minutes. Equilibrium is achieved within a few hours. Adsorption behavior can be described accurately with a surface complexation model.\r\n\r\nGoethite does not oxidize Se(IV) or As(III) in solution at pH .4 and above. However, redox products (Mn(II), Se(VI), As(V)) are observed when Se(IV) or As(III) is added to aqueous suspensions of birnessite. In the arsenite-birnessite system, the rate of As(V) appearance in solution is equal to the rate of As(III) disappearance from solution while the appearance of Mn(II) in solution is slightly slower. In the selenite-birnessite system, uptake of Se(IV) occurs in minutes. Extent of adsorption decreases with increasing pH. The appearance of measurable Se(VI) occurs slowly (time scale of days to weeks) and is a function of adsorbed selenite. This indicates that the rate of selenite oxidation by birnessite is limited by the rate of electron transfer. Rate data from both arsenic and selenium redox systems are successfully described by a reversible four-step kinetic model that accounts for adsorption of the reduced species, electron-transfer, release of the oxidized species, and release of reduced Mn(II).\r\n\r\nThe data suggest that iron oxides provide an adsorptive sink for mobile Se and As oxyanions, while manganese oxides play a major role in accelerating the oxidation of Se(IV) and As(III). Results on the rates of key chemical processes affecting selenium and arsenic should be useful in understanding complex geochemical cycles and in finding solutions to problems in pollutant transport and accumulation in water-sediment systems." }, { "name": "Shimabukuro, Sy Ross", "degree": "PhD", "year": "1991", "title": "Stress Assisted Diffusion in Polymers", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222006-155328", "creators": [ { "name": { "family": "Shimabukuro", "given": "Sy Ross" }, "id": "Shimabukuro-Sy-Ross", "display_name": "Shimabukuro, Sy Ross" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/2g5v-v304", "abstract": "A model for diluent diffusion into a polymer which includes mass flux contributions from both a concentration gradient and pressure gradient is proposed. The pressure is a result of the diluent-induced swelling of the polymer and a constitutive law is incorporated that is analogous to that used in nonlinear thermo-viscoelasticity. The concept of free volume is used as the common basis to relate the relaxation processes for a viscoelastic material to the diffusion of the diluent molecules. The resultant strains (swelling) and stresses must satisfy a strain-displacement relationship and equilibrium equations, respectively.
\r\n\r\nThe governing equations are solved using the finite element technique. An iterative scheme is developed to solve the stress-coupled diffusion process as two separate problems: one for the diffusion process and one for the mechanical response. The two problems are solved individually where the solution from one problem is used as input to the other.
\r\n\r\nNumerical simulations are performed for both one-dimensional and two-dimensional axisymmetric problems in which the diluent is assumed to diffuse along the axis of the cylinder. The results suggest that certain anomalous experimental diffusion results can be explained through the relaxation behavior of the polymer. There are indications that Case II behavior is included in the model by an appropriate choice of material parameters. The results also indicate that typical diffusion experiments may be inadequate to uniquely define the physical model for the diffusion process when more than one type of diffusion driving force exists.
\r\n" }, { "name": "Sivilotti, Massimo Antonio", "degree": "PhD", "year": "1991", "title": "Wiring Considerations in Analog VLSI Systems, with Application to Field-Programmable Networks", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-134330", "creators": [ { "name": { "family": "Sivilotti", "given": "Massimo Antonio" }, "id": "Sivilotti-Massimo-Antonio", "display_name": "Sivilotti, Massimo Antonio" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Bhatt", "given": "Sandeep Nautam" }, "id": "Bhatt-Sandeep-Nautam", "role": "member", "display_name": "Bhatt, Sandeep Nautam" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." } ], "option_major": [ "compsci" ], "doi": "10.7907/stj4-kh72", "abstract": "This thesis develops a theoretical model for the wiring complexity of wide classes of systems, relating the degree of connectivity of a circuit to the dimensionality of its interconnect technology. This model is used to design an efficient, hierarchical interconnection network capable of accommodating large classes of circuits. Predesigned circuit elements can be incorporated into this hierarchy, permitting semi-customization for particular classes of systems (e.g., photoreceptors included on vision chips). A polynomial-time programming algorithm for embedding the desired circuit graph onto the prefabricated routing resources is presented, and is implemented as part of a general design tool for specifying, manipulating and comparing circuit netlists.\r\n\r\nThis thesis presents a system intended to facilitate analog circuit design. At its core is a VLSI chip that is electrically configured in the field by selectively connecting predesigned elements to form a desired circuit, which is then tested electrically. The system may be considered a hardware accelerator for simulation, and its large capacity permits testing system ideas, which is impractical using current means. A fast-turnaround simulator permitting rapid conception and evaluation of circuit ideas is an invaluable aid to developing an understanding of system design in a VLSI context.\r\n\r\nWe have constructed systems using both reconfigurable interconnection switches and laser-programmed interconnect. Prototypes capable of synthesizing circuits consisting of over 1000 transistors have been constructed. The flexibility of the system has been demonstrated, and data from parametric tests have proven the validity of the approach.\r\n\r\nFinally, this thesis presents several new circuits that have become key components in many analog VLSI systems. Fast, dense and provably safe one-phase latches and hierarchical arbiters are presented, as are a low-noise analog switch, an isotropic novelty filter, a dense, active high-resistance element, and a subthreshold differential amplifier with a large linear input range." }, { "name": "Smedley, Keyue Ma", "degree": "PhD", "year": "1991", "title": "Control art of switching converters", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-06062005-152649", "creators": [ { "name": { "family": "Smedley", "given": "Keyue Ma" }, "id": "Smedley-K-M", "display_name": "Smedley, Keyue Ma" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TQG2-GK48", "abstract": "Switching Flow-Graph Model:\n\nThe Switching Flow-Graph is a unified graphical model of large-signal, small-signal and steady-state behavior of pulse-width-modulated (PWM) switching converters. Switching branches are introduced into the flow-graph to represent the switches of the PWM switching converters. The Switching Flow-Graph model is easy to derive, and it provides a visual physical understanding of switching converter systems. The small-signal Switching Flow-Graph generates analytical transfer functions and the large-signal Switching Flow-Graph is compatible with the TUTSIM simulation program. The Switching Flow-Graphs of PWM switching converters reveal a regular pattern, and they predict right-half-plane (RHP) zeros, caused by the imbalanced effects of the duty-ratio control signal on the output of the switching converters. Criteria are found for the design of damping circuits that are capable of eliminating RHP zeros. General models are derived for current-mode controlled switching converters. In addition, the large-signal model and the small-signal model are verified by experiments.\n\nOne-Cycle Control Technique:\n\nThe One-Cycle Control technique is conceived to control the duty-ratio d of the switch in real time such that in each cycle the average of the chopped waveform at the switch output is exactly equal to the control reference. Implementation circuits are found for any type of switch, constant frequency, constant ON-time, constant OFF-time, and variable. One-Cycle Control fully rejects the input signal, and linearly all passes the control signal. This technique turns a nonlinear switch into a linear one. Experiments were conducted using the One-Cycle Control technique on the buck converter and the Cuk converter. One-Cycle Control was found to reject input perturbations and input filter dynamics. The diode voltage of One-Cycle Controlled converters follows the control reference instantaneously in one cycle. One-Cycle Control takes advantage of the pulsed and nonlinear nature of switching converters to achieve instantaneous control of the average value of the diode voltage. This technique is suitable for large-signal control of PWM switching converters and quasi-resonant converters.\n" }, { "name": "Snyder, John Michael", "degree": "PhD", "year": "1991", "title": "Generative Modeling: An Approach to High Level Shape Design for Computer Graphics and CAD", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-07122007-144802", "creators": [ { "name": { "family": "Snyder", "given": "John Michael" }, "id": "Snyder-John-Michael", "display_name": "Snyder, John Michael" } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "compsci" ], "doi": "10.7907/HRFJ-QC74", "abstract": "Generative modeling is an approach to computer-assisted geometric modeling. The goal of the approach is to allow convenient and high-level specification of shapes, and provide tools for rendering and analysis of the specified shapes. Shapes include curves, surfaces, and solids in 3D space, as well as higher-dimensional entities such as surfaces deforming in time, and solids with a spatially varying mass density.
\r\n\r\nShape specification in the approach involves combining low-dimensional entities, especially 2D curves, into higher-dimensional shapes. This combination is specified through a powerful shape description language which builds multidimensional parametric functions. The language is based on a set of primitive operators on parametric functions which include arithmetic operators, vector and matrix operators, integration and differentiation, constraint solution and global optimization. Although each-primitive operator is fairly simple, high-level shapes and shape building operators can be defined using recursive combination of the primitive operators.
\r\n\r\nThe approach encourages the modeler to build parameterized families of shapes rather than single instances. Shapes can be parameterized by scalar parameters (e.g., time or joint angle) or higher-dimensional parameters (e.g., a curve controlling how the scale of a cross section varies as it is translated). Such parameterized shapes allow easy modification of the design, since the modeler can interact with parameters that relate to high-level properties of the shape. In contrast, many geometric modeling systems use a much lower-level specification, such as through sets of many 3D control points.
\r\n\r\nTools for rendering and analysis of generative models are developed using the concept of interval analysis. Each primitive operator on parametric functions has an inclusion function method, which produces an interval bound on the range of the function, given an interval bound on its domain. With these inclusion functions, robust algorithms exist for computing solutions to nonlinear systems of constraints and global minimization problems, when these problems are expressed in the modeling language. These algorithms, in turn, are developed into robust approximation techniques to compute intersections, CSG operations, and offset operations.
" }, { "name": "Stern, Jeffrey Aaron", "degree": "PhD", "year": "1991", "title": "Fabrication and testing of NbN/MgO/NbN tunnel junctions for use as high-frequency heterodyne detectors", "advisor": "Phillips, Thomas G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12202004-091326", "creators": [ { "name": { "family": "Stern", "given": "Jeffrey Aaron" }, "id": "Stern-J-A", "display_name": "Stern, Jeffrey Aaron" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "advisor", "display_name": "Phillips, Thomas G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/AZ4Q-DF35", "abstract": "This thesis describes the development and testing of NbN/MgO/NbN tunnel junctions for use as superconductor-insulator-superconductor (SIS) mixers. SIS mixers are the most sensitive heterodyne detectors in the millimeter wavelength region. Most SIS mixers use Pb alloy tunnel junction. These tunnel junctions have several problems associated with the soft nature of Pb and its low superconducting transition temperature. NbN-based tunnel junctions are being developed to overcome these difficulties. These devices are intended to be used as mixers at millimeter and submillimeter wavelengths. This thesis describes the fabrication process involved in making NbN junctions, and the results of measurements on these devices. The purpose of these measurements is to determine the future possibilities of NbN tunnel junctions as high-frequency mixers.\r\n\r\nThe first chapter is an introduction to SIS mixers and explains how tunnel junction properties affect mixer performance. The basic theory of tunneling and mixing in SIS mixers is first presented. A description of quantum mixer theory is included in this presentation. This theory makes several interesting predictions that cannot be explained using classical theories. This is followed by a description of how real SIS tunnel junctions differ from ideal junctions. The physical origin of these differences is discussed, along with how they affect SIS mixer performance. Finally, the advantages and disadvantages of the various superconducting materials available are discussed. The decision to develop NbN devices is based on these material properties.\r\n\r\nThe second chapter describes the methods used to fabricate small-area NbN/MgO/NbN tunnel junctions. The chapter begins with a description of the various methods that have been used to deposit NbN films. Reactive magnetron sputtering is chosen as the best method for tunnel junction fabrication. Details on the vacuum systems and the methods used for depositing superconducting NbN are discussed. Next, the process used for depositing junction trilayers (NbN/MgO/NbN) is described. The probable growth mode of MgO on NbN is presented. The importance of this growth mode to the junction quality is explained in some detail. Next, standard junction processing steps are reported. The details and limitations of each step are put forth. The standard process allows for the fabrication of 1 [square micron] tunnel junctions. Finally, this chapter discusses several methods of fabaricating submicron junctions that are being pursued. The status of this work is given.\r\n\r\nThe third chapter describes the characterization of NbN films and NbN/Mg0/NbN tunnel junctions. Film properties are described first. The correlation of these properties to deposition conditions is discussed in some detail. Next, values for the various features of the I-V characteristic are given; typical and exceptional values are noted. How these features limit mixer results is described in detail. Several important device attributes were measured using superconducting-quantum-interference-devices (SQUIDs). These attributes are the junction's specific capacitance and the film's magnetic penetration depth. The theory and results of measuring specific capacitance and penetration depth are presented. Following the SQUID results is a large section on RP testing. Mixer tests were made at 205 GHz. The receiver design used, integral inductive tuning circuit used and results are discussed. These results are well understood, with the exception of the temperature dependence of the mixer performance. Finally, measurements of the uniformity of many junctions on a single wafer are presented. The importance of junction uniformity is also described.\r\n\r\nThe final chapter discusses the ultimate limits on NbN mixers, and tells what future work must be done to achieve these limits. The primary high-frequency limit on NbN junctions is the capacitance of NbN/MgO/NbN junctions. The limit imposed by the junction capacitance and circuits used to tune out this capacitance are discussed. Also, the low-frequency limits on NbN junctions are discussed. The status of submicron devices is presented. Junction area is the most immediate limitation on NbN mixer results. The possibility of using other barrier materials to increase the RC speed of NbN junctions is presented. Finally, the possibility of operating NbN junctions at temperatures above 4.2 K is discussed." }, { "name": "Sugioka, Ichiro", "degree": "PhD", "year": "1991", "title": "Particle Transport by Rapid Vaporization of Superheated Liquid", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-082412", "creators": [ { "name": { "family": "Sugioka", "given": "Ichiro" }, "id": "Sugioka-Ichiro", "display_name": "Sugioka, Ichiro" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "co-chair", "display_name": "Hornung, Hans G." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "co-chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Sieh", "given": "Kerry E." }, "id": "Sieh-K-E", "role": "member", "display_name": "Sieh, Kerry E." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZS1H-VE29", "abstract": "Superheated liquid vaporizing explosively in a particle bed inside a cylindrical test cell has been studied using a rapid depressurization apparatus. The experiments provide insights into the explosive vaporization phenomenon and the multiphase flow which is generated by the rapid production of vapor.
\r\n\r\nInside the sealed test cell, spherical glass particles are immersed in a volatile liquid, Refrigerant 12 or 114 at 300K. When the diaphragm at the upper end of the test cell is ruptured, the liquid pressure is reduced to a predetermined pressure within milliseconds. Since the liquid temperature is higher than the boiling temperature at reduced pressure, the liquid achieves a superheated state and nucleate boiling begins among the particles. The particle-liquid-vapor flow produced by the rapid release of vapor has been found to differ depending on whether the pressure is reduced below a critical level, which is 55% of the vapor pressure in the experiments conducted. When the final pressure is greater than critical, vapor pockets continue to grow throughout the particle bed and displace a liquid-particles mixture out from the test cell. When the final pressure is below critical, the particles are dispersed by a wave-like phenomenon (disruption front) where explosive vaporization appears to be localized in a narrow region. A disruption front in R12 travels at about 380 cm/s, and at about 200 cm/s in R114.
\r\n\r\nExperiments have been performed at various conditions to study the vaporization and transport process. High-speed cinematography and fast response pressure gauges have provided data on the particle acceleration process. The inertial effect on particle acceleration has been studied by conducting similar experiments in a centrifuge. Using this data, the transport process associated with the disruption front has been examined in detail. An empirical relationship between the particle weight and viscous drag is presented for this particular case. This study concludes with discussions based on analytical models of the disruption front to approximate flows properties which are intractable experimentally. It is suggested that a disruption front is an expansion process which maximizes vaporization and entropy.
" }, { "name": "Tokumaru, Phillip Takeo", "degree": "PhD", "year": "1991", "title": "Active control of the flow past a cylinder executing rotary motions", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132004-141454", "creators": [ { "name": { "family": "Tokumaru", "given": "Phillip Takeo" }, "id": "Tokumaru-P-T", "display_name": "Tokumaru, Phillip Takeo" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/v7p7-d977", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\t\t\t\t\t\r\nExploratory experiments have been performed on circular cylinders executing forced rotary motions in a steady uniform flow. These motions include harmonic oscillations, steady rotation, and combinations of the two. Flow visualization and laser-Doppler velocimetry measurements were used to characterize the wake structure, and to estimate the convection speed, spacing, and strength of the vortical structures. Laser-Doppler velocimetry measurements were also made to estimate the cylinder drag coefficient and wake displacement thickness. In addition, the periodic flow close the cylinder and in the near wake region was mapped for a particular forced case. The data show that a considerable amount of control can be exerted over the flow by such means. In particular, a large increase, or decrease, in the resulting displacement thickness, estimated cylinder drag, and associated mixing with the free stream can be achieved, depending on the frequency and amplitude of oscillation. In order to assess the effects of oscillatory forcing on a cylinder with a net (mean) rotation rate, a novel method for estimating the steady lift forces was employed. Using this method, it was also found that the addition of forced rotary oscillations to the steady rotation of the cylinder helped to increase [...] in the cases where the wake would normally be separated in the steadily rotating case, and decrease it otherwise. Results obtained for a steadily rotating cylinder (no forced oscillations) compare favorably with similar data published in the literature." }, { "name": "Vakakis, Alexander F.", "degree": "PhD", "year": "1991", "title": "Analysis and identification of linear and nonlinear normal modes in vibrating systems", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-08232004-105610", "creators": [ { "name": { "family": "Vakakis", "given": "Alexander F." }, "id": "Vakakis-A-F", "display_name": "Vakakis, Alexander F." } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "role": "chair", "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/60CA-1Q64", "abstract": "In the first part of this work, the free and forced oscillations of a class of strongly nonlinear, undamped, discrete oscillators, are studied. The free motions are examined by using the notion of \"nonlinear normal mode,\" originally introduced by Rosenberg. Analytical methods for computing similar and nonsimilar normal modes are presented, and the mode stability is analyzed. Normal mode bifurcations are found to exist in these systems, increasing in complexity as the degree of nonlinearity increases.\r\n\r\nA specific application is given with a two degree of freedom, hamiltonian oscillator with cubic nonlinearity. The low energy motions are analyzed by means of Poincare' maps and an approximate averaging technique. When the energy is increased, chaotic motions are observed in the Poincare' maps, resulting from the transverse intersections of the stable and unstable manifolds of an unstable normal mode. Moreover, the generation of subharmonic orbits resulting from the breakdown of invariant KAM Tori is examined by using Subharmonic Melnikov analysis.\r\n\r\nThe similar and nonsimilar forced steady state motions are examined by considering special (nonharmonic) periodic excitations. For the case of cubic nonlinearity, a theorem on the necessary and sufficient conditions that a force should satisfy in order to lead to an exact steady state is given.\r\n\r\nIn the second part of the work, techniques for identifying systems with closely spaced modes and weak nonlinearities are developed. Modal interference in the Complex plane is modeled by expanding the Frequency Response Function of the \"perturbing mode\" in Taylor series, and retaining only the two first terms. The distorted Nyquist plots of systems with stiffness and/or damping nonlinearities are analytically studied, by using the concept of \"equivalent linearization.\" Based on the analytical results, refined identification algorithms are proposed, and their applicability is tested by analyzing theoretical and experimental data.\r\n" }, { "name": "Waitz, Ian Anton", "degree": "PhD", "year": "1991", "title": "An Investigation of Contoured Wall Injectors for Hypervelocity Mixing Augmentation", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-083103", "creators": [ { "name": { "family": "Waitz", "given": "Ian Anton" }, "id": "Waitz-Ian-Anton", "display_name": "Waitz, Ian Anton" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MPJS-1Q71", "abstract": "A parametric study of a class of contoured wall fuel injectors is presented. The injectors were aimed at enabling shock-enhanced mixing for the supersonic combustion ramjet engines currently envisioned for applications on hypersonic vehicles. Short combustor residence time, a requirement for fuel injection parallel to the freestream, and strong sensitivity of overall vehicle performance to combustion efficiency motivated the investigation. Several salient parametric dependencies were investigated. Injector performance was evaluated in terms of mixing, losses, jet penetration and heating considerations.
\r\n\r\nA large portion of the research involved a series of tests conducted at the NASA Langley High - Reynolds Number Mach 6 Wind-Tunnel. Helium was used as an injectant gas to simulate hydrogen fuel. The parameters investigated include injector spacing, boundary layer height, and injectant to freestream pressure and velocity ratios. Conclusions concerning injector performance and parameter dependencies are supported by extensive three-dimensional flow field surveys as well as data from a variety of flow visualization techniques including Rayleigh scattering, Schlieren, spark-shadowgraph, and surface oil flow.
\r\n\r\nAs an adjunct to these experiments, a three-dimensional Navier-Stokes solver was used to conduct a parametric study which closely tracked the experimental effort. The results of these investigations strongly complemented the experimental work. Use of the code also allowed research beyond the fairly rigid bounds of the experimental test matrix. These studies included both basic investigations of shock-enhanced mixing on generic injectors, and applied efforts such as combining film-cooling with the contoured wall injectors.
\r\n\r\nLocation of an oblique shock at the base of the injection plane was found to be a loss-effective method for enhancing hypervelocity mixing through baroclinic generation of vorticity and subsequent convection and diffusion. Injector performance was strongly dependent on the displacement effect of the hypersonic boundary layer which acted to modify the effective wall geometry. Strong dependence on injectant to freestream pressure ratio was also displayed. Mixing enhancement related to interaction of the unsteady component of the boundary layer with both steady and unsteady components of the flow field was found to be secondary, as were effects due to variation in mean shear between the injectant and the freestream in the exit plane.
" }, { "name": "Wang, Shih-Chen", "degree": "PhD", "year": "1991", "title": "Aerosol formation and growth in atmospheric organic/NOx systems", "advisor": "Flagan, Richard C.; Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01112007-152148", "creators": [ { "name": { "family": "Wang", "given": "Shih-Chen" }, "id": "Wang-Shih-Chen", "display_name": "Wang, Shih-Chen" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/npvk-7c22", "abstract": "Secondary atmospheric aerosols are formed by gas-to-particle conversion of condensible vapors produced by reactions of primary species such as organics, NOx, SO2, and NH3. The rates and mechanisms leading to organic aerosol formation are the least well understood aspect of secondary atmospheric aerosols. Gas-phase measurements of organics, NOx, O3, and measurements of particle formation and growth have been made in smog chamber experiments to determine the total aerosol yields of the photochemical oxidation of various organics. Measurements of size distribution dynamics reveal the competition between nucleation and condensation, allowing estimation of the physical properties of the aerosol formed and the likelihood that a particular organic forms aerosol in the atmosphere.\r\n\r\nA new scanning electrical mobility spectrometer (SEMS) was developed to monitor aerosol size distribution dynamics. The measurement of particle size distributions using electrical mobility has been significantly accelerated using a new mode of operating mobility instruments. Rather than changing the electric field in discrete steps to select particles in a given mobility range, the electric field is scanned continuously. The particles are classified in a time-varying electric field, but for an exponential ramp in the field strength, there remains a one-to-one correspondence between the time a particle enters the classifier and the time it leaves. By this method, complete scans of mobility with as many as 100 mobility measurements have been made in 30 seconds using a differential mobility classifier with a condensation nuclei counter as a detector.\r\n\r\nOutdoor smog chamber experiments have been performed to determine the aerosol forming potential of selected C7- and C8- hydrocarbons in sunlight-irradiated hydrocarbon NOx mixtures. Measured aerosol size distributions were used to determine the rates of gas-to-particle conversion and to study the effects of the addition of SO2 and/or NH3 on aerosol formation and growth. The average aerosol yields by mass for the hydrocarbons studied were: \r\n\r\nmethylcyclohexane 9.2% \r\n1-octene 4.2% \r\ntoluene 18.6% \r\nn-octane <0.001% \r\n\r\nAddition of SO2 to the organic/NOx systems led to an early nucleation burst and subsequent rapid growth of the newly formed aerosols. In the presence of NH3, the gas-to-particle conversion rate of the organic/NOx system was enhanced perhaps due to the formation of NH4NO3 or the reaction of NH3 with carboxylic acids. Sustained particle formation was observed when both SO2 and NH3 were present, presumably a result of (NH4)2SO4 formation. We have estimated the complexity of the 1-octene aerosol and identified 5-propyl furanone as a major component of the aerosol.\r\n\r\nAerosol dynamics that were observed in the outdoor smog chamber experiments are simulated by numerical solution of the aerosol general dynamic equation. The vapor source generation rate was estimated directly from the experimental measurements assuming a single surrogate condensing species for each hydrocarbon studied. Sensitivity analysis of the simulated aerosol dynamics to various input parameters revealed that the physical properties of the condensing vapor are important in determining the interplay between nucleation and condensation while the vapor source generation rate is the only factor that determines the eventual total amount of vapor converted to aerosol. The simulations suggest that over 99% of the mass of condensible vapor is converted to aerosol by condensation even when a significant burst of nucleation occurs." }, { "name": "Wedge, Scott William", "degree": "PhD", "year": "1991", "title": "Computer-aided design of low noise microwave circuits", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172003-101254", "creators": [ { "name": { "family": "Wedge", "given": "Scott William" }, "id": "Wedge-S-W", "display_name": "Wedge, Scott William" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "role": "member", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZRTG-GX48", "abstract": "Devoid of most natural and manmade noise, microwave frequencies have detection sensitivities limited by internally generated receiver noise. Low-noise amplifiers are therefore critical components in radio astronomical antennas, communications links, radar systems, and even home satellite dishes. A general technique to accurately predict the noise performance of microwave circuits has been lacking. Current noise analysis methods have been limited to specific circuit topologies or neglect correlation, a strong effect in microwave devices. Presented here are generalized methods, developed for computer-aided design implementation, for the analysis of linear noisy microwave circuits comprised of arbitrarily interconnected components. Included are descriptions of efficient algorithms for the simultaneous analysis of noisy and deterministic circuit parameters based on a wave variable approach. The methods are therefore particularly suited to microwave and millimeter-wave circuits. Noise contributions from lossy passive components and active components with electronic noise are considered. Also presented is a new technique for the measurement of device noise characteristics that offers several advantages over current measurement methods." }, { "name": "Wexler, Anthony Stein", "degree": "PhD", "year": "1991", "title": "Inorganic Components of Atmospheric Aerosols", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-083859", "creators": [ { "name": { "family": "Wexler", "given": "Anthony Stein" }, "id": "Wexler-Anthony-Stein", "display_name": "Wexler, Anthony Stein" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Pandis", "given": "Spyros N." }, "id": "Pandis-S-N", "role": "member", "display_name": "Pandis, Spyros N." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/EYF6-3M05", "abstract": "The inorganic components comprise 15% to 50% of the mass of atmospheric aerosols and, these along with the relative humidity, control the aerosol water content. For about the past 10 years the mass of the inorganic components of atmospheric aerosol was predicted assuming thermodynamic equilibrium between the volatile aerosol-phase inorganic species, NH4NO3 and NH4Cl, and their gas-phase counterparts, NH3, HNO3, and HCl. In this thesis I examine this assumption and prove that 1) the time scales for equilibration between the gas and aerosol phases are often too long for equilibrium to hold, and 2) even when equilibrium holds, transport considerations often govern the size distribution of these aerosol components.
\r\n\r\nWater can comprise a significant portion of atmospheric aerosols under conditions of high relative humidity, whereas under conditions of sufficiently low relative humidity atmospheric aerosols tend to be dry. The deliquescence point is the relative humidity where the aerosol goes from a solid dry phase to an aqueous or mixed solid-aqueous phase. Previous to this thesis little had been known about the temperature and composition dependence of the deliquescence point. In this thesis I first derive an expression for the temperature dependence of the deliquescence point and then prove that in multicomponent solutions the deliquescence point is lower than in the deliquescence point of the individual single component solutions.
\r\n\r\nThese theories of the transport, thermodynamic, and deliquescent properties of atmospheric aerosols are integrated into an aerosol inorganics model, AIM. The equilibrium predictions of AIM compare well to fundamental thermodynamic measurements. Comparison of the prediction of AIM to those of other aerosol equilibrium models show substantial disagreement in the predicted water content at lower relative humidities. The difference is due to the improved treatment of the deliquescence properties of mixed solute aerosols that is contained in AIM.
\r\n\r\nIn the summer and fall of 1987 the California Air Resources Board conducted the Southern California Air Quality Study, SCAQS. During this study the atmospheric aerosols were measured at nine sites in the Los Angeles air basin. The measurements determined the size and composition distributions of the components of the aerosol and the concentrations of their gas phase counterparts during a series of intensive study periods. The comparison of these SCAQS measurements to the predictions of AIM have so much scatter that a departure from equilibrium, that can be attributed to transport limitations, cannot be discerned. When the measured size distributions are compared as another indication of transport-limited departure from equilibrium, we find that different size aerosol particles are not in mutual equilibrium. Although the SCAQS data do not indicate a transport-limited departure from equilibrium, they do support our hypothesis that transport considerations are essential to predicting the size distribution of the volatile inorganic species.
" }, { "name": "Wong, Brian Alan", "degree": "PhD", "year": "1991", "title": "The oxidation of individually levitated char particles", "advisor": "Flagan, Richard C.; Gavalas, George R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07172007-090918", "creators": [ { "name": { "family": "Wong", "given": "Brian Alan" }, "id": "Wong-B-A", "display_name": "Wong, Brian Alan" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "co-advisor", "display_name": "Gavalas, George R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/tm62-ax11", "abstract": "An electrodynamic balance was constructed for use as a single particle thermogravimetric analyzer. The electrodynamic balance uses a vertical DC field to levitate an electrically charged particle. An AC voltage is applied to a ring electrode surrounding the particle between the DC electrodes. This AC field provides a restoring force if the particle is displaced from the center of the balance. A carbon dioxide laser was used to heat the particle. The temperature of the particle was measured by a dual-wavelength optical pyrometer. Two materials were the subject of oxidation studies, a porous synthetic carbon, Spherocarb and char made from PSOC 1451 bituminous coal. Two studies were performed, an ignition study, and a low temperature oxidation study. In the ignition study, a suspended particle was heated by a series of 500 millisecond pulses from the laser, at increasing oxygen concentrations. The particle temperature trace shows the ignition delay as predicted by Semenov's thermal explosion theory. A simple isothermal sphere model was applied with literature values for the physical parameters. A reasonably good match of the data to the model was found. In the low temperature experiments char particles were heated in air to a temperature of about 600\u00b0C. Some of the particles did not react at constant diameter, as expected. In particular, Spherocarb shrank or densified, as noted by others. The char particles formed from a narrow size cut of PSOC 1451 bituminous coal devolatilized at 1200K also shrank in size as it reacted. However the char formed at 1600K did not shrink, but oxidized at constant diameter. The densification phenomenon, then, is dependent on the devolatilization process and charring temperature. Simple char oxidation models will not accurately predict the size changes of these shrinking chars.\n" }, { "name": "Yang, Joseph T.", "degree": "PhD", "year": "1991", "title": "An Analytical and Computational Investigation of Shock-Induced Vortical Flows with Applications to Supersonic Combustion", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092007-155813", "creators": [ { "name": { "family": "Yang", "given": "Joseph T." }, "id": "Yang-Joseph-T", "display_name": "Yang, Joseph T." } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "mecheng" ], "doi": "10.7907/SZQ1-YB88", "abstract": "The motivation for study of shock-induced vortical flows is the problem of achieving rapid and efficient mixing of fuel and oxidizer in a SCRAMJET engine. In particular, the interaction of a shock wave with a jet of light gas generates vorticity which can be used to stir and mix the fluids. This investigation consists of two parts.\r\n\r\nThe first part is a characterization of the basic fluid mechanics of the interaction. The canonical problem is a shock wave passing over a circular light gas inhomogeneity located within a finite channel. The pressure gradient from the shock wave interacts with the density gradient at the edge of the inhomogeneity to deposit vorticity around the perimeter. As time goes on, the structure rolls up into a pair of counter-rotating vortices. This flow is simulated numerically by integrating the governing equations subject to specified initial conditions. From first principles, analytical models are developed to predict the circulation, spacing, and characteristic time for development as a function of initial conditions. From perturbation analysis, another model is developed to predict the vortex pair velocity as a function of the geometrical parameters vortex size/vortex spacing and vortex spacing/channel spacing. The agreement between models and computations is generally good. These models represent the first successful and comprehensive characterization of the fluid mechanics of the canonical flow.\r\n\r\nThe second part is an investigation of mixing efficiencies for various initial configurations. In the canonical flow, stabilization of the vortex pair eventually impairs the mixing. Various initial configurations are considered with the goal of improving the mixing. The mixing is quantified by an asymptotic stretching rate of a material element. Single jet shape perturbations yield little improvement in mixing, but multiple jet arrays do, especially through the phenomenon of entrainment. Another way to improve the mixing is to hit a vortex pair with a reflected shock. Finally, a mathematical correspondence is exhibited between the unsteady 2-D flows considered here and the corresponding 3-D steady flows that may be more typical of real combustor designs." }, { "name": "Yu, Edward Tsu-Wei", "degree": "PhD", "year": "1991", "title": "Physics and applications of semiconductor heterostructures : I. Measurement of band offsets in semiconductor heterojunctions. II. Theoretical and experimental studies of tunneling in semiconductor heterostructure devices", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08232007-120748", "creators": [ { "name": { "family": "Yu", "given": "Edward Tsu-Wei" }, "id": "Yu-E-T", "display_name": "Yu, Edward Tsu-Wei" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/AXNV-8575", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nThis thesis describes investigations concerning the physics and applications of band edge discontinuities in semiconductor heterojunctions. An historical overview and an assessment of the current experimental and theoretical understanding of band offsets are presented in Chapter 1. The physics and potential device applications of tunneling phenomena in semiconductor heterostructures are also introduced.\n\nPart I of the thesis describes measurements of semiconductor heterojunction valence-band offsets by x-ray photoelectron spectroscopy (XPS). In Chapter 2, the basic physical principles of XPS are discussed, with emphasis on capabilities of the technique that are especially relevant in studies of semiconductor interfaces. The experimental procedures and data analysis techniques required to measure band offsets by XPS are also described. A measurement of the GaAs/AlAs (100) valence-band offset is presented in Chapter 3. Our results are discussed in the context of the recent controversy surrounding the value of the GaAs/AlAs band offset. The relationship between band offset commutativity and interfacial quality as elucidated by our experiments and by previously reported results is also explained. A measurement of the valence band offset for the lattice-mismatched Si/Ge (001) heterojunction system is described in Chapter 4. A method developed to extend the applicability of the XPS technique to the determination of strain-dependent band offsets is presented and applied to the Si/Ge (001) material system. Our results demonstrate the profound influence of strain on band offset values in lattice-mismatched heterojunctions. An interpolation scheme for determining band offset values for [...] alloy heterojunctions is described, and is used to demonstrate the consistency of our results with Si/[...] modulation doping experiments that have been reported. Studies of band offsets and interfacial reactions in III-V/II-VI heterojunction systems are reported in Chapter 5. Specifically, band offsets and interface chemistry have been examined in the A1Sb/GaSb/ZnTe material system; the influence of interfacial chemistry on band offset values is demonstrated, and implications of our work for the viability of proposed heterojunction approaches for fabricating visible light emitters are discussed. The measurement of the CdSe/ZnTe (100) valence band offset is described in Chapter 6. Our results are discussed in the context of possible heterojunction approaches for injection of electrons into p-ZnTe for fabricating visible light emitters, and implications of our results for the common anion rule are addressed.\n\nPart II of the thesis describes theoretical and experimental studies of tunneling in semiconductor heterostructures. Various theoretical models we have used to simulate the electrical behavior of a wide variety of heterostructure devices are described in Chapter 7. These techniques are applied to the calculation of current-voltage characteristics for double-barrier tunnel structures proposed in the GaAs/ZnSe and InAs/ZnTe material systems. Theoretical and experimental studies of interband transport in the InAs/GaSb/AlSb material system are described in Chapter 8. Band alignments in the InAs/GaSb/AlSb system and material properties of InAs and GaSb are discussed in the context of both fundamental physics and device applications. Attention is then focused on a theoretical and experimental study of transport in the InAs/GaSb/InAs device structure that helped to clarify the basic nature of interband transport and the coupling between conduction-band and valence-band states in different layers of a heterostructure. In Chapter 9, a theoretical study of hole tunneling times in GaAs/AlAs double-barrier heterostructures is presented. The experimental observation of anomalously short hole tunneling times that motivated this work is reviewed, and a phenomenological model explaining this experimental observation as a consequence of valence-band-mixing is developed." }, { "name": "Allard, Marie-Agn\u00e8s", "degree": "PhD", "year": "1990", "title": "Soil Stress Field Around Driven Piles", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212007-130942", "creators": [ { "name": { "family": "Allard", "given": "Marie-Agn\u00e8s" }, "id": "Allard-Marie-Agn\u00e8s", "display_name": "Allard, Marie-Agn\u00e8s" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "chair", "display_name": "Scott, Ronald F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Allen", "given": "Clarence R." }, "id": "Allen-C-R", "role": "member", "display_name": "Allen, Clarence R." } ], "option_major": [ "civileng" ], "doi": "10.7907/GGE1-GC92", "abstract": "The description, equipment, and results of a series of pile-driving experiments conducted in a centrifuge using a model pile driven in dry sand are presented.
\r\n\r\nThe work was conceived on the basis of the modelling of a soil-structure system under an artificially generated gravitational field, and motivated by the need for experimental data for a better understanding of the complex phenomena involved in the pile-soil interaction during driving. The behavior of the pile itself has been the focus of more attention in the past, but few full-scale or model experimental results have been obtained to the present concerning the soil stress field during pile driving. These are necessary for comparison with analytical and theoretical work. The work presented here appears to be the first attempt to obtain dynamic response of the soil during driving. The objective was to obtain a good understanding of the physical phenomena occurring in the soil and pile during driving.
\r\n\r\nIn order to achieve these objectives both dynamic (transient) and static responses of the soil and pile were measured by means of transducers: accelerometers and strain gages for the pile, pressure transducers for the soil. In particular, the relations between static and dynamic data were explored, which resulted in the modelling of the soil-transducer interaction with a non-linear, history-dependent, model.
\r\n\r\nResults were obtained regarding pile dynamics, soil dynamics, and soil stress field (radial and vertical distribution, stress contours). Both linear and soil-cell model assumptions were used, which enabled a comparison between the two, leading to an estimate that each constitutes a bound of the real stress field, with the linear giving the higher, and the non-linear the lower bound, and the true stress being closer to the lower bound.
\r\n\r\nThe soil response during driving is obtained, filling the gap in the study of the pile-soil system, where only the pile response was known. Recommendations for further work and better experimental procedures are given.
" }, { "name": "Balas, Gary John", "degree": "PhD", "year": "1990", "title": "Robust Control of Flexible Structures: Theory and Experiments", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-10252002-160528", "creators": [ { "name": { "family": "Balas", "given": "Gary John" }, "id": "Balas-Gary-John", "display_name": "Balas, Gary John" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "role": "member", "display_name": "Morari, Manfred" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T7NG-T636", "abstract": "Stringent requirements envisioned for the pointing and shape accuracy of future space missions necessitate advances in the control of large flexible structures. These structures will be extremely flexible, with little natural damping and modes densely packed throughout the frequency domain. Due to their size and complexity, testing of these structures will lead to system models that are inaccurate for control purposes. Therefore, control design methods must be developed to account for model inaccuracies or uncertainties. Such methods should optimize the robustness and performance characteristics of control laws based on the accuracy of the design model.
\r\n\r\nThis thesis focuses on incorporating knowledge of the mismatch between the physical system and its mathematical models into the control design process. Control design models are developed to fit into the structured singular value (\u00b5) framework that is used in the analysis and synthesis of control laws. To validate and verify theoretical developments, a flexible structure experiment is developed to investigate large flexible control problems in a laboratory environment. The Caltech experiment has a number of their attributes: closely spaced, lightly damped modes, collocated and noncollocated sensors and actuators combined with numerous modes in the controller crossover (roll off) region.
\r\n\r\nThe experimental structure is used to investigate several important issues related to control of flexible structures: tradeoffs between robustness and performance associated with uncertainty modeling for flexible structures, robust control of flexible modes in the controller crossover region and benefits and limitations of collocated versus noncollocated control design. A consistent trend in the results indicates that an accurate description of the flexible structure and model errors is required to synthesize high performance, robust control laws for flexible structures.
" }, { "name": "Baskin, John Spencer", "degree": "PhD", "year": "1990", "title": "Real-Time Observation and Analysis of Coherence and Alignment in Molecular Systems: Isolated Molecules and Chemical Reactions", "advisor": "Zewail, Ahmed H.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252003-112746", "creators": [ { "name": { "family": "Baskin", "given": "John Spencer" }, "id": "Baskin-John-Spencer", "display_name": "Baskin, John Spencer" } ], "advisors": [ { "name": { "family": "Zewail", "given": "Ahmed H." }, "id": "Zewail-A-H", "role": "advisor", "display_name": "Zewail, Ahmed H." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Zewail", "given": "Ahmed H." }, "id": "Zewail-A-H", "role": "chair", "display_name": "Zewail, Ahmed H." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Marcus", "given": "Rudolph A." }, "id": "Marcus-R-A", "orcid": "0000-0001-6547-1469", "role": "member", "display_name": "Marcus, Rudolph A." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/H8TF-EE69", "abstract": "Picosecond time-resolved rotational coherence spectroscopy is developed as a probe of excited state rotational level structure and alignment. The measurement technique employs a combination of supersonic cooling by molecular beam expansion, coherent picosecond pulsed laser excitation, and time-resolved and polarization-analyzed detection of spectrally dispersed fluorescence. The requisite measurement system response time of approximately 50 picoseconds is attained using time-correlated single photon counting and a microchannel plate detector.
\r\n\r\nIn the case of purely rotational coherence (PRC), i.e., when rotation may be treated in the rigid rotor approximation, analysis of the polarization-analyzed fluorescence provides direct information about the rotational constants and structure of the molecule's excited vibronic state. This method of structural determination of excited states has the inherent advantages over conventional frequency-domain spectroscopy of sub-Doppler resolution and insensitivity to ground state structure. As a result, it is particularly valuable in investigations of large molecules and complexes. Analyses of PRC measurements on eight different molecular systems are detailed in this thesis. These provide illustrative examples of various aspects of the technique while permitting the derivation of new information about the excited states of six of the eight molecules or complexes studied. Principal among the findings are values of the sum of rotational constants B' and C' of the t-stilbene S\u2081 electronic state (B'+ C' = 0.5132 \u00b1 .0008 GHz) and of all three S\u2081 rotational constants of anthracene.
\r\n\r\nWe also report measurements of time-resolved and polarization-analyzed fluorescence as a function of excess vibrational energy in the S\u2081 electronic states of both t-stilbene and anthracene. We are able to distinguish the contribution of purely rotational coherence from the contributions of purely vibrational (or rovibrational) coherence to the evolution of fluorescence from the vibrationally excited molecule. Our results provide a test of the extent of coupling between vibrational and rotational motion and its influence on intramolecular vibrational energy redistribution.
\r\n\r\nMeasurements of polarization-analyzed fluorescence of dissociation products demonstrate that rotational coherence of the reagent can be transferred to its fragments. In order to interpret the results of these and related experiments, a classical model of fluorescence anisotropy in prompt, impulsive dissociation reactions is developed.
" }, { "name": "Brady, David Jones", "degree": "PhD", "year": "1990", "title": "Photorefractive Volume Holography in Artificial Neural Networks", "advisor": "Psaltis, Demetri; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-05022006-155139", "creators": [ { "name": { "family": "Brady", "given": "David Jones" }, "id": "Brady-David-Jones", "display_name": "Brady, David Jones" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Kimble", "given": "H. Jeff" }, "id": "Kimble-H-J", "role": "member", "display_name": "Kimble, H. Jeff" }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/1YB6-SE42", "abstract": "This thesis describes the use of volume holography to implement large-scale linear transformations on distributed optical fields. Such transformations are useful in the construction of hardware for artificial neural networks. The reconstruction of multiple grating holograms in layers of thin transparencies and in continuous volume media is considered and conditions under which such holograms may be used for linear transformations are derived. The control of the nature of the transformation implemented using fractal sampling grids is reviewed and the impact of such sampling grids on the energy efficiency of the overall system is considered. Information storage in volume holograms is shown to require multiple exposures and the impact of multiple exposures on linear hologram formations in saturable media and photorefractive materials is considered. It is shown for both types of media that the overall diffraction efficiency of a recorded hologram must decrease with the square of the rank of the transformation implemented. A theory for hologram formation in photorefractive materials with multiple trapping species is developed and compared with experimental results. The impact of multiple species and fixing mechanisms on linear hologram formation is evaluated. A method for refreshing the diffraction efficiency of photorefractive holograms in adaptive systems is described and demonstrated. The construction of thick holograms for linear transformations in waveguides is considered. A novel method for controlling such holograms is described and demonstrated. Learning in holographic neural networks is considered and two experimental holographic neural systems are described. The relative strengths of optical and electronic technologies for implementations of neural interconnections are considered.
" }, { "name": "Brinson, Lynda Catherine", "degree": "PhD", "year": "1990", "title": "Time-Temperature Response of Multi-Phase Viscoelastic Solids Through Numerical Analysis", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-112909", "creators": [ { "name": { "family": "Brinson", "given": "Lynda Catherine" }, "id": "Brinson-Lynda-Catherine", "display_name": "Brinson, Lynda Catherine" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Tschoegl", "given": "Nicholas W." }, "id": "Tschoegl-N-W", "role": "member", "display_name": "Tschoegl, Nicholas W." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/SYAS-2A50", "abstract": "A numerical model has been constructed for the study of the properties of multi-phase viscoelastic composites. The model utilizes the dynamic correspondence principle of viscoelasticity in a finite element program to solve boundary value problems simulating uniaxial tension or simple shear and obtains the global complex Young's or shear moduli of the composite.
\r\n\r\nEach phase of the composite is considered to be thermorheologically simple. The resulting modulus properties of the composite however, are thermorheologically complex and this investigation examines the nature of time-temperature behavior of multi-phase composite materials. The specific composite considered throughout this study contains viscoelastic inclusions embedded in a different viscoelastic matrix material. The deviation of the composite moduli from thermorheologically simple behavior of the matrix material is shown to occur at frequencies and temperatures where the glass-to-rubber transition of the included phases are reached.
\r\n\r\nProperties of polystyrene and polybutadiene are used to investigate the thermorheological complexity (non-shiftability) of a Styrene-Butadiene-Styrene (SBS) block copolymer. To achieve congruence of the results with experimental data, it is necessary to consider a transition phase of properties \"intermediate\" to those of styrene and butadiene. Using accurate physical information on the individual phase properties and on the interphase region, it is possible to utilize the numerical model to predict long term properties of multi-phase composites from short term laboratory data. Lacking detailed information on the properties of a particular phase (e.g., the interphase), but knowing the time dependent properties for the composite material at a broad range of temperatures, it is also possible to use the numerical tool to solve an inverse problem and determine the unknown properties of the phase in question.
" }, { "name": "Camassa, Roberto Alfredo", "degree": "PhD", "year": "1990", "title": "Part I: Forced Generation and Stability of Nonlinear Waves. Part II: Chaotic Advection in a Rayleigh-B\u00e9nard Flow", "advisor": "Wu, Theodore Yao-tsu; Wiggins, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02232007-160809", "creators": [ { "name": { "family": "Camassa", "given": "Roberto Alfredo" }, "id": "Camassa-Roberto-Alfredo", "display_name": "Camassa, Roberto Alfredo" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "orcid": "0000-0002-0780-0911", "role": "co-advisor", "display_name": "Wiggins, Stephen R." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "orcid": "0000-0002-0780-0911", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "eng" ], "doi": "10.7907/2MK9-ZD86", "abstract": "Part I
\r\n\r\nThe forced Korteweg-de Vries model has been found satisfactory in predicting the periodic generation of upstream-advancing solitary waves by a bottom topography moving in a layer of shallow water with a steady transcritical velocity. It is also known that with certain characteristic forcing distributions, there exist waves, according to the fKdV model, which can remain steady in accompanying the characteristic forcing, provided such a wave exists initially, whereas for a different initial condition the phenomenon of periodic generation can still manifest itself. The stability of two such transcritically forced steady solitary waves is investigated, with their bifurcation diagrams determined with respect to the velocity and the amplitude of the forcing as parameters. The linear stability analysis is first carried out; it involves solving a singular, non-self-adjoint eigenvalue problem, which is examined by applying techniques of matched asymptotic expansions with suitable multiscales for singular perturbations, about the isolated bifurcation points of the parameters. The eigenvalues and eigenfunctions for the full range of the parameters are then obtained by numerically summing a power series expansion for the solution. The numerical results, which accurately match with the local analysis, show that the eigenvalues have only four branches \u03c3 = \u00b1\u03c3r \u00b1i\u03c3i. The real part \u03c3r is nonvanishing for the velocity less than a certain supercritical value and for the amplitude greater than a certain marginal bound except at a single point in the parametric plane at which the external forcings vanish, reducing the forced waves to the classical free solitary wave. Within this parametric range, the real part of the four eigenvalues is algebraically two to five orders smaller than the imaginary part \u03c3i, wherever \u03c3i exists; such a small \u03c3r indicates physically a weak exponential growth rate of perturbed solutions and mathematically the need of a very accurate numerical method for its determination. Beyond this parametric range, linear stability theory appears to fail because no eigenvalues can there be found to exist. In this latter case a non linear analysis based on the functional Hamiltonian formulation is found to prevail, and our analysis predicts stability. Finally, extensive numerical simulations using various finite difference schemes are pursued, with results providing full confirmation to the predictions made in various regimes by the analysis.
\r\n\r\nWe consider the Korteweg-de Vries equation in the semi-infinite real line with a boundary condition at the origin. The numerical investigations of Chu et al.[2], are revisited and different new forms for the boundary forcing are assumed. In order to provide some qualitative description for the numerical simulations we develop a simple model based on the IST formalism. It is found that the model is also able to provide some quantitative predictions in agreement with the numerical results.
\r\n\r\nPart II
\r\n\r\nThere has been considerable interest recently on chaotic advection, for the first time explored in the context of Rayleigh-B\u00e9nard roll (2D) convection by the experimental work of J. Gollub and collaborators. When the Rayleigh number increases across a (supercritical) value, depending on the wavelength of the rolls, an oscillatory instability sets in. The flow near the onset of the instability can still be modelled by a stream function, which can be split into a time independent part plus a small time dependent perturbation. The motion of fluid particles can therefore be regarded as the flow for a near integrable, \"one-and a half\" degree of freedom Hamiltonian vector field, with the phase space corresponding to the physical domain. In absence of molecular diffusivity, the evolution of a certain region of phase space can thus be viewed as the motion of a dyed part of fluid, when the tracer is perfectly passive. The most important objects for a theory of transport are the invariant manifolds for the Poincar\u00e9 map of the flow homoclinic to fixed points, which physically correspond to the stagnation points. As fluid particles cannot cross invariant lines, these curves constitute a sort of \"template\" for their motion. For the time independent flow, the invariant manifolds connect the stagnation points and define the roll boundaries. Thus, no transport from roll to roll can occur in this case. Switching the perturbation on, these connections are broken and the manifolds are free to wander along the array of rolls. We use segments of stable and unstable manifold to define the time dependent analogue of the roll boundaries. Transport of fluid across a boundary can then be attributed to the way a region bounded by segments of stable and unstable manifold, or \"lobe,\" is evolving under map iterations. This allows us to write explicit formulae for describing the fluid transport in terms of a few of these lobes, for a general cross section defining the Poincar\u00e9 map. Using the symmetries of special cross sections, we are able to further reduce the number of necessary lobes to just one. Furthermore, these symmetries allow us to derive analytically a lower and upper bound for the first time tracer invades a roll, and a lower bound on the stretching of the interface between dyed and clear fluid. These results are independent of the fact that the perturbation is small. When this is the case however, the analytical tools of the Melnikov and subharmonic Melnikov functions are available, so that an approximation to the lobe areas and location and size of the island bands can be determined analytically. It turns out that in our case these approximations are quite good, even for relatively large perturbations. The results we have produced regarding the strong dependence of transport on the period of the oscillation suggest an effect for which no experimental verification is currently available. The presence of molecular diffusivity introduces a (long) time scale into the problem. We discuss the applicability of the theory in this situation, by introducing a simple rule for determining when the effects of diffusivity are negligible, and perform numerical simulations of the flow in this case to provide an example.
" }, { "name": "Ceccio, Steven Louis", "degree": "PhD", "year": "1990", "title": "Observations of the Dynamics and Acoustics of Travelling Bubble Cavitation", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092004-154832", "creators": [ { "name": { "family": "Ceccio", "given": "Steven Louis" }, "id": "Ceccio-Steven-Louis", "display_name": "Ceccio, Steven Louis" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/427S-BC75", "abstract": "Individual travelling cavitation bubbles generated on two axisymmetric headforms were detected using a surface electrode probe. The growth and collapse of the bubbles, almost all of which were quasi-spherical caps moving close to the headform surface, were studied photographically. Although the growth patterns for the two headforms were similar, the collapse mechanisms were quite different. These differences were related to the pressure fields and viscous flow patterns associated with each headform. Measurements of the acoustic impulse generated by the bubble collapse were analyzed and found to correlate with the maximum volume of the bubble for each headform. Numerical solutions of the Rayleigh-Plesset equation were generated for the same flows and compared with the experimental data. The experiments revealed that for smaller bubbles the impulse-volume relationship is determinate, but for larger bubbles the impulse becomes more uncertain. The theoretical impulse was at least a factor of two greater than the measured impulse, and the impulse-volume relationship was related to the details of the collapse mechanism. Acoustic emission of individual cavitation events was spectrally analyzed and the results were compared with relevant theoretical and emperical predictions. Finally, the cavitation nuclei flux was measured and compared to the cavitation event rate and the bubble maximum size distribution through the use of a simple model. The nuclei number distribution was found to vary substantially with tunnel operating conditions, and changes in the nuclei number distribution significantly influenced the cavitation event rate and bubble maximum size distribution. The model estimated the cavitation event rate but failed to predict the bubble maximum size distribution. With the above theoretical and experimental results, the cavitation rate and resulting noise production may be estimated from a knowledge of the non-cavitating flow and the free stream nuclei number distribution.
" }, { "name": "Chen, Howard ZeHua", "degree": "PhD", "year": "1990", "title": "GaAs/Al\u2093Ga\u2081\u208b\u2093As Quantum Well Lasers Grown on GaAs and Si by Molecular Beam Epitaxy", "advisor": "Yariv, Amnon; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212007-153159", "creators": [ { "name": { "family": "Chen", "given": "Howard ZeHua" }, "id": "Chen-Howard-ZeHua", "display_name": "Chen, Howard ZeHua" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/thfh-4627", "abstract": "Molecular beam epitaxy (MBE) has been known as a \"black art\" since its invention in the early 1970's. The main goal of this thesis is to present practical techniques used daily MBE experts which have never been discussed in the literature. If this thesis can make a small step toward a better understanding and utilization of this technology, the author is more than satisfied.
\r\n\r\nThe following is a summary of experimental and theoretical work of GaAs-on-GaAs and GaAs-on-Si material growth by MBE. Except for the relatively new GaAs-on-Si research, background information is presented at a minimum level. Emphasis is made on both theoretical and experimental techniques rather than on general discussions which exist in the literature.
\r\n\r\nThe thesis begins with an introduction, in Chapter 1, to activities in molecular beam epitaxy and related crystal growth methods as well as their applications in the field of optical interconnects using low-threshold lasers and high-speed photodetectors.
\r\n\r\nIn Chapter 2, a Green's function formulation of interface matching problems is presented. A very simple equation can be derived, which can provide some support to a very controversial, yet highly successful and very popular quantum dipole model for Schottky barriers and heterojunctions by J. Tersoff. A simplified model can be obtained, which eliminates the uncertainties in Tersoff's scheme and predicts very well the band offsets for several important semiconductor heterosystems including GaAs/AlAs. The theory is found to be in excellent agreement with a photoelectric measurement on the band offsets of the GaAs/AlGaAs system.
\r\n\r\nChapter 3 deals with details of MBE growth of GaAs/AlGaAs quantum well laser material on GaAs substrates. Various growth techniques and substrate orientations are discussed. The dependence of threshold current density of a GaAs/AlGaAs GRINSCH laser on quantum well thickness is experimentally studied. The experimental results are in good agreement with a qualitative analysis. A theoretical discussion of the effect of quantum well thickness on the threshold current density is used to explain the experimental results. Furthermore, this study has achieved for the first time, threshold current densities below 100 A/cm\u00b2 in any semiconductor laser. The transparency current density obtained in this study, 60 A/cm\u00b2, is very close to the theoretical prediction of 63 A/cm\u00b2. It also establishes a record of lowest threshold current density for any semiconductor lasers.
\r\n\r\nChapter 4 presents some important issues in GaAs-on-Si research. Both the potentialities and limitations of GaAs-on-Si technology are discussed. The main advantage of GaAs-on-Si technology is the special features of Si substrates not available in GaAs substrates.
\r\n\r\nChapter 5 discusses the experimental aspects of GaAs-on-Si laser growth by MBE. The formation and prevention of antiphase domains (APDs) are discussed. Various methods to reduce defect density are presented. The first low threshold current density GaAs-on-Si laser growth by MBE, and the first room temperature continuous wave (CW) operation are described in detail. Important applications such as high-speed modulation of GaAs-on-Si stripe lasers and high-speed GaAs-on-Si p-i-n photodiodes are also presented.
\r\n\r\nAppendix I summarizes the operation and maintenance of a Riber 2300 MBE system from a practical point of view. Only several components in this MBE system are absolutely needed to grow high quality materials. It also discusses the routine material calibrations performed. Appendix II, III, IV, V, and VI deal with the details of material processing and device fabrication.
" }, { "name": "Chua, Kiat", "degree": "PhD", "year": "1990", "title": "Vortex Simulation of Separated Flows in Two and Three Dimensions", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092005-142847", "creators": [ { "name": { "family": "Chua", "given": "Kiat" }, "id": "Chua-Kiat", "display_name": "Chua, Kiat" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9ENS-EP36", "abstract": "This thesis is concerned with the applications of vortex methods to the problem of unsteady, separated flows in two and three dimensions, and can be divided into three parts. In the first part, an improved method for satisfying the boundary conditions on a flat plate is developed and applied to the two-dimensional separated flow problem. In this method, boundary layers on both side of the plate are represented by stacks of multiple vortex panels, the strength of which are determined by enforcing both the no-through flow and no-slip boundary conditions at the plate. Vortex shedding at the sharp edge of the plate is represented as the separation of the boundary vortex elements. Both forced and unforced flows are studied and comparisons to experiments are carried out. For the case without forcing, large discrepancy between calculations and experiments, which is also reported by other workers using a different vortex method or Navier-Stokes calculations, is observed. In the case with forcing, the discrepancy is reduced with lateral forcing at low amplitude; and eliminated, regardless of amplitude, with streamwise forcing (acceleration). In the second part, an improved three-dimensional vortex particle method is developed. In this method, vortex elements of vorticity that move with the local velocity and are stretched and rotated according to the local strain field, are used. To mimic the effects of vorticity cancellations, close pairs of opposite sign vortex elements are replaced by high order dipoles. The method is designed to handle complex high Reynolds number vortical flows and a non-linear viscosity model is included to treat small-scale effects in such flows. Applications to two problems involving strong interactions of vortex tubes are carried out and core deformation with complex internal strucures and induced axial flow within vortex tubes are observed. Qualitative comparison to experiments are encouraging. In the third part, the two-dimensional method developed in the first part is modified and extended to three dimensions. Here, solenoidal condition for vorticity is considered and closed vortex loops are used to represent the boundary layer vorticity and the vorticity at shedding. For the evolution of the vortex wake, the vortex particle method developed in the second part is used. Applications to the flow past a normal square plate is carried out and the early stages of the flow are studied.
" }, { "name": "Deng, Xiaomin", "degree": "PhD", "year": "1990", "title": "Dynamic Crack Propagation in Elastic-Plastic Solids", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062003-112730", "creators": [ { "name": { "family": "Deng", "given": "Xiaomin" }, "id": "Deng-Xiaomin", "display_name": "Deng, Xiaomin" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/WHJV-C644", "abstract": "The present finite element study addresses several issues of interest pertaining to the phenomenon of dynamic crack propagation in elastic-plastic solids. Three classes of materials, namely elastic-perfectly plastic materials, linear hardening materials and power-law hardening materials, are considered. The materials are assumed to obey the von Mises yield criterion and the associated flow rule.
\r\n\r\nUnder conditions of Mode I, plane stress, steady state and small scale yielding, we investigated the structures of the near-tip stress and deformation fields. A preliminary asymptotic analysis for crack-tip stress and velocity fields in elastic-perfectly plastic solids was provided to reveal and explain some special features of the crack tip fields observable only in the case of rapid crack propagation. We studied the theoretical basis of a fracture criterion based on the dynamic stress intensity factor for crack growth in materials which fail in a locally ductile manner. We explored the behavior of crack tip fields under non-K-dominance conditions and its effects on the dynamic fracture toughness vs. crack propagation speed relationship.
\r\n\r\nAn Eulerian finite element scheme is employed. Finite element meshes with extremely small elements near the crack tip are carefully designed. The ratio of the crack tip plastic zone size to that of the element nearest to the crack tip is of the order of 1.6 x 10\u2074. In order to overcome numerical difficulties associated with crack-tip strain singularities and the use of small near-tip elements, an efficient stress integration algorithm is devised. The existing stress state determination procedure is modified to prevent the occurrence of negative plastic flow and to avoid mistakenly treating elastic unloading as plastic flow. The above measures are proven to be essential for the convergence of the numerical solution.
" }, { "name": "Do\u011fanata, Zinnur", "degree": "PhD", "year": "1990", "title": "General Structural Representations for Multi-Input Multi-Output Discrete-Time FIR and IIR Lossless Systems", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02222007-083438", "creators": [ { "name": { "family": "Do\u011fanata", "given": "Zinnur" }, "id": "Do\u011fanata-Zinnur", "display_name": "Do\u011fanata, Zinnur" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/h011-7b66", "abstract": "Discrete-time lossless systems have been found to be of great importance in many signal processing applications. However, a representation for lossless transfer matrices that spans all such matrices with the smallest possible number of parameters has not been proposed earlier. Existing representations are usually for special cases and therefore not general enough. In this study, two general and minimal representations are presented for multi-input, multi-output FIR and IIR lossless systems. The first representation is in terms of planar rotations and it leads to multi-input, multi-output lattice structures. The second representation is in terms of unit-norm vectors and it enables shorter convergence times in optimization applications. A simple modification of this representation leads to structures that remain lossless under quantization. The structures that follow from these representations share some properties such as the orthogonality of the implementations, and minimality of the number of parameters and scalar delays they are. Since all lossless transfer matrices can be spanned by appropriately adjusting their parameters, these structures can be particularly useful in applications that involve optimization under the constraint of losslessness. Some examples of such applications are included.
" }, { "name": "Fric, Thomas Frank", "degree": "PhD", "year": "1990", "title": "Structure in the Near Field of the Transverse Jet", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-02232007-075829", "creators": [ { "name": { "family": "Fric", "given": "Thomas Frank" }, "id": "Fric-Thomas-Frank", "display_name": "Fric, Thomas Frank" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JVHG-E582", "abstract": "Photographs of an axisymmetric turbulent jet issuing from a wall into a crossflow display the four types of vortical structures which exist in the near field: the jet shear layer vortices, the nascent far field vortex pair, the near wall horseshoe vortices, and a system of vortices in the wake of the jet.
\r\n\r\nAdditionally, results of hot-wire measurements in the wake of the transverse jet are presented. Among these results are characteristic wake Strouhal frequencies, which vary with the jet to crossflow velocity ratio, and wake velocity profiles.
\r\n\r\nIt is found that the wake vorticity is not \"shed\" from the jet but is formed from vorticity which originated in the wall boundary layer. Therefore, analogies between the wakes of transverse jets and the wakes of solid cylinders are incorrect. Since the jet is not a solid obstacle to the crossflow, as a cylinder is, new vorticity is not generated at the interface between the jet and the crossflow. Instead, the boundary layer on the wall from which the jet issues separates near the downstream side of the jet because it cannot negotiate the adverse pressure gradient imposed on it by the flow around the jet, which is not \"separated\" as it is for a cylinder. The wake vortices subsequently formed are found to be most coherent near a jet to crossflow velocity ratio of four.
\r\n\r\nThe near field development of the counterrotating vortex pair, which is the dominant structure of the far field jet, is also addressed. It is argued that the source of vorticity for the vortex pair is the vorticity from the boundary layer within the jet nozzle. Estimates for the strength of these vortices are obtained by considering the flux of vorticity emanating from the nozzle.
\r\n\r\nPossible implications for mixing are briefly discussed.
" }, { "name": "Goldstein, David Benjamin", "degree": "PhD", "year": "1990", "title": "Investigations of a Discrete Velocity Gas", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152007-093505", "creators": [ { "name": { "family": "Goldstein", "given": "David Benjamin" }, "id": "Goldstein-David-Benjamin", "display_name": "Goldstein, David Benjamin" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DK4P-AK28", "abstract": "A new model of molecular gasdynamics with discrete molecular velocity components has been implemented for parallel computation. When the suitably normalized velocity components can take only integer values and time is discretized for digital computation, the particles travel between a regular array of points in physical and velocity space, and the gas is called a \"lattice gas.\" Calculations of molecular motions are thereby simplified. The outcome of binary collisions between particles is determined by reflections about axes of symmetry in the center-of-mass frame of reference. The procedure speeds calculations of collisions. Of interest is the insight the discrete model provides into complex physical behavior and the effect that physically realistic simplifications have on the accuracy and speed of parallel calculations of a flow.
\r\n\r\nThe equilibrium state of a discrete-velocity gas and the influence of limited velocity resolution are explained. It is found that the equilibrium velocity distribution functions of the present model agree with those of the discrete Boltzmann equation at very low velocity resolution and the continuous-velocity Boltzmann equation at higher velocity resolution. The time development of non-equilibrium velocity distribution functions is presented. The model is applied to unsteady flows involving strong shock waves, heat transfer between solid surfaces, and unsteady shear layer development.
\r\n\r\nWhen the model is applied to gas mixtures, numerical experiments show that the required number of values of each component of molecular velocity depends strongly upon the mass ratios of the particle species involved. However, fewer than ten values of each velocity component are necessary to produce results of satisfactory accuracy in calculations of a shock wave in a single species gas. A unique, self-adaptive mesh for parallel computation, used either for the present lattice gas model or earlier direct simulation Monte Carlo (Bird, 1976) models, is described. The mesh balances the load between the processors of the multicomputer and maintains the cell size at approximately a fixed number of local mean free paths throughout the flow field.
" }, { "name": "Hayes, Catherine Kent", "degree": "PhD", "year": "1990", "title": "Diffusion and stress driven flow in polymers", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02212007-132113", "creators": [ { "name": { "family": "Hayes", "given": "Catherine Kent" }, "id": "Hayes-C-K", "display_name": "Hayes, Catherine Kent" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/1NE9-1T14", "abstract": "A recently proposed model for non-Fickian diffusion of penetrants into polymers is adapted and used to study a drug-delivery problem. The model modifies Fick's diffusion equation by the addition of stress-induced flux and a bimolecular reaction term. A stress evolution equation incorporating aspects of the Maxwell and Kelvin-Voigt viscoelastic stress models completes the model. The diffusivity and relaxation time in the polymer are taken as functions of the penetrant concentration.\r\n\r\nThe system is first studied on a doubly infinite domain under the assumption that the penetrant's saturation concentration is small. When the diffusivity and relaxation time are taken to be constant, a perturbation analysis is used to show the form and the region of stability of traveling-wave solutions. When the diffusivity and relaxation time are taken as specified functions of the concentration, the shapes of traveling-wave solutions are predicted by perturbation analysis and found to be different when the equations are diffusion-driven than when they are stress-driven. The predictions are verified by numerical integration for specified parameter values.\r\n\r\nThe system is also studied on a finite domain under the assumption that the diffusivity is large. A perturbation analysis is used to demonstrate that the concentration and stress evolve according to a Fickian diffusion equation on a short time scale. After longer time has elapsed, the concentration and stress are shown to exhibit steep fronts in a narrow region within the domain. These predictions are verified numerically. Finally, the equations are studied in the steady state and are found to predict the evolution of shocks.\r\n\r\nWork done on Fisher's equation is presented in an appendix. When the diffusivity is taken in the same nonlinear form as was used in the polymer-penetrant model, a qualitatively new solution of Fisher's equation is found, using a method which is also applied to the polymer-penetrant system" }, { "name": "Hildemann, Lynn Mary", "degree": "PhD", "year": "1990", "title": "A study of the origin of atmospheric organic aerosols", "advisor": "", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222007-143006", "creators": [ { "name": { "family": "Hildemann", "given": "Lynn Mary" }, "id": "Hildemann-L-M", "display_name": "Hildemann, Lynn Mary" } ], "advisors": [], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" } ], "option_major": [ "envreng" ], "doi": "10.7907/XFQA-MH78", "abstract": "The sources of ambient organic particulate matter in urban areas are investigated through a program of emission source measurements, atmospheric measurements, and mathematical modeling of source/receptor relationships. A dilution sampler intended to collect fine organic aerosol from combustion sources is designed to simulate atmospheric cooling and dilution processes, so that organic vapors which condense under ambient conditions will be collected as particulate matter. This system is used to measure the emissions from a boiler burning distillate oil, a home fireplace, catalyst and noncatalyst automobiles, heavy-duty diesel trucks, natural gas home appliances, and meat cooking operations. Alternate techniques are used to sample the particulate matter emitted from cigarette smoking, a roofing tar pot, paved road dust, brake lining wear, tire wear, and vegetative detritus. The bulk chemical characteristics of the fine aerosol fraction are presented for each source. Over half of the fine aerosol mass emitted from automobiles, wood burning, meat cooking, home appliances, cigarettes, and tar pots is shown to consist of organic compounds.\r\n\r\nThe organic material collected from these sources is analyzed using high-resolution gas chromatography. Using a simple analytical protocol, a quantitative, 50-parameter characterization of the elutable fine organic aerosol emitted from each source type is obtained, which proves to be a unique fingerprint that can be used to distinguish most sources from each other.\r\n\r\nA mathematical model is used to predict the characteristics of fine ambient organic aerosol in the Los Angeles area that would prevail if the primary organic emissions are transported without chemical reaction. The model is found to track the seasonal variations observed in the ambient aerosol at the three sites studied. Emissions from vehicles and fireplaces are identified as significant sources of solvent-extractable organic aerosol.\r\n\r\nDifferences between the model predictions and ambient concentrations that could be due to atmospheric chemical reaction are discussed. An upper limit on the amount of secondary organic aerosol present is estimated based on the difference between the acidic organic aerosol present in ambient samples versus that due to primary emissions as computed by the model. Finally, several hypotheses concerning the origin of the acidic organic aerosol are proposed." }, { "name": "Hou, Zhikun", "degree": "PhD", "year": "1990", "title": "Nonstationary Response of Structures and its Application to Earthquake Engineering", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechThesis:03112014-153421620", "creators": [ { "name": { "family": "Hou", "given": "Zhikun" }, "id": "Hou-Zhikun", "display_name": "Hou, Zhikun" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/db5g-6572", "abstract": "This thesis presents a simplified state-variable method to solve for the nonstationary response of linear MDOF systems subjected to a modulated stationary excitation in both time and frequency domains. The resulting covariance matrix and evolutionary spectral density matrix of the response may be expressed as a product of a constant system matrix and a time-dependent matrix, the latter can be explicitly evaluated for most envelopes currently prevailing in engineering. The stationary correlation matrix of the response may be found by taking the limit of the covariance response when a unit step envelope is used. The reliability analysis can then be performed based on the first two moments of the response obtained.
\r\n\r\nThe method presented facilitates obtaining explicit solutions for general linear MDOF systems and is flexible enough to be applied to different stochastic models of excitation such as the stationary models, modulated stationary models, filtered stationary models, and filtered modulated stationary models and their stochastic equivalents including the random pulse train model, filtered shot noise, and some ARMA models in earthquake engineering. This approach may also be readily incorporated into finite element codes for random vibration analysis of linear structures.
\r\n\r\nA set of explicit solutions for the response of simple linear structures subjected to modulated white noise earthquake models with four different envelopes are presented as illustration. In addition, the method has been applied to three selected topics of interest in earthquake engineering, namely, nonstationary analysis of primary-secondary systems with classical or nonclassical dampings, soil layer response and related structural reliability analysis, and the effect of the vertical components on seismic performance of structures. For all the three cases, explicit solutions are obtained, dynamic characteristics of structures are investigated, and some suggestions are given for aseismic design of structures.
" }, { "name": "Jahnke, Craig C.", "degree": "PhD", "year": "1990", "title": "Application of Dynamical Systems Theory to Nonlinear Aircraft Dynamics", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092007-134504", "creators": [ { "name": { "family": "Jahnke", "given": "Craig C." }, "id": "Jahnke-Craig-C", "display_name": "Jahnke, Craig C." } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "orcid": "0000-0002-4903-8419", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9KZS-XC46", "abstract": "A continuation method has been used to determine the steady states of three nonlinear aircraft models: a general aviation aircraft with a canard configuration, a generic jet fighter, and the F-14. The continuation method calculated the steady states of the aircraft as functions of the control surface deflections. Bifurcations of these steady states were determined and shown to cause instabilities which resulted in qualitative changes in the state of the aircraft. A longitudinal instability which resulted in a deep stall was determined for the general aviation aircraft. Roll-coupling and high angle of attack instabilities were determined for the generic jet fighter, and wing rock, directional divergence and high angle of attack instabilities were determined for the F-14.
\r\n\r\nKnowledge of the control surface deflections at which bifurcations occurred was used to either put limits on the control surface deflections or to program the control surface deflections such that a combination of control surface deflections at which bifurcations occur could not be attained. Simple control systems were included in the aircraft models to determine the effects of control systems on the instabilities of each aircraft. Steady spin modes were determined for each aircraft. A successful recovery technique was determined for the general aviation aircraft, but no successful recovery technique could be found for the F-14.
" }, { "name": "Jensen, Hector A.", "degree": "PhD", "year": "1990", "title": "Dynamic Response of Structures with Uncertain Parameters", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechThesis:03112014-155226390", "creators": [ { "name": { "family": "Jensen", "given": "Hector A." }, "id": "Jensen-Hector-A", "display_name": "Jensen, Hector A." } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/5970-fp02", "abstract": "This thesis presents a technique for obtaining the response of linear structural systems with parameter uncertainties subjected to either deterministic or random excitation. The parameter uncertainties are modeled as random variables or random fields, and are assumed to be time-independent. The new method is an extension of the deterministic finite element method to the space of random functions.
\r\n\r\nFirst, the general formulation of the method is developed, in the case where the excitation is deterministic in time. Next, the application of this formulation to systems satisfying the one-dimensional wave equation with uncertainty in their physical properties is described. A particular physical conceptualization of this equation is chosen for study, and some engineering applications are discussed in both an earthquake ground motion and a structural context.
\r\n\r\nFinally, the formulation of the new method is extended to include cases where the excitation is random in time. Application of this formulation to the random response of a primary-secondary system is described. It is found that parameter uncertainties can have a strong effect on the system response characteristics.
" }, { "name": "Jiang, Qing", "degree": "PhD", "year": "1990", "title": "A continuum model for phase transformation in thermoelastic solids", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02232007-155324", "creators": [ { "name": { "family": "Jiang", "given": "Qing" }, "id": "Jiang-Q", "display_name": "Jiang, Qing" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/x4hj-2v63", "abstract": "Under suitable programs of mechanical or thermal loading, many solid materials are capable of undergoing phase transformations from one crystal structure to another. The austenite-martensite transformation that occurs in a variety of metallic alloys, including the so-called shape-memory materials, provides an example. The present paper represents an effort to model coupled thermo-mechanical effects in the macroscopic response of solids that arise from the occurrence of phase transformations. A Helmholtz free energy potential is constructed to describe the thermo-mechanical response of the hypothetical material to be considered here. As a function of strain, the potential is non-convex in a certain range of temperature; this feature is essential for the modeling of phase transformations. Apart from some general preliminary considerations pertaining to finite thermoelasticity, the analysis is carried out in the context of a simple problem, idealized from an experiment, in which an annular cylinder is deformed to a state of radially symmetric, finite anti-plane shear in the presence of differing inner and outer surface temperatures. After constructing all radially symmetric weak solutions involving at most a single surface of discontinuity of strain or temperature gradient, we determine the implications for quasi-static motions of the second law of thermodynamics. The thermo-mechanical phase transformation-induced hysteresis, residual deformation and stress relaxation effects exhibited by this model are discussed and the results concerning creep rate as predicted by the present model are in qualitative agreement with the laboratory observation. Finally, the shape-memory effect as predicted by the present thermo-mechanical model in the setting of finite anti-plane shear is illustrated." }, { "name": "Kalra, Devendra", "degree": "PhD", "year": "1990", "title": "A unified framework for constraint-based modeling", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05042007-134103", "creators": [ { "name": { "family": "Kalra", "given": "Devendra" }, "id": "Kalra-D", "display_name": "Kalra, Devendra" } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/33km-wt29", "abstract": "Constraint-based modeling techniques are emerging as an effective computer graphics approach for modeling and designing objects and their behaviors.\n\nIn this thesis, computer graphics constraint techniques are unified into a single conceptual framework. The central themes of the thesis are methods to partition an arbitrary constraint problem in different domains and at different levels, and to provide a language and computational environment for modeling with constraints. Using partitioning and composition schemes, complex simulations can be built hierarchically from simpler simulations by \"plugging\" together separate modules. Fundamental and basic structures are designed and implemented to provide an \"Assembly Language\" for simulation systems. These structures are put together through a collection of interfaces, much like multiple languages that use the same assembler on a computer.\n\nWe use strategies called refinement and partitioning to integrate seemingly disparate constraint techniques. We present Temporal Sequencing as an approach to design complex time behaviors of simulation systems.\n\nRefinement is a top-down approach of transforming high level representations of a constraint modeling problem into representations that are closer to the basic solution mechanisms available in the constraint environment, such as numerical solution methods. Partitioning is the decomposition of one constraint problem into multiple simpler constraint problems that are then studied separately. Temporal Sequencing is a methodology to design the time behavior of a simulation system by composing time behaviors of the system over subintervals of time.\n\nUsing the above partitioning schemes for the solution and specification of a general constraint problem, we create a unified constraint environment with the capability to both solve constraint problem instances and to create specialized constraint systems. New methods of constraint specification and solution can be added into the same constraint framework as new methods are developed.\n\nBased on the above approach, a modeling system called \"Our Constraint Environment\"(OCE) has been implemented. A programming language as an extension to C++ has been designed to provide an interface to OCE. The language provides the constructs for the partitioning schemes discussed above. Simulations created using OCE have shown the efficacy of our design approach." }, { "name": "Kavranoglu, Davut", "degree": "PhD", "year": "1990", "title": "Elementary solutions for the H infinity- general distance problem- equivalence of H2 and H infinity optimization problems", "advisor": "Sideris, Athanasios", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152007-142515", "creators": [ { "name": { "family": "Kavranoglu", "given": "Davut" }, "id": "Kavranoglu-D", "display_name": "Kavranoglu, Davut" } ], "advisors": [ { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "advisor", "display_name": "Sideris, Athanasios" } ], "committee": [ { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "chair", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "role": "member", "display_name": "Morari, Manfred" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/y2q9-nq75", "abstract": "This thesis addresses the H[infinity] optimal control theory. It is shown that SISO H[infinity] optimal control problems are equivalent to weighted Wiener-Hopf optimization in the sense that there exists a weighting function such that the solution of the weighted H2 optimization problem also solves the given H[infinity] problem. The weight is identified as the maximum magnitude Hankel singular vector of a particular function in H[infinity] constructed from the data of the problem at hand, and thus a state-space expression for it is obtained. An interpretation of the weight as the worst-case disturbance in an optimal disturbance rejection problem is discussed.\n\nA simple approach to obtain all solutions for the Nehari extension problem for a given performance level [gamma] is introduced. By a limit taking procedure we give a parameterization of all optimal solutions for the Nehari's problem.\n\nUsing an imbedding idea [12], it is proven that four-block general distance problem can be treated as a one-block problem. Using this result an elementary method is introduced to find a parameterization for all solutions to the four-block problem for a performance level [gamma].\n\nThe set of optimal solutions for the four-block GDP is obtained by treating the problem as a one-block problem. Several possible kinds of optimality are identified and their solutions are obtained." }, { "name": "Kovacic, Gregor", "degree": "PhD", "year": "1990", "title": "Chaos in a model of the forced and damped sine-Gordon equation", "advisor": "Wiggins, Stephen R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152007-075202", "creators": [ { "name": { "family": "Kovacic", "given": "Gregor" }, "id": "Kovacic-G", "display_name": "Kovacic, Gregor" } ], "advisors": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "advisor", "display_name": "Wiggins, Stephen R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/rg86-2095", "abstract": "We analytically determine two of the mechanisms which cause chaotic dynamics to appear in a model of the forced and damped Sine-Gordon equation. In particular, we find orbits homoclinic to periodic orbits, and orbits homoclinic to fixed points which satisfy conditions sufficient to guarantee the existence of nearby chaotic invariant sets. One of these homoclinic orbits is a so-called Silnikov-type loop. A proof the existence of a symmetric pair of such loops is our main result. This proof consists of a modified Melnikov perturbation analysis, augmented by some techniques from the field of geometric singular perturbation theory.\n" }, { "name": "Lazzaro, John P.", "degree": "PhD", "year": "1990", "title": "Silicon Models of Early Audition", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152007-085000", "creators": [ { "name": { "family": "Lazzaro", "given": "John P." }, "id": "Lazzaro-John-P", "display_name": "Lazzaro, John P." } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" } ], "option_major": [ "compsci" ], "doi": "10.7907/nt1w-ry58", "abstract": "This dissertation describes silicon integrated circuits that model known and proposed physiological structures in the early auditory system. Specifically, it describes silicon models of auditory-nerve response, of auditory localization in the barn owl, and of pitch perception. The integrated circuits model the structure as well as the function of the physiology; all subcircuits in the chips have anatomical correlates. The chips, two of which contain over 100,000 transistors, compute all outputs in real time, using analog, continuous-time processing. In most respects, chip responses approximate physiological or psychophysical response of the modeled biological systems. The dissertation also describes a novel nonlinear-inhibition circuit, which is a key component of two of the silicon models.\r\n" }, { "name": "Levine, Marie-Bernard P.", "degree": "PhD", "year": "1990", "title": "Accelerogram Processing Using Reliability Bounds and Optimal Correction Methods", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechThesis:03112014-160752285", "creators": [ { "name": { "family": "Levine", "given": "Marie-Bernard P." }, "id": "Levine-Marie-Bernard P", "display_name": "Levine, Marie-Bernard P." } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/vnh6-g135", "abstract": "This study addresses the problem of obtaining reliable velocities and displacements from accelerograms, a concern which often arises in earthquake engineering. A closed-form acceleration expression with random parameters is developed to test any strong-motion accelerogram processing method. Integration of this analytical time history yields the exact velocities, displacements and Fourier spectra. Noise and truncation can also be added. A two-step testing procedure is proposed and the original Volume II routine is used as an illustration. The main sources of error are identified and discussed. Although these errors may be reduced, it is impossible to extract the true time histories from an analog or digital accelerogram because of the uncertain noise level and missing data. Based on these uncertainties, a probabilistic approach is proposed as a new accelerogram processing method. A most probable record is presented as well as a reliability interval which reflects the level of error-uncertainty introduced by the recording and digitization process. The data is processed in the frequency domain, under assumptions governing either the initial value or the temporal mean of the time histories. This new processing approach is tested on synthetic records. It induces little error and the digitization noise is adequately bounded. Filtering is intended to be kept to a minimum and two optimal error-reduction methods are proposed. The \"noise filters\" reduce the noise level at each harmonic of the spectrum as a function of the signal-to-noise ratio. However, the correction at low frequencies is not sufficient to significantly reduce the drifts in the integrated time histories. The \"spectral substitution method\" uses optimization techniques to fit spectral models of near-field, far-field or structural motions to the amplitude spectrum of the measured data. The extremes of the spectrum of the recorded data where noise and error prevail are then partly altered, but not removed, and statistical criteria provide the choice of the appropriate cutoff frequencies. This correction method has been applied to existing strong-motion far-field, near-field and structural data with promising results. Since this correction method maintains the whole frequency range of the record, it should prove to be very useful in studying the long-period dynamics of local geology and structures." }, { "name": "Liu, Vincent Cheng-Teh", "degree": "PhD", "year": "1990", "title": "One and two-dimensional digital mutirate systems with applications in sub-sampling and bandlimited signal reconstruction", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092007-130540", "creators": [ { "name": { "family": "Liu", "given": "Vincent Cheng-Teh" }, "id": "Liu-V-C", "display_name": "Liu, Vincent Cheng-Teh" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/cvbb-m844", "abstract": "This thesis deals with the two-dimensional (2D) multirate quadrature mirror filter (QMF) bank and new applications of 1D and 2D multirate filter bank concepts to the periodic nonuniform sampling and reconstruction of bandlimited signals. The potential use of multirate filter banks in the statistically optimal estimation of signals in the presence of wide-sense cyclostationary noise is also examined. The two-dimensional QMF bank is free from aliasing if and only if a certain polyphase matrix product related to the filter bank possesses the 2D pseudo-circulant property. A 2D FIR filter bank can be designed with the perfect reconstruction property if the polyphase matrix of its analysis filter bank is constrained to be a 2D lossless matrix. A design example is included. The losslessness constraint is satisfied by imposing a cascaded structure of first-degree lossless sections on the polyphase matrix. A limited factroization theorem is derived for 2D FIR lossless systems where the order in one of the two dimensions is limited to unity. In the area of nonuniform sampling of multiband bandlimited signals, the filter bank approach is utilized to derive a computationally efficient method for reconstructing bandlimited signals. The above scheme can also be viewed as a mean of compressing and reconstructing an oversampled bandlimited signal. It is shown that such a scheme has lower computational complexity than traditional methods of sampling rate alteration. The results can be extended to nonuniform sampling in two-dimensions using integer lattices. A further application of the multirate filter bank is in signal estimation in the presence of cyclostationary noise. The necessary and sufficient condition for the filter bank to preserve the wide-sense stationarity of the input is derived. Several applications where cyclostationary noise is present are indicated, and through the use of simulations the performance of the optimal filter bank can be compared with the conventional scalar optimal filter. The roundoff noise in orthogonal matrix building blocks is analyzed, since these building blocks are commonly present in filter bank implementations." }, { "name": "Losi, Giancarlo Umberto Maria", "degree": "PhD", "year": "1990", "title": "Nonlinear thermoviscoelastic behavior of polymers", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-103818", "creators": [ { "name": { "family": "Losi", "given": "Giancarlo Umberto Maria" }, "id": "Losi-G-U-M", "display_name": "Losi, Giancarlo Umberto Maria" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2dk7-z575", "abstract": "The rheological behavior of polymers in the neighborhood of the glass transition has been investigated in the framework of the free volume theory of nonlinear viscoelastic behavior. Free volume theory as normally applied above the glass transition was modified to account for the effect of the residual volume of vacancies below the glass transition; this modification was accomplished by modelling the changes in the state of the polymer as the sum of viscoelastic changes and a random disturbance deriving from the thermal collisions between molecules. The changes in mechanical properties going across the glass transition follow from the freezing-in of relaxation mechanisms and of free volume. The pressure dependence of the glass transition was found to be in qualitative agreement with measurements on PVAc, while the ratio of the glassy and rubbery heat capacities was found to coincide with the ratio of the equilibrium bulk compliances in the glassy and rubbery domains. The predictions of the model for the problem of transient and residual thermal stresses were compared with those of two simpler models.\n\nThe second part of the thesis studies the consequences of the nonlinear viscoelastic behavior on the decohesion zone in front of a crack propagating through an adhesive layer. The softening of the material response in the cohesive zone is taken to be effected by free volume induced change in relaxation times of the cohesive material and by void growth; the latter is assumed to depend on a critical value of strain at the beginning of the cohesive zone. The stress intensity factor for steady crack propagation is obtained by imposing the finiteness of strains at the crack tip. For the case where the properties of the adherends are the same as the linearized properties of the adhesive, the predictions show three regimes of crack propagation: a low speed regime where the adherends behave elastically with the rubbery properties, an intermediate range where their response becomes increasingly stiffer, and a high speed regime characterized by glassy behavior of the adherends and control of the crack growth process exclusively by the nonlinearly viscoelastic behavior of the failing material." }, { "name": "Makur, Anamitra", "degree": "PhD", "year": "1990", "title": "Low rate image coding using vector quantization", "advisor": "Posner, Edward C.; Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282007-110244", "creators": [ { "name": { "family": "Makur", "given": "Anamitra" }, "id": "Makur-A", "display_name": "Makur, Anamitra" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "co-advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/GEP0-NG36", "abstract": "This thesis deals with the development and analysis of a computationally simple vector quantization image compression system for coding monochrome images at low bit rate. Vector quantization has been known to be an effective compression scheme when a low bit rate is desirable, but the intensive computation required in a vector quantization encoder has been a handicap in using it for low rate image coding. The present work shows that, without substantially increasing the coder complexity, it is indeed possible to achieve acceptable picture quality while attaining a high compression ratio.\r\n\r\nSeveral modifications to the conventional vector quantization coder are proposed in the thesis. These modifications are shown to offer better subjective quality when compared to the basic coder. Distributed blocks are used instead of spatial blocks to construct the input vectors. A class of input-dependent weighted distortion functions is used to incorporate psychovisual characteristics in the distortion measure. Computationally simple filtering techniques are applied to further improve the decoded image quality. Finally, unique designs of the vector quantization coder using electronic neural networks are described, so that the coding delay is reduced considerably.\r\n\r\nExcept for the basics of the vector quantization described in the first chapter, each chapter is independent from the others because each chapter deals with a separate aspect of the coder. Therefore, each chapter beyond the first can be read separately." }, { "name": "McLachlan, Robert Iain", "degree": "PhD", "year": "1990", "title": "Separated viscous flows via multigrid", "advisor": "Keller, Herbert Bishop; Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03122007-112956", "creators": [ { "name": { "family": "McLachlan", "given": "Robert Iain" }, "id": "McLachlan-R-I", "display_name": "McLachlan, Robert Iain" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "co-advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/8ZMX-HW74", "abstract": "A multigrid code is developed to solve general systems of convection-diffusion equations when the diffusion terms are small, i.e., when the Reynolds number is large. Various upwinding, artificial viscosity and defect correction schemes are considered and compared. The code is applied to the Navier-Stokes equations for various flow configurations and used to study boundary layer separation from a leading edge, with ensuing formation of a downstream eddy. The asymptotic (\"triple deck\") theory of separation is developed for this case, following Sychev, and compared to the numerical calculations at Reynolds numbers of up to 5000. Much better qualitative agreement is obtained than has been reported previously. Together with a plausible choice of two free parameters, the data can be extrapolated to infinite Reynolds number, giving quantitative agreement with triple deck theory with errors of 20% or less. The development of a region of constant vorticity is observed in the downstream eddy, and the global infinite Reynolds number limit is a Prandtl-Batchelor flow; however, when the plate is stationary, the occurrence of secondary separation suggests that the limiting flow contains an infinite sequence of eddies behind the separation point. Secondary separation can be averted by driving the plate, and in this case the limit is a single-vortex Prandtl-Batchelor flow of the type found by Moore, Saffman and Tanveer (1988); we make detailed, encouraging comparisons of the vortex sheet strength and position. By altering the boundary condition on the plate we obtain viscous eddies that approximate different members of the family of inviscid solutions. The code is also used to calculate the flow over a finite flat plate aligned with a uniform free stream; in that case, earlier conflicting results about higher-order corrections to the boundary layer are explained, and the triple deck generally believed to be established around the trailing edge is found to be consistent with the numerical results. There remains a large displacement-like effect in the boundary layer, whose exact origin is unclear." }, { "name": "Mehuys, David Glenn", "degree": "PhD", "year": "1990", "title": "Linear, nonlinear, and tunable guided wave modes for high-power (GaAl)As semiconductor lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012007-144920", "creators": [ { "name": { "family": "Mehuys", "given": "David Glenn" }, "id": "Mehuys-D-G", "display_name": "Mehuys, David Glenn" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/xjjy-2330", "abstract": "High-power, coherent radiation from semiconductor lasers is attractive for such diverse applications as free-space communication, optical data storage, and microsurgery. However, several factors conspire to prevent near-ideal performance from broad area devices and laser arrays. Waveguides wider than a few microns support many lateral modes with poor gain discrimination. Consequently, such modes are easily \"mixed\" by perturbations in gain and refractive index caused by gain saturation, thermal gradients, and inhomogeneities that are due to imperfect crystal growth. This causes spatially localized modes, multimode operation, and reduced spatial coherence, all of which lead to farfields broader than the \"diffraction limit.\"\n\nIn this thesis, we have investigated the influence of gain saturation on the lateral modes of broad area structures and laser arrays. Analytical and numerical techniques have been developed to solve self-consistently for mode shapes and propagation constants as a function of injected current density above threshold. For example, our analysis indicates that the gain-saturated modes of broad area lasers consist of an integer number of phase-locked \"filaments.\" In gain-guided quantum well lasers, these nonlinear modes are observed to oscillate into narrow, single-lobed farfields, which broaden only slightly with increased power output up to the 500mW level. Conversely, laser arrays have been widely touted as structures that suppress unwanted filamentation in favor of spatial mode control. Indeed, in this work we have demonstrated supermode control at the 100 mW power level by varying the diffraction region length in diffraction-coupled arrays. Both theoretically and experimentally, however, we have found the lateral modes of laser arrays to be unstable with increased current injection. Waveguides that are phase-matched below threshold become detuned under the influence of gain saturation, so that interguide power transfer is reduced. This decreases the injection-locking bandwidth, and ultimately, the spatial coherence. While undesirable for a laser oscillator, this property may be attractive for all-optical switching in nonlinear directional couplers.\n\nFinally, we have considered marrying the high-power, coherent output of broad area lasers and laser arrays with the broadband tunability possible in semiconductor lasers. In particular, the steplike density of states unique to quantum well structures results in gain spectra that are broader and flatter than comparable spectra of double heterostructure lasers. Experimentally, we have tuned uncoated, single quantum well stripe lasers in a grating-coupled external cavity over a range >125 nm centered about 800 nm. Similarly tuned broad area lasers output in excess of 200 mW (pulsed) into a single longitudinal mode over 80 nm, and buried heterostructure lasers were operated continuously over 90 nm. We expect that in the future, such devices could provide a compact, rugged, more efficient alternative to dye lasers." }, { "name": "Morlet, Anne Chantal", "degree": "PhD", "year": "1990", "title": "Part I. Numerical experiments for the computation of invariant curves in dynamical systems. Part II. Numerical convergence results for a one-dimensional Stefan problem", "advisor": "Lorenz, Jens; Kreiss, Heinz-Otto", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092007-080826", "creators": [ { "name": { "family": "Morlet", "given": "Anne Chantal" }, "id": "Morlet-A-C", "display_name": "Morlet, Anne Chantal" } ], "advisors": [ { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-J", "role": "advisor", "display_name": "Lorenz, Jens" }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "advisor", "display_name": "Kreiss, Heinz-Otto" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/nfr6-ca66", "abstract": "Part I\n\nWe derive a model equation for the linearized equation of an invariant curve for a Poincare map. We discretize the model equation with a second-order and third-order finite difference schemes, and with a cubic spline interpolation scheme. We also approximate the solution of the model equation with a truncated Fourier expansion. We derive error estimates for the second-order and third-order finite difference schemes and for the cubic spline interpolation scheme. We numerically implement the four schemes we consider and plot some error curves.\n\nPart II\n\nWe show for a one-dimensional Stefan problem, that the numerical solution converges to the solution of the continuous equations in the limit of zero meshsize and timestep. We discretize the continuous equations with a second-order finite difference scheme in space and Crank-Nicholson scheme in time. We derive error equations and we use L2 estimates to bound the error in terms of the truncation errors of the finite difference scheme. We confirm the analysis with numerical computations. We numerically prove that we have fourth-order convergence in space if we discretize the partial differential equations with a fourth-order scheme in space." }, { "name": "Ng, Kit Yin", "degree": "PhD", "year": "1990", "title": "Thermal plumes from staged multiport diffusers in uniform quiescent environment", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05172007-152237", "creators": [ { "name": { "family": "Ng", "given": "Kit Yin" }, "id": "Ng-K-Y", "display_name": "Ng, Kit Yin" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Koh", "given": "Robert C. Y." }, "id": "Koh-R-C-Y", "role": "member", "display_name": "Koh, Robert C. Y." } ], "option_major": [ "envreng" ], "doi": "10.7907/58bk-6222", "abstract": "The behavior of thermal plumes discharged from staged diffusers has been investigated experimentally. A staged diffuser is a type of submerged multiport diffuser characterized by an offshore orientation of the individual nozzles. It is commonly employed for the discharge of heated water from coastal power plants into the ocean because of its effective mixing capability, which does not depend on the prevailing longshore-current directions.\n\nExperiments have been performed to measure the temperature distribution of the plume in a quiescent receiving water. The three-dimensional thermal field is reconstructed from the results of two groups of measurements, the centerline experiments in which the temperature in the vertical plane along the diffuser axis is measured, and the scanning experiments in which the lateral temperature profiles are measured. The emphasis is on a homogeneous ambient receiving water, but a few illustrative experiments with ambient stratification have been carried out. The number of variables associated with the problem is very large, making it difficult to perform a generic study. Nevertheless, five of the variables (the number of ports, n, the initial jet diameter, D0, the horizontal orientation of the jet, [alpha], the total discharge flow rate, QT0, and the water depth, H) have been examined.\n\nExperimental observations support the hypothesis of a near field dominated by momentum jet mixing, and an intermediate field dominated initially by turbulent mixing and eventually by gravitational spreading. H, n and D0 are the governing parameters in both the near field and the intermediate field. By coupling dimensional analysis with experimental results, several empirical relationships have been established to give a first-order approximation relating the mean characteristics of the plume to the governing parameters. It is found that the near-field dilution can be described adequately by the simple jet model with an adjustment factor based on n. The dilution in the intermediate field, however, is relatively insensitive to n. It is also concluded that the horizontal orientation of the jet, at \u00b125\u00b0 to the diffuser axis, helps to spread the plume over a wider extent, thereby reducing the maximum temperature rise. Results from stratified experiments indicate that for weak stratification, the dynamics of the plume is not significantly modified." }, { "name": "Nikzad, Shouleh", "degree": "PhD", "year": "1990", "title": "A Study of Ion Beam Sputtering of Compound Materials with Laser Spectroscopy", "advisor": "Tombrello, Thomas A.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-03022007-090722", "creators": [ { "name": { "family": "Nikzad", "given": "Shouleh" }, "id": "Nikzad-Shouleh", "orcid": "0009-0004-1255-1018", "display_name": "Nikzad, Shouleh" } ], "advisors": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "advisor", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "chair", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "orcid": "0000-0003-0787-1610", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Pellin", "given": "Michael J." }, "id": "Pellin-M-J", "orcid": "0000-0002-8149-9768", "role": "member", "display_name": "Pellin, Michael J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/kgvz-n067", "abstract": "Single crystal metal sulfides of ZnS, CdS, and FeS\u2082 were bombarded with a 3 keV Ar\u207a beam. The secondary neutrals sputtered from the surface of the target were interrogated by laser ionization mass spectrometry and laser fluorescence spectroscopy.
\r\n\r\nThe velocity distribution and yield of sputtered Fe from a FeS\u2082 sample were measured. The velocity distribution of Fe sputtered from the sulfide is qualitatively the same as that of Fe sputtered from the pure metal. The yield of Fe from the sulfide target, after prolonged bombardment, was at most 20% of the yield from the metal. The results are compared with Monte Carlo calculations using the TRIM (transfer of ion in matter) code. Total sputtering yields of ZnS, CdS, and FeS\u2082 were measured by profilometry and were compared with the same measurements of sputtered metal targets.
\r\n\r\nWe have demonstrated the necessity of measuring sputtered molecules and excited state neutrals for accurate yield evaluation. The population distribution of ground state multiplets of sputtered Fe from FeS\u2082 is compared with that measured from an Fe target. The excited state population of sputtered Fe is slightly higher in the FeS\u2082 target (~10%). Molecular yields have also been measured by laser ionization mass spectrometry from ZnS, CdS, and FeS\u2082. S is sputtered predominantly as S\u2082 from all three crystals. Metals are sputtered as the atom, metal sulfide, and metal dimer (except in the case of Fe\u2082). The yield of the metal sulfidemolecules is about 10% of the yield of the metal. Plausible formation mechanisms of molecules and excited state neutrals are discussed.
" }, { "name": "Onyszchuk, Ivan M.", "degree": "PhD", "year": "1990", "title": "On the Performance of Convolutional Codes", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112007-120230", "creators": [ { "name": { "family": "Onyszchuk", "given": "Ivan M." }, "id": "Onyszchuk-Ivan-M", "display_name": "Onyszchuk, Ivan M." } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/7nb5-gy54", "abstract": "This thesis contains error bounds, algorithms, and techniques for evaluating the performance of convolutional codes on the Additive White Gaussian Noise (AWGN) channel. Convolutional encoders are analyzed using simple binary operations in order to determine the longest possible \"zero-run\" output and if \"catastrophic error propagation\" may occur. Methods and algorithms are presented for computing the weight enumerator and other generating functions, associated with convolutional codes, which are used to upper-bound maximum-likelihood (i.e., Viterbi) decoder error rates on memoryless channels. In particular, the complete path enumerator T(D, L, I) is obtained for the memory 6, rate 1/2, NASA standard code. A new, direct technique yields the corresponding bit-error generating function. These procedures may be used to count paths between nodes in a finite directed graph or to calculate transfer functions in circuits and networks modelled by signal flow graphs. A modified Viterbi decoding algorithm is used to obtain numbers for error bound computations.
\r\n\r\nNew bounds and approximations for maximum-likelihood convolutional decoder first-event, bit, and symbol error rates are derived, the latter one for concatenated coding system analysis. Berlekamp's tangential union bound for maximum-likelihood, block decoder word error probability on the AWGN channel is adapted for convolutional codes. Approximations to bit and symbol error rates are obtained that remain within 0.2 dB of simulation results at low signal-to-noise ratios, where many convolutional codes operate but the standard bounds are useless. An upper bound on the loss caused by truncating survivors in a Viterbi decoder leads to estimates of minimum practical truncation lengths. Lastly, the power loss due to quantizing received (demodulated) symbols from the AWGN channel is studied. Effective schemes are described for uniform channel symbol quantization, branch metric calculations, and path metric renormalization in Viterbi decoders.
" }, { "name": "Paslaski, Joel Stephen", "degree": "PhD", "year": "1990", "title": "High Speed Optoelectronics: Photodiodes, Q-Switched Laser Diode and Photoconductive Sampling", "advisor": "Yariv, Amnon; Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092007-084117", "creators": [ { "name": { "family": "Paslaski", "given": "Joel Stephen" }, "id": "Paslaski-Joel-Stephen", "display_name": "Paslaski, Joel Stephen" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "co-advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/dkyt-nc40", "abstract": "In this thesis, a variety of topics related to high speed optoelectronic devices and measurement techniques using ultrafast optical pulses are presented.
\r\n\r\nFollowing a brief introduction, the second chapter describes a Q-switched semi-conductor laser using a multi-quantum well active layer both for gain and as an intracavity loss modulator. While Q-Switching does not produce as short a pulse as modelocking, it does offer the advantage of adjustability of the repetition rate making it attractive as a source for digital communication links. It is also found to be preferred to the similar approach of gain switching due to less demanding requirements on the rf modulation power level and waveform. Results include a pulse width of ~ 20 ps which is fairly independent of the repetition rate, and a limiting repetition rate of 3.2 GHz. The onset of an irregular pulse train which limits the maximum modulation frequency, is analyzed by a graphical approach.
\r\n\r\nThe potential for optical interconnects has motivated a marriage between the two technologies of Si VLSI and GaAs optoelectronics. Direct integration by the growth of GaAs on Si had been impossible, but the MBE and MOCVD techniques now enable the growth of such layers and of a quality suitable for devices. The third chapter describes the operating characteristics of GaAs-on-Si lasers and photodiodes with particular attention to their high speed performance. Both the lasers and photodiodes show comparable high speed performance to similar structures fabricated on GaAs, with most of the shortcomings being in their dc characteristics.
\r\n\r\nIn the fourth chapter, a novel approach to improving the resolution of photoconductive sampling is presented, called differential sampling. This technique obviates the need for carrier lifetime reduction usually used to improve temporal resolution, and is in principal only limited by a small (few ps) RC circuit time. An analysis of the minimum detectable signal voltage shows the technique does quite well compared with lifetime reduction techniques which also tend to reduce mobility and dark resistance. An experimental demonstration of this technique is presented in chapter five. Using a two gap sampler, accurate measurement (10 ps resolution) of a 60 ps pulse response from a photodiode is achieved using photoconductors with a recovery time of only 150 ps. Performance near the fundamental Johnson noise limit is also attained, though the minimum detectable signal is higher than predicted due to low response of the photoconductors (probably due to poor contacts).
\r\n\r\nFinally, in chapter six, the possibility of retrieving an impulse response from its autocorrelation is explored. The use of the logarithmic Hilbert transform for phase retrieval has been discounted in the literature since most such work is concerned with imaging problems for which it is not appropriate due to their symmetric nature. However, causality and the decay nature of transient phenomena make this technique very suitable for use with the impulse response of passive devices. Conditions for the validity of this technique for temporal problems are presented. Simulated retrieval of two functions with similar autocorrelations is demonstrated with sufficient clarity to distinguish them, as well as showing good agreement with the original. Practical limitations and aspects -- such as noise, finite time domain, etc. -- are also simulated and discussed.
" }, { "name": "Popovic, Zoya Basta", "degree": "PhD", "year": "1990", "title": "Grid oscillators", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112007-121926", "creators": [ { "name": { "family": "Popovic", "given": "Zoya Basta" }, "id": "Popovic-Z-B", "display_name": "Popovic, Zoya Basta" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/721n-xr11", "abstract": "In the microwave and millimeter-wave frequency range, solid-state oscillators have limited output power levels. The alternative high-power sources are tubes, which are expensive, bulky, have a limited lifetime and require high-voltage power supplies. Combining a large number of low-power solid-state negative resistance devices becomes attractive. In this work a coherent oscillator that can combine thousands of solid-state devices is presented. The feasibility of a reliable high-power, monolithically integrated microwave and millimeter-wave source is demonstrated. In this approach, the active devices load a two-dimensional metal grid that radiates, and the power combining is done in free-space. Several MESFET grid oscillator designs are presented in this thesis, ranging from a 5 by 5 to a 10 by 10 grid in size. The 100-MESFET hybrid grid oscillator is a planar structure suitable for wafer-scale monolithic integration. This grid locks at 5 GHz, with an ERP of 24 Watts and a conversion efficiency of 20%. An equivalent embedding circuit for the devices in the grid predicts the oscillation frequency. The devices in the grid self-lock with no external locking signal present, but the grid can also be externally injection-locked. Measurements and analysis are presented for the injection-locked planar grid oscillator." }, { "name": "Sayano, Koichi", "degree": "PhD", "year": "1990", "title": "Photorefractive properties of ferroelectric materials for optical phase conjugation, two-beam coupling, and holographic storage", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072006-135048", "creators": [ { "name": { "family": "Sayano", "given": "Koichi" }, "id": "Sayano-K", "display_name": "Sayano, Koichi" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/rc1x-8046", "abstract": "The results of a systematic investigation of doped strontium barium niobate and potassium tantalate niobate for photorefractive beam coupling and optical holographic storage are presented in this thesis. Methods that were successfully employed to increase the magnitude of the photorefractive effect and speed up the response of these materials are also presented. Applications in the area of optical phase conjugation, distortion correction, limiting, and thresholding are also discussed.\n\nIn the first part, the equations governing the photorefractive effect through band transport are introduced. The solutions giving the internal space charge field in photorefractive materials are presented for the one carrier, one species model that approximates the process in strontium barium niobate and most other materials. The coupled equations describing the two-beam coupling effect are also derived.\n\nNext, the results of experiments using as-grown potassium tantalate niobate for holographic diffraction and strontium barium niobate for two-beam coupling are presented. With KTN, the effect of Nb concentration on the phase transition, temperature dependence of diffraction efficiency and dark storage time, and the effects of the bias electric field are discussed. With SBN, the effect of dopant type, temperature dependence of the photorefractive effect, the effects of dark conductivity in Cr-doped SBN:60, and wavelength dependence are presented.\n\nThe third part describes methods and results of increasing the magnitude of the photorefractive effect in SBN. Optimization of the grating period, oxidation and reduction heat treatments, temperature control, and applied fields are discussed. Significant increases in the two-beam coupling constant were observed in Cr-doped SBN:60 with applied fields of up to 10 kV/cm. An order of magnitude reduction of the response time in Rh-doped SBN:60 has been achieved with an applied field of 10 kV/cm.\n\nThe final part discusses applications of these materials, particularly in the areas of phase conjugation, distortion correction, and optical signal processing. A total internal reflection phase conjugate mirror using SBN instead of BaTiO3, a one-way image transmission scheme that can send a signal through a distorting medium, thresholding using a semilinear phase conjugate mirror with grating motion, and a field controlled and enhanced optical limiter are presented.\n" }, { "name": "Shinn-Mendoza, Rachel", "degree": "PhD", "year": "1990", "title": "Shocks and instabilities in traffic", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132007-085544", "creators": [ { "name": { "family": "Shinn-Mendoza", "given": "Rachel" }, "id": "Shinn-Mendoza-R", "display_name": "Shinn-Mendoza, Rachel" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmath" ], "doi": "10.7907/dw5a-sw09", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nIn this thesis, we study several models for traffic flow. Our interest is in finding periodic solutions and to study the effect of including a time lag on the propagation of shocks through a line of cars. The periodic solution was stimulated by a problem from water waves in which a periodic solution is created in the unstable region of the parameters by connecting segments of the growing solution with shocks. This results in a finite amplitude solution in the region of instability. The analysis of this is presented and then applied to a continuum model for traffic flow. We look for a smooth version of this periodic shock solution by considering a car following model for traffic. Car following models define the [...] car's velocity in a line of cars as a function of the distance between the [...] and [...] cars and are thus a system of differential-difference equations which define the motion of the cars.\n\nThe model we study is attributed to G.F. Newell who found a transformation which makes the nonlinear equation linear. We discuss this exact solution and in particular, look at the shock solutions. These solutions, however, do not include the effect of a time lag. When this is included, we have the possibility of instabilities. We look at the shock solutions with the time lag included numerically and find that after some critical value, the smooth shock profile breaks up into oscillations about the final velocity state. We modify the equation by modeling the time lag continuously and look at these same shock solutions. We then find periodic solutions to this in the form of steady profile waves and compare the results with a continuum theory which also has smooth periodic solutions.\n" }, { "name": "Sivarajan, Kumar N.", "degree": "PhD", "year": "1990", "title": "Spectrum efficient frequency assignment for cellular radio", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082007-105043", "creators": [ { "name": { "family": "Sivarajan", "given": "Kumar N." }, "id": "Sivarajan-K-N", "display_name": "Sivarajan, Kumar N." } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "eleceng" ], "doi": "10.7907/q2qb-hh14", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nIn this thesis, we first describe some results on the following generalized chromatic number problem that has its origin in cellular radio (the frequency assignment problem with co-channel constraints only): Given a graph G with vertices V = [...] and an n-vector M = [...] of nonnegative integers (the requirement vector), find the minimum number of colors, [...](G, M), required to assign [...] distinct colors to vertex [...], [...], such that adjacent vertices are assigned disjoint sets of colors. We develop a lower bound on [...](G, M), which generalizes and strengthens the well-known bound [...] n for the usual chromatic number. We show that this bound is sharp for a number of interesting graphs (e.g., perfect graphs and odd cycles), but not for all graphs - the Grotzsch graph being a counterexample. We also give examples of the application of this bound to frequency assignment in cellular radio.\n\nIn the presence of constraints other than just co-channel constraints (e.g., adjacent channel and co-site constraints), the frequency assignment problem is a further generalization of the graph coloring problem. We describe some heuristic algorithms for frequency assignment in cellular radio that we developed by suitably adapting some of the ideas previously introduced in heuristic graph coloring algorithms. These algorithms have yielded optimal, or near-optimal assignments, in many cases.\n\nWe then describe some dynamic channel assignment algorithms for cellular systems that we have developed. In addition to having a considerable advantage over fixed channel assignment in the range of blocking probabilities of interest in current cellular systems (2-4%), these algorithms are feasible for implementation in these systems. Some of these dynamic channel assignment algorithms are also shown to give good performance under overload (heavy traffic conditions).\n\nFinally, we discuss various methods of computing interference probabilities and the formulation of compatibility constraints on channel assignment based on these calculations. We also formulate the channel assignment problem as one of coloring hypergraphs, instead of graphs, and show that, in the case of dynamic channel assignment, this leads to a considerable increase in the carried traffic for the same blocking probability and the same maximum probability of interference." }, { "name": "Smedley, Gregory Todd", "degree": "PhD", "year": "1990", "title": "A study of immiscible liquids, liquid behavior at zero gravity, and dynamic contact lines and angles", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-08182004-154208", "creators": [ { "name": { "family": "Smedley", "given": "Gregory Todd" }, "id": "Smedley-G-T", "display_name": "Smedley, Gregory Todd" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AQR1-4B73", "abstract": "The work reported here covers three topics that were investigated as part of preparation for a space based experiment. The intention of the proposed experiment was to study the relationship between container geometry and interface geometry for a free liquid surface at zero gravity.\n\nA mathematical theory proposed by Paul Concus and Robert Finn in 1974 and recently developed by Finn yields explicit geometrical criteria for the position of the free surface of a liquid at zero gravity in a cylindrical container of specified cross section. It is possible to find geometrical criteria that promise a particular liquid location. A unified graphical presentation of four geometries is given that can be used directly for the design of containments for liquids at zero gravity. As one application of these design curves, a container was built and tested in a series of 2 second droptower experiments at NASA Lewis Research Center.\n\nIt was apparent that the space based experiment would require use of sophisticated optical instrumentation that would be most effective if a pair of immiscible liquids were used rather than a single liquid under its vapor. This work identifies 121 transparent immiscible liquid pairs that have properties compatible with optical instrumentation based on laser-induced fluorescence. Physical data such as specific gravity, index of refraction, viscosity, flash point, and toxicity were found in the literature. Compatibility with plexiglas (PMMA), contact angles of the internal meniscus on glass and PMMA, meniscus formation times, and clearing times were measured. A useful noninvasive technique for determining interfacial tensions is explained and used.\n\nThe contact angle is a critical parameter in the consideration of liquid behavior at zero gravity, therefore, a technique, based on laser light refraction, was developed to objectively measure it. Dynamic contact line experiments were conducted at various velocities, both advancing and receding, using one of the 121 immiscible liquid pairs (nonane/formamide) in contact with glass.\n" }, { "name": "Smith, Roy S.R.", "degree": "PhD", "year": "1990", "title": "Model Validation for Uncertain Systems", "advisor": "Doyle, John Comstock; Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-10252002-162453", "creators": [ { "name": { "family": "Smith", "given": "Roy S.R." }, "id": "Smith-Roy-S-R", "display_name": "Smith, Roy S.R." } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "orcid": "0000-0002-7696-5058", "role": "member", "display_name": "Morari, Manfred" }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7S0Z-ZY41", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nModern robust control synthesis techniques aim at providing robustness with respect to uncertainty in the form of both additive noise and plant perturbations. On the other hand, most popular system identification methods assume that all uncertainty is in the form of additive noise. This has hampered the application of robust control methods to practical problems. This thesis begins to address this disparity by considering the connection between uncertain models and data. The model validation problem addressed here is this: given experimental, data and a model with both additive noise and normbounded perturbations, is it possible that the model could produce the observed inputoutput data? This question is reformulated as an optimization problem: what is the minimum norm noise required to account for the data and meet the constraint imposed by the perturbation uncertainty? The assumptions typically used for robust control analysis are introduced and shown to lead to a constant matrix problem. This problem is studied in detail, and bounds on the size of the required noise are developed. The dimensionality issues that arise in the consideration of the structured singular value ([...]) also arise here.\r\n\r\nA geometric framework is used to introduce a variation on [...]. This is extended to allow the consideration of robust control analysis problems that include input and output data. The more general problem is then used to illustrate the connection between [...] and the model validation theory.\r\n\r\nThe application of the theory is illustrated by a study of a laboratory process control experiment. Typical steps in the identification of a robust control model for a physical system are discussed. It is shown, by example, how the model validation theory can be used to provide insight into the limitations of uncertain models in describing physical systems." }, { "name": "Su, Wen-King", "degree": "PhD", "year": "1990", "title": "Reactive-Process Programming and Distributed Discrete-Event Simulation", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03222012-091423469", "creators": [ { "name": { "family": "Su", "given": "Wen-King" }, "id": "Su-Wen-King", "display_name": "Su, Wen-King" } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Van de Velde", "given": "Eric" }, "id": "van-de-Velde-E", "role": "member", "display_name": "Van de Velde, Eric" } ], "option_major": [ "compsci" ], "doi": "10.7907/9qzd-kv20", "abstract": "The same forces that spurred the development of multicomputers - the demand for\r\nbetter performance and economy - are driving the evolution of multicomputers in\r\nthe direction of more abundant and less expensive computing nodes - the direction\r\nof fine-grain multicomputers. This evolution in multicomputer architecture derives\r\nfrom advances in integrated circuit, packaging, and message-routing technologies,\r\nand carries far-reaching implications in programming and applications. This thesis\r\npursues that trend with a balanced treatment of multicomputer programming and\r\napplications. First, a reactive-process programming system - Reactive-C - is\r\ninvestigated; then, a model application- discrete-event simulation - is developed;\r\nfinally, a number of logic-circuit simulators written in the Reactive-C notation are\r\nevaluated.
\r\n\r\nOne difficulty m multicomputer applications is the inefficiency of many distributed\r\nalgorithms compared to their sequential counterparts. When better formulations\r\nare developed, they often scale poorly with increasing numbers of nodes,\r\nand their beneficial effects eventually vanish when many nodes are used. However,\r\nrules for programming are quite different when nodes are plentiful and cheap: The\r\nprimary concern is to utilize all of the concurrency available in an application, rather\r\nthan to utilize all of the computing cycles available in a machine. We have shown in\r\nour research that it is possible to extract the maximum concurrency of a simulation\r\nsubject, even one as difficult as a logic circuit, when one simulation element is assigned\r\nto each node. Despite the initial inefficiency of a straightforward algorithm,\r\nas the the number of nodes increases, the computation time decreases linearly until\r\nthere are only a few elements in each node. We conclude by suggesting a technique\r\nto further increase the available concurrency when there are many more nodes than\r\nsimulation elements.
" }, { "name": "Tan, Phalkun", "degree": "PhD", "year": "1990", "title": "Numerical simulations of two-dimensional saturated granular media", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232005-154613", "creators": [ { "name": { "family": "Tan", "given": "Phalkun" }, "id": "Tan-P", "display_name": "Tan, Phalkun" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/e02e-mz83", "abstract": "The liquefaction phenomenon in soil has been studied in great detail during the past 20 years. The need to understand this phenomenon has been emphasized by the extent of the damages resulting from soil liquefaction during earthquakes. Although an overall explanation exists for this phenomenon through the concept of effective stress, the basic mechanism of loss of strength of the soil skeleton has not been thoroughly examined and remains unclear.\r\n\r\nThe present study proposes a numerical model for simulations of the behavior of saturated granular media. The model was developed with two main objectives:\r\n\r\n1. To represent the mechanical response of an assemblage of discrete particles having the shape of discs.\r\n\r\n2. To model and represent the interaction of interstitial pore fluid present with the idealized granular media.\r\n\r\nThe representation of the solid skeleton is based on Cundall and Strack's distinct element model, in which discrete particles are modelled as discs in two dimensions, each obeying Newton's laws. Interparticle contacts consisting of springs and frictional element dashpots are included. Assuming a Newtonian incompressible fluid with constant viscosity and density, and quasi-steady flow, the fluid phase is described by Stokes' equations. The solution to Stokes' equations is obtained through the boundary integral element formulation. Several validation test cases are presented along with four simple shear tests on dry and saturated granular assemblages. For these last four tests, the numerical results indicate that the model is able to represent qualitatively the behavior of real soil, while at the same time clarifying the processes occurring at the microscale that influence soil response." }, { "name": "Thyagarajan, Ravi Shanker", "degree": "PhD", "year": "1990", "title": "Modeling and analysis of hysteretic structural behavior", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechThesis:03132014-144907764", "creators": [ { "name": { "family": "Thyagarajan", "given": "Ravi Shanker" }, "display_name": "Thyagarajan, Ravi Shanker" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/r3as-fj34", "abstract": "For damaging response, the force-displacement relationship of a structure is highly nonlinear and history-dependent. For satisfactory analysis of such behavior, it is important to be able to characterize and to model the phenomenon of hysteresis accurately. A number of models have been proposed for response studies of hysteretic structures, some of which are examined in detail in this thesis. There are two popular classes of models used in the analysis of curvilinear hysteretic systems. The first is of the distributed element or assemblage type, which models the physical behavior of the system by using well-known building blocks. The second class of models is of the differential equation type, which is based on the introduction of an extra variable to describe the history dependence of the system.
\r\n\r\nOwing to their mathematical simplicity, the latter models have been used extensively for various applications in structural dynamics, most notably in the estimation of the response statistics of hysteretic systems subjected to stochastic excitation. But the fundamental characteristics of these models are still not clearly understood. A response analysis of systems using both the Distributed Element model and the differential equation model when subjected to a variety of quasi-static and dynamic loading conditions leads to the following conclusion: Caution must be exercised when employing the models belonging to the second class in structural response studies as they can produce misleading results.
\r\n\r\nThe Massing's hypothesis, originally proposed for steady-state loading, can be extended to general transient loading as well, leading to considerable simplification in the analysis of the Distributed Element models. A simple, nonparametric identification technique is also outlined, by means of which an optimal model representation involving one additional state variable is determined for hysteretic systems.
" }, { "name": "Vu, Hoanh Xuan", "degree": "PhD", "year": "1990", "title": "Plasma Collection by an Obstacle", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152007-131939", "creators": [ { "name": { "family": "Vu", "given": "Hoanh Xuan" }, "id": "Vu-Hoanh-Xuan", "display_name": "Vu, Hoanh Xuan" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ctcn-eq94", "abstract": "The problem of plasma collection by an obstacle is investigated systematically to identify potentially important physical effects.\r\n\r\nIn the absence of an ambient toroidal plasma flow, plasma collection by a two-dimensional obstacle of half-width d extending to infinity in the y-direction (slab geometry) is studied in detail. The transport process is taken to be classical. The plasma is assumed to be strongly magnetized. The external magnetic field is assumed to be uniform, and is perpendicular to the obstacle's surface. Our numerical results suggest that both ion viscosity and ion viscous heating can be important in the regions where the ion velocity possesses sharp gradients, e.g., the region near the obstacle's tip.\r\n\r\nA two-dimensional, semi-empirical, model is proposed to account for the effect of anomalous transport due to a low-frequency, microscopic, electrostatic fluctuation of the poloidal electric field. The obstacle has a half-width of d, and is assumed to extend to infinity in the y-direction. The plasma is assumed to be strongly magnetized. The external magnetic field is assumed to be uniform, and is perpendicular to the obstacle's surface. In general, our proposed model suggests the following:\r\n\r\n1. Contrary to that which has been suggested in the literature, the cross-field ion viscosity coefficient (as well as the cross-field ion thermal conductivity) is not enhanced because the cross-field transport is dominated by the fluctuation induced convection.\r\n\r\n2. Viscous heating may have an important effect on the ion temperature when there exists a large velocity gradient. Furthermore, in the presence of anomalous transport, the physical mechanism by which viscous heating is generated is quite different from the case where the transport process is classical. In the absence of an ambient toroidal plasma flow, our numerical results suggest that for realistic plasma parameters, the peaked ion temperature is up to 85% higher than the ambient ion temperature due to ion viscous heating.\r\n\r\nA numerical code based on the above model is developed to deal with the case where the ambient toroidal plasma flow is finite. Such a situation arises in connection with experimental data obtained by the so-called Janus probe or Mach probe. Our numerical results indicate that near the obstacle's tip, the ions on the downstream side are hotter than those on the upstream side." }, { "name": "Washabaugh, Peter D.", "degree": "PhD", "year": "1990", "title": "An experimental investigation of mode-I crack tip deformation", "advisor": "Knauss, Wolfgang Gustav; Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092007-101356", "creators": [ { "name": { "family": "Washabaugh", "given": "Peter D." }, "id": "Washabaugh-P-D", "display_name": "Washabaugh, Peter D." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/wv0e-g535", "abstract": "The out-of-plane displacement of amorphous polymethylmethacrylate plates rupturing at slow (0.1 mm/s), and fast (0.5 to 0.9 mm/\u00b5s) rates are measured using a Twymann-Green interferometer. The measured surface shapes within one plate thickness of the crack-tip do not compare well with the two-dimensional planar asymptotic approximation, but compare favorably with the published slopes for three-dimensional finite element solutions when normalized with the static material properties. Discrepancies, on the order of ten percent, between the magnitude of the three-dimensional finite element solutions suggest that the stress intensity factor does not fully characterize the near tip deformations.\n\nA dynamically propagating crack is found to move in a non-steady, periodic, submicrosecond fashion. This result is supported both by the surface measurements and the fracture morphology. The material toughening, as measured by the surface roughness, correlates well with the stress intensity factor and not with the crack velocity. The details of the sub-microsecond propagation and toughening was not resolvable with the microsecond temporal resolution of the experiment.\n\nInhibiting the material toughening at the crack tip by artificially introducing a weak material plane augments the crack motion to velocities close to the material's shear wave speed. The crack propagates more steadily along the weak plane than through a virgin solid, while maintaining the character of the out-of-plane displacement of a crack propagating in an unsullied material.\n" }, { "name": "Wood, Kristin Lee", "degree": "PhD", "year": "1990", "title": "A method for the representation and manipulation of uncertainties in preliminary engineering design", "advisor": "Antonsson, Erik K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152007-080746", "creators": [ { "name": { "family": "Wood", "given": "Kristin Lee" }, "id": "Wood-K-L", "display_name": "Wood, Kristin Lee" } ], "advisors": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "advisor", "display_name": "Antonsson, Erik K." } ], "committee": [ { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "chair", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "role": "member", "display_name": "Burdick, Joel Wakeman" }, { "name": { "family": "Dubowsky", "given": "Steven" }, "id": "Dubowsky-S", "role": "member", "display_name": "Dubowsky, Steven" } ], "option_major": [ "mecheng" ], "doi": "10.7907/g1hs-p655", "abstract": "Each stage of the engineering design process, and particularly the preliminary phase, includes imprecision, stochastic uncertainty, and possibilistic uncertainty. A technique is presented by which the various levels of imprecision (where imprecision is: \"uncertainty in choosing among alternatives\") in the description of design elements may be represented and manipulated. The calculus of Fuzzy Sets provides the foundation of the approach. An analogous method to representing and manipulating imprecision using probability calculus is presented and compared with the fuzzy calculus technique. Extended Hybrid Numbers are then introduced to combine the effects of imprecision with stochastic and possibilistic uncertainty. Using the results, a preliminary set of metrics is proposed by which a designer can make decisions among alternative configurations in preliminary design.\n\nIn general, the hypothesis underlying the techniques described above is that making more information available than conventional approaches will enhance the decision-making capability of the designer in preliminary design. A number of elemental concepts toward this hypothesis have been formulated during the evolution of this work:\n\t\u2022 Imprecision is a hallmark of preliminary engineering design. To carry out decisions based on the information available to the designer and on basic engineering principles, the imprecise descriptions of possible solution technologies must be formalized and quantified in some way. The application of the fuzzy calculus along with a fundamental interpretation provides a new and straight-forward means by which imprecision can be represented and manipulated.\n\t\u2022 Besides imprecision, other uncertainties, categorized as stochastic and possibilistic, are prevalent in design, even in the early stages of the design process. Providing a method by which these uncertainties can be represented in the context of the imprecision is an important and necessary step when considering the evaluation of a design's performance. Extended Hybrid Numbers have been introduced in this work in order to couple the stochastic and possibilistic components of uncertainty with imprecision such that no information is lost in the process.\n\t\u2022 Because of the size, coupling, and complexity of the functional requirement space in any realistic design, it is difficult to make decisions with regard to the performance of a design, even with an Extended Hybrid Number representation. Defining and utilizing metrics (or figures of merit) in the evaluation of how well a design meets the functional requirements reduces the complexity of this process. \t Such metrics also have merit when we begin to think of languages of design and adding the necessary pragmatics of \"will a generated or proposed design satisfy the performance requirements with respect to the ever-present and unavoidable \t uncertainties?\". These concepts form the central focus of this work. The mathematical methods presented here were developed to support and formalize these ideas." }, { "name": "Xiong, Fulin", "degree": "PhD", "year": "1990", "title": "Characterization and application of MeV ion implanted layers in III-V compound semiconductors", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232002-150110", "creators": [ { "name": { "family": "Xiong", "given": "Fulin" }, "id": "Xiong-Fulin", "display_name": "Xiong, Fulin" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/yjk5-wv20", "abstract": "Ion implantation at keV energies has become a well-established technique for surface modification of solid materials, especially semiconductors. The technique of MeV ion implantation has attracted considerable attention in recent years as it provides an extension of ion implantation technique with a high potential for interface modification of solid materials and for 3-dimensional electronic device fabrication. Extending the ion energy from keV to MeV provides many advantages in terms of the great ion range for deep implantation and the minimized surface damage for modification of deeply buried layers. It also gives rise to many interesting questions about the mechanism of radiation damage and ion-radiation-induced phase transitions. A comprehensive experimental study, from the fundamental to the practical, has been undertaken to investigate MeV ion irradiation effects in III-V compound semiconductors, especially InP and GaAs, and to explore the possibility of its application to optoelectronic semiconductor device fabrication.\r\n\r\nCharacterization of implanted samples has been conducted by a variety of analytical techniques, such as NRRA, ORBS, XRC, XTEM, HRTEX, SIMS, and IVC. The results have not only demonstrated the complementary nature of all these techniques but also have given clear pictures about the implant distribution, profiles and microstructures of radiation damage and lattice defects, structural phase transformation, and the build-up of lattice strain, as well as electrical property changes. They have revealed the physical relation among all of the effects and led to a better understanding of physical processes involved in MeV ion implantation into III-V compound semiconductors. It has been discovered that MeV nitrogen ion implantation can create a deeply buried high resistivity layer in n-type InP crystals, similar to the case where MeV oxygen ion implantation generates a semi-insulating layer in GaAs-AlGaAs systems. Application of this technique to the fabrication of GaAs-AlGaAs quantum well laser devices with MeV oxygen ions for the electrical isolation and carrier confinement has resulted in a device with high quantum efficiency, low current threshold, and excellent electrical characteristics.\r\n\r\nIn this thesis, the experimental studies on MeV ion implanted InP and GaAs are presented. Based on the experimental results obtained, the mechanism of MeV-ion-implantation-induced damage and phase transitions in III-V compound semiconductors is discussed in terms of electronic spikes and nuclear spikes. A mechanism for ion-implantation-induced lattice strain in III-V compound crystals is also proposed. Finally, an example of the application of MeV ion implantaion to semiconductor laser device fabrication is given." }, { "name": "Zarem, Hal", "degree": "PhD", "year": "1990", "title": "Investigations of quantum wires, carrier diffusion lengths, and carrier lifetimes in GaAs/AlGaAs heterostructures", "advisor": "Yariv, Amnon; Vahala, Kerry J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092007-090251", "creators": [ { "name": { "family": "Zarem", "given": "Hal" }, "id": "Zarem-H", "display_name": "Zarem, Hal" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "co-advisor", "display_name": "Vahala, Kerry J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ajzc-wx87", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nNanometer scale wire structures are fabricated by selective disorder of a GaAs/AlGaAs quantum well. These structures are investigated by cathodoluminescence (CL). Spectrally resolved CL images of the structures as well as local CL spectra of the structures are resented. The effects of fabricational variations on quantum wire laser gain spectra and performance are discussed. A new technique for determining carrier diffusion lengths by cathodoluminescence measurements is presented. The technique is extremely accurate and can be applied to a variety of structures. The ambipolar diffusion length and carrier lifetime are measured in [...] for several mole fractions in the interval 0 < [...] < 0.38. These parameters are found to have significantly higher values in the higher mole fraction samples. These increases are attributed to occupation of states in the indirect valleys, and supporting calculations are presented.\n" }, { "name": "Zhuang, Mei", "degree": "PhD", "year": "1990", "title": "An investigation of the inviscid spatial instability of compressible mixing layers", "advisor": "Dimotakis, Paul E.; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132007-094001", "creators": [ { "name": { "family": "Zhuang", "given": "Mei" }, "id": "Zhuang-M", "display_name": "Zhuang, Mei" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "co-advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/650s-9t96", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe behavior of both unbounded and bounded compressible plane mixing layers with respect to two- and three-dimensional, spatially growing wave disturbances is investigated using linear stability analysis. The mixing layer is formed by two parallel streams with different gases and the flow is assumed to be inviscid and non-reacting.\r\n\r\nFor unbounded mixing layers, the effects of the free stream Mach number, velocity ratio, temperature ratio, gas constant (molecular weight) ratio and the ratios of specific heats on the linear spatial instability characteristics of a mixing layer are determined. A nearly universal dependence of the normalized maximum amplification rate on the convective Mach number is found for two-dimensional spatially growing disturbances. The effects of the mean flow profiles on the instability behavior of the mixing layers are also studied. It is shown that decreasing the thickness of the total temperature profile relative to the mean velocity profile, or adding a wake component in the mean velocity profile can make the normalized amplification rate decrease slower as the convective Mach number increases for both subsonic and supersonic convective Mach numbers.\r\n\r\nFor an unbounded mixing layer with subsonic convective Mach numbers, there is only one unstable mode propagating with a phase velocity [...] approximately equal to the isentropically estimated convective velocity of the large scale structures [...]. As the convective Mach number approaches or exceeds unity, there are always two unstable spatial modes. One is with a phase velocity [...] (slow mode and the other is with a phase velocity [...] (fast mode). For the low supersonic convective Mach numbers, the fast mode is more unstable than the slow mode when the heavy gas is on the low speed side and the slow mode is dominant when the heavy gas is on the high speed side.\r\n\r\nThe effect of parallel flow guide walls on a spatially growing mixing layer is also investigated. It is shown that, in this case, if the convective Mach number exceeds a critical value of approximately unity, there are many supersonic unstable modes. The maximum amplification rates of mixing layers approach an asymptotic value and this maximum amplification rate increases to a maximum value and decreases again as the distance between the walls decreases. For a mixing layer inside parallel flow guide walls, the growth rate of three-dimensional modes is larger than the corresponding two-dimensional mode at high convective Mach numbers. But the growth rate of two-dimensional supersonic instability waves has a larger value than their three-dimensional counterparts for a mixing layer inside a rectangular duct (Tam & Hu [1988], [1989]). Contour plots of the pressure perturbation fields for both unbounded and bounded mixing layers indicate that there are waves propagating outward from the mixing layer along the Mach angle, and that the walls provide a feedback mechanism between the growing mixing layer and this compression/expansion wave system. The bounded mixing layers are more unstable than the corresponding free mixing layers for supersonic convective Mach numbers. The streaklines of the flow confirm that the spreading rate of the mixing layer is unusually small for supersonic disturbances.\r\n" }, { "name": "Zimmerman, George Allan", "degree": "PhD", "year": "1990", "title": "Applications of frequency modulation interference cancellers to multiaccess communications systems", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03122014-103214314", "creators": [ { "name": { "family": "Zimmerman", "given": "George Allan" }, "id": "Zimmerman-G-A", "display_name": "Zimmerman, George Allan" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/186j-bd56", "abstract": "Cancellation of interfering frequency-modulated (FM) signals is investigated with emphasis towards applications on the cellular telephone channel as an important example of a multiple access communications system. In order to fairly evaluate analog FM multiaccess systems with respect to more complex digital multiaccess systems, a serious attempt to mitigate interference in the FM systems\r\nmust be made. Information-theoretic results in the field of interference channels are shown to motivate the estimation and subtraction of undesired interfering signals. This thesis briefly examines the relative optimality of the current FM techniques in known interference channels, before pursuing the estimation and subtracting of interfering FM signals.
\r\n\r\nThe capture-effect phenomenon of FM reception is exploited to produce simple interference-cancelling receivers with a cross-coupled topology. The use of phase-locked loop receivers cross-coupled with amplitude-tracking loops to estimate the FM signals is explored. The theory and function of these cross-coupled phase-locked loop (CCPLL) interference cancellers are examined. New interference cancellers inspired by optimal estimation and the CCPLL topology are developed, resulting in simpler receivers than those in prior art. Signal acquisition and capture effects in these complex dynamical systems are explained using the relationship of the dynamical systems to adaptive noise cancellers.
\r\n\r\nFM interference-cancelling receivers are considered for increasing the frequency reuse in a cellular telephone system. Interference mitigation in the cellular environment is seen to require tracking of the desired signal during time intervals when it is not the strongest signal present. Use of interference cancelling in conjunction with dynamic frequency-allocation algorithms is viewed as a way of improving spectrum efficiency. Performance of interference cancellers indicates possibilities for greatly increased\r\nfrequency reuse. The economics of receiver improvements in the cellular system is considered, including both the mobile subscriber equipment and the provider's tower (base station) equipment.
\r\n\r\nThe thesis is divided into four major parts and a summary: the introduction, motivations for the use of interference cancellation, examination of the CCPLL interference canceller, and applications to the cellular channel. The parts are dependent on each other and are meant to be read as a whole.
\r\n" }, { "name": "Ahn, Hojin", "degree": "PhD", "year": "1989", "title": "Experimental and Analytical Investigations of Granular Materials: Shear Flow and Convective Heat Transfer", "advisor": "Sabersky, Rolf H.; Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152004-135555", "creators": [ { "name": { "family": "Ahn", "given": "Hojin" }, "id": "Ahn-Hojin", "display_name": "Ahn, Hojin" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "co-advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Goodwin", "given": "David G." }, "id": "Goodwin-D-G", "role": "member", "display_name": "Goodwin, David G." } ], "option_major": [ "mecheng" ], "doi": "10.7907/XFYT-7909", "abstract": "Granular materials flowing down an inclined chute were studied experimentally and analytically. Characteristics of convective heat transfer to granular flows were also investigated experimentally and numerically.
\r\n\r\nExperiments on continuous, steady flows of granular materials in an inclined chute were conducted with the objectives of understanding the characteristics of chute flows and of acquiring information on the rheological behavior of granular material flow. Two neighboring fibre optic displacement probes were employed to measure mean velocity, one component of velocity fluctuations, and linear concentration at the wall and free surface boundaries. A shear gauge was also developed to make direct measurement of shear stress at the chute base. Measurements of solid fraction, velocity, shear rate, and velocity fluctuations were analyzed to understand the chute flow characteristics, and the rheological behavior of granular materials was studied with the present experimental data. The vertical profiles of mean velocity, velocity fluctuation, and solid fraction were also obtained at the sidewalls.
\r\n\r\nExisting constitutive equations and governing equations were used to solve for fully developed chute flows of granular materials, and thus the boundary value problem was formulated with two parameters (the coefficient of restitution between particles, and the chute inclination) and three boundary values at the chute base wall (the values of solid fraction, granular temperature, and mean velocity at the wall). The boundary value problem was numerically solved by the \"shooting method.\" The boundary conditions at the free surface were satisfied by the proper choice of a gradient of granular temperature at the wall. The results show a significant role played by granular conduction in determining the profiles of granular temperature, solid fraction, and mean velocity in chute flows. These analytical results were also compared with the present experimental measurements and with the computer simulations by other investigators in the literature.
\r\n\r\nExperiments on heat transfer to granular flows over a flat heating plate were conducted with three sizes of glass beads, polystyrene beads, and mustard seeds. A modification on the existing model for the convective heat transfer was made using the effective Nusselt number and the effective Peclet number, which include the effects of solid fraction variations. The slightly modified model could describe the heat transfer characteristics of both fast and slow flows (supercritical and subcritical flows).
\r\n\t\r\nA numerical analysis of the convective heat transfer to granular flows was also performed. The results were compared with the present experimental data, and reasonable agreement was found in the comparison.
" }, { "name": "Anilkumar, A. V.", "degree": "PhD", "year": "1989", "title": "Experimental Studies of High-Speed Dense Dusty Gases", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312006-130447", "creators": [ { "name": { "family": "Anilkumar", "given": "A. V." }, "id": "Anilkumar-A-V", "display_name": "Anilkumar, A. V." } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/5B1B-AY62", "abstract": "An experimental study of the flow of high-speed dense dusty gases has been conducted in a novel shock tube facility. The flow is generated through rapid depressurization and subsequent fluidization of a stationary packed bed of particles loaded under pressure in the vertical driver section of the shock tube. The flow was studied with high-speed photography and fast-response pressure transducers.
\r\n\r\nThe studies have been exploratory in nature. The entire process of lofting and disassembly of packed particle beds has been documented. A wide spectrum of dusty flows with particle loadings ranging from that of a fully packed plug to that of a dilute disperse particle flow was observed in this facility. Only extreme flow fields like packed plug flows and very dilute disperse particle flows were found to be uniform. All other flow fields, with intermediate particle loadings, were characterized by the simultaneous presence of dense filamentary structures and dilute dispersions of particles. Typically, while operating with 0.5 mm glass beads, flows reached speeds of 60 meters per second in a period of 25 milliseconds.
\r\n\r\nTwo lofting configurations of the packed beds were set up. In the first configuration, the rapid depressurization of the interstitial bed fluid and the consequent initiation of bed expansion was examined. Bed expansion starts along horizontal fractures that partition the bed into slabs. While the bed is accelerating, particles rain down from the bottom surfaces of the slabs partitioning the fractures into bubbles with a characteristic honeycomb pattern. The bubbles eventually compete and the dominant ones prevail. The observed instability of the bottom surfaces of the slabs is analogous to the Rayleigh-Taylor instability observed in continuous media. The flow development in this configuration was not influenced by any wall effects.
\r\n\r\nThe second lofting configuration is a high-speed fluidization configuration. Here, the role of the fluid entering from below the bed, in continuing the bed expansion initiated by the rapid depressurization of the interstitial bed fluid, was examined. The bed expansion occurs along expanding and elongating bubbles and the bubble walls are stretched into dense filamentary structures. Beds initially stacked with a gradient in particle size or density or both showed drastic differences in response to fluidization. The morphology of the expanded flow field in all cases was essentially the same: nonuniform, interspersed with dense filamentary structures and dilute dispersions of particles.
\r\n\r\nIn the second lofting configuration, only the late stages of flow development were influenced by wall effects. Wall effects manifest as faster moving fluid along the walls and denser accumulation of flow structures towards the center of the channel. The bottom of the dusty flow is characterized by the presence of a tail; a concentric dense particle column formed by the accumulation of particles, initially present in the bottom regions of the flow. The tail terminates in a bulbous and streamlined bottom from which particles are slowly eroded by the coflowing fluid.
\r\n\r\nA multi-transducer probe was installed in the dusty gas flow for making dynamic pressure measurements and for correlating observations with those made through extensive flow visualization.
" }, { "name": "Beran, Philip Stewart", "degree": "PhD", "year": "1989", "title": "An Investigation of the Bursting of Trailing Vortices Using Numerical Simulation", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012007-105641", "creators": [ { "name": { "family": "Beran", "given": "Philip Stewart" }, "id": "Beran-Philip-Stewart", "display_name": "Beran, Philip Stewart" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/chyb-nk54", "abstract": "Solutions of the Navier-Stokes equations are obtained for the flow of an isolated, trailing vortex, and for the swirling flow through a frictionless pipe. In both cases, the flow is assumed to be steady, incompressible and rotationally symmetric. Solutions are computed using Newton's method and Gaussian elimination for a wide range of values of two parameters: Reynolds number, Re, and vortex strength, V. Pseudo-arclength continuation is employed to facilitate the computation of solution points in the parameter space. The numerical procedure is validated through comparison of solutions with solutions obtained in previous investigations for the case of a trailing vortex. Solutions are also compared with results reported by Brown and Lopez (1988) for the case of flow through a pipe.
\r\n\r\nSolutions of the quasi-cylindrical equations are obtained for the flow of a trailing vortex. Solutions are computed using an explicit, space-marching scheme, and are compared with solutions of the Navier-Stokes equations.
\r\n\r\nProvided that Re is about 200, or larger, four vortex states are observed.
\r\n\r\n1. When V is sufficiently small, the flow is entirely supercritical.
\r\n\r\n2. As V is increased, the flow at an axial station becomes critical and a transition point forms. At the point, the flow departs from an upstream state that is supercritical to a downstream state that is marked by large-amplitude, spatial oscillations of core radius. When Re is large, the downstream state is nearly periodic. The general features of transition are well described by the conjugate-flow theory of Benjamin 1967). Failure of the quasi-cylindrical equations is found to be a necessary and sufficient condition for the existence of a transition point. As V is further increased, the transition point moves upstream. Reversed flow is not observed.
\r\n\r\n3. Over a narrow range of vortex strengths, a small bubble of reversed flow is observed downstream of the transition point.
\r\n\r\n4. When V is large, the entire flow is marked by large-amplitude, spatial oscillations of core radius. A transition point is not evident within the computational domain. Typically, large regions of reversed flow are observed.
" }, { "name": "Brouillette, Martin", "degree": "PhD", "year": "1989", "title": "On the Interaction of Shock Waves with Contact Surfaces Between Gases of Different Densities", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-102505", "creators": [ { "name": { "family": "Brouillette", "given": "Martin" }, "id": "Brouillette-Martin", "display_name": "Brouillette, Martin" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Hornung", "given": "Hans G." }, "id": "Hornung-H-G", "role": "member", "display_name": "Hornung, Hans G." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9JGS-ZX78", "abstract": "The interaction of shock waves with a contact surface between gases of different densities has been studied experimentally and theoretically. The basic mechanism for the instability of perturbations at the interface is baroclinic vorticity generation resulting from the misalignment of the pressure gradient of the shock and the density gradient of the interface. In the present study, the effects of interface density contrast and initial thickness, and incident wave strength on the development of the instability at the interface are investigated. The experiments were performed in a new vertical shock tube facility where the interaction of a shock wave with either a discontinuous interface, formed by a thin (0.5 \u00b5m) plastic membrane, or a continuous interface, created by retracting a metal plate initially separating the two gases, was studied. Air was used on one side of the interface and either helium, carbon dioxide, refrigerant-22 or sulphur hexafluoride was used on the other side as the test gas.
\r\n\r\nExperiments to study the time evolution of quasi-sinusoidal perturbations on a continuous interface have shown that the growth rates are reduced as the interface thickness is increased. It has been observed that growth rates of perturbations of wavelength \u03bb ~ 25 mm on interfaces of thickness \u03b4 ~ 10 mm are about three times smaller than those predicted by the linear theory for the impulsive acceleration of discontinuous interfaces. A new model that accounts for the growth rate reduction caused by the presence of a finite density gradient on the interface has been proposed, and good agreement was obtained with the present experimental results.
\r\n\r\nExperiments were also performed to observe the schlieren visual thickness of plane discontinuous or continuous interfaces with random small-scale perturbations after interaction with the incident shock wave and its reverberations. The interface was initially located near the end wall of the shock tube to permit the observation of the development of the interface phenomena after the arrival of the incident shock and its reverberations. It is found that the interaction of a shock wave with a discontinuous interface causes the appearance of a turbulent mixing zone between the two gases, whose growth rate slows down as time increases, owing to a decrease in turbulence intensity and the action of viscosity. Because of the large uncertainty associated with the measurements a short time after the interaction with the incident shock, the accurate determination of a possible universal power law governing the thickening of the interface is not feasible. Results for the interaction of the first reverberation of the primary wave with the already turbulent interface have demonstrated that this growth is sensitive to the initial pre-growth state of the interface. It also appears that the thickening of the turbulent mixing zone is accomplished by the merging of large structures within the interface. However, since the energy available for the turbulent motions at the impulsively accelerated interface remains constant after the interaction with the shock and also depends on the wavelength of the initial perturbation, it is not certain whether the development of mixing at the interface achieves an asymptotic stage of self-similar turbulence independent of initial conditions, as has been observed for the gravity-driven interfaces. Also, it has been found that the growth rates measured in the present experiments with discontinuous interfaces are nearly an order of magnitude lower than those reported by previous investigators. The continuous interfaces formed by the retracting plate are smoothed by molecular diffusion, and thus the combination of low density gradient and small initial perturbations is such that they exhibit growth only after being perturbed by acoustic noise introduced by the reverberation of waves between the interface, the side walls and the end of the shock tube.
\r\n\r\nThe development of viscous boundary layers on the side walls of the test section can cause the bifurcation of waves reflected from the end wall of the shock tube, and, thereafter, the formation of wall bubbles and interface contaminating jets. Moreover, the generation of vortical structures by the baroclinic instability excited by the interaction of reflected waves with the distorted interface within the boundary layer has been demonstrated. Significant contamination of the test gas can by achieved by these structures, even if reflected-wave bifurcation is absent. Moreover, the strain induced by the vorticity in these wall structures tends to thin the interface; the magnitude of this effect on the growth rates in the present plane interface experiments is estimated to be of order 10% for discontinuous interfaces and 50% for continuous interfaces.
\r\n" }, { "name": "Chao, Chi-chao", "degree": "PhD", "year": "1989", "title": "Error-Correction Coding for Reliable Communication in the Presence of Extreme Noise", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012007-093354", "creators": [ { "name": { "family": "Chao", "given": "Chi-chao" }, "id": "Chao-Chi-chao", "display_name": "Chao, Chi-chao" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Wilson", "given": "Richard M." }, "id": "Wilson-R-M", "role": "member", "display_name": "Wilson, Richard M." }, { "name": { "family": "Swanson", "given": "Laif" }, "id": "Swanson-Laif", "role": "member", "display_name": "Swanson, Laif" } ], "option_major": [ "eleceng" ], "doi": "10.7907/h228-d056", "abstract": "This thesis is a study of error-correcting codes for reliable communication in the presence of extreme noise. We consider very noisy channels, which occur in practice by pushing ordinary channels to their physical limits. Both block codes and convolutional codes are examined.
\r\n\r\nWe show that the family of triply orthogonal codes, defined and studied in this thesis, or orthogonal codes can be used to achieve channel capacity for certain classes of very noisy discrete memoryless channels. The performance of binary block codes on the unquantized additive white Gaussian noise channel at very low signal-to-noise ratios is studied. Expressions are derived for the decoder block error as well as bit error probabilities and the asymptotic coding gain near the point where the signal energy is zero.
\r\n\r\nThe average distance spectrum for the ensemble of time-varying convolutional codes is computed, and the result gives a surprisingly accurate prediction of the growth rate of the number of fundamental paths at large distance for fixed codes. A Gilbert-like free distance lower bound is also given. Finally, a Markov chain model is developed to approximate burst error statistics of Viterbi decoding. The model is validated through computer simulations and is compared with the previously proposed geometric model.
" }, { "name": "Chiueh, Tzi-Dar", "degree": "PhD", "year": "1989", "title": "Pattern Classification and Associative Recall by Neural Networks", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11052012-093038170", "creators": [ { "name": { "family": "Chiueh", "given": "Tzi-Dar" }, "id": "Chiueh-Tzi-Dar", "orcid": "0000-0003-0851-6629", "display_name": "Chiueh, Tzi-Dar" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/pjan-6r82", "abstract": "The first part of this dissertation discusses a new classifier based on a multilayer feed-forward network architecture. The main idea is to map irregularly-distributed prototypes in a classification problem to codewords that are organized in some way. Then the pattern classification problem is transformed into a threshold decoding problem, which is easily solved using simple hard-limiter neurons. At first we propose the new model and introduce two families of good \"internal representation\" codes. Then some analyses and software simulation concerning the storage capacity of this new model are done. The results show that the new classifier is much better than the classifier based on the Hopfield model in terms of both the storage capacity and the ability to classify correlated prototypes.
\r\n\r\nA general model for neural network associative memories with a feedback. structure is proposed. Many existing neural network associative memories can be expressed as special cases of this general model. Among these models, there is a class of associative memories, called correlation associative memories, that are capable of storing a large number of memory patterns. If the function used in the evolution equation is monotonically nondecreasing, then a correlation associative memory can be proved to be asymptotically stable in both the synchronous and asynchronous updating modes.
\r\n\r\nOf these correlation associative memories, one stands out because of its VLSI implementation feasibility and large storage capacity. This memory uses the exponentiation function in its evolution equation; hence it is called exponential correlation associative memory (ECAM). It is further proved that the storage capacity of ECAM scales exponentially with N (the number of components in memory patterns) when N approaches infinity. A programmable ECAM chip is designed, simulated, fabricated, and then tested. The performance of the ECAM chip is shown to be not much worse than that of a computer-simulated ECAM model in terms of error correcting ability (attraction radius). Finally, the speed of the prototype ECAM chip is demonstrated by employing it to do vector quantization on binary images. And it is found that the ECAM chip can process binary images in real time.
" }, { "name": "Chow, David Hsingkuo", "degree": "PhD", "year": "1989", "title": "Growth, Characterization, and Simulation of Novel Semiconductor Tunnel Structures", "advisor": "McGill, Thomas C.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212003-115412", "creators": [ { "name": { "family": "Chow", "given": "David Hsingkuo" }, "id": "Chow-David-Hsingkuo", "display_name": "Chow, David Hsingkuo" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/96gc-kc14", "abstract": "This thesis presents investigations of novel semiconductor heterostructure devices based on quantum mechanical tunneling. Due to their small characteristic dimensions, these devices have extremely fast charge transport properties. Thus, it is expected that tunnel structure devices will be well-suited to high frequency and optoelectronic applications. The work presented here can be divided into three sections. In the first section, a theoretical model for simulating current-voltage behavior in single barrier heterostructures is developed. The simulations are then used to design a novel single barrier negative differential resistance (NDR) device. The second section consists of detailed experimental characterizations of single barrier Hg1-xCdxTe heterostructures, including the first demonstration of the novel single barrier NDR mechanism. Growth of III-V semiconductor heterostructures by molecular beam epitaxy (MBE) is the subject of the third section. Several aspects of tunneling are explored through characterization of these III-V structures.
\r\n\r\nIn chapter 2, a theoretical model is developed to simulate tunneling currents in single barrier heterostructures. The model includes band bending effects and a two band treatment of electron attenuation coefficients in the barrier. It is proposed that certain material systems have the appropriate band alignments to realize a novel single barrier negative differential resistance mechanism. A thorough theoretical analysis of these single barrier NDR structures is presented.
\r\n\r\nThe first experimental demonstration of the single barrier NDR mechanism is reported in chapter 3. The HgCdTe/CdTe material system was selected for the demonstration. In this material system, low temperatures (<20 K) are needed to observe the NDR effect. However, it has been demonstrated recently that room temperature NDR can be obtained from InAs/GaAlSb single barrier structures. High temperature (190-300 K) current-voltage curves from the single barrier Hg1-xCdxTe heterostructures have also been investigated, leading to a direct electrical measurement of the controversial HgTe/CdTe valence band offset.
\r\n\r\nIn chapter 4, results are presented from several studies of III-V heterostructures grown by MBE. A measurement of the GaAs/AlAs valence band offset by xray photoemission spectroscopy yields a value of 0.46 \u00b1 0.07 eV, independent of growth sequence. Optical measurements of electron tunneling times in GaAs/AlAs double barrier heterostructures are performed by growing structures with very thin cap layers. Tunneling times as short as \u2248 12 ps are measured. Triple barrier GaAs/AlAs tunnel structures are found to display strong NDR, indicating that the tunneling process is coherent (as opposed to sequential) in nature. Finally, a technique for depositing high quality InAs buffer layers on GaAs substrates is developed.
" }, { "name": "Coffey, John Timothy", "degree": "PhD", "year": "1989", "title": "On Complexity and Efficiency in Encoding and Decoding Error-correcting Codes", "advisor": "Goodman, Rodney M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06102005-114154", "creators": [ { "name": { "family": "Coffey", "given": "John Timothy" }, "id": "Coffey-John-Timothy", "display_name": "Coffey, John Timothy" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Farrell", "given": "Paddy" }, "id": "Farrell-P", "role": "member", "display_name": "Farrell, Paddy" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Solomon", "given": "Gustave" }, "id": "Solomon-G", "role": "member", "display_name": "Solomon, Gustave" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4jy2-w055", "abstract": "A central paradox of coding theory has been noted for many years, and concerns the existence and construction of the best codes. Virtually every linear code is \"good\" in the sense that it meets the Gilbert-Varshamov bound on distance versus redundancy. Despite the sophisticated constructions for codes derived over the years, however, no one has succeeded in demonstrating a constructive procedure which yields such codes over arbitrary symbol fields. A quarter of a century ago, Wozencraft and Reiffen, in discussing this problem, stated that \"we are tempted to infer that any code of which we cannot think is good.\" Using the theory of Kolmogorov complexity, we show the remarkable fact that this statement holds true in a rigorous mathematical sense: any linear code which is truly random, in the sense that there is no concise way of specifying the code, is good. Furthermore, random selection of a code which does contain some constructive pattern results, with probability bounded away from zero, in a code which does not meet the Gilbert-Varshamov bound regardless of the block length of the code. In contrast to the situation for linear codes, we show that there are effectively random non-linear codes which have no guarantee on distance, and that over all rates, the average non-linear code has much lower distance than the average linear code.
\r\n\r\nThese techniques are used to derive original results on the performance of various classes of codes, including shortened cyclic, generalized Reed-Solomon, and general non-linear codes, under a variety of decoding strategies involving mixed burst- and random-error correction.
\r\n\r\nThe second part of the thesis deals with the problem of finding decoding algorithms for general linear codes. These algorithms are capable of full hard decision decoding or bounded soft decision decoding, and do not rely on any rare structure for their effectiveness.
\r\n\r\nAfter a brief discussion of some aspects of the theory of NP-completeness as it relates to coding theory, we propose a simple model of a general decoding algorithm which is sufficiently powerful to be able to describe most of the known approaches to the problem. We provide asymptotic analysis of the complexity of various approaches to the problem under various decoding strategies (full hard decision decoding and bounded hard- and soft-decision decoding) and show that a generalization of information set decoding gives more efficient algorithms than any other approach known.
\r\n\r\nFinally, we propose a new type of algorithm that synthesizes some of the advantages of information set decoding and other algorithms that exploit the weight structure of the code, such as the zero neighbours algorithm, and discuss its effectiveness.
" }, { "name": "Collett, Jeffrey Lee, Jr.", "degree": "PhD", "year": "1989", "title": "Characterization of Cloudwater and Precipitation Chemistry and Deposition at Elevated Sites in Central and Southern California", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062007-142411", "creators": [ { "name": { "family": "Collett", "given": "Jeffrey Lee, Jr." }, "id": "Collett-Jeffrey-Lee-Jr", "display_name": "Collett, Jeffrey Lee, Jr." } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/fybt-5982", "abstract": "The chemical composition of cloudwater samples collected in the Sierra Nevada Mountains of central California between 1985 and 1988 was dominated by NH\u207a\u2084, NO\u207b\u2083, and SO\u00b2\u207b\u2084. The balance between these three species usually was responsible for determining the cloudwater pH, although inputs of formic and acetic acid also are believed to be important in this regard, particularly for relatively unpolluted samples. The pH of cloudwater sampled in Yosemite National Park, which ranged from 3.8 to 5.2, normally was lower than the pH of samples collected in Sequoia National Park (3.9 to 6.5). Cloudwater pH differences between the two Parks appear to be due to small differences in cloudwater concentrations of NH\u207a\u2084, NO\u207b\u2083, and SO\u00b2\u207b\u2084.
\r\n\r\nThe composition of cloudwater in Sequoia National Park is determined primarily by the concentrations of precursor aerosol and soluble gases. Park aerosol concentrations were observed to increase during the approach of a cold front, producing higher pollutant concentrations in the clouds associated with the frontal activity than would be expected based on typical regional aerosol and gas concentrations.
\r\n\r\nOver 265 hours of cloud interception were observed, during a one-year period of continuous monitoring, at 1860 m elevation in Sequoia National Park. Most interception was observed at elevations above 1500 m -- produced during the passage of convective clouds, associated with cold fronts, across the Sierra. Deposition of pollutants, including acids, to the forest canopy at elevations above 1500 m was estimated to be significant, relative to inputs from precipitation and dry deposition. Cloudwater interception may, in fact, be the dominant deposition mechanism for NH\u207a\u2084 and NO\u207b\u2083, particularly for isolated trees or ridgetop canopies where wind speeds are higher and cloudy air parcels can impact directly on foliar surfaces.
\r\n\r\nA precipitation study, conducted in the South Coast Air Basin surrounding Los Angeles during the winter of 1987, illustrated the rapid scavenging of pollutants from the air column by falling raindrops. Results of a comparison of N(V) and S(VI) deposition during an extended precipitation event with the atmospheric loading of these species over the basin prior to the event suggested that both species were produced in the atmosphere during the rainstorm. Evidence was seen for in-cloud production of SO\u00b2\u207b\u2084, but not of NO\u207b\u2083.
" }, { "name": "Collins, Oliver Michael", "degree": "PhD", "year": "1989", "title": "Coding Beyond the Computational Cutoff Rate", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012007-132507", "creators": [ { "name": { "family": "Collins", "given": "Oliver Michael" }, "id": "Collins-Oliver-Michael", "display_name": "Collins, Oliver Michael" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Solomon", "given": "Gustave" }, "id": "Solomon-G", "role": "member", "display_name": "Solomon, Gustave" }, { "name": { "family": "Wilson", "given": "Richard M." }, "id": "Wilson-R-M", "role": "member", "display_name": "Wilson, Richard M." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/nxwj-1433", "abstract": "This thesis presents a collection of new codes, algorithms, and hardware, which can all be used to reduce the required energy per information bit to noise spectral density ratio on the Gaussian channel. First comes a feedback technique from an outer to an inner code. The basic idea is to perform a second maximum likelihood decoding operation of the inner code that incorporates side information. Next comes a new kind of algebraic outer code which we get from combining Reed Solomon codes with themselves. The most important results, however, deal with the construction of long constraint length Viterbi decoders. One chapter presents a hardware design of a constraint length 15, rate 1/6 decoder. The last chapter gives some results on the partitioning of a deBruijn graph which make the number of interconnections in the design physically realizable.
" }, { "name": "Derry, Pamela Louise", "degree": "PhD", "year": "1989", "title": "Properties of Buried Heterostructure Single Quantum Well (Al,Ga)As Lasers", "advisor": "Yariv, Amnon; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052007-093221", "creators": [ { "name": { "family": "Derry", "given": "Pamela Louise" }, "id": "Derry-Pamela-Louise", "display_name": "Derry, Pamela Louise" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/WSZC-4R60", "abstract": "Unlike conventional semiconductor lasers, single quantum well (SQW) lasers with high reflectivity end facet coatings have dramatically reduced threshold currents as a result of the smaller volume of the (active) quantum well region. A cw threshold current of 0.55 mA was obtained for a buried graded-index separate-confinement heterostructure SQW laser with facet reflectivities of ~80%, a cavity length of 120 \u00b5m, and an active region stripe width of 1 \u00b5m. This is believed to be the lowest threshold current so far reported for any semiconductor laser at room temperature.
\r\n\r\nThe submilliampere threshold currents of these lasers allow them to be modulated at high speed without any current prebias or feedback monitoring. The relaxation oscillation frequency for these lasers was also measured. Values of differential gain derived from these measurements demonstrated that the differential gain in the uncoated lasers is less than in the coated devices. This result was expected because of gain saturation.
\r\n\r\nAs predicted, SQW lasers have substantially narrower spectral linewidths than bulk double heterostructure lasers. This result is attributed to lower internal loss, linewidth enhancement factor, and spontaneous emission factor. A further major reduction (< 3x) in the linewidth of these SQW lasers was observed when the facet reflectivities were enhanced. This observation is explained theoretically on the basis of the very low losses in coated SQW lasers and the value of the spontaneous emission factor.
" }, { "name": "DiChristina, Thomas J.", "degree": "PhD", "year": "1989", "title": "Dissimilative Fe(III) Reduction by Alteromonas putrefaciens Strain 200", "advisor": "Lidstrom, Mary E.; Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052007-153354", "creators": [ { "name": { "family": "DiChristina", "given": "Thomas J." }, "id": "DiChristina-Thomas-J", "display_name": "DiChristina, Thomas J." } ], "advisors": [ { "name": { "family": "Lidstrom", "given": "Mary E." }, "id": "Lidstrom-M-E", "role": "advisor", "display_name": "Lidstrom, Mary E." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "co-advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Lidstrom", "given": "Mary E." }, "id": "Lidstrom-M-E", "role": "chair", "display_name": "Lidstrom, Mary E." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "co-chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Simon", "given": "Melvin I." }, "id": "Simon-M-I", "role": "member", "display_name": "Simon, Melvin I." }, { "name": { "family": "Emr", "given": "Scott D." }, "id": "Emr-S-D", "role": "member", "display_name": "Emr, Scott D." }, { "name": { "family": "Gunsalus", "given": "Robert P." }, "id": "Gunsalus-Robert-P", "role": "member", "display_name": "Gunsalus, Robert P." } ], "option_major": [ "envreng" ], "doi": "10.7907/temn-0p39", "abstract": "Complementary genetic and biochemical analyses have been used to study the (dissimilative) iron reduction system of Alteromonas putrefaciens strain 200. Preliminary kinetic data suggested that A. putrefaciens 200 possessed a ferri-reductase that was physiologically distinct from either cytochrome oxidase or nitrate reductase. A suite of iron-reduction-deficient mutants was generated via chemical (EMS) and transposon (Tn5) mutagenesis procedures. A newly developed screening technique was subsequently used to identify mutants deficient in both high-rate and low-rate iron reduction activity. A conjugal gene transfer system was developed for mobilization of IncP1-based cloning vectors to A. putrefaciens 200. The broad host range (IncPl) cosmid cloning vector pVK100 was used to construct A. putrefaciens 200 gene clone banks in E. coli strains HB101 and S17-1 (mobilizing strain). Both three-way and two-way mating (conjugation) procedures were used to mobilize the gene clone banks into the suite of iron-reduction-deficient mutants during genetic (complementation) analysis. Two iron reduction clones (designated S4-E-2 and S18-F-4) were identified by their ability to restore iron reduction activity to several of the iron-reduction-deficient mutants. Preliminary biochemical characterization of selected mutant strains has indicated that cytochrome content may play an important role in the iron reduction process. Based on the results of the complementary genetic and biochemical studies, the iron reduction mutants have been placed into four classes: Class I (deficient in both high-rate and low-rate iron reduction activity, complemented by clones S4-E-2 and S18-F-4, possible b- or c-type cytochrome mutants), Class II (deficient in both high-rate and low-rate iron reduction activity, complemented by clone S4-E-2 but not by S18-F-4), Class III (proficient in high-rate iron reduction activity, but deficient in low-rate iron reduction activity, not complemented by either clone S4-E-2 or S18-F-4), and Class IV (deficient in both high-rate and low-rate iron reduction activity, but not complemented by either clone S4-E-2 or S18-F-4, possible d-type cytochrome or anaerobic regulatory mutant).
" }, { "name": "Donlon, William Patrick, Jr.", "degree": "PhD", "year": "1989", "title": "Experimental Investigation of the Nonlinear Seismic Response of Concrete Gravity Dams", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232007-074318", "creators": [ { "name": { "family": "Donlon", "given": "William Patrick, Jr." }, "id": "Donlon-William-Patrick-Jr", "display_name": "Donlon, William Patrick, Jr." } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "civileng" ], "doi": "10.7907/4mqw-6z67", "abstract": "The nonlinear seismic response of concrete gravity dams is investigated experimentally through the use of small-scale models. Of primary interest is crack formation, crack opening and closing, and sliding along crack planes. Also of concern is the stability of the structure after cracking. Three small-scale models (length scale - 115) of a single monolith of Pine Flat Dam are tested to determine the extent of such behavior and its effect on structural stability. The models are constructed of one polymer-based and two plaster-based materials developed for these experiments. The plaster-based materials fulfill the strength, stiffness, and density requirements established by the laws of similitude, while the polymer-based material fulfills only the stiffness and density requirements and is used only in the lower part of the dam where cracking is not expected. The excitation is a modified version of the N00E component of the 1940 Imperial Valley earthquake, applied to each model's base in the stream direction through a vibration table with high-frequency capability. Tests are performed with and without water in the reservoir. The response of each earthquake test is presented in the form of acceleration and displacement time histories, Fourier spectra, and frames taken from high-speed films of the model's response. The results of the experiments indicate that the neck region of a concrete gravity dam is most susceptible to cracking, although crack profiles can differ as a result of variations in excitation, material properties, and construction techniques. These results also indicate alternate design techniques which could improve the seismic stability of a cracked gravity dam.
" }, { "name": "El-Aidi, Bahaa", "degree": "PhD", "year": "1989", "title": "Nonlinear Earthquake Response of Concrete Gravity Dam Systems", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06072007-132404", "creators": [ { "name": { "family": "El-Aidi", "given": "Bahaa" }, "id": "El-Aidi-Bahaa", "display_name": "El-Aidi, Bahaa" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "civileng" ], "doi": "10.7907/n2f8-rv33", "abstract": "The earthquake response of concrete gravity dam systems is investigated with emphasis on the nonlinear behavior associated with tensile concrete cracking and water cavitation. A single dam-monolith is considered and is assumed to respond independently as a two-dimensional system under plane stress conditions. The two-dimensional assumption is also extended to model the compressible water body impounded upstream of the dam. Standard displacement-based finite element techniques are used to spatially discretize the field equations and produce a single symmetric matrix equation for the dam-water system. Energy dissipation in the reservoir, through radiation in the infinite upstream direction and absorption at the bottom, is approximately accounted for, and a set of numerical examples is presented to demonstrate the accuracy of the present formulation in modeling the linear earthquake response of infinite reservoirs. An approximate procedure to account for dam-foundation interaction is incorporated based on the response of a rigid plate attached to a three-dimensional viscoelastic half-space.
\r\n\r\nWater cavitation is modeled by a smeared approach which uses a bilinear pressure-strain relation. It is shown that the water response becomes dominated by spurious high frequency oscillations upon closure of cavitated regions, and improved results can be obtained by using some stiffness-proportional damping in the water reservoir. As demonstrated in an example analysis of Pine Flat Dam (linear dam), cavitation occurs in the upper part of the reservoir along the dam face, unlike other investigations which show cavitated regions at considerable distances from the dam, and both the tensile pressure cutoffs and compressive impacts have a minor effect on the dam response.
\r\n\r\nTensile cracks are incorporated using the smeared crack approach, and sliding along closed cracks is allowed. Coupling effects inherent in the finite element formulation are explained, and their influence on open and closed cracks is investigated. Propagation of cracks is monitored in an interactive environment which uses an equivalent strength criterion and allows for user input; remeshing is avoided. The algorithm adopted here produces narrow cracks, unlike many other investigations which show large zones of cracking. An extensive numerical study of Pine Flat Dam demonstrates some interesting features of the nonlinear response of the system, identifies potential failure mechanisms, and reveals a number of difficulties that the analysis encounters. Although no instability of the dam occurs, the numerical difficulties will have to be overcome before definite conclusions regarding stability can be made. It is shown that cracking reduces the hydrodynamic pressures in the reservoir and, hence, reduces water cavitation.
" }, { "name": "Franz, Ronald John", "degree": "PhD", "year": "1989", "title": "Experimental Investigation of the Effect of Cavitation on the Rotordynamic Forces on a Whirling Centrifugal Pump Impeller", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-133417", "creators": [ { "name": { "family": "Franz", "given": "Ronald John" }, "id": "Franz-Ronald-John", "display_name": "Franz, Ronald John" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/5JXT-CZ84", "abstract": "The interaction of a rotating impeller and the working fluid introduce forces on the rotor. These fluid-induced forces can cause self-excited whirl, where the rotor moves away from and whirls along a trajectory eccentric to its undeflected position. When designing a turbomachine, particularly one which is to operate at high speed, it is important to be able to predict the fluid-induced forces, both steady and unsteady, acting on the various components of the machine. The fluid-induced rotordynamic forces acting upon the impeller and therefore on the bearings was investigated for a centrifugal impeller in a spiral volute in the presence of cavitation.\r\n\r\nAn experiment in forced vibration was made to study the fluid-induced rotordynamic force on an impeller whirling around its machine axis of rotation in water. The whirl trajectory of the rotor is prescribed to be a circular orbit of a fixed radius. A dynamometer mounted behind the rotor and rotating with it measures the force on the impeller. The force measured is a combination of a steady radial force due to volute asymmetries and an unsteady force due to the eccentric motion of the rotor. These measurements have been carried out over a full range of whirl/impeller speed ratios at different flow coefficients for various turbomachines. A destabilizing force was observed over a region of positive whirl ratio. Cavitation corresponding to a three percent head loss did not have a significant effect upon this destabilizing force. However, a lesser degree of cavitation at the design point for the impeller-volute combination tested increased this destabilizing force for a particular set of whirl ratios" }, { "name": "James, David Earl", "degree": "PhD", "year": "1989", "title": "Effects of Hydrazine and Other Toxicants on Early Life Stages of California Brown Algae", "advisor": "North, Wheeler J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062007-131016", "creators": [ { "name": { "family": "James", "given": "David Earl" }, "id": "James-David-Earl", "display_name": "James, David Earl" } ], "advisors": [ { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "advisor", "display_name": "North, Wheeler J." } ], "committee": [ { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "chair", "display_name": "North, Wheeler J." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Brokaw", "given": "Charles J." }, "id": "Brokaw-C-J", "role": "member", "display_name": "Brokaw, Charles J." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Jackson", "given": "George" }, "id": "Jackson-George", "role": "member", "display_name": "Jackson, George" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/WRCJ-G589", "abstract": "Toxicity of hydrazine to early life stages of several species of California brown algae was demonstrated to occur at environmentally relevant concentrations. Effects of hydrazine on benthic organisms had not been previously studied.
\r\n\r\nPreliminary studies evaluated toxicity of boric acid, chlorine (as hypochlorite), lithium ion, tributyltin chloride and Zn(II).
\r\n\r\nA reliable bioassay technique was developed using digital image analysis to measure vegetative growth inhibition of brown algal gametophytes. Hydrazine toxicity threshold of Macrocystis pyrifera gametophytes was almost constant in 10 96-hour experiments, ranging from 3 - 5 ppb (96-160 nM).
\r\n\r\nDifferences in resistance to short-term hydrazine exposures were observed among three algal families of the order Laminariales. Two of three tested members of the family Alariaceae, Pterygophora californica and Eisenia arborea were among the most resistant species tested. The three tested species in the family Lessoniaceae, Macrocystis pyrifera, Nereocystis luetkeana and Pelagophycus porra, all fast-growing canopy-formers, were among the most sensitive tested species. Tested representatives of the family Laminariaceae varied in resistance. Laminaria farlowii was resistant. Laminaria dentigera and Laminaria ephemera were fairly sensitive.
\r\n\r\nHydrazine autoxidation rates varied by an order of magnitude in seawater sampled from different locations. Rates showed strong temperature dependence. Autoxidation at 10\u00b0C and below was much slower and indicated a higher activation energy than autoxidation at 20\u00b0C and above.
\r\n\r\nUndiluted trace hydrazine powerplant emissions from a time period when algal community composition changed in the vicinity of an outfall were compared to growth inhibition results from multivariate hydrazine toxicity experiments on Macrocystis gametophytes. Results indicated that several trace hydrazine discharges were of sufficient duration and concentration to have inhibited algal microscopic stages.
" }, { "name": "Johnson, Matthew Bruce", "degree": "PhD", "year": "1989", "title": "Ultrafast Time-Resolved Photoluminescence Studies of GaAs", "advisor": "McGill, Thomas C.; McCaldin, James Oeland; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062007-105824", "creators": [ { "name": { "family": "Johnson", "given": "Matthew Bruce" }, "id": "Johnson-Matthew-Bruce", "display_name": "Johnson, Matthew Bruce" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "advisor", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Cowan", "given": "Eugene W." }, "id": "Cowan-E-W", "role": "member", "display_name": "Cowan, Eugene W." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/9WE7-AP87", "abstract": "This thesis concerns the study of ultrafast phenomena in semiconductor physics. At the heart of this research is the construction of a colliding-pulse mode-locked (CPM) ring-dye laser. This laser outputs ultrashort optical pulses at a high repetition rate. With a CPM laser, ultrafast semiconductor phenomena may be optically probed. In addition, using this laser to drive photoconductive circuit elements (PCEs), ultrafast electrical pulses can be generated and sampled, allowing novel high-speed devices to be electronically probed. For the measurement of ultrafast time-resolved photoluminescence (PL) a new pump/probe technique called photoluminescence excitation correlation spectroscopy (PECS) was used. The technique itself was investigated both theoretically and experimentally; it was applied to a variety of GaAs samples of interest in the development of high-speed devices.
\r\n\r\nChapter 2 discusses the construction and alignment of the CPM laser, and the autocorrelator used to measure the ultrashort pulses. Although the laser can be run with pulse widths of < 100 fs full-width at half maximum (FWHM), in the work of this thesis, the laser was operated with pulse widths in the range 200 to 400 fs, with a repetition rate of about 120 MHz, and average output power of 10 to 30 mW.
\r\n\r\nIn Chapter 3, the PECS method is investigated both experimentally and theoretically. PECS is a pulse-probe technique that measures the cross-correlation of photo-excited populations. PECS is theoretically investigated using a rate equation model for a simple three-level system consisting of an electron and hole band and a single trap level. The model is examined in the limits of radiative band-to-band dominated recombination, and capture-dominated recombination. In the former limit, no PECS signal is observed. However, in the latter limit, the PECS signal from the band-to-band PL measures the cross-correlation of the excited electron-hole population, and, thus, the electron and hole lifetimes. PECS is experimentally investigated using a case study of PL in semi-insulating (SI) GaAs and In-GaAs. At 77 K, the PECS signal behaves as in the simple model, and an electron-hole lifetime in the range 200 ps is measured. This is much less than the expected radiative lifetime, and therefore the recombination in SI GaAs is capture-dominated. At 5 K, the behavior is more complicated, because of an acceptor, which is un-ionized at 5 K. PECS for the PL band-to-band decay, shows two decay modes: the fast decay (about 100 ps) is due to the saturable decay associated with the acceptor and the slow decay (about 1 ns) is due to bulk capture. The acceptor-related PL also shows complicated behavior: A fast decay is associated with the band-to-acceptor transition, and the donor-acceptor PL saturates, producing a PECS signal that is negative and decays slowly.
\r\n\r\nIn Chapter 4, PECS is used to investigate the large band-to-band PL contrast observed near dislocations in In-alloyed GaAs. It is found that the PL intensity contrast between a bright and dark area correlates with the ratio of the lifetimes measured using PECS in these areas. Thus, the PL intensity contrast is due to the difference in the carrier lifetimes in the different regions. The differences in the behavior of the lifetimes in the bright and dark regions with temperature suggest that the lifetime-governing defects in the two regions are different. Moreover, the defects are deep, and from the shortness of the lifetimes, neither defect is EL2. These results agree with earlier research, which indicated that defects are gettered and generated at these dislocations. The effects of surface recombination on the PL intensity and lifetimes in In-alloyed GaAs are important to the investigations of this chapter. These are investigated in Appendix E, where it is shown that both PL intensity and PECS-measured carrier lifetimes are greatly affected by surface properties and by laser dose and surface preparation. This is thought to be due to the creation of defects, which affects the surface recombination directly, and bends the electronic bands at the surface to affect the surface recombination indirectly. These effects are reduced by minimizing the exposure to the laser and by using a recently developed Na2S surface passivation layer.
\r\n\r\nIn Chapter 5, the carrier lifetime of damaged GaAs is correlated to the cross-correlation of the PCEs fabricated on the same material. Implantation of 200 keV H+ ions at doses in the range of 1011 - 1014 cm-2 is used to damage the GaAs. The carrier lifetimes are inversely proportional to the dose for doses > 1012 cm-2, and do not indicate a saturation of the damage within the range investigated. For the highest dose of 1014 cm-2, a lifetime of 0.6 \u00b1 0.2 ps was measured at 77 K. The PCE cross-correlation decreases less quickly than the lifetime, indicating that some effect other than the lifetime is governing the cross-correlation response speed.
\r\n\r\nFinally, two of the appendices present independent research that is worthy of note. Appendix C presents an attempt to grow HgTe on CdTe using a novel low-temperature Hg-rich melt liquid-phase epitaxial (LPE) growth technique, which involves an in situ cleave. Appendix D presents a program that models the behavior of ultrafast voltage pulses on a dispersive waveguide, which includes a lumped device.
" }, { "name": "Jones, Todd Jarrott", "degree": "PhD", "year": "1989", "title": "Radiation-Induced Conductivity in Amorphous Carbon", "advisor": "Tombrello, Thomas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-131335", "creators": [ { "name": { "family": "Jones", "given": "Todd Jarrott" }, "id": "Jones-Todd-Jarrott", "display_name": "Jones, Todd Jarrott" } ], "advisors": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "advisor", "display_name": "Tombrello, Thomas A." } ], "committee": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "chair", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Housley", "given": "Robert M." }, "id": "Housley-Robert-M", "role": "member", "display_name": "Housley, Robert M." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/5A5K-T270", "abstract": "Amorphous carbon films were irradiated with high energy chlorine ions with energies between 1 and 45 MeV. The electrical conductivity was measured in situ over a range of doses from 2 x 1010 to 5 x 1015 ions/cm2. It was found that the conductivity increases over three to four orders of magnitude. The variation of the conductivity with temperature is successfully fitted by a Mott hopping conduction model. The energy sensitivity of the effect (excitation curve) does not parallel the electronic stopping power of chlorine in carbon, but a multihit \u03b4 electron theory based on an ion-track model closely matches the excitation curve. The 1 and 2 MeV irradiations show he effect of nuclear stopping associated with low energy irradiatio" }, { "name": "Krishnaswamy, Sridhar", "degree": "PhD", "year": "1989", "title": "On the Domain of Dominance of the Asymptotic Elastodynamic Crack-Tip Fields", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-134326", "creators": [ { "name": { "family": "Krishnaswamy", "given": "Sridhar" }, "id": "Krishnaswamy-Sridhar", "display_name": "Krishnaswamy, Sridhar" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/cfz9-nk80", "abstract": "A substantial part of the experimental data in dynamic fracture mechanics has been obtained under the assumption that the two-dimensional asymptotic elastodynamic stress-intensity factor field (the KdI-field) is dominant over at least the region around the crack-tip over which the experimental measurements are made. The validity of this assumption is investigated in this thesis both experimentally and through finite-element simulations of the experiments.
\r\n\r\nThe experiments reported in this work were on 4340 steel, three-point bend specimens loaded dynamically using a drop-weight tower. The two cases of dynamically loaded stationary cracks and dynamically propagating cracks were considered. An optical configuration is proposed that leads to a bifocal high-speed camera capable of focusing on two different planes simultaneously. This was used in conjunction with the method of caustics to measure the apparent stress-intensity factor simultaneously from two different regions (initial-curves) around the crack-tip. If the initial-curves lie within the domain of dominance of the asymptotic field, the measured values of the dynamic stress-intensity factor must agree to within experimental error. By suitably adjusting the optical set-up, a range of initial-curves was scanned in an attempt to map the domain of dominance of the KdI-field.
\r\n\r\nThe impact hammer and supports of the drop-weight loading device were instrumented in order to monitor the time dependent loads acting on the specimen. These loads were subsequently used as boundary tractions in dynamic two- and three-dimensional finite-element simulations of the experiments. The simulations were carried only up to the point of crack initiation. Comparison of the numerical simulations with the experimental results help in identifying the role of three-dimensionality and transient conditions on the measured stress-intensity factor values.
\r\n\r\nOn the basis of both the experimental results as well as the numerical simulations, no sizeable annulus of dominance for the asymptotic elastodynamic field was found for the laboratory situation studied. It appears that the assumption of an underlying KdI-dominant (or two-dimensional) field might not hold to a level of accuracy that would warrant many of the conclusions made in the literature regarding the crack-initiation toughness values as well as the uniqueness of the dynamic fracture toughness - crack velocity relation or its specimen and acceleration dependence.
" }, { "name": "Lo, Davy", "degree": "PhD", "year": "1989", "title": "Molecular Dynamics Simulation of Sputtering", "advisor": "Tombrello, Thomas A.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082007-095349", "creators": [ { "name": { "family": "Lo", "given": "Davy" }, "id": "Lo-Davy", "display_name": "Lo, Davy" } ], "advisors": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "advisor", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "chair", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Housley", "given": "Robert M." }, "id": "Housley-Robert-M", "role": "member", "display_name": "Housley, Robert M." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/EVKV-AW57", "abstract": "The sputtering of metals by low-energy (keV) ion bombardment has been investigated with the molecular dynamics technique. This study, based on computer simulations, aims to elucidate experimental observations and to provide valuable theoretical insight. The systems studied include Ar+ ion bombardment of metals, alloys, and isotopic mixtures in either the solid or liquid state. Effects of many-body interactions on the spectrum of sputtered atoms were also examined. Simulation results generally support experimental findings and render many basic assumptions of analytic sputtering theory dubious.
\r\n\r\nThis thesis consists of molecular dynamics studies of several sputtering topics not directly related to each other and is organized accordingly into separate chapters. Each of these chapters will be a summary of corresponding publications published by the author during the course of his graduate study. Reprints of publications are included as appendices at the end of each chapter.
" }, { "name": "Lu, Lun-Tseng", "degree": "PhD", "year": "1989", "title": "Dynamics, Noise Properties, and Spectral Characteristics of Semiconductor Lasers with External Coupling", "advisor": "Yariv, Amnon; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082007-092122", "creators": [ { "name": { "family": "Lu", "given": "Lun-Tseng" }, "id": "Lu-Lun-Tseng", "display_name": "Lu, Lun-Tseng" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Breckinridge", "given": "James B." }, "id": "Breckinridge-James-B", "orcid": "0000-0002-9488-098X", "role": "member", "display_name": "Breckinridge, James B." }, { "name": { "family": "Drever", "given": "Ronald W. P." }, "id": "Drever-R-W-P", "role": "member", "display_name": "Drever, Ronald W. P." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/frs6-t936", "abstract": "This thesis is a study of the dynamics, noise properties, and linewidth of semiconductor lasers with external coupling. In Chapter 2, a general formalism is developed for obtaining the optical-field equations of semiconductor lasers with external coupling. This formalism is applied to three different types of semiconductor lasers: (1) a diode laser coupled to an external mirror, (2) an injection-locked diode laser, and (3) an axially coupled two-section diode laser. The resulting equations are the basis for the studies and discussions given in Chapters 3, 4, and 5.
\r\n\r\nThe third chapter considers, using a small-signal analysis, a single-mode semiconducor laser coupled to an external mirror. Light trapped for many round trips inside the external cavity is taken into account. Analytical expressions for the frequency and relative-intensity fluctuation spectra, the laser linewidth and the small-signal current modulation response are obtained. The fundamental mechanism that prevents the mode locking in semiconductor lasers with an external feedback is identified. The observed data on the intensity noise and the current modulation response are elucidated.
\r\n\r\nAn injection-locked semiconductor laser is studied in Chapter 4. The origin and importance of the facet's amplitude reflectivities are described. The instability occurring in the high-frequency side of the locked range is fully explored. A detailed study of the locking bandwidth is presented. It is shown that, depending on the detuning of the lasing frequency, the relative-intensity noise can be reduced or increased. It is also demonstrated on a general basis that the locked laser linewidth is the same as that of the injected field.
\r\n\r\nThe dynamics and laser linewidth of an axially coupled two-section semiconductor laser are scrutinized in the last chapter. The relative-intensity and frequency fluctuation spectra can be obtained from the results given in this chapter. A formula is obtained for the laser linewidth. This formula explains the experimental observations that the linewidth is nearly inversely proportional to the power with a nonzero intercept. Finally, the contribution to the reduction in dynamic frequency chirping of two-section lasers is clarified.
" }, { "name": "Maboudian, Roya", "degree": "PhD", "year": "1989", "title": "In-Situ Observation of Surface and Near-Surface Modification Using Scattering of Ballistic Phonons", "advisor": "Goodstein, David L.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122007-080335", "creators": [ { "name": { "family": "Maboudian", "given": "Roya" }, "id": "Maboudian-Roya", "orcid": "0000-0002-5121-6560", "display_name": "Maboudian, Roya" } ], "advisors": [ { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "advisor", "display_name": "Goodstein, David L." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "chair", "display_name": "Goodstein, David L." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/w5xh-p756", "abstract": "We have investigated the feasibility of phonon-reflection techniques as non-destructive means to probe surface and/or near-surface damage in otherwise highly perfect crystals. A UHV liquid-helium stage, suitable for phonon-reflection measurements, was installed on a beam line of a tandem van de Graaff accelerator which was used to implant MeV ions into the substrate in order to modify the subsurface region in situ. Here, we report our investigation on the effects of 1 MeV Ar\u207a implantation in Al\u2082O\u2083 single crystals by monitoring the reflection of terahertz (THz) phonons (50 \u00c5 wavelength) from the implanted region. The results are supported by x-ray rocking measurements and Monte Carlo simulations.
\r\n\r\nUsing a 15 kV ion gun on the same beam line we have also bombarded Al\u2082O\u2083 crystals coated with thin films of gold. The effects of a 7.5 keV Ar\u207a irradiation on this Au - Al\u2082O\u2083 system are also discussed in this thesis.
\r\n\r\nThe relevance of this work is discussed in connection to the observations made by other groups and also to our previous work (reported in Appendix 3) on phonon-induced desorption of He atoms as well as the Kapitza anomaly.
" }, { "name": "Maher, Mary Ann Cecilia", "degree": "PhD", "year": "1989", "title": "A Charge-Controlled Model for MOS Transistors", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082007-135328", "creators": [ { "name": { "family": "Maher", "given": "Mary Ann Cecilia" }, "id": "Maher-Mary-Ann-Cecilia", "display_name": "Maher, Mary Ann Cecilia" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Linvill", "given": "John G." }, "id": "Linvill-John-G", "role": "member", "display_name": "Linvill, John G." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "compsci" ], "doi": "10.7907/JHQE-T452", "abstract": "As MOS (metal-oxide-semiconductor) devices scale to submicron lengths, short-channel effects begin to dominate device behavior, and designers of VLSI (very-large-scale-integrated) circuits see an improved transistor model as a necessary tool. A new physically based, charge-controlled model for the DC current, the intrinsic terminal charges, and the transcapacitances in the MOS transistor under quasistatic conditions has been developed. The model expresses the current in the MOS transistor in terms of the mobile charge per unit area in the channel, and uses a complete set of natural units for velocity, voltage, length, charge, and current. The current-flow equation for the transistor includes both a drift term and a diffusion term, so that the formulation applies equally over the subthreshold, saturation, and \"ohmic\" regions of transistor operation and includes the effect of velocity saturation. The solution of this dimensionless current-flow equation using these units is a simple, continuous expression, and is suitable for the computer simulation of integrated circuits. The expression allows the regimes of transistor operation and the behavior of long-channel devices versus short-channel devices to be discerned easily. In particular, the expressions for source and drain terminal charges combine the mobile charge in the channel at the source and drain ends in simple polynomials. Analysis of the model shows a fundamental relation between the transistor transcapacitances and transconductances, and permits the development of efficient simulation models of them.
\r\n\r\nOur physically based transistor model uses parameters derived from the fabrication process by direct measurement and from the dimensions of the device. The zero-order model agrees closely with measurements on the scaling of current with channel length down to submicron channel lengths. For more detailed analog simulations, the model contains several first-order effects calculated as perturbations on the simple model. Comparisons among calculated and measured curves of conductance, capacitance, and drain currents demonstrate the accuracy of the model both above and below threshold for a number of experimental devices of different channel lengths. Results from the model concur with measurements on short-channel transistors down to 0.6-micron channel length. Several analog circuit simulators now contain the model.
" }, { "name": "Maksimovi\u0107, Dragan", "degree": "PhD", "year": "1989", "title": "Synthesis of PWM and Quasi-Resonant DC-to-DC Power Converters", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-02132007-105916", "creators": [ { "name": { "family": "Maksimovi\u0107", "given": "Dragan" }, "id": "Maksimovi\u0107-Dragan", "orcid": "0000-0002-8867-0230", "display_name": "Maksimovi\u0107, Dragan" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "co-advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "chair", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "eleceng" ], "doi": "10.7907/B8XA-2R90", "abstract": "Synthesis of DC-to-DC converter topologies in the two largest families - PWM and Quasi-Resonant (QR) - is completed in this thesis.
\r\n\r\nIn a PWM converter, two linear time-invariant networks, consisting of only capacitors and inductors, source and load, are switched at constant frequency with duty ratio D. From defining assumptions, several general properties of PWM converter networks are derived. The established general properties interrelate the number of elements, attainable DC conversion ratio M(D), and features such as continuous terminal currents or possible coupling of inductors.
\r\n\r\nBased on matrix representation of the converter topology, the systematic synthesis procedure for generation of PWM converters with a given number of reactive elements is constructed. A prescribed set of requirements is the input for the procedure. The requirements may include desired DC conversion ratio, continuous terminal currents, possible coupling of inductors and a given number of switches. In particular, the number of switches implemented as transistors can be specified. Outputs of the procedure are complete classes of PWM converters that satisfy the input requirements. A number of useful PWM topologies, which have not been identified before, are uncovered. A comparison of members of the classes is included.
\r\n\r\nSeveral extensions of PWM converters are considered, including insertion of the isolation transformer and two discontinuous operating modes for which unified DC analyses are completed.
\r\n\r\nQuasi-Resonant converters are defined as two-switch PWM converter networks to which resonant elements are added. Synthesis of QR, converters is based on the recognition that there are only a finite number of topologically distinct positions for resonant elements within a two-switch PWM parent converter. If a single resonant inductor and a single resonant capacitor are added to a two-switch PWM topology, examination of all possible positions yields a total of six QR classes, which come in dual pairs. Two pairs are identified as known QR classes, namely, Zero-Current/Zero-Voltage (ZV/ZC) and Zero-Current/Zero-Voltage Quasi-Square-Wave (ZC-QSW/ZV-QSW). The remaining two classes, named Off-Resonant and On-Resonant Quasi-PWM (Qf-PWM/Qn-PWM), have not been recognized so far. The names originate from the fact that Q-PWM converters can be regarded as PWM converters operating in both discontinuous modes simultaneously. The synthesis procedure can be generalized to encompass additional resonant elements. As an example, classes of Zero-Current and Zero-Voltage Multi-Resonant (ZC-MR/ZV-MR) converters are formally defined.
\r\n\r\nIn contrast to square-wave switch waveforms in PWM converters, all QR topologies exhibit smooth quasi-sinusoidal waveforms and therefore reduced switching losses. Of particular interest are operating modes in which all switching transitions are at zero current or at zero voltage.
\r\n\r\nA study of operating modes and a DC analysis unified with respect to all PWM parents and all topological variations are carried out for four selected classes of QR Converters - Qn-PWM, ZV, ZV-QSW, and ZV-MR. It is emphasized that for a QR converter, topology alone is not sufficient to derive DC conversion properties. Subject to different switch implementations and control timing, the emerging operating modes can result in vastly different behavior of the same converter topology.
\r\n\r\nTwo switch implementations are considered - conventional, with one controllable switch and one diode, and the one that resembles the technique of synchronous rectification - with two controllable switches. In the first case, with the exception of converters in two Q-PWM classes, only variable-frequency control is applicable. However, if both switches are controllable, constant-frequency control is restored in all QR classes, and several novel operating modes of practical interest are uncovered.
\r\n\r\nVarious QR classes and operating modes are compared with respect to sets of switching transitions, sensitivity to parasitic elements, available operating region, frequency range and stresses on switching devices. The role of free parameters in various design trade-offs is exposed, thus allowing a designer to select and realize the topology best suited for a particular application.
" }, { "name": "McChesney, Jon Mearns", "degree": "PhD", "year": "1989", "title": "Observations of Stochastic Ion Heating by Low Frequency Drift Waves", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092007-143250", "creators": [ { "name": { "family": "McChesney", "given": "Jon Mearns" }, "id": "McChesney-Jon-Mearns", "display_name": "McChesney, Jon Mearns" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/vyaq-ye14", "abstract": "Several laser induced fluorescence (LIF) experiments were performed on the Encore tokamak device. These experiments represent the first application of this technique to the majority ions of a tokamak. The main laser system selected consisted of a copper vapor laser (CVL), which pumped a narrowband, tunable dye laser. This system allowed the Doppler-broadened, ion distribution function to be scanned with high resolution, giving accurate ion temperature measurements. As a preliminary test, the diagnostic was used to observe ion heating in the presence of lower hybrid RF power. Ion temperatures were found to increase dramatically with increasing RF power.
\r\n\r\nBy using a second dye laser, actual ion trajectories were determined using the technique of \"optical tagging.\" Tagging involves the use of a so-called \"pump\" laser to alter the fraction of ions in a particular quantum state. As a preliminary test, this technique was used to demonstrate ion gyro-motion in Encore.
\r\n\r\nUsing the ion distribution functions determined by means of LIF, it was possible to make detailed measurements of ion heating during an ohmically heated tokamak discharge. It was found that the observed rate of ion heating was nearly two orders of magnitude faster than expected from collisional energy exchange with the hot electrons. The high ion temperatures inferred from the LIF measurements were later verified by measuring the Landau damping of ion acoustic waves. The observed damping lengths were roughly in accord with those calculated using measured values of Te and Ti.
\r\n\r\nThis enhanced ion heating was correlated with the presence of large amplitude, low frequency (\u03c9 < \u03c9ci), drift-Alfv\u00e9n waves. Using numerical calculations, it was shown that in the presence of electrostatic modes (such as drift waves) of sufficient amplitude, ion motion becomes stochastic or chaotic. In physical terms, stochasticity occurs when the ion displacement that is due to the polarization drift becomes comparable to the perpendicular wavelength, i.e., when \u03b1 = mik2\u22a5\u03c60/qB20 ~ 1. A combination of numerical calculations and experiments was used to demonstrate that stochasticity was indeed responsible for the observed rapid heating.
\r\n\r\nFinally, we concluded by speculating that stochastic heating may also be the cause of the anomalously high ion temperatures observed in reversed field pinches (RFP's) and in field reversed configurations (FRC's). Intrinsic stochasticity is also important in the field of auxiliary plasma heating. As is now well known, a large amplitude RF electric field can heat particles despite a large mismatch between the wave frequency and the gyrofrequency.
" }, { "name": "Miles, Richard Henry", "degree": "PhD", "year": "1989", "title": "Structural and Optical Properties of Strained-Layer Superlattices", "advisor": "McGill, Thomas C.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082007-093744", "creators": [ { "name": { "family": "Miles", "given": "Richard Henry" }, "id": "Miles-Richard-Henry", "display_name": "Miles, Richard Henry" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Chan", "given": "Sunney I." }, "id": "Chan-S-I", "orcid": "0000-0002-5348-2723", "role": "member", "display_name": "Chan, Sunney I." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/042y-d234", "abstract": "This thesis describes investigations into the optical and structural properties of strained-layer superlattices. The purpose of the work was twofold: to establish the merits of strained-layer structures in applications, particularly to optoelectronics; and to examine structural characteristics of superlattices in which the lattice-mismatch between adjacent layers is large. Optical properties of CdTe/ZnTe superlattices have been examined through photoluminescence experiments. Observed band gaps have been compared with those expected from calculations of electronic band structure, including effects that are due to strain. Band gaps of a variety of II-VI superlattices have been calculated based on the agreement between theory and experiment in the CdTe/ZnTe system. The accommodation of lattice mismatch has been investigated for CdTe/ZnTe and Ge0.5Si0.5/Si superlattices. The assumptions behind traditional single-film critical thicknesses and their extensions to multilayer structures were of particular interest in these studies.
\r\n\r\nIn Chapter 2 we use photoluminescence experiments to examine the optical properties of CdTe/ZnTe superlattices grown on a variety of CdxZn1-xTe buffer layers. The work was motivated by interest in wide-band-gap II-VI's as possible visible light emitters and detectors and, more generally, by interest in the effects of strain and dislocations on the optical properties of strained-layer superlattices. Photoluminescence from the superlattices is observed to be several orders of magnitude more intense than from a Cd0.37Zn0.63Te alloy. Spectra are dominated by Gaussian distributions of excitonic lines. The 20-30meV widths of these distributions show that superlattice layer thicknesses were controlled to approximately one monolayer. Identifying the superlattice band gaps as the high-energy edges of the observed excitonic luminescence yields sample energy gaps substantially lower than expected for alloys. Observed gaps are in excellent agreement with those calculated from a \u2192k \u2022 \u2192p model, assuming strain appropriate to a free-standing structure. This configuration is one in which dislocations at the superlattice/buffer-layer interface have redistributed strain within an otherwise dislocation-free superlattice in manner that minimizes the elastic strain energy within the structure. The free-standing configuration is argued to be plausible in view of calculated critical thicknesses and strain relaxation rates. Calculations of the effects of a free-standing strain on the electronic band structure of CdTe/ZnTe superlattices show that strain can substantially reduce band gaps (on the order of 100meV for a 6% mismatch), and causes transitions from type-I to type-II band alignments. Attempts to observe laser oscillation in these CdTe/ZnTe superlattice structures have proven unsuccessful to date, although Cd0.25Zn0.75Te/ZnTe structures have recently been reported to lase.
\r\n\r\nChapter 3 describes a structural study of the CdTe/ZnTe superlattices examined in Chapter 2. Strain fields and dislocation densities are inferred from x-ray diffraction, in situ reflection high-energy electron diffraction (RHEED), and transmission electron microscopy (TEM). All of our samples are observed to exceed the critical thickness for the nucleation of misfit-accommodating dislocations. Although each of the structures appears to be highly defective, the free-standing limit appears to be plausible, as defect densities drop substantially within a micron of the superlattice/buffer-layer interface, regardless of the buffer layer used. Although several samples substantially exceed predicted critical thicknesses, the sample that shows the smallest degree of residual strain lies below limits derived from a previous empirical study. This result demonstrates that dislocation formation in superlattices is not appropriately characterized by applying traditional critical thickness models to an alloy of equivalent total thickness and average composition. Variations in strain fields appear to be correlated with sample growth conditions. As growth parameters are neglected in traditional energy-balancing models of critical thickness, it is argued that activation barriers associated with the nucleation or glide of dislocations can substantially inhibit the relaxation of strain beyond the equilibrium limits.
\r\n\r\nIn Chapter 4 we demonstrate that the accommodation of lattice mismatch in Ge0.5Si0.5/Si superlattices is highly dependent on the conditions under which a sample is grown. Dislocation densities of 1.5 x 105cm-1 drop to levels undetectable by TEM (< 105cm-2) as the growth temperature of compositionally identical superlattices is lowered from 530\u00b0C to 365\u00b0C. Thus, by lowering growth temperatures, it is possible to freeze a structure in a highly strained metastable state well beyond the critical thickness limits calculated by equilibrium theories. There appears to be a large kinetic barrier blocking dislocation nucleation or glide; the effect we observe cannot be explained by mismatched thermal expansion coefficients alone. These results are contrary to initial studies of GexSi1-x alloys, which appear to display critical thicknesses relatively independent of temperature over the ranges described here. Recognizing that defect creation can be inhibited in severely mismatched superlattices should be important in growing heavily strained films of high quality.
\r\n\r\nFinally, the Appendix contains maps of band gap as a function of layer thicknesses for a variety of II-VI superlattice systems, calculated using the Bastard model described in Chapter 2. Agreement with experiment is good for the CdTe/ZnTe superlattices examined here. As mentioned in Chapter 1, comparison of these calculated gaps with those measured experimentally leads to a prediction of \u0394Ev = 1.0 \u00b1 0.1eV for the ZnSe/ZnTe valence band offset.
" }, { "name": "Mittelstein, Michael", "degree": "PhD", "year": "1989", "title": "Theory and Experiments on Unstable-Resonator and Quantum Well GaAs/GaAlAs Lasers", "advisor": "Yariv, Amnon; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082007-125156", "creators": [ { "name": { "family": "Mittelstein", "given": "Michael" }, "id": "Mittelstein-Michael", "display_name": "Mittelstein, Michael" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/p3k2-pp58", "abstract": "Structures of GaAs/GaA1As lasers and their performance characteristics are investigated experimentally and theoretically. A self-consistent model for the longitudinal gain and intensity distribution in injection lasers is introduced. The model is applied to unstable-resonator semiconductor lasers to evaluate their lateral losses and quantum efficiencies, and an advanced design is presented. Symmetric, unstable-resonator semiconductor lasers are manufactured and a virtual source point inside the laser more than an order of magnitude narrower than the width of the near field is demonstrated. Young's double-slit experiment is adopted for lateral coherence measurements in semiconductor lasers. A high degree of lateral coherence is found, indicating operation of the unstable-resonator lasers in predominantly one mode.
\r\n\r\nIn the pulsed measurements on broad-area, single-quantum-well, graded-index wave-guide, separate-confinement-heterostructure lasers, very high quantum efficiencies, very low losses, and very high output powers are observed. The devices are found to exhibit beam divergence narrower than two times the diffraction limit in single-lobed, far-field patterns. Using these single-quantum-well lasers, the \"second quantized-state lasing\" is found experimentally, and a simple model is developed to explain it.
\r\n\r\nA general model for the gain spectrum and required current density of quantum-well lasers is introduced. The eigenfunctions and eigenvalues of the charge carriers and optical mode of the transverse structure are used to derive the gain spectrum and current density from the Einstein coefficients. The two-dimensional density of states for the charge carriers and the effective width of the optical mode (not the width of the quantum well) are identified as the dominant parameters. The model includes a new heuristic approach to account for the observed smeared onset of subbands, eliminating convolution calculations.
\r\n\r\nApplications of the model for a typical structure, a conventional double heterostructure and an advanced structure are presented. Structures providing two- and three-dimensional confinement are discussed and are directly compared to conventional and quantum-well structures in terms of laser parameters. The length scale of confinement structures for the optical mode is found to be two orders of magnitude larger than the corresponding length scale for carrier confinement, implying that the single-quantum-well laser is the most adapted structure.
\r\n\r\nThe gain-flattened condition that single-quantum-well lasers exhibit near the onset of the second quantized-state lasing is introduced. An external grating-tuned resonator is analyzed, and the coupled cavity formalism is employed to examine conditions for continuous tuning. Predictions for tuning ranges of conventional, double-heterostructure and single-quantum-well lasers are made, and the superiority of the latter on account of pump current density is clarified. Experimentally, broadband tunability exceeding a 10% spectral tuning range of an uncoated quantum-well laser in a simple grating-tuned resonator is demonstrated.
" }, { "name": "Mok, Fai Ho", "degree": "PhD", "year": "1989", "title": "Binary Correlators for Optical Computing and Pattern Recognition", "advisor": "Psaltis, Demetri; Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082007-130728", "creators": [ { "name": { "family": "Mok", "given": "Fai Ho" }, "id": "Mok-Fai-Ho", "display_name": "Mok, Fai Ho" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "co-advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" } ], "option_major": [ "eleceng" ], "doi": "10.7907/dwpt-gn93", "abstract": "The matrix-vector multiplier is an important building block in optical information processing architectures, examples of which are correlators for pattern recognition, associative memories, and neural networks. Such architectures are most suitable for implementation by optics due to the ease in realizing dense interconnections optically. The success of the implementation partially relies on the quality of the SLM used to record the information for processing. Limited dynamic range for the representation of the data recorded is a common drawback suffered by most commercially available devices. In this thesis, the importance of the dynamic range of the device on the performance of the implementation is investigated. The effect of limited dynamic range on the signal to noise ratio, probability of error, capacity, and training of various forms of matrix-vector multipliers are addressed. Through the use of theoretical analyses, computer simulations, and optical experiments, it will be shown that a large dynamic range is not essential in most applications. Specifically, it is shown that only one bit of dynamic range, i.e. two gray levels, for the representation of each data point, results in acceptable loss in performance.
" }, { "name": "Munger, James William", "degree": "PhD", "year": "1989", "title": "The Chemical Composition of Fogs and Clouds in Southern California", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02132007-152409", "creators": [ { "name": { "family": "Munger", "given": "James William" }, "id": "Munger-James-William", "display_name": "Munger, James William" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "orcid": "0000-0002-4263-2562", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/YFER-M388", "abstract": "Fogs and clouds are frequent occurrences in Southern California. Their chemical composition is of interest due to their potential role in the transformation of sulfur and nitrogen oxides to sulfuric and nitric acid and in the subsequent deposition of those acids. In addition, cloud and fog droplets may be involved in the chemistry of low-molecular-weight carboxylic acids and carbonyl compounds.
\r\n\r\nThe major inorganic species in cloud and fogwater samples were NH\u2084\u207a, H\u207a, NO\u2083\u207b, and SO\u2084\u00b2\u207b. Concentrations in fogwater samples were 1-10 x 10\u207b\u00b3 M; pH values ranged from \u22432 to 6. Nitrate usually exceeded sulfate. Acidity depended on the availability of NH\u2083 from agricultural operations. Stratus cloudwater had somewhat lower concentrations; pH values were in the range 3 - 4. The major factors accounting for variation in fog- or cloudwater composition were the preexisting aerosol and gas concentrations and variations in liquid water content. Deposition and entrainment or advection of different air masses were also important during extended cloud or fog episodes.
\r\n\r\nThe droplet size dependence of cloudwater composition was investigated on one occasion in an intercepted coastal stratus clouds. The observations were consistent with the hypothesis that small droplets form on small secondary aerosol composed of H\u2082SO\u2084, HNO\u2083 and their NH\u2084\u207a salts, while large droplets form on large sea-salt and soil-dust aerosol. Species that can exist in the gas phase, such as HCl and HNO\u2083, may be found in either droplet-size fraction.
\r\n\r\nConcentrations of S(IV) and CH\u2082O in the range 100 - 1000 \u00b5M were observed in fogwater from urban sites in Southern California. Lower concentrations were observed in stratus clouds. The high levels of S(IV) and CH\u2082O were attributed to the formation of hydroxymethanesulfonate (HMSA), the S(IV) adduct of CH\u2082O. Direct measurement of HMSA in fogwater samples from Bakersfield, CA were made by ion-pairing chromatography. Glyoxal and methyiglyoxal were observed at concentrations comparable to CH\u2082O in fogwater samples from Riverside, CA and in stratus cloudwater samples from sites along the Santa Barbara Channel.
" }, { "name": "Nazaroff, William W.", "degree": "PhD", "year": "1989", "title": "Mathematical Modeling and Control of Pollutant Dynamics in Indoor Air", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092007-144249", "creators": [ { "name": { "family": "Nazaroff", "given": "William W." }, "id": "Nazaroff-William-W", "display_name": "Nazaroff, William W." } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/89WP-N863", "abstract": "To assess the total human-health and material-damage risks associated with air-pollutant exposure, the concentrations and fates of pollutants in indoor atmospheres must be understood. Three observations reinforce this point: (1) concentrations of many pollutants are commonly higher in indoor air than in outdoor air, (2) in many countries, people spend more time indoors than outside; and (3) many of the most precious material possessions of society are kept indoors. In this thesis, mathematical models are developed as tools to improve the understanding of pollutant dynamics in indoor air. These tools are applied to the problem of protecting works of art from damage due to air pollutant exposure, particularly for the purpose of understanding how to control soiling due to airborne particle deposition.
\r\n\r\nA deterministic mathematical model first is formulated to describe the time-dependent concentrations of chemically reactive gases and airborne particles in indoor air, then implemented as a computer program. Using a flexible, multichamber description of a building, the model accounts for the effects of ventilation, filtration, deposition onto surfaces, and direct emission for all pollutants. In addition, the influence of homogeneous photolytic and thermal chemical reactions is computed for gases that are present in the photochemical smog system. The model is capable of determining the chemical composition and size distribution of indoor aerosols, accounting for the effect of coagulation in addition to the processes itemized above. The model computes the fate of pollutants in indoor air, determining the absolute strengths of the sources and sinks for each species.
\r\n\r\nTo permit the simulation of soiling problems, modeling calculations for the deposition of particles and other pollutants onto surfaces are particularly detailed. Equations that predict the rate of pollutant deposition onto indoor surfaces are developed, accounting for the effects of advection, diffusion, and, for particles, gravitational settling and thermophoresis. Three air flow regimes are analyzed: natural convection induced by a temperature difference between the surface and the nearby air, forced laminar flow parallel to a surface, and homogeneous turbulence in the core of the room. The analysis of a vertical isothermal flat plate in natural convection flow shows that, for this flow regime, thermophoresis is an important particle transport process within the boundary layer adjacent to the surface, effectively repelling particles larger than approximately 0.1 \u00b5m in diameter if the surface is even a few degrees K warmer than the nearby air.
\r\n\r\nTo test model performance, and to investigate the dynamic behavior of indoor pollutants, the model is applied to several indoor air quality problems. In one case, modeling predictions are made of pollutant concentrations in a museum gallery in Southern California into which photochemical smog is introduced by the ventilation system. Good agreement is obtained between measured and modeled concentrations of NO, NO\u2082 and O\u2083. The model predicts substantial production of several species, including HNO\u2082, HNO\u2083, NO\u2083, and N\u2082O\u2085, due to chemical reaction within the museum atmosphere. The aerosol mechanics aspects are tested by applying the model to the problem of predicting the evolution of the aerosol size distribution following combustion of a cigarette in a single room having a low air-exchange rate, and good agreement is found between model predictions and measured values.
\r\n\r\nThe completed indoor air quality model next is used to evaluate the soiling hazard to art objects in museums resulting from the deposition of particles containing elemental carbon (soot) or soil dust. Time-resolved measurements of the indoor and outdoor aerosol size distribution in three Southern California museums are reported. Model predictions of indoor aerosol characteristics based on measured outdoor aerosol characteristics and data on building dynamics agree well with measurements. The predictions also show that generally less than 1% of the fine particles (0.05-2 \u00b5m in diameter) entering the museums deposit onto the walls. Nevertheless, deposition calculations indicate that, at the rates determined for the study days, elemental carbon (soot) particles would accumulate on vertical surfaces in the museums at a rate sufficient to yield perceptible soiling in characteristic times of 1-40 years, depending on the museum studied. These are very short periods, considering that many art objects are to be preserved indefinitely.
\r\n\r\nTo test the accuracy of the particle deposition calculations, model predictions are made of the annual mean deposition velocity of particles onto the walls of five Southern California museums, using the results of short-term monitoring of near-wall air velocities and long-term monitoring of surface-air temperature differences. The predictions are compared against the results of measurements in these museums of the deposition velocities of sulfates and of fine particles. The modeling and measurement results generally concur, revealing that the deposition velocities for a given particle size vary by a factor of as much as 30 among the sites studied, with the lowest values associated with laminar forced flow adjacent to the building walls, and highest values found in museums where deposition is driven by turbulence in the core of the room.
\r\n\r\nMethods for reducing the soiling rate of objects displayed in museums are identified and include the following: (1) reducing the rate of supply of outdoor air into the building; (2) increasing the effectiveness of particle filtration; (3) altering the air flow conditions within the building to reduce the particle deposition velocity onto surfaces of concern; (4) placing objects within display cases or framing objects behind glass; (5) managing the building site to achieve low outdoor concentrations; and (6) eliminating indoor particle sources. The mathematical model of indoor aerosol dynamics is combined with experimental data collected at an historic museum in Southern California to determine the potential effectiveness of these control measures. According to model results, with careful design of control measures the soiling rate can be reduced by at least two orders of magnitude, thereby extending to periods of a century or more the time before noticeable soiling will occur.
" }, { "name": "Ngai, John Yee-Keung", "degree": "PhD", "year": "1989", "title": "A Framework for Adaptive Routing in Multicomputer Networks", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02132007-153533", "creators": [ { "name": { "family": "Ngai", "given": "John Yee-Keung" }, "id": "Ngai-John-Yee-Keung", "display_name": "Ngai, John Yee-Keung" } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "chair", "display_name": "Seitz, Charles L." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" } ], "option_major": [ "compsci" ], "doi": "10.7907/a01h-0z81", "abstract": "Message-passing concurrent computers, also known as multicomputers, such as the Caltech Cosmic Cube [47] and its commercial descendents, consist of many computing nodes that interact with each other by sending and receiving messages over communication channels between the nodes. The communication networks of the second-generation machines, such as the Symult Series 2010 and the Intel iPSC2 [2], employ an oblivious wormhole-routing technique that guarantees deadlock freedom. The network performance of this highly evolved oblivious technique has reached a limit of being capable of delivering, under random traffic, a stable maximum sustained throughput of \u2248 45 to 50% of the limit set by the network bisection bandwidth, while maintaining acceptable network latency. This thesis examines the possibility of performing adaptive routing as an approach to further improving upon the performance and reliability of these networks. In an adaptive multipath routing scheme, message trajectories are no longer deterministic, but are continuously perturbed by local message loading. Message packets will tend to follow their shortest-distance routes to destinations in normal traffic loading, but can be detoured to longer but less-loaded routes as local congestion occurs.
\r\n\r\nA simple adaptive cut-through packet-switching framework is described, and a number of fundamental issues concerning the theoretical feasibility of the adaptive approach are studied. Freedom of communication deadlock is achieved by following a coherent channel protocol and by applying voluntary misrouting as needed. Packet deliveries are assured by resolving channel-access conflicts according to a priority assignment. Fairness of network access is assured either by sending round-trip packets or by having each node follow a local injection-synchronization protocol.
\r\n\r\nThe performance behavior of the proposed adaptive cut-through framework is studied with stochastic modeling and analysis, as well as through extensive simulation experiments for the 2D and 3D rectilinear networks. Theoretical bounds on various average network-performance metrics are derived for these rectilinear networks. These bounds provide a standard frame of reference for interpreting the performance results.
\r\n\r\nIn addition to the potential gain in network performance, the adaptive approach offers the potential for exploiting the inherent path redundancy found in richly connected networks in order to perform fault-tolerant routing. Two convexity-related notions are introduced to characterize the conditions under which our adaptive routing formulation is adequate to provide fault-tolerant routing, with minimal change in routing hardware. The effectiveness of these notions is studied through extensive simulations. The 2D octagonal-mesh network is suggested; this displays excellent fault-tolerant potential under the adaptive routing framework. Both performance and reliability behaviors of the octagonal mesh are studied in detail.
\r\n\r\nA number of implementation issues are examined. Encoding schemes for packet headers that admit simple incremental updates while providing all necessary routing information in the first flit of a relatively narrow flit width are developed. A pipelined control structure that allows a packet to cut through an intermediate node with a minimum delay of two cycles is described. A distributed clocking scheme is developed that eliminates the problem of global clock-signal distribution. Under this clocking scheme, the adaptive routers can be tessellated to form a network of arbitrary size.
\r\n\r\n[2] W.C. Athas and C.L. Seitz., \"Multicomputers: Message-Passing Concurrent Computers,\" IEEE Computer, August 1988, pp. 9-24.
\r\n\r\n[47] C.L. Seitz, \"The Cosmic Cube,\" CACM, Vol. 28, No. 1, January 1985, pp. 22-33.
" }, { "name": "Nguyen, Truong Quang", "degree": "PhD", "year": "1989", "title": "Design and Implementation of Linear-Phase and/or Pairwise-Symmetric Perfect-Reconstruction FIR Multirate Filter Banks", "advisor": "Vaidyanathan, P. P.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-091115", "creators": [ { "name": { "family": "Nguyen", "given": "Truong Quang" }, "id": "Nguyen-Truong-Quang", "display_name": "Nguyen, Truong Quang" } ], "advisors": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "advisor", "display_name": "Vaidyanathan, P. P." } ], "committee": [ { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "chair", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Swanson", "given": "Larry W." }, "id": "Swanson-L-W", "role": "member", "display_name": "Swanson, Larry W." } ], "option_major": [ "eleceng" ], "doi": "10.7907/8z2n-y592", "abstract": "This thesis studies the structures, design procedures and implementations of FIR perfect-reconstruction digital filter banks. The first part of the thesis deals with the structures and the design procedures of the perfect-reconstruction filter banks where the polyphase transfer matrices are lossless. These structures are parameterized by a set of rotation angles [37]. The usual procedure is to blindly optimize these angles to minimize an objective function where the objective function consists of all the stopband energies of the filters which we would like to design. This procedure is very time-consuming because of the nonlinear objective function and the large number of parameters to be optimized. The pairwise-symmetry property is imposed on these perfect reconstruction systems as a means of decreasing the number of parameters (rotation angles). The pairwise-symmetric property together with a method to initialize these rotation angles gives a very efficient design procedure. Design examples and complexity of the pairwise-symmetric, perfect-reconstruction FIR filter banks have compared well with the approximate perfect-reconstruction systems.
\r\n\r\nThe second part of the thesis studies the structures and the design procedures of perfect-reconstruction filter banks which yield linear-phase filters. By confining the problem to a class, we are able to count exactly the number of linear-phase, perfect-reconstruction filter banks in this class. For the two-channel filter banks, we have obtained structures and design procedures for all nontrivial systems. Comparison with the approximated perfect-reconstruction systems in terms of complexity and performance is made. In our subclass of linear-phase, perfect-reconstruction, there are three structures for the case of three-channel filter banks. By limiting the problem to one of these systems, we obtain structures which yield linear-phase, perfect-reconstruct ion filters. The implementation complexity is studied. Design examples for all new methods presented here are included, along with tabulation of lattice and filter coefficients.
\r\n\r\n[37] Z. Doganata, P. P. Vaidyanathan, and T. Q. Nguyen, \"General Synthesis procedures for FIR lossless transfer matrices for perfect-reconstruction multirate filter bank applications,\" IEEE Trans. on Acoustics, Speech and Signal Processing, Vol. ASSP-36, 1561-1574, Oct. 1988.
" }, { "name": "Nowak, Paul Scott", "degree": "PhD", "year": "1989", "title": "Effect of Nonuniform Seismic Input on Arch Dams", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042013-091930444", "creators": [ { "name": { "family": "Nowak", "given": "Paul Scott" }, "id": "Nowak-Paul-Scott", "display_name": "Nowak, Paul Scott" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/zbd0-ty45", "abstract": "Standard earthquake analyses of civil engineering structures use uniform ground motions even though considerable variations in both amplitude and phase can occur along the foundation interface for long-span bridges and large dams. The objective of this thesis is to quantify the effect that these nonuniformities have on the structural response.
\r\n\r\nThe nonuniform, free-field motions of the foundation interface are assumed to be caused by incident plane body waves. The medium in which these waves travel is a linear, elastic half-space containing a canyon of uniform cross section in which the structure is placed. The solutions for the free-field motions that are due to incident SH, P and SV waves are calculated using the boundary element method.
\r\n\r\nAn analysis of Pacoima (arch) dam located near Los Angeles, California, is performed for both uniform and nonuniform excitations. The important effect of nonuniformities in the free-field motions, sometimes leading to a decrease in the dam response and sometimes to an increase, is quantified.
" }, { "name": "Platt, John Carlton", "degree": "PhD", "year": "1989", "title": "Constraint Methods for Neural Networks and Computer Graphics", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122007-152609", "creators": [ { "name": { "family": "Platt", "given": "John Carlton" }, "id": "Platt-John-Carlton", "display_name": "Platt, John Carlton" } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "compsci" ], "doi": "10.7907/vnt8-kh55", "abstract": "Both computer graphics and neural networks are related, in that they model natural phenomena. Physically-based models are used by computer graphics researchers to create realistic, natural animation, and neural models are used by neural network researchers to create new algorithms or new circuits. To exploit successfully these graphical and neural models, engineers want models that fulfill designer-specified goals. These goals are converted into mathematical constraints.
\r\n\r\nThis thesis presents constraint methods for computer graphics and neural networks. The mathematical constraint methods modify the differential equations that govern the neural or physically based models. The constraint methods gradually enforce the constraints exactly. This thesis also describes applications of constrained models to real problems.
\r\n\r\nThe first half of this thesis discusses constrained neural networks. The desired models and goals are often converted into constrained optimization problems. These optimization problems are solved using first-order differential equations. There are a series of constraint methods which are applicable to optimization using differential equations: the Penalty Method adds extra terms to the optimization function which penalize violations of constraints, the Differential Multiplier Method adds subsidiary differential equations which estimate Lagrange multipliers to fulfill the constraints gradually and exactly, Rate-Controlled Constraints compute extra terms for the differential equation that force the system to fulfill the constraints exponentially. The applications of constrained neural networks include the creation of constrained circuits, error-correcting codes, symmetric edge detection for computer vision, and heuristics for the traveling salesman problem.
\r\n\r\nThe second half of this thesis discusses constrained computer graphics models. In computer graphics, the desired models and goals become constrained mechanical systems, which are typically simulated with second-order differential equations. The Penalty Method adds springs to the mechanical system to penalize violations of the constraints. Rate-Controlled Constraints add forces and impulses to the mechanical system to fulfill the constraints with critically damped motion. Constrained computer graphics models can be used to make deformable physically-based models follow the directives of a animator.
" }, { "name": "Rasi, Marco", "degree": "PhD", "year": "1989", "title": "Mixing in Density-Stratified Conjugate Flows", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechETD:etd-02152007-155510", "creators": [ { "name": { "family": "Rasi", "given": "Marco" }, "id": "Rasi-Marco", "display_name": "Rasi, Marco" } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "chair", "display_name": "List, E. John" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "civileng" ], "doi": "10.7907/2s6d-kv47", "abstract": "Two-layer stratified shear flows have been studied in the laboratory using combined laser-induced fluorescence and laser-Doppler velocimetry. Use of this high resolution, non-intrusive instrumentation has enabled new insight on the entraining characteristics of supercritical two-layer flows and the phenomenon known as an internal hydraulic jump.
\r\n\r\nIn the experiments, salt water was discharged at a steady flowrate from a rectangular slot located at the bottom of the upstream end of a horizontal channel containing fresh water. The flow of the dense bottom layer was controlled at the downstream end of the channel by either a free overfall or a broad-crested weir. The transition between the wall-jet-like flow near the source and the subcritical downstream counterflow took place through an internal hydraulic jump, characterized by a steep interfacial slope and a local recirculating flow region.
\r\n\r\nA one-dimensional theory based on the assumptions of uniformity of velocity and density distributions downstream of the mixing region was discussed and extended to predict the overall internal flow geometry and the dilution attained by the source fluid across the mixing region. The analysis, which applies to the general case of a mixing channel of finite depth and length, was carried out in three stages. First, the flow at the upstream end of the channel was considered, and a conservation of flow force in the total channel depth across the jump was hypothesized. Second, the gradually-varied counterflow, governed by boundary shear and interfacial momentum transfer, as well as by the critical flow condition at the channel end, was studied by applying the momentum principle to both layers. Finally, the upstream and downstream equations were combined to obtain hydraulic solutions, in a way that clearly establishes that the overall problem can only be solved if the importance of the interplay between source and control is recognized.
\r\n\r\nAn extensive series of experiments confirmed the general predictions of the one-dimensional theory. Four predicted mixing modes (free internal hydraulic jump, flooded jump, upstream-controlled instability, and downstream-controlled instability) were all observed in the experiments. The dependence of the entrainment rate, both on the depth of the ambient water and on the control establishing the critical flow at the end of the channel, has been documented with comprehensive experimental data.
\r\n \r\nThe non-intrusive laser-based instrumentation used has enabled a detailed experimental description of the density and velocity distributions at several locations in the flow field and has pointed out some inaccuracies in the one-dimensional approach. A procedure to overcome these inaccuracies has been proposed.
\r\n\r\nThe ideas developed and the experimental results obtained from this work can be readily extended to further the understanding of many of the two-layer stratified shear flows of interest to engineers and geophysicists.
" }, { "name": "Rom-Kedar, Vered", "degree": "PhD", "year": "1989", "title": "Part I. An Analytical Study of Transport, Mixing and Chaos in an Unsteady Vortical Flow. Part II. Transport in Two Dimensional Maps", "advisor": "Wiggins, Stephen R.; Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03152006-114909", "creators": [ { "name": { "family": "Rom-Kedar", "given": "Vered" }, "id": "Rom-Kedar-Vered", "display_name": "Rom-Kedar, Vered" } ], "advisors": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "advisor", "display_name": "Wiggins, Stephen R." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "co-advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "chair", "display_name": "Wiggins, Stephen R." }, { "name": { "family": "Leal", "given": "L. Gary" }, "id": "Leal-L-G", "role": "member", "display_name": "Leal, L. Gary" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "appmath" ], "doi": "10.7907/EH82-GA67", "abstract": "PART I:
\r\n\r\nWe examine the transport properties of a particular two dimensional, inviscid incompressible flow using dynamical systems techniques. The velocity field is time periodic and consists of the velocity field induced by a vortex pair plus an oscillating strain-rate field. In the absence of the strain-rate field the vortex pair moves with a constant velocity and carries with it a constant body of fluid. When the strain-rate field is added the picture changes dramatically; fluid is entrained and detrained from the neighborhood of the vortices and chaotic particle motion occurs. We investigate the mechanism for this phenomena and study the transport and mixing of fluid in this flow. Our work consists of both numerical and analytical studies. The analytical study includes the interpretation of the invariant manifolds as the underlying structure which govern the transport. Then we use Melnikov's technique to investigate the behavior of the manifolds as the parameters of the problem change and to prove the existence of a horseshoe map and thus the existence of chaotic particle paths in the flows. Using the Melnikov technique once more we develop an analytical estimate of the flux rate into and out of the vortex neighborhood. We develop a technique for determining the residence time distribution for fluid particles near the vortices. The technique involves an understanding of the geometry of the tangling of the stable and unstable manifolds and results in a dramatic reduction in computational effort for the residence time distributions. Additionally, we develop a finite time analog of the Liapunov exponent which measures the effect of, the horseshoes on trajectories passing through the mixing region. The numerical work verifies the analytical predictions regarding the structure of the invariant manifolds, the mechanism for entrainment and detrainment, and the flux rate.
\r\n\r\nPART II:
\r\n\r\nWe study transport in the two dimensional phase space of Cr diffeomorphisms (r \u2265 1) of two manifolds between regions of the phase space bounded by pieces of the stable and unstable manifolds of hyperbolic fixed points. The mechanism for the transport is associated with the dynamics of homoclinic and heteroclinic tangles and the study of this dynamics leads to a general formulation for the transport rates in terms of distributions of small regions in phase space (\"lobes\"). It is shown how the method applies to three geometrical configurations, one of which corresponds to the geometry associated with the Kelvin-Stuart Cat's eye flow undergoing a time periodic perturbation. In this case the formulae imply, for example, that the evolution of only two lobes determines the mass transport from the upper to the lower half plane of the fluid flow. As opposed to previous studies this formulation takes into account the effect of re-entrainment of the lobes, i.e. the implications of the lobes leaving and re-entering the specified regions on the transport rates. The formulation is developed for both area preserving and non area preserving two dimensional diffeomorphisms and does not require the map to be near integrable. The techniques involved in applying this formulation are discussed including the possible use of the generating function for computing the distributions of the lobes in phase space, and the use of Poincar\u00e9 maps which enables one to study the transport in continuous time systems via the above formalism. In particular, we demonstrate how the right choice of the Poincar\u00e9 section can reduce the calculations of the transport rates.
" }, { "name": "Rosakis, Phoebus", "degree": "PhD", "year": "1989", "title": "Ellipticity and Deformations with Discontinous Gradients in Finite Elastostatics", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122007-094508", "creators": [ { "name": { "family": "Rosakis", "given": "Phoebus" }, "id": "Rosakis-Phoebus", "display_name": "Rosakis, Phoebus" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Rice", "given": "James R." }, "id": "Rice-James-R", "role": "member", "display_name": "Rice, James R." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/jn2t-m109", "abstract": "Loss of ellipticity of the equilibrium equations of finite elastostatics is closely related to the possible emergence of elastostatic shocks, i.e., deformations with discontinuous gradients. In certain situations where constitutive response functions are essentially one-dimentional, such as anti-plane shear or bar theories, strong ellipticity is closely related to convexity of the elastic potential and invertibility of certain constitutive response functions.
\r\n\r\nThe present work addresses the analogous issues within the context of three dimensional elastostatics of compressible but not necessarily isotropic hyperelastic materials. A certain direction-dependent resolution of the deformation gradient is introduced and its existence and uniqueness for a given direction are established. The elastic potential is expressed as a function of kinematic variables arising from this resolution. Strong ellipticity is shown to be equivalent to the positive definiteness of the Hessian matrix of this function, thus sufficing for its strict convexity. The underlying variables are interpretable physically as simple shears and extensions. Their work-conjugates define a traction response mapping. It is shown that discontinuous deformation gradients are sustainable if and only if this mapping fails to be invertible. This result is explicit, in the sense that it characterizes the set of all possible piecewise homogeneous deformations given the elastic potential function.
" }, { "name": "Rotenberry, James Michael", "degree": "PhD", "year": "1989", "title": "Effect of Compliant Boundaries on Weakly Nonlinear Shear Waves in Channel Flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02152007-075746", "creators": [ { "name": { "family": "Rotenberry", "given": "James Michael" }, "id": "Rotenberry-James-Michael", "display_name": "Rotenberry, James Michael" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "appmath" ], "doi": "10.7907/gva0-r175", "abstract": "There exists a critical Reynolds number (at which a linear instability first appears for an incompressible fluid flowing in a channel with compliant walls (Hains and Price, [1962]). It is proven that, for fixed non-dimensionalized wall parameters, to any unstable disturbance in three dimensions there corresponds an unstable disturbance in two dimensions at a lower Reynolds number. Consequently, the Ginzburg-Landau equation is used to study the weakly nonlinear two-dimensional evolution of a disturbance in a channel with compliant walls for Reynolds number near its critical value. The coefficients of this equation are found by numerically integrating solutions of the Orr-Sommerfeld equation and its adjoint as well as solutions of the perturbation equations.
\r\n\r\nFor rigid walls the finite amplitude two-dimensional plane wave solution that bifurcates from laminar Poiseuille flow at the critical Reynolds number is itself unstable to two-dimensional disturbances. It is found that for compliant walls this solution is stable to disturbances of the same type.
\r\n\r\nThe formalism developed by Landman [1987] is used to study a class of quasisteady solutions to the Ginzburg-Landau equation. This class includes solutions describing a transition from the laminar solution to finite amplitude states and nonperiodic, \"chaotic\" attracting sets. It is shown that for compliant walls the transition solutions persist while the \"chaotic\" ones do not.
" }, { "name": "Schalit, Mark Alan", "degree": "PhD", "year": "1989", "title": "Oscillating-Field Current-Drive Schemes for Tokamaks", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02132007-141701", "creators": [ { "name": { "family": "Schalit", "given": "Mark Alan" }, "id": "Schalit-Mark-Alan", "display_name": "Schalit, Mark Alan" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Cowan", "given": "Eugene W." }, "id": "Cowan-E-W", "role": "member", "display_name": "Cowan, Eugene W." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/xjrw-pq56", "abstract": "A novel current-drive scheme for steady-state tokamak operation is investigated in which external coils are applied to induce time-periodic fluid-type, fluctuations within the plasma; a nonlinear interaction between these fluctuations results in a time-averaged EMF, which maintains the large-scale magnetic field against Ohmic dissipation. Analytical and numerical modeling of this current-drive scheme is presented for low-frequency schemes (where the nonlinear < u⃗ x b⃗ > EMF is dominant) and for higher-frequency schemes (where the < j⃗ x b⃗ > Hall EMF is dominant). The Hall EMF is dominant at frequencies well above the ion-cyclotron frequency (referred to the strength of the static axial field) - except in the case of the rotamak, where the oscillating electric field is in the same direction as the static axial field.
\r\n\r\nA figure-of-merit for these current-drive schemes is the ratio of the strength of the static axial current to the strength of the oscillating current. This ratio is always much less than unity in all standard MHD calculations. As the electronion collision frequency vanishes, the ratio approaches infinity for the case of the rotamak. The ratio also approaches infinity for the m = 1 analogue of the rotamak - but only in the restrictive case where the static axial field becomes vanishingly small and where the DC magnetic fields are a small fraction of the AC magnetic fields. For the m = 1 analogue, the currents are confined to a skin layer as the axial field becomes very large, with the ratio of DC current strength to the oscillating current strength approaching unity.
\r\n\r\nThe analysis presented here is compared and contrasted with existing theories and to a number of recent experiments.
" }, { "name": "Schneider, Steven Philip", "degree": "PhD", "year": "1989", "title": "Effects of Controlled Three-Dimensional Perturbations on Boundary Layer Transition", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-02142007-094214", "creators": [ { "name": { "family": "Schneider", "given": "Steven Philip" }, "id": "Schneider-Steven-Philip", "display_name": "Schneider, Steven Philip" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZJ0M-GG83", "abstract": "The laminar-turbulent transition in a flat plate boundary layer was studied experimentally using a spanwise array of computer-controlled surface heating elements. The elements were used to introduce disturbances at a point just downstream of the critical Reynolds number. When sinusoidal heating at an unstable frequency is carried out, instability waves develop and grow as they travel downstream. Measurements were made using flush-mounted hot-film wall shear sensors, and the later stages of transition were visualized using dye injection. Oblique Tollmien-Schlichting waves were successfully introduced, and their downstream development into the turbulent regime was studied. Exploratory studies of other types of 3D forcing are also reported.
\r\n\r\nMeasurements of oblique waves in the linear region yielded phase speeds and wave angles that were consistent with the linear theory. Subharmonics of the oblique-wave wall shear were seen downstream, in the nonlinear region. Surprisingly, the amplitude of these subharmonic waves decreased abruptly with increasing oblique-wave angle, so that an oblique wave of about 10 degrees had a subharmonic amplitude which was an order of magnitude below that for a 2D wave. Waves of larger oblique angles did not produce detectable subharmonics. A simple explanation of this behavior is given, in terms of the wave-interaction theory.
\r\n\r\nThe intermittency, defined as the fraction of time in which the wall shear is turbulent, was measured to determine the relative location of transition. These measurements, carried out further downstream, show that the introduction of a 2D wave is most effective in moving the transition point upstream, for a given power input. This upstream movement of transition slowly decreases as the oblique wave angle is increased. The fact that there is no abrupt movement of transition corresponding to the abrupt disappearance of the subharmonic nonlinear breakdown mechanism suggests there should be a simpler explanation for the nonlinear breakdown.
" }, { "name": "Soibelman, Israel", "degree": "PhD", "year": "1989", "title": "A Study of Finite Amplitude Bifurcations in Plane Poiseuille Flow", "advisor": "Meiron, Daniel I.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02142007-080941", "creators": [ { "name": { "family": "Soibelman", "given": "Israel" }, "id": "Soibelman-Israel", "display_name": "Soibelman, Israel" } ], "advisors": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "advisor", "display_name": "Meiron, Daniel I." } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appmath" ], "doi": "10.7907/2xg0-5q97", "abstract": "Plane Poiseuille flow is known to be linearly unstable at a Reynolds number of 5772.22 (Drazin and Reid, 1981). In experiments, however, transition to turbulent flow is seen to occur at a Reynolds number of 1000 (Nishioka and Asai, 1985). In an attempt at resolving this conflict, we search for 2D and 3D nonlinear bifurcations at low Reynolds number.
\r\n\r\nBecause we wish to study secondary bifurcations, we compute the 2D waves which bifurcate from plane Poiseuille flow. These waves were first computed by Zahn, et al., (1975), and the critical Reynolds number, based on constant pressure, was found to be approximately 2900. To find 2D bifurcations, we study the 2D superharmonic stability of the 2D waves. The stability picture is found to change when switching from a constant flux to constant average pressure gradient boundary condition. For both boundary conditions, we find several Hopf bifurcations on the upper branch of the 2D waves.
\r\n\r\nWe calculate the periodic orbits which emanate from these bifurcations and find that no branch extends below the critical 2D wave Reynolds number. We also confirm the results of Jimenez (1988) who detected one of the branches we calculate with a time dependent formulation.
\r\n\r\nTo find 3D bifurcations, we study the 3D stability of the 2D waves. Several branches of 3D waves are calculated. In particular, we study 3D bifurcations at a spanwise wave number of 2. No bifurcations are found to branches which extend to low Reynolds numbers. This result conflicts with those found by Rozhdestvensky and Simakin (1984) with a time dependent formulation.
\r\n\r\nIn addition, we study 3D oblique waves and 3D standing-travelling waves (standing in the streamwise direction) which bifurcate from plane Poiseuille flow. In particular, we study the bifurcation at spanwise wave numbers greater than .365. Contrary to Bridges' (1988) hypothesis, we find that no branches extend to low Reynolds numbers.
" }, { "name": "S\u00e1nchez Pe\u00f1a, Ricardo Salvador", "degree": "PhD", "year": "1989", "title": "Robust Analysis of Feedback Systems with Parametric and Dynamic Structured Uncertainty", "advisor": "Sideris, Athanasios; Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012005-084251", "creators": [ { "name": { "family": "S\u00e1nchez Pe\u00f1a", "given": "Ricardo Salvador" }, "id": "S\u00e1nchez-Pe\u00f1a-Ricardo-Salvador", "display_name": "S\u00e1nchez Pe\u00f1a, Ricardo Salvador" } ], "advisors": [ { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "advisor", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "co-advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "chair", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Lorentz", "given": "G. G." }, "id": "Lorentz-G-G", "role": "member", "display_name": "Lorentz, G. G." }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "role": "member", "display_name": "Morari, Manfred" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/MM2J-E556", "abstract": "This thesis presents the first general program implementation of the algorithm by deGaston and its generalization by Sideris and deGaston to compute the Multivariable stability margin or Structured singular value of a feedback system under real (independent or related) parametric uncertainty. An improved implementation of the algorithm mentioned above is also considered, which simplifies significantly the code and increases the computational speed. The latter also allows a simple and fast analysis by just checking the extreme values of the set of parameters, with a high probability of achieving the actual stability margin; this being supported by an intense statistical analysis performed at the end of this thesis.
\r\n\r\nA great deal of work has recently been done related to this class of uncertain systems initiated by the well known theorem of Kharitonov. A connection is made in Chapter 4 between these procedures and the above ones in terms of generality of the class of uncertain polynomials considered. A theorem characterizing the set of polynomials whose robust stability can be determined by a finite number of tests is addressed. Sufficient conditions to determine when the latter conditions apply are also given, which in some cases can considerably simplify the analysis. In particular cases, polynomials with related uncertain parameters can be treated in the same way as independent parameters as shown in two examples.
\r\n\r\nThe main part of this thesis is concerned with the analysis of more general type of uncertainties. In particular, the analysis of robust stability for the case when unstructured dynamic uncertainty is combined with real parametric uncertainty is treated in Chapter 5. This can also be applied in the analysis of robust performance for plants with parametric uncertainty. Chapter 6 generalizes the latter to the most general case in which structured dynamic and real parametric uncertainty appear simultaneously in the plant. A computational scheme is given in both cases which uses the algorithm mentioned in the first part and is applied to several examples.
\r\n\r\nAt the end, an example of the robust analysis of an experimental aircraft demonstrates how a practical situation can be handled by this procedure.
" }, { "name": "Ting, Francis Chi Kin", "degree": "PhD", "year": "1989", "title": "Interaction of Water Waves with a Density-Stratified Fluid in a Rectangular Trench", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-02152007-151955", "creators": [ { "name": { "family": "Ting", "given": "Francis Chi Kin" }, "id": "Ting-Francis-Chi-Kin", "display_name": "Ting, Francis Chi Kin" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "chair", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "civileng" ], "doi": "10.7907/8bgx-4e53", "abstract": "The interaction of normally incident time-periodic water waves with a density-stratified fluid in a rectangular trench is studied experimentally and theoretically; the fluid outside the trench is homogeneous.
\r\n\r\nThis investigation has focused on the excitation of internal waves in the trench by surface waves, and the effects of the internal oscillations on the waves on the free surface. The study shows that, when the frequency of the incoming surface waves corresponds to the natural frequency of oscillation of the internal waves in the trench, the amplitude of the internal waves becomes large compared to the amplitude of the surface waves. The effects of the internal waves on the surface waves were very small in the experiments.
\r\n\r\nA two-layer model and a three-layer model are developed and applied to a particular constant-depth channel and trench configuration used in the experiments. The two-layer model is also applied to a rectangular trench in an infinite region. These models treat steady-state wave motions of infinitesimal amplitude for all ranges of fluid depth relative to the wavelength of the surface waves, and include a vigorous treatment of the effects of energy dissipation in the laminar boundary layers adjacent to the solid surfaces and at the density interface. In the two-layer model the stratified fluid in the trench is represented by two homogeneous fluids of different densities; in the three-layer model these two fluids are separated in between by a transition region of linear density variation.
\r\n\r\nFresh water and salt water were used to model density stratification in the experiments. The effects of surface wave amplitude and density distribution on the internal motion in the trench were investigated for small density differences compared to the density of water. A new technique using a scanning laser beam and detector system was developed to measure internal wave amplitudes. Satisfactory agreement with the theoretical predictions was obtained. The effects of nonlinearity and viscous dissipation on the internal motions were more pronounced when the depth of the heavier fluid was small compared to the wavelength of the internal waves in the trench.
\r\n\r\nFor a trench in an infinite region, the two-layer model also predicts that large surface wave reflections occur when the trench is \"at internal resonance,\" and a significant portion of the incident wave energy can be dissipated within the trench.
\r\n\r\nThe investigation has provided insight with regard to both the dynamics of wave-trench interaction and the design of navigation channels in density-stratified fluids for reducing the potential of wave-induced internal resonance.
" }, { "name": "Tomita, Yasuo", "degree": "PhD", "year": "1989", "title": "Modal Dispersal of Information and Wave Mixing in Photorefractive Crystals for Information Retrieval, Processing and Sensing", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-02152007-083930", "creators": [ { "name": { "family": "Tomita", "given": "Yasuo" }, "id": "Tomita-Yasuo", "display_name": "Tomita, Yasuo" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Whaling", "given": "Ward" }, "id": "Whaling-W", "role": "member", "display_name": "Whaling, Ward" } ], "option_major": [ "eleceng" ], "doi": "10.7907/vjga-q464", "abstract": "This thesis describes an experimental and theoretical study on modal dispersal of information and wave mixing in photorefractive crystals for vector phase conjugation and real-time information processing. Photorefractive crystals with short drift lengths (BaTiO\u2083 and Ba\u2081\u208b\u2093Sr\u2093Nb\u2082O\u2086) and long drift ones (Bi\u2081\u2082SiO\u2082\u2080 and semi-insulating GaAs) are particularly used in this thesis.
\r\n\r\nIn the first part, the photorefractive effect in electrooptic crystals is described in terms of Kukhtarev's band transport model. The explicit solution of the space-charge electric field for the case of one photorefractive species and one type of charge carrier is extended to the case of two photorefractive species and two types of charge carriers. The enhancement of the space-charge electric field is also described. In particular an approximate solution to Stepanov and Petrov's enhancement method of using AC external electric field is extended to a general case that describes the transient behavior for AC external electric field of arbitrary waveform. The anisotropic refractive index change due to the space-charge field formation is then described in terms of tensorial forms of the nonlinear susceptibility.
\r\n\r\nIn the second part, anisotropic beam coupling in photorefractive crystals is presented and a general set of coupled-wave equations that describes beam coupling in amplitude, phase, and polarization is derived by using the nonlinear and tensorial susceptibility. The polarization properties of the interacting waves are particularly stressed. Two limiting cases, i.e., one for scalar beam coupling and the other for cross-polarization beam coupling, are obtained from the general expression and solved. Experimental results of beam coupling in semi-insulating GaAs are presented, and the signs of dominant charge carriers and the density of photorefractive species are estimated from beam-coupling gain. The enhancement of beam-coupling gain and its temperature dependence are also discussed.
\r\n\r\nIn the third part, four-wave mixing for scalar and vector phase conjugation is described. Self-pumped phase-conjugate mirrors using photorefractive crystals are presented and one of the most interesting properties of these mirrors, i.e., the response to phase changes of inputs, is emphasized both theoretically and experimentally.
\r\n\r\nIn the fourth part, two-wave and four-wave mixing in photorefractive crystals are applied to moving object detection, mathematical operation on images, and one-way image transmission through phase-distorting media. In these applications, polarization properties of interacting waves are particularly utilized.
\r\n\r\nIn the fifth part, a novel method of vector phase conjugation by modal dispersal and scalar phase conjugation is discussed. The propagation characteristics of conjugate waves in strongly scattering media (e.g., mode-scrambling multimode fibers) are described theoretically, followed by the experimental demonstration of vector phase conjugation. In the theory the unitarity and time-reversal symmetry of the scattering matrix are incorporated into the analysis of the coherency matrix of the conjugate field. This theory which describes the physical process of the generation of vector phase conjugation can successfully explain the experimental results of its fidelity.
\r\n\r\nIn the last part, we describe experiments in which the new concept of modal dispersal of information and scalar phase conjugation is used for several novel applications that include nonreciprocal polarization-distortion correction, amplitude-distortion correction, and phase-conjugate multimode fiber-optic sensors. Experiments as well as proposals for these applications are presented.
" }, { "name": "Von Herzen, Brian", "degree": "PhD", "year": "1989", "title": "Applications of Surface Networks to Sampling Problems in Computer Graphics", "advisor": "Barr, Alan H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03132007-083552", "creators": [ { "name": { "family": "Von Herzen", "given": "Brian" }, "id": "Von-Herzen-Brian", "display_name": "Von Herzen, Brian" } ], "advisors": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "advisor", "display_name": "Barr, Alan H." } ], "committee": [ { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "chair", "display_name": "Barr, Alan H." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Burdick", "given": "Joel Wakeman" }, "id": "Burdick-J-W", "orcid": "0000-0002-3091-540X", "role": "member", "display_name": "Burdick, Joel Wakeman" } ], "option_major": [ "compsci" ], "doi": "10.7907/K9AS-GN82", "abstract": "This thesis develops the theory, algorithms and data structures for adaptive sampling of parametric functions, which can represent the shapes and motions of physical objects. For the first time, ensured methods are derived for determining collisions and other interactions for a broad class of parametric functions. A new data structure, called a surface network, is developed for the collision algorithm and for other sampling problems in computer graphics. A surface network organizes a set of parametric samples into a hierarchy. Surface networks are shown to be good for rendering images, for approximating surfaces, and for modeling physical environments. The basic notion of a surface network is generalized to higher-dimensional problems such as collision detection. We may think of a two-dimensional network covering a three-dimensional solid, or an n-dimensional network embedded in a higher-dimensional space. Surface networks are applied to the problems of adaptive sampling of static parametric surfaces, to adaptive sampling of time-dependent parametric surfaces, and to a variety of applications in computer graphics, robotics, and aviation.
\r\n\r\nFirst we develop the theory for adaptive sampling of static surfaces. We explore bounding volumes that enclose static surfaces, subdivision mechanisms that adjust the sampling density, and subdivision criteria that determine where samples should be placed.
\r\n\r\nA new method is developed for creating bounding ellipsoids of parametric surfaces using a Lipschitz condition to place bounds on the derivatives of parametric functions. The bounding volumes are arranged in a hierarchy based on the hierarchy of the surface network. The method ensures that the bounding volume hierarchy contains the parametric surface completely. The bounding volumes are useful for computing surface intersections. They are potentially useful for ray tracing of parametric surfaces.
\r\n\r\nWe develop and examine a variety of subdivision mechanisms to control the sampling process for parametric functions. Some of the methods are shown to improve the robustness of adaptive sampling. Algorithms for one mechanism, using bintrees of right parametric triangles, are particularly simple and robust.
\r\n\r\nA set of empirical subdivision criteria determine where to sample a surface, when we have no additional information about the surface. Parametric samples are concentrated in regions of high curvature, and along intersection boundaries.
\r\n\r\nOnce the foundations of adaptive sampling for static surfaces are described, we examine time-dependent surfaces. Based on results with the empirical subdivision criteria for static surfaces, we derive ensured criteria for collision determination. We develop a new set of rectangular bounding volumes, apply a standard k-dimensional subdivision mechanism called k-d trees, and develop criteria for ensuring that we detect collisions between parametric surfaces.
\r\n\r\nWe produce rectangular bounding boxes using a \"Jacobian\"-style matrix of Lipschitz conditions on the parametric function. The rectangular method produces even tighter bounds on the surface than the ellipsoidal method, and is effective for computing collisions between parametric surfaces.
\r\n\r\nA new collision determination technique is developed that can detect collisions of parametric functions, based on surface network hierarchies. The technique guarantees that the first collision is found, to within the temporal accuracy of the computation, for surfaces with bounded parametric derivatives. Alternatively, it is possible to guarantee that no collisions occur for the same class of surfaces. When a collision is found, the technique reports the location and parameters of the collision as well as the time of first collision.
\r\n\r\nFinally, we examine several applications of the sampling methods. Surface networks are applied to the problem of converting a two-dimensional image, or texture map, into a set of triangles that tile the plane. Many polygon-rendering systems do not provide the capability of rendering surfaces with textures. The technique converts textures to triangles that can be rendered directly by a polygon system. In addition, potential applications of the collision determination techniques are discussed, including robotics and air-traffic control problems.
" }, { "name": "Williams, Wyman Lee", "degree": "PhD", "year": "1989", "title": "Computer-Aided Measurement of Microwave Circuits", "advisor": "Rutledge, David B.; Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-02162007-080706", "creators": [ { "name": { "family": "Williams", "given": "Wyman Lee" }, "id": "Williams-Wyman-Lee", "display_name": "Williams, Wyman Lee" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "co-advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/65XX-PQ66", "abstract": "Instruments that measure the scattering parameters of microwave circuits generally have large systematic errors due to unavoidable parasitics in the instruments. These errors can be modeled analytically, however, and removed through a calibration procedure. A personal computer is well suited to the performance of the required calculations. Combining a personal computer with a microwave network analyzer results in a flexible and accurate automatic instrument. Two such automatic network analyzers are presented here. A new type of network analyzer, known as a sampled-line network analyzer is presented. It is an extension of the six-port network analyzer concept developed at the National Bureau of Standards. It is a particularly simple implementation and shows promise for the construction of relatively low-cost microwave network analyzers. The sampled-line network analyzer is analyzed theoretically and several experimental versions of it are presented. Another personal computer-controlled network analyzer is presented in which a Pascal program automates an HP 8410 network analyzer. The result is an instrument which can measure S-parameters from 0.5 to 18 GHz with a measurement error vector ranging in magnitude from 0.01 in the low frequency range to about 0.03 at 18 GHz.
" }, { "name": "Winckelmans, Gr\u00e9goire St\u00e9phane", "degree": "PhD", "year": "1989", "title": "Topics in Vortex Methods for the Computation of Three- and Two-Dimensional Incompressible Unsteady Flows", "advisor": "Leonard, Anthony", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-112216", "creators": [ { "name": { "family": "Winckelmans", "given": "Gr\u00e9goire St\u00e9phane" }, "id": "Winckelmans-Gr\u00e9goire-St\u00e9phane", "display_name": "Winckelmans, Gr\u00e9goire St\u00e9phane" } ], "advisors": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "advisor", "display_name": "Leonard, Anthony" } ], "committee": [ { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "chair", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/19HD-DF80", "abstract": "Contributions to vortex methods for the computation of incompressible unsteady flows are presented. Three methods are investigated, both theoretically and numerically.
\r\n\r\nThe first method to be considered is the inviscid method of vortex filaments in three dimensions, and the following topics are presented: (a) review of the method of regularized vortex filaments and of convergence results for multiple-filament computations, (b) modeling of a vortex tube by a single filament convected with the regularized Biot-Savart velocity applied on the centerline: velocity of the thin filament vortex ring and dispersion relation of the rectilinear filament, and (c) development of a new regularization of the Biot-Savart law that reproduces the lowest mode dispersion relation of the rectilinear vortex tube in the range of large to medium wavelengths.
\r\n\r\nNext the method of vortex particles in three dimensions is investigated, and the following contributions are discussed: (a) review of the method of singular vortex particles: investigation of different evolution equations for the particle strength vector and weak solutions of the vorticity equation, (b) review of the method of regularized vortex particles and of convergence results, and introduction of a new algebraic smoothing with convergence properties as good as those of Gaussian smoothing, (c) development of a new viscous method in which viscous diffusion is taken into account by a scheme that redistributes the particle strength vectors, and application of the method to the computation of the fusion of two vortex rings at Re = 400, and (d) investigation of the particle method with respect to the conservation laws and derivation of new expressions for the evaluation of the quadratic diagnostics: energy, helicity and enstrophy.
\r\n\r\nThe third method considered is the method of contour dynamics in two dimensions. The particular efforts presented are (a) review of the classical inviscid method and development of a new regularized version of the method, (b) development of a new vector particle version of the method, both singular and regularized: the method of particles of vorticity gradient, (c) development of a viscous version of the method of regularized particles and application of the method to computation of the reconnection of two vortex patches of same sign vorticity, and (d) investigation of the particle method with respect to the conservation laws and derivation of new expressions for the evaluation of linear and quadratic diagnostics.
" }, { "name": "Anlage, Steven Mark", "degree": "PhD", "year": "1988", "title": "Icosahedral Order in Metastable Metallic Alloys", "advisor": "Johnson, William Lewis; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272010-145542274", "creators": [ { "name": { "family": "Anlage", "given": "Steven Mark" }, "id": "Anlage-Steven-Mark", "display_name": "Anlage, Steven Mark" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/mjqp-qr45", "abstract": "We examine the consequences of short-range icosahedral order in metastable metallic alloys. There is evidence, both direct and indirect, for the existence of atomic clustering with icosahedral symmetry in supercooled liquid metals, metastable metallic alloys, and large-unit-cell intermetallic compounds. It is observed that a variety of metallic alloys can exhibit a long-range ordered structure with icosahedral point group symmetry upon rapid quenching from the liquid. We have carefully examined one of these icosahedral phase-forming systems in an effort to understand how the long-range ordered solid develops from the liquid phase. Our studies show that the icosahedral phase nucleates homogeneously from the liquid during the rapid quenching process.
\r\n\r\nWe have developed a theory to explain qualitatively this observation. A model material is proposed, which is endowed with short-range icosahedral order broken up by defect structures. The thermodynamics of this model are described by a Ginzburg-Landau theory. The model displays a strong first-order phase transition from a high-temperature, heavily defected phase to a low-temperature phase with enhanced short-range icosahedral order. This transition is compared to our observations of icosahedral phase formation to fix the values of the theoretical parameters.
\r\n" }, { "name": "Arndt, Norbert Karl Erhard", "degree": "PhD", "year": "1988", "title": "Experimental Investigation of Rotor-Stator Interaction in Diffuser Pumps", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-110354", "creators": [ { "name": { "family": "Arndt", "given": "Norbert Karl Erhard" }, "id": "Arndt-Norbert-Karl-Erhard", "display_name": "Arndt, Norbert Karl Erhard" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/MR43-SR51", "abstract": "The interaction between impeller blades and diffuser vanes in diffuser pumps was investigated. Steady and unsteady pressure measurements were made on the diffuser vanes and on the front shroud wall of a vaned and a vaneless diffuser. Two different impellers were used, one half of the impeller of the double suction pump of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine), and a two-dimensional impeller. The measurements were made for different flow coefficients, shaft speeds, and radial gaps between the impeller blades and the diffuser vanes (1.5% and 4.5% of the impeller discharge radius for the impeller of the HPOTP, and 5% and 8% for the two-dimensional impeller). The vane pressure fluctuations were larger on the vane suction than on the vane pressure side attaining their maximum value, of the same order of magnitude as the total pressure rise across the pump, near the leading edge. The resulting lift on the vane, both steady and unsteady, was computed from the pressure measurements at mid vane height. The magnitude of the fluctuating lift was found to be larger than the steady lift. For the impeller of the HPOTP, pressure measurements on the front shroud of a vaned and a vaneless diffuser showed that the front shroud pressure fluctuations increased with the presence of the diffuser vanes.
\r\n\r\nFor the two-dimensional impeller, also unsteady impeller blade pressure measurements were made. The largest blade pressure fluctuations, of the same magnitude as the large pressure fluctuations on the vane suction side, occurred at the blade trailing edge. However, the dependence of those pressure fluctuations on the flow coefficient was found to be different; on the vane suction side, the fluctuations were largest for maximum flow and decreased with decreasing flow coefficient, whereas at the blade trailing edge, the fluctuations were smallest for maximum flow and increased with decreasing flow coefficient. Increasing the vane number resulted in a significant decrease of the blade pressure fluctuations.
\r\n\r\nLift, vane and blade pressure, and front shroud pressure fluctuations decreased strongly with increasing radial gap.
\r\n" }, { "name": "Avila-Segura, Francisco E.", "degree": "PhD", "year": "1988", "title": "The Creeping Motion of Immiscible Drops Through a Converging/Diverging Tube: I. Non-Newtonian Effects of Viscoelastic Drops. II. Effects of Constant Pressure Gradient Condition for the Flow. III. Motion of Drops Through a Parallel Channel", "advisor": "Leal, L. Gary", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312007-093206", "creators": [ { "name": { "family": "Avila-Segura", "given": "Francisco E." }, "id": "Avila-Segura-Francisco-E", "display_name": "Avila-Segura, Francisco E." } ], "advisors": [ { "name": { "family": "Leal", "given": "L. Gary" }, "id": "Leal-L-G", "role": "advisor", "display_name": "Leal, L. Gary" } ], "committee": [ { "name": { "family": "Leal", "given": "L. Gary" }, "id": "Leal-L-G", "role": "chair", "display_name": "Leal, L. Gary" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "mecheng" ], "doi": "10.7907/1944-bp37", "abstract": "Experimental results are presented for the motion of neutrally buoyant drops of non-Newtonian fluid through a wavy wall tube within a Newtonian suspending fluid. The motion of these drops exhibits very different behavior with respect to both Newtonian drop-Newtonian suspending fluid system and Newtonian drop-viscoelastic suspending fluid system. In particular, drop breakup behavior is strongly modified. At small flow rates (small capillary numbers) viscoelastic drops undergo drop breakup. At large flow rates (large capillary numbers) breakup phenomena do not occur and axial drop elongation is inhibited. For the cases in which drop breakup occurs, it produces important effects on the time-dependent response of the extra pressure drop and on the drop mobility. For high polymer concentration (1%) in the viscoelastic drop, the resulting elastic effects are overshadowed by the increase in viscosity which accompanies the addition of polymer.
\r\n\r\nThe effects of flow type on the dynamics of the drop motion in a wavy wall tube are investigated. According to the nature of the driving mechanism there are two types of flow, each one of them presenting different properties (though identical for non-drop conditions). One flow is susceptible to changes in flow resistance that may appear in the experimental setup, the other is such that the volumetric flow rate is constant. The former is generated by imposing a constant pressure gradient (CPG conditions), the latter is generated by a gear pump (CFR conditions). Drop deformation in a CPG experiment is less severe than it is in a CFR experiment. Also, under CPG conditions, the axial elongation and the mobility of a moving drop are independent of the viscosity ratio, whereas under CFR conditions they depend on it. In addition, the magnitude of the extra pressure drop caused by the passage of the drop through the test section is smaller under CPG conditions than it is under CFR conditions.
\r\n\r\nFinally, a more realistic simulation of flow dynamics in porous media is considered. For this purpose, a parallel channel device was tested under constant pressure gradient conditions. Measurements were taken in both arms of this device for the extra pressure drop caused by the passage of drops through one of the channels (a wavy wall tube). The ratio of the mean value of such measurements is nearly constant regardless of the value of the total volumetric flow, drop size or viscosity ratio. Obviously, the pressure drop measured in the bypass tube is a tangible indication of the increase (or decrease) in the volumetric flow through it, due to the motion of the drop through the other arm of the experimental apparatus.
\r\n" }, { "name": "Bell, Mark Robert", "degree": "PhD", "year": "1988", "title": "Information Theory and Radar: Mutual Information and the Design and Analysis of Radar Waveforms and Systems", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06272005-152700", "creators": [ { "name": { "family": "Bell", "given": "Mark Robert" }, "id": "Bell-Mark-Robert", "display_name": "Bell, Mark Robert" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "eleceng" ], "doi": "10.7907/AYD5-RB83", "abstract": "This thesis examines the use of information theory in the analysis and design of radar, with a particular emphasis on the information-theoretic design of radar waveforms. First, a brief review of information theory is presented and then the applicability of mutual information to the measurement of radar performance is examined. The idea of the radar target channel is introduced. The Radar/Information Theory Problem is formulated and solved for a number of radar target channels, providing insight into the problem of designing radar waveforms that maximize the mutual information between the target and the received radar signal. Radar-scattering models are examined in order to obtain usable models for practical waveform design problems. The target impulse response is introduced as a method of characterizing the spatial range distribution of radar targets. The target impulse response is used to formulate a new generalization of the matched filter in radar that matches a transmitted-waveform/receiver-filter pair to a target of known impulse response, providing the maximum signal-to-noise ratio at the receiver under a constraint on transmitted energy and the time duration of the waveform. Next, the problem is formulated and solved of designing radar waveforms that maximize the mutual information between the target and the received radar waveform for a target characterized by an impulse response that is a finite-energy random process. The characteristics of waveforms for optimum detection and for obtaining maximum information about a target are compared. Finally, the information content of radar images is examined. It is concluded that the information-theoretic viewpoint can improve the performance of practical radar systems.
\r\n" }, { "name": "Cox, Robert William", "degree": "PhD", "year": "1988", "title": "A Model for Stress-Driven Diffusion in Polymers", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01232013-124105465", "creators": [ { "name": { "family": "Cox", "given": "Robert William" }, "id": "Cox-Robert-William", "orcid": "0000-0002-0031-1568", "display_name": "Cox, Robert William" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "chair", "display_name": "Cohen, Donald S." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "appmath" ], "doi": "10.7907/06tx-qh63", "abstract": "Penetration of solvents into polymers is sometimes characterized by steep concentration gradients that move into the polymer and last for long times. The behavior of these fronts cannot be explained by standard diffusion equations, even with concentration dependent diffusion coefficients. The addition of stress terms to the diffusive flux can produce such progressive fronts. Model equations are proposed that include solvent flux due to stress gradients in addition to the Fickian flux. The stress in turn obeys an concentration dependent evolution equation.
\r\n\r\nThe model equations are analyzed in the limit of small diffusivity for the problem of penetration into a semi-infinite medium. Provided that the coefficient functions obey certain monotonicity conditions, the solvent concentration profile is shown to have a steep front that progresses into the medium. A formula governing the progression of the front is developed. After the front decays away, the long time behavior of the solution is shown to be a similarity solution. Two techniques for approximating the solvent concentration and the front position are presented. The first approximation method is a series expansion; formulas are given for the initial speed and deceleration of the front. The second approximation method uses a portion of the long time similarity solution to represent the short time solution behind the front.
\r\n\r\nThe addition of a convective term to the solvent flux is shown to raise the possibility of a traveling wave solution. The existence of the traveling wave solution is shown for certain types of coefficient functions. The way the initial front speed evolves onto the traveling wave speed is sketched out.
\r\n" }, { "name": "Crouch, David Dale", "degree": "PhD", "year": "1988", "title": "A Theoretical Study of the Generation of Squeezed-State Light via Degenerate Parametric Amplification", "advisor": "Caves, Carlton M.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-11022007-131309", "creators": [ { "name": { "family": "Crouch", "given": "David Dale" }, "id": "Crouch-David-Dale", "display_name": "Crouch, David Dale" } ], "advisors": [ { "name": { "family": "Caves", "given": "Carlton M." }, "id": "Caves-C-M", "orcid": "0000-0001-8876-1186", "role": "advisor", "display_name": "Caves, Carlton M." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Thorne", "given": "Kip S." }, "id": "Thorne-K-S", "orcid": "0000-0002-9475-4318", "role": "chair", "display_name": "Thorne, Kip S." }, { "name": { "family": "Caves", "given": "Carlton M." }, "id": "Caves-C-M", "orcid": "0000-0001-8876-1186", "role": "member", "display_name": "Caves, Carlton M." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/55jn-f921", "abstract": "This thesis is primarily a theoretical study of degenerate parametric amplification as a means of generating squeezed-state light.
\r\n\r\ni) A wideband traveling-wave formalism is developed for analyzing quantum mechanically a degenerate parametric amplifier. The formalism is based on spatial differential equations \u2014 spatial Langevin equations \u2014 that propagate temporal Fourier components of the field through the nonlinear medium. In addition to the parametric nonlinearity, the Langevin equations include absorption and associated fluctuations, dispersion, and pump quantum fluctuations. The dominant effects of dispersion and pump quantum fluctuations on the squeezing produced by a degenerate parametric amplifier are analyzed.
\r\n\r\nii) The wideband formalism of i) is used to carry out a more detailed analysis of the effects of phase mismatching. With the assumption of a lossless medium and a classical pump, we find that parametric amplification is capable of generating squeezed-state light over a wide band if materials with large \u03c7(2) nonlinearities can be found, and that the squeezing bandwidth can be enhanced by phase mismatching away from degeneracy.
\r\n\r\niii) We consider again the effect of pump quantum fluctuations on the squeezing produced by parametric amplification. We perform discrete-mode calculations for a parametric amplifier with a quantum pump, and discuss some of the limitations of calculations of this sort in quantum optics. We derive stochastic differential equations (SDEs) for one- and two-mode parametric amplifiers, and from them obtain an iterative solution showing that pump quantum fluctuations impose a limitation on the degree of squeezing obtainable from a parametric amplifier.
\r\n\r\niv) A possible application of squeezing is considered; in particular, we study the effects of squeezing the intracavity noise in a laser oscillator. We solve the classical noise problem of a realistic laser model by making a bold \u2014 and possibly unrealizable \u2014 assumption, that the in-phase and quadrature Langevin sources which are responsible for the \"noisiness\" of the laser can be squeezed. We show that the effect of squeezing the in-phase quadrature is to reduce the phase noise, including the linewidth, of the laser but, due to amplitude-phase coupling, not to eliminate them altogether.
\r\n" }, { "name": "Dowling, David Russell", "degree": "PhD", "year": "1988", "title": "Mixing in Gas Phase Turbulent Jets", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06132005-160404", "creators": [ { "name": { "family": "Dowling", "given": "David Russell" }, "id": "Dowling-David-Russell", "display_name": "Dowling, David Russell" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9233-5476", "abstract": "This work is an experimental investigation of the mixing of the nozzle fluid of a round, turbulent jet with the entrained reservoir fluid, using laser-Rayleigh scattering methods. The measurements, at Reynolds numbers of 5,000 and 16,000, cover the axial range from 20 to 90 jet exit diameters and resolve the full range of temporal and spatial concentration scales. The measured mean and rms values of the concentration, and the mean scalar dissipation rate, when estimated from the time derivative of concentration, are consistent with jet similarity laws. Concentration fluctuation power spectra are found to be self-similar along rays emanating from the virtual origin of the jet, and are consistent with the universal form of scalar spectra proposed by Gibson (1968 II). The probability density functions for the concentration, the time derivative of concentration, and the square of the time derivative of concentration, are compiled and are also found to be self-similar along rays. Features of the measured distributions and spectra are consistent with the existence of large-scale structures within the flow that span the local diameter of the jet's turbulent cone. On the centerline of the jet, the scaled probability density function of jet gas concentration is found to be almost independent of the Reynolds number while the local mixing rate in the inner part of jet is not. The usual assumptions concerning isotropy and correlation of derivatives are found to lead to erroneous results for the probablility density function of the scalar dissipation rate.
" }, { "name": "Dowling, Michael John", "degree": "PhD", "year": "1988", "title": "Nonlinear Seismic Analysis of Arch Dams", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06112008-155515", "creators": [ { "name": { "family": "Dowling", "given": "Michael John" }, "id": "Dowling-Michael-John", "display_name": "Dowling, Michael John" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." } ], "option_major": [ "civileng" ], "doi": "10.7907/DJ4P-9393", "abstract": "A nonlinear finite element procedure for arch dams is described in which the gradual opening and closing of vertical contraction joints and predetermined horizontal cracking planes are considered. A special joint element approximately represents the deformations due to plane sections not remaining plane at each open joint and allows a single shell element discretization in the thickness direction to be used for the dam. Compressive and sliding nonlinearities are not included. Finite element treatments are also used for the water, assumed incompressible, and for the foundation rock, assumed massless, with all degrees of freedom (dof) off the dam condensed out. For efficiency in the computations, the condensed water and foundation matrices are localized in a way which maintains good accuracy. The response of Pacoima Dam to the 1971 San Fernando ground motion recorded on a ridge over one abutment and scaled by two-thirds is computed first for water at the intermediate level that existed during the 1971 earthquake and then for full reservoir. In the first analysis, the dam exhibits pronounced opening and separation of the contraction joints, allowing violation of the no-slip assumption. The presence of a full reservoir greatly increases the dam response, enough to bring some of the assumptions of the analysis into question. Reducing the ground motion scale to 0.44 with full reservoir drops the response back to a reasonable level, but the contraction joint separations remain.
\r\n\r\n" }, { "name": "Dur\u00f3n, Ziyad Hassan", "degree": "PhD", "year": "1988", "title": "Experimental and Finite Element Studies of a Large Arch Dam", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03142013-082003398", "creators": [ { "name": { "family": "Dur\u00f3n", "given": "Ziyad Hassan" }, "id": "Dur\u00f3n-Ziyad-Hassan", "display_name": "Dur\u00f3n, Ziyad Hassan" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." } ], "option_major": [ "civileng" ], "doi": "10.7907/e0rt-g677", "abstract": "Forced vibration field tests and finite element studies have been conducted on Morrow Point (arch) Dam in order to investigate dynamic dam-water interaction and water compressibility. Design of the data acquisition system incorporates several special features to retrieve both amplitude and phase of the response in a low signal to noise environment. These features contributed to the success of the experimental program which, for the first time, produced field evidence of water compressibility; this effect seems to play a significant role only in the symmetric response of Morrow Point Dam in the frequency range examined. In the accompanying analysis, frequency response curves for measured accelerations and water pressures as well as their resonating shapes are compared to predictions from the current state-of-the-art finite element model for which water compressibility is both included and neglected. Calibration of the numerical model employs the antisymmetric response data since they are only slightly affected by water compressibility, and, after calibration, good agreement to the data is obtained whether or not water compressibility is included. In the effort to reproduce the symmetric response data, on which water compressibility has a significant influence, the calibrated model shows better correlation when water compressibility is included, but the agreement is still inadequate. Similar results occur using data obtained previously by others at a low water level. A successful isolation of the fundamental water resonance from the experimental data shows significantly different features from those of the numerical water model, indicating possible inaccuracy in the assumed geometry and/or boundary conditions for the reservoir. However, the investigation does suggest possible directions in which the numerical model can be improved.
" }, { "name": "Freeland, Stephen D.", "degree": "PhD", "year": "1988", "title": "I. A Unified Analysis of Converters with Resonant Switches. II. Input-Current Shaping for Single-Phase Ac-Dc Power Converters", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222006-130413", "creators": [ { "name": { "family": "Freeland", "given": "Stephen D." }, "id": "Freeland-Stephen-D", "display_name": "Freeland, Stephen D." } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "chair", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PVNN-X318", "abstract": "Part I:
\r\n\r\nQuasi-resonant converters are a family of single-switch resonant dc-dc converters featuring zero-current or zero-voltage switching. Recognition of the topological structure uniting these resonant converters--and the rectangular-wave (PWM) converters on which they are based--leads to general models of their dc and low-frequency ac behavior.
\r\n\r\nAn expression is derived that yields the dc conversion ratio of a quasi-resonant converter in terms of the well-known conversion ratio of the underlying PWM topology. A small-signal, low-frequency dynamic model is developed whose parameters also incorporate the PWM conversion ratio. The dc and ac models reveal that any quasi-resonant converter with a full-wave resonant switch has dc and low-frequency behavior identical to that of its PWM parent, with switching-frequency control replacing duty-ratio control. Converters with half-wave resonant switches behave more like PWM converters in discontinuous conduction mode or with current programming, exhibiting lossless damping in the small-signal model and output resistance at dc.
\r\n\r\nAlthough quasi-resonant converters come in an astounding variety of topologies, the dc (and to a large extent ac) behavior of these converters depends only on the underlying PWM topology and the class of resonant switch, and is unchanged by movement of the resonant reactances to various alternative positions.
\r\n\r\nPart 2:
\r\n\r\nThe distorted input-current waveforms of nonlinear electronic loads cause interference and lead to poor utilization of the utility power line, a situation that is rapidly becoming intolerable with the increased application of electronic loads. Input-current shaping, also known as power-factor improvement, addresses the problem of improving current waveforms drawn from the power line. This study is restricted to single-phase ac-dc power conversion systems.
\r\n\r\nCurrent-shaping circuits are shown to fall into just a few categories with common features and limitations. In addition to the more common buck- and boost-based current-shaping converters, a class of circuits with \"automatic\" current shaping is presented and analyzed. A set of rules is derived for determining whether a particular dc-dc converter topology is suitable for use as a current-shaping ac-dc converter, and the rules are used to judge the suitability of several resonant converter topologies for this application. A new, low-cost converter is suggested that combines input-current shaping, isolation, and fast output-voltage regulation.
\r\n\r\nInput-current shaping requires that a converter store significant energy, leading to unfortunate size and weight restrictions. Additional implications of stored energy are examined, along with several methods of reducing the energy storage. It is shown that the ability of a current-shaping converter to regulate its output voltage is severely restricted as a result of the energy requirement. The methods and implications of introducing isolation to a shaping ac-dc converter are also studied.
" }, { "name": "Fuhs, Susan Elizabeth", "degree": "PhD", "year": "1988", "title": "Studies of Inertial Deposition of Particles onto Heat Exchanger Elements", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012007-135053", "creators": [ { "name": { "family": "Fuhs", "given": "Susan Elizabeth" }, "id": "Fuhs-Susan-Elizabeth", "display_name": "Fuhs, Susan Elizabeth" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/jh2a-bh94", "abstract": "Although the magnitude of the fouling problem in heat transfer equipment is well recognized, few investigations have been conducted into the mechanisms that lead to such fouling. The work reported in this thesis has been designed to examine gas-side fouling mechanisms that involve the inertial impaction of small particles onto tubular heat exchanger surfaces.
\r\n\r\nAn aerosol processes wind tunnel has been constructed which facilitates quantitative studies of particle interactions with heat exchanger surfaces. Three sets of experiments were performed. First, single heat exchanger tubes were exposed to a cross-flow of particle laden air. Stainless steel tubes coated with a thin layer of grease to ensure that particle collisions resulted in capture were used to verify a numerical model for the inertial transport of ammonium fluorescein particles to the tube surface. Particle bounce has been quantified for the case of clean tubes and solid particles. Experimental results compared favorably with the results of a numerical simulation based on the concept of a critical incident particle velocity normal to the surface needed to induce the particle to bounce with enough energy to escape collection by the tube.
\r\n\r\nSecond, the transient deposition of particles onto single heat exchanger tubes in cross-flow was studied. It was found that a steady-state condition could be reached for cases in which particle bounce occurred. Finally, the deposition patterns for the aerosol particles as they passed through a tube bank were studied. The quantities of aerosol deposited on various tubes depended on tube surface condition, tube position within the tube bank, and the overall geometry of the bank.
\r\n\r\nConditions have been identified in which the aerosol deposits that lead to gas-side heat exchanger fouling can be kept to very low levels by deliberately selecting high fluid velocities that induce solid particles to bounce upon impact with the heat exchanger surfaces. Transient fouling experiments have identified conditions under which high fluid velocities can be used to achieve very low, steady-state particle accumulations on tubes in a cross-flow of solid particles. Using these findings, heat exchangers can be designed that will resist gas-side fouling.
\r\n" }, { "name": "Giezen, Jurgen Johannes", "degree": "PhD", "year": "1988", "title": "Plastic Buckling of Cylinders Under Biaxial Loading", "advisor": "Babcock, Charles D.; Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212007-083506", "creators": [ { "name": { "family": "Giezen", "given": "Jurgen Johannes" }, "id": "Giezen-Jurgen-Johannes", "display_name": "Giezen, Jurgen Johannes" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "co-advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Singer", "given": "Josef" }, "id": "Singer-J", "role": "member", "display_name": "Singer, Josef" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ycv3-kp17", "abstract": "An experimental investigation is carried out to study the effects of nonproportional loading in the plastic range on a buckling load. The discrepancy between experimental and theoretical results points to some principal shortcoming in the analysis. The problem has been simplified by applying axial tensile load and external press to simple cylindrical shell specimen and observing the buckling load for various nonproportional load-paths. Results are compared to numerical predictions (BOSOR5) using classical type plasticity models such as J\u2082 deformation and J\u2082 incremental theory. Significant discrepancy was found an attributed to inadequate modeling of the nonlinear material behavior. The effects of geometrical imperfections and large deflections were found to insignificant, thereby leading to an idea how much of the discrepancy between test and theory is due to a use of inadequate plastic model. The introduction of the Southwell plot into elastic shell buckling problem reduced the already minor effects of geometric imperfections.
\r\n\r\nThe Christoffersen-Hutchinson corner theory model was introduced into BOSAR5 in its simplest form as presented by Poh-Sang Lam. Results obtained with this model, which allows corners to form on an initially smooth yield surface, displayed better agreement with experimental data. However, increased computational time and problems related to abrupt changes in load-path at the corner are a major concern at this present time.
\r\n" }, { "name": "Green, Sheldon Isaiah", "degree": "PhD", "year": "1988", "title": "Tip Vortices - Single Phase and Cavitating Flow Phenomena", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-104625", "creators": [ { "name": { "family": "Green", "given": "Sheldon Isaiah" }, "id": "Green-Sheldon-Isaiah", "display_name": "Green, Sheldon Isaiah" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/23TX-JF33", "abstract": "Tip vortices occur wherever a lifting surface terminates in a fluid. An understanding of tip vortices is salient to the solution of many engineering problems, including lift induced drag tip inefficiency, the overturning of small planes flown into the tip wake of larger aircraft, and marine propellor tip cavitation.
\r\n\r\nThe tip vortex shed by several rectangular planform wings, fitted with three different tips, was studied in a water tunnel. Four techniques were employed to examine the tip vortex:
\r\n\r\n(i) Surface flow visualization to reveal the early stages of vortex rollup.
\r\n\r\n(ii) Double pulsed holography of buoyant, Lagrangian particle tracers for detailed tangential and axial velocity data around the vortex core. Holograms were also a source of instantaneous core structure information.
\r\n\r\n(iii) Single pulse holography of air bubbles, of uniform, measured, original size. The size of the bubbles is related to the instantaneous local static pressure. The bubbles are driven by the centripetal pressure gradient forces into the vortex core, providing a means of measuring the average and transient vortex core pressure non-intrusively.
\r\n\r\n(iv) Direct observation of vortex cavitation. These measurements are useful in their own right because of the considerable technological significance of tip vortex cavitation. In addition, many single phase tip flow characteristics have cavitating flow counterparts.
\r\n\r\nThe present study has shown that one chord downstream of the wing trailing edge virtually all the foil bound vorticity has rolled up into the trailing vortex. Armed with this knowledge one may a priori evaluate, in the near field, the tangential velocity distribution, the core axial velocity excess, and the core mean pressure. These predictions are in agreement with the experimental measurements. Three aspects of the core flow, first observed in the present study, remain analytically inexplicable:
\r\n\r\n(i) The trend towards a Reynolds number dependent, axial velocity deficit with downstream distance.
\r\n\r\n(ii) The unsteady core velocity, particularly immediately downstream of the foil.
\r\n\r\n(iii) The vortex kinking which is coincident with highly unsteady axial core flow.
\r\n\r\nAs a first approximation, cavitation inception occurs when the core pressure is reduced to the vapour pressure. The large measured fluctuating core pressure explains the occurrence of inception at core pressures somewhat above pv and the dependence of \u03c3i on the dissolved air content.
\r\n\r\nModifying the tip geometry profoundly affects the trailing vortex. Installation of a ring wing tip can reduce the inception index relative to that of a normal rounded tip foil by a factor of three. The reduction was caused primarily by the redistribution, in the Trefftz plane, of the shed vorticity about a line and circle. Fortuitously, this redistribution caused most of the wing bound vorticity to be shed from the ring, decreasing the tip effect lift loss over the foil body.
" }, { "name": "Hern\u00e1ndez Valencia, Enrique Jos\u00e9", "degree": "PhD", "year": "1988", "title": "Queues of Queues in Communication Networks", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-090157", "creators": [ { "name": { "family": "Hern\u00e1ndez Valencia", "given": "Enrique Jos\u00e9" }, "id": "Hern\u00e1ndez-Valencia-Enrique-Jos\u00e9", "display_name": "Hern\u00e1ndez Valencia, Enrique Jos\u00e9" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "chair", "display_name": "Posner, Edward C." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/wygw-0f83", "abstract": "The concept of a camp-on queueing system is related to the idea of having systems of multiple hierarchical queues. Customers requesting service at a service center are queued at one of different queueing stages based on the location of the customer's intended server within the service hierarchy. In many instances, customers in a camp-on model exhibit a dual function customer-server, giving rise to a system with queues of queues. For this model, we assume Poisson distributed arrivals with different classes of customers for each queueing level. The service completion process is regarded as exponentially distributed, a standard assumption for many communication systems.
\r\n\r\nHere we discuss a stationary model for such a Markovian camp-on system. Closed-form solutions are derived for various state occupancy distributions of interest (e.g., joint probability distribution of queue lengths, marginal distributions for subsystems, accumulated workload, etc.), in systems with finite and infinite storage capacity and two queueing levels. Most of these results are also extended to multilevel queueing systems. It is found that this camp-on model is stable whenever all the distinct queues, in isolation, behave as stable systems. The form of the joint probability distribution of queue lengths is not a product of the independent contributions from each subsystem, since it must also account for the relative position of the queues with respect to the initial service center, the root of the service hierarchy.
\r\n\r\nTwo particular applications are discussed in detail: 1) PBX-like communication services, and 2) broadcast delivery services. Performance statistics such as waiting time distributions, blocking probabilities and mean response time are derived. These results show that we do not pay too large a penalty for introducing two or more levels of queueing, and under very extreme conditions (heavy traffic) the delay in response increases only linearly with the number of queueing stages. Broadcast service strategies provide even better performance than conventional point-to-point service, though a broadcast medium is required.
\r\n" }, { "name": "Hong, Pui-Kwan Andrew", "degree": "PhD", "year": "1988", "title": "Catalytic Oxidation of Sulphur Dioxide by Heterogeneous Cobalt-Phthalocyanine", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082007-080528", "creators": [ { "name": { "family": "Hong", "given": "Pui-Kwan Andrew" }, "id": "Hong-Pui-Kwan-Andrew", "display_name": "Hong, Pui-Kwan Andrew" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Bercaw", "given": "John E." }, "id": "Bercaw-J-E", "role": "member", "display_name": "Bercaw, John E." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/nex9-4957", "abstract": "Various homogeneous and hybrid cobalt phthalocyanines were developed. They were shown to be effective catalysts for the catalytic degradation of many aqueous pollutants. The catalytic activity of these systems was attributed to their ability to activate molecular oxygen. Semiconductor titanium dioxide was found to be useful both as solid support and photocatalyst. The electron relay property of cobalt phthalocyanine on the photoactive TiO\u2082 surface was elucidated. The homogeneous and heterogeneous kinetics and mechanisms for the catalytic oxidation of aqueous sulfur dioxide were studied.
\r\n" }, { "name": "Karyeaclis, Michael P.", "degree": "PhD", "year": "1988", "title": "Dynamics of a Semi-Active Impact Damper: Regular and Chaotic Motions", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-07112005-091557", "creators": [ { "name": { "family": "Karyeaclis", "given": "Michael P." }, "id": "Karyeaclis-Michael-P", "display_name": "Karyeaclis, Michael P." } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "orcid": "0000-0002-0780-0911", "role": "member", "display_name": "Wiggins, Stephen R." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "mecheng" ], "doi": "10.7907/aeca-5g55", "abstract": "A study is made of the general behavior of a semi-active impact damper. The system consists of an undamped forced torsional oscillator, and a flywheel which can be locked to the oscillator through a clutch. Clutch engagement takes place instantaneously when the two rotors move in opposite directions. The resulting impact is effective in reducing the vibration amplitude level of the oscillator when it is subjected to bounded excitation.
\r\n\r\nAll solutions of the system are shown to be bounded when the input is bounded. Emphasis is placed on 2 impacts/cycle periodic solutions. Exact symmetric and nonsymmetric solutions are derived analytically and the region of asymptotic stability is determined. The stability analysis leads to the definition of a transition matrix which determines the state of the system immediately after impact from its state after the previous impact. It also leads to the definition of a nonlinear map associated with the impact damper so that periodic solutions of the system correspond to fixed points of the map. The region of stability is defined as the region in parameter space where the eigenvalues of the transition matrix have modulus less than unity.
\r\n\r\nIn the region of instability solutions are quasiperiodic or chaotic. As the parameter of the problem varies, the fixed points of the associated map undergo Hopf bifurcation which results in an invariant circle. Breakdown of the invariant circle leads to chaotic motions by the impact damper. Time histories, phase plane portraits, power spectra and Poincare maps are used as descriptors to observe the evolution of chaotic motions. Computation of the largest Lyapunov exponent verifies the fact that when the structure of the invariant circle in resonance breaks down motions of the system are indeed chaotic.
\r\n\r\nIt is found that under practically realizable conditions the mechanism is an effective damper. Applications include rotating shafts, and numerical simulations of a two-degree-of-freedom torsion bar were also carried out to observe the effects and effectiveness of impact in a multidegree of freedom primary system.
" }, { "name": "Kim, Sung Joon", "degree": "PhD", "year": "1988", "title": "I. Ion-Solid Interactions with Markers. II. Oxidation Phenomena in Silicides and Aluminides", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062007-081348", "creators": [ { "name": { "family": "Kim", "given": "Sung Joon" }, "id": "Kim-Sung-Joon", "display_name": "Kim, Sung Joon" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "chair", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" } ], "option_major": [ "eleceng" ], "doi": "10.7907/av5j-xe20", "abstract": "This thesis consists of two main topics: a) study of ion-solid interactions, or \"ion mixing\", by markers and b) oxidation phenomena of metal silicides and gold aluminides.
\r\n\r\nThere are many well-developed theories describing atomic collisions in solids. However, the basic aspects of ion mixing, such as the magnitude of atomic relocation and the formation of certain compounds, have proven elusive to theoretical understanding. We have conducted experiments that provide a data base for an understanding of atomic motion during ion irradiation. In these experiments the so-called \"marker\" sample configuration was used, where a layer of about 10 \u00c5 of an impurity is buried in an otherwise homogeneous medium. When the sample is irradiated, the layer is dispersed. This irradiation-induced spreading of marker layer is measured by backscattering spectrometry. The different amount of spreading in different samples under various experimental conditions yields insight into the atomic displacement mechanisms.
\r\n\r\nThree major mechanisms are known to contribute to the atomic displacements during ion irradiation on solids: a) collisional displacements, b) intermixing by a thermal spike and c) radiation-enhanced diffusion (see chap. 1 for definitions). At low temperatures only the first two mechanisms play role in the atomic displacements; at high temperatures radiation-enhanced diffusion is significant. The irradiations were conducted at temperatures ranging from 7 to 500 K using Kr and Xe ions of energies from 0.3 to 1.0 MeV. The matrix atoms studied range in mass from C to Au. The marker impurities used go from Al to Bi.
\r\n\r\nAt low temperatures, the effects of material properties and parameters such as -vmass and cohesive energy of the target, damage energy density in the material, thermal diffusivity, and heat of mixing are investigated. At high temperatures, the effects of the defect creation rate in the material by irradiation and the diffusion mechanisms are studied.
\r\n\r\nThe second part of the thesis deals with oxidation phenomena The oxidation of Co and Ni disilicides on SiO\u2082 substrates is investigated. The motivation of this work is the desire to produce an elemental metal film encapsuled by a protective insulating SiO\u2082 layer for low resistivity interconnection in VLSI circuits. Electrical, chemical, and morphological properties of the oxidized films were investigated as a function of oxidation duration under various oxidation conditions and Si content in the silicide films.
\r\n\r\nThe oxidation of Au aluminides was also investigated. Gold bonds on aluminum metallization for semiconductor devices are under constant physical and chemical changes due to joule heating, electromigration and outgassing of packaging materials. Water and oxygen are some of the main undesirable components in the outgassing of packaging material. We investigate the effects of 50, 70, and 100\u00b0 C water and wet oxidation at 773 K on thin films of Al and of all five existing binary Au-Al compounds (AuAl\u2082, AuAl, AU\u2082Al, Au\u2085Al\u2082, and Au\u2084Al) on SiO\u2082 substrates.
" }, { "name": "Larson, Susan Mary", "degree": "PhD", "year": "1988", "title": "A Study of Summer Midday Low-Visibility Events in the Los Angeles Area", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-152224", "creators": [ { "name": { "family": "Larson", "given": "Susan Mary" }, "id": "Larson-Susan-Mary", "display_name": "Larson, Susan Mary" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/33vc-mc45", "abstract": "The reduction of visibility due to air pollutants in the Los Angeles atmosphere can be severe. During summer midday periods, visibility can be reduced to less than a few kilometers. A five-site air monitoring network operated during the summer of 1984 provided data needed to characterize the summer midday visibility problem in the Los Angeles area. Light scattering and absorption by fine aerosol particles was found to account for more than 80% of the light extinction at the five sites studied. Carbonaceous aerosols and sulfates were responsible for approximately half of that fine aerosol burden. The theories of light scattering and absorption, and the data collected describing the physical and chemical characteristics of the suspended particulate matter and gaseous pollutants were used to calculate the light scattering coefficient and extinction coefficent present on each experiment day. The theoretically computed scattering and extinction coefficients are in reasonable agreement with measurements of those quantities.
\r\n\r\nOne method of presenting the results of a visibility model in a readily understood fashion is to produce synthetic photographs that simulate the appearance of the scene of interest in the presence of a specified level of air pollution. A procedure for creating such synthetic photographs is developed, and methods for testing the accuracy of image processing-based visibility models are explored. The contrast reduction observed when objects are viewed through a polluted atmosphere is reproduced in the synthetic photographs, and with the inclusion of a radiative transfer code to calculate sky intensities, the appearance of the sky can be accurately simulated.
\r\n\r\nSince carbonaceous aerosol is the largest single contributor to fine particle concentrations in the Los Angeles atmosphere, pollutant abatement programs directed at visibility improvement must consider the reduction of primary carbon particle concentrations. The effects on visibility of strategies that have been proposed for reducing the emissions of primary carbon particles are examined. It is estimated that the mean light extinction coefficient in the Los Angeles area atmosphere could be reduced by 8% to 15% by means of carbon particle emission controls costing $80.4 x 10\u2076 year\u207b\u00b9. Controls on other emissions would further improve local visibility.
\r\n" }, { "name": "Levendis, Yiannis Angelo", "degree": "PhD", "year": "1988", "title": "A Fundamental Study of Char Oxidation Kinetics Using Model Materials", "advisor": "Flagan, Richard C.; Gavalas, George R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152007-091715", "creators": [ { "name": { "family": "Levendis", "given": "Yiannis Angelo" }, "id": "Levendis-Yiannis-Angelo", "display_name": "Levendis, Yiannis Angelo" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "co-advisor", "display_name": "Gavalas, George R." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "envreng" ], "doi": "10.7907/FQBH-BT69", "abstract": "A fundamental study concerning the reactivity of carbon to oxygen, under conditions pertinent to the combustion of pulverized fuel particles, was conducted. Model, man-made materials have been synthesized and produced to aid in understanding the events that occur during pyrolysis and oxidation of chars. The benefit of employing synthetic materials, along with natural fuels, was that they allowed control of the purity and composition of the chars, as well as enabled production of particles of specific physical properties relevant to modeling combustion processes.
\r\n\r\nMonodisperse, spherical, glassy carbon particles, of various sizes, were manufactured from spraying and thermally treating a carbon-yielding, highly crosslinked polymer. Various pore-forming agents were introduced and copolymerized, aiming to alter the pore structure, density and pore size distribution of the materials. Characterization of the chars, at various stages of pyrolysis and partial oxidation, employed widely varying techniques such as mercury intrusion, gas sorption, helium pycnometry, wide and small-angle scattering and nuclear magnetic resonance. Upon characterization, the influence of the physical factors on the combustion behavior was accounted for and the intrinsic reaction rates of the chars were correlated with their chemical nature. The mechanisms of pore coarsening, opening of pore restrictions and development of a large accessible pore surface area in the interior of the particles, in conjunction to the kinetics of structural ordering and graphitization, have been shown to influence critically the reactivity of chars. furthermore, experiments with calcium treated chars revealed that the catalytic effect of mineral matter on enhancing the combustion rate is very important.
" }, { "name": "Liang, Liyuan", "degree": "PhD", "year": "1988", "title": "Effects of Surface Chemistry on Kinetics of Coagulation of Submicron Iron Oxide Particles (\u03b1-Fe\u2082O\u2083) in Water", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-110812", "creators": [ { "name": { "family": "Liang", "given": "Liyuan" }, "id": "Liang-Liyuan", "display_name": "Liang, Liyuan" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" } ], "option_major": [ "envreng" ], "doi": "10.7907/4XGW-4G55", "abstract": "Particles in the colloidal size range, i.e. smaller than 10\u207b\u2076 meter, are of interest in environmental science and many other fields of science and engineering. Since aqueous oxide particles have high specific surface areas they adsorb ions and molecules from water, and may remain stable in the aqueous phase with respect to coagulation. Submicron particles collide as a result of their thermal energy, and the effective collision rate is slowed by electric repulsion forces. A key to understanding particle stability and coagulation is the role of simple chemical changes in the water altering the electrostatic repulsion forces between particles.
\r\n\r\nExperiments using hematite particles (\u03b1-Fe\u2082O\u2083, 70nm in diameter) reveal important features of coagulation dynamics. Three experimental techniques are employed: (1) Light scattering measurements to yield quantitative information on the rate of the initial coagulation process; (2) electrokinetic measurements to provide information about the sign and magnitude of the electrical charge on the aqueous oxide particles; (3) acid-base titration and equilibrium adsorption to obtain the intrinsic equilibrium constants for surface species.
\r\n\r\nThe acid-base titration data indicate that the pHzpc of the synthesized hematite colloid is 8.5. This is also supported by the electrophoretic mobility measurements. In the presence of non-specific adsorbing ions (such as Na\u207a and Ca\u00b2\u207a, etc.), the coagulation of a hematite colloid is achieved mainly by the compression of diffuse layer and Schulze-Hardy Rule is exhibited for non-specific electrolytes. Specifically adsorbed counter ions (such as phosphate) are able to reduce the surface charge of aqueous oxide particles, and the critical coagulation concentrations are dependent on the value of the pH, and are much less than those predicted by DLVO theory. In inorganic media, we found that the order of the effectiveness in causing hematite particles to coagulate is:
\r\n\r\nphosphate > sulfate > chloride at pH < pHzpc
\r\n\r\nand
\r\n\r\nmagnesium > calcium > sodium~potassium at pH < pHzpc
\r\n\r\nThe adsorption study reveals that phthalate ions specifically adsorb on hematite particles. The process is most likely due to carboxylic group bonding to the surface. The hematite coagulation rates in the presence of poly-aspartic acid (PAA) demonstrate that the polyelectrolyte is very effective in causing the colloid to coagulate. When the PAA concentration is increased beyond the critical coagulation concentration, the particles are stabilized; this is attributed to the reversal of surface potential as a result of the adsorption of PAA. Similar features are observed in the initial coagulation rates when naturally occurring organics (fulvic and humic acid from Suwannee River) are used.
\r\n\r\nThe adsorption of lauric acid on hematite was investigated and the results interpreted in terms of the energy contributed by the specific chemical, electrostatic and hydrophobic interactions. The initial coagulation rates of hematite particles and the electrophoretic mobilities with respect to fatty acid concentration both show systematic variations as a function of the numbers of carbons in the acid. Hydrophobic interaction may account for these observations since the specific chemical energy appears to be the same for all the fatty acids studied, and the electrostatic contribution is also similar at the same extent of adsorption.
\r\n" }, { "name": "Lin, Anne", "degree": "PhD", "year": "1988", "title": "A Numerical Evaluation of the Method of Equivalent Nonlinearization", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082007-084824", "creators": [ { "name": { "family": "Lin", "given": "Anne" }, "id": "Lin-Anne", "display_name": "Lin, Anne" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." } ], "option_major": [ "civileng" ], "doi": "10.7907/31g4-p045", "abstract": "The Method of Equivalent Nonlinearization, an approach for determining the approximate steady-state probability density function for the random response of nonlinear systems, is evaluated based on numerical simulations.
\r\n\r\nThe approach is a natural extension of the well-known Method of Equivalent Linearization, and is based on approximating the original nonlinear system by an equivalent nonlinear system. As such, the approach relies on the existence of exact solutions for the steady-state probability density function of nonlinear systems.
\r\n\r\nThe approach is applied to a class of systems with nonlinear damping, for which there are no exact solutions. The results show an excellent agreement between simulated and predicted probability density functions for displacement, velocity and energy-based envelope. Several examples were solved, including the case of (velocity)m-damping and the Van der Pol equation.
\r\n" }, { "name": "Madhavan, Raghu", "degree": "PhD", "year": "1988", "title": "On the Collapse of Long Thick-Walled Circular Tubes under Biaxial Loading", "advisor": "Babcock, Charles D.; Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062007-080516", "creators": [ { "name": { "family": "Madhavan", "given": "Raghu" }, "id": "Madhavan-Raghu", "display_name": "Madhavan, Raghu" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "co-advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Singer", "given": "Josef" }, "id": "Singer-J", "role": "member", "display_name": "Singer, Josef" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/VPAC-QV51", "abstract": "The collapse phenomenon of long, thick-walled tubes subjected to axial tension and external pressure is investigated. A combined experimental and analytic approach is adopted. The diameter to thickness ratio (DA) of the tubes studied is in the range 10-40.
\r\n\r\nA series of collapse tests are conducted using thick-walled, small diameter tubes of two different materials. Careful measurements of geometrical and material parameters are carried out before each collapse test. Tension-Pressure collapse envelopes are obtained for tubes of different D/t and loading paths. Collapse tests involving initially ovalized tubes are also carried out. The results show that collapse strength is strongly influenced by initial ovality.
\r\n\r\nA two-dimensional model is used for predicting the collapse strength. The limit point behavior of a long tube with initial geometric imperfections has been modeled. The tube is assumed to be under generalized plane strain conditions and the possible variations of material and geometric parameters along the length are not considered. Hill's anisotropic plasticity theory involving a quadratic yield function is used to model the anisotropies in yield shown by drawn tubes. A power law creep model is employed to assess the effect of primary creep on collapse strength.
\r\n\r\nThe interaction between collapse pressure and tension is found to depend on both material and geometric parameters. The yield behavior of the tube material strongly affects the collapse phenomenon. Initial ovality of the tube is shown to be a very important geometric parameter that influences collapse strength. The effect of primary creep on collapse is shown to be not very significant, for the type of materials used (304 stainless steel and 6061-O aluminum).
\r\n" }, { "name": "Majani, Eric Etienne", "degree": "PhD", "year": "1988", "title": "A Model for the Study of Very Noisy Channels, and Applications", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082007-085237", "creators": [ { "name": { "family": "Majani", "given": "Eric Etienne" }, "id": "Majani-Eric-Etienne", "display_name": "Majani, Eric Etienne" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/9AF1-K251", "abstract": "Very Noisy channels (such as the wideband gaussian channel well-known in deep space communications) have the interesting property that although the maximum number of bits transmitted per symbol is close to zero, the maximum number of bits transmitted per second is not! Furthermore, recent results on the ultimate limits of information density indicate that some channels perform better when pushed to their very noisy limit.
\r\n\r\nWe present a general mathematical model of Very Noisy channels which provides an insight in their behavior, and in some interesting cases, tells us about the limiting behavior of the larger class of noisy channels.
\r\n\r\nTwo classes of Very Noisy Channels are identified and efficient algorithms that compute their capacity are presented. We show that for some Very Noisy broadcast channels, the time-shared coding strategy performs as well as the optimal strategy known as broadcast coding in the limit. Finally, with the help of our model, we derive a tight lower bound on the amount of information lost in a Channel Reduction or Data Compression.
\r\n" }, { "name": "Meng, Wen Jin", "degree": "PhD", "year": "1988", "title": "Solid State Amorphization Reactions in thin Film Diffusion Couples", "advisor": "Johnson, William Lewis; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-11022007-094005", "creators": [ { "name": { "family": "Meng", "given": "Wen Jin" }, "id": "Meng-Wen-Jin", "display_name": "Meng, Wen Jin" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/E13T-CN40", "abstract": "Metastable materials including amorphous materials have traditionally been synthesized from either the vapor or the liquid state. Very recently, it has been demonstrated that an amorphous alloy can be obtained by interdiffusion reactions in crystalline binary thin-film diffusion couples. This thesis focuses its study on the formation of amorphous alloys and the subsequent formation of crystalline compounds in thin-film diffusion couples. Both the thermodynamics and kinetics of amorphous phase formation have been examined. The evolution of these diffusion couples has been followed in some detail. Relevant factors governing the evolution of diffusion couples in general will be discussed.
\r\n" }, { "name": "Olson, Terese Marie", "degree": "PhD", "year": "1988", "title": "The Formation Kinetics, Mechanisms, and Thermodynamics of S(IV)-Aldehyde Addition Compounds", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-130323", "creators": [ { "name": { "family": "Olson", "given": "Terese Marie" }, "id": "Olson-Terese-Marie", "display_name": "Olson, Terese Marie" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." } ], "option_major": [ "envreng" ], "doi": "10.7907/rpn9-8403", "abstract": "The reaction kinetics and thermodynamics of the reversible addition of S(IV) and several aldehydes were studied at low pH in order to determine which carbonyl-bisulfite adducts are potential S(IV) reservoirs in atmospheric water droplets. Benzaldehyde, glyoxal, glyoxylic acid, and hydroxyacetaldehyde were chosen as aldehyde substrates.
\r\n\r\nSpectrophotometric methods were employed to study the reaction kinetics. Between pH 1 - 3, the two rate-determining steps for adduct formation were the addition of HSO\u2083\u207b and SO\u2083\u00b2\u207b to the carbonyl carbon atom. The sulfite ion was a much more effective nucleophile than bisulfite; rate constants for sulfite addition are four to five orders of magnitude higher than for bisulfate. Below pH 1, some specific acid catalysis was also observed.
\r\n\r\nAdduct stability constants were determined by spectrophotometry and from microscopic reversibility relationships. Linear-free-energy relationships between carbonyl-bisulfate adduct stabilities and the Taft \u03c3* parameter were found to hold for a limited set of aldehyde substrates. A relatively high correlation exists between bisulfate adduct stability constants and carbonyl hydration constants.
\r\n\r\nCriteria were formulated, which can be used to predict the potential effectiveness of a carbonyl to significantly stabilize S(IV) in droplets. Modeling calculations for an open atmosphere show that adduct formation rates are much slower than mass transfer and S(IV) oxidation rates under most fog- and cloud-water conditions. Formation rates of hydroxyacetaldehyde-, glyoxal-, and glyoxylic acid - bisulfate addition compounds are comparable to, or faster than, formation rates of hydroxymethanesulfonate, which has been identified in droplets. Equilibrium calculations suggest that these three addition compounds can also stabilize a significant excess of SO\u2082 in the liquid phase.
\r\n" }, { "name": "Parsons, Ian Dennis", "degree": "PhD", "year": "1988", "title": "The Application of the Multigrid Method to the Finite Element Solution of Solid Mechanics Problems", "advisor": "Hall, John F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08102006-090020", "creators": [ { "name": { "family": "Parsons", "given": "Ian Dennis" }, "id": "Parsons-Ian-Dennis", "display_name": "Parsons, Ian Dennis" } ], "advisors": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "advisor", "display_name": "Hall, John F." } ], "committee": [ { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "chair", "display_name": "Hall, John F." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" } ], "option_major": [ "civileng" ], "doi": "10.7907/MVMM-ED69", "abstract": "A multigrid algorithm is described that can be used to obtain the finite element solution of linear elastic solid mechanics problems. The method is applied to some simple two and three dimensional problems to evaluate its strengths and weaknesses. The usefulness of the method is demonstrated by solving some large three dimensional problems of practical interest.
\r\n\r\nWhen conditions of near incompressibility are encountered, the multigrid method performs poorly due to a combination of a reduction in the smoothing effect of the Gauss-Seidel relaxation method and coarse mesh locking. These problems can be partially cured by using the Jacobi preconditioned conjugate gradient method to smooth the error, and assembling the coarse mesh stiffness matrices using a reduced integration scheme.
\r\n\r\nIt is also found that the bending behavior of the linear brick and quadrilateral elements used in this thesis slow the convergence of the multigrid method. This effect also causes nonuniform meshes to yield computation times that are not proportional to the problem size; however, the linear dependence can be recovered by increasing the refinement of the finite element meshes. It is demonstrated that reduced integration techniques become less effective in relieving the stiffness of the coarse mesh for nonuniform meshes as the problem size is increased. The solution of a well-conditioned three dimensional test problem shows that the multigrid algorithm requires far less computational effort than a direct method, and that its performance is comparable to that of the Jacobi preconditioned conjugate gradient method.
\r\n\r\nThe usefulness of the multigrid method is demonstrated by applying it to the finite element solution of two solid mechanics problems of engineering interest: the elastostatic state near a three dimensional edge crack, and the relationship between the average offset and the stress drop for two and three dimensional faults in a half-space. The features of the solution to these problems are extensively discussed. It is found that the multigrid method is faster than the Jacobi preconditioned conjugate gradient method when applied to these practical problems.
\r\n\r\nThe investigations described in this thesis reveal some interesting features of the performance of the multigrid method when it is applied to the finite element solution of solid mechanics problems. In particular, the storage requirements of the method are linearly proportional to the problem size. The constant of proportionality depends only on the dimension of the problem. The solution times of the multigrid method are found to be linearly proportional to the problem size if uniform meshes are used. However, this is not true for most of the problems that are solved with nonuniform meshes. The constant of proportionality in the relationship between the problem size and the solution time depends on the particular problem under consideration.
\r\n" }, { "name": "Peng, Chia-Yen", "degree": "PhD", "year": "1988", "title": "Generalized Modal Identification of Linear and Nonlinear Dynamic Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03132013-163747278", "creators": [ { "name": { "family": "Peng", "given": "Chia-Yen" }, "id": "Peng-Chia-Yen", "display_name": "Peng, Chia-Yen" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/e70y-gz66", "abstract": "This dissertation is concerned with the problem of determining the dynamic characteristics of complicated engineering systems and structures from the measurements made during dynamic tests or natural excitations. Particular attention is given to the identification and modeling of the behavior of structural dynamic systems in the nonlinear hysteretic response regime. Once a model for the system has been identified, it is intended to use this model to assess the condition of the system and to predict the response to future excitations.
\r\n\r\nA new identification methodology based upon a generalization of the method of modal identification for multi-degree-of-freedom dynaimcal systems subjected to base motion is developed. The situation considered herein is that in which only the base input and the response of a small number of degrees-of-freedom of the system are measured. In this method, called the generalized modal identification method, the response is separated into \"modes\" which are analogous to those of a linear system. Both parametric and nonparametric models can be employed to extract the unknown nature, hysteretic or nonhysteretic, of the generalized restoring force for each mode.
\r\n\r\nIn this study, a simple four-term nonparametric model is used first to provide a nonhysteretic estimate of the nonlinear stiffness and energy dissipation behavior. To extract the hysteretic nature of nonlinear systems, a two-parameter distributed element model is then employed. This model exploits the results of the nonparametric identification as an initial estimate for the model parameters. This approach greatly improves the convergence of the subsequent optimization process.
\r\n\r\nThe capability of the new method is verified using simulated response data from a three-degree-of-freedom system. The new method is also applied to the analysis of response data obtained from the U.S.-Japan cooperative pseudo-dynamic test of a full-scale six-story steel-frame structure.
\r\n\r\nThe new system identification method described has been found to be both accurate and computationally efficient. It is believed that it will provide a useful tool for the analysis of structural response data.
" }, { "name": "Pilinis, Christodoulos", "degree": "PhD", "year": "1988", "title": "Mathematical Modeling of the Dynamics and Thermodynamics of Multicomponent Atmospheric Aerosols", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-140642", "creators": [ { "name": { "family": "Pilinis", "given": "Christodoulos" }, "id": "Pilinis-Christodoulos", "display_name": "Pilinis, Christodoulos" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/t5w6-2r52", "abstract": "Atmospheric aerosols consist of particles with sizes between 0.01 and 10\u00b5m. These particles, when occurring in urban areas, consist, in general, of aqueous solutions of sulfate, nitrate, ammonium, chloride, sodium and other ionic species, as well as of primary and secondary organics.
\r\n\r\nThis thesis attempts to describe the evolution and fate of atmospheric aerosol particles. The size-composition distribution of atmospheric aerosols is governed by a combination of kinetics and thermodynamics, which, because of their complexity, can be analyzed only with computer simulations. At first, a solution of the General Dynamic Equation in the case of small coagulation, using perturbation techniques, is developed.
\r\n\r\nIn subsequent work, a comprehensive size-sectionalized trajectory aerosol model was developed for simulating the evolution of a multicomponent aerosol size-composition distribution through homogeneous heteromolecular nucleation, condensational growth, coagulation and deposition. The model was employed along a trajectory from Anaheim to Rubidoux, California.
\r\n\r\nIn the process of analyzing this model it became apparent that a detailed treatment of the thermodynamics of the sodium/ sulfate/ nitrate/ ammonium/ chloride/ water system is very important in aerosol predictions. Thus, an equilibrium model for this system that takes into account differences in the composition among particles of different sizes was developed and tested.
\r\n\r\nFinally, the same theory was used in a Eulerian framework, thus producing a three-dimensional Eulerian Urban Gas-Aerosol Model, which was used to predict the aerosol concentration and size distribution throughout the Los Angeles Basin on August 30, 1982. Its prediction is compared with measured values and a statistical evaluation study is presented.
\r\n" }, { "name": "Pugh, Jeffrey David", "degree": "PhD", "year": "1988", "title": "Finite Amplitude Waves in Plane Poiseuille Flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072007-104253", "creators": [ { "name": { "family": "Pugh", "given": "Jeffrey David" }, "id": "Pugh-Jeffrey-David", "display_name": "Pugh, Jeffrey David" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XHFQ-MJ23", "abstract": "Nonlinear behavior in plane Poiseuille flow has attracted theoretical interest over the last decade, both because of its tractability and because it is believed that some of the results may be applicable to phenomena occurring in the boundary layer. We have investigated the existence of three-dimensional finite amplitude waves in plane Poiseuille flow, in the hope of finding candidates for a class of simple flows which might provide insight into the nature of turbulence. These so-called vortical states would exist as attractors for the turbulent flow and mimic many of its properties.
\r\n\r\nOne of the requisite properties of these simple flows is existence at the low Reynolds numbers observed in experimental studies of transition to turbulence in plane Poiseuille flow. Although no such three-dimensional solutions were found in our study, a number of new insights have been made into the structure and stability of two- and three-dimensional steady wave solutions in plane Poiseuille flow. These in turn suggest new areas of investigation for finding vortical states.
" }, { "name": "Rebeiz, Gabriel M.", "degree": "PhD", "year": "1988", "title": "Monolithic Millimeter-Wave Two-Dimensional Horn Imaging Arrays", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082007-111802", "creators": [ { "name": { "family": "Rebeiz", "given": "Gabriel M." }, "id": "Rebeiz-Gabriel-M", "display_name": "Rebeiz, Gabriel M." } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "display_name": "Rutledge, David B." }, { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "display_name": "Elachi, Charles" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "display_name": "Posner, Edward C." }, { "name": { "family": "Fetterman", "given": "Harold" }, "id": "Fetterman-Harold", "display_name": "Fetterman, Harold" } ], "option_major": [ "eleceng" ], "doi": "10.7907/B9FG-6H18", "abstract": "A new monolithic millimeter-wave two-dimensional horn imaging array is presented. In this configuration, a dipole is suspended in an etched pyramidal cavity on a 1-\u00b5m silicon-oxynitride membrane. This approach allows ample space for low-frequency interconnections, while still maintaining efficient diffraction-limited imaging. The fabrication procedure of the horn array and the deposition parameters of the membrane layer are presented in detail. The array is analysed rigorously, by approximating the horn antenna by a structure of multiple rectangular waveguide sections. Pattern measurements at 93 GHz and 242 GHz agree well with the theory. The results show that horn antennas with an opening between 1.0\u03bb and 1.5\u03bb have high aperture efficiencies and would match well appropriate imaging systems. Also, a new wideband log-periodic antennas is integrated on a thin membrane and tuned by a back plane reflector. The antenna patterns are measured at 167 GHz, 370 GHz and 700 GHz, and the effect of the back-plane reflector is investigated at 370 GHz.
" }, { "name": "Regehr, Wade Gordon", "degree": "PhD", "year": "1988", "title": "Neuron-Microdevice Connections", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092007-084226", "creators": [ { "name": { "family": "Regehr", "given": "Wade Gordon" }, "id": "Regehr-Wade-Gordon", "display_name": "Regehr, Wade Gordon" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Lester", "given": "Henry A." }, "id": "Lester-H-A", "role": "member", "display_name": "Lester, Henry A." }, { "name": { "family": "Bower", "given": "James M." }, "id": "Bower-J-M", "role": "member", "display_name": "Bower, James M." }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "member", "display_name": "Pine, Jerome" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/nshf-ww49", "abstract": "A new method for long-term recording and stimulation applicable to cultured neurons has been developed. Silicon-based microelectrodes have been fabricated using integrated-circuit technology and micromachining. The chronic connection is made by positioning the electrode tip into contact with the cell body, and gluing the device to the bottom of the culture dish. These \"diving-board electrodes\" consist of an insulated lead exposed only at the tip sealed to the cell body of a cultured neuron. A two-way electrical connection to Helisoma B19 neurons has been established for up to four days. Preliminary experiments with cultured superior cervical ganglion neurons indicate diving-board electrodes can be used with cultured neurons larger than 20 \u00b5m in diameter.
\r\n\r\nIn a related technique Helisoma neurons grown on special dish containing a multielectrode array were found to seal to the dish electrodes, establishing similar long-term connections. This capability will make it possible to conduct experiments with either diving-board electrodes or dishes that cannot be performed using conventional techniques.
" }, { "name": "Rizvi, Syed Azhar Abbas", "degree": "PhD", "year": "1988", "title": "The Critical Points of Poynting Vector Fields", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082007-131130", "creators": [ { "name": { "family": "Rizvi", "given": "Syed Azhar Abbas" }, "id": "Rizvi-Syed-Azhar-Abbas", "display_name": "Rizvi, Syed Azhar Abbas" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "chair", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "eleceng" ], "doi": "10.7907/gj18-eq28", "abstract": "In a thought provoking paper Maxwell [The Scientific Papers of James Clerk Maxwell, ed. W. D. Niven, vol. 2, 233-240, Dover Publications, New York (1952)] studied the flow of water on the Earth's surface and how this flow is affected by the local geography. His results linking number of hills and lake bottoms to valleys are simple and the conclusions elegant. Critical points such as summits and lake bottoms play a key role in the overall organization and structuring of the flow lines. This is the spirit in which electromagnetic power flow represented by the Poynting vector field (S) is studied in this thesis. The specialized case of a planar S field which arises due to a single electromagnetic field component Ez or Hz is dealt with here in considerable detail.
\r\n\r\nIn order to analyse the behaviour of the flow lines of a plane Poynting vector field in the neighbourhood of a critical point, the S field is expanded in a Taylor series. Critical points can be classified according to their order, degeneracy or structural stability. The order of a critical point refers to the degree of the leading non zero term in the Taylor series. A critical point is non degenerate if this leading term is sufficient to give a qualitative description of the flow lines in the neighbourhood. A critical point is structurally stable if the flow lines in the neighbourhood do not change drastically when there is a small perturbation of the electromagnetic field. It is found that lowest order critical points, i.e., elementary center point and elementary saddle point, are the only structurally stable critical points. These critical points are always non degenerate. All degenerate and non elementary critical points are found to be structurally unstable. A formula for the index of rotation of the S field at a critical point is derived. The behaviour of the electric or the magnetic field component which lies in the x-y plane is also studied. It is shown that structurally unstable configurations of flow lines change into structurally stable configurations under small perturbations in such a way that the index of rotation is conserved. The statements made above in connection with the behaviour of flow lines and structural stability are illustrated with the help of examples involving linearly polarized system of interfering plane and/or cylindrical waves.
\r\n\r\nThe flow lines of the S field in the vicinity of a perfectly conducting surface are studied. It is found that in structurally stable situations these lines are either parallel to the surface or they form critical points of half saddle type on this surface. Two types of problems involving flow lines and conducting surfaces are identified. The interior problem deals with the situations where all the flow lines are inside a region bounded by a perfect conductor. In the exterior problems all the flow lines are outside a region bounded by a perfectly conducting surface. Conclusions regarding the existence of critical points and the behaviour of flow lines are drawn in the two above mentioned problems. These conclusions are verified by computation of flow lines in a few well known problems of scattering and diffraction.
\r\n\r\nFinally the critical points of three dimensional Poynting vector fields are considered. A complete classification of these critical points requires further study at this time. In this thesis only structurally stable critical points are classified for these S fields. An example demonstrating the existence of such critical points is given.
" }, { "name": "Sahu, Ranajit", "degree": "PhD", "year": "1988", "title": "On the Combustion of Bituminous Coal Chars", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132007-081003", "creators": [ { "name": { "family": "Sahu", "given": "Ranajit" }, "id": "Sahu-Ranajit", "display_name": "Sahu, Ranajit" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "mecheng" ], "doi": "10.7907/zrnz-qc25", "abstract": "The combustion of chars from pulverized bituminous coals was experimentally and theoretically investigated. The chars were made by pyrolyzing size-graded PSOC 1451 coal particles in nitrogen at temperatures of 1000-1600K. Sized char particles were then used for further experiments. Low temperature reactivities of such cenospheric chars were measured at 800K on a thermogravimetric analyzer. The effects of initial coal size, char size, pyrolysis temperature, and oxygen concentration were investigated. Single particle combustion experiments were done in both air and 50% oxygen ambients at wall temperatures of 1000-1500K in a drop tube laminar flow furnace. Particle temperatures were measured during the entire course of combustion. From the complete temperature-time histories of such burning particles, the apparent activation energy and pre-exponential factors were inferred, using numerical models and statistical modelling techniques. Questions of particle-particle variability were addressed. The ignition transients of single burning particles were studied and a model that predicted delay times observed experimentally was developed. Char samples were also partially oxidized at temperatures in the range 1200-1500K (particle temperatures) and physically characterized. Methods of characterization included optical and electron microscopy, gas adsorption methods for specific surface area and pore volume distributions, and mercury porosimetry for pore volume distribution measurements. The results of these characterizations were compared with those done on chars oxidized at 500\u00b0C.
\r\n\r\nThe combustion of single char particles was numerically modelled. A continuum model for asymptotic shrinking-core combustion was developed using apparent reaction rates and temperature-dependent properties. Simplified assumptions were made regarding the gas-phase combustion. Parametric sensitivity of this model yielded significant insight into the combustion process. A more general continuum model was then developed. This model treated the internal pore structure more realistically, as inferred from experiments. The steady state diffusion equation was solved inside the particle to determine its theoretical temperature-time history. Good agreement with experiments was found. The model was extended to include the effects of some nonlinear kinetic reaction rate expressions. A discrete model for a cenospheric particle was also developed. This model consists of spherical voids randomly placed in a spherical particle. It simulates the combustion by taking into account the connectivity of the internal pore structure. This connectivity influences the access of reactant to the interior of the particle and, therefore, the extent of internal reaction. The changes in the internal connectivity led to a percolation type behavior in most particles.
" }, { "name": "Smith, Paul Wesley, Jr.", "degree": "PhD", "year": "1988", "title": "Considerations for the Design of Gas-Lubricated Slider Bearings", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132007-092151", "creators": [ { "name": { "family": "Smith", "given": "Paul Wesley, Jr." }, "id": "Smith-Paul-Wesley-Jr", "display_name": "Smith, Paul Wesley, Jr." } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/FYJ3-X454", "abstract": "An approach is developed that simplifies calculation of the dynamic characteristics of a self-acting, gas-lubricated slider bearing system. This technique avoids a lengthy simultaneous solution of the equations of motion of the slider and the time-dependent Reynolds' equation, while providing additional design information that is otherwise unobtainable.
\r\n\r\nThe equilibrium pressure distribution in the gas film is obtained using the Bunov-Galerkin formulation of the finite element method. By considering small perturbations of the slider bearing system about equilibrium, two coupled, second-order partial differential equations are derived, which define the in-phase and out-of-phase perturbation pressures in the gas film. These perturbation pressures are integrated to obtain the frequency dependent, non-symmetrical stiffness and damping matrices for the slider bearing.
\r\n\r\nUsing the stiffness and damping properties of the gas bearing and slider support, the equations of motion for the entire slider bearing system are derived. The frequency dependence of the stiffness and damping matrices renders the eigenvalue problem nonlinear, and the eigensolutions are obtained iteratively using Brent's method.
\r\n\r\nBecause of the non-symmetrical stiffness and damping matrices, a similarity transformation based on the left and right modal matrices is used to decouple the equations of motion. This decoupling is approximate because of the frequency dependence of the stiffness and damping matrices, but the resulting damped natural frequencies are shown to be in excellent agreement with published experimental data. Fractions of critical damping obtained for several slider geometries also successfully predict observed instabilities.
\r\n\r\nThe mode shapes of slider oscillation, unobtainable with other methods, permit calculation of the center of rotation for the coupled, pitch-heave modes; this information can be used to determine the optimum location for the magnetic transducer. Closed-form solutions are obtained for the response to disk surface displacement, and for the response to a random force applied to the slider body. These forced-response solutions are useful in identifying the critical parameters of slider design.
\r\n" }, { "name": "Smyth, Padhraic", "degree": "PhD", "year": "1988", "title": "The Application of Information Theory to Problems in Decision Tree Design and Rule-Based Expert Systems", "advisor": "Goodman, Rodney M.; Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-103549", "creators": [ { "name": { "family": "Smyth", "given": "Padhraic" }, "id": "Smyth-Padhraic", "display_name": "Smyth, Padhraic" } ], "advisors": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "advisor", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "co-advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "chair", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" } ], "option_major": [ "eleceng" ], "doi": "10.7907/cn89-3127", "abstract": "This thesis examines the problems of designing decision trees and expert systems from an information-theoretic viewpoint. A well-known greedy algorithm using mutual information for tree design is analysed. A basic model for tree design is developed leading to a series of bounds relating tree performance parameters. Analogies with prefix-coding and rate-distortion theory lead to interesting interpretations and results. The problem of finding termination rules for such greedy algorithms is discussed in the context of the theoretical models derived earlier, and several experimentally observed phenomena are explained in this manner. In two classification experiments, involving alphanumeric LEDS and local edge detection, the hierarchical approach is seen to offer significant advantages over alternative techniques.
\r\n\r\nThe second part of the thesis begins by analysing the difficulties in designing rule-based expert systems. The inability to model uncertainty in an effective manner is identified as a key limitation of existing approaches. Accordingly, an information-theoretic model for rules and rule-based systems is developed. From a simple definition of rule information content, the ability to specialise and generalise (akin to cognitive processes) in a quantitative manner is demonstrated. The problem of generalised rule induction is posed and the ITRULE algorithm is described which derives optimal rule sets from data. The problem of probabilistic updating in inference nets is discussed and a new maximum-likelihhod rule is proposed based on bounded probabilities. Utility functions and statistical decision theory concepts are used to develop a model of implicit control for rule-based inference. The theory is demonstrated by deriving rules from expert-supplied data and performing backward and forward chaining based on decision-theoretic criteria. The thesis concludes by outlining the many problems which remain to be solved in this area, and by briefly discussing the analogies between rule-based inference nets and neural networks.
" }, { "name": "So, Frank Cheung Tao", "degree": "PhD", "year": "1988", "title": "Diffusion Barriers for VLSI Applications", "advisor": "Nicolet, Marc-Aurele; Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012007-110846", "creators": [ { "name": { "family": "So", "given": "Frank Cheung Tao" }, "id": "So-Frank-Cheung-Tao", "display_name": "So, Frank Cheung Tao" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "co-advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "chair", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7ytp-0932", "abstract": "This thesis is concerned with diffusion barriers in contact structures to semiconductors. Diffusion barriers are indispensable in present contact technologies to preserve device characteristics from the influence of metal-semiconductor interaction during post-metallization processing.
\r\n\r\nThe absence of grain boundaries makes amorphous W-Zr and Ni-W alloy barriers very attractive for high temperature applications. Nevetheless, in the presence of an adjoining metal layer such as Al, these amorphous barriers are chemically dissociated to form compounds with the metal. The usefulness of these barrier in VLSI metallization schemes is severely limited by their high reactivity with Al within normal processing temperature cycles. Such thermal instability can be removed, however, by adding nitrogen to the barrier layers during sputter deposition.
\r\n\r\nBecoming aware of the beneficial effects of nitrogen incorporation, we investigate the performance of nitrogen-doped W barrier films in various contact configurations. Reactively sputtered amorphous and polycrystalline W-N layers are demonstrated to be excellent diffusion barriers against interdiffusion between Si-Al, Si-Ag, GaAs-Ag, and GaAs-Au. A novel idea of utilizing W-N as an interconnect in CMOS fabrication is also discussed.
\r\n\r\nConducting transition metal oxides emerge as a new class of diffusion barriers. Metallic Mo1-xOx films are deposited by reactive sputtering a Mo target in controlled O\u2082/Ar ambients. These Mo1-xOx barriers can effectively protect Si n\u207a-p shallow junctions from Al spiking even beyond the eutectic temperature of Si-Al. RuO\u2082 films are also found to be equally good in suppressing Si-Al interdiffusion. The present study clearly shows that Mo1-xOx and RuO\u2082 barriers are the most outstanding performers among all the passive barriers that have been explored so far.
" }, { "name": "Waas, Anthony Marius", "degree": "PhD", "year": "1988", "title": "Compression Failure of Fibrous Laminated Composites in the Presence of Stress Gradients: Experiment and Analysis", "advisor": "Babcock, Charles D.; Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062003-092741", "creators": [ { "name": { "family": "Waas", "given": "Anthony Marius" }, "id": "Waas-Anthony-Marius", "orcid": "0000-0002-5258-2749", "display_name": "Waas, Anthony Marius" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "co-chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "co-chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Singer", "given": "Josef" }, "id": "Singer-J", "role": "member", "display_name": "Singer, Josef" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PP86-PE50", "abstract": "A series of experiments were performed to determine the mechanism of failure in compressively loaded laminated plates in the presence of stress gradients generated by a circular cutout. Real time holographic interferometry and in-situ photomicrography of the hole surface, were used to observe the progression of failure.
\r\n\r\nThe test specimens are multi-layered composite flat plates, which are loaded in compression. The plates are made of two material systems, T300/BP907 and IM7/8551-7. Two different lay-ups of T300/BP907 and four different lay-ups of IM7/8551-7 are investigated.
\r\n\r\nThe load on the specimen is slowly increased and a series of interferograms are produced during the load cycle. These interferograms are video-recorded. The results obtained from the interferograms and photo-micrographs are substantiated by sectioning studies and ultrasonic C-scanning of some specimens which are unloaded prior to catastrophic failure, but beyond failure initiation. This is made possible by the servo-controlled loading mechanism that regulates the load application and offers the flexibility of unloading a specimen at any given instance in the loadtime history.
\r\n\r\nAn underlying objective of the present investigation is the identification of the physics of the failure initiation process. This required testing specimens with different stacking sequences, for a fixed hole diameter, so that consistent trends in the failure process could be identified.
\r\n\r\nIt is revealed that the failure is initiated as a localized instability in the 0\u00b0 plies at the hole surface, approximately at right angles to the loading direction. This instability emanating at the hole edge and propagating into the interior of the specimen within the 0\u00b0 plies is found to be fiber microbuckling. The microbuckling is found to occur at a local strain level of \u2243 8600 \u00b5strain at the hole edge for the IM material system. This initial failure renders a narrow zone of fibers within the 0\u00b0 plies to loose structural integrity. Subsequent to the 0\u00b0-ply failure, extensive delamination cracking is observed with increasing load. The through thickness location of these delaminations is found to depend on the position of the 0\u00b0 plies.
\r\n\r\nThe delaminated portions spread to the undamaged areas of the laminate by a combination of delamination buckling and growth, the buckling further enhancing the growth. When the delaminated area reaches a critical size, about 75-100% of the hole radius in extent, an accelerated growth rate of the delaminated portions is observed. The culmination of this last event is the complete loss of flexural stiffness of each of the delaminated portions leading to catastrophic failure of the plate. The levels of applied load and the rate at which these events occur depend on the plate stacking sequence.
\r\n\r\nA simple mechanical model is presented for the microbuckling problem. This model addresses the buckling instability of a semi-infinte layered half-plane alternatingly stacked with fibers and matrix, loaded parallel to the surface of the half-plane. The fibers are modelled using Bernoulli-Navier beam theory, and the matrix is assumed to be a linearly elastic foundation. The predicted buckling strains are found to overestimate the experimental result. However, the dependence of the buckling strain on parameters such as the fiber volume fraction, ratio of Youngs moduli of the constituents and Poisson's ratio of the matrix are obtained from the analysis. It is seen that a high fiber volume fraction, increased matrix stiffness, and perfect bonding between fiber and matrix are desirable properties for increasing the compressive strength.
" }, { "name": "Wang, Rueen-Fang Theresa", "degree": "PhD", "year": "1988", "title": "Laboratory Analysis of Settling Velocities of Wastewater Particles in Seawater using Holography", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-152444", "creators": [ { "name": { "family": "Wang", "given": "Rueen-Fang Theresa" }, "id": "Wang-Rueen-Fang-Theresa", "display_name": "Wang, Rueen-Fang Theresa" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." } ], "option_major": [ "envreng" ], "doi": "10.7907/0zds-gj34", "abstract": "Ocean discharge of treated sewage and digested sludge has been a common practice for the disposal of municipal and industrial wastewaters for years. Since the particles in the discharge cause much of the adverse effect on the marine environment, the transport processes and the final destinations of particles and the associated pollutants have to be studied to evaluate the environmental impact and the feasibility of disposal processes. The settling velocity of particles and the possible coagulation inside the discharge plume are among the most important factors that control the transport of particles.
\r\n\r\nA holographic camera system was developed to study the settling characteristics of sewage and sludge particles in seawater after simulated plume mixing with possible coagulation. Particles were first mixed and diluted in a laboratory reactor, which was designed to simulate the mixing conditions inside a rising plume by varying the particle concentration and turbulent shear rate according to predetermined scenarios. Samples were then withdrawn from the reactor at different times for size and settling velocity measurements. Artificial seawater without suspended particles was used for dilution.
\r\n\r\nAn in-line laser holographic technique was employed to measure the size distributions and the settling velocities of the particles. Doubly exposed holograms were used to record the images of particles for the fall velocity measurement. Images of individual particles were reconstructed and displayed on a video monitor. The images were then digitized by computer for calculating the equivalent diameter, the position of the centroid, the deviations along the principal axes, and the orientation of particles. A special analysis procedure was developed to eliminate sampling biases in the computation of cumulative frequency distributions. The principal advantages of this new technique over the conventional settling column (used in the early part of this research) are that: (1) the coagulation and settling processes can be uncoupled by use of extremely small concentrations (less than 2 mg/l) in the holographic sample cell, and (2) the individual particle sizes and shapes can be observed for correlation with measured fall velocities.
\r\n\r\nFour sets of experiments were conducted with blended primary/secondary effluent from the County Sanitation Districts of Los Angeles County and the digested primary sludge from the County Sanitation Districts of Orange County (proposed deep ocean outfall) using different mixing processes. Experimental results show that the sludge and effluent particles have very similar settling characteristics, and that particle coagulation is small under the simulated plume mixing conditions used in these experiments. The median and 90-percentile fall velocities and the fractions of particles with fall velocities larger than 0.01 cm/sec of the digested primary sludge and the effluent are summarized in the following table. The experimental results from the conventional settling column are also included for comparison. In general, the holographic technique indicates slower settling velocities than all the previous investigations by other procedures.
\r\n\r\n[Table; see abstract in scanned thesis for details.]
" }, { "name": "Wengler, Michael James", "degree": "PhD", "year": "1988", "title": "Heterodyne Detection with Superconducting Tunnel Diodes", "advisor": "Phillips, Thomas G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012007-084647", "creators": [ { "name": { "family": "Wengler", "given": "Michael James" }, "id": "Wengler-Michael-James", "display_name": "Wengler, Michael James" } ], "advisors": [ { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "advisor", "display_name": "Phillips, Thomas G." } ], "committee": [ { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "chair", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/TYQQ-RZ71", "abstract": "Heterodyne receivers based on superconductor-insulator-superconductor (SIS) tunnel diodes are the most sensitive available for near-millimeter wavelengths. Since the late seventies, receivers based on SISs have been used for millimeter band observations at radio observatories around the world. The work described here was carried out with the elusive goal in mind of developing ideal SIS receivers for radioastronomy. This thesis describes one researcher's path towards this goal.
\r\n\r\nIn the first chapter, a basic description of SIS diodes, their interaction with radiation, and heterodyne detection are given. The important detailed results of J. R. Tucker's tunnel diode heterodyne theory are described, since subsequent chapters rely on Tucker's work quite heavily. Throughout this introductory chapter, extremely simple (by comparison with the algebraic theoretical results) physical models are used to describe superconductivity, SISs, photon-assisted tunneling, and heterodyne detection. It is the author's experience that these physical models can be used to derive correct theoretical results, long before these results are proved rigorously.
\r\n\r\nThe second chapter presents a fully quantum mechanical theory of heterodyne detection with diodes. This theory was developed because Tucker's theory for tunnel diodes predicts a greater mixer sensitivity than is possible considering Heisenberg's uncertainty principle for radiation. Tucker does not quantize the radiation incident on the SIS, although his treatment of the isolated tunnel diode is completely quantum mechanical. In chapter 2, the quantization of radiation is carried out for heterodyne diode detectors. The formalism is shown to obey quantum limits on sensitivity. Finally, an ideal SIS mixer is shown to have noise properties identical to those of optical mixers based on ideal photodiodes.
\r\n\r\nIn possession of an apparently complete theory for SIS mixers, the third chapter presents a sampling of numerical results from that theory. Four different non-ideal tunnel diodes are used for these calculations so that a quantitative feel for the importance of diode quality can be achieved. The effects of dc and LO bias, signal and image source admittance, frequency of operation, and junction quality are all explored. This information will be useful for the proper engineering of SIS mixers. Finally, the fully optimized performance of the four tunnel diodes is presented as frequency is varied. It is shown that reasonably good quality lead-alloy SISs should behave like photodiodes up to frequencies as high as 1500 GHz.
\r\n\r\nFinally, chapter 4 presents a prototype open-structure SIS mixer. Measurements in the laboratory show this mixer to be quite sensitive for signal frequencies from 115 to 761 GHz. Unlike all other SIS receivers, in which the diode is mounted across a waveguide, this mixer relies on the bowtie-on-quartz antenna structure, which has been investigated by D. B. Rutledge and his students. This difference is essential to the multi-octave spectral coverage of this mixer. It is probable that waveguide designs will never achieve good results above 500 GHz, and as of now, there are no SIS-waveguide mixers which operate well above 300 GHz. Tests at the Owens Valley Radio Observatory verify the suitablility of this mixer for radioastronomy, but these tests have been limited to frequencies of 260 GHz and lower.
" }, { "name": "Whirley, Robert Gary", "degree": "PhD", "year": "1988", "title": "Random Response of Nonlinear Continuous Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03142013-090423420", "creators": [ { "name": { "family": "Whirley", "given": "Robert Gary" }, "id": "Whirley-Robert-Gary", "display_name": "Whirley, Robert Gary" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "mecheng" ], "doi": "10.7907/ezsr-jt33", "abstract": "This thesis presents a technique for obtaining the stochastic response of a nonlinear continuous system. First, the general method of nonstationary continuous equivalent linearization is developed. This technique allows replacement of the original nonlinear system with a time-varying linear continuous system. Next, a numerical implementation is described which allows solution of complex problems on a digital computer. In this procedure, the linear replacement system is discretized by the finite element method. Application of this method to systems satisfying the one-dimensional wave equation with two different types of constitutive nonlinearities is described. Results are discussed for nonlinear stress-strain laws of both hardening and softening types.
" }, { "name": "Woodward, Ted Kirk", "degree": "PhD", "year": "1988", "title": "Experimental Studies of Heterostructure Devices: Resonant Tunneling Transistors and GaAs/AlAs/GaAs Capacitors", "advisor": "McGill, Thomas C.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-093432", "creators": [ { "name": { "family": "Woodward", "given": "Ted Kirk" }, "id": "Woodward-Ted-Kirk", "display_name": "Woodward, Ted Kirk" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/cwz8-my71", "abstract": "This thesis is concerned with the experimental study of two kinds of heterostructure devices. The resonant tunneling transistor (RTT) is the subject of the first part of the thesis. The RTT is a new class of electronic device that has a controllable negative differential resistance (NDR) as its distinguishing characteristic. Since the first realization of a device of this type, in 1985, about 6 types of transistor structures have been reported that exhibit controllable NDR. We report the development of two types of RTTs, which are series integrations of GaAs/Al\u2093Ga\u2081\u208b\u2093As double-barrier heterostructures with field-effect transistors. Samples were produced by metalorganic chemical vapor deposition (MOCVD). Several fundamental applications of these devices are also presented.
\r\n\r\nThe first device is an integration of a resonant tunneling double-barrier heterostructure with a vertical field-effect transistor. The composite device is referred to as a DB/VFET. The device exhibits NDR in its source-drain I-V curve at 77 K, which is controllable with gate bias. Novel device features include the observation of NDR at large voltages (greater than 10 V) in one bias direction. One device exhibits NDR at room temperature. Typical 77 K peak-to-valley current ratios were about 5. Frequency multiplication and microwave oscillations at 0.8 and 3.3 GHz have been observed in this device. This device is discussed in Chapter 3 and Chapter 5.
\r\n\r\nThe second device is an integration of a double-barrier heterostructure with a planar field-effect transistor, in this case a metal-semiconductor field-effect transistor (MESFET). The composite device is referred to as a DB/MESFET. It also exhibits NDR in its source-drain I-V curve, but is qualitatively different from the DB/VFET in its behavior. A variety of output characteristics may be obtained by varying the double-barrier and MESFET parameters. Logic operations are of interest for this device, and a flip-flop circuit is demonstrated with a single DB/MESFET. This device is described in Chapters 4 and 5.
\r\n\r\nIn Part II of the thesis, studies of a different heterostructure are reported. GaAs/AlAs/GaAs single-barrier capacitor structures, characterized by relatively thick AlAs barriers (1000 - 4000 \u00c5) are the subject of this part of the thesis. Samples were grown by MOCVD. A variety of electrical and optical measurements were performed on these structures. These included capacitance-voltage (C-V), current-voltage (I-V), deep-level transient spectroscopy (DLTS), and photoresponse measurements. This structure, a fundamental part of many heterostructure devices, exhibits novel C-V and I-V behavior that can be attributed to significant densities of electron trap states near one of the GaAs/AlAs interfaces, or in the AlAs. Estimates of the deep-level concentration can be made from both C-V and I-V measurements, which have been confirmed with DLTS measurements. DLTS confirmed that the trap levels are localized. These studies are described in Chapter 6. Photoresponse measurements of the structures are interesting, and are described in Chapter 7. These studies explain the observation of zero-bias photocurrent consistent with electron transport from the back of the sample to the front.
" }, { "name": "Wu, Yu-shu George", "degree": "PhD", "year": "1988", "title": "Electronic Properties of II-VI Superlattices and III-V Tunnel Structures", "advisor": "McGill, Thomas C.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-06152006-080033", "creators": [ { "name": { "family": "Wu", "given": "Yu-shu George" }, "id": "Wu-Yu-shu-George", "display_name": "Wu, Yu-shu George" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7sag-9t91", "abstract": "This thesis deals with the electronic properties of a semiconductor superlattice and with electronic tunneling in a semiconductor heterostructure. Chapter 2 presents the theoretical formalism of k.p method for calculating band structures for strained-layer superlattices. A strained-layer superlattice is defined as a structure made up of alternating layers of at least two materials with different lattice constants. In this type of superlattice, a uniform strain, instead of misfit defects, accommodates the difference in the lattice constants. A strain affects the band structure since it changes the atomic position, and hence, crystal field which is the sum of all atomic potentials. The realization of strain effects in the model makes possible the understanding of physical properties of strained-layer superlattices, for example, optical properties and transport phenomena, which both are functions of the band structure. The study of ZnTe-CdTe system illustrates interesting strain effects in a strained-layer ZnTe/CdTe superlattice. The ZnTe/CdTe system has potential applications for visible-light sources and photodetectors. Because this system has a large lattice mismatch (\u2248 6%), the theoretical study shows that strain plays an important role in optical properties.
\r\n\r\nChapter 3 presents the theoretical formalism of k.p method for calculating band structures for semimagnetic semiconductor superlattices. A semimagnetic semiconductor superlattice is defined as a superlattice with one or more constituent materials containing magnetic impurities. When placed in a magnetic field, this type of superlattice exhibits interesting and possibly useful properties such as band gap reduction. These features are associated with the exchange interaction between the itinerant band electrons and localized d electrons on magnetic impurities. The exchange interaction in the theory is included within mean field approximation. Dependences of the band structure on the magnetic field and temperature follow the mean field approximation.
\r\n\r\nChapter 4 presents the results of theoretical study of HgTe-CdTe superlattices. The HgTe-CdTe system has interesting features which make it a candidate superior to the HgCdTe alloy for infrared application. Based on the calculated band structure, the optical properties of the HgTe/CdTe superlattice are discussed. The optical absorptions in the superlattice and alloy are studied and compared. It is shown that the superlattice could have absorptions comparable to or larger than those of the alloy. The effects of strain on the optical properties and transport phenomena are discussed. It is found that the transport phenomena may be greatly affected by even a small strain in the HgTe-CdTe superlattice, where the relative difference between the lattice constants is only 0.3%. The optical properties of the HgTe-CdTe superlattice is studied for a wide range of valence band offset which is defined as the valence band edge of HgTe relative to that of CdTe and whose value is currently an unsettled issue. Both the band gap and absorptions of the superlattice are found to decrease rapidly for both negative and large positive values of offset.
\r\n\r\nChapter 5 considers the wide-gap Cd\u2081\u208b\u2093Mn\u2093Te/Cd\u2081\u208byMnyTe superlattice and the narrow-gap Hg\u2081\u208b\u2093Mn\u2093Te/Cd\u2081\u208byMnyTe superlattices. Currently, the wide-gap system is of great interest because of the possibility of using it as magnetically tunable laser material. In the system spin-splitting is enhanced by the exchange interaction between the localized 3d electrons of Mn\u207a\u207a and band electrons. The spin-splitting reduces the band gap opposing to the Landau level shift which enlarges the gap. However, the spin-splitting is found to dominate in the system. In consequence, the band gap decreases in a magnetic field. However, the relative change in the band gap is shown to be small. This makes suspect the idea of fabricating magnetically tunable laser out of this system. Interesting results concerning dependences of magnetic effects on temperature, magnetic field and layer thicknesses are presented. Generally speaking, temperature randomizes the spin oreintation while magnetic field aligns Mn\u207a\u207a spins. In thin-layer limit, the magnetic effect in the superlattice is found to be just that of an alloy corresponding in composition to the superlattice. In contrast, the narrow-gap system is found to have larger tunability. Due to small effective mass of electrons, the Landau level shift is found to be important. Results regarding dependences of magnetic effects on temperature, magnetic field and valence band offset are shown.
\r\n\r\nChapter 6 presents the theory and results of electronic tunneling in AlGaAs multi-barrier structures. The observation of negative differential resistance of the structure has been reported. However, basic mechanisms of current conduction in the structure have not been fully understood. We have made study of inelastic electronic tunneling due to electron-phonon coupling in a double-barrier structure. The current induced by the inelastic tunneling of electrons is calculated. The main result is that the inelastic process results in a much larger current than the elastic process at the voltage bias where no resonant tunneling occurs. Dependences of the inelastic contribution on doping level and layer thickness are discussed.
" }, { "name": "Yu, Jeffrey Winston", "degree": "PhD", "year": "1988", "title": "Optical Processing Using Photorefractive Crystals", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012007-140044", "creators": [ { "name": { "family": "Yu", "given": "Jeffrey Winston" }, "id": "Yu-Jeffrey-Winston", "display_name": "Yu, Jeffrey Winston" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Breckinridge", "given": "James B." }, "id": "Breckinridge-James-B", "role": "member", "display_name": "Breckinridge, James B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/q49d-bb74", "abstract": "The ability of photorefractive crystals to holographically record an optical image in real time allows one to use them in a variety of optical information processing systems. A number of such systems are presented in this thesis. To form the ground work used in analyzing the performance of photorefractive optical processors, a comparison between the Kukhtarev and Moharam models was done. The regimes where each model sufficiently predicted the response of the photorefractive crystal was determined. In addition, a new model based on a higher perturbation expansion of Kukhtarev's material equation is presented. This method allows one to numerically derive the profile of the space charge field recorded in the crystal and predict the regime where the Kukhtarev and Moharam models are most accurate.
\r\n\r\nThree optical processing systems are presented. The first, a photorefractive incoherent to coherent converter (PICOC), utilizes a photorefractive crystal as a spatial light modulator. Both the Kukhtarev and higher expansion models were used to analyze the performance of the converter. In the second example, the use of a photorefractive crystal as a time integrating detector is presented. By utilizing this crystal in an acousto-optic time integrating correlator, the output correlation is presented without the bias inherent in standard time integrating architectures. This allows one to utilize the full dynamic range of the output detector, thereby increasing the processing gain of the system. The third example utilizes a photorefractive crystal in a VanderLugt correlator. Standard VanderLugt correlators using planar holograms have been used successfully in pattern classification. In this thesis, we will derive the capacity of this system and demonstrate that by using a photorefractive crystal as the storage medium, the volume holographic properties of the crystal results in an increase in the capacity of the system. In addition, the angular selectivity of the crystal allows one to perform multi-category classification. The effect of using a volume hologram in a VanderLugt correlator is analyzed and experimental results presented.
" }, { "name": "Arakeri, Jaywant H.", "degree": "PhD", "year": "1987", "title": "Structure Measurements in a Synthetic Turbulent Boundary Layer", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-085206", "creators": [ { "name": { "family": "Arakeri", "given": "Jaywant H." }, "id": "Arakeri-Jaywant-H", "display_name": "Arakeri, Jaywant H." } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FABW-YZ77", "abstract": "Extensive hot-wire measurements have been made to determine the structure of the large eddy in a synthejc turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number.
\r\n\r\nThe large eddy is composed of a pair of primary counter-rotating vortices about five \u03b4 long in the streamwise direction and about one \u03b4 apart in the spanwise direction, where \u03b4 is the mean boundary-layer thickness. The sense of the primary pair is such as to pump fluid away from the wall in the region between the vortices. A secondary pair of counter-rotating streamwise vortices, having a sense opposite to that of the primary pair, is observed outside of and slightly downstream from the primary vortices. Both pairs of vortices extend across the full thickness of the boundary layer and are inclined at a shallow angle to the surface of the flat plate. The data show that the mean vorticity vectors are not tangential to the large-eddy vortices. In fact, the streamwise and normal vorticity components that signal the presence of the eddy are of the same order of magnitude. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal vorticity in the outer flow. A stretching mechanism is important in matching spanwise vorticity close to the wall to variations in turbulent shearing stress. Regions where the stretching term is large coincide with regions of large wall shearing stress and large turbulence production.
" }, { "name": "Arnold, Robert Glenn", "degree": "PhD", "year": "1987", "title": "Dissimilative Fe(III) Reduction by Pseudomonas sp. 200", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182008-132957", "creators": [ { "name": { "family": "Arnold", "given": "Robert Glenn" }, "id": "Arnold-Robert-Glenn", "display_name": "Arnold, Robert Glenn" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Bailey", "given": "James E." }, "id": "Bailey-J-E", "role": "member", "display_name": "Bailey, James E." }, { "name": { "family": "Emr", "given": "Scott D." }, "id": "Emr-S-D", "role": "member", "display_name": "Emr, Scott D." }, { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "member", "display_name": "North, Wheeler J." } ], "option_major": [ "envreng" ], "doi": "10.7907/xsas-dd69", "abstract": "The feasibilities of (i) liberating free energy from dissimilative iron reduction and (ii) coupling oxidative phosphorylation to electron transport to Fe(III) are sensitive to the aqueous chemistry of iron. The addition of ligands, such as nitrilotriacetic acid (NTA), to solution significantly impacts both the overall thermodynamics and kinetics of dissimilative iron reduction. The overall free-energy change due to electron transfer from glucose or lactate ion to Fe(III) is negative, but when Fe(III) is presented as an iron oxide there may be insufficient free energy in the transformations to permit coupled ATP generation. A systematic investigation of iron-reduction kinetics as a function of Fe(III) speciation indicated that in Pseudomonas sp. 200 (i) iron-reduction rate was functionally related to the concentrations of individual iron species and (ii) direct contact between Fe(III) and the electron-transport chain (ferrireductase) was required for electron transfer. Iron reduction in the absence of microbial activity was negligible. The addition of equimolar quantities of NTA enormously accelerated the initial rate of microbial iron reduction, and the calculated concentration of Fe(NTA)(OH)22- correlated strongly with measured iron-reduction rates.
\r\n\r\nWhen Fe(III) was provided as an iron oxide, the overall reduction rate was much slower, though still dependent upon the concentration of NTA added to solution. Primary factors controlling mineral dissolution and Fe(III) reduction were mineral surface area (or concentration of high-energy surface sites), ligand concentration, and cell number. Saturation kinetics were evident, as indicated by the following relationship governing reductive dissolution of hematite:
\r\n\r\nd[Fe(II)] / dt = Vmax(I)Km(NTA)Vmax(II)[NTA] / Km(NTA) + [NTA] \u2022 [Fe(III)] / Km(Fe) + [Fe(III)]
\r\n\r\nwhere Vmax(I) = 2.8 x 10-5 M\u2022hr-1
\r\n \r\nVmax(II) = 6.3 x 10-4 M\u2022hr-1
\r\n\r\nKmax(NTA) = 1.2 x 10-3 M
\r\n\r\nKmax(Fe) = 1.0 x 10-1 M (as Fe)
\r\n\r\nNTA = nitrilotriacetic acid
\r\n\r\n[Fe(III)] = volume concentration of hematite (as Fe).
\r\n\r\nExperiments involving oxide/microorganism separation indicated that cell/mineral contact was essential to reductive dissolution of goethite.
\r\n\r\nSpecific respiratory inhibitors were utilized to identify elements of electron transport chains involved in reduction of molecular oxygen and Fe(III) and to compare transport-chain compositions of cells grown under high- versus limited-O2 conditions. Pseudomonas sp. 200 expressed both a constitutive (cytochrome o) and an inducible (cytochrome d) cytochrome oxidase. Induction of the alternate transport pathway resulted from growth at low oxygen tension (<0.01 atm.). Induced cells were capable of O2 utilization at moderately increased rates. Pseudomonas sp. 200 also expressed a constitutive and an inducible ferrireductase. Growth at low oxygen tension resulted in acceleration of the overall rate of dissimilative iron reduction by a factor of 6 to 8, but iron reduction appeared to be uncoupled from oxidative phosphorylation. Maximum rates of electron transfer in induced cells were independent of the identity of the electron acceptor indicating a common rate-limiting step. Dissimilative iron reduction occurred via an abbreviated electron transport chain in both the induced and uninduced cases. Electron-transport-chain compositions for the induced and uninduced cases are postulated.
\r\n" }, { "name": "Athas, William C., Jr.", "degree": "PhD", "year": "1987", "title": "Fine Grain Concurrent Computations", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282008-091326", "creators": [ { "name": { "family": "Athas", "given": "William C., Jr." }, "id": "Athas-William-C-Jr", "display_name": "Athas, William C., Jr." } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "chair", "display_name": "Seitz, Charles L." }, { "name": { "family": "Feynman", "given": "Richard Phillips" }, "id": "Feynman-R-P", "role": "member", "display_name": "Feynman, Richard Phillips" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "compsci" ], "doi": "10.7907/63xc-r308", "abstract": "This thesis develops a computational model, a programming notation, and a set of programming principles to further and to demonstrate the practicality of programming fine grain concurrent computers.
\r\n\r\nPrograms are expressed in the computational model as a collection of definitions of autonomous computing agents called objects. In the execution of a program, the objects communicate data and synchronize their actions exclusively by message-passing. An object executes its definition only in response to receiving a message, and its actions may include sending messages, creating new objects, and modifying its own internal state. The number of actions that occur in response to a message is finite; Turing computability is achieved not within a single object, but through the interaction of objects.
\r\n\r\nA new concurrent programming notation Cantor is used to demonstrate the cognitive process of writing programs using the object model. Programs for numerical sieves, sorting, the eight queens problem, and Gaussian elimination are fully described. Each of these programs involve up to thousands of objects in their exectuion. The general programming strategy is to first partition objects by their overall behavior and then to program the behaviors to be self-organizing.
\r\n\r\nThe semantics of Cantor are made precise through the definition of a formal semantics for Cantor and the object model. Objects are modelled as finite automata. The formal semantics is useful for proving program properties and for building frameworks to capture specific properties of object programs. The mathematical frameworks are constructed for building object graphs independently of program execution and for systematically removing objects that are irrelevant to program execution (garbage collection).
\r\n\r\nThe formal semantics are complemented by experiments that allow one to study the dynamics of the execution of Cantor programs on fine grain concurrent computers. The clean semantics of Cantor suggests simple metrics for evaluating the execution of concurrent programs for an ideal, abstract implementation. Program performance is also evaluated for environments where computing resources are limited. From the results of these experiments, hardware and software architectures for organizing fine grain message- passing computations is proposed, including support for fault tolerance and for garbage collection.
" }, { "name": "Bassiri, Sassan", "degree": "PhD", "year": "1987", "title": "Electromagnetic Wave Propagation and Radiation in Chiral Media", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282008-090141", "creators": [ { "name": { "family": "Bassiri", "given": "Sassan" }, "id": "Bassiri-Sassan", "display_name": "Bassiri, Sassan" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "chair", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" } ], "option_major": [ "eleceng" ], "doi": "10.7907/RFST-5K65", "abstract": "Propagation and radiation of electromagnetic waves in a lossless, reciprocal, chiral medium is studied in this thesis. Such a medium is described electromagnetically by the constitutive relations D = \u03b5E + i\u03b3B and H = i\u03b3E + (1/\u00b5)B. The constants \u03b5, \u00b5, \u03b3 are real and have values that are fixed by the size, shape, and the spatial distribution of the elements that collectively compose the medium. The plane wave propagation in an unbounded chiral medium is considered. The propagation constants are obtained and the polarization properties of electromagnetic waves in such a medium are discussed in detail. The problem of reflection from, and transmission through a semi-infinite chiral medium is solved by obtaining the Fresnel equations. The conditions for the total internal reflection of the incident wave from the interface, and the existance of the Brewster angle are obtained. The effects of the chirality on the polarization and intensity of the reflected wave from the chiral half-space are discussed and illustrated by employing the Stokes parameters. The propagation of electromagnetic waves through an infinite slab of chiral medium is formulated for oblique incidence and solved analytically for the case of normal incidence. The radiation emitted by an oscillating dipole in an unbounded, lossless, chiral medium is calculated. From the constitutive relations and from the time-harmonic Maxwell equations \u2207 x E = i\u03c9B and \u2207 x H = J - i\u03c9D, it is seen that the wave equation for such a medium is given by \u2207 x \u2207 x E - \u03c92\u00b5\u03b5E - 2\u03c9\u00b5\u03b3\u2207 x E = i\u03c9\u00b5J where the source term J is the current density of the oscillating dipole and where E is the electric vector of the radiated field. The desired solution of this wave equation is found by the dyadic Green's function method, that is, by first constructing the dyadic Green's function \u0393 and then evaluating the expression E = i\u03c9\u00b5\u222b\u0393(r,r')\u2022J(r')dV'. The dyadic Green's function \u0393 and the components of the radiated electric field E are obtained in closed form. The components of the radiated B, D, and H fields can be derived from knowledge of E by using the Maxwell equation B = (1/i\u03c9)\u2207 x E and the constitutive relations. The wave impedance of the medium and the radiation resistance of the dipole are also obtained. The effects of the chiral medium on the polarization and intensity of the dipole radiation are discussed.
" }, { "name": "Bonnefoi, Alice Ren\u00e9e", "degree": "PhD", "year": "1987", "title": "Electronic Properties and Device Applications of GaAs/Al\u2093Ga\u2081\u208b\u2093As Quantum Barrier and Quantum Well Heterostructures", "advisor": "McGill, Thomas C.; Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012008-132010", "creators": [ { "name": { "family": "Bonnefoi", "given": "Alice Ren\u00e9e" }, "id": "Bonnefoi-Alice-Ren\u00e9e", "display_name": "Bonnefoi, Alice Ren\u00e9e" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "co-advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/c4q6-2176", "abstract": "This thesis presents an experimental and theoretical study of some of the electronic properties and device applications of GaAs/AlxGa1-xAs single and double barrier tunnel structures. In Chapter 2, energy band diagrams are calculated for heterostuctures in which tunneling occurs between two degenerately doped electrodes separated by a single quantum barrier. When a bias voltage is applied to a structure, the energy band profile gives the voltage drop distribution in the cladding layers as well as in the barrier. This distribution may differ significantly from that based on the commonly made assumption that the entire applied voltage drops linearly across the barrier layer. It is shown that band bending effects become more important for larger applied voltages, thicker barriers, smaller electrode doping densities and larger barrier doping concentrations. Energy band diagrams are found to be useful for calculating tunneling currents and determining what the dominant low temperature current transport mechanisms occurring in these structures are. In some cases, they reveal that these mechanisms are different from those predicted when band bending is neglected.
\r\n\r\nIn Chapter 3, elastic and inelastic tunneling processes are investigated in GaAs-AlAs-GaAs single barrier heterostructures grown on [100]-oriented substrates. The GaAs electrodes are degenerately doped n-type with Se, and the AlAs quantum barriers are doped either p-type with Mg or n-type with Se. In p-type barrier structures, low temperature current transport is found to be dominated by elastic and inelastic electron tunneling through the AlAs band gap at the \u0393-point and at the X-point. Anomalous zero-bias conductances obtained from several of the samples are also discussed. A theoretical model, which treats trap levels in the AlAs barrier as intermediate states for two-step tunneling processes shows that impurity-assisted tunneling becomes more important as the tunnel barrier is made thicker. In heterostructures in which the n-type barrier layers are thick enough and/or sufficiently doped, the AlAs conduction band at the X-point is not totally depleted of electrons. The dominant low temperature current transport mechanism is then tunneling through two reduced AlAs X-point barriers separated by a bulk region of AlAs. When the n-type AlAs barrier layer is sufficiently thin, the AlAs conduction band remains fully depleted of carriers. As a result, electrons tunnel through the AlAs band gap at the X-point and/or at the \u0393-point in a one-step process. In these structures, it is found that plasmons located near the GaAs/AlAs interfaces interact with GaAs and AlAs longitudinal optical (LO) phonons when the doping density in the n-type GaAs electrodes is such that the plasma frequency becomes comparable to the LO phonon frequencies.
\r\n\r\nChapter 4 presents a study of resonant tunneling in GaAs/AlxGa1-xAs double barrier heterostructures grown epitaxially in the [100]-direction. In these structures, electrons tunnel through two AlxGa1-xAs quantum barriers separated by a thin GaAs layer forming a quantum well. The resonant energy levels in the GaAs well which produce negative differential resistances in the experimental I-V characteristics are identified by calculating the energy band diagrams of the structures. In samples having pure AlAs barrier layers, tunneling via resonant states confined in the well by the AlAs \u0393-point potential energy barriers is often inconsistent with experimental results. However, the experimental data can usually be explained by tunneling via quasi-stationary levels confined in the well by the AlAs X-point potential energy barriers as well as the AlAs \u0393-point barriers. The relative contributions of tunneling via resonant \u0393- and X-states in the well are found to depend upon the samples studied and sometimes upon the sign of the applied bias. Resonant tunneling is also investigated in double barrier heterostructures in which a low doped GaAs buffer layer is grown before the first AlxGa1-xAs barrier. As a result of this structural asymmetry, the peaks in current corresponding to a given resonant state in the quantum well may be observed in the experimental I-V characteristics at very different applied voltages in reverse bias than in forward bias.
\r\n\r\nIn Chapter 5, we propose and analyze two types of three-terminal devices based upon resonant tunneling through quantum well and quantum barrier heterostructures. The first type includes two configurations in which a base voltage controls the emitter-collector tunneling current by shifting the resonances in a quantum well. In the proposed devices, the relative positions of the base and collector are interchanged with respect to the conventional emitter-base-collector sequence as a means for obtaining negligible base currents and large current transfer ratios. The second type of three-terminal devices includes three configurations in which the current through a double barrier structure is modulated by a Schottky barrier gate placed along the path of the electrons. These devices feature, in their output current-voltage (ID-VD) curves, negative differential resistances controlled by a gate voltage.
\r\n\r\nChapter 6 presents a growth uniformity study performed on several of the heterostructures discussed in the thesis. First, the reproducibility and uniformity of the electrical characteristics of GaAs/AlAs tunnel structures are used to show that the doping concentrations and layer thicknesses are uniform across the samples under test. Secondly, discrete fluctuations in layer thicknesses are discussed in GaAs/Al0.35Ga0.65As double barrier heterostructures. These fluctuations are manifested by non-uniform experimental results and by sequences of negative differential resistances in the I-V characteristics of many devices.
" }, { "name": "Brewster, Mary Elizabeth", "degree": "PhD", "year": "1987", "title": "Asymptotic Analysis of Thin Plates Under Normal Load and Horizontal Edge Thrust", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechTHESIS:03212013-094948659", "creators": [ { "name": { "family": "Brewster", "given": "Mary Elizabeth" }, "id": "Brewster-Mary-Elizabeth", "display_name": "Brewster, Mary Elizabeth" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "chair", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "appmath" ], "doi": "10.7907/DDP9-KW92", "abstract": "We consider the radially symmetric nonlinear von K\u00e1rm\u00e1n plate equations for circular or annular plates in the limit of small thickness. The loads on the plate consist of a radially symmetric pressure load and a uniform edge load. The dependence of the steady states on the edge load and thickness is studied using asymptotics as well as numerical calculations. The von K\u00e1rm\u00e1n plate equations are a singular perturbation of the F\u04e7ppl membrane equation in the asymptotic limit of small thickness. We study the role of compressive membrane solutions in the small thickness asymptotic behavior of the plate solutions.
\r\n\r\nWe give evidence for the existence of a singular compressive solution for the circular membrane and show by a singular perturbation expansion that the nonsingular compressive solutions approach this singular solution as the radial stress at the center of the plate vanishes. In this limit, an infinite number of folds occur with respect to the edge load. Similar behavior is observed for the annular membrane with zero edge load at the inner radius in the limit as the circumferential stress vanishes.
\r\n\r\nWe develop multiscale expansions, which are asymptotic to members of this family for plates with edges that are elastically supported against rotation. At some thicknesses this approximation breaks down and a boundary layer appears at the center of the plate. In the limit of small normal load, the points of breakdown approach the bifurcation points corresponding to buckling of the nondeflected state. A uniform asymptotic expansion for small thickness combining the boundary layer with a multiscale approximation of the outer solution is developed for this case. These approximations complement the well known boundary layer expansions based on tensile membrane solutions in describing the bending and stretching of thin plates. The approximation becomes inconsistent as the clamped state is approached by increasing the resistance against rotation at the edge. We prove that such an expansion for the clamped circular plate cannot exist unless the pressure load is self-equilibrating.
" }, { "name": "Burridge, Paul Brian", "degree": "PhD", "year": "1987", "title": "Failure of Slopes", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012008-132659", "creators": [ { "name": { "family": "Burridge", "given": "Paul Brian" }, "id": "Burridge-Paul-Brian", "display_name": "Burridge, Paul Brian" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "chair", "display_name": "Scott, Ronald F." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Sieh", "given": "Kerry E." }, "id": "Sieh-K-E", "role": "member", "display_name": "Sieh, Kerry E." } ], "option_major": [ "civileng" ], "doi": "10.7907/2C4G-6R71", "abstract": "The dynamic mechanism of slope failure is studied both experimentally and analytically to establish the spatial and temporal process of failure initiation and propagation during collapse of a natural or man-made slope.
\r\n\r\nModel slopes, constructed of a brittle cemented sand material, are tested to collapse in a geotechnical centrifuge and the dynamics of failure recorded by motion picture film and mechanical detectors within the slope specimen. Shear failure is observed to initiate at the toe and propagate rapidly to the crest in the presence of crest tension cracking.
\r\n\r\nA finite difference approach is taken to numerically solve the plane strain slope stability problem under gravity, based on unstable material behavior. Using a Lagrangian differencing scheme in space and explicit integration in time with dynamic relaxation, the numerical method finds the equilibrium state of the slope as the large-time limit of a dynamic problem with artificial parameters. The solution predicts localized shear failure zones which initiate at the slope toe and propagate to the slope crest in the manner and geometry observed in the centrifuge tests. In so doing, the finite difference algorithm also demonstrates an apparent ability to predict shear failure mechanisms in solid continua in general.
\r\n" }, { "name": "Cheng, Yang-Tse", "degree": "PhD", "year": "1987", "title": "Ion-Beam Mixing and the Formation of Amorphous Alloys", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012008-133433", "creators": [ { "name": { "family": "Cheng", "given": "Yang-Tse" }, "id": "Cheng-Yang-Tse", "display_name": "Cheng, Yang-Tse" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/W1Y4-0347", "abstract": "Ion beam interactions with solids have been of significant interest to both academic and industrial researchers for more than half a century. Looking back into the history of its development, one finds prominent names such as Bohr, Fermi, and Bethe, closely associated with the early development of this area of scientific research. Their efforts in understanding the interatomic potential of ions and atoms have led to the knowledge of ion penetration depth and energy loss in solids. It was also one of the early successful applications of the newly born quantum mechanics.
\r\n\r\nThe subsequent development of the range theory by Lindhard, Scharff, and Schioff in the early sixties (LSS theory) enables one to calculate the ion penetration depth in elemental solids to even greater accuracy and provides the basis for the realization of ion implantation technology.
\r\n\r\nSwelling of reactor materials, caused by ion irradiation, was first observed in austenitic steel in 1967 by a group of British scientists. Such radiation damage drew unprecedented attention of people from both academia and industry to the problem of ion-solid interactions. Irradiation-induced structural and phase changes in materials have since become a major part of the active research in ion beam interactions with solids.
\r\n\r\nIon implantation, which originated in the early 1960s, revolutionized the microelectronics industry. Because of the development of the range theory, ion implantation offered precise control over the number and depth of dopant atoms in semiconductor materials, making possible the miniaturization of electronic devices. Meanwhile, various ion beam analysis techniques, such as RBS (Rutherford Backscattering Spectrometry), developed rapidly and were applied to study problems ranging from Moon rocks to electronic devices.
\r\n\r\nAround 1972, while studying ion implantation in Si through an Al overlayer, D. H. Lee, O. J. Marsh, and R. R. Hart of the Hughes Research Laboratories observed coloration of the surface layer. Using RBS and optical reflectance measurements, they determined that the coloration was due to the migration of Si to the surface of the sample under the influence of ion bombardment. In another case, they observed Pt2Si formation due to mixing of the Si and the Pt overlayer caused by ion implantation. Soon it was found that metastable phases as well as equilibrium phases could be obtained by this type of ion beam-induced mixing phenomena, more commonly called ion mixing processes.
\r\n\r\nToday, ion implantation has found further applications in areas such as corrosion resistance, reduction of wear and friction, and improvement of adhesion. Ion mixing has been viewed as a powerful extension of the traditional ion implantation technology. It provides new challenges to fundamental research in ion-solid interactions and offers new promises to further industrial applications.
\r\n\r\nTwo issues are considered of fundamental importance and are treated in this thesis:
\r\n\r\nI. Mechanisms of ion-beam-induced mixing in solids.
\r\n\r\nII. The formation of amorphous alloys.
\r\n\r\nIn Part I, several aspects of the mixing mechanisms, such as the influence of chemical driving force, the influence of cohesive energy, a newly developed phenomenological model of ion mixing, and a correlation between the cohesive energy and the onset of radiation-enhanced diffusion will be discussed. Also in this part, the evolution of collisional cascades will be studied by using a fractal geometry approach. In Part II, mechanisms of amorphous alloy formation are discussed. Comparisons between amorphous alloy formation by ion mixing and by solid-state reaction illustrate various aspects of glass formation.
" }, { "name": "Cheung, Kar-Ming", "degree": "PhD", "year": "1987", "title": "Error-Correction Coding in Data Storage Systems", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282008-133009", "creators": [ { "name": { "family": "Cheung", "given": "Kar-Ming" }, "id": "Cheung-Kar-Ming", "display_name": "Cheung, Kar-Ming" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Swanson", "given": "Larry W." }, "id": "Swanson-L-W", "role": "member", "display_name": "Swanson, Larry W." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/emtw-yh64", "abstract": "This thesis is divided into two parts. The first part is a study of the decoder error probability of linear maximum distance separable (MDS) codes. An exact formula for the decoder error probability of linear MDS codes is derived. The random characteristic of this class of codes is analyzed, and a lower bound for the decoder error probability is given. The second part is a study of error-correction coding in data storage systems, particularly in tape machines. The helical interleaving scheme is generalized from single channel to n parallel channels. A new code, which is specially designed for tape machines, is introduced. This code corrects more error patterns than the AXP code, and it possesses a simple hardware structure. Lastly, a class of error-correcting DC free trellis code, and a class of error-correcting RLL code are introduced.
\r\n" }, { "name": "Chobotov, Michael V.", "degree": "PhD", "year": "1987", "title": "Gravity Currents with Heat Transfer Effects", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-134449", "creators": [ { "name": { "family": "Chobotov", "given": "Michael V." }, "id": "Chobotov-Michael-V", "display_name": "Chobotov, Michael V." } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/3rnv-em84", "abstract": "A two part experimental study of gravity currents flowing in horizontal channels is performed. The first of these examines adiabatic aqueous flows, and the second, heat transferring gaseous currents. Video photography of dyed saline current fronts flowing into a fresh-water-filled duct allows for front velocity measurements and the study of qualitative flow features such as current head structure, mixing, and layer thickness. In conjunction with previous works, a model of gravity current entrainment is presented. The effects of viscosity are examined in the transition from constant velocity flow to a decelerating, viscous dominated flow regime. This transition is shown to occur at a streamwise position that is a function only of the current layer thickness, and not of Reynolds number, as previously believed.
\r\n\r\nTo examine the effects which the reduction of buoyant forces due to heat loss has on gravity current flow, heated gaseous flows in another experimental facility are studied. A smoke flow-visualization technique is developed, and together with fine gauge thermocouples, heat flux gauges, and shadowgraphy, provides for flow measurement. Front velocities, layer thicknesses, wall heat fluxes, layer velocity and temperature profiles, and qualitative flow characteristics are recorded. The thermal front, with its constant channel-ceiling-temperature boundary condition, is found to decelerate as it moves downstream, while the layer thickness is seen to increase. Layer Richardson number is found to be constant along the streamwise direction of the flow, and an empirical relation for Nusselt number versus Reynolds number is obtained. Free convection in the form of longitudinal roll cells is shown to promote the high levels of heat transfer measured. A flow modeling scheme based on experimental observations is also developed.
" }, { "name": "Choo, Young-il", "degree": "PhD", "year": "1987", "title": "Logic from Programming Language Semantics", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282008-111427", "creators": [ { "name": { "family": "Choo", "given": "Young-il" }, "id": "Choo-Young-il", "display_name": "Choo, Young-il" } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "member", "display_name": "Thompson, Frederick B." }, { "name": { "family": "Kechris", "given": "Alexander S." }, "id": "Kechris-A-S", "role": "member", "display_name": "Kechris, Alexander S." }, { "name": { "family": "Moschovakis", "given": "Yiannis N." }, "id": "Moschovakis-Yiannis-N", "role": "member", "display_name": "Moschovakis, Yiannis N." } ], "option_major": [ "compsci" ], "doi": "10.7907/r9hf-1b88", "abstract": "Logic for reasoning about programs must proceed from the programming language semantics. It is our thesis that programs be considered as mathematical objects that can be reasoned about directly, rather than as linguistic expressions whose meanings are embedded in an intermediate formalism.
\r\n\r\nSince the semantics of many programming language features (including recursion, type-free application, infinite structures, self-reference, and reflection) require models that are constructed as limits of partial objects, a logic for dealing with partial objects is required.
\r\n\r\nUsing the D\u221e model of the \u03bb-calculus, a logic (called continuous logic) for reasoning about partial objects is presented. In continuous logic, the logical operations (negation, implication, and quantification) are defined for each of the finite levels and then extended to the limit, giving us a model of type-free logic.
\r\n\r\nThe triples of Hoare Logic are interpreted as partial assertions over the domain of partial states, and contradictions arising from rules for function definitions are analyzed. Recursive procedures and recursive functions are both proved using mathematical induction.
\r\n\r\nA domain of infinite lists is constructed as a model for languages with lazy evaluation and it is compared to an ordinal-heirarchic construction. A model of objects and multiple inheritance is constructed where objects are self-referential states and multiple inheritance is defined using the notion of product of classes. The reflective processor for a language with environment and continuation reflection is constructed as the projective limit of partial reflective processors of finite height.
" }, { "name": "Compton, Richard C.", "degree": "PhD", "year": "1987", "title": "Analysis of Millimeter and Microwave Integrated Circuits", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02282008-135956", "creators": [ { "name": { "family": "Compton", "given": "Richard C." }, "id": "Compton-Richard-C", "display_name": "Compton, Richard C." } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "member", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Pickett", "given": "Herbert M." }, "id": "Pickett-H-M", "role": "member", "display_name": "Pickett, Herbert M." }, { "name": { "family": "Alexopoulos", "given": "Nicolaos G." }, "id": "Alexopoulos-Nicolaos-G", "role": "member", "display_name": "Alexopoulos, Nicolaos G." } ], "option_major": [ "eleceng" ], "doi": "10.7907/P7EA-S138", "abstract": "The design and measurement of millimeter and microwave integrated circuits encompasses a diverse spectrum of interesting disciplines. A number of contrasting approaches used for theoretically and experimentally characterizing circuits in this frequency range will be presented. Rigorous methods for calculating antenna patterns and impedances of the planar bow-tie antenna used in millimeter wave receiver systems have been developed. A 94 GHz antenna measurement system and microwave scale models were constructed to confirm these theoretical predictions. Pattern measurements were also made on a linear array of bow-tie antennas, a long strip antenna, and a log-periodic antenna. In modified form, these techniques were applied to the investigation of planar array structures. An equivalent circuit model for an array of squares joined at the corners by discrete devices was formulated. This model was verified with impedance and pattern measurements. Finally, a set of analysis tools that have been assembled into an interactive computer-aided design program, called Puff, is discussed. Puff has been used in microwave laboratory classes at the California Institute of Technology, Cornell University and the University of California, Los Angeles.
\r\n" }, { "name": "Dailey, Russell Lane", "degree": "PhD", "year": "1987", "title": "Conic Sector Analysis for Digital Control Systems with Structured Uncertainty", "advisor": "Doyle, John Comstock", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-093526", "creators": [ { "name": { "family": "Dailey", "given": "Russell Lane" }, "id": "Dailey-Russell-Lane", "display_name": "Dailey, Russell Lane" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "advisor", "display_name": "Doyle, John Comstock" } ], "committee": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "role": "chair", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/gz0q-x789", "abstract": "This thesis presents a method which greatly reduces the conservativeness of conic sector analysis for sampled data feedback systems. The new method evaluates the stability and closed-loop performance of systems with structured uncertainty in the plant transfer function, including MIMO systems and those with multiple sampling rates. In contrast to most multirate analysis techniques, the sampling rates need not be related by rational numbers; this allows analysis when samplers are not strobed to a common clock.
\r\n\r\nThe method is based on a theorem from P. M. Thompson which shows how to construct a conic sector containing a hybrid operator. Combining this theorem with the Structured Singular Value approach of J. C. Doyle, with its heavy use of diagonal scaling, provides an analysis framework for systems with multiple structured plant perturbations. Chapter 3 presents a theorem for the optimal conic sector radius in the SISO case; a MIMO extension of the the theorem completes the development of the new method. Chapter 5 gives three examples.
\r\n\r\nChapter 6 presents a new method, based on the complex cepstrum, for synthesis of SISO rational functions to match given \"target\" transfer functions. The method offers complete control over stability and right half plane zeros. It solves directly for poles and zeros, avoiding the numerical sensitivity of methods which solve for polynomial coefficients. It can synthesize minimum phase functions to match a given magnitude or phase curve. In an example, it is used to synthesize a low- order digital replacement for an analog compensator which gives no degradation of stability margin or step response.
\r\n\r\nThis thesis also presents a method for Kranc vector switch decomposition in state space; this is for stability analysis and input-output simulation of perturbed multirate systems. Moving the 30-year-old Kranc technique from the frequency domain to the state-space domain simplifies the analysis tremendously. Because the number of states is preserved, the dimensionality problems long associated with the Kranc method disappear. The new method is also useful for simulating intersample ripple behavior.
" }, { "name": "Do\u011fanata, Yurdaer Nezihi", "degree": "PhD", "year": "1987", "title": "Analysis of Traffic Problems of Integrated Networks", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012008-131442", "creators": [ { "name": { "family": "Do\u011fanata", "given": "Yurdaer Nezihi" }, "id": "Do\u011fanata-Yurdaer-Nezihi", "display_name": "Do\u011fanata, Yurdaer Nezihi" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Lorden", "given": "Gary A." }, "id": "Lorden-G-A", "role": "member", "display_name": "Lorden, Gary A." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/d844-3g40", "abstract": "A new approach to the analysis of Markovian queueing networks is developed and applied to traffic problems of voice-data integration networks and trunked mobile radio networks. This approach is shown to be computationally much less complex for large systems compared to previous work.
\r\n\r\nIn the integrated networks we consider, two classes of users share the system facilities. If all the servers are busy, the first class of users are queued, but the second class of users are blocked and cleared from the system. The performance objective of such an integrated network is to trade the time delay performance of the first class of users against the blockage performance of the second class of users to keep the grade of service as high as possible for both classes of traffic.
\r\n\r\nThe key-state approach introduced in this thesis is what makes the analysis of the corresponding Markovian queueing network model of these integrated networks computationally less complex than that of previous work. The performance of integrated networks is investigated under several control strategies and new exact closed-form expressions are obtained for the equilibrium probabilities of the corresponding Markovian models. The results are extended to a more general Markovian process where a bulk of arrivals and departures are allowed.
\r\n\r\nThe key-state approach is expected to become a standard tool for analyzing large queueing networks such as will arise when Integrated Services Digital Networks (ISDN) become widely deployed in the next five years.
" }, { "name": "Fanson, James L.", "degree": "PhD", "year": "1987", "title": "An Experimental Investigation of Vibration Suppression in Large Space Structures Using Positive Position Feedback", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-08112005-104730", "creators": [ { "name": { "family": "Fanson", "given": "James L." }, "id": "Fanson-James-L", "display_name": "Fanson, James L." } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "role": "member", "display_name": "Morari, Manfred" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Chen", "given": "Jay-Chung" }, "id": "Chen-Jay-Chung", "role": "member", "display_name": "Chen, Jay-Chung" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/0SA8-HW86", "abstract": "A new technique for vibration suppression in Large Space Structures is demonstrated in laboratory experiments on a thin cantilever beam, resulting in substantially reduced dynamic response. This technique, called Positive Position Feedback, makes use of generalized displacement measurements to accomplish vibration suppression.
\r\n\r\nThe concept of a piezoelectric active-member is developed in relation to controlling space-truss type structures. The active-member functions dually as a structural member and a control actuator. Piezoelectric ceramic material is adhered to a thin cantilever beam and simulates the use of an active-member. This space-realizable control scheme makes use of strain measurements, a preferred measurement quantity for vibration suppression, and internal control forces which completely decouple the rigid-body motion from the elastic motion.
\r\n\r\nA simple necessary and sufficient condition for stability with Positive Position Feedback is presented. This condition is non-dynamic and is in general easily satisfied. As a result, Positive Position Feedback is demonstrated to have superior robust stability properties. It is also demonstrated that with Positive Position Feedback, all control and observation spillover is stabilizing. Five experiments are described in which the first six modes of vibration of the cantilever beam are controlled.
\r\n" }, { "name": "Hannoun, Imad A.", "degree": "PhD", "year": "1987", "title": "Turbulent Mixing in Stably-Stratified Fluids Subjected to Zero-Mean Shear", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechETD:etd-03032008-132151", "creators": [ { "name": { "family": "Hannoun", "given": "Imad A." }, "id": "Hannoun-Imad-A", "display_name": "Hannoun, Imad A." } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "chair", "display_name": "List, E. John" }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "civileng" ], "doi": "10.7907/N4NS-MP03", "abstract": "The interaction of a sharp density interface with oscillating grid induced shear-free turbulence was experimentally investigated. A linear photodiode array was used in conjunction with laser-induced fluorescence to measure the concentration of a tracer that was initially located in the less dense layer. A laser-Doppler velocimeter was used to measure the vertical component and a horizontal component of velocity near the interface, and also at a point where tracer concentration was measured. Potential refractive index fluctuation problems were avoided using solutes that provided a homogeneous optical environment. The study consists of two major parts.
\r\n\r\nIn the first part of the investigation, energy spectra, velocity correlations, and kinetic energy fluxes were measured. Amplification of the horizontal turbulent velocity fluctuations, coupled with a sharp reduction in the vertical velocity fluctuation level, was observed near the density interface. Moreover, the experiments indicate that the density interface acts in a manner qualitatively similar to a rigid flat plate inserted in the flow. These findings are in agreement with previous results pertaining to shear-free turbulence near rigid walls (Hunt and Graham 1978).
\r\n\r\nIn the second part of the investigation, internal wave spectra, wave amplitudes and velocities, and the interfacial mixing layer thickness were measured. The results indicate that mixing occurs in intermittent bursts and that the local gradient Richardson number J remains constant for a certain range of the overall Richardson number Rj. The spectra of the internal waves decay as f-3 at frequencies below the maximum Brunt-V\u00e4is\u00e4l\u00e4 frequency. These findings give support to a model of oceanic turbulence proposed by Phillips (1977) in which the internal waves are limited in their spectral density by sporadic local instabilities and breakdown to turbulence. The results also indicate that, for a certain Rj range, the thickness of the interfacial layer (normalized by the integral lengths scale of the turbulence)is a decreasing function of Rj. At sufficiently high Rj the interfacial thickness becomes limited by diffusive effects. A simple model for entrainment at a density interface in the presence of shear-free turbulence is presented and compared with the observations.
" }, { "name": "Hauenstein, Robert Joseph", "degree": "PhD", "year": "1987", "title": "Investigations of Single-Crystal Silicide/Silicon Structures", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-082930", "creators": [ { "name": { "family": "Hauenstein", "given": "Robert Joseph" }, "id": "Hauenstein-Robert-Joseph", "display_name": "Hauenstein, Robert Joseph" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8hdm-m814", "abstract": "This thesis concerns the topic of molecular beam epitaxial (MBE) growth on Si, and presents work related to different aspects of this central topic. We have experimentally investigated the electronic properties of structurally near-perfect, metal-semiconductor interfaces involving metallic, transition-metal silicide films, grown epitaxially on Si by MBE. In particular, measurements of the Schottky barrier height of single-crystal, metal-semiconductor structures has been performed. In addition, inelastic electron tunneling spectroscopy has been used to look for elementary excitations of single-crystal, metal-semiconductor interfaces. Other work presented here concerns the building of a \"home-made\" Si MBE growth apparatus. Lastly, we present theoretical work on a topic unrelated to Si MBE; namely, the calculation of vibrational modes of point-defects in semiconductors.
\r\n\r\nIn Chapter 2, the Schottky barrier heights of high quality, type-A and type-B NiSi2/Si structures are measured, with the use of photoresponse and forward I-V techniques. This work is motivated by a recent controversy over the barrier heights of type-A and type-B structures. Our principal finding is that a substantial difference (greater than 0.1 eV) is observed in Schottky barrier height between the type-A and type-B oriented films. For type-A epitaxy, both measurement techniques consistently yield a Schottky barrier height \u03c6Bn of 0.62 \u00b1 0.01 eV. For the case of type-B, the I-V measurement yields a barrier height of 0.69 eV, in apparent disagreement with the photoresponse value (0.77 eV). Interpretation of the type-B photoresponse data is complicated by an unusual curvature in the plot of \u221aphotoresponse vs. photon energy. It is shown that both the detailed shape of the type-B photoresponse data, and the apparent inconsistency between photoresponse- and I-V-determined Schottky barrier height values can be quantitatively explained in terms of a phenomenological model, in which we represent the type-B interface as a mixture of regions of high and low Schottky barrier height (\u03c6hi and \u03c6lo), electrically in parallel with each other. In terms of this model, the type-B interface is explained as a mixed-barrier structure, having 91% areal coverage of \u03c6hi = 0.81 eV, and 9% of \u03c6lo = 0.64 eV.
\r\n\r\nIn Chapter 3, the first electron tunneling spectroscopy experiments on single-crystal, type-A and type-B NiSi2 films are described. For comparison, single-crystal CoSi2 films, and polycrystalline Au films, all grown on similar, degenerate, n-type Si substrates, are also studied. The purpose of this study is to see if crystalline perfection of the interface results in additional or enhanced structure in the electron tunnel spectrum, due to rigorous k||-conservation. This is not observed. Instead, we observe direct evidence of bulk, Si, k-conserving phonons assisting the transport of electrons through the Schottky barrier. Our electron tunneling spectra appear to to be independent of the identity, crystalline perfection, and crystallographic orientation of the metal layer. No enhancements or new features in our tunneling spectra due to the single-crystallinity of the silicide films are evident, suggesting that, the observed inelastic transport is dominated by bulklike processes excited within the tunneling barrier rather than by processes intrinsically related to the metal-semiconductor interface.
\r\n\r\nIn Chapter 4, the design and construction of a Si/silicide MBE growth system is presented. The original contribution in this work is the design of the apparatus: both of the overall system, and of its many detailed components. In particular, the design of this system reflects a number of issues which are of serious concern in state-of-the-art, Si MBE: the problem of unintentional p-type doping, the concern over the flaking of Si inside the growth chamber, and the accurate monitoring and control of substrate temperature. Most of the key assemblies, including the substrate heater, load-lock mechanism, sample holder, cryoshrouds, and shutter mechanism were designed and fabricated at Caltech. Our main result is the successful operation of this system. Preliminary silicide growth attempts demonstrate the ability of the system to perform closed-loop, rate-controlled depositions onto a heated Si substrate.
\r\n\r\nFinally, Chapter 5 involves the theoretical calculation of vibrational modes of point-defects in semiconductors. An understanding of such modes is useful in providing structural information about point-defects. Often, vibrational modes are observable by optical techniques. In our work, three distinct defect systems are investigated: substitutional oxygen on a phosphorus site in GaP (GaP:Op), substitutional and interstitial iron in Si (Si:Fe), and substitutional carbon on an arsenic site in GaAs (GaAs:CAs). Our theoretical method involves modeling the defect, e.g., in terms of masses and springs. In the calculation, the masses are known, but the spring constants near the defect are unknown, and varied as parameters. This requires a comparison with experimental data. For the GaP:Op defect, we predict and fit two main defect modes through the adjustment of parameters, and in the process, find detailed agreement between theory and experiment for several additional modes, also predicted by our calculation, but not involved in the fit. Our calculations provide the first coherent framework to account for details from many different optical measurements on the GaP:Op defect, within a single, theoretical description. We have also calculated the low-energy defect modes associated with Fe substitutional and interstitial defects in Si, to determine whether a frequency shift is expected upon the isotopic substitution, 54Fe \u2192 56Fe. The calculation predicts the existence of a single, low-energy mode, and that a frequency shift should occur, in disagreement with an experimental result. Our calculation demonstrates that the observed mode cannot therefore be due to a defect phonon. Finally, the effect of the natural isotopic variation of Ga in GaAs on the infrared-active defect modes of the GaAs:CAs, system is investigated. The calculated results show detailed agreement with infrared absorption data with respect to defect-mode splittings and relative intensities, and establish conclusively the identity of the impurity substitutional site as an As site.
" }, { "name": "Hong, John Hyunchul", "degree": "PhD", "year": "1987", "title": "Optical Computing for Adaptive Signal Processing and Associative Memories", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-06142006-094757", "creators": [ { "name": { "family": "Hong", "given": "John Hyunchul" }, "id": "Hong-John-Hyunchul", "display_name": "Hong, John Hyunchul" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Sideris", "given": "Athanasios" }, "id": "Sideris-A", "role": "member", "display_name": "Sideris, Athanasios" }, { "name": { "family": "Koch", "given": "Christof" }, "id": "Koch-C", "orcid": "0000-0001-6482-8067", "role": "member", "display_name": "Koch, Christof" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/3vpt-fn50", "abstract": "Optical techniques for performing two computing tasks are investigated. First, acousto-optical systems that implement adaptive filtering structures are presented for operation in environments that are not well characterized a priori or are time-varying. Theoretical analyses along with experimental confirmations are given to identify the important system parameters that affect the performance. Extensions of the systems to the multidimensional domain of phased array signal processing are discussed as well as novel implementations that use photorefractive crystals as time-integrating elements.
\r\n\r\nAlso investigated are various associative memory models. An acousto-optic implementation of the so-called Hopfield model is presented. The system's storage capacity and attraction radius are characterized experimentally and are shown to agree with computer simulations. Secondly, an upper bound is derived for the storage capacity of holographic associative memories that use planar holograms. It is shown that if the space bandwidth product of the hologram is N2, then the holographic memory can store at most N2/N3 associations, where N3 is the number of pixels in each output item. Finally, associative memories whose performance is invariant with respect to shifts in the input pattern position are considered. It is shown that nonlinear interconnections are required to achieve shift invariant operation, and optical implementations are discussed.
\r\n" }, { "name": "Humphrey, Joseph William, III", "degree": "PhD", "year": "1987", "title": "Linear and Nonlinear Acoustics with Nonuniform Entropy in Combustion Chambers", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03032008-105855", "creators": [ { "name": { "family": "Humphrey", "given": "Joseph William, III" }, "id": "Humphrey-Joseph-William-III", "display_name": "Humphrey, Joseph William, III" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/ZXQ4-SA60", "abstract": "A one-dimensional analytical model is presented for calculating the longitudinal acoustic modes of idealized \"dump-type\" ramjet engines. The geometry considered is the coaxial flow type with the inlet flow opening to the combustor at a simple dump plane. Since the frequencies are very low, the dominant modes are the one-dimensional longitudinal modes and allow the predictions to be extended to more complicated geometries (such as side dump combustors) with good success. A plane flame has been studied and incorporated into the combustor model where the flame is allowed to move or oscillate in the combustor. This provides three mechanisms of interaction at the flame sheet: change in mean temperature in the combustor, energy conversion at the sheet due to upstream fluctuations, and fluctuating heat release. A supersonic inlet upstream contains a shock wave in its diffuser section while the downstream exit is terminated by a choked nozzle. The linear coupling of the acoustic and entropy waves at the inlet shock, flame sheet, and exit nozzle along with acoustic admittances at the inlet and exit are combined to determine the stability of the system as well as the acoustic modes. Since the acoustic and entropy waves travel at different velocities, the geometry is a critical factor in determining stability. Typical values of the admittances will produce damped solutions when the entropy is neglected, but, as the ratio of the entropy to acoustic fluctuations is increased, the coupling can either feed acoustic energy into or out of different modes independently. This transfer of energy has a destabilizing or stabilizing effect on the acoustic modes of the system depending on the relative phases between the acoustic and entropy waves.
\r\n\r\nIn the linear case, the entropy and acoustics are decoupled in the flow field. All linear coupling occurs at the boundary conditions. For cases where the entropy fluctuations are of the same order of magnitude as the pressure oscillations and the coupling is of comparable order, the linear stability of the acoustic field is strongly dependent upon the entropy fluctuations. The linear acoustics are predominantly governed by the boundary conditions; thus it is imperative that the entire system of inlet, combustor, and exit be considered together to determine the characteristic eigenvalues (resonant frequencies) and eigenfunctions (mode shapes). In addition, there are two modes of acoustic pressure oscillations: the classical acoustic mode and the entropy-induced mode of pressure oscillation. The nonlinear case treats the quadratic nonlinear fluid mechanic interactions in the coupling of two acoustic modes. The result is that the nonlinear acoustic-entropy interactions are much smaller than the acoustic-acoustic interactions for this case. Hence, the nonlinear acoustic field is influenced by the nonuniform entropy only by its dependence upon the linear solution which can be strongly dependent upon the entropy.
\r\n\r\nThe energy in the acoustics of this model is controlled by the energy loss (gain) at the boundaries balanced with the energy gain (loss) at the flame front. Acoustic energy is typically lost at both the inlet and exit, but fluctuating entropy waves convecting with the mean flow velocity that impinge upon a choked nozzle generate acoustic waves that can, under the proper conditions, feed acoustic energy into the system. In addition, the Rayleigh condition for driving the system with a fluctuating heat release can also contribute to the stability of the system. The plane flame mechanism also contributes to the acoustic energy from the interaction of entropy and acoustic waves at a flame sheet. This allows a systematic study of the influence of entropy-acoustic wave interactions on the linear stability and modes of this combustor system.
\r\n" }, { "name": "Jayakumar, Paramsothy", "degree": "PhD", "year": "1987", "title": "Modeling and Identification in Structural Dynamics", "advisor": "Beck, James L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02272019-105053083", "creators": [ { "name": { "family": "Jayakumar", "given": "Paramsothy" }, "id": "Jayakumar-Paramsothy", "display_name": "Jayakumar, Paramsothy" } ], "advisors": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "advisor", "display_name": "Beck, James L." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "civileng" ], "doi": "10.7907/1wwx-ca82", "abstract": "Analytical modeling of structures subjected to ground motions is an important aspect of fully dynamic earthquake-resistant design. In general, linear models are only sufficient to represent structural responses resulting from earthquake motions of small amplitudes. However, the response of structures during strong ground motions is highly nonlinear and hysteretic.
\r\n\r\nSystem identification 1s an effective tool for developing analytical models from experimental data. Testing of full-scale prototype structures remains the most realistic and reliable source of inelastic seismic response data. Pseudo-dynamic testing is a recently developed quasi-static procedure for subjecting full-scale structures to simulated earthquake response. The present study deals with structural modeling and the determination of optimal linear and nonlinear models by applying system identification techniques to elastic and inelastic pseudo-dynamic data from a full-scale, six-story steel structure.
\r\n\r\nIt is shown that the feedback of experimental errors during the pseudo-dynamic tests significantly affected the higher modes and led to an effective negative damping for the third mode. The contributions of these errors are accounted for and the small-amplitude modal properties of the test structure are determined. These properties are in agreement with the values obtained from a shaking table test of a 0.3 scale model.
\r\n\r\nThe nonlinear hysteretic behavior of the structure during strong ground motions is represented by a general class of Masing models. A simple model belonging to this class is chosen. with parameters which can be estimated theoretically, thereby making this type of model potentially useful during the design stages. The above model is identified from the experimental data and then its prediction capability and application in seismic design and analysis are examined.
" }, { "name": "Jery, Belgacem", "degree": "PhD", "year": "1987", "title": "Experimental Study of Unsteady Hydrodynamic Force Matrices on Whirling Centrifugal Pump Impellers", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-130547", "creators": [ { "name": { "family": "Jery", "given": "Belgacem" }, "id": "Jery-Belgacem", "display_name": "Jery, Belgacem" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Antonsson", "given": "Erik K." }, "id": "Antonsson-E-K", "role": "member", "display_name": "Antonsson, Erik K." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "mecheng" ], "doi": "10.7907/cmn0-qk37", "abstract": "An experimental facility was constructed and instrumented. A study was conducted on a set of centrifugal flow pumps whose impellers were made to follow a controlled circular whirl motion. The aim was to characterize the steady and unsteady fluid forces measured on the impeller under various pump operating conditions. The postulation was that the unsteady lateral forces result from interactions between the impeller and the surrounding diffuser and or volute (via the working fluid), and that under certain flow regimes these forces can drive unstable lateral motions of the pump rotor.
\r\n\r\nThe lateral hydrodynamic forces were decomposed into their steady and unsteady parts, the latter being further expressed in terms of a generalized fluid stiffness matrix. A study of this matrix as a function of the whirl to pump speed ratio supported the following chief conclusions:
\r\n\r\ni) the common assumption of matrix skew-symmetry is justified;
\r\n\r\nii) the magnitudes and signs of the matrix elements are such that rotor whirl can indeed be caused by the hydrodynamic forces, in pumps operated well above their first critical speed,
\r\n\r\niii) as expected, the matrix is very sensitive to the value of the flow coefficient, especially at flow rates below the design;
\r\n\r\niv) the commonly postulated quadratic variation of the matrix elements with the reduced whirl frequency, resulting in the so-called rotordynamic coefficients (stiffness, damping and inertia) is not justified for flow coefficients significantly below design; and
\r\n\r\nv) surprisingly, it was discovered that the presence, number and orientation of diffuser guide vanes have little effect on the forces.
\r\n\r\nConclusions regarding the effect of impeller geometry could not be reached given the similarity of the tested designs. However, other results on phenomena such as skin friction and leakage flow are presented. Some of the findings are compared to experimental and theoretical data from other sources. Finally, the rotordynamic consequences of the results are discussed as the present data were applied by another author to the case of the Space Shuttle Main Engine's (SSME) High Pressure Oxidizer Turbopump (HPOTP).
" }, { "name": "Kamm, James Russell", "degree": "PhD", "year": "1987", "title": "Shape and Stability of Two-Dimensional Uniform Vorticity Regions", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06302004-093810", "creators": [ { "name": { "family": "Kamm", "given": "James Russell" }, "id": "Kamm-James-Russell", "display_name": "Kamm, James Russell" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Wiggins", "given": "Stephen R." }, "id": "Wiggins-S-R", "role": "member", "display_name": "Wiggins, Stephen R." } ], "option_major": [ "appmath" ], "doi": "10.7907/NW61-5178", "abstract": "The steady shapes, linear stability, and energetics of regions of uniform, constant vorticity in an incompressible, inviscid fluid are investigated. The method of Schwarz functions as introduced by Meiron, Saffman and Schatzman [1984] is used in the mathematical formulation of these problems.
\r\n\r\nNumerical and analytical analyses are provided for several configurations. For the single vortex in strained and rotating flow fields, we find new solutions that bifurcate from the branch of steady elliptical solutions. These nonelliptical steady states are determined to be linearly unstable. We examine the corotating vortex pair and numerically confirm the theoretical results of Saffman and Szeto [1980], relating linear stability characteristics to energetics. The stability properties of the infinite single array of vortices are quantified. The pairing instability is found to be the most unstable subharmonic disturbance, and the existence of an area-dependent superharmonic instability (Saffman and Szeto [1981]) is numerically confirmed. These results are exhibited qualitatively by an elliptical vortex model. Lastly, we study the effects of unequal area on the stability of the infinite staggered double array of vortices. We numerically verify the results of the perturbation analysis of Jim\u00e9nez [1986b] by showing that the characteristic subharmonic stability \"cross\" persists for vortex streets of finite but unequal areas.
\r\n" }, { "name": "Kasilingam, Dayalan P.", "degree": "PhD", "year": "1987", "title": "Topics in Millimeter-Wave Imaging Arrays", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012008-134009", "creators": [ { "name": { "family": "Kasilingam", "given": "Dayalan P." }, "id": "Kasilingam-Dayalan-P", "display_name": "Kasilingam, Dayalan P." } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/rt21-jt48", "abstract": "In this thesis two different types of antenna arrays are investigated as possible configurations for two-dimensional diffraction limited imaging arrays. The first configuration is the \"fly's-eye\" array of microlenses. It is shown that this configuration may be utilized to achieve diffraction limited imaging with theoretical coupling efficiencies of around 50%. The other configuration is the two-dimensional horn array. It is shown that in this configuration, wide-angled horns etched into silicon achieve theoretical coupling efficiencies of 60%. A design for a two-dimensional imaging array, using horn elements of aperture size 1.5\u03bb0 was suggested. Also covered in this thesis are the radiation losses and the substrate-mode losses of coplanar transmission lines. It is shown that at millimeter-wave frequencies these losses are prohibitively high. Finally in the appendix a simulation of Schottky diode mixers is described as a possible design tool for analyzing millimeter-wave detector circuits.
" }, { "name": "Kyt\u00f6maa, Harri Kaarlo", "degree": "PhD", "year": "1987", "title": "Stability of the Structure in Multicomponent Flows", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-142052", "creators": [ { "name": { "family": "Kyt\u00f6maa", "given": "Harri Kaarlo" }, "id": "Kyt\u00f6maa-Harri-Kaarlo", "display_name": "Kyt\u00f6maa, Harri Kaarlo" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Herbolzheimer", "given": "Eric" }, "id": "Herbolzheimer-E", "role": "member", "display_name": "Herbolzheimer, Eric" } ], "option_major": [ "mecheng" ], "doi": "10.7907/VNYA-FE49", "abstract": "Friction pressure drop measurements were made in vertical bubbly and particulate flows, and friction factors up to two orders of magnitude higher than pure liquid values were obtained. The two-phase friction multiplier for air-water flows was shown to attain values up to 15 times higher than the predictions given by the Lockhart and Martinelli correlations (1949). These findings exemplify the lack of detailed understanding of multi-component flow phenomena. The lack of understanding of the flow kinematics and the small amount of information available on the topic has been primarily due to the primitive stage of development of flow measuring instrumentation.
\r\n\r\nA shielded, temperature compensated and non-intrusive Impedance Volume Fraction Meter (IVFM) was built and shown to have good spatial and temporal resolution. The dynamic calibration of the device demonstrated that the volume fraction measuring device could also be used to measure both the dispersed medium velocity and concentration. This device enabled us to carry out measurements of small and large amplitude kinematic stability and wave propagation in two-component and three-component flows. The velocities of small amplitude kinematic waves in both air-water and solids-water flows were measured using a cross-correlation technique and these were shown to be non-dispersive. The persistence of flow structure was quantified using the coherence of the IVFM noise at two locations. The structure in solids-water flows was found to be more persistent than in air-water flows, and the most coherent wave length was measured to be of the order of .5 m, or five pipe diameters in both flows. The statistical properties in the inherent noise in the IVFM output was shown to contain valuable information on two- and three-component flow quantities and regime.
\r\n\r\nIn this thesis, we show that much can be learned about the complex nature of multi-component flows with adequate instrumentation, and we emphasize the need for further development of critical flow measuring techniques for use not only in fundamental investigations but also in the monitoring and control of practical multiphase flow processes.
" }, { "name": "Lacerda, Nehemias Lima", "degree": "PhD", "year": "1987", "title": "On the Start Up of Supersonic Underexpanded Jets", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-081340", "creators": [ { "name": { "family": "Lacerda", "given": "Nehemias Lima" }, "id": "Lacerda-Nehemias-Lima", "display_name": "Lacerda, Nehemias Lima" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W3CX-2Z48", "abstract": "An impulsively started jet can be formed by a gas confined in a high pressure reservoir that escapes suddenly through an exit orifice, into a controlled atmosphere. Supersonic gas jets of this type are unsteady and differ from the steady jet that develops later by the presence of a bow shock, a jet head and a nonstationary Mach disk. The effects of the pressure ratio between the high pressure gas inside the reservoir and the lower pressure atmospheric gas, as well as the gas combination used, are studied experimentally. The gases used for the jet and the atmosphere were selected from helium, nitrogen and sulfur hexafluoride.
\r\n\r\nThe data acquisition consisted of: high resolution flash photography to obtain detail from the pictures; high-speed movie pictures to obtain the time development of selected features; and fast-response pressure transducers located at the reservoir end plate, the tank end plate and the jet exit. The initial development of the jet is highly time dependent. During this phase, the shape that the jet assumes varies with pressure ratio and with the choice of gas. In particular an extremely light gas exhausting into a heavy atmosphere, exhibits an uncommon shape. It develops as a bubble wrapped by the bow shock, that increases its volume with flow time and pressure ratio. As the pressure ratio increases, it becomes more tightly wrapped by the bow shock. At later times the jet assumes conventional linear growth.
\r\n\r\nAfter the jet starts, a Mach disk is observed close to the jet exit which moves downstream as the exit pressure builds up. The monotonic increase in exit pressure is caused by the slow breaking of the diaphragm. The position of the Mach disk is furthest from the jet exit when the exit pressure is a maximum. After that it oscillates around the location predicted by the steady theory of Ashkenas and Sherman (1966) at a frequency close to one of the resonant frequencies of the reservoir. The features observed for the inner structure of the jet were verified to agree with those obtained for impulsive flow generated by a muzzle blast.
\r\n\r\nThe frontal part of the jet forms the jet head, whose shape changes with the flow conditions. The initial evolution of the jet head is linear but after propagating a distance of around ten exit diameters, it reaches asymptotic behavior with an evolution that is approximately proportional to square root of time. The head creates a bow shock ahead of it that propagates downstream and increases the pressure of the atmospheric gas. This bow shock was found to be less attenuated than in spherically symmetric explosions. The asymptotic behavior of the bow shock was reached after about eight exit diameters.
" }, { "name": "Lam, Wayne W.", "degree": "PhD", "year": "1987", "title": "Millimeter-Wave Monolithic Schottky Diode-Grid Phase Shifter", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03032008-105407", "creators": [ { "name": { "family": "Lam", "given": "Wayne W." }, "id": "Lam-Wayne-W", "display_name": "Lam, Wayne W." } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "orcid": "0000-0003-1783-1380", "role": "member", "display_name": "Vahala, Kerry J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Luhmann", "given": "Neville C., Jr." }, "id": "Luhmann-Neville-C-Jr", "role": "member", "display_name": "Luhmann, Neville C., Jr." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CGD0-XA98", "abstract": "Many applications at millimeter wavelengths require fast electronic phase shifters. In this study, the design of diode-grid phase shifters is presented, the fabrication of diode-grids on monolithic gallium-arsenide substrates is demonstrated, and the measurement of these grids is discussed. A new computer-aided design tool is developed to provide an interactive environment for design and to form a basis for comparing theory and experimental results. Diode-grids have been fabricated on 2 cm by 3 cm gallium-arsenide wafers with 2000 aluminum Schottky diodes. A novel small aperture reflectometer is computerized to use a wave-front division interference technique to measure the reflection coefficient of the grids. A 70\u00b0 phase shift with a 6.5-dB loss was measured at 93 GHz when the bias on the diode-grid was changed from -3V to +1V.
\r\n" }, { "name": "Landman, Michael J.", "degree": "PhD", "year": "1987", "title": "New Solutions of an Amplitude Equation Describing Transition in a Laminar Shear Flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03032008-130724", "creators": [ { "name": { "family": "Landman", "given": "Michael J." }, "id": "Landman-Michael-J", "display_name": "Landman, Michael J." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "appmath" ], "doi": "10.7907/CYPP-D856", "abstract": "In order to better understand the process of laminar-turbulent transition in parallel shear flows, the study of the stability of viscous flow between parallel plates, known as plane Poiseuille flow, is found to be a good prototype. For Reynolds number near the critical value at which a linear instability first appears, Stewartson and Stuart (1971) developed a weakly nonlinear theory for which an amplitude equation is derived describing the evolution of a disturbance in plane Poiseuille flow in two space dimensions. This nonlinear partial differential equation is now commonly known in the literature as the Ginzburg-Landau equation, and is of the form
\r\n\r\n(\u2202A)/(\u2202t) = (ar + iai)[(\u22022A)/(\u2202x2)] + (Re - Rec)A + (dr + idi)A|A|2.
\r\n\r\nThis dissertation concentrates on analyzing quasi-steady solutions of the Ginzburg-Landau equation, where
\r\n\r\nA = e-i\u03a9t\u03a6(x - ct).
\r\n\r\nThese solutions describe modulations to the wave of primary instability, with amplitude which is steady in an appropriate moving coordinate system. The ordinary differential equation describing the spatial structure of quasi-steady solutions is viewed as a low-dimensional dynamical system. Using numerical continuation and perturbation techniques, new spatially periodic and quasi-periodic solutions are found which bifurcate from the laminar state and undergo a complex series of bifurcations. Moreover, solitary waves and other solutions suggestive of laminar transition are found numerically for Reynolds number on either side of Rec, connecting the laminar state to finite amplitude states, some of the latter corresponding to known solutions of the full fluid equations. The existence of these new spatially quasi-periodic and transition solutions suggests the existence of a similar class of solutions in the Navier Stokes equations, describing pulses and fronts of instability, as observed experimentally in parallel shear flows.
" }, { "name": "Lau, Billy Ying Bui", "degree": "PhD", "year": "1987", "title": "Small-Signal Frequency Response Theory for Ideal Dc-to-Dc Converter Systems", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012008-134552", "creators": [ { "name": { "family": "Lau", "given": "Billy Ying Bui" }, "id": "Lau-Billy-Ying-Bui", "display_name": "Lau, Billy Ying Bui" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "chair", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/mqpe-vz16", "abstract": "The frequency response problem of switching dc-to-dc converter systems is the problem of computing the small-signal frequency response of the system with respect to its inputs. It arises in the study of the small-signal behavior and in the design of a feedback controller for the dc-to-dc converter system. There are two approaches in tackling the problem: the numerical approach and the analytical approach. This thesis is limited to the analytical approach. There are previous efforts in developing approximate analytical methods for solving the problem; however, these methods are unsatisfactory in one way or another because they are applicable only to few special cases, and valid only in limited range of frequency \u2014 less than half the switching frequency in many cases.
\r\n\r\nThe Small-Signal Frequency Response Theory presented in this thesis is developed to overcome the problems encountered in the application of the approximate analytical methods. Instead of finding an approximate model for a dc-to-dc converter system and postulating that the response of the model is the same as that of the converter system, as in the approximate analytical methods, the new theory computes the frequency response of the perturbed output with respect to perturbations at the control-inputs by the direct application of Fourier Analysis. Hence, the theory is exact in the small-signal limit. Unlike the approximate analytical methods, the results given by the theory are valid at all frequencies provided that the system model used in the calculation of frequency response is valid at all frequencies. In short, the Small-Signal Frequency Response Theory is a mathematical theory for the linearization of an ideal dc-to-dc converter system in the vicinity of its periodic steady state solution.
\r\n\r\nIn the derivation of the results of the Small-Signal Frequency Response Theory, two steps are taken: First, find a difference equation that describes the small-signal motion of the system in the vicinity of the given steady state solution. Second, find the equivalent hold that relates the samples of the perturbed state of the system, given by the difference equation, to the analog output signal. The z-transform of the difference equation with z = esT. is used to relate the spectrum of the sampled perturbed control-input to the spectrum of the sampled perturbed output. The frequency response of the converter system given by the theory resembles the frequency response of a classical single-rate sampled-data system.
\r\n\r\nThe prediction given by the theory and the experimental results for three converter circuits are compared. These three converter circuit have the same basic circuit topology, but different control strategies. The control strategies in these three examples are: constant-switching-frequency PWM, constant-switching-frequency programmed, and bang-bang controlled. It is found that the theory consistently gives good predictions, even up to many times of the switching frequency, while, in many cases, the approximate analytical methods break down.
\r\n\r\nThe theory has the best of both the time domain approach and the frequency domain approach for the analysis of switching dc-to-dc converter systems. It has the exactness of the time domain approach, which uses a difference equation to describe the system, and the measurability of the of frequency domain approach. The exactness and the uniformity of the theory, which has not been achieved before, results in significant impact in the fields of computer-aided design and modelling and analysis in power electronics.
" }, { "name": "Leung, Ping-Sang Kenneth", "degree": "PhD", "year": "1987", "title": "Co-Phthalocyanine Catalyzed Autoxidation of Mercaptans", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03032008-095453", "creators": [ { "name": { "family": "Leung", "given": "Ping-Sang Kenneth" }, "id": "Leung-Ping-Sang-Kenneth", "display_name": "Leung, Ping-Sang Kenneth" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/jgax-r052", "abstract": "The kinetics and mechanism of the autoxidation of 2-mercaptoethanol, 2-aminoethanethiol and ethanethiol catalyzed by Co(II)- 4,4',4'',4'''-tetrasulfophthalocyanine, abbreviated as Co(II)TSP, has been examined. Kinetic data showed that the catalytic autoxidation of all three mercaptans proceeded via the same mechanism. The ultimate products of the autoxidation were found to be the corresponding disulfide (RSSR) and hydroxide ion. The kinetic data indicated that 50% to 80% of the disappearance of mercaptans was controlled by the catalytic cycle as opposed to oxidation by the intermediate, H2O2. The overall stoichiometry of the catalytic autoxidation is the sum of the following reactions:
\r\n\r\n[Chemical equation; see abstract in scanned thesis for details]
\r\n\r\nStoichiometric ratio of mercaptan to oxygen of 1:4 was found for each mercaptan.
\r\n\r\nWhen the mercaptan was added, a dimeric Co(II)TSP was formed by the bridging of the two Co(II)TSP monomers by mercaptan anion. This dimer is proposed as the catalytic center for the cycle. The electron transfer from Co(II) to bound O2 forming a superoxide-like species is assumed to be the rate-determining step.
\r\n\r\nThe experimental rate law for the autoxidation of each mercaptan was found to be
\r\n\r\n[Equation; see abstract in scanned thesis for details]
\r\n\r\nand an expression for kobsd of each mercaptans was derived from the postulated mechanism.
\r\n\r\nThe kinetics reveal that the catalytic cycle is sensitive to variations in pH.The pH dependence at pH < 11 can be easily explained by the acid-base equilibria of the mercaptan (RSH \u21cc RS- + H+. However, the pH dependence at pH > 11 suggests that the deprotonation of Co(II)TSP dimer must occur and that pK'1 of the dimer must be between 11 and 13.
\r\n\r\nThe rate of autoxidation of mercaptans follows the relative order of ethanethiol > 2-aminoethanethiol > 2-mercaptoethanol. Linear free energy relationship (LFER) was established 1) between Taft \u03c3* value of the substituent group and the rate constant; 2) between Taft \u03c3* value and the pK'2 where K'2 is the apparent acid dissociation constant of the catalytic dimer.
\r\n\r\nThe hydrogen peroxide produced from the catalytic cycle oxidizes the mercaptan anions giving the disulfide as the product. The stoichiometry is found to be
\r\n\r\n[Chemical equation; see abstract in scanned thesis for details]
\r\n\r\nThe kinetics and mechanism for the oxidation of 2-mercaptoethanol by hydrogen peroxide have been examined. The rate expression for the oxidation is as follows:
\r\n\r\n[Equation; see abstract in scanned thesis for details]
\r\n\r\nk'obsd depends on the apparent acid dissociation constants of HOC2H4SH, HOC2H4S- and H2O2. The kinetics and mechanism of reduction of Co(II)TSP by 2-mercaptoethanol under anoxic conditions were studied. Results from this study provide estimates of the rate of complexation of Co(II)TSP by 2-mercaptoethanol and the acid dissociation constant, Ka1, of the bound water on the Co(II)TSP-RS=Co(II)TSP. Co(II)TSP was reduced to Co(I)TSP by 2-mercaptoethanol. The rate expression is given by
\r\n\r\n[Equation; see abstract in scanned thesis for details]
\r\n\r\nwhere k2 is the rate constant for the electron transfer step, and K1 is the equilibrium constant for the complexation of CoTSP dimer with thioethanol. Ka1 and Ka2 are the apparent acid dissociation constants of HOC2H4SH and HOC2H4S-, respectively; and \u03b1 is K1/(1 + aH+/Ka1 + Ka2/aH+). Results of this system further enhance the argument that the electron transfer step rather than the preceding mercaptan complexation step is the rate-determining step in the oxygenated system.
\r\n\r\nThis study indicates that Co(II)TSP is a very effective catalyst for the autoxidation of mercaptans. pH is an important physiochemical parameter for the autoxidation, whereas the effect of dissolved O2 concentration is rather insignificant. From a practical standpoint, use of the homogeneous catalyst is not very economical because of the relatively expensive recovery process. Solid-supported Co(II)TSP such as (SiO2)-Co(II)TSP, TiO2-Co(II)TSP, and polystyrene-divinyl benzene resin-Co(II)TSP contained in fixed bed reactors may be an economic alternative for mercaptan waste treatment. Nevertheless, the results of this study should provide useful insight into the design of a suitable hybrid system.
" }, { "name": "Lin, Jane Ming-Chin", "degree": "PhD", "year": "1987", "title": "Transient Gas Jets into Liquid", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-04262004-113723", "creators": [ { "name": { "family": "Lin", "given": "Jane Ming-Chin" }, "id": "Lin-Jane-Ming-Chin", "display_name": "Lin, Jane Ming-Chin" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4qp0-4x37", "abstract": "An experimental investigation of the development of high velocity, impulsively initiated gas jets into liquid was conducted in an effort to understand some of the physical processes that occur for a jet of very light fluid into a dense ambient atmosphere. Four gases, refrigerants 12 and 22, nitrogen, and helium were injected into water at nozzle exit Mach numbers from 1.0 to 2.2.
\r\n\r\nThe study showed that a gas jet into water develops in at least three stages: startup, transition, and global steady state. The startup is characterized by bubble growth; the growth rate is well predicted by classical bubble-growth theory. Jet transition is marked by axially directed flow, which penetrates through the startup bubble and which forms a cylindrical protrusion along the axis of symmetry. A combination of strong recirculating flow and liquid entrainment causes the startup bubble to deflate and to lift off and move downstream. In the steady state, instantaneous photographs show small-scale fluctuations of the jet boundary, but time-averaged photographs show the expected conical spreading of the steady jet; the measured spreading angles range from 18-25 degrees.
\r\n\r\nHowever, the most significant finding of this study is that under some conditions, the gas jet into liquid never reaches the global steady state. Instead, the jet boundary exhibits chugging: large nonlinear oscillations which lead to irregular collapses of the gas column followed by explosive outward bursts of gas. The unsteadiness observed is much more violent than the familiar fluctuations typical of constant-density jets. The length scale of the motion is generally on the order of several jet diameters; the time scale is on the order of the period for bubble collapse.
\r\n\r\nIt was found that the amplitude and frequency of chugging are strongly dependent on the ratio of the liquid density to the gas density, the jet Mach number, and the operating pressure ratio. The conditions under which unsteadiness occurs were determined experimentally. In particular, a quantitative measure of jet susceptibility to unsteadiness has been established. Steady jets can be achieved in two ways: by being discharged from deLaval nozzles (increasing the exit Mach number) or by being overpressured.
\r\n\r\nThe unsteady behavior is modeled as the collapse of a bubble in liquid; comparisons of collapse times show good agreement. A mechanism for the unsteadiness is discussed. It is proposed that the chugging is the response of the jet boundary to a pressure difference between the jet and surrounding liquid, which arises as the result of the rapid expansion of a light fluid into a dense ambient atmosphere. The flow is shown to be similar to the discharge of a gas from a nozzle into a channel of larger cross section. An upper limit to the pressure difference is determined based on estimates of the minimum base pressure for such channel flows; a lower limit is established for the collapse time. All experimental values are within the bounds. The derived values indicate that the pressure differences between the jet and liquid may be more than 90 percent of the ambient pressure.
" }, { "name": "Lindsey, Christopher Paul", "degree": "PhD", "year": "1987", "title": "High Power Phased Array and Tailored Gain Semiconductor Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-03032008-143205", "creators": [ { "name": { "family": "Lindsey", "given": "Christopher Paul" }, "id": "Lindsey-Christopher-Paul", "display_name": "Lindsey, Christopher Paul" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/9mh8-wv40", "abstract": "Most phase locked semiconductor laser arrays suffer from undesirable twin lobed farfield patterns, making them unsuitable for many applications. In this thesis we make a detailed theoretical and experimental study of this problem, and solve it by tailoring the spatial gain profile across the array. We demonstrate a tailored gain chirped array which emits 450mW into a single beam 3\u00bd\u00b0 wide.
\r\n\r\nStripe geometry lasers for use in phased arrays are examined in Chapter 2, as are design considerations for evanescently coupled phased arrays. A powerful numerical method for analyzing a nearly arbitrary one-dimensional dielectric waveguide with gain and/or loss is described.
\r\n\r\nChapter 3 analyzes in detail the simplest array of two adjacent waveguides, both real index and gain guided and both weakly and strongly coupled. Chapter 4 discusses why a uniform array has a twin lobed farfield pattern, and introduces the concept of a nonuniform real index guided chirped array of lasers with widths which increase monotonically across the array. Real index guided chirped arrays can, in principle, be made to lase with a single lobed farfield pattern. Since such arrays are difficult to fabricate, and will be at least partially gain guided, we concentrate on gain guided structures. The combination of gain tailoring and a high interchannel gain in a proton implanted chirped array enables us to achieve our goal of fabricating a high power array with the single lobed farfield pattern described above.
\r\n\r\nSuch arrays are actually tailored gain broad area lasers. Chapter 5 demonstrates another method for gain tailoring, the \"halftone\" process, which can create nearly arbitrary two-dimensional spatial gain profiles in an optoelectronic device, thereby offering a new degree of freedom to the designer of semiconductor lasers. Single lobed nearly diffraction limited beams from tailored gain broad area lasers 50\u00b5m wide are obtained.
\r\n\r\nAsymmetric tailored gain waveguides have several unusual properties. The technique of Path Analysis for analyzing these complex waveguides is introduced. Fundamental Fourier Transform relationships relating device structure to farfield patterns yield additional insights. Finally, we close with a measurement of the antiguiding parameter and briefly examine some design criteria for practical tailored gain broad area lasers.
\r\n" }, { "name": "Lyn, Dennis Anthony", "degree": "PhD", "year": "1987", "title": "Turbulence and Turbulent Transport in Sediment-Laden Open-Channel Flows", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-133940", "creators": [ { "name": { "family": "Lyn", "given": "Dennis Anthony" }, "id": "Lyn-Dennis-Anthony", "display_name": "Lyn, Dennis Anthony" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "member", "display_name": "Vanoni, Vito A." } ], "option_major": [ "envreng" ], "doi": "10.7907/G5WF-5K07", "abstract": "Some aspects of turbulence in sediment-laden open-channel flows are examined. A conceptual model based on similarity hypotheses rather than the traditional mixing-length closures is proposed. It is argued that, over a wide range of laboratory conditions, the main effect of the suspended sediment on the flow is confined to a layer near the bed. If such a distinct layer can be discerned, then this is separated from the outer flow by an inertial subregion in which the mean-velocity profile is approximately logarithmic, with an associated von K\u00e0rman constant of \u2248 0.4, i.e., the same value as in single-phase flows. It is further shown that power-law profiles may be derived from general similarity arguments and asymptotic matching. These implications contrast with those of previous models in which changes in the mean-velocity profile are supposed to occur throughout the flow or primarily in the flow far from the bed. Length and concentration scales appropriate to sediment-laden flows are suggested.
\r\n\r\nAn experimental study was also undertaken. Both the saturated case, in which a sand bed was present, and the unsaturated case, in which a sand bed was absent, were investigated. The study was restricted to nominally flat beds, composed of three well sorted sands (median grain diameters ranged from 0.15 mm to 0.24 mm). A two-component laser-Doppler-velocimetry system was used for velocity measurements. Suction sampling was used to measure local mean concentrations. The major points of the conceptual model are supported by the experimental results. Higher-order statistics of the velocity field were found to exhibit little evidence of any effect on the outer flow, supporting the view that the effect of the suspended sediment is felt primarily in the inner region. This contrasts with the predictions of recent models that propose an analogy between sediment-laden flows and weakly stable density-stratified flows.
\r\n" }, { "name": "Mahadevan, Ramaswamy", "degree": "PhD", "year": "1987", "title": "Problems in Analysis, Control, and Design of Switching Inverters and Rectifiers", "advisor": "Middlebrook, Robert David; Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-03052008-091727", "creators": [ { "name": { "family": "Mahadevan", "given": "Ramaswamy" }, "id": "Mahadevan-Ramaswamy", "display_name": "Mahadevan, Ramaswamy" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "co-advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "chair", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Thompson", "given": "Peter M." }, "id": "Thompson-Peter-M", "role": "member", "display_name": "Thompson, Peter M." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2R9K-A588", "abstract": "Control and analysis techniques in switched-mode inversion (dc-ac) and rectification (ac-dc) are examined in this thesis. Current programming and sliding mode control are used to provide regulation and obtain desired dynamic responses. The basic buck, boost, flyback, and buck-boost topologies are used to illustrate the different methods of control and analysis. For illustration, embodiments employ fast switching converters, but the techniques described can be applied to any general converter.
\r\n\r\nDifferent possibilities for the current programming of dc-ac inverters and ac-dc rectifiers are explored and the more practical and advantageous methods noted. Current reference programming improves the dynamic response of the converter and simplifies the design of the main regulatory loop. It also protects the switches from excessive current stresses and enables the parallel operation of many converters to support a common load. Constant frequency current reference programmed converters are, however, subject to oscillations under certain operating conditions.
\r\n\r\nDescribing equations are used to obtain the low frequency characterization of current programmed converters. The system representation is first obtained in the stationary abc reference frame and then transformed to the rotating dq coordinate frame. In the dq coordinate system, the low frequency characterizations of all balanced, polyphase ac converter systems are represented by a set of continuous, time-invariant differential equations. The steady-state and linearized, small signal dynamic responses are then obtained in this rotating reference frame.
\r\n\r\nSliding mode control is applied to inverters and rectifiers to provide regulation and ensure the stability of the system in the presence of small and large signal disturbances. This is a natural method of control for variable structure systems and enables the design of a robust controller that can provide stability and performance in the face of plant uncertainities. However, it requires that all or many of the states of the system be accessible and results in a variable switching frequency in the converter.
\r\n\r\nThe equivalent control method is used to obtain the low frequency properties of the sliding mode system, and can also be used to obtain the low frequency models of duty ratio programmed converters. Different switching strategies can be used to provide sliding mode control, as well as to optimize responses, maximize efficiency, or minimize switching losses. Practical aspects such as hardware implementation, switch realization, and measurement techniques are also discussed.
" }, { "name": "Moser, Michael Anthony", "degree": "PhD", "year": "1987", "title": "The Response of Stick-Slip Systems to Random Seismic Excitation", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04122019-165004448", "creators": [ { "name": { "family": "Moser", "given": "Michael Anthony" }, "id": "Moser-Michael-Anthony", "display_name": "Moser, Michael Anthony" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ntjg-hg45", "abstract": "This thesis examines the response of stick-slip, or frictional, systems to harmonic and random excitation. Two frictional models are considered: constant slip force, or Coulomb, friction, and displacement dependent slip force, used to model a caster, or pivoting wheel. The response to harmonic excitation of systems exhibiting both frictional models is determined using the method of slowly varying parameters. Changes in the response amplitude of both systems caused by the addition of a linear centering mechanism are also examined.
\r\n\r\nThe response of the system with displacement dependent slip force is examined under Gaussian mean zero white noise excitation using the generalized equivalent linearization method. It is shown that a lower bound is obtained from the Coulomb friction system's response.
\r\n\r\nFor filtered random excitation, linearization methods are shown to predict erroneous displacement trends for the Coulomb system when the input has no spectral content at zero frequency. When the excitation is modeled as a Poisson pulse process, an approximate method exhibiting the proper displacement trends can be constructed. The method is shown to be accurate over a broad range of input parameters if overlaps in the input pulses are considered. A set of excitation parameters consistent with seismic events is then used to estimate final rms displacements as a function of coefficient of friction.
" }, { "name": "Natsiavas, Sotirios", "degree": "PhD", "year": "1987", "title": "Response and Failure of Fluid-Filled Tanks under Base Excitation", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062007-092509", "creators": [ { "name": { "family": "Natsiavas", "given": "Sotirios" }, "id": "Natsiavas-Sotirios", "display_name": "Natsiavas, Sotirios" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Bailey", "given": "James E." }, "id": "Bailey-J-E", "role": "chair", "display_name": "Bailey, James E." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Morari", "given": "Manfred" }, "id": "Morari-M", "role": "member", "display_name": "Morari, Manfred" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/CNWT-V417", "abstract": "An analytical model is developed that leads to better understanding of the response of fluid-filled tanks whose bottom may separate from and lift off the foundation, during base excitation. First, the hydrodynamic problem is solved in closed form, for the most general motion of the structure. This eliminates the fluid response unknowns and therefore only the structural degrees-of-freedom need to be considered. Then, application of Hamilton's Principle in the structural domain sets up the system equations of motion. During this procedure, the uplifting behavior is modeled by an appropriate rotational spring, placed between the foundation and the bottom of the tank. Equivalent springs are also used for modeling the ground/structure interaction. Moreover, shell flexibility and liquid sloshing effects are also incorporated and investigated.
\r\n\r\nUsing this model, results are obtained and compared with experimental data. This comparison reveals some interesting effects of the base uplift on the system response. Ground flexibility is found to reduce the effective beam-type stiffness of the structure, but this reduction is much smaller than the substantial stiffness reduction induced by the possibility of uplifting. For the cases examined, the stiffness reduction due to the base uplift changes dramatically the dynamics of the system, which in turn alters the developed hydrodynamic loads, through the fluid/structure coupling process. Also, the shell flexibility effects - which can be important for the anchored tank case - are found to be negligible for an unanchored tank. Knowledge of the structural response leads to direct calculation of the hydrodynamic loads and consequently to prediction of failure. Buckling phenomena observed experimentally at the top and the bottom of scale model tanks are studied and explained.
\r\n" }, { "name": "O'Hern, Timothy John", "degree": "PhD", "year": "1987", "title": "Cavitation Inception Scale Effects: I. Nuclei Distributions in Natural Waters. II. Cavitation Inception in a Turbulent Shear Flow", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04022004-094117", "creators": [ { "name": { "family": "O'Hern", "given": "Timothy John" }, "id": "O'Hern-Timothy-John", "display_name": "O'Hern, Timothy John" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "mecheng" ], "doi": "10.7907/G8TY-K105", "abstract": "Cavitation scale effects can be grouped into two major categories: susceptibility of the water to cavitation, i.e., the amount, size, and type of microbubbles or microparticulates in the water acting as inception nuclei, and flow field effects due to such factors as velocity and pressure distributions, body size and shape, viscous effects, and turbulent phenomena. Experimental investigations into these two aspects of scale effects were performed in the present study.
\r\n\r\nField investigations of marine nuclei populations were made using underwater holography to observe microbubbles and particulates, including microplankton in oceanic waters of Los Angeles Harbor, San Pedro Channel and near Santa Catalina Island. Holographic detection was shown to be a reliable method of measuring the nuclei number concentration density distributions. Overall, very high concentrations of the various types of potential cavitation nuclei were observed at all of the test sites and depths examined, although the statistical significance of these results is strong only in the smaller size ranges (less than 50 \u00b5m), where a significant number of counts were made. Relatively high bubble concentrations during calm sea conditions, and their population inversion below the thermocline where organism activity was high, indicate a possible biological source of bubble production rather than the usual surface mechanisms of breaking waves and whitecaps. The measured population of particulates is somewhat higher than comparable data in the ocean or in cavitation test facilities, and the number density distribution of particulates decreases approximately as the fourth power of the particle size, as often reported in the literature. An increase in particle concentration near the bottom of the thermocline in clear coastal waters is observed. The total concentration of particles and bubbles in a liquid provides an upper bound on the number of potentially active cavitation nuclei. The measured bubble sizes can be used to indicate that the average tensile strength of the ocean waters examined in this study should be on the order of a few thousand Pascals, with a minimum expected value of about one hundred Pascals. The present results support the recommendation of Billet (1985), that a concentration of at least 3 bubbles per cm3 in the 5 to 20 \u00b5m radius range is needed in test facility water in order to model marine conditions.
\r\n\r\nExperimental studies were also made on the inception processes in a large turbulent free shear layer generated by a sharp edged plate in a water tunnel at Reynolds numbers up to 2 x 106. Two distinct types of vortex motion were evident in the shear layer, the primary spanwise and the secondary longitudinal vortices. Cavitation inception occurs consistently in the secondary shear layer vortices and more fully developed cavitation is visible in both structures, with the streamwise cavities primarily confined to the braid regions between adjacent spanwise vortices. A Rankine vortex model indicates that the secondary vortex strength is always less than 10% of that of the primary structure. Measurements of fluctuating pressures in the turbulent shear layer are made by holographically monitoring the size of air bubbles injected into the non-cavitating flow, showing that pressure fluctuations were much stronger than previously reported, with positive and negative pressure peaks as high as 3 times the freestream dynamic pressure, sufficient to explain the occurrence of cavitation inception at high values of the inception index. Cavitation inception indices display a strong dependence on the dissolved air content and thus on the availability of freestream bubble cavitation nuclei. The present inception data do not display a clear dependence on freestream velocity (or Reynolds number) but do fall into the overall range of data of previous bluff body investigations. The occurrence of inception in the secondary vortices of the shear layer, and previous reports of velocity dependence of these cores (Bernal 1981) may provide the key to explaining the commonly observed Reynolds number scaling of the inception index in shear flows.
" }, { "name": "Papamoschou, Dimitri", "degree": "PhD", "year": "1987", "title": "Experimental Investigation of Heterogeneous Compressible Shear Layers", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192007-085328", "creators": [ { "name": { "family": "Papamoschou", "given": "Dimitri" }, "id": "Papamoschou-Dimitri", "display_name": "Papamoschou, Dimitri" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "member", "display_name": "Blandford, Roger D." }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "member", "display_name": "Lees, Lester" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M7PQ-Y494", "abstract": "The compressible, two-dimensional shear layer is investigated experimentally in a novel facility. In this facility, it is possible to flow similar or, dissimilar gases of different densities and to select different Mach numbers for each stream over a wide range of Reynolds numbers. In the current experiments, ten combinations of gases and Mach numbers are studied in which the freestream Mach numbers range from 0.2 to 4, the density ratio varies from 0.2 to 9.2, and the velocity ratio varies from 0.13 to 1. The growth of the turbulent region of the layer is measured by means of pitot pressure profiles obtained at several streamwise locations. The resulting growth rate is estimated to be about 80% of the visual growth rate. The transition from laminar to turbulent flow, as well as the structure of the turbulent layer, are observed with Schlieren photographs of 20 nanosecond duration. Streamwise pressure distribution and total pressures are measured by means of a Scanivalve-pressure transducer system.
\r\n\r\nAn underlying objective of this investigation was the definition of a compressibility-effect parameter that correlates and consolidates the experimental results, especially the turbulent growth rates. A brief analytical investigation of the vortex sheet suggests that such a parameter is the Mach number in a frame of reference moving with the phase speed of the disturbance, called here the convective Mach number. In a similar manner, the convective Mach number of a turbulent shear layer is defined as the one seen by an observer moving with the convective velocity of the dominant waves and structures. It happens to have about the same value for each stream. In the current experiments, it ranges from 0 to 1.9.
\r\n\r\nThe correlations of the growth rate with convective Mach number fall approximately onto one curve when the growth rate is normalized by its incompressible value at the same velocity and density ratios. The normalized growth rate, which is unity for incompressible flow, decreases gradually with increasing convective Mach number, reaching an asymptotic value of about 0.25 for supersonic convective Mach numbers. The above behavior is in qualitative agreement with results of linear stability theory as well as with those of previous, one-stream experiments.
\r\n\r\nLarge-scale structures, resembling those observed in subsonic shear layers, are evident in the Schlieren photographs. It is estimated that the mean structure spacing, normalized by the local thickness, is reduced to about half its incompressible value as the convective Mach number becomes supersonic.
\r\n\r\nAn estimate of the transition Reynolds number has been obtained from the photographs of two shear layers having quite different convective Mach numbers, one low subsonic and the other sonic. In both cases, it is about 2 x 105, based on distance to transition and properties of the high unit Reynolds number stream, thus suggesting that, in this experiment, transition is dominated by instabilities of the wake, rather than of the shear layer.
\r\n" }, { "name": "Paparizos, Leonidas G.", "degree": "PhD", "year": "1987", "title": "Some Observations on the Random Response of Hysteretic Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152019-163242410", "creators": [ { "name": { "family": "Paparizos", "given": "Leonidas G." }, "id": "Paparizos-Leonidas-G", "display_name": "Paparizos, Leonidas G." } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "civileng" ], "doi": "10.7907/w5wv-5f87", "abstract": "In this thesis, the nature of hysteretic response behavior of structures subjected to strong seismic excitation, is examined. The earthquake ground motion is modeled as a stochastic process and the dependence of the response on system and excitation parameters, is examined. Consideration is given to the drift of structural systems and its dependence on the low frequency content of the earthquake spectrum. It is shown that commonly used stochastic excitation models, are not able to accurately represent the low frequency content of the excitation. For this reason, a stochastic model obtained by filtering a modulated white noise signal through a second order linear filter is used in this thesis.
\r\n\r\nA new approach is followed in the analysis of the elasto-plastic system. The problem is formulated in terms of the drift, defined as the sum of yield increments associated with inelastic response. The solution scheme is based on the properties of discrete Markov process models of the yield increment process, while the yield increment statistics are expressed in terms of the probability density of the velocity and elastic component of the displacent response. Using this approach, an approximate exponential and Rayleigh distribution for the yield increment and yield duration, respectively, are established. It is suggested that, for duration of stationary seismic excitation of practical significance, the drift can be considered as Brownian motion. Based on this observation, the approximate Gaussian distribution and the linearly divergent mean square value of the process, as well as an expression for the probability distribution of the peak drift response, are obtained. The validation of these properties is done by means of a Monte Carlo simulation study of the random response of an elastoplastic system.
\r\n\r\nBased on this analysis, the first order probability density and first passage probabilities for the drift are calculated from the probability density of the velocity and elastic component of the response, approximately obtained by generalized equivalent linearization. It is shown that the drift response statistics are strongly dependent on the normalized characteristic frequency and strength of the excitation, while a weaker dependence on the bandwidth of excitation is noted.
" }, { "name": "Rakuljic, George Anthony", "degree": "PhD", "year": "1987", "title": "Photorefractive Properties and Applications of Barium Titanate and Tungsten Bronze Ferroelectrics", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-05052006-103604", "creators": [ { "name": { "family": "Rakuljic", "given": "George Anthony" }, "id": "Rakuljic-George-Anthony", "display_name": "Rakuljic, George Anthony" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Vahala", "given": "Kerry J." }, "id": "Vahala-K-J", "role": "member", "display_name": "Vahala, Kerry J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/8w0w-ea37", "abstract": "This thesis is an experimental and theoretical investigation of the photorefractive properties of barium titanate and tungsten bronze ferroelectrics, and applications thereof. In the first part, the physics of the photorefractive effect is presented. The band transport equations are solved for three cases that describe the photorefractive mechanism in a crystal with one photorefractive species and either one or two types of charge carriers, or in a crystal with two photorefractive species, but only one type of charge carrier.
\r\n\r\nIn the second part, the coupled wave theory of two-wave mixing in photorefractive crystals is reviewed. Effects of energy coupling between the two interacting beams are discussed along with experimental methods for determining the two-beam coupling coefficient and the photorefractive response time.
\r\n\r\nThe photorefractive crystals barium titanate, strontium barium niobate, and barium strontium potassium sodium niobate are described in the third part. A summary of their optical, physical and electrical properties is presented for use in subsequent sections of the thesis.
\r\n\r\nIn the fourth part, the photorefractive properties of these crystals are presented. Data from two-beam coupling experiments are used to obtain the two-beam coupling coefficients and the photorefractive response times of the crystals under a variety of experimental conditions. The band transport models are then applied to these results.
\r\n\r\nFigures of merit are defined in the fifth part that are then used in a comparison of several photorefractive materials, including the barium titanate, the strontium barium niobate, and the barium strontium potassium sodium niobate crystals. Both ferroelectric and non-ferroelectric materials are considered.
\r\n\r\nIn the last part, applications using barium titanate and the tungsten bronze ferroelectrics are described. By using the self-focusing properties of barium titanate and strontium barium niobate, the compensation of nonlinear optical distortions with phase conjugation is demonstrated. A passive phase conjugator that relies on no external mirrors and uses strontium barium niobate as the nonlinear medium is also described. Finally, a thresholding passive phase conjugate mirror is then presented along with several devices that can perform mathematical operations on images such as subtraction and differentiation.
" }, { "name": "Ramarathnam, Narasimhan", "degree": "PhD", "year": "1987", "title": "Mode I, Plane Stress Crack Initiation and Growth in Elastic-Plastic Solids: A Finite Element Analysis", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062003-094350", "creators": [ { "name": { "family": "Ramarathnam", "given": "Narasimhan" }, "id": "Ramarathnam-Narasimhan", "display_name": "Ramarathnam, Narasimhan" } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/RG0C-WF30", "abstract": "A detailed finite element analysis of crack initiation and stable crack extension is performed under Mode I plane stress, small-scale yielding conditions. A small strain, J2 incremental plasticity theory is employed and both elastic-perfectly plastic materials and power law hardening materials are considered.
\r\n\r\nSome issues pertaining to the stationary plane stress crack problem, such as the range of dominance of the asymptotic stress and deformation fields and the amount of non-proportional loading near the crack tip are addressed. Special attention is devoted to the perfectly plastic idealization, by performing a separate singular finite element analysis, to clarify some details about the asymptotic fields near the stationary crack tip. The full-field numerical solution is used to simulate synthetic (optical) caustic patterns at different distances from the crack tip, which are compared with experimental observations and with asymptotic analytical results.
\r\n\r\nA nodal release procedure is used to simulate quasi-static crack extension. It is found that the asymptotic angular extent of the active plastic zone, surrounding the propagating crack tip, is from \u03b8 = 0 to about \u03b8 = 45\u00b0 for the perfectly plastic case. The near-tip angular stress distribution within the active plastic zone is in good agreement with the variation in a centered fan, as predicted by a preliminary asymptotic analysis by Rice, for the perfectly plastic case. It is also observed that the \u03c3rr stress component has a strong radial variation within the active plastic zone. The angular extent of active yielding around the moving tip increases with hardening, while its maximum radial extent ahead of the tip decreases. Clear evidence of an elastic unloading region following the active plastic zone is found, but no secondary (plastic) reloading along the crack flank has been numerically observed for any level of hardening.
\r\n\r\nThe crack tip opening profile during growth is obtained for various levels of hardening. A ductile crack growth criterion is employed to investigate the nature of the J resistance curves under plane stress. Finally, the influence of hardening on the potential for stable crack growth is examined.
" }, { "name": "Rudin, Leonid Iakov", "degree": "PhD", "year": "1987", "title": "Images, Numerical Analysis of Singularities and Shock Filters", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-06192006-090538", "creators": [ { "name": { "family": "Rudin", "given": "Leonid Iakov" }, "id": "Rudin-Leonid-Iakov", "display_name": "Rudin, Leonid Iakov" } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "member", "display_name": "Fender, Derek H." }, { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "member", "display_name": "Thompson, Frederick B." }, { "name": { "family": "Luxemburg", "given": "W. A. J." }, "id": "Luxemburg-W-A-J", "role": "member", "display_name": "Luxemburg, W. A. J." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." } ], "option_major": [ "compsci" ], "doi": "10.7907/5hr8-8412", "abstract": "This work is concerned primarily with establishing a natural mathematical framework for the Numerical Analysis of Singularities, a term which we coined for this new evolving branch of numerical analysis.
\r\n\r\nThe problem of analyzing singular behavior of nonsmooth functions is implicitly or explicitly ingrained in any successful attempt to extract information from images. The abundance of papers on the so called Edge Detection testifies to this statement.
\r\n\r\nWe attempt to make a fresh start by reformulating this old problem in the rigorous context of the Theory of Generalized Functions of several variables with stress put on the computational aspects of essential singularities. We state and prove a variant of the Divergence Theorem for discontinuous functions which we call Fundamental Theorem of Edge Detection, for it is the backbone of the advocated here numerical analysis based on the estimates of contributions furnished by the essential singularities of functions.
\r\n\r\nWe further extend this analysis to arbitrary order singularities by utilization of the Miranda's calculus of tangential derivatives. With this machinery we are able to explore computationally the internal geometry of singularities including singular, i.e., nonsmooth, singularity boundaries. This theory gives rise to singularity detection scheme called \"rotating thin masks\" which is applicable to arbitrary order n-dimensional essential singularities. In the particular implementation we combined first-order detector with derived here various curvature detectors. Preliminary experimental results are presented. We also derive a new class of nonlinear singularity detection schemes based on tensor products of distributions.
\r\n\r\nFinally, a novel computational approach to the problem of image enhancement is presented. We call this construction the Shock Filters, since it is founded on the nonlinear PDE's whose solutions exhibit formation of discontinuous profiles, corresponding to shock waves in gas dynamics. An algorithm for experimental Shock Filter, based on the upwind finite difference scheme is presented and tested on the one and two dimensional data.
" }, { "name": "Schatzle, Paul Russell", "degree": "PhD", "year": "1987", "title": "An Experimental Study of Fusion of Vortex Rings", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232004-092555", "creators": [ { "name": { "family": "Schatzle", "given": "Paul Russell" }, "id": "Schatzle-Paul-Russell", "display_name": "Schatzle, Paul Russell" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KK00-ZJ41", "abstract": "A two-component laser-Doppler velocimeter with frequency bias is used to measure the velocity field produced by the oblique collision of two laminar vortex rings. The Reynolds number, defined here as the ratio of ring circulation to kinematic viscosity, is about 1800. The rings are generated underwater and approach each other along intersecting paths. The plane defined by the two paths is a plane of symmetry, and is the plane in which the measurements were done. The out-of-plane components of vorticity and strain rate are computed from finite differences of the velocity data. The state of the rings prior to the collision is determined in order to provide a set of starting conditions for future numerical simulations. In addition, the circulation of each vortex core is computed as a function of time during the collision.
\r\n\r\nThe principal result of this work is that the circulation of each vortex core is observed to decrease during the interaction; furthermore, the fluid viscosity is shown to be responsible for this decrease. The exact mechanism by which the reduction in circulation is effected is unclear, but it appears to be related to the out-of-plane stretching. A time scale is proposed for this cancellation process which combines the effects of viscosity and stretching.
\r\n\r\nThe measurements also show that the structure of the vorticity field changes during the collision. In particular, each vortex core is observed to split into two vortices under the action of the local in-plane strain field.
" }, { "name": "Sobota, Thomas Henry", "degree": "PhD", "year": "1987", "title": "An Experimental and Numerical Investigation of Swirling Flows in a Rectangular Nozzle", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03052008-091015", "creators": [ { "name": { "family": "Sobota", "given": "Thomas Henry" }, "id": "Sobota-Thomas-Henry", "display_name": "Sobota, Thomas Henry" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "chair", "display_name": "Marble, Frank E." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "mecheng" ], "doi": "10.7907/dw4x-ex64", "abstract": "The high thrust to weight ratios now possible for military aircraft have made thrust vector pitch control more attractive and versatile than aerodynamic surface pitch control. Use of a rectangular nozzle is a natural consequence because articulation and sealing problems are less formidable than for conventional circular nozzles. The rectangular nozzle offers the additional possibility that the exhaust may mix rapidly with the ambient air and thereby reduce the radiative signature of the exhaust. Some previous investigations have suggested that a series of axial vortices may form in the nozzle, as a result of residual swirl from the gas turbine exhaust, and further enhance the mixing rate.
\r\n\r\nA detailed experimental investigation is described in this thesis which demonstrates that the formation of axial vortices in the nozzle is dependant on the vorticity distribution at the turbine exhaust. Further, three mechanisms which provide for the formation of axial vortices are identified.
\r\n\r\nA parallel computational investigation was carried out which not only confirmed the relationship between the turbine exhaust vorticity and the vortex patterns formed in the nozzle but also provided details of the flow field between the turbine discharge and the nozzle exit. On the basis of this more detailed understanding, it is now possible to \"tailor\" the vortex distribution at the nozzle exit by design of the turbine discharge and the intervening passage.
\r\n" }, { "name": "Sterling, James David", "degree": "PhD", "year": "1987", "title": "Longitudinal Mode Combustion Instabilities in Air Breathing Engines", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07022004-165628", "creators": [ { "name": { "family": "Sterling", "given": "James David" }, "id": "Sterling-James-David", "orcid": "0000-0001-6110-0505", "display_name": "Sterling, James David" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" } ], "option_major": [ "mecheng" ], "doi": "10.7907/2WKT-AY26", "abstract": "An investigation of the self-excitation of low frequency (100-600 Hz), longitudinal acoustic modes of a rearward-facing step combustor has been performed. As in combustion instabilities of air breathing propulsion systems, the pressure oscillations are excited by a fluctuating heat release from a flame that is stabilized in a recirculation zone. Flow visualization results and flame radiation intensity data reveal that large vortex structures are responsible for this fluctuating heat release. The vortices are shed at frequencies corresponding to longitudinal acoustic modes of the system or to the first subharmonic of one of the modes.
\r\n\r\nA series of parametric studies were performed to determine the dependence of the vortex shedding frequency upon the step height, mean flow speed, fuel type, and equivalence ratio. It was discovered that the vortex shedding frequency can shift between modes as a result of changes in the chemical reaction time of the reactants or as a result of changes in the mixing process of the cold reactants with the hot products.
\r\n\r\nDetailed investigations into the mechanism of sustenance of the oscillations during instability were performed for several operating conditions. The distribution of the combustion associated with vortex shedding was investigated by measuring the radiation intensity from the flame region. These results were used in Rayleigh's Criterion to determine regions of driving and damping of the oscillations.
\r\n\r\nA one-dimensional linearized acoustic model is used to predict the natural modes of the system and a fluctuating volumetric source is used to model the oscillatory heat release. First, independent driving is applied to determine the system response to driving at different frequencies. One important result is that, the phase difference between the pressure oscillations and the velocity oscillations at the flameholder is very sensitive to the frequency of driving near natural modes of the system.
\r\n\r\nFinally, a velocity-sensitive volumetric source with a time delay is included as feedback to determine the linear stability characteristics of the system. Various mechanisms leading to nonlinear limit cycle behavior are then discussed and compared to experimental data obtained during transition to instability.
" }, { "name": "Toner, Stephen James", "degree": "PhD", "year": "1987", "title": "Entrainment, Chemistry, and Structure of Fire Plumes", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05052006-075204", "creators": [ { "name": { "family": "Toner", "given": "Stephen James" }, "id": "Toner-Stephen-James", "display_name": "Toner, Stephen James" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "mecheng" ], "doi": "10.7907/jazd-8n24", "abstract": "In Part 1, the entrainment in the lowest regions of buoyant fire plumes burning from an environment of quiescent fresh air (lower layer) across an interface into an environment of hot combustion products (upper layer) is investigated. Measurements using 20 to 200 kW natural gas flames formed above a 0.19 m diameter burner show that the entrained mass flux is nearly linear with distance from the fire source and essentially independent of the fuel flow rate. Comparison with previous results suggests that this linear dependence is valid over a wide range of conditions, but that the magnitude of the entrainment near the burner is influenced by the initial buoyancy of the plume.
\r\n\r\nThe chemistry of the products in the upper layer is also investigated. Over the ranges studied, the composition was a function of the upper-layer equivalence ratio only, and independent of the temperature of the upper layer or the residence time of the gas in it. For fuel-lean fires the product composition suggests that the fuel reaction is nearly complete, in contrast to fuel-rich fires where some of the stable intermediates are found to \"freeze out\" of the reaction prior to completion.
\r\n\r\nThe experimental method is extended to entrainment measurements on steady, axisymmetric, fully turbulent jet diffusion flames of hydrogen in air. In the momentum-dominated regions of the flame, the nondimensional mass flux used to characterize this regime is found to be constant as expected. The transition between momentum-dominated and buoyancy-dominated regions is also observed.
\r\n\r\nIn Part 2, a novel diagnostic technique, which makes use of laser light scattered by soot particles, was used in an effort to identify flame sheets within a natural gas diffusion flame. Soot particles, inherently created and consumed in the flame, were used as the scattering medium, which obviated the need for externally supplied seed material. Since no foreign material was added to the flame, the current technique can be considered truly nonintrusive. The soot distribution within a large buoyant natural gas diffusion flame is argued to be a reasonable marker for the presence of a diffusion flame. Measurements made in 47.4 to 190 kW natural gas flames stabilized on a 0.5 m diameter burner show that when soot is present within the outer boundary of the flame, it is observed as thin sheets, which become narrower in regions where the average strain rate is estimated to be greater. The structure of the soot distribution suggests that the combustion occurs along sheets of diffusion flamelets that are highly wrinkled and convoluted. Furthermore, they are distributed fairly uniformly within the volume of the flame, based on images of the associated soot, and occupy about 40 to 60% of the volume.
" }, { "name": "Venkatesh, Santosh Subramanyam", "degree": "PhD", "year": "1987", "title": "Linear Maps with Point Rules: Applications to Pattern Classification and Associative Memory", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-03052008-095021", "creators": [ { "name": { "family": "Venkatesh", "given": "Santosh Subramanyam" }, "id": "Venkatesh-Santosh-Subramanyam", "display_name": "Venkatesh, Santosh Subramanyam" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "eleceng" ], "doi": "10.7907/1YSB-Q028", "abstract": "Generalisations of linear discriminant functions are introduced to tackle problems in pattern classification, and associative memory. The concept of a point rule is defined, and compositions of global linear maps with point rules are incorporated in two distinct structural forms\u2014feedforward and feedback\u2014to increase classification flexibility at low increased complexity. Three performance measures are utilised, and measures of consistency established.
\r\n\r\nFeedforward pattern classification systems based on multi-channel machines are introduced. The concept of independent channels is defined and used to generate independent features. The statistics of multi-channel classifiers are characterised, and specific applications of these structures are considered. It is demonstrated that image classification invariant to image rotation and shift is possible using multi-channel machines incorporating a square-law point rule. The general form of rotation invariant classifier is obtained. The existence of optimal solutions is demonstrated, and good sub-optimal systems are introduced, and characterised. Threshold point rules are utilised to generate a class of low-cost binary filters which yield excellent classification performance. Performance degradation is characterised as a function of statistical side-lobe fluctuations, finite system space-bandwidth, and noise.
\r\n\r\nSimplified neural network models are considered as feedback systems utilising a linear map and a threshold point rule. The efficacy of these models is determined for the associative storage and recall of memories. A precise definition of the associative storage capacity of these structures is provided. The capacity of these networks under various algorithms is rigourously derived, and optimal algorithms proposed. The ultimate storage capacity of neural networks is rigourously characterised. Extensions are considered incorporating higher-order networks yielding considerable increases in capacity.
" }, { "name": "Wagner, Kelvin H.", "degree": "PhD", "year": "1987", "title": "Time and Space Integrating Acousto-Optic Signal Processing", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-05052006-155412", "creators": [ { "name": { "family": "Wagner", "given": "Kelvin H." }, "id": "Wagner-Kelvin-H", "display_name": "Wagner, Kelvin H." } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Masson", "given": "Colin R." }, "id": "Masson-Colin-R", "role": "co-chair", "display_name": "Masson, Colin R." }, { "name": { "family": "Lesh", "given": "James R." }, "id": "Lesh-James-R", "role": "member", "display_name": "Lesh, James R." } ], "option_major": [ "eleceng" ], "doi": "10.7907/4WH0-H941", "abstract": "One dimensional acousto-optic signal processing techniques are examined from the systems and functional viewpoint, and are then used as building blocks to synthesize multidimensional time and space integrating architectures. Time and space integrating signal processing systems are capable of performing 2-dimensional linear transformations upon images or matrices, by sequentially entering rows of the image with a travelling wave acousto-optic Bragg cell. The travelling rows are frozen by a pulsed laser diode, and the stationary diffracted fields are spatially processed by an optical system. The successively transformed rows are sequentially multiplied by a time varying reference wavefront, and accumulated on a time integrating CCD detector array to complete the two dimensional processing. Long 1-dimensional signals can also be linearly transformed by a time and space integrating system, by using a similar strategy upon a folded, or rastered, version of the high time bandwidth product signal. Small pieces of the long signal are slid into the system with an acousto-optic devices, and are spatially transformed over the device aperture. Then, successively transformed portions of the long signal are multiplied by a reference, and appropriately delayed and accumulated on a 2-D CCD in order to perform multichannel time integrations in the orthogonal dimension. The desired high time bandwidth one dimensional linear transformation is represented in the folded coordinate space of the 2-dimensional output detector.
\r\n\r\nThe operational characteristics of the principal active devices used in these time and space integrating systems are examined from the viewpoint of the system architect. The effects of the devices on the overall system operation are discussed, and device designs intended for application in a time and space integrating system operating environment are proposed.
\r\n\r\nThe final chapter is a detailed theoretical and experimental investigation into the particular operating characteristics of systems designed to perform a folded spectrum analysis of very high time bandwidth signals. This spectrum analysis problem has a shift variant transformation kernel, which can be broken down into a succession of smaller temporal and spatial sub transformations. The 1-dimensional space integrating spectrum analysis operation performed by a lens is used to produce a coarse spectral channelization of the input signal, displayed as a one dimensional spatial profile. Each resolvable spectral channel is fine frequency analyzed by temporal integration, producing a resulting intensity variation of each channel in the orthogonal direction, thereby forming a folded representation of the desired high time bandwidth spectrum analysis. The information which is needed to perform the fine frequency analysis is carried on the optical phase, so interferometric techniques are employed in order to detect the phase and transform it to an optical intensity modulation. Various bias terms are produced on the detector by the interferometric detection operation, and techniques for removing the unwanted bias are investigated. These include spatial carrier encoding of the interferometric terms combined with bandpass filtering, and direct bias subtraction techniques.
" }, { "name": "Wawrzynek, John Charles", "degree": "PhD", "year": "1987", "title": "VLSI Concurrent Computation for Music Synthesis", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-03052008-112515", "creators": [ { "name": { "family": "Wawrzynek", "given": "John Charles" }, "id": "Wawrzynek-John-Charles", "display_name": "Wawrzynek, John Charles" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Feynman", "given": "Richard Phillips" }, "id": "Feynman-R-P", "role": "member", "display_name": "Feynman, Richard Phillips" }, { "name": { "family": "Lyon", "given": "Richard F." }, "id": "Lyon-Richard-F", "role": "member", "display_name": "Lyon, Richard F." } ], "option_major": [ "compsci" ], "doi": "10.7907/qjfp-m864", "abstract": "This thesis presents a very large-scale integrated circuit (VLSI) approach to the generation of musical sounds. The approach allows the generation of rich musical sounds using models that are easy to control and have parameters corresponding to many of the physical attributes of musical instruments. The generality of the approach for music synthesis is demonstrated by presenting several primitive sound generation mechanisms. Utilizing these primitives, several musical instruments are assembled to produce struck, plucked, and blown sounds. Refinements of the instruments are easily accomplished by adjusting or rearranging different functional components. A concurrent computing engine supporting the sound generation mechanisms is presented along with details of its VLSI implementation. Involved in the implementation is a new CMOS design methodology. Several alternative architectures for the computing engine are also presented and studied.
" }, { "name": "Wu, Jin Jwang", "degree": "PhD", "year": "1987", "title": "Powder Synthesis in Aerosol Reactors", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06152006-074336", "creators": [ { "name": { "family": "Wu", "given": "Jin Jwang" }, "id": "Wu-Jin-Jwang", "display_name": "Wu, Jin Jwang" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Weinberg", "given": "William Henry" }, "id": "Weinberg-W-H", "role": "member", "display_name": "Weinberg, William Henry" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" } ], "option_major": [ "envreng" ], "doi": "10.7907/njvw-jn75", "abstract": "The onset of homogeneous nucleation of new particles from the products of gas phase chemical reactions has been explored using an aerosol flow reactor. Silicon seed particles were used as a probe to study the transition from seed growth by cluster deposition to runaway nucleation. This transition was found to be very abrupt. The mechanism of formation of solid particles from large excesses of low vapor pressure condensible species has been investigated by studying the microstructure of the product aerosol. A discrete - sectional solution of the aerosol general dynamic equation was derived in order to examine the aerosol evolution associated with fast chemical reactions. This kinetic model quantitatively predicts the aforementioned transition. Application of the understanding of aerosol generation and growth has led to the production of a high quality silicon powder suitable for ceramic applications. This powder was synthesized by the pyrolysis of silane in an aerosol reactor and has nearly ideal characteristics, i.e., controlled size distribution, spherically shaped, nonagglomerated submicron particles. A simple reaction coagulation model was developed to facilitate mapping of the nucleation and growth domains. This, in conjuction with the discrete-sectional model, was used to evaluate the various aerosol processes for powder synthesis. The influence of the initial reactant concentration, reaction rate, temperature profile, seed particle conditions, and residence time on the final powder characteristics were examined. The structure of the particles also depends on the way particles fuse together. Particle fusing was therefore, modeled along with the formation and growth processes to study the effects of coalescence on the extent of agglomeration of the product powder. A recipe for the synthesis of ideal powders was proposed.
\r\n" }, { "name": "Yeh, Xian-Li", "degree": "PhD", "year": "1987", "title": "Reaction of Hydrogen with Crystalline and Amorphous Alloys \u2014 Crystal to Amorphous Transformation Induced by Hydrogen", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-144844", "creators": [ { "name": { "family": "Yeh", "given": "Xian-Li" }, "id": "Yeh-Xian-Li", "display_name": "Yeh, Xian-Li" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/zc2t-pq88", "abstract": "Metastable polycrystalline A1-xBx (A = Zr, Hf, B = Pd, Rh, 0.15 \u2264 x \u2264 0.25) alloys having a fcc structure are reacted with hydrogen gas at temperatures ranging from 25\u00b0C to 250\u00b0C. It is demonstrated for the first time that an amorphous phase can be formed during such a solid state reaction when the temperature lies below 220\u00b0C. Such a reaction is possible only if the following requirements are satisfied: The existence of a thermodynamic driving force (i.e., the amorphous phase must have a lower free energy than the free hydrogen and the crystalline phase from which it forms) and the existence of a kinetic constraint (i.e., the formation of thermodynamically preferred equilibrium phases or phase mixtures must be kinetically suppressed).
\r\n\r\nX-ray diffraction and TEM studies show that the amorphous phase grows at the expense of the crystalline phase during hydrogen absorption by these metastable fcc alloys. The formation of the amorphous hydride phase is observed by TEM to begin at grain boundaries of the polycrystalline alloys much in the same manner that \"melting\" nucleates at grain boundaries. X-ray analysis indicates that the Zr-Zr distance increases as hydrogen is absorbed, suggesting that hydrogen atoms prefer to stay in tetrahedral sites surrounded by four Zr atoms. This provides evidence as to why the amorphous hydride phase is more stable than the fcc hydride phase. The thermal behavior of amorphous hydrides obtained by hydriding metallic glasses and that obtained by hydriding metastable crystalline alloys are compared and found to be similar. The hydrogen distribution and surface effects are investigated using hydrogen depth profiling, SEM and Rutherford backscattering. Hydrogen permeation through the sample surface has been found to be the rate limiting step in the hydriding reaction.
\r\n\r\nBased on the present experiments and an analysis of the relevant free energy curves, we discuss the thermodynamic and kinetic aspects of this phase transformation to explain why an amorphous phase is formed. The mechanism for this can be viewed as melting in the solid state. A simple \"chemical frustration\" model is proposed to explain the kinetics of amorphization via hydriding.
" }, { "name": "Zehnder, Alan T.", "degree": "PhD", "year": "1987", "title": "Dynamic Fracture Initiation and Propagation in Metals: Experimental Results and Techniques", "advisor": "Rosakis, Ares J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03052008-085910", "creators": [ { "name": { "family": "Zehnder", "given": "Alan T." }, "id": "Zehnder-Alan-T", "display_name": "Zehnder, Alan T." } ], "advisors": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "advisor", "display_name": "Rosakis, Ares J." } ], "committee": [ { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "role": "chair", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" } ], "option_major": [ "mecheng" ], "doi": "10.7907/f3zy-j846", "abstract": "Dynamic fracture initiation and propagation in ductile and brittle materials was studied experimentally using the optical method of caustics in conjunction with high speed photography. The drop weight impact test, previously used only for studies of fracture initiation, was adapted to study both dynamic fracture initiation and dynamic fracture propagation.
\r\n\r\nThe results show that for a relatively brittle, quenched and tempered, high strength 4340 steel the dynamic fracture propagation toughness depends on crack tip velocity through a relation that is a material property. In addition, the effect of stress waves on the dynamic response of different specimen geometries is discussed and the micromechanisms of failure for this heat treatment of 4340 steel are investigated.
\r\n\r\nExtension of the optical method of caustics to applications in elastic-plastic fracture was studied with the goal of learning how to measure dynamic fracture initiation toughness in tough, ductile materials. Static experiments were performed on different specimen geometries of a ductile 4340 steel and 1018 cold rolled steel, and were compared to small scale yielding, plane stress, finite element results. Issues studied that are related to the applicability of caustics are the extent of the dominance of the plane stress HRR field, the effect of plasticity on the accuracy of caustics from the elastic region outside the plastic zone, and the extent of the crack tip region of three dimensionality.
\r\n\r\nThe above approach to caustics in ductile materials was based on the assumption of validity of the HRR field. A novel approach to the use of caustics with ductile materials was taken that eliminates the concerns over the region of dominance of the HRR field, etc. In this approach a calibration experiment was performed relating the caustic diameter to the J integral for a particular specimen geometry under conditions of large scale yielding. This approach was successfully applied to optically measure for the first time the J integral under dynamic loading. Measurement of the J integral by means of strain gages was developed and applied to obtain J simultaneously with the caustics measurement.
\r\n\r\nAt the same time (and on the same specimens) additional measurements were made including, load, load-point displacement, strains near the crack tip and out of plane displacements (measured with interferometry). These results are compared with excellent agreement to a three dimensional finite element simulation of the specimen.
" }, { "name": "Zhang, Zhe", "degree": "PhD", "year": "1987", "title": "Coupled-Inductor Magnetics in Power Electronics", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112008-080918", "creators": [ { "name": { "family": "Zhang", "given": "Zhe" }, "id": "Zhang-Zhe", "display_name": "Zhang, Zhe" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "chair", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7T0E-2219", "abstract": "Leakages are inseparably associated with magnetic circuits and are always thought of in three different negative ways: either you have them and you don't want them (transformers), or you don't have them but want them (to limit transformer short circuit currents), or you have them and want them, but you don't have them in the right amount (coupled-inductor magnetic structures). The methods of how to introduce the leakages at appropriate places and in just the right amounts in coupled-inductor magnetic structures are presented here, in order to optimize the performance of switching dc-to-dc converters.
" }, { "name": "Zufiria, Juan Antonio", "degree": "PhD", "year": "1987", "title": "Part I: Symmetry Breaking of Water Waves. Part II: On the Superharmonic Instability of Surface Water Waves", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03052008-090255", "creators": [ { "name": { "family": "Zufiria", "given": "Juan Antonio" }, "id": "Zufiria-Juan-Antonio", "display_name": "Zufiria, Juan Antonio" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "member", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "appmath" ], "doi": "10.7907/4JDZ-9Y53", "abstract": "PART I:
\r\n\r\nA weakly nonlinear Hamiltonian model for two dimensional irrotational waves on water of finite depth is developed. The truncated model is used to study families of periodic travelling waves of permanent form. It is shown that nonsymmetric periodic waves exist, which appear via spontaneous symmetry breaking bifurcations from symmetric waves.
\r\n\r\nIn order to check these results with the full water wave equations, two different methods are used to calculate nonsymmetric gravity waves on deep water. It is found that they exist and the structure of the bifurcation tree is the same as the one found for waves on water of finite depth using the weakly nonlinear Hamiltonian model. One of the methods is based on the quadratic relations between the Stokes coefficients discovered by Longuet-Higgins (1978a). The other method is a new one based on the Hamiltonian structure of the water wave problem.
\r\n\r\nAnother weakly nonlinear model is developed from the Hamiltonian formulation of water waves to study the bifurcation structure of gravity-capillary waves on water of finite depth. It is found that, besides a very rich structure of symmetric solutions, nonsymmetric Wilton ripples exist. They appear via spontaneous symmetry breaking bifurcation from symmetric solutions. The bifurcation tree is similar to that for gravity waves. The solitary wave with surface tension is studied with the same model close to a critical depth. It is found that the solution is not unique, and further nonsymmetric solitary waves are possible. The bifurcation tree has the same structure as for the case of periodic waves. The possibility of checking these results in low gravity experiments is discussed.
\r\n\r\nPART II:
\r\n\r\nSaffman's (1985) theory of the superharmonic stability of two-dimensional irrotational waves on fluid of infinite depth has been generalized to solitary and periodic waves of permanent form on fluid of finite uniform depth. The frame of reference for the calculation of the Hamiltonian for periodic waves of finite depth is found to be the frame in which the mean horizontal velocity is zero.
\r\n\r\nAlso, a simple analytical model has been constructed to demonstrate Saffman's (1985) theory. The model shows the change of geometrical and algebraic multiplicity of the eigenvalues and eigenvectors of the stability equation at the critical height. It confirms the existence of Hamiltonian systems with limit points at which there is no change of stability.
\r\n" }, { "name": "d'Agostino, Luca", "degree": "PhD", "year": "1987", "title": "Experimental and Theoretical Study on Cavitation Inception and Bubbly Flow Dynamics: I. Design, Development and Operation of a Cavitation Susceptibility Meter. II. Linearized Dynamics of Bubbly and Cavitating Flows with Bubble Dynamics Effects", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-150544", "creators": [ { "name": { "family": "d'Agostino", "given": "Luca" }, "id": "d'Agostino-Luca", "display_name": "d'Agostino, Luca" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" } ], "option_major": [ "mecheng" ], "doi": "10.7907/HK8Q-VQ14", "abstract": "The first and main part of this work presents the design, development and operation of a Cavitation Susceptibility Meter based on the use of a venturi tube for the measurement of the content of active cavitation nuclei in water samples. The pressure at the venturi throat is determined from the upstream pressure and the local flow velocity without corrections for viscous effects because the flow possesses a laminar potential core in all operational conditions. The detection of cavitation and the measurement of the flow velocity are carried out optically. The apparatus comprises a Laser Doppler Velocimeter for the measurement of the flow velocity and the detection of cavitation, a custom-made electronic Signal Processor for real time generation and temporary storage of the data and a computerized system for the final acquisition and reduction of the collected data. The various steps and considerations leading to the present design concept are discussed in detail and the implementation of the whole system is described in order to provide the all the information necessary for its calibration and operation. Finally, the results of application of the Cavitation Susceptibility Meter to the measurement of the water quality of tap water samples are presented and critically discussed with reference to other similar or alternative methods of cavitation nuclei detection and to the current state of knowledge on cavitation inception.
\r\n\r\nThe second part of the present work presents the results of an investigation on the linearized dynamics of two-phase bubbly flows with the inclusion of bubble dynamics effects. Two flow configurations have been studied: the time dependent one-dimensional flow of a spherical bubble cloud subject to harmonic excitation of the far field external pressure and the steady state two-dimensional flow of a bubbly mixture on a slender profile of arbitrary shape. The inclusion of bubble dynamic damping and of the relative motion between the two phases and the extension of the results to the case of arbitrary excitation are discussed when examining the second flow configuration. The simple linearized dynamical analysis developed so far clearly demonstrates the importance of the complex phenomena connected to the interaction of the dynamics of the bubbles with the flow and provides an introduction to the study of the same flows with non-linear bubble dynamics.
" }, { "name": "Abdel-Ghaffar, Khaled Ahmed Sabry", "degree": "PhD", "year": "1986", "title": "An Information- and Coding-Theoretic Study of Bursty Channels with Applications to Computer Memories", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252008-093415", "creators": [ { "name": { "family": "Abdel-Ghaffar", "given": "Khaled Ahmed Sabry" }, "id": "Abdel-Ghaffar-Khaled-Ahmed-Sabry", "display_name": "Abdel-Ghaffar, Khaled Ahmed Sabry" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Wilson", "given": "Richard M." }, "id": "Wilson-R-M", "role": "member", "display_name": "Wilson, Richard M." }, { "name": { "family": "Pless", "given": "Vera" }, "id": "Pless-V", "role": "member", "display_name": "Pless, Vera" } ], "option_major": [ "eleceng" ], "doi": "10.7907/gfyh-ss98", "abstract": "This thesis is a study of two-dimensional bursty channels from the information- theoretic as well as the coding-theoretic points of view. An information-theoretic model of bursty channels is defined and analyzed using probabilistic arguments. Two-dimensional burst correcting codes are developed. Their combinatorial and algebraic structures are examined. Two-dimensional bursty channels are used to model computer memories. The results of this thesis give bounds on the storage capacities of computer memories if sophisticated codes are used.
\r\n" }, { "name": "Adkins, Douglas Ray", "degree": "PhD", "year": "1986", "title": "Analyses of Hydrodynamic Forces on Centrifugal Pump Impellers", "advisor": "Brennen, Christopher E.; Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-111453", "creators": [ { "name": { "family": "Adkins", "given": "Douglas Ray" }, "id": "Adkins-Douglas-Ray", "display_name": "Adkins, Douglas Ray" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "co-advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/X6KZ-W852", "abstract": "It has been experimentally determined by previous investigators that hydrodynamic forces can cause a centrifugal pump impeller to whirl in a volute. The present work was undertaken to develop a theoretical model of the interactions that occur between an impeller and a volute, and to identify the source of the hydrodynamic forces. Experiments were then conducted to test the predictions of the model. The theoretical analysis presents a quasi-one dimensional treatment of the flow in the volute and accounts for the disturbance at the impeller discharge that is caused by the volute. The model also considers the lack of perfect guidance through the blade passages. Extending this model allowed for the calculation of hydrodynamic force perturbations that result when the impeller whirls eccentrically in the volute. These force perturbations were shown to encourage, rather than dissipate the whirling motion. The predictions of the model gave reasonable comparisons with the experimental data obtained in this study. Further, it was experimentally observed that pressure forces acting on the front shroud of the impeller could have a major influence on the hydrodynamic force perturbations acting on an eccentrically positioned impeller.
" }, { "name": "Anderson, Mark Carter", "degree": "PhD", "year": "1986", "title": "A Study of the Periodic and Quasi-Periodic Solutions of the Discrete Duffing\r\nEquation", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252008-105035", "creators": [ { "name": { "family": "Anderson", "given": "Mark Carter" }, "id": "Anderson-Mark-Carter", "display_name": "Anderson, Mark Carter" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/RCHW-E496", "abstract": "The present investigation concentrates on the phenomenological and analytically quantitative study of the periodic and quasi-periodic solutions of a class of conservative, autonomous, nonlinear difference equations. In particular, an equation with a cubic nonlinearity, i.e., a form of the discrete Duffing equation, is studied. Following a simple analysis of the equilibrium solutions, the global structures of the phase portraits are illustrated phenomenologically for different values of the equation parameters. Three discrete perturbation procedures are then developed to obtain a consistent approximation for periodic and quasi- periodic solutions. These approximate solutions contain certain \"small divisors\" in every term other than the zero'th order term. An examination of the consequences of the vanishing of such a \"small divisor\" leads to a method of constructing exact periodic solutions in the form of finite Fourier series. The thesis concludes with a discussion of the quasi-periodic approximate solutions and their applicability.\r\n" }, { "name": "Atzmon, Michael", "degree": "PhD", "year": "1986", "title": "A Study of Bulk Amorphous Alloys Formed by Solid-State Reaction in Elemental Composites", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-03212008-081007", "creators": [ { "name": { "family": "Atzmon", "given": "Michael" }, "id": "Atzmon-Michael", "orcid": "0000-0002-7055-1313", "display_name": "Atzmon, Michael" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "member", "display_name": "Ahrens, Thomas J." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/5M6N-SK53", "abstract": "Bulk amorphous Zr- and Er- based alloys have been synthesized by solid-state reaction in elemental composites prepared by mechanical deformation. For the Er- based composites, complete amorphization was achieved by near- isothermal rolling near room temperature. The driving force for the reaction was found to be a large negative enthalpy of mixing between the constituent elements. Strain and interfacial energies have been estimated and found to modify the driving force only slightly. X-ray diffraction and differential scanning calorimetry have been used to characterize the structure and crystallization behavior of the alloys obtained. Comparison to corresponding amorphous alloys prepared by liquid quenching and sputtering gave good agreement.
\r\n\r\nThe diffusion of Au in amorphous Au-Y and Au-La thin films produced by co-evaporation has been studied by means of X-ray diffraction and Rutherford backscattering. An estimated diffusion coefficient agrees with those obtained by other authors for diffusion of Au in several amorphous alloys. The results confirm that there can be bulk self-diffusion in an amorphous alloy without crystallization. Thus, one does not need to assume short-circuit diffusion during the growth of an amorphous phase by solid-state reaction.
" }, { "name": "Banwell, Thomas Clyde", "degree": "PhD", "year": "1986", "title": "Investigations of Atomic Transport Induced by Heavy Ion Irradiation", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242008-133647", "creators": [ { "name": { "family": "Banwell", "given": "Thomas Clyde" }, "id": "Banwell-Thomas-Clyde", "display_name": "Banwell, Thomas Clyde" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3sgh-2m46", "abstract": "The mechanisms of atomic transport induced by ion irradiation generally fall into the categories of anisotropic or isotropic processes. Typical examples of these are recoil implantation and cascade mixing, respectively. Each possesses its own characteristic fluence dependence (linear and square-root, respectively), although both may occur concurrently. In this case, these processes can be distinguished by carefully examining the fluence dependence at low fluences (less that 1015cm-2). Parametric studies can produce added insight.
\r\n\r\nWe have measured the interaction of these processes in the mixing of Ti/SiO2/Si, Cr/SiO2/Si and Ni/SiO2/Si multi-layers irradiated with Xe at fluences of 0.01 - 10x1015cm-2. The fluence dependence of net metal transport into the underlying layers was measured with different thicknesses of SiO2 and different sample temperatures during irradiation (-196 to 500C). There is a linear dependence at low fluences. The initial slope depends on the sample temperature. At high fluences, a square-root behavior predominates. For thin SiO2 layers (< 20 nm), the cross-over point depends on the SiO2 thickness. These results are readily interpreted in terms of competition between the flux of injected atoms and diffusion of the accumulating metal. Metal appears to be the dominant moving species in these systems. The initial linear dependence was not observed in samples without SiO2, which shows that the effect is not due to cascade overlap.
\r\n\r\nThe detailed analysis allows us to speculate on the role of chemical reaction kinetics in controlling the outcome of intra-cascade processes. There is no significant correlation between the reactivity of the metal with SiO2 and the amount of mixing observed when the irradiations are performed at 25C or below. The contribution from primary recoils is quite pronounced since the gross mixing is small. A significant correlation exists between the mixing and the energy deposited through elastic collisions FD. Several models are examined in an attempt to describe the transport process in Ni/SiO2. It is likely that injection of Ni by secondary recoil implantation is primarily responsible for getting Ni into the SiO2. There were a few more objections against the other conceivable limiting cases. Secondary recoil injection is thought to scale with FD. Trends in the mixing rates indicate that the dominant mechanism for Ti and Cr could be the same as for Ni. Nevertheless, the structure of the mixed region is very different for the three metals. The product of chemical reactions were identified with TEM and XPS. The low temperature results suggest that kinetic constraints are responsible for suppressing the chemical reactions that one might anticipate.
\r\n\r\nThe processes of atomic transport and phase formation clearly fail to be separable at higher temperatures. A positive correlation with chemical reactivity emerges at higher irradiation temperatures. This was not pursued beyond preliminary results reported for Ti or Cr. The temperature at which rapid mixing occurs is not much below that for spontaneous thermal reaction. Less Ni is retained in the SiO2 at high irradiation temperatures. Ni incorporated in the SiO2 by low temperature irradiation is not expelled during a consecutive high temperature irradiation. The Ni remains trapped within larger clusters during a sequential 500C irradiation.
\r\n" }, { "name": "Barrett, Christopher Louis", "degree": "PhD", "year": "1986", "title": "On Central Processes in the Temporal Control of Movement", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-085846", "creators": [ { "name": { "family": "Barrett", "given": "Christopher Louis" }, "id": "Barrett-Christopher-Louis", "orcid": "0000-0003-2518-0039", "display_name": "Barrett, Christopher Louis" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "display_name": "Fender, Derek H." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Hamilton", "given": "Charles R." }, "id": "Hamilton-Charles-R", "display_name": "Hamilton, Charles R." }, { "name": { "family": "White", "given": "C. T." }, "id": "White-C-T", "display_name": "White, C. T." } ], "option_major": [ "bioinfo", "eng" ], "doi": "10.7907/9jgx-pa60", "abstract": "Various applied problems in the areas of manual control and biosystems analysis involve the desire to noninvasively monitor cognitive processes during task performance. This thesis addresses the general problem that the usual methods and assumptions of biosystems analysis may not strictly apply where psychological functioning exhibits a controlling influence on behavior. An experimental situation is proposed as such a case, in which the percept of duration seems to have controlling influence on the timing of a fingertap.
\r\n\r\nThe major themes in theories of motor behavior are surveyed and their reference to higher processes examined. A useful taxonomy of mental processes is outlined to clarify the nature of the processes involved.
\r\n\r\nThe notion of representation is basic to the characterization of mental processes. Prevalent views on the relationship of representation and behavior are assessed, leading to a formalization of representation in which a probability measure on the representational structure can be understood as a model of belief or subjective expectation. The model of representation is constructive and satisfies the taxonomy of mental representation.
\r\n\r\nAn information measure and channel analogy of central processes is formed using the probability measure. The channel analogy leads to a definition of representational event. The representational event is used to formalize the idea of a subjectively constant clocktime interval from which first-order predictions of central process effects on periodic behaviors of subjectively constant rate derive. A fingertapping experiment was undertaken to verify these predictions. Two levels of cognitive influences on finger tapping were discernible. The conformance of the data to the predictions suggests that the developments of this thesis could be useful to biosystems and human factors analyses of cognitive level phenomena underlying behavior.
" }, { "name": "Blume, Janet A.", "degree": "PhD", "year": "1986", "title": "Some Issues in the Kinematics of Finite Deformations", "advisor": "Sternberg, Eli", "url": "https://resolver.caltech.edu/CaltechETD:etd-03212008-074451", "creators": [ { "name": { "family": "Blume", "given": "Janet A." }, "id": "Blume-Janet-A", "display_name": "Blume, Janet A." } ], "advisors": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "advisor", "display_name": "Sternberg, Eli" } ], "committee": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "chair", "display_name": "Sternberg, Eli" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Harris", "given": "John Gregory" }, "id": "Harris-John-Gregory", "role": "member", "display_name": "Harris, John Gregory" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/5rhm-hb74", "abstract": "This dissertation deals chiefly with various issues pertaining to the existence and uniqueness of a finite deformation that gives rise to a prescribed right or left Cauchy-Green strain-tensor field.
\r\n\r\nFollowing a review and discussion of available existence and uniqueness theorems appropriate to a pre-assigned right strain field, the extent of uniqueness of a generating deformation is established under minimal smoothness and invertibility assumptions. Further, the compatibility equations of finite continuum kinematics are used to arrive at an analytical proof of Liouville's theorem on conformal deformations, which supplies an exhaustive classification of three-dimensional deformations that preserve all angles.
\r\n\r\nThe remainder of the dissertation is devoted to the more involved corresponding existence and uniqueness questions for a given left strain-tensor field. These questions are first discussed in a three-dimensional setting and are then resolved for the special class of plane deformations. The results thus obtained stand in marked contrast to their counterparts for a given right strain field.
\r\n" }, { "name": "Bruno, William Michael", "degree": "PhD", "year": "1986", "title": "Powder Core Dielectric Waveguides", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-084301", "creators": [ { "name": { "family": "Bruno", "given": "William Michael" }, "id": "Bruno-William-Michael", "display_name": "Bruno, William Michael" } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "chair", "display_name": "Bridges, William B." }, { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "member", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Pickett", "given": "Herbert M." }, "id": "Pickett-H-M", "role": "member", "display_name": "Pickett, Herbert M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/mxe4-ep43", "abstract": "Flexible dielectric waveguides have been demonstrated at 10 GHz and 94 GHz by filling hollow, low dielectric constant polymer tubes with low-loss, high-dielectric constant powders. Flexible guides with losses as low as 0.12 dB/cm were demonstrated at 94 GHz. These guides also exhibited negligible bending loss for radii of curvature greater than 4 cm.
\r\n\r\nThe theory of 3-region cylindrical dielectric waveguide was used to design the powder-filled tube guides, and measured wavelengths for the HE11 mode are in agreement with theoretical values. Sets of dispersion curves were calculated numerically from the theory for waveguide parameters typical to our guides.
\r\n\r\nA powder-filled rectangular groove in the surface of a plastic substrate has also been demonstrated as a dielectric waveguide at 94 GHz. Guide wavelengths measured for these channel guides for various combinations of guide dimensions, powders, and substrate materials agree with values predicted by the approximate theory of Marcatili for the Ey11 mode. Measured transmission losses were as low as 0.09 dB/cm.
\r\n\r\nThe 94 GHz loss tangents of the powders were calculated by extending Marcatili's theory to relate channel guide attenuation to material losses. These calculated values of loss tangent increased with powder packing fraction, as predicted by theories of electromagnetic wave propagation in random heterogeneous media. Estimates of the 94 GHz loss tangents of the solid constituent materials were then obtained from these theories using the powder loss tangents.
\r\n\r\nPowder channel ring resonators had Q's as high as 2400 at 94 GHz in an 8 cm diameter ring. Directional coupling from adjacent straight channel guides was used to form a transmission filter. Marcatili's approximate theory of bending loss for channel guide appears to be inadequate for predicting the curvature losses of these resonators.
\r\n\r\nIn a 10 GHz experiment, the coupling between two parallel powder channel waveguides was measured as a function of their separation. The measured coupling was at variance with that predicted by Marcatili's approximate analysis for parallel channel waveguides.
" }, { "name": "Conklin, Martha Harriet", "degree": "PhD", "year": "1986", "title": "Thermodynamics, Kinetics and Mechanisms of the Reactions of S(IV) with Cu(II) and Fe(III)", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242008-134119", "creators": [ { "name": { "family": "Conklin", "given": "Martha Harriet" }, "id": "Conklin-Martha-Harriet", "display_name": "Conklin, Martha Harriet" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Chan", "given": "Sunney I." }, "id": "Chan-S-I", "orcid": "0000-0002-5348-2723", "role": "member", "display_name": "Chan, Sunney I." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/83k6-ex73", "abstract": "Spectrosopic methods are used to determine the stability constant for the formation of CuSO3, K = 1.8 \u00b1 0.6 x 104 M-1 for \u00b5 = 0.4 M. Infrared and Raman measurements indicate that sulfite binds to the metal through both sulfur and oxygen. These results are compared to those of other first-row transition metal-sulfite complexes.
\r\n\r\nThe reduction of Cu(II) is shown to proceed via (Cu(II))2SO32+ and CuSO3CuOH+ intermediates. Copper(I), SO42- and a mixed valence compound Cu||SO3Cu2|SO3\u20222H2O are determined to be the principal products. The rate law is consistent with consecutive first-order reactions. Results are interpreted in terms of the initial formation of an inner-sphere complex which is followed by a rate-limiting electron transfer step. Previously accepted mechanisms for the trace metal catalysis of the autoxidation of SO32- are discussed in light of these results.
\r\n\r\nA conditional stability constant for the formation of a Fe(III)-S(IV) complex at \u00b5 = 0.4 M and pH 2.1 was determined spectroscopically. Raman measurements indicate that sulfite binds to the metal through oxygen. EPR experiments show that the reduction of Fe(III) to Fe(II) by S(IV) is a slow reaction at pH 2 (\u03c41/2 \u2243 8 min). Various pathways for the formation of the Fe(III)-S(IV) species are examined to determine the most probable equilibrium species. Results are interpreted by comparing the stability and bonding of Fe(III)-S(IV) species with other Fe(III) complexes.
\r\n\r\nThe rates of these internal redox reactions are too slow for this reaction to be important in the atmospheric autoxidation of S(IV), instead ternary metal-oxygen-sulfito complexes are proposed as the active catalytic species in aqueous atmospheric systems. Calculations based on the equilibrium constants obtained in this study indicate that metal-S(IV) complexes may be important equilibrium species in the absence of \u03b1-hydroxyalkylsulfonates. The catalytic autoxidation of SO2 in aqueous systems appears to proceed via the formation of metal-sulfite complexes as a prelude to electron-transfer.
\r\n" }, { "name": "Dally, William James", "degree": "PhD", "year": "1986", "title": "A VLSI Architecture for Concurrent Data Structures", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252008-140428", "creators": [ { "name": { "family": "Dally", "given": "William James" }, "id": "Dally-William-James", "display_name": "Dally, William James" } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "chair", "display_name": "Seitz, Charles L." }, { "name": { "family": "Bryant", "given": "Randal E." }, "id": "Bryant-R", "role": "member", "display_name": "Bryant, Randal E." }, { "name": { "family": "Feynman", "given": "Richard Phillips" }, "id": "Feynman-R-P", "role": "member", "display_name": "Feynman, Richard Phillips" }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "compsci" ], "doi": "10.7907/f8d5-x741", "abstract": "Concurrent data structures simplify the development of concurrent programs by encapsulating commonly used mechanisms for synchronization and communication into data structures. This thesis develops a notation for describing concurrent data structures, presents examples of concurrent data structures, and describes an architecture to support concurrent data structures.
\r\n\r\nConcurrent Smailtalk (CST), a derivative of Smailtalk-80 with extensions for concurrency, is developed to describe concurrent data structures. CST allows the programmer to specify objects that are distributed over the nodes of a concurrent computer. These distributed objects have many constituent objects and thus can process many messages simultaneously. They are the foundation upon which concurrent data structures are built.
\r\n\r\nThe balanced cube is a concurrent data structure for ordered sets. The set is distributed by a balanced recursive partition that maps to the subcubes of a binary n-cube using a Gray code. A search algorithm, VW search, based on the distance properties of the Gray code, searches a balanced cube in O(log N) time. Because it does not have the root bottleneck that limits all tree-based data structures to O(1) concurrency, the balanced cube achieves O(N/log N) concurrency.
\r\n\r\nConsidering graphs as concurrent data structures, graph algorithms are presented for the shortest path problem, the max-flow problem, and graph partitioning. These algorithms introduce new synchronization techniques to achieve better performance than existing algorithms.
\r\n\r\nA message-passing, concurrent architecture is developed that exploits the characteristics of VLSI technology to support concurrent data structures. Interconnection topologies are compared on the basis of dimension. It is shown that minimum latency is achieved with a very low dimensional network. A deadlock-free routing strategy is developed for this class of networks, and a prototype VLSI chip implementing this strategy is described. A message-driven processor complements the network by responding to messages with a very low latency. The processor directly executes messages, eliminating a level of interpretation. To take advantage of the performance offered by specialization while at the same time retaining flexibility, processing elements can be specialized to operate on a single class of objects. These object experts accelerate the performance of all applications using this class.
" }, { "name": "Dauhajre, Abraham A.", "degree": "PhD", "year": "1986", "title": "Modelling and Estimation of Leakage Phenomena in Magnetic Circuits", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-111040", "creators": [ { "name": { "family": "Dauhajre", "given": "Abraham A." }, "id": "Dauhajre-Abraham-A", "display_name": "Dauhajre, Abraham A." } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "chair", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Thompson", "given": "Peter M." }, "id": "Thompson-Peter-M", "role": "member", "display_name": "Thompson, Peter M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/VTCM-S717", "abstract": "A new modelling method for magnetic circuits is presented in this thesis. This method can be used to model magnetic circuits with any number of windings. The models incorporate adequate information about the correct distribution of leakage energy, the presence of gaps throughout the core, the arrangement of the windings, and the type of core used.
\r\n\r\nThese new electric circuit models (physical models) are \"physically natural\"; i.e., the elements in the models have a one-to-one relationship with corresponding physical quantities in the original magnetic structure.
\r\n\r\nSeveral commonly used arrangements such as toroids with uniformly distributed turns, and bobbin core structures with multiple windings were modelled with the new technique. The measured electric circuit model values always compared favorably with the predicted physical values derived with the new method.
\r\n\r\nBy breaking the windings of the magnetic circuit into their separate layers, a more elaborate and accurate set of models (layer-to-layer models) can be obtained. These models incorporate additional information about the correct distribution of the windings and interwinding self-capacitances. Because of the complicated nature of these elaborate models, they are more suitable for computer analysis of magnetic circuits.
" }, { "name": "El-Hamamsy, Sayed-Amr", "degree": "PhD", "year": "1986", "title": "Coupled-Inductor Inversion, Rectification and Cycloconversion", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-092115", "creators": [ { "name": { "family": "El-Hamamsy", "given": "Sayed-Amr" }, "id": "El-Hamamsy-Sayed-Amr", "display_name": "El-Hamamsy, Sayed-Amr" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "chair", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Thompson", "given": "Peter M." }, "id": "Thompson-Peter-M", "role": "member", "display_name": "Thompson, Peter M." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." } ], "option_major": [ "eleceng" ], "doi": "10.7907/BHKX-4J16", "abstract": "A new PWM approach using three state switching of negatively coupled inductors can be applied to any basic dc-to-dc converter to form single-phase dc-to-ac inverters. Current reference programming gives improvements in linearity, small-signal dynamics, and pulsed-load response. The current programming loops of the flyback and boost inverters are stable at all operating points. New multiple output magnetic structures are introduced that apply space and time multiplexing of magnetics to give non-interacting outputs. The magnetics are analysed for different operating conditions. The inverters with two independent outputs are derived by use of the multiple output magnetics. These are used to form the three-phase versions of the inverters, The corresponding three-phase ac-to-dc rectifiers are also derived with close to ideal current waveforms as well as power factor correction capabilities. Finally, to complete the family of power converters the polyphase ac-to-ac cycloconverters are derived incorporating the qualities of both the inverters and the rectifiers.
\r\n" }, { "name": "Gray, Harry Andrew", "degree": "PhD", "year": "1986", "title": "Control of Atmospheric Fine Primary Carbon Particle Concentrations", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252008-092905", "creators": [ { "name": { "family": "Gray", "given": "Harry Andrew" }, "id": "Gray-Harry-Andrew", "display_name": "Gray, Harry Andrew" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/p3dp-1v47", "abstract": "The adverse health effects and urban visibility degradation associated with atmospheric carbon particle concentrations suggest that control of this class of air pollutants is desirable, especially in the event of an increase in the usage of diesel vehicles. In this study, procedures for the engineering design of fine carbonaceous particulate matter abatement strategies have been developed and tested in the Los Angeles area. Carbon particle abatement strategies are evaluated based on the results of an emissions to air quality model, the performance of which is verified by comparison to measurements of ambient aerosol concentrations taken in the South Coast Air Basin during 1982.
\r\n\r\nAs a result of this research, the long\u2014term average behavior of fine aerosol carbon concentrations has been characterized in the Los Angeles area for the first time. The highest concentrations of fine particulate total carbon were observed in areas of heavy traffic density. The annual average fine total carbon concentration at downtown Los Angeles was 12.2 \u00b5g m-3 during 1982, which constituted 37% of the fine aerosol (dp < 2.1 \u00b5m) mass collected at that location. Aerosol carbon concentrations were observed to decrease with distance inland from downtown Los Angeles. The 1982 annual average fine total carbon concentration at Rubidoux, which is about 80 km east of Los Angeles, was only 8.2 \u00b5g m-3. There is a pronounced winter peak and summer minimum in carbonaceous aerosol concentrations in the western portion of the air basin. The monthly average fine total carbon concentration at downtown Los Angeles reached a high of 22.3 \u00b5g m-3 during December 1982, and dropped to 7.4 \u00b5g m-3 during June 1982. At eastern locations in the air basin, the seasonal trend becomes less significant, with monthly average fine total carbon concentrations at Rubidoux observed to be between 6.4 and 10.8 \u00b5g m-3 during all months of 1982.
\r\n\r\nElemental carbon in the atmosphere is inert and is due solely to direct (primary) aerosol emissions from sources, while organic carbon could be directly emitted as primary aerosol or could be formed in part from condensation of the low vapor pressure products of atmospheric chemical reactions (secondary formation). Examination of the spatial and temporal trends of the ratio of fine total carbon to fine elemental carbon concentration leads to the conclusion that secondary organic carbon aerosol formed in the atmosphere from hydrocarbon precursors was not the overwhelming contributor to overall long\u2014term average total carbon levels in the Los Angeles area during the year 1982. At downwind locations, such as Azusa or Rubidoux, it was found that, at most, between 16% and 22% of the annual average total carbon concentration (or 27% to 38% of the organic carbon) may be due to secondary aerosol formation in excess of that found at Lennox (a near\u2014coastal site next to a heavily travelled freeway source of primary aerosol). Comparison of fine elemental and organic carbon particle concentrations against the ratio of those two aerosol species found in basin\u2014wide source emissions further indicates that, over long averaging times during 1982, primary aerosol carbon particle emissions are responsible for the majority of atmospheric carbon particle concentrations.
\r\n\r\nThe particulate air quality data collected during 1982 were used to verify the performance of a mathematical model for long-term average air quality. The Lagrangian particle-in-cell air quality model previously developed by Cass (1977, 1981) was improved to handle near-source dispersion from ground level sources. The model was tested against emissions, elemental carbon air quality, and meteorological data for 1982 in the Los Angeles area. It was found that the model adequately predicts the long-term average concentration of this primary pollutant. The predictions and observations of monthly average elemental carbon particle concentrations have a positive correlation coefficient of 0.78. The model also determines the source classes responsible for fine carbon particle air quality. Many source types, including highway vehicles, charcoal broilers, and fireplaces contribute to primary total carbon particle concentrations, while elemental carbon concentrations are due mostly to emissions from diesel engines.
\r\n\r\nThe source class contributions computed by the air quality model were used to determine the optimal emission control strategy for attaining any desired level of improved carbon particle air quality. Linear programming techniques were employed to solve for the least costly set of emission control measures which would enable an air quality goal to be met. Solutions indicate that application of a few control measures, aimed almost entirely at diesel engines, will reduce the basin\u2014wide maximum annual average fine elemental carbon concentration approximately by half at an annual cost of about $69 million. The maximum annual average fine primary total carbon concentration may be reduced by about 35% at a cost of $102 million per year. A control program for visibility improvement would preferentially require the reduction of atmospheric fine elemental carbon particle concentrations, whereas a program designed to control fine aerosol mass would benefit from total carbon particle concentration reductions. It was determined that a control strategy that is optimal for total carbon control may be near\u2014optimal for elemental carbon control. However, an emissions control strategy designed to optimize for elemental carbon control may produce peak total carbon concentrations that exceed those which would result from a control strategy optimized for total carbon by as much as 8%.
\r\n\r\nIn summary, it has been demonstrated that the air quality model is useful both in predicting long\u2014term average carbon particle air quality and in determining the sources responsible for that air quality outcome. It was found that emissions from diesel engines were responsible for a large portion of the atmospheric fine carbon particle concentrations in the Los Angeles area during 1982. Control of emissions from diesel engines is therefore important, and it was determined that the least costly set of emission control measures for reducing carbon particle concentrations includes many diesel engine emission controls.
" }, { "name": "Gu\u00e9rin, Roch", "degree": "PhD", "year": "1986", "title": "Queueing and Traffic in Cellular Radio", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-140041", "creators": [ { "name": { "family": "Gu\u00e9rin", "given": "Roch" }, "id": "Gu\u00e9rin-Roch", "orcid": "0000-0002-8928-9984", "display_name": "Gu\u00e9rin, Roch" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "chair", "display_name": "McEliece, Robert J." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/WY9Y-FB87", "abstract": "A Cellular Radio system is analyzed from the communications traffic point of view. A cell within a given system is modeled by a multi-server service facility with or without the possibility of queueing some type of customers. Two types of arrivals are distinguished, corresponding to handoff calls (calls already in progress that enter the cell) and originating calls (calls initiated inside the cell). The queueing system used assumes Poisson distributed arrivals with different rates for the two types of customers. We initially assume, as is usually done for telephone communications, an exponential distribution for the service times of the customers. Due to mobility of the subscribers that can travel through several cells in the system, the channel occupancy time is in general different from the total call duration. Using both a simulation of a cellular system and an analytic model we offer evidence that a memory-less distribution may not be too unrealistic for the channel occupancy time.
\r\n\r\nWe derive some traffic policies that give a higher level of protection to handoff calls, and their influence on the other class of customers as well as on the overall traffic is analyzed. The first policies proposed have the advantage of simplicity and provide an efficient way of reducing the blocking probability of handoff calls while only slightly increasing the blocking probability of originating calls. The price paid is, however, a small decrease in the total carried traffic.
\r\n\r\nSome more evolved traffic policies are then introduced that still decrease the blocking probability of handoff calls without much penalizing originating calls whose access to the system will only be slightly delayed. These more evolved policies provide the additional advantage of increasing the total carried traffic, while still providing a higher level of protection to handoff calls.
\r\n" }, { "name": "Haney, Michael William", "degree": "PhD", "year": "1986", "title": "Acousto-Optical Time-and-Space Integrating Processors for Real-Time Synthetic Aperture Radar Imaging", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-121641", "creators": [ { "name": { "family": "Haney", "given": "Michael William" }, "id": "Haney-Michael-William", "orcid": "0009-0001-8071-5561", "display_name": "Haney, Michael William" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "orcid": "009-0002-2156-967X", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Masson", "given": "Colin R." }, "id": "Masson-Colin-R", "role": "member", "display_name": "Masson, Colin R." }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." } ], "option_major": [ "eleceng" ], "doi": "10.7907/64T4-7N83", "abstract": "Acousto-optical processors for Synthetic Aperture Radar (SAR) imaging are presented. The new processors produce images at real-time rates by combining the operations of data collection, storage, and processing into a compact time-and-space integrating (TSI) architecture. In the TSI approach the 2-D SAR imaging problem is decomposed into a cascade of 2 distinct operations: a 1-D spatial integration of light for range compression, and a 1-D temporal integration of light for azimuth compression. These two operations are coupled via a common path interferometric scheme that is insensitive to mechanical vibrations.
\r\n\r\nThe results of an experimental characterization of the TSI approach, with simulated point scatterer radar echoes, are reported. The performance issues of interferometric bias removal, dynamic range, and resolution are addressed. The architecture is generalized to correct for range migration and the results of a range walk compensation experiment are presented. A programmable version of the TSI architecture, in which the fixed azimuth reference mask is replaced by an acousto-optic light modulator, is described. The application of the programmable architecture to both strip-map and spot-light mode SAR is analyzed and experimentally verified.
" }, { "name": "Hendricks, Gavin Julian", "degree": "PhD", "year": "1986", "title": "Two Mechanisms of Vorticity Generation in Combusting Flow Fields", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-104812", "creators": [ { "name": { "family": "Hendricks", "given": "Gavin Julian" }, "id": "Hendricks-Gavin-Julian", "display_name": "Hendricks, Gavin Julian" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "chair", "display_name": "Marble, Frank E." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "mecheng" ], "doi": "10.7907/kj79-eq14", "abstract": "In Part 1 of the thesis the behavior of a diffusion flame in an unbounded flow with an imposed pressure gradient is analysed. The problem is formulated using the compressible boundary layer equations, and the assumption of infinite reaction kinetics is employed. The equations are transformed to the equivalent incompressible equations by the application of the Howarth transformation. Solutions to these equations are obtained for a functional form of the pressure gradient which admits similarity solutions. Two stoichiometric fuel\u2014air ratios are considered, \u03c6 = 1 which yields a symmetric flow field about the flame, and \u03c6 = 0.058 which corresponds to the combustion of methane in air and yields an unsymmetric flow field.
\r\n\r\nFor favorable pressure gradients the fluid in the vicinity of the flame is accelerated more than the fluid in the free stream. The acceleration of the fluid as it is convected downstream causes an augmentation in the fuel mass consumption rate, the mechanism of which is similar to that of a strained diffusion flame in an unbounded counterflow. For adverse pressure gradients a reverse flow develops in the vicinity of the flame which severely affects the mass consumption rate of fuel. For a flame with unit stoichiometry, recirculation zones develop on either side of the flame which eventually lead to extinction. For the stoichiometric ratio corresponding to the combustion of methane in air, the recirculation zones are situated on the fuel side of the flame and no tendency toward extinction is shown.
\r\n\r\nIn Part 2 a numerical study is done to investigate the formation of large vortex structures observed in the combustion chambers of air breathing engines under certain conditions. It has been proposed that these vortex structures are formed by a surging flow over the flameholding device which exists when longitudinal modes of the combustion system are excited. In the present study the surging flow is generated by passing a weak shock wave over a rearward facing step. The fluid entering the chamber is of high density (representing the cold fuel\u2014air mixture) whereas the fluid in the chamber has a low density (the combustion products). The vortex formed by the surging flow induces a downward velocity in the high density fluid toward the lower wall. It is found that larger surge velocities result in the formation of stronger vortices (which induce higher downward velocities), whereas an increase in the mean velocity causes no significant change in the flow field. The time taken for the high density fluid to reach the lower wall is therefore decreased as the surge velocity is increased. By considering these results, a possible model for the sustenance of the vortex shedding mechanism is proposed.
" }, { "name": "Hetzler, Steven Robert", "degree": "PhD", "year": "1986", "title": "Infrared Optical Studies of HgTe-CdTe Superlattices and GaAs", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-084757", "creators": [ { "name": { "family": "Hetzler", "given": "Steven Robert" }, "id": "Hetzler-Steven-Robert", "display_name": "Hetzler, Steven Robert" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/5ptm-z449", "abstract": "This thesis presents two different studies of the infrared optical properties of two different semiconductors. Chapter 2 describes the results of the first infrared photoluminescence (IRPL) measurements of a HgTe-CdTe superlattice. IRPL spectra of two different HgTe-CdTe superlattices from two different sources were measured from 100 to 270K. Sample 1 was grown on (111) Cd0.96Zn0.04Te, and was grown to have 250 repeats of 38 - 40 \u00c5 of HgTe followed by 18 - 20 \u00c5 of CdTe. Sample 2 was grown on (111) CdTe and was grown to have 75 repeats of 50 \u00c5 of HgTe followed by 50 \u00c5 of CdTe. Sample 1 exhibited a single asymmetrical luminescence line at all temperatures studied. (Low signal-to-noise ratio from sample 2 prevented detailed analysis of the lineshape.) The luminescence from both samples occured at significantly lower energies than that from Hg1-xCdxTe alloys with the same Cd concentrations as the average Cd concentrations of the superlattices. At 240 K, the luminescence peak from sample 1 was near 148 meV, with a full width at half-maximum intensity of 42 meV, while the peak from sample 2 was near 242 meV, with a full width at half-maximum intensity of 69 meV. Analysis of the luminescence lineshape from sample 1 showed it to be consistent with wave-vector conserving band-to-band recombination. In this case, the band-gap energy of the superlattice would be near the low energy threshold of the luminescence peak. This study therefore represents the first direct determination of the band gap of an HgTe-CdTe superlattice. A comparison of the lineshapes from both samples with those measured in GaAs-Ga1-xAlxAs super-lattices showed evidence for fluctuations in the layer thicknesses of both the HgTe-CdTe superlattice samples. A comparison was made between the data and a simple theory of the band gaps of HgTe-CdTe superlattices. The theory was shown to be consistent with the experiments, if there were small errors in the measurements of the superlattice layer thicknesses of each sample. The differences in the luminescence properties of the two samples show that it is possible to tailor the band gaps of HgTe-CdTe superlattices.
\r\n\r\nChapter 3 describes the first observation of s-like excited states of a double acceptor in a semiconductor. Two experiments were performed to study the s-like excited states of the 78-meV acceptor in GaAs. The techniques used, selective excitation scattering (SEL) and electronic Raman scattering (ERS), are both sensitive to the detection of s-like excited states of single acceptors in semiconductors. Measurements on two different liquid encapsulated Czochralski GaAs samples showed two s-like excited state transitions of equal magnitude, separated by 4.0 meV. Only one s-like transition is expected in the energy range measured for a single acceptor. A simple effective mass-like model of a double acceptor was developed to account for the two s-like excited states. This model predicted a splitting of the 1s12s1 excited state of a double acceptor to be 2.6 meV, in good agreement with the observed value of 4.0meV. This proved that the 78-meV acceptor in GaAs is due to the first ionization of a double acceptor, the first such identification to be made based on the s-like excited state spectrum. It is therefore possible to identify the valency of an acceptor in a semiconductor by measuring the s-like excited state spectrum.
\r\n\r\nAppendix A describes a novel technique for performing infrared photoluminescence measurements using a Fourier transform infrared spectrophotometer. This technique was developed to perform the experiments described in Chapter 2.
" }, { "name": "Jones, Nicholas Patrick", "degree": "PhD", "year": "1986", "title": "Flow-Induced Vibration of Long Structures", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072006-091025", "creators": [ { "name": { "family": "Jones", "given": "Nicholas Patrick" }, "id": "Jones-Nicholas-Patrick", "display_name": "Jones, Nicholas Patrick" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "civileng" ], "doi": "10.7907/ZXWC-ZZ44", "abstract": "When a body is exposed to a flowing fluid, oscillations can occur due to one or more of several different mechanisms. The resulting large amplitudes of motion and fatigue are potential sources of structural failure. Furthermore, the drag force on a structure can be increased due to the effectively larger cross-sectional area presented to the flow from the oscillation. A complete understanding of the nature of such vibration is essential in the design of many civil and mechanical engineering systems.
\r\n\r\nPrevious solutions to the vortex-induced vibration problem were primarily based on modal analysis, using a one- or two-mode approximation. Use of modal analysis implies a \"locked-in\" condition: the vortex shedding frequency and a natural frequency of the system are coincident. Observations made on long cable systems indicate that the amplitude of response is smaller than is predicted by a conventional modal analysis. The drag forces on such structures are therefore overestimated by current design approaches.
\r\n\r\nIn very long structures, typical of those found in ocean applications, modes are closely spaced, and it is not reasonable to assume total spanwise correlation in the fluid forces or response. The approach used herein attempts to avoid the limitations associated with the modal solution of such problems by implementing a solution based on traveling waves. The technique draws on earlier theoretical and empirical models for the complex vortex-shedding phenomenon, and incorporates these into a new method for analyzing the structural response problem.
\r\n\r\nThe traveling wave approach can be used to model effectively spanwise variable flow environments by summing the calculated responses of adjacent active sections of cable. Until this method was developed, there was no suitable method available for modeling flow characteristics of this type. Modal analysis is effectively limited to systems with uniform flow over all or part of the system.
" }, { "name": "Lang, Robert James", "degree": "PhD", "year": "1986", "title": "Semiconductor Lasers: New Geometries and Spectral Properties", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142007-081143", "creators": [ { "name": { "family": "Lang", "given": "Robert James" }, "id": "Lang-Robert-James", "orcid": "0000-0001-9496-123X", "display_name": "Lang, Robert James" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/rk0z-ma09", "abstract": "This thesis is an investigation into the spectral properties of two broad classes of semiconductor lasers. They are (1) broad-area lasers with non-planar mirrors, specifically, those with an unstable resonator configuration, and (2) coupled-cavity semiconductor lasers.
\r\n\r\nThe use of non-planar mirrors on broad-area lasers can substantially improve their properties. Chapter 2 focuses on the experimental realization of several unstable resonator semiconductor lasers, while chapter 3 presents a method of analyzing the modes of such a device.
\r\n\r\nCoupling two cavities together can drastically alter the dynamic and spectral properties of a semiconductor laser. In chapter 4 we present experimental measurements and explain the properties of a laser consisting of two side-by-side coupled cavities. We then turn to the theoretical problem of analyzing the dynamic properties of multicavity lasers. In chapter 5, we derive a general expression for the dynamic response of a multielement laser. In the process, we develop a formalism for treating the dynamics of any semiconductor laser system with particular ease of application to single-mode multielement lasers. In chapter 6, we show that 2 or more cavities can lead to bistability and bimodality. The quantum fluctuation-induced noise properties of multicavity lasers are analyzed in chapter 7. In chapter 8, we return to the single-element laser and calculate non-quantum noise contributions--specifically, thermal and diffusion noise-- which give rise to a 1/f spectrum. In chapter 9 we present a new method of deriving multicavity rate equations and point out a shortcoming of the existing coupled-mode treatments.
\r\n" }, { "name": "Lee, Hyuk", "degree": "PhD", "year": "1986", "title": "Optical Interactions in a Dielectric Material with Multiple Perturbations", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152019-101001395", "creators": [ { "name": { "family": "Lee", "given": "Hyuk" }, "id": "Lee-Hyuk", "display_name": "Lee, Hyuk" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ek2w-4557", "abstract": "The interaction of light propagating through a dielectric material with multiple perturbations is investigated.
\r\n\r\nA general coupled mode theory of two gratings is presented. The acousto-electro-optic effect is introduced as an example of an indirect interaction due to the acousto-optic and electro-optic effects. The acousto-electro-optic effect is analyzed using the general theory and is demonstrated experimentally. The application of this effect to light modulation and deflection is discussed in detail. Also a correlator that is based on the photorefractive acousto-electrooptic effect is demonstrated and analyzed theoretically.
" }, { "name": "Leong, Harrison Mon Fook", "degree": "PhD", "year": "1986", "title": "Frequency Dependent Electromagnetic Fields: Models Appropriate for the Brain", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-111015", "creators": [ { "name": { "family": "Leong", "given": "Harrison Mon Fook" }, "id": "Leong-Harrison-Mon-Fook", "display_name": "Leong, Harrison Mon Fook" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "chair", "display_name": "Fender, Derek H." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "member", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Hestenes", "given": "John" }, "id": "Hestenes-John", "role": "member", "display_name": "Hestenes, John" }, { "name": { "family": "Hamilton", "given": "Charles R." }, "id": "Hamilton-Charles-R", "role": "member", "display_name": "Hamilton, Charles R." } ], "option_major": [ "bioinfo", "eng" ], "doi": "10.7907/TNQ6-P071", "abstract": "This dissertation addresses the problem of modeling electromagnetic fields in and about the brain-skull-scalp system that are generated by active neural populations. Specifically, frequency dependence of Maxwell's fields is explored for the case of a dipole-like current source embedded in a spherical conductor surrounded by a vacuum. Frequency dependence was found to be small. Loosely, the difference between frequency dependent and frequency independent fields reached approximately 1% at 103 Hz and reached up to 16% at 104 Hz. Frequency dependence was found to be highly dependent on conductivity, the size of the conductor, and on the phase of generated fields. These findings indicate that the degree to which the magnetic field is coupled to the electric field depends on interference patterns occurring within the conductor. Several highly distinguishable exceptions to general trends in the data were found to be consistent with this view.
" }, { "name": "Li, Peyyun Peggy", "degree": "PhD", "year": "1986", "title": "A Parallel Execution Model for Logic Programming", "advisor": "Martin, Alain J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192008-143903", "creators": [ { "name": { "family": "Li", "given": "Peyyun Peggy" }, "id": "Li-Peyyun-Peggy", "display_name": "Li, Peyyun Peggy" } ], "advisors": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "advisor", "display_name": "Martin, Alain J." } ], "committee": [ { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "chair", "display_name": "Martin, Alain J." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Van de Snepscheut", "given": "Jan L. A." }, "id": "Van-de-Snepscheut-J-L-A", "role": "member", "display_name": "Van de Snepscheut, Jan L. A." }, { "name": { "family": "Kechris", "given": "Alexander S." }, "id": "Kechris-A-S", "orcid": "0000-0002-2226-0423", "role": "member", "display_name": "Kechris, Alexander S." } ], "option_major": [ "compsci" ], "doi": "10.7907/2ngs-bp80", "abstract": "The Sync Model, a parallel execution method for logic programming, is proposed. The Sync Model is a multiple-solution data-driven model that realizes AND-parallelism and OR-parallelism in a logic program assuming a message-passing multiprocessor system. AND parallelism is implemented by constructing a dynamic data flow graph of the literals in the clause body with an ordering algorithm. OR parallelism is achieved by adding special Synchronization signals to the stream of partial solutions and synchronizing the multiple streams with a merge algorithm.
\r\n\r\nThe Sync Model is proved to be sound and complete. Soundness means it only generates correct solutions and completeness means it generates all the correct solutions. The soundness and completeness of the Sync Model are implied by the correctness of the merge algorithm.
\r\n\r\nA new class of interconnection networks, the Sneptree, is also presented. The Sneptree is an augmented complete binary tree which can simulate an unbounded complete binary tree optimally. Amongst different connection patterns of the Sneptree, some are regular and extensible so as to be well suited for VLSI implementation. A recursive method is presented to generate the H-structure layout of one type of the Sneptree, called the Cyclic Sneptree. A message routing algorithm between any two leaf nodes of the Cyclic Sneptree is also presented. The routing algorithm, which is of O(n) complexity, gives a good approximation to the shortest path.
\r\n\r\nThe Sneptree is an ideal architecture for the Sync model, in which a dynamic process tree is constructed. With a simple mapping algorithm, the Sync Model can be mapped onto the Sneptree with highly-balanced load and low overhead.
\r\n" }, { "name": "Mosteller, Richard Craig", "degree": "PhD", "year": "1986", "title": "Monte Carlo Methods for 2-D Compaction", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-03202008-091615", "creators": [ { "name": { "family": "Mosteller", "given": "Richard Craig" }, "id": "Mosteller-Richard-Craig", "display_name": "Mosteller, Richard Craig" } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Frey", "given": "Alexander H." }, "id": "Frey-Alexander-H", "role": "member", "display_name": "Frey, Alexander H." }, { "name": { "family": "Goodman", "given": "Rodney M." }, "id": "Goodman-R-M", "role": "member", "display_name": "Goodman, Rodney M." }, { "name": { "family": "Suaya", "given": "Roberto" }, "id": "Suaya-Roberto", "role": "member", "display_name": "Suaya, Roberto" } ], "option_major": [ "compsci" ], "doi": "10.7907/mwrq-t026", "abstract": "A new method of compaction for VLSI circuits is presented. Compaction is done simultaneously in two dimensions and uses a Monte Carlo simulation method often referred to as simulated annealing for optimization. A new curvilinear representation for VLSI circuits, specifically chosen to make the compaction efficient, is developed. Experiments with numerous cells are presented that demonstrate this method to be as good as, or better than the hand compaction previously applied to these cells. Hand compaction was the best previously known method of compaction. An experimental evaluation is presented of how the run time complexity grows as the number, N, of objects in the circuit increases. The results of this evaluation indicates that the run time growth is order O(N log(A))f(d) where f(d) is a function of the density, d, and A is the initial cell area. The function f(d) appears to have negligible or no dependence on N. A hierarchical composition approach is developed which takes advantage of the capability of the curvilinear representation and the 2-dimensional compaction technique.
" }, { "name": "Papantoniou, Dimitris Antony", "degree": "PhD", "year": "1986", "title": "Observations in Turbulent Buoyant Jets by Use of Laser-Induced Fluorescence", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechETD:etd-03142008-142149", "creators": [ { "name": { "family": "Papantoniou", "given": "Dimitris Antony" }, "id": "Papantoniou-Dimitris-Antony", "display_name": "Papantoniou, Dimitris Antony" } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "chair", "display_name": "List, E. John" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "eng" ], "doi": "10.7907/SX4D-3555", "abstract": "The entrainment mechanism and mixing process are investigated in the far field of a liquid phase buoyant jet issuing into an unconfined, quiescent medium, by an experimental technique based on laser-induced fluorescence (LIF). Visualization experiments show the existence of a large scale organization in the far field, with structures spanning the radial extent of the conical flow region. Quantitative, high-resolution measurements of scalar concentration were performed along the radial direction in the far field region. For each data set, a large number of successive instantaneous concentration profiles were obtained by combining LIF techniques with linear photodiode array imaging and high speed data acquisition. The measurements revealed that the instantaneous profile bears no resemblance to the time-averaged profile. The flow interior is characterized by large spatial gradients of concentration, associated with interfaces between mixed jet fluid and fresh, entrained ambient fluid transported to regions deep into the flow. This is inconsistent with the description of transport by gradient diffusion concepts. The probability of finding unmixed ambient fluid and the concentration variance are greatly increased under the action of buoyancy. At any axial location, the arrival of a structure front is marked by a spatially coherent (along the radial direction) increase in the local concentration level. It is found that, within the structure, values of the concentration are generally decreasing in the upstream direction; substantial uniformity within the mixed fluid portion is observed along the radial direction. In the conical flow field of the momentum jet, a central region (in fixed spatial coordinates) may be identified within which the local mixed fluid composition is relatively uniform. This is not the case for the buoyancy driven plume, due to a greater variance in the position of the large structure and the high value of the intermittency. It is suggested that fluid is entrained by vortical motions mainly from the back and side regions of the large structure. Flow visualization reveals vorticity in the axial direction which enhances the mixing process; this vorticity appears stronger in the buoyancy driven flow. The results of these experiments are interpreted through a simple conceptual model of entrainment and mixing that encompasses the observed large scale organization of the buoyant jet flow.
" }, { "name": "Peek, Ralf", "degree": "PhD", "year": "1986", "title": "Analysis of Unanchored Liquid Storage Tanks under Seismic Loads", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10232019-110854163", "creators": [ { "name": { "family": "Peek", "given": "Ralf" }, "id": "Peek-Ralf", "orcid": "0000-0002-2469-3644", "display_name": "Peek, Ralf" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "chair", "display_name": "Jennings, Paul C." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "civileng" ], "doi": "10.7907/w43k-hj54", "abstract": "Because of cost, cylindrical, ground supported liquid storage tanks are often not fixed to their foundation, even in seismic areas. For such an unanchored tank made of steel, the weight of the cylindrical shell is mostly insufficient to prevent local uplift due to seismic overturning moments. Although, for properly designed connecting pipes, uplift itself is not a problem, it results in larger vertical compressive stresses in the tank wall at the base, opposite to where the uplift occurs. These compressive stresses have often caused buckling, even in earthquakes which did not cause much damage to other structures.
\r\n\r\nVarious investigators have studied the behavior of unanchored tanks experimentally, but, due to the complexity of the problem, so far very little theoretical work has been done. Two methods of analysis for static lateral loads are presented: An approximate one in which the restraining action of the base plate is modeled by nonlinear Winkler springs, and a more comprehensive one in which the two dimensional nonlinear contact problem is solved by the finite difference energy method. The theoretical results are compared with existing experimental results and with the approach from current U.S. design standards. The theoretical peak compressive stresses are in good agreement with the experimental results, but in some cases exceed those calculated by the code method by more than 100%.
\r\n\r\nFinally, a new design concept, by which the tank wall is preuplifted all around its circumference by inserting a ring filler is described. It will be shown theoretically and experimentally that this preuplift method substantially improves the lateral load capacity.
" }, { "name": "Robey, Harry Francis, III", "degree": "PhD", "year": "1986", "title": "The Nature of Oblique Instability Waves in Boundary Layer Transition", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-05242007-150746", "creators": [ { "name": { "family": "Robey", "given": "Harry Francis, III" }, "id": "Robey-Harry-Francis-III", "display_name": "Robey, Harry Francis, III" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7VG8-Y513", "abstract": "An experimental study of both the weakly non-linear as well as the three-dimensional nature of boundary layer transition is conducted using the active surface heating technique of Liepmann et al. In the present study, this technique is extended to provide a means for controllably and repeatably introducing three-dimensional disturbances into a laminar boundary layer. A review of the surface heating technique is presented along with a discussion of some peculiarities encountered in extending this technique to three-dimensional geometries. A thorough description of the design and operation of a programmable 32-element heater array and the supporting instrumentation are given as well.
\r\n\r\nThe heater array is first used to study the effect of weak nonlinearity on boundary layer transition. By keeping the forced disturbances as two-dimensional as possible, it is shown that the effects of weak non-linearity are relatively benign. The growth rates are seen to follow the linear theory up to perturbation amplitudes (\u03c4'w\u03c4̅w) of nearly twelve percent. The only deviation from the linear theory arises in the form of non-linearly generated harmonics phase-locked to the fundamental. It is concluded that although these non-linearly generated harmonics do alter the wave behavior to some extent, they are by themselves not sufficient to explain the transition from small linear oscillations to the large amplitude, broad-band, three-dimensional oscillations characteristic of a fully turbulent boundary layer.
\r\n\r\nThe effect of three-dimensionality on boundary layer transition is then investigated through an analytical and experimental study of single oblique instability waves. This subject has remained largely unexplored, as such disturbances were generally thought to be more stable and therefore less dangerous than their two-dimensional counterparts. Through a series of experiments, however, it is shown that certain conditions exist for which oblique waves are observed to be more unstable than any two-dimensional wave. It is shown that oblique waves exhibit a non-stationary period-doubling behavior that is not seen in two-dimensional disturbances. A vortex pairing mechanism is proposed to explain this behavior, and is shown to occur in a manner consistent with the Biot-Savart law for the induced velocity field.
" }, { "name": "Schlesinger, Tuviah Ehud", "degree": "PhD", "year": "1986", "title": "Optical and Opto-Electronic Investigations of Semiconductor Defects and Heterostructures", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechETD:etd-03082008-082632", "creators": [ { "name": { "family": "Schlesinger", "given": "Tuviah Ehud" }, "id": "Schlesinger-Tuviah-Ehud", "display_name": "Schlesinger, Tuviah Ehud" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/0ydw-cg53", "abstract": "This thesis basically consists of two parts. In the first part is discussed photoluminescence experiments performed on p-type silicon doped with B, In, or Tl. These substitiutional dopants were believed to form complexes with interstitial Fe and thought to be the source of some very intense luminescence in the silicon. Also presented are the results of photoluminescence experiments performed on luminescence features which were thought to be due to an isolated Fe complex observe in n-type Si:P. These spectra generally consisted of one or two sharp no-phonon lines followed by a subsidiary peak approximately 9 - 10 meV below the no-phonon line which was identified as a phonon replica of the no-phonon line. This phonon mode was thought to be a local vibrational mode of the Fe. Isotope shift experiments were performed on these luminescence features by diffusing 54Fe and 56Fe into the silicon samples to see whether a change in the phonon energy or a shift in the no-phonon line could be observed (as predicted by theory) and thus more conclusively identify the center. No isotope shift was observed in the case of any of the Fe related centers studied. Similar experiments which were performed on luminescence features attributed to (Cu,Cu) pairs in silicon (using 65Cu and 63Cu) are also described in the first part of this thesis. An isotope shift of the no-phonon line and a change in the characteristic 7 meV phonon mode, seen in this spectrum, were observed. This confirmed the identification of these luminescence features as being due to the presence of Cu. Also this result confirmed that the lack of a shift in the Fe case was real. Possible explanations for the null result in the Fe case are discussed.
\r\n\r\nThe second part of this thesis consists of optical investigations of GaAs/AlAs heterostructures. In these experiments the transport of electrons past a thin (50 \u00c5 to 200 \u00c5) AlAs barrier sandwiched between thick GaAs cladding layers was studied by measuring the voltage developed across these structures as a function of the wavelength of light illuminating the sample. Calculations to model the optical absorption in these structures were also carried out. Based on the data and the calculations the following explanation for the observed photo- voltages was proposed. Electrons, in the degenerately doped GaAs, are optically excited by free carrier absorption to energies greater than that presented by the AlAs barrier and flow from the illuminated side of the AlAs barrier to the back side of the barrier. The driving force for this flow would be the difference in the concentration of optically excited electrons on either side of the barrier. This difference results from the light intensity difference on either side of the barrier as modeled by the calculations. These experiments were conducted for samples with different AlAs layer thicknesses, GaAs layer thicknesses and dopings, and at various temperatures. Further work involved applying a constant dc bias to the structure while measuring the photovoltage spectrum. This, it was found, increased the photovoltage signal (by several orders of magnitude in some cases) and caused some shifts in the spectrum to slightly longer wavelengths. These effects were explained in terms of charge redistribution in the sample, that is, accumulation and depletion on either side of the barrier and the effective band gap narrowing in the GaAs due to the large electric fields that these dc biases can create in the depleted areas of the GaAs.
\r\n" }, { "name": "Schwendeman, Donald William", "degree": "PhD", "year": "1986", "title": "Numerical Shock Propagation Using Geometrical Shock Dynamics", "advisor": "Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechETD:etd-03082008-083041", "creators": [ { "name": { "family": "Schwendeman", "given": "Donald William" }, "id": "Schwendeman-Donald-William", "orcid": "0000-0002-0161-5221", "display_name": "Schwendeman, Donald William" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "chair", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "member", "display_name": "Ahrens, Thomas J." } ], "option_major": [ "appmath" ], "doi": "10.7907/Q5VX-AF72", "abstract": "Various numerical schemes are developed to calculate the motion of shock waves in gases based on Whitham's theory of geometrical shock dynamics. The basic numerical scheme is used to study the propagation of two-dimensional shock waves along walls and in channels, and the self-focusing of initially curved shock- fronts. This scheme is extended to treat shock wave motion in non-uniform media. The extended scheme is used to examine shock wave refraction at both planar and curved interfaces separating gases with different properties. Precursor-irregular refraction patterns are obtained using geometrical shock dynamics. A general numerical scheme designed to propagate a shock surface in three dimensions is presented. Three-dimensional shock focusing and shock propagation in a curved pipe are considered primarily to demonstrate the use of the three-dimensional numerical scheme. The reflection of planar shock waves from curved walls is studied. The motion of the shock is determined using the combined theories of regular reflection and geometrical shock dynamics. A numerical scheme based on the combined theories is discussed. The numerical scheme is used to calculate the reflection and subsequent focusing of weak planar shock waves. Some of the present results are compared with other solutions to the equations of geometrical shock dynamics obtained using different methods. Recent experimental investigations are discussed and compared with our results calculated using geometrical shock dynamics.
\r\n" }, { "name": "Sigurdson, Lorenz Willard", "degree": "PhD", "year": "1986", "title": "The Structure and Control of a Turbulent Reattaching Flow", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-03102008-104655", "creators": [ { "name": { "family": "Sigurdson", "given": "Lorenz Willard" }, "id": "Sigurdson-Lorenz-Willard", "display_name": "Sigurdson, Lorenz Willard" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/prfm-x404", "abstract": "An unsteady and three-dimensional large-scale structure is proposed for the reattachment region of a separation bubble, based on a visualization study of the flow over a plate with a square leading edge and its axisymmetric counterpart, a flat-faced circular cylinder aligned coaxially with the free-stream. The initial free shear layer structures are primarily two-dimensional but evolve into boundary layer type structures as they near reattachment and interact with the wall. Some segments form \"loops\" which convect away from the wall and downstream, while spanwise adjacent parts convect toward the wall and upstream. The loops are sometimes clearly arranged in a staggered pattern. Their legs form a series of counter-rotating streamwise vortex pairs which bridge the reattachment zone. These observations reconcile apparently contradictory propositions concerning the fate of the structures as they encounter reattachment. The interaction between successive vortices at alternating spanwise locations is fundamental to several flows. The structure of turbulent wakes is also discussed.
\r\n\r\nAn experimental study was made of the effect of a periodic velocity perturbation on the separation bubble downstream of the sharp- edged blunt face of a circular cylinder aligned coaxially with the free stream. Velocity fluctuations were produced with an acoustic driver located within the cylinder and a small circumferential gap located immediately downstream of the fixed separation line to allow communication with the external flow. The flow could be considerably modified when forced at frequencies lower than the initial Kelvin-Helmholtz frequencies of the free shear layer, and with associated vortex wavelengths comparable to the bubble height. Reattachment length, bubble height, pressure at separation, and average pressure on the face were all reduced. The effects on the large-scale structures were studied on flow photographs obtained by the smoke-wire technique. The forcing increased the entrainment near the leading edge.
\r\n\r\nIn both forced and unforced cases it was concluded that the final vortex of the shear layer before reattachment is an important element of the flow structure. There are two different instabilities involved, the Kelvin-Helmholtz instability of the free shear layer and the \"shedding\" type instability of the entire bubble. The latter results from an interaction with the image vortices due to the presence of the wall. A method of frequency scaling is proposed that correlates data for a variety of bubbles and supports an analogy with Karman vortex shedding.
\r\n\r\nNew methods for approximating axisymmetric flows are presented. Transition of shear-layers and separation bubbles is also discussed.
" }, { "name": "Silling, Stewart Andrew", "degree": "PhD", "year": "1986", "title": "Singularities and Phase Transitions in Elastic Solids: Numerical Studies and Stability Analysis", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03082008-083510", "creators": [ { "name": { "family": "Silling", "given": "Stewart Andrew" }, "id": "Silling-Stewart-Andrew", "orcid": "0000-0002-4201-2910", "display_name": "Silling, Stewart Andrew" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/0ytn-e775", "abstract": "Numerical studies of the deformation near the tip of a crack are presented for a family of incompressible solids in the context of the theory of finite anti-plane shear of an elastic material. The numerical model computes the near-field and far-field solutions simultaneously, enabling observations of both small-scale and large-scale nonlinearity. The computed near-field solution is compared with a lowest-order asymptotic solution. An approximation for the J-integral under conditions of very large loads is discussed and compared with numerical results. The size of the region over which the lowest-order solution applies is observed.
\r\n\r\nNumerical solutions are presented for the same crack problem with materials for which the equilibrium equation changes in type from elliptic to hyperbolic as a result of deformation. These results show the emergence of surfaces of discontinuity in the displacement field in some cases. In other cases they show a chaotic mixture of elliptic phases near the crack tip.
\r\n\r\nAnalysis of the stability of such coexistent phases is carried out for a specific material, the trilinear material. It is shown that the Maxwell relation, and therefore local stability, cannot in general be satisfied exactly for an arbitrary boundary value problem with this material. However, in those cases where it cannot be satisfied exactly, it may be satisfied in the sense of a limit of a certain sequence of deformations. This sequence produces a progressively chaotic pattern of two coexistent elliptic phases, as was observed numerically. The phases mix over a definite region in a given boundary value problem. This region may be computed using a constitutive relation which characterizes the mixture in the limit of the sequence.
" }, { "name": "Skjelbreia, James Eric", "degree": "PhD", "year": "1986", "title": "Observations of Breaking Waves on Sloping Bottoms by Use of Laser Doppler Velocimetry", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-06142006-112209", "creators": [ { "name": { "family": "Skjelbreia", "given": "James Eric" }, "id": "Skjelbreia-James-Eric", "display_name": "Skjelbreia, James Eric" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "chair", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "civileng" ], "doi": "10.7907/g5bj-2c76", "abstract": "Wave breaking is investigated experimentally by use of laser doppler velocimetry for two cases: a plunging breaker and a spilling breaker. Specifically, emphasis is given to the kinematics at breaking, the early breaking phase, and the turbulent wake generated from wave breaking. A significant contribution is provided on the amplitude behavior for a solitary wave on a beach, as it is the solitary wave that is used to conduct this study. Associated with the use of the solitary wave, a technique of flow field construction by repeated measurement with an LDV is presented.
\r\n\r\nFour well defined regions of the shoaling-through-breaking solitary wave on a beach are identified and termed according to the wave amplitude behavior within each region. They are: the zone of gradual shoaling, the zone of rapid shoaling, the zone of rapid decay and the zone of gradual decay. The plunging wave case studied exhibited a definite transitional zone, between the previously known -1/4 and -1 power laws, following a power law of -3/5.
\r\n\r\nVelocity fields for a plunger and a spiller at the point of breaking are measured and the corresponding acceleration fields are computed for each. The results show good qualitative comparison to those obtained by theoretical approaches, however, no clear mechanism is demonstrated to initiate breaking for the spilling breaker studied.
\r\n\r\nThe existence of counter-rotating vortices, generated from breaking, is established from velocity measurements of the flow taken during the early breaking phase and within the turbulent wake of the plunging breaker studied. The measurements indicate that the size of the vortices are roughly the same as the undisturbed depth at the point of breaking. Turbulent intensities determined within the wake of the plunging breaker illustrate its character and show that level of turbulent intensity does not progressively decrease behind the turbulent source.
" }, { "name": "Smith, John Stephen", "degree": "PhD", "year": "1986", "title": "III-V Molecular Beam Epitaxy Structures for Electronic and Optoelectronic Applications", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-03082008-083912", "creators": [ { "name": { "family": "Smith", "given": "John Stephen" }, "id": "Smith-John-Stephen", "display_name": "Smith, John Stephen" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/r489-8025", "abstract": "Molecular beam epitaxy (MBE), a method for depositing epitaxial semiconductor layers with an extreme degree of control, has previously been limited largely to featureless substrates. This thesis describes a procedure for high quality MBE growth over finely patterned GaAs substrates, which is suitable for device fabrication requiring lateral definition of small (~ 1-2 micron) dimension. The results of series of experiments determining the characteristics of MBE growth over patterned substrates are presented. Temperature and flux ratio dependence of faceting during MBE growth over patterned substrates is shown for temperatures ranging from 580\u00b0 C to 700\u00b0 C and for As/Ga flux ratios from 1.4:1 to 4:1, and surface diffusion lengths for gallium are measured. The (811) and (411) facets are shown to have growth rates which are at a local maximum and minimum, respectively, for facets tilted in the [01̅1] direction, and implications with respect to other experiments on the atomic growth kinetics on (100) facets are discussed. The material grown over facets tilted in the [0111 direction is shown to be of high quality, with electroluminescence equal to that over the (100) plane.
\r\n\r\nThis method was used for the fabrication of an index guided laser structure, with an optical guide similar to that of the liquid phase grown channeled substrate planer laser structure, as well as tightly packed arrays of these lasers. Yields of individual lasers exceeded 90 percent, and thresholds were uniform to 10 percent. Other potential applications for this technique include a vertical structure high electron mobility transistor, formation of \"quantum wire\" structures, and methods of directly contacting quantum well layers for device applications and research purposes.
\r\n\r\nCertain aspects of transport of hot electrons over quantum wells are discussed, with application to several types of devices, including a new type of infrared detector structure, a solid state electron multipler, and a proposed quantum well base transistor.
" }, { "name": "Swaminathan, Kumar", "degree": "PhD", "year": "1986", "title": "Analysis and Demonstration of the Quantile Vocoder", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-07192006-155419", "creators": [ { "name": { "family": "Swaminathan", "given": "Kumar" }, "id": "Swaminathan-Kumar", "display_name": "Swaminathan, Kumar" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "chair", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Vaidyanathan", "given": "P. P." }, "id": "Vaidyanathan-P-P", "orcid": "0000-0003-3003-7042", "role": "member", "display_name": "Vaidyanathan, P. P." }, { "name": { "family": "Townes", "given": "S." }, "id": "Townes-S", "role": "member", "display_name": "Townes, S." } ], "option_major": [ "eleceng" ], "doi": "10.7907/2XFF-5X20", "abstract": "A new scheme for speech compression is proposed, implemented and evaluated in this thesis. In this new scheme, the spectral envelope of the power spectral density of a speech frame is encoded using quartiles or order statistics. The perceptually important features of the spectral envelope are its peaks which correspond to the formant frequencies. The shape of the spectral envelope near the formants can be encoded by a careful choice of the quantiles and quantile orders. Algorithms to choose such a set of quantiles and quantile orders are described. It turns out that this can be done using very few quantiles. Data compression is achieved chiefly this way.
\r\n\r\nThe quantile decoding algorithm estimates the spectral envelope from the quartiles and quantile orders. The first step is to set up a flat spectral density approximation. In this approximation, the spectral envelope is assumed to be constant every interquantile range. This constant value is simply the average power (i.e., ratio of the difference in quantile orders to the difference in quantiles) in that interquantile range. It is shown that the flat spectral density approximation is the maximum entropy solution to the decoding problem. The flat spectral density approximation is then smoothed by fitting an all-pole or autoregressive model. Algorithms to determine the parameters of the autoregressive model are described. These algorithms involve the solution of a system of linear equations, which has a \"Toeplitz plus Hankel\" structure, followed by a standard spectral factorization. The algorithms can easily be extended to pole-zero models as well.
\r\n\r\nThe information about the spectral fine structure is sent through the parameters of the excitation model. A multi-pulse excitation model in cascade with a pitch predictor model has been chosen for this purpose. The theory of the multi-pulse model is reviewed, and algorithms to estimate the parameters of the multi-pulse model as well as the pitch predictor model are presented.
\r\n\r\nQuantization and encoding schemes of various transmission parameters are described. For high and medium bit rate applications, the parameters that need to be transmitted every frame are the quantiles, quantile orders, locations and amplitudes of the excitation pulses, parameters of the pitch predictor model and a gain term. For low bit rate applications, the quantile orders are fixed and so need not be transmitted. The quantization schemes for the quantile orders and for the gain term are shown to be optimal in the sense of minimizing the maximum spectral deviation due to quantization.
\r\n\r\nThe quantile vocoder has been implemented in software at 4.8, 9.6, 16 and 24 Kbits/s. In order to test the vocoder, a speech data base of ten sentences spoken by one male and one female speaker has been used. The so-called segmental signal-to-noise ratio has been used as an objective performance measure to evaluate the vocoder at all bit rates. A subjective method for assessing the quality of the vocoder at various bit rates is also proposed and carried out. The results of the nonreal time quantile vocoder simulations at 4.8, 9.6, 16 and 24 Kbits/s have been recorded and will be played at the end of the talk. The quantile vocoder does indeed seem equivalent to or better than other vocoders at the same bit rates, according to informal listening tests.
" }, { "name": "Synolakis, Constantine Emmanuel", "degree": "PhD", "year": "1986", "title": "The Runup of Long Waves", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122007-111121", "creators": [ { "name": { "family": "Synolakis", "given": "Constantine Emmanuel" }, "id": "Synolakis-Constantine-Emmanuel", "orcid": "0000-0003-0140-5379", "display_name": "Synolakis, Constantine Emmanuel" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "chair", "display_name": "Raichlen, Fredric" }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Imberger", "given": "Jorg" }, "id": "Imberger-J", "role": "member", "display_name": "Imberger, Jorg" } ], "option_major": [ "civileng" ], "doi": "10.7907/REBC-D787", "abstract": "This is a study of the fundamental physical processes of the runup of long waves with the objective to understand some coastal effects of tsunamis.
\r\n\r\nThe runup of nonbreaking long waves on plane beaches is studied and an exact solution is developed for the runup of solitary waves. The maximum runup predicted by this solution is compared to laboratory data from this and other investigations and it is found to be in good agreement. A runup transducer was developed and deployed in the laboratory to provide data for the shape of the runup tongue. The exact solution is shown to model the details of the climb of the wave satisfactorily.
\r\n\r\nThe runup of breaking long waves on plane beaches is investigated in the laboratory by studying different long waves and bores of finite volume. The runup is shown to be a function of a momentum scale determined from the generation characteristics of the incoming wave. The runup number is introduced and it is demonstrated that it models the runup process adequately. It is also observed that arbitrary long waves have runup numbers smaller than, or at most equal to, the runup number of breaking solitary waves, suggesting that on a given plane beach breaking solitary waves run-up further than other long waves with similar generation characteristics.
\r\n\r\nAn exact result is established for the force on an accelerating plate in a fluid with a free surface. The result is used to explain some of the results of this study and other results on the hydrodynamic forces on moving partitions.
\r\n\r\nA technique is developed to generate arbitrary, long, continuously evolving waves at any desired location in a laboratory model. The technique is applied in the laboratory and it is shown to be successful in reproducing complex waveforms.
" }, { "name": "Tan, Thiam-Soon", "degree": "PhD", "year": "1986", "title": "Two-Phase Soil Study: A. Finite Strain Consolidation. B. Centrifuge Scaling Considerations", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03082008-084249", "creators": [ { "name": { "family": "Tan", "given": "Thiam-Soon" }, "id": "Tan-Thiam-Soon", "display_name": "Tan, Thiam-Soon" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "chair", "display_name": "Scott, Ronald F." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." } ], "option_major": [ "civileng" ], "doi": "10.7907/agt3-mf84", "abstract": "Two different aspects of the behavior of soil as a two-phase medium are studied, namely, the consolidation of soil and scaling relations for soils in centrifuge testing.
\r\n\r\nPART A
\r\n\r\nFirst a consistent approach is presented that unifies all current theories of consolidation of soil. For one-dimensional finite strain consolidation, a Lagrangian finite element scheme is then given and tested against three different experiments and found to give consistent results. For a quick solution to a particular problem, the regular perturbation method applied to the formulation in which the dependent variable is the natural strain is shown to give the most consistent results. For the Eulerian formulation, the material derivative contains a convective term. This convective effect is then analytically studied and found not to be negligible for a final natural strain greater than 10%. A method is then introduced that can account for both the moving boundary and the convective effect. This method is tested in a finite difference scheme and found to give identical results with the Lagrangian finite element scheme for the one-dimensional case. Finally the method is used for the axisymmetric problem of consolidation by vertical drain. The solution to this case suggests that arching and subsequent load redistribution should be considered.
\r\n\r\nPART B
\r\n\r\nConceptually, when a centrifuge is used to test models, the centrifuge is assumed to produce an equivalent ng gravitational field (as on another planet) and the behavior of the model in the ng field is then assumed to be similar to that of the prototype. For most static problems, the centrifuge does model the prototype well but for some dynamic problems, these assumptions can break down. To investigate this, the similarity requirements are examined for the case of a single particle moving in a fluid. It is found that for the post-liquefaction process and for seepage flow, unless the Reynolds number is much less than one in both model and prototype, the centrifuge is not a good simulation of the prototype situation. But, perhaps contrary to expectations, the breakdown is due to the fact that the behavior in the ng planet is not similar to the prototype ig planet, whereas the centrifuge does simulate the ng planet well. Further, it is shown that the concept of \"modeling of models\" can lead to misleading results. Lastly, for cratering experiments, it is concluded that the centrifuge will only model the crater shape just after an explosion and not the final crater shape.
" }, { "name": "Tanner, John Edward", "degree": "PhD", "year": "1986", "title": "Integrated Optical Motion Detection", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-03102008-081506", "creators": [ { "name": { "family": "Tanner", "given": "John Edward" }, "id": "Tanner-John-Edward", "display_name": "Tanner, John Edward" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Hopfield", "given": "John J." }, "id": "Hopfield-J-J", "role": "member", "display_name": "Hopfield, John J." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Lyon", "given": "Richard F." }, "id": "Lyon-Richard-F", "role": "member", "display_name": "Lyon, Richard F." }, { "name": { "family": "Van Essen", "given": "David C." }, "id": "Van-Essen-D-C", "orcid": "0000-0001-7044-4721", "role": "member", "display_name": "Van Essen, David C." } ], "option_major": [ "compsci" ], "doi": "10.7907/PK3H-CM61", "abstract": "Two systems for detecting the motion of a scene are described. For both, an image is projected directly onto an integrated circuit that contains photosensors and computing circuitry to extract the motion. The first system, which has been reported earlier, correlates the analog image with a digitized version of the image stored from the previous cycle. The chip reports the motion that corresponds to the maximum analog correlation value. This system represents an advance from previous designs but exhibits some shortcomings.
\r\n\r\nA second completely analog design surpasses the first. The mathematical foundation is derived and the CMOS circuits used in the implementation are given. Test results and characterization of the working chips are reported. The new motion detector is not clocked and exhibits collective behavior. The use of local information extensively avoids the correspondence problem. The system can be thought of as a Hopfield neural net with one important extension\u2014input driven synapses. The motion detector also meshes nicely with the existing computational vision work. Extensions to handle more complex motions are proposed. The suitability of the motion extraction algorithm as a biological vision model is explored.
" }, { "name": "Taylor, Stephen", "degree": "PhD", "year": "1986", "title": "The Effects of Large-Eddy Manipulator Devices on the Turbulent Spot and the Turbulent Boundary Layer", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03102008-083411", "creators": [ { "name": { "family": "Taylor", "given": "Stephen" }, "id": "Taylor-Stephen", "orcid": "0000-0003-0264-1453", "display_name": "Taylor, Stephen" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7520-qj30", "abstract": "Recent experimental studies indicate that net drag reductions can be achieved in a turbulent boundary layer by placing a tandem configuration of large-eddy manipulator blades in the outer region of the boundary layer. However, the mechanisms responsible for the observed wall-shear reductions are not well understood. Furthermore, discrepancies exist among independent experimental studies regarding the magnitude of the attainable net drag reduction.
\r\n\r\nA fundamental argument is made regarding the source of the observed wall-shear reductions. It is shown that the tandem manipulator is not a low-drag device. The implication is that the momentum deficit in the wake of the manipulator is a prominent contributor to the observed wall-shear reductions, not necessarily that the ability of the large eddies to transport momentum is hampered. The behavior of the wall shear downstream of the device, obtained using hot-film wall-shear sensors, is consistent with the entrainment, mixing, and consequent deceleration of low-momentum fluid from the wake of the manipulator.
\r\n\r\nWith the aid of direct measurements of wall shear, an upper bound is placed on the attainable net drag reduction by establishing a lower bound for the device drag. It is concluded that small net reductions (~ 5 percent) may be attained at large downstream distances (\u2273 100 boundary-layer thicknesses). This conclusion is consistent with most net drag assessments made independently by others in which the momentum-balance technique was employed. However, the result is not consistent with reports of large net reductions (~ 20 percent) over shorter distances (~ 50 boundary-layer thicknesses).
\r\n\r\nEfforts are also made to explain the observed effects in terms of turbulent structure. The turbulent spot is employed as a prototype structure for the large-scale, organized motions in the turbulent boundary layer. Dramatic wall-shear reductions occur in the region of the spot occupied by the large vortex structure. Such reductions are also evident when the spot is propagating in transitional and fully turbulent ambient boundary layers. Although the transport properties of the vortex structure may be affected by the manipulator, it is proposed that an important source of the wall-shear reductions is the transport by the large vortex of low-momentum fluid in the wake of the manipulator.
\r\n\r\nSome effects of a three-dimensional manipulator are also explored. The design of the device is based on a crude model of the three-dimensional structure of the turbulent spot. Although it appears that the device inhibits the spanwise growth of the spot, its overall effect on the wall shear of the spot and the turbulent boundary layer does not represent an improvement over the effectiveness of a comparable tandem configuration.
" }, { "name": "Ungsuwarungsri, Tawach", "degree": "PhD", "year": "1986", "title": "The Effect of Strain-Softening Cohesive Material on Crack Stability", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242004-152909", "creators": [ { "name": { "family": "Ungsuwarungsri", "given": "Tawach" }, "id": "Ungsuwarungsri-Tawach", "display_name": "Ungsuwarungsri, Tawach" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/sqjv-pf95", "abstract": "Part I
\r\n\r\nFailure mechanisms of materials under very high strains experienced at and ahead of the crack tip (such as the formation, growth and interaction of microvoids in ductile materials, microcracks in brittle solids or crazes in polymers and adhesives) are represented by one-dimensional, nonlinear stress-strain relations possessing different post-yield softening (unloading) behaviors. These reflect different ways by which the material loses capacity to carry load up to fracture. A DCB type specimen is considered in this study. The nonlinear material is confined to a thin strip between the two elastic beams loaded by a wedge. The problem is first treated as a beam on a nonlinear foundation for which the pertinent equation is solved numerically as a two-point boundary value problem for both the stationary and the quasi-statically propagating crack. A finite element model is then used to model the problem in more detail to assess the adequacy of the beam model for reduction of the experimental data.
\r\n\r\nIt is found that the energy release rate G = 2(\u03b3b) = {3P2\u03b4)2/EI}1/3 derived by assuming the built-in conditions at the crack tip could be used to calculate the fracture (surface) energy more accurately and conveniently than the conventional scheme even in cases where the built-in assumption is invalid. Results for the deformations of the beam prior to or during crack growth suggest ways to approximately characterize the complete material stress-strain behavior, including loading and strain-softening characteristics.
\r\n\r\nPart II
\r\n\r\nThis study investigates the effects of nonlinear fibril behavior on the mechanics of craze and crack growth. We developed a numerical method for determining the equilibrium shape of a craze in an infinite elastic plane whose fibrils exhibit very general nonlinear force-displacement (P-V) behavior, including strain softening characteristics.
\r\n\r\nThe problem formulation is based on the superposition of the relevant elasticity Green's function. The solution is effected by using Picard's successive approximation iterative scheme. Both field equilibrium and the Barenblatt condition for vanishing stress and strain singularities (KI = 0) are satisfied simultaneously, rendering the craze tip profile cusp-like as observed experimentally. The formulation allows the stress distribution profile and the corresponding P-V relation to be computed from experimentally measured craze/crack contours with certain advantages over the methods proposed to date.
\r\n\r\nFurther numerical investigations indicate that only certain classes of the fibril P-V relations are consistent with realistic craze profiles, i.e., profiles with nonnegative displacements at all points. In addition, it is found that for a given P-V relation, nontrivial solutions -- the 'trivial solution' refers to the solution corresponding to a fully closed craze, i.e., zero displacements throughout or, simply: no craze exists -- exist only for certain ranges of craze lengths depending on the P-V characteristics under consideration.
\r\n\r\nQuasi-static growth of a craze with a central crack is analyzed for different nonlinear P-V relations for the craze fibrils. A 'critical crack tip opening displacement' (CTOD) or more precisely, 'critical fibril extension' is employed as the criterion for fracture. The P-V relation is further assumed to be invariant with respect to the craze and crack lengths. For comparison purposes, the results are compared and contrasted with the Dugdale model. The craze zone size and the energy dissipation rate are shown to approach asymptotic values in the limit of long cracks.
\r\n\r\nThe problem of craze growth from a precut crack under increasing far-field loading is then studied. Instability is shown to occur in the case where the P-V relation is monotonically softening: The crack could start to grow unstably before the crack tip opening displacement reaches its critical value.
" }, { "name": "Venkataramanan, Ramanarayanan", "degree": "PhD", "year": "1986", "title": "Sliding Mode Control of Power Converters", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-09222006-170253", "creators": [ { "name": { "family": "Venkataramanan", "given": "Ramanarayanan" }, "id": "Venkataramanan-Ramanarayanan", "display_name": "Venkataramanan, Ramanarayanan" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "chair", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Thompson", "given": "Peter M." }, "id": "Thompson-Peter-M", "role": "member", "display_name": "Thompson, Peter M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/230A-P786", "abstract": "Switched mode power converters are being used extensively for the purpose of efficient power conversion. Such converters are nonlinear, time variant systems. In the past such converters were being modelled using the state space averaging method. The theory of variable structure systems (VSS), and sliding mode control form a mutually complementary analysis and design tools for the control of switched mode power converters. The application of sliding mode control is presented for dc-to-dc converters and electrical motor drives in this thesis. The concept of sliding mode control is brought out through exhaustive examples of second order systems. The equivalent control, an analysis method of VSS, is applied to obtain transfer function description of dc-to-dc power converters. The sliding mode control is applied to the control problem of dc-to-dc power converters and speed controlled electrical drives to develop practical design techniques. The practical design methods are confirmed through experimental results.
" }, { "name": "Waldman, Jed Michael", "degree": "PhD", "year": "1986", "title": "Depositional Aspects of Pollutant Behavior in Fog", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03132008-095317", "creators": [ { "name": { "family": "Waldman", "given": "Jed Michael" }, "id": "Waldman-Jed-Michael", "orcid": "0000-0002-5220-5919", "display_name": "Waldman, Jed Michael" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "orcid": "0000-0002-4263-2562", "role": "member", "display_name": "Yung, Yuk L." } ], "option_major": [ "envreng" ], "doi": "10.7907/6K0F-E189", "abstract": "Droplet deposition during fog is shown to play an important role in the removal of anthropogenic pollutants from the atmosphere. Relevant theoretical principles are reviewed, and a survey of previous investigations is made. Results of extensive field monitoring programs are presented, and characterizations of fog chemistry and deposition in several environments are reported.
\r\n\r\nThe in-cloud scavenging of aerosols and soluble gases coupled with the small size of fog droplets are found to result in higher chemical concentrations in fogwater than in rainwater. In the urban regions of southern California and the southern San Joaquin Valley, fogwater chemistry is dominated by sulfate, nitrate, and ammonium ions, which are measured at millimolar levels. High fog- and cloudwater acidities (pH 2 to 4) are routinely found in the western Los Angeles basin where ammonia emissions are low. San Joaquin Valley fogwater samples are less acidic due to greater ammonia release from local sources.
\r\n\r\nThe formation of fog is shown to accelerate deposition rates for water-scavenged atmospheric constituents. Surrogate-surface measurements made in the San Joaquin Valley indicate that major species were removed at rates 5 to 20 times greater during fogs compared to nonfoggy periods. During stagnation episodes, pollutant removal by ventilation of valley air requires at least 5 days, while the enhancement of deposition by fog formation leads to pollutant lifetimes on the order of 6-12 h. Thus, in an environment characterized by flat, open landscape and low wind speed, droplet sedimentation can be the dominant removal mechanism of pollutants during prolonged stagnation episodes with fog.
" }, { "name": "Zah, Chung-en", "degree": "PhD", "year": "1986", "title": "Millimeter-Wave Monolithic Schottky Diode Imaging Arrays", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112008-080410", "creators": [ { "name": { "family": "Zah", "given": "Chung-en" }, "id": "Zah-Chung-en", "display_name": "Zah, Chung-en" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "member", "display_name": "Pine, Jerome" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Luhmann", "given": "Neville C., Jr." }, "id": "Luhmann-Neville-C-Jr", "role": "member", "display_name": "Luhmann, Neville C., Jr." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/YSN2-8F19", "abstract": "Inexpensive and compact imaging systems with high sensitivity are needed for millimeter waves. In this study, the calculated efficiencies of elementary integrated-circuit feed antennas show that the antennas with substrate lenses are potentially better feeds than those without substrate lenses. Planar Schottky diodes are integrated with bow-tie antennas to form a one dimensional array. The energy is focused onto the antenna through a silicon lens placed on the back of the gallium-arsenide substrate. Putting a polystyrene cap on the silicon lens has been demonstrated to be an effective way to reduce the reflection loss. A self-aligning process together with proton isolation has been developed to make the planar Schottky diodes with a 1.1-THz zero-bias cutoff frequency. The antenna coupling efficiency and imaging properties of the system are studied by video detection measurements at 94 GHz. As a heterodyne receiver, a double-sideband mixer conversion loss of 11.2 dB and noise temperature of 3770\u00b0K have been achieved at a local oscillator frequency of 91 GHz.
\r\n" }, { "name": "Zelt, Jeffrey Alan", "degree": "PhD", "year": "1986", "title": "Tsunamis: The Response of Harbours with Sloping Boundaries to Long Wave Excitation", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-03142008-080030", "creators": [ { "name": { "family": "Zelt", "given": "Jeffrey Alan" }, "id": "Zelt-Jeffrey-Alan", "display_name": "Zelt, Jeffrey Alan" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "chair", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "civileng" ], "doi": "10.7907/QBE6-5409", "abstract": "The influence of sloping boundaries on the long wave response of bays and harbours is studied in this work. Laboratory experiments are performed to help validate the theoretical analysis which is applicable to nonbreaking waves.
\r\n\r\nA set of long wave equations in the Lagrangian description is derived which includes terms to account for nonlinear, dispersive, and dissipative processes for wave propagation in two horizontal coordinates. A finite element model is developed based on these equations which is capable of treating arbitrary geometry and the runup of nonbreaking waves on a beach.
\r\n\r\nAn analytical harbour response model, capable of treating narrow rectangular harbours with variable bathymetry and sidewall geometry, is developed and applied to several simple geometries. The model shows that for a given harbour length and entrance width, the resonant frequencies and the response of a harbour are very dependent on the harbour sidewall geometry and bathymetry.
\r\n\r\nSome of the nonlinear effects of the runup of nonbreaking periodic waves on a plane beach are discussed. In particular, the time average of the water surface time history at a fixed spatial location is negative and the wave crests are smaller than the troughs. Nonlinear effects do not alter the runup maxima or minima and the maximum fluid acceleration occurs at the point of maximum rundown of the \r\nwave.
\r\n\r\nLaboratory experiments were performed to determine the long wave reponse of a narrow rectangular harbour whose still water depth decreases linearly between the harbour entrance and the shoreline. Good agreement with the finite element model was obtained, including the prediction of the depression of the mean water level within the harbour.
\r\n\r\nA three-dimensional application of the finite element model treats the runup of solitary waves on a coastline with variable bottom topography and a curved shoreline. The results indicate that the model can predict the trapping of wave energy along a sloping coastal margin, a process of fundamental importance for predicting potential tsunami damage.
" }, { "name": "Zhu, Jinlin", "degree": "PhD", "year": "1986", "title": "Internal Solitons Generated by Moving Disturbances", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-03122008-080220", "creators": [ { "name": { "family": "Zhu", "given": "Jinlin" }, "id": "Zhu-Jinlin", "display_name": "Zhu, Jinlin" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." } ], "option_major": [ "eng" ], "doi": "10.7907/pspg-vp83", "abstract": "A new phenomenon of the generation of internal solitons is investigated in this thesis by applying theoretical models and is observed in both numerical and experimental results. By imposing an external disturbance, such as a top surface pressure or a bottom bump, that moves with a constant velocity within a trans critical range after an impulsive start from rest, upon a two-layered or a continuously stratified fluid system, a series of solitons are generated, one after another periodically, each surging ahead of the disturbance in turn. Two theoretical models, belonging to the generalized Boussinesq class, are developed to investigate the generation of weakly nonlinear and weakly dispersive long waves and their evolution in an inviscid, immiscible, and incompressible stratified fluid system under the forcing of the external disturbances. The top surface may be either free or covered by a rigid horizontal plate. For the generalized Boussinesq class for two-layered fluid systems, we have derived the FOUR-equation model for the free top-surface case and the THREE-equation model for the rigid horizontal top-surface case; these are extensions of the one-layer homogeneous fluid system previously considered by Wu (1979). For primarily unidirectional motions a forced KdV equation is obtained which represents each normal mode of a two-layer system or a continuously stratified fluid system. Numerical schemes have been successfully developed to solve these equations. Experiments were performed to investigate this phenomenon,henomenon using fresh water to form the upper layer and brine the lower layer. The relationship between the main properties (the amplitude and the period of generation) of the generated solitons and the forcing function configurations is discussed along with comparisons of theoretical, numerical and experimental results. Qualitatively all the results are consistent in exhibiting the salient features of the resulting motion. Quantitatively the numerical results based on the continuously stratified fluid model seem to be more satisfactory than those given by the two-layered fluid model in comparison with the present experiments. The discrepancy between the theory and experiment is supposedly due to the viscous effects, which will be left for future work.
\r\n" }, { "name": "van Zyl, Jakob Johannes", "degree": "PhD", "year": "1986", "title": "On the Importance of Polarization in Radar Scattering Problems", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-06262006-133025", "creators": [ { "name": { "family": "van Zyl", "given": "Jakob Johannes" }, "id": "van-Zyl-Jakob-Johannes", "display_name": "van Zyl, Jakob Johannes" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "chair", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Albee", "given": "Arden Leroy" }, "id": "Albee-A-L", "role": "member", "display_name": "Albee, Arden Leroy" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "orcid": "009-0002-2156-967X", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/QRD0-YE09", "abstract": "In this thesis, the importance of polarization in radar scattering problems is investigated. The different matrix characterizations of scatterers are discussed in detail. The problem of finding the polarizations which would yield an optimum amount of power received from the scatterer is solved for the most general case. This shows that for certain classes of scatterers six optimum polarizations exist. The concept of a polarization spectrum to characterize a scatterer is introduced. The usefulness of these spectrums is illustrated when results, using measured multipolarization synthetic aperture radar data, are discussed. Another useful parameter, the coefficient of variation, is introduced. Measured results show that this parameter may be used to form an idea of the scale over which the scattering properties of the scene being imaged vary. The problem of finding the effective scattering operator of a slab filled with different scatterers is formulated. Detailed expressions are given for the effective single scattering operators. This formulation is illustrated by calculating the effective single scattering operators for models of different types of vegetation.
" }, { "name": "Aaron, Kim Maynard", "degree": "PhD", "year": "1985", "title": "Edgetones and Acoustic Resonances in a Duct", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222007-092606", "creators": [ { "name": { "family": "Aaron", "given": "Kim Maynard" }, "id": "Aaron-Kim-Maynard", "display_name": "Aaron, Kim Maynard" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "chair", "display_name": "Kubota, Toshi" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/bfy8-1995", "abstract": "Undesirable sound generation in the combustion chamber of segmented solid propellant rocket motors has been attributed to vortex shedding from obstructions that are uncovered as the propellant burns back. This phenomenon has been investigated experimentally and the mechanism explained.
\r\n\r\nA pair of aluminum baffles within a lucite duct through which air is drawn models the important aspects which enable the sound generation mechanism to operate. The baffles form an edgetone system which interacts with the longitudinal acoustic modes of the chamber. Acoustic tones occur spontaneously, at frequencies determined by the acoustic resonances, when the spacing between the baffles satisfies certain criteria.
\r\n\r\nFlow visualization using smoke and a strobe light triggered by the pressure oscillations indicate that vortex shedding occurs at the first baffle in phase with the acoustic velocity oscillations there. The interaction of these vortices with the downstream baffle drives the acoustic resonance which, in turn, triggers the formation of new vortices at the upstream separation point.
\r\n\r\nThe phase relations for this feedback to operate require that there be close to an integral number of wavelengths, or vortices, from the separation point to the impingement point.
\r\n\r\nA model has been developed which predicts the experimentally observed behaviour well. Pressure amplitudes are predicted within an order of magnitude. Mean flow rates and baffle spacings yielding maximum response are determined correctly by the model.
" }, { "name": "Bales, Roger Curtis", "degree": "PhD", "year": "1985", "title": "Surface Chemical and Physical Behavior of Chrysotile Asbestos in Natural Waters and Water Treatment", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292010-075726877", "creators": [ { "name": { "family": "Bales", "given": "Roger Curtis" }, "id": "Bales-Roger-Curtis", "orcid": "0000-0002-0811-8535", "display_name": "Bales, Roger Curtis" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/4q42-z892", "abstract": "Chrysotile asbestos fibers enter California waters from physical weathering of magnesium-silicate, serpentine rocks in mountains of the northern and central portions of the state. Chrysotile particles, initially positively charged below pH 8.9 because of their magnesium-hydroxide surface, become negatively charged due to dissolution and adsorption of organic matter. Magnesium release from chrysotile dissolving in 0.1 M inorganic electrolyte at pH 7-10 for up to five days is in excess of the 3:2 Mg:Si to silica molar ratio in the solid. The magnesium release rate exhibits a fractional dependence on hydrogen-ion concentration:
\r\n\r\nr = k1'[H+](0.24)
\r\n\r\nThe observed rate constant, k1', depends on dissolution mechanism, specific surface area of the solid and charge-potential relation at the surface. In terms of a surface site-binding model, the fractional dependence implies that dissolution is limited by a chemical reaction involving less than one adsorbed proton per magnesium ion released. Silica release shows no clear pH dependence.
\r\n\r\nThe rate of magnesium release is independent of the anions NO3-, Cl-, SO42-, HCO3-, oxalate or catechol. Oxalate inhibited and catechol slightly enhanced silica release at pH 7.5-8.5; other anions had no systematic effect. Chrysotile's dissolution rate (10-15.7 mol/cm2\u2022s at pH 8) is consistent with observations on other magnesium silicates and brucite.
\r\n\r\nCatechol adsorption onto chrysotile or aluminum oxide (pH 7.5-8.5) does not reach equilibrium but increases over five days. After one day the maximum adsorption density (Langmuir adsorption equation) on chrysotile is 0.7 x 10-9 mol/cm2 (50 x 10-6 mg C/cm2), approximately one-third of the estimated density for proton exchange. The maximum adsorption density for natural organic matter was near 30 x 10-6 mg C/cm2 on both chrysotile and aluminum oxide.
\r\n\r\nChrysotile adsorbs sufficient natural organic matter within one day to reverse its surface charge. The extent of reversal is larger than observed on aluminum oxide, because of selective dissolution of chrysotile's outer magnesium-hydroxide layer.
\r\n\r\nIn reservoirs, submicron-sized chrysotile particles coagulate with larger (> 2 \u00b5m), negatively-charged particles that subsequently settle out. The rate at which freshly-suspended, positively-charged fibers coagulate is at least ten-fold greater than the rate for aged, negatively-charged fibers coagulate. Capture of chrysotile particles in water filtration is enhanced 10-fold or more by incorporating fibers into larger flocs.
" }, { "name": "Biswas, Pratim", "degree": "PhD", "year": "1985", "title": "Impactors for Aerosol Measurement: Developments and Sampling Biases", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-112738", "creators": [ { "name": { "family": "Biswas", "given": "Pratim" }, "id": "Biswas-Pratim", "display_name": "Biswas, Pratim" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." } ], "option_major": [ "mecheng" ], "doi": "10.7907/YG7P-PX37", "abstract": "This work is subdivided into four parts. The first part consists of characterizing high jet velocity impactors, developing their scaling criteria to facilitate instrument design and prediction of impactor performance under conditions where no calibration data are available.
\r\n\r\nThe second part discusses the problem of distortion of size distributions by aerosol sampling instruments because of particle size changes occurring due to vapor or condensable phase transport to and from the particles. The severity of the problem is demonstrated both theoretically and experimentally for a few commonly used aerosol sampling instruments.
\r\n\r\nThe third part is the development of a 'Particle Trap Impactor' working on the virtual impaction principle. The inherent problems of bounce and re-entrainment in conventional impactors is minimized, without the addition of substrates such as grease, in these impactors. The result of operating the unit at high temperature is also discussed.
\r\n\r\nThe final part is the calculation of the scavenging rate of particles due to differential impaction. The results are used to determine upperbounds on the number concentration of particles entering the impactor to minimize biasing the measurements.
" }, { "name": "Brown, Elliott R.", "degree": "PhD", "year": "1985", "title": "Investigation of Bulk Indium Antimonide as Heterodyne Detector for the Submillimeter Wavelength Region", "advisor": "Phillips, Thomas G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-130847340", "creators": [ { "name": { "family": "Brown", "given": "Elliott R." }, "id": "Brown-Elliott-R", "display_name": "Brown, Elliott R." } ], "advisors": [ { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "advisor", "display_name": "Phillips, Thomas G." } ], "committee": [ { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "chair", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/wm40-4k69", "abstract": "Bulk n-InSb is investigated at a heterodyne detector for the submillimeter wavelength region. Two modes of operation are investigated: (1) the Rollin or hot electron bolometer mode (zero magnetic field), and (2) the Putley mode (quantizing magnetic field). The highlight of the thesis work is the pioneering demonstration or the Putley mode mixer at several frequencies. For example, a double-sideband system noise temperature of about 510K was obtained using a 812 GHz methanol laser for the local oscillator. This performance is at least a factor or 10 more sensitive than any other performance reported to date at the same frequency. In addition, the Putley mode mixer achieved system noise temperatures of 250K at 492 GHz and 350K at 625 GHz. The 492 GHz performance is about 50% better and the 625 GHz is about 100% better than previous best performances established by the Rollin-mode mixer. To achieve these results, it was necessary to design a totally new ultra-low noise, room-temperature preamp to handle the higher source impedance imposed by the Putley mode operation. This preamp has considerably less input capacitance than comparably noisy, ambient designs.
\r\n\r\nIn addition to advancing receiver technology, this thesis also presents several novel results regarding the physics of n-InSb at low temperatures. A Fourier transform spectrometer was constructed and used to measure the submillimeter wave absorption coefficient of relatively pure material at liquid helium temperatures and in zero magnetic field. Below 4.2K, the absorption coefficient was found to decrease with frequency much faster than predicted by Drudian theory. Much better agreement with experiment was obtained using a quantum theory based on inverse-Bremmstrahlung in a solid. Also the noise of the Rollin-mode detector at 4.2K was accurately measured and compared with theory. The power spectrum is found to be well fit by a recent theory of non-equilibrium noise due to Mather. Surprisingly, when biased for optimum detector performance, high purity InSb cooled to liquid helium temperatures generates less noise than that predicted by simple non-equilibrium Johnson noise theory alone. This explains in part the excellent performance of the Rollin-mode detector in the millimeter wavelength region.
\r\n\r\nAgain using the Fourier transform spectrometer, spectra are obtained of the responsivity and direct detection NEP as a function of magnetic field in the range 20-110 cm-1. The results show a discernable peak in the detector response at the conduction electron cyclotron resonance frequency for magnetic fields as low as 3 KG at bath temperatures of 2.0K. The spectra also display the well-known peak due to the cyclotron resonance of electrons bound to impurity states. The magnitude of responsivity at both peaks is roughly constant with magnet1c field and is comparable to the low frequency Rollin-mode response. The NEP at the peaks is found to be much better than previous values at the same frequency and comparable to the best long wavelength results previously reported. For example, a value NEP = 4.5 x 10-13W/Hz1/2 is measured at 4.2K, 6 KG and 40 cm-1. Study of the responsivity under conditions of impact ionization showed a dramatic disappearance of the impurity electron resonance while the conduction electron resonance remained constant. This observation offers the first concrete evidence that the mobility of an electron in the N = 0 and N = 1 Landau levels is different. Finally, these direct detection experiments indicate that the excellent heterodyne performance achieved at 812 GHz should be attainable up to frequencies of at least 1200 GHz.
" }, { "name": "Chelvakumar, Kasivisvanathan", "degree": "PhD", "year": "1985", "title": "A Simple Strain-Space Plasticity Model for Clays", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01022019-123640478", "creators": [ { "name": { "family": "Chelvakumar", "given": "Kasivisvanathan" }, "id": "Chelvakumar-Kasivisvanathan", "display_name": "Chelvakumar, Kasivisvanathan" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "mecheng" ], "doi": "10.7907/kcgf-c188", "abstract": "This thesis develops and demonstrates a simple strain-space constitutive model for wet clays. It has been seen that a strain-space formulation of the constitutive behavior of engineering materials facilitates the solution of boundary value problems involving these materials. Soil, because of its multi-phase granular constitution poses challenging problems in constitutive modeling. Although several stress-space plasticity models exist for soils, they are not used commonly in engineering practice due to their complexity. It is attempted herein to develop and test a simple model which could result in simplified solutions for some soil problems.
\r\n\r\nThe model is based on the experimentally observed physical behavior of soil. Certain approaches alien to conventional plasticity. Are employed so that the material behavior is closely predicted without sacrificing the simplicity of the model.
\r\n\r\nThe model is initially developed for triaxial load systems. Its predictions are then tested against other model predictions and experimental data. The model is then generalized. The generalization renders the model capable of handling general stress-strain states and finite deformations.
\r\n\r\nFinally, the generalized model is used to solve an idealization of a practical problem. The problem of a pile driven into a soil medium is idealized as an expanding cavity in a homogeneous infinite medium. The solution predicted by the strain-space model is compared with other model predictions and test results.
" }, { "name": "Cifuentes, Arturo O.", "degree": "PhD", "year": "1985", "title": "System Identification of Hysteretic Structures", "advisor": "Iwan, Wilfred D.; Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12192018-105342164", "creators": [ { "name": { "family": "Cifuentes", "given": "Arturo O." }, "id": "Cifuentes-Arturo-O", "orcid": "0000-0001-9689-3939", "display_name": "Cifuentes, Arturo O." } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "co-advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "chair", "display_name": "Jennings, Paul C." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/p43n-j428", "abstract": "This thesis is concerned with the earthquake response of hysteretic structures subjected to strong ground acceleration. Several earthquake records corresponding to different instrumented buildings are analyzed. Based on these observations, a new model for the dynamic behavior of reinforced concrete buildings is proposed. In addition, a suitable system identification algorithm to be used with this new model is introduced. This system identification algorithm is based upon matching the restoring force behavior of the structure rather than the time history of the response. As a consequence, the new algorithm exhibits significant advantages from a computational point of view. Same numerical examples using actual earthquake data are discussed.
" }, { "name": "Collins, Reuben Theodore", "degree": "PhD", "year": "1985", "title": "Electronic Properties of Heterostructures and Defects in Compound Semiconductors", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-142511", "creators": [ { "name": { "family": "Collins", "given": "Reuben Theodore" }, "id": "Collins-Reuben-Theodore", "orcid": "0000-0001-7910-3819", "display_name": "Collins, Reuben Theodore" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Lambe", "given": "John" }, "id": "Lambe-John", "role": "chair", "display_name": "Lambe, John" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/pg8h-k549", "abstract": "This thesis deals with the electronic characteristics of semiconductor heterostructures and with the electrical properties of semiconductors which are used in the growth of heterostructures. Chapter 2 describes electrical measurements which were made on heterostructures composed of the compound semiconductors AlAs and GaAs. Specifically, the mechanisms for current transport perpendicular to one or more AlAs layers sandwiched between two degenerate GaAs layers were studied, with an emphasis on elastic and inelastic tunneling through the AlAs layers at low temperatures. Tunneling currents occur because the conduction band offset between AlAs and GaAs causes the AlAs to act as a barrier to electrons in the GaAs. Samples composed of single or multiple layers of AlAs sandwiched between GaAs layers were grown by metal organic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Electron transport perpendicular to the AlAs barriers was studied as a function of temperature, doping, and layer thickness by making I-V, first derivative (dI/dV), and second derivative d2I/dV2 measurements on these samples. The I-V curves give information about current transport mechanisms. If the dominant mechanism is tunneling, the I-V curves reflect mostly elastic tunneling currents, Structure in the derivatives of the I-V curves indicates the presence of inelastic and resonant tunneling processes. The elastic tunneling measurements give an understanding of the structure of the barriers since these measurements depend on barrier thickness, barrier spacings, and barrier height. Inelastic tunneling measurements can be used to identify the fundamental excitations in the tunneling barrier which can couple to the tunneling electrons; thus, inelastic measurements give additional information about the properties of the barrier. First and second derivatives were measured using modulation techniques.
\r\n\r\nThe main results of this study were the identification of the dominant current transport mechanisms across the AlAs barriers as a function of temperature and AlAs layer thickness, the observation of inelastic tunneling currents due to the excitation of phonons, and the observation of resonant tunneling currents. Measurements on MOCVD grown samples with a single p-type AlAs barrier indicated that thermionic emission was the dominant mechanism for current transport over the barrier at room temperature. At low temperatures, leakage currents dominated if the barrier was thicker than approximately 100 \u00c5, while tunneling currents were dominant in the samples with thinner AlAs barriers. Electron self-energy effects due to the coupling of electrons and optical phonons in the GaAs, and the inelastic-excitation of longitudinal optical phonons in the AlAs were observed in the tunneling current through samples with 50 \u00c5 thick AlAs barriers. This was the first observation of these effects in the AlAs/GaAs system. Measurements were also made on MOCVD grown samples with a single, n-type AlAs barrier. I-V curves for these samples did not have the expected dependence on AlAs layer width. Reproducible structure was still present in the second derivative spectra. A possible explanation for the differences between samples with n-type and p-type barriers which is based on band bending in the AlAs barrier is given. Measurements on MOCVD grown samples with AlxGa1-xAs barriers were made with results similar to those for pure AlAs barriers. Negative resistance regions were observed in the I-V curves of samples with multiple AlAs layers, indicating the presence of resonant tunneling effects. Tunneling measurements on MBE grown structures with a single AlAs barrier did not give reproducible or consistent results.
\r\n\r\nChapter 3 presents an investigation of the deep-level defect structure of CdTe using the technique of deep-level transient spectroscopy (DLTS). Layered structures composed of the compound semiconductors CdTe and HgTe or of the alloy Hg1-xCdxTe may have interesting properties. To realize these properties it is important to understand the electrical characteristics of CdTe and HgTe.The electronic properties of CdTe and HgTe are complicated by the fact that native defects may dominate the electrical characteristics of the crystals. An understanding of the deep-level defect structure of CdTe is, thus, important. DLTS measurements can be used to determine the energy of a deep-level with respect to the band edges, the concentration of the level, and its carrier capture cross section. DLTS measurements are made by monitoring changes in the capacitance of a diode caused by capturing carriers at levels in the depletion region of the diode and then thermally emitting the carriers back to the conduction and valence edges.
\r\n\r\nMeasurements were made on a variety of CdTe crystals. Nominally undoped, Cu-doped and In-doped CdTe crystals were studied. Some of the crystals were observed before and after anneals in Cd-vapor, Te-vapor, or in a purified H2 ambient. Characteristics of deep levels which are seen in all of the n-type CdTe samples are presented. These levels were attributed to native crystal defects or to impurities which are commonly incorporated into CdTe. Levels were also observed which were common to all of the p-type crystals. The same explanation was given for the origin of these traps. A few levels which were specific to certain crystals were also observed and were attributed to unidentified impurities. Deep states were present in the In-doped CdTe which were not observed until the sample was illuminated with above band gap light at low temperatures. Other levels were induced to appear by stressing the CdTe crystals. In general, anneal conditions had a large effect on the concentrations of both shallow and deep levels in the crystals, but did not alter which deep levels were present and their relative concentrations. Modest sample heating (400K) during the process of making DLTS measurements could change the amplitude of levels, sometimes causing new levels to appear or previously observed levels to no longer be observed.
" }, { "name": "Dahm, Werner Johann Anton", "degree": "PhD", "year": "1985", "title": "Experiments on Entrainment, Mixing and Chemical Reactions in Turbulent Jets at Large Schmidt Number", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062006-104125", "creators": [ { "name": { "family": "Dahm", "given": "Werner Johann Anton" }, "id": "Dahm-Werner-Johann-Anton", "orcid": "0000-0002-0779-3280", "display_name": "Dahm, Werner Johann Anton" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/k93g-jh12", "abstract": "Entrainment, mixing and chemical reactions are investigated in the far field of steady, axisymmetric, momentum-driven, turbulent jets issuing into an unconfined, quiescent medium in the large Schmidt number (liquid-phase) regime. Visualization experiments using both passive and chemically sensitive planar laser induced fluorescence (LIF) techniques show the importance of large scale transport in the jet far field, and suggest that entrainment, mixing and chemical reactions in the far field are dominated by a large scale organization of the flow. Successive instantaneous profiles of the jet fluid concentration along the axial and radial directions in the jet far field are measured by combining these LIF techniques with direct, high-resolution, linear photodiode array imaging and high-speed digital data acquisition. These imaging measurements have revealed an axial similarity concentration variable for which probability density functions (PDFs) in the jet far field are self-similar along rays. A chemical reaction method is presented which allows the self-similar form of these PDFs to be measured with full resolution at all scales of transport and mixing. Furthermore, these imaging measurements have shown that instantaneous radial profiles of the jet fluid concentration do not resemble the mean concentration profile. Specifically, unmixed ambient fluid is found deep within the jet and the composition of molecularly mixed fluid within large regions in the jet is approximately uniform. The results from these experiments are interpreted in the context of a simple conceptual model for large scale organization of entrainment, mixing and chemical reactions in the far field of turbulent jets.
" }, { "name": "Davies, Simon Henry Richard", "degree": "PhD", "year": "1985", "title": "Mn(II) Oxidation in the Presence of Metal Oxides", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03212005-111003", "creators": [ { "name": { "family": "Davies", "given": "Simon Henry Richard" }, "id": "Davies-Simon-Henry-Richard", "display_name": "Davies, Simon Henry Richard" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Yung", "given": "Yuk L." }, "id": "Yung-Y-L", "orcid": "0000-0002-4263-2562", "role": "member", "display_name": "Yung, Yuk L." }, { "name": { "family": "Bercaw", "given": "John E." }, "id": "Bercaw-J-E", "role": "member", "display_name": "Bercaw, John E." } ], "option_major": [ "envreng" ], "doi": "10.7907/512V-8A90", "abstract": "The oxidation of Mn(II) by oxygen in the presence of goethite (\u03b1-FeOOH), lepidocrocite (\u03b3-FeOOH), silica and alumina was studied. All the solids, except perhaps alumina,enhanced the rate of Mn(II) oxidation. The degree of enhancement was as follows:
\r\n\r\nlepidocrocite > goethite > silica > alumina.
\r\n\r\nAt constant pO2 Mn(II) oxidation on goethite, lepidocrocite and silica can be described by the following equation
\r\n\r\n[Equation; see abstract in scanned thesis for details.]
\r\n\r\nwhere <\u2261SOH> is the concentration of the surface hydroxyl group and a is the solids concentration.
\r\n\r\nMn(II) oxidation in the presence of goethite or lepidocrocite is first order in pO2. Both these reactions are strongly temperature dependent (apparent activation energy ~100 kJ/mol). Normal laboratory lighting has no effect on the rate of these reactions.
\r\n\r\nThe rate of Mn(II) oxidation in the presence of lepidocrocite is about 4 times slower in 0.7M NaClO4, than in 0.1M NaClO4. This reaction is inhibited by the following ions; Mg2+, Ca2+, silicate, salicylate, phosphate, chloride, and sulfate. Phthalate has little or no effect on the rate of this reaction.
\r\n\r\nThe adsorptive behaviour of Mn(II) on the metal oxides studied could be described using a surface complexation model. Using this model it was shown that the rate of Mn(II) oxidation on the metal oxides studied is described by the equation
\r\n\r\n[Equation; see abstract in scanned thesis for details.]
\r\n\r\nwhere (\u2261SOH)2Mn is a bidentate surface complex. It is possible that a hydrolyzed surface complex (\u2261SOMnOH) rather than the bidentate complex is involved in the reaction.
\r\n\r\nThe results of the laboratory studies indicate that in natural waters the important factors which influence Mn(II) on metal oxides are pH, iron oxide concentration, temperature, [Mg2+], [Cl-], and ionic strength. These studies predict that at pH < 7.5 the rate of Mn(II) oxidation in natural waters is slow (t1/2 < 100 days). Mn(II) may be completely oxidized within a few days in iron-rich, high pH waters.
" }, { "name": "Dolgin, Benjamin Paul", "degree": "PhD", "year": "1985", "title": "Kinetics of the Formation of an Amorphous Layer During a Solid State Reaction", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272008-090442", "creators": [ { "name": { "family": "Dolgin", "given": "Benjamin Paul" }, "id": "Dolgin-Benjamin-Paul", "display_name": "Dolgin, Benjamin Paul" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/n0qt-h472", "abstract": "Solid state reaction as a new method of amorphous film fabrication was introduced by R. Schwartz and W. L. Johnson in 1983. A thermodynamic explanation for the process given by the original article provides a clue to understanding the forces making the reaction possible. This thesis emphasizes the kinetic approach to the description of the reaction. The movements of the interfaces as a fundamental mechanism of the reaction is suggested. The reaction in La-Au and Ni-Hf multilayers is described. Resistance measurements, TEM and SIMS techniques, and Rutherford backscattering are used to study the process.
\r\n\r\nThe thesis contains a proof that the final product of the solid state reaction is amorphous. It describes the morphology of the reacting multilayers. The one-dimensional and multi-dimensional processes taking place during the growth are separated. The thesis connects the properties of the reaction with known properties of the \"fast diffusion.\" The phenomenological model for the reaction is introduced. The model consists of a diffusion equation with a new set of boundary conditions. The amorphous layer growth rate in the limit of short time is found to be X = 1 - exp(-At) and X = -1/(A - 1) + (2at)1/2 in the limit of long time. The \"steady state\" approximation as a solution to the diffusion equations in the limit of long time is found to be incorrect. The model shows excellent agreement with the experimental data.
" }, { "name": "Elyada, Dov", "degree": "PhD", "year": "1985", "title": "Structural Analysis of Imperfect Three-Legged Truss Columns for Large Space Structures Applications", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11182004-161353", "creators": [ { "name": { "family": "Elyada", "given": "Dov" }, "id": "Elyada-Dov", "display_name": "Elyada, Dov" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YXNE-YE65", "abstract": "Three-legged truss columns are basic structural components of many envisioned large outer-space structures. They constitute three longerons ('legs') forming, in the column cross-section, the vertices of an equiliateral triangle. Their longerons are held together by uniformly spaced battens while a shear web, usually made of diagonals, restrains shear deformation.
\r\n\r\nThis work deals with configurations characterized by having relatively stiff battens, longerons which are pinned to the battens and prestressed string diagonals. Considered are only simply-supported slender columns having slender longeron segments and relatively thin and lightly preloaded diagonals. The columns are allowed to have global (overall) as well as local (longeron segment) geometrical imperfections - not necessarily small ones.
\r\n\r\nInvestigated is the static structural behavior of such columns when loaded by purely axial compressive concentrated forces acting at the supports. Addressed are the topics of global and local buckling, post-buckling, imperfection sensitivity, global-local mode interaction, complete non-linear response, limit loads and diagonals slackening and post-slackening.
\r\n\r\nThe approach is a theoretical one; a system of non-linear, ordinary differential equations is set up which represents the column, and results, mostly in closed form, are obtained by solving that system for a variety of cases of varying generality.
\r\n\r\nFirst, a highly idealized case is studied in detail, in which the diagonals are removed and infinite shear rigidity is postulated instead. The results exhibit most of the essential features of the more complicated cases. Next, the case of the undeflected or only-slightly deflected column is considered. Results include the prebuckling behavior, slackening and local buckling loads, global buckling load, initial post-buckling behavior and imperfection sensitivities. Diagonals slackening in a deflecting column is studied next. This is done by means of slackening loci constructed in the load-deflection plane. Solutions are obtained for some special cases of a deflecting column. These include a complete analysis of the locally-perfect case and the cases of small load and high defection. Also obtained is an engineering-oriented load-deflection working relation valid for the most general case but based on generalization rather than on rigorous solution. A torsion-compression mode, dominant in post-slackening, is also analyzed. The work is concluded by investigating the error committed in treating continuous longerons as if they were discontinuous-pinned.
\r\n" }, { "name": "Faust, Bruce Charles", "degree": "PhD", "year": "1985", "title": "Photo-Induced Reductive Dissolution of Hematite (\u03b1-Fe\u2082O\u2083) by S(IV) Oxyanions", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-141334", "creators": [ { "name": { "family": "Faust", "given": "Bruce Charles" }, "id": "Faust-Bruce-Charles", "orcid": "0009-0001-2881-6533", "display_name": "Faust, Bruce Charles" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." } ], "option_major": [ "envreng" ], "doi": "10.7907/cj3r-5x15", "abstract": "The kinetics and mechanism of the photo-induced reductive dissolution of hematite (\u03b1-Fe2O3) by S(IV) oxyanions, in aqueous suspensions of hematite, have been investigated. Experimental quantum yields for Fe(II)aq production are reported for deoxygenated hematite suspensions containing S(IV). Quantum yield studies together with spectroscopic information indicate that \u2261Fe(III)-S(IV) surface complexes undergo a photo-induced ligand to metal charge transfer reaction resulting in the reductive dissolution of hematite and production of Fe(II)aq.
\r\n\r\nThe autoxidation of S(IV) in oxygenated hematite suspensions exhibits autocatalytic behavior. This behavior is interpreted in terms of three general processes: i) production of Fe(II)aq from photo-induced ligand to metal charge transfer reactions of \u2261Fe(III)-S(IV) surface complexes, ii) oxidation of Fe(II)aq to Fe(III)aq and, iii) the Fe(III)aq catalyzed autoxidation of S(IV). A numerical model, based on these processes, is developed to predict the disappearance of S(IV) in oxygenated hematite suspensions under illumination.
" }, { "name": "Fier, Jeffrey Michael", "degree": "PhD", "year": "1985", "title": "Part I. Fold Continuation and the Flow Between Rotating, Coaxial Disks. Part II. Equilibrium Chaos. Part III. A Mesh Selection Algorithm for Two-Point Boundary Value Problems", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-150456", "creators": [ { "name": { "family": "Fier", "given": "Jeffrey Michael" }, "id": "Fier-Jeffrey-Michael", "display_name": "Fier, Jeffrey Michael" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "chair", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" } ], "option_major": [ "appmath" ], "doi": "10.7907/cs9b-ft10", "abstract": "Part I:
\r\n\r\nWe consider folds in the solution surface of nonlinear equations with two free parameters. A system of equations whose solutions are fold paths is formulated and proved to be non-singular in a neighborhood of a fold, thus making continuation possible. Efficient numerical algorithms employing block Gaussian elimination are developed for applying Euler-Newton pseudo-arclength continuation to the system, and these are shown to require fewer operations than other methods.
\r\n\r\nTo demonstrate the use of these methods we calculate the flow between two infinite, rotating disks. For Reynold's number less than 1000, six separate solution sheets are found and completely described. Plots of 47 solutions for three values of the disk speed ratio and for Reynold's number equal to 625 are shown. These are compared with the solutions found by previous investigators.
\r\n\r\nPart II:
\r\n\r\nTwo ordinary differential equations with parameters whose solution paths exhibit an infinite sequence of folds clustered about a limiting value are studied. Using phase-plane analysis, expressions for the limiting ratios of the parameter values at which these folds occur are derived and the limiting values are shown to be non-universal.
\r\n\r\nPart III:
\r\n\r\nA mesh selection algorithm for use in a code to solve first-order nonlinear two-point boundary value problems with separated end conditions is described. The method is based on equidistributing the global error of the box scheme, a numerical estimate of which is obtained from Richardson extrapolation. Details of the algorithm and examples of its performance on non-stiff and stiff problems are presented.
\r\n" }, { "name": "Fredrickson, Eric Donald", "degree": "PhD", "year": "1985", "title": "An Experimental and Theoretical Investigation of a Finite Beta Modified Drift Wave", "advisor": "Bellan, Paul Murray", "url": "https://resolver.caltech.edu/CaltechTHESIS:12112018-111733645", "creators": [ { "name": { "family": "Fredrickson", "given": "Eric Donald" }, "id": "Fredrickson-Eric-Donald", "display_name": "Fredrickson, Eric Donald" } ], "advisors": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "advisor", "display_name": "Bellan, Paul Murray" } ], "committee": [ { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "chair", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "member", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Moffet", "given": "Alan Theodore" }, "id": "Moffet-A-T", "role": "member", "display_name": "Moffet, Alan Theodore" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/fdcx-m289", "abstract": "The saturated slate of a low frequency coherent, m=2, global mode has been studied in the Encore tokamak using probe techniques. The mode is found to have large fluctuations in density, electron temperature, space potential and magnetic field. The equilibrium plasma characteristics were also determined with probe measurements. Magnetic probes were used to determine the radial profile of the poloidal magnetic field, from which the rotational transform and current density profiles could be deduced. A Langmuir probe was used to measure radial profiles of the density, electron temperature and space potential.
\r\n\r\nBy comparing the experimental measurements with the predictions of a computer code. the mode was identified as a finite \u03b2\u03c4 modified drift wave. The code is based on a linear, two-fluid theory of the coupling of drift and shear-Alfven modes. Of the two shear-Alfven solutions and the drift branch solution, it was found that the drift wave solution best fit the observed frequency of the mode and the relative amplitudes of the density, space potential and magnetic fluctuations. The identification of the mode as a finite \u03b2\u03c4 modified drift wave means that the mode is more closely related to the higher frequency, turbulent fluctuations observed on larger machines. rather than the lower frequency, coherent Mirnov oscillations.
" }, { "name": "Frost, David Lawrence", "degree": "PhD", "year": "1985", "title": "Effects of Ambient Pressure on the Instability of a Liquid Boiling Explosively at the Superheat Limit", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-081638", "creators": [ { "name": { "family": "Frost", "given": "David Lawrence" }, "id": "Frost-David-Lawrence", "orcid": "0000-0002-3579-6091", "display_name": "Frost, David Lawrence" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8J3K-PS54", "abstract": "The effect of ambient pressure on the dynamical behaviour of a single droplet (1-2 mm diameter) of volatile liquid boiling explosively at the limit of superheat is studied experimentally and theoretically. In a series of experiments it is shown that the evaporative instability, observed earlier by Shepherd & Sturtevant (1982) during the rapid vapourization of butane droplets at atmospheric pressure, is suppressed at high pressure. Three other fluids (pentane, isopentane, and ether) are tested to establish the generality of the instability and other transient processes previously observed. Direct evidence is obtained showing that during violently unstable boiling small liquid particles are torn from the liquid-vapour interface. This ejection of fine droplets from the evaporating surface produces a mass flux orders of magnitude greater than that characteristic of ordinary boiling.
\r\n\r\nRaising the ambient pressure lowers the superheat attained at the superheat limit, which decreases the vapourization rate. At high pressure boiling consists of normal slow vapourization from a smooth interface. Observed bubble growth rates show reasonable agreement with theory. At intermediate pressures a transitional regime of stability occurs in which a drop initially vapourizes stably for several milliseconds while incipient instability waves develop on the evaporating interface. When only a small amount of liquid remains in the drop in the shape of a thin cap, heat transfer from the surrounding hot host fluid initiates violent boiling at the edge of the liquid cap. The subsequent rapid vapourization generates a radiated pressure field two orders of magnitude larger than during stable boiling, and sets the bubble into violent oscillation. The bubble is subject to the Rayleigh-Taylor instability and rapidly disintegrates into a cloud of small bubbles.
\r\n\r\nLowering the ambient pressure decreases the time delay between nucleation and onset of unstable boiling. For example, in ether at atmospheric pressure the instability is triggered less than 8 \u00b5sec after nucleation, shortly after the smooth vapour bubble contacts the droplet surface. Heterogeneous nucleation spreads out along the surface of the drop while disturbances (with a length scale of 100 \u00b5m) distort the unstably evaporating interface within the drop, substantially enhancing the vapourization rate. At early times, droplets torn from the evaporating surface evaporate before the instability-driven jet impinges upon the surrounding fluid, bulging the bubble surface. The last portion of liquid in a drop boils particularly violently and droplets ejected from the evaporating interface at this time remain intact to splatter the bubble surface. At subatmospheric pressures the most rapid vapourization occurs and temperature gradients within a drop produce spatial variations in vapourization rate.
\r\n\r\nThe Landau mechanism for the instability of laminar flames is adapted to the case of evaporation to investigate the effects of variable ambient pressure. A spherical version of the theory, applicable before the vapour bubble contacts the droplet surface, predicts absolute stability at atmospheric pressure. At later times the spherical constraint is inappropriate and planar theory yields results in general agreement with observation. Differences in fluid properties make some fluids more prone to instability than others. The product of the maximum growth rate with the time interval the interface is predicted to be linearly unstable measures the susceptibility to instability. For practical estimates it is suggested that a value of 3 of this parameter be taken as the lower limit for instability. The sensitivity of the instability to temperature suggests that small temperature nonuniformities may be responsible for quantitative departures of the behaviour from predictions.
\r\n" }, { "name": "Hazelton, Lowell Eugene", "degree": "PhD", "year": "1985", "title": "A Study of Hydrogen Mobility in a Glassy Zr\u2082Pd Using Internal Friction", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272008-075843", "creators": [ { "name": { "family": "Hazelton", "given": "Lowell Eugene" }, "id": "Hazelton-Lowell-Eugene", "orcid": "0000-0002-4616-6423", "display_name": "Hazelton, Lowell Eugene" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "member", "display_name": "Ahrens, Thomas J." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/t60e-ft46", "abstract": "Hydrogen-related internal friction peaks have been measured in amorphous Zr2Pd and Y64Fe36, covering a range of hydrogen concentrations up to 0.86 H/M for the former alloy. The internal friction peaks were found to be several times wider than a peak due to a single relaxing defect, and quite asymmetric with a long low temperature tail, as with previous measurements on hydrogen in amorphous metals. They showed a thermally activated relaxation time with a frequency prefactor and a range of activation energies indicative of a point defect source. The evidence is shown to strongly indicate a Snoek-type defect, consisting of single hydrogen atoms in interstitial sites with strongly elliptical or variable strain dipole tensors. The integral equation that gives the internal friction is inverted for the first time to yield the distribution of relaxation times. It is suggested that the main peak in the resulting distribution of activation energies results from hydrogen hopping through three-sided faces, primarily between tetrahedral sites. These sites are found to change at high concentration to have a lower strain dipole ellipticity and to become more well-defined. This is interpreted as signaling a change in the structure of the amorphous metal itself. In addition there appear to be a small number of other deep-well sites where hydrogen is initially trapped at low concentrations. These have a very broad distribution of activation energies ranging from the main peak down to below 0.1 eV. A model is proposed to account for this by hopping of hydrogen between larger sites through distorted four-sided faces in the metal lattice.
" }, { "name": "Henshaw, William Douglas", "degree": "PhD", "year": "1985", "title": "Part I. The Numerical Solution of Hyperbolic Systems of Conservation Laws. Part II. Composite Overlapping Grid Techniques", "advisor": "Kreiss, Heinz-Otto", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312008-100117", "creators": [ { "name": { "family": "Henshaw", "given": "William Douglas" }, "id": "Henshaw-William-Douglas", "orcid": "0009-0008-9088-7229", "display_name": "Henshaw, William Douglas" } ], "advisors": [ { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "advisor", "display_name": "Kreiss, Heinz-Otto" } ], "committee": [ { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "chair", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Lorenz", "given": "Jens" }, "id": "Lorenz-Jens", "role": "member", "display_name": "Lorenz, Jens" } ], "option_major": [ "appmath" ], "doi": "10.7907/kz0y-2j77", "abstract": "Part I
\r\n\r\nA method is described for the numerical solution of hyperbolic systems of conservation laws in one space dimension. The basis of the scheme is to use finite differences where the solution is smooth and the method of characteristics where the solution is not smooth. The method can accurately represent shocks. Results are presented for the solution of the equations of gas dynamics. The examples illustrate the accuracy of the method when discontinuities are present and the code's performance on difficult problems of interacting shocks and shock formation.
\r\n\r\nPart II
\r\n\r\nTechniques for the numerical solution of partial differential equations on composite overlapping meshes are discussed. Methods for the solution of time dependent and elliptic problems are illustrated, including a discussion of implicit time stepping and using the multigrid algorithm for the iterative solution of Poisson's equation. Two model problems are analyzed. The first gives insight into the accuracy of the solution to elliptic equations on overlapping meshes. The second deals with the numerical approximation of boundary conditions for vorticity stream function formulations. Computational results are presented.
" }, { "name": "Hermanson, James Carl", "degree": "PhD", "year": "1985", "title": "Heat Release Effects in a Turbulent, Reacting Shear Layer", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06132007-075717", "creators": [ { "name": { "family": "Hermanson", "given": "James Carl" }, "id": "Hermanson-James-Carl", "display_name": "Hermanson, James Carl" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "chair", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/y722-za34", "abstract": "The effects of heat release were studied in a planar, gaseous reacting mixing layer formed between free streams containing hydrogen and fluorine in inert diluents. Sufficiently high concentrations of reactants were employed to produce adiabatic flame temperature rises of up to 940 K (1240 K absolute). The Reynolds number at the measuring station, based on velocity difference, 1% temperature thickness and cold kinematic viscosity was approximately 6x104. The temperature field was measured with cold wire resistance thermometers and thermocouples. Flow visualization was accomplished by schlieren spark and motion picture photography. Mean velocity information was extracted from mean pitot probe dynamic pressure measurements.
\r\n\r\nThough the displacement thickness of the layer, for zero streamwise pressure gradient, increased with increasing heat release, the actual growth rate of the layer did not increase, but instead decreased slightly. The overall entrainment into the layer was seen to be substantially reduced as a consequence of heat release. Calculations showed that the decrease in layer growth rate can be accounted for by a corresponding reduction in turbulent shear stress.
\r\n\r\nThe mean temperature rise profiles, normalized by the adiabatic flame temperature rise, were not greatly changed in shape by heat release. A small decrease in normalized mean temperature rise with heat release was observed. Large scale coherent structures were observed to persist at all levels of heat release in this investigation. The mean structure spacing decreased with increasing temperature. This decrease exceeded the rate of layer growth rate reduction, and suggests that the mechanisms of vortex amalgamation were, to some extent, inhibited by heat release.
\r\n\r\nImposition of a favorable pressure gradient resulted in additional thinning of the layer, and caused a slight increase in the mixing and amount of chemical product formation. The change in layer growth rate can be shown to be related to a change in free stream velocity ratio induced by pressure gradient.
" }, { "name": "Jacob, Daniel James", "degree": "PhD", "year": "1985", "title": "The Origins of Inorganic Acidity in Fogs", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01112005-133508", "creators": [ { "name": { "family": "Jacob", "given": "Daniel James" }, "id": "Jacob-Daniel-James", "orcid": "0000-0002-6373-3100", "display_name": "Jacob, Daniel James" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." } ], "option_major": [ "envreng" ], "doi": "10.7907/54GV-ZQ97", "abstract": "A rotating arm device to collect large samples of fogwater for chemical analysis was designed and fully characterized. This instrument was used to determine the chemical composition of fogwater at a large number of sites in California. Fogwater at both urban and non-urban sites was frequently found to contain important inorganic acidity. Chemical models were developed to interpret the origins of this acidity in terms of aqueous-phase S(IV) oxidation reactions and acid/base titration processes in the fog and the precursor atmosphere. These models were found to successfully interpret the inorganic acidity in fogwater and aerosol during wintertime stagnation episodes in the San Joaquin Valley of California.
\r\n" }, { "name": "Jeong, Garrett Duane", "degree": "PhD", "year": "1985", "title": "Cumulative Damage of Structures Subjected to Response Spectrum Consistent Random Processes", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04052019-121036771", "creators": [ { "name": { "family": "Jeong", "given": "Garrett Duane" }, "id": "Jeong-Garrett-Duane", "display_name": "Jeong, Garrett Duane" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/97b3-2427", "abstract": "A theoretical analysis of the effect of duration on the damage of structures subjected to earthquakes is presented. Earthquake excitation is modeled as a nonstationary random process. Estimates of the first-passage probability of a simple oscillator are employed to choose modulated Gaussian random processes consistent with a prescribed response spectrum. The response spectrum is assumed to be specified independent of the duration. Expressions for the mean damage of a structure are derived using an approach similar to the Miner-Palmgren rule for failure caused by cyclic loads. The expected damage expressions are then evaluated for a structure subjected to modulated Gaussian random processes of varying duration.
\r\n\r\nTwo types of structures are examined: a steel structure and a reinforced concrete structure. Results are presented for systems with constant linear stiffness and a particular form of softening behavior. The nonlinearity of the softening system is accounted for by statistical linearization. The level of expected damage is found to be a strong function of both the duration of the excitation and the ductility of the response.
" }, { "name": "Kasiraj, Prakash", "degree": "PhD", "year": "1985", "title": "Shock-Wave Consolidation of Metallic Powders", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202002-161800", "creators": [ { "name": { "family": "Kasiraj", "given": "Prakash" }, "id": "Kasiraj-Prakash", "display_name": "Kasiraj, Prakash" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "chair", "display_name": "Vreeland, Thad" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Ahrens", "given": "Thomas J." }, "id": "Ahrens-T-J", "role": "member", "display_name": "Ahrens, Thomas J." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7cxy-vx62", "abstract": "Conventional powder metallurgical techniques have the drawback in that metastable properties of the powder can be lost during the sintering stage. The use of shock waves to bond particles of powder together can, in principle, circumvent this drawback and produce bulk solids which retain metastable properties of the initial powder. However, the effects of the relevant shock and powder parameters on the final properties of the compacts must be understood before this technique can be used optimally.
\r\n\r\nIn the present investigation the influence of shock pressure, shock duration, and surface oxides on the mechanical and metallurgical properties of compacted steel, molybdenum, and nickel-molybdenum alloy powders were studied. In addition, to improve our fundamental understanding of shock waves in metallic powder media, the shock temperature at the junction between two layers of copper and constantan powders was measured via the thermoelectric effect for varying shock pressure and energy.
\r\n\r\nThe measured homogeneous temperatures in the copper-constantan powders varied from 150 C to 940 C as the shock energy was increased from 50 to 360 kJ/kg (shock pressure from 1.3 to 9.4 GPa). These results indicate that almost all of the energy in the shock front is converted into thermal energy. Furthermore, the rise time of the shock front is less than 23 ns which corresponds to a shock front width of less than 37 \u00b5m,a dimension comparable to the powder particle diameter.
\r\n\t\r\nRapidly solidified AISI 9310 steel powders were consolidated and the dependence of the microhardness and the ultimate tensile strength of the compacts on the shock energy from 94 to 770 kJ/kg (3.6 to 19.0 GPa) were measured for an initial powder distension of 1.64 and a shock duration of 2-3 \u00b5s. Photomicrographs and SEM fractographs were used to study the interparticle bonding in the compacts. Results show that, for shock energies below 200 kJ/kg (4.9 GPa), the compacts have negligble strength. However, above this threshold the strength of the compact rises rapidly until a maximum value of 1.3 GPa is reached at a shock energy of 500 kJ/kg (12.4 GPa). This strength which is larger than that of wrought AISI 9310 remains constant before decreasing at the higher shock energies. In marked contrast, with increasing shock energy, the diamond pyramid hardness increases very gradually from a value of 340 for the initial powder to 500 at a shock energy of 500 kJ/kg. Microhardness also begins to decrease at higher shock energies. The maximum strength obtained correlates well with the strength expected from microhardness measurements.
\r\n\r\nThe AISI 9310 powders were also used to study the effect of shock duration on the compact's strength. Results indicate that, for consolidations with a shock energy of 400 kJ/kg (10 GPa), shock durations greater than 0.4 \u00b5s are needed to produce strong compacts. This lower limit on shock duration can be attributed to the condition that the duration of the compressive shock wave must exceed the solidification and strengthening time of the melt produced by the shock wave.
\r\n\t\r\nMolybdenum powders with a distension of 1.67 were used to study the effect of surface oxides. Results indicate that, by reducing the surface oxides, the tensile strength of the compact can be increased from nearly zero to 0.76 GPa for a shock energy of 580 kJ/kg (17.8 GPa). The final strength is comparable to that of bar stock of molybdenum.
\r\n\t\r\nPowders of glass forming Mark-1064 alloy (Ni55.8Mo25.7Cr9.7B8.8) with a distension of 2.0 were used to study the amount of melt produced during the shock consolidation process. Such measurements were possible because the melt was quenched rapidly enough to form the amorphous phase which could be delineated from the microcrystalline phase during metallographic examination. The results indicate that shock energies above 190 kJ/kg (3.4 GPa) are required before the occurence of measurable melting. The amount of melt is much less than the upper bound limit and the melt distribution is nonuniform.
\r\n\t\r\nFinally, the conceptual understanding of the shock consolidation process is discussed and the criteria for producing well-bonded compacts are enumerated. These criteria can be conveniently expressed in terms of a shock consolidation map which plots a dimensionless shock duration versus a dimensionless shock energy. The existing models for the shock consolidation process are evaluated in light of the recently acquired results.
" }, { "name": "Kendall, Elizabeth Ann", "degree": "PhD", "year": "1985", "title": "Range Dependent Signals and Maximum Entropy Methods for Underwater Acoustic Tomography", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-04092008-080843", "creators": [ { "name": { "family": "Kendall", "given": "Elizabeth Ann" }, "id": "Kendall-Elizabeth-Ann", "display_name": "Kendall, Elizabeth Ann" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." } ], "option_major": [ "mecheng" ], "doi": "10.7907/hrqs-cv92", "abstract": "A new method for simulating underwater acoustic signals in range dependent environments is presented, and the approach utilizes Maslov asymptotic theory as developed by C. H. Chapman for synthetic seismograms. The simulated range dependent signals are then used in active underwater acoustic tomography exercises, where changes in observed acoustic transmissions are inverted to obtain information about ocean sound velocity structure. The inversions are performed with both the generalized inverse and the maximum entropy inverse, and a new numerical method for finding the maximum entropy inverse with noisy data is presented. The numerical technique follows the \u03b5 statistic approach proposed by Bryan and Skilling.
\r\n" }, { "name": "Lang, Daniel Bernard", "degree": "PhD", "year": "1985", "title": "Laser Doppler Velocity and Vorticity Measurements in Turbulent Shear Layers", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312005-112325", "creators": [ { "name": { "family": "Lang", "given": "Daniel Bernard" }, "id": "Lang-Daniel-Bernard", "display_name": "Lang, Daniel Bernard" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/YFR4-VE59", "abstract": "A Laser Doppler Velocimeter (LDV) system was developed to measure the instantaneous spanwise vorticity, -wz, in a turbulent shear layer. It was necessary to design and fabricate the LDV optics and processing electronics, as no commercially available LDV systems met the specifications of measuring the velocity at four closely spaced points to the requisite accuracy. Measurements were also made of the instantaneous u, v, u', v', and -u'v'. The instantaneous vorticity was processed to obtain an estimate of its probability density function, from which the mean and rms values were estimated. It was also possible to separate the irrotational fraction of the flow (-wz \u2248 0) from the rotational (intermittent) fraction of the flow (-wz \u2260 0). The development of the intermittency profiles, based on vorticity, as a function of the downstream distance from the splitter plate was studied. A notable feature is that the vorticity is found to have values opposite the mean sense of rotation, i.e., -wz(t) < 0, a significant fraction of the time. Additionally, a detailed study was performed to evaluate the approximation of -\u2202v/\u2202x, in terms of various local temporal derivatives \u2202v/u(y)\u2202t. The optimum choice for u(y) can be found and is influenced by the relative local convection velocities of the small and large scale structures.
\r\n" }, { "name": "Lee, Seung-Joon", "degree": "PhD", "year": "1985", "title": "Generation of Long Water Waves by Moving Disturbances", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012008-151918", "creators": [ { "name": { "family": "Lee", "given": "Seung-Joon" }, "id": "Lee-Seung-Joon", "display_name": "Lee, Seung-Joon" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "chair", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" } ], "option_major": [ "eng" ], "doi": "10.7907/EG1N-VZ69", "abstract": "Several theoretical models are developed to study generation of nonlinear dispersive long waves by moving disturbances. All these models belong to the same class as the original Boussinesq or KdV model. The newly developed models, now with external forcing functions added to the KdV equation and the pair of coupled Boussinesq equations, have been chosen for numerical investigations. A predictor-corrector method is adopted to develop the numerical schemes employed here. In order to make the region of computation reasonably small for the case with moving disturbances, a pseudo-moving frame and the sufficiently transparent open boundary conditions are devised. The numerically obtained surface elevations exhibit a series of positive waves running ahead of the disturbance over a wide range of transcritical speeds of the disturbance. The numerical results show that, for speeds close to the critical value, the generation of such waves appears to continue indefinitely. The numerically obtained wave resistance coefficient is compared to the results given by linear dispersive theory. Numerical solutions have been obtained using the KdV and Boussinesq models with surface pressure and bottom bump as forcing functions. Comparisons are made between these results for various cases. Experiments were conducted for a two-dimensional bottom bump moving steadily in shallow water of a towing tank. Experimental results so attained are compared with the numerical solutions, and the agreement between them is good in terms of both the magnitude and the phase of the waves for the range of parameters used in the current study.
" }, { "name": "Lien, Chuen-Der", "degree": "PhD", "year": "1985", "title": "Thin Film Silicide Formation by Thermal Annealing: Study of Kinetics, Moving Species, Impurity Effect, and Electrical Properties", "advisor": "Nicolet, Marc-Aurele; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272008-074200", "creators": [ { "name": { "family": "Lien", "given": "Chuen-Der" }, "id": "Lien-Chuen-Der", "display_name": "Lien, Chuen-Der" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "co-advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/t5r5-5267", "abstract": "Growth kinetics, dominant moving species (DMS), impurity effect, and electrical properties of thermally formed silicides have been studied by using MeV4He+ Rutherford backscattering spectrometry, 18O(p,\u03b1)15N nuclear reaction analysis, four\u2014point probe measurement, and I\u2014V measurement.
\r\n\r\nThe growth kinetics (including growth rate and activation energy of growth rate) measurements are done for silicides formed on different kinds of Si substrates, viz., single crystalline (100) Si (Sic) and amorphous evaporated Si (Sie). Results show that the substrate can have different effects on different silicides. Some silicides grow much faster on Sie than on Sic (e.g., NiSi2,CoSi2), some show the reverse phenomenon (e.g., Co2Si, CoSi), and some have similar growth rates (e.g., NiSi, Ni2Si, Pt2Si, PtSi) (see Table 2). Some silicides are more uniform and form at lower temperature on Sie than on Sic (e.g., CrSi2, NiSi2, CoSi2). These interesting phenomena are discussed and explained in terms of the different properties between the samples with either substrate (see Chapter 2).
\r\n\r\nWhen studying the formation of a silicide, one would like to know the DMS in silicide during the silicide formation. Not only is it an important property of the silicide but it is closely related to the silicide formation. The DMS is, in general, measured by inert marker experiments. In Chapter 3, we use such marker experiments to study the DMS in a silicide during silicide formation and two other silicide reactions (viz., solid-phase-epitaxy (SPE) of Sie through silicide and silicide oxidation). The reason for measuring the DMS for the two additional types of silicide reactions is that all these reactions are related and additional information can be obtained from this comparison. The results, in fact, show that in all three reactions, the DMS in the silicide is the same when the silicide formation is diffusion\u2014controlled. An explanation is given (with some assumptions) by considering the detailed atomic motion inthe silicide during these reactions (see Chapter 3).
\r\n\r\nInert marker experiments can identify the DMS in a silicide. They cannot, however, distinguish whether the DMS diffuses by an interstitial (or grain boundary) or a vacancy mechanism. One possible way to determine the diffusion mechanism of the moving species is by using tracer experiments. The problem with the tracer studies is that the measured tracer profiles can be (and have been) misinterpreted. We review several models that were used to explain the tracer profiles, point out incorrect considerations and finally give a plausible model to explain what information can be obtained from the tracer experiments (see Chapter 4).
\r\n\r\nDuring marker experiments, one may find that the marker used to monitor the DMS can affect the growth rate of silicide, and sometimes even change the DMS. This points to a general problem, namely, how foreign atoms (impurities) introduced in a sample affect the properties of silicide. Since the effect of impurity is important in our thin film reactions, we have systematically studied the effect of oxygen on the growth rates of silicide, and its redistribution, by using a rare isotope of oxygen, 18O, as an impurity. The results are explained in terms of a modified model which was originally proposed by Scott (see Chapter 5).
\r\n\r\nFinally, we study the electrical properties of Co silicides. Co silicides formed from Sie (silicides thus formed are more uniform than that formed from Sic) are used for the measurements of Schottky barrier height, resistivity, Hall mobility, and carrier concentration. From the result of this study, we suggest that that CoSi2 is a potential candidate for contacts to shallow junctions and as an interconnection material in VLSI (see Chapter 6).
\r\n\r\nFurther works, arising out of the implications of these studies, are suggested and summarized in the last chapter of the thesis.
" }, { "name": "Lien, Sheue-Ling Chang", "degree": "PhD", "year": "1985", "title": "Combining Computation with Geometry", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-142130", "creators": [ { "name": { "family": "Lien", "given": "Sheue-Ling Chang" }, "id": "Lien-Sheue-Ling-Chang", "display_name": "Lien, Sheue-Ling Chang" } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Lewicki", "given": "George W." }, "id": "Lewicki-G-W", "role": "member", "display_name": "Lewicki, George W." }, { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "member", "display_name": "Fender, Derek H." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." } ], "option_major": [ "compsci" ], "doi": "10.7907/n1qe-h846", "abstract": "This thesis seeks to establish mathematical principles and to provide efficient solutions to various time consuming operations in computer-aided geometric design. It contains a discussion of three major topics: (1) design validation by means of object interference detection, (2) object reconstruction through the union, intersection, and subtraction of two polyhedra, and (3) calculation of basic engineering properties such as volume, center of mass, or moments of inertia.
\r\n\r\nTwo criteria are presented for solving the problems of point-polygon enclosure and point-polyhedron enclosure in object interference detection. An algorithm for efficient point-polyhedron-enclosure detection is presented. Singularities encountered in point-polyhedron-enclosure detection are categorized and simple methods for resolving them are also included.
\r\n\r\nA new scheme for representing solid objects, called skeletal polyhedron representation, is proposed. Also included are algorithms for performing set operations on polyhedra (or polygons) represented in skeletal polyhedron representation, algorithms for performing edge-edge intersection and face-face intersection in a set operation, and a perturbation method which can be used to resolve singularities for an easy execution of edge-edge intersection and face-face intersection.
\r\n\r\nA symbolic method for calculating basic engineering properties (such as volume, center of mass, moments of inertia, and similar integral properties of geometrically complex solids) is proposed. The same method is generalized for computing the integral properties of a set combined polyhedron, and for computing the integral properties of an arbitrary polyhedron in m-dimensional (Rm) space.
" }, { "name": "Lin, Tzu-Mu", "degree": "PhD", "year": "1985", "title": "A Hierarchical Timing Simulation Model for Digital Integrated Circuits and Systems", "advisor": "Mead, Carver; Ryser, Herbert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04102008-105646", "creators": [ { "name": { "family": "Lin", "given": "Tzu-Mu" }, "id": "Lin-Tzu-Mu", "display_name": "Lin, Tzu-Mu" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" }, { "name": { "family": "Ryser", "given": "Herbert J." }, "id": "Ryser-H-J", "role": "advisor", "display_name": "Ryser, Herbert J." } ], "committee": [ { "name": { "family": "Ryser", "given": "Herbert J." }, "id": "Ryser-H-J", "role": "chair", "display_name": "Ryser, Herbert J." }, { "name": { "family": "Bryant", "given": "Randy" }, "id": "Bryant-R", "role": "member", "display_name": "Bryant, Randy" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "compsci" ], "doi": "10.7907/41bh-7e43", "abstract": "A hierarchical timing simulation model for digital MOS circuits and systems is presented. This model supports the structured design methodology, and can be applied to both \"structure\" and \"behavior\" representations of designs in a uniform manner. A simulator based on this model can run several orders of magnitude faster than any other simulators that offer the same amount of information.
\r\n\r\nAt the structure (transistor) level, the transient behavior of a digital MOS circuit is approximated by that of an RC network for estimating delays. The Penfield-Rubinstein RC tree model is extended to include the effects of parallel paths and initial charge distributions. As far as delay is concerned, a two-port RC network is characterized by three parameters: R: series resistance, C: loading capacitance and D: internal delay. These parameters can be determined hierarchically as networks are composed in various ways. The composition rules are derived directly from the Kirchoff's current and voltage laws, so that the consistency with physics is established.
\r\n\r\nThe (R, C, D) characterization of two-port RC networks is then generalized to describe the behavior of semantic cells at any level of representation. A semantic cell is a functional block which can be abstracted by its steady-state behavior to interface with other cells in the system. As semantic cells are composed, the parameters of the composite cell can be determined from those of the the component cells either analytically or by simulation. A Smalltalk implementation of the hierarchical timing simulation model is also presented.
" }, { "name": "Maragakis, Emmanuel", "degree": "PhD", "year": "1985", "title": "A Model for the Rigid Body Motions of Skew Bridges", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02132019-102055741", "creators": [ { "name": { "family": "Maragakis", "given": "Emmanuel" }, "id": "Maragakis-Emmanuel", "display_name": "Maragakis, Emmanuel" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "chair", "display_name": "Jennings, Paul C." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "civileng" ], "doi": "10.7907/YWES-NJ36", "abstract": "This thesis investigates the rigid body motions of skew bridges, concentrating on the in-plane translational and rotational displacements of the bridge deck induced by impact between the deck and the abutments. Experience in the San Fernando Earthquake of February 9, 1971 demonstrates that this feature is particularly important for skew bridges.
\r\n\r\nA simple model, in which the bridge deck is represented by a rigid rod restricted by column and abutment springs is examined first. This model illustrates the mechanism by which in-plane rotational vibrations is triggered after the closure of the gap between the bridge deck and the abutment. It also shows that the force-deflection relations of the columns and the abutments are particularly important features for the response of the bridge. Methods for the exact and approximate estimation of the elastic stiffness of elastically founded, tapered bridge columns with octagonal cross section are presented next. The methods are applied to a bridge used later as an example. In addition, the yielding of the columns is examined and the force-deflection relations for bending about two orthogonal axes are estimated.
\r\n\r\nThe abutments are treated as rigid bodies and the soil embankments as Winkler Foundations with elastic spring constants increasing with depth. For the examination of the yielding of soil the Rankine theory is used. Based on these assumptions an approximate force deflection relation for the abutments is constructed.
\r\n\r\nThe response of a more complicated bridge model applied to a bridge near Riverside, California is examined at the end of the thesis and examples of the results are given. This model, in which the bridge deck is still represented as a rigid rod, has three in-plane degrees of freedom: two orthogonal displacements and a rotation, and is capable of capturing many of the more important features of the nonlinear, yielding response of skew bridges during strong earthquake shaking.
" }, { "name": "Matthys, Eric Francois", "degree": "PhD", "year": "1985", "title": "An Experimental Study of Convective Heat Transfer, Friction, and Rheology for Non-Newtonian Fluids: Polymer Solutions, Suspensions of Fibers, and Suspensions of Particulates", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-105407", "creators": [ { "name": { "family": "Matthys", "given": "Eric Francois" }, "id": "Matthys-Eric-Francois", "display_name": "Matthys, Eric Francois" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "chair", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "mecheng" ], "doi": "10.7907/pr91-d523", "abstract": "An experimental investigation was conducted on the convective heat transfer, friction, and rheological properties of various types of non-newtonian fluids in circular tube flows.
\r\n\r\nIf an apparent Reynolds number is used and if the temperature and degradation effects are properly taken into account, the reduced turbulent friction and heat transfer results, respectively, are then shown to be well correlated by the same expressions for different fluids, regardless of the nature of the fluids and whether they are shear-thinning or shear-thickening. This representation can also separate the reductions in turbulent heat transfer and friction that are induced by viscoelasticity from those induced by pseudoplasticity.
\r\n\r\nPolyacrylamide solutions inducing asymptotic and intermediate drag reduction regimes were investigated over a broad range of Reynolds numbers. The minimum heat transfer asymptote was determined for fully-developed conditions and for the very long (up to x/D = 600) entrance region observed. Solutions subjected to various degrees of intentional pre-degradation were studied to separate this effect from that of the degradation induced in the test tube itself.
\r\n\r\nA kerosene-based antimisting polymer solution was also studied. It was found to exhibit a complex viscous behavior involving time-dependency, shear-thickening beyond a critical shear rate, high susceptibility to degradation, and large sensitivity to temperature variations. The unusual friction and heat transfer results obtained with this fluid were, however, reduced to simple correlations for asymptotic drag reduction if an appropriate computational model is used.
\r\n\r\nSuspensions of bentonite of various concentrations were investigated in laminar and turbulent regimes, and the results for fully-developed and entrance flows were well correlated by newtonian relationships when an adequate wall viscosity concept was used. A combination of bentonite and polymer was found to be unusually susceptible to mechanical degradation, which affected significantly the viscosity and the level of drag and heat transfer reductions obtained.
\r\n\r\nA suspension of organic pulp based on tomato puree was shown to exhibit up to 40% of viscoelastic-type reduction in heat transfer and friction coefficients with respect to newtonian fluids in the turbulent regime. For laminar flow, however, these coefficients were larger than expected. Combinations of pulp and polymer were investigated as well.
\r\n\r\nA method was developed to predict the \"diameter effect\" for viscoelastic fluids.
" }, { "name": "Mehra, Madhav", "degree": "PhD", "year": "1985", "title": "The Atomic Structure of Some Metallic Glasses and the Influence of the Preparation Technique on the Amorphous State", "advisor": "Vreeland, Thad; Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272008-101236", "creators": [ { "name": { "family": "Mehra", "given": "Madhav" }, "id": "Mehra-Madhav", "display_name": "Mehra, Madhav" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "co-advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "chair", "display_name": "Vreeland, Thad" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "matsci" ], "doi": "10.7907/6twq-9080", "abstract": "In this work the structure of some new transition metal-metalloid glasses is discussed. Based on the Ru-Zr-B and the Rh-Si-B alloy series, these glasses are unique in that they contain up to 52 atomic percent metalloids. Available dense random packing models are not successful in explaining the structure of these glasses. The presence of a peak in the reduced radial distribution functions, G(r), at a distance of \u221a2 times the nearest-neighbour distance suggests the presence of octahedral coordination. This coordination, absent in the dense random packed models is explained by invoking a packing of trigonal prisms. With this proposed short range order the main features in the experimentally obtained G(r) have been reproduced.
\r\n\r\nAlso presented is a study that compares the amorphous state obtained in the same alloy by two different techniques. Films of (Mo0.6Ru0.4)82B18 obtained by sputtering are found to be more disordered than their liquid quenched counterparts. This increased disorder is evidenced through measurements of the G(r) and superconducting properties. The films have a lower atomic density than liquid quenched films of the same composition. This lower density reflects the presence of more entrapped free volume.
\r\n\r\nFinally, the results of a study on wear resistant amorphous coatings is reported. It is found that, by coating a surface of 52100 bearing steel with a thin film of (W0.6Re0.4)76B24, the wear resistance of the steel is increased by three orders of magnitude. This encouraging result suggests that the technological hopes for amorphous materials may indeed be realised.
" }, { "name": "Pak, Ronald Y.S.", "degree": "PhD", "year": "1985", "title": "Dynamic Response of a Partially Embedded Bar Under Transverse Excitations", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01222019-152401456", "creators": [ { "name": { "family": "Pak", "given": "Ronald Y.S." }, "id": "Pak-Ronald-Y-S", "display_name": "Pak, Ronald Y.S." } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "chair", "display_name": "Jennings, Paul C." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/pp2r-fc10", "abstract": "This dissertation is concerned with the dynamic response of a finite flexible bar partially embedded in a half-space, under transverse loadings. The loadings are applied at the unembedded end of the bar and may, in general, be a combination of time-harmonic shear and moment. The problem is intended to serve as a fundamental idealization for the dynamic analysis of piles or other embedded foundations whose flexibilities are not negligible.
\r\n\r\nBy treating the bar as a one-dimensional structure and the half-space as a three-dimensional elastic continuum, the interaction problem is formulated as a Fredholm integral equation of the second kind. The essential tool required in the formulation is a group of Green's functions which describe the response of an elastic half-space to a finite, distributed, buried source which acts in the lateral direction. By means of a technique developed for a class of three-dimensional asymmetric wave propagation problems, the Green's functions are derived as integral representations. A numerical procedure for the computation of the semi-infinite Hankel-type integrals involved is presented which is free of the basic difficulties commonly encountered in such problems. Owing to the special nature of the kernel function, a numerical scheme which contains the essence of quadrature and collocation techniques is developed for the solution of the governing integral equation. Selected results for the interaction problem are presented to illustrate various basic features of the solution. In addition to furnishing the compliance functions commonly used in soil-structure interaction studies, the solution should prove useful in providing a basis for the assessment and improvement of approximate and numerical models currently employed for such analyses.
" }, { "name": "Patton, James Scott", "degree": "PhD", "year": "1985", "title": "Experimental Study of Shear Flows and Convective Heat Transfer Characteristics of Granular Materials", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11022004-085416", "creators": [ { "name": { "family": "Patton", "given": "James Scott" }, "id": "Patton-James-Scott", "display_name": "Patton, James Scott" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "chair", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "mecheng" ], "doi": "10.7907/f3ja-cj26", "abstract": "An experimental study of granular material shear flows and convective heat transfer characteristics are presented in this investigation. A rectangular chute was used to obtain the results. The experiments were conducted with two sizes of glass beads. In addition, some information was obtained on the shear stress of polyethylene pellets.
\r\n\r\nThe bulk flow properties are used to evaluate the wall shear. The development of a method for determining the bulk density allowed for more accurate calculation of the flow quantities. A derivation of a compressible open channel equation is given for determining the wall shear. The wall shear is presented in terms of several forms of the Froude Number and solid fraction. The experimental results show that the friction coefficient (the ratio of the shear stress to the normal stress) is not a constant but increases with the Froude Number. The presentation of the wall shear as a function of a wide range of solid fractions is the first experimental work that can be directly compared to analytical and computational investigations.
\r\n\r\nThe convective heat transfer properties of flowing granular materials were investigated by examining the flow over a flat heating plate. The method for determining the bulk density of the flow also proved revealing for the heat transfer studies. By using this method, a unique curve for each material was produced in terms of a special Nusselt Number and Peclet Number. The results clearly show that the Nusselt Number reaches a maximum and then decreases for higher values of the Peclet Number. A derivation for convective heat transfer to a flowing granular material is given to predict the heat transfer properties over a wide range of flow conditions.
" }, { "name": "Prabhakar, Arati", "degree": "PhD", "year": "1985", "title": "Investigations of Deep Level Defects in Semiconductor Material Systems", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06212004-160535", "creators": [ { "name": { "family": "Prabhakar", "given": "Arati" }, "id": "Prabhakar-Arati", "display_name": "Prabhakar, Arati" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "chair", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Janda", "given": "Kenneth C." }, "id": "Janda-K-C", "role": "member", "display_name": "Janda, Kenneth C." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/BNQT-B222", "abstract": "In this thesis, we present the results of two groups of investigations of deep level defects in semiconductor material systems.
\r\n\r\nChapter 1 consists of an overview of the thesis, background information on semiconductor impurities, and a description of deep level transient spectroscopy (DLTS).
\r\n\r\nChapter 2 contains discussions of the experiments performed on transition metal silicide-silicon Schottky barrier structures to probe for the existence of deep levels. We investigated platinum, palladium, and nickel silicides on n-type silicon which were annealed at temperatures from 300 to 800\u00b0C. The primary techniques used were DLTS, current-voltage (IV), and capacitance-voltage (C-V) measurements for electronic characterizations, and Rutherford backscattering spectrometry (RBS) to determine the silicide phase and film condition. For our samples, 700\u00b0C was the maximum temperature below which no significant degradation of the barrier or contamination of the underlying silicon were observed in platinum and palladium silicide structures. Nickel silicide structures could only withstand temperatures up to 500\u00b0C. Cobalt, chromium, and erbium silicides were also studied using DLTS. These measurements constitute the first series of studies of deep level contamination of the silicon underlying a transition metal suicide thin film.
\r\n\r\nChapter 3 details our DLTS studies of four different compositions of the alloy In1-xGaxAsyP1-y. Our samples, with bandgaps of 0.75, 0.83, 0.95,and 1.1 eV, covered the range of compositions that are lattice-matched to InP and are used for long-wavelength optoelectronic devices. No traps were observed above the detection limit of 5 x 1013 cm-3. The only exception was one sample, which had a trap that was attributed to a lattice defect in the substrate. These DLTS experiments were the first attempt to investigate deep level defects in In1-xGaxAsyP1-y.
\r\n" }, { "name": "Roberts, Fredrick Allen", "degree": "PhD", "year": "1985", "title": "Effects of a Periodic Disturbance on Structure and Mixing in Turbulent Shear Layers and Wakes", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252008-144801", "creators": [ { "name": { "family": "Roberts", "given": "Fredrick Allen" }, "id": "Roberts-Fredrick-Allen", "display_name": "Roberts, Fredrick Allen" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "chair", "display_name": "Broadwell, James E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/syy5-a334", "abstract": "Large scale structure and mixing processes are investigated in chemically reacting wakes and shear layers to which a periodic disturbance is applied. The experiments employ a diffusion-limited acid-base reaction to directly measure the extent of mixing. Optical diagnostics used include laser absorption and laser induced fluorescence. Absorption of laser light by reacted product provides a measure of cross-stream average product. Fluorescence was measured by a self-scanning linear photodiode array using high speed computer data acquisition to obtain the product distribution across the layer.
\r\n\r\nPrevious results showing that forcing alters the structure and growth rate of shear layers are confirmed. Forcing artificially extends the lifetime of vortices whose size is consistent with the disturbance wavelength. Amalgamation of smaller vortices is enhanced over that in the natural layer until the frequency locked scale is achieved. At high Reynolds number product measurements show reduction of product with forcing. At moderate Reynolds numbers, on the other hand, there is an increase in product when forced. In one case a five fold increase in product was observed. The differences are related to the different effects of forcing on entrainment, composition ratio and secondary structure.
\r\n\r\nA dramatic, order of magnitude increase in mixing was discovered for certain forced wake flows. This effect is strongly associated with an interaction between the spanwise organized wake vortices and the test-section side walls.
\r\n" }, { "name": "Russell, Armistead Goode", "degree": "PhD", "year": "1985", "title": "Formation and Control of Atmospheric Aerosol Nitrate and Nitric Acid", "advisor": "Cass, Glen Rowan", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252008-090855", "creators": [ { "name": { "family": "Russell", "given": "Armistead Goode" }, "id": "Russell-Armistead-Goode", "orcid": "0000-0003-2027-8870", "display_name": "Russell, Armistead Goode" } ], "advisors": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "advisor", "display_name": "Cass, Glen Rowan" } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" } ], "option_major": [ "mecheng" ], "doi": "10.7907/rdz0-9a12", "abstract": "This work focuses on the formation, transport and control of atmospheric nitric acid and nitrate aerosol using both theoretical modeling and experimental techniques. A mathematical model was developed that describes the formation and transport of photochemically produced atmospheric gases and nitrate aerosol, using fundamental thermodynamic data to determine the quantity and state of the aerosol nitrate produced. Model predictions compared favorably with the field data available. A sensitivity study of the model indicated that the predicted aerosol nitrate concentrations are highly dependent on temperature. The trajectory model was used to study the fate of nitrogen oxides emissions and the chemical reactions responsible for the formation of atmospheric nitric acid. A majority of the NOx emissions deposit out within 24 hours, primarily as HNO3. Previously it was believed that almost all of the atmospheric nitric acid was produced during daylight hours, however model results indicate that nighttime reactions can produce comparable quantities, especially in the upper portions of the boundary layer more than a hundred meters above ground.
\r\n\r\nAn experimental program was designed and executed to collect a set of data for use in studying nitrate formation, and for use in evaluating the accuracy of air quality models. A large quantity of aerosol nitrate was observed to accumulate overnight near the coast, presumably due to the reaction between HNO3 and sea salt aerosol or soil dust\u2014like material. This aerosol is then transported inland the following afternoon, and can contribute to the high particulate nitrate levels found inland. Data from the experiment were used to test the hypothesis that atmospheric HNO3 and NH3 are in equilibrium with the aerosol phase. Most of the data are consistent with the assumption that an external mixture containing some pure NH4NO3 is present. Additional improvement is obtained if an internally mixed NH+4-NO-3-SO=4 aerosol is assumed to be present.
\r\n\r\nFurther evaluation of the air quality model against the data described above showed that the model accurately predicts the measured concentrations of O3, NO2, total nitrate, HNO3, and NH3. Representative emission control programs were tested using the model, and results indicated that NOx emission control will reduce HNO3(g), aerosol nitrate and PAN concentrations. For the particular trajectories studied, NOx control would also have reduced the peak O3 concentrations. Reducing NH3 emissions will reduce aerosol nitrate formation at the expense of increasing HNO3 concentrations. Controlling organic gas emissions will reduce O3 and PAN. Further research areas suggested by this work also are presented.
" }, { "name": "R\u00f6sgen, Thomas", "degree": "PhD", "year": "1985", "title": "Second Sound Scattering in Superfluid Helium", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-161340", "creators": [ { "name": { "family": "R\u00f6sgen", "given": "Thomas" }, "id": "R\u00f6sgen-Thomas", "display_name": "R\u00f6sgen, Thomas" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/r8ge-j070", "abstract": "Focusing cavities are used to study the scattering of second sound in liquid helium II. The special geometries reduce wall interference effects and allow measurements in very small test volumes.
\r\n\r\nIn a first experiment, a double elliptical cavity is used to focus a second sound wave onto a small wire target. A thin film bolometer measures the side scattered wave component. The agreement with a theoretical estimate is reasonable, although some problems arise from the small measurement volume and associated alignment requirements.
\r\n\r\nA second cavity is based on confocal parabolas, thus enabling the use of large planar sensors. A cylindrical heater produces again a focused second sound wave. Three sensors monitor the transmitted wave component as well as the side scatter in two different directions. The side looking sensors have very high sensitivities due to their large size and resistance. Specially developed cryogenic amplifiers are used to match them to the signal cables.
\r\n\r\nIn one case, a second auxiliary heater is used to set up a strong counterflow in the focal region. The second sound wave then scatters from the induced fluid disturbances.
\r\n\r\nAttempts to observe scattering from quantized vortex lines in the rotating parabolic cavity ultimately did not succeed, although a theoretical estimate seems to indicate a basic feasibility.
" }, { "name": "Smith, Duane A.", "degree": "PhD", "year": "1985", "title": "An Experimental Study of Acoustically Excited, Vortex Driven, Combustion Instability within a Rearward Facing Step Combustor", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-160540", "creators": [ { "name": { "family": "Smith", "given": "Duane A." }, "id": "Smith-Duane-A", "display_name": "Smith, Duane A." } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "chair", "display_name": "Marble, Frank E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/xn67-7h10", "abstract": "An internal feedback mechanism, capable of sustaining combustion instabilities, is investigated inside a small laboratory combustor in which the flame is stabilized behind a rearward facing step. Pressure and optical measurements are employed to define the acoustic field and heat release rate within the combustor, while shadowgraph records are used to visualize the reacting, kinematic flow field.
\r\n\r\nThe acoustic flow field creates an unsteady flow inside the combustor, which produces an unsteady heat addition. When this fluctuating heat release is in the appropriate phase relationship with the pressure oscillation, energy is supplied to the acoustic field, and the strong acoustic oscillations are sustained.
\r\n\r\nAs a result of the strong acoustic oscillations present during combustion instability, the flow surges into the combustor periodically, and large vortices are formed at the acoustic frequency which produce the large velocity fluctuation in the vicinity of the flameholder. The magnitude of the velocity fluctuation, relative to the mean flow speed, determines whether or not the vortex will form. The frequency of the combustion instability appears to be directly proportional to the amplitude of the velocity fluctuation so that the actual magnitude of the velocity fluctuation determines the instability frequency. The dependence of the instability frequency upon the velocity fluctuation creates the possibility of exciting a large range of frequencies.
\r\n\r\nContinued existence of the combustion instability depends upon the mean flow speed, fuel type, and fuel-air ratio.
\r\n" }, { "name": "Smith, Kenneth Scott", "degree": "PhD", "year": "1985", "title": "Stochastic Analysis of the Seismic Response of Secondary Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02012019-085357846", "creators": [ { "name": { "family": "Smith", "given": "Kenneth Scott" }, "id": "Smith-Kenneth-Scott", "display_name": "Smith, Kenneth Scott" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Lorden", "given": "Gary A." }, "id": "Lorden-G-A", "role": "member", "display_name": "Lorden, Gary A." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/w4cj-w767", "abstract": "This thesis is concerned with the earthquake response of light equipment in structures. The motion of the ground during an earthquake is represented as a stochastic process in order to reflect uncertainty in the prediction of such motion. A number of different stochastic earthquake models are considered, and analytical methods are described for these models.
\r\n\r\nThe response of equipment in a structure to stochastic ground motion is derived, in the case of a single-degree-of-freedom secondary system (equipment) attached to a single-degree-of-freedom structure. The distribution of the envelope of the secondary system displacement is obtained for general transient ground motion. Closed form expressions are computed for the transient response to stationary ground motion.
\r\n\r\nThe effect of the interaction of equipment with the structure is described by the introduction of an equivalent non-interacting system. However, this method applies only to classically damped systems.
\r\n\r\nThe results are applied in a simple way to the problem of the computation of floor spectra. It is found that the ground spectrum is amplified in a simple way, except near resonance, where special considerations must be addressed.
" }, { "name": "Tong, Peter Ping Tak", "degree": "PhD", "year": "1985", "title": "Millimeter-Wave Integrated-Circuit Antenna Arrays", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08172005-102232", "creators": [ { "name": { "family": "Tong", "given": "Peter Ping Tak" }, "id": "Tong-Peter-Ping-Tak", "display_name": "Tong, Peter Ping Tak" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "chair", "display_name": "Rutledge, David B." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ddxq-rj80", "abstract": "This thesis presents three different types of millimeter-wave integrated-circuit antenna array. They are a linearly polarized antenna array that can form polarization and intensity line images, a circularly polarized spiral antenna and a two-dimensional tracking antenna array. They are all integrated-circuit antennas with detectors on quartz substrates using quasi-optical systems to collect and focus the waves.
\r\n" }, { "name": "Vahala, Kerry John", "degree": "PhD", "year": "1985", "title": "Dynamic and Spectral Features of Semiconductor Lasers", "advisor": "Yariv, Amnon; Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02082005-114440", "creators": [ { "name": { "family": "Vahala", "given": "Kerry John" }, "id": "Vahala-Kerry-John", "orcid": "0000-0003-1783-1380", "display_name": "Vahala, Kerry John" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/H7JA-K512", "abstract": "This thesis is divided into two main subject areas: the fluctuation properties of state of the art semiconductor lasers and the improvement of modulation and fluctuation properties in these devices through a technique called detuned loading.
\r\n\r\nThe discussion of fluctuations in lasers is a topic as old as the device itself, and much of the pioneering work in this field was done in the sixties. Surprisingly, however, several new chapters in this field are being written, because of certain pecularities only recently observed in semiconductor lasers. Chapters 2 and 3 of this thesis will consider these pecularities, which, as it turns out, are quite important in many potential system applications of these devices.
\r\n\r\nOne of the driving forces behind the development of semiconductor lasers has been their application as sources and local oscillators in optical communication systems. In general, such applications require lasers which have low phase and intensity noise, and which can be modulated at high data rates. As is often the case, these requirements are to a certain extent mutually exclusive. Chapter 4 introduces a technique which is an exception to this rule. It relies upon the semiconductor laser physics which produces the fluctuation abnormalities discussed in Chapters 2 and 3. The technique can be used to improve modulation speed while simultaneously reducing noise as compared to the conventional device.
" }, { "name": "Wakugawa, Jason Masao", "degree": "PhD", "year": "1985", "title": "On the Existence and Uniqueness of the Solution to the Small-Scale Nonlinear Anti-Plane Shear Crack Problem in Finite Elastostatics", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03212008-094413", "creators": [ { "name": { "family": "Wakugawa", "given": "Jason Masao" }, "id": "Wakugawa-Jason-Masao", "display_name": "Wakugawa, Jason Masao" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Rosakis", "given": "Ares J." }, "id": "Rosakis-A-J", "orcid": "0000-0003-0559-0794", "role": "member", "display_name": "Rosakis, Ares J." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/dfcw-j110", "abstract": "This thesis addresses the issue of existence and uniqueness of the solution to the small-scale nonlinear anti-plane shear crack problem in finite elastostatics. The hodograph transformation, commonly used in the theory of compressible fluid flows, plays an essential role. Existence is established by exhibiting an exact closed form solution, constructed via the hodograph transformation. Uniqueness is established by first proving the uniqueness of the solution to a related boundary-value problem, which is linear by virtue of the hodograph transformation, and then examining the implications of this result on the original problem. The possibility of making some of the conditions imposed on the solution to the small-scale nonlinear crack problem less restrictive is then investigated. This leads to several further results, including estimates of the nonvanishing shear stress component of the stress tensor along the crack faces.
" }, { "name": "Whelan, Daniel Steven", "degree": "PhD", "year": "1985", "title": "ANIMAC: A Multiprocessor Architecture for Real-Time Computer Animation", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-092532", "creators": [ { "name": { "family": "Whelan", "given": "Daniel Steven" }, "id": "Whelan-Daniel-Steven", "display_name": "Whelan, Daniel Steven" } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Blinn", "given": "Jim" }, "id": "Blinn-J", "role": "member", "display_name": "Blinn, Jim" }, { "name": { "family": "Fox", "given": "Geoffrey C." }, "id": "Fox-G-C", "role": "member", "display_name": "Fox, Geoffrey C." } ], "option_major": [ "compsci" ], "doi": "10.7907/0qnw-g372", "abstract": "Advances in integrated circuit technology have been largely responsible for the growth of the computer graphics industry. This technology promises additional growth through the remainder of the century. This dissertation addresses how this future technology can be harnessed and used to construct very high performance real-time computer graphics systems.
\r\n\r\nThis thesis proposes a new architecture for real-time animation engines. The ANIMAC architecture achieves high performance by utilizing a two-dimensional array of processors that determine visible surfaces in parallel. An array of sixteen processors with only nearest neighbor interprocessor communications can produce real-time shadowed images of scenes containing 100, 000 triangles.
\r\n\r\nThe ANIMAC architecture is based upon analysis and simulations of various parallelization techniques. These simulations suggest that the viewing space be spatially subdivided and that each processor produce a visible surface image for several viewing space subvolumes. Simple assignments of viewing space subvolumes to processors are shown to offer high parallel efficiencies.
\r\n\r\nSimulations of parallel algorithms were driven with data derived from real scenes since analysis of scene composition suggested that using simplistic models of scene composition might lead to incorrect results.
\r\n\r\nThe ANIMAC architecture required the development of a shadowing algorithm which was tailored to its parallel environment. This algorithm separates shadowing into local and foreign effects. Its implementation allows individual processors to compute shadowing effects for their image regions utilizing only very local information.
\r\n\r\nThe design of the ANIMAC processors makes extensive use of new VLSI architectures. A formerly proposed processor per object architecture is used to determine visible surfaces while new processor per object and processor per pixel architectures are used to determine shadowing effects.
\r\n\r\nIt is estimated that the ANIMAC architecture can be realized in the early 1990's. Realizing this architecture will require considerable amounts of hardware and capital yet its cost will not be out of line when compared with today's real-time computer graphics systems.
" }, { "name": "Whiting, Douglas Lee", "degree": "PhD", "year": "1985", "title": "Bit-Serial Reed-Solomon Decoders in VLSI", "advisor": "McEliece, Robert J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252008-090414", "creators": [ { "name": { "family": "Whiting", "given": "Douglas Lee" }, "id": "Whiting-Douglas-Lee", "display_name": "Whiting, Douglas Lee" } ], "advisors": [ { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "advisor", "display_name": "McEliece, Robert J." } ], "committee": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "chair", "display_name": "Seitz, Charles L." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Abu-Mostafa", "given": "Yaser S." }, "id": "Abu-Mostafa-Y-S", "role": "member", "display_name": "Abu-Mostafa, Yaser S." }, { "name": { "family": "Berlekamp", "given": "Elwyn Ralph" }, "id": "Berlekamp-Elwyn-Ralph", "role": "member", "display_name": "Berlekamp, Elwyn Ralph" }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." } ], "option_major": [ "compsci" ], "doi": "10.7907/bjd1-9j44", "abstract": "Reed-Solomon codes are known to provide excellent error-correcting capabilities on many types of communication channels. Although efficient decoding algorithms have been known for over fifteen years, currently available decoder systems are large both in size and in power consumption. Such systems typically use a single, very fast, fully parallel finite-field multiplier in a sequential architecture. Thus, more processing time is required as the code redundancy increases. By using many arithmetic units on a single chip, it is possible to exploit the concurrency inherent in the decoding algorithms to attain performance levels previously possible only with large ECL systems.
\r\n\r\nAn investigation into the structure of binary extension fields reveals that the common arithmetic operations used in decoding can be implemented quite efficiently in a bit-serial fashion, using any of several bases over GF(2). Berlekamp's dual-basis multiplier is generalized to the product of two arbitrary field elements, and a necessary and sufficient condition is then derived for the existence of a self-dual basis. Efficient methods for bit-serial multiplicative inversion are also discussed, greatly reducing the complexity traditionally associated with this operation.
\r\n\r\nUsing these bit-serial techniques, several architectures for implementing each phase of the known Reed-Solomon decoding algorithms are presented and compared. Simple methods are presented to allow power-sum syndrome decoders to handle codes with a variety of block lengths and redundancies. Each approach comes within a factor of log n (where n is the block length of the code) of the recently derived asymptotic lower bounds for both time and area. Results from a student project to lay out a prototype decoder chip using the Berlekamp-Massey algorithm are also discussed. By utilizing the parallelism inherent in the key equation solution, these architectures can decode received words at a speed independent of the redundancy of the code.
" }, { "name": "Whitney, Telle Elizabeth", "degree": "PhD", "year": "1985", "title": "Hierarchical Composition of VLSI Circuits", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242008-112135", "creators": [ { "name": { "family": "Whitney", "given": "Telle Elizabeth" }, "id": "Whitney-Telle-Elizabeth", "orcid": "0000-0002-4580-2395", "display_name": "Whitney, Telle Elizabeth" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Barr", "given": "Alan H." }, "id": "Barr-A-H", "role": "member", "display_name": "Barr, Alan H." }, { "name": { "family": "Lyon", "given": "Richard F." }, "id": "Lyon-Richard-F", "role": "member", "display_name": "Lyon, Richard F." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." } ], "option_major": [ "compsci" ], "doi": "10.7907/ykeb-r680", "abstract": "A transistor level representation for VLSI circuits is presented. This representation is simple but general, technology independent, hierarchical, and maintains connectivity, circuit schematic information, and the information for mask geometry.
\r\n\r\nA transistor level cell is represented as the interconnection of devices along with their types, sizes and placement, and the cell's typed ports. Connection is represented explicitly by shared connection points. The ports describe the interface between this cell and other cells. This representation, together with a set of synthesis and analysis rules, enforces the description of strictly legal designs. The synthesis rules ensure that each structure is correct by construction. The analysis rules check for geometrical design rule violations which cannot, by their nature, be enforced by construction.
\r\n\r\nA file of technology dependent information indicates how to implement each transistor type, interconnect type and connection point type, as well as how structure types may interact.
\r\n\r\nCells described in this representation may be composed hierarchically to form larger cells. Given a valid composition, the topology, geometry and connectivity of the composite structure is guaranteed to be legal.
\r\n\r\nA working system supporting this hierarchical representation is also described. This system currently supports design rules for nMOS and cMOS/bulk, and has produced chip descriptions that have been both fabricated and tested.
" }, { "name": "Wie, Chu Ryang", "degree": "PhD", "year": "1985", "title": "Effects Produced in GaAs by MeV Ion Bombardment", "advisor": "Tombrello, Thomas A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10292015-135146919", "creators": [ { "name": { "family": "Wie", "given": "Chu Ryang" }, "id": "Wie-Chu-Ryang", "display_name": "Wie, Chu Ryang" } ], "advisors": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "advisor", "display_name": "Tombrello, Thomas A." } ], "committee": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "chair", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/m4f7-4x30", "abstract": "Presented in the first part of this thesis is work performed on the ionizing energy beam induced adhesion enhancement of thin (~ 500 Angstrom) Au films on GaAs substrates. The ionizing beam, employed in the present thesis, is the MeV ions (i.e., 16O, 19F, and 35Cl), with energies between 1 and 20 MeV. Using the \"Scratch\" test for adhesion measurement, and ESCA for chemical analysis of the film-substrate interface, the native oxide layer at the interface is shown to play an important role in the adhesion enhancement by the ionizing radiation. A model is discussed which explains the experimental data on the the dependence of adhesion enhancement on the energy which was deposited into electronic processes at the interface. The ESCA data indicate that the chemical bonds (or compounds), which are responsible for the increase in the thin film adherence, are hydroxides rather than oxides.
\r\n\r\nIn the second part of the thesis we present a research performed on the radiation damage in GaAs crystals produced by MeV ions. Lattice parameter dilatation in the surface layers of the GaAs crystals becomes saturated after a high dose bombardment at room temperature. The strain produced by nuclear collisions is shown to relax partially due to electronic excitation (with a functional dependence on the nuclear and electronic stopping power of bombarding ions). Data on the GaAs and GaP crystals suggest that low temperature recovery stage defects produce major crystal distortion. The x-ray rocking curve technique with a dynamical diffraction theory analysis provides the depth distribution of the strain and damage in the MeV ion bombarded crystals.
" }, { "name": "Abushagur, Mustafa A. G.", "degree": "PhD", "year": "1984", "title": "Scattering of Light from Large Cylinders", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-102554", "creators": [ { "name": { "family": "Abushagur", "given": "Mustafa A. G." }, "id": "Abushagur-Mustafa-A-G", "display_name": "Abushagur, Mustafa A. G." } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "Cowan", "given": "Eugene W." }, "id": "Cowan-E-W", "role": "chair", "display_name": "Cowan, Eugene W." }, { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "member", "display_name": "George, Nicholas A." }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/akkw-r889", "abstract": "Scattering of a plane electromagnetic wave from circular conducting and dielectric cylinders is analyzed. Both polarizations of the incident electric field, parallel and normal to the axis of the cylinder, are considered. The study of the rigorous solutions gives an insightful understanding of the scattered field and its dependence on the material of the cylinder, the polarizations of the incident field, and the three dimensionality of the object which usually are not considered in Fourier optics. It is shown that a combination of Fourier optics and ray theory can give good approximations for the scattered field from both conducting and dielectric cylinders. It is shown that the scattered pattern from a conducting cylinder consists of a main lobe and a number of side lobes. The spacing between the side lobes decreases as ka increases, where k is the wave number of the incident field and a the radius of the cylinder. It is found that for a certain conducting cylinder the side lobes terminate in a smaller scattering angle when the incident field is polarized parallel to the axis than when the incident field is polarized normal to the axis of the cylinder. The surface current density in the shadow region is found to be larger for the normal polarization case than for the parallel polarization case. The pattern of the scattered field from a dielectric cylinder has fringes all around the cylinder. The contrast of the fringes for the dielectric cylinder is much larger when the polarization of the incident field is parallel to the axis than that when the polarization is normal to the axis. The backscattered field of the dielectric cylinder has a peak which depends in its position on the refractive-index of the cylinder for the parallel polarization case. The fine structure of the scattering by a dielectric cylinder is studied. It is shown that the dielectric cylinder has resonant frequencies which depend on the radius and refractive-index of the cylinder. It is found that there are significant differences in the shape of the scattered pattern depending on whether the cylinder is at-resonance or at off-resonance. Experimental investigations are carried out to verify the theory derived in this study and it is found that both theory and experiments are in good agreement.
" }, { "name": "Alam, Md. Khairul", "degree": "PhD", "year": "1984", "title": "Nucleation and Condensational Growth of Aerosols: Application to Silicon Production", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092005-142825", "creators": [ { "name": { "family": "Alam", "given": "Md. Khairul" }, "id": "Alam-Md-Khairul", "display_name": "Alam, Md. Khairul" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "chair", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "mecheng" ], "doi": "10.7907/t1x1-p304", "abstract": "A theoretical analysis of aerosol nucleation and condensational growth is developed. A growing aerosol depletes the surrounding vapor, leading to the development of a spherically symmetric radial distribution of monomer partial pressure. A symmetric radial temperature profile is simultaneously developed due to release of latent heat of condensation. These local perturbations are analyzed to determine the total effect on the nucleation rate. The analysis forms the basis for building an experimental reactor for production of large particles of silicon for semiconductors and photovoltaic cells. The large size of the silicon particles facilitates separation and processing of the product.
" }, { "name": "Bardet, Jean-Pierre", "degree": "PhD", "year": "1984", "title": "Application of Plasticity Theory to Soil Behavior: A New Sand Model", "advisor": "Scott, Ronald F.; Hughes, Edward Wesley", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-143343", "creators": [ { "name": { "family": "Bardet", "given": "Jean-Pierre" }, "id": "Bardet-Jean-Pierre", "orcid": "0000-0002-9718-3426", "display_name": "Bardet, Jean-Pierre" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." }, { "name": { "family": "Hughes", "given": "Edward Wesley" }, "id": "Hughes-Edward-Wesley", "role": "co-advisor", "display_name": "Hughes, Edward Wesley" } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Hughes", "given": "Edward Wesley" }, "id": "Hughes-Edward-Wesley", "role": "member", "display_name": "Hughes, Edward Wesley" } ], "option_major": [ "civileng" ], "doi": "10.7907/Z23J-9E80", "abstract": "The representation of rheological soil behavior by constitutive equations is a new branch of soil mechanics which has been expanding for 30 years. Based on continuum mechanics, numerical methods (finite elements) and experimental techniques, this new discipline allows practicing engineers to solve complex geotechnical problems. Although all soils are constituted of discrete mineral particles, forces and displacements within them are represented by continuous stresses and strains. Most stress-strain relationships, which describe the soil behavior, are derived from plasticity theory. Originated for metals, the conventional plasticity is presented and illustrated simultaneously with a metal and a soil model. Each plasticity concept may be criticized when applied to soil. A recent theory, called \"bounding surface plasticity,\" generalizes the conventional plasticity and describes more accurately the cyclic responses of metals and clays. This new theory is first presented and linked with the conventional plasticity, then applied to a new material, sand. Step by step a new sand model is constructed, mainly from data analysis with an interactive computer code. In its present development, only monotonic loadings are investigated. In order to verify the model ability to describe sand responses, isotropic, drained and undrained tests on the dense Sacramento River sand are simulated numerically and compared with real test results and predictions with another model. Finally the new constitutive equation, which was formulated in the p-q space for axisymmetric loadings, is generalized in the six-dimensional stress state with the assumption of isotropy and a particular Lode's angle contribution. This new model is ready to be used in finite element codes to represent a sand behavior.
" }, { "name": "Bartur, Meir", "degree": "PhD", "year": "1984", "title": "Utilization of Silicides for VLSI-Contacts with Aluminum and Thermal Oxidation", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032005-130746", "creators": [ { "name": { "family": "Bartur", "given": "Meir" }, "id": "Bartur-Meir", "display_name": "Bartur, Meir" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Lau", "given": "Silvanus S." }, "id": "Lau-Silvanus-S", "role": "chair", "display_name": "Lau, Silvanus S." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/V36Y-BW59", "abstract": "The potential role of silicides in VLSI (very large scale integration) Si technology is described. A survey of trends and requirements exposes two difficult technological issues as the device dimensions shrink: contacts to the individual devices and interconnections between devices or functional blocks on the Si chip. For both, silicides play an important role.
\r\n\r\nThe contact between the Si that contains the device and the top Al layer (Al is the preferred metal for metallization) has to be thermally stable, reproducible, reliable, and have low contact resistivity. After a brief survey of the available diffusion barriers designed to suppress the Al interaction with Si, I concentrate on the sacrificial barrier structure. The generalized layered structure approach, utilizing Si/silicide/sacrificial barrier/Al, is analyzed with Ti, V, or Cr as the sacrificial barrier material. A study of Cr as a barrier between Al and NiSi, Pd2Si, or PtSi reveals that impurities in the as-deposited Cr film determine the barrier properties. The concept of the sacrificial barrier is critically reexamined in the light of these results. A study of a thin W layer, which is probably a stuffed barrier, as a barrier between NiSi and Al is reported. An outlook to future trends and approaches concludes this part of the thesis.
\r\n\r\nA major attribute of silicides as interconnection material is their capability to form SiO2 upon thermal oxidation. A study of the oxidation characteristics of near-noble metal silicides (Co, Ni, Pd, and Pt) is presented in the second part of this thesis. The oxidation kinetics and the mass transport through the silicide during oxidation are explored. The role of mass transport in the oxidation kinetics is reviewed in the light of all the reported experimental results. The effect of oxidation on: a) the epitaxial registration of a silicide on <111> Si substrate (NiSi2, CoSi2, and Pd2Si), and b) the electrical resistivity (NiSi2 and CoSi2), is explored. Properties of SiO2 grown on different (Ti, Co, Ni, Pd and Pt) silicides are found to be the same as for SiO2 grown on Si substrates, except for the lower (~1.5 x 106 V/cm) dielectric breakdown. A preliminary implementation of interconnections with NiSi2 demonstrates the applicabilty of this silicide for VLSI. Finally, a novel interconnection scheme is advanced as a possible method to produce self-confined metal interconnection lines.
\r\n" }, { "name": "Baxter, David Verge", "degree": "PhD", "year": "1984", "title": "EXAFS Studies of La-Ga Metallic Glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072005-153348", "creators": [ { "name": { "family": "Baxter", "given": "David Verge" }, "id": "Baxter-David-Verge", "orcid": "0000-0003-2812-0904", "display_name": "Baxter, David Verge" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Baldeschwieler", "given": "John D." }, "id": "Baldeschwieler-J-D", "role": "member", "display_name": "Baldeschwieler, John D." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/NHED-5T47", "abstract": "Extended X-ray Absorption Fine Structure ( EXAFS ) measurements have been performed on the Ga edge of several La-Ga metallic glasses, using an in-lab spectrometer. The results obtained are compared with earlier experiments on the same materials where X-ray diffraction and isomorphous substitution were used to determine partial pair correlation functions. This is, therefore, a rigorous test of the EXAFS technique when applied to strongly disordered systems, such as metallic glasses. It is found that the glass La80Ga20 has a comparatively simple local Ga environment and that the EXAFS for this glass can be described very well with a single asymmetric shell of La atoms surrounding the Ga. As the Ga concentration is increased, however, it is found that the local Ga environment becomes more complicated. Traditional methods of EXAFS analysis, based on nonlinear least squares curve fitting, are then unable to distinguish between several different possible local Ga environments. Finally a new, essentially non-parametric, method of analyzing EXAFS data is discussed and tests are conducted to demonstrate the circumstances under which this new method could prove advantageous over the more traditional methods.
\r\n" }, { "name": "Cimbala, John Michael", "degree": "PhD", "year": "1984", "title": "Large Structure in the Far Wakes of Two-Dimensional Bluff Bodies", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132005-131650", "creators": [ { "name": { "family": "Cimbala", "given": "John Michael" }, "id": "Cimbala-John-Michael", "orcid": "0000-0003-3210-6347", "display_name": "Cimbala, John Michael" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KZ05-YC02", "abstract": "Smoke-wire flow visualization and hot-wire anemometry have been used to study near and far wakes of two-dimensional bluff bodies. For the case of a circular cylinder at 70 < Re < 2000, a very rapid (exponential) decay of velocity fluctuations at the Karman vortex street frequency is observed. Beyond this region of decay, larger-scale (lower wave-number) structure can be seen. In the far wake (beyond one hundred diameters) a broad band of frequencies is selectively amplified and then damped, the center of the band shifting to lower frequencies as downstream distance is increased.
\r\n\r\nThe far-wake structure does not depend directly on the scale or frequency of the original Karman vortices; the growth of this structure is due to hydro-dynamic instability of the developing mean wake profile; it is not caused by amalgamation of the Karman vortices. Under certain conditions amalgamation can take place, but is purely incidental, and is not the driving mechanism responsible for the growth of larger-scale structure. Similar large structure is observed downstream of porous flat plates (Re \u2248 6000), which do not initially shed Karman-type vortices into the wake.
\r\n\r\nHot-wire measurements show that two-dimensional locally-parallel inviscid linear stability theory is adequate to explain the growth of downstream structure. Namely, measured prominent frequencies in the cylinder wake are in close agreement with those predicted by the theory, when streamwise growth of wake width is taken into account.
\r\n\r\nFinally, three-dimensionality in the far wake of a circular cylinder is briefly discussed.
" }, { "name": "Cornet, Jean-Luc", "degree": "PhD", "year": "1984", "title": "Evaluation of the Unsteady Effects for a Class of Wind Turbines", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082005-093825", "creators": [ { "name": { "family": "Cornet", "given": "Jean-Luc" }, "id": "Cornet-Jean-Luc", "display_name": "Cornet, Jean-Luc" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Yates", "given": "George T." }, "id": "Yates-George-T", "role": "member", "display_name": "Yates, George T." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "eng" ], "doi": "10.7907/JVZE-1485", "abstract": "An investigation of a class of vertical axis wind turbines is carried out with the unsteady effects due to the rotating blade motion fully taken into account. The work is composed of two parts.
\r\n\r\nIn part one, a hydromechanical theory is developed which proceeds from the point of view of unsteady airfoil theory. A rotor comprised of a single blade is used and a two-dimensional analysis is applied to a cross section of the rotor in the limiting mode of operation wherein U \u00ab \u03a9R. Use of linearized theory and of the acceleration potential allows the problem to be expressed in terms of a Riemann-Hilbert boundary value problem. The method of characteristics is used to solve for the remaining unknown function. A uniformly valid first order solution is obtained in closed form after some approximation based on neglecting the variations in the curvature of the path. Explicit expressions of the instantaneous forces and moments acting on the blade are given and the total energy lost by the fluid and the total power input to the turbine are determined.
\r\n\r\nIn part two, the lift acting on a wing crossing a vortex sheet is evaluated by application of a reciprocity theorem in reverse flow. This theorem follows from Green's integral theorem and relates the circulation around a blade having impulsively crossed a vortex wake to the lift acting on a blade continuously crossing a vortex wake. A solution is obtained which indicates that the lift is composed of two parts having different rates of growth, each depending on the apparent flow velocity before and after the crossing.
" }, { "name": "Eriksen, K. Jeffrey", "degree": "PhD", "year": "1984", "title": "Biophysical Source Modeling of Some Exogenous and Endogenous Components of the Human Event-Related Potential", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072005-143659", "creators": [ { "name": { "family": "Eriksen", "given": "K. Jeffrey" }, "id": "Eriksen-K-Jeffrey", "orcid": "0000-0002-0778-9177", "display_name": "Eriksen, K. Jeffrey" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "chair", "display_name": "Fender, Derek H." }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Ary", "given": "James P." }, "id": "Ary-James-P", "role": "member", "display_name": "Ary, James P." }, { "name": { "family": "Hamilton", "given": "Charles R." }, "id": "Hamilton-Charles-R", "role": "member", "display_name": "Hamilton, Charles R." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" } ], "option_major": [ "bioinfo", "eng" ], "doi": "10.7907/SPSG-FX90", "abstract": "Methods of dipole localization were applied to human scalp-recorded electrical activity associated with a simple auditory cognitive discrimination task.
\r\n\r\nHuman neuroanatomy and neurophysiology were reviewed from a biophysical standpoint in order to describe the probable neurogenesis of electrical activity in the brain and on the surface of the head. Topographic electroencephalography (EEG) analysis and source localization methods were historically reviewed in detail, followed by a brief review of the history of non-invasive evoked potential (EP) and magnetic field measurements of human central nervous system activity.
\r\n\r\nFour well known simple cognitive tasks were considered that were known to elicit non-obligatory brain responses, and the odd-ball task chosen. Three subjects listened to a series of two tones, one frequent and one rare, and counted the rare tones. During task performance, 40 to 46 channels of EEG activity were recorded from their scalps.
\r\n\r\nFrom the EEG data, average evoked potentials (aEP) were calculated for the frequent and rare conditions. From these a difference response was calculated. All three of these EPs were plotted as equipotential maps over a schematic of a head for topographic display and the major distribution features discussed. These aEPs and maps matched those previously reported in the literature.
\r\n\r\nFrom estimates of the spatial electrical power over the head, four peak components were selected for analysis by equivalent source modeling (ESM). These were designated the FP40, FP100, FP200, and FP350, where FP stands for field power. ESM demonstrated that one centrally located point dipole or two bilaterally symmetric dipoles could model the empirical data quite well. These results were discussed in relation to other topographic studies, as well as studies of intracranial recordings, lesions, and animal models. The source locations found were consistent with auditory cortical locations for the obligatory sensory peaks (FP40, FP100, FP200) and with brainstem locations as the source of the FP350 cognitive event-related peak.
" }, { "name": "Greene, Glenn Joel", "degree": "PhD", "year": "1984", "title": "ICRF Antenna Coupling and Wave Propagation in a Tokamak Plasma", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-144119", "creators": [ { "name": { "family": "Greene", "given": "Glenn Joel" }, "id": "Greene-Glenn-Joel", "display_name": "Greene, Glenn Joel" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "chair", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "member", "display_name": "Phillips, Thomas G." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ppan-gp26", "abstract": "A variety of experiments are reported pertaining to the excitation, propagation, and damping of waves in the ion cyclotron range of frequencies (ICRF) in the Caltech Research Tokamak.
\r\n\r\nComplex impedance studies on five different RF antennas addressed the nature of the anomalous density-dependent background loading observed previously in several laboratories. A model was proposed which successfully explained many of the observed impedance characteristics solely in terms of particle collection and rectification through the plasma sheath surrounding the antenna electrode. Peaks were observed on the input resistance of the shielded antennas and were coincident with toroidal eigenmode production; their magnitude was explained by a simple coupling theory.
\r\n\r\nThe toroidal eigenmodes were studied in detail with magnetic field probes. The mode dispersion curves in density-frequency space were mapped out and the results compared with various theoretical models. A surprising result was that all of the antennas, both magnetic and electric in nature, coupled to the eigenmodes with comparable efficiency with respect to the antenna excitation current. Wave damping was investigated and found to be considerably higher than predicted by a variety of physical mechanisms. A numerical model of the wave equations permitting an arbitrary radial density profile was developed, and a possible mechanism for enhanced cyclotron damping due to density perturbations was proposed. Toroidal modes were identified using phase measurements between pairs of magnetic probes; they were found to have m = 1 poloidal character and low integral toroidal mode numbers, in accordance with theoretical predictions.
\r\n\r\nA new approach to the study of ICRF wave propagation was investigated: wave-packets were launched and their propagation was followed around the tokamak using magnetic probes. This technique avoided the dominant effect of the eigenmode resonances because it observed propagation on a time scale short compared to the formation time for the modes. The transit time of the packets around the machine yielded the toroidal group velocity, and the results of the experiments were compared with several theoretical models. The inclusion of a vacuum layer at the plasma edge was useful in explaining some of the observations.
\r\n\r\nFinally, a plasma-compatible Rogowski current probe was developed and used to observe, for the first time, RF particle current in a tokamak plasma. The diagnostic permitted investigation of the spatial form of the RF current driven in the edge plasma by the electric field antennas. The results dramatically showed that the current from these antennas flows largely along the toroidal field lines. This highly localized current distribution suggests a mechanism for the good coupling to the eigenmode fields observed with these antennas.
" }, { "name": "Haas, Jean-Fran\u00e7ois Luc", "degree": "PhD", "year": "1984", "title": "Interaction of Weak Shock Waves and Discrete Gas Inhomogeneities", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232005-110318", "creators": [ { "name": { "family": "Haas", "given": "Jean-Fran\u00e7ois Luc" }, "id": "Haas-Jean-Fran\u00e7ois-Luc", "orcid": "0000-0002-7730-5107", "display_name": "Haas, Jean-Fran\u00e7ois Luc" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T37C-X215", "abstract": "An experimental investigation of the interaction of shock waves with discrete gas inhomogeneities is conducted in the GALCIT 15 cm diameter shock tube. The gas volumes are cylindrical refraction cells of 5 cm diameter with a 0.5 \u00b5m thick membrane separating the test gas (helium or Freon 22) from the ambient air and large spherical soap bubbles containing the same gases. The incident wave Mach numbers are nominally 1.09 and 1.22. The wave pattern and the deformation of the gas volumes are documented by shadowgraphs. The transmitted and diffracted wave pressure profiles are recorded by pressure transducers at various distances behind the cylinders. The basic phenomena of acoustic wave refraction, reflection and diffraction by cylindrical acoustic lenses, with indices of refraction appropriate to the gases used in the experiments, are illustrated with computer-generated ray and wave-front diagrams.
\r\n\r\nIn the case of a Freon 22-filled cylinder, the wave diffracted externally around the body precedes the wave transmitted from the interior which goes through a focus just behind the cylinder, while in the case of the helium-filled cylinder the expanding transmitted wave runs ahead of the diffracted wave. Both sets of waves merge a few cylinder diameters downstream. The wave patterns inside the cylinder, showing initially the refracted waves and later the same waves reflected internally, present some interesting phenomena.
\r\n\r\nThe mechanisms by which the gas volumes are transformed into vertical structures by the shock motion are observed. The unique effect of shock acceleration and Rayleigh-Taylor instability on the spherical volume of helium leads to the formation of a strong vortex ring which rapidly separates from the main volume of helium. Measurements of the wave and gas-interface velocities are compared to values calculated for one-dimensional interactions and for a simple model of shock-induced Taylor instability. The behavior of thin liquid membranes accelerated by shocks under varying conditions is documented by high speed photography.
\r\n\r\nIn a related experiment, shock waves of Mach number between 1.005 and 1.36 interact with a dense random array of 2 mm diameter helium filled soap bubbles. Experimental results (based on shadowgraphs and pressure measurements) show that very weak shock waves (Ms \u2264 1.01) are strongly scattered by the array, which is left undisturbed by the shock, and that stronger shock waves, only locally disturbed by each bubble, maintain undisturbed pressure profiles because of nonlinear effects, while the array undergoes shock-induced mixing. A simple criterion for multiple scattering shows that the combined effect of many bubbles is necessary in order to produce important modifications on the shock wave pressure profile.
" }, { "name": "Ho, Kuo Ting", "degree": "PhD", "year": "1984", "title": "Evolution of Nitrogen Impurities in Metal-Silicon Binary Couples and their Effect on Silicide Formation", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072005-080724", "creators": [ { "name": { "family": "Ho", "given": "Kuo Ting" }, "id": "Ho-Kuo-Ting", "display_name": "Ho, Kuo Ting" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Barnes", "given": "Charles A." }, "id": "Barnes-C-A", "role": "chair", "display_name": "Barnes, Charles A." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/tz19-ww79", "abstract": "The possible ways in which nitrogen may be present in and interact with metal silicides are outlined. It is shown that, although contaminant nitrogen can be easily eliminated in deposition systems and processing ambients, understanding the role of nitrogen in metals and metal silicides may be important for various nitridation processes used for VLSI fabrication.
\r\n\r\nNitrogen isotope 15N is controllably introduced into either the metal or silicon in a metal-silicon binary couple. Silicide formation is induced by vacuum annealing. After various thermal treatments, 15N is profiled by the 15N(p,\u03b1)12C nuclear reaction. A detailed description of this technique is given.
\r\n\r\nThe metals investigated are Pd, Ni, Co, Pt, Ta, Mo and Ti. Metal silicides are grouped into three categories according to the moving species during silicide formation: metal, silicon or both. The interpretation of nitrogen evolution during silicide formation is based on the identity of the moving species. A wide variety of nitrogen redistribution patterns (segregation, incorporation, accumulation, dilution and fast diffusion) are observed in different samples, depending on parameters such as nitrogen diffusivity and solubility in its host matrix, and nitrogen bond strength to the silicide forming species.
\r\n\r\nThe presence of nitrogen sometimes will slow down the silicide growth rate. The degree of slowing down generally depends on the amount of nitrogen incorporated. In case of refractory metal, a large concentration up to 25 at% of oxygen is found to be incorporated during metal film deposition. The redistribution of oxygen during annealing is investigated using the 16O(d,\u03b1)14N nuclear reaction.
\r\n\r\nTwo additional studies on different subjects are reported. The first one investigates the dry and wet oxidation behavior of Ti and Hf nitrides. A parabolic oxidation rate is found in all cases except the wet oxidation of HfN. The other study extends the work on dopant enhanced epitaxial regrowth of Si to three substrate orientations. It is found that the enhancement factor is the same, independent of the substrate orientation. An improved crystalline quality is observed for epitaxial Si regrown on an <111> substrate.
\r\n" }, { "name": "Ho, Tai-Ping", "degree": "PhD", "year": "1984", "title": "The Dialogue Designing Dialogue System", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01022007-104438", "creators": [ { "name": { "family": "Ho", "given": "Tai-Ping" }, "id": "Ho-Tai-Ping", "display_name": "Ho, Tai-Ping" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "chair", "display_name": "Thompson, Frederick B." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" }, { "name": { "family": "Tschoegl", "given": "Nicholas W." }, "id": "Tschoegl-N-W", "role": "member", "display_name": "Tschoegl, Nicholas W." }, { "name": { "family": "Thompson", "given": "Bozena H." }, "id": "Thompson-B-H", "role": "member", "display_name": "Thompson, Bozena H." } ], "option_major": [ "compsci" ], "doi": "10.7907/5v76-gn68", "abstract": "This thesis presents an interactive system, the Dialogue Designing Dialogue System, that integrates natural language programming of user dialogues with a natural language system, the ASK system. This interactive system satisfies the basic criteria of a general programming language.
\r\n\r\nThe system presented in this thesis may be referred to as a \"meta-dialogue\" system. Using this meta-dialogue, the user implements domain specific dialogues which he and others can then use, providing highly succinct and efficient interfaces for interaction with the computer.
\r\n\r\nThe system combines the use of a syntax-directed and a semantic-directed system, which gives the user flexibility in specifying additional capabilities, and thus in turn gives the system itself a much broader domain of application. Further, the system integrates natural language programming, dialogue directed user interface, underlying data base, and text handling capabilities, so that it does not require users to have programming background in order to establish an application system for themselves.
" }, { "name": "Houseworth, James Evan", "degree": "PhD", "year": "1984", "title": "Longitudinal Dispersion in Nonuniform, Isotropic Porous Media", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122007-131711", "creators": [ { "name": { "family": "Houseworth", "given": "James Evan" }, "id": "Houseworth-James-Evan", "display_name": "Houseworth, James Evan" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "chair", "display_name": "List, E. John" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Herbolzheimer", "given": "Eric" }, "id": "Herbolzheimer-E", "role": "member", "display_name": "Herbolzheimer, Eric" }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." } ], "option_major": [ "envreng" ], "doi": "10.7907/0vtp-g766", "abstract": "A theoretical and experimental investigation has been made of the longitudinal dispersion of chemically and dynamically passive solutes during flow through nonuniform, isotropic porous media. Both theoretical and experimental results are limited to the high Peclet number, low Reynolds number flow regime. The goal of the theoretical investigation is to provide a quantitative method for calculating the coefficient of longitudinal dispersion using only measurable structural features of the porous medium and the characteristics of the carrying fluid and solute. A nonuniform porous medium contains variations in grain scale pore structure, but is homogeneous at the macroscopic level for quantities such as the permeability or porosity.
\r\n\r\nA random capillary tube network model of nonuniform porous media is developed which uses a pore radius distribution and pore length distribution to characterize the grain scale structure of porous media. The analysis gives the asymptotic longitudinal dispersion coefficient flowing through individual, random capillary tubes. However, shear dispersion within individual capillary tubes (discussed in Appendix C) is found to have negligible impact on the overall longitudinal dispersion in porous media. The dispersion integrals are evaluated using a Monte Carlo integration technique. An analysis of the permeability in nonuniform porous media is used to establish a proper flow field for the analysis of longitudinal dispersion.
\r\n\r\nThe experimental investigation of longitudinal dispersion is carried out by measuring (with conductivity probes) the development of an initially sharp miscible displacement surface. The experimentally determined longitudinal dispersion coefficients are found to be greater in nonuniform media than in uniform media when compared using Peclet numbers based on the geometric mean grain diameter. The experimental breakthrough curves also display highly asymmetrical shapes, in which the \"tail\" of the breakthrough is longer than would be expected from advection-diffusion theory.
\r\n\r\nAlthough the theoretical model does not predict the tailing behavior, it is found that the leading portion of the breakthrough curve is described by advection-diffusion theory. The theoretically determined longitudinal dispersion coefficients lie roughly within a factor of 1.35 of the measured values.
" }, { "name": "Huang, Moh-jiann", "degree": "PhD", "year": "1984", "title": "Investigation of Local Geology Effects on Strong Earthquake Ground Motions", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12122018-092221333", "creators": [ { "name": { "family": "Huang", "given": "Moh-jiann" }, "id": "Huang-Moh-jiann", "display_name": "Huang, Moh-jiann" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "chair", "display_name": "Housner, George W." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" } ], "option_major": [ "civileng" ], "doi": "10.7907/pm3k-w086", "abstract": "Accelerograms recorded at four stations in the Pasadena area during the 1971 San Fernando, the 1970 Lytle Creek, the 1968 Borrego Mountain and the 1952 Kern County earthquakes are analyzed to investigate local geology effects on strong earthquake ground motions. Spatial variations of the ground motions at two nearby stations are also investigated. It is found that the ground motions in this area caused by the local geology effects depend on the 3- dimensional configuration of the local geology and the direction of arriving seismic waves. Local geology effects are less evident on the leading portions of the accelerograms than the trailing portions, indicating the effects of local geology on surface wave propagations. Comparison of the Fourier amplitudes of the motions recorded at the same station during different earthquakes shows that there are no significant spectral peaks can be identified as site periods. Hence, it is not appropriate to characterize such local sites by a site period.
\r\n\r\nA two-dimensional model considering inclined propagating P and S waves in a horizontal-layered structure, which is more realistic and closer to the actual seismic environment within a local geology than the one-dimensional model of vertically propagating waves, is studied. The transfer functions between the free surface and the half-space outcrop for a single incident P, SV or SH wave from the half-space at an incident angle are defined and derived by a matrix method. Two numerical examples are given to demonstrate the effects of incident angle and material damping on the transfer function. It is found that the transfer function between the free surf ace motions and the bedrock outcrop motions to multiple incident waves having different amplitudes, angles and arrival times is quite different from that for a single incident wave. Completely satisfactory results cannot be expected when using the analytical model for evaluating the local geology effects on the motions during a nearby shallow-focus earthquake for which seismic waves emitted from different parts of the fault will approach the bedrock from different directions and at different angles.
\r\n\r\nThe analytical model for assessing local geology effects is evaluated in the light of the data recorded at stations in the Pasadena area during the 1971 San Fernando earthquake. The observed site transfer functions between the alluvial and the rock sites are obtained and compared with the computed results from a two-dimensional model with 7-layers overlying a half-space. Values of model parameters are optimally adjusted to give a best least-squares fit between computed and observed amplitude ratios. It is concluded that the analytical model oversimplifies the local geological structure in the Pasadena area and the actual seismic environment in the area during the 1971 San Fernando earthquake.
\r\n\r\nIt is concluded from these studies that the effects of the source mechanism and the seismic wave travel paths upon the site ground motion can be comparable to the effect of the local geology. The characteristics of the source mechanism, such as type of faulting, direction of fault-slip propagation, nature of stress drop across the fault surface, orientation of fault, depth beneath ground surface, etc., can appreciably influence the ground motion at the site. Also, the travel path can have a significant effect through influencing the types of waves that reach the site, and the directions of approach of the waves. The results of this study indicate that a better understanding of the spatial variation of ground motions, of the role played by different types of waves and their contributions to an accelerogram, and of the propagation directions of the waves is needed for assessing local geology effects on earthquake ground motions. A local array is desirable to provide data for giving a reasonably complete picture of the nature of ground motions in a local area.
" }, { "name": "Hushmand, Behnam", "degree": "PhD", "year": "1984", "title": "Experimental Studies of Dynamic Response of Foundations", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152006-091708", "creators": [ { "name": { "family": "Hushmand", "given": "Behnam" }, "id": "Hushmand-Behnam", "display_name": "Hushmand, Behnam" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "chair", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "civileng" ], "doi": "10.7907/6TJK-6088", "abstract": "An investigation was made into the behavior of rigid foundations and structures resting on the surface or embedded in a cohesionless soil and subjected to transient active or passive excitations and forced vibrations using the centrifuge modeling technique. The investigation was aimed at studying both low and high amplitude vibrations of foundations under machine type loadings, earthquake or wave induced vibrations, and other sources of dynamic loads. Rigid \"prototype\" foundations of mass and size comparable to foundations of a low rise building were simulated in the centrifuge at a centrifugal acceleration of 50g. Rigid model structures (aluminum towers) attached to foundations of different shapes, sizes, masses, and moments of inertia were tested. The effect of soil depth, boundary conditions, and depth of foundation embedment were investigated. Mainly rocking and horizontal modes of vibration were studied. The impulse rocking-horizontal excitation of the models was provided by actively perturbing the model structures using explosive energy or by passively exciting them by shaking the whole soil bucket using a hydraulic shaking system. The forced vibration was produced by a miniature air-driven counterrotating eccentric mass shaker mounted on the model structures. During the tests detailed measurements of the static and dynamic contact pressure distributions, displacement components of the model, and acceleration amplitudes at different elevations of the model structure were obtained. The acceleration ratios were used to determine the modes of vibration of the foundation systems. Natural frequencies and damping coefficients of the modes were calculated by fitting the amplitude-frequency response of a single degree of freedom mass-spring-dashpot oscillator to the experimental response curves derived from the test data. Experimental results provided information regarding the influence of different geometrical, inertial, and loading conditions on the vibrational characteristics of the soil-structure system. In particular the effect of foundation embedment was to increase the model resonant frequencies and to cause an appreciable change in contact pressure distribution underneath the footing. However, the resonant frequencies predicted by the lumped parameter analysis for a simple two-degree-of-freedom (rocking and translation) model were about 20 to 55 per cent higher than those measured experimentally. These results were consistent with the comparisons made in similar theoretical and experimental studies such as those performed by Morris in the Cambridge centrifuge and those performed on full-scale footings by Stokoe and Richart. Damping ratios of the rocking-sliding vibration did not change considerably when footing size or depth of embedment changed. The existence of rigid boundaries around the soil mass in the bucket, and an inefficient contact between soil and the foundation side walls and lower surface could account for these observations. Uplift and nonlinear large amplitude vibrations were consistently observed during the steady-state vibration tests. Uplift led to a softer vibrating system which behaved non-linearly. As a result the frequency of vibration decreased with the amount of lift-off. In transient vibration uplift reduced the intensity of higher frequency vibration. Soil around the foundation edge yielded and plastic deformations and subsequent softening of the contact soil increased the material damping while it decreased the resonant frequency of the system. It was concluded that elastic half-space theory does not satisfy the needs for analysis of foundation behavior under high amplitude vibrations and more sophisticated methods of analysis are required.
" }, { "name": "Koochesfahani, Manoochehr Mohseni", "degree": "PhD", "year": "1984", "title": "Experiments on Turbulent Mixing and Chemical Reactions in a Liquid Mixing Layer", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132006-131143", "creators": [ { "name": { "family": "Koochesfahani", "given": "Manoochehr Mohseni" }, "id": "Koochesfahani-Manoochehr-Mohseni", "orcid": "0000-0002-7001-8455", "display_name": "Koochesfahani, Manoochehr Mohseni" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y7BR-C556", "abstract": "The processes of entrainment and mixing are investigated in reacting and non-reacting, uniform density, liquid mixing layers over a wide range of Reynolds numbers. In non-reacting cases, a passive scalar technique is used to measure the probability density function (pdf) of the composition field. Chemically reacting experiments employ a diffusion-limited acid-base reaction to directly measure the extent of mixing. The diagnostics are based entirely on the laser induced fluorescence technique. The fluorescence signal is measured by self-scanning linear photodiode arrays using high speed, real-time computer data acquisition. The system is capable of yielding species concentration data with a spatial resolution of 100 \u00b5m and a temporal resolution of 0.8 msec.
\r\n\r\nResults show that the vertical structures in the mixing layer initially roll up with a large excess of high speed fluid in the cores. During the mixing transition, not only does the amount of mixed fluid increase, but the composition also changes. It is found that the pdf of the mixed fluid, above the mixing transition, is quite uniform across the entire transverse extent of the layer. Furthermore, it is asymmetric and biased toward the high speed fluid. Experimental evidence indicates that the turbulent transport, in the cases studied, is dominated by large scale structures and is not adequately described by standard gradient-diffusion models. The fluid composition in the mixing layer, suggested by the present results, is in qualitative agreement with many aspects of the recent theoretical model of Broadwell and Breidenthal. The amount of product formed in the layer is compared to Mungal's measurements in gas, and, it is observed that the liquid layer has about 50% less product. The mean concentration of the mixed fluid, for a mixing layer at a velocity ratio of 0.38, becomes constant at 0.57 above the mixing transition. This corresponds to an entrainment ratio of 1.32, in agreement with the gaseous result of Konrad at the same velocity ratio.
" }, { "name": "Mailhiot, Christian", "degree": "PhD", "year": "1984", "title": "Theoretical Investigations of Electron States in Small-Scale Semiconductor Structures", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01112007-111123", "creators": [ { "name": { "family": "Mailhiot", "given": "Christian" }, "id": "Mailhiot-Christian", "display_name": "Mailhiot, Christian" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/0470-nf89", "abstract": "The work presented here is concerned with theoretical investigations of electronic states in small-scale semiconductor structures. This last term encompasses layered structures made up of two dissimilar, but lattice-matched, semiconductors. The semiconductors of interest here are mostly the tetrahedrally bonded zincblende semiconductors GaAs and the alloy Ga1-xAlxAs. The thesis is subdivided in three major chapters. The first chapter is concerned with electrical doping of Ga1-xAlxAs-GaAs-Ga1-xAlxAs quantum well structures. The second chapter addresses the question of the transport of electrons through GaAs-Ga1-xAlxAs double heterojunction structures. In the final chapter, we develop a theory of the electronic structure of semiconductor superlattices particularly suitable for the study of the optical properties and the recombination mechanisms.
\r\n\r\nIn Chapter 2, we study the energy spectrum of ground state and excited states of shallow donor states in Ga1-xAlxAs-GaAs-Ga1-xAlxAs quantum well structures. In this system, an impurity atom is located within a GaAs slab of finite thickness. The GaAs slab is, in turn, centered between two semi-infinite layers of Ga1-xAlxAs. We use a variational method to solve the effective mass equation for the donor envelope function. We study the variation of the binding energy as a function of
\r\n\r\n\u2218 thickness of the GaAs containing the impurity,
\r\n \r\n\u2218 alloy composition x in Ga1-xAlxAs, and
\r\n \r\n\u2218 position of the impurity in the GaAs slab.
\r\n \r\nTwo cases are treated:
\r\n\r\n(i) In the first case we assume that the potential well is formed by finite conduction band offsets at the GaAs-Ga1-xAlxAs interface (imperfect confinement).
\r\n\r\n(ii) In the second case we consider infinite confining potential at the GaAs-Ga1-xAlxAs interface (perfect confinement).
\r\n\r\nThe major result of this study is that the binding energy of the donor ground state is considerably modified as the thickness of the GaAs slab containing the impurity is varied. At large GaAs slab thicknesses, the binding energy is that of shallow donors in bulk GaAs. At small GaAs slab thicknesses, the binding energy is that of shallow donors in bulk Ga1-xAlxAs for the case of imperfect confinement, but corresponds to the two-dimensional Coulomb limit in the case of perfect confinement. It is also found that the binding energy depends on the position of the impurity atom within the GaAs slab. Thus, we have a confinement-induced lifting of the Coulomb energy levels.
\r\n\r\nIn Chapter 3, we study the transport characteristics of electrons through GaAs-Ga1-xAlxAs-GaAs double heterojunction structures. In this system, a Ga1-xAlxAs slab of finite thickness is centered between two semi-infinite layers of GaAs. An electron is incoming from the GaAs onto the Ga1-xAlxAs barrier. Transport coefficients are calculated using the formalism of the complex-k energy band structure within the empirical tight-binding method. Transmission into states derived from different energy extrema of the GaAs lowest conduction band obtained. We consider both the (111) and the (100) GaAs-Ga1-xAlxAs interfaces. Transport coefficients are calculated as a function of
\r\n\r\n\u2218 GaAs conduction band minimum from which the electron state is derived,
\r\n \r\n\u2218 energy of the electron incoming on the Ga1-xAlxAs barrier,
\r\n \r\n\u2218 thickness of the Ga1-xAlxAs barrier, and
\r\n \r\n\u2218 alloy composition x in the Ga1-xAlxAs.
\r\n\r\nThe major result of the study is that states derived from different energy extrema of the GaAs lowest conduction band appear to couple weakly across the GaAs-Ga1-xAlxAs interface. Thus, if we consider the (111) interface, is seems possible to reflect the L-point component of the current while transmitting the \u0393-point component. There exists two regimes of transport: tunneling transport and propagating transport. In the case where the energy incoming electron is below the energy barrier, transmission is small and the transport occurs via a tunneling process. However, in the case where the energy incoming electron is above the energy barrier, transmission is large and the transport occurs via a propagating process. Depending on the Ga1-xAlxAs slab thickness, it is possible to induce resonances whereby the transmission coefficient is unity.
\r\n\r\nIn Chapter 4, we develop a theoretical framework to investigate the electronic structure of semiconductor superlattices. The theoretical formulation is based on the k \u2022 p method derived from an accurate local pseudopotential method. The formalism developed is particularly well suited for the study of the optical properties and the investigation of the recombination mechanisms in semiconductor superlattices. Here again, we make extensive use of the complex-k energy band structure obtained via the k \u2022 p method. Realistic boundary conditions are imposed on the multi-component superlattice envelope function. From these boundary conditions, the energy spectrum of the superlattice is deduced. For the first time, we develop a scheme whereby the superlattice state function in both solids is expanded in terms of the same set of basis functions. By doing so, we relax the often used approximation that assumed that the basis functions are the same for all zincblende semiconductors.
" }, { "name": "Margoliash, Daniel", "degree": "PhD", "year": "1984", "title": "Songbirds, Grandmothers, Templates: a Neuroethological Approach", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11282018-101712728", "creators": [ { "name": { "family": "Margoliash", "given": "Daniel" }, "id": "Margoliash-Daniel", "orcid": "0000-0003-0002-3117", "display_name": "Margoliash, Daniel" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Ary", "given": "James P." }, "id": "Ary-James-P", "role": "chair", "display_name": "Ary, James P." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Konishi", "given": "Masakazu" }, "id": "Konishi-M", "role": "member", "display_name": "Konishi, Masakazu" }, { "name": { "family": "Van Essen", "given": "David C." }, "id": "Van-Essen-D-C", "orcid": "0000-0001-7044-4721", "role": "member", "display_name": "Van Essen, David C." }, { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "member", "display_name": "Fender, Derek H." } ], "option_major": [ "eng" ], "doi": "10.7907/2yhr-5t19", "abstract": "Songbirds such as the white-crowned sparrow memorize the song of conspecific adults during a critical period early in life, and later in life develop song by utilizing auditory feedback. Neurons in one of the telencephalic nuclei controlling song have recently been shown to respond to acoustic stimuli. I investigated the auditory response properties of units in this nucleus using a technique that permitted great flexibility in manipulating complex stimuli such as song. A few of the units exhibited considerable selectivity for the individual's own song. In wild-caught birds, song specific units exhibited intra-dialect selectivity. In those birds that sang abnormal songs due to laboratory manipulation of song exposure during the critical period for song learning, units were selective for the abnormal songs. By systematic modification of a song, and by construction of complex synthetic sounds mimicking song, the acoustic parameters responsible for the response selectivity were identified. Song specific units responded to sequences of two song parts, but not to the parts in isolation. Modification of the frequencies of either part of the sequence, or increasing the interval between the parts, varied the strength of the response. Thus, temporal as well as spectral parameters were important for the response. When sequences of synthetic sounds mimicking song were effective in evoking an excitatory response, the response was sensitive to the aforementioned manipulations. With these techniques it was possible to elucidate the acoustic parameters required to excite song specific units. All songs of the repertoire eliciting a strong excitatory response contained the appropriate parameters, which were missing from all weakly effective, ineffective, or inhibitory songs. These observations suggest that the ontogenetic modification of integrative neural mechanisms underlying song learning or song crystalization is reflected at the level of single neurons.
\r\n" }, { "name": "Neikirk, Dean Paul", "degree": "PhD", "year": "1984", "title": "Integrated Detector Arrays for High Resolution Far-Infrared Imaging", "advisor": "Rutledge, David B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092007-104136", "creators": [ { "name": { "family": "Neikirk", "given": "Dean Paul" }, "id": "Neikirk-Dean-Paul", "display_name": "Neikirk, Dean Paul" } ], "advisors": [ { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "advisor", "display_name": "Rutledge, David B." } ], "committee": [ { "name": { "family": "Pine", "given": "Jerome" }, "id": "Pine-J", "role": "chair", "display_name": "Pine, Jerome" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/jxk1-9t91", "abstract": "Imaging systems designed to operate in the millimeter and submillimeter portion of the spectrum (often referred to as the far-infrared) require the development of focal plane detector arrays to simplify their construction. In this study the general characteristics of an antenna array intended to provide diffraction limited imaging are discussed. Two line-imaging bow-tie antenna arrays utilizing the hyperhemispherical substrate lens optical system and operating at 1.22mm and 119\u00b5m, are demonstrated. Two new far-infrared detectors, the bismuth air-bridge microbolometer and the bismuth-antimony microthermocouple, have been used with these arrays. Thermal models and performance data for these detectors are given. Finally, the photolithographic processes used to fabricate the detectors and antennas are discussed.
\r\n" }, { "name": "Ngo, Khai Doan The", "degree": "PhD", "year": "1984", "title": "Topology and Analysis in PWM Inversion, Rectification, and Cycloconversion", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-04222005-160253", "creators": [ { "name": { "family": "Ngo", "given": "Khai Doan The" }, "id": "Ngo-Khai-Doan-The", "orcid": "0000-0002-0326-3055", "display_name": "Ngo, Khai Doan The" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" } ], "option_major": [ "eleceng" ], "doi": "10.7907/M91H-FZ91", "abstract": "Topologies and analysis techniques in switched-mode dc conversion (dc-to-dc), inversion (dc-to-ac), rectification (ac-to-dc), and cycloconversion (ac-to-ac) are unified in this thesis. The buck, boost, buck-boost, and flyback topologies are used to demonstrate that familiar dc converters can be extended into equivalent ac converters. Although some of these are presented as fast-switching circuits, they have also been found in slow-switching applications. Thus, topology is the unifying factor not only over four fields of power electronics, but also within each field itself.
\r\n\r\nDescribing equations are used to characterize low frequency components of the inputs and outputs in fast-switching networks containing filters, excited by dc or balanced sinusoidal sources, and pulse-width-modulated by dc or balanced sinusoidal duty ratios. They are first written in the stationary (abc) reference frame and then transformed to the rotating (ofb) coordinates. In the ofb coordinates, all balanced ac converters with any number of phases are reduced to a set of continuous, time-invariant differential equations describing a two-phase equivalent.
\r\n\r\nSteady-state, dynamic, and canonical models are then solved in the rotating frame of reference. Emphasis is stressed on circuit ideality - sinusoidal outputs for sinusoidal inputs even though a switched network is nonlinear - and effects of filters on steady-state and small-signal frequency responses. These results are similar for a dc converter, inverter, rectifier, and cycloconverter of the same topology; this similarity again confirms that the four converters are closely related. The cycloconverter is thus established as the generalized converter that degenerates to the other three under special input and output frequencies.
\r\n\r\nPractical issues discussed include the realization of the switches, modification of drive and topology for bidirectionality of power flow, isolation, switched-mode impedance conversion, and measurement techniques.
\r\n" }, { "name": "Papachristidis, Alexandros Christou", "degree": "PhD", "year": "1984", "title": "Heterogeneous Data Base Access", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01022007-110210", "creators": [ { "name": { "family": "Papachristidis", "given": "Alexandros Christou" }, "id": "Papachristidis-Alexandros-Christou", "display_name": "Papachristidis, Alexandros Christou" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "chair", "display_name": "Thompson, Frederick B." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" } ], "option_major": [ "compsci" ], "doi": "10.7907/5sdf-7w07", "abstract": "This thesis presents a design for accessing commercially available data bases and other data base systems from a given, \"local\" data base system. Using this design, data from the local data base and from one or more \"foreign\" data bases will be integrated in framing the response to a single query. The design does not presume any standardization or integration of any kind on the part of a target data base.
\r\n\r\nAn expert system has been designed, to be used by the applications programmer, for acquiring the information about a target data base, the communication path with the target computer, and the protocol for sending a data retrieval request. It also obtains from the applications programmer the nature of the data to be accessed and instructions for converting the incoming data into the \"local\" system's own format. This information is then associated with each word referring to data residing in the \"foreign\" data base, and is stored in the lexicon of the \"local\" system. The design also includes the extension of the underlying, host, system so that this information is properly used at the appropriate points in the processing of a user query.
\r\n\r\nState-of-the-art techniques used for interfacing heterogeneous data bases and natural language front-ends to data base systems are examined. The unique accomplishments of this thesis are identified. At the present time, there are no other systems, either commercial or research, that provide the heterogeneous access capabilities of the design presented here.
\r\n\r\nThe design of Heterogeneous Data Base Access has been implemented as a part of the ASK System, A Simple Knowledgable System, providing natural language interface with the user.
" }, { "name": "Papanicolaou, Panayiotis Nikolas", "degree": "PhD", "year": "1984", "title": "Mass and Momentum Transport in a Turbulent Buoyant Vertical Axisymmetric Jet", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechTHESIS:02202019-095834395", "creators": [ { "name": { "family": "Papanicolaou", "given": "Panayiotis Nikolas" }, "id": "Papanicolaou-Panayiotis-Nikolas", "display_name": "Papanicolaou, Panayiotis Nikolas" } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Reynolds", "given": "William C." }, "id": "Reynolds-William-C", "role": "member", "display_name": "Reynolds, William C." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" } ], "option_major": [ "civileng" ], "doi": "10.7907/6khx-sv30", "abstract": "The entrainment and mixing processes in an axisymmetric vertical turbulent buoyant jet and its transition from a jet to a plume have been studied. The ambient fluid is of uniform density and calm except for the flow induced by the jet, and the density variations are assumed small.
\r\n\r\nA systematic set of experiments was carried out to examine turbulent buoyant jet behavior over a wide range or initial jet Richardson numbers. All experiments were performed in a glass wall tank with dimensions 1.15 m x 1.15 m x 3.30 m deep, equipped with a jet flow source and an instrument carriage to enable velocity and concentration measurements in the entire jet flow field.
\r\n\r\nThe axial and radial velocity components and the concentration of a Rhodamine 6G dye were measured simultaneously at the same point of the jet flow field using a two - reference beam laser - Doppler velocimeter combined with a laser induced fluorescence measuring device. From the time signals of the axial and radial velocity components (w) and (u) and the concentration (c) of a Rhodamine 6G dye, information was obtained concerning the mean values, turbulent fluctuations and correlations between w, u and c, up to 100 jet and 80 plume diameters downstream of the jet exit.
\r\n\r\nMore specifically, the mean flow (including the spreading rate of the mean velocity and tracer concentration profiles and distribution along the jet axis) and the turbulent structure (including the profile of turbulence intensity, turbulent mass flux of a tracer and turbulent momentum flux) were investigated as a function of distance from jet origin made dimensionless by a characteristic length scale based on jet buoyancy and momentum fluxes. The results from a detailed dimensional analysis were verified experimentally. It was determined that the turbulent flux of a tracer (or buoyancy) varied from 6-10% for jets and was 15-20% of the total for plumes. The turbulent momentum flux was found to be 15% of the local momentum flux transported by the mean flow.
\r\n\r\nWhile the profiles of w and c and the turbulent velocity profiles are found to be much the same tor both jets and plumes, the turbulence intensity profiles of the concentration take higher values in plumes than in jets. More rapid dilutions were obtained in buoyancy driven plumes than in momentum driven jets.
\r\n\r\nUseful information concerning engineering applications is provided from the experimental constants derived.
\r\n\r\n\r\n" }, { "name": "Polivka, William M.", "degree": "PhD", "year": "1984", "title": "Applications of Magnetics to Problems in Switched-Mode Power Conversion", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-01022007-112439", "creators": [ { "name": { "family": "Polivka", "given": "William M." }, "id": "Polivka-William-M", "display_name": "Polivka, William M." } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Barnes", "given": "Charles A." }, "id": "Barnes-C-A", "role": "chair", "display_name": "Barnes, Charles A." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/31G4-8128", "abstract": "Two topics are presented which advance the use of magnetic devices in switched-mode power converters. Part I discusses a novel method of detecting impending saturation of magnetic materials. The technique exploits the interaction of perpendicular magnetic fields to provide a simple, direct and continuous measure of the increasing nonlinearity of the material without any elaborate unconventional devices or complex electronic circuitry. Theoretical foundations and applications to ferrite cores in switching converters are given. Specific practical hardware examples are described including magnetics for a 4-kilowatt push-pull buck converter. Part II presents a discussion of the analysis of zero ripple integrated magnetic structures. These complex devices are of great interest in the field of switched mode power conversion because they have the ability to exclude ac currents from some of their windings when they are excited by ac voltages. A thorough analysis is carried out to establish which of the many characteristic parameters of these devices are responsible for the unusual zero ripple behavior. Practical methods of modelling and analysis are developed by which a designer can quickly determine the conditions required for zero ripple. Equivalent electric circuit models are given to aid in the electrical design of converters and to support the simple physical explanations of the observed phenomena including the effects of parasitic quantities. A number of experiments confirm the validity of the models.
" }, { "name": "Robinson, Allen Conrad", "degree": "PhD", "year": "1984", "title": "Existence and Stability of Vortices and Vortex Arrays", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212006-111951", "creators": [ { "name": { "family": "Robinson", "given": "Allen Conrad" }, "id": "Robinson-Allen-Conrad", "orcid": "0000-0001-7345-5223", "display_name": "Robinson, Allen Conrad" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Fornberg", "given": "Bengt" }, "id": "Fornberg-Bengt", "role": "member", "display_name": "Fornberg, Bengt" }, { "name": { "family": "Kath", "given": "William L." }, "id": "Kath-William-L", "role": "member", "display_name": "Kath, William L." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appmath" ], "doi": "10.7907/0db7-mr48", "abstract": "The stability to three-dimensional disturbances of three classical steady vortex configurations in an incompressible inviscid fluid is studied in the limit of small vortex cross-sectional area and long axial disturbance wavelength. The configurations examined are the single infinite vortex row, the Karman vortex street of staggered vortices and the symmetric vortex street. It is shown that the single row is most unstable to a two-dimensional disturbance, while the Karman vortex street is most unstable to a three-dimensional disturbance over a significant range of street spacing ratios. The symmetric vortex street is found to be most unstable to three-dimensional or two-dimensional symmetric disturbances depending on the spacing ratio of the street. Short remarks are made concerning the relevance of the calculations to the observed instabilities in free shear layer, wake and boundary layer type flows.
\r\n\r\nThe three-dimensional linear stability of a steady rectilinear vortex of elliptical cross-section existing in an irrotational straining field is studied numerically in the case of finite strain. It is shown that the instability predicted for weak strain persists for finite strain and that the weak strain results continue to be quantitatively valid for finite strain. Parametric dependence of the growth rates of the unstable modes on the strain and the axial disturbance wavelength is discussed. It is also shown that a three-dimensional instability is always more unstable than a two-dimensional instability in the range of parameters of most interest.
\r\n\r\nThe radially symmetric Burgers' vortex is an example of a solution to the Navier-Stokes equations in which the intensification of vorticity due to vortex stretching is balanced by the diffusion of vorticity through viscosity. We present analytical solutions obtained from a perturbation analysis as well as numerical computations of non-symmetric Burgers' vortices in which the radial flow field in a plane perpendicular to the vorticity is non-symmetric. We also demonstrate the linear stability of the symmetric Burgers' vortex to a restricted class of two-dimensional perturbations.
" }, { "name": "Schulz, Robert", "degree": "PhD", "year": "1984", "title": "Electrical Transport During Phase Transformation in Metallic Glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252007-153245", "creators": [ { "name": { "family": "Schulz", "given": "Robert" }, "id": "Schulz-Robert", "display_name": "Schulz, Robert" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "chair", "display_name": "Duwez, Pol E." }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/yxsm-vx37", "abstract": "Electrical resistivity measurements have been used as a primary tool to study relaxation phenomena and high temperature structural transformations in metallic glasses. We will try to correlate, throughout this work, the resistivity behavior with structural measurements from high and low angle X-ray scattering, transmission electron microscopy, Mossbauer experiments and low temperature superconductivity measurements to get a better understanding of the scattering mechanism during the phase transformation. We will distinguish between topological relaxation and chemical relaxation and in this latter case, emphasis will be given to phase separation. Three systems will be discussed extensively. Amorphous Cu100-xZrx around the equiatomic composition, (Mo0.6Ru0.4)100-xBx for boron concentrations ranging from x = 14 to x = 22 and (Zr1-xHfx)62Ni38 across the concentration range. We will show that upon annealing at temperature above 300\u00b0C, Cu50Zr50 phase separates into two amorphous phases of concentration close to CuZr2 and Cu10Zr7. During the phase separation an anomalous resistivity behavior, similar to the one observed during the early stage of Guinier-Preston zones formation in crystalline alloys is seen. In Mo-Ru-B alloys, the nonlinear behavior in resistivity is correlated with the presence of a peak in the small angle X-ray intensity and is explained in term of spinodal decomposition caused by the diffusion of boron in the amorphous matrix. In (Zr1-xHfx)62Ni38, an exothermic transformation which gives rise to an increase in resistivity but no resolvable Bragg peaks in the high angle X-ray pattern is investigated in detail. The applicability of the Ziman formalism to successfully explain the behavior of the resistivity in all these cases is questioned and an alternative approach, based on d-band conduction, is proposed. New ways of understanding transport phenomena during structural relaxation in metallic glasses follow from these discussions.
" }, { "name": "Senior, Constance Lynn", "degree": "PhD", "year": "1984", "title": "Submicron Aerosol Formation During Combustion of Pulverized Coal", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022007-105020", "creators": [ { "name": { "family": "Senior", "given": "Constance Lynn" }, "id": "Senior-Constance-Lynn", "orcid": "0000-0002-1454-4194", "display_name": "Senior, Constance Lynn" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "chair", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "orcid": "0000-0003-1468-6835", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/70GT-H495", "abstract": "A detailed investigation is conducted into the fundamental processes responsible for the formation of submicron aerosol during combustion of pulverized coal. To this end, both theoretical and experimental tools are developed.
\r\n\r\nThe first part of the work consists of a numerical simulation of the vaporization of ash and formation of aerosol. The work combines a model of a single, burning coal particle with one of the formation of aerosol by nucleation and the growth of aerosol by coagulation. A quasi-steady approach is used to model combustion and aerosol formation and this is shown to be valid a posteriori. Calculations are performed for vaporization of refractory oxides during combustion. The effect of thermophoresis on the transport of aerosol around a burning coal particle is found to be small. For refractory species like silica, nucleation typically occurs within 4-5 particle radii from the surface of the coal particle. Thus, in this case, nucleation is controlled by the combustion process. The vaporization rate is found to be weakly dependent on the presence of aerosol in the gas.
\r\n\r\nThe second part of this work is the development of an experimental system in which to study the aerosol formation processes. A new material is produced that is similar to coal in many respects, but is chemically simpler and more well-characterized. This makes it possible for the first time to study the fundamental aerosol formation processes without interference from the complex chemistry of coal ash. Experiments in a laminar drop-tube furnace confirm that this material burns in a manner similar to coal and that combustion produces an aerosol from vaporization of ash.
" }, { "name": "Simmen, Jeffrey Alan", "degree": "PhD", "year": "1984", "title": "Steady Deep-Water Waves on a Linear Shear Current", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192007-153942", "creators": [ { "name": { "family": "Simmen", "given": "Jeffrey Alan" }, "id": "Simmen-Jeffrey-Alan", "display_name": "Simmen, Jeffrey Alan" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "chair", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Kath", "given": "William L." }, "id": "Kath-William-L", "role": "member", "display_name": "Kath, William L." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appmath" ], "doi": "10.7907/H88C-1G49", "abstract": "The behavior of steady, periodic, deep-water gravity waves on a linear shear current is investigated. A weakly nonlinear approximation for the small amplitude waves is constructed via a variational principle. A local analysis of those large amplitude waves with sharp crests, called extreme waves, is also provided. To construct solutions for all waveheights (especially the limiting ones) a convenient mathematical formulation which involves only the wave profile and some constants of the motion is derived and then solved by numerical means. It is found that for some shear currents the highest waves are not necessarily the extreme waves. Furthermore a certain non-uniqueness in the sense of a fold is shown to exist and a new type of limiting wave is discovered.
\r\n" }, { "name": "Smyth, Noel Frederick", "degree": "PhD", "year": "1984", "title": "Part I: Soliton on a Beach and Related Problems. Part II: Modulated Capillary Waves", "advisor": "Whitham, Gerald Beresford; Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252007-143608", "creators": [ { "name": { "family": "Smyth", "given": "Noel Frederick" }, "id": "Smyth-Noel-Frederick", "orcid": "0000-0002-8787-3175", "display_name": "Smyth, Noel Frederick" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "co-advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "chair", "display_name": "Cohen, Donald S." }, { "name": { "family": "Kath", "given": "William L." }, "id": "Kath-William-L", "role": "member", "display_name": "Kath, William L." }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "member", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "appmath" ], "doi": "10.7907/VXDD-1M21", "abstract": "I. Soliton on a Sloping Beach and Related Problems
\r\n\r\nThe problem of the behaviour of a soliton on a slowly varying beach is considered. It is shown that for a correct description, the full Boussinesq equations rather than a Korteweg-de Vries type approximation must be used. Using both energy conservation and two-timing expansions, the behaviour of the soliton is analysed. The slowly varying soliton is found not to conserve mass and momentum and it has been suggested that to conserve these quantities, both forward and reflected waves must be added behind the soliton, these waves being solutions of the linear shallow water equations. It is shown that to the order of approximation of the Boussinesq equations, only a forward wave (or tail) behind the soliton is necessary to fulfill mass and momentum conservation.
\r\n\r\nA perturbed Korteweg-de Vries equation for which the perturbation adds energy to the soliton is considered. It is found that a tail is formed behind the soliton. The development of this tail into new solitons is analysed.
\r\n\r\nII. Modulated Capillary Waves
\r\n\r\nAn exact hodograph solution for symmetric and antisymmetric capillary waves on a fluid sheet (of possibly infinite thickness) has been previously found. Using this solution, an exact averaged Lagrangian for slowly varying capillary waves is calculated. Modulation equations can be found from this averaged Lagrangian, but due to the algebraic complexity of the equations, the limit of waves on a thin fluid sheet is considered. From the modulation equations, the stability of symmetric and antisymmetric capillary waves on a thin fluid sheet is found. The modulation equations for antisymmetric waves form a hyperbolic system and the simple wave solutions for this system are calculated. These simple wave solutions are interpreted physically.
" }, { "name": "Vorp\u00e9rian, Vatch\u00e9", "degree": "PhD", "year": "1984", "title": "Analysis of Resonant Converters", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-04082005-150525", "creators": [ { "name": { "family": "Vorp\u00e9rian", "given": "Vatch\u00e9" }, "id": "Vorp\u00e9rian-Vatch\u00e9", "orcid": "0000-0002-8534-187X", "display_name": "Vorp\u00e9rian, Vatch\u00e9" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "chair", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" } ], "option_major": [ "eleceng" ], "doi": "10.7907/NWMH-AP27", "abstract": "The load parameter, Q, and the ratio of the switching frequency to the resonant frequency, Fs/Fo, characterize the operation of resonant converters. An accurate do analysis of the series and parallel resonant converters is given in terms of these parameters whereby the conversion ratio, peak stresses, and diode conduction time are determined. An exact and systematic method of small-signal analysis is given whereby the control-to-output transfer function, audio susceptibility, and input impedance are determined at a given operating point. In addition, simple and approximate transfer functions are obtained under high-Q assumption.
" }, { "name": "Wang, Chiun", "degree": "PhD", "year": "1984", "title": "The Effects of Curvature on Turbulent Mixing Layers", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222007-142548", "creators": [ { "name": { "family": "Wang", "given": "Chiun" }, "id": "Wang-Chiun", "display_name": "Wang, Chiun" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BC48-BE98", "abstract": "Experimental studies have been conducted in a curved mixing layer in which both the velocity ratio and the density ratio were variable. Flow visualization studies and profile measurements covered a wide range of experimental conditions. The structures observed experimentally were examined in the light of three different instability mechanisms which can exist in the same mean flow.
\r\n\r\nFor the case of mixing layers with uniform density, it was found that the normal large spanwise vortex structures can be weakened or inhibited by Taylor-Gortler instability if the inner stream is faster than the outer stream. For the case of mixing layers with different densities, three-dimensionality is greatly enhanced by Rayleigh-Taylor instability if the inner stream is heavier than the outer stream, and especially if the inner stream is also faster. In the former case the growth rate of the mixing layer was found to be insensitive to changes in the velocity ratio.
\r\n\r\nThe effects of curvature on the structure of the curved turbulent mixing layer were explored in terms of length scales and celerity for the large spanwise structures where these structures could be observed. Other things being equal, the celerity of the large structures was found to depend on density ratio and velocity ratio but not on the sense of the mean streamline curvature.
" }, { "name": "Warne, Larry Kevin", "degree": "PhD", "year": "1984", "title": "Electromagnetic Radiation and Scattering in a Plasma with an Azimuthal Biasing Field", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232007-143259", "creators": [ { "name": { "family": "Warne", "given": "Larry Kevin" }, "id": "Warne-Larry-Kevin", "display_name": "Warne, Larry Kevin" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "chair", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Kath", "given": "William L." }, "id": "Kath-William-L", "role": "member", "display_name": "Kath, William L." }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" } ], "option_major": [ "eleceng" ], "doi": "10.7907/tja8-zp12", "abstract": "The problem of radiation from an electric line source in a homogeneous, cold, incompressible electron plasma is considered when a large static current is superposed. The static axial current gives rise to a magnetostatic biasing field which is oriented in the azimuthal direction and varies with radial distance. When the driving frequency is greater than the plasma frequency, and the medium is assumed to be unbounded, the presence of the static current reduces the amount of radiation. On the other hand, if the driving frequency is less than the plasma frequency and the medium is assumed to be bounded, the amount of radiation is increased.
\r\n\r\nThe problem of scattering from an axial current in a plasma is also considered. The medium in this problem is taken to be a bounded column of plasma containing a radially distributed axial current. At normal incidence the scattered wave contains a cross polarized field component due to the gyrotropic nature of the column. The scattered cross polarized component vanishes in the incident direction as well as in the backward direction. This null is explained by considering the effect of Faraday rotation on various rays traversing the column. Solutions to the scattering problem when the axial current density varies inversely with radial distance are considered in some detail. This case is labeled \"homogeneous\" since the dielectric tensor does not vary with radial distance and the resulting field equations are thus simplified. The field behavior in the vicinity of the origin is also considered in detail since phenomena similar to those encountered in wedge type media (unbounded fields) occur.
" }, { "name": "White, Jeffrey Owen", "degree": "PhD", "year": "1984", "title": "Four-Wave Mixing and Phase Conjugation in Photorefractive Crystals", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192007-152414", "creators": [ { "name": { "family": "White", "given": "Jeffrey Owen" }, "id": "White-Jeffrey-Owen", "orcid": "0000-0003-3109-193X", "display_name": "White, Jeffrey Owen" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "chair", "display_name": "Bridges, William B." }, { "name": { "family": "Kath", "given": "William L." }, "id": "Kath-William-L", "role": "member", "display_name": "Kath, William L." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/f9ef-m894", "abstract": "This thesis is an experimental and theoretical investigation of nonlinear optics in photo-refractive crystals, and applications thereof. Coherent light is used to induce nonlinear, optical frequency polarizations proportional to the cube of the total optical field within these materials. Equivalently, dynamic holography performed wherein the incident light simultaneously writes, reads and erases index of refraction gratings.
\r\n\r\nThe first part of this thesis is a description of the physics of the photo-refractive effect in such crystals as Bi12SiO20, LiNbO3, KTaO3, and BaTiO3. Previous microscopic rate equation models are extended to include the dynamics of a second photo-refractive center with the aim of explaining several discrepancies with experimental data.
\r\n\r\nThe second part reviews the coupled wave theory of fixed gratings and dynamic gratings formed in photo-refractive media. Coupled nonlinear ordinary differential equations describe the interaction between two optical waves; which is caused by the grating that they create. The analysis is extended to the reflection geometry and the ring resonator geometry. The coupling constant is measured in the reflection geometry. Holographic gain is combined with mirror feedback to demonstrate a unidirectional ring oscillator, wherein a optically pumped photo-refractive crystal functions as a directional gain element.
\r\n\r\nThe third part extends the analysis to the holographic formulation of four-wave mixing, wherein four waves and up to four gratings exist in the crystal. The equations are solved in the single grating approximation. The object of much of the analysis is to calculate the reflectivity of a four-wave mixing photo-refractive phase conjugate mirror. The invention of a passive self-pumped phase conjugate mirror is described.
\r\n\r\nThe last part describes three applications of four-wave mixing. We demonstrate the compensation of intracavity laser distortions by replacing an ordinary mirror in a laser with a passive phase conjugate mirror. We propose and demonstrate a phase conjugate window for one-way transmission of an information bearing optical field through a thin phase distortion. Finally, the multiplicative properties of four-wave mixing are combined with the transforming properties of lenses to construct a coherent optical processor capable of convolving and correlating three input fields containing arbitrary spatial phase and amplitude information.
" }, { "name": "Wilson, John Charles", "degree": "PhD", "year": "1984", "title": "Analysis of the Observed Earthquake Response of a Multiple Span Bridge", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11262018-124513833", "creators": [ { "name": { "family": "Wilson", "given": "John Charles" }, "id": "Wilson-John-Charles", "display_name": "Wilson, John Charles" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "chair", "display_name": "Jennings, Paul C." }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." } ], "option_major": [ "civileng" ], "doi": "10.7907/5321-6p57", "abstract": "Accelerograms obtained during the 1979 Coyote Lake, California earthquake are used to examine the response of a multiple-span, steel girder bridge to strong earthquake loading. The structure studied, the San Juan Bautista 156/101 Separation Bridge, is typical of many highway bridges in seismic regions of the United States. Although the bridge was not damaged, the strong-motion records are of significant engineering interest as they are the first to be recorded on such a structure.
\r\n\r\nAn engineering seismology study suggests that long-period ground displacements at the bridge site were caused by Rayleigh waves. A three-second period, pseudostatic response of the superstructure is attributed to small amounts of differential support motion induced by the surface waves.
\r\n\r\nA time-domain technique of system identification is used to determine linear models which can closely replicate the observed bridge response. Using time-invariant models, two structural modes at 3.50 and 6.33 Hz, are identified in the horizontal direction. Each mode, having approximately ten-percent damping, involves coupled longitudinal and transverse motions of the superstructure. Time-variations of frequency and damping in the horizontal response are also identified using a moving-window analysis.
\r\n\r\nA three-dimensional finite element model which includes soil-structure interaction predicts several important features of the dynamic response of the bridge. The first two computed horizontal frequencies are found to be in excellent agreement with the observed responses provided the model's expansion joints are locked, preventing relative translational motions from occurring across the joints. Locking is confirmed by the observed deformations of the structure in the fundamental mode. Fundamental vertical frequencies of the individual spans, predicted by the finite element model, are in very good agreement with ambient vibration test data. Results of the strong-motion data analysis and the finite element modeling are used to recommend a plan for expansion of the strong-motion instrumentation array on the bridge.
" }, { "name": "Winget, James Michael", "degree": "PhD", "year": "1984", "title": "Element-by-Element Solution Procedures for Nonlinear Transient Heat Conduction Analysis", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252007-132425", "creators": [ { "name": { "family": "Winget", "given": "James Michael" }, "id": "Winget-James-Michael", "display_name": "Winget, James Michael" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hall", "given": "John F." }, "id": "Hall-J-F", "orcid": "0000-0002-7863-5060", "role": "member", "display_name": "Hall, John F." }, { "name": { "family": "Hughes", "given": "Thomas J. R." }, "id": "Hughes-T-J-R", "role": "member", "display_name": "Hughes, Thomas J. R." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/G7VB-EV65", "abstract": "Despite continuing advancements in computer technology, there are many problems of engineering interest that exceed the combined capabilities of today's numerical algorithms and computational hardware. The resources required by traditional finite element algorithms tend to grow geometrically as the \"problem size\" is increased. Thus, for the forseeable future, there will be problems of interest which cannot be adequately modeled using currently available algorithms. For this reason, we have undertaken the development of algorithms whose resource needs grow only linearly with problem size. In addition, these new algorithms will fully exploit the \"parallel-processing\" capability available in the new generation of multi-processor computers.
\r\n\r\nThe approach taken in the element-by-element solution procedures is to approximate the global implicit operator by a product of lower order operators. This type of \"product\" approximation originated with ADI techniques and was further refined into the \"method of fractional steps.\" The current effort involves the use of a more natural operator split for finite element analysis based on \"element operators.\" This choice of operator splitting based on element operators has several advantages. First, it fits easily within the architecture of current FE programs. Second, it allows the development of \"parallel\" algorithms. Finally, the computational expense varies only linearly with the number of elements.
\r\n\r\nThe particular problems considered arise from nonlinear transient heat conduction. The nonlinearity enters through both material temperature dependence and radiation boundary conditions. The latter condition typically introduces a \"stiff\" component in the resultant matrix ODE's which precludes the use of explicit solution techniques. Implicit solution techniques can be prohibitively expensive. Instead, the matrix equations are solved by combining a modified Newton-Raphson iteration scheme with an element-by-element preconditioned conjugate gradient subiteration procedure. The resultant procedure has proven to be both accurate and reliable in the solution of medium-size problems in this class.
\r\n" }, { "name": "Yang, Vigor", "degree": "PhD", "year": "1984", "title": "Pressure Oscillations in Liquid-Fueled Ramjet Engines", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09052006-153951", "creators": [ { "name": { "family": "Yang", "given": "Vigor" }, "id": "Yang-Vigor", "display_name": "Yang, Vigor" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "member", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "mecheng" ], "doi": "10.7907/rfpg-es59", "abstract": "Pressure oscillations in liquid-fueled ramjet engines have been studied both analytically and numerically within the low frequency range. We examine first the linear unsteady motions in coaxial-dump configurations. The flowfield in the dump combustor is approximated by division into three parts: a flow of reactants, a region containing combustion products, and a recirculation zone, separated by two infinitesimally thin sheets: the flame and the vortex sheets. The three zones are matched at these sheets by taking into account kinematic and conservation relations. The oscillatory field in the inlet is coupled to the field in the combustor at the dump plane to determine the complex frequencies characterizing the linear stability of the engine. Favorable comparison with the experimental data obtained at the California Institute of Technology has been obtained.
\r\n\r\nNumerical analysis has been applied to investigate the nonlinear behavior of the shock wave in the inlet diffuser. Both viscous effects and the influences of injecting fuel/air mixture are accounted for. The response of a shock wave to various disturbances, including finite and large amplitude oscillations, has been studied in detail. The results obtained serve as a basis for analyzing the stability characteristics of the inlet flow.
\r\n\r\nNumerical calculations have also been conducted for the pressure oscillations in side-dump ramjet engines. The flowfields have been constructed in two regions: the inlet section, including a region of fuel injection, and a dump combustor. Each region is treated separately and matched with the other at the dump plane. Following the calculation of the mean flowfield, the oscillatory characteristics of the engine are determined by its response to a disturbance imposed on the mean flow. Results for the frequencies and mode shapes have shown good agreement with the experimental data reported by the Naval Weapons Center, China Lake.
\r\n" }, { "name": "Yu, Paul Kit-Lai", "degree": "PhD", "year": "1984", "title": "Long Wavelength InGaAsP/InP Lasers and Optoelectronic Integration", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232007-131641", "creators": [ { "name": { "family": "Yu", "given": "Paul Kit-Lai" }, "id": "Yu-Paul-Kit-Lai", "display_name": "Yu, Paul Kit-Lai" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Margalit", "given": "Shlomo" }, "id": "Margalit-Shlomo", "role": "chair", "display_name": "Margalit, Shlomo" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Neugebauer", "given": "Gerry" }, "id": "Neugebauer-G", "role": "member", "display_name": "Neugebauer, Gerry" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4dk7-wn36", "abstract": "The light sources for optical communications in the 1.3-1.5 \u00b5m range are the quaternary InGaAsP/InP lasers which emit in this low loss region of optical fibers. The structure and properties of some lasers fabricated in this material system as well as their integration into optoelectronics are treated in this thesis.
\r\n\r\nLasers exhibiting low threshold, high power and stable far field are extremely desirable in communication systems. Selective epitaxial growth offers an elegant yet powerful technique of fabricating laser structures with these properties. Its application to, as well as properties of, the resulting laser structures are presented. In particular, a laser with high output power is demonstrated.
\r\n\r\nTo further extend the operating power of index guided laser diodes in a stable fundamental mode, gain stabilization is proposed as an effective means of discriminating against higher order transverse mode operation. The optimal design for gain stabilized fundamental mode operation is formulated theoretically and verified experimentally.
\r\n\r\nPrecipitous increase of threshold current with temperature has been observed in some InGaAsP/InP lasers. Electron leakage over the heterobarrier has been identified as the cause of this abnormality. The origin as well as the control of these leaked carriers is studied.
\r\n\r\nAdvances in optoelectronic integration consisting of diffraction coupled arrays and the demonstration of Laser-MISFET devices and the technique of microcleaved mirrors are described in detail.
\r\n\r\nThe microcleavage technique is applied to the fabrication of very short cavity lasers. The advantages of short cavities are presented.
\r\n" }, { "name": "Zur, Amikam", "degree": "PhD", "year": "1984", "title": "Theoretical Investigations of Solid Interfaces: 1. The Position of the Fermi Level at a Metal-Semiconductor Interface. 2. Geometric Lattice Match and Its Application to Heteroepitaxy. 3. Ab-Initio Calculation of the Elastic Properties of Silicon, Using Small Clusters", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222007-152908", "creators": [ { "name": { "family": "Zur", "given": "Amikam" }, "id": "Zur-Amikam", "display_name": "Zur, Amikam" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/w8vp-2g07", "abstract": "The work presented in this thesis is concerned with theoretical investigations of the electronic, geometric, and elastic properties of solid interfaces. The interfacial electronic property studied was the effect of doping on the Fermi-level position at a metal-semiconductor interface. Geometric lattice match in heteroepitaxy was studied using a novel method of systematically determining every possible orientation of the two crystals which would result in lattice match at the interface between the two crystals. Finally, the parameters of several elastic models that can be used in calculating the elastic properties of silicon interfaces were computed, using ab-initio quantum-chemistry methods. The predictions of these models to bulk elastic properties were compared to experimental results to test the models.
\r\n\r\n(1) Chapter 1 presents the effect of semiconductor doping on the Fermi-level position at a metal-semiconductor interface. A model based on the concept of a dipole layer was used. The number of chargeable defects at the interface required to pin the Fermi level was determined in the limits of thin and thick metallic coverages. The calculations included the metal response to large charge transfer at the interface, using a jellium model for the metal.
\r\n\r\nThe major findings of this chapter are:
\r\n\r\n\u2022 It takes about 1014defects \u2022 cm-2 to pin the Fermi level in a bulk metal-semiconductor interface, but only about 1012defects \u2022 cm-2 during the initial stages of metallization.
\r\n\r\n\u2022 The Fermi-level position at the metal-semiconductor interface may be very different for n- and p- type semiconductors during the initial steps of metallization. These Fermi-level positions seem to stabilize after the creation of about 1012defects \u2022 cm-2 (which usually corresponds to less than a monolayer of metallic coverage). However, as the metallization proceeds, the two Fermi-level positions on n- and p-type semiconductors should merge to within 0.05 eV at the interface (for doping not exceeding 1017 cm-3).
\r\n\r\n\u2022 During the initial steps of metallization most of the carriers required to charge the defects come from the semiconductor. When the metallic overlayer is fully grown, it is the metal that contributes most of the charge.
\r\n\r\n\u2022 The potential difference between the metal surface and bulk, in the jellium model, changes quadratically with charge removed or added to the surface. For a charge density of 1014 electrons/cm2 removed from the surface, the slope of the potential vs. charge removed is of the order of 1V per 1014e \u2022 cm-2 or less.
\r\n\r\n(2) In Chapter 2 the relevance of lattice mismatch to heteroepitaxiall growth was investigated. A novel method to determine all the possible lattice matches between any two given materials, with any given crystal structure, has been developed. This method allows for an arbitrary periodic reconstruction of the interface. Such reconstruction results in two-dimensional superlattices on both sides of the interface, that have to be similar to each other. The input parameters to these calculations, besides the crystal structure of both materials, are the upper bound on the superlattice unit cell areas, and the maximum allowed mismatch in unit cell dimensions. This method was applied to study known heteroepitaxial interfaces of CdTe on GaAs, CdTe on sapphire, silicon on sapphire, and transition-metal silicides on silicon, to determine the relevance of lattice match in heteroepitaxy. For the last class of materials, namely, silicides on silicon, we list many possible lattice matches, including many that have not been grown so far.
\r\n\r\nThe principal results described in Chapter 2 are:
\r\n\r\n\u2022 A good lattice match is not necessary for epitaxial growth of a single crystal on another.
\r\n\r\n\u2022 In those cases checked in which the epitaxial layer is metallic (silicide on silicon) and a single crystal, there is a good lattice match (bulk mismatch of 2.5% or less).
\r\n\r\n\u2022 Even a polycrystalline epitaxial layer may have some epitaxial relations, that is, some preferred orientations of the crystallites with respect to the substrate. In this case mismatches of up to 15% may be present; this means that the lattice match requirement is probably irrelevant.
\r\n\r\n(3) In Chapter 3 the elastic properties of silicon are calculated using four models. The parameters of these models were calculated from the elastic constants of a small silicon cluster (Si5H12) using ab-initio quantum-chemistry methods. The calculated elastic properties were compared to experimental results to assess the quality of the models.
\r\n\r\nThe main findings are:
\r\n\r\n\u2022 All four different models yield a phonon-band structure which is qualitatively correct but not very accurate numerically.
\r\n\r\n\u2022 The deviations of the model predictions from experimental results were attributed to the models and not to the quantum-chemistry methods used to obtain their parameters.
\r\n\r\n\u2022 The LA branch of the phonon-band structure agreed very well with experiment in all the different models used.
\r\n\r\n\u2022 The TA branch of the phonon-band structure was in poor agreement with experiment in all the four models; in particular, the slopes of the TA branch near the \u0393 point (which determine the elastic constants c12 and c44) were inaccurate.
\r\n\r\n\u2022 The accuracy of the calculated optical phonons varied among the four models.
\r\n\r\n\u2022 Elastic properties associated with bond stretching were calculated much more accurately than elastic properties associated with bond bending.
" }, { "name": "Abu-Mostafa, Yaser Said", "degree": "PhD", "year": "1983", "title": "Complexity of Information Extraction", "advisor": "Psaltis, Demetri", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142003-111719", "creators": [ { "name": { "family": "Abu-Mostafa", "given": "Yaser Said" }, "id": "Abu-Mostafa-Yaser-Said", "display_name": "Abu-Mostafa, Yaser Said" } ], "advisors": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "advisor", "display_name": "Psaltis, Demetri" } ], "committee": [ { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "chair", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Kechris", "given": "Alexander S." }, "id": "Kechris-A-S", "orcid": "0000-0002-2226-0423", "role": "member", "display_name": "Kechris, Alexander S." }, { "name": { "family": "McEliece", "given": "Robert J." }, "id": "McEliece-R-J", "role": "member", "display_name": "McEliece, Robert J." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." }, { "name": { "family": "Ryser", "given": "Herbert J." }, "id": "Ryser-H-J", "role": "member", "display_name": "Ryser, Herbert J." }, { "name": { "family": "Wilson", "given": "Richard M." }, "id": "Wilson-R-M", "role": "member", "display_name": "Wilson, Richard M." } ], "option_major": [ "eleceng" ], "doi": "10.7907/FVKM-7J60", "abstract": "This thesis describes a mathematical theory that interrelates the basic concepts of complexity, cost, information and reliability. The accessibility of information, as opposed to its availability, is characterized. Universal bounds for complexity distribution, implementation cost and decision reliability are estimated. These bounds give rise to a methodology for any consistent definition of a complexity measure. The basic notions of pattern recognition and information theory are directly related to computational complexity.
" }, { "name": "Awad, Elias A.", "degree": "PhD", "year": "1983", "title": "Nonlinear Acoustics Instabilities in Combustion Chambers", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182006-131617", "creators": [ { "name": { "family": "Awad", "given": "Elias A." }, "id": "Awad-Elias-A", "display_name": "Awad, Elias A." } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/h9sr-tq76", "abstract": "In this report, we show, following a second order expansion in the pressure amplitude, analytical expressions for the amplitude, and the conditions for existence and stability of limit cycles for pressure oscillations in combustion chambers. Two techniques are used. The first technique is an asymptotic-perturbation technique where the asymptotic oscillatory behavior is sought by expanding the asymptotic solution in a measure of the amplitude of the wave, mainly the amplitude of the fundamental. The second technique is a perturbation-averaging technique where an approximate solution is sought by applying a perturbation method followed by an expansion of the solution in the normal modes of the acoustic field in the chamber. It is shown, to third order in the amplitude of the wave, that both techniques yield the same results regarding the amplitude and the conditions for existence and stability of the limit cycle. However, while the first technique can be extended to higher orders in the pressure amplitude, the second technique suffers serious difficulties. The advantage of the second technique is in its ability to handle easily a large number of modes.
\r\n\r\nA stable limit cycle seems to be unique. The conditions for existence and stability are found to be dependent only on the linear parameters. The nonlinear parameter affects only the wave amplitude. In very special cases, the initial conditions can change the stability of the limit cycle. The imaginary parts of the linear responses, to pressure oscillations, of the different processes in the chamber play an important role in the stability of the limit cycle. They also affect the direction of flow of energy among modes. In the absence of the imaginary parts, in order for an infinitesimal perturbation in the flow to reach a finite amplitude, the lowest mode must be unstable while the highest must be stable; thus energy flows from the lowest mode to the highest one. The same case exists when the imaginary parts are non-zero, but in addition, the contrary situation is possible. There are conditions under which an infinitesimal perturbation may reach a finite amplitude if the lowest mode is stable while the highest is unstable. Thus energy can flow \"backward\" from the highest mode to the lowest one. It is also shown that the imaginary parts increase the final wave amplitude.
\r\n\r\nSecond, the triggering of pressure oscillations in solid propellant rockets is discussed. In order to explain the triggering of the oscillations to a non-trivial stable limit cycle, the treatment of two modes and the inclusion in the combustion response of either a second order nonlinear velocity coupling or a third order nonlinear pressure coupling seem to be sufficient. Moreover, some mechanisms which are likely to be responsible for triggering are identified.
\r\n" }, { "name": "Barzegar, Farhad, Farhad", "degree": "PhD", "year": "1983", "title": "Problems in Switched-Mode DC and AC Power Conversion", "advisor": "Cuk, Slobodan; Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132006-144011", "creators": [ { "name": { "family": "Barzegar, Farhad", "given": "Farhad" }, "id": "Barzegar-Farhad", "display_name": "Barzegar, Farhad, Farhad" } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "chair", "display_name": "Wilts, Charles Harold" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/qr7n-cj36", "abstract": "Several issues in the field of Power Electronics are discussed in this thesis. Part I first reviews the method of state-space averaging to analyze steady state and small-signal behavior of switched-mode dc-to-dc converters. The approach is then generalized to encompass multiple inputs and a general form of feedback system. Since the method involves matrix manipulations it is well suited for computer computation. The Switching Converter Analysis Program is developed to implement the state-space averaging method, and requires computational power only of a small desktop computer. This, together with another program which performs frequency response measurement of the actual system, constitute a powerful design tool for power electronics engineers.
\r\n\r\nPart II extends the basic one-quadrant switching dc-to-dc converter to both current and voltage bidirectionality. The proposed \"push-pull\" power amplifier, being a four-quadrant converter, is capable of interfacing dc and ac ports. This special capability is then exploited to introduce a single-stage ac Uninterruptible Power Supply (UPS), which can process power from dc to ac or from ac to dc. Since with the form used only one of these accomplishments is required at a time, a single converter performs as a complete system. Hence, this UPS system is reliable and economical.
\r\n\r\nFinally, Part III further generalizes the switching power amplifier to polyphase operation in such a way that a minimal number of power converters is required. Then, through a set of steps a new polyphase power amplifier is introduced. The idea is experimentally verified by a 1 hp variable-speed motor drive with regulated output voltages. The technique has many other advantages such as ease of paralleling, dc isolation, and voltage boost, etc. The generality of the technique makes it suitable for many other line related applications such as uninterruptible power supplies, unity power factor battery chargers, and battery-to-three-phase line interfaces.
" }, { "name": "Blauvelt, Henry A.", "degree": "PhD", "year": "1983", "title": "New Structures for AlGaAs Lasers and Avalanche Photodetectors", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-09072006-080636", "creators": [ { "name": { "family": "Blauvelt", "given": "Henry A." }, "id": "Blauvelt-Henry-A", "display_name": "Blauvelt, Henry A." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/DJMZ-S785", "abstract": "This thesis describes the fabrication and the properties of five new semiconductor laser diode structures. All of these devices were grown from the GaAs-AlGaAs ternary system using the liquid phase epitaxial technique. In addition, a new low noise avalanche photodetector is proposed.
\r\n\r\nThe first example is a new technique for fabricating cleaved mirrors without cleaving through the substrate. This technique, called micro-cleavage, has potential applications for both opto-electronic integrated circuits and for the fabrication of short cavity length lasers. In this technique, cantilevers are formed by a sequence of etching steps. These cantilevers are subsequently cleaved using ultrasonic vibrations.
\r\n\r\nThree devices related to high power single mode lasers are described. The first of these is the large optical cavity buried heterostructure window laser. The output power of semiconductor lasers, particularly during pulsed operation is limited by catastrophic mirror damage which occurs at power densities above a pulse width dependent damage threshold. The damage occurs due to local heating up to the melting point of the active region in the vicinity of the cleaved mirror facets. However, catastrophic mirror damage can be avoided by isolating the active layer from the cleaved mirrors, as is done in these window lasers. The second device related to high power that is described is the Inverted Strip Buried Heterostructure laser. These lasers combine many of the best features of both the buried optical guide lasers and the strip buried heterostructure that have been previously developed elsewhere. The inverted strip buried heterostructure lasers have significantly better beam quality than buried optical guide lasers and can be operated in the fundamental spatial mode for larger emitting areas (and therefore greater output power). The third device related to high power lasers is a variation of a buried heterostructure laser in which the injected current is confined to a narrow section in the center of the active layer. The optical gain is therefore also confined to a narrow section in the center of the active layer. By doing so the fundamental mode is much better matched to the optical gain than the higher order spatial modes. The result is that fundamental mode operation is possible for buried heterostructure lasers with active layer widths up to 8 \u00b5m. When the current is injected uniformly into the active layer, fundamental mode operation is possible only for active layer widths less than 2 \u00b5m. In addition to the descriptions of these devices a theoretical chapter on high power single mode lasers is included.
\r\n\r\nThe final laser structure that is described is a single liquid phase epitaxial growth laser structure in which the current is restricted to flow between two narrow stripes located above and below the active layer. This structure, which is fabricated using a meltback-growth technique allows the current injection to be restricted to a very narrow section of the active layer, which results in several interesting properties which are described and explained using a simple model.
\r\n\r\nThe final subject of this thesis is a multilayer avalanche photodetector (APD) which has been proposed for low noise applications. The noise generated by an APD is dependent on the statistics of the carrier multiplication process, since positive feedback effects, which exist when both electrons and holes produce secondary pairs, can greatly amplify any current fluctuations. Significantly more noise is generated if the electron and hole ionization rates (\u03b1, \u03b2) are equal than if only one carrier produces secondary pairs. The multilayer structure described and analyzed in this chapter is expected to have impact ionization which is dominated by electrons and therefore would be of importance for low noise applications.
" }, { "name": "Botelho, Dirceu Luiz Rodrigues", "degree": "PhD", "year": "1983", "title": "An Empirical Model for Vortex-Induced Vibrations", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272018-115401142", "creators": [ { "name": { "family": "Botelho", "given": "Dirceu Luiz Rodrigues" }, "id": "Botelho-Dirceu-Luiz-Rodrigues", "display_name": "Botelho, Dirceu Luiz Rodrigues" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "civileng" ], "doi": "10.7907/T3ZS-SH29", "abstract": "Through an analytical-empirical approach, the vortex-excited transverse oscillations of flexibly-mounted circular cylinders in a uniform flow is studied.
\r\n\r\nA new model is derived, assuming spanwise constant flow velocity within the sub-critical range of Reynolds numbers and using only experimental data obtained from forced cylinders in water.
\r\n\r\nThe steady-state response of flexibly-mounted cylinders is obtained as a function of the structural system and flow parameters and its stability is analyzed. Several characteristics observed experimentally and also present in the model response are discussed.
\r\n\r\nThe resultant model's capability for predicting structural response for a wide range of fluid mediums is illustrated through comparisons between model predictions and results obtained experimentally from flexibly-mounted cylinders in air and in water.
\r\n\r\nThis model developed is expected to yield better results for structures in water, by virtue of being based only on experimental results obtained in water.
" }, { "name": "Chamieh, Dimitri Suhayl", "degree": "PhD", "year": "1983", "title": "Forces on a Whirling Centrifugal Pump-Impeller", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152006-083609", "creators": [ { "name": { "family": "Chamieh", "given": "Dimitri Suhayl" }, "id": "Chamieh-Dimitri-Suhayl", "display_name": "Chamieh, Dimitri Suhayl" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "member", "display_name": "Rannie, W. Duncan" } ], "option_major": [ "mecheng" ], "doi": "10.7907/vnqy-ne26", "abstract": "The present work is an experimental and theoretical investigation of the possible forces of fluid dynamic origin that can act on a turbomachine rotor particularly when it is situated off its normal center position. An experimental facility, the Rotor Force Test Facility, has been designed and constructed in order to measure these kinds of forces acting on a centrifugal pump impeller when the latter is made to whirl in a slightly eccentric circular orbit. The rotor speed, eccentric orbital radii and whirl speed could be varied independently. The scope of the present experimental work consists of measuring quasi-steady forces on the impeller as it whirls slowly about the axis of the pump rotation. These forces are due to interaction between the impeller and volute; they are decomposed into force components relative to the geometric center of the volute and to those proportional to displacement from this center. These latter are interpreted as stiffness matrices. These matrices were measured on two widely differing volute types and both were found to have the property of being skew-symmetric. It can be shown that a stiffness matrix of this type can lead to dynamic instability of the impeller shaft system in certain circumstances. This new experimental finding may explain some operational problems of \"high speed\" hydraulic machinery.
\r\n\r\nIn the theoretical part of this thesis, a somewhat more physical model of a rotor pump is proposed other than has been used heretofore in most works namely an actuator disk having infinitely many blades. As a simplification it is assumed that the flow field is irrotational. Forces and stiffness matrices are calculated on this basis but the stiffness matrix so found does not reveal the skew-symmetric property of the experiments.
" }, { "name": "Chen, Marina Chien-mei", "degree": "PhD", "year": "1983", "title": "Space-time Algorithms: Semantics and Methodology", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312006-094203", "creators": [ { "name": { "family": "Chen", "given": "Marina Chien-mei" }, "id": "Chen-Marina-Chien-mei", "display_name": "Chen, Marina Chien-mei" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Kechris", "given": "Alexander S." }, "id": "Kechris-A-S", "orcid": "0000-0002-2226-0423", "role": "member", "display_name": "Kechris, Alexander S." }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "display_name": "Mead, Carver" } ], "option_major": [ "compsci" ], "doi": "10.7907/bfpj-t811", "abstract": "A methodology for specifying concurrent systems is presented. A model of computation for concurrent systems is presented first. The syntax and semantics of the language CRYSTAL are introduced. The specification of a system is called a space-time algorithm since space and time are explicit parameters in the description. Fixed-point semantics is used for abstracting the behavior of a system from its implementation. The consistency between an implementation and its description can therefore be ensured using this method. Formal semantics for an arbitrary transistor network is given. An \"interpreter\" for space-time algorithms -- a hierarchical simulator -- for VLSI systems is presented. The framework can be viewed as a concurrent programming notation when describing communicating processes and as a hardware description notation when specifying integrated circuits.
" }, { "name": "Chiou, Arthur Er-Terg", "degree": "PhD", "year": "1983", "title": "I. Parametric Study of Optically Pumped Far-Infrared Waveguide Lasers. II. Theory and Experiment of Folded Fabry-Perot Quasi-Optical Ring Resonator Diplexer", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312006-083650", "creators": [ { "name": { "family": "Chiou", "given": "Arthur Er-Terg" }, "id": "Chiou-Arthur-Er-Terg", "display_name": "Chiou, Arthur Er-Terg" } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "chair", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "member", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/eeh1-p029", "abstract": "This thesis consists of two parts, each representing a different aspect of far-infrared (FIR) physics and technology.
\r\n\r\nPart I deals with the problems related to the physics and the design of one of the extremely useful coherent sources in the FIR region of the electromagnetic spectrum: the optically-pumped FIR waveguide laser. The effects of small waveguide diameter were studied here particularly because of their importance to the practical realization of a compact coherent FIR laser. Two known theoretical models were used to analyze the performance of CH3OH 118 \u00b5m laser and CH3F 496 \u00b5m laser; the results from these models were compared with the results of our experimental parametric study on CH3OH 118 \u00b5m laser. A simplified model of Lourtioz and Adde agrees reasonably well, in a semiquantitative sense, with our experimental results. The \u03bb2/a3 dependence of distributed waveguide loss for FIR radiation turns out to be the major factor that limits the waveguide size.
\r\n\r\nPart II deals with a problem related to the physics and design of a diplexer for application in the FIR heterodyne radiometry, where signals from the local oscillator and the received signal have to be directed into a detector for frequency mixing and for further signal processing. Since the signal of interest is typically very weak, the diplexer should serve the dual purpose of directing the two beams and filtering out the unwanted frequency components (noise) to enhance the signal to noise ratio, and do so with minimum loss.
\r\n\r\nThe optimum design parameters for a folded Fabry-Perot quasi-optical ring resonator diplexer were derived, and its performance was investigated both theoretically and experimentally. The results were compared with those of the similar diplexers of non-optimum geometry. The advantages and limitations of the optimum diplexer design are analyzed.
" }, { "name": "Chiu, Liew-Chuang", "degree": "PhD", "year": "1983", "title": "III-V Semiconductor Lasers and Detectors", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062006-131347", "creators": [ { "name": { "family": "Chiu", "given": "Liew-Chuang" }, "id": "Chiu-Liew-Chuang", "display_name": "Chiu, Liew-Chuang" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "chair", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Margalit", "given": "Shlomo" }, "id": "Margalit-Shlomo", "role": "member", "display_name": "Margalit, Shlomo" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Whaling", "given": "Ward" }, "id": "Whaling-W", "role": "member", "display_name": "Whaling, Ward" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ttgs-8a70", "abstract": "The subjects of this thesis can be divided into two main categories: III-V semiconductor lasers and detectors. The first two chapters are concerned with the InGaAsP/InP laser diodes. The final two chapters are related to fundamental problems in the avalanche photodiodes and the new class of quantum well infrared detectors.
\r\n\r\nThe kinetics of the mass transport phenomenon in InP is studied experimentally. Application of this technique to laser fabrication has resulted in very low threshold terrace mesa lasers.
\r\n\r\nThe continuing problem of the excess temperature sensitivity of InGaAsP lasers and light emitting diodes is studied in detail. Non-radiative Auger recombination and electron leakage are found to be important factors affecting the temperature sensitivities of these devices.
\r\n\r\nImpact ionization in the GaAlSb system is investigated. The resonant nature of the enhanced impact ionization of holes is discussed. Further enhancement is predicted to be possible in quantum well structures.
\r\n\r\nThe new class of quantum well infrared detectors is described. Theoretical considerations on absorption coefficients and other parameters essential to device design and performance are discussed.
" }, { "name": "Clemens, Bruce Montgomery", "degree": "PhD", "year": "1983", "title": "Superconductivity as a Structural Characterization Tool in Amorphous Materials", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112002-182754", "creators": [ { "name": { "family": "Clemens", "given": "Bruce Montgomery" }, "id": "Clemens-Bruce-Montgomery", "orcid": "0000-0001-6070-9140", "display_name": "Clemens, Bruce Montgomery" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Mercereau", "given": "James E." }, "id": "Mercereau-J-E", "role": "member", "display_name": "Mercereau, James E." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/GTS1-9E08", "abstract": "This thesis presents the use of superconductivity as a structural probe for studying amorphous and metastable materials. The characteristics of the superconducting state which facilitate its use as a probe are explained, followed by a description of some of the properties of the materials studied. The superconducting measurements performed were critical current, transition temperature and upper critical field. Materials prepared by rapid quench from the melt, sputter deposition and ion beam mixing were studied. The critical current measurements performed on liquid quenched materials reflect three pinning mechanisms. Crystalline inclusions in otherwise amorphous (Mo0.6Ru0.4)80Si10B10 produced a dramatic increase in critical current. The pinning in purely amorphous (Mo0.6Ru0.4)82B18 was shown to be affected by pinning by surface roughness on the sample edges. This contribution can be eliminated by a proper sample geometry and electropolish treatment. The bulk pinning in purely amorphous (Mo0.6Ru0.4)82B18 was shown to first decrease and then increase as a function of annealing time. This reflects the disappearance of quenched in inhomogeneous strains and excess volume defects followed by the growth of an inhomogeneity such as compositional phase segregation during an anneal. The upper critical field was measured for liquid quenched (Mo0.6Ru0.4)1-xBx for x = 0.12, 0.18 and 0.22 both before and after an anneal. The annealed samples exhibited greater transition widths and more curvature in the Hc2(T) curves than the unannealed samples which are evidence for a growth of inhomogeneities upon annealing. Measurements on sputter deposited (Mo0.6Ru0.4)82B18 were performed on samples sputtered in low (5 \u00b5m) and high (75 \u00b5m) Ar pressure, The material sputtered in low Ar pressure had a greater drop in Tc than the liquid quenched material and a pinning profile which exhibited a peak near Hc2. The sample sputtered in high Ar pressure was very inhomogeneous as evidenced by transition width and flux pinning force profile. Measurements were performed on ion beam mixed Mo55Ru45. The structure consisted of an amorphous matrix with crystalline inclusions. The pinning profile was characteristic of a strong pinning mechanism. The pinning force decreased then increased as a function of ion beam dose. This reflects the destruction of the remnants of the original structure followed by the formation of an inhomogeneity such as \u03c3-MoRu or Xe gas bubbles during ion beam irradiation.
" }, { "name": "Connolly, Jeremiah Finbarr", "degree": "PhD", "year": "1983", "title": "Two Problems in Plane Finite Elastostatics", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182006-085128", "creators": [ { "name": { "family": "Connolly", "given": "Jeremiah Finbarr" }, "id": "Connolly-Jeremiah-Finbarr", "display_name": "Connolly, Jeremiah Finbarr" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "chair", "display_name": "Sternberg, Eli" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/yhjy-mb48", "abstract": "In this paper the fully nonlinear equilibrium theory of homogeneous and isotropic incompressible elastic solids is used to study the elastostatic fields in plane strain near the point of application of a concentrated force on a deformed half plane and near the vertex of a circular sector whose plane deformed faces are subjected to prescribed tractions.
\r\n\r\nIn the concentrated force problem, restricting only the form of the elastic potential at large extensional deformations, it is shown that, for materials which \"harden\" in simple shear, the displacement is bounded at the point of application of the load. This is not the case for materials which \"soften\" in shear. Estimates of the true stress tensor near the singular point are given.
\r\n\r\nIn the sector problem, for a class of the materials mentioned, the deformation and stress field near the vertex of the deformed cross-section are derived and discussed.
\r\n" }, { "name": "DeBenedictis, Erik Penn", "degree": "PhD", "year": "1983", "title": "Techniques for Testing Integrated Circuits", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062006-111645", "creators": [ { "name": { "family": "DeBenedictis", "given": "Erik Penn" }, "id": "DeBenedictis-Erik-Penn", "orcid": "0000-0001-6079-4787", "display_name": "DeBenedictis, Erik Penn" } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "chair", "display_name": "Seitz, Charles L." }, { "name": { "family": "Bryant", "given": "Randy" }, "id": "Bryant-R", "role": "member", "display_name": "Bryant, Randy" }, { "name": { "family": "Fox", "given": "Geoffrey C." }, "id": "Fox-G-C", "role": "member", "display_name": "Fox, Geoffrey C." }, { "name": { "family": "Johnsson", "given": "S. Lennart" }, "id": "Johnsson-S-Lennart", "role": "member", "display_name": "Johnsson, S. Lennart" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "compsci" ], "doi": "10.7907/ZKWD-NR73", "abstract": "A language is presented for describing tests of integrated circuits. The language has a high abstractive capability that enables test specifications to follow the structural or logical organization of a design. The test language is applied to a number of current design styles in a series of examples. Methods for designing integrated circuits for testability are demonstrated. An implementation of the test language through a test language interpreter and a tester is discussed. Tester designs are presented that will execute the test language with unusually high efficiency.
" }, { "name": "Dolson, Mark Barry", "degree": "PhD", "year": "1983", "title": "A Tracking Phase Vocoder and its Use in the Analysis of Ensemble Sounds", "advisor": "Pierce, John Robinson", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312006-105836", "creators": [ { "name": { "family": "Dolson", "given": "Mark Barry" }, "id": "Dolson-Mark-Barry", "display_name": "Dolson, Mark Barry" } ], "advisors": [ { "name": { "family": "Pierce", "given": "John Robinson" }, "id": "Pierce-J-R", "display_name": "Pierce, John Robinson" } ], "committee": [ { "name": { "family": "Pierce", "given": "John" }, "id": "Pierce-J", "role": "chair", "display_name": "Pierce, John" }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "member", "display_name": "Posner, Edward C." } ], "option_major": [ "eleceng" ], "doi": "10.7907/0RC3-V146", "abstract": "Additive analysis-synthesis using the phase vocoder is a powerful tool for the exploration of musical timbre. In this research, previous investigations of this subject are extended in two significant directions.
\r\n\r\nFirst, an improved analysis of the phase vocoder is developed to explain the errors introduced by undersampling and modification of the magnitude and phase-derivative signals. Two sources of error are identified. It is shown that the first of these involves crosstalk between adjacent frequency channels, and can be eliminated through the development of a tracking version of the phase vocoder. Alternatively, restrictions can be placed on the phase-derivative signal to preserve the absolute phase. The second source of error appears to be inherent in the phase vocoder formulation.
\r\n\r\nSecondly, the tracking phase vocoder is used to investigate differences between solo and ensemble sounds. A search is conducted for the minimal set of cues which will produce an ensemble sensation. It is shown that the primary requirement is that there be at least four to eight harmonics, each of which has a characteristic amplitude modulation proportional to its frequency. In addition, a number of issues related to the quality of the ensemble sensation and its efficient synthesis are examined.
" }, { "name": "Erickson, Robert Warren, Jr.", "degree": "PhD", "year": "1983", "title": "Large Signals in Switching Converters", "advisor": "Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-01112006-110638", "creators": [ { "name": { "family": "Erickson", "given": "Robert Warren, Jr." }, "id": "Erickson-Robert-Warren", "orcid": "0000-0003-3877-8398", "display_name": "Erickson, Robert Warren, Jr." } ], "advisors": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "chair", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" }, { "name": { "family": "Wood", "given": "Lincoln" }, "id": "Wood-L", "role": "member", "display_name": "Wood, Lincoln" }, { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "member", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CN9A-WY51", "abstract": "The behavior of switching converters under large-signal conditions is modelled and analyzed. Two major problems are of interest: the reduction of the distortion which occurs in switching amplifiers, and the stabilization of switching regulators for all transients which are expected to occur.
\r\n\r\nIn Part 1, a large-signal model is described which predicts the simple harmonic distortion generated inherently by switched-mode amplifiers. The causes of this distortion are identified, and relatively simple design techniques for its reduction to an acceptable level are presented. A particularly attractive feature of the method is the ability to compute harmonic magnitude and phase using linear circuit models and Bode plots.
\r\n\r\nThe method is extended to account for intermodulation distortion. Additional effects not described by the model are also discussed, including crossover distortion and bandwidth limitations.
\r\n\r\nAlthough in its simplest form the buck converter is inherently linear, considerable distortion may arise when it is preceded by an input filter. This problem is solved as an example of the usefulness and circuit-oriented nature of the method.
\r\n\r\nIn Part 2, a large-signal switching regulator model is derived, and prominent features of the transient response are determined. In particular, the various regions of operation are identified in the state plane, analytical expressions are found for the equilibrium points of the system, and computer-generated transient waveforms are obtained.
\r\n\r\nAs an example, a boost regulator is investigated, and is found to be stable for small signals but unstable for large transients. Approximate analytical expressions are found for the waveforms and salient features of the response, and a number of ways of obtaining global stability are discussed.
\r\n\r\nExperimental evidence is presented to verify both the distortion and stability analyses.
" }, { "name": "Gharib, Morteza (Mory)", "degree": "PhD", "year": "1983", "title": "The Effect of Flow Oscillations on Cavity Drag, and a Technique for their Control", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-133001", "creators": [ { "name": { "family": "Gharib", "given": "Morteza (Mory)" }, "id": "Gharib-Morteza", "orcid": "0000-0003-0754-4193", "display_name": "Gharib, Morteza (Mory)" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "member", "display_name": "Blandford, Roger D." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JJYA-CK31", "abstract": "The phenomenon of cavity flow oscillation is investigated to determine the conditions for onset of periodic oscillations and to understand the relationship between the state of the shear layer and the cavity drag. Experiments have been performed in a water tunnel using a 4\" axisymmetric cavity model instrumented with a strip heater on the nose cone and pressure taps in and around the cavity. A complete set of measurements of oscillation phase, amplitude amplification along the flow direction, distribution of shear stress and other momentum flux is obtained by means of a laser Doppler velocimeter. Drag measurements were made by integrating the mean pressure over the solid surfaces of the cavity. Results indicated exponential cavity drag dependence on the length of the cavity. A jump in the cavity drag coefrcient is observed as the cavity flow shows a bluff body wake type behavior. An independent estimate of the drag, which is obtained by integration of shear and mean momentum transfer terms over the peripheral area of the cavity, confirms the exponential dependence of drag on the length of the cavity. Results, also reveal that the drag of the cavity in the non-oscillating mode is less than the case if the cavity were replaced by a solid surface. Natural and forced oscillations of the cavity shear layer spanning the gap are studied. The forced oscillations are introduced by a sinusoidally heated thin-film strip which excites the Tollmein-Schlichting waves in the boundary layer upstream of the gap, For a sufficiently large gap, self-sustained periodic oscillations are observed while for smaller gaps, which do not oscillate naturally, periodic oscillations can be obtained by external forcing through the strip-heater. In the latter case resonance is observed whenever the forcing frequency satisfies the phase criterion \u03c6/(2\u03c0) = N, and its amplitude exceeds certain threshold levels, but the phenomenon is non-self-supporting. The drag of the cavity can be increased by one order of magnitude in the non-oscillating case through external forcing. For naturally occurring oscillations, it is possible for two waves to co-exist in the shear layer (natural and forced). Also, it is possible to completely eliminate mode switching by applying external forcing. For the first time a test is performed to cancel or dampen the amplitude of Kelvin-Helmholtz wave in the cavity shear layer. This is done through introducing an external perturbation with the same frequency of the natural component but having a different phase. Reduction by a factor of 2 is obtained in the amplitude of the oscillation.
" }, { "name": "Goh, Chuen Jin", "degree": "PhD", "year": "1983", "title": "Analysis and Control of Quasi Distributed Parameter Systems", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092005-091223", "creators": [ { "name": { "family": "Goh", "given": "Chuen Jin" }, "id": "Goh-Chuen-Jin", "display_name": "Goh, Chuen Jin" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Wood", "given": "Lincoln" }, "id": "Wood-L", "role": "member", "display_name": "Wood, Lincoln" }, { "name": { "family": "Thompson", "given": "Peter M." }, "id": "Thompson-Peter-M", "role": "member", "display_name": "Thompson, Peter M." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/96PH-6521", "abstract": "As engineering systems become larger and more flexible, serious consideration must be given to the very high order, and consequently very high bandwidth, of these so called quasi-distributed parameter systems. In particular, as practical active control devices such as sensors and actuators have finite bandwidth, great care must be exercised so that control of low frequency modes does not cause instability of intermediate and high frequency modes. In this report, the nature of these stability problems is investigated in the context of direct velocity feedback control, and approximate bounds on the diagonal elements of the modal gain matrix are derived. Two velocity feedback techniques are proposed to alleviate potential instability, but these are dependent on the natural damping of the system, which remains uncertain in practice. Another technique using position feedback is considered. Despite certain additional complications, position feedback control proves to be more advantageous in many ways than velocity feedback. Some preliminary analyses on a quasi-linear vibration suppression technique via damping matrix modification are also presented. The feasibility of these theoretical techniques are confirmed by means of a numerical simulation on a simply supported discrete shear beam.
\r\n" }, { "name": "Harder, Christoph S.", "degree": "PhD", "year": "1983", "title": "Bistability, High Speed Modulation, Noise and Pulsations in GaAlAs Semiconductor Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062006-083609", "creators": [ { "name": { "family": "Harder", "given": "Christoph S." }, "id": "Harder-Christoph-S", "display_name": "Harder, Christoph S." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Peck", "given": "Charles W." }, "id": "Peck-C-W", "role": "member", "display_name": "Peck, Charles W." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" } ], "option_major": [ "eleceng" ], "doi": "10.7907/jxwz-e844", "abstract": "This thesis describes seven different subjects relevant to semiconductor laser diodes which fall in the following three categories: Bistability and pulsations, high speed modulation and noise.
\r\n\r\nBistable semiconductor lasers based on inhomogeneous current injection, achieved with a split contact scheme, were proposed around 20 years ago. However, actual devices showed no or only a small hysteresis and they were in addition beset by pulsations for reasons not well understood at the time. In this thesis we show that lasers with an optimized design can display bistability with a giant hysteresis. Crucial to the understanding of the bistable laser is a negative differential resistance across the absorber section, reminiscent of a tunnel diode characteristic. Depending on the electrical biasing circuit this negative differential resistance leads to bistability or light-jumps and self-pulsations. A simple model based on the conventional rate equations explains the observed behavior. Investigation of the switching dynamics of this optoelectronic device reveals a delay time which is critically dependent on the trigger pulse amplitude and which is typically in the order of a few nanoseconds at a power-delay product of 100pJ. We also investigate the characteristic of this laser coupled to an external optical cavity and we demonstrate that this bistable laser can be used as a self-coupled stylus for optical disk readout. Under a different biasing condition this laser coupled to an external optical cavity can be used to generate ultrashort optical pulses through passive mode locking. Unlike previous mode locking techniques, the method presented here does not rely on absorption introduced by damaging the crystal and is consequently much more reliable.
\r\n\r\nThe high speed modulation behavior of semiconductor lasers is investigated theoretically and experimentally. In this thesis we derive the fundamental limits of injection lasers for pulse modulation and small signal modulation. We place emphasis on developing laser structures optimized for high frequency modulation and experiments on such structures show that they can be modulated at frequencies up to 8GHz. At these frequencies the parasitic elements can no longer be neglected and they are included in the analysis.
\r\n\r\nThe noise equivalent circuit of a semiconductor laser diode is derived from the rate equations including Langevin noise sources. This equivalent circuit allows a straightforward calculation of the noise and frequency modulation characteristics of a laser diode combined with electronic components. The field spectrum of injection lasers is observed also experimentally. It is a unique feature of injection lasers that their linewidth is increased through a strong amplitude phase coupling by the factor (1 + \u03b12) where \u03b1 is the linewidth enhancement factor. A model is developed which shows that the same factor \u03b1 enters in the small signal modulation characteristics and a careful measurement of the small signal amplitude and phase modulation at high frequencies enables us to obtain this important factor \u03b1 for the first time by a direct measurement.
" }, { "name": "Heymans, Luc J.", "degree": "PhD", "year": "1983", "title": "An Engineering Analysis of Polymer Film Adhesion to Rigid Substrates", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152007-111322", "creators": [ { "name": { "family": "Heymans", "given": "Luc J." }, "id": "Heymans-Luc-J", "display_name": "Heymans, Luc J." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Tschoegl", "given": "Nicholas W." }, "id": "Tschoegl-N-W", "role": "member", "display_name": "Tschoegl, Nicholas W." }, { "name": { "family": "Fornberg", "given": "Bengt" }, "id": "Fornberg-Bengt", "role": "member", "display_name": "Fornberg, Bengt" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3GQW-YP87", "abstract": "An important source of interface fracture contributing to adhesive failure in a bimaterial sandwich, consisting of a rigid substrate and a viscoelastic encapsulant material, arises from residual stresses. The encapsulant is often deposited on the substrate above its glass transition temperature region but used below this temperature range. In order to determine the magnitude of the residual stresses a viscoelastic stress analysis of a bimaterial sandwich is carried out, taking into account the time-dependent material properties of the polymeric layer and the environmental \"loading\" conditions. The theoretical analysis is paralleled by an experimental examination of the time-dependent out-of-plane deformation of thin, circular sandwiches.
\r\n\r\nPolyvinyl acetate was chosen as a model material exhibiting significant viscoelastic effects under room test conditions. Therefore the pertinent physical and mechanical properties of PYAc are determined; these include the thermal coefficient of expansion, the shear creep compliance and the relaxation modulus. In the experimental work BK-7 glass is taken as the \"rigid\" substrate. The measurements connected to the stress analysis are monitored with laser interferometry (Newton's rings). A comparison between theory and experiment completes the viscoelastic stress analysis.
\r\n\r\nIn the second part of this study time dependent adhesive failure of rubbery materials is investigated. Polymeric materials are being used increasingly for a wide variety of applications. Some of these materials are applied as protective layers to isolate their substrates from a hostile environment. Others achieve remarkable structural bond strengths thereby displacing the traditional mechanical fasteners like bolts and rivets. If one wants to investigate the long time integrity of a layer assembly the time dependence of the material properties of the adhesives needs to be carefully analyzed. This time dependence is also reflected in the energy required to create new surfaces as interfacial debonding proceeds the adhesive fracture energy is one of the dominant parameters in time dependent adhesive failure. In our investigation it is characterized through peel testing.
\r\n\r\nWith the knowledge of the pertinent material properties as well as of the adhesive fracture energy, we then proceed to formulate a criterion for continuing interfacial crack propagation. The analysis is carried out for elastic solids, with the effect of viscoelastic behavior incorporated later on. Debond tests provide a way to check how well the theoretical predictions correspond to experimental debond results.
" }, { "name": "Hopkins, Stuart Thomas", "degree": "PhD", "year": "1983", "title": "Low Temperature Specific Heat Studies of Molybdenum-Ruthenium Based Superconducting Metallic Glasses", "advisor": "Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102002-125642", "creators": [ { "name": { "family": "Hopkins", "given": "Stuart Thomas" }, "id": "Hopkins-Stuart-Thomas", "display_name": "Hopkins, Stuart Thomas" } ], "advisors": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/TJRF-S955", "abstract": "Low temperature specific heat measurements have been used to investigate the electronic structure and superconducting properties of metallic glasses based on transition metals Mo and Ru alloyed with metalloids B and Si. An apparatus constructed for making these measurements is described. The results obtained are discussed in terms of the dependence of the density of states at the Fermi level N(\u03b5F) and of the Debye temperature \u03b8D on metalloid content, and the influence of these parameters on observed properties. N(\u03b5F) is shown to reflect the short-range order of the metal atoms and in Mo-Ru-B alloys, indicates the existence of two distinct amorphous phases. In addition, N(\u03b5F) strongly influences the superconductivity and electronic properties of these materials. Alloying with metalloids increases the Debye temperature of the amorphous Mo-Ru phase and thus affects the superconductivity through the dependence of the electron-phonon coupling on average phonon frequency. A comparison with elastic properties shows an anomalous effect in the lattice specific heat commonly observed in insulating glasses.
" }, { "name": "Jain, Sudhir Kumar", "degree": "PhD", "year": "1983", "title": "Analytical Models for the Dynamics of Buildings", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08162019-113014700", "creators": [ { "name": { "family": "Jain", "given": "Sudhir Kumar" }, "id": "Jain-Sudhir-Kumar", "display_name": "Jain, Sudhir Kumar" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "chair", "display_name": "Jennings, Paul C." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" } ], "option_major": [ "civileng" ], "doi": "10.7907/4k04-ca84", "abstract": "This thesis investigates the significance of in-plane floor flexibility on the dynamics of buildings, and develops analytical models for structures that have flexible floor diaphragms. Experience with past earthquakes demonstrates that this feature is particularly important for long, narrow buildings and buildings with stiff end walls. In the method developed in this study, the equations of motion and appropriate boundary conditions for various elements of the structure are written in a single coordinate system and then are solved exactly.
\r\n\r\nOne- and two-story buildings with end walls are analyzed by treating their floors and walls as bending and shear beams, respectively. The resulting equations of motion and the boundary conditions are solved to obtain the dynamic properties of the structure. The expected low torsional stiffness of the end walls or frames is confirmed by analysis of a single-story example structure. Study of a similar two-story building showed that the first two modes, dominated by the floor and the roof vibrations, make the largest contributions to the total base shear in the structure.
\r\n\r\nFloors of multistory buildings with end walls (or frames) are idealized as equivalent, distributed beams while the walls or frames are treated as bending or shear beams. Analysis of a nine-story building showed that the structure possesses several lower modes in which floors vibrate essentially as pinned-pinned beams.
\r\n\r\nBuildings with large numbers of uniform stories and frames (or walls) are treated as vertically-oriented anisotropic plates. It is concluded that the floors in such buildings can be assumed rigid for seismic analysis, since the modes involving floor deformations are not excited by uniform ground motion.
\r\n\r\nThe approach can be generalized further to study more complex structures. An example is the Imperial County Services Building, which has two end walls in the upper stories and several walls in the ground story. The analytical model of this building predicts several important features of the complex dynamic behavior of the structure.
\r\n" }, { "name": "Levit, Itzhak", "degree": "PhD", "year": "1983", "title": "A General Solution Strategy for Large Scale Static and Dynamic Nonlinear Finite Element Problems Employing the Element-by-Element Factorization Concept", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09012006-080048", "creators": [ { "name": { "family": "Levit", "given": "Itzhak" }, "id": "Levit-Itzhak", "display_name": "Levit, Itzhak" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hughes", "given": "Thomas J. R." }, "id": "Hughes-T-J-R", "role": "member", "display_name": "Hughes, Thomas J. R." }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "mecheng" ], "doi": "10.7907/jqbq-rc43", "abstract": "It is proposed to solve large-scale finite-element equation systems arising in structural and solid mechanics by way of an element-by-element approximate factorization technique which obviates the need for a global coefficient matrix. The procedure has considerable operation count and I/O advantages over direct elimination schemes and it is easily implemented. Numerical results demonstrate the effectiveness of the method and suggest its potential for the analysis of large-scale systems.
" }, { "name": "Megdal, Barry Bruce", "degree": "PhD", "year": "1983", "title": "VLSI Computational Structures Applied to Fingerprint Image Analysis", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:03202012-091934255", "creators": [ { "name": { "family": "Megdal", "given": "Barry Bruce" }, "id": "Megdal-Barry-Bruce", "display_name": "Megdal, Barry Bruce" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" }, { "name": { "family": "Fox", "given": "Geoffrey C." }, "id": "Fox-G-C", "role": "member", "display_name": "Fox, Geoffrey C." }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "compsci" ], "doi": "10.7907/9tyn-bc11", "abstract": "Advances in integrated circuit technology have made possible the application of LSI and VLSI techniques to a wide range of computational problems. Image processing is one of the areas that stands to benefit most from these techniques. This thesis presents an architecture suitable for VLSI implementations which enables a wide range of image processing operations to be done in a real-time, pipelined fashion. These operations include filtering, thresholding, thinning and feature extraction.
\r\n\r\nThe particular class of images chosen for study are fingerprints. There exists a long history of fingerprint classification and comparison techniques used by humans, but previous attempts at automation have met with little success. This thesis makes use of VLSI image processing operations to create a graph structure representation (minutia graph) of the inter-relationships of various low-level features of fingerprint images. An approach is then presented which allows derivation of a metric for the similarity of these graphs and of the fingerprints which they represent. An efficient algorithm for derivation of maximal common subgraphs of two minutia graphs serves as the basis for computation of this metric, and is itself based upon a specialized clique-finding algorithm. Results of cross comparison of fingerprints from multiple individuals are presented.
" }, { "name": "Moody, Douglas Marion, Jr.", "degree": "PhD", "year": "1983", "title": "I. Numerical Solution of the Superfluid Shock Jump Conditions. II. Experimental Investigation of the Liquid Helium II-Vapor Interface", "advisor": "Goodstein, David L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08312006-081008", "creators": [ { "name": { "family": "Moody", "given": "Douglas Marion, Jr." }, "id": "Moody-Douglas-Marion", "display_name": "Moody, Douglas Marion, Jr." } ], "advisors": [ { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "advisor", "display_name": "Goodstein, David L." } ], "committee": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "chair", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/387M-V435", "abstract": "Numerical Solution of the Superfluid Shock Jump Conditions
\r\n\r\nThe four fundamental conservation equations of superfluid mechanics may be integrated across a one-dimensional discontinuity (shock wave) propagating into undisturbed helium II to yield a set of four algebraic equations (jump conditions) which, when supplemented by thermodynamic state information, establish the equilibrium flow state behind the shock wave for a given wave speed and undisturbed flow state ahead of the shock. These jump conditions have been solved numerically for 19 points on the helium II p-T diagram with upstream Mach number as the independent parameter. Representative results of the calculations are presented for pressure shocks, temperature raising shocks, and temperature lowering shock. The results are compared to previous analytical approximate solutions to test the validity of those approximation. They are also compared to experimental data for shock waves in helium II as a means of testing the correctness of the full, nonlinear two-fluid equations.
\r\n\r\nExperimental Investigation of the Liquid Helium II-Vapor Interface
\r\n\r\nAn apparatus was designed and constructed to measure the linear reflection and transmission coefficients for weak second sound shocks impinging upon the liquid-vapor interface of helium II. The measured reflection coefficients reproduce the work of previous authors, giving values which are roughly 20% higher than those predicted by thermodynamic equilibrium theory. The transmitted pressure wave speed was measured, and was found to be sonic within the limits of experimental precision. Therefore strength could not be deduced from time of flight measurements. Direct amplitude measurements of this weak wave were prevented by the film which coats the sensors in the vapor. For these reasons, the attempted transmission coefficient measurements were unsuccessful.
\r\n" }, { "name": "Mungal, Mark Godfrey", "degree": "PhD", "year": "1983", "title": "Experiments on Mixing and Combustion with Low Heat Release in a Turbulent Shear Flow", "advisor": "Dimotakis, Paul E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142006-144655", "creators": [ { "name": { "family": "Mungal", "given": "Mark Godfrey" }, "id": "Mungal-Mark-Godfrey", "display_name": "Mungal, Mark Godfrey" } ], "advisors": [ { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "advisor", "display_name": "Dimotakis, Paul E." } ], "committee": [ { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "chair", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Broadwell", "given": "James E." }, "id": "Broadwell-J-E", "role": "member", "display_name": "Broadwell, James E." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QZ4F-V692", "abstract": "A new blowdown facility to study mixing and combustion in a turbulent shear layer has been built. The system is capable of 100 m/s for three seconds in a 5 x 20 cm exit area on the high speed side, and 50 m/s in a 10 x 20 cm exit area on the low speed side. Dilute concentrations of hydrogen and fluorine, carried in an inert gas, react when both fluid streams meet at the tip of a splitter plate. The reaction is spontaneous, rapid, and highly exothermic. The resulting temperature field has been studied using a rake of eight fast response thermometers placed across the width of the layer. Runs have been performed for low heat release over a wide range of equivalence (concentration) ratios, at a Reynolds number of 30,800 based on velocity difference and vorticity thickness. The heat release is sufficiently low so that the overall properties of the mixing layer are not significantly changed from the cold case.
\r\n\r\nThe results show the presence of large, hot structures within the flow together with cool, irrotational tongues of freestream fluid that penetrate deep into the layer. Thus, it is possible for the entire width of the layer to be quite hot, owing to the passage of a large structure, or for the layer to be quite cool, owing to the presence of the cool fluid tongues. The mean temperature results from a duty cycle whereby a given point in the flow sees alternating hot and cool fluid which averages into the local mean. The mean temperature profiles do not achieve the adiabatic flame temperature at any location across the layer, with the maximum mean temperature, depending upon the equivalence ratio, varying from 54% to 67% of the adiabatic flame temperature. The location of the maximum mean temperature shifts by about 25% of the visual thickness of the layer for a change of equivalence ratio by a factor of 64. The amount of product formed in the layer is compared to earlier measurements in water, and, it is found that at a speed ratio of 0.40, there exists 20 to 25% more product in gaseous flows, implying that molecular diffusion, or in nondimensional form the Schmidt number, plays a role in mixing at large Reynolds number. The present results compare favorably with the recent theoretical model of Broadwell and Breidenthal for mixing and chemical reaction in a turbulent shear layer. With this model it is possible to bring the results for gases and liquids into quantitative agreement.
" }, { "name": "Neches, Philip Malcolm", "degree": "PhD", "year": "1983", "title": "Hardware Support for Advanced Data Management Systems", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08102006-083426", "creators": [ { "name": { "family": "Neches", "given": "Philip Malcolm" }, "id": "Neches-Philip-Malcolm", "display_name": "Neches, Philip Malcolm" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/BH0Y-Q162", "abstract": "This thesis considers the problem of the optimal hardware architecture for advanced data management systems, of which the REL system can be considered a prototype. Exploration of the space of architectures requires a new technique which applies widely varying work loads, performance constraints, and heuristic configuration rules with an analytic queueing network model to develop cost functions which cover a representative range of organizational requirements. The model computes cost functions, which are the ultimate basis for comparison of architectures, from a technology forecast. The discussion shows the application of the modeling technique to thirty trial architectures which reflect the major classifications of data base machine architectures and memory technologies. The results suggest practical design considerations for advanced data management systems." }, { "name": "Norton, Olin Perry", "degree": "PhD", "year": "1983", "title": "The Effects of a Vortex Field on Flames with Finite Reaction Rates", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112006-111139", "creators": [ { "name": { "family": "Norton", "given": "Olin Perry" }, "id": "Norton-Olin-Perry", "display_name": "Norton, Olin Perry" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "chair", "display_name": "Kubota, Toshi" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/7vn8-4078", "abstract": "A diffusion flame, supported by a one-step chemical reaction, is initiated along the horizontal axis between a fuel occupying the upper half-plane and an oxidizer below. Simultaneously, a vortex of circulation \u0393 is established at the origin. As time progresses the flame is extended and \"wound up\" by the vortex flow field. The effect of distortion of the flame is locally described by the time-dependent straining of a one-dimensional flame. The rate of chemical reaction is represented by the characteristic chemical reaction time, tch, of the system. The combustion field then consists of a totally reacted core region and an external flame region consisting of a pair of spiral arms extending off at large radii toward their original positions.
\r\n\r\nThe presence of the vortex increases the rate of fuel consumption of the flame. For large values of \u0393/D, the augmentation of fuel consumption due to the vortex is proportional to \u03c1\u03932/3D1/3, and is a function of t/tch which approaches a constant value as t \u2192 \u221e. The growth of the fuel consumption rate from zero to its steady value for large times is governed by the time scale tch. If the products of combustion occupy more volume than the original reactants, then the spiral flame will appear as an unsteady volume dilitation for times on the order of the chemical time. An unsteady volume dilitation acts as an acoustic source, so the interaction of a vortex and a diffusion flame is shown to result in the generation of a pressure pulse; the peak pressure occurring after a delay proportional to the chemical time, and the strength of the pulse proportional to \u03932/3D1/3 and inversely proportional to \u221atch.
\r\n\r\nThese results are valid for hypergolic reaction systems in which the reactant temperature does not significantly effect the rates of the chemical reactions. For systems described as having \"large activation energy\", the rates are strongly temperature dependent and another description is appropriate. For these systems, a vortex established on an already ignited flame exhibits, in addition to the features described above, an extinct core of unburned reactants if the circulation of the vortex is large.
\r\n\r\nThe results provide the fundamental structure for the mechanism of combustion instability proposed by Rogers and Marble in 1956.
" }, { "name": "O'Sullivan, Timothy Christopher", "degree": "PhD", "year": "1983", "title": "The Propagation and Arrest of an Edge Crack in an Elastic Half-Space Under Conditions of Anti-Plane Shear: Analytical and Numerical Results", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09052006-082841", "creators": [ { "name": { "family": "O'Sullivan", "given": "Timothy Christopher" }, "id": "O'Sullivan-Timothy-Christopher", "display_name": "O'Sullivan, Timothy Christopher" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "chair", "display_name": "Sternberg, Eli" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "display_name": "Knowles, James K." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/jb3j-5460", "abstract": "The motion of an edge crack extending non-uniformly in an elastic half-space under conditions of anti-plane shear is analyzed. An expression for the stress intensity factor at the crack tip is obtained, and an energy balance crack propagation criterion is used to find the equation of motion of the tip. On solving this equation numerically, it is found that crack arrest occurs before the second reflected wave from the boundary reaches the tip.
\r\n\r\nIn the second half of this investigation, a numerical procedure for studying anti-plane shear crack propagation problems using finite differences is developed. To approximate the elastodynamic field as accurately as possible near the moving crack tip, where singular stresses occur, the local asymptotic displacement field near the tip is incorporated into the finite difference scheme. The numerical procedure is applied to the edge crack problem analyzed in the first part of this study, and the numerical and exact results are compared.
" }, { "name": "Pence, Thomas James", "degree": "PhD", "year": "1983", "title": "The Emergence and Propagation of a Phase Boundary in an Elastic Bar", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09052006-154543", "creators": [ { "name": { "family": "Pence", "given": "Thomas James" }, "id": "Pence-Thomas-James", "orcid": "0000-0002-5136-3384", "display_name": "Pence, Thomas James" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "chair", "display_name": "Sternberg, Eli" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/85D8-5A19", "abstract": "This dissertation is concerned with the dynamical analysis of an elastic bar whose stress-strain relation is not monotonic. Sufficiently large applied loads then require the strain to jump from one ascending branch of the stress-strain curve to another such branch. For a special class of these materials, a nonlinear initial-boundary value problem in one-dimensional elasticity is considered for a semi-infinite bar whose end is subjected to either a monotonically increasing prescribed traction or a monotonically increasing prescribed displacement. If the stress at the end of the bar exceeds the value of the stress at any local maximum of the stress-strain curve a strain discontinuity or \"phase boundary\" emerges at the end of the bar and subsequently propagates into the interior. For classically smooth solutions away from the phase boundary, the problem is reducible to a pair of differential-delay equations for two unknown functions of a single variable. The first of these two functions gives the location of the phase boundary, while the second characterizes the dynamical fields in the high-strain phase of the material. In these equations the former function occurs in the argument of the latter, so that the delays in the functional equations are unknown. A short-time analysis of this system provides an asymptotic description of the emergence and initial propagation of the phase boundary. For large-times, a different analysis indicates that the phase boundary velocity approaches a constant which depends on material properties and on the ultimate level reached by the applied load as well. Higher order corrections depend on the detailed way in which the load is applied. Estimates for the various dynamical field quantities are given and a priori conditions are deduced which determine whether the phase boundary eventually becomes the leading disturbance.
" }, { "name": "Rashed, Ahmed Atef", "degree": "PhD", "year": "1983", "title": "Dynamic Analyses of Fluid-Structure Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01252019-143659174", "creators": [ { "name": { "family": "Rashed", "given": "Ahmed Atef" }, "id": "Rashed-Ahmed-Atef", "display_name": "Rashed, Ahmed Atef" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "chair", "display_name": "Housner, George W." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." } ], "option_major": [ "civileng" ], "doi": "10.7907/1yc0-fm70", "abstract": "Theoretical investigations of the dynamic behavior of some important fluid-structure systems are conducted to seek a better understanding of: 1) the hydrodynamic pressures generated in the fluid as a result of both the rigid body and the vibrational motions of the structure, and 2) the effects of the fluid on the dynamic properties of the structure as well as on its response to earthquake ground motions.
\r\n\r\nExplicit formulas are presented for the hydrodynamic pressures generated in fluid domains having boundaries which can be approximated by simple geometries. Such domains may be reservoirs behind dams, or around intake towers, water around bridge piers or liquids stored in circular cylindrical tanks. The formulas are used to calculate the hydrodynamic pressures analytically and the results are exhibited in a form showing the pressure dependence on the various parameters of the problem.
\r\n\r\nThe fluid-structure interaction problems of long straight walls, having uniform rectangular sections, and long straight gravity dams, having uniform triangular sections, are investigated. The natural frequencies of vibration and the associated mode shapes are found in the former case, through a fully analytical approach for both the structure and the fluid domains, and in the latter, by discretizing the dam into finite elements and treating the reservoir as a continuum by boundary solution techniques. A method is presented for computing the earthquake response of both structures, based on superposition of their free vibrational modes.
\r\n\r\nThe problems of limited length dam or wall-reservoir systems are investigated. The natural frequencies of the structure and the corresponding mode shapes are found by the Rayleigh-Ritz method. This method is also used to obtain the frequency domain response of the structure to all three components of the ground motion. The validity of the two dimensional approximation, often made in the analysis of gravity dams, and the effect of the length to height ratio on the dynamic properties and response of the structure are studied.
\r\n\r\nTime domain responses to arbitrary earthquake ground motions are evaluated by superposing the frequency domain responses, to individual Fourier components of the excitation, through the Fourier Integral. For efficiency of computation, a fast Fourier analysis is used for both the forward transform of the ground excitation and the inverse transform of the Fourier Integral.
" }, { "name": "Sargent, William Stapf", "degree": "PhD", "year": "1983", "title": "Natural Convection Flows and Associated Heat Transfer Processes in Room Fires", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02052007-132409", "creators": [ { "name": { "family": "Sargent", "given": "William Stapf" }, "id": "Sargent-William-Stapf", "display_name": "Sargent, William Stapf" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "chair", "display_name": "Kubota, Toshi" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/n7kr-k165", "abstract": "This report presents the results of experimental investigations of natural convection flows and associated heat transfer processes produced by small fires in rooms with a single door or window opening. Calculation procedures have been developed to model the major aspects of these flows.
\r\n\r\nTwo distinct sets of experiments were undertaken.
\r\n\r\nFirst, in a roughly 1/4 scale facility, a slightly dense solution of brine was allowed to flow into a tank of fresh water. The resulting density difference produced a flow which simulated a very small fire in a room with adiabatic walls. Second, in an approximately 1/2 scale test room, a nearly stoichioinetric mixture of air and natural gas was burned at floor level to model moderate strength fires. In this latter facility, we directly measured the heat conducted through the walls, in addition to determining the gas temperature and composition throughout the room.
\r\n\r\nThese two facilities complemented each other. The former offered good flow visualization and allowed us to observe the basic flow phenomena in the absence of heat transfer effects. On the other hand, the latter, which involved relatively larger fires, was a more realistic simulation of an actual room fire, and allowed us to calculate the convective heat transfer to the ceiling and walls. In addition, the stronger sources present in these 1/2 scale tests produced significant secondary flows. These secondary flows along with heat transfer effects act to modify the gas temperature or density profiles within the room from those observed in the 1/4 scale experiments.
\r\n\r\nSeveral calculation procedures have been developed, based on the far field properties of plumes when the density differences are small (the Boussinesq approximation). The simple point source plume solution is used along with hydraulic analysis of flow through an orifice to estimate the temperatures of the hot ceiling layer gas and of the cooler floor zone fluid, as well as the height of the interface between them. A finite source plume model is combined with conservation equations across the interface to compute the evolution of the plume above the interface. This calculation then provides the starting point for an integral analysis of the flow and heat transfer in the turbulent ceiling jet.
\r\n\r\nThe computed results both for the average floor and ceiling zone gas temperatures, and for the connective heat transfer in the ceiling jet agreed reasonably well with our experimental data. This agreement suggests that our computational procedures can be applied to answer practical questions, such as whether the connective heat flux from a given fire in a real room would be sufficient to trigger sprinklers or other detection systems in a given amount of time.
" }, { "name": "Speriosu, Virgil Simon", "degree": "PhD", "year": "1983", "title": "X-ray Rocking Curve and Ferromagnetic Resonance Investigations of Ion-Implanted Crystals", "advisor": "Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072002-110622", "creators": [ { "name": { "family": "Speriosu", "given": "Virgil Simon" }, "id": "Speriosu-Virgil-Simon", "display_name": "Speriosu, Virgil Simon" } ], "advisors": [ { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles H." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/BET3-1831", "abstract": "A kinematical model for general Bragg case x-ray diffraction in nonuniform films is presented. The model incorporates depth-dependent strain and structure factor. For ion-implanted crystals the change in structure factor attributed to damage is calculated using a spherically symmetric Gaussian distribution of incoherent atomic displacements. Profiles of strain and structure factor are obtained by fitting experimental rocking curves. The method is applicable to ion-implanted, diffused and multilayer crystalline structures such as heterojunctions and superlattices.
\r\n\r\nA comparison is made between profiles of strain and incoherent atomic displacements obtained from rocking curves and from Rutherford backscattering spectrometry in a Gd3Ga5O12 crystal implanted with 100 keV Ne+. The ranges of sensitivity of the two techniques-overlap for about one decade in implantation dose up to the amorphous threshold. Xray diffraction was found to be most sensitive to low damage levels while backscattering was found to be most sensitive to high damage levels. The two techniques are in excellent agreement on the near-surface strain, but differ significantly at depths below \u2243 500A. The discrepancy is attributed to errors caused by steering of channelled particles in backscattering spectrometry. The profiles of number of displaced atoms agree within a factor of two.
\r\n\r\nThe rocking curve method is combined with analysis of ferromagnetic resonance (FMR) spectra for characterization of crystalline and magnetic properties of [111]-oriented Gd,Tm,Ga:YIG films implanted with Ne+, He+, and H2+. For each implanted species the range of doses begins with easily-analyzed effects and ends with paramagnetism or amorphousness. Profiles of normal strain, lateral strain and damage were obtained. For maximum strains up to 1.3% the behavior of the strain with annealing is nearly independent of implanted species or dose. Magnetic profiles obtained before and after annealing were compared with the strain profiles. The local change in uniaxial anisotropy field \u0394Hk with increasing strain shows an initially linear rise for both He+ and Ne+, in quantitative agreement with the magnetostriction effect estimated from the composition. For strain values between 1% and 1.5%, \u0394Hk saturates and for increasing strain, \u0394Hk decreases to nearly zero when the material becomes paramagnetic. For peak strains greater than 1.3% for He+ and 1.1% for Ne+ the relation between uniaxial anisotropy and strain is not unique. Behavior of the saturation magnetization 4\u03c0M, the exchange constant A and the cubic anisotropy H1 was elucidated. For H2+ implantation the total \u0394Hk consists of a magnetostrictive contribution due to strain and of a comparable excess contribution associated with the local concentration of hydrogen. The profile of excess \u0394Hk agrees with calculated LSS range. The presence of hydrogen results in a reduction of 4\u03c0M not attributable to strain or damage. With increasing annealing temperature the excess \u0394Hk diminishes and above 400\u00b0C the only component of \u0394Hk is magnetostrictive.
\r\n\r\nCrystalline properties of Si-implanted [100] GaAs, Si, and Ge were studied by the rocking curve method. Sharp qualitative and quantitative differences were found between the damage in GaAs on one hand and Si and Ge on the other. At a moderate damage level the GaAs crystal undergoes a transition from elastic to plastic behavior. The plastically deformed region presents a barrier to epitaxial regrowth and is consistent with the well-known high defect density in regrown GaAs.
" }, { "name": "Stone, Alan Thomas", "degree": "PhD", "year": "1983", "title": "The Reduction and Dissolution of Manganese(III) and (IV) Oxides by Organics", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112006-133416", "creators": [ { "name": { "family": "Stone", "given": "Alan Thomas" }, "id": "Stone-Alan-Thomas", "orcid": "0000-0002-3660-1129", "display_name": "Stone, Alan Thomas" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "chair", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." }, { "name": { "family": "Anson", "given": "Fred C." }, "id": "Anson-F-C", "role": "member", "display_name": "Anson, Fred C." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "List", "given": "John A." }, "id": "List-J-A", "role": "member", "display_name": "List, John A." } ], "option_major": [ "envreng" ], "doi": "10.7907/MSQ2-M609", "abstract": "Although it is known that manganese oxides are solubilized by reduction in anoxic waters, the chemical processes are poorly understood. A study of the reduction and dissolution of manganese oxide suspensions by twenty-seven organic substrates that have chemical structures similar to those of natural organics was undertaken to determine the rates and mechanisms of the solubilization reactions.
\r\n\r\nDissolution of suspensions by hydroquinone in the pH range 6.5 < pH < 8.5 is described by the following experimental rate law:
\r\n\r\n(d[Mn2+])/dt = k1{H+}0.46[HQ]1.0(MnT - [Mn2+])
\r\n\r\nwhere [Mn2+] is the amount of dissolved manganese, [HQ] is the hydroquinone concentration, and MnT is the initial amount of manganese oxide. The apparent activation energy of the reaction was found to be +37 kJ/mole. The Mn(III,IV) oxide suspension was prepared by oxidizing a Mn(OH)2(s.) suspension with oxygen, and has a composition characterized by MnO1.66. Suspension particles were between 0.2 and 1.0 microns in diameter. Calcium and phosphate were found to inhibit the dissolution reaction, by adsorbing on the oxide surface.
\r\n\r\nDihydroxybenzenes and methoxyphenols dissolved the suspensions at appreciable rates. Of the aliphatic substrates examined, only ascorbate, oxalate, and pyruvate dissolved the oxide. Dissolution by marine fulvic acid was found to be photocatalyzed.
\r\n\r\nA model was developed to explain the observed rate dependence and the relative reactivity of different organic substrates. The model assumes that complexes between substrate and surface sites form prior to electron transfer and dissolution. The pH dependence is not explained by this model; involvement of H+ in the dissolution of reduced surface sites may be responsible for the observed fractional order with respect to H+.
\r\n" }, { "name": "Tatoian, James Zareh", "degree": "PhD", "year": "1983", "title": "An Analytical Study of Electromagnetic Vector Field Propagation in a Nonlinear Electron Plasma", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312005-133116", "creators": [ { "name": { "family": "Tatoian", "given": "James Zareh" }, "id": "Tatoian-James-Zareh", "display_name": "Tatoian, James Zareh" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "chair", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "member", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Fornberg", "given": "Bengt" }, "id": "Fornberg-Bengt", "role": "member", "display_name": "Fornberg, Bengt" }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" } ], "option_major": [ "appmath" ], "doi": "10.7907/hzt3-s585", "abstract": "From the equations of hydrodynamics and electrodynamics, a system of a coupled nonlinear equations governing the propagation of plane electromagnetic waves in a collisionless electron plasma is obtained. It is shown that solitary wave solutions exist for both the longitudinal and transverse components of the electromagnetic field. It is found that the velocity of the electromagnetic vector solitary wave depends on the amplitudes of all components of the field linearly. The relations among the longitudinal and transverse components that support the solitary waves are determined for different values of plasma temperature. It is shown that while transverse solitary waves cannot exist, except when they are supported by longitudinal waves, the latter can exist by themselves. The dynamics of the plasma electrons during the passage of a longitudinal wave is analyzed and the interaction of such waves with each other is studied. An upper bound on the amplitudes of these waves is obtained. The uniqueness and stability of the longitudinal waves are demonstrated. A Lagrangian density function and two conservation laws for the longitudinal wave equation are found. Frequency spectra of the solitary waves are calculated and their low frequency content is emphasized.
\r\n" }, { "name": "Torczynski, John Robert", "degree": "PhD", "year": "1983", "title": "Second Sound Shock Waves in Rotating Superfluid Helium", "advisor": "Corngold, Noel Robert", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032005-113539", "creators": [ { "name": { "family": "Torczynski", "given": "John Robert" }, "id": "Torczynski-John-Robert", "orcid": "0000-0002-6469-895X", "display_name": "Torczynski, John Robert" } ], "advisors": [ { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "advisor", "display_name": "Corngold, Noel Robert" } ], "committee": [ { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "chair", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Mercereau", "given": "James E." }, "id": "Mercereau-J-E", "role": "member", "display_name": "Mercereau, James E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Y2KN-XM66", "abstract": "Second sound shock waves have been used to examine the breakdown of superfluidity in bulk He II. The maximum counterflow velocity achieved in this manner was measured at a variety of temperatures and pressures. The results are found to agree with predictions of vortex nucleation theories (Langer and Fisher, 1967) in their pressure and temperature dependences although it was shown that dissipation occurred only near the heater. A simple scaling argument is suggested, assuming breakdown occurs near the heater. A vortex dynamics model of breakdown (following the method of Turner, private communication) is developed.
\r\n\r\nTo examine the effect of vorticity on breakdown, second sound shocks were produced in rotating helium. Experiments were performed in which the shocks propagated either along or normal to the axis of rotation, called \"axial\" and \"transverse\" cases, respectively. In both cases the decay was seen to increase monotonically with the rotation rate. Furthermore, the decay was ongoing, rather than being confined to a narrow region near the heater. However, the extraordinary dissipation in the transverse case seemed to be related primarily to the arrival of secondary waves from the heater-sidewall boundary. An explanation of this difference is put forth in terms of vortex nucleation in the bulk fluid, using ideas similar to Crocco's Theorem.
\r\n\r\nIn order to examine the breakdown of superfluidity away from walls in nonrotating fluid, spherically converging second sound shocks were produced. The temperature jumps of the waves were measured, and exact numerical solutions of the two-fluid jump conditions (Moody, 1983) were used to calculate the relative velocity in each case. The experiments show that the processes limiting the counterflow velocity still occur at the heater although the strongest final waves produced have relative velocities in excess of 10 m/sec. These are the largest relative velocities ever produced in the bulk fluid.
\r\n" }, { "name": "Trawick, David James", "degree": "PhD", "year": "1983", "title": "Robust Sentence Analysis and Habitability", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032005-154728", "creators": [ { "name": { "family": "Trawick", "given": "David James" }, "id": "Trawick-David-James", "display_name": "Trawick, David James" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "chair", "display_name": "Thompson, Frederick B." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Thompson", "given": "Bozena H." }, "id": "Thompson-B-H", "role": "member", "display_name": "Thompson, Bozena H." }, { "name": { "family": "Tschoegl", "given": "Nicholas W." }, "id": "Tschoegl-N-W", "role": "member", "display_name": "Tschoegl, Nicholas W." } ], "option_major": [ "compsci" ], "doi": "10.7907/re17-h091", "abstract": "Systems for using subsets of English with computers have progressed much in the area of linguistic coverage of well-formed sentences for a specific task. Some methods have also been devised for the treatment of input that is almost well-formed. Nevertheless, it is still quite easy to stray over the bounds imposed by current natural language systems. Without proper diagnosis, this leads to interactive systems that are not habitable, i.e., systems that are not pleasant to use because they are not able to perform up to the user's expectations.
\r\n\r\nThis thesis presents an overall system for the treatment of several areas normally outside the limit of natural language systems, and for the diagnosis of any input. The system, Robust Sentence Analysis, includes procedures for handling ambiguous input, resolving input with anaphors (e.g. pronouns), making several kinds of major and minor corrections to input, and the interaction of all of these areas. The system does not treat every aspect of these methods of human interaction, but does provide for the more prevalent forms as found in simulations of user interaction in several modes: face-to-face, terminal-to-terminal, and human-to-computer (using a previously implemented natural language system). Thus the system incorporates the most likely forms found in human performance. Diagnostics are designed to lead the user back into the boundaries of the system.
\r\n\r\nThe Robust Sentence Analysis system is implemented as a part of the ASK System, A Simple Knowledgeable System.
" }, { "name": "Trimberger, Stephen Mathias", "degree": "PhD", "year": "1983", "title": "Automated Performance Optimization of Custom Integrated Circuits", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072005-081513", "creators": [ { "name": { "family": "Trimberger", "given": "Stephen Mathias" }, "id": "Trimberger-Stephen-Mathias", "orcid": "0009-0006-5482-3362", "display_name": "Trimberger, Stephen Mathias" } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Goldreich", "given": "Peter Martin" }, "id": "Goldreich-P-M", "role": "member", "display_name": "Goldreich, Peter Martin" }, { "name": { "family": "Lewicki", "given": "George W." }, "id": "Lewicki-G-W", "role": "member", "display_name": "Lewicki, George W." } ], "option_major": [ "compsci" ], "doi": "10.7907/8YDZ-G637", "abstract": "The complexity of integrated circuits requires a hierarchical design methodology that allows the user to divide the problem into pieces, design each piece independently, and assemble the pieces into the complete system. The design hierarchy brings out composition problems, problems that are a property of the assembly as a whole, not of one single instance in the hierarchy.
\r\n\r\nRecent research has produced tools that automate part of the composition task - the logical connection of the pieces. However, these tools do not ensure that signals driven over these connections will be driven sufficiently to give reasonable cycle speed of the resulting chips. It is easily possible to specify an assembly in which a small-sized gate is required to drive an enormous load. Parasitic capacitance of the wiring made automatically by the logical connection tool can be the dominant source of delay, so assembly tools can actually worsen the performance of the circuit and hide this fact from the designer.
\r\n\r\nWhen required to make large circuits, automated layout tools such as PLA generators can blindly make layouts that give abysmally poor performance. Here again, the delay is in a part of circuit that the designer did not specify, so it is hidden. Finding and correcting these problems is a difficult and time-consuming task in integrated circuit design, and one that consumes vastly more people's time and computer time than the simple assembly of the chip.
\r\n\r\nThe task of guaranteeing that circuits meet performance specifications has been left mainly to the designer. Computer aided design has provided analysis tools, tools that tell the designer the performance statistics of the current design. It is then the designer's burden to interpret the performance statistics and use them as guides to make changes in the circuit.
\r\n\r\nThis thesis views performance optimization as an electrical composition task. Poor performance as a result of mismatched loads on devices is a problem of composition and should be corrected by the composition tool. Such a tool is presented in this thesis -- a program that automatically sizes transistors in a symbolic description of a chip to match the load the transistors are driving. The results are encouraging: they show that delays can be cut by a factor of two in many current designs.
" }, { "name": "Ullner, Michael K.", "degree": "PhD", "year": "1983", "title": "Parallel Machines for Computer Graphics", "advisor": "Kajiya, James Thomas", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092005-140159", "creators": [ { "name": { "family": "Ullner", "given": "Michael K." }, "id": "Ullner-Michael-K", "display_name": "Ullner, Michael K." } ], "advisors": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "advisor", "display_name": "Kajiya, James Thomas" } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Sutherland", "given": "Ivan Edward" }, "id": "Sutherland-I-E", "role": "member", "display_name": "Sutherland, Ivan Edward" }, { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "member", "display_name": "Thompson, Frederick B." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" } ], "option_major": [ "compsci" ], "doi": "10.7907/wxmq-sx43", "abstract": "Computer graphics provides some ideal applications for the kind of highly parallel implementations made possible by advances in integrated circuit technology. Specifically, hidden line and hidden surface algorithms, while easily defined and simple in concept, entail a substantial amount of computation. This requirement fits the characteristics of integrated circuit technology, where modular designs involving regular communication between many concurrent operations are rewarded with high performance at an acceptable cost.
\r\n\r\nRay tracing is a very flexible technique that can be used to produce some of the most realistic of all computer generated images by simulating the interactions of light rays with surfaces in a modeled scene. Because light rays are mutually independent, many may be processed simultaneously, and the potential for concurrency is great. One architecture for expediting a ray tracing algorithm consists of a conventional computer equipped with a special purpose peripheral device for locating the intersections of rays and surfaces. This intersection computation is the most time consuming aspect of a ray tracing algorithm. Although the attached processor configuration can produce images more quickly than an unaided computer, its performance is limited. Alternatively, a pipeline of surface processors can replace the peripheral device. Each processor computes the intersections of its stored surface with rays that flow through the pipe. Such a machine machine can be quite fast, and its performance can be increased by lengthening the pipeline, but the component processors are not very effectively utilized. A third approach combines the advantages of the prior two machines by using an array of processors, each simulating a distinct subvolume of the modeled world by treating light rays traveling through space as messages flowing between processors. Local communication is sufficient because light rays travel continuously through space.
\r\n\r\nIn real time computer graphics, successive images must be produced in times that are imperceptible to a viewer. Although the ray tracing machines fall short of this performance, it is possible to compromise image quality in order to produce a highly parallel machine capable of real time operation. The processors in such a machine are organized to form a binary tree. Leaf processors scan-convert surfaces, producing a sequence of segments, where a segment is the portion of a surface that appears on a single scan line of the display. Processors towards the root of the tree accept two such segment sequences and produce a third in which all segment overlap has been resolved. The final image is available at the root of the tree. The communication bottleneck that would otherwise occur at the root can be eliminated by breaking out parallel roots, and the resulting tree may be extended to scenes of almost arbitrary complexity merely by increasing the supply of available processors.
\r\n\r\nMassive parallelism can also be applied to the problem of removing hidden edges from line drawings. A suitable architecture takes the form of a pipeline in which each processor is dedicated to the handling of a single polygon edge. These processors successively clip line segments passing through the pipeline to eliminate portions hidden behind surfaces. Each edge processor can be constructed out of little more than three serial multipliers.
\r\n\r\nThe machines described here are varied in organization, and each functions differently, but their treatment of sorting is one ingredient common to all. Sorting is a key component of hidden surface algorithms running on conventional computers, but its extensive communication requirements make it costly for use in a highly integrated design. Consequently, the highly parallel machines described here operate largely without sorting. Instead, they maintain information in sorted order or make use of already sorted information to limit communication requirements.
" }, { "name": "Valioulis, Iraklis Anestis", "degree": "PhD", "year": "1983", "title": "Particle Collisions and Coalescence in Fluids", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechETD:etd-11082005-142054", "creators": [ { "name": { "family": "Valioulis", "given": "Iraklis Anestis" }, "id": "Valioulis-Iraklis-Anestis", "display_name": "Valioulis, Iraklis Anestis" } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "chair", "display_name": "List, E. John" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Herbolzheimer", "given": "Eric" }, "id": "Herbolzheimer-E", "role": "member", "display_name": "Herbolzheimer, Eric" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/w0ax-hs27", "abstract": "Coagulation, in the physical context, is looked upon here first from the fundamental perspective of collision and coalescence of individual particles. A Monte Carlo technique is used to investigate the particle size distribution in a suspension of coagulating particles when one or more collision mechanisms operate. The effect of interparticle forces - hydrodynamic, van der Waals' and electrostatic - on the collision probability of the particles is examined. The results obtained are used to evaluate the well-known dynamic equilibrium hypothesis according to which an equilibrium particle size distribution is assumed to exist under the action of a given collision mechanism. It is shown that dimensional analysis cannot, in general, be used to predict steady state particle size distributions, mainly because of the strong dependence of the interparticle forces on the sizes of the interacting particles.
\r\n\r\nThe insight into particle kinetics thus gained from the Monte Carlo simulation of collision processes is used to develop a numerical simulation of a rectangular settling basin. The computer model follows the spatial and temporal development of the influent particle size distribution towards the outlet of the tank, accounting for all of the basic kinetics of particle collision and coalescence processes and including transport processes such as particle settling, advection, resuspension and turbulent mixing. The influence of the particle size-density relationship and floc deaggregation by turbulent shearing are also modeled. Of necessity, modeling of some of these processes has been somewhat empirical since the physical and biochemical nature of the flocs are unique to a particular suspension and their determination requires experimental work. The results of the simulations performed indicate that the particle size-density relationship, the collision efficiencies between flocs and the influent particle size distribution are of major importance to the performance of the sedimentation basin. Clearly, further modifications, improvements and trials are needed in order to use the model for the design of new facilities. Nevertheless, the computer model may serve as a guide for selection of several design and operation variables for the successful treatment of a particular waste or the selective removal of pollutants whose concentration depends the shape of the effluent particle size distribution.
" }, { "name": "Zee, Layne", "degree": "PhD", "year": "1983", "title": "Ordinary and Strong Ellipticity in the Equilibrium Theory of Incompressible Hyperelastic Solids", "advisor": "Sternberg, Eli", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012005-130640", "creators": [ { "name": { "family": "Zee", "given": "Layne" }, "id": "Zee-Layne", "display_name": "Zee, Layne" } ], "advisors": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "advisor", "display_name": "Sternberg, Eli" } ], "committee": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "chair", "display_name": "Sternberg, Eli" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/jzka-ce91", "abstract": "In this paper explicit necessary and sufficient conditions are established for the ordinary and strong ellipticity of the three-dimensional field equations in the nonlinear equilibrium theory of incompressible, homogeneous and isotropic, hyperelastic solids. The resulting system of inequalities involves the local principal stretches directly and in addition restricts the first and second partial derivatives of the strain-energy density with respect to the deformation invariants or the principal stretches. The conditions of ordinary and strong ellipticity are found to coalesce for materials that obey the Baker-Ericksen inequalities and possess a positive shear modulus at infinitesimal deformations. Various implications of these ellipticity conditions for special classes of materials and deformations are explored.
" }, { "name": "Zondervan, Keith Peter", "degree": "PhD", "year": "1983", "title": "Optimal Low Thrust, Three Burn Orbit Transfers with Large Plane Changes", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-08152005-091409", "creators": [ { "name": { "family": "Zondervan", "given": "Keith Peter" }, "id": "Zondervan-Keith-Peter", "display_name": "Zondervan, Keith Peter" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Wood", "given": "Lincoln" }, "id": "Wood-L", "role": "member", "display_name": "Wood, Lincoln" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/NXPK-GE17", "abstract": "During the last twenty-five years, much attention has been devoted to the problem of optimal orbit transfer. The problem has been conveniently divided into two categories - unlimited thrust (or acceleration) orbit transfers and limited thrust (or acceleration) orbit transfers. The unlimited thrust orbit transfers use infinite thrust, zero burn time burns and hence have also come to be known as impulsive burn orbit transfers. In general it has been found that optimal (i.e., minimum fuel, time-free) solutions to these types of transfers require two or possibly three burns. The limited thrust transfers, in contrast, do not use impulsive burns but use burns which have a finite thrust level and a nonzero burn time and, hence, are also known as finite burn orbit transfers.
\r\n\r\nIf our attention is restricted to finite multi-burn transfers which have burn times less than an orbital period, two classes of transfers emerge. These classes of transfers are either Geometrically Similar to the 2-Burn Impulsive (GS2BI) transfers or Geometrically Similar to the 3-Burn Impulsive (GS3BI) transfers. For example, if a 2-burn impulsive solution has a perigee burn followed by an apogee burn, the GS2BI finite burn transfer would use one or more perigee burns followed by one or more apogee burns.
\r\n\r\nRecent-studies have presented optimal solutions to GS2BI finite burn orbit transfers for various thrust to weight ratios. The current study presents the optimal solutions to GS3BI finite burn orbit transfers between a 28.5\u00b0 inclined low-earth orbit and a series of 63.4\u00b0 inclined circular orbits and a series of 63.4\u00b0 inclined elliptical orbits with twelve hour periods. Also presented are optimal solutions to GS3BI finite burn orbit transfers between 97\u00b0 inclined high-earth orbits and a 57\u00b0 inclined low-earth orbit. Optimal solutions are found to be bounded by a lower limit on the initial thrust to weight ratio. It is shown that as the final perigee altitude is increased, the GS3BI finite burn transfer degenerates to a GS2BI finite burn transfer much as it would for the impulsive case.
\r\n\r\nAnalysis of the optimal steering during various burns reveals a natural division of the steering strategies into two categories based on whether a burn results in a predominant change in the orbit size-or-the orbit plane. The similarity of these optimal steering strategies to previously obtained simple \"near-optimal\" steering strategies is discussed.
" }, { "name": "Anderson, Lisa", "degree": "PhD", "year": "1982", "title": "Iron Reduction and Micronutrient Nutrition of Juvenile Macrocystis pyrifera (L.) C. A. Agardh (Giant Kelp) Determined by a Chemically Defined Medium, Aquil", "advisor": "North, Wheeler J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202006-152443", "creators": [ { "name": { "family": "Anderson", "given": "Lisa" }, "id": "Anderson-Lisa", "display_name": "Anderson, Lisa" } ], "advisors": [ { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "advisor", "display_name": "North, Wheeler J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Lowenstam", "given": "Heinz A." }, "id": "Lowenstam-H-A", "role": "member", "display_name": "Lowenstam, Heinz A." }, { "name": { "family": "Brokaw", "given": "Charles J." }, "id": "Brokaw-C-J", "role": "member", "display_name": "Brokaw, Charles J." }, { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "member", "display_name": "North, Wheeler J." } ], "option_major": [ "envreng" ], "doi": "10.7907/t2eq-ve46", "abstract": "Iron reduction and micronutrient nutrition of juvenile Macrocystis pyrifera (L.) C. A. Agardh (giant kelp) were investigated using a chemically defined artificial seawater medium, Aquil. Juvenile sporophytes were grown and Aquil formulations were prepared in a Class 1000 cleanroom. Weights of the juveniles at the beginning and end of experiments determined the success of the various Aquil formulations.
\r\n\r\nMicronutrient experiments showed that kelp store surprisingly large quantities of Fe, Mn, Cu, Zn, Mo, Co and I, enough for 20- to 30-fold increases in weight. A maximum growth rate of 0.38 per day was measured for juvenile Macrocystis grown in Aquil. X-ray fluorescence analysis of dried, pressed blades determined kelp tissue element concentrations.
\r\n\r\nKelp grew fastest with 250 nM Fe, 5 nM Mn, 100 nM Zn, 1000 tiM No and 300 mM Co. Concentrations of iodine up to 500 nM I- and of copper up to 500 nM produced neither stimulating nor inhibitory responses. Theoretical chemical species concentrations in Aquil formulations were calculated using the thermodynamic equilibrium computer program REDEQL2.
\r\n\r\nKelp reduced Fe(III) to Fe(II) supporting the hypothesis that prior to uptake, iron is reduced in and then dissociates from the chelate complex, Fe-EDTA. This mediation was enhanced by the presence of light. The effects of photoreduction alone on Fe(III) reduction were studied, establishing its minor contribution as a source of Fe(II).
" }, { "name": "Barker, John Wilson", "degree": "PhD", "year": "1982", "title": "I. Interactions of Fast and Slow Waves in Problems with Two Time Scales. II. A Numerical Experiment on the Structure of Two-Dimensional Turbulent Flow", "advisor": "Kreiss, Heinz-Otto", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182006-090057", "creators": [ { "name": { "family": "Barker", "given": "John Wilson" }, "id": "Barker-John-Wilson", "display_name": "Barker, John Wilson" } ], "advisors": [ { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "advisor", "display_name": "Kreiss, Heinz-Otto" } ], "committee": [ { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "chair", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Luxemburg", "given": "W. A. J." }, "id": "Luxemburg-W-A-J", "role": "member", "display_name": "Luxemburg, W. A. J." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Tadmor", "given": "E." }, "id": "Tadmor-E", "role": "member", "display_name": "Tadmor, E." } ], "option_major": [ "appmath" ], "doi": "10.7907/ynsy-nh46", "abstract": "I. Interaction of Fast and Slow Waves in Problems with Two Time Scales
\r\n\r\nWe consider certain symmetric, hyperbolic systems of nonlinear first-order partial differential equations whose solutions vary on two time scales, a 'slow' scale t and a 'fast' scale t/\u03b5. The large (0(\u03b5-1)) part of the spatial operator is assumed to have constant coefficients, but a nonlinear term multiplying the time derivatives (a 'symmetriser') is allowed.
\r\n\r\nIn physical applications, it is often the case that the fast scale motion is of little interest, and it is desired to calculate only the slow scale motion accurately. It is known that solutions with arbitrarily small amounts of fast scale motion can be obtained by careful choice of the initial data, and that an error of amplitude 0(\u03b5p), where p = 2 for one space dimension or p = 3 for two or three space dimensions, in this choice is allowable, resulting in fast scale waves of amplitude 0(\u03b5p) in the solution.
\r\n\r\nWe investigate what happens when the initial data are not prepared correctly for the suppression of the fast scale motion, but contain errors of amplitude 0(\u03b5). We show that then the perturbation in the solution will also be of amplitude 0(\u03b5). Further, we show that if the large part of the spatial operator is nonsingular in the sense that the number of large eigenvalues of the symbol, P(i\u03c9), of the spatial operator is independent of \u03c9, then the error introduced in the slow scale motion will be of amplitude 0(\u03b52), even though fast scale waves of amplitude 0(\u03b5) will be present in the solution. If the symmetriser is a constant, this holds even if the spatial operator is singular, and further if an error 0(\u03b5\u03bc) is made in the initial conditions, for any \u00b5 > 0, the resulting error in the slow scale motion will be 0(\u03b52\u03bc).
\r\n\r\nOur proofs are based on energy estimates which show that spatial derivatives of the solutions are 0(1), even if time derivatives are not, and the development of the solutions in asymptotic expansions.
\r\n\r\nII. A Numerical Experiment on the Structure of Two-Dimensional Turbulent Flow
\r\n\r\nSome previous theories and numerical calculations pertaining to the problem of two-dimensional turburlence are reviewed, and a new numerical experiment is proposed. The purpose of the experiment is to test the hypothesis that narrow regions of concentrated vorticity are produced in two-dimensional flows by advection of vorticity towards dividing streamlines in regions where the local flow is convergent.
\r\n\r\nThe numerical method to be used is described in detail. It integrates the inviscid Euler equations using a Fourier (pseudo-spectral) method for the space derivatives, and a predictor-corrector method due to Hyman (1979) for time stepping. Dissipation is included, following Fornberg (1977), by a chopping of the amplitudes of the higher Fourier modes every few time-steps. This acts as a high-wavenumber energy sink, allowing very high Reynolds number flows to be simulated with relatively little computational effort.
" }, { "name": "Batchelder, John Samuel", "degree": "PhD", "year": "1982", "title": "The Luminescent Solar Concentrator", "advisor": "Zewail, Ahmed H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152004-162115", "creators": [ { "name": { "family": "Batchelder", "given": "John Samuel" }, "id": "Batchelder-John-Samuel", "display_name": "Batchelder, John Samuel" } ], "advisors": [ { "name": { "family": "Zewail", "given": "Ahmed H." }, "id": "Zewail-A-H", "role": "advisor", "display_name": "Zewail, Ahmed H." } ], "committee": [ { "name": { "family": "Zewail", "given": "Ahmed H." }, "id": "Zewail-A-H", "role": "chair", "display_name": "Zewail, Ahmed H." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Murray", "given": "Bruce C." }, "id": "Murray-B-C", "role": "member", "display_name": "Murray, Bruce C." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/W5W7-9660", "abstract": "The Luminescent Solar Concentrator (LSC) allows sunlight to be concentrated through the use of light pipe trapping of luminescence. Such concentrators do not require tracking, and they can reduce the cost of solar energy conversion by reducing the required area of photovoltaic cells. We have conducted the following experimental and theoretical investigations in order to optimize the LSC's performance.
\r\n\r\nThe spectral characteristics of 18 organic laser dyes are studied for their applicability as luminescing centers. The spectral homogeneity and self-absorption characteristics of representative dyes are examined in detail. The relative spectral homogeneity of such dyes is shown to depend upon the surrounding material using narrow band laser excitation. We develop three independent techniques for measuring self-absorption rates; these are time-resolved emission, steady state polarization anisotropy, and spectral convolution. Prototype devices are tested for performance, and the componant dyes are tested for stability to solar exposure.
\r\n\r\nA model is developed which predicts the efficiency and gain of and LSC from the spectroscopic characteristics of its components. A critical optical density (CODE) is assigned to the dyes surveyed which predicts the self-absorption limited performance for a particular dye. The maximum efficiency of an LSC is found using a simple model and the experimentally measured Stokes shift required to minimize self-absorption.
\r\n\r\nWe find that the performance of LSCs which achieve high light concentration is primarily limited by self-absorption and by photodegradation. The maximum efficiency possible is about 9% in such systems, and present devices can achieve about 3%. A typical lifetime for an LSC using organic laser dyes due to photodegradation is on the order of a month.
" }, { "name": "Bauer, Thomas Patrick", "degree": "PhD", "year": "1982", "title": "Low-Thrust Perturbation Guidance", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-08122005-133355", "creators": [ { "name": { "family": "Bauer", "given": "Thomas Patrick" }, "id": "Bauer-Thomas-Patrick", "display_name": "Bauer, Thomas Patrick" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Wood", "given": "Lincoln" }, "id": "Wood-L", "role": "chair", "display_name": "Wood, Lincoln" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Muhleman", "given": "Duane Owen" }, "id": "Muhleman-D-O", "role": "member", "display_name": "Muhleman, Duane Owen" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TVQ3-FV70", "abstract": "Low-thrust perturbation guidance, as applied to the minimum time problem of an Earth to Mars rendezvous, has been reexamined and shown to perform orders of magnitude better, as measured by the terminal state error, than previous studies indicated. The orbits of Earth and Mars were assumed to be inclined and elliptical. The only forces considered were the Sun's gravity and that of the constant thrust rocket engine.
\r\n\r\nFirst order necessary conditions of the calculus of variations were developed for the nominal trajectory. The resulting nonlinear two-point boundary value problem was solved with the Backward Sweep Method. Feedback gain related and trajectory information is stored on a file during the optimization of the nominal trajectory to be retrieved later in the guidance programs by a high order interpolator.
\r\n\r\nTwo guidance schemes, Time-To-Go Guidance and Minimum Distance Guidance, were investigated for several initial perturbations in velocity and position. The performance of the two schemes was found to be clearly acceptable although not quite as good as reoptimization. The two schemes are equivalent in performance. Moreover, a simplified version of the schemes, Current Time Guidance, was found to be comparable in performance to the more elaborate guidance schemes.
\r\n\r\nA comparison of the current results with those of previous studies was made showing that terminal state errors can be reduced 100 to 10,000 times more than found earlier. This apparent improvement may possibly be explained by the use of a high fidelity integrator and other enhancements implemented in the software, although algorithm and programming mistakes in the earlier studies are suspected.
\r\n\r\nA similar minimum time problem, that of a two-dimensional Earth to Mars orbit transfer using a solar sail, was also reexamined. The optimized trajectory was found to be very similar to those obtained by most earlier studies. A recent report which prompted the study was found to have an error in a transversality condition causing anomalous results.
" }, { "name": "Bernier, Robert J. N.", "degree": "PhD", "year": "1982", "title": "Unsteady Two-Phase Flow Instrumentation and Measurement", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122004-092752", "creators": [ { "name": { "family": "Bernier", "given": "Robert J. N." }, "id": "Bernier-Robert-J-N", "display_name": "Bernier, Robert J. N." } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." }, { "name": { "family": "Herbolzheimer", "given": "Eric" }, "id": "Herbolzheimer-E", "role": "member", "display_name": "Herbolzheimer, Eric" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/8KSZ-8796", "abstract": "The performance of a transverse field electromagnetic flowmeter in a steady two-phase flow was investigated analytically for a disperse and an annular flow regime. In both cases the flowmeter output voltage was found to be proportional to the mean velocity of the liquid phase. Experiments in a steady air-water mixture showed good agreement with the analysis.
\r\n\r\nAn impedance void fraction meter was designed and built to conduct measurements of unsteady void fractions. Short electrodes excited by voltages of opposite polarity were used in combination with a highly sensitive signal processor. The steady state calibration indicated that the meter was somewhat sensitive to the void fraction distribution for the bubbly flow regime. However, the transition to a churn turbulent regime greatly affected the meter steady state response. The dynamic capability of the void fraction meter was estimated by comparison of the statistical properties of the voltage fluctuations in a nominally steady bubbly flow with those of a shot-noise process. The filter function associated with the finite volume of the electric field within the fluid cell could be determined from the measured autocorrelation function and was shown to be mainly a function of the velocity of the disperse phase. Also some properties of the disperse phase could be inferred from the statistical analysis.
\r\n\r\nTwo void fraction meters were used to measure the propagation speed of kinematic shocks in an air-water bubbly mixture for various void fractions and water flow rates. The relative velocity of the disperse phase calculated from these measurements decreased with an increase in the disperse phase concentration. However, this effect disappeared at higher water flow rates and the relative velocity became independent of void fraction. Measurements of the propagation speed of shocks of decreasing strength provided a good verification of the kinematic wave theory. The shock thicknesses could also be determined leading to the conclusion that an important diffusion mechanism was responsible for arresting the steepening of the wave.
\r\n\r\nCross-correlations of the fluctuating voltage of two void fraction meters in a steady bubbly flow were determined. The speed measured by this technique was identified as the infinitesimal wave speed of the void fraction and not the velocity of the dispersed phase as postulated by some authors. The normalized cross-correlation maxima showed that the small amplitude void fraction disturbances were short-lived structures, which were created and diffused on a continuous basis. The cross spectral density revealed that the waves present in these disturbances were nondispersive.
" }, { "name": "Brownlie, William Robert", "degree": "PhD", "year": "1982", "title": "Prediction of Flow Depth and Sediment Discharge in Open Channels", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12192006-152351", "creators": [ { "name": { "family": "Brownlie", "given": "William Robert" }, "id": "Brownlie-William-Robert", "display_name": "Brownlie, William Robert" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Koh", "given": "Robert C. Y." }, "id": "Koh-R-C-Y", "role": "member", "display_name": "Koh, Robert C. Y." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "member", "display_name": "Vanoni, Vito A." } ], "option_major": [ "civileng" ], "doi": "10.7907/100Z-Z157", "abstract": "In recent years attempts have been made to develop numerical models for unsteady flows in channels with sediment transport. This work was conducted to analyze two essential ingredients of any numerical model: the relationship between the hydraulic variables (slope, depth, and velocity), and the predictor of sediment concentration.
\r\n\r\nA data base containing 7027 records (5263 laboratory records and 1764 field records) in 77 data files was assembled and is provided (Appendix B). The data base was used to examine existing relationships and to develop new ones. Six existing hydraulic relationships are reworked and examined. Detailed statistical analyses are provided for 13 existing techniques for predicting sediment concentration.
\r\n\r\nRelying heavily on statistical analysis of dimensionless groups, new relationships have been developed. The new hydraulic relationship solves for flow depth for upper and lower regime flow separately and then provides a method for determining which flow regime one might expect. The new method for predicting sediment transport, which is easy to use, appears to be more accurate than the 13 existing methods, and suggests that complex procedures for calculating concentration are not warranted.
\r\n\r\nA four-point implicit finite difference scheme has been presented to demonstrate the feasibility of applying the new hydraulic and sediment relationships to a numerical solution of the differential equations.
" }, { "name": "Campbell, Charles Soutter", "degree": "PhD", "year": "1982", "title": "Shear Flows of Granular Materials", "advisor": "Brennen, Christopher E.; Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242003-104837", "creators": [ { "name": { "family": "Campbell", "given": "Charles Soutter" }, "id": "Campbell-Charles-Soutter", "display_name": "Campbell, Charles Soutter" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "co-advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "chair", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" } ], "option_major": [ "mecheng" ], "doi": "10.7907/QZSF-E358", "abstract": "Many of the macroscopic and microscopic features of shearing granular materials were observed during the course of this investigation.
\r\n\r\nThe principal results were obtained from a computer simulation of the flows in an inclined chute, and in a Couette shear cell. The simulation followed the exact trajectories of two-dimensional discs through a control volume. Properties of the flow were obtained from temporal averages of the instantaneous particle properties. Macroscopic flow characteristics such as velocity and density profiles are presented. Because the simulation follows the exact mechanics of the particles it was also possible to investigate the statistical nature of granular flows. Towards this purpose velocity distributions, collision angle distributions and pair correlation functions were measured.
\r\n\r\nThe results of the simulation draw a picture of a flowing granular material as a self-excited gas. There appears to be a \"temperature\" associated with the random motions of the particles, that is a product of gradients in the mean velocity field. An equation of state is proposed, involving this temperature, to describe the behavior of the density within the flow. A phenomenon reminscent of conduction is observed. The particle velocities appear to obey a Maxwellian distribution based on this temperature.
\r\n\r\nPreliminary experiments were also performed to investigate the flow of glass beads down inclined chutes. It is shown that the flows may be classified as either supercritical or subcritical depending on the local value of the Froude number, and that the classification had a strong influence on the flow properties. In addition, wall friction coefficients were determined.
" }, { "name": "Carroll, Christopher Ralph", "degree": "PhD", "year": "1982", "title": "Hybrid Processing", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132006-131111", "creators": [ { "name": { "family": "Carroll", "given": "Christopher Ralph" }, "id": "Carroll-Christopher-Ralph", "display_name": "Carroll, Christopher Ralph" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Sutherland", "given": "Ivan Edward" }, "id": "Sutherland-I-E", "role": "member", "display_name": "Sutherland, Ivan Edward" }, { "name": { "family": "Johnsson", "given": "S. Lennart" }, "id": "Johnsson-S-Lennart", "role": "member", "display_name": "Johnsson, S. Lennart" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Fox", "given": "Geoffrey C." }, "id": "Fox-G-C", "role": "member", "display_name": "Fox, Geoffrey C." } ], "option_major": [ "compsci" ], "doi": "10.7907/ssgy-ep18", "abstract": "The past decade has witnessed a revolution in digital electronics. As the cost per function has decreased, digital techniques have pushed the older analog methods into the background. This thesis explores a method of merging digital and analog techniques into a hybrid combination of the two. Representing the analog information as continuously variable intervals of time minimizes the effects of noise on the analog data. Ensuring that only digital data pass from one computation to another prevents the accumulation of errors.
\r\n\r\nAs an example of hybrid processing, this thesis includes the design of Large Scale Integrated (LSI) circuit that implements the Lee-Moore maze solving algorithm, extended to cover the two-layer path finding case. The use of digital information to describe the path geometry and analog information to describe the path costs demonstrates the system's hybrid nature.
\r\n\r\nThe design of this system provided several lessons applicable to the design of other hybrid systems. It also unexpectedly demonstrated the importance of the communication structure in determining the costs involved in all kinds of processing. These lessons are summarized in the last chapter.
" }, { "name": "Catherasoo, Christopher Jeyaparan", "degree": "PhD", "year": "1982", "title": "Shock Dynamics in Non-Uniform Media", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132006-143337", "creators": [ { "name": { "family": "Catherasoo", "given": "Christopher Jeyaparan" }, "id": "Catherasoo-Christopher-Jeyaparan", "display_name": "Catherasoo, Christopher Jeyaparan" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7knb-5s50", "abstract": "The theory of shock dynamics in two dimensions is reformulated to treat shock propagation in a non-uniform medium. The analysis yields a system of hyperbolic equations with source terms representing the generation of disturbances on the shock wave as it propagates into the fluid non-uniformities. The theory is applied to problems involving the refraction of a plane shock wave at a free plane gaseous interface. The \"slow-fast\" interface is investigated in detail, while the \"fast-slow\" interface is treated only briefly. Intrinsic to the theory is a relationship analogous to Snell's law of refraction at an interface. The theory predicts both regular and irregular (Mach) refraction, and a criterion is developed for the transition from one to the other. Quantitative results for several different shock strengths, angles of incidence and sound speed ratios are presented. An analogy between shock refraction and the motion of a force field in unsteady one-dimensional gasdynamics is pointed out. Also discussed is the limiting case for a shock front to be continuous at the interface. Comparison of results is made with existing experimental data, with transition calculations based on three-shock theory, and with the simple case of normal interaction.
" }, { "name": "Cetegen, Baki Mehmet", "degree": "PhD", "year": "1982", "title": "Entrainment and Flame Geometry of Fire Plumes", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192006-141619", "creators": [ { "name": { "family": "Cetegen", "given": "Baki Mehmet" }, "id": "Cetegen-Baki-Mehmet", "display_name": "Cetegen, Baki Mehmet" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "chair", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/CJ4E-W053", "abstract": "This study concerns the flame structure and fire plume entrainment of natural gas diffusion flames on 0.10, 0.19 and 0.50 m. diameter burners. The heat release rates ranged from 10 kW to 200 kW. Flame heights based on high speed photography and eye averages show a transition in the dependence of flame height on a dimensionless heat addition parameter around unity. For flames taller than three burner diameters, the initial diameter of the fire does not affect the length of these flames whereas for short flames initial geometry becomes important. Another prominent feature of these flames is the presence of large scale ring vortex-like structures which are formed close to the burner surface more or less regularly. It is found that these structures are responsible for the fluctuations of the flame top.
\r\n\r\nEntrainment measurements spanned heights starting very close to the burner surface to distances about six times the average flame heights. Experiments indicate the presence of three regions; a region close to the burner surface where plume entrainment rates are independent of the fuel flow (or heat release) rates; a far field region above the flame top, where a simple point source model correlates the data reasonably well; and a not so well-defined intermediate region where entrainment seems to be similar to that of a turbulent flame with plume-like characteristics. It is also found that the disturbances in the ambient atmosphere will greatly enhance the fire plume entrainment. Finally, a theoretical study of a steady, buoyant, diffusion flame indicated the importance of the puffing in the entrainment process.
" }, { "name": "Chai, Herzl", "degree": "PhD", "year": "1982", "title": "The Growth of Impact Damage in Compressively Loaded Laminates", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132004-084629", "creators": [ { "name": { "family": "Chai", "given": "Herzl" }, "id": "Chai-Herzl", "display_name": "Chai, Herzl" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "chair", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Corcoran", "given": "William Harrison" }, "id": "Corcoran-W-H", "role": "member", "display_name": "Corcoran, William Harrison" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/58D3-ZZ41", "abstract": "The thesis is divided into two chapters. The first chapter describes an experimental program carried out to determine the phenomenological aspects of composite panel failure (graphite/epoxy laminate) under simultaneous in-plane compression and low velocity transverse impact (0-250 ft/sec). High-speed photography and the shadow moire technique were used to record a full-field surface deformation history of the impacted plate. The information gained from these records, supplemented by plate sectioning and observation for interior damage, has shown that the predominant failure mechanism is the coupled effect of delamination and buckling.
\r\n\r\nIn chapter 2, this process of failure is modelled by delamination buckling wherein the local delamination stability, growth or arrest are governed by an energy release rate criterion. Various degrees of problem simplifications are employed, starting with a one-dimensional, delaminated-beam model. In the most sophisticated treatment, it is assumed that the damaged area has an elliptical shape. It was found that this model is capable of describing the growth conditions and the growth behavior of the damaged area. It was also found that the predominant parameter controlling delamination growth or arrest is the fracture energy associated with delamination.
\r\n\r\nIn the appendix at the end of this work, the fracture energy of a composite laminate is considered. A modified cleavage analysis is developed, and is applied to evaluate this quantity for two composite materials of current interest. The test results are then examined with reference to impact damage tolerance data available for these materials. A viscoelastic characterization of the two resins used to fabricate the two composites mentioned above is also provided. The results of these measurements are then examined with reference to long-term applicability of the matrix material.
" }, { "name": "Chen, Carl Leei", "degree": "PhD", "year": "1982", "title": "Direct Output Feedback Control of Large Flexible Spacecraft", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-143337", "creators": [ { "name": { "family": "Chen", "given": "Carl Leei" }, "id": "Chen-Carl-Leei", "display_name": "Chen, Carl Leei" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/vx2f-yh14", "abstract": "This report addresses the problem of active control of large flexible space structures. The current activities and control schemes in this field are briefly reviewed. A direct output feedback control (DOFC) technique is proposed to control the large flexible space structures. Assuming an N-degree-of-freedom system with n collocated sensor and actuator (S/A) pairs, where N is typically much larger than n, the analysis shows that at least the first n lowest critical vibration modes can be controlled with the system remaining stable. A formula for the selection of the feedback control gain matrix is provided. The DOFC approach is also applicable to the systems with certain types of nonlinearities, as well as systems including sensor/actuator dynamics. A simple criterion for selecting the \"optimal\" location of collocated sensor and actuator pairs is proposed. Numerical examples are given to illustrate the proposed DOFC technique and the \"optimal\" location criterion.
" }, { "name": "Chen, Michael Jiu-Wei", "degree": "PhD", "year": "1982", "title": "A Spatiotemporal Probe of the Human Visual System by Application of Nonlinear Systems Identification Theory", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132006-154529", "creators": [ { "name": { "family": "Chen", "given": "Michael Jiu-Wei" }, "id": "Chen-Michael-Jiu-Wei", "display_name": "Chen, Michael Jiu-Wei" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "chair", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Ary", "given": "James P." }, "id": "Ary-James-P", "role": "member", "display_name": "Ary, James P." }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Allman", "given": "John Morgan" }, "id": "Allman-J-M", "role": "member", "display_name": "Allman, John Morgan" }, { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "member", "display_name": "Fender, Derek H." } ], "option_major": [ "bioinfo", "eng" ], "doi": "10.7907/f613-bd08", "abstract": "This thesis describes an attempt to apply signal processing and systems theory to the task of analyzing and interpreting evoked potential data and locating evoked potential sources by physical principles. Random impulse trains were used as inputs to characterize the human visual system. The method is analogous to the Wiener method for a continuous Gaussian white noise input. The restricted-diagonal Volterra series for discrete inputs is used by making certain restrictions on the integrals in a Volterra series. A modification of Lee and Schetzen's method was used in the estimation of the kernels.
\r\n\r\nForty-channel first-order kernels were computed for briefly appearing checkerboard patterns placed in left or right visual fields. The measured potential distribution showed a radical dependence on stimulus locus. Equivalent dipoles generally give excellent fits to the measured data, and the mapping between the visual field and these equivalent sources is similar to the commonly accepted mapping between the visual field and the visual cortex. Also, the results resemble those using conventional signal averaging.
\r\n\r\nFirst order kernels show better signal-to-noise ratio when compared to conventional signal averaging for the same experiment duration. Multichannel first-order kernels show that sources from early components are deep in the head as expected and in a believable region.
\r\n\r\nResults for the second-order kernels reveal occlusive interactions in the visual system and are interpreted relative to the first-order kernel. These inhibitions display different lengths of memories which suggest that they might arise from different neural origins.
\r\n" }, { "name": "Chen, Pei-Chuang", "degree": "PhD", "year": "1982", "title": "Long Wavelength GaInAsP/InP Semiconductor Lasers for Optical Communications", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132006-133617", "creators": [ { "name": { "family": "Chen", "given": "Pei-Chuang" }, "id": "Chen-Pei-Chuang", "display_name": "Chen, Pei-Chuang" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "chair", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/51sv-sm58", "abstract": "Optical fiber communication systems have shifted toward the long wavelength range of 1.2-1.6 \u00b5m due to lower losses and dispersion available with high quality fibers. The quaternary GaInAsP/InP material system has evolved as the most promising system for light sources in this range.
\r\n\r\nIndium phosphide electronic devices are expected to possess high frequency switching capabilities, but present device technology is still rather primitive. In anticipation of future developments, which will render opto-electronic integration in this system advantageous, two laser structures on semi-insulating InP substrates were demonstrated. The substrate permits electrical isolation between components and thus is ideal in planar integration of the lasers with electronic devices.
\r\n\r\nLow threshold lasers can only be achieved when the active region is properly defined in two dimensions to provide good optical and carrier confinement. Present techniques usually require difficult and intricate growth step of two-step liquid phase epitaxy. Embedded epitaxy, by growth through a mask, offers a simple yet elegant means of two dimensional definition of the active region with only a single growth step. Low threshold lasers were fabricated with this technique and demonstrated its potential applications.
\r\n\r\nAll GaInAsP/InP lasers show accelerated increase of threshold current with temperature of a different nature than similar GaA1As lasers. To understand the origin of this phenomenon, calculations were made of the Auger process in these lasers, and have demonstrated that they play a very important role in the temperature behavior of GaInAsP/InP lasers.
\r\n" }, { "name": "Engheta, Nader", "degree": "PhD", "year": "1982", "title": "On the Radiation Patterns of Interfacial Antennas", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142006-080653", "creators": [ { "name": { "family": "Engheta", "given": "Nader" }, "id": "Engheta-Nader", "orcid": "0000-0003-3219-9520", "display_name": "Engheta, Nader" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "chair", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "orcid": "009-0002-2156-967X", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Kavanagh", "given": "Ralph William" }, "id": "Kavanagh-R-W", "role": "member", "display_name": "Kavanagh, Ralph William" } ], "option_major": [ "eleceng" ], "doi": "10.7907/y86x-2709", "abstract": "The radiation pattern of an interfacial radiating source is obtained for the case where the source is an infinitely long line source lying along the plane interface of two dielectric half-spaces; for the case where the source is an infinitesimal electric dipole vertically located on the interface; and for the case where the dipole is lying horizontally along the interface. For all the three cases, it is found that the radiation pattern at the interface has a null (interface extinction). For the infinitely long line source, it is obtained that the pattern in the upper half-space, whose index of refraction is taken to be less than that of the lower half-space, has a single lobe with a maximum normal to the interface, and that the pattern in the lower half-space (subsurface region) has two maxima straddling symmetrically a minimum. Interpretation of these results in terms of ray optics, Oseen's extinction theorem, and the Cerenkov effect are given. For the vertical dipole, it is found that the radiation pattern along the dipole axis has a null. For the horizontal dipole, it is obtained that the pattern in the upper half-space has a single lobe whose maximum is normal to the interface; that in the lower half-space, in the plane normal to the interface and containing the dipole, the pattern has three lobes; whereas in the plane normal to the interface and normally bisecting the dipole, the pattern has two maxima located symmetrically about a minimum. Interpretation of these results in terms of the Cerenkov effect is also given.
" }, { "name": "Feenstra, Randall Meindert", "degree": "PhD", "year": "1982", "title": "Electronic and Vibrational States of Point Defects in Semiconductors", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142018-171221657", "creators": [ { "name": { "family": "Feenstra", "given": "Randall Meindert" }, "id": "Feenstra-Randall-Meindert", "display_name": "Feenstra, Randall Meindert" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "member", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/p5ph-6811", "abstract": "This thesis deals with the properties of defects in tetrahedrally-bonded semiconductors. The detects which will be studied here are impurity atoms substitutional for host atoms in the crystal. In particular, those defects which produce localized electronic states in the middle of the electronic energy gap (\"deep levels\") will be discussed. The main experimental technique used is photoluminescence. The crystals are excited with a laser, and they emit light due to various electronic transitions at the defects. The energy of this luminescence yields information about the nature of the excited electronic states. Also, excited vibrational states of the defects are apparent in the luminescence, and these vibrational states yield structural information about the defect.
\r\n\r\nThe major system studied here is GaP containing Zn and O impurities. The Zn and O ions experience an attractive Coulomb interaction, so that they tend to occupy lattice sites which are near to each other, forming defect pairs. The energy or luminescence emitted from a (Zn,O) pair depends on the separation of the impurities. Thus, a luminescence spectrum contains information about the number or pairs of each possible separation. I have used this phenomenon to monitor the relative positions of Zn and O impurities in the lattice. I have observed reactions in which the impurity atoms move through the lattice under the influence of laser excitation. Specifically, I observe the dissociation of nearest-neighbor (Zn,O) pairs, and the subsequent formation of further separated pairs. The dissociation of the nearest-neighbor pairs can occur thermally, or by a photoinduced mechanism. At temperatures near 200 C, the intensity of the (Zn,O) luminescence spectra changes with time, a direct observation of the photoinduced reactions in progress. The (Zn,O) pairs are observed to dissociate by purely thermal means at temperatures near 900 C. From the rates of these two types of reactions, I identify the photoinduced pair dissociation as being a \"recombination-enhanced defect reaction\". In the reaction, electron-hole recombination puts the defect into a highly excited vibrational state, leading to the dissociation. This is the first observation of this sort of reaction in a system with known defect types. Thus, my study provides unique information about the electron-phonon interaction at defects. This study also has some practical application. The material GaP:(Zn,O) is used for fabricating red light-emitting-diodes, and the dissociation or the pairs provides an explanation for the degradation of these diodes. Presumably the degradation of some other semiconductor devices proceeds by mechanisms similar to those observed here.
\r\n\r\nThis thesis deals with several other topics aside from GaP:(Zn,O). The geometry or impurity pairs in zinc-blende crystals is discussed. For a given separation or the impurity atoms, there is some number or different possible relative orientations of the impurities. I have derived an analytic form for this distribution of impurity pair separations, and I show how this formula can be used to interpret the observed luminescence spectra of GaP:N. Another system studied here is Si containing In and B impurities. Recombination of excitons bound onto the impurities produces luminescence. From the observed decay times of these luminescence lines, I deduce values of the cross sections for free exciton capture onto In and B impurities. The magnitude of the In cross section indicates the presence of excited states of the In bound exciton. Finally, a theoretical treatment of the vibrational modes of substitutional defects in zinc-blende crystals is presented. The defects consist of an impurity atom, with springs or variable strength connecting it to its neighbors. For the case of oxygen in GaP, the theory predicts the existence or two defect vibrational modes, in agreement with experiment. From the energies of the observed vibrational modes, it appears that the oxygen impurity is quite weakly bonded to its neighboring atoms.
" }, { "name": "Fleming, Graham Christopher", "degree": "PhD", "year": "1982", "title": "Structure and Stability of Buoyant Diffusion Flames", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152006-121855", "creators": [ { "name": { "family": "Fleming", "given": "Graham Christopher" }, "id": "Fleming-Graham-Christopher", "display_name": "Fleming, Graham Christopher" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "chair", "display_name": "Marble, Frank E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Barnes", "given": "Charles A." }, "id": "Barnes-C-A", "role": "member", "display_name": "Barnes, Charles A." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/DVY5-MD93", "abstract": "The structure and stability of the convecting fluid flow generated by a diffusion flame in gaseous reactants has been investigated. The flame extends vertically upwards from a solid horizontal boundary, and separates the fuel from the oxidizer which can be of a different density. Real fuels are modelled by choosing appropriate values for the density difference and stoichiometric ratio of the reaction.
\r\n\r\nA self-similar solution for the steady flow is obtained incorporating the Howarth transformation, which allows the large density variations inherent in the combustion of gases to be accommodated. The stoichiometric ratio and fuel/oxidizer density ratio are varied to examine their effects on the structure and flow properties of the flame.
\r\n\r\nAn Orr-Sommerfeld equation governing the stability of buoyant flows is developed, incorporating all the variable density terms. Two different steady flows are studied, the symmetric flame (unit stoichiometry), and a flame with the stoichiometric ratio corresponding to methane burning in air. It was found that using the Boussinesq approximation which neglects density variations except for a buoyancy term is not applicable for the flame, and also introduced inaccuracy in the stability diagram for the buoyant plume. Although the flame bears a superficial similarity to the buoyant plume, the several differences cause a large difference in their stability. Empirically interpreting the stability diagrams to obtain an expected transition point gives ReT \u2248 250 for the flame compared to the less stable buoyant plume with ReT \u2248 140. A new unstable region consisting of waves with negative phase velocity but positive group velocity was found for both the buoyant flame and the buoyant plume.
\r\n\r\nThe local analysis is inappropriate for disturbances with wavelengths long compared to the flame thickness, therefore an analysis treating the flame and associated plume as negligibly thin was undertaken. This showed that the primary cause of instability was centrifugal forces generated by the momentum flux following a curved path. Reasonably good agreement was obtained with the local analysis.
" }, { "name": "Fowler, Graeme Francis", "degree": "PhD", "year": "1982", "title": "Finite Plane and Anti-Plane Elastostatic Fields with Discontinuous Deformation Gradients Near the Tip of a Crack", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122006-153033", "creators": [ { "name": { "family": "Fowler", "given": "Graeme Francis" }, "id": "Fowler-Graeme-Francis", "display_name": "Fowler, Graeme Francis" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/td0f-kr59", "abstract": "In this paper the fully nonlinear theory of finite deformations of an elastic solid is used to study the elastostatic field near the tip of a crack. The special elastic materials considered are such that the differential equations governing the equilibrium fields may lose ellipticity in the presence of sufficiently severe strains.
\r\n\r\nThe first problem considered involves finite anti-plane shear (Mode III) deformations of a cracked incompressible solid. The analysis is based on a direct asymptotic method, in contrast to earlier approaches which have depended on hodograph procedures.
\r\n\r\nThe second problem treated is that of plane strain of a compressible solid containing a crack under tensile (Mode I) loading conditions. The material is characterized by the so-called Blatz-Ko elastic potential. Again, the analysis involves only direct local considerations.
\r\n\r\nFor both the Mode III and Mode I problems, the loss of equilibrium ellipticity results in the appearance of curves (\"elastostatic shocks\") issuing from the crack-tip across which displacement gradients and stresses are discontinuous.
\r\n" }, { "name": "Hedemann, Mark Allen", "degree": "PhD", "year": "1982", "title": "Measurements of Magnetic Field Fluctuations in the Caltech Research Tokamak", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132006-153307", "creators": [ { "name": { "family": "Hedemann", "given": "Mark Allen" }, "id": "Hedemann-Mark-Allen", "display_name": "Hedemann, Mark Allen" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "chair", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/z70q-f715", "abstract": "An experimental investigation of magnetic field fluctuations in a research tokamak plasma has been performed. The fluctuations were measured with movable probes inserted directly into the plasma. Estimates of the fluctuating field strength, power spectral density, and correlation lengths have been made by calculations on the raw data. The fluctuations were found to be of comparable strength for the radial and poloidal components, while the toroidal component was found to be at least a factor of 5 weaker in strength. The fluctuating field strength showed no apparent dependence on plasma current and safety factor at the edge, but increased with electron density during gas puffing and as the minor radius of measurement was decreased.
\r\n\r\nThe power spectral density indicated that the fluctuations could be divided into two frequency regions. The low frequency region (f < 100 kHz) was dominated by coherent MHD modes with correlation lengths on the order of the tokamak size. The high frequency (f > 100 kHz) region appeared to be turbulent in nature with short correlation lengths in the poloidal direction (< .01 m), but longer correlation lengths in the radial direction (> .04 m). The high frequency region showed a roll-off in frequency of \u03b4Br of approximately f-2.5.
\r\n\r\nThe results are compared with theories of fluctuation sources and the effects of fluctuations on anomalous electron thermal transport. The best fit to the high frequency region spectral density is given by a statistical theory of fluctuations. The fluctuating field strength appears to be more than an order of magnitude too small to account for the anomalous electron thermal transport using stochastic field theory.
" }, { "name": "Karagozian, Ann Renee", "degree": "PhD", "year": "1982", "title": "An Analytical Study of Diffusion Flames in Vortex Structures", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132005-133501", "creators": [ { "name": { "family": "Karagozian", "given": "Ann Renee" }, "id": "Karagozian-Ann-Renee", "orcid": "0000-0002-2847-8773", "display_name": "Karagozian, Ann Renee" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "chair", "display_name": "Marble, Frank E." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/NE3D-T576", "abstract": "The interaction of a laminar diffusion flame with two- and three-dimensional vortex structures is considered, in which the flame becomes severely distorted and is strained in its own plane. Fast chemical kinetics and unity stoichiometry are assumed. The resulting curved flame sheets are treated by applying the boundary layer approximation locally until neighboring flame sheets come sufficiently close to interact and consume the intervening reactant, thus creating a core of combustion products with external isolated flame sheets.
\r\n\r\nThe simplest example is the deformation of a diffusion flame by a viscous vortex of circulation \u0393. For large \u0393 the radius of the core of combustion products increases in proportion to \u03931/3D1/6t1/2, where D is the binary diffusivity, indicating the overall transport quantity to be \u03932/3D1/3. The augmentation of reactant consumption due to the presence of the vortex is time-independent and behaves as \u03932/3D1/3.
\r\n\r\nThe interaction of a laminar flame with a viscous vortex undergoing constant axial straining also is examined. The growth of the core radius has the similarity relation \u03d2 \u00b7 ~ \u03931/3D1/6[(1-e-\u03b5t)1/2]/\u03b51/2 indicating that the core eventually reaches a steady state size. The core continues to store products and the outer flame arms continue to consume reactants independently of time, however, due to axial extension. Hence there exist two different time scales governing the development of the flame: one associated with the flame-vortex interaction and one associated with the external strain rate.
\r\n\r\nThe effect of the release of heat (and subsequent density change) by the reaction on flame structure is examined by considering the interaction of a diffusion flame with a vortex undergoing a density change at the core. The decreased core density shifts the entire flowfleld radially outward, causing the burned core to be increased in size, while the radius of the unburned core decreases as [\u03c11/\u03c12 + 1]-1/6, where \u03c11 is the reactant density and \u03c12 is the product density. The augmented consumption rate of the flame also is reduced, since the flame is being strained further from the viscous core and thus to a lesser extent.
" }, { "name": "Katz, Joseph", "degree": "PhD", "year": "1982", "title": "Cavitation Inception in Separated Flows", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01252005-084230", "creators": [ { "name": { "family": "Katz", "given": "Joseph" }, "id": "Katz-Joseph", "display_name": "Katz, Joseph" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." } ], "option_major": [ "mecheng" ], "doi": "10.7907/VP9N-K847", "abstract": "The phenomenon of cavitation was studied on four axisymmetric bodies whose boundary layers underwent a laminar separation and subsequent turbulent reattachment. The non-cavitating flow was studied by holography and the Schlieren flow visualization technique. Surface distributions of the mean and the fluctuating pressures were also measured. The conditions for cavitation inception and desinence were determined and several holograms were recorded just prior to and at the onset of cavitation. The population of microbubbles and the nature of the subsequent development of visible cavitation was determined from the reconstructed image.
\r\n\r\nHigh rms and peak values of the fluctuating pressure were measured (up to 90 percent of the dynamic head), the negative peaks being larger than the positive ones except for the reattachment zone where large positive peaks existed. The power spectra contained peaks thought to originate within the large eddies of the mixing layer and in one case there were also peaks due to the laminar boundary layer instability waves.
\r\n\r\nCavitation inception occurred in the turbulent shear layer downstream of the transition region. When the separation zone was large the inception region was located within the most developed section of the mixing layer but upstream of the reattachment zone. When the separation region was small inception occurred close to the reattachment zone but still detached from the body surface. A comparison between the surface minimum pressure and the cavitation inception indices also indicated that inception could not occur near the surface of the bodies having a large separation region.
\r\n\r\nThe appearance of visible cavities was preceded by the appearance of a cluster of microbubbles only in the cavitation inception region. The nuclei population in the other sections of the flow field remained fairly uniform. This observation supports the assumption that cavitation is initiated from microscopic free stream nuclei. The rate of cavitation events was estimated from the nuclei population and from the dimensions of the separation region. It was shown for one of the bodies that at least one bubble larger than 10 micrometers radius was exposed every second to a pressure peak which was sufficiently large to cause a cavitation event.
\r\n" }, { "name": "Kavaya, Michael Joseph", "degree": "PhD", "year": "1982", "title": "Optoacoustic Detection Employing Stark Voltage Modulation and Stark Polarization Modulation", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06072006-091651", "creators": [ { "name": { "family": "Kavaya", "given": "Michael Joseph" }, "id": "Kavaya-Michael-Joseph", "display_name": "Kavaya, Michael Joseph" } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "chair", "display_name": "Bridges, William B." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Menzies", "given": "Robert Thomas" }, "id": "Menzies-Robert-Thomas", "role": "member", "display_name": "Menzies, Robert Thomas" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JB2P-3726", "abstract": "The conventional chopped laser radiation technique of optoacoustic detection suffers from a sensitivity-limiting synchronous background signal. This thesis reports on theoretical and experimental studies of two novel optoacoustic modulation techniques designed to reduce the background signal and thereby improve the sensitivity. A specialized optoacoustic detector is described, which is capable of being operated in the conventional chopped-laser modulation mode as well as in the new Stark voltage modulation and Stark polarization modulation modes; experimental results are given using all three modes of operation. Stark voltage modulation produces more than two orders of magnitude improvement in sensitivity over conventional modulation under identical conditions. Even greater sensitivities are shown to be attainable. A basic theory of conventional optoacoustic detection is developed and then applied to the new optoacoustic modulation techniques. An introduction to and history of optoacoustic detection are also presented.
" }, { "name": "Koch, Thomas Lawson", "degree": "PhD", "year": "1982", "title": "Gigawatt Picosecond Dye Lasers and Ultrafast Processes in Semiconductor Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042006-130634", "creators": [ { "name": { "family": "Koch", "given": "Thomas Lawson" }, "id": "Koch-Thomas-Lawson", "display_name": "Koch, Thomas Lawson" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Zewail", "given": "Ahmed H." }, "id": "Zewail-A-H", "role": "member", "display_name": "Zewail, Ahmed H." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/61ca-rp72", "abstract": "This thesis is a theoretical and experimental investigation of a gigawatt picosecond dye laser oscillator-amplifier system, and the application of that system to the study of ultrafast lasing and carrier dynamics in semiconductor lasers.
\r\n\r\nBeginning with a review of traveling wave rate equations, nonlinear pulse propagation in a generalized two-level amplifying/absorbing medium is discussed. This permits a qualitative treatment of synchronously mode-locked dye lasers. The formalism is then refined to provide a quantitative analysis of picosecond dye laser amplifier chains, including amplified spontaneous emission, saturable absorbers used for amplifier stage isolation, gain saturation with \"angular hole-burning\" and triplet losses, and linear and nonlinear pulse shaping effects.
\r\n\r\nExperimentally, the construction and operation of a three stage Nd:YAG laser pumped picosecond dye laser amplifier chain is described. Numerical modeling is used to compare the theoretical analysis with the experimental results. In addition, a brief discussion of picosecond time domain measurement techniques is presented, focussing on nonlinear optical methods. This includes a parametric sum frequency upconversion gating technique used extensively in this work to provide linear, picosecond resolution temporal measurements of optical pulses which are synchronized to the dye laser pulses.
\r\n\r\nThe output of the picosecond dye laser system is used to optically generate high carrier densities in semiconductor lasers, and the ensuing short pulse lasing dynamics are investigated and compared to the predictions of a simple rate equation analysis. Novel effects are observed in the spectrally resolved temporal measurements of the lasing output from picosecond optically pumped buried heterostructure semiconductor lasers. A model is developed which includes both broadband stimulated emission as well as many-valley and hot electron effects in the semiconductor, and the model is in close agreement with the observed behavior. The conclusion is drawn that the picosecond lasing dynamics of semiconductor lasers can be understood if the conventional rate equations are abandoned in favor of a more fundamental analysis which includes not just the dynamics of the optical energy exchange in the laser cavity, but the detailed picosecond dynamics of the semiconductor material as well.
\r\n" }, { "name": "Lang, Charles Richard, Jr.", "degree": "PhD", "year": "1982", "title": "The Extension of Object-Oriented Languages to a Homogeneous, Concurrent Architecture", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142006-085516", "creators": [ { "name": { "family": "Lang", "given": "Charles Richard, Jr." }, "id": "Lang-Charles-Richard", "display_name": "Lang, Charles Richard, Jr." } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Bryant", "given": "Randy" }, "id": "Bryant-R", "role": "chair", "display_name": "Bryant, Randy" }, { "name": { "family": "Fox", "given": "Geoffrey C." }, "id": "Fox-G-C", "role": "member", "display_name": "Fox, Geoffrey C." }, { "name": { "family": "Johnsson", "given": "S. Lennart" }, "id": "Johnsson-S-Lennart", "role": "member", "display_name": "Johnsson, S. Lennart" }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Martin", "given": "Alain J." }, "id": "Martin-A-J", "role": "member", "display_name": "Martin, Alain J." }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." } ], "option_major": [ "compsci" ], "doi": "10.7907/9EVC-2X08", "abstract": "A homogeneous machine architecture, consisting of a regular interconnection of many identical elements, exploits the economic benefits of VLSI technology. A concurrent programming model is presented that is related to object oriented languages such as Simula and Smalltalk. Techniques are developed which permit the execution of general purpose object oriented programs on a homogeneous machine. Both the hardware architecture and the supporting software algorithms are demonstrated to scale their performance with the size of the system.
\r\n\r\nThe program objects communicate by passing messages. Objects may move about in the system and may have an arbitrary pointer topology. A distributed, on-the-fly garbage collection algorithm is presented which operates by message passing. Simulation of the algorithm demonstrates its ability to collect obsolete objects over the entire machine with acceptable overhead costs. Algorithms for maintaining the locality of object references and for implementing a virtual object capability are also presented.
\r\n\r\nTo insure the absence of hardware bottlenecks, a number of interconnection strategies are discussed and simulated for use in a homogeneous machine. Of those considered, the Boolean N-cube connection is demonstrated to provide the necessary characteristics.
\r\n\r\nThe object oriented machine will provide increased performance as its size is increased. It can execute a general purpose, concurrent, object oriented language where the size of the machine and its interconnection topology are transparent to the programmer.
" }, { "name": "Lin, Albert Niu", "degree": "PhD", "year": "1982", "title": "Experimental Observations of the Effect of Foundation Embedment on Structural Response", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162018-100416743", "creators": [ { "name": { "family": "Lin", "given": "Albert Niu" }, "id": "Lin-Albert-Niu", "display_name": "Lin, Albert Niu" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "chair", "display_name": "Housner, George W." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "civileng" ], "doi": "10.7907/ksr8-pf30", "abstract": "Ambient, ring-down, and forced vibration tests were used to determine the effect of foundation embedment on the response of a one-story model structure 10 ft square in plan and 11.4 ft high. The tests, conducted at the full-, half- and unembedded foundation conditions, led to the identification of the fundamental translatory mode in the primary (east-west) and secondary (north-south) directions, and two torsional modes. The forced vibration consisted of horizontally incident SH-waves generated at an excitation structure located 47.5 ft (center-to-center) away. During these tests, detailed measurements of the near-field ground motion and modal displacement ratios were obtained at the fundamental mode in the primary direction. The displacement ratios were used to calculate the structural and foundation-soil stiffnesses and damping coefficients for comparison to theoretical results. Foundation embedment increased the model frequencies and decreased the contribution of the foundation motion to the overall displacement of the superstructure. For the fundamental mode response, which consisted of translatory and rocking motions, the resonant frequency predicted by lumped parameter analysis was higher than that measured experimentally by 25% for the unembedded case. While the experimental and theoretical fundamental mode shapes were in close agreement, the calculated effect of embedment on the response was less than that measured. These results were consistent with the comparison of the impedances and embedment factors. Serious discrepancies between analytical and experimental results were found for the case of torsion; a simple two-degree-of-freedom model was consistent only with the first of the two measured resonant frequencies.
" }, { "name": "Mueller, James Robert", "degree": "PhD", "year": "1982", "title": "I. The Analysis of the Rewetting of a Vertical Slab Using a Wiener-Hopf Technique. II. Asymptotic Expansions of Integrals with Three Coalescing Saddle Points", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142006-131317", "creators": [ { "name": { "family": "Mueller", "given": "James Robert" }, "id": "Mueller-James-Robert", "display_name": "Mueller, James Robert" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/8q9c-pe97", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I: A problem which arises in the analysis of the emergency core cooling system of a nuclear reactor is the rewetting of the fuel rods following a loss of coolant accident. Due to the high initial temperatures in the rods, the emergency coolant initially flashes to steam on contact, effectively insulating the rods from the coolant. It is observed experimentally, however, that a constant velocity traveling quench front is set up on the surface of the rod, moving from the cold to the hot end.\r\n\t\r\nWe approximate the rod by an infinite two-dimensional slab with adiabatic boundary conditions ahead of the quench front, and a constant heat transfer coefficient behind in the wet region. The temperature at the front is found using Fourier transforms and an exact Wierner-Hopf Factorization. Using a reversion of series, the dimensionless velocity of the quench front (Peclet number) for a small dimensionless heat transfer coefficient A (Biot number) is found approximately to lowest order in A. This approximate quench front velocity is found to be in agreement with the known front velocity for a one-dimensional slab.\r\n\r\nPart II: Contour integrals of the form I([...]) = [...]dz are considered for a large parameter [...]. In problems of interest, the exponent w is assumed to have simple saddle points at z = [...], i=1,2,3 which are allowed to coalesce, forming a single saddle of order three. Using a conformal map, the integral I is shown to be asymptotically equivalent to the study of the canonical integral J([...]) = [...]dt, which has simple saddles at t = 0, \u00b1 [...]. By applying the method of steepest descent, the complete asymptotic behavior of J([...]) is obtained for [...], uniformly as [...]." }, { "name": "Nosenchuck, Daniel Mark", "degree": "PhD", "year": "1982", "title": "Passive and Active Control of Boundary Layer Transition", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182006-135720", "creators": [ { "name": { "family": "Nosenchuck", "given": "Daniel Mark" }, "id": "Nosenchuck-Daniel-Mark", "display_name": "Nosenchuck, Daniel Mark" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CKFA-E875", "abstract": "It is well known that laminar-turbulent boundary layer transition is initiated by the formation of Tollmien-Schlichting laminar instability waves. The amplification rates of these waves are strongly dependent on the shape of the boundary layer velocity profile. Consequently, the transition process can be controlled by modifying the velocity profile. This can be accomplished by controlling the pressure gradient (dp/dx), using boundary layer suction, installing surface roughness elements, or by surface heating or cooling. Methods used to modify the transition process through changes in the mean velocity profile are called \"passive\" in this paper. There exists a large set of experiments and theory on the application of passive methods for boundary layer control. In the present work only surface heating will be addressed.
\r\n\r\nTransition measurements were made on a heated flat plate in water. Results are presented for several plate wall temperature distributions. An increase by a factor of 2.5 in transition Reynolds number was observed for a 5\u00b0C isothermal wall overheat. Buoyancy effects on transition were minimal due to the small Richardson and Grashof numbers encountered in the experiments.
\r\n\r\nThe amplification of laminar instability waves is comparatively to process, taking place over many boundary layer thicknesses. After the slow amplification of the laminar instability waves, transition occurs by a strong three dimensional dynamic instability. It appears possible to attenuate (or reinforce) the instability waves by introducing amplitude-and phase-controlled perturbations into the laminar boundary layer using feedback control system. This method is called \"active\" control and forms the larger part of the research reported in this thesis.
\r\n\r\nA combination of sensors, activators and feedback control electronics is required for active control. The sensors used in the experiments are flush-mounted hot film wall shear robes. A new type of activator was developed using thin, flush-mounted surface heating elements to excite instability waves in the laminar boundary layer by periodic (active) heating.
\r\n\r\nExperimental evidence is presented illustrating the effects of periodically heated flush mounted strips in perturbing a flat plate boundary layer in water. The results of superposition of forced laminar instability waves are also given. Finally, an active feedback-control system using a single hot film probe and strip heater was developed to control natural laminar instability waves in real time. It is shown that when the natural waves were attenuated, the transition length was increased by 25%, requiring only 10 watts of strip heater power. To accomplish the same transition delay using passive heating, the internal heating pads had to supply 1900 watts of power.
" }, { "name": "Ooi, Kean Khoon", "degree": "PhD", "year": "1982", "title": "Scale Effects on Cavitation Inception in Submerged Jets", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202006-102904", "creators": [ { "name": { "family": "Ooi", "given": "Kean Khoon" }, "id": "Ooi-Kean-Khoon", "display_name": "Ooi, Kean Khoon" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "chair", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "member", "display_name": "Acosta, Allan J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/qvn5-1075", "abstract": "The present work is an investigation into the scale effects on cavitation inception in submerged water jets. Four scale effects were studied: (i) jet size, (ii) jet velocity, (iii) dissolved air content, and (iv) the nuclei population in the flow. The nuclei population was artificially altered by \"electrolysis seeding.\"
\r\n\r\nHolography and schlieren photography were used to observe the flow. Direct measurements of the nuclei population were also accomplished by holography. In addition, the instantaneous pressure field in the jet was successfully mapped out using specially tailored bubbles as pressure sensors.
\r\n\r\nIt was found that inception did not generally occur in the cores of the turbulent eddies and that the region in which the cavities were first seen were dependent on the size of the jet.
\r\n\r\nPressure measurements showed that negative peak pressure fluctuation intensities of as high as 120 percent of the dynamic head existed in the jet. The results also revealed that the instantaneous pressure fluctuations have a slightly skewed bell shape probability distribution.
\r\n\r\nFor the present tests, the inception index was independent of the exit velocity for a constant size jet. However, when the flow was seeded, the inception number showed a linear dependence on velocity and this dependence increased with increased number of seeded nuclei. The effects of the nuclei number density and pressure fluctuations are incorporated in a \"probable cavitation occurrence\" parameter which shows promise in reducing scatter in this type of experiment.
" }, { "name": "Ortiz, Louis Alexander", "degree": "PhD", "year": "1982", "title": "Dynamic Centrifuge Testing of Cantilever Retaining Walls", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132006-104119", "creators": [ { "name": { "family": "Ortiz", "given": "Louis Alexander" }, "id": "Ortiz-Louis-Alexander", "display_name": "Ortiz, Louis Alexander" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "chair", "display_name": "Beck, James L." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "member", "display_name": "Scott, Ronald F." } ], "option_major": [ "civileng" ], "doi": "10.7907/vep9-1127", "abstract": "An investigation was made into the behavior of flexible cantilever walls retaining a cohesionless soil backfill and subjected to earthquake-type dynamic excitations using the centrifuge modelling technique. The study was motivated by the abundant observations of earth retaining structure damage and failures documented in earthquake damage reports.
\r\n\r\nThe \"prototype\" typical walls were designed using the traditional Mononobe-Okabe dynamic lateral earth pressure theory, were properly scaled for use in the centrifuge at 50 g's and were subjected to lateral earthquake-like motions which were considered to be of realistic levels. The walls were amply instrumented with pressure and displacement transducers, accelerometers, and strain gages. Moment, pressure, shear, and displacement distributions (static, dynamic, and residual) were obtained.
\r\n\r\nFrom the test data, some empirical curves for relating the upper bound responses of the retaining walls to the strong motion characteristics of the applied earthquakes were obtained.
" }, { "name": "Prouty, Dale Austen", "degree": "PhD", "year": "1982", "title": "Investigations of Near-Zone Doppler Effects", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142006-111227", "creators": [ { "name": { "family": "Prouty", "given": "Dale Austen" }, "id": "Prouty-Dale-Austen", "display_name": "Prouty, Dale Austen" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "chair", "display_name": "Wilts, Charles Harold" }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "member", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/vfzj-7d74", "abstract": "Far away from an electromagnetic source the normal Doppler shifts in frequency occur \u2013 a red shift for receding and a blue shift for approaching. As indicated by previous work with an infinitesimal dipole, different frequency shifts occur when the source and observer move closer together, into the near-zone. These \"near-zone Doppler effects\" are investigated for general sources and subsequently two specific examples are presented.
\r\n\r\nThe general results show that near-zone shifts are similar to far-zone shifts, but the local phase velocity must be used, i.e. \u03c9' \u2243 \u03c9(1 \u00b1 (v/vph)). In the far zone the phase velocity is the speed of light; in the near zone it differs. Fundamentally, the distance between surfaces of constant phase in the near zone is changed. The surfaces of constant phase for the waves are no longer spherical, but more ellipsoidal or spheroidal, so that a moving observer sees a different frequency shift.
\r\n\r\nTwo specific examples are presented to indicate the actual magnitude of near-zone effects. The examples include a prolate spheroidal antenna and a circular aperture.
\r\n\r\nOnce the magnitude of the effects is determined, the measurability of near-zone Doppler effects is discussed. The investigation concentrates on Fresnel zone effects due to the measurement problem.
\r\n\r\nFinally, it is shown that for an electrically large wire antenna (the spheroidal example) near-zone Doppler effects are measurable.
" }, { "name": "Psycharis, Ioannis N.", "degree": "PhD", "year": "1982", "title": "Dynamic Behavior of Rocking Structures Allowed to Uplift", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162018-151856693", "creators": [ { "name": { "family": "Psycharis", "given": "Ioannis N." }, "id": "Psycharis-Ioannis-N", "display_name": "Psycharis, Ioannis N." } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." } ], "option_major": [ "civileng" ], "doi": "10.7907/jexq-jr68", "abstract": "Strong shaking of structures during large earthquakes may result in some cases in partial separation of the base of the structure from the soil. This phenomenon of uplifting, which can affect the dynamic behavior of the structure significantly, even if the amount of uplift is small, is examined in this thesis. First the case of a rocking rigid block is investigated and then more complicated, flexible superstructures are introduced. Two foundation models which permit uplift are considered: the Winkler foundation and the much simpler \"two-spring\" foundation. Several energy dissipating mechanisms are also introduced into these models. It is shown that an equivalence between these two models for the foundation can be established, so that one can always work with the much simpler two-spring foundation. In this way complete analytical solutions can be derived in most cases. Moreover, simple approximate methods for the calculation of the apparent fundamental period of the rocking system are developed and simplified methods of analysis are proposed.
\r\n\r\nIn general, uplift leads to a softer vibrating system which behaves nonlinearly, although the response is composed of a sequence of linear responses. As a result, the apparent fundamental resonant frequency of the uplifting system is always less than the fundamental resonant frequency of both the soil-structure interacting system, in which lift-off is not allowed, and the superstructure itself. The second and higher resonant frequencies of the superstructure, however, are not affected significantly by lift-off. For damped foundations, the ratio of critical damping associated with the apparent fundamental mode decreases, in general, with the amount of lift-off. These effects of uplift on the dynamic properties of the rocking system can alter the response of the structure significantly during an earthquake. Nevertheless, it cannot be said a priori whether they are favorable to the behavior or not; this depends on the parameters of the system and the time history of the excitation.
" }, { "name": "Ravi-Chandar, K.", "degree": "PhD", "year": "1982", "title": "An Experimental Investigation into the Mechanics of Dynamic Fracture", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-104624", "creators": [ { "name": { "family": "Ravi-Chandar", "given": "K." }, "id": "Ravi-Chandar-K", "display_name": "Ravi-Chandar, K." } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZSX5-Q128", "abstract": "Current theories of dynamic fracture are based on elastodynamic analyses of mathematically sharp plane cracks and as such do not explain the observed terminal velocities or the phenomenon of crack branching satisfactorily. The present investigation addresses the above problems by using both microscopic and macroscopic interpretations. The experimental scheme that is used in this investigation is the configuration of a pressure loaded semi-infinite crack in an infinite medium. The loading is achieved through an electromagnetic device which provides highly repeatable loading. The method of caustics is used in conjunction with a high speed camera to obtain the time histories of the crack tip stress intensity factor and the crack position.
\r\n\r\nThe problems of crack initiation and crack arrest are explored. The stress intensity factor at initiation is found to be independent of the rate of applied loading when the latter is below about 104MPA/sec, but the initiation stress intensity factor increases considerably when the loading rate is increased further. Crack arrest is obtained in large specimen by using very low energy loading pulses. It was found that the stress intensity factor at crack arrest was constant and also that, within the time resolution of the high speed camera (5 \u03bcsec), the crack comes to a stop abruptly.
\r\n\r\nThe crack propagation and branching aspects were investigated first using post-mortem analysis of the fracture surfaces and high speed photomicrography to get an idea of the microscopic processes that occur in the fracure process. From this investigation, it was found that crack propagation involving high stress intensity factor and high velocity situations takes place by the growth and interaction of microcracks, due to the voids present in the material. A surprising result of this investigation was that cracks propagated at a constant velocity, although the stress intensity factor varied. Current theories of dynamic fracture cannot explain such behaviour. The crack branching process was found to be a continuous process arising out of propagation along a straight line. High speed photomicrographs of the branching process indicated the presence of a number of part-through attempted branches that interact with one another and finally the successful emergence of a few full fledged branches.
\r\n\r\nThe microscopic observations on the crack propagation and branching process leads to a new interpretation of dynamic fracture that attempts to qualitatively explain the constancy of the velocity of propagation, the terminal velocity and crack branching. The crack branching mechanism is a logical continuation of the mechanism for crack propagation.
\r\n" }, { "name": "Reinhall, Per Gustaf", "degree": "PhD", "year": "1982", "title": "The Analysis of a Nonlinear Difference Equation Occurring in Dynamical Systems", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-07082005-102658", "creators": [ { "name": { "family": "Reinhall", "given": "Per Gustaf" }, "id": "Reinhall-Per-Gustaf", "display_name": "Reinhall, Per Gustaf" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/X17F-E253", "abstract": "A difference equation with a cubic nonlinearity is examined. Using a phase plane analysis, both quasi-periodic and chaotically behaving solutions are found. The chaotic behavior is investigated in relation to heteroclinic and homoclinic oscillations of stable and unstable solution manifolds emanating from unstable periodic points. Certain criteria are developed which govern the existence of the stochastic behavior. An approximate solution technique is developed giving expressions for the quasi-periodic solutions close to a stable periodic point and the accuracy of these expressions are investigated. The stability of the solutions is examined and approximate local stability criteria are obtained. Stochastic excitation of a nonlinear difference equation is also considered and an approximate value of the second moment of the solution is obtained.
" }, { "name": "Romero, Louis Anthony", "degree": "PhD", "year": "1982", "title": "I. Similarity Solutions of the Equations of Three Phase Flow through Porous Media. II. The Fingering Problem in a Hele-Shaw Cell", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09082006-131345", "creators": [ { "name": { "family": "Romero", "given": "Louis Anthony" }, "id": "Romero-Louis-Anthony", "display_name": "Romero, Louis Anthony" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "member", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Leal", "given": "L. Gary" }, "id": "Leal-L-G", "role": "member", "display_name": "Leal, L. Gary" } ], "option_major": [ "appmath" ], "doi": "10.7907/MR6S-7C08", "abstract": "I
\r\n\r\nIn part I of this thesis similarity solutions to the equations of three phase flow through porous media are examined. The three phases are water, steam, and a noncondensing phase, most likely oil. The main purpose of analyzing such flows is to gain understanding of the steam flooding of oil fields.
\r\n\r\nProvided steam is being injected at a higher pressure than the initial field pressure, it is shown that there will always be at least two saturation shocks. As one increases the pressure of the injected steam several regimes are encountered; first the flow develops a region where all the steam is completely condensed, then the position of two of the shocks are interchanged, and finally one of the shocks grows weaker and is eventually replaced by an expansion fan.
\r\n\r\nIn sections 12 and 13 the stability of steadily moving condensation fronts in porous media is analyzed. For one special problem it is found that the sign of the jump in pressure gradient at the interface determines whether the interfaces are stable or unstable. This result is applied with some caution to the similarity solutions found in the earlier sections.
\r\n\r\nII
\r\n\r\nRecently McLean analyzed the shapes of fingers in a Hele-Shaw cell, including the effects of surface tension. His work resolved the question of the uniqueness of the shapes first brought up by Saffman and Taylor in their analysis that did not include surface tension. It is however felt that there are still unresolved problems.
\r\n\r\nIn determining the pressure jump across an interface there are two principal radii of curvature. McLean only took into account the effect of the larger of these, assuming that the other was constant along the outline of the finger. Unless the smaller radius is very nearly constant, it should in fact give a larger contribution to the jump in pressure. In this thesis the effect of this smaller radius of curvature is modelled by assuming that it is a function of the normal velocity of the mean two dimensional surface of the finger.
\r\n\r\nIt is found that if one only takes into account the smaller radius of curvature, the problem is not uniquely determined, as in the case with no surface tension at all. When both radii of curvature are taken into account, the effect of the smaller radius of curvature is to modify the finger shapes in a way that is qualitatively in agreement with experimental data. Also, McLean's results are checked by an independent numerical scheme, and the results are found to be in excellent agreement. Using both methods of solution a second solution branch other than that described by McLean was also found.
" }, { "name": "Scheid, Robert Elmer, Jr", "degree": "PhD", "year": "1982", "title": "The Accurate Numerical Solution of Highly Oscillatory Ordinary Differential Equations", "advisor": "Kreiss, Heinz-Otto", "url": "https://resolver.caltech.edu/CaltechETD:etd-05042006-103859", "creators": [ { "name": { "family": "Scheid", "given": "Robert Elmer, Jr" }, "id": "Scheid-Robert-Elmer", "display_name": "Scheid, Robert Elmer, Jr" } ], "advisors": [ { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "advisor", "display_name": "Kreiss, Heinz-Otto" } ], "committee": [ { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "chair", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Tadmor", "given": "E." }, "id": "Tadmor-E", "role": "member", "display_name": "Tadmor, E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "appmath" ], "doi": "10.7907/4JVY-JB67", "abstract": "We consider systems of ordinary differential equations with rapidly oscillating solutions. Conventional numerical methods require an excessively small time step (Δt = 0(εh), where h is the step size necessary for the resolution of a smooth function of t and 1/ε measures the size of the large eigenvalues of the system's Jacobian).
\r\n\r\nFor the linear problem with well-separated large eigenvalues we introduce smooth transformations which lead to the separation of the time scales and computation with a large time step (Δt = 0(h)). For more general problems, including systems with weak polynomial nonlinearities, we develop an asymptotic theory which leads to expansions whose terms are suitable for numerical approximation. Resonances can be detected and resolved often with a large time step (Δt = 0(h)). Passage through resonance in nonautonomous systems can be resolved by a moderate time step (Δt = 0(√εh)).
\r\n" }, { "name": "Schember, Helene R.", "degree": "PhD", "year": "1982", "title": "A New Model for Three-Dimensional Nonlinear Dispersive Long Waves", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232005-153011", "creators": [ { "name": { "family": "Schember", "given": "Helene R." }, "id": "Schember-Helene-R", "display_name": "Schember, Helene R." } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "chair", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "eng" ], "doi": "10.7907/05SA-9135", "abstract": "A new formulation of the pair of Boussinesq-class equations for modelling the propagation of three-dimensional nonlinear dispersive long water waves is presented. This set of model equations permits spatial and temporal variations of the bottom topography. Further, the two resultant equations may be combined into a single equation through the introduction of an irrotational layer-mean velocity. An exact permanent-form solution is derived for the combined equation, which is still of the Boussinesq-class and includes reflection. This solution for the surface height is found to describe a slightly wider wave than the permanent form solution to the uni-directional Korteweg-deVries Equation.
\r\n\r\nA numerical scheme using an implicit finite-difference method is developed to solve the combined equation for propagation over fixed sloping bottom topography. The scheme is tested for various grid sizes using the permanent-form solution, and an oscillatory tail is seen to develop as a result of insufficient mesh refinement.
\r\n\r\nSeveral cases of wave propagation over a straight sloping ramp onto a shelf are solved using the permanent-form solution as initial conditions and the results are found to be in good agreement with previous results obtained by using either the Boussinesq dual-equation set or the single Korteweg-deVries equation. The combined equation is used to solve the related problem in two horizontal dimensions of a wave propagating in a channel having a curved-ramp bottom topography. Depending on the specific topography, focussing or defocussing occurs and the crest is selectively amplified. Indications of cross-channel oscillation are presented. Linear, nondispersive theory is used to solve a case with identical topographical features and initial condition. The solutions using the simplified theory are found to be considerably different from the results for nonlinear, dispersive theory with respect to the overall three-dimensional wave shape as well as in the areas of crest amplification, soliton formation and cross-channel effects.
" }, { "name": "Schweig, Edgard", "degree": "PhD", "year": "1982", "title": "Dielectric Waveguides for Millimeter Waves", "advisor": "Bridges, William B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062006-152644", "creators": [ { "name": { "family": "Schweig", "given": "Edgard" }, "id": "Schweig-Edgard", "display_name": "Schweig, Edgard" } ], "advisors": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "advisor", "display_name": "Bridges, William B." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/05DR-KV58", "abstract": "In this thesis, we analyze high-permittivity dielectric waveguides for use as guiding structures of millimeter waves. Two basic geometries are considered: the circular and rectangular guides.
\r\n\r\nIn Part I, we describe the theory of round fibers surrounded by an infinite cladding. Millimeter wavelengths are comparable to the physical dimensions of the guide. Therefore, a large difference in permittivity between the core and the cladding is required in order to provide for a tight confinement of the fields. We present the results of computations of the propagation characteristics and losses of fibers of very high permittivity. We note that the distribution of the electromagnetic power between the core and the cladding can be deduced from the dispersion curves. Finally, we consider the feasibility of a dielectric fiber made of thallium bromide-iodide (KRS-5) for the long distance transmission of W-band signals (94 GHz). Using our measurements of the dielectric parameters of KRS-5, we find that the losses are several orders of magnitude higher than the losses of conventional metallic waveguides.
\r\n\r\nIn Part II, we analyze rectangular dielectric guides made of high-permittivity materials such as GaAs that would permit the fabrication of active devices directly into the transmission line. We present a new numerical technique base on finite-differences for computing the modes of dielectric guiding structures. This method is simple and efficient in computer storage and computational time. We use it to compute the modes of a rectangular dielectric waveguide and compare the numerical results to those obtained from Marcatili's closed-form solution. We find that this latter one is a good approximation for the dominant mode of a rectangular guide even when the permittivity of the guide is large compared to the outer medium. For higher order modes, Marcatili's solution predicts incorrect propagation curves. We have also observed the presence in our numerical solution of \"spurious modes\" that are thought to be due to the mathematical indefinitiveness of the problem.
\r\n\r\nIn Part III, we present a waveguide technique for the measurement of complex dielectric constants at millimiter wave frequencies: the shorted-waveguide method. Waveguide methods have been extensively used at lower frequencies but this is the first application at 94 GHZ. We use a novel sample preparation technique that allows for an accurate and gap-free positionment of a ductile dielectric material inside a metallic waveguide. We note that the correct choice of sample lengths is critical to the accuracy of the measurement of the loss tangent. Finally, we summarize the results of our measurement of the dielectric constant and loss tangent of thallium bromide-iodide (KRS-5) and thallium bromide-chloride (KRS-6).
" }, { "name": "Scott, David Martin", "degree": "PhD", "year": "1982", "title": "The Effects of Oxygen on the Formation of Ni, Pd, and Pt Silicides", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062006-140245", "creators": [ { "name": { "family": "Scott", "given": "David Martin" }, "id": "Scott-David-Martin", "display_name": "Scott, David Martin" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "chair", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Barnes", "given": "Charles A." }, "id": "Barnes-C-A", "role": "member", "display_name": "Barnes, Charles A." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/234h-2915", "abstract": "A systematic study of the effects of implanted oxygen on the formation of Ni, Pt and Pd silicides has been carried out using 4He+ backscattering spectrometry (BS), 16O(d,\u03b1)14N nuclear reaction analysis (NRA) and x-ray photoelectron spectroscopy (XPS) for the analysis. A detailed presentation of the NRA technique is given as this technique was central to this study and is not as generally known as are BS and XPS (Chapter II). The depth resolution of this technique is found to be ~ 150 to 200 \u00c5 in Ni. The oxygen sensitivity is essentially limited by measurement time (~ 10 hrs) to ~ 1019 to 1020 0/cm2.
\r\n\r\nThe effect of oxygen on the formation of Ni2Si is shown to vary with the initial location of the oxygen (Chapter III). Ni is the dominant diffusing species in Ni2Si formation. Oxygen initially located in the Ni film is found to build up during annealing at the Ni-Ni2Si interface until a diffusion barrier to the Ni is formed. The XPS data shows this barrier to be SiO2. Oxygen picked up during annealing from the ambient also plays a role in the buildup of this barrier. Once Ni2Si growth is halted, the second phase NiSi begins to nucleate and grow. The result is the simultaneous presence of Ni, Ni2Si and NiSi in the implanted samples. The threshold dose \u03d5th necessary for barrier formation is ~ 1.2 x 1016 0/cm2. This is equivalent to ~ 26 \u00c5 of stoichiometric fused quartz if present as a layer. For the oxygen initially present in the Si, the oxygen is incorporated into the Ni2Si layer without an interfacial accumulation taking place. The relative reduction in oxygen density parallels that of the Si density as Si forms Ni2Si.
\r\n\r\nWe model these observations in terms of the asymmetries that are present in this system with regard to the moving species in Ni2Si formation and with regard to the chemical reactivity of oxygen with Ni and Si.
\r\n\r\nThe effects of implanted oxygen on NiSi formation are studied for the case of the oxygen initially present in the Ni2Si film on a Si <100> substrate. Upon annealing, NiSi grows with square root of time in both implanted and unimplanted samples. This disagrees with the linear rate previously reported. The growth is slightly slower for implanted samples. The slowing is uncorrelated with the amount of oxygen, suggesting that a structural change due to ion implantation is the cause. During NiSi formation, oxygen is incorporated into the NiSi film without interfacial accumulation, but the oxygen distribution is seen to move towards the surface. This motion is explained in terms of a simple model based on the chemical affinity of oxygen to Si and Ni and the fact that Ni is the moving species in NiSi growth. The shift in the oxygen peak position during NiSi formation enables the implanted oxygen to act as a diffusion marker. This confirms that Ni is the diffusing species in NiSi formation. The use of implanted oxygen as a diffusion marker in thin film studies is briefly explored.
\r\n\r\nWe have also studied the effect of impurity oxygen initially present in a Pt film on Pt2Si formation (Chapter IV). We found that the redistribution of the oxygen during annealing, subsequent barrier formation and threshold oxygen dose were all identical to that of the corresponding Ni case. This result is shown to be consistent with the asymmetries present in the chemistry of oxygen relative to Pt and Si and in the initial location of the oxygen relative to the moving species (Pt). The case of oxygen initially located in the Si was not investigated as this case most likely is also identical to the corresponding Ni case.
\r\n\r\nFor the impurity oxygen initially present in a Pd film on a Si <100> substrate (Chapter V), we found that the oxygen is incorporated into the Pd2Si without a diffusion barrier being formed. The implanted oxygen has no effect on the growth of Pt2Si. We find oxygen to be mobile in the Pd at an annealing temperature of only 250\u00b0C. Upon annealing the oxygen diffuses to the Pd-Pt2Si interface, to react and form SiO2 there. Simultaneously Si diffuses through the Pd2Si layer and forms additional silicide at the Pd-Pd2Si interface thereby incorporating the SiO2 into the Pd2Si. Thus barrier formation does not occur. We also show that our results identify Si as the dominant diffusing species during Pd2Si formation rather than both Pd and Si as previously reported.
\r\n\r\nGeneralizing from the result of our study of the effects of impurity oxygen on the formation of the silicides of Ni, Pt and Pd we present a conceptual framework for impurity effects in metal silicide formation (Chapter VI). This model relies on the asymmetries present with regard to the initial location of the impurity relative to the moving species and with regard to the chemical affinities of the impurity relative to the reacting species. The results for impurity N in the Ni-Si system are briefly compared with predictions of the model and shown to agree.
\r\n\r\nFurther work suggested by this model is summarized next (Chapter VII). The cases covered are impurity N in the Ni-Si, Pt-Si and Pd-Si systems along with impurity C in the Ni-Si and Pt-Si systems. Also covered are the preliminary results of contact restivity measurements after barrier formation has occurred for the cases of impurity N and O in the Ni-Si system. The results of this additional work are shown to be consistent with the model.
" }, { "name": "Shieh, An Huh", "degree": "PhD", "year": "1982", "title": "Non-Stationary Lattice Theory", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142006-112813", "creators": [ { "name": { "family": "Shieh", "given": "An Huh" }, "id": "Shieh-An-Huh", "display_name": "Shieh, An Huh" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/xknf-r113", "abstract": "No abstract submitted." }, { "name": "Stevenson, John Cary", "degree": "PhD", "year": "1982", "title": "The Rheology of a Bituminous Coal", "advisor": "Corcoran, William Harrison", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122006-151359", "creators": [ { "name": { "family": "Stevenson", "given": "John Cary" }, "id": "Stevenson-John-Cary", "display_name": "Stevenson, John Cary" } ], "advisors": [ { "name": { "family": "Corcoran", "given": "William Harrison" }, "id": "Corcoran-W-H", "role": "advisor", "display_name": "Corcoran, William Harrison" } ], "committee": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "chair", "display_name": "Acosta, Allan J." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "England", "given": "Chris" }, "id": "England-Chris", "role": "member", "display_name": "England, Chris" }, { "name": { "family": "Corcoran", "given": "William Harrison" }, "id": "Corcoran-W-H", "role": "member", "display_name": "Corcoran, William Harrison" } ], "option_major": [ "mecheng" ], "doi": "10.7907/06Q1-DZ20", "abstract": "The fluidity of a rapidly heated, bituminous coal was studied with a capillary rheometer. Quantitative measurements of overall fluidity, of transition from no flow to flow, and of the effects of presence of the gaseous phase were the principal objectives.
\r\n\r\nSeparate measurements of the density of the coal indicated that the major changes in density with time were due to the production of gas by decomposition. The volume fraction of gas was calculated from the density measurements.
\r\n\r\nThe relationships between volumetric flow rate and pressure drop were expressed in terms of an overall, or \"effective,\" viscosity. The overall viscosity displayed values as low as thirty poise, and its rheological classification was Newtonian within the accuracy of the experimental equipment. The transition from no flow to flow was quite sudden, and it was independent of the volume of gas present in the reservoir.
\r\n\r\nThe multi-component, multi-phase flow of coal was considered to be a two-component, two-phase, liquid-gas system. Various correlations found in the literature were applied to the overall viscosity data, and estimates of the viscosity of the liquid phase were made. A constitutive relationship for the density as a function of temperature, time, and pressure was developed. Closed-form solutions of the simplified momentum equation were generated based on definitions of a mean viscosity as a function of the viscosities of the liquid and the gas, and the volume fractions of the liquid and the gas. Because of the magnitude of the volume fraction of gas, the viscosity of the liquid phase was greater than the overall viscosity of the mixture.
\r\n" }, { "name": "Tezduyar, Tayfun Ersin", "degree": "PhD", "year": "1982", "title": "Finite Element Formulations for Hyperbolic Systems with Particular Emphasis on the Compressible Euler Equations", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112006-130749", "creators": [ { "name": { "family": "Tezduyar", "given": "Tayfun Ersin" }, "id": "Tezduyar-Tayfun-Ersin", "display_name": "Tezduyar, Tayfun Ersin" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "chair", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Hughes", "given": "Thomas J. R." }, "id": "Hughes-T-J-R", "role": "member", "display_name": "Hughes, Thomas J. R." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "mecheng" ], "doi": "10.7907/994z-vj07", "abstract": "A Petrov-Galerkin finite element formulation for first-order hyperbolic systems is developed generalizing the streamline approach which has been successfully applied previously to convection-diffusion and incompressible Navier-Stokes equations. The formulation is shown to possess desirable stability and accuracy properties.
\r\n\r\nThe algorithm is applied to the Euler equations in conservation-law form and is shown to be effective in all cases studied, including ones with discontinuous solutions. Accurate and crisp representation of shock fronts in transonic problems is achieved.
" }, { "name": "Trebitz, Bernd Otto", "degree": "PhD", "year": "1982", "title": "Acoustic Transmission Imaging for Flow Diagnostics", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-145444", "creators": [ { "name": { "family": "Trebitz", "given": "Bernd Otto" }, "id": "Trebitz-Bernd-Otto", "display_name": "Trebitz, Bernd Otto" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/pnsp-rk30", "abstract": "Wave propagation through a given flow field can be utilized to obtain information about the flow. Acoustic waves in particular offer the possibility of measuring velocity fields, because sound waves are convected with the flow, and temperature fields, because the acoustic index of refraction is a strong function of temperature. This work concentrates on situations where the first effect is dominating compared to the latter one.
\r\n\r\nA sound system capable of \"illuminating\" a flow field with ultrasonic waves and measuring the amplitude and phase distribution of the transmitted wave as a function of time was constructed. A large area transmitter and a linear receiving array were used as transducers. Parallel signal processing and interleaved data conversion and acquisition result in a maximum frame rate of 10 kHz.
\r\n\r\nThe feasibility of measuring velocity disturbances with ultrasound was demonstrated by transmitting sound through a vortex, which was generated in a duct by an airfoil swirl generator. Assuming an exponential fit for the tangential velocity component, inner core radius and circulation can be determined directly from the phase change of the transmitted wave due to the vortex. A more accurate representation of the radial velocity profile can be found by digital reconstruction via the Abel inversion formula, which allows reconstruction of rotationally symmetric objects from line projections. Even though the flow field under investigation was steady, this is neither a restriction of the technique, nor of the apparatus. However, the repetition rate for consecutive data frames depends on the operating procedure.
" }, { "name": "Young, James Robert", "degree": "PhD", "year": "1982", "title": "A Study of the Adsorption of Ni(II) onto an Amorphous Silica Surface by Chemical and NMR Methods", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062006-143724", "creators": [ { "name": { "family": "Young", "given": "James Robert" }, "id": "Young-James-Robert", "display_name": "Young, James Robert" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Chan", "given": "Sunney I." }, "id": "Chan-S-I", "orcid": "0000-0002-5348-2723", "role": "member", "display_name": "Chan, Sunney I." }, { "name": { "family": "Anson", "given": "Fred C." }, "id": "Anson-F-C", "role": "member", "display_name": "Anson, Fred C." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "envreng" ], "doi": "10.7907/Q574-CG34", "abstract": "The physical structure of the electrical double layer at a metal-oxide surface is not well-known. Adsorption models, which require a knowledge of the location of the adsorbed species, have integrated different descriptions of the electrical double layer into a common coordination chemistry framework.
\r\n\r\nThe goal of this work was to determine the hydration number of Ni(II) species adsorbed unto a silica surface by extending a nuclear magnetic resonance (NMR) technique used to determine the hydration number of paramagnetic metal ions in solution. Information about the environment of the adsorbed Ni(II) species at the molecular level could then be incorporated into state-of-the-art adsorption models.
\r\n\r\nIn order to conduct the NMR experiment, it was necessary to determine the speciation of a Ni(II)-silica system at a high metal-ion loading. Titrations, in 0.1 N NaClO4, were conducted on silica suspensions, nickel solutions and a system where the total amount of Ni(II) was twice the total number of available surface binding sites. The pH dependence of the adsorption process and the maximum adsorption density achievable were investigated.
\r\n\r\nThe amount of charge on a silica surface was found to increase logarithmically with pH. Formation of surface complexes with Na+ provided the necessary mechanism to account for this behavior. All of the Ni(II) present in the Ni(II)-silica system was removed by adsorption processes at a pH of approximately 8. In the same system, removal of Ni(II) by a precipitation process does not occur until Ni(OH)2(s) forms at a pH of approximately 8.5. The adsorption process was not limited by the number of surface hydroxyl groups present. It was shown that the NiOH moiety of a hydrolyzed nickel surface complex could provide the new adsorption centers necessary for a multilayer adsorption process, if the NiOH group functions chemically like an SiOH group. The observation of adsorption of Ni(II) onto a silica surface at coverages greater than one monolayer indicates siliceous soils and sediments may have a greater capacity to bind Ni(II) than previously thought.
\r\n\r\nThe capability of the NMR spectroscopic technique to determine hydration numbers of adsorbed metal ions was demonstrated. Usefulness of the technique was limited by the slowness of water exchange between the first coordination sphere of the adsorbed Ni(II) species and bulk solution. A lower limit for the hydration number of the adsorbed Ni(II) species was calculated to be 4.4. This is at the lower end of the predicted range for this value (4.5 to 6.0). Suggestions were made to improve upon the design of the NMR experiment so as to overcome the limitations encountered.
" }, { "name": "van Ingen, Catharine", "degree": "PhD", "year": "1982", "title": "Observations in a Sediment-Laden Flow by Use of Laser-Doppler Velocimetry", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192007-155029", "creators": [ { "name": { "family": "van Ingen", "given": "Catharine" }, "id": "van-Ingen-Catharine", "display_name": "van Ingen, Catharine" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "member", "display_name": "Vanoni, Vito A." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." } ], "option_major": [ "civileng" ], "doi": "10.7907/X24M-0R50", "abstract": "The laser-Doppler velocimetry technique was adapted for use in sediment-laden flows. The developed instrumentation was used to make one-dimensional, instantaneous measurements of both fluid and sediment grain velocities throughout the water column in such a flow. The velocimetry results were obtained in a steady, uniform flow over a natural sediment bed in the high-transport, flat bed regime.
\r\n\r\nLaser-Doppler velocimetry is particularly attractive for use in sediment-laden flows as no calibration is required and no probe is introduced into the flow field. Measurements of the fluid velocity and the occurrence and velocity of individual sediment grains are possible with the instrumentation developed in this study. The major difficulties encountered are the possible conditional sampling, hence possible biasing, of the fluid velocity data and the failure of the instrumentation to record or resolve individual sediment grains at higher sediment transport rates. The instrumentation employed in this study is still in the developmental stages and suggestions for its improvement are given.
\r\n\r\nDespite the difficulties encountered, the data obtained in this study give some insights into the mechanics of suspension and entrainment of sediment during transport by water. The longitudinal turbulence intensity does not seem to be significantly affected by the presence of suspended sediment; the turbulence intensities observed in the sediment-laden flow of this study do not differ greatly from the values reported by previous investigators for clear fluid flows. The mean and standard deviation of the sediment grain velocity were observed to be less than those for the fluid velocity in the lower portion of the flow, but respectively greater near the water surface.
\r\n\r\nThe data demonstrate the shortcomings of the continuum approach to the mechanics of the suspension of sediment. The length (or time) scales of the fluid turbulence are smaller than the length (or time) scale of a set of sediment grains required to define suspended sediment concentration. Near the water surface, where the velocimeter acts as a grain counter, the probability density functions of the sediment grain inter-arrival times, the time between the detection of successive sediment grains, were observed to be negative exponentials. The transport of individual sediment grains might be modeled as a Poisson process.
\r\n\r\nThis work is the foundation of an ongoing experimental program of direct measurements of the fine-scale, time-fluctuating characteristics of sediment-laden flows. This study developed and implemented instrumentation capable of making such measurements and established a conceptual framework for the subsequent interpretation of the data obtained. Two-dimensional measurements, with improved instrumentation, will give additional insights into the mechanics of sediment transport.
" }, { "name": "Bernal, Luis Paulino", "degree": "PhD", "year": "1981", "title": "The Coherent Structure of Turbulent Mixing Layers. I. Similarity of the Primary Vortex Structure. II. Secondary Streamwise Vortex Structure", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-08262005-154143", "creators": [ { "name": { "family": "Bernal", "given": "Luis Paulino" }, "id": "Bernal-Luis-Paulino", "display_name": "Bernal, Luis Paulino" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "chair", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." }, { "name": { "family": "Ingersoll", "given": "Andrew P." }, "id": "Ingersoll-A-P", "orcid": "0000-0002-2035-9198", "role": "member", "display_name": "Ingersoll, Andrew P." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z52D-SA34", "abstract": "The primary spanwise organized vortex structure and the secondary streamwise vortex structure of turbulent mixing layers have been investigated. Flow visualization motion pictures of a constant density mixing layer were used to measure the properties of the large scale vortices. It was found that after an initial transition region mean properties of the large scale vortices reach the expected linear growth with downstream distance required by similarity. In the self-similar region, the vortex core area and visual thickness increase continuously during its life-span.
\r\n\r\nA theoretical model of probability distribution function for the large-scale vortex circulation was developed. This distribution is found to be lognormal and to have a standard deviation, normalized with the mean of 0.28. From this model the mean life-span of the vortices could also be obtained and was found to be 0.67 times the mean life-span position.
\r\n\r\nThe streamwise streak pattern observed by Konrad (1976) and Breidenthal (1978) in plan-view pictures of the mixing layer was investigated, using flow visualization and spanwise concentration measurements. It was confirmed that this pattern is the result of a secondary vortex structure dominated by streamwise, counterrotating vortices. A detailed description of its spatial relation to the primary, spanwise vortex structure is presented. From time average flow pictures, the onset position and initial scale of the secondary structures were determined. From concentration measurements, spanwise variations in mean properties, resulting from the secondary structure, were found. This also showed an increase of the spanwise scale with downstream distance and the existence of the streamwise vortices in the fully developed turbulent region. In this region the mean spacing is found approximately equal to the vorticity thickness.
" }, { "name": "Brooks, Alexander Nelson", "degree": "PhD", "year": "1981", "title": "A Petrov-Galerkin Finite Element Formulation for Convection Dominated Flows", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012005-161447", "creators": [ { "name": { "family": "Brooks", "given": "Alexander Nelson" }, "id": "Brooks-Alexander-Nelson", "display_name": "Brooks, Alexander Nelson" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "chair", "display_name": "Housner, George W." }, { "name": { "family": "Hughes", "given": "Thomas J. R." }, "id": "Hughes-T-J-R", "role": "member", "display_name": "Hughes, Thomas J. R." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" } ], "option_major": [ "civileng" ], "doi": "10.7907/Q164-VZ22", "abstract": "In this thesis, a new finite element formulation for convection dominated flows is developed. The basis of the formulation is the streamline upwind concept, which provides an accurate multidimensional generalization of optimal one-dimensional upwind schemes. When implemented as a consistent Petrov-Galerkin weighted residual method, it is shown that the new formulation is not subject to the artificial diffusion criticisms associated with many classical upwind methods.
\r\n\r\nThe effectiveness of the streamline upwind/Petrov-Galerkin formulation for the linear advection diffusion equation is demonstrated with numerical examples. The formulation is extended to the treatment of the incompressible Navier-Stokes equations. An efficient implicit pressure/explicit velocity transient algorithm is developed which allows for several treatments of the incompressibility constraint and for multiple iterations within a time step. The algorithm is demonstrated on the problem of vortex shedding from a circular cylinder at a Reynolds number of 100.
" }, { "name": "Brown, Arthur Raymond", "degree": "PhD", "year": "1981", "title": "Topics in the Analysis, Measurement, and Design of High-Performance Switching Regulators", "advisor": "Middlebrook, Robert David; Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-10092006-083114", "creators": [ { "name": { "family": "Brown", "given": "Arthur Raymond" }, "id": "Brown-Arthur-Raymond", "display_name": "Brown, Arthur Raymond" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "co-advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "chair", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "member", "display_name": "Cuk, Slobodan" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-C-H", "role": "member", "display_name": "Wilts, Charles Harold" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SQ09-ZS78", "abstract": "This thesis treats several issues in the analysis, measurements and design of high-performance switching regulator systems. In Part 1 the high-frequency capabilities of two switching regulator modeling techniques, state-space averaging and discrete modeling, are compared, using the subharmonic instability in current-programmed regulators as a test. As a result of this comparison, a new small-signal, linear, time-invariant modeling technique, called sampled-data modeling, is developed. This new method retains the continuous form of state-space averaging but also possesses the accuracy of discrete modeling, and thus it combines the best features of the two techniques.
\r\n\r\nIn Part II the newly developed sampled-data modeling technique is applied to the question of the interpretation of loop gain measurements in high-performance switching regulators. As a result of the inaccuracy of state-space averaging near one-half the switching frequency, conventional loop gain predictions are found to be inadequate in this regime. Sampled-data analysis is employed to develop new theoretical predictions which closely match various kinds of loop gain measurements in high-performance systems.
\r\n\r\nFinally, in Part III attention is turned to a potential sensitivity problem in high-performance switching regulators. For systems whose bandwidths lie close to one-half the switching frequency, even small changes in the operating environment of the power converter may result in dramatic degradation of the system's dynamic characteristics. Formulas for the estimation of this sensitivity are developed, and adaptive control, in which feedback gains are functions of certain important circuit quantities, is proposed as a means of curing the problem. Several different adaptive control schemes are proposed, and the implementation and testing of two of these strategies demonstrate their superiority over a conventional, non-adaptive design.
" }, { "name": "Cohen, Martin", "degree": "PhD", "year": "1981", "title": "Silent Boundary Methods for Transient Wave Analysis", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechThesis:08132021-221014507", "creators": [ { "name": { "family": "Cohen", "given": "Martin" }, "id": "Cohen-Martin", "display_name": "Cohen, Martin" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/xrgh-ag46", "abstract": "This thesis sets forth a dynamic model, designed to absorb infinitely radiating waves in a finite, computational grid. The analysis is primarily directed toward the problem of soil-structure interaction, where energy propagates from a region near a structure, outward toward the boundaries.
\r\n\r\nThe proposed method, called the extended-paraxial boundary, is derived from one-directional, wave theories that have been propounded by other authors. In this thesis, the theory is presented from a more general viewpoint and is studied for its stability properties. This work suggests some modifications to the method as it was first presented. Innovations are also put forward in the boundary's implementation for finite element calculations. These alterations render the boundary an effective wave absorber.
\r\n\r\nThe extended-paraxial boundary is then compared, both analytically and numerically, with two other transmitting (or silent) boundaries currently available -- the standard-viscous and unified-viscous methods. The analytical results indicate that the extended-paraxial boundary enjoys a distinct advantage in cancelling wave reflections; actual numerical tests revealed a small superiority over the viscous approaches.
\r\n\r\nVarious issues are also discussed as they relate to the silent boundaries. These include Rayleigh waves, spherically symmetric and axially symmetric waves, nonlinear waves, anisotropic media, and numerical stability.
" }, { "name": "Gabriel, Andrew Keith", "degree": "PhD", "year": "1981", "title": "Optogalvanic Spectroscopy and Cataphoretic Laser Isotope Separation", "advisor": "Shair, Fredrick H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282010-100527331", "creators": [ { "name": { "family": "Gabriel", "given": "Andrew Keith" }, "id": "Gabriel-Andrew-Keith", "display_name": "Gabriel, Andrew Keith" } ], "advisors": [ { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "advisor", "display_name": "Shair, Fredrick H." } ], "committee": [ { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "chair", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Bellan", "given": "Paul Murray" }, "id": "Bellan-P-M", "orcid": "0000-0002-0886-8782", "role": "member", "display_name": "Bellan, Paul Murray" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/xhjf-aa40", "abstract": "A microscopic theory for the positive column discharge (PCD) is developed using rate equations and power balance equations to model the microscopic discharge processes. Macroscopic variables are calculated from the microscopic parameters. The model is used to characterize a hydrogen-helium PCD.
\r\n\r\nThe equations in the model are modified to account for the presence of resonant (H-alpha) radiation from an external source. The model is then used to predict the voltage change in a hydrogen PCD (the optogalvanic effect) as a function of current, illumination intensity, and gas pressure. The results compare very favorably with experiments conducted to measure the OGE.
\r\n\r\nTransient voltage changes induced by resonant illumination in a PCD are calculated by numerical integration of the model equations. Perturbation theory is applied to the equations to obtain more physical insight into the physics of the transient OGE.
\r\n\r\nThe experimental apparatus used to measure the OGE and that used to measure the electron temperature (double probes) are described. A discussion of experimental problems covers some of the difficulties encountered.
\r\n\r\nThe PCD model and OGE model are used to evaluate the practicality of separating hydrogen and deuterium by optically assisted cataphoresis in the PCD.
\r\n\r\nThe possibility that recombination is a dominant process in the discharge is discussed in detail and rejected.
\r\n\r\nA careful description of the interaction of the illuminating radiation and the PCD plasma is given, with special attention to homogeneous and inhomogeneous broadening processes, saturation of absorption and saturation of the OGE, and the relative bandwidths of the illuminating radiation and discharge gas.
\r\n\r\nSome suggestions are made for future work.
" }, { "name": "Glezer, Ari", "degree": "PhD", "year": "1981", "title": "An Experimental Study of a Turbulent Vortex Ring", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-10092006-080016", "creators": [ { "name": { "family": "Glezer", "given": "Ari" }, "id": "Glezer-Ari", "display_name": "Glezer, Ari" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "chair", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "member", "display_name": "Kubota, Toshi" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RC4P-DA56", "abstract": "An apparatus has been constructed to study the formation and dynamics of vortex rings. The rings are formed in water by a momentary jet discharge downward into a glass tank from an orifice in a submerged plate. The necessary impulse is provided by a pressurized reservoir and is controlled by a fast programmable solenoid valve.
\r\n\r\nA particular turbulent vortex ring with a relatively thin core was chosen for detailed study. The velocity field of this ring was measured at numerous locations in the tank, using a two-channel laser-Doppler velocimeter with digital tracking electronics. Beamsplitting and frequency-shifting were accomplished by two partially-overlapping radial phase gratings driven by hysteresis-synchronous motors.
\r\n\r\nThe main aim of the research was to verify the similarity properties of the turbulent vortex ring and to determine mean particle paths and mean vorticity contours in the appropriate nonsteady similarity coordinates x/t\u00bc, r/t\u00bc. Some novel pattern-recognition techniques were developed to overcome the problem of dispersion in the trajectories of individual vortices.
" }, { "name": "Hall, Shawn Anthony", "degree": "PhD", "year": "1981", "title": "Vortex-Induced Vibrations of Structures", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02222018-150519570", "creators": [ { "name": { "family": "Hall", "given": "Shawn Anthony" }, "id": "Hall-Shawn-Anthony", "display_name": "Hall, Shawn Anthony" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "chair", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Lorden", "given": "Gary A." }, "id": "Lorden-G-A", "role": "member", "display_name": "Lorden, Gary A." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Y4QP-A998", "abstract": "Vortex-induced oscillations, often of concern when a bluff structure is exposed to fluid cross-flow, are considered herein using a semi-empirical modeling approach. Based on the fluid momentum theorem, the model involves a highly simplified abstraction of the complex flow field, and major assumptions concerning the nature of the coupling between the fluid and the oscillating structure.
\r\n\r\nThree prototype problems are studied, including harmonically forced cylinders, spring-mounted cylinders, and taut elastic cables; in each case the structure is assumed to be of circular cross-section and situated in a uniform cross-flow. Only oscillations transverse to the flow are considered. The problem of modal interaction for elastic cables, typically of interest when the fluid flow excites high-mode-number resonances, is given particular attention.
\r\n\r\nThe model produces a set of nonlinear, ordinary differential equations describing the coupled fluid/structure oscillations. Steady-state oscillatory solutions to these equations are found analytically and are examined for stability. Using various regression techniques, the steady-state solutions are then fit to experimental data for forced and spring-mounted cylinders. Finally, the model's predictions for elastic cables are used to postulate a qualitative picture of modal interaction, certain features of which have been observed experimentally.
" }, { "name": "James, Ralph Boyd", "degree": "PhD", "year": "1981", "title": "Theoretical Studies of the Nonlinear Infrared Properties of p-Type Semiconductors", "advisor": "Smith, Darryl L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102006-093346", "creators": [ { "name": { "family": "James", "given": "Ralph Boyd" }, "id": "James-Ralph-Boyd", "display_name": "James, Ralph Boyd" } ], "advisors": [ { "name": { "family": "Smith", "given": "Darryl L." }, "id": "Smith-D-L", "role": "advisor", "display_name": "Smith, Darryl L." } ], "committee": [ { "name": { "family": "Smith", "given": "Darryl L." }, "id": "Smith-D-L", "role": "chair", "display_name": "Smith, Darryl L." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/e2ha-tt71", "abstract": "This thesis presents theoretical studies of the nonlinear optical properties of p-type semiconductors. Chapter 2 is concerned with the intensity dependence of the complex dielectric constant of p-type germanium for light with a wavelength in the 9-11 \u00b5m region. The nonlinear absorption is described by the imaginary part of the complex dielectric constant, and the nonlinear dispersive properties are described by the intensity dependence of the real part of the dielectric constant. Chapter 3 deals with the saturation characteristics of practically all Groups IV and III-V p-type semiconductors and includes a discussion of the systematic dependence of the saturation intensity on the material parameters. Chapters 4 and 5 are concerned with several \"pump-and-probe\" experiments. Here, the transmission of a low-intensity light beam (probe) can be altered by the presence of a high-intensity laser (pump). In these chapters the modulation of the probe transmission is analyzed as a function of the intensity of the pump laser. Chapter 6 treats the intensity dependence of the conductivity of p-Ge for light with a wavelength of 10.6 \u00b5m.
\r\n\r\nIn Chapter 2, we present a theory of the saturation of heavy- to light-hole band transitions in p-type germanium by high-intensity light with a wavelength near 10 \u00b5m. The free-hole distribution function is modified by the high-intensity light, which leads to an intensity dependence in the absorption coefficient and the index of refraction. The absorption coefficient is found to decrease with intensity in a manner closely approximated by an inhomogeneously broadened two-level model. For temperatures and hole concentrations where hole-phonon dominates hole-impurity and hole-hole scattering, the saturation intensity is independent of the hole concentration. For larger hole densities, the saturation intensity is found to increase monotonically with increasing hole concentration. We calculate the saturation intensity as a function of excitation wavelength and temperature for p-Ge. The saturation intensity is found to increase with increasing photon energy and temperature. The calculated results for the absorption saturation are compared with the available experimental data and good agreement is found. In addition to the nonlinear absorption, there exist laser-induced changes in the index of refraction resulting from the saturation of the intervalence-band transitions. Calculations of the intensity dependence of the real part of the dielectric constant are performed for room temperature and for light with a wavelength of 10.6 \u00b5m. The index of refraction is found to increase monotonically with increasing intensity.
\r\n\r\nIn Chapter 3, we present the results of the theory describing the saturation behavior of most p-type semiconductors with the diamond or zincblende crystal structure by high-intensity CO2 light. For materials with large spin-orbit splittings as compared to the excitation wavelength (as for Ge), the dominant absorption mechanism is direct intervalence-band transitions where a free hole in the heavy-hole band absorbs a photon and makes a transition to the light-hole band. For materials with small spin-orbit splittings as compared to the excitation wavelength (as for Si), direct intervalence-band transitions are allowed between the heavy-hole and light-hole, heavy-hole and split-off, and light-hole and split-off hole bands. In each material, values of the saturation intensity are reported as a function of the photon energy and temperature.
\r\n\r\nIn Chapter 4, we present a theory to describe the enhanced transmission of a weak tunable probe laser with a wavelength near 3 \u00b5m in the presence of a high-intensity saturating beam with a wavelength near 10 \u00b5m in p-Ge. The mechanism responsible for the increasing transmission of the probe laser is the depletion of holes in the heavy-hole band by the saturating beam. Room temperature values of the absorption coefficient of the probe are predicted as a function of the intensity of the pump beam.
\r\n\r\nIn Chapter 5, we present a theory of the absorption lineshape of a low-intensity probe laser which is tuned in the vicinity of a high-intensity pump laser with a wavelength of 10.6 \u00b5m. Values for the absorption coefficient of the probe are calculated at room temperature as a function of the intensity of the pump laser. We find the probe absorption can be divided into two contributions: one being due to the depletion of holes in the resonant region of the heavy-hole band by the saturable pump, and the other being due to a coupling of the pump and probe beams which allow the pump photons to be scattered into the probe and vice versa. The calculated results for the composite lineshape of the probe are compared with the experimental data and good agreement is found.
\r\n\r\nIn Chapter 6, we show how the modification of the free hole distribution function by the saturating beam leads to a change in the conductivity of p-Ge. The photoconductive response is calculated as a function of the doping level, temperature and light intensity.
" }, { "name": "Jepson, Allan Douglas", "degree": "PhD", "year": "1981", "title": "I. Asymptotic Boundary Conditions for Ordinary Differential Equations. II. Numerical Hopf Bifurcation", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechETD:etd-08182005-153922", "creators": [ { "name": { "family": "Jepson", "given": "Allan Douglas" }, "id": "Jepson-Allan-Douglas", "display_name": "Jepson, Allan Douglas" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/C2RJ-6F27", "abstract": "Part I. \"Asymptotic Boundary Conditions for Ordinary Differential Equations\"\r\n\r\nThe numerical solution of two point boundary value problems on semi-infinite intervals is often obtained by truncating the interval at some finite point. In this thesis we determine a hierarchy of increasingly accurate boundary conditions for the truncated interval problem. Both linear and nonlinear problems are considered. Numerical techniques for error estimation and the determination of an appropriate truncation point are discussed.\r\n\r\nA Fredholm theory for boundary value problems on semi-infinite intervals is developed, and used to prove the stability of our numerical methods.\r\n\r\nPart II. \"Numerical Hopf Bifurcation\"\r\n\r\nSeveral numerical methods for locating a Hopf bifurcation point of a system of o.d.e.'s or p.d.e.'s are discussed. A new technique for computing the Hopf bifurcation parameters is also presented. Finally, well-known numerical techniques for simple bifurcation problems are adapted for Hopf bifurcation problems. This provides numerical techniques for computing the bifurcating branch of periodic solutions, possibly including turning points and simple bifurcation points. The stability of the periodic solutions is also discussed.\r\n" }, { "name": "Jin, Michael Yih-Hwa", "degree": "PhD", "year": "1981", "title": "Temporal-Spatial Functional Analysis of the Class-II-a1 Motion Detection Cell of the Fly Calliphora phaenicia", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312006-134932", "creators": [ { "name": { "family": "Jin", "given": "Michael Yih-Hwa" }, "id": "Jin-Michael-Yih-Hwa", "display_name": "Jin, Michael Yih-Hwa" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/ccc0-ws70", "abstract": "The physiology of the horizontal motion detection cell class-IIa1 of the fly Calliphora phaenicia was studied by extracellular recording. The receptive field was treated as a multi-input single output system such that Volterra-Wiener functional formalism could be used to describe the input-output relation. The present work has three objectives: (1) To study the functional of a subunit called the basic motion detection unit. Interpretation of the kernel's features was obtained by comparing it with the results of transient type stimuli. (2) To investigate the organization of the nonlinear spatial interactions in relation to the hexagonal array of visual elements along the horizontal and vertical lines of symmetry. Two sets of experiments were done to find the difference in the organizations of this interaction under light and dark adapted conditions. (3) To investigate the binocular interaction between two class-IIa1 cells each located in different lobes.\r\n\r\nThe basic motion detection unit could be modeled by two first and second order self kernels, which are associated with their two channels, and a cross kernel. The modeling response of a single channel is dominated by the contribution from the second order self kernels because the receptive field is of on-off type. The cross kernel predicts the multiplication-like directionally selective motion response. Both white noise and transient type stimuli confirmed that an excitatory effect as well as an inhibitory effect exist when stimulus patterns move in the forward direction and backward direction, respectively. The cross kernel model can be thought of as a correlation model which has delay type linear filters (instead of differential and integration type filters). An inhibition model with four types of inhibitory interactions was developed which adequately explained the function of this basic motion detection unit.\r\n\r\nHorizontally and vertically aligned eight-stripe white noise patterns were used to investigate the receptive field organization. Under dark adapted conditions the interaction was limited to six adjacent columns and rows. The horizontal cross kernels reveal directionally selective characteristics and have significant 'weights' for those describing the interactions between one column and the nearest four adjacent columns. The vertical cross kernels show a mutually excitatory effect, which could be the evidence of neural pooling of photoreceptors. Under light adapted conditions two major differences appeared. They are: (1) Only two horizontal cross kernels, which describe the interactions between one column and the nearest two columns, have significant 'weights'. The interactions outside this range show reversed directionally selective characteristics. (2) All horizontal and vertical cross kernels have negative diagonal components which indicate a mutually inhibitory effect. This could be a nonlinear sensitivity control mechanism. All the above results were studied with monocular preparation.\r\n\r\nThe binocular interaction was studied by stimulus patterns located both within the binocular region and outside it. The results confirmed that a mutually inhibitory relationship exists between the class-IIa1 cell and its mirror image in the opposite lobe." }, { "name": "Johannsen, David Lawrence", "degree": "PhD", "year": "1981", "title": "Silicon Compilation", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092006-140405", "creators": [ { "name": { "family": "Johannsen", "given": "David Lawrence" }, "id": "Johannsen-David-Lawrence", "display_name": "Johannsen, David Lawrence" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "chair", "display_name": "Mead, Carver" }, { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "co-chair", "display_name": "Thompson, Frederick B." }, { "name": { "family": "Kajiya", "given": "James Thomas" }, "id": "Kajiya-J-T", "role": "member", "display_name": "Kajiya, James Thomas" }, { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "member", "display_name": "Seitz, Charles L." }, { "name": { "family": "Ray", "given": "Charles B." }, "id": "Ray-Charles-B", "role": "member", "display_name": "Ray, Charles B." } ], "option_major": [ "compsci" ], "doi": "10.7907/32ha-8453", "abstract": "Modern integrated circuits are among the most complex systems designed by man. Although we have seen a rapid increase in fabrication technology, traditional design methodologies have not evolved at a rate commensurate with the increasing design complexity potential. These circuit design methodologies fail when applied to Very Large Scale Integrated (VLSI) circuit design. This thesis proposes a new design methodology which manages the complexity VLSI design, allowing economical generation of correctly functioning circuits.
\r\n\r\nCost is one measurement of a design methodology's value. A good design methodology rapidly and efficiently translates high level system specifications into working parts. Traditional techniques partition the translation process into many steps; each design tool is focused upon one of these design steps. This partitioning precludes the consideration of global constraints, and introduces a literal explosion of data being transfered between design steps. The design process becomes error-prone and time consuming.
\r\n\r\nThe technique of silicon compilation presented in this thesis automatically translates from high level specifications into correct geometric descriptions. In this approach, the designer interacts at a high level of abstraction, and need not be concerned with lower levels of detail, facilitating exploration of alternate system architectures. Furthermore, since the implementation is algorithmically generated, chip descriptions can be made correct by construction. Finally, the user is given technology independence, because the high level specification need not require knowledge of fabrication details. This flexibility allows the user to take advantage of technology advances.
\r\n\r\nThis thesis explores various aspects of silicon compilation, and presents a prototype compiler, Bristle Blocks. The methodology is demonstrated through the design of several chips. The practicality of the methodology results from the concern for efficiency of the design process and of the chip designs produced by the system.
" }, { "name": "Kath, William Lawrence", "degree": "PhD", "year": "1981", "title": "I. Propagating and Waiting Fronts in Nonlinear Diffusion. II. Sustained Reentry Roll Resonance", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09282006-094746", "creators": [ { "name": { "family": "Kath", "given": "William Lawrence" }, "id": "Kath-William-Lawrence", "display_name": "Kath, William Lawrence" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "chair", "display_name": "Cohen, Donald S." }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "member", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "member", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." } ], "option_major": [ "appmath" ], "doi": "10.7907/bpk3-rt60", "abstract": "Part I
\r\n\r\nWe examine a nonlinear diffusion equation that arises in the study of a number of physical problems, where the equation is nonlinear because the diffusion coefficient is proportional to a power of the concentration. Previous authors have proven using similarity solutions, that this dependence produces fronts (interfaces between regions of zero and nonzero concentration) which propagate with finite speed, as well as waiting-time behavior, where the fronts remain stationary for a finite amount of time before beginning to move. These similarity solutions provide limited information about the solution for general initial conditions, however.
\r\n\r\nTo alleviate this deficiency, we construct approximate solutions for the above nonlinear diffusion equation using singular perturbation theory. We do so by considering the equation in the limit of nearly linear diffusion, but the analysis reveals the basic qualitative behavior outside this limit as well.
\r\n\r\nThe basic behavior follows from the leading-order approximation of a transformed equation, and propagating and waiting fronts are due to the formation (in this approximation) of what we call corner shocks. This enables us to determine for which initial conditions waiting time behavior will occur.
\r\n\r\nThe transformed equation must be solved to first order to find the solution of the original equation to leading order, and when corner shocks occur at a point of nonzero concentration, this first order analysis shows that they become rounded (which we call a corner layer). When a corner shock occurs at a point of zero concentration, this rounding does not take place, and the corner shock remains sharp. This allows us to give a simple procedure for constructing approximate solutions of the nonlinear diffusion equation when corner shocks occur only at points of zero concentration.
\r\n\r\nPart II
\r\n\r\nWe study a model of reentry roll resonance, a situation encountered when an almost axially symmetric vehicle reenters the earth's atmosphere, using the method of near identity transformations. This method allows us to extend previous results for the case of sustained resonance, when roll buildup occurs.
\r\n\r\nIn particular, we give necessary conditions both for entrainmeat to sustained resonance and for sustained resonance to continue. These conditions imply that it is possible for sustained resonance to last for a finite time and then for unlocking of the resonance to occur. In addition, from the analysis we make a conjecture concerning sufficient conditions for sustained resonance.
" }, { "name": "Katz, Joseph", "degree": "PhD", "year": "1981", "title": "AlGaAs Optoelectronic Devices for Optical Communications", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072005-145115", "creators": [ { "name": { "family": "Katz", "given": "Joseph" }, "id": "Katz-Joseph", "display_name": "Katz, Joseph" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Peck", "given": "Charles W." }, "id": "Peck-C-W", "role": "member", "display_name": "Peck, Charles W." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Rauch", "given": "Lawrence L." }, "id": "Rauch-Lawrence-L", "display_name": "Rauch, Lawrence L." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2AXD-2Z75", "abstract": "This thesis describes several semiconductor injection laser diodes and related optoelectronic devices that can be used as light sources for optical communication systems, and develops the intrinsic electrical model of the laser diode. All the devices were grown from the GaAs-GaAlAs ternary system using the liquid phase epitaxy technique. The AlGaAs materials are very useful for the fabrication of both optical devices (sources and detectors) and conventional electronic components, due to their optical and electrical properties.
\r\n\r\nThe first device is the Translaser, a monolithically integrated heterostructure bipolar transistor with an injection laser. The next two types of devices possess bistable electrical characteristics. One is a laser-SCR switch, and the second type consists of multi-PN heterostructure devices. Each of the devices described above performs an electronic function, of modulating the light output of the laser associated with it.
\r\n\r\nFinally, two types of low-threshold single-node laser diodes are presented. Their properties make them attractive candidates for sources in optical fiber communication systems. The first one is the Embedded Stripe Laser, and the second one is a new version of the Buried-Heterostructure laser, fabricated on semi-insulating substrates.
\r\n\r\nAn equivalent circuit of the laser diode is presented in the last chapter. This model provides a better understanding of the operation of the laser diode, which is particularly important in applications which involve its high frequency: operation with other electronic components and when a modification of its frequency response is needed.
\r\n" }, { "name": "Krousgrill, Charles Morton", "degree": "PhD", "year": "1981", "title": "A Linearization Technique for the Dynamic Response of Nonlinear Continua", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechThesis:08202021-231219519", "creators": [ { "name": { "family": "Krousgrill", "given": "Charles Morton" }, "id": "Krousgrill-Charles-Morton", "display_name": "Krousgrill, Charles Morton" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/d5wa-0v91", "abstract": "The efforts of this dissertation are directed toward the development of a technique for understanding the dynamic response of structural elements governed by nonlinear partial differential equations. This technique is based on the concepts of the equivalent linearization method which relies on obtaining an optimal linear set of equations to model the original nonlinear set.
\r\n\r\nIn this method, the linearization is performed at the continuum level. At this level, the equivalent linear stiffness and damping parameters are physically realizable and are defined in such a way that the method can be easily be incorporated into finite element computer codes.
\r\n\r\nThree different approaches to the method are taken with each approach based on the minimization of a distinct difference between the nonlinear system and its linear replacement, Existence and uniqueness properties of the minimizat4on solutions are established.
\r\n\r\nThe method is specialized for the treatment of steady-state solutions to harmonic excitation and of stationary response to random excitation. Procedures for solving the equivalent linearization are also discussed.
\r\n\r\nThe method is applied to three specific examples: one dimensional, hysteretic shear beams, thin plates governed by nonlinear equations of motion and the same nonlinear thin plates but with cutouts. Solutions via the equivalent linearization method using the stress difference minimization compare well with Galerkin's method and numerical integration. The last example is easily handled by the continuum equivalent linearization technique, whereas other methods prove to be inadequate.
" }, { "name": "Kuech, Thomas Francis", "degree": "PhD", "year": "1981", "title": "Investigations of Schottky Barrier Structures in Compound Semiconductors: I. HgTe on CdTe: a Lattice Matched Schottky Barrier. II. Au-Cd Barriers to CdTe. III. AAu Barriers on In\u2093Ga\u2081\u208b\u2093P", "advisor": "McCaldin, James Oeland", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122006-090129", "creators": [ { "name": { "family": "Kuech", "given": "Thomas Francis" }, "id": "Kuech-Thomas-Francis", "display_name": "Kuech, Thomas Francis" } ], "advisors": [ { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "advisor", "display_name": "McCaldin, James Oeland" } ], "committee": [ { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "chair", "display_name": "McCaldin, James Oeland" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8hcw-7421", "abstract": "i) The Au Schottky barrier height to n - InxGa1-xP was measured as a function of alloy composition. The Au barrier, \u03c6p, to p - InxGa1-xP was found to be independent of composition. The barrier, \u03c6p, was determined by the relation \u03c6p + \u03c6n = \u03c6g where \u03c6g is the band gap energy and \u03c6n is the measured barrier height to n - InxGa1-xP. It has been observed that the Au barrier height to p-type material for most compound semiconductors is determined by the anion. This dependence on the anion of the compound has now been seen to extend to the alloy system InxGa1-xP measured here.
\r\n\r\nii) The Schottky barrier height of Cd, Au, and Au-Cd alloys was determined on vacuum cleaved surfaces of n-CdTe. A large barrier of 0.92 eV was found in the case of the Au-Cd alloy contacts. Contacts made with elemental Cd or Au gave barrier heights of 0.45 and 0.65 eV, respectively. The increased barrier height found on Au-Cd alloy contacts may be related to recent UHV observations on Schottky barrier formation where crystal defects play a role in determining the observed barrier height.
\r\n\r\niii) HgTe-CdTe lattice matched heterojunctions were formed by the epitaxial growth of HgTe on CdTe substrates using a new low temperature metal organic chemical vapor deposition (MOCVD) technique. These heterojunctions combine features of the Schottky barrier structure, due to the high carrier concentrations found in the semi-metallic HgTe, with the structural perfection present in a lattice matched heterojunction. The measured Schottky barrier height varied from 0.65 to 0.90 eV depending on the details of the HgTe growth procedure used. Two models of the HgTe-CdTe heterojunction are presented which account for the observed variation in barrier height.
" }, { "name": "Lau, Kam-Yin", "degree": "PhD", "year": "1981", "title": "Ultra-High Frequency Dynamics of Semiconductor Injection Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042006-111807", "creators": [ { "name": { "family": "Lau", "given": "Kam-Yin" }, "id": "Lau-Kam-Yin", "display_name": "Lau, Kam-Yin" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "chair", "display_name": "Bridges, William B." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Psaltis", "given": "Demetri" }, "id": "Psaltis-D", "orcid": "0000-0003-4684-8800", "role": "member", "display_name": "Psaltis, Demetri" }, { "name": { "family": "Walker", "given": "Robert Lee" }, "id": "Walker-R-L", "role": "member", "display_name": "Walker, Robert Lee" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "eleceng" ], "doi": "10.7907/f057-zj77", "abstract": "Experimental and theoretical studies on the high frequency dynamics of (GaAl)As semiconductor lasers center on three main areas: 1) analog modulation response of laser diodes; 2) pulse (pulse code modulation) response of laser diodes and 3) generation and quenching of intensity pulsations in laser diodes coupled to external cavities.
\r\n\r\nThe basic analog modulation and transient characteristics of injection lasers with various structures are studied and compared. The basic limitations on ultrahigh frequency ( > 5GHz) modulation of lasers are considered. Self-pulsations in injection lasers are studied and their interaction with external cavities are clarified. These studies lead to the quenching of self-pulsation and ultra-short short pulse generation in laser diodes by coupling to an external cavity. A novel external fiber resonator is introduced for this purpose. Pattern effects in pulse code modulation of injection lasers are studied and a bipolar pulsing scheme devoid of the above effect is described. The transverse mode shift in a transverse junction laser under ultrashort electrical pulse excitation is investigated. Finally, the frequency response of superluminescent lasers (lasers without mirrors) is analysed.
\r\n" }, { "name": "Lepelletier, Thierry Georges", "degree": "PhD", "year": "1981", "title": "Tsunamis \u2013 Harbor Oscillations Induced by Nonlinear Transient Long Waves", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192007-153149", "creators": [ { "name": { "family": "Lepelletier", "given": "Thierry Georges" }, "id": "Lepelletier-Thierry-Georges", "display_name": "Lepelletier, Thierry Georges" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Kanamori", "given": "Hiroo" }, "id": "Kanamori-H", "orcid": "0000-0001-8219-9428", "role": "member", "display_name": "Kanamori, Hiroo" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "member", "display_name": "Raichlen, Fredric" } ], "option_major": [ "civileng" ], "doi": "10.7907/05TE-BH74", "abstract": "The process of excitation of harbors and bays by transient nonlinear long waves is investigated theoretically and experimentally. In addition, nonlinear shallow water waves generated in a closed rectangular basin by the motion of the basin are also examined.
\r\n\r\nTwo numerical methods based on finite element techniques are used to solve the weakly nonlinear-dispersive-dissipative equations of motion and are applied to the basin excitation problem and the transient harbor oscillation problem, respectively. In the latter case, the open sea conditions are simulated by including a radiative boundary condition in time at a finite distance from the harbor entrance. Various dissipative effects are also included. In addition to the numerical results, analytical solutions are presented to investigate certain particular aspects of basin and harbor oscillations (e.g., the effects of viscous dissipation in a harbor with simple geometry).
\r\n\r\nExperiments conducted in the closed rectangular basin indicate that for a continuous excitation at or near a resonant mode of oscillation the linear theory becomes inadequate and the nonlinear-dispersive-dissipative theory must be used. For a transient excitation the validity of the linear theory depends on the value of the Stokes parameter. Indeed, some features not predicted by the linear theory can be directly inferred from the magnitude of this parameter.
\r\n\r\nExperiments on the continuous wave induced oscillations of a narrow rectangular harbor with constant depth show that at the first resonant mode convective nonlinearities can be neglected and a linear dissipative solution is sufficient to describe the waves inside the harbor. At the second resonant mode which corresponds to a longer harbor relative to the length of the incident wave, nonlinear convective effects become important and must be incorporated into the numerical model. Also the characteristics of various sources of dissipation which reduce resonance in the harbor are investigated experimentally. The sources considered include, among others, laminar boundary friction, leakage losses underneath the harbor walls, and energy dissipation due to flow separation at the entrance of the harbor.
\r\n\r\nThe good agreement obtained between the experiments and the nonlinear numerical model developed in this study suggests that this model could be used with some confidence to predict the response characteristics of prototype harbors. As an example, the results of this study have been applied to the response of Ofunato Bay (Japan) to the tsunami generated by the Tokachi-Oki earthquake of May 16,1968. The model has been used to investigate the effects of convective nonlinearities on the bay oscillations and also to determine the efficiency of the breakwater which was built to reduce the effects of tsunamis at Ofunato.
\r\n" }, { "name": "Liu, Wing Kam", "degree": "PhD", "year": "1981", "title": "Development of Finite Element Procedures for Fluid-Structure Interaction", "advisor": "Hughes, Thomas J. R.", "url": "https://resolver.caltech.edu/CaltechThesis:08202021-235130206", "creators": [ { "name": { "family": "Liu", "given": "Wing Kam" }, "id": "Liu-Wing-Kam", "display_name": "Liu, Wing Kam" } ], "advisors": [ { "name": { "family": "Hughes", "given": "Thomas J. R." }, "id": "Hughes-T-J-R", "role": "advisor", "display_name": "Hughes, Thomas J. R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/4yzv-q979", "abstract": "In this thesis the development of finite element procedures for fluid-structure interaction problems is presented. The areas upon which attention is focused are: numerical transient algorithms which emphasize implicit-explicit finite element concepts; finite element kinematical descriptions for modelling fluid subdomains in fluidstructure interaction problems; finite element methodology for nearly incompressible fluids and solids, and beam, plate and shell structures based upon theories which include transverse shear deformations; and finite rotation effects in numerical integration of rate constitutive equations arising in large-deformation analysis. All these nonlinear methodologies have been integrated into a working finite element computer code. A number of numerical examples are presented to demonstrate the effectiveness of these approaches." }, { "name": "McRae, Gregory John", "degree": "PhD", "year": "1981", "title": "Mathematical Modeling of Photochemical Air Pollution", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05042006-134537", "creators": [ { "name": { "family": "McRae", "given": "Gregory John" }, "id": "McRae-Gregory-John", "display_name": "McRae, Gregory John" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "chair", "display_name": "Brooks, Norman H." }, { "name": { "family": "Kreiss", "given": "Heinz-Otto" }, "id": "Kreiss-H-O", "role": "member", "display_name": "Kreiss, Heinz-Otto" }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Holmes", "given": "John R." }, "id": "Holmes-John-R", "role": "member", "display_name": "Holmes, John R." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "member", "display_name": "Seinfeld, John H." } ], "option_major": [ "envreng" ], "doi": "10.7907/n8p7-f149", "abstract": "Air pollution is an environmental problem that is both pervasive and difficult to control. An important element of any rational control approach is a reliable means for evaluating the air quality impact of alternative abatement measures. This work presents such a capability, in the form of a mathematical description of the production and transport of photochemical oxidants within an urban airshed. The combined influences of advection, turbulent diffusion, chemical reaction, emissions and surface removal processes are all incorporated into a series of models that are based on the species continuity equations. A delineation of the essential assumptions underlying the formulation of a three-dimensional, a Lagrangian trajectory, a vertically integrated and single cell air quality model is presented. Since each model employs common components and input data the simpler forms can be used for rapid screening calculations and the more complex ones for detailed evaluations.
\r\n\r\nThe flow fields, needed for species transport, are constructed using inverse distance weighted polynomial interpolation techniques that map routine monitoring data onto a regular computational mesh. Variational analysis procedures are then employed to adjust the field so that mass is conserved. Initial concentration and mixing height distributions can be established with the same interpolation algorithms.
\r\n\r\nSubgrid scale turbulent transport is characterized by a gradient diffusion hypothesis. Similarity solutions are used to model the surface layer fluxes. Above this layer different treatments of turbulent diffusivity are required to account for variations in atmospheric stability. Convective velocity scaling is utilized to develop eddy diffusivities for unstable conditions. The predicted mixing times are in accord with results obtained during sulfur hexafluoride (SF6) tracer experiments. Conventional models are employed for neutral and stable conditions.
\r\n\r\nA new formulation for gaseous deposition fluxes is presented that provides a means for estimating removal rates as a function of atmospheric stability. The model satisfactorily reproduces measured deposition velocities for reactive materials. In addition it is shown how computational cell size influences the representation of surface removal.
\r\n\r\nChemical interactions between twenty nine chemical species are described by a 52 step kinetic mechanism. The atmospheric hydrocarbon chemistry is modeled by the reactions of six lumped classes: alkanes, ethylene, other olefins, aromatics, formaldehyde and other aldehydes; a grouping that enables representation of a wide range of smog chamber experiments and atmospheric conditions. Chemical lumping minimizes the number of species while maintaining a high degree of detail for the inorganic reactions. Variations in rate data, stoichiometric coefficients and initial conditions have been studied using the Fourier Amplitude Sensitivity Test.
\r\n\r\nThe wide variation in time scales, non-linearity of the chemistry and differences in transport processes complicates selection of numerical algorithms. Operator splitting techniques are used to decompose the governing equation into elemental steps of transport and chemistry. Each transport operator is further split into advective and diffusive components so that linear finite element and compact finite difference schemes can be applied to their best advantage. Because most of the computer time is consumed by the chemical kinetics those species that could be accurately described by pseudo-steady state approximations were identified reducing the number of species, described by differential equations, to 15.
\r\n\r\nWhile the mathematical formulation of the complete system contains no regional or area specific information, performance evaluation studies were carried out using data measured in the South Coast Air Basin of Southern California. Detailed emissions and meteorological information were assembled for the period 26-28 June 1974. A comparison between predictions and observed air quality, during multi-day periods, indicates that the model can satisfactorily describe urban scale atmospheric concentration dynamics.
" }, { "name": "Melton, Ronald Benjamin", "degree": "PhD", "year": "1981", "title": "A Study of Horizontal Cell-Photoreceptor Interaction in the Frog Retina Using a Randomly Modulated Stimulus", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042006-110912", "creators": [ { "name": { "family": "Melton", "given": "Ronald Benjamin" }, "id": "Melton-Ronald-Benjamin", "display_name": "Melton, Ronald Benjamin" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/6dzj-fd89", "abstract": "The intracellular responses of frog horizontal cells and photoreceptors to conventional and randomly modulated stimuli were recorded by intracellular probing using glass micropipettes. The stimuli were designed to test for photoreceptor response compression by surround illumination. The results indicated that the response of photoreceptors is reduced by stimulation of the area surrounding the cell's receptive field. It appeared that the effect is generated by negative feedback from horizontal cells to both rods and cones. These findings are in good agreement with the results of earlier studies by other investigators who established that horizontal cells feed back to cone photoreceptors in many vertebrate species." }, { "name": "Milenkovic, Paul Henry", "degree": "PhD", "year": "1981", "title": "A Systematic Assessment of the Accuracy of Vocal Tract Area Function Estimates Made from the Speech Waveform", "advisor": "Pierce, John Robinson", "url": "https://resolver.caltech.edu/CaltechETD:etd-09282006-135046", "creators": [ { "name": { "family": "Milenkovic", "given": "Paul Henry" }, "id": "Milenkovic-Paul-Henry", "display_name": "Milenkovic, Paul Henry" } ], "advisors": [ { "name": { "family": "Pierce", "given": "John Robinson" }, "id": "Pierce-J-R", "role": "advisor", "display_name": "Pierce, John Robinson" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6ydf-ke74", "abstract": "By performing Linear Predictive Coding (LPC) analysis on the speech waveform, it is possible to determine the cross sectional areas, or area function, of a discrete section acoustic tube model of the vocal tract. It is a matter of controversy, however, as to whether the areas of the acoustic tube model accurately estimate the areas of the actual vocal tract. There are several sources of error which cause the estimated areas to differ from the true areas. A procedure for estimating the spectrum of the vocal tract response in terms of LPC derived formant frequencies and bandwidths is discussed; the areas of the acoustic tube model can be calculated from these frequency and bandwidth values. The accuracy with which formant frequencies and bandwidths can be estimated is evaluated by experiments where the frequency and bandwidth of a one resonator vocal tract model are estimated. The accuracy of the complete procedure for estimating the area function from speech is evaluated by experiments where the area function is estimated from synthetic speech sounds. These speech sounds are synthesized from known vocal tract shapes against which the estimated area function can be compared." }, { "name": "Mitchard, Gordon Stuart", "degree": "PhD", "year": "1981", "title": "Low Temperature Photoluminescence Properties of Silicon and Silicon-Germanium Alloys", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122006-144917", "creators": [ { "name": { "family": "Mitchard", "given": "Gordon Stuart" }, "id": "Mitchard-Gordon-Stuart", "display_name": "Mitchard, Gordon Stuart" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Tombrello", "given": "Thomas A." }, "id": "Tombrello-T-A", "role": "member", "display_name": "Tombrello, Thomas A." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/T3SB-MQ10", "abstract": "In this thesis, three examples of the application of the photoluminescence technique to indirect semiconductors at low temperatures are presented.
\r\n\r\nChapter 2 deals with the effect of increasing impurity concentrations on the photoluminescence spectrum. We present results for the Si:(B,In) system. As the In concentration is increased, we observe quenching of B luminescence. We propose a model based on exciton transfer from B to In impurities, which agrees well with the experimental results when the exchange mechanism is assumed for the transfer. This is the first observation of exciton transfer in Si.
\r\n\r\nChapter 3 deals with the properties of three sharp and relatively intense features in the photoluminescence spectrum of Si:In. We observe these lines, which are labelled \"P,Q,R\", only in the luminescence of Si:In. We present measurements of the lifetimes of P,Q,R luminescence which show that these lines have extremely long lifetimes. These results suggest that the P,Q,R lines are associated with an isoelectronic complex in Si. We present measurements of the temperature dependence of P,Q,R luminescence and P,Q,R lifetimes which support this conclusion. This is the first observation of luminescence associated with an isoelectronic complex in Si. In addition, we present results which show that the P,Q,R luminescence intensities are very sensitive to the sample surface preparation. This is the first observation of surface sensitive photoluminescence.
\r\n\r\nChapter 4 deals with the photoluminescence properties of undoped and In doped Si-rich Si-Ge alloys. We identify the alloy luminescence features on the basis of the temperature dependence, time dependence and pump power dependence of the luminescence intensities. We present results for the band gap shift and free exciton binding energy for each sample examined. In addition, we present a model for the observed broadening of bound exciton luminescence. Finally, we present observations which suggest that excitons bind to local fluctuations in alloy composition at low temperatures. This is the first investigation of the photoluminescence properties of Si-rich Si-Ge alloy semiconductors.
" }, { "name": "Ouimette, James Richard", "degree": "PhD", "year": "1981", "title": "Aerosol Chemical Species Contributions to the Extinction Coefficient", "advisor": "Flagan, Richard C.; Friedlander, Sheldon K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092005-093436", "creators": [ { "name": { "family": "Ouimette", "given": "James Richard" }, "id": "Ouimette-James-Richard", "display_name": "Ouimette, James Richard" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "advisor", "display_name": "Flagan, Richard C." }, { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "advisor", "display_name": "Friedlander, Sheldon K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/s1we-wc48", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA model was developed for determining the contributions of aerosol chemical species to the extinction coefficient. The model assumes that the suspended particles are spherical and that particle volume is conserved with condensation and coagulation.\r\n\r\nIn general, the diameter, refractive index, and chemical composition of each particle must be known to rigorously calculate each species contribution. It is shown that species mass distributions with respect to particle diameter are sufficient to determine the species contributions exactly for some simple aerosols. Requirements were derived for each of the simple aerosols in which linear regression analysis could be legitimately applied to historical species mass concentrations data in order to estimate species contributions to light extinction.\r\n\r\nThe model was field tested at two remote arid locations in the southwestern United States where aerosol water content was ofsumed to be negligible. A low pressure impactor (LPI) was used in this research to size segregate aerosol from 0.05 to 4 [...] aerodynamic diameter for elemental analysis. Two new techniques were developed for analysis of aerosol deposits collected with the LPI. Nanogram sensitivities were achieved for soot and many elements.\r\n\r\nA three-week experiment was conducted in remote northeastern Arizona to calculate the contributions of fine aerosol species to the extinction coefficient. Theoretical mass extinction efficiencies were calculated and numerically integrated with measured mass distributions to determine the contribution of each species to the extinction coefficient. The measured chemical species could account for 94 [plus or minus] 19% of the fine aerosol mass concentration and 85 [plus or minus] 34% of the measured particle extinction coefficient. All important species balances were met, both in total and with respect to size. The satisfactory agreement between the calculated and measured extinction coefficient indicates that the model and experimental technique are useful for determining the contributions to various aerosol species to visibility degradation at an arid site.\r\n\r\nA one-year experiment was conducted at China Lake, California. Multiple regression analysis was applied to the measured particle scattering coefficient and fine aerosol species mass concentrations from 61 filter samples collected during 1979. Contributions of various aerosol species to the particle scattering coefficient, [...], were estimated. The statistically estimated contributions were compared with those determined theoretically using measured aerosol mass distributions. It was found that the statistically inferred species contributions to [...] agreed qualitatively with those calculated theoretically using measured aerosol distributions. Regression analysis overestimated the contribution of sulfate relative to that calculated theoretically. Using measured 1979 values, a light extinction budget was calculated for China Lake. Measured mass extinction coefficients were used to predict the reduction in visibility at China Lake which would occur by increasing the concentrations of various aerosol species." }, { "name": "Ruth, Edward Kenneth", "degree": "PhD", "year": "1981", "title": "Experiments with Unconventional Cross Flow Heat Exchangers", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042006-110003", "creators": [ { "name": { "family": "Ruth", "given": "Edward Kenneth" }, "id": "Ruth-Edward-Kenneth", "display_name": "Ruth, Edward Kenneth" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P6TP-GR40", "abstract": "These experiments consisted of measurements of pressure losses and heat transfer rates for two unconventional crossflow heat exchanger configurations.\r\n\r\nThe first type consisted of an arrangement of circular tubes in a sawtooth pattern. Performance of this type did not appear to be an improvement over more conventional heat exchangers.\r\n\r\nThe second type used exchanger tubes of a special lenticular cross section so spaced as to keep the velocity of the fluid flowing outside the tubes nearly constant in magnitude reducing separation and drag. The lenticular tubes' performance was superior to the conventional types, especially at higher Reynolds numbers." }, { "name": "Schatzman, James Carl", "degree": "PhD", "year": "1981", "title": "A Model for the von K\u00e1rm\u00e1n Vortex Street", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122005-112041", "creators": [ { "name": { "family": "Schatzman", "given": "James Carl" }, "id": "Schatzman-James-Carl", "display_name": "Schatzman, James Carl" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Fornberg", "given": "Bengt" }, "id": "Fornberg-Bengt", "role": "member", "display_name": "Fornberg, Bengt" }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" } ], "option_major": [ "appmath" ], "doi": "10.7907/34YN-H995", "abstract": "In the wake of a two-dimensional bluff body placed in a uniform stream, for sufficiently large but not too large flow velocity a distinctive pattern of vorticity is observed. The pattern consists of \"vortices\" of high vorticity surrounded by nearly irrotational fluid. These vortices are organized in two nearly parallel staggered rows of vortices of opposite direction of rotation. This pattern is called the von K\u00e1rm\u00e1n vortex street.
\r\n\r\nThis thesis is a report on the analysis of a model for the von K\u00e1rm\u00e1n vortex street. The model is inviscid, incompressible, two-dimensional, and consists of vortices of finite area and uniform vorticity. The first part of this thesis contains a brief survey of the work on this problem, and an explanation of the approach used in the present work; the second part describes calculations of steady solutions of the Euler equations of this kind, and the third part describes an analysis of the stability of these steady solutions to two-dimensional disturbances.
\r\n\r\nThe calculations indicate that the vortex wake can be stabilized by sufficiently large area of the vortices. Data are given which (to some approximation) will permit relating the street to the flow past a body; this is proposed as a suitable study for further work.
" }, { "name": "Shepherd, Joseph Emmett", "degree": "PhD", "year": "1981", "title": "Dynamics of Vapor Explosions: Rapid Evaporation and Instability of Butane Droplets Exploding at the Superheat Limit", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-143525", "creators": [ { "name": { "family": "Shepherd", "given": "Joseph Emmett" }, "id": "Shepherd-Joseph-Emmett", "orcid": "0000-0003-3181-9310", "display_name": "Shepherd, Joseph Emmett" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/E3KR-3X92", "abstract": "A preliminary experimental investigation of the vapor explosion of a single droplet (~ 1 mm diameter) of liquid butane at the superheat limit has been completed. These experiments provided the first detailed look at rapid evaporation taking place under conditions such that departures from equilibrium, evaporative fluxes and fluid accelerations are orders of magnitude larger than observed under ordinary circumstances. Single short-exposure photographs and fast-response pressure measurements were used to obtain a description of the complete explosion process within a superheated drop immersed in a bubble-column apparatus. Emphasis was placed on the early (microsecond-time-scale) evaporative stage. Despite the apparant simplicity of the vapor explosion of a single superheated droplet, the present experiments revealed a wide range of phenomina of varying complexity occurring at different stages of the explosion.
\r\n\r\nThe explosion is initiated by the spontaneous formation within the drop of a single vapor bubble, which grows until the drop liquid is completely evaporated. The resulting vapor bubble undergoes volume oscillations and eventually breaks up via Taylor instability. Several new and unusual features of the early evaporative stage of the explosion have been observed, three of which are remarkably repeatable. First, photographs of the evaporative surface show a highly roughened and disturbed interface for most of the evaporative stage. At the earliest observed times (8 [mu]sec) the roughening appears to begin as a rather regular pattern on an otherwise spherical surface, suggestive of a fundamental instability due to evaporative mass flux. Second, due to the asymmetric location of the initial nucleus within the drop, a portion of the evaporating surface contacts the surrounding fluid first and becomes nonevaporating. As the bubble grows, a unique, axisymmetric structure of circumferential waves terminated by a spherical cap appears on this nonevaporating surface. Apparently, these waves are driven by the impinging jet of vapor coming from the opposing evaporating surface. Third, nucleation and initial development of the bubble in the first 10[mu]sec is accompanied by a characteristic two-step pulsating pressure signal, suggesting that a fundamental and repeatable unsteadiness, perhaps connected with the above mentioned instability, is taking place at this stage.
\r\n\r\nA preliminary estimation of the evaporative mass flux has been made from photographically-determined bubble volumes and pressure signals measured in the first 30 [mu]sec. As might have been expected in view of our observations of the highly roughened surface, the inferred mass flux (~ 400 gm/cm[superscript 2]-sec) is two orders of magnitude larger than that predicted by the classical, diffusion-limited theory of bubble growth. We propose that the interface roughening is due to an inertial instability of the evaporative surface. A preliminary calculation for the Landau mechanism of instability, supplemented by an ad hoc correction for sphericity indicates that, indeed, the classical mode of bubble growth would be unstable under the conditions found in the present experiment. An explanation of the present observations that is consistent with this theoretical prediction is that the actual instability does occur in the first 1-2 [mu]sec of bubble growth and the instability has developed well into the nonlinear stage by 8 [mu]sec, the earliest time at which bubbles have been observed in the present experiment.
\r\n\r\nThe present observations are completely different than what might be predicted from previous experiments and analyses of near-equilibrium evaporation. The generality of the present results needs to be verified in detail, but they clearly indicate that evaporation at the superheat limit can be much more complex than previously expected.
" }, { "name": "Shih, Choon-Foo", "degree": "PhD", "year": "1981", "title": "Failure of Liquid Storage Tanks Due to Earthquake Excitation", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04132018-090928397", "creators": [ { "name": { "family": "Shih", "given": "Choon-Foo" }, "id": "Shih-Choon-Foo", "display_name": "Shih, Choon-Foo" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/m0v8-hs31", "abstract": "Above ground liquid storage tanks have suffered serious damage during earthquakes. The damage of tanks can vary from local yielding or buckling of the tank wall, to loss of contents, or to collapse which leads to an unrepairable tank. Considerable work has been carried out on this problem with varying degree of success. However, the results are largely directed toward response rather than failure prediction. The information on failure mechanisms is very limited. The present work consists of scale model testing, correlation with existing analysis and failure prediction with laboratory verification. The scale model testing incorporates dynamic similarity of the fluid/structure interaction problem. The model study shows that small plastic models can be useful in studying the dynamics and buckling of liquid-filled tanks under ground excitation even though the model does not display complete similitude. The buckling criterion proposed in this study is based upon static considerations and the complex stress field in the shell wall is supplanted by a simple field for which analytical/experimental results are available. Harmonic buckling tests demonstrate that the static buckling criterion is satisfactory even though the prebuckling stress field is time dependent. The harmonic buckling tests, when correlated with the stresses from a response analysis, also indicate that the buckling is largely dependent upon the n = 1 response, Transient buckling tests are also carried out and the results show that the linear analysis together with the static buckling criterion gives a good prediction of the failure of a full fluid-filled tank. The test parameters in these buckling tests include water depth, title angle, thickness of tank wall, top end condition, ground excitation pattern, etc. In addition, buckling tests of unanchored tanks are conducted to study the influence of changing the anchorage of the tank base. An analytical model is suggested to predict the response of an unanchored tank due to overturning moment. The current design criterion of an un\u00adanchored tank is also assessed in this study. The results of this investigation, in addition to those carried out previously, provide a better understanding of the forced vibration problem, failure criterion and appropriate design procedure for a liquid storage tank.
\r\n" }, { "name": "Stephenson, Rodney Alan", "degree": "PhD", "year": "1981", "title": "The Equilibrium Field Near the Tip of a Crack for Finite Plane Strain of Incompressible Elastic Materials", "advisor": "Sternberg, Eli", "url": "https://resolver.caltech.edu/CaltechETD:etd-10052006-094802", "creators": [ { "name": { "family": "Stephenson", "given": "Rodney Alan" }, "id": "Stephenson-Rodney-Alan", "display_name": "Stephenson, Rodney Alan" } ], "advisors": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "advisor", "display_name": "Sternberg, Eli" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/y00g-0984", "abstract": "This investigation is concerned with the deformations and stresses in a slab of all-around infinite extent containing a traction-free plane crack, under conditions of plane strain. The analysis is carried out within the framework of the fully nonlinear equilibrium theory of homogeneous and isotropic incompressible elastic solids. For a fairly wide class of such materials and general loading conditions at infinity, asymptotic estimates appropriate to the various field quantities near the crack-tips are deduced. For a subclass of the materials considered, these results -- in contrast to the analogous predictions of the linearized theory -- lead to the conclusion that the crack opens up in a neighborhood of its tips even if the applied loading is antisymmetric about the plane of the crack, (e.g., Mode II loading). It is shown further that the non-linear global crack problem corresponding to such a loading in general cannot admit an antisymmetric solution." }, { "name": "Sung, Windsor", "degree": "PhD", "year": "1981", "title": "Catalytic Effects of the \u03b3-FeOOH (Lepidocrocite) Surface on the Oxygenation Removal Kinetics of the Fe(II) and Mn(II)", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122006-111302", "creators": [ { "name": { "family": "Sung", "given": "Windsor" }, "id": "Sung-Windsor", "display_name": "Sung, Windsor" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Anson", "given": "Fred C." }, "id": "Anson-F-C", "role": "member", "display_name": "Anson, Fred C." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "orcid": "0000-0002-4571-6884", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "member", "display_name": "North, Wheeler J." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "eng" ], "doi": "10.7907/r22w-2c12", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPrevious investigations of Fe(II) oxygenation had resulted in a wide range in the reported rate constant(s). While Fe(II) oxygenation rates are fast in simple laboratory systems (seconds to minutes when pH > 7), actual rates observed in natural waters can be orders of magnitude lower. Conversely, while Mn(II) oxygenation rates are slow in laboratory systems (days when pH < 9), much faster rates are observed in natural waters or implicated in model studies.\r\n\r\nThe influences of ionic strength, temperature and anions on the Fe(II) homogeneous oxygenation rates were examined in this study. Other rate constants from the literature were successfully incorporated into this framework. Complexation by major anions (e.g., [...] and [...]) and ionic strength effects were sufficient to account for the retardation of Fe(II) oxygenation in seawater. Autocatalysis of Fe(II) oxygenation was observed for pH > 7. A general integrated autocatalytic rate expression suitable for Fe(II) or Mn(II) oxygenation was used to interpret laboratory-obtained kinetic data. Oxidation of Fe(II) in various laboratory systems with characteristics like those of natural water was shown to form the allotrope [gamma]-FeOOH. The [gamma]-FeOOH surface was shown to be an excellent catalyst for Fe(II) and Mn(II) oxygenation.\r\n\r\nThe [gamma]-FeOOH surface obtained by oxidizing milli-molar levels of Fe(II) in 0.7 M NaCl was studied in the following ways: surface charge characteristics by acid/base titration; adsorption of Mn(II) and surface oxidation of Mn(II). A rate law was formulated to account for the effects of pH and the amount of surface on the surface oxidation rate of Mn(II). The presence of milli-molar levels of [gamma]-FeOOH was shown to reduce significantly the half-life of Mn(II) in 0.7 M NaCl from hundreds of hours to hours. The [gamma]-FeOOH surface was shown to be as effective as colloidal MnO2 in catalysing Mn(II) oxygenation." }, { "name": "Taylor, Dean Dalton", "degree": "PhD", "year": "1981", "title": "Laboratory Studies of Submicron Particle Formation in Pulverized Coal Combustion", "advisor": "Flagan, Richard C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182006-083816", "creators": [ { "name": { "family": "Taylor", "given": "Dean Dalton" }, "id": "Taylor-Dean-Dalton", "display_name": "Taylor, Dean Dalton" } ], "advisors": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "advisor", "display_name": "Flagan, Richard C." } ], "committee": [ { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "chair", "display_name": "Flagan, Richard C." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-G-R", "role": "member", "display_name": "Cass, Glen Rowan" }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "orcid": "0000-0003-1468-6835", "role": "member", "display_name": "Gavalas, George R." } ], "option_major": [ "mecheng" ], "doi": "10.7907/as3w-nf63", "abstract": "A laboratory furnace was constructed to study the mechanism of submicron particle formation in pulverized coal boilers. Simulation was achieved by matching characteristic kinetic times in laboratory and field units. This was done by matching volumetric heat extraction rates. Reynolds number and geometric scaling were not deemed essential for the simulation.
\r\n\r\nCombustion-generated submicron aerosols from the laboratory furnace were characterized by size and composition distribution measurements using an electrical mobility analyzer and a low-pressure impactor. Elemental analysis of size-classified mass samples was done by alpha particle-induced X-ray emission spectrum analysis.
\r\n\r\nThe influence of macroscopic combustion parameters on the characteristics of fine particle emissions was investigated. Total submicron particle volume concentration was found to depend on burner type and to increase with temperature for each burner type tested. The particle volume concentration was found to increase with exhaust NO concentration.
\r\n\r\nThe fine particle composition was found to differ from that of larger residual ash particles which generally reflected the composition of the bulk ash. It was also found that combustion conditions (overall fuel-air equivalence ratio and wall temperature) influenced the composition of the smallest ash particles.
\r\n\r\nSpecies enrichment data are generally supportive of the vaporization-condensation mechanism of submicron particle formation. Measured dependence of particle volume-mean diameter is consistent with theoretical predictions based on free-molecular Brownian coagulation of particles formed by nucleation of vaporized ash. Strong dependence of submicron particle volume concentration on char particle temperatures in the hot zone further suggests vaporization of ash to be the principal source of material from which fine particles are formed.
\r\n\r\nA semi-quantitative combustion model was formulated to calculate char particle temperature-time histories in the laboratory furnace. An Arrhenius vaporization rate expression was fitted to the laboratory measurements of total submicron particle volume concentration using the particle temperature histories calculated from the combustion model. Estimates of kinetic parameters were compared with those of other investigators. The model calculations suggest that the mass-specific rate of ash vaporization is strongly dependent on parent coal particle size. This is due to higher burning temperatures of smaller particles together with a high apparent activation energy for ash vaporization.
\r\n\r\nRecommendations for further work are given.
" }, { "name": "Tenhover, Michael Alan", "degree": "PhD", "year": "1981", "title": "M\u00f6ssbauer Effect Studies in Yttrium Based Metallic Glasses", "advisor": "McGill, Thomas C.; Johnson, William Lewis", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182006-154115", "creators": [ { "name": { "family": "Tenhover", "given": "Michael Alan" }, "id": "Tenhover-Michael-Alan", "display_name": "Tenhover, Michael Alan" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "advisor", "display_name": "Johnson, William Lewis" } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Boehm", "given": "Felix H." }, "id": "Boehm-F-H", "role": "member", "display_name": "Boehm, Felix H." }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "member", "display_name": "Duwez, Pol E." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/5a6h-a632", "abstract": "The short range order of a variety of Yttrium-3d transition metal glasses has been investigated using Fe57 M\u00f6ssbauer Effect (ME) spectroscopy. We found that the ME spectra of these glasses could best be described in terms of a model which assumes two kinds of sites for the 3d elements. The nature of the two sites is radically different depending on whether the transition metal is Mn, Fe, Co, and Ni or Cu and Zn. We attributed the difference in the structure of these glasses to the same factors which determine whether a C-15 crystalline compound is stable in equilibrium. The microscopic nature of ME spectroscopy provides an interesting comparison between the nature of the short range order in crystalline and amorphous alloys. The process of crystallization has also been studied for a few glasses, and was found to occur in two distinct steps associated with the formation of hcp Y and a C-15 compound. In the final section we use the results of this study to design a novel high field superconducting material.
" }, { "name": "Williams, Arthur Ray", "degree": "PhD", "year": "1981", "title": "Atomic Structure of Transition Metal Based Metallic Glasses", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182006-144351", "creators": [ { "name": { "family": "Williams", "given": "Arthur Ray" }, "id": "Williams-Arthur-Ray", "display_name": "Williams, Arthur Ray" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "chair", "display_name": "McGill, Thomas C." }, { "name": { "family": "Johnson", "given": "William L." }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William L." }, { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "member", "display_name": "Duwez, Pol E." }, { "name": { "family": "Goodstein", "given": "David L." }, "id": "Goodstein-D-L", "role": "member", "display_name": "Goodstein, David L." }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/sb90-n460", "abstract": "The atomic-scale structure of several transition metal-based metallic glasses has been investigated by X-ray diffraction techniques. Current dense random packing models have been found to have only a superficial resemblance to the structure of real amorphous metallic alloys, and a theoretical density for amorphous transition metals has been obtained which might be used as a filter for more realistic single component models in the future. The partial pair distribution functions for individual pairs of atomic species have been obtained for glassy alloys of lanthanum with aluminum, gallium and gold through the use of isomorphous alloys. These systems have been demonstrated to be chemically ordered and the short range order of these alloys has been shown to be quite different from that of typical amorphous transition metal-metalloid alloys.
" }, { "name": "Wilt, Daniel Paul", "degree": "PhD", "year": "1981", "title": "(AlGa)As Semiconductor Lasers and Integrated Optoelectronics", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182006-141505", "creators": [ { "name": { "family": "Wilt", "given": "Daniel Paul" }, "id": "Wilt-Daniel-Paul", "display_name": "Wilt, Daniel Paul" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "member", "display_name": "McGill, Thomas C." }, { "name": { "family": "Rutledge", "given": "David B." }, "id": "Rutledge-D-B", "role": "member", "display_name": "Rutledge, David B." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/f9jz-ez68", "abstract": "Five subjects related to monolithic integration of electronic and optical devices in the (AlGa)As material system are treated in this thesis. They are:
\r\n\r\n1. The Integrated Optoelectronic Repeater:
\r\n\r\nThe design, fabrication, and testing of the first monolithic integrated optical repeater is described. This device consists of an optical detector, electronic gain stage, and current modulated semiconductor laser transmitter integrated in a single crystal chip to perform the function of regenerating an optical signal as might be found in an optical communication system. The device has a measured optical gain (light out to light in) of 10 dB.
\r\n\r\n2. Ion Implanted Lasers and Schottky Gate Field Effect Transistors:
\r\n\r\nThe use of ion implantation as a technique to fabricate both lasers and field effect transistors is described. Devices fabricated include a beryllium implanted laser diode on N type GaAs substrate, a beryllium implanted laser diode on semi-insulating Cr doped GaAs substrate integrated with a field effect transistor driver, and sulfur implanted GaAs field effect transistors.
\r\n\r\n3. A Steady State Lateral Model of the Double Heterostructure Laser:
\r\n\r\nA theoretical model of the double heterostructure laser is described which treats the p-n junction in the device correctly by using fundamental semiconductor relationships and reasonable assumptions about the device heterointerfaces. The model treats both the electronic and optical properties self consistently, making the model valid above lasing threshold. Finite element formalism is adopted as a solution technique to enable the treatment of complicated diode geometries. An example is treated and theoretical and experimental results are compared.
\r\n\r\n4. The Effect of Lateral Carrier Diffusion on the Modulation Response of a Semiconductor Laser:
\r\n\r\nThe effect of lateral carrier diffusion upon the modulation characteristics of the semiconductor laser is investigated. A self consistent analysis of the spatially dependent rate equations is performed using a finite element model. The transverse junction stripe laser is treated as an example and a comparison is made between lateral carrier diffusion and spontaneous emission as damping mechanisms for the resonance peak. Experimental results bear out the conclusion that the relaxation resonance in this device is damped mainly by lateral carrier diffusion. In addition, a simple analytic result is presented which illustrates qualitatively the effect of lateral carrier diffusion upon such devices. The conclusion from this result is that lateral carrier diffusion serves to damp the relaxation resonance in the semiconductor laser quite well, but probably will not serve to improve the upper limit on modulation frequency as might have been suspected.
\r\n\r\n5. Effective Permittivity Formalism and the Design of Buried Heterostructure Lasers:
\r\n\r\nAn approach to effective permittivity formalism is presented which clarifies and extends the use of this technique particularly in the treatment of waveguiding in the semiconductor laser. The scalar wave equation is posed in a variational form, and the effective permittivity formalism is treated as a variational approximation technique. This approach shows clearly the nature and limits of the approximation involved. The formalism is applied to the case of the buried heterostructure laser and the results differ considerably from the conventional application of effective permittivity formalism to this device when a reasonable form is assumed for the variational modal profile.
" }, { "name": "Yu, Kwang-I", "degree": "PhD", "year": "1981", "title": "Communicative Databases", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262006-113134", "creators": [ { "name": { "family": "Yu", "given": "Kwang-I" }, "id": "Yu-Kwang-I", "display_name": "Yu, Kwang-I" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/mga3-1n19", "abstract": "A hierarchical organization stores its information in a large number of databases. These databases are interrelated, forming a closely-coupled database system. Traditional information systems and current database management systems do not have a means of expressing these relationships.\r\n\r\nThis thesis describes a model of the information structure of the hierarchical organization that identifies the nature of database relationships. It also describes the design and implementation of the Communicative Database Management System (CDMS)." }, { "name": "Agmon, Pinchas", "degree": "PhD", "year": "1980", "title": "I. Design, Control, and Characterization of the Passively Mode Locked CW Dye Laser. II. Photoconductive Impulse Response and Excess Carrier Lifetime of Cr-doped GaAs", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-104818", "creators": [ { "name": { "family": "Agmon", "given": "Pinchas" }, "id": "Agmon-Pinchas", "display_name": "Agmon, Pinchas" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "chair", "display_name": "Yariv, Amnon" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." }, { "name": { "family": "Smith", "given": "Darryl L." }, "id": "Smith-D-L", "role": "member", "display_name": "Smith, Darryl L." }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/hr51-0r95", "abstract": "This thesis consists of two parts. The subject of the first part is the design, control, and characterization of the passively mode locked CW dye laser, which is capable of producing a stable continuous train of subpicosecond pulses. Following a description of the laser's elements, the mode stability of its multi-mirror resonator is studied. The monitoring of the laser operational state by pulsewidth and bandwidth measurements is described.
\r\n\r\nIn the second part, the photoconductive impulse response and excess carrier lifetime of semi-insulating Cr:GaAs is studied experimentally and analytically. In the transient photoconductive experiment, the material is irradiated with a continuous train of picosecond light pulses with photon energy above the band-gap energy, generated by the passively mode locked CW dye laser described in part I. A photoconductive decay time of 67 psec is deduced from the observations and interpreted as the result of both bulk and surface recombination. It is shown that it agrees well with longer carrier lifetime in Cr:GaAs measured under steady state conditions with longer illumination wavelengths.
" }, { "name": "Barton, Anthony Francis", "degree": "PhD", "year": "1980", "title": "A Fault Tolerant Integrated Circuit Memory", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03212012-110600634", "creators": [ { "name": { "family": "Barton", "given": "Anthony Francis" }, "id": "Barton-Anthony-Francis", "display_name": "Barton, Anthony Francis" } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/dr7k-qn11", "abstract": "Most commercially produced integrated circuits are incapable of\r\ntolerating manufacturing defects. The area and function of the\r\ncircuits is thus limited by the probability of faults occurring\r\nwithin the circuit. This thesis examines techniques for using\r\nredundancy in memory circuits to provide fault tolerance and to\r\nincrease storage capacity.
\r\n\r\nA hierarchical memory architecture using multiple Hamming codes\r\nis introduced and analysed to determine its resistance to\r\nmanufacturing defects. The results of the analysis indicate that\r\nsubstantial yield improvement is possible with relatively modest\r\nincreases in circuit area. Also, the architecture makes it possible\r\nto build larger memory circuits than is economically feasible\r\nwithout redundancy.
" }, { "name": "Bowser, William Matthew", "degree": "PhD", "year": "1980", "title": "The Development and Utilization of Inelastic Electron Tunneling Spectroscopy as a Surface Vibrational Probe with an Emphasis on the Study of Chemisorption and Heterogeneous Catalysis", "advisor": "Weinberg, William Henry", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132006-131809", "creators": [ { "name": { "family": "Bowser", "given": "William Matthew" }, "id": "Bowser-William-Matthew", "display_name": "Bowser, William Matthew" } ], "advisors": [ { "name": { "family": "Weinberg", "given": "William Henry" }, "id": "Weinberg-W-H", "role": "advisor", "display_name": "Weinberg, William Henry" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/w6b6-t291", "abstract": "Inelastic electron tunneling spectroscopy (IETS) has been used to investigate the vibrational structure of molecular species bound to, or contained in, the insulating layer of Al-insulator Pb tunnel junctions. The insulating layer, prepared by the exposure of the Al electrode to an oxygen plasma discharge, was studied via IETS and was found to be an oxide rather than a hydroxide. An oxide with appreciable hydroxide content could be prepared under certain conditions.\tAn X-ray photoelectron spectroscopic (XPS) study of this oxide layer was also carried out to further facilitate comparison to commercial aluminas. IETS was used to investigate the chemisorption on this oxide of phenol and three derivatives of phenol: catehol, resorcinol and hydroquinone. Phenol adsorbs as a phenixide ion, catechol and resorcinol lose both of their acidic protons upom chemisorption, whereas hydroquinone only loses one proton, bonding as a mono-ion. This study demonstrated the high sensitivity and resolution of IETS. IETS was also used in the study of supported metal catalysts. The adsorption of ethanol on silver particles supported on alumina was studied, extending the use of IETS in supported metal catalysis. An important area of current research is concerned with the fixing of metal cluster compounds on substrated to form catalysis. IETS was used to study the interaction of [RhCl(CO)2]2 on alumina, the first reported study of a metal carbonyl complex via IETS. This complex decomposes upon chemisorption, leaving, predominantly, isolated Rh(CO)2 species on the surface. In contrast, Ru3(CO)12 is seen via IETS, to retain its molecular structure upon adsorption on alumina. A method for heating the IETS sample easily and quickly is also presented." }, { "name": "Braisted, David Miner", "degree": "PhD", "year": "1980", "title": "Cavitation Induced Instabilities Associated with Turbomachines", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232004-091330", "creators": [ { "name": { "family": "Braisted", "given": "David Miner" }, "id": "Braisted-David-Miner", "display_name": "Braisted, David Miner" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/V1WV-V511", "abstract": "Cavitation induced instabilities of hydraulic systems were investigated both experimentally and analytically. The instability, known as auto-oscillation, was found to occur in a well defined region of cavitation numbers just above head breakdown of the inducer. Auto-oscillation is characterized by large amplitude fluctuations in the pressures and mass flow rates throughout the system. The frequency of the oscillations was observed to decrease with a reduction in both the flow coefficient and cavitation number. The amplitudes of the fluctuation increased with a reduction in the flow coefficient. These detailed measurements reflect changes in the dynamic performance of the inducer due to cavitation and the interaction between the dynamics of the inducer and those of the inlet flow field. Some detailed analytical studies were performed to try to understand the nature of this interaction.\r\n\t\r\nA linear stability analysis was developed which was based upon the understanding that auto-oscillation is a function of the entire hydraulic system including the cavitating inducer. Using the experimentally obtained transfer functions of two impellers, the analysis successfully predicted both the onset and frequency of auto-oscillation. The stability of the Dynamic Pump Test Facility is significantly reduced by the increased dynamically active character of the inducers at the lower cavitation number. In addition, the stability of the Dynamic Pump Test Facility was found to be particularly sensitive to the mass flow gain factor and pump impedance." }, { "name": "Browning, Sally Anne", "degree": "PhD", "year": "1980", "title": "The Tree Machine: A Highly Concurrent Computing Environment", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082006-153626", "creators": [ { "name": { "family": "Browning", "given": "Sally Anne" }, "id": "Browning-Sally-Anne", "display_name": "Browning, Sally Anne" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/15zs-9x82", "abstract": "An architecture for a VLSI multiprocessor machine is proposed. The processors are connected together as a binary tree. A collection of algorithms are mapped onto the tree machine. These include heap sort transitive closure, the travelling salesman, and matrix inversion, among others. A model of computational complexity for the tree machine is suggested, and the algorithms are analyzed in the context of that model. A notation for expressing the algorithms is described, a processor design is proposed, and a compiler for the notation and processor is presented." }, { "name": "Chen, Jing-Chang", "degree": "PhD", "year": "1980", "title": "Studies on Gravitational Spreading Currents", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechTHESIS:09302010-090407312", "creators": [ { "name": { "family": "Chen", "given": "Jing-Chang" }, "id": "Chen-Jing-Chang", "display_name": "Chen, Jing-Chang" } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/16RG-AZ72", "abstract": "The objective of this investigation is to examine the buoyancy-driven gravitational spreading currents, especially as applied to ocean disposal of wastewater and the accidental release of hazardous fluids.
\r\n\r\nA series of asymptotic solutions are used to describe the displacement of a gravitationally driven spreading front during an inertial phase of motion and the subsequent viscous phase. Solutions are derived by a force scale analysis and a self-similar technique for flows in stagnant, homogeneous, or linearly density-stratified environments. The self-similar solutions for inertial-buoyancy currents are found using an analogy to the well-known shallow-water wave propagation equations and also to those applicable to a blast wave in gasdynamics. For the viscous-buoyancy currents the analogy is to the viscous long wave approximation to a nonlinear diffusive wave, or thermal wave propagation. Other similarity solutions describing the initial stage of motion of the flow formed by the collapse of a finite volume fluid are developed by analogy to the expansion of a gas cloud into a vacuum. For the case of a continuous discharge there is initially a starting jet flow followed by the buoyancy-driven spreading flow. The jet mixing zone in such flows is described using Prandtl's mixing length theory. Dimensional analysis is used to derive the relevant scaling factors describing these flows.
" }, { "name": "Cheung, Woontong Nathan", "degree": "PhD", "year": "1980", "title": "I. Channeling Studies of Silicon Interfaces. II. Diffusion Barrier Properties of Titanium Nitride", "advisor": "Mayer, James Walter; Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-10122006-090333", "creators": [ { "name": { "family": "Cheung", "given": "Woontong Nathan" }, "id": "Cheung-Woontong-Nathan", "display_name": "Cheung, Woontong Nathan" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/e47n-cg57", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I\r\n\r\nThe channeling effect of MeV ions in crystalline materials has been applied to study the interfaces of metals, silicides and oxides with single-crystal Si substrates. The study was facilitated by the development of thin (1500-5000\u00c5) Si crystals which enabled channeled ions to probe the interfacial region without first traversing the metal or silicide layers. These investigations revealed that a reaction occurs between the silicon and as-deposited metal layers. For the Ni-Si system, about three monolayers of Ni penetrate into Si and occupy interstitial sites. An interfacial layer is also found between silicides and Si. In contrast, an abrupt interface is found between SiO2 and Si.\r\n\r\nWith conventional channeling techniques, the ion beam traverses first the overlayer and then the Si substrate. A Si peak is observed in the energy spectrum and the area of the peak can be converted to Si atoms/cm(2) from known Rutherford scattering cross-sections. The Si peak corresponds to the first few monolayers of crystalline Si (the \"surface peak\"), the non-registered Si at the interface and the amount of Si in the silicide or oxide. From recent theoretical and experimental studies on surfaces, the surface peak contribution can be accurately predicted.\r\n\r\nUsing different overlayer thicknesses, the stoichiometry of silicides and oxides and the interfacial disordered Si can be determined. In the case of metal-Si interfaces, the interfacial reactivity can be monitored by measuring the amount of non-registered Si at the interface. However, the conventional channeling technique is applicable only when the multiple scattering of the incident beam by the overlayer is small (i.e. thin overlayers and low atomic number elements).\r\n\r\nAdditional information on the nature of the interfacial disordered Si can be obtained by the thin-crystal channeling technique which involves the use of thin ([...]), self-supporting Si crystals. With the ions first traversing the Si thin crystal along a channeling direction, the channeled ions are steered away from the atomic rows. At the interfacial region, the channeled ions only interact with the interfacial Si atoms which are displaced [...] laterally from the atomic rows. There is no contribution from the first few crystalline Si layers to the measured Si peak; as there is in the case of conventional channeling. The combination of both conventional and thin-crystal channeling techniques provides further information about the interfacial disorder because of the different sensitivities of the two techniques to lateral displacements. Thin-crystal channeling has also been used to locate the relative position of foreign atoms with respect to the Si lattice near the interfacial region. This technique requires angular scan experiments along various axial and planar channeling directions.\r\n\r\nFor metal-Si interfaces, channeling results show that an interfacial reaction is initiated at room temperature with as-deposited metal layers (Ni, Pd, Cr, V and Au); Ag is the only exception. With the Ni-Si system, the interfacial reaction can be greatly reduced by cooling the substrate to 170\u00b0K during Ni deposition and ion beam analysis. The temperature dependence of the interfacial reactivity emphasizes the kinetic nature of the metal-Si interfaces and the importance of interfacial studies at low temperatures for meaningful comparison with abrupt metal-semiconductor interface models. The amount of disordered interfacial Si is observed to be high for metals which are dominant diffusion species in silicide formation (e.g. Ni and Pd). A lattice location experiment on the Ni-Si interface shows that ~3 monolayers of Ni atoms are situated interstitially at the tetrahedral sites of crystalline Si. This observation supports the interstitial diffusion model which was proposed by Tu to explain the low-temperature formation of silicides.\r\n\r\nInterfaces between Si and Pd2Si, Ni2Si, NiSi or NiSi2 have also been investigated by thin-crystal channeling. The Ni2Si-Si interface shows ~4x10(16) atoms/cm(2) of excess Si above an \"ideal\" Ni2Si-Si interface. The other silicide-Si interfaces all show disordered interfacial Si of <8x10(15) atoms/cm(2). The amount of interfacial disorder correlates with the transformation temperature for the next stable silicide phase. For example, the Ni2Si phase (which exhibits the highest interfacial disorder) transforms to NiSi at ~350\u00b0C. In contrast, the other silicide phases, Pd2Si and NiSi, require a much higher transformation temperature (~700\u00b0C).\r\n\r\nThe SiO2-Si interface has been studied by both conventional and thin-crystal channeling. The results show that thermally grown oxides on (110)Si are stoichiometric SiO2 at least down to a thickness of 4\u00c5. By comparing the channeling data with predictions based on a various number of reconstructed Si layers, an abrupt SiO2-Si interface is deduced with 2 monolayers of the Si single crystal being reconstructed at the interface.\r\n\r\nPart II\r\n\r\nThis part of the thesis is concerned with the deposition and evaluation of titanium nitride (TiN) layers as diffusion barriers in contact metallization on Si devices. The application of TiN to Si solar cell contacts (i.e., the TiN-Ti-Ag metallization scheme) has been demonstrated to withstand a 600\u00b0C, 10 min anneal without degrading the cell's performance.\r\n\r\nTitanium nitride films have been prepared by reactive sputtering of Ti in a nitrogen plasma. The nitride films are identified by TEM and X-ray diffraction to have the NaCl structure with a lattice parameter of 4.24\u00b10.02\u00c5. Electrical properties and atomic composition of the films have been studied as a function of sputtering RF power (500-1500 W) and nitrogen pressure (3-100 mT). Backscattering analysis shows that the films have a composition close to stoichiometric TiN but with a slight tendency for higher nitrogen content. Oxygen is the major contaminant in the nitride films. The oxygen content strongly depends on the sputtering parameters and a high oxygen content corresponds to high electrical resistivity of the TiN films. The lowest resistivity (~170[...]-cm) is obtained by sputtering with high RF power and low nitrogen pressure.\r\n\r\nThe effectiveness of titanium nitride films as a diffusion barrier between various metals and single-crystal Si substrate or Ti on single-crystal Si substrate is investigated by backscattering spectrometry, SEM and EDAX. The temperature range of interest is from 400\u00b0C to 700\u00b0C. Various metals of high electrical conductivity such as Au, Ag, Al, Cu and Pd are used as the top metal layer. By interposing a thin layer of TiN ([...] 1000 \u00c5) between the metal and substrate, the failure temperature (i.e., the temperature at which metal-substrate interdiffusion becomes significant) can be greatly increased. The failure temperature of the TiN layers as a diffusion barrier is related to the metal-silicon eutectic temperature. SEM studies show that the interdiffused layer is laterally non-uniform and is initiated at isolated spots across the sample's surface. It is believed that grain boundaries or pinholes in the TiN films are the weak links in the diffusion barrier properties of TiN.\r\n\r\nAs an application for high-temperature diffusion barriers, the Ag-Ti-TiN metallization scheme has been tested on shallow-junction (~2000A) Si solar cells. The conventional Ti-Pd-Ag metallization scheme has been shown to fail after a 600\u00b0C, 10 min anneal which is required for a glass encapsulation process. With the TiN-Ti-Ag scheme, no degradation of cell performance can be observed after the 600\u00b0C, 10 min anneal if the TiN layer is [...]1500\u00c5." }, { "name": "Coutsias, Evangelos Athanassios", "degree": "PhD", "year": "1980", "title": "Some Effects of Spatial Nonuniformities in Chemically Reacting Mixtures", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072012-130738166", "creators": [ { "name": { "family": "Coutsias", "given": "Evangelos Athanassios" }, "id": "Coutsias-Evangelos-Athanassios", "display_name": "Coutsias, Evangelos Athanassios" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/3wt1-cc54", "abstract": "In Part I, a method is developed for treating reacting-diffusing\r\nsystems whose kinetics lead to a limit cycle behavior with frequency\r\nvarying slowly with position. This is accomplished by including the\r\neffects of the spatial variation in a phase variable that is introduced\r\nto parametrize the limit cycles at each point. The normalization of\r\nthis phase variable is chosen such that the limit cycles at each point\r\nhave the same frequency with respect to this variable. The method is\r\nmotivated by treating the weakly coupled behavior of two oscillators\r\nthat, unlike previous works, are not nearly identical. The analogy\r\nbetween discrete oscillator systems and continuous chemically reacting\r\nmixtures is explored by treating a chain of coupled limit cycle\r\noscillators and considering various limits as the number of oscillators\r\ntends to infinity.
\r\n\r\nIn Part II a different effect of spatial nonuniformities is studied:\r\nthe modification of the simple diffusion approximation to treat situations\r\nof large deviations from equilibrium distributions in a mixture or\r\nproximity to some critical temperature. A technique for treating\r\nbifurcation from the continuous spectrum by introducing a slow space\r\nscale is developed. Using this, the onset of a spatially nonuniform\r\nstate in a model chemically reacting system is studied, occurring\r\nwhen some reaction rate crosses the values at which linearized theory\r\npredicts destabilization of the uniform steady state solutions admitted\r\nby the system. Subs critical bifurcation is also found possible.
" }, { "name": "Elliott, Kenneth Robert", "degree": "PhD", "year": "1980", "title": "Optical Determination of the Properties of Excitons Bound to Impurities in Semiconductors", "advisor": "McGill, Thomas C.; Smith, Darryl L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10252006-081057", "creators": [ { "name": { "family": "Elliott", "given": "Kenneth Robert" }, "id": "Elliott-Kenneth-Robert", "display_name": "Elliott, Kenneth Robert" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Smith", "given": "Darryl L." }, "id": "Smith-D-L", "role": "advisor", "display_name": "Smith, Darryl L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/z105-h928", "abstract": "This thesis deals with the electronic and optical properties of excitons bound to impurities in semiconductors. The first three chapters are concerned with the electronic structure of bound exciton states. The fundamental process in which a bound exciton is formed on a neutral acceptor in silicon is studied. Three lines are observed in the absorption spectra of the acceptors Al, Ga, and In in silicon. Of the various schemes used to explain these lines, it is determined from the relative oscillator strengths that the correct scheme is one in which two j=3/2 holes are coupled to form states with total angular momentum J=0 and J=2. The cubic environment of the crystal in the neighborhood of the impurity leads to a splitting of the J=2 state. In the bound exciton spectra of Si:Tl, four lines are observed in contrast to the three lines observed for the acceptors Al, Ga, and In. The oscillator strength of the thallium bound exciton is measured and continues the trend towards large oscillator strengths for the deep impurities. The excited state structure of the donor bound excitons in GaP is also presented. It is established that excitons bound at these impurities should have a structure which consists of a D- core to which a hole is loosely bound. Two different types of excited states have been identified for the donor bound excitons. Some of these states are excitations of the hole about the D- core of the bound exciton. Other states have been identified which are due to excitations of the D- electron core. These excitations have different symmetry than the ground state.\r\n\r\nThe observation of a low lying excited state of the neutral indium acceptor is reported. This state is interesting because current theories of the electronic states of the acceptor do not predict it. The state may exist as the result of the Jahn-Teller effect.\r\n\r\nThe systematics of the spectroscopy of multiple exciton complexes bound to donors in silicon are reported. It is found that the spectroscopy of these complexes changes very little between different impurities. This suggests that carrier-carrier interactions are more important than the impurity potential in determining the binding of excitons to the complexes. Any model of the structure of the complexes must take this into account.\r\n\r\nMeasurements of the capture cross-section of a free exciton on a neutral In acceptor in silicon are reported. In lightly doped silicon the decay of the luminescence associated with In bound excitons is determined by the rate at which excitons are captured on the indium site. By measuring the decay time of the luminescence as a function of indium concentration and temperature, it is possible to obtain the capture cross-section of a free exciton on a site. The capture cross-section is strongly temperature dependent changing by two orders of magnitude between 10\u00b0K and 30\u00b0K." }, { "name": "Gallagher, Timothy Joseph", "degree": "PhD", "year": "1980", "title": "Domain Wall Dynamics in Ion-Implanted Magnetic Bubble Materials", "advisor": "Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172006-152737", "creators": [ { "name": { "family": "Gallagher", "given": "Timothy Joseph" }, "id": "Gallagher-Timothy-Joseph", "display_name": "Gallagher, Timothy Joseph" } ], "advisors": [ { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/j5xa-xp25", "abstract": "The object of this work is to extend the experimental and theoretical understanding of domain wall dynamics in implanted magnetic bubble materials. The presence of the implanted layer was incorporated into the theory of domain wall dynamics by considering both the modified demagnetizing field and the surface pinning associated with the implanted surface. Using this model, calculations of peak wall velocities were made to explain the velocity asymmetry with respect to in-plane field direction. An experimental technique was developed to determine the influence of implantation on bubble state switching, and the results were interpreted using the surface pinning condition. Based on predictions of the model, a new class of bubble states was found in implanted films and the unique dynamic characteristics of these states were investigated." }, { "name": "Haroun, Medhat Ahmed", "degree": "PhD", "year": "1980", "title": "Dynamic Analyses of Liquid Storage Tanks", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08292019-100431566", "creators": [ { "name": { "family": "Haroun", "given": "Medhat Ahmed" }, "id": "Haroun-Medhat-Ahmed", "display_name": "Haroun, Medhat Ahmed" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/1J74-RH65", "abstract": "Theoretical and experimental investigations of the dynamic behavior of cylindrical liquid storage tanks are conducted to seek possible improvements in the design of such tanks to resist earthquakes. The study is carried out in three phases: 1) a detailed theoretical treatment of the liquid-shell system, 2) an experimental investigation of the dynamic characteristics of full-scale tanks, and 3) a development of an improved design-procedure based on an approximate analysis.
\r\n\r\nNatural frequencies of vibration and the associated mode shapes are found through the use of a discretization scheme in which the elastic shell is modeled by finite elements and the fluid region is treated as a continuum by boundary solution techniques. In this approach, the number of unknowns is substantially less than in those analyses where both tank wall and fluid are subdivided into finite elements. A method is presented to compute the earthquake response of both perfect circular and irregular tanks; it is based on superposition of the free lateral vibrational modes. Detailed numerical examples are presented to illustrate the applicability and effectiveness of the analysis and to investigate the dynamic characteristics of tanks with widely different properties. Ambient and forced vibration tests are conducted on three full-scale water storage tanks to determine their dynamic characteristics. Comparison with previously computed mode shapes and frequencies shows good agreement with the experimental results, thus confirming the reliability of the theoretical analysis. Approximate solutions are also developed to provide practicing engineers with simple, fast, and sufficiently accurate tools for estimating the seismic response of storage tanks.
" }, { "name": "Harris, Jerry Michael", "degree": "PhD", "year": "1980", "title": "The Influence of Random Media on the Propagation and Depolarization of Electromagnetic Waves", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-10162006-082641", "creators": [ { "name": { "family": "Harris", "given": "Jerry Michael" }, "id": "Harris-Jerry-Michael", "display_name": "Harris, Jerry Michael" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/XH76-NK15", "abstract": "Electromagnetic wave propagation and depolarization in an inhomogeneous medium having random fluctuations in its permittivity are studied. The continuous space-time permittivity fluctuations are taken to be frozen-in, homogeneous, and isotropic. We find that the essential effect of the random permittivity is to destroy the time coherence and spatial orthogonality of the vector components of an electromagnetic wave penetrating the medium.
\r\n\r\nTo study this problem, we develop a unique discrete model for the continuous random medium by dividing the volume occupied by the random inhomogeneities into independent elementary scattering volumes. Scattering by each of these elementary volumes is analyzed to obtain the complex amplitude and polarization of the single scattered field. Then multiple scattering among the many elementary volumes is used to estimate the composite values for scattering per unit length and depolarization per unit length of the medium. The manifestation of scattering in the medium is the generation of an incoherent or fluctuating electric wavefield and a coherent or average electric wavefield. It is shown that the total electric wavefield propagating in the medium satisfies an integral equation which is directly reducible to the classical equation for radiation transfer.
\r\n\r\nA novel result of this study is that only two phenomenological parameters are needed to describe the penetration of the wave into a plane-parallel medium, when a polarized plane wave is normally incident. These two parameters appear as diffusion constants in expressions for the solution for the coherency and Stokes matrices. These solutions simply describe how wave energy is progressively converted from the initially coherent and polarized field to an incoherent and unpolarized field as the wave propagates. An initially polarized wave is gradually depolarized, yielding a completely unpolarized wave deep into the medium.
\r\n" }, { "name": "Hess, Gideon David", "degree": "PhD", "year": "1980", "title": "A Software Design System", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182006-082833", "creators": [ { "name": { "family": "Hess", "given": "Gideon David" }, "id": "Hess-Gideon-David", "display_name": "Hess, Gideon David" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/Z9348HB7", "abstract": "The goal of the research described in this thesis was to build a system that supports, without interfering with, the activity of systematic software design and takes upon itself mechanical activities the designer can be spared.
\r\n\r\nTwo of the main activities which constitute the process of software creation are:
\r\n1.Designing a solution to the problem.
\r\n2. Implementing the design.
The activity of design has to be performed by the programmer himself, it can only be aided by the computer. Producing a program from a complete design is a mechanical activity the computer can take upon itself.
\r\n\r\nThese observations lead to the following objectives that a software design system should meet:
\r\n1. Providing tools that support the design activity and enable maximum flexibility.
\r\n2. Recognizing the lowest level primitives of the design as the target language and producing the program in this language.
A system along these guidelines was implemented. It permits the user to write definitions which refine high level design decisions into lower levels and, at the same time, serve as syntax descriptions and translation rules for the languages used in the design.
\r\n\r\nThe system operates in two user-controlled passes. In the first pass the user's definitions are read, either interactively or from external files, and the syntax rules are stored in a dictionary. In the second pass a syntax driven language processor uses the dictionary to compile the user's program into the target language which consists of the lowest level constructs of the design.
\r\n\r\nDue to the freedom the programmer has in design, several kinds of syntactic ambiguities may be introduced with - or without - the user's attention. Unless caused by user errors, the translator tries to resolve these ambiguities to match the designers intentions.
\r\n\r\nIn order to reduce the amount of time and space required for parsing, long texts are divided into subtexts which are translated separately. Guidance as to which subtexts are separately translatable is provided by the user in a natural way by composing the design of statements.
\r\n\r\nA command language enables the user to control the passes, to look at the contents of the dictionary and of external files, to monitor the translation process for debugging purposes, to store dictionaries for later use and retrieve them and to modify special symbols used in definitions.
\r\n\r\nThe system is implemented in Simula. A second system is presently being implemented as part of POL (Problem Oriented Language), a system for writing and using application languages. POL's metalanguage enables the user to build - or extend object languages by writing new syntax rules. The tools of the development system described above are incorporated into the metalanguage in order to aid the application programmer in the design and compilation of the semantic routines of these rules.
" }, { "name": "Hsu, Shi-Ping", "degree": "PhD", "year": "1980", "title": "Problems in Analysis and Design of Switching Regulators: I. Pole Placement Technique for DC-to-DC Switching Regulators. II . Transformer Modelling. III. Cross-Regulation of the Two-Output \u0106uk Converter", "advisor": "Middlebrook, Robert David; Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302006-100214", "creators": [ { "name": { "family": "Hsu", "given": "Shi-Ping" }, "id": "Hsu-Shi-Ping", "display_name": "Hsu, Shi-Ping" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/GV8S-2J15", "abstract": "Power Electronics is an interdisciplinary field which combines three of the major disciplines of electrical engineering--control, power and electronics. The three topics in this thesis arise from problems encountered in these fields.\r\n\r\nPart I is an application of modern control theory to the design of any dc-to-dc switching regulator. By feeding back all the state variables in a regulator, the system closed-loop poles can be placed anywhere desired on the s-plane. This is in contrast to the conventional single-loop design where the closed-loop poles are constrained on the root loci between the open loop poles and zeros. With this total-state feedback technique, the stability margins and transient responses of a switching regulator can be shaped as desired.\r\n\r\nPart II is a study of transformer modelling, which is important in the design of power processing circuits. The simple [pi]-model is used to model two-winding, three-winding and under some special cases, four-winding transformers. In the past, the parameters in the model were expressed in terms of the coupled-inductor coefficients L11, M12, L22 etc., while in this thesis, they are expressed in terms of the permeances which link the model directly to the physical layout of the windings. With this representation, the physical insight of the transformer is explicitly exposed in the model.\r\n\r\nPart III analyzes the cross-regulation problem of a two-output Cuk converter. The unique effect of the unequal discharge of the coupling capacitances on the cross-regulation of a Cuk converter is first discussed. It is pointed out that this effect can be made arbitrarily small by increasing the values of the capacitances. The parasitic effects such as leakage inductances, winding resistances and diode offset voltages are then included in the more general analysis. Quantitative results, which are useful in control and improvement of the cross-regulation, are given at the end." }, { "name": "Hunt, James Robert", "degree": "PhD", "year": "1980", "title": "Coagulation in Continuous Particle Size Distributions: Theory and Experimental Verification", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10242006-104534", "creators": [ { "name": { "family": "Hunt", "given": "James Robert" }, "id": "Hunt-James-Robert", "display_name": "Hunt, James Robert" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "member", "display_name": "List, E. John" }, { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "orcid": "0000-0003-1468-6835", "role": "member", "display_name": "Gavalas, George R." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "member", "display_name": "Friedlander, Sheldon K." } ], "option_major": [ "envreng" ], "doi": "10.7907/dbbb-v854", "abstract": "Previous theories for particle coagulation are not readily applicable to the continuous particle size distributions encountered in natural waters. By extending concepts developed in the analysis of aerosol dynamics, predictions of continuous particle size distributions were obtained dimensionally for size intervals dominated by Brownian, shear, differential sedimentation coagulation and gravitational settling. A dynamic steady state size distribution was assumed to exist, maintained by a constant flux of particle volume through the distribution. Predictions have been successfully compared with the shapes of particle size distributions measured in oceanic waters.\r\n \r\nAn experimental program was designed to test the predictions with cleaned clay and silica minerals in artificial seawater. A series of batch experiments was conducted at fluid shear rates of 1/2 to 32 sec-1 in a rotating cylinder apparatus. During the experiments, total suspended volumes were determined from suspension optical absorbance, and particle size distributions were measured with a Coulter Counter-multichannel analyzer system. The volume flux through the distribution was estimated from the rate of suspended particle volume removal, which was second order in suspended volume and depended on the fluid shear rate.\r\n \r\nThe Brownian and shear coagulation predictions were verified for the kaolinite, illite, and montmorillonite clays. The three clays were significantly different in the regions of Brownian and shear coagulation dominance and in the volume removal rates at low fluid shear rates. At higher shear rates the volume removal rates declined because of aggregate breakup by fluid shear in the rotating cylinder apparatus. Differences in the clay coagulation and breakup characteristics were explained by variations in clay aggregate porosities. Experiments with silica did not agree with predictions because the silica particles were not destabilized in seawater. Predictions for differential sedimentation coagulation and gravitational settling could not be tested because of larger aggregate breakup by the Coulter Counter.\r\n\r\nThe theoretical predictions have direct application to particle coagulation in oceanic waters and possible application to more complex systems, such as estuarine waters and water and wastewater treatment operations." }, { "name": "Koffman, Larry Douglas", "degree": "PhD", "year": "1980", "title": "I. Experimental Observations of the Microlayer in Vapor Bubble Growth on a Heated Solid. II. An Investigation of the Theory of Evaporation and Condensation", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082006-131228", "creators": [ { "name": { "family": "Koffman", "given": "Larry Douglas" }, "id": "Koffman-Larry-Douglas", "display_name": "Koffman, Larry Douglas" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "chair", "display_name": "Plesset, Milton S." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "member", "display_name": "Lees, Lester" }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "eng" ], "doi": "10.7907/M1H1-S690", "abstract": "Two fundamental problems related to the evaporation of the microlayer formed beneath growing vapor bubbles on a solid surface are investigated. First, experimental measurements of microlayer formation and evaporation have been obtained for nucleate boiling of water and ethanol using laser interferometry combined with high speed photography. For pool boiling of water at atmospheric pressure with low subcooling, the initial microlayer profile is wedge-like with a thickness of 1.85 \u00b5m at a radius of 0.25 mm; the thickness for ethanol is approximately 1.6 times that for water. The measured evaporation rates from the microlayer correspond to local heat fluxes of the order of 1000 kW/m2 over the bubble lifetime. The measurement technique of laser interferometry is discussed in detail with emphasis on the difficulties encountered in interpretation of the fringe patterns. In the second investigation, the theory of evaporation and condensation is considered from a kinetic theory approach. The moment method of Lees is used to solve the problem of the flow of vapor between a hot liquid surface and a cold liquid surface. A result of the theory is that the temperature profile in the vapor for the continuum problem is inverted from what would seem physically reasonable. Because of this behavior, the theory is questioned on physical grounds leading to the conclusion that the usually assumed boundary conditions for emission of molecules from a liquid surface are probably incorrect." }, { "name": "Korwar, Vijaya Narayan", "degree": "PhD", "year": "1980", "title": "Degradation of Picture Quality by Speckle in Coherent Mapping Systems", "advisor": "Pierce, John Robinson", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082006-144128", "creators": [ { "name": { "family": "Korwar", "given": "Vijaya Narayan" }, "id": "Korwar-Vijaya-Narayan", "display_name": "Korwar, Vijaya Narayan" } ], "advisors": [ { "name": { "family": "Pierce", "given": "John Robinson" }, "id": "Pierce-J-R", "role": "advisor", "display_name": "Pierce, John Robinson" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/edk6-jc81", "abstract": "When a coherent imaging system is used to map a rough surface, for instance when a synthetic aperture radar (SAR) system is used to map the earth, the resulting picture of the surface is degraded by random intensity fluctuations called speckle. Speckle obscures the intensity variations caused by the inherent reflectivity differences that identify various features in the picture. The problem of specifying the extent of the degradation caused by speckle in pictures meant to be examined by a human observer was investigated. In particular, the problems considered were those in which an observer has to (a) detect a small feature immersed in a somewhat darker background; (b) detect a grating consisting of alternating bright and somewhat darker lines; (c) distinguish between two or four specified geometrical forms. In each case the picture was corrupted by speckle.\r\n\r\nIn investigating each of these problems, a plausible theoretical model was developed for the decision process used by the observer in his detection or discrimination task. This model was used to relate the probability of his making a correct decision to the relevant picture parameters such as contrast ratio between the reflectivities of various parts of the picture, number of looks per pixel, picture size, and dimension of the features or lines. These calculations were verified by experiments in which the decisions made by an observer examining computer simulations of speckle-corrupted pictures were noted.\r\n\r\nResults of calculations for the reasonable SAP parameters of 1 dB contrast ratio and 12 looks per pixel showed that, in order to achieve a probability of correct decision of 0.95, (a) a small square in a 100 by 100 pixel background needs to be about 7 pixels on a side; (b) a 100 by 100 pixel grating of line pairs needs to have lines about 2 pixels wide; (c) a simple geometrical form (a specific one) needs to be at least 12 pixels on a side to be distinguished from another (specific) form of the same size, when these two forms are the only possible alternatives. These results illustrate that detectability of line pairs is a poor criterion for characterizing picture quality, while form discrimination imposes the most stringent requirements on the imaging system." }, { "name": "Kuwabara, James Shigeru", "degree": "PhD", "year": "1980", "title": "Micronutrient Requirements for Macrocystis pyrifera (L.) C. A. Agardh (Giant Kelp) Gametophytes Determined by Means of a Chemically Defined Medium, Aquil", "advisor": "North, Wheeler J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122006-091318", "creators": [ { "name": { "family": "Kuwabara", "given": "James Shigeru" }, "id": "Kuwabara-James-Shigeru", "display_name": "Kuwabara, James Shigeru" } ], "advisors": [ { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "advisor", "display_name": "North, Wheeler J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/ECSY-FZ64", "abstract": "Requirements of Macrocystis pyrifera (L.) C.A. Agardh gametophytes for nine nutrients (Co, Cu, Fe, I, Mn, Mo, N, P and Zn) were established by means of the chemically defined, artificial seawater, Aquil. Optimal growth ranges for total concentrations of Co, Cu, Fe, Mn, Zn and NO3-N and for media temperatures were determined. Effects on Macrocystis gametophytic growth within these optimal ranges were then investigated. Mathematical equations modeling gametophytic length as a function of concentrations of NO3-N, Fe and Zn, and Zn, Mn, Cu and Co were generated by least squares fit of experimental data.\r\n\r\nAn Aquil formulation was developed that consistently produced Macrocystis embryonic sporophytes after 12 culturing days. Sporophyte production was achieved in Aquil using sporophylls from a variety of southern California sampling sites to initiate gametophytic cultures. This marks the first instance that any macroalga has been successfully cultured in a chemically defined artificial seawater medium using ultraclean techniques.\r\n" }, { "name": "Kyriakides, Stelios", "degree": "PhD", "year": "1980", "title": "On the Propagating Buckle and Its Arrest", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-134840", "creators": [ { "name": { "family": "Kyriakides", "given": "Stelios" }, "id": "Kyriakides-Stelios", "display_name": "Kyriakides, Stelios" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/c81x-nk02", "abstract": "If an offshore pipeline locally buckles in the presence of sufficiently large external pressure, a propagating buckle is initiated. The buckle propagates along the pipeline until it encounters a region of adverse conditions -- low pressure or an arresting device. The lowest pressure at which a buckle propagates is defined as the Propagation Pressure. An experimental study of this quantity is presented and a semiempirical expression derived by examining various models of the phenomenon. The dynamics of the Propagating Buckle are also examined and a parametric study of the steady state velocity of Propagation is carried out. A systematic way of empirically deriving the parametric dependence of arresting devices is presented and experimental results of two such arrestors are discussed. During this study a unique \"flip-flop\" mode of propagation was discovered and studied. An explanation of the phenomenon is also attempted." }, { "name": "Levine, Bruce Stephen", "degree": "PhD", "year": "1980", "title": "Particle Confinement and Magnetic Fluctuations in Tokamak Discharges with Gas Puffing", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102006-132249", "creators": [ { "name": { "family": "Levine", "given": "Bruce Stephen" }, "id": "Levine-Bruce-Stephen", "display_name": "Levine, Bruce Stephen" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/rrs7-xm92", "abstract": "An experimental investigation has been made of particle confinement and magnetic fluctuations associated with short (< 1 msec) gas pulses into a Tokamak discharge. The fluctuations are measured with movable pairs of magnetic probes, each containing a poloidal and radial coil and inserted into the outer regions of the plasma.\r\n\r\nWhen neutral gas is added and the current channel contracts, the fluctuation spectra are dominated by an m=2 mode that grows with the classical tearing-mode rate. When the gas feed is terminated, much broader spectra of modes with m up to 15 are observed. The modal frequencies are nearly integer multiples of 11 kHz. The m=2 mode dominates the poloidal spectra, while the radial spectra have numerous modes of appreciable amplitude. Time-delay measurements suggest that many of the higher-order (m > 3) modes originate in deformation of the m=2 and m=3 magnetic islands. A strong m=7 is found to be localized near the limiter in q(a) = 3.8 discharges, hence this mode is identified as an m=7, n=2, It is found that the m=2 mode becomes destabilized for discharges for which the peak puff density approaches the upper limit given by the Murakami scaling relation. The m=2 mode grows at a rate much slower than the classical tearing-mode rate. The threshold in peak puff density for this destabilization coincides with a degradation in particle confinement." }, { "name": "Liechti, Kenneth Macdougall", "degree": "PhD", "year": "1980", "title": "The Application of Optical Interferometry to Time Dependent Unbonding: Parts 1, 2, and 3", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292003-135400", "creators": [ { "name": { "family": "Liechti", "given": "Kenneth Macdougall" }, "id": "Liechti-Kenneth-Macdougall", "display_name": "Liechti, Kenneth Macdougall" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9yk1-v212", "abstract": "Improved methods of adhesive joining for constructing structural elements have led to an increase in the use of bonding. Bonding is already widely used in the aerospace industry. It allows potential for greater weight and manufacturing cost savings when compared to mechanical fastening as well as providing better fatigue resistant capabilities. More accurate design or life prediction based on a better understanding of adhesive joint failure will allow far more extensive and safer use of adhesively bonded structures. The possibility of time dependent failure is introduced in bonding,by the fact that many adhesives are polymers and measurably viscoelastic under many circumstances. Failure can occur by unbonding at the adherend-adhesive interface or totally within the adhesive. Here the time dependent failure by unbonding at the interface is addressed as one initial investigation of the whole problem.\r\n\r\nIn many engineering problems the modelling of failure has been based on linear fracture mechanics. The extent to which the use of the linear theory can be justified is often questionable in view of the nonlinearity of the local crack front deformation field. One aspect of the current investigation is therefore the measurement of the local crack front deformation to examine the limits of the validity for the linear theory and to provide a basis for future modelling, Within this framework, particular attention is paid to the aspects of local failure mode interaction and the time dependence of the unbonding process.\r\n\r\nThe small displacements in the crack front region require a resolution on the order of a wavelength of light. The experimental techniques used are therefore based on optical interferometry. The displacements applied to the adherends are controlled to the same order by a novel, thermally actuated servoloading device.\r\n\r\nThe thesis is divided into three distinct parts. The first part deals with the development of the experimental techniques used to measure the unbound profiles as well as to measure and control the displacements applied to the adherends. For stationary cracks, the second part describes experiments which examine the extent of the nonlinearity in the crack front deformation field while fracture criteria are developed and compared for unbonding rates in steadily propagating cracks. Finally, proposals for improvement of the experimental techniques and further experiments are discussed in the third part." }, { "name": "Liljestrand, Howard Michael", "degree": "PhD", "year": "1980", "title": "Atmospheric Transport of Acidity in Southern California by Wet and Dry Mechanisms", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102006-110816", "creators": [ { "name": { "family": "Liljestrand", "given": "Howard Michael" }, "id": "Liljestrand-Howard-Michael", "display_name": "Liljestrand, Howard Michael" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Anson", "given": "Fred C." }, "id": "Anson-F-C", "role": "member", "display_name": "Anson, Fred C." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." } ], "option_major": [ "envreng" ], "doi": "10.7907/pgev-yh86", "abstract": "Acid precipitation samples collected at Pasadena, California, from February 1976 to April 1979 and at eight other southern California sites for shorter periods were analyzed to determine acid and base composition. The concentrations of major cations (H+, NH4+, Na+, K+, Ca2+, Mg2+) and anions (Cl-, NO2-, Br-, NO3-, SO42) as well as trace weak acids (Fe, Al, Mn, Si(OH)4, RCOOH) were determined. Titrations with base showed acidity predominantly to be due to strong acids (nitric and sulfuric) and weak acids (ammonium ion and carbonic acid). The pH was controlled by strong acidity at the urban sites in the Los Angeles Basin.\r\n\r\nThe chemical composition of precipitation samples collected in ~0.25 in increments is modeled in several ways. Chemical balances are used to determine the contributions of sea salt, soil dust, stationary sources, mobile sources and non-point sources of ammonia. Multiple regression analysis is used to relate ground-level measurements of air quality and atmospheric conditions with rainwater nitrite plus nitrate and sulfate concentrations. Precipitation intensity, ozone, nitric oxide and nitrogen dioxide concentrations are most strongly correlated with rainwater nitrite plus nitrate. Precipitation intensity, ozone, and nitric oxide are most strongly correlated with rainwater sulfate.\r\n\r\nGas-liquid equilibrium models yield the following predictions: Low partial pressures of ammonia (average of 0.001 - 0.006 ppbv within the basin) during precipitation scavenging; total sulfite amounting to less than 25% of the non-sea salt sulfur; and nitrite concentrations from NO and NO2 dissolution which are slightly larger than observed values. Kinetic models of the formation of nitrate and sulfate underestimate the observed concentrations. Spatial distributions of acids and base correspond with local sources. The mountain sites and the more rural eastern sites have significantly less net acidity than the western urban sites.\r\n\r\nEstimates of the dry deposition of atmospheric acids indicate the dry flux is ~6600 equivalents/HA-YR in the Los Angeles Basin compared to ~380 equivalents/HA-YR for the wet flux of strong acidity. The semi-arid climate and high ambient pollutant concentrations cause the large dry flux. Advection of pollutants is the most important mechanism for the removal of acidity from the Los Angeles airshed.\r\n" }, { "name": "Locanthi, Bartholomew Nicholas, III", "degree": "PhD", "year": "1980", "title": "The Homogeneous Machine", "advisor": "Seitz, Charles L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10092006-142135", "creators": [ { "name": { "family": "Locanthi", "given": "Bartholomew Nicholas, III" }, "id": "Locanthi-Bartholomew-Nicholas-III", "display_name": "Locanthi, Bartholomew Nicholas, III" } ], "advisors": [ { "name": { "family": "Seitz", "given": "Charles L." }, "id": "Seitz-C-L", "role": "advisor", "display_name": "Seitz, Charles L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/0jdc-9578", "abstract": "The advance of semiconductor technology is bringing about rapid changes in the scale and performance of integrated systems, thus also in their economics and potential applications. The highly visible and readily quantified changes in measures such as the number of transistors are accompanied by more subtle but increasingly significant shifts in fundamental relationships affecting system design. Specifically, as transistors become smaller, faster, and lower power, the wires used to interconnect them are becoming slower. These shifts, along with the challenge of managing the complexity of designs with millions of switching elements, are forcing a new look at alternative computer architectures which use ensembles of computing elements under restricted and regular interconnection.\r\n\r\nThis thesis addresses the problem of orchestrating many computing elements in the performance of general-purpose computations. There are three major obstacles in the way of this goal. First, it must be possible to express programs in a notation that allows concurrency to be discovered and exploited. Second, it must be possible to map computations onto a physical structure for execution by multiple computing elements. Third, such computing elements must be provided rapid access to storage while at the some time avoiding contention.\r\n\r\nThis thesis presents a scheme which automatically detects and exploits concurrencies in computations expressed in an applicative subset of the LISP programming language. The mapping of numerical and symbolic computations onto array and tree structures is also investigated.\r\n\r\nThis thesis approaches the design of multiprocessor systems as a problem in bandwidth reduction. To this end, the concept of a multi-level cache is introduced. The discussion culminates with a description of a multi-level LISP system implemented on a tree of processors. This implementation provides each processor with a superset of the address space of its immediate ancestor. Memory allocation and garbage collection for this machine are described and a simple example of its operation is given." }, { "name": "McVerry, Graeme Haynes", "degree": "PhD", "year": "1980", "title": "Frequency Domain Identification of Structural Models from Earthquake Record", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechThesis:08232021-222545352", "creators": [ { "name": { "family": "McVerry", "given": "Graeme Haynes" }, "id": "McVerry-Graeme-Haynes", "display_name": "McVerry, Graeme Haynes" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/bpab-qq32", "abstract": "The usefulness of simple linear mathematical models for representing the behaviour of tall buildings during earthquake response is investigated for a variety of structures over a range of motions including the onset of structural damage. The linear models which best reproduce the measured response of the structures are determined from the recorded earthquake motions. In order to improve upon unsatisfactory results obtained by methods using transfer functions, a systematic frequency domain identification technique is developed to determine the optimal models. The periods, dampings and participation factors are estimated for the structural modes which are dominant in the measured response.
\r\n\r\nThe identification is performed by finding the values of the modal parameters which produce a least-squares match over a specified frequency range between the unsmoothed, complex-valued, finite Fourier transform of the acceleration response recorded in the structure and that calculated for the model. It is possible to identify a single linear model appropriate for the entire response, or to approximate the nonlinear behavior exhibited by some structures with a series of models optimal for different segments of the response.
\r\n\r\nThe investigation considered the earthquake records obtained in ten structures ranging in height from seven to forty-two stories. Most of the records were from the San Fernando earthquake. For two of these structures, smaller-amplitude records from more distant earthquakes were also analyzed. The maximum response amplitudes ranged from approximately 0.025 g to 0.40 g.
\r\n\r\nThe very small amplitude responses were reproduced well by linear models with fundamental periods similar to those measured in vibration tests. Most of the San Fernando responses in which no structural damage occurred (typically 0.2g-0.3g maximum accelerations) were also matched closely by linear models. However, the effective fundamental periods in these responses were characteristically 50 percent longer than in vibration tests. The average first mode damping identified from these records was about 5 percent of critical. Only those motions which produced structural damage could not be represented satisfactorily by time-invariant linear models. Segment-by-segment analysis of these records revealed effective periods of two to three times the vibration test values with fundamental mode dampings of 15 to 20 percent.
\r\n\r\nThe systematic identification technique generally achieves better matches of the recorded responses than those produced by models derived by trial-and-error methods, and consequently more reliable estimates of the modal parameters. The close reproductions of the measured motions confirm the accuracy of linear models with only a few modes for representing the behaviour during earthquake response of tall buildings in which no structural damage occurs.
" }, { "name": "Moyer, Richard Harrison", "degree": "PhD", "year": "1980", "title": "I. The Mode Locked Dye Laser. II. Picosecond Photoconductivity of Semi-Insulating Gallium Arsenide", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-06152005-155103", "creators": [ { "name": { "family": "Moyer", "given": "Richard Harrison" }, "id": "Moyer-Richard-Harrison", "display_name": "Moyer, Richard Harrison" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/bhsz-8b41", "abstract": "The first part of this thesis deals with the principles and practice of the passive mode locking of a CW dye laser. This discussion includes the dynamics of picosecond pulse production as well as the techniques of high resolution pulse width measurement. The characterization of the mode locked dye laser through real-time temporal and spectral measurements is also described.\r\n\r\nThe second part of the thesis describes the development and applications of the opto-electronic semiconductor switch. Design considerations of the high speed photoconductive device and results of experiments in which picosecond pulses activate the devices are discussed. The experimental results are interpreted to yield numerical estimates of carrier recombination rates. A new experimental technique of determining these parameters through ultrafast magnetophotoconductivity is introduced as well. The results of this technique show good agreement with the steady state measurements." }, { "name": "Nguyen, Tanh Van", "degree": "PhD", "year": "1980", "title": "Studies in the Flow of Granular Materials", "advisor": "Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062006-150937", "creators": [ { "name": { "family": "Nguyen", "given": "Tanh Van" }, "id": "Nguyen-Tanh-Van", "display_name": "Nguyen, Tanh Van" } ], "advisors": [ { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/dm6x-9s32", "abstract": "A number of problems related to the flow of cohesionless granular materials in hoppers are investigated.\r\n\r\nAn approximate solution to the flow of granular materials in a conical hopper is presented. The material is modeled as a rigid-perfectly plastic continuum which satisfies the Mohr-Coulomb yield condition. Unknown geometries of the upper and lower free surfaces are determined from the stress-free conditions. The results are compared to those based on different constitutive postulates as well as to experimental observations. The computed mass flow rate and wall stress compare well with the experimental measurements made with small and full size hoppers.\r\n\r\nThe flow field in a hopper with a vertical bin is observed to gain a better understanding of the details of the flow field. The observations seem to correspond to the recent results obtained by other investigators using X-ray radiography.\r\n\r\nThe funnel flow regime in hoppers is studied in detail. The different types of flow which exist are identified and classified. The possibility of having a transition from one type of flow into another one is recorded as a function of the material properties and hopper geometry. Finally, the boundary between the moving and stagnant material is studied as a function of the hopper geometry. Other parameters such as the effect of the hopper thickness and wall roughness on the flow field are also studied." }, { "name": "Pepper, David M.", "degree": "PhD", "year": "1980", "title": "Phase Conjugate Optics: On the Theory, Observation, and Utilization of Temporally-Reversed Wavefronts as Generated Via Nonlinear Optical Parametric Interactions", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-10122006-081036", "creators": [ { "name": { "family": "Pepper", "given": "David M." }, "id": "Pepper-David-M", "display_name": "Pepper, David M." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/03GZ-7C28", "abstract": "This thesis describes theoretical and experimental aspects as well as potential applications in the field of coherent optics known as Phase Conjugate Optics (PCO). By utilizing nonlinear optical techniques, real-time phase or wavefront reversal of an arbitrary incident electromagnetic field can be realized. The nonlinear optical interaction gives rise to what is referred to as the \"phase conjugate replica\" (of the incident monochromatic wave) by performing the operation of complex conjugation upon the incident wave's complex spatial amplitude in real time. This conjugate wave, which is also designated as being a \"time-reversed\" wavefront, has the property of exactly retracing the path of the incident field. The ability of the conjugate wave to correct for inhomogeneous linear and nonlinear (intensity-dependent) phase aberrations as well as polarization distortions is proved. In particular, the theory of a degenerate four-wave nonlinear optical interaction as providing for the phase conjugator is presented. The effects of linear and nonlinear losses upon this interaction are discussed. The quantum mechanical origin of the third order nonlinear optical susceptibility responsible for the four-wave mixing process is analyzed for both single and two-photon allowed transitions in an atomic (or molecular) system. The analogies of four-wave mixing with that of real-time holography are discussed. The theory of phase conjugation via four-wave mixing in optical waveguides is presented.\r\n\r\nSeveral of the above characteristics of conjugate fields are verified experimentally where phase conjugate fields via degenerate four-wave mixing were observed both in the bulk and in waveguide geometries, using carbon disulfide as the nonlinear medium. Amplified time-reversed wavefront generation as well as a mirrorless optical parametric mode of oscillation have been observed, both in agreement with theoretical predictions.\r\n\r\nPotential applications of PCO are discussed in three different regimes: spatial-frequency, temporal-frequency, and spatial/temporal frequency domains. In the first category, the ability of PCO to correct for image modal dispersion in optical waveguides as well as the use of PCO to perform real-time coherent image processing and nonlinear microscopy is discussed. Temporal-frequency domain applications of PCO to be analyzed include the use of a nearly degenerate four-wave mixing process as a narrowband, wide field-of-view optical filter, capable of an amplified bandpass. The ability of a PCO interaction to renarrow (transform limited) optical pulses which have been temporally spread due to propagation through (group velocity) dispersive channels is analyzed. A potential application of PCO in the field of nonlinear laser spectroscopy is presented. Specifically, the scattering of a probe photon off a two-photon coherent state (created in a three-level atomic system) is shown to yield a conjugate replica. This conjugate replica is capable of providing sub-Doppler width resolution of the two-photon resonance. Further, in the transient regime, the optical free-induction decay of the conjugate wave is capable of yielding detailed spectral features of the three-level system such as the anharmonic contribution to a (nearly) harmonic potential. This technique, performed in the time domain, is known as [alpha]-beat spectroscopy.\r\n\r\nFinally, a detailed theoretical and experimental study is presented of a laser resonator in which one (or both) of the mirror(s) comprising the optical cavity is replaced by a phase conjugate mirror (PCM). This novel resonator, which is termed a phase conjugate resonator (PCR), combines many of the spatial- and temporal-frequency aspects of PCO interactions discussed above. The stability criterion, transverse and longitudinal mode spectra, and the PCR output energy, as well as the frequency locking features of the laser modes to the PCM are discussed." }, { "name": "Rensink, Loman", "degree": "PhD", "year": "1980", "title": "Switching Regulator Configurations and Circuit Realizations", "advisor": "Middlebrook, Robert David; Cuk, Slobodan", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102006-131020", "creators": [ { "name": { "family": "Rensink", "given": "Loman" }, "id": "Rensink-Loman", "display_name": "Rensink, Loman" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Cuk", "given": "Slobodan" }, "id": "Cuk-S", "role": "advisor", "display_name": "Cuk, Slobodan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PD3T-2V38", "abstract": "Methods for obtaining improved performance from switching regulators with respect to their noise generation characteristics and dynamic response are developed through topology selection, refinement and generation, and by application of modern control techniques to both continuous and discrete time converter models.\r\n\r\nReduction in switching noise is attained by focusing analysis and design effort on rendering the external converter current waveforms as near to the ideal dc quantities as possible. Three techniques, not relying on conventional low-pass filtering, are promoted and several new or refined converter topologies are generated with these methods. In addition, a power-processing elliptic-function filter specifically designed to meet the requirements of the switching conversion environment and applicable to many common converter types is presented. Performance of the new low-noise converter topologies is substantiated by several circuit realizations and laboratory measurements.\r\n\r\nSwitching regulator dynamic performance is optimized by use of modern control theory in conjunction with the state-space-averaging technique. State-vector feedback coefficients which will minimize transient error excursions are determined through use of generally applicable algorithms for optimal linear regulator design.\r\n\r\nAn alternative approach is developed that relies on a discrete-time formulation of converter and regulator that is the dual to state-space-averaging. Among the important results are a simple expression for duty-ratio-controlled inductive current bandwidth of wide applicability, and a general solution for obtaining the fastest possible transient response from a switching regulator. The results of the control analysis are convincingly supported with laboratory measurements." }, { "name": "Rowson, James Allely", "degree": "PhD", "year": "1980", "title": "Understanding Hierarchical Design", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-12062006-104710", "creators": [ { "name": { "family": "Rowson", "given": "James Allely" }, "id": "Rowson-James-Allely", "display_name": "Rowson, James Allely" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/Z9BP00R2", "abstract": "With the exponential improvement in integrated circuit technology comes the problem of how to design systems containing millions of devices. This thesis presents a new look at hierarchical design based on the Caltech structured design methodology.\r\n\r\nThe hierarchy is separated into two parts: leaf cells, containing no instances of other cells, and composition cells, containing only instances of other cells. A leaf cell can be implemented in many different representations. A representation consists of a set of leaf cells and a composition rule that builds correct higher level cells.\r\n\r\nThe separated hierarchy is suitable for mathematical analysis by the use of Curry's theory of combinators. In this form, a hierarchy is represented by a mathematical operator that produces a digital system from the leaf cells. The question of hierarchical equivalence is examined.\r\n\r\nThree sample composition rules, or algorithms, are presented as examples. The SLAP system provides a geometry composition rule that produces the mask description of a system given the geometries of the leaf cells. In analogy to TYPEing in a programming language, two representations that enforce a certain design style are discussed. The first TYPE system guarantees signal integrity. The second TYPE system guarantees mutual exclusion between the sources on a bus." }, { "name": "Sander, Stanley Paul", "degree": "PhD", "year": "1980", "title": "Kinetics Studies of Bromine Monoxide and Methylperoxy Free Radicals by Flash Photolysis", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032006-131828", "creators": [ { "name": { "family": "Sander", "given": "Stanley Paul" }, "id": "Sander-Stanley-Paul", "display_name": "Sander, Stanley Paul" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/9BZ5-X071", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA flash photolysis-ultraviolet absorption system was constructed to study the kinetics of gas-phase free radical reactions over a wide range of pressure and temperature. Because of their atmospheric importance, the reactions of methylperoxy (CH302) and bromine monoxide (BrO) radicals with themselves, and with NO and NO2 were investigated:\r\n\r\n[...]. \r\n\r\nThe rate constants for reactions 1 - 6 were determined by measuring the first-order or second-order decay rates of BrO and CH3O2 radicals by ultraviolet absorption spectrophotometry. The rate constants for reactions 3 and 6 were found to vary significantly with pressure, indicating the formation of a stable adduct. The pressure dependence of the rate constants was discussed in terms of the Troe theory of unimolecular reactions. Measurements of the branching ratio of reaction 4 were used to develop a detailed reaction mechanism for the disproportionation of BrO radicals. Upper limits were also obtained for the rate constants for the reactions\r\n\r\n[...]. \r\n\r\nThe atmospheric implications of the rate constant measurements are discussed." }, { "name": "Sherman, David Carl", "degree": "PhD", "year": "1980", "title": "Natural Convection Film Boiling on a Vertical Surface", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10112006-081638", "creators": [ { "name": { "family": "Sherman", "given": "David Carl" }, "id": "Sherman-David-Carl", "display_name": "Sherman, David Carl" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/MZ76-J054", "abstract": "Experimental results are presented for an investigation of free convection film boiling heat transfer to saturated ethanol, saturated Freon 113, and saturated distilled water from a vertical cylinder. High speed motion pictures of the vapor-liquid interface in film boiling have been obtained. All tests have been conducted at atmospheric pressure over a range of heat flux between 9000 and 37000 BTU/hr ft(2).
\r\n\r\nA study of the stability of the vapor-liquid interface is performed and the results are compared to the photographic data. Parameters influencing the heat transfer process are developed and the experimental data is used to determine their proper relationship.
\r\n\r\nThe heat transfer coefficient in natural convection film boiling of saturated liquids on moderately long vertical surfaces at constant heat flux is shown to be insensitive to vertical position, and to be dependent only on the temperature differential and the fluid properties.
\r\n \r\nLarge scale waves have been observed on the vapor-liquid interface: however, their effect on the heat transfer is minimal. It appears that intense vaporization at the interface plays an important role in the generation of these waves, while surface tension does not.
\r\n\r\nA strong possibility of liquid droplet entrainment in the vapor flow is indicated by the presence of a rough, wavy interface, a relatively high speed vapor-flow, and by the unexpectedly strong dependence of the heat transfer on the latent heat of vaporization.
\r\n" }, { "name": "Subbaiah, Malladi Venkata", "degree": "PhD", "year": "1980", "title": "Non-Steady Behavior of a Flame Spreading from a Point in a Two-Dimensional Duct", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012006-152708", "creators": [ { "name": { "family": "Subbaiah", "given": "Malladi Venkata" }, "id": "Subbaiah-Malladi-Venkata", "display_name": "Subbaiah, Malladi Venkata" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/se8q-9c70", "abstract": "Non-steady behavior of a flame stabilized in a two-dimensional duct is studied in this thesis. The problem is formulated by an integral technique in which the governing equations are integrated across the duct to obtain integral relations for the mean flow variables. The flow fields on either side of the flame sheet are matched by appropriate matching conditions. Fluid flow through the flame surface causes the integral relations to explicitly involve the fluid velocities at the flame. An independent description of the flame shape and the irrotational flow field upstream of the flame is provided by a source distribution on the duct axis.\r\n\r\nThe integral relations are analyzed by a perturbation technique, in which the dominant order solution represents the steady flame development. The steady flame configuration is perturbed by an acoustic wave incident on the compact flame region. The time dependent counterpart of the integral relations describes the ensuing non-steady flow fields. The flame perturbation exhibits a travelling wave pattern with considerable amplification along the flame zone. A simple model to describe the growth of the flame perturbation is put forth, by considering the flame surface as an unstable shear layer.\r\n\r\nAcoustic reflection and transmission coefficients of the flame region are obtained utilizing the time-dependent flame calculations. The response spectra exhibit active responses at certain well defined frequencies. The non-steady flame model is incorporated in a rudimentary afterburner configuration to investigate the low frequency behaviour of the afterburner. The results suggest a possible mechanism of low frequency instability in a combustion system." }, { "name": "Tsaur, Bor-Yeu", "degree": "PhD", "year": "1980", "title": "Ion-Beam-Induced Modifications of Thin Film Structures and Formation of Metastable Phases", "advisor": "Mayer, James Walter; Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102006-094500", "creators": [ { "name": { "family": "Tsaur", "given": "Bor-Yeu" }, "id": "Tsaur-Bor-Yeu", "display_name": "Tsaur, Bor-Yeu" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "chair", "display_name": "Mayer, James Walter" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2v82-tm86", "abstract": "The influences of energetic ion bombardment on the composition and structure of thin film materials and the utilization of ion-beam-mixing techniques to produce compounds and alloys are reported in this thesis.\r\n\r\nMotivated by recent experimental observations that ion bombardment can induce alteration of atomic distributions in composite materials, a systematic study of ion-induced modification of interface profile and structure has been carried out. By bombarding through a thin transition-metal film deposited on a Si substrate, significant atomic mixing was observed near the metal-Si interface at dose levels of ~10(15)cm(-2). The atomic mixing led to the formation of well-defined silicide phases which are identical to those obtained by normal thermal treatment. A macroscopic model based on collision-cascade mixing and radiation-enhanced diffusion mechanisms was proposed to account for the ion-induced interface reaction. The mixing process and its products were found to be strongly influenced by the implantation conditions such as ion energy, mass, fluence and sample temperature, as well as by the intrinsic properties of target material such as thermal diffusivity and radiation stability. Ion-beam-mixing at higher ion doses (~10(16)cm(-2)) led to the formation of more Si-rich phases or disordered metal-Si layers which are difficult to form or, in some cases, inaccessible by normal thermal process. The phenomenon of ion-induced silicide formation is similar to that observed in thermal annealing except that the radiation stability of phase structure is important in determining whether a silicide phase is formed or a disordered metal-Si mixture is formed. (Chapter 2)\r\n\r\nThe ion-beam-mixing process was then utilized to investigate the production of nonequilibrium (or metastable) phases. A metastable silicide phase of a stoichiometry Pt2Si3 has been obtained by heat treating a Si-rich amorphous Pt-Si alloy layer produced by ion-beam-mixing of thin PtSi (or Pt) films on Si. The Pt2Si3 phase is absent in the equilibrium phase diagram of Pt-Si and has not been reported before. X-ray diffraction analysis established the crystal structure of Pt2Si3 to be hexagonal with lattice parameters a = 3.841 \u00c5, c = 11.924 \u00c5 and with 10 atoms per unit cell. The metastable phase was found to exhibit a superconducting transition onset at about 4.2K and to become completely superconductive at temperature below 3.6K. For the first time, a compound of this structure was observed to be a superconductive material. The transformation behavior of the ion-induced amorphous Pt2Si3 alloy has been studied by using resistivity measurements. The amorphous to metastable crystalline transformation occurred at ~400\u00b0C as indicated by an abrupt decrease of resistivity. The metastable phase then gradually decomposed into an equilibrium PtSi and Si mixture at temperatures above 550\u00b0C. The kinetics of amorphous to crystalline transformation have been determined by isothermal treatment over the temperature interval 376-392\u00b0C. The results were interpreted in terms of a classical nucleation and growth mechanism with a t4 (time) dependence and an apparent activation enthalpy of 4.69 eV (108 kcal/mole). The microstructures of the alloys at various stages of transformation were studied by transmission electron microscopy and diffraction. The results were found to correlate well to the phase transformation behavior observed by resistivity measurements. (Chapters 3 and 4)\r\n\r\nTo further investigate the production of metastable phases by ion-beam mixing, experiments have been performed in the simple eutectic system of Au-Si. An amorphous alloy with a uniform composition Au-28 at .% Si (~Au5Si2) was formed by bombarding through a thin Au film on Si, a result distinctly different from that obtained in normal thermal treatment. Upon thermal annealing, the amorphous phase transforms into a metastable crystalline phase at ~100\u00b0C, which then gradually decomposes into an equilibrium Au and Si mixture at higher temperatures. The present observations were compared with those obtained previously by rapid quenching techniques. The comparison of metastable phase formation in the Pt-Si and Au-Si systems revealed a correlation between the existence of metastable phases and eutectic compositions, as well as the importance of sample temperature during implantation for direct observation of metastable phases. (Chapter 5)\r\n\r\nAs an extension of compound formation by ion-beam-mixing of a thin layer on a thick substrate, we investigated the mixing of thin deposited layers as a scheme for producing compounds or alloys of desirable compositions. Multiple-layered samples consisting of thin alternate layers of two elements were prepared by sequential vacuum deposition of the two components onto an inert substrate such as Si02 or Al2O3. The relative thicknesses of the individual layers were adjusted such that the average film composition was equal to a fixed, predetermined value. Ion bombardment was then performed to homogenize the layers on an atomic scale. Formation of supersaturated Ag-Cu and Au-Co solid solutions over a wide range of composition has been achieved. Extensions of alloy solubility and formation of amorphous phases have been obtained in the almost completely immiscible systems of Ag-Ni and Cu-Ta, respectively. The present scheme may promise to be a new technique for producing metastable phases which are difficult to form or unattainable by conventional rapid quenching techniques. (Chapter 6)\r\n\r\nFinally, we consider the possibility of using ion-beam-mixing techniques as an alternative approach to direct high dose implantation for material surface modification. Comparison between ion-beam-mixing and high dose implantation is made to demonstrate the \"effectiveness\" of ion-beam mixing in incorporating Au or Ag in single crystal Cu substrates. A simple diffusion model for the evolution of ion-beam-mixing of a thin surface layer on a thick substrate was then proposed. The model predicts the influence of implantation conditions and material properties on the redistribution of the thin surface layers. From a practical point of view, the technique of introducing foreign species by ion-beam-mixing process exhibits many attractive advantages over direct implantation because of significantly lower ion doses required and the ability to use simple ion sources. (Chapter 7)." }, { "name": "Turner, Timothy Neal", "degree": "PhD", "year": "1980", "title": "Second Sound Shock Waves and Critical Velocities in Liquid Helium II", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132006-075044", "creators": [ { "name": { "family": "Turner", "given": "Timothy Neal" }, "id": "Turner-Timothy-Neal", "display_name": "Turner, Timothy Neal" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/cg05-6436", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nLarge amplitude second-sound shock waves have been generated and the experimental results compared to the theory of nonlinear second-sound. The structure and thickness of second-sound shock fronts is calculated and compared to experimental data. Theoretically it is shown that at T = 1.88\u00b0K, where the nonlinear wave steepening vanishes, the thickness of a very weak shock must diverge. In a region near this temperature, a finite-amplitude shock pulse will evolve into an unusual double-shock configuration consisting of a front steepened, temperature raising shock followed by a temperature lowering shock. Double-shocks are experimentally verified. The theoretical dependence of the shock induce temperature jump on the Mach number is successfully verified for large amplitudes ([...]) after the response of a thin-film superconducting temperature sensor is analyzed.\r\n\r\nThe ability of second-sound shock waves to simultaneously produce and measure very large relative velocities in regions away from the disruptive influence of walls makes them an invaluable tool in the study of critical velocities intrinsic to the fluid. It was experimentally discovered that very large second-sound shock waves initiate a breakdown in the superfluidity of helium II, which is dramatically displayed as a limit to the maximum attainable shock strength. Although the observed breakdown could not be definitely attributed to a critical velocity, the value of the maximum shock-induced relative velocity represents a significant lower bound to the intrinsic critical velocity of helium II. The observed limits within which superfluidity was still maintained (w=3.67 m/sec at T = 1.45\u00b0K, and w = 3.20 m/sec at T = 1.85\u00b0K) are the largest counterflow velocities ever obtained outside of restricted geometries." }, { "name": "Ury, Israel", "degree": "PhD", "year": "1980", "title": "Monolithic Integration of Gallium Arsenide Optoelectronic Devices", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-09282006-090324", "creators": [ { "name": { "family": "Ury", "given": "Israel" }, "id": "Ury-Israel", "display_name": "Ury, Israel" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/s4x6-kk53", "abstract": "The optical properties of GaAs make it a very useful material for the fabrication of optical emitters and detectors. GaAs also possesses electronic properties which permit the fabrication of high speed electronic devices which are superior to conventional silicon devices. This thesis describes three examples of the monolithic integration of optical and electronic devices on semi-insulating GaAs substrates.\r\n\r\nIn the first example, an injection laser was integrated with a Gunn oscillator to yield a high frequency modulated optical source. In the second example, an injection laser was integrated with a metal semiconductor field effect transistor (MESFET). The transistor was used to modulate the current through the laser. In the third example, an integrated optical repeater was demonstrated which consisted of a MESFET optical detector, a current source, a transistor driver, and an injection laser all fabricated on a single chip. The repeater displayed an optical gain of 10 dB.\r\n\r\nIn order to facilitate the fabrication of more complex integrated optoelectronic circuits, a method was sought to form a laser cavity which did not occupy the entire width of a chip. The result was the demonstration of whispering gallery lasers which take the shape of quarter and half rings. The performance of the curved lasers was reduced from that of the straight lasers due to optical scattering at imperfections along the curve. A general theory is developed which describes mode conversion in perturbed dielectric resonators. This theory is applied to the case of the whispering gallery laser and its predictions are compared with experiment." }, { "name": "Vural, Kadri L\u00fctfi", "degree": "PhD", "year": "1980", "title": "Magnetic Domain Wall Dynamics in the Presence of an In-Plane Field", "advisor": "Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechETD:etd-09212004-103313", "creators": [ { "name": { "family": "Vural", "given": "Kadri L\u00fctfi" }, "id": "Vural-Kadri-L\u00fctfi", "display_name": "Vural, Kadri L\u00fctfi" } ], "advisors": [ { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/NPAV-0X78", "abstract": "The purpose of this work is to understand the domain wall dynamics in the presence of high drive fields and inplane fields in magnetic bubble materials. Bubble radial expansion method is used to investigate the non-linear region. Saturation velocity is found at low in-plane fields and a drive dependent region at higher in-plane fields. The in-plane field increases all the velocities. There is velocity anisotropy and the wall along the in-plane field generally has a higher velocity than the one normal to it. The domain wall is dynamically deformed through the thickness at high drive and in-plane fields. This deformation is studied in the bulk of the film by transmission (Faraday) mode and at the surfaces by reflection (Kerr) mode. The mechanism for the deformation is based on the spatial variations of the effective in-plane field through the thickness. This causes different parts of the wall to move with different velocities resulting in a deformed wall. The characteristics of the deformed wall are studied in detail for several samples." }, { "name": "Abeyaratne, Rohan Chandra", "degree": "PhD", "year": "1979", "title": "Discontinuous Deformation Gradients in Plane Finite Elastostatics of Incompressible Materials. (I) General Considerations. (II) An Example", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03012018-170438409", "creators": [ { "name": { "family": "Abeyaratne", "given": "Rohan Chandra" }, "id": "Abeyaratne-Rohan-Chandra", "display_name": "Abeyaratne, Rohan Chandra" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "chair", "display_name": "Knowles, James K." }, { "name": { "family": "Hughes", "given": "Thomas J. R." }, "id": "Hughes-T-J-R", "role": "member", "display_name": "Hughes, Thomas J. R." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "member", "display_name": "Knauss, Wolfgang Gustav" }, { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "member", "display_name": "Sternberg, Eli" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/seym-cd95", "abstract": "This investigation is concerned with the possibility of the change of type of the differential equations governing finite plane elastostatics for incompressible elastic materials, and the related is sue of the existence of equilibrium fields with discontinuous deformation gradients. Explicit necessary and sufficient conditions on the deformation invariants and the material for the ellipticity of the plane displacement equations of equilibrium are established. The issue of the existence, locally, of \"elastostatic shocks\" -- elastostatic fields with continuous displacements and discontinuous deformation gradients -- is then investigated. It is shown that an elastostatic shock exists only if the governing field equations suffer a loss of ellipticity at some deformation. Conversely, if the governing field equations have lost ellipticity at a given deformation at some point, an elastostatic shock can exist, locally, at that point. The results obtained are valid for an arbitrary homogeneous, isotropic, incompressible, elastic material. In order to illustrate the occurrence of elastostatic shocks in a physical problem, a specific displacement boundary value problem is studied. Here, a particular class of isotropic, incompressible, elastic materials which allow for a loss of ellipticity is considered. It is shown that no solution which is smooth in the classical sense exists to this problem for certain ranges of the applied loading. Next, we admit solutions involving elastostatic shocks into the discussion and find that the problem may then be solved completely. When this is done, however, there results a lack of uniqueness of solutions to the boundary value problem. In order to resolve this non-uniqueness, dissipativity and stability are investigated.
" }, { "name": "Au Yeung, John Chen Wei", "degree": "PhD", "year": "1979", "title": "Phase Conjugate Optics and Nonlinear Optical Phenomena in Optical Fibers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:02232026-221505804", "creators": [ { "name": { "family": "Au Yeung", "given": "John Chen Wei" }, "id": "Au Yeung-John-Chen-Wei", "display_name": "Au Yeung, John Chen Wei" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4dcy-fx66", "abstract": "Part I of this thesis describes the theoretical and experimental\r\naspects of a new area in coherent optics known as phase conjugate optics.\r\nBy using nonlinear optical mixing techniques, the complex conjugate of an\r\narbitrary incident monochromatic wave can be generated. In particular,\r\nthe theory of the degenerate four-wave mixing technique is presented.\r\nExperimental observation of phase conjugate wave front generation in a\r\nliquid crystal material (MBBA) is described. The ability of the conjugate\r\nwave front to correct for phase aberration is demonstrated. The quantum\r\nmechanical origin of the nonlinear third order susceptibility responsible\r\nfor the four-wave mixing process is illustrated in an atomic system.\r\nBecause of a finite memory time of such an atomic system, the electromagnetic\r\nwaves taking part in the mixing process need not occur simultaneously.\r\nThe applications of the phase conjugation process to real-time\r\ninformation processing and the characteristics of a phase conjugate resonator\r\nare discussed in detail.
\r\n\r\nThe ability of an optical fiber to confine the propagation of electromagnetic\r\nwaves over a long distance and within a small cross sectional\r\narea implies that large optical intensities can be maintained over a long\r\n\" interaction length even at moderate incident optical power. Part II of\r\nthis thesis describes some third order nonlinear optical phenomena that\r\nhave been observed under this condition. Especially, phase conjugation\r\nby degenerate four-wave mixing in a fiber has been shown to require significantly\r\nless pumping power. The theoretical and experimental studies\r\nof four-wave mixing in a liquid-filled fiber are presented.
\r\n\r\nExtensive experimental efforts have been devoted over the last\r\nfew years to the study of stimulated Raman scattering and the oscillation\r\nof the Stokes radiation inside fibers. A detailed theoretical\r\ntreatment will be given here to describe these effects. The analysis\r\nshows that pump depletion due to the nonlinear process is very important\r\nin describing the stimulated Raman scattering in low loss fibers and is\r\nthe dominant saturation effect in a fiber Raman oscillator. Finally,\r\nthe implications of nonlinear optical phenomena to fiber optic communication\r\nwill be mentioned.
" }, { "name": "Ayres, Ronald Frederick", "degree": "PhD", "year": "1979", "title": "A Language Processor and a Sample Language", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072021-184918786", "creators": [ { "name": { "family": "Ayres", "given": "Ronald Frederick" }, "id": "Ayres-Ronald-Frederick", "display_name": "Ayres, Ronald Frederick" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/r2hy-6x63", "abstract": "This thesis explores shared data in list structures and ambiguity in language processing. Tolerance of ambiguity is necessary to support clear and modular expression. Data sharing is necessary to support ambiguity efficiently. Data sharing is useful also in compiled programs to save memory and time.
\r\n\r\nLet us define some terms. A rewrite grammar is a set of replacement rules each of which specifies that a given phrase may be replaced by another given phrase. Each replacement rule expresses a local translation. A parser finds those sequences of replacements that bring a given text to a machine handleable form. Each such sequence represents a meaning or interpretation for the given text. Tolerance of ambiguity or multiple interpretations for a given text is necessary so that subsequent processing can place further constraints upon the input text.
\r\n\r\nThis thesis presents a parser which efficiently, handles general-rewrite grammars. To conserve computer time and memory, only essential differences among multiple interpretations are represented and processed. If several interpretations for a given text are valid, the parser yields a meaning which represents the ambiguity as, locally as possible. Even an exponential number of distinct meanings may be represented in a polynomial amount of memory.
\r\n\r\nThis thesis also presents a language processing system which supports semantic processing via independent rewrite grammars. Each grammar represents a distinct aspect of the language. A given sequence of grammars becomes a sequence of passes, or process steps. Each pass derives a meaning with respect to one grammar and uses that meaning to generate phrases which will be interpreted by the next pass. Although linguistic specification is usually done with context-free grammars, features of this parser which support general-rewrite grammars are essential for the integration of passes. Not only ambiguity, but also the locality of ambiguity is preserved from one pass to the next. It is necessary to preserve\r\nlocality of ambiguity in order to avoid explosive computation arising from useless action among independent sets of interpretations.
\r\n\r\nI have implemented a general-purpose programming language called ICL with this system. The fact that ICL's datatypes are processed by a rewrite grammar makes it simple to implement both user-defined datatype coercions and functions known as polymorphic operators whose definitions depend on parameter datatypes. Datatype coercions and Polymorphic operators reduce the amount,of specification required in algorithms to such an extent that a user can often modify declarations and achieve optimizations and changes in concept without modifying his algorithmic specification.
\r\n\r\nICL includes a simple and safe policy about pointers so that the user can ignore their existence completely if he wishes. ICL automatically maximizes data sharing and minimizes copying by adopting a \"copy on write\" policy. This policy supports the illusion that each and every reference to a data structure generates a\r\ncomplete copy of that data structure. This same technique is used in the language processor itself to facilitate data sharing among multiple interpretations in ambiguous cases.
" }, { "name": "Beck, James Leslie", "degree": "PhD", "year": "1979", "title": "Determining Models of Structures from Earthquake Records", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212003-110242", "creators": [ { "name": { "family": "Beck", "given": "James Leslie" }, "id": "Beck-James-Leslie", "display_name": "Beck, James Leslie" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "chair", "display_name": "Jennings, Paul C." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "civileng" ], "doi": "10.7907/JP7R-KF57", "abstract": "The problem of determining linear models of structures from seismic response data is studied using ideas from the theory of system identification. The investigation employs a general formulation called the output-error approach, in which optimal estimates of the model parameters are obtained by minimizing a selected measure-of-fit between the responses of the structure and the model. The question of whether the parameters can be determined uniquely and reliably in this way is studied for a general class of linear structural models. Because earthquake records are normally available from only a small number of locations in a structure, and because of measurement noise, it is shown that it is necessary in practice to estimate parameters of the dominant modes in the records, rather than the stiffness and damping matrices.
\r\n\r\nTwo output-error techniques are investigated. Tests of the first, an optimal filter method, show that its advantages are offset by weaknesses which make it unsatisfactory for application to seismic response. A new technique, called the modal minimization method, is developed to overcome these difficulties. It is a reliable and efficient method to determine the optimal estimates of modal parameters for linear structural models.
\r\n\r\nThe modal minimization method is applied to two multi-story buildings that experienced the 1971 San Fernando earthquake. New information is obtained concerning the properties of the higher modes of the taller building and more reliable estimates of the properties of the fundamental modes of both structures are found. The time-varying character of the equivalent linear parameters is also studied for both buildings. It is shown for the two buildings examined that the optimal, time-invariant, linear models with a small number of modes can reproduce the strong-motion records much better than had been supposed from previous work using less systematic techniques.
" }, { "name": "Best, John Stewart", "degree": "PhD", "year": "1979", "title": "Schottky Barriers on Compound Semiconductors: I. HgSe Highly Electronegative Contacts. II. Au Schottky Barriers on n-Ga\u2081\u208b\u2093A1\u2093As", "advisor": "McCaldin, James Oeland", "url": "https://resolver.caltech.edu/CaltechTHESIS:07162014-160535319", "creators": [ { "name": { "family": "Best", "given": "John Stewart" }, "id": "Best-John-Stewart", "display_name": "Best, John Stewart" } ], "advisors": [ { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "advisor", "display_name": "McCaldin, James Oeland" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ysaz-r608", "abstract": "I. HgSe is deposited on various semiconductors, forming a\r\nsemimetal/semiconductor \"Schottky barrier\" structure. Polycrystalline,\r\nevaporated HgSe produces larger Schottky barrier heights on n-type\r\nsemiconductors than does Au, the most electronegative of the elemental\r\nmetals. The barrier heights are about 0.5 eV greater than\r\nthose of Au on ionic semiconductors such as ZnS, and 0.1 to 0.2\r\neV greater for more covalently bonded semiconductors. A novel\r\nstructure,which is both a lattice matched heterostructure and a\r\nSchottky barrier, is fabricated by epitaxial growth of HgSe on\r\nCdSe using hydrogen transport CVD. The Schottky barrier height\r\nfor this structure is 0.73 \u00b1 0.02 eV, as measured by the photoresponse\r\nmethod. This uncertainty is unusually small; and the magnitude is\r\ngreater by about a quarter volt than is achievable with Au, in\r\nqualitative agreement with ionization potential arguments.
\r\n\r\nII . The Schottky barrier height of Au on chemically etched\r\nn-Ga1-x AlxAs was measured as a function of x. As x increases, the\r\nbarrier height rises to a value of about 1.2 eV at x \u2248 0.45 , then\r\ndecreases to about 1.0 eV as x approaches 0.83. The barrier height\r\ndeviates in a linear way from the value predicted by the \"common\r\nanion\" rule as the AlAs mole fraction increases. This behavior is\r\nrelated to chemical reactivity of the Ga1-x AlxAs surface.
\r\n" }, { "name": "Breidenthal, Robert Edward", "degree": "PhD", "year": "1979", "title": "A Chemically Reacting, Turbulent Shear Layer", "advisor": "Roshko, Anatol; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10272006-111937", "creators": [ { "name": { "family": "Breidenthal", "given": "Robert Edward" }, "id": "Breidenthal-Robert-Edward", "display_name": "Breidenthal, Robert Edward" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "chair", "display_name": "Saffman, Philip G." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Dimotakis", "given": "Paul E." }, "id": "Dimotakis-P-E", "role": "member", "display_name": "Dimotakis, Paul E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/hj67-9h91", "abstract": "A chemically reacting turbulent shear layer was investigated in a new, blow-down water tunnel. In a diffusion-limited reaction, a pH indicator, phenolphthalein, in one stream mixed and reacted with a base, sodium hydroxide, in the other stream to form a visible reaction product. Using optical densitometry techniques, the amount of product was measured as a function of Reynolds number, at a relatively high Schmidt number of approximately 600. The results were compared with both the previous mixing measurements of Konrad in a gaseous shear layer (Sc = 0.7) and the simple mixing model of Broadwell.\r\n\r\nThe product was found to be distributed, as expected, in concentrated lumps associated with the large, spanwise-coherent structures of the turbulence. The time averaged amount of product in the layer exhibited a rapid transition at a large-structure Reynolds number of about 5 x 10(3) for a velocity ratio of 0.38. Above the transition, the amount of product within the layer was independent of Reynolds number.\r\n\r\nThis transition is related to the introduction of small scale, three-dimensional motions into the layer. In the initial region, where the flow was already unsteady and contained large structures but was strictly two-dimensional, very little mixing was observed. Downstream the flow became unstable to three-dimensional perturbations and small scale, three-dimensional motions were introduced into the layer. Across this transition, the aqueous mixing increased by an order of magnitude, indicating the sensitivity of mixing to small scales of the turbulence in a high Schmidt number fluid. At high Reynolds numbers, changing the Schmidt number by three orders of magnitude only altered the molecular mixing by about a factor of two or less. The mixing model of Broadwell, which addresses the effect of Schmidt number, is in satisfactory qualitative agreement with the observations.\r\n\r\nThe unique flow visualization of the visible reaction product in water permitted a study of the three-dimensional instability and evolution of small scale motions in the layer. Streamwise streaks which had been previously observed in the Brown-Roshko gas apparatus were found to originate from a spanwise-sinuous wiggle which appeared at a large-structure Reynolds number which varied with velocity ratio, indicating an influence of initial conditions on the instability." }, { "name": "Darcey, Terrance Michael", "degree": "PhD", "year": "1979", "title": "Methods for Localization of Electrical Sources in the Human Brain and Applications to the Visual System", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032026-125501655", "creators": [ { "name": { "family": "Darcey", "given": "Terrance Michael" }, "id": "Darcey-Terrance-Michael", "display_name": "Darcey, Terrance Michael" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/yvch-jm69", "abstract": "Multichannel human visual evoked scalp potential (VESP)\r\nrecording was combined with results from electric field theory and the\r\nmethods of non-linear parameter estimation to see if it was possible\r\nto infer the general spatio-temporal course of brain excitation in the\r\nprocessing of a visual stimulus, To do this, various models of the head\r\nand underlying sources were tested , Head models included a simple\r\nhomogeneous and 2 different piecewise homogeneous volume-conducting\r\nspheres, the latter of which were designed to account for the known\r\nelectrical inhomogeneity and anisotropy provided by the skull and scalp.\r\nSource models studied were single and multiple electrostatic dipoles\r\nand two simple types of extended sources, radial cap and annular sector\r\ndipole layers. Equivalent sources for the experimental data were\r\nfound by taking least-squares estimates of model parameters, minimizing\r\nthe sum of the squared deviations between the actual scalp potentials\r\nand the scalp potentials computed by the model, Since these models were\r\nparameterized for both location and source characteristics (e.g.\r\norientation and magnitude), one could attempt to relate them to the\r\ntopography and functional anatomy of the brain. A working assumption\r\nin relating these was that active cortex could be modeled to a first\r\napproximation as a neuronal layer wherein the neurons are treated as\r\ndiscrete current sources oriented normal or at right-angles to the\r\ncortical surface, Thus, it was assumed that VESP's reflect the\r\ntopography of the tissues that produce them.
\r\n\r\n40-channel VESP measurements were made to briefly appearing\r\ncheckerboard patterns placed in various areas of the visual field.\r\nThese data were analyzed in terms of underlying equivalent sources in\r\nthe brain. Although there were some variations present in the 3\r\nsubjects studied, these may be consistent with known variations in\r\ncortical topography. The measured potential distributions showed a\r\nradical dependence of VESP topography on stimulus locus and indicated\r\nthat these VESP's are probably volume-conducted field effects arising\r\nfrom a small number of fairly localized sources in the brain. Equivalent\r\ndipoles in general give excellent fits to the measured data and\r\nthe mapping between the visual field and these equivalent sources\r\nis similar to the connnonly accepted mapping between the visual field\r\nand visual cortex. As such, it appears that evoked potentials may\r\nbe used as a crude tool for defining the anatomical projection of\r\nlocalized sensory fields onto the cortical surface in humans.
" }, { "name": "Gartrell, Gregory Jr.", "degree": "PhD", "year": "1979", "title": "Studies on the Mixing in a Density-Stratified Shear Flow", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10172017-162001547", "creators": [ { "name": { "family": "Gartrell", "given": "Gregory Jr." }, "id": "Gartrell-Gregory", "display_name": "Gartrell, Gregory Jr." } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/G80K-5566", "abstract": "The objective of this study was to examine in a fundamental way the mixing processes in a stably-stratified shear flow. The results of the experimental program have yielded information on the nature of turbulence and mixing in density-stratified fluids. The results can be applied to such problems as the determination of the spreading and mixing rates of heated effluents discharged to lakes or the ocean, as well as to many geophysical problems.
\r\n \r\nAn experimental investigation was made to measure the mixing in a two-layered density-stratified shear flow in a flume 40-meters long, with a cross-section of 110 cm wide by 60 cm deep. Both mean temperatures and the mean velocities of the two layers could be independently controlled, and steps were taken to ensure that the temperatures and velocities of the two layers remained nearly constant at the inlet. The relative density difference between the layers was 10-3 or less. A laser-Doppler velocimeter, designed for this study, allowed measurements of two components of velocity simultaneously, while a sensitive thermistor was used to measure the temperature. The temperature and velocity measurements were recorded and later analyzed.
\r\n \r\nThe initial mixing layer which developed at the inlet was found to be dominated by large, two-dimensional vortex structures. When the flow was sufficiently stratified, these structures would collapse in a short distance and the flow would develop a laminar shear layer at the interface. It was found that the bulk-Richardson number \u0394\u03c1/\u03c1oglT*/\u0394u-o2, where lT* is the maximum-slope thickness of the temperature profile, attained a maximum value of between 0.25 and 0.3 when the mixing layer collapsed.
\r\n \r\nDownstream, much less turbulent mixing took place in the stratified flows than homogeneous flows. The depth-averaged turbulent diffusivities for heat and momentum were often 30 to 100 times smaller in stratified flows than in homogeneous flows. The turbulence downstream was found to be dominated by large turbulent bursts, during which the vertical turbulent transport of momentum, heat and turbulent kinetic energy are many times larger than their mean values. It was found these bursts were responsible for most of the total turbulent transport of momentum, heat and turbulent kinetic energy, even though the bursts were found only intermittently.
\r\n \r\nThe flux Richardson number, Rf, in the flow was examined and found to be related to the local mean-Richardson number in many cases. When production of turbulent kinetic energy from the mean shear, (-u1v1)‾ \u03d1u‾/\u03d1uy, was the largest source of turbulent kinetic energy, it was found that Rf < 0.3, and when the flow was strongly stratified, then Rf < 0.2. If the diffusion of turbulent kinetic energy 1/2 \u03d1(u'2 + v'2)v'‾/\u03d1y = \u03d1q*2v'/\u03d1y was the largest source of turbulent kinetic energy, then the flux-Richardson number often attained large values, and the quantity was found to be a more useful parameter than Rf. It was found that, in almost all cases, the rate at which the potential energy of the fluid increased due to turbulent mixing was much less than the estimated rate of viscous dissipation of turbulent kinetic energy.
" }, { "name": "Goring, Derek Garard", "degree": "PhD", "year": "1979", "title": "Tsunamis -- The Propagation of Long Waves onto a Shelf", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechTHESIS:10172017-155041868", "creators": [ { "name": { "family": "Goring", "given": "Derek Garard" }, "id": "Goring-Derek-Garard", "display_name": "Goring, Derek Garard" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/Z9W957BN", "abstract": "The various aspects of the propagation of long waves onto a shelf (i.e., reflection, transmission and propagation on the shelf) are examined experimentally and theoretically. The results are applied to tsunamis propagating onto the continental shelf.
\r\n \r\nA numerical method of solving the one-dimensional Boussinesq equations for constant depth using finite element techniques is presented. The method is extended to the case of an arbitrary variation in depth (i.e., gradually to abruptly varying depth) in the direction of wave propagation. The scheme is applied to the propagation of solitary waves over a slope onto a shelf and is confirmed by experiments.
\r\n \r\nA theory is developed for the generation in the laboratory of long waves of permanent form, i.e., solitary and cnoidal waves. The theory, which incorporates the nonlinear aspects of the problem, applies to wave generators which consist of a vertical plate which moves horizontally. Experiments have been conducted and the results agree well with the generation theory. In addition, these results are used to compare the shape, celerity and damping characteristics of the generated waves with the long wave theories.
\r\n \r\nThe solution of the linear nondispersive theory for harmonic waves of a single frequency propagating over a slope onto a shelf is extended to the case of solitary waves. Comparisons of this analysis with the nonlinear dispersive theory and experiments are presented.
\r\n \r\nComparisons of experiments with solitary and cnoidal waves with the predictions of the various theories indicate that, apart from propagation, the reflection of waves from a change in depth is a linear process except in extreme cases. However, the transmission and the propagation of both the transmitted and the reflected waves in general are nonlinear processes. Exceptions are waves with heights which are very small compared to the depth. For these waves, the entire process of propagation onto a shelf in the vicinity of the shelf is linear . Tsunamis propagating from the deep ocean onto the continental shelf probably fall in this class.
" }, { "name": "Grossman, William Mark", "degree": "PhD", "year": "1979", "title": "Combustion of CS\u2082/O\u2082 in a laminar mixing layer and processes in the CO chemical laser", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-104557879", "creators": [ { "name": { "family": "Grossman", "given": "William Mark" }, "id": "Grossman-William-Mark", "display_name": "Grossman, William Mark" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/CAPG-QQ92", "abstract": "The combustion of CS\u2082 and O\u2082 in a free burning laminar mixing layer at low pressure was investigated using emission spectroscopy. The temperature fields, CO vibrational distributions, and CO concentrations were measured. The data indicate that vibration ally excited CO was produced in the mixing layer flames, but that there were no vibrational population inversions. In comparison with the CS\u2082/O\u2082 premixed flames, the mixing layer flames favored greater production of COS and CO\u2082. Computer modeling was used to study the mechanisms responsible for the production of COS and CO\u2082, and to study how the branching chain mechanism responsible for production of CO affects the behavior of the mixing layer flame. The influences of the gas additives, N\u2082O, COS, and CNBr, were also investigated.\r\n" }, { "name": "Hagan, Patrick Shawn", "degree": "PhD", "year": "1979", "title": "The Stability of Traveling Wave Solutions of Parabolic Equations", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03222013-083627751", "creators": [ { "name": { "family": "Hagan", "given": "Patrick Shawn" }, "id": "Hagan-Patrick-Shawn", "display_name": "Hagan, Patrick Shawn" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/yn9e-nm19", "abstract": "A method for determining by inspection the stability or instability of any solution u(t,x) = \u0278(x-ct) of any smooth equation of the form u_t = f(u_(xx),u_x,u where \u2202/\u2202a f(a,b,c) > 0 for all arguments a,b,c, is developed. The connection between the mean wavespeed of solutions u(t,x) and their initial conditions u(0,x) is also explored. The\r\nmean wavespeed results and some of the stability results are then extended\r\nto include equations which contain integrals and also to include some\r\nspecial systems of equations. The results are applied to several physical\r\nexamples." }, { "name": "Hong, Chi-Shain", "degree": "PhD", "year": "1979", "title": "New Optical Waveguide Devices Using Periodic and Chirped Surface Corrugations and Optical Waves in Periodic Layered Structures", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242019-103435948", "creators": [ { "name": { "family": "Hong", "given": "Chi-Shain" }, "id": "Hong-Chi-Shain", "display_name": "Hong, Chi-Shain" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/77TB-4N62", "abstract": "The first part of this work describes theoretical and experimental studies of some corrugated waveguide devices for use in optical communications and integrated optics. These devices include wavelength demultiplexers and broad-band optical filters using chirped corrugations, and optical scanners using the electrooptic effect in the corrugations.
\r\n\r\nThe theory of corrugated waveguides is well described by the coupled mode formalism. The problem is also treated phenomenologically by picturing the incident waveguide mode as a zig-zag ray which is diffracted by the grating surface at every bounce. Principles of the devices are given, and the parameters which characterize the devices are derived.
\r\n\r\nExperimental results on fabrication and evaluation of the devices are presented and compared with the design theory. Various techniques which have been developed during the course of this investigation are described in some detail.
\r\n\r\nThe second part of this work describes the propagation of electromagnetic waves in periodic layered structures.
\r\n\r\nA diagonalization of the unit cell translation operator of a periodic medium is used to obtain exact solutions for the Bloch waves, the dispersion relations, and the band structure of the medium. The general formalism is then applied to deal with such problems as Bragg reflectors, periodic multichannel waveguides, and electromagnetic surface waves.
\r\n" }, { "name": "Hwang, David Li-Shui Quek", "degree": "PhD", "year": "1979", "title": "Propagation of the Fast Magnetosonic Wave in a Tokamak Plasma", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-104710068", "creators": [ { "name": { "family": "Hwang", "given": "David Li-Shui Quek" }, "id": "Hwang-David-Li-Shui-Quek", "display_name": "Hwang, David Li-Shui Quek" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/f15y-jy67", "abstract": "The propagation of the fast magnetosonic wave in a tokamak\r\nplasma has been investigated at low power, between 10 and 300 watts,\r\nas a prelude to future heating experiments.
\r\n\r\nThe attention of the experiments has been focused on the understanding\r\nof the coupling between a loop antenna and a plasma-filled\r\ncavity. Special emphasis has been given to the measurement of the complex\r\nloading impedance of the plasma. The importance of this measurement\r\nis that once the complex loading impedance of the plasma is known,\r\na matching network can be designed so that the r.f. generator impedance\r\ncan be matched to one of the cavity modes, thus delivering maximum\r\npower to the plasma. For future heating experiments it will be essential\r\nto be able to match the generator impedance to a cavity mode in\r\norder to couple the r.f. energy efficiently to the plasma.
\r\n\r\nAs a consequence of the complex impedance measurements, it was\r\ndiscovered that the designs of the transmitting antenna and the impedance\r\nmatching network are both crucial. The losses in the antenna and\r\nthe matching network must be kept below the plasma loading in order to\r\nbe able to detect the complex plasma loading impedance. This is even\r\nmore important in future heating experiments, because the fundamental\r\nbasis for efficient heating before any other consideration is to deliver\r\nmore energy into the plasma than is dissipated in the antenna system.
\r\n\r\nThe characteristics of the magnetosonic cavity modes are confirmed\r\nby three different methods. First, the cavity modes are observed\r\nas voltage maxima at the output of a six-turn receiving probe.\r\nSecond, they also appear as maxima in the input resistance of the transmitting\r\nantenna. Finally, when the real and imaginary parts of the\r\nmeasured complex input impedance of the antenna are plotted in the\r\ncomplex impedance plane, the resulting curves are approximately circles,\r\nindicating a resonance phenomenon.
\r\n\r\nThe observed plasma loading resistances at the various cavity\r\nmodes are as high as 3 to 4 times the basic antenna resistance (~ .4 \u2126).\r\nThe estimated cavity Q\u2019s were between 400 and 700. This means that\r\nefficient energy coupling into the tokamak and low losses in the antenna\r\nsystem are possible.
" }, { "name": "Kushner, Mark Jay", "degree": "PhD", "year": "1979", "title": "Electronic and Kinetic Processes in the Cu/CuCl Double Pulse Laser", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-092719903", "creators": [ { "name": { "family": "Kushner", "given": "Mark Jay" }, "id": "Kushner-Mark-Jay", "display_name": "Kushner, Mark Jay" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/a9bz-sw68", "abstract": "Kinetic and electronic processes in a Cu/CuCl double pulsed\r\nlaser were investigated by measuring discharge and laser pulse characteristics,\r\nand by computer modeling. There are two time scales\r\ninherent to the operation of the Cu/CuCl laser. The first is during\r\nthe interpulse afterglow (tens to hundreds of microseconds). The\r\nsecond is during the pumping pulse (tens of nanoseconds). It was\r\nfound that the character of the pumping pulse is largely determined\r\nby the initial conditions provided by the interpulse afterglow. By\r\ntailoring the dissociation pulse to be long and low energy, and by\r\nconditioning the afterglow, one may select the desired initial conditions\r\nand thereby significantly improve laser performance. With a\r\nlow energy dissociation pulse, the fraction of metastable copper obtained\r\nfrom a CuCl dissociation is low. By maintaining the afterglow,\r\ncontributions to the metastable state from ion recombinations\r\nare prevented, and the plasma impedance remains low thereby increasing\r\nthe rate of current rise during the pumping pulse. Computer models\r\nfor the dissociation pulse, afterglow, pumping pulse and laser pulse\r\nreproduced experimentally observed behavior of laser pulse energy\r\nand power as a function of time delay, pumping pulse characteristics,\r\nand buffer gas pressure. The sensitivity of laser pulse properties\r\non collisional processes (e.g., CuCl reassociation rates)\r\nwas investigated." }, { "name": "Larkin, Ross Martin", "degree": "PhD", "year": "1979", "title": "Photopic Rapid Adaptation in the Electroretinogram: a White Noise Analysis", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03022026-194810149", "creators": [ { "name": { "family": "Larkin", "given": "Ross Martin" }, "id": "Larkin-Ross-Martin", "display_name": "Larkin, Ross Martin" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/0s8a-v524", "abstract": "When light enters the eye it initiates a complicated chain of\r\nevents which eventually lead to the sensation of vision. The\r\nelectroretinogram (ERG) is a widely used indirect measure of the\r\nvisual system, One of the most interesting aspects of the visual\r\nsystem, adaptation, is its ability to function over a very wide range\r\nof incoming light intensities, This thesis is concerned with the\r\nstudy of the retina during small, fast changes in the state of\r\nadaptation.
\r\n\r\nTo study rapid adaptation, a new technique was developed which\r\nmay also be used for looking at other biological systems, Kernels\r\n(a form of cross-correlation), when used with white noise stimuli,\r\nhave proven very useful in the study of the dynamics of photopic\r\nrapid adaptation, Using first order kernels we have probed the wide\r\nrange of adaptation and compared kernels to flash responses, With the\r\nsecond order kernel we found evidence that a late (125 ms) wave in the\r\nERG is caused by rapid adaptation, identified the components of highly\r\nabnormal ERG 1s and obtained basic information about the internal\r\norganization of a system. The third order kernel characterized\r\nsuppression-recovery in the photopic ERG.
\r\n\r\nWe then speculated on the correlation of our results with some of\r\nthe prevailing views of the organization and operation of rapid\r\nadaptation in the photoreceptors of the retina,
" }, { "name": "Liau, Zong-Long", "degree": "PhD", "year": "1979", "title": "Ion Bombardment Effects on Material Compositions: Preferential Sputtering and Atomic Mixing", "advisor": "Mayer, James Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:02182026-213527000", "creators": [ { "name": { "family": "Liau", "given": "Zong-Long" }, "id": "Liau-Zong-Long", "display_name": "Liau, Zong-Long" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/08ty-be56", "abstract": "This thesis reports a study of the effects of ion\r\nbombardment on material composition and their implications\r\nin material modification and analysis. First, composition\r\nchanges in binary alloys and compounds as a result of rare-gas\r\nsputtering were observed by using Rutherford backscattering\r\ntechniques. The heavier components were generally\r\nfound to become enriched in a surface layer whose thickness\r\ncorresponded to the ion range. After an amount of\r\nmaterial comparable to this thickness had been sputter-removed,\r\nthe surface layer reached a steady-state. The\r\nsteady-state surface composition was independent of the\r\nmass and energy of the sputtering ion. (Chapters 2 and 3)
\r\n\r\nThe results were interpreted in terms of a preferential\r\nsputtering, which generated enrichment of the heavy\r\nspecies at surface, in combination with an ion-induced\r\natomic mixing effect, which propagated the composition\r\nchange over a depth comparable to the ion range. A model\r\nbased on this interpretation seemed to combine all experimental\r\nresults into a consistent picture. (Chapter 4)
\r\n\r\nThe model was then extended to study the phenomena of\r\nhigh-dose ion implantation. The idea of preferential\r\nsputtering was used to predict the limits of compositions\r\nachievable by implanting ion species A into material B,\r\nor by implanting A+ into material AB. The formation\r\nkinetics of the implanted surface layer was determined by\r\nboth sputtering and atomic mixing effects. The model\r\nyielded results in good agreement with preliminary experimental\r\nresults. (Chapter 5)
\r\n\r\nOne of the important implications of sputter-induced\r\nsurface layer composition changes has been their effects on\r\nthe use of sputtering in surface-cleaning and in depth-profiling\r\ntechniques. In this respect, we also studied the\r\neffect of atomic mixing and preferential sputtering on the\r\nevolution of very thin surface layers during sputter-etching.\r\nWe observed that, for low ion doses, the atomic mixing\r\neffect first produced a uniformly alloyed surface layer with\r\na thickness comparable to the ion range. Then, during the\r\nsuccessive steps of sputter-etching, the surface layer maintained\r\na constant thickness, but with a decreasing alloy (or\r\nimpurity) concentration. Again, the previously developed\r\nmodel was extended for the present case. It also combined\r\nthe results into a consistent picture. Based on these\r\nstudies, we then extended the model further to predict the\r\neffect of atomic mixing and preferential sputtering on the\r\ndepth-profiling techniques. A simple equation was obtained,\r\nwhich related the \"apparent\" depth profiles to the true\r\nones. (Chapter 6)
\r\n\r\nFinally, the effect of atomic mixing has been studied\r\nin the cases where the ion range penetrated through the\r\ninterface between a surface metal film and an underlying\r\nSi-substrate. Silicide formation at the interface was\r\nobserved for ion doses \u227e 1014cm-2. For higher doses,\r\nmore Si-atoms were incorporated into the surface layer and\r\nthe system appeared to be amorphized. After being\r\nthermally annealed, the samples showed formation of metastable\r\nphases which had not been reported previously.\r\nThe present results suggest that the ion-induced atomic\r\nmixing effect has the potential of producing thin-film\r\nmaterials with any desirable compositions or with\r\ncompositions and structures unachievable by conventional\r\nmetallurgical means. (Chapter 7)
" }, { "name": "Lyon, Stephen Aplin", "degree": "PhD", "year": "1979", "title": "Optical Properties of Excited Silicon and Germanium at Low Temperatures", "advisor": "McGill, Thomas C.; Smith, Darryl L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-141717487", "creators": [ { "name": { "family": "Lyon", "given": "Stephen Aplin" }, "id": "Lyon-Stephen-Aplin", "display_name": "Lyon, Stephen Aplin" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Smith", "given": "Darryl L." }, "id": "Smith-D-L", "role": "advisor", "display_name": "Smith, Darryl L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8gcb-7j35", "abstract": "Part I of this thesis deals with 3 topics concerning the\r\nluminescence from bound multi-exciton complexes in Si. Part II presents a model for the decay of electron-hole droplets in pure and\r\ndoped Ge.
\r\n\r\nPart I.
\r\n\r\nWe present high resolution photoluminescence data for Si doped With Al, Ga, and In. We observe emission lines due to recombination of electron-hole pairs in bound excitons and satellite lines which have been interpreted in terms of complexes of several excitons bound to an impurity. The bound exciton luminescence in Si:Ga and Si:Al consists of three emission lines due to transitions from the ground\r\nstate and two low lying excited states. In Si:Ga, we observe a second triplet of emission lines which precisely mirror the triplet due to the bound exciton. This second triplet is interpreted as due to decay of a two exciton complex into the bound exciton. The observation of the second complete triplet in Si:Ga conclusively demonstrates that more than one exciton will bind to an impurity.\r\nSimilar results are found for Si:Al. The energy of the lines show that the second exciton is less tightly bound than the first in Si:Ga. Other lines are observed at lower energies. The assumption of ground state\r\nto ground-state transitions for the lower energy lines is shown to produce a complicated dependence of binding energy of the last exciton on the number of excitons in a complex. No line attributable to the decay of a two exciton complex is observed in Si:In.
\r\n\r\nWe present measurements of the bound exciton lifetimes for the four common acceptors in Si and for the first two bound multi-exciton complexes in Si:Ga and Si:Al. These results are shown to be in agreement with a calculation by Osbourn and Smith of Auger transition rates for acceptor bound excitons in Si. Kinetics determine the relative populations of complexes of various sizes and work functions, at temperatures which do not allow them to thermalize with respect to one another. It is shown that kinetic limitations may make it impossible to form two-exciton complexes in Si:In from a gas of free excitons.
\r\n\r\nWe present direct thermodynamic measurements of the work functions of bound multi-exciton complexes in Al, B, P and Li doped Si. We find that in general the work functions are smaller than previously believed. These data remove one obstacle to the bound multi-exciton complex picture which has been the need to explain the very large apparent work functions for the larger complexes obtained by assuming\r\nthat some of the observed lines are ground-state to ground-state transitions. None of the measured work functions exceed that of the electron-hole liquid.
\r\n\r\nPart II.
\r\n\r\nA new model for the decay of electron-hole-droplets in Ge is presented. The model is based on the existence of a cloud of droplets within the crystal and incorporates exciton flow among the drops in the cloud and the diffusion of excitons away from the cloud. It is able to fit the experimental luminescence decays for pure Ge at different\r\ntemperatures and pump powers while retaining physically\r\nreasonable parameters for the drops. It predicts the shrinkage of the cloud at higher temperatures which has been verified by spatially and temporally resolved infrared absorption experiments. The model also accounts for the nearly exponential decay of electron-hole-droplets\r\nin lightly doped Ge at higher temperatures.
\r\n" }, { "name": "MacNeal, Bruce Edward", "degree": "PhD", "year": "1979", "title": "Horizontal Bloch Line Motion in Magnetic Bubble Materials", "advisor": "Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-101245424", "creators": [ { "name": { "family": "MacNeal", "given": "Bruce Edward" }, "id": "MacNeal-Bruce-Edward", "display_name": "MacNeal, Bruce Edward" } ], "advisors": [ { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/m96x-g645", "abstract": "The purpose of this work is to extend experimental and theoretical \r\nunderstanding of horizontal Bloch line (HBL) motion in magnetic\r\nbubble materials. The present theory of HBL motion is reviewed, and\r\nthen extended to include transient effects in which the internal\r\ndomain wall structure changes with time. This is accomplished by\r\nnumerically solving the equations of motion for the internal azimuthal\r\nangle \u0278 and the wall position q as functions of z, the coordinate\r\nperpendicular to the thin-film material, and time. The\r\neffects of HBL's on domain wall motion are investigated by comparing\r\nresults from wall oscillation experiments with those from the theory.\r\nIn these experiments, a bias field pulse is used to make a step\r\nchange in equilibrium position of either bubble or stripe domain\r\nwalls, and the wall response is measured by using transient photography. \r\nDuring the initial response, the dynamic wall structure\r\nclosely resembles the initial static structure. The wall accelerates\r\nto a relatively high velocity (\u224820 m/sec), resulting in a short\r\n(\u224822 nsec ) section of initial rapid motion. An HBL gradually forms\r\nnear one of the film surfaces as a result of local dynamic properties,\r\nand moves along the wall surface toward the film center. The presence\r\nof this structure produces low-frequency, triangular-shaped\r\noscillations in which the experimental wall velocity is nearly constant, \r\nvs\u2248 5-8 m/sec. If the HBL reaches the opposite surface,\r\ni.e., if the average internal angle reaches an integer multiple of\r\n\u03c0, the momentum stored in the HBL is lost, and the wall chirality\r\nis reversed. This results in abrupt transitions to overdamped motion\r\nand changes in wall chirality, which are observed as a function of\r\nbias pulse amplitude. The pulse amplitude at which the nth punch-\r\nthrough occurs just as the wall reaches equilibrium is given within\r\n0.2 0e by Hn = (2vsH'/\u03b3)1/2 \u2022 (n\u03c0)1/2 + Hsv), \r\nwhere H' is the effective field gradient from the surrounding domains, and Hsv is a small\r\n(less than 0.03 0e), effective drag field. Observations of wall oscillation\r\nin the presence of in-plane fields parallel to the wall show that HBL\r\nformation is suppressed by fields greater than about 40 0e (\u22482\u03c0Ms),\r\nresulting in the high-frequency, sinusoidal oscillations associated\r\nwith a simple internal wall structure.\r\n" }, { "name": "Mason, Alfred Barr", "degree": "PhD", "year": "1979", "title": "Some Observations on the Random Response of Linear and Nonlinear Dynamical Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechThesis:08232021-215722701", "creators": [ { "name": { "family": "Mason", "given": "Alfred Barr" }, "id": "Mason-Alfred-Barr", "display_name": "Mason, Alfred Barr" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/hvp8-jf64", "abstract": "First examined is the problem of obtaining the nonstationary stochastic response of a nonlinear system subject to deterministically modulated stationary Gaussian random excitation. An extension of the generalized method of equivalent linearization is used to obtain an approximation to this response. The accuracy of this approximate technique is investigated by means of Monte Carlo simulation.
\r\n\r\nAttention is then turned to the first passage problem for the stationary response of a lightly damped linear oscillator excited by white noise. A method is developed to generate approximate values for the limiting decay rate of the corresponding first passage probability density. This method is extended so that an approximate first passage probability distribution may be calculated when the oscillator response is nonstationary. The accuracy of this approximate distribution is examined.
\r\n\r\nAs a practical application, it is indicated how this technique may be used to determine an earthquake-like random process which generates a response spectrum consistent with given data. The accuracy and range of validity of the procedure are indicated by a simulation study.
\r\n\r\nThe approximate solution of the first passage problem is combined with the equivalent linearization technique to yield a procedure for computing approximate first passage probabilities of a weakly nonlinear oscillator. The errors introduced by this procedure are investigated.
" }, { "name": "Oey, Nicolaus Kiam Thian", "degree": "PhD", "year": "1979", "title": "Leading Edge Flutter of a Supercavitating Hydrofoil", "advisor": "Babcock, Charles D.; Brennen, Christopher E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032006-091936", "creators": [ { "name": { "family": "Oey", "given": "Nicolaus Kiam Thian" }, "id": "Oey-Nicolaus-Kiam-Thian", "display_name": "Oey, Nicolaus Kiam Thian" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "advisor", "display_name": "Brennen, Christopher E." } ], "committee": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "chair", "display_name": "Babcock, Charles D." }, { "name": { "family": "Brennen", "given": "Christopher E." }, "id": "Brennen-C-E", "role": "member", "display_name": "Brennen, Christopher E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Davis", "given": "Leverett" }, "id": "Davis-Leverett", "role": "member", "display_name": "Davis, Leverett" }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9DGB-DW93", "abstract": "Leading edge flutter is a problem that is unique to a super-cavitating hydrofoil. At high speed, the leading edge portion has been observed to oscillate while the trailing edge remains motionless.
\r\n\r\nIn this study, several flat plate hydrofoils were tested. The experimental results indicate that the phenomenon is a complex function of speed, angle of attack, cavitation number and mass ratio. Leading edge flutter was also observed to cause cavity pinching. A theoretical study was also conducted. Two mathematical models are presented here. The first one models the flexible chord foil as a rigid chord foil hinged at the trailing edge; the second model treats the fluid-structure interaction problem of a flexible chord foil cantilevered at the trailing edge. Both models resemble leading edge flutter near zero cavitation number in some respects. At short and moderate cavity lengths, leading edge flutter phenomenon is influenced by the cavity closure condition.
\r\n" }, { "name": "Pankow, James Frederick", "degree": "PhD", "year": "1979", "title": "The Dissolution Rates and Mechanisms of Tetragonal Ferrous Sulfide (Mackinawite) in Anoxic Aqueous Systems", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112009-074718", "creators": [ { "name": { "family": "Pankow", "given": "James Frederick" }, "id": "Pankow-James-Frederick", "display_name": "Pankow, James Frederick" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "chair", "display_name": "Morgan, James J." }, { "name": { "family": "Anson", "given": "Fred C." }, "id": "Anson-F-C", "role": "member", "display_name": "Anson, Fred C." }, { "name": { "family": "Revel", "given": "Jean-Paul" }, "id": "Revel-J-P", "role": "member", "display_name": "Revel, Jean-Paul" }, { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "member", "display_name": "Duwez, Pol E." } ], "option_major": [ "envreng" ], "doi": "10.7907/31FS-0Q87", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental study was carried out on the rates and mechanisms of the non-oxidative dissolution of mackinawite (tetragonal FeS) in anoxic aqueous systems of varying pH (3-7), T (5-35\u00b0C), and ionic strength (0.05-0.60 M [M is underscored]). A special glass and teflon dissolution reactor was constructed. The main design criterion was the need to keep the reaction medium absolutely free of oxygen.\r\n\r\nThe flux F[subscript S] (moles/cm[superscript 2]-min) from the surfaces of pellets pressed from [...]l\u03bc FeS particles was found to obey the rate equation\r\n\r\nF[subscript S] = k[subscript 1]a[subscript H superscript +] + k[subscript 2]\r\n\r\nk[subscript 1] and k[subscript 2] are rate constants and a[subscript H superscript +] is the activity of the hydrogen ion At 25\u00b0C, k[subscript 1] = 0.22 cm/min with a relative standard deviation of 18%. The value of k[subscript 2] was measured to be 1.9 moles/cm[superscript 2]-min with a relative standard deviation of 22%. The actual exposed FeS surface area A[...] was related to the projected area A by the expression A[...] = 1.7A. The factor of 1.7 accounts for the roughness of the surface. The actual rate constants k[...] and k[...] were therefore obtained by dividing k[subscript 1] and k[subscript 2] by 1.7: k[...] = 0.13/min and k[...] = 1.1 x 10[superscript -9] moles/cm[superscript 2]-min. The k[...] term dominates at pH < 4.3 and k[...]dominates at pH > 5.6. pH 4.3-5.6 is a transition region.\r\n\r\nIt is argued that these rate constants are relatable to dissolution mechanisms at the FeS crystal surface. k[...] is envisioned to arise from an attack at the surface by H[superscript +]. k[...] is linked to a mechanism which relies upon normal thermal vibrations and H20 solvation effects to liberate lattice constituents. Both k[\u2026] and k[\u2026] are thought to reflect a rate-limiting departure of surficial S(-II) lattice constituents. The activation entropies [...] for these two processes are calculated accordingly. The activation enthalpies [\u2026] were determined from the E[subscript a] data. Concentrations of Cu(II) in the ppm range were found to strongly inhibit the dissolution rate.\r\n\r\nThe k[...] term would dominate at pH's typical of natural waters. This term was used to determine how quickly FeS dissolves when anaerobic sediments are disturbed. When anoxic and oxic sediments are adjacent to one another, the dissolution of FeS in the anoxic portion takes place primarily near the oxic front.\r\n\r\nIf FeS-containing anaerobic sewage sludge is discharged to anoxic receiving waters, the particles of FeS may be expected to dissolve. Expressions were developed by which the lifetimes of such particles may be calculated. Both transport and non-transport controlled situations are analyzed. The effects which the agglomeration of such FeS with other sewage particles would have on the dissolution rate were considered. The implications which this work holds for sediment pyritization rates were also discussed.\r\n" }, { "name": "Petersen, Stephen Vaughn", "degree": "PhD", "year": "1979", "title": "CARTAM : the Cartesian Access Method for Data Structures with n-Dimensional Keys", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072018-133905871", "creators": [ { "name": { "family": "Petersen", "given": "Stephen Vaughn" }, "id": "Petersen-Stephen-Vaughn", "display_name": "Petersen, Stephen Vaughn" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "compsci" ], "doi": "10.7907/va76-8270", "abstract": "The Cartesian Access Method (CARTAM) is a data\r\nstructure and its attendant access program designed to\r\nprovide rapid retrievals from a data file based upon\r\nmulti-dimensional keys: for example, using earth surface points\r\ndefined by latitude and longitude, retrieve all points\r\nwithin x nautical miles. This thesis describes that data\r\nstructure and program in detail and provides the actual\r\nroutines as implemented on the International Business\r\nMachine (IBM) System/370 series of computers. The search\r\ntechnique is analogous to the binary search for a linear\r\nsorted file and seems to run in O(log(N)) time. An\r\nindication of the performance is the extraction, in less\r\nthan 25 milliseconds CPU time on an IBM 370, Model 3033, of\r\nall points within a 10,000-foot circle from a geographic\r\ndata base containing approximately 100,000 basic records." }, { "name": "Powers, Robert Lewis", "degree": "PhD", "year": "1979", "title": "Iontophoretic Studies of Visual Neurons in Drosophila melanogaster", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:04012026-145310276", "creators": [ { "name": { "family": "Powers", "given": "Robert Lewis" }, "id": "Powers-Robert-Lewis", "display_name": "Powers, Robert Lewis" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/sf0b-c827", "abstract": "The physiology of single cells in the visual system of the fly\r\nDrosophila melanogaster is studied by intracellular recording. Iontophoresis\r\nor current passage from the micropipette is used in two distinct\r\nways. The first of these is to yield a short injection of free calcium\r\nion into the photoreceptor or primary sensory neuron. Iontophoresis of\r\nCa++ is shown to have a pronounced but r eversible effect upon the receptor\r\npotential response to light input. The transient change is characterized\r\nby gain suppression and phase delay to sinusoidal stimuli. The phase\r\ndelay is expressed at 10.0 Hz and higher. These changes are, however,\r\ndependent upon the genotype of the animal. Two single-gene mutants of\r\nthis fly have been identified as having lesioned or altered physiology in\r\nthe visual receptors. The location of the lesions is in the casual pathway\r\nafter photon absorption by the photopigment and before ion permeability\r\nchanges are effected at the plasma membrane. The norp AH52 mutant responds \r\nto Ca++ injection in a manner similar to that of wild type. The trp\r\nmutant, however, has a much prolonged recovery period. The recovery, when\r\nfinally begun, is characterized by a transient phase advance with respect\r\nto the normal response. To this author's knowledge this is the first description \r\nof a phase advance in a visual cell potential that does not\r\ninvolve manipulation of the light stimulus.
\r\n\r\nA physiological model for phototransduction is developed to account\r\nfor the results of Ca++ injection and the new distinction in receptor\r\nfunction based upon genotype. This model incorporates both intracellular\r\nCa++ and mitochondrial energy in the early events of the visual sensory\r\nprocess. A study of mathematical models developed to account for the\r\ntime scale of the recovery to injection concludes that the photoreceptor\r\nsequesters free Ca++ following an injection. This conclusion is consistent\r\nwith the physiological model for phototransduction.
\r\n\r\nIontophoresis is used in a second way in a study of membrane properties\r\nof both photoreceptors and second-order neurons of the visual\r\nsystem. Small currents are passed into the cells simultaneously with the\r\napplication of Gaussian white noise light stimulation. The Wiener kernels\r\nobtained for the intracellular potential are used as sensitive assays of\r\nthe dynamics of membrane resistance changes following light input. The\r\nphotoreceptor membrane conductance is approximately a linear function of\r\nlight intensity for the stimuli used. By contrast the monopolar neurons\r\nof the Drosophila visual system, which are proximal to the primary sensory\r\ncells, exhibit an active voltage dependence in the response.
" }, { "name": "Sava\u015f, \u00d6mer", "degree": "PhD", "year": "1979", "title": "Some Measurements in Synthetic Turbulent Boundary Layers", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012006-083249", "creators": [ { "name": { "family": "Sava\u015f", "given": "\u00d6mer" }, "id": "Sava\u015f-\u00d6mer", "display_name": "Sava\u015f, \u00d6mer" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XZ05-2555", "abstract": "Synthetic turbulent boundary layers were constructed on a flat plate by generating systematic moving patterns of turbulent spots in a laminar flow. The experiments were carried out in a wind tunnel at a Reynolds number based on plate length of 1.7 x 106. Spots were generated periodically in space and time near the leading edge to form a regular hexagonal pattern. The disturbance mechanism was a camshaft which displaced small pins momentarily into the laminar flow at frequencies up to 80 Hz. The main instrumentation was a rake of 24 hot wires placed across the flow in a line parallel to the surface. The main measured variable was local intermittency; i.e., the probability of observing turbulent flow at a particular point in space and time. The results are reported in numerous x-t diagrams showing the evolution of various synthetic flows along the plate. The celerity or phase velocity of the large eddies was found to be 0.88, independent of eddy scale. All patterns with sufficiently small scales eventually showed loss of coherence as they moved downstream. A novel phenomenon called eddy transposition was observed in several flows which contained appreciable laminar regions. The large eddies shifted in formation to new positions, intermediate to their original ones, while preserving their hexagonal pattern. The present results, together with some empirical properties of a turbulent spot, were used to estimate the best choice of scales for constructing a synthetic boundary layer suitable for detailed study. The values recommended are: spanwise period/thickness \u22483.2, streamwise period/thickness \u224811." }, { "name": "Vinkler, Aharon P.", "degree": "PhD", "year": "1979", "title": "Optimal Controller Design Methods for linear Systems with Uncertain Parameters: Development, Evaluation and Comparison", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312006-104019", "creators": [ { "name": { "family": "Vinkler", "given": "Aharon P." }, "id": "Vinkler-Aharon-P", "display_name": "Vinkler, Aharon P." } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9fwb-er39", "abstract": "In many physical systems, an accurate knowledge of certain parameters is very difficult or very expensive to obtain. The designer of a remotely piloted vehicle flight control system, for example, frequently has available little data regarding aerodynamic coefficients, due to a lack of wind tunnel tests. Commonly used controller design methods, based on nominal values of plant parameters, often fail to achieve a satisfactory design in the face of parameter uncertainty.\r\n\r\nIn this work two methods have been developed for the design of linear, constant gain feedback controllers for systems with uncertain parameters:\r\n\r\n1) The multistep guaranteed cost control method is based on the concept of minimizing an upper bound of a cost functional in the face of parameter uncertainty. An algorithm has been developed to analyze the effect of parameter uncertainties on closed-loop system stability. An extension of this algorithm results in a technique for choosing constant feedback gains which guarantee a stable closed-loop system that possesses some of the desirable features of optimally designed control systems.\r\n\r\n2) The minimum discrete expected cost method is based on the concept of minimizing the expected value of a cost functional over a finite number of points in the range of parameter uncertainty. The design process makes use of statistical information about the uncertain parameters and incorporates in its cost functional whatever effects accompany a large departure in the plant parameters from their nominal values.\r\n\r\nAn extensive comparison of these two methods, together with the guaranteed cost control method, the minimax method, and the uncertainty weighting method, has been done in the context of the design of a fifth-order lateral autopilot for an RPV with uncertain aerodynamic coefficients. All five methods were evaluated on the bases of performance and design effort required. Both new methods were found to avoid some of the drawbacks associated with other techniques. The two newly developed methods are easy to implement and offer the designer tools for use in real control system design." }, { "name": "Wise, Jack LeRoy, III", "degree": "PhD", "year": "1979", "title": "Experimental Investigation of First- and Second-Sound Shock Waves in liquid Helium II", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032006-095703", "creators": [ { "name": { "family": "Wise", "given": "Jack LeRoy, III" }, "id": "Wise-Jack-LeRoy-III", "display_name": "Wise, Jack LeRoy, III" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/c49w-bh82", "abstract": "The cryogenic shock tube is used to generate a gasdynamic shock which propagates through saturated helium vapor and subsequently reflects from the upper surface of a column of LHeII. Superconducting thin-film detectors, produced by evaporation of aluminum in an oxygen atmosphere, yield highly repeatable arrival time data for the incident gasdynamic shock and the resultant first- and second-sound shocks in the liquid. Accurate x-t diagrams of the shock trajectories have been constructed for initial liquid temperatures of T(0) = 1.522, 1.665, 1.751, 1.832, 1.989, 2.031, and 2.095\u00b0K. Consistent discrepancies are observed between experimental and theoretical wave trajectories.\r\n\r\nThe detector signals qualitatively verify theoretical predictions that the temperature decreases through the pressure shock and increases through the temperature shock. Amplitude measurements based on static detector calibrations indicate that the magnitude of the temperature jump across the pressure shock agrees approximately with the theoretical calculation. Temperature jump measurements for the coupled second-sound shock imply shock-induced relative velocities, w =v(n)-v(s), on the order of 2.5 m/sec.\r\n\r\nFor initial conditions close to the [lambda]-transition (e.g., T(0) = 2.095\u00b0K), the pressure jump across the first-sound shock is sufficient to cause a change in phase from LHeII to LHeI. This change is experimentally evidenced by detector outputs indicating the absence of the temperature shock in the wake of a sufficiently strong pressure shock." }, { "name": "Wong Wooi Yee, Vincent Sydney", "degree": "PhD", "year": "1979", "title": "Computational Structures for Extracting Edge Features from Digital Images for Real-Time Control Applications", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:04272026-225845479", "creators": [ { "name": { "family": "Wong Wooi Yee", "given": "Vincent Sydney" }, "id": "Wong-Wooi-Yee-Vincent-Sydney", "display_name": "Wong Wooi Yee, Vincent Sydney" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5fh0-3b67", "abstract": "This thesis investigates extracting edge features\r\nfrom digital images for real-time control applications. A\r\nsequence of image operations is presented for extracting\r\nedge features from a digital image. This sequence\r\nemphasizes intensity edges, isolates them from the rest of\r\nthe image and then converts them into line data structures\r\nfor further analysis by a higher-level vision processor.\r\nThis way, an image of 500 x 500 pixels is reduced to a few\r\nhundred data elements.
\r\n\r\nIn order to extract edge features from digital\r\nimages fast enough for real-time use, some consideration has\r\nbeen given to the computational structures for performing\r\nthe edge-extraction operations. Past attempts at\r\nconstructing parallel processing arrays to speed up image\r\nprocessing are summarized. From examining these past\r\nefforts, it is concluded that array processing is unsuitable\r\nfor real-time image processing. One of the reasons for\r\nrejecting the use of array processors is the difficulty in\r\nconstructing arrays large enough to cover reasonable-size\r\nimages. A study reveals that this difficulty will remain\r\neven when ultimate LSI gate densities are used in\r\nconstructing\r\nthe arrays.
\r\n\r\nSpecialized processors are found to be more suitable\r\nfor real-time image processing. From examining the\r\ncomputational characteristics of the edge-extraction\r\nalgorithms, it was found that all but one of them could be\r\nsuitably executed by pipeline processors. The exception is\r\nthe chain-coding process, which is more suitably performed\r\nby a random-accessed structure. To demonstrate methodology\r\nand feasibility, a pipeline unit to perform the\r\nedge-enhancement operation in real-time has been designed\r\nand constructed using MOS LSI technology.
\r\n\r\nA vision system for real-time control purposes must\r\nbe able to track moving objects. A brief scenario for using\r\nthe edge features extracted from a sequence of images to\r\ntrack a moving object is presented in the last chapter of\r\nthis thesis.
" }, { "name": "Cass, Glen Rowan", "degree": "PhD", "year": "1978", "title": "Methods for Sulfate Air Quality Management with Applications to Los Angeles", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-06172004-111601", "creators": [ { "name": { "family": "Cass", "given": "Glen Rowan" }, "id": "Cass-Glen-Rowan", "display_name": "Cass, Glen Rowan" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/WWJR-PJ15", "abstract": "Particulate sulfate air pollutants contribute to visibility deterioration and are of current public health concern. This study develops the technical understanding needed for sulfate air quality control strategy design. Methods which link sulfate air quality and air quality impacts on visibility to the cost of controlling sulfur oxides air pollutant emissions are presented. These techniques are tested by application to the Los Angeles Basin over the years 1972 through 1974.\r\n\r\nAn air quality simulation model is developed which directly calculates long-term average sulfate concentrations under unsteady meteorological conditions. Pollutant concentrations are estimated from Lagrangian marked-particle statistics based on the time sequence of historical measured wind speed, wind direction and inversion base height motion. First order chemical reactions and ground level pollutant dry deposition are incorporated within a computational scheme which conserves pollutant mass.\r\n\r\nTechniques are demonstrated for performing both mass balance and energy balance calculations on flows of energy resources containing sulfur throughout the economy of an air quality control region. The energy and sulfur balance approach is used to check the consistency of a spatially and temporally resolved air quality modeling emission inventory for the South Coast Air Basin.\r\n\r\nNext the air quality model is validated against sulfur oxides emissions and sulfate air quality patterns observed in the Los Angeles Basin over each month of the years 1972 through 1974. A seasonal variation in the rate of SO2 oxidation to form sulfates is inferred. Overall average SO2 oxidation rates of about 6% per hour prevail during late spring, summer and early fall, while mean SO2 oxidation rates of between 0.5% per hour and 3% per hour prevail from October through February of our test years. From the model results, it is concluded that three to five major SO2 source classes plus background sulfates must be considered simultaneously at most monitoring sites in order to come close to explaining observed sulfate levels. The implication is that a mixed strategy aimed simultaneously at a number of specified source types will be needed if substantial sulfate air quality improvements are to be achieved within this particular airshed.\r\n\r\nTechniques are developed for analysis of the long-run impact of pollutant concentrations on visibility. Existing statistical models for light scattering by aerosols which use particle chemical composition as a key to particle size and solubility are modified so that the relative humidity dependence of light-scattering by hygroscopic aerosols could be represented in a more physically realistic manner. Coefficients are fitted to the model based on ten years of air pollution control agency routine air monitoring data taken at downtown Los Angeles. Sulfates are found to be the most effective light scatterers in the Los Angeles atmosphere. It is estimated that the visibility impact of reducing sulfates to a half or to a quarter of their measured historic values on each past day of record would be manifested most clearly in a reduction in the number of days per year of less than three-mile visibility. The number of days of average visibility less than ten miles would be little affected.\r\n\r\nTwo retrospective examples are worked to show how the results of the air quality simulation models may be used to define a variety of sulfate air quality control strategy options. It is suggested that a package of technological emissions control measures and institutional changes (including natural gas price deregulation) may provide greater improvements in both sulfate air quality and visibility at less cost than can be obtained from a purely technological solution to the Los Angeles sulfate problem." }, { "name": "Clough, Gene Alan", "degree": "PhD", "year": "1978", "title": "I. A Recirculating Charge-Coupled Device. II. The Mercury Selenide on N-Silicon Schottky Barrier", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-100207238", "creators": [ { "name": { "family": "Clough", "given": "Gene Alan" }, "id": "Clough-Gene-Alan", "display_name": "Clough, Gene Alan" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/dadc-z725", "abstract": "A recirculating charge-coupled device structure has\r\nbeen devised. Entrance and exit gates allow a signal to be\r\nadmitted, recirculated a given number of times, and then\r\nexamined. In this way a small device permits simulation\r\nof a very long shift register without passing the signal\r\nthrough input and output diffusions. An oscilloscope\r\nmotion picture demonstrating degradation of an actual\r\ncirculating signal has been made. The performance of the\r\ndevice in simulating degradation of a signal by a very long\r\nshift register is well fit by a simple model based on\r\ntransfer inefficiency.
\r\n\r\nElectrical properties of the mercury selenide on\r\nn-type chemically-cleaned silicon Schottky barrier have\r\nbeen studied. Barrier heights measured were 0.96 volts\r\nfor the photoresponse technique and 0.90 volts for the\r\ncurrent-voltage technique. These are the highest barriers\r\nyet reported on n-type silicon.
" }, { "name": "De Logi, Walter K.", "degree": "PhD", "year": "1978", "title": "Electromagnetic Wave Generation and Propagation in Gravitational Fields", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:08312017-150019175", "creators": [ { "name": { "family": "De Logi", "given": "Walter K." }, "id": "De-Logi-Walter-K", "display_name": "De Logi, Walter K." } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/es3k-qv56", "abstract": "We use Feynman perturbation techniques to analyze some aspects\r\nof electromagnetic wave generation and propagation in weak gravitational\r\nfields.
\r\n\r\nIn the first part of this report we calculate differential \r\ncross sections d\u03c3/d\u03a9 for the scattering of plane electromagnetic\r\nwaves by weakly gravitating and rotating bodies in the long-wavelength \r\nlimit (wavelength of incident radiation >> radius of scatterer >> mass \r\nof scatterer). We find that the polarization of right (or left) \r\ncircularly polarized electromagnetic waves is unaffected by the \r\nscattering process (i.e., helicity is conserved), and that the two \r\nhelicity states of the photon are scattered differently by a rotating \r\nbody. This coupling between the photon helicity and the angular \r\nmomentum of the scatterer also leads to a partial polarization of \r\nunpolarized incident light.
\r\n\r\n\r\nFor the sake of comparison, we also compute the differential \r\ncross sections for the gravitational scattering of scalar and gravi\u00adtational \r\nwaves. For the latter there is neither helicity conservation \r\nnor helicity-dependent scattering; and the angular momentum has no \r\npolarizing effect on incident, unpolarized gravitational waves.
\r\n\r\nIn the second part of this report, we analyze the conversion \r\nof gravitational waves into electromagnetic waves (and vice versa) \r\nunder the \"catalytic\" action of a static electromagnetic background \r\nfield. Closed-form differential cross sections are presented for \r\nconversion in the Coulomb field of a point charge, electric and \r\nmagnetic dipole fields, and uniform electrostatic and magnetostatic \r\nfields. Using the model calculation of conversion in a Coulomb field, \r\nwe discuss the problems that we must face when calculating non-gauge\u00ad-invariant \r\ntransition amplitudes, as is frequently done in the litera\u00adture.
\r\n\r\n\r\nWe conclude this report by pointing out how charged-particle \r\nbeams may be used (in principle) as direction-sensitive gravitational\u00ad-wave detectors.
\r\n \r\n\r\n\r\n" }, { "name": "Decker, Dwight William", "degree": "PhD", "year": "1978", "title": "Topics in Bifurcation Theory", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechTHESIS:03252013-104520935", "creators": [ { "name": { "family": "Decker", "given": "Dwight William" }, "id": "Decker-Dwight-William", "display_name": "Decker, Dwight William" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/xv6r-jf75", "abstract": "I. Existence and Structure of Bifurcation Branches
\r\n\r\nThe problem of bifurcation is formulated as an operator equation\r\nin a Banach space, depending on relevant control parameters, say of\r\nthe form G(u,\u03bb) = 0. If dimN(G_u(u_O,\u03bb_O)) = m the method of Lyapunov-Schmidt\r\nreduces the problem to the solution of m algebraic equations.\r\nThe possible structure of these equations and the various types of\r\nsolution behaviour are discussed. The equations are normally derived\r\nunder the assumption that G^O_\u03bb\u03b5R(G^O_u). It is shown, however, that\r\nif G^O_\u03bb\u03b5R(G^O_u) then bifurcation still may occur and the local structure\r\nof such branches is determined. A new and compact proof of the\r\nexistence of multiple bifurcation is derived. The linearized\r\nstability near simple bifurcation and \"normal\" limit points is then\r\nindicated.
\r\n\r\nII. Constructive Techniques for the Generation of Solution Branches
\r\n\r\nA method is described in which the dependence of the solution\r\narc on a naturally occurring parameter is replaced by the dependence\r\non a form of pseudo-arclength. This results in continuation procedures\r\nthrough regular and \"normal\" limit points. In the neighborhood\r\nof bifurcation points, however, the associated linear operator\r\nis nearly singular causing difficulty in the convergence of continuation\r\nmethods. A study of the approach to singularity of this\r\noperator yields convergence proofs for an iterative method for determining \r\nthe solution arc in the neighborhood of a simple bifurcation\r\npoint. As a result of these considerations, a new constructive\r\nproof of bifurcation is determined.
" }, { "name": "Delayen, Jean Roger", "degree": "PhD", "year": "1978", "title": "Phase and Amplitude Stabilization of Superconducting Resonators", "advisor": "Mercereau, James E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042008-083340", "creators": [ { "name": { "family": "Delayen", "given": "Jean Roger" }, "id": "Delayen-Jean-Roger", "display_name": "Delayen, Jean Roger" } ], "advisors": [ { "name": { "family": "Mercereau", "given": "James E." }, "id": "Mercereau-J-E", "role": "advisor", "display_name": "Mercereau, James E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ZS1J-1E35", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis, which stemmed from the superconducting heavy-ion accelerator project at Caltech, deals with the problem of phase and amplitude stabilization of the fields in superconducting resonators. The problem arises from the fast ([...]50 Hz) resonator eigenfrequency modulation of magnitude ([...]100 Hz) which is much larger than the resonator bandwidth ([...]10 Hz). The problem is compounded by the fact that the coupling between the electrical and mechanical modes of the resonator can lead to instabilities (ponderomotive instabilities). The solution suggested involves operating the resonators in self-excited loops, and electronically modifying the loop parameters in order to lock the loop oscillations to an external phase and amplitude reference without attempt to modify the instantaneous resonator eigenfrequency. It is found that this method of phase stabilization is well suited to resonators with small energy contents and small eigenfrequency deviations since the power required is equal to their product; this occurs when the loaded bandwidth of the resonator is twice the maximum eigenfrequency deviation to be compensated for. It is also found that when the loop is free-running, the field amplitude is stable and no ponderomotive instabilities are present as long as the non-ideal effects are limited. When the loop is locked to an external phase and amplitude reference, ponderomotive instabilities can occur; however, the loop can be made stable by adjustment of the loop phase shift, and the stable range can be increased by using high amplitude and phase feedback gains. It is also found that under certain feedback conditions, the error on the particle energy gain can be made to vanish, although residual phase and amplitude errors are still present. A microprocessor-controlled feedback system based on this analysis is then described and results of experiments performed in conjunction with a 150 MHz lead (Pb) plated superconducting split-ring resonator are presented. The experiments show excellent agreement with the analysis." }, { "name": "Diner, Daniel Bruce", "degree": "PhD", "year": "1978", "title": "Hysteresis in Human Binocular Fusion: a Second Look", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01232026-225955428", "creators": [ { "name": { "family": "Diner", "given": "Daniel Bruce" }, "id": "Diner-Daniel-Bruce", "display_name": "Diner, Daniel Bruce" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/09sg-tm18", "abstract": "A study of hysteresis in human binocular fusional ranges had been\r\nperformed in order to clarify the nature of the extension of Panum's\r\nFusional Area as demonstrated by Derek Fender and Bela Julesz (1967).
\r\n\r\nUsing binocular retinally stabilized images, a stimulus regime\r\nwas designed to determine the size and location of Panum's Fusional\r\nArea at any given stimulus condition. This regime was employed to\r\nmeasure Panum's fusional area in the non-extended and in the extended\r\nconditions.
\r\n\r\nThe following three results were obtained.
\r\n\r\n1. The nasalward limits of Panum's fusional area and the hysteresis\r\ndemonstrated by the nasalward limits do not differ significantly from\r\nthe temporalward limits of Panum's fusional area and the hysteresis\r\ndemonstrated by the temporalward limits.
\r\n\r\n2. A non-transient (continually presented) stimulus will fuse over\r\na significantly wider range with a transient (flashed) stimulus than\r\nwith another non-transient stimulus. Furthermore, the range of fusion\r\nfor the transient stimulus is dependent upon the non-transient stimuli\r\nthat are present immediately before the transient stimulus is presented.
\r\n\r\n3. The extension of Panum's fusional area, as effected by the\r\nstimulus regime of this thesis, not only includes the recruitment of\r\nretinal locations into Panum's fusional area which are not normally\r\nin Panum's fusional area, but also includes the loss from Panum's\r\nfusional area of certain retinal locations which are normally within\r\nPanum's fusional area. For all subjects, Panum's fusional area is\r\nshifted significantly. For some subjects, Panum's fusional area is\r\nstretched significantly. In some situations, the \"zero disparity\"\r\nretinal location may be lost from, and therefore not included within,\r\nPanum's fusional area.
\r\n\r\nA new definition of \"corresponding retinal points\" is developed\r\nfrom the results of this thesis.
" }, { "name": "Grabbe, Crockett Lane", "degree": "PhD", "year": "1978", "title": "Resonance Cones and Mode Conversion in a Warm Magnetized Bounded Plasma", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-075841435", "creators": [ { "name": { "family": "Grabbe", "given": "Crockett Lane" }, "id": "Grabbe-Crockett-Lane", "display_name": "Grabbe, Crockett Lane" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/BY3Z-2M41", "abstract": "The warm plasma resonance cone structure of the quasistatic field\r\nproduced by a gap source in a bounded magnetized slab plasma is\r\ndetermined theoretically. This is initially determined for a homogeneous\r\nor mildly inhomogeneous plasma with source frequency lying\r\nbetween the lower hybrid frequency and the plasma frequency. It\r\nis then extended to the complicated case of an inhomogeneous plasma\r\nwith two internal lower hybrid layers present, which is of interest\r\nto radio frequency heating of plasmas.
\r\n\r\nIn the first case, the potential is obtained as a sum of multiply\r\nreflected warm plasma resonance cones, each of which has a similar\r\nstructure, but a different size, amplitude, and position. An\r\nimportant interference between nearby multiply-reflected resonance\r\ncones is found. The cones are seen to spread out as they move\r\naway from the source, so that this interference increases and the\r\nindividual resonance cones become obscured far away from the source.
\r\n\r\nIn the second case, the potential is found to be expressible as\r\na sum of multiply-reflected, multiply-tunnelled, and mode converted\r\nresonance cones, each of which has a unique but similar structure.\r\nThe effects of both collisional and collisionless damping are included\r\nand their effects on the decay of the cone structure studied.\r\nVarious properties of the cones such as how they move into and out\r\nof the hybrid layers, through the evanescent region, and transform\r\nat the hybrid layers are determined. It is found that cones can\r\ntunnel through the evanescent layer if the layer is thin,\r\nand the effect of the thin evanescent layer is to subdue the\r\nsecondary maxima of cone relative to the main peak, while slightly\r\nbroadening the main peak and shifting it closer to the cold plasma\r\ncone line.
\r\n\r\nEnergy theorems for quasistatic fields are developed and applied\r\nto determine the power flow and absorption along the individual\r\ncones. This reveals the points of concentration of the flow and the\r\nvarious absorption mechanisms.
" }, { "name": "Hamill, Gregory Prince", "degree": "PhD", "year": "1978", "title": "Analysis of Defect Structures in High Purity Copper Single Crystals Using X-Ray Topographic Techniques", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162002-105352", "creators": [ { "name": { "family": "Hamill", "given": "Gregory Prince" }, "id": "Hamill-Gregory-Prince", "display_name": "Hamill, Gregory Prince" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/51fg-6x90", "abstract": "Copper single crystals were grown in a modified Czochralski system. The \"grown-in\" dislocations and those introduced through selective scratching of the polished (111) surfaces were observed using Berg-Barrett X-ray topography and Borrmann transmission topographic methods.\r\n\r\nSeveral aspects of the dislocation images may be understood on the basis of pure dynamical or kinematical theories of X-ray diffraction. Some observations, however, support the theory that both dynamical and kinematic effects must be considered to properly describe the experimental results.\r\n\r\nStereo depth measurements of the dislocation images were taken under four sets of X-ray geometries. The minimum range of depths observed, approximately 1.0 to 2.0?m from the surface, was obtained for both methods of Berg-Barrett stereo topography. The Borrmann transmission topographs provided an image depth range of approximately 3.0 ?m from the exit surface to 270 ?m from the exit surface. This latter value is equivalent to the crystal thickness, to the accuracy of the present data. Comparison of reflection (Berg-Barrett) and transmission (Borrmann) topographs of the same crystal showed that no image of an individual dislocation on one topograph had a corresponding image on the second topograph.\r\n\r\nAn attempt to mark the surface of the crystal by vapor depositing gold dot \"absorbers\" on the surface was not completely satisfactory due to a shadowing effect in Berg-Barrett topography. The apparent epitaxial growth of the gold dots on the (111) copper surface and the corresponding strain field in the crystal around the dots provided a reference surface for transmission topography, although the true surface was marked only in the asymmetric stereo topographs.\r\n\r\nComputer simulation using finite element analysis is proposed to solve the problems of X-ray image formation." }, { "name": "Holm, Thomas Russell", "degree": "PhD", "year": "1978", "title": "Trace Metals in Fresh Water Plankton", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292014-102557612", "creators": [ { "name": { "family": "Holm", "given": "Thomas Russell" }, "id": "Holm-Thomas-Russell", "display_name": "Holm, Thomas Russell" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/86aa-4708", "abstract": "The uptake of Cu, Zn, and Cd by fresh water plankton was studied\r\nby analyzing samples of water and plankton from six lakes in southern\r\nCalifornia. Co, Pb, Mn, Fe, Na, K, Mg, Ca, Sr, Ba, and Al were also\r\ndetermined in the plankton samples. Special precautions were taken\r\nduring sampling and analysis to avoid metal contamination.
\r\n\r\nThe relation between aqueous metal concentrations and the\r\nconcentrations of metals in plankton was studied by plotting aqueous\r\nand plankton metal concentrations vs time and comparing the plots.\r\nNo plankton metal plot showed the same changes as its corresponding\r\naqueous metal plot, though long-term trends were similar. Thus,\r\npassive sorption did not completely explain plankton metal uptake.
\r\n\r\nThe fractions of Cu, Zn, and Cd in lake water which were\r\nassociated with plankton were calculated and these fractions were\r\nless than 1% in every case.
\r\n\r\nTo see whether or not plankton metal uptake could deplete\r\naqueous metal concentrations by measurable amounts (e.g. 20%) in\r\nshort periods (e.g. less than six days), three integrated rate\r\nequations were used as models of plankton metal sorption.\r\nParameters for the equations were taken from actual field measurements.\r\nMeasurable reductions in concentration within short times were\r\npredicted by all three equations when the concentration factor was\r\ngreater than 10^5. All Cu concentration factors were less than 10^5.
\r\n\r\nThe role of plankton was regulating metal concentrations\r\nconsidered in the context of a model of trace metal chemistry in lakes.\r\nThe model assumes that all particles can be represented by a single\r\nsolid phase and that the solid phase controls aqueous metal\r\nconcentrations. A term for the rate of in situ production of\r\nparticulate matter is included and primary productivity was used\r\nfor this parameter. In San Vicente Reservoir, the test case, the rate of in situ production of particulate matter was of the same order of\r\nmagnitude as the rate of introduction of particulate matter by the\r\ninfluent stream.
\r\n" }, { "name": "Ju, Kochan", "degree": "PhD", "year": "1978", "title": "Magnetic Bubble Domain and Domain Wall Dynamics in Gradient Translation", "advisor": "Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechTHESIS:03092026-221231176", "creators": [ { "name": { "family": "Ju", "given": "Kochan" }, "id": "Ju-Kochan", "display_name": "Ju, Kochan" } ], "advisors": [ { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/pmfh-6n03", "abstract": "The object of this work is to extend both the experimental and\r\ntheoretical understanding of domain wall dynamics in magnetic bubble\r\ntranslation. Bubble motion in the presence of a bias field gradient\r\nhas been investigated in detail, using high-speed sampling microscopy \r\nwith 10 nanosecond laser pulse illumination. Transient\r\nbubble translation was observed and overshoot was confirmed. The\r\nstored momentum formulation was expanded. Creep was discovered and\r\na qualitative model was formulated to explain the various phases of\r\nthe translational motion and the mechanism of momentum storage and\r\nrelease. The model was further confirmed by the transverse distortion\r\nphenomenon observed 1n the high impulse gradient experiment. Equation\r\nof motion for magnetic domain walls and Bloch lines are also\r\nincluded." }, { "name": "Kirkwood, Peter D.", "degree": "PhD", "year": "1978", "title": "Seasonal Patterns in the Growth of the Giant Kelp, Macrocystis pyrifera", "advisor": "North, Wheeler J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072026-110926979", "creators": [ { "name": { "family": "Kirkwood", "given": "Peter D." }, "id": "Kirkwood-Peter-D", "display_name": "Kirkwood, Peter D." } ], "advisors": [ { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "advisor", "display_name": "North, Wheeler J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/5xqk-a593", "abstract": "Field surveys revealed seasonal growth changes in the\r\nGiant Kelp, Macrocystis pyrifera. Frond counts were used\r\nto measure average sporophyte size in the study bed and\r\nto follow vegetative growth of a typical plant for about\r\nsixteen months. Storm induced wave motions and sea urchin\r\ngrazing were primary causes of whole plant losses.
\r\n\r\nThe importance of fish grazing on kelp was estimated\r\nduring field surveys. Average damage varied from light\r\nto moderate during the study period.
\r\n\r\nKelp consumption rates by Opaleye Perch, Girella\r\nnigricans, were measured in aquarium experiments. Preference\r\nfor specific kelp tissues was established.
\r\n\r\nMathematical relationships between kelp growth and\r\nenvironmental conditions were established by multiple\r\nlinear regression analysis. Regression equations modeled\r\ngrowth patterns observed in field surveys. Average frond\r\nnumber was expressed as a function of sunlight, water temperature,\r\nfish grazing, and upwelling index.
\r\n\r\nA regression model was used to hindcast kelp growth\r\nfluctuations for conditions at Point Loma, San Diego\r\nCounty, from 1950 to 1969.
" }, { "name": "Koenig, Keith", "degree": "PhD", "year": "1978", "title": "Interference Effects on the Drag of Bluff Bodies in Tandem", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042006-140552", "creators": [ { "name": { "family": "Koenig", "given": "Keith" }, "id": "Koenig-Keith", "display_name": "Koenig, Keith" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EXEV-R625", "abstract": "The objective of this study is to obtain better understanding of the flow over two tandemly positioned bluff bodies in close enough proximity to strongly interact with each other. This interaction is often beneficial in that the drag of the overall system is reduced. Prototypes for this problem come from tractor-trailer and cab-van combinations and from various add-on devices designed to reduce their drag.\r\n\r\nThe object of the present investigation is an axisymmetric configuration which seems to have first been studied by Saunders (1966). A disc of diameter d1 is coaxially placed in front of a flat faced cylinder of diameter d2. For a given ratio d1/d2, there is a value of gap ratio, g*/d2 for which the drag of the system is a minimum. In the most optimum configuration, d1/d2 = 0.75, g*/d2 = 0.375, and the corresponding drag coefficient is 0.01, a remarkable reduction from the value of 0.72 for the cylinder alone. For each value of d1/d2, the minimum drag configuration g*/d2 appears to correspond to a condition in which the separation streamsurface just matches (joins tangentially onto) the rearbody. Support for this idea is furnished by comparison with results derived from free-streamline theory and from flow visualization experiments. However, when g*/d2 exceeds a critical value of about 0.5, the value of CD, while still optimum, is almost an order of magnitude higher than for subcritical optimum gap ratios. The increase seems to be connected with the onset of cavity oscillations.\r\n\r\nMeasurements of the velocity field in the vicinity of the forebody have been made using a frequency-shifted laser-Doppler velocimeter. These measurements indicate an order of magnitude difference in the shear stress along the separation surface between optimum subcritical and supercritical geometries.\r\n\r\nThe drag characteristics of the axisymmetric forebody system are altered by modifying the shape of the component bodies. Modifications that change the conditions at separation from the frontbody, interfere with the cavity flow or effect the flow on the rearbody face can produce significant changes in the forebody drag.\r\n\r\nFor non-axisymmetric geometry (square cross-sections) the separation surface cannot exactly match the rear body and the subcritical minimum values of drag are higher than for circular cross-sections." }, { "name": "Kubena, Randall Lynn", "degree": "PhD", "year": "1978", "title": "Fluctuations in a Tokamak Plasma", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07222014-154820206", "creators": [ { "name": { "family": "Kubena", "given": "Randall Lynn" }, "id": "Kubena-Randall-Lynn", "display_name": "Kubena, Randall Lynn" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ncb6-bs51", "abstract": "An experimental investigation of low frequency floating potential fluctuations (f \u2264 200 kHz) in a research tokamak plasma using two spatially separated electrostatic probes has been performed. The spectra, correlation length, and the phase velocity of the fluctuations in both the radial and azimuthal direction have been determined. The propagation velocity in the toroidal direction was also measured and was found to be in the direction of electron current flow. The waves traveled azimuthally\r\nin the ion diamagnetic drift direction, even after the usual E x B rotation was taken into account. The electron density fluctuations associated with these oscillations were large, \u03b4n/n \u2243 0.35 - 0.50.
\r\n\r\nThe spectra were found to have regularly spaced peaks which seemed\r\nto be related to specific azimuthal modes (m =1,2,3,...,etc. ) A parametric\r\nstudy was made to determine what effect plasma parameters had on\r\nthese peaks. During periods of high electron density in the first 2 msec\r\nof the plasma lifetime, strong sawtooth type oscillations were observed.\r\nThese oscillations typically had frequencies of approximately 10 kHz and\r\nwere also present when large amounts of neutral gas were added during the\r\ndischarge by a process called \"gas puffing.\"
\r\n\r\nThe results are compared with experimental observations made on\r\nother plasma devices with electric and magnetic probes and with microwave\r\nand CO2 laser scattering techniques. (The scattering measurements are\r\ncomplimentary to the probe measurements since, in the former case, the\r\nwavelength is fixed by the scattering angle, but the oscillations could\r\nnot be spatially localized.) The oscillations in the Caltech torus were\r\nprobably related to a drift-tearing type instability which is thought\r\nto play a major role in the anomalous particle and energy flux observed\r\nin tokamaks. Comparisons are made between current theory and the experimental\r\nresults. However, the theory for the observed oscillations\r\nis still in a rudimentary stage of development, and it is hoped that\r\nthe present investigation will stimulate future analytical work.
" }, { "name": "Latimer, James Laurens", "degree": "PhD", "year": "1978", "title": "Cost and Traffic Analysis of Demand Access Satellite Networks", "advisor": "Posner, Edward C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02252026-221906868", "creators": [ { "name": { "family": "Latimer", "given": "James Laurens" }, "id": "Latimer-James-Laurens", "display_name": "Latimer, James Laurens" } ], "advisors": [ { "name": { "family": "Posner", "given": "Edward C." }, "id": "Posner-E-C", "role": "advisor", "display_name": "Posner, Edward C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/yqxt-hb15", "abstract": "A method using a Markov process model is described and used to analyze the traffic capacity and call blockage probability of an SCPC (single channel per carrier) satellite network. The model is shown to be suitable for telephone traffic. The traffic density for certain networks whose states can be ordered in a linear fashion (birth/death\r\nprocess) is derived and shown to exhibit an Erlang B distribution. The application of the Erlang B distribution to PA (preassigned) and limited cases of FVDA (fully-variable demand access) and SVDA (semi-variable demand access) is demonstrated. The Erlang B equation does not apply when an SVDA network exhibits partial sharing of channels by different earth stations. An example of this is given and the capacity and blockage probability solved exactly by the use of steady state Markov statistics. The traffic capacity and blockage for a satellite with channel switching capability in the repeater is shown to be equivalent to an SVDA network.
\r\n\r\nSCPC should be used in place of preassigned frequency division multiplex (FDM) channels whenever the traffic load of the earth station is very light. In this case it is better to use a few expensive SCPC channels than many less expensive FDM channels. FDM is probably better if two stations have traffic between them requiring more than 15-25 channels.
\r\n\r\nA simulation program was written to determine the blockage probability for those networks too large to do any other way. The goodness of the random number generator was tested and the results of the simulation were compared to known solutions.
\r\n\r\nTraffic data obtained from Latin American and Caribbean nations was used to estimate the number of satellite channels and earth station modems required and the cost of such a network. We have also presented as an example the improvement of SVOA over PA in the case of Jamaica where l/4th as many modems would be required.
\r\n\r\nA rough analysis of earth station costs was made based upon information obtained from several companies. It is shown that a large part of the network cost is in the modems. We estimate the cost of a regional network for Latin America and the Caribbean to be about $25M. The earth stations represent about 40% of this cost, and 65% of the earth station expense is in the modems.
" }, { "name": "Lee, Chien-Ping", "degree": "PhD", "year": "1978", "title": "New Optoelectronic Devices Using GaAs-GaAlAs Epitaxy", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-090759102", "creators": [ { "name": { "family": "Lee", "given": "Chien-Ping" }, "id": "Lee-Chien-Ping", "display_name": "Lee, Chien-Ping" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/RNFQ-GG20", "abstract": "Three subjects related to epitaxial GaAs-GaAlAs optoelectronic\r\ndevices are discussed in this thesis. They are:
\r\n\r\n1. Embedded Epitaxy
\r\n\r\nThis is a technique of selective multilayer growth of GaAs-\r\nGa1-xAlxAs single crystal structures through stripe openings in masking\r\nlayers on GaAs substrates. This technique results in prismatic layers\r\nof GaAs and Ga1-xAlxAs \"embedded\" in each other and leads to controllable\r\nuniform structures terminated by crystal faces. The dependence of the\r\ngrowth habit on the orientation of the stripe openings has been studied.\r\nRoom temperature embedded double heterostructure lasers have been\r\nfabricated using this technique. Threshold current densities as low\r\nas 1.5 KA/cm2 have been achieved.
2. Barrier Controlled PNPN Laser Diode
\r\n\r\nIt is found that the I-V characteristics of a PNPN device can be\r\ncontrolled by using potential barriers in the base regions. Based on\r\nthis principle, GaAs-GaAlAs heterostructure PNPN laser diodes have been\r\nfabricated. GaAlAs potential barriers in the bases control not only\r\nthe electrical but also the optical properties of the device. PNPN lasers\r\nwith low threshold currents and high breakover voltage have been achieved.\r\nNumerical calculations of this barrier controlled structure are presented\r\nin the ranges where the total current is below the holding point and\r\nnear the lasing threshold.
3. Injection Lasers on Semi-Insulating Substrates
\r\n\r\nGaAs-GaAlAs heterostructure lasers fabricated on semi-insulating\r\nsubstrates have been studied. Two different laser structures achieved\r\nare: (1) Crowding effect lasers, (2) Lateral injection lasers. Experimental\r\nresults and the working principles underlying the operation of\r\nthese lasers are presented. The gain induced guiding mechanism is used\r\nto explain the lasers' far field radiation patterns. It is found that\r\nZn diffusion in Ga1-xAlxAs depends on the Al content x, and that GaAs\r\ncan be used as the diffusion mask for Zn diffusion in Ga1-xAlxAs.\r\nLasers having very low threshold currents and operating in a stable\r\nsingle mode have been achieved. Because these lasers are fabricated on\r\nsemi-insulating substrates, it is possible to integrate them with\r\nother electronic devices on the same substrate. An integrated device,\r\nwhich consists of a crowding effect laser and a Gunn oscillator on\r\na common semi-insulating GaAs substrate, has been achieved.
This thesis reports on investigations in two areas of the\r\neconomics of electricity supply. The first chapter examines\r\nempirical evidence to determine whether rate of return regulation\r\nhas produced detectable overcapitalisation in this industry.\r\nThe second chapter studies the determination of optimal pricing\r\nmechanisms for electricity, particularly in the presence of\r\nuncertainty.
\r\n\r\nChapter 1:
\r\n\r\nThree studies which claim to confirm, and one which claims\r\nto reject, the existence of the Averch-Johnson effect in the\r\nelectric power industry, have recently been published. This\r\npaper examines the general problem of what the nature of the\r\nA-J effect might be and what sort of data would be required in\r\norder to confirm its presence. The other studies are then\r\ncritically examined on the basis of this discussion. A modification\r\nof the method used in one previous study is then used\r\nto test a suitably restricted form of the A-J hypothesis, and\r\nno evidence of capital bias is found. The principal conclusion\r\nof this study is that if the A-J effect is significant in distorting\r\ninput choices in the electric utility industry, very\r\ndifferent sorts of data than those that have been used thus far\r\nare going to be required in order to verify its presence. Mechanical\r\nusage of gross input and output numbers, without understanding\r\nof the technological processes involved, leads only to\r\nerroneous conclusions.
\r\n\r\nChapter 2:
\r\n\r\nIn this chapter we examine the issues involved in setting\r\nelectricity prices. The existing literature on peak load\r\npricing and pricing under uncertainty is reviewed. Recent\r\ntechnological developments applicable to metering and load\r\nmanagement of electricity are examined. The pricing problem is\r\nthen reformulated so that its solution may take advantage of\r\nthese innovations. New technologies such as wind power promise\r\nto be economically attractive within this new framework. This\r\nformulation of the problem suggests a method of investment\r\nplanning which would better distribute risk. In addition it\r\nprovides a way in which the generation sector of the industry\r\ncan be made competitive, thus reducing the need for regulation.
" }, { "name": "Medina-Vaillard, Luis Manuel", "degree": "PhD", "year": "1978", "title": "An Engineering Formalization of Computer Systems", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02262026-193717902", "creators": [ { "name": { "family": "Medina-Vaillard", "given": "Luis Manuel" }, "id": "Medina-Vaillard-Luis-Manuel", "display_name": "Medina-Vaillard, Luis Manuel" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/5m4c-hm34", "abstract": "The aim of this work is to develop a formal apparatus\r\nthat defines the elements composing software-hardware\r\ncomputer systems and the relations between them.
\r\n\r\nThe basic tools come from Systems Theory, Mathematical\r\nLogic, Operating Systems and Computer Architecture.\r\nTwo sound engineering principles are fundamental in the\r\nformal apparatus: hierarchical organization and elimination\r\nof time dependent malfunctions (like race conditions in\r\nhardware and mutual exclusion in software).
\r\n\r\nAll the basic elements in a computer system are\r\nidentified as 'singletons.' Typical singletons are:\r\n(sequential) user programs, (concurrent) operating systems,\r\nvirtual machines and hardware machines. A computer system\r\nis just a set of inter-related singletons.
\r\n\r\nVelocity and transparency are defined and used as a\r\nmeasure of the quality of a hierarchy. Computer systems\r\nare analyzed as directed graphs (singletons being the nodes),\r\nand directions for research in optimal structuring are\r\nsuggested. Singletons are analyzed as a hierarchy of\r\nspaces (low level, high level, assertions) and the mappings\r\nbetween them (compiler, programmer).
\r\n\r\nFinally, a real time, special-purpose multiprocessor\r\nsystem (ECOS) is described and analyzed within this formal\r\nframework.
" }, { "name": "Mickelson, Alan Rolf", "degree": "PhD", "year": "1978", "title": "Electromagnetic Wave Propagation in Almost Periodic Media", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:03122012-112325331", "creators": [ { "name": { "family": "Mickelson", "given": "Alan Rolf" }, "id": "Mickelson-Alan-Rolf", "orcid": "0000-0003-2529-8301", "display_name": "Mickelson, Alan Rolf" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "chair", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Langmuir", "given": "Robert V." }, "id": "Langmuir-R-V", "role": "member", "display_name": "Langmuir, Robert V." }, { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "member", "display_name": "Keller, Herbert Bishop" }, { "name": { "family": "Bridges", "given": "William B." }, "id": "Bridges-W-B", "role": "member", "display_name": "Bridges, William B." } ], "option_major": [ "eleceng" ], "doi": "10.7907/SZMY-A964", "abstract": "The problem of electromagnetic wave propagation in almost periodic\r\nmedia is investigated and a solution is obtained directly from Maxwell's\r\nequations. Techniques to evaluate this solution are developed. These\r\ntechniques involve a generalization to almost periodic media of the\r\nBrillouin diagram of periodic media. The method of invariant imbedding\r\nis applied to the coupled mode equations which determine the Brillouin\r\ndiagram for the purpose of transforming them to coupled Riccati equations.\r\nThese coupled Riccati equations, when subjected to a single boundary condition,\r\ndetermine the solutions to both the periodic and almost periodic\r\nboundary value problems. These evaluation techniques are used to place\r\nin evidence similarities and differences of wave propagation in periodic\r\nand almost periodic media. It is shown that although the periodic and\r\nalmost periodic theories agree in many cases of interest, there exist\r\ncases in which distinct differences appear. In cases of multi-tone perturbations,\r\nthe almost periodic theory yields both simpler and more reasonable\r\nresults than the periodic theory." }, { "name": "Poon, Siu-Joe", "degree": "PhD", "year": "1978", "title": "Superconductivity, Spin-Glass Properties, and Ferromagnetism in Amorphous La-Gd-Au Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-144716507", "creators": [ { "name": { "family": "Poon", "given": "Siu-Joe" }, "id": "Poon-Siu-Joe", "display_name": "Poon, Siu-Joe" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/s0jp-gw13", "abstract": "The superconducting and magnetic properties of splat cooled amorphous alloys of \r\ncomposition \r\n(La100-xGdx)80Au20 (0 \u2264 x \u2264 100)\r\nhave been studied. The La80Au20 alloys are ideal type II super-conductors\r\n(critical temperature Tc = 3.5\u00b0 K ). The concentration\r\nrange (x less than 1) where superconductivity and spin-glass freezing n1ight\r\ncoexist has been studied in detail. The spin-glass alloys (0 less than x less than 70)\r\nexhibit susceptibility maxima and thermomagnetic history effects.\r\nIn the absence of complications due to crystal field and enhanced\r\nmatrix effects, a phenomenological model is proposed in which the\r\nmagnetic clusters are treated as single spin entities interacting via\r\nrandom forces using the molecular field approach. The fundamental\r\nparameters (such as the strength of the forces and the size of\r\nclusters) can be deduced from magnetization measurements. The\r\nremanent magnetization is shown to arise from an interplay of the\r\nRKKY and dipolar forces. Magnetoresistivity results are found to be\r\nconsistent with the aforementioned picture. The nature of magnetic\r\ninteractions in an amorphous matrix is also discussed. The moment\r\nper Gd atom (7\u00b5B) is found to be constant and close to that of the\r\ncrystalline value throughout the concentration range investigated.\r\nFinally, a detail study is made of the critical phenomena and\r\nmagnetic properties of the amorphous ferromagnet: Gd80Au20. The\r\nresults are compared with recent theories on amorphous magnetism." }, { "name": "Roth, Scott Darrell", "degree": "PhD", "year": "1978", "title": "Stereo 3-D Perception for a Robot", "advisor": "Sutherland, Ivan", "url": "https://resolver.caltech.edu/CaltechTHESIS:01292026-175231485", "creators": [ { "name": { "family": "Roth", "given": "Scott Darrell" }, "id": "Roth-Scott-Darrell", "display_name": "Roth, Scott Darrell" } ], "advisors": [ { "name": { "family": "Sutherland", "given": "Ivan" }, "id": "Sutherland-I", "role": "advisor", "display_name": "Sutherland, Ivan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/5tjr-7340", "abstract": "This thesis concludes a study of robot vision and presents an\r\nanalysis of the rudimentary vision problem of modeling form in 3-Space.\r\nA stereo \"snapshot\" vision theory for a computer is proposed, based on\r\nan experimental implementation.
\r\n\r\nHere, stereo vision is argued to be essential for modeling natural\r\nor unfamiliar domains. The \"firm\" perception resulting from stereopsis\r\nis second only to kinesthesia/tactility in effectiveness with the\r\nunknown.
\r\n\r\nThe novel mechanism introduced-as the heart of the system-is a\r\nstereopsis algorithm for growing stereo surfaces in natural scones.\r\nFirst, 2-D features are extracted from the stereo pair of digital images\r\nby locating patterns of change in the images' \"gradient-arrow\"\r\nrepresentations. Then, by associating features in the loft imago with\r\nfeatures in the right image, stereo regions or \"matches\" are made. The\r\nstereopsis process fuses the stereo images by growing contexts of\r\nmatched features. Every match defines via the camera geometry a visible\r\nsurface in the scene, interlocking with neighboring matches like the\r\npieces of a 3-D jigsaw puzzle. The resultant surface molds provide a\r\nfirm basis for a polyhedral model of the scene's forms.
" }, { "name": "Scranton, Robert A.", "degree": "PhD", "year": "1978", "title": "Investigations of the Conductor-Semiconductor Interface", "advisor": "McCaldin, James Oeland", "url": "https://resolver.caltech.edu/CaltechTHESIS:07222014-101031867", "creators": [ { "name": { "family": "Scranton", "given": "Robert A." }, "id": "Scranton-Robert-A", "display_name": "Scranton, Robert A." } ], "advisors": [ { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "advisor", "display_name": "McCaldin, James Oeland" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/z9j6-a423", "abstract": "I. Schottky barriers produced by polymeric sulfur nitride,\r\n(SN)x, on nine common III-V and II-VI compound semiconductors\r\nare compared to barriers formed by Au. The\r\nconductor (SN)x produces significantly higher barriers to\r\nn-type semiconductors and lower barriers to p-type semiconductors\r\nthan Au, the most electronegative elemental\r\nmetal. The barrier height improvement, defined as\r\n\u0278(SN)x - \u0278(Au), is smaller on covalent semiconductors\r\nthan on ionic semiconductors; (SN)x barriers follow the\r\nionic-covalent transition. Details of (SN)x film deposition,\r\nsamples preparation, and barrier height measurements\r\nare described.
\r\n\r\nII. The rate of dissolution of amorphous Si into solid\r\nAl is measured. The rate of movement of the amorphous\r\nSi/Al interface is found to be much faster than predicted\r\nby a simple model of the transport of Si through Al.\r\nThis result is related to defects in the growth of epitaxial\r\nSi using the solid phase epitaxy process.
" }, { "name": "Sheby, David", "degree": "PhD", "year": "1978", "title": "Wiener Kernel Analyses of the Functional Microstructure of a Crustacean Visual Field", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:04202026-183922546", "creators": [ { "name": { "family": "Sheby", "given": "David" }, "id": "Sheby-David", "display_name": "Sheby, David" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/xbkw-t179", "abstract": "The microstructure of the excitatory field of the crayfish sustaining\r\nfiber 038 was studied by Wiener kernel analysis. By treating\r\nthe receptive field as a multi-input single-output system, Volterra's,\r\nand Wiener's, nonlinear functional formalisms for such systems could\r\nbe invoked to define the canonical types of interactions that could,\r\nand do, underlie the field.
\r\n\r\nA light emitting diode/fiber optic stimulus package was developed\r\nfor these experiments to provide the required spatial configurations\r\nof independently (noise-) modulated sources; optimally excite the\r\ncrayfish 1s yellow-sensitive visual system; and to eliminate the\r\nartifacts that might arise from conventional light sources' spectral\r\ndependence on drive current.
\r\n\r\nThe second-order cross kernels computed from 2-, and 4-input experiments\r\nindicate that a lateral excitation phenomenon is predominant\r\nin the field. Evidence for lateral inhibition (between yellow channels)\r\nis indirect, but suggestive that inhibition manifests itself through a\r\nthird-order cross term. 038 does receive inputs from yellow and blue\r\nchannels, and their is evidence of yellow channel inhibition of the\r\nblue channel. Periodic structure found in 038 1s spike train response\r\nto multiple stimuli can be modelled by first and second-order self\r\nkernels without the use of cross terms.
\r\n\r\nAnalysis of the kernel dynamics leads to a model of the functional\r\nmicrostructure subserving 038 1s excitatory field.
" }, { "name": "Shellan, Jeffrey B.", "degree": "PhD", "year": "1978", "title": "Aperiodic Structures in Optics and Integrated Optics and the Transverse Bragg Reflector Laser", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212014-142218548", "creators": [ { "name": { "family": "Shellan", "given": "Jeffrey B." }, "id": "Shellan-Jeffrey-B", "display_name": "Shellan, Jeffrey B." } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/662b-ca80", "abstract": "The first part of this work describes the uses of aperiodic\r\nstructures in optics and integrated optics. In particular, devices\r\nare designed, fabricated, tested and analyzed which make use of a\r\nchirped grating corrugation on the surface of a dielectric waveguide.\r\nThese structures can be used as input-output couplers, multiplexers\r\nand demultiplexers, and broad band filters.
\r\n\r\nNext, a theoretical analysis is made of the effects of a random\r\nstatistical variation in the thicknesses of layers in a dielectric\r\nmirror on its reflectivity properties. Unlike the intentional\r\naperiodicity introduced in the chirped gratings, the aperiodicity in\r\nthe Bragg reflector mirrors is unintentional and is present to some\r\nextent in all devices made. The analysis involved in studying these\r\nproblems relies heavily on the coupled mode formalism. The results\r\nare compared with computer experiments, as well as tests of actual\r\nmirrors.
\r\n\r\nThe second part of this work describes a novel method for confining\r\nlight in the transverse direction in an injection laser. These\r\nso-called transverse Bragg reflector lasers confine light normal to\r\nthe junction plane in the active region, through reflection from an\r\nadjacent layered medium. Thus, in principle, it is possible to guide\r\nlight in a dielectric layer whose index is lower than that of the surrounding\r\nmaterial. The design, theory and testing of these diode\r\nlasers are discussed.
\r\n" }, { "name": "Symington, William Allan", "degree": "PhD", "year": "1978", "title": "Analytical Studies of Steady and Non-Steady Motions of a Bubbly Liquid", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08172005-082759", "creators": [ { "name": { "family": "Symington", "given": "William Allan" }, "id": "Symington-William-Allan", "display_name": "Symington, William Allan" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/0ENX-DE36", "abstract": "A consistent set of continuum-like equations which describe, under certain limitations, the flow of bubbly gas-liquid mixtures is developed. These equations are then applied in the solution of a few problems that bear on technological issues of nuclear reactor safety. The solutions of these problems illustrate the importance of the ratio between the viscous relaxation time of the bubbles and the characteristic time of the flow, in scaling experimental results.\r\n\r\nThe choked flow of a bubbly mixture through a contraction in a one dimensional duct is treated. It is found that in many cases the ratio of the contraction residence time to the viscous relaxation time is small, indicating the motion of the bubbles will be dictated largely by the dynamic forces on them. The one-dimensional equations are solved approximately for small values of this ratio.\r\n\r\nA rudimentary experiment on choked bubbly flow through a contraction was conducted using a contraction with gradual changes in area, making the experimental situation amenable to a one-dimensional analysis. Pressures and mass flow rates of liquid and gas were measured. The results compare favorably with theoretical calculations.\r\n\r\nThe rise through a liquid of a uniform cloud of bubbles is also analyzed. Self-preserving wave solutions of the non-linear equations are found to exist. They have the form of transitions between a region of high void fraction below and a region of lower void fraction above. These waves are unstable to small disturbances, so when they are created they will steepen, developing into clumps of bubbles above which are regions of low void fraction. The fact that the bubbles in these clumps may coalesce presents a mechanism for a change in flow regime from bubbly to some other, perhaps slug or annular flow. The effect of bubble-bubble interactions in impeding the formation of these clumps is speculated upon.\r\n\t\r\nFinally, the flow of a bubbly mixture over a wavy wall is analyzed. The solution illustrates that the effect of interactions between bubbles and solid boundaries is lacking in our formalism. It is concluded that more work is required in the area of interactions, both of the bubble-bubble and bubble-boundary varieties." }, { "name": "Titlow, Joseph David", "degree": "PhD", "year": "1978", "title": "Sailing Vessel Dynamics", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152026-212436475", "creators": [ { "name": { "family": "Titlow", "given": "Joseph David" }, "id": "Titlow-Joseph-David", "display_name": "Titlow, Joseph David" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ex17-jw66", "abstract": "A general study has been conducted to determine how the\r\ndynamics of sailing vessels depend on speed and sailing angle. A\r\nsimplified model of the forces acting on a sailing vessel has been\r\nconstructed which includes all rigid body motions and uses the\r\nresults of full scale tests. Numerical solutions for the steady\r\nstate conditions and perturbational motions have been calculated\r\nbased on limited available data. The results for performance and\r\nattitude show good agreement with full scale sailing observations;\r\nthey are close to the optimum conditions reported in practice.\r\nThe normal modes of sailing vessels appear to be strongly\r\ndependent on speed and sailing angle, and they are sensitive to\r\nsuch general parameters as displacement, stiffness, aerodynamic\r\ncharacteristics and rudder effectiveness. Several regions were\r\nfound where unstable solutions exist." }, { "name": "Wadcock, Alan James", "degree": "PhD", "year": "1978", "title": "Flying-Hot-Wire Study of Two-Dimensional Turbulent Separation on an NACA 4412 Airfoil at Maximum Lift", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312006-095330", "creators": [ { "name": { "family": "Wadcock", "given": "Alan James" }, "id": "Wadcock-Alan-James", "display_name": "Wadcock, Alan James" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5TB8-1G75", "abstract": "Hot-wire measurements have been made in the boundary layer, the separated region, and the near wake for flow past an NACA 4412 airfoil at maximum lift. The Reynolds number based on chord was about 1,500,000. Special care was taken to achieve a two-dimensional mean flow. The main instrumentation was a flying hot wire; that is, a hot-wire probe mounted on the end of a rotating arm. The probe velocity was sufficiently high to avoid the usual rectification problem by keeping the relative flow direction always within a range of \u00b130 degrees to the probe axis. A digital computer was used to control synchronized sampling and storage of hot-wire data at closely spaced points along the probe arc. Data were obtained at several thousand locations in the flow field. These data include intermittency, two components of mean velocity, and mean values for three double, four triple, and five quadruple products of two velocity fluctuations. No information was obtained about the third (spanwise) velocity component. The data are available on punched cards in raw form and also in processed form, after use of smoothing and interpolation routines to obtain values on a fine rectangular mesh aligned with the airfoil chord. The data are displayed as contour plots of the fifteen variables." }, { "name": "Westermo, Bruce Donald", "degree": "PhD", "year": "1978", "title": "The Solutions of a Nonlinear Difference Equation Found in Numerical Analysis", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:02082026-093737021", "creators": [ { "name": { "family": "Westermo", "given": "Bruce Donald" }, "id": "Westermo-Bruce-Donald", "display_name": "Westermo, Bruce Donald" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/h972-x606", "abstract": "The solutions of a nonlinear difference equation resulting from\r\nthe trapezoidal quadrature approximation of a piecewise linear differential\r\nequation are examined. A phase plane mapping technique is used\r\nto find the periodic and unbounded solutions of the difference equation and\r\nto determine the stability of these solutions. From the phase plane mappings\r\nof the unbounded solutions it is shown that the energy of the bounded\r\nsolutions can grow and decay by large amounts. The maximum rate of\r\nHamiltonian increase of the unbounded solutions is calculated from the\r\nmapping transformations. It is shown that the stability of a solution can\r\nonly be guaranteed for discrete ranges of the time step with fixed initial\r\nconditions. The solutions of the non-autonomous difference equations\r\nfor a sinusoidal forcing term and the damped difference equations are\r\nalso examined." }, { "name": "Williams, Randall Gary", "degree": "PhD", "year": "1978", "title": "The Stochastic Exit Problem for Dynamical Systems", "advisor": "Franklin, Joel N.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03212013-095136861", "creators": [ { "name": { "family": "Williams", "given": "Randall Gary" }, "id": "Williams-Randall-Gary", "display_name": "Williams, Randall Gary" } ], "advisors": [ { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "advisor", "display_name": "Franklin, Joel N." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/rwka-vz48", "abstract": "The problem of \"exit against a flow\" for dynamical systems\r\nsubject to small Gaussian white noise excitation is studied.\r\nHere the word \"flow\" refers to the behavior in phase space of\r\nthe unperturbed system's state variables. \"Exit against a flow\"\r\noccurs if a perturbation causes the phase point to leave a phase\r\nspace region within which it would normally be confined. In\r\nparticular, there are two components of the problem of exit\r\nagainst a flow:
\r\n\r\ni) the mean exit time
\r\n\r\nii) the phase-space distribution of exit locations.
\r\n\r\nWhen the noise perturbing the dynamical systems is small, the\r\nsolution of each component of the problem of exit against a flow\r\nis, in general, the solution of a singularly perturbed, degenerate\r\nelliptic-parabolic boundary value problem.
\r\n\r\nSingular perturbation techniques are used to express the\r\nasymptotic solution in terms of an unknown parameter. The unknown\r\nparameter is determined using the solution of the adjoint\r\nboundary value problem.
\r\n\r\nThe problem of exit against a flow for several dynamical\r\nsystems of physical interest is considered, and the mean exit\r\ntimes and distributions of exit positions are calculated. The systems\r\nare then simulated numerically, using Monte Carlo techniques,\r\nin order to determine the validity of the asymptotic solutions.
\r\n\r\n" }, { "name": "Williams, Rick Alan", "degree": "PhD", "year": "1978", "title": "The Processing of Velocity Information by the Pursuit Oculomotor System", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02092026-224152317", "creators": [ { "name": { "family": "Williams", "given": "Rick Alan" }, "id": "Williams-Rick-Alan", "display_name": "Williams, Rick Alan" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/p8ae-pz33", "abstract": "A study of human smooth pursuit eye movements has been\r\nperformed in order to clarify the velocity information processing\r\ncapabilities of the visual system.
\r\n\r\nA set of stimuli were designed which, when presented in motion\r\nto the visual system, contained no position information. Thus, the\r\nvelocity sensitive pursuit system was stimulated in isolation from the\r\nsaccadic system, which is position sensitive.
\r\n\r\nThe smooth eye movements which were elicited by step increases\r\nin target velocity from zero velocity were analyzed in detail\r\nby a nonlinear least squares curve fitting procedure. Eye velocity\r\nwas found not to exactly match stimulus velocity, the differences being\r\nunsystematic with velocity amplitude or direction. Response latency\r\nand the duration of eye acceleration were found to vary about average\r\nvalues of 150 and 300 msec, respectively.
\r\n\r\nAveraged velocity and acceleration responses were computed\r\nfrom first and second derivatives of the position responses to\r\nrepeated presentations of the step velocity target motion. Response\r\naverage acceleration pulse amplitude did not vary linearly with stimulus\r\nacceleration pulse amplitude. Increases in stimulus pulse amplitude\r\nwere met with changes in amplitude, shape, and duration of the\r\nresponse pulse.
\r\n\r\nAveraged acceleration responses to two consecutive stimulus\r\nvelocity steps were shown not to correspond with the response\r\npredicted by the linear superposition to two single pulse responses.\r\nThe departure of the actual double pulse response from the predicted\r\nresponse was discussed in terms of possible sources of a such a nonlinearity.
\r\n\r\nThe results of the single and double pulse experiments were\r\nused to design a pseudo-random stimulus acceleration signal which was\r\nsubsequently used in a white-noise type of nonlinear analysis of the\r\npursuit system. The first and second order pursuit system kernels\r\nwhich were obtained from the analysis showed that the technique could\r\nbe used to study interactions within the pursuit-perceptual system.\r\nThe results were not reliable to the extent that a mathematical model\r\ncould be constructed. However, several suggestions for improving\r\nthe pseudo-random input analysis technique were included in the conclusion\r\nchapter.
\r\n\r\nFinally, the experimental results were discussed in terms of\r\nthe relationship between visual perception and the control of smooth\r\npursuit eye n1ovements.
" }, { "name": "Baker, Gregory Richard", "degree": "PhD", "year": "1977", "title": "Studies in Vortex Motion", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03252013-131037625", "creators": [ { "name": { "family": "Baker", "given": "Gregory Richard" }, "id": "Baker-Gregory-Richard", "display_name": "Baker, Gregory Richard" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/4yv1-7109", "abstract": "This thesis covers four different problems in the\r\nunderstanding of vortex sheets, and these are presented in\r\nfour chapters.
\r\n\r\nIn Chapter 1, free streamline theory is used to determine\r\nthe steady solutions of an array of identical, hollow\r\nor stagnant core vortices in an inviscid, incompressible\r\nfluid. Assuming the array is symmetric to rotation through\r\n \u03c0 radians about an axis through any vortex centre, there\r\nare two solutions or no solutions depending on whether A^(1/2)/L\r\nis less than or greater than 0.38 where A is the area of\r\nthe vortex and L is the separation distance. Stability\r\nanalysis shows that the more deformed shape is unstable to\r\ninfinitesimal symmetric disturbances which leave the centres\r\nof the vortices undisplaced.
\r\n\r\nChapter 2 is concerned with the roll-up of vortex\r\nsheets in homogeneous fluid. The flow over conventional and\r\nring wings is used to test the method of Fink and Soh (1974).\r\nDespite modifications which improve the accuracy of the\r\nmethod, unphysical results occur. A possible explanation\r\nfor this is that small scales are important and an alternate\r\nmethod based on \"Cloud-in-Cell\" techniques is introduced.\r\nThe results show small scale growth and amalgamation into\r\nlarger structures.
\r\n\r\nThe motion of a buoyant pair of line vortices of\r\nopposite circulation is considered in Chapter 3. The density\r\ndifference between the fluid carried by the vortices and the\r\nfluid outside is considered small, so that the Boussinesq\r\napproximation may be used. A macroscopic model is developed\r\nwhich shows the formation of a detrainment filament and this\r\nis included as a modification to the model. The results\r\nagree well with the numerical solution as developed by Hill\r\n(1975b) and show that after an initial slowdown, the vortices\r\nbegin to accelerate downwards.
\r\n\r\nChapter 4 reproduces completely a paper that has\r\nalready been published (Baker, Barker, Bofah and Saffman\r\n(1974)) on the effect of \"vortex wandering\" on the measurement\r\nof velocity profiles of the trailing vortices behind a\r\nwing.
\r\n\r\n" }, { "name": "Berg, Dale Evan", "degree": "PhD", "year": "1977", "title": "Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142006-154140", "creators": [ { "name": { "family": "Berg", "given": "Dale Evan" }, "id": "Berg-Dale-Evan", "display_name": "Berg, Dale Evan" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "chair", "display_name": "Kubota, Toshi" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "member", "display_name": "Zukoski, Edward E." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2S44-JV38", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation of the response of a hypersonic turbulent boundary layer to a step change in surface roughness has been performed. The boundary layer on a flat nozzle wall of a Mach 6 wind tunnel was subjected to abrupt changes in surface roughness and its adjustment to the new surface conditions was examined. Both mean and fluctuating flow properties were acquired for smooth-to-rough and rough-to-smooth surface configurations.\r\n\r\nThe boundary layer was found to respond gradually and to attain new equilibrium profiles, for both the mean and the fluctuating properties, some 10 to 25 [...] downstream of the step change. Mean flow self-similarity was the first to establish itself, followed by the mass flux fluctuations, followed in turn by the total temperature fluctuations.\r\n\r\nUse of a modified Van Driest transformation resulted in good correlation of smooth and rough wall data in the form of the incompressible law of the wall. This is true even in the nonequilibrium vicinity of the step for small roughness heights.\r\n\r\nThe present data are found to correlate well with previously published roughness effect data from low and high speed flows when the roughnesses are characterized by an equivalent sand grain roughness height.\r\n\r\nExisting correlations based on low speed data were found to be unsuccessful in predicting the effect of this roughness on the skin friction and velocity profile. The indiscriminate use of low speed roughness effects correlations to predict the effects of roughness on supersonic and hypersonic flows must therefore be regarded as a procedure subject to gross errors.\r\n\r\nSignificant pressure and temperature history effects were observed throughout the boundary layer. The existence of these effects was found to create a nozzle wall boundary layer whose properties were far different than those in a boundary layer on a flat plate in the freestream, raising questions about the validity of simulating the flat plate boundary layer with the nozzle wall boundary layer." }, { "name": "Cadena-Cepeda, Fernando", "degree": "PhD", "year": "1977", "title": "Temperature Effects on the Activity Coefficient of the Bicarbonate Ion", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292014-085219405", "creators": [ { "name": { "family": "Cadena-Cepeda", "given": "Fernando" }, "id": "Cadena-Cepeda-Fernando", "display_name": "Cadena-Cepeda, Fernando" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/DX7Y-8N64", "abstract": "Natural waters may be chemically studied as mixed electrolyte\r\nsolutions. Some important equilibrium properties of natural waters are\r\nintimately related to the activity-concentration ratios (i.e., activity\r\ncoefficients) of the ions in solution. An Ion Interaction Model, which\r\nis based on Pitzer's (1973) thermodynamic model, is proposed in this\r\ndissertation. The proposed model is capable of describing the activity\r\ncoefficient of ions in mixed electrolyte solutions. The effects of\r\ntemperature on the equilibrium conditions of natural waters and on the\r\nactivity coefficients of the ions in solution, may be predicted by means\r\nof the Ion Interaction Model presented in this work.
\r\n\r\nThe bicarbonate ion, HCO3-, is commonly found in natural waters.\r\nThis anion plays an important role in the chemical and thermodynamic\r\nproperties of water bodies. Such properties are usually directly related\r\nto the activity coefficient of HCO3- in solution. The Ion Interaction\r\nModel, as proposed in this dissertation, is used to describe\r\nindirectly measured activity coefficients of HCO3- in mixed electrolyte\r\nsolutions.
\r\n\r\nExperimental pH measurements of MCl-MHCO3 and MCl-H2CO3 solutions\r\nat 25\u00b0C (where M = K+, Na+, NH4+, Ca2+ or Mg2+) are used in this\r\ndissertation to evaluate indirectly the MHCO3 virial coefficients. Such\r\ncoefficients permit the prediction of the activity coefficient of HCO3-\r\nin mixed electrolyte solutions. The Ion Interaction Model is found to\r\nbe an accurate method for predicting the activity coefficient of HCO3-\r\nwithin the experimental ionic strengths (0.2 to 3.0 m). The virial\r\ncoefficients of KHCO3 and NaHCO3 and their respective temperature variations\r\nare obtained from similar experimental measurements at 10\u00b0 and\r\n40\u00b0C. The temperature effects on the NH4HCO3, Ca(HCO3)2, and Mg(HCO3)2\r\nvirial coefficients are estimated based on these results and the temperature\r\nvariations of the virial coefficients of 40 other electrolytes.
\r\n\r\nFinally, the Ion Interaction Model is utilized to solve various\r\nproblems of water chemistry where bicarbonate is present in solution.
" }, { "name": "Cheetham, Craig McClain", "degree": "PhD", "year": "1977", "title": "Perception of Pitch in Pulse Wave Forms whose Power Spectra are Flat", "advisor": "Pierce, John Robinson; Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechTHESIS:12222025-234030485", "creators": [ { "name": { "family": "Cheetham", "given": "Craig McClain" }, "id": "Cheetham-Craig-McClain", "display_name": "Cheetham, Craig McClain" } ], "advisors": [ { "name": { "family": "Pierce", "given": "John Robinson" }, "id": "Pierce-J-R", "role": "advisor", "display_name": "Pierce, John Robinson" }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "co-advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/wdg7-xk25", "abstract": "These experiments were performed to explore the upper limits\r\nof pitch perception based on the time waveform of the stimulus.\r\nFlanagan and Guttman, using pulses with various polarity patterns,\r\nshowed that pitch may be assigned to a sound based on either the time\r\nwaveform or the Fourier spectrum. Their results show these two\r\nmechanisms in conflict in the region between 100 and 200 hertz. The\r\nstimulus used here consisted of a train of uniformly spaced pulses of\r\nequal amplitude whose polarities were randomly chosen. Such a\r\nsignal is shown to have a flat power spectrum and as such should offer\r\nno competition to the time-based pitch mechanism. Subjects listened\r\nalternately to the stimulus and to a unipolar pulse generator whose\r\npulse rate was under their control. The subjects were instructed to\r\nmatch the two pitches. Some musically talented subjects were found\r\nwho could match the pitch even when the random polarity pulse rate\r\nwas as high as 9.5 kHz. Matching is defined to occur when an integral\r\nrelation exists between the pulse rates as set by the experimenter and\r\nthe subject Matching at high rates was found to occur at stimulus\r\nlevels as low as 10 db or when both the stimulus and matching signals\r\nwere high-pass filtered at 8 kHz .
\r\n\r\nInvestigation of the short term spectrum of the random polarity\r\npulse train shows that there are clues to the pulse rate even though\r\nthe long term power spectrum is flat. One of these clues is the\r\ndifferent probability distribution of the amplitude peaks at frequencies\r\nof nfp/2 where fp is the pulse rate. This variability of amplitude\r\ndistribution can be reduced, and the frequencies which then occur\r\nchanged, by using polarity patterns randomly chosen from a certain\r\nset of patterns. However, experiments performed using pulse patterns\r\nshowed little or no change in subjects' ability to match.
" }, { "name": "Chen, Martin Yu-Wen", "degree": "PhD", "year": "1977", "title": "Luminescence Properties of Electron-Hale-Droplets in Pure and Doped Germanium", "advisor": "McGill, Thomas C.; Smith, Darryl L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-143816928", "creators": [ { "name": { "family": "Chen", "given": "Martin Yu-Wen" }, "id": "Chen-Martin-Yu-Wen", "display_name": "Chen, Martin Yu-Wen" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." }, { "name": { "family": "Smith", "given": "Darryl L." }, "id": "Smith-D-L", "role": "advisor", "display_name": "Smith, Darryl L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/9WCK-2W46", "abstract": "This work contains 4 topics dealing with the properties of the\r\nluminescence from Ge.
\r\n\r\nThe temperature, pump-power and time dependences of the photoluminescence\r\nspectra of Li-, As-, Ga-, and Sb-doped Ge crystals were\r\nstudied. For impurity concentrations less than about 1015cm-3, emissions\r\ndue to electron-hole droplets can clearly be identified. For\r\nimpurity concentrations on the order of 1016cm-3, the broad lines in\r\nthe spectra, which have previously been attributed to the emission from\r\nthe electron-hole-droplet, were found to possess pump-power and time\r\ndependent line shape. These properties show that these broad lines cannot\r\nbe due to emission of electron-hole-droplets alone. We interpret\r\nthese lines to be due to a combination of emissions from (1) electron-hole-\r\ndroplets, (2) broadened multiexciton complexes, (3) broadened\r\nbound-exciton, and (4) plasma of electrons and holes. The properties\r\nof the electron-hole-droplet in As-doped Ge were shown to agree with\r\ntheoretical predictions.
\r\n\r\nThe time dependences of the luminescence intensities of the\r\nelectron-hole-droplet in pure and doped Ge were investigated at 2 and\r\n4.2\u00b0K. The decay of the electron-hole-droplet in pure Ge at 4.2\u00b0K\r\nwas found to be pump-power dependent and too slow to be explained by\r\nthe widely accepted model due to Pokrovskii and Hensel et al. Detailed\r\nstudy of the decay of the electron-hole-droplets in doped Ge were\r\ncarried out for the first time, and we find no evidence of evaporation\r\nof excitons by electron-hole-droplets at 4.2\u00b0K. This doped Ge result\r\nis unexplained by the model of Pokrovskii and Hensel et al. It is\r\nshown that a model based on a cloud of electron-hole-droplets generated\r\nin the crystal and incorporating (1) exciton flow among electron-hole-droplets\r\nin the cloud and (2) exciton diffusion away from the cloud is\r\ncapable of explaining the observed results.
\r\n\r\nIt is shown that impurities, introduced during device fabrication,\r\ncan lead to the previously reported differences of the spectra of\r\nlaser-excited high-purity Ge and electrically excited Ge double injection\r\ndevices. By properly choosing the device geometry so as to\r\nminimize this Li contamination, it is shown that the Li concentration\r\nin double injection devices may be reduced to less than about 1015cm-3\r\nand electrically excited luminescence spectra similar to the photoluminescence\r\nspectra of pure Ge may be produced. This proves conclusively\r\nthat electron-hole-droplets may be created in double injection\r\ndevices by electrical excitation.
\r\n\r\nThe ratio of the LA- to TO-phonon-assisted luminescence intensities\r\nof the electron-hole-droplet is demonstrated to be equal to the\r\nhigh temperature limit of the same ratio of the exciton for Ge. This\r\nresult gives one confidence to determine similar ratios for the\r\nelectron-hole-droplet from the corresponding exciton ratio in semiconductors\r\nin which the ratio for the electron-hole-droplet cannot\r\nbe determined (e.g., Si and GaP). Knowing the value of this ratio\r\nfor the electron-hole-droplet, one can obtain accurate values of\r\nmany parameters of the electron-hole-droplet in these semiconductors\r\nspectroscopically.
" }, { "name": "Craig, James Eldon", "degree": "PhD", "year": "1977", "title": "Weak Shocks in Open-Ended Ducts with Complex Geometry", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302006-133224", "creators": [ { "name": { "family": "Craig", "given": "James Eldon" }, "id": "Craig-James-Eldon", "display_name": "Craig, James Eldon" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "member", "display_name": "Culick, Fred E. C." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QAFR-PS29", "abstract": "The dynamics of weak shocks in ducts of complex geometry and the sound radiation produced by the reflection of a weak shock from the open end of a duct have been investigated. Duct geometries include expansion chambers with and without inlet or outlet tubes extended and enclosed perforated tubes. Internal and external pressure histories of the interaction of weak shocks with simple muffler elements have been recorded using a standard one-shot shock tube and a resonating shock tube. The excitation shock Mach number ranged from 1.05 to 1.55. Analytical investigations, including a synthesis of existing works on internal weak-shock interactions of an acoustic treatment of the sound radiation produced by weak shock waves, are presented. Combining the above analyses, models for the reduction in radiated sound per unit of incident shock amplitude, as a result of inserting a muffler between the source and the tailpipe exit, are developed.\r\n\r\nFor expansion chambers with and without extensions, the dependence of the transmitted and reflected waves and of the radiated sound on area ratio is compared with predictions. In particular, measured transmission coefficients for expansion chambers agree reasonably well with the predictions for all shock strengths; however, for large area ratios, the predicted sound attenuation is not observed, as waves diffracted at the upstream junction cause more sound to be radiated. For expansion chambers with internal extensions, sound attenuation is increased for low incident shock strengths; while for increasing incident shock strength, the internal transmission characteristics deteriorate, the reducing the sound attenuation.\r\n\r\nFor enclosed perforated tubes, the dependence of the transmitted and reflected waves and of the radiated sound on the perforated area ratio and incident shock strength is compared with predictions. For perforated tubes with infinite enclosure, the transmission and reflection coefficients depend on both incident shock strength and perforated area ratio, as predicted. However, agreement with data is obtained only after inserting a perforated discharge coefficient with the perforated area ratio in the theory. The reduction of sound radiation with perforated area ratio is measured for one incident shock strength and then compared with predictions. For small area ratios, there is agreement but for large area ratios the measurements show that less sound is radiated than predicted. For large area ratios, gradual compressions with smooth fronts (not shock fronts) are transmitted, resulting in less radiated sound. Enclosures have no effect on the sound attenuation for small perforate area ratios; however, as the perforate area ratio increases, the enclosure eventually inhibits further increase in sound attenuation." }, { "name": "Davidson, Cliff Ian", "degree": "PhD", "year": "1977", "title": "Deposition of Trace Metal-Containing Aerosols on Smooth, Flat Surfaces and on Wild Oat Grass (Avena fatua)", "advisor": "Friedlander, Sheldon K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01122026-165851360", "creators": [ { "name": { "family": "Davidson", "given": "Cliff Ian" }, "id": "Davidson-Cliff-Ian", "orcid": "0000-0002-6872-4094", "display_name": "Davidson, Cliff Ian" } ], "advisors": [ { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "advisor", "display_name": "Friedlander, Sheldon K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/cb91-ae70", "abstract": "A new model for the dry deposition of aerosol particles on\r\nfields of vegetation has been developed. The model, which includes\r\ndiffusion, sedimentation, and impaction as transport mechanisms,\r\nhas been applied to deposition on a field of wild oat grass, Avena\r\nfatua. The model was tested experimentally for the diffusion range,\r\nand applied to predict the deposition of lead for all mechanisms\r\nfor typical wind conditions. Inputs to the model include the airborne\r\nchemical species distribution with respect to particle size,\r\nthe windfield above and within the canopy, and details of the\r\nvegetation elements.
\r\n\r\nDeposition is considered to be a two-step process, namely transport\r\nfrom the open atmosphere into the vegetation followed by filtration\r\nby the vegetation elements. Each step is described by an expression\r\nfor particle flux. The equation for transport from the atmosphere\r\nrelates the flux to the sedimentation velocity and the Brownian and\r\neddy diffusivities. This relation is assumed to apply both above and\r\nwithin the canopy. The filtration equation is used only within the\r\ncanopy, incorporating either convective diffusion or impaction. The\r\ntwo equations are solved simultaneously for the effective concentration\r\nsink and particle flux.
\r\n\r\nAccording to the model, the deposition of unit density, spherical\r\nparticles with diameters smaller than 0.001 \u03bcm and larger than 10 \u03bcm\r\nis controlled by the rate at which particles are delivered to the\r\ncanopy. For particles with diameters between these values, the rate of\r\ndeposition is control led by relatively inefficient filtration within\r\nthe canopy.
\r\n\r\nThe model was tested by measuring profiles of condensation\r\nnuclei above a field of Avena fatua. The atmospheric transport equation\r\nwas used with the profiles to determine the flux. This value\r\ncompared well with fluxes calculated by solving the equations for\r\natmospheric transport and filtration simultaneously. The latter\r\ncalculation used only one concentration measurement at a known height\r\nrather than the entire profile.
\r\n\r\nThe deposition of lead, zinc, and cadmium on flat, smooth\r\nsurfaces exposed to the free atmosphere was also measured. Simultaneous\r\nisokinetic measurements of the airborne size distributions\r\nof these trace metals provided data which were used to calculate\r\nthe sedimentation fluxes. About 70% of the total mass deposition of\r\neach trace metal was due to sedimentation of particles with aerodynamic\r\ndiameter greater than 10 \u03bcm. The airborne fractions of these\r\nlarge particles for lead, zinc, and cadmium were 17%, 32'%, and 37%,\r\nrespectively. Because large airborne particles control led the mass\r\ndeposition, isokinetic sampling was essential.
\r\n\r\nThe isokinetically measured distribution of lead with respect\r\nto particle size was used to calculate deposition on a field of\r\nAvena fatua. Ninety percent of the lead deposition resulted from\r\nimpaction of particles greater than 10 \u03bcm. As with the flat, smooth\r\nsurfaces, the relatively high concentrations of small airborne\r\nlead particles did not contribute significantly to mass deposition.
\r\n\r\nComparing the smooth surface data with the calculations for\r\nAvena fatua fields suggested that the deposition of lead on such\r\nfields is two to three times greater than on a flat, smooth surface.
" }, { "name": "Edwards, Dean Barton", "degree": "PhD", "year": "1977", "title": "Time Domain Analysis of Switching Regulators", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302005-112610", "creators": [ { "name": { "family": "Edwards", "given": "Dean Barton" }, "id": "Edwards-Dean-Barton", "display_name": "Edwards, Dean Barton" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/GRRM-FG16", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe exact expressions for the local stability of a buck regulator are found, and these expressions are simplified when the ratio of the natural frequency to the switching frequency is small. Simplified expressions are also found for the local stability of the boost and buck-boost regulators when the frequency ratio is small and the damping factor is less than the nondimensional switching period, [...]. The feedback constants of the linear control law determine both the local stability and regulation of the linear discrete regulator.\r\n\r\nLiapunov's direct stability method as applied to discrete systems and the method of paired systems due to Kalman are used to obtain sufficient conditions for global stability. The paired system technique is also used to analyze the switching regulators for their global convergence properties." }, { "name": "Foutch, Douglas Allen", "degree": "PhD", "year": "1977", "title": "A Study of the Vibrational Characteristics of Two Multistory Buildings", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312017-102214623", "creators": [ { "name": { "family": "Foutch", "given": "Douglas Allen" }, "id": "Foutch-Douglas-Allen", "display_name": "Foutch, Douglas Allen" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/X944-SG43", "abstract": "Forced vibration tests and associated analysis of two multistory\r\nbuildings are described. In one case, the dynamic properties of the\r\nbuilding measured during the tests are compared to those predicted by\r\nsimple analytical models. A three-dimensional finite element model\r\nof the second building was constructed for the purpose of evaluating\r\nthe accuracy of this type of analysis for predicting the observed\r\ndynamic properties of the structure.
\r\n\r\n\r\nForced vibration tests were performed on Millikan Library, a\r\nnine-story reinforced concrete shear wall building. Measurements of\r\nthree-dimensional motions of approximately 50 points on each of six\r\nfloors (including the basement) were taken for excitation in the N-S and\r\nE-W directions. The results revealed a complex interaction between\r\nlateral and vertical load carrying systems in both directions. The\r\nresults also suggest that a significant change in the foundation response\r\nof the structure occurred in the stiffer N-S direction during the San\r\nFernando earthquake. This phenomenon was investigated through the\r\nuse of two analytical models of the building which included the effects\r\nof soil-structure interaction.
\r\n\r\n\r\nThe Ralph M. Parsons world Headquarters building, a twelve-story\r\nsteel frame structure, was also tested. The natural frequencies,\r\nthree-dimensional mode shapes, and damping coefficients of nine modes\r\nof vibration were determined. Other features of this investigation\r\nincluded the study of nonlinearities associated with increasing levels\r\nof response and the measurement of strain in one of the columns of the\r\nstructure during forced excitation. The dynamic characteristics of\r\nthe building determined by these tests are compared to those predicted\r\nby a finite element model of the structure. The properties of primarily\r\ntranslational modes are predicted reasonably well; but adequate predictions\r\nof torsional motions were not obtained. The comparison\r\nbetween measured and predicted strains suggests that estimates of\r\nstress obtained from finite element analyses of buildings should be\r\nwithin 25 percent of those experienced by the structure for a known\r\nexcitation.
" }, { "name": "Garrott, W. Riley", "degree": "PhD", "year": "1977", "title": "Transient Response of Two-Dimensional Cantilevered Semi-Infinite and Finite Elastic Plates, Subjected to Base Motions", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechTHESIS:11182025-210824229", "creators": [ { "name": { "family": "Garrott", "given": "W. Riley" }, "id": "Garrott-W-Riley", "display_name": "Garrott, W. Riley" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/e3aq-9d16", "abstract": "This research is concerned with the response of a two-dimensional,\r\nisotropic, homogeneous, elastic, cantilevered plate subjected\r\nto a step transverse velocity at the base. The investigation uses a\r\nmethod by Miklowitz which is based on a double Laplace transform and\r\na boundedness condition on the solution.
\r\n\r\nThe case of a semi-infinite plate is solved, for long-time, to\r\nfind the shear and normal stresses at the base. The solution in the interior\r\nof the plate is shown to agree with that obtained by the\r\nBernoulli-Euler approximate theory. The solution is then extended to\r\nthe case of the finite length plate, with traveling wave and vibrational\r\nforms of the solution being found for the interior of the plate.
\r\n\r\nAt the base of the plate the investigation shows that the normal\r\nstress is singular at the corners while the shear stress is non-singular.
" }, { "name": "Gates, Edward Maurice", "degree": "PhD", "year": "1977", "title": "The Influence of Freestream Turbulence, Freestream Nuclei Populations and a Drag-Reducing Polymer on Cavitation Inception on Two Axisymmetric Bodies", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08122014-083534353", "creators": [ { "name": { "family": "Gates", "given": "Edward Maurice" }, "id": "Gates-Edward-Maurice", "display_name": "Gates, Edward Maurice" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/GH1H-3780", "abstract": "The influence upon the basic viscous flow about two axisymmetric\r\nbodies of (i) freestream turbulence level and (ii) the injection\r\nof small amounts of a drag-reducing polymer (Polyox WSR 301) into\r\nthe test model boundary layer was investigated by the schlieren flow\r\nvisualization technique. The changes in the type and occurrence of\r\ncavitation inception caused by the subsequent modifications in the\r\nviscous flow were studied. A nuclei counter using the holographic\r\ntechnique was built to monitor freestream nuclei populations and a\r\nfew preliminary tests investigating the consequences of different populations\r\non cavitation inception were carried out.
\r\n\r\nBoth test models were observed to have a laminar separation\r\nover their respective test Reynolds number ranges. The separation on\r\none test model was found to be insensitive to freestream turbulence\r\nlevels of up to 3.75 percent. The second model was found to be very\r\nsusceptible having its critical velocity reduced from 30 feet per second\r\nat a 0.04 percent turbulence level to 10 feet per second at a 3.75 percent\r\nturbulence level. Cavitation tests on both models at the lowest\r\nturbulence level showed the value of the incipient cavitation number\r\nand the type of cavitation were controlled by the presence of the laminar\r\nseparation. Cavitation tests on the second model at 0.65 percent turbulence \r\nlevel showed no change in the inception index, but the appearance\r\nof the developed cavitation was altered.
\r\n\r\n\r\nThe presence of Polyox in the boundary layer resulted in a\r\ncavitation suppression comparable to that found by other investigators.\r\nThe elimination of the normally occurring laminar separation on these\r\nbodies by a polymer-induced instability in the laminar boundary layer\r\nwas found to be responsible for the suppression of inception.
\r\n\r\nFreestream nuclei populations at test conditions were measured\r\nand it was found that if there were many freestream gas bubbles the\r\nnormally present laminar separation was elminated and travelling bubble\r\ntype cavitation occurred - the value of the inception index then depended\r\nupon the nuclei population. In cases where the laminar separation\r\nwas present it was found that the value of the inception index was\r\ninsensitive to the free stream nuclei populations.
" }, { "name": "Gates, Nathan Craig", "degree": "PhD", "year": "1977", "title": "The Earthquake Response of Deteriorating Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04212017-094508970", "creators": [ { "name": { "family": "Gates", "given": "Nathan Craig" }, "id": "Gates-Nathan-Craig", "display_name": "Gates, Nathan Craig" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/E3AQ-B348", "abstract": "This thesis is concerned with the earthquake response of\r\ndeteriorating systems. A model for stiffness degrading or\r\ndeteriorating systems is used to describe six different single-degree-of-freedom systems. A numerical investigation of the\r\nresponse of these six systems is performed using an ensemble of\r\ntwelve earthquakes. The response is studied at nine nominal\r\nperiods of oscillation. The numerical results are presented as\r\nresponse spectra corresponding to six different ductilities.
\r\n\r\nAn approximate analytical method for calculating the earthquake\r\nresponse of deteriorating systems from a linear response\r\nspectrum is presented. The method, called the average stiffness\r\nand energy method, is based upon the premise that a linear system\r\nmay be defined which is in some sense equivalent to the deteriorating\r\nsystem. The criterion for equivalence in this method is that\r\nthe average stiffness of the deteriorating system be equal to the\r\nstiffness of the linear system and the average energy dissipated\r\nby the linear system be the same as the average energy dissipated\r\nby the deteriorating system.
\r\n\r\nThe new analytical method is compared to existing methods.\r\nComparison with the numerical results is also made. Based upon\r\nthese comparisons, it is concluded that the average stiffness and\r\nenergy method represents a significant improvement over currently\r\navailable methods for predicting the earthquake response of\r\ndeteriorating and nondeteriorating systems.
" }, { "name": "Hesselink, Lambertus", "degree": "PhD", "year": "1977", "title": "An Experimental Investigation on Propagation of Weak Shock Waves in a Random Medium", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-01042006-154703", "creators": [ { "name": { "family": "Hesselink", "given": "Lambertus" }, "id": "Hesselink-Lambertus", "display_name": "Hesselink, Lambertus" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/XKHF-VD55", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn apparatus has been constructed for generating a 25 cm cube of randomly inhomogeneous gas in the GALCIT 17-inch diameter shock tube. It consists of a two-dimensional 7 x 8 array of fine jets alternately of helium and freon-12 behind coarse grids located on opposite sides of a box. The two other side walls of the box are fitted with optical windows for diagnostics. The up-stream and downstream faces of the box are movable and can be opened rapidly just before shock arrival. This process is automated, and the arrival time of the shock wave relative to the decay of the turbulent density field can be varied. The gas mixture is made neutrally buoyant so that the mean interface between the scattering region and the uniform air in the shock tube is parallel to the plane of the incoming wave. Furthermore, the mean acoustic impedance of the mixture is matched to that of the quiescent air in the shock tube to minimize the effect of the air-gas mixture interface on the shock wave.\r\n\r\nIn this experiment shock waves of strengths varying from [...] = 1.007 to 1.1 scatter from random variations of acoustical impedance and index of refraction (defined as the ratio of the sound speed in air to the local, variable, sound speed in the scattering medium) which occur during the turbulent mixing of the two different gases. The scale and amplitude of the fluctuations before interaction with the shock wave are obtained from optical and point density measurements; the method of Uberoi and Kovasznay (Ref. 10) has been used to obtain length scales of the flow from shadowgraph and schlieren pictures, and the Brown-Rebollo (Ref. 11) density probe is used to measure local mean and rms density fluctuations, and space- and cross-correlation functions.\r\n\r\nTo study the interaction of the shock with the turbulence, spark shadowgraph and schlieren pictures have been taken and pressure measurements have been made. Arrays of pressure transducers located in a false endwall downstream of the scattering volume record the shock front topology and the spatial variation of shock amplitude.\r\n\r\nThe pressure measurements indicate a substantial modification of the unperturbed shock profile. Data are presented which indicate the effect of the Mach number on the scattering process.\r\n\r\nOptical measurements show that length scales in the fluid, which is processed by all but the weakest shocks, have changed due to the interaction process." }, { "name": "Higuchi, Hiroshi", "degree": "PhD", "year": "1977", "title": "Experimental Investigation on Axisymmetric Turbulent Wakes with Zero Momentum Defect", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11282006-111227", "creators": [ { "name": { "family": "Higuchi", "given": "Hiroshi" }, "id": "Higuchi-Hiroshi", "display_name": "Higuchi, Hiroshi" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/121B-VN50", "abstract": "An experimental investigation of a turbulent axisymmetric wake with zero momentum defect was carried out. The experiment was conducted in a low speed wind tunnel with a circular tube mounted parallel to the stream. A controlled amount of air was injected into the stream at the end of the model to cancel the drag produced by the turbulent boundary layer on the model. The measurements on the mean flow and the fluctuation quantities were carried up to 90 diameters downstream. By adjusting the strength of the injections the behavior of the pure wake, the co-flowing jet and the matched injection were examined, and the self similar properties both in the mean velocity and the turbulent intensity were found to exist in these cases. Rapid decays off the centerline velocity and the maximum turbulent intensity were observed in the matched injection case. The effect of the initial condition was studied by artificially thickening the boundary layer on the model, and it was observed that the wake relaxes into the final decay law sooner. The unmatched cases, both strong and weak injections, were also investigated; the strong injection case was found to relax into the self-similar weak jet profile and the weaker injection case was observed to approach to the similar wake profile.\r\n\r\nFlow visualization was conducted on the plane of symmetry and the entrainment process by the engulfing large eddies was visualized in the pure wake and in the co-flowing jet.\tA lack of large rotations was observed in the matched injection case and the lack of production of turbulent energy was attributed to the faster decay of the flow properties." }, { "name": "Jaggard, Dwight L.", "degree": "PhD", "year": "1977", "title": "Bragg Interactions in Periodic Media", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:11142025-203411358", "creators": [ { "name": { "family": "Jaggard", "given": "Dwight L." }, "id": "Jaggard-Dwight-L", "orcid": "00-0002-0697-1612", "display_name": "Jaggard, Dwight L." } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6ctw-8m32", "abstract": "The interaction of electromagnetic waves of wavelength \u03bb with periodic structures of spatial period \u039b. are studied. The emphasis of the work is on Bragg interactions where \u03bb \u2243 2/\\/N and the Bragg order N takes on the values 1, 2,... . An extended coupled waves (ECW) theory is developed for the case N \u2265 2 and the results of the theory are found to compare favorably with the exact results of Floquet theory. Numerous numerical results are displayed as Brillouin diagrams for the first few Bragg orders. Moreover, explicit expressions for coupling coefficients, bandgap shifts and bandgap widths are derived for singly periodic media. Particular note is taken of phase speeding effects.
\r\n\r\nThe effects of multiharmonic periodicities on the control of feedback strength are investigated. It is found that with proper phasing the feedback strength becomes zero and the bandgap disappears. Coupling parameters are calculated for typical multiharmonic periodicities for the first three Bragg orders.
\r\n\r\nFor odd Bragg orders, inverted bandgaps and phase slowing occur when the gain or loss of the media is modulated. Also average gain or loss affects the bandgap shape and the spatial or temporal growth or decay. Absolute instabilities are observed and expressions are derived for the instability frequencies, thresholds and growth rates. Under certain conditions, instabilities occur for structures with average loss. The results for the first and second Bragg orders are archetypical of all odd and even orders respectively.
\r\n\r\nApplications of the ECW theory to higher-order DFB filters involve such phenomena as transient propagation, effects of periodicity profiles and the relative coupling due to boundaries and periodicities. The calculation of higher-order DFB laser parameters shows that the mode spectrum is asymmetrically shifted and the threshold gain is greatly dependent upon the periodicity profile. Approximate threshold parameters are calculated for high and low gain and for all Bragg orders. In addition, application of the ECW theory to holographic gratings and beam propagation is made.
" }, { "name": "Johnson, Robert Edward", "degree": "PhD", "year": "1977", "title": "Slender-Body Theory for Stokes Flow and Flagellar Hydrodynamics", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-04212004-114339", "creators": [ { "name": { "family": "Johnson", "given": "Robert Edward" }, "id": "Johnson-Robert-Edward", "display_name": "Johnson, Robert Edward" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/HYMQ-AH77", "abstract": "The singularity method for Stokes flow is used to examine the flow past slender bodies possessing finite centerline curvature, in a viscous, incompressible fluid without any appreciable inertia effects. The motion of a slender toroidal ring in Stokes flow is considered first. The symmetry of the geometry and absence of ends has made an accurate analysis possible; the result of this problem elucidates the general flow characteristics present for bodies moving in an arbitrary manner with a finite centerline curvature. Using the methods developed here it is possible to calculate the force/length to higher orders in the slenderness parameter, \u03f5, than has previously been possible. In particular, we find the Stokeslet strength with an error of O(\u03f5\u00b2). The solution of the torus problem serves as an effective guide in extending the theory to slender bodies of circular cross section with arbitrary centerline configurations and spheroidal ends. In all the cases considered, the no-slip boundary condition is satisfied by distributing appropriate Stokeslets, doublets, rotlets, sources, stresslets, and quadrupoles on the body centerline up to an error term of O(\u03f5\u00b2 ln\u03f5), which is sufficient for practical application. From the general slender body analysis we find an integral equation which determines the Stokeslet strength up to the term of O(\u03f5\u00b2). The general theory is then applied to examine the propulsion of flagellated microorganisms, including an approximate solution for the interaction between cell body and flagella. A final brief note is made on the thrust enhancing capabilities of oscillating non-spherical cell bodies." }, { "name": "Koblasz, Arthur Joseph", "degree": "PhD", "year": "1977", "title": "Nonlinear Analysis of the Human Electroretinogram", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11142025-160635865", "creators": [ { "name": { "family": "Koblasz", "given": "Arthur Joseph" }, "id": "Koblasz-Arthur-Joseph", "display_name": "Koblasz, Arthur Joseph" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/dn67-1t75", "abstract": "The human electroretinogram (ERG) has been studied for\r\nabout a century and has been in use as a clinical tool for perhaps\r\nhalf that time. Like most other biopotentials, the ERG is probably\r\nthe result of nonlinear operations, but there have been surprisingly\r\nfew attempts to study these nonlinear characteristics. We have\r\ncharacterized the human ERG system using Wiener kernels, which\r\nreflect separately the linear and nonlinear operations.
\r\n\r\nOne of the difficulties with conventional analyses of the ERG for\r\nsmall amplitude flash stimuli is the variability of the response, both between\r\nsubjects and for the same subject. This is often the result of poorly\r\ncontrolled experimental conditions rather than pitfalls in the analysis.\r\nFor example, differences in retinal illumination can change both the\r\nstimulus and the system. Also, different placement of electrodes\r\ncan cause different impedence and noise effects. We reduced both\r\nthese artifacts by providing a maxwellian view of the stimulus and by\r\nusing an eyecup electrode of our own design. The inherent nature\r\nof the flash stimulus can produce other artifacts which the quasi-random\r\nstimulus avoids. For example, flash stimuli are more\r\nlikely to evoke nonvisual responses than the random intensity\r\nstimulus. Also large amplitude flashes test the retina with nonp-hysiological\r\nlevels.
\r\n\r\nWe first demonstrated the reliability of the first- and second-order\r\nWiener kernels for characterizing the human ERG system by\r\nmeasuring standard deviations of the kernels for a variety of experimental\r\nconditions. We also used the kernels to predict responses\r\nto flash stimuli. For the cases considered, the first- and second-order\r\nkernels characterized the human ERG system more completely\r\nand accurately than measured flash responses.
\r\n\r\nWe next examined the changes in the kernels for different\r\nmean levels of quasi-random stimuli. The first- and second-order\r\nkernels change suddenly for a step increase or decrease in stimulus\r\nmean. The size and latency of the kernel components increase as\r\nthe stimulus mean decreases and a second b-wave appears as a\r\ndistinct component of the first-order kernel for low stimulus means.
\r\n\r\nThis second b-wave was shown to be attenuated for a red\r\n(663 nm) stimulus and reduced for a Retinitis Pigmentosa patient.\r\nFurthermore, when the stimulus bandwidth is increased, other\r\ncomponents of the first-order kernel increase in size but the second\r\nb-wave remains the same. Hence, the second b-wave of the first-order\r\nkernel probably reflects the functioning of rod systems, much\r\nlike the scotopic b-wave of the flash response.
\r\n\r\nNext we compiled all experimental evidence to construct\r\nmodels of the ERG system which produce the observed adaptation\r\neffects. Separate photopic and scotopic models were derived which\r\noffer a simple interpretation of the first- and second-order Wiener\r\nkernels. The photopic system is described as a cascade of a nonlinear\r\nsystem without memory followed by a linear filter with a long\r\ntime constant. This seems appropriate since the first-order kernel\r\nfor photopic stimulus levels does not change shape with different\r\ndepths of modulation and since the second- and third-order kernels\r\nmain diagonals resemble the shape of the first-order kernel. The\r\ncharacteristics of both elements of the model were estimated using\r\nexperimental observations.
\r\n\r\nA scotopic model is also described which accounts for some of\r\nthe observed changes in dynamics for scotopic stimulus levels. An\r\nadditional linear integrator with a short time constant is added in\r\nseries to the photopic model, positioned in front of the nonlinear\r\nelement. Small changes in the time constant of this linear stage\r\nproduce large changes in the total dynamics of the model. If the\r\nlinear operations of this stage become more complex, then some of\r\nthe structure of the second-order kernel away from the main diagonal\r\ncan be accounted for.
\r\n\r\nFinally, we measured the ERG responses to one and to two\r\nsimultaneous quasi-random stimuli of different wavelengths. The\r\nfirst-order kernels change significantly for different wavelength\r\nstimuli. However, the differences can be accounted for by changes in\r\nthe relative adaptation states of photopic and scotopic components.
\r\n\r\nThe two-input experiments produce cross-kernels which can\r\nindicate cross-talk between receptor systems. However, if all\r\nreceptor systems receive some proportion of both stimuli, then the\r\ncross-kernel can be dominated by self second-order kernels. This is\r\nthe case for two inputs of red (663 nm) plus blue (423 nm) stimuli.
\r\n\r\nOther evidence for interactions between receptor systems is\r\navailable from observing the changes in the first-order kernel for\r\na single input when a second input of different wavelength is added\r\nto the stimulus. For example, the background red stimulus changes\r\nthe response to the blue stimulus, and the background blue stimulus\r\nchanges the response to a red stimulus. However, simple adaptation\r\ndifferences can again account for the observed changes.
\r\n\r\nThe original goal of this project was to prove the feasibility of\r\nanalyzing human retinal function using quasi-random stimuli. The\r\nsmall amplitudes characteristic of the quasi-random stimulus and the\r\nlarge noise levels customary for the human ERG made our analysis\r\ndifficult. Furthermore, subjects would only tolerate a few minutes of\r\nsteady fixation. Results are not presented for about half the subjects\r\ntested because of excessive noise levels. However, the Wiener kernels\r\ncan provide more information about retinal function than alternative\r\ncharacterizations. Changes in the lower order Wiener kernels can be\r\nempirically linked to retinal diseases even when higher order kernels\r\nare ignored. We hope that our procedure and interpretations will provide\r\na means for eventually improving the resolution of the clinical ERG.
" }, { "name": "Konrad, John Harrison", "degree": "PhD", "year": "1977", "title": "An Experimental Investigation of Mixing in Two-Dimensional Turbulent Shear Flows with Applications to Diffusion-Limited Chemical Reactions", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132005-105700", "creators": [ { "name": { "family": "Konrad", "given": "John Harrison" }, "id": "Konrad-John-Harrison", "display_name": "Konrad, John Harrison" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZE81-ZM79", "abstract": "The extent of molecular mixing in several two-dimensional free turbulent shear flows was measured using a concentration probe with a frequency response of 100 kHz and a spatial resolution of 0.1 mm. The flows investigated were (i) a shear layer in which the gases on either side of the layer are of unequal density, (ii) a shear layer in which the gases on either side of the layer are of equal density, and (iii) a wake in which the gases on either side of the wake are of unequal densities. The extent of mixing was measured as a function of Reynolds number for the first case.
\r\n\r\nIt was found that at a critical Reynolds number the extent of molecular mixing sharply increased (25%). Power spectral density curves of the concentration time histories also indicated a marked increase in the high frequency fluctuations above this Reynolds number. A shadowgraph investigation of this phenomenon revealed that three-dimensional Taylor-type vortices whose axes of rotation are basically in the flow direction exist in the flow in addition to the two-dimensional large structures previously observed. These Taylor vortices were found to be unstable above the critical Reynolds number and were producing the increase in molecular mixing. The growth and development of the two-dimensional large structures were found to be basically unaffected by this instability. It is proposed that the fully developed turbulence of shear flows is maintained by a combination of the development of the large structures and of the coupling between the large structures and these unstable Taylor vortices.
\r\n\r\nThese data were also used to predict results for shear flows in which diffusion-limited chemical reactions have been incorporated.
\r\n" }, { "name": "McMurry, Peter Howard", "degree": "PhD", "year": "1977", "title": "On the Relationship Between Aerosol Dynamics and the Rate of Gas-to-Particle Conversion", "advisor": "Friedlander, Sheldon K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01142026-032008026", "creators": [ { "name": { "family": "McMurry", "given": "Peter Howard" }, "id": "McMurry-Peter-Howard", "orcid": "0000-0003-1609-5131", "display_name": "McMurry, Peter Howard" } ], "advisors": [ { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "advisor", "display_name": "Friedlander, Sheldon K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/gxhr-8r33", "abstract": "A theoretical and experimental study of the dynamic behavior of secondary aerosols generated by homogeneous gas phase reactions is presented. The relationship between the rate at which new aerosol is formed by chemical reaction and the development of the aerosol is emphasized. The effect of an initial aerosol, present at the start of gas-to-particle conversion, on aerosol dynamics is also investigated.
\r\nAerosol dynamics in such systems are typically separated into two stages. During the early stage, new particles are often formed by homogeneous nucleation. Particle concentrations rise to a maximum value after timescales of 10-60 minutes, then decrease continually as the coagulation\r\nrate exceeds the rate at which new particles are formed. A new theory which predicts the rate at which new particles of a given size are formed during the early stages of aerosol growth is presented. This rate is shown to be a known function of a single parameter which depends on the rate at which condensable molecules are produced and on the amount of preexisting aerosol surface area per volume of gas. This parameter can be calculated from experimental data.
" }, { "name": "Olowolafe, Johnson Olufemi", "degree": "PhD", "year": "1977", "title": "Silicide Formation and the Interaction of Metals with Polycrystalline Si", "advisor": "Mayer, James Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212014-113955709", "creators": [ { "name": { "family": "Olowolafe", "given": "Johnson Olufemi" }, "id": "Olowolafe-Johnson-Olufemi", "display_name": "Olowolafe, Johnson Olufemi" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/JZBN-0V57", "abstract": "The main factors affecting solid-phase Si-metal interactions are reported in this work. The influence of the orientation of the Si substrates and the presence of impurities in metal films and at the Si-metal interface on the formation of nickel and chromium silicides have been demonstrated. We have observed that the formation and kinetic rate of growth of nickel silicides is strongly dependent on the orientation and crystallinity of the Si substrates; a fact which, up to date, has never been seriously investigated in silicide formation. Impurity contaminations in the Cr film and at the Si-Cr interface are the most dominant influencing factors in the formation and kinetic rate of growth of CrSi2. The potentiality and use of silicides as a diffusion barrier in metallization on silicon devices were also investigated.
\r\n\r\nTwo phases, Ni2Si and NiSi, form simultaneously in two distinct sublayers in the reaction of Ni with amorphous Si, while only the former phase was observed on other substrates. On (111) oriented Si substrates the growth rate is about 2 to 3 times less than that on <100> or polycrystalline Si. Transmission electron micrographs establish-\u00b7that silicide layers grown on different substrates have different microcrystalline structures. The concept of grain-boundary diffusion is speculated to be an important factor in silicide formation.
\r\n\r\nThe composition and kinetic rate of CrSi2 formation are not influenced by the underlying Si substrate. While the orientation of the Si substrate does not affect the formation of CrSi2 , the purity of the Cr film and the state of Si-Cr interface become the predominant factors in the reaction process. With an interposed layer of Pd2Si between the Cr film and the Si substrate, CrSi2 starts to form at a much lower temperature (400\u00b0C) relative to the Si-Cr system. However, the growth rate of CrSi2 is observed to be independent of the thickness of the Pd2Si layer. For both Si-Cr and Si-Pd2Si-Cr samples, the growth rate is linear with time with an activation energy of 1.7 \u00b1 0.1 ev.
\r\n \r\nA tracer technique using radioactive 31Si (T1/2 = 2.26 h) was used to study the formation of CrSi2 on Pd2Si. It is established from this experiment that the growth of CrSi2 takes place partly by transport of Si directly from the Si substrate and partly by breaking Pd2Si bonds, making free Si atoms available for the growth process.
\r\n\r\nThe role of CrSi2 in Pd-Al metallization on Si was studied. It is established that a thin CrSi2 layer can be used as a diffusion barrier to prevent Al from interacting with Pd2Si in the Pd-Al metallization on Si.
\r\n\r\nAs a generalization of what has been observed for polycrystalline-Si-Al interaction, the reactions between polycrystalline Si (poly Si) and other metals were studied. The metals investigated include Ni, Cr, Pd, Ag and Au. For Ni, Cr and Pd, annealing results in silicide formation, at temperatures similar to those observed on single crystal Si substrates. For Al, Ag and Au, which form simple eutectics with Si annealing results in erosion of the poly Si layer and growth of Si crystallites in the metal films.
\r\n\r\nBackscattering spectrometry with 2.0 and 2.3 MeV 4He ions was the main analytical tool used in all our investigations. Other experimental techniques include the Read camera glancing angle x-ray diffraction, scanning electron, optical and transmission electron microscopy. Details of these analytical techniques are given in Chapter II.
\r\n" }, { "name": "Redondo-Mui\u00f1o, Antonio", "degree": "PhD", "year": "1977", "title": "Theoretical Studies of Silicon Surfaces Using Finite Clusters", "advisor": "Goddard, William A., III; McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11182009-101146638", "creators": [ { "name": { "family": "Redondo-Mui\u00f1o", "given": "Antonio" }, "id": "Redondo-Mui\u00f1o-Antonio", "display_name": "Redondo-Mui\u00f1o, Antonio" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "advisor", "display_name": "Goddard, William A., III" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/8M08-WC34", "abstract": "The objective of this thesis is to study the electronic structure, geometries and chemical binding characteristics of the surfaces of silicon and of the initial form of oxygenated Si. We examined the (111), (100), and (110) surfaces, relaxation on the (111) and (100) surfaces and reconstruction on the (100) surfaces. In addition we examined steps on the OM surfaces. In the oxygenated surface we considered the geometry, excited states and ion states of both 0 and 0_2 bonded to the perfect (111) surface.\r\n\r\nThese studies indicated that surfaces and chemisorption lead to localized electronic states for which explicit inclusion of electronic correlation (many body) effects is essential. These effects are included through use of generalized valence bond (GVB) and configuration interaction (CI) techniques. These techniques require use of a finite collection of Si atoms to represent the surface. We find that very small clusters lead to reliable results if the model system is properly tied off with SiH bonds (to represent internal Si-Si bonds).\r\nIn Chapter 1 we report an effective potential for replacing the ten core electrons in calculations involving the Si atom. The potential is obtained directly from ab initio calculations on the states of the Si atom and no empirical data or adjustable parameters are used. The ab initio effective potential is tested by carrying out Hartree-Fock generalized valence bond and configuration interaction calculations on various molecules. We considered Si, Si_2, SiH_3, Si_2H_6 and H_3S10_2 and calculated excitation energies, ionization potentials, and electron affinities both both using the effective potential and without it (ab initio). In essentially all cases the agreement is to better than 0.1 eV, providing strong evidence that the effective potential adequately represents the Si core. This potential is utilized in all of the calculations reported in subsequent chapters. \r\n\r\nIn Chapter 2 we consider clean (111), (100) and (110) silicon surfaces. For the (111) surface the relaxation of silicon surface atoms is studied by means of an Si(SiH_3)_3 cluster. We find that the surface state is accurately described as a dangling bond orbital with 93% p character. We determined the .optimum relaxation of the surface layer to be 0.08\u00c5 toward the second layer. For the positive ion we find that the surface atom relaxes toward the second layer by an additional 0.30\u00c5. Using an Si_3H_6 cluster we find that the interaction between adjacent dangling bond orbitals indicates that they are very weakly coupled (with a splitting of ~0.01 eV between the singlet and triplet spin couplings.) For the (100) surface we used an Si(SiH_3)_2 cluster. We find a relaxation distance of 0.10\u00c5 toward the vacuum. We also considered the 2x1 reconstruction of such surfaces using the results for Si_2H_4 and Si(SiH_3)_2 complexes. It is found that adjacent surface atoms form a bond (1.76 eV bond strength), leading to pairing up. of adjacent silicons with an optimum Si-Si bond length of 2.38\u00c5).\r\n\r\nIn Chapter 3 we consider the electronic structure of divalent steps on (111) silicon surfaces. We find three localized electronic states separated by less than 0.3 eV. These states have quite different electronic structure and are expected to be reactive toward a large range of chemical species.\r\n\r\nIn Chapter 4 we study the chemisorption of oxygen upon Si (111) surfaces. For single oxygen atoms we find an optimum Si-0 bond length of 1.63\u00c5. We also find ionization potentials in the range 11-16 eV. Then we consider a model in which an oxygen molecule chemisorbed onto the silicon surface has, an electronic structure corresponding to a peroxy radical. We find ionization potentials in the range 11-18 eV\r\nin agreement with experiment. We find an optimum 0-0 bond length of 1.37\u00c5 and a Si-0-0 bond angle of 126\u00b0 for the chemisorbed peroxy radical.\r\n" }, { "name": "Roberts, Philip Joseph William", "degree": "PhD", "year": "1977", "title": "Dispersion of Buoyant Waste Water Discharged from Outfall Diffusers of Finite Length", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03142026-094501355", "creators": [ { "name": { "family": "Roberts", "given": "Philip Joseph William" }, "id": "Roberts-Philip-Joseph-William", "orcid": "0000-0003-4125-275X", "display_name": "Roberts, Philip Joseph William" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/5bjx-sh58", "abstract": "The three-dimensional flow field created by a simple line plume\r\nof finite length in a steady current of uniform density was investigated\r\nin a laboratory basin. The results can be used to aid in the prediction\r\nof dispersion of buoyant waste water released from line diffusers,\r\nparticularly sewage discharges into the ocean.
\r\n\r\nThe experimental results for minimum surface dilution, Sm, were\r\nfound to be independent of L/H, in the range 3.7 < L/H < 30 where L is\r\nthe diffuser length and H the water depth, and independent of Reynolds\r\nnumber, Re = 4uH/v, in the range 1190 < Re < 12,900 where u is the\r\ncurrent velocity. The results are expressed graphically in the form:
\r\n\r\nSmq/uH = f(F,\u03b8)
\r\n\r\nwhere q is the volume flux per unit length, and \u03b8 the orientation of the\r\nline diffuser to the current. F is a type of Froude number defined by\r\nF = u3/b, where b is the buoyancy flux per unit length. The initial\r\nmomentum flux is assumed to be small.
\r\n\r\nFor a current perpendicular to the diffuser, and F > 0.2, the\r\neffluent mixes over the receiving water depth due to self-induced\r\nturbulence. When the diffuser is of finite length, the diluted effluent\r\nseparates from the bottom at some point downstream and forms a two-layer\r\nflow. However, currents parallel to the diffuser do not produce mixing\r\nover the depth, and the flow forms a two-layer system immediately,\r\neven for Froude numbers as high as 100.
\r\n\r\nFor F < 0.1, dilution is independent of current speed and direction.\r\nFor F > 0.1, dilutions when the current is perpendicular to the diffuser\r\nare proportional to the current speed. For 0.1 < F < 100 this dilution\r\nis about 60% of that predicted assuming uniform mixing of the effluent\r\nover the receiving water depth. This is due to the development of a\r\nvertically stable density profile. For F > 0.1, a diffuser placed\r\nperpendicular to the current will result in greater dilutions than if\r\nparallel. The ratio of minimum surface dilution when the current is\r\nperpendicular to that when the current is parallel increases with F,\r\nand is equal to about 4 at F = 100.
\r\n\r\nHorizontal spreading of the waste field is governed by buoyancy\r\nforces rather than ambient turbulence. For F \u2265 1 the initial surface\r\nplume spreading is found to be linear, and independent of L/H and Re\r\nfor 3. 7 < L/H < 15, and 2,900 < Re < 13,000. Beyond this initial\r\nlinear spreading zone the rate of plume growth decreases. It is\r\nspeculated that regimes may exist where the surface width grows as the\r\n2/3 or 1/5 power of downstream distance; the results are not adequate\r\nto confirm these growth laws. It is believed that ambient turbulence\r\nhas no significant effect on diluting the waste within several diffuser\r\nlengths from the source.
\r\n\r\nThe results have been presented in a manner which makes them\r\nimmediately applicable for improving outfall designs, and demonstrates\r\nthe error frequently made in assuming two-dimensional flow fields. This\r\nassumption is incorrect even if the diffuser length is an order of\r\nmagnitude greater than the water depth.
" }, { "name": "Shah, Piyush Chimanlal", "degree": "PhD", "year": "1977", "title": "Estimation of Properties in Petroleum Reservoirs", "advisor": "Gavalas, George R.; Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042006-081055", "creators": [ { "name": { "family": "Shah", "given": "Piyush Chimanlal" }, "id": "Shah-Piyush-Chimanlal", "display_name": "Shah, Piyush Chimanlal" } ], "advisors": [ { "name": { "family": "Gavalas", "given": "George R." }, "id": "Gavalas-G-R", "role": "advisor", "display_name": "Gavalas, George R." }, { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7DC3-EX92", "abstract": "The determination of parameters in a dynamical system, on the basis of noisy observations of its state is variously known as parameter estimation, identification or the inverse problem. In this work, the determination of porous rock property distribution in a petroleum reservoir using the production rate records and observed pressures (the history matching problem) is considered.\r\n\r\nThe history matching problem is inherently underdetermined because of the large number of unknown parameters relative to the available data. The number of unknowns can be reduced by representing the distributions by a small number of parameters (parameterization). The commonly used zonation approach involves a parameterization, but introduces a considerable modeling error. In chapter 1, Bayesian estimation theory is extended to history matching as an alternative to zonation; it is sought to alleviate the underdeterminacy through specification of a priori statistical information about the unknown parameters. Application of Bayesian estimation and zonation to the problem of porosity and permeability estimation in a one-dimensional single-phase reservoir indicates that the former yields superior estimates; this holds true even when the prior statistics involve large errors. The application of the conjugate gradient and the Gauss-Newton (or Marquardt's) algorithms for history matching is investigated, and the numerical effort for zonation and Bayesian estimation in one- and two-dimensional reservoirs is estimated in detail.\r\n\r\nIn chapter 2, analytic expressions are derived for the sensitivities of an observed oil pressure to small, arbitrary changes in the porosity and permeability distributions in a one-dimensional reservoir. The results indicate that highly oscillatory components of either have very small influence on the pressure and thus cannot be determined by history matching. Further, the dependence of all the observed pressures on the unknown parameters is linearized, for small deviation, about two reference property distributions. The linear relation is analyzed to yield quantitative information concerning the statistical properties of the problem. Iterative corrections in the history matching algorithms are identified with various pseudo-inverses of the linear relation, thus explaining the properties of the resulting estimates. The nature of the linear relation is found to be not strongly dependent on the reference property distributions used for linearization; thus such analysis can be performed prior to estimation. It is discussed how the linearized analysis can be used to determine the determinacy of any given parameterization.\r\n\r\nThe information derived from the linearized analysis and that in the a priori statistics is synthesized in chapter 3 to predict covariances for the zonation and Bayesian estimates. Since the results of the linearized analysis depend only weakly on the reference distribution, the predicted covariances are valid for a class of reservoirs having \"true\" property distributions with identical prior statistics. A good agreement is found when the predicted variances are compared with actual mean square estimate errors in simulations with four distributions with given prior statistics. The sensitivity of the estimates and their covariance to changes and errors in the specification of the prior statistics are investigated in considerable detail. The determination of zonation with smallest trace of estimate covariance for a given problem is considered. The design of Marquardt's algorithm to yield the smallest expected total estimate error for a given zonation is discussed." }, { "name": "Spanos, Polihronis Thomas Dimitrios", "degree": "PhD", "year": "1977", "title": "Linearization Techniques for Non-Linear Dynamical Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10282024-225753505", "creators": [ { "name": { "family": "Spanos", "given": "Polihronis Thomas Dimitrios" }, "id": "Spanos-Polihronis-Thomas-Dimitrios", "display_name": "Spanos, Polihronis Thomas Dimitrios" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/bxg5-0375", "abstract": "This dissertation is concerned with the application of linearization techniques to the study of the response of non-linear dynamical systems subjected to periodic and random excitations.
\r\n\r\nA general method for generating an approximate solution of a multi-degree-of-freedom non-linear dynamical system is presented. This method relies on solving an optimum equivalent linear sub\u00adstitute of the original system.
\r\n\r\nThe applicability of the method for determination of the amplitudes and phases of the approximate steady-state solution of a multi-degree-of-freedom non-linear system under harmonic monofrequency excitation is considered. The implementation of the method for several special classes of non-linear functions is dis\u00adcussed in detail. In addition, the manner in which the method may be applied to generate an approximate solution for the covariance matrix of the stationary random response of a multi-degree-of\u00ad freedom dynamical system subjected to stationary Gaussian exci\u00adtation is outlined.
\r\n\r\nThe potential of the method to treat transient solutions of non-linear systems is indicated in the context of the non-stationary response of a lightly damped and weakly non-linear oscillator sub\u00adjected to monofrequency harmonic or to a Gaussian white noise disturbance. For both classes of excitation the method produces a first-order differential equation governing the response amplitude. The results pertinent to the harmonically excited oscillator are compared with existing solutions. A non-stationary solution of the Fokker-Planck equation associated with the stochastic differential equation governing the response amplitude of the randomly excited oscillator is accomplished by perturbation techniques; the stationary solution is determined without making any approximation in the Fokker-Planck equation.
\r\n\r\nThe new method for transient response is applied to the random response of a Duffing Oscillator and a Hysteretic System. The solution for the Duffing Oscillator is compared with data obtained by a Monte Carlo study.
" }, { "name": "Srinivas, Sankaran", "degree": "PhD", "year": "1977", "title": "Error Recovery in Robot Systems", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:09102018-150127337", "creators": [ { "name": { "family": "Srinivas", "given": "Sankaran" }, "id": "Srinivas-Sankaran", "display_name": "Srinivas, Sankaran" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/P7QY-KN31", "abstract": "This dissertation addresses itself to the problem faced by a robot in recovering from failures during execution of a task. Failures occur partly because sensory information is inaccurate, partly because effectors do not always perform as expected, and partly because the domain in which the robot operates cannot be characterized exactly. Robot systems with automated planners have traditionally dealt with the problem of error recovery by merely replanning to achieve the desired goal, without attempting to characterize the failure in any way whatsoever.
\r\n\r\nThe central idea in this thesis is that planning recovery from failures has its own special techniques, distinct from those used in conventional planning systems. Two viewpoints, looking at the past for an explanation of the failure, and looking at the current situation to attempt a characterization of the failure state, provide powerful heuristics for error recovery. This thesis suggests that these heuristics can be formalized as failure reason analysis and multiple outcome analysis, and that knowledge relevant for such analysis can be provided through a failure reason model and a multiple outcome model associated with each action.
\r\n\r\nThe failure reason model about why actions provides a means for representing fail, like bumping into an object to be grasped because of servoing errors or because of inaccurate information about the location of the object. The model also provides knowledge required for distinguishing between the different reasons for failure. Finally, it includes recommendations of corrective actions to be taken if failure is attributed to a specific reason. This model in used in failure reason analysis in building a failure tree representing possible explanations of the failure. The explanations represented in the tree are then used in planning recovery.
\r\n\r\nThe multiple outcome model provides a way of representing the possible outcomes of an action, like bumping onto the object or bumping onto the ground in the immediate vicinity of the object, ignoring the fact that these outcomes could be the result of several different reasons. Knowledge required to distinguish between different outcomes is provided as part of the model. In cases where the immediately available information is inadequate to identify the outcome of an action, the multiple outcome model provides a basis for executing actions to serve as information gathering steps. The novel feature here is that information gathering is directed by specific expectations about the state of the world.
\r\n\r\nA computer implementation of a program called MEND has provided a medium for exploring the above idea. MEND has been designed to automate recovery from failures in simple manipulation tasks to be performed by the JPL robot, but the techniques used in MEND have greater generality. A first implementation of MEND established the basis of this investigation. A second version, which has been designed to correct some limitations of the first version, has not yet been fully implemented and integrated with the JPL robot system.
\r\n\r\nThe techniques of planning recovery from failures through failure reason analysis and multiple outcome analysis are contributions to the subject of robotics. More importantly, however, the problem of error recovery is recognized to be a member of a larger class of problems involving knowledge representation and common sense reasoning, both of which are core topics in the study of artificial intelligence. The solution presented in this thesis makes some new contributions to these core topics.
" }, { "name": "Stoll, Michael Edward", "degree": "PhD", "year": "1977", "title": "Spin Dynamics of Pulsed Nuclear Magnetic Double Resonance in Solids", "advisor": "Vaughan, Robert W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212014-160352901", "creators": [ { "name": { "family": "Stoll", "given": "Michael Edward" }, "id": "Stoll-Michael-Edward", "display_name": "Stoll, Michael Edward" } ], "advisors": [ { "name": { "family": "Vaughan", "given": "Robert W." }, "id": "Vaughan-R-W", "role": "advisor", "display_name": "Vaughan, Robert W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/3A2F-RM03", "abstract": "In the first part of this thesis, experiments utilizing an NMR\r\nphase interferometric concept are presented. The spinor character of\r\ntwo-level systems is explicitly demonstrated by using this concept.\r\nFollowing this is the presentation of an experiment which uses this\r\nsame idea to measure relaxation times of off-diagonal density matrix\r\nelements corresponding to magnetic-dipole-forbidden transitions in a\r\n^(13)C-^1H, AX spin system. The theoretical background for these experiments\r\nand the spin dynamics of the interferometry are discussed also.
\r\n\r\nThe second part of this thesis deals with NMR dipolar modulated\r\nchemical shift spectroscopy, with which internuclear bond lengths and\r\nbond angles with respect to the chemical shift principal axis frame\r\nare determined from polycrystalline samples. Experiments using benzene\r\nand calcium formate verify the validity of the technique in heteronuclear\r\n(^(13)C-^1H) systems. Similar experiments on powdered trichloroacetic\r\nacid confirm the validity in homonuclear (^1H- ^1H) systems. The\r\ntheory and spin dynamics are explored in detail, and the effects of a\r\nnumber of multiple pulse sequences are discussed.
\r\n\r\nThe last part deals with an experiment measuring the ^(13)C chemical\r\nshift tensor in K_2Pt(CN)_4Br_(0.3) \u2022 3H_2O, a one-dimensional conductor. The\r\n^(13)C spectra are strongly affected by ^(14)N quadrupolar interactions via\r\nthe ^(13)C - ^(14)N dipolar interaction. Single crystal rotation spectra are\r\nshown.
\r\n\r\nAn appendix discussing the design, construction, and performance\r\nof a single-coil double resonance NMR sample probe is included.
\r\n" }, { "name": "Udupa, Shriram Mahabal", "degree": "PhD", "year": "1977", "title": "Collision Detection and Avoidance in Computer Controlled Manipulators", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:09212018-113534426", "creators": [ { "name": { "family": "Udupa", "given": "Shriram Mahabal" }, "id": "Udupa-Shriram-Mahabal", "display_name": "Udupa, Shriram Mahabal" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/2E18-0E29", "abstract": "This dissertation tackles the problem of planning safe trajectories for computer controlled manipulators with two links and multiple degrees of freedom.
\r\n\r\nThere are two ways to look at safe trajectory planning. The first concerns itself with planning trajectories in empty space; obstacles enter into consideration only indirectly in that they determine what part of the maneuverable space is free. The second considers obstacles alone; free space considerations are of secondary importance. We show how these complementary views can be used to advantage in the safe trajectory planning problem.
\r\n\r\nObstacles are naturally described in cartesian space and trajectories in joint space. If obstacles and trajectories are both represented in one space, collision checks would not require the constant and expensive conversion between the two spaces. We show how it is possible to decompose the planning task so as to get the best of both cartesian space and joint space representations, and yet avoid the constant conversion overhead problem.
\r\n\r\nWe show how the principles of hierarchical decomposition can be used to reduce the complexity of the manipulator trajectory planning problem. Different strategies are used for maneuvering far away from obstacles and for maneuvering close to obstacles. A characterization of large chunks of empty space makes maneuvering far away from obstacles very easy. A characterization of obstacle configuration types simplifies planning of maneuvers close to obstacles.
\r\n\r\nThe key ideas in the representation that make it possible to realize the above claims are:
\r\n\r\n1) the identification of a hierarchy of abstraction spaces that permit simplified manipulator descriptions. These spaces make it possible to model the manipulator as two line segments, a single line segment, or incredibly as a point.
\r\n\r\n2) the identification of primitive trajectory types that make collision detection, trajectory hypothesis and modification numerically tractable.
\r\n\r\n3) the polyhedra-model of obstacles and the identification of one-time-only transformations on obstacles that significantly simplify trajectory planning.
\r\n\r\n4) a neat characterization of empty space. Empty space is approximated by easily describable entities called charts; the approximation is dynamic and under program control; the approximation can be selective, and thus it is easy to make incremental modifications to the charts.
\r\n\r\nThe thesis describes a model for collision detection and avoidance systems for computer controlled manipulators. The justification for the model lies in the computer implementations for 2D and 3D manipulator systems. These systems incorporate a significant portion of the model. The promising performance of the implementation makes fast collision avoiders a distinct possibility.
\r\n\r\nThe solution presented treats manipulators with a sliding joint, and permits the manipulator to transport objects which can be enclosed within the minimum bounding cylinder of the manipulator link. Modifications of the solution that permit handling of large objects are indicated. An extension of the solution that solves the problem for manipulators with only rotary joints is described.
\r\n\r\nA consequence of the investigations into the collision detection and avoidance problem has been the identification of execution-time strategies for terminal phase motion. Guidelines have been presented for incorporating proximity sensors into the manipulator system.
\r\n" }, { "name": "Wojcik, Gregory Lynn", "degree": "PhD", "year": "1977", "title": "Self-Similar Elastodynamic Solutions for the Plane Wedge", "advisor": "Sechler, Ernest Edwin; Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132006-080224", "creators": [ { "name": { "family": "Wojcik", "given": "Gregory Lynn" }, "id": "Wojcik-Gregory-Lynn", "display_name": "Wojcik, Gregory Lynn" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "chair", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "member", "display_name": "Miklowitz, Julius" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E1D3-0T11", "abstract": "Wave propagation in a two-dimensional elastic wedge is fundamental to a large class of problems in elastodynamic theory, however until now analytical solutions to all but certain degenerate cases were unknown. In this thesis a general elastodynamic solution is derived for the wedge in a state of plane strain. Surface tractions are, restricted to uniform normal and shear loads spreading from the wedge vertex at constant velocity. The geometry and loading then allow self-similar solutions of the governing differential equations and boundary conditions in hyperbolic and elliptic domains. Hyperbolic solutions are found in terms of the elliptic solutions by the method of characteristics, while elliptic solutions are reduced using analytic function theory to two independent Fredholm integral equations of the second kind in one dimension. Although numerical solutions are beyond the scope of the investigation, the integral equations are solvable by standard techniques. Such solutions can be used to solve a number of plane elastodynamic problems involving an edge." }, { "name": "Wright, Steven Jay", "degree": "PhD", "year": "1977", "title": "Effects of Ambient Crossflows and Density Stratification of the Characteristic Behavior of Round, Turbulent Buoyant Jets", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03032025-161925415", "creators": [ { "name": { "family": "Wright", "given": "Steven Jay" }, "id": "Wright-Steven-Jay", "display_name": "Wright, Steven Jay" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/424v-vn63", "abstract": "This investigation considers a round, turbulent buoyant jet in\r\nan ambient crossflow that is either of uniform density or with a\r\nlinear density stratification. The primary emphasis is the development\r\nof a fundamental understanding of the jet properties that are\r\nof interest in engineering design problems. These include jet\r\ntrajectories, characteristic dilutions, and in the case of a\r\nstratified crossflow, the maximum and equilibrium heights of rise.
\r\n\r\nMost previous studies of similar buoyant jet flows have used\r\nthe integral method to solve for the jet characteristics. This\r\napproach requires an assumed relation for the rate of entrainment of\r\nambient fluid by the jet, and also depends upon experimental evidence\r\nto estimate values for the coefficients in the assumed relation. Most\r\nprevious experimental studies have been directed toward evaluating\r\nentrainment coefficients and have not considered a systematic investigation\r\nof the effects of the various jet and ambient flow parameters.
\r\n\r\nA major objective of this investigation is to provide a basis\r\nfor the interpretation and extension of the results from previous\r\ntheoretical and experimental investigations. A systematic dimensional\r\nanalysis is performed to define the basic problem and to provide\r\napproximate solutions without using the integral equations. The\r\nanalysis indicates the types of experiments necessary to adequately\r\ndescribe general buoyant jet behavior and also provides a framework\r\nfor the presentation of experimental data.
" }, { "name": "Yates, George Thomas", "degree": "PhD", "year": "1977", "title": "Finite Amplitude Unsteady Slender Body Theory and Experiments", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:03022026-181358157", "creators": [ { "name": { "family": "Yates", "given": "George Thomas" }, "id": "Yates-George-Thomas", "display_name": "Yates, George Thomas" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/z858-hh50", "abstract": "A theoretical study is carried out of the potential flow about\r\nslender bodies. Several theoretical models are discussed and new\r\ndevelopments are directed toward a finite amplitude theory where\r\nflow singularities are distributed along the body centerline, which\r\nmay undergo arbitrary body motion and the body cross section is\r\npresently restricted to being circular. Guided by the example of a\r\ntoroidal ring, for which simple symmetry in shape makes a highly\r\naccurate solution possible, the general theory is developed and results\r\nare given for the force and rate of work done by the fluid on the\r\nmoving body. An example with application to the anguilliform mode\r\nof aquatic animal propulsion is given and compared to observations on\r\na swimming eel (Synbranchus marmoratus).
\r\n\r\nNext, an experimental investigation is discussed, where a\r\ntruly three-dimensional body (modeled after a Chinook salmon) was\r\nused to examine the basic slender body assumptions. Pressure measurements\r\nwere made on the model surface using a set of high sensitivity\r\npressure transducers, and several theoretical solutions are evaluated\r\nand compared with the measured pressure distribution.
" }, { "name": "van der Kogel, Hans", "degree": "PhD", "year": "1977", "title": "Wave Propagation in Saturated Porous Media", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03052010-152258919", "creators": [ { "name": { "family": "van der Kogel", "given": "Hans" }, "id": "van-der-Kogel-Hans", "display_name": "van der Kogel, Hans" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/5REP-HK49", "abstract": "Wave propagation in saturated porous media is investigated in the framework of two models, a theoretical and an experimental one.\r\n\r\nThe theoretical model has two phases, a fluid phase and a solid phase, both modeled as a continuum. The solid phase consists of incompressible grains forming a compressible skeleton. The fluid phase represents a compressible fluid located between the grains. Interactive forces, due to relative motion between the skeleton and the fluid are taken into account. Non-linear balance laws and equations of state are formulated for plane waves. Linearization of the non-linear balance laws yields a set of equations which in limiting cases reduce to well-known results (e.g. consolidation equation, condition for fluidization). The harmonic solution of the linearized field equations contains two modes: one in which the phases move almost together (which is slightly damped) and one in which the phases move in opposite directions (which is highly damped). Solutions are presented in system form.\r\n\r\nApplying a step loading in the variables at the boundary generates, in general, two propagating discontinuities in the variables and these discontinuities decay as they propagate. If we assume that the parameters take \"practical\" values of wet sand then the jump in pore-pressure is always large with respect to the jump in effective pressure along the faster discontinuity propagating into a medium at rest, while velocity differences between the phases are generated if the densities of the phases are different. Non-linear effects due to a non-linear constitutive equation for the fluid oppose the decay of gradients in the variables along the faster propagating discontinuity. The influence of non-linear convective terms can be neglected if the phase velocities are small with respect to the velocities of the discontinuities.\r\n\r\nThe solution to the problem of reflection and refraction of a discontinuity propagating in a fluid and impinging on a two-phase medium is presented. The theory is extended in multi-dimensions, in order to allow shear waves to propagate. The existence of non- propagating discontinuities in dilatant shear is demonstrated.\r\n\r\nThe experimental model consists of a disc configuration, dry and saturated. The interparticle stresses due to impact are visualized by a photo-elastic technique and recorded by a high-speed camera. Changing stress patterns in the discs behind the wavefront are observed. In the dry case a wavefront emerges, behind which the particles are relatively well stressed, while no such definite stress front can be identified in the saturated case. Phase velocity differences occur and separation of particles was observed to take place due to indirect loading of the discs via the fluid." }, { "name": "\u0106uk, Slobodan M.", "degree": "PhD", "year": "1977", "title": "Modelling, Analysis, and Design of Switching Converters", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-110336", "creators": [ { "name": { "family": "\u0106uk", "given": "Slobodan M." }, "id": "\u0106uk-Slobodan-M", "display_name": "\u0106uk, Slobodan M." } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "chair", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "member", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "member", "display_name": "Mead, Carver" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SNGW-0660", "abstract": "The principal objective of this work on modeling and analysis of switching dc-to-dc converters and regulators is to obtain a linear model (either through state-space or linear circuit description), subject to appropriate restrictions, for the inherently nonlinear power state in which the dc conversion is accomplished. A general unified approach to modeling and analysis of switching dc-to-dc converters is developed which is directly applicable to any dc-to-dc operating in either of two conduction modes (continuous or discontinuous inductor current), and which results in a final dynamic linear model either in terms of state-space equations or in terms of their corresponding linear circuit models. In particular, in Part I this analysis technique, called state-space averaging, is applied to the continuous conduction mode of converter operation, while in Part II appropriate extension of the method to the discontinuous conduction mode is made. In each case, the culmination of modeling and analysis is achieved in the development of canonical circuit models which represent any such converter regardless of its detailed configuration.\r\n\r\nThe insights that emerge from the general state-space modeling approach (Parts I and II) lead in Parts III and IV to the design of new converter topologies through the study of generic properties of the cascade connection of basic buck and boost converters. This study paves the way in Part IV to the discovery of a new switching converter based upon capacitive rather than the usual inductive energy transfer. The new converter is shown to have substantial advantages over the conventional converters in its class in efficiency, performance, and also in size and weight.\r\n\r\nBothe the state-space averaged models and their corresponding circuit realizations provide the circuit designer with a powerful tool for analysis of existing converters as well as for synthesis of new converter topologies." }, { "name": "Abdel-Ghaffar, Ahmed Mansour", "degree": "PhD", "year": "1976", "title": "Dynamic Analyses of Suspension Bridge Structures and Some Related Topics", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03012018-135434228", "creators": [ { "name": { "family": "Abdel-Ghaffar", "given": "Ahmed Mansour" }, "id": "Abdel-Ghaffar-Ahmed-Mansour", "display_name": "Abdel-Ghaffar, Ahmed Mansour" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "chair", "display_name": "Housner, George W." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Munger", "given": "Edwin S." }, "id": "Munger-Edwin-S", "role": "member", "display_name": "Munger, Edwin S." } ], "option_major": [ "civileng" ], "doi": "10.7907/Y1XR-WG52", "abstract": "The thesis is divided into two parts. The first part develops a method of dynamic analysis for vertical, torsional and lateral free vibrations of suspension bridges, based on linearized theory and the finite-element approach. The method involves two distinct steps: (1) specification of the potential and kinetic energies of the vibrating members of the continuous structure, leading to derivation of the equations of motion by Hamilton's Principle, (2) use of the finite-element technique to: (a) discretize the structure into equivalent systems of finite elements, (b) select the displacement model most closely approximating the real case, (c) derive element and assemblage stiffness and inertia properties, and finally (d) form the matrix equations of motion and the resulting eigenvalue problems. The stiffness and inertia properties are evaluated by expressing the potential and kinetic energies of the element (or the assemblage) in terms of nodal displacements. Detailed numerical examples are presented to illustrate the applicability and effectiveness of the analysis and to investigate the dynamic characteristics of suspension bridges with widely different properties. This method eliminates the need to solve transcendental frequency equations, simplifies the determination of the energy stored in different members of the bridge, and represents a simple, fast and accurate tool for calculating the natural frequencies and modes of vibration by means of a digital computer. The method is illustrated by calculating the modes and frequencies of a bridge and comparing them with the measured frequencies.
\r\n\r\nThe second part contains two studies on the effect of differential motions of two foundations upon the response of the superstructure of a bridge. The first study deals with the dynamic response of a \"long beam\" model of a bridge to both steady-state and random excitations applied at the supports. The second study develops a method to analyze the dynamic soil-bridge interaction of a simple bridge model erected on an elastic half-space, and the input motion is in the form of incident plane SH-waves. The dynamic response of the bridge and the effect of the radiative damping in the half-space on the interaction of the bridge are also studied.
" }, { "name": "Bofah, Kwasi Kete", "degree": "PhD", "year": "1976", "title": "A Study of the Trailing Vortices Behind a Ring Wing", "advisor": "Liepmann, Hans Wolfgang; Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11092006-132109", "creators": [ { "name": { "family": "Bofah", "given": "Kwasi Kete" }, "id": "Bofah-Kwasi-Kete", "display_name": "Bofah, Kwasi Kete" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/050Z-4228", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe flow field of a laminar vortex wake behind a ring wing was investigated. Experiments were conducted in the GALCIT Low Speed Water Channel, using laser Doppler velocimetry techniques to measure vertical and axial velocity components in the trailing vortex wake. A thin cylindrical ring wing model was tested at various axial angles of attack and free stream velocities. Velocity profiles were measured at several downstream stations from the trailing edge to 45 wing diameters downstream.\r\n\r\nThe inviscid roll-up of the trailing vortex sheet shed by a ring wing was numerically examined. A line vortex representation was used to calculate the evolution of the initially cylindrical vortex sheet. The vortex sheet was found to distort in shape and then smoothly roll up into a pair of doubly connected spirals whose centers originate from approximately the center of gravity of vorticity in the upper quadrants of the ring wing's circular trailing edge. (This origin is at an angle of 38\u00b0 measured from the horizontal wing diameter.)\r\n\r\nThe experimental and flow visualization results are consistent with the numerical data and show that a pair of counter-rotating vortices do develop from the rolling up of the vortex sheet shed by a ring wing in a nonaxial flow. The vortices trail, downstream of the wing, with their vorticity centroids spaced by [...]/4 wing diameters.\r\n\r\nSaffman and Moore's theory of axial flow in laminar trailing vortices was adapted and found to be in reasonable agreement with the experimental results. The flow field near the trailing edge was found to be in fair agreement with Weissinger's inviscid calculations." }, { "name": "Bohn, Mark Stephen", "degree": "PhD", "year": "1976", "title": "Noise Produced by the Interaction of Acoustic Waves and Entropy Waves with High Speed Nozzle Flows", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10152012-130328218", "creators": [ { "name": { "family": "Bohn", "given": "Mark Stephen" }, "id": "Bohn-Mark-Stephen", "display_name": "Bohn, Mark Stephen" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ZP95-5T73", "abstract": "Some aspects of the noise generated internally by a turbojet\r\nengine are considered analytically and experimentally. The emphasis\r\nis placed on the interaction of pressure fluctuations and entropy fluctuations,\r\nproduced by the combustion process in the engine, with\r\ngradients in the mean flow through the turbine blades or the exhaust\r\nnozzle.
\r\n\r\nThe one-dimensional interaction of pressure fluctuations and\r\nentropy fluctuations with a subsonic nozzle is solved analytically. The\r\nacoustic waves produced by each of three independent disturbances\r\nare investigated. It is seen that results for a large number of physically\r\ninteresting nozzles may be presented in a concise manner.
\r\n\r\nSome of the second-order effects which result from the area\r\nvariations in a nozzle are investigated analytically. The interaction\r\nof an entropy wave with a small area variation is investigated and the\r\ntwo-dimensional duct modes, which propagate away from the nozzle,\r\nare calculated.
\r\n\r\nAn experiment is described in which one-dimensional acoustic\r\nwaves and entropy waves are made to interact with a subsonic nozzle.\r\nThe response of the nozzle to these disturbances is measured and\r\ncompared with the response as calculated by the analytical model.
\r\n\r\nThe interaction of two-dimensional entropy waves with a subsonic\r\nnozzle and with a supersonic nozzle is investigated experimentally.\r\nThe results are explained in terms of an analysis of the acoustic\r\nwaves and entropy waves produced by a region of arbitrary heat\r\naddition in a duct with flow.
\r\n\r\n" }, { "name": "Cantwell, Brian Joseph", "degree": "PhD", "year": "1976", "title": "A Flying Hot Wire Study of the Turbulent Near Wake of a Circular Cylinder at a Reynolds Number of 140,000", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-085806", "creators": [ { "name": { "family": "Cantwell", "given": "Brian Joseph" }, "id": "Cantwell-Brian-Joseph", "display_name": "Cantwell, Brian Joseph" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QKGW-CA84", "abstract": "An experiment was performed in the GALCIT 10-foot wind tunnel to study the flow in the near wake of a circular cylinder at a Reynolds number of 140,000.\r\n\r\nThe main objective of this investigation was to study the phenomenology of the processes of vortex formation and transport in the near wake, at a Reynolds number sufficiently high to insure a fully turbulent wake, but low enough to insure a laminar separation. The latter requirement anticipates the eventual use of the results as a test case for advanced calculation codes.\r\n\r\nMuch current experimental work on turbulent flows is concerned with large, coherent, organized vortex structures which have a relatively long lifetime and which account for much of the transport of mass, momentum and heat in turbulent shear flows. High Reynolds number flow past a cylinder is one case where such structures dominate.\r\n\r\nThe apparatus developed for measuring this flow consists of x-array hot wire probes mounted on the ends of a pair of whirling arms. In such a flow, where large changes in flow direction occur, a fixed hot wire would rectify the velocity signal and give ambiguous results. However, by applying a large enough bias velocity to the wires, the relative velocity vector can be maintained within the [+/-]30 degree range of sensitivity of the x-array. One useful property of this technique is that a rotation of the arms in a uniform flow applies a wide range of relative flow angles to the x-arrays, making them inherently self-calibrating in pitch.\r\n\r\nThe most important element of the instrumentation concomitant to the flying hot wire is a computer controlled data acquisition system which is slaved to the position of the rotating arm and which manages, monitors, edits and records the vast profusion of data which is continuously poured out by the device. A fast sensor responding to model surface pressure was used to generate a signal synchronized with the vortex-shedding process. This signal was recorded along with the hot wire data and used later to sort the data into populations having the same phase. Ensemble averages conditioned this way yield an average picture of the instantaneous flow field in which the vortices are frozen as they would be in a photograph.\r\n\r\nIn addition to the conventional velocity, pressure and stress data, results are presented which show the instantaneous (in the sense of an average at constant phase) velocity, intermittency, vorticity and stress fields as a function of phase for the first six diameters of the near wake.\r\n\r\nIn the present study, the Reynolds stresses are broken up into the contribution from large scale periodic motions and that from background or random turbulence, and, when dissected in this way, permit an enlightening look at the anatomy of this turbulent flow. Laid against the background of the instantaneous velocity, vorticity and intermittency, the stresses in the near wake emerge as a concatenation of peaks and valleys, some the result of strong induced motions in the outer flow which cause free stream fluid to move rapidly inward toward the center of the wake, others the result of the random motions of the background turbulence." }, { "name": "Cosner, Raymond Robert", "degree": "PhD", "year": "1976", "title": "Experiments on Thin Airfoils Spanning a Transonic Shear Flow", "advisor": "Zukoski, Edward E.; Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292006-134453", "creators": [ { "name": { "family": "Cosner", "given": "Raymond Robert" }, "id": "Cosner-Raymond-Robert", "display_name": "Cosner, Raymond Robert" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YJNQ-ZP43", "abstract": "A wind tunnel was built at the California Institute of Technology to provide two uniform coflowing streams at Mach numbers of 0.6 and l.4 with a plane mixing layer in between. Preliminary studies were made of this free shear layer, indicating a region of self-similar behavior and general agreement in growth rate with previous studies.\r\n\r\nA program of experimental and theoretical work was completed in which wedges were installed in the supersonic stream to create shock waves incident on the shear layer. Similar studies were performed with wedges in the subsonic stream. Good agreement was found between the analytic first-order theory and experiment in showing that the upstream propagation of pressure disturbances ahead of their source in the uniform subsonic stream is limited to about 0.6 subsonic layer thicknesses.\r\n\r\nThe problem of an airfoil in spanwise-varying transonic shear was studied experimentally with the goal of understanding the interactions in the shear region between the supersonic and subsonic streams, especially in terms of deviations from quasi-two-dimensional behavior. The effect of modest angle of attack was also examined." }, { "name": "Faisst, William Karl", "degree": "PhD", "year": "1976", "title": "Digested Sludge: Delineation and Modeling for Ocean Disposal", "advisor": "McKee, Jack E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04292014-113745649", "creators": [ { "name": { "family": "Faisst", "given": "William Karl" }, "id": "Faisst-William-Karl", "display_name": "Faisst, William Karl" } ], "advisors": [ { "name": { "family": "McKee", "given": "Jack E." }, "id": "McKee-J-E", "role": "advisor", "display_name": "McKee, Jack E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/j7nk-g480", "abstract": "Experimental work was performed to delineate the system of digested\r\nsludge particles and associated trace metals and also to measure the\r\ninteractions of sludge with seawater. Particle-size and particle number\r\ndistributions were measured with a Coulter Counter. Number\r\ncounts in excess of 1012 particles per liter were found in both the City\r\nof Los Angeles Hyperion mesophilic digested sludge and the Los Angeles\r\nCounty Sanitation Districts (LACSD) digested primary sludge. More than\r\n90 percent of the particles had diameters less than 10 microns.
\r\n\r\nTotal and dissolved trace metals (Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb,\r\nand Zn) were measured in LACSD sludge. Manganese was the only metal\r\nwhose dissolved fraction exceeded one percent of the total metal.\r\nSedimentation experiments for several dilutions of LACSD sludge in seawater\r\nshowed that the sedimentation velocities of the sludge particles\r\ndecreased as the dilution factor increased. A tenfold increase in\r\ndilution shifted the sedimentation velocity distribution by an order\r\nof magnitude. Chromium, Cu, Fe, Ni, Pb, and Zn were also followed\r\nduring sedimentation. To a first approximation these metals behaved\r\nlike the particles.
\r\n\r\nSolids and selected trace metals (Cr, Cu, Fe, Ni, Pb, and Zn)\r\nwere monitored in oxic mixtures of both Hyperion and LACSD sludges for\r\nperiods of 10 to 28 days. Less than 10 percent of the filterable\r\nsolids dissolved or were oxidized. Only Ni was mobilized away from\r\nthe particles. The majority of the mobilization was complete in less\r\nthan one day.
\r\n\r\nThe experimental data of this work were combined with oceanographic,\r\nbiological, and geochemical information to propose and model the\r\ndischarge of digested sludge to the San Pedro and Santa Monica Basins.\r\nA hydraulic computer simulation for a round buoyant jet in a density\r\nstratified medium showed that discharges of sludge effluent mixture\r\nat depths of 730 m would rise no more than 120 m. Initial jet mixing\r\nprovided dilution estimates of 450 to 2600. Sedimentation analyses\r\nindicated that the solids would reach the sediments within 10 km of\r\nthe point discharge.
\r\n\r\nMass balances on the oxidizable chemical constituents in sludge\r\nindicated that the nearly anoxic waters of the basins would become wholly\r\nanoxic as a result of proposed discharges. From chemical-equilibrium\r\ncomputer modeling of the sludge digester and dilutions of sludge in\r\nanoxic seawater, it was predicted that the chemistry of all trace\r\nmetals except Cr and Mn will be controlled by the precipitation of metal\r\nsulfide solids. This metal speciation held for dilutions up to\r\n3000.
\r\n\r\nThe net environmental impacts of this scheme should be salutary.\r\nThe trace metals in the sludge should be immobilized in the anaerobic\r\nbottom sediments of the basins. Apparently no lifeforms higher than\r\nbacteria are there to be disrupted. The proposed deep-water discharges\r\nwould remove the need for potentially expensive and energy-intensive\r\nland disposal alternatives and would end the discharge to the highly\r\nproductive water near the ocean surface.
\r\n" }, { "name": "Gover, Avraham", "degree": "PhD", "year": "1976", "title": "Wave Interactions in Periodic Structures and Periodic Dielectric Waveguides", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-155953992", "creators": [ { "name": { "family": "Gover", "given": "Avraham" }, "id": "Gover-Avraham", "display_name": "Gover, Avraham" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Pierce", "given": "John" }, "id": "Pierce-J", "role": "chair", "display_name": "Pierce, John" }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "member", "display_name": "Yariv, Amnon" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/V0RY-GY17", "abstract": "This work is concerned with a general analysis of wave interactions\r\nin periodic structures and particularly periodic thin film\r\ndielectric waveguides.
\r\n\r\nThe electromagnetic wave propagation in an asymmetric dielectric\r\nwaveguide with a periodically perturbed surface is analyzed in\r\nterms of a Floquet mode solution. First order approximate analytical\r\nexpressions for the space harmonics are obtained. The solution is\r\nused to analyze various applications: (1) phase matched second harmonic\r\ngeneration in periodically perturbed optical waveguides;\r\n(2) grating couplers and thin film filters; (3) Bragg reflection devices;\r\n(4) the calculation of the traveling wave interaction impedance\r\nfor solid state and vacuum tube optical traveling wave amplifiers\r\nwhich utilize periodic dielectric waveguides. Some of these applications\r\nare of interest in the field of integrated optics.
\r\n\r\nA special emphasis is put on the analysis of traveling wave\r\ninteraction between electrons and electromagnetic waves in various\r\noperation regimes. Interactions with a finite temperature electron\r\nbeam at the collision-dominated, collisionless, and quantum regimes\r\nare analyzed in detail assuming a one-dimensional model and longitudinal\r\ncoupling.
\r\n\r\nThe analysis is used to examine the possibility of solid state\r\ntraveling wave devices (amplifiers, modulators), and some monolithic\r\nstructures of these devices are suggested, designed to operate at the\r\nsubmillimeter-far infrared frequency regime. The estimates of\r\nattainable traveling wave interaction gain are quite low (on the order\r\nof a few inverse centimeters). However, the possibility of attaining\r\nnet gain with different materials, structures and operation condition\r\nis not ruled out.
\r\n\r\nThe developed model is used to discuss the possibility and\r\nthe theoretical limitations of high frequency (optical) operation of\r\nvacuum electron beam tube; and the relation to other electron-electromagnetic\r\nwave interaction effects (Smith-Purcell and Cerenkov\r\nradiation and the free electron laser) are pointed out. Finally, the\r\ncase where the periodic structure is the natural crystal lattice is\r\nbriefly discussed. The longitudinal component of optical space harmonics\r\nin the crystal is calculated and found to be of the order of\r\nmagnitude of the macroscopic wave, and some comments are made on the\r\npossibility of coherent bremsstrahlung and distributed feedback\r\nlasers in single crystals.
" }, { "name": "Harris, Joe Marion, Jr.", "degree": "PhD", "year": "1976", "title": "Part I. Energy Straggling of \u2074He below 2.0 MeV in Al, Ni, Au, and Pt. Part II. Studies of the Ti-W Metallization System on Si", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-102340032", "creators": [ { "name": { "family": "Harris", "given": "Joe Marion, Jr." }, "id": "Harris-Joe-Marion", "display_name": "Harris, Joe Marion, Jr." } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/C4FY-ZX66", "abstract": "Part I.
\r\n\r\nIn recent years, backscattering spectrometry has become an important\r\ntool for the analysis of thin films. An inherent limitation,\r\nthough, is the loss of depth resolution due to energy straggling of\r\nthe beam. To investigate this, energy straggling of 4He has been\r\nmeasured in thin films of Ni, Al, Au and Pt. Straggling is roughly\r\nproportional to square root of thickness, appears to have a slight\r\nenergy dependence and generally decreases with decreasing atomic\r\nnumber of the adsorber. The results are compared with predictions\r\nof theory and with previous measurements. While Ni measurements are\r\nin fair agreement with Bohr's theory, Al measurements are 30% above\r\nand Au measurements are 40% below predicted values. The Au and Pt\r\nmeasurements give straggling values which are close to one another.
\r\n\r\nPart II.
\r\n\r\nMeV backscattering spectrometry and X-ray diffraction are used to\r\ninvestigate the behavior of sputter-deposited Ti-W mixed films on Si\r\nsubstrates. During vacuum anneals at temperatures near 700\u00b0C for several\r\nhours, the metallization layer reacts with the substrate. Backscattering\r\nanalysis shows that the resulting compound layer is uniform in composition\r\nand contains Ti, Wand Si. The Ti:W ratio in the compound corresponds\r\nto that of the deposited metal film. X-ray analyses with\r\nReed and Guinier cameras reveal the presence of the ternary TixW(1-x)Si2\r\ncompound. Its composition is unaffected by oxygen contamination during\r\nannealing, but the reaction rate is affected. The rate measured on\r\nsamples with about 15% oxygen contamination after annealing is linear, of\r\nthe order of 0.5 \u00c5 per second at 725\u00b0C, and depends on the crystallographic\r\norientation of the substrate and the dc bias during sputter-deposition\r\nof the Ti-W film.
\r\n\r\nAu layers of about 1000 \u00c5 thickness were deposited onto unreacted\r\nTi-W films on Si. When annealed at 400\u00b0C these samples\r\nunderwent a color change,and SEM micrographs of the samples showed\r\nthat an intricate pattern of fissures which were typically 3\u00b5m wide\r\nhad evolved. Analysis by electron microprobe revealed that Au had\r\nsegregated preferentially into the fissures. This result suggests\r\nthat Ti-W is not a barrier to Au-Si intermixing at 400\u00b0C.
" }, { "name": "Hartmann, Alfred C.", "degree": "PhD", "year": "1976", "title": "A Concurrent Pascal Compiler for Minicomputers", "advisor": "Brinch Hansen, Per", "url": "https://resolver.caltech.edu/CaltechTHESIS:01122026-230457533", "creators": [ { "name": { "family": "Hartmann", "given": "Alfred C." }, "id": "Hartmann-Alfred-C.", "display_name": "Hartmann, Alfred C." } ], "advisors": [ { "name": { "family": "Brinch Hansen", "given": "Per" }, "id": "Brinch-Hansen-Per", "role": "advisor", "display_name": "Brinch Hansen, Per" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/27wt-jc79", "abstract": "This paper describes a seven-pass compiler for the\r\nConcurrent Pascal programming language. Concurrent Pascal\r\nis an abstract programming language for computer operating\r\nsystems. The language extends sequential Pascal with the\r\nmonitor concept for structured concurrent programming.\r\nCompilation of Concurrent Pascal on a minicomputer is done\r\nby dividing the compiler into seven sequential passes. The\r\npasses, written in sequential Pascal, generate virtual code\r\nthat can be interpreted on any 16-bit minicomputer. It has\r\nbeen running on a PDP-11/45 computer at Caltech since\r\nJanuary 1975." }, { "name": "Jackson, George Anthony", "degree": "PhD", "year": "1976", "title": "Nutrients and Productivity of the Giant Kelp, Macrocystis Pyrifera, in the Nearshore", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:02172017-101827008", "creators": [ { "name": { "family": "Jackson", "given": "George Anthony" }, "id": "Jackson-George-Anthony", "display_name": "Jackson, George Anthony" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/j42e-c605", "abstract": "The growth of giant kelp, Macrocystis pyrifera was\r\nstudied by field measurements of nutrients and other water\r\nparameters. Gross primary production of the kelp bed at\r\nPoint Loma, California was calculated at 1.5 moles-O2/m2-day\r\nor 14.6 g-C/m2-day. This represents one of the highest\r\nmeasured values of gross primary production. A rate of\r\nproduction twice as high might be attained under optimal\r\nconditions.
\r\n\r\nThe condition most limiting Macrocystis production was\r\nthe low concentration of dissolved nutrients, especially\r\nnitrogenous substances, near the surface. Kelp compensated\r\nfor this limitation by translocating nitrogenous compounds\r\nfrom depths where nutrient concentrations were higher.\r\nSummer dieoff of the surface canopy may be caused by\r\ninability of plants to translocate nutrients due to low\r\navailability of nutrients in deeper water.
\r\n\r\nNutrient concentrations varied seasonally. Surface\r\nnitrate concentrations were low for most of the year\r\n(usually less than 1 \u03bcM), higher during the winter. Nitrate\r\nconcentrations at 6 and 9 meters depth usually exceeded\r\n1 \u03bcM. They were highest during spring upwelling months,\r\nlowest during summer months.
\r\n\r\nNutrient concentrations in the kelp bed were not\r\ndepleted by the kelp or enhanced by sediment nutrient\r\nregeneration, implying relatively fast exchange of water in\r\nthe bed with outside waters.
\r\n\r\nNutrient concentrations varied at different longshore\r\nlocations. Surface nitrate concentrations were more likely\r\nto be higher near the tip of Point Loma than 5 kilometers\r\nfarther north. Localized upwelling caused this.
\r\n\r\nIn the shallow nearshore (depth<5 meters) the nutrient\r\nconcentrations were higher than those in the kelp bed at\r\ncomparable depths. The cause remains unknown.
" }, { "name": "Jensen, Arthur R.", "degree": "PhD", "year": "1976", "title": "Computer Simulation of Surface Water Hydrology and Salinity with an Application to Studies of Colorado River Management", "advisor": "List, E. John; Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01152026-221251934", "creators": [ { "name": { "family": "Jensen", "given": "Arthur R." }, "id": "Jensen-Arthur-R", "display_name": "Jensen, Arthur R." } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "co-advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/jmm5-0x29", "abstract": "Management of a large river basin requires information regarding the\r\ninteractions of variables describing the system. A method has been\r\ndeveloped to determine these interactions so that the resources management\r\nwithin a given river basin can proceed in an optimal way. The\r\nmethod can be used as a planning tool to display how different management\r\nalternatives affect the behavior of the river system. Direct\r\napplication is made to the Colorado River Basin.
\r\n\r\nThe Colorado River has a relatively low and highly variable streamflow.\r\nAllocated rights to the consumptive use of the river water exceed\r\nthe present long-term average flow. The naturally high total dissolved\r\nsolids concentration of the river water continues to increase due to the\r\nactivities of man. Current management policies in the basin have been\r\nthe products of compromises between the seven states and two countries\r\nwhich are traversed by the river or its tributaries. The anticipated\r\nuse of the scarce supply of water in the extraction and processing of\r\nenergy resources in the basin underwrites the need for planning tools\r\nwhich can illuminate many possible management alternatives and their\r\neffects upon water supply, water quality, power production, and the\r\nother concerns of the Colorado River water users.
\r\n\r\nA computer simulation model has been developed and used to simulate\r\nthe effects of various management alternatives upon water conservation,\r\nwater quality, and power production. The model generates synthetic\r\nsequences of streamflows and total dissolved solids (TDS) concentrations.\r\nThe flows of water and TDS are then routed through the major reservoirs\r\nof the system, Lakes Powell and Mead.
\r\n\r\nCharacteristics of system behavior are examined from simulations\r\nusing different streamflow sequences, upstream depletion levels, and\r\nreservoir operating policies. Reservoir evaporation, discharge, discharge\r\nsalinity, and power generating capacity are examined.
\r\n\r\nSimulation outputs show that the probability with which Lake Powell\r\nfails to supply a specified target discharge is highly variable. Simulations\r\nemploying different streamflow sequences result in probabilities\r\nof reservoir failure which differ by as much as 0.1.
\r\n\r\nThree levels of Upper Colorado River Basin demands are imposed on\r\nthe model: 3.8 MAF/yr (4.7 km3 /yr), 4.6 MAF/yr (5.7 km3/yr), and 5.5\r\nMAF/yr (6.8 km3/yr). Two levels of water demand are imposed below\r\nLake Mead: 8.25 MAF/yr (10.2 km3/yr) and 7.0 MAF/yr (6.8 km3/yr).
\r\n\r\nAlthough the effects of reservoir operations upon water quality\r\nare made uncertain by a lack of knowledge regarding the chemical\r\nlimnology of Lake Powell, two possible lake chemistry models have been\r\ndeveloped, and the predicted impacts of changes in reservoir operation\r\nupon water quality are presented.
\r\n\r\nThe current criteria for the operations of Lakes Powell and Mead\r\nare based upon 75 years of compromises and agreements between the various\r\nwater interests in the Colorado River Basin. Simulations show that\r\nLake Powell will be unable to conform to these operating constraints\r\nat the higher levels of water demand.
\r\n\r\nAn alternative form of reservoir operation is defined and compared\r\nto the existing policy on the basis of reliability of water supply, conservation\r\nof water, impact upon water quality, and the effect upon power\r\ngeneration.
\r\n\r\nIgnoring the current institutional operating constraints, and\r\nattempting only to provide a reliable supply of water at the locations\r\nof water demand, is shown to be a superior management policy. This\r\nalternate policy results in the conservation of as much as 0.25 MAF/yr\r\n(0.3 km3/yr) of water. The impact of the alternate operating policy\r\nupon hydroelectric power generation and the potential use of the conserved\r\nwater for development of energy resources is discussed.
" }, { "name": "Lau, Kei-Fung", "degree": "PhD", "year": "1976", "title": "Pulse NMR in Solids: Chemical Shift, Lead Fluoride and Thorium Hydride", "advisor": "Vaughan, Robert W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-132542120", "creators": [ { "name": { "family": "Lau", "given": "Kei-Fung" }, "id": "Lau-Kei-Fung", "display_name": "Lau, Kei-Fung" } ], "advisors": [ { "name": { "family": "Vaughan", "given": "Robert W." }, "id": "Vaughan-R-W", "role": "advisor", "display_name": "Vaughan, Robert W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/FP5F-FD33", "abstract": "Part one of this thesis consists of two sections. In the first\r\nsection the fluorine chemical shift of a single crystal CaF_2 has been\r\nmeasured as a function of external pressure up to 4 kilobar at room\r\ntemperature using multiple pulse NMR techniques. The pressure dependence\r\nof the shift is found to be -1.7 \u00b1 1 ppm/kbar, while a\r\ntheoretical calculation using an overlap model predicts a shift of\r\n-0.46 ppm/kbar. In the second section a separation of the chemical\r\nshift tensor into physically meaningful \"geometrical\" and \"chemical\"\r\ncontributions is presented and a comparison of the proposed model\r\ncalculations with recently reported data on hydroxyl proton chemical\r\nshift tensors demonstrates, that for this system, the geometrical\r\nportion accounts for the qualitative features of the measured tensors.
\r\n\r\nPart two of the thesis consists of a study of fluoride ion motion\r\nin \u03b2-PbF_2 doped with NaF by measurement of the ^(19)F transverse\r\nrelaxation time (T_2), spin lattice relaxation time (T_1) and the spin\r\nlattice relaxation time in the rotating frame (T_(1r)). Measurements\r\nover the temperature range of -50\u00b0C to 160\u00b0C lead to activation\r\nenergies for T_1, T_(1r) and T_2 of 0.205 \u00b1 0.01, 0.29 + 0.02 and 0.27 \u00b1\r\n0.01 ev/ion, and a T_(1r) minimum at 56\u00b0C yields a correlation time of\r\n0.74 \u03bcsec. Pressure dependence of T_1 and T_2 yields activation volumes\r\nof <0.2 cm^3/g-mole and 1.76 \u00b1 0.05 cm^3/g-mole respectively. These\r\ndata along with the measured magnetic field independence of T_1\r\nsuggest that the measured T_1's are not caused by ^(19)F motion, but by\r\nthermally excited carriers.
\r\n\r\nPart three of the thesis consists of a study of two samples of\r\nTh_4H_(15), prepared under different conditions but both having the proper\r\nratio of H/Th (to within 1%). The structure of the Th_4H_(15) as suggested\r\nby X-ray measurements is confirmed through a moment analysis of the\r\nrigid lattice line shape. T_1 and T_2 measurements above 390 K furnish\r\nactivation energies of 16.3 \u00b1 1.2 kcal/mole and 18.0 \u00b1 3.0 kcal/mole,\r\nrespectively. Below 350 K, T_(1r) measurements furnish an activation\r\nenergy of 10.9 \u00b1 0.7 kcal/mole, indicating most probably more than a\r\nsingle mechanism for proton motion. A time-temperature hysteresis\r\neffect of the proton motion was found in one of the two samples and is\r\nstrongly indicative of a phase change. T_1 at room temperature and\r\nbelow is dominated by relaxation due to conduction electrons with the\r\nproduct T_1T being 180 \u00b1 10 K-sec. Using multiple pulse techniques to\r\ngreatly reduce homonuclear dipolar broadening, a temperature-dependent\r\nline shift was observed, and the chemical shift anisotropy is estimated\r\nto be less than 16 ppm.
\r\n" }, { "name": "Marmarelis, Vasilis Zissis", "degree": "PhD", "year": "1976", "title": "Identification of Nonlinear Systems through Quasi-White Test Signals", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:01142026-194640712", "creators": [ { "name": { "family": "Marmarelis", "given": "Vasilis Zissis" }, "id": "Marmarelis-Vasilis-Zissis", "orcid": "0000-0003-1457-813X", "display_name": "Marmarelis, Vasilis Zissis" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/tqrq-3b96", "abstract": "The use of quasi-white test signals, i.e. physically realizable\r\nsignals that approximate the statistical properties of ideal white\r\nnoise, in nonlinear system identification through the crosscorrelation\r\ntechnique is comprehensively studied. Important theoretical aspects\r\nof the subject are illustrated (e. g. the mathematical mechanisms of\r\nkernel estimation through crosscorrelation, the role of the several\r\northogonal functional series, the meaning of the corresponding kernels,\r\nthe accuracy of the obtained truncated models etc.), and useful tools\r\nfor the actual application of the method are developed (e.g. analytical\r\nexpressions for the kernel estimation errors, optimum test procedure\r\netc.).
\r\n\r\nIn addition to the widely known and used band-limited gaussian\r\nwhite noise and pseudorandom signals based on m-sequences, a\r\nnew family of quasi-white test signals is introduced and its properties\r\nare thoroughly studied. The various advantages and disadvantages of\r\nthese three families of quasi-white signals are discussed independently\r\nas well as in a comparative perspective. The accuracy of the several\r\nestimated models is found to be comparable for all these families of\r\nquasi-white signals, with small differences pertaining to the specific\r\nsystem under study or random factors. The theoretical study is\r\nfollowed and confirmed by actual applications on computer simulated\r\nand physiological systems.
\r\n\r\nThe newly introduced family is simplifying, clarifying and\r\nunifying the concept of the quasi-white signal in connection with its use\r\nin the crosscorrelation technique.
\r\n\r\nSome special purpose tests are also presented, with one of\r\nthem (the \"general nonlinearity test\") possessing the potentiality of a\r\ntotally different identification method aiming at the Volterra kernels of\r\nthe system.
" }, { "name": "Miklovic, Donald W.", "degree": "PhD", "year": "1976", "title": "Topics in Linear and Nonlinear Dispersive Waves", "advisor": "Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechTHESIS:03292013-083637190", "creators": [ { "name": { "family": "Miklovic", "given": "Donald W." }, "id": "Miklovic-Donald-W", "display_name": "Miklovic, Donald W." } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/KPRH-JK65", "abstract": "The various singularities and instabilities which arise in the modulation theory of dispersive wavetrains are studied. Primary interest is in the theory of nonlinear waves, but a study of associated questions in linear theory provides background information and is of independent\r\ninterest.
\r\n\r\nThe full modulation theory is developed in general terms.\r\nIn the first approximation for slow modulations, the modulation equations are solved. In both the linear and nonlinear theories, singularities and regions of multivalued modulations are predicted. Higher order effects\r\nare considered to evaluate this first order theory. An improved approximation is presented which gives the true behavior in the singular regions. For the linear case, the end result can be interpreted as the overlap of elementary wavetrains. In the nonlinear case, it is found that a sufficiently strong nonlinearity prevents this overlap. Transition zones with a predictable structure replace the singular regions.
\r\n\r\nFor linear problems, exact solutions are found by Fourier\r\nintegrals and other superposition techniques. These show the true behavior when breaking modulations are predicted.
\r\n\r\nA numerical study is made for the anharmonic lattice to\r\nassess the nonlinear theory. This confirms the theoretical predictions of nonlinear group velocities, group splitting, and wavetrain instability, as well as higher order effects in the singular regions.
\r\n" }, { "name": "Miller, Richard Keith", "degree": "PhD", "year": "1976", "title": "The Steady-State Response of Multidegree-of-Freedom Systems with a Spatially Localized Nonlinearity", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03052014-104111406", "creators": [ { "name": { "family": "Miller", "given": "Richard Keith" }, "id": "Miller-Richard-Keith", "display_name": "Miller, Richard Keith" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/M5NW-Z443", "abstract": "This thesis is concerned with the dynamic response of a\r\nGeneral multidegree-of-freedom linear system with a one dimensional nonlinear constraint attached between two points. The nonlinear constraint is assumed to consist of rate-independent conservative and hysteretic nonlinearities and may contain a viscous dissipation element. The dynamic equations for general spatial and temporal load distributions are derived for both continuous and\r\ndiscrete systems. The method of equivalent linearization is used to develop equations which govern the approximate steady-state response to generally distributed loads with harmonic time dependence.
\r\n\r\nThe qualitative response behavior of a class of undamped\r\nchainlike structures with a nonlinear terminal constraint is\r\ninvestigated. It is shown that the hardening or softening behavior of every resonance curve is similar and is determined by the properties of the constraint. Also examined are the number and location of resonance curves, the boundedness of the forced response, the loci of response extrema, and other characteristics\r\nof the response. Particular consideration is given to the\r\ndependence of the response characteristics on the properties of the linear system, the nonlinear constraint, and the load distribution.
\r\n\r\nNumerical examples of the approximate steady-state response of three structural systems are presented. These examples illustrate the application of the formulation and qualitative theory. It is shown that disconnected response curves and response curves which cross are obtained for base excitation of a uniform shear beam with a cubic spring foundation. Disconnected response curves are also obtained for the steady-state response to a concentrated\r\nload of a chainlike structure with a hardening hysteretic constraint. The accuracy of the approximate response curves is investigated.
\r\n" }, { "name": "Minzoni Alessio, Antonmaria", "degree": "PhD", "year": "1976", "title": "Some Problems of Edge Waves and Standing Waves on Beaches", "advisor": "Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechTHESIS:03252013-104029711", "creators": [ { "name": { "family": "Minzoni Alessio", "given": "Antonmaria" }, "id": "Minzoni-Alessio-Antonmaria", "display_name": "Minzoni Alessio, Antonmaria" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/jyc7-f650", "abstract": "Some problems of edge waves and standing waves on beaches\r\nare examined.
\r\n\r\nThe nonlinear interaction of a wave normally incident on a\r\nsloping beach with a subharmonic edge wave is studied. A two-timing\r\nexpansion is used in the full nonlinear theory to obtain the\r\nmodulation equations which describe the evolution of the waves. It is\r\nshown how large amplitude edge waves are produced; and the results\r\nof the theory are compared with some recent laboratory experiments.
\r\n\r\nTraveling edge waves are considered in two situations. First,\r\nthe full linear theory is examined to find the finite depth effect on the\r\nedge waves produced by a moving pressure disturbance. In the second\r\nsituation, a Stokes' expansion is used to discuss the nonlinear effects\r\nin shallow water edge waves traveling over a bottom of arbitrary\r\nshape. The results are compared with the ones of the full\r\ntheory for a uniformly sloping bottom.
\r\n\r\nThe finite amplitude effects for waves incident on a sloping\r\nbeach, with perfect reflection, are considered. A Stokes' expansion\r\nis used in the full nonlinear theory to find the corrections to the dispersion\r\nrelation for the cases of normal and oblique incidence.
\r\n\r\nFinally, an abstract formulation of the linear water waves\r\nproblem is given in terms of a self adjoint but nonlocal operator. The\r\nappropriate spectral representations are developed for two particular\r\ncases.
\r\n" }, { "name": "Moyls, Adrian Leigh", "degree": "PhD", "year": "1976", "title": "Friction and Heat Transfer Reduction in Turbulent Flow of Dilute Asbestos Fiber Suspensions in Smooth and Rough Tubes", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02022017-132608721", "creators": [ { "name": { "family": "Moyls", "given": "Adrian Leigh" }, "id": "Moyls-Adrian-Leigh", "display_name": "Moyls, Adrian Leigh" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/2395-4706", "abstract": "Friction and heat transfer coefficients were obtained in turbulent\r\nflow of dilute asbestos fiber suspensions through a smooth and a\r\nrough tube. The 3/8 inch nickel tubes were heated electrically. Suspensions\r\nof 50,300 and 600 ppm asbestos fibers were used at Prandtl\r\nnumbers of approximately 2, 6 and 11. These were obtained by varying\r\nthe bulk temperature of the suspension. The surface of the rough tube\r\nconsisted of a close-packed, granular type of roughness with a height-to-diameter \r\nratio of 0.488. The Reynolds number range studies varied\r\nfrom 10,000 (Pr = 11) to 500,000 (Pr = 2).
\r\n\r\nMaximum friction reductions of 76% in the smooth tube and 87%\r\nin the rough tube were observed, along with even greater reductions in\r\nheat transfer rates, namely 86% in the smooth tube and 95% in the rough\r\ntube. (Heat transfer coefficients with asbestos fibers can be lower in a\r\nrough tube than in a smooth tube.) In the present series of experiments\r\nthe mechanism by which the fibers interfere with the flow lost its effectiveness\r\nat high Reynolds numbers.
\r\n\r\nThe data was analyzed in light of analyses developed previously\r\nfor Newtonian fluids and extended to dilute fiber suspensions. The results\r\nindicate that the turbulent diffusivities are reduced in the wall region\r\nand bring about a thicker viscous layer.
\r\n\r\nThe most plausible mechanism which may explain the action of\r\nthe fibers envisions interference of the fibers with the so-called \"bursts\"\r\nwhich are known to originate in the viscous layer.
" }, { "name": "Naheer, Ehud", "degree": "PhD", "year": "1976", "title": "Stability of Bottom Armoring Under the Attack of Solitary Waves", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechTHESIS:02232017-105808087", "creators": [ { "name": { "family": "Naheer", "given": "Ehud" }, "id": "Naheer-Ehud", "display_name": "Naheer, Ehud" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/TMPB-2078", "abstract": "An empirical relationship is presented for the incipient motion\r\nof bottom material under solitary waves. Two special cases\r\nof bottom material are considered: particles of arbitrary shape,\r\nand isolated sphere resting on top of a bed of tightly packed\r\nspheres.
\r\n\r\nThe amount of motion in the bed of particles of arbitrary shape is\r\nshown to depend on a dimensionless shear stress, similar to the Shields\r\nparameter. The mean resistance coefficient used in estimating this\r\nparameter is derived from considerations of energy dissipation, and is\r\nobtained from measurements of the attenuation of waves along a channel. A\r\ntheoretical expression for the mean resistance coefficient is developed\r\nfor the case of laminar flow from the linearized boundary layer equations\r\nand is verified by experiments.
\r\n\r\nFor the case of a single sphere resting on top of a bed of spheres,\r\nthe analysis is based on the hypothesis that at incipient motion the\r\nhydrodynamic moments which tend to remove the sphere are equal to the\r\nrestoring moment due to gravity which tends to keep it in its place. It\r\nis shown that the estimation of the hydrodynamic forces, based on an\r\napproach similar to the so-called \"Morison's formula\", in which the drag,\r\nlift, and inertia coefficients are independent of each other, is inaccurate.\r\nAlternatively, a single coefficient incorporating both drag,\r\ninertia, and lift effects is employed. Approximate values of this coefficient\r\nare described by an empirical relationship which is obtained\r\nfrom the experimental results.
\r\n\r\nA review of existing theories of the solitary wave is presented and\r\nan experimental study is conducted in order to determine which theory\r\nshould be used in the theoretical analysis of the incipient motion of\r\nbottom material.
\r\n\r\nExperiments were conducted in the laboratory in order to determine\r\nthe mean resistance coefficient of the bottom under solitary waves, and\r\nin order to obtain a relationship defining the incipient motion of\r\nbottom material. All the experiments were conducted in a wave tank\r\n40 m long, 110 cm wide with water depths varying from 7 cm to 42 cm.\r\nThe mean resistance coefficient was obtained from measurements of the\r\nattenuation of waves along an 18 m section of the wave tank. Experiments\r\nwere conducted with a smooth bottom and with the bottom roughened with\r\na layer of rock. The incipient motion of particles of arbitrary shape\r\nwas studied by measuring the amount of motion in a 91 cm x 50 cm section\r\ncovered with a 15.9 mm thick layer of material. The materials used had\r\ndifferent densities and mean diameters. The incipient motion of spheres\r\nwas observed for spheres of different diameters and densities placed on\r\na bed of tightly packed spheres. The experiments were conducted with\r\nvarious water depths, and with wave height-to-water depth ratios varying\r\nfrom small values up to that for breaking of the wave.
\r\n\r\nIt was found that: (a) The theories of Boussinesq (1872) and McCowan\r\n(1891) describe the solitary wave fairly accurately. However, the\r\ndifferences between these theories are large when used to predict the forces\r\nwhich are exerted on objects on the bottom, and it was not established which\r\ntheory describes these forces better. (b) The mean resistance coefficient\r\nfor a rough turbulent flow under solitary waves can be described as\r\na function of Ds, h, and H, where Ds is the mean diameter of the\r\nroughness particles, h is the water depth, and H is the wave height.\r\n(c) Small errors in the determination of the dimensionless shear stress\r\nfor incipient motion of rocks result in large errors in the evaluation\r\nof the diameter of the rock required for incipient motion. However, it\r\nwas found that the empirical relationship for the incipient motion of\r\nspheres can be used to determine the size of rock of arbitrary shape for\r\nincipient motion under a given wave, provided the angle of friction of\r\nthe rock can be determined accurately.
\r\n\r\n" }, { "name": "Ng, Sheung-Lip", "degree": "PhD", "year": "1976", "title": "The Dynamic Response of Cavitating Turbomachines", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272003-122146", "creators": [ { "name": { "family": "Ng", "given": "Sheung-Lip" }, "id": "Ng-Sheung-Lip", "display_name": "Ng, Sheung-Lip" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/KC09-P112", "abstract": "Stimulated by the pogo instability encountered in many liquid propellant rockets, the dynamic behavior of cavitating inducers is the subject of the present thesis. An experimental facility where the upstream and downstream flows of a cavitating inducer could be perturbed was constructed and tested. The upstream and downstream pressure and mass flow fluctuations were measured. Matrices representing the transfer functions across the inducer pump were calculated from these measurements and from the hydraulic system characteristics for two impellers in various states of cavitation. The transfer matrices when plotted against the perturbing frequency showed significant departure from steady state or quasi-steady predictions especially at higher frequencies." }, { "name": "Packard, Dennis John", "degree": "PhD", "year": "1976", "title": "Discrete Modeling and Analysis of Switching Regulators", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082008-110208", "creators": [ { "name": { "family": "Packard", "given": "Dennis John" }, "id": "Packard-Dennis-John", "display_name": "Packard, Dennis John" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/VR66-DX76", "abstract": "A simplified method for finding and using discrete small-signal models for switching regulators is presented. With introduction of a new \"straight-line\" approximation, and application of root locus techniques, it is demonstrated that discrete models may be used accurately to predict wide bandwidth closed-loop behavior with methods simple enough to be useful in the initial design phase of a switching regulator. The principal result is a set of converter transfer functions comparable to the set derived by describing function techniques, but not subject to the low frequency restriction of describing function models. Also presented is a set of pulse-width modulator transfer functions which indicates that the potential small-signal transient behavior of a switching regulator is independent of the choice of modulator." }, { "name": "Pearce, James Charles", "degree": "PhD", "year": "1976", "title": "Mechanics of Flowing Granular Media", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04072017-102157703", "creators": [ { "name": { "family": "Pearce", "given": "James Charles" }, "id": "Pearce-James-Charles", "display_name": "Pearce, James Charles" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/46HR-Q850", "abstract": "The flow of a frictional, cohesive solid through plane converging \r\nchannels with Coulomb friction acting along the channel walls is\r\ninvestigated. The constitutive postulates used in the development of\r\nthe solution are discussed and the solution is compared with those obtained\r\nby earlier investigators. Velocity profiles, mass flow rates,\r\nand mean stress distributions along the channel walls predicted by the\r\nanalysis are compared with experimental results. The solution correctly \r\npredicts the trend of the mass flow rate as a function of the\r\nchannel opening angle as well as the magnitude of the mass flow rate in\r\nterms of the flow parameters. The solution also gives an accurate\r\nmeasure of the mean stress acting along the channel walls.
\r\n\r\n\r\nThe problem of predicting the size of the cavity formed below\r\na cylinder in the transverse flow of a frictional, cohesionless material\r\nis investigated experimentally. A correlation which gives the lower\r\nseparation angle as a function of the flow parameters is determined.
\r\n\r\n\r\nFinally, the temperature distribution in the wake of a heated\r\ncylinder in the transverse flow of a granular material is investigated\r\nexperimentally and spanwise temperature profiles are given as a\r\nfunction of downstream location.
\r\n\r\n\r\nThe information gained from the experimental investigation is\r\nintended to be of use in the design of heat exchanger equipment for\r\ngranular media.
" }, { "name": "Ramer, O. Glenn", "degree": "PhD", "year": "1976", "title": "Surface Effects on Spinwave Resonance in Thin Magnetic Films", "advisor": "Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212014-110016606", "creators": [ { "name": { "family": "Ramer", "given": "O. Glenn" }, "id": "Ramer-O-G", "display_name": "Ramer, O. Glenn" } ], "advisors": [ { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/PKCX-X329", "abstract": "Over the past few decades, ferromagnetic spinwave resonance in\r\nmagnetic thin films has been used as a tool for studying the properties\r\nof magnetic materials. A full understanding of the boundary conditions\r\nat the surface of the magnetic material is extremely important. Such\r\nan understanding has been the general objective of this thesis. The\r\napproach has been to investigate various hypotheses of the surface condition\r\nand to compare the results of these models with experimental\r\ndata. The conclusion is that the boundary conditions are largely due\r\nto thin surface regions with magnetic properties different from the bulk.\r\nIn the calculations these regions were usually approximated by uniform\r\nsurface layers; the spins were otherwise unconstrained except by the\r\nsame mechanisms that exist in the bulk (i.e., no special \"pinning\" at\r\nthe surface atomic layer is assumed). The variation of the ferromagnetic\r\nspinwave resonance spectra in YIG films with frequency, temperature,\r\nannealing, and orientation of applied field provided an\r\nexcellent experimental basis for the study.
\r\n\r\nThis thesis can be divided into two parts. The first part is\r\nferromagnetic resonance theory; the second part is the comparison of\r\ncalculated with experimental data in YIG films. Both are essential\r\nin understanding the conclusion that surface regions with properties\r\ndifferent from the bulk are responsible for the resonance phenomena\r\nassociated with boundary conditions.
\r\n\r\nThe theoretical calculations have been made by finding the wave\r\nvectors characteristic of the magnetic fields inside the magnetic\r\nmedium, and then combining the fields associated with these wave\r\nvectors in superposition to match the specified boundary conditions.\r\nIn addition to magnetic boundary conditions required for the surface\r\nlayer model, two phenomenological magnetic boundary conditions are\r\ndiscussed in detail. The wave vectors are easily found by combining\r\nthe Landau-Lifshitz equations with Maxwell's equations. Mode\r\npositions are most easily predicted from the magnetic wave vectors\r\nobtained by neglecting damping, conductivity, and the displacement\r\ncurrent. For an insulator where the driving field is nearly uniform\r\nthroughout the sample, these approximations permit a simple yet accurate\r\ncalculation of the mode intensities. For metal films this\r\ncalculation may be inaccurate but the mode positions are still accurately\r\ndescribed. The techniques necessary for calculating the power\r\nabsorbed by the film under a specific excitation including the effects\r\nof conductivity, displacement current and damping are also presented.
\r\n\r\nIn the second part of the thesis the properties of magnetic\r\ngarnet materials are summarized and the properties believed associated\r\nwith the two surface regions of a YIG film are presented. Finally, the\r\nexperimental data and calculated data for the surface layer model and\r\nother proposed models are compared. The conclusion of this study is\r\nthat the remarkable variety of spinwave spectra that arises from\r\nvarious preparation techniques and subsequent treatments can be explained\r\nby surface regions with magnetic properties different from the\r\nbulk.
" }, { "name": "Shantz, Michael Joe", "degree": "PhD", "year": "1976", "title": "Description and Classification of Neuronal Structure in the Frog Retina", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:07042025-000053559", "creators": [ { "name": { "family": "Shantz", "given": "Michael Joe" }, "id": "Shantz-Michael-Joe", "display_name": "Shantz, Michael Joe" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/9z56-xy92", "abstract": "The intent of this study is to develop and apply an\r\nobjective method for the description and classification of\r\nstructure in a biological system for use in the correlation\r\nof structure and function. The biological system of interest is the frog retina, in particular, the neuronal structures which ramify in the inner plexiform layer of the retina.
\r\nA tree grammar is developed for the description of the\r\nj-dimensional structure of Golgi impregnated retinal neurons\r\nseen in light microscope examination. This descriptive method includes 1) an optical sectioning procedure for automatic digitization of 3-dimensional light microscope\r\nimages, 2) various methods for extracting the neuronal image\r\nfrom noise, 1) the extraction from stereo pairs of the\r\nprimitive elements of the neuronal tree grammar, 4) the use\r\nof the grammar as a tool for investigating the occurrence of\r\nsimple or complex substructures in a neuronal structure, and\r\n5) the use of the grammar as a tool for the quantitative\r\nclassification of neurons.
\r\nThe Weiner - Lee method for characterizing nonlinear\r\nsystems is applied to the various cells of the frog retina\r\nusing a two input, spot-annulus white noise stimulus. These\r\nfunctional studies include Proc1on dye injection of the neurons whose kernels are obtained. Procion dye injection\r\nprovides a way of linking the functional descriptions to the\r\nGolgi-obtained structural descriptors. Correlation of\r\nstructure and function is approached through comparisons of\r\nstructural reconstructions and functional identifications.
\r\nIn short this study employs quantitative descriptors and classifiers to correlate structure and function in the frog retina.
" }, { "name": "Shea, John Richard, III", "degree": "PhD", "year": "1976", "title": "A Chemical Reaction in a Turbulent Jet", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11282006-152216", "creators": [ { "name": { "family": "Shea", "given": "John Richard, III" }, "id": "Shea-John-Richard-III", "display_name": "Shea, John Richard, III" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Shair", "given": "Fredrick H." }, "id": "Shair-F-H", "role": "member", "display_name": "Shair, Fredrick H." }, { "name": { "family": "Wulf", "given": "Oliver Reynolds" }, "id": "Wulf-O-R", "role": "member", "display_name": "Wulf, Oliver Reynolds" }, { "name": { "family": "Setchell", "given": "Robert E." }, "id": "Setchell-R-E", "role": "member", "display_name": "Setchell, Robert E." }, { "name": { "family": "Kaufmann", "given": "Aaron" }, "id": "Kaufmann-A", "role": "member", "display_name": "Kaufmann, Aaron" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BJQT-9A50", "abstract": "The turbulent mixing and subsequent chemical reaction of gases is an essential part of many technological processes ranging from gas furnaces to chemical lasers. Surprisingly, there is very little information, either theoretical or experimental, about the actual rate of the chemical reaction in such processes. Generally the chemical kinetics are well understood, but the process of turbulent mixing is not. Many measurements of mixing in turbulent jets have been made in the past, but they have generally failed to distinguish essentially unmixed gas in the turbulent mixing zone from gas which is mixed on a molecular scale. Knowledge of where turbulent fluid is mixed on a molecular scale is critical for predicting chemical reaction rates in the flow.
\r\n\r\nIn this experiment the rate of a chemical reaction in an axisymmetric turbulent jet is studied, and the results are used to determine the rate of molecular mixing in the jet. A turbulent jet containing dilute ozone in an inert mixture of nitrogen and oxygen flows into a stagnant tank of nitric oxide and nitrogen. When the gases mix on a molecular scale, the ozone and nitric oxide rapidly react to produce oxygen and nitrogen dioxide. The rate at which the mixing and chemical reaction proceeds is determined by using an ultraviolet light absorption technique to measure the time averaged ozone concentration at points throughout the jets mixing zone.
\r\n\r\nThe experiment establishes a criterion for determining when a reaction of known chemical kinetics is sufficiently rapid that chemical nonequilibrium has a negligible effect on the mean reactant profile. When a reacting jet satisfies this criterion for equilibrium chemistry, the reactant profiles are found to be independent of jet Reynolds numbers from 4,000 to 32,000 based on the nozzle diameter.
\r\n\r\nIn addition, a mixing fraction, η, is defined to measure the extent of local molecular scale mixing independently of a chemical reaction occurring in the jet. The fraction assumes values of unity in the unmixed primary jet, zero in unmixed ambient fluid, and intermediate fractions for mixtures of all proportions. Points on nonreacting jet profiles are related to time averages of η. A limiting highly reacting ozone profile, found when a large excess of nitric oxide is present in the ambient fluid, is related to the time average of an intermittency function, J(η), defined equal to unity when η is within a specified neighborhood of one and zero elsewhere. Thus the experimental measurements of ozone profiles are directly related to the statistics of molecular scale mixing in the jet.
" }, { "name": "Suezawa, Yoshitaka", "degree": "PhD", "year": "1976", "title": "Damped Free Oscillation of Magnetization in Ni-Fe Thin Films", "advisor": "Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechTHESIS:02232017-094033612", "creators": [ { "name": { "family": "Suezawa", "given": "Yoshitaka" }, "id": "Suezawa-Yoshitaka", "display_name": "Suezawa, Yoshitaka" } ], "advisors": [ { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MD0Y-D860", "abstract": "Damped free oscillations of the magnetization have been clearly\r\nobserved at the completion of 180\u00b0 flux reversal along both the easy\r\nand the hard axis in Ni-Fe thin films. The flux component perpendicular\r\nto the applied pulse field was observed using a single turn pickup\r\nloop around the film. The frequency of the oscillation was studied\r\nas a function of applied pulse field and compared with the results obtained\r\nby ferromagnetic resonance. The frequency of the damped free\r\noscillation agreed quite well with that obtained by resonance when the\r\nfrequency was measured after the oscillation had damped to small amplitude.\r\nThe damping constant obtained from the decay of the oscillation\r\nagreed quite well with that obtained from the half-power line-width\r\nof the resonance curve.
\r\n\r\nThe Landau-Lifshitz equation proposed for the coherent rotation,\r\nusing the value of the damping constant obtained by resonance, could\r\ndescribe the initial part of the magnetization reversal and the damped\r\nfree oscillation in the films with low angular dispersion. Agreement\r\nbetween the experimental and the calculated transverse flux change for\r\nthe entire waveform could not be obtained by using the value of damping\r\nconstant obtained by resonance. The agreement was better at both\r\nhigher applied field or lower anisotropy dispersion. The effect of\r\neddy currents was negligible on the flux reversal but appeared as a\r\nslight increase of the damping constant obtained by resonance\r\nexperiment.
" }, { "name": "Tangonan, Gregory Ligot", "degree": "PhD", "year": "1976", "title": "The Electrical and Magnetic Properties of Amorphous Pd-Cu-P Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-155504331", "creators": [ { "name": { "family": "Tangonan", "given": "Gregory Ligot" }, "id": "Tangonan-Gregory-Ligot", "display_name": "Tangonan, Gregory Ligot" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/XW4A-2E70", "abstract": "The amorphous phases of the Pd-Cu-P system has been obtained\r\nusing the technique of rapidly quenching from the liquid state.\r\nBroad maxima in the diffraction pattern were obtained in the X-ray\r\ndiffraction studies which are indicative of a glass-like structure.\r\nThe composition range over which the amorphous solid phase is retained\r\nfor the Pd-Cu-P system is (Pd100-xCux)80P20 with 10 \u2264 x \u2264 50 and\r\n(Pd65Cu35)100-yPy with 15 \u2264 y \u2264 24 and (Pd60Cu40)100-yPy with\r\n15 \u2264 y \u2264 24.
\r\n\r\nThe electrical resistivity for the Pd-Cu-P alloys decreases with\r\ntemperature as T2 at low temperatures and as T at high temperatures\r\nup to the crystallization temperature. The structural scattering\r\nmodel of the resistivity proposed by Sinha and the spin-fluctuation\r\nresistivity model proposed by Hasegawa are re-examined in the light\r\nof the similarity of this result to the Pt-Ni-P and Pd-Ni-P systems.\r\nObjections are raised to these interpretations of the resistivity results \r\nand an alternate model is proposed consistent with the new\r\nresults on Pd-Cu-P and the observation of similar effects in crystalline\r\ntransition metal alloys. The observed negative temperature\r\ncoefficients of resistivity in these amorphous alloys are thus interpreted\r\nas being due to the modification of the density of states with\r\ntemperature through the electron-phonon interaction. The weak Pauli\r\nparamagnetism of the Pd-Cu-P, Pt-Ni-P and Pd-Ni-P alloys is interpreted\r\nas being modifications of the transition d-states as a result of the\r\nformation of strong transition metal-metalloid bonds rather than a\r\nlarge transfer of electrons from the glass former atoms (P in this\r\ncase) to the d-band of the transition metal in a rigid band picture.
" }, { "name": "Vuceta, Jasenka", "degree": "PhD", "year": "1976", "title": "Adsorption of Pb(II) and Cu(II) on \u03b1-Quartz from Aqueous Solutions: Influence of pH, Ionic Strength, and Complexing Ligands", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04162014-093109979", "creators": [ { "name": { "family": "Vuceta", "given": "Jasenka" }, "id": "Vuceta-Jasenka", "display_name": "Vuceta, Jasenka" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/71AV-TE55", "abstract": "Adsorption of aqueous Pb(II) and Cu(II) on \u03b1-quartz was studied as a function of time, system surface area, and chemical speciation. Experimental systems contained sodium as a major cation, hydroxide, carbonate, and chloride as major anions, and covered the pH range 4 to 8. In some cases citrate and EDTA were added as representative\r\norganic complexing agents. The adsorption equilibria were reached quickly, regardless of the system surface area. The positions of the adsorption equilibria were found to be strongly dependent on pH, ionic strength and concentration of citrate and EDTA. The addition of these non-adsorbing ligands resulted in a competition between chelation and\r\nadsorption. The experimental work also included the examination of the adsorption behavior of the doubly charged major cations Ca(II) and Mg(II) as a function of pH.
\r\n\r\nThe theoretical description of the experimental systems was obtained by means of chemical equilibrium-plus-adsorption computations using two adsorption models: one mainly electrostatic (the James-Healy Model), and the other mainly chemical (the Ion Exchange-Surface Complex\r\nFormation Model). Comparisons were made between these two\r\nmodels.
\r\n\r\nThe main difficulty in the theoretical predictions of the adsorption behavior of Cu(II) was the lack of the reliable data for the second hydrolysis constant(*\u03b2_2) The choice of the constant was made on the basis of potentiometric titratlons of Cu^(2+)
\r\n\r\nThe experimental data obtained and the resulting theoretical observations were applied in models of the chemical behavior of trace metals in fresh oxic waters, with emphasis on Pb(II) and Cu(II).
\r\n" }, { "name": "Yang, Fang-Chou", "degree": "PhD", "year": "1976", "title": "An Analysis of Linear Induction Motors for Propulsion and Suspension of Magnetically Levitated Vehicles", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:11092017-124408265", "creators": [ { "name": { "family": "Yang", "given": "Fang-Chou" }, "id": "Yang-Fang-Chou", "display_name": "Yang, Fang-Chou" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/DM0P-XW77", "abstract": "A four-layer single-sided LIM used for propulsion and suspension of magnetically levitated vehicles is studied. The track is assumed to be made of conductors with uniaxial \u03bc and \u03c3. A general analysis allows us to exclude unsuitable geometries. The machine performance is given for the promising geometries. A possible way of computing the effective \u03bc and \u03c3 for a composite track is sketched. From the analysis of an extremely simplified geometry, the conditions for the validity of the effective \u03bc and \u03c3 concept are given. Finally, a three-dimensional correction is introduced." }, { "name": "Yen, Huan-wun", "degree": "PhD", "year": "1976", "title": "Gallium Arsenide-Gallium Aluminum Arsenide Distributed Feedback and Distributed Bragg Reflector Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:11252025-193026356", "creators": [ { "name": { "family": "Yen", "given": "Huan-wun" }, "id": "Yen-Huan-wun", "display_name": "Yen, Huan-wun" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/vc0r-rk03", "abstract": "This work describes theoretical and experimental studies of\r\nGaAs/GaAlAs distributed feedback and distributed Bragg reflector\r\nlasers. These lasers are strong candidates as the light source\r\nin integrated optical circuits and optical communication systems.
\r\n\r\nA coupled-mode formalism is used to study the propagation of\r\nelectromagnetic waves in a dielectric waveguide with periodic surface\r\ncorrugation. The reflection and transmission characteristics of\r\nboth passive and active periodic waveguides are found as a function\r\nof wavelength.
\r\n\r\nThese results are used to derive the oscillation conditions of\r\ntwo different laser structures: (1) the distributed feedback laser -\r\nwhere a corrugated active waveguide section is the basic structure,\r\n(2) the distributed Bragg reflector laser - where an active region is\r\nflanked by two sections of passive periodic waveguides.
\r\n\r\nThe procedure of determining the lasing wavelength is outlined.\r\nThe merits and disadvantages of various laser structures are compared\r\nand discussed.
\r\n\r\nExperimental results on fabrication and measurements of GaAs/GaAlAs\r\ndistributed feedback and distributed Bragg reflector lasers\r\nare presented and compared with the theory. Various fabrication and\r\nmeasurement techniques developed during the course of the investigation\r\nare described in some detail.
" }, { "name": "Auerbach, Jerome Martin", "degree": "PhD", "year": "1975", "title": "Experimental Studies of the Noise Produced in a Supersonic Nozzle by Upstream Acoustic and Thermal Disturbances", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10172012-081901085", "creators": [ { "name": { "family": "Auerbach", "given": "Jerome Martin" }, "id": "Auerbach-Jerome-Martin", "display_name": "Auerbach, Jerome Martin" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/z2x3-g471", "abstract": "A novel noise source mechanism whereby sound is produced\r\nby time-dependent temperature nonuniformities in a flow with a mean\r\nvelocity gradient is investigated experimentally. The research is\r\npart of a theoretical and experimental study of this noise source initiated by Professor F. E. Marble.
\r\n\r\nA steady accelerating flow was produced in a rectangular supersonic\r\nnozzle with an entrance Mach number of 0.2, an exit Mach\r\nnumber of 1.38, and a throat area of 1 in.^2. A rotary valve bleed\r\nflow system and an electrical wire resistance heater upstream of the\r\nnozzle introduced mass flow and temperature fluctuations into the\r\nnozzle flow at frequencies up to 500Hz. Sound measurements were\r\nmade at six positions along the nozzle and outside the nozzle assembly,\r\nwhich was enclosed in an anechoic chamber 10 ft. on a side.
\r\n\r\n\r\nAll data acquisition and processing was done with a computer-controlled\r\ndata acquisition system, making the experiment essentially\r\n\"computerized.\u201d By interfacing the control circuitry of the bleed flow\r\nand heater systems to the data acquisition system) a digital signal-averaging\r\ntechnique was developed which enabled the sound produced\r\nby the bleed flow and temperature fluctuations to be detected and accurately\r\nmeasured in high-level backgrounds of turbulent flow noise.
\r\n\r\nBy synchronization of the bleed flow and heater, a pure temperature\r\ndisturbance without an associated pressure disturbance\r\ncaused by heating was produced. This pure temperature disturbance\r\nwas found to produce sound upon being convected through the nozzle.\r\nThe novel noise source mechanism was thus verified.
\r\n\r\nExcellent agreement was found between the nozzle sound\r\nmeasurements and one-dimensional small disturbance theory applied\r\nto the flow occurring in the nozzle.
\r\n\r\nExternal field measurements yielded jet noise levels and spectra\r\nagreeing with other reported studies, spatial variation of the sound\r\nfield due to a pure pressure fluctuation at the nozzle exit, and cross\r\ncorrelation data between the external sound field and the pressure\r\nfluctuations at the nozzle exit.
\r\n" }, { "name": "Berrill, John Beauchamp", "degree": "PhD", "year": "1975", "title": "A Study of High-Frequency Strong Ground Motion from the San Fernando Earthquake", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01312018-100922603", "creators": [ { "name": { "family": "Berrill", "given": "John Beauchamp" }, "id": "Berrill-John-Beauchamp", "display_name": "Berrill, John Beauchamp" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/B04E-Q851", "abstract": "This thesis describes an investigation of the attentuation of\r\nstrong earthquake ground motion in the 0.4 to 16 Hz frequency band\r\nduring the M = 6.4, February 9, 1971, San Fernando, California \r\nearthquake. It is found that Fourier amplitudes of ground acceleration decay\r\naccording to a simple expression incorporating a geometric spreading\r\nterm, and a material attenuation term with constant specific\r\nattentuation Q. The scatter in the amplitude data about an expected\r\nlevel given by the simple decay expression is nearly constant with\r\nrespect to both frequency and focal distance. Fourier amplitudes of\r\nacceleration corrected to a reference hypocentral distance agree\r\nwell with those determined by a two-parameter source model of the\r\nSan Fernando earthquake. Focusing of energy to the south by the\r\nsouthward propagating rupture is observed at frequencies below 8 Hz.\r\nThe propagation of rupture was incoherent with respect to higher-\r\nfrequency components.
\r\n\r\nThe relationship between intensity of ground motion and site \r\ngeology is examined. It is found that while, in general, sedimentary \r\nsites were accelerated more strongly than basement rock sites, no \r\nclear difference could be found between sedimentary sites classified\r\nas \"soft\" by Trifunac and Brady (1975) (generally recent alluvium) and \r\nthose classified as having \"medium\" soil stiffness, generally consisting \r\nof older alluvium and sedimentary rock. The difference between amplitudes \r\nrecorded on basement rock and sediments is more complex. In\r\ngeneral, smoothed amplitude spectra from accelerograms recorded\r\non basement rock are lower than smoothed amplitudes at corresponding \r\nsedimentary sites. However, basement site spectra show marked isolated \r\npeaks, as high as those from sedimentary sites at similar distances.\t\r\nThis is attributed to the focusing effects of the irregular topography \r\nnormally accompanying basement rock outcrops. In the\r\nfrequency band considered, it is concluded that for the purposes \r\nof a seismic design of structures no discrimination should be made \r\nbetween the intensity of ground motion expected on basement rock, \r\nsedimentary rock, and coarse-grained alluvium typical of Southern California.
\r\n\r\nThe agreement between the recorded strong motion amplitudes\r\nand those predicted by a simple two-parameter source model suggests\r\nthat the model can be used for the assessment of strong ground motion\r\nto be used in design procedures. A procedure for estimating design\r\nearthquakes using the source model and the amplitude decay expression\r\nis presented.
" }, { "name": "Brown, Thomas Carl, Jr.", "degree": "PhD", "year": "1975", "title": "A Structured Design Method for Specialized Proof Procedures", "advisor": "Ingargiola, Giorgio", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182011-144905895", "creators": [ { "name": { "family": "Brown", "given": "Thomas Carl, Jr." }, "id": "Brown-Thomas-Carl", "display_name": "Brown, Thomas Carl, Jr." } ], "advisors": [ { "name": { "family": "Ingargiola", "given": "Giorgio" }, "id": "Ingargiola-G", "role": "advisor", "display_name": "Ingargiola, Giorgio" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/nrh8-ka82", "abstract": "A proof procedure verifies relative consequence relations\r\n B \u22a8_E C (1)\r\nin first-order logic with equality by generating a refutation (or proof of contradiction) for some clause-representation C of B \u02d8 {\u00ac C}, using the axioms and inferences of some sound and effective calculus for \u22a8_E. Performance of the procedure depends upon two forms of heuristic knowledge about \u22a8_E. which it may embody:\r\n\r\n(S) Structural knowledge is formalized by a refinement (or decidable subset) of the deductions admitted by the procedure's calculus which acts as a \"search-space filter\": only those deductions from C contained in the refinement are generated.\r\n\r\n(P) Procedural knowledge is formalized by a search strategy (or enqueing function): it determines which of the admissible inferences will be generated next on the basis of the current deduction.\r\n\r\nThis investigation develops a general hierarchical method for the design of refinements embodying structural forms of heuristic knowledge characteristic of expert human problem solvers in an axiomatized problem domain.\r\n\r\nInitially we design refinement \u0394 for E-resolution deductions, whose inferences have the form\r\n{B_1 v q_1,...,B_n v q_n} \u22a2 C (2)\r\nwhere (b_1 -q_1) \u03b8 v ... v (B_n - q_n) \u03b8 \u2265 C \u2265 (B_1 \u03b8 - q_1\u03b8) v...v (B_n\u03b8-q_n\u03b8) and \u03b8 is a substitution (of terms for variables) which makes {q_1\u03b8,...q_n\u03b8} contradictory in E. The unit-clause set {q_1,...,q_n} is called a latent E-contradiction.\r\n\r\nE-resolution is not in general effective: each inference (2) must be realized by finding a \"lower level\" refutation for E \u02d8 {q_1,...,q_n} and extracting \u03b8 from it. For this sub-problem we design and E'-resolution refinement \u0394' where E > E'. The normal composition \u0394 \u2022 \u0394' consists of deductions in \u0394 wherein each inference (2) is \"realized\" by a refutation in \u0394'; \u0394 \u2022 \u0394' is actually an E'-resolution refinement.\r\n\r\nIterating the above (with E' for E), we obtain an E_o-resolution refinement \u0394_M = (...(\u0394_n \u2022 \u0394_(n-1))...\u0394_o) where \u0394_k is an E_k-resolution refinement and E = E_n >...>E_o = unit clauses of E. An E_o-resolution inference is realized by refuting a latent A-contradiction {p,q} where A is a set of equations including E_o\u02d8{[x=x]}. For this sub-problem we design an (E_o-) resolution micro-refinement \u0394_\u00b5 for the set of deductions composed of factoring, binary resolution, and paramodulation inferences.\r\n\r\nNormal refinements \u0394_M \u2022 \u0394_\u00b5 combine the composite structural knowledge embodied in \u0394_M with the effectiveness, efficiency, and most-general inference properties of \u0394_\u00b5.\r\n\r\nHyper-E-resolution (HR(E,\u227b,s)) exemplifies \u0394_\u00b5. \u227b is an \"invariant complexity ordering\" which well-orders constant terms. For each resolution inference {A v p, B v Q} \u22a2 (A v B)\u03b8 in a member of ND(E,\u227b), underlined literals must have been reduced to a \"least complex\" normal form by a chain of \u227b -ordered replacement operations based on equations of E and current derived equations; moreover, t\u03b8 cannot be \"more complex\" than s\u03b8. \"Functional reflexivity\" equations [fx_1...x_n = fx_1...x_n], being sudsumed by [x=x], are excluded from E-normal deductions by strong subsumption-deletion constraints.\r\n\r\nTheorem B. ND (E,\u227b) is refutation complete on unit-clause sets. \r\n\r\nCorollary. If E and \u0394_M are as in Theorem A and no non-unit clause of E contains a (positive) equation then \u0394_M \u2022 ND(E_o,\u227b) is refutation complete on clause-sets whose non-unit clauses each contain at most one equation.\r\n\r\nNormal refinements are illustrated in the solutions of several refutation problems in Group Theory and Integer Arithmetic, where useful forms and complexity orderings are employed." }, { "name": "Cannon, Johnnie B., Jr.", "degree": "PhD", "year": "1975", "title": "Convective Flows Under Conditions Applicable to Fires in High Rise Buildings", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02282018-094023116", "creators": [ { "name": { "family": "Cannon", "given": "Johnnie B., Jr." }, "id": "Cannon-Johnnie-B", "display_name": "Cannon, Johnnie B., Jr." } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/DXY0-9G71", "abstract": "This study was an attempt to analyze convective flow patterns\r\nunder conditions applicable to fires in high rise buildings when natural\r\nconvection alone is the most important driving force. The primary\r\naim of this investigation was to consider the turbulent flow in vertical\r\nshafts caused by hot gases entering the bottom of the shaft which is\r\nalready filled with a cooler (denser) gas, and hence creating an \r\nunstable density field.
\r\n\r\nThe small scale model used to study this problem consisted of \r\na vertical tube of dense fluid placed in an infinite (less dense) fluid\r\nenvironment. General scaling laws were developed for the variation of\r\ndensity with time for the flow set up in the model. Also, an analytical\r\nmodel was developed to account for the observed mixing rates in this\r\nsimple configuration.
\r\n\r\nIn the analysis, the diffusion equation was solved and found to\r\nbe in agreement with the small scale model. The mixing coefficient\r\nfor this unstable system is
\r\n\r\nSee abstract for formula
\r\n\r\nwhere the constant, 0.28, was determined empirically, and the\r\nfundamental time scale that characterizes the mixing in the vertical column\r\nis
\r\n\r\nSee abstract for formula
\r\n\r\nLater, the above techniques were used to investigate in a more\r\nsuperficial way the effects on the mixing rates of geometric variations,\r\nlimited external environments, changes in the internal geometry of the\r\nshafts, gas density ration, and heat transfer.
\r\n\r\n\r\n" }, { "name": "Chang, Liang-Chou", "degree": "PhD", "year": "1975", "title": "Theoretical Investigations of Turbulent Boundary Layer Over a Wavy Surface", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:11122015-115400945", "creators": [ { "name": { "family": "Chang", "given": "Liang-Chou" }, "id": "Chang-Liang-Chou", "display_name": "Chang, Liang-Chou" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ANTA-K262", "abstract": "The important features of the two-dimensional incompressible\r\nturbulent flow over a wavy surface of wavelength comparable with the boundary\r\nlayer thickness are analyzed.
\r\n\r\nA turbulent field method using model equation for turbulent\r\nshear stress similar to the scheme of Bradshaw, Ferriss and Atwell\r\n(1967) is employed with suitable modification to cover the viscous\r\nsublayer. The governing differential equations are linearized based\r\non the small but finite amplitude to wavelength ratio. An orthogonal\r\nwavy coordinate system, accurate to the second order in the amplitude\r\nratio, is adopted to avoid the severe restriction to the validity of\r\nlinearization due to the large mean velocity gradient near the wall.\r\nAnalytic solution up to the second order is obtained by using the method\r\nof matched-asymptotic-expansion based on the large Reynolds number\r\nand hence the small skin friction coefficient.
\r\n\r\nIn the outer part of the layer, the perturbed flow is practically\r\n\"inviscid.\" Solutions for the velocity, Reynolds stress and also the\r\nwall pressure distributions agree well with the experimental measurement. \r\nIn the wall region where the perturbed Reynolds stress plays an\r\nimportant role in the process of momentum transport, only a qualitative\r\nagreement is obtained. The results also show that the nonlinear\r\nsecond-order effect is negligible for amplitude ratio of 0.03.\r\nThe discrepancies in the detailed structure of the velocity, shear\r\nstress, and skin friction distributions near the wall suggest modifications\r\nto the model are required to describe the present problem.
" }, { "name": "Chen, Wilkie Yung-Kee", "degree": "PhD", "year": "1975", "title": "Properties of Superconducting Cu-Rich Composites Containing V\u2083Si or V\u2083Ga", "advisor": "Tsuei, Chang-chyi; Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07172014-081159687", "creators": [ { "name": { "family": "Chen", "given": "Wilkie Yung-Kee" }, "id": "Chen-Wilkie-Yung-Kee", "display_name": "Chen, Wilkie Yung-Kee" } ], "advisors": [ { "name": { "family": "Tsuei", "given": "Chang-chyi" }, "id": "Tsuei-C-C", "role": "co-advisor", "display_name": "Tsuei, Chang-chyi" }, { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/4FAM-6K11", "abstract": "Superconducting Cu-rich composites containing the A-15 compounds\r\nV3Si or V3Ga have been made by the \"Tsuei\" process, which\r\nconsists of melting the constituent elements into ingots followed by\r\nsubsequent cold working and heat treatment. The superconducting\r\ntransition temperatures of the resulting composites have been measured.\r\nX-ray diffraction analyses have been performed to identify\r\nthe phases in the alloys. The microstructures have been studied using\r\nboth the optical metallograph and the scanning electron-microscope.\r\nFor some composites containing V3Ga, the critical current densities\r\nas functions of transverse magnetic field up to 60 kG, and as functions\r\nof temperature from 4.2\u00b0K to 12\u00b0K have been measured. It was\r\nfound that the Tsuei process does not work for the composites containing\r\nV3Si, but works satisfactorily for the composites containing\r\nV3Ga. The reasons are discussed based on the results of microstructure\r\nstudies, electrical resistivity measurements, and also the\r\nrelevant binary phase diagrams. The relations between the measured\r\nproperties and the various metallurgical factors such as the alloy\r\ncompositions, the cross-section reduction ratios of the materials,\r\nand the heat treatment are discussed. The basic mechanism for the\r\nobserved superconductivity in the materials is also discussed. In addition,\r\nit was found that the Tsuei composites are expected to have\r\nhigh inherent magneto-thermal stability based on the stability theory\r\nof superconducting composites." }, { "name": "Daimon-Hagihara, Yoshiaki", "degree": "PhD", "year": "1975", "title": "Change Transfer in Charge Coupled Devices", "advisor": "McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03212022-225418687", "creators": [ { "name": { "family": "Daimon-Hagihara", "given": "Yoshiaki" }, "id": "Daimon-Hagihara-Yoshiaki", "display_name": "Daimon-Hagihara, Yoshiaki" } ], "advisors": [ { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/vx9y-gb03", "abstract": "Theoretical analysis of the dynamics of charge transfer in charge coupled devices is central to the intelligent design and proper estimation of the usefulness of this new device concept. In this report, a detailed study of the electrostatics and dynamics of buried channel charge coupled devices (BCCDs) is presented. Both theoretical and experimental study of BCCD has been very difficult due to the additional complexity in the BCCU structure in contrast to the original simpler structure of surface charge coupled devices (SCCDs). And up to present, no comprehensive study of BCCD which includes the complete electrostatic and dynamic analysis of BCCD operations has been reported. It is the purpose of this thesis to assist physicists, device engineers, and applications engineers interested in BCCD by presenting all essential information on the buried channel CCDs in one place and in a comprehensive form so that the background laid on BCCD can be applied immediately to the case of the SCCD studies achieved in the past and also to the investigation of a future CCD structure.
\r\n\r\nThe work reported in this thesis consists of three major contributions to the rapidly progressing CCD research and is described in the main text, Chapter 1, 4, and 5 of this thesis.
\r\n\r\nIn Chapter 1 the relations between the electrostatic potential and the charge distribution in one dimensional structure for BCCD are analyzed in detail. An expression for the channel potential in terms of salient physical parameters is obtained by depletion approximation. And its implications on doping levels, and profiles; charge storage capacity; geometrical structure and gate voltages are discussed in detail to provide a useful reference and guide-work in design and analysis of buried channel CCDs. The results obtained numerically for the case of Gaussian doping profile are also presented and correlated with the uniform doping model. In Chapter 4 a detailed two dimensional electrostatic analysis of buried channel CCDs is presented. By a simple capacitance network model the two dimensional Poisson equation appropriate for the structure is reduced into a second order differential equation in a single spatial dimension. The resulting equation relates the signal charge and the minimum channel potential under all the relevant electrodes and interelectrode regions. A diffusion equation describing the charge transfer is coupled to this equation in order to incorporate the static model in dynamic charge transfer description. The results of a detailed numerical simulation of the charge transfer process in the resulting realistic model of a high density buried channel CCU remain to be studied in Chapter 5. It is shown that the limitations on the device performance due to incomplete free charge transfer are reduced considerably by powerful field-aided charge transfer. The procedure to estimate the significance of this reduction in terms of the charge remaining as a function of time is formulated analytically.
" }, { "name": "Decker, Stephen K.", "degree": "PhD", "year": "1975", "title": "Investigations of Noise and of Quantum Interference in Proximity Effect Bridges", "advisor": "Mercereau, James E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-085322954", "creators": [ { "name": { "family": "Decker", "given": "Stephen K." }, "id": "Decker-Stephen-K", "display_name": "Decker, Stephen K." } ], "advisors": [ { "name": { "family": "Mercereau", "given": "James E." }, "id": "Mercereau-J-E", "role": "advisor", "display_name": "Mercereau, James E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/HZMZ-3C32", "abstract": "This work reports investigations upon weakly superconducting proximity\r\neffect bridges. These bridges, which exhibit the Josephson\r\neffects, are produced by bisecting a superconductor with a short\r\n(<1\u00b5) region of material whose superconducting transition temperature\r\nis below that of the adjacent superconductors. These bridges are\r\nfabricated from layered refractory metal thin films whose transition\r\ntemperature will depend upon the thickness ratio of the materials\r\ninvolved. The thickness ratio is changed in the area of the bridge\r\nto lower its transition temperature. This is done through novel\r\nphotolithographic techniques described in the text, Chapter 2.
\r\n\r\nIf two such proximity effect bridges are connected in parallel,\r\nthey form a quantum interferometer. The maximum zero voltage current\r\nthrough this circuit is periodically modulated by the magnetic flux\r\nthrough the circuit. At a constant bias current, the modulation of\r\nthe critical current produces a modulation in the dc voltage across\r\nthe bridge. This change in dc voltage has been found to be the result\r\nof a change in the internal dissipation in the device. A simple model\r\nusing lumped circuit theory and treating the bridges as quantum\r\noscillators of frequency \u03c9 = 2eV/h, where V is the time average\r\nvoltage across the device, has been found to adequately describe the\r\nobserved voltage modulation.
\r\n\r\nThe quantum interferometers have been converted to a galvanometer\r\nthrough the inclusion of an integral thin film current path which\r\ncouples magnetic flux through the interferometer. Thus a change in\r\nsignal current produces a change in the voltage across the interferometer\r\nat a constant bias current. This work is described in Chapter\r\n3 of the text.
\r\n\r\nThe sensitivity of any device incorporating proximity effect\r\nbridges will ultimately be determined by the fluctuations in their\r\nelectrical parameters. He have measured the spectral power density of\r\nthe voltage fluctuations in proximity effect bridges using a room\r\ntemperature electronics and a liquid helium temperature transformer\r\nto match the very low (~ 0.1 \u03a9) impedances characteristic of these\r\ndevices.
\r\n\r\nWe find the voltage noise to agree quite well with that predicted\r\nby phonon noise in the normal conduction through the bridge plus a\r\ncontribution from the superconducting pair current through the bridge\r\nwhich is proportional to the ratios of this current to the time average\r\nvoltage across the bridge. The total voltage fluctuations are given\r\nby <V^2(f ) > = 4kTR^2_d I/V where R_d is the dynamic resistance, I the\r\ntotal current, and V the voltage across the bridge . An additional\r\nnoise source appears with a strong 1/f^(n) dependence , 1.5 < n < 2, if the\r\nbridges are fabricated upon a glass substrate. This excess noise,\r\nattributed to thermodynamic temperature fluctuations in the volume of\r\nthe bridge, increases dramatically on a glass substrate due to the\r\ngreatly diminished thermal diffusivity of the glass as compared to sapphire.
\r\n" }, { "name": "Evans, Gary Alan", "degree": "PhD", "year": "1975", "title": "Electromagnetic Theory of Distributed Feedback Lasers in Periodic Dielectric Waveguides", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052007-100020", "creators": [ { "name": { "family": "Evans", "given": "Gary Alan" }, "id": "Evans-Gary-Alan", "display_name": "Evans, Gary Alan" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/QMW8-1287", "abstract": "A theory for distributed feedback lasers in transversely bounded structures is developed. The space harmonics approach is used to discuss the general properties of periodic structures. The coupled mode approach is used to develop expressions for the threshold gain, longitudinal mode structure, and electromagnetic field distribution for distributed feedback lasers.\r\n\r\nThree basic structures are considered for distributed feedback lasers--thin film waveguides, diffusion waveguides, and fiber wave-guides.\r\n\r\nEquations for the amplification of a waveguide mode that extends transversely over both regions with and without gain are derived.\r\n\r\nAnalytical expressions are derived for coupling between modes in periodically perturbed dielectric waveguides. Sinusoidal perturbations of the electric permittivity and of the waveguide boundary are considered.\r\n\r\nTheoretical results indicate that an optimum design of distributed feedback lasers can be achieved by an appropriate choice of geometrical parameters. Regions of optimum design are illustrated in numerous plots of normalized threshold gain versus normalized laser frequency." }, { "name": "Feng, Joseph Shao-Ying", "degree": "PhD", "year": "1975", "title": "I. Stopping Cross Section Additivity for 0-2 MeV \u2074He Ions in Solids. II. Magnetite Thin Films: Fabrication and Electrical Properties", "advisor": "Nicolet, Marc-Aurele; Mayer, James Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:04062012-150944579", "creators": [ { "name": { "family": "Feng", "given": "Joseph Shao-Ying" }, "id": "Feng-Joseph-Shao-Ying", "display_name": "Feng, Joseph Shao-Ying" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" }, { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1C3P-AH34", "abstract": "Part I:
\r\n\r\nRutherford backscattering can be used to determine the depth\r\ndistribution of the constituent elements in the first micron of a sample. The interpretation of the spectra requires an accurate knowledge of the rate at which the probe ions lose their kinetic energy. The microscopic rate of energy loss, the stopping cross section, has been\r\nfairly intensively investigated, both experimentally and theoretically, in elemental targets.
\r\n\r\nIn 1905, Bragg and Kleeman proposed that the rate of energy loss in a compound is a linear superposition of the atomic stopping powers. Because of the experimental difficulties, the uncertainties in the tests of this assumption have been 5-10%. Within the sensitivities of these experiments, Bragg's rule has usually been reported to be valid at high ion velocities (E\u2273I MeV/amu). We describe two new methods of testing Bragg's rule in which the apparent sensitivity limit is below 1%.
\r\n\r\nThe first test requires that Bragg's rule be extended in the obvious way to include at toys and non-stoichiometric compounds. This experiment requires a multi-layered sample in which the components of these layers can somehow be redistributed. If there is no chemical interaction with the ambient, including the substrate, the total energy\r\nloss in this multi-layered structure should be independent of the distribution of the constituent elements. This test was applied to two-layered structures of Au-Ag, Au-Cu, Au-Al, and their alloys or compounds. The total energy loss before and after the two layers were mixed was reproducible to within 1%, as predicted by Bragg's rule.
\r\n\r\nThe second test is particularly useful in those targets in which one of the component elements(or chemical radicals) is not readily available as a separate layer. Some examples that were included in this experiment are the oxides, SiO_2 and Al_2O_3. The analytical procedure\r\nrequired that three assumptions in addition to Bragg's rule be invoked. When this procedure was applied to MgO, SiO_2, Al_2O_3, Fe_2O_3 and Fe_3O_4, it was possible to demonstrate that there is a unique contribution by oxygen\r\nto the molecular stopping cross sections of these compounds. However, this value is apparently 6-22% lower than the value expected from the measured stopping cress section of molecular O_2 in the gas phase.
\r\n\r\nPart II:
\r\n\r\nA low-temperature process for manufacturing magnetite (Fe_3O_4) thin films by converting hematite(\u03b1-Fe_2O_3) thin films is described. The films produced are unambiguously identified as magnetite.
\r\n\r\nResistivity, dc Hall effect and transverse magnetoreslstance measurements were performed on these films from 104\u00b0K to room temperature. The Verwey transition is observed at 123\u00b0K, about 4\u00b0K higher than reported for stoichiometric bulk magnetite. The ordinary and extraordinary Hall coefficients are both negative over the entire temperature range, consistent with negatively charged carriers. The extraordinary Hall coefficient exhibits a \u03c1^(1/3) dependence on the resistivity above T_V and a \u03c1^(2/3) dependence below T_V. The magnetoresistance\r\nis negative at all temperatures and field strengths and its magnitude increases monotonically with the magnetic field at all temperatures. The planar Hall effect signal was below the sensitivity of the present experiment.
\r\n\r\nOne particular anomalous result observed in these measurements is the elevated Verwey transition temperature. To account for this unusual behavior, the Verwey transition in magnetite thin films was investigated by measuring the temperature dependence of the sheet resistivity. It was demonstrated that substrate-induced stresses are responsible for the elevated Verwey transition temperature. The ratio of the resistances in the two states, as evaluated at the transition temperature, is apparently proportional to the thickness of the film and independent of the substrate. The combination of these two results suggests that there is a 600-1200 \u00c5 layer that remains in the high conductivity state at all temperatures and that it is probably at the free surface of the magnetite film.
" }, { "name": "Gomberg, Richard Ira", "degree": "PhD", "year": "1975", "title": "Test Particle Motion in a Lorentz Gas", "advisor": "Corngold, Noel Robert", "url": "https://resolver.caltech.edu/CaltechTHESIS:07102014-094128527", "creators": [ { "name": { "family": "Gomberg", "given": "Richard Ira" }, "id": "Gomberg-Richard-Ira", "display_name": "Gomberg, Richard Ira" } ], "advisors": [ { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "advisor", "display_name": "Corngold, Noel Robert" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/5MDV-YZ10", "abstract": "This is a two-part thesis concerning the motion of a test\r\nparticle in a bath. In part one we use an expansion of the operator\r\nPLeit(1-P)LLP to shape the Zwanzig equation into a generalized\r\nFokker-Planck equation which involves a diffusion tensor depending\r\non the test particle's momentum and the time.
\r\n\r\nIn part two the resultant equation is studied in some detail\r\nfor the case of test particle motion in a weakly coupled Lorentz Gas.\r\nThe diffusion tensor for this system is considered. Some of its\r\nproperties are calculated; it is computed explicitly for the case\r\nof a Gaussian potential of interaction.
\r\n\r\nThe equation for the test particle distribution function can\r\nbe put into the form of an inhomogeneous Schroedinger equation.\r\nThe term corresponding to the potential energy in the Schroedinger\r\nequation is considered. Its structure is studied, and some of its\r\nsimplest features are used to find the Green's function in the\r\nlimiting situations of low density and long time.
" }, { "name": "Horgen, Henri Michel", "degree": "PhD", "year": "1975", "title": "Analysis of Object-Image Relationships in Electron Microscopy by Image Processing Techniques", "advisor": "Villagrana, Robert E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10152002-154431", "creators": [ { "name": { "family": "Horgen", "given": "Henri Michel" }, "id": "Horgen-Henri-Michel", "display_name": "Horgen, Henri Michel" } ], "advisors": [ { "name": { "family": "Villagrana", "given": "Robert E." }, "id": "Villagrana-R-E", "role": "advisor", "display_name": "Villagrana, Robert E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/46Q4-TE10", "abstract": "By considering an electron microscope to be an information channel, it is shown that the correspondence between the object and the image can be linked to the electron optical characteristics of the instrument and to the statistical properties of the noise. A discussion of the image formation of a cluster of atoms is introduced in order to demonstrate the main contrast mechanisms that operate at the atomic level. A direct extension of this analysis to more complex specimens gives rise to a wave optical theory of image formation, which is used to present the concept of the amplitude transfer function. This formalism greatly simplifies in the case of weakly scattering objects, where the total object wave is linearly related to both the projected potential distribution of the specimen and the amplitude attenuation of the incident beam. For this category of specimens, there exists a linear relationship between the image intensity in bright-field and the total object wave. Phase and amplitude contrast transfer functions describe the perturbing influence of the objective lens aberrations on the phase and the amplitude of the object wave. If spatial and chromatic incoherence effects are included in this formalism, it is shown that the linearity between image intensity and object is preserved.\r\n\r\nThe validity of the approximations of the wave optical theory is first checked by studying the effect of defocusing on the transfer conditions of the phase and amplitude contrast mechanisms. A medium resolution experiment is conducted on a bright-field image of bovine liver catalase. The results demonstrate a qualitative agreement between experiment and theory.\r\n\r\nA reconstruction scheme is next implemented on a through-focus series of a specimen of gold on carbon. This scheme is analyzed critically prior to a description of the experimental results. It is demonstrated that under certain conditions this technique is capable of restoring the total object wave and simultaneously achieving a selective contrast enhancement at heavy atom locations. This potential Z discrimination is tested experimentally, and the difficulties encountered during the processing are discussed. A qualitative estimate of all contrast mechanisms that contribute to a high-resolution bright-field micrograph can be inferred from this analysis. The problems which one faces in a quantitative interpretation of micrographs at the atomic level are also discussed, and possible ways to circumvent these problems are mentioned.\r\n\r\nNext, image processing schemes for improving the signal-to-noise ratio of an image are applied to micrographs of crystalline specimens. The enhancement of lattice fringe images is demonstrated for both silicon and gold specimens. Periodic images can be processed in either real space or Fourier space and an analysis of these processing modes is presented.\r\n\r\nBy enhancing a weak-beam image of a dissociated-dislocation dipole in germanium, a quantitative comparison to a simulated image is rendered possible. The resolving power of the weak-beam technique is analyzed for this particular example. It is found that by selecting a diffraction geometry so that the systematic reflections are dynamically interacting, four dislocation peaks are individually resolved. Problems associated with the contrast interpretation are discussed in conjunction with a calculation of the image contrast. Finally, suggestions for further study of the atomic structure of crystalline defects by the weak-beam method are given." }, { "name": "Johnson, William Lewis", "degree": "PhD", "year": "1975", "title": "Superconductivity in Metal-Semiconductor Eutectic Alloys", "advisor": "Tsuei, Chang-chyi; Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05272004-131743", "creators": [ { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-William-Lewis", "display_name": "Johnson, William Lewis" } ], "advisors": [ { "name": { "family": "Tsuei", "given": "Chang-chyi" }, "id": "Tsuei-C-C", "role": "advisor", "display_name": "Tsuei, Chang-chyi" }, { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/ZJ13-0B77", "abstract": "The superconductivity of several metal-semiconductor simple eutectic alloys containing Ge or Si, and one of the metals Al, Be, In, Pb, Sn, or T1 has been investigated. The liquid-quenching technique was used to reduce the characteristic scale of the microstructure in the alloys. It was found in some cases (notably Al-base alloys) that the superconducting transition temperature of the metallic phase was significantly enhanced (from 1.2[degrees]K to ~ 6[degrees]K for Al-base alloys) as a result of liquid-quenching. The characteristic scale of the microstructure was found to be of the order of several hundred angstroms in alloys showing the greatest enhancement effect. The results are discussed in terms of recent theoretical models that predict enhancement of superconductivity due to electronic interactions at a metal-semiconductor interface. The results are also analyzed in terms of the McMillan theory of superconductivity in which the enhancement effect is attributed to a reduction in the characteristic phonon frequencies of the metal. It is concluded that the latter explanation can account for all of the observed properties and, thus, that it is probably unnecessary to invoke an \"excitonic mechanism\" to explain the results.\r\n" }, { "name": "Keller, Stuart Ronald", "degree": "PhD", "year": "1975", "title": "Fluid Mechanical Investigations of Ciliary Propulsion", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:04182012-081505490", "creators": [ { "name": { "family": "Keller", "given": "Stuart Ronald" }, "id": "Keller-Stuart-Ronald", "display_name": "Keller, Stuart Ronald" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/QD11-B584", "abstract": "Fluid mechanical investigations of ciliary propulsion are\r\ncarried out from two points of view. In Part I, using a planar geometry,\r\na model is developed for the fluid flow created by an array of\r\nmetachronally coordinated cilia. The central concept of this model is\r\nto replace the discrete forces of the cilia ensemble by an equivalent\r\ncontinuum distribution of an unsteady body force within the cilia layer.\r\nThis approach facilitates the calculation for the case of finite amplitude\r\nmovement of cilia and takes into account the oscillatory component of\r\nthe flow. Expressions for the flow velocity, pressure, and the energy\r\nexpended by a cilium are obtained for small oscillatory Reynolds numbers.\r\nCalculations are carried out with the data obtained for the two\r\nciliates Opalina ranarurn and Paramecium multimicronucleatum. The\r\nresults are compared with those of previous theoretical models and\r\nsome experimental observations.
\r\n\r\nIn Part II a model is developed for representing the mechanism\r\nof propulsion of a finite ciliated micro-organism having a prolate\r\nspheroidal shape. The basic concept of the model is to replace the\r\nmicro-organism by a prolate spheroidal control surface at which\r\ncertain boundary conditions on the fluid velocity are prescribed. These\r\nboundary conditions, which admit specific tangential and normal\r\ncomponents of the flow velocity relative to the control surface, are\r\nproposed as a reasonable representation of the overall features of the\r\nflow field generated by the motion of the cilia system. Expressions\r\nare obtained for the velocity of propulsion, the rate of energy dissipation\r\nin the fluid exterior to the cilia layer, and the stream\r\nfunction of the motion. The effect of the shape of the organism upon\r\nits locomotion is explored. Experimental streak photographs of the\r\nflow around both freely swimming and inert sedimenting Paramecia\r\nare presented and compared with the theoretical prediction of the\r\nstreamlines.
" }, { "name": "Kotsovinos, Nikolas Evangelos", "degree": "PhD", "year": "1975", "title": "A Study of the Entrainment and Turbulence in a Plane Buoyant Jet", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechETD:etd-05162007-081622", "creators": [ { "name": { "family": "Kotsovinos", "given": "Nikolas Evangelos" }, "id": "Kotsovinos-Nikolas-Evangelos", "display_name": "Kotsovinos, Nikolas Evangelos" } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/JBRN-V548", "abstract": "The entrainment and mixing processes in a two-dimensional vertical turbulent buoyant (heated) jet in its transition state from a pure jet to a pure plume have been studied. The ambient fluid is of uniform density and non-flowing except for the flow induced by the jet. Density variations are assumed small.\r\n\r\nThe equations of motion integrated across the jet have been carefully examined and it has been found that the kinematic buoyancy flux of a heated plume and the kinematic momentum flux of a pure jet are not in general conserved. It has been proven that the flow in a two-dimensional pure jet is not self-preserving.\r\n\r\nA systematic set of experiments was carried out to examine turbulent buoyant jet behavior for a wide range of initial Richardson numbers (or densimetric Froude numbers). Values of the Richardson number, which describes the relative importance of buoyancy in a jet, extended from the value appropriate for a pure jet (zero) to that appropriate for a plume (approximately 0.6). The buoyant jet temperature and velocity fields were measured using calibrated fast response thermistors and a Laser Doppler velocimeter respectively. The velocity and temperature data obtained were recorded magnetically in digital form and subsequently processed to extract both mean and fluctuating values of temperature and velocity.\r\n\r\nThe structure of the mean flow (including the spreading rate of the mean velocity and temperature profiles, velocity and temperature distribution along jet axis, and the heat flux profile), the turbulence structure (including the profile of turbulence intensity and turbulent heat transfer, probability density distribution of temperature and velocity, skewness and flatness factor of temperature fluctuations) and the large scale motions (intermittency, profile of maximum and minimum temperature, frequency of crossing of hot/cold, cold/hot interface) of a buoyant jet were investigated as a function of the jet Richardson number. It was determined that the turbulent heat transfer and the turbulent intensity increase with increasing the Richardson number. The spreading rate of the transverse mean velocity and temperature profiles were found to be independent of the Richardson number. The turbulent buoyancy flux in a fully developed buoyant jet has been found to be a significant fraction (38%) of the axial buoyancy flux." }, { "name": "Kulkarny, Vijay Anand", "degree": "PhD", "year": "1975", "title": "An Experimental Investigation on Focussing of Weak Shock Waves in Air", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042007-082903", "creators": [ { "name": { "family": "Kulkarny", "given": "Vijay Anand" }, "id": "Kulkarny-Vijay-Anand", "display_name": "Kulkarny, Vijay Anand" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KK7V-6827", "abstract": "The behavior of focussing weak shock waves is experimentally investigated with a view to observe and understand the processes occurring near the focus, especially the processes that control the maximum amplitude. Concave reflectors are used against the endwall of a large 17\" diameter shock tube, to focus the plane incident shock. Reflectors producing line and point foci, and cusped and smooth caustics are examined for incident shock Mach numbers ranging between 1.005 to 1.5. The flowfield is observed with spark shadowgraphs to visualize the motion of various wavefronts. Pressure histories measured at various points in the flow with miniature piezoelectric gauges provide additional information about the various processes occurring near the focus.\r\n\r\nShadowgraphs show that for weak shocks, the observed foci are predominantly nonlinear, even though away from the focus, the shockfronts appear to be almost acoustic. Thus a weak shockfront, after the focus, crosses itself and forms a loop, which is an essential feature of acoustic wavefronts. Nonetheless, at the focus, distortion in the geometry of the fronts due to nonlinear effects is very prominent. Inherently nonlinear phenomena, such as formation of three-shock intersections, lead to foci of finite size, in which, as the pressure measurements show, the amplitudes are finite.\r\n\r\nThe amplitude dependence of these phenomena confirms that they are basically nonlinear. The geometrical distortion and the focus are larger for stronger shock waves, and the maximum amplification is smaller. Further, when the distortion becomes significant compared to the size of the initial shockfront, a transition occurs in the geometry of the focussed shockfront. In this case, the focussed front does not cross and remains \"unlooped\", which is consistent with the nonlinear behavior predicted by shock dynamics.\r\n\r\nThe transition in the geometry of the wavefronts is related to the behavior of the three-shock intersections formed near the focus. In fact, it is shown that the occurrence of crossed or uncrossed shockfronts is very parallel to the occurrence of regular or Mach reflection, respectively, in the case of a shock diffracted by a wedge. (The reflecting wedge surface corresponds to the axis of symmetry in a focussing process.) The dependence on the steepness of the approaching waves is also similar in the two cases; rapid convergence of waves suppresses nonlinear effects, whereas in a slow convergence, nonlinear effects gain prominence.\r\n\r\nThe pressure histories at various locations, when correlated with the waves occurring there, show that nonlinear diffraction processes are very important. In fact, it is shown that the formation of the three-shock intersection occurs due to nonlinear distortion and breaking of a compressive diffraction, and that, in the focus, the limiting and reduction of the peak amplitude occurs by a diffracted expansion overtaking the shock due to nonlinear effects." }, { "name": "Laguna, Glenn Alan", "degree": "PhD", "year": "1975", "title": "Second Sound Attenuation in a Liquid Helium Counterflow Jet", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282010-140423372", "creators": [ { "name": { "family": "Laguna", "given": "Glenn Alan" }, "id": "Laguna-Glenn-Alan", "display_name": "Laguna, Glenn Alan" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/7C0G-HK08", "abstract": " The attenuation of a beam of high frequency second sound traversing a counterflow jet in liquid helium has been measured in the temperature range 1.6 to 2.06\u00b0K. Combined use of thin film superconducting thermometers with specially developed low noise amplifiers allowed a temperature resolution of better than one part in 10^8 \u00b0K. The additional attenuation due to the jet was found to be less than 10 percent of the predicted value using the theory of mutual friction in a supercritical counterflow, and consistent with the result of earlier temperature gradient and ion beam attenuation measurements." }, { "name": "Lee, Tsu-wei Frank", "degree": "PhD", "year": "1975", "title": "Deep Levels and High Concentrations of Impurities in Silicon", "advisor": "Mayer, James Walter; McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10122021-201307143", "creators": [ { "name": { "family": "Lee", "given": "Tsu-wei Frank" }, "id": "Lee-Tsu-wei-Frank", "display_name": "Lee, Tsu-wei Frank" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/j2rb-3s97", "abstract": "A study of the electronic levels associated with the divacancy in silicon is reported. The extended H\u00fcckel theory is shown to \r\nreproduce the band structure of silicon near the energy gap. The electronic levels of the divacancy are calculated by considering a periodic array of large unit cells each containing 62 atoms; a 64 atom perfect cell with 2 atoms removed to form the divacancy. The results are found to be in qualitative agreement with the results of EPR and infrared absorption measurements.
\r\n\r\nA theory of the variation of conduction electron density with the temperature for various impurity concentrations is presented. In addition to previously noted effects of conduction band edge lowering and screening of the impurity potential by the conduction electrons, the influence of a finite energy transfer integral and spatial fluctuation in the potential are included. The results show that for ND \u2272 1017 cm-3 silicon one must not view the activation as occurring between a single impurity level and a well defined conduction band edge, but must include the broadening of the impurity level and tailing of the conduction band density of states, Calculations for the shallow donors P, Sb, and As in Si are found to be in satisfactory agreement with experiment.
\r\n\r\nHall and sheet resistivity measurements as a function of temperature combined with layer removal have been used to study Si implanted with Te at energies up to 220 KeV. At low doses (\u2272 4 x 1012 cm-2), Te has a donor level with 140 meV activation energy. The activation energy decreases at higher Te doses and is approximately equal to zero for Te doses \u2273 1015 cm-2. At high dose levels, the number Ns of conduction electrons is more than an order of magnitude below the number of Te cm-2. High temperature anneal treatments followed by quenching did not produce a substantial increase in Ns suggesting that the formation of Te clusters was not responsible for the low value of Ns. Also channeling measurements indicated a high substitutional fraction. Based on differential Hall measurements on P-implanted samples, with and without Si pre-damage, we conclude that residual radiation damage is not a major factor. A theoretical calculation, which includes the effect of decrease of activation energy with increasing impurity concentrations, indicated that the number of conduction electrons could be much less than the number of implanted Te even though the apparent activation energy is almost zero. Although the results of theoretical calculation do not give quantitative agreement with the experimental results, they do confirm the changes in apparent activation energy with concentration.
" }, { "name": "Livanos, Alexander Constantine R.", "degree": "PhD", "year": "1975", "title": "I. Edge Diffraction of a Convergent Wave. II. Diffraction of Laguerre Gaussian Beams by a Circular Aperture", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11112003-093137", "creators": [ { "name": { "family": "Livanos", "given": "Alexander Constantine R." }, "id": "Livanos-Alexander-Constantine-R", "display_name": "Livanos, Alexander Constantine R." } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/KDAN-7033", "abstract": "PART I.\r\n\r\nClosed form solutions have been derived for the focal plane diffraction patterns of (a) a convergent spherical wave illuminating a segment of a circular aperture and (b) a convergent Gaussian beam diffracted by an infinite edge. The theoretical results agree with the experiments showing that the edge produces a spike of light with intensity variation inversely proportional to the squared distance from the center, that the pattern is symmetric in the focal plane, and that in the case of the uniform illumination the intensity has high spatial frequency components while for the Gaussian case the pattern does not ring when the edge is positioned symmetrically in the beam.\r\n\r\nIn addition, the near focus intensity distribution for a convergent uniform amplitude wave illuminating a semicircular aperture is presented, and it is shown that the fact that the radiation pattern is symmetric only at the focal plane can be used very effectively to determine the exact location of that plane.\r\n\r\nPART II.\r\n\r\nThe diffraction of a Laguerre Gaussian beam (TEM[subscript p,l] mode of a laser resonator) by a circular aperture is presented here. We calculate the electric field for the Fresnel region, and study the loss of power as a function of relative aperture size and mode index, showing that the conventional rule of thumb in selecting apertures by \"going out a few times w[subscript o]\" is not accurate for large mode indices." }, { "name": "MacQuigg, David Rodgers", "degree": "PhD", "year": "1975", "title": "The Modulated Grating Hologram", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212014-154218408", "creators": [ { "name": { "family": "MacQuigg", "given": "David Rodgers" }, "id": "MacQuigg-David-Rodgers", "display_name": "MacQuigg, David Rodgers" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/VZN5-MT65", "abstract": "A phase and amplitude, off-axis hologram has been synthesized\r\nfrom three computer-generated transmission masks, using a multiple-exposure\r\nholographic recording method. Each of the masks controls one\r\nfixed-phase component of the complex hologram transmittance. The basic\r\ngrating is generated optically, relieving the computer of the burden of\r\ndrawing details the size of each fringe. The maximum information\r\ncapacity of the computer plotting device can then be applied to the\r\ngeneration of the grating modulation function. By this method large\r\ndigital holograms (25 mm by 25 mm) have been synthesized in dichromated\r\ngelatin. The recording method is applicable to virtually any holographic\r\nmedium.
\r\n\r\nThe modulated grating hologram was designed primarily for the\r\napplication of spatial filtering, in which the requirement is a hologram\r\nwith large dynamic range and large free spectral range. Choice of a\r\nlow-noise, high-efficiency medium such as dichromated gelatin will allow\r\nexceptionally large dynamic range. Independence of the optically-generated\r\ncarrier grating from the computer-generated modulation functions\r\nallows arbitrarily large free spectral range.
\r\n\r\nThe performance of a holographic spatial filter will be limited\r\nultimately by noise originating from imperfections in the holographic\r\nmedium. The characteristics of this noise are analyzed, and in the\r\ncase of a high diffraction efficiency hologram are shown to differ significantly\r\nfrom previous analyses. The dominant noise source in holograms\r\nof high diffraction efficiency will be scattering of the first order\r\nor imaging wave by deformations in the hologram surface or other\r\neffects of low spatial frequency. Experimental measurements in various\r\nlow-noise holographic media verify these predictions.
\r\n" }, { "name": "Marrello, Vincent", "degree": "PhD", "year": "1975", "title": "Part I. Solid-Phase Growth of Germanium Structures. Part II. Condensation of Injected Electrons and Holes in Germanium", "advisor": "Mayer, James Walter; McGill, Thomas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08312021-204039498", "creators": [ { "name": { "family": "Marrello", "given": "Vincent" }, "id": "Marrello-Vincent", "display_name": "Marrello, Vincent" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" }, { "name": { "family": "McGill", "given": "Thomas C." }, "id": "McGill-T-C", "role": "advisor", "display_name": "McGill, Thomas C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/56z0-0h91", "abstract": "Part I
\r\n\r\nSolid-solid reactions between a semiconductor and evaporated metal films can lead to semiconductor crystal growth. In this work, two aspects of solid-phase growth have been investigated; 1) growth of epitaxial Ge layers from a solid solution of Ge in an Al film onto single crystal Ge substrate (solid-phase epitaxy), and 2) growth of Ge crystallites in Al films from amorphous Ge films deposited on the Al film.
\r\n\r\nIn solid-phase epitaxial studies, backscattering measurements with MeV 4He+ ions showed that a solid-solid reaction occurred at temperatures below the Ge/Al eutectic point. Channeling effect measurements with MeV 4He+ ions indicated that the Ge layers were well-ordered and epitaxial. Electron microprobe measurements indicated the Ge layers contained Al. Hall effect measurements showed the Ge layers to be heavily p-doped. These Ge layers have been used to construct p-type contacts on p-n diodes, double injection diodes and nuclear particle detectors.
\r\n\r\nGe crystallite growth in Al films occurs when an amorphous Ge film is deposited on an Al film and is heated at temperatures below the Ge/Al eutectic point. Crystallization of Ge occurs by an initial dissolution of Ge into the Al film followed by diffusion and growth of Ge crystallites in the Al films.
\r\n\r\nThe nature of Ge crystallite growth has been studied by MeV 4He+ ion backscattering techniques, transmission electron diffractometry, scanning electron microscopy and electron microprobe analysis.
\r\n\r\nPart II
\r\n\r\nWe demonstrate for the first time that the condensation of electrons and holes in Ge can be produced by electrical injection of carriers. The condensate occurs in double injection diodes at temperatures of at least up to 5\u00b0K.
\r\n\r\nThe recombination radiation from the condensate was analysed using an infrared spectrometer. The LA- and TO-phonon assisted recombination radiation lines from the condensate occur at 709 meV and 700 meV respectively. The linewidth at half maximum of the 709 meV line is 3 meV. We measure a lifetime for the condensate of 40 \u03bcs. The radiation was emitted almost uniformly from the volume between the contacts of the double injection diode. The radiation intensity increased with increasing current and decreasing temperature.
\r\n\r\nLA-phonon assisted exciton and bound exciton recombination radiation lines at 714 meV and 712 meV respectively were observed from 7 to 15\u00b0K. Above 15\u00b0K, only the exciton line was observed. The recombination radiation lifetime of the exciton at 20\u00b0K is 6 \u03bcs.
" }, { "name": "Melville, Richard Devern Samuels", "degree": "PhD", "year": "1975", "title": "Spatial and Spectral Behavior of Speckle in an Imaging System", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02182005-111421", "creators": [ { "name": { "family": "Melville", "given": "Richard Devern Samuels" }, "id": "Melville-Richard-Devern-Samuels", "display_name": "Melville, Richard Devern Samuels" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2KP8-CT79", "abstract": "When coherent illumination is reflected from or transmitted through a medium which causes random phase changes in the illumination, a random interference pattern termed speckle results.\r\n\r\nWe have studied speckle in an imaging system and have described and measured the effect of polarization of the illumination, the first order statistics of speckle intensity, and the autocorrelation of speckle intensity as a function of space and wavelength variables.\r\n\r\nWe have measured the relationship between the amount of depolarization of a plane polarized input in transmission through opal glass diffusers of various thicknesses and the effect of this phenomenon on the first and second order statistics of speckle intensity. A relationship between diffuser thickness and the probability density function for speckle intensities has been calculated and measured. The autocorrelation of speckle intensities has been calculated and measured as a function of both the spatial dimension of the speckle pattern and the wavelength of the illumination. We find that the spatial behavior of the autocorrelation depends upon the limiting aperture of the optical system, while the wavelength dependence is a function of the roughness of the diffuser and is only very slightly influenced by the imaging system." }, { "name": "Moronval, Marc Jules", "degree": "PhD", "year": "1975", "title": "Optimization of Arch and Shell Structures", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272010-093909310", "creators": [ { "name": { "family": "Moronval", "given": "Marc Jules" }, "id": "Moronval-Marc-Jules", "display_name": "Moronval, Marc Jules" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EMCP-7017", "abstract": "Structural optimization of structures with respect to their shape and thickness distribution is studied using a variational approach. The behavioral constraint is either the state of stress or the stiffness.\r\nThe boundary value problems, derived using Optimal Control theory, are solved with the parallel shooting technique. For statically determinant arches subjected to a uniform pressure, the contribution of the shear force is included in the behavioral constraints to prevent the problems from being singular. For the case of membrane shells of revolution supporting a combined pressure and end traction loading case, solutions were obtained up to a critical value of the load coefficient. A physical interpretation of the singularity is obtained by including the possibility\r\nof discrete rings in the formulation. A set of optimality conditions for shells of revolution described by the bending theory, satisfying a stiffness constraint, is derived. The problem is found to be ill posed when the shear contribution is not included in the structural operator.\r\n" }, { "name": "Nicolaides, Pericles Leonidas", "degree": "PhD", "year": "1975", "title": "RELSIM - An On-Line Language for Discrete Simulation in Social Sciences", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09142021-200416356", "creators": [ { "name": { "family": "Nicolaides", "given": "Pericles Leonidas" }, "id": "Nicolaides-Pericles-Leonidas", "display_name": "Nicolaides, Pericles Leonidas" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/czr0-2x47", "abstract": "With the progress of science, our models of the world or any of its aspects become more and more complex, and therefore less and less susceptible to analytical solution. This is especially true in the field of social sciences, where statistical and stochastic processes are indispensable tools for model examination.
\r\n\r\nAs a result, various simulation languages or packages have been developed to aid in the formulation and testing of such models. This thesis considers the directions that such languages have taken, and introduces a new such language, RELSIM, which attempts to meet present needs of the potential simulation designer. It features a simple structure that is also very flexible, and a timesharing environment, which allows dialogue, gaming and experimentation in the design and the actual simulation run.
\r\n\r\nA full description of RELSIM is given, with examples illustrating its use, and the implementation of the language on the REL system is also discussed.
" }, { "name": "Roberts, Paul Thomas", "degree": "PhD", "year": "1975", "title": "Gas-To-Particle Conversion: Sulfur Dioxide in a Photochemically Reactive System", "advisor": "Friedlander, Sheldon K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10212022-160818228", "creators": [ { "name": { "family": "Roberts", "given": "Paul Thomas" }, "id": "Roberts-Paul-Thomas", "display_name": "Roberts, Paul Thomas" } ], "advisors": [ { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "advisor", "display_name": "Friedlander, Sheldon K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/c8qr-7m43", "abstract": "Particulate phase sulfur compounds are suspected to be major contributors to human health effects and visibility reduction. The formation of such aerosol sulfur compounds in a photochemically reactive system was studied, in both the laboratory and the field.
\r\n\r\nAn aerosol vaporization technique was developed capable of measuring both total filter and cascade impactor aerosol samples for nanogram levels of sulfur compounds. This method measures the total aerosol sulfur species concentration.
\r\n\r\nModel calculations using measured aerosol and gas phase sulfur concentrations and air trajectory analysis provided estimated conversion rates for sulfur dioxide to aerosol sulfur compounds. For afternoon periods in Los Angeles, the pseudo-first order rate constant for SO2 oxidation was from 1 to 15% hr-1. The estimated rates were higher at higher levels of photochemical activity. In the atmosphere and in smog chamber studies, this rate is dependent upon the presence of O3 and olefins, as well as SO2. In smog chamber experiments with 1-heptene, NOx and SO2, the formation of the aerosol organic and sulfur compounds is consistent with the major aerosol producing step being a reaction between SO2 and a reactive intermediate of the O3-1-heptene reaction.
\r\n\r\nThe size distribution of aerosol sulfur species was measured at various locations in the Los Angeles Basin. The sulfur was concentrated in the less than 0.5 \u03bcm size range during periods of high photochemical activity and in the 0.25-1.0 \u03bcm size range during other daylight hours. Measurements of the size distribution of aerosol sulfur species were taken during smog chamber experiments with 1-heptene, NOx and SO2 added to unfiltered ambient air, and irradiated with sunlight. A bimodal distribution developed with 2/3 of the sulfur in a mode below 0.1 \u03bcm and 1/3 in a mode above 0.2 \u03bcm in diameter.
\r\n\r\nThe present and future effects of automobile emissions on aerosol sulfur compounds were estimated. The present contribution of motor vehicles to aerosol sulfur air quality at Pasadena is minimal. The introduction of the catalytic converter on new automobiles is estimated to produce a small increase in aerosol sulfur concentrations at receptor sites; however, the catalytic converter is estimated to produce dramatic increases in aerosol sulfur concentrations near roadways.
" }, { "name": "Sankur, Haluk", "degree": "PhD", "year": "1975", "title": "Part I - Diffusion of Si in Al and Solid Phase Growth of Epitaxial Si Structures in Al. Part II - Investigation on the Si-Au Interface Effects and on the Phase Diagram of Si-Au-Cu", "advisor": "McCaldin, James Oeland", "url": "https://resolver.caltech.edu/CaltechTHESIS:10282021-200925928", "creators": [ { "name": { "family": "Sankur", "given": "Haluk" }, "id": "Sankur-Haluk", "display_name": "Sankur, Haluk" } ], "advisors": [ { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-J-O", "role": "advisor", "display_name": "McCaldin, James Oeland" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/cvpy-tr40", "abstract": "Part I
\r\n\r\nReactions between solid metal films and semiconductors are important in the reliability, operation of semiconductor devices and growth of semiconductor structures in solid state. In this work diffusion and precipitation of Si in Al films and growth of Si epitaxial structures in solid Al have been studied.
\r\n\r\nDiffusivity and solubility of Si in Al films of an integrated circuit structure have been investigated by means of electron microprobe analysis at temperatures between 360\u00b0C and 560\u00b0C. The Si solubility was found to be in essential agreement with values reported in the literature for bulk Al. The Si diffusivity was found to be enhanced with respect to bulk values and the activation energy for diffusion reduced by 42% from bulk value to 0.8 eV. The enhanced diffusivity and reduced activation energy are due to the presence of a large number of structural defects -- mainly dislocations -- in the evaporated Al film.
\r\n\r\nThe thin Al films were also analyzed for the ultimate location of Si precipitation with the electron microprobe. Si in solution in Al becomes supersaturated and precipitates upon cooling from the dissolution temperature. Si in Al considerably less than a diffusion length from the substrate Si was found to regrow there. Elsewhere Si formed precipitates, preferentially near the free surface of the Al film.
\r\n\r\nIn view of the results of the precipitation experiments, investigation of the growth of Si epitaxial structures in solid Al onto crystal Si substrates was performed by means of scanning electron microscopy. A variety of growth structures, such as mesas, faceted structures, thin vertical membranes, large plateaus were observed. The morphology of these structures depended on the amount of Si deposited in the Al film, annealing conditions, stresses in the metal film, crystalline orientation of the substrate surface.
\r\n\r\nPreferential growth was observed to occur at reentrant corners and small diameter oxide cuts. The probable cause for such preferential growth was indicated in pressure experiments which showed that regions in the solid Al under relatively less compression are favored locations for growth.
\r\n\r\nPart II
\r\n\r\nInterface conditions between a metal and a metal or semiconductor are known to affect solid state reactions there. In the present work dissolution reaction of crystalline and amorphous Si into evaporated Au films was studied with electron microprobe and scanning electron microscopy. The dissolution pattern was found to be nonuniform along the plane of the surface and dependent on the crystalline orientation of the Si substrate. The latter behavior was changed upon evaporation of a thin Pd layer between Au and Si, which greatly facilitated the dissolution reaction.
\r\n\r\nInvestigation of Si dissolution in Au by electron microprobe analysis also indicated that Si solubility was below the sensitivity of this analysis technique. A study of Si-Au-Cu ternary solid solution was undertaken in view of the more extensive solubility of Si in Cu compared to that in Au. The analysis, which was performed by powder X-ray diffraction and micrography, indicated that a continuous ternary solid solution existed through most of the Cu-Au solubility range, and that it was in equilibrium with a phase, with cubic lattice structures. The solubility of Si deviated from the linear interpolation of binary solubilities and from a monotonically decreasing behavior going from Cu-rich toward Au-rich corner of the diagram.
" }, { "name": "Sarohia, Virendra", "degree": "PhD", "year": "1975", "title": "Experimental and Analytical Investigation of Oscillations in Flows over Cavities", "advisor": "Roshko, Anatol; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-05032007-131245", "creators": [ { "name": { "family": "Sarohia", "given": "Virendra" }, "id": "Sarohia-Virendra", "display_name": "Sarohia, Virendra" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WJC1-X942", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn this study, an analytical and experimental approach has been used to investigate the phenomenon of flow induced oscillations in cavities. Laminar axisymmetric flows over shallow cavities at low subsonic speeds were experimentally investigated using constant temperature hot-wire anemometry. This study comprised the following: study of the effect of the freestream and cavity configuration on onset of cavity oscillations; measurements of cavity shear layer under a wide range of cavity and flow configurations, and the distribution of the phase of the propagating disturbances during both first and second mode of cavity oscillation for a fixed Reynolds number at the upstream corner. Both motion and instant pictures of cavity shear flow, visualized by smoke injection, were obtained. Experiments were also done to investigate the effect of artificial excitation and of mass injection on the onset of cavity oscillations.\r\n\r\nThe present study indicates that the cavity depth has little effect on oscillations in shallow cavities, except when the depth is of the order of the thickness of the cavity shear flow. For such cavity configurations, measurements indicate a strong stabilizing effect of depth on laminar cavity shear layer. Results of motion pictures and hot-wire surveys of the cavity shear layer show that, close to the downstream cavity corner, large lateral motion of the shear layer occurs, which results in a periodic shedding of vortices at a frequency of cavity oscillations. Mean velocity measurements show growth rates as high as [...] 0.022 where [...] is the shear layer momentum thickness and x is the streamwise coordinate. These are attributed to strong imposed velocity fluctuations on the flow, by the oscillating cavity system.\r\n\r\nPhase measurements indicate that the disturbances propagate at a constant phase speed through the cavity shear layer. The wave length of the propagating disturbance bears an approximate integral relation to cavity width, in each mode of cavity oscillation given by [...] where b is the cavity width, [...] the wave length of the propagating disturbance and N is an integer, which takes values 0, 1, 2, ... etc. depending upon the mode of oscillation.\r\n\r\nStability calculations of the measured mean velocity profile were made by numerically integrating the governing equation of motion. These numerical results were used to compute the phase and the integrated amplification of the growing disturbances, through the cavity shear layer. Finally, the mode of cavity oscillation can be predicted for a given cavity flow by studying simultaneously the phase and integrated amplification of various disturbance frequencies through the shear layer and applying the mode relation." }, { "name": "Satorius, Edgar Harry", "degree": "PhD", "year": "1975", "title": "Electromagnetic Pulses at the Boundary of a Nonlinear Plasma", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:09172021-215240263", "creators": [ { "name": { "family": "Satorius", "given": "Edgar Harry" }, "id": "Satorius-Edgar-Harry", "display_name": "Satorius, Edgar Harry" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/d6ww-a643", "abstract": "This paper describes an investigation of the behavior of strong electromagnetic pulses at the boundary of a nonlinear, cold, collision-less, and uniform plasma. The nonlinearity considered here is due to the nonlinear terms in the fluid equation which is used to describe the plasma.
\r\n\r\nTwo cases are studied. First, we consider the case where there is a voltage pulse applied across the plane boundary of a semi-infinite, nonlinear plasma. Two different voltage pulses are considered: a delta function pulse and a suddenly turned-on sinusoidal pulse. The resulting electromagnetic fields propagating in the nonlinear plasma are found in this case. In the second case, we consider the reflection of incident E-polarized and H-polarized, electromagnetic pulses at various angles of incidence from a nonlinear, semi-infinite plasma. Again, two forms of incident pulses are considered: a delta function pulse and a suddenly turned-on sinusoidal pulse. In case two, the reflected electromagnetic fields are found.
\r\n\r\nIn both cases, the method used for finding the fields is to first solve the fluid equation (which describes the plasma) for the nonlinear conduction current in terms of the electric field using a perturbation method (since the nonlinear effects are assumed to be small). Next, this current is substituted into Maxwell's equations, and finally the electromagnetic fields which satisfy the boundary conditions are found.
" }, { "name": "Sharma, Dhiraj Kumar", "degree": "PhD", "year": "1975", "title": "Predictive Encoding of Digitized TV Pictures", "advisor": "Pierce, John Robinson", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292021-170924946", "creators": [ { "name": { "family": "Sharma", "given": "Dhiraj Kumar" }, "id": "Sharma-Dhiraj-Kumar", "display_name": "Sharma, Dhiraj Kumar" } ], "advisors": [ { "name": { "family": "Pierce", "given": "John Robinson" }, "id": "Pierce-J-R", "role": "advisor", "display_name": "Pierce, John Robinson" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/t5n9-3a07", "abstract": "In this report, we consider the problem of efficient intra-frame encoding of digitized TV pictures using Differential Pulse Code Modulation (DPCM) type encoders. Our goal is to reduce the average number of bits used to encode a pixel while subjective quality of the picture still remains acceptable.
\r\n\r\nTo this end, we propose some new predictors and compare them with the existing ones using the error criteria \"essential maximum\" and \"variance\" of the prediction errors. The two criteria have also been compared with respect to the subjective quality of the final encoded pictures. We propose to design the quantizers using \"mean n-th power\" distortion criterion. Effects of \"n\" on bit rate and subjective quality of the encoded picture have been studied as it varies from 1 to 6. In this way, we achieve reductions up to 6 to 1 in the bit rate with little degradation in the picture quality. We also consider the use of second and third order entropies of the encoded pictures to reduce the bit rate.
\r\n\r\nNext, we adapt the encoding procedure to local structural variations in the picture by first segmenting it in three areas of varying detail and then using the concepts developed for non-adaptive encoding to encode the three areas differently. The resulting encoder yields better picture quality than before and can be used to encode a broad class of pictures.
" }, { "name": "Simons, Donald Alan", "degree": "PhD", "year": "1975", "title": "Scattering of a Rayleigh Wave by the Edge of a Thin Surface Layer", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062019-152855123", "creators": [ { "name": { "family": "Simons", "given": "Donald Alan" }, "id": "Simons-Donald-Alan", "display_name": "Simons, Donald Alan" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/TZ1Z-9M12", "abstract": "This investigation treats the problem of the scattering of a Rayleigh wave by the edge of a thin layer which covers half the surface of an elastic half-space. The interaction between the layer and the half-space is described approximately by means of a model in which the effect of the layer is represented by a pair of boundary conditions at the surface of the half-space. Two parameters- one representing mass and the other, stiffness- are found to characterize the layer. The incident Rayleigh wave impinges normally upon the plated region from the unplated side.
\r\n\r\nIn the case where the mass of the layer vanishes, the problem is solved exactly using Fourier transforms and the Wiener-Hop\u00a3 technique, and numerical results are obtained for the amplitudes of the reflected and transmitted surface waves. In the more general case of a layer possessing both mass and stiffness, a perturbation procedure leads to a sequence of problems, each of which may be solved using Fourier transforms. The zeroth- and first-order problems are solved and the resulting approximate reflection and transmission coefficients are evaluated numerically for various ratios of layer mass to stiffness.
\r\n" }, { "name": "Smith, Gordon Carl", "degree": "PhD", "year": "1975", "title": "An Experimental Investigation of the Dynamic Fracture of a Brittle Material", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042006-082245", "creators": [ { "name": { "family": "Smith", "given": "Gordon Carl" }, "id": "Smith-Gordon-Carl", "display_name": "Smith, Gordon Carl" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/35AK-XJ82", "abstract": "A new method of experimentally investigating the behavior of a crack in a stress wave environment has been developed and used to study the initial stages of dynamic crack propagation in Homalite 100, a polyester. The experimental method, which employs an electromagnetic loading device, permitted the application of pressure pulses to the surfaces of an 18 inch crack. The amplitude (51 psi to 1020 psi) and duration (~ 200 \u00b5sec) of the pulses were highly repeatable. The experimental configuration simulates, in the vicinity of the crack tip, a tension wave impacting a stationary semi-infinite crack in an infinite two-dimensional body where the wave front is parallel to the crack. A high speed framing camera, synchronized with the loading device, was used to record the time required for the crack to begin to propagate and its subsequent extension and velocity. The experimental results were analyzed within the bounds of linearly elastic fracture mechanics and a correlation was made between the dynamic stress intensity factor and the time at which the cracks began to propagate. It was found that the critical stress intensity factor increased dramatically with increasing loading rates at very high rates, which contrasts with quasi-static loading where the critical stress intensity factor decreases with an increasing loading rate. A simple model suggests that temperature effects at the crack tip may account for the observed increase in the critical stress intensity factor at high loading rates. Crack branching of running cracks was observed but unlike previous reports of branching, the cracks in this study branched mostly into three separate fast-running cracks." }, { "name": "Stevens, Thomas", "degree": "PhD", "year": "1975", "title": "Numerical Methods for Ill-Posed, Linear Problems", "advisor": "Franklin, Joel N.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03292013-151040800", "creators": [ { "name": { "family": "Stevens", "given": "Thomas" }, "id": "Stevens-Thomas", "display_name": "Stevens, Thomas" } ], "advisors": [ { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "advisor", "display_name": "Franklin, Joel N." } ], "committee": [ { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "chair", "display_name": "Franklin, Joel N." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" }, { "name": { "family": "Luxemburg", "given": "W. A. J." }, "id": "Luxemburg-W-A-J", "role": "member", "display_name": "Luxemburg, W. A. J." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." } ], "option_major": [ "appmath" ], "doi": "10.7907/ZB0R-1F34", "abstract": "A means of assessing the effectiveness of methods used in the numerical solution of various linear ill-posed problems is outlined. Two methods: Tikhonov' s method of regularization and the quasireversibility method of Latt\u00e8s and Lions are appraised from this point of view.
\r\n\r\nIn the former method, Tikhonov provides a useful means for incorporating a constraint into numerical algorithms. The analysis suggests that the approach can be generalized to embody constraints other than those employed by Tikhonov. This is effected and the general \"T-method\" is the result.
\r\n\r\nA T-method is used on an extended version of the backwards heat equation with spatially variable coefficients. Numerical computations based upon it are performed.
\r\n\r\nThe statistical method developed by Franklin is shown to have an interpretation as a T-method. This interpretation, although somewhat loose, does explain some empirical convergence properties which are difficult to pin down via a purely statistical argument.
" }, { "name": "Sun, Yen-Sheng Edmund", "degree": "PhD", "year": "1975", "title": "Proximity Effect in Ag-Pb Alloys", "advisor": "Duwez, Pol E.; Tsuei, Chang-chyi", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212014-154147234", "creators": [ { "name": { "family": "Sun", "given": "Yen-Sheng Edmund" }, "id": "Sun-Yen-Sheng-Edmund", "display_name": "Sun, Yen-Sheng Edmund" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." }, { "name": { "family": "Tsuei", "given": "Chang-chyi" }, "id": "Tsuei-C-C", "role": "advisor", "display_name": "Tsuei, Chang-chyi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/eqtc-vh77", "abstract": "The superconducting properties and the microstructure of the\r\nAg100-xPbx alloys, 1 \u2264 x \u2264 5, prepared by rapid quenching from the\r\nliquid state with and without subsequent heat treatments, have been\r\nstudied. The x-ray diffraction measurements show that supersaturated\r\nsolid solutions of Pb in Ag can be obtained up to 3.2 at.% Pb as\r\ncompared to less than 0.1 at.% Pb at equilibrium. It was found that\r\nby suitable heat treatment it is possible to vary the size and distribution\r\nof the Pb precipitates in the Ag matrix and reproducible superconducting\r\nproperties in the alloy can be observed. The superconducting\r\ntransition temperature of these samples can be qualitatively explained\r\nby the Silvert and Singh's theoretical calculation. The theory\r\ndeveloped for the case of layer structure can be extended to three dimensions\r\nto explain the critical current versus temperature behavior.\r\nThe critical current versus field behavior of these alloys can be explained\r\nby the modification of the Josephson effect. Combining these\r\nresults together with the critical magnetic field measurements and the\r\nmicrostructure studies of the alloys, it can be concluded that the\r\nthree-dimensional proximity effect is the main mechanism for the superconductivity\r\nin the Ag-Pb alloys. Based on the Hilsch empirical\r\nformula which was based on experimental results obtained on layer\r\nstructures, the experimental data in this investigation show that the\r\nelectron-phonon-electron interaction in silver is attractive. The interaction\r\nparameter NV obtained is approximately 0.06, which would lead\r\nto a value of 10-5 \u00b0K for the superconducting transition temperature of\r\nAg. These values are in agreement with other determinations which\r\nwere done on vapor-deposited metallic film sandwiches. Hence, the\r\nHilsch empirical relation valid for layer structures is also valid in the\r\nthree-dimensional case. Because the transition temperature and the\r\ncritical current can be varied in a wide range by controlling the heat\r\ntreatments, the Ag-Pb superconductors might have some useful applications." }, { "name": "Szolovits, Peter", "degree": "PhD", "year": "1975", "title": "The REL Language Writer's Language: A Metalanguage for Implementing Specialized Application Languages", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10182021-214340088", "creators": [ { "name": { "family": "Szolovits", "given": "Peter" }, "id": "Szolovits-Peter", "display_name": "Szolovits, Peter" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/599s-1283", "abstract": "This thesis is an investigation into the task of implementing specialized computer application languages. It contains a discussion of the conceptual issues which make the development of specialized languages useful, and it motivates the selection of a scheme of syntax directed interpretation as the framework on which specialized languages are to be implemented. The thesis includes a description of the REL Language Writer's Language, in which the semantically primitive data types and operations and the extended syntax of object languages are to be specified. The definition of an illustrative object language for the storage and retrieval of personal bibliographic information is given. Also discussed is the relationship between this manner of language implementation and various alternative technologies.
" }, { "name": "Treweek, Gordon Paul", "degree": "PhD", "year": "1975", "title": "The Flocculation of E. coli with Polyethyleneimine", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04182014-094111781", "creators": [ { "name": { "family": "Treweek", "given": "Gordon Paul" }, "id": "Treweek-Gordon-Paul", "display_name": "Treweek, Gordon Paul" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "McKee", "given": "Jack E." }, "id": "McKee-J-E", "role": "chair", "display_name": "McKee, Jack E." }, { "name": { "family": "Davidson", "given": "Norman R." }, "id": "Davidson-N-R", "role": "member", "display_name": "Davidson, Norman R." }, { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "member", "display_name": "Friedlander, Sheldon K." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "member", "display_name": "Morgan, James J." } ], "option_major": [ "envreng" ], "doi": "10.7907/Y732-V890", "abstract": "A comprehensive study was made of the flocculation of dispersed E. coli bacterial cells by the cationic polymer polyethyleneimine (PEI). The three objectives of this study were to determine the primary mechanism involved in the flocculation of a colloid with an oppositely charged polymer, to determine quantitative correlations between four commonly-used measurements of the extent of flocculation, and to record the effect of varying selected system parameters on the degree of flocculation. The quantitative relationships derived for the four measurements of the extent of flocculation should be of direct assistance to the sanitary engineer in evaluating the effectiveness of specific coagulation processes.
\r\n\r\nA review of prior statistical mechanical treatments of absorbed polymer configuration revealed that at low degrees of surface site coverage, an oppositely- charged polymer molecule is strongly adsorbed to the colloidal surface, with only short loops or end sequences extending into the solution phase. Even for high molecular weight PEI species, these extensions from the surface are theorized to be less than 50 \u00c5 in length. Although the radii of gyration of the five PEI species investigated were found to be large enough to form interparticle bridges, the low surface site coverage at optimum flocculation doses indicates that the predominant mechanism of flocculation is adsorption\r\ncoagulation.
\r\n\r\nThe effectiveness of the high-molecular weight PEI species 1n producing rapid flocculation at small doses is attributed to the formation of a charge mosaic on the oppositely-charged E. coli surfaces. The large adsorbed PEI molecules not only neutralize the surface charge at the adsorption sites, but also cause charge reversal with excess cationic segments. The alignment of these positive surface patches with negative patches on approaching cells results in strong electrostatic attraction in addition to a reduction of the double-layer interaction energies. The comparative ineffectiveness of low-molecular weight PEI species in producing E. coli flocculation is caused by the size of the individual molecules, which is insufficient to both neutralize and reverse the negative E.coli surface charge. Consequently, coagulation produced by low molecular weight species is attributed solely to the reduction of double-layer interaction energies via adsorption.
\r\n\r\nElectrophoretic mobility experiments supported the above conclusions, since only the high-molecular weight species were able to reverse the mobility of the E. coli cells. In addition, electron microscope examination of the seam of agglutination between E. coli cells flocculation by PEI revealed tightly- bound cells, with intercellular\r\nseparation distances of less than 100-200 \u00c5 in most instances. This intercellular separation is partially due to cell shrinkage in preparation of the electron micrographs.
\r\n\r\nThe extent of flocculation was measured as a function of PEl molecular weight, PEl dose, and the intensity of reactor chamber mixing. Neither the intensity of mixing, within the common treatment practice limits, nor the time of mixing for up to four hours appeared to play any significant role in either the size or number of E.coli aggregates formed. The extent of flocculation was highly molecular weight dependent: the high-molecular-weight PEl species produce the larger aggregates, the greater turbidity reductions, and the higher filtration flow rates. The PEl dose required for optimum flocculation decreased as the species molecular weight increased. At large doses\r\nof high-molecular-weight species, redispersion of the macroflocs occurred, caused by excess adsorption of cationic molecules. The excess adsorption reversed the surface charge on the E.coli cells, as recorded by electrophoretic mobility measurements.
\r\n\r\nSuccessful quantitative comparisons were made between changes in suspension turbidity with flocculation and corresponding changes in aggregate size distribution. E. coli aggregates were treated as coalesced spheres, with Mie scattering coefficients determined for spheres in the anomalous diffraction regime. Good quantitative comparisons were also found to exist between the reduction in refiltration time and the reduction of the total colloid surface area caused by flocculation. As with turbidity measurements, a coalesced sphere model was used since the equivalent spherical volume is the only information available from the Coulter particle counter. However, the coalesced sphere model was not applicable to electrophoretic mobility measurements. The aggregates produced at each PEl dose moved at approximately the same vlocity, almost independently of particle size.
\r\n\r\nPEl was found to be an effective flocculant of E. coli cells at weight ratios of 1 mg PEl: 100 mg E. coli. While PEl itself is toxic to E.coli at these levels, similar cationic polymers could be effectively applied to water and wastewater treatment facilities to enhance sedimentation and filtration characteristics.
\r\n" }, { "name": "Vetter, Alan August", "degree": "PhD", "year": "1975", "title": "Kinetics and Structure of the CS\u2082/O\u2082 Flame Laser", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102007-131039", "creators": [ { "name": { "family": "Vetter", "given": "Alan August" }, "id": "Vetter-Alan-August", "display_name": "Vetter, Alan August" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/D6QA-YZ15", "abstract": "This thesis is a study of the interactions of chemical kinetics, relaxation processes, and low-speed fluid mechanics for the deflagration of gaseous carbon disulfide and oxygen under conditions for which laser action has been demonstrated. A four-reaction branching chain reaction mechanism is deduced from experimental evidence and reaction rates to represent the chemical kinetics of CS2/O2 combustion. This chain mechanism is used to explain some explosion phenomena and to obtain the initial conditions and initial chemical kinetics expected for the different types of CS2/O2 chemical lasers. The dynamics of chemical population and relaxation, including selective depopulation, of the vibrational levels of CO are discussed.\r\n\r\nThree analytical methods are employed to solve the premixed laminar flame problem for the CS2/O2 flame. The von Karman approximations and the thermal theory approximation are two of these methods; the third, which considers diffusion of only the chain carrier, is termed the single-species diffusion approximation. The flame speed, which is the eigenvalue of laminar flame propagation theories, was experimentally determined for the low-pressure CS2/O2 flame and compared to the magnitude and dependencies calculated by the analytic methods. Some qualitative measures of flame structure are compared to the calculated structure.\r\n\r\nDetails are given for a multi-slit injector whose design allows complete control over mixing. Results for this burner and premixed configuration burners are discussed.\r\n\r\nCO emission spectra were taken from CS2/O2 flames and the relative vibrational populations determined. The rates of population of the upper vibrational levels are calculated from these experimental spectra." }, { "name": "Wilgen, John Bernard", "degree": "PhD", "year": "1975", "title": "Cyclotron Harmonic Emission in a Penning Discharge", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07232014-141900755", "creators": [ { "name": { "family": "Wilgen", "given": "John Bernard" }, "id": "Wilgen-John-Bernard", "display_name": "Wilgen, John Bernard" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0Y87-V047", "abstract": "Microwave noise emission at the harmonics of the electron cyclotron frequency from the magnetized plasma column of a Penning discharge is investigated experimentally. The harmonic emission spectrum is observed using oxygen gas in a variety of discharge configurations. It is found that grid stabilization of the plasma\r\ncolumn has very little effect on the emission spectrum. Measurements of the shape and location of the harmonic emission lines are described in detail. On the basis of a microwave interferometer measurement of the electron density, it is concluded that the existence of a hybrid layer somewhere on the plasma column is a necessary condition for the observation of harmonic emission. The\r\nrelaxation time and the cathode voltage dependence of the harmonic emission are investigated using a pulse modulation technique. It is found that the emission intensity increases rapidly with the magnitude of the cathode voltage and that the relaxation time decreases with increasing neutral gas pressure. High intensity nonharmonic radiation is observed and identified as resulting from a beam-plasma wave\r\ninstability thereby eliminating the same instability as a possible source of the harmonic emission. It is found that the collective experimental results are in reasonable agreement with the single particle electrostatic radiation theory of Canobbio and Croci.
\r\n" }, { "name": "Wong, Hung Leung", "degree": "PhD", "year": "1975", "title": "Dynamic Soil-Structure Interaction", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05242023-213627945", "creators": [ { "name": { "family": "Wong", "given": "Hung Leung" }, "id": "Wong-Hung-Leung", "display_name": "Wong, Hung Leung" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/yqyx-mg56", "abstract": "The dynamic response of a structure placed on a deformable soil medium subjected to seismic excitation is studied. The basic phenomena of soil-structure interaction was investigated by several analytical models supplemented by experimental observations; a brief review of literature in this discipline is also included.
\r\n\r\nAmong the physical phenomena investigated: the effects caused by local topography, the interaction with other structures, and the dissipation of dynamic energy through the soil medium were described by exact series solutions. Foundations of arbitrary shape, however, were modeled by using an approximate integral representation. This latter method utilizes the principle of superposition and provides flexibility in analyzing numerically the three-dimensional disc foundations placed on the soil surface. The results indicate that the detailed description for the shape of a rigid foundation placed on a deformable soil medium is not essential in the overall response of the superstructure, but the stress distribution under the disc foundation is quite sensitive to these changes in detail.
\r\n\r\nIn this thesis, several methods for the calculation of foundation compliances for several types of foundation models were discussed, some of which have direct practical practical applications. The importance of the base input motion induced by incident seismic waves is also stressed, because the seismic input, along with the foundation compliances, are necessary for a complete analysis of this problem.
" }, { "name": "Blevins, Robert Dilworth", "degree": "PhD", "year": "1974", "title": "Flow Induced Vibration of Bluff Structures", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302005-082356", "creators": [ { "name": { "family": "Blevins", "given": "Robert Dilworth" }, "id": "Blevins-Robert-Dilworth", "display_name": "Blevins, Robert Dilworth" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/F3D4-5Q27", "abstract": "Models are developed for both multi-degree-of-freedom aerodynamic galloping and vortex induced oscillation of bluff structures. These models are useful in the analysis of elastic structures exposed to a steady fluid flow.\r\n\r\nAn asymptotic method, based on the approximation of Bogoliubov and Mitropolsky, is developed for the analysis of the autonomous, internally resonant, nonlinear differential equations produced by the models. It is shown that the solutions of these systems can be divided into two classes by the nature of the secular terms arising in the perturbation equations.\r\n\r\nA model for multi-degree-of-freedom galloping is developed by modeling the aerodynamic forces on the structure as dependent only on the relative magnitude and velocity of the flow to the structure. A simple criterion for the stability of the zero solution is presented. Examples are made with a noninertially coupled system with the torsion and plunge degrees-of-freedom and a cubic curve fit to the aerodynamic coefficients. Examples show that the system is dominated by either a torsion or a plunge mode except when the natural frequencies of these modes are in certain integer multiples. In these cases the two modes interact strongly and they achieve first order limit cycles simultaneously.\r\n\r\nA model for vortex induced vibration of elastic structures is produced from a control volume approach to the vortex shedding process. The model features both fluid and structural oscillators. The model parameters are determined from experimental data by matching the model response to experimental observation for the cases of fixed and forced cylinder motion. A frequency entrainment effect is produced by the model for an elastically mounted cylinder resonating with vortex shedding. The resonant amplitude of an elastically mounted cylinder predicted by the model is in good agreement with experimental data." }, { "name": "Brabston, Donald Campbell, Jr.", "degree": "PhD", "year": "1974", "title": "I. Numerical Solutions of Steady Viscous Flow Past Spheres and Gas Bubbles. II. Numerical Solution of Singular Endpoint Boundary Value Problems", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechETD:etd-08172005-081056", "creators": [ { "name": { "family": "Brabston", "given": "Donald Campbell, Jr." }, "id": "Brabston-Donald-Campbell", "display_name": "Brabston, Donald Campbell, Jr." } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/4719-D351", "abstract": "In Part I, numerical solutions of the Navier-Stokes equations are given for steady, viscous, incompressible, axisymmetric flow past a rigid and a spherical gas bubble. The problem is formulated in terms of a stream function and the vorticity which are expanded in finite Legendre series. The coefficients in these series satisfy a finite system of ordinary differential equations. A finite-difference scheme is used to solve the system with Newton's method used to solve the nonlinear difference equations. The results agree very well with low and high Reynolds number theories.
\r\n\r\nIn Part II, systems of ordinary differential equations with singular points of the first kind are considered. The singular point may be at either end, at both ends, or in the interior of a finite interval. A two-point linear system of boundary conditions is imposed at the endpoints. A theory is developed stating the conditions under which a unique solution will exist A numerical method is developed for solving these problems. In this method, a series solution about the singular point is matched to a finite difference solution away from the singular point. Error estimates are developed, and numerical examples are given.
" }, { "name": "Broome, Norval Lagier", "degree": "PhD", "year": "1974", "title": "Transient Radiation from Coaxial Waveguide and Cylindrical Monopole Antennas", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302005-110310", "creators": [ { "name": { "family": "Broome", "given": "Norval Lagier" }, "id": "Broome-Norval-Lagier", "display_name": "Broome, Norval Lagier" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5MP2-DD24", "abstract": "In this work the coaxial waveguide antenna is treated by the Wiener-Hopf technique and the transient radiation from a cylindrical monopole is developed in the light of the rigorous results obtained from the Wiener-Hopf analysis. Analytic expressions are derived for (1) the electromagnetic fields in the feed line and (2) the far zone radiation fields of the coaxial waveguide antenna, with time harmonic excitation voltage. Complete characterization of the transient behavior is also found for (1) the fields interior to the feed line and (2) the radiated fields for excitation voltages arbitrary in their time dependence to the extent that kb,ka << 1. This corresponds to the case of a thin antenna and excitation voltage with a non-zero rise time, specifically chosen so that frequencies violating the restriction kb,ka << l are negligible.\r\n\r\nThe transient radiation from the cylindrical monopole is developed in a closed analytic form which is relatively easy to interpret and apply. The expressions found offer an alternative to transient analysis by conventional methods requiring numerical techniques involving extensive computer calculations. They are also the basis for an uncomplicated procedure to synthesize a desired behavior of the transient radiation from cylindrical monopole antennas." }, { "name": "Crouse, Charles Brian", "degree": "PhD", "year": "1974", "title": "Engineering Studies of the San Fernando Earthquake", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechThesis:08112021-192505383", "creators": [ { "name": { "family": "Crouse", "given": "Charles Brian" }, "id": "Crouse-Charles-Brian", "display_name": "Crouse, Charles Brian" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/17yn-bc14", "abstract": "A number of accelerograms obtained during the San Fernando earthquake were analyzed to investigate the nature of the strong motion. The particular features studied were soil-structure interaction and the relative influence of local site conditions versus the source mechanism and travel paths of earthquake waves.
\r\n\r\nEvidence of soil-structure interaction in the EW fundamental mode of the Hollywood Storage building is seen in the earthquake data. General agreement exists up to ~ 5 c.p.s. in both lateral directions between theoretical, base to free field transfer functions and transfer functions derived from accelerograms obtained in the basement and adjacent parking lot. There was no evidence of soil-structure interaction in the Millikan Library and Athenaeum buildings on the Caltech campus, and this effect could not account for the major differences in their accelerograms.
\r\n\r\nAccelerogram, Fourier Amplitude Spectra, and Response Spectra data were compared from a group of six tall buildings close together near Wilshire Blvd. and Normandie Ave. in Los Angeles and from seven surrounding buildings, two to three miles away. The data indicated that local site conditions and soil-structure interaction were not major contributors to the observed differences in the response at these sites. There was correlation between the degree of similarity in the response at two sites and their distance apart. A simple wave superposition model with numerical examples confirms this correlation.
" }, { "name": "Dukelow, Robert Alexander", "degree": "PhD", "year": "1974", "title": "An Experimental Investigation of Very Low Frequency Semiconductor Noise", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052005-155759", "creators": [ { "name": { "family": "Dukelow", "given": "Robert Alexander" }, "id": "Dukelow-Robert-Alexande", "display_name": "Dukelow, Robert Alexander" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2E2R-Z765", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis represents an attempt to more accurately characterize the statistics of the very low frequency noise of a particular semi conductor device (a grounded input bipolar integrated operational amplifier) than has previously been achieved. Power spectral density estimates are obtained for frequencies ranging from 250 Hz to [...] Hz. These estimates are based on data recorded over an uninterrupted period of approximately 1 year (355.9 days). Relatively high sample rates are maintained for each source, allowing a high degree of accuracy in these estimates without resorting to the questionable process of averaging the estimates for a number of noise sources [1]. The high sample rate also allows for a reduction in the errors due to aliasing by the use of digital filtering techniques. Spectral density estimates for six separate noise sources are presented.\r\n\r\nThe preliminary objectives of the experiment were to search for a break in the [...] spectral density component of semiconductor noise and to attempt to establish the \"true\" value of [alpha] if a unique value exists. Very long time constant \"popcorn\" noise (ignored by one investigator because it is \"as natural as flicker noise itself\" [1, page 69]), proved to be an obstacle in measuring the \"pure\" l/f noise process and may not only be the reason for the wide range of values for a reported in the literature but, as suggested by some researchers [2], may be the cause of flicker noise. \"Popcorn\" noise was observed with apparent time constants greater than [...] seconds. The statistics of the observed \"popcorn\" noise were investigated and showed good agreement with the results of J. N. Puckett, Jr. [3] (who worked primarily with popcorn noise having time constants on the order of a few milliseconds) except for a few cases in which the waveform resembled that which might be expected if one popcorn component were to modulate another. The work of Puckett was also extended in that a test for burst waiting time dependency was performed. No evidence of dependency could be found. Popcorn noise components which were large enough to be clearly identified were removed in the time domain. This technique was found to be quite useful in improving the spectral estimates.\r\n\r\nAs in previous experiments, power supply regulation and temperature control were found to be essential. In this experiment, however, the temperatures of the noise sources and the power supply fluctuations were measured concurrently with the noise data so that their contribution to the total observed noise could be more accurately ascertained.\r\n\r\nNeither a break frequency in the [...] trend nor a unique [alpha] were established, although the values of [alpha] obtained were all slightly larger than but closer to 1.0 than most reported values. A nearly periodic component (with a period of 1 year) was also observed in two of the noise sources which were contained in a plastic integrated circuit package. Since this component cannot be explained by temperature or power supply voltage it is conjectured that other external parameters such as humidity or barometric pressure (or even cosmic radiation) may account for some of the observed noise, although no such component could be observed in the other four noise sources (which were housed in metal packages)." }, { "name": "Fletcher, Donnie Carlton", "degree": "PhD", "year": "1974", "title": "The Conservation Laws of Three Dimensional Linearized Elasticity Theory", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10122005-085657", "creators": [ { "name": { "family": "Fletcher", "given": "Donnie Carlton" }, "id": "Fletcher-Donnie-Carlton", "display_name": "Fletcher, Donnie Carlton" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/TC8V-H381", "abstract": "For linearized isotropic elastodynamics and elastostatics, Noether's theorem on invariant variational principles is used to obtain all conservation laws arising from a reasonably general group of infinitesimal transformations. A theorem regarding the completeness of the derived laws is proved, and the conservation laws are then used to derive the wave speed equation for the Rayleigh problem on the surface of an anisotropic half space. An example of additional laws following from the same group but from a more general version of Noether's theorem is given in an appendix devoted to a discussion of limitations on the completeness theorem." }, { "name": "Folsom, Blair Allen", "degree": "PhD", "year": "1974", "title": "I. Two-Phase Flow in Vertical and Annular Fluidized Beds. II. Unsteady Disturbances in Axial Compressors", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132005-133650", "creators": [ { "name": { "family": "Folsom", "given": "Blair Allen" }, "id": "Folsom-Blair-Allen", "display_name": "Folsom, Blair Allen" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/SBE9-8D93", "abstract": "Part I is a study of vertical and annular fluidized beds. The vertical fluidized bed was used to determine the responses of a total head probe and an electromagnetic probe to the average velocity through the bed. Both probes indicated velocities substantially higher than the calculated average fluid velocity for the suspension. The fluidized bed consisted of glass beads suspended in water flow and had an aspect ratio of 20. The average concentration distribution was measured over the height of the bed as well and was found to be constant within one tube diameter of the top and bottom of the bed.\r\n\r\nThe annular fluidized bed consisted of a suspension of small nylon spheres in a vortex-sink flow of water in a special annular chamber. The velocity distribution was deduced from pressure measurements in the flat side walls and the concentration distribution of particles was measured with a special optical meter. The drag coefficient of the particles and the wall shear stress were calculated from the measurements. At low concentrations the side wall boundary layers had a major effect on motion of the particles. At higher concentration the drag coefficient of the particles was found to have approximately the same value as for a vertical fluidized bed at the same concentration and Reynolds number. The wall shear stress coefficient was found to be of the same order of magnitude as for channel flow at the same Reynolds number.\r\n\r\nPart II is an analytical study of unsteady disturbances in an axial compressor. The blade forces were represented as a continuous distribution of body forces acting on the fluid and the equations of motion were linearized. Only axial variations in the mean flow were considered and the disturbances were limited to planar pressure and entropy waves. A numerical integration gave results that depended on frequency and indicated that the largest velocity fluctuations inside the compressor always occurred at either the front or rear. Two related problems were also considered. Disturbances were superimposed on the flow through a duct with a restriction, similar to a blade row, and the reflected and transmitted waves were determined as functions of frequency. The response of turning vanes, treated as an actuator disc, to small disturbances was also determined." }, { "name": "Griffin, Jerry Howard", "degree": "PhD", "year": "1974", "title": "Wave Front Analysis in the Scattering of a Plane Compressional Pulse by a Cylindrical Elastic Inclusion", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechETD:etd-10132005-083854", "creators": [ { "name": { "family": "Griffin", "given": "Jerry Howard" }, "id": "Griffin-Jerry-Howard", "display_name": "Griffin, Jerry Howard" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/AKFT-PB89", "abstract": "The plane-strain problem of a stress pulse striking an elastic circular cylindrical inclusion embedded in an infinite elastic medium is treated. The method used determines dominant stress singularities that arise at wave fronts from the focusing of waves refracted into the interior. It is found that a necessary and sufficient condition for the existence of a propagating stress singularity is that the incident pulse has a step discontinuity at its front. The asymptotic wave front behavior of the first few P and SV waves to focus are determined explicitly and it is shown that the contribution from other waves are less important. In the exterior, it is found that in most composite materials the reflected waves have a singularity at their wave front which depends on the angle of reflection. Also the wave front behavior of the first few singular transmitted waves is given explicitly.\r\n\r\nThe analysis is based on the use of a Watson-type lemma, developed here, and Friedlander's method (see his book Sound Pulses, Cambridge, 1958). The lemma relates the asymptotic behavior of the solution at the wave front to the asymptotic behavior of its Fourier transform on time for large values of the transform parameter. Friedlander's method is used to represent the solution in terms of angularly propagating wave forms. This method employs integral transforms on both time and [theta], the circumferential coordinate. The [theta] inversion integral is asymptotically evaluated for large values of the time transform parameter by use of appropriate asymptotics for Bessel and Hankel functions and the method of stationary phase. The Watson-type lemma is then used to determine the behavior of the solution at singular wave fronts.\r\n\r\nThe Watson-type lemma is generally applicable to problems which involve singular loadings or focusing in which wave front behavior is important. It yields the behavior of singular wave fronts whether or not the singular wave is the first to arrive. This application extends Friedlander's method to an interior region and physically interprets the resulting representation in terms of ray theory." }, { "name": "Jain, Atul", "degree": "PhD", "year": "1974", "title": "A Wavelength Diversity Technique for Smoothing of Speckle", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08312011-132624162", "creators": [ { "name": { "family": "Jain", "given": "Atul" }, "id": "Jain-Atul", "display_name": "Jain, Atul" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/02VQ-6128", "abstract": "Theoretical and experimental results are given for the\r\nwavelength dependence of speckle, thus establishing a method for the reduction of speckle noise in holographic microscopy with the use of multitoned illumination and a panchromatic viewing system. A model is presented for a partially diffuse phase type of object and the statistical behavior of t he speckle produced in the image of this\r\nobject is studied. A calculation is made for the spectral autocorrelation function which gives a wavelength spacing required to decouple the speckle patterns produced by two tones, this spacing being found to be inversely proportional to the standard deviation of the heights of the scatterers on the object. A criteria is defined for the degradation of an image due to speckle and the resultant improvement is found to depend on the square root of the\r\nnumber of independent tones used.\r\n\r\nThe wavelength dependence of speckle is verified in a\r\nseries of experiments where we illuminate the object by both laser and bandlimited light. We first demonstrate the averaging of speckle in the image of a pap smear when we use four tones of an argon laser (5145, 4965, 4880 and 4765 \u00c5). We then show that the image of a rough object is speckly even for bandwidths up to 5\u00c5; and then we demonstrate the smoothing of speckle when both a scotch\r\ntape diffuser and a section of an optic nerve is illuminated by six equally spaced bandlimited tones scanning 1,500\u00c5.\r\n\r\nThus, in this study, we demonstrate the feasibility of\r\neliminating objective speckle in holographic microscopy using a multimonochromatic source and also provide a theoretical basis for studying the properties of rough surfaces by studying the wavelength diversity of the speckle produced by them.\r\n\r\n" }, { "name": "Knight, Doyle Dana", "degree": "PhD", "year": "1974", "title": "An Analytical Investigation of Turbulent Flow Over a Wavy Boundary", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-151736905", "creators": [ { "name": { "family": "Knight", "given": "Doyle Dana" }, "id": "Knight-Doyle-Dana", "display_name": "Knight, Doyle Dana" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T9PD-TM13", "abstract": "The linearized, two-dimensional flow of an incompressible fully turbulent fluid over a sinusoidal boundary is solved using the method of matched asymptotic expansions in the limit of vanishing skin friction.\r\nA phenomenological turbulence model due to Saffman\r\n(1970, 1974) is utilized to incorporate the effects of the wavy boundary on the turbulence structure.\r\nArbitrary lowest order wave speed is allowed in order to consider both the stationary wavy wall, and the water wave moving with arbitrary positive or negative velocity.\r\nGood agreement is found with measured tangential velocity profiles and surface normal stress coefficients. The phase shift of the surface normal stress exhibits correct qualitative behavior with both positive and negative wave speeds, although predicted values are low.\r\n" }, { "name": "Lugujjo, Eriabu", "degree": "PhD", "year": "1974", "title": "I. Backscattering and Channeling Effect Studies on Semiconductor-Metal Systems. II. Low Temperature Migration of Silicon through Metal Films", "advisor": "Mayer, James Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:01282021-190841642", "creators": [ { "name": { "family": "Lugujjo", "given": "Eriabu" }, "id": "Lugujjo-Eriabu", "display_name": "Lugujjo, Eriabu" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0zd4-s880", "abstract": "PART I
\r\n\r\nChanneling measurements by backscattering of He and H ions have been made on <111>- and <110>-oriented Si covered with evaporated layers of Al and Au. The energy range was 0.4 - 1.8 MeV and the film thicknesses ranged between 100 and 1100\u00c5 for Au, and between 900 and 3000\u00c5 for Al. As a first approach to analysis of disorder in crystals, we have investigated the effects of simulated disorder in form of metal layers on the surface of Si and Ge. This has an advantage in that particle scattering in the metal films can be controlled independently of scattering in the underlying substrate. The minimum yield, half-width of the angular-yield profile and the depth dependence of aligned yield have been studied as a function of metal-film thickness and beam energy. Comparisons between experimental and calculated values have been made on the basis of two different treatments of plural scattering.
\r\n\r\nThe minimum yield values obtained by applying only a step-function approximation to the angular yield profile were first evaluated as a function of film thickness. The minimum yield, angular-yield profiles and dechanneling dependence on depth obtained witl1 Al films follow the predictions of Meyer's treatment of plural scattering.
\r\n\r\nA detailed study of minimum yield values on covered Si was then made. In this case the minimum yield was calculated from the Meyer treatment and probability curves determined from (i) a step-function approximation to the angular-yield profile, and (ii) two different axial scans on uncovered Si, one of which is azimuthally averaged. The minimum yields calculated using the step-function approximation and average probability curves are in good agreement with experimental results. This suggests that the step-function approximation, although less accurate than the azimuthally averaged procedure, is adequate for use with investigations of disorder in crystals by channeling-effect measurements. On the basis of the step function approximation, we have established universal curves from which minimum yield values as a function of disorder may be obtained.
\r\n\r\nPART II
\r\n\r\nThe backscattering spectrometry using 2 MeV He\u207a ions have been employed to study the phenomenon of low temperature migration of Si through thin films of Au and Ag evaporated on <110> and <111> Si single crystal substrates. The thicknesses of Au films ranged from 200 to 4000\u00c5, and those of Ag from 200 to 800\u00c5. Migration of Si into these metal films is observed when the systems are heat treated in an oxidizing ambient at low temperatures (150\u00b0C for Au, 400\u00b0C for Ag), well below their eutectic points (375\u00b0C for Au and 830\u00b0C for Ag).
\r\n\r\nThe migration of Si is followed by formation of a silicon-oxide layer on top of the metal film. The initial growth of this oxide layer is proportional to (time)\u00bd. The factors controlling this low-temperature oxide formation have been investigated. Both oxidizing ambient and orientation of the substrate influence the oxide growth rate, and the thickness of evaporated film determines the final thickness of the oxide. A model to explain the oxide-growth mechanism is presented.
\r\n\r\nThe migration of Si also has been studied through layers of Au with superimposed layers of Ag, and vice versa. It is found that the interface between Si and the metal film plays a leading role in these low-temperature migration studies.
" }, { "name": "Moeller, Thomas Lee", "degree": "PhD", "year": "1974", "title": "The Dynamics of a Spinning Elastic Disk with Massive Load", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03102021-235835719", "creators": [ { "name": { "family": "Moeller", "given": "Thomas Lee" }, "id": "Moeller-Thomas-Lee", "display_name": "Moeller, Thomas Lee" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/cq6c-nf52", "abstract": "This thesis analyzes the dynamics of a spinning elastic disk. The disk rotates at a constant angular velocity and is acted upon by a load consisting of a mass distributed over a finite area of the disk, a spring, and a dashpot. Using a finite mode approximation, the equation of motion of the transverse deflection of the disk is written as a system of ordinary differential equations with constant coefficients.
\r\n\r\nAnalysis of the eigenvalues of the finite mode approximation yields four distinct types of instability. An instability occurs due to the stiffness of the load, terminal instabilities occur due to both the mass of the load and the damping of the load, and an instability occurs as a result of modal coupling.
\r\n\r\nThe multiple mode approximation used in the spinning disk analysis is applied to a stationary disk with a moving load. Comparison of the spinning and stationary disk shows the influence of the centrifugal stress of the rotating disk.
\r\n\r\nThe direct stability methods of Liapunov are applied to the equation of motion for both the spinning and stationary disk and are used to prove the stability of the systems at speeds below certain critical speeds. Upper bounds for the difference between eigenvalues of the finite mode approximation and eigenvalues of a full infinite mode system are derived. These bounds are calculated for the eigenvalues of a modal coupling instability arising from the finite mode analysis to show that the solution of the full set of equations is also unstable.
" }, { "name": "Myers, Edward Payson", "degree": "PhD", "year": "1974", "title": "The Concentration and Isotopic Composition of Carbon in Marine Sediments Affected by a Sewage Discharge", "advisor": "Epstein, Samuel", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192021-200716816", "creators": [ { "name": { "family": "Myers", "given": "Edward Payson" }, "id": "Myers-Edward-Payson", "display_name": "Myers, Edward Payson" } ], "advisors": [ { "name": { "family": "Epstein", "given": "Samuel" }, "id": "Epstein-S", "role": "advisor", "display_name": "Epstein, Samuel" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/9dd2-v129", "abstract": "The impact of the discharge of primary treated effluent of a high suspended solids concentration on the sedimentary environment of the Palos Verdes Shelf was investigated. Analyses of the carbon content and the isotopic composition of sedimentary organic material with depth in the sediments and the areal distribution of these properties relative to the location of the Los Angeles County Sanitation Districts' ocean outfalls indicate that the outfalls are extremely important in determining the chemical and physical properties of sediments on the Palos Verdes Shelf. The analyses of various sedimentary cores specifically indicate that sludge-like matter has accumulated to depths of as great as twenty centimeters during the past 38 years.
\r\n\r\nCalculation of the accumulation rates of organic carbon suggests that the present outfall-induced sedimentation rate for organic carbon in the immediate vicinity of the discharge is as much as about 260 times that of the natural sedimentation of organic carbon for the Palos Verdes Shelf. One result of this rapid input of organic carbon is the occurrence of a relatively large area of surface anaerobic sediments. The relationship between the mass accumulation rates of organic carbon and the areal extent of surface anaerobic conditions is further discussed as related to the suspended solids concentration of discharged effluent.
\r\n\r\nThe uppermost outfall-influenced sediments are shown to be of high water content and to have a total organic carbon concentration as high as 12 percent which has a \u03b4C13 value of about -24.5 o/oo. Particulate organic carbon discharged from the outfall has narrow-ranged \u03b4C13 values of about -23.5 o/oo, thus indicating that the sedimentary carbon has incurred a diagenetic change resulting in the preferential decay of a higher \u03b4C13 fraction, or that there has been a preferential deposition near the outfall of particulates with a more negative \u03b4C13 value. Other possibilities are also discussed.
\r\n\r\nThe lower pre-outfall natural sediments on the Palos Verdes Shelf have organic carbon concentrations of about one percent. The \u03b4C13 values for these natural sediments are about -22.5 to -23.0 ‰ which is typical of other data reported in the literature for sediments of marine basins offshore of southern California.
" }, { "name": "M\u00e9ndez, Horacio Augusto", "degree": "PhD", "year": "1974", "title": "Shielding Theory of Enclosures with Apertures", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:10192017-142731943", "creators": [ { "name": { "family": "M\u00e9ndez", "given": "Horacio Augusto" }, "id": "M\u00e9ndez-Horacio-Augusto", "display_name": "M\u00e9ndez, Horacio Augusto" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9KW5D7F", "abstract": "Present methods for computing the shielding efficiency of metallic plates with apertures are based on the analysis of a plane wave incident on an infinite conducting sheet. When applied to actual enclosures with internal radiation sources, these methods lose all validity, and obviously fail to predict the measured results. Semi-empirical formulas are available for special cases,\r\nbut no serious analytic investigation has ever been conducted.
\r\n\r\nThis dissertation develops the theory of electromaqnetic radiation from metallic enclosures with apertures, excited by an internal source at frequencies below the fundamental resonance\r\nof the enclosure.
\r\n\r\nThe enclosure with an aperture is analyzed from two different points of view: as a cavity with a small aperture in a wall; and as a waveguide section short-circuited at one end and open at the\r\nother end.
\r\n\r\nRectangular geometries are used throughout, since these are by far the most commonly encountered in practical enclosures and cabinets.
\r\n\r\nUsing the corresponding dyadic Green's functions, the fields generated inside the enclosure by some simple sources are determined. In addition to the case of a Hertzian dipole - the building block for more complicated sources - a center-fed dipole and a square loop antenna are analyzed. The fields radiated through small apertures in a cavity are determined using Bethe's theory of diffraction by small holes. The radiation from an open waveguide is calculated with the help of field equivalence theorems, with assumptions applicable to the case of evanescent waves.
\r\n\r\nThe final step is to derive expressions for the \"Insertion Loss\" of the shield, defined as the ratio of the field strength at a point external to the shield, before and after the insertion\r\nof the enclosure. To accomplish this, the effect of the shield upon the input impedance of the antenna is analyzed, and expressions obtained for the applicable cases.
\r\n\r\nThe resulting insertion loss expressions are numerically evaluated for some representative cases, and graphically compared with a series of measurements performed to obtain experimental\r\nconfirmation. Very good agreement is obtained in all cases, establishing the validity of the analysis.
\r\n\r\nThus, this work provides accurate prediction capabilities for the design of shielded enclosures with apertures, in the presence of internal or external noise sources (the latter is a consequence\r\nof applying the reciprocity theorem). Hence, it constitutes a useful tool in the solution of electromagnetic interference and susceptibility problems.
" }, { "name": "Pashley, Richard Dana", "degree": "PhD", "year": "1974", "title": "Electrical Properties of Ion Implanted Layers in Silicon and Gallium Arsenide", "advisor": "Mayer, James Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:03102021-184153613", "creators": [ { "name": { "family": "Pashley", "given": "Richard Dana" }, "id": "Pashley-Richard-Dana", "display_name": "Pashley, Richard Dana" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/gat7-kp43", "abstract": "Part I
\r\n\r\nWith the advent of ion implantation, it has become possible to introduce many new dopant species into silicon. The electrical behavior of implanted species displaying deep energy levels was investigated in this work. Hall effect and sheet resistivity measurements were taken as a function of temperature to determine the carrier concentration, mobility, compensation, and impurity ionization energy in the implanted layers. However, since these electrical parameters varied with depth in the samples, conventional Hall effect methods were inadequate. Special differential Hall techniques were developed to characterize the inhomogeneous samples.
\r\n\r\nThe validity of this differential technique was demonstrated by investigating the doping effects of indium in silicon. Differential measurements were first made on samples shallow diffused with indium. Then the results were compared with bulk values that had been obtained in a uniformly doped sample by standard methods. In addition, studies were made on indium implanted silicon to determine the influence of radiation effects. In all three cases an indium acceptor level of 160 meV was observed. Mobility plots versus temperature were also consistent with bulk measurements. However, significant compensation effects were noticed in the implanted layers.
\r\n\r\nWith the analysis technique experimentally confirmed, the electrical behavior of tellurium implanted silicon was investigated. Samples were implanted with several doses to study the electrical activity as a function of impurity concentration. Isothermal anneal cycles were performed to determine the anneal temperature necessary to attain peak electrical activity. After anneal, differential Hall measurements were made from 100\u00b0 to 278\u00b0K to characterize the implanted layers. Tellurium was found to behave as a donor with an energy level of 140 meV in ion implanted silicon. For room temperature e1ectron densities above 1017 carriers/cm3, the ionization energy was observed to decrease. In conjunction with this decrease, the doping efficiency of ion implanted tellurium was also observed to decrease for concentrations in excess of 1017/cm3. Both of these effects were attributed to the influence of energy level broadening.
\r\n\r\nPart II
\r\n\r\nIon implantation was investigated as a doping process for the fabrication of submicron n-type layers in GaAs. Tellurium implantation was performed as a function of dose (3 x 1013 - 1 x 1015 Te/cm2) and substrate temperature (23\u00b0C - 350\u00b0C). After implantation, a protective dielectric coating was sputtered on the samples to prevent the GaAs from disassociating during the anneal. The protective qualities of three dielectrics (SiO2, Si3N4, AlN) were compared. Anneal temperatures ranged from 750\u00b0C to 950\u00b0C. The residual radiation damage and defects in the implanted layers were studied by photoluminescence and Rutherford backscatteringmeasurements. The electrical characteristics were analyzed by Schottky barrier capacitance-voltage and Hall effect measurements. Sequential Hall measurements in conjunction with layer removal were used to determine the carrier concentration and mobility profiles in the implanted layers. In addition, junction capacitance-voltae and current-voltage measurements were performed to evaluate the quality of implanted diodes.
\r\n\r\nThe samples implanted at room temperature and subsequently annealed with a SiO2 protective coating displayed almost no electrical activity and had intrinsic regions extending several microns into the GaAs. In contrast, high electrical activity was observed in samples implanted at elevated temperatures followed by anneal with a Si3N4 coating. A doping efficiency of 50% was achieved with a carrier density approaching the maximum attainable in tellurium doped GaAs (7 x 1018 electrons/cm3). However, the electrical activity varied over a wide range for samples with identical implant conditions. This scatter in the electrical measurements was attributed to the poor adherence of the Si3N4 layers to the GaAs surface during the anneal.
\r\n\r\nThe maximum electrical activity achieved using an AlN encapsulent was comparable to the value attained using a Si3N4 coating. However, the electrical activity was consistently high for the AlN protected samples and the AlN displayed better adherence to the GaAs during anneal than Si3N4.
" }, { "name": "Peterson, Lee Louis", "degree": "PhD", "year": "1974", "title": "The Propagation of Sunlight and the Size Distribution of Suspended Particles in a Municipally Polluted Ocean Water", "advisor": "North, Wheeler J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252011-133643810", "creators": [ { "name": { "family": "Peterson", "given": "Lee Louis" }, "id": "Peterson-Lee-Louis", "display_name": "Peterson, Lee Louis" } ], "advisors": [ { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "advisor", "display_name": "North, Wheeler J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/TADP-EA09", "abstract": "Waste discharge by the Los Angeles County Sanitation District (LACSD) affects sunlight in the ocean. Increased sunlight attenuance affects productivity and changes in\r\nocean surface color could be useful for monitoring dispersal.\r\n\r\nTemperature, sunlight irradiance in five colors, light beam attenuance, and particle size distributions were simultaneously measured as a function of water depth. A limited number of samples were analyzed by a co-worker for particulate percent organic carbon and particulate carbon isotope ratio. Background field stations included Catalina, Dana Point, and Rocky Point. Stations in the vicinity of the LACSD outfall at Whites Point represented a dispersing sewage field. The most significant result was that pollutants decreased the optical albedo of ocean water, increasing the extinction of sunlight irradiance as a function of optical depth.\r\n\r\nAdditional findings were that 1) pollutants decreased euphotic zone depths by as much as 60 percent (depending\r\nupon particle concentrations), 2) water surface color spectra indicated that pollutants increased light absorption at short wavelengths (violet, blue and green), 3) the average particle concentration in polluted waters was twice that of background waters, 4) the LACSD discharge caused a bimodal increase in particle numbers as a function of particle size; there was a dramatic increase for particles less than 1.5 microns and a secondary increase at 8 microns, 5) assuming real particle refractive indices (no light absorption by particles), scattering by natural and sewage particles was maximum between particle diameters 3 and 8 microns, 6) calculations assuming complex refractive indices (absorbing particles) indicated that light absorption by sewage particles was maximum for particles less than 1.5 microns in diameter, and 7) heavy (high specific gravity) particles had lower percent organic carbon and a lower carbon isotope ratio." }, { "name": "Prosperetti, Andrea", "degree": "PhD", "year": "1974", "title": "Viscous and Nonlinear Effects in the Oscillations of Drops and Bubbles", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11072006-111631", "creators": [ { "name": { "family": "Prosperetti", "given": "Andrea" }, "id": "Prosperetti-Andrea", "display_name": "Prosperetti, Andrea" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "chair", "display_name": "Plesset, Milton S." }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "member", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" } ], "option_major": [ "eng" ], "doi": "10.7907/FRDP-DV27", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe thesis is divided into three parts. In Part I the nonlinear oscillations of a spherical gas bubble in an incompressible, viscous liquid are investigated analytically by means of an asymptotic method. The effect of surface tension is included, and it is shown that thermal and acoustic damping can be accounted for by the suitable redefinition of one parameter. Approximate analytical solutions for the steady state oscillations are presented for the fundamental mode as well as for the first and second subharmonic and for the first and second harmonic. The transient behaviour is also briefly considered. The first subharmonic is studied in particular detail, and a new explanation of its connection with acoustic cavitation is proposed. The approximate analytical results are compared with some numerical ones and a good agreement is found.\r\n\r\nIn Part II the characteristics of subharmonic and ultraharmonic modes appearing in the forced, steady state oscillations of weakly nonlinear systems are considered from the physical, rather than mathematical, viewpoint. A simple explanation of the differences between the two modes, and in particular of the threshold effect usually exhibited by subharmonic oscillations, is presented. The principal resonance in the case of weak excitation is also briefly considered.\r\n\r\nFinally, in Part III the problem of two viscous, incompressible fluids separated by a nearly spherical free surface is considered in general terms as an initial value problem to first order in the perturbation of the spherical symmetry. As an example of the applications of the theory, the free oscillations of a viscous drop are studied in some detail. In particular, it is shown that the normal mode analysis of this problem available in the literature does not furnish a solution correct for all times, but only an asymptotic one valid as [...]." }, { "name": "Rizk, Magdi Hanna", "degree": "PhD", "year": "1974", "title": "Nonsteady Fluid Mechanics of Vehicles in Tubes", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-152813759", "creators": [ { "name": { "family": "Rizk", "given": "Magdi Hanna" }, "id": "Rizk-Magdi-Hanna", "display_name": "Rizk, Magdi Hanna" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8PJF-8H92", "abstract": "A theoretical study is performed to investigate the drag\r\nexperienced by vehicles travelling in tubes, the pressure distribution and flow velocities resulting from the vehicle's motion. The study deals with both the cases of vehicles accelerating from rest in the tube and vehicles entering a tube at finite speed. The effect of having a vent in the tube is also studied.\r\n\r\nThe unsteady compressible equations are used to describe\r\nthe flow in the tube. Before the boundary layer fills the tube, an inviscid core-boundary layer formulation is used. However, it is found that the simpler one-dimensional formulation is adequate for describing the flow in the tube. The quasi-steady near-field assumption agrees well with the unsteady near-field solution except for the initial period of low velocities.\r\n\r\nThe solution is compared to that in which compressibility\r\nis neglected. It is found that the effect of compressibility is not large for short tubes, low blockage ratios and small velocities. However, its importance increases as the values of these parameters increase. Compressibility may not be neglected during the initial period in the case of vehicles entering tubes at finite speeds.\r\n" }, { "name": "Somekh, Sasson Roger", "degree": "PhD", "year": "1974", "title": "Theory, Fabrication and Performance of Some Integrated Optical Devices", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-08112005-135414", "creators": [ { "name": { "family": "Somekh", "given": "Sasson Roger" }, "id": "Somekh-Sasson-Roger", "display_name": "Somekh, Sasson Roger" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TGHB-PR22", "abstract": "Recent progress in the fabrication of low attenuation optical fibers raises the attractive possibility of optical communications via these waveguides. Integration of different optical functions on one substrate in the form of optical circuits will form ideal terminals for such a communication network. We shall discuss the theory, fabrication and performance of a few \"building stones\" of such optical circuits. Optical directional couplers capable of coupling light from one channel to another will be described and their use as switches will be discussed. Distributed feedback for integrated lasers will be analyzed. Laser action in a GaAs waveguide, in which distributed feedback was supplied by corrugations fabricated on the surface, will be described. Longitudinal and transverse mode control of such a laser will also be discussed. We shall conclude with an analysis of nonlinear interactions in thin films, pointing out new methods for phase matching and ways to implement them." }, { "name": "Stoll, Harold McDowell", "degree": "PhD", "year": "1974", "title": "Proton-Implanted Optical Waveguides and Integrated Optical Detectors in Gallium Arsenide", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:07082021-224732104", "creators": [ { "name": { "family": "Stoll", "given": "Harold McDowell" }, "id": "Stoll-Harold-McDowell", "display_name": "Stoll, Harold McDowell" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/m0zg-j870", "abstract": "Defect-associated energy levels which appear within the forbidden energy gap of proton-irradiated gallium arsenide give rise both to free carrier compensation and to additional near band-edge optical attenuation. These damage-induced changes in the electrical and optical properties of gallium arsenide have been exploited in the fabrication of passive optical waveguides and waveguide-compatible detectors suitable for use in integrated optical circuits. In order to understand the physical processes which underlie the operation of these structures and devices and, thereby, to suggest ways in which the irradiation and post-irradiation fabrication parameters may be optimized, a model has been constructed which explains the experimentally observed electrical and optical properties of proton-irradiated gallium arsenide. Using this model and data obtained by other investigators, a self consistent analysis of the optical confinement and attenuation properties of waveguides formed by irradiating n-type gallium arsenide with 300 keV protons has been made: Optical confinement is found to result from the so-called plasma depression effect; optical attenuation is found to be due to a combination of dissipative scattering and absorption by thermal spikes and dipole-assisted transitions between defect levels and the band continua. The model is also used to make a preliminary analysis of an integrated optical detector fabricated using the same proton-irradiation technique.
" }, { "name": "Uehara, Sachio", "degree": "PhD", "year": "1974", "title": "Theoretical Investigation of Minimum Time Loop Maneuvers of Jet Aircraft", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-111949185", "creators": [ { "name": { "family": "Uehara", "given": "Sachio" }, "id": "Uehara-Sachio", "display_name": "Uehara, Sachio" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZTAZ-J396", "abstract": "Minimum time loop maneuvers of high performance jet aircraft have been investigated by means of the calculus of variations. A number of simplifying assumptions have been made in the atmospheric conditions, aerodynamic parameters, and the number of controls and their upper and lower bounds, in order to obtain general features and basic characteristics of the problem. The optimal control (lift coefficient and thrust) has been determined as a function of the state variables and Lagrange multipliers. It is found that subarcs with variable thrust, or with variable lift coefficient and minimum thrust do not occur on time optimal paths. Possible transitions among the five optimal subarcs have been established by applying the corner conditions of variational calculus. These relationships are applicable to any minimum time maneuver in the vertical plane. The effects of the magnitudes of maximum lift coefficient and maximum thrust on the control program, maneuver time, final speed, and final. horizontal distance for minimum time loop maneuvers are explored through numerical computation. It is found that the control history in lift and thrust and the minimum time required for a loop maneuver depend strongly on the magnitudes of maximum lift coefficient and maximum thrust. A limited numerical exploration using more realistic aerodynamic and atmospheric parameters and a state-dependent maximum thrust yielded results in qualitative agreement with the more extensive analysis based on simplified parameters. Normal acceleration constraints are analyzed by considering the maximum lift coefficient to be a function of altitude and speed. New design criteria for the inlet, duct and engine are suggested by consideration of the problem of engine surge." }, { "name": "Whipple, Christopher George", "degree": "PhD", "year": "1974", "title": "Extension of Rayleigh-Taylor Instability Theory with Applications", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02032021-213518907", "creators": [ { "name": { "family": "Whipple", "given": "Christopher George" }, "id": "Whipple-Christopher-George", "display_name": "Whipple, Christopher George" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/5bc3-w217", "abstract": "A theoretical derivation is presented for interfacial waves, both stable and unstable, which includes viscosity and surface tension. This result is extended to the case where one fluid has a finite thickness and is bounded by a rigid boundary or a free surface. As these solutions present formidable algebraic difficulties, approximate forms of solutions, which are motivated by physical arguments, are also given, and, through the use of a computer, the full theoretical result is shown to be fairly accurately reproduced by these approximations. The theory is used to give an explanation of the bioconvection patterns which have been observed with cultures of microorganisms which have negative geotaxis. Since such organisms tend to collect at the surface of a culture and since they are heavier than the culture medium the conditions for Rayleigh-Taylor instability are met. It is shown that the observed patterns are quite accurately explained by the theory. Similar observations with a viscous liquid loaded with small glass spheres are described. A behavior similar to the bioconvective patterns with microorganisms is found and the results are also explained quantitatively by Rayleigh-Taylor instability theory with viscosity. Further physical considerations of the bioconvection demonstrate the validity of the Rayleigh-Taylor instability model, and describe the steady state circulation of microorganisms. An approximate solution to a viscous fluid of finite depth with an exponential density gradient is developed, and the applicability of this result to certain bioconvective situations is discussed.
" }, { "name": "Apostolakis, George Efstratios", "degree": "PhD", "year": "1973", "title": "Studies in Nuclear Reactor Dynamics. I. The Accuracy of Point Kinetics. II. The Effect of Delayed Neutrons on the Spectrum of the Group Diffusion Operator", "advisor": "Corngold, Noel Robert", "url": "https://resolver.caltech.edu/CaltechTHESIS:07102014-095346884", "creators": [ { "name": { "family": "Apostolakis", "given": "George Efstratios" }, "id": "Apostolakis-George-Efstratios", "display_name": "Apostolakis, George Efstratios" } ], "advisors": [ { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "advisor", "display_name": "Corngold, Noel Robert" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/CJCX-CB43", "abstract": "This thesis is a theoretical work on the space-time dynamic behavior of a nuclear reactor without feedback. Diffusion theory with G-energy groups is used.
\r\n\r\nIn the first part the accuracy of the point kinetics (lumped-parameter description) model is examined. The fundamental approximation of this model is the splitting of the neutron density into a product of a known function of space and an unknown function of time; then the properties of the system can be averaged in space through the use of appropriate weighting functions; as a result a set of ordinary differential equations is obtained for the description of time behavior. It is clear that changes of the shape of the neutron-density distribution due to space-dependent perturbations are neglected. This results to an error in the eigenvalues and it is to this error that bounds are derived. This is done by using the method of weighted residuals to reduce the original eigenvalue problem to that of a real asymmetric matrix. Then Gershgorin-type theorems .are used to find discs in the complex plane in which the eigenvalues are contained. The radii of the discs depend on the perturbation in a simple manner.
\r\n\r\nIn the second part the effect of delayed neutrons on the eigenvalues of the group-diffusion operator is examined. The delayed neutrons cause a shifting of the prompt-neutron eigenvalue s and the appearance of the delayed eigenvalues. Using a simple perturbation method this shifting is calculated and the delayed eigenvalues are predicted with good accuracy.
\r\n" }, { "name": "Arakeri, Vijay Hanumappa", "degree": "PhD", "year": "1973", "title": "Viscous Effects in Inception and Development of Cavitation on Axi-Symmetric Bodies. Part I. Cavitation Inception. Part II. A Semi-Empirical Method to Predict Cavitation Separation on Smooth Bodies", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-081335", "creators": [ { "name": { "family": "Arakeri", "given": "Vijay Hanumappa" }, "id": "Arakeri-Vijay- Hanumappa", "display_name": "Arakeri, Vijay Hanumappa" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/JJ3M-ZA06", "abstract": "The schlieren method was developed as a flow visualization technique for use in water tunnels. The process of cavitation development on two axi-symmetric bodies was studied using this approach and found to be greatly influenced by the presence of a previously unreported viscous laminar separation. On these bodies, cavitation inception was observed to take place within this separated region which occurs far downstream of the minimum pressure point. On one of these bodies, the incipient cavitation index was found to be closely correlated with the negative value of the pressure coefficient at the point of laminar separation. Approximate computations of the position of transition on a body without laminar separation indicate that the incipient cavitation index is closely correlated with the negative value of the pressure coefficient at the predicted point of transition.\r\n\r\nCavitation separation under fully developed conditions is found to be preceded by a viscous laminar boundary layer separation on bodies which possess the latter separation under fully wetted conditions. An empirical method is proposed to compute the position of cavitation separation on such bodies and the method applied to a sphere and a cylinder showed good agreement with experiments" }, { "name": "Bhatia, Prem", "degree": "PhD", "year": "1973", "title": "Buckling of Imperfect Circular Cylindrical Shells", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08302010-162439924", "creators": [ { "name": { "family": "Bhatia", "given": "Prem" }, "id": "Bhatia-Prem", "display_name": "Bhatia, Prem" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FS7M-8D46", "abstract": "In this project, the buckling of imperfect circular cylindrical shells under uniform axial compression has been investigated. The imperfection considered is prismatic and is in the form of flat spots along the complete length of the shell. The problem is solved by considering it as an interaction problem between curved and flat panels. Shell equations are satisfied in the curved portions of the shell while flat plate equations are used in the flat spot regions. At the common edge between two adjacent panels, forces and displacements are matched to arrive at the eigenvalue problem for the critical load of the shell. Two flat spot configurations have been studied. In the first case, a single flat spot along the complete length of the shell is considered. Curved and flat panels join to form sharp corners at their common edges. Numerical results are presented to show the effect of the width of the flat spot, thickness ratio and length to radius ratio of the shell, on the buckling load of the shell. In the second case, the imperfection is in the form of two or more identical flat spots distributed uniformly along the circumference of the shell. Between two consecutive flat spots is a uniform radius cylindrical panel joining smoothly to the flat panels. This analysis is valid for any integral number of identical flat spots. Numerical results are presented for 2, 3, 4, 8-flat spots. The effect of width of flat spots, radius of curved panels, thickness ratio of the shell has been investigated. The results, presented in this paper, clearly demonstrate a very significant reduction in the buckling load of the shell below its classical value. This is true even in the presence of relatively small flat spots. This reduction becomes more severe with a decrease in the thickness of the shell or an increase in the width of the flat spot. " }, { "name": "Bigelow, Richard Henry", "degree": "PhD", "year": "1973", "title": "Computer Languages for Numerical Engineering Problems", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12122017-105710635", "creators": [ { "name": { "family": "Bigelow", "given": "Richard Henry" }, "id": "Bigelow-Richard-Henry", "display_name": "Bigelow, Richard Henry" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/CBA9-Z637", "abstract": "Recent and anticipated advances in computer hardware capabilities have made hardware limitations insignificant for many numerical engineering problems. The difficulties of programming computers now constitute the greatest block to their effective utilization by engineers and scientists. Consequently, new languages that are specialized to numerical engineering problems are needed.
\r\n\r\nRelmath is such a language. It is designed to solve ordinary differential equations and to manipulate the resulting functions. Systems of equations can be stated in a normal mathematical form and solved by a simple statement. Printed and plotted output can be readily obtained.
\r\n\r\nRelmath also allows the definition of procedures for solving differential equations. Its procedural language is quite different from general programming languages. It is restricted to a certain class of algorithms, and the calculations that are common to all these methods are made implicit in the language. The language is highly supportive for procedures in this class. The user need only state the important mathematical steps, such as the formulas defining a Runge-Kutta scheme or the method of estimating the error, if error control is desired.
\r\n\r\nSome considerations for the design and implementation of numerical engineering languages are discussed using Relmath as an example. The decisions involved in the design of Relmath are detailed. The behavior of a representative numerical algorithm in a paging environment is analyzed, which shows the importance of properly designing algorithms for such environments. Relmath's method of compiling its procedures is discussed. The compiled code is as fast as standard library subroutines. Finally, a plan for further research to develop a more supportive environment for the implementation of similar languages is outlined.
" }, { "name": "Bower, Robert William", "degree": "PhD", "year": "1973", "title": "Reaction Kinetics of Pd and Ti-Al Films on Si", "advisor": "Mayer, James Walter; Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-04122004-132122", "creators": [ { "name": { "family": "Bower", "given": "Robert William" }, "id": "Bower-Robert-William", "display_name": "Bower, Robert William" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" }, { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/NY05-4E97", "abstract": "The growth of compound phases from thin film layers of Pd and Ti-Al deposited on Si is described in this work. The growth kinetics and composition of the compound phases were measured utilizing 2 MeV \u2074He backscattering. Crystalline structure and film texture effects of the compounds layers were measured by X-ray diffraction techniques.
\r\n\r\nThe Pd-Si system was first studied by depositing 1000 to 3000\u00c5 of Pd onto a Si substrate and heating to 200 to 700\u00b0C. A single phase of material with a composition Pd2Si developed when specimens were heated to a temperature of 200\u00b0C. The phase grows at a rate proportional to (time)1/2 indicating transport limited growth. The temperature dependence of the growth constant was found to be expressible as a single activation energy of approximately 1.5 eV over the 200 to 275\u00b0C temperature range where growth kinetics were measured.
\r\n\r\nThe X-ray diffraction data indicated that the Pd2Si phase which formed has the crystalline structure of Pd2Si known from metallurgical studies of bulk materials. The Pd2Si layers which formed from the thin film structures were found to be oriented with the hexagonal basal plane parallel to the substrate material. The degree of the preferred orientation of the Pd2Si depends on the Si substrate orientation. By far the highest degree of orientation was found when the Pd2Si was formed on <lll>-Si.
\r\n\r\nThe more complex Si-Ti-Al system is treated following the Pd-Si system. In this case a layer of Ti and then Al was evaporated on Si after which the specimens were heated to temperatures of 400\u00b0 to 500\u00b0C. Backscattering of \u2074He ions was used to measure growth kinetics and composition of compound phases which develop. While the spectra are more complex the same basic analysis techniques developed for the Pd-Si system were applicable. While no measurable reaction of the Si and Ti was found in this temperature range, the Ti-Al reacts to form a phase of TiAl\u2083. The rate of formation of TiAl\u2083 was also found to be proportional to (time)1/2 indicating transport limited growth. The temperature dependence of the growth constant was found to be again expressible by a single activation energy over the temperature range measured. The value of activation energy was found to be approximately 1.85 eV.
\r\n\r\nThe X-ray diffraction analysis indicates that a single phase of TiAl3 forms until the entire Ti layer is consumed. At this point Si reacts with the system displacing most of the Al to form a Si-rich Ti-Al-Si ternary phase.
\r\n\r\nThe Ti-Al metal system is used to make contact to Si in integrated circuit applications. The TiAl\u2083 and subsequent Si-rich Ti-Al-Si ternary formation in this system can be directly related to severe erosion of metal -Si contact areas which result in failure of the integrated circuits.
\r\n\r\nThe measured rate of formation of TiAl\u2083 found from the backscattering measurements allows the thickness of Ti to be chosen large enough so that heat treatments following metal deposition will not cause contact failure. Thus, the rate kinetics of TiAl3 formation measured by 2 MeV \u2074He backscattering is found to have practical application in predicting and controlling a failure mechanism in an integrated circuit metallization scheme.
" }, { "name": "Carne, Thomas Glen", "degree": "PhD", "year": "1973", "title": "Load-Absorption and Interaction of Two Filaments in a Fiber-Reinforced Material", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02062018-115639478", "creators": [ { "name": { "family": "Carne", "given": "Thomas Glen" }, "id": "Carne-Thomas-Glen", "display_name": "Carne, Thomas Glen" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/GDSK-RJ45", "abstract": "This investigation is concerned with the interaction - as far \r\nas load-absorption is concerned - of a pair of identical and parallel elastic \r\nfilaments in a fiber-reinforced composite material. The filaments are \r\nassumed to have uniform circular cross-sections, are taken to be\r\nsemi-infinite, and are supposed to be continuously bonded to an all\u00ad \r\naround infinite matrix of distinct elastic properties. At infinity the\r\nmatrix is subjected to uniaxial tension parallel to the filaments. Two \r\nseparate but related problems are treated. In the first both filaments \r\nextend to infinity in the same direction and their terminal cross-sections \r\nare coplanar. In the second problem the filaments extend to infinity in opposite \r\ndirections and their terminal cross-sections need no longer be coplanar, \r\nthe two filaments being permitted to overlap partly. An approximate scheme \r\nbased in part on three-dimensional linear elasticity and developed originally \r\nby Muki and Sternberg is employed in the analysis. The problems are ultimately \r\nreduced to Fredholm integral equations which characterize the distribution \r\nof the axial filament force. The integral equations are analyzed asymptotically and \r\nnumerically. Results are presented which show the variation of\r\nfilament force with position and the effect on this variation of various relevant \r\ngeometrical and material properties.\r\n" }, { "name": "Chang, Daniel Pan Yih", "degree": "PhD", "year": "1973", "title": "Particle Collection from Aqueous Suspensions by Solid and Hollow Single Fibers", "advisor": "Friedlander, Sheldon K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09232010-142641670", "creators": [ { "name": { "family": "Chang", "given": "Daniel Pan Yih" }, "id": "Chang-Daniel-Pan-Yih", "display_name": "Chang, Daniel Pan Yih" } ], "advisors": [ { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "advisor", "display_name": "Friedlander, Sheldon K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/rs2j-vw31", "abstract": "An investigation of particle capture by single solid and hollow fibers was conducted. The experimental system consisted of a small water tunnel with a test section in which single fibers were inserted. The deposition rate of particles under conditions of controlled flow and chemical composition was measured with an optical microscope. Particles studied included human erythrocytes and latex spheres ranging in size from 2.0 \u00b5m polyvinyltoluene latex to 25.7 \u00b5m styrenedivinylbenzene copolymer latex. The fibers were composed of glass, fluoroethylene-propylene (teflon - FEP), and cellulose acetate. Surface chemistry was found to play a major role in the attachment of micron-size particles to the collector. However, electrical double layer theory could not predict the onset of rapid particle attachment quantitatively. Significant viscous interaction of particles approaching the collector surface was inferred from the data, confirming recent theory.
\r\n\r\nA novel application of hollow fibers with permeable membrane walls was developed. The membrane permeability permits modification of the fiber suspension interface by means of chemical addition and flow alteration. The destabilizing chemicals form a thin concentration boundary layer around the fiber surface, reducing the total amount of chemical needed. Slight suction at the fiber surface reduces the hydrodynamic resistance acting on the particles as they approach the surface. An increase in the collection efficiency can occur when these methods are applied.
" }, { "name": "Cummings, John Chester", "degree": "PhD", "year": "1973", "title": "I. Development of a Cryogenic Shock Tube. II. Experimental Investigation of the Interaction of a Shock Wave with Liquid Helium and I and II", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072010-095321580", "creators": [ { "name": { "family": "Cummings", "given": "John Chester" }, "id": "Cummings-John-Chester", "display_name": "Cummings, John Chester" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AM0F-DB64", "abstract": "I. Development of a cryogenic shock tube
\r\n\r\nA cryogenic shock tube has been developed as a tool for research in fluid mechanics and low temperature physics. The shock tube is designed to operate with the test section immersed in a cryogenic liquid. A unique diaphragm changing mechanism makes this shock tube an economical and practical device.
\r\n\r\nThere are several advantages in operating a shock tube at cryogenic temperatures. Shock waves of very large Mach number can be produced. The flow field can be accurately calculated using ideal shock tube - perfect gas theory. Boundary layer effects are decreased so that long test times are possible.
\r\n\r\nThe cases which have been studied are test gas temperatures of 300, 77, 4.2, and 2.3\u00b0K. Helium is used as both test and driver gas. The largest Mach numbers which have been observed range from 2.4 at 300\u00b0K to 32 at 2.3\u00b0K (several runs at 1.46\u00b0K have produced Mach 40 shocks). As the test gas temperature is decreased the observed Mach numbers approach those calculated using the ideal shock tube equation. The observed test times can be interpreted using laminar or turbulent boundary layer theory if the effects of shock formation distance and wall temperature rise are taken into account.
\r\n\r\nAs a laboratory tool the cryogenic shock tube may be applied in many areas and modified for use in even more. Large Mach number shocks and large Reynolds number flows can be produced with this device. The rapid increase in temperature and pressure across a shock wave is useful for studies of sublimation, evaporation, or chemical reactions. Quantum mechanical effects in cryogenic materials, superconductors, or superfluid helium can also be investigated.
\r\n\r\nII. Experimental investigation of the interaction of a shock wave with liquid helium I and II
\r\n\r\nThe flow field produced by a shock wave reflecting from a helium gas -liquid interface has been investigated using a new cryogenic shock tube. Incident and reflected shock waves have been observed in the gas; transmitted first and second sound shocks have been observed in the liquid. Wave diagrams have been constructed to compare the data to theoretical wave trajectories. Qualitative agreement between data and theory has been shown. Quantitative differences between data and theory indicate a need for further analysis of both the gas-liquid interface and the propagation of nonlinear waves in liquid helium.
\r\n\r\nThis work is essentially a first step in the experimental investigation of a very complex nonequilibrium state. The well controlled jump in temperature and pressure across the incident shock wave provides unique initial conditions for the study of dynamic phenomena in superfluid helium.
\r\n\r\nThe results clearly demonstrate the usefulness of the cryogenic shock tube as a research tool.
" }, { "name": "D'Orazio, Robert Joseph", "degree": "PhD", "year": "1973", "title": "Detection of Mode-Locked Laser Signals", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11122019-160113596", "creators": [ { "name": { "family": "D'Orazio", "given": "Robert Joseph" }, "id": "D'Orazio-Robert-Joseph", "display_name": "D'Orazio, Robert Joseph" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/26D2-8776", "abstract": "In this work we describe our approach to matched-filtering for mode-locked laser signals. Our optical receiver consists of a passive laser cavity controlled in length and a photodetector with its associated electronics. The length of the passive Fabry-Perot cavity is chosen roughly equal to the cavity length of the transmitting laser, but with provision for fine fractional wavelength control of its length. In addition to the selective filtering characteristics of the passive cavity (passbands of unity transmission matching the frequencies of the multi-mode laser), a readout of the vernier length control, peaking the output, provides for an extremely wide range of velocity measurements with either an active or passive vehicle moving relative to the receiver.
\r\n\r\nIn studying the mode-locked laser we use the matched-filter criterion resulting from the optimization of the signal-to-noise ratio. This criterion specifies that the amplitude transmission function be Tm(\u03c9) = AE*(\u03c9)/Sn(\u03c9); where E(\u03c9) is the Fourier transform of the laser signal E1(t); Sn(\u03c9) is the power spectral density of the additive input noise; the asterisk denotes the complex conjugate; and A is any nonzero complex constant. For an actual laser signal, writing E(\u03c9) for the multi-tone laser with finite linewidths \u0394\u03c9\u2113 yields an expression which is comparable on a mode by mode basis to the transmission function for a Fabry-Perot cavity. The resulting matching conditions are that \u0394\u03c9p = \u0394\u03c9\u2113 and ho = h in which \u0394\u03c9p is the linewidth of the receiver cavity of length ho, and h is the length of the transmitter cavity.
\r\n\r\nThe Fabry-Perot cavity is probably as close a physical realization to a matched-filter for the multi-toned laser as can be attained in a passive system. Even so, gain narrowing invariably results in \u0394\u03c9\u2113 < \u0394\u03c9p, thereby limiting the observed improvement in signal-to-noise ratio from its optimal value. For high gain lasers with cavities of low finesse, the receiver can be made closer to the ideal, while greater departures are to be expected in the case of low gain.
\r\n\r\nFurther study of the use of the passive cavity in contrast to no cavity shows that the signal-to-noise ratio improves approximately by the finesse of the cavity which is typically 150. Considering the improvement in signal-to-noise ratio as a function of the number of oscillating modes N we find that the peak value of the temporally varying detected output has a signal-to-noise ratio proportional to N2, i.e., it varies as the peak power of the mode-locked laser.
\r\n\r\nNow, suppose that the mode-locked laser is moving toward our receiver with a velocity v. For TEM waves, an emitted frequency \u03c9' will be observed shifted to \u03c9 given by \u03c9 = \u03b3(1 + v/c)\u03c9' in which \u03b3 = [1 - (v/c)2]-l/2 and c is the speed of light. In this case where there is relative motion, we find that optimal detection of the mode-locked laser signal requires a receiver with a cavity length ho given by ho = h/[\u03b3(1 + v/c)]. Similarly, if the mode-locked laser and the passive cavity were on a common platform, then the echo from a vehicle moving toward this platform with velocity v would be shifted to \u03c9 = (1 + 2v/c)\u03c9', where we have set \u03b3 = 1. So by vernier adjustments of the passive cavity length we can read a large range of approach velocities with a resolution independent of the velocity.
" }, { "name": "Dimotakis, Paul Emmanuel", "degree": "PhD", "year": "1973", "title": "Investigation of Supercritical Heat Flow in Helium II", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-094055", "creators": [ { "name": { "family": "Dimotakis", "given": "Paul Emmanuel" }, "id": "Dimotakis-Paul-Emmanuel", "display_name": "Dimotakis, Paul Emmanuel" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/WMV3-FJ63", "abstract": "To investigate the validity of appending the Gorter-Mellink friction term to the equations of motion of liquid helium the temperature was measured along the axis of a channel carrying a supercritical heat current. A single thermometer on a traversing assembly was used permitting local measurements both in the interior of the channel and in the jet formed in the free fluid.
\r\n\r\nThe temperature gradient in the interior of the channel is found to be in agreement with the Gorter-Mellink law up to the lamda point, but goes to zero within a channel diameter, in the free jet. Since the relative velocity between the two fluids is probably continuous along the axis of the jet in the vicinity of the exit, the disappearance of the temperature gradient appears to be inconsistent with the predictions of the Gorter-Mellink term.
\r\n\r\nThe Gorter-Mellink A(T) was also measured up to the lamda point. A much stronger divergence is found as T\u03bb is approached than was indicated by previous measurements.
" }, { "name": "Eisenberg-Gr\u00fcnberg, Mois\u00e9s", "degree": "PhD", "year": "1973", "title": "Voltage Gateable Ionic Pores Induced by Alamethicin in Black Lipid Membranes", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092006-125321", "creators": [ { "name": { "family": "Eisenberg-Gr\u00fcnberg", "given": "Mois\u00e9s" }, "id": "Eisenberg-Gr\u00fcnberg-Mois\u00e9s", "display_name": "Eisenberg-Gr\u00fcnberg, Mois\u00e9s" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "biology" ], "doi": "10.7907/2YFT-Q653", "abstract": "The strongly surface-active polypeptide antibiotic alamethicin (m.w. ~ 1700) interacts with artificial black lipid membranes to form voltage gateable ionic channels with five discrete conductance states. The channels fluctuate between these states with transition rates which depend little on the applied voltage. Within any conductance state, the behavior is approximately ohmic and similar to bulk solutions. When added on one side only, alamethicin confers upon a phosphatidyl-ethanolamine-decane black film a pronounced asymmetry. The alamethicin channels are only slightly ion selective, their rate of formation is strongly dependent on the alamethicin concentration, on the voltage across the membrane and on the ionic strengths." }, { "name": "Hill, Murray Keith", "degree": "PhD", "year": "1973", "title": "Behavior of Spherical Particles at Low Reynolds Numbers in a Fluctuating Translational Flow", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11132015-144035933", "creators": [ { "name": { "family": "Hill", "given": "Murray Keith" }, "id": "Hill-Murray-Keith", "display_name": "Hill, Murray Keith" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/22ME-5X65", "abstract": "The behavior of spheres in non-steady translational flow\r\nhas been studied experimentally for values of Reynolds number\r\nfrom 0.2 to 3000. The aim of the work was to improve our\r\nqualitative understanding of particle transport in turbulent\r\ngaseous media, a process of extreme importance in power\r\nplants and energy transfer mechanisms.
\r\n\r\nParticles, subjected to sinusoidal oscillations parallel\r\nto the direction of steady translation, were found to have changes\r\nin average drag coefficient depending upon their translational\r\nReynolds number, the density ratio, and the dimensionless\r\nfrequency and amplitude of the oscillations. When the Reynolds\r\nnumber based on sphere diameter was less than 200, the\r\noscillation had negligible effect on the average particle drag.
\r\n\r\nFor Reynolds numbers exceeding 300, the coefficient of\r\nthe mean drag was increased significantly in a particular\r\nfrequency range. For example, at a Reynolds number of\r\n3000, a 25 per cent increase in drag coefficient can be produced\r\nwith an amplitude of oscillation of only 2 per cent of the sphere\r\ndiameter, providing the frequency is near the frequency at which\r\nvortices would be shed in a steady flow at the mean speed. Flow\r\nvisualization shows that over a wide range of frequencies, the\r\nvortex shedding frequency locks in to the oscillation frequency.\r\nMaximum effect at the natural frequency and lock-in show that a\r\nnon-linear interaction between wake vortex shedding and the\r\noscillation is responsible for the increase in drag.
" }, { "name": "Ikawa, Hideo", "degree": "PhD", "year": "1973", "title": "Turbulent Mixing Layer Experiment in Supersonic Flow", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272010-154352889", "creators": [ { "name": { "family": "Ikawa", "given": "Hideo" }, "id": "Ikawa-Hideo", "display_name": "Ikawa, Hideo" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4MBK-D880", "abstract": "A supersonic, two-dimensional, turbulent free mixing layer\r\nwas experimentally investigated in the GALCIT Supersonic wind tunnel to clarify the Mach number dependence of this flow field. The tests were conducted with a nominal Mach number of 2.47 with an ambient stagnation condition. Self similarities of the mean and turbulent flow fields were established.\r\n\r\nThe mean and fluctuating flow measurements were made. In\r\naddition, the actual entrainment rate of the turbulent free mixing layer through the low speed interface was also measured and it was verified that this quantity equals the growth rate of momentum thickness. The spreading rate, the entrainment rate and the maximum shear stress were appreciably smaller than the respective incompressible\r\nvalues. Velocity profile scaled to an incompressible form.\r\nby a linear transformation of the lateral coordinate. The maximum streamwise velocity fluctuation was approximately 1/3 of the incompressible value. The flow field of turbulent free mixing layer was found to be highly dependent upon the supersonic compressibility\r\neffect.\r\n" }, { "name": "Jiang, Ching-Lin", "degree": "PhD", "year": "1973", "title": "Electromagnetic Wave Propagation and Radiation in a Suddenly Created Plasma", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:07112018-141856792", "creators": [ { "name": { "family": "Jiang", "given": "Ching-Lin" }, "id": "Jiang-Ching-Lin", "display_name": "Jiang, Ching-Lin" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/3TKY-YR40", "abstract": "Propagation and radiation of electromagnetic waves from oscillating sources in a suddenly created plasma are studied in this investigation. Field expressions are derived through the use of Laplace transformations. The spatial distribution of sources is taken to be arbitrary but confined.
\r\n\r\nTwo cases are considered in detail: (1) plane wave propagation in a source-free region, and (2) electric point dipole radiation. In the case of plane wave propagation, various aspects such as wave split, frequency shift, phase and group velocities, amplitude changes, power flows and energy relations are discussed. In the case of electric dipole radiation, the electromagnetic fields and instantaneous radiated power are calculated and expressed in terms of Lommel functions of two variables. Asymptotic expressions and graphical results of numerical calculations of these quantities are presented. Many interesting properties of the spherical waves and power radiation are discussed.
" }, { "name": "Jim\u00e9nez Send\u00edn, Javier", "degree": "PhD", "year": "1973", "title": "I. Nonlinear Gas Oscillations in Pipes. II. Wavetrains with Small Dissipation", "advisor": "Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172011-101324443", "creators": [ { "name": { "family": "Jim\u00e9nez Send\u00edn", "given": "Javier" }, "id": "Jim\u00e9nez-Send\u00edn-Javier", "display_name": "Jim\u00e9nez Send\u00edn, Javier" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/HRSK-FC56", "abstract": "In part I of this thesis we study theoretically the problem of forced acoustic oscillations in a pipe. The oscillations are produced by a moving piston in one end of the pipe, while a variety of boundary conditions ranging from a completely closed end to a completely open mouth are considered at the other end. All these boundary conditions are modelled by two parameters: a length correction and a reflection coefficient equivalent to the acoustic impedance.\r\n\r\nThe linear theory predicts large amplitudes near resonance and non-linear effects become crucially important. By expanding the equations of motion in a series of the Mach number, both the amplitude and waveform of the oscillations are predicted there.\r\n\r\nIn both the open and closed-end cases the need for shock waves in some range of parameters is found. The amplitude of the oscillation is different for the two cases, however, being proportional to the square root of the piston amplitude in the closed end case, and to the cube root in the open end.\r\n\r\nThis part of the thesis was first published in the Journal of Fluid Mechanics.\r\n\r\nIn part II we modify the averaged Lagrangian method used by Whitham to analyze slowly varying non-linear wavetrains to include cases with a small dissipation. To do this, we use a pseudo-variational principle introduced by Prigogine in which the Lagrangian depends on the variable and the solution of the problem, and which can be used to describe irreversible processes.\r\n\r\nWe prove the corresponding averaged equations to all orders and describe practical ways to use them to lowest order." }, { "name": "Lee, Peter Hoong-Yee", "degree": "PhD", "year": "1973", "title": "An Investigation of Collisionless Plasma Beam Interaction with a Nonhomogeneous Magnetic Field", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:08262010-104719284", "creators": [ { "name": { "family": "Lee", "given": "Peter Hoong-Yee" }, "id": "Lee-Peter-Hoong-Yee", "display_name": "Lee, Peter Hoong-Yee" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XNF6-9D90", "abstract": "The interaction between a rarefied flowing plasma and an externally imposed nonhomogeneous magnetic field is studied experimentally in a collisionless plasma wind tunnel, where a collisionless plasma beam is directed through a current loop. The collisionless plasma is generated by an electron bombardment engine. Nominal values of ion flow speed, number density, electron temperature and magnetic induction of the loop are U ~10^4 m/s, N ~5 x 10^7/cc, kT_e ~0.2 eV and B ~10 Gauss, respectively. Due to lack of probe theories in the presence of nonhomogeneous magnetic fields and failure of conventional Langmuir probe methods, a new, simple method of diagnostics is developed. This method employs two probes of different geometry and obtains information on the ion density and flow speed from the ion-saturation region of the probe characteristic. Radial density profiles in the wake of the current loop mapped by the \"two-probe\" method indicate annular density \"peaks\" at certain radial positions. In order to understand this non-uniform \"pinching\" process, a theoretical analysis is attempted. It is found that the experimentally observed phenomenon can be qualitatively described by the collision-less two-fluid equations, but turbulent \"friction\" is required to improve the two-fluid model. A heuristic turbulent model is used, and evidence of turbulence in the flow field is also obtained through measurements of the fluctuating probe currents." }, { "name": "Lu, Tyzz-Dwo", "degree": "PhD", "year": "1973", "title": "I. Constitutive Relations for a Granular Material. II. The Distribution of Stresses and Development of Failure at the Toe of a Slope and Around the Tip of a Crack", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132017-144159939", "creators": [ { "name": { "family": "Lu", "given": "Tyzz-Dwo" }, "id": "Lu-Tyzz-Dwo", "display_name": "Lu, Tyzz-Dwo" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/P0H6-TA75", "abstract": "In the first part of this thesis, a three-dimensional rheological \r\nmodel was constructed to represent the deformation behavior of a \r\ngranular material. The constitutive relations for a granular material \r\nwere subsequently derived. The rheological model was conceived\r\nfrom the observed behavior of granular material from laboratory \r\nexperiments and from theoretical considerations. The constitutive \r\nrelations were expressed in incremental forms to account for the\r\nstress history and loading path dependency of a granular material's \r\nbehavior, such as non-linearity, initial or induced anisotropy, history \r\nand path dependency, and shear dilatance.
\r\n\r\nThe qualitative and quantitative behavior of a granular material \r\nsuch as sand under shear stress from experimental results and from \r\nthe proposed constitutive relations was examined and compared. It\r\nwas found that the experimental data and the proposed constitutive\r\nrelations were in close agreement.
\r\n\r\nDue to the number of parameters involved, and the non-symmetrical \r\nresulting stiffness matrix in a general stress-strain formulation, \r\nit is difficult to apply the proposed constitutive in a finite element \r\ncomputer formulation at the present state of the art. Consequently \r\nthe application of finite element methods to non-linear problems was \r\nexamined in more detail as a preliminary step. The effect, or the\r\nresults of the material properties, the finite element mesh size and \r\nthe computational procedure was examined in detail in Part II of this thesis.
\r\n\r\n\r\n" }, { "name": "Maeda, Hisatoshi", "degree": "PhD", "year": "1973", "title": "Theoretical and Experimental Investigations of Saturation Effects in a Gas Laser", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:02092018-113834352", "creators": [ { "name": { "family": "Maeda", "given": "Hisatoshi" }, "id": "Maeda-Hisatoshi", "display_name": "Maeda, Hisatoshi" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/K70K-GS53", "abstract": "Theoretical studies of standing and traveling wave lasers are\r\npresented. The spectral behavior of the amplified spontaneous emission\r\n(superradiance) in a pencil-shaped column is investigated \r\ntheoretically and experimentally. Spectral narrowing followed by rebroadening\r\nhas been observed as predicted by the theory.
\r\n\r\nA geometrical representation of an interacting two-level atomic\r\nsystem has been developed and applied to an optical laser. A semi-classical\r\nmodel for a standing wave laser has been examined using the\r\nrotating wave approximation, and compared to the exact solution.\r\nDepth and width of the Lamb dip are determined theoretically and\r\nexperimentally. The effect of radial profile of the laser field has\r\nbeen studied using the self-consistent-field approach, and the radius\r\nof the beam was measured at various positions from the window.
" }, { "name": "Marzwell, Neville Ingersoll", "degree": "PhD", "year": "1973", "title": "Influence of Composition of the Structure, Electric and Magnetic Properties of Pd-Mn-P and Pd-Co-P Amorphous Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07222014-140906524", "creators": [ { "name": { "family": "Marzwell", "given": "Neville Ingersoll" }, "id": "Marzwell-Neville-Ingersoll", "display_name": "Marzwell, Neville Ingersoll" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/NARJ-BA54", "abstract": "The influence of composition on the structure and on the electric\r\nand magnetic properties of amorphous Pd-Mn-P and Pd-Co-P prepared\r\nby rapid quenching techniques were investigated in terms of (1) the 3d\r\nband filling of the first transition metal group, (2) the phosphorus\r\nconcentration effect which acts as an electron donor and (3) the transition metal concentration.
\r\n\r\nThe structure is essentially characterized by a set of polyhedra\r\nsubunits essentially inverse to the packing of hard spheres in\r\nreal space. Examination of computer generated distribution functions\r\nusing Monte Carlo random statistical distribution of these polyhedra\r\nentities demonstrated tile reproducibility of the experimentally calculated atomic distribution function. As a result, several possible\r\n\"structural parameters\" are proposed such as: the number of nearest\r\nneighbors, the metal-to-metal distance, the degree of short-range order\r\nand the affinity between metal-metal and metal-metalloid. It is shown\r\nthat the degree of disorder increases from Ni to Mn. Similar behavior\r\nis observed with increase in the phosphorus concentration.
\r\n\r\nThe magnetic properties of Pd-Co-P alloys show that they are\r\nferromagnetic with a Curie temperature between 272 and 399\u00b0K as the\r\ncobalt concentration increases from 15 to 50 at.%. Below 20 at.% Co the\r\nshort-range exchange interactions which produce the ferromagnetism are\r\nunable to establish a long-range magnetic order and a peak in the\r\nmagnetization shows up at the lowest temperature range . The electric\r\nresistivity measurements were performed from liquid helium temperatures\r\nup to the vicinity of the melting point (900\u00b0K). The thermomagnetic\r\nanalysis was carried out under an applied field of 6.0 kOe. The\r\nelectrical resistivity of Pd-Co-P shows the coexistence of a Kondo-like\r\nminimum with ferromagnetism. The minimum becomes less important\r\nas the transition metal concentration increases and the coefficients\r\nof \u2113n T and T^2 become smaller and strongly temperature dependent.\r\nThe negative magnetoresistivity is a strong indication of the existence\r\nof localized moment.
\r\n\r\nThe temperature coefficient of resistivity which is positive\r\nfor Pd- Fe-P, Pd-Ni-P, and Pd-Co-P becomes negative for Pd-Mn-P. It is\r\npossible to account for the negative temperature dependence by the\r\nlocalized spin fluctuation model and the high density of states at the\r\nFermi energy which becomes maximum between Mn and Cr. The magnetization\r\ncurves for Pd-Mn-P are typical of those resulting from the interplay of different exchange forces. The established relationship between susceptibility and resistivity confirms the localized spin fluctuation model. The magnetoresistivity of Pd-Mn-P could be interpreted\r\nin tenns of a short-range magnetic ordering that could arise\r\nfrom the Rudennan-Kittel type interactions.
\r\n" }, { "name": "Mohsen, Amr Mohamed", "degree": "PhD", "year": "1973", "title": "Incomplete Charge Transfer in Overlapping Gates Charge Coupled Devices", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:02012018-092625397", "creators": [ { "name": { "family": "Mohsen", "given": "Amr Mohamed" }, "id": "Mohsen-Amr-Mohamed", "display_name": "Mohsen, Amr Mohamed" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CEG6-AR39", "abstract": "We have developed a numerical simulation of the charge transfer\r\nin the overlapping gates charge coupled devices. The transport \r\ndynamics were analyzed in terms of thermal diffusion, self-induced\r\nfields and fringing fields under all the relevant electrodes and the\r\ninterelectrode regions with time varying gate potentials. We have also \r\ndeveloped a lumped circuit model of charge coupled devices. Using\r\nthis model simple analytic expressions describing the charge transfer\r\nwith various clocking waveforms are derived. This model can be used \r\nto study the charge transfer characteristics for other device structures, \r\ndimensions, clocking waveforms and voltages, thus providing\r\npractical charge coupled device and circuit design tools.
\r\n\r\n\r\nUsing the numerical simulation and lumped circuit model, the\r\ninfluence of clocking waveforms and clocking schemes on CCD operation\r\nare studied. It is concluded that increasing the clocking scheme\r\ncomplexity allows a better control of the storage and transfer of the\r\nsignal charge and hence improves the signal dynamic range and charge\r\ntransfer characteristics. It is shown that the performance of charge\r\ncoupled devices is better with push clocks (that push the charge from\r\none storage site to another) than with drop clocks (that create\r\ndeeper potential wells to transfer the charge). The performance of\r\ncharge coupled devices is shown to be basically superior to the MOS\r\nbucket brigade.
\r\n\r\n\r\nWe have also developed a simple model to study the incomplete \r\ncharge transfer due to trapping in the interface states. Incomplete\r\ncharge transfer due to trapping in interface states is shown to limit\r\nthe performance CCDs at low frequencies. The most dominant effect\r\nis trapping in the interface states under the edges of the gates\r\nparallel to the active channel. The influence of the device parameters,\r\ndimensions and clocking waveforms on the signal degradation is discussed.\r\nDesign features of CCD structures which would reduce the \r\nincomplete charge transfer due to interface states are presented. It\r\nis shown that increasing the clock voltages, increasing the signal\r\ncharge or using dynamic push clock reduces the incomplete charge \r\ntransfer due to interface states.
\r\n\r\n\r\nThe contents of this thesis have been published under the\r\nfollowing titles:
\r\n\r\n\"Charge Transfer in Overlapping Gates Charge Coupled Devices\"\r\nA. M. Mohsen, T. C. McGill and C. A. Mead, Journal of Solid State \r\nCircuits, SC-8, No. 3, June 1973.
\r\n\r\n\"The Influence of Interface States on Incomplete Charge \r\nTransfer in Overlapping Gates Charge Coupled Devices\",\r\nA. M. Mohsen, T. C. McGill , Y. Daimon and C. A. Mead, \r\nJournal of Solid State Circuits, SC-8, No. 2, April 1973.
\r\n\r\n\"Push Clocks: A new approach to charge coupled device \r\nclocking\", A. M. Mohsen, T. C. McGill, M. Anthony and\r\nC. A. Mead, Appl. Phys. Letters, 22, 4, February 15, 1973, \r\npp. 172-175.
\r\n\r\n\"Charge Transfer in Charge Coupled Devices\", A. M. Mohsen,\r\nT. C. McGill and C. A. Mead, ISSCC Digest of Technical Papers\r\n15, 1972, pp. 248-249
\r\n\r\nThe contents of this thesis have also been presented in the following\r\nconferences:
\r\n\r\n\"Physics of Charge Coupled Devices\", Invited Review Talk \r\ngiven at the Gordon Research Conference, Meriden, New\r\nHampshire, August 1972.
\r\n\r\n\r\n\"The Influence of Clocking Waveforms of CCD Operation\",\r\npresented at the International Device Research Conference\r\nat Edmonton, Canada, June 1972.
\r\n\r\n\r\n\"Charge Transfer in Charge Coupled Devices\", presented at\r\nthe International Solid State Circuits Conference,\r\nPhiladelphia, Pa., February 1972.
\r\n\r\n\r\nA motion picture simulation of the various stages of the charge trans\u00adfer\r\nprocess with two-phase and four-phase clocking schemes was produced \r\ndirectly from the results of the numerical simulation developed in this \r\nthesis. The CCD movie has been presented in the conferences mentioned\r\nabove and is included in the \"Semiconductor Memory Course\" prepared \r\nby Texas Instruments on video tapes. The CCD movie is published in\r\nthe Journal of Solid State Circuits (June 1973) as three sequences of \r\npage-flip movie.
\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n" }, { "name": "Piliavin, Michael Aron", "degree": "PhD", "year": "1973", "title": "A Theoretical Investigation of the Effect of Intermolecular Correlations upon Properties of Simple Liquids from X-Ray Diffraction", "advisor": "Pings, Cornelius J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08272018-085905047", "creators": [ { "name": { "family": "Piliavin", "given": "Michael Aron" }, "id": "Piliavin-Michael-Aron", "display_name": "Piliavin, Michael Aron" } ], "advisors": [ { "name": { "family": "Pings", "given": "Cornelius J." }, "id": "Pings-C-J", "role": "advisor", "display_name": "Pings, Cornelius J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "abstract": "This work reports a theoretical study on the effect of including intermolecular correlations in x-ray scattering data from simple liquids.
\r\n\r\nAn instantaneous configuration-dependent scattering factor is defined for a molecule in a liquid. Using statistical mechanics and physical principles, an expression is derived that corrects the usual scattering equations, for both coherent and incoherent radiation.
\r\n\r\nComputations, using the new result, were done on liquid helium and argon. Comparison of correlated scattering factors and isolated molecule scattering factors show significant deviations, especially for larger angles of scattering. Incorporating correlation effects into scattering data for these liquids, the resultant radial distribution function peak is depressed an average of 1% and the potential energy is lowered by 5%. Treatment of data in this manner leads to better agreement with theoretical predictions.
\r\n" }, { "name": "Poore, Aubrey Bonner", "degree": "PhD", "year": "1973", "title": "Stability and Bifurcation Phenomena in Chemical Reactor Theory", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07312006-091400", "creators": [ { "name": { "family": "Poore", "given": "Aubrey Bonner" }, "id": "Poore-Aubrey-Bonner", "display_name": "Poore, Aubrey Bonner" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/Y69M-X355", "abstract": "We investigate the nonlinear parabolic equations of chemical tubular reactors. For various ranges of certain physical parameters perturbation procedures are applied to reduce the problem to various questions involving periodicity of solutions of ordinary and partial differential equations, multiplicity of solutions, bifurcation phenomena, existence, and stability of solutions. The main results include an investigation of the implications of the direction and stability of bifurcating branches and the multiplicity of periodic solutions for nonlinear diffusive systems. For the non-adiabatic chemical reactors the response diagrams are given for all relevant ranges of all physical parameters.\r\n" }, { "name": "Rebollo-Rebollo, Manuel", "degree": "PhD", "year": "1973", "title": "Analytical and Experimental Investigation of a Turbulent Mixing Layer of Different Gases in a Pressure Gradient", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072010-091455869", "creators": [ { "name": { "family": "Rebollo-Rebollo", "given": "Manuel" }, "id": "Rebollo-Rebollo-Manuel", "display_name": "Rebollo-Rebollo, Manuel" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6YB5-CJ15", "abstract": "An analytical and experimental study has been made of the turbulent mixing layer in a pressure gradient. Theory predicts the possible existence of equilibrium flows, and this was confirmed experimentally for turbulent shear layers between streams of helium and nitrogen. \r\nThe only case for which similarity is possible is for P2 U_2^2 = P1 U_1^2 since then P_2 (x) = P_1 (x). These equilibrium flows are of the form U_1 ~x^ \u03b1 and \u03b4~X, where \u03b1=x/U_1 dU_1/dx is non \u2013dimensional pressure gradient parameter. \r\nThe experimental investigation was conducted in the facility designed by Brown to produce turbulent flows at pressures up to 10 atmospheres. The adjustable walls of the test section of the apparatus were modified in order to set the pressure gradient. \r\nShadowgraphs of the mixing zone for \u03b1 = 0 and \u03b1 = - 0.18, at different Reynolds numbers, revealed a large scale structure noticeably different for each \u03b1. \r\nThe similarity properties of the shear layer were established from mean profiles of total head and density. In addition, the rms density fluctuations were found to be self-preserving. From the mean profiles, the spreading rate, turbulent mass diffusion, Reynolds stress and Schmidt number distributions were calculated from the equations of motion. \r\nThe experimental results show that the spreading rate for the adverse pressure gradient is 60% A greater than for the \u03b1 = 0 case. The maximum shearing stress is 70% larger and the maximum value of the turbulent mass diffusion is 20% larger than their \u03b1 = 0 counterparts. The maximum rms density fluctuations are approximately 0.2 in both flows. \r\nSurprisingly low values of turbulent Schmidt numbers were found; e. g., at the dividing streamline Sc_t = 0.16 for \u03b1 = 0 and Sc_t = 0. 33 for \u03b1 = - 0. 18.\r\n" }, { "name": "Rupert, Viviane Claude", "degree": "PhD", "year": "1973", "title": "Experimental Study of Shock Wave Strengthening by a Positive Density Gradient in a Cryogenic Shock Tube", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:08272010-083731520", "creators": [ { "name": { "family": "Rupert", "given": "Viviane Claude" }, "id": "Rupert-Viviane-Claude", "display_name": "Rupert, Viviane Claude" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZXBM-7809", "abstract": "An experimental investigation of the strengthening of a shock wave propagating through an isobaric region of increasing density is presented. A new experimental configuration consisting of a pressure-driven shock tube mounted vertically with the test section partially immersed in a cryogenic bath is used. The resulting test gas density distribution consists of a uniform region of low density near the shock tube diaphragm, then a strong local gradient followed by another uniform region of high density. The\r\nMach number of the shock initiated at the diaphragm is determined as the shock emerges from the gradient from velocity and temperature measurements for various initial conditions.\r\nThe experimental data are compared with predictions from approximate theoretical models and a numerical integration of the exact flow equations for the shock-gradient interaction. The measured Mach numbers are considerably higher than these predictions indicating that the models are not adequate to represent the experimental configuration. Calculations show that the additional strengthening of the shock results from multiple interactions between waves generated within the gradient and flow nonuniformities due to the shock formation mechanism.\r\n" }, { "name": "Sinclair, Glenn Bruce", "degree": "PhD", "year": "1973", "title": "On Nonmixed Symmetric End-Load Problems in Elastic Waveguides", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechTHESIS:07102018-114156713", "creators": [ { "name": { "family": "Sinclair", "given": "Glenn Bruce" }, "id": "Sinclair-Glenn-Bruce", "display_name": "Sinclair, Glenn Bruce" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ZDWG-ZG20", "abstract": "This investigation deals with the response of the semi-infinite,\r\nlinear elastic, homogeneous, isotropic plate in plane strain, subject\r\nto symmetric normal loads acting, in the absence of shear stress,\r\non its edge. A double Laplace transform technique is used to obtain\r\nlong-time information for two problems; a uniform load and a line-load.\r\nNear- and far-field approximations are found, the far-field approximations \r\ngiving the integral of the Airy integral for both problems." }, { "name": "Small, Robert Donald", "degree": "PhD", "year": "1973", "title": "Nonlinear Dispersive Waves in Nonlinear Optics", "advisor": "Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechTHESIS:03292013-143344675", "creators": [ { "name": { "family": "Small", "given": "Robert Donald" }, "id": "Small-Robert-Donald", "display_name": "Small, Robert Donald" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/KKBY-7364", "abstract": "A study is made of solutions of the macroscopic Maxwell\r\nequations in nonlinear media. Both nonlinear and dispersive terms are responsible for effects that are not taken into account in the geometrical optics approximation. The nonlinear terms can, depending on the nature of the nonlinearity, cause plane waves to focus when the amplitude varies across the wavefront. The dispersive terms prevent the singularities that nonlinearity alone would produce.\r\nSolutions are found which de scribe periodic plane waves in fully nonlinear media. Equations describing the evolution of the amplitude, frequency and wave number are generated by means of averaged Lagrangian techniques. The equations are solved for near linear media to produce the form of focusing waves which develop a singularity at the focal point. When higher dispersion is included nonlinear\r\nand dispersive effects can balance and one finds amplitude profiles that propagate with straight rays.
\r\n" }, { "name": "Storm, Erik", "degree": "PhD", "year": "1973", "title": "Part I. Investigation of Strong Shock Waves in a Conical Convergent Channel. Part II. Spectroscopic Investigation of Strong Shockwaves in a Conical, Convergent Channel", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042007-104952", "creators": [ { "name": { "family": "Storm", "given": "Erik" }, "id": "Storm-Erik", "display_name": "Storm, Erik" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TJFS-6964", "abstract": "ABSTRACT OF PART I:
\r\n\r\nThe behavior of an initially plane, strong shock wave propagating into a conical convergence is investigated experimentally and theoretically. In the experiment a 10\u00b0 half-angle cone is mounted on the end of a pressure-driven shock tube. Shock waves with initial Mach numbers varying from 6.0 to 10.2 are generated in argon at a pressure of 1.5 torr. During each run local shock velocities at several positions along the cone axis are measured using a thin, multi-crystal piezoelectric probe inserted from the vertex. This technique produces accurate velocity data for both the incident and reflected shock waves. In the corresponding analysis, a simplified characteristics method is used to obtain an approximate solution of the axisymmetric diffraction equations derived by Whitham (1959).
\r\n\r\nBoth the shock velocity measurements and the axisymmetric diffraction solution confirm that the incident shock behavior is dominated by cyclic diffraction processes which originate at the entrance of the cone. Each diffraction cycle is characterized by Mach reflection on the cone wall followed by Mach reflection on the axis. These cycles evidently persist until the shock reaches the cone vertex, where the measured velocity has increased by as much as a factor of three. Real-gas effects, enhanced in the experiment by increasing the initial Mach number and decreasing the pressure, apparently alter the shock wave behavior only in the region near the vertex. Velocity measurements for the reflected shock within the cone show that the shock velocity is nearly constant throughout most of the convergence length.
\r\n\r\nABSTRACT OF PART II:
\r\n\r\nThe thermodynamic conditions behind the incident and reflected shock wave close to the vertex of a convergent channel are investigated spectroscopically. The investigation was initiated in order to better determine the possible uses of such a geometrical device as a tool for high temperature plasma research. Using argon at an initial pressure of 1.5 torr, the shock Mach number prior to the entrance of the cone is 10.2. Two windows are mounted at x/1 = 0.9 in the cone, where the Mach number has increased to 24, and the emitted radiation is monitored for both time-resolved (Monochromator - Photomultiplier) and time-integrated (Spectrograph) analysis. The relative line intensity method is used to measure the electron temperature. The Stark broadened profile of the 6965.4 \u00c5 neutral argon line, and continuum intensity measurements are used to determine the electron number density.
\r\n\r\nFrom initial values of 13200\u00b0K and 1.4 x 10\u00b9\u2077 cm\u207b\u00b3, both the electron temperature and number density profiles behind the incident shock are dominated by the previous shock diffraction processes. The general trend is a gradual increase, presumably due to the continuing compression of the gas shocked at successively earlier times. Superimposed upon this is the effect of hot slugs of gas from previous localized regions of very high Mach number. The reflected shock wave heats and compresses the gas even further. The subsequent expansion results in a series of rapid exponential decreases in temperature, density and pressure. Immediately after the reflected shock wave has passed, the gas appears to be in a nonequilibrium state with a population inversion among the upper excited atomic energy levels. There is an indication of the presence of a second reflected wave. The effects of self-absorption on Stark broadened lines is studied. An equation is derived, demonstrating the effect of individual corrections that are necessary before accurate interpretations of measured quantities can be made. Simple self-absorption correction schemes are demonstrated and shown to be self-consistent.
" }, { "name": "Sullivan, William Noel", "degree": "PhD", "year": "1973", "title": "Heat Transfer to Flowing Granular Media", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-132934", "creators": [ { "name": { "family": "Sullivan", "given": "William Noel" }, "id": "Sullivan-William-Noel", "display_name": "Sullivan, William Noel" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9CC8-A074", "abstract": "The convective heat transfer resulting from a granular flow over a heated surface is investigated. The specific type of flow considered is that in which adjacent material particles are in physical contact. The qualitative features of this type of flow are discussed, and the existing equations of motion are extended. With regard to the equations of motion, an exact solution is shown which has applications concerning the mass flow rate of granular materials through hoppers. The particular heat transfer problem investigated is convection from a flat plate with its long axis parallel to the flow field. An approximate analytical solution, which takes into account the particulate nature of the medium, is developed and experimental measurements obtained. The theory was found to correctly predict the trends of the experimental data. The results indicate that the Nusselt number for this configuration is influenced substantially, under certain conditions, by the noncontinuous nature of the medium. A semi-empirical correlation is presented, based on experimental results obtained with four different granular materials." }, { "name": "Wood, John Holm", "degree": "PhD", "year": "1973", "title": "Earthquake-Induced Soil Pressures on Structures", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechThesis:10152019-101037996", "creators": [ { "name": { "family": "Wood", "given": "John Holm" }, "id": "Wood-John-Holm", "display_name": "Wood, John Holm" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/MZWQ-BA46", "abstract": "The earthquake-induced pressures on soil-retaining structures are investigated. The study was motivated by the lack of suitable earthquake design data for relatively rigid structures on firm foundations in situations where the foundation, structure and retained soil remain essentially elastic.
\r\n\r\nPressures and forces on the walls of a number of idealized wall-soil problems are analyzed. The solutions obtained are evaluated for a range of the important parameters to give results useful for design. In the idealized problems the soil is represented by an elastic layer of finite length bonded to a rigid foundation or rock layer. The wall or structure is represented by a rigid element resting on the rock layer and is permitted to undergo rotational deformation about the base. The mass or moment of inertia of the structure and its rotational stiffness are included as parameters in the idealization. Static and dynamic solutions are obtained using both analytical and finite element methods. Solutions are evaluated for the assumption of perfectly rigid behavior of the wall. The general solution for the deformable wall case was developed by superposition of the solution for the perfectly rigid case and solutions derived for displacement forcing of the wall structure.
\r\n\r\nThe assumption of linear elastic behavior of the wall- soil system is likely to be approximately satisfied in situations where a building or other large civil engineering structure is founded on firm soil or rock strata. In contrast to the linearly elastic assumption made in this study, the commonly used Mononobe-Okabe method employs the assumption of sufficiently large wall deformations to induce a fully plastic stress condition in the soil. It was concluded that both the elastic theory and the Mononobe-Okabe method have valid applications in the design of wall structures subjected to earthquake motions, but that because of significant differences in the solutions obtained from each method, care is required in selecting the most appropriate method for a particular situation.
" }, { "name": "Yu, Thomas King Lin", "degree": "PhD", "year": "1973", "title": "Optimal Filtering for Systems Governed by Coupled Ordinary and Partial Differential Equations", "advisor": "Seinfeld, John H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10202017-140716441", "creators": [ { "name": { "family": "Yu", "given": "Thomas King Lin" }, "id": "Yu-Thomas-King-Lin", "display_name": "Yu, Thomas King Lin" } ], "advisors": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "advisor", "display_name": "Seinfeld, John H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/C7W5-8C39", "abstract": "The recursive estimation of states or parameters of stochastic dynamical systems with partial and imperfect measurements is generally referred to as filtering. The estimator itself is called the filter. In this dissertation optimal filters are derived for three important classes of nonlinear stochastic dynamical systems.
\r\n\r\nThe first class of systems, considered in Chapter II, is that governed by stochastic nonlinear hyperbolic and parabolic partial differential equations in which the dynamical disturbances in the system and in the boundary conditions can be both additive and nonadditive. This class of systems is important for it encompasses a large group of systems of practical interest, such as chemical reactors and heat exchangers. The optimal filter obtained can estimate, not only the state, but also constant parameters appearing at the boundary and in the volume of the system. The computational application of this filter is illustrated in an example of the feedback control of a styrene polymerization reactor.
\r\n\r\nMany physical systems contain time delays in one form or another. Often, this kind of delay system is accompanied by some other processes such as dissipation of mass and energy, fluid mixing, and chemical reaction. In Chapter III within a single framework new optimal filters are obtained for the following classes of stochastic systems:
\r\n\r\n1. Nonlinear lumped parameter systems containing multiple constant and time-varying delays;
\r\n2. Mixed nonlinear lumped and hyperbolic distributed parameter systems; and
\r\n3. Nonlinear lumped parameter systems with functional time delays.
\r\n\r\nThe performance of the filter is illustrated through estimates of the temperatures in a system consisting of a well-stirred chemical reactor and an external heat exchanger.
\r\n\r\nIn Chapter IV filtering equations are derived for a completely general class of stochastic systems governed by coupled nonlinear ordinary and partial differential equations of either first order hyperbolic or parabolic type with both volume and boundary random disturbances. Thus, the results of Chapter III can be shown to be a special case of those obtained in Chapter IV.
\r\n\r\nA related important concept to filtering is observability. For deterministic linear lumped parameter systems, observability refers to the ability to recover some prior state of a dynamical system based on partial observations of the state over some period of time. Under certain conditions, observability of the corresponding deterministic system is a sufficient condition for convergence of the optimal linear filter for a linear system with white noise disturbances. In Chapter V the concept of observability and filter convergence is developed for a class of stochastic linear distributed parameter systems whose solutions can be expressed as eigenfunction expansions. Two important questions examined are: (1) the effect of measurement locations on observability, and (2) the optimal location of measurements for state estimation.
\r\n" }, { "name": "Yuen, Henry Che-Chuen", "degree": "PhD", "year": "1973", "title": "Waves on Vortex Filaments", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252004-113017", "creators": [ { "name": { "family": "Yuen", "given": "Henry Che-Chuen" }, "id": "Yuen-Henry-Che-Chuen", "display_name": "Yuen, Henry Che-Chuen" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/37BW-KF96", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nVarious problems concerning waves on vortex filaments are considered. The local force balance method introduced by Moore and Saffman for the calculation of the induced velocity at a point of a vortex filament with arbitrary structure and shape is used to examine the effect of axial flow on the stability of trailing vortices and vortex rings. It is found that the effect is small in both cases. The method is extended to study the stability of vortex rings carrying electric charges, which are possible models for vortices in liquid helium. Two cases are considered--the conducting ring and the uniformly charged ring. In each of these cases it is found that the velocity of a charged ring is smaller than an uncharged one, and if the charges are strong enough, the ring may reverse its direction of motion. Furthermore, the charged ring becomes unstable when the charge effect is comparable to the vorticity effect. The motion and stability of a buoyant vortex ring are also considered. It is shown that a heavy ring travelling in the direction of gravity decelerates, thins and expands, while a light ring accelerates, fattens and contracts. The heavy ring is stable to disturbances of the centerline, but the light ring is unstable with a growth rate independent of wave number.\r\n\r\nIntrinsic equations governing the curvature [...] and torsion [...] of a vortex filament are obtained. They form a set of coupled nonlinear integro-partial differential equations. By retaining only the leading order term in the singularity of the Biot-Savart integral, which corresponds to the localized induction hypothesis introduced by Arms and Hama, these can be reduced to a single nonlinear Schrodinger equation for the complex variable [...] where s is the arclength. A complete set of steady state solutions for this equation is obtained. This includes the straight vortex, the helical vortex, the vortex ring, and a solitary wave form, all being limiting cases of a general periodic wave structure. A modified scheme is introduced to resolve an apparent nonuniformity of the solitary wave solution in the limit [...]. Non-local effects (effects of the regular part of the Biot-Savart integral) are examined by means of an asymptotic expansion of the intrinsic equations in the small parameter [...] where a is the core radius of the filament. It is shown that even in the tail ends of the solitary wave where the local effect fails to dominate, the solitary wave solution exists to [...]." }, { "name": "Zaidel, Eran", "degree": "PhD", "year": "1973", "title": "Linguistic Competence and Related Functions in the Right Cerebral Hemisphere of Man Following Commissurotomy and Hemispherectomy", "advisor": "Sperry, Roger Wolcott", "url": "https://resolver.caltech.edu/CaltechTHESIS:05062011-142849302", "creators": [ { "name": { "family": "Zaidel", "given": "Eran" }, "id": "Zaidel-Eran", "display_name": "Zaidel, Eran" } ], "advisors": [ { "name": { "family": "Sperry", "given": "Roger Wolcott" }, "id": "Sperry-R-W", "role": "advisor", "display_name": "Sperry, Roger Wolcott" } ], "committee": [ { "name": { "family": "Sperry", "given": "Roger Wolcott" }, "id": "Sperry-R-W", "role": "chair", "display_name": "Sperry, Roger Wolcott" }, { "name": { "family": "Benzer", "given": "Seymour" }, "id": "Benzer-S", "role": "member", "display_name": "Benzer, Seymour" }, { "name": { "family": "Dostert", "given": "Bozena" }, "id": "Dostert-B", "role": "member", "display_name": "Dostert, Bozena" }, { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "member", "display_name": "Fender, Derek H." }, { "name": { "family": "Pierce", "given": "John" }, "id": "Pierce-J", "role": "member", "display_name": "Pierce, John" } ], "option_major": [ "eng" ], "doi": "10.7907/GBH1-QX09", "abstract": "A simple new contact lens technique has been developed to permit the presentation of continuously lateralized visual information to one visual half field at a time. Free unilateral scanning of the information and monitoring of performance in the subjects' lap makes it possible to administer a variety of standard perceptual and cognitive tasks to either hemisphere in order to assess hemispheric specialization under natural conditions. Two representative commissurotomy patients have been fitted with the new device and have undergone an extensive series of language and related studies focusing on the right hemisphere. All tests were administered unilaterally to each hemisphere and subsequently in free vision. The results were correlated with data from a group of three hemispherectomy patients in two of whom the right (non dominant) and in one of whom the left (dominant) cerebral hemisphere has been surgically removed for the treatment of post infantile tumor.
\r\n\r\nThe case of dominant hemispherectomy is particularly rare and permits the study of language competence and performance in a girl whose language lateralization for speech and hearing was well under way (perhaps completed) when the tumor set in. Results of extensive clinical aphasia tests reveal a distinct hierarchy of language functions from a relatively good auditory comprehension through a more severe speech deficit, to almost complete alexia, agraphia and acalculia. Theoretical aphasiological analysis of the pattern of impairment in language functions here shows that in spite of characteristic nonfluency and anomia in speech, the syndrome is unique and does not correspond to either a Broca's or anomic aphasia. The agraphia and especially the alexia in this patient are more severe than in the separated right hemisphere of the two commissurotomy patients which can read a wide range of individual words and even short sentences. This is in contrast to her superior expressive speech relative to the right hemisphere of the same two commissurotomy patients.
\r\n\r\nIn a series of studies comparing the psycholinguistic abilities of the two hemispheres in the two commissurotomy and three hemispherectomy patients it was shown that the right cerebral hemisphere had extensive ability to elicit meaning from pictures and to recognize semantic associations and form concepts. In particular it was able to ignore perceptual for semantic similarity.
\r\n\r\nLateralized tests of visual closure reveal the conditions under which right hemisphere visual feature extraction mechanisms fail. Previous results on superior right hemisphere competence in completing patterns from fragmented information must now be qualified by the provision that when the gestalt of the visual ground is strong and in competition with the figure, the right hemisphere is unable to complete partial patterns. Neither can it recognize complete embedded figures in the face of distracting gestalt in the ground.
\r\n\r\nRight hemisphere competence in various aspects of auditory language comprehension has been investigated with the aid of an experimental paradigm involvingmatching an auditory message to one of unilaterally presented alternative line drawings. Lower limit age estimates for right hemisphere comprehension of vocabulary were obtained and it was shown that the right hemisphere can comprehend not only abstract words but also a variety of syntactic structures including verbs, and sentential transformations and to a lesser degree long nonredundant and semantically abstract references. Right hemisphere pattern of syntactic competence has weak correlation with order of acquisition in children and somewhat stronger with aphasics. In contrast, aural vocabulary in the right hemisphere, although consistently inferior to the left, follows the same function of frequency as the left just as do children and aphasics.
" }, { "name": "Zoltek, John Jr.", "degree": "PhD", "year": "1973", "title": "Interaction of Aqueous Inorganic Orthophosphate and Phosphate Rock", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04182014-102433018", "creators": [ { "name": { "family": "Zoltek", "given": "John Jr." }, "id": "Zoltek-John", "display_name": "Zoltek, John Jr." } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/8957-0Z94", "abstract": "An experimental study was made of the interaction of phosphate\r\nrock and aqueous inorganic orthophosphate, calcium, and hydroxyl\r\nions. A model of the reaction was developed by observing electron\r\ndiffraction patterns in conjunction with concentration changes of\r\nchemical components. The model was applied in explaining the performance\r\nof batch suspensions of powdered phosphate rock and packed\r\ncolumns of granular phosphate rock. In both cases the reaction consisted\r\ninitially of a rapid nucleation phase that occurred in a time\r\nperiod of minutes. In the batch system the calcium phosphate nuclei\r\nthen ripened into larger micro-crystals of hydroxyapatite, which\r\neventually became indistinguishable from the original phosphate rock\r\nsurface. During column operation the high supersaturation ratio that\r\nexisted after the rapid nucleation phase resulted in a layer of small\r\nnuclei that covered a slowly growing hydroxyapatite crystal.
\r\n\r\nThe column steady-state rate constant was found to increase with\r\nincreasing temperature, pH, and fluoride concentration, and to decrease\r\nwith increasing concentrations of magnesium sulfate,\r\nammonium chloride, and bicarbonate ion.
\r\n\r\nAn engineering feasibility study indicated that, based on economic\r\nconsiderations, nucleation of apatite on phosphate rock ore has a\r\npotential use as a wastewater phosphate removal treatment process.
" }, { "name": "Anthony, Michael Paul", "degree": "PhD", "year": "1972", "title": "Electrical and Optical Properties of Beta-Gallium Oxide", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042016-102655753", "creators": [ { "name": { "family": "Anthony", "given": "Michael Paul" }, "id": "Anthony-Michael-Paul", "display_name": "Anthony, Michael Paul" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/HB9S-1F80", "abstract": "An experimental investigation of the optical properties of \u03b2\u2013gallium oxide has been carried out, covering the wavelength range 220-2500 nm.
\r\n\r\nThe refractive index and birefringence have been determined to about \u00b1 1% accuracy over the range 270-2500 nm, by the use of a technique based on the occurrence of fringes in the transmission of a thin sample due to multiple internal reflections in the sample (ie., the \"channelled spectrum\" of the sample.)
\r\n\r\nThe optical absorption coefficient has been determined over the range 220 - 300 nm, which range spans the fundamental absorption edge of \u03b2 \u2013 Ga2O3. Two techniques were used in the absorption coefficient determination: measurement of transmission of a thin sample, and measurement of photocurrent from a Schottky barrier formed on the surface of a sample. Absorption coefficient was measured over a range from 10 to greater than 105, to an accuracy of better than \u00b1 20%. The absorption edge was found to be strongly polarization-dependent.
\r\n\r\nDetailed analyses are presented of all three experimental techniques used. Experimentally determined values of the optical constants are presented in graphical form.
\r\n\r\n" }, { "name": "Bajorek, Christopher Henry", "degree": "PhD", "year": "1972", "title": "Spin Wave Resonance in Ferromagnetic Thin Films", "advisor": "Wilts, Charles H.; Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042016-091637939", "creators": [ { "name": { "family": "Bajorek", "given": "Christopher Henry" }, "id": "Bajorek-Christopher-Henry", "display_name": "Bajorek, Christopher Henry" } ], "advisors": [ { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." }, { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9e70-r690", "abstract": "The objective of this investigation has been a theoretical and experimental understanding of ferromagnetic resonance phenomena in ferromagnetic thin films, and a consequent understanding of several important physical properties of these films. Significant results have been obtained by ferromagnetic resonance, hysteresis, torque magnetometer, He ion backscattering, and X-ray fluorescence measurements for nickel-iron alloy films.
\r\n\r\nTaking into account all relevant magnetic fields, including the applied, demagnetizing, effective anisotropy and exchange fields, the spin wave resonance condition applicable to the thin film geometry is presented. On the basis of the simple exchange interaction model it is concluded that the normal resonance modes of an ideal film are expected to be unpinned. The possibility of nonideality near the surface of a real film was considered by means of surface anisotropy field, inhomogeneity in demagnetizing field and inhomogeneity of magnetization models. Numerical results obtained for reasonable parameters in all cases show\r\nthat they negligibly perturb the resonance fields and the higher order mode shapes from those of the unpinned modes of ideal films for thicknesses greater than 1000 \u00c5. On the other hand for films thinner than 1000 \u00c5 the resonance field deviations can be significant even though the modes are very nearly unpinned. A previously unnoticed but important feature of all three models is that the interpretation of the first resonance mode as the uniform mode of an ideal film allows an accurate\r\nmeasurement of the average effective demagnetizing field over the film volume. Furthermore, it is demonstrated that it is possible to choose parameters which give indistinguishable predictions for all three models, making it difficult to uniquely ascertain the source of spin pinning in real films from resonance measurements alone.
\r\n\r\nSpin wave resonance measurements of 81% Ni-19% Fe coevaporated films 30 to 9000 \u00c5 thick, at frequencies from 1 to 8 GHz, at room temperature, and with the static magnetic field parallel and perpendicular to the film plane have been performed. A self-consistent analysis of the results for films thicker than 1000 \u00c5, in which multiple excitations can be observed, shows for the first time that a unique value of exchange constant A can only be obtained by the use of unpinned mode assignments. This evidence and the resonance behavior of films thinner than 1000 \u00c5 strongly imply that the magnetization at the surfaces of permalloy films is very weakly pinned. However, resonance measurements alone cannot determine whether this pinning is due to a surface anisotropy, an inhomogeneous demagnetizing field or an inhomogeneous magnetization. The above analysis yields\r\na value of 4\u03c0M=10,100 Oe and A = (1.03 \u00b1 .05) x 10-6 erg/cm for this alloy. The ability to obtain a unique value of A suggests that spin wave resonance can be used to accurately characterize the exchange interaction in a ferromagnet.
\r\n\r\nIn an effort to resolve the ambiguity of the source of pinning of the magnetization, a correlation of the ratio of magnetic moment and X-ray film thickness with the value of effective demagnetizing field 4\u03c0NM as determined from resonance, for films 45 to 300 \u00c5 has been performed. The remarkable agreement of both quantities and a comparison with the predictions of five distinct models, strongly imply that the thickness dependence of both quantities is related to a thickness dependent average saturation magnetization, which is far below 10,100 Oe for very thin films. However, a series of complementary experiments shows that this large decrease of average saturation magnetization cannot be simply explained by either oxidation or interdiffusion processes. It can only be satisfactorily explained by an intrinsic decrease of the average saturation magnetization for very thin films, an effect which cannot be justified by any simple physical considerations.
\r\n\r\nRecognizing that this decrease of average saturation magnetization could be due to an oxidation process, a correlation of resonance measurements, He ion backscattering, X-ray fluorescence and torque magnetometer measurements, for films 40 to 3500 \u00c5 thick has been performed. On basis of these measurements it is unambiguously established that the oxide layer on the surface of purposefully oxidized 81% Ni-19% Fe evaporated films is predominantly Fe-oxide, and that in the oxidation process Fe atoms are removed from the bulk of the film to depths of thousands of angstroms. Extrapolation of results for pure Fe films indicates that the oxide is most likely \u03b1-Fe2O3. These conclusions are in agreement with results from old metallurgical studies of high temperature oxidation of bulk Fe and Ni-Fe alloys. However, X-ray fluorescence results for films oxidized at room temperature, show that although the preferential oxidation of Fe also takes place in these films, the extent of this process is by far too small to explain the large variation of their average saturation magnetization with film thickness.
\r\n" }, { "name": "Baker, Mary", "degree": "PhD", "year": "1972", "title": "Double-Slit Photometric Measurement of Velocity Profiles of Blood in Microvessels and Capillary Tubes", "advisor": "Wayland, J. Harold", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162005-112315", "creators": [ { "name": { "family": "Baker", "given": "Mary" }, "id": "Baker-Mary", "display_name": "Baker, Mary" } ], "advisors": [ { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "advisor", "display_name": "Wayland, J. Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/DDWS-GF91", "abstract": "The extreme blunting of velocity profiles for human blood, reported from double-slit photometric measurements, has been shown to be an artifact of the measuring technique. The velocities measured are actually an average of velocities throughout the tube. An equation developed to model this averaging predicts profiles which agree with experimental results. This model explains the increase in blunting with decreasing tube diameter previously reported even if the true profiles remain parabolic.
\r\n\r\nA trial and error method was chosen to extract information about the actual velocity distributions from double-slit measurements. Trial profiles were calculated using a τ versus \u03b3. relationship derived from bulk rheological measurements. The data of Barbee for τW versus ⩂ and for tube relative hematocrit were used. When these trial profiles were averaged with the model for double-slit averaging, they were consistent with double-slit measurements. Neither the calculated nor measured profiles gave any evidence of substantial blunting except for ⩂<2 sec-1 where yield stress becomes important.
\r\n\r\nAlthough the continuum approach was used to calculate trial profiles, limitations in the continuum representation were evident from hematocrit considerations. No hematocrit distribution could be found that resulted in calculated profiles which produced both the correct volume flow rate and correct outflow hematocrit.
\r\n\r\nA simple correction procedure is described for calculating volume flow rates from double-slit centerline velocity measurements.
" }, { "name": "Balanis, George Nick", "degree": "PhD", "year": "1972", "title": "Plasma Inverse Scattering Theory", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:04012016-145403689", "creators": [ { "name": { "family": "Balanis", "given": "George Nick" }, "id": "Balanis-George-Nick", "display_name": "Balanis, George Nick" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7PTN-RV17", "abstract": "The object of this report is to calculate the electron density profile of plane stratified inhomogeneous plasmas. The electron density profile is obtained through a numerical solution of the inverse scattering algorithm.
\r\n\r\nThe inverse scattering algorithm connects the time dependent reflected field resulting from a \u03b4-function field incident normally on the plasma to the inhomogeneous plasma density.
\r\n\r\nExamples show that the method produces uniquely the electron density on or behind maxima of the plasma frequency.
\r\n\r\nIt is shown that the \u03b4-function incident field used in the inverse scattering algorithm can be replaced by a thin square pulse.
\r\n\r\n" }, { "name": "Baligh, Mohsen Mohamed", "degree": "PhD", "year": "1972", "title": "Applications of Plasticity Theory to Selected Problems in Soil Mechanics", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042016-082008001", "creators": [ { "name": { "family": "Baligh", "given": "Mohsen Mohamed" }, "id": "Baligh-Mohsen-Mohamed", "display_name": "Baligh, Mohsen Mohamed" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/EAM0-H226", "abstract": "Two topics in plane strain perfect plasticity are studied using the method of characteristics. The first is the steady-state indentation of an infinite medium by either a rigid wedge having a triangular cross section or a smooth plate inclined to the direction of motion. Solutions are exact and results include deformation patterns and forces of resistance; the latter are also applicable for the case of incipient failure. Experiments on sharp wedges in clay, where forces and deformations are recorded, showed a good agreement with the mechanism of cutting assumed by the theory; on the other hand the indentation process for blunt wedges transforms into that of compression with a rigid part of clay moving with the wedge. Finite element solutions, for a bilinear material model, were obtained to establish a correspondence between the response of the plane strain wedge and its axi-symmetric counterpart, the cone. Results of the study afford a better understanding of the process of indentation of soils by penetrometers and piles as well as the mechanism of failure of deep foundations (piles and anchor\r\nplates).
\r\n\r\nThe second topic concerns the plane strain steady-state free rolling of a rigid roller on clays. The problem is solved approximately for small loads by getting the exact solution of two problems that encompass the one of interest; the first is a steady-state with a geometry that approximates the one of the roller and the second is an instantaneous solution of the rolling process but is not a steady-state. Deformations and rolling resistance are derived. When compared with existing empirical formulae the latter was found to agree closely.
\r\n\r\n" }, { "name": "Barker, Steven Joseph", "degree": "PhD", "year": "1972", "title": "Radiated Noise and Wall Pressure Measurements in Turbulent Boundary Layers in Dilute Polymer Solutions", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechTHESIS:09152010-105211344", "creators": [ { "name": { "family": "Barker", "given": "Steven Joseph" }, "id": "Barker-Steven-Joseph", "display_name": "Barker, Steven Joseph" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/4TVJ-YA39", "abstract": "Measurements of radiated noise and wall pressure\r\nfluctuations in a turbulent boundary layer in water are\r\ndescribed. A comparison is made between measurements in\r\npure water and in dilute solutions of high molecular weight\r\npolymers. To obtain these measurements, a new experimental\r\ngeometry was developed.\r\n\r\nThe principle of the experiment is as follows: A\r\nflat steel plate 205 cm long by 80 cm wide is rolled into a\r\nsingle-turn spiral, with a radial gap of 4.5 cm between the\r\ntwo overlapping ends. The spiral is submerged in water and\r\nrotated about its axis, creating a boundary layer on the\r\ninner surface which leaves the interior of the spiral\r\nthrough the radial gap. The fluid leaving the interior\r\nthrough the gap is replaced through the two open ends of\r\nthe spiral by means of stationary honeycomb filters which\r\nremove residual turbulence and vorticity.\r\n\r\nMeasurements of the mean velocity profile show that\r\nthe turbulent boundary layer on the inside surface of the\r\nspiral resembles that on a flat plate in a uniform free\r\nstream. A Reynolds number based upon plate length of\r\n5 x 10^6 is obtained.\r\n\r\nWall pressure fluctuations under the boundary layer\r\nare measured with piezoelectric transducers mounted flush in\r\nthe wall of the spiral. Radiated noise is measured with a stationary transducer located outside of the boundary layer,\r\nnear the center of the spiral. It is shown that the polymer\r\nadditives cause significant reductions in both the radiated\r\nnoise and wall pressure spectra. The reductions are greatest\r\nat high frequencies, or at Strouhal numbers greater than one.\r\n" }, { "name": "Brockway, George Samuel, II", "degree": "PhD", "year": "1972", "title": "On the Uniqueness of Singular Solutions to Boundary-Initial Value Problems in Linear Elastodynamics", "advisor": "Sternberg, Eli", "url": "https://resolver.caltech.edu/CaltechTHESIS:04012016-123848510", "creators": [ { "name": { "family": "Brockway", "given": "George Samuel, II" }, "id": "Brockway-George-Samuel", "display_name": "Brockway, George Samuel, II" } ], "advisors": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "advisor", "display_name": "Sternberg, Eli" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/WR6E-S243", "abstract": "This investigation deals with certain generalizations of the classical uniqueness theorem for the second boundary-initial value problem in the linearized dynamical theory of not necessarily homogeneous nor isotropic elastic solids. First, the regularity assumptions underlying the foregoing theorem are relaxed by admitting stress fields with suitably restricted finite jump discontinuities. Such singularities are familiar from known solutions to dynamical elasticity problems involving discontinuous surface tractions or non-matching boundary and initial conditions. The proof of the appropriate uniqueness theorem given here rests on a generalization of the usual energy identity to the class of singular elastodynamic\r\nfields under consideration.
\r\n\r\nFollowing this extension of the conventional uniqueness theorem, we turn to a further relaxation of the customary smoothness hypotheses and allow the displacement field to be differentiable merely in a generalized sense, thereby admitting stress fields with square-integrable unbounded local singularities, such as those encountered in the presence of focusing of elastic waves. A statement of the traction problem applicable in these pathological circumstances necessitates the introduction of \"weak solutions'' to the field equations that are accompanied by correspondingly weakened boundary and initial conditions. A uniqueness theorem pertaining to this weak formulation is then proved through an adaptation of an argument used by O. Ladyzhenskaya in connection with the first boundary-initial value problem for a second-order hyperbolic equation in a single dependent\r\nvariable. Moreover, the second uniqueness theorem thus obtained contains, as a special case, a slight modification of the previously established uniqueness theorem covering solutions that exhibit only finite stress-discontinuities.
\r\n\r\n" }, { "name": "Caloyannides, Michael Akylas", "degree": "PhD", "year": "1972", "title": "A Mathematical and Experimental Investigation of Microcycle Spectral Estimates of Semiconductor Flicker Noise", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042016-152719186", "creators": [ { "name": { "family": "Caloyannides", "given": "Michael Akylas" }, "id": "Caloyannides-Michael-Akylas", "display_name": "Caloyannides, Michael Akylas" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MDV9-W982", "abstract": "The experimental portion of this thesis tries to estimate the density of the power spectrum of very low frequency semiconductor noise, from 10-6.3 cps to 1. cps with a greater accuracy than that achieved in previous similar attempts: it is concluded that the spectrum is 1/f\u03b1 with \u03b1 approximately 1.3 over most of the frequency range, but appearing to have a value of about 1 in the lowest decade. The noise sources are, among others, the first stage circuits of a grounded input silicon epitaxial operational amplifier. This thesis also investigates a peculiar form of stationarity which seems to distinguish flicker noise from other semiconductor noise.
\r\n\r\nIn order to decrease by an order of magnitude the pernicious effects of temperature drifts, semiconductor \"aging\", and possible mechanical failures associated with prolonged periods of data taking, 10 independent noise sources were time-multiplexed and their spectral estimates were subsequently averaged. If the sources have similar spectra, it is demonstrated that this reduces the necessary data-taking time by a factor of 10 for a given accuracy.
\r\n\r\nIn view of the measured high temperature sensitivity of the noise sources, it was necessary to combine the passive attenuation of a special-material container with active control. The noise sources were placed in a copper-epoxy container of high heat capacity and medium heat conductivity, and that container was immersed in a temperature controlled circulating ethylene-glycol bath.
\r\n\r\nOther spectra of interest, estimated from data taken concurrently with the semiconductor noise data were the spectra of the bath's controlled temperature, the semiconductor surface temperature, and the power supply voltage amplitude fluctuations. A brief description of the equipment constructed to obtain the aforementioned data is included.
\r\n\r\nThe analytical portion of this work is concerned with the following questions: what is the best final spectral density estimate given 10 statistically independent ones of varying quality and magnitude? How can the Blackman and Tukey algorithm which is used for spectral estimation in this work be improved upon? How can non-equidistant sampling reduce data processing cost? Should one try to remove common trands shared by supposedly statistically independent noise sources and, if so, what are the mathematical difficulties involved? What is a physically\r\nplausible mathematical model that can account for flicker noise and what are the mathematical implications on its statistical properties? Finally, the variance of the spectral estimate obtained through the Blackman/Tukey algorithm is analyzed in greater detail; the variance is shown to diverge for \u03b1 \u2265 1 in an assumed power spectrum of k/|f|\u03b1, unless the assumed spectrum is \"truncated\".
\r\n\r\n" }, { "name": "Candel, Sebastien M.", "degree": "PhD", "year": "1972", "title": "Analytical Studies of Some Acoustic Problems of Jet Engines", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-153104", "creators": [ { "name": { "family": "Candel", "given": "Sebastien M." }, "id": "Candel-Sebastien-M", "orcid": "0000-0003-2286-8460", "display_name": "Candel, Sebastien M." } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/E5DD-ZC41", "abstract": "This thesis presents analytical studies of internal noise generation and transmission in jet engines and its radiation from the duct ends.
\r\n\r\nThe propagation and generation of acoustic waves in a choked nozzle is considered first. Pressure and entropy fluctuations caused by gas stream non-uniformities like \"hot spots,\" are incident on the nozzle entrance. A novel noise-generation mechanism is uncovered where acoustic waves are produced by a distribution of sources of strength proportional to the entrance entropy fluctuation and local gradient of the mean flow velocity.
\r\n\r\nThe propagation of acoustic waves in a moving medium in the presence of semi-infinite or finite boundaries is then considered. A transformation is introduced which relates the solutions of such problems to the solutions of associated problems in a stationary medium. The method is described by discussing the Sommerfeld problem of diffraction of a plane wave by a half plane immersed in a subsonically moving medium. When the plane has a trailing edge, it is shown that both reflection and shadow regions expand; while the opposite occurs for a leading edge, in which circumstance an additional diffracted wave also appears.
\r\n\r\nIn the supersonic case, all the diffraction problems are related to a single reference problem, solved by Fourier transform methods. A decomposition of the pressure field in a \"geometrical optics\" field and a diffracted field is given, showing some remarkable similarities with the subsonic case solution.
\r\n\r\nThe radiation of acoustic modes from a duct immersed in a subsonically moving medium is treated by a similar transform method. The presence of the uniform flow has roughly the same effect as an increase in frequency of the incident wave, at constant mode number. The effect of acoustical lining on the radiation pattern is examined, and side radiation is shown to be greatly reduced for the lower order modes.
\r\n\r\nThe transmission and reflection of acoustic waves incident on a blade row is analyzed by the transform method, and the transmission and reflection coefficients for the blade row immersed in a moving medium are expressed in terms of the basic acoustic characteristics of the blade row in a stationary medium.
" }, { "name": "Chao, Chih Chieh", "degree": "PhD", "year": "1972", "title": "Lattice Anomalies and Magnetic States in Fe\u2085Si\u2083-Mn\u2085Si\u2083 Alloys", "advisor": "Duwez, Pol E.; Tsuei, Chang-chyi", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042016-141241598", "creators": [ { "name": { "family": "Chao", "given": "Chih Chieh" }, "id": "Chao-Chih-Chieh", "display_name": "Chao, Chih Chieh" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." }, { "name": { "family": "Tsuei", "given": "Chang-chyi" }, "id": "Tsuei-C-C", "role": "advisor", "display_name": "Tsuei, Chang-chyi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/X3BM-C979", "abstract": "The lattice anomalies and magnetic states in the (Fe100-xMnx)5Si3 alloys have been investigated. Contrary to what was previously reported, results of x-ray diffraction show a second phase (\u03b1') present in Fe-rich alloys and therefore strictly speaking a complete solid solution does not exist. M\u00f6ssbauer spectra, measured as a function of composition and temperature, indicate the presence of two inequivalent sites, namely 6(g) site (designated as site I) and 4(d) (site II). A two-site model (TSM) has been introduced to interpret the experimental findings. The compositional variation of lattice parameters a and c, determined from the x-ray analysis, exhibits anomalies at x = 22.5 and x = 50, respectively. The former can be attributed to the effect of a ferromagnetic transition; while the latter is due to the effect of preferential substitution between Fe and Mn atoms according to TSM.
\r\n\r\nThe reduced magnetization of these alloys deduced from magnetic hyperfine splittings has been correlated with the magnetic transition temperatures in terms of the molecular field theory. It has been found from both the M\u00f6ssbauer effect and magnetization measurements that for composition 0 \u2264 x \u02c2 50 both sites I and II are ferromagnetic at liquid-nitrogen temperature and possess moments parallel to each other. In the composition range 50 \u02c2 x \u2264 100 , the site II is antiferromagnetic whereas site I is paramagnetic even at a temperature below the bulk N\u00e9el temperatures. In the vicinity of x = 50 however, site II is in a state of transition between ferromagnetism and antiferromagnetism. The present study also suggests that only Mn in site II are responsible for the antiferromagnetism in Mn5Si3 contrary to a previous report.
\r\n\r\nElectrical resistance has also been measured as a function of temperature and composition. The resistive anomalies observed in the Mn-rich alloys are believed to result from the effect of the antiferromagnetic Brillouin zone on the mobility of conduction electrons.
\r\n" }, { "name": "Chapyak, Edward Jay", "degree": "PhD", "year": "1972", "title": "Surface Effects in Simple Molecular Systems", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042016-133123395", "creators": [ { "name": { "family": "Chapyak", "given": "Edward Jay" }, "id": "Chapyak-Edward-Jay", "display_name": "Chapyak, Edward Jay" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/F4N2-0732", "abstract": "This thesis examines two problems concerned with surface effects in simple molecular systems. The first is the problem associated with the interaction of a fluid with a solid boundary, and the second originates from the interaction of a liquid with its own vapor.
\r\n\r\nFor a fluid in contact with a solid wall, two sets of integro-differential equations, involving the molecular distribution functions of the system, are derived. One of these is a particular form of the well-known Bogolyubov-Born-Green-Kirkwood-Yvon equations. For the second set, the derivation, in contrast with the formulation of the B.B.G.K.Y. hierarchy, is independent of the pair-potential assumption. The density of the fluid, expressed as a power series in the uniform fluid density, is obtained by solving these equations under the requirement that the wall be ideal.
\r\n\r\nThe liquid-vapor interface is analyzed with the aid of equations that describe the density and pair-correlation function. These equations are simplified and then solved by employing the superposition and the low vapor density approximations. The solutions are substituted into formulas for the surface energy and surface tension, and numerical results are obtained for selected systems. Finally, the liquid-vapor system near the critical point is examined by means of the lowest order B.B.G.K.Y. equation.
\r\n" }, { "name": "Chen, Jay-Chung", "degree": "PhD", "year": "1972", "title": "Nonlinear Vibration of Cylindrical Shells", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242010-085617930", "creators": [ { "name": { "family": "Chen", "given": "Jay-Chung" }, "id": "Chen-Jay-Chung", "display_name": "Chen, Jay-Chung" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CBC4-MP23", "abstract": "The large amplitude vibrations of a thin-walled cylindrical shell are analyzed using the Donnell's shallow-shell equations. A perturbation method is applied to reduce the nonlinear partial differential equations into a system of linear partial differential equations. The simply-supported boundary condition and the circumferential periodicity condition are satisfied. The resulting solution indicates that in addition to the fundamental modes, the response contains asymmetric modes as well as axisymmetric modes with the frequency twice that of the fundamental modes. In the previous investigations in which the Galerkins procedure was applied, only the additional axisymrnetric modes were assumed.\r\nVibrations involving a single driven mode response are investigated. The results indicate that the nonlinearity is either softening or hardening depending on the mode. The vibrations involving both a driven mode and a companion mode are also investigated. The region where the companion mode participates in the vibration is obtained and the effects due to the participation of the companion mode are studied.\r\nAn experimental investigation is also conducted. The\r\nresults are generally in agreement with the theory. \"Non-stationary4 response is detected at some frequencies for large amplitude response where the amplitude drifts from one value to another. Various nonlinear phenomena are observed and quantitative comparisons with the theoretical results are made.\r\n" }, { "name": "Davis, Joseph Eugene", "degree": "PhD", "year": "1972", "title": "Non-Planar Wings in Non-Planar Ground Effect", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272010-162542308", "creators": [ { "name": { "family": "Davis", "given": "Joseph Eugene" }, "id": "Davis-Joseph-Eugene", "display_name": "Davis, Joseph Eugene" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NNF7-GV39", "abstract": " A numerical method is developed for solving the problem of a wing in arbitrary non-planar ground effect. The linearized equations of unsteady motion for an arbitrary non-planar wing in non-planar ground effect are presented. Numerical calculations were made to determine all the aerodynamic characteristics and stability derivatives for various thin, uncambered planar and non-planar wings (including two wings connected in tandem) in planar and non-planar ground effect. These calculations were incorporated into the equations of unsteady motion to determine the dynamic stability characteristics of these wings in the various ground effect situations. Several wings were found to be longitudinally stable, but only in rare cases were they found to be laterally stable.\r\n \r\n An experiment was conducted to compare some of the numerical calculations with reality. The agreement was reasonable.\r\n" }, { "name": "Debrule, Paul Maurice", "degree": "PhD", "year": "1972", "title": "Friction and Heat Transfer Coefficients in Smooth and Rough Pipes with Dilute Polymer Solutions", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04112016-132300001", "creators": [ { "name": { "family": "Debrule", "given": "Paul Maurice" }, "id": "Debrule-Paul-Maurice", "display_name": "Debrule, Paul Maurice" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/0NA8-5133", "abstract": "Measurements of friction and heat transfer coefficients were obtained with dilute polymer solutions flowing through electrically heated smooth and rough tubes. The polymer used was \"Polyox WSR-301\", and tests were performed at concentrations of 10 and 50 parts per million. The rough tubes contained a close-packed, granular type of surface with roughness-height-to-diameter ratios of 0.0138 and 0.0488 respectively. A Prandtl number range of 4.38 to 10.3 was\r\ninvestigated which was obtained by adjusting the bulk temperature of the solution. The Reynolds numbers in the experiments were varied from =10,000 (Pr= 10.3) to 250,000 (Pr= 4.38).
\r\n\r\nFriction reductions as high as 73% in smooth tubes and 83% in rough tubes were observed, accompanied by an even more drastic heat transfer reduction (as high as 84% in smooth tubes and 93% in rough tubes). The heat transfer coefficients with Polyox can be lower for a rough tube than for a smooth one.
\r\n\r\nThe similarity rules previously developed for heat transfer with a Newtonian fluid were extended to dilute polymer solution pipe flows. A velocity profile similar to the one proposed by Deissler was taken as a model to interpret the friction and heat transfer data in smooth tubes. It was found that the observed results could be explained by assuming that the turbulent diffusivities are reduced in smooth tubes in the vicinity of the wall, which brings about a thickening of the viscous layer.\r\nA possible mechanism describing the effect of the polymer additive on rough pipe flow is also discussed.
\r\n\r\n\r\n" }, { "name": "Furuike, Dennis Masato", "degree": "PhD", "year": "1972", "title": "Dynamic Response of Hysteretic Systems with Application to a System Containing Limited Slip", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082016-132302337", "creators": [ { "name": { "family": "Furuike", "given": "Dennis Masato" }, "id": "Furuike-Dennis-Masato", "display_name": "Furuike, Dennis Masato" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/WENT-KG11", "abstract": "A general class of single degree of freedom systems possessing rate-independent hysteresis is defined. The hysteretic behavior in a system belonging to this class is depicted as a sequence of single-valued functions; at any given time, the current function is determined by some set of mathematical rules concerning the entire previous response of the system. Existence and uniqueness of solutions are established and boundedness of solutions is examined.
\r\n\r\nAn asymptotic solution procedure is used to derive an approximation to the response of viscously damped systems with a small hysteretic nonlinearity and trigonometric excitation. Two properties of the hysteresis loops associated with any given system completely determine this approximation to the response: the area enclosed by each loop, and the average of the ascending and descending branches of each loop.
\r\n\r\nThe approximation, supplemented by numerical calculations, is applied to investigate the steady-state response of a system with limited slip. Such features as disconnected response curves and jumps in response exist for a certain range of system parameters for any finite amount of slip.
\r\n\r\nTo further understand the response of this system, solutions of the initial-value problem are examined. The boundedness of solutions is investigated first. Then the relationship between initial conditions and resulting steady-state solution is examined when multiple steady-state solutions exist. Using the approximate analysis and numerical calculations, it is found that significant regions of initial conditions in the initial condition plane lead to the different asymptotically stable\r\nsteady-state solutions.
\r\n" }, { "name": "Furuya, Okitsugu", "degree": "PhD", "year": "1972", "title": "A Singular Perturbation Method of Calculating the Behavior of Supercavitating Hydrofoils with Rounded Noses", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082016-141758840", "creators": [ { "name": { "family": "Furuya", "given": "Okitsugu" }, "id": "Furuya-Okitsugu", "display_name": "Furuya, Okitsugu" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/A946-HN67", "abstract": "A simple, direct and accurate method to predict the pressure distribution on supercavitating hydrofoils with rounded noses is presented. The thickness of body and cavity is assumed to be small. The method adopted in the present work is that of singular perturbation theory. Far from the leading edge linearized free streamline theory is applied. Near the leading edge, however, where singularities of the linearized theory occur, a non-linear local solution is employed. The two unknown parameters which characterize this local solution are determined by a matching procedure. A uniformly valid solution is then constructed with the aid of the singular perturbation approach.
\r\n\r\nThe present work is divided into two parts. In Part I isolated supercavitating hydrofoils of arbitrary profile shape with parabolic noses are investigated by the present method and its results are compared with the new computational results made with Wu and Wang's exact \"functional iterative\" method. The agreement is very good. In Part II this method is applied to a linear cascade of such hydrofoils\r\nwith elliptic noses. A number of cases are worked out over a range of cascade parameters from which a good idea of the behavior of this type of important flow configuration is obtained.
\r\n\r\nSome of the computational aspects of Wu and Wang's functional iterative method heretofore not successfully applied to this type of problem are described in an appendix.
\r\n\r\n" }, { "name": "Goodwin, Antony Wilfred", "degree": "PhD", "year": "1972", "title": "The Oculomotor System: (1) Vertical-Horizontal Interaction and Signal Recognition. (2) Time Delays and Power Spectra", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082016-145655161", "creators": [ { "name": { "family": "Goodwin", "given": "Antony Wilfred" }, "id": "Goodwin-Antony-Wilfred", "display_name": "Goodwin, Antony Wilfred" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/ETE3-RP39", "abstract": "In the first section of this thesis, two-dimensional properties of the human eye movement control system were studied. The vertical - horizontal interaction was investigated by using a two-dimensional target motion consisting of a sinusoid in one of the directions vertical or horizontal, and low-pass filtered Gaussian random motion of variable bandwidth (and hence information content) in the orthogonal direction. It was found that the random motion reduced the efficiency of the sinusoidal tracking. However, the sinusoidal tracking was only slightly dependent on the bandwidth of the random motion. Thus the system should be thought of as consisting of two independent channels with a small amount of mutual cross-talk.
\r\n\r\nThese target motions were then rotated to discover whether or not the system is capable of recognizing the two-component nature of the target motion. That is, the sinusoid was presented along an oblique line (neither vertical nor horizontal) with the random motion orthogonal to it. The system did not simply track the vertical and horizontal components of motion, but rotated its frame of reference so that its two tracking channels coincided with the directions of the two target motion components. This recognition occurred even when the two orthogonal motions were both random, but with different bandwidths.
\r\n\r\nIn the second section, time delays, prediction and power spectra were examined. Time delays were calculated in response to various periodic signals, various bandwidths of narrow-band Gaussian random motions and sinusoids. It was demonstrated that prediction occurred only when the target motion was periodic, and only if the harmonic content was such that the signal was sufficiently narrow-band. It appears as if general periodic motions are split into predictive and\r\nnon-predictive components.
\r\n\r\nFor unpredictable motions, the relationship between the time delay and the average speed of the retinal image was linear. Based on this I proposed a model explaining the time delays for both random and periodic motions. My experiments did not prove that the system is sampled data, or that it is continuous. However, the model can be interpreted as representative of a sample data system whose sample interval is a function of the target motion.
\r\n\r\nIt was shown that increasing the bandwidth of the low-pass filtered Gaussian random motion resulted in an increase of the eye movement bandwidth. Some properties of the eyeball-muscle dynamics and the extraocular muscle \"active state tension\" were derived.
\r\n\r\n" }, { "name": "Greenfeld, Norton Robert", "degree": "PhD", "year": "1972", "title": "Computer System Support for Data Analysis", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04112016-081827399", "creators": [ { "name": { "family": "Greenfeld", "given": "Norton Robert" }, "id": "Greenfeld-Norton-Robert", "display_name": "Greenfeld, Norton Robert" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/XGAM-XB93", "abstract": "This thesis is an investigation into the nature of data analysis and computer software systems which support this activity.
\r\n\r\nThe first chapter develops the notion of data analysis as an experimental science which has two major components: data-gathering and theory-building. The basic role of language in determining the meaningfulness of theory is stressed, and the informativeness of a language and data base pair is studied. The static and dynamic aspects of data analysis are then considered from this conceptual vantage point. The second chapter surveys the available types of computer systems which may be useful for data analysis. Particular attention is paid to the questions raised in the first chapter about the language restrictions imposed by the computer system and its dynamic properties.
\r\n\r\nThe third chapter discusses the REL data analysis system, which was designed to satisfy the needs of the data analyzer in an operational relational data system. The major limitation on the use of such systems is the amount of access to data stored on a relatively slow secondary memory. This problem of the paging of data is investigated and two classes of data structure representations are found, each of which has desirable paging characteristics for certain types of queries. One representation is used by most of the generalized data base management systems in existence today, but the other is clearly preferred in the data analysis environment, as conceptualized in Chapter I.
\r\n\r\nThis data representation has strong implications for a fundamental process of data analysis -- the quantification of variables. Since quantification is one of the few means of summarizing and abstracting, data analysis systems are under strong\r\npressure to facilitate the process. Two implementations of quantification are studied: one analagous to the form of the lower predicate calculus and another more closely attuned to the data representation. A comparison of these indicates that the use of the \"label class\" method results in orders of magnitude improvement over the lower predicate calculus technique.
\r\n\r\n" }, { "name": "Hammack, Joseph Leonard, Jr.", "degree": "PhD", "year": "1972", "title": "Tsunamis: A Model of Their Generation and Propagation", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechTHESIS:04182016-131851689", "creators": [ { "name": { "family": "Hammack", "given": "Joseph Leonard, Jr." }, "id": "Hammack-Joseph-Leonard", "display_name": "Hammack, Joseph Leonard, Jr." } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/4XTB-TS46", "abstract": "A general solution is presented for water waves generated by an arbitrary movement of the bed (in space and time) in a two-dimensional fluid domain with a uniform depth. The integral solution which is developed is based on a linearized approximation to the complete (nonlinear) set of governing equations. The general solution is evaluated for the specific case of a uniform upthrust or downthrow of a block section of the bed; two time-displacement histories of the bed movement are considered.
\r\n\r\nAn integral solution (based on a linear theory) is also developed for a three-dimensional fluid domain of uniform depth for a class of bed movements which are axially symmetric. The integral solution is evaluated for the specific case of a block upthrust or downthrow of a section of the bed, circular in planform, with a time-displacement history identical to one of the motions used in the two-dimensional\r\nmodel.
\r\n\r\nSince the linear solutions are developed from a linearized approximation of the complete nonlinear description of wave behavior, the applicability of these solutions is investigated. Two types of non-linear effects are found which limit the applicability of the linear theory: (1) large nonlinear effects which occur in the region of generation during the bed movement, and (2) the gradual growth of nonlinear effects during wave propagation.
\r\n\r\nA model of wave behavior, which includes, in an approximate manner, both linear and nonlinear effects is presented for computing wave profiles after the linear theory has become invalid due to the growth of nonlinearities during wave propagation.
\r\n\r\nAn experimental program has been conducted to confirm both the linear model for the two-dimensional fluid domain and the strategy suggested for determining wave profiles during propagation after the linear theory becomes invalid. The effect of a more general time-displacement history of the moving bed than those employed in the theoretical models is also investigated experimentally.
\r\n\r\nThe linear theory is found to accurately approximate the wave behavior in the region of generation whenever the total displacement of the bed is much less than the water depth. Curves are developed and confirmed by the experiments which predict gross features of the lead wave propagating from the region of generation once the values of certain nondimensional parameters (which characterize the generation process) are known. For example, the maximum amplitude of the lead wave propagating from the region of generation has been found to never exceed approximately one-half of the total bed displacement. The gross features of the tsunami resulting from the Alaskan earthquake of 27 March 1964 can be estimated from the results of this study.
\r\n\r\n" }, { "name": "Hoeneisen-Frost, Bruce", "degree": "PhD", "year": "1972", "title": "I. Fundamental Limitations in Microelectronics. II. Power Schottky Diode Design and Comparison with the Junction Diode. III. Permittivity of Strontium Titanate", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:04182016-112301893", "creators": [ { "name": { "family": "Hoeneisen-Frost", "given": "Bruce" }, "id": "Hoeneisen-Frost-Bruce", "display_name": "Hoeneisen-Frost, Bruce" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TVY5-NY24", "abstract": "Part I
\r\n\r\nThe physical phenomena which will ultimately limit the packing density of planar bipolar and MOS integrated circuits are examined. The maximum packing density is obtained by minimizing the supply voltage and the size of the devices. The minimum size of a bipolar transistor is determined by junction breakdown, punch-through and doping fluctuations. The minimum size of a MOS transistor is determined by gate oxide breakdown and drain-source punch-through. The packing density of fully active bipolar or static non-complementary MOS circuits becomes limited by power dissipation. The packing density of circuits which\r\nare not fully active such as read-only memories, becomes limited by the area occupied by the devices, and the frequency is limited by the circuit time constants and by metal migration. The packing density of fully active dynamic or complementary MOS circuits is limited by the area occupied by the devices, and the frequency is limited by power dissipation and metal migration. It is concluded that read-only memories will reach approximately the same performance and packing density with MOS and bipolar technologies, while fully active circuits will reach the highest levels of integration with dynamic MOS or complementary MOS technologies.
\r\n\r\nPart II
\r\n\r\nBecause the Schottky diode is a one-carrier device, it has both advantages and disadvantages with respect to the junction diode which is a two-carrier device. The advantage is that there are practically no excess minority carriers which must be swept out before the diode blocks current in the reverse direction, i.e. a much faster recovery time. The disadvantage of the Schottky diode is that for a high voltage device it is not possible to use conductivity modulation as in the p i n diode; since charge carriers are of one sign, no charge cancellation can occur\r\nand current becomes space charge limited. The Schottky diode design is developed in Section 2 and the characteristics of an optimally designed silicon Schottky diode are summarized in Fig. 9. Design criteria and quantitative comparison of junction and Schottky diodes is given in Table 1 and Fig. 10. Although somewhat approximate, the treatment allows a systematic quantitative comparison of the devices for any given application.
\r\n\r\nPart III
\r\nWe interpret measurements of permittivity of perovskite strontium titanate as a function of orientation, temperature, electric field and frequency performed by Dr. Richard Neville. The free energy of the crystal is calculated as a function of polarization. The Curie-Weiss law and the LST relation are verified. A generalized LST relation is used to calculate the permittivity of strontium titanate from zero to\r\noptic frequencies. Two active optic modes are important. The lower frequency mode is attributed mainly to motion of the strontium ions with respect to the rest of the lattice, while the higher frequency active mode is attributed to motion of the titanium ions with respect to the oxygen lattice. An anomalous resonance which multi-domain strontium titanate crystals exhibit below 65\u00b0K is described and a plausible mechanism which explains the phenomenon is presented.
\r\n\r\n" }, { "name": "Johnson, Gordon Oliver", "degree": "PhD", "year": "1972", "title": "Effects of Magnetostriction and Superlattice Formation in Ferromagnetic Thin Films", "advisor": "Wilts, Charles H.; Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechTHESIS:04182016-145345048", "creators": [ { "name": { "family": "Johnson", "given": "Gordon Oliver" }, "id": "Johnson-Gordon-Oliver", "display_name": "Johnson, Gordon Oliver" } ], "advisors": [ { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." }, { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/DYFK-DQ28", "abstract": "The contribution to the magnetic uniaxial perpendicular anisotropy which arises from substrate constraint through magnetostrictive effects has been measured in Ni-Fe and Ni-Co thin films evaporated on substrates at room temperature. This was accomplished by measuring the perpendicular anisotropy before and after removal of the film from the substrate. Data are given for the fcc crystal structure regions of both alloy systems, but data for Ni-Co include compositions with less than 60% Ni which have a small percentage of the hcp phase mixed with the fcc phase. The constraint contribution to the perpendicular anisotropy correlates well with the value of the bulk magnetostriction constant using the equation \u2206K\u02d4=3/2\u03bbs\u03c3. Measured values of isotropic stress for films thicker than 600 \u00c5 were 1.6 x 1010 dyn/cm2. In films less than 600 \u00c5 thick the isotropic stress decreased with decreasing thickness. After removal of the films from the substrates, the measured perpendicular anisotropy deviated from the expected geometrical shape anisotropy near pure Ni in both alloys. This indicates that additional significant sources of anisotropy exist at these compositions.
\r\n\r\nThe effect of substrate constraint on the crystalline anisotropy K1 of Ni-Fe epitaxial films has been studied by use of a film removal technique, which involves the evaporation of an epitaxial layer of LiF on MgO, the epitaxial growth of the metallic film on the LiF, and the stripping of the film with water soluble tape. Films ranging in composition from 50% to 100% Ni have been studied. For compositions below 90% Ni the experimental values agree reasonably well with the first order theoretical prediction, \u2206K1=[-9/4(C11-C12)\u03bb2 100+9/2C44\u03bb2111].
\r\n\r\nIn order to compare the magnetic properties of epitaxial thin films more completely with the properties of bulk single crystals, Ni-Fe films ranging in composition from 60% to 90% Ni, which were evaporated epitaxially on (100) MgO substrates, have been subsequently annealed at 400\u00b0C in a vacuum of less than 10-7 Torr to form the ordered Ni3Fe structure near the 75% composition. This ordered structure has been confirmed by electron diffraction.
\r\n\r\nThe saturation magnetization at Ni3Fe increased about 6% with ordering which is in good agreement with previous bulk data. Measurements of the magnetocrystalline anisotropy energy K1 for the epitaxial films show the same large changes with ordering as observed in bulk single crystal samples. In the (001) plane the magnetostriction constants \u03bb100, \u03bb111 are directly related to the induced anisotropy due to a uniform uniaxial strain in the [100] and [110] directions respectively. Assuming that the elastic constants of a film are the same as in bulk material and are unchanged by ordering, the changes in strain sensitivity with ordering for the epitaxial films are found to be in good agreement with values predicted from bulk data. The exchange constant A as measured by ferromagnetic resonance has been measured at the Ni3Fe composition and found to increase 25% with ordering. This seems to indicate a significant increase in the Curie temperature which has only been inferred indirectly for bulk material.
\r\n\r\n" }, { "name": "Kavanagh, Robert Nicholas", "degree": "PhD", "year": "1972", "title": "Localization of Sources of Human Evoked Responses", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03212016-135649927", "creators": [ { "name": { "family": "Kavanagh", "given": "Robert Nicholas" }, "id": "Kavanagh-Robert-Nicholas", "display_name": "Kavanagh, Robert Nicholas" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/J35H-XN59", "abstract": "The evoked response, a signal present in the electro-encephalogram when specific sense modalities are stimulated with brief sensory inputs, has not yet revealed as much about brain function as it apparently promised when first recorded in the late 1940's. One of the problems has been to record the responses at a large number of points on the surface of the head; thus in order to achieve greater spatial resolution than previously attained, a 50-channel recording system was designed to monitor experiments with human visually evoked responses.
\r\n\r\nConventional voltage versus time plots of the responses were found inadequate as a means of making qualitative studies of such a large data space. This problem was solved by creating a graphical display of the responses in the form of equipotential maps of the activity at successive instants during the complete response. In order to ascertain the necessary complexity of any models of the responses, factor analytic procedures were used to show that models characterized by only five or six independent parameters could adequately represent the variability in all recording channels.
\r\n\r\nOne type of equivalent source for the responses which meets these specifications is the electrostatic dipole. Two different dipole models were studied: the dipole in a homogeneous sphere and the dipole in a sphere comprised of two spherical shells (of different conductivities) concentric with and enclosing a homogeneous\r\nsphere of a third conductivity. These models were used to determine nonlinear least squares fits of dipole parameters to a given potential distribution on the surface of a spherical approximation to the head. Numerous tests of the procedures were conducted with problems having known solutions. After these\r\ntheoretical studies demonstrated the applicability of the technique, the models were used to determine inverse solutions for the evoked response potentials at various times throughout the responses. It was found that reliable estimates of the location and strength of cortical activity were obtained, and that the two models\r\ndiffered only slightly in their inverse solutions. These techniques enabled information flow in the brain, as indicated by locations and strengths of active sites, to be followed throughout the evoked response.
\r\n\r\n" }, { "name": "Keener, James Paul", "degree": "PhD", "year": "1972", "title": "Some Modified Bifurcation Problems with Application to Imperfection Sensitivity in Buckling", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechTHESIS:03292013-095532634", "creators": [ { "name": { "family": "Keener", "given": "James Paul" }, "id": "Keener-James-Paul", "display_name": "Keener, James Paul" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/8P4J-GD34", "abstract": "The branching theory of solutions of certain nonlinear\r\nelliptic partial differential equations is developed, when the nonlinear\r\nterm is perturbed from unforced to forced. We find\r\nfamilies of branching points and the associated nonisolated solutions\r\nwhich emanate from a bifurcation point of the unforced problem.\r\nNontrivial solution branches are constructed which contain the nonisolated \r\nsolutions, and the branching is exhibited. An iteration\r\nprocedure is used to establish the existence of these solutions, and\r\na formal perturbation theory is shown to give asymptotically valid\r\nresults. The stability of the solutions is examined and certain\r\nsolution branches are shown to consist of minimal positive solutions.\r\nOther solution branches which do not contain branching points are\r\nalso found in a neighborhood of the bifurcation point.
\r\n\r\nThe qualitative features of branching points and their\r\nassociated nonisolated solutions are used to obtain useful information\r\nabout buckling of columns and arches. Global stability characteristics\r\nfor the buckled equilibrium states of imperfect columns and\r\narches are discussed. Asymptotic expansions for the imperfection\r\nsensitive buckling load of a column on a nonlinearly elastic foundation\r\nare found and rigorously justified.
" }, { "name": "Kim, Byung-Koo", "degree": "PhD", "year": "1972", "title": "Piecewise Linear Dynamic Systems with Time Delays", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:06252025-164239697", "creators": [ { "name": { "family": "Kim", "given": "Byung-Koo" }, "id": "Kim-Byung-Koo", "display_name": "Kim, Byung-Koo" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/790y-rk32", "abstract": "A new method of constructing periodic solutions for piecewise\r\nlinear dynamic systems with time delays is investigated. Although the\r\nexistence and the uniqueness of the periodic solution are guaranteed by\r\nwell-known theorems, existing schemes for actually constructing the\r\nperiodic solution are either purely formal or approximate.
\r\n\r\nThe idea of constructing the exact solution is first pursued with\r\nthe linear delay systems. The formal representation of the solution to\r\nthe linear problem is viewed as a system of Fredholm integral equations\r\nof the second kind. Since the matrix kernel for this system of integral\r\nequations is separable, the integral equation can be reduced to a system\r\nof algebraic equations involving certain integral moments of the initial\r\nfunction. These observations lead to a transfer relationship between\r\ntwo state vectors in the form of a matrix equation. Then the problem\r\ncan be posed as either an initial value problem (if one is seeking the\r\ntransient solution), or a periodic solution problem (if one is seeking the\r\nunknown initial data).
\r\n\r\nThis Fredholm Integral Equation Method is used effectively to\r\nconstruct periodic solutions to piecewise linear differential-difference\r\nequations. The periodic solutions are constructed from a cascaded\r\nproduct of matrix equations derived for each linear region. The\r\nstability of the periodic solution is determined by solving an associated\r\neigenvalue problem. The periodic solution and its stability analysis\r\nare exact in the sense that the error induced by the truncation process\r\nin the Fredholm Integral Equation Method can be made exponentially \r\nsmall as the size of the transfer matrix is increased.
" }, { "name": "Lineberry, Michael Jay", "degree": "PhD", "year": "1972", "title": "Neutron Slowing Down with Inelastic Scattering", "advisor": "Corngold, Noel Robert", "url": "https://resolver.caltech.edu/CaltechTHESIS:07102014-110604334", "creators": [ { "name": { "family": "Lineberry", "given": "Michael Jay" }, "id": "Lineberry-Michael-Jay", "display_name": "Lineberry, Michael Jay" } ], "advisors": [ { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "advisor", "display_name": "Corngold, Noel Robert" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/AQAR-2957", "abstract": "The emphasis in reactor physics research has shifted toward\r\ninvestigations of fast reactors. The effects of high energy neutron\r\nprocesses have thus become fundamental to our understanding, and one\r\nof the most important of these processes is nuclear inelastic scattering.\r\nIn this research we include inelastic scattering as a primary energy\r\ntransfer mechanism, and study the resultant neutron energy spectrum\r\nin an infinite medium. We assume that the moderator material has a\r\nhigh mass number, so that in a laboratory coordinate system the\r\nenergy loss of an inelastically scattered neutron may be taken as discrete.\r\nIt is then consistent to treat elastic scattering with an age\r\ntheory expansion. Mathematically these assumptions lead to balance\r\nequations of the differential-difference type.
\r\n\r\nThe steady state problem is explored first by way of Laplace\r\ntransformation of the energy variable. We then develop another steady\r\nstate technique, valid for multiple inelastic level excitations, which\r\ndepends on the level structure satisfying a physically reasonable constraint.\r\nIn all cases the solutions we generate are compared with\r\nresults obtained by modeling inelastic scattering with a separable,\r\nevaporative kernel.
\r\n\r\nThe time dependent problem presents some new difficulties. By\r\nmodeling the elastic scattering cross section in a particular way, we\r\ngenerate solutions to this more interesting problem. We conjecture the\r\nmethod of characteristics may be useful in analyzing time dependent\r\nproblems with general cross sections. These ideas are briefly explored.
" }, { "name": "Logan, Samuel Ernest", "degree": "PhD", "year": "1972", "title": "Laser Velocimeter Measurement of Reynolds Stress and Turbulence in Dilute Polymer Solutions", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202010-110214903", "creators": [ { "name": { "family": "Logan", "given": "Samuel Ernest" }, "id": "Logan-Samuel-Ernest", "display_name": "Logan, Samuel Ernest" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BD39-BV19", "abstract": "Measurements of Reynolds stress and axial and transverse\r\nturbulence intensities have been made in drag-reducing\r\nturbulent pipe flow of a dilute solution of high molecular\r\nweight polymer and compared to measurements made with pure\r\nwater. A newly developed laser velocimeter capable of\r\nmeasuring these turbulence parameters has been utilized and\r\nis described in detail.\r\n\r\nAxial turbulence intensities measured in polymer solution\r\nare consistent with previous polymer results and\r\nviscous sublayer thickening is observed. New results include\r\ndemonstration that the turbulent shearing stress is\r\nreduced in the turbulent core by an amount proportional to\r\nthe observed decrease in pressure gradient at the wall, and\r\nextrapolates to a wall value in agreement with calculated\r\nlocal wall shear. Near the wall polymer solution Reynolds\r\nstress is reduced below that measured for water consistent\r\nwith observed velocity profiles. Polymer radial turbulence\r\nintensities are comparable with those for water in the\r\nturbulent core, but exhibit similar dramatic suppression\r\nnear the wall. These and other recent results strongly\r\nsuggest that dilute polymer solution drag reduction is\r\nprimarily a wall phenomenon. Polymers appear to have little\r\nor no effect on turbulent flow away from a solid boundary\r\nwhere turbulent velocities scale with u_\u03c4, the shear\r\nvelocity based on the observed wall shear.\r\n" }, { "name": "Marmarelis, Panos Zissis", "degree": "PhD", "year": "1972", "title": "Nonlinear Dynamic Transfer Functions for Certain Retinal Neuronal Systems", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072014-142214067", "creators": [ { "name": { "family": "Marmarelis", "given": "Panos Zissis" }, "id": "Marmarelis-Panos-Zissis", "display_name": "Marmarelis, Panos Zissis" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/TBKA-2Q74", "abstract": "The applicability of the white-noise method to the identification\r\nof a nonlinear system is investigated. Subsequently, the method\r\nis applied to certain vertebrate retinal neuronal systems and nonlinear,\r\ndynamic transfer functions are derived which describe quantitatively\r\nthe information transformations starting with the light-pattern stimulus\r\nand culminating in the ganglion response which constitutes the visually-derived\r\ninput to the brain. The retina of the catfish, Ictalurus\r\npunctatus, is used for the experiments.
\r\n\r\nThe Wiener formulation of the white-noise theory is shown to be\r\nimpractical and difficult to apply to a physical system. A different\r\nformulation based on crosscorrelation techniques is shown to be applicable\r\nto a wide range of physical systems provided certain considerations\r\nare taken into account. These considerations include the time-invariancy\r\nof the system, an optimum choice of the white-noise input bandwidth,\r\nnonlinearities that allow a representation in terms of a small number\r\nof characterizing kernels, the memory of the system and the temporal\r\nlength of the characterizing experiment. Error analysis of the kernel\r\nestimates is made taking into account various sources of error such\r\nas noise at the input and output, bandwidth of white-noise input and\r\nthe truncation of the gaussian by the apparatus.
\r\n\r\nNonlinear transfer functions are obtained, as sets of kernels,\r\nfor several neuronal systems: Light \u2192 Receptors, Light \u2192 Horizontal,\r\nHorizontal \u2192 Ganglion, Light \u2192 Ganglion and Light \u2192 ERG. The derived\r\nmodels can predict, with reasonable accuracy, the system response to\r\nany input. Comparison of model and physical system performance showed\r\nclose agreement for a great number of tests, the most stringent of\r\nwhich is comparison of their responses to a white-noise input. Other\r\ntests include step and sine responses and power spectra.
\r\n\r\nMany functional traits are revealed by these models. Some\r\nare: (a) the receptor and horizontal cell systems are nearly linear\r\n(small signal) with certain \"small\" nonlinearities, and become faster\r\n(latency-wise and frequency-response-wise) at higher intensity levels,\r\n(b) all ganglion systems are nonlinear (half-wave rectification), (c)\r\nthe receptive field center to ganglion system is slower (latency-wise\r\nand frequency-response-wise) than the periphery to ganglion system,\r\n(d) the lateral (eccentric) ganglion systems are just as fast (latency\r\nand frequency response) as the concentric ones, (e) (bipolar response)\r\n= (input from receptors) - (input from horizontal cell), (f) receptive\r\nfield center and periphery exert an antagonistic influence on the\r\nganglion response, (g) implications about the origin of ERG, and many\r\nothers.
\r\n\r\nAn analytical solution is obtained for the spatial distribution\r\nof potential in the S-space, which fits very well experimental data.\r\nDifferent synaptic mechanisms of excitation for the external and\r\ninternal horizontal cells are implied.
" }, { "name": "McGovern, Patrick Anthony", "degree": "PhD", "year": "1972", "title": "Electromagnetic Fields in Nonuniform Lossless Transmission Lines", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062016-081741962", "creators": [ { "name": { "family": "McGovern", "given": "Patrick Anthony" }, "id": "McGovern-Patrick-Anthony", "display_name": "McGovern, Patrick Anthony" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/S8QM-4Y57", "abstract": "Methods are developed for electromagnetic field calculations in nonuniform lossless transmission lines which support quasi-one dimensional propagation of a single baseband wave species. Approximate solutions are obtained in perturbation series for smoothly tapered lines by expanding Maxwell's equations and boundary conditions in the dimensionless parameter \u019e, given by the ratio of typical\r\ncross-section dimension to the length of the tapered section. The method emphasizes construction of a single ''warped\" field description rather than the local modal expansions of Schelkunoff's generalized telegraphist's equations.
\r\n\r\nExpansions in Cartesian coordinates yield the traditional distributed circuit parameter equations in the lowest approximation. Correction terms appear in even powers of \u019e, and their effects are shown most clearly by calculating waveform aberrations introduced by line transitions of nominally constant characteristic impedance. Improved field descriptions in nonuniform regions are obtained by reformulating the exact equations in special nonorthogonal coordinate systems more closely related to the essential structure of the field problem. The lowest term of the ordered expansion is now exact for a uniform finite angle taper. New circuit level nonuniform line equations are obtained which reduce to the well-known forms for gradual tapers.
\r\n\r\nThese techniques are extended to treat tapered plate lines with curved center lines and then to give a description of coaxial lines in which the field pattern is locally dominated by the boundaries, and the electrical center line is located in the propagation region. Odd-sequence field distortion terms now appear in third and higher orders. In all the systems investigated, distributed circuit equations give results, outside the nonuniform region, that are valid to within second order terms in the taper scale parameter.
\r\n" }, { "name": "Morel, Fran\u00e7ois M. M.", "degree": "PhD", "year": "1972", "title": "I. A Study of Passive Potassium Efflux From Human Red Blood Cells Using Ion Specific Electrodes. II. Quantitation of Human Red Blood Cell Fixation by Glutaraldehyde", "advisor": "Wayland, J. Harold", "url": "https://resolver.caltech.edu/CaltechETD:etd-12172004-160548", "creators": [ { "name": { "family": "Morel", "given": "Fran\u00e7ois M. M." }, "id": "Morel-Fran\u00e7ois-M-M", "display_name": "Morel, Fran\u00e7ois M. M." } ], "advisors": [ { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "advisor", "display_name": "Wayland, J. Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/WGFY-R705", "abstract": "I. Study of Passive Potassium Efflux From Human Red Blood Cells Using Ion Specific Electrodes.\r\n\r\nIt is shown that, by using ion specific electrodes, the small potassium leakage induced by ouabain in human erythrocytes can be measured continuously and precisely.\r\n\r\nUpon addition of isotonic sucrose solution to a suspension of red cells in physiological saline the passive (ouabain-insensitive) potassium efflux is directly proportional to the chloride ratio. (i. e., an exponential function of the total membrane potential). The same result is obtained upon addition of hypertonic sucrose solution, suggesting that neither osmolarity nor intracellular concentrations have any influence on the passive potassium efflux.\r\n\r\nThe independence of the potassium efflux and osmolarity can be verified by addition of glucose to the cell suspension. Glucose penetrates the red cells leaving the intracellular volume,and thus the membrane potential as well as the intracellular concentrations, unchanged.\r\n\r\nAdding water or hypertonic sodium chloride solution to red blood cell suspensions shows that the potassium efflux increases slightly in more concentrated salt solutions. Inasmuch as this effect can be interpreted as a pure ionic strength effect, the experiments corroborate the hypertonic sucrose solution experiments in demonstrating no dependence of the potassium efflux upon intracellular concentrations.\r\n\r\nThe results of this investigation as well as other studies (LaCelle and Rothstein 1966, Donlon and Rothstein 1969, Cotterrell and Whittam 1971) show that the passive permeability of the human red blood cell to potassium depends uniquely on the membrane potential near physiological conditions, while it depends on parameters such as pH or concentrations for values of the membrane potential over 40mV. This suggests that two different mechanisms of transport might be involved: one would control the permeability under normal conditions; the other would represent a leak through the route normally used by anions and become important only under extreme conditions.\r\n\r\nII. Quantitation of Human Red Blood Cell Fixation by Glutaraldehyde.\r\n\r\nThe uptake of glutaraldehyde by human red blood cells has been measured as a function of time by a freezing point osmometer. The rate of attachment of glutaraldehyde to the cell proteins is high over the first hour, declining to zero over a period of a few days. The number of glutaraldehyde molecules cross-linking with each hemoglobin molecule is of the order of 200, in reasonable agreement with the calculated number of attachment sites. The cell membrane is immediately highly permeable to glutaraldehyde. Selective permeability to ions is lost during fixation. Ionic equilibrium is obtained only after a few hours. An optimum fixation technique for shape preservation is suggested." }, { "name": "Newhall, X X (Nicholas)", "degree": "PhD", "year": "1972", "title": "Two New Integral Transforms and Their Applications", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03272013-154852773", "creators": [ { "name": { "family": "Newhall", "given": "X X (Nicholas)" }, "id": "Newhall-X-X-Nicholas", "display_name": "Newhall, X X (Nicholas)" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/P9CC-E241", "abstract": "This thesis is in two parts. In Part I the independent\r\nvariable \u03b8 in the trigonometric form of Legendre's equation is\r\nextended to the range ( -\u221e, \u221e). The associated spectral\r\nrepresentation is an infinite integral transform whose kernel\r\nis the analytic continuation of the associated Legendre function\r\nof the second kind into the complex \u03b8-plane. This new transform\r\nis applied to the problems of waves on a spherical shell, heat\r\nflow on a spherical shell, and the gravitational potential of a\r\nsphere. In each case the resulting alternative representation of\r\nthe solution is more suited to direct physical interpretation than\r\nthe standard forms.
\r\n\r\nIn Part II separation of variables is applied to the\r\ninitial-value problem of the propagation of acoustic waves in an\r\nunderwater sound channel. The Epstein symmetric profile is taken\r\nto describe the variation of sound with depth. The spectral\r\nrepresentation associated with the separated depth equation is\r\nfound to contain an integral and a series. A point source is\r\nassumed to be located in the channel. The nature of the\r\ndisturbance at a point in the vicinity of the channel far removed\r\nfrom the source is investigated.
" }, { "name": "Owyoung, Adelbert", "degree": "PhD", "year": "1972", "title": "The Origins of the Nonlinear Refractive Indices of Liquids and Glasses", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06132016-142455107", "creators": [ { "name": { "family": "Owyoung", "given": "Adelbert" }, "id": "Owyoung-Adelbert", "display_name": "Owyoung, Adelbert" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/E9HM-AK76", "abstract": "Nonlinear refractive index changes in isotropic media are a consequence of two distinct types of mechanisms. An \"electronic\" mechanism arises from the nonlinear distortion of the electron orbits about the nuclei and a \"nuclear\" mechanism arises from an electric-field-induced change in the motions of nuclei.
\r\n\r\nA general treatment of nonlinear optical phenomena involving a polarization cubic in the electric field strength is given with the topic of nonlinear index changes treated as a special case. A central result of this theory is the following expression for the nonlinear polarization P3(t) in terms of the electric field E(t), the \"electronic\" parameter \u03c3 and the \"nuclear response functions\" a(t) and b(t):
\r\n\r\nP3(t) = \u03c3-2 E(t)\u25aa E(t) E(t) + \u222b a(t-\u03c4)E(\u03c4)\u25aaE(\u03c4)d\u03c4 E(t)
\r\n\r\n+ \u222b b(t-\u03c4)E(\u03c4)\u25aaE(t)E(\u03c4)d\u03c4
\r\n\r\n\r\nIn the theory the relationship between these parameters and the nonlinear susceptibility tensor X3, is established. Several experiments in nonlinear optics are analyzed; in particular, it is shown that Kerr effect measurements lead to a determination of the quantity \u03c3 + \u03b2 (where \u03b2 = \u0283 b(t)dt) whereas measurements of the intensity dependent rotation of the polarization ellipse of a monochromatic optical beam yield the quantity \u03c3 + 2\u03b2. Hence together these two techniques offer a means of uniquely determining both the \"electronic\" parameter a and the \"nuclear\" parameter \u03b2 in any isotropic medium.
\r\n\r\nThe nonlinear susceptibility element X31221 (-\u03c9,\u03c9,\u03c9,-\u03c9) = \u03c3+2\u03b2/24 is calculated from ellipse rotation measurements in fused quartz, BK-7 borosilicate crown glass, and SF-7 dense flint glass giving values of 1.5, 2.3, and 9.9 x 10-15 esu at \u03bb = 6943\u00c5, respectively. These measurements constitute the first observations of ellipse rotation in any solid and (with an absolute accuracy of 11%) are the most accurately known of any nonlinear optical parameter in glasses.
\r\n\r\nAlthough the interpretation of these results along with Kerr, three-wave mixing, and third harmonic generation data nominally indicate that \u03c3 \u02c3\u02c3 \u03b2 for glasses, we hesitate to conclude that the nonlinear refractive indices in glasses are purely \"electronic\" in origin until the uncertainties in the latter measurements are reduced. If it is assumed however that electronic contributions are dominant, these experimental data would indicate that the nonlinear refractive index n2 for a linearly polarized beam in fused quartz, BK-7 glass, and SF-7 glass is 1.2, 1.7, and 6.9 x 10-13 esu respectively.
\r\n\r\nParallel investigations of \"ellipse rotation\" in the symmetric molecule liquid CC14 show that X31221 (-\u03c9,\u03c9,\u03c9,-\u03c9) = 6.1 x 10-15 esu. This value when interpreted along with very accurate Kerr measurements indicate that the fractional electronic contribution to the Kerr constant of CC14 is given by \u03c3/\u03c3+\u03b2 = 0.54 \u00b1 0.17. Hence both electronic and nuclear contributions are significant to nonlinear refractive index changes in CC14.
\r\n\r\n" }, { "name": "Palaniswamy, Karuppagounder", "degree": "PhD", "year": "1972", "title": "Crack Propagation under General In-Plane Loading", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:08252010-104555143", "creators": [ { "name": { "family": "Palaniswamy", "given": "Karuppagounder" }, "id": "Palaniswamy-Karuppagounder", "display_name": "Palaniswamy, Karuppagounder" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M7WW-G964", "abstract": "The problem of crack extension in brittle materials under\r\ngeneral loading conditions is investigated. Methods of solution of the related two-dimensional elasto-static boundary value problem are discussed. Using Kolosov-Muskhelishvili stress functions, an approximate solution is obtained. The effect of the approximation on the results is estimated by solving two related problems exactly. Then using two postulates the critical loads and crack extension direction are determined under loading conditions\r\nunsymmetrical to the crack axis. Results are compared with those obtained using a different set of postulates.\r\n" }, { "name": "Pearson, James Edward", "degree": "PhD", "year": "1972", "title": "Infrared Optical Parametric Fluorescence and Parametric Oscillation", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:06212016-105216322", "creators": [ { "name": { "family": "Pearson", "given": "James Edward" }, "id": "Pearson-James-Edward", "display_name": "Pearson, James Edward" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/HZSX-GD54", "abstract": "The properties of optical parametric fluorescence and parametric oscillation are considered in detail. Parametric fluorescence occurs when a pump light source (usually a laser) is incident on a nonlinear crystal; an input pump photon is \"split\" into two new photons whose energies sum to that of the pump. The frequencies of the fluorescence output can be tuned by varying the nonlinear crystal refractive indices. In a parametric oscillator, an optical resonator is used to provide feedback at the fluorescence frequencies so that coherent oscillations occur. The result is a coherent, narrow bandwidth light source which is wavelength-tunable over thousands of angstroms.
\r\n\r\nFor use in theoretical discussions, the nonlinear equations which describe three-wave parametric interactions are derived from Maxwell's equations. The interaction equations are given in a general form which exhibits the spatial and temporal dependence of the fields. The equations are solved for the case of a steady-state, non-depleted pump, parametric amplifier.
\r\n\r\nThe power, bandwidth, and angular dependence of parametric fluorescence are theoretically discussed in detail. Experimental measurements using a 1.06\u03bc, Nd:YAG laser are in good agreement with the theory. The experiments constitute the first observation of parametric fluorescence in the infrared.
\r\n\r\nThe theoretical properties of parametric oscillators are discussed using a simple but rigorous Fabry-Perot analysis. The analysis gives the threshold and oscillation frequencies of a parametric oscillator and the results are used to provide some insights into an oscillator's bandwidth and stability. The rise time of a pulsed parametric oscillator driven by a Q,-switched pump is analyzed rigorously for the first time. The analysis gives a minimum peak pump power for oscillation which can be substantially larger than the \"cw\" threshold power.
\r\n\r\nMeasurements on a 1.06\u03bc-pumped, internal, LiNb03 parametric oscillator are presented. The threshold, bandwidth, mode spectra, tuning range, and time behavior are discussed and compared to theory. The experimental results show good qualitative agreement with theory except that the bandwidth is nearly an order of magnitude smaller than expected. Peak power conversion efficiencies of 50% are observed along with 10% average power conversion. Several suggestions are made for improving the performance of this type of parametric oscillator.
\r\n" }, { "name": "Pu\u010dik, Thomas Antone", "degree": "PhD", "year": "1972", "title": "Elastostatic Interaction of Cracks in the Infinite Plane", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282010-083924490", "creators": [ { "name": { "family": "Pu\u010dik", "given": "Thomas Antone" }, "id": "Pu\u010dik-Thomas-Antone", "display_name": "Pu\u010dik, Thomas Antone" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BVJ3-BV94", "abstract": " The stress boundary value problem of an infinite, planar region with embedded rectilinear cracks is investigated from the viewpoint of two-dimensional, static, linear elasticity theory (plane strain or generalized stress). Any finite number of cracks may be considered. Their orientation may be arbitrary, so long as they do not intersect. Boundary loadings may take the form of quite general in-plane tractions along the crack surfaces, together with a bounded in-plane stress field at infinity.\r\n\r\n Using Muskhelishvili\u2019s solution for colinear cracks, the problem is reduced to a set of one-dimensional Fredholm integral equations. A simple numerical technique is presented for the approximate solution of these equations. The method is established to possess an extremely high rate of convergence.\r\n\r\n Results are presented for a number of two-crack interaction problems. As expected, the interaction of the cracks generally tends to reduce the fracture strength of a material, relative to the strength that would exist with either crack acting independently. However, for certain orientations, it is found that the interaction phenomenon can actually increase the resistance to fracture." }, { "name": "Setchell, Robert Earle", "degree": "PhD", "year": "1972", "title": "Shock Tube Investigations of Strong Shock Waves in a Convergent Channel", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212003-154300", "creators": [ { "name": { "family": "Setchell", "given": "Robert Earle" }, "id": "Setchell-Robert-Earle", "display_name": "Setchell, Robert Earle" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RVJ0-B836", "abstract": "The behavior of the incident and reflected shock waves in a convergent channel is investigated in order to determine if such a geometrical device could be used as a means of producing high-enthalpy gas samples. A 10\u00b0 half-angle conical convergence is mounted on the end of a pressure-driven, six-inch shock tube. Using argon at an initial pressure of 1.5 torr, initial shock Mach numbers are varied from 6.0 to 10.2. During each run local shock velocities at several positions along the cone axis are measured using a small, multi-crystal, axial piezoelectric probe inserted from the cone vertex.
\r\n\r\nThe incident shock velocity profiles show that the shock behavior is dominated by multiple diffraction processes which originate at the cone entrance. Sudden increases in shock velocity at certain positions along the axis are observed, corresponding to the intersection of stemshocks formed by Mach reflection on the cone wall. These increases are separated by regions of deceleration and acceleration, corresponding to the growth and decline of a center shock formed by Mach reflection on the cone axis. Near the vertex the shock velocity has increased by as much as a factor of three, indicating that high temperatures and pressures are generated. By varying the initial Mach number and pressure, real gas effects are found to influence the diffraction process only in a region near the vertex.
\r\n\r\nReflected shock profiles show that the shock velocity is nearly constant for much of the convergence length, in contrast to the power-law decline predicted by the similarity solution. During this period the shock propagates into fluid originally set into steady, uniform motion outside the cone entrance. Small variations in the velocity result from weak interactions with localized nonuniformities and secondary waves. Beyond the cone entrance the shock decelerates towards the velocity corresponding to reflection from a plane end wall. A departure from ionization equilibrium is likely near the vertex during the rapid expansion which occurs behind the reflected shock.
" }, { "name": "Smith, Richard Ross", "degree": "PhD", "year": "1972", "title": "Collective Effects in Three Pulse Cyclotron Echoes", "advisor": "Harp, Robert S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07122016-145602568", "creators": [ { "name": { "family": "Smith", "given": "Richard Ross" }, "id": "Smith-Richard-Ross", "display_name": "Smith, Richard Ross" } ], "advisors": [ { "name": { "family": "Harp", "given": "Robert S." }, "id": "Harp-Robert-S", "role": "advisor", "display_name": "Harp, Robert S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/PR88-HK58", "abstract": "Three-pulse cyclotron echoes, 3PE, in rare gas afterglow plasmas are investigated. The experiments are performed with the magnetic field parallel to the discharge tube, which passes perpendicularly through an S-band waveguide. The echo properties are experimentally shown to be incompatible with previous models.
\r\n\r\nExperiments on 3PE are performed, which show that the electron density is the most important parameter, especially for the growth and decay of the echo following the first two pulses. The density is shown to have a qualitative as well as quantitative effect on the echo. Periodic modulation of both the emission and absorption of the plasma is observed following the first two pulses, and these additional methods of investigating echo processes will be helpful in formulating a satisfactory theory.
\r\n\r\nA model containing the experimentally important parameters is developed, and it is based upon the relatively simple case of the generation of plasma waves following an impulsive excitation for times\r\nso small that the original transient response has lost negligible energy. Better agreement than with previous theories is obtained, especially in the qualitative dependence of the echo on the electron density. Electron velocity space instabilities are briefly examined and discarded as influences in echo experiments.
\r\n\r\nThe detection and qualitative theoretical explanation of slow wave pulses created inside the plasma by the applied microwave pulses supports the mode conversion echo model.
\r\n\r\n" }, { "name": "Steinhilper, Eric Anthony", "degree": "PhD", "year": "1972", "title": "Electron Beam Measurements of the Shock Wave Structure: Part I. The Inference of Intermolecular Potentials from Shock Wave Experiments. Part II. The Influence of Accommodation on Reflecting Shock Waves", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-09042007-094927", "creators": [ { "name": { "family": "Steinhilper", "given": "Eric Anthony" }, "id": "Steinhilper-Eric-Anthony", "display_name": "Steinhilper, Eric Anthony" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AWTA-PA12", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA technique has been developed in which accurate measurements of shock wave structure and an exact molecular theory of shock waves are used to determine intermolecular potentials. Shock wave density profiles in neon, argon, krypton, and xenon are measured in the GALCIT 17-inch diameter shock tube. The theory is a numerical molecular simulation technique (developed by G. Bird of the University of Sidney) in which the only adjustable parameter is the intermolecular potential. Parameters for the exp-6 and Lennard-Jones potentials are determined by matching the experimental shock wave density profiles with those predicted by the Monte Carlo simulation technique. The experimental data are taken at shock Mach number of about 8; consequently, these results fall in an energy range midway between the molecular beam measurements and low temperature transport property results.\r\n\r\nAfter the potentials for neon, argon, krypton, and xenon have been determined, they are tested for conformity to the Law of Corresponding States. Plots of the potentials in corresponding states coordinates, [...] vs.[...], show that the exp-6 potential model issuperior to the Lennard-Jones. This is an important result, because for the first time this statement can be made on the basis of one set of measurements. Previously it had been necessary to adduce molecular beam results in order toprove that the inverse twelfth-power repulsive part of the Lennard-Jones potential is too strong. Comparisons show that the exp-6, Lennard-Jones, simple repulsive, and hard sphere molecular potentials predict the experimental shock structure with successively decreasing accuracy. However, their accuracy is sufficient that any one of the potentials would predict any flow accurately enough to give an indication of the relative importance of the parameters governing the flow. This point is emphasized by the need for both the most precise experimental measurements and the use of the Law of Corresponding States in order to provide the basis for ranking the potentials. Moreover, changing the potentials has given a better understanding of the mechanisms by which intermolecular forces influence shock structure.\r\n\r\nMeasurements of density profiles during the reflection of thick shock waves in argon from the end wall of the GALCIT 17-inch diameter shock tube were reported previously. A mass balance using these profiles had revealed that as much as 20% of the gas which should have been between the end wall and the reflected shock was simply not present. Comparison with theory was not possible because no theory incorporated a loss of mass. Currently available theories for the reflection process include a Monte Carlo flow simulation technique for a thermally accommodating wall.\r\n\r\nIt is found that this technique can correctly predict either the reflected shock trajectory or the thermal layer near the wall, but the inability to duplicate both implies that there is a second important effect which we assume to be adsorption.\r\n\r\nAdditional experiments are conducted in neon which has a lower thermal accommodation coefficient than argon. If thermal accommodation is the only wall boundary condition, then according to the Monte Carlo calculations the shock should reflect faster in neon, and the thermal layer should be thinner. However, the measured density profiles show that the reflected shock trajectory is nearly the same as in argon but that there is only half as much \"missing\" mass. Thus, the neon results provide the most significant confirmation of adsorption.\r\n\r\nBecause this unexpected violation of the continuity equation was observed, a comprehensive review of instrumental effects and the data reduction technique is made. Several hypothetical effects are shown to have no influence on the loss of mass. However, improving the mass balance calculations accounts for approximately 25% of the missing mass. Correcting for multiple scattering of the electron beam accounts for another 10%, but this correction applies only at the highest densities. Therefore, the \"missing\" mass of the previous experiment is verified but is reduced somewhat in magnitude." }, { "name": "Taylor, Brent Dalton", "degree": "PhD", "year": "1972", "title": "Temperature Effects in Alluvial Streams", "advisor": "Vanoni, Vito A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09062016-161209389", "creators": [ { "name": { "family": "Taylor", "given": "Brent Dalton" }, "id": "Taylor-Brent-Dalton", "display_name": "Taylor, Brent Dalton" } ], "advisors": [ { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "advisor", "display_name": "Vanoni, Vito A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/9XZ5-FA91", "abstract": "A laboratory investigation was conducted to determine the effects of water temperature on sediment discharge close to the bed (bed-load discharge), and on bed roughness and geometry in alluvial, open-channel flows.
\r\n\r\n\r\nThree types of experiments were made: 1) Low-transport, flat-bed experiments in which all of the sediment discharged moved as bed load; 2) high-transport, flat-bed experiments with fine sands wherein there was considerable suspended sediment discharge; and 3) a series of experiments where the discharge was kept constant and the velocity varied to produce ripple, dune, and flat-bed configurations. The experiments were made in pairs. In each pair the velocity and\r\ndepth were the same or nearly the same, but in one experiment the water temperature was from 15\u00b0C to 20\u00b0C higher than in the other.
\r\n\r\n\r\nIt was found that in low-transport, flat-bed flows where particle transport is by rolling and sliding along the bed, a 15\u00b0C to 20\u00b0C increase in water temperature can produce a relatively large change in sediment discharge. The nature of this change depends on the flow condition at the bed. With hydrodynamically smooth flow there is an increase in sediment discharge with increase in water temperature; whereas in transition from smooth to rough an increase in water temperature effects a reduction in sediment discharge. With fully-rough flow which obtains at boundary Reynolds numbers larger than approximately 200, sediment discharge does not depend on water temperature. A phenomenological explanation has been presented for these observed temperature effects on sediment discharge.
\r\n\r\n\r\nIn high-transport, flat-bed flows with suspended sediment transport, it was observed that the temperature effects on bed-load discharge are qualitatively the same as those which obtain in low-transport, flat-bed flows of approximately the same boundary Reynolds numbers.
\r\n\r\n\r\nIt was also found that under certain flow conditions a change in water temperature alone can cause a change in bed form. The nature of this change in bed form seems to be related to the boundary Reynolds numbers R'*b of the flows. For R'*b less than a value near 8 bed form transitions were accomplished at lower velocities in a warm water flow than in a cold water flow at the same discharge; whereas for larger values of R'*b contrary temperature effects on bed form transitions have been observed.
\r\n\r\n" }, { "name": "Thyagaraja, Anantanarayanan", "degree": "PhD", "year": "1972", "title": "Compressible Flows at Small Reynolds Numbers", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03292013-152506285", "creators": [ { "name": { "family": "Thyagaraja", "given": "Anantanarayanan" }, "id": "Thyagaraja-Anantanarayanan", "display_name": "Thyagaraja, Anantanarayanan" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/VVKA-ZS09", "abstract": "The problem of the slow viscous flow of a gas past a sphere is considered. The fluid cannot be treated incompressible in the limit when the Reynolds number Re, and the Mach number M, tend to zero in such a way that Re ~ o(M^2 ). In this case, the lowest order approximation to the steady Navier-Stokes equations of motion leads to a paradox discovered by Lagerstrom and Chester. This paradox is resolved within the framework of continuum mechanics using the classical slip condition and an iteration scheme that takes into account certain terms in the full Navier-Stokes equations that drop out in the approximation used by the above authors. It is found however that the drag predicted by the theory does not agree with R. A. Millikan's classic experiments on sphere drag.
\r\n\r\nThe whole question of the applicability of the Navier-Stokes theory when the Knudsen number M/Re is not small is examined. A new slip condition is proposed. The idea that the Navier-Stokes equations coupled with this condition may adequately describe small Reynolds number flows when the Knudsen number is not too large is looked at in some detail. First, a general discussion of asymptotic solutions of the equations for all such flows is given. The theory is then applied to several concrete problems of fluid motion. The deductions from this theory appear to interpret and summarize the results of Millikan over a much wider range of Knudsen numbers (almost up to the free molecular or kinetic limit) than hitherto Believed possible by a purely continuum theory. Further experimental tests are suggested and certain interesting applications to the theory of dilute suspensions in gases are noted. Some of the questions raised in the main body of the work are explored further in the appendices.
\r\n" }, { "name": "Trijonis, John Charles, Jr.", "degree": "PhD", "year": "1972", "title": "An Economic Air Pollution Control Model-Application: Photochemical Smog in Los Angeles County in 1975", "advisor": "List, E. John", "url": "https://resolver.caltech.edu/CaltechTHESIS:06262014-113258422", "creators": [ { "name": { "family": "Trijonis", "given": "John Charles, Jr." }, "id": "Trijonis-John-Charles", "display_name": "Trijonis, John Charles, Jr." } ], "advisors": [ { "name": { "family": "List", "given": "E. John" }, "id": "List-E-J", "role": "advisor", "display_name": "List, E. John" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/hxbp-pc89", "abstract": "An economic air pollution control model, which determines the least cost of reaching various air quality levels, is formulated. The model takes the form of a general, nonlinear, mathematical programming problem. Primary contaminant emission levels are the independent variables. The objective function is the cost of attaining various emission levels and is to be minimized subject to constraints that given air quality levels be attained.
\r\n\r\nThe model is applied to a simplified statement of the photochemical smog problem in Los Angeles County in 1975 with emissions specified by a two-dimensional vector, total reactive hydrocarbon, (RHC), and nitrogen oxide, (NOx), emissions. Air quality, also two-dimensional, is measured by the expected number of days per year that nitrogen dioxide, (NO2), and mid-day ozone, (O3), exceed standards in Central Los Angeles.
\r\n\r\n\r\nThe minimum cost of reaching various emission levels is found by a linear programming model. The base or \"uncontrolled\" emission levels are those that will exist in 1975 with the present new car control program and with the degree of stationary source control existing in 1971. Controls, basically \"add-on devices\", are considered here for used cars, aircraft, and existing stationary sources. It is found that with these added controls, Los Angeles County emission levels [(1300\r\ntons/day RHC, 1000 tons /day NOx) in 1969] and [(670 tons/day RHC, 790 tons/day NOx) at the base 1975 level], can be reduced to 260 tons/day RHC (minimum RHC program) and 460 tons/day NOx (minimum NOx program).
\r\n\r\n\"Phenomenological\" or statistical air quality models provide the relationship between air quality and emissions. These models estimate the relationship by using atmospheric monitoring data taken at one (yearly) emission level and by using certain simple physical assumptions, (e. g., that emissions are reduced proportionately at all points in space and time). For NO2, (concentrations assumed proportional to NOx emissions), it is found that standard violations in\r\nCentral Los Angeles, (55 in 1969), can be reduced to 25, 5, and 0 days per year by controlling emissions to 800, 550, and 300 tons /day, respectively. A probabilistic model reveals that RHC control is much more effective than NOx control in reducing Central Los Angeles ozone. The 150 days per year ozone violations in 1969 can be reduced to 75, 30, 10, and 0 days per year by abating RHC emissions to 700, 450, 300, and 150 tons/day, respectively, (at the 1969 NOx emission level).
\r\n\r\nThe control cost-emission level and air quality-emission level relationships are combined in a graphical solution of the complete model to find the cost of various air quality levels. Best possible air quality levels with the controls considered here are 8 O3 and 10 NO2 violations per year (minimum ozone program) or 25 O3 and 3 NO2 violations per year (minimum NO2 program) with an annualized cost of $230,000,000 (above the estimated $150,000,000 per year for the new car control program for Los Angeles County motor vehicles in 1975).
\r\n" }, { "name": "Udwadia, Firdaus Erach", "degree": "PhD", "year": "1972", "title": "Investigation of Earthquake and Microtremor Ground Motions", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechThesis:08262021-203716987", "creators": [ { "name": { "family": "Udwadia", "given": "Firdaus Erach" }, "id": "Udwadia-Firdaus-Erach", "display_name": "Udwadia, Firdaus Erach" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/4cv1-wy73", "abstract": "The nature of strong earthquake ground shaking has been investigated based on a study of 15 accelerograms recorded at El Centro in southern California. It is concluded that the characteristics of the source mechanism and the transmission path play a dominant role in determining the details of strong ground shaking at the site. No local site periodicities could be clearly identified, which suggests that source and transmission path effects overshadow the influence of local site conditions.
\r\n\r\nThe method of using microtremor measurements to determine local site characteristics has been tested by direct comparison with strong motion measurements. Microtremor ground motions were recorded at five sites in the El Centro area and measurements were repeated at three of these sites after a period of 24 hours. These low amplitude ground motions have been found to be widely different from the motions caused by strong earthquake ground shaking. Their nonstationary nature over a period of a day or so makes the interpretation of such data from a single microtremor measurement very unreliable. It has been concluded that these microtremor ground motions are forced oscillations of the ground caused by nearby sources of excitation. The microtremor acceleration spectra do not indicate prominent peaks that could be correlated with local site conditions. At this site the use of microtremor measurements to define local subsoil conditions would evidently not be feasible.
" }, { "name": "Wester, Gene Ward", "degree": "PhD", "year": "1972", "title": "Low-Frequency Characterization of Switched dc-de Converters", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechTHESIS:06242010-143228488", "creators": [ { "name": { "family": "Wester", "given": "Gene Ward" }, "id": "Wester-Gene-Ward", "display_name": "Wester, Gene Ward" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/RMBC-4961", "abstract": "Techniques are developed for the approximate representation of switched dc-dc converters by time-averaged models. Simple analytical expressions in terms of the circuit components are derived for the characteristic transient and frequency responses of averaged power-stage models for use in designing and understanding the behavior of the actual switched power stages. High-order systems can be analyzed by the averaging technique without a commensurate increase in complexity.\r\n\r\nTwo functional blocks are necessary to construct a switched converter: the switch controller, which is relatively well understood, and the power stage. When concreteness is necessary, a particular pulse- width modulator is chosen for the switch controller and is thoroughly analyzed. The output of representative power stages (buck, boost, and buck-boost) is a complicated nonlinear function of the switch controller and source input, and since conventional methods of nonlinear analysis are shown to be intractable or uninterpretable, attention is focused on the challenge of obtaining useful design equations.\r\n\r\nThe difficulty encountered in the nonlinear analysis of switched power stages is successfully surmounted by the semiheuristic development of a continuous power-stage model. Since the characteristic response times of state variables in the switched power stage are invariably large with respect to the switching period, discontinuous forcing functions in the equivalent circuits are averaged over a time interval comparable with the switching period without appreciably affecting the nature of the response. Consequently, the averaged model is limited to response times greater than the averaging interval. Equivalent circuits and analytic expressions for the transient and frequency response of each power-stage type are then derived from the averaged models. A linearized control-input transfer function, obtained for small amplitude variations of the averaged control, reveals a dependence of effective circuit component values upon the switch duty ratio, and the possible existence of a positive real zero.\r\n\r\nThe unusual behavior predicted above is confirmed by an analog computer simulation of both the switched and averaged power stages. It is also shown experimentally that closed-loop stability of the switched power stage is adequately predicted by the averaged model. The averaging technique is thus a powerful analytical tool for exposing inherent characteristics of switched circuits.\r\n" }, { "name": "Yagii, Keikichi", "degree": "PhD", "year": "1972", "title": "Effect of Pressure on the Mechanical Behavior of Filled Elastomers", "advisor": "Tschoegl, Nicholas W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07232014-093132642", "creators": [ { "name": { "family": "Yagii", "given": "Keikichi" }, "id": "Yagii-Keikichi", "display_name": "Yagii, Keikichi" } ], "advisors": [ { "name": { "family": "Tschoegl", "given": "Nicholas W." }, "id": "Tschoegl-N-W", "role": "advisor", "display_name": "Tschoegl, Nicholas W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/1vr2-7x25", "abstract": "The Young's modulus, stress-strain curves, and failure\r\nproperties of glass bead-filled EPDM vulcanizates were studied under superposed hydrostatic pressure. The glass bead-filled EPDM was employed as a representation of composite systems, and the hydrostatic pressure controls the filler-elastomer separation under deformation. This separation shows up as a volume change of the system, and its infuence is reflected in the mechanical behavior as a reinforcing effect of variable degree.
\r\n\r\nThe strain energy stored in the composite system in\r\nsimple tension was calculated by introducing a model which\r\nis described as a cylindrical block of elastomer with two\r\nhalf spheres of filler on each end with their centers on the axis of the cylinder. In the derivation of the strain energy, assumptions were made to obtain the strain distribution in the model, and strain energy-strain relation for the elastomer was also assumed. The derivation was carried out for the case of no filler-elastomer separation and was modified to include the case of filler-elastomer separation.
\r\n\r\nThe resulting strain energy, as a function of stretch ratio and volume of the system, was used to obtain stress-strain curves and volume change-strain curves of composite systems under superposed hydrostatic pressure.
\r\n\r\nChanges in the force and the lateral dimension of a ring\r\nspecimen were measured as it was stretched axially under a\r\nsuperposed hydrostatic pressure in order to calculate the mechanical properties mentioned above. A tensile tester was used which is capable of sealing the whole system to carry out a measurement under pressure. A thickness measuring device, based on the Hall effect, was built for the measurement of changes in the lateral\r\ndimension of a specimen.
\r\n\r\nThe theoretical and experimental results of Young's\r\nmodulus and stress-strain curves were compared and showed\r\nfairly good agreement.
\r\n\r\nThe failure data were discussed in terms of failure surfaces, and it was concluded that a failure surface of the glass-bead-filled EPDM consists of two cones.
\r\n" }, { "name": "Adegbola, Mashood Olayide", "degree": "PhD", "year": "1971", "title": "Alias-Free Spectral Estimation of Stochastic Processes", "advisor": "Martel, Hardy Cross; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112017-132121017", "creators": [ { "name": { "family": "Adegbola", "given": "Mashood Olayide" }, "id": "Adegbola-Mashood-Olayide", "display_name": "Adegbola, Mashood Olayide" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "member", "display_name": "George, Nicholas A." }, { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "member", "display_name": "Martel, Hardy Cross" }, { "name": { "family": "Todd", "given": "John" }, "id": "Todd-J", "role": "member", "display_name": "Todd, John" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ymat-1n64", "abstract": "A scheme for the practical estimation of power spectrum from randomly-timed samples is proposed and investigated for wide-sense stationary point processes. The sampling process {tn} is assumed to be stationary point process statistically independent of the sampled process X(t). Stationarity of {tn} admits that joint statistics of tk, tk+n do not depend on k. Closed form analytical formulae are derived for the spectral window Qm(f) and for cov{S^(fr), S^(fq)}, var{S^(fr)} for the particular case of independent identically distributed sampling intervals. Results confirm the alias-free character of the Poisson sampling scheme even for non-bandlimited spectra. It is shown further that for Gaussian processes with very smooth spectra Poisson sampling process can yield more reliable estimates (i.e., with a smaller variance) than the well known method of periodic sampling.
" }, { "name": "Adu, Randolph Ademola", "degree": "PhD", "year": "1971", "title": "Response and Failure of Structures Under Stationary Random Excitation", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302017-155936522", "creators": [ { "name": { "family": "Adu", "given": "Randolph Ademola" }, "id": "Adu-Randolph-Ademola", "display_name": "Adu, Randolph Ademola" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "chair", "display_name": "Housner, George W." }, { "name": { "family": "De Prima", "given": "Charles R." }, "id": "De-Prima-C-R", "role": "member", "display_name": "De Prima, Charles R." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "member", "display_name": "Vreeland, Thad" } ], "option_major": [ "civileng" ], "doi": "10.7907/6304-3X27", "abstract": "The response of simple structural systems to stationary random excitation is considered under two criteria of failure. When failure is specified as the crossing of a maximum tolerable threshold by the response, the reliability of a structure is commonly measured by means of response spectra. These give the expected maximum value of the response parameter for a given excitation level. The statistical variations in these spectra are obtained here for viscously damped linear and elastoplastic single-degree of freedom systems by electronic analog simulation. The results obtained are compared with approximate statistical analyses; for example, the threshold crossing statistics of narrow-band oscillators. It is concluded that such methods give satisfactory, but conservative, estimates of the mean spectral values. It is significant that all the spectra obtained showed a very wide distribution about the mean. This was also true of the Fourier amplitude spectrum of the excita\u00adtion.
\r\n\r\nFor response that are so large that structures actually collapse, the linear model was replaced by an elastoplastic system, and the effect of gravity on the collapse time was considered. Experimental simulation showed that the structural response in this case is essentially that of a linear oscillator with yielding occurring at intermittent intervals. Gravity acts to increasingly bias this yielding in one direction, eventually causing instability in the system. Collapse of the system was sensitive to the distribution of peaks in the excitation and it was found that the wide dispersion in the collapse time can be reasonably represented by a Gamma distribution function.
\r\n\r\nAn analytic method for estimating the mean collapse time was derived by considering the energy distribution of the excitation and its effect on the yielding of the structure. The response process was thus modelled by that of an equivalent linear oscillator whose baseline is biased by the yielding in the structure. It was concluded that this procedure gives a good estimate of the failure time for excitations strong enough to cause failure in less than 20 seconds.
\r\n\r\nA two-degree of freedom elastoplastic hysteretic system with gravity was also simulated. In a certain sense, the qualitative behavior is similar to that of the single-degree of freedom system. It was thus possible to estimate the failure time of the structure from that of a single-degree of freedom system once the transmission of vibration is accounted for by considering a linear two-degree of freedom system.
" }, { "name": "Arnett, David Woods", "degree": "PhD", "year": "1971", "title": "Information Processing by the First Optic Ganglion in Dipterans", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:11212017-105124061", "creators": [ { "name": { "family": "Arnett", "given": "David Woods" }, "id": "Arnett-David-Woods", "display_name": "Arnett, David Woods" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/VSZT-PE65", "abstract": "Information processing properties of the dipteran first optic \r\nganglion were studied by observing and analyzing the discharge behavior \r\nof two units in the intermediate chiasma and the slow potential \r\nbehavior of two units in the first optic ganglion. Both types of\r\nchiasma units (on-off, on-maintained) were centripetal and corres\u00adponded \r\nto second order units in the first optic ganglion. The on-off \r\nunit was characterized by a transient discharge following the onset \r\nand cessation of a light pulse presented anywhere in the receptive \r\nfield which had an elliptical configuration with average major and \r\nminor half directional sensitivity angles of 5.5 and 4.3 degrees,\r\nrespectively. The receptive field of the on-maintained unit was \r\ncomposed of three roughly circular regions arranged adjacently\r\nalong a line, and stimulation of the center region elicited a sustained \r\ndis charge while stimulation of either adjacent region elicited an\r\noff discharge. The average half directional sensitivity angle of the \r\ncenter region was 2.5 degrees which compared well with the\r\nacceptance angle of the photo receptors. The orientation of the major \r\naxes of the on-off and on-maintained unit receptive fields was always \r\nthat of the medio-lateral axis of the compound eye.
\r\n\r\nThe on and off regions of the on-maintained unit receptive \r\nfield were antagonistic, for stimulation of either off region inhibited \r\nor suppressed a discharge resulting from region stimulation.\r\nFurthermore, the off response was inhibited by region stimulation \r\nif the cessation of on region stimulation preceded, by not more than\r\n200 msec., the cessation of off region stimulation.
\r\n\r\nThe discharge patterns of both units were independent of the \r\nstimulus spectral wavelength, and all units studied, of both type, \r\npossessed the same spectral sensitivity which was characterized by \r\ntwo peaks of approximately equal maximum sensitivity centered at \r\n350 m\u00b5 and 485 m\u00b5. It was concluded that these units belonged to the \r\nsystem served by photoreceptors 1-6 and that a photopigment\r\nwith two absorption peaks was responsible for the observed spectral \r\nsensitivities. Neither unit displayed any sensitivity to the plane of \r\npolarized light.
\r\n\r\n\r\nPositive slow potentials were recorded from the first optic \r\nganglion with fine micropipettes, and they were believed to originate \r\nfrom the photo receptor axons. A hyperpolarizing slow potential,\r\nmost likely of intracellular origin, was also recorded, but its \r\nprop\u00aderties were not studied in detail.
\r\n\r\nBased on their information processing properties, the on-off \r\nand on-maintained units were identified with the two type I monopolar \r\nneurons of each cartridge. A model was developed which adequately \r\nexplained the behavior of both types of units, and its structure was \r\ncompared with the known anatomical structure of the first optic \r\nganglion.
\r\n\r\n\r\n\r\n\r\n\r\n" }, { "name": "Ayers, Raymond Dean", "degree": "PhD", "year": "1971", "title": "Hall Coefficient and Resistivity of an Amorphous Palladium-Silicon Alloy", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-105821882", "creators": [ { "name": { "family": "Ayers", "given": "Raymond Dean" }, "id": "Ayers-Raymond-ean", "display_name": "Ayers, Raymond Dean" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/05KN-J366", "abstract": "The Hall coefficient and resistance in several specimens of\r\nan amorphous metallic alloy containing 80 at.% palladium and 20 at.%\r\nsilicon have been investigated at temperatures between 4.2\u00b0K and room\r\ntemperature. An ideal limiting behavior of these transport\r\ncoefficients was analyzed on the basis of the nearly free electron\r\nmodel to yield a carrier density of 9 x 1022 cm.-3, or about 1.7\r\nelectrons per palladium atom, and a mean free path of about 9\u00c5 which\r\nis almost constant with temperature. The deviations of the individual\r\nspecimens from this ideal behavior, which were small but noticeable\r\nin the relative resistivity and much greater in the Hall coefficient,\r\ncan be explained by invoking disk-shaped crystalline regions with low\r\nresistivity and a positive Hall coefficient. A detailed calculation\r\nshows how a volume fraction of such crystalline material too small to\r\nbe noticed in X-ray diffraction could have a significant effect on\r\nthe resistivity and a much greater effect on the Hall coefficient." }, { "name": "Barcelo, Brian Thomas", "degree": "PhD", "year": "1971", "title": "Electron Beam Measurements of the Shock Wave Structure. Part 1. Determination of the Interaction Potential of the Noble Gases from Shock Wave Structure Experiments. Part II. Feasibility of a Modified Electron Beam Densitometer Technique to Measure Diffusive Separation in Shock Waves in Helium-Argon Mixtures", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-04022009-092506", "creators": [ { "name": { "family": "Barcelo", "given": "Brian Thomas" }, "id": "Barcelo-Brian-Thomas", "display_name": "Barcelo, Brian Thomas" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "chair", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "member", "display_name": "Roshko, Anatol" }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QH9Z-BH10", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nShock wave experiments were conducted in the GALCIT* seventeen-inch low density shock tube to measure the interaction potential of the following nonradioactive noble gases: neon, argon, krypton, and xenon. The experimental shock profiles obtained by employing the electron beam densitometer technique were compared to the Monte Carlo numerical simulation of the shock wave structure. The comparison determined the intermolecular potential for these gases, a potential assumed to be of the form [...] = const/r[superscript s]. The values resulting for the free parameter s in the inverse repulsive power law were 9, 10, 11, and 12 for xenon, krypton, argon, and neon, respectively.\r\n\r\nIn a second phase of the experiments, the feasibility of a modified electron beam densitometer technique was investigated for measuring the shock wave structure in a binary mixture of helium and argon. It was desired to obtain both the argon and helium density profiles through the shock wave by varying the electron beam energy in two experiments of identical shock conditions (gas concentrations, Mach number, initial pressure, etc.). Theoretical calculations of the collision cross-section indicated only a slight possibility of separating the density profiles of the two species with the range of electron energy possible in the experimental apparatus (7000 to 15000 volts). Experiments conducted with initial gas concentrations of 10%, 20%, 50%, and 80% argon in shock waves with a Mach number of approximately four confirmed these suspicions but permitted qualitative conclusions in agreement with other similar investigations.\r\n\r\n*Graduate Aeronautical Laboratories California Institute of Technology." }, { "name": "Bielak, Jacobo", "degree": "PhD", "year": "1971", "title": "Earthquake Response of Building-Foundation Systems", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12062017-133056313", "creators": [ { "name": { "family": "Bielak", "given": "Jacobo" }, "id": "Bielak-Jacobo", "display_name": "Bielak, Jacobo" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/YEAJ-FN27", "abstract": "The influence of a deformable foundation on the response of \r\nbuildings to earthquake motion is examined. The study is divided into \r\ntwo parts; the vibration of the base of the building on the foundation \r\nmedium, and the response of the whole building-foundation system.
\r\n\r\nStudied first are the forced horizontal, rocking and vertical \r\nharmonic oscillations of a rigid dis c bonded to an elastic half-space, which \r\nis considered as a mathematical model for the soil. The problem,\r\nformulated in terms of dual integral equations, is reduced to a system \r\nof Fredholm integral equations of the second kind. For the limiting \r\nstatic case these equations yield a closed form solution in agreement\r\nwith that obtained by others.
\r\n\r\nUsing the force-deflection relations for the base, the equations of \r\nmotion of linear building-foundation systems are solved by both direct \r\nand transform methods.\tIt is shown that, under assumptions which \r\nappear to be physically reasonable, the earthquake response of the interaction \r\nsystem reduces to the linear superposition of the responses of \r\ndamped, linear one-degree-of-freedom oscillators subjected to modified \r\nexcitations. This result is valid even for systems that do not possess \r\nclassical normal modes. Explicit approximations in terms of the parameters \r\nof the system are obtained for the dynamic properties of\r\nthe one-degree-of-freedom oscillator which is equivalent to a single \u00adstory \r\nbuilding-foundation system. For multi-story buildings it is shown that the \r\neffect of an elastic foundation, as measured by the change in\r\nthe natural frequencies of the building, is negligible for modes \r\nhigher than the first for many types of building structures.
\r\n\r\n" }, { "name": "Brownlow, Leonard William, Jr.", "degree": "PhD", "year": "1971", "title": "Magnetoelastic Effects in Thin Ferromagnetic Films", "advisor": "Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03302018-114644214", "creators": [ { "name": { "family": "Brownlow", "given": "Leonard William, Jr." }, "id": "Brownlow-Leonard-William", "display_name": "Brownlow, Leonard William, Jr." } ], "advisors": [ { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/G42T-JN47", "abstract": "A method is described for the evaporation of ferromagnetic films\r\nonto a very thin water soluble polymer coating on glass substrates and\r\ntheir subsequent removal onto a liquid glycerin film. Determination of\r\nthe change in magnetic anisotropy on removal provides a measure of the\r\nsubstrate constraint contribution to the anisotropy energy. Data are\r\ngiven for both Ni-Fe and Ni-Co alloys in the entire range 0 to 100% Ni,\r\ndeposited at 100\u00b0C.
\r\n\r\nSignificant changes in anisotropy upon removal were observed for\r\nalmost all Ni-Fe alloys and for Ni-Co alloys in the range 0 to 40% Co.\r\nHowever, essentially a zero percentage change was observed for pure Fe,\r\n83% No-Fe and the entire range 0 to 60% Ni in the Ni-Co alloys. These\r\ndate are in disagreement with present theories of the constraint energy\r\nexcept for qualitative agreement in very limited composition ranges.
\r\n\r\nIt has been suggested that the discrepancy between experimental and\r\ntheoretical prediction for the anisotropy energy in thin films may\r\nresult from the use of bulk material magnetoelastic constants which are\r\ninappropriate for thin films. However, this study of the magnetic\r\nproperties of epitaxial films strongly suggests the equivalence of the\r\nmagnetoelastic parameters in thin films and bulk materials. In this\r\nstudy a technique was developed for the preparation of step-free epitaxial\r\nfilms of Ni-Fe and Ni-Co alloys deposited at 400\u00b0C. The strain\r\nsensitivity \u0394Hk/\u0190 has been measured by ferromagnetic resonance along the\r\n[100] and [110] directions in the (001) plane for compositions ranging\r\nfrom 44 to 87% Ni in the Ni-Fe alloys and from 70 to 82% Ni in the Ni-Co\r\nalloys. The data are in good agreement with the theoretical predictions\r\n3(C11-C12)\u03bb100/M and 6C44\u03bb111/M along the [100] and [110] directions\r\nrespectively, evaluated using bulk parameters.
\r\n\r\nIn addition, the strain sensitivity of polycrystalline films deposited\r\nat 100\u00b0C and 400\u00b0C for Ni-Fe alloys and 400\u00b0C for Ni-Co alloys has\r\nbeen measured. Contrary to previous investigations, a systematic temperature\r\ndependence is found. Moreover, it is shown that the isotropic\r\nmaterial model used previously by others to calculate the strain sensitivity\r\nin polycrystalline films is incorrect. However, the apparent\r\nproper formulation does not predict experimentally determined result.\r\nThis discrepancy remains unexplained.
\r\n\r\nNew data for the crystalline anisotropy constant K1 in constrained\r\nepitaxial films of Ni-Fe and Ni-Co are presented. Significant deviations from\r\nvalues in bulk material are observed. However, these deviations are\r\nbelieved to result from the substrate constraint and not \r\nmaterial differences inherent in thin films.
" }, { "name": "Casperson, Lee Wendel", "degree": "PhD", "year": "1971", "title": "Modes and Spectra of High Gain Lasers", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262004-143412", "creators": [ { "name": { "family": "Casperson", "given": "Lee Wendel" }, "id": "Casperson-Lee-Wendel", "display_name": "Casperson, Lee Wendel" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7JZX-4J40", "abstract": "This research has dealt with various problems related to high gain lasers including: gain and dispersion focusing of the transverse modes, mode pulling and mode splitting of the longitudinal modes, ultrashort pulse propagation, relaxation oscillations, spectral narrowing, dispersion effects on the oscillation line width, and a saturation and power formalism for high gain lasers. Most of these subjects had not been treated previously and it is found that the properties of high gain lasers may differ drastically from the properties of similar low gain lasers. Besides the theoretical treatment of these subjects, experimental verification has been obtained whenever possible. The experiments were conducted using 3.51 micron xenon lasers." }, { "name": "Chwang, Allen Tse-Yung", "degree": "PhD", "year": "1971", "title": "Helical Movements of Flagellated-Propelling Microorganisms", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-141206", "creators": [ { "name": { "family": "Chwang", "given": "Allen Tse-Yung" }, "id": "Chwang-Allen-Tse-Yung", "display_name": "Chwang, Allen Tse-Yung" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/JWFS-FA36", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe helical motion of an infinitely long flagellum with a cross-sectional radius b, along which a helical wave of amplitude h, wave-length [lambda] and phase velocity c is propagated, has been analyzed by using Stokes' equations in a helical coordinate system (r,[xi],x). In order to satisfy all the boundary conditions, namely the no-slip condition on the flagellum surface and zero perturbation velocity at infinity, the flagellum must propel itself with a propulsion velocity U in the opposite direction to the phase velocity c. For small values of kb (where k = 2[pi]/[lambda] is the wave number), by a single-harmonic approximation for the outer region (r > h), the ratio of the propulsion velocity U to the phase velocity c is found to be[...], where K[n](kh) is the modified Bessel function of the second kind.\r\n\r\nA modified and improved version of the Gray and Hancock method has been developed and applied to evaluate helical movements of a freely swimming microorganism with a spherical head of radius a and a tail of finite length and cross-sectional radius b. The propulsion velocity U and the induced angular velocity [omega] of the organism are derived. In order that this type of motion can be realized, it is necessary for the head of the organism to exceed a certain critical size, and some amount of body rotation is inevitable. For fixed kb and kh, an optimum head-tail ratio a/b, at which the propulsion velocity U reaches a maximum, has been discovered. The power required for propulsion by means of helical waves is determined, based on which a hydromechanical efficiency [eta] is defined. This [eta] reaches a maximum at kh [...] 0.9 for microorganisms with optimum head-tail ratios. In the neighborhood of kh = 0.9, the optimum head-tail ratio varies in the range 15 < a/b < 40, the propulsion velocity in 0.08 < U/c < 0.2, and the efficiency in 0.14 < [eta] < 0.24, as kb varies over 0.03 < kb < 0.2.\r\n\r\nThe modified version of the Gray and Hancock method has also been utilized to describe the locomotion of spirochetes. It is found that although a spirochete has no head to resist the induced viscous torque, it can still propel by means of helical waves provided that the spirochete spins with an induced angular velocity [omega]. Thus the 'Spirochete paradox' is resolved. In order to achieve a maximum propulsion velocity, it is discovered that a spirochete should keep its amplitude-wavelength ratio h/[lambda] around 1:6 (or kh [...] 1). At kh = 1, the propulsion velocity varies in the range 0 < U/c < 0.2, and the induced angular velocity in 0.4 < [omega]/[low-case omega] < 1 (where [low-case omega] = kc is the circular frequency of the helical wave), as the radius-amplitude ratio varies over 0 < b/h < 1.\r\n\r\nA series of experiments have been carried out to determine by simulation the relative importance of the so-called 'neighboring' effect and 'end' effect, and results for the case of uniform helical waves are presented" }, { "name": "Davey, Robert Frederick", "degree": "PhD", "year": "1971", "title": "An Experimental Investigation of the Effect of a Density Gradient on Shear Layer Instability", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-04022009-131624", "creators": [ { "name": { "family": "Davey", "given": "Robert Frederick" }, "id": "Davey-Robert-Frederick", "display_name": "Davey, Robert Frederick" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YJF7-DV47", "abstract": "Measurements of mass flow rate and mean density have been made in separated laminar boundary layers having large transverse density gradients. A 3/8 in. by 1 1/2 in. rectangular half-jet was used to generate a two-dimensional shear layer and the density heterogeneity was produced in an incompressible flow by exhausting one gas into a reservoir of another gas having a different molecular weight. Two Freons were used having a density ratio of 1.98 and unique properties which permitted the measurement of the mass flow rate in all mixtures of the gases with a single hot wire.\r\n\r\nMean density and mass flow rate profiles were compared to the Holmboe model used in theoretical hydrodynamic stability analyses. Fluctuations in the mass flow rate were analyzed and the frequency, wave number and amplification rate of the most unstable oscillation were measured and compared to theoretically predicted values. The oscillations were found to have a higher amplification rate, lower wave number and lower frequency than homogeneous flow when the lighter gas flowed into the heavier one, in agreement with the theoretical predictions. Opposite trends were observed with the heavy gas flowing.\r\n\r\nThe development of harmonic frequency oscillations in the non-linear region is discussed briefly." }, { "name": "Delaney, Michael Ernest", "degree": "PhD", "year": "1971", "title": "I. Singular Perturbation Problems Involving Singular Points and Turning Points. II. On the Averaged Lagrangian Technique for Nonlinear Dispersive Waves", "advisor": "Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechTHESIS:04032013-100253267", "creators": [ { "name": { "family": "Delaney", "given": "Michael Ernest" }, "id": "Delaney-Michael-Ernest", "display_name": "Delaney, Michael Ernest" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/D9B7-N756", "abstract": "In Part I a class of linear boundary value problems is considered\r\nwhich is a simple model of boundary layer theory. The effect of zeros and\r\nsingularities of the coefficients of the equations at the point where the\r\nboundary layer occurs is considered. The usual boundary layer techniques\r\nare still applicable in some cases and are used to derive uniform asymptotic\r\nexpansions. In other cases it is shown that the inner and outer expansions\r\ndo not overlap due to the presence of a turning point outside the boundary\r\nlayer. The region near the turning point is described by a two-variable\r\nexpansion. In these cases a related initial value problem is solved and\r\nthen used to show formally that for the boundary value problem either a\r\nsolution exists, except for a discrete set of eigenvalues, whose asymptotic\r\nbehaviour is found, or the solution is non-unique. A proof is given of the\r\nvalidity of the two-variable expansion; in a special case this proof also\r\ndemonstrates the validity of the inner and outer expansions.
\r\n\r\nNonlinear dispersive wave equations which are governed by variational\r\nprinciples are considered in Part II. It is shown that the averaged\r\nLagrangian variational principle is in fact exact. This result is used to\r\nconstruct perturbation schemes to enable higher order terms in the equations\r\nfor the slowly varying quantities to be calculated. A simple scheme\r\napplicable to linear or near-linear equations is first derived. The\r\nspecific form of the first order correction terms is derived for several\r\nexamples. The stability of constant solutions to these equations is considered\r\nand it is shown that the correction terms lead to the instability\r\ncut-off found by Benjamin. A general stability criterion is given which\r\nexplicitly demonstrates the conditions under which this cut-off occurs.\r\nThe corrected set of equations are nonlinear dispersive equations and their\r\nstationary solutions are investigated. A more sophisticated scheme is\r\ndeveloped for fully nonlinear equations by using an extension of the\r\nHamiltonian formalism recently introduced by Whitham. Finally the averaged\r\nLagrangian technique is extended to treat slowly varying multiply-periodic\r\nsolutions. The adiabatic invariants for a separable mechanical system are\r\nderived by this method.
" }, { "name": "Ditmars, John David", "degree": "PhD", "year": "1971", "title": "Mixing of Density-Stratified Impoundments with Buoyant Jets", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02052018-100847353", "creators": [ { "name": { "family": "Ditmars", "given": "John David" }, "id": "Ditmars-John-David", "display_name": "Ditmars, John David" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/4RYG-QZ06", "abstract": "This study is an investigation of the mixing of density-stratified \r\nimpoundments by means of buoyant jets created by a pumping system. \r\nThe deterioration of water quality which often occurs in density-strati\u00adfied \r\nlakes and reservoirs may be counter acted by mixing. The physical aspects \r\nof the mixing process are the primary concern of this study, although \r\nseveral implications regarding changes in water quality are indicated.
\r\n\r\n\r\nA simulation technique is developed to predict the time-history \r\nof changes in the density-depth profiles of an impoundment during \r\nmixing.\tThe simulation model considers the impoundment closed to \r\nall external influences except those due to the pumping system.\tThe \r\nimpoundment is treated in a one-dimensional sense, except for the \r\nfluid mechanics of the three-dimensional jet and selective withdrawal \r\nof pumping system. The numerical solution to the governing equations\r\npredicts density profiles at successive time steps during mixing, given \r\nthe initial density profile, the area-depth relation for the impoundment, \r\nthe elevations of intake and jet discharge tubes, and the jet discharge \r\nand diameter. The changes due to mixing in the profiles of temperature \r\nand of a conservative, non-reacting tracer can be predicted also.
\r\n\r\n\r\nThe results of laboratory experiments and two field mixing \r\nexperiments in which density-stratified impoundments were mixed \r\nusing pumping systems show that the simulation technique predicts the \r\nresponse of the impoundment reasonably well.
\r\n\r\n\r\nThe results of a series of simulated mixing experiments for \r\nimpoundments which have prismatic shapes and initially linear \r\ndensity profiles are given in dimensionless form. For these special \r\nconditions, the efficiency of the pumping system increased as the\r\njet densimetric Froude number decreased, and the time required for \r\ncomplete mixing was a fraction of the characteristic time, T ≤ V/Q \r\n(where V is the impoundment volume included between intake and jet \r\nelevations and Q is the pumped discharge).
\r\n\r\n\r\nRecommendations are made for the application of the\r\ngeneralized results and for the use of the simulation technique for\r\nlakes and reservoirs which are not closed systems.
\r\n\r\n \r\n\r\n\r\n\r\n\r\n\r\n" }, { "name": "Elachi, Charles", "degree": "PhD", "year": "1971", "title": "Electromagnetic Wave Propagation and Source Radiation in Space-Time Periodic Media", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-143115", "creators": [ { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-Charles", "display_name": "Elachi, Charles" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WYFR-GR84", "abstract": "The electromagnetic wave equations for the fields, potentials and Hertz vectors are derived and a Lorentz gauge is given for space-time dependent media. Electromagnetic wave propagation, electric and magnetic dipole radiation, and Cerenkov and transition radiation in sinusoidally space-time periodic dielectric, plasma and uniaxial plasma are studied and numerous radiation patterns are given. A special radiation effect in the uniaxial plasma is investigated. Finally the study is extended to general space-time periodic media (i.e., \u03b5 = \u03b50\u03b5r [1 + \u03b51 f(Kz - \u03a9t)] where f(\u03be) is a periodic function)." }, { "name": "Ellison, James Auby", "degree": "PhD", "year": "1971", "title": "Existence, Uniqueness, and Stability of Solutions of a Class of Nonlinear Partial Differential Equations", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:03292013-085108737", "creators": [ { "name": { "family": "Ellison", "given": "James Auby" }, "id": "Ellison-James-Auby", "display_name": "Ellison, James Auby" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/VBKZ-1R69", "abstract": "In this study we investigate the existence, uniqueness and asymptotic stability of solutions of a class of nonlinear integral equations which are representations for some time dependent non- linear partial differential equations. Sufficient conditions are established which allow one to infer the stability of the nonlinear equations from the stability of the linearized equations. Improved estimates of the domain of stability are obtained using a Liapunov Functional approach. These results are applied to some nonlinear partial differential equations governing the behavior of nonlinear continuous dynamical systems." }, { "name": "Everett, William Warren", "degree": "PhD", "year": "1971", "title": "On the Determination of the Properties of a Medium from its Reflection Coefficient", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03272013-095340267", "creators": [ { "name": { "family": "Everett", "given": "William Warren" }, "id": "Everett-William-Warren", "display_name": "Everett, William Warren" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/fsax-ks83", "abstract": "This thesis demonstrates how the parameters of a slightly\r\nnon-homogeneous medium can be derived approximately from the\r\nreflection coefficient.
\r\n\r\nTwo types of media are investigated. The first is described\r\nby the one-dimensional wave equation, the second by the more\r\ncomplex Timoshenko beam equation. In both cases, the media are\r\nassumed to be infinite in extent, with the media parameters\r\nbecoming homogeneous as the space variable approaches positive or\r\nnegative infinity.
\r\n\r\nMuch effort is placed in deriving properties of the reflection\r\ncoefficient for both cases. The wave equation is considered\r\nprimarily to introduce the techniques used to investigate the more\r\ncomplex Timoshenko equation. In both cases, an approximation is\r\nderived for one of the medium parameters involving the reflection\r\ncoefficient.
" }, { "name": "Hoerner, John Brent", "degree": "PhD", "year": "1971", "title": "Modal Coupling and Earthquake Response of Tall Buildings", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechThesis:10192017-153501109", "creators": [ { "name": { "family": "Hoerner", "given": "John Brent" }, "id": "Hoerner-John-Brent", "display_name": "Hoerner, John Brent" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/0H45-NM32", "abstract": "The major dynamic features of tall buildings are within the scope of a shear beam model. Herein the usual one-dimensional model is extended to three dimensions to include modes with translational and rotational components. The analysis is restricted to the continuous model with linear response.
\r\n\r\nA class of models for tall buildings is presented which possesses three sets of mutually orthogonal coupled modes. The amount of modal coupling is related to the eccentricities divided by the translational-torsional frequency differences. Strong modal coupling can occur if the eccentricities and frequency differences are small, as in a rectangular building with a smooth distribution of columns. A perturbation scheme is developed for buildings almost in this class. The perturbation method is applicable to buildings with nearly vertical mass and rigidity centers and with ith-modes of nearly the same shape.
\r\n\r\nRotational components of earthquake response in buildings primarily results from modal coupling, and it is shown that modal coupling can increase response on the building's perimeter. Furthermore, rectangular buildings with modal coupling can show a beating-type frequency response, for which the more usual r.m.s. combination should be replaced by an absolute sum. These effects can significantly increase certain response parameters. The corners of a rectangular building can have a 95% increase in shear, as compared with 30% implied by a 5% eccentricity in the codes. Base shears and overturning moments can be increased by 40%.
\r\n" }, { "name": "James, Edwin Charles", "degree": "PhD", "year": "1971", "title": "A Small Perturbation Theory for Cycloidal Propellers", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:03242015-131614633", "creators": [ { "name": { "family": "James", "given": "Edwin Charles" }, "id": "James-Edwin-Charles", "display_name": "James, Edwin Charles" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/Z979-K031", "abstract": "A hydromechanical theory is developed for cycloidal propellers\r\nfor two limiting modes of operation wherein U \u00bb \u03a9R and\r\nU \u00ab \u03a9R, with U the rectilinear propeller speed (speed of advance)\r\nand \u03a9R the rotational blade speed. A first order theory is developed\r\nfrom the basic principles of the kinematics and dynamics of fluid\r\nmotion and proceeds from the point of view of unsteady hydrofoil\r\ntheory.
\r\n\r\nExplicit expressions for the instantaneous forces and moments\r\nproduced by blade motions are presented. On the basis of these\r\nresults an optimization procedure is carried out which minimizes\r\nthe energy loss under the constraint of specified mean thrust. Under\r\noptimal conditions the propeller is found to possess high Froude efficiencies\r\nin both the high and low speed modes of propulsion. This\r\nefficiency is defined as the ratio of the average useful work obtained\r\nduring one cycle of propeller operation to the average power input\r\nrequired to sustain the motion of the propeller during the cycle.
" }, { "name": "Jeffers, Robert Humphrey Francis", "degree": "PhD", "year": "1971", "title": "On Two-Dimensional Waves of Finite Amplitude in Elastic Materials of Harmonic Type", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09272017-154819290", "creators": [ { "name": { "family": "Jeffers", "given": "Robert Humphrey Francis" }, "id": "Jeffers-Robert-Humphrey-Francis", "display_name": "Jeffers, Robert Humphrey Francis" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/C2ZB-4K70", "abstract": "In this thesis, two-dimensional waves of finite amplitude in\r\nelastic materials of harmonic type are considered. After specializing\r\nthe basic equations of finite elasticity to these materials,\r\nattention is restricted to plane motions and a new representation\r\ntheorem (analogous to the theorem of Lam\u00e9 in classical linear\r\nelasticity) for the displacements in terms of two potentials is derived.
\r\n\r\n\r\nThe two-dimensional problem of the reflection of an obliquely\r\nincident periodic wave from the free surface of a half-space composed\r\nof an elastic material of harmonic type is formulated. The incident\r\nwave is a member of a special class of exact one-dimensional solutions\r\nof the nonlinear equations for elastic materials of harmonic\r\ntype, and reduces upon linearization to the classical periodic \"shear\r\nwave\" of the linear theory.
\r\n\r\n\r\nA perturbation procedure for the construction of an approximate \r\nsolution of the reflection problem, for the case where the \r\nincident wave is of small but finite amplitude, is constructed. The\r\nprocedure involves series expansions in powers of the ration of the amplitude \r\nto the wavelength of the incident wave and is of the so-called\r\ntwo-variable type. The perturbation scheme is carried far\r\nenough to determine the second-order corrections to the linearized \r\ntheory.
\r\n\r\n\r\nA summary of results for the reflection problem is provided,\r\nin which nonlinear effects on the reflection pattern, on the particle\r\ndisplacements at the free surface and on the behavior at large depth\r\nin the half-space are detailed.
" }, { "name": "Kasper, Dennis Robert", "degree": "PhD", "year": "1971", "title": "Theoretical and Experimental Investigations of the Flocculation of Charged Particles in Aqueous Solution by Polyelectrolytes of Opposite Charge", "advisor": "Morgan, James J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04232014-095415213", "creators": [ { "name": { "family": "Kasper", "given": "Dennis Robert" }, "id": "Kasper-Dennis-Robert", "display_name": "Kasper, Dennis Robert" } ], "advisors": [ { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/K31R-A990", "abstract": "An electrostatic mechanism for the flocculation of charged particles by polyelectrolytes of opposite charge is proposed. The difference between this and previous electrostatic coagulation mechanisms is the formation of charged polyion patches on the oppositely charged surfaces. The size of a patch is primarily a function of polymer molecular weight and the total patch area is a function of the amount of polymer adsorbed. The theoretical predictions\r\nof the model agree with the experimental dependence of the\r\npolymer dose required for flocculation on polymer molecular weight and solution ionic strength.
\r\n\r\nA theoretical analysis based on the Derjaguin-Landau, Verwey- Overbeek electrical double layer theory and statistical mechanical treatments of adsorbed polymer configurations indicates that flocculation of charged particles in aqueous solutions by polyelectrolytes of opposite charge does not occur by the commonly accepted polymerbridge mechanism.
\r\n\r\nA series of 1, 2-dimethyl-5 -vinylpyridinium bromide polymers with a molecular weight range of 6x10^3 to 5x10^6 was synthesized and used to flocculate dilute polystyrene latex and silica suspensions in solutions of various ionic strengths. It was found that with high molecular weight polymers and/or high ionic strengths the polymer\r\ndose required for flocculation is independent of molecular weight. With low molecular weights and/or low ionic strengths, the flocculation dose decreases with increasing molecular weight.
\r\n" }, { "name": "Kim, Jong Hyun", "degree": "PhD", "year": "1971", "title": "The Unsteady Cavity in Internal Flows", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112018-095816439", "creators": [ { "name": { "family": "Kim", "given": "Jong Hyun" }, "id": "Kim-Jong-Hyun", "display_name": "Kim, Jong Hyun" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Q343-FG73", "abstract": "The problems of the two-dimensional unsteady cavity in internal flow are treated and linear theories are developed. In Part I, the two- dimensional supercavitating flow past a flat plate heaving and pitching with small amplitudes in a choked tunnel is investigated and a linearized solution is obtained using the acceleration potential. The flat plate is inclined at a small angle of attack to the oncoming flow and the cavity pressure is assumed to be constant. Force and moment coefficients are calculated for the case of the foil placed in the middle of the walls as functions of reduced frequency and the ratio of tunnel height to chord length. The pressure disturbances caused by the unsteady motion of the foil do not die out far upstream; these also depend on the chord-tunnel height ratio and reduced frequency.
\r\n\r\nAnother type of cavity problem in an internal flow is studied in Part II. Here, the finite cavity flow over a wedge held stationary in the middle of a tunnel is investigated. A salient feature of the problem is that the mass oscillation is allowed. Also the pressure on the cavity is allowed to vary in a prescribed manner. The problem is linearized using the complex perturbation velocity and the formal solution is obtained. The choked case in the presence of the overall mass fluctuation is obtained as a limiting case. Throughout the analysis, it is assumed that the change of the cavity length with time is small.
\r\n" }, { "name": "Kurtin, Stephen L.", "degree": "PhD", "year": "1971", "title": "Current Flow in Thin Solid Films: Thermionic Emission and Tunneling", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112018-102411958", "creators": [ { "name": { "family": "Kurtin", "given": "Stephen L." }, "id": "Kurtin-Stephen-L", "display_name": "Kurtin, Stephen L." } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Y9SR-D889", "abstract": "Current flow in metal-GaSe-metal sandwiches is investigated. These structures are particularly well suited to the study of current flow mechanisms because sandwiches containing uniform, single crystal films of gallium selenide can be easily fabricated. The well-defined nature of these structures allows sufficient a priori knowledge of their properties to make quantitative calculation of the predictions of appropriate models of current flow meaningful.
\r\n\r\nAs discussed in Part I, for gallium selenide films between 200 \u00c5 and 1000 \u00c5 thick, experimentally observed currents are in excellent agreement with a simple model of thermionic contact-limited current flow. This investigation presents the first unequivocal evidence for contact-limited thermionic currents in solids.
\r\n\r\nIn Part II films less than 100 \u00c5 thick are studied. For this thickness range, direct, inter-electrode tunneling is shown to be the dominant mechanism of current flow and an accurate energy-momentum dispersion relation within the forbidden gap of GaSe is obtained. This work represents the first quantitative calculation of tunneling currents in a metal-insulator-metal structure with all parameters relevant to the experiment independently determined.
\r\n" }, { "name": "Langford, William Finlay", "degree": "PhD", "year": "1971", "title": "Bifurcation Theory of Nonlinear Boundary Value Problems", "advisor": "Keller, Herbert Bishop", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082013-100223262", "creators": [ { "name": { "family": "Langford", "given": "William Finlay" }, "id": "Langford-William-Finlay", "display_name": "Langford, William Finlay" } ], "advisors": [ { "name": { "family": "Keller", "given": "Herbert Bishop" }, "id": "Keller-H-B", "role": "advisor", "display_name": "Keller, Herbert Bishop" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/BP03-ZM29", "abstract": "The theory of bifurcation of solutions to two-point boundary\r\nvalue problems is developed for a system of nonlinear first order\r\nordinary differential equations in which the bifurcation parameter is\r\nallowed to appear nonlinearly. An iteration method is used to\r\nestablish necessary and sufficient conditions for bifurcation and to\r\nconstruct a unique bifurcated branch in a neighborhood of a bifurcation\r\npoint which is a simple eigenvalue of the linearized problem. The\r\nproblem of bifurcation at a degenerate eigenvalue of the linearized\r\nproblem is reduced to that of solving a system of algebraic equations.\r\nCases with no bifurcation and with multiple bifurcation at a\r\ndegenerate eigenvalue are considered.
\r\n\r\nThe iteration method employed is shown to generate\r\napproximate solutions which contain those obtained by formal\r\nperturbation theory. Thus the formal perturbation solutions are\r\nrigorously justified. A theory of continuation of a solution branch\r\nout of the neighborhood of its bifurcation point is presented. Several\r\ngeneralizations and extensions of the theory to other types of\r\nproblems, such as systems of partial differential equations, are\r\ndescribed.
\r\n\r\nThe theory is applied to the problem of the axisymmetric\r\nbuckling of thin spherical shells. Results are obtained which\r\nconfirm recent numerical computations.
" }, { "name": "Madhukar, Anupam", "degree": "PhD", "year": "1971", "title": "Theory of s-d Exchange Scattering in Dilute Magnetic Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07242014-134709339", "creators": [ { "name": { "family": "Madhukar", "given": "Anupam" }, "id": "Madhukar-Anupam", "display_name": "Madhukar, Anupam" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/A2J0-9P67", "abstract": "The problem of s-d exchange scattering of conduction electrons\r\noff localized magnetic moments in dilute magnetic alloys is considered\r\nemploying formal methods of quantum field theoretical scattering. It\r\nis shown that such a treatment not only allows for the first time, the\r\ninclusion of multiparticle intermediate states in single particle\r\nscattering equations but also results in extremely simple and straight\r\nforward mathematical analysis. These equations are proved to be\r\nexact in the thermodynamic limit. A self-consistent integral equation\r\nfor electron self energy is derived and approximately solved. The\r\nground state and physical parameters of dilute magnetic alloys are\r\ndiscussed in terms of the theoretical results. Within the approximation\r\nof single particle intermediate states our results reduce to\r\nearlier versions. The following additional features are found as a\r\nconsequence of the inclusion of multiparticle intermediate states;
\r\n\r\n(i) A non analytic binding energy is pre sent for both,\r\nantiferromagnetic (J < o) and ferromagnetic (J > o)\r\ncouplings of the electron plus impurity system.
\r\n\r\n(ii) The correct behavior of the energy difference of the\r\nconduction electron plus impurity system and the\r\nfree electron system is found which is free of unphysical\r\nsingularities present in earlier versions\r\nof the theories.
\r\n\r\n(iii) The ground state of the conduction electron plus\r\nimpurity system is shown to be a many-body condensate\r\nstate for J < o and J > o, both. However,\r\na distinction is made between the usual terminology\r\nof \"Singlet\" and \"Triplet\" ground states and nature\r\nof our ground state.
\r\n\r\n(iv) It is shown that a long range ordering, leading to\r\nan ordering of the magnetic moments can result\r\nfrom a contact interaction such as the s-d exchange\r\ninteraction.
\r\n\r\n(v) The explicit dependence of the excess specific heat\r\nof the Kondo systems is obtained and found to be\r\nlinear in temperatures as T\u2192 o and T \u2113nT for\r\n0.3 T_K \u2264 T \u2264 0.6 T_K. A rise in (\u0394C/T) for\r\ntemperatures in the region 0 < T \u2264 0.1 T_K is\r\npredicted. These results are found to be in excellent\r\nagreement with experiments.
\r\n\r\n(vi) The existence of a critical temperature for Ferromagnetic\r\ncoupling (J > o) is shown. On the basis of\r\nthis the apparent contradiction of the simultaneous\r\nexistence of giant moments and Kondo effect is\r\nresolved.
\r\n " }, { "name": "McFarlane, Harold Finley", "degree": "PhD", "year": "1971", "title": "Pulsed Neutron Experiments in Graphite", "advisor": "Shapiro, Jerome L.; Corngold, Noel Robert", "url": "https://resolver.caltech.edu/CaltechTHESIS:07102014-141504536", "creators": [ { "name": { "family": "McFarlane", "given": "Harold Finley" }, "id": "McFarlane-Harold-Finley", "display_name": "McFarlane, Harold Finley" } ], "advisors": [ { "name": { "family": "Shapiro", "given": "Jerome L." }, "id": "Shapiro-J-L", "role": "advisor", "display_name": "Shapiro, Jerome L." }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "advisor", "display_name": "Corngold, Noel Robert" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/GJ42-CD26", "abstract": "Detailed pulsed neutron measurements have been performed\r\nin graphite assemblies ranging in size from 30.48 cm x 38.10 cm x 38.10 cm to 91.44 cm x 66.67 cm x 66.67 cm. Results of the measurement have been compared to a modeled theoretical computation.
\r\n\r\nIn the first set of experiments, we measured the effective decay constant of the neutron population in ten graphite stacks as a function of time after the source burst. We found the decay to be non-exponential in the six smallest assemblies, while in three larger assemblies the decay was exponential over a significant portion of the total measuring interval. The decay in the largest\r\nstack was exponential over the entire ten millisecond measuring interval. The non-exponential decay mode occurred when the effective decay constant exceeded 1600 sec^( -1).
\r\n\r\nIn a second set of experiments, we measured the spatial\r\ndependence of the neutron population in four graphite stacks as a function of time after the source pulse. By doing an harmonic analysis of the spatial shape of the neutron distribution, we were able to compute the effective decay constants of the first two spatial modes. In addition, we were able to compute the time dependent\r\neffective wave number of neutron distribution in the stacks.
\r\n\r\nFinally, we used a Laplace transform technique and a\r\nsimple modeled scattering kernel to solve a diffusion equation for the time and energy dependence of the neutron distribution in the graphite stacks. Comparison of these theoretical results with the results of the first set of experiments indicated that more exact theoretical analysis would be required to adequately describe the experiments.
\r\n\r\nThe implications of our experimental results for the theory of pulsed neutron experiments in polycrystalline media are discussed\r\nin the last chapter.
\r\n" }, { "name": "Neville, Richard Coulston", "degree": "PhD", "year": "1971", "title": "Some Electronic Properties of ZnO and SrTiO\u2083", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:06132018-121037092", "creators": [ { "name": { "family": "Neville", "given": "Richard Coulston" }, "id": "Neville-Richard-Coulston", "display_name": "Neville, Richard Coulston" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZF7V-1G45", "abstract": "The surface barrier systems consisting of gold and palladium on both chemically prepared and cleaved zinc oxide have been studied in detail.\r\nSurface barrier energies on non-degenerate chemically prepared zinc oxide were found to be 0.66 and 0.60 eV respectively for gold and palladium, as determined by four independent methods: photoresponse, current-voltage characteristics, thermal activation energy, and capacitance variation with voltage. The Bethe diode theory as modified by image force lowering was found to be an excellent description of the voltage-current characteristics. Thermionic field and pure tunneling currents were observed for surface barriers on degenerate zinc oxide at room and liquid nitrogen temperatures, respectively. The voltage dependence of these currents was in excellent agreement with the thermionic field and tunneling theories. Although dependence on impurity concentration was functionally in agreement with theory the predicted currents were too high by an order of magnitude. This effect is attributed to deficiencies in the theory.
\r\n\r\nThe second material investigated was strontium titanate. The surface barrier systems consisting of gold, palladium, copper, and indium on both chemically prepared and cleaved single crystal strontium titanate were examined in detail. Surface barrier energies were determined, and the current versus voltage characteristics were examined in light of Bethe diode theory as modified by image force lowering. The relative permittivity of strontium titanate was determined over a temperature range from\r\n4.2\u00b0K to 300\u00b0K as a function of applied electrical bias. No evidence of a ferroelectric transition was observed. A phenomonological description of the free energy involved in the titanium atom motion, which is responsible for the large relative permittivity, was derived. Evidence for domain interaction is discussed.
\r\n" }, { "name": "Nielsen, Richard Carl", "degree": "PhD", "year": "1971", "title": "Transient Heating in B\u00e9nard Convection", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10112005-093233", "creators": [ { "name": { "family": "Nielsen", "given": "Richard Carl" }, "id": "Nielsen-Richard-Carl", "display_name": "Nielsen, Richard Carl" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/WPPS-5214", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperimental results are presented for a study of the effects of time-dependent heating on Benard convection, where the fluids were 5 centistoke (cs), 100 cs and 500 cs viscosity grades of silicone oil. Fluid layer depths were 0.00635m, 0.01270m and 0.01905m. For each run the heat flux at the lower surface was approximately constant, which in dimensionless units was between [...] and [...]. The study examined the effects of different heating rates on the onset of convection, the change of the Rayleigh number with time and the development of motion. Visual observations were made from shadowgraph images, which were recorded photographically.\r\n\r\nA supplementary analytical analysis of the onset of motion was performed. The results of the work support the trends of the critical time data found in the experiments.\r\n\r\nOn the basis of the experimental results the conculsions are that as the heat flux at the lower surface is increased, the temperature difference required for the initiation of convection increases while the time to the onset of motion decreases. For the higher heating rates a \"new\" small closed cell pattern is observed shortly after the onset of motion. This pattern does not appear in the steady-state system. Because of the \"large\" (approximately greater than 100) Prandtl number, specifying the time and the heat flux at the lower surface is sufficient to characterize the state of the fluid layer." }, { "name": "Okoye, Josephat Kanayo", "degree": "PhD", "year": "1971", "title": "Characteristics of Transverse Mixing in Open-Channel Flows", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05142018-094038251", "creators": [ { "name": { "family": "Okoye", "given": "Josephat Kanayo" }, "id": "Okoye-Josephat-Kanayo", "display_name": "Okoye, Josephat Kanayo" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "envreng" ], "doi": "10.7907/JTHM-FS72", "abstract": "The transverse spreading of a plume generated by a point source in a uniform open-channel flow is investigated. A neutrally buoyant tracer was injected continuously at ambient velocity through a small round source at a point within the flow. Tracer concentration was measured in situ at several points downstream of the source using conductivity probes.
\r\n\r\nTracer concentration was analyzed in two phases.
\r\n\r\nIn Phase I, time-averaged concentration was evaluated, its distribution within the plume determined, and characteristic coefficients of transverse mixing calculated. It was shown that the transverse mixing coefficient varied with the flow level and was highest near the water surface where the flow velocity was greatest. In contrast to previous speculation, the ratio of the depth-averaged coefficient of transverse mixing -Dz to the product of the (bed) shear velocity u* and the flow depth d was not a constant but depended on the aspect ratio \u03bb= d/W, where W = flume width. For laboratory experiments-Dz/u*d decreased from o. 24 to 0.093\r\nas \u03bb increased from O. 015 to O. 200.
\r\n\r\nIn Phase II, the temporal fluctuation of tracer concentration was studied in three sections. In the first, the intermittency factor technique was used to delineate three regions of the plume cross section: an inner core where tracer concentration c(t) was always greater than the background Cb; an intermittency region where c(t) was only intermittently greater than Cb; and the outer region\r\nWhere cb was never exceeded. Dimensional analysis furnished universal curves for prediction of the geometric characteristics of the three regions. In the second section, the entire plume, at a fixed station, was treated as a fluctuating cloud. Variances characterizing the fluctuation of the plume centroid and the variation of the plume width were calculated and compared. In the third section, the intensity and probability density of the concentration fluctuations at fixed points were calculated. The distribution of the peak-to-average ratio was also determined.
\r\n\r\nFinally the results of the two phases of study were interrelated to evaluate their contributions to the transverse spreading of the plume.
\r\n" }, { "name": "Puckett, Jason Niles, Jr.", "degree": "PhD", "year": "1971", "title": "An Electrical and Statistical Study of Burst Noise", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042018-105756176", "creators": [ { "name": { "family": "Puckett", "given": "Jason Niles, Jr." }, "id": "Puckett-Jason-Niles", "display_name": "Puckett, Jason Niles, Jr." } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/D816-7C55", "abstract": "Burst noise is a normally undesirable phenomenon occasionally \r\nfound in bipolar semiconductors and other current carrying devices. It \r\nis an electrical fluctuation which exhibits itself as one or more rectangular \r\nwaveforms possessing constant amplitude but random pulse duration. The \r\nexperimental portion of this study relates only to burst noise in bipolar \r\ntransistors and operational amplifiers.
\r\n\r\nBurst noise is not Gaussian as are the more common fluctuations\r\nin semiconductors. That fact was established by estimation of the amplitude\r\ndistribution, a technique found to be sensitive in the\r\ndetection of burst noise obscured by quantities of conventional noise.
\r\n\r\nThe amplitude of burst noise varies with the parameters of\r\nbase-emitter, voltage temperature and source resistance. An exponential \r\nincrease of amplitude with Vbe and a lack of dependence on collector \r\nvoltage implied that the noise originates in the base-emitter junction.\r\nA noise magnitude linearly proportional to source resistance over several\r\ndecades leads one to infer the equivalent circuit of a current source\r\nbetween base and emitter. Current amplitudes of 10-10 to nearly 10-6\r\nampere p-p were observed.
\r\n\r\nBurst noise pulse durations were found as brief as 10 \u00b5sec and as \r\nlong as some 29 hours; neither an upper nor a lower bound was established. The \r\ntwo noise states (high and low, in the rectangular\r\nwaveform) were treated separately in the duration experiments. Careful\r\nmeasurements on the relative frequency with which the pulse occurred\r\ngave duration probability densities of 1/\u03c4 e -t/\u03c4 for each state.\r\nThat density also applies to a single particle alternately being trapped\r\nand escaping and is consistent with the physical theory due to Mead and\r\nWhittier relating burst noise to trapping phenomena. Measurements on\r\nnoise pulse durations in both states as a function of Vbe lent support \r\nto the theory and indicated both trapping and recombination-generation centers \r\nwere present in samples examined. Another theory, due to Leonard and Jaskolsky, \r\nwas found inconsistent with the evidence for burst noise's origin in the base-emitter \r\njunction. Duration versus temperature dependence indicated activation \r\nenergies of roughly .5 eV.
\r\n\r\nAlthough suggestions in the literature for the power spectrum of burst noise \r\nhave been inconsistent, digital spectral estimation and judicious use of a \r\nwave analyzer showed the spectrum to be flat at low frequencies and to fall as \r\n1/f2 at higher ones. Proceeding only from the measured pulse duration \r\nprobability density, the power spectrum was deduced on theoretical grounds \r\nfor the first time. The method entailed the derivation of burst noise's \r\nautocorrelation function which, when Fourier transformed, yielded
\r\n\r\nS(w) = 2/(\u03c41 + \u03c40)[(1/\u03c41 + 1/\u03c40)2 + w2]
\r\n\r\nwhere \u03c41 and \u03c40 are the average durations in the two noise estates.\r\nThe expression proved consistent with experiment.
\r\n\r\n" }, { "name": "Ramaswamy, Mathagondapally A.", "degree": "PhD", "year": "1971", "title": "Experimental Investigation of the Effect of Cooling on Near Wake of Circular Cylinder at Mach Number Six", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152011-112031398", "creators": [ { "name": { "family": "Ramaswamy", "given": "Mathagondapally A." }, "id": "Ramaswamy-Mathagondapally-A", "display_name": "Ramaswamy, Mathagondapally A." } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8ZZ8-PC49", "abstract": "An experimental investigation has been conducted to study the near wake of a two-dimensional circular cylinder of 0.2 in. diameter at M_\u221e = 6. Mean flow properties were determined from Pitot pressure, static pressure, and hot-wire recovery temperature measurements at free stream Reynolds number of 0.905 X 10^4 and 2.95 X 10^4 for both adiabatic and cooled models, the latter at 0.19 T_o.
\r\n\r\nThe near-wake was laminar for the adiabatic model at both\r\nthe Reynolds numbers tested. For the cold model, the near-wake was laminar for the lower Reynolds number and transition occurred in the near wake at the higher Reynolds number. The wake shocks, the shear layer edge and the thermal layer edge moved closer to the wake centerline with cooling and with increase in Reynolds number. The base pressure decreased with cooling and the sonic point moved closer to the model on cooling. In the recirculating region, the total temperature distributions exhibited a minimum close to the dividing stream line for all the cases, and the total temperature on the centerline was nearly constant and equal to the value at the rear stagnation point (0.5 T_o for the cold models) indicating that the heat transfer in this region was mainly by convection. The existence of a thin thermal layer on the base was evident for the cold models.
\r\n\r\nPreliminary experiments on the two-dimensionality of the\r\nflow and an emperical formulation for the viscous corrections to the measured Pitot pressure have been included in the Appendices.
\r\n" }, { "name": "Sharon, Thomas Edward", "degree": "PhD", "year": "1971", "title": "Magnetism in an Amorphous Fe-Pd-P Alloy System", "advisor": "Duwez, Pol E.; Tsuei, Chang-chyi", "url": "https://resolver.caltech.edu/CaltechTHESIS:04122018-091817826", "creators": [ { "name": { "family": "Sharon", "given": "Thomas Edward" }, "id": "Sharon-Thomas-Edward", "display_name": "Sharon, Thomas Edward" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." }, { "name": { "family": "Tsuei", "given": "Chang-chyi" }, "id": "Tsuei-C-C", "role": "advisor", "display_name": "Tsuei, Chang-chyi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/SKE6-7667", "abstract": "Amorphous alloys of composition FexPd80-xP20 (13 ≤ x ≤ 44) have been prepared by rapid quenching from the liquid state. The\r\nM\u00f6ssbauer effect in Fe57 has been used to study the magnetic\r\nproperties of these materials. The hyperfine field distributions have\r\nbeen determined from these experiments, as a function of composition\r\nand temperature. The results indicate that the electronic state of\r\nFe in these alloys remains essentially constant throughout the\r\ncomposition range, and that the Pd d band is filled by electron\r\ntransfer from phosphorus.
\r\n\r\nThe variation of the magnetic transition temperature with\r\ncomposition has been determined by combining the M\u00f6ssbauer effect\r\nresults with complementary magnetic measurements. There is a\r\nsharp change in the slope in this curve at x \u2243 26. Below this \r\nconcentration, the long range magnetic order which prevails in the higher\r\nFe concentration alloys has broken down, giving rise to a more\r\nlocal ordering.
\r\n\r\nThe M\u00f6ssbauer effect results confirm the existence of weakly \r\ncoupled Fe atoms in all the amorphous Fe-Pd-P alloys. These\r\natoms reside in low effective fields, and can participate in the\r\nspin-flip scattering process which produces a Kondo effect (resistivity\r\nminimum). The large critical concentration observed is also an\r\nindication that the spin correlations are greatly reduced in these\r\namorphous alloys.
" }, { "name": "Shollenberger, Carl Alvin", "degree": "PhD", "year": "1971", "title": "An Investigation of a Two-Dimensional Propulsive Lifting System", "advisor": "Lissaman, Peter B. S.; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:08312010-081235652", "creators": [ { "name": { "family": "Shollenberger", "given": "Carl Alvin" }, "id": "Shollenberger-Carl-Alvin", "display_name": "Shollenberger, Carl Alvin" } ], "advisors": [ { "name": { "family": "Lissaman", "given": "Peter B. S." }, "id": "Lissaman-P-B-S", "role": "advisor", "display_name": "Lissaman, Peter B. S." }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GZNT-1X61", "abstract": " Several aspects of the nonhomogeneous flow associated with a system combining lifting and propulsive requirements of an aircraft are considered in detail by analytical and experimental methods. The basic geometry of the problem is that of two lifting surfaces with an actuator disk located between them. The resulting flow consists of two regions of different total energies.\r\n\r\n Propulsive lift systems are prototypes of many similar multi-energy flow problems. The principles governing flow with energy addition are examined. Basic equations and boundary conditions are developed for the complete inviscid and incompressible analysis for the two-dimensional case. The corresponding flow singularities are discussed and the integral equations which completely specify the system are derived.\r\n \r\n The two special cases of small and large energy addition are considered in detail including solutions.\r\n\r\n A numerical procedure is developed to solve the full problem including allowance for the wake deflection. Appropriate vorticity forms are used to represent the entire system. Wake vorticity is provided the freedom to move in the plane. An iterative scheme is presented which rapidly converges to a solution for the magnitude and location of the system vorticity distributions. Forces and moments are evaluated on the propulsive lift system.\r\n\r\n Analytical results are given from the numerical solution for various values of the geometric and energy parameters. Comparison of the numerical result with the solutions for extreme values of energizing is given.\r\n\r\n Results from a wind tunnel study of the two-dimensional propulsive-lift system provide a check on the importance of real effects. Comparison of the analytical and experimental results is given in detail. The experimentally determined wake development is observed to be similar to the predicted shape. In addition, the lift augmentation is similar for the theoretical and experimental cases. Further, the airfoil pressure distributions and resulting pitching moments are seen to exhibit the behavior expected from the calculations.\r\n" }, { "name": "Sigal, Asher", "degree": "PhD", "year": "1971", "title": "An Experimental Investigation of the Turbulent Boundary Layer Over a Wavy Wall", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:09232010-101022816", "creators": [ { "name": { "family": "Sigal", "given": "Asher" }, "id": "Sigal-Asher", "display_name": "Sigal, Asher" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VK9A-XA44", "abstract": " An experimental investigation of turbulent boundary layer flow over wavy surfaces was conducted at low speed.\r\n\r\n Two models with the ratio of the amplitude to the wave length a/\u03bb = 0.03 and wave lengths \u03bb = 6\" and 12\" were tested in an open-circuit wind tunnel. The free stream velocity was 15.4 m/sec, giving Reynolds number Re = 2.54 X 10^4 per inch. Boundary-layer thickness varied from \u03b4 = 1.5\" to \u03b4 = 4. 1\" by means of boundary-layer trips of various height, in order to change the ratio \u03bb/6.\r\n \r\n The following measurements were taken:\r\n * Wall pressure distribution\r\n * Average velocity and turbulence level, using a single element hot-wire probe\r\n * Wall stress distribution, using Preston's tube\r\n * Static and total pressures\r\n * Turbulence intensities and shear stress using X-array hot-wire probe.\r\n\r\n An appreciable modulation of all the flow quantities, imposed by the wavy boundary, is observed throughout the investigation. Wall pressure is much lower than predicted by uniform, inviscid theory and is slightly non-symmetric. Wall stress distribution has a peak with C_f/C_fo = 1.2 upstream of the crest and a dip of C_f/C_fo = 0. 6 upstream of the trough. Static pressure decays exponentially in the outer layer while its gradient is decreased toward the surface in the wall layer.\r\n\r\n The turbulence intensities and shear stress distributions near the wall show oscillatory modulation superimposed on the reference flat plate profiles. The amplitude of the oscillations decay exponentially toward the edge of the layer, so that in the outer part of the layer the turbulence quantities are practically independent of the longitudinal position.\r\n\r\n It was found that Coles' Law of the Wall does not apply in the present situation because of the modulation of the slope of the semi-logarithmic portion of the velocity profiles. A presentation of velocity profiles is suggested through the use of total velocity defined by U^t = (U^2 + 2(p\u2013p_\u221e)/p)^(1/2). This quantity obeys the Law of the Wake. Mixing length and eddy viscosity profiles based on the derivative \u2202U^t/\u2202y are reduced into one curve which is the reference flat plate distribution.\r\n" }, { "name": "Singh, Nagendra", "degree": "PhD", "year": "1971", "title": "Radiation from a Short Electric Dipole Antenna in a Hot Uniaxial Plasma", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07232014-083706438", "creators": [ { "name": { "family": "Singh", "given": "Nagendra" }, "id": "Singh-Nagendra", "display_name": "Singh, Nagendra" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/R9Z4-RG15", "abstract": "The effects of electron temperature on the radiation fields\r\nand the resistance of a short dipole antenna embedded in a uniaxial\r\nplasma have been studied. It is found that for \u03c9 < \u03c9_p the antenna \r\nexcites two waves, a slow wave and a fast wave. These waves propagate\r\nonly within a cone whose axis is parallel to the biasing magnetostatic\r\nfield B_o and whose semicone angle is slightly less than sin ^(-1) (\u03c9/\u03c9_p).\r\nIn the case of \u03c9 > \u03c9_p the antenna excites two separate modes of \r\nradiation. One of the modes is the electromagnetic mode, while the\r\nother mode is of hot plasma origin. A characteristic interference\r\nstructure is noted in the angular distribution of the field. The far\r\nfields are evaluated by asymptotic methods, while the near fields are\r\ncalculated numerically. The effects of antenna length \u2113, electron\r\nthermal speed, collisional and Landau damping on the near field patterns \r\nhave been studied.
\r\n\r\nThe input and the radiation resistances are calculated and are\r\nshown to remain finite for nonzero electron thermal velocities. The\r\neffect of Landau damping and the antenna length on the input and\r\nradiation resistances has been considered.
\r\n\r\nThe radiation condition for solving Maxwell's equations is\r\ndiscussed and the phase and group velocities for propagation given.\r\nIt is found that for \u03c9 < \u03c9_p in the radial direction (cylindrical coordinates) the power flow is in the opposite direction to that of the phase propagation. For \u03c9 > \u03c9_p the hot plasma mode has similar characteristics.
\r\n\r\n" }, { "name": "Skattum, Knut Sverre", "degree": "PhD", "year": "1971", "title": "Dynamic Analysis of Coupled Shear Walls and Sandwich Beams", "advisor": "Jennings, Paul C.", "url": "https://resolver.caltech.edu/CaltechThesis:10192017-151943526", "creators": [ { "name": { "family": "Skattum", "given": "Knut Sverre" }, "id": "Skattum-Knut-Sverre", "display_name": "Skattum, Knut Sverre" } ], "advisors": [ { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/SMJ0-W112", "abstract": "A study is made of the free vibration of planar coupled shear walls, a common lateral load-resisting configuration in building construction where two walls are coupled together by a system of discrete spandrel beams. The differential equations and boundary conditions are obtained by the variational method, and by assuming that the spandrels can be replaced by a continuous system of laminae, or small beams.
\r\n\r\nNatural frequencies and mode shapes are determined, and the results are presented in a number of figures from which the natural frequencies of any coupled shear wall can be extracted. The importance of including vertical displacement in the analysis is discussed, and a study of the effect of neglecting the vertical inertia term is given. These cases are illustrated with graphs and with one specific example. Investigations are also made of the asymptotic behavior of the system as the spandrels become weak, as they become stiff, and as the frequencies become large.
\r\n\r\nFinally, the theory of sandwich beams is presented and compared to that for coupled shear walls. It is observed that for most cases of constant properties, the differential equations (and boundary conditions) reduce to the same mathematical form for both theories.
" }, { "name": "Stahl, Karl John", "degree": "PhD", "year": "1971", "title": "Dynamic Response of Circular Plates Subjected to Moving Massive Loads", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04182018-103519413", "creators": [ { "name": { "family": "Stahl", "given": "Karl John" }, "id": "Stahl-Karl-John", "display_name": "Stahl, Karl John" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/1R1H-0G28", "abstract": "Techniques are presented for studying the dynamic response of circular disks excited by moving loads. The loading system, consisting of a mass, spring, and dashpot, travels in a circular path concentric with the disk at constant angular velocity. For cases involving elastically-supported rigid disks, the equations of motion for the disk and moving load may be written as a set of coupled Hill\u00ad\r\nMathieu equations, typical of moving mass problems. By applying relatively simple transformations the equations may be rewritten as a set of coupled linear differential equations with constant coefficients. The problem is then reduced to solving an ordinary eigenvalue problem.
\r\n\r\nWhen the eigenvalues are pure imaginary numbers, they\r\ncorrespond to the frequency components in the motion of the moving mass, and describe the disk motion as well. In certain regions the eigenvalues have positive real parts, corresponding to motions which are unbounded in time. There are three distinct regions of instability which appear in the rigid disk problem.\tA stiffness in stability region occurs immediately above the critical speed of the disk, and is caused by load stiffness. At higher speeds, a region of instability due to modal coupling appears. Finally, if the load speed exceeds a certain terminal velocity (determined primarily by the mass of the load), an unstable solution will always exist.
\r\n\r\nThe dynamic response of circular elastic disk s with similar loading is investigated using the conventional eigenfunction expansion technique. The system of coupled Hill-Mathieu equations obtained by applying this method r educes to an ordinary eigenvalue problem when certain transformations are made. Thus, many modes may be included in the solution, although it is generally sufficient to consider only a few modes. Solutions to the eigenvalue problem reveal regions of instability directly analogous to those observed in the rigid disk examples.
\r\n" }, { "name": "Vijayaraghavan, Alwar", "degree": "PhD", "year": "1971", "title": "Free and Forced Oscillations in a Class of Piecewise-Linear Dynamic Systems", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:12062017-105553336", "creators": [ { "name": { "family": "Vijayaraghavan", "given": "Alwar" }, "id": "Vijayaraghavan-Alwar", "display_name": "Vijayaraghavan, Alwar" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/11SF-5Q09", "abstract": "A study is made of the free and forced oscillations in dynamic\r\nsystems with hysteresis, on the basis of a piecewise-linear, nonlinear\r\nmodel proposed by Reid. The existence, uniqueness, boundedness\r\nand periodicity of the solutions for a single degree of freedom\r\nsystem are established under appropriate conditions using topological\r\nmethods and Brouwer's fixed-point theorem. Exact periodic solutions\r\nof a specified symmetry class are obtained and their stability is also\r\nexamined. Approximate solutions have been derived by the Krylov-Bogoliubov-Van der Pol\r\nmethod and comparison is made with the exact solutions.
\r\n\r\n\r\nFor dynamic systems with several degrees of freedom, consisting\r\nof \"Reid oscillators\", exact periodic solutions are derived under\r\ncertain restricted forms of \"modal excitation\" and the stability of the\r\nperiodic solutions has been studied. For a slightly more general form\r\nof sinusodial excitation, a simple way of obtaining approximate solutions\r\nby \"apparent superposition\" has been indicated. Examples are\r\npresented on the exact and approximate periodic solutions in a dynamic\r\nsystem with two degrees of freedom.
" }, { "name": "Willus, Charles Arthur", "degree": "PhD", "year": "1971", "title": "An Experimental Investigation of Particle Motion in Liquid Fluidized Beds", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-09292006-113348", "creators": [ { "name": { "family": "Willus", "given": "Charles Arthur" }, "id": "Willus-Charles-Arthur", "display_name": "Willus, Charles Arthur" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/2086-K074", "abstract": "A laboratory study was made on particle motion in liquid fluidized beds. In Part 1, experiments made in a bed of 4-inch inside diameter with a large length-to-diameter ratio of 24 to 1 are described. Particle motion in the bed was found to be essentially a diffusion process. Diffusion coefficients for motion in the vertical direction were measured for glass beads of .236-inch diameter at a range of average bead concentrations. Vertical diffusion was independent of radial position in the bed.\r\n\r\nThe experimental findings on particle diffusion in the bed were compared to principles of diffusion of a turbulent fluid. A significant correlation between two successive vertical step lengths of short duration suggested that a bead is within an eddy of beads and fluid for a short time. The diffusion coefficients of the beads were much larger than the diffusion coefficients of the turbulent fluid in the absence of the beads, indicating that particles in a liquid fluidized bed augment instabilities.\r\n\r\nSteady and quasi-steady patterns of particle circulation were observed in both a cylindrical bed with a length-to-diameter ratio of 5 to 1 and in beds of conical shape, and are described in Part 2. Weak waves also formed in this cylindrical bed; the observed propagating speed compared roughly to that estimated using the theory of kinematical waves.\r\n\r\nPhotographic materials on pages 17, 18, 65, and 94 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered." }, { "name": "Wilson, Michael Barron", "degree": "PhD", "year": "1971", "title": "A Michell Oseen-Flow Theory for Thin Ships", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-154052", "creators": [ { "name": { "family": "Wilson", "given": "Michael Barron" }, "id": "Wilson-Michael-Barron", "display_name": "Wilson, Michael Barron" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/4ZZV-F953", "abstract": "A linear theory is developed for the steady free surface flow of a viscous fluid past a general system of submerged flow disturbances (a point mass source and three orthogonal point forcelets). The viscous character of the flow is approximated by using the Oseen linearization of the Navier-Stokes equations.
\r\n\r\nSolution of the fundamental problem (point flow disturbances) using double Fourier transforms furnishes formal representations of all the interesting flow quantities: the wave height, the three components of the perturbation velocity, and the dynamic pressure. Asymptotic expansions are presented for the 'free' or propagating parts of the flow quantities as they would appear far downstream.
\r\n\r\nCenterplane distributions of the flow disturbance singularities are used to model the flow about a symmetric thin ship. From the application of the momentum theorem, general formulae are derived for the total fluid drag on a ship in a viscous flow. These results are then specialized for use with the Oseen equations. The wave resistance formulae are of particular interest because they contain the strengths of the three forcelet distributions as well as the mass source distribution.
\r\n\r\nA numerical example of a wave resistance calculation is presented in which the four distribution functions are prescribed. The results are compared to known experimental curves. These indicate that significant features in the character of ship wave resistance can be qualitatively described by including the strengths of local viscous forces acting on the body.
" }, { "name": "Baskes, Michael I.", "degree": "PhD", "year": "1970", "title": "A Generalized Treatment of the Order-Disorder Transformation in Alloys and its Effect on their Magnetic Properties", "advisor": "Buffington, Francis S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09102015-152741604", "creators": [ { "name": { "family": "Baskes", "given": "Michael I." }, "id": "Baskes-Michael-I", "display_name": "Baskes, Michael I." } ], "advisors": [ { "name": { "family": "Buffington", "given": "Francis S." }, "id": "Buffington-Francis-S", "role": "advisor", "display_name": "Buffington, Francis S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/GH0V-AX93", "abstract": "A theory of the order-disorder transformation is developed in\r\ncomplete generality. The general theory is used to calculate long\r\nrange order parameters, short range order parameters, energy, and\r\nphase diagrams for a face centered cubic binary alloy. The theoretical\r\nresults are compared to the experimental determination of the copper-gold\r\nsystem, Values for the two adjustable parameters are obtained.
\r\n\r\nAn explanation for the behavior of magnetic alloys is developed,\r\nCurie temperatures and magnetic moments of the first transition series\r\nelements and their alloys in both the ordered and disordered states are\r\npredicted. Experimental agreement is excellent in most cases. It is\r\npredicted that the state of order can effect the magnetic properties of\r\nan alloy to a considerable extent in alloys such as Ni3Mn. The values\r\nof the adjustable parameter used to fix the level of the Curie temperature,\r\nand the adjustable parameter that expresses the effect of ordering on the\r\nCurie temperature are obtained.
" }, { "name": "Bilow, Henry Joel", "degree": "PhD", "year": "1970", "title": "Electromagnetic Wave Propagation and Scattering in a Randomly-Inhomogeneous Dielectric Sphere", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:08282015-131240078", "creators": [ { "name": { "family": "Bilow", "given": "Henry Joel" }, "id": "Bilow-Henry-Joel", "display_name": "Bilow, Henry Joel" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CMVZ-RR78", "abstract": "Electromagnetic wave propagation and scattering in a sphere composed of an inhomogeneous medium having random variations in its permittivity are studied by utilizing the Born approximation in solving the vector wave equation. The variations in the permittivity are taken to be isotropic and homogeneous, and are spatially characterized by a Gaussian correlation function. Temporal variations in the medium are not considered.
\r\n\r\nTwo particular problems are considered: i) finding the far-zone electric field when an electric or magnetic dipole is situated at the center of the sphere, and ii) finding the electric field at the sphere's center when a linearly polarized plane wave is incident upon it. Expressions are obtained for the mean-square magnitudes of the scattered field components; it is found that the mean of the product of any two transverse components vanishes. The cases where the wavelength is much shorter than correlation distance of the medium and where it is much longer than it are both considered.
\r\n" }, { "name": "Blumenthal, Donald Lawrence", "degree": "PhD", "year": "1970", "title": "Experimental Study of Satellite Wakes in a Simulated Ionospheric Plasma", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:07092010-100552106", "creators": [ { "name": { "family": "Blumenthal", "given": "Donald Lawrence" }, "id": "Blumenthal-Donald-Lawrence", "display_name": "Blumenthal, Donald Lawrence" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PYM3-H107", "abstract": "Wakes of simple bodies (discs, strips) were investigated using an electrostatically accelerated stream of argon \r\n\r\nions and electrons. Typical conditions are: beam ion energy is 80 eV, ion density is 10^7-10^8 cm^(-3), electron \r\n\r\ntemperature 1-3 eV, ion thermal speed very small compared to mean ion velocity. The dimensionless parameters \r\n\r\nclosely approximate satellite flight conditions, with the exception of the electron-ion temperature ratio, which \r\n\r\nis near unity in flight and large in these experiments.\r\n\r\nThe dependence of principal near wake features (such as the large ion current peak on the centerline behind the \r\n\r\nbody) on the shape of the body was investigated systematically. All trends can be explained qualitatively by \r\n\r\nrecognizing the dominant role of those portions of the sheath where the free stream ion velocity is tangential to \r\n\r\nthe body.\r\n\r\nThe far wake of a strip (downstream of the ion current peak) displays a decaying radial distribution on the scale \r\n\r\nof the body size, somewhat similar to what is expected from a neutral gas. For axial symmetric models, the far \r\n\r\nwake displays a small structure on the scale of the ion current peak. The evolution of these disturbances\r\nis qualitatively explained by a simple, linearized two fluid theory. These features are initiated by the \r\n\r\ninteraction of the inwardly deflected ion streams behind the body. At least in certain regions of the flow field, \r\n\r\nthis interaction involves two-humped ion distribution functions, which may play a role in the further development \r\n\r\nof the far wake.\r\n\r\nThe effects on the simulation of varying the vacuum chamber background pressure was also examined in detail.\r\n" }, { "name": "Cassady, Phillip Earl", "degree": "PhD", "year": "1970", "title": "An Investigation of Non-Equilibrium Effects in an Argon Free-Jet Plasma", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012010-092851271", "creators": [ { "name": { "family": "Cassady", "given": "Phillip Earl" }, "id": "Cassady-Phillip-Earl", "display_name": "Cassady, Phillip Earl" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WHYP-RZ81", "abstract": "The non-equilibrium effects present in the formation of a strong normal shock wave in a low density, slightly ionized argon flow field, particularly as evidenced by the appearance of a dark region upstream of the shock wave, have been analyzed both theoretically and experimentally. A model for the flow through the shock wave was formulated which incorporates a quantum mechanical theory to explain the existence of the dark region, and the problem was solved numerically to yield flow field property distributions. A precursor region of high electron temperature was found to exist upstream of the main body of the heavy-particle shock wave.\r\n\r\nAn experimental investigation of the phenomenon was carried out in an arc heated free jet flow field. A test facility was constructed in which the goal has been to attain operation at low enough enthalpies to allow precise and extensive diagnostic testing while still high enough to exhibit the interesting non-equilibrium effects. Extensive study was carried out on the effect of electrode design and gas flow phenomena on the stability of the arc discharge. The completed unit was instrumented fully for measurement of the operating parameters and a computer program was developed to monitor its operation as a supply of slightly ionized argon for free-jet experiments.\r\n\r\nThe non-equilibrium aspects of the free-jet were analyzed both theoretically and experimentally. A theoretical model was developed and numerically solved for the free-jet expansion of slightly ionized argon. Pitot pressure measurements were completed and compared favorably with predictions calculated from this theoretical model.\r\n\r\nElectron temperature and ion density profiles were measured both along the axis of the empty free-jet and through the normal shock wave in front of a cooled blunt body using a new type of cooled Langmuir probe, the operation of which was theoretically analyzed. The existence of a region of electron temperature in front of a strong normal shock wave coincident with the observed dark region was experimentally verified." }, { "name": "Casten, Richard Guy", "degree": "PhD", "year": "1970", "title": "Methods for Deriving Conservation Laws", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04192012-114039484", "creators": [ { "name": { "family": "Casten", "given": "Richard Guy" }, "id": "Casten-Richard-Guy", "display_name": "Casten, Richard Guy" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/RMSA-DS35", "abstract": "Systematic methods are used to find all possible conservation laws of a given type for certain systems of partial differential equations, including some from fluid mechanics. The necessary and sufficient conditions for a vector to be divergence-free are found in the form of a system of first order, linear, homogeneous partial differential equations, usually overdetermined. Incompressible, inviscid fluid flow is treated in the unsteady two-dimensional and steady three-dimensional cases. A theorem about the degrees of freedom of partial differential equations, needed for finding conservation laws, is proven. Derivatives of the dependent variables are then included in the divergence-free vectors. Conservation laws for Laplace's equation are found with the aid of complex variables, used also to treat the two-dimensional steady flow case when first derivatives are included in the vectors. Conservation laws, depending on an arbitrary number of derivatives, are found for a general first order quasi-linear equation in two independent variables, using two differential operators, which are associated with the derivatives with respect to the independent variables. Linear totally hyperbolic systems are then treated using an obvious generalization of the above operators." }, { "name": "Chapman, Richard Bruce", "degree": "PhD", "year": "1970", "title": "Nonspherical Vapor Bubble Collapse", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04142011-083038797", "creators": [ { "name": { "family": "Chapman", "given": "Richard Bruce" }, "id": "Chapman-Richard-Bruce", "display_name": "Chapman, Richard Bruce" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/TDCB-D645", "abstract": "Vapor bubble collapse problems lacking spherical symmetry are solved using a method of simulation designed especially for these problems. Viscosity and compressibility in the liquid are neglected. The method of simulation uses finite time steps and features an iterative technique for applying the boundary conditions at infinity directly to the liquid a finite distance from the free surface. Two cases of initially spherical bubbles collapsing near a plane solid wall were simulated, a bubble initially in contact with the wall and a bubble initially half its radius from the wall. at the closest point. In both cases the bubble developed a jet directed towards the wall. Free surface shapes and velocities are presented at various stages in the collapses. Velocities are scaled like \u221a^(\u2206p)/_ \u03c1 where p is the density of the liquid and \u2206p is the difference between the ambient liquid pressure and the vapor pressure. For ^(\u2206p)/_ \u03c1 = 10^6 (^(cm)/_(sec))^2 \u2248 ^(1 atm.)/_(density of water) the jet had a speed of about 130m/ sec in the first case and 170 m/ sec in the second when it struck the opposite side of the bubble. Collapse in a homogeneous liquid was simulated for bubbles with nonspherical initial shapes described by the radii r_s = R_o [1 + 1/10 P_2(cos \u03b8)] and r_s = R_o [l \u2013 1/10 P_2(cos \u03b8)] where P_2 (cos \u03b8) is the second degree Legendre polynomial. Bubble shapes in both cases were close to those predicted by linearized theory. A simple perturbation study of the effect of a small pressure gradient on a collapsing bubble shows that gravity is ordinarily negligible for bubbles initially one cm. in radius or less.\r\n" }, { "name": "Chu, Billie Mae", "degree": "PhD", "year": "1970", "title": "Rheological Properties of Soft Extensible Animal Tissue in Both Living and Excised States", "advisor": "Wayland, J. Harold", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072010-153606301", "creators": [ { "name": { "family": "Chu", "given": "Billie Mae" }, "id": "Chu-Billie-Mae", "display_name": "Chu, Billie Mae" } ], "advisors": [ { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "advisor", "display_name": "Wayland, J. Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/48T9-AD89", "abstract": "A mechanical characterization, over a wide range of response, \r\nof a particular soft extensible animal tissue, the mesentery of the cat, \r\nis presented. The structure of the mesenteric tissue is made up of a \r\ncomplicated array of components and the mechanical response is \r\ninfluenced not only by local factors, but also by adjustments of higher \r\ncontrol centers of the animal. Certain individual aspects of the \r\nresponse of living mesenteric membrane per se have been studied and \r\ncontrasted with (1) membrane strongly influenced by or containing \r\nlarge blood vessels, (2) excised membrane and (3) membrane after \r\ncirculatory collapse and accompanying sustained gut contraction.\r\n\r\n\tA freely floating segment of mesentery exists in a state of \r\ntension which can be demonstrated by making an incision through the \r\nplane of the mesentery. A technique has been developed to determine \r\nthe magnitude of this tension and also the corresponding stretch which \r\nis designated here as the initial configuration length. The tension \r\nlevel in the tissue at the initial configuration length is not unique but \r\ncan vary significantly according to the activity of the components of \r\nthe membrane per se as well as the state of the gut and the large \r\nblood vessels. The most nearly unique length of the tissue which can \r\nbe detected by these experimental methods is a relaxed length determined \r\nby excising a piece of tissue of known dimensions and \r\nmeasuring the freely floating (in a physiologic solution) dimensions\r\nto which the tissue relaxes. There is no marked material anisotropy\r\nin the plane of the membrane, i.e. the two principal dimensions in the \r\nplane of the mesentery do not vary by more than five percent even with \r\nwide history variations just prior to excision.\r\n\r\n\tThe temperature of the test preparation was monitored during \r\nthe course of the tests and maintained at the level of the core temperature \r\nof the animal. Since this temperature could drop as much as \r\nthree or four \u00b0C as a result of the anesthesia, the influence of \r\ntemperature variations on the force-stretch response of the tissue was \r\nstudied and was found to be less significant than the influence of \r\nmechanical degradation in successive loading cycles.\r\n\r\n\tA theoretical characterization that correlates rather well with \r\nthe data of the loading curves for the various tissues has been \r\nproposed. The limitations and assumptions incorporated in this \r\ntreatment have been discussed and when appropriate additional experimental \r\ndata are procured then the analytical treatment can likewise be \r\nextended to a more adequate characterization.\r\n\r\n\tPhotographic materials on pp. 53, 54, 55, 56, 58, 59, 60, 61, \r\n63, 64, 66, 67, 71, 72, 83, 89, 90 and 93 are essential and will not \r\nreproduce clearly on Xerox copies. Photographic copies should be \r\nordered.\r\n" }, { "name": "Damlamayan, Dikran", "degree": "PhD", "year": "1970", "title": "Analysis of Aperture Antennas in Inhomogeneous Media", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:04152011-101450645", "creators": [ { "name": { "family": "Damlamayan", "given": "Dikran" }, "id": "Damlamayan-Dikran", "display_name": "Damlamayan, Dikran" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8GWH-NP26", "abstract": "The object of this report is to calculate the admittance and the radiation pattern of aperture antennas fed by waveguides of arbitrary cross-section and radiating into dielectric slabs, whose constitutive parameters may be functions of position along the direction normal to the slab faces.
\r\n\r\nFor a given aperture field distribution the antenna aperture admittance and the radiation field are expressed here, for the first time, in terms of two auxiliary quantities directly related to the plane wave reflection and transmission coefficients of the dielectric slab. These quantities are the input admittance of the dielectric slab and the ratio of the total electric field amplitude transmitted at one end of the slab to the transverse field at the other, both calculated for plane waves as a function of incident propagation direction. This approach introduces a great simplification in the solution of the problem, particularly in the case of an antenna radiating into an inhomogeneous dielectric slab.
\r\n\r\nA simple and powerful method has been devised for the computation of the input admittance of an inhomogeneous dielectric slab as well as for the electric field ratio. In this case the impracticability of obtaining analytical results has necessitated the use of numerical techniques.
\r\n\r\nExamples of the application of the theory to typical dielectric slabs are given and the results are discussed.
" }, { "name": "Davey, Theodore Herbert", "degree": "PhD", "year": "1970", "title": "The Conjugate Representation of Signal Envelope", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202015-153803402", "creators": [ { "name": { "family": "Davey", "given": "Theodore Herbert" }, "id": "Davey-Theodore-Herbert", "display_name": "Davey, Theodore Herbert" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/F0TV-2421", "abstract": "The problem of the representation of signal envelope is treated, motivated by the classical Hilbert representation in which the envelope is represented in terms of the received signal and its Hilbert transform. It is shown that the Hilbert representation is the proper one if the received signal is strictly bandlimited but that some other filter is more appropriate in the bandunlimited case. A specific alternative filter, the conjugate filter, is proposed and the overall envelope estimation error is evaluated to show that for a specific received signal power spectral density the proposed filter yields a lower envelope error than the Hilbert filter.
" }, { "name": "Dill, John Cedric", "degree": "PhD", "year": "1970", "title": "A Computer-Aided Investigation of Motion Detection Units in the Fly", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202015-141724571", "creators": [ { "name": { "family": "Dill", "given": "John Cedric" }, "id": "Dill-John-Cedric", "display_name": "Dill, John Cedric" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/06J6-SK55", "abstract": "This work deals with two related areas: processing of visual information in the central nervous system, and the application of computer systems to research in neurophysiology.
\r\n\r\nCertain classes of interneurons in the brain and optic lobes of the blowfly Calliphora phaenicia were previously shown to be sensitive to the direction of motion of visual stimuli. These units were identified by visual field, preferred direction of motion, and anatomical location from which recorded. The present work is addressed to the questions: (1) is there interaction between pairs of these units, and (2) if such relationships can be found, what is their nature. To answer these questions, it is essential to record from two or more units simultaneously, and to use more than a single recording electrode if recording points are to be chosen independently. Accordingly, such techniques were developed and are described.
\r\n\r\nOne must also have practical, convenient means for analyzing the large volumes of data so obtained. It is shown that use of an appropriately designed computer system is a profitable approach to this problem. Both hardware and software requirements for a suitable system are discussed and an approach to computer-aided data analysis developed. A description is given of members of a collection of application programs developed for analysis of neuro-physiological data and operated in the environment of and with support from an appropriate computer system. In particular, techniques developed for classification of multiple units recorded on the same electrode are illustrated as are methods for convenient graphical manipulation of data via a computer-driven display.
\r\n\r\nBy means of multiple electrode techniques and the computer-aided data acquisition and analysis system, the path followed by one of the motion detection units was traced from open optic lobe through the brain and into the opposite lobe. It is further shown that this unit and its mirror image in the opposite lobe have a mutually inhibitory relationship. This relationship is investigated. The existence of interaction between other pairs of units is also shown. For pairs of units responding to motion in the same direction, the relationship is of an excitatory nature; for those responding to motion in opposed directions, it is inhibitory.
\r\n\r\nExperience gained from use of the computer system is discussed and a critical review of the current system is given. The most useful features of the system were found to be the fast response, the ability to go from one analysis technique to another rapidly and conveniently, and the interactive nature of the display system. The shortcomings of the system were problems in real-time use and the programming barrier\u2014the fact that building new analysis techniques requires a high degree of programming knowledge and skill. It is concluded that computer system of the kind discussed will play an increasingly important role in studies of the central nervous system.
\r\n" }, { "name": "Early, Benjamin Nathaniel", "degree": "PhD", "year": "1970", "title": "Stochastic Optimal Control", "advisor": "Sridhar, Rangasami", "url": "https://resolver.caltech.edu/CaltechTHESIS:08282015-143654533", "creators": [ { "name": { "family": "Early", "given": "Benjamin Nathaniel" }, "id": "Early-Benjamin-Nathaniel", "display_name": "Early, Benjamin Nathaniel" } ], "advisors": [ { "name": { "family": "Sridhar", "given": "Rangasami" }, "id": "Sridhar-Rangasami", "role": "advisor", "display_name": "Sridhar, Rangasami" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2F63-GT04", "abstract": "H. J. Kushner has obtained the differential equation\r\nsatisfied by the optimal feedback control law for a\r\nstochastic control system in which the plant dynamics\r\nand observations are perturbed by independent additive\r\nGaussian white noise processes. However, the differentiation\r\nincludes the first and second functional derivatives and,\r\nexcept for a restricted set of systems, is too complex to\r\nsolve with present techniques.
\r\n\r\nThis investigation studies the optimal control law\r\nfor the open loop system and incorporates it in a sub-optimal \r\nfeedback control law. This suboptimal control\r\nlaw's performance is at least as good as that of the\r\noptimal control function and satisfies a differential\r\nequation involving only the first functional derivative.\r\nThe solution of this equation is equivalent to solving\r\ntwo two-point boundary valued integro-partial differential\r\nequations. An approximate solution has advantages over\r\nthe conventional approximate solution of Kushner's equation.
\r\n\r\nAs a result of this study, well known results of\r\ndeterministic optimal control are deduced from the analysis\r\nof optimal open loop control.
" }, { "name": "El Raheb, Michel Sadek", "degree": "PhD", "year": "1970", "title": "Some Approximations in the Dynamic Shell Equations", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02212013-152121344", "creators": [ { "name": { "family": "El Raheb", "given": "Michel Sadek" }, "id": "El-Raheb-Michel-Sadek", "display_name": "El Raheb, Michel Sadek" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ejzn-dy90", "abstract": "A theoretical analysis was performed on the linear dynamic\r\nequations of thin cylindrical shells to find the error committed by the\r\nDonnell assumption and the neglect of inplane inertia.
\r\n\r\nThe Donnell approximation was found to be valid at high\r\nfrequencies as compared to the ring frequencies, for all admissible\r\nsets of boundary conditions for finite length thin shells.
\r\n\r\nThe error from neglecting tangential inertia is appreciable for\r\nlong circumferential and axial wave lengths, independent of shell\r\nthickness.
\r\n\r\nThe effect of boundary conditions was investigated from an\r\nexact solution of the linear eigenvalue problem. The inplane boundary\r\nconditions proved to be very influential in the neighborhood of the\r\nminimum frequency. An approximate technique which accounts for the\r\ninplane boundary conditions was then developed and shown to be in good\r\nagreement with the exact solution.
\r\n\r\nFinally, the effect of an elastic end ring on the eigenfrequencies\r\nwas studied. The out-of-plane and torsional rigidities of the ring were\r\nfound to govern the overall shell stiffness. Considerable mode inter action\r\nwas noticed at low circumferential wave numbers for low values\r\nof ring stiffness. The computed eigenfrequencies were found to be in\r\ngood agreement with the experimental results.
\r\n\r\n" }, { "name": "French, Jonathan Akin", "degree": "PhD", "year": "1970", "title": "Wave Uplift Pressures on Horizontal Platforms", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechTHESIS:08052015-104412384", "creators": [ { "name": { "family": "French", "given": "Jonathan Akin" }, "id": "French-Jonathan-Akin", "display_name": "French, Jonathan Akin" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/AKKA-X706", "abstract": "The major objective of the study has been to investigate in detail\r\nthe rapidly-varying peak uplift pressure and the slowly-varying positive\r\nand negative uplift pressures that are known to be exerted by\r\nwaves against the underside of a horizontal pier or platform located\r\nabove the still water level, but not higher than the crests of the incident\r\nwaves.
\r\n\r\nIn a \"two-dimensional\" laboratory study conducted in a 100-ft\r\nlong by 15-in.-wide by 2-ft-deep wave tank with a horizontal smooth\r\nbottom, individually generated solitary waves struck a rigid, fixed,\r\nhorizontal platform extending the width of the tank. Pressure transducers\r\n were mounted flush with the smooth soffit, or underside, of\r\nthe platform. The location of the transducers could be varied.
\r\n\r\nThe problem of a d equate dynamic and spatial response of the\r\ntransducers was investigated in detail. It was found that unless the\r\nradius of the sensitive area of a pressure transducer is smaller than\r\nabout one-third of the characteristic width of the pressure distribution,\r\nthe peak pressure and the rise-time will not be recorded\r\naccurately. A procedure was devised to correct peak pressures and\r\nrise-times for this transducer defect.
\r\n\r\nThe hydrodynamics of the flow beneath the platform are described \r\nqualitatively by a si1nple analysis, which relates peak pressure\r\nand positive slowly-varying pressure to the celerity of the wave front\r\npropagating beneath the platform, and relates negative slowly-varying\r\npressure to the process by which fluid recedes from the platform\r\nafter the wave has passed. As the wave front propagates beneath the\r\nplatform, its celerity increases to a maximum, then decreases. The\r\npeak pressure similarly increases with distance from the seaward\r\nedge of the platform, then decreases.
\r\n\r\nMeasured peak pressure head, always found to be less than five\r\ntimes the incident wave height above still water level, is an order of\r\nmagnitude less than reported shock pressures due to waves breaking\r\nagainst vertical walls; the product of peak pressure and rise-time,\r\nconsidered as peak impulse, is of the order of 20% of reported shock\r\nimpulse due to waves breaking against vertical walls. The maximum\r\nmeasured slowly-varying uplift pressure head is approximately equal\r\nto the incident wave height less the soffit clearance above still water\r\nlevel. The normalized magnitude and duration of negative pressure\r\nappears to depend principally on the ratio of soffit clearance to still\r\nwater depth and on the ratio of platform length to still water depth.
\r\n" }, { "name": "Goodman, Seymour Evan", "degree": "PhD", "year": "1970", "title": "The Hydro-Kinetic Theory of Liquid Helium II", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04032013-114325644", "creators": [ { "name": { "family": "Goodman", "given": "Seymour Evan" }, "id": "Goodman-Seymour-Evan", "display_name": "Goodman, Seymour Evan" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/X8EM-S579", "abstract": "In Part I the kinetic theory of excitations in flowing liquid He II\r\nis developed to a higher order than that carried out previously, by\r\nLandau and Khalatnikov, in order to demonstrate the existence of\r\nnon-equilibrium terms of a new nature in the hydrodynamic equations.\r\nIt is then shown that these terms can lead to spontaneous destabilization\r\nin counter currents when the relative velocity of the normal\r\nand super fluids exceeds a critical value that depends on the temperature,\r\nbut not on geometry. There are no adjustable parameters\r\nin the theory. The critical velocities are estimated to be in the\r\n14-20 m/sec range for T \u2264 2.0\u00b0 K, but tend to zero as T \u2192 T_\u03bb. The\r\npossibility that these critical velocities may be related to the experimentally observed \"intrinsic\" critical velocities is discussed.
\r\n\r\nPart II consists of a semi-classical investigation of rotonquantized\r\nvortex line interactions. An essentially classical model\r\nis used for the collision and the behavior of the roton in the vortex\r\nfield is investigated in detail. From this model it is possible to\r\nderive the HVBK mutual friction terms that appear in the phenomenalogical\r\nequations of motion for rotating liquid He II. Estimates of\r\nthe Hall and Vinen B and B' coefficients are in good agreement with\r\nexperiments. The claim is made that the theory does not contain\r\nany arbitrary adjustable parameters.
" }, { "name": "Govindaraju, Shakkottai P.", "degree": "PhD", "year": "1970", "title": "Part I. An Analysis of Reiner's Centripetal Pump. Part II. A Study of Some Turbulent Flows Using a Model for Inhomogeneous Turbulence", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-150404", "creators": [ { "name": { "family": "Govindaraju", "given": "Shakkottai P." }, "id": "Govindaraju-Shakkottai-P", "display_name": "Govindaraju, Shakkottai P." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/C143-TT24", "abstract": "Part I:\tA centripetal pump consists of a self-aligning rotor in rotation close to a fixed plane stator. In such an apparatus Reiner observed an excess air pressure in the gap between the discs over ambient and a consequent repulsive force between the discs. Reiner interpreted this repulsive force to be the result of non-Newtonian properties of air. Since this hypothesis is in contradiction with known behavior of air in other similar situations, we try to explain it as due to imperfections of the apparatus used and consider three possibilities: dynamic unbalance of the rotor, instability of the rotor and vibrations of the stator. The results of the analyses show that the third possibility can explain Reiner's observations under some reasonable assumptions. It is concluded that Reiner's hypothesis is unjustified.
\r\n\r\nPart II: A model for inhomogeneous turbulence, due to Saffman, describes turbulence in terms of two scalar densities governed by nonlinear diffusion equations. Using this model some turbulent flows are studied to assess the value of the model as a basis for analyzing turbulent flows. The specific problems studied include the two-dimensional wake, the two-dimensional jet, the turbulent couette flow, flow in a channel and the turbulent trailing vortex. Predictions based on the model agree fairly well with experimental results except for the turbulent trailing vortex. Some shortcomings of the model as evident from the application are discussed.
" }, { "name": "Gran, Robert Lee", "degree": "PhD", "year": "1970", "title": "Step Induced Separation of a Turbulent Boundary Layer: Part I. Experiments in Supersonic Flow. Part II. A Model for Incompressible Flow in a Channel", "advisor": "Zukoski, Edward E.; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-082033", "creators": [ { "name": { "family": "Gran", "given": "Robert Lee" }, "id": "Gran-Robert-Lee", "display_name": "Gran, Robert Lee" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/XZZS-AR89", "abstract": "This thesis is concerned with the separation of a two-dimensional turbulent boundary layer caused by a forward facing step. The two major flow regimes considered here are in the realms of supersonic flow and incompressible flow in a channel.
\r\n\r\nFor the case of supersonic turbulent boundary layer separation, a series of experiments were conducted. The upstream pressure field for step sizes in the range from 5% to 150% of the local boundary layer thickness was determined and correlated with \"large\" step data. The separated shear layer was found to be approaching a constant pressure and self-similar flow in a distance of around 6-10 initial boundary layer thicknesses. Fluctuation measurements were conducted near the similar flow region. In addition, the low-frequency unsteady behavior associated with the separation phenomenon was examined and is presumed to be caused by a standing wave acoustic in the subsonic separated region.
\r\n\r\nFor the incompressible flow over a step in a channel, an inviscid model utilizing free streamline theory and based on experimental observations was constructed and solved with the aim of predicting the upstream flow field. Although the solution is not in \"closed form\" (two experimental parameters are required) it does show that the far upstream pressure field is predominately fixed by the flow geometry as opposed to viscous effects such as the Reynolds number or step height-to-boundary layer thickness ratio. Close to the step these effects do, however, become important and are unaccounted for here. The effect of finite blockage ratio (step height-to-channel height ratio) is shown to be substantial for quite modest values (greater than 2%). The precise values of the two experimental parameters are not required for accurate prediction of the upstream influence.
" }, { "name": "Horgan, Cornelius Oliver", "degree": "PhD", "year": "1970", "title": "Eigenvalue Problems Associated With Korn's Inequalities in the Theory of Elasticity", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08062015-145439790", "creators": [ { "name": { "family": "Horgan", "given": "Cornelius Oliver" }, "id": "Horgan-Cornelius-Oliver", "display_name": "Horgan, Cornelius Oliver" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/3VYK-2B81", "abstract": "Interest in the possible applications of a priori inequalities in \r\nlinear elasticity theory motivated the present investigation. Korn's\r\ninequality under various side conditions is considered, with emphasis\r\non the Korn's constant. In the \"second case\" of Korn's inequality, a\r\nvariational approach leads to an eigenvalue problem; it is shown that,\r\nfor simply-connected two-dimensional regions, the problem of determining \r\nthe spectrum of this eigenvalue problem is equivalent to finding\r\nthe values of Poisson's ratio for which the displacement boundary-value\r\nproblem of linear homogeneous isotropic elastostatics has a non-unique solution.
\r\n\r\nPrevious work on the uniqueness and non-uniqueness issue for\r\nthe latter problem is examined and the results applied to the spectrum\r\nof the Korn eigenvalue problem. In this way, further information on\r\nthe Korn constant for general regions is obtained.
\r\n\r\nA generalization of the \"main case\" of Korn's inequality is introduced\r\nand the associated eigenvalue problem is a gain related to the\r\ndisplacement boundary-value problem of linear elastostatics in two\r\ndimensions.
\r\n" }, { "name": "Jassby, Kenneth Mark", "degree": "PhD", "year": "1970", "title": "An Experimental Study of the Mobility of Edge Dislocations in Pure Copper Single Crystals", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-114729703", "creators": [ { "name": { "family": "Jassby", "given": "Kenneth Mark" }, "id": "Jassby-Kenneth-Mark", "display_name": "Jassby, Kenneth Mark" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/8J8A-7T18", "abstract": "The velocity of selectively-introduced edge dislocations in\r\n99.999 percent pure copper crystals has been measured as a function\r\nof stress at temperatures from 66\u00b0K to 373\u00b0K by means of a torsion\r\ntechnique. The range of resolved shear stress was 0 to 15 megadynes/\r\ncm^2 for seven temperatures (66\u00b0K, 74\u00b0K, 83\u00b0K, 123\u00b0K, 173\u00b0K, 296\u00b0K, 296\u00b0K, 373\u00b0K.
\r\n\r\nDislocation mobility is characterized by two distinct features;\r\n(a) relatively high velocity at low stress (maximum velocities of about\r\n9000 em/sec were realized at low temperatures), and (b) increasing\r\nvelocity with decreasing temperature at constant stress.
\r\n\r\nThe relation between dislocation velocity and resolved shear\r\nstress is:
\r\n\r\nv = v_o(\u03c4_r/\u03c4_o)^n
\r\n\r\nwhere v is the dislocation velocity at resolved shear stress \u03c4_r, v_o\r\nis a constant velocity chosen equal to 2000 cm/ sec, \u03c4_o\r\nis the resolved shear stress required to maintain velocity v_o, and n is the mobility coefficient. The experimental results indicate that \u03c4_o decreases from 16.3 x 10^6 to 3.3 x 10^6 dynes/cm^2 and n increases from about 0.9 to 1.1 as the temperature is lowered from 296\u00b0K to 66\u00b0K.
\r\n\r\nThe experimental dislocation behavior is consistent with an\r\ninterpretation on the basis of phonon drag. However, the complete\r\ntemperature dependence of dislocation mobility could not be closely\r\napproximated by the predictions of one or a combination of mechanisms.
\r\n" }, { "name": "Kerber, Ronald Lee", "degree": "PhD", "year": "1970", "title": "Phase Transitions from the Solid State of Monatomic Elements", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08072015-110010138", "creators": [ { "name": { "family": "Kerber", "given": "Ronald Lee" }, "id": "Kerber-Ronald-Lee", "display_name": "Kerber, Ronald Lee" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/7B4C-H074", "abstract": "The principle aims of this thesis include the development of\r\nmodels of sublimation and melting from first principles and the application\r\nof these models to the rare gases.
\r\n\r\nA simple physical model is constructed to represent the sublimation\r\nof monatomic elements. According to this model, the solid\r\nand gas phases are two states of a single physical system. The nature\r\nof the phase transition is clearly revealed, and the relations between\r\nthe vapor pressure, the latent heat, and the transition temperature\r\nare derived. The resulting theory is applied to argon, krypton, and\r\nxenon, and good agreement with experiment is found.
\r\n\r\nFor the melting transition, the solid is represented by an anharmonic\r\nmodel and the liquid is described by the Percus-Yevick approximation.\r\nThe behavior of the liquid at high densities is studied\r\non the isotherms kT/\u2208 = 1.3, 1.8, and 2.0, where k is\r\nBoltzmann's constant, T is the temperature, and e is the well depth\r\nof the Lennard-Jones 12-6 pair potential. No solutions of the PercusYevick\r\nequation were found for \u03c1\u03c33 above 1.3, where \u03c1 is the\r\nparticle density and \u03c3 is the radial parameter of the Lennard-Jones\r\npotential. The liquid structure is found to be very different from the\r\nsolid structure near the melting line. The liquid pressures are about\r\n50 percent low for experimental melting densities of argon. This\r\ndiscrepancy gives rise to melting pressures up to twice the experimental\r\nvalues.
" }, { "name": "Koester, John Kent", "degree": "PhD", "year": "1970", "title": "Analytical and Experimental Studies of Thermionically Emitting Electrodes in Contact with Dense, Seeded Plasmas", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04202011-112053777", "creators": [ { "name": { "family": "Koester", "given": "John Kent" }, "id": "Koester-John-Kent", "display_name": "Koester, John Kent" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/VK0B-6955", "abstract": "The electrode current-voltage characteristics and the limiting cathode current density for thermionically emitting electrodes in contact with high-pressure, seeded, non-equilibrium MHD plasmas were determined analytically and experimentally. The theoretical model was based on the coupling of the adsorption phenomena of alkali metal seed particles onto electrode surfaces with that behavior due to the plasma in the electric boundary layer adjacent to the electrode surface. The desorption rates of electrons and seed atoms and ions (which were given by quoted functions of the surface temperature, the surface degree of coverage, and the electric field at the surface) were related to the appropriate boundary conditions for the governing continuum-type plasma equations in the electric boundary layer.\r\n\r\nAn algorithm was given for the simultaneous solutions of both the surface state and the electric boundary layer. Machine computed results were presented for a potassium-seeded argon plasma (at 2000\u00b0K and one atmosphere pressure) in axially-symmetric stagnation flow over a tungsten electrode and displayed the effects of varying the parameters: surface temperature and seed fraction. These results indicated an order of magnitude increase in the thermionic limiting current density due to coupling effects.\r\n\r\nExperimentally, the electrode phenomena were studied in a non-equilibrium discharge produced in the same plasma-electrode system as used for the machine computations. The electrode behavior was determined from voltage probes, photomultiplier measurements, and photographs. As the thermionic limit was approached, a transition to an arc mode of cathode operation occurred at some breakdown voltage drop. The experimental current-voltage characteristics for the cathode agreed with the machine results, and the predicted enhancement of the thermionic limiting current density was observed experimentally." }, { "name": "Kryder, Mark Howard", "degree": "PhD", "year": "1970", "title": "Flux Reversal in Ferromagnetic Thin Films", "advisor": "Humphrey, Floyd Bernard; Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03222012-143256016", "creators": [ { "name": { "family": "Kryder", "given": "Mark Howard" }, "id": "Kryder-Mark-Howard", "display_name": "Kryder, Mark Howard" } ], "advisors": [ { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" }, { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "co-advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/AP2X-M430", "abstract": "Flux reversal in Ni-Fe thin films has been studied with the use of\r\n10 nsec exposure time Kerr magneto-optic photographs which depict the\r\ndynamic magnetization configuration with 10 \u00b5 resolution during the\r\nreversal process. The photographs show that at least five mechanisms\r\nare involved in the reversal of thin films: (1) domain wall motion,\r\n(2) coherent rotation, (3) diffuse boundary propagation, (4) nucleation\r\nand subsequent reversal of partially reversed regions, and (5) noncoherent\r\nrotation. The present investigation has been concerned mainly\r\nwith the latter three mechanisms as they have either been previously\r\nunreported or poorly understood.
\r\n\r\nNon-coherent rotation is a complex rotational reversal process\r\nwherein the rate of the magnetization rotation varies over the surface of the magnetic film. It occurs only when transverse fields are applied.\r\nThe Kerr magneto-optic photographs show that initially there is a fast\r\nrelaxation of the ripple and a coherent rotation of the magnetization during the risetime of the pulse field, followed by a breakup of the\r\nconfiguration after the field exceeds the\r\nStoner-Wohlfarth threshold. With fields just exceeding the Stoner-Wohlfarth\r\nthreshold, after the stripes form, regions of reversed magnetization\r\nnucleate throughout the stripes and complete the reversal process.\r\nWith larger applied fields, the reversal is completed by the slow (as compared to coherent rotation) rotation of the magnetization which\r\nis accompanied by a gradual decrease in amplitude of the stripes. The\r\nangle at which the stripes form is dependent on the applied field and\r\nvaries from film to film, but indicates that the magnetization rotates coherently to angles significantly greater (5\u00b0 to 20\u00b0) than the critical angle for reversal. The previously proposed fast relaxation models of Stein and Harte both predict that the coherent rotation should cease before the critical angle and therefore do not agree with the data. A model, based on ripple theory, has been constructed to show\r\nthat after the magnetization rotates past the critical angle, an instability\r\nshould occur in the ripple and cause a striped configuration at the observed angles.
\r\n\r\nThe nucleation and subsequent reversal of partially reversed\r\nregions is a reversal process occuring predominantly with zero or small\r\ntransverse fields. During this process the magnetization reverses in\r\nsmall (0.01 mm^2) regions of the film sequentially in time. With zero\r\ntransverse field, the nucleation occurs with longitudinal fields exceeding\r\na well defined nucleation threshold (>H_k) to fields greater\r\nthan 2H_k. Anisotropy dispersion and magnetostatic stray fields are\r\nbelieved to be important in the nucleation process.
\r\n\r\nDiffuse boundary propagation involves a poorly defined, jagged,\r\nand diffuse boundary separating regions of anti-parallel magnetization.\r\nWith zero transverse field the boundary lies transverse to the easy axis\r\nand propagates in the longitudinal direction -- just the opposite of\r\ndomain wall motion. When a transverse field is applied, the boundary\r\npropagates rapidly from diffuse tips pointing in the direction of the\r\nstripes which are observed during non-coherent rotation. The boundary\r\nvelocity varies roughly as the fifth power of the field and ranges from 0.033 cm/\u00b5sec at fields near H_c to 1.25 cm/\u00b5sec at 1.3 H_k which is one\r\nto three order of magnitude faster than domain wall motion. The high velocity is in part attributed to the large width of the boundary which\r\nwidens from 0.2 mm to 2 mm as the field is increased.
\r\n\r\nPhotographs taken when the drive field is terminated before\r\nsaturation of the magnetic film show that the magnetization configuration\r\ncontinues to change for more than 200 nsec in the absence of an applied\r\nfield. The diffuse boundaries become more sharply defined, though still\r\nquite jagged, and are found to change structure and propagate more\r\nslowly during subsequent pulses. Many of the partially reversed nucleated regions revert to the non-reversed state when the field is terminated. The striped partially rotated magnetization of the noncoherent\r\nrotation process, depending on the direction of the magnetization\r\nand the magnitude of the magnetostatic fields arising from the\r\nstripes, either relaxes to the non-reversed state or continues to reverse.\r\nUsually the static state shows no evidence of the stripes, and\r\nthose which are observed are broken up by nucleated regions and frequently\r\nlie at different angles than the dynamic stripes. The large\r\nchanges which occur after the field is terminated show that it is misleading\r\nto try to infer the dynamic state from the final static state\r\nas has been previously done. The long relaxation time is attributed to\r\nthe sequential nature of the relaxation process.
" }, { "name": "Lee, Jiin-Jen", "degree": "PhD", "year": "1970", "title": "Wave Induced Oscillations in Harbors of Arbitrary Shape", "advisor": "Raichlen, Fredric", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072015-163443717", "creators": [ { "name": { "family": "Lee", "given": "Jiin-Jen" }, "id": "Lee-Jiin-Jen", "display_name": "Lee, Jiin-Jen" } ], "advisors": [ { "name": { "family": "Raichlen", "given": "Fredric" }, "id": "Raichlen-F", "role": "advisor", "display_name": "Raichlen, Fredric" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/SEBX-ZE52", "abstract": "Theoretical and experimental studies were conducted to investigate the wave induced oscillations in an arbitrary shaped harbor with constant depth which is connected to the open-sea.
\r\n\r\nA theory termed the \u201carbitrary shaped harbor\u201d theory is developed. The solution of the Helmholtz equation, \u22072f + k2f = 0, is formulated as an integral equation; an approximate method is employed to solve the integral equation by converting it to a matrix equation. The final solution is obtained by equating, at the harbor entrance, the wave amplitude and its normal derivative obtained from the solutions for the regions outside and inside the harbor.
\r\n\r\nTwo special theories called the circular harbor theory and the rectangular harbor theory are also developed. The coordinates inside a circular and a rectangular harbor are separable; therefore, the solution for the region inside these harbors is obtained by the method of separation of variables. For the solution in the open-sea region, the same method is used as that employed for the arbitrary shaped harbor theory. The final solution is also obtained by a matching procedure similar to that used for the arbitrary shaped harbor theory. These two special theories provide a useful analytical check on the arbitrary shaped harbor theory.
\r\n\r\nExperiments were conducted to verify the theories in a wave basin 15 ft wide by 31 ft long with an effective system of wave energy dissipators mounted along the boundary to simulate the open-sea condition.
\r\n\r\nFour harbors were investigated theoretically and experimentally: circular harbors with a 10\u00b0 opening and a 60\u00b0 opening, a rectangular harbor, and a model of the East and West Basins of Long Beach Harbor located in Long Beach, California.
\r\n\r\nTheoretical solutions for these four harbors using the arbitrary shaped harbor theory were obtained. In addition, the theoretical solutions for the circular harbors and the rectangular harbor using the two special theories were also obtained. In each case, the theories have proven to agree well with the experimental data.
\r\n\r\nIt is found that: (1) the resonant frequencies for a specific harbor are predicted correctly by the theory, although the amplification factors at resonance are somewhat larger than those found experimentally,(2) for the circular harbors, as the width of the harbor entrance increases, the amplification at resonance decreases, but the wave number bandwidth at resonance increases, (3) each peak in the curve of entrance velocity vs incident wave period corresponds to a distinct mode of resonant oscillation inside the harbor, thus the velocity at the harbor entrance appears to be a good indicator for resonance in harbors of complicated shape, (4) the results show that the present theory can be applied with confidence to prototype harbors with relatively uniform depth and reflective interior boundaries.
\r\n" }, { "name": "Newkirk, Lawrence Ronald", "degree": "PhD", "year": "1970", "title": "Band Structure and Transport Properties of Simple Cubic Tellurium-Base Alloys", "advisor": "Duwez, Pol E.; Tsuei, Chang-chyi", "url": "https://resolver.caltech.edu/CaltechTHESIS:07222014-092932572", "creators": [ { "name": { "family": "Newkirk", "given": "Lawrence Ronald" }, "id": "Newkirk-Lawrence-Ronald", "display_name": "Newkirk, Lawrence Ronald" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." }, { "name": { "family": "Tsuei", "given": "Chang-chyi" }, "id": "Tsuei-C-C", "role": "advisor", "display_name": "Tsuei, Chang-chyi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/ZJJ1-7T20", "abstract": "The electrical transport properties and lattice spacings of simple cubic Te-Au, Te-Au-Fe, and Te-Au-Mn alloys, prepared by rapid quenching from the liquid state, hove been measured and correlated with a proposed bond structure. The variations of superconducting transition temperature, absolute thermoelectric power, and lattice spacing with Te concentration all showed related anomalies in the binary Te-Au alloys. The unusual behavior of these properties has been interpreted by using nearly free electron theory to predict the effect of the second Brillouin zone boundary on the area of the Fermi surface, and the electronic density of states. The behavior of the superconducting transition temperature and the lattice parameter as Fe and Mn ore added further supports the proposed interpretation as well as providing information on the existence of localized magnetic states in the ternary alloys. In addition, it was found that a very distinct bond structure effect on the transition temperatures of the Te-Au-Fe alloys could be identified.
\r\n" }, { "name": "Parker, Gerhard Hans", "degree": "PhD", "year": "1970", "title": "Tunneling in Schottky Barriers", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-06212004-113629", "creators": [ { "name": { "family": "Parker", "given": "Gerhard Hans" }, "id": "Parker-Gerhard-Hans", "display_name": "Parker, Gerhard Hans" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/QC24-Z481", "abstract": "The tunneling characteristics of metal contacts on n-type CdTe and p-type InAs have been measured. Both the forward and reverse bias characteristics on CdTe are in good agreement with the two-band model for the energy vs. complex momentum relationship. The presence of trapping states increased the magnitude of the tunneling current at low voltage levels by providing a two-step transition. The slope of the forward bias log J vs. V curves for tunneling through the intermediate states was reduced by a factor of 2. The approximate density and energy of the trapping states was calculated from the observed J-V characteristics. The E-k dispersion relation for InAs was also determined and found to be in excellent agreement with the two-band model.\r\n" }, { "name": "Patula, Edward John", "degree": "PhD", "year": "1970", "title": "Equivalent Differential Equations for Nonlinear Dynamical Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182015-085203745", "creators": [ { "name": { "family": "Patula", "given": "Edward John" }, "id": "Patula-Edward-John", "display_name": "Patula, Edward John" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/4PEG-2Q54", "abstract": "A technique for obtaining approximate periodic solutions to nonlinear ordinary differential equations is investigated. The approach is based on defining an equivalent differential equation whose exact periodic solution is known. Emphasis is placed on the mathematical justification of the approach. The relationship between the differential equation error and the solution error is investigated, and, under certain conditions, bounds are obtained on the latter. The technique employed is to consider the equation governing the exact solution error as a two point boundary value problem. Among other things, the analysis indicates that if an exact periodic solution to the original system exists, it is always possible to bound the error by selecting an appropriate equivalent system.
\r\nThree equivalence criteria for minimizing the differential equation error are compared, namely, minimum mean square error, minimum mean absolute value error, and minimum maximum absolute value error. The problem is analyzed by way of example, and it is concluded that, on the average, the minimum mean square error is the most appropriate criterion to use.
\r\nA comparison is made between the use of linear and cubic auxiliary systems for obtaining approximate solutions. In the examples considered, the cubic system provides noticeable improvement over the linear system in describing periodic response.
\r\nA comparison of the present approach to some of the more classical techniques is included. It is shown that certain of the standard approaches where a solution form is assumed can yield erroneous qualitative results.
\r\n" }, { "name": "Perry, Edward Harris", "degree": "PhD", "year": "1970", "title": "Investigations of the T-Burner and its Role in Combustion Instability Studies", "advisor": "Culick, Fred E. C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312008-132130", "creators": [ { "name": { "family": "Perry", "given": "Edward Harris" }, "id": "Perry-Edward-Harris", "display_name": "Perry, Edward Harris" } ], "advisors": [ { "name": { "family": "Culick", "given": "Fred E. C." }, "id": "Culick-F-E-C", "role": "advisor", "display_name": "Culick, Fred E. C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/J91E-7262", "abstract": "Of several devices introduced to study combustion instability in solid rocket propellants, one, known as the \"T-burner,\" has become the most widely used. With this device the response of a burning propellant to a small pressure disturbance can be measured. Such information is vital both to the understanding of unsteady combustion processes as well as to the assessment of the stability characteristics of solid rocket motors.\r\n\r\nAlthough the T-burner has been used for several years, several questions concerning the device have arisen and, for the most part, have remained unanswered. Moreover, little effort has been given toward showing the relevance of T-burner data to predictions of instability in rocket motors.\r\n\r\nThe present investigations, comprising over 400 test firings in T-burners of various lengths and diameters, were undertaken with the major objective of gaining a better understanding of the T-burner itself in order to answer some of these unresolved questions. Another objective was to compare T-burner predictions of rocket motor instability with actual observations made in a previous study.\r\n\r\nAmong the investigations was a comparison of several ignition procedures which showed clearly that a poor, uneven ignition can seriously affect the test results. Included among the ignition studies were tests conducted in transparent chambers to permit high-speed motion photography of the firings. These tests confirmed the common assumption that the T-burner is basically a one-dimensional device.\r\n\r\nTests using burners of different diameters showed that although the acoustic losses of the T-burner are nearly independent of diameter, the limiting amplitude of the oscillations is strongly dependent on the latter. The dilemma raised by these observations was resolved by measurements which indicate that the heat transfer from the combustion gases to the burner wall is strongly dependent on the amplitude of the waves. From these measurements emerged a nonlinear description of the damping in the T-burner which accounts for both the behavior of the losses as well as that of the limiting amplitude.\r\n\r\nWhen two independent T-burner methods were compared, the results obtained were initially in very poor agreement. However, when the T-burner losses were assumed to be non-linear as mentioned earlier, excellent agreement was observed.\r\n\r\nFinally, the T-burner predictions of instability in rocket motors were in rather poor agreement with direct observations made in a previous study. Although this lack of agreement is not understood, it is doubtful in the light of the present investigations that the major error lies in the T-burner measurements, for these should be relatively accurate. Moreover, these results indicate the need for more comparisons of this type in order to determine the usefulness of the T-burner in predicting combustion instability in solid propellant rockets." }, { "name": "Pogorzelski, Ronald James", "degree": "PhD", "year": "1970", "title": "Investigations in the Theory of Electromagnetic Scattering from Expanding Dielectric Obstacles", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202015-163157997", "creators": [ { "name": { "family": "Pogorzelski", "given": "Ronald James" }, "id": "Pogorzelski-Ronald-James", "display_name": "Pogorzelski, Ronald James" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/G2F7-EJ85", "abstract": "An equation for the reflection which results when an expanding dielectric slab scatters normally incident plane electromagnetic waves is derived using the invariant imbedding concept. The equation is solved approximately and the character of the solution is investigated. Also, an equation for the radiation transmitted through such a slab is similarly obtained. An alternative formulation of the slab problem is presented which is applicable to the analogous problem in spherical geometry. The form of an equation for the modal reflections from a nonrelativistically expanding sphere is obtained and some salient features of the solution are described. In all cases the material is assumed to be a nondispersive, nonmagnetic dielectric whose rest frame properties are slowly varying.
" }, { "name": "Prelewicz, Daniel Adam", "degree": "PhD", "year": "1970", "title": "Range of Validity of the Method of Averaging", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:09012015-094327595", "creators": [ { "name": { "family": "Prelewicz", "given": "Daniel Adam" }, "id": "Prelewicz-Daniel-Adam", "display_name": "Prelewicz, Daniel Adam" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/4S5M-N506", "abstract": "Sufficient conditions are derived for the validity of approximate periodic solutions of a class of second order ordinary nonlinear differential equations. An approximate solution is defined to be valid if an exact solution exists in a neighborhood of the approximation.
\r\n\r\nTwo classes of validity criteria are developed. Existence is obtained using the contraction mapping principle in one case, and the Schauder-Leray fixed point theorem in the other. Both classes of validity criteria make use of symmetry properties of periodic functions, and both classes yield an upper bound on a norm of the difference between the approximate and exact solution. This bound is used in a procedure which establishes sufficient stability conditions for the approximated solution.
\r\n\r\nApplication to a system with piecewise linear restoring force (bilinear system) reveals that the approximate solution obtained by the method of averaging is valid away from regions where the response exhibits vertical tangents. A narrow instability region is obtained near one-half the natural frequency of the equivalent linear system. Sufficient conditions for the validity of resonant solutions are also derived, and two term harmonic balance approximate solutions which exhibit ultraharmonic and subharmonic resonances are studied.
\r\n" }, { "name": "Prych, Edmund Andrew", "degree": "PhD", "year": "1970", "title": "Effects of Density Differences on Lateral Mixing in Open-Channel Flows", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08252015-081521032", "creators": [ { "name": { "family": "Prych", "given": "Edmund Andrew" }, "id": "Prych-Edmund-Andrew", "display_name": "Prych, Edmund Andrew" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/WEDF-B722", "abstract": "This study investigates lateral mixing of tracer fluids in turbulent open-channel flows when the tracer and ambient fluids have different densities. Longitudinal dispersion in flows with longitudinal density gradients is investigated also.
\r\n\r\nLateral mixing was studied in a laboratory flume by introducing fluid tracers at the ambient flow velocity continuously and uniformly across a fraction of the flume width and over the entire depth of the ambient flow. Fluid samples were taken to obtain concentration distributions in cross-sections at various distances, x, downstream from the tracer source. The data were used to calculate variances of the lateral distributions of the depth-averaged concentration. When there was a difference in density between the tracer and the ambient fluids, lateral mixing close to the source was enhanced by density-induced secondary flows; however, far downstream where the density gradients were small, lateral mixing rates were independent of the initial density difference. A dimensional analysis of the problem and the data show that the normalized variance is a function of only three dimensionless numbers, which represent: (1) the x-coordinate, (2) the source width, and (3) the buoyancy flux from the source.
\r\n\r\nA simplified set of equations of motion for a fluid with a horizontal density gradient was integrated to give an expression for the density-induced velocity distribution. The dispersion coefficient due to this velocity distribution was also obtained. Using this dispersion coefficient in an analysis for predicting lateral mixing rates in the experiments of this investigation gave only qualitative agreement with the data. However, predicted longitudinal salinity distributions in an idealized laboratory estuary agree well with published data.
\r\n" }, { "name": "Randall, David Lawrence", "degree": "PhD", "year": "1970", "title": "Formal Methods in the Foundations of Science", "advisor": "McCann, Gilbert Donald; Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08252015-104226727", "creators": [ { "name": { "family": "Randall", "given": "David Lawrence" }, "id": "Randall-David-Lawrence", "display_name": "Randall, David Lawrence" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/KB5H-4F11", "abstract": "The intent of this study is to provide formal apparatus which facilitates the investigation of problems in the methodology of science. The introduction contains several examples of such problems and motivates the subsequent formalism.
\r\n\r\nA general definition of a formal language is presented, and this definition is used to characterize an individual\u2019s view of the world around him. A notion of empirical observation is developed which is independent of language. The interplay of formal language and observation is taken as the central theme. The process of science is conceived as the finding of that formal language that best expresses the available experimental evidence.
\r\n\r\nTo characterize the manner in which a formal language imposes structure on its universe of discourse, the fundamental concepts of elements and states of a formal language are introduced. Using these, the notion of a basis for a formal language is developed as a collection of minimal states distinguishable within the language. The relation of these concepts to those of model theory is discussed.
\r\n\r\nAn a priori probability defined on sets of observations is postulated as a reflection of an individual\u2019s ontology. This probability, in conjunction with a formal language and a basis for that language, induces a subjective probability describing an individual\u2019s conceptual view of admissible configurations of the universe. As a function of this subjective probability, and consequently of language, a measure of the informativeness of empirical observations is introduced and is shown to be intuitively plausible \u2013 particularly in the case of scientific experimentation.
\r\n\r\nThe developed formalism is then systematically applied to the general problems presented in the introduction. The relationship of scientific theories to empirical observations is discussed and the need for certain tacit, unstatable knowledge is shown to be necessary to fully comprehend the meaning of realistic theories. The idea that many common concepts can be specified only by drawing on knowledge obtained from an infinite number of observations is presented, and the problems of reductionism are examined in this context.
\r\n\r\nA definition of when one formal language can be considered to be more expressive than another is presented, and the change in the informativeness of an observation as language changes is investigated. In this regard it is shown that the information inherent in an observation may decrease for a more expressive language.
\r\n\r\nThe general problem of induction and its relation to the scientific method are discussed. Two hypotheses concerning an individual\u2019s selection of an optimal language for a particular domain of discourse are presented and specific examples from the introduction are examined.
\r\n" }, { "name": "Rastogi, Prabhat Kumar", "degree": "PhD", "year": "1970", "title": "Part I. Kinetics of Coarsening of the Gamma-Prime Precipitate in Ni-Si Alloys. Part II. Rate of Crystallization of an Amorphous Fe-P-C Alloy", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-131630839", "creators": [ { "name": { "family": "Rastogi", "given": "Prabhat Kumar" }, "id": "Rastogi-Prabhat-Kumar", "display_name": "Rastogi, Prabhat Kumar" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/NQW7-SH65", "abstract": "The coarsening kinetics of Ni3 Si(\u03b3') precipitate in a binary\r\nNi-Si alloy containing 6.5 wt. % silicon was studied by magnetic techniques and transmission electronmicroscopy. A calibration curve was\r\nestablished to determine the concentration of silicon in the matrix.\r\nThe variation of the Si content of the Ni-rich matrix as a function of\r\ntime follows Lifshitz and Wagner theory for diffusion controlled\r\ncoarsening phenomena. The estimated values of equilibrium solubility\r\nof silicon in the matrix represent the true coherent equilibrium solubilities.
\r\n\r\nThe experimental particle-size distributions and average particle\r\nsize were determined from dark field electron micrographs. The\r\naverage particle size varies linearly with t-1/3 as suggested by Lifshitz\r\nand Wagner. The experimental distributions of particle sizes differ\r\nslightly from the theoretical curve at the early stages of aging, but\r\nthe agreement is satisfactory at the later stages. The values of diffusion\r\ncoefficient of silicon, interfacial free energy and activation energy\r\nwere calculated from the results of coarsening kinetics. The experimental\r\nvalue of effective diffusion coefficient is in satisfactory agreement\r\nwith the value predicted by the application of irreversible the rmodynamics\r\nto the process of volume constrained growth of coherent precipitate\r\nduring coarsening. The coherent \u03b3' particles in Ni-Sialloy unlike\r\nthose in Ni-Al and Ni-Ti seem to lose coherency at high temperature.\r\nA mechanism for the formation of semi-coherent precipitate is suggested.
" }, { "name": "Starnes, James Herbert, Jr.", "degree": "PhD", "year": "1970", "title": "The Effect of a Circular Hole on the Buckling of Cylindrical Shells", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012009-110903", "creators": [ { "name": { "family": "Starnes", "given": "James Herbert, Jr." }, "id": "Starnes-James-Herbert-Jr", "display_name": "Starnes, James Herbert, Jr." } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VGHN-EQ52", "abstract": "An experimental and theoretical investigation of the effect of a circular hole on the buckling of thin cylindrical shells under axial compression was carried out. The experimental program consisted of tests performed on seamless electroformed copper shells and Mylar shells with a lap joint seam. The copper shells were tested in a controlled displacement testing machine equipped with a noncontacting surface displacement measuring device. Three-dimensional surface plots obtained in this manner showed the changes in the displacement field over the entire shell, including the hole region, as the applied load was increased. The Mylar shells were tested in a controlled load testing machine and demonstrated the effect of increasing the hole radius on the buckling loads of the cylinder.
\r\n\r\nThe theoretical solution was based on a Rayleigh-Ritz approximation. The solution provided an upper bound for the buckling stresses of the cylinders tested for hole radii less than ten per cent of the shell radii. The theoretical solution also identified the governing parameter of the problem as being related to the hole radius, the shell radius, and the shell thickness.
\r\n\r\nThe theoretical part of the investigation showed that even a small hole should significantly reduce the buckling stresses of circular cylinders. Experimentally, it was found that the effect of a small hole is masked by the effects of initial deformations but, at larger hole radii, the reduction in buckling stress took the form predicted by the theory. The experimental results also showed that the character of the shell buckling was dependent on the hole size. For very small holes the shell buckled into the general collapse configuration and there was no apparent effect of the hole on the buckling mode of the shell. For slightly larger holes the shell still buckled into the general collapse configuration, but the buckling stresses of the shell were sharply reduced as the hole size increased. For still larger holes the buckling stresses did not decrease as sharply as the hole size increased and the shell buckled into a stable local buckling configuration.
\r\n" }, { "name": "Stenzel, Reiner Ludwig", "degree": "PhD", "year": "1970", "title": "Microwave Absorption and Emission from Magnetized Afterglow Plasmas", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07232014-095313314", "creators": [ { "name": { "family": "Stenzel", "given": "Reiner Ludwig" }, "id": "Stenzel-Reiner- Ludwig", "display_name": "Stenzel, Reiner Ludwig" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PFRP-ZW64", "abstract": "The microwave scattering properties of an axially magnetized\r\nafterglow plasma column in an S-band waveguide have been investigated\r\nexperimentally. The column axis is perpendicular to the electric field\r\nand the direction of wave propagation in the H_(10)-mode waveguide.\r\nStrong absorption is found in the range of upper hybrid frequencies, \r\n\u03c9_c \u2264 \u03c9 \u2264 [\u03c9^2_c + \u03c9^2_p(r,t)]^(1/2) where \u03c9_c is the electron cyclotron frequency and \u03c9_p is the locally and temporally varying electron plasma frequency. With the high absorption the noise emission approaches the\r\nblackbody limit. A microwave radiometer has been used to measure the\r\nnoise power and with a comparison and null-technique the electron temperature. As emission and absorption are largely confined to a resonant layer, spatially resolved temperature data are obtained.\r\nTime resolution is obtained by gating the radiometer. The peak\r\nelectron density is derived from the emission or absorption onset at\r\nthe maximum upper hybrid frequency and confirmed by independent measurements. With this diagnostic technique the electron density and temperature decay has been studied under a variety of experimental\r\nconditions. Ambipolar diffusion and collisional cooling essentially\r\naccount for the plasma decay, but impurities and metastable ions\r\nplay an important role. The diagnostic method is successfully applied\r\nin a microwave heating experiment. The existence of absorbing\r\nresonant layers is shown by a peak in the radial temperature profile\r\nwhere the local upper hybrid frequency equals the heating frequency.\r\nThe knowledge of the plasma parameters is important in the study of hot plasma effects. Buchsbaum-Hasegawa modes are investigated in a wide range of magnetic fields (.5 < \u03c9_c/\u03c9 < .985).\r\n" }, { "name": "Taynai, Joseph Dean", "degree": "PhD", "year": "1970", "title": "Properties of \u03b1-Monoclinic Selenium", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072014-094710539", "creators": [ { "name": { "family": "Taynai", "given": "Joseph Dean" }, "id": "Taynai-Joseph-Dean", "display_name": "Taynai, Joseph Dean" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2T9A-6F21", "abstract": "The growth of bulky and platelet shaped \u03b1-monoclinic crystals is discussed. A simple method is devised for identifying and orienting them.
\r\nThe density, previously in disagreement with the value calculated from x-ray studies, is carefully redetermined, and found to be in good agreement with the latter.
\r\n\r\nThe relative dielectric constant is determined, an effort being made to eliminate errors inherent in previous measurements, which have not been in agreement. A two parameter model is derived which explains the anisotropy in the relative dielectric constant of orthorhombic sulfur, which is also composed of 8-atom puckered ring molecules. The model works less well for \u03b1-monoclinic selenium. The relative dielectric constant anisotropy is quite noticeable, being 6.06 along the crystal b axis, and 8.52-8.93 normal to the axis.
\r\n\r\nThin crystal platelets of \u03b1-monoclinic selenium (less than 1\u00b5 thick) are used to extend optical transmission measurements up to 4.5eV. Previously the measurements extended up to 2.1 eV, limited by the thickness of the available crystals. The absorption edge is at 2.20 eV, with changes in slope of the absorption coefficient occurring at 2.85 eV and 3.8 eV. Measurement of transmission through solutions of selenium in CS_2 and trichlorethylene yield an absorption edge of 2.75 eV. There is evidence the selenium exists in solution partly as Se_8 rings, the building block of monoclinic selenium. Transmission is measured at low temperatures (80\u00b0K and 10\u00b0K) using the platelets. The absorption edge is at 2.38 eV and 2.39 eV, respectively, for the two temperatures. Measurements at low temperatures with polarized and unpolarized light reveal interesting absorption anisotropy near 2.65 eV.
\r\n" }, { "name": "Trenholme, John Burgess", "degree": "PhD", "year": "1970", "title": "Superconducting Proximity Effect Currents in Indium Above its Transition Temperature", "advisor": "Mathews, Jon", "url": "https://resolver.caltech.edu/CaltechTHESIS:07272011-091553750", "creators": [ { "name": { "family": "Trenholme", "given": "John Burgess" }, "id": "Trenholme-John-Burgess", "display_name": "Trenholme, John Burgess" } ], "advisors": [ { "name": { "family": "Mathews", "given": "Jon" }, "id": "Mathews-J", "role": "advisor", "display_name": "Mathews, Jon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/EHQZ-DY93", "abstract": "The superconducting proximity effect, in which superconductivity diffuses from a superconductor into an adjacent nonsuperconductor, was investigated using the SNS sandwich method in order to test the predictions of the de Gennes-Werthamer theory of temperature dependence of the Ginzburg-Landau equation. Sandwiches were made in which Pb injected superconductivity into a central layer of In, so that the maximum lossless current through the In could be found as a function of temperature down to the In transition temperature (3.4K). Techniques were used to insure uniform current flow, and to avoid annealing. The log of the critical current density of the sandwiches decreased linearly with temperature above the In transition; the current became much larger below the transition. The de Gennes-Werthamer theory was extended by the addition of the nonlinear term in the Ginzburg-Landau equation; exact solutions of the one-dimensional Ginzburg-Landau equation in the presence of current (but with A_ = 0) were used to find the theoretical temperature variation of the critical current density. The experimental and theoretical curves showed the same linear behavior (although there were slope and value variations), thus verifying the de Gennes-Werthamer theory near the transition temperature of a material." }, { "name": "Vu, Quat Thuong", "degree": "PhD", "year": "1970", "title": "Space-Charge-Limited Current in Fast Neutron Irradiated Silicon", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062014-162429098", "creators": [ { "name": { "family": "Vu", "given": "Quat Thuong" }, "id": "Vu-Quat-Thuong", "display_name": "Vu, Quat Thuong" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/T93C-DG21", "abstract": "DC and transient measurements of space-charge-limited currents through alloyed and symmetrical n^+\u03bd n^+ structures made of nominally 75 k\u03a9cm \u03bd-type silicon are studied before and after the introduction of defects by 14 MeV neutron radiation. In the transient measurements, the current response to a large turn-on voltage step is analyzed. Right after the voltage step is applied, the current transient reaches a value which we shall call \"initial current\" value. At longer times, the transient current decays from the initial current value if traps are present.
\r\n\r\nBefore the irradiation, the initial current density-voltage characteristics J(V) agree quantitatively with the theory of trap-free space-charge-limited current in solids. We obtain for the electron mobility a temperature dependence which indicates that scattering due to impurities is weak. This is expected for the high purity silicon used. The drift velocity-field relationships for electrons at room temperature and 77\u00b0K, derived from the initial current density-voltage characteristics, are shown to fit the relationships obtained with other methods by other workers. The transient current response for t > 0 remains practically constant at the initial value, thus indicating negligible trapping.
\r\n\r\nMeasurement of the initial (trap-free) current density-voltage characteristics after the irradiation indicates that the drift velocity-field relationship of electrons in silicon is affected by the radiation only at low temperature in the low field range. The effect is not sufficiently pronounced to be readily analyzed and no formal description of it is offered. In the transient response after irradiation for t > 0, the current decays from its initial value, thus revealing the presence of traps. To study these traps, in addition to transient measurements, the DC current characteristics were measured and shown to follow the theory of trap-dominated space-charge-limited current in solids. This theory was applied to a model consisting of two discrete levels in the forbidden band gap. Calculations and experiments agreed and the capture cross-sections of the trapping levels were obtained. This is the first experimental case known to us through which the flow of space-charge-limited current is so simply representable.
\r\n\r\nThese results demonstrate the sensitivity of space-charge-limited current flow as a tool to detect traps and changes in the drift velocity-field relationship of carriers caused by radiation. They also establish that devices based on the mode of space-charge-limited current flow will be affected considerably by any type of radiation capable of introducing traps. This point has generally been overlooked so far, but is obviously quite significant.
\r\n" }, { "name": "Wilcox, David Clinton", "degree": "PhD", "year": "1970", "title": "The Motion of a Disc at Angle of Attack in a Rapidly Rotating Fluid", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04032009-113521", "creators": [ { "name": { "family": "Wilcox", "given": "David Clinton" }, "id": "Wilcox-David-Clinton", "display_name": "Wilcox, David Clinton" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EJBR-X182", "abstract": "The motion of a thin disc in a slightly viscous incompressible rotating fluid is studied. The axis of rotation is termed the vertical axis and the fluid and disc are in a container which is bounded by horizontal planes. Nonlinear inertia terms and unsteady effects are assumed small relative to the Coriolis acceleration and hence neglected. Of most importance is the fact that the disc is inclined to the container walls at an angle, \u03b1, which is not necessarily small. The angle is assumed to be large enough so that there are no closed geostrophic contours between the disc and the walls.\r\n\r\nSince the equations of motion are linear, the motions in the six degrees of freedom are considered independently. In all cases, a Taylor column is present although, in all but one case, there is fluid flowing across the boundary of the column. The detailed structure of the shear column is examined for infinitesimal angle of incidence. It is shown that it is possible to solve for the geostrophic flow without actually doing the detailed solution for the shear column structure.\r\n\r\nA static stability study is done and the disc is found to be unstable to small disturbances.\r\n\r\nThe motion of an elliptical plate at finite angle of attack for which the Taylor column is circular is studied. Using the techniques developed for infinitesimal \u03b1, an equation relating the geostrophic flow inside and outside the Taylor column is proposed. This equation is general enough to be used for arbitrary motion of any thin plate. However, only the solution for horizontal translation in a specific direction of the elliptical plate is done.\r\n" }, { "name": "Wiscombe, Warren Jackman", "degree": "PhD", "year": "1970", "title": "Non-Linear Dispersive Waves with a Small Dissipation", "advisor": "Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechTHESIS:04042013-095120206", "creators": [ { "name": { "family": "Wiscombe", "given": "Warren Jackman" }, "id": "Wiscombe-Warren-Jackman", "display_name": "Wiscombe, Warren Jackman" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/4QJW-9809", "abstract": "The general theory of Whitham for slowly-varying non-linear wavetrains is extended to the case where some of the defining partial differential equations cannot be put into conservation form. Typical examples are considered\r\nin plasma dynamics and water waves in which the\r\nlack of a conservation form is due to dissipation; an\r\nadditional non-conservative element, the presence of an\r\nexternal force, is treated for the plasma dynamics \r\nexample. Certain numerical solutions of the water waves\r\nproblem (the Korteweg-de Vries equation with dissipation)\r\nare considered and compared with perturbation expansions\r\nabout the linearized solution; it is found that the first\r\ncorrection term in the perturbation expansion is an\r\nexcellent qualitative indicator of the deviation of the\r\ndissipative decay rate from linearity.
\r\n\r\nA method for deriving necessary and sufficient conditions\r\nfor the existence of a general uniform wavetrain\r\nsolution is presented and illustrated in the plasma\r\ndynamics problem. Peaking of the plasma wave is demonstrated, and it is shown that the necessary and sufficient existence conditions are essentially equivalent to the statement that no wave may have an amplitude larger than the peaked wave.
\r\n\r\nA new type of fully non-linear stability criterion is developed for the plasma uniform wavetrain. It is\r\nshown explicitly that this wavetrain is stable in the\r\nnear-linear limit. The nature of this new type of\r\nstability is discussed.
\r\n\r\nSteady shock solutions are also considered. By a\r\nquite general method, it is demonstrated that the plasma\r\nequations studied here have no steady shock solutions\r\nwhatsoever. A special type of steady shock is proposed,\r\nin which a uniform wavetrain joins across a jump discontinuity to a constant state. Such shocks may indeed\r\nexist for the Korteweg-de Vries equation, but are barred\r\nfrom the plasma problem because entropy would decrease\r\nacross the shock front.
\r\n\r\nFinally, a way of including the Landau damping\r\nmechanism in the plasma equations is given. It involves\r\nputting in a dissipation term of convolution integral\r\nform, and parallels a similar approach of Whitham in\r\nwater wave theory. An important application of this\r\nwould be towards resolving long-standing difficulties\r\nabout the \"collisionless\" shock.
" }, { "name": "Yang, I-Min", "degree": "PhD", "year": "1970", "title": "Stationary Random Response of Multidegree-of-Freedom Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09012015-113504472", "creators": [ { "name": { "family": "Yang", "given": "I-Min" }, "id": "Yang-I-Min", "display_name": "Yang, I-Min" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ZX37-5J02", "abstract": "An approximate approach is presented for determining the stationary random response of a general multidegree-of-freedom nonlinear system under stationary Gaussian excitation. This approach relies on defining an equivalent linear system for the nonlinear system. Two particular systems which possess exact solutions have been solved by this approach, and it is concluded that this approach can generate reasonable solutions even for systems with fairly large nonlinearities. The approximate approach has also been applied to two examples for which no exact or approximate solutions were previously available.
\r\n\r\nAlso presented is a matrix algebra approach for determining the stationary random response of a general multidegree-of-freedom linear system. Its derivation involves only matrix algebra and some properties of the instantaneous correlation matricies of a stationary process. It is therefore very direct and straightforward. The application of this matrix algebra approach is in general simpler than that of commonly used approaches.
" }, { "name": "Ash, Gerald Richard", "degree": "PhD", "year": "1969", "title": "Optimal Guidance of Low-Thrust Interplanetary Space Vehicles", "advisor": "Sridhar, Rangasami", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192014-095711728", "creators": [ { "name": { "family": "Ash", "given": "Gerald Richard" }, "id": "Ash-Gerald-Richard", "display_name": "Ash, Gerald Richard" } ], "advisors": [ { "name": { "family": "Sridhar", "given": "Rangasami" }, "id": "Sridhar-Rangasami", "role": "advisor", "display_name": "Sridhar, Rangasami" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/RDY0-PH47", "abstract": "The low-thrust guidance problem is defined as the minimum terminal variance (MTV) control of a space vehicle subjected to random perturbations of its trajectory. To accomplish this control task, only bounded thrust level and thrust angle deviations are allowed, and these must be calculated based solely on the information gained from noisy, partial observations of the state. In order to establish the validity of various approximations, the problem is first investigated under the idealized conditions of perfect state information and negligible dynamic errors. To check each approximate model, an algorithm is developed to facilitate the computation of the open loop trajectories for the nonlinear bang-bang system. Using the results of this phase in conjunction with the Ornstein-Uhlenbeck process as a model for the random inputs to the system, the MTV guidance problem is reformulated as a stochastic, bang-bang, optimal control problem. Since a complete analytic solution seems to be unattainable, asymptotic solutions are developed by numerical methods. However, it is shown analytically that a Kalman filter in cascade with an appropriate nonlinear MTV controller is an optimal configuration. The resulting system is simulated using the Monte Carlo technique and is compared to other guidance schemes of current interest." }, { "name": "Baum, Carl Edward", "degree": "PhD", "year": "1969", "title": "A Scaling Technique for the Design of Idealized Electromagnetic Lenses", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:01252016-081748086", "creators": [ { "name": { "family": "Baum", "given": "Carl Edward" }, "id": "Baum-Carl-Edward", "display_name": "Baum, Carl Edward" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/N9WZ-SP03", "abstract": "A technique is developed for the design of lenses for transitioning TEM waves between conical and/or cylindrical transmission lines, ideally with no reflection or distortion of the waves. These lenses utilize isotropic but inhomogeneous media and are based on a solution of Maxwell's equations instead of just geometrical optics. The technique employs the expression of the constitutive parameters, \u025b and \u03bc, plus Maxwell's equations, in a general orthogonal curvilinear coordinate system in tensor form, giving what we term as formal quantities. Solving the problem for certain types of formal constitutive parameters, these are transformed to give \u025b and \u03bc as functions of position. Several examples of such lenses are considered in detail.
" }, { "name": "Blum, Joseph William", "degree": "PhD", "year": "1969", "title": "Wave Propagation in an Inhomogeneous Medium", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082013-143307592", "creators": [ { "name": { "family": "Blum", "given": "Joseph William" }, "id": "Blum-Joseph-William", "display_name": "Blum, Joseph William" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/CQ38-0N14", "abstract": "This paper is in two parts. In the first part we give a qualitative study of wave propagation in an inhomogeneous medium principally by geometrical optics and ray theory. The inhomogeneity is represented by a sound-speed profile which is dependent upon one coordinate, namely the depth; and we discuss the general characteristics of wave propagation which result from a source placed on the sound channel axis. We show that our mathematical model of the sound- speed in the ocean actually predicts some of the behavior of the observed physical phenomena in the underwater sound channel. Using ray theoretic techniques we\r\ninvestigate the implications of our profile on the following characteristics of SOFAR propagation: (i) the sound energy traveling further away from the axis takes less time to travel from source to receiver than sound energy traveling closer to the axis, (ii) the focusing of sound energy in the sound channel at certain ranges, (iii) the overall ray picture in the sound channel.
\r\n\r\nIn the second part a more penetrating quantitative study is done by means of analytical techniques on the governing equations. We study the transient problem for the Epstein profile by employing a double transform to formally derive an integral representation for the acoustic pressure amplitude, and from this representation we obtain several\r\nalternative representations. We study the case where both source and receiver are on the channel axis and greatly separated. In particular we verify some of the earlier results derived by ray theory and obtain asymptotic results for the acoustic pressure in the far-field.
\r\n" }, { "name": "Brinker, Gary Duane", "degree": "PhD", "year": "1969", "title": "A Kinetic Theory Description for External Spherical Flows with Arbitrary Knudsen Number by a Moment Method", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechTHESIS:01112016-132852787", "creators": [ { "name": { "family": "Brinker", "given": "Gary Duane" }, "id": "Brinker-Gary-Duane", "display_name": "Brinker, Gary Duane" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/B115-B274", "abstract": "The Maxwell integral equations of transfer are applied to a series of problems involving flows of arbitrary density gases about spheres. As suggested by Lees a two sided Maxwellian-like weighting function containing a number of free parameters is utilized and a sufficient number of partial differential moment equations is used to determine these parameters. Maxwell's inverse fifth-power force law is used to simplify the evaluation of the collision integrals appearing in the moment equations. All flow quantities are then determined by integration of the weighting function which results from the solution of the differential moment system. Three problems are treated: the heat-flux from a slightly heated sphere at rest in an infinite gas; the velocity field and drag of a slowly moving sphere in an unbounded space; the velocity field and drag torque on a slowly rotating sphere. Solutions to the third problem are found to both first and second-order in surface Mach number with the secondary centrifugal fan motion being of particular interest. Singular aspects of the moment method are encountered in the last two problems and an asymptotic study of these difficulties leads to a formal criterion for a \"well posed\" moment system. The previously unanswered question of just how many moments must be used in a specific problem is now clarified to a great extent.
" }, { "name": "Butman, Jerry", "degree": "PhD", "year": "1969", "title": "Phase-Incoherent Feedback Communication", "advisor": "Grettenberg, Thomas L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102002-144406", "creators": [ { "name": { "family": "Butman", "given": "Jerry" }, "id": "Butman-Jerry", "display_name": "Butman, Jerry" } ], "advisors": [ { "name": { "family": "Grettenberg", "given": "Thomas L." }, "id": "Grettenberg-T-L", "role": "advisor", "display_name": "Grettenberg, Thomas L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/HN11-MK65", "abstract": "Nonlinear feedback communication schemes proposed up to now have been restricted to coherent channels. This paper describes a scheme which not only lacks this restriction but yields performance better than the coherent ones that have been analyzed. Block coded orthogonal signals together with incoherent receiver forms are used on both forward and feedback links. It is assumed that the transmitter has a high peak power capability. However, it is shown that by increasing the code length the duty cycle of this mode can be made sufficiently small so that the contribution to average power is negligible. It is found that the probability of error for every message is upper-bounded by exp[-E(R)T], where T represents the code length and E(R) is a function of the transmission rate, R , the capacities of the forward and feedback channels, and a parameter that determines the rate with which the duty cycle decreases with increasing code length. When the forward and feedback capacities are equal, say C , the E(R) versus R curve can be made to approach a curve that starts at 2C and decreases monotonically to the value C at R = C . This contrasts with the corresponding curve without feedback which starts at C/2 and decreases to zero at R = C . The main advantage of information feedback over no feedback, namely E(R = C) > 0 , where C is the forward channel capacity, can also be obtained even when the capacity of the feedback channel is less than that of the forward. To obtain such behavior, existing schemes require that the feedback channel capacity be at least as great as the forward." }, { "name": "Caywood, John Millard", "degree": "PhD", "year": "1969", "title": "Optical and Electrical Properties of \u03b1-Monoclinic Selenium", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112002-170638", "creators": [ { "name": { "family": "Caywood", "given": "John Millard" }, "id": "Caywood-John-Millard", "display_name": "Caywood, John Millard" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WWWK-4431", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe optical absorption of [alpha]-monoclinic selenium has been measured over the range in wavelength 1.15 [micron] to 0.2775 [micron]. The data show a well defined absorption edge at 2.25 eV with further structure appearing as changes in [...] at 2.85 eV and 3.75 eV. For comparison the absorption of selenium in solutions in which it is believed to exist in the same eight-membered puckered ring as in the crystal was measured. This absorption is qualitatively different from that of the crystal.\r\n\r\nThe existence of surface barriers on [alpha]-monoclinic selenium crystals has been demonstrated. Photometric measurements indicate electron barrier heights of 1.05 eV and 1.3 eV, respectively, for Ga and Au contacts. The mobilities of holes and electrons have been measured by a time-of-flight technique to be about 0.2 [centimeters squared]/V-sec and 1.6 [centimeters squared]/V-sec, respectively, at room temperature. The hole mobility was found to be limited by traps 0.23 [plus/minus] .01 eV above the valence levels, while the electron mobility is an intrinsic mobility limited only by scattering. It was found that in the region of low carrier density (i.e. no space charge effects) the number of carriers which crossed the sample was determined by the interplay of the applied field (carrying carriers across the sample) and diffusion (carrying carriers into the metal contact where they relax). The dielectric constant, K, was determined to be 9.2 [plus/minus] .6 over the range 100 [kilohertz] to 100 [megahertz]." }, { "name": "Chang, Milton M.T.", "degree": "PhD", "year": "1969", "title": "Holographic Dielectric Gratings: Theory and Practice", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072002-134846", "creators": [ { "name": { "family": "Chang", "given": "Milton M.T." }, "id": "Chang-Milton-M-T", "display_name": "Chang, Milton M.T." } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CWA9-QS54", "abstract": "A holographic dielectric grating is a diffraction grating comprised of a periodic variation of the refractive index of a medium, and is produced by the interference pattern of two monochromatic waves. Emphasis is placed upon photographic emulsion as the medium for recording the pattern, but the treatment is general and includes any material that can have an internal modulation of the refractive index. Three topics are treated: the effective dielectric constant of the emulsion, the diffraction of light by dielectric gratings, and the techniques for producing gratings with high efficiency and good resolution.
\r\n\r\nThe photographic emulsion is treated as an artificially loaded material, i.e. as a suspension of grains in a gelatin base. A Mie scattering theory analysis is used and the effect of adjacent scatterers on the local field is accounted for by the Lorentz-Lorenz relation. The optical density of the emulsion is shown to be proportional to the number of grains present. The effective index variation after bleaching is proportional to the pre-bleached optical density, which implies that the emulsion should have a linear density vs. exposure curve to effect a sinusoidally modulated index of refraction. A relation between the modulation transfer function (MTF) of bleached and unbleached emulsion is derived. Means for improvement of the MTF is also obtained analytically.
\r\n\r\nThe diffraction of light by a dielectric grating is analyzed using the Raman-Nath formalism which is generalized to include loss. Graphs are presented showing the diffraction efficiency versus the index modulation for a wide range of thicknesses and loss. The peak efficiency for arbitrary emulsion thickness can be obtained from measurements at a specific thickness. The conclusion is reached that presently available emulsion should be made thicker, preferably in the 20-30 micron range.
\r\n\r\nThe basic physical processes of various holographic materials are described. The processing techniques of photographic emulsion are emphasized and the merits of various bleaches are evaluated. It is found that resolution can be increased by using a reversal process. The dielectric grains in an emulsion processed this way are round in shape. A desensitizing dye can be used to stabilize the grains. A method of extending the dynamic range of the photographic emulsion using a pre-flashing exposure technique is also described.
\r\n\r\nSeveral experiments are proposed, and recommendations are made which may serve as guide-lines for the development of more suitable materials for holographic recording.
" }, { "name": "Charette, Wilfred Peter", "degree": "PhD", "year": "1969", "title": "Control Systems Theory Applied to Metabolic Homeostatic System and the Derivation and Identification of Mathematical Models", "advisor": "Sridhar, Rangasami", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072002-135255", "creators": [ { "name": { "family": "Charette", "given": "Wilfred Peter" }, "id": "Charette-Wilfred-Peter", "display_name": "Charette, Wilfred Peter" } ], "advisors": [ { "name": { "family": "Sridhar", "given": "Rangasami" }, "id": "Sridhar-Rangasami", "role": "advisor", "display_name": "Sridhar, Rangasami" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/W419-NS94", "abstract": "The relations among organs and processes resulting in the hormonal control of human metabolism are interpreted mathematically for the derivation and analysis of models using control systems theory and systems engineering techniques. A dynamic nonlinear model for glucose homeostasis including four controlling hormones is derived from the current biological knowledge of the normal system and simulated for comparison with experimental data. Mathematical algorithms are developed and demonstrated for the identification of the parameters of the proposed model and a series of experiments is proposed to yield the minimal requisite data for the application of the method. Control systems analyses are undertaken on the proposed model to demonstrate a consistent methodology for investigations of complex metabolic control systems in the intact animal" }, { "name": "Cheung, Man Cheong", "degree": "PhD", "year": "1969", "title": "The Static and Dynamic Stability of Clamped Shallow Circular Arches", "advisor": "Babcock, Charles D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11162005-081618", "creators": [ { "name": { "family": "Cheung", "given": "Man Cheong" }, "id": "Cheung-Man-Cheong", "display_name": "Cheung, Man Cheong" } ], "advisors": [ { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "advisor", "display_name": "Babcock, Charles D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8MXG-DE89", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation of the relationship between the dynamic buckling and the static buckling phenomenon was carried out.\r\n\r\nThe first half of the paper studies the stability of shallow arches subjected to lateral forces. Concentrated static and step loads were applied to circular arches with geometric parameters 7 < [...] < 20. Equilibrium path and the dynamic response at the loading position were recorded. Dynamic buckling is distinct. Supercritical and subcritical responses were separated by [...] of the total load. The sensitivity of the arch to loading imperfection was studied. The effect was pronounced in the static tests but moderate in the dynamic responses.\r\n\r\nThe second half of the paper studies the response of clamped circular arches under lateral impulse. The motion of the arch was recorded by a high speed camera and the deflected arch shape was measured in detail. The response was expressed in terms of the average displacement and three generalized displacement coordinates representing the amplitudes of the assumed mode shapes. The critical impulse is defined as the impulse level at the inflection point of the curve of maximum response versus impulse." }, { "name": "Collins, Donald James", "degree": "PhD", "year": "1969", "title": "The Near Wake of a Two-Dimensional Hypersonic Blunt Body with Mass Addition", "advisor": "Roshko, Anatol; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072002-144356", "creators": [ { "name": { "family": "Collins", "given": "Donald James" }, "id": "Collins-Donald-James", "display_name": "Collins, Donald James" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZHBC-A772", "abstract": "An experimental investigation of the steady, laminar nearwake flow field of a two-dimensional, adiabatic, circular cylinder with surface mass transfer has been made at a free-stream Mach number of 6. 0, and free-stream Reynolds numbers Re\u221e,d=0.9 and 3.0x104.
\r\n\r\nA flush-mounted porous section was used to transfer argon, nitrogen or helium into the near wake of the circular cylinder to determine the flow field associated with the addition of a passive scalar. Two cases were studied: mass transfer from the forward stagnation region, and mass transfer from the base. The pressure field was mapped by standard Pitot- and static-pressure measurements. The mass-concentration field was monitored by a continuous sampling mass-spectrometer system which utilized the output of a single mass peak to determine the relative mass-concentration levels.
\r\n\r\nFor mass addition from the base, a recirculating vortex remains in the near-wake flow and the characteristic near-wake pressure is the pressure at the stagnation point created by the interaction of the reversed flow with the injected fluid. This pressure, and the entire near-wake flow field, correlates with the ratio of the momentum flux of the injected fluid to the momentum flux in the cylinder boundary layer upstream of separation, and not the mass flow of the injected fluid as predicted by Chapman.
\r\n\r\nFor mass addition from the base, the axial mass concentration decays rapidly away from the base as a consequence of the countercurrent diffusion of mass into the oncoming recirculating flow. In addition, strong transverse mass-concentration gradients exist in the region between the two stagnation points and a local maximum occurs in the vicinity of the u = 0 locus for those cases in which ReSc > 0(1) for the reversed flow.
\r\n\r\nWith moderate mass addition from the forward stagnation region, the near-wake pressure field is unperturbed. In addition, because there is no source in the base region, the near-wake mass-concentration field is nearly uniform in the region of reversed flow. Bounding the uniform region, in the vicinity of the viscous shear layers, narrow diffusion layers govern the transport of mass into the outer flow.
\r\n\r\nIn the intermediate-wake region, immediately downstream of the neck, the mass-concentration fields for both forward and base injection are explained by a single model which incorporates the influence both of the accelerating axial velocity and of an assumed Gaussian distribution for the mass-concentration of argon. This model predicts the axial decay of mass concentration in the intermediate wake, and establishes the location of the virtual origin of the asymptotic far wake in terms of the mass-concentration profile parameters at the neck.
\r\n" }, { "name": "Curro, John Gillette", "degree": "PhD", "year": "1969", "title": "Theoretical Investigation of the Effect of Intramolecular Interactions on the Configuration of Polymeric Chains", "advisor": "Pings, Cornelius J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072002-145049", "creators": [ { "name": { "family": "Curro", "given": "John Gillette" }, "id": "Curro-John-Gillette", "display_name": "Curro, John Gillette" } ], "advisors": [ { "name": { "family": "Pings", "given": "Cornelius J." }, "id": "Pings-C-J", "role": "advisor", "display_name": "Pings, Cornelius J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/8KEP-R512", "abstract": "A theoretical investigation of the effect of intramolecular interactions on the configurational statistics of a polymer molecule is presented. This problem has been studied by many authors and is known as the \"excluded volume problem\" in the literature. A statistical mechanical approach is used. Many of the similarities between the theory of \"classical fluids\" and the excluded volume problem are exploited.
\r\n\r\nThe configurational statistics of 2 and 3 segment chains are computed exactly for the \"hard sphere potential\". The integrations were performed by introducing bipolar and tripolar coordinate systems. It was found that the mean square end-to-end distance for these cases was n1.33 where n is the number of segments. These results are of no practical use in predicting the properties of real polymer chains which are much longer. It is instructive, however, to compare these exact results with approximate theories in the limit of short chain length.
\r\n\r\nA \"cluster expansion\" is written for the partition function of a polymer chain with the ends of the chain fixed. This is analogous to the cluster expansion for the partition function of an imperfect gas. The first-order term in this expansion is evaluated for the hard core potential. In the limit of small hard core diameters, the first-order term leads to the wellknown first-order perturbation theory for the mean square end-to-end distance. The exact results of this first-order correction term are used to construct higher-order terms of a specified \"isolated topology\". If only these terms are used in the cluster expansion, incorrect results are obtained for the mean square end-to-end distance. This indicates that higher-order terms of complicated topology are significant for longer chain length.
\r\n\r\nVarious approximate integral equations for the restricted partition function of a polymer chain are presented. The most promising of these equations is the analog of the well-known Percus-Yevick equation in the theory of liquids. In deriving this equation two topologically distinct types of graphs are defined. These are the \"nodal and elementary\" graphs. An exact equation relating these types of graphs is presented. The analog of the Percus-Yevick approximation is made which leads to an integro-difference equation. This equation is solved exactly using the hard core potential for the special case of the hard core diameter equal to the polymer segment length. Results of numerical calculations are given for other intermediate values of this diameter ranging from zero to the segment length (the \"pearl necklace\" model). This leads to values of \u03b3 ranging correspondingly from 1.0 to 2.0 where <r21N \u221d M\u03b3> with <r21N the mean square end-to-end distance and M the molecular weight. The numerical results for <r21N as a function of chain length are in good agreement with the second-order perturbation theory of Fixman for small hard core diameters.
" }, { "name": "Fernandez, Fernando Lawrence", "degree": "PhD", "year": "1969", "title": "Two-Dimensional Viscous Flows with Large Distributed Surface Injection. Part I. Boundary Layer Flows with Large Injection and Heat Transfer. Part II. Experiments in Supersonic Turbulent Flow with Large Distributed Surface Injection. Part III. The Effect of Finite Plate Length", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-155216", "creators": [ { "name": { "family": "Fernandez", "given": "Fernando Lawrence" }, "id": "Fernandez-Fernando-Lawrence", "display_name": "Fernandez, Fernando Lawrence" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TCCK-HT69", "abstract": "This report is concerned primarily with the effect of surface injection on viscous two-dimensional flows. More precisely, the investigation centers on surface injection rates where the wall shear has been considerably reduced below the no-injection value, but where the momentum of the injectant is still negligible compared to that in the free stream. Three separate problems are investigated to try to obtain an understanding of the physical mechanisms which control the flow.
\r\n\t\r\nFor the case of laminar boundary-layer flow, asymptotic solutions are obtained for large injection and heat transfer. It is found in this case that the boundary layer may be divided into two regions: (1) an inner region adjacent to the surface where viscous mixing plays a minor role; (2) a viscous layer where the transition occurs from the inner solution to the inviscid flow outside the boundary layer. In the case of the insulated wall the viscous layer contributes only small corrections to the boundary-layer properties. For the highly-cooled wall the boundary layer is strongly influenced by the viscous mixing between the inviscid outer flow and the high density low-speed gas adjacent to the wall.
\r\n\t\r\nFor turbulent flow, experiments with constant distributed surface injection at M\u221e=2.6 have been performed. These show that large injection leads to a constant pressure self-similar flow with linear growth. The experimental results are shown to be in good agreement with low Mach number experiments when the normal coordinate is stretched by using a Howarth-Dorodnitsyn transformation at the same value of the ratio of wall mass flow per unit area to that in the free stream.
\r\n\t\r\nFinally, the third part considers the upstream effect of the termination of injection on the flow in the \"blown\" layer. An analysis, using an integral approach is presented which agrees with the experimentally observed effects. In particular, as injection rates approaching the maximum value which can be entrained by a constant pressure mixing layer are approached, the analysis predicts that virtually the entire porous region experiences a falling pressure. It is postulated that this effect provides for a smooth transition from a boundary-layer flow to one where mixing is negligible, except in a thin layer near the streamline which divides the injected and freestream gas. Therefore, the analysis provides the step which gives a quantitative estimate for the range of injection rates in turbulent flow where the effect of mixing can be neglected and inviscid flow models utilized.
" }, { "name": "Foster, Michael Ralph", "degree": "PhD", "year": "1969", "title": "I. The Rotation of a Gravitating Sphere in a Monatomic Gas. II. The Drag of a Body Moving Transversely in a Confined Stratified Fluid", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01132006-084851", "creators": [ { "name": { "family": "Foster", "given": "Michael Ralph" }, "id": "Foster-Michael-Ralph", "display_name": "Foster, Michael Ralph" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/89KW-B656", "abstract": "Part I - The Rotation of a Gravitating Sphere in a Monatomic Gas
\r\n\r\nThe flow resulting from the steady rotation of a gravitating sphere in a monatomic gas at rest is studied in a variety of special cases. The low speed rotation problem involves the solution of non-uniform Stokes equations and exhibits the interesting property that, if the field is large enough to make a \"scale height\" very small compared to the sphere radius, the motion is very weak and occurs primarily in a thin boundary layer on the sphere. The asymptotic theory for the gravitational field strength very large with arbitrary rotation speed shows essentially the same boundary layer, regardless of Reynolds number; the perturbation theory presents some interesting mathematical problems as well. The high speed rotation case is finally considered, and solutions have been obtained only for a gas with small Prandtl number. Even then, the flow structure is very complex. Depending on the relative sizes of the Prandtl number and inverse Reynolds number, there are six possibilities. In every case, there is a thin Prandtl boundary layer on the surface of the sphere and an essentially incompressible jet in the equatorial plane. In some cases, a thermal layer outside the Prandtl boundary layer is required to adjust the temperature, and in every case but one, it is necessary to infer the existence of still another layer, which is inviscid but rotational, that adjusts the uniform flow into the layer required by the strong hydrostatic constraints on the outer flow to that necessary for Prandtl boundary layer entrainment. In some cases these layers are unstable to small disturbances if the temperature on the sphere is sufficiently large.
\r\n\r\nPart II - The Drag of a Body Moving Transversely in a Confined Stratified Fluid
\r\n\r\nThe motion of a body through a stratified fluid bounded by vertical plates is studied in the case when the motion of the body is sufficiently slow to make the inertia of the fluid negligible. The case studied is for a very small coefficient of diffusion (for salt in water, for example). The density changes are quite large, and the drag is quite easily computed without appeal to the structure of any boundary layers or shear layers, depending only on changes of potential energy of the fluid. The solution exhibits regions where the fluid is unstably stratified, and hence mixes. Depending upon how complete the mixing process is, the body might experience a thrust!
\r\n\r\nThe equations for boundary layers are given, but details of their solution are not dealt with here, because of their quasi-linear nature. The horizontal shear layers consist of a simple density adjustment layer surrounded by a thicker and quite complicated non linear dynamical layer. The more conventional Stewartson layers do not appear here, these layers, because of the non linearities, are quite complex, and details of their structure have not yet been fully worked out.
" }, { "name": "Gakenheimer, David Charles", "degree": "PhD", "year": "1969", "title": "Transient Excitation of an Elastic Half-Space by a Point Load Traveling on the Surface", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechETD:etd-03022006-134535", "creators": [ { "name": { "family": "Gakenheimer", "given": "David Charles" }, "id": "Gakenheimer-David-Charles", "display_name": "Gakenheimer, David Charles" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/5FEH-EG57", "abstract": "The propagation of transient waves in an elastic half-space excited by a traveling normal point load is investigated. The load is suddenly applied and then it moves rectilinearly at a constant speed along the free surface. The displacements are computed for all points of the half-space as well as for all load speeds.\r\n\r\nThe disturbance is analyzed by using multi-integral transforms and an inversion scheme based on the well-known Cagniard technique. This reduces the displacements to single integral and algebraic contributions, each of which is identified as the disturbance behind a specific wave front. The same solution is valid for all load speeds, even though the wave front geometry varies greatly, depending on the speed of the load relative to the body wave speeds. Moreover, the surface displacements are obtained from the interior ones, but only after the Rayleigh waves are computed by a separate calculation. Then, by taking advantage of the form of the exact solution, wave front expansions and Rayleigh wave approximations are computed for all load speeds.\r\n\r\nSeveral other analytical results are obtained for restricted values of the load speed. In particular, when it exceeds both of the body wave speeds the steady-state displacement field is separated from the transient one and reduced to algebraic form. Also, for the limit case of zero load speed a new representation of the interior displacements for Lamb's point load problem is displayed in terms of single integrals." }, { "name": "Green, Richard Rutherford", "degree": "PhD", "year": "1969", "title": "Decoding Cosets of First-Order Reed-Muller Codes", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechTHESIS:03182016-151447208", "creators": [ { "name": { "family": "Green", "given": "Richard Rutherford" }, "id": "Green-Richard-Rutherford", "display_name": "Green, Richard Rutherford" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/wfs6-ej43", "abstract": "Proper encoding of transmitted information can improve the performance of a communication system. To recover the information at the receiver it is necessary to decode the received signal. For many codes the complexity and slowness of the decoder is so severe that the code is not feasible for practical use. This thesis considers the decoding problem for one such class of codes, the comma-free codes related to the first-order Reed-Muller codes.
\r\n\r\nA factorization of the code matrix is found which leads to a simple, fast, minimum memory, decoder. The decoder is modular and only n modules are needed to decode a code of length 2n. The relevant factorization is extended to any code defined by a sequence of Kronecker products.
\r\n\r\nThe problem of monitoring the correct synchronization position is also considered. A general answer seems to depend upon more detailed knowledge of the structure of comma-free codes. However, a technique is presented which gives useful results in many specific cases.
\r\n" }, { "name": "Grinthal, Edward Ted", "degree": "PhD", "year": "1969", "title": "Derivation and Interpretation of a Generalized Charge-Control Theory and Reciprocity for a Bipolar Transistor", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechTHESIS:03282017-092448714", "creators": [ { "name": { "family": "Grinthal", "given": "Edward Ted" }, "id": "Grinthal-Edward-Ted", "display_name": "Grinthal, Edward Ted" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PFHF-HV33", "abstract": "The charge-control relations are rigorously derived from the\r\ncarrier transport and continuity equations for a bipolar transistor\r\nwith an arbitrary three-dimensional geometry, arbitrary base impurity\r\ndistribution, arbitrary recombination mechanisms (including spatial\r\nnonuniformity), and for both low and high injection levels. A one-to-one\r\ncorrespondence is maintained between internal processes and the\r\ncharge-control parameters, so that conceptual understanding of, and\r\ninsight into, device operation is enhanced. In the absence of recombination,\r\nthe average carrier velocity is used to obtain the average\r\ncarrier transit time across the base region. The current is then obtained\r\nas the ratio of injected base charge to the average transit\r\ntime. In the presence of recombination, the injected carriers are\r\ndivided into two groups according to whether they recombine or are\r\ncollected. The collected current is then obtained as the ratio of the\r\ncollected charge to the average transit time of the collected carriers.\r\nThe Beaufoy-Sparkes \"collector time constant\" is related to the carrier\r\ntransit time and is given a conceptual interpretation as a collection\r\nlifetime in analogy with the recombination lifetime. A recombination\r\ntransit time is introduced in analogy with the collection transit time.
\r\n\r\n\r\nThe theory, which is generally valid up to frequencies of the\r\norder of the reciprocal transit time, is extended to include high injection\r\nlevels and some second-order phenomena, such as the Early effect\r\nand nonideal base contacts. It is pointed out that the integration of\r\nthe basic equations over the base region may lead to a loss of detailed\r\ninformation, so that the charge-control theory may accurately describe\r\nonly the average behavior of the device; a solution of this difficulty\r\nis suggested. The Ebers-Moll circuit relations are derived from charge-control\r\nprinciples so that a charge-control interpretation of the Ebers-Moll\r\nparameters and an electrical interpretation of the charge-control\r\nparameters is obtained. This leads to the conclusion that the short-circuit\r\nsaturation currents are of more fundamental significance than\r\nare the open-circuit saturation currents.
\r\n\r\nFinally, the separation of injected carriers into recombining\r\nand nonrecombining components is used to obtain a conceptually clear\r\nderivation of the principle of reciprocity for a transistor.
\r\n" }, { "name": "Haas, Roger Allison", "degree": "PhD", "year": "1969", "title": "Particle Kinetics of Gas-Solid Particle Mixtures", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03272017-145900980", "creators": [ { "name": { "family": "Haas", "given": "Roger Allison" }, "id": "Haas-Roger-Allison", "orcid": "0000-0002-6929-6132", "display_name": "Haas, Roger Allison" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/BT3R-BW68", "abstract": "In this thesis the interaction of a normal gas dynamic shock\r\nwave with a gas containing a distribution of small solid spherical\r\nparticles of two distinct radii, \u03c31 and \u03c32, is studied (1) to demonstrate\r\nthat the methods of kinetic theory can be extended to treat solid\r\nparticle collision phenomena in multidimensional gas-particle flows;\r\n(2) to elucidate some of the essential physical characteristics associated\r\nwith particle-particle collision processes; and (3) to give some\r\nindication regarding the importance of particle collisions in particle-laden\r\ngas flows. It is assumed that upstream of the shock wave\r\nparticles \u03c31 are uniformly distributed while particles \u03c32 are non-uniformly\r\ndistributed parallel to the shock face and in much smaller\r\nnumbers than particles \u03c31. Under these conditions the gas-particle\r\n\u03c31 flow downstream of the shock wave is very nearly one-dimensional\r\nand independent of the presence of particles \u03c32. The usual shock\r\nrelaxation zone is established by the interaction of particles \u03c3 and\r\nthe gas downstream of the shock wave. The collisional model pro-\r\nposed by Marble3 is then extended and used with a modified form\r\nof the mean free path method of kinetic theory to calculate the macroscopic\r\ndistribution and velocity of particles \u03c32 as determined by the\r\nparticle \u03c31- particle \u03c32 and particle \u03c32-gas interactions. Within the\r\ncondition that the random velocity imparted to a particle \u03c32 by a\r\ncollision is damped by its viscous interaction with the gas before it\r\nsuffers another collision, the kinetic theory method established here\r\nmay be extended to include more general particle-particle and particle-gas\r\ninteraction laws than those used by Marble. However, the\r\ncollisional model employed is particularly important because the\r\ncriteria for its application are easy to establish and because it\r\nadmits a wide class of physically interesting situations.
\r\n\r\nWithin the restrictions of this collision model, it is possible\r\nto analyze the macroscopic motion of particles \u03c32 in three important\r\nlimiting cases: (\u03c32/\u03c31)2 >> \u22a5,(\u03c32/\u03c31)2 << \u22a5\r\nand (\u03c32/\u03c31)2 ~ \u22a5. It is found that when\r\n(\u03c32/\u03c31)2 >> \u22a5 there\r\nis essentially no redistribution of particles \u03c32 normal to the gas flow.\r\nThe only effect of particle \u03c31 -particle \u03c32 encounters is a drag force\r\nacting to slow down particles \u03c32. When (\u03c32/\u03c31)2 << \u22a5 it is found\r\nthat particles \u03c32. may have many collisions during their passage\r\nthrough the shock relaxation zone. As a consequence there may be\r\na substantial redistribution of particles \u03c32 downstream of the shock\r\nwave. The physical features of this process are studied in detail\r\ntogether with the range of validity of this diffusion model. The case\r\n(\u03c32/\u03c31)2 ~ \u22a5 is analyzed under the condition particles \u03c32 have\r\nat most one collision during their passage through the shock relaxation\r\nzone. It is found that when the gas or particle \u03c31 density is low,\r\nthe single collision effects may be important even when \u03c32/\u03c31 differs\r\nsignificantly from unity and the particles are not very small.
\r\n\r\n\r\nUnder most conditions of practical significance, because there\r\nis invariably a distribution of particles sizes present in a dusty gas,\r\nthe calculation of the particle distribution in the shock relaxation zone\r\nshould account for the effects of particle-particle encounters. It is\r\nsuggested that an experimental observation of particle size distribution\r\nin a shock relaxation zone can yield significant information on particle-particle\r\nand particle-gas interaction laws.
\r\n" }, { "name": "Hasegawa, Ryusuke", "degree": "PhD", "year": "1969", "title": "Conduction-Electron Localized-Moment Interaction in Palladium-Silicon Base Amorphous Alloys Containing Transition Metals", "advisor": "Duwez, Pol E.; Tsuei, Chang-chyi", "url": "https://resolver.caltech.edu/CaltechTHESIS:07182014-141610391", "creators": [ { "name": { "family": "Hasegawa", "given": "Ryusuke" }, "id": "Hasegawa-Ryusuke", "display_name": "Hasegawa, Ryusuke" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." }, { "name": { "family": "Tsuei", "given": "Chang-chyi" }, "id": "Tsuei-C-C", "role": "co-advisor", "display_name": "Tsuei, Chang-chyi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/V806-3R45", "abstract": "The electrical and magnetic properties of amorphous alloys\r\nobtained by rapid quenching from the liquid state have been studied.\r\nThe composition of these alloys corresponds to the general formula\r\nMxPd80-xSi20, in which M stands for a metal of the first transition\r\nseries between chromium and nickel and x is its atomic concentration.\r\nThe concentration ranges within which an amorphous structure could be\r\nobtained were: from 0 to 7 for Cr, Mn and Fe, from 0 to 11 for Co\r\nand from 0 to 15 for Ni. A well-defined minimum in the resistivity vs\r\ntemperature curve was observed for all alloys except those containing\r\nnickel. The alloys for which a resistivity minimum was observed had a\r\nnegative magnetoresistivity approximately proportional to the square\r\nof the magnetization and their susceptibility obeyed the Curie-Weiss\r\nlaw in a wide temperature range. For concentrated Fe and Co alloys\r\nthe resistivity minimum was found to coexist with ferromagnetism.\r\nThese observations lead to the conclusion that the present results\r\nare due to a s-d exchange interaction. The unusually high resistivity\r\nminimum temperature observed in the Cr alloys is interpreted as a\r\nresult of a high Kondo temperature and a large s-d exchange integral.\r\nA low Fermi energy of the amorphous alloys (3.5 eV) is also responsible\r\nfor the anomalies due to the s-d exchange interaction." }, { "name": "Heitner, Kenneth Leon", "degree": "PhD", "year": "1969", "title": "A Mathematical Model for Calculation of the Run-Up of Tsunamis", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312017-150238598", "creators": [ { "name": { "family": "Heitner", "given": "Kenneth Leon" }, "id": "Heitner-Kenneth-Leon", "display_name": "Heitner, Kenneth Leon" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/GVM3-N517", "abstract": "To understand the engineering implications of possible wave\r\nrun-up resulting from tsunamis, a formulation of the run-up process\r\ncapable of giving quantitative answers is required. In this\r\nthesis, a new mathematical run-up model suitable for computer\r\nevaluation is proposed and tested. The two-dimensional model uses\r\na flow constrained so that the horizontal velocity is uniform in depth.\r\nHowever, unlike the usual shallow water theory, the terms representing\r\nthe kinetic energy of the vertical motion are retained. It is\r\nshown that this formulation allows a solitary-like wave to propagate\r\nas well as giving a more accurate indication of wave breaking. An\r\n'artificial viscosity' term is used to allow the formation of hydraulic\r\nshocks. The effects of bottom friction are also included. The\r\nmodel is derived for a linear beach slope, in Lagrangian coordinates.\r\nA finite element formulation of the problem is derived that is suitable\r\nfor digital computer evaluation.
\r\n\r\nCalculations with the model agree satisfactorily with experimental\r\nresults for the fun-up of solitary waves and bores. The model\r\nis used to obtain run-up data on tsunami-like waves, which show the danger of large run-up \r\nfrom low initial steepness waves on shallow slopes.\r\nHowever, the data also show that bottom friction values can\r\nsignificantly attenuate run-up, especially on shallow slopes.
\r\n\r\n\r\nWaves generated by a dipole-like displacement of the simulated\r\nocean floor show that the run-up is usually larger when the upwards\r\ndisplacement is nearest the beach than when the downwards displacement\r\nis nearest the beach.
" }, { "name": "Ko, Denny Ru-sue", "degree": "PhD", "year": "1969", "title": "I. Supersonic Laminar Boundary Layer Along a Two-Dimensional Adiabatic Curved Ramp. II. Non-Linear Stability Theory for a Laminar, Incompressible Wake", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102003-093156", "creators": [ { "name": { "family": "Ko", "given": "Denny Ru-sue" }, "id": "Ko-Denny-Ru-sue", "display_name": "Ko, Denny Ru-sue" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DM2V-N712", "abstract": "In Part I, the integral method of Lees and Reeves is applied to study a supersonic laminar boundary layer along a two-dimensional adiabatic curved ramp. The present method of solution requires no prior knowledge of the separation point and can be used to treat relatively weak interaction, including a fully attached flow. It starts with small perturbations of the self-induced interaction on a flat plate; consequently, it can be applied to flows with the hypersonic interaction parameter \u03a7\u0305, based on the distance of the beginning station of interaction to the leading edge, of the order 1. The effect of the radius of curvature on the separation phenomena is then investigated using this method. The effect of finite ramp length on the interaction is examined by making use of the characteristics of the singularities associated with the set of moment equations. Satisfactory agreement with the theory is obtained for the corresponding experiments conducted in the Mach 6 wind tunnel at the Graduate Aeronautical Laboratories of the California Institute of Technology.
\r\n\r\nIn Part II, a non-linear theory for the stability of the laminar wake behind a flat plate in an incompressible flow is presented. An integral method is used to investigate the effects of a finite amplitude disturbance on the flow. The flow is decomposed into a mean part, which is independent of time and a fluctuating part, which has a zero time average. The mean flow is assumed to be characterized by two parameters: the centerline velocity defect w[subscript c] and the wake half-width b. By using a two-length expansion procedure, the assumption of local, parallel mean flow is justified for the solution of the fluctuating component to the order considered in the present study. The fluctuation is assumed to be represented by an ascending power series of the amplitude A. The coefficients of the power series, as functions of the radial distance y, are then obtained in terms of the two mean flow parameters wc and b. The three unknowns b, wc and A are then obtained by solving the integral conservation equations of mean momentum, mean energy and fluctuation energy. In this integral method, the higher-order effects are introduced systematically by truncating the expansion for the fluctuation at various orders. The coupling between the mean flow and the fluctuation is found to be the most important mechanism in limiting the fluctuation amplitude and determining the mean flow. Satisfactory agreements with the experiment of Sato-Kuriki in the mean flow quantities and the relative development of the fluctuations are obtained, including the observed effect of free-stream Reynolds number.
" }, { "name": "Lake, Bruce Meno", "degree": "PhD", "year": "1969", "title": "Velocity Measurements Ahead of a Semi-Infinite Body in Magnetohydrodynamic Flow with Aligned Fields", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-142805", "creators": [ { "name": { "family": "Lake", "given": "Bruce Meno" }, "id": "Lake-Bruce-Meno", "display_name": "Lake, Bruce Meno" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PN2X-JB97", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nExperiments are described in which velocities were measured ahead of a semi-infinite Rankine body moving parallel to a uniform magnetic field in a conducting fluid. The flow disturbance in front of the body is found to increase in length as [...], where N is the interaction parameter. In most of the experiments this parameter was varied from 4 to about 50. Measurements made along the axis of symmetry in the flow show that there is a relatively short region of stagnant fluid directly ahead of the body. The major part of the disturbance is found to consist of a much longer region in which the flow undergoes transition from conditions in the freestream to conditions near the body. Velocity profiles across the flow in this region show that for increased N, at a fixed distance ahead of the body, the velocity defect increases and the disturbance becomes more confined radially. Although the radial gradients in the flow increase with N, they are found to be much smaller than would be expected in a flow containing thin current layers. A physical model of the flow which has currents and pressures consistent with these results is discussed." }, { "name": "Laussade, Jean-Pierre Raymond Henri", "degree": "PhD", "year": "1969", "title": "I. Mode Locking and Ultrashort Laser Pulses by a Refractive Index Nonlinearity. II. A Theoretical Study of Optical Wave Propagation Through a Random Medium and its Application to Optical Communication", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:06262017-154848811", "creators": [ { "name": { "family": "Laussade", "given": "Jean-Pierre Raymond Henri" }, "id": "Laussade-Jean-Pierre-Raymond-Henri", "display_name": "Laussade, Jean-Pierre Raymond Henri" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/82JD-BB21", "abstract": "Part I. Mode Locking and Ultrashort Laser Pulses by a Refractive Index Nonlinearity
\r\n\r\nA new method for locking the longitudinal modes of a laser\r\nresonator and generating ultrashort pulses of light has been found.\r\nThe cavity modes are coupled together when a medium possessing a\r\nrefractive index nonlinearity is placed inside the cavity.
\r\n\r\n\r\nA theoretical study is presented which analyzes the mode\r\nstructure of a laser resonator containing a cell filled with an\r\nanisotropic molecular liquid. It is found that under certain conditions\r\nthe energy exchange between the modes gives rise to a mode\r\nlocked spectrum and to the attendant generation of ultrashort pulses\r\nof light (~10-11 sec for a ruby laser, ~10-12 sec for a Nd3+ glass laser).
\r\n\r\n\r\nAn experimental investigation is reported. The presence of\r\nultrashort pulses in the output of a Q-switched ruby laser is observed\r\nwhen a liquid cell containing nitrobenzene or \u03b1-chloronaphthalene is\r\nplaced inside the cavity.
\r\n\r\n\r\nPart II. A Theoretical Study of Optical Wave Propagation Through a Random Medium and its Application to Optical Communication
\r\n\r\nIn this report we are interested in a theoretical study of\r\nwave propagation in a randomly turbulent medium and the application\r\nof the results to the evaluation of optical communication systems\r\nthrough the atmospheric turbulence.
\r\n\r\nWe first derive a power series expansion solution for the\r\nwave function u(\u2192x) of a wave propagating through a medium with a\r\nrandom index of refraction. The average wave function u(\u2192x) and the\r\ncorrelation function u(\u2192x1) u*(\u2192x2) are calculated in terms of the\r\ncorrelation function of the index of refraction, the only assumption\r\nbeing that the wavelength of the wave is much smaller than the smallest\r\nsize of the turbulence. The intensity correlation function\r\nI(\u2192x1) I(\u2192x2) is investigated and recent experimental results concerning\r\nthe behavior of the intensity fluctuations are discussed.
\r\n\r\n\r\nNext, the performances of two schemes of optical communication\r\nthrough the random atmospheric turbulence are compared: (a) heterodyne\r\ndetection, (b) video communication. It is found that for long propagation\r\npaths and strong turbulences, scheme (b) is preferable to scheme\r\n(a). This is due to the cancellation of the phase fluctuations between\r\n\"reference\" and \"signal\" parts of the beam in the video communication\r\nscheme.
\r\n\r\n" }, { "name": "Lee, Don Howard", "degree": "PhD", "year": "1969", "title": "Double-Injection: High Frequency Noise and Temperature Dependence", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechTHESIS:10072014-144607202", "creators": [ { "name": { "family": "Lee", "given": "Don Howard" }, "id": "Lee-Don-Howard", "display_name": "Lee, Don Howard" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/964x-ab98", "abstract": "Noise measurements from 140\u00b0K to 350\u00b0K ambient temperature and between 10kHz and 22MHz performed on a double injection silicon diode as a function of operating point indicate that the high frequency noise depends linearly on the ambient temperature T and on the differential conductance g measured at the same frequency. The noise is represented quantitatively by\u3008i^2\u3009 = \u03b1\u20224kTg\u0394f. A new interpretation demands Nyquist noise with \u03b1 \u2261 1 in these devices at high frequencies. This is in accord with an equivalent circuit derived for the double injection process. The effects of diode geometry on the static I-V characteristic as well as on the ac properties are illustrated. Investigation of the temperature dependence of double injection yields measurements of the temperature variation of the common high-level lifetime \u03c4(\u03c4 \u221d T^2), the hole conductivity mobility \u00b5_p (\u00b5_p \u221d T^(-2.18)) and the electron conductivity mobility \u00b5_n(\u00b5_n \u221d T^(-1.75)).
" }, { "name": "Maitrepierre, Philippe Louis", "degree": "PhD", "year": "1969", "title": "Influence of Composition on the Structure and Properties of Fe-Pd-P and Ni-Pd-P Amorphous Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192014-085423804", "creators": [ { "name": { "family": "Maitrepierre", "given": "Philippe Louis" }, "id": "Maitrepierre-Philippe-Louis", "display_name": "Maitrepierre, Philippe Louis" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/8VCG-6E08", "abstract": "Ternary alloys of nickel-palladium-phosphorus and iron-palladium-phosphorus containing 20 atomic % phosphorus were rapidly quenched from the liquid state. The structure of the quenched alloys was investigated by X-ray diffraction. Broad maxima in the diffraction patterns, indicative of a glass-like structure, were obtained for 13 to 73 atomic % nickel and 13 to 44 atomic % iron, with palladium adding up to 80%.
\r\n\r\nRadial distribution functions were computed from the diffraction data and yielded average interatomic distances and coordination numbers. The structure of the amorphous alloys could be explained in terms of structural units analogous to those existing in the crystalline Pd3P, Ni3P and Fe3P phases, with iron or nickel substituting for\r\npalladium. A linear relationship between interatomic distances and composition, similar to Vegard's law, was shown for these metallic glasses.
\r\n\r\nElectrical resistivity measurements showed that the quenched alloys were metallic. Measurements were performed from liquid helium temperatures (4.2\u00b0K) up to the vicinity of the melting points (900\u00b0K-1000\u00b0K). The temperature coefficient in the glassy state was very low, of the order of 10-4/\u00b0K. A resistivity minimum was found at low temperature, varying between 9\u00b0K and 14\u00b0K for Nix-Pd80-x -P20 and between 17\u00b0K and 96\u00b0K for Fex-Pd80-x -P20, indicating the presence of a Kondo effect. Resistivity measurements, with a constant heating rate of about 1.5\u00b0C/min,showed progressive crystallization above approximately 600\u00b0K.
\r\n\r\nThe magnetic moments of the amorphous Fe-Pd-P alloys were measured as a function of magnetic field and temperature. True ferromagnetism was found for the alloys Fe32-Pd48-P20 and Fe44-Pd36-P20 with Curie points at 165\u00b0 K and 380\u00b0 K respectively. Extrapolated values of the saturation magnetic moments to 0\u00b0 K were 1.70 \u00b5B and 2.10 \u00b5B respectively. The amorphous alloy Fe23-Pd57-P20 was assumed to be superparamagnetic. The experimental data indicate that phosphorus contributes to the decrease of moments by electron transfer, whereas palladium atoms probably have a small magnetic moment. A preliminary investigation of the Ni-Pd-P amorphous alloys showed that these alloys are weakly paramagnetic.
" }, { "name": "McCrickerd, John Thomas", "degree": "PhD", "year": "1969", "title": "The Holographic Stereogram", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04062017-144815513", "creators": [ { "name": { "family": "McCrickerd", "given": "John Thomas" }, "id": "McCrickerd-John-Thomas", "display_name": "McCrickerd, John Thomas" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/gq8t-k869", "abstract": "The holographic stereogram, a hologram synthesized from ordinary\r\nstereoscopic component photographs, is investigated as an alternative to classical\r\nholograms and to previous types of stereograms for three-dimensional perfect\r\nimagery. The process is partly holographic in nature, but it provides images of\r\nnaturally illuminated objects, and its application is not limited by the technology\r\nof laser illumination. The pinhole camera stereogram and the fly's eye lens\r\nstereogram are also analyzed, since the principles of their operation are similar.\r\nPinhole camera stereogram imagery is shown to have several deficiencies, among\r\nwhich is the necessity for small camera-object distances. The fly's eye lens is\r\nmuch superior, but is limited in practice by aberrations, a difficulty which the\r\nholographic stereogram overcomes. Also treated are the full-color, the focused type,\r\nand the distortionless-scaled holographic stereogram, and optical spatial\r\nfiltering of holographic stereogram images.
\r\n\r\nThe achromatically imaged Fresnel zone plate is analyzed as a technique\r\nof very general applicability which compensates for source incoherency in two-beam\r\ntype holographic arrangements. The emphasis is on physical interpretation\r\nrather than mathematical formulation. Two simple graphical mnemonics are\r\ndeveloped for rapid analytical inspection of the effects of, respectively, temporal\r\nand spatial incoherence of the source in any achromatically imaged zone plate\r\nor Gabor in-line type holographic system.
\r\n\r\nThe scalar wave function approximation of physical optics is used\r\nthroughout.
\r\n" }, { "name": "McGill, Thomas Conley, Jr.", "degree": "PhD", "year": "1969", "title": "The Evaluation of E-k Curves from Tunneling Currents", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122006-092025", "creators": [ { "name": { "family": "McGill", "given": "Thomas Conley, Jr." }, "id": "McGill-Thomas-Conley-Jr", "display_name": "McGill, Thomas Conley, Jr." } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/D3BX-RQ47", "abstract": "The basis for interpreting I-V data taken on metal-insulator-metal structures with insulator thicknesses of less than 100 \u00c5 is examined carefully. A set of experimental tests for determining the applicability of the equation linking the I-V data to the E-k curve is presented. These tests are found to be a stringent requirement on the experimental data and to support strongly the interpretation of the experimental I-V in terms of the E-k curve for the insulator. A numerical technique for obtaining the E-k curve from I-V data is presented, and applied to data taken on Al-AlN-(Mg,Au) structures where it allows the evaluation of the E-k curve for AlN throughout the forbidden gap." }, { "name": "Mo, Tse Chin", "degree": "PhD", "year": "1969", "title": "Theory of Electrodynamics of Media in Non-Inertial Frames and Applications", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:03282017-111748813", "creators": [ { "name": { "family": "Mo", "given": "Tse Chin" }, "id": "Mo-Tse-Chin", "display_name": "Mo, Tse Chin" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1Z64-YS50", "abstract": "In the first half of this thesis a local electrodynamics of\r\nmedia in given non-inertial frames*, within Maxwell-Einstein classical\r\nfield theory, is constructed in terms of observable EM fields and\r\nco-moving local physical media parameters. Localization of tensors to\r\nobservables is introduced and justified, and a relation is obtained\r\nconnecting tensor transforms to instantaneous Lorentz transforms for\r\nobservers in different frames. A constitutive tensor, explicitly\r\nexpressed by the four-velocity and the local properties in co-moving\r\nframe of a linear medium, is found for the first time. Previous mistakes\r\nin confusing the tensors, in which forms the physical quantities\r\ncombine with the non- flatness of frames to be used in covariant equations\r\nand thus make geometrical quantities, with observables are\r\ncleared. Also a Lagrangian formulation for both lossless and lossy\r\nmedia is constructed, and boundary conditions, local conservation laws,\r\nand energy momentum tensor are obtained.
\r\n\r\n\r\nThe second half concerns application to motions in SRT, such\r\nas uniform linear (hyperbolic) acceleration and steady rotation. For\r\nthese local Maxwell equations in co-moving frames are obtained, and\r\napproximate solutions are found for special cases. An EM wave\r\npropagating in the direction of acceleration is studied in the\r\naccelerating frame. The first order propagation shows a frequency\r\nshift and amplitude change which have very simple physical significances\r\nof instantaneous Doppler shift and photon density in media\r\nand which agree with familiar results in the vacuum limit. A particle\r\nmodel for this wave shows that the \"mass dressed\" photon is dragged by\r\nthe medium and does not follow a geodesic path. In the rotating medium\r\ncase a plane wave scattered by a rotating sphere is solved by an integral\r\niteration method in the laboratory frame. The scattered field\r\npurely associated to the rotation of the medium is separated from the\r\nMie scattering. Its first order amplitudes are found and plotted for\r\nincidences perpendicular and parallel to the rotation axis. Particular\r\nsynunetry and shapes of scattering amplitude in the results agree with\r\nintuition and resemble radiation patterns of appropriately induced\r\ntraveling electric and magnetic dipole sheaths.
\r\n\r\n*The contribution of EM field to g\u00b5v is neglected.
" }, { "name": "Molinder, John Irving", "degree": "PhD", "year": "1969", "title": "Binary Coding Using Standard Run Lengths", "advisor": "Grettenberg, Thomas L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03282017-150849634", "creators": [ { "name": { "family": "Molinder", "given": "John Irving" }, "id": "Molinder-John-Irving", "display_name": "Molinder, John Irving" } ], "advisors": [ { "name": { "family": "Grettenberg", "given": "Thomas L." }, "id": "Grettenberg-T-L", "role": "advisor", "display_name": "Grettenberg, Thomas L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/n2yk-3382", "abstract": "Run length coding using standard run lengths has been proposed by Cherry et al [7]. Their analysis has been mostly experimental for specific types of data.
\r\n\r\nIn this thesis the globally optimum single standard run length has been derived for the binary independent source and globally optimum single standard run lengths of zeros and ones have been derived for the binary first order Markov source. It is assumed that the output symbols are subsequently block coded in each case. A recursion relationship between standard run lengths is derived for two specific coding algorithms. A simple single standard run length scheme using a non-block code on the output symbols has also been derived for the binary independent source.
" }, { "name": "Norgard, John Dennis", "degree": "PhD", "year": "1969", "title": "Radiation from an Antenna Entering the Martian Atmosphere", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:03242017-095341798", "creators": [ { "name": { "family": "Norgard", "given": "John Dennis" }, "id": "Norgard-John-Dennis", "display_name": "Norgard, John Dennis" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/pd64-rx94", "abstract": "The interaction between the ionized wake of a capsule entering\r\nthe Martian atmosphere and the circularly polarized radiation emitted\r\nby an antenna located on the aft part of the capsule is theoretically\r\ninvestigated in this study. A simplified mathematical model of the\r\natmosphere of Mars, the entry-trajectory of the capsule, and the flow\r\nfield surrounding the capsule are used in the analysis. The near wake\r\nof the capsule is approximated by a cylindrically stratified plasma\r\nshell consisting of n plasma regions. The plasma in each region is\r\nassumed to be homogeneous, anisotropic, and conducting, and moving at\r\na uniform velocity relative to the antenna. The antenna is represented\r\nby a turnstile antenna located off-axis \u03bbo/4 above an infinite ground\r\nplane and operates at the signal frequencies of 400 MHz and 2.295 GHz.
\r\n\r\nIntegral expressions for the cylindrical components of the\r\nfield vectors are obtained by a rigorous relativistic formulation of\r\nthe problem, and are evaluated using the techniques of asymptotic\r\nexpansions to yield the radiation patterns of the antenna. Radiation\r\npatterns for the special case of an on-axis antenna radiating through\r\na uniform, lossless, and isotropic plasma shell are presented and are\r\ncompared with the free space patterns.
\r\n\r\nThe analysis shows that blackout occurs during the entry of\r\na capsule into the Martian atmosphere, Before and after blackout,\r\nthe radiation patterns of the antenna exhibit an on-axis null region\r\nwhose angular extent is proportional to the electron concentration of\r\nthe plasma. Also, sharp peaks which are attributed to leaky wave radiation,\r\nare present in the null region of the patterns. For the non-null\r\nregion of the patterns, the values of the gain function of the antenna\r\noscillate about the free space values. As the electron concentration\r\nof the plasma increases, the peaks in the radiation patterns become more\r\nnumerous and more sharply defined. The effects of the motion of the\r\nplasma on the radiation emitted by the antenna are to shift the peaks\r\nof the radiation patterns to smaller cone angles and to introduce more\r\npeaks into the patterns.
\r\n\r\nFor the low velocity case corresponding to an entry into the\r\nMartian atmosphere, no serious motional or depolarization effects\r\noccur, and communications with the capsule can be satisfactorily carried\r\nout when the condition of blackout does not exist.
" }, { "name": "Ohtakay, Hiroshi", "degree": "PhD", "year": "1969", "title": "Variable Lift Control of a Space Vehicle During the Re-Entry into Martian Atmosphere", "advisor": "Sridhar, Rangasami", "url": "https://resolver.caltech.edu/CaltechTHESIS:09262017-101951259", "creators": [ { "name": { "family": "Ohtakay", "given": "Hiroshi" }, "id": "Ohtakay-Hiroshi", "display_name": "Ohtakay, Hiroshi" } ], "advisors": [ { "name": { "family": "Sridhar", "given": "Rangasami" }, "id": "Sridhar-Rangasami", "role": "advisor", "display_name": "Sridhar, Rangasami" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/NAF8-Q357", "abstract": "Re-entry trajectory design problem of a space capsule into the Martian atmosphere is investigated within the context of modern control theory. The optimal control law which minimizes the heat generated on the surface of the capsule is obtained analytically. This in turn allows the capsule to make a successful softlanding on Mars through the partially known atmosphere of the planet. The investigation is also extended to the guidance of the capsule in a stochastic disturbance environment. An attempt is made to simplify the stochastic control law so that the mechanization of the resulting control law is within the grasp of current engineering technology." }, { "name": "Parthasarathy, Shakkottai P.", "degree": "PhD", "year": "1969", "title": "I. The Transient Boundary Layer Produced by a Sink on a Plane Wall. II. Flow of Dusty Gases", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012009-085458", "creators": [ { "name": { "family": "Parthasarathy", "given": "Shakkottai P." }, "id": "Parthasarathy-Shakkottai-P", "display_name": "Parthasarathy, Shakkottai P." } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GAFK-2R04", "abstract": "Part I: The solution for the problem of the transient boundary layers generated by a sink on a plane wall is obtained by an integral method. The incompressible flow is similar and the similarity solutions are obtained for the two dimensional and axisymmetric cases. The velocity layer reaches a steady state and the thermal layer does not. For large times, when the thermal layer is much thicker than the velocity layer, a solution for the temperature field is obtained ignoring the velocity layer. With some approximations to the flow near the sink, similar solutions for compressible flow are also obtained.\r\n\r\nPart IIa: By using the integrated equations of motion, the development of a laminar, two-dimensional, dusty jet issuing from a slit is considered. The solutions are simple in the limits \u03c4 \u2192 0 and \u03c4 \u2192 \u221e, where \u03c4 is the particle relaxation time. For arbitrary \u03c4, a numerical example is given. With some assumptions, the turbulent dusty jet is also considered.\r\n\r\nPart IIb: There are three parameters in the problem of steady motion of a dusty gas around a sphere. These are the Reynolds number R, particle parameter \u03c3 and the mass concentration of dust f[subscript \u221e]. Solutions are obtained by the perturbation method by expanding in terms of R with \u03c3 or \u03c3/R fixed, in the limit R \u2192 0. Solutions are also obtained for the limit R tending to infinity with f < < 1. In both cases critical values of \u03c3 exist, below which the sphere does not capture dust. The efficiency of capture as a function of \u03c3 is calculated in both cases." }, { "name": "Pfeiffer, Wayne Wallace", "degree": "PhD", "year": "1969", "title": "Reflection and Transmission Functions in Reactor Physics", "advisor": "Shapiro, Jerome L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072017-101556497", "creators": [ { "name": { "family": "Pfeiffer", "given": "Wayne Wallace" }, "id": "Pfeiffer-Wayne-Wallace", "display_name": "Pfeiffer, Wayne Wallace" } ], "advisors": [ { "name": { "family": "Shapiro", "given": "Jerome L." }, "id": "Shapiro-J-L", "role": "advisor", "display_name": "Shapiro, Jerome L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/73BQ-HK18", "abstract": "The utility of reflection and transmission function (or collectively,\r\nresponse function) concepts in reactor physics is extensively\r\ninvestigated. Previously obtained differential (invariant imbedding)\r\nand functional (adding) equations for the response functions are re-derived\r\nin a unified manner. In addition a numerical halving technique\r\nis developed from the adding relations.
\r\n\r\n\r\nExisting response function calculations are summarized and\r\nextended by combining the invariant imbedding and functional equations.\r\nFor deep-penetration shielding problems in slab geometry,\r\nthis combined response function approach is shown to be more efficient\r\nthan conventional Monte Carlo or discrete ordinates techniques.\r\nThe response function approach is also shown to be efficient for a\r\ncriticality search in slab geometry. As a step toward a more general\r\ntreatment, invariant imbedding equations are derived, but not solved,\r\nin finite cylindrical geometry.
\r\n\r\n\r\nFinally the feasibility of performing response function experiments\r\nto obtain cross-section and criticality information is examined.\r\nThe envisioned experimental set-up is described and calculations are\r\ncarried out to verify the analytical procedures, with particular emphasis\r\non the propagation of errors. Cross-sections can be determined\r\nusing the halving scheme, which provides a theoretically sound\r\ntechnique for multiple scattering correction. Thus experiments may\r\nbe done on moderately thick slabs. Criticality parameters can be\r\nobtained from measured response functions using the criticality\r\nsearch procedure. Because response function experiments are\r\nexpected to be relatively quick and cheap compared to present cross-section\r\nand critical experiments, it is concluded that response\r\nfunction experiments should be carried out as soon as possible to\r\ndetermine whether they are as useful as our analysis indicates.
" }, { "name": "Picraux, Samuel Thomas", "degree": "PhD", "year": "1969", "title": "Channeling in Semiconductors and its Application to the Study of Ion Implantation", "advisor": "Mayer, James Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:05102017-142717261", "creators": [ { "name": { "family": "Picraux", "given": "Samuel Thomas" }, "id": "Picraux-Samuel-Thomas", "display_name": "Picraux, Samuel Thomas" } ], "advisors": [ { "name": { "family": "Mayer", "given": "James Walter" }, "id": "Mayer-J-W", "role": "advisor", "display_name": "Mayer, James Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/EBXR-QS35", "abstract": "The channeling characteristics of protons and helium ions in various\r\ndiamond-type lattices (diamond, Si, Ge, GaP, GaAs, GaSb) have been\r\nstudied by means of elastic backscattering in the 0.5 to 2 MeV range.\r\nCritical angles (\u03c8\u00bd) and minimum yields (\u03c8\u00bd) have been measured and\r\ncompared to theory. The values of \u03c8\u00bd for axial channeling have a functional\r\ndependence which agrees well with calculations based on the average\r\npotential along the row - both for uniform and for non-uniform spacing\r\nand (in the case of the compound semiconductors) for mixed atomic\r\ncomposition. Planar critical angles also show a functional dependence\r\nin agreement with average potential calculations. However, it is necessary\r\nto include in the calculation the effect of surface transmission\r\nwhich becomes increasingly important for higher order planar directions\r\n(e.g. lower atomic density of the planes). Measured full angular distributions\r\nare compared with calculated distributions for planar channeling. \r\nFor both axial and planar channeling the measured critical\r\nangles are \u2248 25% lower in absolute magnitude than calculated.
\r\n\r\n\r\nChanneling and electrical measurements are combined to study ion\r\nimplanted impurities in silicon. The lattice disorder and impurity atom\r\nlattice location are investigated by channeling effect measurements\r\nusing a 1 MeV helium ion analyzing beam. The electrical type, number of\r\ncarriers/cm2 and mobility are determined by use of Hall effect and sheet\r\nresistivity measurements.
\r\n\r\n\r\nThe anneal behavior of Cd and Te implantations (20-50 keV) into Si\r\nat substrate temperatures of 23\u00b0C and 350\u00b0C were investigated. The room\r\ntemperature Te implants showed substitutional behavior and donor action\r\nafter anneal at 600\u00b0C. In room temperature Cd implantations, outdiffusion\r\nof the Cd was observed when the disordered layer annealed. Implantations\r\nof Cd at 350\u00b0C indicated the presence of an interstitial\r\ncomponent and n-type behavior was observed.
\r\n" }, { "name": "Randles, Philip Wayne", "degree": "PhD", "year": "1969", "title": "Modal Representations for the High-Frequency Response of Elastic Plates", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-101810031", "creators": [ { "name": { "family": "Randles", "given": "Philip Wayne" }, "id": "Randles-Philip-Wayne", "display_name": "Randles, Philip Wayne" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/F4BM-J980", "abstract": "Representations for the high-frequency response of a\r\nsuddenly loaded infinite plate are obtained from the modal\r\nform of the exact solution. The method of approach is presented\r\nby treating a linearly elastic, homogeneous, isotropic\r\nplate subjected to a normal impulsive line load on\r\none face.
\r\n\r\n\r\nAn investigation of the branches of the governing\r\nRayleigh-Lamb frequency equation is given. These branches\r\nare closely related to the modes of propagation, the sum\r\nof which is the modal solution. The relationship between\r\nthe high-frequency portions of the underlying frequency\r\nspectra and the high-frequency response is brought out.
\r\n\r\n\r\nSeries representations for the branches are used to\r\nfacilitate a summation over the branch (or mode) numbers.\r\nThis results in convenient high-frequency representations,\r\nwhich exhibit all of the expected singular wave fronts in\r\nthe plate.
\r\n\r\n\r\nThe method appears to be applicable to a broader\r\nclass of problems than other methods which have been used\r\nfor the high-frequency response of a plate.
" }, { "name": "Robinson, William McKinley, Jr.", "degree": "PhD", "year": "1969", "title": "Mass Spectrometric Studies of Ionization Precursors Ahead of Strong Shock Waves", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11222005-155153", "creators": [ { "name": { "family": "Robinson", "given": "William McKinley, Jr." }, "id": "Robinson-William-McKinley-Jr", "display_name": "Robinson, William McKinley, Jr." } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0QN4-MY03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental study was conducted to identify the nature and origin of precursor ions produced by photoionization ahead of strong shock waves in xenon. A magnetic mass spectrometer is mounted at the end of a hydrogen-driven shock tube. Ions produced upstream of a shock wave are sampled by the spectrometer and the collected current provides a continuous time history of a particular ionic species. A mass spectrum is obtained in the precursor region for all impurities found in the shock tube. The incident shock Mach number is varied from 11.9 to 21.3, the initial pressure is varied from 0.050 to 0.500 torr, and the impurity level is altered. In all the conditions studied, the dominant ion present in the precursor is Xe+, although in certain instances, the impurity ion currents are found to be of the same order of magnitude as the xenon ion current. For small impurity levels, photoionization processes in xenon and impurities are apparently independent. Independent double probe measurements determine the total ion density to be about [...] at the shock front, the observable precursor extending about 150 cm from the shock wave.\r\n\r\nA theoretical model accounting for one-step and multi-step photoionization of xenon and impurities is used to find the ionization level ahead of a shock wave. The calculated ion density profiles agree well with experimental observations at the low pressures, where it appears that one-step photoionization predominates. Lack of agreement at high pressures, where, apparently, multi-step ionization is more efficient than the single-step process, suggests inadequacies in the treatment of photoexcitation and multi-step photoionization. Additional areas for experimental study are suggested.\r\n\r\nThe mass spectrometric data yield a better understanding of the role of radiation in shock structure, of the kinetics of photoionization processes in rare gases, and of the influence of impurities in the experimental facility on the radiation mechanisms." }, { "name": "Rodriguez, Valentin", "degree": "PhD", "year": "1969", "title": "Measurement of the Electron Drift Velocity in Silicon", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-09272002-164439", "creators": [ { "name": { "family": "Rodriguez", "given": "Valentin" }, "id": "Rodriguez-Valentin", "display_name": "Rodriguez, Valentin" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/B8ER-9195", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nThe drift velocity of electrons in silicon at high electric fields is measured in the <111> direction over the range of lattice temperatures from 4.2[degrees]K to 300[degrees]K. This information is obtained from measurements of pure unipolar (sclc) space-charge-limited current. Structures of the type [n^+ n n^+] and [n^+ p n^+] have been manufactured to study this current. The experimental V-I characteristics obtained from these structures offer a consistent picture. The theoretical models adopted are simple and adequate.\r\n\r\nThe drift velocity is found to increase monotonically with electric field strength in the range of lattice temperatures covered. It is established that a limiting drift velocity exists at high electric fields. Its temperature dependence is measured from 4.2[degrees]K to 300[degrees]K. No indication of a negative differential mobility - as observed in GaAs and Ge below 77[degrees]K - is present. At 300[degrees]K and 77[degrees]K the velocity-field relationship is determined from the linear (low field) range up to a field strength of the order of [10^5] volt/cm. A comparison with results obtained by other authors at those two temperatures yields good agreement, in particular at 300[degrees]K.\r\n\r\nA fairly complete treatment of the influence on unipolar sclc of: (1) trapping, (2) geometry, (3) ionized impurities, (4) illumination, and (5) thermal carriers, is presented. In particular, the effect of giant trapping and normal trapping is studied in detail. The threshold voltage is measured as a function of lattice temperature from 4.2[degrees]K to 300[degrees]K. In the range from 4.2[degrees]K to 50[degrees]K, its temperature dependence is correlated to that of the trapping crosssection for the compensated donor atoms. Above 77[degrees]K, the temperature dependence of the threshold voltage is linked to that of the Debye length. From this analysis, the degree of compensation of the material is derived in a simple way." }, { "name": "Rose, James Robert", "degree": "PhD", "year": "1969", "title": "An Analysis of the Incompressible Two-Dimensional Jet Ejector", "advisor": "Lissaman, Peter B. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-093813", "creators": [ { "name": { "family": "Rose", "given": "James Robert" }, "id": "Rose-James-Robert", "display_name": "Rose, James Robert" } ], "advisors": [ { "name": { "family": "Lissaman", "given": "Peter B. S." }, "id": "Lissaman-P-B-S", "role": "advisor", "display_name": "Lissaman, Peter B. S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q1EZ-AW49", "abstract": "A general method for calculating the performance of two-dimensional jet ejector systems is presented, with special emphasis on those qualities desired in thrust augmenter devices. The nature of the viscous-inviscid interaction problem is examined and a \"frictionless\" model is defined. The equations are solved for the particular parametric problem of a single jet in a finite length shroud of uniform height. The flow in the \"recovery\" or confined-mixing region is discussed for this model and techniques are developed which may be applied to devices with diffusing systems.\r\n\r\nThe solutions presented for the free-mixing or interaction region are shown to agree with the simple channel flow studied analytically and experimentally by Curtet." }, { "name": "Sahinkaya, Yilmaz Esref", "degree": "PhD", "year": "1969", "title": "Minimum Energy Control of Electric Propulsion Vehicles", "advisor": "Sridhar, Rangasami", "url": "https://resolver.caltech.edu/CaltechETD:etd-10032002-120235", "creators": [ { "name": { "family": "Sahinkaya", "given": "Yilmaz Esref" }, "id": "Sahinkaya-Yilmaz-Esref", "display_name": "Sahinkaya, Yilmaz Esref" } ], "advisors": [ { "name": { "family": "Sridhar", "given": "Rangasami" }, "id": "Sridhar-Rangasami", "role": "advisor", "display_name": "Sridhar, Rangasami" } ], "committee": [ { "name": { "family": "Sridhar", "given": "Rangasami" }, "id": "Sridhar-Rangasami", "role": "chair", "display_name": "Sridhar, Rangasami" }, { "name": { "family": "Grettenberg", "given": "Thomas L." }, "id": "Grettenberg-T-L", "role": "member", "display_name": "Grettenberg, Thomas L." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Langmuir", "given": "Robert V." }, "id": "Langmuir-R-V", "role": "member", "display_name": "Langmuir, Robert V." } ], "option_major": [ "eleceng" ], "doi": "10.7907/24NJ-WQ58", "abstract": "Minimum-energy control problems for various electric propulsion vehicles are formulated and solved using modern control theory and systems engineering techniques. Analytical results are obtained by making several simplifications and approximations in the dynamical equations of each system whose performance index is related to the minimization of the system energy consumption for a required control action. An attempt is made to implement the resulting control laws using the current engineering practice.\r\n\r\n" }, { "name": "Schlueter, Roger Selig", "degree": "PhD", "year": "1969", "title": "Thermal Wave Propagation in Helium II", "advisor": "Hsieh, Din-Yu", "url": "https://resolver.caltech.edu/CaltechTHESIS:03312017-093136052", "creators": [ { "name": { "family": "Schlueter", "given": "Roger Selig" }, "id": "Schlueter-Roger-Selig", "display_name": "Schlueter, Roger Selig" } ], "advisors": [ { "name": { "family": "Hsieh", "given": "Din-Yu" }, "id": "Hsieh-Din-Yu", "role": "advisor", "display_name": "Hsieh, Din-Yu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/3T5S-CN85", "abstract": "Landau's equations for the two-fluid model of liquid helium II\r\nare us ed as the basis for an investigation of the properties of thermal\r\nwave propagation. A number of assumptions are made which reduce\r\nthe four original equations to a system of two non-linear partial differential equations valid to first order in the relative velocity of the\r\ntwo components. These equations are analogous to Riemann's equations\r\nwhich describe pressure waves in a classical fluid.
\r\n\r\n\r\nThis system of equations, when reduced to just one space\r\ndimension is shown to be hyperbolic and a set of characteristics and\r\ninvariants is found. A particularly simple, one-dimensional problem\r\nis then formulated and an explicit solution is given. This solution is\r\nthen studied in detail to show the distortion of a temperature pulse as\r\nit propagates and also to show effects such as non-linear breaking.
\r\n\r\n\r\nSubsequently, the restrictive assumptions are eliminated\r\nindividually and the equations are then valid to second order in the\r\nrelative velocity; the effects of including thermal expansion and using\r\nthe relative velocity as a thermodynamic variable are given. Also,\r\nsome effects due to the interaction of first and second sound are\r\ninvestigated. In all cases, the results are compared with other\r\nresults based on equations differing from the Landau equations and\r\nwith results found by using perturbation techniques.
\r\n\r\nFinally, equations based on the same Landau equations are\r\nderived and discussed which describe steady state shock (discontinuous)\r\nsolutions.
\r\n\r\nSuggestions for further theoretical and experimental work are\r\nmade.
\r\n\r\n " }, { "name": "Srinivasan, Ramachandra", "degree": "PhD", "year": "1969", "title": "A Nonlinear Systems Model for the Control Mechanism of Free Fatty Acid-Glucose Metabolism in Normal Humans", "advisor": "Sridhar, Rangasami", "url": "https://resolver.caltech.edu/CaltechTHESIS:02262016-130953115", "creators": [ { "name": { "family": "Srinivasan", "given": "Ramachandra" }, "id": "Srinivasan-Ramachandra", "display_name": "Srinivasan, Ramachandra" } ], "advisors": [ { "name": { "family": "Sridhar", "given": "Rangasami" }, "id": "Sridhar-Rangasami", "role": "advisor", "display_name": "Sridhar, Rangasami" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CV4F-WW33", "abstract": "A mathematical model is proposed in this thesis for the control mechanism of free fatty acid-glucose metabolism in healthy individuals under resting conditions. The objective is to explain in a consistent manner some clinical laboratory observations such as glucose, insulin and free fatty acid responses to intravenous injection of glucose, insulin, etc. Responses up to only about two hours from the beginning of infusion are considered. The model is an extension of the one for glucose homeostasis proposed by Charette, Kadish and Sridhar (Modeling and Control Aspects of Glucose Homeostasis. Mathematical Biosciences, 1969). It is based upon a systems approach and agrees with the current theories of glucose and free fatty acid metabolism. The description is in terms of ordinary differential equations. Validation of the model is based on clinical laboratory data available at the present time. Finally procedures are suggested for systematically identifying the parameters associated with the free fatty acid portion of the model.\r\n\r\n" }, { "name": "St-Cyr, Gaetan Joseph", "degree": "PhD", "year": "1969", "title": "Control Mechanisms in the Human Binocular Oculomotor System", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02262016-115946369", "creators": [ { "name": { "family": "St-Cyr", "given": "Gaetan Joseph" }, "id": "St-Cyr-Gaetan-Joseph", "display_name": "St-Cyr, Gaetan Joseph" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/HWV2-8062", "abstract": "A study of human eye movements was made in order to elucidate the nature of the control mechanism in the binocular oculomotor system.
\r\n\r\nWe first examined spontaneous eye movements during monocular and binocular fixation in order to determine the corrective roles of flicks and drifts. It was found that both types of motion correct fixational errors, although flicks are somewhat more active in this respect. Vergence error is a stimulus for correction by drifts but not by flicks, while binocular vertical discrepancy of the visual axes does not trigger corrective movements.
\r\n\r\nSecond, we investigated the non-linearities of the oculomotor system by examining the eye movement responses to point targets moving in two dimensions in a subjectively unpredictable manner. Such motions consisted of hand-limited Gaussian random motion and also of the sum of several non-integrally related sinusoids. We found that there is no direct relationship between the phase and the\r\ngain of the oculomotor system. Delay of eye movements relative to target motion is determined by the necessity of generating a minimum afferent (input) signal at the retina in order to trigger corrective eye movements. The amplitude of the response is a function of the biological constraints of the efferent (output) portion of the system: for target motions of narrow bandwidth, the system responds preferentially to the highest frequency; for large bandwidth motions, the system distributes the available energy equally over all frequencies. Third, the power spectra of spontaneous eye movements were compared with the spectra of tracking eye movements for Gaussian random target motions of varying bandwidths. It was found that there is essentially no difference among the various curves. The oculomotor system tracks a target, not by increasing the mean rate of impulses along the motoneurons of the extra-ocular muscles, but rather by coordinating those spontaneous impulses which propagate along the motoneurons during stationary fixation. Thus, the system operates at full output at all times.
\r\n\r\n\r\nFourth, we examined the relative magnitude and phase of motions of the left and the right visual axes during monocular and binocular viewing. We found that the two visual axes move vertically in perfect synchronization at all frequencies for any viewing condition. This is not true for horizontal motions: the amount of vergence noise is highest for stationary fixation and diminishes for tracking tasks as\r\nthe bandwidth of the target motion increases. Furthermore, movements of the occluded eye are larger than those of the seeing eye in monocular viewing. This effect is more pronounced for horizontal motions, for stationary fixation, and for lower frequencies.
\r\n\r\nFinally, we have related our findings to previously known facts about the pertinent nerve pathways in order to postulate a model for the neurological binocular control of the visual axes.
\r\n" }, { "name": "Suzuki, Takao", "degree": "PhD", "year": "1969", "title": "I. Anisotropy and Crystal Structure of Ferromagnetic Thin Films. II. Investigations into Magnetic Microstructure by Lorentz Microscopy", "advisor": "Wilts, Charles H.; Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechTHESIS:02222016-085859004", "creators": [ { "name": { "family": "Suzuki", "given": "Takao" }, "id": "Suzuki-Takao", "display_name": "Suzuki, Takao" } ], "advisors": [ { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." }, { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4gb0-gj02", "abstract": "The induced magnetic uniaxial anisotropy of Ni-Fe alloy films has been shown to be related to the crystal structure of the film. By use of electron diffraction, the crystal structure or vacuum-deposited films was determined over the composition range 5% to 85% Ni, with substrate temperature during deposition at various temperatures in the range 25\u00b0 to 500\u00b0 C. The phase diagram determined in this way has boundaries which are in fair agreement with the equilibrium boundaries for bulk material above 400\u00b0C. The (\u03b1+ \u0264) mixture phase disappears below 100\u00b0C.
\r\n\r\nThe measurement of uniaxial anisotropy field for 25% Ni-Fe alloy films deposited at temperatures in the range -80\u00b0C to 375\u00b0C has been carried out. Comparison of the crystal structure phase diagram with the present data and those published by Wilts indicates that the\r\nanisotropy is strongly sensitive to crystal structure. Others have proposed pair ordering as an important source of anisotropy because of an apparent peak in the anisotropy energy at about 50% Ni composition. The present work shows no such peak, and leads to the conclusion that\r\npair ordering cannot be a dominant contributor.
\r\n\r\nWidth of the 180\u00b0 domain wall in 76% Ni-Fe alloy films as a function of film thickness up to 1800 \u00c5 was measured using the defocused mode of Lorentz microscopy. For the thinner films, the measured wall widths are in good agreement with earlier data obtained by Fuchs. For films thicker than 800 \u00c5, the wall width increases with film thickness to about 9000 \u00c5 at 1800 \u00c5 film thickness. Similar measurements for polycrystalline Co films with thickness from 200 to 1500 \u00c5 have been made. The wall width increases from 3000 \u00c5 at 400 \u00c5 film thickness to about 6000 \u00c5 at 1500 \u00c5 film thickness. The wall widths for Ni-Fe and Co films are much greater than predicted by present theories. The validity of the classical determination of wall width is discussed,\r\nand the comparison of the present data with theoretical results is given.
\r\n\r\nFinally, an experimental study of ripple by Lorentz microscopy in Ni-Fe alloy films has been carried out. The following should be noted: (1) the only practical way to determine experimentally a meaningful wavelength is to find a well-defined ripple periodicity by\r\nvisual inspection of a photomicrograph. (2) The average wavelength is of the order of 1\u00b5. This value is in reasonable agreement with the main wavelength predicted by the theories developed by others. The dependence of wavelength on substrate deposition temperature, alloy\r\ncomposition and the external magnetic field has been also studied and the results are compared with theoretical predictions. (3) The experimental fact that the ripple structure could not be observed in completely epitaxial films gives confirmation that the ripple results from the randomness of crystallite orientation. Furthermore, the experimental observation that the ripple disappeared in the range 71 and 75% Ni supports the theory that the ripple amplitude is directly\r\ndependent on the crystalline anisotropy. An attempt to experimentally determine the order of magnitude of the ripple angle was carried out. The measured angle was about 0.02 rad. The discrepancy between the experimental data and the theoretical prediction is serious. The accurate experimental determination of ripple angle is an unsolved problem.
\r\n\r\n" }, { "name": "Tombach, Ivar Harald", "degree": "PhD", "year": "1969", "title": "Velocity Measurements with a New Probe in Inhomogeneous Turbulent Jets", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-110134", "creators": [ { "name": { "family": "Tombach", "given": "Ivar Harald" }, "id": "Tombach-Ivar-Harald", "display_name": "Tombach, Ivar Harald" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V2CR-0Q19", "abstract": "Velocity profiles have been measured in subsonic, inhomogeneous, axisymmetric turbulent jets, using a new velocity measuring probe. This probe creates a train of heat pulses at one point in the flow and measures the time interval between the time a pulse is created and the time at which it is convected by the flow past a sensing wire a short distance downstream. In a turbulent flow the detected pulses are highly disturbed, but reconstruction of a mean pulse, by a digital computer, from several hundred pulses enabled calculation of a mean velocity and a velocity fluctuation level.\r\n\r\nMeasurements were made with this probe from near the nozzle to 48 diameters downstream in several combinations of jet gas and ambient gas (air-air, air-He, He-air, and He-SF[subfield 6]) having a range of jet/ambient density ratios from 0.03 to 7.25. Axial profiles of the variation with the density ratio of the jet width, mean velocity, and turbulence level were obtained from these measurements, showing the entrainment and approach to homogeneity of the inhomogeneous jet. A jet which is less dense than the ambient fluid is seen to entrain the ambient fluid more vigorously than the denser jet, as is demonstrated by its higher turbulence levels, more rapid growth, and more rapid axial decay of the mean velocity." }, { "name": "Trifunac, Mihailo Dimitrije", "degree": "PhD", "year": "1969", "title": "Investigation of Strong Earthquake Ground Motion", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192016-120838514", "creators": [ { "name": { "family": "Trifunac", "given": "Mihailo Dimitrije" }, "id": "Trifunac-Mihailo-Dimitrije", "display_name": "Trifunac, Mihailo Dimitrije" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/FE4G-RF61", "abstract": "The pattern of energy release during the Imperial Valley, California, earthquake of 1940 is studied by analysing the El Centro strong motion seismograph record and records from the Tinemaha seismograph station, 546 km from the epicenter. The earthquake was a multiple event sequence with at least 4 events recorded at El Centro in the first 25 seconds, followed by 9 events recorded in the next 5 minutes. Clear P, S and surface waves were observed on the strong motion record. Although the main part of the earthquake energy was released during the first 15 seconds, some of the later events were as large as M = 5.8 and thus are important for earthquake engineering studies. The moment calculated using Fourier analysis of surface waves agrees with the moment estimated from field measurements of fault offset after the earthquake. The earthquake engineering significance of the complex pattern of energy release is discussed. It is concluded that a cumulative increase in amplitudes of building vibration resulting from the present sequence of shocks would be significant only for structures with relatively long natural period of vibration. However, progressive weakening effects may also lead to greater damage for multiple event earthquakes.
\r\n\r\nThe model with surface Love waves propagating through a single layer as a surface wave guide is studied. It is expected that the derived properties for this simple model illustrate well several phenomena associated with strong earthquake ground motion. First, it is shown that a surface layer, or several layers, will cause the main part of the high frequency energy, radiated from the nearby earthquake, to be confined to the layer as a wave guide. The existence of the surface layer will thus increase the rate of the energy transfer into the man-made structures on or near the surface of the layer. Secondly, the surface amplitude of the guided SH waves will decrease if the energy of the wave is essentially confined to the layer and if the wave propagates towards an increasing layer thickness. It is also shown that the constructive interference of SH waves will cause the zeroes and the peaks in the Fourier amplitude spectrum of the surface ground motion to be continuously displaced towards the longer periods as the distance from the source of the energy release increases.
\r\n" }, { "name": "Tsai, Nien Chien", "degree": "PhD", "year": "1969", "title": "Influence of Local Geology on Earthquake Ground Motion", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192016-125600857", "creators": [ { "name": { "family": "Tsai", "given": "Nien Chien" }, "id": "Tsai-Nien-Chien", "display_name": "Tsai, Nien Chien" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/RFBJ-0Y82", "abstract": "As a simplified approach for estimating theoretically the influence of local subsoils upon the ground motion during an earthquake, the problem of an idealized layered system subjected to vertically incident plane body waves was studied. Both the technique of steady-state analysis and the technique of transient analysis have been used to analyze the problem.
\r\n\r\nIn the steady-state analysis, a recursion formula has been derived for obtaining the response of a layered system to sinusoidally steady-state input. Several conclusions are drawn concerning the nature of the amplification spectrum of a nonviscous layered system having its layer stiffnesses increasing with depth. Numerical examples are given to demonstrate the effect of layer parameters on the amplification spectrum of a layered system.
\r\n\r\nIn the transient analysis, two modified shear beam models have been established for obtaining approximately the response of a layered system to earthquake-like excitation. The method of continuous modal analysis was adopted for approximate analysis of the models, with energy dissipation in the layers, if any, taken into account. Numerical examples are given to demonstrate the accuracy of the models and the effect of a layered system in modifying the input motion.
\r\n\r\nConditions are established, under which the theory is applicable to predict the influence of local subsoils on the ground motion during an earthquake. To demonstrate the applicability of the models to actual cases, three examples of actually recorded earthquake events are examined. It is concluded that significant modification of the incoming seismic waves, as predicted by the theory, is likely to occur in well defined soft subsoils during an earthquake, provided that certain conditions concerning the nature of the incoming seismic waves are satisfied.
\r\n" }, { "name": "Turner, Arthur Piers Legh", "degree": "PhD", "year": "1969", "title": "The Effect of Stress and Temperature on the Velocity of Dislocations in Pure Iron Monocrystals", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-163154", "creators": [ { "name": { "family": "Turner", "given": "Arthur Piers Legh" }, "id": "Turner-Arthur-Piers-Legh", "display_name": "Turner, Arthur Piers Legh" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/RQXY-BZ41", "abstract": "The velocity of dislocations in pure iron monocrystals as a function of applied stress was measured by observing the change in length of dislocation slip bands after the application of a constant stress amplitude load pulse. Measurements covered a range of stresses from 10 to 500 Mdynes/cm2 and temperatures of 393, 295, 198, and 77\u00b0K.
\r\n\r\nThe dislocation velocity at constant stress was found to be a sensitive function of temperature. However, the nature of the variation of the velocity with temperature was found to be inconsistent with theoretical formulations of thermally assisted dislocation motion. The nature of the disagreement between the experimental results and the thermal activation models is similar to that previously observed in niobium and Fe-3%Si . The decrease in dislocation velocity with decreasing temperature was also found to be too large to be attributed to hardening from the small amounts of impurities in the crystals.
\r\n\r\nThe behavior of the dislocations as determined by this study was found to be consistent with predictions made from measurements of the macroscopic yield stress. However, the results of this study differ markedly from the behavior predicted from measurements of the strain rate sensitivity of the flow stress.
" }, { "name": "Victoria, Keith Jordis", "degree": "PhD", "year": "1969", "title": "The Hypersonic Laminar Boundary Layer Near a Sharp Expansion Corner", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-06172009-151827", "creators": [ { "name": { "family": "Victoria", "given": "Keith Jordis" }, "id": "Victoria-Keith-Jordis", "display_name": "Victoria, Keith Jordis" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EZX3-M918", "abstract": "The integral moment method for treating interactions between a laminar boundary layer and an external supersonic flow is applied to the problem of the hypersonic laminar boundary layer near sharp and slightly rounded convex (expansion) corners. The general features of this type of interacting flow are established by an analytical solution of the integral equations using the method of matched asymptotic expansions for the case of small interaction parameter. Numerical solutions are obtained for flows for which the interaction parameter can no longer be considered small.
\r\n\r\nAn experimental study is carried out in the GALCIT Mach 8 hypersonic wind tunnel in order to study the two-dimensional laminar boundary layer expansion. Major emphasis is placed on the acquisition of detailed data near the corner region. The basic measurements consist of the model surface pressure distribution and pitot pressure surveys of the boundary layer and inviscid flow field between the boundary layer and the leading edge shock wave both upstream and downstream of the corner region. The surface pressure measurements illustrate the striking departure of the flow field at hypersonic speeds from the classical Prandtl-Meyer description.
\r\n\r\nThese data with appropriate assumptions made regarding the static pressure and temperature fields at points away from the model surface allow calculation of the distributions of profile functions defined in the integral moment method formulation. These distributions along with the surface pressure distribution are compared directly with solutions of the moment equations.
\r\n" }, { "name": "Wheeler, Lewis Turner", "degree": "PhD", "year": "1969", "title": "Some Theorems in Classical Elastodynamics", "advisor": "Sternberg, Eli", "url": "https://resolver.caltech.edu/CaltechTHESIS:01252016-143403275", "creators": [ { "name": { "family": "Wheeler", "given": "Lewis Turner" }, "id": "Wheeler-Lewis-Turner", "display_name": "Wheeler, Lewis Turner" } ], "advisors": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "advisor", "display_name": "Sternberg, Eli" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/N9HD-N641", "abstract": "This investigation is concerned with various fundamental aspects of the linearized dynamical theory for mechanically homogeneous and isotropic elastic solids. First, the uniqueness and reciprocal theorems of dynamic elasticity are extended to unbounded domains with the aid of a generalized energy identity and a lemma on the prolonged quiescence of the far field, which are established for this purpose. Next, the basic singular solutions of elastodynamics are studied and used to generate systematically Love's integral identity for the displacement field, as well as an associated identity for the field of stress. These results, in conjunction with suitably defined Green's functions, are applied to the construction of integral representations for the solution of the first and second boundary-initial value problem. Finally, a uniqueness theorem for dynamic concentrated-load problems is obtained.
" }, { "name": "Whitney, Arthur Karl", "degree": "PhD", "year": "1969", "title": "Minimum Drag Profiles in Infinite Cavity Flow", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192016-150014870", "creators": [ { "name": { "family": "Whitney", "given": "Arthur Karl" }, "id": "Whitney-Arthur-Karl", "display_name": "Whitney, Arthur Karl" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/QM8Z-5141", "abstract": "The problem considered is that of minimizing the drag of a symmetric plate in infinite cavity flow under the constraints of fixed arclength and fixed chord. The flow is assumed to be steady, irrotational, and incompressible. The effects of gravity and viscosity are ignored.
\r\n\r\nUsing complex variables, expressions for the drag, arclength, and chord, are derived in terms of two hodograph variables, \u0393 (the logarithm of the speed) and \u03b2 (the flow angle), and two real parameters, a magnification factor and a parameter which determines how much of the plate is a free-streamline.
\r\n\r\nTwo methods are employed for optimization:
\r\n\r\n(1) The parameter method. \u0393 and \u03b2 are expanded in finite orthogonal series of N terms. Optimization is performed with respect to the N coefficients in these series and the magnification and free-streamline parameters. This method is carried out for the case N = 1 and minimum drag profiles and drag coefficients are found for all values of the ratio of arclength to chord.
\r\n\r\n(2) The variational method. A variational calculus method for minimizing integral functionals of a function and its finite Hilbert transform is introduced, This method is applied to functionals of quadratic form and a necessary condition for the existence of a minimum solution is derived. The variational method is applied to the minimum drag problem and a nonlinear integral equation is derived but not solved.
\r\n" }, { "name": "Wong, Felix Shek Ho", "degree": "PhD", "year": "1969", "title": "Large Plane Deformations of Thin Elastic Sheets of Neo-Hookean Material", "advisor": "Shield, Richard T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02222016-101835821", "creators": [ { "name": { "family": "Wong", "given": "Felix Shek Ho" }, "id": "Wong-Felix-Shek-Ho", "display_name": "Wong, Felix Shek Ho" } ], "advisors": [ { "name": { "family": "Shield", "given": "Richard T." }, "id": "Shield-R-T", "role": "advisor", "display_name": "Shield, Richard T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/M380-M034", "abstract": "Large plane deformations of thin elastic sheets of neo-Hookean material are considered and a method of successive substitutions is developed to solve problems within the two-dimensional theory of finite plane stress. The first approximation is determined by linear boundary value problems on two harmonic functions, and it is approached asymptotically at very large extensions in the plane of the sheet. The second and higher approximations are obtained by solving\r\nPoisson equations. The method requires modification when the membrane has a traction-free edge.
\r\n\r\nSeveral problems are treated involving infinite sheets under uniform biaxial stretching at infinity. First approximations are obtained when a circular or elliptic inclusion is present and when the sheet has a circular or elliptic hole, including the limiting cases of a line inclusion and a straight crack or slit. Good agreement with exact solutions is found for circularly symmetric deformations. Other examples discuss the stretching of a short wide strip, the deformation near a boundary corner which is traction-free, and the application of a concentrated load to a boundary point.
\r\n" }, { "name": "Yoh, James", "degree": "PhD", "year": "1969", "title": "Gas Laser Discharge Noise and its Effect on the Laser Output", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03212016-082302712", "creators": [ { "name": { "family": "Yoh", "given": "James" }, "id": "Yoh-James", "display_name": "Yoh, James" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ysmv-qp80", "abstract": "A large portion of the noise in the light output of a laser oscillator is associated with the noise in the laser discharge. The effect of the discharge noise on the laser output has been studied.\r\nThe discharge noise has been explained through an ac equivalent circuit of the laser discharge tube.
\r\n\r\nThe discharge noise corresponds to time-varying spatial fluctuations in the electron density, the inverted population density and the dielectric permittivity of the laser medium from their equilibrium values. These fluctuations cause a shift in the resonant frequencies of the laser cavity. When the fluctuation in the dielectric permittivity of the laser medium is a longitudinally traveling wave (corresponding to the case in which moving striations exist in the positive column of the laser discharge), the laser output is frequency modulated.
\r\n\r\nThe discharge noise has been analyzed by representing the laser discharge by an equivalent circuit. An appropriate ac equivalent circuit of a laser discharge tube has been obtained by considering the frequency spectrum of the current response of the discharge tube to an ac voltage modulation. It consist of a series \u03c1LC circuit, which represents the discharge region, in parallel with a capacitance C', which comes mainly from the stray wiring. The equivalent inductance and capacitance of the discharge region have been calculated from the values of the resonant frequencies measured on discharge currents, gas pressures and lengths of the positive column. The experimental data provide for a set of typical values and dependencies on the discharge parameters for the equivalent inductance and capacitance of a discharge under laser\r\noperating conditions. It has been concluded from the experimental data that the equivalent inductance originates mainly from the positive column while the equivalent capacitance is due to the discharge region other than the positive column.
\r\n\r\nThe ac equivalent circuit of the laser discharge has been shown analytically and experimentally to be applicable to analyzing the internal discharge noise. Experimental measurements have been made on the frequency of moving striations in a laser discharge. Its experimental dependence on the discharge current agrees very well with the expected dependence obtained from an analysis of the circuit and the experimental data on the equivalent circuit elements. The agreement confirms the validity of representing a laser discharge tube by its ac equivalent circuit in analyzing the striation phenomenon and other low frequency noises. Data have also been obtained for the variation of the striation frequency with an externally-applied longitudinal magnetic field and the increase in frequency has been attributed to a decrease in the equivalent inductance of the laser discharge.
\r\n\r\n" }, { "name": "Arbocz, Johann", "degree": "PhD", "year": "1968", "title": "The Effect of General Imperfections on the Buckling of Cylindrical SheIls.", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292005-080202", "creators": [ { "name": { "family": "Arbocz", "given": "Johann" }, "id": "Arbocz-Johann", "display_name": "Arbocz, Johann" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DSCT-G640", "abstract": "An experimental and theoretical investigation of the effect of general imperfections on the buckling load of a circular cylindrical shell under axial compression was carried out.\r\n\r\nA non-contact probe has been used to make complete imperfection surveys on electroformed copper shells before and during the loading process up to the buckling load. The data recording process has been fully automated and the data reduction was done on an IBM 7094. Three-dimensional plots were obtained of the measured initial imperfection surfaces and of the growth of these imperfections under increasing axial load. The modal components of the measured imperfection surfaces were also obtained.\r\n\r\nThe theoretical solution located the limit points of the post-buckled states. A simplified imperfection model was used consisting of one axisymmetric and one asymmetric component. For global buckling the correlation between the theoretical buckling loads and the experimental values was found to be good." }, { "name": "Bauer, Luc-Olivier Edouard", "degree": "PhD", "year": "1968", "title": "Experimental Study of the Upper Hybrid Echo in Plasmas", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:07232014-114203833", "creators": [ { "name": { "family": "Bauer", "given": "Luc-Olivier Edouard" }, "id": "Bauer-Luc-Olivier-Edouard", "display_name": "Bauer, Luc-Olivier Edouard" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/6GB4-EF52", "abstract": "The two-pulse stimulated radiation of dense (109/cm3 < ne \u2264 1011/cm3) nonuniform neon and argon afterglow plasma columns longitudinally immersed in a magnetic field is studied. The magnetic field is very homogeneous over the plasma volume (\u2206B/B ~ .01%). If the S-band microwave pulses' center frequency is such that they resonantly excite a narrow band of plasma upper hybrid oscillations close to the maximum upper hybrid frequency of the column, strong two pulse echoes are observed. This new echo process is called the upper hybrid echo. The echo spectrum, echo power and echo width were studied as a function of the pulse peak power P, pulse separation \u03c4, relative density (\u03c9po/\u03c9)2, and relative cyclotron frequency (\u03c9c/\u03c9). The complex but systematic variations of the echo properties as a function of the above-mentioned parameters arc found to be in qualitative agreement with those predicted by a theory of Gould and Blum based upon a simple nonuniform unidimensional cold plasma slab model. The possible effects of electron neutral and electron ion collisions not retained in the theoretical model are discussed.
\r\n\r\nThe existence of a new type of cyclotron echo, different from that of Hill and Kaplan and not predicted by the Blum and Gould model is documented. It is believed to be also of a collective effect nature and can probably be described in terms of a theory retaining some hot plasma effects.
\r\n" }, { "name": "Bell, Lon Edward", "degree": "PhD", "year": "1968", "title": "Energy Transport by Combined Radiation and Conduction", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-102306", "creators": [ { "name": { "family": "Bell", "given": "Lon Edward" }, "id": "Bell-Lon-Edward", "display_name": "Bell, Lon Edward" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/1T27-2S89", "abstract": "The problem of one-dimensional radiative and conductive heat transfer in a medium bounded by two infinite parallel walls is treated. The medium isotropically absorbs, scatters, and emits radiation. The walls absorb and reflect isotropically, and transmit diffusely. Thermal conductivity, as well as all radiative properties, are assumed independent of temperature and wavelength. Steady state solutions are sought.\r\n\r\nApproximate solutions are developed for the temperature distribution and the heat transfer rate. The temperature distribution is expanded in a power series in a dimensionless variable that is a measure of the ratio of radiative to conductive energy transport. The first two terms are retained in the expansion. This allows the radiation integrals that appear in the basic equations to be expressed in a simple, readily evaluated form. Values for the heat transfer rate and temperature distribution are computed and compared with those of other investigators, and the range of validity of the approximation is examined.\r\n\r\nThe problem of two adjacent slabs with different optical properties is discussed. The analysis shows the interaction between the radiative and conductive transport mechanisms and displays the relative importance of each with changes in temperature. The problem of a coating of finite optical depth irradiated by an external source is also treated. The results indicate the conditions under which a coating may be characterized by an emissivity and the conditions under which it must be described in terms of its conductive and optical properties." }, { "name": "Benson, David Bernard", "degree": "PhD", "year": "1968", "title": "Formal Languages, Part Theory and Change", "advisor": "Thompson, Frederick B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03072016-161303982", "creators": [ { "name": { "family": "Benson", "given": "David Bernard" }, "id": "Benson-David-Bernard", "display_name": "Benson, David Bernard" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Frederick B." }, "id": "Thompson-F-B", "role": "advisor", "display_name": "Thompson, Frederick B." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/MY2Y-F179", "abstract": "A general definition of interpreted formal language is presented. The notion \u201cis a part of\" is formally developed and models of the resulting part theory are used as universes of discourse of the formal languages. It is shown that certain Boolean algebras are models of part theory.
\r\n\r\nWith this development, the structure imposed upon the universe of discourse by a formal language is characterized by a group of automorphisms of the model of part theory. If the model of part theory is thought of as a static world, the automorphisms become the changes which take place in the world. Using this formalism, we discuss a notion of abstraction and the concept of definability. A\r\nGalois connection between the groups characterizing formal languages and a language-like closure over the groups is determined.
\r\n\r\nIt is shown that a set theory can be developed within models of part theory such that certain strong formal languages can be said to determine their own set theory. This development is such that for a given formal language whose universe of discourse is a model of part theory, a set theory can be imbedded as a submodel of part theory so that the formal language has parts which are sets as its discursive entities.
\r\n\r\n" }, { "name": "Bluman, George Wallace", "degree": "PhD", "year": "1968", "title": "Construction of Solutions to Partial Differential Equations by the Use of Transformation Groups", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04082005-155822", "creators": [ { "name": { "family": "Bluman", "given": "George Wallace" }, "id": "Bluman-George-Wallace", "display_name": "Bluman, George Wallace" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/X1E8-1E61", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA systematic approach is given for finding similarity solutions to partial differential equations by the use of transformation groups.\r\n\r\nIf a one-parameter group of transformations leaves invariant a partial differential equation and its accompanying boundary conditions, then the number of variables can be reduced by one. In order to find the group of a given partial differential equation, the \"classical\" and \"non-classical\" methods are discussed. Initially no special boundary conditions are imposed since the invariances of the equation are used to find the general class of invariant boundary conditions.\r\n\r\nNew exact solutions to the heat equation are derived. In addition new exact solutions are found for the transition probability density function corresponding to a particular class of first order nonlinear stochastic differential equations. The equation of nonlinear heat conduction is considered from the classical point of view.\r\n\r\nThe conformal group in n \"space-like\" and m \"time-like\" dimensions, C(n, m), which is the group leaving invariant [...], is shown to be locally isomorphic to S O (n+l, m+l) for n + m >= 3. Thus locally compact operators, besides pure rotations, leave invariant Laplace's equation in n >= 3 dimensions. These are used to find closed bounded geometries for which the number of variables in Laplace's equation can be reduced." }, { "name": "Brock, Richard Runyon", "degree": "PhD", "year": "1968", "title": "Development of Roll Waves in Open Channels", "advisor": "Vanoni, Vito A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302015-161200702", "creators": [ { "name": { "family": "Brock", "given": "Richard Runyon" }, "id": "Brock-Richard-Runyon", "display_name": "Brock, Richard Runyon" } ], "advisors": [ { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "advisor", "display_name": "Vanoni, Vito A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/E2V8-1794", "abstract": "This study is concerned with some of the properties of roll waves that develop naturally from a turbulent uniform flow in a wide rectangular channel on a constant steep slope . The wave properties considered were depth at the wave crest, depth at the wave trough, wave period, and wave velocity . The primary focus was on the mean values and standard deviations of the crest depths and wave periods at a given station and how these quantities varied with distance along the channel.
\r\n\r\nThe wave properties were measured in a laboratory channel in which roll waves developed naturally from a uniform flow . The Froude number F (F = un/\u221aghn, un = normal velocity , hn = normal depth, g =acceleration of gravity) ranged from 3. 4 to 6. 0 for channel slopes So of . 05 and . 12 respectively . In the initial phase of their development the roll waves appeared as small amplitude waves with a continuous water surface profile . These small amplitude waves subsequently developed into large amplitude shock waves. Shock waves were found to overtake and combine with other shock waves with the result that the crest depth of the combined wave was larger than the crest depths before the overtake. Once roll waves began to develop, the mean value of the crest depths hnmax increased with distance . Once the shock waves began to overtake, the mean wave period Tav increased approximately\r\nlinearly with distance.
\r\n\r\nFor a given Froude number and channel slope the observed quantities h-max/hn , T' (T' = So Tav \u221ag/hn), and the standard deviations of h-max/hn and T', could be expressed as unique functions of l/hn (l = distance from beginning of channel) for the two-fold change in hn occurring in the observed flows . A given value of h-max/hn occurred at smaller values of l/hn as the Froude number was increased. For a given value of h /hh-max/hn the growth rate of \u03b4h-max/h-max\u03b4l of the shock waves increased as the Froude number was increased.
\r\n\r\nA laboratory channel was also used to measure the wave properties of periodic permanent roll waves. For a given Froude number and channel slope the h-max/hn vs. T' relation did not agree with a theory in which the weight of the shock front was neglected. After the theory was modified to include this weight, the observed values of h-max/hn were within an average of 6.5 percent of the predicted values, and the maximum discrepancy was 13.5 percent.
\r\n\r\nFor h-max/hn sufficiently large (h-max/hn > approximately 1.5) it was found that the h-max/hn vs. T' relation for natural roll waves was practically identical to the h-max/hn vs. T' relation for periodic permanent roll waves at the same Froude number and slope. As a result of this correspondence between periodic and natural roll waves, the growth rate \u03b4h-max/h-max\u03b4l of shock waves was predicted to depend on the channel slope, and this slope dependence was observed in the experiments.
" }, { "name": "Conn, Robert William", "degree": "PhD", "year": "1968", "title": "The Theory of Pulsed Neutron Experiments in Polycrystalline Moderators", "advisor": "Corngold, Noel Robert", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-101627", "creators": [ { "name": { "family": "Conn", "given": "Robert William" }, "id": "Conn-Robert-William", "display_name": "Conn, Robert William" } ], "advisors": [ { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "advisor", "display_name": "Corngold, Noel Robert" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/5M90-H174", "abstract": "This thesis is a theoretical investigation of pulsed neutron experiments in thermal non-multiplying, polycrystalline moderators. A transport approximation is used to model the spatial dependence of the neutron distribution function.
\r\n\r\nThe first part is concerned with the initial value problem for the Boltzmann equation describing the decay of thermal neutrons in a finite, polycrystalline system. The scattering kernel employed contains an isotropic. square-integrable component describing inelastic scattering and a term of the form v\u03a3el(v)\u03b4(v'2-v2) that models elastic scattering. Laplace transform methods are applied to the Boltzmann equation which lead to an unsuspected structure in the transform variable plane. Discrete eigenvalue existence theorems are re-examined and the role of new continuum terms in the total solution are considered. The variation of the lowest eigenvalue with system size, i.e., the dispersion law, is thoroughly investigated. An alternate representation of the dispersion law is developed which aids in explaining experimental results.
\r\n\r\nIn the second part of this thesis, a simplified model of the inelastic scattering kernel is used to investigate and expand the ideas in the first part ad to examine the role of various continuum contributions to the total solution. The dispersion law is examined in some detail both analytically and numerically. Comparisons are made with experimental data and multi-group calculations in beryllium and graphite.
\r\n\r\nThe implication of results for experiment and multi-group calculations are indicated throughout chapters II and III. Several results of major significance are examined together with suggestions for future work.
" }, { "name": "Crespo Mart\u00ednez, Antonio", "degree": "PhD", "year": "1968", "title": "I. Theoretical Investigation of the Reflection of Ionizing Shocks. II. Theoretical Study of Sound and Shock Waves in a Two-Phase Flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05102005-094142", "creators": [ { "name": { "family": "Crespo Mart\u00ednez", "given": "Antonio" }, "id": "Crespo-Mart\u00ednez-Antonio", "display_name": "Crespo Mart\u00ednez, Antonio" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3XYJ-AC18", "abstract": "PART I\r\n\r\nThe reflection of an ionizing shock from the end wall of a shock tube is studied theoretically following the experimental model of J. Smith. The observed perturbations in the wall pressure history are found to agree with this theory. To describe the first perturbation, a decrease in pressure due to the ionization part in the reflected shock structure, the flow equations are linearized but the rate equations are used in nonlinear form. The second perturbation, an increase in pressure due to the ionization part of the incident shock structure, is studied using Whitham's theory and assuming equilibrium behind the reflected shock.\r\n\r\nPART II\r\n\r\nThe propagation of sound and shock waves in a two-phase medium is studied theoretically using the flow equations for each component. It is shown that the assumption of constant mass ratio during the sound propagation, used previously in the literature for the case of bubbles suspended in a liquid, is only valid for low frequencies. For high frequencies a larger sound speed is obtained. These two sound speeds give two different Mach numbers. It is found that when both Mach numbers are larger than one, the shock structure in a liquid containing bubbles is given by an initial increase of the pressure, followed by a region in which it oscillates around its final equilibrium value. When the low frequency Mach number is larger than one, and the high frequency Mach number smaller than one, the oscillations disappear and the transition is uniform.\r\n\r\nThe speed of sound of the mixture is also calculated by evaluating the scattering by the suspended phase." }, { "name": "De Balbine, Guy", "degree": "PhD", "year": "1968", "title": "Computational Analysis of the Random Components Induced by a Binary Equivalence Relation", "advisor": "Franklin, Joel N.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-145557", "creators": [ { "name": { "family": "De Balbine", "given": "Guy" }, "id": "De-Balbine-Guy", "display_name": "De Balbine, Guy" } ], "advisors": [ { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "display_name": "Franklin, Joel N." } ], "committee": [ { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "chair", "display_name": "Franklin, Joel N." }, { "name": { "family": "Knuth", "given": "Donald E." }, "id": "Knuth-D-E", "role": "member", "display_name": "Knuth, Donald E." }, { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "member", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "Locke", "given": "Kenneth" }, "id": "Locke-K", "role": "member", "display_name": "Locke, Kenneth" } ], "option_major": [ "eng" ], "doi": "10.7907/2A9K-P464", "abstract": "The problem of partitioning into classes by means of a binary equivalence relation is investigated. Several algorithms for determining the number of components in the graph associated with a particular set of elements are constructed and compared. When the classification process operates on independently drawn samples of n distinct elements from a population, the expected number of components is shown to be obtainable recursively for a class of problems called separable; in all cases, estimates are available to reach any desired level of accuracy. Clustering models in Euclidean space are analyzed in detail and asymptotic formulas obtained to complement experiments. Conjectures concerning the general behavior of the expected number of components are presented also. Finally, several computational tools of general interest are improved significantly." }, { "name": "De Mari, Andrea", "degree": "PhD", "year": "1968", "title": "Accurate Numerical Steady-State and Transient One-Dimensional Solutions of Semiconductor Devices", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-154912", "creators": [ { "name": { "family": "De Mari", "given": "Andrea" }, "id": "De-Mari-Andrea", "display_name": "De Mari, Andrea" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WS5D-0211", "abstract": "Numerical iterative methods of solution of the one-dimensional basic two-carrier transport equations describing the behavior of semiconductor junctions under both steady-state and transient conditions are presented. The methods are of a very general character: none of the conventional assumptions and restrictions are introduced, and freedom is available in the choice of the doping profile, generation-recombination law, mobility dependencies, injection level., and boundary conditions applied solely at the external contacts. For a specified arbitrary input signal of either current or voltage (as a function of time) the solution yields terminal properties and all the quantities of interest in the interior of the device, such as carrier densities, electric field, electrostatic potential, particle and displacement currents, as functions of position (and time).
\r\n\r\nThe work is divided into two parts. In Part I a numerical method of solution of the steady-state problem, already available in the literature, is improved and extended, and is applied to a two-contact and a three-contact device. The analytical formulation of the original method is shown to be unsuitable for generating a sound numerical algorithm sufficiently accurate and valid for high reverse bias conditions. Difficulties and limitations are exposed and overcome by an improved formulation extended to any bias condition. As a simple application of the improved formulation, \"exact\" and first-order theory results for an idealized N-P structure are presented and compared. The poorness of some of the basic assumptions of the conventional first-order theory is exposed, in spite of a satisfactory agreement between the exact and first-order results of the terminal properties for particular bias conditions. Results for an N-P-N transistor are also reported and the inadequacy of the one-dimensional model discussed.
\r\n\r\nThe time-dependent analysis of the problem is presented in Part II. The fundamental equations are rearranged to an equivalent set of three non-linear partial differential equations more suitable for numerical methods. A highly non-uniform two-dimensional mesh, subject to maintenance of constant truncation errors in both spatial and time domains of certain pointwise operations, is chosen for the discretization of the problem, in view of the variation of most quantities over extreme ranges within short regions. Consequently an implicit discretization scheme is selected for the second-order partial differential equations of the parabolic type in order to avoid restrictions on the mesh size, without endangering numerical stability. An iterative procedure is necessary at each instant of time to cope with the several non-linearities of the problem and to achieve consistency between the internal distributions and the generating equations. This procedure is easily generalized to incorporate equations pertinent to networks of passive elements and ideal generators connected to the semiconductor device. Results for a particular single-junction structure under typical time-dependent excitations of external current and terminal voltage, and for an N-P diode interacting with an external resistor under switching conditions., are reported and discussed in detail.
\r\n\r\nConsiderable attention is focused on the numerical analysis of the steady-state and transient problems in order to achieve a numerical algorithm sufficiently sound and efficient to cope with the several difficulties of the problem, such as the small differences between nearly equal numbers, the variation of most quantities over extremely wide ranges in short regions, and the stability conditions related to the discretization of partial differential equations of the parabolic type.
" }, { "name": "DeLong, Raymond Kay", "degree": "PhD", "year": "1968", "title": "The Unsteady Forces on Slender Delta Wing Hydrofoils Oscillating in Heave", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072015-164403874", "creators": [ { "name": { "family": "DeLong", "given": "Raymond Kay" }, "id": "Delong-Raymond-Kay", "display_name": "DeLong, Raymond Kay" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/H7R1-KF18", "abstract": "The investigations described herein are both experimental and theoretical. An experimental technique is described by which the models tested could be oscillated sinusoidally in heave. The apparatus used to gather the unsteady lift, drag and pitching moment data is also described.
\r\n\r\nThe models tested were two flat delta wings with apex angles of 15\u00b0 and 30\u00b0 and they had sharp leading edges to insure flow separation. The models were fabricated from 0.25 inch aluminum plate and were approximately one foot in length.
\r\nThree distinct types of flow were investigated: 1) fully wetted, 2) ventilated and 3) planing. The experimental data are compared with existing theories for steady motions in the case of fully wetted delta wings. Ventilation measurements, made only for the 30\u00b0 model at 20\u00b0 angle of attack, of lift and drag are presented.
\r\n\r\nA correction of the theory proposed by M.P. Tulin for high speed planing of slender bodies is presented and it is extended to unsteady motions. This is compared to the experimental measurements made at 6\u00b0 and 12\u00b0 angle of attack for the two models previously described.
\r\n\r\nThis is the first extensive measurement of unsteady drag for any shape wing, the first measurement of unsteady planing forces, the first quantitative documentation of unstable oscillations near a free surface, and the first measurements of the unsteady forces on ventilated delta wings. The results of these investigations, both theoretical and experimental, are discussed and further investigations suggested.
\r\n" }, { "name": "Duderstadt, James Johnson", "degree": "PhD", "year": "1968", "title": "The Theory of Neutron Wave Propagation", "advisor": "Lurie, Harold; Corngold, Noel Robert", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032004-144322", "creators": [ { "name": { "family": "Duderstadt", "given": "James Johnson" }, "id": "Duderstadt-James-Johnson", "display_name": "Duderstadt, James Johnson" } ], "advisors": [ { "name": { "family": "Lurie", "given": "Harold" }, "id": "Lurie-H", "role": "advisor", "display_name": "Lurie, Harold" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "advisor", "display_name": "Corngold, Noel Robert" } ], "committee": [ { "name": { "family": "Lurie", "given": "Harold" }, "id": "Lurie-H", "role": "chair", "display_name": "Lurie, Harold" }, { "name": { "family": "Corngold", "given": "Noel Robert" }, "id": "Corngold-N-R", "role": "member", "display_name": "Corngold, Noel Robert" }, { "name": { "family": "Shapiro", "given": "Jerome L." }, "id": "Shapiro-J-L", "role": "member", "display_name": "Shapiro, Jerome L." }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" } ], "option_major": [ "eng" ], "doi": "10.7907/2X5F-DQ88", "abstract": "The objectives of this thesis include the development of an exact theory of neutron wave propagation in non-multiplying media as well as the application of this theory to analyze current experimental work.
\r\n\r\nAn initial study is made of the eigenvalue spectrum of the velocity-dependent Boltzmann transport operator for plane wave propagation in both noncrystalline and polycrystalline moderators. The point spectrum is discussed in detail, and a theorem concerning the existence of discrete eigenvalues for high frequency, high absorption, and/or small transverse dimensions is demonstrated. The limiting cases of low and high frequency behavior are analyzed. A physical interpretation of the discrete and continuum eigenfunctions (plane wave modes) is given, and the point spectrum existence theorem is explained in the light of such interpretations.
\r\n\r\nUsing this spectral representation, a technique for solving full-range boundary value problems for a general noncrystalline scattering kernel ~s presented. Orthogonality and completeness of the eigenfunctions are demonstrated, and the problem of a plane source at the origin of an infinite medium is solved. This solution is compared with that obtained by a Fourier transform technique. A procedure for solving half- range boundary value problems is presented for a one-term separable kernel model. For purposes of illustration, the problem of an oscillating source incident upon the boundary of a half-space is solved. The difficulty in extending the half-range theory to more general scattering models is discussed.
\r\n\r\nThe second part of the thesis proceeds to demonstrate this theory in more detail by applying it to analyze recent neutron wave experiments in graphite and D2O parallelepipeds. To facilitate the interpretation of the general solution, the inelastic scattering kernel is approximated by a separable kernel, while the elastic scattering is modeled with a Dirac \u03b4-function. The eigenvalue spectrum is analyzed in some detail, revealing several interesting conclusions concerning the experimental data and methods of data analysis. Several modifications in experimental design and analysis are suggested.
\r\n\r\nThe agreement of the theory with experiment is sufficient to warrant its application to the analysis of more complicated experiments (multiple\u00b7-region, multiplying media, pulse propagation, etc.). Several suggestions for such extensions are indicated.
" }, { "name": "Farber, Steven Mark", "degree": "PhD", "year": "1968", "title": "On the Signal Selection Problem for Phase Coherent and Incoherent Communication Channels", "advisor": "Grettenberg, Thomas L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11052012-151028981", "creators": [ { "name": { "family": "Farber", "given": "Steven Mark" }, "id": "Farber-Steven-Mark", "display_name": "Farber, Steven Mark" } ], "advisors": [ { "name": { "family": "Grettenberg", "given": "Thomas L." }, "id": "Grettenberg-T-L", "role": "advisor", "display_name": "Grettenberg, Thomas L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2JDG-ST74", "abstract": "Landau and Slepian [10] have recently obtained a lower bound for \r\nthe probability of error for any equienergy signal set in the infinite\r\nband Gaussian, additive noise channel. They further claim that the\r\nregular simplex signal set achieves equality in their lower bound and\r\nthereby proves the optimality of this set.
\r\n\r\nIn the following paper it is proven that the simplex signals\r\nachieve equality in the lower bound of Landau and Slepian only when\r\nthe dimension n is less than or equal to three. There is also\r\nshown to be an equivalence between certain optimal signal sets for the\r\nphase coherent channel described by Landau and Slepian and certain\r\noptimal signal sets for the incoherent case which have been recently\r\ndiscovered by Schaffner and Krieger [11] and [12].
" }, { "name": "Fersht, Rena Scher", "degree": "PhD", "year": "1968", "title": "Buckling of Cylindrical Shells with Random Imperfections", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142005-105632", "creators": [ { "name": { "family": "Fersht", "given": "Rena Scher" }, "id": "Fersht-Rena-Scher", "display_name": "Fersht, Rena Scher" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KF7B-XA89", "abstract": "The buckling stability analysis of long cylindrical shells with random imperfections subjected to axial load is treated using two different approaches. The first study is based on a Lyapunov method which enables one to establish sufficient conditions for buckling stability of a long cylindrical shell with axisymmetric random imperfections. A perturbed system of equations in the neighborhood of the prebuckling solution is investigated. By reducing the problem to a system of integral equations, it is observed that the stability boundary value problem of a long shell is similar to that of a dynamical system with random parametric excitations.\r\n\r\nInitial imperfections were assumed to have Gaussian distribution and an exponential cosine correlation function. The critical load was obtained as a function of the root mean square of the imperfections. Results obtained are qualitatively similar to those of Koiter for a periodic imperfection (Ref. 1).\r\n\r\nThe second part is based on the approximate method of truncated hierarchy. The prebuckling state of equilibrium for asymmetric imperfections is found by a successive substitution technique. A homogeneous variational system of equations is set up in order to examine the existence of bifurcation in the neighborhood of the equilibrium state. These last equations involve random parametric terms. The truncated hierarchy method is applied and characteristic equations are obtained. Various exponential cosine correlation functions associated with asymmetric imperfections are examined numerically. Qualitatively the results obtained are as anticipated." }, { "name": "Gilpin, Robert Ridgeway", "degree": "PhD", "year": "1968", "title": "Experimental and Theoretical Studies of the Electrothermal Instability in a Nonequilibrium Plasma", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072015-140402720", "creators": [ { "name": { "family": "Gilpin", "given": "Robert Ridgeway" }, "id": "Gilpin-Robert-Ridgeway", "display_name": "Gilpin, Robert Ridgeway" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/H7BQ-RD31", "abstract": "Experimental and theoretical studies have been made of the electrothermal waves occurring in a nonequilibrium MHD plasma. These waves are caused by an instability that occurs when a plasma having a dependence of conductivity on current density is subjected to crossed electric and magnetic fields. Theoretically, these waves were studied by developing and solving the equations of a steady, one-dimensional nonuniformity in electron density. From these nonlinear equations, predictions of the maximum amplitude and of the half width of steady waves could be obtained. Experimentally, the waves were studied in a nonequilibrium discharge produced in a potassium-seeded argon plasma at 2000\u00b0K and 1 atm. pressure. The behavior of such a discharge with four different configurations of electrodes was determined from photographs, photomultiplier measurements, and voltage probes. These four configurations were chosen to produce steady waves, to check the stability of steady waves, and to observe the manifestation of the waves in a MHD generator or accelerator configuration.
\r\n\r\nSteady, one-dimensional waves were found to exist in a number of situations, and where they existed, their characteristics agreed with the predictions of the steady theory. Some extensions of this theory were necessary, however, to describe the transient phenomena occurring in the inlet region of a discharge transverse to the gas flow. It was also found that in a discharge away from the stabilizing effect of the electrodes, steady waves became unstable for large Hall parameters. Methods of prediction of the effective electrical conductivity and Hall parameter of a plasma with nonuniformities caused by the electrothermal waves were also studied. Using these methods and the values of amplitude predicted by the steady theory, it was found that the measured decrease in transverse conductivity of a MHD device, 50 per cent at a Hall parameter of 5, could be accounted for in terms of the electrothermal instability.
\r\n" }, { "name": "Gorman, Jeffrey Archibald", "degree": "PhD", "year": "1968", "title": "The Mobility of Dislocations in High Purity Aluminum", "advisor": "Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232002-114109", "creators": [ { "name": { "family": "Gorman", "given": "Jeffrey Archibald" }, "id": "Gorman-Jeffrey-Archibald", "display_name": "Gorman, Jeffrey Archibald" } ], "advisors": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/5S7G-HJ46", "abstract": "This thesis presents the results of measurements of the velocities of edge and mixed dislocations in aluminum as a function of temperature and applied shear stress. All tests were conducted on 99.999% purity aluminum single crystals. Dislocation velocities were determined by observing the positions of dislocations by the Berg-Barrett X-ray technique before and after applying a stress pulse. Torsion stress pulses of microsecond duration were applied by propagating torsional waves along the axes of cylindrical crystals. Resolved shear stress up to 16 x 106 dynes/cm2 were applied at temperatures from -150\u00b0C to 70\u00b0C. Measured dislocation velocities ranged from 10 to 2750 cm/sec. The velocities measured are believed to be characteristic of single straight dislocations moving through essentially perfect crystals, where the velocity is not significantly influenced by dislocation curvature, impurities or dislocation-dislocation interactions.
\r\n \r\nThe results of this study indicate that the velocity of edge and mixed dislocations is linearly proportional to the applied resolved shear stress, in the temperature range studied. Dislocation velocity increases as temperature is decreased. These results are compared to the predictions of theories which treat the interaction between moving dislocations and the lattice (phonon interactions). The theoretically predicted variation of dislocation velocity with temperature and stress agrees fairy well with the experimental results, but the predicted velocities are about six times less than the experimental velocities. Possible reasons for this discrepancy are discussed.
\r\n\r\n" }, { "name": "Gruber, William Paul", "degree": "PhD", "year": "1968", "title": "Formation of Jets by Impulsive Acceleration of a Curved Free Surface", "advisor": "Ellis, Albert T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072015-132454281", "creators": [ { "name": { "family": "Gruber", "given": "William Paul" }, "id": "Gruber-William-Paul", "display_name": "Gruber, William Paul" } ], "advisors": [ { "name": { "family": "Ellis", "given": "Albert T." }, "id": "Ellis-A-T", "role": "advisor", "display_name": "Ellis, Albert T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/SWXB-0X23", "abstract": "The sudden axial acceleration of a column of liquid bounded at one end by a concave free surface has been found, experimentally, to produce a jet which issues from the free surface with a speed several times that imparted to the column.
\r\nTheoretical approximations to such flows, valid for small time, are formulated subject to the assumption that the fluid is inviscid and incompressible. In a special two-dimensional case, it is found that, for vanishingly small time, the velocity at the point on the free surface from which the jet emanates is \u03c0/2 times the velocity imparted to the column. The solutions to several problems in two and three dimensions assuming that the initial curvature of the free surface is small, lead to values for this ratio dependent upon the curvature\u2014the initial velocity in the case of axial symmetry exceeding that of the analogous two-dimensional problem by approximately 25%.
\r\nExperiments conducted upon the phenomenon give values systematically in excess of those predicted by the theory, although theory and experiment are in qualitative agreement with respect to the displacement of the free surface. It is suggested that the discrepancy is attributable to effects of finite curvature having been imperfectly accounted for in the axially-symmetric analysis.
\r\nPhotographic materials on pp. 115, 120, and 121 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.
\r\n" }, { "name": "Ho, Chee Leung", "degree": "PhD", "year": "1968", "title": "Energy Inequalities and Error Estimates for Axisymmetric Torsion of Thin Elastic Shells of Revolution", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072015-103241369", "creators": [ { "name": { "family": "Ho", "given": "Chee Leung" }, "id": "Ho-Chee-Leung", "display_name": "Ho, Chee Leung" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ARTK-6968", "abstract": "The problem motivating this investigation is that of pure axisymmetric torsion of an elastic shell of revolution. The analysis is carried out within the framework of the three-dimensional linear theory of elastic equilibrium for homogeneous, isotropic solids. The objective is the rigorous estimation of errors involved in the use of approximations based on thin shell theory.
\r\nThe underlying boundary value problem is one of Neumann type for a second order elliptic operator. A systematic procedure for constructing pointwise estimates for the solution and its first derivatives is given for a general class of second-order elliptic boundary-value problems which includes the torsion problem as a special case.
\r\nThe method used here rests on the construction of \u201cenergy inequalities\u201d and on the subsequent deduction of pointwise estimates from the energy inequalities. This method removes certain drawbacks characteristic of pointwise estimates derived in some investigations of related areas.
\r\nSpecial interest is directed towards thin shells of constant thickness. The method enables us to estimate the error involved in a stress analysis in which the exact solution is replaced by an approximate one, and thus provides us with a means of assessing the quality of approximate solutions for axisymmetric torsion of thin shells.
\r\nFinally, the results of the present study are applied to the stress analysis of a circular cylindrical shell, and the quality of stress estimates derived here and those from a previous related publication are discussed.
\r\n" }, { "name": "Kenny, John Joseph", "degree": "PhD", "year": "1968", "title": "Electric Dipole Radiation in Isotropic and Uniaxial Plasmas", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-09242002-082113", "creators": [ { "name": { "family": "Kenny", "given": "John Joseph" }, "id": "Kenny-John-Joseph", "display_name": "Kenny, John Joseph" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2Q1Z-GS04", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis paper describes an investigation of radiation from an electric point dipole situated in a cold, collisionless, homogeneous, electronic plasma medium. Two limiting cases of a gyroelectric medium are studied. The magnetostatic biasing field [...] is first taken to be equal to zero, making the medium isotropic, and then it is taken to be infinite, causing a uniaxial anisotropy. The retarded electromagnetic fields and the instantaneous and averaged values of irreversibly radiated power [...] are calculated.\r\n\r\nIn each medium, the partial differential equations resulting from the two-sided Laplace transformation of Maxwell's equations with an oscillating electric dipole source and the constitutive equations (derived from the appropriate form of the Lorentz force equation) are solved. A particular path deformation of the Laplace inversion integral reveals that the electromagnetic fields and [...] are exactly expressible in terms of circular, cylindrical, and two-variabled Lommel functions. Asymptotic expressions and graphical results of numerical calculations of these quantities are presented.\r\n\r\nFor the isotropic case, it is shown that the retarded fields are well behaved for all space and time (excluding the origin, of course). [...] eventually settles down to the result derived from the conventional time-harmonic analysis when the dipole oscillation frequency [...] is greater than the plasma frequency [...] . When the value of [...] is less than that of [...], [...] eventually oscillates at a frequency [.....] with zero average value.\r\n\r\nWhen the medium is uniaxial, the fields are finite everywhere except at the dipole. The amplitude of the fields does, however, increase with increasing time. This is quite different from the ordinary time-harmonic solution which ignores all time variations different from [...] and which is singular on a conical surface defined by [...] for [...]. The value of [...] in a uniaxial medium is found to be equal to the value of [.....] of a dipole in vacuum. It is also shown that the so-called conventional expression for time-averaged radiated power will not give a sensible result since it contains the retarded electric field which never settles down to a steady-state variation with time. The quantity [...], on the other hand, does not increase with time, oscillates only at the source frequency, and has a well-defined time average." }, { "name": "Klineberg, John Michael", "degree": "PhD", "year": "1968", "title": "Theory of Laminar Viscous-Inviscid Interactions in Supersonic Flow", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-09252002-110303", "creators": [ { "name": { "family": "Klineberg", "given": "John Michael" }, "id": "Klineberg-John-Michael", "display_name": "Klineberg, John Michael" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P246-JJ81", "abstract": "This investigation is concerned with those fluid-mechanical problems in which the pressure distribution is determined by the interaction between an external, supersonic inviscid flow and an inner, laminar viscous layer. The boundary-layer approximations are assumed to remain valid throughout the viscous region, and the integral or moment method of Lees and Reeves, extended to include flows with heat transfer; is used in the analysis.\r\n\r\nThe general features of interacting flows are established, including the important distinctions between subcritical and supercritical viscous layers. The eigensolution representing self-induced boundary-layer flow along a semi-infinite flat plate is determined, and a consistent set of departure conditions is derived for determining solutions to interactions caused by external disturbances. Complete viscous-inviscid interactions are discussed in detail, with emphasis on methods of solution for both subcritical and supercritical flows. The method is also shown to be capable of predicting the laminar flow field in the near wake of blunt bodies.\r\n\r\nResults of the present theory are shown to be in good agreement with the measurements of Lewis for boundary-layer separation in adiabatic and non-adiabatic compression corners, and with the near-wake experiments of Dewey and McCarthy for adiabatic flow over a circular cylinder. Extensions of the method to flows with mass injection at the surface and to subsonic interactions are indicated." }, { "name": "Krause, Daniel Julius", "degree": "PhD", "year": "1968", "title": "Discontinuous Yielding and Fracture Initiation Near a Notch in Mild Steel", "advisor": "Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212014-092153135", "creators": [ { "name": { "family": "Krause", "given": "Daniel Julius" }, "id": "Krause-Daniel-Julius", "display_name": "Krause, Daniel Julius" } ], "advisors": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/4PP6-QN96", "abstract": "This thesis presents the results of an experimental investigation of the initiation of brittle fracture and the nature of discontinuous yielding in small plastic enclaves in an annealed mild steel. Upper and lower yield stress data have been obtained from unnotched specimens and nominal fracture stress data have been obtained from specimens of two scale factors and two grain sizes over a range of nominal stress rates from 102 to 107 lb/in.2 sec at -111\u00b0F and -200\u00b0F. The size and shape of plastic enclaves near the notches were revealed by an etch technique.
\r\n\r\nA stress analysis utilizing slip-line field theory in the plastic region has been developed for the notched specimen geometry employed in this investigation. The yield stress of the material in the plastic enclaves near the notch root has been correlated with the lower yield stress measured on unnotched specimens through a consideration of the plastic boundary velocity under dynamic loading. A maximum tensile stress of about 122,000 lb/in.2 at the instant of fracture initiation was calculated with the aid of the stress analysis for the large scale specimens of ASTM grain size 8 1/4.
\r\n\r\nThe plastic strain state adjacent to a plastic-elastic interface has been shown to cause the maximum shear stress to have a larger value on the elastic than the plastic side of the interface. This characteristic of dis continuous yielding is instrumental in causing the plastic boundaries to be nearly parallel to the slip-line field where the plastic strain is of the order of the L\u00fcder's strain.
\r\n" }, { "name": "Kurosaka, Mitsuru", "degree": "PhD", "year": "1968", "title": "Approximate Theory for the Flow Through a Cascade of Cambered Airfoils", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechTHESIS:02182015-150154875", "creators": [ { "name": { "family": "Kurosaka", "given": "Mitsuru" }, "id": "Kurosaka-Mitsuru", "orcid": "0000-0002-8290-9255", "display_name": "Kurosaka, Mitsuru" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ENJQ-9M06", "abstract": "An approximate theory for steady irrotational flow through a\r\ncascade of thin cambered airfoils is developed. Isolated thin airfoils\r\nhave only slight camber is most applications, and the well known\r\nmethods that replace the source and vorticity distributions of the\r\ncurved camber line by similar distributions on the straight chord line\r\nare adequate. In cascades, however, the camber is usually appreciable,\r\nand significant errors are introduced if the vorticity and source\r\ndistributions on the camber line are approximated by the same distribution\r\non the chord line.
\r\n\r\nThe calculation of the flow field becomes very clumsy in\r\npractice if the vorticity and source distributions are not confined to a\r\nstraight line. A new method is proposed and investigated; in this\r\nmethod, at each point on the camber line, the vorticity and sources\r\nare assumed to be distributed along a straight line tangent to the camber\r\nline at that point, and corrections are determined to account for\r\nthe deviation of the actual camber line from the tangent line. Hence,\r\nthe basic calculation for the cambered airfoils is reduced to the\r\nsimpler calculation of the straight line airfoils, with the equivalent\r\nstraight line airfoils changing from point to point.
\r\n\r\nThe results of the approximate method are compared with\r\nnumerical solutions for cambers as high as 25 per cent of the chord.\r\nThe leaving angles of flow are predicted quite well, even at this high\r\nvalue of the camber. The present method also gives the functional\r\nrelationship between the exit angle and the other parameters such as\r\nairfoil shape and cascade geometry.
" }, { "name": "Laetsch, Theodore Willis", "degree": "PhD", "year": "1968", "title": "Eigenvalue Problems for Positive Monotonic Nonlinear Operators", "advisor": "Cohen, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09252002-110658", "creators": [ { "name": { "family": "Laetsch", "given": "Theodore Willis" }, "id": "Laetsch-Theodore-Willis", "display_name": "Laetsch, Theodore Willis" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "advisor", "display_name": "Cohen, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/R8T3-TJ18", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nThe determination of the set [Lambda] of values of [lambda] for which a family of operators {A[subscript lambda]} on a real, partially-ordered Banach space has positive fixed points and the description of the behavior of the fixed points as functions of [lambda] are considered. The operators A[subscript lambda] are usually assumed to be compact monotonic operators which satisfy A[subscript lambda] 0 > 0, and the elements A[subscript lambda]u are assumed to be continuous increasing functions of [lambda] for every positive u. It is shown that [Lambda] is an interval, that for each [lambda] the operator A[subscript lambda] has a smallest positive fixed point u[?]([lambda]), and that u[?]([lambda]) is an increasing function of [lambda] which is continuous from the left in -[lambda]. Conditions are given which guarantee the uniqueness of the fixed point of A[subscript lambda] for each [lambda] and permit the precise determination of the set [Lambda].\r\n\r\nWhen sup [Lambda][...][Lambda] and A[subscript lambda]u satisfies certain differentiability conditions, the behavior of u[...]([lambda]) for near sup [Lambda] is described and the existence of a second positive fixed point for [lambda] near sup [Lambda] is proved. The asymptotic behavior of A[subscript lambda]u for large positive u is used to determine the behavior of the fixed points of large norm and the existence and value of a number [mu subscript 1] such that the norms of a sequence of fixed points approach infinity as the corresponding values of [lambda] approach [mu subscript 1]. The existence of a second positive fixed point is proved under various conditions, including the case when the operators A[subscript lambda] are Frechet differentiable and 0 < [mu subscript 1] < sup [Lambda][member symbol][Lambda] . More precise results are obtained when the operators A[subscript lambda] are concave or convex.\r\n\r\nThese results are used to study the eigenvalue problem for Hammerstein integral equations and nonlinear ordinary differential equations. For certain ordinary differential equations with convex nonlinearities, the existence of precisely two positive fixed points is proved. Finally, an independent treatment is given of the eigenvalue problem for the equation u''+[lambda]f(u)=0 with the boundary conditions u(0) = u(1) = 0; use is made of the first integral of the differential equation and a study of the equation in the phase plane." }, { "name": "Latham, Raymond Walter", "degree": "PhD", "year": "1968", "title": "Electromagnetic Scattering From Cylindrically and Spherically Stratified Bodies", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212015-110440537", "creators": [ { "name": { "family": "Latham", "given": "Raymond Walter" }, "id": "Latham-Raymond-Walter", "display_name": "Latham, Raymond Walter" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/QGVG-1464", "abstract": "A method is developed for calculating the electromagnetic field scattered by certain types of bodies. The bodies consist of inhomogeneous media whose constitutive parameters vary only with the distance from some axis or point of symmetry. The method consists in an extension of the invariant imbedding method for treating wave problems. This method, which is familiar in the case of a one-dimensional inhomogeneity, is extended to handle special types of two and three-dimensional inhomogeneities. Comparisons are made with other methods which have been proposed for treating these kinds of problems. Examples of applications of the method are given, some of which are of interest in themselves." }, { "name": "Lau, Joseph Po-keung", "degree": "PhD", "year": "1968", "title": "Steady Surface Wave Pattern in Shear Flow", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212015-100519870", "creators": [ { "name": { "family": "Lau", "given": "Joseph Po-keung" }, "id": "Lau-Joseph-Po-keung", "display_name": "Lau, Joseph Po-keung" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/PEET-KY40", "abstract": "The subject under investigation concerns the steady surface wave patterns created by small concentrated disturbances acting on a non-uniform flow of a heavy fluid. The initial value problem of a point disturbance in a primary flow having an arbitrary velocity distribution (U(y), 0, 0) in a direction parallel to the undisturbed free surface is formulated. A geometric optics method and the classical integral transformation method are employed as two different methods of solution for this problem. Whenever necessary, the special case of linear shear (i.e. U(y) = 1+\u03f5y)) is chosen for the purpose of facilitating the final integration of the solution.
\r\nThe asymptotic form of the solution obtained by the method of integral transforms agrees with the leading terms of the solution obtained by geometric optics when the latter is expanded in powers of small \u03f5 r.
\r\nThe overall effect of the shear is to confine the wave field on the downstream side of the disturbance to a region which is smaller than the wave region in the case of uniform flows. If U(y) vanishes, and changes sign at a critical plane y = ycr (e.g. \u03f5ycr = -1 for the case of linear shear), then the boundary of this asymmetric wave field approaches this critical vertical plane. On this boundary the wave crests are all perpendicular to the x-axis, indicating that waves are reflected at this boundary.
\r\nInside the wave field, as in the case of a point disturbance in a uniform primary flow, there exist two wave systems. The loci of constant phases (such as the crests or troughs) of these wave systems are not symmetric with respect to the x-axis. The geometric optics method and the integral transform method yield the same result of these loci for the special case of U(y) = Uo(1 + \u03f5y) and for large Kr (\u03f5r \u02c2\u02c2 1 \u02c2\u02c2 Kr).
\r\n\r\nAn expression for the variation of the amplitude of the waves in the wave field is obtained by the integral transform method. This is in the form of an expansion in small \u03f5r. The zeroth order is identical to the expression for the uniform stream case and is thus not applicable near the boundary of the wave region because it becomes infinite in that neighborhood. Throughout this investigation the viscous terms in the equations of motion are neglected, a reasonable assumption which can be justified when the wavelengths of the resulting waves are sufficiently large.
\r\n" }, { "name": "Lavenberg, Stephen Stuart", "degree": "PhD", "year": "1968", "title": "Feedback Communication Using Orthogonal Signals", "advisor": "Grettenberg, Thomas L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212015-093040606", "creators": [ { "name": { "family": "Lavenberg", "given": "Stephen Stuart" }, "id": "Lavenberg-Stephen-Stuart", "display_name": "Lavenberg, Stephen Stuart" } ], "advisors": [ { "name": { "family": "Grettenberg", "given": "Thomas L." }, "id": "Grettenberg-T-L", "role": "advisor", "display_name": "Grettenberg, Thomas L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WKWH-7823", "abstract": "This research is concerned with block coding for a feedback communication system in which the forward and feedback channels are independently disturbed by additive white Gaussian noise and average power constrained. Two coding schemes are proposed in which the messages to be coded for transmission over the forward channel are realized as a set of orthogonal waveforms. A finite number of forward and feedback transmissions (iterations) per message is made. Information received over the feedback channel is used to modify the waveform transmitted on successive forward iterations in such a way that the expected value of forward signal energy is zero on all iterations after the first. Similarly, information is sent over the feedback channel in such a way that the expected value of feedback signal energy is also zero on all iterations after the first. These schemes are shown to achieve a lower probability of error than the best one-way coding scheme at all rates up to the forward channel capacity, provided only that the feedback channel capacity be greater than the forward channel capacity. These schemes make more efficient use of the available feedback power than existing feedback coding schemes, and therefore require less feedback power to achieve a given error performance." }, { "name": "Lin, Stephen Chung-Hsiung", "degree": "PhD", "year": "1968", "title": "Structure and Properties of an Amorphous Ferromagnetic Alloy", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07242014-133125205", "creators": [ { "name": { "family": "Lin", "given": "Stephen Chung-Hsiung" }, "id": "Lin-Stephen-Chung-Hsiung", "display_name": "Lin, Stephen Chung-Hsiung" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/2sdt-pf07", "abstract": "The structure and the electrical and magnetic properties of an amorphous alloy containing approximately 80 at .% iron, 13 at.% phos\r\nphorus and 7 at.% carbon (Fe_(80)Fe_(13)C_7) obtained by rapid quenching from \r\nthe liquid state have been studied. Transmission electron diffraction data confirm the amorphous nature of this alloy. An analysis of the radial distribution function obtained from X-ray diffraction data indicates that the number of nearest neighbors is approximately seven, at a distance of 2.6A. The structure of the alloy can be related to that of silicate glasses and is based on a random arrangement of trigonal prisms of Fe_2P and Fe_3C types in which the iron atoms have an average ligancy of seven. Electrical resistance measurements show that the alloys are metallic. A minimum in the electrical resistivity vs. temperature curve is observed between 10\u00b0 K to 50\u00b0 K depending on the specimen, and the temperature at which the minimum occurs is related to the degree of local ordering. The Fe-P-C amorphous alloys are ferromagnetic. The Curie temperature measured by the induction method and by Mossbauer spectroscopy is 315\u00b0 C. The field dependence of the magneto-resistance at temperatures from liquid helium to room temperature is similar to that found in crystalline iron. The ordinary Hall coefficient is approximately 10^(-11) volt-cm/amp-G. The spontaneous Hall coefficient is about \r\n0.6 x 10^(-9) volt-cm/amp-G and is practically independent of temperature from liquid helium temperature up to 300\u00b0 c.\r\n
\r\n" }, { "name": "MacDowell, Thomas William", "degree": "PhD", "year": "1968", "title": "Boundary Value Problems for Stochastic Differential Equations", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:04022013-104632972", "creators": [ { "name": { "family": "MacDowell", "given": "Thomas William" }, "id": "MacDowell-Thomas-William", "display_name": "MacDowell, Thomas William" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/JR7J-9W71", "abstract": "A theory of two-point boundary value problems analogous\r\nto the theory of initial value problems for stochastic ordinary\r\ndifferential equations whose solutions form Markov processes is\r\ndeveloped. The theory of initial value problems consists of\r\nthree main parts: the proof that the solution process is\r\nmarkovian and diffusive; the construction of the Kolmogorov\r\nor Fokker-Planck equation of the process; and the proof that\r\nthe transistion probability density of the process is a unique\r\nsolution of the Fokker-Planck equation.
\r\n\r\nIt is assumed here that the stochastic differential equation\r\nunder consideration has, as an initial value problem, a diffusive\r\nmarkovian solution process. When a given boundary value problem\r\nfor this stochastic equation almost surely has unique solutions,\r\nwe show that the solution process of the boundary value problem\r\nis also a diffusive Markov process. Since a boundary value\r\nproblem, unlike an initial value problem, has no preferred\r\ndirection for the parameter set, we find that there are two\r\nFokker-Planck equations, one for each direction. It is shown\r\nthat the density of the solution process of the boundary value\r\nproblem is the unique simultaneous solution of this pair of\r\nFokker-Planck equations.
\r\n\r\nThis theory is then applied to the problem of a vibrating\r\nstring with stochastic density.
\r\n\r\n" }, { "name": "Mortell, Michael Philip", "degree": "PhD", "year": "1968", "title": "Some Approximate Solutions of Dyn01nic Problems in the Linear Theory of Thin Elastic Shells", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04052013-144005487", "creators": [ { "name": { "family": "Mortell", "given": "Michael Philip" }, "id": "Mortell-Michael-Philip", "display_name": "Mortell, Michael Philip" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/11GT-4V56", "abstract": "Some aspects of wave propagation in thin elastic shells are considered.\r\nThe governing equations are derived by a method which makes their\r\nrelationship to the exact equations of linear elasticity quite clear.\r\nFinite wave propagation speeds are ensured by the inclusion of the appropriate\r\nphysical effects.
\r\n\r\nThe problem of a constant pressure front moving with constant\r\nvelocity along a semi-infinite circular cylindrical shell is studied. The\r\nbehavior of the solution immediately under the leading wave is found, as\r\nwell as the short time solution behind the characteristic wavefronts. The\r\nmain long time disturbance is found to travel with the velocity of very\r\nlong longitudinal waves in a bar and an expression for this part of the\r\nsolution is given.
\r\n\r\nWhen a constant moment is applied to the lip of an open spherical\r\nshell, there is an interesting effect due to the focusing of the waves.\r\nThis phenomenon is studied and an expression is derived for the wavefront\r\nbehavior for the first passage of the leading wave and its first reflection.
\r\n\r\nFor the two problems mentioned, the method used involves reducing\r\nthe governing partial differential equations to ordinary differential equations\r\nby means of a Laplace transform in time. The information sought is\r\nthen extracted by doing the appropriate asymptotic expansion with the Laplace\r\nvariable as parameter.
" }, { "name": "Mrstik, Adolph Vincent, Jr.", "degree": "PhD", "year": "1968", "title": "The Resolution of the Thermodynamic Paradox and the Theory of Guided Wave Propagation in Anisotropic Media", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:12182015-135931289", "creators": [ { "name": { "family": "Mrstik", "given": "Adolph Vincent, Jr." }, "id": "Mrstik-Adolph-Vincent", "display_name": "Mrstik, Adolph Vincent, Jr." } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5DAY-XC29", "abstract": "The resolution of the so-called thermodynamic paradox is presented in this paper. It is shown, in direct contradiction to the results of several previously published papers, that the cutoff modes (evanescent modes having complex propagation constants) can carry power in a waveguide containing ferrite. The errors in all previous \u201cproofs\u201d which purport to show that the cutoff modes cannot carry power are uncovered. The boundary value problem underlying the paradox is studied in detail; it is shown that, although the solution is somewhat complicated, there is nothing paradoxical about it.
\r\n\r\nThe general problem of electromagnetic wave propagation through rectangular guides filled inhomogeneously in cross-section with transversely magnetized ferrite is also studied. Application of the standard waveguide techniques reduces the TM part to the well-known self-adjoint Sturm Liouville eigenvalue equation. The TE part, however, leads in general to a non-self-adjoint eigenvalue equation. This equation and the associated expansion problem are studied in detail. Expansion coefficients and actual fields are determined for a particular problem.
\r\n" }, { "name": "Mueller, Hans-Karl Christian Alfred", "degree": "PhD", "year": "1968", "title": "Stable Crack Propagation in a Viscoelastic Strip", "advisor": "Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-142505", "creators": [ { "name": { "family": "Mueller", "given": "Hans-Karl Christian Alfred" }, "id": "Mueller-Hans-Karl-Christian-Alfred", "display_name": "Mueller, Hans-Karl Christian Alfred" } ], "advisors": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MGSD-R362", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA crack of length 2a which propagates with small, constant speed through a viscoelastic strip of width 2b is considered. The strip is strained by displacing its shearfree edges. Linear theory is applied. The stress on the line of crack advancement and the shape of the crack surface are calculated for a state of plane stress.\r\n\r\nThe stress intensity factor which is independent of material properties is given as a function of a/b. It exhibits a maximum at [...]. For a/b > 1.5 the stress intensity factor becomes essentially independent of crack length. The crack surface deflection is obtained in the form of a superposition integral and is a function of material properties and crack speed.\r\n\r\nThe energy which is released when the crack extends a small distancee is calculated. This crack energy depends on the crack speed and involves the creep function of the material. A characteristic length enters in the course of its derivation. This length does not appear in the case of an elastic material and is considered as an additional material property necessary to describe viscoelastic crack propagation.\r\n\r\nThe energy conservation equation is established by considering a small control volume surrounding the crack tip. A relationship emerges from this equation which implicitly gives a stable crack speed as a function of applied strain, temperature, and material properties. The creep function is the controlling factor in this equation.\r\n\r\nThe relevant material properties are discussed and presented for a Polyurethane rubber (Solithane 113 - 50/50). The lower bound of the surface energy is determined from fracture tests on the swollen material. The results of the material characterization are used to calculate the crack speed as a function of applied strain and temperature. Good agreement is found to exist between theory and experiment." }, { "name": "O'Sullivan, Michael John", "degree": "PhD", "year": "1968", "title": "On the Dynamic Behavior of Thin Elastic Plates", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10022002-113310", "creators": [ { "name": { "family": "O'Sullivan", "given": "Michael John" }, "id": "O'Sullivan-Michael-John", "display_name": "O'Sullivan, Michael John" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/2095-RQ32", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nTwo wave propagation problems are considered: the propagation of acoustic waves in a fluid slab and the propagation of elastic waves in an elastic slab.\r\n\r\nWhen formulated in terms of nondimensional variables these problems depend explicitly on two small parameters [epsilon] and [delta]. The parameter [epsilon] provides a measure of the thinness of the slabs considered and the parameter [delta] measures the impulsiveness of the applied excitation or loading. Approximation solutions of the problems considered are obtained consisting of several parts, each part having the form of a power series expansion in the parameters [epsilon] and [delta].\r\n\r\nThe most important result obtained is the development of the approximate theories - the plate wave equation and the Euler-Bernoulli plate equation - directly from the full equations of dynamic elasticity using a rational perturbation expansion technique." }, { "name": "Pincince, Albert Bernard", "degree": "PhD", "year": "1968", "title": "Oxygen Relationships in Intermittent Sand Filtration of Wastewaters", "advisor": "McKee, Jack E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212015-162348721", "creators": [ { "name": { "family": "Pincince", "given": "Albert Bernard" }, "id": "Pincince-Albert-Bernard", "display_name": "Pincince, Albert Bernard" } ], "advisors": [ { "name": { "family": "McKee", "given": "Jack E." }, "id": "McKee-J-E", "role": "advisor", "display_name": "McKee, Jack E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/AVVX-TN81", "abstract": "A model for some of the many physical-chemical and biological processes in intermittent sand filtration of wastewaters is described and an expression for oxygen transfer is formulated.
\r\n\r\nThe model assumes that aerobic bacterial activity within the sand or soil matrix is limited, mostly by oxygen deficiency, while the surface is ponded with wastewater. Atmospheric oxygen reenters into the soil after infiltration ends. Aerobic activity is resumed, but the extent of penetration of oxygen is limited and some depths may be always anaerobic. These assumptions lead to the conclusion that the percolate shows large variations with respect to the concentration of certain contaminants, with some portions showing little change in a specific contaminant. Analyses of soil moisture in field studies and of effluent from laboratory sand columns substantiated the model.
\r\n\r\nThe oxygen content of the system at sufficiently long times after addition of wastes can be described by a quasi-steady-state diffusion equation including a term for an oxygen sink. Measurements of oxygen content during laboratory and field studies show that the oxygen profile changes only slightly up to two days after the quasi-steady state is attained.
\r\n\r\nResults of these hypotheses and experimental verification can be applied in the operation of existing facilities and in the interpretation of data from pilot plant-studies.
\r\n" }, { "name": "Piva, Hugo de Oliveira", "degree": "PhD", "year": "1968", "title": "Electron Beam Measurements of Density in Shock Waves Reflecting From a Cold Wall", "advisor": "Sturtevant, Bradford", "url": "https://resolver.caltech.edu/CaltechETD:etd-11292005-131010", "creators": [ { "name": { "family": "Piva", "given": "Hugo de Oliveira" }, "id": "Piva-Hugo-de-Oliveira", "display_name": "Piva, Hugo de Oliveira" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EDZS-EA78", "abstract": "The normal shock wave is a rarefied-gas flow in which large departures from thermodynamic equilibrium and strong non-linearities occur and it is the simplest such flow due to its one-dimensionality and the absence of solid boundaries. Because of this, both theoretical and experimental studies of the structure of normal shock waves have been used successfully in recent years to get a better understanding of such phenomena. The present work is an extension of the earlier studies to the more complicated problem of shock-wave reflection. The density distribution of a normal shock wave in argon is measured during its reflection from a heat-conducting wall using an electron beam densitometer in the GALCIT 17-in diameter shock tube at incident Mach numbers 6.00, 4.00 and 2.96.\r\n\r\nDuring each run a density history is obtained at a certain distance from the wall by measuring electron-beam current as a function of time. By defining a consistent zero of time for all runs at the same conditions, these histories are converted by a cross-plot to families of density profiles at different times. x-t diagrams are obtained from the density history plots, and a wall-density history is obtained from the density profiles. Measured in terms of the ideal conditions behind the incident shock wave, the distances extend from 0.25 to 56 mean free paths from the wall and the times to 160 mean collision times after the beginning of the reflection.\r\n\r\nThe results presented here give both quantitative and qualitative information about the interaction of the incident shock wave with the wall, the effects of the wall heat transfer and accommodation on the density near the wall, the formation of the reflected shock wave, its strength and trajectory on the x-t diagram, and the nature of the flow field lying between the thermal layer and the reflected shock wave at large times." }, { "name": "Schaffner, Charles Albert", "degree": "PhD", "year": "1968", "title": "The Global Optimization of Phase-Incoherent Signals", "advisor": "Grettenberg, Thomas L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212015-144937012", "creators": [ { "name": { "family": "Schaffner", "given": "Charles Albert" }, "id": "Schaffner-Charles-Albert", "display_name": "Schaffner, Charles Albert" } ], "advisors": [ { "name": { "family": "Grettenberg", "given": "Thomas L." }, "id": "Grettenberg-T-L", "role": "advisor", "display_name": "Grettenberg, Thomas L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/t799-rn87", "abstract": "The problem of global optimization of M phase-incoherent signals in N complex dimensions is formulated. Then, by using the geometric approach of Landau and Slepian, conditions for optimality are established for N = 2 and the optimal signal sets are determined for M = 2, 3, 4, 6, and 12.
\r\n\r\nThe method is the following: The signals are assumed to be equally probable and to have equal energy, and thus are represented by points \u1e61i, i = 1, 2, \u2026, M, on the unit sphere S1 in CN. If Wik is the halfspace determined by \u1e61i and \u1e61k and containing \u1e61i, i.e. Wik = {\u1e59\u03f5CN:| \u2265 | \u02c2\u1e59, \u1e61k\u02c3|}, then the \u01a6i = \u2229/k\u2260i Wik, i = 1, 2, \u2026, M, the maximum likelihood decision regions, partition S1. For additive complex Gaussian noise \u1e45 and a received signal \u1e59 = \u1e61iej\u03f4 + \u1e45, where \u03f4 is uniformly distributed over [0, 2\u03c0], the probability of correct decoding is PC = 1/\u03c0N \u221e/\u0283/0 r2N-1e-(r2+1)U(r)dr, where U(r) = 1/M M/\u01a9/i=1 \u01a6i \u0283/\u2229 S1 I0(2r | \u02c2\u1e61, \u1e61i\u02c3|)d\u03c3(\u1e61), and r = \u01c1\u1e59\u01c1.
\r\n\r\nFor N = 2, it is proved that U(r) \u2264 \u0283/C\u03b1 I0(2r|\u02c2\u1e61, \u1e61i\u02c3|)d\u03c3(\u1e61) \u2013 2K/M. h(1/2K [M\u03c3(C\u03b1)-\u03c3(S1)]), where C\u03b1 = {\u1e61\u03f5S1:|\u02c2\u1e61, \u1e61i\u02c3| \u2265 \u03b1}, K is the total number of boundaries of the net on S1 determined by the decision regions, and h is the strictly increasing strictly convex function of \u03c3(C\u03b1\u2229W), (where W is a halfspace not containing \u1e61i), given by h = \u0283/C\u03b1\u2229W I0 (2r|\u02c2\u1e61, \u1e61i\u02c3|)d\u03c3(\u1e61). Conditions for equality are established and these give rise to the globally optimal signal sets for M = 2, 3, 4, 6, and 12.
\r\n" }, { "name": "Schmulian, Robert Jay", "degree": "PhD", "year": "1968", "title": "Nearly Free Molecular Heat Transfer from a Sphere", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04052013-154128630", "creators": [ { "name": { "family": "Schmulian", "given": "Robert Jay" }, "id": "Schmulian-Robert-Jay", "display_name": "Schmulian, Robert Jay" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/KZ16-1X08", "abstract": "Consider a sphere immersed in a rarefied monatomic gas with\r\nzero mean flow. The distribution function of the molecules at infinity\r\nis chosen to be a Maxwellian. The boundary condition at the body is\r\ndiffuse reflection with perfect accommodation to the surface temperature.\r\nThe microscopic flow of particles about the sphere is modeled\r\nkinetically by the Boltzmann equation with the Krook collision term.\r\nAppropriate normalizations in the near and far fields lead to a perturbation\r\nsolution of the problem, expanded in terms of the ratio of\r\nbody diameter to mean free path (inverse Knudsen number). The distribution\r\nfunction is found directly in each region, and intermediate\r\nmatching is demonstrated. The heat transfer from the sphere is then\r\ncalculated as an integral over this distribution function in the inner\r\nregion. Final results indicate that the heat transfer may at first\r\nincrease over its free flow value before falling to the continuum level." }, { "name": "Seliger, Robert Lewis", "degree": "PhD", "year": "1968", "title": "Part I. On the Breaking of Nonlinear Dispersive Waves. Part II. Variational Principles in Continuum Mechanics", "advisor": "Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechTHESIS:04032013-094741062", "creators": [ { "name": { "family": "Seliger", "given": "Robert Lewis" }, "id": "Seliger-Robert-Lewis", "display_name": "Seliger, Robert Lewis" } ], "advisors": [ { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/K2AZ-JX87", "abstract": "A model equation for water waves has been suggested by Whitham to study, qualitatively at least, the different kinds of breaking. This is an integro-differential equation which combines a typical nonlinear convection term with an integral for the dispersive effects and is of independent mathematical interest. For an approximate kernel of the form e^(-b|x|) it is shown first that solitary waves have a maximum height with sharp crests and secondly that waves which are sufficiently asymmetric break into \"bores.\" The second part applies to a wide class of bounded kernels, but the kernel giving the correct dispersion effects of water waves has a square root singularity and the\r\npresent argument does not go through. Nevertheless the\r\npossibility of the two kinds of breaking in such integro-differential equations is demonstrated.
\r\n\r\nDifficulties arise in finding variational principles for\r\ncontinuum mechanics problems in the Eulerian (field) description. The reason is found to be that continuum equations in the original field variables lack a mathematical \"self-adjointness\" property which is necessary for Euler equations. This is a feature of\r\nthe Eulerian description and occurs in non-dissipative problems which have variational principles for their Lagrangian description. To overcome this difficulty a \"potential representation\" approach is used which consists of transforming to new (Eulerian) variables\r\nwhose equations are self-adjoint. The transformations to the velocity potential or stream function in fluids or the scaler and vector potentials in electromagnetism often lead to variational principles in this way. As yet no general procedure is available for finding suitable transformations. Existing variational principles for the inviscid fluid equations in the Eulerian description are reviewed and some ideas on the form of the appropriate transformations and Lagrangians for fluid problems are obtained. These ideas are developed in a series of examples which include finding variational principles for Rossby waves and for the internal waves of a stratified fluid.
\r\n" }, { "name": "Shankar, Pattamadai Narasimhan", "degree": "PhD", "year": "1968", "title": "I. The Effect of Droplet Solidification Upon Two-Phase Flow in a Rocket Nozzle. II. A Kinetic Theory Investigation of Some Condensation-Evaporation Phenomena by a Moment Method", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12212015-140557422", "creators": [ { "name": { "family": "Shankar", "given": "Pattamadai Narasimhan" }, "id": "Shankar-Pattamadai-Narasimhan", "display_name": "Shankar, Pattamadai Narasimhan" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/X1YG-2K03", "abstract": "Part I:
\r\n\r\nThe perturbation technique developed by Rannie and Marble is used to study the effect of droplet solidification upon two-phase flow in a rocket nozzle. It is shown that under certain conditions an equilibrium flow exists, where the gas and particle phases have the same velocity and temperature at each section of the nozzle. The flow is divided into three regions: the first region, where the particles are all in the form of liquid droplets; a second region, over which the droplets solidify at constant freezing temperature; and a third region, where the particles are all solid. By a perturbation about the equilibrium flow, a solution is obtained for small particle slip velocities using the Stokes drag law and the corresponding approximation for heat transfer between the particle and gas phases. Singular perturbation procedure is required to handle the problem at points where solidification first starts and where it is complete. The effects of solidification are noticeable.
\r\n\r\nPart II:
\r\n\r\nWhen a liquid surface, in contact with only its pure vapor, is not in the thermodynamic equilibrium with it, a net condensation or evaporation of fluid occurs. This phenomenon is studied from a kinetic theory viewpoint by means of moment method developed by Lees. The evaporation-condensation rate is calculated for a spherical droplet and for a liquid sheet, when the temperatures and pressures are not too far removed from their equilibrium values. The solutions are valid for the whole range of Knudsen numbers from the free molecule to the continuum limit. In the continuum limit, the mass flux rate is proportional to the pressure difference alone.
\r\n" }, { "name": "Shen, Cheng-Chung", "degree": "PhD", "year": "1968", "title": "I. Stokes Flow Past a Thin Screen. II. Viscous Flows Past Porous Bodies of Finite Size", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:01112016-094200312", "creators": [ { "name": { "family": "Shen", "given": "Cheng-Chung" }, "id": "Shen-Cheng-Chung", "display_name": "Shen, Cheng-Chung" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/H3WJ-6N43", "abstract": "Part I
\r\n\r\nThe slow, viscous flow past a thin screen is analyzed based on Stokes equations. The problem is reduced to an associated electric potential problem as introduced by Roscoe. Alternatively, the problem is formulated in terms of a Stokeslet distribution, which turns out to be equivalent to the first approach.
\r\n\r\nSpecial interest is directed towards the solution of the Stokes flow past a circular annulus. A \"Stokeslet\" formulation is used in this analysis. The problem is finally reduced to solving a Fredholm integral equation of the second kind. Numerical data for the drag coefficient and the mean velocity through the hole of the annulus are obtained.
\r\n\r\nStokes flow past a circular screen with numerous holes is also attempted by assuming a set of approximate boundary conditions. An \"electric potential\" formulation is used, and the problem is also reduced to solving a Fredholm integral equation of the second kind. Drag coefficient and mean velocity through the screen are computed.
\r\n\r\nPart II
\r\n\r\nThe purpose of this investigation is to formulate correctly a set of boundary conditions to be prescribed at the interface between a viscous flow region and a porous medium so that the problem of a viscous flow past a porous body can be solved.
\r\n\r\nGeneral macroscopic equations of motion for flow through porous media are first derived by averaging Stokes equations over a volume element of the medium. These equations, including viscous stresses for the description, are more general than Darcy's law. They reduce to Darcy's law when the Darcy number becomes extremely small.
\r\n\r\nThe interface boundary conditions of the first kind are then formulated with respect to the general macroscopic equations applied within the porous region. An application of such equations and boundary conditions to a Poiseuille shear flow problem demonstrates that there usually exists a thin interface layer immediately inside the porous medium in which the tangential velocity varies exponentially and Darcy's law does not apply.
\r\n\r\nWith Darcy's law assumed within the porous region, interface boundary conditions of the second kind are established which relate the flow variables across the interface layer. The primary feature is a jump condition on the tangential velocity, which is found to be directly proportional to the normal gradient of the tangential velocity immediately outside the porous medium. This is in agreement with the experimental results of Beavers, et al.
\r\n\r\nThe derived boundary conditions are applied in the solutions of two other problems: (1) Viscous flow between a rotating solid cylinder and a stationary porous cylinder, and (2) Stokes flow past a porous sphere.
\r\n" }, { "name": "Thompson, Ansel Frederick, Jr.", "degree": "PhD", "year": "1968", "title": "The Ultrafiltration of Salt-Polyelectrolyte Solutions", "advisor": "Gram, Andrew L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-160148", "creators": [ { "name": { "family": "Thompson", "given": "Ansel Frederick, Jr." }, "id": "Thompson-Ansel-Frederick", "display_name": "Thompson, Ansel Frederick, Jr." } ], "advisors": [ { "name": { "family": "Gram", "given": "Andrew L." }, "id": "Gram-Andrew-L", "role": "advisor", "display_name": "Gram, Andrew L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/NAJK-3T94", "abstract": "The ultrafiltration of sodium chloride - sodium polyacrylate solutions was studied using a membrane completely impermeable to the polyelectrolyte but permeable to water and simple salts. The membrane was a synthetic, hydrated polymer membrane with an ionic cross-linked structure. The activity of sodium chloride in the filtration cell was measured using a sodium-sensitive glass electrode/silver-silver chloride electrode pair. The continuous flow filtration cell used contained a stirring blade that was used to eliminate concentration polarization at the membrane surface. The effect of stirring speed was observed. The membrane salt-rejection and permeability characteristics were determined using distilled water and NaCl solutions. Independent salt activity measurements in NaCl-NaPA solutions were also made.
\r\n\r\nThe sodium chloride activity data were compared with the simple additivity rule or dissociation theory for the activity of simple salts in polyelectrolyte solutions and with theory based upon the cylindrical electrostatic model. Agreement with the electrostatic model was good; expressions based upon the simple dissociation theory underestimated the activity.
\r\n\r\nConcentration polarization effects during filtration were eliminated only in the case of the lower polyelectrolyte concentrations studied and at relatively low filtration rates using high stirring speeds. Under these conditions, the filtrate flow rate and salt concentration were accurately predicted by flux equations typical of the thermodynamics of irreversible processes. At the solution-membrane interface, where the polyelectrolyte separation takes place, equilibration of the salt leads to an effective concentration equal to the equilibrium salt concentration; thus, the filtrate salt concentration is significantly greater than the salt concentration in the salt-polyelectrolyte solution being filtered. Results of experiments involving concentration polarization were compared with a simple boundary-layer model with only fair success.
\r\n\r\nThe motivation for the research was the possibility of developing a desalination process upon the Donnan membrane equilibrium. The process is described and its performance is evaluated for various operating conditions. Economic considerations indicate only limited use for the process.
" }, { "name": "Turteltaub, Matias Jose", "degree": "PhD", "year": "1968", "title": "On Concentrated Loads and Green's Functions in Elastostatics", "advisor": "Sternberg, Eli", "url": "https://resolver.caltech.edu/CaltechTHESIS:01042016-162513340", "creators": [ { "name": { "family": "Turteltaub", "given": "Matias Jose" }, "id": "Turteltaub-Matias-Jose", "display_name": "Turteltaub, Matias Jose" } ], "advisors": [ { "name": { "family": "Sternberg", "given": "Eli" }, "id": "Sternberg-E", "role": "advisor", "display_name": "Sternberg, Eli" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/NZ29-8943", "abstract": "This investigation is concerned with the notion of concentrated loads in classical elastostatics and related issues. Following a limit treatment of problems involving concentrated internal and surface loads, the orders of the ensuing displacements and stress singularities, as well as the stress resultants of the latter, are determined. These conclusions are taken as a basis for an alternative direct formulation of concentrated-load problems, the completeness of which is established through an appropriate uniqueness theorem. In addition, the present work supplies a reciprocal theorem and an integral representation-theorem applicable to singular problems of the type under consideration. Finally, in the course of the analysis presented here, the theory of Green's functions in elastostatics is extended.
" }, { "name": "Varvatsis, Athanassios Demetrius", "degree": "PhD", "year": "1968", "title": "A Multiple Scattering Problem", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:01142016-141500284", "creators": [ { "name": { "family": "Varvatsis", "given": "Athanassios Demetrius" }, "id": "Varvatsis-Athanassios-Demetrius", "display_name": "Varvatsis, Athanassios Demetrius" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/02K5-V111", "abstract": "The present work deals with the problem of the interaction of the electromagnetic radiation with a statistical distribution of nonmagnetic dielectric particles immersed in an infinite homogeneous isotropic, non-magnetic medium. The wavelength of the incident radiation can be less, equal or greater than the linear dimension of a particle. The distance between any two particles is several wavelengths. A single particle in the absence of the others is assumed to scatter like a Rayleigh-Gans particle, i.e. interaction between the volume elements (self-interaction) is neglected. The interaction of the particles is taken into account (multiple scattering) and conditions are set up for the case of a lossless medium which guarantee that the multiple scattering contribution is more important than the self-interaction one. These conditions relate the wavelength \u03bb and the linear dimensions of a particle a and of the region occupied by the particles D. It is found that for constant \u03bb/a, D is proportional to\r\n\u03bb and that |\u0394\u03c7|, where \u0394\u03c7 is the difference in the dielectric susceptibilities between particle and medium, has to lie within a certain range.
\r\n\r\n\r\nThe total scattering field is obtained as a series the several terms of which represent the corresponding multiple scattering orders. The first term is a single scattering term. The ensemble average of the total scattering intensity is then obtained as a series which does not involve terms due to products between terms of different orders. Thus the waves corresponding to different orders are independent and their Stokes parameters add.
\r\n\r\n\r\nThe second and third order intensity terms are explicitly computed. The method used suggests a general approach for computing any order. It is found that in general the first order scattering intensity pattern (or phase function) peaks in the forward direction \u0398 = 0. The second order tends to smooth out the pattern giving a maximum in the \u0398 = \u03c0/2 direction and minima in the \u0398 = 0 , \u0398 = \u03c0 directions. This ceases to be true if ka (where k = 2\u03c0/\u03bb) becomes large (> 20). For large ka the forward direction is further enhanced. Similar features are expected from the higher orders even though the critical value of ka may increase with the order.
\r\n\r\n\r\nThe first order polarization of the scattered wave is determined. The ensemble average of the Stokes parameters of the scattered wave is explicitly computed for the second order. A similar method can be applied for any order. It is found that the polarization of the scattered wave depends on the polarization of the incident wave. If the latter is elliptically polarized then the first order scattered wave is elliptically polarized, but in the \u0398 = \u03c0/2 direction is linearly polarized. If the incident wave is circularly polarized the first order scattered wave is elliptically polarized except for the directions \u0398 = \u03c0/2 (linearly polarized) and \u0398 = 0, \u03c0 (circularly polarized). The handedness of the \u0398 = 0 wave is the same as that of the incident whereas the handedness of the \u0398 = \u03c0 wave is opposite. If the incident wave is linearly polarized the first order scattered wave is also linearly polarized. The second order makes the total scattered wave to be elliptically polarized for any \u0398 no matter what the incident wave is. However, the handedness of the total scattered wave is not altered by the second order. Higher orders have similar effects as the second order.
\r\n\r\n\r\nIf the medium is lossy the general approach employed for the lossless case is still valid. Only the algebra increases in complexity. It is found that the results of the lossless case are insensitive in the first order of kimD where kim = imaginary part of the wave vector k and D a linear characteristic dimension of the region occupied by the particles. Thus moderately extended regions and small losses make (kimD)2 \u226a 1 and the lossy character of the medium does not alter the results of the lossless case. In general the presence of the losses tends to reduce the forward scattering.
\r\n" }, { "name": "Weiner, Martin Eric", "degree": "PhD", "year": "1968", "title": "Magnetic Moments In Amorphous Palladium-Cobalt-Silicon Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07222014-134811615", "creators": [ { "name": { "family": "Weiner", "given": "Martin Eric" }, "id": "Weiner-Martin-Eric", "display_name": "Weiner, Martin Eric" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/NZ2B-DN76", "abstract": "The magnetic moments of amorphous ternary alloys containing Pd,\r\nCo and Si in atomic concentrations corresponding to Pd_(80-x)Co_xSi_(20) in\r\nwhich x is 3, 5, 7, 9, 10 and 11, have been measured between 1.8 and\r\n300\u00b0K and in magnetic fields up to 8.35 kOe. The alloys were obtained\r\nby rapid quenching of a liquid droplet and their structures were\r\nanalyzed by X-ray diffraction. The measurements were made in a null-coil\r\npendulum magnetometer in which the temperature could be\r\nvaried continuously without immersing the sample in a cryogenic liquid.\r\nThe alloys containing 9 at.% Co or less obeyed Curie's Law over certain\r\ntemperature ranges, and had negligible permanent moments at room\r\ntemperature. Those containing 10 and 11 at.% Co followed Curie's Law\r\nonly above approximately 200\u00b0K and had significant permanent moments\r\nat room temperature. For all alloys, the moments calculated from\r\nCurie's Law were too high to be accounted for by the moments of individual\r\nCo atoms. To explain these findings, a model based on the\r\nexistence of superparamagnetic clustering is proposed. The cluster\r\nsizes calculated from the model are consistent with the rapid onset of\r\nferromagnetism in the alloys containing 10 and 11 at.% Co and with the\r\nmagnetic moments in an alloy containing 7 at.% Co heat treated in such\r\na manner as to contain a small amount of a crystalline phase. In\r\nalloys containing 7 at.% Co or less, a maximum in the magnetization vs\r\ntemperature curve was observed around 10\u00b0K. This maximum was eliminated\r\nby cooling the alloy in a magnetic field, and an explanation for\r\nthis observation is suggested.\r\n" }, { "name": "Yeh, Tyan", "degree": "PhD", "year": "1968", "title": "I. Nonexistence of Looping Trajectories in Hydromagnetic Waves of Finite Amplitude. II. Breaking of Waves in a Cold Collision-Free Plasma in a Magnetic Field. III. On Stability of Periodic Waves in a Cold Collision-Free Plasma in a Magnetic Field", "advisor": "Saffman, Philip G.; Whitham, Gerald Beresford", "url": "https://resolver.caltech.edu/CaltechTHESIS:04022013-142811896", "creators": [ { "name": { "family": "Yeh", "given": "Tyan" }, "id": "Yeh-Tyan", "display_name": "Yeh, Tyan" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "advisor", "display_name": "Whitham, Gerald Beresford" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appmath" ], "doi": "10.7907/5T79-R738", "abstract": "This dissertation consists of three parts. In Part I, it is shown that looping trajectories cannot exist in finite amplitude stationary hydromagnetic waves propagating across a magnetic field in a quasi-neutral cold collision-free\r\nplasma. In Part II, time-dependent solutions in series\r\nexpansion are presented for the magnetic piston problem,\r\nwhich describes waves propagating into a quasi-neutral cold\r\ncollision-free plasma, ensuing from magnetic disturbances\r\non the boundary of the plasma. The expansion is equivalent\r\nto Picard's successive approximations. It is then shown\r\nthat orbit crossings of plasma particles occur on the boundary for strong disturbances and inside the plasma for weak disturbances. In Part III, the existence of periodic waves propagating at an arbitrary angle to the magnetic field in a plasma is demonstrated by Stokes expansions in amplitude. Then stability analysis is made for such periodic waves with respect to side-band frequency disturbances. It is shown that waves of slow mode are unstable whereas waves of fast mode are stable if the frequency is below the cutoff frequency. The cutoff frequency depends on the propagation angle. For longitudinal propagation the cutoff frequency is equal to one-fourth of the electron's gyrofrequency. For transverse propagation the cutoff frequency is so high that waves of all frequencies are stable.
\r\n" }, { "name": "Zoutendyk, Peter John Andrew", "degree": "PhD", "year": "1968", "title": "Spontaneous and Stimulated Light Emission Due to Radiative Recombination in Forward Biased Lead Telluride P-N Junctions", "advisor": "Yariv, Amnon", "url": "https://resolver.caltech.edu/CaltechTHESIS:01042016-150017432", "creators": [ { "name": { "family": "Zoutendyk", "given": "Peter John Andrew" }, "id": "Zoutendyk-Peter-John-Andrew", "display_name": "Zoutendyk, Peter John Andrew" } ], "advisors": [ { "name": { "family": "Yariv", "given": "Amnon" }, "id": "Yariv-A", "role": "advisor", "display_name": "Yariv, Amnon" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/AK38-EQ82", "abstract": "Since the discovery in 1962 of laser action in semiconductor diodes made from GaAs, the study of spontaneous and stimulated light emission from semiconductors has become an exciting new field of semiconductor physics and quantum electronics combined. Included in the limited number of direct-gap semiconductor materials suitable for laser action are the members of the lead salt family, i.e . PbS, PbSe and PbTe. The material used for the experiments described herein is PbTe . The semiconductor PbTe is a narrow band- gap material (Eg = 0.19 electron volt at a temperature of 4.2\u00b0K). Therefore, the radiative recombination of electron-hole pairs between the conduction and valence bands produces photons whose wavelength is in the infrared (\u03bb \u2248 6.5 microns in air).
\r\n\r\nThe p-n junction diode is a convenient device in which the spontaneous and stimulated emission of light can be achieved via current flow in the forward-bias direction. Consequently, the experimental devices consist of a group of PbTe p-n junction diodes made from p \u2013type single crystal bulk material. The p - n junctions were formed by an n-type vapor- phase diffusion perpendicular to the (100) plane, with a junction depth of approximately 75 microns. Opposite ends of the diode structure were cleaved to give parallel reflectors, thereby forming the Fabry-Perot cavity needed for a laser oscillator. Since the emission of light originates from the recombination of injected current carriers, the nature of the radiation depends on the injection mechanism.
\r\n\r\nThe total intensity of the light emitted from the PbTe diodes was observed over a current range of three to four orders of magnitude. At the low current levels, the light intensity data were correlated with data obtained on the electrical characteristics of the diodes. In the low current region (region A), the light intensity, current-voltage and capacitance-voltage data are consistent with the model for photon-assisted tunneling. As the current is increased, the light intensity data indicate the occurrence of a change in the current injection mechanism from photon-assisted tunneling (region A) to thermionic emission (region B). With the further increase of the injection level, the photon-field due to light emission in the diode builds up to the point where stimulated emission (oscillation) occurs. The threshold current at which oscillation begins marks the beginning of a region (region C) where the total light intensity increases very rapidly with the increase in current. This rapid increase in intensity is accompanied by an increase in the number of narrow-band oscillating modes. As the photon density in the cavity continues to increase with the injection level, the intensity gradually enters a region of linear dependence on current (region D), i.e. a region of constant (differential) quantum efficiency.
\r\n\r\nData obtained from measurements of the stimulated-mode light-intensity profile and the far-field diffraction pattern (both in the direction perpendicular to the junction-plane) indicate that the active region of high gain (i.e. the region where a population inversion exists) extends to approximately a diffusion length on both sides of the junction. The data also indicate that the confinement of the oscillating modes within the diode cavity is due to a variation in the real part of the dielectric constant, caused by the gain in the medium. A value of \u03c4 \u2248 10-9 second for the minority- carrier recombination lifetime (at a diode temperature of 20.4\u00b0K) is obtained from the above measurements. This value for \u03c4 is consistent with other data obtained independently for PbTe crystals.
\r\n\r\nData on the threshold current for stimulated emission (for a diode temperature of 20. 4\u00b0K) as a function of the reciprocal cavity length were obtained. These data yield a value of J\u2019th = (400 \u00b1 80) amp/cm2 for the threshold current in the limit of an infinitely long diode-cavity. A value of \u03b1 = (30 \u00b1 15) cm-1 is obtained for the total (bulk) cavity loss constant, in general agreement with independent measurements of free- carrier absorption in PbTe. In addition, the data provide a value of ns \u2248 10% for the internal spontaneous quantum efficiency. The above value for ns yields values of tb \u2248 \u03c4 \u2248 10-9 second and ts \u2248 10-8 second for the nonradiative and the spontaneous (radiative) lifetimes, respectively.
\r\n\r\nThe external quantum efficiency (nd) for stimulated emission from diode J-2 (at 20.4\u00b0 K) was calculated by using the total light intensity vs. diode current data, plus accepted values for the material parameters of the mercury- doped germanium detector used for the measurements. The resulting value is nd \u2243 10%-20% for emission from both ends of the cavity. The corresponding radiative power output (at \u03bb = 6.5 micron) is 120-240 milliwatts for a diode current of 6 amps.
\r\n" }, { "name": "Alber, Irwin Emanuel", "degree": "PhD", "year": "1967", "title": "Integral Theory for Turbulent Base Flows at Subsonic and Supersonic Speeds", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-141417", "creators": [ { "name": { "family": "Alber", "given": "Irwin Emanuel" }, "id": "Alber-Irwin-Emanuel", "display_name": "Alber, Irwin Emanuel" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "chair", "display_name": "Lees, Lester" }, { "name": { "family": "Babcock", "given": "Charles D." }, "id": "Babcock-C-D", "role": "member", "display_name": "Babcock, Charles D." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "member", "display_name": "Coles, Donald Earl" }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "member", "display_name": "Saffman, Philip G." }, { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "member", "display_name": "Wu, Theodore Yao-tsu" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0YEZ-H062", "abstract": "The integral near wake analysis of Reeves and Lees developed for supersonic laminar base flows is extended to the case of fully turbulent separated adiabatic flow behind a rearward facing step at both subsonic and supersonic speeds. A turbulent eddy viscosity model is formulated for the shear stress scaling of the dissipation integral in the mechanical energy equation. It is shown that the eddy viscosity can be described simply by one incompressible constant (valid for both shear layers and wakes) and one reference density \u03c1r. Using a compressibility transformation, theoretical solutions for the spreading rates of free shear layers are found to agree with experiment when the reference density is chosen to be the centerline density for the wake flow.
\r\n\r\nTwo alternate methods are presented for joining the wake flow solution to the body first, through a turbulent free shear layer mixing solution, and then through the use of a two parameter family of velocity profiles valid near the body. A simple conservation model is presented to relate the viscous sublayer after expansion to the initial boundary layer ahead of the step.
\r\n\r\nFor free stream Mach numbers M1 \u2264 2.3, the integral theory is found to give good estimates for the length scales and centerline pressure variations measured experimentally for both wake flows and step flows (where reattachment is to a solid surface).
\r\n\r\nAn iterative method of solution for the incompressible wake flow problem is presented as an extension of the work of Green. The calculation proposes the proper criteria for obtaining a convergent solution. The base pressure coefficient is found to be equal to the difference between the momentum thicknesses in the far wake and at the base.
\r\n" }, { "name": "Atkinson, John David", "degree": "PhD", "year": "1967", "title": "Spectral Density of First Order Piecewise Linear Systems Excited by White Noise", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:11022015-090737162", "creators": [ { "name": { "family": "Atkinson", "given": "John David" }, "id": "Atkinson-John-David", "display_name": "Atkinson, John David" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/V6YX-7864", "abstract": "The Fokker-Planck (FP) equation is used to develop a general method for finding the spectral density for a class of randomly excited first order systems. This class consists of systems satisfying stochastic differential equations of form \u1e8b + f(x) = m/\u01a9/j = 1 hj(x)nj(t) where f and the hj are piecewise linear functions (not necessarily continuous), and the nj are stationary Gaussian white noise. For such systems, it is shown how the Laplace-transformed FP equation can be solved for the transformed transition probability density. By manipulation of the FP equation and its adjoint, a formula is derived for the transformed autocorrelation function in terms of the transformed transition density. From this, the spectral density is readily obtained. The method generalizes that of Caughey and Dienes, J. Appl. Phys., 32.11.
\r\n\r\nThis method is applied to 4 subclasses: (1) m = 1, h1 = const. (forcing function excitation); (2) m = 1, h1 = f (parametric excitation); (3) m = 2, h1 = const., h2 = f, n1 and n2 correlated; (4) the same, uncorrelated. Many special cases, especially in subclass (1), are worked through to obtain explicit formulas for the spectral density, most of which have not been obtained before. Some results are graphed.
\r\n\r\nDealing with parametrically excited first order systems leads to two complications. There is some controversy concerning the form of the FP equation involved (see Gray and Caughey, J. Math. Phys., 44.3); and the conditions which apply at irregular points, where the second order coefficient of the FP equation vanishes, are not obvious but require use of the mathematical theory of diffusion processes developed by Feller and others. These points are discussed in the first chapter, relevant results from various sources being summarized and applied. Also discussed is the steady-state density (the limit of the transition density as t \u2192 \u221e).
\r\n" }, { "name": "Batt, Richard George", "degree": "PhD", "year": "1967", "title": "Experimental Investigation of Wakes Behind Two-Dimensional Slender Bodies at Mach Number Six", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12292005-132450", "creators": [ { "name": { "family": "Batt", "given": "Richard George" }, "id": "Batt-Richard-George", "display_name": "Batt, Richard George" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3WW3-B746", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation has been conducted to determine mean flow properties for both near and far wakes behind several two-dimensional slender bodies at M[...] = 6. Three adiabatic wall models consisting of a flat plate model and two 20 [degree] included angle wedge models (H = .15\", H = .3\") were tested. The effect of wall temperature on wake properties was examined by cooling the larger of these two wedge models with the internal flow of liquid nitrogen ([...] = .19). Free stream Reynolds numbers were varied from [...] to [...] for each of these four configurations. In the far wake, measurements of total temperature, as determined with hot wire probes, and Pitot and static pressures were used to derive all other mean flow properties. The effect of transition on these far wake data was determined. Near wake flows were laminar for all adiabatic wall tests and at least for the two lowest test Reynolds numbers of the cold wall wedge. Base region flow field mappings and shear layer profiles were obtained for the .3\"H wedge model by combining Pitot pressure data with hot wire measurements of total temperature and mass flux. These results illustrated that for slender bodies with flat bases, the basic structure for laminar near wakes is appreciably more complex for hypersonic than for supersonic flow primarily because, in hypersonic flow, the corner expansion fan extends into the separated shear layers and base region shocks now become imbedded within the viscous portion of the shear layers." }, { "name": "Blish, Richard Clark, III", "degree": "PhD", "year": "1967", "title": "Dislocation Velocity and Slip on the {1\u030521\u03052} <12\u030513> Systems of Zinc", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172002-144540", "creators": [ { "name": { "family": "Blish", "given": "Richard Clark, III" }, "id": "Blish-Richard-Clark-III", "display_name": "Blish, Richard Clark, III" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "chair", "display_name": "Vreeland, Thad" }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "member", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Buffington", "given": "Francis Stephan" }, "id": "Buffington-F-S", "role": "member", "display_name": "Buffington, Francis Stephan" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "member", "display_name": "Duwez, Pol E." } ], "option_major": [ "matsci" ], "doi": "10.7907/AEDX-C287", "abstract": "Slip bands on the {‾12‾12} <1‾213> systems of zinc were produced by stress pulses and were observed by etch pitting.. Edge and screw dislocation velocities as a function of stress and temperature (77\u00b0 to 323\u00b0K) were deduced by measurement of the size of the slip bands. For the low temperature range of 77\u00b0 to 110\u00b0K it is found that dislocation velocity is proportional to (stress) exp(-U/kT) where U = 0.182 ev. Screw dislocation velocity is found to be larger than edge dislocation velocity at a constant stress. It is suggested that a Peierls mechanism controls the dislocation velocity for the low temperature range. Above 110\u00b0K the slip bands start to become wider as cross glide takes precedence over the Peierls mechanism for the limitation of dislocation velocity. It is found that dislocation velocity decreases and the amount of cross glide increases with increasing temperature. It is suggested that the dislocations are retarded by an increasing number of dragging dipoles. The experimentally measured dislocation velocities are also related to the macroscopic measurements of the yield stress and the work hardening coefficient." }, { "name": "Butman, Stanley", "degree": "PhD", "year": "1967", "title": "Optimum Linear Coding for Additive Noise Systems Using Information Feedback", "advisor": "Grettenberg, Thomas L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262015-143321124", "creators": [ { "name": { "family": "Butman", "given": "Stanley" }, "id": "Butman-Stanley", "display_name": "Butman, Stanley" } ], "advisors": [ { "name": { "family": "Grettenberg", "given": "Thomas L." }, "id": "Grettenberg-T-L", "role": "advisor", "display_name": "Grettenberg, Thomas L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7ZSR-4928", "abstract": "The feedback coding problem for Gaussian systems in which the noise is neither white nor statistically independent between channels is formulated in terms of arbitrary linear codes at the transmitter and at the receiver. This new formulation is used to determine a number of feedback communication systems. In particular, the optimum linear code that satisfies an average power constraint on the transmitted signals is derived for a system with noiseless feedback and forward noise of arbitrary covariance. The noisy feedback problem is considered and signal sets for the forward and feedback channels are obtained with an average power constraint on each. The general formulation and results are valid for non-Gaussian systems in which the second order statistics are known, the results being applicable to the determination of error bounds via the Chebychev inequality.
" }, { "name": "Dickerson, John Randall", "degree": "PhD", "year": "1967", "title": "Stability of Parametrically Excited Differential Equations", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:11232015-113606191", "creators": [ { "name": { "family": "Dickerson", "given": "John Randall" }, "id": "Dickerson-John-Randall", "display_name": "Dickerson, John Randall" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/62VM-QG37", "abstract": "Sufficient stability criteria for classes of parametrically excited differential equations are developed and applied to example problems of a dynamical nature.
\r\nStability requirements are presented in terms of 1) the modulus of the amplitude of the parametric terms, 2) the modulus of the integral of the parametric terms and 3) the modulus of the derivative of the parametric terms.
\r\nThe methods employed to show stability are Liapunov\u2019s Direct Method and the Gronwall Lemma. The type of stability is generally referred to as asymptotic stability in the sense of Liapunov.
\r\nThe results indicate that if the equation of the system with the parametric terms set equal to zero exhibits stability and possesses bounded operators, then the system will be stable under sufficiently small modulus of the parametric terms or sufficiently small modulus of the integral of the parametric terms (high frequency). On the other hand, if the equation of the system exhibits individual stability for all values that the parameter assumes in the time interval, then the actual system will be stable under sufficiently small modulus of the derivative of the parametric terms (slowly varying).
\r\n" }, { "name": "Fan, Loh-Nien", "degree": "PhD", "year": "1967", "title": "Turbulent Buoyant Jets into Stratified or Flowing Ambient Fluids", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11232015-162414440", "creators": [ { "name": { "family": "Fan", "given": "Loh-Nien" }, "id": "Fan-Loh-Nien", "display_name": "Fan, Loh-Nien" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/C69V-BE23", "abstract": "Theoretical and experimental studies were made on two classes of buoyant jet problems, namely:
\r\n1) an inclined, round buoyant yet in a stagnant environment with linear density-stratification;
\r\n2) a round buoyant jet in a uniform cross stream of homogenous density.
\r\nUsing the integral technique of analysis, assuming similarity, predictions can be made for jet trajectory, widths, and dilution ratios, in a density-stratified or flowing environment. Such information is of great importance in the design of disposal systems for sewage effluent into the ocean or waste gases into the atmosphere.
\r\nThe present study of a buoyant jet in a stagnant environment has extended the Morton type of analysis to cover the effect of the initial angle of discharge. Numerical solutions have been presented for a range of initial conditions. Laboratory experiments were conducted for photographic observations of the trajectories of dyed jets. In general the observed jet forms agreed well with the calculated trajectories and nominal half widths when the value of the entrainment coefficient was taken to be \u03b1 = 0.082, as previously suggested by Morton.
\r\nThe problem of a buoyant jet in a uniform cross stream was analyzed by assuming an entrainment mechanism based upon the vector difference between the characteristic jet velocity and the ambient velocity. The effect of the unbalanced pressure field on the sides of the jet flow was approximated by a gross drag term. Laboratory flume experiments with sinking jets which are directly analogous to buoyant jets were performed. Salt solutions were injected into fresh water at the free surface in a flume. The jet trajectories, dilution ratios and jet half widths were determined by conductivity measurements. The entrainment coefficient, \u03b1, and drag coefficient, Cd, were found from the observed jet trajectories and dilution ratios. In the ten cases studied where jet Froude number ranged from 10 to 80 and velocity ratio (jet: current) K from 4 to 16, \u03b1 varied from 0.4 to 0.5 and Cd from 1.7 to 0.1. The jet mixing motion for distance within 250D was found to be dominated by the self-generated turbulence, rather than the free-stream turbulence. Similarity of concentration profiles has also been discussed.
\r\n" }, { "name": "Flandro, Gary Arnold", "degree": "PhD", "year": "1967", "title": "Rotating Flows in Acoustically Unstable Rocket Motors", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272004-154250", "creators": [ { "name": { "family": "Flandro", "given": "Gary Arnold" }, "id": "Flandro-Gary-Arnold", "display_name": "Flandro, Gary Arnold" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BYWJ-5Q96", "abstract": "One of the most interesting manifestations of acoustic combustion instability in solid propellant rocket motors is the formation of strong vortices in the combustion chamber. A single vortex filament stretching along the motor axis from the head-end has been observed in several experiments in association with gas oscillations in the frequently occurring traveling tangential mode of instability. These flows are sometimes accompanied by a quite noticeable axial torque on the motor itself, and this effect has given rise to flight performance difficulties in a number of instances. Previous theoretical studies of the vortex generation effect have been inadequate in several respects. The present work is an attempt to place the theory on a more firm base and to clarify the connection between traveling wave motions and the generation of vortices and torques.
\r\n\r\nIt is readily shown that traveling waves transport momentum, and in the case of traveling tangential waves in a cylindrical combustion chamber this represents a steady axial component of angular momentum in the gas. This observation gives rise to a simple conceptual model of the vortex generation effect. Thus the presence of a steady mass flux about the axis implies the existence of a layer of vorticity at the chamber walls which may be represented by a vortex sheet composed of axially oriented bound vortex filaments. In the three-dimensional case these vortices are shed either at the end of propellant grain or at the periphery of the nozzle; the other ends of the filaments traverse the fore-end closure to the center and are combined and shed in an intense vortex filament along the symmetry axis of the motor.
\r\n\r\nDue to the production of gas at the chamber wall, tangential forces at the wall are produced by the interaction of this mean flow with the bound vortices. Angular momentum arguments must be used in this conceptual mechanism to estimate the strength of the axial vortex filament, and it is readily shown that the sense of the vortex must be opposite to the direction of travel of the waves. The direction and magnitude of the torque on the motor depend on the mean flow Mach number at the wall and must be established by calculation of the wall shear stresses.
\r\n\r\nThe detailed calculations are guided by the mechanism just outlined. All physical features of the problem which appear to be significant are simulated mathematically. In particular, the effects of the three dimensional mean flow pattern in the chamber and the pressure-sensitive combustion region at the burning surface are represented. Also considered are the effects of freedom of motion of the rocket motor in the plane normal to the symmetry axis. Both inviscid and viscous theories are developed using multi-parameter asymptotic perturbation expansion techniques. It is proved that traveling tangential waves are subject to amplification under conditions existing in typical solid propellant rockets, and that a steady transport of gas about the chamber axis accompanies this motion as a second-order perturbation. The equations of motion admit of only a vortex-like steady second-order azimuthal solution. This must be superimposed on the acoustic wave motions in such a way that angular momentum is conserved (due consideration being given to body forces on the gas and tangential forces at the wall). Thus the net pattern of steady circumfer vential mass flux at a given motor cross-section consists of a drift of fluid in the direction of the wave adjacent to the wall with a rapid transition to an oppositely spinning vortex flow as the longitudinal axis is approached. Introduction of the viscous corrections gives rise to a boundary. condition which sets the vortex strength, and a formal connection with the classical acoustic streaming effect is established. Since momentum is dissipated in the shear region at the wall, a torque appears on the chamber itself. This roll moment is opposite in sense to the wave travel during amplification of the acoustic waves, and numerical calculations give torque magnitudes which are in agreement with experimental data from several sources.
\r\n" }, { "name": "Giberson, Melbourne Fernald", "degree": "PhD", "year": "1967", "title": "The Response of Nonlinear Multi-Story Structures Subjected to Earthquake Excitation", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182002-085426", "creators": [ { "name": { "family": "Giberson", "given": "Melbourne Fernald" }, "id": "Giberson-Melbourne-Fernald", "display_name": "Giberson, Melbourne Fernald" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/W8D4-3W95", "abstract": "The dynamic responses of a 20-story nonlinear structural frame representative of a modern high rise building are analyzed with the aid of a digital computer. Related analytical studies of continuous systems are carried out. Quantitative information is provided on the importance of a wide range of modes to the various responses of a multistory structure during an earthquake. The effect of yielding on the response is observed. The magnitude of the structural responses are compared with common measurements of earthquake strength.\r\n\r\nAt the ends of each girder and column of the structural frame are yield hinges which have bilinear bending moment-rotation hysteretic characteristics. Two beam models having such characteristics are studied; one of these models can treat curvilinear hysteretic behavior. Three definitions of ductility factor are discussed, one of which is applicable to both bilinear and curvilinear hysteresis loops. In the computer program, the frame is subjected to the time history of an earthquake accelerogram, the equations of motion are stepwise integrated, and the various structural responses - displacement, bending moments, incurred yielding, etc. - are determined.\r\n\r\nThe agreement between the response parameters resulting from excitation by seven different earthquake ground motions indicates that these response characteristics are determined more by the properties of the structure than by the earthquake. These results throw some light on extreme value statistics of the response of yielding structures subjected to earthquakes. The characteristic patterns observed in the computed responses of the nonlinear structure can be related to analytical studies of linear elastic, shear-type, uniform and tapered continuous cantilever beams" }, { "name": "Greenman, William Franklin", "degree": "PhD", "year": "1967", "title": "Dislocation Mobility in Pure Copper Single Crystals", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192002-153519", "creators": [ { "name": { "family": "Greenman", "given": "William Franklin" }, "id": "Greenman-William-Franklin", "display_name": "Greenman, William Franklin" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/072F-RC63", "abstract": "This thesis presents the results of an experimental investigation of the stress dependence of dislocation velocity in 99.999 per cent copper single crystals. Dislocation displacements were detected by etch pitting dislocation sites on {100} planes. Stress pulses of microsecond duration were applied to single crystal test specimens by means of a torsion impulse machine. Maximum applied, resolved shear stresses ranged from 29 g/mm\u00b2 to 236 g/mm\u00b2, and calculated dislocation velocities ranged from 160 cm/sec to 710 cm/sec. The dislocations were presumably predominantly edge-oriented.
\r\n\r\nThe growth of copper single crystals, the spark and chemical machining of single crystal test specimens, and the behavior of the etchants which reveal dislocation sites on {100} planes are also discussed.
\r\n\t\r\nThe experimental data have been found to obey a linear relation between dislocation velocity and applied, resolved shear stress. This finding does not correlate with the explanation of the low strain rate sensitivity of the flow stress in copper as proposed by Cottrell (46)*, which predicts that dislocation velocity should be proportional to stress raised to a power of about 200. The low strain rate sensitivity of the flow stress in copper is explained by the high velocity of dislocations at low stresses and the strong stress dependence of the mobile dislocation density. This high velocity is interpreted as enabling the strain essentially to achieve its equilibrium value even at relatively high strain rates.
\r\n\r\n*One- and two-digit numbers appearing in parentheses indicate references listed at the end of the thesis.
" }, { "name": "Hallanger, Lawrence William", "degree": "PhD", "year": "1967", "title": "The Dynamic Stability of an Unbalanced Mass Exciter", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162002-110654", "creators": [ { "name": { "family": "Hallanger", "given": "Lawrence William" }, "id": "Hallanger-Lawrence-William", "display_name": "Hallanger, Lawrence William" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/2REC-VT88", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe dynamic stability of single- and multi-degree-of-freedom unbalanced mass exciter systems is discussed. Previous work concerning this subject by A. Sommerfield, Y. Rocard, R. Maz? V. O. Kononenko, Y. G. Panovko and I. I. Gubanova is summarized. A single-degree-of-freedom system consisting of a linear mechanical oscillator with a rotating unbalanced mass connected rigidly to it is defined as the basic single-degree-of-freedom system. This system is mathematically equivalent to the one used by Rocard in his analysis. The differential equations of motion for the system are obtained by using Lagrange's Equations. Global stability, stability in the sense of Laplace, is proved using Liapunov's second method. Four separate local stability analyses of this system are developed, two of which assume a constant angular velocity, [omega], of the unbalanced mass and two which allow for periodic variations in [omega]. These analyses are termed zero and first order respectively.\r\n\r\nThe first zero order analysis is based directly on the differential equations of motion and the zero order steady state solution. The steady state torque output of the vibration exciter motor and the steady state torque requirements of the oscillator are obtained as functions of the operating frequency. Stability is determined by examining the behavior of the system in the vicinity of the intersection points of these two functions. The second zero order analysis examines the behavior of small perturbations added to the steady state solution. The system is considered stable if these perturbations disappear with time. The first first order analysis is a perturbation type, but is based on a steady state solution which allows for periodic variations in [omega]. The second first order analysis is also based on the first order perturbed equations of motion but is a Floquet type analysis. Validity criteria for the zero and first order analyses are obtained, and the zero order region of validity is plotted graphically. A representative set of systems is analyzed numerically, and the results are presented in a figure showing the stability boundary as a function of the system parameters in non-dimensional form.\r\n\r\nTwo distinct types of multi-degree-of-freedom systems are discussed. The first consists of a single oscillator mass that is free to perform planar motion. It is shown that when an unbalanced mass exciter with a uniaxial force output is mounted on the oscillator in such a way that only one mode is excited, the problem reduces to the single-degree-of-freedom problem. The second system consists of a series of linear single-degree-of-freedom oscillators with an unbalanced mass exciter mounted on one of them. The special case of a three oscillator system with equal masses is used to demonstrate that, for systems with widely separated resonances, the \"equivalent\" single-degree-of-freedom analysis presented by Kononenko is valid. From these results it is concluded that, in any multi-degree-of-freedom system, an \"equivalent\" single-degree-of-freedom analysis may be used to examine the stability of the system near any resonance as long as that particular mode is the only one which is being significantly excited.\r\n\r\nAppendices covering the details of Rocard's analysis, and of the unbalanced mass exciters designed and built at the California Institute of Technology are included." }, { "name": "Harstad, Kenneth Gunder", "degree": "PhD", "year": "1967", "title": "Steady Laminar Compressible Magneto-Fluid-Dynamic Gas Flows in Channels.", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172002-144944", "creators": [ { "name": { "family": "Harstad", "given": "Kenneth Gunder" }, "id": "Harstad-Kenneth-Gunder", "display_name": "Harstad, Kenneth Gunder" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5T8X-8S80", "abstract": "Numerical computations are carried out for the core flow of subsonic MFD generator channels with a large length-to-height ratio and fine electrode segmentation. The working fluid is taken as potassium seeded argon. Variable transport properties and radiation effects are considered. It is shown that transverse variations in fluid properties are very important in Faraday generators; a one-dimensional analysis of the flow is not adequate. Axial currents in nonequilibrium flows can be kept low if the right value of the Hall parameter can be obtained; this also depends critically on the Mach number and load parameter. Mach numbers much less than one and high load parameters are to be avoided. Attainment of very large Hall parameters and fields cannot be expected." }, { "name": "Hoffman, Alan Lowell", "degree": "PhD", "year": "1967", "title": "Magnetohydrodynamic Shock Production and Current Sheet Diffusion", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12292005-135853", "creators": [ { "name": { "family": "Hoffman", "given": "Alan Lowell" }, "id": "Hoffman-Alan-Lowell", "display_name": "Hoffman, Alan Lowell" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4WVH-W290", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nCurrent sheets in inverse pinch MHD shock tubes exhibit the strange property of forming shocks in the very rear of the sheet when accelerating heavy gases. When accelerating light gases, shocks are formed further to the front in the sheet, but in no case do the shocks separate from the driving current sheet. This \"piston dragging shock\" effect is explained on the basis of a single-fluid model with variable conductivity. Shocks are shown to always form within current sheets which move at supersonic speeds with respect to the driven gas. The relevant parameters for determining the shock position are the Mach number and the magnetic Reynolds number. Large magnetic Reynolds numbers and small Mach numbers enhance forward shock formation. These conditions are obtained in light gases with high speeds of sound. Similarity methods are developed to estimate gas conductivities, electron temperatures, and degrees of ionization for the experiments which are conducted. In hydrogen typical electron temperatures of 4 ev are produced by the ohmic heating, but twice this value is shown necessary to achieve separation at the current sheet speeds of 2-3 [...] used. Higher current sheet speeds produce shocks in the rear of the current sheet where separation can never occur. The correct method of procedure and the relevant design parameters to achieve separation are given. The success of single-fluid methods in explaining plasma phenomena is especially notable, and these methods can be extended to other similar problems. Based on these methods, multiple-fluid and microscopic effects are easily detectable and can be accounted for." }, { "name": "Husid, Ra\u00fal", "degree": "PhD", "year": "1967", "title": "Gravity Effects on the Earthquake Response of Yielding Structures", "advisor": "Housner, George W.; Jennings, Paul C.; Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202002-143339", "creators": [ { "name": { "family": "Husid", "given": "Ra\u00fal" }, "id": "Husid-Ra\u00fal", "display_name": "Husid, Ra\u00fal" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "advisor", "display_name": "Jennings, Paul C." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "chair", "display_name": "Housner, George W." }, { "name": { "family": "Jennings", "given": "Paul C." }, "id": "Jennings-P-C", "role": "member", "display_name": "Jennings, Paul C." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "civileng" ], "doi": "10.7907/9XAB-6V59", "abstract": "The effect of gravity on the earthquake response of one degree of freedom yielding structures is studied by subjecting them to earthquake-like excitation. Interest is centered on the time required for yielding to progress to the point of collapse. The results show that the effect of gravity is to increase significantly the development of permanent set over that occurring when gravity is ignored. Because the gravity effect increases as the deflection grows, the permanent set increases rapidly just prior to failure.\r\n\r\nA statistical study of the time to failure for elasto-plastic structures indicates that the average time to failure is inversely proportional to the square of the ratio of the earthquake strength to the lateral yield level of the structure, implying that an earthquake of short duration would have to possess significantly higher accelerations than a longer earthquake in order to cause failure of a given structure.\r\n\r\nIt was found that for the range of periods considered the average time to collapse for the yielding structures was independent of period. For the bilinear hysteretic structure the results show a large increase in the time of failure when the second slope increases from zero.\r\n\r\nCalculations made with simultaneous vertical and horizontal excitation, and with recorded strong earthquake accelerograms, indicate that the thesis results, obtained from artificial earthquakes, should be applicable for strong earthquake excitation.\r\n\r\nComparison of the results with those of a one-dimensional random walk indicates that on the average a yielding structure will collapse after the input of a certain amount of energy." }, { "name": "James, David Fielding", "degree": "PhD", "year": "1967", "title": "Laminar Flow of Dilute Polymer Solutions Around Circular Cylinders", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132002-124902", "creators": [ { "name": { "family": "James", "given": "David Fielding" }, "id": "James-David-Fielding", "display_name": "James, David Fielding" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/G1Z1-PH10", "abstract": "Experimental results are presented for heat transfer by free and forced convection at low velocities from small heated cylinders in dilute solutions of polyethylene oxide in water. The experiments were conducted for a range of velocities (less than 1. 0 ft/sec) and polymer concentrations, with several cylinder diameters, and for several polymer molecular weights. Experimental results are also presented for the drag of a small cylinder in similar liquids and for a comparable range of velocities.\r\n\r\nThe heat transfer and drag results at low velocities were identical to those for a Newtonian liquid; at high velocities, the measured values departed considerably from Newtonian results. These departures result from the viscoelastic nature of the polymer solutions. Visualization studies of the flow around a cylinder and of a minute laminar jet were conducted to determine the gross magnitude of the viscoelastic effects. Due to the liquid's elasticity, a significant enlargement of the flow field was observed for both configurations above a critical Reynolds number. An attempt is made to explain the heat transfer and drag results in light of these observations.\r\n\r\nPhotographic materials on pp. 111 - 149 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered" }, { "name": "Klein, Alan Frank", "degree": "PhD", "year": "1967", "title": "I. The Use of a Large Conventional Shock Tube as a Pre-Ionizer for an Inverse Pinch Shock Tube. II. The Application of Thin-Film Heat Transfer Gauges and Flush Electrostatic Probes to Partially Ionized Flows in Shock Tubes", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12292005-133945", "creators": [ { "name": { "family": "Klein", "given": "Alan Frank" }, "id": "Klein-Alan-Frank", "display_name": "Klein, Alan Frank" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G7GV-GX76", "abstract": "Part 1.
\r\n\r\nA large diameter (17\"), conventional shock tube has been used as the pre-ionizer for an inverse pinch shock tube in an attempt to achieve separation of the shock front and the current sheath in the inverse pinch. The inverse pinch was mounted in the endwall of the shock tube and was operated without an anode, either behind the incident or reflected shock wave generated by the pre-ionizer shock tube. The test gases used were Xenon, Argon, and Helium. Separation was not achieved, but in Argon the pressure front did move closer to the front of the current sheath. In Xenon, no improvement in the performance of the inverse pinch was observed as a result of the pre-ionization, and in one case it was noticeably degraded, with the piston appearing to leak excessively. Because of test time limitations it was only possible to operate the inverse pinch behind the incident shock wave in Xenon. By measuring the ionization relaxation time in Xenon it was found that for all the conditions of the present experiments, ionization equilibrium was not attained in the times available. Therefore, the inverse pinch was being operated in a slightly ionized, relaxing gas. The electrical conductivity of such a gas was calculated for Xenon and Argon and the results in Argon were found to be in good agreement with previous shock tube measurements of the conductivity. The relaxation time measurements, conducted primarily in the GALCIT 6\" shock tube, show that P\u2081\u03c4, the product of the initial pressure and the relaxation time behind the incident shock, depends strongly upon the magnitude of P\u2081, especially for P\u2081 < .5 mm Hg of Xenon. The dependence decreases as the Mach number is increased in the range 10 < Ms < 20.6.
\r\n\r\nPart 2.
\r\n\r\nPrevious shock tube observations of \"spurious\" signals in the output of thin-film heat gauges at Mach number for which the shocked gas becomes partially ionized are summarized. It is shown that these effects, and those observed the the present experiments in Xenon, cannot be explained in terms of a shorting gauge model. It is demonstrated that the effects are due to the gauge acting more as an electrostatic probe than as a heat gauge. Under these conditions it is shown that the heat gauge provides an accurate measurement of the ionization relaxation time as well as still being useful for determining the shock velocity. The thin-film is also operated as a flush electrostatic probe to measure the ion density in the shock tube wall boundary layer, and the experimental results are in good agreement with the theoretical predictions of two solutions of the boundary layer problem: one based on an approximate solution of the transformed boundary layer equations, and the other based on the solution of the equivalent Couette flow problems. The applicability of these solutions is found to be limited to conditions for which the ionization relaxation time is either very long or very short. Because of the computational simplifications involved it is seen that the Couette flow solution is preferred under most conditions.
" }, { "name": "Lewis, John Eldon", "degree": "PhD", "year": "1967", "title": "Experimental Investigation of Supersonic, Laminar, Two-Dimensional, Boundary Layer Separation in a Compression Corner with and without Cooling", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-11162005-102455", "creators": [ { "name": { "family": "Lewis", "given": "John Eldon" }, "id": "Lewis-John-Eldon", "display_name": "Lewis, John Eldon" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R0FB-DD20", "abstract": "An experimental investigation of the boundary layer separation associated with a compression corner was conducted in the GALCIT Mach 6 wind tunnel, and a supplementary study was performed in the JPL supersonic wind tunnel. Special emphasis was placed on the development of a wind tunnel model which approximated true two-dimensional flow, and which could be run in either a highly cooled or an adiabatic configuration. The basic measurements consist of the model surface pressure and temperature, and Pitot surveys of the boundary layer. The surface pressure distributions for the adiabatic wall configurations are compared with the theory of Lees and Reeves (modified by Klineberg and Lees). The surface pressure distribution for the cold wall was compared with the adiabatic configuration for a laminar interaction, and the dependence on Reynolds number for both laminar and transitional interactions are observed. The \"free interaction\" similarity suggested by Chapman is empirically tested and found to be a good approximation for the adiabatic configuration, but it fails to correlate the cooled with the adiabatic case. The scaling suggested by Curle was tested and found to eliminate this deficiency." }, { "name": "Lutes, Loren Daniel", "degree": "PhD", "year": "1967", "title": "Stationary Random Response of Bilinear Hysteretic Systems", "advisor": "Iwan, Wilfred D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-103426", "creators": [ { "name": { "family": "Lutes", "given": "Loren Daniel" }, "id": "Lutes-Loren-Daniel", "display_name": "Lutes, Loren Daniel" } ], "advisors": [ { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "advisor", "display_name": "Iwan, Wilfred D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/Q4HZ-TM03", "abstract": "This study of the stationary random vibration of single degree of freedom bilinear hysteretic oscillators consists of both experimental investigations and approximate analytical investigations. The experimental results are obtained from a differential analyzer electrical analog computer excited by an approximately white, Gaussian source. Measurements of mean squared levels, power spectral density and probability distribution of oscillator response are reported. The applicability of certain approximate analytical techniques is investigated by comparing analytical predictions and experimental measurements of the statistics of the response.\r\n\r\nThe analog computer results indicate that for a system containing viscous damping, yielding may sometimes act to increase the rms level of displacement response. In addition, the experimental results show that yielding has a marked effect on the response power spectral density, and in some instances this statistic has the general character of that for a two mode linear system. The response probability distribution is also affected by yielding and is generally not Gaussian.\r\n\r\nAn extension of the Krylov-Bogoliubov method of equivalent linearization and a method based on defining an approximately equivalent nonlinear nonhysteretic system are considered. The Krylov-Bogoliubov method gives a reasonable estimate of the rms velocity response for all cases considered but gives meaningful information about the rms displacement response only for cases of moderate nonlinearity. The second approximate method is shown to be quite good for predicting rms levels of response for cases of high yield level where the Krylov-Bogoliubov method is less successful. The application of the second method to other cases and to the problem of predicting probability distributions is also discussed." }, { "name": "Mani, Ramani", "degree": "PhD", "year": "1967", "title": "Quasi Two-Dimensional Flows Through Cascades", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-093723", "creators": [ { "name": { "family": "Mani", "given": "Ramani" }, "id": "Mani-Ramani", "display_name": "Mani, Ramani" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/01sg-we85", "abstract": "The present thesis is an attempt to develop a thin airfoil theory for an airfoil which spans the gap between a pair of stream surfaces which are slowly diverging or converging, the motivation being to predict, theoretically, the effect of varying axial velocity on cascade performance of axial flow compressor rows.
\r\n\r\nThe procedure involves, firstly, derivation of approximate equations satisfied by suitably defined average potentials and stream functions in such quasi two-dimensional flows. The flow is assumed to be inviscid, irrotational, and incompressible, but as will be argued later, the quasi two-dimensional type equations also result from less restrictive assumptions. Next, fundamental solutions to these equations, corresponding to bound, line sources and vortices, are found. A distribution of such solutions is used to formulate the airfoil problem, using the condition that the flow be tangential to the airfoil contour. The vorticity distribution appears as the solution to a singular integral equation, which is solved by an approximate method. Simple yet physically realistic assumptions are made concerning the gap width as a function of the streamwise length, to obtain numerical results for the effect of contraction of the stream surfaces. Varying degrees of approximation, later discussed, are used in the calculation procedures. A wide variety of the location and the extent of the contraction, with respect to the airfoil, is investigated.
\r\n\r\nIn all cascade calculations the contraction of the stream surfaces was assumed to be in the same direction as the cascade axis. The main conclusions of the thesis can be summarized as below:
\r\n\r\n1. The theory predicts a lesser circulation round an airfoil in a contracting flow as compared to the circulation round the same airfoil in a plane flow. There is a similar reduction of circulation for a cascade of airfoils. The percentage reduction of circulation is greater for the cascade case as compared to the isolated case, assuming the contractions to be geometrically similar in both cases. The effect on the circulation of contractions, considered physically reasonable in extent and magnitude, either fully upstream or fully downstream of the airfoil, is quite small.
\r\n\r\n2. As a very rough rule of thumb, it may be stated that the reduction of circulation as compared to the two-dimensional theory, in the range of parameters applicable to compressors, has about the same magnitude as the reduction of gap between the stream surfaces taking place across the airfoil chords.
\r\n\r\n3. In a comparison with fixed mean angle of attack, the change in flow turning and deviation angles of the flow are much smaller than changes of circulation and may be stated to be of the order of one degree or less for contraction extents and magnitudes considered realistic for compressor cascades.
\r\n" }, { "name": "Marshall, Franklin Lester", "degree": "PhD", "year": "1967", "title": "I. Surface Deformations in a Draining Cylindrical Tank. II. Stability of a Laminar Film on an Inclined Plane", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-104737", "creators": [ { "name": { "family": "Marshall", "given": "Franklin Lester" }, "id": "Marshall-Franklin-Lester", "display_name": "Marshall, Franklin Lester" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/HFTH-5W53", "abstract": "I. The problem of draining of a liquid from a cylindrical tank through a hole in the bottom is considered. The flow is irrotational, and the free surface boundary conditions are linearized. Solutions are obtained and the shape of the free surface determined for any constant mass flow rate. At large mass flow rates, the free surface deforms appreciably when the mean depth is about 40 per cent or less of the tank diameter.\r\n\r\nThe initial acceleration distribution of the free surface and the transient behavior of the mass flow rate are determined for a flow started impulsively from rest as a result of a constant pressure head.\r\n\r\nAt large Froude numbers it is possible to compare the results with the recent experiments of Gluck, Gille, Zukoski, and Simkin, and the present analysis is consistent with the experimental observations.\r\n\r\nII. The stability characteristics of a laminar film with a free surface flowing under the action of gravity down an inclined plane are examined. Approximate solutions of the Orr-Sommerfeld equation are obtained. These are valid as long as the wave speed of the disturbance is somewhat larger than the maximum velocity of the undisturbed flow. Curves of neutral stability as functions of Reynolds number of the undisturbed flow and wave number of the disturbance are found. These are valid over a larger domain of Reynolds number and wave number than the previous results of Benjamin.\r\n\r\nThe special case of a vertical wall and zero surface tension is also discussed. It is shown that undamped waves of the type predicted by Yih (and tentatively suggested by Benjamin) cannot exist, and a source of error in Yih's analysis is suggested." }, { "name": "Matthews, John Wallace", "degree": "PhD", "year": "1967", "title": "Theory of Holography", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-113521", "creators": [ { "name": { "family": "Matthews", "given": "John Wallace" }, "id": "Matthews-John-Wallace", "display_name": "Matthews, John Wallace" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/qznw-p178", "abstract": "Computation of the amplitudes of the diffracted fields which are produced when a reflection hologram or a \"thick\" transmission hologram is illuminated requires that the 3-dimensional nature of the hologram be accounted for. A general analytical method is formulated for computing the diffracted fields in terms of the initial exposing field, the film characteristics, and the illumination field, taking into account the entire emulsion volume. This method, which is applicable to both transmission and reflection holograms, involves characterizing the emulsion volume by the volume density of scattering particles, with the diffracted field being found by coherently summing the scattered waves, neglecting multiple scattering. The initial exposing field and the illumination field are expressed in the form of a sum of plane or quasi-plane waves, and the diffracted field is expressed as a sum of waves, each of which is found by solving a variation of the same basic problem. This problem consists of computing the directions, amplitudes, and phases of the first-order diffracted waves produced when a 3-dimensional array of scattering particles having a sinusoidal density distribution is illuminated by a plane wave. The solution of this problem is considered, with the directions and phases of the diffracted fields being computed for both transmission and reflection holograms. The amplitudes are computed for the case of transmission holograms and the analytical expressions are evaluated numerically for a number of particular cases to determine the effect of varying different parameters on the amplitudes of the diffracted waves. The results are compared with experimental data obtained by making a careful study of different holographic diffraction gratings.\r\n \r\nThe results of the analytical method described above are compared with the results of the method whereby the hologram is characterized by the transmittance, and it is shown that with respect to the computation of the directions and phases of the diffracted waves, the two methods are equivalent for the case of transmission holograms.\r\n\r\nThe case where the reference beam is composed of a series of waves (ghost imaging) is considered using both of the above methods, and the translational sensitivity and background noise which arise in this case are investigated. An experiment dealing with translational sensitivity was carried out and the experimental results were found to be in good agreement with the theory.\r\n\r\nThe duplication of holograms is considered and the duplication process is described in terms of making a hologram of a hologram, rather than in terms of making a contact print. Experimental results are presented to support this point of view and the effects of varying the characteristics of the illumination wave are described. The duplication of both transmission and reflection holograms is dealt with and a simple method for duplicating reflection holograms is proposed and discussed.\r\n" }, { "name": "McCloskey, David James", "degree": "PhD", "year": "1967", "title": "Multiple Scattering of Acoustical Waves", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-153230", "creators": [ { "name": { "family": "McCloskey", "given": "David James" }, "id": "McCloskey-David-James", "display_name": "McCloskey, David James" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/HC3V-M545", "abstract": "The general theory of the multiple scattering of acoustical waves by a random distribution of isotropic point scatterers is considered. Configurational averages are taken of the equations of multiple scattering and integral equations governing these configurational averages are obtained; the physical consequences of these equations are examined in detail. A complete theoretical picture is obtained of the propagation of the coherent and incoherent radiation and of the connections between the coherent and incoherent contributions to the average sound intensity and current.\r\n\r\nThe problem of the transmission of sound from a plane sound source into a scattering half-space is studied; numerical results are presented for the average sound intensity and current. The reflection of an incident plane wave, inclined at an arbitrary angle to a scattering half-space is considered; an expression for the reflection coefficient, including both the coherent and incoherent reflection of sound, is obtained. The foregoing results are then applied to sound propagation in a liquid containing a large number of small gas bubbles." }, { "name": "Nigam, Navin Chandra", "degree": "PhD", "year": "1967", "title": "Inelastic Interactions in the Dynamic Response of Structures", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10022002-084916", "creators": [ { "name": { "family": "Nigam", "given": "Navin Chandra" }, "id": "Nigam-Navin-Chandra", "display_name": "Nigam, Navin Chandra" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/00JT-C362", "abstract": "The dynamic response of structures is examined under a general condition of loading. It is shown that the inelastic response of structures depends on the interaction between forces and displacements existing at a section during yielding. A theory of yielding is developed in terms of forces and displacements incorporating the effects of such interactions. Based on this theory, a force-displacement relationship is derived under a general condition of loading. The use of this relationship to study the response of structures is discussed and equations of motion are derived for a simple frame subjected to simultaneous base excitation along its principal directions.\r\n\r\nTo study the inelastic response of structures, under a general condition of loading, it is necessary to derive the equation of the yield surface in terms of forces acting at a section. For the special case of bending about the principal axes of a section, equations of yield surfaces are derived for various structural sections.\r\n\r\nThe response of a simple frame, subjected to sinusoidal base excitation, is obtained for elastic behavior, elasto-plastic behavior and elasto-plastic behavior with interaction. The response for these behaviors is compared and it is shown that interaction causes significant changes in the response. The response of the frame is also investigated for earthquake type excitation and a series of curves are presented to show the effect of interaction on various response parameters. Use of these curves for inelastic design of structures is indicated and the implications of the effects of interaction are examined." }, { "name": "Norwood, Frederick Reyes", "degree": "PhD", "year": "1967", "title": "Diffraction of Transient Elastic Waves by a Spherical Cavity", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechETD:etd-10022002-110856", "creators": [ { "name": { "family": "Norwood", "given": "Frederick Reyes" }, "id": "Norwood-Frederick-Reyes", "display_name": "Norwood, Frederick Reyes" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/ps9n-9z78", "abstract": "The diffraction of transient elastic waves by a spherical cavity is treated. Two cases are considered: (a) a suddenly applied normal point load, and (b) the impingement of a plane transient pulse on the cavity. The method used determines the solution only in the shadow zones; that is, those points which cannot be connected to the source of disturbance by straight-line rays. Analytical results are obtained and evaluated for the displacements at the cavity wall.
\r\n\r\nThe analysis is based on the Laplace transform (on time) and the Watson transformation. This well-known transformation makes it possible to convert an infinite series involving a discrete real wave number into one involving a generalized wave number. This leads to transient solutions the components of which have a one-to-one correspondence with the modes of the underlying frequency equation. These solutions have a form convenient for numerical analysis and for obtaining approximate solutions.
\r\n\r\nThe results given here are for the displacements evaluated at the cavity wall. It is found that the behavior of the diffracted wave fronts is similar to that associated with the simpler equations governing scalar diffraction problems (see Friedlander, \"Sound Pulses\" , Cambridge, 1958). In both problems the Rayleigh disturbance predominates for long time, being singular at its arrival time in the point load case and non-singular in the plane wave case.
\r\n\r\n" }, { "name": "Patton, Carl Elliot, III", "degree": "PhD", "year": "1967", "title": "Dynamic Processes in Magnetic Thin Films. Domain Wall Motion and Ferromagnetic Resonance", "advisor": "Humphrey, Floyd Bernard; Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10032002-102713", "creators": [ { "name": { "family": "Patton", "given": "Carl Elliot, III" }, "id": "Patton-Carl-Elliot", "display_name": "Patton, Carl Elliot, III" } ], "advisors": [ { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" }, { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/YST3-KN23", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe objective of the present investigation has been threefold: (1) To characterize domain wall motion in thin ferromagnetic films experimentally and to determine what film properties influence wall mobility. (2) To investigate ferromagnetic resonance relaxation in thin films over a wide range of temperature, frequency, and thickness and to determine what physical relaxation processes contribute to the resonance linewidth. (3) To correlate the losses for wall motion with relaxation processes for ferromagnetic resonance.\r\n\r\nDomain wall mobility for Ni-Fe alloy films has been measured as a function of film thickness from 300 to 1650 [angstroms]. Between 300 and 800 [angstroms] the mobility decreases with increasing film thickness, ranging from 8 x 10[superscript 3] cm/sec-0e at 300 [angstroms] to 3 x 10[superscript 3] cm/sec-0e at 800 [angstroms]. Between 900 and 1000 [angstroms], the mobility increases rapidly with increasing film thickness to about 7 x 10[superscript 3] cm/sec-0e. Above 1000 [angstroms], the mobility increases slowly with film thickness. Predictions based on Lorentz microscopy static wall shape measurements are in good agreement with the data for a constant value of the Landau-Lifshitz damping parameter [alpha] = 0.014. Eddy-current losses are negligible. The crosstie and Bloch line structures associated with domain walls in thin films do not appear to influence the mobility. The sharp increase in mobility between 900 and 1000 [angstroms] is associated with a wall structure transition in this region.\r\n\r\nFerromagnetic resonance linewidth measurements have been made for films 150 to 3200 [angstroms] thick at frequencies from 1 to 9 Gc/sec and temperature from 2[degrees]K to 300[degrees]K with the static field in the film plane. Linewidths between 3 0e (1 Gc/sec) and 50 0e (9 Gc/sec) were observed. For fixed thickness, the 300[degrees]K linewidth increases monotonically with anisotropy dispersion. To eliminate dispersion, samples with the smallest linewidth [...] were selected for each thickness. For thickness less than a critical thickness [...]. [...] is independent of thickness, but increases with thickness for D > D[...]. The data are in good agreement with predictions based on two-magnon scattering between the uniform mode and degenerate magnons. Eddy-current losses are not important. The phenomenological damping varies from 0.005 (D = 400[angstroms] to 0.009 (D = 3200[angstroms]) for the 300[degrees]K data. As a function of temperature, the linewidth exhibits a maximum at about 80[degrees]K which is generally larger in thinner films. The amplitude of the peak (as high as 15 0e) is independent of frequency and the peak shifts to slightly higher temperatures with increasing frequency. Two annealing treatments at 150[degrees]C, one in a vacuum and one in hydrogen or oxygen, indicate that the temperature dependence is associated with a surface oxide layer. Two mechanisms, valence exchange and exchange anisotropy, may be important.\r\n\r\nEven though phenomenological damping parameters for the two processes, wall motion and resonance, are quite different (at 300[degrees]K), there is a definite connection between the losses. Changes in the wall mobility between 300[degrees]K and 77[degrees]K have been measured for films exhibiting, to varying degrees, the above linewidth effect. From these mobility and linewidth data, the losses for wall motion were found to be directly related to the losses for resonance from 300[degrees]K to 77[degrees]K. There is a definite connection between the relaxation processes which are important for wall motion and those involved in resonance." }, { "name": "Poeschel, Robert Leslie", "degree": "PhD", "year": "1967", "title": "A Nonlinear Study of Beam Plasma Amplification", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-10032002-160203", "creators": [ { "name": { "family": "Poeschel", "given": "Robert Leslie" }, "id": "Poeschel-Robert-Leslie", "display_name": "Poeschel, Robert Leslie" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2Z3J-2V17", "abstract": "The interaction between an electron beam and the plasma oscillations it excites in traversing a plasma region effectively changes the magnitude and direction of the force between beam electrons. This effect has been studied theoretically and experimentally by computing and observing beam electron velocities and phases for a beam which is initially velocity modulated at frequency \u03c9 and allowed to drift through a plasma filled region of plasma frequency \u03c9p. When \u03c9 > \u03c9p the force between electrons is repulsive and effectively increases in magnitude as \u03c9 approaches \u03c9p. When \u03c9 < \u03c9p, the force between electrons becomes a force of attraction, to within a given inter-electron spacing, and the maximum effect is also at the resonance condition \u03c9 ~ \u03c9p. This property could be used to improve the efficiency of electron bunching in a klystron type amplifier by filling the drift space with a plasma of appropriate density.
\r\n\r\nThe beam behavior is studied theoretically by computing in an exact, nonlinear manner, the trajectories of a disc model electron beam which traverses a linear, dielectric model plasma. The parameters varied are the beam space charge conditions (beam current), the degree of initial velocity modulation, and the ratio of modulation frequency to plasma frequency (\u03c9/\u03c9p) Computations show that it is possible to bunch the beam electrons to within 85% of delta function bunching under some beam and plasma conditions. The electron beam behavior is studied experimentally by observing the beam electron velocity phase distribution with a crossed-field velocity analyzer, and observing the beam current waveform (density-phase distribution) using a wide-band sampling oscilloscope. Experimental results show essentially the same beam behavior as predicted by the computations with some differences which are attributed to variation in the plasma density along the beam path.
\r\n" }, { "name": "Pope, David Peter", "degree": "PhD", "year": "1967", "title": "The Mobility of Edge Dislocations in the Basal Slip System of Zinc", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-081427", "creators": [ { "name": { "family": "Pope", "given": "David Peter" }, "id": "Pope-David-Peter", "display_name": "Pope, David Peter" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/1XNZ-CE29", "abstract": "This thesis presents the results of measurements of the velocities of edge dislocations in the basal slip system of zinc as a function of applied shear stress. All tests were conducted at room temperature on 99.999 per cent purity zinc monocrystals. Dislocations were revealed by means of the Berg-Barrett x-ray technique. Stress pulses of microsecond duration were applied to the test specimens by means of a torsion testing machine. Applied resolved shear stresses ranged from 0 to 17.2 x 10\u2076 dynes/cm\u00b2 and measured dislocation velocities ranged from 40 to 700 cm/sec.
\r\n\r\nThe results of this study indicate that the velocity of edge dislocations in the basal slip system of zinc is linearly proportional to the applied resolved shear stress. These results are analyzed in terms of the phonon drag theory. Agreement between this theory and the results reported in this thesis is quite good. Further work is suggested that will provide a more definitive test of the phonon drag theory for limiting dislocation motion in metallic crystals.
" }, { "name": "Reihman, Thomas Charles", "degree": "PhD", "year": "1967", "title": "Laminar Flow Over Transverse Rectangular Cavities", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09272002-153158", "creators": [ { "name": { "family": "Reihman", "given": "Thomas Charles" }, "id": "Reihman-Thomas-Charles", "display_name": "Reihman, Thomas Charles" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Y7T9-3M41", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation was conducted on the laminar flow of water over transverse rectangular cavities. Most of the cavities were square ranging in size from 1/8 in. to 1 in. The flow over the cavities was observed for an [epsilon]* range of from 16 to 400. The quantity [epsilon]* may be regarded as a Reynolds number for the cavity. It is defined as [...] where [epsilon] is the cavity depth, [...] is the shear velocity, and [...] is the kinematic viscosity of the fluid. The desired flow approaching the cavities was obtained one foot from the leading edge of a flat plate suspended in an open surface water tunnel at free stream velocities from 0.125 to 0.75 ft/sec. Visual studies, instantaneous velocity measurements, and velocity profile determinations confirmed that the flow was laminar. The velocity measurements were obtained by means of a hot-film anemometer.\r\n\r\nThe primary goal of the investigation was to determine whether the strong random mass-exchange activity observed in identical cavities in turbulent flow in the same [epsilon]* range was due to an inherent instability of the cavity flow or due to the excitation from turbulent fluctuations at the cavity opening. As the present experiments showed no such strong mass exchange, it was concluded that the latter mechanism was indeed the essential factor. In conjunction with these studies the flow patterns in the cavities were examined by visualization techniques and cavity velocity measurements were made. The cavity vortex velocities were found to be less than 8 percent of the free stream velocity in the range of [epsilon]* examined. In addition a laminar oscillation was observed in the shear layer at the cavity opening and its frequencies are reported.\r\n\r\nPhotographic material on pp. 93-133 are essential and will not clearly reproduce on Xerox copies. Photographic copies should be ordered." }, { "name": "Rispin, Peter Paul Augustine", "degree": "PhD", "year": "1967", "title": "A Singular Perturbation Method for Non-Linear Water Waves Past an Obstacle", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechETD:etd-09272002-161056", "creators": [ { "name": { "family": "Rispin", "given": "Peter Paul Augustine" }, "id": "Rispin-Peter-Paul-Augustine", "display_name": "Rispin, Peter Paul Augustine" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/D0P9-9109", "abstract": "The method of matched singular perturbation expansions is used to solve the problem of a steady two-dimensional flow of a perfect fluid with a free surface under the influence of gravity. A flat plate of length \u2113 is inclined at an angle [alpha] to the horizontal and its trailing edge is immersed to a depth h below the surface of an otherwise uniform stream of infinite depth, the velocity at upstream infinity being U. A parameter \u03b2 = g\u2113/U\u00b2 (Froude number F = \u03b2-1/2) is assumed small so that the flow separates smoothly at the leading and trailing edges, giving rise to n upward jet and gravity waves in the downstream. An inner solution for the velocity field is obtained which is valid near the plate and an outer solution which holds far away. These are determined through the orders 1, \u03b2 log \u03b2, \u03b2, \u03b2\u00b2 log\u00b2 \u03b2, \u03b2\u00b2 log \u03b2 up to order \u03b2\u00b2, and are matched with one another to these orders. In contrast with linearized planing theory, the depth of submergence can be prescribed as a parameter. The lift coefficient is calculated for several values of \u03b1, h/\u2113 and \u03b2. The results reduce to known ones in certain limits.
" }, { "name": "Smith, Jerome Allan", "degree": "PhD", "year": "1967", "title": "An Experimental Investigation of the Structure of Reflecting, Ionizing Shocks in Xenon", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-10092002-160549", "creators": [ { "name": { "family": "Smith", "given": "Jerome Allan" }, "id": "Smith-Jerome-Allan", "display_name": "Smith, Jerome Allan" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KSPH-2V57", "abstract": "The results of an experimental investigation of the reflection of strong shocks in xenon from the end wall of the GALCIT 6\" shock tube are presented. The reflection of the incident shock structure, consisting of a frozen shock front, a region of relatively uniform frozen flow, and an ionization front, was observed with a fast-rise (0.3 [mu] sec) pressure gauge mounted in the shock tube end wall. The interaction between the reflecting shock and the ionizing gas in the incident shock structure was of particular interest. This interaction produces a complicated series of shock and rarefaction waves; those waves that propagate back to the end wall were observed with the pressure gauge. The incident shock Mach number was varied from 11 to 20, and the initial pressure was varied from 0.1 to 1.5 mm Hg.\r\n\r\nA simple model which includes the gross features of the shock reflection process is used to calculate end wall pressures. The calculated pressures agree well with the experimental observations. In addition, ionization relaxation times for xenon behind the incident and reflected shocks are determined from this simple model and the measured pressure histories. The relaxation time data yield a better understanding of the ionization relaxation process in monatomic gases and provide an estimate for the electron-atom, inelastic excitation cross section for xenon." }, { "name": "Spaeth, Edmund Eugene", "degree": "PhD", "year": "1967", "title": "The Convective Diffusion of Oxygen, Carbon Dioxide and Inert Gas in Blood", "advisor": "Friedlander, Sheldon K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-134827", "creators": [ { "name": { "family": "Spaeth", "given": "Edmund Eugene" }, "id": "Spaeth-Edmund-Eugene", "display_name": "Spaeth, Edmund Eugene" } ], "advisors": [ { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "advisor", "display_name": "Friedlander, Sheldon K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/TFHB-C781", "abstract": "In modern membrane-type artificial lungs, the major resistance to gas transfer is offered by the blood and not the membrane. Thus, a suitable theory for convective diffusion in blood must be available in order to design these devices. A general equation for the convective diffusion of gases in blood is presented in this work, and numerical solutions to this equation are compared with experimentally measured rates of oxygen, carbon dioxide, and krypton exchange with citrated blood in a boundary layer flow. The measurements were made in a new type of rotating disk apparatus which is especially suited to the study of gas transfer in complex fluids.\r\n\r\nSolutions of the general equation based on velocities derived from the Navier-Stokes equations are shown to predict the measured transfer rates, even though blood is known to be non-Newtonian at low shear rates. The desorption rate of oxygen from blood at low oxygen partial pressures was found to be up to four times the corresponding transfer rate of inert gas. This effect is described somewhat conservatively by a simple local equilibrium form of the general convective diffusion equation. The carbon dioxide transfer rate in blood near venous conditions was found to be about twice that of inert gas. This great an augmentation is not predicted by any simple form of the general convective diffusion equation. The behavior of the membrane lung system was studied numerically using these results, and the practical implications of this study are discussed." }, { "name": "Tyson, Thomas Janney", "degree": "PhD", "year": "1967", "title": "Laminar Boundary Layers in the Neighborhood of Abrupt Spatial Disturbances", "advisor": "Sechler, Ernest Edwin; Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-111459", "creators": [ { "name": { "family": "Tyson", "given": "Thomas Janney" }, "id": "Tyson-Thomas-Janney", "display_name": "Tyson, Thomas Janney" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/S72R-AM75", "abstract": "Supersonic, steady laminar boundary layers exhibiting \"strong\" local interaction with the outer flow are considered. The general behavior of such flows on a flat adiabatic plate are studied by means of the \"moment method\" equations and by finite difference solutions of the full boundary layer equations, including the transverse momentum equation. A one-parameter family of \"free interaction\" solutions is generated with the finite difference approach. These include separated reverse flow solutions. The infinite plate solution is established from the leading edge through weak interaction by both techniques. Expansive corner flow solutions are developed using both methods. In the \"moment method\" study the nature of the leading edge, Blasius point and \"critical\" line singularities is developed by numerical investigation." }, { "name": "Walsh, Myles Alexander, III", "degree": "PhD", "year": "1967", "title": "On the Turbulent Flow of Dilute Polymer Solutions", "advisor": "Blatz, Paul J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-140727", "creators": [ { "name": { "family": "Walsh", "given": "Myles Alexander, III" }, "id": "Walsh-Myles-Alexander", "display_name": "Walsh, Myles Alexander, III" } ], "advisors": [ { "name": { "family": "Blatz", "given": "Paul J." }, "id": "Blatz-P-J", "role": "advisor", "display_name": "Blatz, Paul J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6NTP-AH77", "abstract": "This paper is concerned with the problem of explaining the anomalous decrease in turbulent skin friction observed in the turbulent flow of very dilute polymer solutions.\r\n\r\nThe experimental evidence for dilute solutions is summarized.\r\n\r\nThe polymer molecule in solution is examined from a theoretical point of view, using the Rouse model. It is found that the model predicts that the molecule will locally store energy as a function of the local strain rate of the solution.\r\n\r\nThe experimental evidence is reexamined and it is concluded that the anomalous decrease in turbulent momentum transport results because the molecules manage to alter the energy balance of the small disturbances at the edge of the viscous sublayer. By slightly altering this balance the molecules allow viscous dissipation to destroy disturbances which would have had sufficient energy to grow had the molecules not been present. By decreasing the number of small disturbances which grow per unit area and time and move out from the edge of the viscous sublayer, the addition of polymer molecules ultimately changes the structure of the turbulence in the outer part of the boundary layer. This change results in lower Reynolds stresses and hence lower turbulent momentum transport.\r\n\r\nWith the help of the relation for local energy storage derived from the Rouse model, parameters are developed to characterize the phenomenon. These parameters appear to be useful in understanding the experimental evidence to date." }, { "name": "Wang, Charles Chang-Ping", "degree": "PhD", "year": "1967", "title": "Mass Spectrometric Studies of Ionization in Shock Heated Gas Mixtures", "advisor": "Sturtevant, Bradford; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11142005-104254", "creators": [ { "name": { "family": "Wang", "given": "Charles Chang-Ping" }, "id": "Wang-Charles-Chang-Ping", "display_name": "Wang, Charles Chang-Ping" } ], "advisors": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "advisor", "display_name": "Sturtevant, Bradford" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GN3Q-Y356", "abstract": "The initial stage of thermal ionization in gas mixtures behind strong normal shock waves has been studied using a mass spectrometer. The sampling process, the unique role of mass spectrometric analysis, the ionization mechanism and the effect of impurities on the ionization relaxation time of the inert gases are discussed. A detailed analysis of ion diffusion through the end wall thermal boundary layer to investigate the effect of the sampling process on the reaction and reaction products are described. The experiments were conducted in argon and xenon at temperatures of from 10,000 \u00baK to 30,000 \u00baK and pressures from 15 mmHg to 80 mmHg. A large number of different ions were detected in \"pure\" (the estimated level of naturally occurring impurities was 50 ppm) argon. H+ and O+ were found in much greater amounts than any of the other products. The roles of H and O were studied further by mixing a small amount of H2 or O2 in argon. The activation energy and the effective cross section for ionization were obtained from the measured ionization rate. For argon, the activation energy agrees within experimental accuracy with the result of Kelly (1966). For hydrogen the activation energy is about 10 ev, and this value coincides with its first excited state. The effective cross section is a thousand times larger than the corresponding effective cross section for the ionization of argon. This explains why small amounts of hydrogen affect the argon ionization relaxation time." }, { "name": "Wesseling, Pieter", "degree": "PhD", "year": "1967", "title": "The Driving Mechanism of Strongly Developed Taylor Vortex Flow", "advisor": "Lagerstrom, Paco A.; Saffman, Philip G.; Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechTHESIS:06132025-213106117", "creators": [ { "name": { "family": "Wesseling", "given": "Pieter" }, "id": "Wesseling-Pieter", "display_name": "Wesseling, Pieter" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." }, { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/00y0-xt20", "abstract": "The purpose of this thesis is to explain how strongly\r\ndeveloped Taylor vortex flow is kept motion. On the basis of this\r\nexplanation approximate torque calculations for high Taylor numbers\r\nhave been made. Agreement with experiment is satisfactory. Axial\r\nsymmetry is assumed throughout." }, { "name": "Witte, Arvel Benjamin", "degree": "PhD", "year": "1967", "title": "Part I. Experimental Investigation of an Arc-Heated Supersonic Free Jet. Part II. Analysis of One-Dimensional Isentropic Flow for Partially Ionized Argon", "advisor": "Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022005-082626", "creators": [ { "name": { "family": "Witte", "given": "Arvel Benjamin" }, "id": "Witte-Arvel-Benjamin", "display_name": "Witte, Arvel Benjamin" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/STEK-4N18", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nI. Experimental Investigation of an Arc-Heated Supersonic Free Jet.\r\n\r\nAn experimental investigation of the flow field of a highly ionized supersonic free jet has been carried out in a continuous-flow test facility. Measurements of impact pressure, mass flux, total enthalpy and stagnation point heat transfer profile were made in this flow field with two water cooled probes.\r\n\r\nArgon gas, at a flowrate of 0.5 gm/sec, was heated in a magneto-plasma-dynamic arc heater without an external magnetic field operating from between 200 amp and 40 volts to 1000 amp and 25 volts. The total pressure ranged from between 20 and 35 mm Hg, at constant flowrate, and the atom-ion number density was approximately [...] cm[...] at the exit plane. The average total enthalpy calculated from a heat balance ranged from between about 5,000 to 10,000 BTU/[...], while the probe measurements showed that the peak total enthalpy on the jet centerline near the exit plane was about three times the average total enthalpy.\r\n\r\nThe impact and mass flux measurements showed that the flow was hypersonic, source-like, chemically frozen, and in other details very much like the under-expanded free jet flow of a perfect gas. By combining these measurements with the total enthalpy measurements it was shown that the fraction of the total energy contained in ionization was about 0.6 which is quite close to the equilibrium stagnation value. For equilibrium stagnation conditions, the total temperature ranges from between 12,000\u00b0 to 20,000\u00b0K. The species mass fraction ranges from 0.2 for the atoms and 0.8 for the singly-ionized ions, to 0.8 for the singly-ionized ions and 0.2 for doubly-ionized ions.\r\n\r\nExamination of the electron energy equation showed that within a few diameters from the exit plane the electrons become energetically isolated from the ions and the electron heat conduction term dominates.\r\n\r\nA preliminary attempt to correlate the stagnation point heat transfer measurements along the axis shows that the electron temperature (TE [...] TI in general) plays an important role.\r\n\r\nII. Analysis of One-Dimensional Isentropic Flow for Partially Ionized Argon.\r\n\r\nOne-dimensional isentropic-flow variables of partially ionized argon have been calculated by coupling the isentropic flow equations with the partition-function method of deriving equilibrium thermodynamic properties. Tabulated gas properties and flow variables are presented for stagnation conditions of 0.1, 0.5, 1.0, 2.0, and 3.0 atm pressure and temperatures from 6,000 to 14,000\u00b0K in 1,000\u00b0K increments. The gas properties computed for this flow process include the sound speed, entropy, enthalpy, electron concentration, ionization fraction, electrical conductivity and static-to-stagnation ratios of temperature, pressure, and density. Flow variables include velocity, mass flux, area ratio, and Reynolds number per centimeter. Compared to results obtainable from perfect gas relationships (neglecting excitation and ionization), the results indicate that electronic excitation, and especially ionization effects, significantly alter the flow variables, particularly at the lower stagnation pressures and higher temperatures considered. However, with the exception of the effect of one excited state (the first excited state of the ion) on the equilibrium-composition equation, the thermodynamic properties calculated by neglecting excitation yielded results which were within 1% of those predicted by including excitation." }, { "name": "Wooten, David Clark", "degree": "PhD", "year": "1967", "title": "I. The Attenuation and Dispersion of Sound in a Condensing Medium. II. The Flow of a Gas-Particle Mixture Downstream of a Normal Shock in a Nozzle", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302015-130932926", "creators": [ { "name": { "family": "Wooten", "given": "David Clark" }, "id": "Wooten-David-Clark", "display_name": "Wooten, David Clark" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/T68P-M138", "abstract": "I. The attenuation of sound due to particles suspended in a gas was first calculated by Sewell and later by Epstein in their classical works on the propagation of sound in a two-phase medium. In their work, and in more recent works which include calculations of sound dispersion, the calculations were made for systems in which there was no mass transfer between the two phases. In the present work, mass transfer between phases is included in the calculations.
\r\nThe attenuation and dispersion of sound in a two-phase condensing medium are calculated as functions of frequency. The medium in which the sound propagates consists of a gaseous phase, a mixture of inert gas and condensable vapor, which contains condensable liquid droplets. The droplets, which interact with the gaseous phase through the interchange of momentum, energy, and mass (through evaporation and condensation), are treated from the continuum viewpoint. Limiting cases, for flow either frozen or in equilibrium with respect to the various exchange processes, help demonstrate the effects of mass transfer between phases. Included in the calculation is the effect of thermal relaxation within droplets. Pressure relaxation between the two phases is examined, but is not included as a contributing factor because it is of interest only at much higher frequencies than the other relaxation processes. The results for a system typical of sodium droplets in sodium vapor are compared to calculations in which there is no mass exchange between phases. It is found that the maximum attenuation is about 25 per cent greater and occurs at about one-half the frequency for the case which includes mass transfer, and that the dispersion at low frequencies is about 35 per cent greater. Results for different values of latent heat are compared.
\r\nII. In the flow of a gas-particle mixture through a nozzle, a normal shock may exist in the diverging section of the nozzle. In Marble\u2019s calculation for a shock in a constant area duct, the shock was described as a usual gas-dynamic shock followed by a relaxation zone in which the gas and particles return to equilibrium. The thickness of this zone, which is the total shock thickness in the gas-particle mixture, is of the order of the relaxation distance for a particle in the gas. In a nozzle, the area may change significantly over this relaxation zone so that the solution for a constant area duct is no longer adequate to describe the flow. In the present work, an asymptotic solution, which accounts for the area change, is obtained for the flow of a gas-particle mixture downstream of the shock in a nozzle, under the assumption of small slip between the particles and gas. This amounts to the assumption that the shock thickness is small compared with the length of the nozzle. The shock solution, valid in the region near the shock, is matched to the well known small-slip solution, which is valid in the flow downstream of the shock, to obtain a composite solution valid for the entire flow region. The solution is applied to a conical nozzle. A discussion of methods of finding the location of a shock in a nozzle is included.
" }, { "name": "Zien, Tse-Fou", "degree": "PhD", "year": "1967", "title": "A Class of Three-Dimensional Optimum Wings in Hypersonic Flow", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11302005-135648", "creators": [ { "name": { "family": "Zien", "given": "Tse-Fou" }, "id": "Zien-Tse-Fou", "display_name": "Zien, Tse-Fou" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X1J8-JK85", "abstract": "The idea of using streamlines of a certain known flow field to construct generally three-dimensional lifting surfaces together with the method of evaluating the aerodynamic forces on the surfaces, developed by Nonweiler, Jones and Woods, has been extended and applied to axisymmetric hypersonic flow fields associated with a class of slender power-law shock waves of the form r ~ \u03c4xn in the limit of infinite free stream Mach number. For this purpose, the basic flow fields associated with concave shocks (n > 1) have first been calculated numerically at a fixed value of the ratio of specific heats \u03b3 = 1.40, and the results are presented in tabulated form, covering a wide range of values of n. The method of constructing a lifting surface either by prescribing its leading edge shape on the basic shock or by specifying its trailing edge shape in the plane x = 1 is then discussed. Expressions for lift and drag on the surface are derived. A class of optimum shapes giving minimum pressure drag at a fixed value of lift has been determined for every basic flow field with n ranging from 1/2 to 10 at \u03b3 = 1.40.\r\n" }, { "name": "Zung, Laurence Bei-Yu", "degree": "PhD", "year": "1967", "title": "Particle Fluid Mechanics in Shear Flows, Acoustic Waves, and Shock Waves", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11302015-140521884", "creators": [ { "name": { "family": "Zung", "given": "Laurence Bei-Yu" }, "id": "Zung-Laurence-Bei-Yu", "display_name": "Zung, Laurence Bei-Yu" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/4T4F-9359", "abstract": "Three different categories of flow problems of a fluid containing small particles are being considered here. They are: (i) a fluid containing small, non-reacting particles (Parts I and II); (ii) a fluid containing reacting particles (Parts III and IV); and (iii) a fluid containing particles of two distinct sizes with collisions between two groups of particles (Part V).
\r\nPart I
\r\nA numerical solution is obtained for a fluid containing small particles flowing over an infinite disc rotating at a constant angular velocity. It is a boundary layer type flow, and the boundary layer thickness for the mixture is estimated. For large Reynolds number, the solution suggests the boundary layer approximation of a fluid-particle mixture by assuming W = Wp. The error introduced is consistent with the Prandtl\u2019s boundary layer approximation. Outside the boundary layer, the flow field has to satisfy the \u201cinviscid equation\u201d in which the viscous stress terms are absent while the drag force between the particle cloud and the fluid is still important. Increase of particle concentration reduces the boundary layer thickness and the amount of mixture being transported outwardly is reduced. A new parameter, \u03b2 = 1/\u03a9 \u03c4v, is introduced which is also proportional to \u03bc. The secondary flow of the particle cloud depends very much on \u03b2. For small values of \u03b2, the particle cloud velocity attains its maximum value on the surface of the disc, and for infinitely large values of \u03b2, both the radial and axial particle velocity components vanish on the surface of the disc.
\r\nPart II
\r\nThe \u201cinviscid\u201d equation for a gas-particle mixture is linearized to describe the flow over a wavy wall. Corresponding to the Prandtl-Glauert equation for pure gas, a fourth order partial differential equation in terms of the velocity potential \u03d5 is obtained for the mixture. The solution is obtained for the flow over a periodic wavy wall. For equilibrium flows where \u03bbv and \u03bbT approach zero and frozen flows in which \u03bbv and \u03bbT become infinitely large, the flow problem is basically similar to that obtained by Ackeret for a pure gas. For finite values of \u03bbv and \u03bbT, all quantities except v are not in phase with the wavy wall. Thus the drag coefficient CD is present even in the subsonic case, and similarly, all quantities decay exponentially for supersonic flows. The phase shift and the attenuation factor increase for increasing particle concentration.
\r\nPart III
\r\nUsing the boundary layer approximation, the initial development of the combustion zone between the laminar mixing of two parallel streams of oxidizing agent and small, solid, combustible particles suspended in an inert gas is investigated. For the special case when the two streams are moving at the same speed, a Green\u2019s function exists for the differential equations describing first order gas temperature and oxidizer concentration. Solutions in terms of error functions and exponential integrals are obtained. Reactions occur within a relatively thin region of the order of \u03bbD. Thus, it seems advantageous in the general study of two-dimensional laminar flame problems to introduce a chemical boundary layer of thickness \u03bbD within which reactions take place. Outside this chemical boundary layer, the flow field corresponds to the ordinary fluid dynamics without chemical reaction.
\r\nPart IV
\r\nThe shock wave structure in a condensing medium of small liquid droplets suspended in a homogeneous gas-vapor mixture consists of the conventional compressive wave followed by a relaxation region in which the particle cloud and gas mixture attain momentum and thermal equilibrium. Immediately following the compressive wave, the partial pressure corresponding to the vapor concentration in the gas mixture is higher than the vapor pressure of the liquid droplets and condensation sets in. Farther downstream of the shock, evaporation appears when the particle temperature is raised by the hot surrounding gas mixture. The thickness of the condensation region depends very much on the latent heat. For relatively high latent heat, the condensation zone is small compared with \u0245D.
\r\nFor solid particles suspended initially in an inert gas, the relaxation zone immediately following the compression wave consists of a region where the particle temperature is first being raised to its melting point. When the particles are totally melted as the particle temperature is further increased, evaporation of the particles also plays a role.
\r\nThe equilibrium condition downstream of the shock can be calculated and is independent of the model of the particle-gas mixture interaction.
\r\nPart V
\r\nFor a gas containing particles of two distinct sizes and satisfying certain conditions, momentum transfer due to collisions between the two groups of particles can be taken into consideration using the classical elastic spherical ball model. Both in the relatively simple problem of normal shock wave and the perturbation solutions for the nozzle flow, the transfer of momentum due to collisions which decreases the velocity difference between the two groups of particles is clearly demonstrated. The difference in temperature as compared with the collisionless case is quite negligible.
\r\n" }, { "name": "Beebe, Wayne Metcalf", "degree": "PhD", "year": "1966", "title": "An Experimental Investigation of Dynamic Crack Propagation in Plastic and Metals", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262005-152806", "creators": [ { "name": { "family": "Beebe", "given": "Wayne Metcalf" }, "id": "Beebe-Wayne-Metcalf", "display_name": "Beebe, Wayne Metcalf" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PC0B-4P13", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nCrack propagation experiments were conducted in polyester resin sheets containing a central crack. Uniaxial tension loading at several loading rates was applied perpendicular to the crack direction. Two types of experiments were conducted: (1) High loading rate tests at 24\u00b0C and -45\u00b0C, with a constant loading rate to study the acceleration characteristics of cracks running in a glassy material, and (2) high temperature-low loading rate tests to study slow crack propagation when appreciable viscous dissipation could occur.\r\n\r\nDuring crack propagation, full frame photographs were taken of the photoviscoelastic isochromatic patterns and crack tip position at framing rates from 250 to 100,000 frames per second. The principal conclusions were as follows:\r\n\r\n1. Even at loading rates exceeding [...] psi per sec, isochromatic patterns prior to crack propagation compare closely with static patterns.\r\n\r\n2. Constant crack velocities were achieved in the high loading rate tests and it was found that the isochromatic patterns compare closely with the theoretical solution of Broberg.\r\n\r\n3. During the crack acceleration period, the experimental data could not be represented adequately by the Berry elastic theory.\r\n\r\n4. For the early phase of the slow (viscous) crack growth period, the crack length could be predicted using a simple theory proposed by Schapery and Williams.\r\n\r\nSeveral tests were conducted on silicon-iron metal sheets; it was concluded that the same testing technique can be applied to the study of crack growth in metals." }, { "name": "Behrens, Hermann Wilhelm", "degree": "PhD", "year": "1966", "title": "Flow Field and Stability of the Far Wake Behind Cylinders at Hypersonic Speeds", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172010-151639253", "creators": [ { "name": { "family": "Behrens", "given": "Hermann Wilhelm" }, "id": "Behrens-Hermann-Wilhelm", "display_name": "Behrens, Hermann Wilhelm" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K0KH-9W58", "abstract": "An experimental study of the mean wake flow field and its stability has been carried out in the far wake of circular cylinders at a Mach number of 6. The Reynolds numbers ranged from 200 to 4000 with a few measurements at higher Reynolds number. Pitot pressure, static pressure and mean flow hot wire measurements were done at many axial stations behind cylinders up to (x/d) = 2400.
\r\n\r\nThe inner wake formed from the cylinder boundary layers is laminar and loses its identity within the first 60 diameters or less depending on the Reynolds numbers so that only the outer wake, caused by the bow shock, has to be considered. Within a certain region the experimental results compare well with linear laminar theory, but the wake profiles are not similar up to the farthest downstream station (x/d = 2400). At four Reynolds numbers strong deviations from steady laminar behavior were observed far behind the cylinder, indicating breakdown of the flow because of non-linear instability effects.
\r\n\r\nIn the instability study hot wire fluctuation measurements were made over the whole frequency range (f = 1 - 320 KC) and also at particular frequencies in a band width of 1 KC up to x/d = 12000 at the lowest Reynolds number. Two instability regions were found and investigated: the linear growth region and the non-linear region. In the linear region there is quite a close correspondence with linear stability theory. The onset of non-linearity is characterized by the simultaneous strong deviation of the mean flow from laminar steady behavior, the increase of the fundamental frequency fluctuation component on the wake axis and the sudden rise of the first harmonic frequency component. The non-linear region is compared with the non-linear wake region at low speeds behind a flat plate. On the basis of these measurements a tentative picture is given of the onset of non-linearity and/or transition in the inner and outer wake behind blunt bodies at hypersonic speeds.
\r\n" }, { "name": "Billings, Charles Edgar", "degree": "PhD", "year": "1966", "title": "Effects of Particle Accumulation in Aerosol Filtration", "advisor": "Friedlander, Sheldon K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172002-113217", "creators": [ { "name": { "family": "Billings", "given": "Charles Edgar" }, "id": "Billings-Charles-Edgar", "display_name": "Billings, Charles Edgar" } ], "advisors": [ { "name": { "family": "Friedlander", "given": "Sheldon K." }, "id": "Friedlander-S-K", "role": "advisor", "display_name": "Friedlander, Sheldon K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/T733-0G47", "abstract": "The filtration of solid aerosol particles produces a decrease in filter penetration and an increase in filter resistance because of the accumulation of deposited material. Functions are derived for the effects of particle accumulation on filter penetration and resistance. A new aerosol tunnel is described which provides a uniform field of particle and fluid flow for extended periods. Data are presented on the effects of accumulation of 1.3-micron polystyrene particles on the performance of filter mats tested in the aerosol tunnel. A quantitative microscopic study of accumulation of 1.3-micron particles on single isolated 10-micron glass fibers is described. Photographs of deposit structure and measurements of aggregate size are included." }, { "name": "Blakemore, David Jordan", "degree": "PhD", "year": "1966", "title": "Microcycle Spectral Estimation", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172002-142819", "creators": [ { "name": { "family": "Blakemore", "given": "David Jordan" }, "id": "Blakemore-David-Jordan", "display_name": "Blakemore, David Jordan" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PH0Z-0431", "abstract": "This thesis attempts to estimate the power spectral density of low frequency semiconductor noise over a range of 10 decades, from a microcycle (10-6 cps) to 10 kilocycles (10+4 cps). It is concluded that the behavior is more complex than a simple inverse proportionality to frequency. The spectrum is approximately 1/f in the region around 100 cps and changes gradually to 1/f2 as the frequency decreases to the microcycle region. These spectra represent the noise properties of the first stage transistors of a grounded input dc differential amplifier. The estimated spectra at very low frequencies still reflect strong temperature influences.
\r\n\r\nIn order to obtain these measurements it was necessary to control the temperature environment of the noise source. This was accomplished first by passive attenuation and later by active control. The noise source was placed in a circulating oil bath whose temperature was sensed electrically and controlled to a .001\u00b0 C range. In conjunction with the temperature control activity the power spectral density of room temperature variations was estimated in the frequency range from .1 cps down to 5 x 10-8 cps. Other spectra of interest estimated over the low frequency range were for line voltage amplitude fluctuations and operational amplifier drift. A brief description of the equipment constructed to obtain sample functions of the noise processes is included.
\r\n\r\nThe analytical portion of this work is concerned with the mathematical techniques employed in obtaining power spectral density estimates. The basic scheme employed is that of Blackman and Tukey which consists of estimating the auto-correlation function and Fourier transforming the result. A formula is developed for calculating the variance of the spectral estimator actually employed in the computations. The bias and variability are presented for the estimator when estimating a spectra containing a spectral line. A confidence interval approach to the variability of the spectral estimator is examined. A confidence interval which depends only on the data is constructed around the spectral density estimate. A technique for utilizing the available knowledge concerning the expected variability of the spectral estimate is developed. The result is formulated in terms of a maximum liklihood estimator for the average spectral density when several independent estimates are available. Some possible sources of low frequency bias in the spectral estimate are considered in detail. Among these are the effect of mean removal and certain deterministic disturbances such as steps. Prewhitening for 1/f and 1/f2 spectra is examined and shown to lead to very great improvement in the spectral estimate. Some suggestions as to more efficient methods of spectral estimation data collection and processing are offered.
" }, { "name": "Bowman, Robert Marcus", "degree": "PhD", "year": "1966", "title": "Investigation of Shock Front Topography in Shock Tubes", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-105038", "creators": [ { "name": { "family": "Bowman", "given": "Robert Marcus" }, "id": "Bowman-Robert-Marcus", "display_name": "Bowman, Robert Marcus" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XPM1-ZZ53", "abstract": "An experimental investigation of the shape of shock waves in a circular shock tube is conducted. It is found that there are three distinct regimes governed, in a given tube, by the initial pressure in the test section.
\r\n\r\nAt very low pressures, where the shock thickness is greater than about half the tube radius, the axial extent (deviation from a plane) of the shock is roughly constant and dominated by the viscous interaction between the \"shock\", the boundary layer, and the driving piston of gas. This range of pressures is called the viscosity-dominated regime.
\r\n\r\nAt intermediate pressures, the shape of the shock is very nearly that predicted by the theory of de Boer, the shock curvature being produced by the boundary layer and the axial extent being roughly inversely proportional to the square root of the initial pressure. This is the boundary layer regime. de Boer's work is extended and the shock shapes for both the two-dimensional and axisymmetric cases are computed and plotted.
\r\n\r\nAt high pressures, the shape of the shock is complex and varies periodically down the tube. This shape is determined by transverse waves produced at the diaphragm (or other upstream disturbance) and reflecting back and forth across the tube, decaying with the square root of the distance down the tube. In this transverse wave regime, the axial extent of the shock is essentially independent of initial pressure and is much greater than had been expected.
\r\n\r\nThe square root decay of the transverse wave disturbances is in contrast to the 3/2 power decay predicted by Freeman and apparently verified by Lapworth. The experimental data of Lapworth is re-plotted and it is shown that if this data is analyzed in a slightly different manner it appears to exhibit square root decay.
\r\n\r\nIt is shown that the shock perturbations which exist in the transverse wave regime are absent at lower pressures. The transition region where these disturbances suddenly disappear seems to correspond approximately to the initial pressure at which the boundary layer (appropriately defined) at the disturbance fills the tube.
\r\n\r\nA rule of thumb is developed from which it should be possible to predict the transition initial pressure (which separates the transverse wave and boundary layer regimes) in any given shock tube. This pressure occurs when the quantity L/p1R2 is of order one, the tube dimensions being in millimeters and the initial pressure in millimeters of mercury. This rule of thumb is used to analyze the results of several shock tube experiments published by other researchers.
\r\n\r\nUsing this rule of thumb as an important constraint, a low pressure shock tube design chart is developed, from which, given the type of experiments contemplated and the nature of the instrumentation available, the proper shock tube dimensions and operating pressures may be determined.
\r\n\r\nFinally, avenues of future research are suggested, wherein it may be possible to design a new type of \"hi-fi\" shock tube, capable of producing more nearly plane shock fronts for use in shock structure and relaxation time studies, especially where methods such as integrated schlieren, optical reflectivity, or electron beam scattering are to be used.
\r\n" }, { "name": "Brady, Arthur Gerald", "degree": "PhD", "year": "1966", "title": "Studies of Response to Earthquake Ground Motion", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09152015-111110090", "creators": [ { "name": { "family": "Brady", "given": "Arthur Gerald" }, "id": "Brady-Arthur-Gerald", "display_name": "Brady, Arthur Gerald" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/48HF-MX48", "abstract": "A study is made of the accuracy of electronic digital computer calculations of ground displacement and response spectra from strong-motion earthquake accelerograms. This involves an investigation of methods of the preparatory reduction of accelerograms into a form useful for the digital computation and of the accuracy of subsequent digital calculations. Various checks are made for both the ground displacement and response spectra results, and it is concluded that the main errors are those involved in digitizing the original record. Differences resulting from various investigators digitizing the same experimental record may become as large as 100% of the maximum computed ground displacements. The spread of the results of ground displacement calculations is greater than that of the response spectra calculations. Standardized methods of adjustment and calculation are recommended, to minimize such errors.
\r\n\r\nStudies are made of the spread of response spectral values about their mean. The distribution is investigated experimentally by Monte Carlo techniques using an electric analog system with white noise excitation, and histograms are presented indicating the dependence of the distribution on the damping and period of the structure. Approximate distributions are obtained analytically by confirming and extending existing results with accurate digital computer calculations. A comparison of the experimental and analytical approaches indicates good agreement for low damping values where the approximations are valid. A family of distribution curves to be used in conjunction with existing average spectra is presented. The combination of analog and digital computations used with Monte Carlo techniques is a promising approach to the statistical problems of earthquake engineering.
\r\n\r\nMethods of analysis of very small earthquake ground motion records obtained simultaneously at different sites are discussed. The advantages of Fourier spectrum analysis for certain types of studies and methods of calculation of Fourier spectra are presented. The digitizing and analysis of several earthquake records is described and checks are made of the dependence of results on digitizing procedure, earthquake duration and integration step length. Possible dangers of a direct ratio comparison of Fourier spectra curves are pointed out and the necessity for some type of smoothing procedure before comparison is established. A standard method of analysis for the study of comparative ground motion at different sites is recommended.
\r\n" }, { "name": "Chan, Tsiu Chiu", "degree": "PhD", "year": "1966", "title": "A Study of Nonlinear Phenomena in the Propagation of Electromagnetic Waves in a Weakly Ionized Gas", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:09102015-131924711", "creators": [ { "name": { "family": "Chan", "given": "Tsiu Chiu" }, "id": "Chan-Tsiu-Chiu", "display_name": "Chan, Tsiu Chiu" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/E932-CW77", "abstract": "This thesis is a study of nonlinear phenomena in the propagation of electromagnetic waves in a weakly ionized gas externally biased with a magnetostatic field. The present study is restricted to the nonlinear phenomena rising from the interaction of electromagnetic waves in the ionized gas. The important effects of nonlinearity are wave-form distortion leads to cross modulation of one wave by a second amplitude-modulated wave.
\r\n\r\nThe nonlinear effects are assumed to be small so that a perturbation method can be used. Boltzmann\u2019s kinetic equation with an appropriate expression for the collision term is solved by expanding the electron distribution function into spherical harmonics in velocity space. In turn, the electron convection current density and the conductivity tensors of the nonlinear ionized gas are found from the distribution function. Finally, the expression for the current density and Maxwell\u2019s equations are employed to investigate the effects of nonlinearity on the propagation of electromagnetic waves in the ionized gas, and also on the reflection of waves from an ionized gas of semi-infinite extent.
\r\n" }, { "name": "Clausing, Don Paul", "degree": "PhD", "year": "1966", "title": "The Tensile Fracture of Mild Steel", "advisor": "Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechTHESIS:07222014-133942786", "creators": [ { "name": { "family": "Clausing", "given": "Don Paul" }, "id": "Clausing-Don-Paul", "display_name": "Clausing, Don Paul" } ], "advisors": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/1VYF-8756", "abstract": "The fibrous and cleavage tensile fracture of an annealed mild\r\nsteel was investigated. Round tensile specimens of two geometries,\r\none straight and one with a circumferential notch, were pulled at\r\ntemperatures between room temperature and liquid nitrogen temperature.\r\nTensile fractures occurred at average strains from 0.02 to\r\n0.87. The mechanism of fibrous fracture at room temperature was\r\ninvestigated metallographically. The stress-strain values at which\r\nfibrous and cleavage fractures are initiated were determined.
\r\n\r\nMany fine microcracks, which are associated with pearlite\r\ncolonies and inclusion stringers, develop prior to fibrous fracture.\r\nThe macrofracture, which leads to final separation of the tensile\r\nspecimen, is initiated by the propagation of a microcrack beyond the\r\nmicrostructural feature with which it is associated. Thus, the fibrous\r\nfracture of mild steel does not develop by the gradual growth and coalescence\r\nof voids that are large enough to be visible in the optical\r\nmicroscope. When the microcracks begin to open and propagate,\r\nfinal fracture quickly follows. Axial cracks are a prominent feature\r\nof the macrofracture that forms in the interior of the specimen immediately\r\nbefore final fracture.
\r\n\r\nThe Bridgman distribution of stresses is not valid in a notched\r\ntensile specimen. Fibrous and cleavage fractures occur at approximately\r\nthe same value of maximum tensile stress. When the maximum\r\ntensile stress that is necessary for cleavage fracture is plotted\r\nagainst the corresponding maximum tensile strain, the result is an\r\nunique locus.
" }, { "name": "Cookson, John Thomas, Jr.", "degree": "PhD", "year": "1966", "title": "Kinetics and Mechanisms of Adsorption of Escherichia coli Bacteriophage T\u2084 to Activated Carbon", "advisor": "North, Wheeler J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212015-112716330", "creators": [ { "name": { "family": "Cookson", "given": "John Thomas, Jr." }, "id": "Cookson-John-Thomas", "display_name": "Cookson, John Thomas, Jr." } ], "advisors": [ { "name": { "family": "North", "given": "Wheeler J." }, "id": "North-W-J", "role": "advisor", "display_name": "North, Wheeler J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/BKTQ-2Q52", "abstract": "A study was conducted on the adsorption of Escherichia coli bacteriophage T4 to activated carbon. Preliminary adsorption experiments were also made with poliovirus Type III. The effectiveness of such adsorbents as diatomaceous earth, Ottawa sand, and coconut charcoal was also tested for virus adsorption.
\r\n\r\nThe kinetics of adsorption were studied in an agitated solution containing virus and carbon. The mechanism of attachment and site characteristics were investigated by varying pH and ionic strength and using site-blocking reagents.
\r\n\r\nPlaque assay procedures were developed for bacteriophage T4 on Escherichia coli cells and poliovirus Type III on monkey kidney cells. Factors influencing the efficiency of plaque formation were investigated.
\r\n\r\nThe kinetics of bacteriophage T4 adsorption to activated carbon can be described by a reversible second-order equation. The reaction order was first order with respect to both virus and carbon concentration. This kinetic representation, however, is probably incorrect at optimum adsorption conditions, which occurred at a pH of 7.0 and ionic strength of 0.08. At optimum conditions the adsorption rate was satisfactorily described by a diffusion-limited process. Interpretation of adsorption data by a development of the diffusion equation for Langmuir adsorption yielded a diffusion coefficient of 12 X 10-8 cm2/sec for bacteriophage T4. This diffusion coefficient is in excellent agreement with the accepted value of 8 X 10-8 cm2/sec. A diffusion-limited theory may also represent adsorption at conditions other than the maximal. A clear conclusion on the limiting process cannot be made.
\r\n\r\nAdsorption of bacteriophage T4 to activated carbon obeys the Langmuir isotherm and is thermodynamically reversible. Thus virus is not inactivated by adsorption. Adsorption is unimolecular with very inefficient use of the available carbon surface area. The virus is probably completely excluded from pores due to its size.
\r\n\r\nAdsorption is of a physical nature and independent of temperature. Attraction is due to electrostatic forces between the virus and carbon. Effects of pH and ionic strength indicated that carboxyl groups, amino groups, and the virus's tail fibers are involved in the attachment of virus to carbon. The active sites on activated carbon for adsorption of bacteriophage T4 are carboxyl groups. Adsorption can be completely blocked by esterifying these groups.
\r\n" }, { "name": "Crewdson, Richard Clark", "degree": "PhD", "year": "1966", "title": "Structure and Properties of Amorphous Palladium Silicon Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11132008-104638", "creators": [ { "name": { "family": "Crewdson", "given": "Richard Clark" }, "id": "Crewdson-Richard-Clark", "display_name": "Crewdson, Richard Clark" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/JASN-J126", "abstract": "A study has been made of the structure and electrical properties of an amorphous phase containing 80 at. % Pd and 20 at. % Si, obtained by rapid quenching from the liquid state. The radial distribution function, which was computed for this phase from the x-ray diffraction pattern, indicates an atomic arrangement with 11.6 nearest neighbors at an average distance of 2.79 \u00c5. This is very similar to that of pure Pd which has twelve nearest neighbors at 2.77 \u00c5. The diffuse diffraction pattern found by electron diffraction and the absence of detectible structure in transmission electron microscopy help to confirm the amorphous structure of the alloy. The electrical resistivity of the amorphous alloy is characterized by a very small temperature coefficient (about 9 x 10[superscript -5]/\u00b0K between 4\u00b0K and 625\u00b0K). The resistivity of the liquid alloy was also measured between 1073\u00b0 K and 1400\u00b0K. A correlation was established between the resistivity of the amorphous and liquid phases. These findings are discussed on the basis of the nearly free electron theory of liquid conductors. The crystallization of the amorphous alloy was observed by transmission electron microscopy and the rate of crystallization was measured in a temperature range from 280\u00b0 to 350\u00b0C." }, { "name": "Cronin, Donald Leslie", "degree": "PhD", "year": "1966", "title": "Response of Linear, Viscous Damped Systems to Excitations Having Time-Varying Frequency", "advisor": "Crede, Charles E.; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:09152015-094552278", "creators": [ { "name": { "family": "Cronin", "given": "Donald Leslie" }, "id": "Cronin-Donald-Leslie", "display_name": "Cronin, Donald Leslie" } ], "advisors": [ { "name": { "family": "Crede", "given": "Charles E." }, "id": "Crede-C-E", "role": "advisor", "display_name": "Crede, Charles E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/NR49-C405", "abstract": "The response of linear, viscous damped systems to excitations having time-varying frequency is the subject of exact and approximate analyses, which are supplemented by an analog computer study of single degree of freedom system response to excitations having frequencies depending linearly and exponentially on time.
\r\n\r\nThe technique of small perturbations and the methods of stationary phase and saddle-point integration, as well as a novel bounding procedure, are utilized to derive approximate expressions characterizing the system response envelope\u2014particularly near resonances\u2014for the general time-varying excitation frequency.
\r\n\r\nDescriptive measurements of system resonant behavior recorded during the course of the analog study\u2014maximum response, excitation frequency at which maximum response occurs, and the width of the response peak at the half-power level\u2014are investigated to determine dependence upon natural frequency, damping, and the functional form of the excitation frequency.
\r\n\r\nThe laboratory problem of determining the properties of a physical system from records of its response to excitations of this class is considered, and the transient phenomenon known as \u201cringing\u201d is treated briefly.
\r\n\r\nIt is shown that system resonant behavior, as portrayed by the above measurements and expressions, is relatively insensitive to the specifics of the excitation frequency-time relation and may be described to good order in terms of parameters combining system properties with the time derivative of excitation frequency evaluated at resonance.
\r\n\r\nOne of these parameters is shown useful for predicting whether or not a given excitation having a time-varying frequency will produce strong or subtle changes in the response envelope of a given system relative to the steady-state response envelope. The parameter is shown, additionally, to be useful for predicting whether or not a particular response record will exhibit the \u201cringing\u201d phenomenon.
\r\n" }, { "name": "Crow, Steven Collins", "degree": "PhD", "year": "1966", "title": "1. The Spanwise Perturbation of Two-Dimensional Boundary Layers. 2. The Turbulent Rayleigh Problem. 3. The Propagation of Free Turbulence in a Mean Shear Flow", "advisor": "Saffman, Philip G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11172005-144841", "creators": [ { "name": { "family": "Crow", "given": "Steven Collins" }, "id": "Crow-Steven-Collins", "display_name": "Crow, Steven Collins" } ], "advisors": [ { "name": { "family": "Saffman", "given": "Philip G." }, "id": "Saffman-P-G", "role": "advisor", "display_name": "Saffman, Philip G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/75J2-GM72", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n1. The Spanwise Perturbation of Two-Dimensional Boundary Layers.\r\n\r\nLarge spanwise variations of boundary-layer thickness have recently been found in wind tunnels designed to maintain two-dimensional flow. Bradshaw argues that these variations are caused by minute deflections of the free-stream flow rather than an intrinsic boundary-layer instability. The effect of a small, periodic transverse flow on a flat-plate boundary layer is studied in this chapter. The transverse flow is found to produce spanwise thickness variations whose amplitude increases linearly with distance downstream.\r\n\r\n2. The Turbulent Rayleigh Problem.\r\n\r\nRayleigh flow is the non-steady motion of fluid above a flat plate accelerated suddenly into motion. Laminar Rayleigh flow is closely analogous to laminar boundary-layer flow but does not involve the analytical difficulty of non-linear convection. In this chapter, turbulent Rayleigh flow is studied to illuminate physical ideas used recently in boundary-layer theory. Boundary layers have nearly similar profiles for certain rates of pressure change. The Rayleigh problem is shown to have a class of exactly similar solutions. Townsend's energy balance argument for the wall layer and Clauser's constant eddy viscosity assumption for the outer layer are adapted to the Rayleigh problem to fix the relation between shear and stress. The resulting non-linear, ordinary differential equation of motion is solved exactly for constant wall stress, analogous to zero pressure gradient in the boundary-layer problem, and for zero wall stress, analogous to continuously separating flow. Finally, the boundary-layer equations are expanded in powers of the skin friction parameter [...], and the zeroth order problem is shown to be identical to the Rayleigh problem. The turbulent Rayleigh problem is not merely an analogy, but is a rational approximation to the turbulent boundary-layer problem.\r\n\r\n3. The Propagation of Free Turbulence in a Mean Shear Flow\r\n\r\nThis chapter begins with the assumption that the propagation of turbulence through a rapidly shearing flow depends primarily on random stretching of mean vorticity. The Reynolds stress [...] acting on a mean flow [...] in the x direction is computed from the linearized equations of motion. Turbulence homogeneous in x, z and concentrated near y = 0 was expected to catalyze the growth of turbulence further out by stretching mean vorticity, but [...] is found to become steady as [...]. As far as Reynolds stress is a measure of turbulent intensity, random stretching of mean vorticity alone cannot yield steadily propagating turbulence.\r\n\r\nThe problem is simplified by assuming that all flow properties are independent of x. Eddy motion in the y, z plane is then independent of the x momentum it transports, and the mean speed U(y,t) is diffused passively. The equations of motion are partially linearized by neglecting convection of eddies in the y, z plane, and wave equations for [...] and U(y,t) are derived. The solutions are worthless, however, for large times. Turbulence artificially steady in the y, z plane forces the mean speed gradient steadily to zero. In a real flow the eddies disperse as fast as U diffuses.\r\n\r\nNumerical experiments are designed to find how quickly concentrated vortex columns parallel to x disperse over the y, z plane and how effectively they diffuse U. It is shown that unless a lower limit on the distance between any two vortices is imposed, computational errors can dominate the solution no matter how small a time increment is used. Vortices which approach closely must be united. Uniting vortices during the computations is justified by finding a capture cross section for two vortices interacting in a strain field. The experiments confirm the result that columnar eddies disperse as fast as they transport momentum." }, { "name": "Currie, Iain George", "degree": "PhD", "year": "1966", "title": "The Instability of Fluids with Time Dependent Heating", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechTHESIS:09102015-161601825", "creators": [ { "name": { "family": "Currie", "given": "Iain George" }, "id": "Currie-Iain-George", "display_name": "Currie, Iain George" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/TH7H-TH69", "abstract": "The stability of a fluid having a non-uniform temperature stratification is examined analytically for the response of infinitesimal disturbances. The growth rates of disturbances have been established for a semi-infinite fluid for Rayleigh numbers of 103, 104, and 105 and for Prandtl numbers of 7.0 and 0.7.
\r\n\r\nThe critical Rayleigh number for a semi-infinite fluid, based on the effective fluid depth, is found to be 32, while it is shown that for a finite fluid layer the critical Rayleigh number depends on the rate of heating. The minimum critical Rayleigh number, based on the depth of a fluid layer, is found to be 1340.
\r\n\r\nThe stability of a finite fluid layer is examined for two special forms of heating. The first is constant flux heating, while in the second, the temperature of the lower surface is increased uniformly in time. In both cases, it is shown that for moderate rates of heating the critical Rayleigh number is reduced, over the value for very slow heating, while for very rapid heating the critical Rayleigh number is greatly increased. These results agree with published experimental observations.
\r\n\r\nThe question of steady, non-cellular convection is given qualitative consideration. It is concluded that, although the motion may originate from infinitesimal disturbances during non-uniform heating, the final flow field is intrinsically non-linear.
\r\n" }, { "name": "Erdmann, Robert Charles", "degree": "PhD", "year": "1966", "title": "Time-Dependent Monoenergetic Neutron Transport in Two Adjacent Semi-infinite Media", "advisor": "Lurie, Harold", "url": "https://resolver.caltech.edu/CaltechTHESIS:10022015-101429428", "creators": [ { "name": { "family": "Erdmann", "given": "Robert Charles" }, "id": "Erdmann-Robert-Charles", "display_name": "Erdmann, Robert Charles" } ], "advisors": [ { "name": { "family": "Lurie", "given": "Harold" }, "id": "Lurie-H", "role": "advisor", "display_name": "Lurie, Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/00R6-9A13", "abstract": "An exact solution to the monoenergetic Boltzmann equation is\r\nobtained for the case of a plane isotropic burst of neutrons introduced\r\nat the interface separating two adjacent, dissimilar, semi-infinite\r\nmedia. The method of solution used is to remove the time dependence\r\nby a Laplace transformation, solve the transformed equation by the\r\nnormal mode expansion method, and then invert to recover the time\r\ndependence.
\r\n\r\nThe general result is expressed as a sum of definite, multiple\r\nintegrals, one of which contains the uncollided wave of neutrons\r\noriginating at the source plane. It is possible to obtain a simplified\r\nform for the solution at the interface, and certain numerical calculations\r\nare made there.
\r\n\r\nThe interface flux in two adjacent moderators is calculated and\r\nplotted as a function of time for several moderator materials. For\r\neach case it is found that the flux decay curve has an asymptotic slope\r\ngiven accurately by diffusion theory. Furthermore, the interface current\r\nis observed to change directions when the scattering and absorption\r\ncross sections of the two moderator materials are related in a\r\ncertain manner. More specifically, the reflection process in two\r\nadjacent moderators appears to depend initially on the scattering\r\nproperties and for long times on the absorption properties of the media.
\r\n\r\nThis analysis contains both the single infinite and semi-infinite\r\nmedium problems as special cases. The results in these\r\ntwo special cases provide a check on the accuracy of the general\r\nsolution since they agree with solutions of these problems obtained\r\nby separate analyses.
\r\n" }, { "name": "Fischer, Hugo Breed", "degree": "PhD", "year": "1966", "title": "LongitudinaI Dispersion in Laboratory and Natural Streams", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292015-082820697", "creators": [ { "name": { "family": "Fischer", "given": "Hugo Breed" }, "id": "Fischer-Hugo-Breed", "display_name": "Fischer, Hugo Breed" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/8D5C-BV11", "abstract": "This study concerns the longitudinal dispersion of fluid particles which are initially distributed uninformly over one cross section of a uniform, steady, turbulent open channel flow. The primary focus is on developing a method to predict the rate of dispersion in a natural stream.
\r\n\r\nTaylor's method of determining a dispersion coefficient, previously applied to flow in pipes and two-dimensional open channels, is extended to a class of three-dimensional flows which have large width-to-depth ratios, and in which the velocity varies continuously with lateral cross-sectional position. Most natural streams are included. The dispersion coefficient for a natural stream may be predicted from measurements of the channel cross-sectional geometry, the cross-sectional distribution of velocity, and the overall channel shear velocity. Tracer experiments are not required.
\r\n\r\nLarge values of the dimensionless dispersion coefficient D/rU* are explained by lateral variations in downstream velocity. In effect, the characteristic length of the cross section is shown to be proportional to the width, rather than the hydraulic radius. The dimensionless dispersion coefficient depends approximately on the square of the width to depth ratio.
\r\n\r\nA numerical program is given which is capable of generating the entire dispersion pattern downstream from an instantaneous point or plane source of pollutant. The program is verified by the theory for two-dimensional flow, and gives results in good agreement with laboratory and field experiments.
\r\n\r\nBoth laboratory and field experiments are described. Twenty-one laboratory experiments were conducted: thirteen in two-dimensional flows, over both smooth and roughened bottoms; and eight in three-dimensional flows, formed by adding extreme side roughness to produce lateral velocity variations. Four field experiments were conducted in the Green-Duwamish River, Washington.
\r\n\r\nBoth laboratory and flume experiments prove that in three-dimensional flow the dominant mechanism for dispersion is lateral velocity variation. For instance, in one laboratory experiment the dimensionless dispersion coefficient D/rU* (where r is the hydraulic radius and U* the shear velocity) was increased by a factory of ten by roughening the channel banks. In three-dimensional laboratory flow, D/rU* varied from 190 to 640, a typical range for natural streams. For each experiment, the measured dispersion coefficient agreed with that predicted by the extension of Taylor's analysis within a maximum error of 15%. For the Green-Duwamish River, the average experimentally measured dispersion coefficient was within 5% of the prediction.
" }, { "name": "Hauptmann, Edward Gerald", "degree": "PhD", "year": "1966", "title": "An Experimental Investigation of Forced Convective Heat Transfer to a Fluid in the Region of its Critical Point", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182002-110836", "creators": [ { "name": { "family": "Hauptmann", "given": "Edward Gerald" }, "id": "Hauptmann-Edward-Gerald", "display_name": "Hauptmann, Edward Gerald" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/8KYC-F077", "abstract": "Experimental results are presented for forced convective heat transfer from a heated flat plate in carbon dioxide near the thermodynamic critical point. The heated plate was in a horizontal position and most measurements were made in the fully turbulent downstream portion, with the heated surface facing both up and down.\r\n\r\nThe bulk conditions of the carbon dioxide were varied from below the pseudocritical temperature (\"liquid-like\" region) to above the pseudocritical temperature (\"vapor-like\" region), and in some instances the bulk and wall temperatures were on either side of the pseudocritical temperature. Some limited observations on the effect of free stream velocity were made, and experiments were also conducted below the critical pressure in order to obtain a comparison with boiling.\r\n\r\nOne of the principal objectives was to observe the nature of the heated boundary layer. High speed movie films were taken using a color schlieren apparatus, modified to obtain semi-focusing effects. Although the experimentally determined heat transfer coefficient became high whenever the wall temperature approached the pseudocritical, no significant change in the gross nature of the flow field could be observed. A few exploratory hot wire measurements of the velocity fluctuations near the plate were also made, and they confirmed that no significant increase in turbulence was associated with the regions of high heat transfer coefficients.\r\n\r\nOn the basis of the results it is concluded that the high heat transfer coefficients observed were due to the large values of thermodynamic and transport properties occurring near the critical point, and not because of the occurrence of a \"pseudo-boiling\" phenomena. It is further concluded that the \"pseudo-boiling\" phenomena does not occur with this particular heater geometry or in the range of parameters investigated, although it may in others.\r\n\r\nBecause of the similarity of fully turbulent boundary layers to turbulent pipe flow, it is felt these conclusion may be extended to cover the latter case as well.\r\n\r\nPhotographic materials on pages 171-175 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered." }, { "name": "Hu, Paul Yu-fei", "degree": "PhD", "year": "1966", "title": "Analytical and Experimental Studies of Random Vibration", "advisor": "Crede, Charles E.; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202002-101725", "creators": [ { "name": { "family": "Hu", "given": "Paul Yu-fei" }, "id": "Hu-Paul-Yu-fei", "display_name": "Hu, Paul Yu-fei" } ], "advisors": [ { "name": { "family": "Crede", "given": "Charles E." }, "id": "Crede-C-E", "role": "advisor", "display_name": "Crede, Charles E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/8wxv-qh07", "abstract": "Analytical and experimental investigations are made of the response of linear systems subject to magnitude-limited Gaussian broadband random excitation. A mathematical analysis for determining the statistical properties of this excitation is developed. Experimental studies on the probabilistic response of linear systems with magnitude-limited input are also presented.
\r\n\r\nSecondly the peak characteristics of the response of linear systems subject to Gaussian broadband random excitation are investigated. It is shown that the number of peaks per unit time of the response of a single degree of freedom system increases as the frequency bandwidth of the excitation increases. Analytical and experimental techniques are developed to study the peak distribution characteristics of multi-degree of freedom systems and continuous systems. It is found that the normal mode random variables are statistically independent if the system damping is small, and the modal frequencies are sufficiently separated.
\r\n\r\nFinally the method of Fokker-Planck is used to obtain the statistical properties of the response of a first order Coulomb damped system. The first order probability density function of displacement of this nonlinear system is determined. A simplified method for developing the autocorrelation function, and the power spectral density is discussed and applied to the above problem. The results are further substantiated by experiment. Experimental investigations are also carried out to determine the power spectral density of the response of a second order nonlinear system with Coulomb restoring force to white noise input. The results are compared with those given by Wolaver.
" }, { "name": "Kerdemelidis, Vassilios", "degree": "PhD", "year": "1966", "title": "A Study of Cross-Polarization Effects in Paraboloidal Antennas", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-09242002-083513", "creators": [ { "name": { "family": "Kerdemelidis", "given": "Vassilios" }, "id": "Kerdemelidis-Vassilios", "display_name": "Kerdemelidis, Vassilios" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/3SFB-WB47", "abstract": "In this report the induced surface current method is used to investigate the spatial structure of the radiated electric field for a number of paraboloidal antennas. The paraboloids are excited by three different types of feeds, namely, a small electric dipole, an elemental plane wave source, and a rectangular horn.\r\n\r\nFor the case of electric dipole excitation, formulas are derived that show the following characteristics:\r\n\r\n(i) For a reflector of constant ratio of focal length to the aperture diameter the magnitude of the cross-polarized lobe nearest to the antenna axis (paraboloid axis) remains constant relative to the maximum of the main lobe of the principally-polarized wave and is independent of the aperture size.\r\n\r\n(ii) For a given aperture size the magnitude of the cross-polarized component relative to its own principally-polarized maximum decreases with the focal length.\r\n\r\n(iii) The position of the maximum of the cross-polarized lobe depends only on the aperture size and is independent of the focal length.\r\n\r\nThe problem of cross-polarization is also solved by using a simple model which gives results that are in surprisingly close agreement with those obtained by the more complete expressions. In addition this crude model explains the angular variation of the amplitude of cross-polarization component at angles not necessarily small from the paraboloid axis.\r\n\r\nFor a paraboloid excited by an elemental Huyghens source the cross-polarization in the forward direction is reduced but the component in the laterally-directed radiation is increased relative to that of an electric dipole.\r\n\r\nIn the case of the horn-excited paraboloid we obtain a formula that explains the experimentally-observed large crosspolarization.\r\n\r\nFinally, we show that the problems of the paraboloids excited by a small electric dipole and a plane (Huyghens) source are merely particular cases of the horn excitation problem." }, { "name": "Klose, Gerhard Joachim", "degree": "PhD", "year": "1966", "title": "Unsteady Forces on Oscillating Hydrofoils", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09252002-112500", "creators": [ { "name": { "family": "Klose", "given": "Gerhard Joachim" }, "id": "Klose-Gerhard-Joachim", "display_name": "Klose, Gerhard Joachim" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/96CP-GE12", "abstract": "An experimental apparatus is described which has proved to be well suited to the determination of the unsteady lift forces on a hydrofoil oscillating in heave under a free surface.\r\n\r\nResults are presented for tests covering a wide range of reduced frequency with several foil models in fully wetted, base-ventilated, and supercavitating flow. Tests were performed with aspect ratio one foils and also in two-dimensional flow. The effects of submergence depth below the free surface, angle of attack, and oscillation amplitude were investigated. The experimental findings for the fully wetted foils generally agree fairly well with the available theoretical results.\r\n\r\nIn supercavitating flow, the cavities were established by forced ventilation. The characteristics of the ventilated cavities under oscillation are discussed. The variation in the unsteady lift coefficients with cavity length, and the attendant unsteady cavity pressure, are also presented. The average values of the unsteady lift coefficients are found to differ appreciable from theoretical calculations, and some factors which may contribute to this difference are considered.\r\n\r\nThe present work represents the first extensive set of unsteady force measurements on oscillating hydrofoils, and several new phenomena are revealed by the results. The implications of these findings for practical problems are discussed, and some suggestions are offered for further investigations." }, { "name": "Ko, Hon-Yim", "degree": "PhD", "year": "1966", "title": "Static Stress-Deformation Characteristics of Sand", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09252002-133202", "creators": [ { "name": { "family": "Ko", "given": "Hon-Yim" }, "id": "Ko-Hon-Yim", "display_name": "Ko, Hon-Yim" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/WWZB-SM07", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in.pdf document.\r\n\r\nA soil test box, capable of applying any combination of principal stresses to a cubical soil sample, was developed for the experimental investigation of the behavior of granular soils under static loading. A stress control device was also developed, enabling a continuous and proportionate change to be made in the stresses along a stress path and considerably simplifying the calculation of the stress state in the sample. The apparatus was used to investigate (a) the hydrostatic compression of an Ottawa sand, and (b) the behavior of the same soil under various deviatoric stress paths in both loading and unloading conditions.\r\n\r\nA theoretical \"holey\" model was postulated for sand under hydrostatic stress and the results of the analysis of this model were found to correlate closely with the experimental data.\r\n\r\nThe qualitative behavior of sand under shear stresses was examined from a particulate point of view. Specially designed tests were performed on the Ottawa sand with loading and unloading along stress paths which involved different combinations of hydrostatic and deviatoric stresses, with the purpose of examining the proportions of recoverable and irrecoverable deformations. A failure envelope was obtained for a medium dense and a medium loose sand by monotonically increasing [...] while keeping [...] constant under various conditions of stress distribution, and it was found that the value of equivalent Coulomb [...] increased from 42? in triaxial compression to 48? in triaxial extension for the medium dense sand and from 36? in triaxial compression to 44? in triaxial extension for the medium loose sand." }, { "name": "Lee, Jen-shih", "degree": "PhD", "year": "1966", "title": "Application of Finite Elastic Theory to the Deformation of Cylindrical Tubes", "advisor": "Fung, Yuan-cheng; Frasher, Wallace G.; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052005-150440", "creators": [ { "name": { "family": "Lee", "given": "Jen-shih" }, "id": "Lee-Jen-shih", "display_name": "Lee, Jen-shih" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Frasher", "given": "Wallace G." }, "id": "Frasher-W-G", "role": "advisor", "display_name": "Frasher, Wallace G." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HM2E-AX28", "abstract": "In Part I three types of symmetrical deformations of thin cylindrical rubber tubes are discussed. In the first type a rubber tube is deformed into another circular cylindrical tube of different length and diameter by simultaneous inflation and extension of the tube. This deformation is useful in determining the mechanical properties of tube-like material and it was found that Rivlin-Saunder form of strain-energy fitted a particular latex rubber used in our experiments. The second and third types of deformation are a tube deformed by a longitudinal stretching or an increase in internal pressure to a curved surface of revolution. A number of numerical examples were worked out with a view toward designing experiments to determine mechanical properties of short cylindrical tubes.
\r\n\r\nIn Part II experimental studies on the overall mechanical properties of large blood vessels are presented. Two Lagrangian stresses and two extension ratios are used to describe the stress and strain states of the vessels subjected to symmetrical deformations. The interested deformation range is about ten to twenty percent in the neighborhood of the natural state.
\r\n\r\nTests consisted of (1) a longitudinal stretching while the diameter of the vessels was maintained, (2) a lateral distension with the length of the vessels unchanged, and (3) repeated stretching of the vessels at low frequency.
\r\n\r\nThe first two tests show that the stress-strain law of the vessels tested is highly nonlinear and the vessels behave more rigidly in the longitudinal direction than in the lateral direction. The last test shows that the vessels are more likely to behave as a plastic elastic metal and a higher tangential modulus was observed for the vessels stretched at a smaller oscillation amplitude.
" }, { "name": "Letcher, John Seymour", "degree": "PhD", "year": "1966", "title": "Transverse Hydrodynamic Forces on Slender Bodies in Free-Surface Flows at Low Speed", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11112005-154228", "creators": [ { "name": { "family": "Letcher", "given": "John Seymour" }, "id": "Letcher-John-Seymour", "display_name": "Letcher, John Seymour" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M8NJ-KC21", "abstract": "The forces and moments on a moving body partially immersed in the surface of a deep ocean of heavy fluid are considered in the limit of small Froude number, F. Asymptotic expressions for velocity potential and free surface elevation are developed. The choice of the first terms of the asymptotic sequence is indicated by the behavior, at small F, of the classical results of \"small disturbance theory\" - analysis starting from the linearized free-surface boundary conditions. It is found that the leading terms depend on the local disturbance, which can be expanded as a power series in F. The wave pattern contributes higher-order terms which are not analytic about F = 0; only estimates of the order of these terms are obtained. Consequently the present work does not estimate drag but is confined to consideration of transverse forces and moments.\r\n\r\nOnce the asymptotic sequence is assumed, perturbation of the exact equations and boundary conditions about F = 0 is straightforward. The zero-order potential is that of the \"reflection-plane\" model of Davidson. For a restricted class of shapes, the slender body theory is applied to the zero-order and first-order problems. A general method is developed using conformal mapping to solve the first order problem for sufficiently slender shapes of arbitrary cross-section. This method is applied to two particular shapes, viz. a wing of zero thickness and a half-submerged body of revolution, both in sideslip. The correction to the reflection plane model is found to be generally quite small in the range of F for which this theory is expected to apply." }, { "name": "Lewicki, George Wladimir", "degree": "PhD", "year": "1966", "title": "Electron Tunneling through Thin Films of Aluminum Nitride", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-09272002-150142", "creators": [ { "name": { "family": "Lewicki", "given": "George Wladimir" }, "id": "Lewicki-George-Wladimir", "display_name": "Lewicki, George Wladimir" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/QDH7-C768", "abstract": "Thin film structures involving Aluminum as the base electrode, Aluminum Nitride as the insulating layer, Magnesium, Aluminum or Gold as the counterelectrodes were fabricated by nitriding a freshly deposited Aluminum film in a Nitrogen glow discharge with the thickness of the insulator varying from some thirty to ninety Angstroms with the express purpose of studying currents arising from the tunneling of electrons through the forbidden band of the insulator. Currents understood on the basis of the presently existing tunneling theory were observed for structures having thinner insulating regions. For structures having thicker insulating regions a temperature independent excess current was observed which could not be accounted for by the present tunneling theory.\r\n\r\nThe usual analysis of tunneling assumes the energy momentum relation of the insulator forbidden band to be parabolic and the shape of the barrier separating the two metal electrodes to be trapezoidal. Any deviation from the current voltage characteristic predicted by this model is normally attributed to the lack of validity in the assumption concerning the barrier shape. Data obtained in this research indicated that the barriers of the structures investigated were trapezoidal but that the insulator energy momentum relationship was non-parabolic. Consequently, the analysis was extended to cover the case of a trapezoidal barrier with a semi-arbitrary energy momentum relationship. Greater freedom was obtained for the current voltage characteristics but certain relations between these characteristics and the insulator thickness were retained which could be used to determine whether or not the barrier of a particular structure was trapezoidal. These same relations also suggested a means of experimentally determining the insulator energy momentum relationship if the barrier could be considered trapezoidal.\r\n\r\nThe analysis was applied to the experimental data and a complete self consistent model for electron tunneling through thin insulating layers of Aluminum Nitride was obtained." }, { "name": "Lindsey, Gerald Herbert", "degree": "PhD", "year": "1966", "title": "Hydrostatic Tensile Fracture of a Polyurethane Elastomer", "advisor": "Williams, Max L.; Knauss, Wolfgang Gustav", "url": "https://resolver.caltech.edu/CaltechETD:etd-11232005-113650", "creators": [ { "name": { "family": "Lindsey", "given": "Gerald Herbert" }, "id": "Lindsey-Gerald-Herbert", "display_name": "Lindsey, Gerald Herbert" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." }, { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-W-G", "role": "advisor", "display_name": "Knauss, Wolfgang Gustav" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K12J-X907", "abstract": "The investigation of fracture of polymeric materials in hydrostatic tensile fields constitutes an avenue of approach to the study of fracture in more general three-dimensional environments. The advantages created by the symmetry of the stress field are considerable and, in one of the cases studied, facilitates a theoretical treatment that includes large deformations, which are characteristic of this class of materials.\r\n\r\nThe analysis is developed through the concept of fracture originating from a flaw, which in this instance is taken to be a spherical cavity. Through the application of energy principles, a theoretical prediction of ultimate strength is made for hydrostatic tensile fields.\r\n\r\nExperiments were conducted to demonstrate the existence of such flaws and to evaluate the theory. Results of the tests on specimens containing both residual flaws and artificially inserted ones indicate a fundamental difference in behavior as contrasted with cracks.\r\n\r\nAn explanation is given linking experimental results and theoretical predictions. It is based on the concept that a flaw \"grows\" in the material under load using the cavity as a nucleating point. Upon this hypothesis is built a theory of rupture in which planar cracks grow radially from the center of the cavity in the form of Saturn-ring cracks." }, { "name": "Lissaman, Peter Barry Stuart", "degree": "PhD", "year": "1966", "title": "A Linear Solution for the Jet Flap in Ground Effect", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302002-123622", "creators": [ { "name": { "family": "Lissaman", "given": "Peter Barry Stuart" }, "id": "Lissaman-Peter-Barry-Stuart", "display_name": "Lissaman, Peter Barry Stuart" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "co-advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PWFF-E933", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nThe paper presents the solution of the problem of the Jet Flap airfoil in a plane inviscid flow in the presence of the ground.\r\n\r\nThe basic flow equations are derived and the non-linearity of the boundary conditions are discussed. The problem is then linearized as in thin airfoil theory. By a conformal transformation the flow field is mapped into one having very simple geometry. The singularities of the mapping are identified and the asymptotic character of the flow fields derived. The basic integro-differential equation is developed; this has singular Hilbert type kernels and discontinuous boundary conditions.\r\n\r\nBy considerations of the second order effects, significant relationships between the lift slopes with angle of attack, with jet angle and jet coefficient are developed. These are further simplified by introduction of a new geometrical parameter developed from the mapping.\r\n\r\nThe lift coefficient of the airfoil is expressed in three parts, of which two may be evaluated in simple closed form. The remaining part depends on the solution of the integro-differential equation. This equation is then solved at N points by assuming a piecewise smooth velocity distribution and generating an N x N matrix: numerical results are obtained from an IBM 7094 computer. It is proved that this approximation converges to the exact solution.\r\n\r\nThe limiting cases, when the height to chord ratio, h/c, or jet coefficient, C[subscript J], approach zero or infinity are developed, exploiting the decomposition of the lifting components; and an asymptotic result for small C[subscript J] is presented.\r\n\r\nA linearized theory for wake blockage is given, which also gives an indication of the restrictions on the various parameters implied by the basic linear approach.\r\n\r\nThe results for [...] correlate excellently with Spence's solution for [...]. For low values of h/c the results agree quite well with the limited applicable test data." }, { "name": "Ludewig, Hans", "degree": "PhD", "year": "1966", "title": "Geometrical Effects on the Resonance Absorption of Neutrons", "advisor": "Lurie, Harold", "url": "https://resolver.caltech.edu/CaltechTHESIS:09242015-135757893", "creators": [ { "name": { "family": "Ludewig", "given": "Hans" }, "id": "Ludewig-Hans", "display_name": "Ludewig, Hans" } ], "advisors": [ { "name": { "family": "Lurie", "given": "Harold" }, "id": "Lurie-H", "role": "advisor", "display_name": "Lurie, Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/DDW9-CY15", "abstract": "An investigation was conducted to estimate the error when the flat-flux approximation is used to compute the resonance integral for a single absorber element embedded in a neutron source.
\r\n\r\nThe investigation was initiated by assuming a parabolic flux distribution in computing the flux-averaged escape probability which occurs in the collision density equation. Furthermore, also assumed were both wide resonance and narrow resonance expressions for the resonance integral. The fact that this simple model demonstrated a decrease in the resonance integral motivated the more detailed investigation of the thesis.
\r\n\r\nAn integral equation describing the collision density as a function of energy, position and angle is constructed and is subsequently specialized to the case of energy and spatial dependence. This equation is further simplified by expanding the spatial dependence in a series of Legendre polynomials (since a one-dimensional case is considered). In this form, the effects of slowing-down and flux depression may be accounted for to any degree of accuracy desired. The resulting integral equation for the energy dependence is thus solved numerically, considering the slowing down model and the infinite mass model as separate cases.
\r\n\r\nFrom the solution obtained by the above method, the error ascribable to the flat-flux approximation is obtained. In addition to this, the error introduced in the resonance integral in assuming no slowing down in the absorber is deduced. Results by Chernick for bismuth rods, and by Corngold for uranium slabs, are compared to the latter case, and these agree to within the approximations made.
\r\n" }, { "name": "Maserjian, Joseph", "degree": "PhD", "year": "1966", "title": "Conduction Through Thin Titanium Dioxide Films", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:07222014-092322045", "creators": [ { "name": { "family": "Maserjian", "given": "Joseph" }, "id": "Maserjian-Joseph", "display_name": "Maserjian, Joseph" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/MNGD-M461", "abstract": "Conduction through TiO2 films of thickness 100 to 450 \u00c5\r\nhave been investigated. The samples were prepared by either\r\nanodization of Ti evaporation of TiO2, with Au or Al evaporated\r\nfor contacts. The anodized samples exhibited considerable hysteresis due to electrical forming, however it was\r\npossible to avoid this problem with the evaporated samples\r\nfrom which complete sets of experimental results were obtained\r\nand used in the analysis. Electrical measurements\r\nincluded: the dependence of current and capacitance on dc\r\nvoltage and temperature; the dependence of capacitance and\r\nconductance on frequency and temperature; and transient\r\nmeasurements of current and capacitance. A thick (3000 \u00c5)\r\nevaporated TiO2 film was used for measuring the dielectric\r\nconstant (27.5) and the optical dispersion, the latter being\r\nsimilar to that for rutile. An electron transmission diffraction\r\npattern of a evaporated film indicated an essentially\r\namorphous structure with a short range order that could be\r\nrelated to rutile. Photoresponse measurements indicated the\r\nsame band gap of about 3 ev for anodized and evaporated\r\nfilms and reduced rutile crystals and gave the barrier energies\r\nat the contacts.
\r\n\r\nThe results are interpreted in a self consistent manner\r\nby considering the effect of a large impurity concentration in\r\nthe films and a correspondingly large ionic space charge.\r\nThe resulting potential profile in the oxide film leads to a\r\nthermally assisted tunneling process between the contacts and\r\nthe interior of the oxide. A general relation is derived for\r\nthe steady state current through structures of this kind. This\r\nin turn is expressed quantitatively for each of two possible\r\nlimiting types of impurity distributions, where one type gives\r\nbarriers of an exponential shape and leads to quantitative predictions\r\nin c lose agreement with the experimental results.\r\nFor films somewhat greater than 100 \u00c5, the theory is formulated\r\nessentially in terms of only the independently measured\r\nbarrier energies and a characteristic parameter of the oxide\r\nthat depends primarily on the maximum impurity concentration\r\nat the contacts. A single value of this parameter gives consistent\r\nagreement with the experimentally observed dependence\r\nof both current and capacitance on dc voltage and temperature,\r\nwith the maximum impurity concentration found to be approximately\r\nthe saturation concentration quoted for rutile. This explains \r\nthe relative insensitivity of the electrical properties of \r\nthe films on the exact conditions of formation.
" }, { "name": "Moon, Donald Wayne", "degree": "PhD", "year": "1966", "title": "Influence of Dislocation Mobility on the Yield in Silicon-Iron", "advisor": "Vreeland, Thad", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-164657", "creators": [ { "name": { "family": "Moon", "given": "Donald Wayne" }, "id": "Moon-Donald-Wayne", "display_name": "Moon, Donald Wayne" } ], "advisors": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-T", "role": "advisor", "display_name": "Vreeland, Thad" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/SJWH-6240", "abstract": "This thesis presents the results of an experimental investigation of the yielding phenomenon during the transition from elastic to plastic behavior in 3 per cent silicon-iron alloy. Static load tests, constant strain-rate tests and square wave rapid loading tests were conducted on single crystal. and polycrystalline specimens in order to determine the dislocation configurations at various stages in the yielding process. An electrolytic etching technique was used to reveal dislocation intersections with the observation surface.\r\n\r\nGrain boundaries were found to be the primary source of dislocations for slip band formation in fully annealed material. The velocity of mobile dislocations was found to be an extremely sensitive function of the applied stress.\r\n\r\nA true static upper yield point was found to be consistent with theories of the upper yield point based upon dislocation kinetics. The delay-time for yielding at constant applied stress was found to depend upon the dynamics of dislocation motion, the anisotropic stress concentration, the stress concentration due to relaxation of individual grains and the Schmid factor of the least favorably oriented grains.\r\n\r\nDislocation dynamics and dislocation configurations at various stages of plastic deformation were capable of accounting for a true upper yield point, the shape of the strain-time curve at constant stress and the Luder's band propagation velocity in polycrystalline specimens." }, { "name": "Murthy, K. R. Ananda", "degree": "PhD", "year": "1966", "title": "A Possible Analytical Explanation for the Micrometeorite Concentration near the Earth", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11152005-144237", "creators": [ { "name": { "family": "Murthy", "given": "K. R. Ananda" }, "id": "Murthy-K-R-Ananda", "display_name": "Murthy, K. R. Ananda" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D8XP-4Q06", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe Keplerian motion of a single particle in a dissipating medium, such as air, is analysed and a theory of micrometeorite capture and resulting orbital lifetime is developed. The equations of motion are derived for a planar, two-dimensional model, and all orbital variables are assumed to be perturbed slightly from their Keplerian values. The equations are then linearized and solved. Then a statistical model of the interplanetary micrometeorite flux is developed in which the distribution of velocities at infinity relative to the earth and masses of the particles are taken into account. The velocity distribution is taken to be [...]. The distribution of the masses is taken as a constant number of particle flux M(m) at infinity. Finally, this statistical model is combined with the theory of capture and lifetime to furnish a possible explanation for the micrometeorite concentration near the earth." }, { "name": "Olson, Mervyn Daniel", "degree": "PhD", "year": "1966", "title": "Supersonic Flutter of Circular Cylindrical Shells", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022005-075701", "creators": [ { "name": { "family": "Olson", "given": "Mervyn Daniel" }, "id": "Olson-Mervyn-Daniel", "display_name": "Olson, Mervyn Daniel" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/32AP-C463", "abstract": "Various experimental and theoretical studies on the supersonic flutter of circular cylindrical shells are discussed.
\r\n\r\nResults of experiments in the Mach number range 2.5 - 3.5 are presented. Three shells with radius-to-thickness ratios of 2,000 were subjected to radial external pressure loadings and to combinations of axial compressive loading and internal pressurization while in the presence of an external axially-directed supersonic flow.
\r\n\r\nSmall amounts of internal pressurization were very stabilizing with respect to flutter, but moderate amounts reduced stability to the unpressurized level. However, high internal pressures completely stabilized the shells. The axial compressive loading was slightly destabilizing for moderate amounts of internal pressurization.
\r\n\r\nThe flutter modes (which were standing waves in the axial direction with zero, one or two circumferential nodal lines) contained many waves around the circumference (of the order of 20) that travelled in the circumferential direction. This circumferentially travelling wave phenomenon possibly results from the nonlinear nature of cylindrical shells.
\r\n\r\nModel integrity was not threatened by even the most violent flutter which occurred just prior to buckling under radial external pressure loading and just after buckling under axial compressive loading. Buckled portions of a shell did not flutter. It appears that the large local curvatures encountered in the buckling of a cylindrical shell tend to stabilize the shell locally. However, it also appears that the localized buckling usually encountered in practice reduces the stability of any unbuckled regions of the shell.
\r\n\r\nThe experimental flutter boundaries are compared with various theoretical predictions. Following Voss a modal analysis which satisfies the so-called freely supported shell boundary conditions is used in conjunction with different aerodynamic approximations - namely piston theory and the potential theory of Leonard and Hedgepeth. It was found that the pressurized cylindrical shells fluttered at a lower level of free stream energy than predicted by the theory. Of the two results, that using piston theory appears to correspond closest to the experiment both in stability boundary and in critical values of circumferential wave number. Both predictions yield a larger stabilizing influence of the shell internal pressure than observed in the experiment.
\r\n\r\nAn analysis is presented for calculating the final limiting amplitudes of flutter based on a two-mode, piston theory approximation. A Galerkin procedure is used to reduce the nonlinear shallow shell equations of Marguerre to two coupled nonlinear ordinary differential equations for the modal amplitudes. An approximate limit cycle solution to these equations is obtained by the method of Krylov and Bogoliubov. The results indicate that for practical purposes cylindrical shell flutter does not occur below the stability boundary for infinitesimal disturbances. The limit cycle amplitudes predicted by this analysis seem to agree very well with the experimental ones. The results further indicate that the flutter amplitude, frequency and mode shape should change discontinuously (or jump) as the aerodynamic pressure is increased beyond the value for first flutter.
" }, { "name": "Rocke, Richard Dale", "degree": "PhD", "year": "1966", "title": "Transmission Matrices and Lumped Parameter Models for Continuous Systems", "advisor": "Crede, Charles E.; Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10192015-155737101", "creators": [ { "name": { "family": "Rocke", "given": "Richard Dale" }, "id": "Rocke-Richard-Dale", "display_name": "Rocke, Richard Dale" } ], "advisors": [ { "name": { "family": "Crede", "given": "Charles E." }, "id": "Crede-C-E", "role": "advisor", "display_name": "Crede, Charles E." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/4K3H-1E57", "abstract": "The use of transmission matrices and lumped parameter models for describing continuous systems is the subject of this study. Non-uniform continuous systems which play important roles in practical vibration problems, e.g., torsional oscillations in bars, transverse bending vibrations of beams, etc., are of primary importance.
\r\n\r\nA new approach for deriving closed form transmission matrices is applied to several classes of non-uniform continuous segments of one dimensional and beam systems. A power series expansion method is presented for determining approximate transmission matrices of any order for segments of non-uniform systems whose solutions cannot be found in closed form. This direct series method is shown to give results comparable to those of the improved lumped parameter models for one dimensional systems.
\r\n\r\nFour types of lumped parameter models are evaluated on the basis of the uniform continuous one dimensional system by comparing the behavior of the frequency root errors. The lumped parameter models which are based upon a close fit to the low frequency approximation of the exact transmission matrix, at the segment level, are shown to be superior. On this basis an improved lumped parameter model is recommended for approximating non-uniform segments. This new model is compared to a uniform segment approximation and error curves are presented for systems whose areas very quadratically and linearly. The effect of varying segment lengths is investigated for one dimensional systems and results indicate very little improvement in comparison to the use of equal length segments. For purposes of completeness, a brief summary of various lumped parameter models and other techniques which have previously been used to approximate the uniform Bernoulli-Euler beam is a given.
\r\n" }, { "name": "Schwartz, Henry Gerard", "degree": "PhD", "year": "1966", "title": "Studies on Adsorption and Microbial Degradation of the Pesticides Isopropyl N-(3-Chlorophenyl) Carbamate and 2,4-Dichlorophenoxyacetic Acid in Aqueous Solutions", "advisor": "Samples, William R.; Morgan, James J.; McKee, Jack E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06252004-114224", "creators": [ { "name": { "family": "Schwartz", "given": "Henry Gerard" }, "id": "Schwartz-Henry-Gerard", "display_name": "Schwartz, Henry Gerard" } ], "advisors": [ { "name": { "family": "Samples", "given": "William R." }, "id": "Samples-W-R", "role": "advisor", "display_name": "Samples, William R." }, { "name": { "family": "Morgan", "given": "James J." }, "id": "Morgan-J-J", "role": "advisor", "display_name": "Morgan, James J." }, { "name": { "family": "McKee", "given": "Jack E." }, "id": "McKee-J-E", "role": "advisor", "display_name": "McKee, Jack E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/1E55-D295", "abstract": "The adsorption and microbial degradation in aqueous solution of two selected pesticides, isopropyl N-(3-chlorophenyl) carbamate (CIPC) and 2,4-dichlorophenoxyacetic acid (2,4-D), were studied to better understand the influence of these processes on the persistence of pesticides in natural waters. Based on the experimental results, certain inferences have been made concerning natural water systems. Radioactive tracer techniques were utilized to follow the adsorption and degradation of the two pesticides. Additional information about the disappearance of the phenyl carbon atoms from CIPC adaptation cultures was obtained from ultraviolet spectra.
\r\n\r\n2,4-D was found strongly resistant to microbial degradation in a liquid medium of mineral salts. Less than 40 percent of the acetic acid portion of the molecule disappeared from solution in six months, even in the presence of additional sources of organic carbon. CIPC was degraded much more rapidly than 2,4-D. The isopropyl segment of the CIPC molecule was completely metabolized. Metabolism of the carbon atoms in the ring structure ceased after 40 to 60 percent of the atoms had disappeared from solution. A partial metabolic pathway for the degradation of CIPC is proposed.
\r\n\r\nThe clay minerals, illite, kaolinite, and montmorillonite, suspended in dilute pesticide solutions adsorbed very little 2,4-D or CIPC. CIPC was adsorbed extensively from water solutions with powdered activated carbon. The equilibrium for the adsorption of CIPC on activated carbon was represented closely by a Freundlich isotherm. The adsorption appeared to involve physical or weak chemical bonding. There was some indication that the adsorption of CIPC on activated carbon in a well-stirred system was diffusion controlled.
\r\n\r\nThe addition of activated carbon decreased the overall rate of degradation of CIPC. It is proposed that the decomposition of CIPC in the presence of powdered activated carbon occurs principally in the aqueous phase or at the interface between the liquid and the exterior surface of the activated carbon. As CIPC is degraded in solution, additional quantities desorb. The adsorption equilibrium of the activated carbon-CIPC system is influenced by the presence of bacterial cells and metabolic intermediates.
\r\n" }, { "name": "Sorrell, Furman Yates, Jr.", "degree": "PhD", "year": "1966", "title": "On the Generation of Shock Waves in an Inverse Pinch", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03312009-155713", "creators": [ { "name": { "family": "Sorrell", "given": "Furman Yates, Jr." }, "id": "Sorrell-Furman-Yates", "display_name": "Sorrell, Furman Yates, Jr." } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZCDM-SF32", "abstract": "A problem inherent in magnetic shock tubes is the difficulty of achieving separation of the driving current sheet and the shock wave. If such devices are to be applied to produce shock waves for experimentation, then separation will usually be a necessary requirement. In the present experiments in an inverse pinch shock tube, preliminary measurements showed that not only was separation not achieved, but under certain conditions the shock was actually found to be located far behind the front of the current sheet. This appeared to be a paradoxical case of the shock wave pushing the piston. Moreover, measurements of the current sheet velocity indicated that the interaction of the current sheet with the gas should be strong enough to sweep up all the gas encountered by the current sheet and thus to produce a shock wave moving ahead of it. In order to find explanations for the absence of separation and for some other puzzling aspects of these early experiments, further measurements were made to study in more detail the processes taking place in the device. These included measurements of the radial electric field with electrostatic probes and of the ionization levels by the technique of spectral line broadening. The results of these measurements show that the degree of ionization is surprisingly low and that the amount of gas leaking through the current sheet is significantly high in some cases. The conclusion is then reached that although the so-called \"snowplow model\" is successful in predicting the current sheet velocity, it does not lead to the correct picture of the physical processes taking place. Finally, conditions for which separation may be achievable are inferred from the experiments." }, { "name": "Sutherland, Alexander James", "degree": "PhD", "year": "1966", "title": "Entrainment of Fine Sediments by Turbulent Flows", "advisor": "Vanoni, Vito A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262015-133211952", "creators": [ { "name": { "family": "Sutherland", "given": "Alexander James" }, "id": "Sutherland-Alexander-James", "display_name": "Sutherland, Alexander James" } ], "advisors": [ { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "advisor", "display_name": "Vanoni, Vito A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/F86N-A080", "abstract": "A study was made of the means by which turbulent flows entrain sediment grains from alluvial stream beds. Entrainment was considered to include both the initiation of sediment motion and the suspension of grains by the flow. Observations of grain motion induced by turbulent flows led to the formulation of an entrainment hypothesis. It was based on the concept of turbulent eddies disrupting the viscous sublayer and impinging directly onto the grain surface. It is suggested that entrainment results from the interaction between fluid elements within an eddy and the sediment grains.
\r\n\r\nA pulsating jet was used to simulate the flow conditions in a turbulent boundary layer. Evidence is presented to establish the validity of this representation. Experiments were made to determine the dependence of jet strength, defined below, upon sediment and fluid properties. For a given sediment and fluid, and fixed jet geometry there were two critical values of jet strength: one at which grains started to roll across the bed, and one at which grains were projected up from the bed. The jet strength K, is a function of the pulse frequency, \u03c9, and the pulse amplitude, A, defined by
\r\n\r\nK = A\u03c9-s
\r\n\r\nWhere s is the slope of a plot of log A against log \u03c9. Pulse amplitude is equal to the volume of fluid ejected at each pulse divided by the cross sectional area of the jet tube.
\r\n\r\nDimensional analysis was used to determine the parameters by which the data from the experiments could be correlated. Based on this, a method was devised for computing the pulse amplitude and frequency necessary either to move or project grains from the bed for any specified fluid and sediment combination.
\r\n\r\nExperiments made in a laboratory flume with a turbulent flow over a sediment bed are described. Dye injection was used to show the presence, in a turbulent boundary layer, of two important aspects of the pulsating jet model and the impinging eddy hypothesis. These were the intermittent nature of the sublayer and the presence of velocities with vertical components adjacent to the sediment bed.
\r\n\r\nA discussion of flow conditions, and the resultant grain motion, that occurred over sediment beds of different form is given. The observed effects of the sediment and fluid interaction are explained, in each case, in terms of the entrainment hypothesis.
\r\n\r\nThe study does not suggest that the proposed entrainment mechanism is the only one by which grains can be entrained. However, in the writer\u2019s opinion, the evidence presented strongly suggests that the impingement of turbulent eddies onto a sediment bed plays a dominant role in the process.
\r\n" }, { "name": "Tam, Christopher Kwong-Wah", "degree": "PhD", "year": "1966", "title": "On the Transport Properties of Fluid-Particle Flow", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262015-101523465", "creators": [ { "name": { "family": "Tam", "given": "Christopher Kwong-Wah" }, "id": "Tam-Christopher-Kwong-Wah", "display_name": "Tam, Christopher Kwong-Wah" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/X7YD-5B20", "abstract": "The hydrodynamic forces acting on a solid particle in a viscous, incompressible fluid medium at low Reynolds number flow is investigated mathematically as a prerequisite to the understanding of transport processes in two-phase flow involving solid particles and fluid. Viscous interaction between a small number of spherical particles and continuous solid boundaries as well as fluid interface are analyzed under a \u201cpoint-force\u201d approximation. Non-spherical and elastic spherical particles in a simple shear flow area are then considered. Non-steady motion of a spherical particle is briefly touched upon to illustrate the transient effect of particle motion.
\r\n\r\nA macroscopic continuum description of particle-fluid flow is formulated in terms of spatial averages yielding a set of particle continuum and bulk fluid equations. Phenomenological formulas describing the transport processes in a fluid medium are extended to cases where the volume concentration of solid particles is sufficiently high to exert an important influence. Hydrodynamic forces acting on a spherical solid particle in such a system, e.g. drag, torque, rotational coupling force, and viscous collision force between streams of different sized particles moving relative to each other are obtained. Phenomenological constants, such as the shear viscosity coefficient, and the diffusion coefficient of the bulk fluid, are found as a function of the material properties of the constituents of the two-phase system and the volume concentration of solid. For transient heat conduction phenomena, it is found that the introduction of a complex conductivity for the bulk fluid permits a simple mathematical description of this otherwise complicated process. The rate of heat transfer between particle continuum and bulk fluid is also investigated by means of an Oseen-type approximation to the energy equation.
\r\n" }, { "name": "Thornber, Karvel Kuhn", "degree": "PhD", "year": "1966", "title": "l. Electronic Processes in \u03b1-Sulfur. II. Polaron Motion in a D.C. Electric Field", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechTHESIS:10262015-112021684", "creators": [ { "name": { "family": "Thornber", "given": "Karvel Kuhn" }, "id": "Thornber-Karvel-Kuhn", "display_name": "Thornber, Karvel Kuhn" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/RK39-A748", "abstract": "Part I: The mobilities of photo-generated electrons and holes in orthorhombic sulfur are determined by drift mobility techniques. At room temperature electron mobilities between 0.4 cm2/V-sec and 4.8 cm2/V-sec and hole mobilities of about 5.0 cm2/V-sec are reported. The temperature dependence of the electron mobility is attributed to a level of traps whose effective depth is about 0.12 eV. This value is further supported by both the voltage dependence of the space-charge-limited, D.C. photocurrents and the photocurrent versus photon energy measurements.
\r\n\r\nAs the field is increased from 10 kV/cm to 30 kV/cm a second mechanism for electron transport becomes appreciable and eventually dominates. Evidence that this is due to impurity band conduction at an appreciably lower mobility (4.10-4 cm2/V-sec) is presented. No low mobility hole current could be detected. When fields exceeding 30 kV/cm for electron transport and 35 kV/cm for hole transport are applied, avalanche phenomena are observed. The results obtained are consistent with recent energy gap studies in sulfur.
\r\n\r\nThe theory of the transport of photo-generated carriers is modified to include the case of appreciable thermos-regeneration from the traps in one transit time.
\r\n\r\nPart II: An explicit formula for the electric field E necessary to accelerate an electron to a steady-state velocity v in a polarizable crystal at arbitrary temperature is determined via two methods utilizing Feynman Path Integrals. No approximation is made regarding the magnitude of the velocity or the strength of the field. However, the actual electron-lattice Coulombic interaction is approximated by a distribution of harmonic oscillator potentials. One may be able to find the \u201cbest possible\u201d distribution of oscillators using a variational principle, but we have not been able to find the expected criterion. However, our result is relatively insensitive to the actual distribution of oscillators used, and our E-v relationship exhibits the physical behavior expected for the polaron. Threshold fields for ejecting the electron for the polaron state are calculated for several substances using numerical results for a simple oscillator distribution.
\r\n" }, { "name": "Tong, Pin", "degree": "PhD", "year": "1966", "title": "Liquid Sloshing in an Elastic Container", "advisor": "Fung, Yuan-cheng; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202010-092311496", "creators": [ { "name": { "family": "Tong", "given": "Pin" }, "id": "Tong-Pin", "display_name": "Tong, Pin" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WYZD-Q384", "abstract": "The motion of a liquid in a flexible container is important for rocket structural dynamics. The purpose of this paper is to study the dynamic response of the liquid, the sloshing frequencies and the stability of the free surface of the liquid in an elastic container.
\r\n\r\nThe variational principle for the problem of an incompressible, inviscid fluid in an elastic container is presented by considering the pressure energy of the fluid, the surface energy, and the Lagrangian of the elastic thin shell. The corresponding linearized equations are studied in terms of eigenvalues and eigenfunctions.
\r\n\r\nThe effects of the gravitation, the surface tension, the rigidity of the container, the free surface contact angle and its dynamic variation, on the natural frequencies and the stability of the free surface are discussed.
\r\n\r\nIt is found that the flexibility of the container always lowers the natural frequencies and also induces a mean oscillatory motion of the liquid that creates an oscillatory force on the container in the vertical direction. The equilibrium contact angle and its dynamic variation have an important effect on the limit of stability.
\r\n\r\nThe motion of a liquid in a circular cylindrical container with a flat flexible bottom is worked out in detail analytically by means of eigenfunctions. Some results are presented graphically. A numerical scheme using finite elements method is developed for an arbitrary container. Methods for improving the solution systematically are indicated.
\r\n" }, { "name": "Tsuei, Chang-chyi", "degree": "PhD", "year": "1966", "title": "Electrical Resistance and Thermoelectric Power of the Metastable Phases in Tellurium-Base Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07222014-110401626", "creators": [ { "name": { "family": "Tsuei", "given": "Chang-chyi" }, "id": "Tsuei-Chang-chyi", "display_name": "Tsuei, Chang-chyi" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/4NR0-FE43", "abstract": "By using techniques of rapid quenching from the melt, metastable phases have been obtained in ternary alloys which contain tellurium as a major component and two of the three noble metals (Cu, Ag, Au) as minor components. The metastable phases found in this investigation are either simple cubic or amorphous. The formation of the simple cubic phase is discussed. The electrical resistance and the thermoelectric power of the simple cubic alloy (Au30Te70) have been measured and interpreted in terms of atomic bondings. The semiconducting properties of a metastable amorphous alloy Au5Cu25Te70) have been measured. The experimental results are discussed in connection with a theoretical consideration of the validity of band theory in an amorphous solid. The existence of extrinsic conduction in an amorphous semiconductor is suggested by the result of electrical resistance and thermoelectric power measurements." }, { "name": "Williams, Richard R.", "degree": "PhD", "year": "1966", "title": "Application of the Two Variable Expansion Procedure to the Commensurable Planar Restricted Three-Body Problem", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11162005-082219", "creators": [ { "name": { "family": "Williams", "given": "Richard R." }, "id": "Williams-Richard-R", "display_name": "Williams, Richard R." } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PYNV-5723", "abstract": "The nearly commensurable case of the planar restricted three-body problem is treated by application of the two variable expansion procedure. The polar angle of the infinitesimal body, rather than the time, is taken as the independent variable. A set of four coupled first order differential equations, which govern the long-period behavior of the orbital elements, is obtained by imposing the requirement that the assumed form of the expansions must be self-consistent. The independent variable in these equations is the \"slow variable\". It is then found that the short-period perturbations of the motion of the infinitesimal body do not contain small divisors or secular terms.\r\n\r\nApproximate solutions for the orbital elements are given, for two different cases. Both libratory and non-libratory solutions are found, depending upon the initial conditions. Numerical results are calculated from these solutions, and are compared to numerical computations recently reported in the literature." }, { "name": "Yonas, Gerold", "degree": "PhD", "year": "1966", "title": "Aligned Fields Magneto-Fluid Dynamic Flow Past Bodies", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-094628", "creators": [ { "name": { "family": "Yonas", "given": "Gerold" }, "id": "Yonas-Gerold", "display_name": "Yonas, Gerold" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/XGWS-3X78", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe drag of spheres and disks has been measured in a flow of liquid sodium with an aligned magnetic field. The experiments were carried out for 10[superscript 4] < Re < 25 x 10 [superscript 4] and N , the interaction parameter, satisfying 0.1 < N < 80 . The sphere C[subscript D] was not a function of N for N < or = 0.3, began to increase appreciably for N ~ 1.0 , and reached an asymptotic dependence proportional to [square root]N for N > 10 . The disk gave a C[subscript D] which was relatively unchanged for N< 10 , began to increase for N~10 , and had approximately the same value as for spheres for N > 20 . We conclude, that for high N , flows are characterized by C[subscript D] insensitive to body shape and emphasize this range in our discussion. A physical model is presented which involves stagnant regions which grow in length as N increases, and are separated from the outer flow by thin dissipation layers. A singular perturbation technique is suggested for the theoretical treatment of such layers." }, { "name": "Argyropoulos, George S.", "degree": "PhD", "year": "1965", "title": "Anisotropies and Interactions in Shear Flow of Macromolecular Suspensions", "advisor": "Wayland, J. Harold; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01102003-103458", "creators": [ { "name": { "family": "Argyropoulos", "given": "George S." }, "id": "Argyropoulos-G-S", "display_name": "Argyropoulos, George S." } ], "advisors": [ { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "advisor", "display_name": "Wayland, J. Harold" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/8KNM-5225", "abstract": "The problem of determining the orientation distribution function for rigid particles of arbitrary shape is formulated in a general stochastic approach to consider the influence of any acting orientation mechanism, stochastic or deterministic. The effect of the various orientation mechanisms on the partial differential equation of the problem, an equation of the Fokker-Planck type, is analyzed. The question of linearity or non-linearity of the superposition of the effects due to different orientation mechanisms is examined.\r\n \r\nThe orientation of rigid ellipsoidal particles in uniform shear flow is studied in detail, for different cases of acting orientation mechanisms. When only the viscous stresses act on the particles, the problem for the orientation distribution function becomes a deterministic first-order initial value problem, and its solution displays periodic behavior. In the case of macromolecules, when the Brownian influence is predominant, we examine the effect of a third orientation mechanism acting on the macromolecules in addition to the viscous stresses and the Brownian impulses. In Couette flow between concentric cylinders, the third orientation mechanism is considered to be a deterministic force field in the radial direction x, varying linearly with x. The steady state orientation distribution function is then determined to the third order, and the theory of streaming birefringence of a dilute suspension of rigid ellipsoidal macromolecules in Couette flow is generalized to include the effect of the additional influence. The direction of the isocline and the amount of birefringence are calculated to the second order.\r\n\r\nWhen spherical macromolecules are added to the suspension in increasing concentration, the effect of hydrodynamic interactions between the two species on the orientation of the ellipsoidal particles is examined in Couette flow. It is shown that an effect of the presence of the spheres is to decrease the drift velocity of the ellipsoids--and thus decrease the amount of birefringence--and that the effect can be described as a decrease in the effective velocity gradient. The theoretical result for this decrease is in good agreement with experimental results for sphere concentrations comparable to the concentration of ellipsoids. On the other hand, as the concentration of spheres increases, the effect of their presence on the rotational diffusion constant of the asymmetrical particles can be large enough to reverse the trend and lead to a positive variation of the amount of birefringence with sphere concentration." }, { "name": "Asmus, John Fredrich", "degree": "PhD", "year": "1965", "title": "An Analysis of Perturbed Confocal Resonators", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01132003-084119", "creators": [ { "name": { "family": "Asmus", "given": "John Fredrich" }, "id": "Asmus-John-Fredrich", "display_name": "Asmus, John Fredrich" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/74wn-7319", "abstract": "An analytical technique is developed for computing mode functions and associated diffraction losses of perturbed multimode optical resonators. It is based upon a consistent field formulation of resonance in an open two-mirror system.
\r\n\r\nTo illustrate the method the theory of confocal resonators is extended to include configurations differing from the confocal case by small geometrical perturbations. This involves computing and expanding a perturbed Green's function for such near confocal resonators. Diffraction losses for certain statistical and deterministic perturbations are computed and related to disturbances arising from an imperfect figure, polish or alignment of the mirrors.
\r\n\r\nThe design and construction of a stable laser spectrometer consisting of a single mode tuneable gas laser and a swept interferometer are described. Measurements of the diffraction losses of perturbed confocal resonators are found to be in agreement with the above analysis.
\r\n" }, { "name": "Beeler, George Wood", "degree": "PhD", "year": "1965", "title": "Stochastic Processes in the Human Eye Movement Control System", "advisor": "Fender, Derek H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142003-092707", "creators": [ { "name": { "family": "Beeler", "given": "George Wood" }, "id": "Beeler-George-Wood", "display_name": "Beeler, George Wood" } ], "advisors": [ { "name": { "family": "Fender", "given": "Derek H." }, "id": "Fender-D-H", "role": "advisor", "display_name": "Fender, Derek H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/84W2-8N43", "abstract": "Experiments have been performed to investigate several of the stochastic processes involved in the control of eye movements, particularly where these processes apply to saccades. Previous models have linearized the eye positioning system, and as a result some of the more important features have been lost in the analysis.\r\n\r\nThe experiments concentrated on four areas. The first of these was temporal prediction by saccades when tracking square wave target motions. This predictor function generates a response saccade approximately 100 msec before the stimulus step. The mean response time, however, never precedes the stimulus by more than 50 msec, and actually occurs after the stimulus when tracking either very short or long period square waves. These changes in mean response time are caused by a shift in the predictive lead at short periods, and by failures of the predictive mechanism at longer periods. This failure results in a delayed response 200 msec after the stimulus.\r\n\r\nThe second area investigated was the non-predictive saccadic response system. The investigation revealed that the sampled data effect previously reported is actually the result of the combination of a time delay and a refractory unit in the response mechanism. The characteristic times of these functions were investigated, along with the ability of the system to alter a response when additional retinal information arrives before the initial response saccade is elicited.\r\n\r\nThirdly, the role of spontaneous flicks in steady fixation tasks was investigated utilizing two-dimensional analysis. It was found that the majority of these events are of stochastic origin, whereas previous studies, analyzing only the horizontal components, indicated that the flicks are only used to correct fixation error. A generator for the random flicks can be postulated, and the source of the spontaneous drift motion was identified.\r\n\r\nFinally, experiments were performed on the perceptual effects of saccades. It was found that the visual system is incapable of detecting small target motions when they occur within ?40 msec of a flick. This suppression of movement detection by the saccades led to a re-evaluation of the efference copy mechanism, and the effect of this reevaluation on eye movement control is discussed." }, { "name": "Bell, James Melvin", "degree": "PhD", "year": "1965", "title": "Stress-Strain Characteristics of Cohesionless Granular Materials Subjected to Statically Applied Homogeneous Loads in an Open System", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242003-102726", "creators": [ { "name": { "family": "Bell", "given": "James Melvin" }, "id": "Bell-James-Melvin", "display_name": "Bell, James Melvin" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "chair", "display_name": "Scott, Ronald F." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "McCormick", "given": "Caleb W." }, "id": "McCormick-C-W", "role": "member", "display_name": "McCormick, Caleb W." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "member", "display_name": "Brooks, Norman H." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." } ], "option_major": [ "civileng" ], "doi": "10.7907/066B-HV20", "abstract": "A general stress-strain relationship in incremental and invariant form is derived for sand on the basis of experimental evidence. The resulting expression does not include the yield condition but makes allowance for the direction of loading and the state of stress. Two new modified and dimensionless invariant functions are introduced and a detailed description and classification of stress paths presented. A new first yield criterion for sand stressed to yield along one stress path is developed from experimental evidence. The friction angle in triaxial compression was minimum and 14[degrees] less than that in triaxial extension. The Mohr-Coulomb yield criterion extended to three dimensions is rejected.\r\n\r\nEmphasis is placed on the importance of obtaining homogeneous stress in physical experiments. A new spherical compression apparatus was developed to study the behavior of sand under spherical compression. Disadvantages of former apparatuses were largely overcome by elimination of frictional loading, and a homogeneous state of stress was obtained. A new stress controlled three-dimensional compression apparatus capable of applying principal stresses to a rectangular, plate sample was developed to study the behavior of sand under a general stress state, particularly under deviatoric stress. This apparatus provided for the independent measurement of volumetric strain and allowed for the development of considerable deformation in obtaining yield." }, { "name": "Bond, Robert Harold", "degree": "PhD", "year": "1965", "title": "Directed Electron Velocity Distributions in Rare Gas Discharges Using Guard Ring Probes", "advisor": "Langmuir, Robert V.; Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-144942", "creators": [ { "name": { "family": "Bond", "given": "Robert Harold" }, "id": "Bond-Robert-Harold", "display_name": "Bond, Robert Harold" } ], "advisors": [ { "name": { "family": "Langmuir", "given": "Robert V." }, "id": "Langmuir-R-V", "role": "advisor", "display_name": "Langmuir, Robert V." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/VZM2-A856", "abstract": "An experimental technique for determining detailed properties of anisotropic electron velocity distributions is described. For a planar Langmuir probe it is shown that g(vz) = - [(m\u2202Jp)/(e2\u2202Vp)] where vz = \u221a[2(e/m)Vp] and g(vz) gives the density of electrons with velocities normal to the probe in the range vz to vz + dvz. This expression is valid for any distribution function making it possible to study anisotropies merely by changing the orientation of the probe. If the distribution function is isotropic the above expres- sion is valid for cylindrical and small spherical probes as well.
\r\n\r\nThis technique is applied to the measurement of the directional properties of electron velocity distributions in the positive column of neon and helium hot cathode discharges. The necessary planar probe consists of a 0.01 inch diameter circular probe surrounded by a 0.090 inch square guard-ring. The measured distributions were Druyvesteyn in form except that all electrons were shifted in energy (in the direction of the external field) by an amount proportional to E\u03bb(vz). Here E is the magnitude of the external electric field and \u03bb(vz) the electron mean free path as a function of vz. The experimental conditions are shown to be identical with those necessary in the derivation of the Druyvesteyn distribution.
" }, { "name": "Buczek, Carl James", "degree": "PhD", "year": "1965", "title": "Spontaneously Radiating Atoms in Cavity Fields", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102002-134828", "creators": [ { "name": { "family": "Buczek", "given": "Carl James" }, "id": "Buczek-Carl-James", "display_name": "Buczek, Carl James" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CCD3-4P11", "abstract": "Spontaneous emission competes with stimulated emission in many interactions of light with matter. In the usual analyses which describe the interaction of an atom with a coherent optical field, the spontaneous emission characteristics, e.g., probability and spectral distribution, are not determined. The spontaneous emission from an atom which interacts with a coherent light wave is considered. The competition between coherent photons and spontaneous photons is treated in detail for a system consisting of a stationary atom, an open cavity and spatial fields. In the model chosen, a multilevel atom which spontaneously decays by interacting with spatial fields has two nondegenerate states coupled by an interaction with a single mode of the cavity. The Laplace-transformed Schrodinger equation is solved for specified initial conditions of the system. It is found that the interaction with the coherent field modifies the spectral distribution of spontaneous radiation from the atom. For spontaneous transitions involving an atomic state which interacts with the coherent field, the spectral distributions can no longer be described by Lorentzian functions. The new distributions exhibit a broadening and splitting for strong interactions between the atom and the coherent field. It is shown that the qualitative features of these distributions can be predicted from the energy-level diagram of the atom-cavity system. The net probability of the system gaining a coherent or cavity photon is calculated by integrating over the emitted spontaneous frequencies. The equivalence of this approach to the method of computing probabilities by integrating over time is demonstrated by using Parseval's theorem." }, { "name": "Chao, Chang-Chih", "degree": "PhD", "year": "1965", "title": "A Study of CsCI Type Intermediate Phases Involving Rare Earth Elements", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112002-171500", "creators": [ { "name": { "family": "Chao", "given": "Chang-Chih" }, "id": "Chao-Chang-Chih", "display_name": "Chao, Chang-Chih" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/EKPF-2Q83", "abstract": "This thesis presents the results of a systematic study of CsCl type phases in binary alloys of rare earth elements with other metals. Thirty-nine new phases of this type have been found. The linear variation of the lattice parameter of CsCl phases with the trivalent ionic radius of the rare earth metal previously established for a limited number of alloys, has been extended to seventy-nine phases. This linear relationship leads to some interesting qualitative arguments on the ionic size of the non-rare earth element in these phases. The electrical resistivities of nineteen CsCl type phases of rare earths with copper, silver and gold were measured between 4.2 [degrees] K and about 260 [degrees] K. With the exception of the yttrium-silver phase, all others exhibited an anomaly in the resistivity-temperature curve which is attributed to an antiferromagnetic transition. This conclusion is confirmed by previously published results of neutron diffraction experiments and magnetic susceptibility measurements. A qualitative interpretation of the resistivity results based on the indirect exchange interaction between the ions of the same type (magnetic or non-magnetic) and between the ions of the different type (magnetic and non-magnetic) is proposed." }, { "name": "Close, Donald Henry", "degree": "PhD", "year": "1965", "title": "Nonlinear Effects in Traveling Wave Laser AmpIfiers", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-090900", "creators": [ { "name": { "family": "Close", "given": "Donald Henry" }, "id": "Close-Donald-Henry", "display_name": "Close, Donald Henry" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Y5FC-GV56", "abstract": "Using semiclassical radiation theory, a formalism similar to that used by Lamb in his \"Theory of an Optical Maser\" is developed for studying the amplification of vector traveling waves in a laser-type medium. The effect of the medium on the waves is given in terms of space (or time) dependent field amplitudes and phases and a nonlinear index of refraction. With particular emphasis on typical gaseous media, the effects of Doppler broadening are treated in detail for arbitrary ratios of natural to Doppler linewidths. Polarization and propagation vectors in various directions are considered, and the nonlinear effects are found to make an isotropic medium effectively anisotropic.\r\n\r\nLowest order nonlinear effects (due to a polarization cubic in the field amplitudes) are studied extensively, and the frequency dependence of several of these processes is presented in graphical form. In particular, the introduction of fields at new frequencies and polarization effects are considered. The characteristics of these nonlinear processes peculiar to Doppler broadened lines are discussed, and the processes are interpreted in terms of saturation and coherent modulation of the population inversion density.\r\n\r\nStrong nonlinear effects are considered in a more approximate way and are found to consist of saturation of the various linear and nonlinear processes previously considered. These strong nonlinear effects should occur at low enough intensities to be easily observed in practice on a CW basis. With the present formalism, the analytical results of Gordon, White and Rigden regarding gain saturation in laser amplifiers are obtained, and the extension is made to include frequencies away from line center and the effects of multiple spectral components. Again, the introduction of fields at new frequencies is considered in detail. These results are also discussed in terms of saturation and coherent modulation of the populations and \"hole burning\"." }, { "name": "Cohen, Jules Bernard", "degree": "PhD", "year": "1965", "title": "Effects of Ionizing Radiation on Aqueous Solutions of the Detergent Al!tylbenzenesulfonate and Several Lower Homologs", "advisor": "Samples, William R.; McKee, Jack E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-091628", "creators": [ { "name": { "family": "Cohen", "given": "Jules Bernard" }, "id": "Cohen-Jules-Bernard", "display_name": "Cohen, Jules Bernard" } ], "advisors": [ { "name": { "family": "Samples", "given": "William R." }, "id": "Samples-W-R", "role": "advisor", "display_name": "Samples, William R." }, { "name": { "family": "McKee", "given": "Jack E." }, "id": "McKee-J-E", "role": "advisor", "display_name": "McKee, Jack E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/67ES-AK62", "abstract": "A study was conducted of the degradation of benzene-, p-toluene-, and alkylbenzenesulfonates under the action of ionizing radiation from a 3400 curie, Cobalt-60 irradiator.\r\n\r\nEffects of varying solute concentrations, pH, and dissolved oxygen concentrations were observed as functions of the energy absorbed by the solutions. The rates of oxygen depletion and the rates of hydrogen peroxide, enol, and sulfate production were followed by irradiating the solutions for varying periods of time.\r\n\r\nResults of the irradiations indicate that, in aerated solutions, the major mode of degradation is by desulfonation of the molecule. Degradation was accompanied by significant losses in oxygen, possibly a result of direct oxidation of the solute by radiation, rather than by free radical reactions. Enols were also found to occur, but at very low concentrations. The product formed as a result of desulfonation of benzenesulfonic acid appeared to be quinonoid rather than phenolic in nature.\r\n\r\nIn deaerated solutions, enol yields were found to decrease, while sulfates were not observed. A more rapid decrease in the ultraviolet absorption peaks of these homologs in deaerated solutions was attributed to the formation of dimers.\r\n\r\nThe study indicates that the use of radiation, as a water or wastewater treatment process for degrading organic compounds, would necessarily be limited to aerated solutions in situations where the large losses of oxygen would not be detrimental" }, { "name": "Cool, Terrill Alan", "degree": "PhD", "year": "1965", "title": "Recombination, Ionization, and Nonequilibrium Electrical Conductivity in Seeded Plasmas", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-115831", "creators": [ { "name": { "family": "Cool", "given": "Terrill Alan" }, "id": "Cool-Terrill-Alan", "display_name": "Cool, Terrill Alan" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/JB0S-4521", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nThis study is concerned with the theoretical and experimental description of the behavior of dense seeded plasmas under the influence of applied electric fields under steady-state conditions as well as during electronic ionizational and recombinational relaxations. Extensive experimental measurements of nonequilibrium electrical conductivities, electron temperatures, recombination rates, and ionization rates have been performed in dense potassium-seeded plasmas. Measurements have been made under conditions of practical importance for proposed MHD energy converters in argon-potassium and helium-potassium plasmas. Translational gas temperatures ranged from 1250 to 2000 [degrees]K; seed concentrations were varied between .1 and 1 mole percent; and the total gas pressure was 1 atmosphere.\r\n\r\nExtensive steady-state measurements of nonequilibrium electrical conductivity, and the influence upon it of variations in gas temperatures, seed concentrations, atomic cross sections, current densities, electric field strengths, and energy loss processes have been made. This detailed experimental work has led to important modifications of existing theory which have enabled an accurate description of the plasma in terms of a simple physical model. Electron temperature measurements provide a conclusive and quantitative verification of the validity of this physical model. The essential theoretical modifications made here are the inclusion of both inelastic and elastic electronic collisional energy loss mechanisms in a manner which accurately reflects the essential physical differences between these two processes in terms of fundamental atomic properties, and employs no adjustable parameters. Additionally, consideration of the detailed energy dependence of the atomic cross sections and the inclusion of both electron-ion and electron-atom interactions has been essential in accurately describing the experimental results.\r\n\r\nExperimental measurements of recombination rates, ionization rates, and electronic collisional relaxation characteristics of potassium seeded plasmas have been performed. Measured recombination and ionization rates for potassium show good agreement with theoretical calculations based upon a formulation employing the Gryzinski classical inelastic collision cross sections and a simple physical model of the relaxing plasma" }, { "name": "Davison, Lee Walker", "degree": "PhD", "year": "1965", "title": "Propagation of Finite Amplitude Waves in Elastic Solids", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10032002-104227", "creators": [ { "name": { "family": "Davison", "given": "Lee Walker" }, "id": "Davison-Lee-Walker", "display_name": "Davison, Lee Walker" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/Q1QQ-VG41", "abstract": "This thesis is devoted to consideration of finite amplitude waves propagating into an elastic half-space in a direction normal to the boundary. Excitation is by means of strains applied at the boundary as step functions of time.\r\n\r\nThe solutions obtained are combinations of centered simple waves and shock waves. Longitudinal waves may appear alone but waves with transverse displacement components are always accompanied by longitudinal waves. The foregoing solutions are discussed in general and are illustrated by an example problem involving a special nonlinear, compressible, hyperelastic material. A perturbation method, based on the use of characteristic coordinates, which facilitates approximate solution of the problem for arbitrarily prescribed strain boundary conditions is described." }, { "name": "Goddard, William Andrew, III", "degree": "PhD", "year": "1965", "title": "An Improved Many-Electron Theory for Atoms and Molecules Which Uses Eigenfunctions of Total Spin", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04112003-083311", "creators": [ { "name": { "family": "Goddard", "given": "William Andrew, III" }, "id": "Goddard-William-Andrew-III", "display_name": "Goddard, William Andrew, III" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "chair", "display_name": "Duwez, Pol E." }, { "name": { "family": "Barnes", "given": "Charles A." }, "id": "Barnes-C-A", "role": "member", "display_name": "Barnes, Charles A." }, { "name": { "family": "Chan", "given": "Sunney I." }, "id": "Chan-S-I", "role": "member", "display_name": "Chan, Sunney I." }, { "name": { "family": "Pitzer", "given": "Robert M." }, "id": "Pitzer-R-M", "role": "member", "display_name": "Pitzer, Robert M." } ], "option_major": [ "eng" ], "doi": "10.7907/K8HN-5208", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\t\t\r\nThe object is to obtain good approximations for the ground state wave function and energy for atoms and simple molecules (e.g., H[subscript 2], HF, H[subscript 2]O, CH[subscript 4]). We neglect relativistic effects including all spin couplings and we fix the nuclear positions; thus, the Hamiltonian for a molecule with N electrons is H =[...], where V(r[subscript i]) is theelectrostatic interaction between the electrons and the nuclear framework. Since the Hamiltonian does not contain spin interactions, then the many electron wave function is an eigenfunction of S[superscript 2]; in addition, the many-electron wave function must satisfy Pauli's principle.\r\n\r\nA method has been developed to obtain explicitly (for any N) many-electron wave functions which simultaneously are eigenfunctions of S[superscript 2] and satisfy Pauli's principle. The method is simple and elegant and lends itself readily to applications. Given any function of the spatial coordinates of N particles,[...], and any function of the spin coordinates of N particles,[...], then [...] is an eigenfunction of S[superscript 2] and satisfies Pauli's principle. We will be particularly interested in the best description of the ground state of the many-electron system by a single [...]. The primary reason for this is that such a description is readily interpretable and, in addition, the energy promises to be rather accurate.\r\n\r\nWith no further restrictions (two different sets of orthonormal one-electron functions are used as the basis for the spatial space, i.e.,different orbitals for different spins, the components of [...] are any N of these one-electron functions) the best [...] approximation to the many-electron wave function is found for any N (number of electrons), any S (total spin), and any nuclear configuration. For a given compound calculations can be made for the various nuclear configurations to determine the molecular structure for each possible value of spin. The optimum set of orbitals are each the solution of a one-electron Hamiltonian and thus can be interpreted as the state of an electron moving in the potential due to the other electrons. In addition, these orbitals are not required to be basis functions of the irreducible representations of the spatial symmetry group (as are the Hartree-Fock orbitals) thus, they may be somewhat localized. These optimum orbitals may be of chemical significance.\r\n\r\nThe very much more restrictive case is considered where only one set of orthonormal basis functions spanning spatial space is used from which to select the N components of [...]. Due to the presence of doubly-occupied orbitals this method leads to rather large correlation errors. Using the [...] method the Hartree-Fock equations and the first order perturbed wave functions thereof are derived.\r\n\r\nThe VO[subscript 2] distorted rutile crystal structure is explained and the (uninvestigated) magnetic structure predicted." }, { "name": "Hanson, Robert Duane", "degree": "PhD", "year": "1965", "title": "Post-Elastic Dynamic Response of Mild Steel Structures", "advisor": "Housner, George W.; Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04152003-093000", "creators": [ { "name": { "family": "Hanson", "given": "Robert Duane" }, "id": "Hanson-Robert-Duane", "display_name": "Hanson, Robert Duane" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/76XX-4687", "abstract": "The current philosophy of earthquake resistant design is that a structure should be able to withstand an extremely strong motion earthquake without collapsing, even though a certain amount of damage is incurred. To make such a design requires a knowledge of the dynamic behavior of structures under large amplitude vibrations. The objective of the work reported here was to investigate the dynamic frequency response characteristics of a mild steel structure vibrating in the plastic range. Comparisons were made of the static, the dynamic, and the theoretical responses of the yielding structure.\r\n\r\nThe behavior of single-story structures having structural steel columns was investigated experimentally by means of horizontally applied forces generated by a shaking machine. The experimentally determined dynamic response showed the decrease in resonant frequency for increases in deflection amplitude which is characteristic of a \"softening spring\" type of nonlinearity. Ultraharmonic response was also observed. Under steady-state oscillations the fraction of equivalent viscous damping varied from 0.0016 at small, elastic deflections to 0.089 at large, plastic deflections. Structural deterioration was observed in both the static and dynamic experiments with a recovery of strength occurring between tests. A completely stable hysteretic loop was not attained at large deflection amplitudes, and the hysteresis loop did not become completely stable until the deflection amplitude was reduced to almost the initial yield value. However, the change in the hysteretic loop per cycle for the large deflections was small enough to permit assuming that a steady-state dynamic condition existed over a limited number of cycles.\r\n\r\nDiscrepancies between the theoretical and the experimental virgin force-deflection curves were found and these are shown to be the result of simplifying approximations introduced in the structural analysis. It was found that the resonant vibrational amplitude of the structure can be predicted within 20%, and the resonant natural frequency within 2-1/2%, on the basis of the static virgin force-deflection curve. For large, plastic deflections at an excitation frequency of 3 cps, it was found that the differences between the dynamic and the static hysteresis loops were less than the changes in the static loops resulting from the deterioration caused by repeated cycles of loading." }, { "name": "Hertel, Robert Henry", "degree": "PhD", "year": "1965", "title": "An Experimental Study of the Hydromagnetic Waveguide", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-04112003-095820", "creators": [ { "name": { "family": "Hertel", "given": "Robert Henry" }, "id": "Hertel-Robert-Henry", "display_name": "Hertel, Robert Henry" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6RG2-ND30", "abstract": "The hydromagnetic waveguide consists of a cylindrical metal tube filled with a longitudinally magnetized plasma. Among the classes of waves which propagate in this system are the compressional hydromagnetic modes, characterized by a waveguide cutoff at low frequencies and by a resonance at the electron cyclotron frequency. This paper presents the results of observations of the propagation of such waves in a decaying hydrogen plasma at frequencies from 0.8 to 3.4 times the ion cyclotron frequency. The phase shift and attenuation of the waves are interpreted in terms of the ion density and the temperature by applying a theory based on a three-fluid description of the plasma. Spectroscopic measurements of the H[subscript beta] line profile and absolute intensity are used to check the density and temperature inferred from the wave measurements.\r\n\r\nThe results of this study indicate that a simple approximate relationship between the phase factor and density obtained by neglecting dissipation gives densities which agree well with the spectroscopic measurements. As a diagnostic tool this method may yield densities to within ? 25%, over a range of two decades. In the case of amplitude measurements only semiquantitative agreement between the wave and spectroscopic measurements is found, but the amplitude curves do show evidence of interferences between modes and a sharp cutoff at a critical density, both effects predicted by the theory." }, { "name": "Hwang, Li-San", "degree": "PhD", "year": "1965", "title": "Flow Resistance of Dunes in Alluvial Streams", "advisor": "Vanoni, Vito A.; Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092003-173224", "creators": [ { "name": { "family": "Hwang", "given": "Li-San" }, "id": "Hwang-Li-San", "display_name": "Hwang, Li-San" } ], "advisors": [ { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "advisor", "display_name": "Vanoni, Vito A." }, { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/HRDZ-N222", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nStudies were made of the hydrodynamic resistance of channels with beds covered with dunes generated by flows over granular sediments of the kind normally found in alluvial rivers. The principal objectives of the studies were to determine the pertinent geometric properties of a dune bed by means of which one can express the dune resistance and to establish a quantitative relation between resistance and these geometric quantities. The main results reported here were obtained through experiments in laboratory flumes.\r\n\r\nA series of 23 experiments with flows over dune-covered beds of fine sand were performed in tilting flumes 130 ft. and 40 ft. in length respectively. In addition, two dune beds generated by different flows were stabilized chemically without disturbing their surface configurations and texture. By doing this, it was possible to explore velocity and pressure distributions in the flow fields and to determine the effect of Reynolds number on the friction factor of the dune beds.\r\n\r\nIt was found that the hydrodynamic roughness of a dune field can be described by the average dune height and the exposure parameter which is the fraction of the total bed area occupied by the horizontal projection of the steep lee slopes of the dunes. It was also found from the results of flume experiments that the bed friction factor due to dunes is a function of the modified relative roughness, [...] , where r[?] is the bed hydraulic radius, e is the exposure parameter defined above and [...] is the average dune height.\r\n\r\nA function for dune resistance in straight uniform channels, that is, Equation (6-1) was established from experimental results obtained in the flume. Friction factors for typical alluvial rivers cannot be calculated from Equation (6-1) above because some important features of streams, such as meandering, which contribute to resistance are not reproduced in flumes." }, { "name": "Kelly, Arnold James", "degree": "PhD", "year": "1965", "title": "Atom-Atom Ionization Mechanisms and Cross Sections in Noble Gases and Noble Gas Mixtures", "advisor": "Marble, Frank E.; Jahn, Robert G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04142003-122732", "creators": [ { "name": { "family": "Kelly", "given": "Arnold James" }, "id": "Kelly-Arnold-James", "display_name": "Kelly, Arnold James" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." }, { "name": { "family": "Jahn", "given": "Robert G." }, "id": "Jahn-R-G", "role": "advisor", "display_name": "Jahn, Robert G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/6CHH-Z732", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation of the initial phase of shock produced ionization in argon, krypton, xenon, and argon-xenon mixtures has been conducted in order to elucidate the atom-atom ionization reaction and to determine the atom-atom ionization cross sections for the gases noted. A high-purity shock tube was employed to heat these gases to temperatures in the range 5000[degrees]K to 9000[degrees]K at neutral particle densities of 4.41x10[superscript 17] cm[superscript -3], 6.96x10[superscript 17] cm[superscript -3], and 13.76x10 [superscript 17] cm[superscript -3], and impurity levels of around 10[superscript -6]. A K-band (24 gcps) microwave system situated so that the microwave beam propagation direction was normal to the shock tube monitored the ionization relaxation process occurring immediately after the passage of the shock front. Electron density was calculated from the microwave data using a plane wave - plane plasma slab interaction theory corrected for near-field effects associated with the coupling of the microwave energy to the plasma. These data, adjusted to compensate for the effects of shock attenuation, verified that the dominant electron generation process involves a two-step, atom-atom ionization reaction, the first step (excitation to the first excited states) being rate determining. The quadratic dependence on neutral density associated with this reaction was experimentally demonstrated (with an uncertainty of [...] 15 per cent). The cross section, characterized as having a constant slope from threshold (first excited-energy level), represented as the cross-sectional slope constant C, was found to be equal to 1.2x10[superscript -19] [...] 15 per cent cm[superscript 2]/ev, 1.4x10 [superscript -19] [...] 15 per cent cm[superscript 2]/ev, 1.8x10 [superscript -20] [...] 15 per cent cm[superscript 2]/ev for argon, krypton, and xenon, respectively. The C factor for argon ionizing xenon was determined to be equal with an uncertainty of [...] 20 per cent to the xenon-xenon C factor, i.e., 1.8x10[superscript -20] cm[superscript 2]/ev. This would imply that, for atom-atom processes in the noble gases at about 1 atmosphere pressure and temperature of about 1 ev, the ionization cross section is independent of the electronic structure of the projectile atom. The electron-atom elastic momentum-exchange cross sections derived from the microwave data correlated quite well with Maxwell-averaged beam data, the agreement for the case of argon being [...] 20 per cent; krypton, [...] 30 per cent; and xenon, within a factor of 2." }, { "name": "Knapp, Karl Kent", "degree": "PhD", "year": "1965", "title": "An Experimental Investigation of Free Convection Heat Transfer to Carbon Dioxide in the Region of its Critical Point", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08262011-100648981", "creators": [ { "name": { "family": "Knapp", "given": "Karl Kent" }, "id": "Knapp-Karl-Kent", "display_name": "Knapp, Karl Kent" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/A4PD-0R66", "abstract": "Experimental results are presented for an investigation of free convection heat transfer to carbon dioxide in the region of its critical point. Shadowgraph images of the flow patterns accompanying the heat transfer have been recorded photographically. A horizontal 0.010-inch-diameter cylindrical Nichrome wire was used as the test section for the primary investigation. Tests were conducted in carbon dioxide with pressures from 1000 psia to 1500 psia and bulk temperatures from 49.0\u00b0 to 137.0\u00b0F.\r\n\r\n\"Bubble-like\" and oscillating flow conditions were observed in the experiments conducted with the cylindrical test section. The occurrence of \"bubble-like\" flow conditions, along with pronounced changes in the fluid properties, resulted in significant improvements\r\nin the heat transfer process, as compared to heat transfer resulting with laminar flow at lower heat fluxes. Additional experiments with a vertical wire and a horizontal strip indicated that the occurrence of the \"bubble-like\" flow depends on the shape and orientation of the heat transfer surface. The results of heat transfer with the \"bubble-like\" flow condition in supercritical carbon dioxide are compared with heat transfer results with\" boiling at subcritical pressures.\r\n" }, { "name": "List, Ericson John", "degree": "PhD", "year": "1965", "title": "The Stability and Mixing of a Density-Stratified Horizontal Flow in a Saturated Porous Medium", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302002-124434", "creators": [ { "name": { "family": "List", "given": "Ericson John" }, "id": "List-Ericson-John", "display_name": "List, Ericson John" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/3THV-YS27", "abstract": "The mixing of two miscible fluids in motion in a saturated isotropic porous medium and the stability of the density interface between them has been studied. The density interface was formed by a line source introducing a denser fluid into a uniform confined horizontal flow. It was shown that the half-body thus formed may be approximated to within the density difference by the shape when the densities are equal. The mixing of the two fluids by lateral dispersion along such an interface was investigated experimentally and it was found that up to density differences of at least 1 per cent there was no observable effect on the lateral dispersion coefficient.\r\n\r\nA theoretical investigation has been made of the stability of the uniform two-dimensional horizontal motion of two miscible fluids of different density in a saturated, isotropic, homogeneous porous medium. The fluid of higher density overlay the lower density fluid and both were moving with the same seepage velocity in the same direction. The analytical solution for the stability was obtained from the continuity equation, Darcy's law and the dispersion equation by investigating the stability of arbitrary sinusoidal perturbations to the velocity vector and the density profile prescribed by the lateral dispersion of one fluid into the other. A stability equation similar to the Orr-Sommerfeld equation was obtained and a neutral stability curve in a wave number - Rayleigh number plane was found by two approximate methods. The growth rates of instabilities were investigated for a linear density profile and it has been found that although the flow was always unstable the growth rates of unstable waves could be so low as to form a quasi-stable flow; examples of such flows have been demonstrated experimentally." }, { "name": "Malhotra, Rajeshwar Kumar", "degree": "PhD", "year": "1965", "title": "Free and Forced Oscillations of a Class of Self-Excited Oscillators", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-092546", "creators": [ { "name": { "family": "Malhotra", "given": "Rajeshwar Kumar" }, "id": "Malhotra-Rajeshwar-Kumar", "display_name": "Malhotra, Rajeshwar Kumar" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "member", "display_name": "Housner, George W." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "member", "display_name": "Knowles, James K." }, { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "member", "display_name": "Sabersky, Rolf H." } ], "option_major": [ "appliedmech" ], "doi": "10.7907/81MF-FT73", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nFree and forced oscillations in oscillators governed by the equation [...] are studied with appropriate constraints on [...]. Theorems are proved on the existence and uniqueness of stable periodic solutions for free oscillations using the Poincare-Bendixson theory in the phase-plane. There follow several examples to illustrate the theorems and limit cycles are obtained for these examples by the Leinard construction. A result on the existence of periodic solutions in the forced case is obtained by use of Brouwer's fixed point theorem. The part on topological methods is concluded by applying Yoshizawa's results on ultimate boundedness of solutions to the forced case.\r\n\r\nApproximate analytical solutions are obtained for specific examples for different regions of validity of the parameter [...]. For free oscillations, the perturbation solution is obtained for small [...]. A Fourier series approximation is given for other values of [...] and the limit cycle for the case [...] is obtained. Finally, the first order solution for forced oscillations is obtained by the method of slowly varying parameters and the stability of this solution is examined." }, { "name": "Masri, Sami Faiz", "degree": "PhD", "year": "1965", "title": "Analytical and Experimental Studies of Impact Dampers", "advisor": "Crede, Charles E.; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-04172003-091816", "creators": [ { "name": { "family": "Masri", "given": "Sami Faiz" }, "id": "Masri-Sami-Faiz", "display_name": "Masri, Sami Faiz" } ], "advisors": [ { "name": { "family": "Crede", "given": "Charles E." }, "id": "Crede-C-E", "role": "advisor", "display_name": "Crede, Charles E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "chair", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Crede", "given": "Charles E." }, "id": "Crede-C-E", "role": "member", "display_name": "Crede, Charles E." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Iwan", "given": "Wilfred D." }, "id": "Iwan-W-D", "role": "member", "display_name": "Iwan, Wilfred D." } ], "option_major": [ "mecheng" ], "doi": "10.7907/XK0P-R658", "abstract": "A study is made of the general behavior of a single particle impact damper, with the main emphasis on symmetric 2 impacts/cycle motion. The exact solution for this case is derived analytically and its asymptotically stable regions are determined. The stability analysis defines the zones where the modulus of all the eigenvalues of a certain matrix relating conditions after each of two consecutive impacts is less than unity.\r\n\r\nResults of the analysis are supplemented and verified by experimental studies with a mechanical model and an analog computer. Additional numerical investigations are made with a digital computer.\r\n\r\nIt is found that, under practically realizable conditions, impact damping is effective in reducing the vibration amplitude levels resulting from sinusoidal, random, or impulse-like excitation." }, { "name": "Pawula, Robert Francis", "degree": "PhD", "year": "1965", "title": "Generalizations and Extensions of the Fokker-Planck-Kolmogorov Equations", "advisor": "Braverman, David J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03182015-145729313", "creators": [ { "name": { "family": "Pawula", "given": "Robert Francis" }, "id": "Pawula-Robert-Francis", "display_name": "Pawula, Robert Francis" } ], "advisors": [ { "name": { "family": "Braverman", "given": "David J." }, "id": "Braverman-D-J", "role": "advisor", "display_name": "Braverman, David J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/K713-DX65", "abstract": "The problem of determining probability density functions of general transformations of random processes is considered in this thesis. A method of solution is developed in which partial differential equations satisfied by the unknown density function are derived. These partial differential equations are interpreted as generalized forms of the classical Fokker-Planck-Kolmogorov equations and are shown to imply the classical equations for certain classes of Markov processes. Extensions of the generalized equations which overcome degeneracy occurring in the steady-state case are also obtained.
\r\n\r\nThe equations of Darling and Siegert are derived as special cases of the generalized equations thereby providing unity to two previously existing theories. A technique for treating non-Markov processes by studying closely related Markov processes is proposed and is seen to yield the Darling and Siegert equations directly from the classical Fokker-Planck-Kolmogorov equations.
\r\n\r\nAs illustrations of their applicability, the generalized Fokker-Planck-Kolmogorov equations are presented for certain joint probability density functions associated with the linear filter. These equations are solved for the density of the output of an arbitrary linear filter excited by Markov Gaussian noise and for the density of the output of an RC filter excited by the Poisson square wave. This latter density is also found by using the extensions of the generalized equations mentioned above. Finally, some new approaches for finding the output probability density function of an RC filter-limiter-RC filter system driven by white Gaussian noise are included. The results in this case exhibit the data required for complete solution and clearly illustrate some of the mathematical difficulties inherent to the use of the generalized equations.
" }, { "name": "Peck, Jerry Clifford", "degree": "PhD", "year": "1965", "title": "Plane-Strain Diffraction of Transient Elastic Waves by a Circular Cavity", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-144633", "creators": [ { "name": { "family": "Peck", "given": "Jerry Clifford" }, "id": "Peck-Jerry-Clifford", "display_name": "Peck, Jerry Clifford" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/GDNE-E586", "abstract": "The plane-strain problem of the diffraction of a transient plane dilatation wave by a circular cavity in an elastic medium is treated. The method used determines the (total) solution only in the shadow zone, i.e., those points which cannot be connected to the source of disturbance by straight-line rays. Numerical results are obtained for the velocities and displacements on the \"back\" surface of the cavity caused by a step-stress incident wave.\r\n\r\nThe analysis is based on a method devised by Friedlander (see his book Sound Pulses, Cambridge, 1958) for the analogous acoustic diffraction problem. This method converges most rapidly at short time, in contrast to Fourier series methods. The Friedlander method essentially employs integral transforms on both time and [Theta], the circumferential coordinate. In the shadow zone, the [Theta]-inversion can be performed by residue theory, the residues resulting from poles at the roots of a \"frequency equation.\" The roots are infinite in number, and may be regarded as forming a dispersion spectrum relating the frequencies and angular wave numbers of a series of circumferential propagation modes. The time-transform inversion is carried out by contour integration and subsequent numerical evaluation.\r\n\r\nThe transient response results are found to compare well with the Fourier-series solutions at moderate to long times, but at short time the differences are marked, as would be expected. The fact that the present technique yields good long-time results suggests it is even more powerful than might be expected. The major limitation of the numerical method is its restriction to the shadow zone." }, { "name": "Specht, Walter Albert", "degree": "PhD", "year": "1965", "title": "Part I. Modes in Spherical-Mirror Resonators. Part II. Dominant Mode Calculations in Output-Coupled Infinite Strip Mirror Resonators", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122004-102010", "creators": [ { "name": { "family": "Specht", "given": "Walter Albert" }, "id": "Specht-Walter-Albert", "display_name": "Specht, Walter Albert" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/P9W2-EX19", "abstract": "PART I\r\n\r\nThis work is the examination of a cavity mode approach to the mode structure of a laser. Solutions of the vector wave equation for electromagnetic fields in and between perfectly conducting oblate spheroidal cavities are examined for the case of wavelengths much less than cavity dimensions. These solutions are the field modes in Fabry-Perot type resonators with equal-radius concave spherical mirrors, or with concave-convex spherical mirrors, when the parameters of the oblate spheroids are chosen so that the radii of curvature and spacing on the axis of rotation match those of the resonator mirrors. Expressions for the transverse and longitudinal mode structures are derived. The eigenvalue equations are written, and are solved for the case of the two lowest order modes.\r\n\r\nPart II\r\n\r\nThis work is the numerical calculation of the steady state lowest order even and odd symmetry electromagnetic field patterns at the mirrors of the multimode resonator formed by two plane-parallel infinite strip mirrors, modified for output coupling by central strips of zero reflectivity. The equation solved is the scalar Huyghens-Fresnel integral equation (a transverse electromagnetic wave approximation to the vector integral equation, valid when the wavelength is much less than the cavity dimensions) relating the fields at the two mirrors, converted to an eigenvalue equation, and approximated for calculations by a matrix eigenvalue equation. The mode structure, power loss and phase shift per transit, and output coupling are discussed." }, { "name": "Swedlow, Jerold Lindsay", "degree": "PhD", "year": "1965", "title": "The Thickness Effect and Plastic Flow in Cracked Plates", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-100109", "creators": [ { "name": { "family": "Swedlow", "given": "Jerold Lindsay" }, "id": "Swedlow-Jerold-Lindsay", "display_name": "Swedlow, Jerold Lindsay" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0WVE-W364", "abstract": "Over a range of plate thickness, it is well known that the fracture behavior of flat plates is substantially different from that predicted by classical fracture analyses. Finiteness of the plate thickness causes a variety of failure mechanisms to occur, and qualitative features of the associated stress and strain fields may be deduced. It is indicated that both the three-dimensional nature of the stress field and the plastic deformations will be needed for an accurate prediction of the thickness effect.\r\n\r\nAs a contribution to the three-dimensional analysis, an appropriate elastic boundary value problem is given limited consideration. It is observed that the three in-plane stresses can be singular, in accord with the two-dimensional results, but the transverse components appear to be bounded at the crack tip.\r\n\r\nEquations which include plastic behavior are outlined, and a plane stress problem is solved using numerical methods. Comparison with analytical and experimental results is made and found to be satisfactory. One important result indicates that, compared to the elastic solution, the intensity of stress at the crack point decreases with load, while that for strain increases.\r\n\r\nThe results do not include determination of a fracture stress, as this further step requires the development of an elastoplastic fracture criterion. Comments on this extension are included, together with other aspects of future work." }, { "name": "Townes, Harry Warren", "degree": "PhD", "year": "1965", "title": "Flow Over a Rough Surface", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01292004-094820", "creators": [ { "name": { "family": "Townes", "given": "Harry Warren" }, "id": "Townes-Harry-Warren", "display_name": "Townes, Harry Warren" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/NTR6-2Q13", "abstract": "NOTE: text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation was conducted on the flow over a rough surface. The roughness consisted of sets of square cavities ranging in size from 1/8 to 1 in. The flow over this series of roughness was observed for a range of [...] values from 11 to 260. The quantity [...] may be regarded as a Reynolds number for the roughness and it is the essential parameter governing the flow over the roughness elements. It is defined as [...] where [...] is the cavity depth, [...] is the shear velocity, and [...] the kinematic viscosity of the fluid. The desired approaching flow was obtained in an open surface water channel at free stream velocities of from 0.1 to 0.75 ft/sec. The velocity profile showed the characteristics of a turbulent boundary layer. The velocity measurements necessary to determine the profile were obtained by means of a hot film anemometer.\r\n\r\nVisualization of the flow in the cavities lead to the classification of five characteristic flow types or modes. The observations could be described consistently in terms of these modes and as a function of [...]. At values of [...] below 100 different mode forms appeared periodically and large disturbances of the fluid within the cavity were noted. This type of flow had not been observed previously. At values of [...] beyond about 200 a rather stable vortex formed in the cavities, as had been reported by previous experimenters. Some possible effects of the flow behavior on heat transfer are discussed.\r\n\t\r\nPhotographic materials on pp. 106-150 are essential and will not clearly reproduce on Xerox copies. Photographic copies should be ordered." }, { "name": "Van Atta, Charles William", "degree": "PhD", "year": "1965", "title": "Spiral Turbulence in Circular Couette Flow", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262004-102054", "creators": [ { "name": { "family": "Van Atta", "given": "Charles William" }, "id": "Van-Atta-Charles-William", "display_name": "Van Atta, Charles William" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/73GQ-A629", "abstract": "Under certain conditions, the fluid motion between counter-rotating concentric cylinders is made up of alternate helical stripes of laminar and turbulent flow. The present experiments show that, over a large range of cylinder Reynolds numbers, this helical pattern of turbulence rotates steadily at very nearly the mean angular velocity of the two cylinders. When the speed of the outer cylinder is held fixed and the speed of the inner cylinder increases from rest in the opposite direction, spiral turbulence follows a catastrophic breakdown of the toroidal vortices arising from Taylor instability.\r\n\r\nThe ultimate objective of the present experiments is to measure the local rate of energy transfer between the turbulence and the mean motion in a typical spiral turbulent flow. The working fluid is air, and the instrumentation consists of hot-wire anemometers together with a variety of devices for operating on the resulting signals. Each cycle of the mixed laminar-turbulent flow (as observed by a probe mounted on one or the other cylinder) is treated as a member of an ensemble of realizations. The energy transfer (in a coordinate system rotating with the mean velocity of the turbulence) can be determined by averaging over a large number of instantaneous velocity samples taken at corresponding points in successive cycles of the turbulence.\r\n\r\nAfter some exploratory measurements, particular flow was selected for which the laminar-turbulent interfaces were sharply delineated across the entire annular gap and for which the dispersion in interface location was a minimum. This flow is about half laminar and half turbulent: it is characterized by a nose of turbulence associated with the leading interface and projecting into the laminar region near the outer cylinder, while a corresponding tail near the inner cylinder is associated with the trailing interface. The helical pattern is lefthanded and makes an angle of about 62 degrees with the axis of the cylinders.\r\n\r\nFor the flow in question, analog voltage signals from a calibrated array of four hot wires were first recorded on magnetic tape. Several thousand cycles of turbulence were recorded at each of 17 different radial positions. Sampled values from these signals were then obtained and stored in digital form on magnetic tape, and were finally processed by a large electronic computer to restore the voltage data to the original laboratory units. The total amount of didital information available to describe the turbulence is roughly 180,000,000 bits. The amount of noise introduced into the individual sampled voltages by the recording, playback, digitizing, and processing operations so far carried out is believed to be no more than 3 parts in 10,000.\r\n" }, { "name": "Venezian, Giulio", "degree": "PhD", "year": "1965", "title": "I. Fluid Flow in a Precessing Spherical Cavity. II. Electromagnetic Radiation from an Expanding Sphere in a Magnetic Field", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222004-095044", "creators": [ { "name": { "family": "Venezian", "given": "Giulio" }, "id": "Venezian-Giulio", "display_name": "Venezian, Giulio" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/CVPG-CK78", "abstract": "In Part I the flow of an incompressible fluid inside a precessing spherical cavity is studied. The precession angle is assumed small and the equations of motion are linearized. For the case of large viscosity an expansion is developed in inverse powers of the viscosity by expanding the velocity field in vector spherical harmonics. The flow obtained is essentially rigid body motion. The case of low viscosity is also studied. At low precession rates difficulties arise in the boundary layer treatment and the inviscid equations. A modified boundary layer equation is derived and an approximate solution obtained. The flow consists essentially of rotation about the average axis of rotation. Some geophysical aspects of the problem, and in particular its relevance to dynamo theories of the earth's magnetic field are discussed.\r\n\r\nPart II deals with the electromagnetic fields about a perfectly conducting sphere which is placed in a uniform magnetic field. The radiation fields that result when the radius of the sphere is allowed to change are investigated. Explicit expressions are obtained for the cases of a sphere expanding or collapsing at a uniform rate. In the latter case it is found that wave propagation and energy propagation are in opposite directions. Constant speed oscillations are also investigated and the effect of the amplitude on the power radiated is considered. The case of arbitrary motions of the radius is also discussed." }, { "name": "Wade, Richard Bernard", "degree": "PhD", "year": "1965", "title": "Investigations on Cavitating Hydrofoils", "advisor": "Acosta, Allan J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222004-112658", "creators": [ { "name": { "family": "Wade", "given": "Richard Bernard" }, "id": "Wade-Richard-Bernard", "display_name": "Wade, Richard Bernard" } ], "advisors": [ { "name": { "family": "Acosta", "given": "Allan J." }, "id": "Acosta-A-J", "role": "advisor", "display_name": "Acosta, Allan J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/8YEC-DS05", "abstract": "Experimental and theoretical results are presented for the non-cavitating and cavitating performances of a plano-convex hydrofoil in both the isolated and cascade configurations.\r\n\r\nIn the isolated hydrofoil tests special emphasis is placed on the unsteady region of cavitation separating the partially cavitating region from the fully cavitating region. The detailed behavior of the oscillating cavity together with the magnitude of the force vibrations that occur in this region are investigated from both a qualitative and a quantitative viewpoint. The dependence of the reduced frequency of these oscillations on the angle of attack, cavitation number and flow velocity is also discussed.\r\n\r\nThe performance of the hydrofoil under steady conditions in both the cavitating and non-cavitating regions is also presented. Details of the test equipment and procedures used and various data corrections made are given.\r\n\r\nA linearized partially cavitating theory for this plano-convex hydrofoil is also developed which includes camber and thickness effects. The results from this theory are compared with the experimental data obtained.\r\n\r\nIn the cascade experiments a feasibility study is undertaken to determine the possibility of using the high speed water tunnel at the California Institute of Technology as a cascade tunnel for investigating the cavitating performance of compressor and turbine cascades. A comprehensive design study is given of the modifications made to the existing tunnel to achieve this aim. The experimental procedures used in conducting the experiments are then discussed. Tests are performed on two compressor cascades of plano-convex hydrofoils having solidities of 1.25 and 0.625 and cascade angle of 45 degrees, for all conditions of cavitation from the fully wetted to the fully choked conditions. A study is also made of a turbine cascade of solidity 1.25 for the same cascade angle in the non-cavitating region only. Comparisons of the experimental data with several theories indicate that the cascade tests are indeed fulfilling their purpose in proving the methods used in simulating cascade conditions in the tunnel.\r\n\r\nProposals for modifying the system used to avoid several experimental difficulties are presented. Finally, a linearized theory for a cascade of partially cavitating flat plate hydrofoils is developed which is compared with the data obtained." }, { "name": "Wiberg, Donald Martin", "degree": "PhD", "year": "1965", "title": "Optimal Feedback Control of Spatial Xenon Oscillations in a Nuclear Reactor", "advisor": "Shapiro, Jerome L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222004-113136", "creators": [ { "name": { "family": "Wiberg", "given": "Donald Martin" }, "id": "Wiberg-Donald-Martin", "display_name": "Wiberg, Donald Martin" } ], "advisors": [ { "name": { "family": "Shapiro", "given": "Jerome L." }, "id": "Shapiro-J-L", "role": "advisor", "display_name": "Shapiro, Jerome L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/KFA4-3K71", "abstract": "A kinetic model of spatial processes in a nuclear power reactor is formulated according to the state space approach. The model is very general, and may include the spatial effects of control rods, temperature, and almost any other deterministic spatial process that can be described by a finite set of partial differential equations. It is noted that any locally unstable process may induce a spatial instability, and that a spatial instability will occur only if a local process is unstable. The concept of a temperature coefficient of reactivity is extended to include spatial variations. A linearization about an operating point is performed, and the resulting linear equations are solved by using a non-interacting modal expansion. Some properties of this type of mode and applications to other physical processes are discussed. It is shown that non-interacting modes exist whenever any other modal expansion exists. An efficient computational procedure for exact numerical solution for the non-interacting modes is given in the case of spatial separability. Simple linear stability estimates for spatial processes are formed by variational techniques which permit evaluation of the effects of spatially varying parameters upon stability. A theorem presents mathematical proof of the linear controllability of any finite number of modes by very few control rods. The circumstances under which an infinite number of modes can be controlled are discussed. Finally, methods of optimal feedback control are used for the analytical design of a spatial control system for minimum integrated quadratic loss, and detailed examples are given." }, { "name": "Wu, Jain-Ming", "degree": "PhD", "year": "1965", "title": "A Satellite Theory and its Applications", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-104844", "creators": [ { "name": { "family": "Wu", "given": "Jain-Ming" }, "id": "Wu-Jain-Ming", "display_name": "Wu, Jain-Ming" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2XH7-1828", "abstract": "A theory of an Earth satellite has been developed by considering the Earth's bulge, atmospheric drag and the rotation of the atmosphere simultaneously. The equations of motion have been set up on a tilted equatorial plane coordinate system. All of the orbital variables have been expanded in a series in terms of a perturbative force parameter based on the Keplerian orbit. These equations have been linearized and then solved. By means of geometrical arguments, all of the above solutions have been expressed in the form of conventional orbital elements. In the limiting case, these solutions agree with the classical values. One previously neglected effect, the rotation of the line of apsides by drag, is identified and evaluated. The results have been used to show the correction due to the effect of the above-mentioned forces on the Earth's gravitational potential." }, { "name": "de Pencier, Robert Dewey", "degree": "PhD", "year": "1965", "title": "Genesis of a Machine : a Production Paper Cutter", "advisor": "Morelli, Dino A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242003-104639", "creators": [ { "name": { "family": "de Pencier", "given": "Robert Dewey" }, "id": "de-Pencier-Robert-Dewey", "display_name": "de Pencier, Robert Dewey" } ], "advisors": [ { "name": { "family": "Morelli", "given": "Dino A." }, "id": "Morelli-D-A", "role": "advisor", "display_name": "Morelli, Dino A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/WTQD-CQ41", "abstract": "The evolution of a new machine is described, from an idea conceived in 1960 to a prototype operative in September 1964. The emphasis is on the decisions, methods, criteria, and results incorporated in the machine rather than on analytical aspects of the design. The primary criterion guiding the design was to provide a machine more economical for users to own.
\r\n\r\nA description is given of the machine, PC 64, which is a new completely hydraulic 42 in. x 4 in. capacity production paper cutter of the guillotine type, weighing less than 3000 lbs. Introduction of the essentials of a guillotine cutter and analysis of a 1960 commercial machine are used to establish reference limits for the new machine. Results of cutting tests performed to determine the most advantageous cutting angle are included.
\r\n\r\nImportant new features of PC 64 include a single shear straightline motion knife drive powered by a single hydraulic cylinder, and a hydraulically driven and controlled backstop. Optional automatic control for the backstop is accomplished by means of notched program bars affording trimout cuts to .015 in. It is shown that for any cutting angle selected, the height, width, and length of PC 64 cannot be reduced further.
\r\n\r\nThe machine is evaluated by comparison with commercial cutters marketed prior to and during the project. From the comparison it is concluded that features of PC 64 have commercial potential and that the primary criterion has been met.
\r\n\r\nPhotographic materials on pages 11, 48, 49, 162, 163 and 181 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.
" }, { "name": "Arenz, Robert James", "degree": "PhD", "year": "1964", "title": "Theoretical and Experimental Studies of Wave Propagation in Viscoelastic Materials", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09072002-150755", "creators": [ { "name": { "family": "Arenz", "given": "Robert James" }, "id": "Arenz-Robert-James", "display_name": "Arenz, Robert James" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E8KM-6M98", "abstract": "The phenomenon of wave propagation in viscoelastic materials is investigated both theoretically and experimentally, with attention directed to two areas. First, analytical methods of solution are developed for certain wave propagation problems in one and two dimensions utilizing realistic material properties. This is accomplished by use of time-dependent material property characterization through a Dirichlet series representation to overcome the limitations of the widely-used simple spring and dashpot models involving two or three elements. The Laplace transformed solutions are then inverted by an extension of the Schapery collocation method to dynamic situations.\r\nThe second topic deals with dynamic photoelasticity applied to viscoelastic materials. It is shown that the relationships between stress optic and strain optic coefficients for linearly viscoelastic materials can be formulated. Then the time-dependent birefringence characteristics of a typical low modulus polymer material are determined from constant strain rate tests for a full range of dynamic loading rates by taking advantage of the time-temperature shift phenomenon. Much recent work in dynamic photoviscoelasticity has been based on static calibrations only. Hence to put the technique on a firm foundation and indicate the general necessity of including the time dependency in treatment of material properties, a comparison is made of predicted fringe patterns with experimental results for both one- and two-dimensional situations. The cases considered are the rod and semi-infinite plate geometries under quasistep pressure inputs, for which viscoelastic solutions are obtained from the wave propagation analysis in the first part of the thesis. The results indicate the feasibility of quantitative photoviscoelasticity for dynamic stress analysis." }, { "name": "Auksmann, Boris", "degree": "PhD", "year": "1964", "title": "Investigation of Mechanical Seals", "advisor": "Morelli, Dino A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162002-110114", "creators": [ { "name": { "family": "Auksmann", "given": "Boris" }, "id": "Auksmann-Boris", "display_name": "Auksmann, Boris" } ], "advisors": [ { "name": { "family": "Morelli", "given": "Dino A." }, "id": "Morelli-D-A", "role": "advisor", "display_name": "Morelli, Dino A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/41WJ-PW93", "abstract": "A general description of the mechanical seal problem is given with references to historical background.\r\n\r\nThe design criteria, establishing the basic configuration, and the evolution of the final design of the experimental apparatus are presented in detail. The description of the supporting equipment and instrumentation is given; calibration curves are included in the appendix. The modifications and suggested improvements in the apparatus are discussed in detail. A complete set of manufacturing drawings for the apparatus that was built and used for the experimental work is on file in the Mechanical Engineering Department of California Institute of Technology; the drawings are not included in the thesis, but prints or microfilm copies are available.\r\n\r\nIn the experimental work, the qualitative determination of the clearance geometry and the fluid film behavior in the clearance of an operating seal are described. Measured leakage rates and friction coefficients are presented in graphical form together with the pertinent operating variables. Photographs of typical interference fringe patterns and seal face failures at various stages are included.\r\n\r\nThe sealing mechanism is established and discussed with references to the photographs and numerical data. The usefulness of the balance ratio of a mechanical seal as a basic parameter is established; the correlation of leakage rates and friction coefficient values with the balance ratio and other operating variables is discussed. The frictional heat rate per unit seal area is shown to be the important criterion for predicting seal failures under different operating conditions. An evaluation of experimental errors is included.\r\n\r\nIn conclusion a program is proposed for continuation of the experimental work and salient points in the results are summarized.\r\n" }, { "name": "Baganoff, Donald", "degree": "PhD", "year": "1964", "title": "Experiments on the Wall-Pressure History in Shock Reflection Processes", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-083236", "creators": [ { "name": { "family": "Baganoff", "given": "Donald" }, "id": "Baganoff-Donald", "display_name": "Baganoff, Donald" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XK5D-HZ55", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe normal reflection of a plane shock from a plane wall is investigated experimentally using a pressure gauge which has a risetime of 0.1 [....] and no overshoot. Pressure histories of 5 [.....] duration can be obtained with this gauge. The experiments were conducted on the end wall of the GALCIT 17-in.-diameter shock tube.\r\n\r\nExperimental results for three aspects of the reflection process are discussed: (1) profile for the reflected shock front, (2) effect of a cold wall, and (3) effect of a real gas.\r\n\r\nIt is concluded that the effect of a cold wall must play a comparatively minor role in the reflection process since the thickness of the recorded profile is comparable to the thickness of the incident shock, and the pressure jump across the profile is about 85 per cent of the ideal value. Also, the pressure history immediately behind the reflected shock can be approximated by boundary layer theory. The effect of a real gas was studied in carbon dioxide and it is shown that the relaxation process behind the incident shock produces a large effect on the recorded pressure history which provides a method of measuring the vibrational relaxation time in carbon dioxide for high temperatures." }, { "name": "Bush, William B.", "degree": "PhD", "year": "1964", "title": "On the Viscous Hypersonic Blunt-Body Problem", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102002-143008", "creators": [ { "name": { "family": "Bush", "given": "William B." }, "id": "Bush-William-B", "display_name": "Bush, William B." } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QCBK-ZD50", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nThe viscous hypersonic flow past an axisyrnmetric blunt-body is analyzed based upon the Navier-Stokes equations for a perfect gas having constant specific heats, a constant Prandtl number, P, whose numerical value is of order one, and a viscosity varying as a power, [...], of the absolute temperature, as the free-stream Mach number, M, and the freestream Reynolds number based on the body nose radius, R, go to infinity, and [...] (where [gamma] is the ratio of the specific heats) and [...] go to zero.\r\n\r\nThrough the use of strict asymptotic expansions, the behavior of the flow in the three distinct regions that comprise the interior of the \"shock structure\" is found, as well as for the one, two, or three regions that make up the \"shock layer\" depending on whether the quantity [...] is equal to [...], equal to [...], or greater than [...], respectively." }, { "name": "Clark, Peter Osgoode", "degree": "PhD", "year": "1964", "title": "An Analysis of Multireflector Optical Resonators", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112002-181405", "creators": [ { "name": { "family": "Clark", "given": "Peter Osgoode" }, "id": "Clark-Peter-Osgoode", "display_name": "Clark, Peter Osgoode" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/M4PW-BM47", "abstract": "Geometrical optics and self-consistent field techniques are used to determine the properties of multireflector optical resonators in which the field distributions are multiply-reflected and travel in clockwise and counter-clockwise directions in the cavity. Two types of resonators are considered, a symmetric N-mirror resonator whose axis is a regular N-sided polygon and a nonsymmetric four-mirror resonator whose axis is a parallelogram.\r\n\r\nThe geometrical optics approach leads to sets of coupled nonlinear difference equations which describe the paths of optical rays in the resonators. Approximate solutions to the equations are obtained and a calculation of the first correction term is carried out in the case of the symmetric cavity. It is shown that the approximate analysis may also be formulated in a chain matrix representation. Stability conditions are obtained which determine the mirror curvatures and spacings for high or low-loss multireflector resonators. The set of difference equations may be reduced to recurrence relations which enable the path of an optical ray in the cavity to be calculated exactly using a digital computer.\r\n\r\nIntegral equations are obtained which determine the mode distributions in the symmetric N-mirror and nonsymmetric four-mirror cavities. The equations are not solved exactly except in the particular case of a \"pseudo-confocal\" symmetric resonator which has non-spherical mirrors. Solutions to the general integral equations are determined in the zero wavelength limit. Resonance conditions and detailed descriptions of the field distributions are obtained for both the symmetric and nonsymmetric resonators. For the particular cases of the symmetric three and four-mirror resonators the diffraction losses are obtained by transforming the integral equations to a form such that existing numerical solutions may be used.\r\n\r\nTwo-mirror cavities are treated as simplifications of the multireflector theory. The results of other authors are obtained and extended. The expressions for the resonance condition and minimum mode volume for the symmetric nonconfocal resonator are found to differ slightly from those previously derived. Amplitude and phase distributions throughout the volume of a plane-parallel Fabry-Perot resonator are calculated numerically on an IBM 7090 computer." }, { "name": "Collette, Ren\u00e9 Cl\u00e9ment", "degree": "PhD", "year": "1964", "title": "Domain Walls, Demagnetizing Fields and Anisotropy in Thin Ferromagnetic Films", "advisor": "Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-092748", "creators": [ { "name": { "family": "Collette", "given": "Ren\u00e9 Cl\u00e9ment" }, "id": "Collette-Ren\u00e9-Cl\u00e9ment", "display_name": "Collette, Ren\u00e9 Cl\u00e9ment" } ], "advisors": [ { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/BSKM-G135", "abstract": "The so-called Neel walls separating antiparallel domains in very thin ferromagnetic films are found, on the basis of accurate calculations, to have a shape differing significantly from the linear rotation model suggested by Neel. In this 180 [degree] rotation, three regions can be distinguished: a central one where the magnetization [...] rotates rapidly (positive demagnetizing energy) and two adjacent regions extending in the neighboring domains where the rotation is very much slower. In these \"tail\" portions of the curve, the direction of [...] is determined mostly by a balance between the anisotropy torque and the torque due to the internal field. The calculations have been performed for permalloy films with thicknesses ranging from 0 to 200 [angstroms]. The walls extend up to several microns, in each of the adjacent domains (of the order of 15 [microns] at a thickness of 200 [angstroms].\r\n\r\nAs a continuation of the study of infinite Neel walls, the case of double walls (360 [degree] rotation) and of cross-tie walls is also analysed on a semiquantitative basis. The main characteristics of these two configurations can be explained on the basis of the new model found for the pure Neel walls.\r\n\r\nIn a second section, the internal demagnetizing field H[subscript i] is calculated as a function of the shape, the thickness and the edge profile of the film. Along the edges perpendicular to the easy direction, the growth of peaks of reverse magnetization is studied when the external field varies. Also the detailed configuration of the internal field at the edge is found to depend strongly on the profile of the latter. By varying the slope of a tapered edge, it is shown that (H[subscript i])[...] can be reduced to such a small value that nucleation will take place only at an external field larger in absolute value than the normal coercive force of the film. Thus the hysteresis curve along the easy direction is noticeably altered and very square.\r\n\r\nIn a third section, an instrument is presented for the study of the magnetic anisotropy in the plane of the film. This apparatus is particularly suitable for determining the anisotropy field, the single domain state being preserved at all times" }, { "name": "Evensen, David Arthur", "degree": "PhD", "year": "1964", "title": "Non-Linear Flexural Vibrations of Thin Circular Rings", "advisor": "Sechler, Ernest Edwin; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-165232", "creators": [ { "name": { "family": "Evensen", "given": "David Arthur" }, "id": "Evensen-David-Arthur", "display_name": "Evensen, David Arthur" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7D5J-3C40", "abstract": "The non-linear flexural vibrations of thin circular rings are analyzed by means of the appropriate \"shallow shell\" equations. These partial differential equations are reduced to non-linear ordinary differential equations by assuming vibration modes and applying Galerkin's procedure. Vibrations involving primarily a single bending mode are investigated for three distinct cases, and the results indicate that the basic features of the problem are exhibited by an inextensional analysis.\r\n\r\nThis information is then applied to simplify the analysis of vibrations in which several modes participate. A study of \"self-coupled\" bending modes shows that the single mode solution is valid only for certain combinations of amplitude and frequency: when the single mode exceeds a \"critical amplitude\", its companion mode is parametrically excited and participates in the motion.\r\n\r\nThe general inextensional case (involving an infinite number of modes) is examined for two important sets of forces, and possible solutions are shown to be the excitation of primarily one or two bending modes. Stability analyses of these solutions indicate that when certain restrictions are met, all other bending modes play only a minor part in the vibration.\r\n\r\nAn experimental study of the problem was also conducted. Theory and experiment both indicate a non-linearity of the softening type, the presence of ultraharmonic responses, and the appearance of the companion mode. Measurements of the steady-state response are in good agreement with the calculated values, and the experimentally determined mode shapes agree with the form of the assumed deflection.\r\n\r\nThe analytical and experimental results exhibit several features that are common to the non-linear vibration of axisymmetric systems in general and to circular cylindrical shells in particular." }, { "name": "Fehlberg, William Thomas", "degree": "PhD", "year": "1964", "title": "Thermal Neutron Distributions near Material Discontinuities", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132002-091916", "creators": [ { "name": { "family": "Fehlberg", "given": "William Thomas" }, "id": "Fehlberg-William-Thomas", "display_name": "Fehlberg, William Thomas" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/GSNH-HP15", "abstract": "A method is presented for the approximate calculation of the neutron flux near plane interfaces between different heavy monatomic gaseous media with absorption cross sections inversely proportional to the neutron velocity. Approximate analytic results are obtained for both the diffusion theory and transport theory models. It is found that the flux on each side of the interface can be approximated by the sum of two terms. One term has the same energy dependence that would exist in an infinite medium composed of the heavy monatomic gas that is on that side of the interface. The spatial dependence of this term is determined by diffusion theory. The other term, called a boundary layer correction, makes an appreciable contribution to the flux only near the interface. The procedure presented develops equations and boundary conditions which determine the different terms of the approximate flux. It is found that the approximate flux at the interface, for both diffusion and transport theory, is the average of the two infinite medium fluxes." }, { "name": "Folias, Efthymios Stefanos", "degree": "PhD", "year": "1964", "title": "The Stresses in a Spherical Shell Containing a Crack", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132002-104440", "creators": [ { "name": { "family": "Folias", "given": "Efthymios Stefanos" }, "id": "Folias-Efthymios-Stefanos", "display_name": "Folias, Efthymios Stefanos" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/N4ST-K607", "abstract": "NOTE: There is a 3-page Notation Eqivalency Chart preceding the Introduction. \r\nNOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Introduction is included in .pdf document.\r\n\r\nChapter I \r\n\r\nIntroduction\r\n\r\nOne of the problems in fracture mechanics which apparently has not received extensive theoretical treatment is that concerning the effect of initial curvature upon the stress distribution in a thin sheet containing a crack. Considerable work has been carried out on initially flat sheets subjected to either extensional or bending stresses, and for small deformations the superposition of these separate effects [1] is permissible. On the other hand, if a thin sheet is initially curved, a bending load will generally produce both bending and extensional stresses, and similarly a stretching load will also induce both bending and extensional stresses. The subject of eventual concern therefore is that of the simultaneous stress fields produced in an initially curved sheet containing a crack.\r\n\r\nTwo geometries immediately come to mind: a spherical shell, and a cylindrical shell. In the latter case one of the principal radii of curvature is infinite and the other constant. It might appear therefore that this geometric simplicity leads to a rather straightforward analytical solution. However, the fact that the curvature varies between zero and a constant as one considers different angular positions - say around the point of a crack which is aligned parallel to the cylinder axis - more than obviates the initial geometric simplification. For this reason a spherical section of a large radius of curvature constant in all directions is chosen for consideration.\r\n\r\nIt is of some practical value to be able to correlate flat sheet behavior with that of initially curved specimens. In experimental work, for example, considerable time could be saved if a reliable prediction of curved sheet response behavior could be made from flat sheet tests. For this reason an exploratory study was undertaken to assess analytically how the two problems might be related. Although it is recognized that elastic analysis is not directly applicable to fracture prediction because of the plastic flow near the crack tip, considerable information can be obtained.\r\n\r\nChapter II lists the basic assumptions and equations of shallow spherical shells. Then the complementary problem of a cracked spherical shell is formulated in terms of Reissner's shallow shell equations in Chapter III where the problem is separated into two parts, symmetric and antisymmetric. In Chapters IV and V the solutions to the symmetric and antisymmetric parts respectively are expressed in integral form. They are then reduced to the solution of a pair of coupled singular integral equations, which are solved by successive approximations for small values of the characteristic shell parameter [...]. No effort was made to convert the pair of singular integral equations to a corresponding Fredholm type, however Appendix II shows that the two methods are equivalent.\r\n\r\nThe particular example of a clamped segment of a thin shallow spherical shell is considered in Chapter VI which serves to illustrate how the local solution may be combined in a particular case. Then in Chapter VII, Griffith's criterion is extended to the local region of an initially spherical curved sheet and an expression for its critical crack length is obtained.\r\n\r\nFinally, Chapter VIII compares the experimental and theoretical results for the particular problem described in Chapter VI." }, { "name": "Gibson, Edward George", "degree": "PhD", "year": "1964", "title": "Ionization Phenomena in a Gas-Particle Plasma", "advisor": "Zukoski, Edward E.; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182002-091822", "creators": [ { "name": { "family": "Gibson", "given": "Edward George" }, "id": "Gibson-Edward-George", "display_name": "Gibson, Edward George" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/B2A5-KH20", "abstract": "Several interesting and practically important types of ionization phenomena which occur in a plasma that is composed of thermionically-emitting particles and an ionized gas, have been investigated. There are many interactions that can take place between the particles and the gas which are able to alter the electron density of the plasma appreciably from what it would be in the absence of the particles. Several of these interactions have been explored. Throughout all of the analysis, the emphasis has been placed on gaining a physical understanding of the basic phenomena which are involved.\r\n\r\nIn order to determine the nature of the potential and charge distributions which exist in a gas - particle plasma, the problem in which there is no gaseous ionization and equilibrium prevails has first been thoroughly investigated. Using a family of numerical solutions to Poisson's equation, it has been shown that these distributions can be divided into two characteristic regimes and that a simple algebraic expression, which has been derived, is a good approximation to the potential distribution in one of them. A readily applied method of calculation of the electron density in the plasma and a study of the dependence of this density on the initial parameters which enter the problem have been presented.\r\n\r\nThe relations which are required in order to analyze non-equilibrium ionization phenomena in a gas - particle plasma have been formulated and then applied to various special cases. The case which has received the major emphasis is that in which the particles are hotter than the gas and an enhancement in the gaseous ionization results. It has been shown that this enhancement could be quite large. Electron absorption by the particles, particle quenching of the gaseous ionization, and the supression of either particle or gas ionization, due to the presence of the other, have also been investigated" }, { "name": "Goldstein, Robert", "degree": "PhD", "year": "1964", "title": "Quantitative Spectroscopic Studies on the Infrared Absorption by Water Vapor and Liquid Water", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09182002-095900", "creators": [ { "name": { "family": "Goldstein", "given": "Robert" }, "id": "Goldstein-Robert", "display_name": "Goldstein, Robert" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/5NW0-JM56", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nMeasurements have been made of the integrated intensities and spectral absorption coefficients of water vapor in the 1.38[micron], 1,87[micron], 2.7[micron], and 6.3[micron] regions at temperatures up to [...], using sufficient self-broadening to remove the rotational fine structure. The experiments were performed in a specially designed, isothermal high-pressure absorption cell supplied with vapor from a liquid water reservoir submerged in a constant temperature oil bath.\r\n\r\nIn addition, theoretical calculations of the spectral absorption coefficients of water vapor at elevated temperatures have been performed using a just-overlapping line model and the results have been compared with the experimental data.\r\n\r\nThe spectral absorption coefficients of liquid water have been measured in the wave number regions from 2200 to 3000 cm[superscript -1] and from 3700 to 7600 cm[superscript -1] at temperatures of 27, 89, 159, and 209[degrees]C. From these data, the integrated intensities of the absorption bands at 1.45[microns] and 1.93[microns] have been determined. The experimental data have also been used, in a highly simplified analysis, for the determination of hydrogen bonding in liquid water on the assumption of clusters containing only zero, one or two hydrogen bonds per molecule.\r\n\r\nThe change in the infrared absorption of gaseous and liquid water has been further investigated by measuring the transmission of infrared radiation through equal optical depths of liquid water and of water vapor near the limits of saturation." }, { "name": "Gray, Augustine Heard", "degree": "PhD", "year": "1964", "title": "Stability and Related Problems in Randomly Excited Systems", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192002-104048", "creators": [ { "name": { "family": "Gray", "given": "Augustine Heard" }, "id": "Gray-Augustine-Heard", "display_name": "Gray, Augustine Heard" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/FS96-6Q62", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Introductions to parts are included in .pdf document.\r\n\r\nPart 1. THE CONTINUOUS MARKOV PROCESS\r\n\r\nSince the first treatments of Brownian Motion as an example of a continuous Markov Process, the applications of Markov Processes in physical situations have extended over a wide range which includes such extremes as barometric pressure distributions and structural responses to earthquakes.\r\n\r\nIn this part, the notion of a continuous Markov Process is presented and described in terms of a transition probability and a Fokker-Planck Equation. Two uniqueness theorems are presented here, as well as a heuristic discussion of the large time behavior of such a process.\r\n\r\nPart 2. THE MARKOV PROCESS AS GENERATED BY DIFFERENTIAL EQUATIONS WITH RANDOM COEFFICIENTS\r\n\r\nIn Part 1, the Markov Process was treated from the point of view of the Fokker-Planck Equation alone, and no discussion was presented treating the process itself. In this part, it will be demonstrated that a system of differential equations can define a Markov Process, and the Fokker-Planck Equation for such a process will be derived.\r\n\r\nParticular emphasis is given to a discussion of the differing results of various authors in the case of \"parametric white noise.\" These differing results have led to a controversy concerning the coefficients A[subscript k] of the Fokker-Planck Equation, Eq. 1.14, even in some of the simplest examples.\r\n\r\nAmong the examples given will be the general linear differential equation with \"parametric white noise,\" and an \"equivalent\" linear differential equation with no parametric white noise will be derived.\r\n\r\nPart 3. SOME SUFFICIENT STABILITY CONDITIONS FOR LINEAR SYSTEMS WITH RANDOM (NON-WHITE) COEFFICIENTS\r\n\r\nAs pointed out in Part 2, the stability and instability of linear systems whose coefficients are sums of constants and Gaussian White Noise can be determined by Laplace transforms applied to appropriate moment equations. This will lead explicitly to stability boundaries for the various moments, and is most often useful in determining \"mean square stability.\" Unfortunately, such a procedure cannot be extended to cover non-white parameters. At present, there is no general method that may be used to show instability when the coefficients are random but not white, and only conservative sufficient conditions for various forms of stability can be obtained.\r\n\r\nSome attempts at determining stability boundaries have been published by Chelpanov (11) and Samuels (12). In the former paper, correlation times of the random parameters were assumed to be much smaller than the natural times of the system, thus, as described in Part 2 of this thesis, making the random signals essentially white. The latter paper is unfortunately erroneous in parts, and its results are questionable.\r\n\r\nIn a later paper, F. Kozin (7) treated sufficient stability conditions by utilizing an ergodic property of the random terms and by using the Gronwall-Bellman Lemma (14). Less conservative conditions have been obtained by T. K. Caughey* [*Communicated verbally to the author] by using an appropriate Lyaponof function and the same ergodic property.\r\n\r\nCaughey's Lyaponof function was quadratic in form, and suggested the possibility of using a general quadratic Lyaponov function. Herein is presented an approach for obtaining sufficient conditions for stability, utilizing a general quadratic Lyaponov function.\r\n\r\nPart 4. FIRST PASSAGE TIMES IN A SECOND ORDER SYSTEM\r\n\r\nOf major interest in vibrational systems with random excitation is the mean and mean square time for the system to get from one state to another. A more general problem is that of determining the probability distribution of the elapsed time in getting from one state to another.\r\n\r\nIn principle, this problem can be solved for a stationary Markov Process. Using the notation of Part 1 (Sections 1.2.0 and 1.2.1), if one defines T(z/x,t) as the probability density for the time of passage, t, to get from the point x to the point z in n dimensional phase space, and if P[subscript T](z/x,t) represents the transition probability for the variable z, then Eq. 1.4 of Part 1 states that [...]. By using Laplace Transform techniques, the convolution equation indicated by Eq. 4.1 can be readily solved, giving T(z/x,t) as the inverse Laplace Transform of a ratio of Laplace Transform of P[subscript T](z/x,t) and P[subscript T}(z/z,t). In general, the calculations necessary are far too difficult to perform, except in the simple case of a one-dimensional Markov Process, generated by the linear differential equation [...], where n(t) is white noise.\r\n\r\nA similar problem, that of the evaluation of the frequency with which a variable y(t) crosses a given value z, has been worked out by Rice (16), for the case where y(t) is a stationary random variable. In particular, when y(t) is a Gaussian variable with zero mean, then the mean number of times per unit time that y is equal to z is given by [...], where [...].\r\n\r\nConsider the resonant system defined by [...], where n(t) is white noise, with an autocorrelation function given by [...]. Such a system is used as an approximation of a structural response to an earthquake.* [*See Rosenblueth and Bustamante (17).] A desired result is that of the \"probability of failure\" which is the probability that in a given interval of length T, [...] will have exceeded a fixed value of X at least once. Another desired result if the \"mean time to failure,\" or the mean time to get from one value of [...] to the fixed level X. Neither of these desired results fall into the type of problems just discusses.\r\n\r\nThough this problem does not appear complex on the surface, there is no known technique for solving it. Messrs. Rosenblueth and Bustamante (17) have utilized approximations and boundary value techniques to obtain approximate solutions for the probability of failure. Their approach will be justified here by the obtaining of the same results in another manner, and further the mean and mean square times to failure will be calculated. It will be assumed that the system is highly resonant, so that b < < w, and that the fixed level X will be such that [...]. This latter condition will be satisfied if X is much larger than the steady state standard deviation of y, for the [...]." }, { "name": "Grimes, Charles Kenneth", "degree": "PhD", "year": "1964", "title": "Studies on the Propagation of Elastic Waves in Solid Media", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09192002-160252", "creators": [ { "name": { "family": "Grimes", "given": "Charles Kenneth" }, "id": "Grimes-Charles Kenneth", "display_name": "Grimes, Charles Kenneth" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EW57-KB61", "abstract": "Several aspects of three basic problems concerned with the propagation of elastic waves in solid media are explored.\r\n\r\nStress and displacement correction terms resulting from application of a subsonically moving point load to the free surface of the infinite half-space are obtained using Fourier transform techniques (the load moves subsonically with respect to the longitudinal and transverse wave speeds). It is shown, for the supersonically travelling point load, that the solution is given, in the limit as the load velocity becomes large, by the well known solution of Sauter for the impulsive point load.\r\n\r\nAnalytic function theory is used to predict the existence of Rayleigh waves on the free surface of the infinite halfspace and Stoneley waves along the welded interface between two dissimilar solid media. A brief analysis shows that free-running waves are also possible on the interior surface of an infinitely long cylindrical cavity. These waves are dispersive, however, because of the introduction of a characteristic length.\r\n\r\nThe early and long time approximations for the hoop stress generated through scattering of a plane dilatational wave by a cylindrical cavity in an infinite medium are developed. Use is made of Friedlandler's Riemann surface representation (early time) and expansion in Fourier series (long time)." }, { "name": "Hegemier, Gilbert Arthur", "degree": "PhD", "year": "1964", "title": "Stability of Thin Cylindrical Shells Subjected to a Class of Axially Symmetric Moving Loads", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-10112002-121702", "creators": [ { "name": { "family": "Hegemier", "given": "Gilbert Arthur" }, "id": "Hegemier-Gilbert-Arthur", "display_name": "Hegemier, Gilbert Arthur" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4P8K-YN54", "abstract": "The stability of an infinite-length cylindrical shell subjected to a broad class of axially symmetric moving loads with constant velocity is studied by utilizing a large deflection Donnell theory. Special cases of the general loading function include the moving ring, step and decayed step loads.\r\n\r\nStability is defined on the basis of the boundedness or divergence of an infinitesimal nonsymmetric disturbed motion about an initial nonlinear steady-state symmetric response. Following the determination of the symmetric response, under this concept of stability, the analysis is reduced to a study of a system of linear partial differential equations or so-called variational equations; these are analyzed by use of a double Laplace transform technique and the original stability problem is replaced by a simpler one of determining the location of the poles of a certain function. A scheme for accomplishing this task is outlined. Extension of the method to include more exact equations of motion and to a class of static problems involving finite length shells is discussed.\r\n\r\nA related problem concerning a moving concentrated load on a nonlinear elastic cylindrical membrane (nonlinearity in both geometric and constitutive relations) and a string on a nonlinear foundation is discussed in an appendix to the text. Interesting analogies in both analysis and physical behavior of the string and shell systems are found." }, { "name": "Hughes, Gordon Frierson", "degree": "PhD", "year": "1964", "title": "A Threshold Gate Feed-Forward Switching Net Algorithm", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202002-135451", "creators": [ { "name": { "family": "Hughes", "given": "Gordon Frierson" }, "id": "Hughes-Gordon-Frierson", "display_name": "Hughes, Gordon Frierson" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/K8X1-1697", "abstract": "A general algorithm is presented for the efficient computation of feed-forward nets of general threshold gates which realize given bi-valued switching functions. A simplified version of the algorithm is presented for the case of symmetric threshold nets which realize symmetric switching functions.\r\n\r\nThese algorithms produce near-minimal gate nets, and the results of a digital computer program for the general algorithm are presented to illustrate the degree of efficiency and minimality obtained in practice.\r\n\r\nBoth algorithms are proved to give a minimal one-gate net if one exists for a given switching function; a necessary criterion is given for the symmetric algorithm to produce a minimal two-gate net if one exists; and two-gate minimality is also demonstrated for the general algorithm, for a certain class of two-gate switching functions.\r\n\r\nThe case of partially defined switching functions is also treated." }, { "name": "Jacobson, Alexander Donald", "degree": "PhD", "year": "1964", "title": "On the Theory of Noise-like Electromagnetic Fields of Arbitrary Spectral Width", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132002-124223", "creators": [ { "name": { "family": "Jacobson", "given": "Alexander Donald" }, "id": "Jacobson-Alexander-Donald", "display_name": "Jacobson, Alexander Donald" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/QH8J-B561", "abstract": "A mathematical theory of noise-like electromagnetic fields of arbitrary spectral width is formulated. Attention is restricted to fields whose random fluctuations result exclusively from the chaotic nature of the source. The theory is expressed in terms of the second order moment of the field vector; hence, it is a tensor theory. Moreover, to make it applicable to fields of arbitrary spectral width, the theory is formulated in terms of a spectral representation, rather than directly in terms of the autocorrelation function of the vector field. The principal field quantity, the dyadic field spectral density (DFS), is interpreted from both a statistical and a physical standpoint. In particular, a statistical analysis of partial polarization is presented with the aim of providing a physical interpretation of the polarization of a quasi-monochromatic field. The differential equations that govern the behavior of the DFS are derived in the presence of a source, in a source free region, and in a generalized dielectric medium. Boundary conditions are derived for the DFS at a dielectric interface, at a perfectly conducting interface, and at infinity. The differential equations are integrated for various cases with the aid of the dyadic Green's function. The resulting integral representation for the DFS is employed to analyze an experiment that involves the measurement of a partially polarized, incoherent, discrete radio star by means of a two-element radio interferometer" }, { "name": "Keightley, Willard Otis", "degree": "PhD", "year": "1964", "title": "Vibration Tests of Structures", "advisor": "Housner, George W.; Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232002-113912", "creators": [ { "name": { "family": "Keightley", "given": "Willard Otis" }, "id": "Keightley-Willard-Otis", "display_name": "Keightley, Willard Otis" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/E95Z-HW51", "abstract": "Dynamic tests of three structures are described. In two cases linear vibration theory is applied to explain the behavior of the structures. In the third case a new method of analyzing the vibration records is introduced to define nonlinear properties of the structure.\r\n\r\nFree and forced vibration tests were conducted on a reservoir outlet structure consisting of a reinforced concrete tower, 149 feet in height, with a steel truss bridge, 339 feet long, connected to the tower near the top. Measurements revealed five natural frequencies and mode shapes, and indicated the extent and significance of foundation movements. A detailed theoretical analysis of linear vibrations of the structure is carried out to show good agreement with the observations and to illustrate a general technique for the dynamic analysis of framed structures.\r\n\r\nAn earth dam 485 feet long by 60 feet in height by 450 feet thick at the base was subjected to a sinusoidal lateral exciting force at the top. Application of the theory of a truncated wedge vibrating in shear modes is made to determine an effective shear wave velocity in the earth fill and to estimate damping in the modes.\r\n\r\nA general procedure is presented for experimentally determining the restoring and dissipating functions in lumped mass structures, linear or nonlinear. An experiment on a single degree of freedom laboratory structure with bolted joints is used to illustrate the method.\r\n\r\nThe question of instrumentation suitable for structural dynamic work is considered and recommendations are made on the basis of tests and examination of many commercially available components." }, { "name": "Koh, Robert Ching-Yee", "degree": "PhD", "year": "1964", "title": "Viscous Stratified Flow Towards a Line Sink", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09252002-135207", "creators": [ { "name": { "family": "Koh", "given": "Robert Ching-Yee" }, "id": "Koh-Robert-Ching-Yee", "display_name": "Koh, Robert Ching-Yee" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/YXY3-GG82", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA theoretical and experimental investigation has been made for the problem of two-dimensional viscous, incompressible, steady, slightly-stratified flow towards a line sink. The analytical solution was obtained from the Navier Stokes equations, the continuity equation, and the diffusion equation by first making a boundary-layer-type assumption and then using a small perturbation technique based on a perturbation parameter proportional to the sink strength q. The effects of the viscosity, the diffusivity, and the gravity have been included while the inertia effect is neglected in the zeroth order solution. The solution indicates that there exists a withdrawal layer which grows in thickness with the distance x from the sink at the rate x[superscript 1/3] and that the velocity distributions u(y) are similar from one station x to another.\r\n\r\nTwenty-five tank experiments were performed using water stratified by means of either salt or temperature. Detailed measurements of the velocity field were made by means of photographs of vertical dye lines. The experiments verify the shape of the velocity profiles as well as their similarity in x as predicted by the theory.\r\n\r\nExcept for scale, this is very similar to the problem of selective withdrawal from a reservoir." }, { "name": "Lee, Kelvin Shun-Hung", "degree": "PhD", "year": "1964", "title": "On the Doppler Effect in a Medium", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-120946", "creators": [ { "name": { "family": "Lee", "given": "Kelvin Shun-Hung" }, "id": "Lee-Kelvin-Shun-Hung", "display_name": "Lee, Kelvin Shun-Hung" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WGHV-8G71", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe problem of calculating the frequency of the wave scattered by a body moving in a medium is formulated from field-theoretic considerations. The Doppler equation for a homogeneous dispersive medium is obtained on the basis of the fact that the frequency and the wave vector of a plane wave form a 4-vector. It is found that the solutions of the Doppler equation can be classified into two kinds. In one kind, the solutions are close to the frequency of the incident wave. In the other kind they appear near the poles of the refractive index of the medium on the [omega]-axis. In the case of an isotropic plasma, the monochromaticity of the incident wave is shown to be preserved after the wave is scattered by a moving body. However, in the case of a magneto-active plasma, the scattered wave contains more than one frequency for a monochromatic incident wave. The physical interpretationsof these frequencies are given. In an inhomogeneous medium the Doppler equation has to be derived from a different starting point. The crucial point of the derivation is to perform spectral decompositions of the transformed fields and then to apply, under the assumption of gradual inhomogeneity, the method of stationary phase to determine the critical points. It is shown how the phase functions of the fields can be obtained by transforming Maxwell's equations into equations of Riccati-type. Approximate solutions of the Doppler equation are obtained for isotropic as well as for gyroelectric stratified media" }, { "name": "Levinson, Mark", "degree": "PhD", "year": "1964", "title": "Variational Principles and Applications in Finite Elastic Strain Theory", "advisor": "Blatz, Paul J.; Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09272002-145537", "creators": [ { "name": { "family": "Levinson", "given": "Mark" }, "id": "Levinson-Mark", "display_name": "Levinson, Mark" } ], "advisors": [ { "name": { "family": "Blatz", "given": "Paul J." }, "id": "Blatz-P-J", "role": "advisor", "display_name": "Blatz, Paul J." }, { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PK58-HQ71", "abstract": "The variational principles of finite elastostatic strain theory are presented in a unified manner for both compressible and incompressible bodies. Whereas the principle of stationary potential energy, a restricted case of the general principle of Hu and Washizu, is valid for any elastic deformation, it is found that the principle of stationary complementary energy is valid only for infinitesimal elastic strains. Consequently, Reissner's Theorem is the appropriate stationary principle to use in finite elastic strain theory when the complementary strain energy density is to be the argument function.\r\n\r\nThe potential energy principle is applied to several problems dealing with the finite straining of a neo-Hookean material. All but one of these problems are concerned with plane strain deformations; the one other problem, in a spherical geometry, involves an unusual stability question. Approximate solutions are obtained for some mixed boundary value problems which are not amenable to the semi-inverse methods of solution frequently used in finite elastic strain theory.\r\n\r\nAnother plane strain problem, requiring more detailed stress information than can be obtained from the potential energy principle, is studied approximately by means of Reissner's Theorem." }, { "name": "Lieberman, Alfred George", "degree": "PhD", "year": "1964", "title": "Mode Excitation and Propagation in Waveguides Containing Anistropic Plasmas", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-09302002-120628", "creators": [ { "name": { "family": "Lieberman", "given": "Alfred George" }, "id": "Lieberman-Alfred-George", "display_name": "Lieberman, Alfred George" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/DCTN-2N35", "abstract": "An analysis is presented of perfectly-conducting cylindrical structures completely filled with cold, anisotropic plasmas. Major, but not exclusive, consideration is directed to the circular waveguide containing a lossless, longitudinally magnetized plasma. The modes are generally a mixture of TE and TM fields with the result that the conventional orthogonality relations must be replaced by appropriate generalizations. The orthogonality relations are used to determine the fields excited in a longitudinally magnetized plasmaguide*by a coaxial current loop. At cut-off, resonance, and at limiting values of the system's parameters, the modes reduce to simple TE or TM waves. The field configuration and dispersion are examined at these limiting conditions as well as at intermediate values of the parameters. Numerical results are provided for the cut-off frequencies and dispersion relation.\r\n\r\n*Plasmaguide is the generic name given to any metallic waveguide containing an anisotropic plasma. In this manuscript it will refer to the longitudinally-magnetized, plasma-filled waveguide." }, { "name": "Linde, Ronald Keith", "degree": "PhD", "year": "1964", "title": "Kinetics of Transformation of Metastable Silver-Copper Solid Solutions", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172002-121425", "creators": [ { "name": { "family": "Linde", "given": "Ronald Keith" }, "id": "Linde-Ronald-Keith", "display_name": "Linde, Ronald Keith" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/9F9D-3011", "abstract": "Metastable solid solutions were obtained at compositions across the entire range from 0 at. % Ag;Cu to 100 at. % Ag;Cu by rapid-quenching from the liquid state. Lattice parameters were measured by x-ray diffraction in Debye-Scherrer powder cameras. The enthalpy of solution of the 75.0 at. % Ag;Cu composition was determined calorimetrically and is discussed in relation to the predictions of existing theories.\r\n\r\nThe process of transformation of the metastable solid solutions into the equilibrium phases was studied by means of x-ray diffraction intensity measurements, electrical resistance measurements, and optical microscopy. Results are compared with those for an alloy quenched from the solid state at a composition which exists as a solid solution at elevated temperatures. Activation energies were computed and are shown to be compatible with a diffusion controlled growth process in which most of the nuclei are present very early in the process. A model for the transformation process is postulated and discussed in terms of experimental results.\r\n\r\nPhotographic materials on pages 26, 50, 51, 52, 55, 76, 77, 78, 105, and 107 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered." }, { "name": "Liu, Joseph Tsu Chieh", "degree": "PhD", "year": "1964", "title": "Problems in Particle-Fluid Mechanics", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172002-122957", "creators": [ { "name": { "family": "Liu", "given": "Joseph Tsu Chieh" }, "id": "Liu-Joseph-Tsu-Chieh", "display_name": "Liu, Joseph Tsu Chieh" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/11Y4-2H39", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe continuum equations describing the motion of a fluid containing small solid particles are discussed and stated. The examples considered fall into two categories: (1) when the fluid is incompressible and viscous, with simultaneous occurrence of particle-fluid momentum relaxation and fluid viscous diffusion; and (2) when the fluid can be considered as \"inviscid\" but compressible, with simultaneous occurrence of coupled particle-fluid momentum and thermal relaxations and fluid compressibility.\r\n\r\nUnder (1), the low Mach-number Rayleigh problem is studied. Many of the physical features of the non-linear steady (constant pressure) laminar boundary-layer problem are recovered from appropriate expansions from this exact solution. One obtains answers to questions about the modifications on the boundary layer growth and skin friction; particularly their transition from the \"frozen\" value near the leading edge, where the viscous layer is \"thin\" and the fluid viscous diffusion behaves as if in the absence of particles with the ordinary fluid kinematic viscosity,[.....], to the ultimate \"equilibrium\" value far downstream where the mixture then behaves as a single heavier fluid and viscous diffusion takes place with the \"equilibrium\" kinematic viscosity augmented by the particle density [.....].The uncoupled thermal Rayleigh problem (small relative temperature differences) is directly inferred, and this answers questions about the modifications on the surface heat-transfer rates and particularly about the possibility of similarity with the velocity boundary layer. Similarity of the two boundary layers is possible when, in addition to lateral diffusion effects being similar as indicated by Prandtl number unity, the streamwise relaxation processes must also be similar. The infinite flat plate oscillating in its own plane is studied, and appropriate expansions from the exact solutions point out how approximate treatment of periodic boundary layers in the absence of a mean flow may be made.\r\n\r\nUnder (2), the first-order small perturbation theory is discussed, leading from the equation for acoustic propagation to that for linearized supersonic flow. The two-dimensional steady case, or the Ackeret problem, is considered in detail. The Mach wave structure induced by a thin obstacle is deduced and shows a rapid damping of the disturbance along the \"frozen\" Mach wave (based on the sound speed of a gas in the absence of particles), both damping and diffusiveness along an intermediary Mach wave, and diffusiveness along the \"equilibrium\" Mach wave (based on the sound speed of an equilibrium mixture of gas and particles) and along which the bulk of the disturbance is carried to regions far from the obstacle. An exact form of the pressure coefficient is obtained for any surface shape (consistent with the linear theory), and involves a convolution integral of two Bessel functions with imaginary argument which is analytically evaluated. When the particle-fluid density ratio is small, the \"frozen\" and \"equilibrium\" Mach waves are very closely clustered together. A \"boundary layer technique\", based on the fact that changes across the Mach waves are rapid compared to changes along Mach waves, is then applied to obtain a simplified version of the linearized equation that describes Mach waves inclined toward the downstream direction only. While the Mach wave structure is consistent with the exact treatment, the pressure coefficient takes on the much simpler form of decreasing exponentials. The transition is, again, from the \"frozen\" value at the leading edge towards the \"equilibrium\" value in the downstream direction insofar as the surface shape permits.\r\n" }, { "name": "Luo, Huey-Lin", "degree": "PhD", "year": "1964", "title": "Metastable Amorphous Phase of Tellurium-Base Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10022002-140252", "creators": [ { "name": { "family": "Luo", "given": "Huey-Lin" }, "id": "Luo-Huey-Lin", "display_name": "Luo, Huey-Lin" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/GC87-HJ15", "abstract": "Amorphous phases have been found in tellurium base alloys very rapidly cooled from the liquid state. These phases, which are stable at room temperature, exist in binary alloys containing from approximately 10 to 25 at. % germanium, and from 10 to 30 at. % of gallium or indium. The structure of these alloys was studied by x-ray diffraction (Debye-Scherrer method), using molybdenum Ka radiation monochromatized by the (200) plane of a lithium fluoride crystal. Radial distribution functions were obtained for several alloys and within the experimental accuracy neither the nature of the alloying element nor its concentration had a noticeable effect on the shape of the distribution function. The atomic arrangement in the amorphous alloys is very similar to that found in liquid tellurium which is itself closely related to the crystal structure of solid tellurium. The existence of amorphous phases in tellurium base alloys is discussed in relation with previously published ideas on the various factors governing glass formation in solids." }, { "name": "McColl, Malcolm", "degree": "PhD", "year": "1964", "title": "Electron Current Through Thin Mica Films", "advisor": "Mead, Carver", "url": "https://resolver.caltech.edu/CaltechETD:etd-10142002-162916", "creators": [ { "name": { "family": "McColl", "given": "Malcolm" }, "id": "McColl-Malcolm", "display_name": "McColl, Malcolm" } ], "advisors": [ { "name": { "family": "Mead", "given": "Carver" }, "id": "Mead-C-A", "orcid": "0000-0003-4051-0462", "role": "advisor", "display_name": "Mead, Carver" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7ENX-8503", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nMuscovite mica, cleaving every 10[Angstroms], provides a crystalline insulator with uniformly parallel surfaces of well known separation ideally suited to the study of electron transport phenomena. Using a micro-splitting technique similar to that developed by Foote and Kazan, muscovite was cleaved in a vacuum of 10(^6) Torr and metal electrodes evaporated, aluminum on one side, gold on the other. The current through 30 and 40[Angstrom] films was measured as a function of voltage and temperature and analyzed in terms of the tunneling theory of Stratton. Using the actual image-force barrier shape, the approximately symmetrical volt-ampere data gave barrier heights of [?] = 0.95 and 0.93eV for the 40 and 30[Angstrom] films, respectively, for an effective mass ratio of m*/m =0.92. The theoretical temperature dependence was observed in the 40[Angstrom] film from room temperature down to liquid nitrogen temperature (77[degrees]K). Thicker films 50 to 10,000 [Angstroms], exhibited temperature dependent volt-ampere curves linear in log I versus [square root of]V over a factor of 10:1 in voltage and a thermal activation energy of 0.55eV, lower than [t]he barrier height above possibly because of injection into polaron states. Preliminary photoelectric response data yielded [?] = 0.8eV, raising some question as to the real meaning of the [?] found from tunneling theory." }, { "name": "Mitzner, Kenneth Martin", "degree": "PhD", "year": "1964", "title": "Theory of the Scattering of Electromagnetic Waves by Irregular Interfaces", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182002-092308", "creators": [ { "name": { "family": "Mitzner", "given": "Kenneth Martin" }, "id": "Mitzner-Kenneth-Martin", "display_name": "Mitzner, Kenneth Martin" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/HBEY-GT07", "abstract": "Two problems involving electromagnetic scattering from irregular interfaces are treated, both deterministic and statistical irregularities being considered.\r\n\r\nFirst, reflection of a partially polarized plane wave from a plane interface with large irregularities is studied using geometrical optics. Matrix transformations relating incident and reflected waves are obtained for reflection from a single specular point and from an extended area containing many independent reflectors. The properties of a wave reflected from a diffusely illuminated rough interface are found, and these results are used to study reflection noise reduction when a polarization-sensitive detector viewing near the Brewster angle is used in infrared temperature measurements.\r\n\r\nSecond, the method of small perturbations is used to study scattering of an arbitrary completely polarized wave from an irregular interface of general underlying shape. The irregularities are replaced by equivalent surface currents and then the field in space is found using the dyadic Green's functions of the unperturbed problem. The results obtained are valid when the irregularity has small slope and amplitude small compared to the wavelength and local radii of curvature. To facilitate applications, the theory of dyadic Green's functions is developed, and the necessary functions are evaluated for simple geometries. As an example, the first perturbation is calculated for scattering from a perfectly conducting cylinder with sinusoidal irregularities." }, { "name": "Nagelberg, Elliott Robert", "degree": "PhD", "year": "1964", "title": "Microwave Interaction with Bounded Gyroelectric Plasmas", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-10182002-100544", "creators": [ { "name": { "family": "Nagelberg", "given": "Elliott Robert" }, "id": "Nagelberg-Elliott-Robert", "display_name": "Nagelberg, Elliott Robert" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WG7A-PS41", "abstract": "In the following we investigate, theoretically, the interaction of microwaves with gyroelectric plasmas of finite extent, particularly those having cylindrical or spherical boundaries. Within the latter class of problems, only those involving the axially magnetized column with circular cross section are amenable to rigorous analysis. We find that one of the important effects of the anisotropy is to induce changes in the polarization of the scattered field resulting from interaction with an obliquely incident plane wave.\r\n\r\nAs a means of solving problems which involve uniform but arbitrarily directed magnetization, we develop the perturbation theory of microwave interaction in which the static magnetic field is regarded as a small perturbation of the isotropic plasma. The field equations are derived for all orders but only those of first order, linear in the magnitude of the static magnetic field, are solved. This solution is carried out in general, the only restriction being that the fields for the isotropic problem are assumed to be known.\r\n\r\nThe first order theory is then applied to cylindrical and spherical problems. When the approximate solution for the axially magnetized column is compared with the exact result, agreement is obtained provided that the static magnetic field is weak, as expected. Finally we consider the problem of a magnetic dipole radiating from within a weakly magnetized plasma sphere." }, { "name": "Nielsen, Niels Norby", "degree": "PhD", "year": "1964", "title": "Dynamic Response of Multistory Buildings", "advisor": "Hudson, Donald E.; Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10212002-111231", "creators": [ { "name": { "family": "Nielsen", "given": "Niels Norby" }, "id": "Nielsen-Niels-Norby", "display_name": "Nielsen, Niels Norby" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/KN80-YN39", "abstract": "Two modern multistory buildings, one a five-story reinforced concrete building, the other a nine-story steel frame building, have been the subjects of an extensive series of dynamic tests. The vibrations of the buildings were induced by means of synchronized vibration exciters. The mathematical analysis needed in order to determine the stiffness and damping matrices from the experimentally determined modal properties of a structure has been developed.\r\n\r\nThree translational and one torsional mode of vibration of the reinforced concrete building were investigated in considerable detail. The damping in each mode and the resonant frequency was determined under various levels of excitation. Complete mode shapes were determined as well. The measurements of the resonant frequencies show a well-defined nonlinearity that can be well explained from the hysteretic material properties. The values of damping were for all modes approximately 2% with a tendency for the value of damping to increase with increasing force levels.\r\n\r\nA total of seven translational and three torsional modes of vibration of the nine-story steel frame building were investigated in detail. A mode in which the floor slabs vibrate horizontally as free-free beams was excited as well. The lowest translational modes in the two principal directions of the building had damping values of about 0.5%. The second lowest translational modes had damping values of approximately 1.0%. For both buildings the damping values are considerably less than the values usually mentioned in the literature. Since most earlier tests used run-down tests rather than the steady-state tests used in the present work, comparison tests were run to explore possible differences in the test results. It was concluded that run-down tests could easily overestimate the values of damping by several hundred per cent. A new method for the measurements of natural periods of vibration of structures is proposed. The new method has several important advantages over wind-excited vibration tests which have been used extensively in the past to measure the natural periods of vibration of structures." }, { "name": "O'Kelly, Michael Edmond James", "degree": "PhD", "year": "1964", "title": "Vibration of Viscously Damped Linear Dynamic Systems", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-10142002-084201", "creators": [ { "name": { "family": "O'Kelly", "given": "Michael Edmond James" }, "id": "O'Kelly-Michael-Edmond-James", "display_name": "O'Kelly, Michael Edmond James" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/XGD9-0W17", "abstract": "A general theory of vibration of damped linear dynamic systems is given. The limitations on the use of the usual normal mode theory in determining the response of damped systems were first studied systematically by Caughey when he derived necessary and sufficient conditions for the uncoupling of systems in N-space. Systems which cannot be uncoupled in N-space may still be solvable by modal methods on transforming them to 2N-space and using the results of Foss. However there exist systems which cannot be solved by the usual modal techniques in either N-space or 2N-space. Such systems which include some passive physically realizable systems require the general theory for a complete determination of their motion. For weakly coupled systems the simple perturbation analysis presented gives surprisingly accurate approximations to the actual response of the systems. In any design problem questions of stability arise, particularly when dealing with non-symmetric systems, and therefore a discussion on the stability of these systems is given.\r\n\r\nThe second part of the thesis is concerned with linear continuous systems. Exactly solvable continuous systems are rare and in general recourse must be had to numerical methods. The interchangeability of the differential and integral formulation of continuous systems is noted. As in the discrete systems constructive necessary and sufficient conditions are derived for a damped system to possess the same set of complete eigenfunctions as the undamped system. In the discretization of continuous systems the main problem of practical interest is the error bounds on the solution of these discrete approximations when compared to the exact solution. Unfortunately the literature is very poor in this area but what is known is applied to the systems under discussion." }, { "name": "O'Regan, Patrick Gerard", "degree": "PhD", "year": "1964", "title": "The Application of Tunnel Diodes to Switching and Logical Circuits", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-10222002-085219", "creators": [ { "name": { "family": "O'Regan", "given": "Patrick Gerard" }, "id": "O'Regan-Patrick-Gerard", "display_name": "O'Regan, Patrick Gerard" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZPA2-X230", "abstract": "No abstract submitted." }, { "name": "Parmerter, Robert Reid", "degree": "PhD", "year": "1964", "title": "The Buckling of Clamped Shallow Spherical Shells Under Uniform Pressure", "advisor": "Fung, Yuan-cheng; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-10212002-112304", "creators": [ { "name": { "family": "Parmerter", "given": "Robert Reid" }, "id": "Parmerter-Robert-Reid", "display_name": "Parmerter, Robert Reid" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R18G-ZC96", "abstract": "In view of the wide discrepancy between previous theoretical and experimental results the problem of the buckling of clamped spherical shells under uniform external pressure is reexamined.\r\n\r\nA theoretical study is carried out to determine if asymmetrical modes participate in the snap-through process. It is shown that asymmetrical buckling does occur in a certain range of a geometric parameter, at loads which are significantly less than those predicted from symmetrical theory. Additional effects can be expected if the shell has symmetrical or asymmetrical imperfections, however, the present study considers only the perfect shell.\r\n\r\nExperiments were carried out with copper shells fabricated by an electroforming process. The initial imperfections in the test specimens were of the order of 1/10 of the thickness. The buckling loads of these shells exceeded the loads which have previously been reported by as much as a factor of two at higher values of the geometrical parameter [lamda].\r\n\r\nGood agreement is found between theory and experiment, and with the recently published asymmetrical theory of Huang." }, { "name": "Patch, Richard Walker", "degree": "PhD", "year": "1964", "title": "Part I. Radiative Transfer Studies and Opacity Calculations for Heated Gases. Part II. Absolute Intensity Measurements for the 2.7 \u00b5 Band of Water Vapor in a Shock Tube", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292002-112946", "creators": [ { "name": { "family": "Patch", "given": "Richard Walker" }, "id": "Patch-Richard-Walker", "display_name": "Patch, Richard Walker" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/G92Q-ED75", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPART I. \r\n\r\nEquations for radiative transfer of energy in hot gases are presented for cases involving absorption, spontaneous emission, induced emission, and isotropic scattering. Application of these equations to energy transfer between two infinite parallel plates and also to energy transfer to the nose cone of a reentry vehicle are reviewed.\r\n\r\nThe Planck and Rosseland mean free paths for radiation are derived. It is shown that the treatments by Nachbar and Simon can be combined to give the continuity, momentum, and energy equations for a reacting, multicomponent gas mixture with radiative energy transfer. The resulting equations are then nondimensionalized. The coupling of radiation and convection in detached shock layers is reviewed.\r\n\r\nA simplified method for calculating spectral absorption coefficients for electronic bands of diatomic molecules is presented. A simplified method for calculating continuum radiation in plasmas is reviewed.\r\n\r\nPART II.\r\n\r\nThe apparent spectral absorption coefficients of the H2O infrared bands in the vicinity of 2.7 [microns] were measured in a shock tube behind reflected shock waves in an H20-Ar mixture.\r\n\r\nBy interrupting an infrared beam at a 60 kc rate and projecting this beam across the shock tube to a monochromator, it was possible to simultaneously measure both emission and absorption of H2O at 1000[degrees]K. The spectral absorption coefficients obtained from emission measurements averaged 9.8% higher than absorption coefficients obtained from absorption measurements, probably due to experimental errors (smaller than usually encountered in shock tube measurements). At 1933[degrees]K experimental difficulties precluded simultaneous measurement of infrared emission and absorption, so measurements were restricted to emission.\r\n\r\nThe apparent absorption coefficients were integrated to give the integrated absorption coefficients for the collections of bands near 2.7[microns]. Integrated absorption coefficients were 49.8 cm[superscript -2] atm[superscript -1], 54.7 cm[superscript -2] atm[superscript -1], and 31.6 cm[superscript -2] atm[superscript -1] for absorption at 1000[degrees]K, emission at 1000[degrees]K, and emission at 1933[degrees]K, respectively. The two values at 1000[degrees]K were in good agreement with those of Goldstein, who made no measurements above this temperature.\r\n\r\nPhotographic materials on pp. 100, 107, 111, 123, and 128 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered." }, { "name": "Reardon, Bernard Charles", "degree": "PhD", "year": "1964", "title": "Deposited Loops Coupling Magnetic Films as Fast Computer Elements", "advisor": "McCann, Gilbert Donald; Humphrey, Floyd Bernard", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302002-083025", "creators": [ { "name": { "family": "Reardon", "given": "Bernard Charles" }, "id": "Reardon-Bernard-Charles", "display_name": "Reardon, Bernard Charles" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "Humphrey", "given": "Floyd Bernard" }, "id": "Humphrey-F-B", "role": "advisor", "display_name": "Humphrey, Floyd Bernard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1FZC-JY74", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental study of the fast switching properties of the film-loop assemblies indicated that a line charge model for a rectangular magnetic film represents the external flux distribution of the film with good ([...]10%) accuracy. The flux linkage of a deposited loop equals 100% of the film flux. A 20% decrease in film flux was measured at both ends of the film easy axis and a quadratic flux distribution is consistent with the experimental results. Eddy current and circulating loop current fields affect the nanosecond range switching of magnetic films. Eddy current fields increase rapidly with the fraction of magnetic film perimeter covered by the loop conductors. Capacitive loop current fields cause a small increase in film switching time. Resistive loop loading can slow film switching significantly. The bias and drive field properties of deposited loops can be predicted from the loop dimensions. The deposition of complete film assemblies was effected without opening the vacuum of the system. The film switching test equipment incorporated a new method for the integration of fast switching signals and had a response time of 0.8 nsec. A theoretical study of the coupling loop circuitry indicated that the loop attenuation and the spatial distribution of loop induced voltage distort the film output signal. These effects are small, but not negligible, for a loop with conductor separation of 50,000 A and conductor thicknesses of 4000 A, enclosing a 1 cm[superscript 2] film switching in 1 nsec.\r\n\r\nThe use of integrated deposited circuitry containing magnetic films is feasible for fast computers. A set of logic elements suitable for a deposited configuration has reasonable fan-in and fan-out potentialities. Theoretical miniaturization limits for deposited film logic circuitry depend chiefly on the resistivity of the coupling loops. Operation of such circuitry at low temperature reduces the limit of film size to about 14 microns. Miniaturization alleviates the effect of loop currents and attenuation on film switching signals, leading to low power, short switching time circuitry." }, { "name": "Richer, Ira", "degree": "PhD", "year": "1964", "title": "Properties of an Arbitrarily Doped Field-Effect Transistor", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechETD:etd-09272002-160258", "creators": [ { "name": { "family": "Richer", "given": "Ira" }, "id": "Richer-Ira", "display_name": "Richer, Ira" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/E5RR-2P55", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe properties of p-n junction field-effect transistors (FET's) are formulated on a general basis, in terms of an arbitrary doping profile (i.e. arbitrary gate-channel impurity distribution). The external behavior is shown to be quite insensitive to the doping profile, provided that the profile satisfies certain weak restrictions. Essentially all practical structures are included in the restricted theory. A theoretical basis is thus provided for the much-used empirical conclusion that widely different types of FET's exhibit similar functional behavior. More specifically, upper and lower bounds are obtained on the normalized transconductance, drain current, input capacitance, and bias point for zero temperature coefficient of the drain current, and on the voltage-dependent parts of various figures of merit. In each case the bounds represent the solutions of two analytically simple structures, a step-junction FET and a delta-junction FET. Many practical implications stem from these results.\r\n\r\nFinally, a complete, small-signal, low-frequency equivalent circuit for an arbitrarily doped FET is developed by considering the capacitive current that flows between the channel and the gate. Beyond pinch-off a \"new\" element, the forward transfer capacitance, is present in the circuit. Below pinch-off the theory predicts that the output capacitance [C22] and the reverse transfer capacitance [C12] differ, and in fact that [C22 - C12 < 0], whereas earlier theories and intuition indicate that [C22 - C12 = 0]. Measurements on a wide variety of FET's substantiate these theoretical results. The frequency limitations of the equivalent circuit and, indeed, of all the results obtained are shown to arise from the breakdown of the gradual approximation." }, { "name": "Schwarz, Steven Emanuel", "degree": "PhD", "year": "1964", "title": "Plasma Diagnosis by Means of Photon-Electron Scattering", "advisor": "George, Nicholas A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-124348", "creators": [ { "name": { "family": "Schwarz", "given": "Steven Emanuel" }, "id": "Schwarz-Steven-Emanuel", "display_name": "Schwarz, Steven Emanuel" } ], "advisors": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "advisor", "display_name": "George, Nicholas A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7Y36-RP09", "abstract": "When a pulse of intense light from a giant-pulse laser passes through a plasma, a very small fraction of the light is scattered out of the beam as a result of (\"Thomson\") scattering by free electrons. Under suitable conditions the intensity of the scattered light is proportional to the density of free electrons, while its spectral distribution is related to the velocity distribution of the free electrons through the Doppler formula.\r\n\r\nTheoretical considerations, relating to the conditions of validity of the method, are discussed. Various mechanisms which could interfere with the diagnostic technique are mentioned and their importance considered. Design considerations for diagnostic experiments are then taken up, and signal-to-noise ratios calculated.\r\n\r\nAn apparatus for conducting scattering experiments has been constructed. Phenomenological checks indicate that the observed scattering is by free electrons. Measurements conducted at various times in the development of an afterglow plasma indicate Doppler broadening of the scattered light; the broadening disappears as the electrons cool during the first three microseconds of the afterglow. Measurements of electron density as a function of time are made in the afterglow, and are calibrated by means of Rayleigh scattering from gas at a known pressure.\r\n\r\nTwo unexpected laser-plasma interactions have been observed. The first is designated as \"induced plasma luminosity\" and the second as \"giant scattering.\" Both effects appear to be related to the presence of hydrocarbon impurities in the gas." }, { "name": "Scott, Richard Anthony", "degree": "PhD", "year": "1964", "title": "Transient Wave Propagation in Elastic Plates with Cylindrical Boundaries, Studied with the Aid of Multi-integral Transforms", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-130206", "creators": [ { "name": { "family": "Scott", "given": "Richard Anthony" }, "id": "Scott-Richard-Anthony", "display_name": "Scott, Richard Anthony" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/G7HA-F836", "abstract": "Some mixed time dependent boundary value problems for isotropic elastic plates with circular cylindrical boundaries are studied using the linear equations of elasticity. A multi-integral transform approach is employed, necessitating the introduction of extended Hankel transforms, and formal solutions are obtained with the aid of residue theory. Some properties of the Rayleigh-Lamb frequency equation, pertinent to the inversion processes, are derived. The problem of a free infinite plate with a circular cylindrical cavity subjected to a step normal displacement is studied in detail and numerical information for the far-field, showing the effect of the cavity radius on the displacements, is obtained using stationary phase techniques.\r\n\r\nThe generation of transient elastic waves in free isotropic infinite elastic plates by time dependent body forces is also treated and the results for a radial body force, with step time-dependence, are compared with the corresponding platecavity results. Good agreement between the two is found in the far-field.\r\n\r\nSimilar problems for a free, transversely isotropic, semi-infinite plate (slab) are also studied and some numerical information for the farfield is obtained using the head of the pulse method. Stationary phase solutions for an isotropic slab subjected to a step edge displacement are obtained and compared with the corresponding plate-cavity results. It is found that at a fixed station the plate cavity solutions approach those for the slab, as the cavity radius goes to zero. A comparison between the head of the pulse and stationary pulse results for the isotropic slab is also made and some discrepancies between the two are found." }, { "name": "Shackleford, William Lewis", "degree": "PhD", "year": "1964", "title": "Part I. Measurement of gf-Values for Singly Ionized Chromium Using the Reflected Wave Region of a Shock Tube. Part II. Experimental Investigation of the Approach to Equilibrium Ionization and Electronic Excitation in Shock-Heated Mixtures of Chromium and Argon. Part III. Approximate Spectral Absorption Coefficient Calculations for Electronic Band Systems Belonging to Diatomic Molecules", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-101246", "creators": [ { "name": { "family": "Shackleford", "given": "William Lewis" }, "id": "Shackleford-William-Lewis", "display_name": "Shackleford, William Lewis" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/RAAH-J388", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I.\r\n\r\nAbsolute gf-values for 21 lines of singly ionized chromium (Cr II) in the spectral region 3118-4559 [angstroms] are presented. Mixtures of Cr(CO)[subscript 6] and argon, heated by reflected shock waves to temperatures in the range 7920[degrees]K to 8730[degrees]K, were used to measure the emission intensity of ionized chromium lines. A three inch diameter shock tube was employed, with the light being observed along the shock tube axis in order to observe directly the curve of growth of each spectral line. The emitted intensities observed were converted to gf-values by means of a comparison with a calibrated tungsten strip lamp. Results are compared with values obtained from arc spectra by Corliss and Bozman[superscript 1] at the National Bureau of Standards. In general, our results are a factor of 9 below the latter measurements. Possible reasons for this discrepancy are discussed.\r\n\r\nPart II.\r\n\r\nAn experimental investigation of the approach to equilibrium ionization and electronic excitation for chromium behind shock waves in Cr(CO)[subscript 6]-argon mixtures is described. Mixtures composed of from 0.0043% to 0.036%o Cr(CO)[subscript 6] were heated by reflected shock waves to temperatures between 6170[degrees]K and 8600[degrees]K, and the emission from excited states of Cr I and Cr II was simultaneously measured by photoelectric means with a time resolution of about 3 microseconds. Relaxation toward equilibrium ionization and excited state population was observed to occur within from 12 to 60 microseconds, depending upon the temperature and chromium concentration behind the reflected shock.\r\n\r\nIn measurements in which equilibrium ionization is 95% or more, the populations of excited states of Cr I show a pronounced \"overshoot\" as these states become populated before ionization has depleted the supply of neutral chromium. From a study of the relaxation of Cr I and Cr II upper state populations, it is concluded that ionization proceeds by a multistep autocatalytic process dominated by collisions between chromium atoms and electrons released in prior ionization of chromium. The dependence of the relaxation rates upon the temperature behind the reflected shock wave and upon the concentration of chromium was determined. If it is assumed that the electron and atom temperatures did not differ appreciably during the relaxation period, the variation in the relaxation rate with temperature indicates a 3.1 [plus or minus] 0.3 ev activation energy for chromium ionization, which is significantly less than the ionization potential (6.74 ev).\r\n\r\nA simplified reaction mechanism is proposed which qualitatively explains the observed relaxation behavior of Cr I and Cr II.\r\n\r\nPart III.\r\n\r\nThe spectral absorption coefficients in electronic band systems of diatomic emitters have been computed in the past by models that may be described as \"the just overlapping line model\" and a model \"utilizing a smeared out rotational structure\". Although the basic relations are obtained by utilizing somewhat different physical arguments, the resulting equations are, in fact, identical.\r\n\r\nSpectral absorption coefficients have been calculated for the NO [...]-bands at 2000[degrees]K by using the approximate theoretical relations. The calculated results are in good agreement with estimates derived by numerical calculations in which, however, the absorption coefficient data were averaged over intervals of 2000 cm.[superscript -1]." }, { "name": "Shumka, Alex", "degree": "PhD", "year": "1964", "title": "Space-Charge-Limited Current in Germanium", "advisor": "Nicolet, Marc-Aurele", "url": "https://resolver.caltech.edu/CaltechETD:etd-10082002-102055", "creators": [ { "name": { "family": "Shumka", "given": "Alex" }, "id": "Shumka-Alex", "display_name": "Shumka, Alex" } ], "advisors": [ { "name": { "family": "Nicolet", "given": "Marc-Aurele" }, "id": "Nicolet-M-A", "role": "advisor", "display_name": "Nicolet, Marc-Aurele" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/EV7W-8D66", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nAn experimental verification of the theory of space-charge-limited hole current in germanium is presented. Alloyed p-np solid-state diodes of various base widths W are fabricated. The V-I characteristic of each diode is measured at an ambient temperature of 78[degrees]K. These results are compared with theory. Dacey (4) predicts: J = 1.43[epsilon][epsilon][subscript omikron] [mu][subscript omikron] E[subscript c][superscript 1/2]V[superscript 3/2]W[superscript -5/2] where [mu][subscript omikron] is the low field mobility of the holes and E[subscript c] is the critical electric field. This expression assumes a field dependence of hole mobility of [mu] = [mu][subscript omikron](E[subscript c]/E)[superscript 1/2].\r\n\r\nThe three halves power relationship between current and voltage is observed over nearly two current decades. In that same current range, a direct proportionality of V with W[superscript 5/3] at a constant current density is also observed to within the accuracy of base width and area measurements which are better than 5%. The value of the critical electric field obtained agrees with that estimated by Shockley's model (11).\r\n\r\nMeasurements are also made at higher ambient temperatures. The current decreases as expected from hot carrier considerations.\r\n\r\nThese results represent the first detailed verification of the validity of the theory of pure space-charge-limited current of hot carriers in solids. The measured peak current density of 180 a/cm[superscript 2] is greater than any value reported on space-charge-limited current in solids by an order of magnitude.\r\n\r\nPhotographic materials on pp. 39, 40, 68, 89 and 91 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.\r\n" }, { "name": "Singleton, Robert Edmund", "degree": "PhD", "year": "1964", "title": "Fluid Mechanics of Gas-Solid Particle Flow in Boundary Layers", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10092002-155700", "creators": [ { "name": { "family": "Singleton", "given": "Robert Edmund" }, "id": "Singleton-Robert-Edmund", "display_name": "Singleton, Robert Edmund" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/X9TM-K912", "abstract": "It is shown that the boundary layer approximation is applicable to two-phase flow over a semi-infinite flat plate and about a circular stationary cylinder, provided the particle density is of the order of [rho] in the boundary layer. In the boundary layer equations, the importance of a new parameter, [lamda][subscript m]/x, which is the ratio of the distance required for particle velocity to reach that of the fluid to the length measured downstream from the stagnation point, is pointed out, and expansions are made in terms of this parameter in such a way that a similarity variable can be found for the semi-infinite flat plate. This analysis is carried out for both an incompressible and a compressible gas on the semi-infinite flat plate. New shear coefficients and heat transfer coefficients are derived from this analysis. Also, an integral method is applied to the semi-infinite flat plate when the gas is incompressible to compare with the numerical solution of the same problem. The boundary layer analysis of the stationary circular cylinder demonstrates effects of curvature on two-phase flow." }, { "name": "Skidmore, Lionel Joseph", "degree": "PhD", "year": "1964", "title": "Discrete and Continuous Estimation in Correlated Noise with Finite Observation Time", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-10102002-090435", "creators": [ { "name": { "family": "Skidmore", "given": "Lionel Joseph" }, "id": "Skidmore-Lionel-Joseph", "display_name": "Skidmore, Lionel Joseph" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1V5T-2J86", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn this thesis analytic formulas are derived for the elements of the inverse covariance matrix of sampled rational noise. It is shown that the number of terms composing these formulas is dependent only on the order of the noise and not on the dimension of the covariance matrix. Some special cases are worked out in detail.\r\n\r\nThe estimation of the parameter [theta] in the process y(t) = [theta]S(t) + n(t), where t is in the interval [0,L], n(t) is rational noise, and S(t) is deterministic, is considered in detail for first and second order noise. A minimum variance continuous filter, f(t), which gives an estimate of [....] through [....] and its associated variance are computed. Also computed is a discrete minimum variance estimate of the form, [....] where the [....] are the \"weights\" for the sampled data and T is the sampling period. It is shown that the discrete weighting function and its variance approaches the continuous weighting function and its variance when the density of observations approaches infinity. It is seen that in general the discrete weighting function does not create the equivalent of a delta function and its derivatives by a simple differencing operation through the use of Kronecker deltas.\r\n\r\nAsymptotic properties of the variance of the discrete estimate are considered. The asymptotic term is defined as the first order term in the power series expansion of the variance. It is seen that for a smooth S(t) and first order noise, the asymptotic term is zero. In the special case of S(t) equal to a constant and second order noise it is shown that the asymptotic term is zero if the noise has zeros in its spectral density and nonzero if the noise is all pole.\r\n\r\nThe connection between autoregressive noise and rational noise is considered in detail for second order noise. It is seen that rational noise will have autoregressive properties only for a special pole-zero configuration and a particular sampling rate. The advantages of sampling at this rate are discussed and a special case is considered.\r\n\r\nIt is shown that the results obtained for one parameter, one signal, and one noise can be easily extended to a vector of parameters, a matrix of signals, and a vector of noises. The only restriction is that the components of the noise vector be uncorrelated." }, { "name": "Spaid, Frank William", "degree": "PhD", "year": "1964", "title": "A Study of Secondary Injection of Gases into a Supersonic Flow", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10312002-082315", "creators": [ { "name": { "family": "Spaid", "given": "Frank William" }, "id": "Spaid-Frank-William", "display_name": "Spaid, Frank William" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/T76G-2R21", "abstract": "The flow field around the injection port for secondary injection of a gas normal to a supersonic stream has been studied in a series of wind tunnel experiments. The experiments were conducted at free-stream Mach numbers of 1.38 to 4.54. Gaseous nitrogen, argon, and helium were injected through a circular hole or a transverse slot with sonic flow at the injection orifice. Data are presented which include static pressure distributions on the wall in the region of the injector, shock shapes, and injectant mass fraction, total pressure, and velocity profiles downstream of the injector. A scale parameter has been calculated, based on a simple, inviscid model of the flow field. This scale parameter gives a good general correlation of the data. Use of this scale parameter allows the prediction of a simple scaling law for the normal forces on a wall produced by secondary injection. For the case of injection through a slot, this scaling law has been compared with experimental results reported by other workers. This comparison indicates that further work will be necessary to clarify the effect of free-stream Mach number on the flow field. For the case of injection through a hole, the force scaling law is in approximate agreement with existing rocket motor test results." }, { "name": "Squire, William Dean", "degree": "PhD", "year": "1964", "title": "The Effects of Bias on Polarity-Coincidence Detection", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092002-094452", "creators": [ { "name": { "family": "Squire", "given": "William Dean" }, "id": "Squire-William-Dean", "display_name": "Squire, William Dean" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MDEF-MH25", "abstract": "A polarity-coincidence detector with biased polarity indicators (biased hard limiters) is studied to determine the effects of the bias on the detector output mean value, output variance, and output signal-to-noise power ratio.\r\n\r\nThe mean value of the detector output is derived for the case of Gaussian input signal and Gaussian input noise, with arbitrary spectra for the signal and noise. The mean value is expressed as a function of the input signal-to-noise power ratio, and as a function of the biases in the input channel and the reference channel polarity indicators. It is shown that the effect of bias is to introduce a spurious component in the output mean value.\r\n\r\nThe variance of the defector output is derived for the cage of Gaussian input signal and Gaussian input noise, with RC low-pass spectra for signal and noise, for small input signal-to-noise power ratios only. The variance is expressed as a function of the biases in the input channel and reference channel polarity indicators, and as a function of the input signal-to-noise band-width radio. It is shown that the effect of bias is to introduce a spurious component in the output variance.\r\n\r\nThe output signal-to-noise power ratio (the square of the output mean divided by the output variance) is derived for both an ideal polarity-coincidence detector (no bias) and for a biased polarity-coincidence detector. The output signal-to-noise power ratio is expressed as a function of the input signal-to-noise power ratio, the biases in the input channel and the reference channel polarity indicators, and input signal-to-noise band-width ratio, for small input signal-to-noise power ratios only. \r\n\r\nIt is shown that the output signal-to-noise power ratio of an ideal polarity-coincidence detector is degraded from that of a correlation detector. When the input signal-to-noise band-width ratio is unity, the degradation is about 1.4 db. The degradation increases to about 2.2 db. when the input signal-to noise band-width ratio becomes either very small or very large. It is also shown that the output signal-to-noise power ratio of a biased polarity-coincidence detector is degraded from that of an ideal polarity-coincidence detector. A simple expression for the degradation is presented. Limits on the biases are given, such that when the biases are smaller than these limits, the degradation of the output signal-to-noise power ratio is negligible." }, { "name": "Thomas, Mitchell", "degree": "PhD", "year": "1964", "title": "Radiative Transfer and Opacity Calculations", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092002-103956", "creators": [ { "name": { "family": "Thomas", "given": "Mitchell" }, "id": "Thomas-Mitchell", "display_name": "Thomas, Mitchell" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/EAA2-7R56", "abstract": "The similarity groups for multicomponent, reacting gas mixtures with radiative energy transport are derived. The resulting relations are used to consider the feasibility of scaling for flow processes with radiative energy transport under highly simplified conditions. Next the scaling parameters are derived for radiant energy emission from isobaric and isothermal gases for arbitrary opacities and various spectral line and molecular band models.\r\n\r\nThe radiative scaling properties for representative temperature profiles for both collision-broadened and Doppler-broadened line profiles have been found for a spectral line belonging to a molecular vibration-rotational spectral band on the basis of exact numerical calculations. Representative calculations are also given for radiant energy transfer through non-isothermal, high-temperature air.\r\n\r\nScaling parameters for radiant energy emission from isobaric but non-isothermal systems are discussed for arbitrary opacities and various spectral line and molecular band models under the restrictions imposed on the allowed temperature profiles for dispersion and Doppler lines by the Eddington-Barbier approximation. An examination is made of the failure of the Eddington-Barbier approximation in radiative heat transfer for line radiation.\r\n\r\nThe relative importance of thermal conduction and radiation in heated air is specified through the use of the pertinent similarity group. Finally, a procedure is given that may be used to obtain approximate continuum opacity estimates in polyelectronic plasmas." }, { "name": "Tracy, Richard Ripley", "degree": "PhD", "year": "1964", "title": "Hypersonic Flow Over a Yawed Circular Cone", "advisor": "Lees, Lester; Kubota, Toshi", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042002-161203", "creators": [ { "name": { "family": "Tracy", "given": "Richard Ripley" }, "id": "Tracy-Richard-Ripley", "display_name": "Tracy, Richard Ripley" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RMWT-TH67", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA 10[degree] semi-apex, circular cone is tested in air at Mach 8 and at yaw angles to 24[degrees]; surface pressure, heat transfer, and pitot-pressure throughout the flow field are presented. The nominal surface temperature is 40% of the free stream stagnation temperature, and the Reynolds number, based on cone generator length, is varied from 0.5 x 10[^5] to 4.2 x 10[^5]. Heat transfer is measured at higher surface temperature ratios (up to 56%) and Reynolds numbers (up to 7.3 x 10[^5]) by reducing the free stream stagnation temperature. All raw data consist of continuous circumferential distributions of each quantity and are included in a supplement.\r\n\r\nThe surface pressure data are compared with the theories of Stone-Kopal and Cheng; Reshotko's theory of heat transfer to the windward generator is compared with experiment. The probe data delineate the boundary between viscous and inviscid flow and determine the shape of the outer shock wave as well as the secondary shocks which appear in the flow field at large yaw. The probe data are sufficient to determine the flow field in the plane of symmetry and permit an approximate representation of the Mach number profiles of the separated viscous flow in the leeward meridian plane beyond a moderate yaw angle." }, { "name": "Tso, Wai Keung", "degree": "PhD", "year": "1964", "title": "Dynamics of Thin-Walled Beams of Open Section", "advisor": "Housner, George W.; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102002-085320", "creators": [ { "name": { "family": "Tso", "given": "Wai Keung" }, "id": "Tso-Wai-Keung", "display_name": "Tso, Wai Keung" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/9S14-CQ21", "abstract": "A study of the coupled torsional and bending vibrations of thin-walled beams of asymmetric open section is made. The formal solution to Gere's theory for the case of a monosymmetric section under general loading conditions and boundary conditions is presented.\r\n\r\nA higher order theory including the effect of shear strain induced by bending and warping of the beam is derived. Spectrum curves of the higher order theory are compared with those from the elementary theory for various boundary conditions for a special family of monosymmetric sections. A study is made to assess the effect of the shape of the cross section of the beam to the differences of the spectrum curves from the two theories. An experiment is performed on two specimens to determine their natural frequencies at different beam lengths and the experimental results are compared to those predicted from the two theories. It is concluded that when the beam is long, the elementary theory is adequate to predict the natural frequencies for torsion predominant modes, but is inadequate for bending predominant modes. For bending predominant modes, the higher order theory should be used. The higher order theory also serves as a guide for the range of validity of the elementary theory.\r\n\r\nCertain nonlinear behavior of the beam is observed in the experiment. When the beam is excited at resonance at a higher mode, under special circumstances, there is a tendency for the beam to shift from the higher resonant mode to vibrate at its fundamental mode, resulting in a high order subharmonic oscillation. An analysis is made to show the possibility of such behavior if the inherently nonlinear governing equations for coupled torsional and bending vibrations are used." }, { "name": "Ahlstrom, Harlow Garth", "degree": "PhD", "year": "1963", "title": "Experiments on the Upstream Wake in Magneto-Fluid Dynamics", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-111323", "creators": [ { "name": { "family": "Ahlstrom", "given": "Harlow Garth" }, "id": "Ahlstrom-Harlow-Garth", "display_name": "Ahlstrom, Harlow Garth" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "chair", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "member", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Lauritsen", "given": "Thomas" }, "id": "Lauritsen-T", "role": "member", "display_name": "Lauritsen, Thomas" }, { "name": { "family": "Whitham", "given": "Gerald Beresford" }, "id": "Whitham-G-B", "role": "member", "display_name": "Whitham, Gerald Beresford" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NAR6-M485", "abstract": "Measurements have been made of the perturbation magnetic field in front of a semi-infinite Rankine body moving parallel to a uniform impressed magnetic field in a conducting fluid. The purpose of these experiments was to investigate the so-called upstream wake effect which has been predicted by theory. It is believed that these are the first experiments in which the upstream wake was observed. Although the wake was found to exist as predicted when the Alfv\u00e9n number is greater than one, its decay behavior was remarkably different from that which was predicted. The solutions for infinite medium predicted that in the wake the perturbations should decay inversely as the distance from the body. However the experiments showed that the perturbations decayed exponentially. It was finally shown that this change in the decay behavior was an effect of the walls and the conducting material surrounding the fluid.
\r\n" }, { "name": "Anderson, William Judson", "degree": "PhD", "year": "1963", "title": "Studies in Panel Flutter at Higher Mach Numbers: I. Flat and Slightly Curved Panels at Mach Number 2.81. II. Cylindrical Shells with Boundary Layer", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152005-081824", "creators": [ { "name": { "family": "Anderson", "given": "William Judson" }, "id": "Anderson-William-Judson", "display_name": "Anderson, William Judson" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E3ZX-JG81", "abstract": "Part I.
\r\n\r\nTwo series of panel flutter tests were carried out in the Jet Propulsion Laboratory's 12 inch supersonic wind tunnel. Flat and slightly curved panels were tested at Mach number 2.81.
\r\n\r\nThe flat, rectangular panels were designed to study two-dimensional flutter. They were clamped at front and rear with free sides which extended into the boundary layer at the sides of the tunnel. These panels fluttered in a two-dimensional mode which occurred at a thickness ratio approximately 15 per cent different from the predictions of existing theory. One of the panels exhibited a three-dimensional \"rocking\" flutter which has not been observed or discussed before. A theory is developed for this type of flutter.
\r\n\r\nThe slightly curved panels were shallow circular cylindrical shells with the generators perpendicular to the flow direction. These panels were all of aspect ratio one. It was found that the effect of curvature was destabilizing and that the effect of internal pressurization was stabilizing.
\r\n\r\nPart II.
\r\n\r\nThe effect of a boundary layer on the flutter of a cylindrical shell is studied. The aerodynamic forces are developed for a shell of infinite length. The boundary layer is idealized as an annular region of uniform subsonic flow surrounding the shell. This boundary layer is of constant thickness along the shell and has a constant velocity distribution through its thickness. The external supersonic flow is also taken to be of uniform velocity, resulting in a \"stepped\" velocity profile through the boundary layer. Small perturbation theory is used in the boundary layer region and linear piston theory is used for the supersonic flow.
\r\n\r\nIn order to replace a physical boundary layer with an idealization for calculations, a procedure is developed for choosing the boundary layer parameters of velocity, pressure, etc. in a consistent way.
\r\n\r\nThe forces which are found through this boundary layer theory are compared with those obtained using piston theory directly. It is found that the forces on a mode with many circumferential waves are much smaller than the forces given by piston theory - - a reduction in amplitude of 95 per cent is possible. Phase changes also occur. The effect of the boundary layer on axisymmetric modes is not so great.
\r\n\r\nFlutter boundaries are obtained for axisymmetric flutter under several conditions and illustrate the effect of boundary layer thickness and structural damping.
\r\n" }, { "name": "Boyle, William Charles", "degree": "PhD", "year": "1963", "title": "Studies on the Biochemistry of Disinfection by Monochloramine", "advisor": "Johansson, Karl Richard", "url": "https://resolver.caltech.edu/CaltechTHESIS:09192011-095341446", "creators": [ { "name": { "family": "Boyle", "given": "William Charles" }, "id": "Boyle-William-Charles", "display_name": "Boyle, William Charles" } ], "advisors": [ { "name": { "family": "Johansson", "given": "Karl Richard" }, "id": "Johansson-K-R", "role": "advisor", "display_name": "Johansson, Karl Richard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "abstract": "The chemical characteristics of monochloramine and some of its effects on Escherichia coli were studied. Under certain conditions monochloramine-treated cells recovered in the presence of excess thiols or thiosulfate. Such recovery could not be attributed to activation of sulfur containing respiratory enzymes.
\r\n\r\nA mechanism of the reaction of monochloramine with amino acids was proposed. The sulfur containing groups were most reactive, followed by the guanidino, amino, imidazoyl and indole groups, and purines and pyrimidines. Sugars (lactose, glucose, ribose) were very unreactive. It was estimated that most of the cellular reactivity with monochloramine was instantaneous, resulting from reactions with sulfur groups.
\r\n\r\nMonochloramination of resting cells inhibited: (a) the oxidation of glucose, succinate, acetate and pyruvate; (b) the fermentation of glucose, fructose-l,6-diphosphate and pyruvate; and (c) the dehydrogenation of succinate, lactate, formate and fructose-1, 6-diphosphate.\r\nFermentation was the most sensitive, and formate and lactate dehydrogenases the least sensitive. In general, inhibition of enzyme activity by monochlorarmine was less than loss in viability. The induction of \u03b2-D-galactosidase was considerably less sensitive than any systems tested to monochloramine.
\r\n\r\nResults of these investigations implicate no one biochemical site of monochloramine action. Attempts to isolate monochloramine induced auxotrophic and monochloramine-resistant mutants were unsuccessful.
\r\n" }, { "name": "Dewey, Clarence Forbes", "degree": "PhD", "year": "1963", "title": "Measurements in Highly Dissipative Regions of Hypersonic Flows. Part I. Hot-Wire Measurements in Low Reynolds Number Hypersonic Flows. Part II. The Near Wake of a Blunt Body at Hypers0nic Speeds", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-083759", "creators": [ { "name": { "family": "Dewey", "given": "Clarence Forbes" }, "id": "Dewey-Clarence-Forbes", "display_name": "Dewey, Clarence Forbes" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XG0Q-ZA42", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I:\r\n\r\nMeasurements were made of the heat loss and recovery temperature of a fine hot-wire at a nominal Mach number of 5.8. Data were obtained over an eight-fold range of Reynolds numbers in the transitional regime between continuum and free-molecule flow. At high Reynolds numbers, the heat transfer data agree well with the results of Laufer and McClellan, which were obtained at lower Mach numbers. At lower Reynolds numbers, the results indicate a monotonic transition between continuum and free molecule heat transfer laws. The slope of the heat transfer correlation also appears to vary monotonically, with Nu [...] at high Reynolds numbers and Nu ~ Re for Re< < 1.\r\n\r\nData on the wire recovery temperature (corresponding to zero net heat transfer) were obtained for free-stream Knudsen numbers between 0.4 and 3.0. Comparison with previous supersonic data suggests that for Mach numbers greater than about two the normalized variation of recovery temperature in the transitional regime is a unique function of the free-stream Knudsen number. The recent data of Vrebalovich (33) suggests that the relation between the normalized recovery temperature and Knudsen number found in this investigation also applies to subsonic and transonic flow.\r\n\r\nThe steady-state hot-wire may be used to obtain two thermodynamic measurements: the rate of heat transfer from the wire and the wire recovery temperature. An illustrative experiment was performed in the wake of a transverse cylinder, using both hot-wire and pressure instruments in a redundant system of measurements. It was shown that good accuracy may be obtained with a hot-wire even when the Reynolds number based on wire diameter is small.\r\n\r\nPart II:\r\n\r\nA theoretical model of the near wake is derived following the ideas of Chapman. This model is based on the postulates of mass conservation in the base flow region, thin viscous shear layers, and a recompression process which is independent of Reynolds number. The analysis, which includes the effects of initial shear layer thickness and base flow temperature, shows that the characteristics of the near wake (base pressure, shear layer angle, etc.) are independent of Reynolds number, and that the shear layer and initial wake thicknesses are proportional to Re[...].\r\n\r\nA series of experiments are presented which show that the postulate of thin shear layers is invalid for Reynolds numbers less than about [...]. At higher Reynolds numbers, the theory is qualitatively incorrect if the Mach number [...] external to the shear layer is large. Detailed measurements with a steady-state hot-wire in the near wake of a two-dimensional circular cylinder indicate that the compression process at the neck is not isentropic, and that the maximum pressure rise occurs downstream of the stagnation point formed by the merging shear layers. Comparison between the experimental and theoretical results points out the importance of the base flow temperature and the initial shear layer profile in determining the observable characteristics of the near wake." }, { "name": "Fourney, Michael Eugene", "degree": "PhD", "year": "1963", "title": "I. On the Application of a Laser to High Speed Photography. II. Torsional Magnetoelastic Waves in a Circular Cylinder", "advisor": "Ellis, Albert T.; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-131705", "creators": [ { "name": { "family": "Fourney", "given": "Michael Eugene" }, "id": "Fourney-Michael-Eugene", "display_name": "Fourney, Michael Eugene" } ], "advisors": [ { "name": { "family": "Ellis", "given": "Albert T." }, "id": "Ellis-A-T", "role": "advisor", "display_name": "Ellis, Albert T." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6M9E-V056", "abstract": "The first part of this thesis deals with the application of a ruby laser to high speed photography. The light that is emitted from a ruby laser is monochromatic, collimated, coherent, linearly polarized, and highly intense. It has been demonstrated that these properties make the laser a very useful tool for research in areas involving photographic techniques.\r\n\r\nA method has been devised by which the output of the laser is controlled and is emitted in the form of a series of light pulses. The rate at which these pulses are generated can be controlled and repetition rates of over 1.6 Mc/sec have been achieved. The 30 nsec duration of an individual pulse represents the exposure time for a high speed laser camera which has been developed. Pictures have been taken at rates of over 1.2 million frames per second. This exposure time represents a reduction of an order of magnitude over that previously possible, with an increase of three orders of magnitude in intensity. In applications where a particular characteristic of the laser light is required, such as the monochromatic nature desired in photoelasticity, this improvement of four orders of magnitude is further increased.\r\n\r\nWhen a series of light pulses is generated in the manner described above it is found that the amplitude of the pulse train becomes stable above a certain critical frequency. This critical frequency is determined to be a function of the laser cavity length. The amplitude of the stabilized pulse train is a function of the repetition rate and the cavity length. The nature of this variation is established and a mechanistic explanation of the phenomena involved is presented." }, { "name": "Gold, Harris", "degree": "PhD", "year": "1963", "title": "Stability of Laminar Wakes", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-152513", "creators": [ { "name": { "family": "Gold", "given": "Harris" }, "id": "Gold-Harris", "display_name": "Gold, Harris" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X1TJ-MG72", "abstract": "This investigation deals with the effects of compressibility on the hydrodynamic stability of wake flows. It is found that the effect of temperature is two-fold: (1), as the wake core temperature increases, the range of Mach numbers over which neutral and self-excited subsonic disturbances can exist also increases; (2) as long as the relative Mach number is below the critical Mach number the neutral inviscid wave number will decrease with increasing core temperature, implying that a hot wake will be more stable than a cool one.\r\n\r\nThe analysis of Batchelor and Gill for the inviscid stability of axi-symmetric incompressible jets has been extended to the more general problem of compressible wakes and jets. It is shown that the results are directly analogous to those obtained for the two-dimensional problem. The sinuous (n = 1) mode is the most unstable allowable mode. This unstable mode is observed in a hypersonic wake." }, { "name": "Gray, Louise Dillon", "degree": "PhD", "year": "1963", "title": "Part I. Theoretical Calculations of Equilibrium Infrared Gas Emissivities from Spectroscopic Data. Part II. Representative Radiative Energy Transfer Calculations for Transparent and Optically Dense Media", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04182012-135901615", "creators": [ { "name": { "family": "Gray", "given": "Louise Dillon" }, "id": "Gray-Louise-Dillon", "display_name": "Gray, Louise Dillon" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/79HT-JK40", "abstract": "Part I. Measured data for carbon dioxide emissivities at temperatures up to 1800\u00b0K have been correlated by postulating (a) that the effective spectral region widths, in which significant contributions are made to the total emission of radiant energy, increase with temperature and optical depth, and (b) that unknown combination and harmonic bands make contributions to the integrated intensities of selected spectral regions in such a way that the absolute values of the integrated intensities (cm^(-2)atm^(-1) remain invariant with temperature.
\r\n\r\nSpectral emissivities have been calculated in the infrared for hydrogen chloride to the rigid-rotator harmonic oscillator approximation using the \"smeared-out\" rotational line model for temperatures of 600 and 2400\u00b0K. In the weak-line approximation, this model gives reasonable agreement with numerical calculations. In the strongline approximation, there is quite a large discrepancy, particularly in the P-branch, at 2400\u00b0K; much better agreement is obtained if vibration-rotation interaction and anharmonicity terms are included in the calculation.
\r\n\r\nEquilibrium spectral emissivities have been computed for water vapor by using available low-temperature spectroscopic data. Satisfactory agreement with experimental results at 1111\u00b0K is obtained if the nearly symmetric top expressions for integrated intensities are used in conjunction with the just-overlapping line model.
\r\n\r\nPart II. The general equations of radiative energy transfer are presented. When the absorption coefficients and/ or the gas volume are sufficiently large, the general transport equation can be approximated by the \"diffusion approximation\". This approximation is applied to a two-phase system consisting of carbon- particles dispersed in a gas. The Rosseland mean absorption coefficients are calculated for spherical carbon particles of 200 and 987 A radius at temperatures of 1000 and 2000\u00b0K, and a comparison is made of the relative magnitudes of conductive and radiative heat transfer for this system.
\r\n\r\nIn the special case when scattering may be neglected, and the temperature and pressure of the gas are constant, the transport equation can be integrated for a particular direction. The total radiant energy transfer to any given element of area depends upon geometrical interchange factors. These interchange factors have been evaluated for centrally located areas in cylindrical and conical chambers; simple relations are given for a transparent gas and an optically dense gas. A represei1ative calculation has been carried out for the radiant energy transfer to a centrally-located area element at the plane of intersection of two truncated cones.
\r\n" }, { "name": "Harwell, Kenneth Edwin", "degree": "PhD", "year": "1963", "title": "Initial Ionization Rates in Shock-Heated Argon, Krypton, and Xenon", "advisor": "Jahn, Robert G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-144544", "creators": [ { "name": { "family": "Harwell", "given": "Kenneth Edwin" }, "id": "Harwell-Kenneth-Edwin", "display_name": "Harwell, Kenneth Edwin" } ], "advisors": [ { "name": { "family": "Jahn", "given": "Robert G." }, "id": "Jahn-R-G", "role": "advisor", "display_name": "Jahn, Robert G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HW2S-MW55", "abstract": "The rates of ionization behind strong shock waves in argon, krypton, and xenon are observed by a transverse microwave probe over a range of electron densities low enough that atom-atom inelastic collisions are the rate determining mechanism. Shocks of Mach number 7.0 to 10.0 propagate down a 5 cm square aluminum shock tube into ambient gases at pressures of 3 to 17 mm Hg, heating them abruptly to atomic temperatures of 5500\u00b0K to 9600\u00b0K. The subsequent relaxation toward ionization equilibrium is examined in its early stages by the reflection, transmission, and phase shifts of a 24.0 Kmc (1.25 cm) transverse microwave beam propagating between two rectangular horns abreast a glass test section. The data yield effective activation energies of 11.9 +/- 0.5 ev for argon, 10.4 +/- 0.5 ev for krypton, and 8.6 +/- 0.6 ev for xenon. These coincide, within experimental error, with the first excitation potentials, rather than the ionization potentials of the gases, indicating that in this range, ionization proceeds via a two-step process involving the first excited electronic state. Within experimental error, the pressure dependence is found to be proportional to the number density squared." }, { "name": "Hickling, Robert", "degree": "PhD", "year": "1963", "title": "I. Acoustic Radiation and Reflection from Spheres. II. Some Effects of Thermal Conduction and Compressibility in the Collapse of a Cavity in a Liquid", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08182006-160354", "creators": [ { "name": { "family": "Hickling", "given": "Robert" }, "id": "Hickling-Robert", "display_name": "Hickling, Robert" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/N27T-0Y47", "abstract": "This thesis presents the results of computations for four problems: two in the field of acoustics and two on the collapse of a cavity in a liquid. The first is an analysis of echoes from a solid homogeneous sphere in water, and demonstrates that the vibrations induced in the solid material by incident sound waves have an important effect on the form of the echo. Various materials are examined and the theory is shown to provide a satisfactory explanation for echoes observed in sonar work. The second problem deals with the far-field radiation patterns formed by different types of source distributions on the surface of a rigid sphere, and demonstrates the effect of the shape of a transducer and its housing on such radiation patterns. The problem of the binaural localization of sound sources is also considered. The third problem is concerned with the behavior of a thermally conducting gas inside a collapsing cavity in a liquid. It is shown that, for bubbles of an appropriate size, thermal conduction in the gas can account for the varying intensities of sonoluminescence which have been observed when different gases are dissolved in water. In the final problem, the shock waves which form in the liquid as a result of a cavity collapse are investigated. It is estimated that such shock waves could be a potent cause of cavitation damage." }, { "name": "Intaglietta, Marcos", "degree": "PhD", "year": "1963", "title": "Streaming Birefringence Study of the Interactions of Submicroscopic Particles", "advisor": "Wayland, J. Harold", "url": "https://resolver.caltech.edu/CaltechTHESIS:04232012-082753882", "creators": [ { "name": { "family": "Intaglietta", "given": "Marcos" }, "id": "Intaglietta-Marcos", "display_name": "Intaglietta, Marcos" } ], "advisors": [ { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "advisor", "display_name": "Wayland, J. Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/G7G4-1K34", "abstract": "An apparatus for the observation of streaming birefringence\r\nwith photoelectric detection, in which the output signal near the null is\r\nlinear with respect to the angular distance to the null, was built and\r\ntested. It was found that such an apparatus is able to establish the position\r\nof the isocline with an accuracy of one degree for a relative\r\nretardation of 10^(-9).
\r\n\r\nThe apparatus was subsequently used to study the streaming birefringence of tobacco mosaic virus and of mixtures of tobacco mosaic virus and southern bean mosaic virus. Accurate measurements of the angle of isocline of both types of solutions showed that no significant difference exists between the experimental and theoretical\r\nresults, once all the sources of extraneous birefringences are accounted\r\nfor.
\r\n\r\nThe amount of retardation of the mixtures was found to be lower\r\nthan that for pure tobacco mosaic virus at equal concentrations of the\r\nlatter and equal velocity gradients. This experimental result is explained\r\nby considering that the random motion of the spherical particles\r\ninteracts with the orderly rotation of the rod-like particles, decreasing\r\nthe amount of aligned material, and thus the amount of retardation.
" }, { "name": "Jennings, Paul Christian", "degree": "PhD", "year": "1963", "title": "Response of Simple Yielding Structures to Earthquake Excitation", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102004-142721", "creators": [ { "name": { "family": "Jennings", "given": "Paul Christian" }, "id": "Jennings-Paul-Christian", "display_name": "Jennings, Paul Christian" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "chair", "display_name": "Housner, George W." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "member", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "civileng" ], "doi": "10.7907/C017-RF39", "abstract": "A method is developed for generating a random process that has the pertinent properties of recorded strong-motion earthquake accelerograms. The model accelerograms are sections of a stationary, Gaussian, random process with a power spectral density found from the average undamped velocity spectrum. Eight pseudo-earthquakes of thirty seconds duration are generated on the digital computer and the velocities, displacements, and velocity spectra calculated. The average velocity spectra of the real and pseudo-earthquakes correspond closely and the velocities, displacements, and velocity spectra of the real and pseudo-earthquakes exhibit similar statistical behavior. It is concluded that the pseudoearthquakes are satisfactory models of strongmotion earthquakes for the purposes of structural analysis.\r\n\r\nA general nonlinear hysteretic force-deflection relation for dynamic studies is presented. The relation is a continuous, smooth function and includes the linear and elasto-plastic relations as limiting cases. The steady-state response to sinusoidal excitation is studied in detail and the results presented. It is concluded that the hysteretic relation is general enough to be useful in structural analysis and that comparison of test results and theory may enable the dynamic force deflection relations of real structures to be approximated.\r\n\r\nA class of yielding structures suitable for earthquake response studies is defined by the geometry of the hysteresis curves and the law describing yielding behavior. The general yielding relation is included in this class as are the linear, the elasto-plastic and the bilinear hysteretic relations. The equation of motion and the energy equation for the response of yielding structures to earthquake motion are examined and a typical yielding structure is subjected to the ensemble of pseudo-earthquakes." }, { "name": "Knauss, Wolfgang Gustav", "degree": "PhD", "year": "1963", "title": "Rupture Phenomena in Viscoelastic Materials", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11052003-091542", "creators": [ { "name": { "family": "Knauss", "given": "Wolfgang Gustav" }, "id": "Knauss-Wolfgang-Gustav", "display_name": "Knauss, Wolfgang Gustav" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KZSV-0Y32", "abstract": "A failure theory for high polymers is developed from the hypothesis that weak regions exist in the material. Defects nucleate in these regions through bond rupture until the defects reach a size which is critical for the applied boundary loading. This critical condition is based on energy balance considerations.\r\n\r\nBy considering the relaxation of the polymer chain in terms of the phenomenological stress-strain behavior and the rupture of chemical bonds in terms of an Arrhenius type rate law, the theory is able to accommodate an arbitrary stress or strain history, and shows reasonably good agreement with experiments which cover a large range of conditions.\r\n\r\nIn addition the stress analysis of a special crack geometry is presented. The geometry consists of a thin infinite strip containing a semi-infinite crack. For a uniform separation of the infinite boundaries an infinitesimal elasticity solution is obtained with the help of the Fourier transform and Wiener-Hopf techniques. The effect of large strains on the stresses near the crack tip is studied experimentally and a surprising correlation with the infinitesimal elasticity solution is found." }, { "name": "Ko, William L.", "degree": "PhD", "year": "1963", "title": "Application of Finite Elastic Theory to the Behavior of Rubber-Like Materials", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03012004-143718", "creators": [ { "name": { "family": "Ko", "given": "William L." }, "id": "Ko-William-L", "display_name": "Ko, William L." } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WMS4-A521", "abstract": "In Part I, methods for determining the strain energy function and the associated constitutive stress-deformation law for rubber-like materials is undertaken and the mechanics of data reduction needed to determine some parameters of the theory are displayed. Experiments were performed in four different stress fields on a foamed polyurethane rubber (dilatable rubber) and on several kinds of continuum rubbers. A new strain energy function and the associated stress-deformation law for a foamed rubber are generated which correlate most of the data to a high degree of accuracy. A parameter appearing in the functional expression for a foam rubber has the same significance as Poisson's ratio in infinitesimal elastic theory. For continuum rubbers, the isotropic Neo-Hookean representations of quasi-static behavior is found to be sufficient over most of the whole range of extension.\r\n\r\nIn Part II, geometrical representations of an isotropic failure surface based on various criteria are depicted both in principal stress and principal stretch spaces for elastic materials. The experimental data are compared with all criteria and the results are discussed.\r\n\t\r\nIn Part III, finite elastic theory is used to determine the stress and deformation fields around the base of a radial crack in an infinitely long rubber log opened by a facially bonded rigid wedge-shaped bellow.\r\n\t\r\nIn the last Part, the topology of interstices idealized as closest packed spherical holes (idealized foam structure) is investigated. Equivalent elastic constants are calculated for rubbery interstices of both hexagonal and face-centered cubic closest packings under small displacement." }, { "name": "McMichael, Francis Clay", "degree": "PhD", "year": "1963", "title": "Suspensions of Granular Particles Generated by an Upward Flow", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04242012-142541079", "creators": [ { "name": { "family": "McMichael", "given": "Francis Clay" }, "id": "McMichael-Francis-Clay", "display_name": "McMichael, Francis Clay" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/E8SA-YB56", "abstract": "A laboratory study was made of the local properties of suspensions\r\nof granular particles generated by an upward flow of water. Four\r\ngranular materials covering a range of particle sizes having particle\r\nReynolds numbers between 10 and 70 were studied by making detailed\r\nmeasurements within ten suspensions. Measurements were made of the\r\nmean properties of over one hundred suspensions. Concentrations in\r\nthe suspensions generated by upward flow were generally greater than\r\nthose of typical hindered settling experiments, but less than those of\r\ntypical fluidization experiments by chemical engineers.
\r\n\r\nMeasurements of the mean concentration for an entire suspension\r\nand the ratio of superficial velocity to particle free-fall velocity yielded\r\na separate relationship for each material studied. These relationships\r\nare strongly dependent on the standard deviation of particle sizes for\r\nthe parent materials.
\r\n\r\nRecognizing that granular materials are never perfectly uniform,\r\nmeasurements of concentration and particle size were made on a local\r\nbasis. The suspensions were found to sort themselves with the fine particles\r\nnear the top and the coarse particles at the bottom, and the local\r\nconcentration was observed to decrease from the bottom to the top of\r\nthe suspension.
\r\n\r\nGranular particles with mass densities approximately two and\r\none-half times the density of water and having particle Reynolds numbers\r\nin the range from 10 to 70 produce highly turbulent systems when fluidized\r\nwith water. It was observed that there is local generation of\r\nturbulence throughout the suspension with the highest intensity of turbulence\r\nbeing in the region where the local concentration is the largest.
\r\n\r\nMeasurements of the hindered settling velocity of a suspension\r\nand the superficial velocity necessary to maintain the suspension show\r\nthe two quantities to be identical for all practical purposes. The turbulence\r\nwas observed visually to be less for the settling suspension than\r\nfor the fluidized suspension.
" }, { "name": "Mei, Chiang Chung", "degree": "PhD", "year": "1963", "title": "Part One. On the Initial Value Problems of Radiation and Scattering of Water Waves by Immersed Obstacles. Part Two. Gravity Waves Due to a Point Disturbance in a Stratified Flow", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032012-150157340", "creators": [ { "name": { "family": "Mei", "given": "Chiang Chung" }, "id": "Mei-Chiang-Chung", "display_name": "Mei, Chiang Chung" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/1C5K-TF68", "abstract": "I. Some initial value problems are studied regarding the radiation and scattering of gravity waves by finite bodies in an infinitely deep ocean. Emphasis is placed on the case where a finite number of thin plates lie on a vertical line, for which the general solution is obtained by transforming the boundary value problem to one of the Riemann-Hilbert type. Explicit investigations are made for the large time behavior of the free surface elevation for the case of a rolling plate, and for the Cauchy-Poisson problems in the presence of a stationary plate. By taking the limit as t \u2192 \u221e, the steady state solution is derived for a harmonic point pressure acting on the free surface near a vertical barrier. Finally a formal asymptotic representation of the free surface elevation is given for large time when the geometry of the submerged bodies is arbitrary.
\r\n\r\nII. The subject gravity waves in the two dimensional flow of a vertically stratified fluid is investigated with regard to the dynamic effects of a submerged singularity. Love's linearized equations are adopted as the basis for the theory. Two specific cases are treated according as the parameter N\u00b2 being a constant or a function of depth, where
\r\n\r\nN\u00b2 = g/P\u2092 dP\u2092/dy
\r\n\r\ncharacterizes the density variation in the fluid. The first example of constant N\u00b2 is physically a hypothetical case but can be given an exact mathematical analysis; it is found that in a deep ocean with such a density variation the interval waves are local in nature, i.e., their amplitudes diminish to zero as the distance from the singularity becomes very large. In the second example an asymptotic theory for small Froude number, U\u00b2/gL \u00ab 1, is developed when N\u00b2(y) assumes the profile roughly resembling the actual situation in an ocean where a pronounced maximum called a seasonal thermocline occurs. Internal waves are now progagated to the downstream infinity in a manner analogous to the channel propagation of sound in an inhomogenous medium.
" }, { "name": "Petty, James Sibley", "degree": "PhD", "year": "1963", "title": "Linearized Transonic Flow About Non-Lifting, Thin Symmetric Airfoils", "advisor": "Royce, Winston W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-135856", "creators": [ { "name": { "family": "Petty", "given": "James Sibley" }, "id": "Petty-James-Sibley", "display_name": "Petty, James Sibley" } ], "advisors": [ { "name": { "family": "Royce", "given": "Winston W." }, "id": "Royce-W-W", "role": "advisor", "display_name": "Royce, Winston W." } ], "committee": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "chair", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Royce", "given": "Winston W." }, "id": "Royce-W-W", "role": "member", "display_name": "Royce, Winston W." }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "member", "display_name": "Cole, Julian D." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3ZC0-7Y26", "abstract": "Transonic flow about symmetric, non-lifting airfoils is treated by solving an approximate linear differential equation of mixed type in place of the exact small-perturbation equations. The pressure distribution and drag coefficient are obtained in closed form for power series airfoils. The technique of local linearization is also applied to improve the accuracy of the results, particularly near the leading edge where the linearizing approximation is found to be invalid. Numerical results are obtained for the parabolic arc and single wedge airfoils and are found to compare favorably with experimental data and with previous theoretical results.\r\n" }, { "name": "Pinchak, Alfred Cyril", "degree": "PhD", "year": "1963", "title": "Experimental Investigation of Gas Phase and Surface Phenomena in a Seeded Plasma", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05182011-164000438", "creators": [ { "name": { "family": "Pinchak", "given": "Alfred Cyril" }, "id": "Pinchak-Alfred-Cyril", "display_name": "Pinchak, Alfred Cyril" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/951D-2728", "abstract": "This thesis deals with some recent experiments conducted with low-temperature seeded plasmas at atmospheric pressure. A simple arc jet was utilized to heat a steady flow of argon gas which was subsequently mixed with a small amount of potassium vapor. The resulting mixture was then channeled through a suitable electrode configuration.\r\n\r\nResults of the experiments indicated two modes of steady, stable current conduction between the electrodes. The data indicated that thermionic emission was sufficient to provide the observed currents during both modes of operation. In the first, or normal, mode the effect of gas phase phenomena predominated in fixing the current.\r\n\r\nUnder certain conditions, a transition to a second mode of operation occurred. In this mode, the current was found to be thermionically limited, and thus was determined solely by electrode surface effects. A quantitative comparison between the observed voltage-current characteristics and two current conduction theories is presented.\r\n\r\nThe aforementioned comparison, along with a quantitative examination of the experimentally observed elevated electron temperatures, indicated that both Joule heating and some non-equilibrium process must be considered in order to obtain a satisfactory understanding of the current conduction phenomena.\r\n\r\nElectrode heat transfer was studied by observing variation of the electrode temperatures with magnitude and polarity of the current. Analysis of the data indicated that an important heat transfer mechanism was the penetration of the surface work function barrier as electrons entered or left the surface." }, { "name": "Porter, John William", "degree": "PhD", "year": "1963", "title": "Part I. Chemical Reactions During Flow in Rocket Nozzles. Part II. Gas Discharge Rates Through De Laval Nozzles and the Experimental Determination of Desorption Rates", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05162012-073100475", "creators": [ { "name": { "family": "Porter", "given": "John William" }, "id": "Porter-John-William", "display_name": "Porter, John William" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/MYSG-P786", "abstract": "In Part I, some of the important physical ideas that have been used in an analysis of chemical changes in rocket nozzles are reviewed with particular reference to the three-body recombination reaction. Modified forma of the simple near-equilibrium flow criterion developed about 15 years ago are shown to lead to results that are substantially equivalent to estimates derived from a criterion\r\nof Bray. The influence of surface-catalyzed processes on atomic recombination rates in rocket nozzles is considered and found likely to be important in present solid-propellant rocket engines.
\r\n\r\nIn Part II, studies of the effective desorption rates of gases (Ar, He, and CO_2) from sand and from silica gel are described. These rates have been determined experimentally by measuring, as a function of time, the pressure drop in a vessel containing the solids when the gases are allowed to discharge through a small de Laval nozzle. The dependence of the desorption rate on temperature has been investigated. A theoretical expression for the rate of desorption from porous solids has been developed assuming that the overall process is diffusion controlled. The experimentally determined desorption rates of Ar, He, and CO_2 from silica gel have been compared with this theoretical expression.
\r\n" }, { "name": "Schmidt, Louis Vincent", "degree": "PhD", "year": "1963", "title": "Measurements of Fluctuating Air Loads on a Circular Cylinder", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-06102008-110237", "creators": [ { "name": { "family": "Schmidt", "given": "Louis Vincent" }, "id": "Schmidt-Louis-Vincent", "display_name": "Schmidt, Louis Vincent" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8714-PJ73", "abstract": "Measurements were made of the unsteady air loads, both lift and drag, developed on a circular cylinder when exposed to flow in the supercritical Reynolds number range from 0.38 x 106 to 0.75 x 106. The three dimensional nature of the flow, which is a consequence of the flow separation effects, is recognized. The statistical character of spatially varying random type fluctuating air loads is presented in the form of cross-spectral densities and cross-correlation coefficients. Information of this type has application to the problem of determining the response of a cylindrical structure when exposed to air loads.
\r\n\r\nThe extreme sensitivity of the flow to surface irregularities in the supercritical Reynolds number region is reported including the effects upon the local and spatial character of the fluctuating loads. Local values of steady state lift could be induced by suitably orienting surface disturbances on the forward portion of the cylinder.
\r\n" }, { "name": "Shi, Yun-Yuan", "degree": "PhD", "year": "1963", "title": "Low Reynolds Number Flow Past Finite Cylinders of Large Aspect Ratio", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172005-152936", "creators": [ { "name": { "family": "Shi", "given": "Yun-Yuan" }, "id": "Shi-Yun-Yuan", "display_name": "Shi, Yun-Yuan" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JA8T-4N67", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nLow Reynolds number flow past finite cylinders of large aspect ratio is considered in this thesis. The first cylinder under consideration consists of a finite cylinder of constant radius [...] with two hemispherical caps attached to each end. The axis of the cylinder is perpendicular to uniform flow at infinity and the half length of the cylinder is L. Therefore, two Reynolds numbers can be formed in the present study, namely, Re=[...] and, [...] . The low Reynolds number flow is studied in the limit [...] for [...] fixed. This clearly shows that the body is of large aspect ratio.\r\n\r\nThe other cylinder under consideration is an ellipsoid of revolution whose half-axis parallel to the flow is [...] and whose half-axis perpendicular to the flow is L. The same limiting case as that for the first finite cylinder is studied.\r\n\r\nAsymptotic expansions of the solution valid for the limiting case [...] are obtained by applying singular perturbation procedures with proper use of the idea of the intermediate solution. The nature of the end source variation and the order of magnitude of various effects are clarified in the present study. In addition, certain general remarks have been made about the difference between the end effects for \"tapered\" and \"untapered\" bodies. It is found that the \"taper\" at the ends plays an essential role." }, { "name": "Titsworth, Robert Clem", "degree": "PhD", "year": "1963", "title": "Correlation Properties of Cyclic Sequences", "advisor": "Golomb, Solomon W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09092005-130635", "creators": [ { "name": { "family": "Titsworth", "given": "Robert Clem" }, "id": "Titsworth-Robert-Clem", "display_name": "Titsworth, Robert Clem" } ], "advisors": [ { "name": { "family": "Golomb", "given": "Solomon W." }, "id": "Golomb-S-W", "role": "advisor", "display_name": "Golomb, Solomon W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/XE6F-BM96", "abstract": "In the unconstrained channel with additive Gaussian noise, where the optimum detector is based on correlation or matched filters, the quality of a code can be expressed as a function of the correlation values between code words. For a cyclic-sequence code, optimality reduces to a criterion to be met by the autocorrelation function of the sequence. Methods are presented here for determining cyclic sequences with given correlation properties.
\r\n\r\nWhen the amount of equipment in the receiver is limited, matched filtering is no longer the optimal detection scheme. A better system, as is shown here, is one which, by the use of a Boolean function, combines several \"component\" sequences to generate the transmitted signal; the receiver consists of filters matched to each component. The logic, the number of components, the requirements of the component sequences to optimize the system, and a general method for treating Boolean logics are given in this work.
" }, { "name": "Vlases, George Charpentier", "degree": "PhD", "year": "1963", "title": "Experiments in a Cylindrical Magnetic Shock Tube", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:10092012-110749746", "creators": [ { "name": { "family": "Vlases", "given": "George Charpentier" }, "id": "Vlases-George-Charpentier", "display_name": "Vlases, George Charpentier" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1EHZ-AZ30", "abstract": "An investigation has been conducted with the two-fold purpose\r\nof producing very high Mach number shock waves and studying their\r\ninteraction with an external magnetic field parallel to the shock front.\r\nBy means of the technique of electromagnetic driving, stable reproducible, outward-going cylindrical shock waves in the Mach number\r\nrange from 20 to 100 have been produced and studied.
\r\n\r\nTheory predicts fundamental differences between the interaction\r\nof a magnetic field with a shock moving into a highly conducting\r\nfluid and the interaction of a field with a strong gas-ionizing shock.\r\nIn the former case a true mhd shock is produced. In the latter the\r\nfield interacts directly only with the piston and the shock remains\r\nan ordinary one. The effect of a conducting wall surrounding the\r\nchamber also differs substantially in the two cases.
\r\n\r\nDetailed experiments have been carried out on gas-ionizing\r\nshocks. While the overall motion is very nearly that predicted by the\r\ntheory, anomalies have arisen in the details of the flow and are\r\nexplained in a qualitative manner.
\r\n\r\nMethods of producing sufficient initial conductivity to obtain a\r\nthin magnetohydrodynamic shock are discussed, together with some\r\npreliminary experiments along these lines.
" }, { "name": "Watson, Ronald", "degree": "PhD", "year": "1963", "title": "I. Experimental Spectroscopic Temperature Measurements in the Reflected Wave Region of a Shock Tube Using the OH \u00b2\u03a3 \u2192 \u00b2\u03c0 Band System. II. Shock Tube Measurements of the Absorption Oscillator Strength for the \u00b2\u03a3 \u2192 \u00b2\u03c0 Band System of OH", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10092012-155504520", "creators": [ { "name": { "family": "Watson", "given": "Ronald" }, "id": "Watson-Ronald", "display_name": "Watson, Ronald" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/20T1-5E54", "abstract": "I. Experimental measurements of the population temperature\r\nbehind the reflected shock in a shock tube are presented. Emission\r\nfrom two wavelength intervals of the OH ^2\u01a9 \u2192 ^2\u03c0 electronic band\r\nsystem was measured photoelectrically, the signals observed being\r\ngenerated by a narrow core of hot gas in the reflected shock region\r\nlooking axially up the tube. The ratio of the rate of increase of\r\nintensity with unit increase of optical depth in the two spectral regions\r\nis a unique function of the temperature for a transparent gas. The\r\nlinearity of the signal increase with time represents an experimental\r\nverification of the transparency and equilibration of the test gas.
\r\n\r\nIn the temperature range of 3300-4300\u00b0 K(M_s ~ 4), the\r\nmeasured spectroscopic temperature was in good agreement with the\r\ncalculated equilibrium temperature, the estimated accuracy of the\r\nspectroscopic temperature being \u00b175\u00b0K. A relaxation time of about\r\n25 \u00b5sec was observed for the (2,2) and (3,3) vibration bands to reach\r\nstatistical equilibrium with the lower (0,0) and (1,1) vibrational levels\r\nin the ^2\u01a9 state from which the emission occurred.
\r\n\r\nII. Previous shock tube measurements of the oscillator strength\r\nof the OH ^2\u01a9 \u2192 ^2\u03c0 band system made in this Laboratory^(1) have been\r\ncorrected. Light scattering in the absolute intensity calibration has\r\nbeen eliminated and a continuous flushing technique was used for preparation\r\nand introduction of the water vapor-argon test gas mixture\r\ninto the tube. The experimental technique remains essentially the\r\nsame as in the earlier studies: hot gas samples at 3100-3500\u00b0 K were\r\nproduced behind the reflected shock and the linear rate of increase of\r\nabsolute spectral intensity in the transparent gas region was measured\r\nby monitoring emission from axial observations in the shock tube.
\r\n\r\nThe absorption electronic f-number for the ^2\u01a9 \u2192 ^2\u03c0 band\r\nsystem has been determined from the measurements as (3.9 \u00b1 0.9) x\r\n10^(-3). This value should be compared with Carrington's ^(2) result of\r\n1.4 x 10^(-3) from absorption measurements in flames, and Oldenberg\r\nand Rieke's^(3) value of 1.3 x 10^(-3) and Dyne's ^(4) value of 0.7 x 10^(-3)\r\nfrom measurements in absorption cells.
" }, { "name": "Wu, Ying-Chu Lin Susan", "degree": "PhD", "year": "1963", "title": "Flow Generated by Suddenly Heated Flat Plate", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-10052004-163535", "creators": [ { "name": { "family": "Wu", "given": "Ying-Chu Lin Susan" }, "id": "Wu-Ying-Chu-Lin-Susan", "display_name": "Wu, Ying-Chu Lin Susan" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "chair", "display_name": "Lees, Lester" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "member", "display_name": "Plesset, Milton S." }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "member", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Lauritsen", "given": "Thomas" }, "id": "Lauritsen-T", "role": "member", "display_name": "Lauritsen, Thomas" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CPQD-RQ29", "abstract": "By employing the two-sided Maxwellian in Maxwell's moment method a kinetic theory description is obtained of the flow generated by a step-function increase in the temperature of an infinite flat plate. Four moments are employed in order to satisfy the three conservation equations, plus one additional equation involving the heat flux in the direction normal to the plate. For a small temperature rise the equations are linearized, and closed-form solutions are obtained for small and large time in terms of the average collision time.
\r\n\r\nInitially the disturbances propagate along two distinct characteristics, but the discontinuities across these waves damp out as time increases. At large time the main disturbance propagates with the isentropic sound speed. Solutions for mean normal velocity and temperature show the transition from the nearly collision-free regime to the Navier-Stokes-Fourier regime, which is characterized by a boundary layer near the plate surface merging into a diffuse \"wave\". The classical continuum equations, plus a temperature jump boundary condition, seem to be perfectly adequate to describe the flow beyond a few collision times, provided one accounts properly for the interaction between the inner thermal layer and the outer diffuse wave.
" }, { "name": "de Barbeyrac Saint-Maurice, Jacques J.", "degree": "PhD", "year": "1963", "title": "Minimal Time Deadbeat Regulation and Control of Linear, Stationary, Sampled-Data Systems", "advisor": "Mullin, Francis J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04052012-083321157", "creators": [ { "name": { "family": "de Barbeyrac Saint-Maurice", "given": "Jacques J." }, "id": "de-Barbeyrac-de Barbeyrac-Saint-Maurice-Jacques-J", "display_name": "de Barbeyrac Saint-Maurice, Jacques J." } ], "advisors": [ { "name": { "family": "Mullin", "given": "Francis J." }, "id": "Mullin-F-J", "role": "advisor", "display_name": "Mullin, Francis J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/X0XR-4J34", "abstract": "The problem of minimal time deadbeat regulation and control of linear, stationary, sampled-data systems is studied in this dissertation,\r\nassuming that only a limited number of the state variables are directly observable. The problem is first solved for the usual one-input one-output systems. The existing techniques for deadbeat digital compensation\r\nare all derived under the assumption that a specific initial state always exists; it will be shown that if this condition is violated and a digital controller is designed using the existing methods, the system has a transient response with time constants corresponding to the stable\r\npoles of the open-loop system. A technique to overcome this difficulty is developed using both a state-space and a z-transform approach to the problem. A digital controller which in a sense first identifies the complete state and then proceeds to control it in a deadbeat fashion is\r\nsynthesized.
\r\n\r\nThe problem is next solved for multi-input, multi-output\r\nsystems, using a state-space approach different from the one used for the one-input, one-output systems. It is first shown that if all the state variables are directly observable and the system is completely controllable in N sampling periods, there always exists at least one\r\nstationary, linear feedback law which will regulate the system in N sampling periods. If only a limited number of the state variables are directly observable, but the system is completely observable in N sampling periods, then there exist \"discrete compensators\" which will regulate the system in (N + N') sampling periods.
" }, { "name": "Albini, Frank Addison", "degree": "PhD", "year": "1962", "title": "I. Relaxation Time of One-Dimensional, Laminar Deflagration for First Order Reactions. II. Reflection and Transmission of Electromagnetic Waves at Electron Density Gradients", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07262011-115318209", "creators": [ { "name": { "family": "Albini", "given": "Frank Addison" }, "id": "Albini-Frank-Addison", "display_name": "Albini, Frank Addison" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "chair", "display_name": "Marble, Frank E." }, { "name": { "family": "De Prima", "given": "Charles R." }, "id": "De-Prima-C-R", "role": "member", "display_name": "De Prima, Charles R." }, { "name": { "family": "Jahn", "given": "Robert G." }, "id": "Jahn-R-G", "role": "member", "display_name": "Jahn, Robert G." }, { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "member", "display_name": "Papas, Charles Herach" }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "member", "display_name": "Rannie, W. Duncan" } ], "option_major": [ "mecheng" ], "doi": "10.7907/TYH3-ZQ11", "abstract": "Part I
\r\n\r\nThe one-dimensional, time-dependent equations describing laminar deflagration are solved by an integral method, under the assumption of a physical model for the flame structure and behavior, with restrictions on the type of deviation from steady-state behavior. By virtue of application of a hot-boundary approximation of the von K\u00e1rm\u00e1n type, certain sensitive integrals are expressed in a form independent of the temperature profile assumed. Two cases are considered: the \"thermal theory\" neglecting diffusion, and the case of unity Lewis number (temperature/concentration similarity). Only first order reactions are considered. Arguments supporting the generality of the results are included, along with a discussion of accuracy, and some comparison with experimental work. Graphical display of the results anticipates the utility of the theory for correlating and cross-checking experimental data.
\r\n\r\nIt is concluded that the relaxation time is closely related to the time required for the gas undergoing rapid chemical reaction to pass through the flame.
\r\n\r\nPart II
\r\n\r\nThe interaction of an electromagnetic wave with a mildly ionized gas is described by an ensemble average treatment of electron motion, and under this description, electromagnetic wave propagation parameters derived. Motivated by the fact that mildly ionized gases in general exhibit inhomogeneous boundary regions, exemplary transition zones are described in terms of varying electron density but constant collision frequency, in order to simplify the solution of wave problems. The half-space reflection problem with a linear transition zone is solved exactly and under two approximations. It is discovered that the reflection and transmission coefficients are strong functions of zone thickness for thin zones. A piecewise-linear transition zone solution exemplifies the procedure for constructing an approximate solution to an arbitrary profile and illustrates the relative insensitivity of reflection and transmission coefficients to detailed zone structure. The \"slab\" reflection problem with symmetrical, linear transition zones is solved exactly, and it is discovered that the basic periodicity of reflection and transmission coefficients with slab thickness is unchanged, although shifted to higher values of slab thickness/wavelength. The text is supported by fairly extensive graphical presentation of results.
" }, { "name": "Babcock, Charles Dwight", "degree": "PhD", "year": "1962", "title": "The Buckling of Cylindrical Shells with an Initial Imperfection Under Axial Compression Loading", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242004-151013", "creators": [ { "name": { "family": "Babcock", "given": "Charles Dwight" }, "id": "Babcock-Charles-Dwight", "display_name": "Babcock, Charles Dwight" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0P4A-SA39", "abstract": "An experimental and theoretical investigation of the effect of a specific type of initial imperfection on the buckling load of a circular cylindrical shell under axial compression loading was carried out. The imperfection studied was axially symmetric in shape and had the form of a half sine wave in the length direction. Both inward and outward bowing imperfections were considered.\r\n\r\nThe experiments were carried out with shells fabricated by a copper electroforming process. The shells had no longitudinal seams and had unintended imperfections of the order of the wall thickness. The buckling stress for the intended imperfection studied was only slightly influenced over a considerable range of imperfection amplitudes.\r\n\r\nThe theoretical solution located the bifurcation points of the prebuckled axially symmetric state. The solution showed that outward bowing shells should have the same buckling stress as a perfect cylindrical shell and inward bowing shells should have a lower buckling stress than the perfect cylinder." }, { "name": "Brown, Wilbur Parker", "degree": "PhD", "year": "1962", "title": "A Theoretical Study of the Scattering of Electromagnetic Impulses by Finite Obstacles", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:07262011-163527834", "creators": [ { "name": { "family": "Brown", "given": "Wilbur Parker" }, "id": "Brown-Wilbur-Parker", "display_name": "Brown, Wilbur Parker" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4892-CE13", "abstract": "A general approach to the solution of pulse scattering by\r\nfinite obstacles is formulated. The essential feature of this approach is the identification and separate treatment of the individual terms in a wavefront expansion of the transforms of the field vectors. It is demonstrated that the dispersive effect of a finite conductivity in the scattering obstacle can be neglected for all metals but that it may be significant for poorly conducting\r\nmaterials such as dry earth. The wavefront technique is\r\nemployed to solve the problems of the transmission of a delta pulse through a conducting dielectric slab and the reflection and diffraction of a delta pulse from a perfectly conducting sphere. The transmission problem results provide a convenient example of the usefulness of the wavefront approach. The results for the sphere problem indicate that the nature of the waves observed at a\r\ngiven spatial point change in time, It is shown that the penumbra and the caustic region in the vicinity of the focal line \u03b8 = \u03c0 are initially of zero extent. The rates of expansion of these regions with increasing time are obtained by a consideration of the error terms in the asymptotic expansions of the fields. The temporal behavior of the near and far field zones is obtained in a similar manner." }, { "name": "Cummings, Benjamin Edgar", "degree": "PhD", "year": "1962", "title": "Some Nonlinear Vibration and Response Problems of Cylindrical Panels and Shells", "advisor": "Fung, Yuan-cheng; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-115144", "creators": [ { "name": { "family": "Cummings", "given": "Benjamin Edgar" }, "id": "Cummings-Benjamin-Edgar", "display_name": "Cummings, Benjamin Edgar" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/AXC2-6P94", "abstract": "Large amplitude vibrations and forced responses of curved panels and shells are studied by the application of the shallow shell equation. The Galerkin procedure is used to reduce the nonlinear partial differential equations to ordinary nonlinear equations. Marked differences are found between the behavior of curved panels and cylindrical shells. Relations for the dependence of the free vibration period on amplitude are given. A two mode analysis of the cylindrical shell problem is included.
\r\n\r\nThe curved panel is found to exhibit a buckling phenomenon for the simple \"breathing modes\". Shock response methods are used to predict dynamic buckling of the curved panel and the predictions are verified by numerical integration.
\r\n\r\nThe cylindrical shell vibrations and responses are found to be governed by Duffing's equation and certain of the well-known properties of Duffing's equation are applied to the cylindrical shell dynamics.
\r\n\r\nThe two mode analysis of the cylindrical shell is shown to exhibit weak coupling, allowing the separate excitation of the coupled modes.
\r\n\r\nSome numerical results are given.
" }, { "name": "DiLoreto, Aldo Gene", "degree": "PhD", "year": "1962", "title": "Noise Optimization Techniques for Linear Transistor Amplifiers", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192011-090320424", "creators": [ { "name": { "family": "DiLoreto", "given": "Aldo Gene" }, "id": "DiLoreto-Aldo-Gene", "display_name": "DiLoreto, Aldo Gene" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5JV3-EZ18", "abstract": "Methods of minimizing the effects of internally generated noise in transistor amplifiers are described. The study is both theoretical and experimental in nature, the greater part of the theoretical portion being based on van der Ziel\u2019s transistor noise model. From this model, analytical\r\nexpressions are formulated giving (in terms of easily measurable transistor parameters) the operating point and source resistance that will optimize the noise performance of the amplifier. The derived equations are substantiated by an experimental study. Both audio and radio frequency\r\namplifiers are considered. At audio frequencies, the work is primarily experimental in nature. Here, attention is focused on developing a simplified optimization procedure. For the radio frequency amplifier, formulas are also derived that describe the effect of source reactance on the amplifier\u2019s noise performance.\r\n\r\nFormulas giving the noise figures of the transformer- coupled transistor amplifier are included. From these equations, analytical expressions are formulated that describe the emitter current and transformer turns ratio\r\nwhich will minimize the effects of internally generated noise. An experimental investigation verified the results.\r\n\r\nA portion of the work is devoted to a theoretical and experimental study of temperature and its effect on the noise performance of transistor amplifiers. This study, which considers temperatures from 77 to 320\u00b0 K, differs\r\nfrom those previously conducted in that a wide range of source resistances are used.\r\n\r\nEquations describing the degradation in noise performance produced by resistive stabilizing components are given.\r\n\r\nAlso included is an analytical description of the methods used to obtain noise-factor measurements.\r\n" }, { "name": "Eiselen, Everett Truman", "degree": "PhD", "year": "1962", "title": "Sound Propagation in Small Diameter Tubes", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechTHESIS:07282011-152915773", "creators": [ { "name": { "family": "Eiselen", "given": "Everett Truman" }, "id": "Eiselen-Everett-Truman", "display_name": "Eiselen, Everett Truman" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/5WXZ-NS91", "abstract": "A detailed study of the propagation of sound in small diameter tubes has been made. The physical configuration studied, is typical of instrument systems. The transient response has been determined in addition to the frequency response. The solutions have been programmed on a high speed digital computer and evaluated.\r\n\r\nSeveral approximate solutions have been compared. Iberall's\r\nresults have been expanded to provide a solution of the transient problem. The range of applicability of the various approximations, and their deviation from the more precise solution including heat conduction, has\r\nbeen determined. A detailed analysis of the restrictions that are made on the more precise solution is given.\r\n\r\nThe results have been put in a dimensionless form to provide more general applicability. The proper parameter to describe the damping of the tube has been determined. A knowledge of this parameter and the volume on the end of the tube permits a quite accurate prediction of the\r\nresponse of the system. The value of this parameter required for optimization has been found.\r\n" }, { "name": "Goldstein, Richard Morris", "degree": "PhD", "year": "1962", "title": "Radar Exploration of Venus", "advisor": "Martel, Hardy Cross", "url": "https://resolver.caltech.edu/CaltechTHESIS:07212010-095208070", "creators": [ { "name": { "family": "Goldstein", "given": "Richard Morris" }, "id": "Goldstein-Richard-Morris", "display_name": "Goldstein, Richard Morris" } ], "advisors": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-H-C", "role": "advisor", "display_name": "Martel, Hardy Cross" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/EB99-8T09", "abstract": "The feasibility of studying Venus by radar was demonstrated on the tenth of March, 1961, when an echo from Venus was first detected in real time.\r\n\r\nThe spectrum of the echo may be expected to be broadened by the doppler shifts produced by any rotation Venus might have. In order to measure this broadening, a novel technique for accurate spectral estimation of this extremely weak signal was devised, analyzed and implemented. The results of the measurements indicate that Venus rotates only once for each of its years, so that one hemisphere always faces the sun. In addition, the spectral measurements together with some polarization measurements enable one to infer some scattering properties of the surface.\r\n\r\nTime of flight measurements were also made, using a cross-correlation technique. These, compared with standard astronomical tables, provide a new value for the Astronomical Unit. The standard deviation of these measurements is only a few parts in 10^7." }, { "name": "Guttman, Andrew", "degree": "PhD", "year": "1962", "title": "I. Quantitative Studies of the N0\u2082- N\u20820\u2084 System in the Infrared. II. Emission of Diffuse Bands of Sodium Behind Shock Fronts", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07292011-110936010", "creators": [ { "name": { "family": "Guttman", "given": "Andrew" }, "id": "Guttman-Andrew", "display_name": "Guttman, Andrew" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/BKS0-GN58", "abstract": "integrated intensities as a function of temperature have been measured for one NO_2 and for four N_2O_4 combination bands in the spectral region from one to five microns. The temperature was varied from 50 to 100\u00b0C for the gas-phase studies and from 25 to 100\u00b0C for the liquid-phase experiments. In the spectral region from 5 to 15 microns, integrated intensities at 25\u00b0C were measured for one NO_2 and for three N_2O_4 fundamental bands. Results from a series of absorption spectra were interpreted in accordance with the Wilson\u2013Wells-Penner-Weber method. Saturated vapors were used in all experiments; the optical depth was varied by using a series of spacers in a specially designed infrared absorption cell capable of handling both liquid and gas. Measured intensities for N_2O_4 combination bands in the liquid and gas phases were compared and found to differ by less than 16% for three out of four combination bands studied; for the fourth band, the observed difference was about 50%. Results for all of the combination bands investigated indicate that the integrated intensities vary approximately as 1/T in the temperature range under consideration.
\r\n\r\nAbsolute intensity data may be used for a spectroscopic determination of the heat of dissociation for gases in chemical equilibrium. For the reaction N_2O_4 -> 2NO_2, we have found the value of \u0394H\u00b0 ,using the temperature dependence of the absorption bands, to be 13.1 Kcal/(mole N_2O_4); this value is in fair agreement with the value of 13.7 Kcal/(mole N_2O_4); obtained by techniques utilizing density measurements.
\r\n\r\nIn Chapter II, shock tube studies are descri.bed of a diffuse emission band, centered near the resonance lines of sodium and attributed to van der Waals molecules Na_2. A small quantity of finely ground sodium salt (e.g., NaCl, NaBr, or Na_2CO_3) was placed at the end of the low-pressure section of a shock tube containing an argon atmosphere. Spectra were recorded photographically with a 1.5 m grating spectrograph.
" }, { "name": "Hoult, David Parks", "degree": "PhD", "year": "1962", "title": "Magnetohydrodynamic Surface Waves", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262008-082838", "creators": [ { "name": { "family": "Hoult", "given": "David Parks" }, "id": "Hoult-David- Parks", "display_name": "Hoult, David Parks" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RVM0-1T80", "abstract": "This is an experimental and theoretical study of deep water gravity-like waves which are induced in a liquid metal by a changing magnetic field. The dominant feature of such waves is the emission of Alfven waves from the free surface. A linearized theory is derived and compared with experiments." }, { "name": "King, Kenneth Robert", "degree": "PhD", "year": "1962", "title": "Dynamic Shear Deformation in Zinc Crystals", "advisor": "Wood, David Shotwell; Clark, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08012011-141442374", "creators": [ { "name": { "family": "King", "given": "Kenneth Robert" }, "id": "King-Kenneth-Robert", "display_name": "King, Kenneth Robert" } ], "advisors": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "matsci" ], "doi": "10.7907/J5Q8-5C31", "abstract": "The initial stages of yielding in single crystals of zinc have been investigated at temperatures of -292\u00b0F (-180\u00b0C), -93\u00b0F (-70\u00b0C) and +75\u00b0F (24\u00b0C), by means of rapidly applied constant stress pulses to produce slip along the basal planes of these crystals.
\r\n\r\nThe experimental results are interpreted in terms of a dislocation mechanism based upon the assumptions that the average velocity of dislocations remains constant during the period of constant applied stress and that the density of moving dislocations increases in linear proportion to the plastic strain. The experimental curves of plastic strain vs. time exhibit the form predicted by the assumed dislocation mechanism. The average dislocation velocity is found to be proportional to the 2.5 power of the excess of the applied stress over the static yield stress. The purity of the specimen and the test temperature are found to influence the average dislocation velocity only through their influence upon the static yield stress.
\r\n\r\nThese results show that the behavior of basal slip dislocations in zinc is qualitatively the same as the behavior of slip dislocations in lithium fluoride and silicon-iron, as reported by Johnston and Gilman and by Stein and Low, respectively. Hence it is concluded that the concept of a lattice resistance to dislocation motion proposed by Gilman to explain the observed behavior of lithium fluoride and silicon-iron can be applied equally well to explain the observed behavior of zinc, and in fact that this is the only explanation consistent with the observed results.
" }, { "name": "Klement, William, Jr.", "degree": "PhD", "year": "1962", "title": "Metastable Structures in Alloys Rapidly Cooled from the Melt", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192011-104507587", "creators": [ { "name": { "family": "Klement", "given": "William, Jr." }, "id": "Klement-William", "display_name": "Klement, William, Jr." } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/HHG6-AY94", "abstract": "Small amounts of liquid alloys are cooled to the solid\r\nstate very rapidly by means of a technique which is described in detail. Procedures for studying the resultant thin, irregular foils are discussed; most of the results are obtained from x-ray diffraction experiments. Among the nonequilibrium structures found in various alloys are cited the metastable solid solutions in silver-copper and gallium\r\nantimonide-germanium alloys, the extended primary solid\r\nsolutions in some silver-base alloys, and the metastable\r\nhexagonal close-packed structures in silver-germanium\r\nalloys. The quenching technique is discussed and tentative\r\ncriteria for the prediction and rationalization of certain\r\nmetastable structures in alloy systems are inferred from an\r\nanalysis of the process.\r\n" }, { "name": "Lathrop, Kaye Don", "degree": "PhD", "year": "1962", "title": "Neutron Thermalization in Solids", "advisor": "Lurie, Harold", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122005-162942", "creators": [ { "name": { "family": "Lathrop", "given": "Kaye Don" }, "id": "Lathrop-Kaye-Don", "display_name": "Lathrop, Kaye Don" } ], "advisors": [ { "name": { "family": "Lurie", "given": "Harold" }, "id": "Lurie-H", "role": "advisor", "display_name": "Lurie, Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/K87B-FC98", "abstract": "To describe neutron thermalization in solid media, two simplified models are formulated to describe the motions of atoms bound in solids. One atomic model postulates that the atoms of solids are linear, classical, randomly oriented, harmonic oscillators characterized by a single energy; and the other model postulates the same basic oscillator but permits a distribution of oscillator energies. With atom speed distributions derived from these models, energy exchange cross sections are evaluated analytically assuming a free particle neutron-atom interaction. With these energy exchange cross sections, integral equations are formulated describing thermalization of neutrons in infinite homogeneous media containing a 1/v absorber. The integral equations of both atomic models are solved numerically for the neutron density speed distribution. Numerical results for the single energy atomic oscillator of unit mass are compared with experimental results for neutron thermalization in zirconium hydride. Results for the averaged energy atomic oscillator of unit mass are compared with the neutron density calculated from the Wigner-Wilkins monatomic gas model. This comparison is made for three values of absorption. Numerical results for averaged energy atomic oscillators of masses 1, 2, 9, and 12 are examined to determine the effect of atomic mass upon the neutron density distribution." }, { "name": "Liu, Chung-Yen", "degree": "PhD", "year": "1962", "title": "Part I. Kinetic Theory Description of Plane, Compressible Couette Flow. Part II. Kinetic Theory Description of Conductive Heat Transfer from a Fine Wire", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-133941", "creators": [ { "name": { "family": "Liu", "given": "Chung-Yen" }, "id": "Liu-Chung-Yen", "display_name": "Liu, Chung-Yen" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q16R-JR92", "abstract": "PART I: \r\n \r\nBy utilizing the two-stream Maxwellian in Maxwell's integral equations of transfer we are able to find a closed-form solution of the problem of compressible plane Couette flow over the whole range of gas density from free molecule flow to atmospheric. The ratio of shear stress to the product of ordinary viscosity and velocity gradient, which is unity for a Newtonian fluid, here depends also on the gas density, the plate temperatures and the plate spacing. For example, this ratio decreases rapidly with increasing plate Mach number when the plate temperatures are fixed. On the other hand, at a fixed Mach number based on the temperature of one plate, this ratio approaches unity as the temperature of the other plate increases. Similar remarks can be made for the ratio of heat flux to the product of ordinary heat conduction coefficient and temperature gradient.\r\n\r\nThe effect of gas density on the skin friction and heat transfer coefficients is described in terms of a single rarefaction parameter, which amounts to evaluating gas properties at a certain \"kinetic temperature\" defined in terms of plate Mach number and plate temperature ratio. One interesting result is the effect of plate temperature on velocity \"slip\". In the Navier-Stokes regime most of the gas follows the hot plate, because the gas viscosity is larger there. As the gas density decreases the situation is reversed, because the velocity slip is larger at the hot plate than at the cold plate. In the limiting case of a highly rarefied gas most of the gas follows the cold plate.\r\n\r\nLimitations of the present six-moment approximation at high plate Mach numbers are discussed and it is concluded that an eight-moment approximation would eliminate these difficulties. The results obtained in this simple geometry suggest certain conclusions about hypersonic flow over solid bodies when the surface temperature is much lower than the kinetic temperature.\r\n\r\nPART II:\r\n\r\nThe Maxwell moment method utilizing the two-sided Maxwellian distribution function is applied to the problem of conductive heat transfer between two concentric clylinders at rest. Analytical solutions are obtained for small temperature differences between the cylinders. The predicted heat transfer agrees very well with experiments performed by Bomelburg, Schafer-Rating and Eucken. Comparison with results given by the Grad's thirteen moment equations, and with those given by Fourier's \"law\" plus Maxwell-Smoluchowski temperature-jump boundary condition shows that the two-sided character in the distribution function is a crucial factor in problems involving surface curvature." }, { "name": "Lloyd, James Reily", "degree": "PhD", "year": "1962", "title": "Wave Propagation in an Elastic Plate Resting on an Elastic Foundation", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172011-153814513", "creators": [ { "name": { "family": "Lloyd", "given": "James Reily" }, "id": "Lloyd-James-Reily", "display_name": "Lloyd, James Reily" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/D5NC-XR09", "abstract": "Presented is an analysis of wave propagation in an infinite elastic plate or beam on an elastic foundation. The results are presented in two parts:\r\n\r\n1. The frequency spectra (frequency as a function of wave number) for the problem based on existing approximate bending theories are compared with the spectra based on the exact equations of motion from linear elasticity theory. The existence of complex wave numbers is established in each case. A distinct similarity is found between the\r\nspectrum representing the more exact theory of bending (Timoshenko bending mechanism) and the exact Rayleigh-Lamb spectrum for symmetric waves in a free elastic plate. Good agreement between approximate theories and the exact equations is found for soft foundations under the usual restrictions of low frequency-long waves.\r\n\r\n2. The transient response is considered for the exact theory and the more exact theory of bending. In both cases suddenly applied line loads are considered. In the latter case the related point load problem is also studied. Two distinct integral transform methods of solution are\r\npresented and used in these problems. For one of these methods the contributions from the various modes, including the complex arms, are identified with certain integrals that are components of the solution. Results from numerical computation of these integrals are presented and\r\nanalyzed for the more exact theory of bending using two different foundation stiffnesses.\r\n" }, { "name": "Lock, Kenneth", "degree": "PhD", "year": "1962", "title": "A Digital-Computer-Programmed Topological Method of Coordinate Selection for Numerical Computations in an Electrical Network", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192011-102613198", "creators": [ { "name": { "family": "Lock", "given": "Kenneth" }, "id": "Lock-Kenneth", "display_name": "Lock, Kenneth" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/1KC2-ZF72", "abstract": "In this thesis an algorithm is developed for setting up the\r\ndifferential equations and initial conditions of an electrical network of arbitrarily connected capacitors, resistors, inductors, multiwinding ideal transformers, and ideal voltage and current sources that topologically represents a large class of systems. The algorithm\r\nformulates the equation in a set of coordinates such that all matrices to be inverted are nonsingular. The topological description of the circuit is used to select a nonsingular set of coordinates which enables the computation of the transient responses and the short circuit\r\nadmittances to a set of arbitrarily chosen ports of a network. Transformers are accounted for by appropriately selecting a set of dependent variables from the set of transformer linear equations. The algorithm\r\nfor selecting a nonsingular set of coordinates, being mainly symbol manipulations, is coded in LISP. It is also shown that the same method may be applied to systems with nonlinear parameter matrices." }, { "name": "Malmuth, Norman David", "degree": "PhD", "year": "1962", "title": "Perturbations on Hypersonic Wedge Flow", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152005-133232", "creators": [ { "name": { "family": "Malmuth", "given": "Norman David" }, "id": "Malmuth-Norman-David", "display_name": "Malmuth, Norman David" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KE9Q-XN81", "abstract": "The hypersonic inviscid flow over a configuration representing a small perturbation about a two-dimensional wedge is analyzed. Equations and boundary conditions are obtained for a class of general perturbations within the framework of Hypersonic Small Disturbance Theory.\tA specialization of this formulation is made to the case where the resultant perturbation consists of semi-infinite flat plates of slightly different incidence to the freestream. The flow over such a shape is divided into an outlying uniform region and a central conefield. Here, the outlying, uniform region solution is found to be trivial. The determination of the conefield gives rise to an elliptic boundary value problem which is solved with the aid of the Tschaplygin transformation and other conformal mappings.\r\n\r\nCalculations are presented using the Fourier series solution for the perturbation pressure indicating the surface loads associated with the perturbation as well as the shock distortion function. Integral representations are obtained for the downwash and sidewash perturbations using the pressure solution.\r\n\r\nThe results are compared qualitatively with an analogous linear supersonic flow.\r\n\r\nFinally, a solution for more general profiles is obtained under the further restriction that the specific heat ratio [gamma] is close to one. This solution is specialized to the case considered previously and a qualitative evaluation of the physical significance of the results is made." }, { "name": "Marlotte, Gary Lynn", "degree": "PhD", "year": "1962", "title": "An Experimental Investigation of the Effect of a Transverse Hypersonic Flow Velocity upon a Low-Density D.C. Electrical Discharge in Air", "advisor": "Demetriades, Anthony; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12132005-105051", "creators": [ { "name": { "family": "Marlotte", "given": "Gary Lynn" }, "id": "Marlotte-Gary-Lynn", "display_name": "Marlotte, Gary Lynn" } ], "advisors": [ { "name": { "family": "Demetriades", "given": "Anthony" }, "id": "Demetriades-A", "role": "advisor", "display_name": "Demetriades, Anthony" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3BR3-ZT02", "abstract": "The low-density D.C. electrical discharge in a uniform gas stationary with respect to the electrodes has been studied extensively. However, when the gas moves at a hypersonic speed transverse to the electrodes, several completely new effects are introduced. Experiments were carried out with air in the GALCIT 5-inch by 5-inch hypersonic wind tunnel with a nominal Mach number of 5.8. D.C. breakdown voltages and steady-state sub-normal glow voltages were measured across a channel formed by two sharp-edged insulating flat plates in which flat-plate \"Rogowski\" electrodes were embedded. Segmented electrodes were then used in the normal glow regime to measure current distributions at each electrode for various electrode segment combinations, total currents, and densities.\r\n\r\nSome important results of the present study are the following. For the characteristic dimensions and speeds involved, the explicit dependence of electrical breakdown upon the velocity of the stream is small compared to the effect of boundary layer density defects. A theoretical treatment of breakdown is given and qualitative agreement with experiments is obtained. In the normal glow regime using segmented electrodes, an unmistakable explicit flow velocity effect was observed, with the discharge current paths being displaced downstream compared to static bell-jar tests at equivalent densities." }, { "name": "Marxman, Gerald Albert", "degree": "PhD", "year": "1962", "title": "Heat Transfer in Reacting Gas Mixtures with Large Pressure Gradients.", "advisor": "Marble, Frank E.; Kerrebrock, Jack L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08032011-150229292", "creators": [ { "name": { "family": "Marxman", "given": "Gerald Albert" }, "id": "Marxman-Gerald-Albert", "display_name": "Marxman, Gerald Albert" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." }, { "name": { "family": "Kerrebrock", "given": "Jack L." }, "id": "Kerrebrock-J-L", "role": "advisor", "display_name": "Kerrebrock, Jack L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/61YR-1468", "abstract": "Energy transport by conduction and diffusion is considered in chemically-reacting, gaseous mixtures which have a pressure gradient parallel to the temperature gradient. As a consequence of pressure diffusion and other mechanisms, the pressure gradient can influence energy transport, and this effect is given particular emphasis. The use of an idealized flow model and a perturbation technique makes it possible, with a relatively simple analysis, to deduce many of the features of energy transport in multicomponent, gaseous media.
\r\n\r\nThe dissociation reaction of a diatomic gas, with the ratio (reaction rate/diffusion rate) either large or small, is studied. When the flow is chemically frozen, the extension of the analysis to include any number of components would be straightforward, in principle. However, when the gas is in local chemical equilibrium, the binary case is unique in that the diffusion velocities are then proportional to the local temperature gradient, but independent of the local pressure gradient. Consequently, there exists an effective thermal conductivity. The order of the governing set of equations is therefore the same as for a simple, single-component gas, and the effect of the wall surfaces on reaction rates is confined to reaction boundary layers. Two other examples illustrate that the order of the equations is higher when the equilibrium flow comprises more than two components, although there are still reaction boundary layers. The additional boundary conditions associated with the higher order are determined, through integral conditions, by the proportions of the chemical elements present.
\r\n\r\nThe results show that in many high-temperature gasdynamics problems of current interest the presence of a pressure gradient may have an important influence on energy transport.
\r\n" }, { "name": "Mason, Peter Vroman", "degree": "PhD", "year": "1962", "title": "Surface Impedance of Thin Superconducting Films", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:08032011-113156194", "creators": [ { "name": { "family": "Mason", "given": "Peter Vroman" }, "id": "Mason-Peter-Vroman", "orcid": "0000-0002-7963-7420", "display_name": "Mason, Peter Vroman" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/F5XN-7E70", "abstract": "Theoretical analysis and experimental measurements have been made of the propagation of electromagnetic waves in a structure consisting of two planar superconductors which are of the order of a penetration depth apart. One superconductor is tantalum and is much thicker than a penetration depth; the other is a vacuum evaporated indium film and may be as thin as a penetration depth.
\r\n\r\nIt is shown that such a structure will propagate waves at a phase velocity less than the speed of light in the medium separating the superconductors, a phenomenon that is the result of an inductive component in the surface impedance of the superconductors. The exact velocity is shown to be a function of the thickness parameters in a manner which depends on the law relating the vector potential and the supercurrent in the indium.
\r\n\r\nExperimental measurements indicate that the relationship between vector potential and current in the vacuum evaporated indium is characterized by a coherence distance which is considerably smaller than that found for pure metals by the measurements of Pippard and the theory of Bardeen, Cooper and Schrieffer.
\r\n\r\nThe penetration depth at zero temperature is deduced from dependence of phase velocity on the thicknesses of the indium and dielectric. For indium \u03bb is found to be 650 \u00b1 75\u00c5, in good agreement with Lock's value of 640\u00c5 and Toxen's range from 625 to 725\u00c5. For tantalum \u03bb is found to be 500 \u00b1 175\u00c5. This is believed to be the first measurement. The value of \u03bb for indium is also deduced from the dependence of phase velocity on temperature. It is found to be 704 \u00b1 120\u00c5.
\r\n\r\nSurface resistance of the two superconductors is found to increase \u03c92, in good agreement with theory, and to depend on temperature according to an empirical law proposed by Pippard.
\r\n" }, { "name": "McCarthy, John Francis", "degree": "PhD", "year": "1962", "title": "Hypersonic Wakes", "advisor": "Kubota, Toshi; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-092458", "creators": [ { "name": { "family": "McCarthy", "given": "John Francis" }, "id": "McCarthy-John-Francis", "display_name": "McCarthy, John Francis" } ], "advisors": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-T", "role": "advisor", "display_name": "Kubota, Toshi" }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/63NK-AG38", "abstract": "An experimental investigation was made of the flow field behind a two-dimensional circular cylinder at a nominal Mach number of 5.7. The free-stream Reynolds number based on the cylinder diameter was varied over a range from 4300 to 66, 500 by changing both the diameter of the cylinder and the stagnation pressure of the wind tunnel. Pitot-pressure, static-pressure, and total-temperature measurements were made at various distances behind the cylindrical rod in order to determine the state properties in the wake. Base-pressure measurements were also taken at various Reynolds numbers.\r\n\r\nFrom these measurements, the transition from laminar to turbulent flow in the wake was determined and successfully correlated with other data. A transition Reynolds number based on local conditions and the length of laminar run was determined. Extensive comparison of the experimental data with Kubota's theory for laminar flow was then made. A satisfactory comparison was made between theory and experiment. Because of the nature of the tests conducted, only a qualitative comparison was made with the theory of Lees and Hromas for turbulent flow." }, { "name": "Messick, Roger Edwin", "degree": "PhD", "year": "1962", "title": "Applications of an Edge-and Corner Layer Technique to Elastic Plates and Shells", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192011-135729811", "creators": [ { "name": { "family": "Messick", "given": "Roger Edwin" }, "id": "Messick-Roger-Edwin", "display_name": "Messick, Roger Edwin" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/W4AN-YY85", "abstract": "This paper contains several problems that can be formulated\r\nmathematically as two-dimensional boundary value problems for partial differential equations containing a parameter. A method is given which leads directly to asymptotic solutions for large values of the parameter without resorting to the exact solutions. The examples discussed involve linear differential equations and are drawn primarily from various problems in the theory of elasticity.\r\n\r\nThe method involves consideration of what are termed corner-layers in addition to the well known boundary-layers. The need for considering these corner-layers arises from the fact that the problems treated lead to boundary-layer differential equations which contain derivatives, not only with respect to the boundary-layer variable, but also with respect to the remaining independent variable. Thus, the\r\nsolution of such boundary-layer equations requires knowledge of boundary conditions in addition to those needed in standard boundary-layer problems.\r\n\r\nThe applications include: a heat conduction problem, two problems with transverse bending of stretched plates, and two problems from elastic shell theory.\r\n\r\nThe shell problems concern the bending of both the shallow and the non-shallow helicoidal shell. It is found that these shells have boundary-layers whose characteristic length is proportional to the one-third power of the thickness parameter. This may be contrasted with shells\r\nof revolution, where this characteristic length is proportional to the one-half power of the thickness parameter.\r\n" }, { "name": "Muller, Richard Stephen", "degree": "PhD", "year": "1962", "title": "Electronic Processes in Au-CdS-In Diodes", "advisor": "Middlebrook, Robert David", "url": "https://resolver.caltech.edu/CaltechTHESIS:08042011-100847730", "creators": [ { "name": { "family": "Muller", "given": "Richard Stephen" }, "id": "Muller-Richard-Stephen", "display_name": "Muller, Richard Stephen" } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JF60-HN20", "abstract": "A study of various electronic processes in a class of solid-state diodes which function analogously to thermionic-emission vacuum tube rectifiers is made. For experimental work, such diodes were fabricated from an insulating crystal (cadmium sulfide) to which an ohmic contact (indium) and a blocking contact (gold) were affixed. The properties of the diodes that are most rigorously\r\ninvestigated are the equilibrium space-charge-limited current voltage characteristic, the behavior of the blocking contact under high reverse fields, and the capacitance dependence upon crystal trapping-state kinetics. Electron trapping is demonstrated to have a marked influence on most of the electronic properties\r\nof analogue diodes. Mathematical analysis based upon the premise that these traps are volume-distributed in the crystals of CdS is corroborated by the experimental results.\r\n\r\nAn analytical method, which treats various trapping configurations with energy in a unified fashion, is employed to calculate the expected influence of traps on the space-charge-limited current characteristic. Correspondence of this analysis with experimental observations permits the deduction, in some cases, of trap densities and trap depths. The theoretical treatment\r\nof the influence of volume-distributed trapping states on\r\nterminal capacitance is also shown to be consistent with measurements designed to test the physical model. Use of this theory to interpret measured capacitance variation allowed the determination of some of the kinetic properties of trapping states, thus demonstrating a new technique for obtaining this information. Correspondence with the results from other methods is good. Trapping-state concentrations in actual crystals are shown to constrain practical solid-state analogue devices to very small dimensions.\r\n" }, { "name": "Rosenfeld, Robert Leopold", "degree": "PhD", "year": "1962", "title": "Analysis of Long Compressional Elastic Waves in Rods of Arbitrary Cross Section and Elastic Wave Fronts in Plates and Circular Rods", "advisor": "Miklowitz, Julius", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192011-084654605", "creators": [ { "name": { "family": "Rosenfeld", "given": "Robert Leopold" }, "id": "Rosenfeld-Robert-Leopold", "display_name": "Rosenfeld, Robert Leopold" } ], "advisors": [ { "name": { "family": "Miklowitz", "given": "Julius" }, "id": "Miklowitz-J", "role": "advisor", "display_name": "Miklowitz, Julius" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "appliedmech" ], "doi": "10.7907/WVNP-Z097", "abstract": "Long waves in elastic rods of arbitrary cross section are studied by writing a general expansion of the exact solution for three dimensional linear elasticity. The solution holds for transient excitation of the end of\r\na semi-infinite cylinder and is in terms of the harmonic modes of wave propagation for the infinite elastic cylinder. The major contribution to the solution for large distances from the end of the rod is found by making\r\napproximations to the infinitely long wave length part of the solution. This is aided by using a perturbation method for long wave length to study the modes of propagation. An approximate theory for rods of arbitrary cross section is developed and compared to the exact theory for harmonic\r\nwaves of infinitely long wave lengths.\r\n\r\nThe amplitudes and locations of all wave fronts caused by certain suddenly applied loads on elastic plates and circular rods are presented. Both end loads on the rod and plate as well as normal line and point forces on the plate are considered. The problems are solved by expanding\r\ndouble transforms into a series of terms, each term representing the disturbance following a single wave front. Evaluation of the terms for the wave front behavior is accomplished by Cagniard's method and the saddle point method. Ray theory aids in the interpretation of the\r\nresults and also serves to verify most of the formulas. The solution by Cagniard's method is exact for the plane strain problems studied and is plotted and compared to experiments.\r\n" }, { "name": "Schapery, Richard Allan", "degree": "PhD", "year": "1962", "title": "Irreversible Thermodynamics and Variational Principles with Applications to Viscoelasticity", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08092011-111909246", "creators": [ { "name": { "family": "Schapery", "given": "Richard Allan" }, "id": "Schapery-Richard-Allan", "display_name": "Schapery, Richard Allan" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QEB0-N308", "abstract": "A unified theory of the thermo-mechanical behavior of\r\nviscoelastic media is developed from studying the thermodynamics of irreversible processes, and includes discussions of the general equations of motion, crack propagation, variational principles, and approximate methods of stress analysis.\r\n\r\nThe equations of motion in terms of generalized coordinates\r\nand forces are derived for systems in the neighborhood of a stable equilibrium state. They represent a modification of Biot's theory in that they contain explicit temperature dependence, and a thermodynamically consistent inclusion of the time-temperature superposition principle for treating media with temperature-dependent viscosity coefficients. The stress-strain-temperature and energy equations for viscoelastic solids follow immediately from the general\r\nequations and, along with equilibrium and strain-displacement relations, they form a complete set for the description of the thermomechanical behavior of media with temperature-dependent viscosity. In addition, an energy equation for crack propagation is derived and examined briefly for its essential features by applying it to a specific problem.\r\n\r\nThe thermodynamic equations of motion are then used to\r\ndeduce new variational principles for generalized coordinates and forces, employing convolution-type functionals. Anticipating various engineering applications, the formulation is phrased alternately in terms of mechanical displacement, stresses, entropy displacement, and temperature in thermally and mechanically linear solids. Some special variational principles are also suggested for applications wherein the nonlinear thermal effects of temperature dependent viscosity and dissipation may be important. \r\n\r\nBuilding upon the basic variational formulation, it is next\r\nshown that when these convolution functionals are Laplace-transformed with respect to time, some convenient minimum principles result which can be employed for the approximate calculation of transformed, viscoelastic responses. The characteristic time dependence of exact and approximate solutions is then derived and used in relating error\r\nin approximate viscoelastic solutions to error in the associated elastic solutions.\r\n\r\nThe dissertation is concluded with a study of some approximate methods of viscoelastic analysis. First, the important problem of inverting complicated Laplace transforms to physical time-dependent solutions is resolved by advancing two easily applied, approximate methods of transform inversion. These inversion methods and\r\nvariational principles are then used in some illustrative, numerical, examples of stress and heat conduction analysis.\r\n" }, { "name": "Shimabukuro, Fred Ichiro", "degree": "PhD", "year": "1962", "title": "A Study of Dispersion in Plasmas", "advisor": "Dow, Daniel G.; Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172011-135421197", "creators": [ { "name": { "family": "Shimabukuro", "given": "Fred Ichiro" }, "id": "Shimabukuro-Fred-Ichiro", "display_name": "Shimabukuro, Fred Ichiro" } ], "advisors": [ { "name": { "family": "Dow", "given": "Daniel G." }, "id": "Dow-D-G", "role": "advisor", "display_name": "Dow, Daniel G." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/W2HJ-XE62", "abstract": "The wave propagation characteristics in a stationary unbounded plasma in a static arbitrary magnetic field are reviewed. If the plasma is drifting, a Lorentz transformation can be made to obtain the \u03c9-k relations in the reference frame where the plasma is moving. The transformation is a simple one for the slow waves with non-relativistic drift velocities. The modified waves for the drifting plasma have an important bearing on the instability of the transverse modes in a system of a drifting plasma in a plasma.\r\n\r\nThe dispersion for bounded (cylindrical geometry) plasmas is\r\nstudied, where the propagation vector is along the z-axis. The salient features of these waves are obtained by studying the circularly symmetric mode. The general features predicted by the quasi-static approximation are verified and the exact and quasi-static solutions are compared. The range of validity of the quasi-static\r\napproximation is determined and the h-values are plotted. As the radius becomes larger these modes evolve into the plane wave cases of the unbounded plasma.\r\n\r\nWhen a fast beam of charged particles, electrons, ions or a plasma, traverses a stationary plasma in a magnetic field, there is a possibility of unstable transverse modes of propagation. If the drifting particles are either electrons or ions, the circularly polarized waves exhibit an instability over a very narrow frequency range near the ion and electron cyclotron frequencies respectively. When a plasma drifts through a plasma, in addition to the instabilities noted above, there can be an instability near zero frequency, and the growth condition is determined. For typical parameter values these transverse modes have greater growth constants than the longitudinal mode. These unstable transverse modes have possible applications in the generation of high frequencies, and are possible explanations for various instabilities in the ionosphere.\r\n" }, { "name": "Stiffler, Jack Justin", "degree": "PhD", "year": "1962", "title": "Self-Synchronizing Binary Telemetry Codes", "advisor": "Golomb, Solomon W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092009-113403691", "creators": [ { "name": { "family": "Stiffler", "given": "Jack Justin" }, "id": "Stiffler-Jack-Justin", "display_name": "Stiffler, Jack Justin" } ], "advisors": [ { "name": { "family": "Golomb", "given": "Solomon W." }, "id": "Golomb-S-W", "role": "advisor", "display_name": "Golomb, Solomon W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/G956-8Z21", "abstract": "The past decade has witnessed significant advances in the techniques for communication, with high reliability, over noisy channels and, in particular, in the methods of encoding for these channels. However, for many of these encodings, including the so-called block codes, efficient reception demands that the receiver know the instant in time that one block of data ends and the succeeding block begins. This synchronization problem, as applied to an important class of block codes, which are optimum or nearly optimum over the continuous white Gaussian channel, is the central topic treated in this thesis. Two synchronization methods are presented, and upper bounds on the time necessary for their operation are determined. The first involves almost no additional encoding or decoding equipment, but is dependent upon the randomness of the received message. The second technique, while necessitating more complex decoding apparatus, is, in general, considerably more rapid than the first and is, moreover, independent of the statistical properties of the data. Neither method decreases the information capacity of the channel. The performance of both these techniques in conjunction with the binary symmetric channel is also investigated.\r\n" }, { "name": "Stofel, Edwin Jule", "degree": "PhD", "year": "1962", "title": "Plastic Flow and Fracture of Zinc Single Crystals", "advisor": "Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechETD:etd-07012004-154735", "creators": [ { "name": { "family": "Stofel", "given": "Edwin Jule" }, "id": "Stofel-Edwin-Jule", "display_name": "Stofel, Edwin Jule" } ], "advisors": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/EQK7-RS94", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPlastic flow and fracture of zinc single crystals subjected to tension parallel to the hexagonal crystallographic axis, torsion about that axis, and combinations of such tension and torsion have been investigated experimentally at 25[degrees]C and -77[degrees]C. The results show that under tension alone, cleavage fracture on the basal plane is preceded by plastic elongation in the direction of the hexagonal crystallographic axis. Some evidence is presented which indicates that this newly discovered mode of plastic deformation of zinc crystals probably occurs by slip on [...] planes in [...] directions. The temperature dependence of this mode of plastic deformation is anomalous. The tensile stress required to produce a given amount of plastic strain is greater at 25[degrees]C than at -77[degrees]C.\r\n\r\nThe critical resolved shear stress for basal slip, as determined from the results of torsional tests, is increased markedly by prior tensile plastic deformation. The tensile stress-strain relation is raised moderately by prior basal slip.\r\n\r\nFracture was always found to occur by cleavage on a basal plane. The observed combinations of tensile stress and shear stress on the basal plane at fracture are not consistent with predictions based upon current dislocation theories for the initiation of cleavage fracture in zinc. The present results indicate that dislocations having Burgers vectors that do not lie in the basal plane may be of crucial importance in the dislocation mechanism of cleavage fracture of zinc. Such dislocations have not been considered in previously proposed theories." }, { "name": "Wang, Duen-Pao", "degree": "PhD", "year": "1962", "title": "A Perturbation Theory for Unsteady Cavity Flows", "advisor": "Wu, Theodore Yao-tsu", "url": "https://resolver.caltech.edu/CaltechTHESIS:08192011-142844454", "creators": [ { "name": { "family": "Wang", "given": "Duen-Pao" }, "id": "Wang-Duen-Pao", "display_name": "Wang, Duen-Pao" } ], "advisors": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Wu-T-Y-T", "role": "advisor", "display_name": "Wu, Theodore Yao-tsu" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/NKPW-4612", "abstract": "This investigation deals with a perturbation theory for unsteady cavity flows in which the time-dependent part of the flow may be considered as a small perturbation superimposed on an established steady cavity flow of an ideal fluid, the gravity effect being neglected in this study. In order to make a comparison between the various existing steady-cavity-flow models when applied to unsteady motions, some of these models have been employed to evaluate the small time behavior of, and the initial reaction to an unsteady disturbance. Furthermore, the mechanism by which the cavity volume may be changed with time is studied and the initial hydrodynamic force resulting from such change is calculated.
\r\n\r\nThe second kind of unsteady cavity flow problems treated here is characterized by the fact that the disturbances are limited to be small for all time instants. Based on a systematic linearization with respect to the steady basic flow, a general perturbation theory for unsteady cavity flows is formulated. From this perturbation theory the generation of surface waves along the cavity boundary is revealed, much in the same way as the classical gravity waves in water, except with the centrifugal acceleration due to the curvature of the free-streamlines in the basic flow playing the role of an equivalent gravity effect.
" }, { "name": "Wang, Neng-Ming", "degree": "PhD", "year": "1962", "title": "Bending of Thin Elastic Plates Containing Line Discontinuities", "advisor": "Knowles, James K.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182011-105727536", "creators": [ { "name": { "family": "Wang", "given": "Neng-Ming" }, "id": "Wang-Neng-Ming", "display_name": "Wang, Neng-Ming" } ], "advisors": [ { "name": { "family": "Knowles", "given": "James K." }, "id": "Knowles-J-K", "role": "advisor", "display_name": "Knowles, James K." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/9WFR-W284", "abstract": "The purpose of this work is to examine the stress distribution caused by the bending of a thin elastic plate containing a line discontinuity. Specifically, the plate under consideration is of constant thickness and occupies a whole plane exterior to the line discontinuity. The line discontinuity is either a crack or a rigid inclusion.\r\n\r\nThe loading is applied to the plate at infinity by certain combinations of tractions which leave the plate in equilibirum.\r\n\r\nThe analysis of the problems considered here is based on\r\nan approximate theory which is more refined than the classical theory ordinarily applied to problems of bending of plates. This is because results based on the classical theory may be incorrect, even in first approximation for thin plates, near a boundary, and it is precisely the region near a boundary (in this case, the line\r\ndiscontinuity) which is of primary interest in these problems. In fact one of the principal objectives in this work is to compare the stress distributions near the line discontinuity as predicted by the two theories.\r\n\r\nThe principal techniques used in this work are based on integral equations and the calculus of variations.\r\n\r\nResults based on the two theories are found to agree for\r\nthin plates away from the line discontinuity, but differ significantly in the vicinity of the discontinuity, even for very thin plates.\r\n" }, { "name": "Yeh, Cavour Wei-Hou", "degree": "PhD", "year": "1962", "title": "Electromagnetic Surface-Wave Propagation along a Dielectric Cylinder of Elliptical Cross Section", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechTHESIS:08182011-142633204", "creators": [ { "name": { "family": "Yeh", "given": "Cavour Wei-Hou" }, "id": "Yeh-Cavour-Wei-Hou", "display_name": "Yeh, Cavour Wei-Hou" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/A13E-BB49", "abstract": "The problem of electromagnetic wave propagation along a dielectric cylinder of elliptical cross section is considered. Two infinite determinants representing the characteristic equations for the two types of hybrid waves (the _eHE_(mn) and the _oHE_(mn) waves) are derived.\r\nThese waves degenerate to the well-known HE_(mn) wave of the circular dielectric rod as the eccentricity of the elliptical rod approaches zero. It is found that there exist two dominant waves which possess zero cutoff frequencies. The characteristic roots of these two\r\ndominant waves are computed for various values of eccentricity and relative dielectric constant. Also given are the attenuation characteristics and the field distribution of the dominant modes. It is shown that a flattened dielectric rod supporting the _eHE_(11) wave offers less loss than a circular rod having the same cross-sectional area and supporting the HE_(11) wave. Theoretical propagation characteristics (the guide wavelength, the field distribution and the attenuation constant) of the dominant waves are verified by experiments. The Q's of a dielectric rod cavity resonator supporting the dominant waves are also presented.\r\n" }, { "name": "Zukerman, Abraham", "degree": "PhD", "year": "1962", "title": "Analytical Approximations to the Solutions of the Equations of Motion in the Earth-Moon Space", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-091409", "creators": [ { "name": { "family": "Zukerman", "given": "Abraham" }, "id": "Zukerman-Abraham", "display_name": "Zukerman, Abraham" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZFV9-4018", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\t\r\nTwo methods of obtaining approximate solutions of the equations of motion in the Earth-Moon space are derived. The first method - asymptotic expansions of the solutions of the equations of motion - is a power series expansion of the solutions in powers of the inverse maximum velocity [...]. A comparison of the results of numerical integration with the asymptotic expansions is presented, which shows the range of applicability of this method.\r\n\r\nThe second method is similar to the small perturbation approach. In this method the zeroth order solution is a Keplerian orbit about the Earth (the Moon's effect being neglected). The first order solution corrects for the lunar gravity effects on the zeroth order trajectory. To demonstrate the computational difficulties involved in the application of this method, a straight line Keplerian trajectory was used as the zeroth order solution. Several applications of the solutions are discussed." }, { "name": "Ai, Daniel Kwoh-i", "degree": "PhD", "year": "1961", "title": "Part I. Cylindrical Couette Flow in a Rarefied Gas According to Grad's Equation. Part II. Small Perturbations in the Unsteady Flow of a Rarefied Gas Based on Grad's Thirteen Moment Approximation", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-131707", "creators": [ { "name": { "family": "Ai", "given": "Daniel Kwoh-i" }, "id": "Ai-Daniel-Kwoh-i", "display_name": "Ai, Daniel Kwoh-i" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "chair", "display_name": "Lees, Lester" }, { "name": { "family": "Goetz", "given": "Alexander" }, "id": "Goetz-Alexander", "role": "member", "display_name": "Goetz, Alexander" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Royce", "given": "Winston W." }, "id": "Royce-W-W", "role": "member", "display_name": "Royce, Winston W." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9P2N-HF23", "abstract": "Part I
\r\n\r\nGrad's thirteen moment method is applied to the problem of the shear flow and heat conduction between two concentric, rotating cylinders of infinite length. In order to concentrate on the effects of curvature the problem is linearized by requiring that the Mach number is small compared with unity, and that the temperature difference between the two cylinders is small compared with the mean temperature. The solutions of the linearized Grad equations show a qualitatively correct transition of the cylinder drag from free-molecule flow to the classical Navier-Stokes regime. However the magnitude of the curvature effect on the drag in rarefied flow is not given correctly, because Grad's distribution function ignores the wedge-like domains of influence of the two cylinders.
\r\n\r\nThe solution obtained for the heat transfer rate is physically unrealistic in the free-molecule flow limit, and this result is produced by a cross-coupling between the normal stresses and the radial heat flux imposed by Grad's distribution function. In this simple problem the difficulty can be eliminated by taking the normal stresses to be identically zero and employing a truncated moment method. However, in general this device cannot be utilized in problems involving curved solid boundaries, or when dissipation is considered. One concludes that the choice of the distribution function to be employed in Maxwell's moment equations is dictated by the requirements imposed in the limiting case of highly rarefied gas flows, as well as in the Navier-Stokes regime.
\r\n\r\nPart II
\r\n\r\nIn this paper, the unsteady one-dimensional flow of a compressible, viscous and heat conducting fluid is treated, based on linearized Grad's thirteen moment equations. The fluid, initially at rest, is set into motion by some small external disturbances. Our interest is to examine the nature of all the responses. The fluid field extends to infinity in both directions; thus no length is involved, and also there is no solid wall boundary existing in the problem. The nature of the external disturbances is restricted to having a unit impulse in the momentum equation and a unit heat addition in the energy equation. The disturbances are located on an infinite plane normal to the flow direction; and the responses induced correspond to fundamental solutions of the problem. The method of Laplace transforms is applied, and the inverse transforms of all quantities are obtained in integral form. Because of the complicated expressions of the integrands involved, we consider only certain limiting cases which correspond to small and large times from the start of the motion, compared to the average time between molecular collisions. In order to study these limiting cases, it is essential to understand the behavior of the integrand in the complex plane; hence all singularities and branch points are obtained.
\r\n\r\nWhen t is small, the integrand is expanded in powers of t to obtain a wave front approximation. All discontinuities are propagated along the characteristics of the linearized system, and a damping term also appears.
\r\n\r\nAt large values of time, the integrand gets its main contribution around the branch points, and these solutions are identical to those obtained from the Navier-Stokes equation. The fundamental solution of the one-dimensional unsteady flow, idealized as it seems to be, offers itself as a tool to understand other related problems. The piston problem, as well as the normal quantities in Rayleigh's problem (e.g., normal velocity, normal stress, and thermodynamical quantities), are governed by the same set of equations. Hence, certain parts of the fundamental solutions can be applied directly to these problems. The limiting forms of the normal quantities in Rayleigh's problem are expected to be worked out in another paper in the near future.
" }, { "name": "Aron, Richard Michael", "degree": "PhD", "year": "1961", "title": "Bandwidth Limitations and Synthesis Procedures for Negative Resistance and Variable Reactance Amplifiers", "advisor": "Dow, Daniel G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232006-141908", "creators": [ { "name": { "family": "Aron", "given": "Richard Michael" }, "id": "Aron-Richard-Michael", "display_name": "Aron, Richard Michael" } ], "advisors": [ { "name": { "family": "Dow", "given": "Daniel G." }, "id": "Dow-D-G", "role": "advisor", "display_name": "Dow, Daniel G." } ], "committee": [ { "name": { "family": "Dow", "given": "Daniel G." }, "id": "Dow-Daniel-G", "role": "chair", "display_name": "Dow, Daniel G." }, { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-N-A", "role": "member", "display_name": "George, Nicholas A." }, { "name": { "family": "Mullin", "given": "Francis J." }, "id": "Mullin-Francis-J", "role": "member", "display_name": "Mullin, Francis J." }, { "name": { "family": "Franklin", "given": "Joel N." }, "id": "Franklin-J-N", "role": "member", "display_name": "Franklin, Joel N." } ], "option_major": [ "eleceng" ], "doi": "10.7907/NF7W-1K08", "abstract": "The bandwidth limitation on the reflection coefficient of circuits containing a reactance limited negative conductance such as a tunnel diode is derived, and the insertion loss method of modern network theory is adapted to the synthesis of low pass ladder equivalents of amplifiers containing these elements. Amplifiers which have a considerable bandwidth advantage over simple single tuned circuits, and which approach the ultimate bandwidth limit as rapidly as possible as the number of passive components is increased, are demonstrated.\r\n\r\nFundamental bandwidth limitations of three-frequency nonlinear reactance amplifiers, parametric amplifiers, and non-inverting upconverters are also found. A low pass ladder equivalent circuit and the insertion loss method are shown to be useful tools for synthesis of these amplifiers. Considerable bandwidth advantage over single-tuned circuits is again demonstrated. Syntheses which yield the ultimate bandwidth as the number of circuit elements is increased are found.\r\n\r\nThese synthesis methods and the reverse predistortion technique are used to synthesize stable amplifiers whose bandwidth capability increases almost linearly with the number of active elements employed.\r\n\r\nRelationships between physically achievable amplifier circuits and the low pass equivalents are shown, and the general compatibility of presently available active elements with these circuits is considered.\r\n" }, { "name": "Boedtker, Olaf Alexander", "degree": "PhD", "year": "1961", "title": "Delay Time in the Alpha to Gamma Transformation of Iron", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172006-110102", "creators": [ { "name": { "family": "Boedtker", "given": "Olaf Alexander" }, "id": "Boedtker-Olaf-Alexander", "display_name": "Boedtker, Olaf Alexander" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z8WG-R830", "abstract": "Iron, containing a certain amount of carbon and nitrogen, was pulse-heated from an initial temperature in the alpha phase into a final temperature within the gamma phase. The bulk of the allotropic transformation took place a certain time after the final temperature had been reached. The relationship between this delay time and the final temperature follows an Arrhenius type rate equation with a heat of activation of 20,500 \u00b1 1400 cal per mole. It was also established that under the present experimental conditions alpha iron can be heated directly into the delta phase without going through the gamma phase. The effect of the rate of heating on the alpha to gamma transformation temperature can be deduced from the measurements of the delay time.\r\n\r\nAn interpretation of a possible transformation mechanism is given. It is assumed that the transformation takes place in two steps: (1) A relatively slow diffusion-like growth of nuclei of the new phase in the old matrix to their critical size, followed by (2) a very, fast shear transformation." }, { "name": "Cann, Gordon Lawrence", "degree": "PhD", "year": "1961", "title": "Energy Transfer Processes in a Partially Ionized Gas", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12202005-133300", "creators": [ { "name": { "family": "Cann", "given": "Gordon Lawrence" }, "id": "Cann-Gordon-Lawrence", "display_name": "Cann, Gordon Lawrence" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XV8R-MM73", "abstract": "The following paper is divided into three more or less separate sections. The first section (Chapters II - VI) deals with an analysis of the transport properties of a partially ionized gas subject to the constraint that the average random energy of all constituent particles is exactly equal (equipartition of energy). This constraint is necessary so that the formal Chapman-Enskog solution of Boltzman's equation can be used to evaluate the various transport coefficients. Subject to this constraint, a set of tractable equations describing the mass and energy diffusion in a partially ionized gas is obtained that includes all terms correct to the order of the square root of the ratio of the electron to atom mass compared to one. The transport coefficients are evaluated for helium and argon over the complete range of partial ionization assuming that the species particle densities are quite close to their equilibrium values.\r\n\r\nThe analysis indicates that the electron and ion diffusion velocities are more closely coupled than the equations of Chapman and Cowling show. The added coupling implicitly applies the constraint of zero mass velocity to the gas locally. Because of this constraint a current in the direction of (E x B) x B occurs in addition to the direct and Hall currents.\r\n\r\nIt is shown that the only part of the thermal conductivity that can be influenced by a magnetic field is that part of the energy carried by the diffusion of the charged particles. For this reason, magnetic fields, in general, cannot be nearly as effective in reducing heat transfer rates as was previously thought, e. g., a magnetic field will have no influence on the thermal conductivity in a fully ionized gas, except through its influence on the current density and the thermal diffusion.\r\n\r\nChapters VII - IX comprise the second section of this paper and deal with the development of a similarity solution for axially symmetric electric discharges. A number of parameters are obtained and discussed. The solution is evaluated for a discharge in argon gas at one atmosphere pressure in which the temperature on the axis of the discharge varies from 6,000\u00b0K to 19,000\u00b0K. The current-voltage characteristic obtained from this solution is compared with an experimentally determined curve of H. Maecker.\r\n\r\nThe third section of this paper (Chapters X - XIII) is concerned with the mechanisms of energy transfer in arc jet devices. Use is made of the previous sections of the paper to determine the relative magnitude of the amount of energy that is transferred to the gas in the various parts of the electric discharge. The various possible electrode configurations are discussed in detail and compared. The design and performance of an annular electrode arc heater with a rotating arc is next described and discussed. Because of a number of undesirable performance characteristics of this type of electrode configuration, a modified heater was constructed with the cathode emission occurring along the axis of the applied magnetic field. Details of the unexpectedly good performance of this configuration are given. It is shown that the arc potential drop depends primarily on the strength of the applied magnetic field and the gas enthalpy downstream of the arc. The dependence of the arc potential drop on the arc current and the ambient pressure is shown to be weak over the ranges tested, e. g., 50 to 300 amperes for the current and 1 to 4 atmospheres for the pressure. Some heat transfer measurements taken with this equipment are presented.\r\n\r\nAppendix I is concerned with the evaluation of the transport coefficients in a partially ionized gas. Formulae are developed for determining the viscosity, thermal conductivity, and electric conductivity of the plasma. These coefficients are computed for argon and helium at one atmosphere pressure and over the temperature range of partial ionization." }, { "name": "Childress, William Stephen", "degree": "PhD", "year": "1961", "title": "Asymptotic Expansion of Navier-Stokes Solutions in Three Dimensions for Large Distances", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-113027", "creators": [ { "name": { "family": "Childress", "given": "William Stephen" }, "id": "Childress-William-Stephen", "display_name": "Childress, William Stephen" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A77G-P071", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis studies the stationary flow field at large distances from a finite obstacle moving uniformly in a viscous, incompressible fluid. The principal results consist of asymptotic expansions, uniformly valid for large distance, of the velocity and the pressure of the flow field.\r\n\r\nThe expansion procedure employed is based upon the introduction of a small, extraneous parameter; the construction is thus recast as a perturbation for small values of the parameter. Owing to the presence of a viscous wake, the perturbation is in general a singular one, and is treated accordingly, using methods developed for related hydrodynamical problems.\r\n\r\nThe calculated results include the following: for the case of axially-symmetric flow, a uniformly valid expansion of the velocity to order [...] inclusive, and of the pressure to order [...] inclusive, r being the distance from the obstacle; for the general case, an expansion of the velocity to order [...] and of the pressure to order [...], inclusive." }, { "name": "Christiansen, Walter Henry", "degree": "PhD", "year": "1961", "title": "Development and Calibration of a Cold Wire Probe for Use in Shock Tubes", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12142005-124939", "creators": [ { "name": { "family": "Christiansen", "given": "Walter Henry" }, "id": "Christiansen-Walter-Henry", "display_name": "Christiansen, Walter Henry" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QGS9-WZ66", "abstract": "The use of a fine unheated wire for making shock tube flow measurements is investigated. The operation of the instrument depends on the transient nature of the shock tube flow. The wire is referred to here as a cold wire; it operates in a non-steady manner which is completely different from the usual hot wire operation. This report describes the construction and calibration of the cold wire.\r\n\r\nThe experimental law for the rate of gain of heat to the wire in air is determined over a range of Mach numbers from 0.4 to 1.9 and a range of Reynolds numbers from 0.035 to 3,500 based on the wire diameter and the conditions in the hot flow following the initial shock wave. Similar measurements are reported for argon. The heat transfer measurements cover the continuum region, the slip and transitional regions, and extend into the free-molecule flow region. The dimensionless results are compared with hot wire measurements obtained in wind tunnels and are found to differ slightly. A difference exists because the cold wire gains heat from the fluid while the hot wire loses heat to the fluid. The measurements are very repeatable and self-consistent, and they indicate that the wire can be used to give an accurate flow measurement in the shock tube.\r\n\r\nSome potential applications of the wire for the study of shocktube flows are presented. It is concluded that the fine unheated wire is a versatile tool that can be used to great advantage in the shock tube." }, { "name": "Collins, Daniel Joseph", "degree": "PhD", "year": "1961", "title": "A Study of Hydrodynamic Interactions of Macromolecules in Solution by Means of Precision Viscometry", "advisor": "Wayland, J. Harold", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172006-131142", "creators": [ { "name": { "family": "Collins", "given": "Daniel Joseph" }, "id": "Collins-Daniel-Joseph", "display_name": "Collins, Daniel Joseph" } ], "advisors": [ { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "advisor", "display_name": "Wayland, J. Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/Z3VF-FW62", "abstract": "A precision capillary viscometer with a photoelectric timer has been designed and built for these investigations. On the assumption that the relative viscosity can be expanded in a power series in concentration, the intrinsic viscosity and the coefficient of the second order term have been measured for suspensions of sperical and rigid rodlike macromolecules. The viscosity of a known heterogenous suspension of rods and spheres has been determined and has been interpreted in terms of interaction coefficients.\r\n\r\nThe Einstein theory of viscosity of dilute suspensions of spheres has been modified to form, together with the approaches of Burgers and Jeffery, a logically consistent theory for the intrinsic viscosity of spherical molecules in particular, and ellipsoid particles in general.\r\n\r\nThe second order theory in volume fraction for the viscosity of suspensions was reviewed. Previous work in this field was found to be in error. It was shown that, when properly interpreted, the linear solution of Burgers to the problem of the viscosity of dilute suspensions of spheres fully explains the variation of the relative viscosity with concentration. The linear theory of Burgers did not adequately explain the variation of the relative viscosity of rod-like molecules with concecntration. This was attributed to mutual orientation effects. The study of the system consisting of rods and spheres also indicated that orientation effects might be important.\r\n" }, { "name": "Dienes, John Kalman", "degree": "PhD", "year": "1961", "title": "Some Applications of the Theory of Continuous Markoff Processes to Random Oscillation Problems", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-04102006-132153", "creators": [ { "name": { "family": "Dienes", "given": "John Kalman" }, "id": "Dienes-John-Kalman", "display_name": "Dienes, John Kalman" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/R51Y-W418", "abstract": "Many random problems of engineering interest can be looked upon as examples of continuous Markoff processes. Such processes are completely determined if a certain function, the transition probability, is prescribed. It is shown that all of the functions of interest in random problems can be derived from the transition probability.
\r\n\r\nSome of the concepts of probability theory and of spectral analysis are reviewed and using these results, the Gaussian white noise function is defined. A new derivation of the Fokker-Planck equation is given which emphasizes the role of the Gaussian white input in the analysis of Markoff processes. The transition probability is the fundamental solution of this equation.
\r\n\r\nIt is then shown that the autocorrelation is closely related to the mean motion of a system and can be calculated from the transition probability. This relation can be used, in principle at least, to determine the autocorrelation of nonlinear systems. The Method of Equivalent Linearization for random problems and the First Passage Problem are discussed briefly.
\r\n\r\nThese methods are used to solve a number of problems. A discussion of linear systems is presented, and by a similar treatment the solution to a problem in random parametric excitation is given. Next, the first probability density of a class of nonlinear problems is discussed. Finally, the power spectra for two nonlinear systems are calculated.
" }, { "name": "Dipprey, Duane Floyd", "degree": "PhD", "year": "1961", "title": "An Experimental Investigation of Heat and Momentum Transfer in Smooth and Rough Tubes at Various Prandtl Numbers", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04082005-110724", "creators": [ { "name": { "family": "Dipprey", "given": "Duane Floyd" }, "id": "Dipprey-Duane-Floyd", "display_name": "Dipprey, Duane Floyd" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/WRNM-4K03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nResults are presented from an experimental investigation of the relation between heat transfer and friction in smooth and rough tubes. Three rough tubes and one smooth tube were formed from electroplated nickel. The rough tubes contained a close-packed, granular type of surface with roughness-height-to-diameter ratios ranging from 0.0024 to 0.049. Measurements of the heat transfer coefficients [...] and the friction coefficients [...] were obtained with distilled water flowing through the electrically heated tubes. A Prandtl number range of 1.20 to 5.94 was investigated by adjusting the bulk temperature of the water. Results were obtained for Reynolds numbers from 6 x [...] to 5 x [...] and from 1.4 x [...] to 1.2 x [...] at the lowest and highest Prandtl number respectively.\r\n\r\nA similarity rule for heat transfer was used to correlate, interpret and extend the experimental results. The results were compared with previously existing results, both theoretical and experimental. Increases in [...] due to roughness of as high as 270 percent were obtained. These increases were, in general, accompanied by even larger increases in [...]. An exception to this general behavior occurs at high Prandtl number in the region of transition between the \"smooth\" and the \"fully rough\" [...] characteristic." }, { "name": "Evtuhov, Viktor", "degree": "PhD", "year": "1961", "title": "Theory of the Valence Band Energy Level Structures of Germanium and Silicon in an External Magnetic Field", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-08092007-144751", "creators": [ { "name": { "family": "Evtuhov", "given": "Viktor" }, "id": "Evtuhov-Viktor", "display_name": "Evtuhov, Viktor" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ZTF9-GX67", "abstract": "The problem of the valence band structure of Ge and Si in the presence of an external magnetic field is considered from a quantum mechanical point of view. The analysis is carried out using first and second order perturbation theory. The approach is, in principle, similar to that of W. Shockley and E. O. Kane, but is modified in some important essentials to include the effects of the magnetic field. The analytical results obtained are somewhat more general than those of J. M. Luttinger but reduce to the latter if certain approximations are introduced. Numerical calculations of the Landau energy levels are carried out for certain special cases, of which the most important are the following:
\r\n\r\n1. Magnetic field \u03f0 in the [001] direction, kH = 0; nonspherical symmetry character of energy bands and the coupling of V1 and V2 bands to the V3 band included.
\r\n\r\n2. Magnetic field \u03f0 in the [001] direction, kH \u2260 0; nonspherical symmetry character of energy bands included, decoupling of V1 and V2 bands from the V3 band assumed.
\r\n\r\nIn addition, a set of algebraic equations is derived whose solution should yield the valence band Landau levels for the cases of the magnetic field in the [101] and the [111] directions. However, no numerical calculations are performed for these cases.
\r\n\r\nThe results of the calculations indicate the presence of some interesting transitions between the Landau levels of Ge and Si, as well as the possible presence of other interesting effects which may be observable. Certain of these seem to offer potential millimeter-wave applications possibilities, some of which are discussed.
\r\n" }, { "name": "Iwan, Wilfred Dean", "degree": "PhD", "year": "1961", "title": "The Dynamic Response of Bilinear Hysteretic Systems", "advisor": "Caughey, Thomas Kirk; Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10052004-162528", "creators": [ { "name": { "family": "Iwan", "given": "Wilfred Dean" }, "id": "Iwan-Wilfred-Dean", "display_name": "Iwan, Wilfred Dean" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Y32J-KT73", "abstract": "A study is made of the dynamic response of one and two degree of freedom systems having a bilinear hysteretic restoring force. In the case of the one degree of freedom system exact steady state solutions are obtained for both square wave and trigonometric excitation. It is thereby shown that the system exhibits a soft type resonance and that there exists a critical level of excitation above which the system displays unbounded resonance. An approximate steady state theory for the one degree of freedom system is investigated and on the basis of this theory it is found that the system is stable and possesses a single locus of vertical tangency. The results of the exact and approximate steady state theories are supplemented by electric analog studies of both the harmonic and ultraharmonic response.\r\n\r\nThe response of the one degree of freedom system to transient excitation of finite duration is also examined and it is noted that certain rather general conclusions may be made about the final state of the system without reference to the specific time history of the excitation.\r\n\r\nA first order approximate theory for the steady state response of the two degree of freedom system is formulated and it is shown that there are two critical levels of excitation for unbounded resonance. The existence of loci of vertical tangency is demonstrated and the stability problem is treated in limiting cases. Direct numerical integration of the equations of motion is carried out for a number of specific cases as a check of the approximate theory." }, { "name": "Jones, Orval Elmer", "degree": "PhD", "year": "1961", "title": "Theoretical and Experimental Studies on the Propagation of Longitudinal Elastic Strain Pulses in Wide Rectangular Bars", "advisor": "Ellis, Albert T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06142006-103619", "creators": [ { "name": { "family": "Jones", "given": "Orval Elmer" }, "id": "Jones-Orval-Elmer", "display_name": "Jones, Orval Elmer" } ], "advisors": [ { "name": { "family": "Ellis", "given": "Albert T." }, "id": "Ellis-A-T", "role": "advisor", "display_name": "Ellis, Albert T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/KXTS-1Y59", "abstract": "The method of birefringent coatings is considered as an experimental means of studying wave propagation phenomena in metals. Experiments using the Ellis ultra-high-speed camera and a rectangular aluminum bar having a birefringent coating of PhotoStress indicate that transient fringe patterns resulting from impact can be successfully photographed using existing film and light sources at exposure times of 0.05 microseconds. Pronounced fringe curvatures, indicating the warping of plane sections, were observed in the pictures during the passage of the strain pulse.\r\n\r\nThe propagation of a longitudinal elastic strain pulse in a wide rectangular bar is considered on the basis of the approximate plane-stress equations of motion. Asymptotic expressions are obtained which, for large distances of travel, describe the propagation in a semi-infinite strip with stress free lateral edges, subject to the conditions that a uniform normal stress with a step-function time dependence is applied to the end and that the end undergoes no lateral extension. These expressions are shown to qualitatively predict the warping of plane sections observed in the high-speed pictures and in the dynamic photoelastic pictures obtained by other investigators.\r\n\r\nMeasurements using conventional measuring techniques are described in which wide rectangular aluminum bars of several thicknesses were subjected to a step-function pressure loading produced by a shock tube. Comparisons show that the gross features of the experimental records for the head of the pulse are qualitatively predicted by the plane-stress theory. Both theory and experiment show that short-wavelength second mode disturbances arrive very early. Experimentally it is observed that these disturbances are accompanied by thickness mode activity which cannot be accounted for by the two-dimensional plane-stress theory." }, { "name": "Kevorkian, Jirair Kevork", "degree": "PhD", "year": "1961", "title": "The Uniformly Valid Asymptotic Approximations to the Solutions of Certain Non-Linear Ordinary Differential Equations", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12222005-092728", "creators": [ { "name": { "family": "Kevorkian", "given": "Jirair Kevork" }, "id": "Kevorkian-Jirair-Kevork", "display_name": "Kevorkian, Jirair Kevork" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K8NE-5X16", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis work deals with the application of an expansion procedure in terms of two independent time variables for the uniform asymptotic representation of solutions representing certain mechanical systems.\r\n\r\nThe method is first applied to systems governed by the equation [...] where [...] is a small parameter, and f has the character of a damping (i. e. y is a bounded function of t for all t [...] 0).\r\n\r\nIt is shown that the physical problems which can be brought to the above non-dimensional form possess two characteristic time scales, one associated with the oscillatory behavior of the solution, while the other measures the time interval in which the effects of the non-linear term become apparent.\r\n\r\nThe dependence of the solution on these time scales is not simple, in the sense that an asymptotic representation of the exact solution which is valid for large times cannot be obtained by a limit process in which a non-dimensional time variable is held fixed. This fact has motivated the introduction of an expansion procedure in functions of two time variables, and it is shown that with the use of certain simple boundedness criteria a uniform asymptotic representation can be derived.\r\n\r\nIn addition to the above mentioned class of problems a variety of examples possessing certain boundedness properties is studied by this method, including, for example, the Mathieu equation.\r\n\r\nThe main emphasis of this paper is on the constructive rather than general approach to the solutions of specific examples. These examples are introduced in turn to illustrate the underlying ideas of the method, whose main advantage is its simplicity especially for computing the higher approximations." }, { "name": "Lock, Malcolm Harvey", "degree": "PhD", "year": "1961", "title": "A Study of Two-Dimensional Panel Flutter", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12142005-124410", "creators": [ { "name": { "family": "Lock", "given": "Malcolm Harvey" }, "id": "Lock-Malcolm-Harvey", "display_name": "Lock, Malcolm Harvey" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NZ2V-H267", "abstract": "An investigation of the problem of the flutter of two-dimensional flat panels is undertaken. The research is largely devoted to investigating the adequacy of the ideal flutter theory that has been employed to predict flutter boundaries for such panels. A series of panel flutter experiments carried out in the GALCIT 4\u201d x 10\u201d transonic wind tunnel at Mach numbers up to 1.5 are described in detail. Before the results of these experiments are compared with the predictions of the theory some further analytical studies of the flutter problem are presented that enable a more critical comparison of theory and experiment to be made. These analyses treat some aspects of the problems of transonic and supersonic panel flutter. The nature of the energy exchange at flutter is also considered. This latter study throws considerable light upon the flutter process as described by the ideal theory and also clarifies the breakdown of certain approximate unsteady aerodynamic theories in the low supersonic flow region (1 < M < 1.5). Comparison of theory and experiment reveals considerable differences between the theoretical and experimental flutter boundaries at the lower supersonic Mach numbers. The agreement between theory and experiment improves at Mach numbers above about 1.4. The possible sources of the apparent inadequacy of the theory at the lower supersonic Mach numbers are discussed." }, { "name": "Long, Dennis Vernon", "degree": "PhD", "year": "1961", "title": "Mechanics of Consolidation with Reference to Experimentally Sedimented Clays", "advisor": "Scott, Ronald F.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05042006-130711", "creators": [ { "name": { "family": "Long", "given": "Dennis Vernon" }, "id": "Long-Dennis-Vernon", "display_name": "Long, Dennis Vernon" } ], "advisors": [ { "name": { "family": "Scott", "given": "Ronald F." }, "id": "Scott-R-F", "role": "advisor", "display_name": "Scott, Ronald F." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/1KZR-E375", "abstract": "The problem of large strain consolidation in soils is investigated by analysis and experiment. A mathematical model is formulated to include the effects of large strains. Analytic and numerical solutions are discussed.\r\n\r\nThe design, fabrication and operation of apparatus to study consolidation and other phenomena in sedimented clays is described. Results of experiments on two types of clay are presented. Finally, the consolidation characteristics of one of these clays are shown to be in close agreement with a particular solution of the large strain consolidation equation." }, { "name": "Lynn, Yen-Mow", "degree": "PhD", "year": "1961", "title": "Isentropic Plane Waves in Magnetohydrodynamics", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-134709", "creators": [ { "name": { "family": "Lynn", "given": "Yen-Mow" }, "id": "Lynn-Yen-Mow", "display_name": "Lynn, Yen-Mow" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/K49C-2N76", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPlane waves propagating in a perfectly electrically conducting polytropic gas of otherwise uniform state in the presence of an arbitrarily oriented uniform magnetic field are studied; they correspond to plane simple waves in magnetohydrodynamics. Riemann invariants across finite amplitude waves in ordinary gasdynamics are generalized herein to take into account all possible magnetohydrodynamics effects. There exist totally seven types of waves, namely, contact surfaces, forward and backward facing transverse simple waves and forward and backward facing coupled (fast and slow) simple waves. But of these only coupled waves are genuinely nonlinear and receive most of our attention. The mathematical theory of simple waves is discussed first to give a general picture of the underlying structure of solutions. Contact surfaces and transverse simple wave solutions are given next with particular emphasis on the case of the contact surface adjacent to a vacuum, region. An exact analytical solution of coupled waves for gases of arbitrary value of [...] is obtained in terms of generalized Riemann invariants; some of these invariants are expressed in terms of definite integrals of a parameter [...]. The invariant relations among several physical quantities are thus expressed in a parametric form. An alternative method of solving coupled waves by graphical means is proposed and some detailed calculations are presented. General properties of physical variables across coupled waves are mentioned. For the special case of gas in a purely transverse magnetic field, a scheme of solving arbitrary flow problems is discussed briefly. The corresponding case of coupled wave solutions is given in terms of a hypergeometric function. Finally, some examples are shown to illustrate the application of the solutions to actual physical problems." }, { "name": "Marin, Jean-Fran\u00e7ois", "degree": "PhD", "year": "1961", "title": "Transitions in Chromium", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04102006-131108", "creators": [ { "name": { "family": "Marin", "given": "Jean-Fran\u00e7ois" }, "id": "Marin-Jean-Fran\u00e7ois", "display_name": "Marin, Jean-Fran\u00e7ois" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/MP9B-B768", "abstract": "The presence of a transition in pure chromium around 40C (from 25C to 65C according to the specimen investigated) is evidenced by the anomalous behavior of various physical properties in the vicinity of the transition. Four different properties - electrical resistivity, Young's modulus and Poisson's ratio, Hall coefficient, specific heat - have been investigated on some of five different specimens in temperature ranges including the transition temperature.\r\n\r\nThe shape and magnitude of the observed anomalies for different properties and different specimens are compared, together with the possible effect of impurities on the transition. The relationship between these anomalies and the transition from an antiferromagnetic to a paramagnetic structure is discussed in connection with neutron diffraction experiments and anomalies in other antiferromagnetic materials reported by other workers." }, { "name": "Merchant, Howard Carl", "degree": "PhD", "year": "1961", "title": "Mode Superposition Methods Applied to Linear Mechanical Systems Under Earthquake Type Excitation", "advisor": "Hudson, Donald E.; Caughey, Thomas Kirk; Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04132006-153621", "creators": [ { "name": { "family": "Merchant", "given": "Howard Carl" }, "id": "Merchant-Howard-Carl", "display_name": "Merchant, Howard Carl" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" }, { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/KMKT-B363", "abstract": "The determination of the maximum dynamic responses of a multidegree of freedom mechanical system under earthquake type excitation using mode superposition methods is the general problem considered. The experimental work was carried out using a special purpose electronic differential analyzer involving a three degree of freedom system, or a three mode approximation to a larger system.\r\n\r\nThe results indicate that a suitably weighted average of the sum of the absolute values and the square root of the sum of the squares of the individual mode contributions gives a practical design criterion for the base shear forces. For critical designs this weighted average reduces to the absolute sum of the modes, which will be close to the true value for a significantly high percentage of the cases. The base moment may be more accurately approximated than the base shear by use of the first mode alone." }, { "name": "Narasimha, Roddam", "degree": "PhD", "year": "1961", "title": "Some Flow Problems in Rarefied Gas Dynamics", "advisor": "Liepmann, Hans Wolfgang; Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11042003-095050", "creators": [ { "name": { "family": "Narasimha", "given": "Roddam" }, "id": "Narasimha-Roddam", "display_name": "Narasimha, Roddam" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1S8T-QA38", "abstract": "This thesis discusses three rather loosely connected problems in free molecule and nearly free molecule flow. First the expansion of a gas cloud into perfect vacuum is considered on the basis of the collision-less Boltzmann equation, and it is shown that if the initial distribution is an isothermal Maxwellian, the density obeys a diffusion equation with a diffusion coefficient proportional to the time. This leads to the description of the free expansion of symmetric clouds in terms of a thick 'diffusion front' traveling at the initial isothermal speed of sound. The expansion of asymmetric clouds and the flow due to sources and jets are also studied.\r\n\r\nSecond, a method of iteration proposed by Willis for calculating nearly free molecular flow is extended to general unsteady flows; it is then applied to the flow through an orifice to show that the correction to the mass flow is of the first order in the inverse Knudsen number. The coefficient, estimated by making some reasonable assumptions about the three-dimensional nature of the flow, is found to agree quite well with Liepmann's measurements.\r\n\r\nFinally a physical basis is suggested for Krook's collision model used in the above calculations. Several consequences of the model are then derived, including the important one that, in the Navier-Stokes limit, the model implies a Stokesian gas with a Prandtl number of unity. The value to be given to the parameter in the model is also discussed at some length." }, { "name": "Pinson, Elliot Neil", "degree": "PhD", "year": "1961", "title": "An Adaptive Control Technique for Systems with Lightly Damped Resonances", "advisor": "Mullin, Francis J.; Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04122011-150702576", "creators": [ { "name": { "family": "Pinson", "given": "Elliot Neil" }, "id": "Pinson-Elliot-Neil", "display_name": "Pinson, Elliot Neil" } ], "advisors": [ { "name": { "family": "Mullin", "given": "Francis J." }, "id": "Mullin-F-J", "role": "advisor", "display_name": "Mullin, Francis J." }, { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6HPW-4V89", "abstract": "An Adaptive Controller capable of stabilizing dynamic systems containing multiple lightly damped resonances is synthesized. The controller acts to stabilize the dynamic system by introducing cascade compensation which has zeros of transmission very close to the critical resonant frequencies. Very little a priori knowledge is needed about the frequencies at which the resonances occur because the Adaptive Controller itself measures these frequencies while the system is operating. It then adjusts its internal parameters on the basis of these measurements to insure that the overall system performance is satisfactory. Since the measurement process can be performed continually, this adaptive control technique is applicable to systems whose resonant frequencies change slowly with time. \r\n\r\nBoth the measurement and compensation functions are performed by a digital computer. The resonant frequencies are measured by cross-correlating a signal generated by the dynamic system with a set of periodic signals whose frequencies span the frequency intervals in which the resonances are known to occur. The necessary compensation is instrumented in a set of difference equations stored in the digital computer. Certain coefficients which appear in these difference equations are adjusted according to logic programmed into the computer. \r\n\r\nNecessary and sufficient conditions are derived to describe the conditions under which the proposed system can be successful. The fact that the system can perform successfully is demonstrated by a detailed digital simulation of an adaptive autopilot for a highly flexible ballistic missile." }, { "name": "Russell, David Allison", "degree": "PhD", "year": "1961", "title": "Studies of the Effects of Cross-Sectional Area Change and Boundary-Layer Growth on the Motion of a Shock Wave", "advisor": "Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212003-155010", "creators": [ { "name": { "family": "Russell", "given": "David Allison" }, "id": "Russell-David-Allison", "display_name": "Russell, David Allison" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HXQP-VQ30", "abstract": "Three problems concerned with the motion of a shock wave are discussed. The first is an analytical and experimental study of the performance of a shock tube with area change near the diaphragm. Interesting results of this section are the development of a simple shock-speed control through the use of area change, and the fact that a spread-out dissipation region was shown to exist for a configuration where a non-stationary secondary shock wave was originally expected. A general discussion of the use of this type of area change is also included.\r\n\r\nThe second problem is a study of the effects of boundary-layer growth on the motion of a shock wave. A simple theory for predicting the attenuation of a shock wave on entering an upstream-facing tube is developed from the analysis of Spence and Woods. When simple laminar boundary-layer approximations are applied, the theory shows good agreement with measurements.\r\n\r\nThe final problem is an experimental study of the motion of a shock wave downstream of a finite-length area contraction. Normalized results are presented which show that the shock wave emerges from the area change at a speed close to the \"linearized\" theory value, and is then attenuated by second-order disturbances until it reaches the speed predicted for the steady-state configuration. The results are presented in a form which is shown to be insensitive to both the incident shock Mach number and the amount of the area reduction." }, { "name": "Stearman, Ronald Oran", "degree": "PhD", "year": "1961", "title": "Part I. The Stability of a Membrane in a Subsonic Flow. Part II. The Stability of a Grid of Panels in a Supersonic Flow", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12212005-160627", "creators": [ { "name": { "family": "Stearman", "given": "Ronald Oran" }, "id": "Stearman-Ronald-Oran", "display_name": "Stearman, Ronald Oran" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TE64-4652", "abstract": "Part I.
\r\n\r\nAn experimental investigation has been made on the stability of small aspect ratio rectangular membranes in a subsonic flow. The leading and trailing edges of the membrane were attached to rigid streamlined supports while the two streamwise edges were free. Both surfaces of the membrane were exposed to the airstream, and the membrane tension was applied through the trailing edge.
\r\n\r\nThe results of the test show that two types of flutter (instability) occur. The first to appear as the wind speed was increased from zero, with a fixed tension level in the membrane, was a small amplitude flutter which has a shallow wave like motion traveling in the streamwise direction. At higher wind speeds this motion was damped out. A narrow equilibrium zone or boundary existed which separated the first type of flutter from a second type of motion having a traveling wave of larger amplitude and greater speed. This second type of flutter had no tendency to damp out, but became more violent as the wind speed was increased.
\r\n\r\nThe span of the slender membrane is the physical parameter that uniquely determines and controls the first flutter boundary; its mass plays no part here, but does affect the equilibrium zones.
\r\n\r\nAppendix A contains an obvious formulation of the slender membrane flutter problem.
\r\n\r\nPart II.
\r\n\r\nA theoretical investigation has been made on the stability of a grid of panels in a supersonic flow. The problem is formulated by considering this structure as a limiting case of a more general configuration composed of a ring of panels (i.e. an axially stiffened cylindrical shell) whose outer surface is exposed to a supersonic flow parallel to its axis. It is shown that the stability analysis of this more general configuration can be reduced to the analysis of an \"equivalent\" single panel using the circulant matrix idea. The reduction procedure, applicable to most cyclic configurations, allows for all types of inter-element (panel) coupling and is subject to the sole restriction that the dynamic phenomenon be satisfactorily described by linear theory.
\r\n\r\nIt is shown that at least five different multi-panel configurations can be obtained from this general problem by taking the appropriate limiting process. The stability (flutter) analysis of one of these limiting cases is discussed for high Mach number flows where only an elastic coupling exists between neighboring panels.
" }, { "name": "Willens, Ronald Howard", "degree": "PhD", "year": "1961", "title": "I. A Vacuum X-Ray Diffractometer for High Temperature Studies. II. An Investigation of the Allotropic Transformation of Titanium", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04112011-155942415", "creators": [ { "name": { "family": "Willens", "given": "Ronald Howard" }, "id": "Willens-Ronald-Howard", "display_name": "Willens, Ronald Howard" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/W8TJ-XN31", "abstract": "A vacuum high temperature x-ray diffractometer has been designed and constructed to study metals, sensitive to oxygen and nitrogen contamination, up to 1200\u00b0C. The factors which affect the accuracy of the diffractometer method and the proper choice of extrapolation functions are discussed. It is shown that this instrument can determine lattice parameters with an accuracy of one part in forty thousand. The thermal expansion of titanium has been investigated to 650\u00b0C and the c/a parameter is found to increase rapidly above 400\u00b0C. This variation of c/a is correlated with other properties of titanium to formulate a band model. On the basis of this model it is shown that the electrons can give an appreciable positive contribution to the free energy as the transformation temperature is approached and it is proposed that this is the main factor causing the instability of the low temperature modification of titanium." }, { "name": "Fleming, Edward Richard", "degree": "PhD", "year": "1960", "title": "Non-Linear Flutter", "advisor": "Fung, Yuan-cheng; Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-133349", "creators": [ { "name": { "family": "Fleming", "given": "Edward Richard" }, "id": "Fleming-Edward-Richard", "display_name": "Fleming, Edward Richard" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" }, { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/CSNK-SA02", "abstract": "The problem of two degree of freedom flutter in the presence of structural non-linearities is investigated. The specific problem chosen for investigation is that of bending-torsion flutter of a two-dimensional airfoil in a supersonic flow. The Kryloff-Bogoliuboff assumption of nearly sinusoidal response with slowly varying amplitude and phase is made and aerodynamic piston theory is used throughout the analysis.
\r\n\r\nFormulas for flutter limit cycles are developed in terms of general structural non-linearities. Necessary and sufficient conditions are developed for the existence of stable flutter limit cycles in the case of an airfoil with torsional stiffness. Several numerical examples of this case are given including a case which exhibits flutter for large disturbances but is stable at all airspeeds for small disturbances.
\r\n\r\nAn analog computer investigation of flutter dependence on initial conditions is given.
\r\n" }, { "name": "Forster, Donald Charles", "degree": "PhD", "year": "1960", "title": "Theory of Parametrically-Pumped Longitudinal-Field Electron Beams", "advisor": "Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-02222006-091619", "creators": [ { "name": { "family": "Forster", "given": "Donald Charles" }, "id": "Forster-Donald-Charles", "display_name": "Forster, Donald Charles" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WNEA-DF59", "abstract": "The general equations describing electron beams which have been excited by both a moderately strong pump source (or local oscillator) and a weak signal source are formulated in terms of coupled modes, including coupling to slow-wave circuits, and solved numerically for four problems of interest:
\r\n\r\na) space-charge pumped longitudinal parametric amplifiers
\r\n\r\nb) circuit-pumped longitudinal parametric amplifiers
\r\n\r\nc) parametric cooling of slow space-charge waves, and
\r\n\r\nd) traveling-wave tubes with pump space-charge waves excited on the electron stream.
\r\n\r\nEmphasis is placed on the parametric amplifier solutions, and realization of noise temperatures as low as 55\u00b0K are indicated. A discussion of the form of the general equations leads to new concepts about the coupling of positive and negative energy carriers through the action of parametric pumping.
\r\n\r\nExperimental results are presented which tend to verify qualitatively some of the theoretical predictions for the behavior of the parametric amplifiers.
\r\n" }, { "name": "Glick, Herbert Seymour", "degree": "PhD", "year": "1960", "title": "Modified Crocco-Lees Mixing Theory for Supersonic Separated and Reattaching Flows", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12082005-132722", "creators": [ { "name": { "family": "Glick", "given": "Herbert Seymour" }, "id": "Glick-Herbert-Seymour", "display_name": "Glick, Herbert Seymour" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0V7K-QS61", "abstract": "Re-examination of the Crocco-Lees method has shown that the previous quantitative disagreement between theory and experiment in the region of flow up to separation was caused primarily by the improper C(K) relation assumed. A new C(K) correlation, based on low-speed theoretical and experimental data and on supersonic experimental results, has been developed and found to be satisfactory for accurate calculation of two-dimensional laminar supersonic flows up to separation.\r\n\r\nA study of separated and reattaching regions of flow has led to a physical model which incorporates the concept of the \"dividing\" streamline and the results of experiment. According to this physical model, viscous momentum transport is the essential mechanism in the zone between separation and the beginning of reattachment, while the reattachment process is, on the contrary, an essentially inviscid process. This physical model has been translated into Crocco-Lees language using a semi-empirical approach, and approximate C(K) and F(K) relations have been determined for the separated and reattaching regions. The results of this analysis have been applied to the problem of shock wave-laminar boundary layer interaction, and satisfactory quantitative agreement with experiment has been achieved." }, { "name": "Gorecki, Jacek Piotr", "degree": "PhD", "year": "1960", "title": "An Investigation of Temperature Fluctuations on Bluff Bodies", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242006-083641", "creators": [ { "name": { "family": "Gorecki", "given": "Jacek Piotr" }, "id": "Gorecki-Jacek-Piotr", "display_name": "Gorecki, Jacek Piotr" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KV3S-CJ64", "abstract": "Temperature fluctuations and recovery temperatures on the surface of a circular cylinder (with axis normal to a subsonic compressible flow) and the field of flow about the cylinder, particularly the wake area, are investigated experimentally in range between M = 0.35, Re = 117,000 and M = 0.70, Re = 201,000.\r\n\r\nSpectral analysis of fluctuations on body surface and other evidence indicate that formation of discrete vortex cores from the separated shear layers is initially an impulsive random process (of the generalized \"shot effect\" type), although the wake farther downstream from the model has a definitely periodic structure.\r\n\r\nImpulsive formation of vortex cores can be enhanced by wind tunnel resonance or by a high turbulence level in the free stream and is accompanied by abnormal cooling of the model surface in the separated area - the mechanism of these effects is also investigated." }, { "name": "Gourdine, Meredith Charles", "degree": "PhD", "year": "1960", "title": "On Magnetohydrodynamic Flow over Solids", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162005-083621", "creators": [ { "name": { "family": "Gourdine", "given": "Meredith Charles" }, "id": "Gourdine-Meredith-Charles", "display_name": "Gourdine, Meredith Charles" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/5AMT-CM66", "abstract": "The steady flow of a viscous, incompressible and electrically conducting fluid over a solid, in the presence of an applied magnetic field parallel to the main flow, is considered. The equations of magnetohydrodynamics (MHD) are linearized by assuming that the solid only slightly perturbs the velocity and magnetic field. Fundamental solutions of the linearized equations are derived, and they are used to construct MHD flows over solids. The MHD drag formulas for the finite flat plate and the sphere are derived. The special cases of zero viscosity and infinite conductivity are studied, and general formulas for MHD forces on a solid are presented. The problem is generalized to include an electrical generator in the body.\r\n\r\nSteady flow over a flat, circular, broadside-on disk in the presence of a parallel magnetic field is solved as a boundary value problem. The flow solution and drag formulas are valid for all values of the three parameters, Reynolds number, Magnetic Reynolds number, and Alfven number. The drag is calculated for large and small magnetic interaction; in the latter case the drag is proportional to the Alfven number. A special diffusion model applicable for large Hartmann number flows is also presented." }, { "name": "Hsieh, Din-Yu", "degree": "PhD", "year": "1960", "title": "Theory of Gas Bubble Dynamics in Oscillating Pressure Fields", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06152006-093844", "creators": [ { "name": { "family": "Hsieh", "given": "Din-Yu" }, "id": "Hsieh-Din-Yu", "display_name": "Hsieh, Din-Yu" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/3VCA-FH77", "abstract": "The behavior of a permanent gas bubble in liquids under oscillating pressure fields is studied by a linearized theory. The derived thermodynamic relation tends to indicate average isothermality for high frequency limit, contrary to the usual intuitive reasonings. The growth of the gas bubble under the oscillating pressure fields due to the effect of rectification of mass is also investigated. The effect is small, being of second order, but accumulating. The absence of resulting large bubbles is explained briefly by the considerations on the stability of spherical shape of the bubbles." }, { "name": "Hunter, Herbert Erwin", "degree": "PhD", "year": "1960", "title": "Application of Asymptotic Expansion Procedures to Low Reynolds Number Flows about Infinite Bodies", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092005-134820", "creators": [ { "name": { "family": "Hunter", "given": "Herbert Erwin" }, "id": "Hunter-Herbert-Erwin", "display_name": "Hunter, Herbert Erwin" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5PBX-0J36", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nSeveral limiting cases for viscous incompressible flow are considered for two examples. The first example considered is that of the flow past an expanding infinite cylinder at an angle of attack. The time dependence of the radius of the cylinder is given by the power law R = [...]. The second example considered is the flow past a semi-infinite power law body of revolution (i. e. R = [...]) at zero angle of attack. Both examples are considered for the limiting case of small Reynolds number. The Reynolds number is based on a characteristic length obtained from the parameters in the expression for the radius. The second example is also considered for the limiting case of the flow far down stream.\r\n\r\nAsymptotic expansions of the solution valid for the limiting cases considered (i. e, low Reynolds number or flow far down stream) are obtained by applying singular perturbation procedures. These expansions are obtained for 0 <= n < 1 for the first example and for 0 <= n <= 1/2 for the second example. For the second example the terms in the low Reynolds number expansion are not obtained in closed form, except for n = 1/2. For n < 1/2 the low Reynolds number expansion of the Navier-Stokes equations is expressed in terms of the solution of the corresponding Stokes flow problem. The expansions obtained for the flow far down stream on the power law body of revolution have the character of a very viscous flow although they are valid for any fixed Reynolds number." }, { "name": "Jacobs, Theodore Alan", "degree": "PhD", "year": "1960", "title": "Part 1. An Investigation of Relaxation Processes. Part 2. Studies in Combustion", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10042005-105327", "creators": [ { "name": { "family": "Jacobs", "given": "Theodore Alan" }, "id": "Jacobs-Theodore-Alan", "display_name": "Jacobs, Theodore Alan" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/9YND-DS33", "abstract": "Part 1\r\n\r\nI. The rate of the homogeneous thermal decomposition of NH3 in NH3-Ar mixtures has been measured in a shock tube by monitoring the radiation emitted by the NH3 in the 3 micron wavelength region. For the temperature range 2000-3000\u00baK an apparent activation energy of about 52 Kcal was found.\r\n\r\nII. The vibrational relaxation of isothermal, dilute gas mixtures after excitation by an external radiation field has been investigated, leading to a proposed experiment for the measurement of collision transition probabilities.\r\n\r\nPart 2\r\n\r\nI. A review of recent papers in the field of combustion has been prepared for the 1960 Edition of Annual Reviews of Physical Chemistry.\r\n\r\nII. An approximate theoretical performance evaluation for a diverging rocket has been performed. A paper describing the evaluation has been published in Astronautics Acta." }, { "name": "Kelly, Peter M.", "degree": "PhD", "year": "1960", "title": "A Unified Approach to Two-Terminal Network Synthesis", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechETD:etd-06292006-085436", "creators": [ { "name": { "family": "Kelly", "given": "Peter M." }, "id": "Kelly-Peter-M", "display_name": "Kelly, Peter M." } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WP7M-PE92", "abstract": "The advantages are considered of developing dual approaches to two terminal lumped constant network synthesis. The first is the usual S-plane approach emphasizing the positive-real concept; the second treats the reflection coefficient, involves unitary modular functions, and is related to the older wave filter theory. The second viewpoint is developed in some detail and used to unify the various existing methods of two-terminal synthesis on a common mathematical basis. The synthesis techniques of Foster, Cauer, Brune, Bott-Duffin, Failkow-Gerst, and Miyata are re-examined in terms of the reflection coefficient and some alternate methods of synthesis are suggested. It is found that all of these synthesis techniques may be derived as applications of the Schwarz' lemma." }, { "name": "Kennedy, John Fisher", "degree": "PhD", "year": "1960", "title": "Stationary Waves and Antidunes in Alluvial Channels", "advisor": "Brooks, Norman H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06222006-153051", "creators": [ { "name": { "family": "Kennedy", "given": "John Fisher" }, "id": "Kennedy-John-Fisher", "display_name": "Kennedy, John Fisher" } ], "advisors": [ { "name": { "family": "Brooks", "given": "Norman H." }, "id": "Brooks-N-H", "role": "advisor", "display_name": "Brooks, Norman H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/Y27F-NR79", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA theoretical and laboratory investigation was made of antidunes and associated stationary waves. The objectives were to determine the factors involved in the formation of antidunes, the characteristics of the stationary waves, and the effects of antidunes and waves on the friction factor and sediment transport capacity of streams.\r\n\r\nIn the potential flow solution for flow over a wavy bed it was hypothesized that the flow shapes the erodible sand bed by scour and deposition to conform to a streamline of the flow configuration for which the energy is a minimum. Under this hypothesis, flow over antidunes is the same as the segment of flow above an intermediate streamline of the fluid motion associated with stationary gravity waves (waves with celerity equal and opposite to the flow velocity) in a fluid of infinite depth. For a velocity V the wave length, [lambda] is given by [lambda] and waves break when their height reaches 0.142[lambda]. Laboratory and field data for two-dimensional antidunes confirmed these relations.\r\n\r\nForty-three experimental runs in laboratory flumes were made for different depths and velocities and bed sands of two different sizes (0.55 mm and 0.23 mm). No general criterion for the formation of antidunes or the occurrence of breaking waves could be formulated because of inadequate knowledge of the complex sediment transport phenomenon. Qualitatively, it was found that for a given sand, the critical Froude number for the occurrence of breaking waves decreased as the depth was increased. Over a certain range of depth and velocity it was found that the flow formed waves and antidunes or was uniform depending on whether or not the flow was disturbed to form an initial wave. Waves that did not break had no measurable effect on the transport capacity or friction factor, but breaking waves increased both of these quantities." }, { "name": "Lapp, Marshall", "degree": "PhD", "year": "1960", "title": "Part 1. Emissivity Calculations for CO\u2082. Part 2 Shock Tube f-Number Measurement for OH", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07052006-080623", "creators": [ { "name": { "family": "Lapp", "given": "Marshall" }, "id": "Lapp-Marshall", "display_name": "Lapp, Marshall" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/BW2K-2M27", "abstract": "Part 1: A model has been developed for the calculation of total emissivities of polyatomic molecules at elevated temperatures in terms of room temperature measurements and of a few parameters characteristic of the major known regions of emission. The model involves a statistical redistribution of the theoretically available intensities throughout these regions. Using this model, emissivities of CO2 have been calculated at 600\u00b0K for optical depths up to 3 ft-atm which agree with the experimental data of Hottel within 8%. Calculations made at temperatures up to 1750\u00b0K for optical depths of 0.1 to 2.0 ft-atm agree with the experimental data within 30%.
\r\n\r\nIt appears that the proposed model for calculating the emissivities of CO2 constitutes a good approximation at elevated temperatures and that the required parameters have been obtained with fair accuracy from a semi-empirical fit to total emissivity data measured at 300\u00b0K. It is apparent that a closer correlation with empirical data could have been obtained if an \"optimal adjustment\" had been made for the three variable parameters by fitting our theoretical formulae to high-temperature emissivity measurements. However, this \"optimal fit\" would not constitute as stringent a test of our model as the calculations described in this analysis.
\r\n\r\nWe note that the success of these calculations does not depend upon a fit to Hottel's data at 300\u00b0K since (a) we are able to calculate the total emissivity at 300\u00b0K with fair accuracy from spectroscopic data and (b) we are able to estimate the parameters required by our model directly from available spectroscopic information. The use of Hottel's data is adopted only as a convenience for this test calculation in order to provide a consistent check on our method of calculating emissivities at elevated temperatures.
\r\n\r\nPart 2: The f-number for the (0,0)-band of the 2\u03a3 \u2192 2\u03a0 transitions of OH has been found to be (0.9 \u00b1 0.5) x 10-3. A shock tube was used to produce hot gas samples at temperatures from 3300 to 3900\u00b0K with equilibrium partial pressures of OH of 0.004 to 0.02 atm. The emission intensities were measured photoelectrically as a function of time behind the reflected shock in a selected spectral interval. These results were then related to the f-number by means of an absolute intensity calibration.
\r\n" }, { "name": "MacGillivray, Dean", "degree": "PhD", "year": "1960", "title": "Motion of a Current Element Through a Fluid of Low Electrical Conductivity", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12072005-131316", "creators": [ { "name": { "family": "MacGillivray", "given": "Dean" }, "id": "MacGillivray-Dean", "display_name": "MacGillivray, Dean" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B0AW-TR02", "abstract": "Two-dimensional flow of an incompressible, viscous, electrically conducting fluid past a current element is studied. A solution in the form of an asymptotic development is obtained, valid as a certain dimensionless parameter (essentially the product of the electrical conductivity and the current) tends to zero. An expression for the drag on the current element is computed, and is found to be independent of viscosity." }, { "name": "Mead, Carver A.", "degree": "PhD", "year": "1960", "title": "Transistor Switching Analysis", "advisor": "Middlebrook, Robert David; Langmuir, Robert V.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05182006-084112", "creators": [ { "name": { "family": "Mead", "given": "Carver A." }, "id": "Mead-Carver-A", "orcid": "0000-0003-4051-0462", "display_name": "Mead, Carver A." } ], "advisors": [ { "name": { "family": "Middlebrook", "given": "Robert David" }, "id": "Middlebrook-R-D", "role": "advisor", "display_name": "Middlebrook, Robert David" }, { "name": { "family": "Langmuir", "given": "Robert V." }, "id": "Langmuir-R-V", "role": "co-advisor", "display_name": "Langmuir, Robert V." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0Q5Z-KA62", "abstract": "With the widespread application of junction transistors in switching applications, the need for a general method of analysis useful in the region of collector voltage saturation has become apparent. Linear equivalent circuits using lumped elements have long been used for small signal calculations of normally biased transistors, but a comparable method for saturated transistors has been lacking. Recently Linvill (3) proposed the method of lumped models which allows the analysis of complex switching problems with the ease of linear circuit calculations. In Part I the method is shown to be equivalent to a well-known linear equivalent circuit under normal bias conditions. Examples of the application of the method and the use of approximations are drawn from practical circuit problems. Emphasis is placed upon the understanding of the physical phenomena involved, a necessary prerequisite to intelligent circuit design. In Part II the operation of transistors at relatively large collector currents is considered. Several effects which contribute to non-linear operation are analyzed. It is shown that at both high and low injection levels, a decrease in current gain is to be expected as a result of the self bias cutoff effect.
\r\n\r\nEmitter efficiency is shown to be important at high levels because of its contribution on the self bias effect.
\r\n\r\nThe operation of both alloy and diffused base transistors as saturated switches is discussed, with particular reference to the nonlinear effects. Theoretical expressions are derived for the saturation voltage as a function of collector and base current for both types.
" }, { "name": "Naud\u00e9, Charl Fran\u00e7ois", "degree": "PhD", "year": "1960", "title": "On the Mechanism of Cavitation Damage by Non-Hemispherical Cavities Collapsing in Contact with a Solid Boundary", "advisor": "Ellis, Albert T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06302006-081114", "creators": [ { "name": { "family": "Naud\u00e9", "given": "Charl Fran\u00e7ois" }, "id": "Naud\u00e9-Charl-Fran\u00e7ois", "display_name": "Naud\u00e9, Charl Fran\u00e7ois" } ], "advisors": [ { "name": { "family": "Ellis", "given": "Albert T." }, "id": "Ellis-A-T", "role": "advisor", "display_name": "Ellis, Albert T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/QACP-9A29", "abstract": "A perfect fluid perturbation theory, which neglects the effect of gravity, and which assumes that the pressure inside a cavitation bubble remains constant during the collapse process, is given for the case of a non-hemispherical, but axially symmetric cavity which collapses in contact with a solid boundary. The theory suggests the possibility that such cavities may deform to the extent that the cavity wall strikes the solid surface before minimum cavity volume is reached.\r\n\r\nHigh speed motion pictures of cavities generated by spark methods are used to test the theory experimentally. It is found that the theory describes the change of shape of such cavities fairly well, and that the phenomenon of the cavity wall striking the solid boundary does indeed occur.\r\n\r\nBy studying the damaging effects of various cavities of this type on aluminum samples, it is shown that pressures resulting from the cavity wall striking the surface are much higher than pressures caused by compression of gases inside the cavity. It is furthermore found that the estimated impact velocities of the cavity walls on the solid boundary can account for water hammer pressures sufficiently large to have caused the observed damage." }, { "name": "Olfe, Daniel Burrhus", "degree": "PhD", "year": "1960", "title": "Gas Emissivities and Radiative Transfer Studies", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06292006-152959", "creators": [ { "name": { "family": "Olfe", "given": "Daniel Burrhus" }, "id": "Olfe-Daniel-Burrhus", "display_name": "Olfe, Daniel Burrhus" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/FZWR-9J22", "abstract": "In Chapter 1 theoretical expressions are derived for the relations between gas absorptivities and emissivities for the limit of zero optical depth and for various models of vibration-rotation bands. Some of the band models for which useful results are obtained are bands with constant average absorption coefficients and well-defined widths, bands composed of non-overlapping spectral lines with dispersion or Doppler contour, and bands composed of randomly distributed lines with dispersion contour. The theoretical formulae are shown to provide a good correlation for the available experimental data on CO2, H2O, and CO.\r\n\r\nRepresentative estimates for the radiant energy emission from the combustion products formed by a burning ammonium perchlorate propellant grain are made in Chapter 2. The listed compilations of data may be used to estimate the radiant heat transfer to the burning propellant surface, as well as the radiant energy loss from the combustion products, since emission and absorption of radiation by the gases in the reaction zone are shown to be negligibly small.\r\n\r\nThe study in Chapter 3 on radiant energy transfer from non-isothermal molecular emitters with non-overlapping dispersion lines complements earlier work done on overlapping lines and on randomly distributed dispersion lines. In addition to the transparent gas approximation for gases of small optical depth, a \"square root\" approximation is found to be valid for large optical depths, provided the temperature gradient in the slab of gas nearest to the observer is not too large. These approximations are used to derive explicit expressions for the radiant energy flux from two adjacent isothermal regions at different temperatures.\r\n\r\nIn Chapter 4, the important equilibrium emission processes in a hydrogen plasma are investigated in the temperature range between 300\u00b0K and 10,000\u00b0K for pressures up to several hundred atmospheres. It is found that the pressure-induced spectrum of the H2 molecule makes an important emissivity contribution at the lower temperatures (below approximately 4500\u00b0K) whereas, at the higher temperatures, the bound-free and free-free transitions of the H ion and the continuum and line spectrum of the H atom are the most important contributors to the emissivity. The problems of the very broad wings of the Lyman a line and of the lowering of the ionization potentials by the fields of the plasma ions are considered." }, { "name": "Reichenbach, Roy Earl", "degree": "PhD", "year": "1960", "title": "Combustion Research", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06282006-143052", "creators": [ { "name": { "family": "Reichenbach", "given": "Roy Earl" }, "id": "Reichenbach-Roy-Earl", "display_name": "Reichenbach, Roy Earl" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/8CB5-TG80", "abstract": "In Part 1 an iterative procedure is described for the solution of nozzle flow problems with one-step, reversible chemical reactions. The efficiency of the method of calculation is illustrated by comparing the results with data obtained through the use of machine computations for the recombination of hydrogen atoms in a deLaval nozzle.\r\n\r\nTwo topics concerned with droplet burning are considered in Part 2. Droplets of several important propellants, viz., RP-1, UDMH and N2H4, were burnt in air and in oxygen. The (effective) evaporation constants were determined experimentally for these fuels. The second topic involves the determination of the propagation rates and mechanism of propagation of a flame in a one-dimensional array of n-octane droplets. The flame propagation rates were found to be a function of the initial droplet size, of the droplet spacing, and directly of the depth of immersion of the droplet in the hot-gas zone.\r\n\r\nPart 3 consists of a study of the effect of an inert diluent on spectral intensity ratios in propane-oxygen-nitrogen flames. Experiments were conducted with inert diluent contents of 50, 60, 70, and 80 percent nitrogen (by mass) and with equivalence ratios of 0.6, 0.8, 1.0, 1.2, 1.4 and 1.6. The spectral intensity ratio was found to be a function not only of the equivalence ratio but also of the percentage of inert diluent. Hence it is not possible, in general, to use spectral intensity ratios as measures of mixture composition, a procedure that has been used erroneously by a number of investigators." }, { "name": "Reshotko, Eli", "degree": "PhD", "year": "1960", "title": "Stability of the Compressible Laminar Boundary Layer", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-01042006-141741", "creators": [ { "name": { "family": "Reshotko", "given": "Eli" }, "id": "Reshotko-Eli", "display_name": "Reshotko, Eli" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M6HG-WW29", "abstract": "In previous theoretical treatments of the stability of the compressible laminar boundary layer the effect of the temperature fluctuations on the \"viscous\" (rapidly varying) disturbances is either ignored (Lees-Lin), or is accounted for incompletely (Dunn-Lin). A thorough reexamination of this problem shows that temperature fluctuations have a profound influence on both the \"inviscid\" (slowly varying) and viscous disturbances above a Mach number of about 2.0. The present analysis includes the effect of temperature fluctuations on the viscosity and thermal conductivity, and also introduces the viscous dissipation term that was dropped in the earlier theoretical treatments.\r\n\r\nSome important results of the present study are: (1), the rate of conversion of energy from the mean flow to the disturbance flow through the action of viscosity in the vicinity of the wall increases with Mach number; (2), instead of being nearly constant across the boundary layer, the amplitude of inviscid pressure fluctuations for Mach numbers greater than 3 decreases markedly with distance outward from the plate surface. This behavior means that the jump in magnitude of the Reynolds stress in the neighborhood of the critical layer is greatly reduced; (3), at Mach numbers less than about 2 dissipation effects are minor, but they become extremely important at higher Mach numbers since for neutral disturbances they must compensate for the generally destabilizing effects of items (1) and (2).\r\n\r\nNumerical examples illustrating the effects of compressibility (including neutral stability characteristics) are obtained and are compared with the experimental results of Laufer and Vrebalovich at M = 2.2, and of Demetriades at M = 5.8." }, { "name": "Stumpf, Henry John", "degree": "PhD", "year": "1960", "title": "Response of Mechanical Systems to Random Excitation", "advisor": "Caughey, Thomas Kirk", "url": "https://resolver.caltech.edu/CaltechETD:etd-07262006-142737", "creators": [ { "name": { "family": "Stumpf", "given": "Henry John" }, "id": "Stumpf-Henry-John", "display_name": "Stumpf, Henry John" } ], "advisors": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-T-K", "role": "advisor", "display_name": "Caughey, Thomas Kirk" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/NJSA-T820", "abstract": "The Fourier Series and Fokker-Planck Methods, the available techniques for solving vibration problems when the exciting force is a stochastic process, are reviewed and several detailed examples are given. In particular a two-degree-of-freedom system is considered which is excited by a non-stationary input and which possesses a general type of viscous damping.\r\n\r\nSeveral typical engineering problems involving stochastic processes are considered. In the case of fatigue it is shown that a criterion for fatugue failure in multi-degree-of-freedom systems may be established using Miner's cumulative damage hypothesis and the number of zero crossings per second.\r\n\r\nIn the earthquake problem it is shown that when certain inequalities involving the natural frequencies of the building are valid, cross-product terms may be neglected in computing mean square displacements.\r\n\r\nTwo problems involving beams are considered. In one case it is demonstrated that a convergent expression for the mean square bending moment may be obtained for a Bernoulli-Eular beam excited by white noise, provided a finite cutoff frequency is used. In the other case involving random end motion, a one-term approximation to the mean square bending moment may be obtained, when the correlation time is not too small.\r\n\r\nThe isolation problem is considered and the concept of the \"white spectrum fragility curve\" is established as a criterion for adequate isolation.\r\n\r\nFinally the motion of a single-degree-of-freedom system over a rough surface is considered. It is shown that for an exponentional type of auto-correlation the mean square displacement is finite for unaccelerated motion and diverges when the system is accelerated." }, { "name": "Sturtevant, Bradford", "degree": "PhD", "year": "1960", "title": "The Effusion of Charged Particles from a Shock Heated Gas", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12302004-145356", "creators": [ { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-Bradford", "display_name": "Sturtevant, Bradford" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PCNN-DW03", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental and theoretical investigation is made of the application of a molecular beam type sampling device for studying low density shock tube flows to the case of slowly ionizing argon behind a reflected shock wave. The flux of charged particles from a gas heated to about 10,OOO[degrees]K and 20 mm. Hg. through a small orifice in the shock tube end wall is measured. The processes determining this flux are the initial stages of ionization in argon and the diffusion of charged particles to a cold metallic wall. Providing the diffusion process is understood, the measurements constitute a direct observation of incipient ionization ([...]).\r\n\r\nThe transient charge diffusion mechanism is studied in detail theoretically, avoiding the assumption of ambipolar diffusion. It is concluded that the major problem lies in the understanding of the wall-gas interaction as represented by boundary conditions at the wall. An approximate relation for charge effusion is derived.\r\n\r\nIt is concluded from the experimental results that the initial ionization can not be due to a single step, electron-atom collision process but must result from a series of several atom-atom collisions resulting in the ionization of argon atoms." }, { "name": "Sutera, Salvatore Philip", "degree": "PhD", "year": "1960", "title": "Streaming Birefringence as a Hydrodynamic Research Tool", "advisor": "Wayland, J. Harold", "url": "https://resolver.caltech.edu/CaltechETD:etd-07062006-080514", "creators": [ { "name": { "family": "Sutera", "given": "Salvatore Philip" }, "id": "Sutera-Salvatore-Philip", "display_name": "Sutera, Salvatore Philip" } ], "advisors": [ { "name": { "family": "Wayland", "given": "J. Harold" }, "id": "Wayland-J-H", "role": "advisor", "display_name": "Wayland, J. Harold" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/DDJZ-7X80", "abstract": "An optical system capable of providing precise pointwise measurements of streaming birefringence (SBR) was used to explore the flow of dilute solutions of tobacco mosaic virus between rotating eccentric cylinders. The local relationship between the observed optical anisotropy and the rate of strain tensor calculated from the theoretical solution for the particular flow field was studied. The relationship is apparently in accord with the conclusions of the orientation theory for a sufficiently dilute solution of rigid macromolecules in generalized two-dimensional flow.\r\n\r\nThe general problem of using streaming birefringence of colloidal solutions to visualize two-dimensional laminar flows is considered. The conclusion is reached that a clear and unambiguous kinematic interpretation of SBR in such fluids is possible only for a restricted class of flows. If the flow is such that the angle between the streamline and the principal rate of strain axes is not less than 35\u00b0, then to a good approximation SBR can give the magnitude and direction of the principal strain rates. This information, it is shown, is sufficient to permit calculation of the entire velocity field if the velocity is known on all boundaries.\r\n\r\nIn the most general flow situations, SBR of colloidal solutions cannot indicate the orientation of the rate of strain tensor. SBR in certain birefringent pure liquids may yield the necessary information even in the most general flows. These pure liquids hold promise of being valuable flow visualization agents." }, { "name": "Boyd, Gary Delane", "degree": "PhD", "year": "1959", "title": "Experiments on the Interaction of a Modulated Electron Beam with a Plasma", "advisor": "Gould, Roy Walter; Field, Lester M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01312006-141144", "creators": [ { "name": { "family": "Boyd", "given": "Gary Delane" }, "id": "Boyd-Gary-Delane", "display_name": "Boyd, Gary Delane" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Field", "given": "Lester M." }, "id": "Field-L-M", "role": "advisor", "display_name": "Field, Lester M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JAAT-0J83", "abstract": "New experiments are performed concerning the high frequency interactions of electron beams and plasmas. A modulated (500 Mc and 3000 Mc) electron beam is passed through a uniform plasma region of a mercury arc discharge, after which it is demodulated. Exponentially growing wave amplification along the electron beam is observed for the first time at a modulation frequency equal to the plasma frequency. No constant magnetic fields are used in these experiments. Calculations based on the one dimensional analysis of Bohm and Gross of an electron beam passing through a plasma are made to predict the effects of the random energy of the plasma electrons and collisions. By studying the interaction of a finite diameter beam and a plasma with no thermals or collisions, it is shown that the effect of the finite geometry is to reduce the growth constant.
\r\n\r\nRecent work by Trivelpiece and Gould has pointed out that a plasma column in free space may propagate forward and backward waves at a velocity small compared to the velocity of light. The experimental techniques of passing a modulated electron beam through the plasma, as described above, are applied to observe traveling wave type of interaction with the slow wave mode of propagation in the absence of any magnetic fields. Theory predicting experimental rates of growth is presented. Experimental results in good agreement with theory are presented.
\r\n\r\nIn the course of verifying plasma density measurements, the excitation of the dipole resonance of a plasma column is considered. Multiple resonances are observed and discussed.
" }, { "name": "Briceland, Richard Harald", "degree": "PhD", "year": "1959", "title": "Secondary Flow in a Cascade of Airfoils", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-01312006-134201", "creators": [ { "name": { "family": "Briceland", "given": "Richard Harald" }, "id": "Briceland-Richard-Harald", "display_name": "Briceland, Richard Harald" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/EYF1-2Y08", "abstract": "Secondary flows were studied experimentally in a diffusing cascade. A family of screens were installed ahead of the blade row at the midspan position to produce a controlled distortion of the up-stream velocity profile. In this way it was possible to focus attention on those regions of the flow field which were distant from the tunnel walls and to thereby restrict the investigation to a study of small disturbance phenomena.\r\n\r\nIt was found that the general behavior of the flow at the cascade exit plane was satisfactorily described by a modified channel-theory analysis in which a simple iterative correction was included to account for the spanwise self-transport effects of the induced secondary flows.\r\n\r\nTwo methods are proposed for evaluating the spanwise distribution of blade loading when the approach velocity into the cascade is non-uniform; these methods were tested experimentally and were found to give results which were in good agreement with measured data." }, { "name": "Broman, Gunnar Erik", "degree": "PhD", "year": "1959", "title": "Experimental Investigation of Flame Stabilization in a Deflected Jet", "advisor": "Zukoski, Edward E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022006-105147", "creators": [ { "name": { "family": "Broman", "given": "Gunnar Erik" }, "id": "Broman-Gunnar-Erik", "display_name": "Broman, Gunnar Erik" } ], "advisors": [ { "name": { "family": "Zukoski", "given": "Edward E." }, "id": "Zukoski-E-E", "role": "advisor", "display_name": "Zukoski, Edward E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/J5D1-MX07", "abstract": "An experimental investigation has been made of flame stabilization in a two-dimensiona1 deflected jet of propane-air mixture at 70\u00b0F and atmospheric pressure. By a 90\u00b0 deflection of the jet entering a combustion chamber duct through a slot, a recirculation zone is created which serves as a heat source in the flow. The chemical reaction in mixing zone between the fresh mixture in the jet and the hot gas in the recirculation zone supplies heat for the stabilization of a flame in the flow.\r\n\r\nThe influence of the flow parameters on the stability was determined by changing the burner size and geometry. When the geometry was changed by variation of the ratio between slot width and burner height, two types of flow were observed. First, for large ratios, the mixing zone was covered by the flow of fresh mixture along the complete length of the mixing zone. This type of flow with a free mixing zone shows a great deal of similarity with the flow of the bluff body flameholder. The characteristic time introduced for the bluff body flameholder was also found to be a satisfactory correlation parameter for stability of burners of different size and geometry.\r\n\r\nIn the second type of flow found for small slot to height ratios, the mixing zone reached the burner wall before the end of the recirculation zone. By a detailed study of flow, it was shown that the actual residence time in the mixing zone was the primary parameter for stability. Comparisons between burners with small slot to height ratios and the can burner also suggest that the same concept can be applied to the can burners.\r\n\r\nThe results of the present investigation show that the ignition delay concept, on which the characteristic time for the bluff body flameholder is based, can be extended to flame stabilization in a deflected jet." }, { "name": "Brownlee, Wilmot Grant", "degree": "PhD", "year": "1959", "title": "An Experimental Investigation of Unstable Combustion in Solid Propellant Rocket Motors", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02012006-132933", "creators": [ { "name": { "family": "Brownlee", "given": "Wilmot Grant" }, "id": "Brownlee-Wilmot-Grant", "display_name": "Brownlee, Wilmot Grant" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/84XQ-AA28", "abstract": "Unstable combustion in solid propellant rocket motors is characterized by high frequency chamber pressure oscillations, often accompanied by changes in the mean burning rate. Experiments with case-bonded, cylindrically perforated motors were reproducible as a result of careful manufacturing control and extended propellant curing time. In these motors the oscillations were in the fundamental pseudo-standing tangential mode and were accompanied by increases in the average burning rate. At sufficiently high pressure levels all firings were stable. Reduction of the operating level led to mild instability. A sufficient further reduction produced a sudden change to maximum instability. Continued reduction in pressure level from this point resulted in a gradual decrease in degree of instability but it could not be experimentally verified that a low pressure stable region existed. The levels at which these events took place were frequency dependent and generally increased as the tangential frequency was reduced. At given operating level, the instability became less severe when the grain length was reduced below a critical value. Increasing the length above the critical value moved the point of maximum instability to somewhat higher levels but did not affect the level at which the motors became stable. The pressure levels for stability and for maximum instability moved to lower values with decreases in the propellant grain temperature in a manner not entirely accounted for by the effect of grain temperature on burning rate. Stable, mildly unstable and severely unstable operation was observed throughout the range -80\u00b0F to 180\u00b0F. The maximum instability decreased with grain temperature.\r\n\r\nSlab motors with opposed-plane grain surfaces exhibited oscillations in the transverse sloshing mode but no accompanying changes in the burning rate. Tangential oscillation of equivalent amplitude strongly affected the burning rate in the cylindric motors; hence it appears that increases in the burning rate are associated with tangential velocities rather than pressure fluctuations." }, { "name": "Chang, I-Dee", "degree": "PhD", "year": "1959", "title": "Navier-Stokes Solutions at Large Distances from a Finite Object", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062006-083016", "creators": [ { "name": { "family": "Chang", "given": "I-Dee" }, "id": "Chang-I-Dee", "display_name": "Chang, I-Dee" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SMPS-TA29", "abstract": "The asymptotic expansion of the Navier-Stokes solutions at fixed Reynolds numbers and large distances from a finite object for an incompressible, stationary and two-dimensional flow is studied. The expansion is a coordinate-type expansion and differs in many mathematical aspects from the more familiar parameter-type expansions for large and small Reynolds number flows. These differences are noted and discussed in some detail. The technique chosen for dealing with the problem is that of the use of an artificial parameter. This is one possible method for using some of the techniques of parameter-type expansions. In particular, at large distances from the object one may distinguish a viscous wake region and a potential (\"outer\") flow region. The relation between these regions is very similar to the relation between the viscous boundary layer and the potential flow region for flow at large Reynolds numbers.\r\n\r\nSeveral terms of the expansion are computed. However, the main emphasis is placed on discussing the methods for deriving these terms. The special features of expansions in artificial parameters are discussed in detail. The role of various properties of Navier-Stokes solutions, such as validity of integral theorems and rapid decay of vorticity is also brought out.\r\n\r\nThe original motivation of the study was an attempt to understand the Filon's paradox which historically was an error in evaluating the momentum, integral of the asymptotic flow field. The present study, however, deals with the general problem of the flow at large distances from a finite object, and, more generally, with expansion techniques for similar problems. The author's explanation of Filon's paradox is only an incidental result." }, { "name": "George, Nicholas A.", "degree": "PhD", "year": "1959", "title": "Spatial Distribution of Thermal Radiation at Microwave Frequencies", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022006-142926", "creators": [ { "name": { "family": "George", "given": "Nicholas A." }, "id": "George-Nicholas-A", "display_name": "George, Nicholas A." } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CERS-Y395", "abstract": "Theoretical and experimental radiation patterns are given in spectral form for the thermal radiation from thin slots or heated wires having dimensions of the order of the comparison wavelength. Maxwell's equations and noise theory form the basis of the analyses in which three independent methods are used to predict a spatial distribution which exhibits interference minima and maxima. In the first, the wave equation is solved for a noise-excited transmission line which is suddenly short- and open-circuited at alternate ends. By a study of the trapped noise currents, it is found that the radiation pattern has an interference structure which is smoothed as the loss is increased. Secondly, a formula is derived for the radiation pattern of a heated wire by a computation of its absorption in an isothermal enclosure and by an application of the principle of detailed balancing. Finally, the pattern of a long thin slot is computed directly using the Lpontovich-Rytov distributed source generalization of Nyquist's noise formula.
\r\n\r\nFraunhofer pattern measurements are taken for a thin slot excited by a gaseous discharge at 10,100 \u00b1 200\u00b0K. The pattern measuring apparatus is a Dicke radiometer having the following characteristics: frequency 9200 mc/s, bandwidth to the detector 16 mc/s, modulation frequency 1000 c/s, and residual noise level 0.3 rms\u00b0K.
\r\n\r\nThe theory and the experiment demonstrate an interference phenomenon even though the source excitation is spatially extended and uncorrelated in time and space. The patterns are not even approximately Lambertian, e.g., a thin slot of 9.5 pi radians length exhibits a pattern having nine relative maxima in 180\u00b0 with the maximum emission at 63\u00b0 from the normal.
" }, { "name": "Golden, Roger Morse", "degree": "PhD", "year": "1959", "title": "Experiments in Very Low-Frequency Radio Propagation", "advisor": "Langmuir, Robert V.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022006-091215", "creators": [ { "name": { "family": "Golden", "given": "Roger Morse" }, "id": "Golden-Roger-Morse", "display_name": "Golden, Roger Morse" } ], "advisors": [ { "name": { "family": "Langmuir", "given": "Robert V." }, "id": "Langmuir-R-V", "role": "advisor", "display_name": "Langmuir, Robert V." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/E1C7-K279", "abstract": "In an effort to extend experimentally determined data on the characteristics of very low-frequency radio waves, a vlf transmitting station (8.4 kc) was established at Shaver Lake, California.\r\n\r\nThe establishment of this station permitted controlled experiments in long distance propagation, ionospheric vertical sounding measurements, and attempts at the generation of round trip gyroelectric-echoes.\r\n\r\nThe long distance measurements indicated that at vlf, the ground or surface wave radiated by the antenna, can be detected at great distances. The ionospheric vertical incidence measurements showed rapid fading of the received signal around local sunrise and sunset.\r\n\r\nPropagation in the presence of the ionosphere is considered in the theoretical form of propagation in a homogeneous gyroelectric medium. The results of this analysis are tabulated in graphical form so that the dispersive qualities of the medium can be readily examined. With the aid of these results, an examination of the natural phenomena of whistlers is presented in order to determine the feasibility of generating gyroelectric-echoes. Reflection and transmission coefficients are presented for vertical incidence in order to ascertain the order of magnitude of such an echo. Experiments thus far performed have not yielded echoes but with modifications in the transmitting and receiving equipment, echoes may be detected.\r\n\r\nA complete description of the experimental equipment used is given along with a proposal for a more sophisticated receiving system." }, { "name": "Kuehl, Hans Henry", "degree": "PhD", "year": "1959", "title": "Asymmetrically Excited Electromagnetic Radiation from Circular Cylinders of Finite Length and Prolate Spheroids", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-02172006-084352", "creators": [ { "name": { "family": "Kuehl", "given": "Hans Henry" }, "id": "Kuehl-Hans-Henry", "display_name": "Kuehl, Hans Henry" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/KDNQ-NR51", "abstract": "The far zone radiation from two types of asymmetrically excited systems is considered. The first is a finite cylinder excited by an electric dipole in the radial direction near the cylinder. The second is a prolate spheroid excited by a narrow belt of electric field around the surface of the spheroid. In both cases the body considered is perfectly conducting and the excitation is not necessarily centered at the midplane of the body. In the case of the finite cylinder excited by a radial dipole, an approximate method is used in which the current on the finite cylinder is taken to be identical with the current which would exist on an infinite cylinder under the same excitation. This approximation is shown to be valid analytically and experimentally if the cylinder is not short. The analytic and experimental results are compared for two cylinder lengths. The turnstile antenna mounted on a finite cylinder is considered analytically and the modification of the radiation by the cylinder is exhibited. In the case of the prolate spheroid excited by a narrow belt of electric field, experimental results are compared to analytic expressions. The differences between the experimental and analytic results are considered. The considerations in obtaining accurate experimental results in both asymmetrically excited systems are discussed.
\r\n" }, { "name": "Oates, Gordon Cedric", "degree": "PhD", "year": "1959", "title": "Throughflow in Axial Turbomachines with Variable Wall Geometry", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02172006-093110", "creators": [ { "name": { "family": "Oates", "given": "Gordon Cedric" }, "id": "Oates-Gordon-Cedric", "display_name": "Oates, Gordon Cedric" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ZR3D-NR88", "abstract": "The theory of three-dimensional flow in axial turbomachines was extended to include the effects of variable hub and tip radii such as occur in the entrance stages of conventional axial flow compressors and, to a larger extent, in mixed flow compressors. The problem is simplified by assuming an infinite number of infinitely thin blades in each blade row, so that axially symmetric fluid motion results.\r\n\r\nThe effect of variable hub and tip radii of the annulus walls is investigated when the tangential velocities are small but arbitrary, and when they are large but of special form. The combined effect of heavily loaded inlet guide vanes and variable hub radius is also investigated for the case in which the inlet guide vanes impart a motion very nearly of the solid-body type. The boundary conditions for the variable hub radius require linearization, thus restricting the magnitude of perturbation to be induced by the wall. Finally, the effect of a loaded blade row placed behind the inlet guide vane is determined.\r\n\r\nThe local axial and tangential velocities induced by the variable wall radius were found to be of the same general magnitude as the velocities induced by a normal rotor or stator blade row. Although the forms of the solutions are somewhat complex for routine application in turbomachine design, a sufficiently simple approximate result is obtained for one case and it is indicated how the method of approximation may be extended." }, { "name": "Pietrokowsky, Paul", "degree": "PhD", "year": "1959", "title": "A Study of Conformal Phases in Metal Alloy Systems", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02172006-113424", "creators": [ { "name": { "family": "Pietrokowsky", "given": "Paul" }, "id": "Pietrokowsky-Paul", "display_name": "Pietrokowsky, Paul" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/J221-2G70", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe atomic motifs of the intermediate phases TiAu4 have been investigated. Both crystal structures are tetragonal. Lattice parameters of TiAu4, 80 atomic percent gold, are a2 = b2 = 6.460(5) [angstroms] and c2 = 3.976(5) [angstroms]. There are ten atoms in the unit cell; two titanium atoms were placed in positions (a) and eight gold atoms were placed in (h) of space group [...]. The positional parameters were determined to be [...]. Lattice parameters of TiPt8 are [...]. The unit cell contains eighteen atoms. Space group [...] was used: the two titanium atoms were placed in (a), eight gold atoms in (h) with parameter x1, and eight gold atoms in (i) with parameter x2. The positional parameters were determined to be x1 = 0.333 and x2 = 0.327. The use of conformal transformations in these investigations is discussed.\r\n\r\nA result of this investigation has been the redetermination of the partial constitution diagram TiAu2-Au. Two intermediate phases were established. The phase TiAu2 is congruent melting. It is tetragonal with lattice parameters a = b = 3.4192 [angstroms] and c = 8.513 [angstroms]. The crystal structure has been determined. The two titanium atoms are in (a), of space group [...], and the four gold atoms are in (e) with z = 0.337. A second intermediate phase, TiAu4, displays a hidden maximum. The solubility limit of titanium in gold has been studied as a function of temperature. In addition, the region of homogeneity of TiAu4 has been investigated.\r\n\r\nThe alloys TiFe, TiCo, and TiNi have been investigated by X-ray diffraction methods. Evidence for long-range order in these phases has been established. Thus these alloys are of the CsCl type crystal structure type." }, { "name": "Royce, Winston Walker", "degree": "PhD", "year": "1959", "title": "Transonic Flow Over a Non-Lifting Slender Body of Revolution", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092006-153522", "creators": [ { "name": { "family": "Royce", "given": "Winston Walker" }, "id": "Royce-Winston-Walker", "display_name": "Royce, Winston Walker" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NFVH-YH92", "abstract": "Sonic flow past a non-lifting, slender body of revolution is investigated by the use of small disturbance theory. An approximation for the local Mach number distribution is used to linearize the transonic potential equation. Solutions for the velocity components, pressure distribution, and drag are obtained in terms of simple integrals involving the body geometry. An extension to other Mach numbers in the transonic range is given. The theoretical pressure distribution and drag are found to give good agreement with experimental data." }, { "name": "Rusch, Willard Van Tuyl", "degree": "PhD", "year": "1959", "title": "A New Transmitting Antenna System for Very Low Radio Frequencies", "advisor": "MacMillan, Robert Smith", "url": "https://resolver.caltech.edu/CaltechETD:etd-02172006-091240", "creators": [ { "name": { "family": "Rusch", "given": "Willard Van Tuyl" }, "id": "Rusch-Willard-Van-Tuyl", "display_name": "Rusch, Willard Van Tuyl" } ], "advisors": [ { "name": { "family": "MacMillan", "given": "Robert Smith" }, "id": "MacMillan-R-S", "role": "advisor", "display_name": "MacMillan, Robert Smith" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/BXK9-YY23", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nRecent widespread interest in very low-frequency radio propagation has increased the importance of developing adequate vlf transmitting systems. After briefly examining conventional vertical vlf antennas, a system is presented which employs resonant loading circuits to convert a section of an existing power line into a horizontal vlf transmitting antenna. The simplicity, low cost, and useful radiation pattern of this horizontal antenna are well suited for many experimental applications.\r\n\r\nThe theoretical antenna problem is solved using a normal mode expansion of the current distribution. A matrix method is developed to compute the current distribution of a thin, linear antenna loaded with lumped-circuit elements. The series is found to converge relatively fast. A digital computer is used to solve the matrix equations. Results are obtained for a full-wave linear antenna symmetrically loaded with real impedances [...], one half-wavelength apart. Current distributions, feedpoint impedances, radiation patterns, etc., are presented as functions of [...]. Results of the idealized problem are applied to the power-line antenna. The matrix method can also be extended to the general linear antenna with any type of loading or feeding.\r\n\r\nSystem components and performance of the Dinkey Creek power-line antenna are described. The problem of interference with nearby audio-frequency communication systems is examined.\r\n\r\nThe 8.4 kc propagation experiments using the Dinkey Creek antenna are described. The series of whistler-mode propagations to probe the exosphere has not been completed. However, ionospheric soundings have yielded considerable information about the properties of the ionosphere at vlf. Successful long-distance propagation experiments are also described, and samples of the results are presented." }, { "name": "Vernon, Frank Lee", "degree": "PhD", "year": "1959", "title": "The Theory of a General Quantum System Interacting with a Linear Dissipative System", "advisor": "Feynman, Richard Phillips", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242006-154616", "creators": [ { "name": { "family": "Vernon", "given": "Frank Lee" }, "id": "Vernon-Frank-Lee", "display_name": "Vernon, Frank Lee" } ], "advisors": [ { "name": { "family": "Feynman", "given": "Richard Phillips" }, "id": "Feynman-R-P", "role": "advisor", "display_name": "Feynman, Richard Phillips" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JNJ1-QZ83", "abstract": "A formalism has been developed, using Feynman's space-time formulation of non-relativistic quantum mechanics whereby the behavior of a system of interest, which is coupled to other external quantum systems, may be calculated in terms of its own variables only. It is shown that the effect of the external systems in such a formalism can always be included in a general class of functionals (influence functionals) of the coordinates of the system only. The properties of influence functionals for general systems are examined. Then, specific forms of influence functionals representing the effect of definite and random classical forces, linear dissipative systems at finite temperatures, and combinations of these are analyzed in detail. The linear system analysis is first done for perfectly linear systems composed of combinations of harmonic oscillators, loss being introduced by continuous distributions of oscillators. Then approximately linear systems and restrictions necessary for the linear behavior are considered. Influence functionals for all linear systems are shown to have the same form in terms of their classical response functions. In addition, a fluctuation-dissipation theorem is derived relating temperature and dissipation of the linear system to a fluctuating classical potential acting on the system of interest which reduces to the Nyquist-Johnson relation for noise in the case of electric circuits. Sample calculations of transition probabilities for the spontaneous emission of an atom in free space and in a cavity are made. Finally, a theorem is proved showing that within the requirements of linearity all sources of noise or quantum fluctuation introduced by maser type amplification devices are accounted for by a classical calculation of the characteristics of the maser." }, { "name": "Weyers, Paul Frederik Robert", "degree": "PhD", "year": "1959", "title": "The Vibration and Acoustic Radiation of Thin-Walled Cylinders Caused by Internal Turbulent Flow", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-02062006-134627", "creators": [ { "name": { "family": "Weyers", "given": "Paul Frederik Robert" }, "id": "Weyers-Paul-Frederick-Robert", "display_name": "Weyers, Paul Frederik Robert" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QTM4-9Z19", "abstract": "The investigation concerned noise produced by turbulent flow adjacent to a flexible wall. Measurements of the spectrum and intensity of the pressure field outside thin-walled Mylar cylinders containing turbulent pipe flow have been made. The resulting spectra could be interpreted in relation to the elastic properties of the cylinders and the character of the turbulent fluctuations inside the flow. The eigen frequencies of the cylinders could be identified and similarity parameters for the spectra were established. The effect of cylinder wall thickness on the spectrum and intensity of the pressure fluctuations was investigated. It was found that the intensity of the external pressure field scaled with the fifth power of the velocity at the center of the pipe.
\r\n\r\nFor one particular case the spectrum and intensity of the pressure fluctuations exerted by the turbulent flow on the wall were measured. The intensity of the pressure fluctuations at the wall scaled with the fourth power of the velocity as expected. The ratio of the root-mean-square wall pressure to the dynamic pressure was found to be independent of Mach number and equal to a constant (0.0078). Similarity laws for the spectra of the wall pressure fluctuations were also confirmed.
" }, { "name": "Ang, Dang Dinh", "degree": "PhD", "year": "1958", "title": "Some Radiation Problems in Elastodynamics", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072004-092112", "creators": [ { "name": { "family": "Ang", "given": "Dang Dinh" }, "id": "Ang-Dang-Dinh", "display_name": "Ang, Dang Dinh" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/TF74-2977", "abstract": "Three elastodynamic problems are studied. The first deals with waves generated by instantaneous and uniform closure of a semi-infinite crack, while in the second, a semi-infinite crack is suddenly initiated in a continuous medium initially subjected to uniform tension. The last of the three deals with a force moving at uniform velocity along a semi-infinite crack, starting from the edge. The problems are solved by means of the Wiener-Hopf integral methods. The characteristic wave patterns and stress singularities are discussed." }, { "name": "Barker, Calvin LaRue", "degree": "PhD", "year": "1958", "title": "Experiments Concerning the Occurrence and Mechanism of High-Frequency Combustion Instability", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072004-092728", "creators": [ { "name": { "family": "Barker", "given": "Calvin LaRue" }, "id": "Barker-Calvin-LaRue", "display_name": "Barker, Calvin LaRue" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/F39S-MP16", "abstract": "The phenomenon of screeching combustion was examined experimentally with particular reference to the significance of the time lag proposed by Rogers and Marble.\r\n\r\nThis investigation was conducted in a 1- x 4-inch rectangular cross-section water-cooled combustor in which was burned a premixed air - fuel mixture. This combustor contained a 70 % blockage solid V-wedge flameholder.\r\n\r\nVortices were generated at the flameholder lips during smooth combustion by impinging a shock wave on the flamefront. These vortices were compared with those generated during screeching combustion and found to be similar to them in all major respects. Thus the common assumption that vortices are generated by the action of the oscillating velocity is a sound one.\r\n\r\nThe fact that screech excitation occurs in the shear layers immediately downstream of the flameholders was demonstrated by injection of air into this region. Such injection was found to suppress the tendency of the combustor to screech.\r\n\r\nBy comparison of observations of the screech limit with ignition time delay data obtained from bluff-body flameholding studies it was shown that the mechanism of screech excitation is indeed controlled by a characteristic time. A procedure, based on this result, was developed for determining in advance the behavior of the screech limit in a family of geometrically similar combustors under variations of fuel type and inlet temperature." }, { "name": "Bell, Richard William", "degree": "PhD", "year": "1958", "title": "The Elastic Instability of Thin Cantilever Struts on Elastic Supports with Axial and Transverse Loads at the Free End", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072004-093255", "creators": [ { "name": { "family": "Bell", "given": "Richard William" }, "id": "Bell-Richard-William", "display_name": "Bell, Richard William" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5FEX-RT33", "abstract": "An analysis is made of the elastic instability of thin, tapered cantilever struts subjected to a general concentrated load acting in the plane of the strut at its tip. The strut is supported at its root on a structure permitting elastic rotations of the root section in the buckled mode. The influence of the support on the minimum buckling load is one of the main points of interest. It is shown that the general linearized problem can be formulated in one second order differential equation with variable coefficients, and two associated boundary conditions. This homogeneous eigenvalue system constitutes a simplified statement of the problem which permits the easy extension of exact linear theory to a wide class of taper functions, including the effect of elastic supports. The solution emerges in terms of a generalized deflection parameter, rather than of either the torsional or the bending components of the coupled buckling mode, which are governed respectively by third and fourth order differential equations.\r\n\r\nSpecific solutions are derived for some \"natural\" taper forms of the strut. The general solutions for the deflection mode are power series, which are rapidly convergent for certain limiting geometries. The problems of convergence of the series, some singular physical aspects associated with pointed tips, and the increasing numerical difficulty for large taper ratio are correlated with the behavior of the singular points of the equation. Numerical results showing the effects of the elastic supports on minimum buckling loads are presented for the uniform strut and for a simple case of the tapered strut. The series solutions for more general cases are given in a form which can be applied to digital computers.\r\n" }, { "name": "Braham, Harold Stanley", "degree": "PhD", "year": "1958", "title": "An Investigation of the Use of Feedback Control to Raise the Flutter Speed of an Aeroelastic System", "advisor": "McCann, Gilbert Donald; Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10082004-111321", "creators": [ { "name": { "family": "Braham", "given": "Harold Stanley" }, "id": "Braham-Harold-Stanley", "display_name": "Braham, Harold Stanley" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "co-advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5EVF-4945", "abstract": "This study deals with the possibility of raising the flutter speed of an aeroelastic system by feedback control. Emphasis is given to feedback control through a control surface driven by a powered actuator. It is shown that only for certain aeroelastic systems is it possible to significantly raise the flutter speed by this type of feedback control.\r\n\r\nIn addition, a second type of feedback control is considered, a jet reaction torquer acting on the wing itself. A marked increase in flutter speed is possible in essentially all aeroelastic systems with this form of control. Despite the fact that this type of controller requires more power than the control surface actuator, its use may be practical in many cases.\r\n\r\nThe question of the reliability of the feedback control used to raise flutter speed is becoming less important in this era of missiles where the entire system is controlled by automatic devices.\r\n\r\nPart I discusses the basic problem. Parts II and III develop a general feedback theory. This theory, when applied to a specific aeroelastic system, permits ready determination of whether an increase in flutter speed is possible for that system. Parts IV and V consider numerical investigations of many systems using a control surface actuator. Analyses are made by both the general feedback theory and by analog computer, showing similar numerical results. Part VI considers the jet reaction torquer and the increase in flutter speed that it can achieve. Conclusions are presented in Part VII." }, { "name": "Demetriades, Anthony", "degree": "PhD", "year": "1958", "title": "An Experimental Investigation of the Stability of the Hypersonic Laminar Boundary Layer", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-09232004-093013", "creators": [ { "name": { "family": "Demetriades", "given": "Anthony" }, "id": "Demetriades-Anthony", "display_name": "Demetriades, Anthony" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7SR9-9M59", "abstract": "NOTE: text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental investigation of the stability of the hypersonic laminar boundary layer was carried out for the case of a flat insulated surface at zero angle of attack. The stream-wise amplitude variation of both \"natural\" disturbances (i.e., flow fluctuations existing naturally in the boundary layer) and of disturbances artificially excited with a \"siren\" mechanism was studied with the aid of a hot-wire anemometer. In both cases it was found that such small fluctuations amplify for certain ranges of the fluctuation frequency and the Reynolds number [...], and damp for others. The demarcation boundaries for the amplification (instability) zone were found to resemble the corresponding boundaries of boundary layer instability at lower speeds. A \"line of maximum amplification\" of disturbances was also found. The amplification rates and hence the degree of \"selectivity\" of the hypersonic layer were found, however, to be considerably lower than those at the lower speeds. The disturbances selected by the layer for maximum amplification have a wavelength estimated at about twenty times the boundary-layer thickness [...], which is appreciably longer than the corresponding wave-lengths for low-speed boundary-layer flow." }, { "name": "Fuhs, Allen Eugene", "degree": "PhD", "year": "1958", "title": "Part I. Experimental and Theoretical Studies on Heterogeneous Diffusion Flames. Part II. Spectroscopic Studies of Flames", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10262004-152916", "creators": [ { "name": { "family": "Fuhs", "given": "Allen Eugene" }, "id": "Fuhs-Allen-Eugene", "display_name": "Fuhs, Allen Eugene" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ENEM-BM84", "abstract": "Three topics concerned with heterogeneous diffusion flames are considered in Part I.\r\n\r\nExperiments have been conducted to determine the interference effects during burning for droplet arrays. The burning rate law applicable for single droplets has been found to be valid also for two-, five-, and nine-droplet arrays.\r\n\r\nA heterogeneous diffusion flame formed between liquid sodium and gaseous titanium tetrachloride was found to deposit small particles of titanium on the combustion chamber wall. The burning rate of liquid sodium, which is related to the rate of production of titanium, was determined experimentally.\r\n\r\nThe scaling procedures developed by several authors for liquid-fuel rocket engines have been generalized. In these theoretical studies we have used the functional results derived in our investigations of droplet burning. The generalized analysis indicates that an attempt to maintain complete similarity on scaling results in contradictions. For this reason a program on selected scaling procedures is indicated.\r\n\r\nIn Part II the apparent emission profiles of a turbulent flame are described in terms of a wrinkled laminar flame model. A distribution function, which assigns a probability for the occurrence of the laminar flame at a particular position within the turbulent flame brush, determines the apparent emission profiles. The inverse problem of determining the probability function from observed emission profiles has also been solved.\r\n\r\nIt is possible to correlate the ratio of the apparent spectral intensities of two rotational lines with the equivalence ratio of a laminar flame. Assuming that this correlation applies also to other flames, we have determined the equivalence ratio in the critical zone of a reverse-jet stabilized flame in a duct. The equivalence ratio as a function of radial distance from the duct axis has also been measured. The results indicate that there appears to be a single equivalence ratio curve at blow-off, regardless of jet composition, provided the blow-off velocity is considered to be a function of critical zone equivalence ratio." }, { "name": "Heimer, Harry James", "degree": "PhD", "year": "1958", "title": "Balanced Flap Type Supersonic Control Surfaces", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012004-142134", "creators": [ { "name": { "family": "Heimer", "given": "Harry James" }, "id": "Heimer-Harry-James", "display_name": "Heimer, Harry James" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YVYN-ZD39", "abstract": "The purpose of this investigation is to qualitatively explain the flow phenomena which occur on a balanced flap type control surface at supersonic speeds and to find means of calculating the pressure distributions occurring. The popular and generally useful linearized flow theory, and in fact any inviscid theory, cannot be used since viscosity plays a predominant part in the determination of the flow. It is shown that the flow often involves shock induced separation and reflection of shock waves by these separated wakes. Experimental data in the form of pressure distributions and shadowgraph pictures of the flow are used to arrive at a description of the flow. By use of the empirical results given, a method of predicting the pressure distributions for this type of surface is derived. This procedure is then used to calculate several pressure distributions which are compared with those experimentally determined.\r\n\r\nThe separation effects that occur at the larger angles of attack and/or control surface deflection angles cause the control effectiveness and hinge moments to be very non-linear. It is shown that the use of a gap between the wing and control surface delays or eliminates separation depending on the size of the gap used. Data are presented for a typical control surface, in which the hinge moments were reduced by a factor of 8 or 10 by using a gap between the wing and control surface. A method is given for estimating the size gap necessary to achieve this reduction." }, { "name": "Hooker, William Joseph", "degree": "PhD", "year": "1958", "title": "Shock-Induced C\u2082H\u2082 Pyrolysis and CO Emissivity", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10072004-144737", "creators": [ { "name": { "family": "Hooker", "given": "William Joseph" }, "id": "Hooker-William-Joseph", "display_name": "Hooker, William Joseph" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/J37Y-C144", "abstract": "PART I: Shock Tube Studies of Acetylene Decomposition
\r\n\r\nExtensive experimental studies have been conducted on the rate of decomposition of argon-acetylene mixtures by means of shock waves. Activation energies of 26 and 33 kcal/mole, respectively, have been found for the first- and second-order decomposition reactions of acetylene.
\r\n\r\nA well defined curve of temperature versus induction time for incipient carbon formation has been established. Analysis of these data suggests that possibly a somewhat better correlation is obtained for decomposition reactions of order n=1 and n=1.5 than for n=2. The corresponding activation energies are 10, 13 and 16 kcal/mole for n= 1, 1.5 and 2, respectively.
\r\n\r\nThe effects of impurity and diluent gas radiation, as well as molecular and solid particle light scattering, have been shown to have a negligibly small influence on the results.
\r\n \r\nPART II: An Analysis of Equilibrium Infrared Gas Emissivities for Diatomic Molecules Based on a Just-overlapping Rotational Line Model
\r\n\r\nGeneral equations are developed for the engineering emissivity of diatomic molecules with equally intense R- and P-branches and just-overlapping rotational line structures. Integral expressions for the emissivity are evaluated by exact numerical integration and by approximate series representations.
\r\n\r\nThe results are applied to the molecules CO and HC \u2113. Comparisons are made with emissivity predictions for the same molecules with a completely overlapped rotational line model and an isolated rotational line model. The theoretical emissivity calculations for CO are in fair accord with empirically determined estimates.
" }, { "name": "Katz, Robert", "degree": "PhD", "year": "1958", "title": "Performance of Axial Compressors with Asymmetric Inlet Flows", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11012004-143844", "creators": [ { "name": { "family": "Katz", "given": "Robert" }, "id": "Katz-Robert", "display_name": "Katz, Robert" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/5214-1S06", "abstract": "An experimental and analytical investigation was undertaken to determine the influence of asymmetric inlet flows on the performance of axial turbomachinery.\r\n\r\nOverall performance measurements and circumferential surveys of total pressures, velocities and flow angles were obtained in an axial compressor with inlet disturbances covering approximately 25% of the inlet annulus area. Three configurations were tested to find the principal effects in a single rotor, a complete stage and a multi-stage machine. A two-dimensional linearized theory was developed which includes the effect of losses and leaving angle deviations in the blade rows. The analysis may also be applied to propagating stall so that this theory allows a unified treatment of the two phenomena.\r\n\r\nIntroducing the inlet disturbances did not alter the two-dimensional character of the flow in the compressor. Considerable attenuation of the disturbances occurred through a single rotor and the disturbances were almost completely attenuated downstream of a three stage configuration. The mutual interference of the blade rows with small axial spacing was responsible for significant stator losses. The overall performance deteriorated primarily due to losses occurring in the blade rows. In the three configurations tested the inception of propagating stall, as based on the mean flow rate, was essentially unchanged. The theory qualitatively described the flow behavior and a simple application of the theory would give an estimate of the blade forces." }, { "name": "McLaughlin, Ronald Theodore", "degree": "PhD", "year": "1958", "title": "On the Mechanics of Sedimentation in Artificial Basins", "advisor": "McKee, Jack E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022006-084546", "creators": [ { "name": { "family": "McLaughlin", "given": "Ronald Theodore" }, "id": "McLaughlin-Ronald-Theodore", "display_name": "McLaughlin, Ronald Theodore" } ], "advisors": [ { "name": { "family": "McKee", "given": "Jack E." }, "id": "McKee-J-E", "role": "advisor", "display_name": "McKee, Jack E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/0AB9-FS61", "abstract": "A theoretical and experimental study was made of the quiescent settling of the particles of a suspension in order to determine what governs the removal of particles when the suspension passes through a sedimentation basin. Settling column experiments were performed in tubes ranging from one foot to four feet in depth. Glass spheres in water, alum and clay in water, and Pasadena sewage were used as suspensions. While the suspensions settled in the columns, samples were withdrawn at time intervals at several depths. These were analyzed for concentration of suspended particles.\r\n\r\nIt was found that for free, quiescent settling of discrete particles, the removal of particles can be calculated in advance if the frequency distribution of particle settling velocities and the particle concentration are known as functions of position in the suspension at the beginning of settling.\r\n\r\nFor a suspension of flocculent particles it was almost impossible to predict removal without measuring the settling properties of each individual suspension. There is no single universal property of a settling tank with which removal is correlated. It was found that while for some flocculent suspensions removal may be strongly dependent upon detention time, no strong dependence on overflow rate was indicated.\r\n\r\nSince so many suspensions encountered in settling tanks have flocculent particles, the kinetics of flocculation was studied qualitatively by theory and experiment." }, { "name": "McMahon, Howard Martin", "degree": "PhD", "year": "1958", "title": "An Experimental Study of the Effect of Mass Injection at the Stagnation Point of a Blunt Body", "advisor": "Lees, Lester; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-01262006-142812", "creators": [ { "name": { "family": "McMahon", "given": "Howard Martin" }, "id": "McMahon-Howard-Martin", "display_name": "McMahon, Howard Martin" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PWSC-6787", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental study of the effect of the injection of nitrogen and helium coolant gases at the stagnation point of a blunt body was carried out in the GALCIT Hypersonic Wind Tunnel at a Mach number of 5.8. The gases were injected straight out of the stagnation point and also tangential to the body surface. The model was also fitted with flow separation spikes.\r\n\r\nThe injection of the coolant gas resulted in a marked reduction in the model equilibrium temperature, and this cooling effect persisted over the entire length of the model. For the same mass flow, helium was a better coolant than nitrogen.\r\n\r\nThe average heat transfer near the nose of the body was reduced almost to zero by injecting a mass of helium as small as 1/2 per cent of the mass flow of free-stream air contained in the \"capture\" area [...] of the spherical nose.\r\n\r\nSeparation near the spike tip was observed up to a ratio of spike length to spherical nose diameter of 1.78 and a free-stream Reynolds number based on nose diameter of 2.84 x 10(5), resulting in a value of the foredrag coefficient which was one-third the value with no spike attached." }, { "name": "Russell, Thomas Lee", "degree": "PhD", "year": "1958", "title": "The Effect of Grain Size on the Yielding Behavior of Very Low Carbon Steel.", "advisor": "Wood, David Shotwell; Clark, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232006-153919", "creators": [ { "name": { "family": "Russell", "given": "Thomas Lee" }, "id": "Russell-Thomas-Lee", "display_name": "Russell, Thomas Lee" } ], "advisors": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/77XQ-5M30", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis presents the results of an experimental investigation of the effect of grain size on the yielding behavior of very low-carbon steel. Steel specimens of five grain sizes were produced for testing. The average grain diameter of these specimens ranged from 1.1 x 10(-3) in. to 8.1 x 10(-3) in. Two types of tensile tests were performed, one by the application of very low loading rates and the other by the rapid application of a constant stress. Both types of tests were performed at temperatures of 72\u00b0F and -320\u00b0F, while a few rapid loading tests were performed at a temperature of -109\u00b0F.\r\n\r\nBoth the static upper and lower yield points are observed to increase linearly with [...], where d equals the average grain diameter. Delay time and pre-yield micro strain for specimens that exhibited a yield point were determined from the rapid loading tests conducted at room temperature. Delay time decreases with increasing grain diameter for a given stress.\r\n\r\nThe experimental results are compared with several dislocation models for yielding. These models are shown to be incapable of describing the experimental results of this investigation. A more detailed model, based on Cottrell's yielding mechanism, is described.\r\n\r\nPlastic deformation by twinning occurred in both static and rapid loading tests performed at a temperature of -320\u00b0F. A critical stress for twinning was observed. This stress is independent of stress rate in the range from [...] to [...]. The critical twinning stress increases linearly with [...]. The existence of a critical stress for twinning is shown to be compatible with Cottrell and Bilby's theory for the formation of twin bands." }, { "name": "Sedin, James Walter", "degree": "PhD", "year": "1958", "title": "A Large-Signal Analysis of Beam-Type Crossed-Field Traveling-Wave Tubes", "advisor": "Gould, Roy Walter; Field, Lester M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01132006-083726", "creators": [ { "name": { "family": "Sedin", "given": "James Walter" }, "id": "Sedin-James-Walter", "display_name": "Sedin, James Walter" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Field", "given": "Lester M." }, "id": "Field-L-M", "role": "advisor", "display_name": "Field, Lester M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/5MN5-D881", "abstract": "The equations governing the behavior of beam-type, crossed-field, traveling-wave tubes are formulated and presented. The geometry is assumed to be two-dimensional. The electron beam is treated as a number of cylinders of charge (it can be regarded as a number of layers of pencils the axes of which are parallel; these pencils can move in the two dimensions perpendicular to their axes) and space-charge forces are included by calculating the field due to these cylinders when they are placed between two perfectly conducting planes. The nonlinear equations are re-expressed in terms of normalized variables suitable for machine computation, and the procedure for solving these equations numerically is discussed. The equations are solved for a number of thin-beam, small-signal cases and the results are compared with previous analytical work. Numerical difficulties are encountered because the electric field approaches infinity in the neighborhood of a line charge. These difficulties are circumvented by a modification of the electric field in the vicinity of a line charge. Large-signal calculations are carried out for the special case of a thin sheet beam which would travel in a straight line in the absence of r-f effects. The computations are carried out for both forward- and backward-wave interaction by using several values of a space-charge parameter that cover typical operating conditions." }, { "name": "Tanaka, Richard Isamu", "degree": "PhD", "year": "1958", "title": "The Logical Design of a Serial General-Purpose Computer with Micro-Program Capabilities", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-01202006-130420", "creators": [ { "name": { "family": "Tanaka", "given": "Richard Isamu" }, "id": "Tanaka-Richard-Isamu", "display_name": "Tanaka, Richard Isamu" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TE7V-ZX24", "abstract": "This thesis presents the detailed logical design of a serial, general-purpose digital computer with micro-program capabilities. The machine is a medium-speed computer with a magnetic drum memory, and includes a modest magnetic core memory for storing micro-orders.\r\n\r\nThe micro-program feature relates to the command structure of the machine. Micro-orders enable the programmer to specify many of the elementary internal operations; these micro-orders are arranged into micro-routines which synthesize computation sequences equivalent to commands in more conventional computers. Therefore, effectively, the machine has an extremely long command list.\r\n\r\nIncluded are descriptions of the internal organization of the machine, and the detailed logical equations which are directly applicable to the construction of the computer. A few micro-routines, for both usual and uncommon commands, are also shown, to illustrate possible applications of the machine." }, { "name": "Thomson, James Alex Lloyd", "degree": "PhD", "year": "1958", "title": "Emissivities and Absorptivities of Gases", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232006-143205", "creators": [ { "name": { "family": "Thomson", "given": "James Alex Lloyd" }, "id": "Thomson-James-Alex-Lloyd", "display_name": "Thomson, James Alex Lloyd" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/2HJG-SD13", "abstract": "Equilibrium emissivities and absorptivities of heated gases have been computed from spectroscopic data. Several problems have been studied:\r\n\r\n(1) The relation between equilibrium absorptivities and equilibrium emissivities for diatomic and polyatomic molecules has been investigated. Our theoretical results provide a satisfactory correlation of available experimental data for heated water vapor but not for carbon dioxide. The origin of the failure of the theory for carbon dioxide is discussed in detail.\r\n\r\n(2) The available, empirically determined, emissivity data for water vapor have been correlated in terms of a statistical model for the distribution of spectral lines within well-defined wavelength regions corresponding to the stronger vibration-rotation bands. This correlation provides a useful framework for the extrapolation of measured emissivity data to temperatures and pressures somewhat different from those used to obtain the experimental data.\r\n\r\n(3) The equilibrium emissivity of heated NO has been calculated for the conditions under which this molecule exists in high-temperature air during reentry of hypersonic missiles. An extension of the Mayer-Goody statistical model was used for emissivity calculations on NO. Our semi-analytical results are in acceptable agreement with a simpler numerical analysis of Kivel, Mayer and Bethe.\r\n\r\nThe original investigations of gas absorptivities and emissivities are introduced with a brief survey of basic theoretical results. An attempt has also been made to calculate the dipole moments and low energy transition probabilities for HF, HCl, and HBr. In this study it was found that the intensities of lines lying in the infrared are very sensitive to the details of the approximating wavefunctions. A considerably more detailed description of the wavefunctions than is available at present is required to make confident predictions of absolute intensities from first principles." }, { "name": "Thorman, Herman Carl", "degree": "PhD", "year": "1958", "title": "Boundary Layer Measurements on an Axisymmetric Body with Spin and Yaw", "advisor": "Stewart, Homer Joseph; Millikan, Clark Blanchard; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192006-132244", "creators": [ { "name": { "family": "Thorman", "given": "Herman Carl" }, "id": "Thorman-Herman-Carl", "display_name": "Thorman, Herman Carl" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R54D-S906", "abstract": "A directionally-sensitive hot-wire anemometer was developed for measuring the three-dimensional boundary-layer flow on a spinning, axisymmetric body in a low-speed wind tunnel. Boundary-layer velocity profiles at numerous positions around the body are presented for several spin rates at incidence angles of zero and 3 degrees. Displacement thickness distributions, based on integration of the velocity profiles, are also included.\r\n\r\nThe asymmetries in the azimuthal distribution of the boundary layer around the spinning body at a small angle of incidence (3\u00b0) are examined by means of a Fourier analysis of the experimental data. The experimental results are compared with the results of certain theoretical analyses (BRL 870 (Revised), NAVORD 5036) which provide a method for determining Magnus force (and also normal force) due to the displacement effect of the boundary layer." }, { "name": "Trivelpiece, Alvin William", "degree": "PhD", "year": "1958", "title": "Slow Wave Propagation in Plasma Waveguides", "advisor": "Gould, Roy Walter; Field, Lester M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07012004-112216", "creators": [ { "name": { "family": "Trivelpiece", "given": "Alvin William" }, "id": "Trivelpiece-Alvin-William", "display_name": "Trivelpiece, Alvin William" } ], "advisors": [ { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" }, { "name": { "family": "Field", "given": "Lester M." }, "id": "Field-L-M", "role": "advisor", "display_name": "Field, Lester M." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WNSZ-2Y08", "abstract": "It is shown that the space charge wave modes of propagation which are usually associated with the drifting motion of an electron beam can also propagate and carry energy in stationary electron beams or plasmas of finite transverse cross section. The properties of these modes of propagation have been studied by considering the plasma as a dielectric and solving the field equations. The effect of d.c. magnetic fields have been included, while ion motion and thermal velocities have been neglected. These modes have phase velocities which are generally much less than the velocity of light. Two distinct types of propagation are reported; the first involves charge density variation within the plasma (body wave) and the second involves a perturbation of the surface of the plasma (surface wave). Both of these types have modes which exist down to zero frequency as well as backward wave modes. The angular dependent modes can exhibit Faraday rotation.\r\n\r\nOne of the potentially useful features of these modes of propagation is that of plasma diagnostics. The effect of radial charge density variation within the plasma column has been investigated and methods for experimentally determining this variation, as well as the average charge density, are suggested. The effect of collisions on wave attenuation is examined approximately.\r\n\r\nThe interaction of a moving electron beam with these modes is considered, as well as the backward wave start oscillation conditions for backward wave interaction. A qualitative explanation of these modes is given in terms of an equivalent electrical circuit transmission line. Many of the features of these modes have been verified experimentally by measuring the phase velocity along a mercury arc discharge column in an axial magnetic field.\r\n" }, { "name": "Turcotte, Donald Lawson", "degree": "PhD", "year": "1958", "title": "An Experimental Investigation of Flame Stabilization in a Heated Turbulent Boundary Layer", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07162004-110746", "creators": [ { "name": { "family": "Turcotte", "given": "Donald Lawson" }, "id": "Turcotte-Donald-Lawson", "display_name": "Turcotte, Donald Lawson" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XT75-T174", "abstract": "For a number of years the significant parameters governing flame stabilization in moving streams have been known. In high speed applications the chemical time delay plays a fundamental role. For the low speed problems the normal flame speed and quenching distance govern stabilization. Unfortunately the transition region between the two groups of problems has not been investigated. Also the actual relation between these parameters and the properties of the combustible mixture has not been established.\r\n\r\nTo investigate these fundamental questions an experiment was set up to study flame stabilization in heated turbulent boundary layers. For wall temperatures above about 1700[degrees]F. the chemical time delay, represented by the length of the heated flame holder wall required for stabilization, was found to be a systematic and reproducible variable. A rational explanation was made for the transition from the low speed stabilization mechanism known to be applicable in unheated turbulent boundary layers and heated laminar boundary layers to the ignition mechanism applicable in heated turbulent boundary layers.\r\n\r\nAn attempt was made to relate the observed stabilization measurements to a theoretical solution based on ignition in a laminar sub-layer. The present methods of solution for such problems were found to be inadequate. A similarity solution yielded an interesting result which agreed fairly well with experiments." }, { "name": "Williams, Forman Arthur", "degree": "PhD", "year": "1958", "title": "Theoretical Studies in Heterogeneous Combustion", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122006-130627", "creators": [ { "name": { "family": "Williams", "given": "Forman Arthur" }, "id": "Williams-Forman-Arthur", "display_name": "Williams, Forman Arthur" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/F9A8-VN10", "abstract": "The theory of the steady-state burning of a single spherically-symmetric liquid monopropellant droplet in an infinite inert atmosphere is formulated. Numerical solutions for the temperature and composition profiles and burning rate are obtained in the case of a one-step chemical reaction of the second order. It is shown that the size and location of the reaction zone depend strongly upon the activation energy. Approximate analytical solutions for the burning rate which are valid for large activation energies are obtained for arbitrary chemical reactions. The results indicate that the mass burning rate is proportional to the droplet radius raised to a power which varies from two at small activation energies to unity at large activation energies.\r\n\r\nThe Shvab-Zeldovich formulation of the problem of burning of initially unmixed systems is developed and applied to the case of a single fuel droplet burning in an infinite oxidizing atmosphere. Some simplification over other methods for treating this problem is obtained, and the burning rate is shown to be unaffected by a distributed reaction zone when the Lewis number is unity.\r\n\r\nA general statistical formalism for describing the behavior of sprays is presented, which includes the effects of droplet growth, the formation of new droplets, collisions and aerodynamic forces. The method is applied to the problem of the determination of the size distribution of a spray formed by the impingement of two streams of droplets of known properties. It is shown that if the two incident jets have a size distribution of a generalized Rosin-Rammler type, then the resulting spray belongs to the same class of distributions. The size history of evaporating sprays is also obtained from the theory. A spray combustion analysis given by Probert is extended to include more general size distributions and the effects of droplet interactions and relative motion of the droplets and the fluid. It is shown that sprays of a uniform size yield the highest combustion efficiency." }, { "name": "Benenson, David Maurice", "degree": "PhD", "year": "1957", "title": "Characteristics of Propagating Stall in Axial-Flow Compressors", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-07082004-133942", "creators": [ { "name": { "family": "Benenson", "given": "David Maurice" }, "id": "Benenson-David-Maurice", "display_name": "Benenson, David Maurice" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q6J5-C011", "abstract": "Both small and large amplitude propagating stalls have been observed experimentally and their characteristics distinguished. The characteristics of the small amplitude propagating stall are such that the phenomenon can be described well by linearized theory. The characteristics of the large amplitude stall (which is the propagating stall phenomenon generally found in compressors) are such that the linearized theory is not adequate to describe the stall.\r\n\r\nThe propagating stall speeds determined from the small amplitude propagating stall experiments are in good agreement with those predicted by a particular formulation of the linearized theory." }, { "name": "Beutler, Fredrick Joseph", "degree": "PhD", "year": "1957", "title": "A Generalization of Wiener Optimum Filtering and Prediction", "advisor": "De Prima, Charles R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07082004-135353", "creators": [ { "name": { "family": "Beutler", "given": "Fredrick Joseph" }, "id": "Beutler-Fredrick-Joseph", "display_name": "Beutler, Fredrick Joseph" } ], "advisors": [ { "name": { "family": "De Prima", "given": "Charles R." }, "id": "De-Prima-C-R", "role": "advisor", "display_name": "De Prima, Charles R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/D8FV-4255", "abstract": "This work generalizes the Wiener-Kolmogorov theory of optimum linear filtering and prediction of stationary random inputs. It is assumed that signal and noise have passed through a random device before being available for filtering and prediction. A random device is a unit whose behavior depends on an unknown parameter for which an a priori probability distribution is given.\r\n\r\nUse of representation theorems and a Hilbert space structure make it possible to present the mathematical theory without the ambiguities encountered in engineering derivations. This approach also leads to a proof of the essential identity between the operator solution and a realizable lumped parameter filter.\r\n\r\nA number of engineering applications are cited. A few of these are worked out in some detail to illustrate the optimization procedure." }, { "name": "Goddard, Frank Eber", "degree": "PhD", "year": "1957", "title": "The Effect of Uniformly Distributed Roughness on Turbulent Skin Friction Drag at Supersonic Speeds", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-07132004-115342", "creators": [ { "name": { "family": "Goddard", "given": "Frank Eber" }, "id": "Goddard-Frank-Eber", "display_name": "Goddard, Frank Eber" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BA5G-7H43", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn experimental program was carried out in the 18 x 20-inch supersonic wind tunnel of the Jet Propulsion Laboratory at the California Institute of Technology to determine the effect of uniformly distributed sand-grain roughness on the skin friction drag of a body of revolution for the case of a turbulent boundary layer. The Mach-number range covered was 1.98 to 4.54 and the Reynolds number varied from about [...] to [...]. Some data were also obtained at a Mach-number of 0.70.\r\n\r\nAt speeds up to a Mach number of 5 and for roughness sizes such that the quadratic resistance law holds, the compressibility effect is indirect and the skin friction drag is a function only of the roughness Reynolds number, [...], just as in the incompressible case.\r\n\r\nThe critical roughness below which the surface is hydraulically smooth is [...] and this is equal to the thickness of the laminar sublayer for a smooth surface for both compressible and incompressible flows.\r\n\r\nOver the range of roughness sizes considered here there appears to be no wave drag associated with the drag due to roughness.\r\n\r\nThe shift in the turbulent velocity profile [...] for a rough surface at supersonic speeds is a function only of the roughness Reynolds number, [...], and quantitatively follows identically the same law as in the incompressible case." }, { "name": "Harshbarger, Frederick Clay", "degree": "PhD", "year": "1957", "title": "Physico-Chemical Processes Behind Shock Fronts", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07132004-150103", "creators": [ { "name": { "family": "Harshbarger", "given": "Frederick Clay" }, "id": "Harshbarger-Frederick-Clay", "display_name": "Harshbarger, Frederick Clay" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/YYJF-HM80", "abstract": "Part I: Introduction to the Study of Physico-Chemical Phenomena by the Use of Shock Tubes.\r\n\r\nThe use of the shock tube for the determination of physico-chemical parameters at elevated temperatures is surveyed. We first describe the principles and performance of various shock-tube designs. Next the use of a number of measuring techniques suitable for shock-tube studies is discussed. This section is followed by a summary of representative determinations of physico-chemical parameters behind incident and reflected shock waves.\r\n\r\nPart II: Experimental Studies of Reactions Behind Shocks.\r\n\r\nThe original experimental research involved the study of two chemical reactions. First we describe an unsuccessful attempt to produce hydrazine from ammonia. Second, carbon formation from acetylene is considered theoretically and experimentally. In the calculations, the state of the gas is determined behind the incident and reflected shocks, preceding chemical reaction. Estimates are made for the minimum times spent by the gas in a uniform state at the elevated temperatures behind reflected shocks. The experimental studies led to a new method for making simultaneous light emission and absorption measurements. A kinetic interpretation is given to the induction time necessary to form carbon after the passage of the reflected shock. Spectroscopic studies are presented which indicate that the emitted radiation associated with carbon formation follows a blackbody distribution law. A two-color method has been developed for the determination of temperature as a function of time behind carbon-forming shocks." }, { "name": "Hartwig, Frederic William", "degree": "PhD", "year": "1957", "title": "Development and Application of a Technique for Steady State Aerodynamic Heat Transfer Measurements", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-07132004-161800", "creators": [ { "name": { "family": "Hartwig", "given": "Frederic William" }, "id": "Hartwig-Frederic-William", "display_name": "Hartwig, Frederic William" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Y2JY-A341", "abstract": "A technique was developed for measuring steady state heat transfer on a hemisphere cylinder and the results are compared with theory. The instrumentation consisted of a miniaturized thermopile of silver-constantan thermocouples approximately 1/8\" x 1/16\" x 1/100\". The repeatability of readings with this device was found to be excellent. These heat measuring devices, or heat meters, were installed in both a ceramic hemisphere cylinder and in a similar metal one. There were obtained three different heat flow rates at each of six different combinations of tunnel pressure and temperature.
\r\n\r\nThe results compared very well with a theory developed by Lester Lees based upon the assumption of local similarity.
\r\n" }, { "name": "Hendrickson, James Arnold", "degree": "PhD", "year": "1957", "title": "The Initiation of Yielding and Brittle Fracture in Annealed Mild Steel", "advisor": "Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechETD:etd-07272004-155051", "creators": [ { "name": { "family": "Hendrickson", "given": "James Arnold" }, "id": "Hendrickson-James-Arnold", "display_name": "Hendrickson, James Arnold" } ], "advisors": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9Z18-5Q34", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe initiation of brittle fracture and the transition between ductile and brittle behavior of an annealed mild steel has been investigated. A theoretical and experimental investigation has been made on notched tensile specimens to determine the state of stress beneath a notch which governs the initiation of a brittle fracture. The experimental investigation was conducted for constant rates of stress application of from [...] to [...] [...] sec at temperatures of -110[degrees] F (-79 [degrees] C) and -200[degrees] F (-129[degrees] C). The stress analysis of the notched specimen includes the effect of limited plastic deformation known to precede brittle fracture.\r\n\r\nThe true tensile stress at the position and instant of initiation of brittle fracture in the notched tensile specimens is determined from the experimental results, a knowledge of the yielding behavior of the material, and the elastic-plastic stress analysis. In this manner it is shown that brittle fracture occurs when a critical value of the maximum tensile stress is attained. This critical value of the tensile stress is found to be constant, independent of rate and temperature, and is shown to occur at the elastic-plastic boundary beneath the root of the notch.\r\n\r\nThe information gained from the investigation of the initiation of brittle fracture in notched tensile specimens is applied to the prediction of the transition temperature in the case of the Izod impact test. The prediction is checked by experiment and the agreement is found to be good." }, { "name": "Kubota, Toshi", "degree": "PhD", "year": "1957", "title": "Investigation of Flow Around Simple Bodies in Hypersonic Flow", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-07142004-143403", "creators": [ { "name": { "family": "Kubota", "given": "Toshi" }, "id": "Kubota-Toshi", "display_name": "Kubota, Toshi" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZVPP-FK96", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA theoretical analysis of the flow around slender blunt-nosed bodies was made by applying the flow similarity concept to the hypersonic small-disturbance equations. The flow field around a class of bodies of the form [...] exhibits a certain similarity in the sense that the pressure, density and transverse velocity are described by relations of the form Q(x,r)/Q(R) = f(r/R), where R is the distance from the axis to the shock wave. This similarity holds when the Mach number is infinitely large, and when the exponent in the equation defining the body shape lies in the range [...] for axially-symmetric bodies and in the range [...] for two-dimensional bodies. For large but finite Mach numbers a second approximation was obtained by expanding solutions in series of powers of [...].\r\n\r\nAn experimental investigation of the flow around \"similar-flow\" bodies of revolution was conducted at Mach number 7.7 in the GALCIT hypersonic wind tunnel. The surface pressure distributions agreed closely with the theoretical predictions, after a simplified correction was made for the boundary-layer displacement effect. The results indicated that the boundary layer interaction effect needs a further investigation." }, { "name": "Messiter, Arthur Frederic", "degree": "PhD", "year": "1957", "title": "Expansion Procedures and Similarity Laws for Transonic Flow", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-07152004-091254", "creators": [ { "name": { "family": "Messiter", "given": "Arthur Frederic" }, "id": "Messiter-Arthur-Frederic", "display_name": "Messiter, Arthur Frederic" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4HK0-K279", "abstract": "The transonic flow past slender bodies and thin wings is investigated with the use of a general theory of expansion procedures. It is assumed that the solutions for the velocity components possess asymptotic expansions of a very general form, and the differential equations and boundary conditions for the first and higher approximations are obtained by applying appropriate limiting procedures to the full equations. The following cases are treated: 1) bodies of revolution at zero incidence; 2) bodies of nearly circular cross-section, at zero incidence; 3) bodies of revolution at an angle of attack; and 4) thin wings at zero incidence. Certain first-order similarity laws are derived for these problems, and the order of magnitude of the error is stated in each case." }, { "name": "Neustein, Joseph", "degree": "PhD", "year": "1957", "title": "Low Reynolds Number Experiments in an Axial Flow Turbomachine", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-07152004-095340", "creators": [ { "name": { "family": "Neustein", "given": "Joseph" }, "id": "Neustein-Joseph", "display_name": "Neustein, Joseph" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7EKE-PD84", "abstract": "The performance of a single stage, axial flow turbomachine was studied experimentally at very low Reynolds numbers. The investigation had two primary objectives: first, a quantitative evaluation of overall performance as a function of Reynolds number, and second, a study of the flow within the blade rows.\r\n\r\nThe investigation established that sudden or critical changes in performance do not occur in the type of machine tested between a Reynolds number (based on rotor tip speed and rotor chord) of 150,000 and 20,000. The deterioration of performance is explained in terms of viscous flow phenomena within the blade rows." }, { "name": "Plapp, John Elmer", "degree": "PhD", "year": "1957", "title": "I. Laminar Boundary Layer Stability in Free Convection. II. Laminar Free Convection with Variable Fluid Properties", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-09142004-153230", "creators": [ { "name": { "family": "Plapp", "given": "John Elmer" }, "id": "Plapp-John-Elmer", "display_name": "Plapp, John Elmer" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/6DDP-8W66", "abstract": "I. LAMINAR BOUNDARY LAYER STABILITY IN FREE CONVECTION\r\n\r\nThe stability with respect to transition to turbulent flow of laminar free convection flow along a semi-infinite flat plate was studied analytically by the method of small oscillations. Six procedures of varying degrees of mathematical complexity for solving approximately the stability problem were developed according to different assumptions regarding the presence or absence of heat conduction and viscous and body forces. The procedure which considers that only inertial, pressure, and viscous forces control the stability was applied to the case of free convection of air along a vertical plate. It was found that the analytic predictions agreed qualitatively but not quantitatively with experimental observations made by other investigators of the appearance of instability in such a flow.\r\n\r\nII. LAMINAR FREE CONVECTION WITH VARIABLE FLUID PROPERTIES\r\n\r\nHeat transfer by laminar free convection along a semi-infinite flat plate was analyzed with the assumption that the density, specific heat, viscosity, and thermal conductivity of the fluid are functions of the temperature. An approximate method for obtaining heat-transfer rates was developed and was applied to cases of heating and cooling oils with large changes in their Prandtl numbers. By comparison, it was found that earlier and more general analyses based on essentially constant-property assumptions give good results in the variable-property case when they are based on the properties of the fluid at the plate surface." }, { "name": "Rabinowicz, Josef", "degree": "PhD", "year": "1957", "title": "Aerodynamic Studies in the Shock Tube", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152004-142813", "creators": [ { "name": { "family": "Rabinowicz", "given": "Josef" }, "id": "Rabinowicz-Josef", "display_name": "Rabinowicz, Josef" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MXH9-5H80", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nIn order to utilize the shock tube for quantitative investigations of some aerodynamic problems a thin platinum film resistance thermometer was developed for heat transfer rate measurements. The present report describes the construction and calibration of the heat transfer gage. Since the experimental technique presents a major problem this investigation has been carried out in the straight section of the shock tube where the flow conditions are well defined and readily measured. These flow conditions were calculated utilizing the most recent NBS data on air properties at high temperatures. The flow conditions were also measured utilizing the heat transfer gage and, several independent experimental techniques, and good agreement was found with the equilibrium flow calculations after an initial period of 30 - 50 [...]sec. Measurements of the heat transfer rate at the forward stagnation point and on the circumference of a circular cylinder are reported and compared with the theoretical calculations of L. Lees. A method for deduction of surface pressure distribution from the laminar boundary-layer heat transfer data is also presented." }, { "name": "Richmond, Ronald LeRoy", "degree": "PhD", "year": "1957", "title": "Experimental Investigation of Thick, Axially Symmetric Boundary Layers on Cylinders at Subsonic and Hypersonic Speeds", "advisor": "Coles, Donald Earl", "url": "https://resolver.caltech.edu/CaltechETD:etd-08242004-093622", "creators": [ { "name": { "family": "Richmond", "given": "Ronald LeRoy" }, "id": "Richmond-Ronald-LeRoy", "display_name": "Richmond, Ronald LeRoy" } ], "advisors": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-D-E", "role": "advisor", "display_name": "Coles, Donald Earl" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/A8P6-BA17", "abstract": "An experimental investigation of the transverse curvature effect on laminar and turbulent axially symmetric boundary layers was conducted in two subsonic wind tunnels and in the GALCIT 5 x 5 inch hypersonic wind tunnel.\r\n\r\nSubsonic turbulent skin friction coefficients were estimated from velocity profiles with axial flow on a 0.024 inch diameter cylinder and a 1.00 inch diameter cylinder. A considerable increase over the flat plate skin friction coefficient at the same momentum thickness Reynolds number was found.\r\n\r\nHypersonic laminar and turbulent skin friction coefficients with axial flow on an insulated 0.250 inch diameter cylinder were measured by the floating element technique and indicated, respectively, several times and 1.5 times the laminar and turbulent flat plate skin friction coefficients at the same momentum thickness Reynolds numbers. Turbulent skin friction coefficients were estimated from pitot profiles with axial flow on a 0.064 inch diameter cylinder and on a 0.024 inch diameter cylinder at M1 = 5.8 and indicate double the value to be found for an insulated flat plate at the same momentum thickness Reynolds number." }, { "name": "Shapiro, Haskell", "degree": "PhD", "year": "1957", "title": "Electromagnetic Scattering Properties of a Resonant Plasma", "advisor": "Papas, Charles Herach", "url": "https://resolver.caltech.edu/CaltechETD:etd-08062004-143419", "creators": [ { "name": { "family": "Shapiro", "given": "Haskell" }, "id": "Shapiro-Haskell", "display_name": "Shapiro, Haskell" } ], "advisors": [ { "name": { "family": "Papas", "given": "Charles Herach" }, "id": "Papas-C-H", "role": "advisor", "display_name": "Papas, Charles Herach" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/60W8-N371", "abstract": "A column of ionized mercury vapor is placed in a parallel plate transmission line and the resulting reflection coefficient observed. From the measurement of reflection coefficient as a function of discharge current, plasma resonance is demonstrated. In accordance with the theory applied, but in contrast to the results of other investigators, resonance is found at only one value of discharge current. The discharge current required to produce resonance is measured as a function of frequency. The functional dependence observed is as predicted by theory, but the current is higher than the theoretical value. The discharge current required to produce resonance is measured as a function of gas pressure. The dependence that is found follows that predicted theoretically at higher gas pressures, but deviates sharply from the theoretical form at lower gas pressures.
\r\n" }, { "name": "Buchman, William W.", "degree": "PhD", "year": "1956", "title": "Field Theory of Travelling-Wave with Loss: Application to the Study of Attenuator Saturation Effects", "advisor": "Field, Lester M.; Gould, Roy Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182004-155923", "creators": [ { "name": { "family": "Buchman", "given": "William W." }, "id": "Buchman-William-W", "display_name": "Buchman, William W." } ], "advisors": [ { "name": { "family": "Field", "given": "Lester M." }, "id": "Field-L-M", "role": "advisor", "display_name": "Field, Lester M." }, { "name": { "family": "Gould", "given": "Roy Walter" }, "id": "Gould-R-W", "role": "advisor", "display_name": "Gould, Roy Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/F74C-PD63", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPropagation constants have been calculated for a lossy traveling-wave tube by means of a field theory. These results have been applied to the prediction of an attenuator power loss of the order of 2 or 3 db. compared to attenuatorless operation. It is shown that the gain of the higher order modes is negligible. Admittance matching by means of radial admittance transformation is the underlying method used throughout.\r\n\r\nThe Pierce-Fletcher theory in common use at this time is examined in some detail to determine its range of validity. It is found to break down when the ratio of beam to helix radius is almost unity and when [...] is small. Furthermore, it is shown that complex parameters must replace the real ones, Q, K, and C, if one wants to extend the Pierce notation correctly to lossy tubes. Not doing so leads to discrepancies of approximately 10% in the propagation constants calculated here. There is reason to believe that parameters other than those used here will not result in greater discrepancy.\r\n\r\nThe effects of space charge bunching on saturation has been treated. Criteria have been set for determining whether bunching is important or not in determining saturation." }, { "name": "Campbell, George Stuart", "degree": "PhD", "year": "1956", "title": "Turbulence in the Wake of a Thin Airfoil at Low Speeds", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192004-142218", "creators": [ { "name": { "family": "Campbell", "given": "George Stuart" }, "id": "Campbell-George-Stuart", "display_name": "Campbell, George Stuart" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T35K-QF86", "abstract": "Experiments have been made to determine the nature of turbulence in the wake of a two-dimensional airfoil at low speeds. The experiments were motivated by the need for data which can be used for analysis of the tail-buffeting problem in aircraft design. Turbulent intensity and power spectra of the velocity fluctuations were measured at a Reynolds number 1.6 x 10[superscript 5] for several angles of attack. Total-head measurements were also obtained in an attempt to relate steady and fluctuating wake properties.\r\n\r\nMean-square downwash was found to have nearly the same dependence on vertical position in the wake as that shown by total-head loss. For this particular wing, turbulent intensity, integrated across the wake, increased roughly as the 3 /2 power of the drag coefficient.\r\n\r\nPower-spectrum measurements indicated a decrease in frequency as wing angle of attack was increased. The average frequency in the wake was proportional to the ratio of mean wake velocity to wake width." }, { "name": "Dooley, Donald Allen", "degree": "PhD", "year": "1956", "title": "Combustion in Laminar Mixing Regions and Boundary Layers", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03222004-162749", "creators": [ { "name": { "family": "Dooley", "given": "Donald Allen" }, "id": "Dooley-Donald-Allen", "display_name": "Dooley, Donald Allen" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MGTH-TS83", "abstract": "The governing relations for gaseous flow systems with chemical reaction are briefly discussed. A mixture of mechanically similar Maxwellian molecules is assumed and the general relations are then reduced to the simplified forms appropriate for reacting, laminar boundary layer type flow systems. One-step unopposed, \"global\" reactions following first-order, second-order, and third-order kinetics are considered.\r\n\r\nThe simplified governing relations are transformed to an equivalent constant density plane by application of the Howarth transformation. A similarity function relating the specie concentrations to the local temperature is found for the case of equal Prandtl and Schmidt numbers. The similarity function is shown to be equal to the dimensionless streamwise velocity when the Prandtl and Schmidt numbers are both equal to unity. The remaining governing relations are then transformed to the Blasius plane in which the velocity field has known solutions. The energy equation is solved by an iteration process; a general analytic solution for the N'th approximation is obtained.\r\n\r\nThe analytic techniques developed are applied to the problems of combustion within laminar mixing regions and boundary layers. Temperature and concentration profiles are calculated and the dependence of the characteristic stay time upon the parameters of the system is determined. The application of the similarity techniques to the problem of chemical reaction within a hypersonic boundary layer is briefly discussed in an Appendix." }, { "name": "Eisley, Joe Griffin", "degree": "PhD", "year": "1956", "title": "Panel Flutter in Supersonic Flow", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-03222004-163442", "creators": [ { "name": { "family": "Eisley", "given": "Joe Griffin" }, "id": "Eisley-Joe-Griffin", "display_name": "Eisley, Joe Griffin" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZF04-TK14", "abstract": "The problem of panel flutter in a supersonic flow is treated in three parts. In the first the flutter of a simply supported rectangular plate is studied. Only small deflections are considered so that linear plate theory may be used. The flutter mode is described by a series expansion in terms of the normal modes of oscillation of the plate in a vacuum. Linearized aerodynamic theory is used. The exact aerodynamic solution as well as two simplifications--strip theory and quasi-steady theory--are discussed. Numerical calculations were made to determine flutter boundaries for plates of varying aspect ratio using strip theory aerodynamics for M = 2 and M = \u221a2. The flutter mode was described by considering only two or three normal modes in the calculations.
\r\n\r\nThe flutter of a two-dimensional buckled panel with clamped edges is studied both theoretically and experimentally. The flutter mode is described by a series expansion of functions which satisfy the boundary conditions for clamped edges. Quasi-steady linearized aerodynamics is used. Large deflections of the panel are considered. Numerical calculations have been made considering only the first two terms of the series expansion. The theoretical and experimental results are compared.
" }, { "name": "Hartlieb, Robert Joseph", "degree": "PhD", "year": "1956", "title": "The Cancellation of Random Disturbances in Automatic Control Systems", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232004-132254", "creators": [ { "name": { "family": "Hartlieb", "given": "Robert Joseph" }, "id": "Hartlieb-Robert-Joseph", "display_name": "Hartlieb, Robert Joseph" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/SCBZ-3H18", "abstract": "A disturbance-cancelling feedback transfer function is proposed in a preliminary study for linear systems with constant coefficients. This idea is then experimentally demonstrated.\r\n\r\nIn the main theory for more general systems, expressions are obtained for a computer which generates a cancelling input from measurements of the disturbances. The cases where there are fewer measurements than disturbances and also noisy measurements are treated. Three schemes and a basis for comparison are given. An example is calculated." }, { "name": "Johnson, Robert Royce", "degree": "PhD", "year": "1956", "title": "An Electronic Digital Polynomial Root Extractor", "advisor": "Frankel, Stanley P.; McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-03242004-145118", "creators": [ { "name": { "family": "Johnson", "given": "Robert Royce" }, "id": "Johnson-Robert-Royce", "display_name": "Johnson, Robert Royce" } ], "advisors": [ { "name": { "family": "Frankel", "given": "Stanley P." }, "id": "Frankel-S-P", "role": "advisor", "display_name": "Frankel, Stanley P." }, { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/XSCJ-XT27", "abstract": "Many mathematical techniques exist for factoring algebraic polynomials. Most require much computation and programming and are practical methods only with large machine computers. A special purpose electronic digital computer designed to factor polynomials of high degree is described. The mathematical method is an adaptation of a Taylor serial approximation used to connect the problem and its formulation with a special machine implementation. The computer uses a small rotating magnetic drum, about 200 germanium diodes, and 20 logical flip-flops. Unique features of the system are the simple algebraic logical design techniques and the ease of programming. The result is a small, simple, and useful computer." }, { "name": "Karamcheti, Krishnamurty", "degree": "PhD", "year": "1956", "title": "Sound Radiation from Surface Cutouts in High Speed Flow", "advisor": "Roshko, Anatol; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262004-114458", "creators": [ { "name": { "family": "Karamcheti", "given": "Krishnamurty" }, "id": "Karamcheti-Krishnamurty", "display_name": "Karamcheti, Krishnamurty" } ], "advisors": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1CRR-9Y28", "abstract": "In an experimental investigation of subsonic and supersonic flows of air past rectangular cavities cut into a flat surface it was discovered that the cavities emit a strong acoustic radiation.\r\n\r\nThe frequency of the sound-producing oscillations measured by a hot wire in the cavity was found to be inversely proportional to the breadth for fixed depth. For fixed breadth the frequency was found to increase, though not systematically, with a decrease in depth.\r\n\r\nA non-dimensional frequency S is defined in terms of the frequency of emission, the gap breadth, and the free stream velocity. The dependence of S on the various parameters in the problem, such as Mach number, Reynolds number and ratio of the boundary layer thickness to a dimension of the cavity, is discussed in light of appropriate experiments.\r\n\r\nAn estimate of the intensity of the radiation was obtained by means of an optical interferometer of the Mach-Zehnder type. For points located at 3 to 4 cavity breadths from the cavity, intensities of the order of 100 - 150 decibels were found for sound fields from cavities 0.1\" deep and 0.1 to 0.2 inch broad at Mach numbers 0.7 to 0.85.\r\n\r\nPossible mechanisms for the sound production by the cavities are discussed." }, { "name": "Kendall, James Madison", "degree": "PhD", "year": "1956", "title": "An Experimental Investigation of Leading Edge Shock Wave-Boundary Layer Interaction at Hypersonic Speeds", "advisor": "Nagamatsu, Henry T.; Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252004-153340", "creators": [ { "name": { "family": "Kendall", "given": "James Madison" }, "id": "Kendall-James-Madison", "display_name": "Kendall, James Madison" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." }, { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6XVK-B331", "abstract": "The boundary layer on a slender body tends to be very thick at hypersonic speeds. It interacts with the external flow by producing larger flow deflections near the leading edge than those due to the body alone. The increased shock strength affects the boundary layer growth. The flow around the boundary layer gives rise to an induced pressure with a negative gradient which thins the boundary layer and increases the skin friction with respect to the zero pressure gradient value.
\r\n\r\nExperiments on a flat plate with a sharp leading edge (Re\u209c < 100) have been performed in the GALCIT 5 x 5 inch Mach 5.8 hypersonic wind tunnel. The induced pressure was measured by means of orifices in the plate surface. Profiles of Mach number, velocity, mass flow, pressure, and momentum deficiency were calculated from impact pressure surveys normal to the plate surface made at various distances from the leading edge.
\r\n\r\nThe results are as follows: (1) The induced pressures are 25 per cent higher than the weak interaction theory. (2) The boundary layer and the external flow are distinctly separate for Re\u2093 as low as 6000. (3) The shock wave location is in good agreement with that predicted by the Friedrichs theory for a body shape equivalent to the observed boundary layer displacement thickness. (4) Expansion waves reflected from the shock are weak. (5) The average skin friction coefficient tends toward and nearly matches the zero pressure gradient value downstream, but increases to approximately twice that value as the leading edge is approached.
" }, { "name": "Kerrebrock, Jack Leo", "degree": "PhD", "year": "1956", "title": "The Interaction of Flow Discontinuities with Small Disturbances in a Compressible Fluid", "advisor": "Tsien, Hsue Shen; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04142004-150412", "creators": [ { "name": { "family": "Kerrebrock", "given": "Jack Leo" }, "id": "Kerrebrock-Jack-Leo", "display_name": "Kerrebrock, Jack Leo" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9EN8-WZ61", "abstract": "The interaction of a random small disturbance field in a compressible fluid with shock waves and flame fronts is analyzed. The disturbance field, which may consist of fluctuations of pressure, entropy and vorticity, is found to be modified in passing through the shock or flame.\r\n\r\nIn the case of the shock wave, it is found that all of the the three types of disturbances are generated in comparable strength in the downstream flow by the presence of any of the three in the upstream flow. Moderate fluctuations of either vorticity (turbulence) or entropy will produce intense noise fields in the downstream flow. If the shock is normal, the frequency of this noise field is much lower for very weak shocks than for strong shocks, given the same upstream velocity and disturbance wave length. If the weak shock is oblique to the flow, the frequency of the noise is increased.\r\n\r\nFor the flame front, also, it is found that all three types of disturbances are generated in the downstream flow by the presence of one of them in the upstream flow. In this case, however, the normal propagation Mach number of the flame enters as a small parameter. It is found that the intensity of the downstream turbulence generated by sound waves inpinging on the upstream face of the flame is proportional to the reciprocal of this Mach number times the intensity of the upstream pressure fluctuation. Hence, rather strong turbulence may be generated downstream of a flame by comparatively weak sound upstream. The pressure amplitudes of the sound fields generated by entropy and vorticity fluctuations in the upstream flow are proportional, respectively, to the Mach number squared and cubed. For ordinary hydrocarbon flames, ten percent turbulent velocity fluctuations, or one percent entropy (temperature) fluctuations will cause audible sound to be emitted. The fequency is in the range of 20 to perhaps 100 cycles per second for an input disturbance wave length of one inch.\r\n\r\nAlthough the analysis is carried out for an isolated infinite discontinuity, it is felt that the results are applicable, at least qualitatively, to the complicated configuration of shock waves found in under or over-expanded nozzles, and to the flame configurations found in actual combustion processes" }, { "name": "Lamson, Philip", "degree": "PhD", "year": "1956", "title": "Measurements of Lift Fluctuations Due to Turbulence", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262004-115115", "creators": [ { "name": { "family": "Lamson", "given": "Philip" }, "id": "Lamson-Philip", "display_name": "Lamson, Philip" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2ZDV-9T79", "abstract": "The fluctuating lift of a rigid wing in turbulent flow is studied. The power spectra of the lift and of the turbulent fluctuations are measured. From these measurements the aerodynamic admittance of the wing is obtained.\r\n\r\nThe ratio of span/scale of turbulence is varied by means of movable end plates. For a distance between the end plates of the order of the scale of turbulence the aerodynamic admittance is expected to approach the computed values of Sears.\r\n\r\nThis is shown to be the case if the reduced frequencies are larger than k = 0.8. For smaller k the experimental admittance falls below Sears' values. For large ratios of span/scale of turbulence the aerodynamic admittance is decreased for all frequencies and becomes nearly independent of frequency in the investigated range 0.2 <= k <= 2.\r\n\r\nIn general the measurements support the simplifying assumptions made in the statistical approach to gust loads and buffeting initiated by Clementson and by Liepmann." }, { "name": "Lindley, Charles Alexander", "degree": "PhD", "year": "1956", "title": "Secondary Flow in Compressor Cascades", "advisor": "Rannie, W. Duncan; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04022009-083759", "creators": [ { "name": { "family": "Lindley", "given": "Charles Alexander" }, "id": "Lindley-Charles-Alexander", "display_name": "Lindley, Charles Alexander" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2RYC-QB23", "abstract": "An experimental study was made of the secondary flow in a compressor cascade. Detailed surveys of the entire flow channel at various operating conditions are presented. The chief difference of the experimental results from those predicted by linearized theory was the presence of a turbulent separation region at the corner of the wall and the low pressure surface of the blade. While the actual losses involved were small, the effects on the succeeding stages of a turbomachine might be more severe." }, { "name": "Martel, Hardy Cross", "degree": "PhD", "year": "1956", "title": "An Investigation of the Omegatron Type Mass Spectrometer", "advisor": "Langmuir, Robert V.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06072004-153528", "creators": [ { "name": { "family": "Martel", "given": "Hardy Cross" }, "id": "Martel-Hardy-Cross", "display_name": "Martel, Hardy Cross" } ], "advisors": [ { "name": { "family": "Langmuir", "given": "Robert V." }, "id": "Langmuir-R-V", "role": "advisor", "display_name": "Langmuir, Robert V." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/71EX-5M05", "abstract": "An Omegatron type mass spectrometer has been investigated both theoretically and experimentally to determine its detailed operation and limitations. Resolution, peak height, shape and frequency have been calculated theoretically and compared experimentally. A method is given for sketching ion trajectories in the nonlinear case (e.g., with space charge). Using this method, it is shown that a small amount of space charge will seriously hamper the operation of the Omegatron in that it will limit the maximum excursion of a resonant ion and thus limit the possible resolution. It is shown that under normal operating conditions a trapping voltage is necessary to maintain ion collection efficiency, and that this trapping voltage causes a space charge sufficient in size to result in nonlinear ion trajectories and poor operation.\r\n\r\nIt is concluded that in order to get good operation of the Omegatron some method will have to be found for eliminating the space charge or its effects. Several possibilities for doing this are suggested, the most intriguing one being to use a dipole type of RF electric field rather then a uniform one." }, { "name": "Mitchell, Thomas Patrick", "degree": "PhD", "year": "1956", "title": "I. The Propagation of Shock Waves in Non-Uniform Gases. II. The Stability of the Spherical Shape of a Vapor Cavity in a Liquid", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06142004-153608", "creators": [ { "name": { "family": "Mitchell", "given": "Thomas Patrick" }, "id": "Mitchell-Thomas-Patrick", "display_name": "Mitchell, Thomas Patrick" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/PDMS-YT82", "abstract": "I. The one-dimensional propagation of shock waves in a perfect gas in which the pressure and the density are not necessarily uniform is investigated by seeking similarity solutions of the equations describing the non-isentropic motion of the gas. It is shown that such solutions can be found and that they can be related to specific types of compressive piston motion. In particular, the propagation of the shock resulting from the uniform compressive motion of a piston in a non-uniform gas is studied. For this case a first order, ordinary, non-linear differential equation which determines the shock strength as a function of distance is derived. An analytic solution of this equation is obtained for a gas in which the pressure is constant but the density varies, and for which the ratio of the specific heats, [gamma], is 3/2. There is no restriction placed upon the permissible density variations. In situations in which the pressure and the density distributions are variable, and in which general values of [gamma] are allowed, numerical results are presented. It is not possible in such cases to derive analytic solutions of the equation. The discussion of the shock propagated by the non-uniform motion of a piston is more difficult. However, some details are given in the case of strong and weak shocks resulting from a decelerative piston motion.\r\n\r\nII. The stability of the spherical shape of a gas bubble in a liquid is investigated for the case in which the difference between the pressure in the bubble, P[subscript i] and the pressure in the liquid, P[subscript o], is constant. These conditions apply approximately to a vapor bubble growing, (P[subscript i] > P[subscript o]), or collapsing, (P[subscript i] < P[subscript o]), in a liquid at constant external pressure. The general solution for the behavior of a small deformation in the spherical shape of the cavity is readily determined when surface tension is neglected. For a growing bubble the deformation increases slowly and monotonically; for a collapsing bubble the deformation oscillates with small amplitude until the mean radius of the bubble approaches zero, when the magnitude of the deformation increases rapidly. The consistency and applicability of the small amplitude theory is thus demonstrated. A solution is also obtained which includes the effect of surface tension. In this case the distortion amplitude decreases with increasing radius for the expanding bubble and the singularity in the distortion amplitude for the collapsing bubble at zero radius persists." }, { "name": "Nomicos, George Nicolas", "degree": "PhD", "year": "1956", "title": "Effects of Sediment Load on the Velocity Field and Friction Factor of Turbulent Flow in an Open Channel", "advisor": "Vanoni, Vito A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06182004-105138", "creators": [ { "name": { "family": "Nomicos", "given": "George Nicolas" }, "id": "Nomicos-George-Nicolas", "display_name": "Nomicos, George Nicolas" } ], "advisors": [ { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "advisor", "display_name": "Vanoni, Vito A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/QZ0J-A652", "abstract": "An experimental investigation was made of the friction characteristics of streams with sediment load. Measurements of velocity and sediment profiles, and calculations of friction factor, f, and von Karman's constant, k, were made in a 40-foot tilting flume. Several runs were made with uniform flow and various bed configurations using sands of two sizes (.10 mm and .16 mm). For better understanding of the effect of sediment on von Karman's constant k and the friction factor, uniform clear water flows were established on stabilized natural sand beds. The depth and the mean velocity were kept the same as those of the movable bed stream for which the sand bed was stabilized, and a direct comparison was made. Then, by adding loose sand in steps and establishing uniform flow, the change in von Karman's constant and the friction factor with sediment load was studied. It was found that both the friction coefficient f, and von Karman's k, decreased as the sediment load was increased, although the coefficient f decreased by a much smaller percentage than the constant k. It is hypothesized that the sediment load appreciably reduces the rate of turbulent energy diffusion, thus reducing the turbulence level of the fully established uniform flow and changing the balance of turbulence energy.\r\n\r\nIn a very small region near the bed the turbulent energy production, diffusion, viscous action and dissipation of energy due to sediment in suspension are all of about equal importance. A theoretical study was made of the distribution of both the production of turbulent energy and the dissipation of energy by the sediment along a vertical profile for hydrodynamically smooth bed,and it was made possible to integrate them to the bottom of the stream." }, { "name": "Rethorst, Scott Carson", "degree": "PhD", "year": "1956", "title": "Characteristics of an Airfoil Extending Through a Circular Jet", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-153000", "creators": [ { "name": { "family": "Rethorst", "given": "Scott Carson" }, "id": "Rethorst-Scott-Carson", "display_name": "Rethorst, Scott Carson" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7PS7-T859", "abstract": "A method has been derived for the determination of the downwash in the field of an airfoil extending through a circular jet. This solution has been applied particularly to the region aft of the lifting line in the plane of the airfoil, to determine the lift distribution on a wing extending through a circular jet.\r\n\r\nThe method of solution is essentially based on a division of the flow induced by the jet boundary into parts which are even and odd with respect to the direction of flow. The analysis due to the even part alone is similar to previous theories, which in effect disregarded the odd part. Such previous results based on the even part alone differ considerably from the experimental values. The results based on the total of the even and odd parts show good agreement with the experiments, illustrating the necessity of including the odd part of the flow when the segment of the wing immersed in the jet is of low aspect ratio.\r\n\r\nThe problem has been solved in parametric form, so that the results may be employed to determine the characteristics of any geometry wing-jet combination at any jet velocity ratio." }, { "name": "Rodriguez, Alexander Martin", "degree": "PhD", "year": "1956", "title": "Theorems Concerning the Reduction of Drag for Supersonic Aircraft", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08302006-133358", "creators": [ { "name": { "family": "Rodriguez", "given": "Alexander Martin" }, "id": "Rodriguez-Alexander-Martin", "display_name": "Rodriguez, Alexander Martin" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R1JD-WT10", "abstract": "In this report the problem of drag reduction or minimization for aircraft in supersonic flight is investigated within the framework of linearized theory of inviscid flow for fixed flight Mach number.\r\n\r\nGeneral theorems applicable to complete aircraft configurations are developed. These theorems state defining properties of distributions of thickness and normal force restricted to a particular region of the aircraft configurations that minimize the drag of the complete aircraft under the condition that the distribution of thickness and normal force on the remainder of the aircraft is specified in advance. These optimum distributions are further required to satisfy some of the various types of constraints that are commonly specified for aircraft.\r\n\r\nThe problem of finding the optimum distribution of thickness, lift and sideforce on a slender body of revolution is also studied under the assumption that the body carries no total lift or sideforce and can be represented by placing the distributions along the body axis. The case for which the Mach envelope of the body does not include all of the remaining portion of the aircraft configuration, upon with the thickness and normal force are specified, is solved. This solution covers the previously known case for which the Mach envelope of the body includes the entire aircraft." }, { "name": "Rubin, Sheldon", "degree": "PhD", "year": "1956", "title": "Transient Motion Measurements for Structural Response Analysis", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06252004-104122", "creators": [ { "name": { "family": "Rubin", "given": "Sheldon" }, "id": "Rubin-Sheldon", "display_name": "Rubin, Sheldon" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ND1B-3V27", "abstract": "The theory of the design of instruments suitable for the measurement of the acceleration-time history of a transient motion is considered. It is assumed that the primary purpose of the acceleration-time record is the calculation of structural response. As a criterion of instrument behavior, it is proposed that the correct reproduction of the response spectrum of the transient motion be adopted. The application of this response spectrum criterion to some selected acceleration pulses indicates that the optimum instrument parameters for a transient measurement are essentially the same as for the measurement of periodic motions.\r\n\r\nA general theory for the multiple degree of freedom seismic accelerometer characteristics is established. The particular case of a two degree of freedom accelerometer is studied and it is shown that the sensitivity to acceleration can be increased to about five times that of a single degree of freedom instrument having the same useful frequency range.\r\n\r\nAn instrument which can be used to obtain structural response information directly, without the necessity of an acceleration-time recording is studied. This instrument, the reed gage, gives directly information concerning the transient response of a single degree of freedom system or of individual modes of a complex structure. The total response of a complex structure can be determined from reed gage information by the superposition of the maximum responses in the individual modes. An analysis is made of the errors in total response inherent in this superposition process. It is found that in many practical problems the distribution of mode frequencies and the form of the excitation is such that the total error due to superposition is not a significant factor in the problem." }, { "name": "Shen, Yung-chung", "degree": "PhD", "year": "1956", "title": "Similarity Solution for Transonic Flow Past a Cone", "advisor": "Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06282004-095155", "creators": [ { "name": { "family": "Shen", "given": "Yung-chung" }, "id": "Shen-Yung-chung", "display_name": "Shen, Yung-chung" } ], "advisors": [ { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/74PX-HS89", "abstract": "By applying a transonic expansion procedure to a conical flow field, a system of approximate transonic equations, boundary conditions, and shock relations is derived. A similarity law for the pressure coefficient on the surface of slender cones is established. The surface pressure is computed by solving the approximate equations.\r\n\r\nBy use of similarity, the second order differential equations of the first two steps of the approximation scheme are reduced to first order equations. The solution of the first step is carried out numerically in great detail for different transonic parameters; the procedure for solving the latter is explained in the Appendix.\r\n\r\nThe results are compared with the exact solution, and a highly satisfactory agreement is reached." }, { "name": "Statler, Irving Carl", "degree": "PhD", "year": "1956", "title": "The Effects of Nonstationary Aerodynamics on the Rigid-Body Dynamic Stability of an Airplane", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-06302004-095128", "creators": [ { "name": { "family": "Statler", "given": "Irving Carl" }, "id": "Statler-Irving-Carl", "display_name": "Statler, Irving Carl" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1EHQ-B547", "abstract": "A first order in frequency theory is developed for the aerodynamic loads on a harmonically oscillating thin wing of finite aspect ratio in a subsonic compressible flow. The downwash in the vicinity of a horizontal tail behind such a wing is also evaluated to the same order in frequency. The results are then used to determine the stability derivatives of a conventional-type airplane and to set up the stick-free longitudinal equations of motion including the unsteady flow effects.\r\n\r\nAn important conclusion of this study is that, within the limitations of a \"lifting-strip\" theory, the airloads on the oscillating finite span wing are linear in frequency in the neighborhood of zero frequency. This is in contrast with the two-dimensional results which show a logarithmic singularity there.\r\n\r\nAs an example of a practical application, calculations are made of the frequency, damping and transient responses of the stick-free longitudinal motion of an F-80A airplane and the results compared with those obtained using quasisteady aerodynamic coefficients. The indications are that, while nonsteady flow considerations show considerable influence upon the control surface motion, they have a negligibly small effect upon the airplane motion." }, { "name": "Williams, Harry Edwin", "degree": "PhD", "year": "1956", "title": "Stresses and Strains in Cylindrical Shells", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-143555", "creators": [ { "name": { "family": "Williams", "given": "Harry Edwin" }, "id": "Williams-Harry-Edwin", "display_name": "Williams, Harry Edwin" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/1EB7-W116", "abstract": "As a consequence of assuming that the circumferential normal strain and in-plane shear strain of a cylindrical shell vanish, a relatively simple differential equation is derived which can be readily solved. An investigation of the frequencies of harmonic vibration of each Fourier component of the shell leads to a criterion determining a range of wave numbers within which the approximate method leads to satisfactory results. Experimental measurements show that solutions of the approximate equation are accurate except in the vicinity of a sharp variation of the load intensity, and so long as the length to diameter ratio of the shell is sufficiently large" }, { "name": "Zima, Gordon Everett", "degree": "PhD", "year": "1956", "title": "Some High Temperature Oxidation Characteristics of Nickel with Chromium Additions", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05252004-103520", "creators": [ { "name": { "family": "Zima", "given": "Gordon Everett" }, "id": "Zima-Gordon-Everett", "display_name": "Zima, Gordon Everett" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/8MC2-WR66", "abstract": "The relationship between alloy chromium content and oxidation rate has been determined for nickel-chromium alloys containing up to 17At% chromium. The tests were conducted at 1096C, under one atmosphere of oxygen. The observed structural and phase changes in the oxide were related to the oxidation rate. It has been found that increasing amounts of chromium in the NiO phase govern the oxidation rate for alloys containing less than 2At% chromium. For alloys of greater than 2At% chromium, a complex exchange of chromium among three phases--NiO, Cr2O3 and the spinel, NiCr2O4--has been detected. This chromium exchange was reflected in the lattice parameter of the NiO phase, and in the rate of increase of oxidation rate with chromium addition to the alloy. The present work indicates that an interstitial diffusion mechanism may become dominant in the oxides of high chromium content. Within the scope of the present work, the high oxidation stability of nickel-chromium alloys has been correlated with the presence of Cr2O3 in the oxide layer.\r\n\r\nOxidation rates for high purity nickel have been determined at temperatures of 980, 1096, and 1260C, under one atmosphere of oxygen. The present data, combined with lower temperature data obtained by Gulbransen and Andrew, yielded an activation energy of 45.1Kcal/mole for the oxidation of nickel." }, { "name": "Berndt, Sune Bertil", "degree": "PhD", "year": "1955", "title": "On the Influence of Wall Boundary Layers in Closed Transonic Test Sections", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052003-143311", "creators": [ { "name": { "family": "Berndt", "given": "Sune Bertil" }, "id": "Berndt-Sune-Bertil", "display_name": "Berndt, Sune Bertil" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T014-DR86", "abstract": "The boundary layers at the test section walls of a transonic wind tunnel are known to reduce the wall interference. In the present paper this effect is studied by means of small perturbation theory, assuming viscosity to be negligible when perturbing a turbulent boundary layer. An approximation for thin boundary layers leads to a modified boundary condition at the wall of the test section, expressing the normal streamline slope induced by changes in mass flow density and crossflow within the boundary layer. This boundary condition is applied to the linearized equations of subsonic flow and to the non-linear transonic equations at choking, the cases of plane and circular test sections only being treated in detail.\r\n\r\nThe results of linear theory show that all corrections except the three-dimensional angle-of-attack correction are considerably reduced by the presence of the boundary layers at Mach numbers greater than 0.9, the essential part of their influence being due to the change of mass flow density with pressure. In the case of choking the analysis indicates that the presence of boundary layers will increase the maximum model size for which the flow can be interpreted as corresponding to Mach number one in free flight. Finally, the technique of using artificial thickening of the wall boundary layers for reduction of wall interference is considered, though without reaching a definite conclusion as to its value compared to other techniques." }, { "name": "Burggraf, Odus Roy", "degree": "PhD", "year": "1955", "title": "A Theory of Stall Propagation in Axial Compressors on the Basis of Airfoil Characteristics", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11242003-103851", "creators": [ { "name": { "family": "Burggraf", "given": "Odus Roy" }, "id": "Burggraf-Odus-Roy", "display_name": "Burggraf, Odus Roy" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HQV0-7S12", "abstract": "The process of stall propagation in an axial flow compressor is represented by nonlinear airfoil lift and drag characteristics, with a time lag associated with the stalling mechanism. A pair of nonlinear integro-differential equations express the lift and drag as a function of time for a given airfoil in an isolated plane cascade representing an annulus with only a finite number of blades. Approximate solutions of these integro-differential equations are obtained by considering only the fundamental frequency in the Fourier series representing the blade loadings. Qualitative results are obtained for three cases: (a) only blade circulation is considered to be of importance in the mechanism of propagating stall, (b) blade drag is of predominant importance, and (c) combined effects of lift and drag are considered. Comparisons are made of the propagating speeds calculated for a finite number of blades with the values obtained by the approximation of an infinite number of blades. The magnitudes of the fluctuations in lift and drag are calculated as well as limiting angles of attack for which stall propagation can occur." }, { "name": "Carlson, John Arthur", "degree": "PhD", "year": "1955", "title": "Analytical and Experimental Studies of Vehicle Dynamics Behavior", "advisor": "Kyropoulos, Peter R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022003-114913", "creators": [ { "name": { "family": "Carlson", "given": "John Arthur" }, "id": "Carlson-John-Arthur", "display_name": "Carlson, John Arthur" } ], "advisors": [ { "name": { "family": "Kyropoulos", "given": "Peter R." }, "id": "Kyropoulos-P-R", "role": "advisor", "display_name": "Kyropoulos, Peter R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/4TY3-Y818", "abstract": "This thesis represents one step in the development of analysis in the field of vehicle dynamics made possible by modern computational techniques. A research program was set up, the main object of which was to conduct an appraisal of analysis by comparing the results of analysis with actual vehicle tests. Both experiment and theory are included in this one investigation.\r\n\r\nThe following general conclusions were drawn from the results of the research program:\r\n\r\n1. Relatively simple systems giving good quantitative results can be used to represent a vehicle in motion over a variety of courses.\r\n\r\n2. The effects of varying vehicle properties (spring rates, damping characteristics, masses) can be studied by using these simple systems. The results obtained are of sufficient accuracy to be used for design purposes. \r\n\r\nAn example of a design study demonstrating the application of analysis to a specific problem is presented. The problem was to investigate the possible use of the engine as a dynamic vibration absorber. The conclusion reached is that the engine mount stiffness may be chosen such that the shake of the frame caused by wheel bounce may be reduced.\r\n\r\nConclusions reached on the effects of some automobile properties (suspension bump stops, suspension damping, and tire damping) are summarized." }, { "name": "Chase, Robert Apperson", "degree": "PhD", "year": "1955", "title": "Pressurized Fuselage Stress Analysis", "advisor": "Williams, Max L.; Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022003-161233", "creators": [ { "name": { "family": "Chase", "given": "Robert Apperson" }, "id": "Chase-Robert-Apperson", "display_name": "Chase, Robert Apperson" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZCGR-N460", "abstract": "Theoretical methods for obtaining the complete stress analysis of a pressurized, stiffened circular cylinder of special geometry are presented. In certain limiting cases, the exact solutions are tractable, but in general the solutions lead to approximate results. There are practical cases for which none of the solutions is applicable. Accompanying the theoretical analysis is a short experimental program consisting of the strain gage instrumentation and testing of a Lucite and cellulose acetate model of typical aircraft structural geometry. The results compare favorably with the theoretical analysis." }, { "name": "Crumb, Stephen Franklin", "degree": "PhD", "year": "1955", "title": "A Study of the Effects of Damping on Normal Modes of Electrical and Mechanical Systems", "advisor": "McCann, Gilbert Donald; MacNeal, Richard H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-110450", "creators": [ { "name": { "family": "Crumb", "given": "Stephen Franklin" }, "id": "Crumb-Stephen-Franklin", "display_name": "Crumb, Stephen Franklin" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "MacNeal", "given": "Richard H." }, "id": "MacNeal-R-H", "role": "advisor", "display_name": "MacNeal, Richard H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/YESX-K771", "abstract": "This thesis is a general investigation of some of the properties of free and forced vibrations in linear, non-conservative systems. Particular emphasis is placed upon the problems which arise in normal mode studies made on the electric analog computer at the California Institute of Technology.\r\n\r\nIn Part I the major problems are defined, and limitations of the study are discussed. Part II is a review of the basic theory of normal modes included primarily to establish familiarity with the notation to be used later. In Part III, modifications of normal mode concepts, as applied to damped systems, are examined. \"Small damping\" criteria are discussed, and a set of theorems of small damping is presented.\r\n\r\nIn Part IV a series of normal mode analog circuits for damped systems are developed. Part V is a study of uniform damping, generalizing and extending some of the work of Rayleigh, Bode, and Guillemin. It is shown that for any type of uniform damping, all of the basic normal mode concepts are preserved.\r\n\r\nIn Part VI the theory of mode separation in uniformly damped systems is considered. Criteria for determining mode frequencies and mode parameters are developed. A multiple drive method of exciting normal modes is proposed. In Part VII, some of the methods of Part VI are extended to non-uniformly damped systems. Equivalent orthogonal systems are proposed to approximate the behavior of systems with moderately non-uniform damping. A quantitative measure of non-uniformity is presented.\r\n\r\nIn Part VIII, numerical examples and experimental results in support of the theory are presented. Concluding remarks are made in Part IX.\r\n" }, { "name": "Denney, Joseph Myers", "degree": "PhD", "year": "1955", "title": "A Study of Electron Effects in Solid Solution Alloys of Titanium", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-092120", "creators": [ { "name": { "family": "Denney", "given": "Joseph Myers" }, "id": "Denney-Joseph-Myers", "display_name": "Denney, Joseph Myers" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/MJ3D-CA66", "abstract": "Anomalous behavior of the lattice parameters of solid solution alloys of aluminum and gallium in titanium were observed at approximately 3 atomic percent solute. Alloys of silver in titanium did not exhibit similar anomalies. Anomalies also were observed in the resistivity and in the coefficient of magneto-resistance for solutes of Al and Ga. No significant evidence of anomalous behavior of the Hall coefficient or the magnetic susceptibility with solute concentration was found.\r\n\r\nThe effect of solute valency in producing the observed anomalous changes in physical properties is interpreted; using the Bloch-Brillouin approximation, as evidence of interaction between the Fermi surface and the Brillouin Zones. The effects produced by monovalent Ag and trivalent Al and Ga solutes indicate that titanium has an alloying valency between 1 and 3 in these alloys. The Brillouin Zone interpretation indicates that the alloying valency of titanium is about 1.5 electrons per atom.\r\n\r\nThe absence of an effect of solute addition on the susceptibility, the susceptibility-temperature data of Squire and Kaufmann, and the magnitude of the susceptibility indicate that titanium is anti-ferromagnetic. The suggested antiferromagnetism is in agreement with the interpretation of the effects of solute additions on the other observed physical properties. It is, therefore, concluded that titanium has approximately 2 electrons per atom in antiferromagnetic coupling between neighboring atoms, and about 2 electrons per atom in the conduction band. Neutron diffraction experiments to verify the suggested existence of a simple hexagonal antiferromagnetic superlattice in titanium are urged." }, { "name": "Feldman, Saul", "degree": "PhD", "year": "1955", "title": "On the Hydrodynamic Stability of Two Viscous Incompressible Fluids in Parallel Uniform Shearing Motion", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-093226", "creators": [ { "name": { "family": "Feldman", "given": "Saul" }, "id": "Feldman-Saul", "display_name": "Feldman, Saul" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/X62Y-2070", "abstract": "A new problem in hydrodynamic stability is investigated. Given two contiguous plane sheets of viscous incompressible fluids, bounded on one side by a solid wall and unbounded on the other, the problem is to study the hydrodynamic stability when the fluids are in longitudinal, laminar, uniform shearing motion. The mathematical analysis, based on small disturbance theory, leads to a characteristic vague problem in a system of two linear ordinary differential equations. The case for which forces due to gravity and surface tension are negligible compared with inertia and viscous forces is studied in detail, and the results are presented graphically for all fluid combinations of possible interest." }, { "name": "Gleghorn, George Jay, Jr.", "degree": "PhD", "year": "1955", "title": "An Analog Computer for the Solution of Eigenvalue Problems", "advisor": "MacNeal, Richard H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152003-110324", "creators": [ { "name": { "family": "Gleghorn", "given": "George Jay, Jr." }, "id": "Gleghorn-George-Jay", "display_name": "Gleghorn, George Jay, Jr." } ], "advisors": [ { "name": { "family": "MacNeal", "given": "Richard H." }, "id": "MacNeal-R-H", "role": "advisor", "display_name": "MacNeal, Richard H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/FK46-6J12", "abstract": "This thesis describes a computer suitable for the determination of the eigenvalues and eigenvectors of conservative mechanical and electrical systems.\r\n\r\nIn essence, the computer consists of several active circuits with input impedances which act as negative resistances at the operating frequency of the computer. These negative resistances are interconnected with passive resistors and transformers to form a circuit analogous to the system being studied. For any setting of the control the analog represents the original system at a single frequency only, consequently it cannot be used for transient analysis.\r\n\r\nIt is shown that the analog circuit is, in general, unstable at the control settings that are of interest, but that the application of suitable constraints suppresses the oscillations so that measurements may be made. The negative resistance circuits are designed so that parasitic impedances have little effect on the results. The computer has been found to produce results accurate to one per cent in most cases." }, { "name": "Goldsmith, Martin", "degree": "PhD", "year": "1955", "title": "The Burning of Single Drops of Fuel in Oxidizing Atmospheres", "advisor": "Penner, Stanford S.; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-12182003-091848", "creators": [ { "name": { "family": "Goldsmith", "given": "Martin" }, "id": "Goldsmith-Martin", "display_name": "Goldsmith, Martin" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "chair", "display_name": "Penner, Stanford S." }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "member", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "member", "display_name": "Cole, Julian D." }, { "name": { "family": "Kyropoulos", "given": "Peter R." }, "id": "Kyropoulos-P-R", "role": "member", "display_name": "Kyropoulos, Peter R." }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "member", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Leighton", "given": "Robert B." }, "id": "Leighton-R-B", "role": "member", "display_name": "Leighton, Robert B." } ], "option_major": [ "mecheng" ], "doi": "10.7907/E4YT-5B12", "abstract": "The burning of single, isolated drops of fuel in a quiescent oxidizing atmosphere has been investigated theoretically and experimentally. Two theories are presented. The first, called the diffusion theory, rests on the assumption that the rate of burning is determined by the rate at which the reactants are delivered by diffusion to the flame front surrounding the liquid drop. The second, or thermal theory is based on the assumption that chemical reaction rates govern the rate of burning of the droplet.
\r\n\r\nThe effects on droplet burning rate of changes in the composition, temperature, and pressure of the surrounding oxidizing atmosphere have been investigated experimentally. A preliminary study has also been made of the effect of forced convection on droplet burning.
\r\n\r\nIt is found that the thermal theory of droplet burning does not adequately explain the observed variations in droplet burning rate as the composition and temperature of the surrounding atmosphere are varied. On the other hand, substantial agreement is found between the results of the diffusion theory and experimental data.
" }, { "name": "Lal, Shankar", "degree": "PhD", "year": "1955", "title": "Heat Transfer in Compressible Laminar Boundary-Layers", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-095744", "creators": [ { "name": { "family": "Lal", "given": "Shankar" }, "id": "Lal-Shankar", "display_name": "Lal, Shankar" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BRKX-WV81", "abstract": "This report is concerned with the investigation of skin-friction and heat-transfer in the two-dimensional flow of a viscous compressible fluid.
\r\n\r\nThe boundary-layer equations are first transformed by the Howarth-Stewartson transformation and then it is shown that for fluids of Prandtl Number unity, if the Chapman viscosity law be assumed to hold, then any boundary-layer problem with the free stream Mach Number different from zero can be formally reduced to a problem for which the free stream Mach Number is equal to zero.
\r\n\r\nThe momentum method is then used to solve the boundary-layer equations in the Howarth-Stewartson form, for the case when the free stream Mach Number is zero. The basic equations developed are first used to solve the case of those specific pressure gradients which lead to \"similarity flows\". Other investigators have solved the exact equation for these flows on the differential analyser. The results obtained in this report, with the aid of very simple methods, agree to within a few percent with these more exact but laborious computations.
\r\n\r\nThe use of the method for the case of arbitrary pressure gradients is then developed. Three ways of solving the resulting equations are discussed. In particular, an integral solution for the square of the momentum thickness, analogous to the one existing for incompressible fluids but with different exponents, is given. The application of the method is demonstrated by solving an illustrative example.
" }, { "name": "Magnus, Richard Jeffrey", "degree": "PhD", "year": "1955", "title": "An Experimental Investigation of the Transfer of Heat from Small Wires to a Viscous Compressible Fluid", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-100200", "creators": [ { "name": { "family": "Magnus", "given": "Richard Jeffrey" }, "id": "Magnus-Richard-Jeffrey", "display_name": "Magnus, Richard Jeffrey" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4ZYH-PF56", "abstract": "A steam tunnel, suitable for making experimental measurements of the heat transfer from fine wires to a viscous compressible fluid, was developed and constructed.\r\n\r\nMeasurements of Nusselt numbers and recovery temperatures were carried out using small-diameter (0.00038 to 0.00254 cm.) tungsten wires in steam flow with Reynolds numbers ranging from about 1 to 12 and with nominal Mach numbers of 0.5 to 1.7.\r\n\r\nConsiderable difference was found between the Nusselt numbers for wires in subsonic and supersonic flow at corresponding Reynolds numbers. The results could be fairly well represented by an available theory based on the assumption that a temperature discontinuity of the fluid existed at the wire surface; however, they did not agree very well with other available data in the same range of Mach and Reynolds numbers.\r\n\r\nIn supersonic flow, the wire recovery temperatures were found to be consistently higher than the tunnel stagnation temperature.\r\n\r\nAn experimental procedure for making end-loss corrections to the heat transfer and temperature recovery tests was used and found to give satisfactory correlation of data taken with wires ranging in aspect ratio from 220 to 3040. Some experiments were performed to check the validity of the simple linear theory which is usually used to calculate end loss corrections; the theory was found to be adequate in the experimental range covered." }, { "name": "Marks, Craig", "degree": "PhD", "year": "1955", "title": "The Effects of Chamber Geometry, Surface Characteristics, and Temperature Boundary Conditions on the Hydrogen-Oxygen Reaction", "advisor": "Kyropoulos, Peter R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-145332", "creators": [ { "name": { "family": "Marks", "given": "Craig" }, "id": "Marks-Craig", "display_name": "Marks, Craig" } ], "advisors": [ { "name": { "family": "Kyropoulos", "given": "Peter R." }, "id": "Kyropoulos-P-R", "role": "advisor", "display_name": "Kyropoulos, Peter R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/76DZ-EH40", "abstract": "The established mechanism of the hydrogen-oxygen reaction is reviewed and calculated results presented concerning the rates of reaction and the explosion temperatures expected with various concentrations of water vapor. A simplified theory is developed to predict the overall rate of reaction in the case where a strong temperature gradient exists. Experiments are described in which stoichiometric mixtures of hydrogen and oxygen are introduced to a closed, shallow, nickel plated, cylindrical combustion chamber and measurements made of the pressure change with time. The top surface of the chamber is heated while the bottom surface is either heated or cooled to provide isothermal or gradient conditions, respectively. A large catalytic reaction due to the nickel surfaces is observed. The measured reaction rates and the conditions for explosion with isothermal heating are consistent with predictions based on the established reaction scheme. With gradient heating the rates measured are larger than those predicted. by the simplified theory with temperatures of the top surface above 1300[degrees]R. This fact is believed to be caused by the diffusion of active intermediate reaction products from hot regions into the cooler reactants. These intermediate products are neglected in the simplified analysis. No explosion was observed with gradient heating even when the hot plate was above the temperature which caused isothermal explosion. This fact is explained on the basis of the strong inhibiting effect which water vapor exhibits toward the hydrogen-oxygen reaction." }, { "name": "Ormsbee, Allen Ives", "degree": "PhD", "year": "1955", "title": "Conical Techniques for Incompressible Non-Viscous Flow", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-12052003-093114", "creators": [ { "name": { "family": "Ormsbee", "given": "Allen Ives" }, "id": "Ormsbee-Allen-Ives", "display_name": "Ormsbee, Allen Ives" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/77MG-6Z64", "abstract": "An analytical investigation was made of incompressible potential flow fields in which the velocity components are homogeneous of order zero. Superpositions of such fields were then made and expressions were derived for the flow fields associated with constant-strength source and vortex sheets of finite extent.\r\n\r\nThe constant strength source-sheets were then applied to the construction of aerodynamic models of thin non-lifting wings of polygonal platform and airfoil section.\r\n\r\nBy use of the constant strength vortex-sheets, several approximate aerodynamic models were constructed for the determination of the pressure distribution on thin lifting wings at small angles of attack." }, { "name": "Scarbrough, Alfred Dale", "degree": "PhD", "year": "1955", "title": "The Use of Junction Transistors in Switching Circuits", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122004-100148", "creators": [ { "name": { "family": "Scarbrough", "given": "Alfred Dale" }, "id": "Scarbrough-Alfred-Dale", "display_name": "Scarbrough, Alfred Dale" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WSS7-8P71", "abstract": "The theory of small signal linear junction transistor amplifiers is extended to develop design techniques which can be applied to the non-linear problems of switching circuit design. Many of these techniques differ materially from the corresponding techniques of vacuum tube amplifier design.\r\n\r\nThe linear theory is oriented toward the study of moderate-gain wide-band amplifiers driving non-inductive loads and being driven from non-inductive sources since switching circuit amplifiers commonly fall into this category, but many of the concepts have application to other amplifiers as well.\r\n\r\nAs outgrowth of the linear theory, the transistor parameters which are important in flip-flop operation are discussed, and a new way to measure these parameters is described.\r\n\r\nThe general theory of flip-flop design is discussed in some details and design data is presented for the most useful of the basic flip-flop circuits. Flip-flops were designed by the method presented here and their measured performance compared with the predicted performance. The generally good agreement between theory and experiment is taken as verification of the usefulness of both the design data and the basic concepts used in the derivation of the design data.\r\n\r\nIt is concluded from this study that junction transistors are practical switching circuit elements, and it is confidently predicted that they will eventually see wide use." }, { "name": "Serdengecti, Sedat", "degree": "PhD", "year": "1955", "title": "Analysis of Optimalizing Control Systems witb Special Reference to Noise Interference Effects", "advisor": "Tsien, Hsue Shen; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12112003-090547", "creators": [ { "name": { "family": "Serdengecti", "given": "Sedat" }, "id": "Serdengecti-Sedat", "display_name": "Serdengecti, Sedat" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/TMXZ-AJ80", "abstract": "The optimalizing control system is designed to search out automatically the optimum state of operation of the controlled system and to confine the operation to a region near this optimum state. The performance of the system is affected by the dynamics of the controlled system and by the noise interference.\r\n\r\nThe dynamic effects of the controlled system on the performance of a peak-holding optimalizing control is analyzed under the assumption that the controlled system dynamics may be represented by a first order input linear group and a first order output linear group. Design charts are constructed for determining the required input drive speed and consequent hunting loss with specified time constants of the input and output linear groups, the hunting period, and the critical indicated difference for input drive reversal.\r\n\r\nThe noise interference effects on the control system performance led to a new type of optimalizing control system which is a modification of the peak-holding optimalizing controller. Performance of the modified optimalizing controller is analyzed and several possible procedures are discussed for detecting and eliminating the incorrect operation modes. A statistical analysis is made to demonstrate the efficiency of a typical detection procedure, namely, the method of filtering through cross-correlation.\r\n\r\nThe modified optimalizing controller can utilize any periodically varying input. An example of this, a sinusoidal input controller, is analyzed to show the dynamic effects of the controlled system and to demonstrate the effect of noise interference on the performance of the modified optimalizing controller." }, { "name": "Skinner, George Tolmie", "degree": "PhD", "year": "1955", "title": "A Time Correlator for Problems in Aerodynamics", "advisor": "Liepmann, Hans Wolfgang; Lagerstrom, Paco A.; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-092906", "creators": [ { "name": { "family": "Skinner", "given": "George Tolmie" }, "id": "Skinner-George-Tolmie", "display_name": "Skinner, George Tolmie" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6B8H-3139", "abstract": "An instrument, of fairly simple design, for measuring time correlation functions of two stationary random electrical signals is discussed. It is intended primarily for use in problems connected with aerodynamically produced acoustic fields, but has suitable properties for application to a rather wide range of aerodynamic problems involving turbulent fields. It has been designed and constructed with a view to economy, and simplicity of operation, and makes extensive use of the general statistical properties of the problems for which it is intended.\r\n\r\nA few experimentally determined auto-correlation functions are given in order to indicate the degree of accuracy achieved, and the Fourier transform of the auto-correlation function of a random input is compared with the power-spectrum of the same function.\r\n\r\nSome practical points of general interest are discussed." }, { "name": "Sutton, George Walter", "degree": "PhD", "year": "1955", "title": "A Study of the Application of Photoelasticity to the Investigation of Stress Waves", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-094948", "creators": [ { "name": { "family": "Sutton", "given": "George Walter" }, "id": "Sutton-George-Walter", "display_name": "Sutton, George Walter" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ZQCE-ZN61", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe object of this investigation is to determine the suitability of photoelasticity for the purpose of quantitatively investigating stress waves in solids. Specifically, procedures for determining the dynamic mechanical and optical properties of a common photoelastic plastic, CR-39, were investigated, as well as the techniques for recording dynamic fringe lines.\r\n\r\nThe dynamic mechanical properties of CR-39 were determined from the frequency and decay of free-free longitudinal vibrations of bars. It was found that CR-39 is a viscoelastic plastic whose wave speed, complex modulus, and damping depends on frequency. The stress-strain relationship for CR-39 was found to be slightly nonlinear.\r\n\r\nThe birefringent properties of CR-39 were determined from impact tests in which the fringe order was detected by a phototube, and strain was measured by means of bonded wire strain gages. The results show that CR-39 has a strain-fringe constant of 3.42 x 10[superscript -4] in/fringe [plus or minus] 3%, which is the same as the static value within experimental error. Thus this constant is independent of the rate of loading. CR-39 is not stress-birefringent, which is the usual law quoted for photoelastic plastics.\r\n\r\nAn approximate theory of longitudinal stress waves in elastic bars is derived, which shows that the Boussinesq theory, if used to calculate the stress-fringe constant from sharp impacts, leads to serious error.\r\n\r\nUsing the Ellis camera, strain wave isochromatics can be photographed at framing rates up to 400, 000 per second. An RCA. 1P21 multiplier phototube was found to be extremely sensitive to optical retardation, by using it to detect the time duration of transient strains caused by cavitation. The tube has a frequency response of at least 18 megacycles." }, { "name": "Wright, William Vale", "degree": "PhD", "year": "1955", "title": "Precipitation Embrittlement Studies in Vacuum Melted Iron-Chromium Alloys", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272004-092755", "creators": [ { "name": { "family": "Wright", "given": "William Vale" }, "id": "Wright-William-Vale", "display_name": "Wright, William Vale" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/007T-MG19", "abstract": "This thesis presents the results of an experimental study on the nature of precipitation embrittlement (475[degrees]C embrittlement) in iron-chromium alloys. Electrical resistance, hardness, tension properties, and microstructure were studied using 19, 25, 34, 42, and 49 per cent chromium-iron vacuum melted alloys.\r\n\r\nPrecipitation embrittlement was found to occur from 450[degrees]C to about 540[degrees]C with the rate of embrittlement increasing with teiriperature. Maximum embrittlement occurs near 500[degrees]C. Increasing the chromium content from 19 to 49 per cent increases the rate and magnitude of precipitation embrittlement. An activation energy of 60,000 cal/mol was established for the process.\r\n\r\nPrecipitation embrittlement was found to be analogous to precipitation hardening in alloys where the formation of a coherent precipitate is responsible for property changes in the alloy. A chromium rich body centered cubic ferrite with slightly larger lattice parameter than the iron rich matrix is proposed as the non-equilibrium coherent precipitate which eventually decomposes to form gross sigma phase." }, { "name": "Yang, Hsun-Tiao", "degree": "PhD", "year": "1955", "title": "Rayleigh's Problem at Lo\\w Mach Number According to the Kinetic Theory of Gases", "advisor": "Lees, Lester", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-105335", "creators": [ { "name": { "family": "Yang", "given": "Hsun-Tiao" }, "id": "Yang-Hsun-Tiao", "display_name": "Yang, Hsun-Tiao" } ], "advisors": [ { "name": { "family": "Lees", "given": "Lester" }, "id": "Lees-L", "role": "advisor", "display_name": "Lees, Lester" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2VK2-FC14", "abstract": "Rayleigh's problem of an infinite flat plate set into uniform motion impulsively in its own plane is studied by using Grad's equations and boundary conditions developed from the kinetic theory of gases. For a heat insulated plate and a small impulsive velocity (low Mach number), only tangential shear stress and velocity and energy (heat) flow parallel to the plate are generated, while the pressure, density, and temperature of the gas remain unchanged. Moreover, no normal velocity, normal stress, or normal energy flow is developed. Near the start of the motion the flow behaves like a \"free-molecule flow\", and all physical quantities are analytic functions of the flow parameters and time. The results obtained for \"large time\", however, add to the growing lack of confidence in the Burnett-type series expansions in powers of mean free path. Although such expansions are obtained here, they are poorly convergent and inappropriate to the problem. To replace these unsatisfactory solutions, approximate closed-form solutions valid for all values of the time are developed, which agree with the free-molecule values for small time and the classical Rayleigh solution for large time. This technique may be useful in studying more general flow problems within the framework of the kinetic theory of gases." }, { "name": "Adamson, Thomas Charles, Jr.", "degree": "PhD", "year": "1954", "title": "Ignition and Combustion in a Laminar Mixing Zone", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-11202003-135437", "creators": [ { "name": { "family": "Adamson", "given": "Thomas Charles, Jr." }, "id": "Adamson-Thomas-Charles", "display_name": "Adamson, Thomas Charles, Jr." } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "chair", "display_name": "Marble, Frank E." }, { "name": { "family": "Bohnenblust", "given": "Henri Frederic" }, "id": "Bohnenblust-H-F", "role": "member", "display_name": "Bohnenblust, Henri Frederic" }, { "name": { "family": "Felberg", "given": "Fredrick H." }, "id": "Felberg-Fredrick-H", "role": "member", "display_name": "Felberg, Fredrick H." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "member", "display_name": "Penner, Stanford S." }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "member", "display_name": "Tsien, Hsue Shen" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q9A7-T088", "abstract": "The equations describing combustion in a flow field are modified for use in laminar flows where the so called boundary layer approximations may be employed. These equations are transformed into a corresponding incompressible flow with the Howarth transformation.
\r\n\r\nAs an example of the use of boundary layer concepts this analysis considers the ignition and combustion in the laminar mixing zone between two parallel moving gas streams. One stream consists of a cool combustible mixture, the second is hot combustion products. The two streams come into contact at a given point and a laminar mixing process follows in which the velocity distribution is modified by viscosity, and the temperature and composition distributions by conduction, diffusion and chemical reaction. The decomposition of the combustible stream is assumed to follow first-order reaction kinetics with temperature dependence according to the Arrhenius law. For a given initial velocity, composition, and temperature distribution, the questions to be answered are: (1) Does the combustible material ignite and (2) How far downstream of the initial contact point does the flame appear and what is the detailed process of development?
\r\n\r\nSince the hot stream is of infinite extent it is found that ignition always takes place at some point of the stream. However when the temperature of the hot stream drops below a certain value, the distance required for ignition increases so enormously that it essentially does not occur in a physical apparatus of finite dimension. The complete development of the laminar flame front is computed using an approximation similar to the von Karman integral technique in boundary layer theory.
\r\n" }, { "name": "Basin, Michael Abram", "degree": "PhD", "year": "1954", "title": "Electric Analog Computer Study of Supersonic Flutter of Elastic Delta Wings", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252003-111202", "creators": [ { "name": { "family": "Basin", "given": "Michael Abram" }, "id": "Basin-Michael-Abram", "display_name": "Basin, Michael Abram" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/FHFK-QR87", "abstract": "This thesis presents a method for the solution of the supersonic flutter problem for elastic delta wings with supersonic leading edges.\r\n\r\nIn Part I, the necessary aerodynamic equations are developed, first in integral form, and then in a power series expansion in order to obtain a practical expression for the pressure at a point on the wing due to the motion of the wing surface in a supersonic air stream.\r\n\r\nPart II gives a method for computing the lifts on a partitioned wing, and sets up cell division criteria. These methods are then applied to a specific wing form.\r\n\r\nParts III and IV present the electrical analogs for the aerodynamic lifts, and for the elastic wing structure respectively. These analogs are then applied to the example of part II.\r\n\r\nPart V presents the results of the actual flutter study performed on the above wing on the California Institute of Technology Electric Analog Computer.\r\n\r\nPart VI contains the conclusions of the study, and recommendations and suggestions for further research." }, { "name": "Berger, Howard Martin", "degree": "PhD", "year": "1954", "title": "A New Approach to the Analysis of Large Deflections of Plates", "advisor": "Williams, Max L.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-163054", "creators": [ { "name": { "family": "Berger", "given": "Howard Martin" }, "id": "Berger-Howard-Martin", "display_name": "Berger, Howard Martin" } ], "advisors": [ { "name": { "family": "Williams", "given": "Max L." }, "id": "Williams-M-L", "role": "advisor", "display_name": "Williams, Max L." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FA0E-1X79", "abstract": "As a result of the assumption that the strain energy due to the second invariant of the middle surface strains can be neglected when deriving the differential equations for a flat plate with large deflections, simplified equations are derived that can be solved readily. Computations using the solution of these simplified equations are carried out for the deflection of uniformly loaded circular and rectangular plates with various boundary conditions. Comparisons are made with available numerical solutions of the exact equations. The deflections found by this approach are then used to obtain the stresses, and the resulting stresses are compared with existing solutions. In all the cases where comparisons could be made, the deflections and stresses agree with the exact solutions within the accuracy required for engineering purposes." }, { "name": "Brooks, Norman Herrick", "degree": "PhD", "year": "1954", "title": "Laboratory Studies of the Mechanics of Streams Flowing over a Movable Bed of Fine Sand", "advisor": "Vanoni, Vito A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152003-113520", "creators": [ { "name": { "family": "Brooks", "given": "Norman Herrick" }, "id": "Brooks-Norman-Herrick", "display_name": "Brooks, Norman Herrick" } ], "advisors": [ { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "advisor", "display_name": "Vanoni, Vito A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/JB2P-1H91", "abstract": "A laboratory study was made of the characteristics of streams flowing over a loose bed of fine sand in order to determine what factors govern the equilibrium rate of transportation of fine sand in suspensions. Twenty-two experimental runs were performed in a 40-foot tilting flume for various conditions with bed sand of two different sizes (0.10 mm and 0.16 mm). Each run represented a uniform open-channel flow in equilibrium with the sand bed.
\r\n\r\nIt was found that more than one equilibrium flow velocity and sediment discharge existed for a given depth, slope, and size of sand because of the extreme variability of channel roughness. At low velocities, the large irregular dunes which formed on the stream bed made the bed friction factor over six times larger than the friction factor for the smooth sand beds obtained at higher flow rates. Thus the transportation rate could not be expressed as a unique function of the bed shear stress, the channel geometry, and properties of the sand as has been supposed in all previous theories for the equilibrium transportation rate of suspended load.
\r\n\r\nBy using the mean velocity and the depth (or the water discharge and sediment discharge) as independent variables, and slope as a dependent variable, an orderly qualitative relationship between the pertinent variables was obtained.
\r\n\r\nBecause of the importance of the dunes in the mechanics of sediment-laden streams, a special study was made of their characteristics and the mechanisms of their formation and movement. The studies also included some theoretical and experimental investigations of the distribution of velocity and suspended sediment within the flow for runs with a smooth bed.
" }, { "name": "Caughey, Thomas Kirk", "degree": "PhD", "year": "1954", "title": "The Existence and Stability of Periodic Motions in Forced Non-Linear Oscillations", "advisor": "Hudson, Donald E.; De Prima, Charles R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04072003-115022", "creators": [ { "name": { "family": "Caughey", "given": "Thomas Kirk" }, "id": "Caughey-Thomas-Kirk", "display_name": "Caughey, Thomas Kirk" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." }, { "name": { "family": "De Prima", "given": "Charles R." }, "id": "De-Prima-C-R", "role": "advisor", "display_name": "De Prima, Charles R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/6MNJ-8N71", "abstract": "A general first order theory is presented for treating forced oscillations in multiple degree of freedom quasi-linear systems. It is shown that under suitable conditions ultraharmonic or subharmonic motion may exist in addition to the harmonic motion which a linearized theory would predict. A general study of the stability of such motions reveals that a sufficient condition for the instability, and consequent jump phenomena, of forced oscillations, is that the amplitude frequency response curves possess a vertical tangent. By considering some fairly general two degree of freedom systems it has been shown that a necessary and sufficient condition for stable forced oscillations in non-linear passive systems is that the amplitude lie outside the region enclosed by the loci of vertical tangency. For systems containing an energy source there is, in addition, a restriction on the magnitude of the non-linear damping force.\r\n\r\nThe general theory has also been applied to ultraharmonic and subharmonic motion in a one degree of freedom system having a cubic non-linearity in the restoring force. It has been shown here also, that a necessary and sufficient condition for stability is that the amplitude of forced oscillation lie outside the region enclosed by the loci of vertical tangency.\r\n\r\nA study of the dependence of the motion on the initial conditions reveals that, while ultraharmonic and harmonic motions are relatively insensitive to the initial conditions, the existence of subharmonic motion can be achieved only for a rather restrictive set of initial conditions." }, { "name": "Dailey, Charles Lee", "degree": "PhD", "year": "1954", "title": "Supersonic Diffuser Instability", "advisor": "Liepmann, Hans Wolfgang; Stewart, Homer Joseph; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102003-101604", "creators": [ { "name": { "family": "Dailey", "given": "Charles Lee" }, "id": "Dailey-Charles-Lee", "display_name": "Dailey, Charles Lee" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/V9XM-W683", "abstract": "Steady operation of supersonic diffusers near critical mass flow is interrupted by a transient process known as buzz. This phenomenon consists of a random sequence of individual relaxation cycles. Mass flow entering the diffuser during steady operation is suddenly cut off by a strong interaction between the subcritical shock and boundary layer on the surface of the external compression generator, which blocks the inlet. Air in the plenum chamber, stored at high pressure, then ?blows down? until the inlet can restart. The subsequent supercritical flow entering the diffuser exceeds the flow rate at the exit and the plenum chamber is re-charged to the original condition.\r\n\r\nA distinction is drawn between this phenomenon and a high frequency wave-type resonance noticed at low mass flows and during an individual buzz cycle after the diffuser shock system has been expelled. For the large diffuser tested here, this high frequency oscillation compares well to the 8th closed-end organ pipe mode of the diffuser at low mass flows and to the 9th mode during the shock-expelled phase of the buzz cycle.\r\n\r\nIt is shown that burning almost always ceases in the presence of buzz. When burning was maintained during buzz, it was found to have no qualitative effect on the buzz cycle." }, { "name": "Diederich, Franklin Wolfgang", "degree": "PhD", "year": "1954", "title": "The Response of an Airplane to Random Atmospheric Disturbances", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12102003-105523", "creators": [ { "name": { "family": "Diederich", "given": "Franklin Wolfgang" }, "id": "Diederich-Franklin-Wolfgang", "display_name": "Diederich, Franklin Wolfgang" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XPKW-QH24", "abstract": "The statistical approach to the gust-loads problem is extended by considering the aerodynamic forces due to the lateral and longitudinal variation of instantaneous gust intensity and using them in dynamic analyses of rigid and flexible airplanes free to move vertically, in pitch, and in roll, based on the assumptions of stationarity of the process (in the statistical sense) and of linearity of the forces involved. The effect on the wing stresses of the interaction of longitudinal, vertical and lateral gusts is considered.\r\n\r\nThe method of analyzing the rigid-body motions is similar to that used for analyses of the dynamic stability of airplanes, in that the equations of motion are referred to stability axes and expressed in terms of conventional stability derivatives. The method of analyzing the dynamic effects of structural flexibility consists of an extension of a numerical-integration approach to the static aeroelastic problem and is in a form which offers the possibility of calculating divergence and flutter speeds with relatively little additional effort.\r\n\r\nThe mean-square values, correlation functions and power spectra of some of the aerodynamic forces required in this type of analysis are calculated for certain special correlation functions of the atmospheric turbulence and certain special lift distributions. It is shown, for instance, that the mean-square lift is substantially reduced due to the difference in instantaneous intensity of the turbulent velocity along the span if the span is relatively large compared to the integral scale of turbulence, but that the mean-square pitching moment is substantially increased if the tail length is relatively large. Also, the wing stresses due to vertical, horizontal and side gusts are shown to be statistically independent under certain conditions." }, { "name": "Ergin, Erdem I.", "degree": "PhD", "year": "1954", "title": "Transient Response of Non-linear Spring-Mass Systems", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-092544", "creators": [ { "name": { "family": "Ergin", "given": "Erdem I." }, "id": "Ergin-Erdem-I", "display_name": "Ergin, Erdem I." } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/0528-K973", "abstract": "The purpose of this thesis is: \r\n\r\n1) To investigate the applicability and to compare the accuracy of existing perturbation methods of non-linear mechanics for the solution of transient response problems, and\r\n\r\n2) To describe a new analytical approximate method for the solution of certain types of non-linear problems involving pulse excitation. This new method combines the advantages of engineering accuracy with ease of applicability.\r\n\r\nIn the course of this study it is found that the solution of homogeneous non-linear equations can be obtained readily and with sufficient accuracy by the perturbation methods of Kryloff and Bogoliuboff or Lindstedt, even for large nonlinearities. Greater accuracy can be attained by the use of the newly developed bi-linear approximation. The advantage of the bi-linear method becomes more pronounced when the step function or the single pulse response of the system is investigated. It is shown that the bi-linear method is the only convenient analytical approximate method available for the solution of general pulse excitation problems involving non-linear spring-mass systems." }, { "name": "Hakkinen, Raimo Jaakko", "degree": "PhD", "year": "1954", "title": "Measurements of Skin Friction in Turbulent Boundary Layers at Transonic Speeds", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12152003-084052", "creators": [ { "name": { "family": "Hakkinen", "given": "Raimo Jaakko" }, "id": "Hakkinen-Raimo Jaakko", "display_name": "Hakkinen, Raimo Jaakko" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WAX3-QV41", "abstract": "The first part of this report describes the design and construction of a floating element skin friction balance. This instrument, which is essentially an improved version of Dhawan's balance, was applied to measurements of local skin friction in the turbulent boundary layer of a smooth flat plate at high subsonic Mach numbers and supersonic Mach numbers up to M = 1.75. The measured skin friction coefficients are consistent with the results of other investigations at subsonic and also at high supersonic speeds. The principal difficulties which exist in comparing skin friction coefficients at various Mach numbers are discussed.\r\n\r\nThe second part of this report describes the application of the Stanton tube technique to skin friction measurements near the base of a shock wave impinging upon a turbulent boundary layer. The floating element technique is inherently difficult to apply for skin friction measurements in non-uniform flow. Hence, a Stanton tube is calibrated by means of a floating element balance in a uniform flow field and then used to measure skin friction near the base of an impinging shock. Oblique shock waves were produced by two wedges of 2.5[degree] and 4.6[degree] semi-angles and a normal shock was generated by a choked channel. Skin friction and velocity profiles were obtained for these three cases at a free stream Mach number of 1.48." }, { "name": "Hlavka, George Elmer", "degree": "PhD", "year": "1954", "title": "An Approximate Theory for Potential Flow Through Cascades of Airfoils", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12162003-153722", "creators": [ { "name": { "family": "Hlavka", "given": "George Elmer" }, "id": "Hlavka-George-Elmer", "display_name": "Hlavka, George Elmer" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Q30C-J875", "abstract": "A new analytic theory is presented for predicting certain characteristics of the plane potential flow through a cascade. The analysis is based on the assumption that the airfoils of the cascade deviate only slightly from straight lines.\r\n\r\nThe theory provides a means for obtaining higher order approximations than have been found heretofore. As a result it has been possible to evaluate the accuracy of existing first-order approximations.\r\n\r\nIn addition the first-order theory has been extended by the addition of a means for obtaining the variation of flow velocity and pressure at the airfoils, and the removal of certain restrictions on angle of attack." }, { "name": "Kaplan, Abner", "degree": "PhD", "year": "1954", "title": "Finite Deflections and Buckling of Slightly Curved Beams and Shallow Spherical Shells under Lateral Loads", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-110343", "creators": [ { "name": { "family": "Kaplan", "given": "Abner" }, "id": "Kaplan-Abner", "display_name": "Kaplan, Abner" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Q1HV-T474", "abstract": "This research consists in the experimental and theoretical investigation of the finite deflection and buckling of two similar structures; the low arch or slightly curved beam and the shallow spherical dome, both subjected to lateral loads. These structures are of interest because the large interaction between bending and axial forces causes their load-deflection behavior to become nonlinear at very low values of the deflection. Due to the wide difference in the methods of solution of these two problems they are separated into two parts, each having its own abstract.
\r\n\r\n[Part I]
\r\n\r\nWhen a low arch (a thin curved beam of small curvature) is subjected to a lateral loading acting toward the center of curvature, the axial thrust induced by the bending of the arch may cause the arch to buckle so that the curvature becomes suddenly reversed. The critical lateral loading depends on the dimensions and rigidity of the arch, the elasticity of the the end fixation, the type of load distribution, and the initial curvature of the arch. A general solution of the problem is given in this paper, using the classical buckling criterion which is based on the stability with respect to infinitesimal displacements about the equilibrium positions.
\r\n\r\nFor a sinusoidal arch under sinusoidal loading, the critical load can be expressed exactly as a simple function of the beam dimension parameters. For other arch shapes and load distributions, approximate values of the critical load can be obtained by summing a few terms of a rapidly converging Fourier series. The effect of initial end thrust and axial and lateral elastic support are discussed.
\r\n\r\nThe buckling load based on the energy criterion of Karman and Tsien is also calculated. The results for both the classical and the energy criteria are compared with experiments made on a series of centrally loaded, pin-ended arches. For larger values of a dimensionless parameter [gamma subscript l], which is proportional to the ratio of the arch rise to the arch thickness, the experimental critical buckling loads agreed quite well with the classical criterion, but, for smaller values of [gamma subscript l], the experimental critical loads were appreciably below those calculated from the classical criterion, although they were always above those obtained from the energy criterion.
\r\n\r\n[Part II] The shallow spherical dome subjected to lateral pressure is a structure for which the deformation departs appreciably from the linear theory at very small values of the deflection amplitude. It is also. one for which the buckling process is characterized by a rapid decrease in the equilibrium load once the buckling load has been surpassed. For structures having this type of buckling characteristic, the question arises as to whether the proper buckling criterion to apply is the classical criterion, which considers equilibrium with respect to infinitesimal displacements or the finite displacement \"energy criterion\" proposed by Tsien.
\r\n\r\nIn this paper the problem of the finite displacement and buckling of a shallow spherical dome is investigated both theoretically and experimentally. In the theoretical approach the nonlinear equations are converted into a sequence of linear equations by expanding all of the variables in powers of the center deflection and then equating the coefficients of equal powers. The basic parameter for the shallow dome is proportional to the ratio of the central height of the dome, h, to its thickness, t. For small values of this ratio the expansions converge rapidly and enough terms are computed to determine the buckling load. For higher values of h/t, convergence deteriorates rapidly and the buckling, load is not computed. However, even for these higher values of h/t the deflection shapes are determined for deflection amplitudes below the amplitude at which buckling occurs. These deflection shapes are characterized by their rapid change as h/t increases and by the fact that, over most of the range of h/t studied, the maximum deflection does not occur at the center of the dome.
\r\n\r\nThe experimental program was carried out on a series of clamped-edge, eight inch base diameter shells, subjected to uniform pressure. The deflection shapes and the buckling loads agreed quite well with the values computed theoretically. It was also found that there was no significant difference between the buckling loads observed using air pressure and those observed using oil pressure. Thus it is concluded that for the shallow domes studied the classical buckling criterion holds rather than the \"energy criterion\" proposed by Tsien.
" }, { "name": "Kaplun, Saul", "degree": "PhD", "year": "1954", "title": "The Role of Coordinate Systems in Boundary Layer Theory", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-111930", "creators": [ { "name": { "family": "Kaplun", "given": "Saul" }, "id": "Kaplun-Saul", "display_name": "Kaplun, Saul" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9QZM-8W36", "abstract": "The boundary layer approximation to a given flow problem is not invariant if different coordinate systems are used in the approximation process. However, a correlation theorem (Theorem 1) is given, which states that the boundary layer solution with respect to any given system can be found, by a simple substitution, from that with respect to any other system. On the basis of this theorem, the dependence of the solution on the choice of coordinates is investigated in detail. The skin friction is invariant, but the flow field is not invariant. At large distances from the wall, the flow field given by boundary layer theory depends almost entirely on the choice of coordinates, rather than on the physical problem.\r\n\r\nThis dependence may be used to obtain a complete matching between the boundary layer solution and the external flow, in the following sense: Theorem 2 states how a coordinate system can be found such that the boundary layer solution with respect to this system is valid as an approximation for the entire flow field. It contains the external flow and the flow due to displacement thickness.\r\n\r\nThe discussion is restricted to steady, two-dimensional, incompressible flow without separation. These restrictions, however, are not essential for many of the results." }, { "name": "Knuth, Eldon Luverne", "degree": "PhD", "year": "1954", "title": "The Mechanics of Film Cooling", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-12032003-112656", "creators": [ { "name": { "family": "Knuth", "given": "Eldon Luverne" }, "id": "Knuth-Eldon-Luverne", "display_name": "Knuth, Eldon Luverne" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G4AT-5P75", "abstract": "Thin liquid wall films flowing under the influence of high-velocity turbulent gas streams were studied for the purpose of obtaining an understanding of the mechanics of film cooling. Conditions which insure liquid-film attachment to solid surfaces without loss of unevaporated liquid to the gas stream when simple radial-hole injectors are used were found; the maximum allowable coolant-flow rate for a stable coolant film was determined (a stable coolant film is obtained when no unevaporated coolant is entrained by the gas stream as the result of interfacial disturbances); and a method for calculating the evaporation rate and the surface temperature for a stable inert coolant film was found." }, { "name": "Korkegi, Robert Hani", "degree": "PhD", "year": "1954", "title": "Transition Studies and Skin Friction Measurements on an Insulated Flat Plate at a Hypersonic Mach Number", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01072004-114554", "creators": [ { "name": { "family": "Korkegi", "given": "Robert Hani" }, "id": "Korkegi-Robert-Hani", "display_name": "Korkegi, Robert Hani" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/X3B9-VW73", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn investigation of transition and skin friction on an insulated flat plate, 5 x 26 inches, was made in the GALCIT 5 x 5 inch Hypersonic Wind Tunnel, Leg No. 1, at a nominal Mach number of 5.8.\r\n\r\nThe phosphorescent lacquer technique was used for transition detection and was found to be in good agreement with total-head rake measurements along the plate surface and pitot boundary layer surveys. It was found that the boundary layer was laminar at Reynolds numbers of at least 5 x 10[superscript 6]. It was also observed that transverse contamination due to the turbulent boundary layer on the tunnel sidewall originated far downstream of the flat plate leading edge at Reynolds numbers of 1.5 to 2 x 10[superscript 6], and spread at a uniform angle of 5 1/2[degrees] compared with 9 1/2[degrees] in low speed flow.\r\n\r\nThe effect of two-dimensional and local disturbances was investigated. The technique of air injection into the boundary layer as a means of stimulating transition was extensively used. It was observed that, although the onset of transition occurred at Reynolds numbers down to 10[superscript 6], a fully developed turbulent boundary layer was not obtained at Reynolds numbers much below 2 x 10[superscript 6] regardless of the amount of air injected.\r\n\r\nA qualitative discussion of these results is given with emphasis on the possibility of a greater stability of the laminar boundary layer in hypersonic flow than at lower speeds.\r\n\r\nDirect skin friction measurements were made by means of the floating element technique incorporating a null system using chain loading, over a range of Reynolds numbers (based on distance from leading edge) from 10[superscript 6] to 4 x 10[superscript 6]. Without artificial tripping, the boundary layer was verified as being laminar over the complete range. With air injection, turbulent shear was obtained only for Reynolds numbers greater than 2 x 10[superscript 6] , this value being in good agreement with earlier results of this investigation. The turbulent skin friction coefficient was found to be approximately 0.40 of that for incompressible flow for a constant value of R[subscript theta], and 0.46 for an effective Reynolds number between 5 and 6 x 10[superscript 6]." }, { "name": "Lampert, Seymour", "degree": "PhD", "year": "1954", "title": "Homogeneous Flow Fields of Degree Greater than Zero", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092004-094836", "creators": [ { "name": { "family": "Lampert", "given": "Seymour" }, "id": "Lampert-Seymour", "display_name": "Lampert, Seymour" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/W215-QX89", "abstract": "Solutions to the Prandtl-Glauert differential equation expressed in terms of polynomial type Lame functions can be applied to the problem of the thin delta wings with subsonic leading edges in a supersonic flow field. It is demonstrated how these functions of different species and degrees of homogeneity may be employed to obtain previously known results for certain lifting cases. For the non-lifting or thickness case which is treated in detail in this paper it is shown that a large class of thickness distributions with blunt leading edges my be obtained by systematically studying the Lame functions of the first species. In particular these functions have been investigated up to, and including, n = 5. It is further shown by the methods of this paper that the prescription of the pressure distribution in problems of this sort is not always sufficient to determine the thickness distribution uniquely." }, { "name": "Loh, Eugene Yu-Cheng", "degree": "PhD", "year": "1954", "title": "Study of the Kinetics of the Order-Disorder Transformation in the Alloy MnNi\u2083", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01082004-103918", "creators": [ { "name": { "family": "Loh", "given": "Eugene Yu-Cheng" }, "id": "Loh-Eugene-Yu-Cheng", "display_name": "Loh, Eugene Yu-Cheng" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/D45V-WR30", "abstract": "MnNi3 is one of many alloys, which, in equilibrium have disordered (random) and ordered atomic arrangements at temperatures above and below the so-called transition temperature respectively.\r\n\r\nSpecimens of MnNi3, previously quenched from a temperature at which the structure is disordered, were heated at different constant temperatures below the transition temperature. The magnetization and resistance of these specimens were measured after different intervals of time at these temperatures for the purpose of obtaining data for a study of the kinetics of the isothermal ordering process.\r\n\r\nThe mechanism of the isothermal ordering process of MnNi3 can be interpreted as first local ordering and then the growth of ordered domains. This mechanism is the same as that qualitatively described by Sykes in 1935 for AuCu3. The mechanism of the local ordering, however, is viewed in the present work as the sharpening of the Gaussian distribution curve of local composition within the alloy.\r\n\r\nPrevious studies on the kinetics of ordering in MnNi3, AuCu, CoPt and AuCu3 are also reviewed and analyzed; and three different types of ordering mechanisms are proposed." }, { "name": "Macmillan, Robert Smith", "degree": "PhD", "year": "1954", "title": "Some Properties of the Ionosphere at Low Radio Frequencies", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-090820", "creators": [ { "name": { "family": "Macmillan", "given": "Robert Smith" }, "id": "Macmillan-Robert-Smith", "display_name": "Macmillan, Robert Smith" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ETPM-E198", "abstract": "Low-frequency ionospheric polarization, relative virtual height, and relative reflection coefficient measurements were made at near vertical incidence during October 1952. These measurements were made at a frequency of 50 kc/s.\r\n\r\nA new, continuous-wave, phase-measuring technique was employed. The essential features of the system are (1) a horizontal transmitting antenna near the surface of the ground which is resonant at the operating frequency and which radiates no ground wave in the direction of the receiver and (2) a receiving station located within line-of-sight of the transmitter at which the phase of the low-frequency sky wave is directly compared with a reference phase transmitted over a very-high-frequency link. The transmitting antenna is considered in detail, and the electronics system is briefly described.\r\n\r\nSome of the general features of the earth's atmosphere and the ionosphere are presented. The magneto-ionic theory is developed, and the propagation of electromagnetic waves in an ionized atmosphere is discussed. This material is presented in order that the 50-kc/s ionospheric data may be properly interpreted. The applicability of the quasi-homogeneous, magneto-ionic theory to low-frequency-propagation problems is considered.\r\n\r\nThe virtual height of the E-layer was found to change by approximately 7.5 km during the sunrise and sunset periods. Rapid fluctuations in the virtual height and reflection coefficients of the E-layer are attributed to (1) strong magneto-ionic splitting, (2) fluctuating ionization gradients in the lower nighttime E-region, (3) interference effects due to the presence of two or more partially reflecting layers (i.e. the fine structure of the E-layer), and (4) interference effects due to the interaction of the two magneto-ionic components. Not all of the polarization results are consistent with the predictions of the quasi-homogeneous, magneto-ionic theory.\r\n\r\nLow-frequency noise measurements were also made during October 1952. The 50-kc/s atmospheric noise field strength reached a maximum value during the middle of the night. The atmospheric noise received in the east-west direction reached a much higher maximum value than that received in the north-south direction." }, { "name": "Mark, Richard Muin", "degree": "PhD", "year": "1954", "title": "Laminar Boundary Layers on Slender Bodies of Revolution in Axial Flow", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-155216", "creators": [ { "name": { "family": "Mark", "given": "Richard Muin" }, "id": "Mark-Richard-Muin", "display_name": "Mark, Richard Muin" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4H6Z-K569", "abstract": "An exact similar solution of the modified boundary layer equations has been obtained for the axial incompressible flow past paraboloids of revolution. It has been shown that the usual boundary layer assumptions are justified and that the local skin friction increases as the boundary layer thickness becomes large compared with the body radius.\r\n\r\nAn approximate method for obtaining the local skin friction on arbitrary slender bodies of revolution in axial incompressible flow has been developed. A comparison of the approximate results with the exact solutions for paraboloids of revolution and circular cylinders shows good agreement.\r\n\r\nThe existence of energy integrals of the modified compressible boundary layer equations is established. Similarity of the governing equations for the axial compressible flow past paraboloids of revolution has been shown; for the same bodies, a hypersonic similarity law is deduced.\r\n\r\nAn approximate method for obtaining the local skin friction on arbitrary slender insulated bodies of revolution in axial compressible flow has been developed. The results show that compressibility counterbalances the rise in local skin friction due to curvature at high Reynolds numbers (based on a characteristic length of the body) and increases the local skin friction at sufficiently low Reynolds numbers.\r\n\r\nVelocity profiles on a slender ogive-cylinder have been obtained experimentally at a Mach number of 5.8 and at different Reynolds numbers. The results indicate a curvature effect when compared with flat plate results." }, { "name": "Marschner, Bernard Walter", "degree": "PhD", "year": "1954", "title": "The Flow over a Body in a Choked Wind Tunnel and in a Sonic Free-Jet", "advisor": "Guderley, Karl Gottfried", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-100833", "creators": [ { "name": { "family": "Marschner", "given": "Bernard Walter" }, "id": "Marschner-Bernard-Walter", "display_name": "Marschner, Bernard Walter" } ], "advisors": [ { "name": { "family": "Guderley", "given": "Karl Gottfried" }, "id": "Guderley-Karl-Gottfried", "role": "advisor", "display_name": "Guderley, Karl Gottfried" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/P4DG-RV54", "abstract": "The pressure distribution over a double wedge airfoil under free flight conditions with Mach number one is compared with the pressure distribution over the same airfoil in a choked closed wind tunnel and in a sonic free-jet.\r\n\r\nThe computation is carried out as a development with respect to a parameter which indicates the deviation from free flight conditions with Mach number one. The results are of interest for the question of wind tunnel wall influences. It is found that the deviatiors of the pressure distribution for a sonic free-jet from the distribution in an infinite air flow are somewhat larger than the deviations in a closed wind tunnel under choked flow conditions. For a specific exam of a wedge of a length of 13% of the tunnel height and a thickness ratio of 10%, the deviation of the pressure distribution does not go much beyond the usual experimental scatter.\r\n\r\nThe results are quite encouraging for the application of closed throat wind tunnels in transonic testing although the axial symmetric case may not show entirely the same desirable behavior." }, { "name": "McCaldin, James Oeland", "degree": "PhD", "year": "1954", "title": "The Influence of Isotopic Mass on Some Physical Properties of Iron", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01152004-100956", "creators": [ { "name": { "family": "McCaldin", "given": "James Oeland" }, "id": "McCaldin-James-Oeland", "display_name": "McCaldin, James Oeland" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/NYAY-8G77", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis presents the results of an experimental study to determine whether atomic mass has an appreciable influence on certain physical properties of metals. Iron was chosen for this investigation, several specimens of natural iron of high purity and two specimens of iron enriched in the isotopes Fe54 and Fe57 being available.\r\n\r\nMeasurements of the temperature coefficients of electric resistance between 67[degrees] and 270[degrees]K indicate an isotopic effect in qualitative agreement with deductions from the Gruneisen theory. The previous results of Tuyn may also be interpreted to give agreement with this theory and therefore are preferred to other previous work in disagreement with the theory.\r\n\r\nNo isotopic influence on thermoelectric power at temperatures between 80[degrees] and 270[degrees]K is found. If such an influence does exist however, it is probably less than 0.5[...]V/[degrees]K for a thermocouple made of Fe54 and Fe57.\r\n\r\nMeasurements of the temperature of the alpha-gamma allotropic transformation do not indicate an isotopic effect on this temperature. A difference of 2.5[degrees]C in the transformation temperatures of the isotopes Fe54 and Fe57 which is suggested by theoretical considerations, cannot be excluded on the basis of the present measurements, however, because of the hysteresis observed in the present study." }, { "name": "Morgan, Merle Loren", "degree": "PhD", "year": "1954", "title": "A Computer for Algebraic Functions of a Complex Variable", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechETD:etd-01232004-135703", "creators": [ { "name": { "family": "Morgan", "given": "Merle Loren" }, "id": "Morgan-Merle-Loren", "display_name": "Morgan, Merle Loren" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/19YT-MN23", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAny rational algebraic function of a complex variable, and certain irrational functions, can be factored in either of the equivalent forms: [...] or [...]. In these expressions, F is a function of the complex variable z; each m represents a positive or negative constant, and the other letters represent complex constants. A theory is developed for computers for such functions, in which voltages proportional to the logarithmic components of each factor are obtained from the electrical potential distributions on a pair of uniform resistive sheets. The electrical summation of the voltages representing the factors then yields readings of the logarithmic components of the function.\r\n\r\nAn actual computer, built to test and demonstrate the theory, is described. This computer accepts information in the form of the magnitude (absolute value, modulus) and the phase (angle, argument, amplitude) of each constant and of z in either of the above expressions, and yields answers in the form of the magnitude and phase of the function F. The computer is useful for applications requiring the evaluation of F at a large number of values of z; it is even more valuable for the inverse problem--that of determining by trial (by root locus tracing) the values of z (the roots) for a given value of F." }, { "name": "Neiswander, Robert South", "degree": "PhD", "year": "1954", "title": "Techniques in Treating Nonlinear Closed-Cycle Systems", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-12042003-111341", "creators": [ { "name": { "family": "Neiswander", "given": "Robert South" }, "id": "Neiswander-Robert-South", "display_name": "Neiswander, Robert South" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8T8F-3S33", "abstract": "The objective of this research is to examine and to develop methods of treating nonlinear closed-cycle, single loop systems. Analytical and graphical methods are immediately rejected for their failure to include the complexities of realistic systems. Experimental techniques as, for example, electrical analog modeling are flexible and can accommodate complicated system descriptions. Associated with such a technique are three important steps: 1) selection of suitable analog elements, 2) arraying or modeling these elements to properly simulate the actual system, and 3) devising an experimental test procedure that produces appropriate insight into the cause and the control of results.\r\n\r\nDesigned for the exploratory testing of nonlinear systems the electronic, logarithm type function generator is a nonlinear element that creates an easily modified function of two or more input variables. Its computing speed is sufficient for oscilloscope monitoring of solutions.\r\n\r\nSystem modeling is the most critical step; as demonstrated by two system examples, the deceptively simple hydraulic servomechanism. and the supersonic diffuser instability.\r\n\r\nBased upon a limited Taylor series approximation of the input function the experimental procedure used to design a realistic servomechanism for best saturated performance is quite simple. It utilizes intentional shaping of the rate feedback function (or the static error). Performance within the systems customarily linear region can be improved by intentional saturation." }, { "name": "Rains, Dean Arthur", "degree": "PhD", "year": "1954", "title": "Tip Clearance Flows in Axial Compressors and Pumps", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-04152003-112816", "creators": [ { "name": { "family": "Rains", "given": "Dean Arthur" }, "id": "Rains-Dean-Arthur", "display_name": "Rains, Dean Arthur" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/MR84-WZ87", "abstract": "Flow in the clearance at the rotor blade tips of axial flow compressors and pumps was studied experimentally and theoretically with particular attention to losses. It is shown that losses due to blade tip clearances can be evaluated in a simple manner for high efficiency turbomachines. A vortex sheet formed by the clearance flow was found to roll up into a vortex of such strength that cavitation in axial flow pumps begins in the vortex rather than on the blade surface." }, { "name": "Shennum, Robert Herman", "degree": "PhD", "year": "1954", "title": "The Dielectric Recovery of Parallel Arcs", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-092252", "creators": [ { "name": { "family": "Shennum", "given": "Robert Herman" }, "id": "Shennum-Robert-Herman", "display_name": "Shennum, Robert Herman" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/G0V3-BW26", "abstract": "A study of the factors which influence the stability of simultaneous, distributed arcs on power lines is reported. The types of arcs studied were through air between iron electrodes, flashover along a wood-air boundary between copper electrodes and arcs confined in expulsion-tube lightning arrestors.\r\n\r\nVariations of line geometry influence line characteristic impedance, series and shunt impedances and equivalent length. The studies indicate that of these factors, only the series impedance between the simultaneous arcs is important unless the line length separating the two arcs is very short.\r\n\r\nThe analysis illustrates that it is possible to calculate approximate critical spacing of a test gap in terms of the geometry and material of arc electrodes and the potential at the gap. This potential was shown to depend upon both the power frequency conduction characteristics of the remainder of the circuit and upon the nature of the surge initiating the arc. The relative importance of these two factors was estimated.\r\n\r\nThe studies show that it is possible for arcs to rob one another after they have been independently initiated on power distribution systems. Consequently, with appropriate placement of lightning arrestors it is possible to protect a system so that even though a direct stroke of lightning may initiate an arc at a location remote from the arrestors, the arrestors can still rob the open arc of current and hence extinguish it." }, { "name": "Stallkamp, John Albert", "degree": "PhD", "year": "1954", "title": "Hydrodynamic Forces on Prolate Ellipsoidal Bodies", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122003-093537", "creators": [ { "name": { "family": "Stallkamp", "given": "John Albert" }, "id": "Stallkamp-John-Albert", "display_name": "Stallkamp, John Albert" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/D5TA-HR09", "abstract": "The hydrodynamic forces and moment on submerged bodies of prolate ellipsoidal shape are investigated for two dimensional motion. The specific motion consisted of constant relative linear velocity of the fluid and body and small angular oscillation of the body about its geometric center. The average position of the long axis of the body was in the direction of constant linear motion. The components of the lateral force and of the moment proportional to angular position, velocity, and acceleration are measured for motion in water. These reactions are compared with the reactions derived from perfect fluid theory. It is concluded that the force proportional to angular position is the principal real fluid reaction not predicted by the perfect fluid theory. The deviations of the other components from the theoretical values are small." }, { "name": "Upthegrove, Harry Nelson", "degree": "PhD", "year": "1954", "title": "An Investigation of the Influence of Fuselage Elasticity on the Pitching Motion of a Controlled Missile", "advisor": "McCann, Gilbert Donald; Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-104429", "creators": [ { "name": { "family": "Upthegrove", "given": "Harry Nelson" }, "id": "Upthegrove-Harry-Nelson", "display_name": "Upthegrove, Harry Nelson" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/B4FA-2254", "abstract": "This thesis describes an investigation of the effects of elastic deformation on the performance of a guided missile type of aircraft. An imaginary typical missile is selected, and an electric model is devised to represent the missile with its associated aerodynamic forces and control functions. The results of measurements on this model are presented in the form of oscillographs, and their significance is discussed.\r\n\r\nIt is determined that elasticity effects can rarely be ignored, and that improvement in missile and control system performance will probably require more rather than less consideration of elastic deformation of the aircraft structure." }, { "name": "Valluri, Sitaram Rao", "degree": "PhD", "year": "1954", "title": "Some Studies in the Fundamental Parameters of Fatigue", "advisor": "Sechler, Ernest Edwin; Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-01292004-104442", "creators": [ { "name": { "family": "Valluri", "given": "Sitaram Rao" }, "id": "Valluri-Sitaram-Rao", "display_name": "Valluri, Sitaram Rao" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/5Y4Z-CW45", "abstract": "A torsional fatigue testing machine of the resonant vibrator type has been designed in order to investigate the fatigue and internal friction properties of 3S-O aluminum. This machine uses an elastic restraint on an a-c motor to create resonant conditions and uses a photocell electronic system for the measurement of internal friction by the method of measuring the logarithmic decrement of free oscillations.\r\n\r\nIt has been established that for 3S-O aluminum at torsion stress levels below 112 psi, the stress history does not affect damping and that, for an annealed specimen, the material exhibits a maximum value of internal friction at 375[degrees]F. \"Temporary mobility\" aspects of the slip bands have been investigated and in addition, variation of internal friction as a function of stress amplitude in repeated torsional loading, temperature, and number of reversals has been obtained. At room temperature (75[degrees]F) the internal friction increases with the number of stress reversals in the 0 to 10[superscript 5] range. This increment in general increases with increasing amplitude of stress. At test temperatures of 225[degrees] and 525[degrees]F it was found that this increment does not show any regular variation with stress. In addition, however, it was found that at 375[degrees]F the internal friction decreases with stress reversals in the 0 to 10[superscript 5] range for all stresses. The variation of internal friction with stress history after a large number of stress reversals of the order 10[superscript 6] cycles, is quite complex, giving rise to random patterns of increase and decrease.\r\n\r\nThis work is exploratory in nature and suggestions for further work are indicated." }, { "name": "Vrebalovich, Thomas", "degree": "PhD", "year": "1954", "title": "The Development of Direct and Alternating Current Glow Discharge Anemometers for the Study of Turbulence Phenomena in Supersonic Flow", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222004-111758", "creators": [ { "name": { "family": "Vrebalovich", "given": "Thomas" }, "id": "Vrebalovich-Thomas", "display_name": "Vrebalovich, Thomas" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/95XT-RN93", "abstract": "A direct current glow discharge anemometer (D.C. glow) was designed and constructed. This instrument was calibrated in low speed flow. Shock tube experiments with the D.C. glow indicated that its frequency response was greater than 50 kc. However, the shortcomings of the D.C. glow such as sputtering and asymmetric burning properties of the discharge became apparent. Therefore, a 700 kc. alternating current (A.C.) glow was designed and constructed. The time stability properties of this instrument were found to be much better than those of the D.C. glow. Since no frequency compensation circuits were used with the A.C. glow, the signal to noise ratio was much higher than that of a hot wire. This A.C. glow was used to survey the profile of the fluctuations in a turbulent boundary layer in supersonic flow at Mach numbers between 1.3 and 4. Power spectrum measurements of the fluctuations in this boundary layer were also made with the A.C. glow. These measurements indicated that there was energy in the spectrum above 100 kc. Finally, measurements of frequencies in excess of 100 kc. were made by the A.C. glow in a sound field produced by a source of single frequency ultrasonic sound waves in supersonic flow." }, { "name": "Willmarth, William Walter", "degree": "PhD", "year": "1954", "title": "The Lift of Thin Airfoils at High-Subsonic Speeds", "advisor": "Liepmann, Hans Wolfgang; Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01222004-114509", "creators": [ { "name": { "family": "Willmarth", "given": "William Walter" }, "id": "Willmarth-William-Walter", "display_name": "Willmarth, William Walter" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DFFC-8041", "abstract": "Experimental results are presented for the lift characteristics of thin, two-dimensional airfoils at high-subsonic speeds and small angles of attack. Symmetrical airfoils with different locations of maximum thickness were investigated using a surface pressure probe technique which should find use in other applications.\r\n\r\nThe flow fields over each airfoil are discussed and the quantitative results for the lift and location of the center of lift are compared with theory whenever possible. The effects of flow separation caused by boundary-layer shock-wave interaction are noted and discussed. In particular, the possibility of the forced oscillation of control surfaces due to boundary layer separation is mentioned." }, { "name": "Wohlwill, Hans Emil", "degree": "PhD", "year": "1954", "title": "A Resonant Cavity Method of Measuring the Velocity of Light", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechETD:etd-01272004-090208", "creators": [ { "name": { "family": "Wohlwill", "given": "Hans Emil" }, "id": "Wohlwill-Hans-Emil", "display_name": "Wohlwill, Hans Emil" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9JQK-Y835", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA contribution to the precision measurement of the velocity of light is described. The experiment makes use of a circular cylindrical cavity operating in the [...] mode and resonant in the 3 centimeter region. For a particular length-to-diameter ratio the resonance frequency is only a function of the cavity volume and the velocity of propagation of electromagnetic waves. The latter can be calculated from an experimental determination of resonance frequency and cavity volume.\r\n\r\nThe object of this experiment was to attain an accuracy of one part in 150,000 for each individual determination. The resonant frequency was measured with a precision of one part in a million; the precision of the volume measurement was one part in 180,000. The corrections applying to both of these measurements can be calculated with sufficient accuracy to correspond to the above figures. Unfortunately, however, a time limit prevented a proper experimental determination of one correction; this concerns the shift in resonant frequency due to the iris coupling between the input wave guide and the cavity. It would be difficult to assign a numerical value to the uncertainty introduced by the lack of this information, but a minimum value for the velocity of light can be obtained.\r\n\r\nThe experiments led to a probable result of 299,809 km/sec, measured with a precision of [plus or minus]1 km/sec. The extreme value of the uncertainty in the iris correction corresponds to -19 km/sec, indicating a minimum value of 299,790 km/sec.\r\n\r\nThis is to be compared to the best two recent determinations whose results are 299,789 km/sec and 299,793 km/sec." }, { "name": "Yoler, Yusuf Amon", "degree": "PhD", "year": "1954", "title": "The Hypersonic Shock Tube", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02112004-115540", "creators": [ { "name": { "family": "Yoler", "given": "Yusuf Amon" }, "id": "Yoler-Yusuf-Amon", "display_name": "Yoler, Yusuf Amon" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/853G-K555", "abstract": "The feasibility of using a shock tube for quantitative investigations of hypersonic flow phenomena at temperatures simulating free flight conditions is studied theoretically and experimentally. In the theoretical part, various aspects of the hypersonic shock tube problem are treated in logical order. Methods of producing high Mach numbers, limitations on the test section Mach number, methods of generating strong shock waves, flows with variable specific heats and dissociation, types of problems amenable to study with the hypersonic shock tube are discussed.\r\n\r\nTo verify and supplement some of the theoretical results, a shock tube of a somewhat unconventional design has been built. The bulk of the experimental investigations undertaken to date have dealt with pressure studies using piezoelectric gages, and schlieren studies of the flow, The results obtained so far with flow Mach numbers in excess of six, stagnation temperatures up to 9000[degrees]R and stagnation pressures up to 200 psi, have not only contributed to a much greater understanding of this relatively new field of application of the shock tube, but have indicated a well defined course along Which future investigations will continue." }, { "name": "Zukoski, Edward Edom", "degree": "PhD", "year": "1954", "title": "Flame Stabilization on Bluff Bodies at Low and Intermediate Reynolds Numbers", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01142004-105717", "creators": [ { "name": { "family": "Zukoski", "given": "Edward Edom" }, "id": "Zukoski-Edward-Edom", "display_name": "Zukoski, Edward Edom" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E9V0-GM76", "abstract": "The problem of attaining stable combustion in ramjet power plants and in afterburners of turbojet engines has led to rather extensive studies of the processes involved in stabilizing flames on bluff bodies. One of the results of these studies was to indicate that the flame stabilization mechanism changes significantly at low Reynolds Numbers; the velocity at which flames may be stabilized drops abruptly as the Reynolds Number is decreased, and the mixture ratio for which maximum velocity of flame holding occurs shifts markedly from the stoichiometric value.\r\n\r\nThis abrupt change in the mechanism of flame stabilization is investigated through photographic studies of the flame front near the flame holder. A transition from a laminar to a turbulent surface of the flame front immediately downstream from the flame holder is shown to account for the change in flame stabilization characteristics. This transition was found to occur independently of fuel type and flame holder geometry.\r\n\r\nThe behavior of the low Reynolds Number stabilization limits is attributed to a diffusion process; in particular, the shift found for the mixture ratio corresponding to the maximum blowoff velocity is explained on the basis of the difference in the diffusion rate of fuel and oxygen. Detailed experiments including blowoff results, chemical analysis of gas taken from the flame holder wake, and measurements of wake temperatures are shown to confirm the suggested diffusion mechanism.\r\n\r\nOnce the transition phenomenon is appreciated, re-examination of high Reynolds Number blowoff data is found possible. The results of previous experiments are found to show that the blowoff velocity depends on the square root of the characteristic dimension if the transition Reynolds Number is exceeded and if the flame holder is a bluff body of small fineness ratio." }, { "name": "Anderson, Jack Steele", "degree": "PhD", "year": "1953", "title": "An Analysis of Servomechanisms Containing a Dependent Variable Nonlinearity", "advisor": "McCann, Gilbert Donald; Pickering, William Hayward; Wilts, Charles H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04212003-105744", "creators": [ { "name": { "family": "Anderson", "given": "Jack Steele" }, "id": "Anderson-Jack-Steele", "display_name": "Anderson, Jack Steele" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" }, { "name": { "family": "Wilts", "given": "Charles H." }, "id": "Wilts-C-H", "role": "advisor", "display_name": "Wilts, Charles H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/SQ9A-3G13", "abstract": "A method is developed for obtaining the transient response of an automatic control system containing a nonlinearity in which one dependent variable may be expressed as a unique function of another variable. This method involves obtaining a mathematical expression for the nonlinear characteristic by an expansion in Legendre polynomials, introducing this expression into the equations describing the control system behavior thus obtaining a nonlinear equation in a power series of a dependent variable and solving this nonlinear equation by means of an assumed infinite series solution technique. The rules governing application of the method are discussed.\r\n\r\nA saturation type nonlinearity is used to illustrate the application of the method. A second order system is employed to illustrate the accuracy of the method and to present a numerical technique for solving the series of equations arising from the infinite series method of solving the nonlinear system equation. The stability of a fourth order missile control equation with a saturation limit on the control surface is investigated by the method.\r\n" }, { "name": "Anderson, Roger Alan", "degree": "PhD", "year": "1953", "title": "Transient Response of Uniform Beams", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04212003-111122", "creators": [ { "name": { "family": "Anderson", "given": "Roger Alan" }, "id": "Anderson-Roger-Alan", "display_name": "Anderson, Roger Alan" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/ZVM1-7T63", "abstract": "Several special topics relating to the transient flexural vibrations of a uniform beam predicted by the usual elementary or Bernoulli-Euler equation are discussed. The effect on the beam response of the concentration of an applied transient force in space and in time is studied. In the case of an applied step force, it is shown that the dynamic team response can be larger than twice the response to an equal force statically applied. It is demonstrated that the beam response in the higher modes is independent of the boundary conditions.\r\n\r\nA new, general series solution of the mode superposition type is given for the flexural vibrations of a uniform beam according to the more refined Timoshenko equations including the secondary effects of shear deflections and rotatory inertia. As a special case, the solution is presented for a pin-ended beam. These solutions are characterized by two series, each of the form of the series solution of the Bernoulli-Euler equation.\r\n\r\nFor the special case of a concentrated transient force applied at the midpoint of a pin-ended beam, the bending moment and shear force solutions for the Timoshenko and Bernoulli-Euler equations are compared.\r\n" }, { "name": "Chuan, Raymond Lu-Po", "degree": "PhD", "year": "1953", "title": "The Development and Utilization of Some Equipment for Low Reynolds Number Supersonic Flow Research", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-04292003-103202", "creators": [ { "name": { "family": "Chuan", "given": "Raymond Lu-Po" }, "id": "Chuan-Raymond-Lu-Po", "display_name": "Chuan, Raymond Lu-Po" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/B6T3-QB91", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA low Reynolds number supersonic wind tunnel is a useful tool for the investigation of viscous effects in a high-speed flow. In order to avoid some of the difficulties inherent in a conventional wind tunnel system when operating at low Reynolds numbers, a two-phase cycle is proposed. By examining the thermodynamics of the wind tunnel the relative merits of two methods of operation -- the one-phase cycle and the two-phase cycle -- are compared, indicating certain advantages the two-phase cycle possesses over the conventional one-phase cycle when the tunnel is operated at high-speed and low Reynolds number. The design, construction and operation of a small (about 5 cm.[superscript 2] test section area) supersonic (M[.....]2) wind tunnel using a two-phase cycle with water (in liquid and vapor phases) as the working medium are described.\r\n\r\nDifficulties in pressure measurement and flow visualization, due to the nature of the working medium and the low density of the flow, are encountered. Means of meeting these difficulties are proposed, including a critical analysis of the schlieren technique, from which is evolved a workable arrangement for visualizing the low Reynolds number flow.\r\n\r\nAs an example of the possible utilizations of the tunnel, the curvature, due to viscosity, of the attached shock wave on a wedge in uniform supersonic flow is investigated, using schlieren photography. The effective shape of the wedge is deduced from the shape of the shock wave, and is compared to theory with satisfactory qualitative agreement." }, { "name": "Coles, Donald Earl", "degree": "PhD", "year": "1953", "title": "Measurements in the Boundary Layer on a Smooth Flat Plate in Supersonic Flow", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092003-180051", "creators": [ { "name": { "family": "Coles", "given": "Donald Earl" }, "id": "Coles-Donald-Earl", "display_name": "Coles, Donald Earl" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0DDW-9S38", "abstract": "In Section I available measurements in low-speed turbulent boundary layer flow are compared with a simple analysis based on functional similarity, and the boundary layer is found to be unique within the accuracy of the experimental data. Some consequences of the mean equations of motion are obtained, including the distribution of shearing stress through the boundary layer, and an attempt is made to generalize the relationship known as the law of the wall to flows with variable density.
\r\n\r\nIn Section II some problems encountered in the development and use of the floating surface element and other instrumentation are discussed in detail.
\r\n\r\nIn Section III are presented measurements of mean and local surface friction carried out on a flat plate model in the 20-inch supersonic wind tunnel at the Jet Propulsion Laboratory. The boundary layer flow is studied for free stream Mach numbers of 2.0, 2.6, 3.7, and 4.5. The experiments, which involve nominal Reynolds numbers from 2 x 105 to 9 x 106, include a few measurements in laminar flow, but emphasize transition and the turbulent regime. The effectiveness of various tripping devices is mentioned, and the problem of defining an effective Reynolds number for the fully turbulent flow is discussed at length. Finally, turbulent boundary layer profile measurements are examined for consistency with low-speed data, with a generalized mixing length theory, and with the analysis of Section I of the present report.
" }, { "name": "DeLauer, Richard Daniel", "degree": "PhD", "year": "1953", "title": "Experimental Heat Transfer at Hypersonic Mach Number", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04222003-111626", "creators": [ { "name": { "family": "DeLauer", "given": "Richard Daniel" }, "id": "DeLauer-Richard-Daniel", "display_name": "DeLauer, Richard Daniel" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/59SJ-TR03", "abstract": "An experimental investigation was conducted in Leg 1 of the GALCIT 5 x 5 inch Hypersonic Wind Tunnel to determine the heat transfer coefficients of the laminar boundary layer on a cooled flat plate at a nominal Mach number of 5.8. As a consequence of the investigation, flat plate recovery factors were determined and the effect of condensation on heat transfer was noted. In addition qualitative results as to the laminar boundary layer transition and separation are also presented.
\r\n\r\nThe tests were conducted with a ratio of wall temperature to free stream temperature (Tw/T\u03b4) of approximately 6.2; but under stagnation temperature conditions ranging from 200\u00b0F to 285\u00b0F. The stagnation pressure range of 60 psia to 115.5 psia provided a maximum Reynolds number of 2.1 x 106.
\r\n\r\nA flat plate temperature recovery factor of .858 \u00b1 .004 was determined, and it was concluded that the temperature recovery factor range of Mach number independence could be extended to a Mach number of 5.8. The independence of the recovery factor on Reynolds number up to the beginning of the laminar boundary layer transition was also substantiated.
\r\n\r\nThe heat transfer coefficients were obtained for a negative temperature gradient over a considerable portion of the plate. The effect of these gradients produced values considerably higher than would be expected for an isothermal surface. These results, when related the constant temperature case by a theoretical calculation, were in good agreement, with the theoretical results and the results of a friction investigation carried out at the same Mach number. The accuracy of the results was estimated to be \u00b110% from a value of Nu/Re1/2Pr1/3 - .285.
\r\n \r\nThere was no apparent effect on the heat transfer coefficient by condensation, but the adiabatic wall temperature appeared to be 2% lower than for the condensation free flow. Due to a step increase in thickness of the model at the ten inch station, the shock wave-boundary layer interaction appears to produce laminar boundary layer transition at a Reynolds number of 1.3 x 106, and upon reducing the Reynolds number further, the transition point is subjected to an adverse pressure gradient which results in a boundary layer separation.
" }, { "name": "Delson, Jerome King", "degree": "PhD", "year": "1953", "title": "Networks Involving Ideal Transformers", "advisor": "MacNeal, Richard H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04222003-140332", "creators": [ { "name": { "family": "Delson", "given": "Jerome King" }, "id": "Delson-Jerome-King", "display_name": "Delson, Jerome King" } ], "advisors": [ { "name": { "family": "MacNeal", "given": "Richard H." }, "id": "MacNeal-R-H", "role": "advisor", "display_name": "MacNeal, Richard H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JY4D-QP61", "abstract": "The concept of the ideal transformer is presented in terms of flux relations contrasting a non-ideal transformer, which may be represented by an impedance matrix, to an ideal transformer which may not. The interchangeability of the considerations of a transformer, first, as a constraint on the currents (a \"multiwinding\" transformer) and, second, as a constraint on the voltages (a \"multilimb\" transformer) is formulated. Mesh and nodal analysis is extended to include networks involving ideal transformers by the use of Lagrange multipliers. These multipliers are eliminated from the equations by a procedure, in terms of compound matrices, that is facilitated by reduction of the transformers to a standard form. The procedure is also interpreted as a set of rules such that the mesh and nodal equations of a general network can be written by inspection. The possible degeneracies in network equations are considered, and a \"scattering matrix\" procedure presented to cover these cases. The orientation of the branches in a dual network is analyzed and the dual of an ideal transformer is given. The duality concept in electrical networks is considered in terms of matrices that describe the sets of branches belonging to the various meshes (connection matrix) and belonging to the various node-pairs (branch, node-pair matrix). Using the extension of the duality principle to nonplanar networks, a procedure is presented for drawing a network diagram from its connection matrix. As an application, a general procedure is given for finding the electrical analog of a mechanical structure. Also, the role of gyrators and network duality is mentioned. The problem of minimizing the number of transformers in a network is approached by a circuit reduction technique. Networks uniformly dependent on frequency are first synthesized by Cause's technique. The conditions are derived for then eliminating the transformers from this circuit, one by one, for the particular case of a network with three grounded terminal-pairs." }, { "name": "Duesterhoeft, William Charles", "degree": "PhD", "year": "1953", "title": "Temperature Measurements of Large Power Arcs and the Relation of Temperature to Dielectric Recovery", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-095829", "creators": [ { "name": { "family": "Duesterhoeft", "given": "William Charles" }, "id": "Duesterhoeft-William-Charles", "display_name": "Duesterhoeft, William Charles" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/XRPC-8159", "abstract": "A study of the basic mechanisms of dielectric recovery of power frequency arcs in air is reported. The particular arc studied is that of a standard 6 inch rod gap conducting 300 or 800 amperes crest for 1/2 cycle of a 60 cycle per second current.\r\n\r\nThe temperature of the arc space and the variation of the arc temperature with time are measured. The temperature is measured by spectrographic and velocity of sound techniques. The temperature at current zero is 5000 degrees Kelvin. The temperature is 720 degrees K. 77 milliseconds after current zero and 415 degrees K. 196 milliseconds after current zero.\r\n\r\nThe temperature is correlated to the dielectric strength during the recovery period. During the recovery period the arc space is at atmospheric pressure. The gas density is reduced due to the high temperatures existing in the arc space. Evidence is given that the low gas density is reduced due to the high temperatures existing in the arc space. Evidence is given that the low gas density is the major factor causing the reduced dielectric strength.\r\n\r\nResidual ions in the arc space also contribute to reducing the dielectric strength. A criterion for recovery breakdown is given including the effect of the residual ions. The ion density after current zero decreases due to electron recombination with a recombination coefficient [alpha] = 2.0 x 10[superscript -9] cubic centimeter per ion-second. The loss of ions by diffusion appears negligible." }, { "name": "Eimer, Manfred", "degree": "PhD", "year": "1953", "title": "Direct Measurement of Laminar Skin Friction at Hypersonic Speeds", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04292003-112020", "creators": [ { "name": { "family": "Eimer", "given": "Manfred" }, "id": "Eimer-Manfred", "display_name": "Eimer, Manfred" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "role": "member", "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MK2E-1P76", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA direct measurement of flat plate laminar local skin friction was undertaken at M = 5.8 in the GALCIT Hypersonic Wind Tunnel, Leg No. 1. A new balance particularly suited to the requirements of hypersonic experimentation was designed.\r\n\r\nBy means of the fluorescent lacquer technique for indicating boundary layer transition, unexpectedly high natural transition Reynolds numbers were observed. The several methods of forcing transition which were used were unsuccessful in producing transition at a Reynolds number of two million.\r\n\r\nObservation of the leading edge shock wave and boundary layer by means of a schlieren system indicated that at M = 5.8 the shock wave and boundary layer are separated by appreciable distances wherever the boundary layer equations hold.\r\n \r\nSkin friction force measurements were made at five Reynolds numbers in condensation-free flow. The discrepancies between the observed low values of C[subscript f][...]Re and existing laminar boundary layer calculations are reconciled by means of a qualitative analysis.\r\n\r\nA theory describing the properties of the viscous boundary layer for flows with condensation in the free stream is presented. It is predicted that for a specified nozzle geometry and stagnation temperature, skin friction remains unchanged in the presence of moderate amounts of condensation, while heat transfer for a given wall temperature is affected by the presence of condensation which produces major changes in the adiabatic wall temperature." }, { "name": "Ellion, Max Edmund", "degree": "PhD", "year": "1953", "title": "A Study of the Mechanism of Boiling Heat Transfer", "advisor": "Sabersky, Rolf H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232003-095944", "creators": [ { "name": { "family": "Ellion", "given": "Max Edmund" }, "id": "Ellion-Max-Edmund", "display_name": "Ellion, Max Edmund" } ], "advisors": [ { "name": { "family": "Sabersky", "given": "Rolf H." }, "id": "Sabersky-R-H", "role": "advisor", "display_name": "Sabersky, Rolf H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/9KF8-S513", "abstract": "Part I. An Experimental Study of Partial and Complete Film Boiling with Forced Convection.
\r\n\r\nAn apparatus was developed to investigate the regions of peak heat flux, partial film boiling, and complete film boiling. High-speed motion pictures and experimental data were taken to study the effects of liquid velocity, pressure, and temperature on the boiling heat transfer in subcooled-distilled-degassed water. The motion pictures showed the types of vapor formation which occur in each of the three regions and indicated that the heat transfer at the transition from nucleate boiling to partial film boiling was about 90 per cent of the peak heat flux.
\r\n\r\nPart II. A Detailed Photographic Study of Nucleate Pool Boiling.
\r\n\r\nThe dynamics of nucleate bubbles in aerated and degassed liquids was studied by means of high-speed motion picture cameras. A mechanism is proposed for the growth and collapse of nucleate bubbles which successfully predicts the effects of liquid properties and conditions on bubble dynamics.
\r\n\r\nThe liquids chosen for this study were distilled water and carbon tetrachloride because of their widely different physical properties. The influence of surface tension on the bubble dynamics was investigated separately by adding a surface-tension depressor to the water. For a range of liquid temperature experimental data are presented including the size and lifetime of the bubbles as well as the peak heat flux values.
" }, { "name": "Ellis, Albert Tromly", "degree": "PhD", "year": "1953", "title": "Observations on Cavitation Bubble Collapse", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142003-140023", "creators": [ { "name": { "family": "Ellis", "given": "Albert Tromly" }, "id": "Ellis-Albert-Tromly", "display_name": "Ellis, Albert Tromly" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/EWJ4-R705", "abstract": "Experimental observations are made on collapsing cavitation bubbles. Bubbles generated by two different methods are studied. The first method consists of bubble generation and collapse by flow over a submerged body. This work is done in the High-Speed Water Tunnel of the Hydrodynamics Laboratory. Existing photographic equipment and experimental techniques are employed. The second method consists of bubble generation and collapse by variation of the hydrostatic pressure. Much improved time and space resolution of the collapse is obtained in the latter case by design and construction of a high-speed photographic system. Bubble collapse pictures are taken at 105 frames per sec and an effective exposure time of 5 x 10-8 sec. A magnification of eight diameters from object to image is attained. This equipment reveals new details of cavitation bubble collapse.
\r\n\r\nNumerical solutions of the spherical bubble collapse equations are compared with experimental results. A consistently longer collapse time is observed in all cases. Observed bubble asymmetries are shown to be caused by pressure gradients. A large degree of coupling is shown to exist between the radial motion and the translational motion of the bubble centroid. Bubble collapse is observed to be much less stable than bubble growth.
" }, { "name": "Holmquist, Carl Oreal", "degree": "PhD", "year": "1953", "title": "An Approximate Method of Calculating Three-Dimensional Compressible Flow in Axial Turbomachines", "advisor": "Rannie, W. Duncan; Tsien, Hsue Shen; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232003-115022", "creators": [ { "name": { "family": "Holmquist", "given": "Carl Oreal" }, "id": "Holmquist-Carl-Oreal", "display_name": "Holmquist, Carl Oreal" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3FB2-G132", "abstract": "The two principal existing methods of calculating axially-symmetric compressible flow in turbomachines are: (1) a simplified one-dimensional analysis, and (2) numerical methods using the complete or linearized flow equations. The first is not satisfactory for multi-stage turbines with appreciable wall divergence; the second is very tedious and time consuming. The purpose of this investigation is to extend the approximate methods, successfully used in calculating incompressible flow in compressors with constant blade height, to the analysis of compressible flow in turbomachines with variable blade height. Assuming that the blades can be completely defined by the exit flow angle, and neglecting the influence of downstream blades, the analysis is made considering the flow between successive blade rows only. With these restrictions, subsonic and isentropic supersonic flow patterns can be determined for arbitrary boundary shapes as long as separation does not occur. Average losses can be accounted for by the use of a polytropic law, and the effect of radial variations in stagnation temperature can be included without difficulty. Examples illustrating the flexibility and practical value of the iteration method, and the rapid convergence of successive solutions are given." }, { "name": "Howard, Robert Charles", "degree": "PhD", "year": "1953", "title": "A Special Purpose Electric Analog Computer and its Application to the Solution of Certain Nonlinear Differential Equations", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechETD:etd-05062003-110154", "creators": [ { "name": { "family": "Howard", "given": "Robert Charles" }, "id": "Howard-Robert-Charles", "display_name": "Howard, Robert Charles" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Y018-YQ64", "abstract": "This thesis consists of three parts. (1) An analog computer investigation was made of certain phenomena that can be found among the solutions of a simple nonlinear differential equation. (2) An arbitrary function generator and associated equipment were developed to be used in the solution of more difficult nonlinear equations such as those representing nonlinear servomechanisms. This function generator operates on the logarithmic principle and can be likened to an electronic slide rule. (3) The operation of the function generator was demonstrated by forming a nonlinear computer using the generator and other active and passive circuit elements. This computer was used to investigate the solutions to several modifications of Van der Pol's equation." }, { "name": "Iura, Toru", "degree": "PhD", "year": "1953", "title": "Experimental Investigations of Stall Propagation in Axial-Flow Compressors", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092003-181816", "creators": [ { "name": { "family": "Iura", "given": "Toru" }, "id": "Iura-Toru", "display_name": "Iura, Toru" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7K4C-DA90", "abstract": "Hot-wire anemometer measurements of the velocity fluctuations in stalled operation of an axial-flow compressor have demonstrated that stalling occurs as more or less well-defined regions of retarded flow which rotate in the compressor annulus without changing shape. These regions propagate in the direction of the blade rotation with a speed proportional to, but of smaller magnitude than, the rotor speed. Two principal types of propagating stall were observed. The one with the stalled region or regions extending over part of the blade height was defined as partial stall, and the other with a single stalled region over the entire blade height was defined as full stall." }, { "name": "Johnson, James Edgar", "degree": "PhD", "year": "1953", "title": "The Dynamic Stress-Strain Relation of Annealed 2S Aluminum Under Compression Impact", "advisor": "Clark, Donald S.; Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechETD:etd-09242002-112143", "creators": [ { "name": { "family": "Johnson", "given": "James Edgar" }, "id": "Johnson-James-Edgar", "display_name": "Johnson, James Edgar" } ], "advisors": [ { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/3CM0-PH78", "abstract": "This thesis presents the results of a study of the stress-strain relation of a metal when subjected to compression impact. An annealed 2S aluminum is used for this investigation. Two methods of securing the dynamic stress-strain curve are considered; namely, from the measurement of impact stress and of maximum plastic strain as functions of the impact velocity from 3.15 to 125 ft/sec. The dynamic stress-strain relations obtained by these methods are compared with the static stress-strain curve. Both of the dynamic stress-strain relations lie considerably above the static curve. However, the two dynamic relations are not coincident which indicates that a single dynamic stress-strain curve cannot properly describe the behavior of the material for all impact velocities. A family of stress-strain curves is postulated in order to explain the difference between these two relations. Each curve of the family depends upon the final strain or impact velocity.\r\n\r\nIt is further concluded that the rise of the stress-strain curve under dynamic loading cannot be induced by moderate loading rates." }, { "name": "Mager, Artur", "degree": "PhD", "year": "1953", "title": "Laminar Boundary Layer Problems Associated with Flow Through Turbomachines", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-100849", "creators": [ { "name": { "family": "Mager", "given": "Artur" }, "id": "Mager-Artur", "display_name": "Mager, Artur" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/49CS-2731", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis analysis deals with three-dimensional boundary layer flows which are of particular interest in the design of turbomachinery. By assuming only small lateral pressure gradients and applying perturbation procedure to the steady, laminar boundary layer equations of motion a set of zeroth and first order equations is found. While the zeroth order equations are just the two-dimensional ones for flow over flat plate, the first order equations retain the characteristic Blasius similarity for a family of external flows expressible by [?] (where U* [and] W* are the perturbation velocities, x [and] z are the coordinates and A [and] B are arbitrary constants). For various types of such external flows (which may or may not be rotational) boundary layer velocity distributions were found by a numerical solution.\r\n\r\nThe investigation is divided into two parts, the first one dealing with boundary layer flows over plane surfaces and the second one considering such flows over surfaces with very sharply varying lateral curvature. In order to obtain solutions in the second part it was necessary to expand the appropriate equations in terms of the product of the local surface curvature and the boundary layer thickness. In addition, the effects of compressibility and rotation (of the surface) on the flows over a plane surface were quantitatively evaluated.\r\n\r\nComparison of the present results with the more exact solutions of other investigators in certain special cases, and with the visual studies of three-dimensional boundary layer flow in cascades, indicates a fair qualitative agreement." }, { "name": "Meghreblian, Robert Vartan", "degree": "PhD", "year": "1953", "title": "Thermodynamic Functions of Polyelectronic Atoms at Very High Temperatures", "advisor": "Penner, Stanford S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252003-104736", "creators": [ { "name": { "family": "Meghreblian", "given": "Robert Vartan" }, "id": "Meghreblian-Robert-Vartan", "display_name": "Meghreblian, Robert Vartan" } ], "advisors": [ { "name": { "family": "Penner", "given": "Stanford S." }, "id": "Penner-S-S", "role": "advisor", "display_name": "Penner, Stanford S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/88PE-S208", "abstract": "A convergent series representation for the internal partition function of polyelectronic atoms is obtained by assuming a covolume equation of state for the gas as previously applied by Fermi and Urey to the hydrogen atom.
\r\n\r\nThe present investigation is limited to those cases wherein only extranuclear electronic excitation occurs. The contribution of these electronic states to the thermodynamic functions is obtained from an acceptable approximation to the sum of the convergent series for the partition function.
\r\n\r\nIt is shown that at relatively low temperatures (3000 degrees K), the customary method of evaluating the internal partition function (based on the assumption of an ideal gas) agrees to within a few percent with the results obtained from the covolume treatment. However, at higher temperatures the increase in size of the excited atoms, along with the appearance of charged particles produced by ionization, render the ideal gas treatment inadequate. Since the interaction potentials of charged particles are not known in general, an approximate procedure, which neglects these interactions, is suggested for analyzing a system wherein ions and free electrons constitute a small fraction of the total population. This procedure should be useful for treating gaseous mixtures to temperatures of about 10,000 degrees K.
" }, { "name": "Ponsford, Henry Thomas", "degree": "PhD", "year": "1953", "title": "The Effects of Stiffness on the Buckling of Cylinders with Moderate Wall Thickness", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05082003-160210", "creators": [ { "name": { "family": "Ponsford", "given": "Henry Thomas" }, "id": "Ponsford-Henry-Thomas", "display_name": "Ponsford, Henry Thomas" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JAYX-PF29", "abstract": "A series of 25 complete cylinders was tested experimentally to determine the effects of stiffening elements on the buckling of cylinders with moderate wall thickness, and to present a physical basis for an understanding of the mechanism of cylinder buckling.\r\n\r\nIt was found that both axial and circumferential stiffeners spaced at distances comparable to the buckle wave length of the unstiffened cylinder will raise the buckling stress, reduce the wave length, and alter the shape of the buckling waves. It was shown that for cylinders of D/t = 400, the addition of axial stiffening as little as 2% or 3% of the cylinder wall material can raise the buckling stress by 30% over the unstiffened case.\r\n\r\nThe experiments of this study lend support to a theory developed by Donnell and Wan which ascribes the reduction of the buckling stress of a real cylinder below the classical theoretical value to the initial imperfections of construction in the real cylinder. Conversely, the results cast doubt on the validity of the theory which explains the \"premature\" failure on the basis of external energy disturbances present in the testing laboratory.\r\n\r\nIt was shown that the buckling waves of a reasonably well-made cylinder develop with extreme rapidity without the necessity of a change in cylinder length, and are fully developed in their lateral dimensions throughout the buckling process. Some previous results of Kanemitsu and Nojima which exhibited an essentially different buckling mechanism were explained as the consequence of excessive initial imperfection.\r\n\r\nA brief study of the vibrations of a cylinder under axial load demonstrated an approximate correlation between the vibration and buckling modes of the cylinder." }, { "name": "Savant, Clement Joseph", "degree": "PhD", "year": "1953", "title": "A Non-Linear Computer for the Solution of Servomechanism Problems", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-083454", "creators": [ { "name": { "family": "Savant", "given": "Clement Joseph" }, "id": "Savant-Clement-Joseph", "display_name": "Savant, Clement Joseph" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MV47-XY14", "abstract": "This thesis describes the details of an electronic computer capable of generating arbitrary functions of one or more dependent variables. The design of the essential equipment is discussed, and operating instructions as well as complete circuit diagrams are included for easy reference of future researchers.\r\n\r\nThe computer is used to generate arbitrary functions of an independent variable, and a wide range of functions is shown. Various classical nonlinear problems including Duffing's equation and Van der Pol's equation are solved on the computer and compared with known theory. A discussion, augmented by oscillograms, is presented on nonlinear damping. The computer then is used to improve the response of two feedback control systems. Both systems, which were taken from actual devices met in practice, have inherent nonlinearities. With the aid of the electronic computer the response of these systems is improved. In the solution of the servo system, an interesting nonlinear phenomenon was discovered which is discussed in detail." }, { "name": "Skjelbreia, Lars", "degree": "PhD", "year": "1953", "title": "Stress Analysis of Prismatic and Cylindrical Shells", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-093311", "creators": [ { "name": { "family": "Skjelbreia", "given": "Lars" }, "id": "Skjelbreia-Lars", "display_name": "Skjelbreia, Lars" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/5DQX-4V47", "abstract": "This thesis consists essentially of two distinct parts. The first part deals with the development of the theory and the second part deals with experimental verification of the theory.\r\n\r\nThe theory developed in this paper applies to the analysis of prismatic shells, also called hipped-plate structures or \"Faltwerke\", and uses only techniques commonly employed in structural engineering analysis. A cylindrical shell is approximated by a prismatic shell and analysed as such. In the analysis, extensive use is made of a relaxation or distribution method. Both simply supported and continuous shells are treated.\r\n\r\nFor the purpose of verifying the theory several test models were built, both prismatic and cylindrical. Stresses were measured with electric strain gages, and close agreement was found between theory and experiments." }, { "name": "Solomon, George Edward", "degree": "PhD", "year": "1953", "title": "Transonic Flow Past Cone-Cylinders", "advisor": "Liepmann, Hans Wolfgang; Cole, Julian D.; Roshko, Anatol", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-103200", "creators": [ { "name": { "family": "Solomon", "given": "George Edward" }, "id": "Solomon-George-Edward", "display_name": "Solomon, George Edward" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." }, { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-A", "role": "advisor", "display_name": "Roshko, Anatol" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DE4W-ZJ43", "abstract": "Experimental results are presented for transonic flow past cone-cylinder, axially symmetric bodies. The drag coefficient, surface Mach number, etc. are studied as the free stream Mach number is varied and, wherever possible, the experimental results are compared with theoretical predictions. Interferometric results for several typical flow configurations are shown and an example of shock-free supersonic to subsonic compression is experimentally demonstrated.\r\n\r\nThe theoretical problem of transonic flow past finite cones is discussed briefly and an approximate solution of the axially symmetric transonic equations, valid for a semi-infinite cone, is presented." }, { "name": "Solverson, Robert Richard", "degree": "PhD", "year": "1953", "title": "Stress Concentrations in Fillets", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-105323", "creators": [ { "name": { "family": "Solverson", "given": "Robert Richard" }, "id": "Solverson-Robert-Richard", "display_name": "Solverson, Robert Richard" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/M29Q-K453", "abstract": "The stress concentrations arising in the fillets of fan and turbine blades, tie down rods, and bolt heads from axially symmetric centrifugal or static force loadings are treated two dimensionally by photoelastic and theoretical methods. The effects of the fillet radius, the height of the base, the mode of application of retention forces, and the distance between the retention reactions and fillet tangencies are considered. The stress concentration factor, K, was found to increase with decreasing radius and decreasing base height and, for small radii, to decrease at first with the distance between the reaction and fillet tangency but, in general, to increase with this distance. Comparisons with other experiments and stress concentration configurations are also made.\r\n\r\nAn approximate theoretical solution is derived by selecting a convenient region from the whole base and replacing, where necessary, the exact boundary conditions with relaxed or integral conditions. The problem is formulated in terms of the classical Airy stress function. Agreement between theory and experiment is reasonable." }, { "name": "Stoolman, Leo", "degree": "PhD", "year": "1953", "title": "Investigation of an Instability Phenomena Occurring in Supersonic Diffusors", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05122003-115303", "creators": [ { "name": { "family": "Stoolman", "given": "Leo" }, "id": "Stoolman-Leo", "display_name": "Stoolman, Leo" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EG52-8V58", "abstract": "Experimental investigations of supersonic normal shock type diffusors have shown the existence of self-excited oscillations that occur as the internal mass flow is reduced somewhat below its maximum value. There is a lower bound of free stream Mach number (of the order of 1.8) below which no instability could be observed. However, as free stream Mach number was increased above this lower bound, instability occurred at increasing values of the internal mass flow. Also, the frequency at instability was of the order of the natural frequency of the internal duct acting as organ pipe.\r\n\r\nFirst-order theoretical investigations of the above phenomena indicate that the instability may (in part) be interpreted as intrinsic, that is, independent of viscous effects at the duct inlet or within the diffusor. The fundamental cause of the instability is shown to be due to the nature of the oscillatory inlet flow conditions that occur as a consequence of the external compression from the shock wave to the inlet, and the type of reflections suffered at the shock wave by upstream traveling pressure waves." }, { "name": "Acosta, Allan James", "degree": "PhD", "year": "1952", "title": "An Experimental and Theoretical Investigation of Two-Dimensional Centrifugal Pump Impellers", "advisor": "Hollander, Aladar", "url": "https://resolver.caltech.edu/CaltechETD:etd-04072003-091659", "creators": [ { "name": { "family": "Acosta", "given": "Allan James" }, "id": "Acosta-Allan-James", "display_name": "Acosta, Allan James" } ], "advisors": [ { "name": { "family": "Hollander", "given": "Aladar" }, "id": "Hollander-Alandar", "role": "advisor", "display_name": "Hollander, Aladar" } ], "committee": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "chair", "display_name": "Plesset, Milton S." }, { "name": { "family": "Erd\u00e9lyi", "given": "Arthur" }, "id": "Erd\u00e9lyi-Arthur", "role": "member", "display_name": "Erd\u00e9lyi, Arthur" }, { "name": { "family": "Hollander", "given": "Aladar" }, "id": "Hollander-Aladar", "role": "member", "display_name": "Hollander, Aladar" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "member", "display_name": "Hudson, Donald E." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "member", "display_name": "Rannie, W. Duncan" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" } ], "option_major": [ "mecheng" ], "doi": "10.7907/159P-SA35", "abstract": "An experimental and theoretical investigation on a series of three centrifugal pump impellers has been made in order to determine the usefulness and validity of tyro-dimensional potential theory for the description of the flow. Computed values of the developed head and distribution of pressure on the vane surfaces are compared with measurements an two-, four-, and six- bladed impellers which have 30\u00b0 logarithmic spiral vanes and a radius ratio of about one-half.
\r\n\r\nIt is found that for operating points where the influence on the flow into the impeller by the inlet turn is least, the agreement between the observed and predicted values is reasonably good, while for other flow rates large discrepancies occur. Although the impeller efficiency is relatively high when the flow is least disturbed by the inlet, the slope of the work coefficient line is steeper than the theoretically predicted value. This deviation is attributed to boundary layers which are observed on the vane surfaces.
" }, { "name": "Arthur, Paul David", "degree": "PhD", "year": "1952", "title": "Effects of Impurities on the Supersaturation of Nitrogen in a Hypersonic Wind Tunnel", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-152948", "creators": [ { "name": { "family": "Arthur", "given": "Paul David" }, "id": "Arthur-Paul-David", "display_name": "Arthur, Paul David" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PBSD-2V70", "abstract": "An experimental investigation was conducted to determine the effects of additives on the supersaturation of commercial bottled nitrogen expanded in a hypersonic nozzle. In particular, enough oxygen was added to duplicate air proportions. A stainless steel two-dimensional source-flow nozzle of one-inch width was used to conduct the tests.\r\n\r\nCommercially pure nitrogen, expanded from room temperature and 8-1/3 atm. pressure, was found to supersaturate by approximately 18\u00b0 K or 1.2 Mach number. The supersaturation of the nitrogen was decreased by the addition of impurities, and only a fraction of a percent of carbon dioxide or water vapor was required to eliminate completely all supersaturation. Addition of argon and oxygen was found to be much less effective in decreasing the supersaturation. For the synthetic air, the supersaturation was 16\u00b0 K or 0.9 Mach number based on air vapor pressure values.\r\n\r\nDuring the collapse of the supersaturated state, the static pressure gradually increased above the isentropic value because of the heat release of the condensing gas. As has been shown before, there was no evidence of condensation shock with nitrogen. The impact pressure was only slightly changed from the isentropic value by the presence of condensation in the flow. After the collapse of the supersaturated state, the flow approximated that of a condensation shock.\r\n\r\nFrom these tests it is concluded that condensation of nitrogen, containing slightly more impurities than present in the commercial nitrogen, and of air of the same purity principally caused by foreign impurities, not by spontaneous self-nucleation." }, { "name": "Buhler, Rolf Dietrich", "degree": "PhD", "year": "1952", "title": "Condensation of Air Components in Hypersonic Wind Tunnels: Theoretical Calculations and Comparison with Experiment", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01162007-152444", "creators": [ { "name": { "family": "Buhler", "given": "Rolf Dietrich" }, "id": "Buhler-Rolf-Dietrich", "display_name": "Buhler, Rolf Dietrich" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0J8Q-9Z82", "abstract": "The effect of condensation on the flow in hypersonic wind tunnels is bracketed by equilibrium saturated expansion and by instantaneous condensation. By calculation of shock waves with evaporation, direct comparison of theoretical and measured pressures is made possible. Satisfactory agreement between saturated expansion theory and experiment is obtained after the collapse of the supersaturated state.\r\n\r\nThe droplet growth theory (for free molecule regime) is reexamined, and a good approximate solution is obtained for the nonsteady case (i.e., rapidly changing vapor properties). Limits of validity of the quasi-steady theory are defined, and an upper limiting (zero growth) drop size given for expanding flow.\r\n\r\nA simplified method is presented for calculating the pressure time history of the collapse of the supersaturated state in nozzles. From this, most effective nucleus sizes for given total mass of impurities are calculated. Thus the earliest possible collapse in a nozzle due to impurities is estimated theoretically for low impurity concentrations. The agreement of the predicted trend with experimental results in nitrogen appears to justify the assumed mechanism of the collapse, which is condensation on existing foreign nuclei formed upstream of the collapse.\r\n" }, { "name": "Cheng, Che-Min", "degree": "PhD", "year": "1952", "title": "Studies on Thermal Stresses in Elastic Solids", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechTHESIS:10142011-154227820", "creators": [ { "name": { "family": "Cheng", "given": "Che-Min" }, "id": "Cheng-Che-Min", "display_name": "Cheng, Che-Min" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/06BJ-3W12", "abstract": "Some results, following Gibbs and Murnaghan, on the\r\ngeneral thermodynamical properties of a continuous and\r\nisotropic medium are reviewed in Part I. These discussions\r\nlead to the formulation of various thermodynamic functions\r\nfor a thermo-elastic solid in small strain. The expression\r\nfor the free energy is useful, in particular, for approximate solutions of thermal stress problems involving either steady or transient heating. Also in Part I, a rather general condition is established under which the inertia effect due to transient thermal expansions may be neglected. Conditions under which temperature distributions may be calculated independently of stresses and strains are also given. Attention is given to the order of approximations involved in such simplifications.
\r\n\r\nThe general results in Part I are applied to two problems\r\nin Part II and Part III. The problem of thermal shock,\r\na type of failure due to sudden heating or cooling, is\r\nstudied in Part II. The analytic results obtained there\r\nare compared with the experimental results on thermal shock\r\ncarried out by N.A.C.A. investigators on circular ceramic\r\nand ceramal dics. The correlation between theory and\r\nexperiment is considered satisfactory.
\r\n\r\nThermal stresses in thin cylindrical shells and plates\r\nare formulated and discussed in Part III. It is assumed that\r\nthe temperature varies only across the thickness, and the Young's modulus may be an arbitrary function of temperature. A convention regarding the choice of the reference surface is introduced, by means of which the present theory becomes comparable to the ordinary theory of plates and shells. Methods based on similarity considerations are devised such that the resulting stresses and strains in a shell or plate caused by temperature gradient and external loads can be predicted by experimenting with a similar specimen at a uniform temperature. These considerations are motivated by the necessity to overcome the difficulties both in analytic\r\ncalculations and experimental measurements of stresses\r\nand strains at elevated temperatures, especially when\r\ntransient heating and complicated loads are involved. Such\r\na situation arises, for example, in the combustion chamber\r\nof a rocket engine, where stresses produced by supporting\r\nseats are often too complicated to compute by purely\r\nanalytical methods.
" }, { "name": "Dergarabedian, Paul", "degree": "PhD", "year": "1952", "title": "The Rate of Growth of Vapor Bubbles in Superheated Water", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-112120", "creators": [ { "name": { "family": "Dergarabedian", "given": "Paul" }, "id": "Dergarabedian-Paul", "display_name": "Dergarabedian, Paul" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/M5Q9-M126", "abstract": "Calculations are presented for the dynamic stability of vapor and air bubbles in superheated water. These calculations indicate that the values of the bubble radii for which the equilibrium is unstable are restricted to a finite range of radii whose values are governed by the temperature of the water and the initial air content in the bubble.\r\n\r\nTwo theoretical solutions for the rate of growth of these unstable bubbles are considered. The first, is a solution of the equation of motion of the bubble radius with the assumption that there is no heat diffusion across the bubble wall. The second, is a solution which includes the effect of heat diffusion. The two solutions differ appreciably.\r\n\r\nThese two solutions are then compared with the experimental data on the growth of the vapor bubbles in superheated water. This comparison shows agreement with the solution with the effect of heat diffusion included." }, { "name": "Dixon, William Joseph", "degree": "PhD", "year": "1952", "title": "An Analysis of Errors in the Electric-Analog Computer", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:11202017-110318862", "creators": [ { "name": { "family": "Dixon", "given": "William Joseph" }, "id": "Dixon-William-Joseph", "display_name": "Dixon, William Joseph" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/JZ9T-BA74", "abstract": "This thesis is the result of work done in connection \r\nwith the California Institute of Technology Electric\u00ad \r\nAnalog Computer. Several methods are developed for \r\ndetermining the accuracy of the solutions of various types \r\nof problems by electric circuit analogies. These are \r\nused to obtain expressions for the errors involved in the \r\nsolutions of specific examples.
\r\n\r\n\r\nThe first part deals with the error involved in the\r\nsolution of problems with continuously distributed physical\r\nproperties by means of circuit analogies of lumped parameters.\r\nThe errors of mode frequencies of several mechanical\r\nvibration problems are given in the form of asymptotic\r\nseries.
\r\n\r\n\r\nIn the second part, investigation is made of the effect\r\nof the statistical deviation of the actual values of the\r\ncomputer elements from their nominal values. This effect\r\nis computed for circuits for some of the problems considered\r\nin the first section.
\r\n\r\n\r\nThe third part describes the analog computer solution of\r\nthe transient stresses in a model airplane wing under\r\nlanding impact. This solution is compared with another\r\ncomputed solution and with an experimental test of the\r\nsame model wing.
" }, { "name": "Grey, Jerry", "degree": "PhD", "year": "1952", "title": "The Effects of Air Condensation on Properties of Flow and their Measurement in Hypersonic Wind Tunnels", "advisor": "Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-061157", "creators": [ { "name": { "family": "Grey", "given": "Jerry" }, "id": "Grey-Jerry", "display_name": "Grey, Jerry" } ], "advisors": [ { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HFHE-HR77", "abstract": "Some of the fundamental problems encountered in the measurement of flow properties in condensing air have been discussed, and were investigated experimentally in the GALCIT 9 Hypersonic Wind Tunnel. The saturated expansion theory of flow in a condensing fluid as developed by Buhler was corroborated, and some of the unknown properties of the theory have been clarified by analysis of the wind tunnel tests. Several experimental techniques for the measurement of two-phase fluid properties were developed and the results were used to supply additional information concerning the nature of phenomena such as supersaturation and normal and oblique shock waves. No definite conclusions could be reached with regard to future application of condensed air wind tunnel data on the basis of these tests, but the subject of similarity parameters comparable to the Mach number in flow of a perfect gas has been discussed at some length." }, { "name": "Luo, Peilin", "degree": "PhD", "year": "1952", "title": "On the Theory of Salient Pole Alternators with Electromagnet and with Permanent Magnet Excitations", "advisor": "Sorensen, Royal Wasson", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072012-090301560", "creators": [ { "name": { "family": "Luo", "given": "Peilin" }, "id": "Luo-Peilin", "display_name": "Luo, Peilin" } ], "advisors": [ { "name": { "family": "Sorensen", "given": "Royal Wasson" }, "id": "Sorensen-R-W", "role": "advisor", "display_name": "Sorensen, Royal Wasson" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/M0ZN-HQ87", "abstract": "I.The synchronous reactances of alternators with permanent magnet excitation and alternators with skewed armature slots:
\r\n\r\nThe method for calculating the two reactances of salient pole alternators\r\nwith permanent magnet excitation has been developed. Owing\r\nto the presence of the magnets, the direct axis armature reactance\r\nhas been found to be much smaller than in electromagnet excited\r\nmachines of similar sizes. The quadrature axis reactance is thus\r\nfound to be likely the greater of the two.
\r\n\r\nThe influence of skewing the armature slots has been studied,\r\nboth for electromagnet excited and permanent magnet excited\r\nmachines. It has been found that the general influence is to\r\ndecrease the armature reaction reactances and to increase the leakage\r\nreactances. The influence upon the total reactances is to a\r\ncertain extent to reduce the difference between the reactances\r\nalong the two axes. Formulae are given for both types of excitation.
\r\n\r\nThe practical correctness of the formulae when saturation is\r\nnot appreciable has been confirmed indirectly by comparing calculated\r\nand tested regulation curves of two existing machines.
\r\n\r\nII. The cardioid diagram method of determining the voltage regulation of salient pole alternators and the load voltage increase phenomenon in alternators with permanent magnet excitation:
\r\n\r\nA graphical method has been developed for rapidly determining from two reactances the\r\nregulation of alternators for a wide range of power factor. The\r\nsame method is used to study the performance of alternators with\r\npermanent magnet excitation. The study shows that it is possible\r\nto develop a system applicable to uniform rising regulation curves\r\nover a wide range of power factors from unity to that due to purely\r\ninductive load.
\r\n\r\nIII. The optimum proportions of the field structure of permanent magnet excited alternators:
\r\n\r\nThe optimum design of the field structure of\r\npermanent magnet excited alternators with specified lengths of air\r\ngap and stability has been obtained for two types of problems; viz.,\r\n1) when given space, to find the required maximum flux density in\r\nthe air gap, and 2) when both space and the air gap flux density\r\nare known and the requirement is minimum weight of the magnets. A\r\nmethod of specifying the stability of the excitation magnets has\r\nbeen suggested.
\r\n\r\nIt has been shown that appreciable improvements are possible\r\nfor many existing designs.
" }, { "name": "MacCready, Paul Beattie", "degree": "PhD", "year": "1952", "title": "Investigation of Atmospheric Turbulence", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-104542", "creators": [ { "name": { "family": "MacCready", "given": "Paul Beattie" }, "id": "MacCready-Paul-Beattie", "display_name": "MacCready, Paul Beattie" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F8AR-VH67", "abstract": "Satisfactory measurement techniques were developed which overcame the four principal experimental problems arising in the investigation of atmospheric turbulence.\r\n\r\n1) The data are made reproducible for statistical analyses by recording them on a portable magnetic tape recorder.\r\n\r\n2) Measurements at elevations up to several hundred meters are made feasible by the use of a multi-cable tethering system for a balloon which supports the measuring devices.\r\n\r\n3) and 4) The problems of measuring wind velocity fluctuations over broad ranges (frequencies between 0 and 50 cycles per second, and magnitudes between 1/4 and 20 meters per second) are solved by using hot wire anemometers together with non-linear amplifiers.\r\n\r\nThe statistical analysis of recordings made under various meteorological conditions indicates that Kolmogoroff's similarity hypothesis, concerning the isotropy of turbulence in a certain inertial sub-range of eddy sizes, is directly applicable to eddies of sizes ranging from under 10 cm. to dimensions larger than the elevation of measurement. Over this range the \"2/3 law\" holds for the autocorrelation coefficient and the \"-5/3 law\" holds for the energy spectrum, within the accuracy of the measurements. The large eddy limit of the range of the \"2/3 law\" appears to be considerably extended by strong thermal instability. Heat flux measurements from the correlation between temperature and vertical velocity agree reasonably with the heat flux measured with heat meters. At 70 cm. under moderate wind conditions over half the heat flux is due to eddies of periods less than two seconds. Momentum flux measurements from velocity correlations were inconclusive." }, { "name": "Parkin, Blaine Raphael", "degree": "PhD", "year": "1952", "title": "Scale Effects in Cavitating Flow", "advisor": "Plesset, Milton S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03302009-081459", "creators": [ { "name": { "family": "Parkin", "given": "Blaine Raphael" }, "id": "Parkin-Blaine-Raphael", "display_name": "Parkin, Blaine Raphael" } ], "advisors": [ { "name": { "family": "Plesset", "given": "Milton S." }, "id": "Plesset-M-S", "role": "advisor", "display_name": "Plesset, Milton S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DWKE-J388", "abstract": "Scale effects in cavitating flow are considered for the so-called limited cavitation flow regime. The roles of nuclei and air diffusion in ordinary water and the kinetic theory of liquids for pure water are considered as to their bearing on cavitation scale effects.\r\n\r\nThe attack on the problem is concentrated in three general areas. First, dynamic similarity considerations for individual bubble growth show that no useful scaling laws can be established from such arguments. Aside from changes due to Reynolds number, it is concluded that scale effects are dependent upon the time required for a nucleus to grow from its original microscopic size to a macroscopic size. Second, a series of experiments shows that the cavitation behaves in a systematic way as the scale of the immersed body is changed. In certain instances, the inception of cavitation depends on both model size and free stream velocity. Third, a theoretical study is made to gain insight into the relationships that must hold between the parameters which affect the inception of cavitation. A simplified theory gives only rough qualitative agreement with experiment." }, { "name": "Pauw, Adrian", "degree": "PhD", "year": "1952", "title": "A Rational Design Procedure for Machine Foundations", "advisor": "Martel, Romeo Raoul; Converse, Frederick James", "url": "https://resolver.caltech.edu/CaltechTHESIS:12012017-090837077", "creators": [ { "name": { "family": "Pauw", "given": "Adrian" }, "id": "Pauw-Adrian", "display_name": "Pauw, Adrian" } ], "advisors": [ { "name": { "family": "Martel", "given": "Romeo Raoul" }, "id": "Martel-R-R", "role": "advisor", "display_name": "Martel, Romeo Raoul" }, { "name": { "family": "Converse", "given": "Frederick James" }, "id": "Converse-F-J", "role": "advisor", "display_name": "Converse, Frederick James" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/MZVV-X944", "abstract": "The problem involved in the design of machine foundations are\r\ndiscussed, followed by a short review of the literature of the subject.\r\nThe general theory of vibration for single and multiple degree of freedom\r\nsystems is briefly reviewed, with special emphasis on its application\r\nto machine foundation design. A procedure for the analysis of machine\r\nfoundations is then developed on the basis of a simplified equivalent\r\nsystem. Procedures for determining the elastic coefficients and the \r\ninertia parameters of the soil are next considered.
\r\n\r\n\r\nThe purpose and extent of the experimental investigations are\r\ndiscussed, followed by a description of the instrumentation used and\r\nthe nature and accuracy of the data obtained. The data is then\r\nanalyzed and checked against the theory presented. The data required for\r\nthe design of machine foundations is discussed, and a procedure for\r\ndesign and analysis is recommended. In conclusion recommendations for\r\nfurther study and research are made.
" }, { "name": "Roshko, Anatol", "degree": "PhD", "year": "1952", "title": "On the Development of Turbulent Wakes from Vortex Streets", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-144124", "creators": [ { "name": { "family": "Roshko", "given": "Anatol" }, "id": "Roshko-Anatol", "display_name": "Roshko, Anatol" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4WDN-9807", "abstract": "Wave development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low speed wind tunnel. Standard hot-wire techniques were used to study the velocity fluctuations.\r\n\r\nThe Reynolds number range of periodic vortex \"shedding\" is divided into two distinct sub-ranges. At R = 40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. R = 150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. This transition first occurs in the range R = 150 to 300.\r\n\r\nSpectrum and statistical measurements were made to study the velocity fluctuations. In the stable range the vortices decay by viscous diffusion. In the irregular range the diffusion is turbulent and the wake becomes fully turbulent in 40 to 50 diameters downstream.\r\n\r\nIt was found that in the stable range the vortex street has a periodic spanwise structure.\r\n\r\nThe dependence of shedding frequency on velocity was successfully used to measure flow velocity.\r\n\r\nMeasurements in the wake of a ring showed that an \"annular\" vortex street is developed." }, { "name": "Thiene, Paul George, Jr.", "degree": "PhD", "year": "1952", "title": "Studies on Absorptive Transitions Between Rotational Sublevels of Symmetric-Top Molecules in a Static Electric Field", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechTHESIS:04172018-105411908", "creators": [ { "name": { "family": "Thiene", "given": "Paul George, Jr." }, "id": "Thiene-Paul-George", "display_name": "Thiene, Paul George, Jr." } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/MS6H-6Z64", "abstract": "The topic of this research is the hitherto uninvestigated\r\nabsorption of electromagnetic energy by polar symmetric-top\r\nmolecules in a static electric field, which arises by virtue of\r\ndirect transitions between sublevels of a single rotational\r\nstate. A short theoretical treatment of the Stark effect of a\r\nrigid molecule is included. The factors governing the absorption\r\nof quanta from the surrounding radiation field are discussed\r\nin a rudimentary derivation of a formula for the maximum linear\r\nabsorption coefficient of a gas.
\r\n\r\nA new microwave Stark-effect spectrometer constructed for\r\nan exploratory investigation is described. The instrument\r\noperates in an unusual manner whereby the spectral position of\r\nthe absorption line is varied, while the frequency of the incident\r\nradiation is held fixed. Included also is a treatment of the \r\nfactors which determine and limit the sensitivity of the\r\nspectrometer.
\r\n\r\nExperiments which strongly indicate the existence of these\r\nfield-created absorption lines are reported.
" }, { "name": "Vreeland, Thad", "degree": "PhD", "year": "1952", "title": "A Study of the Initiation of Yielding in Mild Steel", "advisor": "Clark, Donald S.; Wood, David Shotwell", "url": "https://resolver.caltech.edu/CaltechETD:etd-10222002-101824", "creators": [ { "name": { "family": "Vreeland", "given": "Thad" }, "id": "Vreeland-Thad", "display_name": "Vreeland, Thad" } ], "advisors": [ { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." }, { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-D-S", "role": "advisor", "display_name": "Wood, David Shotwell" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/7ZK4-D555", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. \r\n\r\nThis thesis presents the results of an experimental investigation of the behavior of an annealed low-carbon steel subjected to rapidly applied constant stress and to repeated short duration stress-pulses. The magnitude of the stresses in the short duration stress-pulses was greater than the upper yield stress. The material was aged at various temperatures between stress-pulses, and the effect of the time of aging on the number of stress-pulses to induce yielding was determined.\r\n\r\nPlastic and anelastic microstrain of 4 x 10[superscript -6] in./in. to 37 x 10[superscript -6] in./in. is observed prior to the onset of yielding in rapidly applied constant stress tests and in repeated stress-pulse tests. The relation between equilibrium microstrain and stress is determined for stresses below the static upper yield stress. Aging of the specimens for a sufficient length of time at a given temperature between stress-pulses induces recovery in the material such that yielding does not occur in repeated stress-pulse and aging cycles. The activation energy of the recovery process corresponds, within the limits of the experimental accuracy, to the activation energies of carbon and nitrogen diffusion in the material.\r\n\r\nThese effects are discussed in terms of the dislocation theory of yielding. The recovery process is attributed to the diffusion of carbon and nitrogen to dislocations which have been displaced, thus stabilizing the array of dislocations for the particular stress condition.\r\n\r\nEquilibrium microstrain produced by a particular configuration of dislocations is theoretically investigated. An electrostatic analogy of the dislocation model is used in estimating the microstrain. Comparison of the theory and the experimental data leads to the determination of a characteristic length of dislocation which agrees with previous concepts of a mosaic block structure. The delayed yield phenomenon may be qualitatively described by the action of the theoretical dislocation model.\r\n\r\n" }, { "name": "Ward, William W.", "degree": "PhD", "year": "1952", "title": "Problems in Network Theory", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechTHESIS:07242025-211857136", "creators": [ { "name": { "family": "Ward", "given": "William W." }, "id": "Ward-William-W", "display_name": "Ward, William W." } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/bt8j-7129", "abstract": "After a brief philosophical consideration of the status\r\nand function of the theoretician in modern technology, the\r\ncentral objectives of the paper are stated; to investigate \r\nsome of the restrictions on the design and synthesis of linear\r\nphysical systems which are inherent in the mathematical \r\nconstructs and methods by which systems are studied. The\r\nprincipal tools are the Laplace transformation and the theory\r\nof functions of a complex variable.
\r\n\r\nIt is shown that many of the commonly encountered generalizations\r\nto linear distributed-parameter systems of familiar\r\nlumped-parameter-system ideas are valid. These generalizations\r\nare perhaps intuitively obvious, but the details are gone\r\nthrough here once and for all.
\r\n\r\nThe implications in regard to these matters of the principle\r\nof analytic continuation are considered. Tests are\r\nderived to enable one to decide whether or not there is any \r\nchance of realizing a prescribed transfer characteristic T(jw),\r\nw1 less than w less than w2 (analytically expressed data),\r\nand what would be the consequences in terms of T(s) outside this range. The\r\nparadox of the idealized low-pass filter is examined in this\r\nlight. The questions are shown to be unanswerable in the case\r\nof graphically expressed data.
\r\n\r\nIt is shown that the results of the study are in agreement\r\nwith the allied work of others, and a problem of filter\r\nrealization posed by Wallman is solved. The results of the\r\ninvestigations are summarized and reviewed in terms of what\r\ntheoreticians can accomplish in general.
" }, { "name": "Wu, Theodore Yao-tsu", "degree": "PhD", "year": "1952", "title": "On Problems of Heat Conduction in a Compressible Fluid", "advisor": "Lagerstrom, Paco A.; Cole, Julian D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06032004-135328", "creators": [ { "name": { "family": "Wu", "given": "Theodore Yao-tsu" }, "id": "Theodore-Yao-tsu", "display_name": "Wu, Theodore Yao-tsu" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "advisor", "display_name": "Cole, Julian D." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/G8DW-K988", "abstract": "The present work starts with a study of heat conduction in a non-viscous compressible fluid based on a linearized theory which is similar to that used in the theory of sound. Important features of exact equations of motion and their corresponding linearized equations are studied briefly. For this linear system, which preserves many of the features of the original non-linear system, the fundamental solutions are found and discussed. The additional role played by viscosity in the heat conduction problem is then investigated. The fundamental solutions for this compressible, viscous, heat-conducting flow problem are found and compared with the non-viscous case. The problem of heat conduction in a two-dimensional stationary flow of a viscous compressible fluid is further studied by finding the fundamental solutions and discussing the result in some detail. As an example proposed to show how a superposition of these fundamental solutions can be used to solve a boundary value problem, the problem of the anemometry of a heated flat plate is solved for both large and small values of the Reynolds number. The result obtained herein is discussed and compared with some existing theories and experiments. The causes of the discrepancy resulting from this linearized theory are briefly explained." }, { "name": "Bleviss, Zegmund Oscar", "degree": "PhD", "year": "1951", "title": "Interference Effects in Supersonic Flow", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182009-105100", "creators": [ { "name": { "family": "Bleviss", "given": "Zegmund Oscar" }, "id": "Bleviss-Zegmund-Oscar", "display_name": "Bleviss, Zegmund Oscar" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YDMK-MS28", "abstract": "A study is made of interference problems with emphasis on low-aspect-ratio supersonic missile configurations. The configurations are composed of slender pointed bodies with circular cross section, plane or cruciform delta wings, and tails which are not specified. For fin-fin interference (no body) general multi-fin delta wings are studied for the roll problems.\r\n\r\nThree types of interferences are studied. They are (1) fin-fin interference, (2) fin-fin and wing-body interferences combined, and (3) wing-body-tail interference. Where possible, three aerodynamic problems are studied under each of these interferences. They are (1) lift and incidence, (2) roll due to aileron deflection, and (3) damping in roll.\r\n\r\nA survey of the theoretical work on supersonic interference problems is included.\r\n\r\nLinearized theory is used throughout for all problems treated by the writer. Work by other writers which fits naturally into the scheme of the present work is summarized briefly. For most of the problems it is not possible to obtain exact linearized solutions without excessive labor. Where possible, approximations to or estimates of the exact solutions are obtained. It is hoped that these results will be useful for engineering estimates of the interference effects.\r\n\r\nTheoretical results for the roll problems--exact, approximate, and estimated--are presented for fin-fin interference for cruciform and more general multi-fin delta wings with subsonic and supersonic leading edges.\r\n\r\nFor fin-fin and wing-body interferences combined, theoretical results which bracket the exact solutions are obtained for the roll problems.\r\n\r\nFor wing-body-tail interference, the vorticity distributions, rolled-up vortex strengths, and initial vortex positions at the trailing edges are estimated for lift, incidence, aileron deflection, and damping in roll problems. Both plane and cruciform delta wing body configurations are studied.\r\n\r\nA qualitative discussion of some of the nonlinear, viscous, and gap effects is included.\r\n\r\nRecommendations for future research are made." }, { "name": "Bryson, Arthur Earl", "degree": "PhD", "year": "1951", "title": "An Experimental Investigation of Transonic Flow Past Two-Dimensional Wedge and Circular Arc Sections Using a Mach-Zehnder Interferometer", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062003-114932", "creators": [ { "name": { "family": "Bryson", "given": "Arthur Earl" }, "id": "Bryson-Arthur-Earl", "display_name": "Bryson, Arthur Earl" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/S45R-FG17", "abstract": "Interferometer measurements are given of the flow fields near two-dimensional wedge and circular arc sections at zero angle of attack at high subsonic and low subsonic velocities. Both subsonic flow with local supersonic zone and supersonic flow with detached shock wave have been investigated. Pressure distributions and drag coefficients as functions of Mach number have been obtained. The wedge data are compared with the theoretical work on flow past wedge sections of Guderley and Yoshihara, Vincenti and Wagoner, and Cole.
\r\n\r\nIt is shown that the local Mach number at any point on the surface of a finite three-dimensional body or an unswept two-dimensional body, moving through an infinite fluid, is a stationary value at Mach number one and, in fact, remains nearly constant for a range of speeds below and above Mach number one. On the basis of this concept and the experimental data, pressure distributions and drag coefficients for the wedge and circular arc sections are presented throughout the entire transonic range of velocities.
" }, { "name": "Dhawan, Satish", "degree": "PhD", "year": "1951", "title": "Direct Measurements of Skin Friction", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09262002-155504", "creators": [ { "name": { "family": "Dhawan", "given": "Satish" }, "id": "Dhawan-Satish", "display_name": "Dhawan, Satish" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1S03-8631", "abstract": "A device has been developed to measure local skin friction on a flat plate by measuring the force exerted upon a very small movable part of the surface of a flat plate. These forces, which range from about 1 milligram to about 100 milligrams, are measured by means of a reluctance measuring device. The apparatus was first applied to measurements in the low-speed range, both for laminar and turbulent boundary layers. The measured skin friction coefficients show excellent agreement with Blasius' and Karman's results respectively. The device was then applied to high-speed subsonic flow and the turbulent skin friction coefficients were determined up to a Mach number of about 0.8. A few measurements in supersonic floor were also made.
\r\n\r\nThe paper describes the design and construction of the device and the results of the measurements.
" }, { "name": "Dixon, Howard Henry", "degree": "PhD", "year": "1951", "title": "Stresses and Deflections of Unswept and Swept Thin-Walled Beams", "advisor": "Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-093729", "creators": [ { "name": { "family": "Dixon", "given": "Howard Henry" }, "id": "Dixon-Howard-Henry", "display_name": "Dixon, Howard Henry" } ], "advisors": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/7D5X-ZN05", "abstract": "A method is presented for the determination of the stresses and deflections of unswept and swept, thin-walled beams of uniform closed cross section. The cross section, loading distribution and boundary conditions are assumed to be arbitrary. The method is based on the differential equation governing the behavior of orthogonal elastic shells. The differential equation is transformed into a difference equation and the solution obtained by the relaxation technique. A comparison of the theoretical solution and experimental data for a swept back wing with a carry through bay under symmetrical bending showed good agreement.
\r\n\r\nA tapered wing may be treated by approximating the variation by a series of spanwise steps.
\r\n\r\nAs the difference equations are a system of simultaneous algebraic equations, they may be solved by automatic calculating equipment or by electric analogue computers as well as by the relaxation technique.
\r\n" }, { "name": "Ellis, Harry McPhee", "degree": "PhD", "year": "1951", "title": "Factors Affecting the Rate of Dielectric Recovery of Power Arcs in Long Gaps", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112017-102446992", "creators": [ { "name": { "family": "Ellis", "given": "Harry McPhee" }, "id": "Ellis-Harry-McPhee", "display_name": "Ellis, Harry McPhee" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/KAYK-Z254", "abstract": "A satisfactory testing technique is developed for investigating \r\nthe recovery characteristics of various power system insulations.
\r\n\r\n\r\nDuration of the fault current, for a vertical test gap, has little \r\neffect on the dielectric recovery. Five cycle fault current duration \r\ndecreases the initial rate of recovery, for a horizontal test gap, \r\nbelow that for a half cycle, but for longer time delays thermal \r\ncon\u00advection increases the rate of recovery above that for a half cycle \r\nduration.
\r\n\r\n\r\nThe 11 inch test gap has a lower percentage recovery than the 6\r\ninch test gap. The lower the boiling point and the lower the ioniza\u00adtion \r\npotential of the electrode material, the lower the rate of recovery.
\r\n\r\n\r\n\r\nThe increase in the rate of recovery produced by winds up to 1000 \r\nfeet per minute is mainly due to displacement of the ionized gases from \r\nthe test electrodes. For recovery based on this displacement of the \r\nionized gases from the electrodes, the axial wind recovery should be \r\nhalf of the perpendicular. However, the axial wind decreases the cross \r\nsection of the arc, heat transfer away from the ionized gases is \r\nin\u00adcreased, and the axial recovery is greater than half of the perpendicu\u00adlar \r\nrecovery. Wind velocities less than 100 feet per minute have a \r\nnegligible effect on the dielectric recovery characteristics.
\r\n\r\nA 3000 frame per second camera is used to make a high speed photo\u00adgraphic \r\nstudy of the arc. By using a system of mirrors, two mutually \r\nperpendicular views of the arc are obtained simultaneously, on each \r\nframe of the film. Breakdown occurs in the weakest path through the \r\nionized gases, even though this path is 2 to 3 times as long as the \r\nelectrode separation.
\r\n\r\n\r\nThe extent of ionization of the luminous gases is obtained with \r\nthe aid of a microphotometer by taking density readings directly from \r\nthe image of the arc on the 16 mm. negative film. The average density \r\nvariation with time follows the general shape of the curve based on\r\ndiffusion as the only important deionizing agent, for a short time after \r\ncurrent zero.
\r\n\r\n\r\nThe local coefficient of heat transfer obtained from the analogy \r\nof the arc to a hot cylindrical solid body increases with the wind \r\nvelocity and the density of ionization of the luminous gases decreases \r\nwith increasing wind velocity.
\r\n\r\nThe diameter and density of the arc are obtained from the photo\u00adgraphic \r\nstudy and the recovery voltage calculated, at various time de\u00adlays, \r\nfrom Slepian's theory for the critical breakdown gradient of the \r\narc column. The results are in general qualitative agreement with the \r\nexperimental results.
\r\n\r\nThe minimum reclosing time for high-speed automatic-reclosing cir\u00adcuit \r\nbreakers on a transmission system can be reduced by a factor of \r\nfive for a wind of 1000 feet per minute (15 miles per hour) blowing \r\nacross the ionized fault path.
\r\n" }, { "name": "Gates, Clarence Rollins", "degree": "PhD", "year": "1951", "title": "Probability Distributions of the Zeros of Random Noise", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechTHESIS:06262025-155547253", "creators": [ { "name": { "family": "Gates", "given": "Clarence Rollins" }, "id": "Gates-Clarence-Rollins", "display_name": "Gates, Clarence Rollins" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2drf-q802", "abstract": "A complete expression for the probability distribution\r\nof the zero crossing periods of filtered random noise\r\nis given. The first term of this expression is evaluated\r\nand extended to include narrow, symmetrical spectra. The\r\nbehavior of the frequency function about the second and\r\nfurther half-periods is investigated.
\r\n\r\nApparatus has been designed and constructed which\r\ngives directly the distribution function of the zeros of\r\nfiltered random noise. Distribution functions corresponding\r\nto several filters are shown. Correlation between\r\ntheoretical and experimental distributions is good.
" }, { "name": "Greenwood, Donald Theodore", "degree": "PhD", "year": "1951", "title": "Analog Methods of Nonlinear Vibration Analysis", "advisor": "McCann, Gilbert Donald", "url": "https://resolver.caltech.edu/CaltechTHESIS:03242016-111828484", "creators": [ { "name": { "family": "Greenwood", "given": "Donald Theodore" }, "id": "Greenwood-Donald-Theodore", "display_name": "Greenwood, Donald Theodore" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0DNR-VB14", "abstract": "This thesis presents methods by which electrical analogies can be obtained for nonlinear systems. The accuracy of these methods is investigated and several specific types of nonlinear equations are studied in detail.
\r\n\r\nIn Part I a general method is given for obtaining electrical analogs of nonlinear systems with one degree of freedom. Loop and node methods are compared and the stability of the loop analogy is briefly considered.
\r\n\r\nParts II and III give a description of the equipment and a discussion of its accuracy. Comparisons are made between experimental and analytic solutions of linear systems.
\r\n\r\nPart IV is concerned with systems having a nonlinear restoring force. In particular, solutions of Duffing's equation are obtained, both by using the electrical analogy and also by approximate analytical methods.
\r\n\r\nSystems with nonlinear damping are considered in Part V. Two specific examples are chosen: (1) forced oscillations and (2) self-excited oscillations (van der Pol\u2019s equation). Comparisons are made with approximate analytic solutions.
\r\n\r\nPart VI gives experimental data for a system obeying\r\nMathieu's equation. Regions of stability are obtained. Examples of subharmonic, ultraharmonic, and ultrasubharmonic oscillat1ons are shown.
\r\n" }, { "name": "Hipsh, Harold Marvin", "degree": "PhD", "year": "1951", "title": "Harmonic Oscillations of a Narrow Delta Wing in Supersonic Flow", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03112009-125900", "creators": [ { "name": { "family": "Hipsh", "given": "Harold Marvin" }, "id": "Hipsh-Harold-Marvin", "display_name": "Hipsh, Harold Marvin" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VRVK-HB35", "abstract": "A theory is presented for the calculation of the velocity potential of a harmonically oscillating delta wing having subsonic leading edges in a supersonic flow. The velocity potential is expanded in a power series in powers of the reduced frequency. Two modes of oscillation, plunging and pitching, are considered. For both modes the analysis is carried through the term linear in reduced frequency, this being generally sufficient for dynamic stability analyses. The results thus obtained for the pitching mode verify those of Miles (Ref. 9) obtained by an integral transformation of the steady-state solution. In addition, the term that is quadratic in the reduced frequency is presented for the plunging mode to illustrate the general procedure.\r\n\r\nLift and pitching moment coefficients are calculated from the velocity potential and numerical results valid for low frequency oscillations are presented." }, { "name": "Jensen, Arnold Axtell", "degree": "PhD", "year": "1951", "title": "A Slender Cone Starting Impulsively", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03102009-074636", "creators": [ { "name": { "family": "Jensen", "given": "Arnold Axtell" }, "id": "Jensen-Arnold-Axtell", "display_name": "Jensen, Arnold Axtell" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/19KD-1M64", "abstract": "The problem of a semi-infinite slender cone which starts impulsively from rest so that it suddenly has a constant supersonic velocity is considered. It is treated by using the acoustic wave equation for the air at rest at infinity. The problem is reduced to that of dealing with the radial velocity in two conical variables in space-time.\r\n\r\nIt is shown that there are three fundamental regions from the physical or mathematical standpoint. The boundary conditions and equations for each of these regions are developed so that a numerical solution of the problem may be obtained for a given Mach number and cone angle. From the solution of the radial velocity the potential and thence the pressure on the cone are obtained.\r\n\r\nAn approximation to the pressure far back on the cone where the curvature is small is obtained as an improvement on the piston value for zero curvature. This is done by suppressing variations in the axial direction and solving the resulting equation by Riemann's integration method.\r\n\r\nAn attempt to solve the problem by distributing sources on the axis with resulting difficulties is discussed." }, { "name": "Lassen, Herbert Arthur", "degree": "PhD", "year": "1951", "title": "The Analytical Computation of Residual Thermal Stresses", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02072012-112201922", "creators": [ { "name": { "family": "Lassen", "given": "Herbert Arthur" }, "id": "Lassen-Herbert-Arthur", "display_name": "Lassen, Herbert Arthur" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/XH09-8359", "abstract": "An analytical method is developed in detail whereby it is possible to calculate, with arbitrary accuracy, the temperature, the stresses, and the residual strains as a function of the radial position and time induced in an infinitely long solid isotropic cylinder by a quench in a large body of fluid, assuming that all of the pertinent parameters are known (graphical) functions of the temperature.
\r\n\r\nIn the course of this development, a general theory is presented whereby it is theoretically possible to predict the stresses and the residual strains in an isotropic body at any time during a thermal and mechanical history if the following very general assumptions are satisfied.
\r\n\r\n1) The temperature and the boundary conditions are known functions of the position and time and the free thermal expansion is a known function of the temperature.
\r\n\r\n2) There are values of E, G and v which are known functions of the temperature and which relate, through Hooke's Law, the changes in the stresses with the changes in the strains which occur if the stresses are removed from an infinitesmal element of the body.
\r\n\r\n3) There is a theory of strength available which either predicts the maximum stresses which the material can sustain, as a function of the temperature and the past history, or which predicts the plastic strain rates as a function of the stresses, the temperature and the past history.
\r\n\r\nSelecting the values of the pertinent parameters from the literature, a numerical calculation of the residual stresses is made for a specific case of a quenched solid cylinder. The results axe compared with experimental\r\nvalues for the same case determined by other investigators.
\r\n\r\nThe developments for a solid cylinder are extended to a hollow cylinder and a flat plate. Various suitable theories of strength are considered. The modifications to the general theory and the additional information required if a phase change is involved are briefly indicated.
" }, { "name": "Lo, Shih-Chun", "degree": "PhD", "year": "1951", "title": "Oscillating Airfoil in Parallel Streams Separated by an Interface", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-100524", "creators": [ { "name": { "family": "Lo", "given": "Shih-Chun" }, "id": "Lo-Shih-Chun", "display_name": "Lo, Shih-Chun" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HR3R-5994", "abstract": "A new approach to tail buffeting is made by studying the problem of a thin airfoil performing a periodic oscillation of small amplitude in the presence of an interface across which the flow undergoes a constant change in density and velocity. A general solution to the problem is found. Lift and moment for some special cases are obtained in simple forms and are plotted in Figs. 3 and 4 for the two basic modes of oscillation: bending and torsion. A typical application to flutter analysis is made and it is found that tail flutter at low speeds is possible for the tail lying in the wake of the wing." }, { "name": "Michelson, Irving", "degree": "PhD", "year": "1951", "title": "I. On the Dust Devils. II. Linearized Theory of Conical Turbomachines", "advisor": "Stewart, Homer Joseph; Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042009-142746", "creators": [ { "name": { "family": "Michelson", "given": "Irving" }, "id": "Michelson-Irving", "display_name": "Michelson, Irving" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "co-advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PZKM-9280", "abstract": "Dust devils are small-scale atmospheric motions of instability arising from the development of large thermal stratifications in the lowest layers above the surface of the earth. A theory is proposed in Part I to describe the conditions of formation of these motions and depends on the new result that shear provides a powerful stabilizing influence even in non-viscous fluid motions in which denser fluid is situated above less dense. Those features of the flow which can be predicted by the theory and compared with observations are found to be in reasonably good agreement, and it is therefore indicated that the theory, which is based on a highly simplified model of flow, furnishes at least a qualitatively correct correlation of the basic ideas involved in the stable flow of very slightly viscous fluids containing density inversions. Applications to technically interesting flows of this type, in large-scale atmospheric motions as well as in high speed aerodynamic boundary layers, are indicated but not analyzed in detail.\r\n\r\nIn Part II the perfect fluid flow is determined for a turbomachine of conical shape and prescribed blade loading. On the basis of the assumption that the stream surfaces are conical in shape, a linear, elliptic partial differential equation of the second order is obtained. The associated boundary value problem is of the Sturm-Liouville type and is solved completely. An asymptotic representation of the solution is determined which is convenient for computational purposes." }, { "name": "Monroe, Gerald Morgan", "degree": "PhD", "year": "1951", "title": "A Study of Compressible Perfect Fluid Motion in Turbomachines with Infinitely Many Blades", "advisor": "Marble, Frank E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03182009-151729", "creators": [ { "name": { "family": "Monroe", "given": "Gerald Morgan" }, "id": "Monroe-Gerald-Morgan", "display_name": "Monroe, Gerald Morgan" } ], "advisors": [ { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "advisor", "display_name": "Marble, Frank E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HQD3-G406", "abstract": "A study is made of compressible perfect fluid motion in turbomachines having infinitely many blades and a general theory is developed. An underlying concept of the theory is that force fields which represent the action of infinitely many blades belong to a special class described as pseudo-conservative and can be expressed as the product of a scalar function and the gradient of a potential. The scalar function is simply the rate at which energy is imparted to the fluid by the blades, and the potential is simply the family of the equations for the blade surfaces. The introduction of these two functions to express the force field casts an entirely new light on problems of mixed-flow turbomachines having infinitely many blades of arbitrary shape.\r\n\r\nIn the formulation of the problem the non-linear action of rotationality and compressibility is regarded as a force tending to displace the streamsurfaces from their irrotational, incompressible position. It is shown that the character of the problem is determined by a governing velocity: the velocity relative to the blades where blades are present, or the meridional velocity, where blades are not present. Where the governing velocity is subsonic the problem is essentially elliptic, where supersonic, hyperbolic.\r\n\r\nThe theory and the examples lead to conclusions which are believed to explain in part the unexpected efficiencies observed for compressors having transonic governing velocities. These conclusions, which indicate that transonic compressors could perhaps be profitably developed, are as follows: The deflection of the streamsurfaces induced by a given strength of vorticity at a certain point in the flow has one sense when the governing velocity at the point is subsonic, the opposite sense when it is supersonic, and becomes zero as it becomes sonic. The deflection of the streamsurfaces brought about by a given distribution of vorticity in a region is less when the governing velocity in the region is transonic than when it is entirely subsonic or entirely supersonic.\r\n\r\nExamples of incompressible flow through a mixed flow compressor with prescribed blades, and subsonic and transonic flow through actuator disks, were solved by the method of finite differences, applying simultaneously the relaxation technique and an iteration process." }, { "name": "Morgan, Antony John Andrew", "degree": "PhD", "year": "1951", "title": "A General Similarity Theory of Partial Differential Equations and its Use in the Solution of Problems in Aeronautics", "advisor": "Michal, Aristotle D.; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-03192009-091419", "creators": [ { "name": { "family": "Morgan", "given": "Antony John Andrew" }, "id": "Morgan-Antony-John-Andrew", "display_name": "Morgan, Antony John Andrew" } ], "advisors": [ { "name": { "family": "Michal", "given": "Aristotle D." }, "id": "Michal-A-D", "role": "advisor", "display_name": "Michal, Aristotle D." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Michal", "given": "Aristotle D." }, "id": "Michal-A-D", "role": "chair", "display_name": "Michal, Aristotle D." }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "member", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "member", "display_name": "Fung, Yuan-cheng" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9142-KZ49", "abstract": "A general similarity theory of systems of partial differential equations of any order in any number of independent variables is developed with the aid of the theory of continuous one-parameter groups of transformations. The theory is illustrated by means of several known examples of similarity equations, previously given without motivation, in Hydrodynamics. With the aid of the theory two new examples of similarity equations, one in Elasticity and one in Fluid Mechanics, have been found; these are discussed in the text.\r\n" }, { "name": "Nielsen, Jack Norman", "degree": "PhD", "year": "1951", "title": "Supersonic Wing-Body Interference", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03252009-150359", "creators": [ { "name": { "family": "Nielsen", "given": "Jack Norman" }, "id": "Nielsen-Jack-Norman", "display_name": "Nielsen, Jack Norman" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E6Z2-SM31", "abstract": "A method of solving wing-body problems for circular bodies employing wings with supersonic edges has been developed. The method is based on decomposing the wing-body combination into a wing alone plus a number of Fourier component wing-body combinations corresponding to the Fourier series for the normal velocity induced at the body surface by the wing alone. The problem is then solved for each component by a method based on Laplace transform theory, and the method is then shown to be equivalent to a distributed-solution method analogous to that used by Karman and Moore to solve problems of bodies of revolution at supersonic speeds. Two sets of universal functions are presented. The first set is used to obtain the strength distribution of the fundamental solutions distributed along the body axis, from which the entire interference pressure field can be obtained. The second set permits a direct determination of the pressures acting on the body.\r\n\r\nAs an example in the use of the theory, calculations are carried out for the technologically important case of a flat rectangular wing mounted at zero incidence on a body at zero angle of attack. The calculations are carried out for four Fourier components. It was found that all four components were necessary to get good accuracy in determining the pressures at some points in the field, while only one component was required to get a fair determination of the span loading of the combination. From the example much insight into the mechanism of wing-body interference was obtained. The use of the universal functions to obtain pressures due to protuberances on nearly cylindrical bodies is discussed." }, { "name": "Oswald, Telford Wilbert", "degree": "PhD", "year": "1951", "title": "The Influence of Variable Air Density and of Nonlinear Aerodynamic Characteristics on Dynamic Behavior at Supersonic Speeds", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-02242006-160420", "creators": [ { "name": { "family": "Oswald", "given": "Telford Wilbert" }, "id": "Oswald-Telford-Wilbert", "display_name": "Oswald, Telford Wilbert" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VG6Q-C753", "abstract": "The effect of the variable density of the Standard Atmosphere on the dynamic stability of a missile in vertical flight is considered. The analysis is restricted to small disturbances from steady rectilinear flight. The exponential decrease of density with altitude characteristic of the Standard Stratosphere is introduced into the equations of motion and a stability criterion for the dynamic behavior immediately following a small disturbance is found. Alternatively, a hyperbolic variation of density with altitude is used to approximate the Standard Atmosphere and the identical stability criterion is obtained.\r\n\r\nThe effect of non-linear pitching moment and lift variations with angle of attack on the dynamic response to a sudden change in angle of attack is considered. An approximate solution to the non-linear equation of motion is developed. Several numerical examples are considered, and the results of the approximate solution are compared with the very accurate results of numerical integration as well as the classical linearized solution. The effect of a non-linear moment curve on the determination of stability derivatives from flight test data is discussed in the light of these examples." }, { "name": "Parkinson, Geoffrey Vernon", "degree": "PhD", "year": "1951", "title": "Unit-Step Motion of a Wide Delta-Wing", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-05052006-090936", "creators": [ { "name": { "family": "Parkinson", "given": "Geoffrey Vernon" }, "id": "Parkinson-Geoffrey-Vernon", "display_name": "Parkinson, Geoffrey Vernon" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/73TW-ZE47", "abstract": "The effect on a wide delta wing in supersonic flight of the sudden imposition of a small velocity perturbation normal to the plane of the wing is considered. The resulting pressure field on the wing is found in closed form in terms of elementary functions. The corresponding solution for the infinite swept wing with supersonic edges is obtained as a by-product, and for this the terms of the transient pressure coefficient are shown to have geometric significance. The force and moment coefficients are obtained by means of a method of descent, which simplifies the calculations and shows the nature of the dependence of these coefficients on the wing planform. Because of the short duration and moderate strength of the transient effects of the unit-step motion, it is considered to be of little practical importance. However, because of the simplicity of the solutions for the motion, it is also considered to be of possible theoretical value as a basis for Duhamel integration to obtain solutions for more general time-dependent motions of the wide delta wing." }, { "name": "Rannie, William Duncan", "degree": "PhD", "year": "1951", "title": "Heat Transfer in Turbulent Shear Flow", "advisor": "Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172004-135406", "creators": [ { "name": { "family": "Rannie", "given": "William Duncan" }, "id": "Rannie-William-Duncan", "display_name": "Rannie, William Duncan" } ], "advisors": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/9G0F-9R87", "abstract": "A new and relatively simple description is proposed for the velocity profile in turbulent flow close to a smooth wall. Heat transfer coefficients are calculated from the description and are shown to agree better with experiment than other theories. The analysis is extended to transport processes in liquids where the viscosity has a large variation close to the wall.\r\n" }, { "name": "Rosen, Harold Alvin", "degree": "PhD", "year": "1951", "title": "Applications of the Potential Analogy in Network Analysis", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechETD:etd-06242004-143821", "creators": [ { "name": { "family": "Rosen", "given": "Harold Alvin" }, "id": "Rosen-Harold-Alvin", "display_name": "Rosen, Harold Alvin" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2249-6Z06", "abstract": "The analogy existing between linear, lumped parameter network functions and the complex potential function of line charges is applied to various problems in network analysis and synthesis. A means of determining the stream function directly is described. It is shown how the analogy may be used for both steady state and transient analysis when the zeros and poles of the network function are known. In addition, methods of determining the poles of special networks by means of the analogy are described." }, { "name": "Steenson, Bernard Owen", "degree": "PhD", "year": "1951", "title": "Radar Methods for the Exploration of Glaciers", "advisor": "Pickering, William Hayward; Sharp, Robert P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10092014-103732963", "creators": [ { "name": { "family": "Steenson", "given": "Bernard Owen" }, "id": "Steenson-Bernard-Owen", "display_name": "Steenson, Bernard Owen" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" }, { "name": { "family": "Sharp", "given": "Robert P." }, "id": "Sharp-R-P", "role": "co-advisor", "display_name": "Sharp, Robert P." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/3YY8-XC87", "abstract": "The problem of finding the depths of glaciers and the current methods are discussed briefly. Radar methods are suggested as a possible improvement for, or adjunct to, seismic and gravity survey methods. The feasibility of propagating electromagnetic waves in ice and the maximum range to be expected are then investigated theoretically with the aid of experimental data on the dielectric properties of ice. It is found that the maximum expected range is great enough to measure the depth of many glaciers at the lower radar frequencies if there is not too much liquid water present. Greater ranges can be attained by going to lower frequencies.
\r\n\r\nThe results are given of two expeditions in two different years to the Seward Glacier in the Yukon Territory. Experiments were conducted on a small valley glacier whose depth was determined by seismic sounding. Many echoes were received but their identification was uncertain. Using the best echoes, a profile was obtained each year, but they were not in exact agreement with each other. It could not be definitely established that echoes had been received from bedrock. Agreement with seismic methods for a considerable number of glaciers would have to be\r\nobtained before radar methods could be relied upon. The presence of liquid water in the ice is believed to be one of the greatest obstacles. Besides increasing the attenuation and possibly reflecting energy, it makes it impossible to predict the velocity of propagation. The equipment used was far from adequate for such purposes, so many of the difficulties could be attributed to this. Partly because of this, and the fact that there are glaciers with very little liquid water present, radar methods are believed to be worthy of further research for the\r\nexploration of glaciers.
" }, { "name": "Wylly, Alexander", "degree": "PhD", "year": "1951", "title": "A Second-Order Solution for an Oscillating, Two-Dimensional, Supersonic Airfoil", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232009-084121", "creators": [ { "name": { "family": "Wylly", "given": "Alexander" }, "id": "Wylly-Alexander", "display_name": "Wylly, Alexander" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/YA8A-4R06", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nIn this paper a second-order solution, for the forces and moments produced by an oscillating two-dimensional airfoil of arbitrary cross section, has been determined. This solution was obtained by means of an iteration procedure. In the iteration procedure it was necessary to have a linearized solution of simple, closed form which was valid throughout the whole x, y plane. Existing solutions did not satisfy these requirements, thus, it was first necessary to develop a new linearized or first-order velocity potential. This potential was developed as a power series approximation, in frequency, to the exact linearized solution. Six terms of this series were developed and this sixth-order solution shown to be within a few percent of the exact linearized solution for reduced frequencies [...] less than 1.3.\r\n\r\nThe first two terms of the series approximation were then used in the iteration process to produce the second-order solution in thickness. This solution which is valid to second-order in thickness and frequency has been determined for an oscillating airfoil of general cross section.\r\n\r\nThe second-order terms were found to have a relatively strong influence on the final solution, particularly for the pitching moment. It will be seen in Section V that in many cases the second-order terms are larger in magnitude than the corresponding first order-terms and thus reverse the tendencies indicated by first-order theory. In particular, it was shown that the theoretical instability predicted by linearized theory for an airfoil of zero thickness is completely eliminated for an airfoil having a thickness ratio as small as three percent." }, { "name": "Adler, Fred Peter", "degree": "PhD", "year": "1950", "title": "Measurement of the Complex Conductivity of an Ionized Gas at Microwave Frequencies", "advisor": "Pickering, William Hayward; Mackeown, Samuel Stuart", "url": "https://resolver.caltech.edu/CaltechTHESIS:01222018-114138209", "creators": [ { "name": { "family": "Adler", "given": "Fred Peter" }, "id": "Adler-Fred-Peter", "display_name": "Adler, Fred Peter" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" }, { "name": { "family": "Mackeown", "given": "Samuel Stuart" }, "id": "Mackeown-S-S", "role": "advisor", "display_name": "Mackeown, Samuel Stuart" } ], "committee": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "chair", "display_name": "Pickering, William Hayward" }, { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "member", "display_name": "Lindvall, Frederick C." }, { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "member", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "Neher", "given": "Henry Victor" }, "id": "Neher-H-V", "role": "member", "display_name": "Neher, Henry Victor" }, { "name": { "family": "Ramo", "given": "Simon" }, "id": "Ram-Simon", "role": "member", "display_name": "Ramo, Simon" }, { "name": { "family": "Smythe", "given": "William Ralph" }, "id": "Smythe-W-R", "role": "member", "display_name": "Smythe, William Ralph" }, { "name": { "family": "Sorensen", "given": "Royal Wasson" }, "id": "Sorensen-R-W", "role": "member", "display_name": "Sorensen, Royal Wasson" } ], "option_major": [ "eleceng" ], "doi": "10.7907/705A-3B21", "abstract": "The positive column of a glow discharge is placed along the axis of a cylindrical cavity excited in the TM010 mode. The transmission of 3 cm waves through the cavity and the shift in resonant frequency are observed as a function of discharge current. It is shown that from these measurements values of the complex conductivity of the electron gas can be calculated. Curves of the measured conductivity components as functions of pressure and current are given. From theoretical expressions for the conductivity values of electron density are calculated. Langmuir probe studies are carried out and adequate agreement is found. Finally, mean free path and mean free time between collisions are calculated from the conductivity values and hence the variation of collision cross-section with temperature is found.
" }, { "name": "Alford, Jack Leland", "degree": "PhD", "year": "1950", "title": "Internal Friction in Metals", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-080746", "creators": [ { "name": { "family": "Alford", "given": "Jack Leland" }, "id": "Alford-Jack-Leland", "display_name": "Alford, Jack Leland" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/J7H1-BJ17", "abstract": "A summary of the current knowledge on the subject of internal friction is presented. An experimental investigation of the variation of specific damping capacity with torsional stress for three metals is described. It is found that the specific damping capacity can be represented. Calculations are made of the effect on specific damping capacity of type of stress and of non-uniform distribution of stress; the calculations are compared with the available experimental data. An expression is proposed to describe the manner in which energy dissipation varies with stress amplitude" }, { "name": "Alperin, Morton", "degree": "PhD", "year": "1950", "title": "A Study of Detached Shock Waves in Two-Dimensions", "advisor": "Stewart, Homer Joseph; Nagamatsu, Henry T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022009-081306", "creators": [ { "name": { "family": "Alperin", "given": "Morton" }, "id": "Alperin-Morton", "display_name": "Alperin, Morton" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Nagamatsu", "given": "Henry T." }, "id": "Nagamatsu-H-T", "role": "advisor", "display_name": "Nagamatsu, Henry T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NW30-HY03", "abstract": "The present report contains results of an experimental and theoretical investigation of the detached shock wave phenomenon. The experimental phase of this study was actually carried out at the Jet Propulsion Laboratory at California Institute of Technology, in a two-dimensional wind tunnel which is briefly described in Section I.
\r\n\r\nSection II contains a description of the experiments on circular cylinders. The circular cylinder was used in this series of tests primarily because of its simplicity. The investigation discussed in II-1 required a large variation of model shapes and would have required much more time had it been based on a more complicated body shape. In addition to data on the shock wave position and shape, the pressure distribution was also obtained at M=1.546 for a two-dimensional circular cylinder. From this pressure distribution, the drag was calculated.
\r\n\r\nAlthough the theoretical knowledge of flow involving detached shock waves is in a rather primitive state, a review of the existing theoretical work and comparison with experimental data is made in section III.
\r\n\r\nIn section IV a method is presented for finding the stream function or velocity potential for the subsonic region behind the detached shock wave. This method depends upon the hypothesis that the flow can be considered to be irrotational in this region without introducing a serious error. The results appear to be in good agreement with the experiments although the example carried out does not apply strictly to the circular cylinder body shape used in the experiments.
\r\n\r\nA general discussion of the existing theories and their comparison with experimental data is presented in section V.
" }, { "name": "Baen, Spencer Roe", "degree": "PhD", "year": "1950", "title": "The Ternary System Iron-Chromium-Molybdenum at 1200\u00b0F", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06112025-183909499", "creators": [ { "name": { "family": "Baen", "given": "Spencer Roe" }, "id": "Baen-Spencer-Roe", "display_name": "Baen, Spencer Roe" } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/t7vf-ez47", "abstract": "The phase boundaries of the iron-chromium-molybdenum ternary\r\nsystem. have been investigated at 1200\u00b0 F. One-hundred and eighty\r\nalloys were prepared by the method of powder metallurgy for this\r\nstudy. The alloys ware aged in vacuum (10-4 mm Hg or better) for\r\nten days at 1200\u00b0 F. Following the aging treatment the alloys were\r\nrapidly cooled to room temperature. The primary research tools\r\nwere the methods of X-ray diffraction and microscopy as applied to\r\nthe determination of phase boundaries in alloy systems. Microhardness\r\ntests ware used in conjunction with microscopy for the\r\nidentification of phases for some alloys. The results of the\r\npresent investigation in the three binary systems are compared\r\nwith the results of previous investigators. It was found that the\r\nsigma phase or the Fe-Cr binary system is stabilized by the addition\r\nof molybdenum and that this brittle phase is present over a\r\nlarge range of compositions." }, { "name": "Benscoter, Stanley Urner", "degree": "PhD", "year": "1950", "title": "Secondary Stresses in Thin-Walled Beams with Closed Cross-Sections", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02022009-084840", "creators": [ { "name": { "family": "Benscoter", "given": "Stanley Urner" }, "id": "Benscoter-Stanley-Urner", "display_name": "Benscoter, Stanley Urner" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/XKAT-E346", "abstract": "An accurate method of determining secondary stresses in thin-walled, uniform beams of closed cross-section is herein presented. The cross-sections are assumed to be preserved by closely spaced rigid diaphragms. In part I the integro-differential equation governing axial displacements is formulated and solved for a beam without longitudinal stiffeners. In Part II the corresponding summation-difference equation is developed and solved for a beam with stiffeners (flanges and stringers). The cross-section, loading distribution and end conditions are assumed to be arbitrary.\r\n\r\nBy introducing generalized difference equations the mathematical analysis for the stiffened beam may be performed in a manner exactly analogous to the process used for the unstiffened beam. A separation of variables in the homogeneous equation leads to the natural stress or displacement modes for a cross-section. The solution of the non-homogeneous equation is then expressed as an expansion in terms of the natural stress modes. Particular attention is given to cross-sections with single symmetry and double symmetry." }, { "name": "Chang, Chieh-Chien", "degree": "PhD", "year": "1950", "title": "The Linearized Wing Theory of the Supersonic Flow with the Karman's Fourier Integral Method", "advisor": "von K\u00e1rm\u00e1n, Theodore; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042009-110100", "creators": [ { "name": { "family": "Chang", "given": "Chieh-Chien" }, "id": "Chang-Chieh-Chien", "display_name": "Chang, Chieh-Chien" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/67DX-1V06", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nPart I gives a short introduction and some physical interpretation of von armAn's Fourier integral method applied to the supersonic wing theory. A short review of other current contributions to the Linearized supersonic wing theory is also given.\r\n\r\nPart II presents the general formulation of the von [...] method from the view-point of the elementary harmonic sources and doublets. First, the disturbance potential and the velocity components of a general flat body with symmetrical airfoil are derived. Next, the disturbance potential of the lifting surface is presented. In contrast to the well-known conical flow method, the von [...] Fourier integral method can treat a complicated plan-form as a whole, without considering the detailed geometry, as long as the airfoil sections are similar.\r\n\r\nPart III applies the method to the investigation of the wave drag of the non-lifting wing in supersonic flight. A general solution of the wave drag is obtained for the wing with a diamond- shaped airfoil. This solution allows a free choice of a number of the important geometrical parameters. For instance, the wing may be swept forward or backward, tapered or reversed tapered to any ratio. A number of the limiting cases are also investigated. For the practical aerodynamic problems, two useful families of wing plan-form with the fixed taper ratios 0.2 and 0.5, any swept angle, aspect ratio and Mach number are shown in the graphs. A particular application is demonstrated.\r\n\r\nThe reversed flow theorem on wave drag as shown by von [...] and Hayes checks well with the consequence of the general solution. This method shows a certain elegance as no conical flow assumption is needed, and the mathematics is powerful enough to obtain a general solution covering all possible geometrical arrangements without detailed considerations.\r\n\r\nWhile in recent years, the direct problem of finding the lift distribution with given angle of attack on the wing has been well solved by the method of conical flow and others, the present treatment in Part IV, on the other hand, investigates the inverse problem, i.e., to find the downwash distribution in the plane of the wing with a pre- assigned lift distribution. This is particularly favorable with the present method. The general solution of the downwash of the tapered swept wings is derived for the case that a constant lift distribution on the wing is pre-assigned. Of course, the method may be applied to any lift or pressure distribution along the wing chord and span. The corresponding angle of attack on the wing and the downwash can be determined everywhere in the plane of the wing. To demonstrate the downwash distribution as given by the general solution, graphs are given to show the downwash of a number of wings including a swept-back tapered wing with supersonic trailing edge and a delta wing.\r\n" }, { "name": "Chuang, Feng-Kan", "degree": "PhD", "year": "1950", "title": "On the Statistical Theory of Turbulence", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-154021", "creators": [ { "name": { "family": "Chuang", "given": "Feng-Kan" }, "id": "Chuang-Feng-Kan", "display_name": "Chuang, Feng-Kan" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2TJM-BK44", "abstract": "The present work starts with a study of isotropic turbulence which was introduced by G. I. Taylor in 1935. The different notions of averages are critically examined. The notion of stochastic average is then introduced and the general transport equation is developed. After a detailed study of kinematics of turbulence, the concept of correlation and spectrum, the correspondence between the Karman-Howarth equation and the spectrum equation is made. The turbulence decay is studied. A theory for turbulence decay at large Reynolds number is proposed. In the study of turbulence spectrum, different assumptions on the transfer function are critically discussed and the solution using Heisenberg's assumption is obtained explicitly. The spectrum is further studied by trying to fit the turbulence phenomenon into a general scheme of stochastic processes. In the second part of the work, an entirely different approach to the statistical theory is made. Linearized vorticity transport theory is developed and finally the non-linear effects in turbulence are studied." }, { "name": "DeGroff, Harold Miller", "degree": "PhD", "year": "1950", "title": "Aerodynamic Forces on a Propeller in Non-Stationary Motion", "advisor": "Stewart, Homer Joseph; Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272009-083100", "creators": [ { "name": { "family": "DeGroff", "given": "Harold Miller" }, "id": "DeGroff-Harold-Miller", "display_name": "DeGroff, Harold Miller" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "chair", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "member", "display_name": "Fung, Yuan-cheng" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DYT6-1W82", "abstract": "The non-stationary lift and moment of an oscillating propeller blade element are determined. The solutions are obtained in the form of double definite integrals which are evaluated for one numerical example in Appendix A.
\r\n\r\nThe three-dimensional nature of the problem is accounted for by determination of the induced velocity field due to an approximate vorticity distribution in the propeller wake. The corresponding blade element circulation is calculated by means of the classical Munk integral theorem. The two dimensional results for non-stationary lift and moment, expressed in terms of the circulation, are then used to obtain the results of this paper. Derivations of the lift and moment equations are included.
\r\n\r\nThe resultant forces on the blade element are resolved into thrust and torque. Also, a qualitative discussion of the effects of compressibility is made based upon the Prandtl-Glauert transformation.
\r\n\r\nFinally, the results are compared with two dimensional theory and a discussion of the application to problems of flutter and forced oscillations of propellers is made. The discussion is illustrated by means of the numerical example.
\r\n" }, { "name": "Froehlich, Jack Edward", "degree": "PhD", "year": "1950", "title": "Non-Stationary Motion of Purely Supersonic Wings", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-02122009-155907", "creators": [ { "name": { "family": "Froehlich", "given": "Jack Edward" }, "id": "Froehlich-Jack Edward", "display_name": "Froehlich, Jack Edward" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FCGZ-7P23", "abstract": "A general theory is presented for the calculation of the total forces acting on purely supersonic wings. The method applies to wings having an arbitrary downwash distribution (stationary or non-stationary) and is valid whenever all of the wing edges are supersonic. The general three-dimensional non-stationary problem is reduced to an equivalent two-dimensional problem. In the case of harmonic oscillations the aerodynamic coefficients are expressed in terms of known or tabulated functions. The specific example of an oscillating delta wing is considered and values of the aerodynamic coefficients for plunging, pitching, and rolling oscillations are calculated for two Mach numbers." }, { "name": "Green, Leon, Jr.", "degree": "PhD", "year": "1950", "title": "I. The Permeability of a Bed of Smooth Spherical Particles. II. Non-Steady Flow of Gas through a Porous Wall", "advisor": "Duwez, Pol E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08132025-225352011", "creators": [ { "name": { "family": "Green", "given": "Leon, Jr." }, "id": "Green-Leon", "display_name": "Green, Leon, Jr." } ], "advisors": [ { "name": { "family": "Duwez", "given": "Pol E." }, "id": "Duwez-P-E", "role": "advisor", "display_name": "Duwez, Pol E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/p2m3-ce79", "abstract": "Part I
\r\n\r\nThe resistance of a bed of smooth spherical particles to gas\r\nflow in both Darcy and quasi-turbulent regimes was investigated \r\nexperimentally in order to check the accuracy of two conflicting\r\nresistance equations widely reported in the literature. Variations\r\nin specific surface and porosity of the bed independent of one another\r\nwere realized by the use of spheres of different sizes\r\nsystematically packed in different configurations. The experimental\r\nresults are correlated on the basis of a general pressure drop\r\nequation defining two length parameters which are necessary for\r\ncomplete characterization of an arbitrary porous structure. These\r\nresults are used to extend the range of validity of the more\r\naccurate of the two conflicting sphere bed resistance expressions.\r\nA general definition of the Reynold number of a fluid flowing\r\nthrough a porous structure of arbitrary complexity is suggested, and\r\nthe special conditions which permit a sphere bed to be characterized\r\nby a single length parameter are discussed.
\r\n\r\nPart II
\r\n\r\nThe results of a calculation of the time required for establishment\r\nof steady flow of gas through a porous wall following the sudden\r\napplication of a pressure difference across the wall are presented in \r\ndimensionless form. The calculation was made by using an electrical\r\nanalogy to satisfy the non-linear partial differential equation\r\ngoverning the pressure distribution in the wall.
" }, { "name": "Hermes, Richard Manning", "degree": "PhD", "year": "1950", "title": "A Study of Modeling for Dynamic Stress Similitude", "advisor": "Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06172025-163448277", "creators": [ { "name": { "family": "Hermes", "given": "Richard Manning" }, "id": "Hermes-Richard-Manning", "display_name": "Hermes, Richard Manning" } ], "advisors": [ { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/z4kw-mb84", "abstract": "The prediction of stresses developed in structures subjected\r\nto dynamic loading constitutes a problem which is\r\nreceiving increased attention on the part of engineers. The\r\nuse of models for this prediction offers an economical and\r\npractical solution to this problem. In this paper the modeling \r\nparameters for vibrating beams are developed through an\r\nanalysis in which the equations of motion are reduced to\r\ndimensionless form. The validity of these modeling parameters\r\nhus been tested experimentally. These experiments\r\nare reported herein. It is further shown that this method\r\nof analysis can be extended to problems involving plates\r\nand frames." }, { "name": "Li, Ting-Yi", "degree": "PhD", "year": "1950", "title": "Periodic Supersonic Motions of a Thin Wing of Finite Span", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03172009-110456", "creators": [ { "name": { "family": "Li", "given": "Ting-Yi" }, "id": "Li-Ting-Yi", "display_name": "Li, Ting-Yi" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/VZX8-E374", "abstract": "The present paper supplies some general theorems with which periodic supersonic motions of a thin wing of fairly general planform may be analyzed to yield valuable three-dimensional results. It is shown that the method developed by Evvard (Refs. 1,2) for treating the steady supersonic motion of a thin wing with subsonic leading or side edges is valid for an oscillating wing of similar planform. Illustrations of the application of these general theorems are furnished by a careful study of several types of periodic oscillations of a rectangular wing. The present report includes a complete analysis for the case of plunging oscillations. Important steps have also been taken towards solution of the cases of pitching and rolling oscillations. The essential results are presented in a number of vector diagrams giving the magnitudes and phase angles of the lift and moment. Computations are made for several aspect ratios at two Mach numbers (M=10/7,2) when the reduced frequency (k) ranges from 0 to 2.0. It is found that the lift and moment vectors acting on a rectangular wing with supersonic plunging oscillations have positive phase angles within certain ranges of Mach numbers and aspect ratios, while the corresponding vectors acting on a wing of infinite span with the same kind of motion have negative phase angles for every Mach number. This new discovery indicates strongly the necessity of revising present day wing flutter calculations.\r\n" }, { "name": "Lurie, Harold", "degree": "PhD", "year": "1950", "title": "Lateral Vibrations as Related to Structural Stability", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-07092007-131041", "creators": [ { "name": { "family": "Lurie", "given": "Harold" }, "id": "Lurie-Harold", "display_name": "Lurie, Harold" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/0P9M-XM21", "abstract": "The apparently different physical problems of lateral vibration and elastic stability are limiting cases of a single phenomenon, the most general expression being the mode of vibration with end thrust. The theory of straight beams and flat plates is discussed in detail, and it is shown that the square of the frequency of lateral vibration is approximately linearly related to the end load. The linear relationship is exact if the mode of free vibrations is identical to the buckling mode. In all cases, the load corresponding to zero frequency is the critical buckling load. The analysis is valid only if the boundary conditions do not change with load.\r\n\r\nExperimental tests were conducted on elastically restrained columns in the form of rigid rectangular frames. It is found that the relationship between the square of the frequency and the load is practically linear, and that the extrapolated load corresponding to zero frequency coincides with the buckling load. Determining the critical load by frequency measurements seems to have the advantage of predicting that load corresponding to the actual boundary conditions which prevail, whereas a theoretical calculation may unjustifiably assume certain conditions which are not exactly realized.\r\n\r\nIn the case of flat plates, tests showed that the linear relationship is not achieved in practice. It is shown that this is probably due to the fact that the linear plate equations are not valid due to initial curvatures in the plate.\r\n\r\nRigid-joint trusses were also tested. Due to the change of end restraint with load, in some cases the relationship between the square of the frequency and the load deviates considerably from linearity. The amount of deviation appears to depend on the section properties of the members of the truss." }, { "name": "Martin, Harold Clifford", "degree": "PhD", "year": "1950", "title": "Elastic Instability of Cantilever Struts Under Combined Axial and Transverse Forces at the Free End", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-02272009-130215", "creators": [ { "name": { "family": "Martin", "given": "Harold Clifford" }, "id": "Martin-Harold-Clifford", "display_name": "Martin, Harold Clifford" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F3YJ-3D63", "abstract": "This investigation considers the elastic instability of cantilever struts under applied axial and transverse forces at the free end. Fig.1 shows the general case of such a strut.\r\n\r\nFirst the strut of uniform depth and without sweep is studied. This is shown in Fig. 2. A derivation is given for the governing differential equation and boundary conditions. These are then solved for the minim coupled eigenvalues, which correspond to the critical load combinations. Fig. 10 is a plot of these calculated critical loadings.\r\n\r\nNext an experimental investigation, whose main purpose was to provide a check on the above theoretical calculations, is presented. Various difficulties are discussed in addition to the techniques finally adopted. Experimental values are shown to check theory within several per cent. See Fig. 16. Also Southwell\u2019s experimental procedure for determining instability loading is shown to apply to this case of coupled loading.\r\n\r\nThe theory is then extended to include the problem of the tapered strut. Equations and boundary conditions are given for the arbitrary taper case and a solution presented for the limiting strut having complete taper. These results are given in Fig. 24.\r\n\r\nIn the concluding Part some of the more important unsolved problems are discussed in detail. These include the strut with arbitrary taper, the swept strut, and the strut which buckles inelastically.\r\n\r\nThe Appendix derives the differential equation for the non-tapered strut by variational procedure." }, { "name": "Rasof, Bernard", "degree": "PhD", "year": "1950", "title": "Supersonic Source Flow Past Thin Air Foils", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-03052009-084956", "creators": [ { "name": { "family": "Rasof", "given": "Bernard" }, "id": "Rasof-Bernard", "display_name": "Rasof, Bernard" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NCKK-3A63", "abstract": "In this thesis the supersonic source flow over a thin sharp- edged airfoil is formulated as a linearized problem. A new potential equation is derived, using a system of spherical coordinates centered at the source; as a simplification only wings symmetrical about the z axis are considered, and of these only the limiting cases of ring- and annular- airfoils are treated.
\r\n\r\nAfter transforming to characteristic coordinates in the hodograph plane, the potential equation (which has variable coefficients) is shown to be approximated by two classical equations -- one holding for the ring wing and the other applying to the annular wing. The flow over a specific annular wing is computed by en application of the Riemann method to the telegraph equation, which is the appropriate approximation to the governing equation for this case.
\r\n\r\nThe linearized potential equation is also solved by the Method of Characteristics, using a numerical equivalent of the Mono, procedure for quasilinear partial differential equations. A complete set of compatibility equations is exhibited, allowing the computation of the perturbation velocity components at any point of the zone of influence of an airfoil set in the supersonic source flow. Two numerical examples are presented, illustrating the application to the computation of the flow over each of a ring- and annular- wing.
\r\n\r\nFinally in an appendix the usually powerful method of separation of variables is shown to be unsuitable as a procedure for solving the potential equation governing the present problem.
\r\n" }, { "name": "Rechtin, Eberhardt", "degree": "PhD", "year": "1950", "title": "Application of a New Technique for Radio Wave Propagation Study to Experimental Confirmation of the Phase Characteristics of Norton's Ground Wave Propagation Theory", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232004-145009", "creators": [ { "name": { "family": "Rechtin", "given": "Eberhardt" }, "id": "Rechtin-Eberhardt", "display_name": "Rechtin, Eberhardt" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/6M4E-4539", "abstract": "The basic purpose of this work is to investigate experimentally the phase characteristics of radio waves propagated along the surface of the earth as proposed by K.A. Norton (reference 1). Norton's theory indicates that the ground wave phase at distances of the order of tens of miles is greater than the corresponding space wave phase by not more than 180 degrees. From a radio surveying point of view, range errors of tens of feet may result. To avoid difficulties inherent in the direct and absolute approach, that of comparison of optical surveying with radio surveying over actual terrain at normally used frequencies (200 kilocycles per second to 15 megacycles per second), a new technique is developed.\r\n\r\nIt is proposed that the propagation of radio waves may be studied by use of appropriate scale models, permitting experiments otherwise impossible because of the gigantic size of the equivalent true scale systems. Further, relative measurements may be obtained directly in a model system by proper choice of paths as contrasted with the absolute measurements usually made in a full-scale system.\r\n\r\nThe technique is demonstrated by a preliminary experimental confirmation of Norton's theory. Suggestions for technique improvement and for further investigation possibilities are given." }, { "name": "Roney, Robert Kenneth", "degree": "PhD", "year": "1950", "title": "The Influence of Metal Grain Structure on the Attenuation of an Ultrasonic Acoustic Wave", "advisor": "Lindvall, Frederick C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01052007-131306", "creators": [ { "name": { "family": "Roney", "given": "Robert Kenneth" }, "id": "Roney-Robert-Kenneth", "display_name": "Roney, Robert Kenneth" } ], "advisors": [ { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "advisor", "display_name": "Lindvall, Frederick C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/V3FK-SM37", "abstract": "Apparatus is described for the study of the propagation of ultrasonic acoustic waves in solid bodies and its applications in metallurgy. In particular, the anisotropy of attenuation in cold worked aluminum and the effect of anneal are demonstrated. Reflections from individual crystal faces are identifiable in bodies with average grain diameter of 0.17 mm. A critical discussion is given of a theoretical effect of grain size on wave attenuation as advanced by Mason and McSkimin(9), and an empirical relation reported by Roth(7). The theory is extended to cover the complete range from that explored by Mason to that reported by Roth. Experimental deviation from the theoretical effect indicates other factors besides average grain size are effective in materials with asymmetrical grain structure." }, { "name": "Russell, William Treloar", "degree": "PhD", "year": "1950", "title": "Lumped Parameter Analogies for Continuous Mechanical Systems", "advisor": "Housner, George W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:07102025-014554988", "creators": [ { "name": { "family": "Russell", "given": "William Treloar" }, "id": "Russell-William-Treloar", "display_name": "Russell, William Treloar" } ], "advisors": [ { "name": { "family": "Housner", "given": "George W." }, "id": "Housner-G-W", "role": "advisor", "display_name": "Housner, George W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/pv3j-w995", "abstract": "This thesis is an investigation of the analogies between lumped or continuous mechanical systems and electric circuits. Methods are developed for obtaining electric circuit analogs of linearized mechanical systems. Essential features of the development are the use of coordinate transformations and the transformation properties of certain fundamental matrices. These make possible a general treatment of the problem of obtaining efficient analogs.
\r\nThe general theory is developed in part II and it is shown that an electric circuit using linear passive, bi-lateral elements and ideal transformers may be constructed for any of the linear mechanical systems considered.
\r\nIn part III a new approach to the problem of circuit analogies for beams is developed and the methods of part II are applied to obtain new and more accurate analogies for the dynamic behavior of beams with up to six degrees of freedom. A discussion of analogies for frames is given and the effects of the so-called shear deflection and of combined lateral and axial loads in beams is investigated.
\r\nIn part IV the errors due to lumping of distributed mass and distributed external force are investigated for some simple systems.
\r\nA discussion and summary of the thesis is given on pages 11 to 14.
" }, { "name": "Schurman, Glenn August", "degree": "PhD", "year": "1950", "title": "An Investigation of the Autoignition of a Combustible Mixture Due to the Presence of a Heated Surface", "advisor": "Kyropoulos, Peter R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-084015", "creators": [ { "name": { "family": "Schurman", "given": "Glenn August" }, "id": "Schurman-Glenn-August", "display_name": "Schurman, Glenn August" } ], "advisors": [ { "name": { "family": "Kyropoulos", "given": "Peter R." }, "id": "Kyropoulos-P-R", "role": "advisor", "display_name": "Kyropoulos, Peter R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/3QCH-T047", "abstract": "An experimental investigation regarding the nature of the hydrogen-oxygen reaction in the vicinity of a heated surface is described. The experimental work was conducted at atmospheric pressure in a shallow rectangular combustion chamber. The upper surface of this chamber is heated to temperatures ranging from room temperature to 1615\u00b0 R; the lower surface is maintained at a constant temperature of 550\u00b0 R. The temperature distribution of the mixture between the two plates is the primary experimental measurement. This measurement was made with a Mach-Zehnder optical interferometer. The maximum temperature of the upper plate at which experiments were made was 1615\u00b0 R. The maximum temperature at which interferograms were taken was limited by the presence of a nonuniform temperature distribution along the light path. It was found that the central area of the heated surface of the combustion chamber could be held at a temperature of 1710\u00b0 R without an explosion occurring. The chemical reaction could not be detected below an upper plate temperature of 1500 \u00b1 10\u00b0 R. There is evidence that large composition gradients exist in the combustion chamber. These gradients persist for a much longer time than that predicted from the diffusion theory. Accordingly, the overall rate at which the reactants combine is much lower than that expected. The exact reasons for the suppression of the explosion and the reduced reaction rate are not understood. Two possible explanations are suggested." }, { "name": "Williams, Max Lea", "degree": "PhD", "year": "1950", "title": "The Plate Problem for a Cantilever Sector of Uniform Thickness", "advisor": "Sechler, Ernest Edwin; Fung, Yuan-cheng", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202004-095445", "creators": [ { "name": { "family": "Williams", "given": "Max Lea" }, "id": "Williams-Max-Lea", "display_name": "Williams, Max Lea" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng", "role": "advisor", "display_name": "Fung, Yuan-cheng" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/WFM9-RR55", "abstract": "As one approach to the problem of analyzing missile wings of approximately delta configuration for stress and deflection characteristics, a uniformly thin plate of sector planform clamped along one radial edge has been considered.\r\n\r\nIt is shown that an infinite set of deflection functions, resulting from a product solution to the double Laplacian, may be generated, but practical utility is impeded because the functions are non-orthogonal. It is believed that should the importance of the solution warrant, the deflection of a sector under normal loading may be found by using a combination of the deflection functions, the Trefftz variational method, and high speed computing machinery.\r\n\r\nAnother section of the report is devoted to a study of the stress along the clamped edge in the vicinity of the corner, and it is shown that the stress varies from zero to a mathematical infinity as the opening angle of the sector increases from zero through ninety degrees with the stress singularity becoming progressivev stronger as the opening angle is increased. Experimental data are included that show engineering agreement with the theoretical results, for the case of a delta plate of thirty degree opening angle and varying trailing edge angle.\r\n\r\nIn conclusion, some remarks are made upon the application of the sector results to swept rectangular plates by mans of a hydrodynamic analogy wherein the possibility of obtaining approximate overall stress distributions is indicated.\r\n" }, { "name": "Bennett, Robert Royce", "degree": "PhD", "year": "1949", "title": "Electric Analog Computer Techniques Applied to Certain Mechanical Vibration Problems", "advisor": "McCann, Gilbert Donald; Lindvall, Frederick C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072025-081037970", "creators": [ { "name": { "family": "Bennett", "given": "Robert Royce" }, "id": "Bennett-Robert-Royce", "display_name": "Bennett, Robert Royce" } ], "advisors": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-G-D", "role": "advisor", "display_name": "McCann, Gilbert Donald" }, { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "advisor", "display_name": "Lindvall, Frederick C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/xwsf-nf22", "abstract": "Solutions are given for two distinct types of vibration problems\r\nof importance in the field of applied mechanics. These solutions\r\nare of themselves useful, and in addition they represent the development\r\nof basic electric analog computer techniques which may be applied\r\nto the solution of a vast number of hitherto unsolved engineering\r\nproblems.
\r\n\r\nPart One treats the problem of a linear system excited by one\r\nor more forces of varying frequency. An analytical solution is\r\ngiven for the case in which the exciting force is of constant amplitude\r\nand of a frequency which varies linearly with time. A device\r\nwhich generates electric forces of varying frequency is discussed,\r\nand the results of its application to the solution of time-varying\r\nfrequency problems are shown. A detailed study is made of a low\r\nloss two degree of freedom system excited by a force of constant\r\namplitude and a frequency varying linearly with time. This study\r\ndemonstrates the tremendous saving in time which may be effected by\r\nelectric analog computation methods. It is demonstrated how forces\r\nof time-varying frequency may be used to rapidly obtain a qualitative\r\nmeasure of a system's steady state frequency response.
\r\n\r\nThe transient draft gear forces existing during the braking of\r\na long train are treated in Part Two. An analytical solution and an\r\nElectric Analog Computer solution are given for a train of identical\r\ncars and draft gears assumed to behave as perfect springs. The\r\nelectric analog for a nonlinear draft gear is developed. A computer\r\nsolution is presented for a train containing nonlinear draft gears\r\nand, in addition, for certain distributions of cars of unequal weights.\r\nThis problem, involving a system of fifty nonlinear elements and\r\nfifty separate excitation forces would be completely impracticable\r\nby even the best available digital computation methods.
" }, { "name": "Biehl, Arthur Trew", "degree": "PhD", "year": "1949", "title": "Statistical Studies of Cosmic Rays at High Altitudes", "advisor": "Neher, Henry Victor; Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092025-184929895", "creators": [ { "name": { "family": "Biehl", "given": "Arthur Trew" }, "id": "Biehl-Arthur-Trew", "display_name": "Biehl, Arthur Trew" } ], "advisors": [ { "name": { "family": "Neher", "given": "Henry Victor" }, "id": "Neher-H-V", "role": "advisor", "display_name": "Neher, Henry Victor" }, { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9mb2-6n05", "abstract": "A description or the equipment used in measuring cosmic ray\r\nintensities at high altitudes by both balloon and airplane is given.\r\nResults of a series or 15 balloon nights throughout the United States\r\nand Canada are discussed.
\r\n\r\nA B-29 airplane flight to Peru \u00a3or measuring the latitude effect\r\nis discussed and conclusions drawn as to the charge of the primary\r\ncosmic rays. In particular, time variations of cosmic rays at high\r\naltitude are analyzed.
\r\n\r\nA series of B-29 flights made under identical conditions expressly\r\nfor the purpose of studying time variations or cosmic rays are analyzed.\r\nIt is found that there is a general pattern to the variations which\r\nmight be explained by the eccentricity of the sun's magnetic dipole\r\nfrom the sun's rotational axis.
" }, { "name": "Bowen, John Thomas", "degree": "PhD", "year": "1949", "title": "Some Viscosity Effects in Axial Flow Compressors", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292025-223029268", "creators": [ { "name": { "family": "Bowen", "given": "John Thomas" }, "id": "Bowen-John-Thomas", "display_name": "Bowen, John Thomas" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/6de9-xf55", "abstract": "1. A thirty-six inch tip diameter axial flow air compressor,\r\nauxiliary apparatus and instrun1entation have\r\nbeen constructed and have been successfully operated\r\nfor securing accurate test data.
\r\n\r\n2. Special instruments for detailed flow measurements\r\nnear bounding surfaces have been constructed and successfully\r\nused.
\r\n\r\n3. On the basis of data secured from the test installation,\r\nit has been established that flow energy losses\r\nwhich result from fluid friction on actual compressor\r\nblade surfaces are considerably greater than would be\r\nexpected from measured or calculated two-dimensional\r\nresults. Furthermore, the range of low-loss operation\r\nis significantly reduced.
\r\n\r\n4. Test results indicate that the outer and inner wall\r\nboundary regions, which are affected by fluid friction,\r\nmay or may not become more extensive through several\r\nstages of an axial flow compressor, depending on the\r\nspecific compressor design.
\r\n\r\n5. Measurements indicate that a considerable portion\r\nof overall compressor losses occur near the outer end\r\ninner extremes of the blade sets because of poor flow\r\nincidence conditions in the wall boundary regions.
" }, { "name": "Cole, Julian David", "degree": "PhD", "year": "1949", "title": "Problems in Transonic Flow", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04202004-105506", "creators": [ { "name": { "family": "Cole", "given": "Julian David" }, "id": "Cole-Julian-David", "display_name": "Cole, Julian David" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "chair", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "De Prima", "given": "Charles R." }, "id": "De-Prima-C-R", "role": "member", "display_name": "De Prima, Charles R." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "member", "display_name": "Liepmann, Hans Wolfgang" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QS66-WA09", "abstract": "No Abstract." }, { "name": "Gruenberg, Harry", "degree": "PhD", "year": "1949", "title": "A Resonant Cavity Method of Measuring the Velocity of Light", "advisor": "Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222025-165427391", "creators": [ { "name": { "family": "Gruenberg", "given": "Harry" }, "id": "Gruenberg-Harry", "display_name": "Gruenberg, Harry" } ], "advisors": [ { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/61cd-fx41", "abstract": "A method is proposed to determine the velocity of\r\npropagation of electromagnetic waves by means of a resonant\r\ncavity. A circular cylindrical cavity is used operating\r\nin the TE011 mode. It is shown that for a particular length-to-\r\ndiameter ratio, the resonance frequency is only a function\r\nof the cavity volume and the velocity of electromagnetic\r\nwaves. The latter can be calculated, when resonance\r\nfrequency and cavity volume are determined experimentally.\r\nThe main advantage of this method is, that the volume\r\nhas to be measured only to one-third the accuracy which\r\nis desired for the propagation velocity. Linear dimensions,\r\non the other hand, have to be determined to the same accuracy.\r\nFurthermore, the volume method requires only reasonable\r\ntolerances in the construction of the cavity.
\r\n\r\nThe effects of various cavity imperfections on the\r\nresonance frequency were analysed. The frequency shifts\r\ndue to, the finite conductivity of the walls, the deformations\r\nin the boundary surface, grooves, and coupling irises,\r\nwere calculated. The problem of a thick iris was treated\r\nnumerically.
" }, { "name": "Head, Richard Moore", "degree": "PhD", "year": "1949", "title": "Investigations of Spontaneous Condensation Phenomena", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechTHESIS:04212011-134533762", "creators": [ { "name": { "family": "Head", "given": "Richard Moore" }, "id": "Head-Richard-Moore", "display_name": "Head, Richard Moore" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/06R8-C778", "abstract": "The results of a systematic wind tunnel investigation into the attainment and ultimate collapse of the supersaturated state of water vapor are presented. These results, together with those of other recent investigations, are collected and compared with the theory. It is found that the deviations from the quasi-stationary conditions upon which the theory is based are very pronounced in the supersonic wind tunnel. A much higher degree of supersaturation can, therefore, be attained before condensation occurs than is predicted theoretically.\r\n\r\nMeasurements at low temperatures indicate that if the water vapor reaches a temperature of about 153 \u00b0K, without the occurrence of condensation, the vapor will not condense upon further expansion, regardless of how highly supersaturated it becomes. This observation is in agreement with some recent Wilson Cloud Chamber investigations.\r\n\r\nThe shock relations for flow-involving condensation are discussed. It is shown that two types of discontinuities can occur; the condensation shock and the shock with condensation (or vaporization). The latter solution has been disregarded in the past, but it is shown that the shock with vaporization is of importance and can result in appreciable errors in Mach number determination when droplets are present in the flow.\r\n\r\nVarious techniques of measurement of the condensation processes in supersonic flow are considered.\r\n" }, { "name": "Ismail, Hassan Mohamed", "degree": "PhD", "year": "1949", "title": "Study of Suspended Sediment in Closed Channels", "advisor": "Vanoni, Vito A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04262004-152823", "creators": [ { "name": { "family": "Ismail", "given": "Hassan Mohamed" }, "id": "Ismail-Hassan-Mohamed", "display_name": "Ismail, Hassan Mohamed" } ], "advisors": [ { "name": { "family": "Vanoni", "given": "Vito A." }, "id": "Vanoni-V-A", "role": "advisor", "display_name": "Vanoni, Vito A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/FR64-QE92", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nTests on a rectangular channel 10.5 by 3 inches in cross-section transporting water mixed with different amounts of sand are described in this thesis. Two sizes of sand were used. They are of mean sedimentation diameter of 0.10 mm. and 0.16 mm.\r\n\r\nTh experimental data were used to study both the effects of the presence of sand in suspension on the characteristics of the flow, and the concentration transfer coefficient at the middle of the channel, assuming a two-dimensional flow.\r\n\r\nIt was found the the von Karman universal constant of turbulent exchange k decreases with the increase of the suspended material. k decreased to 0.20 when a total load of about 25 kilograms was added to the flume, i.e., 43 grams were added to each liter. No limit was approached for the decreased of k. The friction coefficient [...] was hardly affected by the presence of the sand when the velocity of flow was higher than a certain velocity. This critical velocity increased with the total load in the flume and the size of the sand used. It is related to the bed load and it is the velocity at which all the dunes on the bed are carried in suuspension. Below that critical velocity [...] exceeds that of clear water.\r\n\r\nThe sediment transfer coefficient [...] was found to be equal to 1.5, the momentum transfer coefficient [...] for the 0.10 mm. sand, and to 1.3 [...] for the 0.16 mm. sand. [...] follows the normal parabolic form of [...] at the outer two-thirds of the channel and has a constant value at the middle third." }, { "name": "MacNeal, Richard Henri", "degree": "PhD", "year": "1949", "title": "The Solution of Partial Differential Equations by Means of Electrical Networks", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-04282004-143609", "creators": [ { "name": { "family": "MacNeal", "given": "Richard Henri" }, "id": "MacNeal-Richard-Henri", "display_name": "MacNeal, Richard Henri" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PZ04-5290", "abstract": "The material in this thesis is the result of a year's experience in the solution of problems on the Caltech Electric Analog Computer. Although much work has been done elsewhere, the solution of partial differential equations is a relatively new field for the Caltech Computer. It is natural that such an undertaking should initiate points of view and techniques that differ from those of other investigators., This thesis contains the development of certain ideas that have been useful to the author in the solution of problems on the computer.\r\n\r\nIn Part I, finite difference methods are treated with reference to problems with one space variable. Techniques are developed for the representation of differential operators by means of electrical networks and the question of unequal lumping is discussed.\r\n\r\nThe solutions of the fourth order differential equations of a beam are treated in Part II. Such practical considerations as the effects of parasitic impedances and cell size are investigated. Solutions are presented for the normal modes of a cantilever beam, the transient vibration of a cantilever beam, and the coupled modes of vibration of an airplane wing.\r\n\r\nProblems involving the scalar Laplacian operator are treated in Part III. A general asymmetric network is developed that is useful for problems with irregular boundaries and for problems where it is desired to have variable cell size. These techniques are illustrated with respect to a cavity resonator problem and an electromagnetic radiation problem.\r\n\r\nElastic plate problems are treated in Part IV. The analogy for the elastic plate is an extension of the beam analogy to two dimensions. Here the difficult problems are those relating to the representation of boundary conditions, particularly of boundary conditions along an irregular edge.\r\n\r\nSome conclusions regarding the construction of a network analyzer designed specifically for the solution of partial differential equations are given in Part V. The chief conclusion is that such a computer must contain a much larger number of electrical elements than are at present available in the Caltech Computer." }, { "name": "Mettler, Ruben Fred", "degree": "PhD", "year": "1949", "title": "The Anemometric Application of an Electrical Glow Discharge in Transverse Air Streams", "advisor": "Lindvall, Frederick C.; Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11032003-110318", "creators": [ { "name": { "family": "Mettler", "given": "Ruben Fred" }, "id": "Mettler-Ruben-Fred", "display_name": "Mettler, Ruben Fred" } ], "advisors": [ { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "advisor", "display_name": "Lindvall, Frederick C." }, { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/RTBA-4692", "abstract": "The possibility of using an electrical glow discharge for quantitative turbulence measurements is experimentally investigated. It is found that a glow discharge is stable in a transverse air stream throughout the subsonic velocity range, and at supersonic air velocities up to a Mach number of 1.5, with no indication that this Mach number represents an upper velocity limit. A calibration procedure is developed and used in measuring the decay of turbulence behind a grid at low subsonic velocities. Comparison with decay measurements made independently with a hot wire anemometer under similar flow conditions shows that the glow discharge data is as yet quite badly scattered and somewhat inconsistent.\r\n\r\nA quantitative theory of the dark current anemometer is presented and gives results which agree in form with reported experimental results. A qualitative theory of the mechanism of the glow discharge anemometer and the first steps of the corresponding quantitative analysis are also presented." }, { "name": "Morikawa, George Kiyoshi", "degree": "PhD", "year": "1949", "title": "The Wing-Body Problem for Linearized Supersonic Flow", "advisor": "Stewart, Homer Joseph; Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-01282009-112820", "creators": [ { "name": { "family": "Morikawa", "given": "George Kiyoshi" }, "id": "Morikawa-George-Kiyoshi", "display_name": "Morikawa, George Kiyoshi" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" }, { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "co-advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/PJZP-YG35", "abstract": "This work is concerned with one of the important problems remaining in the theory of linearized supersonic flow: the study of non-planar systems dealing with configurations which cannot be completely solved with the existing theory - in particular, the study of interaction or interference between fuselage and lifting or control surfaces in supersonic flow.\r\n\r\nIn Sections 1.2 and 1.3 the non-planar problems are classified and the problem considered to be the fundamental wing body problem for linearized supersonic flow is presented. In Part II, this and related problems are formulated in a manner suitable for Laplace transform methods and subsequently the transformed solutions are presented in a general form by the Green's function method.\r\n\r\nDue to the inherent difficulties arising in non-planar problems, related planar problems are solved in Part III. In Part IV, the fundamental wing-body problem is discussed in detail and in the light of the results of Part III an approximate solution (in terms of the pressure) in the region of greatest interest is presented; and a quantitative estimate of the increase in lift due to the interaction between wing and body is indicated." }, { "name": "Nagamatsu, Henry Takeshi", "degree": "PhD", "year": "1949", "title": "Theoretical Investigation of Detached Shock Waves", "advisor": "Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092009-130132", "creators": [ { "name": { "family": "Nagamatsu", "given": "Henry Takeshi" }, "id": "Nagamatsu-Henry-Takeshi", "display_name": "Nagamatsu, Henry Takeshi" } ], "advisors": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HW36-ZP15", "abstract": "The problems associated with the detached shock wave are considered from the analytical standpoint in this report. For considering the general case for the detached shock wave, the nonstationary isentropic differential equation is derived. In general the stationary detached shock wave is curved and thus the flow back of the shock is rotational. The effect of rotational flow upon the velocity and pressure distribution over a circular cylinder is analyzed for a parabolic velocity distribution in the disturbed region.\r\n\r\nThe basic equations for both normal and oblique shock waves are presented and the significance of these equations to the problem of detached shock is discussed. The condition for the shock wave to be detached are presented and the mathematical formulation of the Tricomi type of differential equation for the detached shock wave is given.\r\n\r\nThe first approximation to the location of the detached shock wave is derived and the analytical results are correlated with the perimental data for spheres obtained from the supersonic wind tunnel and the ballistic range. The agreement was found to be satisfactory.\r\n\r\nThe existence and uniqueness of a potential solution for an infinite wedge with normal detached shock wave moving at constant velocity is presented. It is shown that, even for an infinite wedge with normal detached shock wave the potential solution does not exist." }, { "name": "Peterson, Norman Charles", "degree": "PhD", "year": "1949", "title": "Noncircular Fuselages in Supersonic Flow", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-02032009-125355", "creators": [ { "name": { "family": "Peterson", "given": "Norman Charles" }, "id": "Peterson-Norman-Charles", "display_name": "Peterson, Norman Charles" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JCZX-0749", "abstract": "The applicability of linearized theory to the aerodynamic study of slender, three-dimensional bodies in supersonic flow is considered in detail, and figures are presented which show the limitations of body shape and mach number to be observed if quantitatively reliable results are to be achieved. Then methods are developed and evaluated for calculating the supersonic flow about slender noncircular bodies, other than wings.\r\n\r\nSections I and II are concerned with the velocity and pressure predictions of the linearized theory. It is shown that these quantities do not converge to the corresponding predictions of the exact solutions for vanishing disturbance, and the reason therefore is found. In Section III the inapplicability of wing theory methods and the theory of slender circular bodies to the present study is reviewed, and the problem is carried to the fundamental nonrotationally symmetrical solutions of the wave equation; the properties of the noncircular functions are developed in Section IV. Section V contains a description of the Lorentz transformation for obtaining solutions singular on a yawed line, and Section VI a simple statement of the Gothert transformation for changing the Mach number.\r\n\r\nSections VII and VIII contain an exposition of the use of the theory developed in the previous Sections. Bodies in supersonic flow are classified according to size and orientation, an appropriate methods for each are presented and evaluated.\r\n\r\nThe Appendices present tables of the functions used in the analysis, along with sample computations." }, { "name": "Puckett, Allen Emerson", "degree": "PhD", "year": "1949", "title": "Supersonic Wave Drag of Thin Airfoils", "advisor": "von K\u00e1rm\u00e1n, Theodore; Stewart, Homer Joseph", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232004-141931", "creators": [ { "name": { "family": "Puckett", "given": "Allen Emerson" }, "id": "Puckett-Allen-Emerson", "display_name": "Puckett, Allen Emerson" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-H-J", "role": "advisor", "display_name": "Stewart, Homer Joseph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HYJJ-3241", "abstract": "The linearization of the equations of motion for the supersonic flow of a perfect fluid is discussed, and methods of solution using elementary source sink solutions are developed. These methods are applied to the calculation of performance of several types of three-dimensional supersonic airfoils; in particular, the drag at zero lift of a family of almost triangular, symmetrical wings is calculated. The significance of the results is discussed.\r\n" }, { "name": "Quinlan, Patrick Michael", "degree": "PhD", "year": "1949", "title": "A Fourier Integral Approach to an Aeolotropic Medium", "advisor": "Martel, Romeo Raoul; Converse, Frederick James", "url": "https://resolver.caltech.edu/CaltechETD:etd-04142009-143250", "creators": [ { "name": { "family": "Quinlan", "given": "Patrick Michael" }, "id": "Quinlan-Patrick-Michael", "display_name": "Quinlan, Patrick Michael" } ], "advisors": [ { "name": { "family": "Martel", "given": "Romeo Raoul" }, "id": "Martel-R-R", "role": "advisor", "display_name": "Martel, Romeo Raoul" }, { "name": { "family": "Converse", "given": "Frederick James" }, "id": "Converse-F-J", "role": "advisor", "display_name": "Converse, Frederick James" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/CTQV-V186", "abstract": "Chapter I: The equations of equilibrium in terms of the displacement components for an axially symmetric aeolotropic medium are developed from the strain-energy function of the medium. Then follows a discussion of the literature of the subject, and an outline of the scope of the present thesis.\r\n\r\nCharter II: The solution is carried through using Fourier Integral technique for the two dimensional plane strain case. Stresses and displacements are obtained for a concentrated line load.\r\n\r\nChapter III: The results of Chapter II are applied to determine the surface settlements, vertical pressures, and shears for a symmetrically loaded strip called \"the unit strip\" of width two units. The following special load distributions are investigated: concentrated, uniform, parabolic, inverted parabolic, hollow wall, and rigid wall. Extension is then made to a strip of any arbitrary width 2a, and settlements are obtained by means of influence factors, (Graph I). An examination is made of the influence of the type of load distribution, demonstrating St. Venant's principle of equipollent loads.\r\n \r\nChapter IV: The equations of Chapter I are solved for an axially symmetric loading by transforming to polar co-ordinates and using Fourier-Bessel Integral technique. The solution is carried through for the concentrated load case, and the results check those given by Mitchell (6).\r\n\r\nChapter V: An investigation similar to that made in Chapter III is made for a loaded circular area of unit radius. The results are then extended to a circle of any arbitrary width a. Surface settlements are obtained quickly by means of influence factors (Graph II). In the latter part of the Chapter series expansions are obtained for the stresses and displacements at any point in the mass, and application is made to some of the more practical load distributions.\r\n\r\nChapter VI: Corresponding results for an elastic isotropic medium, to those given in above chapters, are obtained by the application of a limiting technique to above results. The ease with which the results are obtained is striking. A discussion is given of the infinite surface displacements that are usually obtained in two-dimensional problems.\r\n\r\nChapter VII: In this chapter a review is made of the literature of the three constant medium. The physical significance of the assumptions and the measure of fulfillment of these assumptions by some types of wood, and by some crystals, is examined. Some errors are noted, and corrected. Finally all are shown to be just particular cases of the medium of Chapter II, without having the redeeming feature of simplicity over the more general theory.\r\n\r\nChapter VIII: Results for Orthotropic plates are deduced from those given in Chapter II by a change of constants.\r\n\r\nChapter IX: Typical problems in soil mechanics connected with a loaded column, and with a loaded wall, are worked out in detail. Graph III shows for a particular case the effect aeolotropy may have on the vertical stress distributions in a loaded soil. A brief outline is made of some other problems in an aeolotropic medium capable of solution by the methods of this thesis.\r\n\r\nAppendix F: Practical methods are given for the determination of the required constants. The value of skew samples is shown. The results obtained in this thesis for an aeolotropic medium, apart from the concentrated case given by Mitchell(6), are new. A good test of the accuracy of the work is provided by the known isotropic elastic results obtained by a limiting procedure in Chapter VI. As far as the author is aware, some of the results of Chapter VI are new also. The direct application of Fourier Integral technique to the displacement equations of equilibrium is very rare in elastic problems. This thesis illustrates the power and simplicity of such an approach. Finally, as shown in Chapter IX the results are very readily adapted to practical use." }, { "name": "Sabersky, Rolf Heinrich", "degree": "PhD", "year": "1949", "title": "Experimental and Theoretical Investigations on the General Flow Patterns in Axial Flow Compressors", "advisor": "Rannie, W. Duncan", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142003-142428", "creators": [ { "name": { "family": "Sabersky", "given": "Rolf Heinrich" }, "id": "Sabersky-Rolf-Heinrich", "display_name": "Sabersky, Rolf Heinrich" } ], "advisors": [ { "name": { "family": "Rannie", "given": "W. Duncan" }, "id": "Rannie-W-D", "role": "advisor", "display_name": "Rannie, W. Duncan" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng", "physics" ], "doi": "10.7907/6H98-MT27", "abstract": "1. An axial flow compressor and the corresponding test facilities including instrumentation have been designed and constructed. The compressor has a blade tip diameter of 36 inches, is designed for a top speed of 2000 rpm, and is powered by a 125 hp dynamometer. The unit is in operation and has been used extensively for the experiments of this thesis.
\r\n\r\n2. A number of blade types were designed, all having the same overall performance. Criteria were established characterizing the individual properties of each type and a comparison was made on this basis. It vas shown that some of these blade types are often more suitable than the \"free vortex\" blading which is most commonly used at present.
\r\n\r\n3. Two sets of blades were constructed, the types having been selected from the blade study. Single stage experiments were carried out with each type and detailed measurements of flow patterns as well as overall performance measurements were made at various flow conditions. The experimental data were compared to those calculated by means of the compressor theory of Professor W.D. Rannie. Excellent agreement was obtained; this was interpreted as a verification of the theory. As a further result, measurements of the maximum efficiency of each blade type have established that a blading with an essentially three-dimensional flow pattern can equal the efficiency of the conventional \"free vortex\" blading which has a two-dimensional flow pattern.
" }, { "name": "Schneider, Arthur John Rudolph", "degree": "PhD", "year": "1949", "title": "Some Compressibility Effects in Cavitation Bubble Dynamics", "advisor": "Hollander, Aladar", "url": "https://resolver.caltech.edu/CaltechTHESIS:12072010-114721933", "creators": [ { "name": { "family": "Schneider", "given": "Arthur John Rudolph" }, "id": "Schneider-Arthur-John-Rudolph", "display_name": "Schneider, Arthur John Rudolph" } ], "advisors": [ { "name": { "family": "Hollander", "given": "Aladar" }, "id": "Hollander-Alandar", "role": "advisor", "display_name": "Hollander, Aladar" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/C2VH-HM56", "abstract": "1. Theories on the dynamics of cavitation are critically\r\nexamined, and are found to need clarification.\r\n2. The contents of a bubble formed from a submicroscopic\r\nnucleus are agreed to be almost entirely water vapor.\r\nThis water vapor is shown to be unable to offer decisive\r\nresistance to inward flow during the finite portion of\r\nthe collapse.\r\n3. The effect of compressibility of the liquid is analyzed\r\nin detail. It is found to reduce velocities noticeably,\r\nbut does not, in itself, eliminate the anomaly of an infinite collapse velocity as the bubble radius approaches\r\nzero. The pressures in the fluid surrounding the bubble\r\nare found to be markedly reduced by the assumption of\r\ncompressibility.\r\n4. Energy is found to be continually transported inward\r\nduring the collapse period.\r\n5. The mechanism of rebound of a compressible liquid is\r\nexamined when the bubble collapse is arrested by an immovable barrier of finite radius. A shock wave is formed\r\nfollowed by a tension wave responsible for rupturing the\r\nliquid.\r\n6. The shock wave is estimated to carry off 47% of available\r\nenergy, and limit rebound to 81% of former size.\r\n7. The maximum pressure in the outgoing shock wave is\r\nfound to be incapable of damaging a metallic wall when\r\nthe point of collapse is not on that boundary." }, { "name": "Van Dyke, Milton Denman", "degree": "PhD", "year": "1949", "title": "A Study of Second-Order Supersonic Flow", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12062017-085319714", "creators": [ { "name": { "family": "Van Dyke", "given": "Milton Denman" }, "id": "Van-Dyke-Milton-Denman", "display_name": "Van Dyke, Milton Denman" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MMKH-KT11", "abstract": "An attempt is made to develop a second approximation to the solution of problems of supersonic flow which can be solved by existing first-order theory. The method of attack adopted is an iteration procedure using the linearized solution as the first step.
\r\n\r\nSeveral simple problems are studied first in order to understand the limitations of the method. These suggest certain conjectures regarding convergence. A second-order solution is found for the cone which represents a considerable improvement over the linearized result.
\r\n\r\nFor plane and axially-symmetric flows it is discovered that a particular integral of the iteration equation can be written down at once in terms of the first-order solution. This reduces the second-order problem to the form of the first-order problem, so that it is effectively solved. Comparison with solutions by the method of characteristics indicates that the method is useful for bodies of revolution which have continuous slope.
\r\n\r\nFor full three-dimensional flow, only a partial particular integral has been found. As an example of a more general problem, the solution is derived for a cone at an angle. The possibility of treating other bodies of revolution at angle of attack and three-dimensional wings is discussed briefly.
" }, { "name": "Wood, David Shotwell", "degree": "PhD", "year": "1949", "title": "The Influence of Stress and Temperature upon the Time to Initiate Plastic Deformation in an Annealed Low Carbon Steel", "advisor": "Clark, Donald S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10222002-111754", "creators": [ { "name": { "family": "Wood", "given": "David Shotwell" }, "id": "Wood-David-Shotwell", "display_name": "Wood, David Shotwell" } ], "advisors": [ { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng", "physics" ], "doi": "10.7907/5355-1Z24", "abstract": "An experimental investigation of the time delay for initiation of plastic deformation in an annealed low carbon steel is described. The delay time is determined as a function of the applied stress at temperatures of -75\u00b0F, 73\u00b0F, 150\u00b0F, and 250\u00b0F. The stress is applied in a continuous manner within a period of about 7 millisec, and the stress is maintained substantially constant thereafter, until plastic deformation begins. At any given temperature, the relation between the logarithm of the delay time and the stress is found to consist of two straight lines which join together at a point in the delay time and the stress plane. One is a line of constant stress, and the other is a line along which the logarithm of the delay time decreases linearly as the stress is increased above the constant stress line. The experimental results are compared with a dislocation theory of yielding in low carbon steel which has been given by A.H. Cottrell and B. A. Bilby (21)*. It is shown that this theory, in its present form, does not describe the experimental results adequately. Two suggestions are made for modification and addition to the theory which might lead to satisfactory agreement with the experimental observations.
\r\n\r\n*The figures appearing in the parentheses refer to the references listed at the end of this thesis.
\r\n" }, { "name": "Begovich, Nicholas Anthony", "degree": "PhD", "year": "1948", "title": "A Contribution to the Theory of Thermionic Vacuum Tubes", "advisor": "Neher, Henry Victor", "url": "https://resolver.caltech.edu/CaltechTHESIS:03082024-172323594", "creators": [ { "name": { "family": "Begovich", "given": "Nicholas Anthony" }, "id": "Begovich-Nicholas-Anthony", "display_name": "Begovich, Nicholas Anthony" } ], "advisors": [ { "name": { "family": "Neher", "given": "Henry Victor" }, "id": "Neher-H-V", "role": "advisor", "display_name": "Neher, Henry Victor" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/jv0b-2n11", "abstract": "The elementary treatment of electron streams in vacuum\r\ntubes is based on the assumption that the velocity of the stream\r\ncan be represented by a single valued function of the spatial\r\ncoordinate. The Lagrangian method of treating the resulti11g\r\nelectronic equations was introduced by Muller and extended by\r\nLlewellyn to general boundary conditions. In part III, this method\r\nis carried to the second order solution, which is important in the\r\ncomputation of distortion and detection properties of vacuum tubes\r\nat medium frequencies.
\r\n\r\nWith the refinement of electronic techniques in the past\r\ndecade, the useful radio frequency range for communication has been\r\nincreased. In treating very high frequency tunes, the assumption of\r\nsingle valued velocity electron streams in close spaced vacuum tubes\r\ndiverges sharply from physical fact. There arises a need for an\r\nelectronic theory which includes the velocity spread of the electron\r\nstream. In part IV, the foundation of a multi-velocity theory is\r\nlaid. Though in part IV treatment has been confined to one dimensional\r\nelectron motion with only an electric field, the method can\r\nbe readily extended to two or three dimensional flow with magnetic\r\nfields. The multi-velocity theory is based on a combination of\r\nMaxwell's equations and Liouville's Theorem of classical statistical\r\nmechanics. This fundamental approach in treating vacuum tubes, by\r\nfocusing attention on the electron motion instead of boundary parameters,\r\nhas been bypassed by prior investigators. The theory contains\r\nwithin its structure the explanation of all previously obtained\r\nresults on one dimensional electron flow plus new answers to multi-velocity\r\nproblems. In part V, some examples of stationary electron\r\nflow are treated; and in part VI, the time dependent solutions are\r\nformulated (though not carried out in complete detail).
\r\n\r\nIn part VII, an interesting high frequency loading\r\nphenomena, observed by a number of investigators, is treated. From\r\nthe results of the stationary flow in part V, this problem can be\r\nsolved without the general theory developed in part VI. The\r\nsolution obtained suggests a modification in the construction of very\r\nhigh frequency close spaced vacuum tubes.
" }, { "name": "Chapman, Dean Roden", "degree": "PhD", "year": "1948", "title": "Base Pressure at Supersonic Velocities", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12122008-143236", "creators": [ { "name": { "family": "Chapman", "given": "Dean Roden" }, "id": "Chapman-Dean-Roden", "display_name": "Chapman, Dean Roden" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F2ZC-4B47", "abstract": "The existing theories of base pressure are described in detail and are shown to be unsatisfactory. An \"exact\" analysis is then made of the base pressure in an inviscid fluid, both for two-dimensional and axially-symmetric flow. It is shown that for a given body there are, in general, an infinite number of possible solutions satisfying all necessary boundary conditions. For the particular case of inviscid flow about projectile-shaped bodies only one solution is possible, but it corresponds to zero base drag. This latter result is generalized and the following conjecture made: it is impossible for a steady axially-symmetric inviscid supersonic flow to converge toward, and to meet the axis at a finite (non-zero) angle.\r\n\r\nSince the inviscid-fluid theory does not adequately describe the conditions in a real fluid, an approximate theory for base pressure in a viscous fluid is developed. This latter theory is based in part on the inviscid-flow calculations and in part on dimensional analysis. It includes the effects of Mach number, Reynolds number, body shape, and type of boundary-layer flow. A comparison of the theory with the available experimental data indicates satisfactory agreement.\r\n\r\nIt is shown that under certain conditions the airfoil contour for minimum profile drag in a viscous fluid necessarily has a blunt trailing edge. Approximate calculations indicate that very substantial reductions in profile drag are possible by designing airfoils with blunt trailing edges. Consideration is briefly given to the interference of a support rod on base pressure measurements in a supersonic wind tunnel.\r\n" }, { "name": "Fung, Yuan-cheng", "degree": "PhD", "year": "1948", "title": "Elastostatic and Aereolastic Problems Relating to Thin Wings of High Speed Airplanes", "advisor": "Sechler, Ernest Edwin", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222003-165709", "creators": [ { "name": { "family": "Fung", "given": "Yuan-cheng" }, "id": "Fung-Yuan-cheng-B", "display_name": "Fung, Yuan-cheng" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JK8Q-RH35", "abstract": "This report is concerned with the statics and dynamics of very thin wings of high speed airplanes. With the modern tendency towards sweepback, which is necessary for supersonic airplanes, the wing construction tend more and more to an ideal structure, hence for the static problem of this report, the wing is idealized to a thin cantilever elastic plate.
\r\n\r\nPart I gives a general formulation of the fundamental equations of deformation of thin elastic plates and the direct methods of solution. For small deflection of plates, the equations and boundary conditions are derived from the three-dimensional equations of elasticity developed in power series of the thickness of the plate. It is shown that the classical Poisson-Kirchhoff theory is coincident with the first approximation in this development. These equations are then transformed into oblique coordinates for treating problems concerning swept plates. Since the problem of the cantilever plate is very difficult to solve from the standpoint of biharmonic analysis, emphasis is laid on the direct methods of solution which lead to useful approximate solutions with desired accuracy. Section 1.21 discusses the relation between plate problems and equivalent variational problems. Section 1.22 contains a systematic review of the Rayleigh-Ritz method of relaxation of boundary conditions, including the Trefftz method as one instance.
\r\n\r\nPart II discusses the general aeroelastic problems of high speed airplanes. For airplanes accelerating or decelerating through the transonic region, the coefficients in the aeroelasticity equations are of transient nature. Such transient perturbations are new phenomena in aeronautics but are sufficiently important to warrant detailed investigation. A general mathematical treatment is given, though due to lack of aerodynamic data at present, no specific example is included. A general solution is obtained and this solution is expanded into a generalized power series which proves to be particularly useful when the transient perturbation is small. The present result includes the ordinary small perturbation theory for finite degrees of freedom as a particular case. Several results regarding small perturbations are given in section 2.6.
\r\n\r\nThe next two parts give a detailed computation on the deflection of and stresses in cantilever plates. The deflection of rectangular cantilever plates is solved both by the Rayleigh-Ritz method and the method of relaxation of boundary conditions. For swept plates the Rayleigh-Ritz method is used. A theory of stress approximation without using the intermediate deflection function is developed in Part IV, and is applied to rectangular plates.
" }, { "name": "Ho, Chung Pen", "degree": "PhD", "year": "1948", "title": "Forecasting Mean Weekly Temperature by Statistical Synoptic Considerations", "advisor": "Elliott, Robert Dunshee", "url": "https://resolver.caltech.edu/CaltechTHESIS:05092025-161206674", "creators": [ { "name": { "family": "Ho", "given": "Chung Pen" }, "id": "Ho-Chung-Pen", "display_name": "Ho, Chung Pen" } ], "advisors": [ { "name": { "family": "Elliott", "given": "Robert Dunshee" }, "id": "Elliott-Robert-Dunshee", "role": "advisor", "display_name": "Elliott, Robert Dunshee" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "meteor" ], "doi": "10.7907/hmdc-jx81", "abstract": "The scope of this thesis is to explore the relation between\r\nthe weekly temperature anomaly at a test location and the general\r\ntemperature anomaly pattern for the preceding week. Since the\r\ngeneral pattern of circulation of a given week has a close relationship \r\nto that of the preceding week, and because the circulation\r\npattern establishes the temperature anomaly pattern, it seems\r\nlogical to infer that the temperature anomalies of two consecutive\r\nweeks are correlated. Moreover, as far as the properties of air\r\nmass are concerned, temperature is the more conservative property.
\r\n\r\nA test location is chosen and twenty to thirty other stations\r\nin an evenly scattered network around the United States are used\r\nin representing the temperature anomaly pattern during the preceding\r\nweek. The weekly temperature distribution curves are then prepared\r\nfor each station and a division into five ranges or categories is\r\nmade. Contingency tables are then prepared showing the relation\r\nbetween the temperature anomalies of the test station and those\r\nof each network station during the preceding week. The mean\r\nnumber of matches are found and the standard deviation computed.\r\nThe difference between the mean number of matches and actual number\r\nof matches divided by standard deviation gives the normal deviate.\r\nThere exists a positive correlation if the normal deviate is positive\r\nand vice versa.
\r\n\r\nUsing the calculated normal deviate at each of the network\r\nstations a contour map of this number is drawn. The result is interpreted\r\non a synoptic basis. If some parts are inconsistent\r\nfrom the viewpoint; of synoptic considerations, then those parts are\r\ndisregarded as a forecasting basis.
\r\n\r\nIn practical application, the relationships would be established\r\nfor a large number of test or key stations and thus a weekly forecast\r\ntemperature anomaly pattern could be made.
" }, { "name": "Kyropoulos, Peter Rudolf", "degree": "PhD", "year": "1948", "title": "Dynamic Effects on the Gas Exchange Process in Two Stroke Cycle Engines", "advisor": "Daugherty, Robert Long; Lindvall, Frederick C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05132003-163847", "creators": [ { "name": { "family": "Kyropoulos", "given": "Peter Rudolf" }, "id": "Kyropoulos-Peter-Rudolf", "display_name": "Kyropoulos, Peter Rudolf" } ], "advisors": [ { "name": { "family": "Daugherty", "given": "Robert Long" }, "id": "Daugherty-Robert-Long", "role": "advisor", "display_name": "Daugherty, Robert Long" }, { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "display_name": "Lindvall, Frederick C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng", "mecheng" ], "doi": "10.7907/EDNA-1J88", "abstract": "Recent investigations of fuel injection in spark ignition engines have aroused new interest in two stroke cycle engines. The performance of such engines is very much affected by the dynamic behaviour of the fresh air introduced and the exhaust leaving the cylinder through ports, receivers and silencers. The present investigation has as its aim the clarification and establishment of trends in the performance of two stroke engines with particular reference to crank case scavenged engines.\r\n\r\nThe basic relations governing the flow of air and gas through the whole system are investigated one by one and their interdependence is established. The investigation covers: pulsations in the cylinder, accelerations in the ducts, effect of variable port area, effect of throttling in the ports. The basic differential equation for free oscillation of the exhaust gas in the system comprising receiver, exhaust pipe, and silencer is set up and a method is developed which allows calculation of an equivalent length for the system. With this equivalent length, the natural frequency of the system can be calculated.\r\n\r\nAn experimental investigation is presented which was carried out on a single cylinder compression ignition engine with crank case scavenging. The volumetric efficiency of the engine was determined as a function of exhaust system configuration at various brake mean effective pressures and at constant engine speed. The pressure in the exhaust near the port was measured (by means of a quartz and crystal pickup) as a function of crank angle.\r\n\r\nThe results are presented in the form of plots of volumetric efficiencies as function of brake mean effective pressure for various configurations and as photographic records of pressure as a function of crank angle.\r\n\r\nIt is concluded that a simple frequency analysis is insufficient for the determination of the exhaust behaviour. Criteria for good exhaust systems are established. The trends predicted in the theoretical analysis of the report are, in general, well verified.\r\n\r\nThe need for further investigation is indicated and an outline of research is presented." }, { "name": "Laufer, John", "degree": "PhD", "year": "1948", "title": "Investigation of Turbulent Flow in a Two-Dimensional Channel", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152005-133021", "creators": [ { "name": { "family": "Laufer", "given": "John" }, "id": "Laufer-John", "display_name": "Laufer, John" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6ZYC-HJ88", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA detailed exploration of the field of mean and fluctuating quantities in a two-dimensional turbulent channel flow is presented. The measurements were repeated at three Reynolds numbers, 1.23 x 10\u2075, 3.08 x 10\u2075 and 6.16 x 10\u2075, based on the half width of the channel and the maximum velocity. A channel of 5\" width and 12:1 aspect ratio was used for the investigation.
\r\n\r\nMean speed and axial fluctuation measurements were made well within the laminar sublayer. The semi-theoretical predictions concerning the extent of the laminar sublayer were confirmed. It was found that the viscosity has a more profound influence on the fluctuations than on the mean velocity, the region of influence being approximately four times as wide.
\r\n\r\nFluctuations perpendicular to the flow direction v', w' and the correlation coefficient [...] were measured, and the turbulent shear distribution calculated. Shear calculations from independent methods using the measured velocity gradient at the wall and pressure gradient along the channel furnished a good check on the values of the shearing stress in all cases with the exception of the highest Reynolds number where \u03a4 obtained from the fluctuation measurements is approximately 25% lower. All mean fluctuating quantities were found to decrease with increasing Reynolds number. Measurements of the scales Ly, Lz and micro-scales of turbulence \u03bby, \u03bbz across the channel are presented and their variation with Reynolds number is discussed. Using a new technique, values for \u03bbx were obtained; a method for estimating Lx is also given.
\r\n\r\nThe energy balance in the turbulent flow field was calculated from the measured quantities. From this calculation it is possible to give a descriptive picture of turbulent energy diffusion in the center portion of the channel cross-section.
" }, { "name": "Marble, Frank Earl", "degree": "PhD", "year": "1948", "title": "Some Problems Concerning the Rotational Motion of a Perfect Fluid", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-104144", "creators": [ { "name": { "family": "Marble", "given": "Frank Earl" }, "id": "Marble-Frank-Earl", "display_name": "Marble, Frank Earl" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2JGF-0Z67", "abstract": "In an effort to obtain some understanding of the processes involved in the rotational motion of a perfect fluid several particular linearized examples of rotational flow are solved in detail. The first part discusses some types of boundary value problem which arise. The solution of the non-linear partial differential equation by a particular iteration process is considered and the process is shown to converge for an extended version of the problem when the vorticity distribution is sufficiently smooth. The first step of the iteration process may constitute a good approximation in these cases and is taken as the basis of linearized solutions studied in the remainder of the work.\r\n\r\nThe process of straightening a non-uniform velocity profile by means of an idealized screen is considered in Part II as a problem in rotational motion of an ideal fluid with the screen replaced by an appropriate non-conservative force field. The detailed solution is given for both the linearized problem and the second approximation, The complete second order correction is less than 6 percent of the local velocity given by the linear solution for a rather severe case, The corrections arising from the various physical processes involved are analyzed and found to exceed 6 percent in same cases but are inherently compensating.\r\n\r\nThe two-dimensional rotational flow about a closed body is obtained in Part III by utilizing the Green's function method of solving the inhomogeneous differential equation involved. The conformal transformation which maps the given contour into a circle is used to find the appropriate Green's function for the contour. Solutions are then written down for any body, the Riemann mapping function of which is known, The Blasius force and moment formula are extended to include the case of general rotational motion, the relations of Kuo appearing as special forms where the vorticity distribution is uniform.\r\n\r\nIn the final part the theory of the three-dimensional. flow through an axial turbomachine, associated with variation of circulation along the blade length, is described as an extension of the classical theory of finite wings and is simplified to a problem in axially symmetric rotational fluid motion by considering an infinite number of blades in each row. The linearized problem is solved for the radial, tangential, and axial velocity components induced by a single row of stationary or rotating blades with finite chord and prescribed loading. The particular case for which the blade chord approaches zero, and the tangential velocity changes discontinuously, is associated with the theory of the Prandtl lifting line for finite wings, The complete solution is given for a single stationary or rotating blade row of given loading with a hub/tip ratio of 0.6 and blade aspect ratio of 2. The corresponding discontinuous approximation is compared with the more nearly exact solution and is shown to constitute a useful approximation to the solution for a finite blade chord when the discontinuity is located appropriately. An exponential approximation for the velocity components, deduced from the analysis, allows rapid estimation of the rate at which the equilibrium velocity profiles develop ahead of and behind a blade row and, using the superposition principle, provides a simple means or approximating the velocity distribution in a multistage turbomachine and of discussing mutual interference of blade rows." }, { "name": "Trilling, Leon", "degree": "PhD", "year": "1948", "title": "Investigation into the Flow of a Viscous Heat Conducting Compressible Fluid", "advisor": "Lagerstrom, Paco A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-12242008-101248", "creators": [ { "name": { "family": "Trilling", "given": "Leon" }, "id": "Trilling-Leon", "display_name": "Trilling, Leon" } ], "advisors": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "advisor", "display_name": "Lagerstrom, Paco A." } ], "committee": [ { "name": { "family": "Lagerstrom", "given": "Paco A." }, "id": "Lagerstrom-P-A", "role": "chair", "display_name": "Lagerstrom, Paco A." }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Marble", "given": "Frank E." }, "id": "Marble-F-E", "role": "member", "display_name": "Marble, Frank E." }, { "name": { "family": "Cole", "given": "Julian D." }, "id": "Cole-J-D", "role": "member", "display_name": "Cole, Julian D." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/14DR-5V68", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe present investigation is concerned with the effect of a small viscosity and heat conduction coefficient on the flow of a compressible fluid. It is well known that, in the case of an incompressible fluid, such an investigation leads to the boundary layer theory.\r\n\r\nThe chief purpose of this paper is to determine whether the main result of boundary layer theory, namely, that viscosity plays a negligible part in the flow outside a very narrow region in the immediate vicinity of any solid boundary in the fluid, is still valid for a compressible fluid. To investigate that point, a very simple type of flow is selected: the flow past a semi-infinite two-dimensional flat plate parallel to the main stream direction. The problem is further simplified as follows: on the basis of experimental results, the existence of a layer influenced by viscosity is assumed, and the boundary conditions are applied near the outer edge of this layer. This allows a linearization of the equation of motion, and gives information on the interaction between the outer edge of this layer and the main field of flow.\r\n\r\nThe analysis is carried out by the methods based on the theory of the Laplace Transformation. The results are essentially, that if the flow is subsonic, the boundary layer theory developed for incompressible fluids may be extended without qualitative changes. However, in a supersonic flow, one must expect two related effects: one finds the boundary layer, which, as a first approximation, in similar to the boundary layer of an incompressible fluid, and a shock-wave along the Mach line which starts at the leading edge of the flat palate, and whose strength is given by the expression:\r\n[...] where [...] is the normal velocity across the shock, M is the free stream Mach number, [...] is the distance from the leading edge of the flat plate along the shock, [...] is the distance normal to the shock, [...] is sonic velocity of the free stream and [...] is the mean effective free stream kinematic viscosity of the fluid." }, { "name": "Wilts, Charles Harold", "degree": "PhD", "year": "1948", "title": "Measurements of the Ratio of Charge to Mass of Free Electrons Using a Resonant Cavity", "advisor": "Smythe, William Ralph", "url": "https://resolver.caltech.edu/CaltechETD:etd-11212003-110622", "creators": [ { "name": { "family": "Wilts", "given": "Charles Harold" }, "id": "Wilts-Charles-Harold", "display_name": "Wilts, Charles Harold" } ], "advisors": [ { "name": { "family": "Smythe", "given": "William Ralph" }, "id": "Smythe-W-R", "role": "advisor", "display_name": "Smythe, William Ralph" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4HDY-1E79", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA deflection method for measuring (e/m[subscript o]) for free electrons is described. A beam of electrons is directed along the axis of a cylindrical cavity excited in the TM[...] mode. A null in the subsequent deflection of the beam occurs when the transit time is nearly equal to an integral number of cycles of the cavity oscillation. The average velocity of the electron beam is calculated from knowledge of the cavity dimensions and the resonant frequency of the cavity. The value of (e/m[subscript o]) is obtained by equating the energy required to accelerate the electrons and their kinetic energy. Three quantities must be measured, a distance, a frequency and a difference of potential, and two very small corrections most be made. Errors due to unmeasurable work function potentials, etc., are eliminated by taking two sets of data with different transit times and subtracting the two energy equations. A probable error of less than 1 part in 10,000 sees to be achievable. Preliminary apparatus gave a value (e/m[subscript o]) = 1.759 [plus or minus] .007 (10)[superscript 7] emu per gram." }, { "name": "Ballhaus, William Francis", "degree": "PhD", "year": "1947", "title": "Aerodynamic and Geometric Parameters Affecting Aircraft Weight", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302003-152006", "creators": [ { "name": { "family": "Ballhaus", "given": "William Francis" }, "id": "Ballhaus-William-Francis", "display_name": "Ballhaus, William Francis" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/T60T-F120", "abstract": "A number of single engine conventional aircraft are studied to investigate the possibility of applying statistical methods to the problem of aircraft weight estimation. It is shown that the statistical treatment is definitely useful. It is also shown that, without proper care and judgment, such a statistical treatment leads to somewhat misleading results. The need for structural and aerodynamic training and experience together with essential weight estimating experience is evident. Such experience is requisite to arriving at proper weight estimates when basing these estimates upon the weights of aircraft which have previously been designed and built.
\r\n\r\nIt was hoped that the effects of all of the important aerodynamic and geometric parameters upon aircraft weight would be found from this study of successful single engine aircraft. It was further hoped that the results of this study would be applicable to the difficult problem of estimating the weight of new aircraft. The number of aircraft in the sample for which pertinent information was available was not large enough to permit the evaluation of the effects of all of the parameters although most of the important parameters and their essential effects have been indicated. Lack of complete information due to the restricted or confidential nature of the data was one of the most troublesome handicaps. The latter problem of obtaining weight estimating procedure has, however, been solved since satisfactory weight estimating formulas have been developed for use in basic design weight estimates.
\r\n\r\nIt is this latter result for which the entire study was made. That is, the study was initiated to offer assistance to practicing preliminary design engineers by providing usable information concerning the effects of such factors as gross weight, load factor, and wing span upon aircraft weight. Such information should be invaluable to assist in arriving at the optimum aircraft design with respect to performance, maneuverability, and utility.
\r\n\r\nAll the useful estimating formulas are summarized on page 43. Also included are the calculated probable errors of estimate.
" }, { "name": "Corrsin, Stanley", "degree": "PhD", "year": "1947", "title": "I. Extended Applications of the Hotwire Anemometer. II. Investigations of the Flow in Round, Turbulent Jets", "advisor": "Liepmann, Hans Wolfgang", "url": "https://resolver.caltech.edu/CaltechETD:etd-12092008-105044", "creators": [ { "name": { "family": "Corrsin", "given": "Stanley" }, "id": "Corrsin-Stanley", "display_name": "Corrsin, Stanley" } ], "advisors": [ { "name": { "family": "Liepmann", "given": "Hans Wolfgang" }, "id": "Liepmann-H-W", "role": "advisor", "display_name": "Liepmann, Hans Wolfgang" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/NB53-K411", "abstract": "Part 1:\r\n\r\nTwo new fields of application of the hot-wire anemometer are proposed, and the appropriate response equations and measuring procedures are developed.\r\n\r\nThe first analysis leads to a method for the measurement of physically significant statistical quantities in a turbulent flow with heat transfer: for example the turbulence levels, the temperature fluctuation level, the turbulent heat transfer coefficient, the velocity scale, the temperature scale and some spectra.\r\n\r\nThe second analysis involves the use of the hot-wire in the turbulent isothermal mixing of two appropriately different gases. If the thermal conductivity of the mixture is known and is a monotonic function of the relative concentration, it is possible to measure the mean velocity and mean concentration at any point. If no data are available on the thermal conductivity of the mixture, this additional unknown can be determined by an additional measurement. Furthermore, it is also possible to measure the various statistical functions of the fluctuating velocities and the local concentration fluctuation, provided, again, that the thermal conductivity is a known monotonic function of the concentration.\r\n\r\nAlthough the details of the present analysis are dependent upon the accuracy of King's equation for the rate of heat loss from fine wires, the general approach is equally valid for any (possibly more accurate) equation that may be deduced.\r\n\r\nPart 2: \r\n\r\nA detailed investigation has been made of the flow in a round turbulent air jet, heated slightly to permit measurement of mean temperature.\r\n\r\nOscillograms of the velocity fluctuation plus direct measurement of the turbulent shear both show that the flow in a fully developed \"turbulent\" jet is completely turbulent only out to approximately the radius at which the extreme outer edge is in the nature of a \"laminar collar\", with predominantly radial (inward) mean velocity, and in between the turbulent core and the laminar collar is a rather wide annular transition region.\r\n\r\nA study of the downstream history of the radial distribution of turbulent velocity shows that the fully developed state of this round jet is reached between 15 and 20 diameters. This conclusion is corroborated by examination of the partition between turbulent motion and mean motion, of total kinetic energy crossing planes perpendicular to the axis in unit time.\r\n\r\nThe directly measured shear distribution is checked roughly by a computation of the same quantity from the mean velocity distribution.\r\n\r\nA measurement of the double correlation function between points symmetrical about the jet axis shows considerable similarity to the corresponding function in isotropic turbulence, and permits calculation of scale and microscale.\r\n\r\nWith the assumption of constant microscale across a section, a rough estimate is made of the energy balance distribution of production, dissipation and diffusion of turbulent energy.\r\n\r\nA comparison with momentum transfer, modified vorticity transfer and constant exchange coefficient theories show that none of them is satisfactory.\r\n\r\nA comparison of mean velocity and temperature distributions verifies Ruden's result that the lateral rate of heat transfer in turbulent shear flow is appreciably greater that the lateral rate of momentum transfer.\r\n\r\nThe use of considerably increased heating, in a second jet unit, has permitted direct measurement of the temperature fluctuation level. Velocity fluctuations were also measured in this case for comparison, and they were found to be the same order of magnitude.\r\n\r\nThe final result is the direct measurement of temperature-velocity correlation and of velocity correlation in the hot jet. This gives a direct measure of the turbulent heat transfer and momentum transfer in the jet, and directly verifies the fact that the former is appreciably greater than the latter.\r\n" }, { "name": "Schamberg, Richard", "degree": "PhD", "year": "1947", "title": "The Fundamental Differential Equations and the Boundary Conditions for High Speed Slip-Flow, and their Application to Several Specific Problems", "advisor": "Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-12272004-161736", "creators": [ { "name": { "family": "Schamberg", "given": "Richard" }, "id": "Schamberg-Richard", "display_name": "Schamberg, Richard" } ], "advisors": [ { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/F44D-FG36", "abstract": "The differential equations of motion and the associated boundary conditions for the slip-flow regime of fluid mechanics are derived from the point of view of the kinetic theory of non-uniform gases. The slip-flow regime comprises the flow of gases whose molecular mean free path is smaller than but not negligible relative to the macroscopic dimension characterizing the gas flow.\r\n\r\nA systematic review is presented of the methods of Hilbert and Burnett for obtaining a successive approximation solution to the Boltzmann integro-differential equation. The complete second approximation to the molecular velocity distribution function is calculated for the molecular model of Maxwell. This molecular distribution function is employed for the derivation of the macroscopic differential equations of motion and the associated boundary conditions. It is shown that the same number of boundary conditions are required for slip flows as for gas-dynamical flows, although the differential equations of motion for slip flows are of higher order than those of continuum gas-dynamics. Expressions for the second approximations to the slip velocity and temperature jump are obtained.\r\n\r\nThe general equations obtained are applied to three specific problems: the propagation of sound waves in rarefied gases, high-speed Couette flow of a rarefied gas, and slip-flow between concentric cylinders in relative rotary motion. It is found that the rarefaction of a gas increases the damping of sound waves, whereas the propagation speed differs from the ordinary adiabatic sound velocity by less than two percent. The Couette flow solution indicates that the slippage of gas and the temperature discontinuity at a solid boundary may reduce the gas-dynamical friction coefficient and heat transfer, respectively, by ten percent under approximate conditions. When applied to the flight of aircraft through the rarefied atmosphere, the theory presented is applicable to an altitude range from 100,000 to 300,000 feet.\r\n" }, { "name": "Baller, Howard", "degree": "PhD", "year": "1946", "title": "Losses in Cavity Resonators", "advisor": "Mackeown, Samuel Stuart; Pickering, William Hayward", "url": "https://resolver.caltech.edu/CaltechTHESIS:05052025-205823464", "creators": [ { "name": { "family": "Baller", "given": "Howard" }, "id": "Baller-Howard", "display_name": "Baller, Howard" } ], "advisors": [ { "name": { "family": "Mackeown", "given": "Samuel Stuart" }, "id": "Mackeown-S-S", "role": "advisor", "display_name": "Mackeown, Samuel Stuart" }, { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "role": "advisor", "display_name": "Pickering, William Hayward" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/nncw-zq91", "abstract": "No abstract." }, { "name": "Baller, Howard", "degree": "PhD", "year": "1946", "title": "Losses in Cavity Resonators", "advisor": "Mackeown, Samuel Stuart; Pickering, William Hayward; Hagelbarger, David", "url": "https://resolver.caltech.edu/CaltechTHESIS:05032025-230624898", "creators": [ { "name": { "family": "Baller", "given": "Howard" }, "id": "Baller-Howard", "display_name": "Baller, Howard" } ], "advisors": [ { "name": { "family": "Mackeown", "given": "Samuel Stuart" }, "id": "Mackeown-S-S", "display_name": "Mackeown, Samuel Stuart" }, { "name": { "family": "Pickering", "given": "William Hayward" }, "id": "Pickering-W-H", "display_name": "Pickering, William Hayward" }, { "name": { "family": "Hagelbarger", "given": "David" }, "id": "Hagelbarger-David", "display_name": "Hagelbarger, David" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/nmmx-dk82", "abstract": "The problem investigated was the measurement of the Q, or figure of merit, of a resonant cavity and observation of the variation in Q with changes in the size and shape of the coupling holes. A method of measurement was developed using a spectrum analyzer as a detector and a signal with a known spectrum to calibrate the analyzer for frequency changes. The results indicate that the Q is lowered if the size of the coupling windows is increased. There are two contributions to the losses which may be considered separately; the losses on the inner walls of the resonator, and the losses due to energy radiated out of the coupling hole." }, { "name": "Charyk, Joseph Vincent", "degree": "PhD", "year": "1946", "title": "Condensation Phenomena in Supersonic Flows", "advisor": "von K\u00e1rm\u00e1n, Theodore; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-11062003-165637", "creators": [ { "name": { "family": "Charyk", "given": "Joseph Vincent" }, "id": "Charyk-Joseph-Vincent", "display_name": "Charyk, Joseph Vincent" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RSQH-W442", "abstract": "With the very rapid development of jet propulsion systems, the attainment of speeds which seemed to be well beyond reach a few years ago now appears to be at hand. The war has produced many examples of guided missiles traveling at supersonic speeds such as the famed German A-4 rocket, more commonly referred to in this country as the V-2. Today a supersonic airplane is no longer a designer's dream but practically an accomplished fact. Despite the impressive array of symbols of apparent mastery of high speed flight, there exists a large gap of fundamental knowledge that the theoretician working with the experimentalist must fill before true mastery of transonic and supersonic speeds can be said to be at hand. It was only due to the efforts of pioneers in high speed fluid mechanics like de Laval, Riemann, Hugoniot, Lord Rayleigh and Tschaplygin (see for example Ref. 1 to 4) and later the applications of such basic knowledge to the new field of high speed aerodynamics by men with foresight such as Prandtl, Ackeret, von Karman Taylor and Busemann (see for example Ref. 5 to 9) that tools for the engineer and designer were available when the need for them suddenly arose.
\r\n\r\nToday the emphasis of the aeronautical profession is on the basic problems of transonic and supersonic flows. One of the important and at first mystifying phenomena that emerged from experimental investigations in supersonic wind tunnels was the condensation shock. Later such shocks were noticed in the flow over an airfoil in experiments conducted at the California Institute of Technology by Kate Liepmann in 1941. In more recent years their appearance has been noted in actual flight at high speeds. The importance of such shocks in connection with the aerodynamic characteristics of airfoils in supercritical transonic flow has been pointed out by Tsien and Fejer (Ref. 10). Apparently, however, no detailed investigation of the phenomenon has been made with a view to studying the fundamental aspects of the condensation shock in order to develop practical methods for predicting the occurrence, location, strength and effect of such shocks. It has been the basic purpose of this research to study the detailed aspects of this problem and to endeavor to develop a means of accomplishing the aims noted. It is felt that though crude in many respects, the results of this investigation can provide practical knowledge of basic importance in understanding and treating the problems of condensation shocks when they appear and can point the way towards more refined and detailed future analyses of this problem.
\r\n\r\nIn attacking this problem, an examination of the phenomenon of the sudden collapse of the supersaturated state of the moist air is first made. The assumptions necessary for the determination of the critical stability limit of the supersaturated air are analyzed and the necessity for further investigation, especially from the kinetic point of view, is pointed out. The study reveals that the temperature of air at which this collapse occurs is approximately a function only of the amount of water contained in the air and does not depend upon the pressure. This enables an important simplification in the analysis to be made.
\r\n\r\nThe condition for collapse of the supersaturated state is then applied to the special case of normal condensation shocks. Because of this relatively small amount of water present in air, the effect of the presence of the water on the properties of the air can be neglected except at the shock where the release of the latent heat of vaporization upon condensation is of vital importance. A simple consideration of this heating process yields the interesting result that the flow after the shock must always be supersonic. An important simplification in treating the general condensation problem is an approximation to the actual saturation vapor pressure versus temperature curve by means of an exponential curve. Mathematically this means an approximate integration of the Clausius-Clapeyron equation in the sense that the specific volume of the fluid phase is neglected as compared to the specific volume of the vapor phase. This simplification enables a closed form solution to be obtained.
\r\n\r\nThe oblique condensation shock is then analyzed and its application to the flow over an airfoil or other body in a stream of moist air is treated.
\r\n\r\nThe possibility of a continuous condensation instead of an abrupt condensation of a combination of the two is discussed for the case of a one-dimensional flow. Certain interesting results emerge from such a consideration and experimentation will be required to determine whether under certain conditions such a condensation process can take place.
\r\n\r\nA considerable number of charts are provided which may be of use in making calculations in practical cases. In instances where a different range of values is necessary, additional charts can readily be constructed.
" }, { "name": "Morelli, Dino Anthony", "degree": "PhD", "year": "1946", "title": "Some Contributions to the Theory of the Stiffened Suspension Bridge", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142003-112733", "creators": [ { "name": { "family": "Morelli", "given": "Dino Anthony" }, "id": "Morelli-Dino-Anthony", "display_name": "Morelli, Dino Anthony" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/ZAVX-HG34", "abstract": "Part I of this thesis contains a review of the basic theory of the cable and stiffening girder combination according to the method of Dr. Rode which takes into account the inevitable longitudinal displacements of the suspender connections, when the cable is deflected from its normal configuration.
\r\n\r\nNumerical calculations have been carried out to establish the order of magnitude of approximations in the ordinary deflection theory as developed in this country by F. E. Turneare from the work of J. Melan. Besides the essential omission which is evident in the comparison of the fundamental differential equation of Rode's theory with that of the ordinary deflection theory, the most significant error is the neglect of the effect of inclination of the suspenders on cable deflection. It would appear that an error of three percent can arise from this source which although unimportant from the structural engineer's point of view, is important as a limit on accuracy required of any theory which neglects it.
\r\n\r\nRode's differential equation is not integrable and an approximation has been developed which is tractable by the methods of Part II and yet does not sacrifice entirely the improved representation of structural action given by Rode's theory.
\r\n\r\nPart II utilizes trigonometric series for the development of a simple method of determination of the deflections and girder bending moments in a span. As applied to the ordinary deflection theory there result formulae of extreme simplicity which bring into sharp perspective the related functions of cable and stiffening girder. From these formulae a pictorial representation of bridge stiffness in terms of certain basic parameters has been developed.
\r\n\r\nThe theory and method of computation have then been extended to take into account the effect of a prestress introduced by arbitrary adjustment of suspender lengths which may be necessary in the rehabilitation of old structures or reduction of peak bending stresses in new designs.
\r\n\r\nThe approximation to Rode's theory developed in Part I is then solved in terms of the methods developed for the simple theory and formulae result which are but slightly more complicated than the elegant formulae of the previous work. The practicability of application has been tested by examples.
\r\n\r\nFinally, in order to dispel certain erroneous conceptions of the efficacy of the stiffening girder in controlling the bending moments, (and consequently, the deflections) in a span, the method has been extended to permit the investigation of the influence of variation in flexural rigidity of the girder. This leads to formulae, not overly lengthy, which show in proper relation the influence of the various harmonic components of the flexural rigidity of the girder.
\r\n\r\nThe methods of this thesis are simple in conception and application while still retaining a proper physical basis, and are capable of extension beyond the bounds of current methods without loss of algebraical and arithmetical tractability.
" }, { "name": "Daily, James Wallace", "degree": "PhD", "year": "1945", "title": "The Hydrodynamic Forces and the High Frequency Noise Resulting from Cavitation on Underwater Bodies", "advisor": "Knapp, Robert T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03262007-103144", "creators": [ { "name": { "family": "Daily", "given": "James Wallace" }, "id": "Daily-James-Wallace", "display_name": "Daily, James Wallace" } ], "advisors": [ { "name": { "family": "Knapp", "given": "Robert T." }, "id": "Knapp-R-T", "role": "advisor", "display_name": "Knapp, Robert T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/5S51-F383", "abstract": "Water Tunnel measurements were made of the hydrodynamic forces and moments, and of the high frequency noise resulting from cavitation on underwater bodies. All stages of cavitation from incipient to the full cavity were covered by the investigations.\r\n\r\nThe main findings of the force measurements are:\r\n1. There is no sudden increase in drag with inception of cavitation. The sharp rise occurs only after the normal flow pattern is completely altered by an appreciable amount of visible cavitation. \r\n2. A qualitative comparison of cavitation and separation indicates that they have the same basic effect on the flow in the boundary layer, and hence on the skin friction drag. For blunt bodies with severe separation for noncavitating conditions, the first appearance of cavitation does not immediately alter the flow pattern nor the drag.\r\n3. Cavity drag measurements agree closely with values calculated from measured pressure distributions and for a given value of the cavitation parameter, K, are proportional to the bubble size relative to the diameter of the body.\r\n4. Cavity cross force and moment depend on the cavity shape, and hence on the shape of the body at the point where cavity separation occurs. With spherical tipped noses so proportioned that the cavity separates on the spherical segment, not only at zero but at the maximum yaw, the cross force is zero independent of yaw, and the moment is caused by the drag only. Other shapes produce asymmetrical cavities and definite cross forces and moments.\r\n5. With complete projectiles the conditions for cavity flow with tail sticking through the side of the cavity are reproduced. A low cross force with a zero or stabilizing moment is obtained.\r\n\r\nMeasurements of the sound emitted in the 20 to 100 KC frequency range with the beginning and growth of cavitation show:\r\n1. With appearance of the slightest trace of cavitation, the acoustic pressure increases to several times the value of the background noise.\r\n2. The maximum noise is measured when the zone of cavitation is limited to a very narrow band of small bubbles. With further growth the measured sound drops off.\r\n3. The main source of sound is in the region of the trailing edge of the cavitation zone where the vapor bubbles are collapsing. If, as at advanced stages, the vapor bubbles are entrained and swept down stream before collapsing, the noise level drops" }, { "name": "Fej\u00e9r, Andrej (Andrew)", "degree": "PhD", "year": "1945", "title": "Lifting Line Theory in Linearly Varying Flow", "advisor": "von-K\u00e1rm\u00e1n, Theodore; Tsien, Hsue Shen", "url": "https://resolver.caltech.edu/CaltechETD:etd-11202008-133148", "creators": [ { "name": { "family": "Fej\u00e9r", "given": "Andrej (Andrew)" }, "id": "Fej\u00e9r-Andrej", "display_name": "Fej\u00e9r, Andrej (Andrew)" } ], "advisors": [ { "name": { "family": "von-K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von-K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-H-S", "role": "advisor", "display_name": "Tsien, Hsue Shen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EJJN-XF31", "abstract": "The problem of a wing placed in a flow that is nonuniform in the spanwise direction is of interest to the aerodynamicist as well as to the designer of rotating machinery. The portion of a wing located in the slip stream of the propeller, the blades of propellers and fans, wind-tunnel models in nonuniform airstreams are some of the examples. Prandtl's three dimensional wing theory assumes a uniform undisturbed flow and thus it is not valid in these cases. Some authors tried to modify Prandtl's theory in order to make it applicable to such problems. The work of F. Vandrey (Ref. 1) and K. Bausch (Ref. 2) may be mentioned in this connection. A discussion of their work is given in Section 7 of Part I of this analysis. Lately Th. von Karman and H. S. Tsien presented a general solution of the problem, of a wing placed in a flow with the velocity varying in both directions normal to and parallel with the wing span (Ref. 3). In the following the author will utilize the results of von Karman and Tsien for the simpler case of the velocity varying linearly and in the direction of the span only and solve the \"third problem of airfoil theory\" (finding the lift distribution for an airfoil of given shape) for a finite wing in an infinite fluid and for the case of a wing between two parallel walls. The wing in an infinite fluid is treated in Part I while Part II contains the solution of the problem of the wing between walls.\r\n" }, { "name": "Hiltner, Walter Frederick", "degree": "PhD", "year": "1945", "title": "Development of a Portable Celestial Navigation Instrument for the Direct-Reading of Terrestrial Position", "advisor": "Thomas, Franklin", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192025-202602237", "creators": [ { "name": { "family": "Hiltner", "given": "Walter Frederick" }, "id": "Hiltner-Walter-Frederick", "display_name": "Hiltner, Walter Frederick" } ], "advisors": [ { "name": { "family": "Thomas", "given": "Franklin" }, "id": "Thomas-Franklin", "role": "advisor", "display_name": "Thomas, Franklin" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/mhz6-py61", "abstract": "No abstract." }, { "name": "Kuo, Yung-Huai", "degree": "PhD", "year": "1945", "title": "Two-Dimensional Irrotational Mixed Subsonic and Supersonic Flow of a Compressible Fluid and the Upper Critical Mach Number", "advisor": "von-K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172010-111715951", "creators": [ { "name": { "family": "Kuo", "given": "Yung-Huai" }, "id": "Kuo-Yung-Huai", "display_name": "Kuo, Yung-Huai" } ], "advisors": [ { "name": { "family": "von-K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von-K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/D9ME-DD61", "abstract": "No abstract." }, { "name": "Wagner, Warren Orval", "degree": "PhD", "year": "1945", "title": "Repression of High Velocity Flow Phenomena Around Sharp Bends in Supercritically Sloped Open Channels", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:06302025-210853671", "creators": [ { "name": { "family": "Wagner", "given": "Warren Orval" }, "id": "Wagner-Warren-Orval", "display_name": "Wagner, Warren Orval" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/e7z9-rm42", "abstract": "No abstract." }, { "name": "Boehnlein, Charles Thompson", "degree": "PhD", "year": "1944", "title": "Aerodynamic Theory of the Oscillating Wing-Aileron of Finite Span", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechTHESIS:04142011-111534450", "creators": [ { "name": { "family": "Boehnlein", "given": "Charles Thompson" }, "id": "Boehnlein-Charles-Thompson", "display_name": "Boehnlein, Charles Thompson" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KJZ7-FG07", "abstract": "No abstract." }, { "name": "Lin, Chia-Chiao", "degree": "PhD", "year": "1944", "title": "On the Development of Turbulence", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232004-140148", "creators": [ { "name": { "family": "Lin", "given": "Chia-Chiao" }, "id": "Lin-Chia-Chiao", "display_name": "Lin, Chia-Chiao" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZF3F-AN21", "abstract": "The stability of two-dimensional parallel flows of an incompressible fluid is investigated, based upon a study of the equation of Orr and Sommerfeld along the lines initiated by Heisenberg. The theory of Heisenberg is carefully examined and further developed to obtain several general and specific results on hydrodynamic stability. Most of the disputes in the existing theories are clearly brought out and carefully settled. It is further shown that all symmetrical and all boundary-layer types of velocity distributions are unstable above a certain minimum critical Reynolds number, whose approximate value can be easily calculated from equations (12.24) and (12.25) respectively. General characteristics of the curve of neutral stability are obtained (Fig. 9). Complete numerical calculations of this curve have been carried through for the plane Poiseuille flow and the Blasius flow. In the first case, the minimum critical Reynolds number is found to be 16000, based upon the maximun velocity and the width of the channel. In the second case, the number is 400, based upon the free stream velocity and the displacement thickness of the boundary layer. Physical interpretations of the results obtained are given, based upon the conservation of vorticity in a perfect fluid and its diffusion by viscous forces. Indications are also given to connect the stability theory with Taylor's theory of transition to turbulence. It is hoped that this work may remove all the doubts of applying the theory of small oscillations to the treatment of hydrodynamic stability using Navier-Stokes equations for an incompressible fluid.\r\n" }, { "name": "McMaster, Robert Charles", "degree": "PhD", "year": "1944", "title": "The Non-Destructive Testing Spotwelds in Alclad Aluminum Alloy Sheets", "advisor": "Lindvall, Frederick C.; Sorensen, Royal Wasson; Clark, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08252025-221021251", "creators": [ { "name": { "family": "McMaster", "given": "Robert Charles" }, "id": "McMaster-Robert-Charles", "display_name": "McMaster, Robert Charles" } ], "advisors": [ { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "advisor", "display_name": "Lindvall, Frederick C." }, { "name": { "family": "Sorensen", "given": "Royal Wasson" }, "id": "Sorensen-R-W", "role": "advisor", "display_name": "Sorensen, Royal Wasson" }, { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/yqs7-mv19", "abstract": "No abstract." }, { "name": "Zarem, A. Mordecai", "degree": "PhD", "year": "1944", "title": "I. The Explosion of Ether-Air Mixtures by Electric Sparks. II. The Dynamic Resistance of a Spark", "advisor": "Mackeown, Samuel Stuart", "url": "https://resolver.caltech.edu/CaltechETD:etd-07202004-154931", "creators": [ { "name": { "family": "Zarem", "given": "A. Mordecai" }, "id": "Zarem-A-Mordecai", "display_name": "Zarem, A. Mordecai" } ], "advisors": [ { "name": { "family": "Mackeown", "given": "Samuel Stuart" }, "id": "Mackeown-S-S", "role": "advisor", "display_name": "Mackeown, Samuel Stuart" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/WRM8-4W23", "abstract": "The work of previous investigators, on the initiation of explosion, is reviewed. Several researches are described in detail in order to indicate the basic requirements that must be satisfied by a coordinated theory of the explosion process.\r\n\r\nThe possibility that a correlation may exist between the ability of a \"capacitor spark\" to ignite a combustible mixture, and the electrical charactor of the discharge was investigated. The results of experiments with a 4% ether air mixture are presented and discussed.\r\n\r\nIt is shown that the energy dissipated in a spark is not by itself a measure of the ignitibility of the spark. Neither is the total charge passed during a discharge. The sparking potential, however, greatly affects the \"exploding power\" of a spark.\r\n\r\nFor sparking potentials between 2000 volts and 4000 volts no correlation has been found to exist between the igniting ability of a spark and the maximum, effective, or average discharge current.\r\n\r\nThe results of experiments with corona discharges of potentials up to 35,000 volts indicate that explosion could not be intiated by this type of discharge. The suggestion that current density in a spark may be a critical factor in determining its ability to cause explosion, is advanced. Further experiments are sugggested.\r\n" }, { "name": "Brumfield, Robert Clarence", "degree": "PhD", "year": "1943", "title": "A Method for Recording and Studying Crack Growth in the Corrosion Fatigue of Metals", "advisor": "Clapp, William Howard; Hudson, Donald E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04092025-172608308", "creators": [ { "name": { "family": "Brumfield", "given": "Robert Clarence" }, "id": "Brumfield-Robert-Clarence", "display_name": "Brumfield, Robert Clarence" } ], "advisors": [ { "name": { "family": "Clapp", "given": "William Howard" }, "id": "Clapp-W-H", "role": "advisor", "display_name": "Clapp, William Howard" }, { "name": { "family": "Hudson", "given": "Donald E." }, "id": "Hudson-D-E", "role": "advisor", "display_name": "Hudson, Donald E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/vrcj-q687", "abstract": "No abstract." }, { "name": "Hudson, Donald Ellis", "degree": "PhD", "year": "1942", "title": "Internal Friction in Metals", "advisor": "Lindvall, Frederick C.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05232003-090926", "creators": [ { "name": { "family": "Hudson", "given": "Donald Ellis" }, "id": "Hudson-Donald-Ellis", "display_name": "Hudson, Donald Ellis" } ], "advisors": [ { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "advisor", "display_name": "Lindvall, Frederick C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z2V9-C551", "abstract": "(1) The mean damping capacity of steel over a stress range of several hundred pounds per square inch is a physical property of the material, the value of which can be checked accurately by successive tests on the same specimen, with the apparatus and method developed in the course of this investigation.
\r\n\r\n(2) The results of the damping capacity test can be duplicated accurately for successive specimens of the same material.
\r\n\r\n(3) There is a strong possibility that although the general trend of the stress-damping capacity relationship may follow a simple law, the true relationship for a material such as steel is extremely complex and somewhat erratic.
\r\n\r\n(4) The stress-damping capacity relationship indicates that for steel the damping does not follow the viscous friction law, although for low stresses the assumption of constant damping would not be far in error. In the case of brass, the internal friction was practically independent of stress for the stress range covered in the tests.
\r\n\r\n(5) The damping capacity of the specimens tested was found to be a function of the maximum torsional stress set up in the specimen rather than a function of the maximum shear stress or of the maximum normal stress.
\r\n\r\n(6) In the case of materials whose damping capacity decreases with decreasing stress, the apparent damping capacity measured from a solid test specimen is lower than the true specific damping capacity of the material.
" }, { "name": "Wouk, Victor", "degree": "PhD", "year": "1942", "title": "Static Electricity Generated During the Distribution of Gasolene", "advisor": "Mackeown, Samuel Stuart", "url": "https://resolver.caltech.edu/CaltechETD:etd-12022004-153844", "creators": [ { "name": { "family": "Wouk", "given": "Victor" }, "id": "Wouk-Victor", "display_name": "Wouk, Victor" } ], "advisors": [ { "name": { "family": "Mackeown", "given": "Samuel Stuart" }, "id": "Mackeown-S-S", "role": "advisor", "display_name": "Mackeown, Samuel Stuart" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9HN9-EE76", "abstract": "This research project was undertaken to determine the exact hazard represented by static electricity when it is generated during the distribution of gasolene. \"Equivalent electrical circuits\" have been utilized which, with the knowledge of the magnitude of charge developed under different conditions, enable one to predict the voltages that will be present and the subsequent chances of sparks occurring and possible fires or explosions resulting.
\r\n\r\nThe amount of charge developed when gasolenes are pumped through pipes has been measured, and several factors influencing the magnitude of this charge have been determined. The problem of \"tire static\" was investigated, and the general order of magnitude of currents generated by trucks or other rubber-tired vehicles in motion, has been established.
\r\n\r\nA series of experiments was made in an attempt to determine the amount of energy needed in a spark, caused by a condenser discharge, to ignite a combustible mixture of gasolene and air. It was found that relatively small amounts of resistance in series with a spark gap may, in certain cases completely eliminate the ability of a spark to ignite gasolene vapors. There is apparently a minimum wattage required to ignite combustible mixtures.
\r\n\r\nAll the measurements and analyses indicate that the precautions commonly practiced in the petroleum industry are more than adequate to eliminate all the hazard of fire or explosion due to static electricity.
" }, { "name": "Yuan, Shao Wen", "degree": "PhD", "year": "1942", "title": "Thin Cylindrical Shells Subjected to Various Types of Concentrated Loads", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04232008-152804", "creators": [ { "name": { "family": "Yuan", "given": "Shao Wen" }, "id": "Yuan-Shao-Wen", "display_name": "Yuan, Shao Wen" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QSE5-ZP85", "abstract": "The bending of thin cylinder shells based on the general theory of elasticity is of interest not only to the mathematician but also to the engineer. The general theory of the shells has recently been developed to the point that it is now being used by engineers as a basis for the design of this type of structure.\r\n" }, { "name": "Cobb, Charles Lewis", "degree": "PhD", "year": "1941", "title": "An Investigation of the Deflection Curve for a Pile Due to a Horizontal Load", "advisor": "Martel, Romeo Raoul", "url": "https://resolver.caltech.edu/CaltechTHESIS:02122025-180025793", "creators": [ { "name": { "family": "Cobb", "given": "Charles Lewis" }, "id": "Cobb-Charles-Lewis", "display_name": "Cobb, Charles Lewis" } ], "advisors": [ { "name": { "family": "Martel", "given": "Romeo Raoul" }, "id": "Martel-R-R", "role": "advisor", "display_name": "Martel, Romeo Raoul" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "abstract": "No abstract." }, { "name": "Griffis, LeVan", "degree": "PhD", "year": "1941", "title": "The Influence of the Rate of Deformation on the Strength of Materials in Tension", "advisor": "Clark, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02212025-193949654", "creators": [ { "name": { "family": "Griffis", "given": "LeVan" }, "id": "Griffis-LeVan", "display_name": "Griffis, LeVan" } ], "advisors": [ { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/p0k1-8035", "abstract": "There is growing significance to the tension impact test in\r\ncomparing the usefulness of materials for service conditions in which\r\ndynamic loading occurs. Many recent investigations have begun the\r\nstudy of the dynamic properties of materials, and have attempted to\r\ncorrelate. their results with the existing theories of strength of\r\nmaterials. Few investigators have succeeded in developing their\r\nexperimental procedure in impact testing to the point of determining\r\nbasic tensile properties measured by the stress-strain diagram.
\r\n\r\nThis thesis discusses a method of determining stress-strain\r\nrelations for materials under tension impact loads at various speeds.\r\nTension characteristics of eight different engineering alloys are discussed\r\nfor rates of deformation from 10 to 190 feet per second.\r\nComparison with results from static tests is made for these materials,\r\nand the influence of the rate of deformation is noted.
\r\n\r\nThe results indicate that in general, for the materials\r\ntested, the yield and ultimate stresses under dynamic conditions are\r\nhigher than for static conditions; and quantitative data are tabulated\r\nas a function of the rate of deformation. The dynamic energies absorbed\r\nin tension impact are usually larger than the static values,\r\nbut they may decrease in the case of certain heat treated steels.\r\nResults do not indicate a critical velocity of embrittlement for any\r\nof the materials tested within the range of velocities reported. Use\r\nof any single type of geometrical deformation of the material as a\r\nmeasure of the resistance of the material to dynamic loads is not found\r\npossible.
\r\n\r\nApplication of this test procedure is suggested as a basis\r\nfor investigating the relative usefulness of different heat treatments\r\nand alloying of metals for service conditions involving dynamic tensile\r\nloading.
" }, { "name": "Housner, George William", "degree": "PhD", "year": "1941", "title": "An Investigation of the Effects of Earthquakes on Buildings", "advisor": "Martel, Romeo Raoul", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092003-152001", "creators": [ { "name": { "family": "Housner", "given": "George William" }, "id": "Housner-George-William", "display_name": "Housner, George William" } ], "advisors": [ { "name": { "family": "Martel", "given": "Romeo Raoul" }, "id": "Martel-R-R", "role": "advisor", "display_name": "Martel, Romeo Raoul" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/CTJR-HD62", "abstract": "The forces induced in buildings by earthquakes are here investigated. The effects of some of the physical properties of structures are determined and from an analysis of earthquake records the general character of earthquakes is deduced. An investigation is also made of the dissipation of energy of vibration to the propagation of elastic waves in the ground.\r\n\r\nThis thesis was written to contribute to the program of earthquake research that Professor Martel has been carrying on for the past ten years. As such, it is a continuation of the work done by M. A. Biot and M. P. White. Acknowledgment is made of the financial support of the County of Los Angeles which made possible the analysis of the earthquake records.\r\n\r\nSincere appreciation is expressed to Professor R. R. Martel for the advice he has given and the interest he has shown.\r\n\r\nSUMMARY\r\n\r\nAll the earthquakes analysed are of the same general character. There are no special features distinguishing any one earthquake from another. There is no evidence that the physical properties of the ground have any effect on the character of the earthquake.\r\n\r\nIn the range of periods from 2/10 seconds to 2 seconds, all ground waves are of approximately equal importance. There are no predominating periods of ground waves.\r\n\r\nThe analysis of records provides a convenient method of measuring the intensities of earthquakes. A scale of intensities constructed in this manner is shown in the following table:\r\n\r\nScale of Earthquake Intensities\r\n\r\nEl Centro, May, 1940 -- 100\r\nLong Beach, March, 1933, (at Vernon) -- 65\r\nEl Centro, December, 1934 -- 60\r\nHelena, Montana, October 31, 1935 -- 55\r\nFerndale, September, 1938 -- 40\r\nLos Angeles, October, 1933 ? 17\r\n\r\nThe analysis of the records shows that there is no so-called \"dominant ground period\".\r\n\r\nFor undamped structures, with periods of vibration longer than about 2/10 of a second, the maximum shearing force at the base is, for practical purposes, independent of the height of the structure and independent of the period of vibration.\r\n\r\nFor such structures the maximum shearing forces are independent of the total mass of the structure but for ordinary construction vary in direct ratio as the mass per floor level.\r\n\r\nWhen the height of a structure is increased, the shearing forces in the upper portions of the structure are increased.\r\n\r\nOnly the first few modes of vibration are of importance in producing shearing forces.\r\n\r\nFor undamped structures flexibility and lightness of construction will reduce the magnitudes of the shearing forces. However, the flexibility of the first story alone has little effect upon the maximum shearing force at the base of the structure, although it does reduce the shearing forces in the upper portions of the structure.\r\n\r\nConsiderable elastic yielding of the ground may take place at the base of a structure without having sufficient effect on the accelerogram to be distinguished by analysis of the record.\r\n\r\nThe energy dissipated into the ground may be an important factor in reducing the shearing forces. The analysis shows that the reduction in shearing forces due to energy lost in wave propagation is greater for high frequencies than for low frequencies, and is greater for ground of low rigidity than for ground with high rigidity. Tables are constructed which indicate that structures with high frequencies may have their shearing forces appreciably reduced by this energy dissipation. It appears, however, that structures with periods of about 1 second will be little affected." }, { "name": "Wetmore, William Owen", "degree": "PhD", "year": "1941", "title": "An Investigation of Some Silver Alloy Steels", "advisor": "Clark, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02082025-233859174", "creators": [ { "name": { "family": "Wetmore", "given": "William Owen" }, "id": "Wetmore-William-Owen", "display_name": "Wetmore, William Owen" } ], "advisors": [ { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/v2ch-sj29", "abstract": "The object of this research project was to develop an alloy steel containing an appreciable amount of silver and possessing desirable properties. Investigation revealed that the solubility of silver alone in steel was exceedingly small, less than 0.02 per cent. It was necessary, therefore,\r\nto develop some means of increasing the solubility of silver in steel. By alloying silver with copper before adding to steel, it was found that 0.3 per cent silver could be alloyed with the steel. An investigation was conducted on some of the properties of the silver copper steels. The results indicate that additions of silver with copper have little effect on the thermal critical temperatures, on some of the mechanical properties, on the corrosion resistance, on the austenitic grain size, and on the microstructure of 0.15 per cent and 0.35 per cent carbon steels." }, { "name": "Byrne, Ralph Edward", "degree": "PhD", "year": "1940", "title": "The Analysis of Stresses in a Thin Cylindrical Shell of Circular Cross-Section", "advisor": "Martel, Romeo Raoul", "url": "https://resolver.caltech.edu/CaltechETD:etd-06192007-131244", "creators": [ { "name": { "family": "Byrne", "given": "Ralph Edward" }, "id": "Byrne-Ralph-Edward", "display_name": "Byrne, Ralph Edward" } ], "advisors": [ { "name": { "family": "Martel", "given": "Romeo Raoul" }, "id": "Martel-R-R", "role": "advisor", "display_name": "Martel, Romeo Raoul" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/4542-J330", "abstract": "In Part I., the equations of equilibrium and expressions for the strain components are set up, for a thin shell of a general shape, by the use of the methods of vector analysis. The simplicity of the vector method of approach to this problem is shown.\r\n\r\nIn Part II., the theory developed in Part I. is particularized for the case of a circular cylindrical shell. Expressions for force components are obtained in terms of the deformation components, and three equations of equilibrium in terms of the three deformation components are derived.\r\n\r\nIn Part III., the expression for strain energy for a circular cylindrical shell is set up, and, by means of the Principle of Virtual Work, equilibrium equations and boundary conditions for a general type of boundary are deduced. The boundary conditions are then particularized for the cases in which the boundaries are parametric curves.\r\n\r\nIn Part IV., an exact solution of the differential equations derived in Parts II. and III. is obtained. This solution is applicable to circular cylindrical shells of the type which occurs in the problem of the design and construction of barrel roofs.\r\n\r\nIn Part V., the exact solution of Part IV. is carried out numerically for two particular cases.\r\n\r\nIn Part VI., an account of several approximate methods of solution of this problem is given. A brief summary of some of the 1iterature on this subject is included. The thesis is concluded with a rather detailed account of several of the methods by which the author attempted to obtain short and approximate solutions of this problem." }, { "name": "Dunn, Louis Gerhardus", "degree": "PhD", "year": "1940", "title": "An Investigation of Sheet-Stiffener Panels Subjected to Compression Loads with Particular Reference to Torsionally Weak Stiffeners", "advisor": "Sechler, Ernest Edwin; von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04202004-154649", "creators": [ { "name": { "family": "Dunn", "given": "Louis Gerhardus" }, "id": "Dunn-Louis-Gerhardus", "display_name": "Dunn, Louis Gerhardus" } ], "advisors": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/84RM-ZH50", "abstract": "A total of 183 panel specimens of 24ST alloy with nominal thicknesses of 0.020, 0.025, and 0.040 inch with extruded bulb-angle sections of 12 shapes spaced 4 and 5 inches as stiffeners were tested to obtain the buckling stress and the amplitude of the maximum wave when buckled. Bulb angles from 3 to 27-1/2 inches long were tested as pin-end columns. The experimental data are presented as stress-strain and column curves and in tabular form. Some comparisons with theoretical results are presented.
\r\n\r\nAnalytical methods are developed that make it possible for the designer to predict with reasonable accuracy the buckling stress and the maximum-wave amplitude of the sheet in stiffened-panel combinations. The scope of the test was insufficient to formulate general design criteria but the results are presented as a guide for design and an indictaion of the type of theoretical and experimental work needed.
" }, { "name": "Harrison, Arthur Elliot", "degree": "PhD", "year": "1940", "title": "Cathode Beam Behavior in a High Speed Oscillograph", "advisor": "Sorensen, Royal Wasson", "url": "https://resolver.caltech.edu/CaltechTHESIS:12172024-211553369", "creators": [ { "name": { "family": "Harrison", "given": "Arthur Elliot" }, "id": "Harrison-Arthur-Elliot", "display_name": "Harrison, Arthur Elliot" } ], "advisors": [ { "name": { "family": "Sorensen", "given": "Royal Wasson" }, "id": "Sorensen-R-W", "role": "advisor", "display_name": "Sorensen, Royal Wasson" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ptan-cr41", "abstract": "No abstract." }, { "name": "Hsu, Chang-Pen", "degree": "PhD", "year": "1940", "title": "Propagation of Electromagnetic Waves Inside a Cylindrical Metal Tube and Along Other Types of Guides", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:12132012-155518935", "creators": [ { "name": { "family": "Hsu", "given": "Chang-Pen" }, "id": "Hsu-Chang-Pen", "display_name": "Hsu, Chang-Pen" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/PE3J-AP78", "abstract": "The prime purpose of this paper is to base the discussion of\r\nthe properties of propagation of electromagnetic waves inside a\r\nmetal tube upon the theory of complex functions. The general\r\nexpressions for the field components for different types of excitation\r\nsystems are obtained in a rigorous manner starting from that\r\nof an electric and a magnetic dipole. The formal mathematical\r\ngeneralization is achieved by means of the transformation formulae\r\nof cylindrical functions and the results of the theory of integral\r\nequations. The integral equations thus obtained are expanded into\r\nseries by aid of residual calculus for actual numerical calculation.
\r\n\r\nThe residues at the poles of singularities give rise to different\r\n\"distinct modes\" of propagation and thereby a comprehensive discussion\r\nof all the important physical properties is made. At the same time,\r\nproblems arising in practical applications, say for long distance\r\ntransmission for television purposes, are analyzed and some interesting\r\nconclusions obtained. The unique and rigorous analysis is only\r\nmade possible by the free use of the results of the theory of\r\ncomplex functions.
\r\n\r\nA comparison of the properties of propagation with regard\r\nespecially to the attenuations and the velocities of propagation\r\ninside a hollow cylindrical metal tube guide and that of a\r\nconcentric system is made. It is hoped that the conclusions\r\nobtained therefrom will throw some light on the merits of both\r\nsystems and will point out those things which require careful\r\nconsideration in practical design.
" }, { "name": "Malina, Frank Joseph", "degree": "PhD", "year": "1940", "title": "Characteristics of the Rocket Motor and Flight Analyses of the Sounding Rocket", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechTHESIS:08202010-143142441", "creators": [ { "name": { "family": "Malina", "given": "Frank Joseph" }, "id": "Malina-Frank-Joseph", "display_name": "Malina, Frank Joseph" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/MF80-9W14", "abstract": "No abstract." }, { "name": "Oliver, Bernard More", "degree": "PhD", "year": "1940", "title": "The Measurement of Dielectric Losses at a Frequency of One Hundred Megacycles per Second", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-06182004-135230", "creators": [ { "name": { "family": "Oliver", "given": "Bernard More" }, "id": "Oliver-Bernard-More", "display_name": "Oliver, Bernard More" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TW6X-AB09", "abstract": "No Abstract Submitted." }, { "name": "Pai, Shih-I", "degree": "PhD", "year": "1940", "title": "On Turbulent Flow Between Rotating Cylinders", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-01092006-143245", "creators": [ { "name": { "family": "Pai", "given": "Shih-I" }, "id": "Pai-Shih-I", "display_name": "Pai, Shih-I" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6VD9-HY80", "abstract": "The present work had as its purpose the investigation of the velocity and turbulence distributions in the turbulent flow between two co-axial cylinders, the inner of which rotated. The radius of the inner cylinder was 7-7/8\". Two aspect ratios were used, one 10\" to 1-1/16\", the other 10\" to 17/32\". All velocity and turbulence measurements were made with hot-wire technique, using a special holder which reduced spindle interference to a minimum.\r\n\r\nThe circumferential velocity of the inner rotating cylinder was several hundred times the critical speed for instability of the laminar flow as given by G. I. Taylor.\r\n\r\nIt was found that velocity distributions in which the circumferential velocity of the fluid increases outward actually exist and cannot be explained by the shadow effect of the measuring instrument as G. I. Taylor suggested. Also the flow between the rotating cylinders is three-dimensional. The mean velocity distribution depends on whether the transfer of shear is carried out by turbulent fluctuations or by secondary motion. The regions, where the secondary motion is negligible, the mean velocity distribution is logarithmic which was shown by Dr. von Karman to be the distribution in Couette's case of turbulent flow.\r\n\r\nThe analysis of the measurements indicated that the secondary flow can be described by assuming ring-shaped vortices between the cylinders. It was known that such ring-shaped vortices introduce the instability of the laminar flow (see Ref. 1); but it was not known that such vortices exist at speeds as high as several hundred times the critical speed for instability, although their shapes are distorted. The sizes of the vortices and their numbers depend on the speed of the inner cylinder. The vortices can only exist in pairs, and at certain critical speeds the flow pattern may change suddenly due to the loss or gain of a pair of vortices. At high speeds the number of the vortices tends to decrease.\r\n\r\nThe two-dimensional theories for turbulent flow between rotating cylinders are discussed. They can not even be taken as a first approximation for this three dimensional vortex-ring flow." }, { "name": "Stewart, Homer Joseph", "degree": "PhD", "year": "1940", "title": "The Effect of Shear Instability on the Transverse Circulation in the Atmosphere", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-05222003-084939", "creators": [ { "name": { "family": "Stewart", "given": "Homer Joseph" }, "id": "Stewart-Homer-Joseph", "display_name": "Stewart, Homer Joseph" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/1FW3-YN51", "abstract": "In this paper it is shown that the shear fields on either side of the westerlies are dynamically unstable and will roll up to form discrete eddies. A study of the stable vortex systems into which these eddies might collect shows that a \"vortex street\" is stable for a certain range of the ratio of width to vortex spacing. It is also shown that a formation with vortices placed on the corners of a regular polygon is stable if the number of vortices is less than seven. This still holds if the effect of the shear field north of the westerlies is stimulated by a fixed polar cyclone. It further appears that with a strong general circulation, i.e. strong westerlies, only two or three high pressure cells should be found while the numbers, up to six, should be found with weaker circulations. This conclusion is verified by Northern Hemisphere mean pressure charts." }, { "name": "Van Driest, Edward Reginald", "degree": "PhD", "year": "1940", "title": "An Experimental Investigation of Turbulence Mixing as a Factor in the Transportation of Sediment in Open Channel Flow", "advisor": "Knapp, Robert T.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09282006-141455", "creators": [ { "name": { "family": "Van Driest", "given": "Edward Reginald" }, "id": "Van-Driest-Edward-Reginald", "display_name": "Van Driest, Edward Reginald" } ], "advisors": [ { "name": { "family": "Knapp", "given": "Robert T." }, "id": "Knapp-R-T", "role": "advisor", "display_name": "Knapp, Robert T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eng" ], "doi": "10.7907/NPRA-FT23", "abstract": "This investigation was conducted for the purpose of making a thorough study of the fundamental properties of the turbulence mixing process involved in the flow of water in an open channel.\r\n\r\nA channel 10 1/2 in. wide, 10 in. deep, and 40 ft. long was constructed in such a manner that illuminated globules formed by the injection of an immiscible fluid into the water could be photographed. A statistical analysis of the displacements of the globules from the origin yielded the intensity of turbulence and the correlation of successive velocities of a particle of fluid.\r\n\r\nThrough these measurements of the intensity of turbulence and the correlation of velocities, the nature of the turbulence in open channel flow was determined. The results of the investigation led to the conclusion that similarity of diffusion exists throughout the vertical center line of open channel flow. Due to this similarity, the mising length may be proportional to the root-mean-square velocity fluctuation and the mixing coefficient proportional to the mean-square velocity fluctuation or energy of turbulence. The concept of a particle of fluid losing its identity in the surrounding fluid was found to be untrue for the flows investigated herein.\r\n\r\nThis study was conducted under the direction of Robert T. Knapp, Associate Professor of Hydraulic Engineering, California Institute of Technology." }, { "name": "Vanoni, Vito August", "degree": "PhD", "year": "1940", "title": "Experiments on the Transportation of Suspended Sediment by Water", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-05142003-162057", "creators": [ { "name": { "family": "Vanoni", "given": "Vito August" }, "id": "Vanoni-Vito-August", "display_name": "Vanoni, Vito August" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/CYT2-W932", "abstract": "Measurements of the sediment and velocity distributions in a laboratory flume were made for various values of rate of flow, slope of channel, and size and amount of suspended load. The experimental sediment-distribution measurements were compared with the theoretical distribution which assumes that the coefficient for the turbulent transfer of suspended sediment is the same as the coefficient for the turbulent transfer of momentum.
\r\n\r\nThe following are the main findings:
\r\n\r\n(1) The measured sediment distributions have the same form as the theoretical distribution but do not agree quantitatively with them, thus showing, as was anticipated, the invalidity of the assumption that the transfer coefficient for sediment was equal to that for momentum. In general the measurements gave larger concentrations than the theory when the suspended load was fine, while as the size of the sediment was increased the agreement improved up to a certain size of sediment beyond which the tendency was in the opposite direction.
\r\n\r\n(2) Suspended sediment in a flow tends to reduce appreciably the turbulent transfer of momentum and hence the resistance to flow, allowing the sediment-laden water to flow more rapidly than a comparable clear water flow. This effect increases with the total sediment load and with a decrease in the grain size of the sediment.
\r\n\r\n(3) Suspended load in a flow tends to produce instability and may be a factor in causing the secondary circulation observed in rivers.
\r\n" }, { "name": "Atsumi, John Shoichi", "degree": "PhD", "year": "1939", "title": "Correlation and Decay of Turbulence Produced by Various Grids in a Wind Tunnel", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092024-180737116", "creators": [ { "name": { "family": "Atsumi", "given": "John Shoichi" }, "id": "Atsumi- John-Shoichi", "display_name": "Atsumi, John Shoichi" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/yq2d-wt47", "abstract": "No abstract." }, { "name": "Budenholzer, Roland Anthony", "degree": "PhD", "year": "1939", "title": "Some Thermodynamic Properties of Hydrocarbon Mixtures", "advisor": "Sage, Bruce H.; Lacey, William Noble", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192025-193812180", "creators": [ { "name": { "family": "Budenholzer", "given": "Roland Anthony" }, "id": "Budenholzer-Roland-Anthony", "display_name": "Budenholzer, Roland Anthony" } ], "advisors": [ { "name": { "family": "Sage", "given": "Bruce H." }, "id": "Sage-B-H", "role": "advisor", "display_name": "Sage, Bruce H." }, { "name": { "family": "Lacey", "given": "William Noble" }, "id": "Lacey-W-N", "role": "advisor", "display_name": "Lacey, William Noble" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/nrwe-sb95", "abstract": "No abstract." }, { "name": "Christensen, Nephi Albert", "degree": "PhD", "year": "1939", "title": "Some Aspects of Gully Development, Classification and Control", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:11262024-164738159", "creators": [ { "name": { "family": "Christensen", "given": "Nephi Albert" }, "id": "Christensen-Nephi-Albert", "display_name": "Christensen, Nephi Albert" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/ag6k-9d93", "abstract": "The various types of gully cross-sections are described\r\nand shown to be dependent upon the relative importance or\r\ndown-scour, side-scour and bank degradation, and it is shown\r\nthat the type of the mean cross-section is determined by the\r\ndominant one of these three processes. Not only is the relative\r\nimportance of the developmental process indicated by the\r\nmean cross-section, but also the stage of developnent of the\r\ngully. A means by which the stage of development may be\r\nascertained is important because it is the first step in selecting\r\nthe best method of treatment.
\r\n\r\nA discussion of the forces underlying the developmental\r\nprocesses is given, and the conditions for complete stability\r\nare indicated.
\r\n\r\nThe effects of grade reduction, stream sorting, and sediment\r\nload upon the development of gullies are deduced. The\r\nartificial treatments by man are discussed in the light of\r\nthese deductions.
\r\n\r\nA method for reclaiming major gullies, which are in the\r\nearly stages of development, is given.
" }, { "name": "Howland, Walter Lavern", "degree": "PhD", "year": "1939", "title": "Strength of Thin-Walled Elliptical Cylinders Supported at the Minor Axis", "advisor": "von K\u00e1rm\u00e1n, Theodore; Sechler, Ernest Edwin; Millikan, Clark Blanchard; Klein, Arthur Louis", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012015-161848918", "creators": [ { "name": { "family": "Howland", "given": "Walter Lavern" }, "id": "Howland-Walter-Lavern", "display_name": "Howland, Walter Lavern" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "advisor", "display_name": "Sechler, Ernest Edwin" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "advisor", "display_name": "Klein, Arthur Louis" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/KQK7-V396", "abstract": "In this investigation it was found that the\r\ninstability failure of curved sheet is nearly\r\nindependent of the type of loading and is primarily\r\na function of the maximum stress, radius-thickness\r\nration and modulus of elasticity. A method of\r\ncorrelating the critical stress of thin sheet\r\nunder several different types of loading is given.\r\nAn explanation for the experimental critical stress\r\nof thin walled cylinders under bending being\r\ngreater than that for pure compression is given.\r\nThe strength of unstiffened thin walled circular\r\nnose sections under pure bending was found to be \r\ncontrolled by local instability of the section,\r\nrather than a large scale instability. The equation\r\nof local instability of curved sheet gives values\r\nwhich are in fair agreement with those found experimentally.
\r\n\r\nThe strength of elliptical cylinders supported\r\nat the minor axis under bending plus shear loads is\r\ngoverned primarily by the bending strength, and is\r\nlittle effected by the sheer force unless the amount\r\nof shear is quite large with respect to the moment.\r\nThe effect of increasing the amount of elliptically\r\ngreatly reduces the bending and shear strength of nose\r\nsections. Under torsional loads the stress at\r\nbuckling falls off as the ration of the major to minor \r\naxis increases but the failure stress decreases\r\nat a slower rate than the buckling stress. The\r\nlength effect of semi-circular sections under torsion\r\nis similar to that of a circular tube, and can be\r\nobtained by Donnell's theoretical equation.
\r\n" }, { "name": "Knoblock, Frederick Delbridge", "degree": "PhD", "year": "1939", "title": "Investigations on the Applications of the Hot Wire Anemometer for Turbulence Measurements", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-04252008-094935", "creators": [ { "name": { "family": "Knoblock", "given": "Frederick Delbridge" }, "id": "Knoblock-Frederick-Delbridge", "display_name": "Knoblock, Frederick Delbridge" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/DKG6-T043", "abstract": "The principle reasons for using the hot wire type of anemometer for turbulence measurements are outlined and some of the objectionable features limiting the applicability of the conventional type anemometer are pointed out. A brief historical background of the hot wire anemometer is followed by a consideration of various possibilities of improving the method of measuring the intensity of turbulence. This analysis purposes to show why such improvements can only be realized by a direct calibration of the hot wire\u2019s response to velocity fluctuations.\r\n\r\nThe consequent development of a new technique, referred to as the \u201cVibrator Method,\u201d is then explained. A general discussion of the results of a series of investigations using the Vibrator method is then presented and includes: a comparison with the orthodox method; the response of the hot wire to periodic fluctuations relative to the validity of the theory of hot wire lag; an extension of the method to correlation measurements using two hot wires, and other applications.\r\n\r\nThe paper concludes with a detailed description of various hot wire anemometer equipment which has been developed for use with the Vibrator method of measuring turbulence intensity.\r\n" }, { "name": "Lombard, Albert Eaton", "degree": "PhD", "year": "1939", "title": "An Investigation of the Conditions for the Occurrence of Flutter in Aircraft and the Development of Criteria for the Prediction and Elimination of Such Flutter", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-07182007-091133", "creators": [ { "name": { "family": "Lombard", "given": "Albert Eaton" }, "id": "Lombard-Albert-Eaton", "display_name": "Lombard, Albert Eaton" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/80H8-TB52", "abstract": "A review is presented of the work done by other investigators on the effects of inertia couplings in producing flutter in control surfaces that are not mass balanced. The conclusion is reached that for the prevention of such flutter complete dynamic balance should always maintain.\r\n\r\nFlexural-torsional flutter is investigated in considerable detail from the consideration of the dynamical equations for steady state forced oscillations of the two dimensional case. A complete set of response curves for two typical cases are included to show the types of responses that should be observed in flight with vibration pick-up equipment. The important fact is brought out that the response and behavior of the wing at its natural bending frequency has little or no correlation with the behavior of the wing at the stability limit of flutter. Curves are presented to show that, for normal airplanes, the most important parameters which determine flutter in this mode are (a) the position of the inertia axis, (b) the torsional frequency, end (c) the radius of gyration of the wing mass about the inertia axis.\r\n\r\nThe dynamical equations are set up for the cases of flexural-aileron, torsional-aileron, and flexural-torsional-aileron flutter in the two-dimensional case and an example is given of the determination of the stability limit of a specific example of the first of these modes.\r\n\r\nAn extension of the two-dimensional case to the three-dimensional case is presented with particular reference to determining the flexural-torsional flutter speed of a tail surface with vertical surfaces on the tips of the horizontals. The method of attack is outlined for the calculation of natural frequencies at zero airspeed to use in determining the flutter speed.\r\n\r\nStatistical data in a graphical form show the variations of natural frequencies of the various components of airplanes with the size of such airplanes.\r\n\r\nThe conclusion is reached that the speed of airplanes should be restricted to two-thirds of the critical speed for any mode of flutter, divergence, or aileron reversal." }, { "name": "McCann, Gilbert Donald", "degree": "PhD", "year": "1939", "title": "The Impulse Characteristics of Oil Gaps from the Standpoint of Insulation Coordination", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-05132003-170005", "creators": [ { "name": { "family": "McCann", "given": "Gilbert Donald" }, "id": "McCann-Gilbert-Donald", "display_name": "McCann, Gilbert Donald" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/TBA2-0272", "abstract": "The development and use of high voltage surge generating equipment are described in this thesis.
\r\n\r\nImpulse equipment capable of producing and recording standard test surges up to 2,000,000 volts for both research and commercial testing have been developed.
\r\n\r\nThe present status of insulation coordination shows the need for more data on the impulse characteristics of large oil gaps.
\r\n\r\nA new type of oil test tank has been constructed which permits less gap field distortion and better conditioning of oil and electrodes than was formerly possible for large gaps at high voltage.
\r\n\r\nThe impulse characteristics of oil gaps having spacings ranging from one-half to eight inches formed by circular brass rods with spherical ends from one-fourth to two inches in diameter have been determined.
\r\n\r\nIt is found that such gaps have impulse strengths which are greatly affected by slight changes in conditions of both the oil and electrode surfaces.
\r\n\r\nTheir impulse values are much higher than their 60-cycle strengths and are functions of the wave shape of the surge.
\r\n\r\nThe most probable type of breakdown mechanism was found to be the thermal electric breakdown initiated by impurities in the oil.
" }, { "name": "Schairer, Robert Sorg", "degree": "PhD", "year": "1939", "title": "Unsymmetrical Lift Distributions on a Stalled Monoplane Wing", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-12282005-110200", "creators": [ { "name": { "family": "Schairer", "given": "Robert Sorg" }, "id": "Schairer-Robert-Sorg", "display_name": "Schairer, Robert Sorg" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/3WX9-JZ33", "abstract": "The purpose of the research was to find if it is possible to have an unsymmetrical span load distribution on a monoplane wing at the stall without a rolling velocity. The investigation is based upon the Prandtl first order wing theory. It is shown that it is possible to have an unsymmetrical lift distribution at the stall if a certain shape is assumed for the curve of section lift coefficient vs. effective angle of attack. Two methods of determining such a solution for any particular wing shape are discussed. Curves are presented showing unsymmetrical solutions for a number of different wing shapes and also showing the resulting lift and rolling moment coefficients. The important conclusions are as follows:\r\n\r\n1. An unsymmetrical lift distribution across the span of a monoplane wing at the stall is possible.\r\n\r\n2. The unsymmetrical solution produces a rolling moment of the same order of magnitude as that caused by a fully deflected aileron.\r\n\r\n3. The unsymmetrical distribution can occur only in a very small range of angles of attack after the wing begins to stall.\r\n\r\n4. The magnitude of the maximum rolling moment coefficient and the difference between the angle of attack at which the maximum rolling moment occurs and the angle of attack for first stall are nearly the same for all of the wing shapes investigated." }, { "name": "Tsien, Hsue Shen", "degree": "PhD", "year": "1939", "title": "Problems in Motion of Compressible Fluids and Reaction Propulsion", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-01122004-105646", "creators": [ { "name": { "family": "Tsien", "given": "Hsue Shen" }, "id": "Tsien-Hsue-Shen", "display_name": "Tsien, Hsue Shen" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/2698-R671", "abstract": "none" }, { "name": "Baker, Ralph Doris", "degree": "PhD", "year": "1938", "title": "The Effect of Surface Roughness on Skin Friction and Turbulence in Two Dimensional Flow", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02092006-154408", "creators": [ { "name": { "family": "Baker", "given": "Ralph Doris" }, "id": "Baker-Ralph-Doris", "display_name": "Baker, Ralph Doris" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6BXC-TP03", "abstract": "This investigation is divided into two parts. Part I deals with the effect of roughness and pressure drop and skin friction, and Part II covers the effect of surface roughness and the turbulent velocity fluctuations, and the correlation between these fluctuations in the direction of the mean flow and those normal to the channel walls.
\r\n\r\nThe roughness for both investigations was the same, and consisted of corrugated paper glued to the inside walls of a channel of 4.9 cm. wide by 85 cm. (inside dimensions). The roughness was changed by removing every other one of the corrugations, as illustrated in Fig. 6.
\r\n\r\nPressure and velocity distribution measurements were made at various stations and the results compared to Karman\u2019s equation, u/v* = Ar + B log y/k for rough walls, where u is the velocity in the channel, v* is the friction velocity = \u221a\u03c4o/\u2113, y = distance from wall, \u03c5 = the kinematic viscosity, k = the roughness height.
\r\n\r\nKarman\u2019s analysis showed B to be a universal constant independent of the wall roughness. Some investigators have given slightly different values to this constant. Their results were carried out in pipes or channels of near square cross section. These results appear to fall within 3% of those of Nikuradse as far as the value of B is concerned. However, a value of B a little less than 5.75 would fit the points better.
\r\n\r\nThese experiments were undertaken to add some information to this subject with flow in deep narrow channels and with other types of rough surfaces which had not been investigated.
\r\n\r\nThe turbulence measurements were determined with a hot-wire anemometer using a vibrating wire to calibrate it with. These results show that the correlation coefficient u'v'/(u')2 increases with speed for smooth walls and varies materially with the type of roughness with no definite systematic trend as to this change.
" }, { "name": "Charters, Alexander Crane", "degree": "PhD", "year": "1938", "title": "The Effect of Curvature on Boundary Layer Transition", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard", "url": "https://resolver.caltech.edu/CaltechETD:etd-04292008-110647", "creators": [ { "name": { "family": "Charters", "given": "Alexander Crane" }, "id": "Charters-Alexander-Crane", "display_name": "Charters, Alexander Crane" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z13V-F628", "abstract": "Discrepancies in the boundary layer profiles of NACA T.N. 613, * and recent work done at Cambridge University, England, on the effect of inclination on transition required the reinvestigation of the effect of curvature on boundary layer transition using a more fundamentally sound experimental technique than previously. This technique consisted in comparing velocity profiles taken at different speeds at each measuring station with the universal Blasius laminar profile; a further indication of transition was obtained by measuring the local shear coefficient with a small total head tube pressed against the surface. Agreement between the two methods was complete in all but one case. The effect of inclination was investigated by rotating the working section of the tunnel as a whole around a fixed pivot. Unfavorable inclination produced a decrease in transition Reynolds number on either side of the sheet but a neutral region was found to exist in which inclination had no effect on the transition and in which the effect of curvature alone acted. The effect of the curvature could be expressed as a function of the single variable 1000\u03b4m/rc. As to the exact nature of the (R\u03b4m)T vs 1000\u03b4m/rc curve, little as yet can be said since a sufficient range of 1000\u03b4m/rc has not been investigated as yet. The results of T.N. 613 were thus validated qualitatively but the values of transition given there were found to be too large.
\r\n\r\n* National Advisory Committee for Aeronautics Technical Note.
\r\n" }, { "name": "Doll, Edward Bushnell", "degree": "PhD", "year": "1938", "title": "Radio Field Strength Measurements at 41 Megacycles", "advisor": "Mackeown, Samuel Stuart", "url": "https://resolver.caltech.edu/CaltechTHESIS:12022024-233356078", "creators": [ { "name": { "family": "Doll", "given": "Edward Bushnell" }, "id": "Doll-Edward-Bushnell", "display_name": "Doll, Edward Bushnell" } ], "advisors": [ { "name": { "family": "Mackeown", "given": "Samuel Stuart" }, "id": "Mackeown-S-S", "role": "advisor", "display_name": "Mackeown, Samuel Stuart" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/9j13-5y87", "abstract": "No abstract." }, { "name": "Huang, Hsia-Chien", "degree": "PhD", "year": "1938", "title": "Frontogenetic Regions in the Far East", "advisor": "Krick, Irving Parkhurst", "url": "https://resolver.caltech.edu/CaltechTHESIS:01312025-213644065", "creators": [ { "name": { "family": "Huang", "given": "Hsia-Chien" }, "id": "Huang-Hsia-Chien", "display_name": "Huang, Hsia-Chien" } ], "advisors": [ { "name": { "family": "Krick", "given": "Irving Parkhurst" }, "id": "Krick-I-P", "role": "advisor", "display_name": "Krick, Irving Parkhurst" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "meteor" ], "doi": "10.7907/e6jy-3360", "abstract": "No abstract." }, { "name": "Rader, Louis Telemacus", "degree": "PhD", "year": "1938", "title": "Dielectric Recovery of Short A-C Arcs Between High-Boiling-Point Electrodes", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-06232004-143113", "creators": [ { "name": { "family": "Rader", "given": "Louis Telemacus" }, "id": "Rader-Louis-Telemacus", "display_name": "Rader, Louis Telemacus" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/BXYB-0G14", "abstract": "No Abstract." }, { "name": "Sears, William Rees", "degree": "PhD", "year": "1938", "title": "A Systematic Presentation of the Theory of Thin Airfoils in Non-Uniform Motion", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-06252004-134954", "creators": [ { "name": { "family": "Sears", "given": "William Rees" }, "id": "Sears-William-Rees", "display_name": "Sears, William Rees" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/EM5X-CZ66", "abstract": "The basic conceptions of the circulation theory of airfoils are reviewed briefly, and the mechanism by which a \"wake\" of vorticity is produced by an airfoil in non-uniform motion is pointed out. After a calculation of the induction effects of a wake vortex, it is shown how the lift and moment acting upon an airfoil in the two-dimensional case may be calculated directly from simple physical considerations of momentum and moment of momentum. Formulae for the lift and moment are then obtained which are applicable to all cases of motion of a two-dimensional thin airfoil in which the wake produced is approximately flat; i.e., in which the movement of the airfoil normal to its mean path is small.
\r\n\t\r\nThe general results are applied first to the case of an oscillating airfoil, and vector diagrams giving the magnitudes and phase angles of the lift and moment are obtained. The results of a sudden change of angle of attack are then determined, and a general method for handling transient cases is set up. This method is applied to the calculation of the lift and moment acting on an airfoil entering sharp-edged and graded gusts. The case of a series of sinusoidal gusts is also considered.
\r\n\t\r\nA method of calculating the distribution of forces over the airfoil chord is then shown, and it is applied to the steady-state oscillation. The paper concludes with a discussion of the applicability of certain results to the explanation of observed phenomena beyond the stall.
\r\n" }, { "name": "Clauser, Francis Hettinger", "degree": "PhD", "year": "1937", "title": "New Methods of Solving the Equations for the Flow of a Compressible Fluid", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-175229", "creators": [ { "name": { "family": "Clauser", "given": "Francis Hettinger" }, "id": "Clauser-Francis-Hettinger", "display_name": "Clauser, Francis Hettinger" }, { "name": { "family": "Clauser", "given": "Milton Ure" }, "id": "Clauser-Milton-Ure", "display_name": "Clauser, Milton Ure" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZAWH-VK93", "abstract": "The usual equations for the flow of a compressible fluid are non-linear in character and difficult to solve. It has been found that if the components of velocity are taken as independent variables, the resulting equations are linear. These equations are developed and new forms introduced.
\r\n\r\nA new function, \u0393 is introduced and a method advanced for effecting the transformation from the plane where the velocity components are coordinates, to the physical plane where x and y are coordinates.
\r\n\r\nA new way of finding plausible solutions to investigate is given and the case of flow in a corner is worked out in detail. The flow is found to have an anomalous behavior, the reason for which is explained. This solution is applied to the flow behind a curved shock wave.
" }, { "name": "Clauser, Milton Ure", "degree": "PhD", "year": "1937", "title": "The Effect of Curvature on the Transition from Laminar to the Turbulent Boundary Layer", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Robert Andrews", "url": "https://resolver.caltech.edu/CaltechETD:etd-11122003-174320", "creators": [ { "name": { "family": "Clauser", "given": "Milton Ure" }, "id": "Clauser-Milton-Ure", "display_name": "Clauser, Milton Ure" }, { "name": { "family": "Clauser", "given": "Francis Hettinger" }, "id": "Clauser-Francis-Hettinger", "display_name": "Clauser, Francis Hettinger" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Robert Andrews" }, "id": "Millikan-R-A", "role": "advisor", "display_name": "Millikan, Robert Andrews" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/E5EQ-DA15", "abstract": "In the flow over the upper surface of a wing, a discrepancy between the predicted and actual point of transition from laminar to turbulent boundary layer had been found. This effect may be due to the comparatively small radius of curvature of the upper surface of the wing. The present tests were undertaken to investigate this effect.
\r\n\r\nAs no available channel was suitable for this work, a new channel with two working sections was built. One working section had a wall with a twenty inch radius of curvature and the other section had a flat wall.
\r\n\r\nThree types of measurements were made: a. Traverses were made with a total head tube to determine the character of the boundary layer at various Reynolds numbers. b. The turbulence distribution in the boundary layer was investigated by means of a hot wire and a vacuum tube amplifier. c. A similar investigation of the mean velocity distribution in the boundary layer was made by means of a hot wire anemometer.
\r\n\r\nIt was found that by using an abbreviated form of the turbulence level traverses, critical Reynolds Numbers of the transitions could be established. These critical Reynolds are plotted as a function of x/r (x being the distance of the transition from the leading edge of the plate; r being radius of curvature of the plate) for both the convex and concave side of the plate.
" }, { "name": "Griest, Raymond Howard", "degree": "PhD", "year": "1937", "title": "A Low-Voltage High Speed Cathode-Ray Oscillograph", "advisor": "Sorensen, Royal Wasson", "url": "https://resolver.caltech.edu/CaltechTHESIS:10062021-184222765", "creators": [ { "name": { "family": "Griest", "given": "Raymond Howard" }, "id": "Griest-Raymond-Howard", "display_name": "Griest, Raymond Howard" } ], "advisors": [ { "name": { "family": "Sorensen", "given": "Royal Wasson" }, "id": "Sorensen-R-W", "role": "advisor", "display_name": "Sorensen, Royal Wasson" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/artw-qn46", "abstract": "This thesis is a description of the development of a compact,\r\ncontinuously pumped, metal cathode-ray oscillograph. The design\r\nincorporates several features which it is hoped will prove to be\r\na useful contribution to the subject. In particular, the design\r\nand operation of a discharge tube which is both simple and reliable\r\nis discussed. The tube operates at about 10,000 volts and the\r\nbeam is sufficiently intense to permit a recording speed in excess\r\nof 108 centimeters per second. The principle of \"pre-concentration\",\r\nas suggested by Rogowski, has been utilized and seems to offer some\r\nadvantage in increasing the efficiency of the discharge tube; in\r\naddition, it permits ready visual observation of the cathode surface\r\nby adjusting the two magnetic focusing coils to act as an electron\r\nmicroscope. Roll film mounted in the evacuated space is used to\r\nrecord phenomena by a means which seems to overcome some of the\r\ninherent difficulties of this method. Two circuits used in conjunction\r\nwith this tube, one of which having some advantage over the\r\nmore common types, are briefly discussed. The performance of the\r\napparatus is illustrated by several records." }, { "name": "Hawley, Paul Frederick", "degree": "PhD", "year": "1937", "title": "Design and Operation of a Cathode-Ray Oscillograph for External Photography", "advisor": "Lindvall, Frederick C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05232024-215513766", "creators": [ { "name": { "family": "Hawley", "given": "Paul Frederick" }, "id": "Paul-Frederick-Hawley", "display_name": "Hawley, Paul Frederick" } ], "advisors": [ { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "advisor", "display_name": "Lindvall, Frederick C." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/jvh3-bq94", "abstract": "The prominent features in the design of the instrument are\r\ndiscussed. Novel among these are the design of the metal discharge\r\ntube, Lenard window and associated apparatus, and the\r\ntime sweep and blocking circuits. Investigation of the metal\r\ndischarge tube showed that there was an optimum spacing between\r\ncathode and anode, that decreasing the diameter of the tube\r\nincreased the ratio of beam current to cathode current, and that\r\nraising the cathode voltage increased the current density in the\r\nbeam. A 2\u00bd x 3\u00bd inch Lenard window using cellophane foil\r\nsupported by a metal grid is used, and has proved to be quite\r\nsatisfactory and durable. The sweep and blocking circuits are\r\nintegral, operating from a triple sphere gap, and are so arranged\r\nthat the beam sweeps clear across the window without any auxiliary\r\nbiasing arrangement. Tripping is either automatic from an\r\nincoming surge, or semi-manual from a second set of gaps set to\r\ntrip at convenient intervals. A number of sweep speeds are\r\navailable, controlled by a selector switch.
\r\n\r\nThe various factors involved in Lenard photography are\r\ntabulated and the majority are investigated. The radial current\r\ndensity in the recording spot is measured, and the effects of\r\nchanges in discharge tube design in this regard are evaluated.\r\nSeveral types of films were tested to find the most sensitive.\r\nEastman Process Nitrate film was finally adopted as sensitive\r\nas most and mechanically superior to the others. The best\r\ndevelopment time to use for typical oscillograms in several\r\ndevelopers was determined. From a photometric investigation of\r\noscillograms taken with a wide range of velocities and cathode\r\nvoltages, the blackening of this film by cathode rays was\r\nestablished as a function of incident charge density and\r\ncathode voltage. An empirical formula B = K \u221aq is found\r\nto express the blackening as a function of charge density for a\r\ngiven cathode voltage. From these data the maximum recording\r\nspeed is computed to be 30,000 km./sec.
\r\n\r\nOperating experience with the tube is given. Typical\r\nosoillograms illustrating automatic recording of surge phenomena,\r\netc., are shown. Various types of distortion encountered in\r\noperation are illustrated, and methods for eliminating them\r\nare given.
" }, { "name": "McRae, James Wilson", "degree": "PhD", "year": "1937", "title": "The Measurement of Dielectric Loss in Solid Dielectrics at Very High Frequencies", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:02192025-191650445", "creators": [ { "name": { "family": "McRae", "given": "James Wilson" }, "id": "McRae-James-Wilson", "display_name": "McRae, James Wilson" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/hpzm-bs17", "abstract": "No abstract." }, { "name": "Binder, Raymond Charles", "degree": "PhD", "year": "1936", "title": "Investigation of the Instantaneous Velocity Distribution in the Volute of a Centrifugal Pump", "advisor": "Knapp, Robert T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11052024-211420363", "creators": [ { "name": { "family": "Binder", "given": "Raymond Charles" }, "id": "Binder-Raymond-Charles", "display_name": "Binder, Raymond Charles" } ], "advisors": [ { "name": { "family": "Knapp", "given": "Robert T." }, "id": "Knapp-R-T", "role": "advisor", "display_name": "Knapp, Robert T." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/vc5c-xj91", "abstract": "No abstract." }, { "name": "Bollay, William", "degree": "PhD", "year": "1936", "title": "A New Theory for Wings of Small Aspect Ratio", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-01112006-081734", "creators": [ { "name": { "family": "Bollay", "given": "William" }, "id": "Bollay-William", "display_name": "Bollay, William" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/8BV2-QH84", "abstract": "Experiments on wings have shown that a very different kind of flow takes place for very small aspect ratios than for large aspect ratios. The lift curve continues up to about 45\u00b0 before stalling occurs. During this range it has a concave curvature upward rather than downward as the lifting line or lifting surface theories predict. No theoretical explanation of this effect has yet been given since it was generally supposed to be a stalling phenomenon and thus not adaptable to perfect fluid theories. The present paper shows that this curvature effect is due to the fact that the trailing vortices leave at an angle \u03b1 to the plate. For the limiting case of a plate with finite span and infinite chord it is shown that the bound vorticity and induced downwash are constant across the span, and the trailing vortices leave the wing at the half-angle of attack, \u03b1=\u03b8/2. These results are carried over into the assumptions for the analysis of the finite rectangular flat plate of very small aspect ratio. A surface distribution of vorticity over the plate is assumed, constant across the span, and varying according to the formula \u03b3 = \u03b30\u221at/2-x/t/2+x along the chord. Straight trailing vortices are assumed leaving the plate at an undetermined angle \u03b1. The boundary condition assumed is that the mean value of the induced velocity along the center line of the span is equal to the normal component of the free-stream velocity. This determines the constant \u03b30 and thus the normal force coefficient CN as a function of \u03b8. The parameter \u03b1 is still undetermined; however, its limits are given. For very small aspect ratios \u03b1=\u03b8/2, for large aspect ratios it approaches \u03b8. Winter\u2019s experiments on a wing of aspect ratio \u03ba=1/30 are checked very closely by this theory assuming \u03b1=\u03b8/2. At larger aspect ratios up to about \u03ba=1 the experimental curves lie between the theoretically predicted curves corresponding to \u03b1=\u03b8/2 and \u03b1=\u03b8, moving toward the latter limit at \u03ba=1." }, { "name": "Browne, Thomas Everett", "degree": "PhD", "year": "1936", "title": "Dielectric Recovery of Short A-C Arcs Between Low-Boiling-Point Electrodes", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:10012015-143909827", "creators": [ { "name": { "family": "Browne", "given": "Thomas Everett" }, "id": "Browne-Thomas-Everett", "display_name": "Browne, Thomas Everett" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/2G7K-6814", "abstract": "The re-ignition characteristics (variation of re-ignition\r\nvoltage with time after current zero) of short alternating\r\ncurrent arcs between plane brass electrodes in air were studied\r\nby observing the average re-ignition voltages on the screen of a\r\ncathode-ray oscilloscope and controlling the rates of rise of\r\nvoltage by varying the shunting capacitance and hence the natural\r\nperiod of oscillation of the reactors used to limit the current.\r\nThe shape of these characteristics and the effects on them of\r\nvarying the electrode separation, air pressure, and current\r\nstrength were determined.
\r\n\r\nThe results show that short arc spaces recover dielectric\r\nstrength in two distinct stages. The first stage agrees in shape\r\nand magnitude with a previously developed theory that all voltage\r\nis concentrated across a partially deionized space charge layer\r\nwhich increases its breakdown voltage with diminishing density of\r\nionization in the field-tree space. The second stage appears to\r\nfollow complete deionization by the electric field due to displacement\r\nof the field-free region by the space charge layer, its\r\nmagnitude and shape appearing to be due simply to increase in gas\r\ndensity due to cooling. Temperatures calculated from this second\r\nstage and ion densities determined from the first stage by means\r\nof the space charge equation and an extrapolation of the temperature\r\ncurve are consistent with recent measurements of arc value by\r\nother methods. Analysis or the decrease with time of the\r\napparent ion density shows that diffusion alone is adequate to\r\nexplain the results and that volume recombination is not.\r\nThe effects on the characteristics of variations in the parameters\r\ninvestigated are found to be in accord with previous results and\r\nwith the theory if deionization mainly by diffusion be assumed.
" }, { "name": "Freeman, Robert Braman", "degree": "PhD", "year": "1936", "title": "The Relative Sliding Wear Resistance of Some Hard Alloys", "advisor": "Clark, Donald S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112024-145918852", "creators": [ { "name": { "family": "Freeman", "given": "Robert Braman" }, "id": "Freeman-Robert-Braman", "display_name": "Freeman, Robert Braman" } ], "advisors": [ { "name": { "family": "Clark", "given": "Donald S." }, "id": "Clark-D-S", "role": "advisor", "display_name": "Clark, Donald S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/1htx-tq50", "abstract": "No abstract." }, { "name": "Ippen, Arthur Thomas", "degree": "PhD", "year": "1936", "title": "An Analytical and Experimental Study of High Velocity Flow in Curved Sections of Open Channels", "advisor": "Knapp, Robert T.; von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-03272007-135513", "creators": [ { "name": { "family": "Ippen", "given": "Arthur Thomas" }, "id": "Ippen-Arthur-Thomas", "display_name": "Ippen, Arthur Thomas" } ], "advisors": [ { "name": { "family": "Knapp", "given": "Robert T." }, "id": "Knapp-R-T", "role": "advisor", "display_name": "Knapp, Robert T." }, { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/162E-WA65", "abstract": "In the theory of flow in open channels two stages of flow with principally different characteristics have to be considered, streaming flow and shooting flow. The velocity of flow in the first case is smaller than the velocity of propagation of translatory waves, in the latter case it is larger. The phenomena occurring in streaming flow are well known and theoretically solved, if we neglect the influence of friction. This latter simplification means that the velocity has a constant value for each point of the cross-section. For this assumption also the theory of the hydraulic jump has been successfully attacked, where the stage of flow changes from the shooting to the streaming condition. The present paper, however, deals with problems of flow of the shooting stage only and extends the theory of hydraulics to all cases of supercritical flow, where the variation of depths and velocities due to changes in the direction of flow is desired.
\r\n\r\nAn outstanding example of such a type of flow is the case of curved sections in a rectangular open channel. This case has been investigated in the following analytically by the principles developed, and its solution was then compared to an extensive experimental investigation. It is shown that an adequate solution of the case of high velocity flow in curved sections of open channels has been found.
" }, { "name": "Pierce, John Robinson", "degree": "PhD", "year": "1936", "title": "An Ink Recording Oscillograph for Steady State A.C. Phenomena in the Audio Range", "advisor": "Maxstadt, Francis W.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06252004-100232", "creators": [ { "name": { "family": "Pierce", "given": "John Robinson" }, "id": "Pierce-John-Robinson", "display_name": "Pierce, John Robinson" } ], "advisors": [ { "name": { "family": "Maxstadt", "given": "Francis W." }, "id": "Maxstadt-F-W", "role": "advisor", "display_name": "Maxstadt, Francis W." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/F2B9-4M08", "abstract": "An oscillograph has been designed and constructed which will reproduce in ink on paper tape the wave form of steady state a.c. voltages or currents in the frequency range 50 to 25,000 cycles. The tracing is done at a speed of approximately 1 cycle in 3 seconds, and represents a recording of the instantaneous voltage or current progressively at different phase positions in the cycle.
\r\n\r\nThe principle of the device is that of the Rosa curve tracer, but operation has been made automatic by the introduction of several new features, including an electrical phase shifter, a new type of electronic switch, and a recording milliammeter.
\r\n\r\nThe sources of error in the apparatus are analyzed and are shown to be reasonably small in magnitude and the error capable of further reduction.
\r\n\r\nAn appendix describes the use of the instrument as an harmonic analyzer.
\r\n" }, { "name": "Pipes, Louis Albert", "degree": "PhD", "year": "1936", "title": "Cable and Damper Vibration Studies", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:11122024-164018432", "creators": [ { "name": { "family": "Pipes", "given": "Louis Albert" }, "id": "Pipes-Louis-Albert", "display_name": "Pipes, Louis Albert" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/sqk6-y791", "abstract": "The increase in the diameter of the cables used in overhead\r\ntransmission lines has focused the attention of the Electrical \r\nEngineering profession on the mechanical vibrations which are\r\nset up in these lines by the action of the wind. These vibrations\r\nhave been the important cause of failures in many cases
\r\n\r\nA study of the literature of the subject shows the very\r\nhaphazard state in which the theory of these vibrations finds\r\nitself. It is the purpose of this paper to correlate some of the\r\nobserved phenomena by a mathematical analysis and hence to place\r\nthe subject on a more scientific basis.
\r\n\r\nThe thesis concerns itself with an analysis based on certain\r\nsimplifying assumptions which are well substantiated in practical\r\ncases. The analysis comprises the following topics:
\r\n\r\n1. Imperfect flexibility of conductor.
\r\n\r\n2. Travelling waves.
\r\n\r\n3. Damped Vibrations.
\r\n\r\n4. Forced Oscillations.
\r\n\r\n5. An Analysis of a Simplified Vibration Damper.
\r\n\r\n6. The Effect of Movable Extremities.
\r\n\r\n7. Reflection from a Damper.
\r\n\r\n8. An analysis of Preswerk's Vibrationless Cable.
\r\n\r\nThe results of the analyses of the various topics discussed\r\nare tabulated throughout the body of the paper and the derivation\r\nof the equations is carried out in the appendix.
" }, { "name": "Ramo, Simon", "degree": "PhD", "year": "1936", "title": "A Proposed New Standard for High Voltage Measurements", "advisor": "Sorensen, Royal Wasson", "url": "https://resolver.caltech.edu/CaltechTHESIS:03232012-125331634", "creators": [ { "name": { "family": "Ramo", "given": "Simon" }, "id": "Ramo-Simon", "display_name": "Ramo, Simon" } ], "advisors": [ { "name": { "family": "Sorensen", "given": "Royal Wasson" }, "id": "Sorensen-R-W", "role": "advisor", "display_name": "Sorensen, Royal Wasson" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/7ZP0-G010", "abstract": "It is suggested that the electrostatic force of attraction between spheres, rather than the sparking voltage, be adopted as the standard method of measuring high voltage. This proposal is based on the following investigations and results:
\r\n\r\n1. The sparking voltage of 50 centimeter standard testing spheres varies considerably even when corrections are made for changing air density. At larger spacings, the gap is influenced by the unavoidable presence of ground planes.
\r\n\r\n2. Accurate force measurements made over a period of several months gave a mean sparking voltage curve which differs by a few per cent from a newly recommended A.I.E.E. standard curve.
\r\n\r\n3. Only one correction factor, to account for the presence of extraneous bodies in the laboratory, need be applied to voltage computed from measured forces. It is shown that this factor is small and a technique is described for its precise computation.
\r\n\r\n4. Computations have been made for the effect of the spheres' shanks and the laboratory floor and walls on the attractive force between spheres.
\r\n\r\nThe main results of this research have been published in a paper, \"The Sparkless Sphere Gap Voltmeter II\", Electrical Engineering, Vol. 55, No. 5, by R.W. Sorensen and the author. This paper has been scheduled for a discussion at the A.I.E.E. 1936 summer convention.
" }, { "name": "Vaile, Robert Brainard, Jr.", "degree": "PhD", "year": "1936", "title": "A Determination of the Deviation of the Calibration Constant of a Force Voltmeter from its Theoretical Value for Isolated Spheres Due to the Presence of Other Bodies", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062024-212741052", "creators": [ { "name": { "family": "Vaile", "given": "Robert Brainard, Jr." }, "id": "Vaile-Robert-Brainard", "display_name": "Vaile, Robert Brainard, Jr." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8ajh-qt69", "abstract": "No abstract." }, { "name": "Widess, Moses B.", "degree": "PhD", "year": "1936", "title": "A Clarification of Heaviside's Operational Calculus", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:11192024-180047006", "creators": [ { "name": { "family": "Widess", "given": "Moses B." }, "id": "Widess-Moses-B", "display_name": "Widess, Moses B." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/4jkh-wk78", "abstract": "No abstract." }, { "name": "Genachte, Paul Frank", "degree": "PhD", "year": "1935", "title": "Deforming of the Front of Travelling Waves Along Power Lines Under Corona Conditions", "advisor": "Lindvall, Frederick C.; Mackeown, Samuel Stuart", "url": "https://resolver.caltech.edu/CaltechTHESIS:10112024-222723327", "creators": [ { "name": { "family": "Genachte", "given": "Paul Frank" }, "id": "Genachte-Paul-Frank", "display_name": "Genachte, Paul Frank" } ], "advisors": [ { "name": { "family": "Lindvall", "given": "Frederick C." }, "id": "Lindvall-F-C", "role": "advisor", "display_name": "Lindvall, Frederick C." }, { "name": { "family": "Mackeown", "given": "Samuel Stuart" }, "id": "Mackeown-S-S", "role": "advisor", "display_name": "Mackeown, Samuel Stuart" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/enzk-p071", "abstract": "No abstract." }, { "name": "Hobson, Jesse Edward", "degree": "PhD", "year": "1935", "title": "High Voltage Precision Measurements", "advisor": "Sorensen, Royal Wasson", "url": "https://resolver.caltech.edu/CaltechTHESIS:10302024-204151379", "creators": [ { "name": { "family": "Hobson", "given": "Jesse Edward" }, "id": "Hobson-Jesse-Edward", "display_name": "Hobson, Jesse Edward" } ], "advisors": [ { "name": { "family": "Sorensen", "given": "Royal Wasson" }, "id": "Sorensen-R-W", "role": "advisor", "display_name": "Sorensen, Royal Wasson" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0qx0-5576", "abstract": "No abstract." }, { "name": "Lipp, James Everett", "degree": "PhD", "year": "1935", "title": "Strength of Thin Walled Cylinders Subjected to Combined Compression and Torsion", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-01192006-141156", "creators": [ { "name": { "family": "Lipp", "given": "James Everett" }, "id": "Lipp-James-Everett", "display_name": "Lipp, James Everett" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "member", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-E-E", "role": "member", "display_name": "Sechler, Ernest Edwin" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/6Z0W-XJ59", "abstract": "This thesis is an extension of the work which was started by Dr. Donnell and Lieutenant Bridget on the problem of thin metal cylinders under combined torsion and direct stress. An explanation of the shape of the compression vs. torsion curve is found by calculating the yield failure of an element of sheet considered as a column with both transverse and end loads. Several causes of variation in that curve shape have been brought to light, but must wait for very complete and accurate experiments or a complete theoretical treatment for verification.
\r\n\r\nExperiments have been extended to several new materials, and have given results which parallel the previous work on steel. In order to cover as wide a range of cylinders as possible, the data of reference no. 1 have been included with the present series of tests.
" }, { "name": "Mills, Roscoe Harlan", "degree": "PhD", "year": "1935", "title": "The Boundary Layer for Some Axial Symmetric Flows", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-05022008-122728", "creators": [ { "name": { "family": "Mills", "given": "Roscoe Harlan" }, "id": "Mills-Roscoe-Harlan", "display_name": "Mills, Roscoe Harlan" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "member", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "member", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Tollmien", "given": "Walter" }, "id": "Tollmien-W", "role": "member", "display_name": "Tollmien, Walter" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/R7Q5-V769", "abstract": "The following thesis consists of two sections. Part 1. deals with \"The Boundary Layer for Some Axial Symmetric Flows\", Part 2. with \"Preliminary Experiments on the Flow between Two Circular Disks\"." }, { "name": "White, Merit Penniman", "degree": "PhD", "year": "1935", "title": "Analytical Studies of the Dynamic Response of Certain Structures to Assumed Ground Movements", "advisor": "Martel, Romeo Raoul", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112007-075818", "creators": [ { "name": { "family": "White", "given": "Merit Penniman" }, "id": "White-Merit-Penniman", "display_name": "White, Merit Penniman" } ], "advisors": [ { "name": { "family": "Martel", "given": "Romeo Raoul" }, "id": "Martel-R-R", "role": "advisor", "display_name": "Martel, Romeo Raoul" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "civileng" ], "doi": "10.7907/3Y5W-NG36", "abstract": "This investigation is chiefly concerned with the effects of earthquakes upon various structures. Several of the chapters are quite far afield but are included with the thought that they deal either with earthquakes or with structures, and are, at least to some extent, related to the principal subject of this discussion.\r\n" }, { "name": "Wolfe, Halley", "degree": "PhD", "year": "1935", "title": "An Electrical Method of Measuring Earth Pressures Against Structures", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:10182024-215442697", "creators": [ { "name": { "family": "Wolfe", "given": "Halley" }, "id": "Wolfe-Halley", "display_name": "Wolfe, Halley" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/hf51-4h88", "abstract": "No abstract." }, { "name": "Clark, Donald Sherman", "degree": "PhD", "year": "1934", "title": "Metallographic Investigation of the Iron, Iron-Carbide, Iron-Boride System", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-05132003-154630", "creators": [ { "name": { "family": "Clark", "given": "Donald Sherman" }, "id": "Clark-Donald-Sherman", "display_name": "Clark, Donald Sherman" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/KKRD-7J80", "abstract": "No abstract." }, { "name": "Cobine, James Dillon", "degree": "PhD", "year": "1934", "title": "The Reignition of an Arc at Low Pressures", "advisor": "Mackeown, Samuel Stuart", "url": "https://resolver.caltech.edu/CaltechTHESIS:11072024-000607344", "creators": [ { "name": { "family": "Cobine", "given": "James Dillon" }, "id": "Cobine-James-Dillon", "display_name": "Cobine, James Dillon" } ], "advisors": [ { "name": { "family": "Mackeown", "given": "Samuel Stuart" }, "id": "Mackeown-S-S", "role": "advisor", "display_name": "Mackeown, Samuel Stuart" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/ae7x-sk16", "abstract": "No abstract." }, { "name": "Gainder, Melvin Earnest", "degree": "PhD", "year": "1934", "title": "Impulse Voltages in Windings", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:10022024-204244331", "creators": [ { "name": { "family": "Gainder", "given": "Melvin Earnest" }, "id": "Gainder-Melvin-Earnest", "display_name": "Gainder, Melvin Earnest" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8jct-jh08", "abstract": "An outline of the technique of making impulse voltage\r\nmeasurements by cathode ray oscillograph is given.\r\nCircuits for operating, timing and synchronizing of oscillograph\r\nand impulse generator are discussed. Certain details\r\nof the technique of operating an oscillograph and of\r\nimpulse testing are also mentioned.
\r\n\r\nThe results of experimental determination of the effects\r\nof impulse voltages on distribution transformers are given\r\nin the form of oscillograms and conclusions derived therefrom.\r\nIt may be said that, in general, the characteristics\r\nof such transformers are similar to those of power transformers.
\r\n\r\nA brief study of the literature of the subject is included.
\r\n\r\nA study of the mechanism of transient voltage production\r\nin transformers has led to development of a semi-empirical\r\nform of analysis which permits calculation of terminal transients\r\nafter certain empirical constants are obtained by\r\ntest. The method is essentially that of finding the response\r\nof the transformer to infinite rectangular applied wave from\r\na few cathode ray oscillograph tests. By application of the\r\nsuperposition theorem, the response to any arbitrary wave can\r\nthen be determined.
" }, { "name": "Moore, Norton Bartlett", "degree": "PhD", "year": "1934", "title": "The Boundary Layer and Skin Friction for a Body of Revolution at Large Reynold's Numbers", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-02072006-152924", "creators": [ { "name": { "family": "Moore", "given": "Norton Bartlett" }, "id": "Moore-Norton-Bartlett", "display_name": "Moore, Norton Bartlett" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/JZW9-JZ15", "abstract": "Clark Millikan\u2019s work on the boundary layer and skin friction for a figure of revolution is extended, with particular reference to the completely turbulent boundary layer, in two ways:
\r\n\r\na) His expressions for the completely turbulent regime are generalized so as to hold for the assumption of a one n-th power law for the velocity distribution in the boundary layer;
\r\n\r\nb) Von Karman\u2019s logarithmic velocity distribution is introduced into the analysis.
\r\n\r\nb){sic} leads to a practical method by which the drag of a full-scale dirigible can be predicted from wind tunnel tests.
\r\n\r\nComparison of the theory as gotten from b) with experiments leads to the conclusion that the present theory can be safely used to predict drags at large Reynolds\u2019 numbers, whereas drags predicted on the basis of a one seventh power law may be from 20% to 30% low.
" }, { "name": "Sechler, Ernest Edwin", "degree": "PhD", "year": "1934", "title": "The Ultimate Compressive Strength of Thin Sheet Metal Panels", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-05212003-155534", "creators": [ { "name": { "family": "Sechler", "given": "Ernest Edwin" }, "id": "Sechler-Ernest-Edwin", "display_name": "Sechler, Ernest Edwin" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/HX3P-3Y69", "abstract": "No abstract. " }, { "name": "Wislicenus, George Friedrich", "degree": "PhD", "year": "1934", "title": "Cavitation and Separation in Pumps and Turbines", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:11112024-181310694", "creators": [ { "name": { "family": "Wislicenus", "given": "George Friedrich" }, "id": "Wislicenus-George-Friedrich", "display_name": "Wislicenus, George Friedrich" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/28qb-kc88", "abstract": "No abstract." }, { "name": "Ager, Raymond Wellington", "degree": "PhD", "year": "1933", "title": "The Power Factor of Dielectrics when Subjected to Fifty Cycle Voltages", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:09132024-203044077", "creators": [ { "name": { "family": "Ager", "given": "Raymond Wellington" }, "id": "Ager-Raymond-Wellington", "display_name": "Ager, Raymond Wellington" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/qzx8-9m91", "abstract": "No abstract." }, { "name": "Beckwith, Sterling", "degree": "PhD", "year": "1933", "title": "A New Power Factor Bridge and its Application to Synchronous Machine Testing", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:10212024-203816811", "creators": [ { "name": { "family": "Beckwith", "given": "Sterling" }, "id": "Beckwith-Sterling", "display_name": "Beckwith, Sterling" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/pbcz-zg06", "abstract": "No abstract." }, { "name": "Harness, George Thomas, Jr.", "degree": "PhD", "year": "1933", "title": "A Comparison of Arc Characteristics in Switching in Vacuum and in Oil", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:02282017-092613459", "creators": [ { "name": { "family": "Harness", "given": "George Thomas, Jr." }, "id": "Harness-George-Thomas-Jr.", "display_name": "Harness, George Thomas, Jr." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "mecheng" ], "doi": "10.7907/29CA-HX70", "abstract": "This thesis describes the results of an investigation\r\nof the arc end glow discharges occurring between the contacts\r\nwhen an alternating current is interrupted by an oil circuit\r\nbreaker; and a comparison with similar phenomena in the\r\nvacuum circuit breaker is made. This investigation was made\r\nby taking cathode-ray oscillograms of the variation of\r\nvoltage across the contacts, and the current through the\r\ndischarge, with time, and the variation of the voltage across\r\nthe contacts with the current through the discharge. Circuit\r\nvoltages of 15,000 and 2300 were used, and currents up to\r\n45 amperes were interrupted.
\r\n\r\nThe discharges across the separating contacts of an\r\noil circuit breaker are discussed in detail, and an analysis\r\nof the variations near the zero of the current wave is made.\r\nThis investigation shows that for a brief period, of the\r\norder of 300 microseconds, at the end of each half cycle of\r\nthe current wave the current between the contacts is of a very\r\nsmall magnitude, and may be considered essentially zero. During\r\nthis interval the voltage completes a part of an oscillation,\r\nthe frequency of which is apparently determined by the constants\r\nof the connected circuit, and rises in the reverse direction\r\nuntil a certain maximum is reached. After this value is reached\r\ncurrent again flows end the usual glow and arc phenomena are\r\nobserved.
" }, { "name": "Pleasants, John Gibson", "degree": "PhD", "year": "1933", "title": "Observations on the Theory and Characteristics of Electrical Figures on Plates in Air with Particular Reference to their Speed of Growth", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:03232017-092147859", "creators": [ { "name": { "family": "Pleasants", "given": "John Gibson" }, "id": "Pleasants-John-Gibson", "display_name": "Pleasants, John Gibson" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8EFG-G165", "abstract": "The fact that electrical figures in air at atmospheric pressure\r\ngrow with average velocities which lie in the range of from 10 to 103\r\nkm./sec., and which may extend beyond this range, depending on the\r\nmagnitude of the voltage applied and the physical constants of the\r\nplate is verified. The velocity decreases with increasing size of the\r\nfigure. The effect of a variation in the capacitance between surfaces\r\nper unit area of the plate has been found to be greater for negative\r\nthan for positive figures, and has been found to decrease with increasing\r\nvoltage, for figures at the same stage of development. The maximum\r\ncurrent intake has been observed to be 22.5 amp. (an average for two figures in\r\nparallel) at 30 kv., rising to a value of 60 amp. at 42.5 kv.. The\r\neffective capacitance (of two figures in parallel) in one case rose\r\nfrom an initial value of practically zero to more than 8,000 cm., resulting\r\nin a reduction in maximum value of the voltage wave applied of\r\n25% of the open line value. The reduction in rate of rise of voltage\r\nfor the same case was 30%. The possibility of the use of such an\r\narrangement for protection against over voltages is suggested. The\r\npolarity difference in the figures is a result of the difference in\r\ndirection of the flow of charge, and is dependent on the constants of\r\nthe plate, - - no predisposition to a fixed ratio being noted. The\r\nbehavior of the figures is such as to verify the conclusions of other\r\nauthors that figures of both polarities are formed by the movement of\r\nelectrons alone." }, { "name": "Wattendorf, Frank Leslie", "degree": "PhD", "year": "1933", "title": "A Study of the Effect of Curvature on Fully Developed Turbulent Flow", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-08182006-154158", "creators": [ { "name": { "family": "Wattendorf", "given": "Frank Leslie" }, "id": "Wattendorf-Frank-Leslie", "display_name": "Wattendorf, Frank Leslie" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "chair", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Klein", "given": "Arthur Louis" }, "id": "Klein-A-L", "role": "member", "display_name": "Klein, Arthur Louis" }, { "name": { "family": "Tollmien", "given": "Walter" }, "id": "Tollmien-W", "role": "member", "display_name": "Tollmien, Walter" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/RWZE-DP61", "abstract": "In aeronautics we are especially interested in the flow of air adjacent to surfaces, such as airfoils. There are two main types of flow of real fluids, laminar and turbulent and it is turbulent flow which is of practical importance in aeronautics. We should like to be able to predict the skin friction and flow conditions for any surface of any shape. There has recently been much success with the problem of predicting flow along a flat plate parallel to the direction of flow, and the problem was attacked by investigation of fully developed turbulent flow in straight channels, and direct application of the semi-empirical laws obtained, to the flow along a flat plate. However, surfaces met with in practice are, in general, curved, so that it would be important to be able to predict the effect of curvature on turbulent flow. Most of the previous work in curved flow, however, has been with curved pipes and channels where the behavior of the flow was complicated by secondary vortices.
\r\n\r\nThe present work had the purposes of isolating as far as possible the effect of curvature on a fully developed turbulent flow, with two dimensional mean motion. The curved channels used were 5 cm. in breadth and 90 cm. in depth, and had straight entrance sections over 60 x breadth in length to produce a fully developed straight flow before subjecting it to the effect of curvature. Channel I had inner radius 45 cm. and outer radius 50 cm., while channel II had inner radius 20 cm. and outer 25 cm. In addition, measurements were made in an appratus consisting of two concentric cylinders, the inner one of radius 20 cm. and rotating, the outer of radius 25.4 cm. and fixed. The curvature was made of the same order as channel II for purpose of comparison.
\r\n\r\nMeasurements on the channels consisted of pressure drop along the channel walls at several speeds, velocity distribution at 30\u00b0 intervals around the curved portion, velocity distributions at several speeds, and for channel II, determination of the shearing stress at the walls of one of the curved sections.
\r\n\r\nMeasurements on the cylinders consisted of velocity distributions at two speeds and determination of shearing stress at the outer wall.
\r\n\r\nEvaluation of results included: calculation of resistance law, calculation of the shearing stress, distribution in radial direction across the curved portion, determination of the exponential law for the velocity distribution near the walls in the various cases, calculation of the \"mixing length\" 1, from turbulent exchange theory, and several dimensionless methods of plotting velocity distributions to show similarity between measurements in the channels and in the concentric cylinders.
\r\n\r\nAlso included are calculations of the laminar flow distribution in a curved channel, and a discussion of Rayleigh's stability criterion.
\r\n\r\nIt appears that the distribution of centrifugal force has a strong influence on the stability of the flow, and affects materially the velocity distribution. The fact that similarity can be obtained for several cases by proper dimensionless reduction based on the effective breadth of the mixing region looks hopeful, and it remains for future investigations to determine more facts about the effective breadth of the mixing region.
" }, { "name": "Biot, Maurice A.", "degree": "PhD", "year": "1932", "title": "Transient Oscillations in Elastic Systems", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-11252003-113841", "creators": [ { "name": { "family": "Biot", "given": "Maurice A." }, "id": "Biot-Maurice-A", "display_name": "Biot, Maurice A." } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/ZHSH-T443", "abstract": "No abstract." }, { "name": "Brahtz, John Henry Augustus", "degree": "PhD", "year": "1932", "title": "Stresses at Two-Dimensional Corners for Various Force Distributions", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062007-140731", "creators": [ { "name": { "family": "Brahtz", "given": "John Henry Augustus" }, "id": "Brahtz-John-Henry-Augustus", "display_name": "Brahtz, John Henry Augustus" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/4QRC-A816", "abstract": "This paper deals with the stress distribution under plain strain in a corner of any angular magnitude, i.e., a plane with an angular incision or notch.
\r\n\r\nThe Introduction contains a brief statement of the method employed by Dr. Theodor von Karman in his exact treatment of a beam in bending (Aachen Abhandlungen, Heft 7, 1927).
\r\n\r\nIn Part I a generalization of this method is outlined which is applicable to the corner for any force distribution over the straight boundaries. Solutions are found in the 3/4-plane for:
\r\n1. Concentrated load at any point of the straight boundaries.
\r\n2. Uniform distribution between the vertex and a point of the boundary.
\r\n3. Linear distribution in the same region.
\r\n4. Superposition of 2 and 3.
Certain stresses are determined and plotted and shown to be infinite at the vertex for partial loadings of the boundaries.
\r\n\r\nIn Part II an alternate method is given to obtain a solution for case 1.
\r\n\r\nThe discussion points out the very interesting paradox that stresses may be finite for certain continuous loadings, but become infinite if a portion of the load is removed.
" }, { "name": "Folsom, Richard Gilman", "degree": "PhD", "year": "1932", "title": "An Experimental Investigation of the Phenomena Produced by the Highly Turbulent Flow of Water Past a Series of Sharp Obstacles", "advisor": "von K\u00e1rm\u00e1n, Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-06042004-104603", "creators": [ { "name": { "family": "Folsom", "given": "Richard Gilman" }, "id": "Folsom-Richard-Gilman", "display_name": "Folsom, Richard Gilman" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/BJ70-1607", "abstract": "A knowledge of the resistance to flow of a body placed in a stream of fluid is necessary for many problems in hydraulics, aeronautics, and ventilation. A large amount of experimental and theoretical effort has been expended investigating the drag characteristics of single bodies and small groups of similar bodies. Only a small amount of incomplete data is available regarding the performance of a long series of similar obstacles. This latter material was obtained for air flowing past supporting timber sets in mines. Since the dimensions of the mine shafts varied at different sections, the results of the experiments merely indicated the possibilities of obtaining different pressure losses depending on the size, shape, and spacing of the timber sets. Therefore, more data are needed regarding the drag characteristics of long series of obstacles." }, { "name": "Haeff, Andrew Vasily", "degree": "PhD", "year": "1932", "title": "Ultra High Frequency Oscillators", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:09212010-105300778", "creators": [ { "name": { "family": "Haeff", "given": "Andrew Vasily" }, "id": "Haeff-Andrew-Vasily", "display_name": "Haeff, Andrew Vasily" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/GAKG-W998", "abstract": "No abstract." }, { "name": "Oswald, W. Bailey", "degree": "PhD", "year": "1932", "title": "The Transverse Force Distribution on Ellipsoidal and Nearly Ellipsoidal Bodies Moving in an Arbitrary Potential Flow", "advisor": "von K\u00e1rm\u00e1n, Theodore; Millikan, Clark Blanchard; Tollmien, Walter", "url": "https://resolver.caltech.edu/CaltechETD:etd-09062007-141717", "creators": [ { "name": { "family": "Oswald", "given": "W. Bailey" }, "id": "Oswald-W-Bailey", "display_name": "Oswald, W. Bailey" } ], "advisors": [ { "name": { "family": "von K\u00e1rm\u00e1n", "given": "Theodore" }, "id": "von-K\u00e1rm\u00e1n-Th", "role": "advisor", "display_name": "von K\u00e1rm\u00e1n, Theodore" }, { "name": { "family": "Millikan", "given": "Clark Blanchard" }, "id": "Millikan-C-B", "role": "advisor", "display_name": "Millikan, Clark Blanchard" }, { "name": { "family": "Tollmien", "given": "Walter" }, "id": "Tollmien-W", "role": "advisor", "display_name": "Tollmien, Walter" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/QK4H-C181", "abstract": "The forces acting on an airship moving in a certain field of flow and the resulting path of motion are the result of numerous aerodynamic factors. These factors are principally skin friction drag, form drag, induced drag, aerodynamic transverse force distribution, lateral and longitudinal inertial and static force distribution, lift, and moments arising from all above factors. With the exception of aerodynamic transverse force distribution, lift, and induced drag, these factors are either small or may be determined by methods now available." }, { "name": "Wolfe, Karl Morgan", "degree": "PhD", "year": "1932", "title": "Design of an Optical Oscillograph for the Investigation of Lightning Phenomena", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:09132024-214202659", "creators": [ { "name": { "family": "Wolfe", "given": "Karl Morgan" }, "id": "Wolfe-Karl-Morgan", "display_name": "Wolfe, Karl Morgan" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/s7rp-jr31", "abstract": "No abstract." }, { "name": "Hoover, Vaino Alexander", "degree": "PhD", "year": "1931", "title": "Correlation of Induction Motor Design Factors and Determination of the End Turn Reactance of Polyphase Machines", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:09102024-201957310", "creators": [ { "name": { "family": "Hoover", "given": "Vaino Alexander" }, "id": "Hoover-Vaino-Alexander", "display_name": "Hoover, Vaino Alexander" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/8zys-8x86", "abstract": "No abstract." }, { "name": "Lash, Charles Coyle", "degree": "PhD", "year": "1931", "title": "Study of Electric Transients in the Vacuum Switch by Means of the Cathode Ray Oscillograph", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-09132005-154707", "creators": [ { "name": { "family": "Lash", "given": "Charles Coyle" }, "id": "Lash-Charles-Coyle", "display_name": "Lash, Charles Coyle" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/M45S-A062", "abstract": "The opening of an electric circuit by means of a vacuum switch is a complex performance which is analyzed into a sequence of stages according to the phenomena involved. First, the voltage difference between the opening contacts will increase more rapidly than the electrode spacing, producing successive discharges, which physically are field currents. If the energy delivered is sufficient, an arc is formed; if not, the transients persist for a time. The arc, if formed, continues until a minimum current is reached, when the current suddenly drops to zero. Immediately before and just after this drop occurs, the current is unsteady, many surges being superimposed on the otherwise simple characteristic. The sudden drop to zero current induces a damped sinusoidal voltage oscillation of appreciable magnitude in the external circuit. Such an oscillation of small magnitude follows the field currents when the interrupted current is too small to form an arc. As can be seen, the circuit is normally cleared in the first half cycle.
\r\n\r\nHayward\u2019s work disclosed, but left incomplete, the question of an apparent power storage in the arc. This thesis presents considerable new data from which it appears we may conclude that there is no storage of energy in an arc such as appeared to be the case. While several hypotheses may explain why Hayward\u2019s results were not duplicated, it is probable that his current measurement was erroneous, due to a time lag in his current coil deflections.
\r\n\r\nWhile the equipment available did not permit the determination of the kva. limit of the vacuum switch, the tests made indicated that it will handle its tasks well.
" }, { "name": "Maxstadt, Francis William", "degree": "PhD", "year": "1931", "title": "High Air-Efficiency insulation", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-05132003-123414", "creators": [ { "name": { "family": "Maxstadt", "given": "Francis William" }, "id": "Maxstadt-Francis-William", "display_name": "Maxstadt, Francis William" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/M7PR-FS48", "abstract": "The subject is introduced by a review of some of the work of others which seems not to be generally known. Its beginning is traced to the application of three well known principles of eleotrostatics which are presented in detail. Examples of the limitations of elementary electrostatic theory are set forth.
\r\n\r\nTaken in the order of their influence, each of ten or more factors which control the arc-over strength of solid insulators in air are analyzed, with experimental data accompanying each analysis.
\r\n\r\nA new means of increasing the arc-over strength of an insulator is suggested and experimental results for a few samples are presented.
\r\n\r\nTime did not permit extending the investigation to the arc-over strength of insulators under oil, but many of the factors herein analyzed for insulators in air apply almost directly to oil.
\r\n\r\nA mechanism of arc-over of solids in air is suggested although a great deal more data will be necessary to justify it.
\r\n\r\n1. Namely the behavior of dielectrics of different specific inductive capacity when used in series, in parallel, and in some intermediate arrangement.
" }, { "name": "Hayward, Claude DeWayne", "degree": "PhD", "year": "1929", "title": "A Study of Vacuum Switch Arc Phenomena with the Cathode Ray Oscillograph", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:08212024-152601231", "creators": [ { "name": { "family": "Hayward", "given": "Claude DeWayne" }, "id": "Hayward-Claude-DeWayne", "display_name": "Hayward, Claude DeWayne" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/0stk-t522", "abstract": "No abstract." }, { "name": "Lewis, William Abbett, Jr.", "degree": "PhD", "year": "1929", "title": "Design and Development of a Precision Speed Control Electric Drive for the Guggenheim Aeronautics Wind Tunnel", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292020-170525368", "creators": [ { "name": { "family": "Lewis", "given": "William Abbett, Jr." }, "id": "Lewis-William-Abbett-Jr", "display_name": "Lewis, William Abbett, Jr." } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/y12g-2785", "abstract": "The problem and solution described in this report is that of designing and building a suitable electric drive for the propeller which drives the air in the wind tunnel of the Guggenheim Aeronautics Laboratory. Specifications were written for a suitable direct current motor and a motor-generator set for furnishing the direct current, and a complete control system was designed and installed. The control system is arranged so that a minimum number of operations is required to start and stop the equipment and to adjust the speed of the propeller. All intermediate processes are automatically controlled and the equipment is interlocked so that operations can not occur out of proper sequence. Adequate protective features prevent serious injury to the equipment, even though the equipment is neither visible nor audible from the point of control. Two types of speed control are provided, one known as hand control and the other as regulated control. When under regulated control the speed of the propeller is regulated to a constant value with a high degree of precision for equipment of this size, and the value of the regulated speed can be adjusted at the will of the operator over a wide range. Speed control of both kinds may be obtained at conveniently located stations by operation of a transfer switch.
" }, { "name": "Oboukhoff, Nicolas Mikhailovich", "degree": "PhD", "year": "1929", "title": "A Method of Designing Medium and High Frequency Alternators with a Special Reference to the Inductor Type", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechTHESIS:08162024-200618128", "creators": [ { "name": { "family": "Oboukhoff", "given": "Nicolas Mikhailovich" }, "id": "Oboukhoff-Nicolas-Mikhailovich", "display_name": "Oboukhoff, Nicolas Mikhailovich" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/fgd1-7v75", "abstract": "No abstract." }, { "name": "Hamilton, James Hugh", "degree": "PhD", "year": "1928", "title": "Measurement of Arc Voltage Across Opening Switch Contacts", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-02182005-095331", "creators": [ { "name": { "family": "Hamilton", "given": "James Hugh" }, "id": "Hamilton-James-Hugh", "display_name": "Hamilton, James Hugh" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/CPH6-SH82", "abstract": "No abstract." }, { "name": "Lindvall, Frederick Charles", "degree": "PhD", "year": "1928", "title": "Contact Behavior and Gas Phenomena in a Vacuum Switch", "advisor": "Unknown, Unknown", "url": "https://resolver.caltech.edu/CaltechETD:etd-03042005-110623", "creators": [ { "name": { "family": "Lindvall", "given": "Frederick Charles" }, "id": "Lindvall-Frederick-Charles", "display_name": "Lindvall, Frederick Charles" } ], "advisors": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "eleceng" ], "doi": "10.7907/P2G2-C358", "abstract": "Initially a conditioned vacuum switch opens a circuit with a small, momentary arc. This arcing releases gas from the electrodes so that with continued operation a definite rise in gas pressure within the switch was observed. The rate at which gas is evolved was seen to depend both on the value of the interrupted current and on the circuit voltage, increasing either for increasing current or for increasing voltage. Further, definite evidence of getter-action or electrical clean-up of gas in the switch was obtained. Thus the resulting gas pressure was found to be due to that part of the evolved gas not removed by getter-action; and a limiting equilibrium case was found in which the gas evolution and getter-action balance each other to give a constant operating pressure for indefinitely continued switch operation. Moreover, the pressure range throughout which satisfactory operation in possible was determined to be from that of the best obtainable vacuum to one of the order of 10-3 mm. In addition, the tests included rupture of currents that gave excessively high current densities, and demonstrated that current break is possible even with severe heating of the contacts. Similarly, a limiting value of current density of the order of 10,000 amperes per square inch appeared to be permissible without effecting serious damage to the contacts. And, in general, copper, the metal most desirable from a commercial standpoint, was found to give better operating results than either of the other two metals investigated." } ]